Short Thermal Stress Research Articles

Effect of temporal thermal stress on Penaeus vannamei: Growth performance and physiological plasticity.

The present study evaluated the effect of temporal periods of hypothermia and hyperthermia, followed by an optimal temperature recovery phase on the growth, survival, and physiological response of Penaeus vannamei. Post-larvae were exposed to stress periods for 7 and 14 days at 22 °C and 32 °C each, followed by a recovery phase at 28 °C to complete seven experimental weeks, and were compared with a control group maintained at 28 °C. Weight gain, specific growth rate, feed intake, feed conversion ratio, and survival were weekly determined. Muscle, hepatopancreas, and hemolymph were sampled on the 14th day of the recovery phase for biochemical composition, and antioxidant and digestive enzyme activities determination. The shrimp presented a higher growth rate during short-term hyperthermia in contrast to shrimp under hypothermia that presented compensatory growth after thermal stress when the temperature was restored at 28 °C. Hyperthermia increased 12–13% the feed intake while this was diminished 21–29% by the hypothermia periods. Shrimp undergo metabolic adjustments following thermal stress, with short hypothermia increasing the lipase activity and lipid storage in the hepatopancreas, while short hyperthermia also enhances chymotrypsin activity and leads to higher protein and lipid accumulation. Conversely, prolonged hyperthermia induces greater energy consumption, depleting lipid and glycogen stores, while hypothermia causes scarce mobilization of energy reserves during recovery phase. Antioxidant enzyme activities were not affected by short-thermal stress (7d), while prolonged thermal stress (14d) significantly affected SOD, CAT, and GPx activities. The present study provides important insights into the physiological plasticity of P. vannamei during recovery from thermal stress.

Analysis of the Influence of a Short Term Thermal Stress on the Performance and the Characteristics of Lithium Ion Cells

For several years lithium-ion batteries have been commercially used in small portable devices such as camcorders, laptop computers, cell phones and other electronic devices. Battery lifetime plays only a minor role in such applications due to rapid innovation and strong competition. However, the increasing demand for lithium-ion batteries in the automobile market requires drastic increase in battery lifetime and safety.[1]All compounds in a lithium-ion battery are sensitive to higher temperatures. For example the electrolyte, which is critical in forming the Solid Electrolyte Interface (SEI), is extremely reactive with humid air and has the lowest boiling point of all battery compounds. Equally sensitive is the separator, which has a melting temperature of 130 to 165°C. [2] The majority of existing life-time and performance prognoses are based on long term temperature influences over numerous charging/discharging cycles (such as in a climate chamber at 40°C). Automotive lithium-ion cells must endure multiple production processes during the fabrication of a high-end battery system, such as contact welding, where the cells are exposed to elevated temperatures for a short period of time.This research analyzes the behavior and performance of lithium-ion cells after a short thermal stress. A new laboratory cell in two electrode arrangement has been developed in this study in order to perform in-situ short term thermal stress tests on both electrodes. For the current study commercially available lithium cobalt oxide (LiCoO2) cathodes, graphite anodes and an electrolyte consisting of a solution of lithium salt (e.g. LiPF6) in a mixed organic solvent have been used. This novel cell allows for the exact targeting of various components with heat. The thermal stress has been performed after the cell formation with different temperatures ranging from 60 to 250°C. Electrochemical impedance spectroscopy (EIS) has been used to detect changes, caused by the temporary thermal stress. The morphology and the 3D structure of the thermally stressed electrodes has been examined using Scanning Electron Microscope (SEM) and high resolution Computer Tomography (CT). In addition the thermal characteristics such as the thermal conductivity of the electrodes has been studied using Differential Scanning Calorimetry (DSC) and Laser Flash Analysis (LFA) in order to estimate the temperature propagation in automotive lithium-ion cells during pack assembly.[1] J. Vetter, P. Novák, M.R. Wagner, C. Veit, K.-C. Möller, J.O. Besenhard, M. Winter, M. Wohlfahrt-Mehrens, C. Vogler, A. Hammouche; Ageing mechanisms in lithium-ion batteries. J. Power Sources 147 (2005) 269–281[2] M. Yoshio, R.J. Brodd, A. Kozawa; Lithium-Ion Batteries, Science and Technologies; Springer (2009)

Luciferase activity and synthesis of Hsp70 and Hsp90 are insensitive to 50Hz electromagnetic fields

The activity of luciferase expressed in transfected 34i cells has been monitored under 50Hz EMF and heat shock. While heat shock decreased the luciferase activity, short exposure to EMFs did not, the luciferase expressed in cells exposed to EMFs at 300–3000μ T showing the same activity as that of control cells. To further analyse whether EMF and thermal stress display similar effects, the relative rate of Hsp90 and Hsp70 synthesis was investigated. Hsp90 and Hsp70 synthesis, while induced by a short thermal stress, was not increased by EMF exposure. These results, contrary to previously proposed similarities between thermal stress and EMF effects at a cellular level, indicate that protein denaturation and misfolding caused by thermal stress and responsible both for a loss of luciferase activity and for an induction of Hsp, are not necessarily induced by exposure to EMFs.