35,996 research outputs found
Ensuring Trust in One Time Exchanges: Solving the QoS Problem
We describe a pricing structure for the provision of IT services that ensures
trust without requiring repeated interactions between service providers and
users. It does so by offering a pricing structure that elicits truthful
reporting of quality of service (QoS) by providers while making them
profitable. This mechanism also induces truth-telling on the part of users
reserving the service
One-point Statistics of the Cosmic Density Field in Real and Redshift Spaces with A Multiresolutional Decomposition
In this paper, we develop a method of performing the one-point statistics of
a perturbed density field with a multiresolutional decomposition based on the
discrete wavelet transform (DWT). We establish the algorithm of the one-point
variable and its moments in considering the effects of Poisson sampling and
selection function. We also establish the mapping between the DWT one-point
statistics in redshift space and real space, i.e. the algorithm for recovering
the DWT one-point statistics from the redshift distortion of bulk velocity,
velocity dispersion, and selection function. Numerical tests on N-body
simulation samples show that this algorithm works well on scales from a few
hundreds to a few Mpc/h for four popular cold dark matter models.
Taking the advantage that the DWT one-point variable is dependent on both the
scale and the shape (configuration) of decomposition modes, one can design
estimators of the redshift distortion parameter (beta) from combinations of DWT
modes. When the non-linear redshift distortion is not negligible, the beta
estimator from quadrupole-to-monopole ratio is a function of scale. This
estimator would not work without adding information about the scale-dependence,
such as the power-spectrum index or the real-space correlation function of the
random field. The DWT beta estimators, however, do not need such extra
information. Numerical tests show that the proposed DWT estimators are able to
determine beta robustly with less than 15% uncertainty in the redshift range 0
< z < 3.Comment: 39 pages, 12 figures, ApJ accepte
Cross-correlating the Thermal Sunyaev-Zel'dovich Effect and the Distribution of Galaxy Clusters
We present the analytical formulas, derived based on the halo model, to
compute the cross-correlation between the thermal Sunyaev-Zel'dovich (SZ)
effect and the distribution of galaxy clusters. By binning the clusters
according to their redshifts and masses, this cross-correlation, the so-called
stacked SZ signal, reveals the average SZ profile around the clusters. The
stacked SZ signal is obtainable from a joint analysis of an
arcminute-resolution cosmic microwave background (CMB) experiment and an
overlapping optical survey, which allows for detection of the SZ signals for
clusters whose masses are below the individual cluster detection threshold. We
derive the error covariance matrix for measuring the stacked SZ signal, and
then forecast for its detection from ongoing and forthcoming combined
CMB-optical surveys. We find that, over a wide range of mass and redshift, the
stacked SZ signal can be detected with a significant signal to noise ratio
(total S/N \gsim 10), whose value peaks for the clusters with intermediate
masses and redshifts. Our calculation also shows that the stacking method
allows for probing the clusters' SZ profiles over a wide range of scales, even
out to projected radii as large as the virial radius, thereby providing a
promising way to study gas physics at the outskirts of galaxy clusters.Comment: 11 pages, 6 figures, 3 tables, minor revisions reflect PRD published
versio
Local electronic nematicity in the one-band Hubbard model
Nematicity is a well known property of liquid crystals and has been recently
discussed in the context of strongly interacting electrons. An electronic
nematic phase has been seen by many experiments in certain strongly correlated
materials, in particular, in the pseudogap phase generic to many hole-doped
cuprate superconductors. Recent measurements in high superconductors has
shown even if the lattice is perfectly rotationally symmetric, the ground state
can still have strongly nematic local properties. Our study of the
two-dimensional Hubbard model provides strong support of the recent
experimental results on local rotational symmetry breaking. The
variational cluster approach is used here to show the possibility of an
electronic nematic state and the proximity of the underlying symmetry-breaking
ground state within the Hubbard model. We identify this nematic phase in the
overdoped region and show that the local nematicity decreases with increasing
electron filling. Our results also indicate that strong Coulomb interaction may
drive the nematic phase into a phase similar to the stripe structure. The
calculated spin (magnetic) correlation function in momentum space shows the
effects resulting from real-space nematicity
Inhomogeneity Induces Resonance Coherence Peaks in Superconducting BSCCO
In this paper we analyze, using scanning tunneling spectroscopy, the density
of electronic states in nearly optimally doped BSCCO in zero field. Focusing on
the superconducting gap, we find patches of what appear to be two different
phases in a background of some average gap, one with a relatively small gap and
sharp large coherence peaks and one characterized by a large gap with broad
weak coherence peaks. We compare these spectra with calculations of the local
density of states for a simple phenomenological model in which a 2 xi_0 * 2
xi_0 patch with an enhanced or supressed d-wave gap amplitude is embedded in a
region with a uniform average d-wave gap.Comment: 4 pages, 3 figure
Groundwater flow in a sandy tidal beach 2. Two-dimensional finite element analysis.
Two-dimensional finite element techniques are described that model closely the complicated fluctuations osbserved in the water table of an ocean beach. The use of triangular elements permits the specification of more realistic boundary conditions than the use of line elements in a one-dimensional model. Also, results obtained from the two-dimensional model for the region closet o the ocean compare more favorably with field data than results obtained from the one-dimensional finite element model
Is the cosmic UV background fluctuating at redshift z ~ 6 ?
We study the Gunn-Peterson effect of the photo-ionized intergalactic
medium(IGM) in the redshift range 5< z <6.4 using semi-analytic simulations
based on the lognormal model. Assuming a rapidly evolved and spatially uniform
ionizing background, the simulation can produce all the observed abnormal
statistical features near redshift z ~ 6. They include: 1) rapidly increase of
absorption depths; 2) large scatter in the optical depths; 3) long-tailed
distributions of transmitted flux and 4) long dark gaps in spectra. These
abnormal features are mainly due to rare events, which correspond to the
long-tailed probability distribution of the IGM density field, and therefore,
they may not imply significantly spatial fluctuations in the UV ionizing
background at z ~ 6.Comment: 12 pages, 4 figs, accepted by ApJ
The coexistence of superconductivity and ferromagnetism in nano-scale metallic grains
A nano-scale metallic grain in which the single-particle dynamics are chaotic
is described by the so-called universal Hamiltonian. This Hamiltonian includes
a superconducting pairing term and a ferromagnetic exchange term that compete
with each other: pairing correlations favor minimal ground-state spin, while
the exchange interaction favors maximal spin polarization. Of particular
interest is the fluctuation-dominated regime where the bulk pairing gap is
comparable to or smaller than the single-particle mean level spacing and the
Bardeen-Cooper-Schrieffer theory of superconductivity breaks down.
Superconductivity and ferromagnetism can coexist in this regime. We identify
signatures of the competition between superconductivity and ferromagnetism in a
number of quantities: ground-state spin, conductance fluctuations when the
grain is weakly coupled to external leads and the thermodynamic properties of
the grain, such as heat capacity and spin susceptibility.Comment: 13 pages, 13 figures, Proceedings of the Conference on the Frontiers
of Quantum and Mesoscopic Thermodynamics (FQMT11
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