8,313 research outputs found
Charge-to-spin conversion of electron entanglement states and spin-interaction-free solid-state quantum computation
Without resorting to spin-spin coupling, we propose a scalable spin quantum
computing scheme assisted with a semiconductor multiple-quantum-dot structure.
The techniques of single electron transitions and the nanostructure of
quantum-dot cellular automata (QCA) are used to generate charge entangled
states of two electrons, which are then converted into spin entanglement states
using single-spin rotations only. Deterministic two-qubit quantum gates are
also manipulated using only single-spin rotations with the help of QCA. A
single-shot readout of spin states can be carried out by coupling the multiple
dot structure to a quantum point contact. As a result, deterministic
spin-interaction-free quantum computing can be implemented in semiconductor
nanostructure.Comment: 5 pages, 4 figures, the revised version of quant-ph/0502002 for
publication in Phys. Rev. B (to be appear on the issue of Oct. 15, 2007
Dynamic disorder in receptor-ligand forced dissociation experiments
Recently experiments showed that some biological noncovalent bonds increase
their lifetimes when they are stretched by an external force, and their
lifetimes will decrease when the force increases further. Several specific
quantitative models have been proposed to explain the intriguing transitions
from the "catch-bond" to the "slip-bond". Different from the previous efforts,
in this work we propose that the dynamic disorder of the force-dependent
dissociation rate can account for the counterintuitive behaviors of the bonds.
A Gaussian stochastic rate model is used to quantitatively describe the
transitions observed recently in the single bond P-selctin glycoprotein ligand
1(PSGL-1)P-selectin force rupture experiment [Marshall, {\it et al.}, (2003)
Nature {\bf 423}, 190-193]. Our model agrees well to the experimental data. We
conclude that the catch bonds could arise from the stronger positive
correlation between the height of the intrinsic energy barrier and the distance
from the bound state to the barrier; classical pathway scenario or {\it a
priori} catch bond assumption is not essential.Comment: 4 pages, 2 figure
Do Globular Clusters Harbor Black Holes?
It has been firmly established that there exists a tight correlation between
the central black hole mass and velocity dispersion (or luminosity) of
elliptical galaxies, ``pseudobulges'' and bulges of galaxies, although the
nature of this correlation still remains unclear. In this letter, we explore
the possibility of extrapolating such a correlation to less massive, spherical
systems like globular clusters. In particular, motivated by the apparent
success in globular cluster M15, we present an estimate of the central black
hole mass for a number of globular clusters with available velocity dispersion
in the literature.Comment: 6 pages, 2 figures, 1 table; accepted for publication in CJA
The Structure of Active Merger Remnant NGC 6240 from IRAC Observations
NGC 6240 is a rare object in the local universe: an active merger remnant
viewed at the point of merging where two active galactic nuclei are visible. We
present IRAC data of this object, providing high sensitivity maps of the
stellar and PAH distribution in this complicated system. We use photometry to
analyze the variation in these distributions with radius and provide an SED in
the four IRAC bands: 3.6 microns, 4.5 microns, 5.8 microns and 8.0 microns. We
fit the radial profiles of the 3.6 micron band to r^.25 and exponential
profiles to evaluate the structure of the remnant. Finally, we compare the IRAC
images with multi-wavelength data and examine how outflows in the X-ray, Halpha
and CO correlate with 8 micron emission. The results support the general
picture of NGC 6240 as a system experiencing a major merger and transitioning
from a disk galaxy to a spheroid. The sensitivity of IRAC to low surface
brightness mid-infrared features provides detailed information on the extended
distributions of stars and dust in this rare system.Comment: Accepted for publication in Ap
Spatiotemporal Fluctuation Induced Transition in a Tumor Model with Immune Surveillance
We report on a simple model of spatial extend anti-tumor system with a
fluctuation in growth rate, which can undergo a nonequilibrium phase
transition. Three states as excited, sub-excited and non-excited states of a
tumor are defined to describe its growth. The multiplicative noise is found to
be double-face: The positive effect on a non-excited tumor and the negative
effect on an excited tumor.Comment: 8pages,5figure
Electronic structure of the candidate 2D Dirac semimetal SrMnSb2: a combined experimental and theoretical study
SrMnSb is suggested to be a magnetic topological semimetal. It contains
square, 2D Sb planes with non-symmorphic crystal symmetries that could protect
band crossings, offering the possibility of a quasi-2D, robust Dirac semi-metal
in the form of a stable, bulk (3D) crystal. Here, we report a combined and
comprehensive experimental and theoretical investigation of the electronic
structure of SrMnSb, including the first ARPES data on this compound.
SrMnSb possesses a small Fermi surface originating from highly 2D, sharp
and linearly dispersing bands (the Y-states) around the (0,/a)-point in
-space. The ARPES Fermi surface agrees perfectly with that from
bulk-sensitive Shubnikov de Haas data from the same crystals, proving the
Ystates to be responsible for electrical conductivity in SrMnSb. DFT and
tight binding (TB) methods are used to model the electronic states, and both
show good agreement with the ARPES data. Despite the great promise of the
latter, both theory approaches show the Y-states to be gapped above E,
suggesting trivial topology. Subsequent analysis within both theory approaches
shows the Berry phase to be zero, indicating the non-topological character of
the transport in SrMnSb, a conclusion backed up by the analysis of the
quantum oscillation data from our crystals.Comment: 26 pages, 10 figures, revised submission to SciPost after including
changes requested by referees. All referee reports are open and can be viewed
here: https://scipost.org/submissions/1711.07165v2
Thermodynamic properties of binary HCP solution phases from special quasirandom structures
Three different special quasirandom structures (SQS) of the substitutional
hcp binary random solutions (, 0.5, and 0.75) are
presented. These structures are able to mimic the most important pair and
multi-site correlation functions corresponding to perfectly random hcp
solutions at those compositions. Due to the relatively small size of the
generated structures, they can be used to calculate the properties of random
hcp alloys via first-principles methods. The structures are relaxed in order to
find their lowest energy configurations at each composition. In some cases, it
was found that full relaxation resulted in complete loss of their parental
symmetry as hcp so geometry optimizations in which no local relaxations are
allowed were also performed. In general, the first-principles results for the
seven binary systems (Cd-Mg, Mg-Zr, Al-Mg, Mo-Ru, Hf-Ti, Hf-Zr, and Ti-Zr) show
good agreement with both formation enthalpy and lattice parameters measurements
from experiments. It is concluded that the SQS's presented in this work can be
widely used to study the behavior of random hcp solutions.Comment: 15 pages, 8 figure
Nuclear matter incompressibility coefficient in relativistic and nonrelativistic microscopic models
We systematically analyze the recent claim that nonrelativistic and
relativistic mean field (RMF) based random phase approximation (RPA)
calculations for the centroid energy E_0 of the isoscalar giant monopole
resonance yield for the nuclear matter incompressibility coefficient, K_{nm},
values which differ by about 20%. For an appropriate comparison with the RMF
based RPA calculations, we obtain the parameters for the Skyrme force used in
the nonrelativistic model by adopting the same procedure as employed in the
determination of the NL3 parameter set of an effective Lagrangian used in the
RMF model. Our investigation suggest that the discrepancy between the values of
K_{nm} predicted by the relativistic and nonrelativistic models is
significantly less than 20%.Comment: Revtex file (13 pages), appearing in PRC-Rapid Com
Resonant phenomena in extended chaotic systems subject to external noise: the Lorenz'96 model case
We investigate the effects of a time-correlated noise on an extended chaotic
system. The chosen model is the Lorenz'96, a kind of "toy" model used for
climate studies. Through the analysis of the system's time evolution and its
time and space correlations, we have obtained numerical evidence for two
stochastic resonance-like behavior. Such behavior is seen when both, the usual
and a generalized signal-to-noise ratio function are depicted as a function of
the external noise intensity or the system size. The underlying mechanism seems
to be associated to a "noise-induced chaos reduction". The possible relevance
of these and other findings for an "optimal" climate prediction are discussed.Comment: Submitted to Europhysics Letters (LaTex, 12 pgs, 5 figures
Intestinal transplantation in children under FK 506 immunosuppression
Intestinal transplantation, solitary (n = 3) or in combination with the liver (n = 7), was performed in 10 pediatric patients with intestinal failure. The liver was only replaced if there was liver failure and portal hypertension. Immunosuppression was based on FK 506. Two patients died, one of graft-versus-host disease and one of lymphoproliferative disease. One patient was still in the intensive care unit 1 month posttransplantation due to perioperative complications. The function of the intestinal grafts in the remaining patients is normal. All nutrition and medications including immunosuppression are being administered enterally. This series indicates that small bowel transplantation, alone or in combination with the liver, is feasible in pediatric patients. © 1993
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