Pairing correlations beyond the mean field

We discuss dynamical pairing correlations in the context of configuration mixing of projected self-consistent mean-field states, and the origin of a divergence that might appear when such calculations are done using an energy functional in the spirit of a naive generalized density functional theory.Comment: Proceedings of the XIII Nuclear Physics Workshop ``Maria and Pierre Curie'' on ``Pairing and beyond - 50 years of the BCS model'', held at Kazimierz Dolny, Poland, September 27 - October 1, 2006. Int. J. Mod. Phys. E, in prin

Computational Multiscale Methods for Linear Poroelasticity with High Contrast

In this work, we employ the Constraint Energy Minimizing Generalized Multiscale Finite Element Method (CEM-GMsFEM) to solve the problem of linear heterogeneous poroelasticity with coefficients of high contrast. The proposed method makes use of the idea of energy minimization with suitable constraints in order to generate efficient basis functions for the displacement and the pressure. These basis functions are constructed by solving a class of local auxiliary optimization problems based on eigenfunctions containing local information on the heterogeneity. Techniques of oversampling are adapted to enhance the computational performance. Convergence of first order is shown and illustrated by a number of numerical tests.Comment: 14 pages, 9 figure

Spin correlations in the electron-doped high-transition-temperature superconductor Nd{2-x}Ce{x}CuO{4+/-delta}

High-transition-temperature (high-Tc) superconductivity develops near antiferromagnetic phases, and it is possible that magnetic excitations contribute to the superconducting pairing mechanism. To assess the role of antiferromagnetism, it is essential to understand the doping and temperature dependence of the two-dimensional antiferromagnetic spin correlations. The phase diagram is asymmetric with respect to electron and hole doping, and for the comparatively less-studied electron-doped materials, the antiferromagnetic phase extends much further with doping [1, 2] and appears to overlap with the superconducting phase. The archetypical electron-doped compound Nd{2-x}Ce{x}CuO{4\pm\delta} (NCCO) shows bulk superconductivity above x \approx 0.13 [3, 4], while evidence for antiferromagnetic order has been found up to x \approx 0.17 [2, 5, 6]. Here we report inelastic magnetic neutron-scattering measurements that point to the distinct possibility that genuine long-range antiferromagnetism and superconductivity do not coexist. The data reveal a magnetic quantum critical point where superconductivity first appears, consistent with an exotic quantum phase transition between the two phases [7]. We also demonstrate that the pseudogap phenomenon in the electron-doped materials, which is associated with pronounced charge anomalies [8-11], arises from a build-up of spin correlations, in agreement with recent theoretical proposals [12, 13].Comment: 5 pages, 4 figure

No spin-localization phase transition in the spin-boson model without local field

We explore the spin-boson model in a special case, i.e., with zero local field. In contrast to previous studies, we find no possibility for quantum phase transition (QPT) happening between the localized and delocalized phases, and the behavior of the model can be fully characterized by the even or odd parity as well as the parity breaking, instead of the QPT, owned by the ground state of the system. Our analytical treatment about the eigensolution of the ground state of the model presents for the first time a rigorous proof of no-degeneracy for the ground state of the model, which is independent of the bath type, the degrees of freedom of the bath and the calculation precision. We argue that the QPT mentioned previously appears due to unreasonable treatment of the ground state of the model or of the infrared divergence existing in the spectral functions for Ohmic and sub-Ohmic dissipations.Comment: 5 pages, 1 figure. Comments are welcom

On-Board Oxygen Generation Using High Performance Molecular Sieve

The majority of high performance combat aircrafts presently being operated by Indian air Force are fitted with conventional oxygen systems in which a replenishable store of oxygen is carried, most often as liquid oxygen and the flow of gas to each crew member is controlled by an individual pressure demand regulator in which the oxygen is diluted with cabin air to provide breathing gas.Moreover, in-flight refueling capability of present generation fighter aircraft has made it possible to fly for long durations (6 to 8 hours). In such case, the oxygen source becomes one of the limiting factors. In order to meet this requirement, a large supply of Gaseous Oxygen (GASOX) or Liquid Oxygen (LOX) have proven to be a costly affair and the Onboard Oxygen Generating System (OBOGS) has become a very convenient and attractive proposal. The OBOGS employs molecular sieves to adsorb nitrogen from engine bleed air using pressure swing adsorption (PSA) technique, wherein two molecular sieve beds are continuously cycled between steps of pressurization (adsorption) and depressurization (desorption) to generate oxygen enriched breathing gas for aircrew. This paper describes the design of OBOGS using high performance Lithium based Low Silica X-type (Li-LSX) molecular sieves and its performance characteristics. It consists of two Zeolite beds filled with Li-LSX material which adsorbs nitrogen fromengine bleed air tapped from Environmental Control System pipe line. The two beds are cycled by a 5/2 way solenoid valve. The input air is supplied to the solenoid valve through a coalescent filter to reduce moisture from it and a pressure regulator is fitted at the upstream of solenoid valve to regulate the system pressure. The experimental setup for evaluation of OBOGS is also discussed. The OBOGS, presented in this paper, meets all the performance requirements as specified in MIL-C-85521 (AS).

Synergistic effects of bombesin and epidermal growth factor on cancers.

Bombesin and gastrin-releasing peptide act as autocrine mitogens in various cancers. Bombesin antagonist RC-3095 inhibited growth in some cancers and slowed the progression of premalignant lesions, possibly by down-regulating epidermal growth factor (EGF) receptors. Since the EGF receptor mitogen response involves tyrosine kinase stimulation, we tested the hypotheses that bombesin stimulates, and RC-3095 inhibits, phosphorylation; EGF and bombesin promote the phosphorylation of the same substrates; and EGF and bombesin act synergistically on phosphorylation. Therefore, in vitro assays for phosphorylation were performed in the presence or absence of EGF, bombesin, RC-3095, and combinations in samples derived from tumor, tissue surrounding tumor, cell lines, and normal and transforming tissue derived from the 9,10-dimethyl-1,2-benzanthracene-induced squamous cell lesions of the hamster cheek pouch. Bombesin increased, and RC-3095 decreased, phosphorylation in these samples. In the human hepatoma sample and surrounding tissue, these ligands altered the phosphorylation of the same substrates affected by EGF. EGF and bombesin stimulated phosphorylation synergistically in the hamster samples and the hepatoma. Bombesin-induced phosphorylation was greater in tissue surrounding the hepatoma, whereas RC-3095 was more effective in inhibiting phosphorylation in the hepatoma itself. This cancer, therefore, could be endogenously stimulated by gastrin-releasing peptide. These observations support the hypothesis that bombesin stimulates growth of tissues and tumors by amplifying the phosphorylation response to EGF. The growth inhibitory response to RC-3095, or other bombesin analogues, of individual tumors may be prognosed by in vitro phosphorylation assays using the samples from the patient's tumor