Regression Analysis of PEM Fuel Cell Transient Response

To develop operating strategies in polymer electrolyte membrane (PEM) fuel cell-powered applications, precise computationally efficient models of the fuel cell stack voltage are required. Models are needed for all operating conditions, including transients. In this work, transient evolutions of voltage, in response to load changes, are modeled with a sum of three exponential decay functions. Amplitude factors are correlated to steady-state operating data (temperature, humidity, average current, resistance, and voltage). The obtained time constants reflect known processes of the membrane heat/water transport. These model parameters can form the basis for the prediction of voltage overshoot/undershoot used in computational-based control systems, used in real-time simulation. Furthermore, the results provide an empirical basis for the estimation of the magnitude of temporary voltage loss to be expected with sudden load changes, as well as a systematic method for the analysis of experimental data. Its applicability is currently limited to thin membranes with low to moderate humidity gases, and with adequately high reactant-gas stoichiometry

The Effects of Time Varying Curvature on Species Transport in Coronary Arteries

Alterations in mass transport patterns of low-density lipoproteins (LDL) and oxygen are known to cause atherosclerosis in larger arteries. We hypothesise that the species transport processes in coronary arteries may be affected by their physiological motion, a factor which has not been considered widely in mass transfer studies. Hence, we numerically simulated the mass transport of LDL and oxygen in an idealized moving coronary artery model under both steady and pulsatile flow conditions. A physiological inlet velocity and a sinusoidal curvature waveform were specified as velocity and wall motion boundary conditions. The results predicted elevation of LDL flux, impaired oxygen flux and low wall shear stress (WSS) along the inner wall of curvature, a predilection site for atherosclerosis. The wall motion induced changes in the velocity and WSS patterns were only secondary to the pulsatile flow effects. The temporal variations in flow and WSS due to the flow pulsation and wall motion did not affect temporal changes in the species wall flux. However, the wall motion did alter the time-averaged oxygen and LDL flux in the order of 26% and 12% respectively. Taken together, these results suggest that the wall motion may play an important role in coronary arterial transport processes and emphasise the need for further investigation

Digital elevation model validation with no ground control: application to the topodata dem in Brazil

Digital Elevation Model (DEM) validation is often carried out by comparing the data with a set of ground control points. However, the quality of a DEM can also be considered in terms of shape realism. Beyond visual analysis, it can be verified that physical and statistical properties of the terrestrial relief are fulfilled. This approach is applied to an extract of Topodata, a DEM obtained by resampling the SRTM DEM over the Brazilian territory with a geostatistical approach. Several statistical indicators are computed, and they show that the quality of Topodata in terms of shape rendering is improved with regards to SRTM

Caracterização de uso e cobertura da terra na Amazônia utilizando imagens duais multitemporais do COSMO-SkyMed

The use of radar imagery is an alternative source of information to support the monitoring of the Amazon region, since the optical images have imaging limitations in tropical areas due to the occurrence of clouds. Therefore, the goal of this study is to analyze the radar images in X-band multi-temporal polarized obtained by COSMO-SkyMed satellite (COnstellation of small Satellites for Mediterranean basin Observation), in the intensity mode, isolated and/or combined with textural information, to thematic characterization of land use/land cover in the Humaitá, Amazonas State region. The methodology used includes: analysis of the dual images obtained during two subsequent acquisitions, in order to explore the potential of the dataset as a quad-pol intensity; extraction of textural attributes from the co-occurrence matrix (Gray Level Co-occurrence Matrix) and subsequent contextual classification; statistical assessment of the thematic performance of the intensity and textural images, isolated and in polarized groups. Within the results achieved, the group formed only by the intensity images presented a better performance if compared to those containing the textural attributes. In this discrimination, the classes involved were forest, alluvial forest, reforestation, savannah, pasture and burned areas, yielding 66% overall accuracy and a Kappa value of 0.55. The results showed that X band images, from COSMO-SkyMed, StripMap mode (Ping-Pong), multi-polarized, presents a moderate potential to characterize and monitor the dynamics of land use/land land cover in the Brazilian Amazon.A utilização de imagens de radar é fonte alternativa de informações para subsidiar o monitoramento da região amazônica, visto que as imagens ópticas têm limitações de imageamento em zonas tropicais face a ocorrência de nuvens. Por conseguinte este trabalho teve como objetivo analisar a capacidade das imagens-radar de banda X multitemporais e polarizadas obtidas pelo satélite COSMO-SkyMed (COnstellation of small Satellites for Mediterranean basin Observation), no modo intensidade, isoladamente e agregados às informações texturais, na caracterização temática de uso e cobertura da terra no município de Humaitá/AM. A metodologia empregada consistiu daanálise das imagens duais obtidas em duas aquisições subsequentes, de forma a explorar a potencialidade do conjunto de dados na forma quad-pol intensidade; extração dos atributos texturais a partir da matriz de coocorrência (Gray Level Co-occurrence Matrix) e posterior classificação contextual; avaliação estatística de desempenho temático das imagens intensidade e texturais, isoladas e em grupos polarizados. Dentre os vários resultados alcançados, foi verificado que o grupo formado somente pelas imagens intensidade apresentou o melhor desempenho, comparado àqueles contendo os atributos texturais. Nesta separabilidade, estavam envolvidas as classes de floresta, floresta aluvial, reflorestamento, savana, pasto e queimada, obtendo-se 66% de acurácia total e valor Kappa de 0,55. Os resultados mostraram que as imagens de banda X do COSMO-SkyMed, modo StripMap (Ping-Pong), multipolarizadas, têm potencial moderado para a caracterização e monitoramento da dinâmica de uso e cobertura da terra na Amazônia brasileira

Effects of sleep loss and strenuous physical activity on the rest-activity circadian rhythm : a study on 500 Km and 1000 Km dogsled racers

Objective. Rest-activity circadian rhythm is strongly linked to an organism's entrainment. Sleep loss and prolonged fatigue could affect the circadian system, inducing neurobehavioral deficits. The Finnmarksl\uf8pet is Europe's longest dogsled race. In this competition, lasting up to 7 days, participants (mushers) are physically active most of the time, having little and fragmented rest. Therefore, the race provides an opportunity to investigate the effects of prolonged fatigue and sleep loss. Methods. Ten mushers, participating in the 500 km and 1,000 km categories, underwent continuous actigraph monitoring (5 days) before and after the race. During the competition, heart rate (HR) was recorded by an HR monitor. Results. There was a reduction in the average activity values during the 24-hr cycle after the race. Although there were signs of a forward phase shift, these were weak and unstable. Nonparametric circadian rhythm analysis (NPCRA) showed reductions in interdaily stability (IS) and relative amplitude (RA). 1,000 km mushers also showed sleep disturbances. Conclusion. A period of 3 days of little and fragmented sleep (3-4 hr of total rest per day), in which subjects were engaged in a prolonged physical effort, was enough to significantly affect the rest-activity rhythm. A longer period (5 days) in such a condition induced even more accentuated alterations, with a disturbance in nocturnal sleep. Disrupted sleep is common among hospitalized patients and those working long shifts. This study demonstrates changes in the structure of the rest-activity circadian rhythm that can result and may suggest opportunities for intervention

Methodological issues for studyng the rest-activity cycle and sleep disturbances : a chronobiological approach using actigraphy data

Shift work schedules, intensive physical exercise late in the day, psychological stress, or a busy lifestyle might induce disorders of the circadian structure, which can affect health on both the physiological and neurobehavioral levels. Rest-activity rhythm is strongly connected with an organism's circadian structure, and irregular sleep-wake patterns can lead to a disruption of entrainment, resulting in physiological and neurobehavioral dysfunction. Shift nurses are often subject to disturbances in the quality and duration of their sleep, raising the possibility of negative impacts on their health and their patients' safety. Researchers have used actigraphy in a number of studies to assess sleep patterns. Because of the close connection between sleep and circadian structure, it may be useful to extend the evaluation of actigraphy data to the analysis of the rest-activity rhythm with rhythmometric procedures to provide a better understanding of possible sleep disorders in relation to entrainment. Actigraphy is an easy and reliable way to study these rhythms and identify possible circadian-rhythm disorders. In this article, the authors discuss methodological issues concerning the evaluation of the rest-activity rhythm, with a focus on actigraphy

Intensity pacing strategy and downhill strategy during a cross country ski race

INTRODUCTION During a cross country ski race the intensity pacing strategy could be affected by different variables. It\u2019s not easy to choose the winner strategy. In a previous analysis we found no correlation between the mean heart rate (HR) during the race and the time of the race (RT). In a downhill, the HR normally decreases until the beginning of next flat or uphill. The HR-trend during downhill can be influenced by the payment of oxygen debt and different downhill strategy (Mognoni et al., 2001). The aim of this study was to investigate which intensity pacing strategy would give the best race time during a cross country ski race. METHODS During a 10 km interval start skating race, HR of 9 male cross country skiers (Category U-23) was recorded by Polar RS400\uae (Hz.5sec). We found that all the racers had a clear decrease in HR at about 7 km, in correspondence with a long downhill. We considered the percentage of HR max given by the subjects (%HRmax) pre and post the downhill (% 06HR=%HRpre 12%HRpost). In order to study the influence of downhill strategies on the RT, we calculated the correlation index between % 06HR and RT for all the skiers. As indicator of intensity pacing strategy, we used the angular coefficient of the linear regression for all the HR profiles. HR data were analyzed by Polar Pro Trainer\uae and Microsoft Excel 2003\uae. RESULTS From angular coefficients, we noticed that all the subjects incremented their HR from the start to the end. There were no correlation between the angular coefficient and RT (R2=0.013), and between % 06HR and the RT for all the skiers (R2=0.005), showing that the capacity of recovery during the downhill did not influence RT. The decrease in HR changes from subject to subject. DISCUSSION The increment of HR from the start to the end, as the angular coefficients show, has not a linear relationship with RT. This is in opposition with which was found by Lima-Silva (2010) in 10-km running race. The decrease in HR during the downhill, changing for each subject strategy, did not influence RT. The skiers could push faster to increase speed or let the ski flow to recover (Bilodeau et al., 1991). % 06HR could be influenced by individual technique, ski wax, athletic condition and the kind of work during the downhill. The final part of the race reflects higher intensity as compared to the initial, even if each skier chose his preferred strategy both during the whole race and the downhill. We hypothesise that the skiers used different pacing and downhill strategies during this downhill, a new study is prepared to focus upon this. REFERENCES Bilodeau B. et al. (1991). Int. J. Sports Med. 12:71-76. Lima-Silva A.E. et al. (2010). Eur. J. Appl. Physiol. 108:1045-1053. Mognoni P. et al. (2001). Eur. J. Appl. Physiol. 85:62-27

Effects of sleep loss and strenuous physical activity on the rest-activity circadian rhythm : a study on 500 Km and 1000 Km dogsled racers

Objective. Rest-activity circadian rhythm is strongly linked to an organism's entrainment. Sleep loss and prolonged fatigue could affect the circadian system, inducing neurobehavioral deficits. The Finnmarksl\uf8pet is Europe's longest dogsled race. In this competition, lasting up to 7 days, participants (mushers) are physically active most of the time, having little and fragmented rest. Therefore, the race provides an opportunity to investigate the effects of prolonged fatigue and sleep loss. Methods. Ten mushers, participating in the 500 km and 1,000 km categories, underwent continuous actigraph monitoring (5 days) before and after the race. During the competition, heart rate (HR) was recorded by an HR monitor. Results. There was a reduction in the average activity values during the 24-hr cycle after the race. Although there were signs of a forward phase shift, these were weak and unstable. Nonparametric circadian rhythm analysis (NPCRA) showed reductions in interdaily stability (IS) and relative amplitude (RA). 1,000 km mushers also showed sleep disturbances. Conclusion. A period of 3 days of little and fragmented sleep (3-4 hr of total rest per day), in which subjects were engaged in a prolonged physical effort, was enough to significantly affect the rest-activity rhythm. A longer period (5 days) in such a condition induced even more accentuated alterations, with a disturbance in nocturnal sleep. Disrupted sleep is common among hospitalized patients and those working long shifts. This study demonstrates changes in the structure of the rest-activity circadian rhythm that can result and may suggest opportunities for intervention

Influence of chronotype on responses to a standardized, self-paced walking task in the morning vs afternoon : a pilot study

The response to sub-maximal physical activity performed in the morning and late afternoon by individuals with different chronotypes was investigated. 22 participants filled out the Morningness-Eveningness Questionnaire and underwent a self-paced walking task that consisted of walking from the top to the bottom of a hill and back three times (1,836 meters, with a slope of 14.16%). The task was repeated twice: late afternoon (16:30) and early morning (08:30). Walking speed (time for completion in seconds), heart rate, and perceived exertion were measured during each task, with overall results given as a general descriptive analysis. Preliminary findings suggest that chronotype is likely to influence the responses to exercise, mostly with evening-types seeming at a disadvantage when performing a physical task in the morning. Individuals can be classified by circadian typology or chronotype, which is the propensity to be a morning-type, evening-type, or neither-type. The circadian typology, commonly referred to as being a morning person or an evening person or somewhere in between, is involved not only in the expression of physiological rhythms, but also in habits and lifestyles, such as sleeping patterns (Park, Matsumoto, Seo, & Shinkoda, 1999) that emerge especially during adolescence (Park, Matsumoto, Seo, Kang, & Nagashima, 2002) and remain throughout adult life (Koukkari & Sothern, 2006)