Vacuum skin packaging and its effect on selected properties of beef and pork meat

Physicochemical, instrumental and microbiological examinations of steaks of beef and pork (m. longissimus lumborum) in vacuum skin packaging (VSP), conventional vacuum packing (CVP) and modified atmosphere packaging (MAP) were performed. Samples were stored at 2 ± 0.5 °C for 3 (pork) or 5 (beef) weeks. No statistically significant changes in pH values were recorded. Statistically significant (p < 0.001) changes in the thiobarbituric reactive substances content in modified atmosphere packed beef samples, and differences between samples in MAP and VSP or CVP were found from week 2 of the experiment onwards. The biggest changes in colour parameters were found in beef samples in MAP. The lowest and highest purge loss was recorded in samples in VSP and CVP, respectively. Vacuum packing enhanced the growth of lactic acid bacteria (LAB). At the end of the experiment, their numbers ranged from 4.31 log₁₀ cfu g^?1 (pork in CVP) to 5.14 log₁₀ cfu g^?1 (beef in VSP). LAB populations reached 2 log₁₀ cfu g^?1 in MAP beef and pork samples. On the other hand, MAP enabled the development of bacteria of the genus Pseudomonas and Brochothrix thermosphacta. The highest increase in coliform bacteria counts was recorded in vacuum-packed pork.     

Homogeneous nucleation rate at various initial supersaturations in a closed system

The rate of formation of nuclei in a closed system is studied by numerical solution of kinetic equations at various supersaturations. Depletion of vapor (decrease of supersaturation) due to the phase transition process is taken into account. At a relatively low value of initial supersaturations, the decrease of supersaturation is negligible. At somewhat higher initial supersaturations, the phase transition process is more intense and the decrease of supersaturation plays an important role. As a consequence the nucleation rate after reaching a maximum decreases with time and for sufficiently long times only the nuclei of certain size are formed. At high initial supersaturation the nucleation rate for subcritical cluster sizes is negative, i.e. the number of subcritical clusters tends to get reduced. Critical size increases with time due to lowered supersaturation.     

Specific surfaces of coals determined by small-angle X-ray scattering and by adsorption of methanol

The specific surfaces of twenty samples of Czechoslovak coals were determined by the method of small-angle scattering of X-rays and the results were compared with the values of specific surfaces obtained by adsorption of methanol at 20 °C. The results of both methods used, when determining specific surfaces of brown coals and lignites were found to be similar, but for hard coals the specific surfaces obtained by adsorption of methanol were seldom half as large. The differences are readily explained, and the X-ray method is considered to provide the best approximation to an absolute upper limit.     

Fatigue Behavior of Bodies with Thermally Sprayed Metallic and Ceramic Deposits

This paper summarizes the basic results of fatigue testing of bodies with both metallic and ceramic thermally sprayed coatings. Three kinds of ceramic coatings (Al₂O₃, Cr₂O₃, and olivine) sprayed with DC plasma under identical conditions were investigated together with metallic Ni-5wt.%Al coatings sprayed by wire arc, DC plasma, and HVOF. The elastic modulus of the deposited coatings was investigated using four point bending and resonance method. Bending fatigue tests at resonance frequency were performed with cantilever beam specimens. The processes taking place during the fatigue test are identified and discussed. The morphology of the fracture surfaces was investigated together with microstructure and porosity of the coatings.     

Size Effect on Strength of Quasibrittle Structures with Reentrant Corners Symmetrically Loaded in Tension

The effect of V-notches (or reentrant corners) on fracture propagation has been analyzed for brittle materials, but not for quasibrittle materials such as concrete, marked by a large material characteristic length producing a strong size effect transitional between plasticity and linear elastic fracture mechanics. A simple size effect law for the nominal strength of quasibrittle structures with symmetrically loaded notches, incorporating the effect of notch angle, is derived by asymptotic matching of the following five limit cases: (1) Ba?ant’s size effect law for quasibrittle structures with large cracks for notch angle approaching zero; (2) absence of size effect for vanishing structure size; (3) absence of size effect for notch angle approaching π; (4) plasticity-based notch angle effect for vanishing size; and (5) the notch angle effect on crack initiation in brittle structures, which represents the large-size limit of quasibrittle structures. Accuracy for the brittle large-size limit, with notch angle effect only, is first verified by extensive finite-element analyses of bodies with various notch angles. Then a cohesive crack characterized by a softening stress-separation law is considered to emanate from the notch tip, and the same finite-element model is used to verify and calibrate the proposed law for size and angle effects in the transitional size range in which the body is not far larger than Irwin’s material characteristic length. Experimental verification of the notch angle effect is obtained by comparisons with Dunn et al.’s extensive tests of three-point-bend notched beams made of plexiglass (polymethyl methacrylate), and Seweryn’s tests of double-edge-notched tension specimens, one set made of plexiglass and another of aluminum alloy.     

Sandwich buckling formulas and applicability of standard computational algorithm for finite strain

Although, for homogeneous columns, the differences between Engesser's and Haringx's formulas for shear buckling have been explained in 1971 by the dependence of shear modulus on the axial stress, for soft-core sandwich columns the choice of the correct formula has baffled engineers for half a century. Recently, Ba ant explained this difference by a variational analysis which showed that an agreement is achieved if the shear modulus of the light core is considered to depend on the compressive stress in the skins even when small-strain elasticity applies. To clarify this paradoxical dependence, first the variational framework is briefly reviewed. Subsequently, the mathematical results from Ba ant's recent study are physically reinterpreted, with the conclusion that only the Engesser-type theory (rather than Haringx-type theory) corresponds to constant shear moduli as obtained, for example, by the torsional test of a tube made from the foam. This is a rather fundamental point for applications because the discrepancy between these two theories can be very large in the case of short columns with thin skins. The implications for standard finite element programs are then explored by computing the critical loads of several sandwich columns with different material and geometric properties. The finite element computations show agreement with the Engesser-type formula predictions, while the Haringx-type prediction can be obtained with the finite element program somewhat artificially—by updating the core modulus as a function of the axial stress in the skins.     

Influence of non-axial magnetic field in a 3D3V Particle-In-Cell plasma model

In this article we report on results obtained using a newly developed self-consistent fully 3D Particle-In-Cell code for modelling of plasma-solid interaction.The model presented here involves a hollow cylindrical chamber opened to the plasma, with a thin cylindrical guard at the inlet and a strong external magnetic field limiting access of charged particles to the cylindrical wall. This model layout might provide more insight into processes taking place during magnetron deposition of thin films onto porous media. It is also a basis for probe diagnostics in fusion plasma research.The magnetic field is either parallel or slightly inclined with respect to the cylindrical axis. The results presented are axial and azimuthal ion current densities and cumulative distribution functions of ions impinging on the cylindrical surface for several angles of magnetic field inclination. They confirm the importance of proper alignment with magnetic field in certain geometries.Efficiency and possibilities of further extensions to the 3D model are also briefly discussed.     

Thermodynamic Properties of He@C60

Abstract

Contributions to thermodynamic properties of the endohedral He@C₆₀, resulting from motion of He inside the cage, are calculated. The contribution to C _v shows a maximum at low temperatures. The maxima for ³He@C₆₀ and ⁴He@C₆₀ are at about 41 K and 30 K, respectively.     

Improved prediction model for time-dependent deformations of concrete: Part 1-Shrinkage

This paper is the first in a series of papers that present a new prediction model for creep and shrinkage of concrete, called for brevity the BP−KX model. This model represents an update and improvement of the BP model published in this journal in 1978–79. The improvement is possible because further experimental data became available in the literature and at the same time knowledge of physical concepts and mechanisms has improved. This first paper presents a prediction model for the mean (overall) shrinkage strain in cross-sections of long members, which takes into account the influence of environmental humidity, the effective thickness of the member, the effect of cross-section shape, the effect of age at the start of drying, and the effect of temperature. The proposed basic form of the shrinkage formulae is fustified by nonlinear diffusion theory for the movement of moisture through concrete. Extensive comparisons with important test data from the literature, altogether 23 data sets, reveal that the predictions are better than with the previous models. Statistics of prediction are also given. The main error of prediction arises from the estimation of the shrinkage parameters from concrete strength and composition. If limited short-time shrinkage data are available, the predictions can be greatly improved.

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Resume Ce rapport est le premier d’une série présentant un nouveau modèle de prédiction du fluage et du retrait du béton dénommé, pour abréger, modèle BKP. Ce modèle représente une mise à jour et une amélioration du modèle BP décrit dans ce journal en 1978/79. Des données expérimentales ultérieures disponibles dans la littérature, en même temps qu’une meilleure connaissance des concepts et mécanismes physiques, ont permis ce progrès. Ce premier rapport présente un modèle de prédiction pour une contrainte de retrait moyenne dans les sections transversales de longs éléments, qui prend en compte l’influence de l’humidité ambiante, l’épaisseur effective de l’élément, l’influence de la forme de la section, de l’age au début du séchage et de la température. On justifie l’expression de base des formules de retrait par la théorie de la diffusion non linéaire pour la circulation de l’humidité dans le béton. De vastes comparaisons avec d’importantes données d’essai prises dans la littérature-en tout 23 séries d’essai-ont montré que les prédictions étaient meilleures qu’avec les modèles précédents. On donne aussi des statistiques de prédiction. L’erreur de prédiction principale provient de l’évaluation des paramètres de retrait à partir de la composition et de la résistance du béton. Si l’on dispose de données de retrait limité, les prédictions peuvent être considérablement améliorées.

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Deceased 1989.     

Time lag in measuring pore humidity in concrete by a gage in finite cavity

Measurements of the relative humidity of water vapor in concrete are important for understanding, predicting and controlling the shrinkage and creep of concrete, as well as other processes such as the ASR. A sufficient time is required for the pore water to diffuse into (or out of) the gage cavity. To determine this time, the nonlinear partial differential equation of diffusion of moisture through concrete is solved numerically. The cavity is simplified as spherical and its volume is considered to be far smaller than the volume of surrounding concrete, which permits assuming spherical symmetry of the pore humidity field. The body of the surrounding concrete is assumed to be so large that the water escape into (or intake from) the cavity does not change the pore humidity in concrete appreciably. For the current measurement practice, the humidity difference between the concrete pores and the cavity is found to drop below the inevitable error of the gage after the lapse of about 24 h, and an acceptable error of about 1% is achieved in about 10 h. It is shown that extrapolation by a decaying power function of time can shorten this time to 2 h. A further shortening could be achieved by reducing the volume of the cavity, although any contact of the gage with the concrete must be avoided.