28,941 research outputs found
Effect of hybridization on the magnetic properties of correlated two-band metals
The magnetic properties of transition-like metals are discussed within the
single site approximation, which is a picture to take into account electron
correlations. The metal is described by two hybridized bands one of which
includes Coulomb correlation. The presented results indicate that
ferromagnetism arises for adequate values of hybridization (V), correlation (U)
and occupation number(). Some similarities with Dynamical
Mean-Field Theory (DMFT) are indicated.Comment: 3 pages, 3 figures, presented at the 53rd MMM08 conference in Austin,
200
Abrasion of flat rotating shapes
We report on the erosion of flat linoleum "pebbles" under steady rotation in
a slurry of abrasive grit. To quantify shape as a function of time, we develop
a general method in which the pebble is photographed from multiple angles with
respect to the grid of pixels in a digital camera. This reduces digitization
noise, and allows the local curvature of the contour to be computed with a
controllable degree of uncertainty. Several shape descriptors are then employed
to follow the evolution of different initial shapes toward a circle, where
abrasion halts. The results are in good quantitative agreement with a simple
model, where we propose that points along the contour move radially inward in
proportion to the product of the radius and the derivative of radius with
respect to angle
Where is the fuzz? Undetected Lyman alpha nebulae around QSOs at z~2.3
We observed a small sample of 5 radio-quiet QSOs with integral field
spectroscopy to search for possible extended emission in the Ly line.
We subtracted the QSO point sources using a simple PSF self-calibration
technique that takes advantage of the simultaneous availability of spatial and
spectral information. In 4 of the 5 objects we find no significant traces of
extended Ly emission beyond the contribution of the QSO nuclei itself,
while in UM 247 there is evidence for a weak and spatially quite compact excess
in the Ly line at several kpc outside the nucleus. For all objects in
our sample we estimated detection limits for extended, smoothly distributed
Ly emission by adding fake nebulosities into the datacubes and trying
to recover them after PSF subtraction. Our observations are consistent with
other studies showing that giant Ly nebulae such as those found
recently around some quasars are very rare. Ly fuzz around typical
radio-quiet QSOs is fainter, less extended and is therefore much harder to
detect. The faintness of these structures is consistent with the idea that
radio-quiet QSOs typically reside in dark matter haloes of modest masses.Comment: 12 Pages, Accepted for publication in A&
Hadronic multiparticle production in extensive air showers and accelerator experiments
Using CORSIKA for simulating extensive air showers, we study the relation
between the shower characteristics and features of hadronic multiparticle
production at low energies. We report about investigations of typical energies
and phase space regions of secondary particles which are important for muon
production in extensive air showers. Possibilities to measure relevant
quantities of hadron production in existing and planned accelerator experiments
are discussed.Comment: To be published in Proceedings of ICRC 2005, 29th International
Cosmic Ray Conferenc
Stable schedule matching under revealed preference
Baiou and Balinski (Math. Oper. Res., 27 (2002) 485) studied schedule matching where one determines the partnerships that form and how much time they spend together, under the assumption that each agent has a ranking on all potential partners. Here we study schedule matching under more general preferences that extend the substitutable preferences in Roth (Econometrica 52 (1984) 47) by an extension of the revealed preference approach in Alkan (Econom. Theory 19 (2002) 737). We give a generalization of the GaleShapley algorithm and show that some familiar properties of ordinary stable matchings continue to hold. Our main result is that, when preferences satisfy an additional property called size monotonicity, stable matchings are a lattice under the joint preferences of all agents on each side and have other interesting structural properties
A likelihood method to cross-calibrate air-shower detectors
We present a detailed statistical treatment of the energy calibration of
hybrid air-shower detectors, which combine a surface detector array and a
fluorescence detector, to obtain an unbiased estimate of the calibration curve.
The special features of calibration data from air showers prevent unbiased
results, if a standard least-squares fit is applied to the problem. We develop
a general maximum-likelihood approach, based on the detailed statistical model,
to solve the problem. Our approach was developed for the Pierre Auger
Observatory, but the applied principles are general and can be transferred to
other air-shower experiments, even to the cross-calibration of other
observables. Since our general likelihood function is expensive to compute, we
derive two approximations with significantly smaller computational cost. In the
recent years both have been used to calibrate data of the Pierre Auger
Observatory. We demonstrate that these approximations introduce negligible bias
when they are applied to simulated toy experiments, which mimic realistic
experimental conditions.Comment: 10 pages, 7 figure
Manipulation Strategies for the Rank Maximal Matching Problem
We consider manipulation strategies for the rank-maximal matching problem. In
the rank-maximal matching problem we are given a bipartite graph such that denotes a set of applicants and a set of posts. Each
applicant has a preference list over the set of his neighbours in
, possibly involving ties. Preference lists are represented by ranks on the
edges - an edge has rank , denoted as , if post
belongs to one of 's -th choices. A rank-maximal matching is one in which
the maximum number of applicants is matched to their rank one posts and subject
to this condition, the maximum number of applicants is matched to their rank
two posts, and so on. A rank-maximal matching can be computed in time, where denotes the number of applicants, the
number of edges and the maximum rank of an edge in an optimal solution.
A central authority matches applicants to posts. It does so using one of the
rank-maximal matchings. Since there may be more than one rank- maximal matching
of , we assume that the central authority chooses any one of them randomly.
Let be a manipulative applicant, who knows the preference lists of all
the other applicants and wants to falsify his preference list so that he has a
chance of getting better posts than if he were truthful. In the first problem
addressed in this paper the manipulative applicant wants to ensure that
he is never matched to any post worse than the most preferred among those of
rank greater than one and obtainable when he is truthful. In the second problem
the manipulator wants to construct such a preference list that the worst post
he can become matched to by the central authority is best possible or in other
words, wants to minimize the maximal rank of a post he can become matched
to
Spin-orbital excitation continuum and anomalous electron-phonon interaction in the Mott insulator LaTiO
Raman scattering experiments on stoichiometric, Mott-insulating LaTiO
over a wide range of excitation energies reveal a broad electronic continuum
which is featureless in the paramagnetic state, but develops a gap of cm upon cooling below the N\'eel temperature K. In the
antiferromagnetic state, the spectral weight below the gap is transferred to
well-defined spectral features due to spin and orbital excitations. Low-energy
phonons exhibit pronounced Fano anomalies indicative of strong interaction with
the electron system for , but become sharp and symmetric for . The electronic continuum and the marked renormalization of the phonon
lifetime by the onset of magnetic order are highly unusual for Mott insulators
and indicate liquid-like correlations between spins and orbitals.Comment: to appear in Phys. Rev. Let
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