OPERATIONAL CONDITIONS AND THE STRESS-STRAIN RELATIONSHIP OF SOLID FOODS—THEORETICAL EVALUATION1

Many textural evaluation techniques are based on test procedures that involve large compressive deformations and constant deformation rates. These imply that the specimen undergoes a straining history which depends on the specimen length and in which the true strain rate increases progressively. Mathematical simulation of the real conditions in simplified rheological models indicated that single stress-strain curves may provide misleading information on the true characteristics of the material. I t is shown that the stress-strain curves of different materials can cross one another a t stmin levels that depend on test conditions. Any comparison under such circumstances may result in inconsistent conclusions. It is suggested that relaxation data may provide the complementary information for the comprehensive characterization of the mechanical properties of foods.     

Nonlinear multiresolution: a shape-from-shading example

A method for image resolution reduction that simulates the reduction of shape resolution and is to be used with shape-from-shading algorithms is presented. Resolution reduction is used for accelerating shape-from-shading algorithms using multiresolution pyramids. The goal of this correspondence is to show that resolution reduction based only on image intensities can be inferior to resolution reduction using knowledge of the surface reflectance. This is true for all cases of parameter estimation from intensity images, when the intensity is not a linear function of the parameters. Since optical reduction of images, as when moving a camera away from the object, is a simple gray-level averaging a question is cast on the general scheme of shape-from-shading. It is concluded that for accurate shape-from-shading one needs to know the distance from the object, and the shape should also be known in advance     

Optimal scale translations in noisy measurement systems

In engineering, medicine, biology and agriculture, it is often desired to replace an invasive or slow measurement method, by nondestructive, faster or less expensive methods. The inevitable question is whether the two measurement methods are interchangeable. To answer this question, the common practice is to use linear regression based equations, as scale translation rules. It is shown that this approach is not optimal, when both measurement methods are noisy. Accordingly, a new approach for method comparisons is proposed, by high fidelity translation of the readings taken on the scale of one test, to the scale of another test, and vice versa. The proposed scale translation mode is based on minimizing the sum of squares of the differences between the absolute values of the fast Fourier transform (FFT) series, derived from the readings of the compared measurement methods. Whereas regression methods attempt to find the parameters of a line that provides the best fit to the observed data pairs, the FFT equalization method strives to find the parameters of a line that can render the difference between the translated readings as close to zero as possible. The line taken is illustrated by a comparative study on several artificial datasets of linearly related paired X, Y readings, with various levels of measurement noise. Quality criteria were developed for quantitative comparison of linear regression based, scale translation models versus the new method, while using the results from the artificially generated datasets for illustration. The comparisons indicate that scale translation by the FFT equalization method is optimal in terms of these quality indexes.     

Distributed algorithms for partitioning a swarm of autonomous mobile robots

A number of recent studies address systems of mobile autonomous robots from a distributed computing point of view. Although such systems employ robots that are relatively weak and simple (i.e., dimensionless, oblivious and anonymous), they are nevertheless expected to have strong fault tolerance capabilities as a group. This paper studies the partitioning problem, where n$n$ robots must divide themselves into k$k$ size-balanced groups, and examines the impact of common orientation on the solvability of this problem. First, deterministic crash-fault-tolerant algorithms are given for the problem in the asynchronous full-compass and semi-synchronous half-compass models, and a randomized algorithm is given for the semi-synchronous no-compass model. Next, the role of common orientation shared by the robots is examined. Necessary and sufficient conditions for the partitioning problem to be solvable are given in the different timing models. Finally, the problem is proved to be unsolvable in the no-compass synchronous model.     

Enhanced red cell sodium-hydrogen exchange in microvascular angina

OBJECTIVES: Enhanced calcium content in arterial smooth muscle cells and altered reactivity of coronary vessels to alkalinization have been reported in angina pectoris due to impaired motility of coronary arteries. An altered function of sodium-hydrogen exchange, a ubiquitous membrane transport system that links proton efflux to calcium drifts, may mediate these phenomena. DESIGN AND SUBJECTS: Twenty patients with microvascular angina (stable effort angina, reversible perfusion defects during effort thallium 201 heart scintigraphy, and angiographically normal coronary arteries) were compared to 20 patients with stable effort angina due to coronary atherosclerosis and 20 healthy subjects. The sodium-hydrogen exchange was defined as the initial fraction of the amiloride-sensitive proton efflux from red cells with inhibited anion exchanger (pHi 6.00-6.05) into an Na(+)-containing medium (pHo 8.00-8.05). 12-0-tetradecanoylphorbol-13-acetate (TPA, 600 nmol.l-1) and staurosporine (100 nmol.l-1) were used as phosphorylation modulators in vitro. RESULTS: The mean red blood cell Na+/H+ exchange was increased in patients with microvascular angina (451 +/- 37 vs 142 +/- 17 and 124 +/- 21 umol H+.1 cells-1.min-1, P < 0.01). TPA and staurosporine abolished differences between the groups. CONCLUSIONS: Microvascular angina is associated with enhanced Na+/H+ exchange in erythrocytes, probably due to more extensive phosphorylation of the membrane antiporter sites.     

Models for the compressibility of layered polymeric sponges

The characteristic sigmoid compressive stress-strain relationships of sponges and their layered arrays are described by two kinds of mathematical models having three experimentally determined parameters. Since sponge compression is not accompanied by a significant cross-sectional area expansion, it was assumed that the stress in a multilayered array is the same in each layer. This enables prediction of the array's stress-strain relationship from the parameters of the individual layers and their known thickness. The applicability of the method is demonstrated with experimental data of two kinds of double-layered arrays of polyurethane sponges. It is shown that the arrays' compressive behavior can be satisfactorily predicted irrespective of the mathematical form of the model and whether the strain is expressed as engineering strain or Hencky's.