Unlocking the power of LiOH: Key to next-generation ultra-compact thermal energy storage systems.

This study explores the potential of untapped lithium hydroxide (LiOH) as a phase change material for thermal energy storage. By overcoming the challenges associated with the liquid LiOH leakage, we successfully thermal-cycled LiOH in a laboratory scale experimentation, and observed its stability (>500 thermal cycles), without chemical decomposition. This step has never been performed to date. Its solid-to-liquid reversible transitions temperatures and related solidification/melting enthalpies values have been verified. Then, the first experimental characterization of LiOH's thermal properties shows unexpected values for its heat capacity, thermal conductivity and diffusivity, in contradiction with the few ones available in literature. This opens avenues for LiOH's applications for the storage of sensible and latent heat, as shown through the increased cycle efficiency potential of a thermal energy storage system if based on its energy storage capacity; up to six times more volumetric energy density compared to traditional Solar Salt-based systems used in the solar tower plant (4.5 GJ/m3 vs. 0.76 GJ/m3 over 1000 thermal cycles). Additionally, we observed a softening phenomenon that occurs inconsistently during heating, but which may account for its excellent melting properties and the interplay with other raw chemicals. This new insight contributes certainly to the underlying mechanisms in the synthesis of another promising heat storage material in development: the peritectic compound Li4Br(OH)3. This pioneering work suggests LiOH as a promising ultra-compact thermal energy storage material for filling the intermediary gap from current to next-generation solar power plants, although its large-scale application requires further investigation to achieve economic viability.

Imaging subsurface damage of grinded fused silica optics by confocal fluorescence microscopy.

We report an experimental investigation of fluorescence confocal microscopy as a tool to measure subsurface damage on grinded fused silica optics. Confocal fluorescence microscopy was performed with an excitation at the wavelength of 405 nm on fixed abrasive diamond grinded fused silica samples. We detail the measured fluorescence spectrums and compare them to those of oil based coolants and grinding slurries. We evidence that oil based coolant used in diamond grinding induces a fluorescence that marks the subsurface damages and eases its observation. Such residual traces might also be involved in the laser damage process.

Pressure ulcer risk factors in persons with spinal cord injury part 2: the chronic stage.

INTRODUCTION: Pressure ulcers (PUs) are a common complication following spinal cord injury (SCI). Prevalence for persons in the chronic SCI stage varies between 15 and 30%. The risk assessment scales used nowadays were designed on pathophysiological concepts and are not SCI-specific. Recently, an epidemiological approach to PU risk factors has been proposed for designing an SCI-specific assessment tool. The first results seem quite disappointing, probably because of the level of evidence of the risk factors used. OBJECTIVE: To determine PU risk factors correlated to the chronic stage of SCI. MATERIALS AND METHODS: Systematic review of the literature. RESULTS: There are several PU risk factors for chronic SCI stage: socio-demographics, neurological, medical or behavioral. The level of evidence varies: it is quite high for the socio-demographics and neurological factors and low for behavioral factors. DISCUSSION AND CONCLUSION: Behavioral risk factors (relieving the pressure, careful skin monitoring, smoking) are probably the ones for which a preventive strategy can be established. It is important to develop specific assessment tools for these behavioral risk factors to determine their relevance and evaluate the effect of therapeutic educational programs on persons with SCI.

Self-perception of health and fitness among French and Tunisian men and women.

This work examines the effects of sex and culture on physical self-perceptions. The aim was to compare the perception of physical fitness of French and Tunisian men and women. 400 individuals ages 20 to 35 years assessed their own fitness, endurance, strength, flexibility, body composition, and health according to specific category scales by completing a questionnaire. In general, the Tunisian group rated themselves higher than the French group. It appears that perceived physical fitness was related mainly to perceived endurance for both groups. Some disparities were observed between the two nationalities. Analysis showed an interaction between sex and culture (French vs Tunisian). For French men and women and Tunisian men, perceived physical fitness was more associated with perceived endurance, whereas for Tunisian women, perceived physical fitness was more strongly associated with flexibility. These data show that self-perception of physical fitness is a dimension which varies between individuals from different cultures.

[Female prostitutes in Phnom Penh, Cambodia: changes in knowledge, attitudes and practices between 2000 and 2004]. / Femmes prostituées à Phnom Penh (Cambodge): évolution des connaissances, attitudes et pratiques entre 2000 et 2004.

A survey was carried out to evaluate the knowledge, attitudes and practice of female prostitutes In Phnom Penh (Cambodia) in 2000 and 2004. A total of 131 women were included both years. The population was 75% Cambodian and 25% Vietnamese. Average age was 22.9 years in 2000 and 25.5 years in 2004. Sixty-seven percent of the women surveyed stated that prostitution was a "voluntary" choice. The awareness rate for sexual transmitted diseases (STD) including AIDS and its main clinical signs and of the protective value of condoms was 90% in 2000 and 96% in 2004. However 30% reported unprotected sexual relations with at least one of their last 10 clients. Twenty-five percent performed oral sex usually without precaution. Drug use was limited to methamphetamines. Monthly income ranged from 15 dollars to 22.5 dollars (mean, 66 dollars). This amount is higher than the salary of a factory worker. Despite good knowledge of STD and prevention measures, prostitutes in Phnom Penh appear to have unsafe sexual practices.

Antioxidants and mitochondrial respiration in lung, diaphragm, and locomotor muscles: effect of exercise.

Previous studies have shown that exhaustive exercise may increase reactive oxygen species (ROS) generation in oxidative muscles that may in turn impair mitochondrial respiration. Locomotor muscles have been extensively examined, but there is few report about diaphragm or lung. The later is a privileged site for oxygen transit. To compare the antioxidant defense system and mitochondrial function in lung, diaphragm and locomotor muscles after exercise, 24 young adult male rats were randomly assigned to a control (C) or exercise (E) group. E group rats performed an exhaustive running test on a motorized treadmill at 80-85% VO2max Mean exercise duration was 66+/-2.7 min. Lung, costal diaphragm, mixed gastrocnemius, and oxidative muscles (red gastrocnemius and soleus: RG/SOL homogenate) were sampled. Mitochondrial respiration was assessed in tissue homogenates by respiratory control index (RCI: rate of uncoupled respiration/rate of basal respiration) measurement. Lipid peroxidation was evaluated by malondialdehyde concentration (MDA) and we determined the activity of two antioxidant enzymes: superoxide dismutase (SOD) and glutathione peroxidase (GPX). We found elevated basal (C group data) SOD and GPX activities in both lung and diaphragm compared to locomotor muscles (p<.001). Exercise led to a rise in GPX activity in red locomotor muscles homogenate (GR/SOL; C = 10.3+/-0.29 and E = 14.4+/-1.51 micromol x min(-1) x gww(-1); p<.05), whereas there was no significant change in lung and diaphragm. MDA concentration and mitochondrial RCI values were not significantly changed after exercise. We conclude that lung and diaphragm had higher antioxidant protection than locomotor muscles. The exercise test did not lead to significant oxidative stress or alteration in mitochondrial respiration, suggesting that antioxidant function was adequate in both lung and diaphragm in the experimental condition.

Time course of muscular blood metabolites during forearm rhythmic exercise in hypoxia.

O2 concentration, PO2, PCO2, pH, osmolarity, lactate (LA), and hemoglobin (Hb) concentrations in deep forearm venous blood were repeatedly measured during submaximal exercise of forearm muscles. Concentrations of arterial blood gases were determined at rest and during exercise. Experiments were conducted under normoxia and hypobaric hypoxia (PB = 465 Torr). In arterial blood, data obtained during exercise were the same as those obtained during rest under either normoxia or hypoxia. In venous muscular blood, PO2 and O2 concentration were lower at rest and during exercise in hypoxia. The muscular arteriovenous O2 difference during exercise in hypoxia was increased by no more than 10% compared with normoxia, which implied that muscular blood flow during exercise also increased by the same percentage, if we assume that exercise O2 consumption was not affected by hypoxia. Despite increased [LA], the magnitude of changes in PCO2 and pH in hypoxia were smaller than in normoxia during exercise and recovery; this finding is probably due to the increased blood buffer value induced by the greater amount of reduced Hb in hypoxia. Hence all the changes occurring in hypoxia showed that local metabolism was less affected than we expected from the decrease in arterial PO2. The rise in [Hb] that occurred during exercise was lower in hypoxia. Possible underlying mechanisms of the [Hb] rise during exercise are discussed.

Variability in energy cost and walking gait during race walking in competitive race walkers.

PURPOSE: The aim of this study was to examine the variability of energy cost (Cw) and race walking gait after a 3-h walk at the competition pace in race walkers of the same performance level. METHODS: Nine competitive race walkers were studied. In the same week, after a first test of VO2max determination, each subject completed two submaximal treadmill walks (6 min length, 0% grade, 12 km X h(-1) speed) before and after a 3-h overground test completed at the individual competition speed of the race walker. During the two submaximal tests, subjects were filmed between the 2nd and the 4th min, and physiological parameters were recorded between the 4th and the 6th min. RESULTS: Results showed two trends. On the one hand, we observed a significant and systematic increase in energy cost of walking (mean deltaCw = 8.4%), whereas no variation in the gait kinematics prescribed by the rules of race walking was recorded. On the other hand, this increase in metabolic energy demand was accompanied by variations of different magnitude and direction of stride length, of the excursion of the heel and of the maximal ankle flexion at toe-off among the race walkers. CONCLUSION: These results indicated that competitive race walkers are able to maintain their walking gait with exercise duration apart from a systematic increase in energy cost. Moreover, in this form of locomotion the effect of fatigue on the gait variability seems to be an individual function of the race walk constraints and the constraints of the performer.

Long-term relationship between acute rhabdomyolysis and abnormal high-energy phosphate metabolism potentiated by ischemic exercise.

Relative concentrations of inorganic phosphate [Pi]r, creatine phosphate [CP]r, adenosine triphosphate [ATP]r, and intracellular pH (pHi) were determined by 31P-NMR spectroscopy in the flexores digitorum muscles. The measurements were performed at rest, during bouts of rhythmic exercises at different powers, including one with restricted blood supply, and during recovery. Normal subjects (N) and subjects with previous histories of exercise hyperthermia (EH) were compared. No significant difference was found between N and EH subjects at rest. During exercise [ATP]r was not affected, except in EH subjects exercising under partial muscle ischemia (P less than 0.001); in both N and EH, [CP]r and pHi decreased, and the higher the load the more pronounced the reduction. These changes were significantly larger in EH patients than in N (P less than 0.05), and the differences were dramatically increased by reducing blood supply (P less than 0.001). During recovery, the return to the control values was much slower in EH patients than in N, in particular for pHi after the exercise under partial ischemia. In conclusion, the fact that metabolic disorders are still patent long after the EH occurrence supports the possibility of latent myopathy and of a persistent metabolic disorder. Thus, 31P-NMR spectroscopy could be a useful noninvasive test to detect EH susceptibility in at-risk subjects.

SEMG power spectrum changes during a sustained 50% Maximum Voluntary Isometric Torque do not depend upon the prior knowledge of the exercise duration.

Endurance time (Tlim) is a relevant indicator of muscular resistance to fatigue. It has been recently shown that SEMG changes computed during shorter periods (sub-maximal durations) than the whole test duration could serve to predict Tlim. The aim of the present study was to test whether the prior knowledge of the sub-maximal duration had any influence on Tlim prediction throughout SEMG changes. For this purpose, we compared myoelectric changes estimated over a 30-s isometric contraction whose duration was known by the subjects, to those changes measured during the first 30 s of a test prolonged until exhaustion. The effort intensity was set at 50% of the maximal voluntary isometric torque (MVIT). The myoelectric manifestations of muscle fatigue appeared to change in a similar way during both sessions for temporal and spectral analyses. In conclusion, the prior knowledge of the duration of sustained isometric contraction did not influence the motor unit recruitment strategy throughout surface EMG evaluation. These results confirmed that the use of SEMG changes computed over shorter periods than expected endurance time may be applied to investigate the capability of the initial rate of SEMG changes to predict muscle endurance capacity at 50%MVIT. This may be of particular interest for patient evaluation in the clinical field.

Does arterial PCO2 interfere with hypoxia in muscular metabolism in man?

To answer the question whether PCO2 affects the muscular metabolism, PO2, PCO2, pH, lactic acid concentration and hemoglobin were measured in the efferent muscular venous blood from common flexor digitorum, during forearm rhythmic exercise corresponding to VO2max. Exercise was carried out either in hypocapnic hypoxia i.e. in permanent high altitude residents and translocated lowlanders, or in hypercapnic hypoxia i.e. in chronic obstructive lung disease (COLD) patients. The results show that, during exercise: i) PO2 in muscular venous blood remains around 20 Torr in normoxia and hypocapnic hypoxia and even higher (25 torr) in COLD patients, despite low arterial PaO2, and ii) arterial and/or local PCO2 play a role in the control of the muscular blood flow. But we cannot conclude that a change in PaCO2 affects muscular metabolism itself, because lactic acid in the muscular venous blood, that we used to check this effect, is likely dependent on mechanisms other than anaerobic glycolysis, such as a change in lactic acid efflux from the myocytes. The increase in muscular venous PCO2 may enhance the myocyte permeability to lactic acid during exercise.

Variability in energy cost of running during one training season in high level runners.

The purpose of this study was to investigate the effect of training specificity on a possible change in the energy cost of running over a period of one training season in high level competition runners. Four middle distance and four long distance runners participated in treadmill tests on three sessions after a specific training period. In each session, every subject participated in two tests to determine, in the first test the maximal oxygen consumption and in the second test the energy cost of running. The second test was performed at 60% and 80% of Vmax (maximal speed reached during the first test, respectively 12 and 16 km.h-1), and at 0% grade. The maximal oxygen uptake (VO2max, ml.kg-1.min-1) increased significantly between the first and the last session (p < 0.05). For all the tests, long distance runners showed higher values of VO2max than middle distance runners (p < 0.001). During the year, there were no significant changes in energy cost (C, ml/kg-1.km-1) between the first and the last session (respectively at 60% and 80% vmax: 165 +/- 5.8 vs 164 +/- 4.9 and 167.5 +/- 3.5 vs 166.8 +/- 3.3), and no differences were found between middle and long distance runners. An addition, no changes were found in lactate concentration or in respiratory exchange ratio during all the training season. Discussion set out the difficulty to conclude to a stability in energy cost of running. First by the fact that the energy cost reflects both positive and negative effects of training.(ABSTRACT TRUNCATED AT 250 WORDS)

Running economy, preferred step length correlated to body dimensions in elite middle distance runners.

The purpose of this research was to study the relationship between running economy, step length, and body dimensions. Elite middle distance runners were tested for one high submaximal volocity very close to usual training speeds, near the anaerobic threshold (15 km.h-1) and one low submaximal velocity very different to usual training speeds, near the speed transition between walking and running (9 km.h-1). All the subjects were selected after a maximal protocol to be homogeneous on VO2max (65.7 +/- 2.3 ml.kg-1.min-1). Then they were monitored during two submaximal tread-mill tests at 54.4 +/- 2.2% (9 km.h-1) and 78.5 +/- 3.9% VO2max (15 km.h-1). Body weight, body fat, height, sitting height, low extremity length (height - sitting height), relative low extremity length, leg length, thigh length, foot length were determined. The results indicate an effect of the running speed on the relationship between body dimensions, step length and VO2. The relation was inverse between running economy, body dimensions at 9 and 15 km.h-1 and no significant correlation was found for running economy between these two speeds. Furthermore, the mode of expressing VO2 in ml.kg-0.75.min-1 affects these relations. Thus, this result allows us to make the assumption that mechanisms of adaptation can be different according to the running speed, and the specific constraints that it represents for each subject.

Night heart rate variability during overtraining in male endurance athletes.

AIM: The purpose of the study was to examine whether an unaccustomed increase in training volume would result in characteristics changes in heart rate variability (HRV), in order to determine if this marker can be used to diagnose overtraining. METHODS: Nine experienced endurance athletes increased their usual amount of training by 100% within 4 weeks. Night ECG was recorded before (baseline) and after (OVER) this period of overload, and after 2 weeks of recovery (REC). RESULTS: We diagnosed overtraining in 6 subjects using both physiological and psychological criteria. No difference was noted in heart rate for night periods (56+/-12, 55+/-10 and 53+/-15 bpm, respectively; p>0.05). We found no significant changes of LF/HF (1.10+/-0.92, 0.96+/-0.57 and 0.59+/-0.43, respectively; p>0.05) or HF expressed in normalized units (54.81+/-20.12, 53.81+/-11.35 and 66.15+/-15.12%, respectively; p>0.05). CONCLUSION: In the conditions of the present study, HRV during sleep does not seem to be a valid marker of overtraining in male endurance athletes. Before concluding to the uselessness of this tool in the monitoring of the syndrome, longitudinal studies with elite or sub-elite athletes are needed to determine if spontaneously developed overtraining results in the same response.

Use of energy cost and variability in stride length to assess an optimal running adaptation.

The aim of this study was to analyse how subjects' running adaptation was affected after a training overload. 14 middle-distance runners were tested before and after a training protocol of 15 days conducted only at one training pace. The efficacy of this training protocol to improve energy cost of running was observed only at the training pace. This improvement was correlated with a particular systematic variation in stride length whereas no changes in stability of stride length were recorded. The data were interpreted in terms of specificity of training for which energy cost and stability of stride length could be considered criteria of an optimal adaptation to the training pace.

Self-perception of fitness and personality traits.

Our aim was to analyze how subjects perceive their own physical fitness. In Study 1 the 247 subjects assessed their own fitness, endurance, strength, flexibility, and body composition according to specific category scales. Analyses showed that self-perceived physical fitness was mainly related to perceived cardiovascular endurance. According to sex and age, strength, flexibility, and body composition could have a significant influence. The scores obtained on the five scales were highly correlated, suggesting they were overdetermined by a more general factor assimilated to physical self-worth. In Study 2 the 91 subjects completed the same five scales, the Spielberger State-Trait Anxiety Inventory, the Coopersmith Self-esteem Inventory, and the Bem Sex-role Inventory. Results confirmed the hierarchical model of Fox and Corbin (1989) and showed that physical self-worth is related to self-esteem, anxiety, and masculinity.