Compression, in general, aims to reduce file size, with or without decreasing data quality of the original file. Digital Imaging and Communication in Medicine (DICOM) is a medical imaging file standard used to store multiple information such as patient data, imaging procedures, and the image itself. With the rising usage of medical imaging in clinical diagnosis, there is a need for a fast and secure method to share large number of medical images between healthcare practitioners, and compression has always been an option. This work analyses the Huffman coding compression method, one of the lossless compression techniques, as an alternative method to compress a DICOM file in open PACS settings. The idea of the Huffman coding compression method is to provide codeword with less number of bits for the symbol that has a higher value of byte frequency distribution. Experiments using different type of DICOM images are conducted, and the analysis on the performances in terms of compression ratio and compression/decompression time, as well as security, is provided. The experimental results showed that the Huffman coding technique has the capability to compress the DICOM file up to 1 : 3.7010 ratio and up to 72.98% space savings. DICOM  is a file standard used to handle, store, print, and send information in medical imaging. All modern medical imaging devices  such as X-ray, CT (computed tomography) scan, and MRI (magnetic resonance imaging) use DICOM as their standardized file output. A DICOM file consists of a few data elements or attributes capable to store some information, such as patient data , imaging procedure , and the information of the image itself  . Due to Data compression is one of the solutions to overcome this problem. Data compression is to convert the input data source into the output data that has a smaller size . The maiLossy data compression is usually used for generating higher compression ratio, without considering the loss of information in the image . The latThe lossless JPEG2000 is the popular data compression method used in various PACS and considered the standard for DICOM compression  despite Existing work on Huffman coding adoption to compress the DICOM image by Kavinder  did not Huffman coding has been used for many cases of data compression. In 2015, Ezhilarasu et al.  reviewedAnother related research work was done by Medeiros et al. in 2014 [Research has been conducted on DICOM image file compression using various techniques. In fact, several studies combined lossless and lossy data compression techniques. In 2013, Kavinder  combinedIn previous studies, the lossy data compression technique generates high compression ratio but decreases the quality metrics of the peak signal-to-noise ratio (PSNR), which is generally used to analyse the quality of an image. The higher the PSNR is, the better the quality of the compressed or reconstructed image is. Thus, the lossless technique should be applied for the enhancement of the compression of the same PSNR. An image can be compressed without the loss of significant details through Huffman coding. In the perspective of a DICOM file, we expect that the DICOM image has intact quality and metadata after its compression and decompression. Standard DICOM compression method is in JPEG2000, and thus, we compare the performance analysis between JPEG2000 and Huffman coding as an alternative DICOM compression method. The lossless criteria of Huffman coding are the foundation of this work. Image quality after decompression is a vital point here and is the reason for selecting Huffman coding as the methodology.  00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  44 49 43 4d 02 00 00 00 55 4c 04 00 be 00 00 00  82 04 82 04 82 04 82 04 82 04 82 04 82 04 82 04  7d 04 78 04 78 04 78 04 78 04 78 04 69 04 5a 04  5a 04 00 00 00 00 00 00 00 00 00 00 00 00 00 00The input DICOM file is compressed in the first step. The byte distribution on file is read and calculated with BFD. Next, a prefix tree is created for the acquisition of codewords that will substitute the byte distribution on the input file used for generating a new smaller file. The data used for encoding are the byte distributions, which are compiled in the DICOM file, as shown in the following :The BFD, which is a table storing the frequency of occurrence value from every byte that compiles the file, is calculated for each DICOM file. For example, when the FF byte (255) occurs 887 times in a file, the value of the FF byte (255) in the BFD table is 288700. Once the calculation of BFD is completed, a prefix tree is created for the acquisition of appropriate codewords as substitutes of byte distribution .  Table Bit padding is the process of adding one or more bits into the data flow to fit into the minimum 8-bit computer architecture. In the example, when the generated data size is 7 bit, then 1-bit padding is required to fulfill the 8 bit (1 bytes), and if the generated data size was 28 bit, then 4-bit padding is required to fulfill the 32 bit (4 byte), and so on.The View part comprises the features that are built as the user interface. This part shows to the user the compressed DICOM image, which is displayed in accordance with the original size or the size of the provided canvas. This part is called the DICOM Viewer in other systems. The View loads the image from the DICOM file, determines the DICOM image frame to be displayed and the window level and width to be configured, resizes the image, and reads and displays the pixel distribution of the image. The View describes the metadata of the DICOM file.The Huffman decode decompresses the file to be restored in its original file. The part starts with the reading of the data flow of the compressed file, creation of a prefix tree from previously stored data into data flow in the encoding process, and construction of a lookup table that contains codewords and symbols to be changed back into the original byte structure before the compression . HoweverThe lookup table contains codewords and represents symbols generated from the results of the search of the prefix tree created previously. The table is used for changing the codeword thread from the data flow back into the original byte distribution. After reading the codeword thread of the compressed file data flow, the generated codeword is changed into an original byte distribution or symbol according to the created lookup table. This step is conducted by reading every bit of data flow, then determining whether the bit is in the lookup table. If not, the next bit is read and threaded with the previous bit; then, the search is repeated in the lookup table. If the thread of bit is found as one of the codewords that represents a symbol, then the bit is changed into the symbol. The process is done continuously until the number of the returned symbols achieve the original data size.The programming language used in this research is VB.NET, while the operating system used is Windows 7 Ultimate 64 bit SP1. The computer specification is Intel i5 450M in processor unit, 4 GB RAM, 500 GB HDD, and ATI Radeon HD 5470 in graphic card.http://www.mmnt.net/, and another set of the anonymized DICOM image from computed tomography is collected randomly from the University Hospital RS USU Medan. The files used were 20 DICOM image files with the extension ∗.dcm. The specifications of all DICOM files are described in The data used in this research work are several sets of DICOM image files available at Tables One of the factors that affect the compression ratio is the number of nodes or symbols, which creates a prefix tree of the image file. The tree is shown in CT-MONO2-16-ankle.dcm and CT-MONO2-16-brain.dcm files, which nearly have the same original size (±525 kB) but have different compression ratios. The CT-MONO2-16-ankle.dcm file was twice as large as the CT-MONO2-16-brain.dcm file with respect to the compression ratio.Compared to other image data sets in The BFD of the CT0013.dcm file spreads more evenly than that of the CT0014.dcm file. This feature causes the length of the codeword from the former to exceed that of the latter. For instance, if the assumption for the length of codewords for byte 00 is 2, byte 03 is 5, and byte FE is 6, then the obtained size of CT0013.dcm file when other bytes are disregarded is as follows:In the experimental results, we also observe a limitation of Huffman coding where one case generates a compression ratio of less than 1 (ratio < 1), causing the generated compressed file size is larger than the original file size.n) depth, where n is the total number of symbols . The generated codeword for each symbol has a length in the amount of depth from the created prefix tree, log  2(256) = 8 bit. In this case, no compression was generated from the generated codeword. Another issue in using Huffman coding occurs when all bytes or symbols have the same occurrence frequency, and the generated prefix tree has a log  2. From this state, we can obtain a traversed prefix tree for the collection of symbol codewords, which can be represented according to the construction time of the prefix tree's best and worst cases.In Huffman coding, inputted data are traversed when they receive a BFD value and when they are assigning a codeword for every symbol. If the input file size is defined as The time required for decompressing depends on the compressed file size, which is caused by the search to decompress all the bits in the file from the initial to the last bit. ∗ log  2|∑|, and if we assume the length of the data is n, the best case complexity will become 2 ∗ n+|∑| ∗ log  2|∑| or O(n+|∑| ∗ log  2|∑|).The best case in Huffman coding occurs when the constructed prefix tree forms a shape of perfectly height-balanced tree, where subtrees in the left and the right form one node that has similar height. In the perfectly height-balanced prefix tree, the traversed time for each symbol will take log  2|∑|. Therefore, every symbol will take |∑| ∗|∑|=|∑|2. Thus, the time complexity for worst case becomes 2 ∗ n+|∑|2 or O(n+|∑|2).The worst case in Huffman coding occurs when the constructed prefix tree forms a shape of a degenerated or linear tree, which is called the unbalanced tree. This case takes time to reach one node as |∑|. Therefore, reaching a codeword for every symbol takes |∑|Lossless JPEG2000 compression implementation was applied to the same set of DICOM files listed in Nevertheless, Huffman coding maintains the original file format and size while JPEG2000, being not backward compatible, changes the original size upon decompression. This comparable performance gives Huffman coding an advantage to be an alternative implementation of DICOM image compression in open PACS settings due to JPEG2000 proprietary implementation.Huffman coding can generate compressed DICOM file with the value of the compression ratio up to 1 : 3.7010 and space savings of 72.98%. The compression ratio and percentage of the space savings are influenced by several factors, such as number of symbols or initial node used to create prefix tree and the pattern of BFD spread from the compressed file. The time required for compressing and decompressing is proportional to the compressed file size. That is, the larger the compressed file size, the longer the time required to compress or to decompress the file.O(n+|∑|∗  log  2|∑|), and space complexity, O(|∑|), where n is the read input file size and |∑| is the number of symbols or initial nodes used to compile the prefix tree.Huffman coding has time complexity, The structure of the compressed file cannot be easily interpreted as a DICOM file by using a general text editor, such as Notepad or WordPad. In addition, Huffman coding is able to compress and decompress with preserving any information in the original DICOM file.There is a limitation which is at one time; the technique stops compressing when each symbol or node from the compressed file has the same occurrence frequency .Compression of the DICOM image can be conducted only in the pixel data from the image without changing the overall file structure, so the generated compressed file is still be able to be directly read as the DICOM file in the compressed pixel data size. Thus, for future research, encryption for the important information of DICOM files, such as patient ID, name, and date of birth, is considered to strengthen the secureness of the data.Lastly, we also plan to further evaluate Huffman coding implementation for inclusion in the popular dcm4HCEE open PACS implementation. Such study will focus on transfer time, compression, and decompression until the image reading quality evaluation.


P = 0·004); if the school meals were paid for the use was limited and no difference in change in dietary quality was found (P = 0·343). The school food programme had no difference in effect according to age (P = 0·083). In conclusion, offering a free school meal had a positive effect on dietary quality of the lunches consumed by school children aged 7–13 years. No effect was measured when the school meals were not provided for free. The dietary effect did not depend on age.Strategies are needed to improve the dietary habits of children. The aim of the present study was to evaluate the effect of implementing a school food programme on the dietary quality of lunches consumed by school children aged 7–13 years compared with packed lunches brought from home. A secondary objective was to investigate if a possible effect would differ between the younger children and the older. A quasi-experimental study design with four intervention schools and four matched control schools was conducted. In total, 984 school children participated. Data on packed lunches were collected at baseline. At the 1st follow-up the children in the intervention schools were offered free school meals and at the 2nd follow-up children paid for their school meals. The control group had packed lunches at all measurements. A digital photographic method combined with a Meal Index of dietary Quality  was used for dietary assessment. Multilevel modelling was employed for data analyses. The quality of dietary intake was improved when free school meals were offered ( Some evidence exists that nutrition behaviours track from childhood into adulthood, and thus it is important to establish healthy dietary habits early in life.Healthy dietary habits during childhood promote optimal health, growth and cognitive development of the child, and may contribute to the prevention of chronic diseases in later life, as well as for children in other Western countries, call for improvement. Data from the recent Danish National Survey of Dietary Habits and Physical Activity revealed that to meet the official nutrition recommendations and the food-based dietary guidelines Danish children should consume less fat, especially saturated fat, less added sugar and increase their intake of fruits, vegetables, whole grains and fish. Thus, there is a need for strategies to promote and provide healthy dietary habits among children. The school has been recognised as an important setting for such a health promotion strategy, because health-related behaviours can be influenced, especially healthy eating habits(–). The school reaches all school-aged children of diverse ethnic and socio-economic groups and offers an environment that is accessible to all on equal terms.The dietary habits of children in Denmark. Studies in Denmark as well as in other countries(–) have shown that the dietary quality of packed lunches do not always meet dietary guidelines. Cross-sectional studies have compared the nutritional quality of packed lunches and school meals provided by schools and have reported that children who eat school meals generally have a healthier lunch compared with children who eat a packed lunch(–). Many studies and reviews on school-based intervention studies have been published. The interventions vary to a great extent in terms of intervention , duration of the intervention, outcome measures and significance of results(–). We found only one study substituting the whole lunch meal. Andersen et al. found an increase in the dietary quality of lunches consumed among school children when they had a school meal based on New Nordic Diet principles compared with packed lunches.In Denmark 85 % of children aged 7–14 years eat a packed lunch brought from home during school hours found that some interventions appeared to vary in effectiveness according to, for example, the age of the children. Also a Danish cross-sectional study showed that students had different attitudes toward school food programmes. The younger children, representing the 3rd grade (9–10 years), appreciated packed lunches brought from home but children from the 6th (12–13 years) grade were happier with school meals. The prevalence of children who bring their lunch from home decreases with age. The younger school children are comfortable with their packed lunches, but the growing age and youth culture influences the status of the packed lunch among the older school children; thus it is possible that the effect of a school food programme could depend on the age of the children involved.In a recent systematic review Brown & SummerbellThe aim of the present study was to evaluate the effect of implementing a school food programme on the dietary quality of lunches consumed by school children aged 7–13 years compared with packed lunches brought from home. A secondary objective was to investigate if a possible effect would differ between the younger school children (2nd–3rd grades) and the older (5th–6th grades).We conducted a quasi-experimental study with a pre- and post-intervention design. In 2008, thirty-eight schools received funds from the Danish Food Industry Agency to implement a school food programme. In the first 2 months the school meals were free; this was followed by a period where the school children could buy their school meals. To evaluate the dietary effect of the school food programmes four intervention schools from the thirty-eight schools were selected, taking into account representation of different geographic locations and size of the school. Four schools were selected randomly and afterwards contacted. The four schools all accepted to participate in the study. Four control schools were selected among schools without any school food programme and matched with the four intervention schools with respect to municipality, size (number of children) and families’ social background.Power calculations using an α level of 0·05 and a β level of 0·8 estimated that fifty children were required in order to detect a difference of 2·29 g saturated fat intake, estimating the intra-class correlation to be 0·02. To examine if a possible nutritional effect of the school food programme was different between students from the 2nd–3rd grades and 5th–6th grades approximately fifty students in each age group in each of the eight participating schools were selected.Children from forty-six school classes at the eight participating schools were invited to participate in the study. In total 984 children participated, 493 school children from the 2nd and 3rd grades and 491 students from the 5th and 6th grades. For flow of schools, participants and number of meals, see The present study adheres to Danish ethical standards and has been approved by the Danish Data Protection Agency (reference 2008-54-0497) and reported to the regional ethics committee for the Capital Region of Denmark. They concluded that formal ethics approval was not required because no human biological material was collected.When schools were invited to participate, written information targeting the school management and the teachers was sent to all schools explaining the implications of participation. Teachers, children and their parents at the participating schools were informed that participation was voluntary, that their information would be used for research purposes only and treated confidentially and of the possibility of withdrawing during any stage of the study. Parents were informed of the study and the possibility of withdrawing their child from the study by written information indicating the purpose of the study, the implication for and involvement of their child. If the parents had further questions, they could call the project manager.At baseline (T1), data on packed lunches were collected in both intervention and control schools. At the 1st follow-up (T2) the control schools still had packed lunches brought from home, and the intervention schools were offered free school meals. At the 2nd follow-up (T3) the controls had packed lunches and at the intervention schools the school meals were no longer for free, so the school children would either have paid school meals or brought packed lunches . The datCollection of data covered three consecutive days during a week to cover the variability of the lunches over a week.. At the beginning of the lunch break, the children were asked to place their lunch meals on a plate distributed to them, and all meals were photographed. Where it was difficult to determine what a sandwich contained the child was asked to open the sandwich for viewing. At the end of the lunch break, the plates were again photographed with or without leftovers. In addition, for non-visible food items, the participants were asked questions if the research staff assessed that it would be difficult to see on the digital image. The research staff attended a training session on the use of the digital photographic method before the data were collected.A validated standardised digital photographic method was used to collect dietary data for the packed lunches or the school mealsAt the four intervention schools, thirty-one different lunches provided by the schools were served at the 1st and 2nd follow-ups. Recipes and product specifications for lunches provided by the schools were collected. Two of each school meals were bought and the weights of the food items registered. The data on the packed lunches and the school meals were collected during August–December and February–April.. The total score for the Meal IQ ranged from 0 to 28. Each of the seven components scored from 0 (lack of compliance) to 4 (full compliance), with intermediate scores reflecting levels of attainment towards dietary recommendations.The dietary quality of the lunches was assessed using a validated Meal Index of dietary Quality , which is a tool that we developed for the purpose. The Meal IQ consists of seven components: total fat, saturated fat, whole grains, snack products, fruit, vegetables and fish, selected with the aim of assessing the overall dietary quality of the lunches. Fruits, vegetables and fish were estimated in g. To estimate total fat, saturated fat, whole grains and snack products in the lunch meals, units were defined in terms of household measures, such as slices, cups and piecesA database was developed in Microsoft Excel for the dietary assessment of the digital images in order to make the necessary notes on the dietary components in the Meal IQ while watching the digital image. If there were any doubts about the food items on the digital image decisions were made based on consensus between the two digital image analysts; if consensus was not possible the digital image was excluded from the study. and the paper on the validation of the digital photographic method.More thorough details about the Meal IQ are given in the previous paper describing the development and validation of the Meal IQ. The Danish Occupational Social Class (DOSC) measure was used to assess the social background of the child's family.A questionnaire was used to collect data on sociodemographic characteristic of the participating children. The students from the 2nd and 3rd grades were interviewed and the students from the 5th and 6th grades filled out the questionnaires themselves. The majority of the questions used were developed, validated and used in the Pro Children project2). The measures were taken in light clothing and without shoes. Weight was measured to the nearest 0·1 kg using a Soehnle Verona 63749 digital scale; height was registered to the nearest 1·0 cm using a Soehnle 5003 digital height rod.At baseline the height and weight of the students were measured to calculate BMI , μ0 is the intercept , b is the BMI value at baseline, gr represents the grades (2nd–3rd grades and 5th–6th grades), t represents the measurement times (T2 and T3), in represents two groups (intervention and control), s represents the social status, ge represent the sex, k is the Meal IQ score at baseline, t × b, t × gr, t × in, t × s, t × ge and t × k represent the two-way interactions with time, and t and gr × in × t represents the three-way interaction term. In addition to the deterministic variables the model given above included a number of stochastic variables which took into account the clustering of children within schools and classes and the repeated measurements of the same child. Thus the following hieratical structure was included in the model:SC represents the schools and is nested with intervention (IN), C represents the classes and is nested with school and intervention, and IP represents a personal index for each child's participation in the study and is nested with school, class and intervention.The dietary effect of the school food programme was examined using the Meal IQ score which were measured as repeated measurements for the same group of children at baseline (T1), 1st follow-up (T2) and 2nd follow-up (T3). The analyses were conducted on the differences of the Meal IQ score compared with baseline by using the following model:t × in).The two-way interaction terms were included in the model to test whether the development in the mean changes in Meal IQ score were parallel over time, for example, in intervention and control schools .P < 0·0001). This difference occurred due to more 3rd-grade students in the control group. Regarding the quality of the dietary intake  from the packed lunches brought from home there were no differences between the intervention and the control groups.in × t (time × intervention) (P < 0·0001) (P = 0·004). At T3, about 4 months after the intervention, no significant difference between the dietary quality of lunch consumed in the intervention and control schools was found (P = 0·343). When the children had to buy the school meals the use of the school food programme was limited. At T3 only 7 % of the lunch meals collected were school meals. At two schools the children did not use the opportunity to buy a school meal and at the other two schools, 21 and 6 % of the lunch meals consumed, respectively, were school meals. Overall, only 7 % of the lunch meals collected at the intervention schools at T3 were school meals.A different development over time was seen between the intervention group and the control group illustrated by a significant interaction term  0·0001) . The oveP < 0·0001). The mean Meal IQ scores for the younger and older age group were, respectively, 11·7 (sd 4·5) and 11·1 (sd 5·4). Furthermore, a significant interaction between time and grade was found (P < 0·0001) (P = 0·083), which shows that there is no different effect of the school food programme at T2 and T3 between children in the 2nd–3rd grades and 5th–6th grades. Thus the differences between age groups seen in The Meal IQ scores of the two age groups divided into 2nd–3rd grades and 5th–6th grades were significantly different at baseline ( 0·0001) , indicatP values and the parameter effect estimates of the explanatory variables significantly associated with the change in dietary quality for the final model.m  was accounted for in the model as a new explanatory variable, the variable gr (grade) was no longer significant and was taken out of the model since most of the reason for a difference between the grades was explained by this ‘new’ variable.Some of the different effects of age can be explained by the fact that more children in the 5th and 6th grades did not bring a packed lunch or skipped a meal compared with the children in the 2nd and 3rd grades. When this effect P = 0·0006) and no difference was detected at T3 (P = 0·553).If a child does not eat a meal at all in the timetabled lunch break the Meal IQ score is 0. These observations of children not eating lunch were included in the multilevel analyses. Analyses were also done where the skipped meals were excluded. These analyses showed the same overall results, that a significant difference between the intervention and control groups was found at time point T2  is caused by a reduction in total fat and saturated fat and intake of snack products. The consumption of vegetables and fish increased and the intake of whole grains and fruits decreased .Table 3The study showed that the dietary quality of the lunch eaten at school was improved when Danish school children aged 7–13 years had free school meals instead of packed lunches. When the school meals were not provided for free the use was limited and no difference in dietary effect was found between children at the intervention and control schools. Furthermore, the study showed that there was no different effect of the school food programme according to age group. Most of the reason for the different development in changes in the Meal IQ score between children in the 2nd–3rd grades and 5th–6th grades is explained by more skipped meals in the older age group. including a meta-analysis, on seven studies, where Evans et al. compared British school meals and packed lunches from 1990 to 2007 measuring lunchtime nutrient intake in children aged 5–11 years. The cross-sectional design is weaker than that of the intervention studies according to their ability to provide evidence for causal relationships. To our knowledge our study is the first intervention study to examine if the dietary quality of the lunch consumed was different when school children had school meals instead of packed lunches. Other school-based intervention studies have not exchanged a whole meal, but instead focused on single food groups, for example fruit and vegetables(–), or nutrients, such as fat or whole grains.The improved dietary quality when students have school meals is consistent with the results from several cross-sectional studieset al. conducted a review on forty-two European intervention studies with the purpose of summarising the effectiveness of school-based interventions to promote a healthy diet in children (6–12 years) and adolescents (13–18 years). They concluded that in children (6–12 years) strong evidence was found of effects of multicomponent interventions on fruit and vegetable intake. The overall conclusion was that evidence was found for the effectiveness of especially multicomponent interventions promoting a healthy diet in school-aged children in European Union countries on self-reported dietary behaviour.School-based interventions are heterogeneous in terms of design, participants, intervention, outcomes and duration, making it difficult to generalise about which intervention components are most effective. Van Cauwenberghe et al. reviewed the evidence of school-based interventions promoting a healthy diet together with healthy physical activity habits on behavioural determinants, healthy diets and physical activity habits and measures of obesity in primary and secondary school children in Europe. In younger children (6–12 years) the evidence was found to be inconclusive as to multicomponent interventions having a positive impact on child obesity in the European context. Overall they suggest that combining educational and environmental components that focus on both healthy diet and physical activity give better and more relevant effects.De Bourdeaudhuij This study attempted to influence eating behaviour in school children via availability (T2) or accessibility (T3) of school meals. Nevertheless, it seems that interventions operating at several levels could be an important strategy when children's dietary habits should be improved. So it is possible that another intervention design, e.g. a multicomponent version, may have improved the sustainability of the dietary effect. and a cross-sectional study have reported different results of school food programmes/interventions according to age. However, the differences between age groups in the present study were not due to the school food programme but could be explained by a higher prevalence of skipped meals among children in the 5th and 6th grades compared with children in the 2nd and 3rd grades. Especially at T3 the older children often skipped a lunch meal (10 % did not bring or eat lunch on any of the days at T3); for the younger age group this applied to 0·5 %. The reason why the older school children did not bring a packed lunch could be that they had already eaten their lunch or maybe they eat after school. According to the literature the growing age and youth culture could also explain why packed lunches are not so popular among children in the 5th and 6th grades.A reviewIn the present study the quality of the dietary intake from the lunches was no longer significantly different between the intervention and the comparison schools at the 2nd follow-up. This could be explained by the limited use of the school food programme when the school meals were no longer provided for free and thus relatively few school meals (7 %) were represented at the intervention schools at this measurement. This result indicates strongly that the economic perspective of the school food programme is important for the general dietary effects and the sustainability of school food programmes. and the other study suggested that the difference according to type of meal persisted assessing the nutrient intake of the whole day. This issue has to be investigated further.In this study the food eaten in the timetabled lunch break was measured. It is not known if the overall dietary quality of the diet for the whole day is influenced by the dietary quality of the lunch or if a poor or healthy dietary intake is compensated for during the rest of the day. Two cross-sectional studies have compared packed lunches and school meals and also measured the whole day's energy and nutrient intake. One study suggested that the differences in intakes were compensated for by other foods consumed during the day, such that daily nutrient intakes were not significantly different. The Meal IQ score that was used, which has been shown to be a valid indicator of the overall dietary quality, was developed with the purpose of being simple, flexible with regard to the different types of meals, and also being sensitive enough to measure relevant differences when children were having school meals instead of packed lunches. The Meal IQ does not give information on the energy or the exact nutrient content of the meals, but as a tool for evaluation of school-based interventions or interventions in other settings it seems very suitable.It is a challenge to assess dietary intake among children. Using a validated digital photographic method overcomes the recall problems and difficulties in estimating portion sizes that exist when collecting dietary data on children, and has the positive side effect that it minimises the burden of the respondentThe effect of the school food programme resulted in a significant increase in the Meal IQ score of 2·34 points. A challenge when using indices to assess dietary quality is that the total score covers both positive and negative changes. In this study the positive effect of the free school lunches was due to a decrease of total fat, saturated fat and snack products and an increase in the consumption of vegetables and fish. The result also included a decrease in whole grains and fruits. The dietary change shown in this study is of importance. The decrease in saturated fat goes from 1·77 units at baseline (T1) to 0·80 units at the 1st follow-up (T2). A fat unit was defined as 5 g fat. Also, if the fat units are animal-based they were counted and used as an approximation of the content of saturated fat in the meal. More than half of the content of fat in a saturated fat unit comes from saturated fat. A decrease of 0·97 units from the component of saturated fat in the Meal IQ is thus of dietary relevance, and corresponds to a reduction of at least 2·4 g of saturated fat and thus a reduction of 3–4 % of energy from saturated fat among children in this age group. The increase in intake of fish was not very high, going from 1·5 to 4·2 g. Such a change is not of dietary relevance now, but more children have been introduced to fish and that could perhaps have a positive perspective in the future.A limitation of this study was the randomisation procedure, where a complete randomisation was not possible because the intervention schools were selected among the group of schools receiving funds from the Danish Food Industry Agency for implementing the school food programme. However, the study schools were matched with controls on key variables.. We adjusted our analyses for various known or potential confounders, but we cannot exclude confounding through factors that were not considered.In the present study, multilevel analysis was used, which is a strength, as it takes into account the study design and also the structure of the data. Not all school-based studies have utilised the hierarchical structure of the data (students nested within schools and students within classes) in their statistical analysis, which might have led to biased conclusions regarding the effect of school. The results of the present study suggest important national implications for school food programmes as a potential relevant health-promoting strategy which may improve the quality of dietary intake at lunch. However, this requires additional research on how school food programmes can be better implemented, including knowledge about the economic perspective of this area.Most Danish school children bring their packed lunch from home and the lunches do not in general meet the dietary guidelinesIn conclusion, the implementation of the school food programme had a positive effect on the dietary quality of the lunches consumed by students aged 7–13 years in the period where the school meals were offered for free, but when the school meals were paid by the parents the use was limited and no overall effect on dietary quality was measured. The dietary effect of the school food programme did not differ between the children in the 2nd–3rd grades and 5th–6th grades.


Acoustic illusion devices present a novel approach for defeating detection systems such as sonar by misrepresenting information about the target. These devices are currently designed for a predetermined illusion using metamaterials. We present the first active acoustic illusion utilizing monopole control sources and error sensors arranged circumferentially around a rigid object to generate the desired illusion in the global acoustic field. We also utilize control sources and error sensors in a line array to generate an illusion in the forward-scatter region of the object. Multiple types of illusions are achieved for a given control configuration. Cloaking renders an object invisible whilst illusions misrepresent the true nature of an object being perceived. Yang et al.6 proposed the first optical illusion using a metamaterial shell to increase the scattered field of an object, making the object appear larger than its actual size. In contrast, Jiang et al.7 employed the use of metamaterials to visually shrink an object. Lai et al.8 created an illusion device using two distinct metamaterial shells, where one shell comprised negative permittivity and negative permeability to cancel an optical region, whilst the other shell comprised a homogenous medium with positive anisotropic permeability to project an illusion within the cancelled region. Using a similar approach, Jiang et al.13 experimentally developed a radar illusion device comprising two metamaterial shells which was able to modify the scattered field of a metallic cylinder to be that of a dielectric cylinder. McManus et al.18 proposed an illusion device in which a subwavelength coating of an anisotropic material was applied to a flat plate to reproduce the scattering properties of a curved surface, and vice versa. Recently, Yang et al.21 proposed a dual purpose homogenous illusion device, which could either cloak an object or misrepresent its location.The last decade has seen an unprecedented level of control for electromagnetic and acoustic wave manipulation. Pendry 34 and acoustic illusions37. Kan et al.35 utilized positive anisotropic metamaterials to generate acoustic illusions near boundaries of curved geometry. They numerically and experimentally demonstrated the transformation of scattered waves from a cylinder to appear as scattered waves from a rectangular prism35. Liu and He37 also employed positive isotropic materials to exchange the acoustic scattering potential of an object with that of the desired illusion.Transformation optics was soon generalized to acoustics which allowed for manipulation of the scattered field using analogous counterparts, to achieve acoustic cloaking41. Ma et al.38 experimentally produced an illusional field for a defined region on a conducting plate, by modulating the voltage of control sources arranged circumferentially around the region. Similar to our active approach, Cao et al.39 employed different control configurations comprising closed and open arrangements in which control sources completely circumscribed the object or were localised to certain areas. Using a fixed control configuration, they demonstrated the ability to generate different optical illusions that misrepresented either the orientation or location of the object. Similar to the work by Cao et al.39, we herein employ a fixed control configuration to generate single-type illusions; however we further demonstrate the ability to generate multiple illusions simultaneously. Zheng et al.40 numerically presented an active control configuration comprising three multipole sources surrounding an apple-shaped object, to create the optical illusion of the scattered field corresponding to a banana-shaped object. Our work extends the capability by Zheng et al.40 to actively generate an illusion such that the acoustic field arising from scattering by a rigid body for a given incident excitation can be replaced with a different incident field.The aforementioned optical and acoustical illusions were generated employing passive approaches, primarily using metamaterials. As an alternative, active techniques have also been utilized to create optical illusion effects46; however, no active approaches have been employed to generate acoustic illusions. Herein we present the first active acoustic illusions utilizing arrays of monopole control sources and error sensors to misrepresent the acoustic fields due to scattering by a rigid object. Acoustic illusions are generated to change the apparent size of the object, shift the location of the object, and to simultaneously change the size and location of the object. Unlike their passively produced counterparts, the aforementioned active acoustic illusions are achieved with no required changes to the control configuration. Further, we actively modify the acoustic response of an object due to an incident field to resemble a different incident field.Active control techniques for acoustic cloaking have also been implemented, seea. The acoustic field arising from scattering by the incident excitation is herein known as the primary acoustic field. We implement a multichannel control configuration utilising W control sources and L error sensors. Figure Let’s consider a time-harmonic incident excitation corresponding to either a plane wave or a single monopole source impinging on a rigid 2D cylinder of radius 47. Our active control strategy requires modification to a cost function to accommodate a two-stage process. The first stage is used to completely remove the total acoustic field at the error sensor locations (sound cancellation). The second stage is then employed to generate the desired acoustic illusion (sound reproduction). The cost function for cancellation of the total acoustic field is defined as the sum of the squared acoustic pressures at the error sensor locations, given byH denotes the Hermitian transpose operator and e is a vector denoting the total acoustic field at the error sensors arising from scattering by both the incident excitation and the secondary monopole control sources. This vector can be expressed aspp denotes the primary acoustic pressure at the L error sensor locations, Z is an L × W matrix of complex transfer functions representing the secondary field due to W monopole control sources at L error sensor locations, and q is the vector of W complex control source strengths to be optimized upon minimization of the total acoustic pressure given by Eq.  and horizontally aligned with the cylinder centroid, both at 200 Hz. We herein show results for acoustic pressure in Pascal. Figure a (left) and 0.5a (right), showing greater and reduced scattering effects due to the larger and smaller sized object, respectively. Figure a has been actively modified to resemble the acoustic fields in Fig. a (left) or 0.5a (right). A global acoustic illusion in the exterior acoustic field transpires beyond the control sources located at 2a.Two different excitation cases are considered corresponding to a plane wave propagating from left to right, or a single monopole source located 4a in the back-scatter region. Figure a, in which the effect of cylindrical spreading can be clearly observed. Figure a (left) and a smaller sized cylinder of radius 0.5a (right). Figure Figure a. The targeted acoustic fields now correspond to that of a larger sized cylinder of radius 2a shifted to the left (in the back-scatter region) by a distance a  and monopole source located 4a upstream of the cylinder (right). Figure a to 60a. Further, it was not possible to actively generate an illusional field in the back-scatter region using the line array configuration due to the requirement to cancel the primary incident field.The acoustic illusions in Figs sing Eq. , wherebyθ = 0, for the illusions presented in Fig. a due to plane wave excitation (Fig. a in the back-scatter region (Fig. a in the back-scatter region. Similarly, as per the acoustic illusion field in Fig. a.Figure ion Fig.  or a sinion Fig. . As per In summary, we present a method to generate active acoustic illusions for a rigid body. An illusion in the global acoustic domain beyond the control source perimeter can be achieved using control sources and error sensors fully circumscribing the object. An illusion in the forward-scatter region was demonstrated using a line array of control sources and error sensors, for which the size of the acoustic domain of the illusion is strongly dependent on the number of control sources and sensors. Using a fixed control configuration, active acoustic illusions were generated for single and multiple type illusions. We also demonstrated the ability to replace the acoustic field arising from scattering by a rigid body for a given incident excitation with a different incident field. The proposed technique depends on prior knowledge of the incident field as well as the primary acoustic field arising from scattering of an incident field by a rigid body. As such, the technique can work effectively for a rigid body of arbitrary shape whereby a numerical solution to obtain the primary and secondary acoustic responses can be implemented. Applications of the proposed technique include masking of unwanted sound and misrepresenting information about a target for stealth purposes.45. Analytical results for the incident and scattered acoustic fields for both plane wave and monopole source excitation were numerically validated using COMSOL Multiphysics 5.4. The fluid medium was considered to be inviscid and free of losses for the analytical and numerical simulations. The system parameters comprise a 2D rigid cylinder of radius a = 0.6 m in air of density ρf = 1.225 kg/m3 and speed of sound cf = 343 m/s, with negligible material damping.The analytical simulations of the active illusions presented in this paper were conducted within MATLAB. The incident and scattered acoustic fields of the rigid cylinder were approximated using truncated multipole expansions given in


Congenital constriction ring syndrome (CCRS) is a well-described pathological entity that is caused by fibrous bands that entrap parts of the fetus. The manifestations of this syndrome may vary a lot. We present a case of an almost intrauterine amputation of a fetus’s upper limb. Our case is infrequent because the constriction band caused a fracture of the fetus's forearm during pregnancy. Both the band and the fracture resulted in ischemia to the hand and a salvage procedure was applied after birth.Not many authors have reported fractures due to constriction ring bands and even less have reported fractures of the upper limb. A literature review of this rare entity was conducted. The etiology of congenital constriction ring syndrome (CCRS) is unknown and many theories have been proposed. The three most commonly referred to in the literature are the intrinsic theory, the theory of spontaneous rupture of amnion early in the second trimester of pregnancy, and the theory of intrauterine trauma .CCRS may present with a wide range of pathology. This depends on the site of the band and the proportion of constriction that is caused. Most bands are wrapped around distal extremities, usually fingers and toes. The rest of the limbs are less commonly affected. Although most patients are only superficially affected, both neurovascular and functional damage are frequently reported. So the syndrome may be manifested with amputations, constriction bands, and pseudosyndactylism. The syndrome may also present with multiple craniofacial, visceral, and trunk anomalies.By reviewing the literature, we came across only a few reports of bone defects. This dramatically decreases when the forearm is involved. Only a few limbs have been reported to be fractured. Most limbs that appear with osseous defects are thought to be pseudarthroses and not a recent fracture. To our knowledge, there has never been a report of a fracture of the forearm of a neonate due to an amniotic band.A 31 weeks preterm male was born by cesarian section to a 30-year-old mother. His birth weight was 1080 gm and the circumference of his head was 27 cm. Apgar scores were 6 (1 min), 5 (5 min), and 5 (10 min). His left hand was swollen due to a constriction band and, therefore, put in an elevated position. Due to respiratory distress syndrome (RDS), non-invasive positive pressure ventilation (NIPPV) was applied for two days. Also renal failure with anuria and ischemic encephalopathy were diagnosed during the next few days. The neonate's general clinical condition was critical.Prenatal history included twin-to-twin transfusion syndrome. At the 17th week of gestation, there was an attempt to separate the fetuses, but two days later, one of them was diagnosed dead. Three days before the delivery, the fetus was diagnosed with a constriction band around its left forearm.The neonate was transferred to our institution’s neonatal intensive care unit on the second day after birth. A constriction band around the distal third of the forearm was noticed. Severe swelling and vascular compromise of the hand were evident Figure . CapillaWe decided to perform a reduction of the fracture and release the band. Under anesthesia and sterile preparation, a 5 mm longitudinal incision with an 11 blade scalpel over the dorsal part of the band was performed. Due to the swelling of the hand, a second 5 mm longitudinal incision was made dorsally in order to decompress it. Wounds were left open. Finally, the fracture was reduced and immobilized with a palmar cast in order to decompress the compartment syndrome Figure . The hanCCRS is not an uncommon pathologic entity. Most cases are of mild emergence, such as a simple cutaneous constriction around a specific part of the body, but in some cases, a more severe outcome may be present. Many cases of defects that involve craniofacial, visceral, and trunk anomalies have been reported in the literature. Limbs are affected with a wide spectrum of deformity manifestation. Osseous anomalies of the limbs are not usual since the annular defect is either too deep and, therefore, causes partial or complete amputation or it is superficial and causes only cosmetic or various degrees of neurovascular compromise.Only a few cases of limb defects have been reported and most of them concern pseudarthrosis of the tibia and fibula -8. Most As far as the upper limb is concerned, we have only come across two cases of pseudarthrosis of the forearm in the literature. Zionts et al. report a case of an identical twin with pseudarthrosis of the radius and ulna at the level of a congenital band around the forearm and a congenital amputation of the opposite forearm. This was treated by simple cast immobilization, and bone healing was achieved. The second infant had a band around the leg that caused minimum constriction . Ho et aFinally, we have found only one case of recent fracture due to an amniotic band in the literature. Masmoudi et al. report a fracture of the tibia and fibula that was caused in late pregnancy at the site of the annular defect due to the increasing mechanical stress on the bones related to fetal growth within the confines of the uterine cavity. They have treated their case only with immobilization and report good outcome .In our case, the radiographs indicated a recent fracture since the edges of the fractures were sharp, there were no signs of sclerosis on them, and no callus formation or periosteal reaction was present. We also believe that the fracture occurred only in late pregnancy. Probably, mechanical stress was applied to the hand at its most yielding site and this lead to the fracture. Alignment of the hand was lost and this caused vascular compromise along with the vascular distress caused by the band.We have reported an unusual case of a forearm fracture at the site of an annular defect in a male neonate treated with debridement, reduction, and immobilization. Fractures due to amniotic bands are rare. Pseudarthrosis defects are more common. Osseous defects reported in the forearm are not common. Before amputation is considered, in some cases, a more conservative approach may be considered.


Such a smaller set gives a scalable way to exploit pan-genomic information in further analyses . Optimizing the founder set is an NP-hard problem, but there is a segmentation formulation that can be solved in polynomial time, defined as follows. Given a threshold L and a set m strings (haplotype sequences), each having length n, the minimum segmentation problem for founder reconstruction is to partition  into set P of disjoint segments such that each segment L and the number a, b] is minimized over  We study a preprocessing routine relevant in pan-genomic analyses: consider a set of aligned haplotype sequences of complete human chromosomes. Due to the enormous size of such data, one would like to represent this input set with a few O(mn) time (i.e. linear time in the input size) algorithm to solve the minimum segmentation problem for founder reconstruction, improving over an earlier  We give an https://github.com/tsnorri/founder-sequences. Our improvement enables to apply the formulation on an input of thousands of complete human chromosomes. We implemented the new algorithm and give experimental evidence on its practicality. The implementation is available in  A set n is called a founder set of n] into disjoint subsegments such that, for each parse ofin terms ofparse ofin terms ofa and crossover points; thus, in particular, 1 and The input for our problem is the set It follows from the definition that, in practice, it makes sense to consider founder sets only for pre-aligned recombinants. Throughout the paper we implicitly assume that this is the case, although all our algorithms, clearly, work in the unaligned setting too but the produce results may hardly make any sense.m of this founder set is in most cases unacceptably large. Following Ukkonen’s approach, we consider compromise parameterized solutions. The minimum founder set problem is, given a bound L and a set of recombinants L ; conversely, if L and The minimum founder set problem and the minimum segmentation problem are connected: any segmentation O(mn) time (linear in the input size). The solution normally does not uniquely define a founder set of S are Our main result is an algorithm that solves the minimum segmentation problem in O(m), which is a natural assumption considering that the typical alphabet size is 4 in our problem. It is sometimes convenient to view the set m rows and n columns. We say that an algorithm processing the recombinants streaming if it reads the input from left to right “columnwise”, for each k from 1 to n, and outputs an answer for each set of recombinants Hereafter, we assume that the input alphabet Given a boundLand recombinantseach having lengthn, there is an algorithm that computes (in a streaming fashion inO(mn) time andspace. Using an additional array of lengthn, one can also find inO(n) time a segmentation on which  is equal to the solution (Given a bound  Ukkonen  proposedmentclass2pt{minimM(k) can be computed in O(m) time using  total time and For a given entclass1pt{minimaM(n), we build along with the values M(k) an array of size n whose kth element, for each O(n) time. In order to maintain the array, our algorithm computes, for each j on which these minima are attained (see below). Further details are straightforward and, thence, omitted.To reconstruct a segmentation corresponding to the found solution n, a positional Burrows–Wheeler transform (pBWT), as defined by Durbin [m] such that Let us fix y Durbin , is a pareversed sequences Consider the following example, where mentclass2pt{minimO(m) time on the binary alphabet. Mäkinen and Norri  stores the position of the last seen b in the sequence b occurs for the first time. Thus, The last three lines of the algorithm are responsible for computing O(1) time, we build a range maximum query (RMQ) data structure on the array O(m) time  and partitions of the rows of X of a segment  and an induced set Y of a segment XY forms the content F of some founder F, then this concatenation causes Assume  that each segment in Problem of maximum intersection between two partitions. Let a be an integer. Given two partitions Maximum Intersection Between two Partitions (MIBP) is to find the bijection f from By using the bipartite graph defined between the elements of We can define the greedy algorithm related to MIBP as the the greedy algorithm related to the problem of maximum weight perfect matching in the previous bipartite graph. As the greedy algorithm for maximum weight perfect matching is ximation , we haveLetandbe two partitions ofwithWe can compute the greedy algorithm for MIBP ofandinO(a) time.E be a partition of E, we denote by E of size a such that for all i, a. By using Radix sort, we can compute in O(a) the sorted array of elements of O(a) the ordered list O(a) two arrays f and Let Optimal founder set for the special case. Now we can solve independently the MIBP problem for each pair of consecutive segments, resulting to the following theorems, where the first one follows directly also from earlier constructions [ructions , and theGiven a segmentationofsuch that each segment induces exactlyKdistinct substrings inthen we can construct an optimal parseof(and hence the corresponding set of founders) in polynomial time. Given aGiven a segmentationofsuch that each segment induces exactlyKdistinct substrings inthen we can construct a greedy parseof(and hence the corresponding set of founders) that has at most twice as many crossovers than the optimal parse intime andspace.M(n) distinct substrings. We turn such segments to the special case by duplicating some of the substrings. The choices made have dependencies between segments, and this is the reason we believe this general case is NP-hard to solve optimally. Hence, we aim just to locally optimize the chances of minimizing crossovers by duplicating distinct substrings in proportion they cover E of x of E. We make M(n) and update the last one such that In the general case, there are segments inducing less than see Fig. . The facL using the recursion in Eq. We implemented the segmentation algorithm using Algorithm 2 to build the pBWT arrays and computed the minimum number of founders with the given value of  library .L to generate a segmentation suitable for this purpose. In particular, we wanted to have the length of most segments clearly above a typical read length, such that most reads could be aligned without hitting a recombination site.As our goal is to produce reference sequences for aligning short reads, we wanted to find a good value of We used the chromosome 6 variants from the phase 3 data of the 1000 Genomes Project  as the sL fixed to 10 to verify the usability of the tool in terms of running time and memory consumption. The tests were run on a Ubuntu Linux 16.04 server. The server had 96 Intel Xeon E7-4830 v3 CPUs running at 2.10GHz and 1.4 TB of memory. In addition to our own RMQ data structure, we tested with a general-purpose RMQ from the SDSL library. As seen in Fig. We used an increasing number of the generated sequences as an input to our tool with the value of L on the number of founders as well as the length of the segments. The results have been summarized in Table L ranging from 10 to 80. After generating the founders, we mapped the segment co-ordinates back to the original sequences to determine the segment lengths. The results are shown in Figs. L to conclude that decreasing L further rapidly makes the situation more difficult. On the other hand, setting Our second experiment was to see the effect of the minimum length Random matching which corresponds to concatenating the consecutive fragments in random order, a Perfect matching which takes an optimal solution of the maximum weight perfect matching problem as the order for the concatenation of the fragments, and a Greedy matching which solves the matching problem greedily. For evaluating the different concatenation strategies, we mapped each one of the original sequences to the founders, using a simple greedy algorithm that is also optimal [L to 10 and mapped an increasing number of input sequences to a set of founder sequences generated with the same input sequences. In the second one, we used all of the 5009 input sequences and varied the value of L. The results are shown in Figs. We proceeded with two tests in which we measured the number of recombinations needed to express each of the original sequences with the generated founder sequences depending on the method of concatenating the fragments into the set of founder sequences. Using the method given earlier, we began by duplicating some fragments so that each segment had exactly the same amount of fragments. For these tests, we implemented the three concatenation strategies: a  optimal . In the The results look promising, as using 130 founders instead of 5009 haplotypes as the input to our pan-genome indexing approach  will resOur intention was to compare our tool to an implementation of Ukkonen’s algorithm . HoweverPanVC [As our experiments indicate that one can reduce 5009 haplotypes down to 130 founders with the average distance of two crossovers being 9624 bases, one can expect short read alignment and variant calling to become practical on such pan-genomic setting. We are investigating this on our tool PanVC , where oFinally, it will be interesting to see how much the contiguity of the founder sequences can still be improved with different formulations of the segmentation problem. We are investigating a variant with the number of founder sequenced fixed.


Atta colombica), a set of local priority rules were isolated and it was proposed that these rules govern the temporal and spatial organization of the traffic on the trails. Here we introduce a model based on these priority rules to investigate whether they are sufficient to produce traffic similar to that observed in the experiments on both a narrow and a wider trail. We establish that the model is able to reproduce key characteristics of the traffic on the trails. In particular, we show that the proposed priority rules induce de-synchronization into clusters of inbound and outbound ants on a narrow trail, and that priority-type dependent segregated traffic emerges on a wider trail. Due to the generic nature of the proposed priority rules we speculate that they may be used to model traffic organization in a variety of other ant species.Ants, termites and humans often form well-organized and highly efficient trails between different locations. Yet the microscopic traffic rules responsible for this organization and efficiency are not fully understood. In previous experimental studies with leaf-cutting ants ( Ants often form trails to transport food and supplies they find back to their nest. These trails have a function similar to the roads that connect people’s homes with the local mall, but while the traffic rules that cars on our roads are supposed to follow are well known the traffic rules ants use on their trails are still relatively unknown. Earlier experiments with leaf-cutting ants have suggested a set of simple traffic rules that ants may be attempting to follow on their trails. However, it is difficult to experimentally verify the link between the proposed rules and the observed traffic organization. Modeling is a useful way to link the behaviors isolated at the individual level and the pattern recorded at the collective level. Here we present and analyze a computational model based on the proposed traffic rules. We find that, with some modifications, the proposed rules are indeed sufficient to reproduce key features of the overall ant traffic observed in the experiments. Strengthening our belief that these traffic rules might be employed by the leaf-cutting ants to regulate traffic organization and due of their simplicity we speculate that similar rules may be used by other ant species. Animal collective movement is a widespread phenomenon that occurs at various spatial and temporal scales in a variety of living organisms from cells to pedestrians –4. OftenIn many situations the motion within the collective is unidirectional because it is related to migratory phenomena and involve individuals moving in the same direction. Social insects and humans are some of the rare organisms in which the movements within the collective are predominantly bidirectional –12. In pTraffic in ants can be organized either on a spatial or on a temporal scale . SpatialAtta colombica on a narrow trail [In an attempt to isolate the microscopic traffic rules experimental studies on traffic organization in leaf-cutting ants ow trail  and on aow trail  were perow trail  or on a ow trail . On the ow trail , 22. HowThere are many well known models for ant traffic, most of which are mean-field models studying the macroscopic properties of the traffic on trails –31. HoweAtta colombica on a narrow trail [Here we introduce a self-propelled particle model to reproduce the experiments with leaf-cutting ants ow trail  and on aow trail , and to sOU = 2.3 cm/s for both types of particles. The speed of laden particles (L) is set to sL = 1.9 cm/s  in several ways. In particular, particles are assumed to have constant length 1cm and constant type dependent speeds. Mimicking the experimental setup the particles move on a 300 cm long one-dimensional trail connecting the nest and a leaf source. Particles leave the nest and the leaf source according to a Poisson process characterized by the rate parameter μ. At the beginning of each simulation particles are present at the nest and the leaf source. Following the experimental work we consider three types of particles: outbound (O), inbound unladen (U) and laden particles (L). The probability of a particle being laden when leaving the leaf source is 0.24 as observed in the experiment . Due to 1.9 cm/s .x(t) is the x-coordinate of the particle on the trail at time t (the nest is at x = 0 and the leaf source at x = 300), s ∈ {sOU, sL} is the speed of the particle, h ∈ {−1, 1} is the heading of the particle (1 for outbound and -1 for inbound particles), and Δt = 0.1 is the time step. The value of δ(t) ∈ {0, 1} depends on the interactions between particles at time t. δ(t) is 1 if the particle is given the way, and 0 if the particle stops and gives the way. Two particles interact when they are within a distance of 1 + 2 Δt sOU of each other to account for the size of the particles. The interactions between particles are specified by a set of local priority rules identified in [On the narrow trail the positional update formula for each particle is given byified in ;1. An unladen particle (U) does not attempt to pass a laden particle (L) ahead of it. Instead it stops and waits until the laden ant has moved forward enough for it to take another step.2. An outbound particle (O) stops and gives way to a laden particle (L), and potentially a number of unladen particles (U) following the laden particle (See The cooperative rule below).3. An unladen particle (U) stops and gives way to an outbound particle (O), unless the outbound particle (O) is waiting following an interaction with a laden particle (See The cooperative rule below).In order to cover all interaction possibilities we also included the following two rules not quantified in ;4. A particle of any type  does not attempt to pass another particle of the same type ahead of it. Instead it stops and waits until the particle has moved forward enough for it to take another step.5. A laden particle (L) does not stop for stationary inbound unladen particles (U) ahead of it.n = 0,1, …,15) of unladen particles traveling in line behind the laden ant may also be allowed passage. This phenomenon was referred to as “the cooperative rule” in [n unladen ants benefited from the passage of a laden ant in this way in the experiments was quantified and presented in  waits for τ = 0.8n seconds after encountering the laden particle before it starts to move again. Once the outbound particle starts to move it has priority over unladen particles again. The traffic rules for particles on the narrow trail are summarized in When an outbound particle gives way to a laden particle a number . Here wμ associated with the Poisson process dictating the flow of particles leaving the nest and the leaf source. We know from the experiments [There is one unknown parameter in the model: the rate parameter eriments  that theThe wide trail experiment  was condThe main difference between the narrow and wide trail settings is that there is room for ants/particles to turn on the wide trail so they are not forced to stop when encountering an ant/particle with higher priority. Instead the ant/particle can turn to avoid collision and we adapted the narrow trail model to the wide trail by replacing all instances of stop with turn. The traffic rules for particles on the wide trail are presented in x(t) is the x-coordinate of the particle on the trail at time t (the nest is at x = 0 and the leaf source at x = 300), w(t) is the w-coordinate of the particle at time t , s ∈ {sOU, sL} is the speed of the particle, Δt = 0.1 is the time step, and θ(t) is the heading of the particle at time t. The heading θ(t) = θd +θI(t) is composed of two components:θd ∈ {0, π} which is equal to 0 for outbound and π for inbound particles, and θI ∈ {−π/2,0,π/2} which is the turning angle resulting from an interaction and depends on the traffic rules (i will not turn (θI = 0) if it is given the way by particle j. It will turn if it is not given the way by particle j. In that latter case, it will turn up if wi (t) ≥ wj (t) or down if wi (t) < wj (t). Note that when a particle turns its displacement in the x-direction is 0, because t = 0.1s by each turn time step.The positional update formula for each particle in the wide trail model isic rules . During μ associated with the Poisson process of ants leaving the nest and leaf source. The average flow in the wide trail experiments was 8803 ants/hour and choosing μ = 0.8 results in a flow of 8999.4 (s.d. 97.8) and we use this value for the simulations. Unlike in the narrow trail case, where all ants entered and moved on the trail at the same vertical position, on the wide trail ants entered the trail from the nest via a small opening centered on the trail and from the leaf source via a narrow wooden stick attached to the center of the trail. So the ants entered close to the center on both sides of the trail and then scattered in the w-direction. To model this we assume that the vertical entry position (w(0)) for each ant is normally distributed with mean 2.5 (center of the trail) and standard deviation 0.8. This ensures that almost all entry positions lie between 0 and 5 and if the generated w(0)>5 we set w(0) = 4.99 and if w(0)<0 we set w(0) = 0.01.The cooperative rule where unladen following a laden are sometimes allowed passage is not relevant in the wide trail setting because particles are turning instead of stopping. As in the narrow trail case we use the experimentally observed total flow to set the rate parameter To analyze the model we ran 1000 simulations and calculated the proportion of each particle type in each zone of the trail, in addition to the mean and maximum group sizes, and compared the results with the experimental results . We alsoN, (iii) proportion of laden ants at position P in a group, and (iv) proportion of groups of size N led by a laden ant. A comparison of the experimentally observed distributions and the distributions generated from simulations are presented in 74  more frequently travelled in the marginal zones of the trail. For outbound ants (O) about two thirds of them travelled in the central zone of the trail. The asterisks in Our self-propelled particle model based on the local priority rules presented in  generateThis suggests that it is plausible that the priority rules proposed in  are key Understanding the basic principles that govern traffic organization on trails and identifying the factors that influence the movements of ants on trails are of fundamental importance in the biology of social insect colonies. When ants were forced to move on a narrow trail the formation of alternating groups of inbound and outbound ants was observed. Groups of inbound ants were frequently headed by laden ants, which are slower, followed by unladen ants. The model replicates this behavior, most likely due to the rule that dictates that inbound unladen ants do not attempt to overtake laden ants in front of them (Rule 1). This behavior may appear detrimental because unladen ants move slower by staying behind a laden ant instead of progressing more rapidly by moving at its desired speed. However, the model also includes the so-called cooperative rule that allows for the possibility of unladen ants following a laden ant to benefit from the passage of the laden (See rules 2 and 3). These unladen ants avoid head-on collisions with outbound ants and thus spare time they would otherwise waste by stopping as they normally do when they meet an outbound ant. Moreover, this organization promotes information transfer about the level of leaf availability by increasing the number of contacts between outbound and inbound laden ants which stimulate the former to cut and retrieve leaf fragments when reaching the end of the trail –53. FollAtta cephalotes [Formica rufa [are collecting leaves, outbound ants have the second highest priority and they are potentially going to collect leaves, and inbound unladen ants have the lowest priority and they are not collecting leaves. We speculate that priority rules in other species are likely to correspond to the potential utility of each type of ant with respect to the colony’s foraging activity.Our findings suggest that the ants may be using the same generic priority rules on both trails and the observed differences results from constraints imposed by the environment. In particular, on a wider trail there is room to turn during an encounter whereas on a narrow trail this option is not available so the ants have to stop when giving way. In fact, due to the simplicity of these rules we believe that they could be valid, with appropriate modifications, for other species of ant under similar conditions. For example, the same priority rule between laden and unladen ants has been observed in another leaf-cutting ant phalotes  and in tica rufa . In addiica rufa . We alsoOur model distinguishes itself from earlier spp-models of ant traffic in several ways. In particular, we model three types of ants  whereas ,45 only One often thinks about the similarities between ant traffic, pedestrian traffic and vehicular traffic. These analogies have inspired multiple investigations –58. HoweS1 TableN indicates the number of observation used to obtain the mean value or rule.From  based on(DOCX)Click here for additional data file.S2 TableFrom  based on(DOCX)Click here for additional data file.S1 FigAt time 0 there are outbound particles (red dots), inbound unladen particles (blue dots), and an inbound laden particle (black dot) near the middle of the trail. Over time the red particles will move towards the leaf source (right) and the black and blue particles towards the nest (left), and when a particle crosses the middle of the trail we record a crossing as +1 if it is outbound, -1 if inbound unladen, and -2 if inbound laden. We note that on time steps 1 and 2 we record inbound crossings (-1). On time step 3 the first interaction where one unladen particle steps off the trail in order to give way to an outbound ant. This process continues according to the model rules and by the time step 14 we have collected the sequence -1,-1,+1,+1,+1,-2,-1,-1,-1 and from this we calculate group size by counting consecutive entries with the same sign. Here we first had a group of 2 inbound particles , then a group of 3 outbound particles , and then a group of 4 inbound particles . This phenomenon is referred to as a de-synchronization of inbound and outbound traffic involving the formation of alternating groups of inbound and outbound ants in  and we u(TIF)Click here for additional data file.


We read with interest the editorial by Chawla and PehThe statement from the authors that the inclusion of an erect abdominal radiograph, in addition to the supine projection, will double the radiation dose 0.7–1.4 mSv) does require challenging. Physical measurement data obtained from 168 patients collected for the SEPRAIDD project mSv doesWe recognise the desire to reduce the number of abdominal radiographs performed in the acute setting, but they still have value to the clinicianThe authors declare no conflict of interest.