3,633 research outputs found

    Elastic response of the electron fluid in intrinsic graphene: The collisionless regime

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    The elastic response of an electron fluid at finite frequencies is defined by the electron viscosity η(ω)\eta(\omega). We determine η(ω)\eta(\omega) for graphene at the charge neutrality point in the collisionless regime, including the leading corrections due to the electron-electron Coulomb interaction. We find interaction corrections to η(ω)\eta(\omega) that are significantly larger if compared to the corresponding corrections to the optical conductivity. In addition, we find comparable contributions to the dynamic momentum flux due to single-particle and many-particle effects. We also demonstrate that η(ω)\eta(\omega) is directly related to the nonlocal energy-flow response of graphene at the Dirac point. The viscosity in the collisionless regime is determined with the help of the strain generators in the Kubo formalism. Here, the pseudo-spin of graphene describing its two sublattices plays an important role in obtaining a viscosity tensor that fulfills the symmetry properties of a rotationally symmetric system.Comment: 18 pages, 5 figure

    Universal collisionless transport of graphene

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    The impact of the electron-electron Coulomb interaction on the optical conductivity of graphene has led to a controversy that calls into question the universality of collisionless transport in this and other Dirac materials. Using a lattice calculation that avoids divergences present in previous nodal Dirac approaches, our work settles this controversy and obtains results in quantitative agreement with experiment over a wide frequency range. We also demonstrate that dimensional regularization methods agree, as long as the scaling properties of the conductivity and the regularization of the theory in modified dimension are correctly implemented. Tight-binding lattice and nodal Dirac theory calculations are shown to coincide at low energies even when the non-zero size of the atomic orbital wave function is included, conclusively demonstrating the universality of the optical conductivity of graphene.Comment: 4+ pages,4 figures; includes Supplemental Material (18 pages, 2 figures

    Regulation of hematopoietic stem cell activity by inflammation

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    Hematopoietic stem cells (HSCs) are quiescent cells with self-renewal capacity and the ability to generate all mature blood cells. HSCs normally reside in specialized niches in the bone marrow that help maintain their quiescence and long-term repopulating activity. There is emerging evidence that certain cytokines induced during inflammation have significant effects on HSCs in the bone marrow. Type I and II interferons, tumor necrosis factor, and LPS directly stimulate HSC proliferation and differentiation, thereby increasing the short-term output of mature effector leukocytes. However, chronic inflammatory cytokine signaling can lead to HSC exhaustion and may contribute the development of hematopoietic malignancies. Pro-inflammatory cytokines such as G-CSF can also indirectly affect HSCs by altering the bone marrow microenvironment, disrupting the stem cell niche and leading to HSC mobilization into the blood. Herein, we review our current understanding of the effects of inflammatory mediators on HSCs, and we discuss the potential clinical implications of these findings with respect to bone marrow failure and leukemogenesis

    Expression profiling of snoRNAs in normal hematopoiesis and AML

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    Key Points A subset of snoRNAs is expressed in a developmental- and lineage-specific manner during human hematopoiesis. Neither host gene expression nor alternative splicing accounted for the observed differential expression of snoRNAs in a subset of AML.</jats:p

    Atlas: analysis tools for low-depth and ancient samples

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    Summary: Post-mortem damage (PMD) obstructs the proper analysis of ancient DNA samples and can currently only be addressed by removing or down-weighting potentially damaged data. Here we present ATLAS, a suite of methods to accurately genotype and estimate genetic diversity from ancient samples, while accounting for PMD. It works directly from raw BAM files and enables the building of complete and customized pipelines for the analysis of ancient and other low-depth samples in a very user-friendly way. Based on simulations we show that, in the presence of PMD, a dedicated pipeline of ATLAS calls genotypes more accurately than the state-of-the-art pipeline of GATK combined with mapDamage 2.0. Availability: ATLAS is an open- source C++ program freely available at https://bitbucket.org/phaentu/atlas

    Evaluation of radiological workstations and web-browser-based image distribution clients for a PACS project in hands-on workshops

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    The methodology and outcome of a hands-on workshop for the evaluation of PACS (picture archiving and communication system) software for a multihospital PACS project are described. The following radiological workstations and web-browser-based image distribution software clients were evaluated as part of a multistep evaluation of PACS vendors in March 2001: Impax DS 3000 V 4.1/Impax Web1000 (Agfa-Gevaert, Mortsel, Belgium); PathSpeed V 8.0/PathSpeed Web (GE Medical Systems, Milwaukee, Wis., USA); ID Report/ID Web (Image Devices, Idstein, Germany); EasyVision DX/EasyWeb (Philips Medical Systems, Eindhoven, Netherlands); and MagicView 1000 VB33a/MagicWeb (Siemens Medical Systems, Erlangen, Germany). A set of anonymized DICOM test data was provided to enable direct image comparison. Radiologists (n=44) evaluated the radiological workstations and nonradiologists (n=53) evaluated the image distribution software clients using different questionnaires. One vendor was not able to import the provided DICOM data set. Another vendor had problems in displaying imported cross-sectional studies in the correct stack order. Three vendors (Agfa-Gevaert, GE, Philips) presented server-client solutions with web access. Two (Siemens, Image Devices) presented stand-alone solutions. The highest scores in the class of radiological workstations were achieved by ID Report from Image Devices (p<0.005). In the class of image distribution clients, the differences were statistically not significant. Questionnaire-based evaluation was shown to be useful for guaranteeing systematic assessment. The workshop was a great success in raising interest in the PACS project in a large group of future clinical users. The methodology used in the present study may be useful for other hospitals evaluating PAC
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