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Thermal Stress (thermal + stress)
Selected AbstractsDifferential Responses of the Activities of Antioxidant Enzymes to Thermal Stresses between Two Invasive Eupatorium Species in ChinaJOURNAL OF INTEGRATIVE PLANT BIOLOGY, Issue 4 2008Ping Lu Abstract The effect of thermal stress on the antioxidant system was investigated in two invasive plants, Eupatorium adenophorum Spreng. and E. odoratum L. The former is sensitive to high temperature, whereas the latter is sensitive to low temperature. Our aim was to explore the relationship between the response of antioxidant enzymes and temperature in the two invasive weeds with different distribution patterns in China. Plants were transferred from glasshouse to growth chambers at a constant 25 °C for 1 week to acclimatize to the environment. For the heat treatments, temperature was increased stepwise to 30, 35, 38 and finally to 42 °C. For the cold treatments, temperature was decreased stepwise to 20, 15, 10 and finally to 5 °C. Plants were kept in the growth chambers for 24 h at each temperature step. In E. adenophorum, the coordinated increase of the activities of antioxidant enzymes was effective in protecting the plant from the accumulation of active oxygen species (AOS) at low temperature, but the activities of catalase (CAT), guaiacol peroxidase (POD), ascorbate peroxidase (APX), glutathione reductase (GR), and monodehydroascorbate reductase (MDAR) were not accompanied by the increase of superoxide dismutase (SOD) during the heat treatments. As a result, the level of lipid peroxidation in E. adenophorum was higher under heat stress than under cold stress. In E. odoratum, however, the lesser degree of membrane damage, as indicated by low monodehydroascorbate content, and the coordinated increase of the oxygen. Detoxifying enzymes were observed in heat-treated plants, but the antioxidant enzymes were unable to operate in cold stress. This indicates that the plants have a higher capacity for scavenging oxygen radicals in heat stress than in cold stress. The different responses of antioxidant enzymes may be one of the possible mechanisms of the differences in temperature sensitivities of the two plant species. [source] Modeling of Thermal Stresses in Joining Two Layers with Multi- and Graded InterlayersJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2006C. H. Hsueh The technique of introducing interlayers has been used extensively to mitigate residual thermal stresses in joining dissimilar materials. Finite-element analyses have often been used to quantify thermal stresses in these layered structures in case-by-case studies. Recently, simple analytical models containing only three unknowns have been developed to derive closed-form solutions for elastic thermal stresses in both multilayer systems and two layers joined by a graded junction. The analytical solutions are exact for locations away from the free edges of the system. Application of these solutions is shown here to provide a systematic study of thermal stresses in Si3N4 and Al2O3 layers joined by various sialon polytypoid-based multi- and graded interlayers. The effects of the thickness, stiffness, and coefficient of thermal expansion of the interlayer on thermal stresses in the system are examined. The differences in thermal stresses resulting from multi- and graded interlayers are shown. [source] Long-term stability of dye-sensitised solar cellsPROGRESS IN PHOTOVOLTAICS: RESEARCH & APPLICATIONS, Issue 6 2001A. Hinsch Accelerated ageing tests on large numbers of nanocrystalline dye-sensitised solar cells (nc-DSC) show that, to first order, separation between the effects of the stresses of visible light soaking, UV illumination and thermal treatment on long-term stability is possible. The corresponding mechanisms are electrochemical, photochemical and purely chemical in nature. It was found that visible light soaking alone is not a dominant stress factor. A dramatic improvement in UV stability has been achieved by using MgI2 as additive to the electrolyte. Thermal stress appears to be one of the most critical factors determining the long-term stability of nc-DSC and is strongly related to the chemical composition of electrolyte solvents and additives. Encouraging stability results have been obtained for cells based on pure nitrile-based solvents: (1) A minor decrease in performance of initially 5.5% solar efficient cells has been found after 2000 h at 60°C without light soaking; (2) After 900 h ageing at 85°C, a decrease of 30% in maximum power has been observed; (3) After 3400 h of combined thermal stress and continuous light soaking (45°C, 1 sun equivalent) good stability with 15% decrease in maximum power can be demonstrated. It should be noted that such good thermal stability has not been reported previously for dye-sensitised solar cells so far. Copyright © 2001 John Wiley & Sons, Ltd. [source] Determination of elastic modulus of demineralized resin-infiltrated dentin by self-etch adhesivesEUROPEAN JOURNAL OF ORAL SCIENCES, Issue 1 2007Genta Yasuda The purpose of this study was to determine ultrasonically the changes in elastic modulus of demineralized adhesive-infiltrated dentin. Dentin disks were obtained from bovine incisors and shaped into a rectangular form. The specimens were immersed in single-step self-etch adhesives, then stored in distilled water and run through thermal cycles between 5 and 60°C. The longitudinal and shear wave sound velocities and the elastic modulus were determined using ultrasonic equipment composed of a pulser-receiver, transducers, and an oscilloscope. After 24 h of storage, the elastic modulus of mineralized dentin was 16.9 GPa and that of demineralized dentin was 2.1 GPa. The immersion of demineralized dentin in adhesives significantly increased the elastic modulus to 3.3,5.9 GPa. After 30,000 thermal cycles, the elastic modulus of dentin was 32.4 GPa, whereas that of demineralized adhesive infiltrated dentin was 3.1,4.1 GPa. Thermal stresses did not cause adhesive-infiltrated demineralized dentin to deteriorate, as measured by elastic modulus. [source] Optical studies on ZnO films prepared by sol-gel methodCRYSTAL RESEARCH AND TECHNOLOGY, Issue 8 2009T. Ghosh Abstract A standard sol-gel method was used to deposit ZnO thin films of suitable thickness on glass substrate. The optical characteristics of the visible to infrared range on thermal stress were critically observed. Morphological signature of the films was detected by X-ray diffraction (XRD) and the crystallite size determined by Scherrer method from XRD data were consistent with grain size estimated from spectroscopic data through Meulenkamp equation. The optical band gap value from the transmission spectrum was found to corroborate with the existing works. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] What Is the mechanism of SIDS?DEVELOPMENTAL PSYCHOBIOLOGY, Issue 3 2009Clues from epidemiology Abstract The cause of sudden infant death syndrome (SIDS) is unknown. Many mechanisms have been postulated, although thermal stress, rebreathing of expired gases and infection/inflammation seem the most viable hypotheses for the causation of SIDS. Deaths from SIDS have reduced dramatically following the recommendation not to place infants to sleep prone. Epidemiological data have shown that prone sleeping position is more risky in winter, colder latitudes, higher altitudes, if the infant is unwell or has excessive bedding or clothing. This suggests prone sleeping position involves either directly or indirectly a thermal mechanism. SIDS caused by an infective/inflammatory mechanism might be associated with deaths occurring during the night. Rebreathing of expired gases, airway obstruction, long QT syndrome and other genetic conditions may explain a small number of sudden unexpected deaths in infancy. © 2009 Wiley Periodicals, Inc. Dev Psychobiol 51: 215,222, 2009 [source] Tafoni development in a cryotic environment: an example from Northern Victoria Land, AntarcticaEARTH SURFACE PROCESSES AND LANDFORMS, Issue 10 2008Andrea Strini Abstract Tafoni are a type of cavernous weathering widespread around the world. Despite the extensive distribution of the tafoni, their genesis is not clear and is still a matter of debate, also because they occur in such different climatic conditions and on so many different types of substrate. Geomorphological characterization of more than 60 tafoni in three different Antarctic sites (two coastal and one inland) between 74 and 76° S with sampling of weathering products and salt occurrences are described together with thermal data (on different surfaces) and wind speed recorded in different periods of the year in a selected tafone close to the Italian Antarctic station. The aim of this present study is to provide further information to help understand the processes involved in the growth of tafoni in a cryotic environment, and the relationship of these processes to climate, with particular attention to the thermal regime and the role of wind. The new data presented in this paper suggest that there is no single key factor that drives the tafoni development, although thermal stress seems the most efficient process, particularly if we consider the short-term fluctuations. The data also confirm that other thermal processes, such as freezing,thawing cycles and thermal shock, are not really effective for the development of tafoni in this area. The wind speed measured within the tafoni is half that recorded outside, thus favouring snow accumulation within the tafoni and therefore promoting salt crystallization. On the other hand, the wind effect on the thermal regime within the tafoni seems negligible. While both salt weathering and thermal stress appear active in this cryotic environment, these are azonal processes and are therefore active in other climatic areas where tafoni are widespread (such as the Mediterranean region). Copyright © 2007 John Wiley & Sons, Ltd. [source] Rock thermal data at the grain scale: applicability to granular disintegration in cold environmentsEARTH SURFACE PROCESSES AND LANDFORMS, Issue 8 2003Kevin 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 (,0·15 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] Variability in responses to thermal stress in parasitoidsECOLOGICAL ENTOMOLOGY, Issue 6 2008GAËLLE AMICE Abstract 1.,To study phenotypic effects of stress, a stress is applied to cohorts of organisms with an increasing intensity. In the absence of mortality the response of traits will be a decreasing function of stress intensity because of increasing physiological costs. We call such decreasing functions type A responses. 2.,However, when stress caused mortality, some studies have found that for high stress intensities, survivors performed as well as control individuals (type B responses). We proposed that type A responses are caused by the physiological cost of stress whereas type B responses are caused by a mixture of physiological costs and selection. 3.,The present study exposed Aphidius picipes wasps to an increasing duration of cold storage (cold stress), and obtained variable responses as predicted when both physiological costs and selection of resistant individuals determine the outcome. 4.,When cold storage of parasitoids for biological control is desirable, research should be carried out to find (i) the temperature regime and duration of storage and (ii) the least sensitive stage for storage to minimise losses from mortality and reduction of fitness of survivors. 5.,Selection by cold stress as observed in the present study could result in rapid adaptation of populations exposed to such stress. [source] High Performance SiC Oxidation Protective Coating with ZrO2 Particle Dispersion for Carbon/Carbon Composites,ADVANCED ENGINEERING MATERIALS, Issue 10 2008Y.-L. Zhang High performance SiC oxidation protective coating with ZrO2 particle dispersion for C/C composites was prepared by slurry and pack cementation. Isothermal oxidation tests at 1873,K in air showed that the as-prepared coating could effectively protect C/C composites from oxidation for 100,h. The excellent oxidation protective ability can be attributed to the introduction of ZrO2 particles in the SiC coating, which can baffle the enlargement of cracks and suppress the generation of the thermal stress. [source] Bonded aircraft repairs under variable amplitude fatigue loading and at low temperaturesFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 1 2000Vlot Bonded repairs can replace mechanically fastened repairs for aircraft structures. Compared to mechanical fastening, adhesive bonding provides a more uniform and efficient load transfer into the patch, and can reduce the risk of high stress concentrations caused by additional fastener holes necessary for riveted repairs. Previous fatigue tests on bonded Glare (glass-reinforced aluminium laminate) repairs were performed at room temperature and under constant amplitude fatigue loading. However, the realistic operating temperature of ,40 °C may degrade the material and will cause unfavourable thermal stresses. Bonded repair specimens were tested at ,40 °C and other specimens were tested at room temperature after subjecting them to temperature cycles. Also, tests were performed with a realistic C-5A Galaxy fuselage fatigue spectrum at room temperature. The behaviour of Glare repair patches was compared with boron/epoxy ones with equal extensional stiffness. The thermal cycles before fatigue cycling did not degrade the repair. A constant temperature of ,40 °C during the mechanical fatigue load had a favourable effect on the fatigue crack growth rate. Glare repair patches showed lower crack growth rates than boron/epoxy repairs. Finite element analyses revealed that the higher crack growth rates for boron/epoxy repairs are caused by the higher thermal stresses induced by the curing of the adhesive. The fatigue crack growth rate under spectrum loading could be accurately predicted with stress intensity factors calculated by finite element modelling and cycle-by-cycle integration that neglected interaction effects of the different stress amplitudes, which is possible because stress intensities at the crack tip under the repair patch remain small. For an accurate prediction it was necessary to use an effective stress intensity factor that is a function of the stress ratio at the crack tip Rcrack tip including the thermal stress under the bonded patch. [source] Highly diverse community structure in a remote central Tibetan geothermal spring does not display monotonic variation to thermal stressFEMS MICROBIOLOGY ECOLOGY, Issue 1 2006Lau Chui Yim Abstract We report an assessment of whole-community diversity for an extremely isolated geothermal location with considerable phylogenetic and phylogeographic novelty. We further demonstrate, using multiple statistical analyses of sequence data, that the response of community diversity is not monotonic to thermal stress along a gradient of 52,83°C. A combination of domain- and division-specific PCR was used to obtain a broad spectrum of community phylotypes, which were resolved by denaturing gradient gel electrophoresis. Among 58 sequences obtained from microbial mats and streamers, some 95% suggest novel archaeal and bacterial diversity at the species level or higher. Moreover, new phylogeographic and thermally defined lineages among the Cyanobacteria, Chloroflexi, Eubacterium and Thermus are identified. Shannon,Wiener diversity estimates suggest that mats at 63°C supported highest diversity, but when alternate models were applied [Average Taxonomic Distinctness (AvTD) and Variation in Taxonomic Distinctness (VarTD)] that also take into account the phylogenetic relationships between phylotypes, it is evident that greatest taxonomic diversity (AvTD) occurred in streamers at 65,70°C, whereas greatest phylogenetic distance between taxa (VarTD) occurred in streamers of 83°C. All models demonstrated that diversity is not related to thermal stress in a linear fashion. [source] Vertically Aligned Nanocomposite Thin Films as a Cathode/Electrolyte Interface Layer for Thin-Film Solid Oxide Fuel CellsADVANCED FUNCTIONAL MATERIALS, Issue 24 2009Jongsik Yoon Abstract A thin layer of a vertically aligned nanocomposite (VAN) structure is deposited between the electrolyte, Ce0.9Gd0.1O1.95 (CGO), and the thin-film cathode layer, La0.5Sr0.5CoO3 (LSCO), of a thin-film solid-oxide fuel cell (TFSOFC). The self-assembled VAN nanostructure contains highly ordered alternating vertical columns of CGO and LSCO formed through a one-step thin-film deposition process that uses pulsed laser deposition. The VAN structure significantly improves the overall performance of the TFSOFC by increasing the interfacial area between the electrolyte and cathode. Low cathode polarization resistances of 9,×,10,4 and 2.39,, were measured for the cells with the VAN interlayer at 600 and 400,°C, respectively. Furthermore, anode-supported single cells with LSCO/CGO VAN interlayer demonstrate maximum power densities of 329, 546, 718, and 812,mW cm,2 at 550, 600, 650, and 700,°C, respectively, with an open-circuit voltage (OCV) of 1.13,V at 550,°C. The cells with the interlayer triple the overall power output at 650,°C compared to that achieved with the cells without an interlayer. The binary VAN interlayer could also act as a transition layer that improves adhesion and relieves both thermal stress and lattice strain between the cathode and the electrolyte. [source] Water temperature determines strength of top-down control in a stream food webFRESHWATER BIOLOGY, Issue 8 2005DAISUKE KISHI Summary 1. We examined effects of water temperature on the community structure of a three trophic level food chain (predatory fish, herbivorous caddisfly larvae and periphyton) in boreal streams. We used laboratory experiments to examine (i) the effects of water temperature on feeding activities of fish and caddisfly larvae and on periphyton productivity, to evaluate the thermal effects on each trophic level (species-level experiment), and (ii) the effects of water temperature on predation pressure of fish on abundance of the lower trophic levels, to evaluate how temperature affects top-down control by fish (community-level experiment). 2. In the species-level experiment, feeding activity of fish was high at 12 °C, which coincides with the mean summer temperature in forested streams of Hokkaido, Japan, but was depressed at 3 °C, which coincides with the mean winter temperature, and also above 18 °C, which coincides with the near maximum summer temperatures. Periphyton productivity increased over the range of water temperatures. 3. In the community-level experiments, a top-down effect of fish on the abundance of caddisfly larvae and periphyton was clear at 12 °C. This effect was not observed at 3 and 21 °C because of low predation pressure of fish at these temperatures. 4. These experiments revealed that trophic cascading effects may vary with temperature even in the presence of abundant predators. Physiological depression of predators because of thermal stress can alter top-down control and lead to changes in community structure. 5. We suggest that thermal habitat alteration can change food web structure via combinations of direct and indirect trophic interactions. [source] New insights into global patterns of ocean temperature anomalies: implications for coral reef health and managementGLOBAL ECOLOGY, Issue 3 2010Elizabeth R. Selig ABSTRACT Aim, Coral reefs are widely considered to be particularly vulnerable to changes in ocean temperatures, yet we understand little about the broad-scale spatio-temporal patterns that may cause coral mortality from bleaching and disease. Our study aimed to characterize these ocean temperature patterns at biologically relevant scales. Location, Global, with a focus on coral reefs. Methods, We created a 4-km resolution, 21-year global ocean temperature anomaly (deviations from long-term means) database to quantify the spatial and temporal characteristics of temperature anomalies related to both coral bleaching and disease. Then we tested how patterns varied in several key metrics of disturbance severity, including anomaly frequency, magnitude, duration and size. Results, Our analyses found both global variation in temperature anomalies and fine-grained spatial variability in the frequency, duration and magnitude of temperature anomalies. However, we discovered that even during major climatic events with strong spatial signatures, like the El Niño,Southern Oscillation, areas that had high numbers of anomalies varied between years. In addition, we found that 48% of bleaching-related anomalies and 44% of disease-related anomalies were less than 50 km2, much smaller than the resolution of most models used to forecast climate changes. Main conclusions, The fine-scale variability in temperature anomalies has several key implications for understanding spatial patterns in coral bleaching- and disease-related anomalies as well as for designing protected areas to conserve coral reefs in a changing climate. Spatial heterogeneity in temperature anomalies suggests that certain reefs could be targeted for protection because they exhibit differences in thermal stress. However, temporal variability in anomalies could complicate efforts to protect reefs, because high anomalies in one year are not necessarily predictive of future patterns of stress. Together, our results suggest that temperature anomalies related to coral bleaching and disease are likely to be highly heterogeneous and could produce more localized impacts of climate change. [source] High Molar Extinction Coefficient Ion-Coordinating Ruthenium Sensitizer for Efficient and Stable Mesoscopic Dye-Sensitized Solar Cells,ADVANCED FUNCTIONAL MATERIALS, Issue 1 2007D. Kuang Abstract Ru(4,4-dicarboxylic acid-2,2,-bipyridine) (4,4,-bis(2-(4-(1,4,7,10-tetraoxyundecyl)phenyl)ethenyl)-2,2,-bipyridine) (NCS)2, a new high molar extinction coefficient ion-coordinating ruthenium sensitizer was synthesized and characterized using 1H,NMR, Fourier transform IR (FTIR), and UV/vis spectroscopies and cyclic voltammetry. Using this sensitizer in combination with a nonvolatile organic-solvent-based electrolyte, we obtain a photovoltaic efficiency of 8.4,% under standard global AM,1.5 sunlight. These devices exhibit excellent stability when subjected to continuous thermal stress at 80,°C or light soaking at 60,°C for 1000,h. An electrochemical impedance spectroscopy study revealed that device stability is maintained by stabilizing the TiO2/dye/electrolyte and Pt/electrolyte interface during the aging process. The influence of Li+ present in the electrolyte on the device photovoltaic parameters was studied, and the FTIR spectral and photovoltage transient study showed that Li+ coordinates to the triethyleneoxide methylether side chains on the K60 sensitizer molecules. [source] Thermally Driven AFM for NanoenergeticsIMAGING & MICROSCOPY (ELECTRONIC), Issue 2 2009A Method to Investigate the Decomposition on the Nanoscale Abstract A fundamental understanding of the decomposition of energetic nanocompounds infiltrated in porous host matrixes requires the investigation of their behavior on a nanoscale during a thermal stress. Up to now, the decomposition of pure energetic nanomaterials has only been observed on a macroscopic scale. Thermally driven AFM revealed that the decomposition of the energetic material present in the pores of a Cr2O3 matrix induces a spatial expansion of the oxide on the nanometric scale. [source] Transient thermal modelling of heat recovery steam generators in combined cycle power plantsINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 11 2007Sepehr Sanaye Abstract Heat recovery steam generator (HRSG) is a major component of a combined cycle power plant (CCPP). This equipment is particularly subject to severe thermal stress especially during cold start-up period. Hence, it is important to predict the operational parameters of HRSGs such as temperature of steam, water, hot gas and tube metal of heating elements as well as pressure change in drums during transient and steady-state operation. These parameters may be used for estimating thermal and mechanical stresses which are important in HRSG design and operation. In this paper, the results of a developed thermal model for predicting the working conditions of HRSG elements during transient and steady-state operations are reported. The model is capable of analysing arbitrary number of pressure levels and any number of elements such as superheater, evaporator, economizer, deaerator, desuperheater, reheater, as well as duct burners. To assess the correct performance of the developed model two kinds of data verification were performed. In the first kind of data verification, the program output was compared with the measured data collected from a cold start-up of an HRSG at Tehran CCPP. The variations of gas, water/steam and metal temperatures at various sections of HRSG, and pressure in drums were among the studied parameters. Mean differences of about 3.8% for temperature and about 9.2% for pressure were observed in this data comparison. In the second kind of data verification, the steady-state numerical output of the model was checked with the output of the well-known commercial software. An average difference of about 1.5% was found between the two latter groups of data. Copyright © 2007 John Wiley & Sons, Ltd. [source] Estimating thermal stress in BIPV modulesINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 15 2006Petri Konttinen Abstract The thermal stress on building-integrated photovoltaic modules (BIPV) in Espoo, Finland, was studied with field-testing of amorphous silicon modules. Based on these results, the thermal stress at two other European locations (Paris and Lisbon) was estimated. The estimation procedure entailed thermal modelling of heat transfer in the façade with meteorological data as input. The results indicate that the thermal stress on BIPV modules in Lisbon is, in this case, approximately 50% higher that in Espoo and between 80 and 200% higher than in Paris, depending on the activation energy of the degradation process. The difference in stress between a BIPV module and a free-standing module in Espoo was 50,200%. Copyright © 2006 John Wiley & Sons, Ltd. [source] An analytical and experimental analysis of a very fast thermal transientINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 11 2001C. 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] Numerical analysis on thermal characteristics for chip scale package by integrating 2D/3D modelsINTERNATIONAL JOURNAL OF NUMERICAL MODELLING: ELECTRONIC NETWORKS, DEVICES AND FIELDS, Issue 1 2009Ping Yang Abstract The objective of this paper is to investigate stress and strain of a special scale package-substrate on chip for reliability evaluation or manufacture strategy in deep-seated situation. A two-dimensional model with one-half of cross-section (2D model) and a three-dimensional model with one-fourth of whole package (3D model) were built, respectively, to simulate the thermal stress and strain of CSP-SOC under the condition of the standard industry thermal cycling temperature ,40 to125°C. The different locations can be processed by using the two models, respectively, based on different modeling simplified modes. By using 2D model, the numerical simulation shows that the maximum deformation of the prototype occurs in printed circuit board (PCB), the maximum stress and strain occurs in the outer solder balls. In the meantime, by the results of 3D model, the simulation shows that the maximum elastic strain occurs in the interface between the solder balls and PCB, the minimum strain occurs in the underfill tape, the maximum packaging stress occurs in the edge area of the chip. The result from 3D model maybe more impersonal to reflect the stress and strain characteristics because the third direction is considered in modeling. The analysis by integrating the 2D model and 3D model can get a more comprehensive profile for the thermal investigation of chip scale package (CSP) than by using any single model. The investigation built a basis for improving reliability in engineering design of CSP product. Copyright © 2008 John Wiley & Sons, Ltd. [source] Asymmetric coexistence: bidirectional abiotic and biotic effects between goose barnacles and musselsJOURNAL OF ANIMAL ECOLOGY, Issue 4 2006TAKASHI KAWAI Summary 1Species coexistence depends on the net effect of interacting species, representing the sum of multiple interaction components that may act simultaneously and vary independently depending on ambient environmental conditions. Consequently, for a comprehensive understanding of the compound nature of species interactions and coexistence, a mechanistic approach that allows a separate evaluation of each interaction component is required. 2Two sessile filter-feeders, the goose barnacle Capitulum mitella and the mussel Septifer virgatus, coexist on moderately wave-exposed rocky shores in south-western Japan. In the upper intertidal, Capitulum positively influenced Septifer survivorship and growth through amelioration of thermal stress and of physical disturbance. On the other hand, these species are potential competitors as they have similar body sizes and modes of resource utilization. These opposite processes, facilitation and competition, are based on abiotic characteristics and biotic functions of the two species, respectively. 3In order to quantify the bidirectional abiotic, biotic and net effects, a series of experimental manipulations was conducted involving the use of living neighbours with both abiotic and biotic effects, and artificial mimics to simulate abiotic effects without biotic effects. 4Capitulum had strong positive abiotic effects on the mussel survivorship in most experimental periods, while the biotic effect was negligible or weakly negative, suggesting that the net effect of Capitulum on mussel survival was largely attributable to the abiotic effect. In contrast, a significantly negative biotic effect on the mussel growth rate was always present, though this was cancelled out by the larger, positive abiotic effect. In the case of Septifer, its abiotic and biotic effects on the survivorship of goose barnacles were negligible, while those on the growth rate showed temporal variation. 5With respect to the relationship between species interaction and environmental conditions, the strength of abiotic facilitative effect of Capitulum on mussel survival increased with increasing abiotic stress, while the strength of biotic effect was negligible or weakly negative. As regards the effects of mussels on goose barnacles, our study indicated no obvious relationship. These results point to the importance of decomposing interaction for an accurate, mechanistic understanding of species relations and coexistence. [source] Thermal evolution of pre-adult life history traits, geometric size and shape, and developmental stability in Drosophila subobscuraJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 6 2006M. SANTOS Abstract Replicated lines of Drosophila subobscura originating from a large outbred stock collected at the estimated Chilean epicentre (Puerto Montt) of the original New World invasion were allowed to evolve under controlled conditions of larval crowding for 3.5 years at three temperature levels (13, 18 and 22 °C). Several pre-adult life history traits (development time, survival and competitive ability), adult life history related traits (wing size, wing shape and wing-aspect ratio), and wing size and shape asymmetries were measured at the three temperatures. Cold-adapted (13 °C) populations evolved longer development times and showed lower survival at the highest developmental temperature. No divergence for wing size was detected following adaptation to temperature extremes (13 and 22 °C), in agreement with earlier observations, but wing shape changes were obvious as a result of both thermal adaptation and development at different temperatures. However, the evolutionary trends observed for the wing-aspect ratio were inconsistent with an adaptive hypothesis. There was some indication that wing shape asymmetry has evolutionarily increased in warm-adapted populations, which suggests that there is additive genetic variation for fluctuating asymmetry and that it can evolve under rapid environmental changes caused by thermal stress. Overall, our results cast strong doubts on the hypothesis that body size itself is the target of selection, and suggest that pre-adult life history traits are more closely related to thermal adaptation. [source] Temperature-dependent changes in energy metabolism, intracellular pH and blood oxygen tension in the Atlantic codJOURNAL OF FISH BIOLOGY, Issue 6 2003F. J. Sartoris The effect of acute increase in temperature on oxygen partial pressure (Po2) was measured in the gill arches of Atlantic cod Gadus morhua between 10 and 19° C by use of oxygen microoptodes. Oxygen saturation of the gill blood under control conditions varied between 90 and 15% reflecting a variable percentage of arterial or venous blood in accordance with the position of each optode in the gill arch. The data obtained suggested that arterial Po2 remained more or less constant and arterial oxygen uptake did not become limiting during warming. A progressive drop in venous Po2, however, was observed at >10° C indicating that excessive oxygen uptake from the blood is not fully compensated for by circulatory performance, until finally, Po2 levels fully collapse. In a second set of experiments energy and acid,base status of white muscle of Atlantic cod in vivo was measured by magnetic resonance (31P-NMR) spectroscopy in unanaesthetized and unimmobilized fish in the temperature range between 13 and 21° C. A decrease in white muscle intracellular pH (pHi) with temperature occurred between 10 and 16° C (,pH per ° C = ,0·025 per ° C). In white muscle temperature changes had no influence on high-energy phosphates such as phosphocreatine (PCr) or ATP except during exposure to high critical temperatures (>16° C), indicating that white muscle energy status appears to be relatively insensitive to thermal stress if compared to the thermal sensitivity of the whole animal. The data were consistent with the hypothesis of an oxygen limitation of thermal tolerance in animals, which is set by limited capacity of oxygen supply mechanisms. In the case of Atlantic cod circulatory rather than ventilatory performance may be the first process to cause oxygen deficiency during heat stress. [source] Differential Responses of the Activities of Antioxidant Enzymes to Thermal Stresses between Two Invasive Eupatorium Species in ChinaJOURNAL OF INTEGRATIVE PLANT BIOLOGY, Issue 4 2008Ping Lu Abstract The effect of thermal stress on the antioxidant system was investigated in two invasive plants, Eupatorium adenophorum Spreng. and E. odoratum L. The former is sensitive to high temperature, whereas the latter is sensitive to low temperature. Our aim was to explore the relationship between the response of antioxidant enzymes and temperature in the two invasive weeds with different distribution patterns in China. Plants were transferred from glasshouse to growth chambers at a constant 25 °C for 1 week to acclimatize to the environment. For the heat treatments, temperature was increased stepwise to 30, 35, 38 and finally to 42 °C. For the cold treatments, temperature was decreased stepwise to 20, 15, 10 and finally to 5 °C. Plants were kept in the growth chambers for 24 h at each temperature step. In E. adenophorum, the coordinated increase of the activities of antioxidant enzymes was effective in protecting the plant from the accumulation of active oxygen species (AOS) at low temperature, but the activities of catalase (CAT), guaiacol peroxidase (POD), ascorbate peroxidase (APX), glutathione reductase (GR), and monodehydroascorbate reductase (MDAR) were not accompanied by the increase of superoxide dismutase (SOD) during the heat treatments. As a result, the level of lipid peroxidation in E. adenophorum was higher under heat stress than under cold stress. In E. odoratum, however, the lesser degree of membrane damage, as indicated by low monodehydroascorbate content, and the coordinated increase of the oxygen. Detoxifying enzymes were observed in heat-treated plants, but the antioxidant enzymes were unable to operate in cold stress. This indicates that the plants have a higher capacity for scavenging oxygen radicals in heat stress than in cold stress. The different responses of antioxidant enzymes may be one of the possible mechanisms of the differences in temperature sensitivities of the two plant species. [source] Heat Shock Transcription Factors and the hsp70 Induction Response in Brain and Kidney of the Hyperthermic Rat During Postnatal DevelopmentJOURNAL OF NEUROCHEMISTRY, Issue 1 2000Andrew J. Morrison Abstract : Heat shock transcription factor (HSF) 1 levels increase in brain regions and decline in kidney during postnatal rat development. In both neonatal and adult rats, levels of HSF1 protein in brain and kidney are proportional to the levels of HSF DNA-binding activity and the magnitude of heat shock protein hsp70 induction after thermal stress. There appears to be more HSF1 protein in adult brain than is needed for induction of hsp70 after thermal stress, suggesting that HSF1 may have other functions in addition to its role as a stress-inducible activator of heat shock genes. HSF2 protein levels decline during postnatal rat development in brain regions and kidney. Gel mobility shift analysis shows that HSF2 is not in a DNA-binding form in the neonatal brain and kidney, suggesting that HSF2 may not be involved in the constitutive expression of hsps in early postnatal development. There is no apparent relationship between levels of HSF2 protein and basal levels of hsp90, hsp70, heat shock cognate protein hsc70, and hsp60. [source] Molecular dynamic simulations of nanomechanic chaperone peptide and effects of in silico His mutations on nanostructured functionJOURNAL OF PEPTIDE SCIENCE, Issue 11 2008Abolfazl Barzegar Abstract The nanoscale peptide YSGVCHTDLHAWHGDWPLPVK exhibits molecular chaperone activity and prevents protein aggregation under chemical and/or thermal stress. Here, His mutations of this peptide and their impact on chaperone activity were evaluated using theoretical techniques. Molecular dynamic (MD) simulations with simulated annealing (SA) of different mutant nanopeptides were employed to determine the contribution of the scaffolding His residues (H45, H49, H52), when mutated to Pro, on chaperone action in vitro. The in silico mutations of His residues to Pro (H45P, H49P, H52P) revealed loss of secondary ordered strand structure. However, a small part of the strand conformation was formed in the middle region of the native chaperone peptide. The His-to-Pro mutations resulted in decreased gyration radius (Rg) values and surface accessibility of the mutant peptides under the simulation times. The invariant dihedral angle (,) values and the disrupting effects of the Pro residues indicated the coil conformation of mutant peptides. The failure of the chaperone-like action in the Pro mutant peptides was consistent with their decreased effective accessible surfaces. The high variation of , value for His residues in native chaperone peptide leads to high flexibility, such as a minichaperone acting as a nanomachine at the molecular level. Our findings demonstrate that the peptide strand conformation motif with high flexibility at nanoscale is critical for chaperone activity. Copyright © 2008 European Peptide Society and John Wiley & Sons, Ltd. [source] Characterization of ultrasound extrudated and cut citric acid/paracetamol blendsJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 6 2009P. Hoppu Abstract The purpose of the present work was to study the effect of ultrasound extrusion and cutting on the physical stability of a viscous and sticky supercooled melt containing (50/50, w/w, %) citric acid anhydrate and paracetamol. Samples were extrudated at temperatures of 50, 60, and 70°C using power levels of 0, 50, 100, and 150 W. Similarly, extrudates prepared at 60°C were cut at temperatures ranging from 25,60°C with an ultrasound knife in the range 0, 50, and 100 W. The characterization methods used were: high performance liquid chromatography, differential scanning calorimetry, Karl Fischer titration, X-ray powder diffraction, Fourier transform infrared microscopy, optical- and stereomicroscopy. There was no physical difference in extrudates or cut surfaces whether processed with or without ultrasound. During 1-year aging time in dry conditions, all the samples were observed to crystallize slowly and ultrasound processing did not enhance the crystallization. Ultrasound thus holds some promise for processing of viscous and sticky pharmaceuticals, provided the material is physically stable enough to withstand mechanical and thermal stress. Processing of sticky and viscous material would be difficult without ultrasound with the methods currently used in pharmaceutical industry. © 2008 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 98:2140,2148, 2009 [source] Solid-state properties of warfarin sodium 2-propanol solvateJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 11 2004Agam R. Sheth Abstract The goal of the present work was to understand the effect of relative humidity (RH) and temperature on the molecular structure, crystal structure, and physical properties of warfarin sodium 2-propanol solvate (W). After previous determination of the crystal structure of W, which corresponds to a 1:1 2-propanol solvate, the present work shows that W has a critical RH (60%,<,RH0,,,68%), below which minimal uptake of water occurs, due to surface adsorption, but above which gradual and continuous uptake of water occurs, due to deliquescence. Deliquescence begins at the surface and proceeds inward into the bulk of the crystal. Single crystal X-ray diffractometry indicates no change in the crystal and molecular structure of W during the initial stages of deliquescence. Studies of the unit cell and volume computations of W show that water can neither find space to enter the crystal lattice, nor can replace 2-propanol. Thus, water does not exchange with 2-propanol within the lattice, contrary to previous reports. Storage of single crystals of W at 120°C for 23 h produces shrinkage cracks along the needle (b) axis, which are interpreted as a reduction in d -spacing of the 00l planes. Thus, under thermal stress, W crystals undergo amorphization with concurrent loss of 2-propanol, which may proceed via an intermediate crystalline phase. The phase changes of W, which depend on RH and temperature, are explained at the molecular level. © 2004 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 93:2669,2680, 2004 [source] 122 Local to Coastal-Scale Macrophyte Community Structure: Surprizing Patterns and Possible MechanismsJOURNAL OF PHYCOLOGY, Issue 2003B. A. Menge Understanding large-scale patterns in ecological communities is a central goal of ecology, and yet, rigorous quantitative geographic data on distribution, abundance and diversity are almost totally lacking. Even in rocky intertidal habitats, our data on community structure are spatially and temporally limited, with most surveys limited to a few sites over short time periods. When linked to studies of community dynamics on similar scales, such studies should provide insights into the determinants of pattern at more relevant scales. In 1999 PISCO, the Partnership for Interdisciplinary Studies of Coastal Oceans, initiated survey programs aimed at determining patterns of community structure along the US west coast from Washington to Baja California. Sites are regularly spaced along the coast in a nested design, and were physically similar. Surveys used randomly placed quadrats in transects run parallel to shore in high, mid and low zones. Results show that, contrary to expectation, macroalgal diversity along the northern coast was higher, not lower than that along the southern coast. Possible factors associated with this unexpected pattern include along-coast variation in tidal amplitude, time of tide, thermal stress, upwelling intensity and resulting nutrient gradients, disturbance from storms or sand burial, and grazing. We review evidence relevant to these factors, and focus on the possible role of grazing, using field experiments done under differing oceanographic conditions along the Oregon coast as a model. Although short-term grazing rates can vary with oceanographic condition, we hypothesize that despite these results and those of many similar studies showing strong grazing effects on local spatial and short time scales, that bottom-up factors are stronger determinants of macroalgal community structure on larger spatial scales and longer time scales. [source] | ||||||||||||||||||||||||||||||||||||||||