3,193 research outputs found
Persistent Currents in the Presence of a Transport Current
We have considered a system of a metallic ring coupled to two electron
reservoirs. We show that in the presence of a transport current, the persistent
current can flow in a ring, even in the absence of magnetic field. This is
purely a quantum effect and is related to the current magnification in the
loop. These persistent currents can be observed if one tunes the Fermi energy
near the antiresonances of the total transmission coefficient or the two port
conductance.Comment: To appear in Phys. Rev. B. Three figures available on reques
See What You Feel: A Crossmodal Tool for Measuring Haptic Size Illusions
The purpose of this research is to present the employment of a simple-to-use crossmodal method for measuring haptic size illusions. The method, that we call See what you feel, was tested by employing Uznadze’s classic haptic aftereffect in which two spheres physically identical (test spheres) appear different in size after that the hands holding them underwent an adaptation session with other two spheres (adapting spheres), one bigger and the other smaller than the two test spheres. To measure the entity of the illusion, a three-dimensional visual scale was created and participants were asked to find on it the spheres that corresponded in size to the spheres they were holding in their hands out of sight. The method, tested on 160 right-handed participants, is robust and easily understood by participants
Geographical distribution of Phagocata vivida in the Far East
Phagocata vivida (Ijima et Kaburaki, 1916) is common in cold-water habitats in mountainous and hilly regions in Japan; in Northern Japan it occurs in lowland areas. Comparative studies of the material from South Korea and Primorskiy in Northeast Siberia, Russia, show that Ph. vivida is distributed widely in these geographic areas. Phagocata miyadii Okugawa, 1939, reported from North Korea and Northeastern China is a synonym of Ph vivida. Geographical distribution of this species in the Japanese Islands now becomes very clear. Judging by its geographical and vertical distributions, the species probably is a preglacial faunal element that entered Japan by the northern route to Old Honshû Island along the coast of the Old Sea of Japan. © 1995, Kluwer Academic Publishers. All rights reserved
A deeply branching thermophilic bacterium with an ancient acetyl-CoA pathway dominates a subsurface ecosystem
<div><p>A nearly complete genome sequence of <em>Candidatus</em> ‘Acetothermum autotrophicum’, a presently uncultivated bacterium in candidate division OP1, was revealed by metagenomic analysis of a subsurface thermophilic microbial mat community. Phylogenetic analysis based on the concatenated sequences of proteins common among 367 prokaryotes suggests that <em>Ca.</em> ‘A. autotrophicum’ is one of the earliest diverging bacterial lineages. It possesses a folate-dependent Wood-Ljungdahl (acetyl-CoA) pathway of CO<sub>2</sub> fixation, is predicted to have an acetogenic lifestyle, and possesses the newly discovered archaeal-autotrophic type of bifunctional fructose 1,6-bisphosphate aldolase/phosphatase. A phylogenetic analysis of the core gene cluster of the acethyl-CoA pathway, shared by acetogens, methanogens, some sulfur- and iron-reducers and dechlorinators, supports the hypothesis that the core gene cluster of <em>Ca.</em> ‘A. autotrophicum’ is a particularly ancient bacterial pathway. The habitat, physiology and phylogenetic position of <em>Ca.</em> ‘A. autotrophicum’ support the view that the first bacterial and archaeal lineages were H<sub>2</sub>-dependent acetogens and methanogenes living in hydrothermal environments.</p> </div
Magneto-transport in periodic and quasiperiodic arrays of mesoscopic rings
We study theoretically the transmission properties of serially connected
mesoscopic rings threaded by a magnetic flux. Within a tight-binding formalism
we derive exact analytical results for the transmission through periodic and
quasiperiodic Fibonacci arrays of rings of two different sizes. The role played
by the number of scatterers in each arm of the ring is analyzed in some detail.
The behavior of the transmission coefficient at a particular value of the
energy of the incident electron is studied as a function of the magnetic flux
(and vice versa) for both the periodic and quasiperiodic arrays of rings having
different number of atoms in the arms. We find interesting resonance properties
at specific values of the flux, as well as a power-law decay in the
transmission coefficient as the number of rings increases, when the magnetic
field is switched off. For the quasiperiodic Fibonacci sequence we discuss
various features of the transmission characteristics as functions of energy and
flux, including one special case where, at a special value of the energy and in
the absence of any magnetic field, the transmittivity changes periodically as a
function of the system size.Comment: 9 pages with 7 .eps figures included, submitted to PR
Persistent currents in coupled mesoscopic rings
We have analysed the nature of persistent currents in open coupled mesoscopic
rings. Our system is comprised of two ideal loops connected to an electron
reservoir. We have obtained analytical expressions for the persistent current
densities in two rings in the presence of a magnetic field. We show that the
known even-odd parity effects in isolated single loops have to be generalised
for the case of coupled rings. We also show that when the two rings have
unequal circumferences, it is possible to observe opposite currents
(diamagnetic or paramagnetic) in the two rings for a given Fermi level.Comment: Submitted to PRB. 9 figures availabel on reques
Hard probes in heavy ion collisions at the LHC: heavy flavour physics
We present the results from the heavy quarks and quarkonia working group.
This report gives benchmark heavy quark and quarkonium cross sections for
and collisions at the LHC against which the rates can be compared in
the study of the quark-gluon plasma. We also provide an assessment of the
theoretical uncertainties in these benchmarks. We then discuss some of the cold
matter effects on quarkonia production, including nuclear absorption,
scattering by produced hadrons, and energy loss in the medium. Hot matter
effects that could reduce the observed quarkonium rates such as color screening
and thermal activation are then discussed. Possible quarkonium enhancement
through coalescence of uncorrelated heavy quarks and antiquarks is also
described. Finally, we discuss the capabilities of the LHC detectors to measure
heavy quarks and quarkonia as well as the Monte Carlo generators used in the
data analysis.Comment: 126 pages Latex; 96 figures included. Subgroup report, to appear in
the CERN Yellow Book of the workshop: Hard Probes in Heavy Ion Collisions at
the LHC. See also http://a.home.cern.ch/f/frixione/www/hvq.html for a version
with better quality for a few plot
Culture dependent and independent analyses of 16S rRNA and ATP citrate lyase genes : a comparison of microbial communities from different black smoker chimneys on the Mid-Atlantic Ridge
Author Posting. © Springer, 2008. This is the author's version of the work. It is posted here by permission of Springer for personal use, not for redistribution. The definitive version was published in Extremophiles 12 (2008): 627-640, doi:10.1007/s00792-008-0167-5.The bacterial and archaeal communities of three deep-sea hydrothermal vent systems
located on the Mid-Atlantic Ridge (MAR; Rainbow, Logatchev and Broken Spur) were
investigated using an integrated culture-dependent and independent approach.
Comparative molecular phylogenetic analyses, using the 16S rRNA gene and the deduced
amino acid sequences of the alpha and beta subunits of the ATP citrate lyase encoding
genes were carried out on natural microbial communities, on an enrichment culture
obtained from the Broken Spur chimney, and on novel chemolithoautotrophic bacteria
and reference strains originally isolated from several different deep-sea vents. Our data
showed that the three MAR hydrothermal vent chimneys investigated in this study host
very different microbial assemblages. The microbial community of the Rainbow chimney
was dominated by thermophilic, autotrophic, hydrogen-oxidizing, sulfur- and nitrate
reducing Epsilonproteobacteria related to the genus Caminibacter. The detection of
sequences related to sulfur-reducing bacteria and archaea (Archaeoglobus) indicated that
thermophilic sulfate reduction might also be occurring at this site. The Logatchev
bacterial community included several sequences related to mesophilic sulfur-oxidizing
bacteria, while the archaeal component of this chimney was dominated by sequences
related to the ANME-2 lineage, suggesting that anaerobic oxidation of methane may be
occurring at this site. Comparative analyses of the ATP citrate lyase encoding genes from
natural microbial communities suggested that Epsilonproteobacteria were the dominant
primary producers using the reverse TCA cycle (rTCA) at Rainbow, while Aquificales of
the genera Desulfurobacterium and Persephonella were prevalent in the Broken Spur
chimney.This research was supported by NSF grants MCB 04-56676 (C.V.), OCE 03-27353 (C.V.), MCB 04-56689 (S.M.S.), a grant from the New Jersey Agricultural Experiment Station to C.V., and a NIH Ph.D. Training
Program in Biotechnology Fellowship (NIH NIGMS 5 T32 GM08339) to J.V. M.H. was
supported through a postdoctoral scholarship from the Woods Hole Oceanographic
Institution
Origin of anomalously long interatomic distances in suspended gold chains
The discovery of long bonds in gold atom chains has represented a challenge
for physical interpretation. In fact, interatomic distances frequently attain
3.0-3.6 A values and, distances as large as 5.0 A may be seldom observed. Here,
we studied gold chains by transmission electron microscopy and performed
theoretical calculations using cluster ab initio density functional formalism.
We show that the insertion of two carbon atoms is required to account for the
longest bonds, while distances above 3 A may be due to a mixture of clean and
one C atom contaminated bonds.Comment: 4 pages, 4 Postscript figures, to be published in Physical Review
Letter
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