588 research outputs found
Nonequilibrium-induced metal-superconductor quantum phase transition in graphene
We study the effects of dissipation and time-independent nonequilibrium drive
on an open superconducting graphene. In particular, we investigate how
dissipation and nonequilibrium effects modify the semi-metal-BCS quantum phase
transition that occurs at half-filling in equilibrium graphene with attractive
interactions. Our system consists of a graphene sheet sandwiched by two
semi-infinite three-dimensional Fermi liquid reservoirs, which act both as a
particle pump/sink and a source of decoherence. A steady-state charge current
is established in the system by equilibrating the two reservoirs at different,
but constant, chemical potentials. The nonequilibrium BCS superconductivity in
graphene is formulated using the Keldysh path integral formalism, and we obtain
generalized gap and number density equations valid for both zero and finite
voltages. The behaviour of the gap is discussed as a function of both
attractive interaction strength and electron densities for various
graphene-reservoir couplings and voltages. We discuss how tracing out the
dissipative environment (with or without voltage) leads to decoherence of
Cooper pairs in the graphene sheet, hence to a general suppression of the gap
order parameter at all densities. For weak enough attractive interactions we
show that the gap vanishes even for electron densities away from half-filling,
and illustrate the possibility of a dissipation-induced metal-superconductor
quantum phase transition. We find that the application of small voltages does
not alter the essential features of the gap as compared to the case when the
system is subject to dissipation alone (i.e. zero voltage).Comment: 13 pages, 8 figure
Electron-fluctuation interaction in a non-Fermi superconductor
We studied the influence of the amplitude fluctuations of a non-Fermi
superconductor on the energy spectrum of the 2D Anderson non-Fermi system. The
classical fluctuations give a temperature dependence in the pseudogap induced
in the fermionic excitations.Comment: revtex fil
Isolation and characterization of equine native MSC populations
Abstract Background In contrast to humans in which mesenchymal stem/stromal cell (MSC) therapies are still largely in the clinical trial phase, MSCs have been used therapeutically in horses for over 15Â years, thus constituting a valuable preclinical model for humans. In human tissues, MSCs have been shown to originate from perivascular cells, namely pericytes and adventitial cells, which are identified by the presence of the cell surface markers CD146 and CD34, respectively. In contrast, the origin of MSCs in equine tissues has not been established, preventing the isolation and culture of defined cell populations in that species. Moreover, a comparison between perivascular CD146+ and CD34+ cell populations has not been performed in any species. Methods Immunohistochemistry was used to identify adventitial cells (CD34+) and pericytes (CD146+) and to determine their localization in relation to MSCs in equine tissues. Isolation of CD34+ (CD34+/CD146â/CD144â/CD45â) and CD146+ (CD146+/CD34â/CD144â/CD45â) cell fractions from equine adipose tissue was achieved by fluorescence-activated cell sorting. The isolated cell fractions were cultured and analyzed for the expression of MSC markers, using qPCR and flow cytometry, and for the ability to undergo trilineage differentiation. Angiogenic properties were analyzed in vivo using a chorioallantoic membrane (CAM) assay. Results Both CD34+ and CD146+ cells displayed typical MSC features, namely growth in uncoated tissue culture dishes, clonal growth when seeded at low density, expression of typical MSC markers, and multipotency shown by the capacity for trilineage differentiation. Of note, CD146+ cells were distinctly angiogenic compared with CD34+ and non-sorted cells (conventional MSCs), demonstrated by the induction of blood vessels in a CAM assay, expression of elevated levels of VEGFA and ANGPT1, and association with vascular networks in cocultures with endothelial cells, indicating that CD146+ cells maintain a pericyte phenotype in culture. Conclusion This study reports for the first time the successful isolation and culture of CD146+ and CD34+ cell populations from equine tissues. Characterization of these cells evidenced their distinct properties and MSC-like phenotype, and identified CD146+ cells as distinctly angiogenic, which may provide a novel source for enhanced regenerative therapies
Physics at a Neutrino Factory
In response to the growing interest in building a Neutrino Factory to produce
high intensity beams of electron- and muon-neutrinos and antineutrinos, in
October 1999 the Fermilab Directorate initiated two six-month studies. The
first study, organized by N. Holtkamp and D. Finley, was to investigate the
technical feasibility of an intense neutrino source based on a muon storage
ring. This design study has produced a report in which the basic conclusion is
that a Neutrino Factory is technically feasible, although it requires an
aggressive R&D program. The second study, which is the subject of this report,
was to explore the physics potential of a Neutrino Factory as a function of the
muon beam energy and intensity, and for oscillation physics, the potential as a
function of baseline.Comment: 133 pages, 64 figures. Report to the Fermilab Directorate. Available
from http://www.fnal.gov/projects/muon_collider/ This version fixes some
printing problem
High-Tc Superconductivity and Antiferromagnetism in Multilayered Copper Oxides - A New Paradigm of Superconducting Mechanism -
High-temperature superconductivity (HTSC) in copper oxides emerges on a
layered CuO2 plane when an antiferromagnetic Mott insulator is doped with
mobile hole carriers. We review extensive studies of multilayered copper oxides
by site-selective nuclear magnetic resonance (NMR), which have uncovered the
intrinsic phase diagram of antiferromagnetism (AFM) and HTSC for a
disorder-free CuO2 plane with hole carriers. We present our experimental
findings such as the existence of the AFM metallic state in doped Mott
insulators, the uniformly mixed phase of AFM and HTSC, and the emergence of
d-wave SC with a maximum Tc just outside a critical carrier density, at which
the AFM moment on a CuO2 plane disappears. These results can be accounted for
by the Mott physics based on the t-J model. The superexchange interaction J_in
among spins plays a vital role as a glue for Cooper pairs or mobile
spin-singlet pairs, in contrast to the phonon-mediated attractive interaction
among electrons established in the Bardeen-Cooper-Schrieffer (BCS) theory. We
remark that the attractive interaction for raising the of HTSC up to
temperatures as high as 160 K is the large J_in (~0.12 eV), which binds
electrons of opposite spins to be on neighboring sites, and that there are no
bosonic glues. It is the Coulomb repulsive interaction U(> 6 eV) among Cu-3d
electrons that plays a central role in the physics behind high-Tc phenomena. A
new paradigm of the SC mechanism opens to strongly correlated electron matter.Comment: 20 pages, 25 figures, Special topics "Recent Developments in
Superconductivity" in J. Phys. Soc. Jpn., Published December 26, 201
Runx1+ vascular smooth muscle cells are essential for hematopoietic stem and progenitor cell development in vivo
Hematopoietic stem cells (HSCs) produce all essential cellular components of the blood. Stromal cell lines supporting HSCs follow a vascular smooth muscle cell (vSMC) differentiation pathway, suggesting that some hematopoiesis-supporting cells originate from vSMC precursors. These pericyte-like precursors were recently identified in the aorta-gonad-mesonephros (AGM) region; however, their role in the hematopoietic development in vivo remains unknown. Here, we identify a subpopulation of NG2 +Runx1 + perivascular cells that display a sclerotome-derived vSMC transcriptomic profile. We show that deleting Runx1 in NG2 + cells impairs the hematopoietic development in vivo and causes transcriptional changes in pericytes/vSMCs, endothelial cells and hematopoietic cells in the murine AGM. Importantly, this deletion leads also to a significant reduction of HSC reconstitution potential in the bone marrow in vivo. This defect is developmental, as NG2 +Runx1 + cells were not detected in the adult bone marrow, demonstrating the existence of a specialised pericyte population in the HSC-generating niche, unique to the embryo. </p
Subject specific demands of teaching: Implications for out-of-field teachers
This chapter provides a framework for thinking about the subject-specific nature of teaching in terms of the
knowledge, modes of inquiry and discursive practices that delineate one subject from another in the
traditional school curriculum. The chapter will explore how these disciplinary traits are translated into
teaching as curriculum, knowledge and pedagogy, and how this subject-specificity of teaching is
juxtaposed against the more generic aspects of teaching. The chapter explores the idea that if a teacherâs
expertise can be situated within a field, then they can also be positioned out-of-field. Implications for
teaching out-of-field are discussed in terms of the subject-specific knowledge, processes and skills, and the
difficulties associated with teacher practice. English and Australian illustrations of teacher practices from
in-field and out-of-field situations are provided, in particular highlighting the demands of moving across
subject boundaries. Cross-fertilisation is especially evident when subjects are integrated, therefore, the
issues associated with integrated curriculum are discussed where the traditional subject boundaries are
being challenged as schools are reorganised to integrate subjects through, for example, STEM teaching, or
holistic curriculum designs
Peptide nanofiber scaffolds for multipotent stromal cell culturing
Self-assembled peptide nanofibers are versatile materials providing suitable platforms for regenerative medicine applications. This chapter describes the use of peptide nanofibers as extracellular matrix mimetic scaffolds for two-dimensional (2D) and three-dimensional (3D) multipotent stromal cell culture systems and procedures for in vitro experiments using these scaffolds. Preparation of 2D and 3D peptide nanofiber scaffolds and cell culturing procedures are presented as part of in vitro experiments including cell adhesion, viability, and spreading analysis. Analysis of cellular differentiation on peptide nanofiber scaffolds is described through immunocytochemistry, qRT-PCR, and other biochemical experiments towards osteogenic and chondrogenic lineage. © Springer Science+Business Media New York 2013
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