The glass transition temperature of mixtures of trehalose and hydroxyethyl starch

Although mixtures of HES and sugars are used to preserve cells during freezing or drying, little is known about the glass transition of HES, or how mixtures of HES and sugars vitrify. These difficulties may be due to the polydispersity between HES samples or differences in preparation techniques, as well as problems in measuring the glass transition temperature (T(g)) using differential scanning calorimetry (DSC). In this report, we examine the T(g) of mixtures of HES and trehalose sugar with <1% moisture content using DSC measurements. By extrapolating these measurements to pure HES using the Gordon-Taylor and Fox equations, we were able to estimate the T(g) of our HES sample at 44 degrees C. These results were additionally confirmed by using mixtures of glucose-HES which yielded a similar extrapolated T(g) value. Our approach to estimating the glass transition temperature of HES may be useful in other cases where glass transitions are not easily identified.     

Calorimetric studies on dry pectinlyase preparations: impact of glass transition on inactivation kinetics

The glass transition temperature (T(g)) of a dry ultrafiltrated pectinlyase (PL) preparation decreased from 56 to 24 degrees C when water content increased to 20%. The thermal transition temperature (T(p)) for protein denaturation decreased greatly up to 40% moisture; above 40% no further changes in T(p) were observed. In the glassy state, a lag period of approximately 7 days with no PL activity loss was observed; after that, PL activity was lost. Above T(g), the rates of PL inactivation greatly increased. In the glassy state E(a) was 16.6 kJ/mol. When the system was in a higher mobility state (rubbery), E(a) increased to 66.5 kJ/mol.     

The glass transition temperatures of amorphous trehalose-water mixtures and the mobility of water: an experimental and in silico study

Isothermal-isobaric molecular dynamics simulations are used to calculate the specific volume of models of trehalose and three amorphous trehalose-water mixtures (2.9%, 4.5% and 5.3% (w/w) water, respectively) as a function of temperature. Plots of specific volume versus temperature exhibit a characteristic change in slope when the amorphous systems change from the glassy to the rubbery state and the intersection of the two regression lines provides an estimate of the glass transition temperature T(g). A comparison of the calculated and experimental T(g) values, as obtained from differential scanning calorimetry, shows that despite the predicted values being systematically higher (about 21-26K), the trend and the incremental differences between the T(g) values have been computed correctly: T(g)(5.3%(w/w))相似文献   

Estimating the size of European rabbits consumed by predators: Relationship between body mass and tooth dimensions

A method for estimating body mass of European rabbitsOryctolagus cuniculus (Linnaeus, 1758) based on tooth dimensions is proposed. Regression models identified significant relationships between the body mass of 87 rabbits and individual tooth length, breadth, product of tooth length and breadth, and whether or not the individual was infected with myxomatosis. Dimensions of 10 of 14 different teeth explained over 80% of variation in body mass, and those teeth were selected as adequate predictors of rabbit body mass. Models were tested using teeth from 16 additional rabbits of known body mass. Body mass, predicted on the basis of 9 of the 10 selected teeth, was statistically indistinguishable from the observed values for all 16 individuals. When myxomatosis infection status of the rabbit was included in the model, all 10 selected teeth yielded predictions statistically indistinguishable from those observed. Prediction errors can be computed permitting statistical comparison of the average predicted value of body mass from different samples of rabbits. The model is useful in estimating rabbit body masses from teeth recovered from feces of predators and it will facilitate testing of hypotheses on size-selective predation. The method was applied to rabbit teeth found in fecal samples from the Iberian lynxLynx pardinus collected over a one-year period. Lynx preyed preferentially upon younger rabbits during the peak breeding period of this lagomorph.     

Glass transition and enthalpy relaxation of amorphous lactose glass

The glass transition temperature, T(g), and enthalpy relaxation of amorphous lactose glass were investigated by differential scanning calorimetry (DSC) for isothermal aging periods at various temperatures (25, 60, 75, and 90 degrees C) below T(g). Both T(g) and enthalpy relaxation were found to increase with increasing aging time and temperature. The enthalpy relaxation increased approximately exponentially with aging time at a temperature (90 degrees C) close to T(g) (102 degrees C). There was no significant change observed in the enthalpy relaxation around room temperature (25 degrees C) over an aging period of 1month. The Kohlrausch-Williams-Watts (KWW) model was able to fit the experimental enthalpy relaxation data well. The relaxation distribution parameter (beta) was determined to be in the range 0.81-0.89. The enthalpy relaxation time constant (tau) increased with decreasing aging temperature. The observed enthalpy relaxation data showed that molecular mobility in amorphous lactose glass was higher at temperatures closer to T(g). Lactose glass was stable for a long time at 25 degrees C. These findings should be helpful for improving the processing and storage stability of amorphous lactose and lactose containing food and pharmaceutical products.     

Numerical modeling and uncertainties in rate coefficients for methane utilization and TCE cometabolism by a methane-oxidizing mixed culture

The rates of methane utilization and trichloroethylene (TCE) cometabolism by a methanotrophic mixed culture were characterized in batch and pseudo-steady-state studies. Procedures for determination of the rate coefficients and their uncertainties by fitting a numerical model to experimental data are described. The model consisted of a system of differential equations for the rates of Monod kinetics, cell growth on methane and inactivation due to TCE transformation product toxicity, gas/liquid mass transfer of methane and TCE, and the rate of passive losses of TCE. The maximum specific rate of methane utilization (k(CH(4) )) was determined by fitting the numerical model to batch experimental data, with the initial concentration of active methane-oxidizing cells (X(0) (a)) also used as a model fitting parameter. The best estimate of k(CH(4) ) was 2.2 g CH(4)/g cells-d with excess copper available, with a single-parameter 95% confidence interval of 2.0-2.4 mg/mg-d. The joint 95% confidence region for k(CH(4) ) and X(0) (a) is presented graphically. The half-velocity coefficient (K(S,CH(4) )) was 0.07 mg CH(4)/L with excess copper available and 0.47 mg CH(4)/L under copper limitation, with 95% confidence intervals of 0.02-0.11 and 0.35-0.59 mg/L, respectively. Unique values of the TCE rate coefficients k(TCE) and K(S,TCE) could not be determined because they were found to be highly correlated in the model fitting analysis. However, the ratio k(TCE)/K(S,TCE) and the TCE transformation capacity (T(C)) were well defined, with values of 0.35 L/mg-day and 0.21 g TCE/g active cells, respectively, for cells transforming TCE in the absence of methane or supplemental formate. The single-parameter 95% confidence intervals for k(TCE)/K(S,TCE) and T(C) were 0.27-0.43 L/mg-d and 0.18-0.24 g TCE/g active cells, respectively. The joint 95% confidence regions for k(TCE)/K(S,TCE) and T(C) are presented graphically. (c) 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 53: 320-331, 1997.     

Evidence for "diminishing returns" from the scaling of stem diameter and specific leaf area

Research indicates that increases in total leaf area (A(T)) may fail to keep pace with increases in total leaf mass (M(L)) across plants differing in size (e.g., as measured by stem diameter, D). This "diminishing returns" hypothesis predicts that the scaling exponent for A(T) vs. M(L) will be less than one and that the exponent for specific leaf mass (i.e., A(T) / M(L)) vs. D will be negative. These predictions were examined using data from 46 plants ranging between 0.125 cm ≤ D ≤ 0.485 m across 25 woody dicot species. Standardized major axis slopes were used to quantify scaling exponents and random effects models were used to quantify species and size effects on the numerical values of exponents. The exponents for A(T) vs. M(L) and A(T) / M(L) vs. D differed among species and different species groupings. In general, the exponent for A(T) vs. M(L) was less than one and the exponent for A(T) / M(L) vs. D was negative, as predicted. However, random effects models indicated that species effects overshadowed size effects, although size effects were statistically significant. The diminishing returns hypothesis therefore receives statistical support, i.e., although the numerical values of exponents are "species-dependent," they are less than unity, as predicted by theory.     

A physiological systems approach to modeling and resetting of mouse thermoregulation under heat stress

Heat stroke (HS) is a serious civilian and military health issue. Due to the limited amount of experimental data available in humans, this study was conducted on a mouse mathematical model fitted on experimental data collected from mice under HS conditions, with the assumption there is good agreement among mammals. Core temperature (T(c)) recovery responses in a mouse model consist of hypothermia and delayed fever during 24 h of recovery that represent potential biomarkers of HS severity. The objective of this study was to develop a simulation model of mouse T(c) responses and identify optimal treatment windows for HS recovery using a three-dimensional predictive heat transfer simulation model. Several bioenergetic simulation variables, including nonlinear metabolic heat production (W/m3), temperature-dependent convective heat transfer through blood mass perfusion (W/m3), and activity-related changes in circadian T(c) were used for model simulation. The simulation results predicted the experimental data with few disparities. Using this simulation model, we tested a series of ambient temperature treatment strategies to minimize hypothermia and delayed fever to accelerate HS recovery. Using a genetic algorithm, we identified eight time segments (ambient temperature = 27, 30, 31, 29, 28, 28, 27, 26°C) of 110 min total duration that optimized HS recovery in our model simulation.     

Thermal behavior of native and hydrophobized wheat gluten, gliadin and glutenin-rich fractions by modulated DSC

The glass transition temperature (T(g)) of hydrophobized and native wheat gluten and its protein fractions, with water mass fraction from 0 to 0.2, was studied using modulated differential scanning calorimetry. The T(g) values of unplasticized products were approximately 175 degrees C whatever the treatment (hydrophobization) or the fraction tested, except for the gliadin-rich fraction (162 degrees C). Experimental change in heat capacity at the glass transition (DeltaC(p)) ranged from 0.32 to 0. 50 J/g/ degrees C depending on the gluten fractions. The Gordon-Taylor fit of T(g) evolution as a function of water content showed that glutenin-rich fractions were more sensitive to water plasticization than the gliadin-rich fraction. The Kwei equation gave better fit to experimental data and demonstrated that the water plasticization of gluten and its fractions is influenced by secondary interactions. However, the application of the Couchman-Karasz equation without fitting predicts satisfactorily the plasticization of gluten proteins by water.     

Mold appearance and modeling on selected corn stover components during moisture sorption

Occurrence of mold was visually monitored for 26days on samples of major anatomical components of corn stover maintained at several storage temperatures (T) and water activities (a(w)). Glass desiccators with saturated salt solutions placed in temperature controlled chambers provided simulated storage conditions with temperatures ranging from 10 degrees C to 40 degrees C and water activities ranging from 0.11 to 0.98. Mold affected leaf, stalk skin, and stalk pith equally at water activity greater than 0.9. As expected, a combination of increased water activity greater than 0.9 and temperatures greater than 30 degrees C was conducive to mold growth. Based on material moisture content during the initial mold growth, it was postulated that among the corn stover components the stalk pith was the least resistant to mold growth followed by stalk skin and leaf for the studied range of temperature and water activity. Mold growth models fitted well with the observation. A linear mold-free days predictions using a three-parameter regression model (T, a(w), and T x a(w)) was superior (R(2)=0.99) to other models considered. The exponential spoilage model using two parameter T and a(w) also gave comparable performance (R(2)=0.95). Among the independent factors, T x a(w) product was the most significant (p=0.0069) followed by T (p=0.0114), and a(w) (p=0.3140) in explaining the experimental data. The developed models can be applied to predict the safe storage period of corn stover components exposed to various temperature and moisture environmental conditions.     

Solid-state fermentation for xylanase production by Thermoascus aurantiacus using response surface methodology

We investigated xylanase production by Thermoascus aurantiacus using semisolid fermentation. Multivariant statistical approaches were employed to evaluate the effects of several variables (initial moisture in the medium, cultivation time, inoculum level, and bagasse mass) on xylanase production. The initial moisture content and bagasse mass were the most important factors affecting xylanase activity. The xylanase activity produced by the fungus under the optimized conditions (81% moisture content and 17 g bagasse) was found to be 2700 U per gram of initial dry matter, whereas its value predicted by a polynomial model was 2400 U per gram of initial dry matter. Received: 4 December 1998 / Received revision: 15 March 1999 / Accepted: 16 May 1999     

干燥中果蔬内部质热传递的数值模拟

根据果蔬多孔质特点,建立了热风、远红外和微波干燥果蔬过程中同时考虑温度、水分影响的内部质热传递模型．并进行理论计算和实测比较．热风干燥时温度水分和微波干燥时水分的模拟值与实测值十分接近;微波干燥时的物料温度和远红外干燥时的温度水分模拟值与实测值略有差异．分析了产生差异的原因．     

Estimation of oxygen mass transfer coefficient in stirred tank reactors using artificial neural networks

The estimation of volumetric mass transfer coefficient, k(L)a, in stirred tank reactors using artificial neural networks has been studied. Several operational conditions (N and V(s)), properties of fluid (μ(a)) and geometrical parameters (D and T) have been taken into account. Learning sets of input-output patterns were obtained by k(L)a experimental data in stirred tank reactors of different volumes. The inclusion of prior knowledge as an approach which improves the neural network prediction has been considered. The hybrid model combining a neural network together with an empirical equation provides a better representation of the estimated parameter values. The outputs predicted by the hybrid neural network are compared with experimental data and some correlations previously proposed in the literature for tanks of different sizes.     

Xylanase production in solid state fermentation by Aspergillus niger mutant using statistical experimental designs

The initial moisture content, cultivation time, inoculum size and concentration of basal medium were optimized in solid state fermentation (SSF) for the production of xylanase by an Aspergillus niger mutant using statistical experimental designs. The cultivation time and concentration of basal medium were the most important factors affecting xylanase activity. An inoculum size of 5 x 10(5) spores/g, initial moisture content of 65%, cultivation time of 5 days and 10 times concentration of basal medium containing 50 times concentration of corn steep liquor were optimum for xylanase production in SSF. Under the optimized conditions, the activity and productivity of xylanase obtained after 5 days of fermentation were 5,071 IU/g of rice straw and 14,790 IU l(-1) h(-1), respectively. The xylanase activity predicted by a polynomial model was 5,484 IU/g of rice straw.     

Solute exclusion from cellulose in packed columns: process modeling and analysis

In this investigation, process modeling and analysis were used to explore the behavior of solute exclusion from cellulose in packed columns. The study focused on modeling the effects of dispersion, mass transport, and pore diffusion. Three mathematical models were used to predict the behavior of the columns: an equilibrium model, a mass transfer model, and a combined mass transfer and pore diffusion model. Computer implementations of these models were tested against experimental conditions where cellulose particle size and solution velocity were used to either amplify or minimize dispersion or skewness in the elution curves. For small cellulose particles (200-300 mesh), all three models accurately predicted the shape of the elution curve and the particle porosity. For larger particles (45-60 mesh), the mass transfer model and the combined mass and pore diffusion model best represented the behavior of the column. At high solution velocities (0.63 cm(3) min(-1)) and large particles, only the combined mass transfer and pore diffusion model accurately represent the column behavior. Sensitivity analysis revealed that the mass transfer coefficient had little effect on the elution curves for the range of values (10(-6)-10(-3) cm s(-1)) calculated from the experimental data. The combined mass transfer and pore diffusion model presented in this article can be used to design solute exclusion measurement experiments for the larger cellulose particles found in a commercial cellulose-to-ethanol plant.     

Metabolism, body temperature and thermal conductance of fruit-doves (Aves: Columbidae, Treroninae)

Basal metabolic rate (MR), body temperature (T(b)) and wet thermal conductance (C(wet)) of three tropical species of fruit-doves were investigated at ambient temperatures (T(a)) of 11-33 degrees C in activity (alpha) and rest (rho) phases to investigate the possible effect of obligate frugivory on the physiology of columbids. The basal metabolic rates of Ptilinopus melanospila (black-naped fruit-dove, 94 g), Drepanoptila holosericea (cloven-feathered dove, 198 g) and Ducula pinon (Pinon's imperial pigeon, 748 g) are 20-38% lower than predicted for all birds, including granivorous columbid species from temperate and tropical regions. The MR was minimal at a T(a) value of approximately 30 degrees C (=lower critical temperature, T(lc)) for all three species, indicating that these rainforest birds are not able to withstand high ambient temperatures as well as arid-adapted members of the pigeon family. Minimal wet-thermal conductance was, on average, higher than expected, indicating poor insulation in these tropical birds. Body temperatures were as expected; however, below T(lc) the body temperatures decreased to levels of 35-36 degrees C (T(a)=12 degrees C).     

Dynamic thermal balance in the leaf-eared mouse: the interplay among ambient temperature,body size,and behavior

Endotherms maintain constant body temperature through physiological and behavioral adjustments. Behavioral thermoregulation is an important factor influencing energy balance. We exposed the leaf-eared mouse, Phyllotis darwini, to temperatures corresponding to its natural thermal range and studied two forms of behavioral thermoregulation: diminishing surface to volume ratio by huddling and heat dissipation by increasing physical contact with the substrate (flattening). We predicted that at low ambient temperatures (T(a)) huddling would be used as a heat conservation mechanism and at high T(a) flattening would be used for heat loss. We simultaneously measured oxygen consumption (VO2) and flattening, in response to three independent factors: huddling, T(a), and body mass. Each experiment was a 6-h VO2 trial where five virgin females were measured at constant T(a). We performed this protocol for two body mass groups, small (ca. 40 g) and large (ca. 70 g), in a metabolic chamber. Treatments were groups with and without the ability to huddle at five different T(a), ranging from 5 degrees to 35 degrees C. A significant interaction between all three factors was found. Huddling and flattening were used as strategies for conserving or dissipating heat, respectively, and the shift between both strategies occurred at the lower limit of thermoneutrality. At T(a) below thermoneutrality, huddling was a more effective way of reducing metabolic requirements and was more efficient (H(E)) in small individuals than large individuals. So, by huddling, small individuals save more energy. At high T(a), flattening appeared to be an equally useful mechanism for heat loss, for both large and small animals.     

斜纹夜蛾和烟青虫在烟草上的生态位

斜纹夜蛾和烟青虫同是烟草上食叶类的重要害虫,对烟叶产量和品质均可构成严重的影响.研究两者在烟草上的生态位和种间关系,结果表明斜纹夜蛾的空间生态位宽度和空间生态位重叠指数均略大于烟青虫,两者空间生态位的比例相似性为0.0973,说明两种害虫在空间资源上几乎不存在竞争.斜纹夜蛾和烟青虫的时间生态位及时间生态位重叠指数很接近,时间生态位的比例相似性高达0.9485.斜纹夜蛾和烟青虫在烟草植株上、中、下部叶片共存的比例分别为6.11%、3.23%和0.51%.由于对空间垂直资源的不同选择,使它们可以同时在同株烟草上为害而互不干扰.     

Craniofacial variation,body size and ecological factors in aboriginal populations from central Patagonia (2000–200 years B.P.)

Previous studies have shown that ecological factors had a significant role in shaping the patterns of craniofacial variation among South American populations. Here, we evaluate whether temperature and diet contributed to facial diversification in small geographic areas. Facial size and shape of 9 osteological samples from central Patagonia (Argentina) were described using 2D landmarks and semilandmarks. Data on mean annual temperature, diet composition (δ¹³C and δ¹⁵N values) and femoral head maximum breadth, used as a proxy of body mass, were obtained for each sample. We then tested the association of body mass and the ecological variables with facial morphology using spatial regression techniques and a model selection approach. Akaike Information Criterion produced disparate results for both components of facial morphology. The best model for facial size included temperature and body mass proxy, and accounted for more than 80% of variation in size. Lower temperatures were related to larger facial sizes. Body mass was negatively associated with facial size and showed no relationship with the temperature. This suggests a relatively independent variation of cranial traits and body mass at the spatial scale studied here. Facial shape was not associated with the temperature or diet composition, contrasting with the patterns observed at larger spatial scales. Our results point out that the effect of climatic variables on cranial traits might be a source of morphological differentiation not only at large scales but also in small geographic areas, and that size and shape display a differential preservation of environmental signals.     

干湿交替格局下黄土高原小麦田土壤呼吸的温湿度模型

全球气候变化的直接后果是气温升高,同时还可能引起强降雨增多和干旱频发,形成干湿交替的格局.土壤呼吸在全球变化过程中发挥着重要作用.以黄土高原沟壑区小麦田土壤为研究对象,采用3个全自动多通量箱以及相应的气象监测系统,对土壤呼吸和环境因子全天候连续测定,利用已有的单因子模型、双因子模型对测定的土壤呼吸与气温和湿度的关系进行了拟合,通过优化,根据实际情况提出E-Q(exponential-quadratic)模型.结果表明:(1)干湿交替格局下,基于气温的单因子模型(指数模型,幂函数模型和线性模型)不适合模拟土壤呼吸;(2)基于土壤湿度的单因子模型中,二次曲线模型最适合模拟干湿交替格局下土壤呼吸的响应情况;(3)基于气温和土壤湿度的双因子模型中,E-Q模型SR=aebT(c+dW+fW2)g,既能反映土壤呼吸随气温的正向指数变化,又能表现土壤湿度对土壤呼吸的双向调节作用,解释了土壤呼吸73.05%的变化情况,比其他双因子模型和单因子模型更能有效描述干湿交替情况下土壤呼吸对气温和土壤湿度协同变化的响应特征.