2,265 research outputs found
Modelling convection in A star atmospheres. Bisectors and lineshapes of HD108642
We present a code, VeDyn, for modelling envelopes and atmospheres of A to F
stars focusing on accurate treatment of convective processes. VeDyn implements
the highly sophisticated convection model of Canuto and Dubovikov (1998) but is
fast and handy enough to be used in practical astrophysical applications. We
developed the HME envelope solver for this convection model furtheron to
consistently model the envelope together with the stellar atmosphere. The
synthesis code SynthV was extended to account for the resulting velocity
structure. Finally, we tested our approach on atomic line bisectors. It is
shown that our synthetic line bisectors of HD108642 bend towards the blue and
are of a magnitude comparable to the observed ones. Even though this approach
of modelling convection requires the solution of a coupled system of nonlinear
differential equations, it is fast enough to be applicable to many of the
investigation techniques relying on model atmospheres.Comment: 3 pages, 3 figure
Frustration and thermalization in an artificial magnetic quasicrystal
Artificial frustrated systems offer a playground to study the emergent properties of interacting systems. Most work to date has been on spatially periodic systems, known as artificial spin ices when the interacting elements are magnetic. Here we have studied artificial magnetic quasicrystals based on quasiperiodic Penrose tiling patterns of interacting nanomagnets. We construct a low-energy configuration from a step-by-step approach that we propose as a ground state. Topologically induced emergent frustration means that this configuration cannot be constructed from vertices in their ground states. It has two parts, a quasi-one-dimensional ‘skeleton’ that spans the entire pattern and is capable of long-range order, surrounding ‘flippable’ clusters of macrospins that lead to macroscopic degeneracy. Magnetic force microscopy imaging of Penrose tiling arrays revealed superdomains that are larger for more strongly coupled arrays, especially after annealing the array above its blocking temperature
Asymptotic behavior of small solutions for the discrete nonlinear Schr\"odinger and Klein-Gordon equations
We show decay estimates for the propagator of the discrete Schr\"odinger and
Klein-Gordon equations in the form \norm{U(t)f}{l^\infty}\leq C
(1+|t|)^{-d/3}\norm{f}{l^1}. This implies a corresponding (restricted) set of
Strichartz estimates. Applications of the latter include the existence of
excitation thresholds for certain regimes of the parameters and the decay of
small initial data for relevant norms. The analytical decay estimates are
corroborated with numerical results.Comment: 13 pages, 4 figure
Separable and Low-Rank Continuous Games
In this paper, we study nonzero-sum separable games, which are continuous
games whose payoffs take a sum-of-products form. Included in this subclass are
all finite games and polynomial games. We investigate the structure of
equilibria in separable games. We show that these games admit finitely
supported Nash equilibria. Motivated by the bounds on the supports of mixed
equilibria in two-player finite games in terms of the ranks of the payoff
matrices, we define the notion of the rank of an n-player continuous game and
use this to provide bounds on the cardinality of the support of equilibrium
strategies. We present a general characterization theorem that states that a
continuous game has finite rank if and only if it is separable. Using our rank
results, we present an efficient algorithm for computing approximate equilibria
of two-player separable games with fixed strategy spaces in time polynomial in
the rank of the game
On right conjugacy closed loops of twice prime order
The right conjugacy closed loops of order 2p, where p is an odd prime, are
classified up to isomorphism.Comment: Clarified definitions, added some remarks and a tabl
Binary choice models for external auditors decisions in Asian banks
Summarization: The present study investigates the efficiency of four classification techniques, namely discriminant analysis, logit analysis, UTADIS multicriteria decision aid, and nearest neighbours, in the development of classification models that could assist auditors during the examination of Asian commercial banks. To develop the auditing models and examine their classification ability, the dataset is split into two distinct samples. The training sample consists of 1,701 unqualified financial statements and 146 ones that received a qualified opinion over the period 1996–2001. The models are tested in a holdout sample of 527 unqualified financial statements and 52 ones that received a qualified opinion over the period 2002–2004. The results show that the developed auditing models can discriminate between financial statements that should receive qualified opinions from the ones that should receive unqualified opinions with an out-of-sample accuracy around 60%. The highest classification accuracy is achieved by UTADIS, followed by logit analysis, nearest neighbours and discriminant analysis. Both financial variables and the environment in which banks operate appear to be important factors.Presented on: Operational Research, An International Journa
The possible existence of Hs in nature from a geochemical point of view
A hypothesis of the existence of a long-lived isotope 271Hs in natural
molybdenites and osmirides is considered from a geochemical point of view. It
is shown that the presence of Hs in these minerals can be explained only by
making an additional ad hoc assumption on the existence of an isobaric pair of
271Bh-271Hs. This assumption could be tested by mass-spectrometric measurements
of U, Pb, Kr, Xe, and Zr isotopic shifts.Comment: 5 pages, no figures. Physics of Particles and Nuclei Letters, 2006,
Vol. 3, No. 3, pp. 165-168 in pres
A stitch in time: Efficient computation of genomic DNA melting bubbles
Background: It is of biological interest to make genome-wide predictions of
the locations of DNA melting bubbles using statistical mechanics models.
Computationally, this poses the challenge that a generic search through all
combinations of bubble starts and ends is quadratic.
Results: An efficient algorithm is described, which shows that the time
complexity of the task is O(NlogN) rather than quadratic. The algorithm
exploits that bubble lengths may be limited, but without a prior assumption of
a maximal bubble length. No approximations, such as windowing, have been
introduced to reduce the time complexity. More than just finding the bubbles,
the algorithm produces a stitch profile, which is a probabilistic graphical
model of bubbles and helical regions. The algorithm applies a probability peak
finding method based on a hierarchical analysis of the energy barriers in the
Poland-Scheraga model.
Conclusions: Exact and fast computation of genomic stitch profiles is thus
feasible. Sequences of several megabases have been computed, only limited by
computer memory. Possible applications are the genome-wide comparisons of
bubbles with promotors, TSS, viral integration sites, and other melting-related
regions.Comment: 16 pages, 10 figure
Electronic excitations in J=0 Os halides studied by RIXS and optical spectroscopy
We demonstrate that the cubic antifluorite-type halides KOsCl,
KOsBr, and RbOsBr are excellent realizations of non-magnetic
J=0 compounds. The magnetic susceptibility shows the corresponding Van-Vleck
type behavior and no sign of defects. We investigate the electronic excitations
with two complementary techniques, resonant inelastic x-ray scattering (RIXS)
and optical spectroscopy. This powerful combination allows us to thoroughly
study, e.g., on-site intra- excitations and -to-
excitations as well as inter-site excitations across the Mott gap and an
exciton below the gap. In this way, we determine the electronic parameters with
high accuracy, altogether yielding a comprehensive picture. In KOsCl,
we find the spin-orbit coupling constant =0.34 eV, Hund's coupling
=0.43 eV, the onset of excitations across the Mott gap at =2.2 eV,
the cubic crystal-field splitting 10Dq=3.3 eV, and the charge-transfer energy
=4.6 eV. With =1.3, KOsCl is in the
intermediate-coupling regime. In a -only Kanamori picture, the above
values correspond to =0.41 eV and =0.28 eV, which is
very close to results reported for related iridates. In the tetragonal
phase at 5 K, the non-cubic crystal field causes a peak splitting of the J=1
state as small as 4 meV. Compared to KOsCl, the bromides KOsBr
and RbOsBr show about 12-14 % smaller values of 10Dq and ,
while the spin-orbit-entangled intra- excitations below 2 eV and hence
and are reduced by less than 4 %. Furthermore, the Mott gap in
KOsBr is reduced to about 1.8 eV.Comment: 14 pages, 14 figure
Chylous ascites and chylothorax: a case study
No Abstract. 
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