27,883 research outputs found
Heat and spin transport in a cold atomic Fermi gas
Motivated by recent experiments measuring the spin transport in ultracold
unitary atomic Fermi gases (Sommer et al., 2011; Sommer et al., 2011), we
explore the theory of spin and heat transport in a three-dimensional
spin-polarized atomic Fermi gas. We develop estimates of spin and thermal
diffusivities and discuss magnetocaloric effects, namely the the spin Seebeck
and spin Peltier effects. We estimate these transport coefficients using a
Boltzmann kinetic equation in the classical regime and present experimentally
accessible signatures of the spin Seebeck effect. We study an exactly solvable
model that illustrates the role of momentum-dependent scattering in the
magnetocaloric effects.Comment: 18 pages, 6 figures, slight notation changes from previous versio
Training Churches in Faith and Work Discipleship
The goal of this study is to evaluate the effectiveness of two training mechanisms to equip churches to run an intensive faith and work discipleship program called the Gotham Fellowship. The first training involves participation in a week-long summer intensive training and the second training will happen through the development of a leaders’ handbook for implementing the Gotham Fellowship.
Building upon the framework of the normative, existential and situational perspectives extensively outlined in this study, these church leaders will be equipped to lead a Gotham-like Fellows program in their churches to lay a foundation for a robust faith and work ministry. This training corresponds to the three perspectives. Normatively, those who will lead the Fellows program will learn a foundational biblical theology of work highlighting five passages of Scripture. Existentially, they will experience spiritually formative practices that highlight the need to engage God personally through adaptations of ancient devotional practices. Situationally, they will acquire and be trained to utilize tools that help apply the gospel’s power into the three areas of heart, community, and world through corresponding projects.
CFW will utilize two main online surveys to assess the effectiveness of this training—the first survey will be sent out shortly after the summer intensive with a follow-up survey sent out after the completion of the first-year Gotham program. Through these two surveys, the hope is to improve these two training tools so that CFW can more effectively prepare churches to launch Gotham programs that will accelerate faith and work ministries around the world
A VLT/FORS2 Multi-Slit Search for Lyman-alpha Emitting Galaxies at z~6.5
We present results from a deep spectroscopic search in the 9150A atmospheric
window for z~6.5 Lyman-alpha emitting galaxies using the VLT/FORS2. Our
multi-slit+narrow-band filter survey covers a total spatial area of 17.6 sq.
arcmin in four different fields and reaches fluxes down to 5x10^(-18)
erg/s/cm^2 (7 sigma detection). Our detection limit is significantly fainter
than narrow-band searches at this redshift and fainter also than the unlensed
brightness of Hu et al.'s HCM6A at z=6.56, and thus provides better overlap
with surveys at much lower redshifts. Eighty secure emission line galaxies are
detected. However, based on their clear continuum emission shortward of the
line or the presence of multiple lines, none of these can be Ly-alpha emission
at z~6.5. Our null result of finding no z~6.5 Ly-alpha emitters suggests that
the number density of Ly-alpha emitters with L>2x10^(42) erg/s declines by ~2
between z~3 and z~6.5.Comment: accepted by ApJ Letters (originally submitted June 11, 2004
Hyperspectral Image Processing Using Locally Linear Embedding
We describe a method of processing hyperspectral images of natural scenes that uses a combination of k-means clustering and locally linear embedding (LLE). The primary goal is to assist anomaly detection by preserving spectral uniqueness among the pixels. In order to reduce redundancy among the pixels, adjacent pixels which are spectrally similar are grouped using the k-means clustering algorithm. Representative pixels from each cluster are chosen and passed to the LLE algorithm, where the high dimensional spectral vectors are encoded by a low dimensional mapping. Finally, monochromatic and tri-chromatic images are constructed from the k-means cluster assignments and LLE vector mappings. The method generates images where differences in the original spectra are reflected in differences in the output vector assignments. An additional benefit of mapping to a lower dimensional space is reduced data size. When spectral irregularities are added to a patch of the hyperspectral images, again the method successfully generated color assignments that detected the changes in the spectra
Non-Gaussianity in Axion N-flation Models
We study perturbations in the multifield axion N-flation model, taking account of the full cosine potential. We find significant differences from previous analyses which made a quadratic approximation to the potential. The tensor-to-scalar ratio and the scalar spectral index move to lower values, which nevertheless provide an acceptable fit to observation. Most significantly, we find that the bispectrum non-Gaussianity parameter fNL may be large, typically of order 10 for moderate values of the axion decay constant, increasing to of order 100 for decay constants slightly smaller than the Planck scale. Such a non-Gaussian fraction is detectable. We argue that this property is generic in multifield models of hilltop inflation
Searching for Dust around Hyper Metal-Poor Stars
We examine the mid-infrared fluxes and spectral energy distributions for
metal-poor stars with iron abundances [Fe/H] , as well as two
CEMP-no stars, to eliminate the possibility that their low metallicities are
related to the depletion of elements onto dust grains in the formation of a
debris disk. Six out of seven stars examined here show no mid-IR excess. These
non-detections rule out many types of circumstellar disks, e.g. a warm debris
disk ( K), or debris disks with inner radii AU, such as
those associated with the chemically peculiar post-AGB spectroscopic binaries
and RV Tau variables. However, we cannot rule out cooler debris disks, nor
those with lower flux ratios to their host stars due to, e.g. a smaller disk
mass, a larger inner disk radius, an absence of small grains, or even a
multicomponent structure, as often found with the chemically peculiar Lambda
Bootis stars. The only exception is HE0107-5240, for which a small mid-IR
excess near 10 microns is detected at the 2- level; if the excess is
real and associated with this star, it may indicate the presence of (recent)
dust-gas winnowing or a binary system.Comment: Accepted for publication in Ap
Approximation Algorithms for Scheduling with Resource and Precedence Constraints
We study non-preemptive scheduling problems on identical parallel machines and uniformly related machines under both resource constraints and general precedence constraints between jobs. Our first result is an O(logn)-approximation algorithm for the objective of minimizing the makespan on parallel identical machines under resource and general precedence constraints. We then use this result as a subroutine to obtain an O(logn)-approximation algorithm for the
more general objective of minimizing the total weighted completion time on parallel identical machines under both constraints. Finally, we present an O(logm logn)-approximation algorithm for scheduling under these constraints on uniformly related machines. We show that these results can all be generalized to include the case where each job has a release time. This is the first upper bound on the approximability of this class of scheduling problems where both resource and general precedence constraints must be satisfied simultaneously
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