2,736 research outputs found
Short versus long range interactions and the size of two-body weakly bound objects
Very weakly bound systems may manifest intriguing "universal" properties,
independent of the specific interaction which keeps the system bound. An
interesting example is given by relations between the size of the system and
the separation energy, or scaling laws. So far, scaling laws have been
investigated for short-range and long-range (repulsive) potentials. We report
here on scaling laws for weakly bound two-body systems valid for a larger class
of potentials, i.e. short-range potentials having a repulsive core and
long-range attractive potentials. We emphasize analogies and differences
between the short- and the long-range case. In particular, we show that the
emergence of halos is a threshold phenomenon which can arise when the system is
bound not only by short-range interactions but also by long-range ones, and
this for any value of the orbital angular momentum . These results
enlarge the image of halo systems we are accustomed to.Comment: 6 pages, 1 figure. To be published in the Proceedings of the Workshop
"Hirschegg 2003: Nuclear Structure and Dynamics at the Limits", Hirschegg,
January 12 - 18, 200
Description of Heavy Quark Systems by means of Energy Dependent Potentials
We apply, for the first time, an energy dependent Schrodinger equation to
describe static properties of heavy quark systems, i.e. charmonium and
bottonium. We show that a good description of the eigenstates and reasonable
values for the widths can be obtained. Values of the radii and of the density
at the origin are also given. We compare the results to those deduced with a
Schrodinger equation implemented with potentials used so far. We note that the
energy dependence of the confining potential provides a natural mechanism for
the saturation of the spectra. Our results introduce a new class of potentials
for the description of heavy quark systems.Comment: 3 page
The development of an advanced system to cool a man in a pressure suit
Conductive cooling system for cooling man in pressurized space sui
Development of an internal restraint system for an integrated restraint-pressure suit system Report, 7 Jun. 1965 - 28 Jun. 1966
Internal restraint system, composed of liquid filled garment and separate auxiliary system, for integrated restraint pressure suit for acceleration protection and thermal transpor
Proton-helium elastic scattering: a possible high-energy polarimeter at RHIC-BNL
We examine a suggestion to use elastic scattering, as an
absolute polarimeter for high-energy polarized proton beams, by means of a
Coulomb-Nuclear Interference effect for the single-spin asymmetry ,
around the diffractive minimum of the differential cross section . Although this reaction has a fairly simple dynamical structure, our
theoretical uncertainties and the present experimental inaccuracy of the
differential cross section in this region, allows one to generate dramatic
effects for , which will be discussed.Comment: 8 pages, Latex, 4 figure
Free and smooth boundaries in 2-D finite-difference schemes for transient elastic waves
A method is proposed for accurately describing arbitrary-shaped free
boundaries in single-grid finite-difference schemes for elastodynamics, in a
time-domain velocity-stress framework. The basic idea is as follows: fictitious
values of the solution are built in vacuum, and injected into the numerical
integration scheme near boundaries. The most original feature of this method is
the way in which these fictitious values are calculated. They are based on
boundary conditions and compatibility conditions satisfied by the successive
spatial derivatives of the solution, up to a given order that depends on the
spatial accuracy of the integration scheme adopted. Since the work is mostly
done during the preprocessing step, the extra computational cost is negligible.
Stress-free conditions can be designed at any arbitrary order without any
numerical instability, as numerically checked. Using 10 grid nodes per minimal
S-wavelength with a propagation distance of 50 wavelengths yields highly
accurate results. With 5 grid nodes per minimal S-wavelength, the solution is
less accurate but still acceptable. A subcell resolution of the boundary inside
the Cartesian meshing is obtained, and the spurious diffractions induced by
staircase descriptions of boundaries are avoided. Contrary to what occurs with
the vacuum method, the quality of the numerical solution obtained with this
method is almost independent of the angle between the free boundary and the
Cartesian meshing.Comment: accepted and to be published in Geophys. J. In
ELEVATED SERUM LEVELS OF TNF SOLUBLE RECEPTORS IN PATIENTS WITH POSITIVE ANTI-NEUTROPHIL CYTOPLASMIC ANTIBODIES
ANCA are found in various systemic vasculitis and are supposed to play a role in the pathogenesis of the disease, in cooperation with other factors such as cytokines. A total of 36 ANCA-positive and 10 ANCA-negative serum samples were analysed for the presence of TNF soluble receptors (TNF-sR), which are shed from the surface of activated cells and may act as TNF inhibitors. Of the ANCA-positive samples, 67% had elevated TNF-sR75 and 72% had elevated TNF-sR55 compared to ANCA-negative specimens (mean [S.E.] 18.7 [17.3] vs 3.6 [1.5] and 10.5 [9.7] vs 1.9 [0.7] ng/ml, P<0.01). Elevation of TNF-sR in patients with ANCA suggests that cytokines and their inhibitors are involved in the pathogenesis of ANCA-associated autoimmune disease
The size of two-body weakly bound objects : short versus long range potentials
The variation of the size of two-body objects is investigated, as the
separation energy approaches zero, with both long range potentials and short
range potentials having a repulsive core. It is shown that long range
potentials can also give rise to very extended systems. The asymptotic laws
derived for states with angular momentum l=1,2 differ from the ones obtained
with short range potentials. The sensitivity of the asymptotic laws on the
shape and length of short range potentials defined by two and three parameters
is studied. These ideas as well as the transition from the short to the long
range regime for the l=0 case are illustrated using the Kratzer potential.Comment: 5 pages, 3 figures, submitted to Physical Review Letter
Evaluation of Vascular Control Mechanisms Utilizing Video Microscopy of Isolated Resistance Arteries of Rats
This protocol describes the use of in vitro television microscopy to evaluate vascular function in isolated cerebral resistance arteries (and other vessels), and describes techniques for evaluating tissue perfusion using Laser Doppler Flowmetry (LDF) and microvessel density utilizing fluorescently labeled Griffonia simplicifolia (GS1) lectin. Current methods for studying isolated resistance arteries at transmural pressures encountered in vivo and in the absence of parenchymal cell influences provide a critical link between in vivo studies and information gained from molecular reductionist approaches that provide limited insight into integrative responses at the whole animal level. LDF and techniques to selectively identify arterioles and capillaries with fluorescently-labeled GS1 lectin provide practical solutions to enable investigators to extend the knowledge gained from studies of isolated resistance arteries. This paper describes the application of these techniques to gain fundamental knowledge of vascular physiology and pathology in the rat as a general experimental model, and in a variety of specialized genetically engineered designer rat strains that can provide important insight into the influence of specific genes on important vascular phenotypes. Utilizing these valuable experimental approaches in rat strains developed by selective breeding strategies and new technologies for producing gene knockout models in the rat, will expand the rigor of scientific premises developed in knockout mouse models and extend that knowledge to a more relevant animal model, with a well understood physiological background and suitability for physiological studies because of its larger size
Supplemented low-protein diets : are they superior in chronic renal failure?
CITATION: Herselman, M. G. et al 1995. Supplemented low-protein diets : are they superior in chronic renal failure? South African Medical Journal, 85(5):361-365.The original publication is available at http://www.samj.org.zaTwenty-two patients with chronic renal failure were randomly assigned to a conventional low-protein diet containing 0,6g protein/kg/day or a very-low-protein diet containing 0,6g protein/kg/day supplemented with essential amino acids; they were followed up for 9 months. There were no significant changes in body mass index, arm muscle area, percentage body fat, serum albumin and transferrin levels in any of the groups; neither was there any difference between the groups in respect of these parameters. Renal function, as measured by the reciprocal of serum creatinine over time, stabilised in both groups during intervention, with no significant difference between the groups. There was however no correlation between changes in renal function and changes in blood pressure, or dietary intake of protein, phosphorus, cholesterol, polyunsaturated and saturated fatty acids. There were also no significant changes and no significant differences between the groups in serum levels of parathyroid hormone and alkaline phosphatase, urine cyclic adenosine monophosphate, tubular reabsorption of phosphate, and the theoretical renal threshold for phosphate. The results of this study suggest that the supplemented very-low-protein diet was not superior to the conventional low-protein diet in terms of its effect on protein-energy status, renal function and biochemical parameters of renal osteodystrophy.Publisher’s versio
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