4,607 research outputs found
Classical Representation of a Quantum System at Equilibrium
A quantum system at equilibrium is represented by a corresponding classical
system, chosen to reproduce the thermodynamic and structural properties. The
objective is to develop a means for exploiting strong coupling classical
methods (e.g., MD, integral equations, DFT) to describe quantum systems. The
classical system has an effective temperature, local chemical potential, and
pair interaction that are defined by requiring equivalence of the grand
potential and its functional derivatives with respect to the external and pair
potentials for the classical and quantum systems. Practical inversion of this
mapping for the classical properties is effected via the hypernetted chain
approximation, leading to representations as functionals of the quantum pair
correlation function. As an illustration, the parameters of the classical
system are determined approximately such that ideal gas and weak coupling RPA
limits are preserved
Exploring the link between market orientation and innovation in the European and US insurance markets
Despite the increasing research importance of market orientation concept in the marketing literature, few comparative studies between Europe and U.S. have been conducted. Consequently, this void limits the understanding of marketing orientation strategy in global markets. The empirical study reported in this article investigates (a) the influence of competitive environments on the understanding and uses of market orientation in insurance flrms in Europe and U.S. and (b) the effects of market orientation on firms innovativeness. The results not only provide empirical support of the concept of market orientation as defmed in the literature, but also expands it
Estimating the power spectrum covariance matrix with fewer mock samples
The covariance matrices of power-spectrum (P(k)) measurements from galaxy
surveys are difficult to compute theoretically. The current best practice is to
estimate covariance matrices by computing a sample covariance of a large number
of mock catalogues. The next generation of galaxy surveys will require
thousands of large volume mocks to determine the covariance matrices to desired
accuracy. The errors in the inverse covariance matrix are larger and scale with
the number of P(k) bins, making the problem even more acute. We develop a
method of estimating covariance matrices using a theoretically justified,
few-parameter model, calibrated with mock catalogues. Using a set of 600 BOSS
DR11 mock catalogues, we show that a seven parameter model is sufficient to fit
the covariance matrix of BOSS DR11 P(k) measurements. The covariance computed
with this method is better than the sample covariance at any number of mocks
and only ~100 mocks are required for it to fully converge and the inverse
covariance matrix converges at the same rate. This method should work equally
well for the next generation of galaxy surveys, although a demand for higher
accuracy may require adding extra parameters to the fitting function.Comment: 7 pages, 7 figure
A Detection of the Baryon Acoustic Oscillation Features in the SDSS BOSS DR12 Galaxy Bispectrum
We present the first high significance detection () of the Baryon
Acoustic Oscillations (BAO) feature in the galaxy bispectrum of the twelfth
data release (DR12) of the Baryon Oscillation Spectroscopic Survey (BOSS) CMASS
sample (). We measured the scale dilation parameter,
, using the power spectrum, bispectrum, and both simultaneously for
DR12, plus 2048 MultiDark-PATCHY mocks in the North and South Galactic Caps
(NGC and SGC, respectively), and the volume weighted averages of those two
samples (N+SGC). The fitting to the mocks validated our analysis pipeline,
yielding values consistent with the mock cosmology. By fitting to the power
spectrum and bispectrum separately, we tested the robustness of our results,
finding consistent values from the NGC, SGC and N+SGC in all cases. We found
Mpc,
Mpc, and
Mpc from
the N+SGC power spectrum, bispectrum and simultaneous fitting, respectively.Comment: Submitted to Monthly Notices of the Royal Astronomical Society. 13
pages, 11 figure
Noncollinear magnetic phases and edge states in graphene quantum Hall bars
Application of a perpendicular magnetic field to charge neutral graphene is
expected to result in a variety of broken symmetry phases, including
antiferromagnetic, canted and ferromagnetic. All these phases open a gap in
bulk but have very different edge states and non-collinear spin order, recently
confirmed experimentally. Here we provide an integrated description of both
edge and bulk for the various magnetic phases of graphene Hall bars making use
of a non-collinear mean field Hubbard model. Our calculations show that, at the
edges, the three types of magnetic order are either enhanced (zigzag) or
suppressed (armchair). Interestingly, we find that preformed local moments in
zigzag edges interact with the quantum Spin Hall like edge states of the
ferromagnetic phase and can induce back-scattering.Comment: 5 pages, 4 figure
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