The effect of ethanol and oxygen absorption on the shelf-life of packed sliced rye bread

The effect of ethanol emitters, 1% (v/v) ethanol-containing gases and oxygen absorbers on the shelf-life of whole grain rye bread was investigated in two 6 week storage experiments. The bread slices (215 g) were packed in 500 ml plastic containers with headspace volumes of 240 ml. The biggest ethanol emitters (2 and 3 G) extended the microbial shelf-life of rye bread from 8–12 to 26–27 days in the two experiments, and oxygen absorbers correspondingly to the end of the storage period (42 days). Small ethanol emitters (0.6 and 1 G) and 1% (v/v) ethanol-containing gases had no influence on the microbial shelf-life. Ethanol and oxygen absorbers had no effect on changes in texture and moisture during storage. The overall sensory quality of the samples without microbial growth was evaluated as rather good at the end of the storage period. The flavour of ethanol was discovered not to prevent the use of ethanol for the preservation of bread, since ethanol was detected only a few times in the panellist sensory evaluation     

Twyman effect mechanics in grinding and microgrinding

In the Twyman effect (1905), when one side of a thin plate with both sides polished is ground, the plate bends: The ground side becomes convex and is in a state of compressive residual stress, described in terms of force per unit length (Newtons per meter) induced by grinding, the stress (Newtons per square meter) induced by grinding, and the depth of the compressive layer (micrometers). We describe and correlate experiments on optical glasses from the literature in conditions of loose abrasive grinding (lapping at fixed nominal pressure, with abrasives 4-400 μm in size) and deterministic microgrinding experiments (at a fixed infeed rate) conducted at the Center for Optics Manufacturing with bound diamond abrasive tools (with a diamond size of 3-40 μm, embedded in metallic bond) and loose abrasive microgrinding (abrasives of less than 3 μm in size). In brittle grinding conditions, the grinding force and the depth of the compressive layer correlate well with glass mechanical properties describing the fracture process, such as indentation crack size. The maximum surface residual compressive stress decreases, and the depth of the compressive layer increases with increasing abrasive size. In lapping conditions the depth of the abrasive grain penetration into the glass surface scales with the surface roughness, and both are determined primarily by glass hardness and secondarily by Young's modulus for various abrasive sizes and coolants. In the limit of small abrasive size (ductile-mode grinding), the maximum surface compressive stress achieved is near the yield stress of the glass, in agreement with finite-element simulations of indentation in elastic-plastic solids.     

The effect of packaging materials and oxygen on the colour stability of sliced bologna

The aim of the study was to determine the effect of packaging materials with different oxygen permeability, residual oxygen concentration in the package and light upon discoloration of the surface of sliced bologna. The packaging material caused significant differences in the discolouration of vacuum-packed, sliced bologna. The surface colour of sliced bologna packed in films with an oxygen transmission rate lower than 10cm³/m²/24h/atm was not affected by illuminated storage. Packages of sliced bologna with 0% oxygen in the head space showed good colour stability after 28 days of illuminated storage at 4 C. The discolouration of bologna was almost directly proportional to oxygen concentration in the package. Bologna stored in a high oxygen concentration developed more off-odour; 1% and 2% oxygen in the packages caused higher worst spot colour, discolouration and off-odour scores after 3 days of storage.     

重晶石湿法超细研磨中的机械力化学效应研究

研究了重晶石在搅拌磨湿法超细研磨过程中产生的机械力化学效应。结果表明，湿法超细粉碎重晶石可导致颗粒晶体结构发生整体变形、晶格畸变和非晶化。粉碎机械力化学效应使重晶石产生了高活性表面和化学活性点，从而为利用其制备功能材料提供了前提。     

Coolant pH control for optimum ceramic grinding Part II Influence of the rebinder effect on the surface grinding of aluminum oxide

Variations in the grinding (machining) properties of aluminum oxide attributable to the Rebinder effect, an environment-caused variation in the hardness of rock, ceramic, or glass, were investigated using conventional surface grinding equipment. Systematic variation in normal force, tangential force, roughness average, waviness average, and post grinding flexural strength were attributable to the grinding condition (coarse or fine) and the pH of the coolant. Observations in this study are consistent with a ductile/brittle grinding transition for fine grinding, a brittle/brittle grinding transition for coarse grinding and pH control of plastic deformation.     

骨料粒径对混凝土动态拉伸强度及尺寸效应影响分析

骨料粒径是影响混凝土力学性能及破坏机理的重要因素。从细观角度出发,将混凝土看作由骨料颗粒、砂浆基质及界面过渡区组成的三相复合材料,考虑细观组分的应变率效应,建立了混凝土动态拉伸破坏行为研究的细观力学分析模型,模拟研究了不同骨料粒径下混凝土动态拉伸破坏行为,并揭示了动态拉伸强度的尺寸效应规律。研究表明:低应变率下骨料不发生破坏,骨料粒径对混凝土动态拉伸破坏模式及拉伸强度影响显著,且拉伸强度的尺寸效应随骨料粒径的减小而削弱;高应变率下裂缝将贯穿骨料,骨料粒径的大小对混凝土动态拉伸强度及尺寸效应影响可忽略。最后,结合应变率效应的影响机制,建立了混凝土拉伸强度的"静动态统一"尺寸效应理论公式,该公式可以较好描述各骨料粒径下混凝土动态拉伸强度与试件尺寸的定量关系。     

On crack closure and the notch size effect in fatigue

A method for determining the fatigue notch-size-effect is presented based upon the development of closure in the wake of a newly formed crack growing from a notch. A comparison with experimental results is in accord with predictions. The effect of crack closure on the formation of non-propagating cracks at notches and on notch sensitivity is also discussed.     

The study of grain size distribution and morphometric characteristics of synthetic and natural diamond grinding powders

The paper summarizes the results of a comparative study of grain size distribution and morphometric characteristics of synthetic and natural diamond grinding powders For the first time the morphometric characteristics of natural diamond grinding powders have been comprehensively identified and the uniformity of the powders have been quantitatively assessed by the system-criteria method.     

The effect of the degree of grinding on the flotation of celestite ore

In a study to investigate how the degree of grinding influenced the concentration of celestite, the concentrate was found to increase in celestite (SrSO₄) content from 52 to 65 mass% when the size was reduced from 80/100 (177/149) to 160/200 mesh (88/74 μm). Experiments were conducted for the concentration of celestite ore by flotation using a mechanical cell with a 3 l capacity for particles sizes ranging between 80 and <400 mesh (177 and <37 μm), and modifying both ph in the flotation cell and collector (sodium oleate) concentration. the results obtained show that, although recovery percentages are low, celestite content in the concentrate is approximately 70 mass%.     

The role of defects in the quantum size effect

Many macroscopic properties of films exhibit an oscillatory dependence on thickness when the thickness is comparable with the de Broglie wavelength of an electron at the Fermi surface. This behavior is called the quantum size effect. In this paper the influence of defects in thin semimetal films on the electrical conductivity is explored by extending the work of Sandomirskiǐ to include a scattering potential of finite range. An isotropic sample bounded by infinitely high potential walls is assumed, and the Greenwood-Peierls formula is the starting point for this calculation. The potential selected and the approach taken allow the conductivity to be calculated with correction terms which have not previously been given. Within this model the calculations show that for δ-function scattering, Sandomirski?'s results are exact. Compared with Sandomirski?'s work, the calculations in this paper predict a reduction in the amplitude of the oscillations in addition to an overall decrease in the conductivity. A physical explanation of the results is given.     

球磨仪研磨硫磺粉的静电作用

采用高频振动球磨仪研磨硫磺,对研磨过程中硫磺粉的起电特性进行测试和分析。结果表明:控制研磨转速分别为1 200、1 500、1 800 r/min时,薄片状硫磺带静电量到达饱和值的时间为40、60、100 s,荷质比增大速率为0.269、0.470、0.700 nC/(g·s),粉状硫磺所带静电量到达饱和值的时间分别为30、40、70 s,荷质比增大速率为0.416、0.701、0.979 nC/(g·s);采用碳化钨材质的研磨体,研磨后的硫磺粉所带静电量最小,不锈钢研磨材质的是碳化钨的1.39倍,氧化锆研磨材质的是碳化钨的3.82倍;增大硫磺粉的湿基含水量能够有效减小研磨过程中硫磺粉所带的静电量,当湿基含水量为0.8%时,研磨硫磺粉的饱和静电量几乎减小为0。     

The effect of grinding on the flexural strength of a sialon ceramic

The effect of selected grinding parameters on the flexural strength of a sialon ceramic was studied. Support compliance was found to have no significant effect, while depth of incursion and grinding direction did. Weibull statistics and analysis of variance techniques were used to detect these effects which are explained through flaw magnitude and direction.     

The effect of the pulse electric current treatment on residual stresses arising in grinding

We show experimentally that the passing of a pulse electric current through a strip of stainless steel with a surface layer containing grinding-induced tensile stresses substantially reduces their level. In this case, the effect of treatment is not related to the macro-heating of the strip metal.     

Cohesive stresses and size effect in quasi-brittle materials

A novel approach to the derivation of Bažant’s size effect law is presented. Contrarily to the original Lagrangian derivation which hinged on energetic consideration, a Newtonian approach based on local stress intensity factors is presented. Through this approach, it is shown that Bažant’s size effect law is the first (and dominant) term in a series expansion for the nominal stress. Furthermore, analytical expressions forB are derived for selected specimen geometries.     

Quantum size effect in thin films

When the thickness of a film is of the order of the de Broglie wavelength of the electron, size effects appear in the electrical properties of the material. In this paper we derive the current in the presence of a magnetic field perpendicular to the plane of the film. We use the quantum mechanical density-matrix formalism. Unlike previous works we obtain an exact expression for the current. It is found that the current has a non-linear behavior with the electric field. The current also oscillates with the thickness of the film.     

The size effect in metal cutting

When metal is removed by machining there is substantial increase in the specific energy required with decrease in chip size. It is generally believed this is due to the fact that all metals contain defects (grain boundaries, missing and impurity atoms, etc.), and when the size of the material removed decreases, the probability of encountering a stress-reducing defect decreases. Since the shear stress and strain in metal cutting is unusually high, discontinuous microcracks usually form on the metal-cutting shear plane. If the material being cut is very brittle, or the compressive stress on the shear plane is relatively low, microcracks grow into gross cracks giving rise to discontinuous chip formation. When discontinuous microcracks form on the shear plane they weld and reform as strain proceeds, thus joining the transport of dislocations in accounting for the total slip of the shear plane. In the presence of a contaminant, such as CCI₄ vapour at a low cutting speed, the rewelding of microcracks decreases, resulting in decrease in the cutting force required for chip formation. A number of special experiments are described in the paper that support the transport of microcracks across the shear plane, and the important role compressive stress plays on the shear plane. Relatively recently, an alternative explanation for the size effect in cutting was provided based on the premise that shear stress increases with increase in strain rate. When an attempt is made to apply this to metal cutting by Dineshet al (2001) it is assumed in the analysis that the von Mises criterion pertains to the shear plane. This is inconsistent with the experimental findings of Merchant. Until this difficulty is taken care of, together with the promised experimental verification of the strain rate approach, it should be assumed that the strain rate effect may be responsible for some notion of the size effect in metal cutting. However, based on the many experiments discussed here, it is very unlikely that it is totally responsible for the size effect in metal cutting as inferred in Dineshet al (2001).