967 research outputs found
PPARÎł2 Regulates a Molecular Signature of Marrow Mesenchymal Stem Cells
Bone formation and hematopoiesis are anatomically juxtaposed and share common regulatory mechanisms. Bone marrow mesenchymal stromal/stem cells (MSC) contain a compartment that provides progeny with bone forming osteoblasts and fat laden adipocytes as well as fibroblasts, chondrocytes, and muscle cells. In addition, marrow MSC provide an environment for support of hematopoiesis, including the development of bone resorbing osteoclasts. The PPARÎł2 nuclear receptor is an adipocyte-specific transcription factor that controls marrow MSC lineage allocation toward adipocytes and osteoblasts. Increased expression of PPARÎł2 with aging correlates with changes in the MSC status in respect to both their intrinsic differentiation potential and production of signaling molecules that contribute to the formation of a specific marrow micro-environment. Here, we investigated the effect of PPARÎł2 on MSC molecular signature in respect to the expression of gene markers associated exclusively with stem cell phenotype, as well as genes involved in the formation of a stem cell
supporting marrow environment. We found that PPARÎł2 is a powerful modulator of stem cell-related gene expression. In general, PPARÎł2 affects the expression of genes specific for the maintenance of stem cell phenotype, including LIF, LIF receptor, Kit ligand, SDF-1, Rex-1/Zfp42, and Oct-4. Moreover, the antidiabetic PPARÎł agonist TZD rosiglitazone specifically affects the expression of âstemnessâ genes, including ABCG2, Egfr, and CD44. Our data indicate that aging and anti-diabetic TZD therapy may affect mesenchymal stem cell phenotype through modulation of PPARÎł2 activity. These observations may have important therapeutic consequences and indicate a need for more detailed studies of PPARÎł2 role in stem cell biology
Chiral Symmetry Versus the Lattice
After mentioning some of the difficulties arising in lattice gauge theory
from chiral symmetry, I discuss one of the recent attempts to resolve these
issues using fermionic surface states in an extra space-time dimension. This
picture can be understood in terms of end states on a simple ladder molecule.Comment: Talk at the meeting "Computer simulations studies in condensed matter
physics XIV" Athens, Georgia, Feb. 19-24, 2001. 14 page
Stationary states and phase diagram for a model of the Gunn effect under realistic boundary conditions
A general formulation of boundary conditions for semiconductor-metal contacts
follows from a phenomenological procedure sketched here. The resulting boundary
conditions, which incorporate only physically well-defined parameters, are used
to study the classical unipolar drift-diffusion model for the Gunn effect. The
analysis of its stationary solutions reveals the presence of bistability and
hysteresis for a certain range of contact parameters. Several types of Gunn
effect are predicted to occur in the model, when no stable stationary solution
exists, depending on the value of the parameters of the injecting contact
appearing in the boundary condition. In this way, the critical role played by
contacts in the Gunn effect is clearly stablished.Comment: 10 pages, 6 Post-Script figure
Modifying the surface electronic properties of YBa2Cu3O7-delta with cryogenic scanning probe microscopy
We report the results of a cryogenic study of the modification of
YBa2Cu3O7-delta surface electronic properties with the probe of a scanning
tunneling microscope (STM). A negative voltage applied to the sample during STM
tunneling is found to modify locally the conductance of the native degraded
surface layer. When the degraded layer is removed by etching, the effect
disappears. An additional surface effect is identified using Scanning Kelvin
Probe Microscopy in combination with STM. We observe reversible surface
charging for both etched and unetched samples, indicating the presence of a
defect layer even on a surface never exposed to air.Comment: 6 pages, 4 figures. To appear in Superconductor Science and
Technolog
Vector like gauge theories with almost massless fermions on the lattice
A truncation of the overlap (domain wall fermions) is studied and a criterion
for reliability of the approximation is obtained by comparison to the exact
overlap formula describing massless quarks. We also present a truncated version
of regularized, pure gauge, supersymmetric models. The mechanism for generating
almost masslessness is shown to be a generalized see-saw which can also be
viewed as a version of Froggatt-Nielsen's method for obtaining natural large
mass hierarchies. Viewed in this way the mechanism preserving the mass
hierarchy naturally avoids preserving even approximately axial U(1). The new
insights into the source of the mass hierarchy suggest ways to increase the
efficiency of numerical simulations of QCD employing the truncated overlap.Comment: 35 pages, TeX, 4 figures using eps
Silicon Atomic Quantum Dots Enable Beyond-CMOS Electronics
We review our recent efforts in building atom-scale quantum-dot cellular
automata circuits on a silicon surface. Our building block consists of silicon
dangling bond on a H-Si(001) surface, which has been shown to act as a quantum
dot. First the fabrication, experimental imaging, and charging character of the
dangling bond are discussed. We then show how precise assemblies of such dots
can be created to form artificial molecules. Such complex structures can be
used as systems with custom optical properties, circuit elements for
quantum-dot cellular automata, and quantum computing. Considerations on
macro-to-atom connections are discussed.Comment: 28 pages, 19 figure
Probing photo-carrier collection efficiencies of individual silicon nanowire diodes on a wafer substrate
Timescales of Massive Human Entrainment
The past two decades have seen an upsurge of interest in the collective
behaviors of complex systems composed of many agents entrained to each other
and to external events. In this paper, we extend concepts of entrainment to the
dynamics of human collective attention. We conducted a detailed investigation
of the unfolding of human entrainment - as expressed by the content and
patterns of hundreds of thousands of messages on Twitter - during the 2012 US
presidential debates. By time locking these data sources, we quantify the
impact of the unfolding debate on human attention. We show that collective
social behavior covaries second-by-second to the interactional dynamics of the
debates: A candidate speaking induces rapid increases in mentions of his name
on social media and decreases in mentions of the other candidate. Moreover,
interruptions by an interlocutor increase the attention received. We also
highlight a distinct time scale for the impact of salient moments in the
debate: Mentions in social media start within 5-10 seconds after the moment;
peak at approximately one minute; and slowly decay in a consistent fashion
across well-known events during the debates. Finally, we show that public
attention after an initial burst slowly decays through the course of the
debates. Thus we demonstrate that large-scale human entrainment may hold across
a number of distinct scales, in an exquisitely time-locked fashion. The methods
and results pave the way for careful study of the dynamics and mechanisms of
large-scale human entrainment.Comment: 20 pages, 7 figures, 6 tables, 4 supplementary figures. 2nd version
revised according to peer reviewers' comments: more detailed explanation of
the methods, and grounding of the hypothese
Theoretical studies of the historical development of the accounting discipline: a review and evidence
Many existing studies of the development of accounting thought have either been atheoretical or have adopted Kuhn's model of scientific growth. The limitations of this 35-year-old model are discussed. Four different general neo-Kuhnian models of scholarly knowledge development are reviewed and compared with reference to an analytical matrix. The models are found to be mutually consistent, with each focusing on a different aspect of development. A composite model is proposed. Based on a hand-crafted database, author co-citation analysis is used to map empirically the entire literature structure of the accounting discipline during two consecutive time periods, 1972â81 and 1982â90. The changing structure of the accounting literature is interpreted using the proposed composite model of scholarly knowledge development
Low energy spin dynamics in the antiferromagnetic phase of CaFe2As2
We present 75As nuclear magnetic resonance data in the paramagnetic and
magnetic states of single crystal CaFe2As2. The electric field gradient and the
internal magnetic field at the As sites change discontinuously below the first
order structural transition at T0 = 169 K. In the magnetic state, we find a
single value of the internal hyperfine field consistent with commensurate
antiferromagnetic order of Fe moments pointing in the ab plane. The spin
lattice relaxation rate shows Korringa behavior for T<T0/3, reflecting the
metallic nature of the ordered state. Surprisingly, 1/T1 exhibits a small peak
at 10 K, revealing the presence of slow spin fluctuations that may be
associated with domain wall motion.Comment: 11 pages, 8 figure
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