3,161 research outputs found
Assembling, storing and ginning cotton in the Mississippi Delta
The Agricultural Experiment Stations of Arizona, Arkansas, Georgia, Louisiana, Mississippi, Missouri, New Mexico, Tennessee, and Texas, cooperating.Includes bibliographical references
Letter to Sonora Dodd from Leon V. Metcalf, May 6, 1945
Letter to Sonora Dodd from Leon V. Metcalf, with envelope.https://digitalcommons.whitworth.edu/fathers-day-correspondence/1136/thumbnail.jp
Initializing a Quantum Register from Mott Insulator States in Optical Lattices
We propose and quantitatively develop two schemes to quickly and accurately
generate a stable initial configuration of neutral atoms in optical microtraps
by extraction from the Mott insulator state in optical lattices. We show that
thousands of atoms may be extracted and stored in the ground states of optical
microtrap arrays with one atom per trap in one operational process
demonstrating massive scalability. The failure probability during extraction in
the first scheme can be made sufficiently small (10^{-4}) to initialize a large
scale quantum register with high fidelity. A complementary faster scheme with
more extracted atoms but lower fidelity is also developed.Comment: 5 pages, 3 figure
Early diffusion evidence of retrograde transsynaptic degeneration in the human visual system
We investigated whether diffusion tensor imaging (DTI) indices of white matter integrity would offer early markers of retrograde transsynaptic degeneration (RTD) in the visual system after stroke
Objective: We investigated whether diffusion tensor imaging (DTI) indices of white matter integrity
would offer early markers of retrograde transsynaptic degeneration (RTD) in the visual system
after stroke.
Methods: We performed a prospective longitudinal analysis of the sensitivity of DTI markers of
optic tract health in 12 patients with postsynaptic visual pathway stroke, 12 stroke controls,
and 28 healthy controls. We examined group differences in (1) optic tract fractional anisotropy
(FA-asymmetry), (2) perimetric measures of visual impairment, and (3) the relationship between
FA-asymmetry and perimetric assessment.
Results: FA-asymmetry was higher in patients with visual pathway lesions than in control groups.
These differences were evident 3 months from the time of injury and did not change significantly
at 12 months. Perimetric measures showed evidence of impairment in participants with visual
pathway stroke but not in control groups. A significant association was observed between
FA-asymmetry and perimetric measures at 3 months, which persisted at 12 months.
Conclusions: DTI markers of RTD are apparent 3 months from the time of injury. This represents
the earliest noninvasive evidence of RTD in any species. Furthermore, these measures associate
with measures of visual impairment. DTI measures offer a reproducible, noninvasive, and sensitive
method of investigating RTD and its role in visual impairment
Doppler cooling with coherent trains of laser pulses and tunable "velocity comb"
We explore the possibility of decelerating and Doppler cooling of an ensemble
of two-level atoms by a coherent train of short, non-overlapping laser pulses.
We develop a simple analytical model for dynamics of a two-level system driven
by the resulting frequency comb field. We find that the effective scattering
force mimics the underlying frequency comb structure. The force pattern depends
strongly on the ratio of the atomic lifetime to the repetition time and pulse
area. For example, in the limit of short lifetimes, the frequency peaks of the
optical force wash out. We show that laser cooling with pulse trains results in
a "velocity comb", a series of narrow peaks in the velocity space
Continuous Loading of a Conservative Trap from an Atomic Beam
We demonstrate the fast accumulation of Cr atoms in a conservative potential
from a magnetically guided atomic beam. Without laser cooling on a cycling
transition, a single dissipative step realized by optical pumping allows to
load atoms at a rate of 2*10^7 1/s in the trap. Within less than 100 ms we
reach the collisionally dense regime, from which we directly produce a
Bose-Einstein condensate with subsequent evaporative cooling. This constitutes
a new approach to degeneracy where, provided a slow beam of particles can be
produced by some means, Bose-Einstein condensation can be reached for species
without a cycling transition.Comment: 4 pages, 4 figure
Probing -Spin Correlations in Optical Lattices
We propose a technique to measure multi-spin correlation functions of
arbitrary range as determined by the ground states of spinful cold atoms in
optical lattices. We show that an observation of the atomic version of the
Stokes parameters, using focused lasers and microwave pulsing, can be related
to -spin correlators. We discuss the possibility of detecting not only
ground state static spin correlations, but also time-dependent spin wave
dynamics as a demonstrative example using our proposed technique.Comment: 7 pages, 4 figure
Constraining Warm Dark Matter using QSO gravitational lensing
Warm Dark Matter (WDM) has been invoked to resolve apparent conflicts of Cold
Dark Matter (CDM) models with observations on subgalactic scales. In this work
we provide a new and independent lower limit for the WDM particle mass (e.g.
sterile neutrino) through the analysis of image fluxes in gravitationally
lensed QSOs.
Starting from a theoretical unperturbed cusp configuration we analyze the
effects of intergalactic haloes in modifying the fluxes of QSO multiple images,
giving rise to the so-called anomalous flux ratio. We found that the global
effect of such haloes strongly depends on their mass/abundance ratio and it is
maximized for haloes in the mass range 10^6-10^8 \Msun.
This result opens up a new possibility to constrain CDM predictions on small
scales and test different warm candidates, since free streaming of warm dark
matter particles can considerably dampen the matter power spectrum in this mass
range. As a consequence, while a ()CDM model is able to produce flux
anomalies at a level similar to those observed, a WDM model, with an
insufficiently massive particle, fails to reproduce the observational
evidences.
Our analysis suggests a lower limit of a few keV () for the
mass of warm dark matter candidates in the form of a sterile neutrino. This
result makes sterile neutrino Warm Dark Matter less attractive as an
alternative to Cold Dark Matter, in good agreement with previous findings from
Lyman- forest and Cosmic Microwave Background analysis.Comment: One equation added, typo in eq: 5 corrected, minor changes to match
the accepted version by MNRA
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