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Heat Loss (heat + loss)
Selected AbstractsMetabolic Heat Production, Heat Loss and the Circadian Rhythm of Body Temperature in the RatEXPERIMENTAL PHYSIOLOGY, Issue 3 2003Roberto Refinetti Metabolic heat production (calculated from oxygen consumption), dry heat loss (measured in a calorimeter) and body temperature (measured by telemetry) were recorded simultaneously at 6 min intervals over five consecutive days in rats maintained in constant darkness. Robust circadian rhythmicity (confirmed by chi square periodogram analysis) was observed in all three variables. The rhythm of heat production was phase-advanced by about half an hour in relation to the body temperature rhythm, whereas the rhythm of heat loss was phase-delayed by about half an hour. The balance of heat production and heat loss exhibited a daily oscillation 180 deg out of phase with the oscillation in body temperature. Computations indicated that the amount of heat associated with the generation of the body temperature rhythm (1.6 kJ) corresponds to less than 1% of the total daily energy budget (172 kJ) in this species. Because of the small magnitude of the fraction of heat balance associated with the body temperature rhythm, it is likely that the daily oscillation in heat balance has a very slow effect on body temperature, thus accounting for the 180 deg phase difference between the rhythms of heat balance and body temperature. [source] Investigation of the derived fuel rod formation from auto shredder residue using an extrusion apparatusENVIRONMENTAL PROGRESS & SUSTAINABLE ENERGY, Issue 3 2006Hua-Shan Tai Abstract The objective of this study was to form auto shredder residue,derived fuel (ASRDF) by using an extrusion apparatus, to solve the disposal problems of auto shredder residue (ASR) and to recover the heat value in its combustible content. ASR is the waste material produced by shredding vehicles. In general, these materials contain 20,30% of each vehicle by weight. ASR should be preprocessed into extruded rods before being used for fuel to remove about 20,30% inorganic, incombustible materials and to accommodate easy transportation and storage. The analytical results of ASR indicated the moisture content to be <2%, ash was <20%, and combustibles were nearly 80% by weight. Concentrations of N and S in the ASR were very low, although the chlorine content of ASR was in the range of 1.32,2.79%, which is the main burden of the ASR utilization. The heat content of ASR was about 5000,6000 kcal kg,1 (9000,10,800 BTU lb,1). Particle size had no significant effect on the analytical chemical composition. All the data indicated that ASR had a significant potential use as RDF. Through observations of the appearance and density of the ASRDF rod, we found that better appearance and higher densities could be achieved at higher extrusion temperature and pressure. The heat content of ASRDF was much lower than that of ASR, and it decreased with increasing extrusion temperature and pressure. The reasons for the better appearance, higher densities, and heat loss on the conditions of higher extrusion temperature and pressure may be explained by the proposed die swell ratio and skin,core effect. © 2006 American Institute of Chemical Engineers Environ Prog, 2006 [source] Metabolic Heat Production, Heat Loss and the Circadian Rhythm of Body Temperature in the RatEXPERIMENTAL PHYSIOLOGY, Issue 3 2003Roberto Refinetti Metabolic heat production (calculated from oxygen consumption), dry heat loss (measured in a calorimeter) and body temperature (measured by telemetry) were recorded simultaneously at 6 min intervals over five consecutive days in rats maintained in constant darkness. Robust circadian rhythmicity (confirmed by chi square periodogram analysis) was observed in all three variables. The rhythm of heat production was phase-advanced by about half an hour in relation to the body temperature rhythm, whereas the rhythm of heat loss was phase-delayed by about half an hour. The balance of heat production and heat loss exhibited a daily oscillation 180 deg out of phase with the oscillation in body temperature. Computations indicated that the amount of heat associated with the generation of the body temperature rhythm (1.6 kJ) corresponds to less than 1% of the total daily energy budget (172 kJ) in this species. Because of the small magnitude of the fraction of heat balance associated with the body temperature rhythm, it is likely that the daily oscillation in heat balance has a very slow effect on body temperature, thus accounting for the 180 deg phase difference between the rhythms of heat balance and body temperature. [source] Ecophysiological significance of leaf size variation in Proteaceae from the Cape Floristic RegionFUNCTIONAL ECOLOGY, Issue 3 2010Megan J. Yates Summary 1.,Small leaves of species endemic to Mediterranean-type climate areas have been associated with both low rainfall and nutrient availability, but the physiological reasons for this association remain unknown. 2.,We postulated that small leaves have thin boundary layers that facilitate transpiration in winter and sensible heat loss in summer. High transpiration rates when water is available may facilitate nutrient acquisition in winter, whereas efficient sensible heat loss reduces the requirement for transpirational leaf cooling in summer. 3.,The consequences of varying leaf sizes for water and heat loss in Cape Proteaceae were examined at two scales. At the leaf level, gas exchange and thermoregulatory capacities of 15 Proteaceae species with varying leaf size were assessed under controlled conditions using phylogenetically independent contrasts. At an environmental level, leaf attributes of Proteaceae occurring in the winter-rainfall area of the Cape Floristic Region were correlated with climatic environments derived from distribution data for each species. 4.,Leaf temperature was positively correlated with leaf size when wind speed was negligible. However, transpiration decreased significantly with increasing leaf size when measured on individual leaves, detached branches and when expressed on a per stoma basis. 5.,From multiple stepwise regression analysis of climatic variables obtained from distribution data, leaf size was negatively correlated with A-Pan evaporation, mean annual temperatures and water stress in January. We conclude that leaf size is conservative for survival over relatively rare periods of hot dry conditions with low wind speeds. 6.,Narrow leaves enable plants to shed heat through sensible heat loss during summer droughts, without the need for transpirational cooling. Additionally, small leaf dimensions confer a capacity for high transpiration when evaporative demand is low and water is abundant (i.e. winter). This may be a particularly important strategy for driving nutrient mass-flow to the roots of plants that take up most of their nutrients in the wet winter/spring months from nutrient-poor soils. [source] Allometric scaling of maximum metabolic rate: the influence of temperatureFUNCTIONAL ECOLOGY, Issue 4 2008C. R. White Summary 1Maximum aerobic metabolic rate, measured in terms of rate of oxygen consumption during exercise (), is well known to scale to body mass (M) with an exponent greater than the value of 0·75 predicted by models based on the geometry of systems that supply nutrients. 2Recently, the observed scaling for (,M0·872) has been hypothesized to arise because of the temperature dependence of biological processes, and because large species show a greater increase in muscle temperature when exercising than do small species. 3Based on this hypothesis, we predicted that will be positively related to ambient temperature, because heat loss is restricted at high temperatures and body temperature is likely to be elevated to a greater extent than during exercise in the cold. 4This prediction was tested using a comparative phylogenetic generalized least-squares (PGLS) approach, and 34 measurements of six species of rodent (20·5,939 g) maximally exercising at temperatures from ,16 to 30 °C. 5 is unrelated to testing temperature, but is negatively related to acclimation temperature. We conclude that prolonged cold exposure increases exercise-induced by acting as a form of aerobic training in mammals, and that elevated muscle temperatures of large species do not explain the scaling of across taxa. [source] Single, twin and triple buried heating pipes: on potential savings in heat losses and costsINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 14 2005Benny Bøhm Abstract In order to make district heating systems competitive in areas with single family houses or in other areas with low heat demands it is necessary to reduce the heat losses from the pipes. In recent years the twin pipe has become popular in the Nordic countries. In the article we describe how the heat loss and the heat loss coefficients can be calculated. We introduce the triple pipe with three media pipes (two supply pipes and one return pipe). The temperature dependency and the ageing of polyurethane insulation are briefly discussed. A comparison is made for different 80 mm distribution pipes and for different service pipes with respect to heat losses and to resources, i.e. materials needed for the casing and polyurethane insulation and the gravel in the excavations. For the distribution pipe we found that an egg-shaped twin pipe can reduce the heat loss by 37% and the investments by 12% compared with a pair of single pipes. For the service pipes we found that the triple pipe reduces the heat loss by 45% compared with a common pair of single pipes and by 24% compared with circular twin pipes. The reduction in investment index is 21%. The article also addresses the question of the heat exchange between the two media pipes in a twin pipe. Copyright © 2005 John Wiley & Sons, Ltd. [source] Gasification of char particles in packed beds: analysis and resultsINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 12 2001S. Dasappa Abstract In this paper a packed bed of char particles is considered for experimental study and analysis. The packed char bed is modelled by extending the single-particle analysis (Dasappa et al., 1994a, Chem. Eng. Sci.49,2:223,232. Dasappa et al., 1994b, Twenty-fifth Symposium (International) on Combustion, pp. 1619,1628. Dasappa et al., 1998, Twenty-seventh Symposium (International) on Combustion, pp. 1335,1342.). All the reactions related to gasification are introduced into the reaction system as in Dasappa et al. (1998). The propagation of the reaction front into the packed char bed against the air stream is modelled. The results are compared with the experimental data on a model quartz reactor using charcoal. Experimental data of propagation of the reaction front through the packed bed from the present study and of Groeneveld's charcoal gasifier are used for comparison. Using the analysis of Dosanjh et al. 1987 (Combust. Flame68:131,142), it is shown that heat loss dominates the heat generation at the quench condition. It is also shown that increasing the oxygen fraction in air has resulted in flame front to propagate into the char bed. The critical air mass flux for peak propagation rate in a bed of char is found to be 0.1 kg m,2 s. Copyright © 2001 John Wiley & Sons, Ltd. [source] Nursing and medical staff knowledge regarding the monitoring and management of accidental or exposure hypothermia in adult major trauma patientsINTERNATIONAL JOURNAL OF NURSING PRACTICE, Issue 6 2006Sharyn Ireland RN Dip.HSc B.Nurs CritCareCert ACCN M.Ed Recording a patient's vital signs is a basic requirement that in part informs clinical decision-making. Practice suggests that recording a trauma patient's temperature is occasionally overlooked in the emergency department. A staff survey was undertaken to gain an appreciation of knowledge and understanding of the issues that surround accidental or exposure hypothermia in trauma patients. Results demonstrate that nurses and doctors are unsure of how to define hypothermia and are not conversant with simple ways to prevent heat loss or rewarm patients. Complications from hypothermia such as coagulopathy and metabolic acidosis were seldom identified. Issues that limit staff recording temperature include patient access and acuity, lack of knowledge and confidence and access to temperature-measuring devices. These results emphasize the need for regular education. Implications for clinical practice were considered; an algorithm to guide staff on ways to improve the monitoring and management of temperature in trauma patients was developed. Opportunities for ongoing and further research were identified. [source] Improved thermal design of a compression moldADVANCES IN POLYMER TECHNOLOGY, Issue 2 2007Maria A. Kuczmarski Abstract An analysis of the heat transfer in a tool for producing neat resin disks was conducted to determine how to bring about a better agreement between the tool temperature and the applied temperature profile. Using the commercial code FLUENT to investigate the relative effects of heat conduction into the tool and heat loss from the tool by convection, it was shown that convective heat transfer appears more important than conduction in controlling the tool performance. Decreasing the height of the tool was predicted to decrease the heat losses by convection. Redesigning of the tool based on this analysis resulted in the tool experiencing the applied temperature profile. © 2007 Wiley Periodicals, Inc. Adv Polym Techn 26:86,99, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20091 [source] Evaluation of numerical simulation methods in reactive extrusionADVANCES IN POLYMER TECHNOLOGY, Issue 3 2005Linjie Zhu Abstract Reactive extrusion is a complex process, and numerical simulation is an important method in optimizing operational parameters. In the current work, two different simulation methods, one-dimensional (1D) model and three-dimensional (3D) model, were introduced to predict the polymerization of ,-caprolactone in fully filled screw elements. The predicted results of polymerization progression under different simulation conditions based on these two methods were compared. The simulation results show that the simplifications and assumptions in 1D model make it difficult to capture the complex mixing mechanism, heat generation, and heat loss in reactive extrusion. 1D model is feasible only under particular conditions, such as low screw rotating speed, small heat from reaction, and small screw diameter, whereas 3D model is a more powerful simulation tool for much wider processing conditions. © 2005 Wiley Periodicals, Inc. Adv Polym Techn 24: 183,193, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20041 [source] Raised thermoregulatory costs at exposed song posts increase the energetic cost of singing for willow warblers Phylloscopus trochilusJOURNAL OF AVIAN BIOLOGY, Issue 4 2005Sally Ward Sexually selected displays, such as bird song, are expected to be costly. We examined a novel potential cost to bird song: whether a less favourable microclimate at exposed song posts would be predicted to raise metabolic rate. We measured the microclimate and height at which willow warblers Phylloscopus trochilus sang and foraged. Song posts were higher than foraging sites. The wind speed was 0.6±0.3 ms,1 greater at song posts (mean±SD, N=12 birds). Song rate and song post selection were not influenced consistently by temperature or wind speed, but the birds sang from lower positions on one particularly windy day. This may have resulted from difficulty in holding on to exposed branches in windy conditions rather than a thermoregulatory constraint. The results suggest that the extra thermoregulatory costs at song posts would increase metabolic rate by an average of 10±4% and a maximum of 25±8% (N=12 birds) relative to birds singing at foraging sites. We estimated that metabolic rate would be 3,8% greater during singing than during quiet respiration because of heat and evaporative water loss in exhaled gases. The combined energy requirements for sound production, thermoregulation at exposed song posts and additional heat loss in exhaled air could increase the metabolic rate of willow warblers by an average of 14,23%, and a maximum of 42,63%, during singing. The energetic cost of singing may thus be much greater for birds in a cold, windy environment than for birds singing in laboratory conditions. [source] Gold-Tip Electrodes,A New "Deep Lesion" Technology for Catheter Ablation?JOURNAL OF CARDIOVASCULAR ELECTROPHYSIOLOGY, Issue 7 2005In Vitro Comparison of a Gold Alloy Versus Platinum, Iridium Tip Electrode Ablation Catheter Radiofrequency (RF) catheter ablation is widely used to induce focal myocardial necrosis using the effect of resistive heating through high-frequency current delivery. It is current standard to limit the target tissue,electrode interface temperature to a maximum of 60,70°C to avoid char formation. Gold (Au) exhibits a thermal conductivity of nearly four times greater than platinum (Pt,Ir) (3.17 W/cm Kelvin vs 0.716 W/cm Kelvin), it was therefore hypothesized that RF ablation using a gold electrode would create broader and deeper lesions as a result of a better heat conduction from the tissue,electrode interface and additional cooling of the gold electrode by "heat loss" to the intracardiac blood. Both mechanisms would allow applying more RF power to the tissue before the electrode,tissue interface temperature limit is reached. To test this hypothesis, we performed in vitro isolated liver and pig heart investigations comparing lesion depths of a new Au-alloy-tip electrode to standard Pt,Ir electrode material. Mean lesion depth in liver tissue for Pt,Ir was 4.33 ± 0.45 mm (n = 60) whereas Au electrode was able to achieve significantly deeper lesions (5.86 ± 0.37 mm [n = 60; P < 0.001]). The mean power delivered using Pt,Ir was 6.95 ± 2.41 W whereas Au tip electrode delivered 9.64 ± 3.78 W indicating a statistically significant difference (P < 0.05). In vitro pig heart tissue Au ablation (n = 20) increased significantly the lesion depth (Au: 4.85 ± 1.01 mm, Pt,Ir: 2.96 ± 0.81 mm, n = 20; P < 0.001). Au tip electrode again applied significantly more power (P < 0.001). Gold-tip electrode catheters were able to induce deeper lesions using RF ablation in vitro as compared to Pt,Ir tip electrode material. In liver and in pig heart tissue, the increase in lesion depth was associated with a significant increase in the average power applied with the gold electrode at the same level of electrode,tissue temperature as compared to platinum material. [source] The role of water abundance, thermoregulation, perceived predation risk and interference competition in water access by African herbivoresAFRICAN JOURNAL OF ECOLOGY, Issue 3 2008Marion Valeix Abstract In African savannas, surface water can become limiting and an understanding of how animals address the trade-offs between different constraints to access this resource is needed. Here, we describe water access by ten African herbivore species in Hwange National Park, Zimbabwe, and we explore four possible determinants of the observed behaviours: water abundance, thermoregulation, perceived predation risk and interference competition. On average, herbivores were observed to drink in 80% of visits to a waterhole. The probability of drinking was higher in 2003 (474 mm) than in 2004 (770 mm), and at the end of the dry season than at its beginning. For larger species, this probability may also be related to risks of interference competition with elephants or other herbivores. For smaller species, this probability may also be related to the perceived risk of predation. We also investigate the time spent accessing water to drink. The influence of herd size and the presence of young on the time spent accessing water for most species suggests that perceived predation risk plays a role. Thermoregulation also affects this time: during the hottest periods, herbivores spend less time in open areas, unless when wind is strong, probably owing to evapotranspired heat loss. Résumé Dans les savanes africaines, l'eau de surface disponible peut devenir un facteur limitant et il est nécessaire de comprendre comment les animaux agissent face aux différentes contraintes que pose l'accès à cette ressource. Nous décrivons ici l'accès à l'eau de dix herbivores africains du Parc National de Hwange, au Zimbabwe, et nous explorons quatre facteurs qui sont peut-être déterminants dans les comportements observés: l'abondance de l'eau, la thermorégulation, le risque de prédation ressenti et la compétition/ interférence. En moyenne, on a observé que les herbivores buvaient lors de 80% de leurs visites au point d'eau. La probabilité qu'ils boivent étai plus forte en 2003 (474 mm) qu'en 2004 (770 mm), et à la fin de la saison sèche qu'au début. Pour les plus grandes espèces, cette probabilité pourrait aussi être liée aux risques de compétition par interférence avec les éléphants ou d'autres herbivores. Pour les plus petites espèces, cette probabilité pourrait aussi être liée au risque de prédation ressenti. Nous avons aussi étudié le temps passéà se rendre au point d'eau pour y boire. L'influence de la taille du groupe et de la présence de jeunes sur le temps pris par la plupart des espèces pour se rendre au point d'eau laisse penser que la perception du risque de prédation joue un rôle. La thermorégulation affecte aussi cette durée: pendant les périodes les plus chaudes, les herbivores passent moins de temps dans les espaces ouverts, sauf si le vent est fort, probablement à cause de la perte de chaleur par évapotranspiration. [source] Heat capacity measurement by flow calorimetry: An exact analysisAICHE JOURNAL, Issue 1 2009T. K. Hei Abstract The principal unsolved problem in flow calorimetry for liquid heat capacity measurement accurate accounting for heat loss from the heater lead-in wires as a function of system properties is analyzed by exact procedures for a five-zone calorimeter model. Temperature distributions in the fluid, and bi-metal wire are obtained from solutions of the governing third-order ODE in the fluid temperature for realistic boundary conditions. Conductive heat losses at the fluid exit qHL/q, are large (up to 20% of energy input), and physical property and flow rate dependent. A new correlating equation for (qHL/q,) gives separately and explicitly, for the first time, its dependence on calorimeter characteristics, flow rates and fluid properties. Experiments on five pure liquids confirmed the predictions of the theoretical model and produced Cp values in close agreement with literature data. Fluid friction and small convection heat losses (UiAi (,T)lm) were accounted for experimentally. © 2008 American Institute of Chemical Engineers AIChE J, 2009 [source] Thermoregulation and Heat Loss Prevention After Birth and During Neonatal Intensive-Care Unit Stabilization of Extremely Low-Birthweight InfantsJOURNAL OF OBSTETRIC, GYNECOLOGIC & NEONATAL NURSING, Issue 3 2007Robin Knobel Extremely low-birthweight infants have inefficient thermoregulation due to immaturity and may exhibit cold body temperatures after birth and during their first 12 hours of life. Hypothermia in these infants can lead to increased morbidity and mortality. Anecdotal notes made during our recent study revealed extremely low-birthweight infants' temperatures decreased with caregiver procedures such as umbilical line insertion, intubations, obtaining chest x-rays, manipulating intravenous lines, repositioning, suctioning, and taking vital signs during the first 12 hours of life. Therefore, nursing interventions should be undertaken to prevent heat loss during these caregiver procedures. Nurses can improve the thermal environment for extremely low-birthweight infants by prewarming the delivery room and placing the infant in a plastic bag up to the neck during delivery room stabilization to prevent heat loss. JOGNN, 36, 280-287 ; 2007. DOI: 10.1111/J.1552-6909.2007.00149.x [source] Individualized and time-variant model for the functional link between thermoregulation and sleep onsetJOURNAL OF SLEEP RESEARCH, Issue 2 2006STIJN QUANTEN Summary This study makes use of control system model identification techniques to examine the relationship between thermoregulation and sleep regulation. Specifically, data-based mechanistic (DBM) modelling is used to formulate and experimentally test the hypothesis, put forth by Gilbert et al. [Sleep Med. Rev.8 (2004) 81], that there exists a connection between distal heat loss and sleepiness. Six healthy sleepers each spent three nights and the following day in the sleep laboratory: an adaptation, a cognitive arousal and a neutral testing day. In the cognitive arousal condition, a visit of a television camera crew took place and subjects were asked to be interviewed. During each of the three 25-min driving simulator tasks per day, the distal-to-proximal gradient and the electroencephalogram are recorded. It is observed from these experimental data that there exists a feedback connection between thermoregulation and sleep. In addition to providing experimental evidence in support of the Gilbert et al. (2004) hypothesis, the authors propose that the nature of the feedback connection is determined by the nature of sleep/wake state (i.e. NREM sleep versus unwanted sleepiness in active subjects). Besides this, an individualized and time-variant model for the linkage between thermoregulation and sleep onset is presented. This compact model feeds on real-time data regarding distal heat loss and sleepiness and contains a physically meaningful parameter that delivers an individual- and time-depending quantification of a well known biological features in the field of thermoregulation: the thermoregulatory error signal Thypo(t),Tset(t). A validation of these physical/biological features emphasizes the reliability and power of DBM in describing individual differences related to the sleep process. [source] Pressureless Rapid Sintering of UO2 Assisted by High-frequency Induction Heating ProcessJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2008Jae Ho Yang Heat generation of uranium dioxide (UO2) powder and its pressureless rapid sintering behaviors have been studied using a high-frequency induction heating apparatus. The porous graphite housing has been used to prevent heat loss and to preheat the uranium oxides, simultaneously. At an elevated temperature, UO2 powder generated extra heat by itself. The synergism of individual heat generation between the graphite and UO2 powder could effectively heat the UO2 to the sintering temperature of 1700°C. Using this process, densification behavior of cylindrical and disk-type UO2 green pellets according to the heating rate and grain structure of sintered UO2 pellets were investigated. Rapid sintering caused a large crack around the circumference of the sintered pellet. The formation of cracks could be avoided when the heating rate or sample dimension are properly reduced. A dense and crack-free UO2 pellet with a relative density of up to 96% was produced within 5 min of the process time. The induction heat sintering process can be a potential candidate for the rapid fabrication of ceramics and composites. [source] Abstracts of the 8th Meeting of the Italian Peripheral Nerve Study Group: 84JOURNAL OF THE PERIPHERAL NERVOUS SYSTEM, Issue 1 2003V Donadio The aim of the study is to determine the site of autonomic lesion in a patient with Holmes-Adie Syndrome (HAS) who subsequently developed generalized anhydrosis. We describe a 38-year-old woman who from age 33 showed a right pupil larger than the left and from age 34 complained of focal and, a year later, generalized anhydrosis. Neurological examination showed absent tendon reflexes and right mydriatic pupil. Brain MRI, EEG, motor and sensory conduction studies were normal. Serologic screening for autoimmune disease was negative. To determine the site of the autonomic lesion the patient underwent the following investigations: pupillary tests with a diluted solution of pilocarpine (0.062%) and adrenaline (0.1%); cardiovascular reflexes; thermoregulatory sweat test (TST); circadian rhythm of body core temperature (CRT°); sympathetic skin response (SSR); microneurography recording of skin sympathetic activity (SSA) from median and peroneal nerves, and muscle sympathetic activity (MSA) from peroneal nerve; skin biopsy to evaluated the eccrine glands. Pupillary tests showed postganglionic parasympathetic and sympathetic denervation only of the right pupil. TST showed complete anhydrosis, SSR and SSA were absent and skin biopsy revealed normal morphology of the eccrine glands with hypotrophy of their structures. These results indicated a lesion of the postganglionic skin sympathetic fibers. Mechanisms for heat loss and conservation, cardiovascular reflexes and MSA were normal excluding a hypothalamic dysfunction or a more diffuse involvement of the autonomic nervous system. In conclusion, our patient showed a HAS associated with generalized anhydrosis and the autonomic investigations suggested underlying postganglionic parasympathetic and sympathetic autonomic lesions. [source] The value of infrared thermography for research on mammals: previous applications and future directionsMAMMAL REVIEW, Issue 3 2007DOMINIC J. MCCAFFERTY ABSTRACT 1Infrared thermography (IRT) involves the precise measurement of infrared radiation which allows surface temperature to be determined according to simple physical laws. This review describes previous applications of IRT in studies of thermal physiology, veterinary diagnosis of disease or injury and population surveys on domestic and wild mammals. 2IRT is a useful technique because it is non-invasive and measurements can be made at distances of <1 m to examine specific sites of heat loss to >1000 m to count large mammals. Detailed measurements of surface temperature variation can be made where large numbers of temperature sensors would otherwise be required and where conventional solid sensors can give false readings on mammal coats. Studies need to take into account sources of error due to variation in emissivity, evaporative cooling and radiative heating of the coat. 3Recent advances in thermal imaging technology have produced lightweight, portable systems that store digital images with high temperature and spatial resolution. For these reasons, there are many further opportunities for IRT in studies of captive and wild mammals. [source] Differences among forced-air warming systems with upper body blankets are small.ACTA ANAESTHESIOLOGICA SCANDINAVICA, Issue 9 2003A randomized trial for heat transfer in volunteers Background:, Forced-air warming is known as an effective procedure in prevention and treatment of perioperative hypothermia. Significant differences have been described between forced-air warming systems in combination with full body blankets. We investigated four forced-air warming systems in combination with upper body blankets for existing differences in heat transfer. Methods:, After approval of the local Ethics Committee and written informed consent, four forced-air warming systems combined with upper body blankets were investigated in a randomized cross-over trial on six healthy volunteers: (1) BairHuggerÔ 505 and Upper Body Blanket 520, Augustine Medical; (2) ThermaCareÔ TC 3003, GaymarÔ and OptisanÔ Upper Body Blanket, Brinkhaus; (3) WarmAirÔ 134 and FilteredFlowÔ Upper Body Blanket, CSZ; and (4) WarmTouchÔ 5800 and CareDrapeÔ Upper Body Blanket, Mallinckrodt. Heat transfer from the blanket to the body surface was measured with 11 calibrated heat flux transducers (HFTs) with integrated thermistors on the upper body. Additionally, the blanket temperature was measured 1 cm above the HFT. After a preparation time of 60 min measurements were started for 20 min. Mean values were calculated over 20 min. The t -test for matched pairs with Bonferroni-Holm-correcture for multiple testing was used for statistical evaluation at a P -level of 0.05. The values are presented as mean±SD. Results:, The WarmTouchÔ blower with the CareDrapeÔ blanket obtained the best heat flux (17.0±3.5 W). The BairHuggerÔ system gave the lowest heat transfer (8.1±1.1 W). The heat transfer of the ThermaCareÔ system and WarmAirÔ systems were intermediate with 14.3±2.1 W and 11.3±1.0 W. Conclusions:, Based on an estimated heat loss from the covered area of 38 W the heat balance is changed by 46.1 W to 55 W by forced-air warming systems with upper body blankets. Although the differences in heat transfer are significant, the clinical relevance of this difference is small. [source] Interannual changes in seasonal ground freezing and near-surface heat flow beneath bottom-fast ice in the near-shore zone, Mackenzie Delta, NWT, CanadaPERMAFROST AND PERIGLACIAL PROCESSES, Issue 3 2010Christopher W. Stevens Abstract Interannual changes in seasonal ground freezing and near-surface heat flow beneath zones of bottom-fast ice (BFI) were examined over the winters of 2005,06 and 2006,07 within the near-shore zone of the Mackenzie Delta, Canada. Winter variability in ground thermal conditions was determined at three monitoring sites. Ground-penetrating radar surveys were conducted in late winter to determine spatial variability in landfast ice conditions and the extent of ice-bonded sediments. Shallow water sites (<0.5,m-water depth) were characterised by early onset of BFI, freezeback of the active layer and mean winter sediment bed temperatures ranging between ,3°C and ,10°C. In contrast, deep water sites (>1,m of water) experienced prolonged periods of floating ice, which limited the duration of ice contact with the sediment bed and the depth of seasonal frost, and resulted in warmer winter ground temperatures (between ,0.5°C and ,2.6°C). Under similar water depths, interannual changes in ice growth altered the timing of BFI and winter heat loss from the ground. When comparing conditions over the two winters, 2005,06 was characterised by a decrease in ice thickness that limited the extent of BFI and seasonal cooling of the ground. These changes in ice conditions had a greater effect on the thermal conditions at sites where water depths were close to the maximum ice thickness. The short ice contact times at these sites are important to the thermal state of permafrost, as only minimal heat exchange contributing to permafrost cooling occurs prior to freezeback of the active layer. Copyright © 2010 John Wiley & Sons, Ltd. [source] Numerical investigation of the influence of material properties and adhesive layer thickness on the heating efficiency of microwave curing of an adhesive-bonded jointPOLYMER ENGINEERING & SCIENCE, Issue 8 2004H. W. So In the process of microwave curing of an adhesive-bonded joint, both the adhesive layer and the adherends affected the heating efficiency of the joint. As an extension of previous studies, the influences of changing the properties of the components of the joint on the heating efficiency were predicted by simulations that were based on the numerical model developed previously. The influence of adhesive thickness was also studied. The properties that directly affected power dissipation and heat loss of the adhesive layer were found to be important to the heating efficiency of the process. The heating rate was also sensitive to the thickness of the adhesive layer. Polym. Eng. Sci. 44:1414,1418, 2004. © 2004 Society of Plastics Engineers. [source] Performance of symmetric polygonal fins with and without tip loss , A comparison of different methods of predictionTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 2 2000Balaram Kundu Abstract No analytical solution exists for estimating the efficiency of symmetric polygonal fins (SPFs) circumscribing circular tubes. Performance of such fins is conventionally determined from either of the two approximate techniques, namely, the equivalent annulus method and the sector method. The present work aims to judge the relative merits and applicability of these two methods critically. To this end, the results obtained from the approximate techniques have compared with those obtained from a semi-analytical technique. It has been noted that, with the increase of the tip heat loss, the accuracy of prediction from any of the approximate methods decreases. For the sector method, a modification has been suggested. The prediction from the modified version of the sector method is always more accurate than that from the equivalent annulus method. It has been further illustrated that though the approximate techniques can be employed for the prediction of efficiency, they cannot be used to predict the tip temperatures accurately. Il n'existe pas de solution analytique pour estimer l'efficacité des ailettes polygonales symétriques (5PF) circonscrivant des tubes circulaires. La performance de telles ailettes est traditonnellement déterminée par l'une ou l'autre des techniques approximatives, à savoir la méthode de l'espace annulaire équivalent et la méthode des secteurs. Ce travail a pour but de juger des mérites et de l'applicabilité relatifs de ces deux méthodes de manière critique. à cette fin, les résultats obtenus par ces techniques approximatives sont cornparés à ceux d'une technique semi-analytique. On a constatè que, avec l'augmentation de la perte de chaleur aux extrémités, la précision de la prédiction de ces méthodes approximatives diminue. Pour la méthode des secteurs, une modification est proposée. La prédiction de la version modifiée de la méthode des secteun est toujours plus précise qu'avec la méthode de l'espace annulaire équivalent. On illustre par ailleurs le fait que bien que les techniques approximatives puissent servir à la prédiction de l'efficacitè, elles ne permettent pas de prédire avec précision les températures aux extrémités. [source] Chlorpyrifos-Induced Hypothermia and Vasodilation in the Tail of the Rat: Blockade by Scopolamine,BASIC AND CLINICAL PHARMACOLOGY & TOXICOLOGY, Issue 1 2000Christopher J. Gordon Organophosphate pesticides such as chlorpyrifos reduce core temperature (Tc) in laboratory rodents. The mechanism(s) responsible for the chlorpyrifos-induced hypothermia are not well known. This study assessed the role of a key effector for thermoregulation in the rat, vasomotor control of heat loss from the tail, and its possible cholinergic control during chlorpyrifos-induced hypothermia. Tc and motor activity were monitored by telemetry in female Long-Evans rats maintained at an ambient temperature (Ta) of 25°. Tail skin temperature (Tsk(t)) was measured hourly. Rats were dosed with chlorpyrifos (0 or 25 mg/kg orally). Two hr later the rats were dosed with saline or scopolamine (1.0 mg/kg intraperitoneally). Two hr after chlorpyrifos treatment there was a marked elevation in Tsk(t) concomitant with a 0.5° reduction in Tc. Scopolamine administered to control rats led to a marked elevation in Tc with little change in Tsk(t). Rats treated with chlorpyrifos and administered scopolamine underwent a marked vasoconstriction and elevation in Tc. Vasodilation of the tail is an important thermoeffector to reduce Tc during the acute stages of chlorpyrifos exposure. The blockade of the response by scopolamine suggests that the hypothermic and vasodilatory response to chlorpyrifos is mediated via a cholinergic muscarinic pathway in the CNS. [source] Partial-body exposure of human volunteers to 2450,MHz pulsed or CW fields provokes similar thermoregulatory responses,BIOELECTROMAGNETICS, Issue 4 2001Eleanor R. Adair Abstract Many reports describe data showing that continuous wave (CW) and pulsed (PW) radiofrequency (RF) fields, at the same frequency and average power density (PD), yield similar response changes in the exposed organism. During whole-body exposure of squirrel monkeys at 2450 MHz CW and PW fields, heat production and heat loss responses were nearly identical. To explore this question in humans, we exposed two different groups of volunteers to 2450,MHz CW (two females, five males) and PW (65,,s pulse width, 104,pps; three females, three males) RF fields. We measured thermophysiological responses of heat production and heat loss (esophageal and six skin temperatures, metabolic heat production, local skin blood flow, and local sweat rate) under a standardized protocol (30,min baseline, 45,min RF or sham exposure, 10,min baseline), conducted in three ambient temperatures (Ta,=,24, 28, and 31°C). At each Ta, average PDs studied were 0, 27, and 35,mW/cm2 (Specific absorption rate (SAR),=,0, 5.94, and 7.7,W/kg). Mean data for each group showed minimal changes in core temperature and metabolic heat production for all test conditions and no reliable differences between CW and PW exposure. Local skin temperatures showed similar trends for CW and PW exposure that were PD-dependent; only the skin temperature of the upper back (facing the antenna) showed a reliably greater increase (P,=,.005) during PW exposure than during CW exposure. Local sweat rate and skin blood flow were both Ta - and PD-dependent and showed greater variability than other measures between CW and PW exposures; this variability was attributable primarily to the characteristics of the two subject groups. With one noted exception, no clear evidence for a differential response to CW and PW fields was found. Bioelectromagnetics 22:246,259, 2001. © 2001 Wiley-Liss, Inc. [source] Infants sleeping outdoors in a northern winter climate: skin temperature and duration of sleepACTA PAEDIATRICA, Issue 9 2010Marjo Tourula Abstract Aim:, The aim of the study is to describe the relationships among thermal environment, skin temperatures and infants' daytime outdoor sleep duration in northern winter conditions. Methods:, This study is a cross-over observational study. Skin temperatures of three-month-old infants were recorded from seven skin sites continuously throughout outdoor (n = 34) and indoor sleep (n = 33) in the families' homes. The duration of the sleep was observed, and temperature and the air velocity of the environment were recorded. Results:, Skin temperatures increased towards the end of indoor sleeping, whereas they decreased during outdoor sleeping. The cooling rate of mean skin temperature (Tsk) increased in lower outdoor temperatures (rs = 0.628, p < 0.001) in spite of increased clothing. On some occasions, cold extremities were observed, suggesting slight deviations from thermoneutrality. Sleep time was 92 min longer in outdoors than in indoors. However, outdoor sleep duration was shortened when the cooling rate of Tsk increased (rs = 0.611, p < 0.001). Conclusion:, The longest sleep was recorded outdoors when the cooling rate of Tsk was minimal. Restriction of movements by clothing probably increases the length of sleep, and a cold environment makes swaddling possible without overheating. A decrease in ambient temperature increased the cooling rate, suggesting that the cold protection of the clothing compensated only partly for the increased heat loss. [source] Frontal Polymerization Synthesis of Starch-Grafted Hydrogels: Effect of Temperature and Tube Size on Propagating Front and Properties of HydrogelsCHEMISTRY - A EUROPEAN JOURNAL, Issue 12 2006Qing-Zhi Yan Prof. Dr. Abstract The frontal polymerization process was used to produce superabsorbent hydrogels based on acrylic acid monomers grafted onto starch. Using a simple test tube which was nonadiabatic and permitted contact with air, the effects of initial temperature and tube size on the propagating front of grafting copolymerization and the properties of hydrogels were explored. The unrestricted access of the reaction mixture to oxygen delayed the formation of self-propagating polymerization front. The ignition time was markedly lengthened with the increasing of tube size attributed to the formation of large amounts of peroxy radicals. The front velocity dependence on initial temperature could be fit to an Arrhenius function with the average apparent activation energy of 24 kJ,mol,1, and on tube size to a function of higher order. The increase of the initial temperature increased the front temperature, which lead to more soluble oligomers and higher degree of crosslinking. The interplay of two opposite effects of oligomer and crosslinking determined the sol and gel content. An increase in tube size had two effects on the propagating front. One was to reduce heat loss. The other effect was to increase the number of escaping gas bubbles. The combined action of the two effects resulted in a maximum value of front temperature, an increase in sol content and a reduction in gel content with tube size. The highest swelling capacity of hydrogels was obtained when the initial temperature or tube size favored a formation of porous microstructure of hydrogels. [source] Application of a simple enthalpy-based pyrolysis model in numerical simulations of pyrolysis of charring materialsFIRE AND MATERIALS, Issue 1 2010S. R. Wasan Abstract A new, simple pyrolysis model for charring materials is applied to several numerical and experimental test cases with variable externally imposed heat fluxes. The model is based on enthalpy. A piecewise linear temperature field representation is adopted, in combination with an estimate for the pyrolysis front position. Chemical kinetics are not accounted for: the pyrolysis process takes place in an infinitely thin front, at the ,pyrolysis temperature'. The evolution in time of pyrolysis gases mass flow rates and surface temperatures is discussed. The presented model is able to reproduce numerical reference results, which were obtained with the more complex moving mesh model. It performs better than the integral model. We illustrate good agreement with numerical reference results for variable thickness and boundary conditions. This reveals that the model provides good results for the entire range of thermally thin and thermally thick materials. It also shows that possible interruption of the pyrolysis process, due to excessive heat losses, is automatically predicted with the present approach. Finally, an experimental test case is considered. Copyright © 2009 John Wiley & Sons, Ltd. [source] Modelling radiation and moisture content in fire spreadINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 9 2007L. Ferragut Abstract A numerical method is developed for fire spread simulation modelling. The model is a two-dimensional one which takes into account moisture content and radiation. We consider the combustion of a porous solid, where a simplified energy conservation equation is applied. The effect of the vegetation moisture and endothermic pyrolysis is incorporated in the model by means of a multivalued function representing the enthalpy. Some of the three-dimensional effects are incorporated in the model, i.e. heat losses in the vertical direction and non-local radiation from the flame above the vegetal layer. Also the radiation model allows to cope with wind and slope effects. The approximate solution is obtained using a finite element method. A semi-implicit Euler algorithm in time is applied. The resolution of the multivalued operator is done using the Yosida approximation of a perturbed multivalued operator. The characteristic method combined with a discrete ordinate method is used to solve the radiation equation. Finally, several representative examples are solved and compared with experimental data. Copyright © 2006 John Wiley & Sons, Ltd. [source] Single, twin and triple buried heating pipes: on potential savings in heat losses and costsINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 14 2005Benny Bøhm Abstract In order to make district heating systems competitive in areas with single family houses or in other areas with low heat demands it is necessary to reduce the heat losses from the pipes. In recent years the twin pipe has become popular in the Nordic countries. In the article we describe how the heat loss and the heat loss coefficients can be calculated. We introduce the triple pipe with three media pipes (two supply pipes and one return pipe). The temperature dependency and the ageing of polyurethane insulation are briefly discussed. A comparison is made for different 80 mm distribution pipes and for different service pipes with respect to heat losses and to resources, i.e. materials needed for the casing and polyurethane insulation and the gravel in the excavations. For the distribution pipe we found that an egg-shaped twin pipe can reduce the heat loss by 37% and the investments by 12% compared with a pair of single pipes. For the service pipes we found that the triple pipe reduces the heat loss by 45% compared with a common pair of single pipes and by 24% compared with circular twin pipes. The reduction in investment index is 21%. The article also addresses the question of the heat exchange between the two media pipes in a twin pipe. Copyright © 2005 John Wiley & Sons, Ltd. [source] | |||||||||||||||||||||||||