493 research outputs found
Random background charges and Coulomb blockade in one-dimensional tunnel junction arrays
We have numerically studied the behavior of one dimensional tunnel junction
arrays when random background charges are included using the ``orthodox''
theory of single electron tunneling. Random background charge distributions are
verified in both amplitude and density. The use of a uniform array as a
transistor is discussed both with and without random background charges. An
analytic expression for the gain near zero gate voltage in a uniform array with
no background charges is derived. The gate modulation with background charges
present is simulated.Comment: 10 pages, 7 figure
On testing the violation of the Clausius inequality in nanoscale electric circuits
The Clausius inequality, one of the classical formulations of the second law,
was recently found to be violated in the quantum regime. Here this result is
formulated in the context of a mesoscopic or nanoscale linear RLC circuit
interacting with a thermal bath. Previous experiments in this and related
fields are analyzed and possibilities of experimental detection of the
violation are pointed out. It is discussed that recent experiments reached the
range of temperatures, where the effect should be visible, and that a part of
the proposal was already confirmed.Comment: 5 pages revtex 4. No figure
Dynamics near the Surface Reconstruction of W(100)
Using Brownian molecular dynamics simulation, we study the surface dynamics
near the reconstruction transition of W(100) via a model Hamiltonian. Results
for the softening and broadening of the surface phonon spectrum near the
transition are compared with previous calculations and with He atom scattering
data. From the critical behavior of the central peak in the dynamical structure
factor, we also estimate the exponent of the power law anomaly for adatom
diffusion near the transition temperature.Comment: 8 pages, 8 figures, to appear in Phys. Rev.
From Fractional Chern Insulators to a Fractional Quantum Spin Hall Effect
We investigate the algebraic structure of flat energy bands a partial filling
of which may give rise to a fractional quantum anomalous Hall effect (or a
fractional Chern insulator) and a fractional quantum spin Hall effect. Both
effects arise in the case of a sufficiently flat energy band as well as a
roughly flat and homogeneous Berry curvature, such that the global Chern
number, which is a topological invariant, may be associated with a local
non-commutative geometry. This geometry is similar to the more familiar
situation of the fractional quantum Hall effect in two-dimensional electron
systems in a strong magnetic field.Comment: 8 pages, 3 figure; published version with labels in Figs. 2 and 3
correcte
Baculovirus Transduction of Mesenchymal Stem Cells: In Vitro Responses and In Vivo Immune Responses After Cell Transplantation
Baculovirus holds great promise for the genetic modification of mesenchymal stem cells (MSCs). However, whether baculovirus transduction provokes undesired MSCs responses that might compromise their in vivo applications has yet to be examined. Hereby, we unraveled that baculovirus transduction of human MSCs upregulated the transcription of interleukin (IL)-1 beta, interferon (IFN)-alpha and IL-6, but not tumor necrosis factor (TNF)-alpha and IFN-gamma. However, only IL-6 secretion was detectable by enzyme-linked immunosorbent assay (ELISA). Baculovirus transduction also stimulated transient, low level upregulation of human leukocyte antigen I (HLA-I) on the human MSCs surface, yet it did not either altered the HLA-II expression or impaired the MSCs ability to inhibit lymphocyte proliferation. After transplantation into allogeneic rats, the transduced rat MSCs elicited transient, mild macrophage responses, but the cells remained tolerant as judged by the persistence of transplanted cells and absence of CD8(+) T cells infiltration. Besides, transplantation of the transduced MSCs did not provoke systemic induction of monocytes and CD8(+) T cells. This study, for the first time, explores the responses of MSCs to virus transduction and confirms the safety of transplanting baculovirus-engineered MSCs into immunocompetent animals for cell-based gene therapy
Partial Wave Analysis of
BES data on are presented. The
contribution peaks strongly near threshold. It is fitted with a
broad resonance with mass MeV, width MeV. A broad resonance peaking at 2020 MeV is also required
with width MeV. There is further evidence for a component
peaking at 2.55 GeV. The non- contribution is close to phase
space; it peaks at 2.6 GeV and is very different from .Comment: 15 pages, 6 figures, 1 table, Submitted to PL
Temperature-dependence of spin-polarized transport in ferromagnet / unconventional superconductor junctions
Tunneling conductance in ferromagnet / unconventional superconductor
junctions is studied theoretically as a function of temperatures and
spin-polarization in feromagnets. In d-wave superconductor junctions, the
existence of a zero-energy Andreev bound state drastically affects the
temperature-dependence of the zero-bias conductance (ZBC). In p-wave triplet
superconductor junctions, numerical results show a wide variety in
temperature-dependence of the ZBC depending on the direction of the magnetic
moment in ferromagnets and the pairing symmetry in superconductors such as
, and -wave pair potential. The last one is a
promising symmetry of SrRuO. From these characteristic features in the
conductance, we may obtain the information about the degree of
spin-polarization in ferromagnets and the direction of the -vector in
triplet superconductors
Tomonaga-Luttinger parameters for quantum wires
The low-energy properties of a homogeneous one-dimensional electron system
are completely specified by two Tomonaga-Luttinger parameters and
. In this paper we discuss microscopic estimates of the values of
these parameters in semiconductor quantum wires that exploit their relationship
to thermodynamic properties. Motivated by the recognized similarity between
correlations in the ground state of a one-dimensional electron liquid and
correlations in a Wigner crystal, we evaluate these thermodynamic quantities in
a self-consistent Hartree-Fock approximation. According to our calculations,
the Hartree-Fock approximation ground state is a Wigner crystal at all electron
densities and has antiferromagnetic order that gradually evolves from
spin-density-wave to localized in character as the density is lowered. Our
results for are in good agreement with weak-coupling perturbative
estimates at high densities, but deviate strongly at low
densities, especially when the electron-electron interaction is screened at
long distances. vanishes at small carrier density
whereas we conjecture that when , implying that
should pass through a minimum at an intermediate density.
Observation of such a non-monotonic dependence on particle density would allow
to measure the range of the microscopic interaction. In the spin sector we find
that the spin velocity decreases with increasing interaction strength or
decreasing . Strong correlation effects make it difficult to obtain fully
consistent estimates of from Hartree-Fock calculations. We
conjecture that v_{\sigma}/\vf\propto n/V_0 in the limit where
is the interaction strength.Comment: RevTeX, 23 pages, 8 figures include
Mechanics of Reversible Unzipping
We study the mechanics of a reversible decohesion (unzipping) of an elastic
layer subjected to quasi-static end-point loading. At the micro level the
system is simulated by an elastic chain of particles interacting with a rigid
foundation through breakable springs. Such system can be viewed as prototypical
for the description of a wide range of phenomena from peeling of polymeric
tapes, to rolling of cells, working of gecko's fibrillar structures and
denaturation of DNA. We construct a rigorous continuum limit of the discrete
model which captures both stable and metastable configurations and present a
detailed parametric study of the interplay between elastic and cohesive
interactions. We show that the model reproduces the experimentally observed
abrupt transition from an incremental evolution of the adhesion front to a
sudden complete decohesion of a macroscopic segment of the adhesion layer. As
the microscopic parameters vary the macroscopic response changes from
quasi-ductile to quasi-brittle, with corresponding decrease in the size of the
adhesion hysteresis. At the micro-scale this corresponds to a transition from a
`localized' to a `diffuse' structure of the decohesion front (domain wall). We
obtain an explicit expression for the critical debonding threshold in the limit
when the internal length scales are much smaller than the size of the system.
The achieved parametric control of the microscopic mechanism can be used in the
design of new biological inspired adhesion devices and machines
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