Thermal Conditions (thermal + condition)

Distribution by Scientific Domains

Selected Abstracts

ChemInform Abstract: Iridium Catalyzed Alkylation of 4-Hydroxy Coumarin, 4-Hydroxy-2-quinolones and Quinolin-4(1H)-one with Alcohols under Solvent-Free Thermal Conditions.

CHEMINFORM, Issue 3 2010
Ronald Grigg
Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source]

Cardiovascular function in the heat-stressed human

C. G. Crandall
Abstract Heat stress, whether passive (i.e. exposure to elevated environmental temperatures) or via exercise, results in pronounced cardiovascular adjustments that are necessary for adequate temperature regulation as well as perfusion of the exercising muscle, heart and brain. The available data suggest that generally during passive heat stress baroreflex control of heart rate and sympathetic nerve activity are unchanged, while baroreflex control of systemic vascular resistance may be impaired perhaps due to attenuated vasoconstrictor responsiveness of the cutaneous circulation. Heat stress improves left ventricular systolic function, evidenced by increased cardiac contractility, thereby maintaining stroke volume despite large reductions in ventricular filling pressures. Heat stress-induced reductions in cerebral perfusion likely contribute to the recognized effect of this thermal condition in reducing orthostatic tolerance, although the mechanism(s) by which this occurs is not completely understood. The combination of intense whole-body exercise and environmental heat stress or dehydration-induced hyperthermia results in significant cardiovascular strain prior to exhaustion, which is characterized by reductions in cardiac output, stroke volume, arterial pressure and blood flow to the brain, skin and exercising muscle. These alterations in cardiovascular function and regulation late in heat stress/dehydration exercise might involve the interplay of both local and central reflexes, the contribution of which is presently unresolved. [source]

A basic study on humidity recovery by using micro-porous media (Effects of thermal condition of fluids and geometrical condition of apparatus on transport performance)

Shixue Wang
Abstract Using an experimental apparatus to examine the performance of heat and mass transfer between constant-temperature water and dry air through a porous plate having extremely small pores, the effects of the thermal conditions in the fluids and the geometric condition of the apparatus on moisture transport were measured. The effects of water temperature, thickness of the porous plate, and channel height of the flowing air on moisture transport are noticeable. However, the effect of air temperature in the channel inlet on moisture transport is slight. In addition, in order to evaluate the degree of air humidity absorption, a parameter called the moisture absorption rate was introduced. The moisture absorption rate was shown to decrease with increasing air velocity and varies only slightly for a plate thickness of 1 mm and decreases for a plate thickness of 3.5 mm with increasing water temperature. 2006 Wiley Periodicals, Inc. Heat Trans Asian Res, 35(8): 568,581, 2006; Published online in Wiley InterScience ( DOI 10.1002/htj.20133 [source]

Differences between young adults and elderly in thermal comfort, productivity, and thermal physiology in response to a moderate temperature drift and a steady-state condition

INDOOR AIR, Issue 4 2010
L. Schellen
Abstract, Results from naturally ventilated buildings show that allowing the indoor temperature to drift does not necessarily result in thermal discomfort and may allow for a reduction in energy use. However, for stationary conditions, several studies indicate that the thermal neutral temperature and optimum thermal condition differ between young adults and elderly. There is a lack of studies that describe the effect of aging on thermal comfort and productivity during a moderate temperature drift. In this study, the effect of a moderate temperature drift on physiological responses, thermal comfort, and productivity of eight young adults (age 22,25 year) and eight older subjects (age 67,73 year) was investigated. They were exposed to two different conditions: S1-a control condition; constant temperature of 21.5C; duration: 8 h; and S2-a transient condition; temperature range: 17,25C, duration: 8 h, temperature drift: first 4 h: +2 K/h, last 4 h: ,2 K/h. The results indicate that thermal sensation of the elderly was, in general, 0.5 scale units lower in comparison with their younger counterparts. Furthermore, the elderly showed more distal vasoconstriction during both conditions. Nevertheless, TS of the elderly was related to air temperature only, while TS of the younger adults also was related to skin temperature. During the constant temperature session, the elderly preferred a higher temperature in comparison with the young adults. Practical Implications ,Because the stock of fossil fuels is limited, energy savings play an important role. Thermal comfort is one of the most important performance indicators to successfully apply measures to reduce the energy need in buildings. Allowing drifts in indoor temperature is one of the options to reduce the energy demand. This study contributes to the knowledge concerning the effects of a moderate temperature drift and the age of the inhabitants on their thermal comfort. [source]

An experimental and mathematical study of efforts of a novel photovoltaic-Trombe wall on a test room

Ji Jie
Abstract A novel photovoltaic-Trombe wall (PV-TW) is proposed and investigated experimentally and theoretically in this paper. The PV-TW was installed at the south-facing external wall of an environmental chamber that carried two identical test rooms. Both of the test rooms have a double window of the same size. One test room was installed with the PV-TW (known as the PV-TW room), and the other without PV-TW (known as the reference room). The influence of the PV-TW on the thermal environment of the test room was investigated under different operating conditions. The experimental results show the dual benefits of the PV-TW system: improving the room thermal condition and at the same time generating electricity. Compared with the reference room, the maximum indoor temperature was found to be 5,7C higher in winter, and the daily electrical output reached about 0.3,kWh with a PV cell area of 0.72,m2. Also, a detailed model is given to evaluate the performance of PV-TW theoretically, and the PV-TW room is simulated under one certain operating condition. The simulated and measured air temperatures of PV-TW room are found to be in good agreement. Copyright 2007 John Wiley & Sons, Ltd. [source]

Absence of arterial baroreflex modulation of skin sympathetic activity and sweat rate during whole-body heating in humans

Thad E. Wilson
1Prior findings suggest that baroreflexes are capable of modulating skin blood flow, but the effects of baroreceptor loading/unloading on sweating are less clear. Therefore, this project tested the hypothesis that pharmacologically induced alterations in arterial blood pressure in heated humans would lead to baroreflex-mediated changes in both skin sympathetic nerve activity (SSNA) and sweat rate. 2In seven subjects mean arterial blood pressure was lowered (,8 mmHg) and then raised (,13 mmHg) by bolus injections of sodium nitroprusside and phenylephrine, respectively. Moreover, in a separate protocol, arterial blood pressure was reduced via steady-state administration of sodium nitroprusside. In both normothermia and heat-stress conditions the following responses were monitored: sublingual and mean skin temperatures, heart rate, beat-by-beat blood pressure, skin blood flow (laser-Doppler flowmetry), local sweat rate and SSNA (microneurography from peroneal nerve). 3Whole-body heating increased skin and sublingual temperatures, heart rate, cutaneous blood flow, sweat rate and SSNA, but did not change arterial blood pressure. Heart rate was significantly elevated (from 74 3 to 92 4 beats min,1; P < 0.001) during bolus sodium nitroprusside-induced reductions in blood pressure, and significantly reduced (from 92 4 to 68 4 beats min,1; P < 0.001) during bolus phenylephrine-induced elevations in blood pressure, thereby demonstrating normal baroreflex function in these subjects. 4Neither SSNA nor sweat rate was altered by rapid (bolus infusion) or sustained (steady-state infusion) changes in blood pressure regardless of the thermal condition. 5These data suggest that SSNA and sweat rate are not modulated by arterial baroreflexes in normothermic or moderately heated individuals. [source]

Rock thermal data at the grain scale: applicability to granular disintegration in cold environments

Kevin Hall
Abstract Consideration of the mechanisms associated with the granular disintegration of rock has been limited by available data. In most instances, both the size of the transducer and the nature of the study have negated any applicability of the resulting data to the understanding of grain-to-grain separation within rock. The application of microthermocouples (,015 mm diameter) and high-frequency logging (20 s intervals) at a taffoni site on southern Alexander Island and from a rock outcrop on Adelaide Island (Antarctica) provide new data pertaining to the thermal conditions, at the grain scale, of the rock surface. The results show that thermal changes (,T/t) can be very high, with values of 22 C min,1 being recorded. Although available data indicate that there can be differences in frequency and magnitude of ,uctuations as a function of aspect, all aspects experienced some large magnitude (,2 C min,1) ,uctuations. Further, in many instances, large thermal changes in more than one direction could occur within 1 min or in subsequent minutes. These data suggest that the surface grains experience rapidly changing stress ,elds that may, with time, effect fatigue at the grain boundaries; albedo differences between grains and the resulting thermal variations are thought to exacerbate this. The available data failed to show any indication of water freezing (an exotherm) and thus it is suggested that microgelivation may not play as large a role in granular breakdown as is often postulated for cold regions, and that in this dry, Antarctic region thermal stress may play a signi,cant role. Copyright 2003 John Wiley & Sons, Ltd. [source]

Oviposition Preferences in Newts: Does Temperature Matter?

ETHOLOGY, Issue 6 2009
Jan Dvo
A female's decision where and when to place her eggs has important fitness consequences for her offspring. Although temperature is considered among the most relevant abiotic factors affecting female oviposition site choice in ectotherms, little is known about the relative importance of temperature cues in complex oviposition decisions. In this study, we examined female's oviposition choice under conflicting demands for temperature and embryo protection by studying oviposition behaviour in female alpine newts, Triturus alpestris, exposed to various thermal conditions and the availability of egg-wrapping vegetation. Females oviposited between 12.5 and 22.5C in the aquatic thermal gradient (5,32.5C) with the unrestricted availability of oviposition vegetation. The removal of the vegetation from predominantly chosen oviposition temperatures (15,20C) induced egg-retention in most females. This suggests that both temperature and the presence of egg-wrapping vegetation play important roles in oviposition site choice of alpine newts. [source]

Costs of Refuge Use Affect Escape Decisions of Iberian Rock Lizards Lacerta monticola

ETHOLOGY, Issue 6 2000
Jos Martn
Theoretical models of anti-predator escape behaviour suggest that prey may adjust their escape response such that the optimal flight distance is the point at which the costs of staying exceed the costs of fleeing. Anti-predatory decisions should be made based also on consequences for long-term expected fitness, such as the costs of refuge use. For example, in lizards, the maintenance of an optimal body temperature is essential to maximize physiological processes. However, if unfavourable thermal conditions of refuges can decrease the body temperature of lizards, their escape decision should be influenced by refuge conditions. Analyses of the variation in flight distances and emergence latency from a refuge for the lizard Lacerta monticola under two different predation risk levels, and their relationship with the thermal environment, supported these predictions. When risk increased, lizards had longer emergence latencies, and thus costs of refuge use increased (a greater loss of time and body temperature). In the low-risk situation, lizards that were farther from the refuge had longer flight distances, whereas thermal conditions were less important. When risk increased, lizards had longer flight distances when refuges were farther off, but also when the external heating rate and the refuge cooling rate were lower. The results suggest that, in addition to the risk of predation, expected long-term fitness costs of refuges can also affect escape decisions. [source]

3D Architecture and Load Partition in Eutectic Al-Si Alloys,

Guillermo Requena
Abstract The changes of the three dimensional architecture of a eutectic AlSi12 alloy during heat treatment are revealed by means of synchrotron holotomography. The non-destructive nature of the holotomography technique allows to analyze the same volumes in different thermal conditions. The results show a disintegration of the interconnected eutectic Si-lamellae into isolated elongated particles. The load carrying capacity of both types of Si morphologies is studied by in situ neutron diffraction during compression tests. The experimental results are compared to those obtained using a micromechanical model developed for metal matrix composites based on a homogenization approach. The correlation between experiments and calculations shows that the interconnectivity of Si must be considered to account for the strength exhibited by the eutectic alloy. The present study bridges the gap between the already available two-dimensional studies of architecture and properties of the binary AlSi12 alloy and new three-dimensional studies of more complex systems based on this alloy. [source]

Aromatic and Benzylic C,H Bond Functionalization Upon Reaction between Nitriles and Perfluoroalkyl Sulfoxides

Yohan Mac
Abstract We studied the thermal behavior of some intermediates formed by reaction of nitriles with perfluoroalkyl sulfoxides upon trifluoromethanesulfonic anhydride activation. Bistriflate ketal 3, precursor of sulfilimine 1, may undergo a rearrangement to sulfanyl nitrile 5 after triflic acid elimination under thermal conditions. With p -tolyl trifluoromethyl sulfoxide, remote triflic acid elimination from intermediate 4 leads to benzamide 8 formation. These reactions involve, respectively, selective functionalization of the aromatic ortho C,H bond or the benzylic C,H bond para to the sulfoxide group. ( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source]

Factors influencing the service-like thermomechanical fatigue test cycle endurance of 1% CrMoV rotor steel

ABSTRACT Service-like thermomechanical fatigue tests have been performed in order to characterize the endurance of 1% CrMoV rotor steel under such transient thermal conditions. The key features of these tests are low strain rates (,10,5 s,1) and longer hold periods. In all testpieces, ratcheting with progressive section reduction is observed in the central portion of the gauge length accompanied by local amplification of the strain range. The finite-element-based analysis of this phenomenon allows the measured endurances to be rationalized with those determined from isothermal tests. Post-test inspection has revealed the development of two concurrent damaging mechanisms in the testpieces: (i) fatigue at the surface and (ii) creep in the interior. Different methods of damage calculation for creep,fatigue interaction are applied and compared in their predictive capabilities. [source]

Effects of ontogeny, temperature, and light on vertical movements of larval Pacific cod (Gadus macrocephalus)

Abstract The role of behavior, especially vertical migration, is recognized as a critical component of realistic models of larval fish dispersion. Unfortunately, our understanding of these behaviors lags well behind our ability to construct three-dimensional flow-field models. Previous field studies of vertical behavior of larval Pacific cod (Gadus macrocephalus) were limited to small, preflexion stages (,11 mm SL) in a narrow range of thermal conditions. To develop a more complete picture of larval behavior, we examined the effects of ontogeny, temperature, and light on vertical responses of larval Pacific cod in experimental columns. While eggs were strictly demersal, yolk-sac larvae displayed a strong surface orientation as early as 1 day post hatch (, 5 mm SL). Consistent with field observations, small preflexion larvae (<10 mm SL) showed no response to varying light levels. However, there was a direct effect of temperature on larval behavior: Pacific cod larvae exhibited a stronger surface orientation at 4C than at 8C. The behavior of larger, postflexion larvae (>15 mm SL) in experimental columns was consistent with a diel vertical migration and independent of water temperature: fish were more widely distributed in the column, and median positions were consistently deeper at higher light levels. These laboratory observations are combined with observations from discrete-depth (MOCNESS) sampling in the Gulf of Alaska to characterize the vertical distribution of larval Pacific cod and contrast ontogenetic patterns with walleye pollock (Theragra chalcogramma). The vertical movements of larval Pacific cod described here will be applied in the development of dispersal projections from Gulf of Alaska spawning grounds. [source]

Temperature dependence of stream benthic respiration in an Alpine river network under global warming

Summary 1. Global warming has increased the mean surface temperature of the Earth by 0.6 C in the past century, and temperature is probably to increase by an additional 3 C by 2100. Water temperature has also increased, which in turn can affect metabolic rate in rivers. Such an increase in metabolic rate could alter the role of river networks in the global C cycle, because the fraction of allochthonous organic C that is respired may increase. 2. Laboratory-based incubations at increasing water temperature were used to estimate the temperature dependence of benthic respiration in streams. These experiments were performed on stones taken from seven reaches with different thermal conditions (mean temperature ranging 8,19 C) within the pre-alpine Thur River network in Switzerland, June,October 2007. 3. The activation energy of respiration in different reaches along the river network (0.53 0.12 eV, n = 94) was similar, indicating that respiration was constrained by the activation energy of the respiratory complex (E = 0.62 eV). Water temperature and the thickness of the benthic biofilm influence the temperature dependence of respiration and our results suggest that an increase of 2.5 C will increase river respiration by an average of 20 1.6%. [source]

Thermal adaptation of Arctic charr: experimental studies of growth in eleven charr populations from Sweden, Norway and Britain

Summary 1. Experimental growth data for Arctic charr (Salvelinus alpinus L.), all fed on excess rations, from 11 European watercourses between 54 and 70N were analysed and fitted to a new general growth model for fish. The model was validated by comparing its predictions with the growth rate of charr in the wild. 2. Growth performance varied among populations, mainly because of variation in the maximum growth potential, whereas the thermal response curves were similar. The estimated lower and upper temperatures for growth varied between ,1.7 to 5.3 and 20.8,23.2 C, respectively, while maximum growth occurred between 14.4 and 17.2 C. 3. There was no geographical or climatic trend in growth performance among populations and therefore no indication of thermal adaptation. The growth potential of charr from different populations correlated positively with fish body length at maturity and maximum weight in the wild. Charr from populations including large piscivorous fish had higher growth rates under standardised conditions than those from populations feeding on zoobenthos or zooplankton. Therefore, the adaptive variation in growth potential was related to life-history characteristics and diet, rather than to thermal conditions. [source]

Inaccurate or disparate temperature cues?

Seasonal acclimation of terrestrial, aquatic locomotor capacity in newts
Summary 1.,Many organisms respond to seasonal temperature fluctuations by the reversible modification of whole-animal performance. Semiaquatic ectotherms, which possess this acclimatory capacity in swimming speed, lack the plastic response in terrestrial locomotor performance and vice versa. Theory predicts that the presence of reversible (seasonal) thermal acclimation or fixed phenotypes depends on the predictability of future thermal conditions (i.e. accuracy of temperature cues) in a given environment. Alternatively, comparative data suggest that thermal acclimation is induced by disparate temperature cues in water and on land. 2.,We tested both predictions by examining the seasonal acclimation response in thermal sensitivity of maximal swimming and running speed in adult alpine newts, Ichthyosaura (formerly Triturus) alpestris. 3.,Following the seasonal variation in environmental temperatures, we exposed newts to 5 C from November to March and, after a gradual temperature increase, to either a constant (15 C) or fluctuating (10,20 C) thermal regime from May to June. At the end of each treatment, we measured newt swimming and running capacity at five temperatures (range 5,25 C). In the field, hourly temperatures were recorded in various aquatic and terrestrial microhabitats to obtain information about the predictability of thermal conditions in both environments. 4.,Seasonal acclimation shaped the thermal sensitivity of swimming speed under both constant and fluctuating temperature treatments. Thermal sensitivity of running speed was markedly modified by a fluctuating thermal regime so that newts ran at the highest test temperature faster than cold-acclimated individuals. Natural thermal environment contained a similar proportion of predictable variation in water and on land. 5.,Complex seasonal acclimation of locomotor capacity in newts was influenced by the disparate thermal cues, i.e. mean acclimation temperature or diel temperature fluctuations, rather than by the different accuracy of these cues in water and on land. Future confrontations of theory with empirical data will require more attention not only on the assumptions of adaptive thermal acclimation but also on the ecologically relevant thermal conditions during acclimation experiments. [source]

What limits insect fecundity?

Body size-, oviposition in a butterfly, temperature-dependent egg maturation
Summary 1Large female insects usually have high potential fecundity. Therefore selection should favour an increase in body size given that these females get opportunities to realize their potential advantage by maturing and laying more eggs. However, ectotherm physiology is strongly temperature-dependent, and activities are carried out sufficiently only within certain temperature ranges. Thus it remains unclear if the fecundity advantage of a large size is fully realized in natural environments, where thermal conditions are limiting. 2Insect fecundity might be limited by temperature at two levels; first eggs need to mature, and then the female needs time for strategic ovipositing of the egg. Since a female cannot foresee the number of oviposition opportunities that she will encounter on a given day, the optimal rate of egg maturation will be governed by trade-offs associated with egg- and time-limited oviposition. As females of different sizes will have different amounts of body reserves, size-dependent allocation trade-offs between the mother's condition and her egg production might be expected. 3In the temperate butterfly Pararge aegeria, the time and temperature dependence of oviposition and egg maturation, and the interrelatedness of these two processes were investigated in a series of laboratory experiments, allowing a decoupling of the time budgets for the respective processes. 4The results show that realized fecundity of this species can be limited by both the temperature dependence of egg maturation and oviposition under certain thermal regimes. Furthermore, rates of oviposition and egg maturation seemed to have regulatory effects upon each other. Early reproductive output was correlated with short life span, indicating a cost of reproduction. Finally, large females matured more eggs than small females when deprived of oviposition opportunities. Thus, the optimal allocation of resources to egg production seems dependent on female size. 5This study highlights the complexity of processes underlying rates of egg maturation and oviposition in ectotherms under natural conditions. We further discuss the importance of temperature variation for egg- vs. time-limited fecundity and the consequences for the evolution of female body size in insects. [source]

Thermal performance of juvenile Atlantic Salmon, Salmo salar L.

Summary 1,Experimental data for maximum growth and food consumption of Atlantic Salmon (Salmo salar L.) parr from five Norwegian rivers situated between 59 and 70N were analysed and modelled. The growth and feeding models were also applied to groups of Atlantic Salmon growing and feeding at rates below the maximum. The data were fitted to the Ratkowsky model, originally developed for bacterial growth. 2,The rates of growth and food consumption varied significantly among populations but the variation appeared unrelated to thermal conditions in the river of population origins. No correlation was found between the thermal conditions and limits for growth, thermal growth optima or maximum growth, and hypotheses of population-specific thermal adaptation were not supported. Estimated optimum temperatures for growth were between 16 and 20 C. 3, Model parameter estimates differed among growth-groups in that maximum growth and the performance breadth decreased from fast to slow growing individuals. The optimum temperature for growth did not change with growth rate. 4, The model for food consumption (expressed in energy terms) peaked at 19,21 C, which is only slightly higher than the optimal temperature for growth. Growth appeared directly related to food consumption. Consumption was initiated ,2 C below the lower temperature for growth and terminated ,15 C above the upper critical temperature for growth. Model parameter estimates for consumption differed among growth-groups in a manner similar to the growth models. 5,By combining the growth and consumption models, growth efficiencies were estimated. The maximum efficiencies were high, 42,58%, and higher in rivers offering hostile than benign feeding and growth opportunities. [source]

Body size, locomotor speed and antipredator behaviour in a tropical snake (Tropidonophis mairii, Colubridae): the influence of incubation environments and genetic factors

J. K. Webb
Summary 1,The physical conditions experienced by reptile embryos inside natural nests can influence the size, shape and behaviour of the resultant hatchlings. Although most reptiles are tropical, the effects of incubation temperatures on offspring phenotypes have received little attention in tropical species. 2,The consequences of differences in thermal variance during incubation on offspring were studied in a tropical natricine snake (the Keelback Tropidonophismairii), which lays eggs in soil cracks of varying depths. Some 253 eggs from 19 clutches were incubated under two thermal regimes with identical mean temperatures (256 C), but temperatures in the ,variable' treatment fluctuated more (218,296 C) than those in the ,constant' temperature treatment (252,265 C). These thermal regimes were similar to those of shallow (20 cm deep) and deep (40 cm deep) soil cracks, respectively, and represent thermal conditions inside natural nests and potential nest sites. 3,Incubation temperatures affected body size, shape and antipredator behaviour of hatchling snakes. Snakes from constant temperature incubation were longer and thinner than snakes from high variance incubation. Clutch effects influenced all offspring traits, with significant interactions between clutch of origin and incubation treatment for body size, but not swimming speed or behaviour. 4,There was a significant interaction between incubation treatment and offspring sex on neonate swimming speed. Incubation under cycling thermal regimes significantly increased swimming speeds of females, but had little effect on males. Such sex differences in phenotypic responses of hatchling snakes support a major assumption of the Charnov,Bull hypothesis for the evolution of temperature-dependent sex determination. [source]

Regional scale relationships between ecosystem structure and functioning: the case of the Patagonian steppes

GLOBAL ECOLOGY, Issue 5 2004
Jos M. Paruelo
ABSTRACT Aims, 1. To characterize ecosystem functioning by focusing on above-ground net primary production (ANPP), and 2. to relate the spatial heterogeneity of both functional and structural attributes of vegetation to environmental factors and landscape structure. We discuss the relationship between vegetation structure and functioning found in Patagonia in terms of the capabilities of remote sensing techniques to monitor and assess desertification. Location, Western portion of the Patagonian steppes in Argentina (3930, S to 4527, S). Methods, We used remotely-sensed data from Landsat TM and AVHRR/NOAA sensors to characterize vegetation structure (physiognomic units) and ecosystem functioning (ANPP and its seasonal and interannual variation). We combined the satellite information with floristic relevs and field estimates of ANPP. We built an empirical relationship between the Landsat TM-derived normalized difference vegetation index (NDVI) and field ANPP. Using stepwise regressions we explored the relationship between ANPP and both environmental variables (precipitation and temperature surrogates) and structural attributes of the landscape (proportion and diversity of different physiognomic classes (PCs)). Results, PCs were quite heterogeneous in floristic terms, probably reflecting degradation processes. Regional estimates of ANPP showed differences of one order of magnitude among physiognomic classes. Fifty percent of the spatial variance in ANPP was accounted for by longitude, reflecting the dependency of ANPP on precipitation. The proportion of prairies and semideserts, latitude and, to a lesser extent, the number of PCs within an 8 8 km cell accounted for an additional 33% of the ANPP variability. ANPP spatial heterogeneity (calculated from Landsat TM data) within an 8 8 km cell was positively associated with the mean AVHRR/NOAA NDVI and with the diversity of physiognomic classes. Main conclusions, Our results suggest that the spatial and temporal patterns of ecosystem functioning described from ANPP result not only from water availability and thermal conditions but also from landscape structure (proportion and diversity of different PCs). The structural classification performed using remotely-sensed data captured the spatial variability in physiognomy. Such capability will allow the use of spectral classifications to monitor desertification. [source]

A basic study on humidity recovery by using micro-porous media (Effects of thermal condition of fluids and geometrical condition of apparatus on transport performance)

Shixue Wang
Abstract Using an experimental apparatus to examine the performance of heat and mass transfer between constant-temperature water and dry air through a porous plate having extremely small pores, the effects of the thermal conditions in the fluids and the geometric condition of the apparatus on moisture transport were measured. The effects of water temperature, thickness of the porous plate, and channel height of the flowing air on moisture transport are noticeable. However, the effect of air temperature in the channel inlet on moisture transport is slight. In addition, in order to evaluate the degree of air humidity absorption, a parameter called the moisture absorption rate was introduced. The moisture absorption rate was shown to decrease with increasing air velocity and varies only slightly for a plate thickness of 1 mm and decreases for a plate thickness of 3.5 mm with increasing water temperature. 2006 Wiley Periodicals, Inc. Heat Trans Asian Res, 35(8): 568,581, 2006; Published online in Wiley InterScience ( DOI 10.1002/htj.20133 [source]

Prediction of thermal sensation based on simulation of temperature distribution in a vehicle cabin

Takuya Kataoka
Abstract Thermal comfort in an automobile is predicted with numerical simulation. The flow field and temperature distribution are solved with a grid system based on many small cubic elements which are generated automatically with cabin and passenger configuration. Simulation of temperature is combined with simulation of cooling cycle and calculation of heat transfer at the wall including solar radiation to treat transient and actual driving conditions of the vehicle. In order to evaluate thermal comfort, transitional effective temperature is calculated from simulated thermal conditions and physiologic values which are calculated by a simple model of a human thermal system. This system can well predict thermal sensation of passengers in a short period of time. 2001 Scripta Technica, Heat Trans Asian Res, 30(3): 195,212, 2001 [source]

Reactivity and Selectivity of Captodative Olefins as Dienes in Hetero -Diels,Alder Reactions

Rubn Sanabria
Abstract The reactivity and selectivity of the the captodative olefins 1-acylvinyl benzoates 1a,1f and 3a as heterodienes in hetero -Diels,Alder reactions in the presence of electron-rich dienophiles is described. Heterodienes 1 undergo regioselective cycloaddition with the alkyl vinyl etherdienophiles 6a,b and 9 to give the corresponding dihydro-2H -pyrans 7, 8, and 10 under thermal conditions. The reactivity of these cycloadditions depends, to a large extent, on the electronic demand of the substituent in the aroyloxy group of the heterodiene. Frontier-molecular-orbital (FMO; ab initio) and density-functional-theory (DFT) calculations of the ground and transition states account for the reactivity and regioselectivity observed in these processes. [source]

Inverse design of directional solidification processes in the presence of a strong external magnetic field

Rajiv Sampath
Abstract A computational method for the design of directional alloy solidification processes is addressed such that a desired growth velocity ,f under stable growth conditions is achieved. An externally imposed magnetic field is introduced to facilitate the design process and to reduce macrosegregation by the damping of melt flow. The design problem is posed as a functional optimization problem. The unknowns of the design problem are the thermal boundary conditions. The cost functional is taken as the square of the L2 norm of an expression representing the deviation of the freezing interface thermal conditions from the conditions corresponding to local thermodynamic equilibrium. The adjoint method for the inverse design of continuum processes is adopted in this work. A continuum adjoint system is derived to calculate the adjoint temperature, concentration, velocity and electric potential fields such that the gradient of the L2 cost functional can be expressed analytically. The cost functional minimization process is realized by the conjugate gradient method via the FE solutions of the continuum direct, sensitivity and adjoint problems. The developed formulation is demonstrated with an example of designing the boundary thermal fluxes for the directional growth of a germanium melt with dopant impurities in the presence of an externally applied magnetic field. The design is shown to achieve a stable interface growth at a prescribed desired growth rate. Copyright 2001 John Wiley & Sons, Ltd. [source]

Air temperature changes in the arctic from 1801 to 1920

Rajmund Przybylak
Abstract In this paper, the results of an investigation into the thermal conditions in the Arctic in the period from 1801 to 1920 are presented. For this ,early instrumental' period limited meteorological data exist. Generally, the first meteorological stations in the Arctic were established in the second half of the 19th century and almost all of them were located in the coastal parts of Greenland. In order to get at least a rough idea of thermal conditions in the Arctic in the study period, data from different land and marine expeditions were collected. A total of 118 temperature series of monthly means have been gathered. Although the area and time periods covered by the data are variable, it is still possible to describe the general character of the temperature conditions. The results show that the areally averaged Arctic temperature in the early instrumental period was 0.8 C lower than the next 60-year period (1861,1920). In comparison to present-day conditions, winter and autumn were significantly colder (winter by 1.6 C and autumn by 0.9 C) than were summer (colder by 0.4 C) and spring (colder by only 0.2 C). The air temperature in the real Arctic during the first International Polar Year (IPY) was, on average, colder than today by 1.0,1.5 C. Winter was exceptionally cold with the average temperature being lower by more than 3 C in all months except February. On the other hand, spring (March,May) was slightly warmer than today, and April was exceptionally warm (1.1 C above present norm). The temperature differences calculated between historical and modern mean monthly temperatures show that majority of them lie within one standard deviation (SD) from present long-term mean. Thus, it means that the climate in the early instrumental period was not as cold as some proxy data suggest. Copyright 2009 Royal Meteorological Society [source]

An analytical and experimental analysis of a very fast thermal transient

C. Aprea
Abstract According to some international standards, some products, developed for use under heavy thermal conditions, have to be tested by subjecting them for a short time to a particular heating and cooling thermal stress to allow them an acceptable future operative life. It is possible to obtain these fast thermal gradients in confined environments, called climatic chambers where the air is heated by an electrical resistance and is cooled with a finned evaporator which is linked to a vapour compression system subjected to a particular control system of the refrigerating power. In particular, in this paper the air and object tested thermal transients are studied from an analytical and experimental point of view. The study of the mathematical model is realized assuming simplified hypotheses about the air, the object and the air cooled evaporator temperature. The most complex circumstances are related to a very fast temperature decrease because under this working condition the mathematical model is characterized by a nonlinear differential system. The nonlinear term is represented by the refrigerating power that varies in a definite range with the evaporator temperature according to a sinusoid trend. For this power a suitable analytical expression, derived by the control system performance and by the compressor characteristic, has been found. The analytical,experimental comparison during a cooling thermal stress of typical products subjected to international standard tests as the electronic boards, has been carried out showing acceptable results. The model presented is useful to foresee the climatic chamber performances in the presence of a specific refrigerating power trend; this is the start-point for the design of the vapour compression plant and its control system. Copyright 2001 John Wiley & Sons, Ltd. [source]

External morphology of a Slovenian population of pumpkinseed Lepomis gibbosus (L.) from a habitat with extreme thermal conditions

Summary The external morphology and growth variability of morphometric characters of pumpkinseed (n = 141) from an oxbow (River Sava, Slovenia) that receives thermal effluent were examined using triple regression analysis. Differences in external morphology between pumpkinseed from the oxbow and both native North American (River Otonabee, Looncall Lake, Canada) and non-native Central European populations (side arms of the River Danube, Slovakia) were evaluated. Two possible morphotypes among adults were observed, whereas the morphology of juveniles appears rather uniform across geographical location (i.e. Otonabee, Looncall, Danube). This suggests that environmental conditions, i.e. epigenetical information, seem to be responsible for most of variability in pumpkinseed morphology, which represents a function of epigenetical mechanisms. However, further investigation into epigenetical interactions, especially early development, fecundity, number of spawning acts per season, parental care, egg size and age at maturation are necessary to test this hypothesis. [source]

A modelling analysis of the genetic variation of phenology between tree populations

I. Chuine
Summary 1 The phenology of temperate woody plants is commonly assumed to be locally adapted to climate. 2 However, the high gene flow expected in forest tree species, the high between year variance of thermal conditions at a given place and the high plasticity of phenology regarding temperature, lead us to hypothesize that genetic variation of phenology between populations is likely to be insignificant for many lowland tree species. 3 Using phenological models, we investigated variation in the timing of flowering between locations for four European clonal trees and between different populations of a further five species. 4 Models were also used to study the responses of the different populations to climate change by simulating transfers of each population to different locations. 5 While clinal variations can be observed in the phenological response to temperature between populations, only one species (Corylus avellana) showed significantly different responses between populations and even then only one of three populations could be separated from the others. 6 Hypothetical transfers show that the differences observed between populations depend on the thermal conditions at the location of transfer, and that these differences are less marked in warmer conditions. 7 Our results indicate that local adaptation will probably not be a serious constraint in predicting the phenological responses of temperate lowland tree species to global warming. [source]

The diapause decision as a cascade switch for adaptive developmental plasticity in body mass in a butterfly

Abstract Switch-induced developmental plasticity, such as the diapause decision in insects, is a major form of adaptation to variable environments. As individuals that follow alternative developmental pathways will experience different selective environments the diapause decision may evolve to a cascade switch that induces additional adaptive developmental differences downstream of the diapause decision. Here, we show that individuals following alternative developmental pathways in a Swedish population of the butterfly, Pararge aegeria, display differential optimization of adult body mass as a likely response to predictable differences in thermal conditions during reproduction. In a more northern population where this type of selection is absent no similar difference in adult mass among pathways was found. We conclude that the diapause decision in the southern population appears to act as a cascade switch, coordinating development downstream of the diapause decision, to produce adult phenotypes adapted to the typical thermal conditions of their expected reproductive period. [source]

Latitudinal variations in age and size at maturity among allis shad Alosa alosa populations

G. Lassalle
Age and total length (LT) at maturity of allis shad Alosa alosa exhibited a significant negative latitudinal gradient over the species' distribution range. Particular thermal conditions experienced over the distribution area could be the key factor involved to explain this negative trend. [source]