971 research outputs found
Probing Isospin Dynamics in Halo Nuclei
Nuclear many-body theory is used to study nuclear matter and finite nuclei at
extreme isospin. In-medium interactions in asymmetric nuclear matter are
obtained from (Dirac-) Brueckner theory. Neutron skin formation in Ni and Sn
isotopes is investigated by relativistic mean-field calculations in DDRH theory
with density dependent meson-nucleon vertices. Applications to light nuclei are
discussed with special emphasis on pairing and core polarization in weakly
bound nuclei. Approaches accounting for continuum coupling in dripline pairing
and core polarization are presented. Calculations for the halo nuclei B,
Be and C show that shell structures are dissolving when the
driplines are approached. Relativistic breakup data are well described by
eikonal calculations.Comment: 10 pages, 8 figure
National Geodetic Satellite Program, Part II: Smithsonian Astrophysical Observatory
A sequence of advances in the determination of geodetic parameters presented by the Smithsonian Astrophysical Observatory are described. A Baker-Nunn photographic system was used in addition to a ruby-laser ranging system to obtain data for refinement of geodetic parameters. A summary of the data employed to: (1) derive coordinates for the locations of various tracking stations; and (2) determine the gravitational potential of the earth, is presented
Effects of oxidized low density lipoprotein, lipid mediators and statins on vascular cell interactions
The integrin heterodimer CD11b/CD18 (alpha M beta 2, Mac-1, CR3) expressed on monocytes or polymorphonuclear leukocytes (PMN) is a receptor for iC3b, fibrinogen, heparin, and for intercellular adhesion molecule (ICAM)-1 on endothelium, crucially contributing to vascular cell interactions in inflammation and atherosclerosis. In this report, we summarize our findings on the effects of lipid mediators and lipid-lowering drugs. Exposure of endothelial cells to oxidized low density lipoprotein (oxLDL) induces upregulation of ICAM-1 and increases adhesion of monocytic cells expressing Mac-1. Inhibition experiments show that monocytes use distinct ligands, i.e. ICAM-1 and heparan sulfate proteoglycans for adhesion to oxLDL-treated endothelium. An albumin-transferable oxLDL activity is inhibited by the antioxidant pyrrolidine dithiocarbamate (PDTC), while 8-epi-prostaglandin F2 alpha (8-epi-PGF2 alpha) or lysophosphatidylcholine had no effect, implicating yet unidentified radicals. Sequential adhesive! and signaling events lead to the firm adhesion of rolling PMN on activated and adherent platelets, which may occupy areas of endothelial denudation. Shear resistant arrest of PMN on thrombin-stimulated platelets in flow conditions requires distinct regions of Mac-1, involving its interactions with fibrinogen bound to platelet alpha llb beta 3, and with other platelet ligands. Both arrest and adhesion strengthening under flow are stimulated by platelet-activating factor and leukotriene B4, but not by the chemokine receptor CXCR2. We tested whether Mac-1-dependent monocyte adhesiveness is affected by inhibitors of hydroxy-methylglutaryl-Coenzyme A reductase (statins) which improve morbidity and survival of patients with coronary heart disease. As compared to controls, adhesion of isolated monocytes to endothelium ex vivo was increased in patients with hypercholesterolemia. Treatment with statins decreased total and low density lipoprotein (LDL) cholesterol plasma levels, surface expression of Mac-1, and resulted in a dramatic reduction of Mac,mediated monocyte adhesion to endothelium. The inhibition of monocyte adhesion was reversed by mevalonate but not LDL in vitro,indicating that isoprenoid precursors are crucial for adhesiveness of Mac-1. Such effects may crucially contribute to the clinical benefit of statins, independent of cholesterol-lowering, and may represent a paradigm for novel, anti-inflammatory mechanisms of action by this class of drugs
Delocalizing effect of the Hubbard repulsion for electrons on a two-dimensional disordered lattice
We study numerically the ground-state properties of the repulsive Hubbard
model for spin-1/2 electrons on two-dimensional lattices with disordered
on-site energies. The projector quantum Monte Carlo method is used to obtain
very accurate values of the ground-state charge density distributions with
and particles. The difference in these charge densities allows us
to study the localization properties of an added particle. The results obtained
at quarter-filling on finite clusters show that the Hubbard repulsion has a
strong delocalizing effect on the electrons in disordered 2D lattices. However,
numerical restrictions do not allow us to reach a definite conclusion about the
existence of a metal-insulator transition in the thermodynamic limit in
two-dimensions.Comment: revtex, 7 pages, 7 figure
A quark model framework for the study of nuclear medium effects
A quark-model framework for studying nuclear medium effects on nucleon
resonances is described and applied here to pion photoproduction on the
deuteron, which is the simplest composite nucleon system and serves as a first
test case. Pion photoproduction on nuclei is discussed within a chiral
constituent quark model in which the quark degrees of freedom are explicitly
introduced through an effective chiral Lagrangian for the
quark-pseudoscalar-meson coupling. The advantage of this model is that a
complete set of nucleon resonances can be systematically included with a
limited number of parameters. Also, the systematic description of the nucleon
and its resonances at quark level allows us to self-consistently relate the
nuclear medium's influence on the baryon properties to the intrinsic dynamic
aspects of the baryons. As the simplest composite nucleus, the deuteron
represents the first application of this effective theory for meson
photoproduction on light nuclei. The influence of the medium on the transition
operators for a free nucleon is investigated in the Delta resonance region. No
evidence is found for a change of the Delta properties in the pion
photoproduction reaction on the deuteron since the nuclear medium here involves
just one other nucleon and the low binding energy implies low nuclear density.
However, we show that the reaction mechanism is in principle sensitive to
changes of Delta properties that would be produced by the denser nuclear medium
of heavier nuclei through the modification of the quark model parameters.Comment: Revtex, 8 pages, 4 figure
Uptake and transport of novel amphiphilic polyelectrolyte-insulin nanocomplexes by caco-2 cells - towards oral insulin
“The original publication is available at www.springerlink.com”. Copyright SpringerPurpose: The influence of polymer architecture on cellular uptake and transport across Caco-2 cells of novel amphiphilic polyelectrolyte-insulin nanocomplexes was investigated. Method: Polyallylamine (PAA) (15 kDa) was grafted with palmitoyl chains (Pa) and subsequently modified with quaternary ammonium moieties (QPa). These two amphiphilic polyelectrolytes (APs) were tagged with rhodamine and their uptake by Caco-2 cells or their polyelectrolyte complexes (PECs) with fluorescein isothiocyanate-insulin (FITC-insulin) uptake were investigated using fluorescence microscopy. The integrity of the monolayer was determined by measurement of transepithelial electrical resistance (TEER). Insulin transport through Caco-2 monolayers was determined during TEER experiments. Result: Pa and insulin were co-localised in the cell membranes while QPa complexes were found within the cytoplasm. QPa complex uptake was not affected by calcium, cytochalasin D or nocodazole. Uptake was reduced by co-incubation with sodium azide, an active transport inhibitor. Both polymers opened tight junctions reversibly where the TEER values fell by up to 35 % within 30 minutes incubation with Caco-2 cells. Insulin transport through monolayers increased when QPa was used (0.27 ngmL-1 of insulin in basal compartment) compared to Pa (0.14 ngmL-1 of insulin in basal compartment) after 2 hours. Conclusion: These APs have been shown to be taken up by Caco-2 cells and reversibly open tight cell junctions. Further work is required to optimise these formulations with a view to maximising their potential to facilitate oral delivery of insulin.Peer reviewe
Nucleon propagation through nuclear matter in chiral effective field theory
We treat the propagation of nucleon in nuclear matter by evaluating the
ensemble average of the two-point function of nucleon currents in the framework
of the chiral effective field theory. We first derive the effective parameters
of nucleon to one loop. The resulting formula for the effective mass was known
previously and gives an absurd value at normal nuclear density. We then modify
it following Weinberg's method for the two-nucleon system in the effective
theory. Our results for the effective mass and the width of nucleon are
compared with those in the literature.Comment: 11 pages including 4 figures. To appear in Eur. J. Phys.
The selective phosphodiesterase 4 inhibitor roflumilast and phosphodiesterase 3/4 inhibitor pumafentrine reduce clinical score and TNF expression in experimental colitis in mice.
The specific inhibition of phosphodiesterase (PDE)4 and dual inhibition of PDE3 and PDE4 has been shown to decrease inflammation by suppression of pro-inflammatory cytokine synthesis. We examined the effect of roflumilast, a selective PDE4 inhibitor marketed for severe COPD, and the investigational compound pumafentrine, a dual PDE3/PDE4 inhibitor, in the preventive dextran sodium sulfate (DSS)-induced colitis model. The clinical score, colon length, histologic score and colon cytokine production from mice with DSS-induced colitis (3.5% DSS in drinking water for 11 days) receiving either roflumilast (1 or 5 mg/kg body weight/d p.o.) or pumafentrine (1.5 or 5 mg/kg/d p.o.) were determined and compared to vehicle treated control mice. In the pumafentrine-treated animals, splenocytes were analyzed for interferon-γ (IFNγ) production and CD69 expression. Roflumilast treatment resulted in dose-dependent improvements of clinical score (weight loss, stool consistency and bleeding), colon length, and local tumor necrosis factor-α (TNFα) production in the colonic tissue. These findings, however, were not associated with an improvement of the histologic score. Administration of pumafentrine at 5 mg/kg/d alleviated the clinical score, the colon length shortening, and local TNFα production. In vitro stimulated splenocytes after in vivo treatment with pumafentrine showed a significantly lower state of activation and production of IFNγ compared to no treatment in vivo. These series of experiments document the ameliorating effect of roflumilast and pumafentrine on the clinical score and TNF expression of experimental colitis in mice
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