15,596 research outputs found
Phase Transitions of Neural Networks
The cooperative behaviour of interacting neurons and synapses is studied
using models and methods from statistical physics. The competition between
training error and entropy may lead to discontinuous properties of the neural
network. This is demonstrated for a few examples: Perceptron, associative
memory, learning from examples, generalization, multilayer networks, structure
recognition, Bayesian estimate, on-line training, noise estimation and time
series generation.Comment: Plenary talk for MINERVA workshop on mesoscopics, fractals and neural
networks, Eilat, March 1997 Postscript Fil
Visualization of leukocyte transendothelial and interstitial migration using reflected light oblique transillumination in intravital video microscopy
Dynamic visualization of the intravascular events leading to the extravasation of leukocytes into tissues by intravital microscopy has significantly expanded our understanding of the underlying molecular processes. In contrast, the detailed observation of leukocyte transendothelial and interstitial migration in vivo has been hampered by the poor image contrast of cells within turbid media that is obtainable by conventional brightfield microscopy. Here we present a microscopic method, termed reflected light oblique transillumination microscopy, that makes use of the optical interference phenomena generated by oblique transillumination to visualize subtle gradients of refractive indices within tissues for enhanced image contrast. Using the mouse cremaster muscle, we demonstrate that this technique makes possible the reliable quantification of extravasated leukocytes as well as the characterization of morphological phenomena of leukocyte transendothelial and interstitial migration
High density culturing of porcine hepatocytes immobilized on nonwoven polyurethane-based biomatrices
Objective: Hepatocytes are increasingly used as functional units in bioartificial liver devices. The objective of the present study was to investigate the feasibility of culturing porcine hepatocytes in high density on a novel polyurethane-based nonwoven three-dimensional matrix. We investigated (1) the optimal cell density within this culture configuration, (2) the maintenance of liver-specific morphology and cell functions over long-term periods and (3) the necessity to apply an additional extracellular matrix component (collagen gel). Methods: Nonwoven polyurethane matrices were manufactured by a specially developed fiber extrusion technology. Pig hepatocytes were cultured at various cell densities of 0.1, 0.25, 0.5, 0.75, 1 and 2 x 10(6) cells/cm(2) on three-dimensional networks of nonwoven polyurethane matrices and cell adhesion as well as functional parameters (DNA of nonattached/attached cells, lactate dehydrogenase release and cytochrome P450 activity) were determined. To assess the performance of cells within this configuration albumin and urea excretion was measured over 8 days. The potentially beneficial effect of an additional extracellular matrix configuration was evaluated by comparing the average albumin synthesis in groups of identical cell numbers. Results: The optimal cell density in this three-dimensional culture configuration was 1 x 10(6) cells/cm(2). The functional capacity of hepatocytes was stable for 8 days at an average level of 53.7 +/- 5.6 ng/h/mug DNA and of 1.8 +/- 0.14 mug/h/mug DNA for albumin and urea excretion, respectively. The supplementation of an extracellular matrix configuration did not improve functional activity of cells. Average albumin synthesis was 35.6 ng/h/mug DNA (28.7, 42.8) and 32.7 ng/h/mug DNA (23.4, 49.2) for collagen-immobilized and control cultures, respectively, Conclusion: The results of the study indicate that nonwoven polyurethane sheets supply a biocompatible support structure for functionally active high density cultures. Thus, nonwoven polyurethane matrices should be further investigated on with respect to their role in the development, optimization and design of bioartificial liver systems. Copyright (C) 2001 S.Karger AG, Basel
European surveillance of infections in cancer patients - ESIC
Major advances in cancer therapy result from development of multidrug chemotherapy regimens. Besides death from tumor progression, infections are currently one of the major causes of mortality and morbidity. Because of the risk of complications and mortality, the treatment for febrile neutropenia is admission to hospital and administration of broad-spectrum antibiotics. Response rates of initial antimicrobial treatment vary considerably (40-92%). Due to the heterogeneity of populations in randomized studies, comparison of efficacy and identification of risk factors is limited. This is the main reason why the European Society of Biomodulation and Chemotherapy (ESBiC) is conducting a surveillance study that concentrates more on the evaluation of risk factors than on the therapeutic outcome of prospective randomized antimicrobial regimens: European Surveillance of Infections in Cancer Patients (ESIC). The present contribution is to determine which cancer patients are at low risk for fever, and can benefit from first-line treatment with treatment options such as monotherapy as well as on an outpatient basis
On the concepts of radial and angular kinetic energies
We consider a general central-field system in D dimensions and show that the
division of the kinetic energy into radial and angular parts proceeds
differently in the wavefunction picture and the Weyl-Wigner phase-space
picture. Thus, the radial and angular kinetic energies are different quantities
in the two pictures, containing different physical information, but the
relation between them is well defined. We discuss this relation and illustrate
its nature by examples referring to a free particle and to a ground-state
hydrogen atom.Comment: 10 pages, 2 figures, accepted by Phys. Rev.
A combined ion-sputtering and electron-beam annealing device for the in vacuo postpreparation of scanning probes
Universal quantum computer from a quantum magnet
We show that a local Hamiltonian of spin-3/2 particles with only two-body
nearest-neighbor Affleck-Kennedy-Lieb-Tasaki and exchange-type interactions has
an unique ground state, which can be used to implement universal quantum
computation merely with single-spin measurements. We prove that the Hamiltonian
is gapped, independent of the system size. Our result provides a further step
towards utilizing systems with condensed matter-type interactions for
measurement-based quantum computation.Comment: 5 pages, 3 figure
Histologic, Immunohistochemical and Morphometric Study of the Mucosa of the total gastric antrum in Patients with carcinoma of the stomach.
Conformational transformations induced by the charge-curvature interaction at finite temperature
The role of thermal fluctuations on the conformational dynamics of a single
closed filament is studied. It is shown that, due to the interaction between
charges and bending degrees of freedom, initially circular aggregates may
undergo transformation to polygonal shape. The transition occurs both in the
case of hardening and softening charge-bending interaction. In the former case
the charge and curvature are smoothly distributed along the chain while in the
latter spontaneous kink formation is initiated. The transition to a
non-circular conformation is analogous to the phase transition of the second
kind.Comment: 23 pages (Latex), 10 figures (Postscript), 2 biblio file (bib-file
and bbl-file
Isolation and characterization of cGMP phosphodiesterase from bovine rod outer segments
Journal ArticleA simple purification method has been developed for isolation of bovine cGMP phosphodiesterase from photoreceptor rod outer segments. The enzyme is peripherally membrane bound in its native state and is present in relatively high concentrations. In the bovine photoreceptors its molar ratio to rhodopsin can be estimated to be as great as 1:40 and not lower than 1: 170. The isolated enzyme is purified to homogeneity as demonstrated by gel electrophoresis under native and denaturing conditions and analytical ultracentrifuga- Con. The core enzyme has a molecular weight of approximately 170,000, as demonstrated by sucrose gradient centrifugation and analytical ultracentrifugation, and is composed of two major subunits, 88,000 (CY) and 84,000 (p), augmented by a small subunit of 13,000 (y). In its purified state, the enzyme is activated neither by light nor GTP in contrast to the native membranebound enzyme. As isolated, the molar activity of the enzyme is 45 mol of cGMP hydrolized s-' mol-' with a Km = 150 PM (cGMP) and Km > 4 XnM (CAMP). Protamine activates the enzyme to 360 mol of cGMP see-' mol-' @-fold) and limited digestion by trypsin activates it to as great as 2100 mol of cGMP s-l mol-' @O-fold)
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