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Freezing Point (freezing + point)
Selected AbstractsDevelopmental and environmental regulation of antifreeze proteins in the mealworm beetle Tenebrio molitorFEBS JOURNAL, Issue 21 2000Laurie A. Graham The yellow mealworm beetle, Tenebrio molitor, contains a family of small Cys-rich and Thr-rich thermal hysteresis proteins that depress the hemolymph freezing point below the melting point by as much as 5.5 °C (,T = thermal hysteresis). Thermal hysteresis protein expression was evaluated throughout development and after exposure to altered environmental conditions. Under favorable growth conditions, small larvae (11,13 mg) had only low levels of thermal hysteresis proteins or thermal hysteresis protein message, but these levels increased 10-fold and 18-fold, respectively, by the final larval instar (> 190 mg), resulting in thermal hysteresis >,3 °C. Exposure of small larvae (11,13 mg) to 4 weeks of cold (4 °C) caused an ,,20-fold increase in thermal hysteresis protein concentration, well in excess of the less than threefold developmental increase seen after 4 weeks at 22 °C. Exposure of large larvae (100,120 mg) to cold caused 12-fold and sixfold increases in thermal hysteresis protein message and protein levels, respectively, approximately double the maximum levels they would have attained in the final larval instar at 22 °C. Thus, thermal hysteresis increased to similar levels (> 4 °C) in the cold, irrespective of the size of the larvae (the overwintering stage). At pupation, thermal hysteresis protein message levels decreased >,20-fold and remained low thereafter, but thermal hysteresis activity decreased much more slowly. Exposure to cold did not reverse this decline. Desiccation or starvation of larvae had comparable effects to cold exposure, but surprisingly, short daylength photoperiod or total darkness had no effect on either thermal hysteresis or message levels. As all environmental conditions that caused increased thermal hysteresis also inhibited growth, we postulate that developmental arrest is a primary factor in the regulation of T. molitor thermal hysteresis proteins. [source] Growth kinetics of microorganisms isolated from Alaskan soil and permafrost in solid media frozen down to ,35°CFEMS MICROBIOLOGY ECOLOGY, Issue 2 2007Nicolai S. Panikov Abstract We developed a procedure to culture microorganisms below freezing point on solid media (cellulose powder or plastic film) with ethanol as the sole carbon source without using artificial antifreezes. Enrichment from soil and permafrost obtained on such frozen solid media contained mainly fungi, and further purification resulted in isolation of basidiomycetous yeasts of the genera Mrakia and Leucosporidium as well as ascomycetous fungi of the genus Geomyces. Contrary to solid frozen media, the enrichment of liquid nutrient solutions at 0°C or supercooled solutions stabilized by glycerol at ,1 to ,5°C led to the isolation of bacteria representing the genera Polaromonas, Pseudomonas and Arthrobacter. The growth of fungi on ethanol,microcrystalline cellulose media at ,8°C was exponential with generation times of 4.6,34 days, while bacteria displayed a linear or progressively declining curvilinear dynamic. At ,17 to ,0°C the growth of isolates and entire soil community on 14C-ethanol was continuous and characterized by yields of 0.27,0.52 g cell C (g of C-substrate),1, similar to growth above the freezing point. The ,state of maintenance,' implying measurable catabolic activity of non-growing cells, was not confirmed. Below ,18 to ,35°C, the isolated organisms were able to grow only transiently for 3 weeks after cooling with measurable respiratory and biosynthetic (14CO2 uptake) activity. Then metabolic activity declined to zero, and microorganisms entered a state of reversible dormancy. [source] Experimental study and analysis of the application of ice-storage capsules in an air conditioning systemHEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 1 2002Shuiquan Ye Abstract Ice-storage capsules are used in an energy-efficient air conditioning system. Experiments and numerical simulations were conducted to investigate the effects of different structural configurations of the capsules on the freezing and melting processes of the refrigerant solution sealed inside the capsules. The predictions of the numerical simulation are in good agreement with the test results. The results show that the freezing speed of the capsules equipped with a metal core is 30% to 50% faster than for capsules without the metal core. In addition, it was found that the special refrigerant solution used in the experiment had a lower freezing point and a higher freezing speed than water. The effects of the size of the metal core, and the coolant temperatures are also investigated. © 2001 Scripta Technica, Heat Trans Asian Res, 31(1): 21,27, 2002 [source] Photovoltaic-powered cold store and its performanceINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 5 2001J. Nagaraju Abstract A photovoltaic-powered cold store plant, the first of its kind, has been developed to store 10 tons of frozen fish at ,15°C. It consists of a photovoltaic array (4 kW peak), a battery bank (96 V DC, 180 A H), a vapour compression refrigeration system (1 ton), electronic controls for automatic operation of plant and an insulated cold chamber. Experiments were conducted on the system to evaluate its performance with no heat load (frozen fish at ,15°C) and with different heat loads. It is observed that the system can be operated with a maximum heat load of 2350 W to maintain the walk-in-cooler temperature below the freezing point of fish (,2°C). The performance studies conducted on these subsystems viz., photovoltaic array and battery bank showed that their output has deteriorated in 5 years. Copyright © 2001 John Wiley & Sons, Ltd. [source] CFD modelling and experimental investigation of an ejector refrigeration system using methanol as the working fluidINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 2 2001S. B. Riffat Abstract This paper presents results of computational fluid dynamic (CFD) analysis and experimental investigation of an ejector refrigeration system using methanol as the working fluid. The CFD modelling was used to investigate the effect of the relative position of the primary nozzle exit within the mixing chamber on the performance of the ejector. The results of the CFD were used to obtain the optimum geometry of the ejector, which was then used to design, construct and test a small-scale experimental ejector refrigeration system. Methanol was used as the working fluid, as it has the advantage of being an ,environmentally friendly' refrigerant that does not contribute to global warming and ozone layer depletion. In addition, use of methanol allows the ejector refrigeration system to produce cooling at temperatures below the freezing point of the water, which of course would not be possible with a water ejector refrigeration system. CFD results showed that positioning the nozzle exit at least 0.21 length of the mixing chamber throat's diameter upstream of the entrance of the mixing chamber gave better performance than pushing it into the mixing chamber. Experimental values of coefficient of performance (COP) between 0.2 and 0.4 were obtained at operating conditions achievable using low-grade heat such as solar energy and waste heat. Copyright © 2001 John Wiley & Sons, Ltd. [source] Freeze-drying using vacuum-induced surface freezingJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 2 2002Martin Kramer Abstract A method of freezing during freeze-drying, which avoids undercooling of a solution and allows growth of large, dendritic ice crystals, was investigated. Aqueous solutions of mannitol, sucrose, or glycine were placed under a chamber vacuum of approximately 1 mbar at a shelf temperature of,+,10°C. Under these conditions, the solutions exhibit surface freezing to form an ice layer of approximately 1,3 mm thickness. On releasing the vacuum and lowering the shelf temperature to below the freezing point of the ice in the solution, crystal growth occurs to yield large, chimney-like ice crystals. The duration of primary drying of a frozen cake,as measured by using inverse comparative pressure measurement,was up to 20% shorter than when using a "moderate" freezing procedure (2 K shelf temperature per min). With mannitol, however, the residual moisture content of the final dried product was higher than with moderate freezing, and with sucrose and glycine there was no difference. These findings are related to the structures of the dried cakes formed during freezing, as examined by light microscopy and wide-angle X-ray diffraction. The introduction of an annealing step (4 h at a shelf temperature slightly above the onset melting point of the ice in the frozen cake) combined with the vacuum-induced surface freezing procedure maintains the rapid primary drying and produces a low residual moisture (0.2%) for the freeze-dried mannitol solution. © 2002 Wiley-Liss, Inc. and the American Pharmaceutical Association J Pharm Sci 91:433,443, 2002 [source] Physiological, hormonal and molecular mechanisms regulating chilling injury in horticultural species.JOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 4 2009Postharvest technologies applied to reduce its impact Abstract The storage of fruits and vegetables at low temperature near the freezing point is the foremost technology applied to retard postharvest ripening and to extend the shelf-life period of agricultural products. However, most tropical and subtropical produce is sensitive to chilling injury, which constitutes a set of physiological alterations caused by exposure to low temperatures for variable time periods, to the detriment of quality. This article is a thorough review of the physiological, hormonal and molecular mechanisms involved in the induction and development of this physiopathy. Also, the different postharvest technologies of a chemical, physical or biotechnological nature assayed in research or applied in the agro-food industry with the aim of inhibiting or delaying the emergence of chilling injury in sensitive plant produce of agricultural interest are reviewed. Copyright © 2009 Society of Chemical Industry [source] Antifreeze Properties of Polyglycidol Block CopolymersMACROMOLECULAR RAPID COMMUNICATIONS, Issue 23 2007Eti Baruch Abstract In this paper, we describe a new biomimetic approach to the synthesis of block copolymers with antifreeze properties. Our approach focuses on the design of block copolymers that mimic the structure and functionality of antifreeze proteins. Hyperbranched copolymers containing poly(ethylene oxide)-polyethyleneimine blocks and polyglycidol side chains were synthesized and their antifreeze properties were studied. It is shown that these block copolymers can lower the freezing point of water up to 0.8,°C at a relatively low concentration (1 mg,·,mL,1). From DSC measurements it is proven that polyglycidol block copolymers slow down the crystallization kinetics of ice and lead to changes in the ice crystal morphology, as observed by cryo-optical microscopy. [source] Geophysical surveys designed to delineate the altitudinal limit of mountain permafrost: an example from Jotunheimen, NorwayPERMAFROST AND PERIGLACIAL PROCESSES, Issue 3 2004Christian Hauck Abstract Three geophysical methods have been applied to delineate the altitudinal limit of permafrost at Juvvasshøe/Jotunheimen in southern Norway. By using each method in a complementary way according to its applicability, the permafrost distribution could be analysed on both large and small scales. In addition, temperature-based methods such as the BTS method (bottom temperature of snow cover) were used to validate the results. On a large scale, electromagnetic induction profiling with the EM-31 was used to detect the location of the transition area between frozen and unfrozen ground. Within this area direct-current (DC) resistivity and refraction seismic tomography were also applied to further characterize and visualize the permafrost transition. The large scale surveys revealed a sharp increase in conductivity, indicating an increase in unfrozen water content, near 1400,m a.s.l., with a possible transition zone between 1500,m a.s.l. and 1380,m a.s.l. The small scale investigation delineated the altitudinal limit of permafrost between 1470,m a.s.l. and 1410,m a.s.l., with sporadic ground ice occurrences and temperatures near the freezing point. Copyright © 2004 John Wiley & Sons, Ltd. [source] Liver Transplantation Using Liver Grafts Preserved Under High PressureARTIFICIAL ORGANS, Issue 10 2005Takuya Ueno Abstract: To extend organ preservation time, we attempted to establish a unique method of maintaining a preservation solution in a stable unfrozen state below its freezing point by pressurizing the solution. Livers removed from Lewis rats (RT1l) were stored in UW solution pressurized at the prescribed pressure. After the termination of preservation, orthotopic liver transplantation was performed. Experiment 1: Liver grafts were pressurized up to 30, 40, 50, and 70 MPa and preserved at 0°C for 60 min. Experiment 2: Liver grafts were compressed at a rate of 1.32 or 0.04 MPa/s to 35 MPa and preserved for 60 min at 0°C. Experiments 3 and 4: Liver grafts were pressurized up to 5, 10, 20, and 30 MPa and preserved at ,2°C (Exp. 3), ,3°C or ,4°C (Exp. 4) for 5 h. All rats transplanted with livers pressurized up to 30 MPa (Exp. 1), all rats in the 5 MPa and control groups at ,2°C (Exp. 3), and all rats in the 5 MPa group at ,3°C (Exp. 4) survived for 2 weeks. In light microscopy, diffuse hemorrhage and vacuolar degeneration of hepatocytes were observed in a pressure-dependent manner. Liver grafts preserved under pressurized, subzero nonfrozen condition have sufficient function to sustain the life of rats after orthotopic transplantation. [source] | |||||||||||||