Effect of low temperature

The effect of low temperatures affecting the ortho para ratio is more important for light... 

Hence if a laboratory measurement at 25°C yields a conductivity of 100 pS/m the same liquid at -10°C will have a conductivity of about 30 pS/m. The effects of low temperature combined with the elevated dielectric constants of many nonconductive chemicals support use of the 100 pS/m demarcation for nonconductive liquids (5-2.5) rather than the 50 pS/m demarcation used since the 1950s by the petroleum industry. For most hydrocarbons used as fuels, the dielectric constant is roughly 2 and a demarcation of 50 pS/m is adequate, provided the conductivity is determined at the lowest probable handling temperature. 

Notch sensitivity Effect of low temperature Maximum transition temperature ( O... 

Because of the effect of low temperatures on structural steel, it will be no use to change (decrease) the allowable unit stresses mentioned in the preceding paragraphs titled Allowable Stresses. Low temperature phenomena in steel are well established in principle. Structures to be used under extreme conditions should use special materials that have been, and are being, developed for this application. 

Tinplate and Solder. The tests were carried out to determine the effect of low temperature irradiation on the metallurgical properties of the tinpalte, solder, and soldered lap joints. Two types of tinplate were used 43 kg (95 lb), Type MR-TU and 43 kg (95 lb), Type MR-T2, both coated with No. 25 electrolytic tinplate. The test specimens were 20 X 20 cm panels. 

Tinplate and Solder. Metallurgical studies were performed to determine the effect of irradiation at low temperature on the corrosion resistance of tinplate and on the mechanical properties and microstructure of tinplate and side-seam solder of the tinplate container. The area of major interest was the effect of low-temperature irradiation on the possible conversion of the tin from the beta form to the alpha form. In the case of pure tin, the transition occurs at 18 °C. It was feared that low-temperature irradiation would create dislocations in the crystal lattice of tin and enhance the conversion of tin from the silvery form to a powdery form rendering the tin coating ineffective in protecting the base steel. Tin used for industrial consumption contains trace amounts of soluble impurities of lead and antimony to retard this conversion for several years. 

The rate of catalysis of membrane bound enzymes (Plot B, Figure 1) is more greatly affected than soluble enzymes by lowering the temperature. This is due to the effect of low temperatures on the solidification of the membranes. Thus, an Arrhenius plot of the rate of a membrane-bound enzyme as a function of temperature often shows a discontinuity with a sharp break point (transition temperature) and loss of activity at the temperature where the membrane becomes a gel or more solid phase. 

When testing the effect of low temperatures on elastomers it is rarely sufficient merely to enclose the standard apparatus in a refrigerated chamber special procedures are necessary. The relevant standard is BS 903 Part A13. Method for determination of stiffness at low temperatures (Gehman test). 

Kondo S, Kittikom M and Kanlayanarat S. 2005. Preharvest antioxidant activities of tropical fruit and the effect of low temperature storage on antioxidants and jasmonates. Potharv Biol Technol 36(3) 309—318. 

Box 3.3 Hibernation, migration or insulation in warm-blooded animals. Manipulations to overcome the effects of low temperatures... 

Coffin, R. H., Yada, R. Y, Parkin, K. L., Grodzinski, B., Stanley, D. W. (1987). Effect of low-temperature storage on sugar concentrations and chip color of certain proeessing potato cultivars and selections. Journal of Food Science, 52, 639-645. 

Abu-Ghannam,N., Crowley, H. (2006). The effect of low temperature blanching on the texture of whole processed new potatoes. J. Food Eng., 74,335-344. 

Griffiths, D. W., Bain, H., Dale, M. F. B. (1997). The effect of low-temperature storage on the glycoalka-loid content of potato (Solanum tuberosum) tubers. Journal of the Science of Food and Agriculture, 74, 301-307. 

The analysis conducted in this Chapter dealing with different theoretical approaches to the kinetics of accumulation of the Frenkel defects in irradiated solids (the bimolecular A + B —> 0 reaction with a permanent particle source) with account taken of many-particle effects has shown that all the theories confirm the effect of low-temperature radiation-stimulated aggregation of similar neutral defects and its substantial influence on the spatial distribution of defects and their concentration at saturation in the region of large radiation doses. The aggregation effect must be taken into account in a quantitative analysis of the experimental curves of the low-temperature kinetics of accumulation of the Frenkel defects in crystals of the most varied nature - from metals to wide-gap insulators it is universal, and does not depend on the micro-mechanism of recombination of dissimilar defects - whether by annihilation of atom-vacancy pairs (in metals) or tunnelling recombination (charge transfer) in insulators. 

The optimum reoxidation temperature, shown in Fig. 20, is about 600°C. This depends to some extent on the type of support. Highly titanated samples produce peak melt indexes at only 300°C. Probably the temperature is needed to bind the chromium to the dehydroxylated support. Above 600°C the activity remains high, but the promotional effect of low temperature attachment is lost, and the MI drops. 

The most straightforward way to measure the effect of low temperatures on recovery is by means of a compression set or tension set test. Tests in compression are favoured and a method has been standardised internationally. The procedure is essentially the same as set measurements at normal or elevated temperatures and has been discussed in Chapter 10, Section 3.1. As the recovery of the rubber becomes more sluggish with reduction of temperature the dynamic loss tangent becomes larger and the resilience lower (see Chapter 9), and these parameters are sensitive measures of the effects of low temperatures. Procedures have not been standardized, but rebound resilience tests are inherently simple and quite commonly carried out as a function of temperature. It is found that resilience becomes a minimum when the rubber is in its most leathery state and rises again as the rubber becomes hard and brittle. 

It would appear that the common standard low temperature tests are not thought totally suitable for measuring effects of crystallisation because a hardness tests has been standardised for this purpose, even although hardness tests are not so commonly used for measuring the immediate effect of low temperature. The international method ISO 338733 and the British method BS 903 Part A6334 are the same and are applicable to unvulcanised as well as vulcanised rubber. This is probably one reason why the hardness test has been introduced because the other methods would not be satisfactory... 

Figure 14 Effect of low temperature on hydration of bovine casein micelles and of interfacially bound protein in ice cream mix with (+E) and without (-E) emulsifier (saturated mono-diglyceride).

J.E. Plum, The Effect of Low Temperature on the Impact Sensitivity of TNT , Masters Thesis, Naval Postgraduate School, Monterey... 

The exposure of plants to low temperatures induces many changes in physiological and biochemical parameters. Many studies have attempted to investigate the relationship between low temperature and enzyme activities. The effects of low temperature treatments on the protein levels and on activity of some plant cell enzymes are reported in Table 1. 

Huner, N.P.A. Macdowall, F.D.H. (1979). The effects of low temperature acclimation on the catalytic properties of its ribulose bisphosphate carboxylase-oxygenase. Canadian Journal of Biochemistry 57, 1036-41. 

Eliassen, E., Leivestad, H. and Muller (1960). The effect of low temperature on the freezing point of plasma and on the potassium/sodium ratio in the muscles of some boreal and subarctic fishes. Bergens Universitet Arbok, Matematisk-Naturvitenskapelig Ser. 1960 (14), 24pp. 

Casellas, G. B. (2005). Effect of low temperature fermentation and nitrogen content on wine yeast metabolism. Universitat Rovira i Virgili, Tese de Doutoramento. 

The effect of low temperatures affecting the ortho para ratio is more important for light molecules, such as F and 2H2, than for heavy ones, such as 19F2 and 14N2. The reason is that the separation of the J= 0 and J= 1 levels is smaller for a heavier molecule and a lower temperature is required before a significant deviation from the normal ortho para ratio is observed. 

The discoveries of Csp s and trigger factor may represent the tip of a large iceberg. In view of the pervasive effects of low temperature on the structures of all classes of macromolecules, it is reasonable to conjecture that many more types of proteins will be discovered whose roles are to offset the effects of cold shock on the cell. Some of these molecules may be expressed constitutively and may be part of the normal machinery of the cell. For example, certain ribosomal proteins are thought to function as RNA chaperones, and if present in sufficient amounts, these proteins may allow the cell to cope with the effects of cold shock on the structures of certain classes of RNAs. In yeast, a constitutively expressed ribosomal protein has helicase activity, and mutation in the gene encoding the protein confers on the cells a cold-sensitive phenotype (Schmid and Linder, 1992). Perhaps the apparent absence of cold-induced RNA chaperones in eukaryotic cells is... 

For hypothermia, one major possible difficulty involves the effect of low temperature on metabolism and enzyme activity. Many pharmaceutical agents have reduced biological activity at lower temperature compared with higher temperature. The thrombolytic activity of recombinant tissue plasminogen activator (rt-PA), for example, is clearly temperature dependent, with decreased activity at lower temperature (1). Thus, the assumption that hypothermia will not have an adverse effect on other treatment agents cannot be presumed. Hypothermia is also known to reduce the activity of inflammatory and antiinfectious biological processes. This could potentially result in increased susceptibility to infection. This possibility is of particular concern because infections are a major cause of morbidity in stroke patients (2). Therefore, combination therapy with hypothermia and antiinflammatory agents could potentially worsen outcome. 

Chapman, H.R., Sharpe, M.E., Law, B.A. 1976. Some effects of low-temperature storage of milk on cheese production and Cheddar cheese flavor. Dairy Ind. Int. 41, 42-45. 

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