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Same Temperature (same + temperature)
Terms modified by Same Temperature Selected AbstractsKinetic studies on the influence of temperature and growth rate history on crystal growthCRYSTAL RESEARCH AND TECHNOLOGY, Issue 12 2008P. M. Martins Abstract Crystallization experiments of sucrose were performed in a batch crystallizer to study the effect of temperature and growth rate history on the crystal growth kinetics. In one of the growth methods adopted, the isothermal volumetric growth rate (RV) is determined as a function of supersaturation (S) at 35, 40 and 45 ºC. In the other, crystals are allowed to grow at constant supersaturation by automatically controlling the solution temperature as the solute concentration decreased. Using the latter method RV is calculated as the solution is cooled. The obtained results are interpreted using empirical, engineering and fundamental perspectives of crystal growth. Firstly, the overall activation energy (EA) is determined from the empirical growth constants obtained in the isothermal method. The concept of falsified kinetics, widely used in chemical reaction engineering, is then extended to the crystal growth of sucrose in order to estimate the true activation energy (ET) from the diffusion-affected constant, EA. The differences found in the isothermal and constant supersaturation methods are explained from the viewpoint of the spiral nucleation mechanism, taking into account different crystal surface properties caused by the growth rate history in each method. Finally, the crystal growth curve obtained in the batch crystallizer at 40 ºC is compared with the one obtained in a fluidized bed crystallizer at the same temperature. Apparently divergent results are explained by the effects of crystal size, hydrodynamic conditions and growth rate history on the crystallization kinetics of sucrose. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Influence of filling fat type on praline products with nougat fillingEUROPEAN JOURNAL OF LIPID SCIENCE AND TECHNOLOGY, Issue 12 2007Biljana Pajin Abstract The aim of this research was to examine the composition and functional characteristics of three samples of commercial filling fat intended for the making of nougat fillings for confectionary products. The crystallization rate of the fats was measured under static conditions using the NMR technique and under dynamic conditions as well as using a rotational rheometer. The functional characteristics of the fats were estimated by means of sensory values of the prepared praline product. Under the static conditions, all investigated filling fats showed a fast crystallization rate (,2,4%/min). The sample with the highest lauric acid contents started to crystallize immediately (no induction period). The longest induction period was found for the sample with the lowest saturated fatty acid and trans fatty acid contents. During the crystallization under dynamic conditions, all investigated samples started to crystallize more rapidly (rapid viscosity increase) at practically the same temperature (,17,°C). Measuring solid fat content and viscosity are two approaches of determining the suitability of a filling fat to be used in pralines. Both measurements provide valuable information, and particularly viscosity build-up is very important from the view of production on factory scale. [source] Cost-Affordable Technique Involving Equal Channel Angular Pressing for the Manufacturing of Ultrafine Grained Sheets of an Al,Li,Mg,Sc Alloy,ADVANCED ENGINEERING MATERIALS, Issue 8 2010Rustam Kaibyshev A two-step process consisting of modified equal channel angular pressing (ECAP) and subsequent isothermal rolling (IR) was developed to produce thin sheets of aluminum alloys with ultra-fine grained (UFG) structure. Significant increase in the efficiency of ECAP was attained by using flat billets and a back pressure system. The incorporation of final IR into technologic route provides a reduced strain which is necessary to impose for the fabrication of thin sheets with UFG structure. In addition, it allows producing relatively "long billets." In order to demonstrate the feasibility of this technique an Al,5.1Mg,2.1Li,0.17Sc,0.08Zr (wt %) alloy was subjected to ECAP at 325,°C to a total strain of ,8 using processing route CX. The operation time of this processing did not exceed 15,min. Subsequent IR at the same temperature with a total reduction of 88% was applied to produce thin sheets with a 1.8,mm thickness and an average size of recrystallized grains of ,1.6,µm. These sheets exhibit extraordinary high superplastic ductilities. In addition, this material demonstrated almost isotropic mechanical behavior at room temperature. The maximum elongation-to-failure of ,2700% was attained at a temperature of 450,°C and an initial strain rate of 1.4,×,10,2 s,1. Thus it was demonstrated that the two-step processing consisting of ECAP with a back pressure followed by IR was a simple technique providing potential capability for the fabrication of superplastic sheets from an Al,Mg,Li,Sc alloy on a commercial scale. [source] Liquid,vapour partition of ethanol in bakery productsFLAVOUR AND FRAGRANCE JOURNAL, Issue 1 2006Paola Pittia Abstract Ethanol is a common ingredient in formulated foods, naturally present or added in liquid form in order to achieve the desired sensorial properties. In many complex foods this volatile compound could also serve interesting technological functions, as well as extending their shelf-lives, owing to its capacity to inhibit or reduce the rate of microbial growth. At the European level there are no known restrictions regarding the use of ethanol in foods as a preservative, while in Italy, current regulations allow its addition as an anti-moulding agent in pre-packed bread, at a maximum concentration of 2% on a dry weight basis. This research studied the effect of water activity (aw) and water content on the ethanol vapour pressure of sliced white bread, previously equilibrated at various aw values and with 2% ethanol added. Different aw values were obtained by both rehydration from previously freeze-dried bread, and dehydration from the fresh product. The results showed that both aw and moisture affected the vapour pressure of ethanol as a consequence of water,solute and ethanol,solute interactions in the matrix. These interactions varied according to the modality of equilibration (desorption or absorption) at a given aw. The results are discussed in terms of ethanol activity (ae), computed as the ratio between the ethanol vapour pressure in bread and the vapour pressure of pure ethanol at the same temperature. This index, analogous to aw, proved to be useful in evaluating the ,freedom' of the ethanol present in a food matrix to be released in the vapour phase. Copyright © 2006 John Wiley & Sons, Ltd. [source] Temperature sensitivity and substrate quality in soil organic matter decomposition: results of an incubation study with three substratesGLOBAL CHANGE BIOLOGY, Issue 6 2010J. Å. MARTIN WETTERSTEDT Abstract Kinetic theory suggests that the temperature sensitivity of decomposition of soil organic matter should increase with increasing recalcitrance. This ,temperature,quality hypothesis' was tested in a laboratory experiment. Microcosms with wheat straw, spruce needle litter and mor humus were initially placed at 5, 15 and 25 °C until the same cumulative amount of CO2 had been respired. Thereafter, microcosms from each single temperature were moved to a final set of incubation temperatures of 5, 15 and 25 °C. Straw decomposed faster than needle litter at 25 and 15 °C, but slower than needle litter at 5 °C, and showed a higher temperature sensitivity (expressed as Q10) than needle litter at low temperatures. When moved to the same temperature, needle litter initially incubated at 5 and 15 °C had significantly higher respiration rates in the final incubation than litters initially placed at 25 °C. Mor humus placed at equal temperatures during the initial and final incubations had higher cumulative respiration during the final incubation than humus experiencing a shift in temperature, both up- and downwards. These results indicate that other factors than substrate quality are needed to fully explain the temperature dependence. In agreement with the hypothesis, Q10 was always higher for the temperature step between 5 and 15 °C than between 15 and 25 °C. Also in agreement with the temperature,quality hypothesis, Q10 significantly increased with increasing degree of decomposition in five out of the six constant temperature treatments with needle litter and mor humus. Q10s for substrates moved between temperatures tended to be higher than for substrates remaining at the initial temperature and an upward shift in temperature increased Q10 more than a downward shift. This study largely supports the temperature,quality hypothesis. However, other factors like acclimation and synthesis of recalcitrant compounds can modify the temperature response. [source] Elevated metabolic costs while resting on water in a surface feeder: the Black-legged Kittiwake Rissa tridactylaIBIS, Issue 1 2007ELIZABETH M. HUMPHREYS Measurements of the energy costs of individual behaviours provide insights into how animals trade-off resource allocation and energy acquisition decisions. The energetic costs while resting on water are poorly known for seabirds but could comprise a substantial proportion of their daily energy expenditure. We measured the cost of resting on water in Black-legged Kittiwakes Rissa tridactyla, a species which does not fly during the night and for which estimating energy expenditure while resting on the water is therefore important. Their resting metabolic rate on water at 12.5 °C was at least 40% higher compared with resting at the same temperature in air. This indicates that, at comparable temperatures, metabolic costs are elevated for birds resting at sea compared with on land. We argue that Kittiwakes meet much of this extra thermoregulatory demand by dedicated metabolic activity. During the winter months, their costs are likely to be even higher owing to lower sea temperatures. Accordingly, we suggest that migration to milder latitudes, following breeding, will provide enhanced benefits, particularly to seabirds such as Kittiwakes which rest on the sea surface during darkness. [source] Absorption kinetics of oxygen scavengersINTERNATIONAL JOURNAL OF FOOD SCIENCE & TECHNOLOGY, Issue 2 2002Gaurav Tewari The oxygen (O2) absorption kinetics of six commercial O2 scavengers were studied. The scavengers were placed in bags which were filled with 240 mL of air, 4.5 L N2 + 15 mL of air, or 3.5 L CO2 + 9 mL of air. The O2 concentration in each bag was measured at hourly intervals for 8 h. The effects of variability among individual scavengers, initial O2 concentrations of 20% or 500 ppm (0.05%), temperatures of 25, 12, 2 or ,1.5 °C, and scavenger capacity on the O2 absorption rate were determined. In addition, the effect of placing scavengers within over-wrapped trays within bags, was examined. Rates of O2 absorption varied by factors of up to 2 between individual O2 scavengers of the same type, but rates of absorption by groups of four scavengers of the same type were similar. Low temperatures gave longer O2 half-life when compared with those at higher temperatures, e.g. O2 half-lives of 7.1 and 1.0 h at ,1.5 and 25 °C, respectively, were obtained for one scavenger type. Shorter O2 half-lives were obtained in air than in N2 atmospheres at the same temperature, e.g. O2 half-lives of 1.0 and 3.3 h in air and N2 at 25 °C, respectively, were obtained for one scavenger type. The O2 absorption reactions were of first order for both high and low initial O2 concentrations. However, O2 concentration was the primary limiting factor for O2 absorption in atmospheres having O2 concentration of 500 ppm because of the dominance of diffusion. Scavengers, when placed within over-wrapped trays within bags had up to 12 times longer O2 half-lives, indicating that the O2 permeable film acts as an O2 barrier when pack atmosphere has low O2 concentrations. To obtain consistent and reproducible results, it is recommended that multiple scavengers be used in a packaging system. The appropriate number should be based on scavenger type, desired O2 absorption rate, storage temperature, and pack atmosphere (air/N2/CO2). [source] Synthesis of polymer-supported metal-ion complexes and evaluation of their catalytic activitiesJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2008K. C. Gupta Abstract Polymer-supported transition-metal-ion complexes of the N,N,-bis(o -hydroxy acetophenone) propylenediamine (HPPn) Schiff base were prepared by the complexation of iron(III), cobalt(II), and nickel(II) ions on a polymer-anchored N,N,-bis(5-amino- o -hydroxy acetophenone) propylenediamine Schiff base. The complexation of iron(III), cobalt(II), and nickel(II) ions on the polymer-anchored HPPn Schiff base was 83.44, 82.92, and 89.58 wt%, respectively, whereas the unsupported HPPn Schiff base showed 82.29, 81.18, and 87.29 wt % complexation of these metal ions. The iron(III) ion complexes of the HPPn Schiff base showed octahedral geometry, whereas the cobalt(II) and nickel(II) ion complexes were square planar in shape, as suggested by spectral and magnetic measurements. The thermal stability of the HPPn Schiff base increased with the complexation of metal ions, as evidenced by thermogravimetric analysis. The HPPn Schiff base showed a weight loss of 51.0 wt % at 500°C, but its iron(III), cobalt(II), and nickel(II) ion complexes showed weight losses of 27.0, 35.0, and 44.7 wt % at the same temperature. The catalytic activity of the unsupported and supported metal-ion complexes was analyzed by the study of the oxidation of phenol and epoxidation of cyclohexene in the presence of hydrogen peroxide. The supported HPPn Schiff base complexes of iron(III) ions showed a 73.0 wt % maximum conversion of phenol and 90.6 wt % epoxidation of cyclohexene, but unsupported complexes of iron(III) ions showed 63.8 wt % conversion of phenol and 83.2 wt % epoxidation of cyclohexene. The product selectivity for catechol (CTL) and epoxy cyclohexane (ECH) was 93.1 wt % and 98.1 wt % with the supported HPPn Schiff base complexes of iron(III) ions, but it was low with the supported Schiff base complexes of cobalt(II) and nickel(II) ions. The selectivity for CTL and ECH varied with the molar ratio of the metal ions but remained unaffected by the molar ratio of hydrogen peroxide to the substrate. The energy of activation for the epoxidation of cyclohexene and oxidation of phenol with the polymer-supported Schiff base complexes of iron(III) ions was 10.0 and 12.7 kJ/mol, respectively, but it was found to be higher with the supported HPPn Schiff base complexes of cobalt(II) and nickel(II) ions and with the unsupported HPPn Schiff base complexes of iron(III), cobalt(II), and nickel(II) ions. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci 2008 [source] Energy reserves during food deprivation and compensatory growth in juvenile roach: the importance of season and temperatureJOURNAL OF FISH BIOLOGY, Issue 1 2005P. L. M. Van Dijk The effect of 21 days of starvation, followed by a period of compensatory growth during refeeding, was studied in juvenile roach Rutilus rutilus during winter and summer, at 4, 20 and 27° C acclimation temperature and at a constant photoperiod (12L : 12D). Although light conditions were the same during summer and winter experiments and fish were acclimated to the same temperatures, there were significant differences in a range of variables between summer and winter. Generally winter fish were better prepared to face starvation than summer fish, especially when acclimated at a realistic cold season water temperature of 4° C. In winter, the cold acclimated fish had a two to three-fold larger relative liver size with an approximately double fractional lipid content, in comparison to summer animals at the same temperature. Their white muscle protein and glycogen concentration, but not their lipid content, were significantly higher. Season, independent of photoperiod or reproductive cycle, was therefore an important factor that determined the physiological status of the animal, and should generally be taken into account when fish are acclimated to different temperature regimes. There were no significant differences between seasons with respect to growth. Juvenile roach showed compensatory growth at all three acclimation temperatures with maximal rates of compensatory growth at 27° C. The replenishment of body energy stores, which were utilized during the starvation period, was responsible for the observed mass gain at 4° C. The contribution of the different energy resources (protein, glycogen and lipid) was dependent on acclimation temperature. In 20 and 27° C acclimated roach, the energetic needs during food deprivation were met by metabolizing white muscle energy stores. While the concentration of white muscle glycogen had decreased after the fasting period, the concentrations of white muscle lipid and protein remained more or less constant. The mobilization of protein and fat was revealed by the reduced size of the muscle after fasting, which was reflected in a decrease in condition factor. At 20° C, liver lipids and glycogen were mobilized, which caused a decrease both in the relative liver size and in the concentration of these substrates. Liver size was also decreased after fasting in the 4° C acclimated fish, but the substrate concentrations remained stable. This experimental group additionally utilized white muscle glycogen during food deprivation. Almost all measured variables were back at the control level within 7 days of refeeding. [source] IMPINGEMENT DRYING OF POTATO CHIPSJOURNAL OF FOOD PROCESS ENGINEERING, Issue 1 2002ALINE T. CAIXETA ABSTRACT The effect of superheated steam temperature (115, 130, and 145C) and convective heat transfer coefficient (100 and 160 W/m2C) on the drying rate and product quality attributes (shrinkage, density, porosity, color, texture, and nutrition loss) of potato chips was investigated. Furthermore, potato chips dried by impinging superheated steam (130 and 145C, h = 100 W/m2C) were compared to air dried (same conditions), commercial, and fried potato chips. Temperature and convective heat transfer coefficient had a significant effect on the drying rate during superheated steam impingement drying. Potato chips dried at higher drying temperature and convective heat transfer coefficient showed less shrinkage, lower bulk density, higher porosity, and darker color when compared to chips dried at lower temperatures and convective heat transfer coefficients. They were also less hard and had a lower vitamin C content. A higher rate of evaporation during the falling rate period was obtained when superheated steam drying was compared to air impingement drying. Potato chips produced using superheated steam impingement drying showed more shrinkage, higher bulk density, lower porosity, and lighter color than chips dried with air under the same temperature and with the same convective heat transfer coefficient (130, and 145C, h = 100 W/m2C). Moreover, superheated steam-dried potato chips retained more vitamin C during the drying process. [source] EFFECT OF CaCl2 AND CONVECTIVE-OSMOTIC DRYING ON TEXTURE AND PREFERENCE OF APPLEJOURNAL OF FOOD QUALITY, Issue 6 2006L.A. OCHOA-MARTÍNEZ ABSTRACT Conventional air-drying combined with osmotic dehydration was researched as a potential method for drying apple cubes of superior quality. Samples were pretreated with CaCl2 at different temperatures and times. Pretreated apple cubes were dehydrated in a tray dryer. Then, osmotic dehydration with sucrose solutions was carried out. The curves for osmotic dehydration showed that the gain of solids was higher when 40% of water was removed by convective drying while the loss of weight was lower at the same level of dehydration at 65°Brix. Texture measurements indicated that the temperature of pretreatment affected the hardness and cohesiveness. Hardness values were higher at 40C, while cohesiveness values were lower at the same temperature. The CaCl2 at a given temperature did not have a significant effect on texture. Sensory evaluation showed that samples pretreated at 25C and osmotically dried at 50°Brix had the higher preference by the judges. [source] Effect of Temperature (,5 to 130 °C) and Fiber Direction on the Dielectric Properties of Beef Semitendinosus at Radio Frequency and Microwave FrequenciesJOURNAL OF FOOD SCIENCE, Issue 6 2008N. Basaran-Akgul ABSTRACT:, The dielectric properties must be defined to design efficient radio frequency (RF) and microwave (MW) processes by the food manufacturers. The objective of this study was to understand how frequency, temperature, and muscle fiber orientation influence the dielectric properties. The eye of round (Semitendinosus) muscle was selected because it contains large, relatively uniform muscle cells with similar muscle fiber orientation and relatively uniform chemical composition throughout the tissue. Dielectric properties were measured using an open-ended coaxial probe technique at 27, 915, and 1800 MHz and temperatures between ,5 and 130 °C. Power penetration depth was calculated. Since many commercially prepared, thermally processed, ready-to-eat entrees are made with frozen meat, dielectric property measurements were started from ,5 °C. The dielectric constant and dielectric loss factors were often higher for muscle with the muscle fiber measured in a parallel orientation to the probe compared to samples of the same treatment (for example, fresh or frozen) in a perpendicular tissue orientation at the same frequency and temperature. Dielectric constant and loss values for frozen beef tended to be higher than fresh beef at the same temperature and frequency. Tissue orientation appeared to have a greater effect on dielectric loss values at lower frequencies. Penetration depth tended to be greater when the direction of propagation was perpendicular to the muscle fiber. [source] Inactivation of Shigella boydii 18 IDPH and Listeria monocytogenes Scott A with Power Ultrasound at Different Acoustic Energy Densities and TemperaturesJOURNAL OF FOOD SCIENCE, Issue 4 2007Edgar Ugarte-Romero ABSTRACT:, The effect of acoustic energy density (AED) on inactivation of Shigella boydii 18 IDPH and Listeria monocytogenes Scott A in a cell suspension was studied at sublethal temperatures and at AEDs of 0.49, 0.85, and 1.43 W/mL. The effect of temperature on ultrasonic inactivation of L. monocytogenes Scott A at 35, 50, and 65 °C was examined at an AED of 1.43 W/mL. Increasing AED increased the rate of inactivation for both S. boydii and L. monocytogenes. The destruction of S. boydii and L. monocytogenes followed 1st order kinetics in a 20-min treatment, except for S. boydii inactivation at 1.43 W/mL where a tailing effect was observed after 15 min. At sublethal temperatures, the D-values of S. boydii were 8.8, 4.3, and 2.5 min for AEDs of 0.49, 0.85, and 1.43 W/mL, whereas those for L. monocytogenes at the 3 AED levels were 31.5, 13.5, and 7.3 min, respectively. Ultrasonic treatment of L. monocytogenes at 35 and 50 °C enhanced inactivation. However, at 65 °C, application of ultrasound did not result in additional inactivation compared to thermal treatment alone at the same temperature. With the experimental conditions and the ultrasound system used in this study, an upper temperature limit for thermosonication was evident above which no added killing due to ultrasound was observed. [source] Diffusion-controlled growth of wollastonite rims between quartz and calcite: comparison between nature and experimentJOURNAL OF METAMORPHIC GEOLOGY, Issue 5 2002R. Milke Abstract Growth rates of wollastonite reaction rims between quartz and calcite were experimentally determined at 0.1 and 1 GPa and temperatures from 850 to 1200 °C. Rim growth follows a parabolic rate law indicating that this reaction is diffusion-controlled. From the rate constants, the D,,-values of the rate-limiting species were derived, i.e. the product of grain boundary diffusion coefficient D, and the effective grain boundary width, ,. In dry runs at 0.1 GPa, wollastonite grew exclusively on quartz surfaces. From volume considerations it is inferred that (D,CaO,)/(D,SiO2,),1.33, and that SiO2 diffusion controls rim growth. D,SiO2, increases from about 10,25 to 10,23 m3 s,1 as temperature increases from 850 to 1000 °C, yielding an apparent activation energy of 330±36 kJ mol,1. In runs at 1 GPa, performed in a piston-cylinder apparatus, there were always small amounts of water present. Here, wollastonite rims always overgrew calcite. Rims around calcite grains in quartz matrix are porous and their growth rates are controlled by a complex diffusion-advection mechanism. Rim growth on matrix calcite around quartz grains is controlled by grain boundary diffusion, but it is not clear whether CaO or SiO2 diffusion is rate-limiting. D,, increases from about 10,21 to 10,20 m3 s,1 as temperature increases from 1100 to 1200 °C. D,SiO2, or D,CaO, in rims on calcite is c. 10 times larger than D,SiO2, in dry rims at the same temperature. Growth structures of the experimentally produced rims are very similar to contact-metamorphic wollastonite rims between metachert bands and limestone in the Bufa del Diente aureole, Mexico, whereby noninfiltrated metacherts correspond to dry and brine-infiltrated metacherts to water-bearing experiments. However, the observed diffusivities were 4 to 5 orders of magnitude larger during contact-metamorphism as compared to our experimental results. [source] Molecular dynamics simulations of hydrotropic solubilization and self-aggregation of nicotinamideJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 7 2010Yong Cui Abstract Hydrotropy is a phenomenon where the presence of a large quantity of one solute enhances the solubility of another solute. The mechanism of this phenomenon remains elusive and a topic of debate. This study employed molecular dynamics simulation to investigate the hydrotropic mechanism of a model system consisting of a hydrotropic agent, nicotinamide (NA), a poorly water-soluble solute, PG-300995 (PG), and water. Our study demonstrates that NA and PG undergo significant aggregation in the aqueous solution, a result correlating closely to the self-aggregation of NA under the same conditions. The correlations are found both structurally and dynamically, suggesting that the self-aggregation of NA may be a prerequisite, or at least a major contributor, to its hydrotropic effects. The self-aggregation of NA allows the segregation of the hydrophobic solute from water, a key step to ease the energy increase to the system. Energetic evidences directly show that the hydrotropic solubilization is favored in the presence of NA aggregation. These results are in strong support of the molecular aggregation hypothesis for hydrotropic solubilization. Additionally, it is found that the restoration of water,water HBs from the interference of the NA and PG molecules plays an important role for the aggregation. The HBs between the solute and the hydrotrope may contribute, but is not vital, to the aggregation and hence the hydrotropic effects. The dynamic data confirm that the aggregates, while remain in liquid state, are much more active dynamically than a pure NA amorphous/liquid phase under the same temperature and pressure. By equilibrating an NA amorphous agglomerate with water, it is found that the aggregation state, rather than an NA,water two phase system, is the equilibrium state of the NA,+,water system. © 2010 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 99:3048,3059, 2010 [source] TEMPERATURE INDUCED PHOTOINHIBITION IN OUTDOOR CULTURES OF MONODUS SUBTERRANEUSJOURNAL OF PHYCOLOGY, Issue 2000A. Vonshak Outdoor algal cultures are continuously exposed to changes in environmental conditions, particularly irradiance and temperature. While the changes in light intensity take place in a range of one to two hours, the increase in temperature is a slower process and takes about four to five hours. This de-synchronization between the two important environmental factors governing photosynthesis and growth of algae results in a unique stress condition where photoinhibition can be induced at relatively low light intensity. Outdoors the early morning culture temperature was found to be about 12 to 14° C, and reaches 25 to 28° C at mid-day. In an experiment, such a natural temperature regime was compared to another one in which the morning temperature of the culture was increased to 20° C by using a heating system. A fast decline in the maximal photochemical efficiency of PSII (Fv/Fm) was observed starting as soon as sunrise. The decline was faster in the non-heated culture and was to a lower value. The diurnal changes in the electron transfer rate (ETR) and in the non-photochemical quenching (NPQ) of the cultures, indicated that the early morning exposure of cells to sub-optimal temperature results in a fast inactivation of PSII activity which was reflected in an inhibition of the photosynthetic activity even when the two cultures finally reached the same temperature at mid-day. Thus, under the same light and temperature mid-day conditions the ETR was higher and the NPQ was significantly lower in the heated culture. Significant changes in productivity of the cultures also were observed. [source] Propylene polymerization with nickel,diimine complexes containing pseudohalidesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 1 2006Marcos L. Dias Abstract DADNiX2 nickel,diimine complexes [DAD = 2,6- iPr2C6H3NC(Me)C(Me)N2,6- iPr2C6H3] containing nonchelating pseudohalide ligands [X = isothiocyanate (NCS) for complex 1 and isoselenocyanate (NCSe) for complex 2] were synthesized, and the propylene polymerization with these complexes and also with the Br ligand (X = Br for complex 3) activated by methylaluminoxane (MAO) were investigated (systems 1, 2, and 3/MAO). The polypropylenes obtained with systems 1, 2, and 3 were amorphous polymers and had high molecular weights and narrow molecular weight distributions. Catalyst system 1 showed a relatively high activity even at a low Al/Ni ratio and reached the maximum activity at the molar ratio of Al/Ni = 500, unlike system 3. Increases in the reaction temperature and propylene pressure favored an increase in the catalytic activity. The spectra of polypropylenes looked like those of propylene,ethylene copolymers containing syndiotactic propylene and ethylene sequences. At the same temperature and pressure, system 2 presented the highest number of propylene sequences, and system 3 presented the lowest. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 458,466, 2006 [source] Living radical polymerization of vinyl chloride initiated with iodoform and catalyzed by nascent Cu0/tris(2-aminoethyl)amine or polyethyleneimine in water at 25 °C proceeds by a new competing pathways mechanismJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 21 2003Virgil Percec Abstract The first example of living radical polymerization of vinyl chloride carried out in water at 25 °C is reported. This polymerization was initiated by iodoform and catalyzed by nascent Cu0 produced by the disproportionation of CuI in the presence of strongly CuII binding ligands such as tris(2-aminoethyl)amine or polyethyleneimine. The resulting poly(vinyl chloride) was free of structural defects, had controlled molecular weight and narrow molecular weight distribution, contained two ,CHClI active chain ends, and had a higher syndiotacticity (62%) than the one obtained by conventional free-radical polymerization at the same temperature (56%). This novel polymerization proceeds, most probably, by a combination of competitive pathways that involves activation by single electron transfer mediated by nascent Cu0 and degenerative chain transfer. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3283,3299, 2003 [source] PHYSICAL, SENSORY AND FLOW PROPERTIES OF WHEAT STARCH,DAIRY BY-PRODUCT SPRAY-DRIED PEKMEZ MIXTURESJOURNAL OF TEXTURE STUDIES, Issue 2 2008DURMU ABSTRACT Pekmez, also known as a concentrated grape juice, was spray dried in a laboratory-type pilot drying unit to obtain pekmez powder (PP). The flow characteristics of PP, wheat starch (WS) and some dairy by-products (whey powder, skim milk powder, calcium caseinate and sodium caseinate) systems as binary and ternary mixtures were studied. The empirical power law model fitted the apparent viscosity,rotational speed data. PP,dairy by-product and WS,dairy by-product mixed solutions exhibited a shear-thinning behavior at 21C with flow behavior index (n) values of 0.86 , n , 0.92 and 0.06 , n , 0.27, respectively. WS,dairy by-product mixed solutions showed high shear-thinning behavior with the highest consistency index (k = 25,425,180,599 mPa·sn). However, PP,WS and PP,WS,dairy by-product mixed solutions at the same temperature exhibited the shear-thickening behavior with flow behavior index (n) values of 1.05 , n , 1.18. PRACTICAL APPLICATIONS Pekmez has become popular as a healthy food product; therefore, its rheologic properties were extensively studied by some researchers. However, pekmez powder (PP) is a new product and has not been produced yet in the food industry. Spray drying of foods has been spread recently in almost all food industry branches because it provides some advantages such as extending the shelf life, storage stability, decreasing the storage costs of the food products, etc. For this reason, production technology is first developed; PP is produced and studied in this study. There is no published data informing the rheologic, physical and sensory properties of pekmez or PP as binary and ternary mixtures with other components such as wheat starch (WS) and any dairy by-product. The purpose of this study was mainly to characterize the rheologic behavior of the PP,WS,dairy by-product mixed solutions and determine their physical and sensory properties. [source] Reproducible Solvent,Thermal Synthesis, Controlled Microstructure, and Photoluminescence of REPO4:Eu3+, Tb3+ (RE=Y, La, and Gd) NanophosphorsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2010Xiuzhen Xiao By altering the temperature and solvents, we have synthesized hydrated and dehydrated Eu3+/Tb3+ -doped REPO4 (RE=Y, La, and Gd) nanophosphors via a solvo-thermal technology. X-ray powder diffraction and scanning electronic microscopy reveal that they have different structures and different morphologies. REPO4 prepared under subsequent heating at 80°, 120°, and 160°C for 1 day, respectively, present larger particle size than that formed by heating at 160°C for 3 days. Moreover, at the same temperature of 160°C and pH 3, three different solvents (ethanol, N,N -dimethylformamide (DMF), and water) were used, whose influence on the microstructure of LaPO4 has been examined. As a result, LaPO4 samples from anhydrous ethanol solvent show a pure hexagonal phase and nanowire morphology, just like that prepared from the water solvent. On the other hand, the microstructure of LaPO4 samples from DMF,H2O-mixed solvents have been changed: with the increasing volume ratio of DMF to H2O, the crystal phase of LaPO4 has been changed from hexagonal phase to monoclinic phase and the morphology from nanowires to nanoparticles. Finally, the photoluminescence properties of these Eu3+ (Tb3+)-activated rare earth phosphates have been investigated, indicating that the photoluminescent behavior are related to their crystal phases and microstructures. [source] Crack Healing Behavior of Silicon Carbide CeramicsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2000Jan Korou This study focuses on the crack healing behavior of three kinds of commercial SiC ceramics. Specimens with and without cracks were subjected to thermal treatment at different temperatures, and their strengths were measured by a three-point bending test in accordance with JIS standards. The tests were performed in air at both room temperature and elevated temperatures between 600° and 1500°C. The healed specimens showed a complete recovery of strength at room temperature for the investigated crack sizes of 2c, 100 ,m and 2c, 200 ,m, and their strength increased in accordance with the healing temperature. The behavior of the healed specimens at elevated temperatures was influenced by the material used and the test temperature. Generally, the strength decreased at a high temperature, but the degree of strength reduction was determined by the kind of ceramic. The most important difference between the healed and smooth specimens was exhibited in material A. It was observed that at 1400°C, the bending strength of the healed specimens made from this ceramic was about 37% of the value for specimens in an as-received state. Static fatigue tests were also performed for ceramic B at 900° and 1000°C. The experiment demonstrated that the static fatigue limit of a healed specimen is about 75% of the monotonic bending strength at the same temperature. [source] Using pit solution chemistry for evaluation of metastable pitting stability of austenitic stainless steelMATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 3 2005M. H. Moayed Abstract The stability of a corrosion pit is directly related to the pit solution chemistry. In order to know the stability of a meastable pit, the product of corrosion current density and diffusion depth (pit radius for an open hemisphere pit) is compared to the stability product obtained from the artificial pit electrode results. In this paper the stability of a metastable pit recorded on a 904L stainless at 54°C (2°C below the alloy CPT) is investigated. Assuming the geometry result of such a transient is an open hemisphere, pick current density and pit radius were calculated from Faraday's equation and then pit stability product (i·a) was calculated. This value was compared with the product of i·a associated with the pit solution chemistries (critical, saturation and supersaturation concentrations) which were obtained from the investigation on artificial pit electrode at the same temperature. SEM investigations on pit cavity generated from large metastable pit current transients with the stability product greater than the stability product associated with supersaturation concentration of pit environment proves that measured pit solution chemistry from artificial pit electrode is a reliable step for evaluation of pit stability. [source] Quantifying oxygen diffusion in paraffin oil used in oocyte and embryo cultureMOLECULAR REPRODUCTION & DEVELOPMENT, Issue 12 2009Yvonne M. StokesArticle first published online: 11 AUG 200 Oxygen diffusion through oil is important in the culture of oocytes and embryos. A diffusion coefficient two orders of magnitude smaller than that of oxygen in water has been thought possible, and this has led to concerns of anoxia in cultures. Using an assay for determining the oxygen consumption rate of embryos and oocytes, along with a mathematical model, it is here shown that the oxygen diffusion rate in paraffin oil at 37°C is about two-thirds of that in water at the same temperature. Although not previously recognised for the assay in question, the geometry is such that anoxia does occur for a period of time in excess of 1,hr and, by the completion of the assay, 30,40% of the medium is anoxic. Hence the quantity of oxygen consumed is less than would be consumed in conditions of plentiful oxygen supply. Nevertheless, using a model with a concentration dependent oxygen consumption rate, the oxygen consumption rate can be estimated. Mol. Reprod. Dev. 76: 1178,1187, 2009. © 2009 Wiley-Liss, Inc. [source] SWNT probed by multi-frequency EPR and nonresonant microwave absorptionPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 10 2008B. Corzilius Abstract In addition to g = 2.00 signals seen frequently in EPR spectra of SWNT, signals at g = 2.07 of SWNT prepared by CVD were detected, exhibiting a Pauli susceptibility temperature dependence. This Pauli magnetism in combination with the large g shift is taken as evidence that these signals originate from itinerant electrons of metallic nanotubes. At temperatures below 150 K, a dominant narrow signal develops at g = 2.00. By applying multifrequency EPR up to 319 GHz, its inhomogeneous nature was confirmed. This signal is assigned to defects of the carbon network of the tubes. Comparing room temperature EPR spectra of CVD and arc-grown SWNT, we found a much lower concentration of metallic tubes in arc material. No g = 2.07 signals of itinerant spins could be observed, which might be also caused by the high amount of residing catalyst. A drastic increase in nonresonant microwave absorption is observed below 10 K for both types of samples, if a threshold microwave power level is passed. In the same temperature range a drop in EPR intensity is also detected. These observations are taken as evidence for a transition into a superconducting phase of part of the sample. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Growth of A -plane (11-20) In-rich InGaN on R -plane (10-12) sapphire by RF-MBEPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2007M. Noda Abstract Non-polar A -plane (11-20) high In content (In-rich) InGaN was grown on R -plane (10-12) sapphire with an InN template by radio-frequency plasma assisted molecular beam epitaxy (RF-MBE). Nitridation of R -plane sapphire was carried out at 300 °C for 2 hours by RF-nitrogen plasma. A template of A -plane InN was grown at 400 °C. The In-rich InGaN films were then grown at the same temperature on the InN template. We characterized the films using reflection high-energy electron diffraction (RHEED), X-ray diffraction (XRD), scanning electron microscopy (SEM) and photo-luminescence (PL). These results indicated clearly that non-polar In0.71Ga0.29N was successfully obtained with a PL emission at approximately 1.1 eV. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Growth of InGaN quantum dots on GaN by MOVPE, employing a growth temperature nitrogen annealPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2003R. A. Oliver Abstract We have studied the growth of InGaN epitaxial layers on GaN by MOVPE (metal-organic vapour phase epitaxy), and have discovered that nanostructures may be formed if a flat epilayer is annealed in molecular nitrogen immediately after growth. The size and density of the nanostructures are shown to be dependent on the growth/anneal temperature. We demonstrated the quantum dot nature of our nanostructures by performing spatially resolved photoluminescence on samples that had been capped with a layer of GaN, grown at the same temperature as the InGaN epilayer. This revealed narrow, delta-function-like lines in the luminescence spectrum with full width at half maximum (FWHM) limited by the resolution of the spectrometer at 4.2 K. Measurement of the FWHM as a function of temperature revealed significant broadening above 20 K. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Effects of thermoperiods on diapause induction in the cabbage beetle, Colaphellus bowringi (Coleoptera: Chrysomelidae)PHYSIOLOGICAL ENTOMOLOGY, Issue 5 2004Xiao-Ping Wang Abstract., The effects of thermoperiods on diapause induction in continuous darkness or under a 12 : 12 h LD photoperiod were investigated in the cabbage beetle, Colaphellus bowringi Baly, a typical short-day species. The diapause response curves both at different constant temperatures and at the thermocycle of format CT x: (24 , x) h (16 : 28 °C) under continuously dark rearing conditions showed that the incidence of diapause depended mainly on whether or not the mean temperature was ,20 °C or >20 °C. If the mean temperature was ,20 °C, all individuals entered diapause; if >20 °C, the incidence of diapause declined gradually with increasing mean temperatures. The thermocycle (CT 12 : 12 h) with a series of different cryophases (8,22 °C) and thermophases (24,32 °C) under continuous darkness demonstrated a cryophase response threshold temperature of approximately 19 °C and a thermophase response threshold temperature of approximately 31 °C. Thermoperiodic amplitude (temperature difference between cryophase and thermophase) was shown to have a significant influence on diapause induction at the mean temperatures of 22, 23 and 24 °C, but not at ,25 °C. Thermoperiodic responses under LD 12 : 12 h clearly showed that the incidence of diapause was influenced strongly by the photophase temperature. The thermoperiod under LD 12 : 12 h induced a much lower incidence of diapause than the thermoperiod with the same temperature in continuous darkness. The ecological significance of thermoperiodic induction of diapause in this species is discussed. [source] Implications of foliar terpene content and hydration on leaf flammability of Quercus ilex and Pinus halepensisPLANT BIOLOGY, Issue 1 2008G. A. Alessio Abstract We investigated the implications of foliar hydration and terpene content on leaf flammability in two widely distributed forest species of the Mediterranean basin, Quercus ilex, which does not store terpenes, and Pinus halepensis, a terpene-storing species. The experiments were carried out in plants grown under different water regimes that generated a wide range of foliar hydration and terpene contents. We monitored the temperatures and time elapsed to reach the smoke, pyrolysis and flame phases. Smoke appeared much earlier (37 versus 101 s) and at lower temperatures (96 versus 139 °C) in Quercus ilex than in Pinus halepensis. Quercus ilex reached pyrolysis earlier than Pinus halepensis (278 versus 338 s) but at the same temperature (365,371 °C). There were no significant differences in time elapsed nor in temperature for flammability (386,422 s; 505,487 °C in both species). Quercus ilex had lower water hydration than Pinus halepensis (41 versus 100%) and the leaf content of terpenes in Quercus was three orders of magnitude lower. The results of this study show no differences in the flame phase between the two species and the absence of a significant relationship between temperature and elapsed time of the different flammability phases in relation to monoterpene content; thus indicating that the role of monoterpenes in flammability phases is smaller than that of the water content. This, however, does not exclude the effects of terpene content on plant combustibility and fire propagation once fires start. [source] Sub-optimal morning temperature induces photoinhibition in dense outdoor cultures of the alga Monodus subterraneus (Eustigmatophyta)PLANT CELL & ENVIRONMENT, Issue 10 2001A. Vonshak Abstract Diel changes in photosynthetic oxygen evolution and several photochemical parameters measured by chlorophyll fluorescence quenching and induction were measured in outdoor dense cultures of the alga Monodus subterraneus (Eustigmatophyta). Cultures were maintained under two temperature regimes. In one, a rise in temperature was initiated in the morning by the increase in solar radiation up to the optimal temperature of 28 °C; in the other, a heating device was used to increase the rate of warming up in early morning. Although the two cultures were maintained at the same temperature and light intensity for most of the day, cultures exposed for only a short time to suboptimal morning temperature showed a larger decrease in almost all the photosynthetic parameters. By comparing the diel changes in maximal photochemistry efficiency of photosystem II, the electron transport rate and the photochemical and non-photochemical chlorophyll fluorescence quenching of the cultures, we concluded that even a relatively short exposure to suboptimal morning temperatures induced photoinhibitory damage. The higher photochemical activity of the heated culture was also reflected in a significant increase in productivity, which was 60% higher in the morning heated cultures than in the non-heated cultures. [source] Environmental stress cracking of a chemical nature in a PBT/PBA co-poly(ester ester)POLYMER ENGINEERING & SCIENCE, Issue 7 2004N. B. Kuipers The Environmental Stress Cracking (ESC) of a poly(butylene terephthalate)/poly(butylene adipate) (PBT/PBA) copoly(ester ester) was studied by constant-load time-to-failure (TTF) tests performed on sharply notched tensile specimens in water and phosphoric acid solution at 353 K. For comparison, tests were also performed in air at the same temperature. It was found that the time to failure is significantly reduced both in water and in an acid solution as compared with air. ESC implies a mutual intensification of the destructive effect of loading and environment. Owing to the intrinsic hydrolytic instability of polyesters, a failure mechanism due to hydrolysis has to be excluded here to prove the ESC. Therefore the ESC test results are compared with measurements of the exclusive influence of hydrolysis on the degradation of mechanical properties. It was found that the PBT/PBA copoly(ester ester) tested is susceptible to environmental stress cracking in water and even more in a phosphoric acid solution, both at 353 K. From the comparison of the influence of water and a phosphoric acid solution on the time to failure, it was concluded that the ESC of PBT/PBA copoly(ester ester) in a phosphoric acid solution is mainly of a chemical nature. Polym. Eng. Sci. 44:1319,1327, 2004. © 2004 Society of Plastics Engineers. [source] | ||||||||||||||||||||||