21,192 research outputs found
Approximate Treatment of Hermitian Effective Interactions and a Bound on the Error
The Hermitian effective interaction can be well-approximated by
(R+R^dagger)/2 if the eigenvalues of omega^dagger omega are small or
state-independent(degenerate), where R is the standard non-Hermitian effective
interaction and omega maps the model-space states onto the excluded space. An
error bound on this approximation is given.Comment: 13 page
CMBR Constraint on a Modified Chaplygin Gas Model
In this paper, a modified Chaplygin gas model of unifying dark energy and
dark matter with exotic equation of state
which can also explain the recent accelerated expansion of the universe is
investigated by the means of constraining the location of the peak of the CMBR
spectrum. We find that the result of CMBR measurements does not exclude the
nonzero value of parameter , but allows it in the range .Comment: 4 pages, 3 figure
Enhancement of singly and multiply strangeness in p-Pb and Pb-Pb collisions at 158A GeV/c
The idea that the reduction of the strange quark suppression in string
fragmentation leads to the enhancement of strange particle yield in
nucleus-nucleus collisions is applied to study the singly and multiply strange
particle production in p-Pb and Pb-Pb collisions at 158A GeV/c. In this
mechanism the strange quark suppression factor is related to the effective
string tension, which increases in turn with the increase of the energy, of the
centrality and of the mass of colliding system. The WA97 observation that the
strange particle enhancement increases with the increasing of centrality and of
strange quark content in multiply strange particles in Pb-Pb collisions with
respect to p-Pb collisions was accounted reasonably.Comment: 8 pages, 3 PostScript figures, in Latex form. submitted to PR
Investigating the intrinsic noise limit of Dayem bridge NanoSQUIDs
NanoSQUIDs made from Nb thin films have been produced with nanometre loop sizes down to 200 nm, using weak-link junctions with dimensions less than 60 nm. These composite (W/Nb) single layer thin film devices, patterned by FIB milling, show extremely good low-noise performance ∼170 nΦ0 at temperatures between 5 and 8.5 K and can operate in rather high magnetic fields (at least up to 1 T). The devices produced so far have a limited operating temperature range, typically only 1–2 K. We have the goal of achieving operation at 4.2 K, to be compatible with the best SQUID series array (SSA) preamplifier available. Using the SSA to readout the nanoSQUIDs provides us with a means of investigating the intrinsic noise of the former. In this paper we report improved white noise levels of these nanoSQUIDs, enabling potential detection of a single electronic spin flip in a 1-Hz bandwidth. At low frequencies the noise performance is already limited by SSA preamplifier noise
Density-functional theory for 1D harmonically trapped Bose-Fermi mixture
We present a density-functional theory for the one dimensional harmonically
trapped Bose-Fermi mixture with repulsive contact interactions. The ground
state density distribution of each component is obtained by solving the
Kohn-Sham equations numerically based on the Local Density Approximation and
the exact solution for the homogeneous system given by Bethe ansatz method. It
is shown that for strong enough interaction, a considerable amount of fermions
are repelled out of the central region of the trap, exhibiting partial phase
separation of Bose and Fermi components. Oscillations emerge in the Bose
density curves reflecting the strong correlation with Fermions. For infinite
strong interaction, the ground state energy of the mixture and the total
density are consistent with the scenario that all atoms in the mixture are
fully fermionized.Comment: 10 pages, 8 figure
Phenomenological theory of a scalar electronic order: application to skutterudite PrFe4P12
By phenomenological Landau analysis, it is shown that a scalar order
parameter with the point-group symmetry explains most properties
associated with the phase transition in PrFeP at 6.5 K. The
scalar-order model reproduces magnetic and elastic properties in
PrFeP consistently such as (i) the anomaly of the magnetic
susceptibility and elastic constant at the transition temperature, (ii)
anisotropy of the magnetic susceptibility in the presence of uniaxial pressure,
and (iii) the anomaly in the elastic constant in magnetic field. An Ehrenfest
relation is derived which relates the anomaly of the magnetic susceptibility to
that of the elastic constant at the transition.Comment: 16 pages, 9 figure
Quantum Monte Carlo study of a magnetic-field-driven 2D superconductor-insulator transition
We numerically study the superconductor-insulator phase transition in a model
disordered 2D superconductor as a function of applied magnetic field. The
calculation involves quantum Monte Carlo calculations of the (2+1)D XY model in
the presence of both disorder and magnetic field. The XY coupling is assumed to
have the form -J\cos(\theta_i-\theta_j-A_{ij}), where A_{ij} has a mean of zero
and a standard deviation \Delta A_{ij}. In a real system, such a model would be
approximately realized by a 2D array of small Josephson-coupled grains with
slight spatial disorder and a uniform applied magnetic field. The different
values \Delta A_{ij} then corresponds to an applied field such that the average
number of flux quanta per plaquette has various integer values N: larger N
corresponds to larger \Delta A_{ij}. For any value of \Delta A_{ij}, there
appears to be a critical coupling constant K_c(\Delta
A_{ij})=\sqrt{[J/(2U)]_c}, where U is the charging energy, above which the
system is a Mott insulator; there is also a corresponding critical conductivity
\sigma^*(\Delta A_{ij}) at the transition. For \Delta A_{ij}=\infty, the order
parameter of the transition is a renormalized coupling constant g. Using a
numerical technique appropriate for disordered systems, we show that the
transition at this value of \Delta A_{ij} takes place from an insulating (I)
phase to a Bose glass (BG) phase, and that the dynamical critical exponent
characterizing this transition is z \sim 1.3. By contrast, z=1 for this model
at \Delta A_{ij}=0. We suggest that the superconductor to insulator transition
is actually of this I to BG class at all nonzero \Delta A_{ij}'s, and we
support this interpretation by both numerical evidence and an analytical
argument based on the Harris criterion.Comment: 17 pages, 23 figures, accepted for publication in Phys. Rev.
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Wearable activity sensors and early pain after total joint arthroplasty.
A prospective observational cohort of 20 primary total hip arthroplasty (n = 12) and total knee arthroplasty (n = 8) patients (mean age: 63 ± 6 years) was passively monitored with a consumer-level wearable activity sensor before and 6 weeks after surgery. Patients were clustered by minimal change or decreased activity using sensor data. Decreased postoperative activity was associated with greater pain reduction (-5.5 vs -2.0, P = .03). All patients surpassed minimal clinical benefit thresholds of total joint arthroplasty (TJA) (Hip Disability and Osteoarthritis Score Junior 30.5 vs 20.8, P = .23; Knee Injury and Osteoarthritis Outcome Score Junior 23.3 vs 18.2, P = .77) within 6 weeks. Patients who objectively "take it easy" after TJA may experience less pain with no difference in early subjective outcome. Remote, passive analysis of outpatient wearable sensor data may permit real-time detection of early problems after TJA
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