887 research outputs found
Binary black holes on a budget: Simulations using workstations
Binary black hole simulations have traditionally been computationally very
expensive: current simulations are performed in supercomputers involving dozens
if not hundreds of processors, thus systematic studies of the parameter space
of binary black hole encounters still seem prohibitive with current technology.
Here we show how the multi-layered refinement level code BAM can be used on
dual processor workstations to simulate certain binary black hole systems. BAM,
based on the moving punctures method, provides grid structures composed of
boxes of increasing resolution near the center of the grid. In the case of
binaries, the highest resolution boxes are placed around each black hole and
they track them in their orbits until the final merger when a single set of
levels surrounds the black hole remnant. This is particularly useful when
simulating spinning black holes since the gravitational fields gradients are
larger. We present simulations of binaries with equal mass black holes with
spins parallel to the binary axis and intrinsic magnitude of S/m^2= 0.75. Our
results compare favorably to those of previous simulations of this particular
system. We show that the moving punctures method produces stable simulations at
maximum spatial resolutions up to M/160 and for durations of up to the
equivalent of 20 orbital periods.Comment: 20 pages, 8 figures. Final version, to appear in a special issue of
Class. Quantum Grav. based on the New Frontiers in Numerical Relativity
Conference, Golm, July 200
Strong decays of radially excited mesons in a chiral approach
We study radial excitations of pseudoscalar and vector (q bar q) mesons
within a chiral approach. We derive a general form for a chiral Lagrangian
describing processes involving excited pseudoscalar and vector mesons. The
parameters of the chiral Lagrangian are fitted using data and previous
calculations in the framework of the 3P0 model. Finite-width effects are
examined and predictions for mesons previously not discussed are given.
Available experimental data is analyzed whenever possible. Possible hints for
exotic mesons and open interpretation-issues are discussed.Comment: 16 page
A simple model for the vibrational modes in honeycomb lattices
The classical lattice dynamics of honeycomb lattices is studied in the
harmonic approximation. Interactions between nearest neighbors are represented
by springs connecting them. A short and necessary introduction of the lattice
structure is presented. The dynamical matrix of the vibrational modes is then
derived, and its eigenvalue problem is solved analytically. The solution may
provide deeper insight into the nature of the vibrational modes. Numerical
results for the vibrational frequencies are presented. To show that how
effective our method used for the case of honeycomb lattice is, we also apply
it to triangular and square lattice structures. A few suggested problems are
listed in the concluding section.Comment: 9 pages, 12 figures, submitted to American Journal of Physic
BSSN in Spherical Symmetry
The BSSN (Baumgarte-Shapiro-Shibata-Nakamura) formulation of the Einstein
evolution equations is written in spherical symmetry. These equations can be
used to address a number of technical and conceptual issues in numerical
relativity in the context of a single Schwarzschild black hole. One of the
benefits of spherical symmetry is that the numerical grid points can be tracked
on a Kruskal--Szekeres diagram. Boundary conditions suitable for puncture
evolution of a Schwarzschild black hole are presented. Several results are
shown for puncture evolution using a fourth--order finite difference
implementation of the equations.Comment: This is the final version to be published in CQG. It contains much
more information and detail than the original versio
Cost-effectiveness analysis of ceftazidime/avibactam compared to imipenem as empirical treatment for complicated urinary tract infections
Ceftazidime/avibactam (CAZ-AVI) is a novel, fixed-dose combination antibiotic that has been approved in Europe and the United States for patients with complicated urinary tract infections (cUTIs) based on results of a Phase III, randomized, comparative study (RECAPTURE study). The present analysis evaluated cost-effectiveness of CAZ-AVI as an empirical treatment for hospitalized patients with cUTIs from the Italian publicly funded healthcare (third-party payer) perspective. A sequential, patient-level simulation model was developed that followed the clinical course of cUTI and generated 5000 pairs of identical patients (CAZ-AVI or imipenem as empirical treatment). The model included additional impact of resistant pathogens; patients who did not respond to empirical treatment were switched to second-line treatment of colistin+high dose carbapenem in both groups. The time horizon of the model was five years, with an annual discount rate of 3% applied to both costs and quality-adjusted life-years (QALYs). The analysis demonstrated that an intervention sequence (CAZ-AVI followed by colistin+high dose carbapenem) compared with a comparator sequence (imipenem followed by colistin+high dose carbapenem) was associated with a net incremental cost of €1015 per patient but provided better health outcomes in terms of clinical cure (97.65% vs. 91.08%; ∆ = 6.57%), shorter hospital stays (10.65 vs. 12.55 days; ∆ = 1.90 days), and QALYs gained per patient (4.190 vs. 4.063; ∆ = 0.126). The incremental cost-effectiveness ratio was €8039/QALY, which is well below the willingness-to-pay threshold of €30 000/QALY in Italy. The results showed that CAZ-AVI is expected to be a cost-effective treatment compared with imipenem for cUTI in Italy
Many-particle interference beyond many-boson and many-fermion statistics
Identical particles exhibit correlations even in the absence of
inter-particle interaction, due to the exchange (anti)symmetry of the
many-particle wavefunction. Two fermions obey the Pauli principle and
anti-bunch, whereas two bosons favor bunched, doubly occupied states. Here, we
show that the collective interference of three or more particles leads to a
much more diverse behavior than expected from the boson-fermion dichotomy known
from quantum statistical mechanics. The emerging complexity of many-particle
interference is tamed by a simple law for the strict suppression of events in
the Bell multiport beam splitter. The law shows that counting events are
governed by widely species-independent interference, such that bosons and
fermions can even exhibit identical interference signatures, while their
statistical character remains subordinate. Recent progress in the preparation
of tailored many-particle states of bosonic and fermionic atoms promises
experimental verification and applications in novel many-particle
interferometers.Comment: 12 pages, 5 figure
Beyond the Bowen-York extrinsic curvature for spinning black holes
It is well-known that Bowen-York initial data contain spurious radiation.
Although this ``junk'' radiation has been seen to be small for non-spinning
black-hole binaries in circular orbit, its magnitude increases when the black
holes are given spin. It is possible to reduce the spurious radiation by
applying the puncture approach to multiple Kerr black holes, as we demonstrate
for examples of head-on collisions of equal-mass black-hole binaries.Comment: 10 pages, 2 figures, submitted to special "New Frontiers in Numerical
Relativity" issue of Classical and Quantum Gravit
Tur\'an Graphs, Stability Number, and Fibonacci Index
The Fibonacci index of a graph is the number of its stable sets. This
parameter is widely studied and has applications in chemical graph theory. In
this paper, we establish tight upper bounds for the Fibonacci index in terms of
the stability number and the order of general graphs and connected graphs.
Tur\'an graphs frequently appear in extremal graph theory. We show that Tur\'an
graphs and a connected variant of them are also extremal for these particular
problems.Comment: 11 pages, 3 figure
International human resource management strategies of Chinese multinationals operating abroad
Strategic international human resource management (SIHRM) is crucial for the effective leveraging of human resources in organizations to achieve the desired business strategies. There is a rich collection of studies on western multinational corporations (MNCs) in China, but few studies that explore the SIHRM of Chinese MNCs operating overseas. This study utilizes cross-level, in-depth interviews to analyse SIHRM of three large Chinese multinationals. The paper contributes to literature by addressing two contextual SIHRM issues, namely the characteristics of the SIHRM for Chinese multinationals and how their SIHRM orientation facilitates their international investment and operation. The findings indicate that organizational transformation is the starting point for latecomers matching their international HRM strategies. Their SIHRM approaches, such as forming learning organizations, reliance on host-country nationals, reconciling both home and host-country effects and promoting ‘best practices’, facilitate their international operations
Asymptotically Matched Spacetime Metric for Non-Precessing, Spinning Black Hole Binaries
We construct a closed-form, fully analytical 4-metric that approximately
represents the spacetime evolution of non-precessing, spinning black hole
binaries from infinite separations up to a few orbits prior to merger. We
employ the technique of asymptotic matching to join a perturbed Kerr metric in
the neighborhood of each spinning black hole to a near-zone, post-Newtonian
metric farther out. The latter is already naturally matched to a far-zone,
post-Minkowskian metric that accounts for full temporal retardation. The result
is a 4-metric that is approximately valid everywhere in space and in a small
bundle of spatial hypersurfaces. We here restrict our attention to quasi-
circular orbits, but the method is valid for any orbital motion or physical
scenario, provided an overlapping region of validity or buffer zone exists. A
simple extension of such a metric will allow for future studies of the
accretion disk and jet dynamics around spinning back hole binaries
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