Changes In Heat Resistance Research Articles

Thermophysical Properties of Composite Metal-Filled Copolymers of Polyvinylpyrrolidone

The effect of the presence of finely dispersed metal fillers of various natures (Zn, Co, Ni) on the thermophysical characteristics (Vick heat resistance, glass transition temperature) of polyvinylpyrrolidone block copolymers with 2-hydroxyethylmethacrylate was studied. It was found that the heat resistance of the obtained composites significantly exceeds the heat resistance of unfilled copolymers and is in the range of 360-395K, depending on the nature and content of the metal filler. The change in heat resistance correlates with the change in glass transition temperature, which was evaluated according to the results of thermomechanical and dynamic mechanical thermal analyses. The results of this work are an additional source to characterize the structure of metal-filled copolymers: they confirm the participation of metal filler particles in the formation of the nodes of the copolymer spatial network, and also prove the formation of a different polymer network structure in the interfacial layer on the surface of the metal particle and in the polymer volume.

Analysis of heat transfer and factors affecting the thermal propertieson rib 1x1 knitwear

Clothing comfort is very important feature which is considered as a result of different process of heat exchange between human body, clothing and environment. The purpose of this paper is to analyse the impact of clothing insulation on the heat transfer. The measurements were carried out on commercially 1x1 RIB knitted fabrics used for the production of next-to-skin shirts. The one group of samples are made from 100% cotton yarn and another with 96% cotton and 4%lycra. It is noticed that knitted material composition affected the change in heat resistance. Also, this paper presents and verifies the correlation between the measured values of thermal resistance (Rct) and the knitwear thickness (dpl), the covering factor (K), the porosity of the twists (e) and the surface coefficient (dp). Based on these results, a mathematical model for calculating thermal resistance is proposed. Comparing the results obtained with the proposed equation and the measured results, we can see that the deviations are minimal. The highest deviation for sample C4 is 0.05%,while the largest deviation for sample CL4 is 4.6%.

Моделирование изменения предела длительной прочности сплавов на основе никеля с использованием байесовских искусственных нейронных сетей

Моделирование изменения предела длительной прочности сплавов на основе никеля с использованием байесовских искусственных нейронных сетей

Physicochemical characterization of polyimide (PI) / p-aramid: New functional and safe materials with improved heat resistance by a simple coating of polyimide on the surface of p-aramid

With excellent heat resistance and chemical resistance, p-aramid is used in a variety of industrial applications. In this study, the polyimide (PI) precursor was coated on the surface of p-aramid yarn and studied the changes in heat resistance and physicochemical properties of composite PI / p-aramid yarns. Changes in peaks by imidization of PI using XRD and FT-IR, surface characteristics through SEM, and thermal properties analyzed by TMA and TG-DTA were measured. The degree of imidization of PI films were quantitatively investigated by FT-IR analysis. Through these analyzes, the following results were revealed: (1) the imidization of the PI was confirmed that the thermal imidization process at 350 °C was suitable; (2) the physical properties of the PI film were affected by the imidization temperature, the heat treatment time and the amount of the catalyst; and (3) the tensile strength of PI / p-aramid coated yarn was higher than that of conventional uncoated p-aramid yarn at 200–350 °C. Therefore, PI/ p-aramid composite yarns formed through the stepwise coating were found to improve thermal properties including initial thermal degradation temperature compared to no PI coating.

Influence of the Length and Concentration of Carbon and Glass Fibers on the Properties of Polyphenylene Sulfone

The influence of the length and concentration of carbon (CF) and glass (GF) fibers on the rheological, physicomechanical and thermal properties of high-temperature polyphenylene sulfone thermoplastic with a filler content up to 40% (by mass) was investigated. Carbon and glass fibers 0.2- and 3-mm long were used as fillers. The introduction of CF and GF leads to a noticeable decrease in the melt flow index and the impact strength of polyphenylene sulfone, while the yield stress disappears on the stress-strain diagram, which is caused by a decrease in the material’s ability to plastic deformations. With an increase in the fiber content, the elastic modulus and tensile strength of the composite increase both in bending and in tension. A significant increase in heat resistance occurs with an increase in the CF content, and samples with a CF content of 0.2 mm have a higher mass loss temperature. In the case of composites with GF, there are no significant changes in heat resistance.

THERMAL STABILITY ANALYSIS OF IRON-ORE PELLETS PRODUCED USING THE TECHNOLOGY OF HEAT-SPRAYING OF WET CHARGE

The article presents the results of the study of thermal stability of wet iron-ore pellets obtained by heat-spraying technology of wet charge on charge pelletizer skull, as well as on the clumping off-grade pellets. The experiments involve the pellets obtained by the technology of nucle- ation by spraying and additional clumping and the technology of nucleation, pelletizing and spraying. These pellets have structural heterogeneity on the moisture content. The former has the reduced moisture content in the center of the pellet; the second one has lower moisture content in the coat of the formed pellets. It is established that the cracking temperature and shock fracture increase signifi cantly with the decrease of moisture content in the center (nucleation by spraying and additional clumping) and in the coat (the technology of nucleation, pelletizing and spraying) of pellets as compared with the conventional technology. It was found out that in case of equality of the total moisture content of the pellets obtained by the technology of nucleation by spraying and additional clumping and the technology of nucleation, pelletizing and spraying, their fracturing temperatures differ signifi cantly. The boundaries of the moisture ratio of the surface layer and the central part of the pellet, achieved by each of the offered technologies and affect directly the heat resistance parameters are also different from each other. In particular, the structural heterogeneity of the pellets according to the moisture content at which a minimum amount of moisture is contained in the central area of the pellet (the technology of nucleation by spraying and additional clumping), has the largest interval of the moisture ratio. For the pellets, obtained according to the technology of nucleation by spraying and additional clumping in the interval of the moisture ratio, it is possible to raise the cracking temperature at 240 °C compared to pellets formed according to the technology of nucleation, pelletizing (560 °C). The pellets, obtained according to the technology of nucleation, pelletizing and spraying, have the boundaries of the moisture ratio in the surface and central parts, which are signifi cantly less. Within these boundaries the change in heat resistance according to the criterion of crack formation does not exceed 40 °C.

Effect of finishing treatments on heat resistance of one- and two-layered fabrics

A series of cotton knitted fabrics was produced and finished according to three different recipes in order to compare the changes of their heat resistances. The heat resistance was measured using the sweating guarded hotplate. Measurements were carried out on one layer of produced knitted fabrics, as well as on two layers of fabrics. The results indicated significant influence of all carried finishing treatments to the decrease of heat resistance of knitted fabrics. It was shown that the high influence of finishing treatment to the total heat transfer trough fabric remains if the fabric is worn with additional knitted fabric layer. The presented results and performed statistical analysis indicated significant effect of finishing treatments to the changes of fabric parameters and furthermore to the changes of heat resistance what directly affects the total thermophysiological comfort of knitwear.

Use of marination for controlling Salmonella enterica and Listeria monocytogenes in raw beef

The effect of marination on the survival and growth of the pathogens Salmonella enterica and Listeria monocytogenes on beef pieces was investigated.Five marinades were used: soy sauce base marinade without (SB) or with lactic acid (SBLA), red wine base marinade without (WB) or with 0.5% v/v oregano essential oil (WBO), and sterile saline used as control (C). Inoculated fresh beef pieces were marinated for 18 h at 5 °C, removed from the marinade and subjected to storage trials at 5 °C and 15 °C. Heat inactivation studies were also performed on the isolates after exposure to the marinades to determine if marination affects heat resistance of the pathogens.The marinades with antimicrobials caused a significant decrease in viable count of the pathogens during marinations at 5 °C for 18 h of up to 2.1 and 3.4 log cfu cm−2 for Salmonella and L. monocytogenes, respectively. Marinades without antimicrobials were less bactericidal resulting to reductions ranging from 0.3 to 0.4 and 1.3 to 2.0 log cfu cm−2 for Salmonella and L. monocytogenes, respectively. Growth of L. monocytogenes was observed in the controls at both tested temperatures, while growth of Salmonella was observed in the controls stored at 15 °C. No growth of the pathogens was observed in any of the marinated samples at both temperature tested. No significant changes of heat resistance of the tested pathogens after exposure to the marinades were observed demonstrating the enhanced safety of the marinated beef product.

Analysis of individual changes in heat resistance of Daphnia magna clones at initial stages of cultivation

We studied 30 daphnia clones with respect to the organism’s heat resistance (HR) at the initial stages of cultivation: ten clones died before the appearance of offspring in F2, while the remaining clones successfully reproduced and produced subsequent generations. Based on changes in F1 of the individual HR level of clones as compared with their ancestors, the conclusion was drawn that there is a disturbance of the work of mechanisms of physiological homeostasis in the population of dead clones. In the remaining clones, there was observed a high negative correlation between the initial individual resistance level and its change in F1 and F2, as well as a sharp narrowing of the variability diapason in F1. In this group of animals, a significant lability of the individual stability level was noted, as well as its ability to regulate the shift of its resistance, which provides a satisfactory work of mechanisms of physiological homeostasis.

Characterization of poly(vinyl alcohol)/gold nanocomposites obtained by in situ gamma‐irradiation method

AbstractGamma‐irradiation induced reduction of gold (Au) ions was performed in aqueous poly(vinyl alcohol) (PVA) solution. PVA/Au nanocomposites with different contents of inorganic phase were prepared by solvent evaporation. The colloids and corresponding nanocomposites show visible light absorption with strong excitonic peak in the wavelength range from 520 to 550 nm. Morphological and structural characterizations of gold nanoparticles (Au NPs) and nanocomposites were performed by TEM, XRD, and FTIR measurements. Also, Mie and Maxwell‐Garnett theories were applied to calculate optical properties of Au colloids and PVA/Au nanocomposites, respectively. The changes of heat resistance upon the increase of inorganic phase were correlated to the decrease in crystal perfection of polymer. Improvement of thermal stability of nanocomposites, compared with the neat PVA, was observed when the content of inorganic phase exceeds 1 wt %. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Thermal Inactivation of Avian Viral and Bacterial Pathogens in an Effluent Treatment System within a Biosafety Level 2 and 3 Enhanced Facility

Avian influenza (AI) virus, avian paramyxovirus Type 1 (APMV-1 or NDV), reovirus, rotavirus, turkey astrovirus (TAst), avian metapneumovirus (aMPV), Marek's disease virus (MDV-1), avian parvovirus (ChPV), and Salmonella enterica serovar Enteritidis are significant biosafety level 2 (BSL-2) or biosafety level 3 enhanced (BSL-3E) pathogens of poultry that are studied in veterinary medical research laboratories worldwide. The purpose of this study was to determine the effectiveness of a moderate temperature, effluent decontamination system (EDS) to inactivate avian pathogens. First, the thermal inactivation processes for AI virus, APMV-1, reovirus, and rotaviruses were determined in phosphate-buffered saline (PBS) using in vitro assays from which thermal death rates (Dt) and changes in heat resistance (zD) of the AI virus and APMV-1 were determined at various time/temperature parameters. The PBS validation process demonstrated that 6 log10 reduction was achieved following heating at 82.2°C within 30 seconds for AI virus and APMV-1, 1.8 minutes for astrovirus, while reoviruses and rotaviruses were destroyed within 3 minutes. Second, to determine whether pathogens were adequately inactivated in a moderate temperature EDS system, vials containing avian viruses (5.1-11.1 log10 TCID, EID50/ml, or infectious particle/ml) and bacteria (9.1 log10 cfu/ml) were placed in the effluent tank and exposed to a standard cycle of 82.2°C for 6 hours. The EDS process totally inactivated enveloped and non-enveloped viruses with complete inactivation of greater than 5.1-11.1 log10 TCID/ml of specific pathogens. The data from the inactivation models and the EDS validation test showed that the 6 log10 reduction required for a sanitary assurance level of effluent was achieved with a significant margin of safety.

Validated empirical models describing the combined effect of water activity and pH on the heat resistance of spores of a psychrotolerant Bacillus cereus strain in broth and béchamel sauce.

The major objective of this study was to evaluate and model the combined effect of the water activity (a(w)) and pH of the heating menstrum on the heat resistance of spores of a psychrotolerant Bacillus cereus strain isolated from béchamel sauce. Two models, a quadratic polynomial equation and a reparameterized function, were assessed for their ability to describe the combined influence of a(w) and pH on the D(85°C)-values of the B. cereus isolate in tryptone soy broth. The performance of the models was validated by challenging the models with data independently collected in broth and béchamel sauce. Both models were found to adequately describe the validation data obtained in broth. However, it was determined that in béchamel sauce the predictions of the polynomial function not only showed bias (bias factor = 1.156) but were also fail-dangerous, as they deviated from the validation data by 17.2%. The reparameterized function was determined to be a good predictor of the D(85°C)-values in béchamel sauce as it showed no bias (bias factor = 1.033) and its predictions differed by only 7.9% from the validation data. The reparameterized function can be used to provide estimates of the minimum processing conditions required to achieve desired levels of spore inactivation within the a(w) and pH ranges studied and to determine the potential changes in heat resistance of B. cereus spores when a(w) and pH are changed, for example, during product reformulation. As validation of heat resistance models is rarely performed, let alone in actual food products, the models evaluated and validated in this study (in particular the reparameterized function) are of immediate relevance to the food industry.

Thermal inactivation of avian influenza virus and Newcastle disease virus in a fat-free egg product.

High-pathogenicity avian influenza (HPAI) virus, low-pathogenicity avian influenza (LPAI) virus, virulent Newcastle disease virus (vNDV) and low-virulent Newcastle disease virus (lNDV) can be present on the eggshell surface, and HPAI viruses and vNDV can be present in the internal contents of chicken eggs laid by infected hens. With the increase in global trade, egg products could present potential biosecurity problems and affect international trade in liquid and dried egg products. Therefore, the generation of survival curves to determine decimal reduction times (D(T)-values) and change in heat resistance of the viruses (z(D)-value) within fat-free egg product could provide valuable information for development of risk reduction strategies. Thermal inactivation studies using A/chicken/Pennsylvania/1370/83 (H5N2) HPAI virus resulted in D(55)-, D(56)-, D(56.7)-, D(57)-, D(58)-, and D(59)-values of 18.6, 8.5, 3.6, 2.5, 0.4, and 0.4 min, respectively. The z(D)-value was 4.4 °C. LPAI virus A/chicken/New York/13142/94 (H7N2) had D(55)-, D(56.7)-, D(57)-, D(58)-, D(59)-, and D(60)-values of 2.9, 1.4, 0.8, 0.7, 0.7, and 0.5 min, respectively, and a z-value of 0.4 °C. vNDV avian paramyxoviruses of serotype 1 (AMPV-1)/chicken/California/212676/2002 had D(55)-, D(56)-, D(56.7)-, D(57)-, D(58)-, and D(59)-values of 12.4, 9.3, 6.2, 5, 3.7, and 1.7 min, respectively. The z(D)-value was 4.7 °C. lNDV AMPV-1/chicken/United States/B1/1948 had D(55)-, D(57)-, D(58)-, D(59)-, D(61)-, and D(63)-values of 5.3, 2.2, 1.1, 0.55, 0.19, and 0.17 min, respectively, and a z(D)-value of 1.0 °C. Use of these data in developing egg pasteurization standards for AI and NDV-infected countries should allow safer trade in liquid egg products.

Relationship between membrane fatty acid composition and heat resistance of acid and cold stressed Salmonella senftenberg CECT 4384

This study evaluates the adaptative response to heat (63 °C) and the modifications in membrane fatty acid composition of Salmonella senftenberg after its growth in an acidified medium and after its exposure to combinations of acid and cold stresses. Cells were grown in Brain Heart Infusion (BHI) buffered at pH 7.0 and acidified up to pH 4.5 (fresh cultures) and kept at refrigeration temperature (4 °C) for 7 days (refrigerated cultures). The results indicate that previous adaptation to a low pH increased the bacterial heat resistance, but combinations of sublethal stresses reduced S. senftenberg heat tolerance, specially when the growth medium pH was decreased. Acid-adapted cells showed D 63-values ranging from 3.10 to 6.27 min, while non-acid-adapted cells showed D 63-values of 1.07 min. As pH decreased, over the pH range studied (7.4–4.5), D 63-values of the resulting cells increased. However, refrigerated acid-adapted cells showed lower D 63-values, which ranged from 0.95 to 0.49 min. A linear relationship between the thermotolerance of S. senftenberg cells and the previous growth medium pH was found in both fresh and refrigerated cultures, which allowed us to predict changes in heat resistance of S. senftenberg that occur at any pH value within the range used in the present study in which most foodstuffs are included. Both acidification of the growth medium and refrigeration storage of cells induced modifications in membrane fatty acid composition, which were clearly linked to their heat resistance. Acid-adapted cells, regardless of the pH value of the growth medium, showed the lowest UFA/SFA ratio and a CFA content 1.5–2-fold higher than that observed for non-acid-adapted cells. On the other hand, the UFA/SFA ratio found for S. senftenberg cells exposed to a cold stress was 1.2–1.8-fold higher than that observed for non-refrigerated cultures. This increase in the UFA/SFA ratio was specially high for acid-adapted cells. The highest thermotolerance was observed for cells with low UFA/SFA ratio, and, consequently, having a low membrane fluidity. However, changes observed in CFA content did not explain the great heat sensitivity of refrigerated acid-adapted cells.

Radiolytic synthesis and characterization of Ag-PVA nanocomposites

The Ag-PVA nanocomposites with different contents of inorganic phase were prepared by reduction of Ag + ions in aqueous PVA solution by gamma irradiation followed by solvent evaporation. Optical properties of the colloidal solutions and the nanocomposite films were investigated using UV–vis spectroscopy. Structural characterization of the Ag nanoparticles was performed by TEM and XRD. Interaction of the Ag nanoparticles with polymer matrix and the heat resistance of the nanocomposites were followed by IR spectroscopy and DSC analysis. IR spectra indicated that Ag nanofiller interact with PVA chain over OH groups. The changes of heat resistance upon the increase of the content of inorganic phase are correlated to the adsorption of polymer chains on the surface of Ag nanoparticles.

Heat sensitivity of photosynthetic electron transport varies during the day due to changes in sugars and osmotic potential

In water-stressed leaves, accumulation of neutral osmotica enhances the heat tolerance of photosynthetic electron transport. There are large diurnal and day-to-day changes in leaf sugar content because of variations in net photosynthetic production, respiration and retranslocation. To test the hypothesis that diurnal and day-to-day variations in leaf sugar content and osmotic potential significantly modify the responses to temperature of photosynthetic electron transport rate, we studied chlorophyll fluorescence rise temperatures (i.e. critical temperatures at break-points in fluorescence versus temperature response curves, corresponding to enhanced damage of PSII centers and detachment of pigment-binding complexes) in the dark at a background of weak far-red light (T(FR)) and under actinic light (T(L)), and responses of foliar photosynthetic electron transport rate to temperature using gas-exchange and chlorophyll fluorescence techniques in the temperate tree Populus tremula L. Sucrose and sorbitol feeding experiments demonstrated strong increases of fluorescence rise temperatures T(FR) and T(L) with decreasing leaf osmotic potential and increasing internal sugar concentration. Similar T(FR) and T(L) changes were observed in response to natural variation in leaf sugar concentration throughout the day. Increases in leaf sugar concentration led to an overall down-regulation of the rate of photosynthetic electron transport (J), but increases in the optimum temperature (Topt) of J. For the entire dataset, Topt varied from 33.8 degrees C to 43 degrees C due to natural variation in sugars and from 33.8 degrees C to 52.6 degrees C in the sugar feeding experiments, underscoring the importance of sugars in modifying the response of J to temperature. However, the correlations between the sugar concentration and fluorescence rise temperature varied between the days. This variation in fluorescence rise temperature was best explained by the average temperature of the preceding 5 or 6 days. In addition, there was a significant year-to-year variation in heat sensitivity of photosynthetic electron transport that was associated with year-to-year differences in endogenous sugar content. Our data demonstrate a diurnal variation in leaf heat tolerance due to changes in sugar concentration, but they also show that this short-term modification in heat tolerance is super-imposed by long-term changes in heat resistance driven by average temperature of preceding days.

Changes in Heat Resistance of the Muscle and Glycerinated Muscle Fibers of Green Toad (Bufo viridis complex)

Heat resistance of muscles and actomyosin proteins was determined at damaging temperatures of 41, 42, and 43 degrees C in three green toad (Bufo viridis complex) populations from different climatic zones of Uzbekistan. The highest muscle and model resistance to these temperatures was revealed in toads living in the warmest plain regions of the country, while the lowest resistance was specific for animals from the piedmont and mountain regions. The variability of heat resistance of the muscle and models was also the highest in toads of the first group. Divergence going in this animal species is proposed.

Changes in Heat Resistance Resulting from pH and Nutritional Shifts of Acid-Adapted and Non–Acid-Adapted Listeria monocytogenes Scott A

Stationary-phase Listeria monocytogenes cells that were either pH dependent acid adapted or not acid adapted were heat challenged at 60°C in a two-level full factorial design for three variables. The three variables and the levels consisted of tryptic soy broth (TSB) and sterile cell-free culture supernatant (sterile TSB), the presence and absence of 1% added glucose, and pH 4.8 and pH 7. Non–acid-adapted cells were most heat resistant when challenged in TSB (mean decimal reduction times at 60°C: D60 = 1.16 min). In the absence of added glucose, non–acid-adapted cells had similar D60-values for inactivations at pH 4.8 and pH 7; however, the presence of glucose caused non–acid-adapted cells challenged at pH 4.8 to be more heat sensitive (D60 = 0.65 min) than those inactivated at pH 7 (D60 = 1.03 min), indicating an interaction between glucose and pH. Overall, the significantly decreased heat resistance of the acid-adapted cells was due to the presence of glucose (D60 = 0.78 min without glucose, D60 = 0.59 min with glucose). Acid-adapted cells heat challenged in TSB had similar D60-values for inactivations at pH 4.8 and pH 7; however, acid-adapted cells in sterile TSB challenged at pH 4.8 (D60 = 0.52 min) had significantly lower heat resistance than did cells challenged at pH 7 (D60 = 0.76 min), indicating an interaction between the medium and pH. The L. monocytogenes survivor data were modeled to extract information on the frequency distribution of heat resistance within heat-challenged populations, and the frequency distribution characteristics of mean, mode, and variance were compared among treatment conditions. Significant differences in the frequency distribution data were compared with the D60-values. These data indicated that the presence and level of cross-protection is highly dependent on the physiological state of the cells and nutrient availability at the time of heat challenge. Such conditions should be considered to ensure that stressed pathogens in foods are destroyed or inactivated.

Ultradian rhythm of trehalose levels coupled to heat resistance in continuous cultures of the yeast Saccharomyces cerevisiae

Heat resistance appears to cycle in concert with energy metabolism in continuous culture of the yeast Saccharomyces cerevisiae. To study the mechanism of this oscillation, the authors first examined if heat shock proteins (Hsps) are involved. Neither the protein levels of major Hsps nor the expression of the β-galactosidase gene as a reporter under the control of the promoter carrying heat-shock element oscillated during the metabolic oscillation. The level of trehalose in yeast cycled with the same periodicity, as did energy metabolism. This oscillation was not found in a GTS1-deleted mutant that also did not show cyclic changes in heat resistance. These results suggest that heat resistance oscillation is induced by fluctuations in trehalose level and not by an oscillatory expression of Hsps. The increase in trehalose began at the start of the respiro-fermentative phase and the decrease began after the elevation of the cyclic adenosine monophosphate (cAMP) level. The authors hypothesize that the synthesis of trehalose parallels the activation of the glycolytic pathway and that trehalose is degraded by trehalase activated by cAMP coupled with the metabolic oscillation in the continuous culture of yeast.

The effect of culture growth phase on induction of the heat shock response in Yersinia enterocolitica and Listeria monocytogenes.

The effect of culture growth phase on induction of the heat shock response in Yersinia enterocolitica and Listeria monocytogenes, was examined. Exponential or stationary preconditioned cultures were heat shocked and survivor numbers estimated using selective and overlay/resuscitation recovery techniques. The results indicate that prior heat shock induced increased heat resistance in both micro-organisms to higher heat treatments. Heat-shocked cells of each micro-organism were able to survive much longer than non-heat-shocked cells when heated at 55 degrees C. The size of the change in heat resistance between heat-shocked and non-heat-shocked cells was greatest for exponential cultures (X:X). Results indicate that the overall relative thermal resistance of each pathogen was dependent on cell growth phase. Stationary cultures (S:S) were significantly (P < 0.01) more thermotolerant than exponential cultures (X:X) under identical processing conditions. Under most conditions, the use of an overlay/resuscitation recovery medium resulted in higher D-values (P < 0.05) compared with a selective recovery medium.