Although exercise prevents cardiovascular disease and mortality, vigorous exercise and endurance athletics can cause atrial fibrillation (AF). However, no large cohort study has assessed the relationship between physical activity and AF in the general population. We assessed the effect of physical activity at different energy expenditures on the incidence of AF. We studied 501,690 individuals without pre-existing AF  included in the Korean National Health Insurance Service database. The physical activity level was assessed using a standardized self-reported questionnaire at baseline. During a median follow-up of 4 years, 3,443 participants  developed AF. The overall incidence of AF at follow-up was 1.79 per 1,000 person-years. The subjects who met the recommended physical activity level  had a 12% decreased AF risk , but not the insufficiently  and highly active subjects . The recommended minimum key target range of physical activity level was associated with the maximum benefit for reduced AF risk in the general population. The dose-response relationship between physical activity level and AF risk showed a U-shaped pattern. Although exceeding the key target range attenuated this benefit, it did not increase the AF risk beyond that during inactivity. The lifetime AF risk is one in four individuals aged >40 years4. Its prevalence will increase rapidly with the aging society, and the public health burden imposed by AF and AF-related morbidity is enormous. The population attributable risk of AF for lifestyle based risk factors is more than half5. Regular physical activity has favorable effects on cardiovascular risk factors, including significant reductions in cardiovascular morbidity and mortality for those meeting the recommended level.Atrial fibrillation (AF) is the most common cardiac arrhythmia worldwide and can increase the risk of stroke, heart failure, dementia, and mortality10. Thus, the effect of different physical activity levels on the incidence of AF varies. However, no eligible studies have addressed whether the public health guideline-recommended physical activity level can positively affect the AF risk. Moreover, the optimal target range for AF prevention remains undefined.The potential benefit of regular physical activity in reducing AF risk may be considerable. However, the relationship between physical activity level and AF risk remains unclear; the reported relationship varied among studies. Moderate physical activity is related to reduced AF risk, while high-intensity or endurance exercise is associated with increased AF risk in younger athletes and middle-aged menIn this study, we evaluated the association of physical activity level and new-onset AF in a community-based database in Korea, which includes >500,000 individuals who underwent health examinations. Moreover, we assessed the effect of different physical activity levels on the incidence of AF and aimed to suggest the optimal target range of physical activity for AF prevention.11. The death registration database of the Korea National Statistical Office, including the date and cause of the death, was linked with the NHIS cohort database. Every population in the sample cohort was linked by the Korean social security numbers, and all social security numbers were deleted after constructing the cohort by providing serial numbers to prevent leakage of personal information. This study was approved by the Institutional Review Board (IRB) of Yonsei University College of Medicine in Seoul, Republic of Korea. The IRB waived the requirement to obtain informed consent, and this study was conducted in accordance with the tenets of the Declaration of Helsinki.This study was based on the Korean National Health Insurance Service (NHIS) sample cohort (from 2002 to 2013) database released in 2015. The NHIS manages all Korean health service databases as a single-insurer system. The sample cohort was extracted via probability sampling from all beneficiaries of the NHIS and National Medical Aid depending on the entire national cohort information. The sample cohort database consisted of the dataset of the sociodemographic information of the beneficiaries; medical claims dataset, including information on the diagnosis based on the 10th revision of the International Classification of Disease (ICD-10) codes, treatment, and admission; and National Health Screening dataset. The National Health Screening dataset comprised a health check-up database conducted for the entire Korean population from 2002 to 2013 by the National Health Insurance Corporation. The National Health Screening Program included chest X-ray, blood test, physical examination, anthropometric measurement, and use of a questionnaire related to physical activity. Approximately 70% of the entire cohort underwent a national health screening program13. The participants were followed up at the time of incident AF, disqualification by the NHIS , or end of the study . The details regarding profile of this cohort and definition of AF have been well described in previously published articles15.This study investigated adults without AF aged >18 years receiving the National Health Screening Program in 2009 among the total population included in the sample cohort. Data of 501,690 participants were available for analyses. To include only newly diagnosed AF, we selected all patients with AF not diagnosed during the 3-year blanking period from January 2002 to December 2004. AF was defined according to ICD-10 code I48 and presence of one hospitalization or two outpatient visits. To evaluate the accuracy of our definition of AF, we conducted a validation study in two hospitals with 628 randomly selected patients with ICD-10 code I48. Their electrocardiograms were reviewed by two physicians. The patients were ascertained to have AF, with a positive predictive value of 94.1%17. Each participant was asked to report the frequency of physical activity weekly in three categories: vigorous (20-minute increments), moderate (30-minute increments), and walking (30-minute increments). Vigorous-intensity physical activity was defined as intense exercise that causes severe shortness of breath such as running. Moderate-intensity physical activity was defined as exercise that causes mild shortness of breath such as brisk walking and bicycling at a usual speed. Walking was defined as usual-pace walking for at least 10 minutes at a time, including transportation. Each type of activity was assigned a metabolic equivalent task (MET) score based on the energy cost19. We computed the energy expended in each activity by multiplying the associated MET score by the minutes on the activity and summed the energy expended across the moderate- to vigorous-intensity activities to estimate the total energy expenditure per week.The National Health Screening Program included health examination and interview. The health interview included a self-administered standardized questionnaire for ascertaining the physical activity status21.The participants were stratified on the basis of their weekly physical activity levels as follows: (1) inactive group: no leisure-time physical activity (LTPA) beyond basic movements; (2) insufficiently active group: having less than the key guideline target range (1–500 MET-minutes/week); (3) active group: meeting the key guideline target range ; and (4) highly active group: exceeding the key guideline target range Descriptive statistics were used to characterize the baseline characteristics and comorbidities. The values were presented as means ± standard deviations or as percentages, as appropriate. Cox proportional hazard regression was used to assess the association between AF and LTPA. Models for clinical variable adjustments were used to assess the association. A multivariable model was adjusted for age, sex, body mass index (BMI), heart failure, hypertension, diabetes, previous myocardial infarction (MI), prior stroke or transient ischemic attack, chronic kidney disease (CKD), smoking, and alcohol drinking. To assess the dose-response relationship LTPA and mortality, we used restricted cubic spline model. We further examined the physical activity levels by separating moderate-intensity and vigorous-intensity activities and creating mutually adjusted models. We also stratified them by potential effect modifiers of age, sex, BMI, waist circumflex, heart failure, hypertension, blood pressure, diabetes, CKD, previous MI, dyslipidemia, smoking, and alcohol drinking. A p-value of <0.05 was considered statistically significant. Statistical analysis was performed using the Statistical Package for Social Sciences version 23.0  and R version 3.4.4 .In total, 501,690 participants (50% women) with a mean age of 47.6 ± 14.3 years were included in the analyses. The baseline characteristics of the study participants stratified according to their LTPA are compared in Table During a median follow-up of 4 years, 3,443 participants  developed AF. The overall incidence of AF at follow-up was 1.79 per 1,000 person-years. The cumulative incidence of AF according to physical activity levels presented in Supplementary Fig. Cox models with cubic splines showed a shape of the dose-response curve for the relationship between physical activity and risk of AF  was associated with the largest benefit for reduced AF risk in the general population, whereas insufficient activity (1–500 MET-minutes/week) and high activity  attenuated the benefit for AF risk reduction. Our analysis found an incremental reduction in incident AF after moderate-intensity physical activity; higher-intensity physical activity had no beneficial effect. The dose-response relationship between physical activity level and AF risk appeared to follow a U-shaped pattern.The present study investigated the association between LTPA and development of AF in a nationwide general population. We assessed the effect of LTPA at different energy expenditures as indicated in public health guidelines for physical activity23.The health benefits of regular physical activity have been well described, including significant reductions in cardiovascular mortality and morbidity for those meeting the recommended key target range. Furthermore, an additional benefit occurred with increasing physical activity level. At the minimum recommended physical activity level, the risk of mortality, coronary heart disease, and heart failure decreased; at two times the minimum recommended level, the risk decreased further24. Some previous studies reported that increasing physical activity was probably associated with an increased risk of AF in men and a decreased risk in women26. However, our study did not find a gender-specific increased risk of AF with high volume physical activity. We believe the conflict results from different study populations. Previous studies reporting increased risk with higher physical activity level were mainly conducted among middle aged men or endurance athletes28, whereas our analyses conducted from general population with broad age. Zhu et al.25 meta-analysis reported that male individuals with intensive physical activity had a slightly higher risk of developing AF, but there was a significantly reduced risk of incident AF in female. Interestingly, the meta-analysis showed that increasing physical activity was probably associated with an increased risk of AF in middle- or young-aged men. In addition, the meta-analysis included only western countries data. The pattern of risk for AF with increasing physical activity level vary according to study characteristics. Therefore, self-reported physical activity, widely varying categorizing of the activity, vary in definition of AF and different cultural patterns of sport seem to limit the comparative interpretation of existing studies30.In this nationwide population-based large cohort study, the subjects who met the key minimum recommended target range by performing moderate- or vigorous-intensity LTPA had a 12% lower AF risk than the inactive subjects. Those exceeding the key minimum recommended target range had no significant risk reduction. Our findings are consistent with those of previous studies supporting that moderate but not vigorous physical activity decreases the AF risk. However, a higher activity level did not significantly increase the risk of AF compared with inactivity. The subjects who engaged in highly active LTPA did not appear to be at an increased risk of AF compared with those who had no LTPA. A meta-analysis including 18 cohort studies and one cross-sectional study reported that the dose-relationship between physical activity and AF had a J-shaped pattern, and a physical activity exceeding 1,200 MET-minutes/week was not associated with AF risk7. Our findings indicate the uncertainty of the nature of the relationship at higher physical activity levels and the complex role of physical activity in modifying the risk of AF.Interestingly, there was no difference in the cumulative incidence of AF between highly active and inactive groups in men (Supplementary Fig. 31.There are several mechanisms underlying the complex association between physical activity and AF. Physical activity can potentially reduce the risk of AF through beneficial effects on cardiovascular risk factors. Conversely, long-term high exercise levels may lead to remodeling of the heart and alteration of the autonomic nervous system32. In the separate intensity model, the AF risk significantly decreased after moderate-intensity LTPA but not after vigorous-intensity LTPA. A small number of studies have reported the AF risk according to the intensity of physical activity. The relationship between exercise intensity and AF risk suggests a curvilinear response with diminishing benefit or even a risk with the most intense exercise33. Mozaffarian et al. reported that a significant reduction in the AF risk could be observed with moderate- but not high-intensity exercise6. Similarly, a Norwegian community-based cohort study reported that a significant reduction in the AF risk could be observed with moderate-intensity activities such as walking and cycling, but not higher-intensity activities30. We believe our data are of interest because they expand our understanding of the complex role of physical activity in modifying the risk of AF in the general population. Moderate physical activity may reduce the risk of AF via modified cardiovascular risk factors, e.g., by improving weight, blood pressure, inflammation, glucose level, and lipid control36.The current public health guideline did not specifically consider the relative value of different physical activity levels such as moderate- and vigorous-intensity physical activities37, increased atrial ectopic burden38, vagal enhancement39, and atrial dilatation and fibrosis40. These mechanisms are widely documented in long-endurance training and could counteract the beneficial effect of moderate physical activity on the AF risk41. Further studies designed to measure physical activity exposure in terms of energy expenditure are needed to clarify the relationship between different intensities of physical activity and AF risk.However, this favorable effect of moderate physical activity on AF may be mitigated by chronic exposure to vigorous physical activity, which generates structural and functional cardiac adaptations that hinder the reduction of the risk of AF. The possible mechanism of the increased AF risk in subjects exposed to vigorous physical activity may be higher inflammation and oxidative stressA major strength of this study is its large sample size with a broad age range from a representative nationwide cohort, and that the uniform physical activity categories used matched the levels described in the current public guidelines. In addition, limited data are available to evaluate the AF in relation to LTPA in Asian population. To the best of our knowledge, this was the largest Asian population-based study investigating the association between physical activity and AF. However, some limitations must also be considered.42, and validity of IPAQ based self-reported physical activity questionnaire has been confirmed in several studies and has yielded valuable results to date43. In addition, although the South Korean society has changed radically and has become more westernized, caution is needed for generalization of our results to western countries owing to racial, ethnic, and geographic restrictions. This study is potentially susceptible to errors arising from coding inaccuracies and cases of asymptomatic paroxysmal AF may have been missed because the research used administrative database. To minimize this problem, we applied the definition that we already validated in previous studies that used the Korean NHIS sample cohort and the diagnostic reliability of cohort data was high15. The validity of hazard ratios depend on the completeness of follow-up because the analysis was performed retrospectively. The NHIS in Korea is a universal coverage and single-insurer system, we believe that very small participants were lost to follow-up. Unfortunately, we were unable to adjust for variables that were not included in the cohort, such as occupational physical activity, echocardiogram and obstructive sleep apnea data.The limitations of this study include the reliance on the self-reported physical activity, which was reported at a single time point. This may cause inaccurate measurements of self-reported LTPA habits, and the conditions at the time of questionnaire completion may not represent the actual LTPA conditions throughout life. Further, behavioral changes during the follow-up period could not be assessed in our study. Nevertheless, self-report questionnaires may provide a reliable approximation of PA at a population levelMeeting the recommended key target range of physical activity was associated with the maximum benefit for AF risk reduction in the general population. The dose-response relationship between physical activity level and AF risk showed a U-shaped pattern. Although exceeding the key target range attenuated this benefit, it did not increase the risk of AF beyond that during inactivity. Our findings support the current public guideline-recommended 150-minute/week moderate-intensity physical activity for achieving health benefits. Although vigorous LTPA should not be discouraged for those who want a higher intensity of activity, our results indicate that moderate-intensity exercise is more recommended to achieve substantial health benefits for AF risk reduction.Supplementary Information


This study examines the impact of the transition from ICD-9-CM to ICD-10-CM diagnosis coding on the recording of mental health disorders in electronic health records (EHRs) and claims data in ten large health systems. We present rates of these diagnoses across two years spanning the October 2015 transition.Mental health diagnoses were identified from claims and EHR data at ten health care systems in the Mental Health Research Network (MHRN). Corresponding ICD-9-CM and ICD-10-CM codes were compiled and monthly rates of people receiving these diagnoses were calculated for one year before and after the coding transition.For seven of eight diagnostic categories, monthly rates were comparable during the year before and the year after the ICD-10-CM transition. In the remaining category, psychosis excluding schizophrenia spectrum disorders, aggregate monthly rates of decreased markedly with the ICD-10-CM transition, from 48 to 33 per 100,000. We propose that the change is due to features of General Equivalence Mappings (GEMS) embedded in the EHR.For most mental health conditions, the transition to ICD-10-CM appears to have had minimal impact. The decrease seen for psychosis diagnoses in these health systems is likely due to changes associated with EHR implementation of ICD-10-CM coding rather than an actual change in disease prevalence. It is important to consider the impact of the ICD-10-CM transition for all diagnostic criteria used in research studies, quality measurement, and financial analysis during this interval. Although the International Classification of Diseases Ninth Revision, Clinical Modification (ICD-9-CM) was developed for systematic study of illness, it is an essential component of the structured language of health care financing and evaluation of medical care. Electronic health records (EHRs), incentivized by the Health Information Technology for Economic and Clinical Health (HITECH) Act of 2009, significantly changed the process for collecting diagnosis data, eliminating paper and shifting the workflows of providers and coders 2. Most cIn contrast, the recent adoption of International Classification of Diseases Tenth Revision, Clinical Modification (ICD-10-CM) coding in the United States occurred nationwide on October 1, 2015. ICD-10-CM represents a major revision, designed to better support the role of coding in reimbursement, quality measurement and monitoring 7 and in An abrupt shift in coding or terminology mapping would be more problematic for activities dependent on a stable longitudinal relationship between diagnostic codes and clinical reality. That stability is essential for public health surveillance, health care quality metrics, and evaluating the impact of care improvement interventions. For example, amid increasing opioid-related mortality and federal and state efforts to halt and reverse the trend, ICD-10-CM expanded the number of relevant codes almost 5-fold. Analysis of opioid-related hospitalizations, which increased 5 percent and 3.5 percent per quarter before and after the ICD-10-CM, respectively, increased 14.1 percent between the last quarter coded in ICD-9-CM and the first quarter coded in ICD-9-CM  and to e79The Health Care Systems Research Network Virtual Data Warehouse (HCSRN VDW)  providesDiagnoses were extracted from federated data warehouses containing electronic medical record and insurance claims data  from OctHealthPartners (Minnesota)Harvard Pilgrim Health Care (Massachusetts)Henry Ford Health System (Michigan)Baylor, Scott & White Health (Texas)Six Kaiser Permanente regionsColoradoGeorgiaHawaiiSouthern CaliforniaWashingtonNorthwestThese health care systems serve an annual population of over 8 million members which reflects the demographic diversity of the associated geographic areas . Responshttps://github.com/MHResearchNetwork/Diagnosis-Codes. In each health system the monthly diagnosis rates for each class of 8 categories of diagnoses were calculated as the total number of enrolled members receiving at least one diagnosis in that category during that calendar month divided by the total number of members enrolled during that calendar month.Definitions of mental health conditions for ICD-10-CM were developed using the ICD-9-CM definitions developed by the MHRN  and mappWhere discontinuities were found, we stratified results by site and demographic variables. We also explored the source EHR data supporting the interface allowing clinicians to search for diagnosis codes. As with most EHRs, clinicians’ recording of encounter or billing diagnoses at these sites allowed either direct entry of diagnosis or entry of free text leading to suggested diagnosis codes. Each EHR database may include several commonly used free-text terms mapping to a single ICD-9-CM or ICD-10-CM diagnosis code.Figure In contrast, the rate of psychotic disorder diagnoses other than schizophrenia decreased by almost 40 percent at the time of the transition to ICD-10-CM and remained relatively stable thereafter. Figure Sites 1 and 4 were chosen for investigation of text associations with diagnosis codes in the EHR clinical interface because of a larger and smaller relative decrease in rate of other psychotic disorder diagnoses. As shown in Table At site 1, ICD-9-CM code 298.9 was linked to 31 possible text descriptions. Of these 31 descriptions, eleven contained the word “psychosis”, eleven contained the word “confusion” and five contained the word “dementia.” Only 16 of these 31 terms were mapped to a corresponding ICD-10-CM code of F29 . As shown in Figure Figure Using medical records data from ten large health systems, we find that rates of many mental health diagnosis categories remained relatively stable or increased or declined gradually during the two years before and after the transition from ICD-9-CM to ICD-10-CM, and these trends were generally similar across the ten individual health systems. Our findings were also consistent with the analysis by Yoon and Chow, who found significant but small changes in annual rates of depression, schizophrenia, and bipolar disorder between 2014 and 2016 in the Veterans Affairs (VA) health care system .Uniquely, psychotic disorder diagnosis rates decreased abruptly in October 2015 by more than one third; this decrease in other psychotic disorder diagnoses was unexpected. Although schizoaffective disorder moves from a subtype of schizophrenia to its own category, and three ICD-9-CM codes for other psychosis map to a single ICD-10 code as shown in Table The decrease in rates of psychosis, specifically unspecified psychosis, is significant for early intervention efforts . In our However, data presented here were limited to diagnostic codes ascertained from health system EHRs or insurance claims. We were not able to investigate or confirm accuracy of diagnoses using actual clinical records. Neither were we able to conduct any structured examinations or other standardized assessments. Consequently, we cannot directly assess the validity or rate of false positive error for diagnoses before or after the transition to ICD-10-CM. Although chart review akin to that performed for ICD-9-CM codes  will be All sites in this study shared the same EHR software vendor, although methods of implementing the ICD-10-CM schema differed. We cannot be certain that our findings would generalize to other settings using different EHR systems. In fact, the effect of the transition to ICD-10-CM on rates of psychosis diagnoses varied considerably among the ten health systems contributing data to this analysis. The pattern of text labels for ICD-9-CM and ICD-10-CM codes we observe in these health systems may vary across EHR products or across different implementations of the same product. The most general implication of our findings is that the specific EHR algorithms used to facilitate diagnosis code selection can impact the apparent frequency of a condition, and changes in the incidence or prevalence of any diagnosis during the period from 2015 to 2017 should be carefully interpreted and further investigated.The strengths of this study include a large sample size and the ability to investigate the functioning of the clinical user interface. In addition to offering reassurance regarding 7 of the 8 mental health conditions we analyzed and specific guidance about interpretation of changes in coding of psychotic disorders, our findings also illustrate generalizable principles for exploring anomalies or unexpected findings in data derived from health records. First, analyses stratified by health system, data source, and/or demographic groups are often illuminating. In this study, the finding of sudden decrease in diagnosis of other psychotic disorder was further explored with analyses stratified by health system and age. The marked site and age differences seen in those stratified analyses pointed to differences in coding systems with a preferential effect on older adults. Second, local knowledge of technical and organizational influences on coding or recording is invaluable. In this specific case, local examination of the mapping of text descriptors to a single diagnosis code led to the putative source of a dramatic, but artefactual, shift in diagnosis rates.The impact of the transition from ICD-9-CM to ICD-10-CM appeared to be minimal for 7 of 8 mental health diagnosis categories assessed. For the exception, psychotic disorders excluding schizophrenia and schizoaffective disorder, our findings suggest that the implementation of ICD-10-CM may have resulted in more specific use of certain codes in ten health systems, resulting in a spurious decrease in the rate of recorded diagnosis for psychosis. A more general lesson from these results is that the linkage of diagnosis codes with specific search terms in clinical terminology tools can impact clinical usage enough to cause an apparent change in prevalence. These findings support the recommendation that trend analysis and validation of diagnosis codes after the ICD-10-CM transition is necessary for all users of this clinical data.The additional file for this article can be found as follows:10.5334/egems.281.s1Supplemental Figure 1.Monthly rates of six mental health conditions, by site.


Severe plastic deformation techniques, such as high-pressure torsion (HPT), have been increasingly applied on powder materials to consolidate bulk nanostructured materials. In this context, the aim of the present study is to compare the plastic deformation characteristics during HPT of two distinct Mg-based powder precursors: (i) atomized micro-sized powder and (ii) condensed and passivated nanopowder. Dynamic recrystallization could take place during HPT consolidation of the atomized powder particles while the oxide pinning of the grain boundaries restricted it for the condensed powder. Consequently, there have been substantial differences in the development of the microstructure, texture, local strain heterogeneities, and hardness in the two types of consolidated products. Different types of local strain heterogeneities were also revealed in the consolidated products. The associated diversity in microstructure within the same consolidated product has been demonstrated to have an effect on the hydrogen activation kinetics to form hydrides for these Mg-based materials that could be suitable for solid state H-storage applications. Severe plastic deformation (SPD) techniques are well known for their effective potential to produce ultrafine-grained/nanocrystalline bulk materials with enhanced mechanical and functional properties for a large variety of metal systems ,2. It isMagnesium-based materials are regarded as potential structural elements in the automotive, aerospace, and biomedical applications mainly due to their lightweight, low cost and excellent specific strength . The des95Zn4.3Y0.7 alloy was processed by HPT consolidation at room temperature as well as at 100 °C, and the superior mechanical properties of this alloy were associated with the ultrafine-grained microstructures accompanied with a high density of dislocations and also due to the significant equilibrium grain boundaries attained at elevated temperature [To date, there have been limited studies ,27,28,29Although the feasibility of HPT processing is, in the vast majority of cases, appreciated for fabricating thin samples with thickness of around 1 mm ,11,12,13In this context, motivated by the potential advantages of SPD powder consolidation, and also by the difficulties associated with the conventional processing of Mg-based materials, the present study focuses on HPT consolidation of two kinds of Mg powder precursors: atomized micro-sized powder produced by gas atomization and condensed ultrafine powder obtained by arc-plasma condensation. Since the initial powder particles were very different , it coulTwo kinds of Mg powder precursors—atomized micro-sized powder produced by gas atomization and condensed ultrafine powder obtained by arc-plasma condensation—were employed for HPT-assisted powder consolidation at room temperature. Commercial purity Mg (99.8%) was gas atomized by SFM SA  to produce micro-sized Mg powder with a particle size distribution in the range of 10–70 µm. Both Mg powder precursors were separately processed by HPT processing at room temperature. A two-step HPT procedure was followed: step 1—a pre-compacted body in disk shape was produced by uniaxial compression of the powder, and step 2—torsional straining by HPT was imposed on the intermediate disk. Both steps were carried out at room temperature. Details can be found in our recent publication  where a The phases in the initial powders as well as in the HPT-consolidated products were identified by X-ray diffraction (XRD) using a powder X-ray diffraction apparatus  using a diffracted beam monochromator and a conventional copper target x-ray tube set to 40 KV and 30 mA. The XRD data were obtained under the following conditions: step size 0.02°, scan speed 10°/min. The JADE software  [The morphology and the microstructure of the initial powders and their consolidated products were examined by scanning electron microscopy (SEM) using a field emission gun scanning electron microscope . Mechanical polishing was preliminary carried out on these specimens and was found sufficient to observe the secondary phases, while a subsequent etching with an acetic glycol solution was required to reveal the grain boundaries. The grain orientations and the related microtexture were materialized by using regular electron backscatter diffraction (EBSD) technique for the micro-HPT product, and a SEM-based transmission Kikuchi diffraction (SEM-TKD) facility for the nano-HPT product. For the EBSD preparation, the samples were mechanically polished down to 0.05 μm diamond using a mixture of glycerol and ethanol (Ratio 1 for 3) lubricant and a final rising using pure ethanol. The details of this TKD facility and its acquisition techniques can be found in Ref. . AccordiR, 0.3R, 0.5R, 0.7R, and 0.9R radial positions in the middle plane and also on some additional cross-sectional planes across the thickness-height .For hardness measurements, the HPT-disks were cut diagonally, and the cross-sections were polished mechanically with abrasive papers and with cloths using diamond paste to a mirror-like finishing. Vickers microhardness was measured using a Leitz Micro Hardness tester, for a dwell time of 15 s with a load of 50 g. In order to obtain the radial as well as axial distributions of the microhardness, the measurements were conducted at 0.1The hydrogen activation characteristics of the two HPT-consolidated products were investigated using a Sievert-type pressure-composition-temperature (PCT) volumetric apparatus . Prior to hydrogenation, the bulk HPT-products were broken into micrometer size particles (using a ceramic mortar) to fit into the testing vessel. The hydrogen activation was carried out at 400 °C for 8 h under a hydrogen pressure of 3.5 MPa. In order to get insights into the effects of severe plastic deformation (SPD) processing routes on the hydrogen sorption properties of Mg, the initial powder precursors were also tested using identical experimental conditions.2 was also identified through its (101) reflexion in the condensed powder and its nano-HPT product. This phase along with MgO oxide was formed during the controlled passivation process conducted in the mixture of Ar + normal air. In contrast, the atomized powder and its micro-HPT product did not show such kinds of additional peaks  for both powder systems under identical experimental conditions. Grain orientation mapping for the deformed samples was carefully acquired by using a normal EBSD technique for the micro-HPT product, while a SEM-based TKD technique was used for the nano-HPT products due to their ultra-fine structures. The local EBSD and TKD measurements were carried out at the periphery and on the middle-thickness of the HPT-disk, and the corresponding results are described in the following subsections for the two types of consolidated products.In order to gain some insights into the HPT consolidation deformation behavior of the Mg powder particles, some additional samples were processed at lower level of shear strains .The HPT consolidation of atomized powder only up to 1/2 turn has led to the formation of recovered/recrystallized microstructures see a. The grtextures . It has textures , or in Htextures  of pure Further torsional straining by 3/4 and 2 turns led to recrystallized microstructures accompanied with equiaxed grain-structures see d,g. The The microstructure of the HPT-compacted nanopowder was examined by transmission Kikuchi diffraction (TKD) because of the much smaller grain size. The TKD technique used in our laboratory is unique in the sense that it is applied in a direct on-axis configuration permitting rapid and accurate measurements . At the c-axes should be positioned at the top and bottom parts of the pole figure in At the early stages of deformation , the TKD orientation map in For the subsequent deformation through 3/4 and 2 turns, a rather homogeneously deformed microstructure was developed in the HPT-products see d,g. In bThe mechanical strengths of the 2 turns HPT products were characterized by Vickers microhardness across the radial as well as the axial directions; the results are shown in Because of the presence of finer grains and oxide particles, the hardness of the nano-HPT product is always twice higher than that of the micro-HPT product. It is apparent from As recalled by the data given in In the case of the nano-HPT product see , the harThe 2 turns HPT products were analyzed for H-sorption properties during the first hydrogenation. For the ultrafine condensed powder and its nano-HPT product see b, the efIt was revealed from the present study that the nature of the initial powder precursors had significant impacts on the powder consolidation behavior. The evolutions of the microstructure, the texture and the microhardness for the two HPT-consolidated products were significantly dissimilar in nature. They also showed distinct hydrogen sorption characteristics for the first hydrogenation cycle. These aspects will be discussed hereafter.It has been a great concern for long time that processing of Mg based materials through powder metallurgy routes inherently induces significant difficulties due to the high reactivity of the powder particles towards atmosphere that rapidly generates impervious oxide layer around the powder particles that prevent subsequent sintering ,22,23. DThe nature of the powder precursors had significant influences on the development of the microstructure. This is particularly true for the final attainable grain size which depended essentially on the amount of oxide particles present in the deformed products. While a saturation grain size of about 2 to 3 µm is generally obtained for dynamically recrystallized HPT Mg disk deformed from bulk precursors that did not contain oxides ,36, the B fibre was somewhat deviated from its ideal position with increasing shear strain; it was tilted against the shear sense  the HPT-consolidated products always showed faster absorption kinetics in comparison with their original powder precursors. Indeed, the torsional straining of the powder particles introduced numerous structural defects in the Mg matrix  that are known to promote the hydrogen activation ,37,52,53 hydride ,55, must[2 layer . When th[2 layer , an inte[2 layer ,34,35.The aim of the present study was to compare the plastic deformation characteristics of 3 mm thick disc obtained by high-pressure torsion (HPT) of two distinct powder precursors: (i) atomized micro-sized Mg (10–70 µm) powder particles containing 2–5 µm grains to consolidate into the so-called micro-HPT disk and (ii) condensed nano-sized Mg (50–800 nm) single grain powder particles that were subsequently passivated to consolidate into the so-called nano-HPT Mg/MgO disk.The nature of the initial powder precursors had significant influences on the microstructure and texture evolutions in the two types of HPT products as well as on the development of local strain heterogeneities.The HPT consolidation of the atomized powder particles led to heterogeneous microstructures across the through thickness: recrystallized equiaxed 1 µm grains at the middle section that sustained the highest strain and rather heterogeneously deformed microstructures at the top and bottom regions of the disk.The HPT consolidation of the condensed powder particles led to a Mg + 5%MgO composite having a rather more homogeneously deformed microstructure consisting of elongated recovered nanometric Mg domains pinned by the nano-sized Mg oxide particles. Some strain heterogeneities have, however, developed from bottom to top of the disk where the average thickness of the elongated recovered grains varied from about 100 to 500 nm.Due to the plastic shear deformation and subsequent dynamic recrystallization, a strong basal texture has developed in the micro-HPT product. Comparatively, the presence of oxides that promoted dynamic recovery and possible powder particle sliding, have hindered the evolution towards the ideal shear texture in the nano-HPT product.The hardness being essentially affected by the local grain size and local amount of oxide particles, the hardness of the nano-HPT product obtained from the fine condensed and passivated powder exhibited twice higher hardness than the micro-HPT product: 108 Hv and 55 Hv, respectively. Also, the hardness values in our micro-HPT product obtained from the atomized powder precursor are always higher than the ones reported on HPT deformed disk of pure Mg for which the precursor was a bulk sample ,36.The local hardness varied in the consolidated products with the local amount of strain and depended on the mechanism of deformation accommodation. For the micro-HPT product obtained from the atomized powder, the increasing amount of local strain hardened the materials until dynamic recrystallization occurred. Comparatively, for the nano-HPT product obtained from the nano-sized Mg/MgO core-shell powder, the dynamic recovery process led a continuous decrease in local hardness with the amount of strain.After HPT deformation, likely due to an increase in nucleation sites for the hydride formation, the kinetics of the H pick up was significantly improved. For example, the nano-HPT product took only 5 min to reach 4 wt.% H-uptake compared to 68 min for its initial condensed powder precursor. For the heterogeneous micro-HPT product, the fastest kinetics was reported for the central part of the product that was properly deformed and developed a finer recrystallized microstructure. Unfortunately, this faster kinetics was always accompanied with a lower H-storage capacity. For example, in the case of the condensed nano-sized powder, the capacity was reduced from 7.2 wt.% to 5.7 wt.% after HPT.The effect of the powder type was examined in terms of (i) microstructure and texture evolution mechanisms, (ii) development of strain heterogeneities and related local mechanical strength (by microhardness), and (iii) H-activation ability by hydrogenation measurements. The following main conclusions are listed hereafter.


We report a self-triggered asynchronous optical sampling terahertz spectroscopy system based on a single bidirectional mode-locked fiber laser and plasmonics-enhanced photoconductive nanoantennas. The fiber laser generates two optical mutually coherent pulse trains with a stable repetition rate difference, enabling time-domain terahertz spectroscopy without using any mechanical delay line, stabilization electronics, or external trigger. The resolved terahertz spectra over a 0.1–2 THz frequency range and a 30-second measurement time show more than a 70-dB dynamic range, revealing water absorption lines matching the HITRAN database, through a light-weight and compact spectroscopy setup. However, most experimental implementations make deployment of the technology outside the laboratory environment difficult due to complex measurement requirements.Time-domain terahertz spectroscopy (THz-TDS) has diverse applications in material characterization, chemical detection, and industrial quality controlTHz-TDS systems consist of a pulsed terahertz source and detector triggered by a femtosecond optical pump and probe beam, respectively. Generated terahertz pulses are incident on the sample to be analyzed and the transmitted or reflected terahertz pulses, which carry the sample’s spectral signature, are detected. A variable time-delay between the pump and probe beams allows temporal scanning of the generated terahertz pulses after interaction with the analyzed sample. The first THz-TDS systems used mechanical delay lines to scan across the temporal width of terahertz pulses, obtaining timing precision using quality optomechanics. The use of such delay lines however constrained THz-TDS designs in terms of acquisition speed, frequency resolution, and overall size of the measurement apparatus. These limitations were also found in optical pump-probe experiments in which scanning delay lines were used.14, which controls the time-delay by tuning the repetition rate of the femtosecond laser. Although high spectroscopy speeds can be achieved using this approach, the tuning range constraint of the femtosecond laser repetition rate limits the frequency resolution of the spectroscopy system. In addition, the scanning time window is predefined when using this approach and an additional optical delay stage should be added to the system for an initial calibration. Another alternative technique for achieving high spectroscopy speeds is electronically-controlled optical sampling (ECOPS)15, which uses two femtosecond lasers. The difference between the repetition rates of these lasers is controlled electronically, usually by a piezoelectric transducer tuning the cavity length of one of the lasers. However, similar to OSCAT systems, an additional optical delay stage is necessary for an initial system calibration and adjustment of the scanning time window. Moreover, the use of two femtosecond lasers makes the system less compact than the traditional THz-TDS systems. High-speed THz-TDS using a single laser was recently demonstrated through polarization-controlled optical sampling (SLAPCOPS)16. The system uses a unique laser consisting of two ring resonators sharing the same pump diode and gain section. However, similar to OSCAT and ECOPS techniques, SLAPCOPS THz-TDS requires a phase control unit to precisely control the repetition rate difference between the pump and probe laser pulse trains and the jitter in the phase-control electronics can have detrimental effects on the spectral accuracy, dynamic range, and bandwidth of the spectroscopy system.A promising alternative for introducing a variable time-delay between the pump and probe beams is optical sampling by cavity tuning (OSCAT)19. Later, it was proved to have similar utility in THz-TDS and terahertz asynchronous optical sampling systems (ASOPS-THz-TDS) based on electronic delay lines or multiple lasers were developed over the last few years23. ASOPS-based terahertz dual-comb spectroscopy systems were also developed, which provide frequency resolutions finer than those of ASOPS-THz-TDS systems25. These ASOPS-based terahertz spectroscopy systems also eliminate mechanical delay lines and speed up data acquisition considerably. However, mechanical complexity is traded for electronic complexity, often requiring numerous phase-locked loops or stabilization electronics. Moreover, these systems often utilize two femtosecond lasers, which increase the complexity, size, and cost of THz-TDS systems.Another promising alternative for high-speed THz-TDS is asynchronous optical sampling (ASOPS). ASOPS was first demonstrated in the context of optical pump-probe experiments to address the limitations of mechanical delay lines40. In some of these systems, the difference in repetition rates is stable enough to support ASOPS-THz-TDS and dual THz comb heterodyning37. For all MML platforms, pulse repetition rate differences are determined predominantly by linear effects of group velocity dispersion and birefringence. The effect of dispersion and birefringence on group delay, τ, and repetition rate difference, Dnet (ps/nm) is the net cavity dispersion, l is the cavity length. When there is no average birefringence between the two pulse trains and the oscillator is wavelength multiplexed with a filtering mechanism, as in the recent demonstrations of ASOPS-THz-TDS and dual THz comb heterodyning37, very small sampling steps may only be accomplished by cavity dispersion management since there is a practical limit to repetition rate. By contrast, bidirectional schemes and polarization multiplexed systems do not have this limitation since they do not constrain the difference in center wavelength, and polarization multiplexed systems have the additional ability to offset group dispersion delay with birefringence40.A number of multiplexed mode-locked laser (MML) platforms have emerged recently, which are capable of emitting the pump and probe pulses from a single cavity simultaneously. An improved timing performance can be achieved by MMLs in free-running mode since environmental effects such as vibration and temperature variations tend to affect both pump and probe repetition rates similarly. MMLs may be multiplexed in wavelength, polarization, or propagation direction41 and the efficient terahertz power generation and detection of plasmonics-enhanced photoconductive nanoantennas49. In doing so we eliminate the mechanical and electronic complexity and perform THz-TDS over a 0.1–2 THz bandwidth with dynamic range of more than 70 dB, without using any moving parts and/or servo control electronics.In this report, we demonstrate a system for self-triggered ASOPS-THz-TDS using bidirectional operation of a single mode-locked fiber laser27. The oscillator is a dispersion-managed soliton bidirectional oscillator with a net anomalous cavity dispersion41, which uses a carbon nanotube saturable absorber and requires tuning of a polarization controller to obtain bidirectional mode-locking. The oscillator has two outputs in the clockwise (CW) and counterclockwise (CCW) directions. Both oscillator outputs are made polarization maintaining (PM) to align the optical pump and probe fields reliably along the optimum axis of the plasmonics-enhanced photoconductive nanoantennas. These outputs are only 0.5 nm apart in center wavelength  anti-correlated and their noises add:Assuming that the repetition rate σM/M, which we term the ‘magnification deviation’, directly relates to the error in the asynchronous sampling rate, yielding non-uniform sampling. While each repetition rate fr may have a deviation /fr of 1 part in 107–109 over a single trace , for the repetition rate difference ∆fr a comparable stability would require a µHz or lower over the same duration26. Thus, it is clear that even though experiments have shown repetition rate differences to drift together in multiplexed single-oscillator systems like ours, the drift in ∆fr is the dominant factor controlling the quality of the ASOPS-THz-TDS. In this experiment we observed a slow drift in ∆fr, which nevertheless allowed for averaging of 1000 traces over a ∼ 30 second interval to enhance the dynamic range of our ASOPS-THz-TDS.The quantity 46. The generated terahertz radiation is routed and focused onto a plasmonic photoconductive nanoantenna detector array47 fabricated on a low-temperature-grown GaAs substrate using two off-axis parabolic mirrors. The plasmonic photoconductive nanoantenna detector array is designed to operate at ~780 nm wavelength, so the other laser output passes through a periodically-poled Lithium Niobate (PPLN) crystal for second harmonic generation and the generated optical beam is focused onto the plasmonic photoconductive nanoantenna detector array. The generated photocurrent by the terahertz detector is amplified using a current amplifier  and recorded using a PCI digitizer card (AlazarTech ATS660). A trigger signal is typically required in ASOPS THz-TDS measurements to create an accurate time-base for the captured temporal traces. To generate this trigger signal, a small portion of the two laser output pulses is coupled and the interfered beam is sent to a photodetector (New Focus Model 1611). The photodetector output passes through a bandpass filter to obtain the generated interferogram from the two overlapping optical pulses. The generated interferogram, which serves as the trigger signal, is sent to the PCI digitizer for data acquisition and time-base creation.A schematic diagram of the THz-TDS setup is sketched in Fig. 30. The spectral lines of water vapor at 0.557 THz and 0.753 THz are clearly observed in the resolved power spectrum.The acquisition time of a single photocurrent trace is inversely proportional to the repetition rate difference of the two laser outputs. The single-trace photocurrent acquisition time for the constructed THz-TDS system is 33 ms. Figure fr, stays almost constant over a long time, no post-processing is required to fix the time-base of different captured photocurrent pulses. To demonstrate the effect of averaging multiple photocurrent traces, power spectra obtained over different acquisition times are compared in Fig. In order to reduce the noise level, increase the bandwidth and dynamic range of the obtained terahertz spectrum, multiple photocurrent traces are recorded and averaged. Since the repetition rate difference, ∆Next, the trigger system is eliminated and a self-triggered ASOPS THz-TDS system is constructed, which uses the generated photocurrent by the terahertz detector to trigger the digitizer card. The resolved power spectrum of the self-triggered THz-TDS system for a 30-second data acquisition time is shown in Fig. 51 or interleaved sampling53, at the expense of a higher noise and reduced dynamic range.The ultimate factor that limits the frequency resolution of the ASOPS-THz-TDS system is the repetition rate of the laser outputs. However, the frequency resolution cannot usually reach this limit because of the uncertainties added due to the drift in the repetition rate difference of the two laser outputs. Additionally, the output photocurrent time-window duration used for calculating the power spectrum adds another limitation to the frequency resolution. The theoretical limit for the spectral resolution of the presented ASOPS THz-TDS system determined by the repetition rate of the laser outputs is 62 MHz. However, the use of an 800-ps time-window results in a 1.2 GHz spectral resolution. The spectral resolution can be further reduced to 62 MHz by using the full photocurrent temporal span, which naturally results in an increase in noise level and reduction in dynamic range. Moreover, sub-repetition-rate frequency resolution can be achieved by utilizing a dual-comb terahertz spectroscopy system through recording the terahertz pulse trains over long time-windows54 (Fig. To verify the accuracy of the resolved spectra, the frequency of the water spectral lines observed with the ASOPS THz-TDS system based on the bidirectional mode-locked laser is compared with the water absorption lines obtained from the HITRAN databaseEven though we show that there is no difference in terms of operation bandwidth and dynamic range between self-trigger and external-trigger operations, one should remember that the external trigger is necessary to have accurate knowledge of the timescale. Even though self-triggered operation is more than sufficient for various applications of terahertz science and technology, a time reference is still needed for many unique applications of THz-TDS where the temporal position of the measured signal is important.56. Several factors have limited the dynamic range and bandwidth of the demonstrated ASOPS THz-TDS system.Although we have demonstrated ASOPS-THz-TDS with a single free-running laser, reducing the need for a second laser, mechanical delay line, and locking electronics, the performance of the system can still be improved to offer higher dynamic ranges and broader bandwidths than the achieved 70 dB dynamic range over the 0.1–2 THz frequency rangeThe main limitation on the system performance is the shape and duration of the optical pulses generated in the amplifiers using a soliton-compression scheme. Even though CW and CCW arms offer 65- and 75-fs FWHM pulses, respectively, their relatively large pulse pedestals broaden the overall pulse-width used for pumping/probing the terahertz source/detector, thus, ultimately producing slower transient photocurrent and narrower operation bandwidth for the ASOPS-THz-TDS system.fr, is another important factor impacting the most important specifications of the spectroscopy system. These deviations can cause two serious problems: aperiodic sampling with random fluctuations and time-base distortion. As the repetition rate difference drifts during data acquisition, the time difference between the two output pulses from the bidirectional laser varies uncontrollably, leading to random fluctuations in data sampling. An analogy can be made between this uncertainty in the repetition rate difference and the uncertainty in the position of mechanical delay stages used in traditional THz-TDS systems. A delay stage with low accuracy can cause such fluctuations in sampling as well, which are proven to limit the dynamic range of the spectroscopy system57. Similarly, the aperiodic sampling due to the deviations in the repetition rate difference of the two laser outputs is one of the main factors limiting the dynamic range of the presented spectroscopy system. The negative impact of the time-base distortion in the recorded output photocurrent traces is more apparent when averaging multiple traces. If the time-base of the traces are not the same, averaging can degrade the spectral resolution, add undesirable artifacts to the spectrum, and decrease the sharpness of the resolved spectral lines. Again, an analogy can be made between this time-base distortion and the time-base distortion caused by the repeatability of delay stage positions in traditional THz-TDS systems58.Deviations in the repetition rate difference of the two laser outputs, ∆M. While phase-locking electronics may be complex and costly with two laser systems, single multiplexed oscillator ASOPS-THz-TDS might only require stabilizing one degree of freedom for high resolution performance, especially when using an external trigger.Mode-locked oscillators with polarization control are typically sensitive to movement and environmental perturbations like temperature fluctuations and vibration. Thermal stabilization and vibration isolation can help to minimize the fluctuations in optical output power level and deviation of 47. Therefore, adding another amplification stage to the laser would help to increase the dynamic range and operation bandwidth of the ASOPS-THz-TDS system. Moreover, the terahertz detector used in this experiment is designed to operate at a 780-nm wavelength. Second harmonic generation is achieved with 40% conversion efficiency by using a PPLN crystal. The performance of the system would improve with a terahertz detector operating at the laser wavelength while offering similar performance.Both the terahertz emitter and the detector have better performance under higher-power optical illuminationSelf-triggered ASOPS-THz-TDS has been demonstrated with a single bidirectional mode-locked fiber laser and plasmonics-enhanced photoconductive nanoantennas. Terahertz spectra over a 0.1–2 THz frequency range with more than a 70 dB dynamic range are resolved for a 30-second measurement time, revealing water absorption lines matching the HITRAN database, through a light-weight and compact spectroscopy setup.


It has been reported that the frequency bandwidth of capacitive micro-machined ultrasonic transducers (CMUTs) is relatively broader than that of other ceramic-based conventional ultrasonic transducers. In this paper, a feasibility study for orthogonal chirp coded excitation to efficiently make use of the wide bandwidth characteristic of CMUT array is presented. The experimental result shows that the two orthogonal chirps mixed and simultaneously fired in CMUT array can be perfectly separated in decoding process of the received echo signal without sacrificing the frequency bandwidth each chirp. The experimental study also shows that frequency band-divided orthogonal chirps are successfully compressed to two short pulses having the −6 dB axial beam-width of 0.26- and 0.31-micro second for high frequency and low frequency chirp, respectively. B-mode image simulations are performed using Field II to estimate the improvement of image quality assuming that the orthogonal chirps designed for the experiments are used for simultaneous transmission multiple-zone focusing (STMF) technique. The simulation results show that the STMF technique used in CMUT array can improve the lateral resolution up to 77.1% and the contrast resolution up to 74.7%, respectively. It is shown that the penetration depth also increases by more than 3 cm.  Coded excitation, which has employed pulse compression techniques used in radar and sonar systems for decades, can improve the signal to noise ratio (SNR) of medical ultrasound imaging by increasing average power without affecting instantaneous peak power ,2,3,4. AAs an approach to achieve high lateral resolution, synthetic transmit aperture techniques that can provide two-way dynamic focused beam fields in both transmission (Tx) and reception (Rx) have been studied and developed ,17,18. HTo improve the lateral resolution of traditional ultrasound B-mode image without reducing the frame rate, simultaneous transmission multiple-zone focusing (STMF) techniques using orthogonal chirp or Golay coded excitation were introduced ,24,25,26Meanwhile, it has been known that capacitive micro-machined ultrasonic transducer (CMUT) technologies provide unique opportunities to minimize the size and cost of ultrasound scanners by fabricating and interconnecting the front-end circuits into CMUT array with higher performance in terms of features and image qualities ,28,29. MHence, the aim of this study is to demonstrate the feasibility that the 2-D CMUT-on-ASIC array can maximize the advantage of FDMA based STMF technique using orthogonal chirps in both simulation and experimental setups. In this paper, an experimental study on orthogonal chirp coded excitation in CMUT array is conducted which is a world-first work. In the experimental study, 2-D CMUT array integrated with front-end ASICs called 2-D CMUT-on-ASIC array which was previously developed and introduced is used ,36,37,38L sub-band signals are designed inside the frequency bandwidth of a given transducer to have both compression and orthogonal properties. The mutually orthogonal signals are focused at L different depths and simultaneously transmitted with different transmission (Tx) delays. Tx beamformer calculates the Tx time delays for the L sub-band signals according to the Tx foci which are selected by the user. For example, the Tx focusing delays for each focal depth i and j are applied to the corresponding chirps L sub-band signals are transmitted to the medium. On reception (Rx), the received RF (radio frequency) echo signals are amplified in a low noise amplifier (LNA) and a variable gain amplifier (VGA) for the time-gain compensation (TGC), digitized by the analog-to-digital converters (ADCs), and dynamically focused in the Rx beamformer. The Rx beamformer output is then fed to correlators for matched filter processing. The L orthogonal sub-band signals which are individually focused in Tx are separated and compressed into each short pulse. The focused beams are combined to form an ultrasound image by the conventional zone-blending method. Therefore, the final B-mode image with improved image quality is provided by using a conventional echo-processing and digital scan conversion (DSC). An example of the composition result of multiple-zone focused beam-patterns is shown in the left side of L beam-patterns for the focal zones 1 to L are combined. In this way, the lateral resolution is improved by obtaining the multiple-zone focused Tx beam-pattern.The improvement aspect of lateral beampattern is also illustrated in This section describes the encoding and decoding process of the orthogonal chirp coded excitation for the FDMA based STMF technique. The linear FM signal whose instantaneous angular frequency varies linearly with time, called a chirp, can be defined as ,41,42:, yielding:Then, the delayed RF-echo signal is given by:L compressed chirps are independently focused and then each beam having different focal depth is combined to provide the dynamically transmit-focused beam along each scan line. The STMF method can easily be extended for an arbitrary number L, and the L orthogonal chirps are designed based on frequency division within a given transducer bandwidth.Finally, the An experimental setup is shown in For the experiment, all channels for 256 elements were used for plane wave Tx and were measured for Rx echo test. As the property of the CMUT array and ASIC device was introduced in ,34 and tIn the simulation study, the STMF method using the orthogonal chirps designed within the frequency bandwidth of CMUT array is compared to the conventional single-zone focusing (SF) method using a pulsed-wave. The mimicking tissue phantom used in B-mode simulation contains nine point targets, five anechoic cysts located at −10 mm in lateral direction with a start depth of 30 mm, and five hyperechoic masses located at 10 mm in lateral direction with a start depth of 30 mm, and 200,000 random scatters for speckles. The anechoic and hyperechoic targets are separated by 10 mm in depth. All anechoic cysts have a gain of 0, and an increased radius by 0.5 mm from 1 mm to 3 mm in depth. All hyperechoic masses have an amplitude gain of 20 dB compared to the surrounding speckles, and a decreased radius by 0.5 mm from 3 mm to 1 mm in depth.The design details about the 2-D CMUT-on-ASIC array and the property of all the elements are not described here for succinctness and one can refer to ,36,37,38The −6 dB fractional bandwidth of the CMUT-on-ASIC array is 114% of the center frequency of 4.66 MHz as shown in ut 40 dB ,26. To mTx foci of the two chirps are set to six (6) combinations as seen in Two sub-band chirps designed for the experiment are displayed in o (GSNR) ,46. Assuo (GSNR) ,48. TherThe results also demonstrate that the coded excitation technique can be used in lower voltage transmission applications as well. The use of low voltage transmission in CMUT array can be an approach to solve an issue about the generation of harmonic components due to the intrinsic behavior of CMUT array .Comparing the frequency spectrums between before and after matched filtering, it could be seen that the frequency bandwidth after matched filtering narrowed from In the experiment, two sub-band chirps considering different time delay were added and transmitted at the same time. e target ,52. ThusIt was demonstrated that the major benefit adopting STMF technique using orthogonal chirp coded excitation in CMUT was the improvement of contrast resolution. As shown in c2) was focused at this depth in those Figures. Compared to c1) was focused at 60 mm, CNR improvement in At the C1 region (30 mm) which was the focused depth of In terms of contrast resolution based on the evaluation of CNR values, c1 used in c2 used in c2 was used for focusing at 50 mm (P4), which was better than c1 was focused at 50 mm. At P5 target (60 mm), The lateral resolution of B-mode images adopting the STMF technique was improved at every depth (P1~P7) except P3 (40 mm) which was the focus depth of SF method. At P1 target (20 mm) which was the focused depth for low frequency chirp c1 and 18.8% for the high frequency chirp c2 as described in To maintain the axial resolution in this simulation, orthogonal chirps were designed to have almost same bandwidth as that of the pulsed-wave. The −6 dB frequency bandwidth of the two orthogonal chirps were 2.46 MHz (A phantom and in vivo experiment need to be performed to investigate the effects of inhomogeneity and nonlinearity in tissues and the effectiveness in clinical application though the simulation results obtained using the proven and well-established simulator are adequate to ascertain the features and expected benefits of orthogonal chirp coded excitation in the CMUT array.The main goal of this work was to validate that the 2-D CMUT-on-ASIC array can maximize the advantage of FDMA based STMF technique using orthogonal chirps in both simulation and experimental studies. In this preliminary study, experiments were conducted to show that simultaneously transmitted orthogonal chirps designed within the frequency bandwidth of CMUT were successfully separated and compressed into two short pulses from the received signal by performing the pulse compression and separation with the correlators. The experimental results validate that the orthogonal chirp coded excitation in the 2-D CMUT-on-ASIC array is feasible without any distortion in frequency characteristics of transmitted chirps. It has been observed that the frequency bandwidth after matched filtering narrows in the experiment and this should be considered in the design of orthogonal chirps used for the STMF technique. The simulation study was also conducted to quantitatively and qualitatively evaluate the image quality of STMF technique using orthogonal chirp coded excitation in CMUT array. It has been shown that orthogonal chirp coded excitation for the STMF technique in CMUT array provides more improved quality of images in terms of contrast resolution and lateral resolution than previous works. It has been demonstrated that higher frequency chirp provides higher contrast and spatial resolution, and the various combination of Tx foci for orthogonal chirps is feasible for STMF technique in CMUT array. The simulation results support that the image quality can be improved in the STMF technique using two orthogonal chirps designed to be utilized in CMUT array. It has been shown that the axial resolution was better than any other results which were previously introduced as the axial beam-width is not sacrificed due to the wide bandwidth characteristic of the CMUT array in both simulation and experimental results. Accordingly, the wide bandwidth characteristic of CMUT array can maximize the benefit of STMF technique using frequency band-divided sub-band signals without sacrificing the frame rate and axial resolution. The phantom and in vivo study should be performed after the ultrasound system and the CMUT-ASIC array is integrated and the arbitrary waveform generation for orthogonal chirp coded excitation in the integrated system is enabled.


In this paper, metasurfaces with both cross-polarization conversion and vortex beam-generating are proposed. The proposed finite metasurface designs are able to change the polarization of incident electromagnetic (EM) waves to its cross-polarization. In addition, they also can modulate the incidences into beams carrying orbital angular momentum (OAM) with different orders ( The topological charge corresponds to the OAM mode and, theoretically, the OAM mode is vast.The orbital angular momentum of electromagnetic waves has been explored in recent years for its potential applications in wireless communications ,2,3 and The OAM in EM waves is typically generated using techniques like spiral phase plates ,7, spiraCompared to these methods, metasurfaces for generation of beams carrying OAM have advantages including low profile and simple EM wave control, i.e., the magnitude/phase/polarization of the EM waves can be manipulated simply by changing the shape, geometry, size, orientation and arrangement of the structures . ReflectIn this paper, multi-layered metasurfaces generating OAM beams with efficient linear polarization conversion were proposed. The patches on the outer sides of the designed metasurface receive and re-radiate the incident wave, respectively. The cross-polarized transmission is higher than −1 dB around 5.15 GHz with an extremely low co-polarized transmission below −35 dB. The transmission phase can be fully controlled by the length of the stripline in the middle layer. By arranging the metasurface unit cells according to desired phase distributions, the proposed metasurfaces can generate EM beams carrying different modes of OAM. This design method was demonstrated by both simulation and measurement.This paper is organized as follows: p = 17.92 mm, R = 16.64 mm, r = 0.8 mm, w = 1.2 mm, S varies from 1.66 mm to 8.49 mm to achieve a 360A flowchart illustrating the main goal and the adopted methodology of this study is presented in x and y directions), that the polarization of the transmitted wave is converted.The unit cell design takes its inspiration from the patch antenna. The top/bottom layer couples the y-polarized/x-polarized incident wave into the guided mode in the stripline structure and then, the bottom/top layer decouples the guided wave into the x-polarized/y-polarized free space propagation. It is by selecting the positions of the vias in orthogonal direction  on top and bottom layers are shown in The simulated distributions of the electric field component perpendicular to the unit cell  using periodic boundary in l is the topological charge. Therefore, EM beams carrying OAM with an order of l experiences an azimuthal phase change of l defines the helicity of the vortex beam phase distribution. To generate vortex beam-carrying OAM of orders z directions, these two designs have opposite helicities and generate EM beams carrying OAM with orders of The helical wavefront of vortex beams can be expressed by the term The two finite full structure models containing y-polarization and along z direction with a x-polarization, respectively. The simulated transmitted electric field distributions at a transverse plane 250 mm away from the metasurface are depicted in The transmitted phase distributions are shown in The proposed metasurface was fabricated using PCB processing as shown in The fabricated metasurfaces were measured using a vector network analyzer Agilent E8363b  and a two-dimensional near field scanning measurement system. The metasurface was placed between a lens horn antenna (used as the excitation) and a WR-229 open-ended rectangular waveguide probe (used for receiving the OAM carrying beams). The measurement was conducted in the anechoic chamber. The response calibration was used to eliminate the effect of external noise during the measurement. The polarization conversion was confirmed by receiving and analyzing the co-polarization and cross-polarization components of the EM waves, which was realized by rotating the open-ended rectangular waveguide probe. A schema of the measurement devices and settings is depicted in x-polarized transmitted wave with a y-polarized excitation propagating along y-polarized transmitted wave with an x-polarized excitation propagating along z direction. The amplitude distributions shown in The measured amplitude and phase distributions of the cross-polarized transmitted electric field at a transverse plane 250 mm away from the metasurface are shown in The simulated and measured amplitudes of the co-polarized transmitted wave are shown in In conclusion, two polarization conversion metasurfaces generating four different orders of OAM carrying beams (


Millions of Americans have low health literacy, potentially leading to a number of issues including medication errors, hospital admissions, unnecessary emergency department visits, skipped screenings and shots, and misinterpretation of treatment plans. People with low health literacy have less knowledge of illness management, less ability to share in decision-making, and poorer self-reported health status. Addressing health literacy is necessary to improve health care quality, reduce costs, and reduce disparities.The How to Talk to Your Doctor (HTTTYD) HANDbook Program addresses health literacy among rural participants who have low incomes, with a focus on improving health communication among populations that are medically vulnerable by using the HANDbook tool.Participants were recruited from 55 rural counties by county extension agents (CEA) to participate in the 1-hour HTTTYD session. Pre- and post-test surveys were completed. A subset of the sample completed a 3-month follow-up survey.M = 15.99) to post-test (M = 17.76), , was noted. A subset of 166 participants also completed the 3-month follow-up survey. A significant increase in health literacy after participation in the HTTTYD HANDbook program from pre-test to 3-month follow-up was noted; effect sizes ranged from moderate to large.Of the 548 participants who fully completed the survey, a Wilcoxon Signed-Rank Test was performed on 484 of the participants who completed both the pre- and post-test. A statistically significant median increase in overall confidence among the participants from pre- :e103–e109.][The HTTTYD HANDbook program meets recommendations for successful health literacy programs; significant positive outcomes demonstrate program effectiveness. HTTTYD HANDbook program delivery in rural communities by CEAs demonstrates access to understudied and often difficult-to-reach populations. The How to Talk to Your Doctor HANDbook program delivered by county extension agents in rural communities showed capacity to access understudied and often difficult-to-reach populations. The significant, sustained improvement in health literacy noted among program participants demonstrated program effectiveness among those with low health literacy. Health literacy is the degree to which one has the capacity to obtain, process, and understand basic health information and services needed to make appropriate health decisions . Over 80Interventions to improve health literacy in rural populations are particularly important due to the high prevalence of chronic disease and poor health indicators in these communities including high rates of obesity, hypertension, diabetes, and food insecurity . It is cIn response to health literacy concerns, each of the 50 states has created for its own citizens programs intended to improve health literacy . EvidencHealth literacy has different dimensions including reading, comprehending, and communicating medical and health information . Health The HTTTYD HANDbook program was developed and field tested as a single-session program designed for delivery in community-based settings by health educators. HTTTYD sessions typically lasted for 1 hour and were delivered by county Extension educators and trained volunteers in various settings . Site selection is key as the National Academies of Sciences, Engineering, and Medicine  highlighThe HTTTYD HANDbook includes five steps to prepare a person for health care provider appointments. Each step is represented by an individual finger on a hand: (1) remember the things you need to take to your visit; (2) two-minute history: tell your doctor your health problems in 2 minutes; (3) words: repeat instructions and information back in your own words; (4) FORms: don't forget to fill out all your FORms completely; and (5) take your meds: take medications as labeled and take all your medications to your doctor's visit. Teaching techniques used modeling, scenarios, role-play, and Teach Back, which provided participants opportunities to practice new communication skills. Examples of recommended strategies included getting assistance to make a list of questions to take to appointments, writing down prescriptions to take to appointment, writing down reasons for the visit and changes in health status, taking notes during the visit, and requesting written instructions for medicine and treatments. Sessions were designed to minimize confusion and eliminate barriers common for audiences with low literacy. For example, one piece of paperwork was passed out at a time , and question and answer response options were read aloud. HTTTYD HANDbook sessions were most often delivered in small group settings allowing for interactions between participants and trainers. Readability assessment of the HTTTYD Handbook revealed a mean level of 4th grade .This study was designed to answer two fundamental research questions: “What changes were noted in participants' confidence in engaging in communication with their doctors after participation in the HTTTYD HANDbook' program?” and “Were those changes sustained after 3 months?”After Institutional Review Board Approval at the University of Arkansas, participants were recruited from 55 rural counties by County Extension Agents (CEA) by advertising and hosting their own programs or through existing groups at established sites . Participants completed a sign-in slip to document attendance and indicated if they gave permission for a member of the research team to contact them in 3 months to ask follow-up questions. Criteria for participation in the study included written consent from the participant, older than age 18 years, and able to read and write in English at a basic level.1.“How confident are you at being prepared to talk to your doctor?”2.“How confident are you at telling your doctor everything he or she needs to know in a short visit?”3.“How confident are you at repeating back what your doctor tells you in your own words?”4.“How confident are you at taking your meds like the label says to?”The first question was a validated health literacy screening question, “How confident are you at filling out medical forms by yourself?” . Four adThese questions were asked at three different time points: the beginning of the session to establish a baseline, the end of the session to measure immediate impact of the intervention, and at 3 months to measure sustainability of changes. All participants agreeing to participate in the research were administered pre- and post-test questions. Those participants who also agreed to follow-up surveys to were contacted 3 months later using their indicated preferred communication method . Nonrespondents were contacted using their preferred method 3 times, each 1 week apart.Readability of the questions was assessed using three formulas, each yielding a grade level result: Flesch-Kincaid, FORCAST, and Fry Readability. The mean readability result for the questions was a 4.8 grade level, which is interpreted to be “easy to read.” For studies using participants with low literacy, the reading level should be at or below the 5th or 6th grade level .n = 460), White (n = 362), older than age 65 years (n = 362), and from a rural area (n = 417) (Table 1).Fifty separate training sessions were held in 33 of the 55 targeted counties. Approximately 75% of the training was conducted by 21 CEAs. Five hundred and forty-nine participants completed the pre- and post-tests. One survey was disregarded due to missing a properly signed consent form. The final sample for the pre- and post-analysis was 548. Most of the participants were female  to post- test (M = 17.76), . See Table 2 for details on individual question analysis for the pre- and post-tests.No statistically significant differences were found between counties, training locations, or trainers when participants' age, gender, or race were analyzed. The data did not meet the assumptions of normality; therefore, a Wilcoxon Signed-Rank Test was performed on 484 participants who completed both the pre- and post- test. Of those participants, the HTTTYD HANDbook Program improved participant confidence among 296 (61.2%) participants, whereas 45 (9.3%) participant scores decreased from pre- to post-test, and 143 (29.5%) participant scores remained unchanged. The HTTTYD HANDbook program elicited a statistically significant mean increase in overall confidence among the participants from pre- (Table 1). Comparison of the repeated measures was performed using Friedman's test for each of the pre-, post-, and 3-month follow-up questions for this subset of participants. The pre- to post-testing score increased on each of the health literacy questions. A slight decrease in mean score was found from post-test to 3-month follow up for confidence in repeating back what one's doctor tells them in his or her own words as well as the overall mean scores. All other scores increased from post-test to 3-month follow up (Table 2).Of the 548 participants, 166 completed the 3-month follow-up survey .A Wilcoxon Signed Ranks test with a Bonferroni correction was performed for each pre-, post-test, and 3-month follow-up question to determine at which points and in which direction significant changes occurred. As indicated in Of primary importance in this study is the sustained improvement in health literacy after participation in the program. Improvements were noted at the post-test and at the 3-month follow up. Previous studies show mixed results for other health literacy interventions . Much ofDespite sustained improvements in each skill from pre-test to 3-month follow-up, one question, confidence in repeating back what one's doctor tells them in his or her own words, did not demonstrate the same sustained improvement. Doctor-patient communication impacts compliance, patient satisfaction, and ultimately health , and manUse of participatory methods in HTTTYD HANDbook development enhanced the quality and the appropriateness of the program . DespiteAnother important aspect of the program is that sessions were delivered by university-affiliated CEAs and trained volunteers. Both groups are trusted, credible community members . BecauseFuture implementation of the HANDbook program could be expanded to include role play with simulated providers. Opportunities for participants to practice and demonstrate competencies asking and answering questions and giving their 2-minute histories with “providers” may result in increased engagement and shared decision-making in real clinical settings. Future research on this implementation expansion and its impact is needed.Some limitations apply to the analyses presented. The sample was a convenience sample of relatively homogeneous participants. Caution should be taken concerning generalizing these results to other populations, although the analyzed sample is similar to the study area population. The one-group pre-test and post-test quasi-experimental design can be considered weak and particularly vulnerable to internal validity threats because it has no control group , althougThe National Action Plan to Improve Health Literacy contains seven goals along with several strategies to achieve these goals . One goa


Introduction: In people with Parkinson's disease (PD) many aspects of walking ability deteriorate with advancing disease. Clinical tests typically evaluate single aspects of walking and to a lesser extent assess more complex walking tasks involving a combination of the three key aspects of walking ability . The Interactive Walkway allows for assessing more complex walking tasks to address features that are relevant for daily life walking of patients, including adaptive walking and dual-task walking.Methods: To evaluate the expected added value of Interactive Walkway assessments in people with PD, we first evaluated its known-groups validity for outcome measures of unconstrained walking, adaptive walking and dual-task walking. Subsequently, these outcome measures were related to commonly used clinical test scores. Finally, we evaluated the expected added value of these outcomes over clinical tests scores in discriminating people with PD with and without freezing of gait.Results: Interactive Walkway outcome measures showed significant differences between freezers, non-freezers and healthy controls, in expected directions. Most Interactive Walkway outcome measures were not or at best moderately correlated with clinical test scores. Finally, Interactive Walkway outcome measures of adaptive walking slightly better discriminated freezers from non-freezers than clinical tests scores.Conclusion: We confirmed the added value of Interactive Walkway assessments, which provides a comprehensive evaluation of walking ability incorporating features of its three key aspects. Future studies are warranted to examine the potential of the Interactive Walkway for the assessment of fall risk and informing on tailored falls prevention programs in people with PD and in other populations with impaired walking ability. Walking ability is a multifaceted construct which includes the ability to generate stepping, to maintain postural equilibrium, and to adjust walking to meet behavioral goals and environmental demands . In ParkThis study aimed to evaluate the expected added value of IWW assessments in people with PD, which includes an assessment of more complex walking tasks. The IWW utilizes multiple external sensors for a validated quick markerless 3D full-body motion registration of unconstrained walking . MoreoveWalking ability was assessed in 30 people with PD and 30 age- and sex-matched healthy controls Table . People We used clinical tests of gait and balance impairment that have previously been suggested or recommended for use in people with PD . Two tesThe IWW was used to assess unconstrained walking, adaptive walking and dual-task walking  for one-way ANOVAs and eta squared (η2) for Kurskal–Wallis tests. There was no correction for multiple comparisons due to the explorative character of the study and given the dependency between the outcome measures.IBM SPSS Statistics for Windows, version 24  was used to perform the statistical analyses. With regard to the known-groups validity we examined the effect of group  on clinical test scores and IWW outcome measures of unconstrained walking, adaptive walking and dual-task walking using one-way ANOVAs or the Kruskal-Wallis test if the assumption of normality was violated . For one-way ANOVAs, the assumption of homogeneity of variance was checked using the Levene's test. If significant, the Welch test was used and main effects were examined using Games-Howell Pearson's correlation coefficients were determined between clinical test scores and IWW outcome measures for people with PD only. Absolute correlations between 0-0.499, 0.500-0.699, 0.700-0.899, and 0.900-1.000 were regarded as low, moderate, high and very high correlations, respectively .Stepwise discriminant analyses were conducted to determine the added value of IWW outcome measures over clinical test scores in discriminating freezers from non-freezers, using Wilks' lambda method  in four different models. Predictor variables were clinical test scores (model 1), IWW gait characteristics of unconstrained walking (model 2), IWW outcome measures of adaptive walking (model 3) and IWW outcome measures of dual-task walking  were significant, out of which 17 (40.5%) were high and 1 (2.4%) was moderate Figure . Signifip = 0.025, Wilks' lambda = 0.791, Canonical correlation = 0.457), the sole predictor variable contributing significantly to the model. Five of ten freezers (50.0%) and 13 of 14 non-freezers (92.9%) were correctly classified. The accuracy of model 1 and its cross validation were both 75.0%. For model 2 (IWW gait characteristics), none of the predictor variables contributed significantly to the model. For model 3 , group membership was predicted using stepping accuracy on symmetric stepping stones of the goal-directed stepping task and turning time of full turns  such that 7 of 10 freezers (70.0%) and 12 of 14 non-freezers (85.7%) were correctly classified, with an accuracy of 79.2%. The accuracy of the cross-validated model was 70.8%. For model 4 , none of the predictor variables contributed significantly to the model. The results of an exact McNemar's test demonstrated that there was no statistical significant difference in the proportion of freezers and non-freezers identified with models 1 and 3 (p = 0.688).For model 1 , group membership  was predicted using only the 10-m walking test at comfortable walking speed  is needed for a successful task performance. Indeed, for most IWW tasks a combination was required strongly tapping into the aspect of walking adaptability, while adaptation was not or only moderately targeted by commonly-used clinical tests that mainly measure steady-state gait and static balance as evidenced by the low correlations Figure . While hThis study also aimed to determine the expected added value of the IWW over clinical tests in discriminating freezers from non-freezers. We indeed found that IWW adaptive walking tasks discriminated better than clinical tests, although the added value was somewhat limited and the proportion of freezers and non-freezers identified with model 3 did not differ significantly from model 1. Clinical tests performed slightly worse compared to adaptive walking tasks with regard to the percentage of freezers correctly classified . The percentage of non-freezers correctly classified was high for both models . IWW gait characteristics and IWW outcome measures of dual-task walking did not contribute significantly to the discriminant analysis. Although we could discriminate freezers from non-freezers, the freezing phenomenon itself was rarely observed. IWW tasks elicited FOG episodes in only 12 out of 466 (2.6%) trials, concerning five freezers and mostly during tasks that included turning . ExplanThe latter is also a limitation of this study, since medication may improve gait impairments and could therefore lead to smaller group differences in walking ability. However, we still found significant between-groups differences, which may indicate that the IWW is a sensitive evaluation tool of walking ability. Another limitation is the relatively small sample size of the discriminant analyses . We therefore needed to pre-select predictor variables for the models to prevent overfitting, since the smallest group needs to exceed the number of predictor variables. Finally, the significant difference between freezers and non-freezers in disease severity . In addition, since the impairments in walking ability evaluated with the IWW are linked to walking-related falls, future studies are warranted to examine the clinical potential of the IWW for assessing fall risk and informing on tailored falls prevention programs in people with PD or other populations prone to declines in walking ability . Note that the current study is helpful in that regard, by informing on the subtasks and associated outcome measures providing complementary information with a decent between-groups contrast.The raw data supporting the conclusions of this manuscript will be made available by the authors, without undue reservation, to any qualified researcher.All subjects gave written informed consent, and the study was approved by the local medical ethics committee (P15.232).DG conceived and designed the study, acquired the data, analyzed, and interpreted the data and wrote the paper. MR, JM, and JvH conceived and designed the study and wrote the paper. Each of the authors has read and concurs with the content in the final manuscript.The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.