16,050 research outputs found
Cumulative identical spin rotation effects in collisionless trapped atomic gases
We discuss the strong spin segregation in a dilute trapped Fermi gas recently
observed by Du et al. with "anomalous" large time scale and amplitude. In a
collisionless regime, the atoms oscillate rapidly in the trap and average the
inhomogeneous external field in an energy dependent way, which controls their
transverse spin precession frequency. During interactions between atoms with
different spin directions, the identical spin rotation effect (ISRE) transfers
atoms to the up or down spin state, depending on their motional energy. Since
low energy atoms are closer to the center of the trap than high energy atoms,
the final outcome is a strong correlation between spins and positions.Comment: 4 pages, 2 figures; v2: comparison to experimental data adde
Hard discs under steady shear: comparison of Brownian dynamics simulations and mode coupling theory
Brownian dynamics simulations of bidisperse hard discs moving in two
dimensions in a given steady and homogeneous shear flow are presented close to
and above the glasstransition density. The stationary structure functions and
stresses of shear-melted glass are compared quantitatively to parameter-free
numerical calculations of monodisperse hard discs using mode coupling theory
within the integration through transients framework. Theory qualitatively
explains the properties of the yielding glass but quantitatively
overestimatesthe shear-driven stresses and structural anisotropies.Comment: 1. The original Phil. Trans. R. Soc. contains an error in the caption
of the y-axes of the upper left panel in figure 9: There's a factor
\dot{\gamma} missing in the denominato
Variable-speed Generators with Flux Weakening
A cost-competitive, permanent-magnet 20 kW generator is designed such that the following criteria are satisfied: an (over) load capability of at least 30 kW over the entire speed range of 60-120 rpm, generator weight of about 550 lbs with a maximum radial stator flux density of 0.82 T at low speed, unity power factor operation, acceptably small synchronous reactances and operation without a gear box. To justify this final design four different generator designs are investigated: the first two designs are studied to obtain a speed range from 20 to 200 rpm employing rotor field weakening, and the latter two are investigated to obtain a maximum speed range of 40 to 160 rpm based on field weakening via the stator excitation. The generator reactances and induced voltages are computed using finite element/difference solutions. Generator losses and efficiencies are presented for all four designs at rated temperature of Tr=120C
Deterministic Digital Clustering of Wireless Ad Hoc Networks
We consider deterministic distributed communication in wireless ad hoc
networks of identical weak devices under the SINR model without predefined
infrastructure. Most algorithmic results in this model rely on various
additional features or capabilities, e.g., randomization, access to geographic
coordinates, power control, carrier sensing with various precision of
measurements, and/or interference cancellation. We study a pure scenario, when
no such properties are available. As a general tool, we develop a deterministic
distributed clustering algorithm. Our solution relies on a new type of
combinatorial structures (selectors), which might be of independent interest.
Using the clustering, we develop a deterministic distributed local broadcast
algorithm accomplishing this task in rounds, where
is the density of the network. To the best of our knowledge, this is
the first solution in pure scenario which is only polylog away from the
universal lower bound , valid also for scenarios with
randomization and other features. Therefore, none of these features
substantially helps in performing the local broadcast task. Using clustering,
we also build a deterministic global broadcast algorithm that terminates within
rounds, where is the diameter of the
network. This result is complemented by a lower bound , where is the path-loss parameter of the
environment. This lower bound shows that randomization or knowledge of own
location substantially help (by a factor polynomial in ) in the global
broadcast. Therefore, unlike in the case of local broadcast, some additional
model features may help in global broadcast
Fanleaf degeneration/decline disease of grapevines
NYS IPM Type: Fruits IPM Fact SheetFanleaf degeneration/decline disease is one of the most severe viral disease complexes of grapevine worldwide. It is also one of the oldest known viral diseases of Vitis vinifera with descriptions of symptoms being reported in Europe as early as 1841. This disease is now known to affect grapevines in all temperate regions where Vitis vinifera and hybrid rootstocks are grown. Within the United States, fanleaf degeneration/decline is widespread in California, but has also been observed in Washington State, Maryland, Pennsylvania, New York and Missouri
Spin self-rephasing and very long coherence times in a trapped atomic ensemble
We perform Ramsey spectroscopy on the ground state of ultra-cold 87Rb atoms
magnetically trapped on a chip in the Knudsen regime. Field inhomogeneities
over the sample should limit the 1/e contrast decay time to about 3 s, while
decay times of 58 s are actually observed. We explain this surprising result by
a spin self-rephasing mechanism induced by the identical spin rotation effect
originating from particle indistinguishability. We propose a theory of this
synchronization mechanism and obtain good agreement with the experimental
observations. The effect is general and susceptible to appear in other physical
systems.Comment: Revised version; improved description of the theoretical treatmen
Intrinsic defects in silicon carbide LED as a perspective room temperature single photon source in near infrared
Generation of single photons has been demonstrated in several systems.
However, none of them satisfies all the conditions, e.g. room temperature
functionality, telecom wavelength operation, high efficiency, as required for
practical applications. Here, we report the fabrication of light emitting
diodes (LEDs) based on intrinsic defects in silicon carbide (SiC). To fabricate
our devices we used a standard semiconductor manufacturing technology in
combination with high-energy electron irradiation. The room temperature
electroluminescence (EL) of our LEDs reveals two strong emission bands in
visible and near infrared (NIR), associated with two different intrinsic
defects. As these defects can potentially be generated at a low or even single
defect level, our approach can be used to realize electrically driven single
photon source for quantum telecommunication and information processing
Exact marginality in open string field theory: a general framework
We construct analytic solutions of open bosonic string field theory for any
exactly marginal deformation in any boundary conformal field theory when
properly renormalized operator products of the marginal operator are given. We
explicitly provide such renormalized operator products for a class of marginal
deformations which include the deformations of flat D-branes in flat
backgrounds by constant massless modes of the gauge field and of the scalar
fields on the D-branes, the cosine potential for a space-like coordinate, and
the hyperbolic cosine potential for the time-like coordinate. In our
construction we use integrated vertex operators, which are closely related to
finite deformations in boundary conformal field theory, while previous analytic
solutions were based on unintegrated vertex operators. We also introduce a
modified star product to formulate string field theory around the deformed
background.Comment: 63 pages, 10 figures, LaTeX2
Neuroactive compounds in the brain of the honeybee during imaginal life.
1. In the brains of worker honeybees (Apis mellifera carnica) corresponding to different stages in the life span, we measured the content of GABA, glutamate, acetylcholine, eholine, norepinephrine, dopamine and serotonin. 2. The highest concentrations were found for GABA, glutamate and acetylcholine. 3. Biogenic amines occur in considerably lower concentrations in comparison to the above mentioned transmitters. 4. Age-correlated changes were found for different neuroactive substances. 5. GABA and glutamate show a well marked rise and fall of their concentrations with a maximum at day 10. 6. The results are discussed in comparison to other species and with respect to age polyethism of worker honeybees
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