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PubMed2004

Statistical mechanical theory for the structure of steady state systems: application to a Lennard-Jones fluid with applied temperature gradient.

The constrained entropy and probability distribution are given for the structure that develops in response to an applied thermodynamic gradient, as occurs in driven steady state systems. The theory is linear but is applicable to gradients with arbitrary spatial variation. The phase space probability distribution is also given, and it is surprisingly simple with a straightforward physical interpretation. With it, all of the known methods of equilibrium statistical mechanics for inhomogeneous systems may now be applied to determining the structure of nonequilibrium steady state systems. The theory is illustrated by performing Monte Carlo simulations on a Lennard-Jones fluid with externally imposed temperature and chemical potential gradients. The induced energy and density moments are obtained, as well as the moment susceptibilities that give the rate of change of these with imposed gradient and which also give the fluctuations in the moments. It is shown that these moment susceptibilities can be written in terms of bulk susceptibilities and also that the Soret coefficient can be expressed in terms of them.

Journal Article↗
PubMed1997

Immunons revisited: binding of multivalent antigens to B cells.

The T-independent B cell response induced by highly multivalent hapten polymer preparations has been studied extensively. The in vitro measured dose-response curve tends to be roughly bell-shaped with the peak response occurring at very low ligand concentrations, between 0.1-1 ng/ml for a variety of different ligands. Furthermore, polymers with more than approximately 10 haptens tend to be stimulatory, whereas polymers with fewer than 10 haptens conjugated, tend to be inhibitory. These observations have been perplexing when viewed within the context of standard theories of receptor ligation by multivalent ligands. We present a new analysis of these previous experiments that reconciles the differences between theory and experiment. From this theory it is concluded that the peak in the observed dose response curve only weakly reflects properties of the ligand and the affinity of surface immunoglobulin for the hapten, but depends strongly on the density of antigen-specific B cells in the culture. The number of responding cells decreases at low ligand concentrations, because cells have to share limiting amounts of ligand and not because of the decreasing probability of receptors and ligands meeting each other. Our theory leads to the same conclusion as made by previous researchers, namely that a minimum number of receptor sites, of the order of 10, need to be bound to a single ligand in order to stimulate a B cell. While this conclusion was based on the lack of immunogenicity of antigens carrying less than a minimum number of haptens, the quantitative results of this study, derived from fitting experimental dose response curves obtained with highly multivalent antigens, provide evidence for the immunon hypothesis that is based upon the degree of receptor aggregation. Our theory also provides quantitative agreement with experimental observations on systems, in which both stimulatory and non-stimulatory polymers are mixed in the same system.

Dose-Response Relationship, Immunologic↗
PubMed1996

Exploration strategies for hydrothermal deposits.

With unlimited money the most certain strategy for finding most hydrothermal metal deposits would be by drilling to 5000 m at 50 m spacing. However, the cost would far outweigh the benefit of the discoveries. Geological knowledge and exploration techniques may be used to obtain the greatest benefit for minimum cost, and to concentrate human and material resources in the most economic way in areas with the highest probability of discovery. This paper reviews the economic theory of exploration based on expected value, and the application of geological concepts and exploration techniques to exploration for hydrothermal deposits. Exploration techniques for hydrothermal-systems on Mars would include geochemistry and particularly passive geophysical methods.

Alpha Particles↗
PubMed1980

Within-species brain-body weight variability: a reexamination of the Danish data and other primate species.

A restudy of the Danish brain weight data published by Pakkenberg and Voigt ('64), using partial correlation techniques, confirms and extends their earlier conclusions regarding a much stronger allometric relationship between height and brain weight than between body weight and brain weight. The relationship is particularly strong in males, and not in females, which is hypothesized to be related to higher fat components in the latter. Comparative data for smaller samples of Pan, Gorilla, Pongo, Macaca, Papio, and Saimiri using body weights, suggest that such relationships also hold more strongly in males than females, although more reliable data are greatly needed. In addition to providing within-species ranges of variability for variously derived neural statistics (e.g., encephalization quotients, "extra neurons," etc.), for "normal" primates, it is suggested that while allometric trends do exist within species, and particularly males, evolutionary pressures leading to larger brain size were probably very diverse, and that any one homogenistic theory is unlikely.

Adolescent↗
PubMed2000

Detection of nuclear resonance signals: modification of the receiver operating characteristics using feedback.

The performance of a nuclear resonance detection system can be quantified using binary detection theory. Within this framework, signal averaging increases the probability of a correct detection and decreases the probability of a false alarm by reducing the variance of the noise in the average signal. In conjunction with signal averaging, we propose another method based on feedback control concepts that further improves detection performance. By maximizing the nuclear resonance signal amplitude, feedback raises the probability of correct detection. Furthermore, information generated by the feedback algorithm can be used to reduce the probability of false alarm. We discuss the advantages afforded by feedback that cannot be obtained using signal averaging. As an example, we show how this method is applicable to the detection of explosives using nuclear quadrupole resonance.

Algorithms↗
PubMed1995

Analytical solutions of the dinucleotide probability after and before random mutations.

The mutation process is a classical evolutionary genetic process mainly based on the (random) substitutions of one base (A = Adenine, C = Cytosine, G = Guanine, T = Thymine) for another. Two analytical solutions derived here allow us to analyse in genes the occurrence probabilities of motifs (e.g. dinucleotides) after substitutions (in the evolutionary sense: from the past to the present) and, unexpectedly, also before substitutions (after back substitutions, in the inverse evolutionary sense: from the present to the past). We generalize on the alphabet [A, C, G, T] of the analytical solutions and of the properties derived on the alphabet [R, Y] (R = purine = A or G, Y = pyrimidine = C or T). Application of the theory is based on the analytical solution giving the probabilities of the 16 dinucleotides AA, ..., TT in the protein (coding) genes of (nuclear) eukaryotes, viruses and prokaryotes and in (eukaryotic) introns after back substitutions (called primitive genes). After back substitutions, four of 16 dinucleotides--CG, TA, GT and AC--occur with low probabilities in each of these four primitive gene populations, except for CG in the primitive prokaryotic protein genes. In the primitive eukaryotic protein genes, the dinucleotide AT has also a significant low probability. We present the properties of the two analytical solutions, and the functions which may have these five dinucleotides in primitive genes are described in terms of biological signals.

Animals↗
PubMed1987

Evolution, games theory and polyhedra.

The problem of finding an Evolutionary Stable Strategy (ESS) for an animal species is defined. It is shown how such strategies are a subset of the equilibrium solutions for a particular non-zero sum game. These equilibrium solutions are then shown to arise from the vertices of a particular convex polyhedron. A method of finding these equilibrium solutions through the vertices and then the ESS solutions is given. This is illustrated by a number of numerical examples taken from the literature. Finally an alternative approach based on solving a Linear Complementarity Problem is discussed.

Animals↗
PubMed1992

Pathogenesis of diastematomyelia: can a surgical model in the chick embryo give some clues about the human malformation?

To reproduce diastematomyelia, a sagittal incision was carried out at the level of the rhomboidal sinus of 36- to 40-h-old chick embryos. A small piece of membrane shell, a small agar screen, or a piece of quail isochronous isotopic notochord was inserted into the gap. The embryos were killed and fixed after 9 days' incubation. Diastematomyelia was obtained in several embryos treated with interposition of a membrane screen or a piece of quail notochord. Microscopic examination revealed two hemicords, each containing its own central canal; in some cases one of the cords showed hydromyelia. Absence of the rump was seen in association with experimental diastematomyelia. The interposition of a resorbable agar screen did not succeed in reproducing diastematomyelia. The results of these surgical manipulations suggest that diastematomyelia cannot be explained by a primary disorder of neurulation. It supports the theory of noninvolution of a firm midline structure (probably the neurenteric canal, rapidly surrounded by mesodermal cells originating from the notochord), which prevents the fusion of the separated parts.

Animals↗
PubMed1980

A transducer function for threshold and suprathreshold human vision.

A nonlinear function is derived to describe the contrast transduction process for human visual mechanisms. This function is sigmoid in form, having an accelerating nonlinearity at low contrasts and a compressive nonlinearity at high contrasts. The resulting formulation is consistent with both signal detection theory and with Quick's (1974) equation for probability summation. Similarities between the present description of human vision and properties of complex cells in cat visual cortex are noted.

Animals↗
PubMed1981

Entropy measures of signal in the presence of noise: evidence for 'byte' versus 'bit' processing in the nervous system.

A method for detecting signal in the presence of noise in a highly specific way is described. Using action potential interval data from 12 neurons in rat cerebellum, we have demonstrated that the sequential ordering of spike intervals contains both noise and signal. We have identified and quantified the magnitude of relative entropy (uncertainty) of specified sets of interval patterns, ranging in length from 3-5 successive intervals. Some of these sets have exceptionally low entropy and thus seem to be especially meaningful as a set ('word') to the brain.

Action Potentials↗
PubMed1986

The effect of the myotoxic agent iodoacetate on dystrophic mice 129/Re.

Three groups of dystrophic and non-dystrophic mice 129/Re were used for studying the effect of the myotoxic agent iodoacetate on dystrophic muscle. The mice of the first group were given intramuscular injections of iodoacetate. The mice of the second group were injected with normal saline and the third group was maintained as untreated controls. The most severe histopathological changes were found in the dystrophic mice treated with iodoacetate. The non-dystrophic mice of the same group showed a significant increase in the number of internal nuclei. Moderate changes were observed in saline-treated dystrophic controls. There was no significant decrease in the life expectancy in any of the groups. The body weight of dystrophic mice was reduced throughout the experiment. On the contrary the non-dystrophic group showed an increased in weight, regardless of the treatment. The aggravation of the histopathological changes of dystrophic mice by iodoacetate would probably give support to the cyclical necrosis/abnormal regeneration theory of pathogenesis of muscular dystrophy.

Animals↗
PubMed1985

The stochastic determinants of hospital-bed supply.

This paper uses a general queuing-theoretic model to derive more appropriate measures of hospital quality, such as turn-away probabilities and patient's expected waiting time, than have been used in recent empirical work [e.g., Joskow (1980)].

Health Facility Size↗