28,576 research outputs found
Thermal detector model for cryogenic composite detectors for the dark matter experiments CRESST and EURECA
The CRESST (Cryogenic Rare Event Search with Superconducting Thermometers)
and the EURECA (European Underground Rare Event Calorimeter Array) experiments
are direct dark matter search experiments where cryogenic detectors are used to
detect spin-independent, coherent WIMP (Weakly Interacting Massive
Particle)-nucleon scattering events by means of the recoil energy. The
cryogenic detectors use a massive single crystal as absorber which is equipped
with a TES (transition edge sensor) for signal read-out. They are operated at
mK-temperatures. In order to enable a mass production of these detectors, as
needed for the EURECA experiment, a so-called composite detector design (CDD)
that allows decoupling of the TES fabrication from the optimization procedure
of the absorber single-crystal was developed and studied. To further
investigate, understand and optimize the performance of composite detectors a
detailed thermal detector model which takes into account the CDD has been
developed.Comment: To appear in Journal of Physics: Conference Series; Proceedings of
Neutrino 2008, Christchurch, New Zealan
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
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
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
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
Magnon Heat Conductivity and Mean Free Paths in Two-Leg Spin Ladders: A Model-Independent Determination
The magnon thermal conductivity of the spin ladders
in has been investigated at low doping levels
, 0.125, 0.25, 0.5 and 0.75. The Zn-impurities generate nonmagnetic
defects which define an upper limit for and therefore allow
a clear-cut relation between and to
be established independently of any model. Over a large temperature range we
observe a progressive suppression of with increasing
Zn-content and find in particular that with respect to pure is strongly suppressed even in
the case of tiny impurity densities where ~{\AA}.
This shows unambiguously that large ~{\AA} which
have been reported for and on basis of a kinetic model are in the correct order
of magnitude
Sensitivity Kernels for Flows in Time-Distance Helioseismology: Extension to Spherical Geometry
We extend an existing Born approximation method for calculating the linear
sensitivity of helioseismic travel times to flows from Cartesian to spherical
geometry. This development is necessary for using the Born approximation for
inferring large-scale flows in the deep solar interior. In a first sanity
check, we compare two mode kernels from our spherical method and from an
existing Cartesian method. The horizontal and total integrals agree to within
0.3 %. As a second consistency test, we consider a uniformly rotating Sun and a
travel distance of 42 degrees. The analytical travel-time difference agrees
with the forward-modelled travel-time difference to within 2 %. In addition, we
evaluate the impact of different choices of filter functions on the kernels for
a meridional travel distance of 42 degrees. For all filters, the sensitivity is
found to be distributed over a large fraction of the convection zone. We show
that the kernels depend on the filter function employed in the data analysis
process. If modes of higher harmonic degree () are
permitted, a noisy pattern of a spatial scale corresponding to
appears near the surface. When mainly low-degree modes are used
(), the sensitivity is concentrated in the deepest regions and it
visually resembles a ray-path-like structure. Among the different low-degree
filters used, we find the kernel for phase-speed filtered measurements to be
best localized in depth.Comment: 17 pages, 5 figures, 2 tables, accepted for publication in ApJ. v2:
typo in arXiv author list correcte
Microscopic two-nucleon overlaps and knockout reactions from C
The nuclear structure dependence of direct reactions that remove a pair of
like or unlike nucleons from a fast C projectile beam are considered.
Specifically, we study the differences in the two-nucleon correlations present
and the predicted removal cross sections when using -shell shell-model and
multi- no-core shell-model (NCSM) descriptions of the two-nucleon
overlaps for the transitions to the mass =10 projectile residues. The NCSM
calculations use modern chiral two-nucleon and three-nucleon (NN+3N)
interactions. The -removal cross sections to low-lying =0, B
final states are enhanced when using the NCSM two-nucleon amplitudes. The
calculated absolute and relative partial cross sections to the low energy
B final states show a significant sensitivity to the interactions used,
suggesting that assessments of the overlap functions for these transitions and
confirmations of their structure could be made using final-state-exclusive
measurements of the -removal cross sections and the associated momentum
distributions of the forward travelling projectile-like residues.Comment: 9 pages, 7 figure
Dynamics of ligand substitution in labile cobalt complexes resolved by ultrafast T-jump
Ligand exchange of hydrated metal complexes is common in chemical and biological systems. Using the ultrafast T-jump, we examined this process, specifically the transformation of aqua cobalt (II) complexes to their fully halogenated species. The results reveal a stepwise mechanism with time scales varying from hundreds of picoseconds to nanoseconds. The dynamics are significantly faster when the structure is retained but becomes rate-limited when the octahedral-to-tetrahedral structural change bottlenecks the transformation. Evidence is presented, from bimolecular kinetics and energetics (enthalpic and entropic), for a reaction in which the ligand assists the displacement of water molecules, with the retention of the entering ligand in the activated state. The reaction time scale deviates by one to two orders of magnitude from that of ionic diffusion, suggesting the involvement of a collisional barrier between the ion and the much larger complex
- …