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In most freeze tolerant insects, the tolerance of the formation of internal body ice is arrived at by a two-step process: (S-1) a period of supercooling of the body fluids that is followed by (S-2) the freezing event. To date, the necessity of S-1 remains to be questioned seriously. The present study reports evidence that S-1 may be almost completely substituted or superseded in large-bodied insects by integumental buffering. In the New Zealand alpine grasshopper Sigaus australis Hutton, there is a substantial difference between external and body core temperatures at the moment when internal ice nucleation is registered. Using the invagination of the pleural suture as a nondetrimental proxy for the core and the sclerotized postnotum as a measure of surface temperature, comparisons of the temperature of crystallization (Tc) show a highly significant difference (P

A phenomenological model for thermal relaxation and wave propagation in ideal polyatomic gases is developed by introducing a dynamical non-equilibrium temperature. The system of equations governing the evolution of the gas is derived and the speeds of propagation of thermo-mechanical disturbances together with the Rankine-Hugoniot jump conditions for shock waves are calculated. The hyperbolic theories of heat propagation in incompressible fluids and rigid solids are recovered as particular cases. For rigid solids, the well posedness of the Cauchy problem is proved by a classical method.

Non-isothermal miscible viscous flow in homogeneous porous media is studied through nonlinear simulation of the process and analysis of breakthrough efficiency. The main focus is on the effect of heat exchange between the displacing fluid and the solid matrix on the resulting instability. Higher diffusion rate of heat in the fluids reduces the effect of lagging between the fronts due to heat exchange. Hence, sweep efficiency of the injected solvent is less sensitive to thermal lag coefficient as the diffusion ratio increases. Variation of heat sweep efficiency with thermal lag coefficient and thermal log mobility ratio has been analysed as well. © 2012 Canadian Society for Chemical Engineering

Thermal death kinetic parameters for Bacillus stearothermophilusspores were evaluated in sugarcane must (21.5°Brix, pH = 6.14) at temperatures ranging from 98 to 130C, using the thermal-death-time tube method and survivors count. Resulting survival curves showed strong nonlinearity and different shapes according to heating temperature. The 98 and 110C curves showed an initial shoulder or thermal lag and were adjusted to the logistic model. At the temperature range of 120–125C, the two-term exponential model for population with heterogeneous heat resistance was fitted, and at 130C, the classic linear model was suitable. It was shown that rate constants are influenced by temperature according to two irreconcilable methods: the Arrhenius and the Bigelow methods. Activation energy (Ea) obtained was 249.52 kJ/mol while thermal resistance parameter (z-value) calculated from Ea and the Bigelow method were 11.48 and 9.19C, respectively. Thermal death kinetic constant, k values, varied from 0.019 to 13.63/min. PRACTICAL APPLICATIONS The thermal degradation kinetics from this work, in conjunction with the appropriate sugar degradation kinetic data (Nolasco Junior 2005, Nolasco Junior and De Massaguer 2006), can be used to properly design an optimal thermal process to inactivate sugarcane must contaminants with optimal sugar content retention. Contaminant control in ethanolic fermentation processes could namely be based on temperature, a physical agent, instead of the current control practice based on antibiotics. Besides, the data from this research meet the more frequently found nonlinear microbial thermal death kinetic model application.

First and second order thermal transitions have been characterized for a number of cis/trans-polypentenamer copolymers, for blends of high cis and high trans polymers, and for high trans polypentenamer containing oil and carbon black. The extrapolated value of Tg for 100% trans polypentenamer is −91°C at a heating rate of 10°C/min. At the same heating rate the maximum, equilibrium melting point is estimated to be 44°C. Correcting for the thermal lag in the experiment (i.e., extrapolating to infinitely slow heating rate), the above value is 40°C. The heat of fusion of trans-polypentenamer is 1.93 ± 0.11 K cal/mole. The presence of crystalline polypentenamer slightly raises the glass transition temperature of the amorphous phase. This effect becomes measurable when the trans content is greater than 80%. Once calibrated by infrared or other spectroscopic determination of composition, thermal analysis is a rapid, precise method for measuring cis/trans contents in polypentenamers.

The isoconversional approach proposed by Vyazovkin for evaluating the Hoffman-Lauritzen parameters from overall rates of non-isothermal crystallization was critically applied to two new and fast crystallizing polymers, poly(propylene terephthalate) and poly(butylene naphthalate), which are used for the production of fibers. Non-isothermal crystallization data were corrected for the effect of the thermal lag and the effective activation energy as a function of temperature was calculated using the method of Friedman. The estimated Hoffman-Lauritzen parameters, U* and K g , were consistent with corresponding values from isothermal crystallization experiments obtained either from DSC measurements or using polarized optical microscopy (POM). It was found that the proposed method could simulate the experimental data very well, and the temperature interval under consideration did not allow the detection of any critical breakpoints denoting regime transitions.

The Nakamura equation is used to model the crystallization kinetics of syndiotactic polystyrene. Model constants are generated by fitting available data under isothermal conditions. The resulting fit is then applied to available data under constant-cooling-rate conditions, with notable agreement provided the measurements include corrections for thermal lag. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2402–2406, 2004

Differential scanning calorimetry (DSC) can be used to infer the distribution of lamellar crystal thickness l. For homopolymers, the relation between melting temperature T and thickness is described by the Gibbs relation. In this case the weight distribution function of thickness g(l) ∝ P(T)(T − T)2, where P(T) is DSC power and T is the melting temperature of an infinitely thick crystal. Copolymer melting is affected by the concentration of noncrystallizable comonomer in the melt as well as lamellar thickness. Unknown melt composition in copolymers with nonequilibrium crystallinity makes determination of the correct distribution g(l) from DSC impossible. An approximate distribution g2(l) ∝ P(T)(T − T)2 is proposed, where T is based on Flory's equilibrium crystallization theory. This approximate distribution is most accurate when crystallinity is small, that is, near the upper end of the melting range. Results are reported for polyethylene homopolymer and model ethylene–butene random copolymers. Corrections were not made for distortion of the DSC endotherms by thermal lag or by melting and recrystallization; these experiments are primarily to illustrate the effect of analysis in terms of an incorrect g3(l) ∝ P(T). Average crystal thicknesses are about 20 nm for polyethylene and 5 nm for the copolymers. Distributions are characterized by lw /ln ≤ 1.1 in all cases. Width of the melting range is not a reliable indicator of the breadth of the thickness distribution. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 3131–3140, 1999

A study was conducted of the temperature dependence of the thermal diffusivity and thermal expansion of an alumina–aluminum titanate composite heated to a range of maximum temperatures followed by cooling to room temperature. Heating to temperatures above about 600°C resulted in a hysteresis behavior in which the data on cooling differed from the data obtained during heating. For both the thermal diffusivity and thermal expansion, the degree of hysteresis increased with increasing maximum temperature. On return to room temperature, following heating to a temperature of about 1200°C, the thermal diffusivity exhibited a significant decrease, with a corresponding increase in specimen size. This effect was attributed to an increase in microcrack density over the corresponding value prior to heating. On subsequent cycles of heating and cooling for a maximum temperature of 1200°C this decrease in thermal diffusivity was partially recovered, indicative of the structural integrity of the alumina–aluminum titanate composite of this study in practical applications involving temperatures of at least 1200°C.

Dew forms on cocoa pods after sunrise when the dew-point temperature of air in the canopy rises faster than the surface temperature of the pods. Exchanges of heat and water vapour are estimated by treating a pod as an isothermal body with homogeneous thermal properties. Two treatments of this simple model are discussed. First, the heat balance equation is simplified to a form which allows the environmental limits for condensation to be derived explicitly. Second, the equation is solved numerically to find the duration and mean depth of wetness as a function of environmental variables. Consistent with observation, the thermal lag of the pod is about 1 to 3K; condensation to a depth of 10 to μm occurs when air at sunrise is almost saturated and windspeed is light. Condensation on cocoa pods is likely to be significant in the spread of Black Pod, a serious fungal disease.

The heat resistance of proteolytic C. botulinum type F strains Langeland, PC and 4YRC was studied by the thermal death time tube method in phosphate buffer; 4Y,RC was also studied in crabmeat. Correction of exposure time for thermal lag and lethality during lag was made by the graphic method. Decimal reduction times in minutes (D) were calculated by Schmidt's probability method, using the Karber LD50. For these 3 strains, D curves in phosphate buffer traversed one log cycle in 18.1–25.3°F (z); extrapolated they gave 0.14–0.23 for D250. The z of the 4YRC crabmeat D curve was 23, extrapolating to 0.17–0.18 for D250. Proteolytic type F, therefore, resembles other proteolytic C. botulinurn types.

Differential scanning calorimetry (DSC) was used to study the effect of chlorine treatment of wheat flour on the heat of gelatinization of the wheat flour and starch. The DSC thermograms were corrected for heat capacity changes and thermal lag. An endothermic transition occurred in both flours and starches at a temperature commonly associated with starch gelatinization. The enthalpy (ΔH) for the starches was concentration dependent. The chlorine treatment did not affect significantly the transition temperatures nor enthalpies of either the flour or the starch isolated from it. Addition of sucrose delayed the onset of gelatinization and increased the ΔH for both treated and untreated wheat flours and starches.

Techniques for measuring the enthalpy change during isothermal aging of polymer glasses are discussed. Critical analysis of conventional scanning calorimetry reveals that its accuracy may be suspect under certain circumstances due to the thermal lag inherent in a temperature scanning experiment. An additional problem is that the conventional technique is restricted to certain kinds of paths for reaching the aging temperature. It is proposed that both problems can be overcome by analyzing the output of a scanning calorimeter not only during steady heating but also during the transients at the beginning and end of a heating scan. This data analysis method represents an extension of a method used previously by others in accurate measurements of the much larger heat of fusion of crystalline polymers. Practical feasibility of the improved technique is demonstrated by preliminary measurements of enthalpy relaxation during aging of well-characterized polystyrene at 80°C. In particular, the initial departure from equilibrium of a glass prepared by 5°C/min cooling from the liquid state is found to be 6.9 ± 0.6 J/g. This measured value agrees with a value calculated on the basis of the glass transition temperature corresponding to 5°C/min cooling and heat-capacity data from the literature.

The effect of a spatial variation of the thermal conductivity on the magnitude of the maximum tensile thermal stress in a solid circular cylinder subjected to sudden convective heating was calculated by finite element methods. The general results show that by lowering the thermal conductivity in the surface region of the cylinder, the magnitude of the maximum tensile thermal stress at the center of the cylinder is reduced significantly. The negative temperature dependence of the thermal conductivity in dielectric materials, which indirectly creates a spatial variation in thermal conductivity, also causes a significant decrease in the magnitude of the tensile thermal stresses, as demonstrated by a numerical example for aluminum oxide. It is also shown that a spatial variation in thermal conductivity can significantly affect the time to maximum tensile stress as well.

An increase in the accuracy and precision of thermal diffusivity (α) was observed when estimated from thermal process data using the analytical heat conduction equation as compared to using the process fh value. Differences in α for the two methods ranged from 2.4 to 3.5%. Correcting for the presence of the thermocouple probe became more important with smaller can sizes. The analytical solution to the heat conduction equation proved to be a very sensitive model with regard to prolonged retort come-up time and heat conduction along the thermocouple probe.