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At least 649 records · Page 36Linked to original sources
PubMed2006

Determining biodegradability of plastic materials under controlled and natural composting environments.

With the advent of recently promulgated Government regulations on plastics in Mauritius, a study was initiated to examine the biodegradability of two different types of plastic, namely Willow Ridge Plastics - PDQ-H additive (Plastic A) and Ecosafe Plastic - TDPA additive (Plastic B) under controlled and natural composting environments. The results obtained from the controlled composting environment showed that the cumulative carbon dioxide evolution for Plastic A was much higher than that for Plastic B. Plastic A therefore showed a higher level of biodegradation in terms of CO2 evolution than Plastic B. However, from the regression analysis, it was found that the level of CO2 varying with time fitted the sigmoid type curves with very high correlation coefficients (R2 values: 0.9928, 0.9921 and 0.9816, for reference material, inoculum and Plastic A, respectively). The corresponding F-values obtained from the ANOVA analysis together with significance levels of p<0.05 indicated that the three treatments analysed in the biodegradability experiment were significant. The other experiment was undertaken to observe any physical change of Plastics A and B as compared to a reference plastic, namely, compostable plastic bag (Mater-Bi product-Plastic C), when exposed to a natural composting environment. Thermophilic temperatures were obtained for about 3-5 days of composting and the moisture content was in the range of 60-80% throughout the degradation process. It was observed that after 55 days of composting, Plastic C degraded completely while Plastic A and Plastic B did not undergo any significant degradation. It can be concluded that naturally based plastic made of starch would degrade completely in a time frame of 60 days, whereas plastics with biodegradable additive would require a longer time.

Aerobiosis↗
PubMed1986

The role of polyunsaturated fatty acids in fish.

The physical properties of polyunsaturated and saturated fatty acids are compared in relation to melting points and fluidity. The role of polyunsaturated fatty acids on membrane fluidity and membrane bound enzyme activity is discussed. The influence of the environment, particularly temperature, on poikilothermic animals is considered in relation to membrane fatty acid composition and metabolism. The metabolic role of polyunsaturated fatty acids of the (n-3) series and their interaction with arachidonate metabolism is discussed.

Animals↗
PubMed1986

Readdressing personal cooling with ice.

An ice-based system of personal, non-restrictive cooling of workers exposed to high temperature work environments in nuclear power plants was evaluated. The garments were designed to be worn under the protective clothing donned for penetration into radiation areas. The cooling system consisted of direct body contact with small packets of frozen water enclosed in the pockets of a shirt in high ambient temperatures (55 degrees C) and moderate metabolic heat production (200-300 kcal/hr). Mean exposure time without cooling (control) was 52 min for workloads demanding 200 kcal/hr energy expenditure. A long garment with 7.2 kg of frozen water (LFWG) increased mean exposure time over the control by 242% (163% for the same garment with 6.2 kg of frozen water). A short version garment with 3.8 kg of frozen water (SFWG) increased the stay time by 115%. In field observations, the LFWG with 6.2 kg of frozen water improved stay time by 125%. The leveling off of the body temperatures and heart rates during the work both in the laboratory and in the field confirmed a reduction of heat strain associated with the use of these garments. Calculated heat balance equations of heat uptake by the ice predicted these results very closely. It was concluded that direct body contact with frozen water provided predictable adequate body cooling for the work and ambient conditions investigated in this study.

Adult↗
PubMed2004

Geographic variation in the life history of the sagebrush lizard: the role of thermal constraints on activity.

Thermal constraints on the time available for activity have been proposed as a proximate mechanism to explain variation in suites of life history traits. The longer that an ectotherm can maintain activity, the more time it has to forage and the greater chance that it will encounter a predator and be eaten. Thus, the thermal environment may produce a trade off between growth and survival when variation in the environment favors increased activity. I used mark-recapture data from a demographic study of three natural populations of the sagebrush lizard (Sceloporus graciosus) and estimates of thermal opportunity for each population to evaluate whether variation in the thermal environment can explain patterns of growth and survival that occur over an elevational gradient. Lizards from the highest elevation population exhibited higher individual growth rates than those of lizards from lower elevation, while mortality rates increased with elevation for these populations. The covariation of fast growth and high mortality with increased thermal opportunity is the opposite trend expected if the thermal environment alone is to explain patterns of life history in these lizards. Additional factors including thermal heterogeneity in the distribution of microhabitats of lizards, adaptation to local environmental conditions, and a potential trade-off between resource acquisition and predation risk need to be addressed to obtain a satisfactory explanation of the causative mechanisms producing life history variation.

Animals↗
PubMed1999

Pharmacokinetics of melphalan in isolated limb perfusion.

The pharmacokinetics of melphalan was studied by sampling of tissue and plasma in 72 rats that underwent isolated hyperthermic limb perfusion under different conditions. A miniaturized extracorporeal circulation system for small animals was used for perfusion of the rat hindlimb. Melphalan levels (L-phenylalanine mustard, L-PAM) were determined by high-performance liquid chromatography (HPLC). The temperature of the perfusate plasma and tissue, pH, administration method, and flow rate were modified and compared with regard to their influence on pharmacokinetic parameters. The highest tissue penetration of melphalan was observed under the following conditions: (a) pH range of the perfusate plasma between 7.3 and 7.7 (physiological environment), (b) temperature range of the perfusate from 40 degrees to 41.5 degrees C (destruction of cellular carrier systems at higher temperatures and increased inactivation by hydrolysis of melphalan above 41.5 degrees C), (c) application of melphalan as a single dose into the reservoir of the extracorporeal circuit (optimal tissue penetration), and (d) reduced perfusate flow (prolonged contact time between perfusate and tissue).

Algorithms↗
PubMed2005

Acrylic bone cements: mechanical and physical properties.

Mechanical and physical properties are of particular significance for the performance of acrylic bone cement. Several mechanical test methods are described in the literature to characterize the mechanical performance of bone cements. The simulation of the in vivo situation is extremely difficult, however, because of the complex mechanism of loading in the bone. The usefulness of the different mechanical and physical test methods, several results of commercial acrylic bone cements, and the influence of different parameters, such as temperature, test environment, and preparation of specimens on these results are discussed in this article.

Bone Cements↗
PubMed1990

Growth characteristics of motile Aeromonas spp. isolated from different environments.

The growth of 80 strains of motile Aeromonas spp. derived from environments with temperatures above 25 degrees C and below 15 degrees C, respectively, were examined at five temperatures (5 degrees C, 10 degrees C, 25 degrees C, 37 degrees C and 44 degrees C) and four salt levels (0.05%, 2%, 4% and 6% NaCl). Sixty-one strains were further examined at two pH levels (pH 7.3 and pH 5.3). All strains grew at 25 degrees C and 10 degrees C with the majority of the isolates proliferating from approx. 10(2) to approx. 10(7) cfu/ml within 1 and 3 days, respectively. In contrast, there were significant differences in the proportion of isolates able to grow at 5 degrees C and 37 degrees C depending on the temperature of their source of isolation. The ecological background of the organisms thus influences their thermal growth range and their ability to proliferate at body temperature, a highly significant factor in infective disease. At 25 degrees C and pH 7.3, all strains grew in 0.05% NaCl, 96% grew in 2% NaCl, 96% grew in 2% NaCl while few grew in broth containing 4% or 6% NaCl. Lowering the pH to 5.3 with lactic acid caused a marked increase in the lag phase at 25 degrees C and prevented growth of a large number of isolates at suboptimal conditions. Thus, none of the isolates from warm environments and only 8% of the isolates from cold environments grew at this pH at 5 degrees C. The observed differences in growth optima between strains from different environments are discussed in relation to food- or waterborne infection.

Aeromonas↗
PubMed2005

Degradation of biodiesel under different storage conditions.

This paper aimed to investigate the biodiesel degradation characteristics under different storage conditions. The qualities of twelve biodiesel samples, which were divided into 3 groups and stored at different temperatures and environments, were monitored at regular interval over a period of 52 weeks. Experimental results demonstrated that the biodiesel under test degraded less than 10% within 52 weeks for those samples stored at 4 and 20 degrees C while nearly 40% degradation was found for those samples stored at a higher temperature, i.e. 40 degrees C. The results suggested that high temperature, together with air exposure, greatly increase the biodiesel degradation rate. The temperature or air exposure alone, however, had little effect on biodiesel degradation. Water content in biodiesel will enhance biodiesel degradation due to hydrolysis but its effect is much less than the above two factors.

Bioelectric Energy Sources↗
PubMed1995

Cold water immersion simulations using the Wissler Texas Thermal Model: validation and sensitivity analysis.

BACKGROUND: Wissler's Texas Thermal Model (TM) has been used to simulate the effects of thermal stresses on individuals under a variety of conditions. As part of a U.S. Navy effort to develop integrated protection garments, TM was modified to predict tolerance to cold water immersion (CWI) with garments with clo values less than 0.1 (15). METHODS: With these modifications, TM predictions were validated using experimental data obtained from 39 males and females during anti-exposure suit CWI assessments. Data analyses were based on changes in rectal (Tre) and various skin temperatures (Tsk). A sensitivity analysis was also performed to determine which TM parameters were most affected during simulated CWI. The condition tested was head-out immersion in 4.4 degrees C water by a 72.6 kg man (10 mm mean skinfold thickness). RESULTS: For most of the subject pool, the estimated change in Tre, chest, thigh, calf, and arm temperatures were not statistically different from experimental values. However, TM predictions were less accurate with respect to female responses. Based on thermal end points, TM predictions indicated that the following body segments were most sensitive to changes in insulation level (ordered from most to least important): chest and abdomen, leg, head, and arm. The physical parameters mean skinfold thickness, basal metabolic rate, body weight, and exercise metabolic rate had the most impact on TM predictions. CONCLUSIONS: The relative benefit of increased insulation on individual body segments was identified to aid garment design. Further, the relative importance of model physical parameters was identified so that judicious initial conditions could be selected to ensure that only garment design changes would be reflected in model predictions.

Abdomen↗
PubMed1988

Geographic patterns of childhood insulin-dependent diabetes mellitus. Diabetes Epidemiology Research International Group.

Population-based registries of insulin-dependent diabetes mellitus (IDDM) worldwide have reached the critical mass needed to investigate global patterns of the disease. International collaboration of 24 registries from 15 countries resulted in the first set of standardized incidence measures among divergent areas and ethnic groups. The average annual age-adjusted incidence under age 15 yr ranged from 1.7/100,000 person-yr in Hokkaido, Japan, to 29.5/100,000 person-yr in Finland during the years 1978-1980. The geographic differences in IDDM in childhood are rarely seen among chronic diseases. It appears that the risk for IDDM is determined by factor(s) correlated to the average yearly temperature of environment and to the ethnicity of the population at risk.

Adolescent↗
PubMed2005

Competing failure risk analysis using evidence theory.

Safety systems are important components of high-consequence systems that are intended to prevent the unintended operation of the system and thus the potentially significant negative consequences that could result from such an operation. This presentation investigates and illustrates formal procedures for assessing the uncertainty in the probability that a safety system will fail to operate as intended in an accident environment. Probability theory and evidence theory are introduced as possible mathematical structures for the representation of the epistemic uncertainty associated with the performance of safety systems, and a representation of this type is illustrated with a hypothetical safety system involving one weak link and one strong link that is exposed to a high temperature fire environment. Topics considered include (1) the nature of diffuse uncertainty information involving a system and its environment, (2) the conversion of diffuse uncertainty information into the mathematical structures associated with probability theory and evidence theory, and (3) the propagation of these uncertainty structures through a model for a safety system to obtain representations in the context of probability theory and evidence theory of the uncertainty in the probability that the safety system will fail to operate as intended. The results suggest that evidence theory provides a potentially valuable representational tool for the display of the implications of significant epistemic uncertainty in inputs to complex analyses.

Journal Article↗
PubMed1975

Thermoregulatory behavior and body temperature in chicks of willow grouse (Lagopus lagopus lagopus).

Clocal temperatures (Tcl) of outdoor living captive willow grouse chicks (Lagopus lagopus lagopus) were found to increase from 39.4 +/- 0.5 degrees C. the first day to 40.3 +/- 0.5 degrees C. the twelfth day after hatching. Average Tcl of adults was 40.7 +/- 0.3 degrees C. When left alone for 30 min. in a controlled test environment providing temperatures ranging from 21 degrees C. to 46 degrees C., the one day old chicks preferred significantly higher ambient temperatures than eight day old birds. Tcl was significantly lower in the chicks tested the day after hatching than in the older chicks. It is concluded that the chicks' thermoregulatory behavior is essential for maintaining homeothermia, and that the birds' thermoregulatory set-point is low the day after hatching and climbs to adult level during the first week.

Animals↗
PubMed1975

Temperature regulation training in a cooling environment.

Twelve young men were given biofeedback training to enable them to increase finger temperature at will. They were dressed in warm clothing, including gloves, and placed six at a time in an environmental chamber at 7 degrees C for three hours daily for eight work days. Each was to attempt six rewarmings per session. Finger temperature was presented to the subject on a multipoint recorder. Data from 554 attempts were analyzed. A training effect was not noted, but successful rewarmings were present from the start. The 12 subjects varied considerably in ability to rewarm, from 89% to 28% successes. They were divided into the most and least consistent who, nevertheless, remained over 10 degrees C above air temperature. These performances were compared with another group wearing identical, or even much more insulative, handwear under roughly comparable conditions but without voluntary rewarming; the advantage of periodic feedback rewarming to maintain finger temperature in such conditions was obvious.

Body Temperature↗
PubMed1997

Calcineurin is required for virulence of Cryptococcus neoformans.

Cyclosporin A (CsA) and FK506 are antimicrobial, immunosuppressive natural products that inhibit signal transduction. In T cells and Saccharomyces cerevisiae, CsA and FK506 bind to the immunophilins cyclophilin A and FKBP12 and the resulting complexes inhibit the Ca2+-regulated protein phosphatase calcineurin. We find that growth of the opportunistic fungal pathogen Cryptococcus neoformans is sensitive to CsA and FK506 at 37 degrees C but not at 24 degrees C, suggesting that CsA and FK506 inhibit a protein required for C. neoformans growth at elevated temperature. Genetic evidence supports a model in which immunophilin-drug complexes inhibit calcineurin to prevent growth at 37 degrees C. The gene encoding the C. neoformans calcineurin A catalytic subunit was cloned and disrupted by homologous recombination. Calcineurin mutant strains are viable but do not survive in vitro conditions that mimic the host environment (elevated temperature, 5% CO2 or alkaline pH) and are no longer pathogenic in an animal model of cryptococcal meningitis. Introduction of the wild-type calcineurin A gene complemented these growth defects and restored virulence. Our findings demonstrate that calcineurin is required for C. neoformans virulence and may define signal transduction elements required for fungal pathogenesis that could be targets for therapeutic intervention.

Amino Acid Sequence↗
PubMed2002

Bulk shear viscosities of endogenous and exogenous lung surfactants.

Bulk shear viscosities were measured with a cone and plate microviscometer as a function of concentration, shear rate, and temperature for lavaged calf lung surfactant (LS), Exosurf, Infasurf, Survanta, and synthetic lipid mixtures dispersed in normal saline. Viscosity increased with phospholipid concentration for all surfactants, but its magnitude and shear dependence varied widely among the different preparations. Saline dispersions of Exosurf and synthetic phospholipids had low viscosities of only a few centipoise (cp) and exhibited minimal shear dependence. LS, Infasurf, Survanta, and lipid mixtures containing palmitic acid and tripalmitin had larger non-Newtonian viscosities that increased as shear rate decreased. At 35 mg of phospholipid/ml and 37 degrees C, viscosity values were 52.3 cp (Survanta), 31.1 cp (LS), and 25 cp (Infasurf) at a shear rate of 77 s(-1) and 16.9 cp (Survanta), 10.1 cp (LS), and 6.6 cp (Infasurf) at 770 s(-1). At 25 mg of phospholipid/ml and 37 degrees C, viscosity values at 77 s(-1) were 28.8 cp (Survanta), 4.7 cp (LS), and 12.5 cp (Infasurf). At fixed shear rate, viscosity was substantially decreased at 23 degrees C compared with 37 degrees C for LS and Infasurf but was increased for Survanta. Calcium (5 mM) greatly reduced the viscosity of both Survanta and Infasurf at 37 degrees C. Studies on synthetic mixtures indicated that phospholipid/apoprotein interactions were important in the rheology of lung-derived surfactants and that palmitic acid and tripalmitin contributed to the increased viscosity of Survanta. The viscous behavior of clinical exogenous surfactants potentially influences their delivery and distribution in lungs and varies significantly with composition, concentration, temperature, ionic environment, and physical formulation.

Animals↗
PubMed1989

Seasonal changes of plasma serotonin and related parameters: correlation with environmental measures.

Seasonal changes of several serotonin-related measures in plasma and whole blood of healthy individuals were determined every 4 weeks. Plasma serotonin (5-HT) shows very marked changes throughout the year, with maximum values during the summer and lowest values in the fall, whereas its metabolite 5-hydroxyindoleacetic acid (5-HIAA) follows a somewhat contrary pattern. The sum of 5-HT plus 5-HIAA in plasma thus does not change significantly during the year and follows the evolution of total plasma tryptophan (TP). The difference of 5-HIAA minus 5-HT in plasma, which is indicative of the efficacy of degradative processes of 5-HT in the periphery, is strongly dependent on the season and suggests a higher degradation of 5-HT during fall-winter. Unlike plasma TP and whole blood 5-HT, significant correlations among plasma 5-HT, 5-HIAA, and the ambient temperature were found. The possible significance and relationship of these findings to the seasonality of major depression is discussed.

Adult↗
PubMed1978

Imparied thermoregulation in pregnant rabbits at term.

Pregnant and nonpregnant female rabbits were placed in hot (33 degrees C) and cold (3 degrees C) environments and their core temperatures measured. Pregnant rabbits during the 3 days before giving birth were less able to maintain normal body temperatures in thermally adverse environments than were nonpregnant rabbits. This alteration in thermoregulatory ability may permit an environmental temperature change that is not dangerous to nonpregnant rabbits to be potentially harmful or lethal to both mother and offspring.

Animals↗