All available knowledge related to relevant confounding factors was considered in this re-analysis. This more realistic approach led us to establish a correlation between changes in mammal abundance with both the time elapsed since the last snowfall and the dose rate to which they were exposed. This relationship was also observed when distinguishing prey from predators. The dose rates resulting from our re-analysis are in agreement with exposure levels reported in the literature as likely to induce physiological disorders in mammals that could explain the decrease in their abundance in the CEZ. Our results contribute to informing the Weight of Evidence approach to demonstrate effects on wildlife resulting from its field exposure to ionizing radiation.We re-analyzed field data concerning potential effects of ionizing radiation on the abundance of mammals collected in the Chernobyl Exclusion Zone (CEZ) to interpret these findings from current knowledge of radiological dose–response relationships, here mammal response in terms of abundance. In line with recent work at Fukushima, and exploiting a census conducted in February 2009 in the CEZ, we reconstructed the radiological dose for 12 species of mammals observed at 161 sites. We used this new information rather than the measured ambient dose rate (from 0.0146 to 225 µGy h However, whatever their conclusions, these studies do not sufficiently often analyze the underlying data with respect to the most relevant indicator of total exposure when attempting to quantify the dose–response relationship that characterizes the effects of animal exposure to ionizing radiation. As explained by Beresford et al.4 simplistic measurements of exposure, such as ambient dose rates or soil concentration activities, cannot encompass all the complexity of actual exposure of wildlife. Contributions of internal and external irradiation pathways to the total dose rates have both to be considered, and this balance depends on radionuclides (type and energy of emitted radiation) and on animal species . Largely used for humans, the dose reconstruction process would also allow the accurate characterization of wildlife exposure required to interpret it in terms of effect. It should be acknowledged that this approach incorporates larger uncertainties than for humans as it deals with interspecific variation in addition to inter-individual differences. However, it is an unavoidable step for a correct analysis of the dose–response relationship.Thirty years after the accident at the Chernobyl nuclear power plant (Ch-NPP), the subject of its consequences for wildlife living in the Exclusion Zone  is still hotly debated between scientists arguing it had a negative ecological impact5, we revisited the results of a field census of mammals in the CEZ1, where tracks in the snow were counted along line transects in 2009. The study sites were located west of the Ch-NPP, inside or very close to the CEZ, over an area of 800 km2  that we reconstructed for individual mammals. We assessed both the external and internal components of the dose (rate) on the basis of (i) the simplified morphological and ecological characteristics of the mammals of interest (Tables S1–S4), and (ii) the radioisotope concentrations in soils, crossing GPS information with the most relevant available data describing soil contamination. We re-analyzed the abundance data considering the reconstructed total dose as an explanatory variable for mammal individuals, with the same environmental descriptors as confounding variables. Optimization of the statistical methods applicable to this dataset led to grouping of data according to two hierarchical taxonomic levels of description. The first analysis focused on all identified mammals, with an additional analysis of “predators” and “prey”. This re-analysis confirmed the results previously obtained1, which concluded a relationship between exposure to ionizing radiation and the abundance of mammals. The added value of our work consisted first of assessing a realistic value of the dose absorbed by exposed mammals, applying recognized and fully traceable methods. Second, we checked the consistency of our results with the state of the art with regard to dose (rate)–effect relationships.Combining life history traits describing the mammals species located by Møller and Mousseautdj). Depending on a species and its home range, basic data were more or less complete. We compared the tdj values for the two mammals having the greatest difference in generation time . We reported on the same graph , (Time since snow)2, Bush cover , and Grass cover .The possible confounding variables included as fixed effects in the Generalized Linear Mixed Models (GLMM) were identified as follows: TTDi, including the four possible confounding variables previously identified. The relationship between animal abundance and the TTD is significantly negative (Table 2 (time × time) since last snowfall also explained a significant proportion of the number of mammals observed along a transect. The three remaining factors had no influence on the mammal abundance.The first GLMM fitted expressed variation in mammal abundance with increase in ve Table , that is1, we first distinguished prey and predators, applying the same approach as for the entire mammal category. The number of prey was significantly negatively influenced by TTDi and positively affected by time since snowfall 2. Adding the number of prey as a potential new confounding variable did not add significantly to the data analysis. The robustness of this first category of analysis is already strongly constrained by the small numbers of prey and predators per transect. Additionally, the grouping of species into prey and predators was arbitrary based on their diet, considering carnivorous and omnivorous mammals as potential predators and other mammals as potential prey. The reality of the prey-predator relationship between the species of interest has not been considered . According to this well identified limitation of the number of individuals, we decided not to investigate finer scale divisions among taxa as frequencies for most species were too low to permit a robust statistical analysis.The next step of our analysis consisted of exploring ways to refine the analysis per subgroup of mammals. Following the example of Møller and Mousseau12. However, most investigators agree that the poor estimate of actual levels of exposures in terms of doses to wildlife is one of the highly relevant explanations that could underlie differences in opinions concerning radiation effects on wildlife14. This led to recommendations with regard to the nature of data to acquire when conducting field studies15. Suggested good practices, such as more thoughtful sampling protocols, should apply to future studies. However, it would be wasteful to not better value existing data as often as possible, through their re-analysis and reinterpretation if and when needed. The current study clearly illustrates the value of such an approach. By proposing such re-interpretations, there are inevitable issues related to data availability, assumptions to be made, and additional uncertainties. Of particular note, is that a robust analysis of field data related to ionizing radiation requires the most accurate dose assessment possible16. When re-analyzing past studies, this implies the implementation of a dose reconstruction that combines ecological and radiological aspects. The present study required that we adapt the available historical data to our spatial and temporal needs in order to assess soil contamination levels. Generic life history and morphological information were collected for all mammal species, ignoring their potential site-specific characteristics. From this, we made the best use of the initial dataset and the additional information that we were able to gather.There has been considerable discussion and some disagreement concerning the possible effects of low to moderate dose of ionizing radiation on natural populationsDue to limitations in the initial dataset and constraints imposed by statistical models, we were only able to robustly analyze patterns of variation for the entire mammal assemblage, and predators and their prey. Because of the rarity of many species, there was insufficient variation among sites to permit a more detailed analysis at any lower taxonomic level. Future studies should endeavor to increase overall sample sizes as well as promote the development of new statistical models better able to accommodate sparse data.1 confirmed their first conclusion. There is a correlation between the increasing exposure to ionizing radiation of mammals due to radionuclides emitted during the NPP accident and the decrease in their abundance. In terms of dose rates, the range of the lowest values across all sites varied from 6.6 × 10–3 µGy h−1 (stoat outside the CEZ) to ca 10–1 µGy h−1 (wild boar outside the CEZ). At the opposite end, the highest dose rates ranged from 4.4 µGy h−1  to 6.1 × 102 µGy h−1 . On average across the 145 transects, the highest dose rate was recorded for the Przewalski’s horse (7.0–101 µGy h-1), and the lowest for the wolf (1.8 µGy h−1). These values were calculated for an average individual of each species, which is supposed to be representative for the mean exposure of populations of this species. The area on which the dose rates were assessed was the species home range, that is to say the area sufficient for individuals of this species to carry out their normal functions. This area is also considered of relevance to the maintenance of populations17.The first result of this re-analysis of the dataset collected by Møller and Mousseau18. For mammalian reference animals (RAPs)19, the range of background exposure varied from 5.0 × 10–2 to 1.4 × 10–1 µGy h–1. This corresponds to the lowest values we estimated outside the CEZ, that is to say two to three orders of magnitude lower than the highest dose rates we calculated for wolf and mouse. These latest values are consistent with other assessments made in the CEZ, for example for small rodents (38 to 61 µGy h–1 at the western edge of the Red Forest20).Natural background exposure dose rates would constitute a relevant point of reference to put in context the additional dose rates we assessed. Their characterization is scarce, and spatially limited. Some data have been reported for terrestrial wildlife in parts of the UK–1 adopted by the International Commission on Radiological Protection (ICRP) for mammalian RAPs. Just above this DCRL, defined as the band of dose rate for which there is very low probability of effects occurring to individuals of mammals, the ICRP recognizes a potential for reduce reproductive success which could explain a decrease in abundance of mammals. Additionally, the two ranges of values include the generic screening benchmark defined as “safe” at the ecosystem level during the ERICA project21 (10 µGy h–1). Looking more precisely at ecosystem sub-levels, vertebrates among which mammals would be protected by respecting a maximal dose rate value of 2 µGy h–1 established as a first estimate22. Both the 10 µGy h–1 and the 2 µGy h–1 values were derived on the basis of effects observed at the individual level, applying recognized methods to extrapolate at the population level22. A look in the FREDERICA database23 suggests that the range of dose rates reported here could result in various observable effects on individuals of a variety of mammals including the otter (10 µGy h–1: minor decrease in body weight and moderate decrease in population density24), mice  and vole . The actual consequences for population, and a good way to asses them, of such effects and any other effect observed on individuals are an area of intensive research in the field of radiation protection of wildlife. However, the global view obtained from the combination of the whole set of effects data gives an intrinsically consistent panorama which may partly explain the reduction in mammal abundance described in the CEZ by Møller and Mousseau1  of 4.2 to 42 µGy h137Cs and 90Sr that differ by up to ca. three orders of magnitude on the same transect, and by five orders of magnitude across the whole study area. Use of simple ambient dose rates in such cases led to (i) ignorance of this variation and (ii) to the conclusion that effects could occur at dose rates up to a factor three lower than those actually estimated (10–2 to 2.3 × 102 µGy h−1 vs. 6.6 × 10–3 to 6.1 × 102 µGy h−1). The ambient dose rate is in general neither representative of the minimal nor maximal value of the dose rate assessed per transect using our reanalysis  was associated with a decrease of ca 60% of the number of all mammals, 66% of the number of prey, and about 50% of the number of predators , and were located along roadsides  and environmental factors . Ambient radiation levels were determined from averaged repeated measurements (2–3) at ground level with a hand-held Geiger counter .We used a number of additional descriptors for each site as covariates in our analysis, as described by Møller and Mousseau5 (SI). According to this method, we estimated for the mammal species j and the radionuclide r the external and internal dose rates  and IDR; µGy h−1, see supporting Excel® file) absorbed by mammals of a given species. We used radionuclide activity concentrations measured in soils and calculated for animals, multiplied by the ad-hoc Dose Coefficients . These coefficients, specific for the combination of radionuclides, species and irradiation pathway, were determined per radionuclide and daughter element(s) for adult stage of each species with the EDEN v3.1 software27.The principles for reconstruction of total radiological doses absorbed by animals were described in detail in a previous similar study of dose reconstruction for birds in the Fukushima area5 . The total dose rate absorbed by the mammal species j, TDRj, is the sum of the internal and external dose rates assessed for each radionuclide, applied to all radionuclides of interest (SI Excel® file).The internal and external irradiation dose rates absorbed by mammal species were calculated according to the equations described elsewherej considering that adult individuals are exposed to ionizing radiation at a constant dose rate during a period that corresponds to the generation time LGj of the species . Consequently, the total dose absorbed by each species j at a given transect i noted tdj,i resulted fromWe assessed the total dose to a given mammal species This total dose was calculated for each species and each transect, whether the presence of the species on this given transect has been confirmed or not. This is the theoretical total dose the animal would receive if living there.tdj,i values presented large ranges of variation . Their geometric mean for all species on a given transect i was calculated as the most relevant indicator, named Transect Total Dose and abbreviated TTDi. Calculating the mean on all species, whatever they have been counted on the transect or not, gives a highly representative estimate of the level of exposure on the considered transect, not of the exposure of the counted species. This was also justified because we considered the zero count as relevant information. Such a number may have two origins: either the species has never occupied the surroundings of the transect (e.g. area not suitable for its needs) or it has disappeared. In both cases, the series of possible confounding variables considered in our statistical analyses will allow us to include this information  identified at the study sites vary according to their exposure to ionizing radiation. We needed a unique value of dose per transect, representative of the average exposure of all animals indirectly observed along this transect. The We deliberately chose to limit our analysis to adults in order to minimize the assumptions required to achieve our calculations. It is generally recognized that juveniles may be more sensitive to exposure to pollutants than adults. Juvenile development and growth mobilize resources that are no longer available for their protection. Juveniles differ from adults in their diet, behavior and physiological characteristics. Moreover, these characteristics change with time from birth to maturity. Such changes can have large implications in terms of dose reconstruction and associated uncertainties. Thus it is necessary to identify periods of development during which individual characteristics can be considered constant, and to be able to collect data corresponding to the needs for dose reconstruction. This approach is possible for a single species, but would be much more speculative for all 12 of our species of interest. Since our understanding of adult life history is likely to be more robust than that of juveniles for the purposes of dose reconstruction, we have ignored juvenile stages for this analysis. Moreover, time from birth to maturity is generally short with regard to generation time Table , and dis30. By default for site-specific data, the choice was made to refer to best-estimates published in an international compilation of data31. All data depending on the nature of the radionuclide were collected or calculated for the elements Cs and Sr and their isotopes present in the accidental releases for the Chernobyl NPP accident . 137Cs and 90Sr soil activities were assessed for each transect. We took into account both the transect length (100 m) and the species home range  and the radionuclide periods (about 30 years for both 137Cs and 90Sr). This assumption contributes to the conservatism of the approach. The final dataset included three values of soil activity concentration per radionuclide (137Cs and 90Sr) for each species on each transect . We arbitrarily decided not to use more complex data treatment such as krieging. Due to the highly heterogenous “leopard skin” pattern of the soil contamination, we considered such approaches not particularly robust as they give an apparent continuity to soil contamination between measured values. Using only actually measured values helped to limit the number of assumptions required by our calculation, already high. We acknowledge however that a spatialized statistical approach to better assess the soil contamination is an interesting perspective to refine the dose reconstruction.Measurements of soil radionuclide activity concentrations have been extensively conducted in the CEZ and around since the accident. To best cover the spatial and temporal scales of our study, we combined different data sourcesge Table  to definge Table . This ciThe first source of uncertainty in this study was its field protocol, which did not allow screening of the possibility of a double count of the same animal. This is a well-known weakness of such census methods. This “old fashioned” approach of field counting was largely applied in the past, as it is something relatively easy and simple to implement, requiring relatively few resources in contrast to more technological methods. The related and inherent disadvantage is the uncertainty around the count that is difficult to quantify. The way the census was conducted was though to reduce this uncertainty, by exploring somewhat distant transects in a short period of time. This is not a guarantee that individuals have not been counted more than once, but the application of recommended best practices when using such methods.31. Using these values under-predicted the transfer of 137Cs to predatory versus to prey species31. Wood et al.36 reported from previous studies that the transfer of cesium to carnivorous species such as those classified in our study as predatory was suggested to be higher than for mammals at lower trophic levels. At the opposite, values summarized by the IAEA showed a significantly higher transfer of cesium to omnivorous and herbivorous mammals, as data in this database relate31 mainly to insectivorous small mammals rather than to species similar to our predatory mammals. In the absence of site-specific CR values, the use of best-estimates remained the best option.Other sources of uncertainty appear in such a dose reconstruction, which is a highly uncertain exercise requiring numerous assumptions. The use of CRs was previously acknowledged as a major source of uncertainty that we managed by constraining the value by the diet and using preferentially site-specific values or by default best-estimates such as CR values provided by the IAEAWe applied this logic to any other ecological or biological parameter required by the dose calculation . Our choice was to make an assessment as specific and realistic as possible, without propagating uncertainty characterized at a global scale. For all parameters, there were insufficient local data to characterize their local variation. Soil activities showed rapid spatial change. This is a well-known characteristic of the contamination in the CEZ and it was the only data that we were able to characterize locally in terms of range of variation. We decided to consider only this site-specific uncertainty in our calculations.A last source of uncertainty in approaches such as the one applied here is the existence of confounding factors. A number of additional variables are known as potentially affecting mammal abundance, such as environmental characteristics or human activities. The first problem consists in identifying these variables, and then to characterize them. What are the necessary and sufficient parameters to collect, when and how? Regarding the description of the environment, the minimal dataset usually acknowledged as relevant has been collected during the census . If time data provide objective information, soil cover is observer dependent. This uncertainty was reduced due to observations done by a single observer. This ensured a high comparability between transects. The interaction between animal abundance and human activities is somewhat more complex to characterize. The nature of the CEZ led us to consider only the potential for repulsion of industrial activity linked with the NPP or attraction of farming areas. Characterizing the latest areas was highly uncertain (see dedicated paragraph in SI). There may be a significant time shift between the time of required data were acquired and the time of census. There may be also problems of spatial definition due to labels used in the available sources of information.The re-analysis of the dataset gave the opportunity to investigate the role of complementary data related to the impact of human activities. Potential spatial interactions between industrial and farming activities, present in the CEZ, and exposure areas of all or parts of the mammals were considered before to be dismissed as non-significant in the conditions of this study (see SI). The set of confounding variables finally retained was the same as for the initial study, that is to say the environmental descriptors that were recorded during the census .37. We first tested the variation in mammal abundance with the TTDi increase through the development of a Generalized Linear Mixed Model (GLMM), assuming Poisson error distribution. The main predictor (TTDi) was log-transformed and then centered on the mean and scaled by the standard deviation. The multicollinearity between possible confounding variables was checked through the Pearson correlation coefficient , in order to include in the non collinear standardized variables in the model. Site was introduced as a random effect, and transects were treated as statistically independent observations. Secondly, the variation in abundance of mammal subgroups (predators and prey) was tested in the same way with regard to the TTDi increase. The same fixed and random effects were considered. The last analysis aimed to analyze the variation in predator abundance with TTDi, while considering the number of prey as an additional fixed effect.All statistical analyses were performed in RFinally, four GLMMs were used to test the following hypotheses (where No means number):39. For each model, we computed adjusted p-values using the multcomp package in order to take into account the multiple null hypotheses tested simultaneously40.All GLMMs were fitted with the lme4 packageThe effect of exposure to ionizing radiation for wild mammal populations in the Chernobyl Exclusion zone was examined. Our re-analysis of exposure levels included measures of animal life history and past and contemporary radionuclide levels in order to estimate total doses for individual organisms in a manner not previously conducted. This novel approach led to new insights that suggest that likely doses to some animals were often much higher than those estimated using simple measures of ambient radiation levels with doses consistent with those expected to generate deleterious effects based on conventional radiological protection criteria for ecosystems. Our new analysis suggests that a tenfold increase of the mean dose absorbed by mammals over their generation time corresponds to a decrease in total abundance of about 60%. These findings tend to confirm the linkage established by the initial study, by revising upwards the dose rate responsible for the observed effects. They remain however fragile, due to the many associated uncertainties. Especially, despite our effort to consider as many as possible confounding factors, the difficult characterization of some did not allow their fully satisfactory interpretation.The process of dose reconstruction has proven necessary and useful, as this revision led to estimated levels of exposure correlated to observed effects on mammals consistent with the available knowledge on the toxicity of ionizing radiation on these animals. In large part, this new analysis resolves some of the conflicts that were mentioned in the introduction. However, dose reconstruction alone is not sufficient to demonstrate a causal relationship between exposure and the observed effects. But, it is a step in the right direction and, when combined with the large spatial scale of the Chernobyl disaster and the ability to survey biological consequences at multiple locations across a regional landscape, one can at least have some confidence that the observations are realistic in the light of current knowledge of radiation effects. Our results should be seen as one line in a larger Weight of Evidence approach to demonstrate in situ the effects of exposure to ionizing radiation on wildlife.More generally, our re-analysis indicates that existing datasets can be a valuable source of new knowledge regarding effects of exposure to ionizing radiation for wildlife in the field, as long as dose reconstruction is possible. This reconstruction process may be long and complex, and there are unavoidable assumptions required to fill each data gap that may introduce additional uncertainties. However, the current study indicates that it may be productive, constructive and useful to implement modern re-analyses to review initial findings that did not fit “conventional wisdom”.The findings of this study highlight two general issues that apply to all ecological research. The first issue relates to the care that must be taken in designing and planning field studies. It is crucial to pay sufficient attention to and adequately characterize the environmental conditions under which the study is conducted and to report these additional data as completely as possible when publishing so that subsequent re-analysis might be conducted if needed. The second issue concerns the need for sensitivity and uncertainty analyses in dose reconstruction processes . It is only by collecting appropriate and relevant qualitative and quantitative information that field observations may be properly interpreted.Supplementary Information 1.Supplementary Information 2.Supplementary Information 3.


To investigate the cross‐section shape of the femoral neck isthmus (FNI) in three‐dimensional reconstruction model of the femoral neck.From December 2009 to December 2012, computed tomography (CT) data of bilateral hip joint from 200 consecutive patients  who underwent surgical treatments for proximal femoral fracture were retrospectively reviewed. The 3D model of the proximal femur was reconstructed, and the “inertia axis” method, which was applied to measure the long and short axes of the cross‐section of the FNI, was established. The cross‐sectional area and perimeter were calculated by a formula using the length of the long and short axes and then compared with the actual measured values by the software. Correlation between the descriptive parameters of the FNI cross‐section  and patients' demographics  was analyzed. Stepwise linear regression analysis was used to determine the main relevant factors.2vs 731.62 ± 128.15 mm2, P = 0.322). The perimeter using the two methods showed narrow while significant difference , the actual measured values were about 5 mm greater than the predicted values. The parameters  were significantly larger in male than female (P < 0.001). A positive correlation between the cross‐sectional area, perimeter, height, and weight was observed. The stepwise linear regression analysis showed that the regression equation of the FNI area was as follows: Y = −1083.75 + 1033.86 × HEIGHT + 1.92 × WEIGHT, R2 = 0.489.The ICC results showed excellent data reproducibility ranged from 0.989 to 0.996. There was no significant difference in the cross‐sectional area of the FNI between the actual measured values and the predicted values using the formula , are of great significance for the spatial configuration of the screws used in the internal fixation of femoral neck fractures. This study utilizes the three‐dimensional model of the proximal femur to segment the FNI plane. We found that the actual measured data of FNI cross‐section was in line with the values calculated using elliptical equations, thus proving that FNI cross‐section was approximately elliptical. Femoral neck fracture is a common fracture in orthopaedic trauma, which occurred in approximately 3.61% of the systemic fracture and 50%–60% of the hip fractureet al. found that the cross‐section of the femoral neck of a gorilla and a modern human gradually changed from a circular shape to an oval shape from the proximal to the distal endResearch on the effectiveness of internal fixation involves multiple fields, including anatomy studies, biomechanical studies, and comparative clinical trials. One of the important factors that affect the implant selection and mechanical properties of femoral neck internal fixation is the spatial shape of the femoral neck canal, especially the morphological characteristics of the cross‐section of the femoral neck isthmus, which directly affects both the spatial configuration and type of the cannulated screwset al. compared the single‐cylinder method with the two‐angled cylinder method and found that the continuous ellipse method using the 3D reconstruction was more accurate in identifying the morphology of the femoral neck. Moreover, the regression analysis showed that the continuous cross‐section ellipse model might be a better way to describe the structure of the femoral neckCurrently, the diverse configuration of implants is controversial among surgeons and causes subjective deviations and mismatching of implantsThe purpose of this study was to: (i) reconstruct and reslice the cross‐section of the FNI according to inertia axis in the 3D model; (ii) employ the mathematical tools to measure and analyze the geometric features of the femoral neck and FNI; (iii) predict factors associated with the area of the FNI cross‐section using correlation analysis, and calculate equations using regression analysis to guide the implant of screws in osteosynthesis of femoral neck fractures. This study hypothesized that actual measured values of the cross‐section of FNI were in line with the predicted values using the elliptical equation.After obtaining the approval of the Institutional Review Board (IRB) of the General Hospital of the Chinese People's Liberation Army, computed tomography (CT) data of bilateral hip joint from 213 consecutive patients who underwent surgical treatments for proximal femoral fracture at our hospital from December 2009 to December 2012 were retrospectively reviewed. The patients received a completed CT scan  of the bilateral hip joint and the slice thickness was 1.2 mm. The exclusion criteria are set as follows: (i) patient with a history of femoral neck fractures or surgery of the hip joint; (ii) patient with a history of congenital deformities, like developmental dysplasia of the hip, coxa vara, and retroversion; (iii) patient with necrosis of femoral head; and (iv) patient with severe hip or knee arthritis. Two hundred patients with bilateral CT images of the hip joint were included in this study. The study population comprised 137 males and 63 females with a mean age of 69.41 ± 9.21 years, ranging from 50–85 years. The group’s demographic data according to gender was listed in Table In this study, the 3D model of the proximal femur was reconstructed using Mimics 20.0 software  according to the standard methodsThe perimeter and area of the FNI cross‐section were automatically calculated in the 3‐Matic and defined as the actual measured value Fig. .2].The “inertia axis” method was used to determine the long and short axes of the FNI cross‐sectionAll data were analyzed using SPSS software . All measurements had passed the normality test, and then the paired t‐test was used to compare the difference between the calculated area and perimeter and the measured values. Furthermore, the area and perimeter of the FNI were also grouped by sex and sides and compared. Pearson's Correlation Analysis was then used to elucidate the correlation between the morphological parameters of the cross‐section of the femoral neck and the patient's demographics . Finally, the factors that affected the morphological parameters of the cross‐section of the femoral neck were determined by stepwise linear regression analysis.α = 0.05, 1‐β = 0.65) according to the study by Walter and Eliasziw et al.P‐value of less than 0.05 was statistically significant. Finally, measurements of 200 patients were randomly numbered using the digital table method, and data of a senior physician (RYZ) was adopted for this study.At least 180 samples were required for the linear regression . The perimeter calculated by the two methods showed a narrow while significant difference , the actual measured values were about 5 mm greater than the predicted values , perimeter , and weak correlation with the elliptical eccentricity of the FNI . In addition, there was a moderate correlation between the patient weight and cross‐sectional area , perimeter . There was also a slightly negative correlation between the cross‐sectional area of the isthmus and the age of patients was observed .The correlation results between the morphological parameters of the femoral neck cross‐section and the parameters of the demographics were listed as following Table : The patY = −1083.75 + 1033.86 × HEIGHT + 1.92 × WEIGHT, and R2 = 0.489.Results of the stepwise linear regression showed that the regression equation of the cross‐sectional area of the FNI was: In this study, the main finding was there is no significant difference between the actual measured value and the equation‐predicted value on the cross‐sectional area of the FNI. There was a significant difference in the perimeter of FNI between the two methods, the actual measured value was larger than the calculated value, and the difference was narrow (approximately 5 mm). The results indicate that the cross‐section of the femoral neck could be described using the elliptic equations, and has an approximate oval‐like shape mathematically.Regarding the narrow gap in the perimeter of FNI between the actual value and the formula value, there may be two main factors affecting this result. One is the elliptic equation in the mathematical model is not completely suitable for the FNI due to the systematic bias, and the other is that the inner surface of the femoral neck is not smooth. Generally, the cross‐sectional perimeter of a smooth object was smaller than that of an object with an equal cross‐section but with a rough surface.The correlation analysis showed a highly positive correlation between the cross‐sectional area or perimeter and height, which is consistent with the effect of height on bone morphology that has been reported in the literature, namely, that height is proportional to the bone development of the femoral neckSurgical treatments of the femoral neck fractures were not yet perfect for orthopaedic doctors. Minimally invasive internal fixation is the first choice for young and middle‐aged patients. Studies regarding internal fixation treatments for femoral neck fractures have shown that surgeons still prefer using three screw fixations in a parallel pattern. Due to the unique anatomical structure of the femoral neck, the incidence of postoperative complications  can reach up to 40%According to the previous studies and our research finding, the morphology of the cross‐section of the femoral neck is more like an ellipsis. Furthermore, some researchers have reported that the femoral neck has a specific torsion angleR2 value was 0.489 in the regression equation of the cross‐sectional area of the FNI. It is worthy mentioning that the more the value approached +1 or − 1, the more it fits the model. Therefore, further investigations are needed to strengthen the robustness of the equation.This study has several limitations. One is the use of the outer boundary of the femoral neck cortex to analyze the morphology of the cross‐section of the femoral neck, which does not completely reflect the morphology of the medullary cavity of the femoral neck out of the cortex thickness. This might explain the difference between the actual measured value and software value. The other is that we measured the characteristics of the cross‐section of the FNI but did not study the morphological changes in the femoral neck from the proximal to the distal end. Researchers need a more continuous analysis of the femoral neck based on approximate anatomical landmarks. At last, the This study supported the notion that the cross‐section shape of the FNI appears to be oval‐like in the 3D model, separated according to the inertia axis. The size of the FNI cross‐section was correlated with height and weight. The findings of this study proposed an anatomical basis for further study of the spatial configuration of cannulated screws in the treatment of femoral neck fractures.LCZ and PFT conceived the study. RYZ and YPZ wrote the manuscript. RYZ, YPZ, and XYS performed the study. RYZ, YPZ, XYS, JTL, and ZJX contributed to the data collection and interpretation of the results. All authors read and approved the final manuscript and consented to publish this manuscript.


Few studies have examined public opinion about the health care system in the former Soviet region. The objective of our study was to evaluate the population’s satisfaction with the health care system and identify factors associated with it in Armenia.We conducted a cross-sectional telephone survey among 576 adult residents of the capital Yerevan using Random Digit Dialing technique. Simple and multivariate logistic regression explored associations between potential determinants and satisfaction.A substantial proportion of respondents (45.5%) were dissatisfied or very dissatisfied with the health system. About 49% of respondents negatively evaluated the ability of the system to provide equal access to care. About 69% of respondents thought that the responsibility for an individual’s health should be equally shared between the individual and the government or that the government’s share should be larger. The adjusted odds of satisfaction were higher among individuals with better health status, those who positively rated equal access and respect to patients in the system, those thinking that the responsibility for health should be equally shared between the individual and the government, and those who tended to trust the government.This study enriched our understanding of factors that shape the population’s satisfaction with the health care system in different cultural and political environments. We recommend further exploration of public opinion about those system attributes that are not directly linked to patient experiences with care, but might be equally important for explaining the phenomenon of satisfaction.Supplementary information accompanies this paper at 10.1186/s12913-020-05863-6. The importance of assessing patient satisfaction as an essential component of health care outcomes has been long recognized . While mIn Armenia, as well as in many other former Soviet countries, the health care system destabilized following independence in 1991, leading to a substantial decline in access to and quality of health care –6. The gThe government has attempted to improve access to care through several programs. The Basic Benefit Package (BBP), which was introduced in 1996, specifies services that are either fully or partially funded for socially vulnerable groups and the entire population , 9. As oIn 2006, to ensure access to free and quality maternity services for all women, the Government of Armenia introduced the Obstetric Care State Certificate. The reform substantially reduced out-of-pocket payments for deliveries among the Armenian women . AnotherThe periodical review of BBP with the expansion or reduction of services and/or population groups covered led to certain a level of confusion among service users and health care providers . The limDespite continuous gaps in the system, the study conducted in nine former Soviet countries has shown a high level of satisfaction with the system in Armenia 53.8%) in 2010 [.8% in 20The above-mentioned study has not provided a detailed analysis of factors influencing satisfaction with health care in Armenia. The direct exploration of the Armenian population’s expectations, beliefs and values that might shape the satisfaction levels could therefore be a valuable contribution to the limited existing evidence in the field.The investigation of public opinion can foster a clearer communication of what citizens expect from the system and what can be reasonably provided, and serve as a groundwork for public inclusion in decision-making processes , 12. WhiThe primary aim of this study was to assess the Armenian population’s satisfaction level with the health care system and explore associated factors.We conducted a cross-sectional telephone survey among the adult population of capital Yerevan, where roughly 37% of Armenia’s population are located . To be iThe survey respondents were sampled using Stratified Random Sampling proportionate to size of the population living in each district of Yerevan. Random Digit Dialing (RDD) of landline phone numbers was used to enroll the participants . RepeateWe used a structured questionnaire developed based on the tools from similar studies conducted internationally and in Armenia, located through extensive literature search , 16–19.The questionnaire was pre-tested prior to data collection and contained domains on satisfaction with health care system, health status and utilization of health care services, awareness about recent health care reforms, the relative importance of health system characteristics, government’s responsibility for the health of individuals and socio-demographic characteristics of participants. In total, the questionnaire included 27 survey questions.The dependent variable was the respondents’ satisfaction with the health care system in Armenia. Satisfaction was measured by a Likert scale type question with balanced response options of “very satisfied”, “satisfied”, “neither satisfied nor dissatisfied”, “dissatisfied”, and “very dissatisfied”. The independent variables included socio-demographic characteristics, self-rated health status, use of health care services in the last 12 months, awareness about governmental reforms to improve access to care, evaluation of six system attributes  in the current system, opinion about the role of the government in preserving individual’s health, and trust in the government.The data was entered, cleaned and analyzed using SPSS 22 and STATA 13 software . Descriptive analysis was followed by bivariate and multivariate logistic regression to reveal crude and independent associations between independent and dependent variables. The responses of those who chose the neutral option of the satisfaction variable were excluded from the binary outcome used in bivariate and multivariate analysis.The Institutional Review Board of the American University of Armenia approved the study (#AUA-2016-017). Oral informed consent was obtained from all participants.Overall, 5851 call attempts were made to reach the study participants, resulting in 2030 contacts. Out of the contacted respondents, 30.8% did not meet the inclusion criteria. About 57% of the remaining respondents refused to participate in the study, with the most commonly cited reason being having no time. Overall, 576 completed interviews were obtained. There were twenty-seven incomplete interviews. Table Approximately 46% of the respondents were either dissatisfied or very dissatisfied with the health care system as opposed to 25.4% who were satisfied or very satisfied  or good 28.2%). About 66% of the respondents used health care services in the last 12 months. Approximately 16% of them were very satisfied and 50.8% were satisfied with the services received (Table 8.2%. AboThe overwhelming majority of the respondents knew about major reforms carried out by the government to improve access to care (78 to 87% awareness about each program). However, most of them (53.4%) thought that the listed reforms did not help to improve access to care for Armenian citizens. When asked to explain why the reforms were not helpful, most of them said that the improvements did not work as expected (60.7%). Equal proportions thought that the improvements apply to narrow population groups (34.7%) or to limited services (34.7%).The respondents were asked to rate the state of several health system attributes in the Armenian system Table . The abiThe largest proportion of the respondents thought that the responsibility for health should be shared between the individual and the government, but the government’s responsibility is larger (34.7%). A similar proportion (34.2%) thought that there should be an equal share of responsibility. Approximately 17% thought that the individual’s responsibility should be larger, 10% thought that it is solely the government’s responsibility, and 4% thought that it is solely the individual’s responsibility.Participants were asked about whether they tend to trust or not to trust the government. About 66% said that they tend not to trust the government, 17.5% said that they tend to trust it, and 16.3% refused to answer.p < 0.1 level in bivariate analysis were entered into the adjusted logistic regression model (Table All variables which were associated with satisfaction at el Table . The varp = 0.012). Positive rating of equal access to care in the Armenian health care system was associated with substantially higher odds of satisfaction  as compared to negative assessments. Similarly, those who positively evaluated respect to patients in the system were 2.69 times more likely to be satisfied with it  than those who had not.In the adjusted analysis, those who reported fair/poor health status were less likely to be satisfied with the health care system as compared to those who had excellent or very good status .Those who thought that the responsibility for health of the individual is equally shared between the individual and the government were more likely to be satisfied with the health care system than those who thought that it is solely the government’s responsibility or that the responsibility is shared but the government’s share is larger at the marginal level of significance with the OR of 1.93 .Not trusting the government was associated with substantially lower odds of satisfaction  reported being either dissatisfied or very dissatisfied with the system. Only 25.4% were satisfied or very satisfied, while the remaining proportion was neutral. Participants’ health status, ratings of equal access to care and respect to patients in the system, opinion on whether the responsibility for health lies with the government or the individual, and trust in government were found to be associated with satisfaction in the adjusted analysis.The level of dissatisfaction found in this study closely resembles the one reported in the study which explored patient satisfaction in nine former Soviet countries, where 46.2% of Armenian respondents were either quite dissatisfied or definitely dissatisfied with health care . HoweverInterestingly, the rate of satisfaction with the services received in the last 12 months was substantially higher than the overall satisfaction rate with the system recorded in this study , which is in agreement with the studies conducted in other regions of the world . This diA solid proportion of respondents who have not used health care services in the last 12 months (31.4%) mentioned the inability to pay for health services as the reason for not using them, which is quite close to the findings of previous studies conducted in 2010 and 2016 , 22 and Although the awareness about major health sector reforms was pretty high, from the perspective of most of the surveyed respondents the reforms did not help to meet their needs. This wide disapproval of the reforms combined with high awareness about them might reflect the actual poor implementation of the reforms in Armenia rather than inadequate communication about them to the public, which has also been alleged by some authors , 9.The highest proportions of respondents in our study thought that responsibility for health should be either equally shared between the individual and the government or that the government’s share should be larger. Our data resemble the findings of the Global Trends 2014 survey in Russia where the majority of the respondents (52%) thought that it is the government’s responsibility to support the healthy lifestyle of the population as opposed to individual responsibility – the highest proportion across 20 surveyed countries . On the Our finding that fair/poor health status is associated with lower satisfaction is in line with the results of studies conducted in the same region and in other countries in Europe , 3, 26. Out of six system attributes, only equal access to care for all citizens and respect to patients seemed to influence patients’ satisfaction with the system. Respect for patients is one element of responsiveness, a concept developed by WHO, which refers to how the system performs in non-health aspects . In addiWe believe that our finding of higher satisfaction among those respondents who favored equal share of responsibility for individual’s health by the government and the individual as opposed to those who thought it is fully or largely government’s responsibility points out to the importance of studying new ways of measuring patient expectations, embodied with this particular variable in our study. The researchers exploring the concept of satisfaction often use proxy measures for patient expectations such as education, income, age, rurality, and others –4. The nTrust in government was associated with higher satisfaction in our study. The concept of trust in government includes individuals’ attitudes toward government based on their assessments of how well elected officials and public organizations meet individual expectations . This asThis study has several limitations. First of all, the restriction of the sample to the urban Yerevan population, and having the majority of educated and female respondents in the sample might limit the generalizability of our results. Although the landline phone coverage in Yerevan is substantial , the excAnother limitation is the exclusion of responses of those who chose the neutral option of the satisfaction variable from bivariate and multivariate analysis, which decreased the sample size available for the logistic regression analysis.This study makes an important contribution to the international literature published on the topic of satisfaction with the health care system, as it helps to improve our knowledge about factors that influence it in different cultural and political environments. In democratic countries public norms and opinions are widely believed to affect policy . HoweverAdditional file 1. Survey questionnaire.


In this work, a cellular automata (CA) approach was used to generate 3D structures of polyamide and carbon aerogels. Experimental results are used as initial data for materials’ digital representations and to verify the developed CA models. Based on the generated digital structures, a computer study of aerogels’ mechanical properties was conducted. The offered CA models can be applied for the development of new nanoporous materials such as aerogels of different nature and allow for a reduction in the amount of required full-scale experiments, consequently decreasing development time and costs of new material formulations. Development of new functional materials with certain properties is an important scientific direction, accelerated by growing requirements of different practical fields. Increasing markets and fast data exchange claim a creation of new tools, making R&D process faster and more efficient. Taking into account these modern tendencies, we tried to build new models focused on material design and present in this paper the results obtained within a case study of new perspective nanomaterials—polyamide and carbon aerogels.3, and its porosity can exceed 90%. The specific surface area of aerogels varies from 100 to 2000 m2/g ; pored is the pore diameter, d100 = 100 nm. This relationship was obtained empirically by carrying out a large number of computational experiments with test structures. Silica–carbon composites obtained from silica–resorcinol formaldehyde aerogels via pyrolysis were used as test structures. Pyrolysis was carried out inside an electric furnace under 700 °C.The developed model has the following assumptions:Identification of all pores.The diameter of each pore is increased with the calculated probability by the fixed step, and all the “polyamide” inside pores with new diameters is removed.Step 2 is repeated until the required fraction of “polyamide” is removed.Changing the state all “polyamide” cells to “carbon”.The algorithm of the developed model can be represented by the following steps:In the pyrolysis model program, pores are recognized as follows: In each empty cell, the program tries to place a pore with a certain diameter where the considered cell acts as the center of the spherical pore. If there are cells with substance inside the pore or the placed pore overlaps with the others too much, then the pore is removed. Otherwise, this pore is not removed from the structure, and its cells are marked as “pore cells”. After all the structure empty cells are considered, a certain diameter is reduced and the procedure is repeated. Algorithms are carried out until all possible pore diameters from the maximum level to the minimum one are considered. The pore volume is calculated from the number of pore cells that belong to each diameter. The input parameters of the model are an aerogel modelled structure  and the amount of substance that must be removed. The amount of substance that must be removed is calculated from the amount of carbon in the experimental PA-C sample.


An overview of the gas-phase endstation with the multi-coincidence setup at the FinEstBeAMS beamline in the MAX IV 1.5 GeV storage ring is presented. A detailed description of the functional design of the endstation together with the data acquisition concept and first test measurements is given. 2 and thiophene (C4H4S) molecules have demonstrated that the setup can be used for many-particle coincidence spectroscopy. The measurements of the Ar 3p photoelectron spectra by linear horizontal and vertical polarization show that angle-resolved experiments can also be performed. The possibility to compare the electron spectroscopic results of diluted samples with solid targets in the case of Co2O3 and Fe2O3 at the Co and Fe L2,3-absorption edges in the same experimental session is also demonstrated. Because the photon energy range of the FinEstBeAMS beamline extends from 4.4 eV up to 1000 eV, electron, ion and coincidence spectroscopy studies can be executed in a very broad photon energy range.Since spring 2019 The photoabsorption of VUV photons up to 20–30 eV usually causes single ionization while at higher photon energies multiple ionization becomes possible, producing positive ions, neutral fragments and electrons (photoelectrons and Auger electrons).Molecular photofragmentation is one of the important branches of studies concerning molecular reaction dynamics. The simplest example of photodissociation processes is a two-body reaction of diatomic molecules, in which a parent ion breaks into just two pieces. In this case the kinematic and energetic information about one single fragment is sufficient to acquire almost complete knowledge of the dynamics of the whole photodissociation event. Photoionization of more complex systems may lead to the creation of more than two fragments. In general, if the number of products from a photoionization event is et al., 2002abet al., 2013et al., 1991et al., 2005et al., 2011et al., 2003et al., 2007et al., 2004et al., 2005et al., 2016The detection and correlation of photoions and photoelectrons (or Auger electrons) from the same photoionization process can provide a dynamically complete description of the photofragmentation reactions  of the FinEstBeAMS beamline in the 1.5 GeV storage ring at the MAX IV Laboratory in Lund, Sweden. The tunable photon energy range of this beamline (4.4–1000 eV) enables electron, ion and coincidence spectroscopic studies of the valence and core levels of a variety of sample systems such as molecules, clusters, nanoparticles and liquids. An overview of the experimental configurations of the GPES and its opportunities is given. The selected examples of measurements are not given as novel scientific results, but to illustrate the capabilities of the present setup.2.2.1.et al., 2017et al., 1993−1 and 92 lines mm−1). High orders of diffracted light at low photon energies can be eliminated by the combination of gas and thin film filters . The spot size at the focus of the endstation is 100 µm × 100 µm. The overall resolving power is in the range 5000–10000. The highest photon energy resolution is about 1.2 meV at 21.58 eV and 30–40 meV at 401 eV. The photon flux in the photon energy range 50–100 eV stays above 1013 photons s−1 using a resolving power of 5000. Photon flux at 1000 eV is about 4 × 109 photons s−1.The design and optical concept of the FinEstBeAMS beamline was described in detail in an earlier paper . These windowless pumping stages permit pressure differences between the beamline and GPES of up to five orders of magnitude, avoiding contamination of the beamline optics with gas phase samples from the experimental sections. The endstation is designed and planned for experimental techniques like high-resolution electron spectroscopy, ion TOF mass spectroscopy, velocity mapping and multiparticle coincidence spectroscopy. Also time-resolved studies can be conducted at the GPES but generally they require both single-bunch operation of the storage ring and a beam chopper clusters, free-standing nanoparticles as well as liquids. The free-standing nanoparticles are injected into the experimental chamber from the colloidal solution by atomizer or nebulizer system or by liquid micro-jet setup. The freestanding nanoparticles are not desorbed to any surfaces, but can be injected into the X-ray beam by carrier gas  or by solvent liquid. In order to maintain ultra-high vacuum (UHV) conditions at the FinEstBeAMS beamline, the GPES is connected to the beamline via a differential pumping section, consisting of three stages (a 300 l sa)]. The movement enables either chamber to be brought into the focus of the photon beam. The upstream chamber (further referred to as the coincidence chamber) hosts a permanent electron spectrometer (SCIENTA R4000) and a momentum-resolving ion TOF (TOF) spectrometer [Fig. 1a)] and is equipped with an inner mu-metal shielding to block out external magnetic fields. The coincidence chamber can be considered as the main installation of the GPES.From the beginning of the design phase, the aim was to create a versatile, modular and portable experimental configuration, which would be compatible with different sample injection systems. The starting point was a crossed-beams configuration in which a signal detection axis, flight axis of sample particles and the photon beam propagation axis cross. The endstation consists of two separate experimental chambers that include crossed-beams configurations and can be mounted after each other on a rail system, which allows movement along the beam axis . Both chambers have separate stands and they can be connected by means of a rotary seal and a flexible bellow that have three radial DN16CF ports for mounting different diagnostic or measurement instruments [Fig. 1b)]. The chambers can also be isolated from each other by a manual gate valve.When experiments are performed in the user chamber the beam goes through the coincidence chamber. In addition to the variable polarization of the undulator radiation, both chambers can be rotated around the photon beam axis over a 90° range. The coincidence chamber can be rotated by an integral independent support system and does not require an external crane for lifting and support [see Fig. 1b)]. The distance of these DN150CF ports from the chamber axis is kept at minimum in order to retain flexibility for mounting different instruments and sample systems. In order to reduce the distance between the focal points of the upstreams and downstreams chambers and the movement needed when bringing either of the chambers to the focal position of the photon beam, the four-way DN150CF crosses are located asymmetrically depending on the centre between the two DN200CF end-ports. The focal positions of the two chambers are normally separated by 550–600 mm. The movement and alignment of the GPES is accomplished using a linear rail system, which is cast on the experimental hall’s floor and three alignment sliders [Fig. 1a)].The principal design of both chambers consists of a cylindrical main body with two DN200CF end flanges and with DN150CF four-way crosses that determine the measurement and sample injection planes [see Fig. 1b)]. On the plane of the DN150CF four-way cross, there is an additional DN16CF port and its axis is directed to the focal point of the chamber at 45° relative to the normals of the DN150CF ports. Additional ports  can be used, for instance, for a pressure gauge, a viewport for alignment, a quartz crystal microbalance or a shutter of the sample source, respectively.The axes of two DN38CF ports for user equipment pass through the focal point of the chamber and intersect with the main (beam) axis at a 45° angle  and TOF is its flight time. The lens voltage, however, can be used to adjust the ion trajectories and the size of the momentum image, while keeping the desired TOF range of the ion spectrum.The TOF spectrometer has four elements with adjustable potentials – the ion repeller and the extractor grid, the aperture (‘lens’) in front of the drift tube and the entire drift tube assembly together with its entrance aperture Fig. 2. In stan+ ions with the initial kinetic energy equal to 4 eV – a typical value obtained in the dissociation of et al., 2016Igor Pro software environment (WaveMetrics Company) and the ion flight trajectories were then traced through the grid.Initial values for the suitable TOF spectrometer’s voltage settings can be obtained by numerical simulations of the spectrometer, which also provide useful insight into the operational conditions in the pulsed-field coincidence mode. For the measurements reported here, we modelled the ion flight trajectories of NFirst, a acceleration voltage satisfying the Wiley–McLaren space focusing condition and the optimal TOF resolution  corresponds to the conditions where ions emitted at ±θ are detected at the same radius, giving the best resolution for determining the transverse momentum component from the image. The lens voltage for this condition was −380 V.Then, the momentum imaging conditions were optimized by varying the lens voltage. Fig. 3Td = 500 ns delay was applied in the second simulations shown in Fig. 3b), where closer inspection shows that the ions now originate from a circle around the nominal source point . The radius of this circle is Rd = (2Ekin/M)1/2 Td, the spread from the point source in an initially field-free sample region by the time the extraction pulse is applied. If Rd becomes comparable with the dimensions of the sample region, the effect on the ion trajectories is significant, as seen in Fig. 3b). The momentum image becomes considerably compressed and also the momentum resolution deteriorates.The above simulation does not take into account the delay between the creation of the ions and the application of the extraction pulse. In the coincidence mode where the electron provides the trigger for applying the extraction pulse, the contributions to the delay are: (i) the electron flight time in the lens system of the electron spectrometer, (ii) electron flight time in the hemispherical analyzer and (iii) delays in the electronic circuit. The first depends on the electron kinetic energy, the pass energy and various lens voltages, and the second is determined only by the pass energy. Low kinetic and pass energy settings cause longer pulse delays. The electronic contribution presently forms (for common pass energy and electron kinetic energy ranges of 10–100 eV) approximately two-thirds of the total delay that is of the order of 500 ns. This M ≳ 30) ions. In order to minimize the total delay time in the present setup, future upgrades with faster electronic components are planned.The simulation shows that the effect of the extraction pulse delay in a pulsed-field coincidence setup cannot be ignored. The delay affects the detector image more, whereas the TOF spectrum is not sensitive to it and is more pronounced at low electron kinetic and/or pass energy settings. The influence of the pulse delay diminishes rapidly with the decreasing initial velocity of the ions, and is generally negligible for heavier (c) shows the simulation where the lens voltage value was optimized empirically in the experiment, by obtaining the momentum image with the best contrast. The value of −300 V was obtained and used also for the measurements reported below . The simulation demonstrates the effect of adjusting the size of the momentum image by the relatively small variations of the lens voltage. Why the experimental optimization did not arrive at exactly the simulated optimum lens settings can be due to several reasons: the chosen voltage could partly compensate for the distortions due to the pulse delay, the smaller momentum image could exhibit sharper features even if the actual momentum resolution is not improved and, finally, the accuracy of the experimental optimization was limited.Finally, Fig. 33.2.In this section the main elements of a data acquisition and triggering scheme are described ]. The first one, output A, is a short pulse that is converted to a nuclear instrumentation module (NIM) signal by a logic converter (ORTEC 9307) and it triggers the waveform acquisition cards in the Roentdek computer. The second one, output B, from the TTL generator triggers the HV pulse and determines the duration for which the extraction field is present in the ion source region.Regular ion TOF measurements are performed at fixed frequency (up to ∼20 kHz) of extraction pulses. Two TTL output channels are in use [see Fig. 4b)]. If the coordinate voltage value is close to zero, it means no valid electron position was available from the position analyzer. This situation corresponds to either a generated constant-frequency trigger (as opposed to electron trigger) or a fault in encoding the electron position from the resistive anode.In the case of coincidence measurements the ion extraction HV pulse must be synchronized with the arrival time of the electrons which is provided by the electron detector of the Scienta R4000 electron spectrometer. In order to retrieve the kinetic energy distribution of detected electrons from each coincidence event the electron hit position on the axis of the detector in the energy-dispersive direction must be saved for each trigger separately. The setup utilizes a Roentdek waveform capture input channel that is not required to decode the ion hit position from the delay-line Hexanode. The electron-dispersive position (kinetic energy) information from the analog output of the Quantar position analyzer is forwarded to that input channel of the Roentdek and the position value is recorded as the (maximum running average of the) trace height for each triggered acquisition , the ions with high radial velocity pass close to the edge of the aperture of the lens element, where electro-optical aberrations are strong.The red dots in Fig. 5+ ions detected, by doubling the energy values, and (ii) through coincidence analysis of N+ ion pairs, as a distribution of the sum of their kinetic energies. As the figure shows, the latter method yields a considerably better resolved KER distribution, since only ions that form true coincidence pairs can be chosen by checking that their momentum vectors are antiparallel as required by momentum conservation. The first method can give a rough estimate for KER in a faster experiment with trigger rates too high for a coincidence analysis.After determining the momenta of the ions, kinetic energy release (KER) in the charge-symmetric dissociation of molecular nitrogen dications, 2 . The centre of the kinetic energy window was set at 138 eV to capture the S LVV Auger electrons, and the width of the energy window at the given pass energy was 12 eV. The voltage settings of the ion TOF spectrometer Usource = ±200 V, Ulens = −400 V, Udrift = −1240 V were used.A demonstration of a coincidence measurement of a core ionized medium-sized organic molecule is shown in the example of thiophene – a molecule exhibiting a rich dissociation landscape with well defined features in the corresponding ion–ion coincidence map  and 1b)The vacuum chamber of the GPES can be rotated in the dipole plane along the photon beam [see Figs. 1. The spectra at each photon energy were recorded immediately after each other by only changing the direction of the polarization and the undulator gap in between the measurements, i.e. the settings of the monochromator were not touched. No kinetic energy shift was observed in any of the measurements within the accuracy of Gaussian fitting; a shift could have indicated a movement of the photon beam upon the change of the polarization. A pass energy of 10 eV was used in the measurements. The inset of Fig. 8Ihor and Ivert are the intensities (areas) of the photoelectron lines measured with the horizontal and vertical linear polarization, respectively. Our results for β are compared with those of Houlgate et al.  or mixed (Co3O4) charge state is possible  to a DN150CF inlet flange. The sample is introduced via needle at the end of 6 mm stainless steel tube. The length of the presently used needle is around 50 mm, inner diameter 110 µm and outer diameter 0.25 mm. The cross section of the needle is chosen as small as possible in order to avoid distortions of electric fields in the interaction region of spectrometers. The minimized gas conductance of the inlet needle also moderates pressure fluctuations in the experimental chamber. However, it is possible to replace the needle by a wider one if it is necessary due to low vapour pressure of the sample. The sample pressure in the vacuum chamber can be adjusted by a gas inlet valve between the inlet system and sample gas container.5.2.−1). The expansion chamber needs to be connected to the experimental section through gas flow limiters such as apertures, flow tubes or skimmers. The coincidence chamber of the GPES has two opposite DN150CF flanges on the axis that is perpendicular to the axis of the electron and ion TOF spectrometers’ mounting flanges. One of these flanges can be used for mounting an expansion chamber with a gas flow limiter and specific user determined sample source. At the moment the GPES is equipped with a DN150CF five-way cross with a liquid-nitrogen trap and three HiPace 700 (Pfeiffer) pumps to enable a pumping speed of more than 2000 l s−1 of the sample sources with high gas load. This pumping speed is satisfactory for most well constructed liquid microjet  and liquid microjet setups need an expansion chamber and (turbo)pumps with a pumping speed for high gas load  molecules with the multi-coincidence setup at the GPES demonstrated the possibility to use the GPES in many-particle coincidence spectroscopy. The measurements of Ar 3p photoelectron spectra with linear horizontal and vertical polarization show that the setup can be used to perform angle-resolved experiments. We have also demonstrated the possibility to compare the electron spectroscopic results of diluted samples with the solid targets in the case of Co2O3 and Fe2O3 at the Co, Fe L2,3-absorption edges in the same experimental beam time.The GPES enables users to study different samples in the gas phase such as atoms, molecules, microclusters and liquids. Electron, ion and coincidence spectroscopy studies can be executed in a broad photon energy range from 4.4 eV up to 1000 eV. The configuration of three perpendicular axes in the experimental chambers enables users to mount different sample inlet systems easily. In this way the electron spectrometer of the GPES can be used even for experiments of nanoparticles and liquid samples. The first test measurements of N


The number of Internet of Things (IoT) devices has experienced a large growth during the last decade, as well as the data volume gathered from remote sensors. Satellites are still a suitable communication method and may be preferable for a remote ubiquitous sensor network (USN), which sometimes are located in places without much communications infrastructure where coverage is the principal drawback. Alternatively, the proposed solution for this article aims at a near-vertical incidence skywave (NVIS) channel for high frequencies (HF) with a low-cost platform, allowing a low-power transmissions coverage area up to 250 km for USN. The HF standards are focused on generic communication channels not being robust for NVIS communications. In this article we study and test an alternative based on orthogonal frequency-division multiplexing (OFDM) modulations to make them more robust and less dependent on the channel NVIS communications. For that purpose, we test the HF standard modulations and a designed OFDM modulation to prove the robustness of each. This study has been tested between Barcelona and Tarragona, using different transmission power levels and modulation orders. It is not news that the number of sensors and mobile devices is increasing enormously every day in the current world. The infrastructure of the communications for these devices is very extended in areas with a high population. However, some areas in the world do not have such infrastructure due to complex orography, which makes communications between the transmitter and receptor almost impossible. Normally, the most extended way to communicate in these places is the use of satellite services, which do not need any terrestrial network infrastructure. Nowadays, the environmental impact of satellite deployments  and theiRemote sensing became an extended study focus making use of new technologies such as light detection and ranging (LIDAR), artificial intelligence (AI) , machineAs an alternative to satellite communications, the use of ionospheric reflection has been under study for several years even in scenarios such as Antarctica where there is almost no kind of infrastructure, and the deployment of network communications are practically unfeasible due to its complicated terrain . Near-veTo maintain a standard for NVIS communications, high-frequency (HF) frame protocols MIL-STD 188 110C Appendix D  and STANIn this paper we present an alternative to the standards by the use of a wideband OFDM modulation for NVIS based on a low-cost and low-power platform for remote sensors, which can be a solution to multipath. This solution aims to improve NVIS communications and make a more robust system. To achieve this solution, this study has two principal goals: the proposal of a new ionospheric transmission configuration and to have the ideal trade-off between narrow-band modulations and OFDM in terms of power consumption for low-power systems. If we take into account the possible applications, the starting point is the battery consumption for remote sensors. For that reason, the input back off (IBO) plays an essential role in the OFDM modulation. This parameter lets us increase the average power cutting the peaks that the OFDM produces due to the subcarriers division and is more adequate for the ubiquity for portable sensors.Moreover, to improve NVIS, the use of two different waves, known as the ordinary and extraordinary waves, can benefit the communication. These waves are caused birefringence nature of the ionospheric plasma in the presence of the geomagnetic field . Also, tThis article is organized as follows. In This section introduces the basis of the NVIS characteristics and the leading technologies present in the developed platform used to achieve the study, as different techniques are used in the optimization of the platform. Additionally, an overall vision of the components and software are explained.NVIS propagation consists of the transmission of HF electromagnetic waves between 3 to 10 MHz with an angle above 70° to the ionosphere which can make this signal rebound and reach distances up to 250 km . The rebThe main challenge of this kind of communications is the availability of the rebounds. This fact relies on the ionosphere layers, which are D, E and F. D appears during the day but prevents the rebounds under 10 MHz and attenuates the signal. The E layer is the first which allows the HF signals to rebound followed by the F layer, which is divided into F1 and F2. Both are present during the day, but during the night the F1 disappears. The F2 due to its stability is the layer with which the test transmissions have been performed.Lastly, the ionosphere with NVIS has some difficulties in the design because of the channel effects produced by the ionosphere rebounds as studied by Vilella , JodalenAlso, this protocol has a SIMO technique which overcomes results that sustain the study of different polarization ways in order to receive the NVIS signal studied by Erhel . In our A preliminary experimental approach of the noise level in channels between 3 and 24 KHz was studied by Bechet, Bechet and Miclaus , but theThe current platform allows a continuous transmission with a radius of 250 km because of the NVIS channel. Talking about costs and pollution, the developed NVIS platform is affordable compared to any satellite.The system description is explained below, taking into account all different parts, and finally, a graphical scheme is shown in Software-Defined Radio (SDR)/Red PitayaSDR is key to the development of the platform  due to iRaspberry Pi 3The time synchronization between transmitter and receiver is performed with GPS controlled as a peripheral from Raspberries Pi 3 . In the Amplifier and Low Noise Amplifier (LNA)For our lab tests, an amplifier of 48.5 dB is used in order to reach 50 dBm signal transmissions. Bonn BLWA 0103-250 class A is the chosen model, which can works correctly between 1.5 and 30 MHz . In contFilterA band pass filter (BPF) is needed to limit the frequencies used for NVIS channel (3–10 MHz). Due to strong interferences in that band, we have used a 2 MHz BPF centered on 5.4 MHz to avoid the saturation of the ADC at the reception.AntennaOur system needs to be easily deployed, and the election of the antennas is intended for this purpose as far as possible. The chosen antennas are an inverted V which have a gain of 6.8 dBi , with a One of the three antennas is placed in the transmitter, while the other two are set perpendicularly at the receiver with the purpose of receiving both right-handed circular polarization and left-handed circular polarization waves simultaneously. To receive both waves, the antenna configuration on the receiving requires a phasing network as we can see in The aforementioned phasing box was developed in order to perform the delays explained using coaxial cables. Each of the antenna inputs is divided into two identical signals with a radio frequency splitter, generating 4 signals (2 for each antenna). The paths followed by each antenna are identical. One of the cables is lengthened with a quarter wave phasing line, providing a 90° phase shift, while the other signal is connected directly to an RF combiner. This process is repeated identically for both antenna wires, resulting in an output of two dipole antennas with a phase difference of either +90° or −90° between each other. Equation (1) shows the unification of the two antennas which includes the non-phased wave in (2) and the 90° phased wave in (3). It is important to mention that this system has been designed for a unique frequency. For wideband studies, the phasing network should be frequency adaptive and implemented in the FPGA.The narrow-band modulations  studied in previous works are good enough for remote-sensing applications, but in low-multipath scenarios. Our OFDM proposal is suited to manage strong multipath with easy equalization methods. The study of this modulation lies in its capacity to avoid the multipath effect and the easy way to equalize it. It is known that in ionospheric communications the evening transmissions are plenty of multipath compared to the morning, being the OFDM an excellent option to avoid those effects .The spectral efficiency is a good characteristic as well as the computational efficiency due to the FFT and IFFT. The modulation process is done by the IFFT of all the M-QAM or M-PSK symbols, which form the OFDM symbols. Equation (4) describes the IFFT process of the symbols where Nsc is the number of subcarriers and Sk is the modulated symbols in QAM/PSK. This process ensures data transmission in multiple parallel subtransmissions at lower speed, but in a robust way, which helps the stability of any communication system.As a drawback, the OFDM peak consumption is higher than any other narrow-band modulations because of the subcarrier division creates peaks having as a result a high peak to average power ratio (PAPR) which is the difference between the peak power and the average power.The configuration of the OFDM to be transmitted in our tests is based to be the most similar as the HF standards to maintain the most similar comparison. The design of the OFDM configuration requires a previous study of the channel to define every parameter. This channel analysis and definition of the OFDM configuration for high multipath is defined in a previous article . Taking The delay spread is a key measure of the multipath received, being the time between the first and the last path received. In  this wasOne of the weak points of the OFDM is the high PAPR, as mentioned, the OFDM modulation produces high peaks which reduce the average power of the modulation. Also, this is reduced by the IBO application to crop the peaks and then rising the average power. In  the IBO The initial design is done with an IBO of 3 dB because the average power was too small compared to the narrow-band modulations. After doing the first comparison, more IBO values  are studied to make the OFDM more efficient. The bits in use are calculated by multiplying the bits/symbol, the number of data OFDM symbols and the number of data subcarriers. Finally, the summarized configuration of the OFDM is shown in Diversity techniques are being applied in many communication fields. Spatial diversity, frequency diversity and time diversity are methods applied in many frequency bands and scenarios. Polarization diversity is a diversity mode that may be applied in very specific environments and is based on two different channels with particular properties.The ionosphere is an ionized layer of the atmosphere due to solar radiation. Its electrons vibrate at the frequency of the incoming waves, acting as small dipoles. These vibrations are usually elliptical in shape and occur in both directions. Because of this, the ionosphere creates two opposite channels due to the movement of the electrons. These channels are completely decorrelated and change the polarization of the wave to a circular one, even if the emitted signal is linearly polarized .b/N0.When having two isolated channels, multiple input multiple output (MIMO) appears as a method to exploit their multipath propagation. This work focuses on the ionospheric channel and the development of a SIMO system that benefits from the two characteristic waves, the ordinary and the extraordinary waves. Both MIMO and SIMO are valid solutions, with the MIMO being the one that can provide better results as more antennas are involved in the scenario and more techniques can be applied . A SIMO scenario  demonstrb/N0 and then ignores the worse result. On the other hand, EGC makes the coherent sum of both channels to get an increase of the bit energy [Despite these gains, the HF antennas are too big and most of the times it is necessary to install a mast. The use of diversity-polarization makes sense in the receiver side because it can help to minimize the power consumption and the size of the transmitter antenna. This article studies the SC and equal gain combining (EGC) techniques to outperform results. SC compares the two different signals received (two different channels) in terms of Et energy .Geoscience and the complete understanding of how the atmosphere’s layers work take a leading role in the development and implementation of telecommunication’s applications. Remote sensing, for instance, can directly benefit from the ionosphere’s studies by the application of techniques based on the ionospheric properties. This paper shows, for example the usage of polarization diversity as an improvement of a remote-sensing network.In this section, we explain the area where we tested the different transmissions with an NVIS channel and the organization of the tests to be transmitted.There were two different tests: the first one was dedicated to a simple comparison between the narrow-band and the multicarrier-band modulation to know the viability and efficiency respect narrow-band modulations, and the second one was to optimize the OFDM transmitted making use of the IBO which helps to find a power transmission for a low-consumption system which means smaller batteries.In La Salle University URL  there is an inverted V antenna acting as a transmitter NVIS node. The receptor is approximately 97 km away  where La Salle has a specific lab with the same antenna but making use of SIMO technique, so there are two of them and the phasing box. The tests follow a 10-minute plan, in which the first 5 min the platform does not transmit, and throughout the next 5 min, we increase the order of modulation for each modulation (from 2 to 32) after each minute. This process is repeated six times during one hour but increasing the transmission power by 3 dBs from 35 dBm to 50 dBm every 10 min. The summary is shown in Each transmission includes a 6th PN sequence with a resampling of 8 and 5 ms length as in  that is Each transmission contains 200 packets (50 for each modulation) of 162 symbols with a resample of 34 to achieve 3 KHz of channel bandwidth. In the A good point of study is the optimization of the average power of the OFDM due to the high peaks produced by the multiple subcarriers. This optimization allows the platform to have greater autonomy or smaller batteries to be integrated in low-power applications. Numerous techniques overcome the results of the OFDM bit error rate (BER) due to the increase of the average power. However, we opted for the IBO study.The initial tests start with IBO = 3 dBs just to reduce the principal peaks and compared directly with narrow-band modulations. After that, there is a specific IBO sweep to obtain the optimal one (same structure as before), which also helps the reduction of power consumption indirectly. Is true that high values of IBO increase the average power (energy) and overcome the bit error, but thanks to that, the peak power could be decreased.b/N0, the cumulative distribution function (CDF) of BER for a specific Eb/N0, the PAPR, average power and peak power obtained depending on the IBO, the CDF BER depending on the IBO and the improvement of the communication by using polarization techniques at the receiver system. These tests took around two weeks transmitting and receiving a total amount of 28 MB of data.The most relevant results obtained from the test performed will be shown in this section. We will analyze the BER obtained depending on the Eb/N0 for each transmitted modulation and modulation order symbolized with M. These results show us the robustness of each modulation in front of the NVIS channel. The results are better when the line takes lower values.At first, we will analyze the BER obtained depending on the Eb/N0 of 18 dB we can obtain a BER of 6 × 10−5 by using an OFDM modulation, a BER of 10−3 by using a 4QAM and a BER of 6 × 10−3 by using a 4FSK. For a lower Eb/N0 as 10 dB, we can see that the results are more similar with a BER of 4 × 10−3 for the OFDM, a BER of 8 × 10−3 for the 4QAM and a BER of 3 × 10−2 for the 4FSK.In b/N0 of 10 dB we can obtain a BER of 4 × 10−3 by using an OFDM modulation, a BER of 2 × 10−3 by using an 8QAM and a BER of 8 × 10−1 by using an 8FSK. For a lower Eb/N0 as 5 dB, we can see that we obtain a BER of 4 × 10−2 for the OFDM, a BER of 7 × 10−2 for the 8QAM and a BER of 2 × 10−1 for the 8FSK.In b/N0 and 16QAM the most robust modulation for low Eb/N0. As we can see for an Eb/N0 of 10 dB we can obtain a BER of 2 × 10−2 by using an OFDM modulation, a BER of 3 × 10−3 by using a 16QAM, a BER of 7 × 10−2 by using an 8PSK and a BER of 2 × 10−1 by using a 16FSK. For lower Eb/N0 as 5 dB, we can see that we obtain a BER of 6 × 10−2 for the 16QAM, a BER of 10−1 by using an OFDM, a BER of 10−1 for the 16PSK and a BER of 2 × 10−1 for the 16FSK.In b/N0 it is important to analyze for each Eb/N0 the CDF of the modulations depending on the order of modulation. By this test, we can obtain more information about the robustness of each modulation with low energy per bit and the probabilities of obtaining a low BER. All graphics of this section shows us in the Y-axis the probability of obtaining a BER lower than a value Xo represented on the X-axis. The results are better when the line is at the top left.Once analyzed the BER depending on the Eb/N0 of 5 dB the behavior of each modulation and robustness. We can see that the OFDM and QAM have the best results in a very similar way. The 4QAM have a probability of 79% to obtain a BER lower than 2 × 10−3 and the OFDM have a probability of a 78% to obtain a BER lower than 3 × 10−3. The 4FSK as we can see is highly affected by the low energy bit transmission with a probability of a 4% to obtain a BER lower than 2 × 10−3. As we can see in this graphic, the OFDM is shown to be a little bit worse than the 4QAM even though in the graphic of −1 we have a probability of 98% for the OFDM, a probability of 95% for the 4QAM and a probability of 64% for the 4FSK. For this reason, for a low Eb/N0 of 5 dB, the OFDM obtains better results in terms of average but for transmission with the minimum errors it is better to use the 4QAM.In b/N0 of 5 dB and order of modulation 8. As we can see, in this case, the OFDM obtains the best results in comparison of the 8PSK and the 8FSK. To obtain a BER lower than 2 × 10−3 we have a probability of 56% for the OFDM and a probability of 45% for the 8PSK. For the 8FSK, we have a probability of a 1% to obtain a BER lower than 4 × 10−3.In b/N0 of 5 dB and order of modulation of 16. In this case, contrary to −3 we have a probability of 54% for the 16QAM, a probability of 10% for the 16PSK, and a probability of a 4% for the OFDM. At this figure, the OFDM is highly affected due to the increase of modulation order. Finally, in this case, the 16FSK has a probability of 10% to obtain a BER lower than 10−1.In b/N0 of 5 dB are analyzed, we will analyze the same modulations with a Eb/N0 of 8 dB. At b/N0. To obtain a BER lower than 6 × 10−3 we have a probability of 97% for the OFDM, a probability of 95% for the 4QAM and a probability of 61% for the 4FSK. For this Eb/N0, we can see in Once the order modulations with a low E−3 we have a probability of 95% for the OFDM, a probability of 88% for the 8PSK and a probability of 4% for the 8FSK.At −2 the OFDM has the same results as the 16QAM. For a lower BER, the 16QAM and the 16PSK are better. In −3 we have a probability of 70% for the 16QAM, a probability of 34% for the 16PSK and a probability of 30% to obtain a BER lower than 2 × 10−3 for the OFDM.At −2 we have a probability of 87% to for the OFDM and 16QAM, a probability of 58% for the 16PSK and a probability of 3% for the 16FSK.For higher BER, to obtain a BER lower than 2 × 10b/N0 and b/N0 received can have high variations. At Taking into account the results obtained in −3, the OFDM with a 4QAM modulation has a probability of 46% to receive a BER lower than 3 × 10−3, the 8PSK have a probability 25% to receive a BER lower than 4 × 10−3 and the OFDM with an 8PSK has 1% to receive a BER lower than 4 × 10−3. As we can see, the OFDM with a 8PSK is shown to be the less robust modulation due to the lack of power to achieve Eb/N0 of 8 dB to maintain its robustness.At Taking into account the results obtained in To achieve that goal, a simple IBOs sweep to find the optimal value has been simulated as is shown below. The simulations have been set with a Rayleigh distribution with an SNR of 0 dB and a second path delayed 250 ms from the first one with half of the power. In The results show that values of IBOs between around 9 and 10 dBs can reduce the BER around 46% in relation to the IBO of 3 dB, so a priori the increase of the IBO value from the initial one, must overcome the results of the tests already done. That improvement makes it possible to make the OFDM more robust than the 4QAM of In a real scenario, we performed several tests to verify the simulated IBO results and analyzed the best option to apply. In addition, IoT needs to have a low power system, so we limit the real tests up to 5 W of average power. Different studies such as ,29,30 sh−3 we have a probability of 80% for the configuration #4, a probability of a 77% for the configuration #3 and a probability of a 71% for the configuration #2, #8 and #9. The rest of results obtained are lower to assure stable communication, as we can see, to obtain the same BER we have a probability of 63% for the configuration #1, we have a probability of 40% for the configuration #6, and we have a probability of 31% for the configuration #5.Through the realization of this test, at By the variation of the IBO, we can analyze that the OFDM with a 4QAM modulation is more robust than the results achieved with the 4QAM narrowband modulation of −3 to a probability of 87% in front of the EGC which improves the probability to receive a BER lower than 3 × 10−3 to an 82%.Finally, by the results obtained, we can apply SIMO techniques by the addition of a second antenna at the receiver system. In Finally, we can conclude that OFDM overcomes narrow-band modulations in scenarios with high multipath such as mornings and evenings for NVIS communications. As we have studied, the OFDM is a good alternative but requires the IBO to be well configured to decrease the PAPR of the modulation signal. This factor is very important for remote sensing where the power consumption is a critical issue.b/N0 graphics, the OFDM modulation seems to be the best option with an IBO of 3 dB and a modulation order 4 in front of the narrowband modulations, as we have seen in b/N0 and we analyze the BER on a CDF, the results change and the 4QAM seems to be the best option. As analyzed, the 4QAM modulation requires less Eb/N0 to obtain better results as we can see at Through the study performed, in terms of robustness if we analyze the BER EFurthermore, to make the NVIS communication more robust, as studied, the addition of a second antenna at the receiver system to apply SIMO techniques, can improve the link. By the use of the polarization technique using the ordinary and the extraordinary waves and the SC polarization technique, the BER results have been improved in a 9% the results obtained as we can see at As analyzed, the mix of the OFDM and QAM depending on the channel scenario is the right approach, especially with the rapid changes of the ionosphere. Through the results obtained, in terms of applications, the OFDM can assure the use of NVIS communication for remote sensors in distances under 250 km, with low-power transmissions and a higher robustness than the HF standards modulations based on narrowband. We conclude that the study of multicarrier modulations benefits the robustness of NVIS communications giving a wide range of possibilities for sensors which need ubiquity to monitoring or sensing multiple facts.−3. In the case of adding a second antenna in the receiver system, the probability will increase to 87% to obtain a BER lower than 3 × 10−3. In the case of need to reduce the average power of the system more than 4.6 W, the receiver node will receive low Eb/N0 signals. In this case, the use of a 4QAM will be more robust than the OFDM modulation.Finally, through the results obtained we propose as the best option for NVIS remote sensing the use of an OFDM modulation for high multipath scenarios with 4QAM subcarriers and an average power transmission of 4.6 W. This configuration offers a bitrate of 2.139 Kbps and a probability of 80% to obtain a BER lower than 3 × 10In