11,278 research outputs found
Organs from animals for man
In the following review some of the problems of xenotransplantation shall be discussed, based on the few experimental data available so far and on reports in the literature describing investigations which may be of importance for xenotransplantation. The impact of gravity on the upright posture of man versus almost all other mammals, the dysfunction between enzymes and hormones in different species and the lack of interactions between interleukins, cytokines and vasoactive substances will be taken into consideration. The question must be asked whether different levels of carrier molecules or serum proteins play a role in the physiological network. Even though the development of transgenic animals or other imaginative manipulations may lead to the acceptance of any type of xenografted organ, it has to be established for how long the products of the xenografts are able to act in the multifactorial orchestra. We are far from understanding xenogeneic molecular mechanisms involved in toxicity, necrosis and apoptosis or even reperfusion injury and ischemia in addition to the immediate mechanisms of the hyperacute xenogeneic rejection. Here, cell adhesion, blood clotting and vasomotion collide and bring micro-and macrocirculation to a standstill. All types of xenogeneic immunological mechanisms studied so far were found to have a more serious impact than those seen in allogeneic transplantation. In addition we are now only beginning to understand that so-called immunological parameters in allogeneic mechanisms act also in a true physiological manner in the xenogeneic situation. These molecular mechanisms occur behind the curtain of hyperacute, accelerated, acute or chronic xenograft rejection of which only some folds have been lifted to allow glimpses of part of the total scene. Other obstacles are likely to arise when long-term survival is achieved. These obstacles include retroviral infections, transfer of prions and severe side effects of the massive immunosuppression which will be needed. Moral, ethical and religious concerns are under debate and the species-specific production of proteins of the foreign donor species developed for clinical use suddenly appears to be a greater problem than anticipated
Effective field theory description of halo nuclei
Nuclear halos emerge as new degrees of freedom near the neutron and proton
driplines. They consist of a core and one or a few nucleons which spend most of
their time in the classically-forbidden region outside the range of the
interaction. Individual nucleons inside the core are thus unresolved in the
halo configuration, and the low-energy effective interactions are short-range
forces between the core and the valence nucleons. Similar phenomena occur in
clusters of He atoms, cold atomic gases near a Feshbach resonance, and some
exotic hadrons. In these weakly-bound quantum systems universal scaling laws
for s-wave binding emerge that are independent of the details of the
interaction. Effective field theory (EFT) exposes these correlations and
permits the calculation of non-universal corrections to them due to
short-distance effects, as well as the extension of these ideas to systems
involving the Coulomb interaction and/or binding in higher angular-momentum
channels. Halo nuclei exhibit all these features. Halo EFT, the EFT for halo
nuclei, has been used to compute the properties of single-neutron, two-neutron,
and single-proton halos of s-wave and p-wave type. This review summarizes these
results for halo binding energies, radii, Coulomb dissociation, and radiative
capture, as well as the connection of these properties to scattering
parameters, thereby elucidating the universal correlations between all these
observables. We also discuss how Halo EFT's encoding of the long-distance
physics of halo nuclei can be used to check and extend ab initio calculations
that include detailed modeling of their short-distance dynamics.Comment: 104 pages, 31 figures. Topical Review for Journal of Physics G. v2
incorporates several modifications, particularly to the Introduction, in
response to referee reports. It also corrects multiple typos in the original
submission. It corresponds to the published versio
Microjansky sources at 1.4 GHz
We present a deep 1.4 GHz survey made with the Australia Telescope Compact
Array (ATCA), having a background RMS of 9 microJy near the image phase centre,
up to 25 microJy at the edge of a 50' field of view. Over 770 radio sources
brighter than 45 microJy have been catalogued in the field. The differential
source counts in the deep field provide tentative support for the growing
evidence that the microjansky radio population exhibits significantly higher
clustering than found at higher flux density cutoffs. The optical
identification rate on CCD images is approximately 50% to R=22.5, and the
optical counterparts of the faintest radio sources appear to be mainly single
galaxies close to this optical magnitude limit.Comment: 6 pages, 4 figures, accepted by ApJ Letters 4 May 199
Ascent control studies of the 049 and ATP parallel burn solid rocket motor shuttle configurations
The control authority approach is discussed as a major problem of the parallel burn soil shuttle configuration due to the many resulting system impacts regardless of the approach. The major trade studies and their results, which led to the recommendation of an SRB TVC control authority approach are presented
Coherent polychotomous waves from an attractive well
A novel effect of a wave packet scattering off an attractive one- dimensional
well is found numerically and analytically. For a wave packet narrower than the
width of the well, the scattering proceeds through a quasi-bound state of
almost zero energy. The wave reflected from the well is a polychotomous
(multiple peak) monochromatic and coherent train. The transmitted wave is a
spreading smooth wave packet. The effect is strong for low average speeds of
the packet, and it disappears for wide packets.Comment: Latex, 8 eps figure
Recent Developments in the Nuclear Many-Body Problem
The study of quantum chromodynamics (QCD) over the past quarter century has
had relatively little impact on the traditional approach to the low-energy
nuclear many-body problem. Recent developments are changing this situation. New
experimental capabilities and theoretical approaches are opening windows into
the richness of many-body phenomena in QCD. A common theme is the use of
effective field theory (EFT) methods, which exploit the separation of scales in
physical systems. At low energies, effective field theory can explain how
existing phenomenology emerges from QCD and how to refine it systematically.
More generally, the application of EFT methods to many-body problems promises
insight into the analytic structure of observables, the identification of new
expansion parameters, and a consistent organization of many-body corrections,
with reliable error estimates.Comment: 15 pages, 10 figures, plenary talk at the 11th Conference on Recent
Progress in Many-Body Theories (MB 11), Manchester, England, 9-13 Jul 200
Xenogeneic, extracorporeal liver perfusion in primates improves the ratio of branched-chain amino acids to aromatic amino acids (Fischer's ratio)
In fulminant hepatic failure (FHF), the development of hepatic encephalopathy is associated with grossly abnormal concentrations of plasma amino acids (PAA). Normalization of the ratio of branched-chain amino acids to aromatic amino acids (Fischer's ratio) correlates with clinical improvement. This study evaluated changes in PAA metabolism during 4 h of isolated, normothermic extracorporeal liver perfusion using a newly designed system containing human blood and a rhesus monkey liver. Bile and urea production were within the physiological range. Release of the transaminases AST, ALT and LDH were minimal. The ratio of branched (valine, leucine, isoleucine) to aromatic (tyrosine, phenylalanine) amino acids increased significantly. These results indicate that a xenogeneic extracorporeal liver perfusion system is capable of significantly increasing Fischer's ratio and may play a role in treating and bridging patients in FHF in the future
Generalized Swiss-cheese cosmologies: Mass scales
We generalize the Swiss-cheese cosmologies so as to include nonzero linear
momenta of the associated boundary surfaces. The evolution of mass scales in
these generalized cosmologies is studied for a variety of models for the
background without having to specify any details within the local
inhomogeneities. We find that the final effective gravitational mass and size
of the evolving inhomogeneities depends on their linear momenta but these
properties are essentially unaffected by the details of the background model.Comment: 10 pages, 14 figures, 1 table, revtex4, Published form (with minor
corrections
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