The effects of holding raw milk under carbon dioxide pressures of 68 to 689 kPa at temperatures of 5, 6.1, 10, and 20°C on the indigenous microbiota were investigated. These pressure-temperature combinations did not cause precipitation of proteins from the milk. Standard plate counts from treated milks demonstrated significantly lower growth rate compared with untreated controls at all temperatures, and in some cases, the treatment was microcidal. Raw milk treated with CO2 and held at 6.1°C for 4 d exhibited reduced bacterial growth rates at pressures of 68, 172, 344, and 516 kPa; and at 689 kPa, demonstrated a significant loss of viability in standard plate count assays. The 689-kPa treatment also reduced gram-negative bacteria and total Lactobacillus spp. The time required for raw milk treated at 689 kPa and held at 4°C to reach 4.30 log10 cfu/mL increased by 4 d compared with untreated controls. Total coliform counts in the treated milk were maintained at 1.95 log10 cfu/mL by d 9 of treatment, whereas counts in the control significantly increased to 2.61 log10 cfu/mL by d 4 and 2.89 log10 cfu/mL by d 9. At d 8, Escherichia coli counts had not significantly changed in treated milk, but significantly increased in the control milk. Thermoduric bacteria counts after 8 d were 1.32 log10 cfu/mL in treated milk and 1.98 log10 cfu/mL in control milk. These data indicated that holding raw milk at low CO2 pressure reduces bacterial growth rates without causing milk protein precipitation. Combining low CO2 pressure and refrigeration would improve the microbiological quality and safety of raw milk and may be an effective strategy for shipping raw single strength or concentrated milk over long distances. 相似文献
The goal of this work was to construct Escherichia coli strains capable of enhanced arginine production. The arginine biosynthetic capacity of previously engineered E. coli strains with a derepressed arginine regulon was limited by the availability of endogenous ornithine (M. Tuchman, B. S. Rajagopal, M. T. McCann, and M. H. Malamy, Appl. Environ. Microbiol. 63:33-38, 1997). Ornithine biosynthesis is limited due to feedback inhibition by arginine of N-acetylglutamate synthetase (NAGS), the product of the argA gene and the first enzyme in the pathway of arginine biosynthesis in E. coli. To circumvent this inhibition, the argA genes from E. coli mutants with feedback-resistant (fbr) NAGS were cloned into plasmids that contain "arg boxes," which titrate the ArgR repressor protein, with or without the E. coli carAB genes encoding carbamyl phosphate synthetase and the argI gene for ornithine transcarbamylase. The free arginine production rates of "arg-derepressed" E. coli cells overexpressing plasmid-encoded carAB, argI, and fbr argA genes were 3- to 15-fold higher than that of an equivalent system overexpressing feedback-sensitive wild-type (wt) argA. The expression system with fbr argA produced 7- to 35-fold more arginine than a system overexpressing carAB and argI genes on a plasmid in a strain with a wt argA gene on the chromosome. The arginine biosynthetic capacity of arg-derepressed DH5 alpha strains with plasmids containing only the fbr argA gene was similar to that of cells with plasmids also containing the carAB and argI genes. Plasmids containing wt or fbr argA were stably maintained under normal growth conditions for at least 18 generations. DNA sequencing identified different point mutations in each of the fbr argA mutants, specifically H15Y, Y19C, S54N, R58H, G287S, and Q432R. 相似文献
We propose a modified Fitzhugh-Nagumo neuron (MFNN) model. Based on this model, an integer-order MFNN system (case A) and a fractional-order MFNN system (case B) were investigated. In the presence of electromagnetic induction and radiation, memductance and induction can show a variety of distributions. Fractional-order magnetic flux can then be considered. Indeed, a fractional-order setting can be acceptable for non-uniform diffusion. In the case of an MFNN system with integer-order discontinuous magnetic flux, the system has chaotic and non-chaotic attractors. Dynamical analysis of the system shows the birth and death of period doubling, which is a sign of antimonotonicity. Such a behavior has not been studied previously in the dynamics of neurons. In an MFNN system with fractional-order discontinuous magnetic flux, different attractors such as chaotic and periodic attractors can be observed. However, there is no sign of antimonotonicity.
In this study, a locking-free n-sided C1 polygonal finite element is presented for nonlinear analysis of laminated plates. The plate kinematics is based on Reddy's third-order shear deformation theory (TSDT). The in-plane displacements are approximated using barycentric form of Lagrange shape functions. The weak-form Galerkin formulation based on the kinematics of TSDT requires the C1 approximation of the transverse displacement over the polygonal element. This is achieved by embedding the C0 Lagrange interpolants over a cubic Bernstein-Bezier patch defined over the n-sided polygonal element. Such an approach ensures the continuity of the derivative field at the inter-element edges. In addition, Eringen's stress-gradient nonlocal constitutive equations are used in the present formulation to account for nonlocality. The effect of geometric nonlinearity is taken by considering the von Kármán geometric nonlinearity. Examples are presented to show the effect of nonlocality, geometric nonlinearity, and the lamination scheme on the bending behavior of laminated composite plates. The results are compared with analytical solutions, conventional FEM results, and with those available in the literature. Shear locking is addressed considering reduced integration and consistent interpolation techniques. The patch test is used to check the convergence of the element developed. 相似文献
A theory describing the behavior of chemically non-reacting binary mixtures can be based on a detailed formulation of the governing equations for the individual components of the mixture or on treating the mixture as a single homogenized continuous medium. We argue that if we accept that both approaches can be used to describe the behavior of the given mixture, then the requirement on the equivalence of these approaches places restrictions on the possible structure of the internal energy, entropy, Helmholtz potential, and also of the diffusive, energy, and entropy fluxes. (The equivalence of the approaches is understood in the sense that the quantities used in one approach can be interpreted in terms of the quantities used in the other approach and vice versa. Further, both approaches must lead to the same predictions concerning the evolution of the physical system under consideration). In the case of a general chemically non-reacting binary mixture of components at the same temperature, we show that these restrictions can indeed be obtained by purely algebraic manipulations. An important outcome of this analysis is, for example, a general form of the evolution equation for the diffusive flux. The restrictions can be further exploited in the specification of thermodynamically consistent constitutive relations for quantities such as the interaction (drag) force or the Cauchy stress tensor. As an example of the application of the current framework, we derive, among others, a generalization of Fick’s law and we recover several non-trivial results obtained by other techniques. The qualitative features of the derived generalization of Fick’s law are demonstrated by a numerical experiment. 相似文献
We explore tradeoffs between organization and number of ALUs and clock frequency in a stream processor. The tool provides candidate low-power configurations and estimates of their real-time performance. The tool relates instruction-level, subword, and data parallelism to functional units' organization and utilization. The exploration methodology is applicable to all embedded-processor designs in signal and media processing. 相似文献
Stress corrosion cracking of a commercial 0.19 pct C steel (SA-516 Grade 70) was studied in hot (92 ‡C) caustic solutions
of NaOH and NaOH plus aluminate (AlO−2) species. Potentiostatically controlled tests were conducted near the active-passive transition, using fracture mechanics
testing techniques and fatigue precracked double cantilever beam specimens. Crack propagation rates (Ν) were determined for
a range of stress intensities (Kl). In simple NaOH solutions, Region I (K1-dependent) and Region II (K1-independent) cracking behavior were observed. Increasing the concentration of NaOH from2m to8m decreasedKISCC and displaced Region I and the onset of Region II to lowerK1 levels. The presence of AlO−2 produced a comparable effect, with Region II being extended to lowerKI-Ν levels relative to simple NaOH solutions of similar hydroxyl anion concentration. The overallKI -Νv behavior and fractography were consistent with a dissolution mechanism of crack advance based on the general principles of
the film rupture-dissolution model. The effect of environment composition uponKI— Ν behavior was attributed to changes in repassivation kinetics.
Formerly Graduate Student at the University of British Columbia 相似文献
It has been shown recently that the class of elastic bodies is much larger than the classical Cauchy and Green elastic bodies, if by an elastic body one means a body incapable of dissipation (converting working into heat). In this paper, we study the boundary value problem of a hole in a finite nonlinear elastic plate that belongs to a subset of this class of the generalization of elastic bodies, subject to a uniaxial state of traction at the boundary (see Fig. 1). We consider several different specific models, including one that exhibits limiting strain. As the plate is finite, we have to solve the problem numerically, and we use the finite element method to solve the problem. In marked contrast to the results for the classical linearized elastic body, we find that the strains grow far slower than the stress. 相似文献
We present our results on successful synthesis of pyrazine–MoO3 nanorod hybrids by using pyrazine and MoO3 nanorods. On the first stage, MoO3 nanorods were grown hydrothermally and, on the second stage, their mixture with pyrazine was again involved in a hydrothermal reaction to produce organic–inorganic hybrids. To understand the growth mechanism of the hybrids we varied time and temperature of the hydrothermal process. Intercalation of pyrazine was confirmed through X-ray diffraction analysis, X-ray photoelectron spectroscopy, X-ray emission spectroscopy, scanning electron microscopy methods. Upon calcinations, pyrazine was deintercalated, i.e. removed from the MoO3 hybrid system, and the MoO3 nanorods were found to bind together resulting in formation of MoO3 microslabs with increased surface area. Photodecomposition performance of the MoO3 nanorods, pyrazine–MoO3 hybrids and MoO3 microcrystals was studied against Procion Red MX-5B textile dye. A high photodecomposition performance was found to decrease when going from MoO3 nanorods to MoO3 microcrystal and, further, to pyrazine–MoO3 hybrids. 相似文献