3,425 research outputs found
Benchmarking Fast-to-Alfven Mode Conversion in a Cold MHD Plasma
Alfv\'en waves may be generated via mode conversion from fast
magneto-acoustic waves near their reflection level in the solar atmosphere,
with implications both for coronal oscillations and for active region
helio-seismology. In active regions this reflection typically occurs high
enough that the Alfv\'en speed greatly exceeds the sound speed , well
above the level where the fast and slow modes interact. In order to focus
on the fundamental characteristics of fast/Alfv\'en conversion, stripped of
unnecessary detail, it is therefore useful to freeze out the slow mode by
adopting the gravitationally stratified cold MHD model . This provides a
benchmark for fast-to-Alfv\'en mode conversion in more complex atmospheres.
Assuming a uniform inclined magnetic field and an exponential Alfv\'en speed
profile with density scale height , the Alfv\'en conversion coefficient
depends on three variables only; the dimensionless
transverse-to-the-stratification wavenumber , the magnetic field
inclination from the stratification direction , and the polarization
angle of the wavevector relative to the plane containing the
stratification and magnetic field directions. We present an extensive
exploration of mode conversion in this parameter space and conclude that
near-total conversion to outward-propagating Alfv\'en waves typically occurs
for small and large (--), though it is
absent entirely when is exactly zero (vertical field). For wavenumbers
of helioseismic interest, the conversion region is broad enough to encompass
the whole chromosphere.Comment: 14 pages plus supplementary tables. Astrophys J (accepted 25 May
2011). Two ancillary animations (animated gif) attache
Forest resource information system, phase 3
There are no author-identified significant results in this report
Global-Scale Genetic Identification of Hammerhead Sharks: Application to Assessment of the International Fin Trade and Law Enforcement
The future status of sharks is an issue of widespread conservation concern due to declines in many species in the face of high levels of exploitation to satisfy market demands for products, especially fins. Substantial declines in the large-bodied hammerhead sharks, Sphyrna lewini, S. mokarran and S. zygaena, even in regions where some management occurs, indicate that informed conservation measures are warranted for these circumglobally distributed species. Despite the importance of assessing shark catch and trade on a species-specific basis to detect potential overexploitation of individual species, achieving this goal for hammerheads has proven elusive due to difficulties in identification of their products. Here, we present the development and application of a diagnostic, streamlined, five-primer multiplex polymerase chain reaction assay utilizing species-specific primers based on nuclear ribosomal ITS2 for the three hammerhead species throughout their global distribution. Application of this assay to investigations of the fin market confirmed the presence of hammerhead fins in the international trade. A study of the world’s largest fin market in Hong Kong revealed a high concordance between specific Chinese-name trade categories and fins from these three species (‘‘Bai Chun’’ with S. lewini, ‘‘Gui Chun’’ with S. zygaena and ‘‘Gu Pian’’ with S. mokarran), and clear species preferences. This concordance information allows the use of market records for monitoring species-specific trends in trade and exploitation rates. The assay is also proving useful for identification of shark body parts in U.S. fisheries law-enforcement activities. Screening of morphologically identified ‘‘S. lewini’’ from globally distributed areas using this assay with subsequent whole ITS2 sequencing suggests a cryptic species closely related to S. lewini occurs off the SE USA coast
Cavitation-induced force transition in confined viscous liquids under traction
We perform traction experiments on simple liquids highly confined between
parallel plates. At small separation rates, we observe a simple response
corresponding to a convergent Poiseuille flow. Dramatic changes in the force
response occur at high separation rates, with the appearance of a force plateau
followed by an abrupt drop. By direct observation in the course of the
experiment, we show that cavitation accounts for these features which are
reminiscent of the utmost complex behavior of adhesive films under traction.
Surprisingly enough, this is observed here in purely viscous fluids.Comment: Submitted to Physical Review Letters on May 31, 2002. Related
informations on http://www.crpp.u-bordeaux.fr/tack.htm
Identification of Species Composition in the Hong Kong Shark Fin Trade using Genetic Techniques and Trader Records
Trade in shark fins represents one of the most serious threats to shark populations worldwide. Previous studies have indicated that certain types of fins are more valued than others, but due to the largely unregulated and often covert nature of the trade, information on actual species composition has been anecdotal and unverified. In order to examine the potential impacts of the shark fin trade on the abundance of various shark species, a study of the species composition in the world’s largest shark fin trading center, Hong Kong, was initiated. Several approaches for distinguishing the species identity of dried fins were evaluated including visual differentiation (shape, color and morphometrics), denticle recognition, and DNA-based methods. This assessment found that genetic analyses were necessary to reliably determine species identity, and a technique involving application of polymerase chain reactions (PCR) with species-specific primers was selected. A sampling program was developed based on the requirements of the PCR technique, the practicalities of accessing samples, and the ability to draw statistically robust conclusions. Shark fins from twelve market categories were sampled and analyzed across a broad range of traders to investigate the concordance between trader names for fins and the associated species identity. Preliminary results indicating an initial matching of trade names and species identities will be presented. These data will subsequently be used in combination with daily shark fin auction records to estimate verified, speciesspecific proportions and quantities of shark fins in the trade
A Deployment of Spreadsheets
Many steganographers would agree that, had it not been for the appropriate unification of the partition table and cache coherence, the unproven unification of IPv7 and architecture might never have occurred. In fact, few researchers would disagree with the evaluation of evolutionary programming. Our focus here is not on whether the much-touted replicated algorithm for the deployment of forward-error correction by Gupta and White runs in Ω(n) time, but rather on presenting a semantic tool for deploying operating systems (Taw)
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Photoactivatable genetically encoded calcium indicators for targeted neuronal imaging.
Circuit mapping requires knowledge of both structural and functional connectivity between cells. Although optical tools have been made to assess either the morphology and projections of neurons or their activity and functional connections, few probes integrate this information. We have generated a family of photoactivatable genetically encoded Ca(2+) indicators that combines attributes of high-contrast photolabeling with high-sensitivity Ca(2+) detection in a single-color protein sensor. We demonstrated in cultured neurons and in fruit fly and zebrafish larvae how single cells could be selected out of dense populations for visualization of morphology and high signal-to-noise measurements of activity, synaptic transmission and connectivity. Our design strategy is transferrable to other sensors based on circularly permutated GFP (cpGFP)
Benchmarking Fast-to-Alfv\'en Mode Conversion in a Cold MHD Plasma. II. How to get Alfv\'en waves through the Solar Transition Region
Alfv\'en waves may be difficult to excite at the photosphere due to low
ionization fraction and suffer near-total reflection at the transition region
(TR). Yet they are ubiquitous in the corona and heliosphere. To overcome these
difficulties, we show that they may instead be generated high in the
chromosphere by conversion from reflecting fast magnetohydrodynamic waves, and
that Alfv\'enic transition region reflection is greatly reduced if the fast
reflection point is within a few scale heights of the TR. The influence of mode
conversion on the phase of the reflected fast wave is also explored. This phase
can potentially be misinterpreted as a travel speed perturbation, with
implications for the practical seismic probing of active regions.Comment: 13 pages, 10 figures, accepted by ApJ 17 March 201
Hadronic Parity Violation: a New View through the Looking Glass
Studies of the strangeness changing hadronic weak interaction have produced a
number of puzzles that have so far evaded a complete explanation within the
Standard Model. Their origin may lie either in dynamics peculiar to weak
interactions involving strange quarks or in more general aspects of the
interplay between strong and weak interactions. In principle, studies of the
strangeness conserving hadronic weak interaction using parity violating
hadronic and nuclear observables provide a complementary window on this
question. However, progress in this direction has been hampered by the lack of
a suitable theoretical framework for interpreting hadronic parity violation
measurements in a model-independent way. Recent work involving effective field
theory ideas has led to the formulation of such a framework while motivating
the development of a number of new hadronic parity violation experiments in
few-body systems. In this article, we review these recent developments and
discuss the prospects and opportunities for further experimental and
theoretical progress.Comment: Manuscript submitted to Annual Reviews of Nuclear and Particle
Scienc
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