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Temperature Changes (temperature + change)
Selected AbstractsCHARACTERISTICS OF CHAMBER TEMPERATURE CHANGE DURING VACUUM COOLINGJOURNAL OF FOOD PROCESS ENGINEERING, Issue 2 2009RUI ZHAO ABSTRACT In order to investigate the dynamic changing pattern of the chamber temperature with chamber pressure during vacuum cooling, 10 repeated experiments were conducted to evaluate the time-dependent temperature and pressure in the vacuum chamber during vacuum cooling of water. Water was chosen in the experiment as it is the main component of most foods. The results showed that the temperature in the vacuum chamber significantly depended on variation in pressure at different pumping stages. The temperature changes in the chamber generally followed a certain pattern. In the early stage of vacuum cooling, the chamber temperature dropped very quickly (0.26 K/s), while at the end of vacuum cooling, it increased rapidly (0.22 K/s), and was about 11.8 K higher than the ambient temperature when the vacuum was released with ambient air flowing back to the chamber. PRACTICAL APPLICATIONS Vacuum cooling is a rapid cooling method for the food industry; further understanding of the vacuum cooling mechanism can help to control and improve this cooling process. Temperature changing pattern and distribution affects the quality of the food product in vacuum cooling process. As the main component of most foods is water, it is necessary to investigate the dynamic temperature changing pattern and distribution with vacuum pressure during vacuum cooling of water so that the information obtained could be used as a reference for vacuum cooling of food products. [source] RADIO FREQUENCY (RF) HEATING OF STARCH SOLUTIONS UNDER CONTINUOUS FLOW CONDITIONS: EFFECT OF SYSTEM AND PRODUCT PARAMETERS ON TEMPERATURE CHANGE ACROSS THE APPLICATOR TUBEJOURNAL OF FOOD PROCESS ENGINEERING, Issue 3 2002G.B. AWUAH ABSTRACT Studies were conducted to evaluate the effect of system and product parameters on the temperature change (,T) across a 1.5 kW radio frequency heater operating at 27.12 MHz. Starch solutions (1 to 4% w/w) were used at three different flow rates (0.35, 0.5 and 1 L/min) and four power levels (672, 912, 1152 and 1392 W). The average heating rate of starch solutions varied from 6 to 19C/min depending on flow rate, concentration and power level. The corresponding residence time varied from 1.5 to 4.3 min. Central composite designs involving power (830 to 1234 W) and starch concentration (1 to 4% w/w) at 0.5 L/min were used to study the effects of salt, pH and sugar. As expected fluid flow rate, power level and salt concentration had significant impact (P ± 0.05) on temperature change (,T) across the applicator tube. Although the interaction effect of salt and concentration influenced ,T (P < 0.05), observed trends were not clear cut. Sugar and pH had no significant (P >0.05) influence on ,T due probably to their relatively lower conductivities. However, the interaction effect of sugar and starch concentration affected ,T. Correlations were developed for estimating ,T across the tube as a function of power level, concentration, pH, added salt and sugar. Finally, dimensionless correlations involving the generalized Reynolds, Prandtl, Grashof numbers, dimensionless power and loss-factor ratios were developed for estimating the temperature ratio (U) across the RF applicator. [source] Temperature change within gutta-percha induced by the System-B Heat SourceINTERNATIONAL ENDODONTIC JOURNAL, Issue 9 2002M. Venturi No abstract is available for this article. [source] Physical characterization of starch extrudates as a function of melting transitions and extrusion conditionsADVANCES IN POLYMER TECHNOLOGY, Issue 4 2004Stéphanie Blanche Abstract The objective of this study was to investigate the relationships between starch melt transition characteristics, extrusion conditions, and final product properties. Cornstarch was extruded using a corotating twin-screw extruder at varying moisture content, medium/high screw configuration, and 300/400-rpm screw speeds. Extrudates were evaluated for bulk density, expansion ratio, cell structure, bending strength, thermal and pasting properties. Temperature change (,T) was defined as the temperature difference between the native starch melting temperature and its melt temperature just behind the die during extrusion at a given moisture content. ,T was significantly affected by starch moisture content and mechanical shearing, which controlled the melting behavior of the starch in the barrel. Amylose,lipid complex formation during extrusion increased as ,T increased and leveled off at ,T of about 20°C. Pasting peak viscosity of the starch extrudates decreased as ,T increased and leveled off at ,T of about 15°C. Within the same range of mechanical shearing intensity, extrudate bulk density and bending strength decreased linearly as ,T increased. Extrudate expansion was negatively correlated to bulk density. © 2004 Wiley Periodicals, Inc. Adv Polym Techn 23: 277,290, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20017 [source] Electromechanical reshaping of septal cartilage,,THE LARYNGOSCOPE, Issue 11 2003Ki-Hong Kevin Ho BS Abstract Objectives: This study describes the process of tissue electroforming and how shape changes in cartilage can be produced by the application of direct current (DC). The dependence of shape change on voltage and application time is explored. Study Design: Basic investigation using ex vivo porcine septal cartilage grafts and electromechanical cartilage deformation focused on development of a new surgical technique. Methods: Uniform flat porcine nasal septal cartilage specimens were mechanically deformed between two semicircular aluminum electrodes. DC current was applied to establish charge separation and electrical streaming potential. Voltage (0,3.5 V) and application time (0,5 minutes) were varied. Shape change was measured, and shape retention was calculated using analytic representation. The effect of the direction of applied current on shape change was evaluated by switching the polarities of electrodes and using parameters of 0 to 5.5 V and 5 minutes. Temperature during reshaping was monitored with a thermocouple, and surface features were evaluated using light microscopy. Results: Reshaped specimen demonstrated mechanical stability similar to native cartilage tissue. Shape retention strongly correlated with increasing voltage and application time. Only a small current (<0.1 A) through the tissue was measured. Temperature change was less than 2°C during electroforming, suggesting that electroforming likely results from some nonthermal mechanisms. Surface features indicated that electrodeposition may occur depending on electrode material and magnitude of the applied voltage. Conclusions: These findings demonstrate that cartilage can be reshaped through the process we have described as "electroforming" by generating intrinsic differences in charge separation with negligible heat production. [source] Post-ictal fever: a rare symptom of partial seizuresEUROPEAN JOURNAL OF NEUROLOGY, Issue 5 2007A. O. Rossetti Although fever may induce seizures, especially in children, its occurrence following epileptic spells has been rarely described, except from generalized convulsive status epilepticus. We present two patients suffering from focal seizures accompanied by episodes of post-ictal fever, and review similar reports in the literature of the last 40 years. Temperature changes following non-convulsive seizures might be induced by gene upregulation occurring in the hypothalamus, the nucleus tractus solitarius, or in other brain regions, producing a local inflammatory response. Direct propagation of electrical discharges seems less consistent with the timing of development of this symptom. Heterogeneity of reported clinical features argues against the assumption of a definite localizing or lateralizing value for post-ictal fever. [source] Noninvasive temperature mapping with MRI using chemical shift water-fat separationMAGNETIC RESONANCE IN MEDICINE, Issue 5 2010Brian J. Soher Abstract Tissues containing both water and lipids, e.g., breast, confound standard MR proton reference frequency-shift methods for mapping temperatures due to the lack of temperature-induced frequency shift in lipid protons. Generalized Dixon chemical shift,based water-fat separation methods, such as GE's iterative decomposition of water and fat with echo asymmetry and least-squares estimation method, can result in complex water and fat images. Once separated, the phase change over time of the water signal can be used to map temperature. Phase change of the lipid signal can be used to correct for non-temperature-dependent phase changes, such as amplitude of static field drift. In this work, an image acquisition and postprocessing method, called water and fat thermal MRI, is demonstrated in phantoms containing 30:70, 50:50, and 70:30 water-to-fat by volume. Noninvasive heating was applied in an Off1-On-Off2 pattern over 50 min, using a miniannular phased radiofrequency array. Temperature changes were referenced to the first image acquisition. Four fiber optic temperature probes were placed inside the phantoms for temperature comparison. Region of interest (ROI) temperature values colocated with the probes showed excellent agreement (global mean ± standard deviation: ,0.09 ± 0.34°C) despite significant amplitude of static field drift during the experiments. Magn Reson Med 63:1238,1246, 2010. © 2010 Wiley-Liss, Inc. [source] Temperature changes in dental pulp associated with use of power grinding equipment on equine teethAUSTRALIAN VETERINARY JOURNAL, Issue 1-2 2005GJ WILSON Objective To quantify the temperature changes in the dental pulp associated with equine dental procedures using power grinding equipment. Design A matrix experimental design with replication on the same sample was followed to allow the following independent variables to be assessed: horse age (young or old), tooth type (premolar or molar), powered grinding instrument (rotating disc or die grinder), grinding time (15 or 20 seconds) and the presence or absence of water coolant. Procedure Sound premolar and molar teeth from a 6-year-old horse and a 15-year-old horse, which had been removed postmortem, were sectioned parallel to the occlusal plane to allow placement of a miniature thermocouple at the level of the dental pulp. The maximum temperature increase, the time taken to reach this maximum and the cooling time were measured (n=10 in each study). The teeth were placed in a vice and the instrument used on the tooth as per clinical situation. Results Significant differences were recorded for horse age (P < 0.001), instrument type (P < 0.001), grinding time (P < 0.001) and presence or absence of coolant (P < 0.001). There was no significant difference for tooth type. Conclusion Thermal insult to the dental pulp from the use of power instruments poses a significant risk to the tooth. This risk can be reduced or eliminated by appropriate selection of treatment time and by the use of water irrigation as a coolant. The increased dentine thickness in older horses appears to mitigate against thermal injury from frictional heat. [source] Processes controlling rapid temperature variations on rock surfaces,EARTH SURFACE PROCESSES AND LANDFORMS, Issue 5 2010Jamie L. Molaro Abstract In arid environments, thermal oscillations are an important source of rock weathering. Measurements of temperature have been made on the surface of rocks in a desert environment at a sampling interval of 0·375,s, with simultaneous measurements of wind speed, air temperature, and incoming shortwave radiation. Over timescales of hours, the temperature of the rock surface was determined primarily by shortwave radiation and air temperature, while rapid temperature variations, high dT/dt, at intervals of seconds or less, were determined by wind speed. The maximum values of temperature change and time spent above 2°C,min,1 increased at high measurement rates and were much higher than previously reported. The maximum recorded value of dT/dt was 137°C,min,1 and the average percentage time spent above 2°C,min,1 was ,70 ± 13%. Maximum values of dT/dt did not correlate with the maximum values of time spent above 2°C,min,1. Simultaneous measurements of two thermocouples 5·5,cm apart on a single rock surface had similar temperature and dT/dt values, but were not correlated at sampling intervals of less than 10,s. It is suggested that this is resulting from rapid fluctuations due to small spatial and timescale wind effects that are averaged out when data is taken at longer sampling intervals, ,10,s or greater. Published in 2010 by John Wiley & Sons, Ltd. [source] Contrasting spatial and temporal global change impacts on butterfly species richness during the 20th centuryECOGRAPHY, Issue 6 2006Peter White Regional patterns of species richness are often explained by models using temperature or measures habitat suitability. Generally, species richness is positively associated with temperature, and negatively associated with habitat degradation. While these models have been well tested across spatial scales, they have rarely been tested on a temporal scale , in part due to the difficulty in ascertaining accurate historical data at an appropriate resolution. In this study, we compared the results of temporal and spatial models, each incorporating two predictors of species richness: temperature, and human population density (as a surrogate of human-related habitat impacts). We found that the change in species richness from the early to late part of the 20th century was positively correlated with temperature change, and negatively correlated with human population density change. When we compared these results to two spatial models using contemporary and historic data, the spatial effects of temperature on butterfly richness were similar to its temporal effects, while the effect of human population density through time is the opposite of its spatial effect. More generally, the assumption that spatial patterns are equivalent to temporal ones when applying macroecological data to global change is clearly unreliable. [source] Effect of temperature change on the composition of the bacterial and archaeal community potentially involved in the turnover of acetate and propionate in methanogenic rice field soilFEMS MICROBIOLOGY ECOLOGY, Issue 2 2010Matthias Noll Abstract The microbial community structure was investigated together with the path of methane production in Italian rice field soil incubated at moderate (35 °C) and high (45 °C) temperature using terminal restriction fragment length polymorphism and stable isotope fractionation. The structure of both the archaeal and bacterial communities differed at 35 °C compared with 45 °C, and acetoclastic and hydrogenotrophic methanogenesis dominated, respectively. Changing the incubation of the 45 °C soil to different temperatures (25, 30, 35, 40, 45, 50 °C) resulted in a dynamic change of both microbial community structure and stable isotope fractionation. In all treatments, acetate first accumulated and then decreased. Propionate was also transiently produced and consumed. It is noteworthy that acetate was also consumed at thermophilic conditions, although archaeal community composition and stable isotope fractionation indicated that acetoclastic methanogenesis did not operate. Instead, acetate must have been consumed by syntrophic acetate oxidizers. The transient accumulation and subsequent consumption of acetate at thermophilic conditions was specifically paralleled by terminal restriction fragments characteristic for clostridial cluster I, whereas those of clostridial clusters I and III, Acidaminococcaceae and Heliobacteraceae, paralleled the thermophilic turnover of both acetate and propionate. [source] Remote extinguishing of large fires with powder aerosolsFIRE AND MATERIALS, Issue 5 2006Article first published online: 9 JAN 200, Mikhail Krasnyansky Abstract A new method for distant extinguishing of fire spreading in an extended closed volume such as a mine working, storehouse, subway tunnel, electric cable channels, etc. is proposed. A novel extinguishing agent based on a stable mixture of superfine ammonium phosphate [NH4H2PO4] and modified fumed silica [SiO2,CH3] is supplied to the fire by a powerful ventilator. The properties of the extinguishing agent (average particle size, airborne residence time, distance of transfer by the air stream) have been studied in an experimental chamber (100 m3). A test extinguishing of a large-scale fire has been performed in an experimental tunnel 180 m in length. Extinguishing agent consumption, dynamics of temperature change over the tunnel length and composition of fire gases were recorded in this test. The influence of foam concentration, addition of nitrogen and halons to aerosol, were also studied. Copyright © 2006 John Wiley & Sons, Ltd. [source] Numerical modeling of hydrothermal zinc silicate and sulfide mineralization in the Vazante deposit, BrazilGEOFLUIDS (ELECTRONIC), Issue 2 2009M. S. APPOLD Abstract The Vazante zinc deposit in central Brazil is currently the world's largest known example of a hypogene nonsulfide (i.e. willemite-dominant) zinc deposit. The mineralization is hypothesized to have formed as a result of mixing between a hot, acidic, reducing, metal-rich brine and a cool, more basic and dilute, metal-poor meteoric fluid. The present study sought to investigate this scenario by quantifying the individual effects of temperature, pH, salinity, and oxidation state on willemite and sphalerite solubility, and modeling their combined effects during mixing through reaction path and reactive transport modeling. Solubility calculations showed that in an initially hot, moderately acidic, reducing, metal-rich ore fluid saturated with respect to silica, willemite solubility is relatively insensitive to changes in temperature and log , but highly sensitive to changes in pH and salinity. In contrast, sphalerite solubility was highly sensitive to changes in temperature and log , as well as salinity, and was less sensitive than willemite to changes in pH. Reaction path models sought to extend these observations by modeling the geochemistry of mixing. The results show that mixing is able to produce most of the major zinc ore and gangue minerals observed in the field, though not necessarily at the same paragenetic stages, and that both compositional and temperature changes from mixing are needed. Reactive transport models were formulated to investigate spatial patterns of mineralization. The results showed that sphalerite deposition was strongly controlled by temperature and concentrated in the regions of greatest temperature change. Willemite deposition was concentrated along the interface between the metal-rich ore fluid and the surrounding meteoric fluid. The more rapid transport of solute than heat, in conjunction with the higher concentration of silica than sulfide in both fluids meant that willemite mineralization developed over a broader region and in greater concentrations compared with sphalerite. [source] A 2000-YEAR CONTEXT FOR MODERN CLIMATE CHANGEGEOGRAFISKA ANNALER SERIES A: PHYSICAL GEOGRAPHY, Issue 1 2005K.A. MAASCH ABSTRACT. Although considerable attention has been paid to the record of temperature change over the last few centuries, the range and rate of change of atmospheric circulation and hydrology remain elusive. Here, eight latitudinally well-distributed (pole-equator-pole), highly resolved (annual to decadal) climate proxy records are presented that demonstrate major changes in these variables over the last 2000 years. A comparison between atmospheric 14C and these changes in climate demonstrates a first-order relationship between a variable Sun and climate. The relationship is seen on a global scale. [source] Statistical theory of weak field thermoremanent magnetization in multidomain particle ensemblesGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 2 2003Karl Fabian SUMMARY A non-equilibrium statistical theory of multidomain thermoremanent magnetization (TRM) is developed, which describes thermal magnetization changes as continuous inhomogeneous Markov processes. The proposed theory relies on three very general physical properties of TRM: (a) The probability that a magnetization state Sj is transformed during an infinitesimal temperature change into state Si depends only on external conditions and on Sj, but not on previously assumed states. (b) Due to time inversion symmetry of the Maxwell equations, the magnetic energies are invariant with respect to inversion of all spins in zero field. (c) The probability that an energy barrier between two magnetization states is overcome during a thermal process is governed by Boltzmann statistics. From these properties, the linearity of TRM with field is derived for generic multidomain particle ensembles. The general validity of Thellier's law of additivity of partial TRM's in weak fields is established and a method for proving a large class of similar additivity laws is developed. The theory allows consistent treatment of blocking and unblocking of remanence in multidomain particle ensembles and naturally explains apparent differences between blocking and unblocking temperatures. [source] Ecological relevance of laboratory determined temperature limits: colonization potential, biogeography and resilience of Antarctic invertebrates to environmental changeGLOBAL CHANGE BIOLOGY, Issue 11 2010D. K. A. BARNES Abstract The relevance of laboratory experiments in predicting effects of climate change has been questioned, especially in Antarctica where sea temperatures are remarkably stable. Laboratory studies of Southern Ocean marine animal capacities to survive increasing temperature mainly utilize rapid temperature elevations, 100 ×,10 000 × faster than sea temperature is predicted to rise. However, due to small-scale temperature fluctuations these studies may be crucial for understanding colonization patterns and predicting survival particularly through interactions between thermal tolerance and migration. The colonization of disjunct shelves around Antarctica by larvae or adult drift requires crossing or exposure to, rapid temperature changes of up to 2,4 °C over days to weeks. Analyses of responses to warming at varying rates of temperature change in the laboratory allow better predictions of the potential species have for colonizing disjunct shelf areas (such as the Scotia Arc). Inhabiting greater diversities of localities increases the geographic and thermal range species experience. We suggest a strong link between short-term temperature tolerance, environmental range and prospects for surviving changing environments. [source] European phenological response to climate change matches the warming patternGLOBAL CHANGE BIOLOGY, Issue 10 2006ANNETTE MENZEL Abstract Global climate change impacts can already be tracked in many physical and biological systems; in particular, terrestrial ecosystems provide a consistent picture of observed changes. One of the preferred indicators is phenology, the science of natural recurring events, as their recorded dates provide a high-temporal resolution of ongoing changes. Thus, numerous analyses have demonstrated an earlier onset of spring events for mid and higher latitudes and a lengthening of the growing season. However, published single-site or single-species studies are particularly open to suspicion of being biased towards predominantly reporting climate change-induced impacts. No comprehensive study or meta-analysis has so far examined the possible lack of evidence for changes or shifts at sites where no temperature change is observed. We used an enormous systematic phenological network data set of more than 125 000 observational series of 542 plant and 19 animal species in 21 European countries (1971,2000). Our results showed that 78% of all leafing, flowering and fruiting records advanced (30% significantly) and only 3% were significantly delayed, whereas the signal of leaf colouring/fall is ambiguous. We conclude that previously published results of phenological changes were not biased by reporting or publication predisposition: the average advance of spring/summer was 2.5 days decade,1 in Europe. Our analysis of 254 mean national time series undoubtedly demonstrates that species' phenology is responsive to temperature of the preceding months (mean advance of spring/summer by 2.5 days°C,1, delay of leaf colouring and fall by 1.0 day°C,1). The pattern of observed change in spring efficiently matches measured national warming across 19 European countries (correlation coefficient r=,0.69, P<0.001). [source] Effect of global atmospheric carbon dioxide on glacial,interglacial vegetation changeGLOBAL ECOLOGY, Issue 5 2000K. D. Bennett Abstract Global vegetation changes at the time-scale of the Earth's orbital variations (104,105 years) have been interpreted as a direct effect of consequential climatic changes, especially temperature. At mid- and high latitudes, the evidence from fossil data and general circulation models (GCMs) supporting this hypothesis is strong, but at low latitudes there is a major discrepancy. GCMs predict temperature changes that are less than those inferred from palaeoclimatic data, including the plant fossil record. However, changes in atmospheric CO2 concentrations can account for a high proportion of the low-latitude vegetation change hitherto attributed to temperature change, and may thus explain the discrepancy. The implications of this finding are considerable for understanding patterns of macroevolution and ecosystem development throughout the geological record. [source] Climate change and grasslands through the ages: an overviewGRASS & FORAGE SCIENCE, Issue 2 2007L. 't Mannetje Summary Change from cool to warm temperatures and vice versa have occurred throughout geological time. During the Jurassic and Cretaceous periods (206,65 million years ago, Ma) the climate was more uniformly warm and moist than at present and tropical rainforests were widespread. Grasses evolved during the Jurassic period and they expanded greatly as the climate differentiated with reduced rainfall and temperatures. C4 -grasses probably arose during the Oligocene period (24,35 Ma). During the Miocene period (23·8,5·3 Ma) grasslands expanded into huge areas (e.g. prairies in the USA, steppe in Eurasia, and pampas and llanos in South America). During the Quaternary period (1·8 Ma till now) some twenty-two different ice ages with periodicities of about 100 000 years occurred. Eighteen-thousand years ago, north-western Europe had a polar climate with tundra vegetation and the Mediterranean region was covered by steppe. During that time Amazonia was so dry that it was covered in extensive areas of savanna and the Sahara expanded rapidly. Only in the last 10 000 years has a closed rainforest covered the Amazonian region again. However, 9000 years ago a brief period of global warming caused excessive rains, which caused the sea and river levels to rise in north-western Europe with tremendous loss of life. The present period of extreme dryness in the Sahara only started some 5000 years ago and then the desert expanded rapidly into the Sahel. Before that the Sahara was covered by steppe. Global warming took place between about ad 900 and about ad 1200 or 1300 just before the Little Ice Age (1550,1700 ad). The article concludes with a description of temperature and vegetation changes that are occurring in Europe at present. It is predicted that C4 -grasses, which are already present in southern Europe, will further expand but that, in the short term, land abandonment will have much more deleterious effects than temperature change due to increased wild fires, loss of biodiversity and desertification. [source] Evaluation of Noble Gas Recharge Temperatures in a Shallow Unconfined AquiferGROUND WATER, Issue 5 2009Bradley D. Cey Water table temperatures inferred from dissolved noble gas concentrations (noble gas temperatures, NGT) are useful as a quantitative proxy for air temperature change since the last glacial maximum. Despite their importance in paleoclimate research, few studies have investigated the relationship between NGT and actual recharge temperatures in field settings. This study presents dissolved noble gas data from a shallow unconfined aquifer heavily impacted by agriculture. Considering samples unaffected by degassing, NGT calculated from common physically based interpretive gas dissolution models that correct measured noble gas concentrations for "excess air" agreed with measured water table temperatures (WTT). The ability to fit data to multiple interpretive models indicates that model goodness-of-fit does not necessarily mean that the model reflects actual gas dissolution processes. Although NGT are useful in that they reflect WTT, caution is recommended when using these interpretive models. There was no measurable difference in excess air characteristics (amount and degree of fractionation) between two recharge regimes studied (higher flux recharge primarily during spring and summer vs. continuous, low flux recharge). Approximately 20% of samples had dissolved gas concentrations below equilibrium concentration with respect to atmospheric pressure, indicating degassing. Geochemical and dissolved gas data indicate that saturated zone denitrification caused degassing by gas stripping. Modeling indicates that minor degassing (<10% ,Ne) may cause underestimation of ground water recharge temperature by up to 2°C. Such errors are problematic because degassing may not be apparent and degassed samples may be fit by a model with a high degree of certainty. [source] Application of inverse solution in two-dimensional heat conduction problem using Laplace transformationHEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 7 2003Masanori Monde Abstract An inverse solution has been explicitly derived for two-dimensional heat conduction in cylindrical coordinates using the Laplace transformation. The applicability of the inverse solution is checked using the numerical temperatures with a normal random error calculated from the corresponding direct solution. For a gradual temperature change in a solid, the surface heat flux and temperature can be satisfactorily predicted, while for a rapid change in the temperature this method needs the help of a time partition method, in which the entire measurement time is split into several partitions. The solution with the time partitions is found to make an improvement in the prediction of the surface heat flux and temperature. It is found that the solution can be applied to experimental data, leading to good prediction. © 2003 Wiley Periodicals, Inc. Heat Trans Asian Res, 32(7): 602,617, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.10115 [source] Electrocaloric Materials for Solid-State RefrigerationADVANCED MATERIALS, Issue 19 2009Sheng-Guo Lu Abstract The electrocaloric effect (ECE) in dielectric materials has great potential in realizing solid-state cooling devices with compact size and high efficiency, which are highly desirable for a broad range of applications. This paper presents the general considerations for dielectric materials to achieve large ECE and reviews the experimental efforts investigating ECE in various polar dielectrics. For practical cooling devices, an ECE material must possess a large isothermal entropy change besides a large adiabatic temperature change. We show that polar dielectrics operated at temperatures near order,disorder transition have potential to achieve large ECE due to the possibility of large change in polarization induced by electric field and large entropy change associated with the polarization change. We further show that indeed the ferroelectric poly(vinylidene fluoride,trifluoroethylene)-based polymers display a large ECE, i.e., an isothermal entropy change of more than 55,J,(kgK),1 and an adiabatic temperature change of more than 12,°C, at temperatures above the order,disorder transition. [source] Fluid dynamic numerical simulation coupled with heat transfer and reaction in the tubular reactor of industrial cracking furnacesINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 4 2010Chufu Li Abstract The thermal cracking furnace is the heart of the ethylene production process in a petrochemical plant. This paper presents a comprehensive mathematical model containing equations for mass, momentum and heat transfer combined with Kumar molecular kinetic model to describe dynamic behaviors of fluid flow, heat transfer and reaction in the tubular reactor of thermal cracking furnaces. The ,flow-reaction' decomposition strategy is adopted to solve the complex model for implementing the fluid dynamic simulation coupled with heat transfer and reaction in the tubular reactor by a conventional procedure. The proposed mathematical model and the decomposition algorithm are successfully applied to the fluid dynamic simulation in the tubular reactor of a millisecond industrial cracking furnace. The results of dynamic simulation reveal the various transient behaviors of fluid flow, temperature change and species content variation in the tubular reactor under the step disturbance of inlet feedrate. Finally, the performance of the decomposition algorithm is also investigated. Copyright © 2009 John Wiley & Sons, Ltd. [source] Annual temperature history in Southwest Tibet during the last 400 years recorded by tree ringsINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 7 2010Bao Yang Abstract We present a tree ring-width record from the southern Tibetan Plateau (TP) which spans from 1612,1998 AD (387 years). The series was developed from Tibetan juniper (Juniperus tibetica Kom) growing at sites near the western distribution limit of the species. Two versions of the chronology, a traditionally standardized chronology (TSC) and a regional curve standardization (RCS)chronology were developed. Linear regression models between ring width and mean annual temperature account for 41% (TSC) and 43% (RCS) of the annual (July,June) temperature variance for the period 1957,1998. According to the TSC reconstruction, warm periods occurred during the 1620s, 1650,1675, 1720s, 1740,1790, 1810s, 1850s,1890s, 1935,1950, and 1957,1964 and since 1980. Cold conditions prevailed during the 1630s,1640s, 1680s,1710s, 1730s, 1820,1840s, 1900s,1920s and the 1970s. Within the last 400 years, the late-20th century warming is distinctive but still within the range of natural climatic variability of this region. Comparison of our TSC reconstruction with proxy temperature records from other parts of the TP shows that the cold conditions during the 1730s, 1900s,1920s, and 1970s, and the warm periods during the 1770,1800, 1850s,1890s, 1935,1950, and 1957,1964 and since 1980 were synchronously occurring broad-scale climate anomalies on the whole TP. Differences between the reconstructions are found during the 17th century and around 1760, which were probably caused by local differences in temperature change and different sensitivity in seasonality. The RCS series portrays low-frequency variations such as warm periods during 1620,1640, 1650,1690, 1715,1790, and 1845,1875, and cold conditions during 1640,1650, 1690,1715, and 1875,1995. These long-term trends need to be verified by developing other proxy records that target to capture low-frequency signals in the future. Copyright © 2009 Royal Meteorological Society [source] Consistency of modelled and observed temperature trends in the tropical troposphereINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 13 2008B. D. Santer Abstract A recent report of the U.S. Climate Change Science Program (CCSP) identified a ,potentially serious inconsistency' between modelled and observed trends in tropical lapse rates (Karl et al., 2006). Early versions of satellite and radiosonde datasets suggested that the tropical surface had warmed more than the troposphere, while climate models consistently showed tropospheric amplification of surface warming in response to human-caused increases in well-mixed greenhouse gases (GHGs). We revisit such comparisons here using new observational estimates of surface and tropospheric temperature changes. We find that there is no longer a serious discrepancy between modelled and observed trends in tropical lapse rates. This emerging reconciliation of models and observations has two primary explanations. First, because of changes in the treatment of buoy and satellite information, new surface temperature datasets yield slightly reduced tropical warming relative to earlier versions. Second, recently developed satellite and radiosonde datasets show larger warming of the tropical lower troposphere. In the case of a new satellite dataset from Remote Sensing Systems (RSS), enhanced warming is due to an improved procedure of adjusting for inter-satellite biases. When the RSS-derived tropospheric temperature trend is compared with four different observed estimates of surface temperature change, the surface warming is invariably amplified in the tropical troposphere, consistent with model results. Even if we use data from a second satellite dataset with smaller tropospheric warming than in RSS, observed tropical lapse rate trends are not significantly different from those in all other model simulations. Our results contradict a recent claim that all simulated temperature trends in the tropical troposphere and in tropical lapse rates are inconsistent with observations. This claim was based on use of older radiosonde and satellite datasets, and on two methodological errors: the neglect of observational trend uncertainties introduced by interannual climate variability, and application of an inappropriate statistical ,consistency test'. Copyright © 2008 Royal Meteorological Society [source] Mass balance of a slope glacier on Kilimanjaro and its sensitivity to climateINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 7 2008Thomas Mölg Abstract Meteorological and glaciological measurements obtained at 5873 m a.s.l. on Kersten Glacier, a slope glacier on the southern flanks of Kilimanjaro, are used to run a physically-based mass balance model for the period February 2005 to January 2006. This shows that net shortwave radiation is the most variable energy flux at the glacier-atmosphere interface, governed by surface albedo. The majority of the mass loss (,65%) is due to sublimation (direct conversion of snow/ice to water vapour), with melting of secondary importance. Sensitivity experiments reveal that glacier mass balance is 2,4 times more sensitive to a 20% precipitation change than to a 1 °C air temperature change. These figures also hold when the model is run with input data representative of a longer term (1979,2004) mean period. Results suggest that a regional-scale moisture projection for the 21st century is crucial to a physically-based prediction of glacier retention on Africa's highest mountain. Copyright © 2007 Royal Meteorological Society [source] January northern hemisphere circumpolar vortex variability and its relationship with hemispheric temperature and regional teleconnectionsINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 11 2005Robert V. Rohli Abstract Variability in the hemispheric-scale atmospheric circulation can be directly linked to variations in surface environmental features, such as temperature, precipitation, salinity of water bodies, and pollutant transport. One indicator of the behavior of the hemispheric-scale circulation is the circumpolar vortex (CPV). This research utilizes a geographic information system approach to characterize variability in the Northern Hemispheric (NH) CPV. Specifically, the area, shape, and centroid of the January NHCPV are analyzed for 1959,2001 because it may provide insight about relationships between hemispheric-scale circulation and global temperature change. We also use a new means of characterizing the hemispheric-scale circulation using a ,circularity ratio' (Rc). Results suggest that the January NHCPV has exhibited no long-term trends in area or shape, and that the mean centroid is positioned at approximately 85.3°N, 178.0°W. Regional patterns emerge, which suggest that the area and circularity are associated with variability in surface temperature and moist static energy. Furthermore, the area of the January NHCPV is associated with variability in the Arctic Oscillation, while the shape is tied to variability in the Pacific-North American teleconnection pattern. These results will facilitate understanding of the relationship between hemispheric-scale circulation, regional circulation, and local temperatures. Copyright © 2005 Royal Meteorological Society. [source] Sensitivity of an Arctic regional climate model to the horizontal resolution during winter: implications for aerosol simulationINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 11 2005Eric Girard Abstract Our ability to properly simulate current climate and its future change depends upon the exactitude of the physical processes that are parameterized on the one hand, and on model configuration on the other hand. In this paper, we focus on the latter and investigate the effect of the horizontal grid resolution on the simulation of a month of January over the Arctic. A limited-area numerical climate model is used to simulate the month of January 1990 over a grid that includes the Arctic and sub-Arctic regions. Two grid resolutions are used: 50 km and 100 km. Results show that finer details appear for regional circulation, temperature, and humidity when increasing horizontal resolution. This is particularly true for continental and sea ice boundaries, which are much better resolved by high-resolution model simulations. The Canadian Archipelago and rivers in northern Russia appear to benefit the most from higher horizontal resolution. High-resolution simulations capture some frozen rivers and narrow straits between islands. Therefore, much colder surface air temperature is simulated over these areas. Precipitation is generally increased in those areas and over topography due to a better representation of surface heterogeneities when increasing resolution. Large-scale atmospheric circulation is substantially changed when horizontal resolution is increased. Feedback processes occur between surface air temperature change over heterogeneous surfaces and atmospheric circulation. High-resolution simulations develop a stronger polar vortex. The mean sea-level pressure increases over the western Arctic and Iceland and decreases over the eastern Arctic. This circulation leads to a substantial cooling of the eastern Arctic and enhanced synoptic activity over the Arctic associated with an intensification of the baroclinic zone. Aerosol mass loading, which is simulated explicitly in this model, is significantly altered by the grid resolution change with the largest differences in aerosol concentration over areas where precipitation and atmospheric circulation are the most affected. The implications of this sensitivity study to the evaluation of indirect radiative effects of anthropogenic aerosols are discussed. Copyright © 2005 Royal Meteorological Society. [source] Change in mean temperature as a predictor of extreme temperature change in the Asia,Pacific regionINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 10 2005G. M. Griffiths Abstract Trends (1961,2003) in daily maximum and minimum temperatures, extremes and variance were found to be spatially coherent across the Asia,Pacific region. The majority of stations exhibited significant trends: increases in mean maximum and mean minimum temperature, decreases in cold nights and cool days, and increases in warm nights. No station showed a significant increase in cold days or cold nights, but a few sites showed significant decreases in hot days and warm nights. Significant decreases were observed in both maximum and minimum temperature standard deviation in China, Korea and some stations in Japan (probably reflecting urbanization effects), but also for some Thailand and coastal Australian sites. The South Pacific convergence zone (SPCZ) region between Fiji and the Solomon Islands showed a significant increase in maximum temperature variability. Correlations between mean temperature and the frequency of extreme temperatures were strongest in the tropical Pacific Ocean from French Polynesia to Papua New Guinea, Malaysia, the Philippines, Thailand and southern Japan. Correlations were weaker at continental or higher latitude locations, which may partly reflect urbanization. For non-urban stations, the dominant distribution change for both maximum and minimum temperature involved a change in the mean, impacting on one or both extremes, with no change in standard deviation. This occurred from French Polynesia to Papua New Guinea (except for maximum temperature changes near the SPCZ), in Malaysia, the Philippines, and several outlying Japanese islands. For urbanized stations the dominant change was a change in the mean and variance, impacting on one or both extremes. This result was particularly evident for minimum temperature. The results presented here, for non-urban tropical and maritime locations in the Asia,Pacific region, support the hypothesis that changes in mean temperature may be used to predict changes in extreme temperatures. At urbanized or higher latitude locations, changes in variance should be incorporated. Copyright © 2005 Royal Meteorological Society. [source] Signals of anthropogenic influence on European warming as seen in the trend patterns of daily temperature varianceINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 1 2005A. M. G. Klein Tank Abstract Signals of anthropogenic warming over Europe are searched for in the spatial trend patterns for the variance and skewness (expressed by the 10th and 90th percentiles) of the distribution of daily mean temperature. Comparisons are made between these patterns in the station records of the European Climate Assessment dataset for the 1976,99 period, the patterns associated with natural variability in the observations (which were empirically derived from the observations in the 1946,75 period), and the patterns of future warming and natural variability as simulated by the National Center for Atmospheric Research Community Climate System Model in the Challenge ensemble experiment. The results indicate that, on the basis of the patterns for the variance, a distinction can be made between temperature change due to natural variability and temperature change due to changes in external forcing. The observed variance trend patterns for the spring (March,May) and summer (June,August) warming 1976,99 are clearly different from the patterns for the change in variance associated with a warming due to natural variability in the observations. This led us to conclude that a change in an external forcing has to be invoked to explain the observed spring and summer warming. From the evaluation of the greenhouse and natural variability patterns in the climate model simulations, we infer that the observed spring and summer variance trend patterns contain imprints consistent with anthropogenic warming. The analysis of the variance trend patterns for the winter (December,February) season is inconclusive about identifying causes of the observed warming for that season. Unlike the other three seasons, the autumn (September,November) is for Europe a period of cooling in recent decades. The observed variance trend pattern for this season closely resembles the estimated pattern for the change in variance associated with a cooling due to natural variability, indicating that the observed autumn cooling can be ascribed to random weather variations in the period under consideration. 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