7,648 research outputs found
Optimal pricing using online auction experiments: A P\'olya tree approach
We show how a retailer can estimate the optimal price of a new product using
observed transaction prices from online second-price auction experiments. For
this purpose we propose a Bayesian P\'olya tree approach which, given the
limited nature of the data, requires a specially tailored implementation.
Avoiding the need for a priori parametric assumptions, the P\'olya tree
approach allows for flexible inference of the valuation distribution, leading
to more robust estimation of optimal price than competing parametric
approaches. In collaboration with an online jewelry retailer, we illustrate how
our methodology can be combined with managerial prior knowledge to estimate the
profit maximizing price of a new jewelry product.Comment: Published in at http://dx.doi.org/10.1214/11-AOAS503 the Annals of
Applied Statistics (http://www.imstat.org/aoas/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Observation of intrinsic inverse spin Hall effect
We report observation of intrinsic inverse spin Hall effect in un-doped GaAs
multiple quantum wells with a sample temperature of 10 K. A transient ballistic
pure spin current is injected by a pair of laser pulses through quantum
interference. By time-resolving the dynamics of the pure spin current, the
momentum relaxation time is deduced, which sets the lower limit of the
scattering time between electrons and holes. The transverse charge current
generated by the pure spin current via the inverse spin Hall effect is
simultaneously resolved. We find that the charge current is generated well
before the first electron-hole scattering event. Generation of the transverse
current in the scattering-free ballistic transport regime provides unambiguous
evidence for the intrinsic inverse spin Hall effect.Comment: 4 pages, 3 figure
Discovery of an optical counterpart to the hyperluminous X-ray source in ESO 243-49
The existence of black holes of masses ~ 10^2-10^5 Msun has important
implications for the formation and evolution of star clusters and supermassive
black holes. One of the strongest candidates to date is the hyperluminous X-ray
source HLX1, possibly located in the S0-a galaxy ESO243-49, but the lack of an
identifiable optical counterpart had hampered its interpretation. Using the
Magellan telescope, we have discovered an unresolved optical source with R =
(23.80 +/- 0.25) mag and V = (24.5 +/- 0.3) mag within HLX1's positional error
circle. This implies an average X-ray/optical flux ratio ~ 500. Taking the same
distance as ESO243-49, we obtain an intrinsic brightness M_R = (-11.0 +/- 0.3)
mag, comparable to that of a massive globular cluster. Alternatively, the
optical source is consistent with a main-sequence M star in the Galactic halo
(for example an M4.4 star at ~ 2.5 kpc). We also examined the properties of
ESO243-49 by combining Swift/UVOT observations with stellar population
modelling. We found that the overall emission is dominated by a ~5 Gyr old
stellar population, but the UV emission at ~2000 Ang is mostly due to ongoing
star-formation at a rate of ~ 0.03 Msun/yr. The UV emission is more intense (at
least a 9-sigma enhancement above the mean) North East of the nucleus, in the
same quadrant as HLX1. With the combined optical and X-ray measurements, we put
constraints on the nature of HLX1. We rule out a foreground star and a
background AGN. Two alternative scenarios are still viable. HLX1 could be an
accreting intermediate-mass black hole in a star cluster, which may itself be
the stripped nucleus of a dwarf galaxy that passed through ESO243-49, an event
which might have caused the current episode of star formation. Or, it could be
a neutron star in the Galactic halo, accreting from an M4-M5 donor star.Comment: 7 pages, accepted by MNRAS. Several improvements from Oct 7 version:
stronger evidence of the optical counterpart; more accurate estimate of its
brightness (a factor of 2 brighter than previously estimated); use of a
larger set of Swift/UVOT data to measure the recent star formation rate in
ESO243-49; improved discussion and comparison of the competing scenario
Non-LTE Spectra of Accretion Disks Around Intermediate-Mass Black Holes
We have calculated the structures and the emergent spectra of stationary,
geometrically thin accretion disks around 100 and 1000 M_sun black holes in
both the Schwarzschild and extreme Kerr metrics. Equations of radiative
transfer, hydrostatic equilibrium, energy balance, ionization equilibrium, and
statistical equilibrium are solved simultaneously and consistently. The six
most astrophysically abundant elements (H, He, C, N, O, and Fe) are included,
as well as energy transfer by Comptonization. The observed spectrum as a
function of viewing angle is computed incorporating all general relativistic
effects. We find that, in contrast with the predictions of the commonly-used
multi-color disk (MCD) model, opacity associated with photoionization of heavy
elements can significantly alter the spectrum near its peak. These ionization
edges can create spectral breaks visible in the spectra of slowly-spinning
black holes viewed from almost all angles and in the spectra of
rapidly-spinning black holes seen approximately pole-on. For fixed mass and
accretion rate relative to Eddington, both the black hole spin and the viewing
angle can significantly shift the observed peak energy of the spectrum,
particularly for rapid spin viewed obliquely or edge-on. We present a detailed
test of the approximations made in various forms of the MCD model. Linear
limb-darkening is confirmed to be a reasonable approximation for the integrated
flux, but not for many specific frequencies of interest.Comment: 30 pages, 11 eps figures, accepted for publication in Ap
Structure and dielectric response in the high ferroelectric Bi(Zn,Ti)O-PbTiO solid solutions
Theoretical {\em ab initio} and experimental methods were used to investigate
the Bi(Zn,Ti)O-(1-)PbTiO (BZT-PT) solid solution. We find that
hybridization between Zn 4 and O 2 orbitals allows the formation of
short, covalent Zn-O bonds, enabling favorable coupling between A-site and
B-site displacements. This leads to large polarization, strong tetragonality
and an elevated ferroelectric to paraelectric phase transition temperature.
nhomogeneities in local structure near the 90 domain boundaries can be
deduced from the asymetric peak broadening in the neutron and x-ray diffraction
spectra. These extrinsic effects make the ferroelectric to paraelectric phase
transition diffuse in BZT-PT solid solutions
Microscopic analytical theory of a correlated, two-dimensional N-electron gas in a magnetic field
We present a microscopic, analytical theory describing a confined N-electron
gas in two dimensions subject to an external magnetic field. The number of
electrons N and strength of the electron-electron interaction can be
arbitrarily large, and all Landau levels are included implicitly. A possible
connection with the Integer and Fractional Quantum Hall Effects is proposed.Comment: The revised version contains minor changes to text. To be published
in J. Phys: Condens. Mat
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