464 research outputs found
Solving the Richardson equations for Fermions
Forty years ago Richardson showed that the eigenstates of the pairing
Hamiltonian with constant interaction strength can be calculated by solving a
set of non-linear coupled equations. However, in the case of Fermions these
equations lead to singularities which made them very hard to solve. This letter
explains how these singularities can be avoided through a change of variables
making the Fermionic pairing problem numerically solvable for arbitrary single
particle energies and degeneracies.Comment: 5 pages, 4 figures, submitted to Phys.Rev.
A Sub-Picojoule per Bit Integrated Magneto-Optic Modulator on Silicon: Modeling and Experimental Demonstration
Integrated magneto-optic (MO) modulators are an attractive but not fully explored alternative to electro-optic (EO) modulators. They are current driven, structurally simple, and could potentially achieve high efficiency in cryogenic and room temperature environments where fJ bit−1 optical interfaces are needed. In this paper, the performance and energy efficiency of a novel MO modulator at room temperature are for the first time assessed. First, a model of the micro-ring-based modulator is implemented to investigate the design parameters and their influence on the performance. Then, a fabricated device is experimentally characterized to assess its performance in terms of bit rate and energy efficiency. The model shows efficient operation at 1.2 Gbps using a 16 mA drive current, consuming only 155 fJ bit−1. The experimental results show that the MO effect is suitable for modulation, achieving error-free operation above 16 mA with a power consumption of 258 fJ bit−1 at a transient limited data rate of 1.2 Gbps
A quantum Monte-Carlo method for fermions, free of discretization errors
In this work we present a novel quantum Monte-Carlo method for fermions,
based on an exact decomposition of the Boltzmann operator . It
can be seen as a synthesis of several related methods. It has the advantage
that it is free of discretization errors, and applicable to general
interactions, both for ground-state and finite-temperature calculations. The
decomposition is based on low-rank matrices, which allows faster calculations.
As an illustration, the method is applied to an analytically solvable model
(pairing in a degenerate shell) and to the Hubbard model.Comment: 5 pages, 4 figures, submitted to Phys. Rev. Let
Continuous Time Quantum Monte Carlo Method for Fermions: Beyond Auxiliary Field Framework
Numerically exact continuous-time Quantum Monte Carlo algorithm for finite
fermionic systems with non-local interactions is proposed. The scheme is
particularly applicable for general multi-band time-dependent correlations
since it does not invoke Hubbard-Stratonovich transformation. The present
determinantal grand-canonical method is based on a stochastic series expansion
for the partition function in the interaction representation. The results for
the Green function and for the time-dependent susceptibility of multi-orbital
super-symmetric impurity model with a spin-flip interaction are presented
IL-6-induced anaemia in rats:Possible pathogenetic implications for anaemia observed in chronic inflammations
Anaemia of chronic disease (ACD) is frequently found in rheumatoid arthritis (RA). In the pathogenesis of ACD both cytokines, such as tumour necrosis factor-alpha (TNF-α), IL-1 and IL-6 as well as a relative deficiency of erythropoietin (EPO), are thought to play a key role. In the present study the role of IL-6 in the pathogenesis of this anaemia was investigated. IL-6 was administered intraperitoneally to rats for 14 sequential days. It appeared that IL-6 was able to induce anaemia. No evidence for suppression of bone marrow erythropoiesis or enhanced sequestration of erythrocytes in the liver was found. However, decreased plasma and bone marrow iron contents were observed in anaemic rats. Blood loss in intestinal tissue was demonstrated using erythrocyte labelling with 99mtechnetium. Histologically this was associated with inflammatory cell infiltration, oedema and bleeding in the intestinal wall. In conclusion, IL-6 induced anaemia in rats. This anaemia was caused by intestinal blood loss.</p
Brane-bulk matter relation for a purely conical codimension-2 brane world
We study gravity on an infinitely thin codimension-2 brane world, with purely
conical singularities and in the presence of an induced gravity term on the
brane. We show that in this approximation, the energy momentum tensor of the
bulk is strongly related to the energy momentum tensor of the brane and thus
the gravity dynamics on the brane are induced by the bulk content. This is in
contrast with the gravity dynamics on a codimension-1 brane. We show how this
strong result is relaxed after including a Gauss-Bonnet term in the bulk.Comment: 12 pages, mistake corrected, references adde
Level density and thermal properties in rare earth nuclei
A convergent method to extract the nuclear level density and the gamma-ray
strength function from primary gamma-ray spectra has been established.
Thermodynamical quantities have been obtained within the microcanonical and
canonical ensemble theory. Structures in the caloric curve and in the heat
capacity curve are interpreted as fingerprints of breaking of Cooper pairs and
quenching of pairing correlations. The strength function can be described using
models and common parameterizations for the E1, M1 and pygmy resonance
strength. However, a significant decrease of the pygmy resonance strength at
finite temperatures has been observed.Comment: 15 pages including 8 figures. Proceedings article for the conference
Nuclear Structure and Related Topics, Dubna, Russia, June 6-10, 200
Evaluation of NV556, a Novel Cyclophilin Inhibitor, as a Potential Antifibrotic Compound for Liver Fibrosis
Hepatic fibrosis can result as a pathological response to nonalcoholic steatohepatitis (NASH). Cirrhosis, the late stage of fibrosis, has been linked to poor survival and an increased risk of developing hepatocellular carcinoma, with limited treatment options available. Therefore, there is an unmet need for novel effective antifibrotic compounds. Cyclophilins are peptidyl-prolyl cis-trans isomerases that facilitate protein folding and conformational changes affecting the function of the targeted proteins. Due to their activity, cyclophilins have been presented as key factors in several stages of the fibrotic process. In this study, we investigated the antifibrotic effects of NV556, a novel potent sanglifehrin-based cyclophilin inhibitor, in vitro and in vivo. NV556 potential antifibrotic effect was evaluated in two well-established animal models of NASH, STAM, and methionine-choline-deficient (MCD) mice, as well as in an in vitro 3D human liver ECM culture of LX2 cells, a human hepatic stellate cell line. We demonstrate that NV556 decreased liver fibrosis in both STAM and MCD in vivo models and decreased collagen production in TGFβ1-activated hepatic stellate cells in vitro. Taken together, these results present NV556 as a potential candidate for the treatment of liver fibrosis
Decellularized human liver as a natural 3D-scaffold for liver bioengineering and transplantation
Liver synthetic and metabolic function can only be optimised by the growth of cells within a supportive liver matrix. This can be achieved by the utilisation of decellularised human liver tissue. Here we demonstrate complete decellularization of whole human liver and lobes to form an extracellular matrix scaffold with a preserved architecture. Decellularized human liver cubic scaffolds were repopulated for up to 21 days using human cell lines hepatic stellate cells (LX2), hepatocellular carcinoma (Sk-Hep-1) and hepatoblastoma (HepG2), with excellent viability, motility and proliferation and remodelling of the extracellular matrix. Biocompatibility was demonstrated by either omental or subcutaneous xenotransplantation of liver scaffold cubes (5 × 5 × 5 mm) into immune competent mice resulting in absent foreign body responses. We demonstrate decellularization of human liver and repopulation with derived human liver cells. This is a key advance in bioartificial liver development
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