566 research outputs found
Surface characterization and surface electronic structure of organic quasi-one-dimensional charge transfer salts
We have thoroughly characterized the surfaces of the organic charge-transfer
salts TTF-TCNQ and (TMTSF)2PF6 which are generally acknowledged as prototypical
examples of one-dimensional conductors. In particular x-ray induced
photoemission spectroscopy turns out to be a valuable non-destructive
diagnostic tool. We show that the observation of generic one-dimensional
signatures in photoemission spectra of the valence band close to the Fermi
level can be strongly affected by surface effects. Especially, great care must
be exercised taking evidence for an unusual one-dimensional many-body state
exclusively from the observation of a pseudogap.Comment: 11 pages, 12 figures, v2: minor changes in text and figure labellin
String theory duals of Lifshitz-Chern-Simons gauge theories
We propose candidate gravity duals for a class of non-Abelian z=2 Lifshitz
Chern-Simons (LCS) gauge theories studied by Mulligan, Kachru and Nayak. These
are nonrelativistic gauge theories in 2+1 dimensions in which parity and
time-reversal symmetries are explicitly broken by the presence of a
Chern-Simons term. We show that these field theories can be realized as
deformations of DLCQ N=4 super Yang-Mills theory. Using the holographic
dictionary, we identify the bulk fields that are dual to these deformations.
The geometries describing the groundstates of the non-Abelian LCS gauge
theories realized here exhibit a mass gap.Comment: 25+14 pages, 3 figures; v2: significant corrections regarding IR
geometry, resulting in new section 5; journal versio
Large-density field theory, viscosity, and "" singularities from string duals
We analyze systems where an effective large-N expansion arises naturally in
gauge theories without a large number of colors: a sufficiently large charge
density alone can produce a perturbative string ('tHooft) expansion. One
example is simply the well-known NS5/F1 system dual to , here viewed as a 5+1 dimensional theory at finite density. This model is
completely stable, and we find that the existing string-theoretic solution of
this model yields two interesting results. First, it indicates that the shear
viscosity is not corrected by effects in this system. For flow
perpendicular to the F1 strings the viscosity to entropy ratio take the usual
value , but for flow parallel to the F1's it vanishes as at low
temperature. Secondly, it encodes singularities in correlation functions coming
from low-frequency modes at a finite value of the momentum along the
directions. This may provide a strong coupling analogue of finite density
condensed matter systems for which fermionic constituents of larger operators
contribute so-called "" singularities. In the NS5/F1 example, stretched
strings on the gravity side play the role of these composite operators. We
explore the analogue for our system of the Luttinger relation between charge
density and the volume bounded by these singular surfaces. This model provides
a clean example where the string-theoretic UV completion of the gravity dual to
a finite density field theory plays a significant and calculable role.Comment: 28 pages. v2: added reference
Cube law, condition factor and weight-length relationships: history, meta-analysis and recommendations
This study presents a historical review, a meta-analysis, and recommendations for users about weight–length relationships, condition factors and relative weight equations. The historical review traces the developments of the respective concepts. The meta-analysis explores 3929 weight–length relationships of the type W = aLb for 1773 species of fishes. It shows that 82% of the variance in a plot of log a over b can be explained by allometric versus isometric growth patterns and by different body shapes of the respective species. Across species median b = 3.03 is significantly larger than 3.0, thus indicating a tendency towards slightly positive-allometric growth (increase in relative body thickness or plumpness) in most fishes. The expected range of 2.5 < b < 3.5 is confirmed. Mean estimates of b outside this range are often based on only one or two weight–length relationships per species. However, true cases of strong allometric growth do exist and three examples are given. Within species, a plot of log a vs b can be used to detect outliers in weight–length relationships. An equation to calculate mean condition factors from weight–length relationships is given as Kmean = 100aLb−3. Relative weight Wrm = 100W/(amLbm) can be used for comparing the condition of individuals across populations, where am is the geometric mean of a and bm is the mean of b across all available weight–length relationships for a given species. Twelve recommendations for proper use and presentation of weight–length relationships, condition factors and relative weight are given
Moduli Spaces of Cold Holographic Matter
We use holography to study (3+1)-dimensional N=4 supersymmetric Yang-Mills
theory with gauge group SU(Nc), in the large-Nc and large-coupling limits,
coupled to a single massless (n+1)-dimensional hypermultiplet in the
fundamental representation of SU(Nc), with n=3,2,1. In particular, we study
zero-temperature states with a nonzero baryon number charge density, which we
call holographic matter. We demonstrate that a moduli space of such states
exists in these theories, specifically a Higgs branch parameterized by the
expectation values of scalar operators bilinear in the hypermultiplet scalars.
At a generic point on the Higgs branch, the R-symmetry and gauge group are
spontaneously broken to subgroups. Our holographic calculation consists of
introducing a single probe Dp-brane into AdS5 times S^5, with p=2n+1=7,5,3,
introducing an electric flux of the Dp-brane worldvolume U(1) gauge field, and
then obtaining explicit solutions for the worldvolume fields dual to the scalar
operators that parameterize the Higgs branch. In all three cases, we can
express these solutions as non-singular self-dual U(1) instantons in a
four-dimensional space with a metric determined by the electric flux. We
speculate on the possibility that the existence of Higgs branches may point the
way to a counting of the microstates producing a nonzero entropy in holographic
matter. Additionally, we speculate on the possible classification of
zero-temperature, nonzero-density states described holographically by probe
D-branes with worldvolume electric flux.Comment: 56 pages, 8 PDF images, 4 figure
Entanglement Entropy from a Holographic Viewpoint
The entanglement entropy has been historically studied by many authors in
order to obtain quantum mechanical interpretations of the gravitational
entropy. The discovery of AdS/CFT correspondence leads to the idea of
holographic entanglement entropy, which is a clear solution to this important
problem in gravity. In this article, we would like to give a quick survey of
recent progresses on the holographic entanglement entropy. We focus on its
gravitational aspects, so that it is comprehensible to those who are familiar
with general relativity and basics of quantum field theory.Comment: Latex, 30 pages, invited review for Classical and Quantum Gravity,
minor correction
COMPUTER-CONTROLLED GAS CHROMATOGRAPH CAPABLE OF ''REAL-TIME'' READOUT OF HIGH-PRECISION DATA.
A gas chromatograph has been assembled which provides computer control of sample injection, column temperature, and flow rate, plus direct computer readout of inlet pressure, mass flow rate, and detector response. Data processing yields, in real-time, a standard deviation of less than 0.05% in retention time, which is comparable to previous results obtained using an off-line computer. However, corrected retention volumes determined in real-time had a standard deviation of about 0.4% which reflected primarily the uncertainty in flow measurement
Enhanced multiplex genome engineering through co-operative oligonucleotide co-selection
Genome-scale engineering of living organisms requires precise and economical methods to efficiently modify many loci within chromosomes. One such example is the directed integration of chemically synthesized single-stranded deoxyribonucleic acid (oligonucleotides) into the chromosome of Escherichia coli during replication. Herein, we present a general co-selection strategy in multiplex genome engineering that yields highly modified cells. We demonstrate that disparate sites throughout the genome can be easily modified simultaneously by leveraging selectable markers within 500 kb of the target sites. We apply this technique to the modification of 80 sites in the E. coli genome.United States. Dept. of Energy. Genomes To Life (DE-FG02-03ER6344)National Science Foundation (U.S.). Genes and Genomes Systems Cluster (0719344)National Science Foundation (U.S.). Center for Bits and Atoms (0122419)National Science Foundation (U.S.). Synthetic Biology Engineering Research Center (0540879
Modified bases enable high-efficiency oligonucleotide-mediated allelic replacement via mismatch repair evasion
Genome engineering using single-stranded oligonucleotides is an efficient method for generating small chromosomal and episomal modifications in a variety of host organisms. The efficiency of this allelic replacement strategy is highly dependent on avoidance of the endogenous mismatch repair (MMR) machinery. However, global MMR inactivation generally results in significant accumulation of undesired background mutations. Here, we present a novel strategy using oligos containing chemically modified bases (2′-Fluoro-Uridine, 5-Methyl-deoxyCytidine, 2,6-Diaminopurine or Iso-deoxyGuanosine) in place of the standard T, C, A or G to avoid mismatch detection and repair, which we tested in Escherichia coli. This strategy increases transient allelic-replacement efficiencies by up to 20-fold, while maintaining a 100-fold lower background mutation level. We further show that the mismatched bases between the full length oligo and the chromosome are often not incorporated at the target site, probably due to nuclease activity at the 5′ and 3′ termini of the oligo. These results further elucidate the mechanism of oligo-mediated allelic replacement (OMAR) and enable improved methodologies for efficient, large-scale engineering of genomes.Synthetic Biology Engineering Research CenterNational Science Foundation (U.S.) (Grant #SA5283-11210)United States. Dept. of Energy (Genomes to Life Center) (Grant #DE-FG02-03ER6344)Wyss Institute for Biologically Inspired Engineerin
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