1,493 research outputs found
A subsurface particle maximum layer and enhanced microbial activity in the secondary nitrite maximum of the northeastern tropical Pacific Ocean
Profiles of light transmission, dissolved oxygen, dissolved nutrients, electron transport system (ETS) activity, temperature and salinity were made in the northeastern tropical Pacific Ocean. A particle maximum at 150–300 m within the oxygen minimum and secondary nitrite maximum was associated with the salinity maximum of Subtropical Subsurface Water. A subsurface maximum in ETS activity was also found to be associated with the secondary nitrite maximum and the particle maximum. Persistence of these features at a constant depth and their location within a minimum in vertical static stability suggest an advective and/or in situ origin for the particles and an in situ development of the associated chemical and biochemical extremes
Electron-beam-induced shift in the apparent position of a pinned vortex in a thin superconducting film
When an electron beam strikes a superconducting thin film near a pinned
vortex, it locally increases the temperature-dependent London penetration depth
and perturbs the circulating supercurrent, thereby distorting the vortex's
magnetic field toward the heated spot. This phenomenon has been used to
visualize vortices pinned in SQUIDs using low-temperature scanning electron
microscopy. In this paper I develop a quantitative theory to calculate the
displacement of the vortex-generated magnetic-flux distribution as a function
of the distance of the beam spot from the vortex core. The results are
calculated using four different models for the spatial distribution of the
thermal power deposited by the electron beam.Comment: 9 pages, 6 figures, resubmitted to PRB with referee-suggested
revisions, includes new paragraph on numerical evaluatio
Submillimeter satellite radiometer Final engineering report
All solid-state superheterodyne Dicke radiometer for submillimeter wavelength
Unused Medication Collection: An Emerging Service-Learning Experience for Pharmacy Students
While the U.S. makes up around 5% of the world’s population, we consume approximately 75% of the world’s prescription drugs—well over 4 billion prescriptions per year. Approximately one third of those are never used, creating an array of public health challenges. These challenges include land and water pollution; unintentional inappropriate use and unintentional human, pet, and wildlife poisonings; and intentional drug abuse and diversion. Misuse of prescription drugs now exceeds that of all illegal drugs combined. Reducing the number of medications prescribed is of primary importance, as well as collecting unnecessary medications from households and disposing of them through environmentally friendly methods. There are a variety of medication collection methods, including public take-back events, permanent drop boxes at pharmacies, collection by police departments, as well as prepaid mailers available from some pharmacies and the Internet. When bulk medication is collected at take-back events or by police departments, it is generally quantified as “pounds collected,” with no determination of specific medications collected, quantities of prescribed medications left unused, or length of household storage beyond the expiration date. Pharmacy students are uniquely positioned to explore these unknowns and develop solutions with their high level of drug expertise. This research study combined with community service events involved the collaboration of pharmacy students with environmentalists, community volunteers, and law enforcement officers to collect and analyze unwanted medications, as well as explore factors pertinent to this public hazard
Normal Modes of a Vortex in a Trapped Bose-Einstein Condensate
A hydrodynamic description is used to study the normal modes of a vortex in a
zero-temperature Bose-Einstein condensate. In the Thomas-Fermi (TF) limit, the
circulating superfluid velocity far from the vortex core provides a small
perturbation that splits the originally degenerate normal modes of a
vortex-free condensate. The relative frequency shifts are small in all cases
considered (they vanish for the lowest dipole mode with |m|=1), suggesting that
the vortex is stable. The Bogoliubov equations serve to verify the existence of
helical waves, similar to those of a vortex line in an unbounded weakly
interacting Bose gas. In the large-condensate (small-core) limit, the
condensate wave function reduces to that of a straight vortex in an unbounded
condensate; the corresponding Bogoliubov equations have no bound-state
solutions that are uniform along the symmetry axis and decay exponentially far
from the vortex core.Comment: 15 pages, REVTEX, 2 Postscript figures, to appear in Phys. Rev. A. We
have altered the material in Secs. 3B and 4 in connection with the normal
modes that have |m|=1. Our present treatment satisfies the condition that the
fundamental dipole mode of a condensate with (or without) a vortex should
have the bare frequency $\omega_\perp
Transition from synchronous to asynchronous superfluid phase slippage in an aperture array
We have investigated the dynamics of superfluid phase slippage in an array of
apertures. The magnitude of the dissipative phase slips shows that they occur
simultaneously in all the apertures when the temperature is around 10 mK below
the superfluid transition, and subsequently lose their simultaneity as the
temperature is lowered. We find that when periodic synchronous phase slippage
occurs, the synchronicity exists from the very first phase slip, and therefore
is not due to mode locking of interacting oscillators. When the system is
allowed to relax freely from a given initial energy, the total number of phase
slips that occur and the energy left in the system after the last phase slip
depends reproducibly on the initial energy. We find the energy remaining after
the final phase slip is a periodic function of the initial system energy. This
dependence directly reveals the discrete and dissipative nature of the phase
slips and is a powerful diagnostic for investigation of synchronicity in the
array. When the array slips synchronously, this periodic energy function is a
sharp sawtooth. As the temperature is lowered and the degree of synchronicity
drops, the peak of this sawtooth becomes rounded, suggesting a broadening of
the time interval over which the array slips. The underlying mechanism for the
higher temperature synchronous behavior and the following loss of synchronicity
at lower temperatures is not yet understood. We discuss the implications of our
measurements and pose several questions that need to be resolved by a theory
explaining the synchronous behavior in this quantum system. An understanding of
the array phase slip process is essential to the optimization of superfluid
`dc-SQUID' gyroscopes and interferometers.Comment: 10 pages, 4 figure
Anomalous modes drive vortex dynamics in confined Bose-Einstein condensates
The dynamics of vortices in trapped Bose-Einstein condensates are
investigated both analytically and numerically. In axially symmetric traps, the
critical rotation frequency for the metastability of an isolated vortex
coincides with the largest vortex precession frequency (or anomalous mode) in
the Bogoliubov excitation spectrum. As the condensate becomes more elongated,
the number of anomalous modes increases. The largest frequency of these modes
exceeds both the thermodynamic critical frequency and the nucleation frequency
at which vortices are created dynamically. Thus, anomalous modes describe not
only the critical rotation frequency for creation of the first vortex in an
elongated condensate but also the vortex precession in a single-component
spherical condensate.Comment: 4 pages revtex, 3 embedded figure
Nucleation of vortex arrays in rotating anisotropic Bose-Einstein condensates
The nucleation of vortices and the resulting structures of vortex arrays in
dilute, trapped, zero-temperature Bose-Einstein condensates are investigated
numerically. Vortices are generated by rotating a three-dimensional,
anisotropic harmonic atom trap. The condensate ground state is obtained by
propagating the Gross-Pitaevskii equation in imaginary time. Vortices first
appear at a rotation frequency significantly larger than the critical frequency
for vortex stabilization. This is consistent with a critical velocity mechanism
for vortex nucleation. At higher frequencies, the structures of the vortex
arrays are strongly influenced by trap geometry.Comment: 5 pages, two embedded figures. To appear in Phys. Rev. A (RC
Shape deformations and angular momentum transfer in trapped Bose-Einstein condensates
Angular momentum can be transferred to a trapped Bose-Einstein condensate by
distorting its shape with an external rotating field, provided the rotational
frequency is larger than a critical frequency fixed by the energy and angular
momentum of the excited states of the system. By using the Gross-Pitaevskii
equation and sum rules, we explore the dependence of such a critical frequency
on the multipolarity of the excitations and the asymmetry of the confining
potential. We also discuss its possible relevance for vortex nucleation in
rotating traps.Comment: 4 pages revtex, 2 figures include
Engineering a rare-cutting restriction enzyme: genetic screening and selection of NotI variants
Restriction endonucleases (REases) with 8-base specificity are rare specimens in nature. NotI from Nocardia otitidis-caviarum (recognition sequence 5′-GCGGCCGC-3′) has been cloned, thus allowing for mutagenesis and screening for enzymes with altered 8-base recognition and cleavage activity. Variants possessing altered specificity have been isolated by the application of two genetic methods. In step 1, variant E156K was isolated by its ability to induce DNA-damage in an indicator strain expressing M.EagI (to protect 5′-NCGGCCGN-3′ sites). In step 2, the E156K allele was mutagenized with the objective of increasing enzyme activity towards the alternative substrate site: 5′-GCTGCCGC-3′. In this procedure, clones of interest were selected by their ability to eliminate a conditionally toxic substrate vector and induce the SOS response. Thus, specific DNA cleavage was linked to cell survival. The secondary substitutions M91V, F157C and V348M were each found to have a positive effect on specific activity when paired with E156K. For example, variant M91V/E156K cleaves 5′-GCTGCCGC-3′ with a specific activity of 8.2 × 10(4) U/mg, a 32-fold increase over variant E156K. A comprehensive analysis indicates that the cleavage specificity of M91V/E156K is relaxed to a small set of 8 bp substrates while retaining activity towards the NotI sequence
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