275 research outputs found

    Calculation of NMR Properties of Solitons in Superfluid 3He-A

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    Superfluid 3He-A has domain-wall-like structures, which are called solitons. We calculate numerically the structure of a splay soliton. We study the effect of solitons on the nuclear-magnetic-resonance spectrum by calculating the frequency shifts and the amplitudes of the soliton peaks for both longitudinal and transverse oscillations of magnetization. The effect of dissipation caused by normal-superfluid conversion and spin diffusion is calculated. The calculations are in good agreement with experiments, except a problem in the transverse resonance frequency of the splay soliton or in magnetic-field dependence of reduced resonance frequencies.Comment: 15 pages, 10 figures, updated to the published versio

    Theory of Flux-Flow Resistivity near Hc2H_{c2} for s-wave Type-II Superconductors

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    This paper presents a microscopic calculation of the flux-flow resistivity ρf\rho_{f} for s-wave type-II superconductors with arbitrary impurity concentrations near the upper critical field Hc2H_{c2}. It is found that, as the mean free path ll becomes longer, ρf\rho_{f} increases gradually from the dirty-limit result of Thompson [Phys. Rev. B{\bf 1}, 327 (1970)] and Takayama and Ebisawa [Prog. Theor. Phys. {\bf 44}, 1450 (1970)]. The limiting behaviors suggest that ρf(H)\rho_{f}(H) at low temperatures may change from convex downward to upward as ll increases, thus deviating substantially from the linear dependence ρfH/Hc2\rho_{f}\propto H/H_{c2} predicted by the Bardeen-Stephen theory [Phys. Rev. {\bf 140}, A1197 (1965)]

    Adenosine Kinase on Deoxyribonucleic Acid Methylation: Adenosine Receptor-Independent Pathway in Cancer Therapy

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    Methylation is an important mechanism contributing to cancer pathology. Methylation of tumor suppressor genes and oncogenes has been closely associated with tumor occurrence and development. New insights regarding the potential role of the adenosine receptor-independent pathway in the epigenetic modulation of DNA methylation offer the possibility of new interventional strategies for cancer therapy. Targeting DNA methylation of cancer-related genes is a promising therapeutic strategy; drugs like 5-Aza-2′-deoxycytidine (5-AZA-CdR, decitabine) effectively reverse DNA methylation and cancer cell growth. However, current anti-methylation (or methylation modifiers) are associated with severe side effects; thus, there is an urgent need for safer and more specific inhibitors of DNA methylation (or DNA methylation modifiers). The adenosine signaling pathway is reported to be involved in cancer pathology and participates in the development of tumors by altering DNA methylation. Most recently, an adenosine metabolic clearance enzyme, adenosine kinase (ADK), has been shown to influence methylation on tumor suppressor genes and tumor development and progression. This review article focuses on recent updates on ADK and its two isoforms, and its actions in adenosine receptor-independent pathways, including methylation modification and epigenetic changes in cancer pathology

    Quasiparticle Band Structure and Density Functional Theory: Single-Particle Excitations and Band Gaps in Lattice Models

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    We compare the quasiparticle band structure for a model insulator obtained from the fluctuation exchange approximation (FEA) with the eigenvalues of the corresponding density functional theory (DFT) and local density approximation (LDA). The discontinuity in the exchange-correlation potential for this model is small and the FEA and DFT band structures are in good agreement. In contrast to conventional wisdom, the LDA for this model overestimates the size of the band gap. We argue that this is a consequence of an FEA self-energy that is strongly frequency dependent, but essentially local.Comment: 8 pages, and 5 figure

    Pair fluctuation induced pseudogap in the normal phase of the two-dimensional attractive Hubbard model at weak coupling

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    One-particle spectral properties in the normal phase of the two-dimensional attractive Hubbard model are investigated in the weak coupling regime using the non-selfconsistent T-matrix approximation. The corresponding equations are evaluated numerically directly on the real frequency axis. For temperatures sufficiently close to the superconducting transition temperature a pseudogap in the one-particle spectral function is observed, which can be assigned to the increasing importance of pair fluctuations.Comment: 22 pages, 13 figure

    Alpha-Synuclein Oligomers Interact with Metal Ions to Induce Oxidative Stress and Neuronal Death in Parkinson's Disease

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    Protein aggregation and oxidative stress are both key pathogenic processes in Parkinson's disease, although the mechanism by which misfolded proteins induce oxidative stress and neuronal death remains unknown. In this study, we describe how aggregation of alpha-synuclein (α-S) from its monomeric form to its soluble oligomeric state results in aberrant free radical production and neuronal toxicity

    A planar diagram approach to the correlation problem

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    We transpose an idea of 't Hooft from its context of Yang and Mills' theory of strongly interacting quarks to that of strongly correlated electrons in transition metal oxides and show that a Hubbard model of N interacting electron species reduces, to leading orders in N, to a sum of almost planar diagrams. The resulting generating functional and integral equations are very similar to those of the FLEX approximation of Bickers and Scalapino. This adds the Hubbard model at large N to the list of solvable models of strongly correlated electrons. PACS Numbers: 71.27.+a 71.10.-w 71.10.FdComment: revtex, 5 pages, with 3 eps figure

    Air-Independent Solid Oxide Fuel Cells for NASA's LOX-CH4 Landers

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    Gemini, Apollo, and Space Shuttle used fuel cells as main power source for vehicle and water source for life support and thermal PEM (Gemini) and Alkaline (Apollo, Shuttle) fuel cells were used Ideal for short (less than 3 weeks) missions when the required O2 and H2 can be launched with the vehicle. New missions that might require longduration stays in orbit or at a habitat, cannot rely on the availability of pure reactants but should also aim to be sunindependent - a problem for which Solid Oxide Fuel Cells might be the answer. Recently, NASA has investigated & developed LOX/CH4propelled landers (Altair, MORPHEUS). In order to preserve mission flexibility, fuel cells are being studied as a potential power source. Much of NASA's fuel cell development has been focused on creating a deadheaded, nonflow through PEM fuel cells which would weigh less and be more reliable than the existing Alkaline and PEM technology; however, LOX/CH4 as a propellant introduces SOFCs as a power option due to their ability to accept those reactants without much reforming
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