1,561 research outputs found
Coulomb parameters and photoemission for the molecular metal TTF-TCNQ
We employ density-functional theory to calculate realistic parameters for an
extended Hubbard model of the molecular metal TTF-TCNQ. Considering both intra-
and intermolecular screening in the crystal, we find significant longer-range
Coulomb interactions along the molecular stacks, as well as inter-stack
coupling. We show that the long-range Coulomb term of the extended Hubbard
model leads to a broadening of the spectral density, likely resolving the
problems with the interpretation of photoemission experiments using a simple
Hubbard model only.Comment: 4 pages, 2 figure
Membrane solitons in eight-dimensional hyper-Kaehler backgrounds
We derive the BPS equations satisfied by lump solitons in -dimensional
sigma models with toric 8-dimensional hyper-K\"ahler () target spaces
and check they preserve 1/2 of the supersymmetry. We show how these solitons
are realised in M theory as M2-branes wrapping holomorphic 2-cycles in the
\bE^{1,2}\times {HK}_8 background. Using the -symmetry of a probe
M2-brane in this background we determine the supersymmetry they preserve, and
note that there is a discrepancy in the fraction of supersymmetry preserved by
these solitons as viewed from the low energy effective sigma model description
of the M2-brane dynamics or the full M theory. Toric manifolds are
dual to a Hanany-Witten setup of D3-branes suspended between 5-branes. In this
picture the lumps correspond to vortices of the three dimensional or theory.Comment: 12+1 pages. LaTex. v2: Typos corrected and references adde
Theory for transport through a single magnetic molecule: Endohedral N@C60
We consider transport through a single N@C60 molecule, weakly coupled to
metallic leads. Employing a density-matrix formalism we derive rate equations
for the occupation probabilities of many-particle states of the molecule. We
calculate the current-voltage characteristics and the differential conductance
for N@C60 in a break junction. Our results reveal Coulomb-blockade behavior as
well as a fine structure of the Coulomb-blockade peaks due to the exchange
coupling of the C60 spin to the spin of the encapsulated nitrogen atom.Comment: 5 pages, 4 figures, v2: version as publishe
Using Fill Terraces to Understand Incision Rates and Evolution of the Colorado River in Eastern Grand Canyon, Arizona
The incision and aggradation of the Colorado River in eastern Grand Canyon through middle to late Quaternary time can be traced in detail using well-exposed fill terraces dated by a combination of optically stimulated luminescence, uranium series, and cosmogenic nuclide dating. This fluvial history provides the best bedrock incision rate for this important landscape and highlights the complications and advantages of fill terrace records for understanding river long-profile evolution and incision. The use of fill terraces, as distinct from strath terraces, for calculating incision rates is complicated by the cyclic alluviation and incision they record. In the example of the Grand Canyon this has led to various rates being reported by different workers and rates that tend to be overestimates in shorter records. We illustrate that a meaningful long-term bedrock incision rate of 140 m/m.y. can be extracted from the Grand Canyon record by linking episodes when the Colorado River is floored on bedrock. Variable incision rates reported in the greater region may be, to some degree, due to inconsistent calculations. Our data also highlight that the Colorado River has been a mixed alluvial-bedrock river through both time and space and has been a bedrock river for less than half of its Pleistocene history. This strong temporal variation, combined with the varying bedrock the river encounters on its path, heightens the challenge of understanding the tectonic, climatic, and drainage integration controls on the form and evolution of the Colorado Riverâs long profile
Discovering and verifying DNA polymorphisms in a mung bean [V. radiata (L.) R. Wilczek] collection by EcoTILLING and sequencing
<p>Abstract</p> <p>Background</p> <p><it>Vigna radiata</it>, which is classified in the family Fabaceae, is an important economic crop and a dietary staple in many developing countries. The species <it>radiata </it>can be further subdivided into varieties of which the variety <it>sublobata </it>is currently acknowledged as the putative progenitor of <it>radiata</it>. EcoTILLING was employed to identify single nucleotide polymorphisms (SNPs) and small insertions/deletions (INDELS) in a collection of <it>Vigna radiata </it>accessions.</p> <p>Findings</p> <p>A total of 157 DNA polymorphisms in the collection were produced from ten primer sets when using <it>V. radiata </it>var. <it>sublobata </it>as the reference. The majority of polymorphisms detected were found in putative introns. The banding patterns varied from simple to complex as the number of DNA polymorphisms between two pooled samples increased. Numerous SNPs and INDELS ranging from 4â24 and 1â6, respectively, were detected in all fragments when pooling <it>V. radiata </it>var. <it>sublobata </it>with <it>V. radiata </it>var. <it>radiata</it>. On the other hand, when accessions of <it>V. radiata </it>var. <it>radiata </it>were mixed together and digested with CEL I relatively few SNPs and no INDELS were detected.</p> <p>Conclusion</p> <p>EcoTILLING was utilized to identify polymorphisms in a collection of mung bean, which previously showed limited molecular genetic diversity and limited morphological diversity in the flowers and pod descriptors. Overall, EcoTILLING proved to be a powerful genetic analysis tool providing the rapid identification of naturally occurring variation.</p
Describing interruptions, multi-tasking and task-switching in the community pharmacy: A qualitative study in England
Background: There is growing evidence base around interruptions and distractions in the community pharmacy setting. There is also evidence to suggest these practices may be associated with dispensing errors. Up to date, qualitative research on this subject is limited.
Objective: To explore interruptions and distractions in the community setting; utilising an ethnographic approach to be able to provide a detailed description of the circumstances surrounding such practices.
Setting: Community pharmacies in England, July to October 2011.
Method: An ethnographic approach was taken. Non participant, unstructured observations were utilised to make records of pharmacistsâ every activities. Case studies were formed by combining field notes with detailed information on pharmacists and their respective pharmacy businesses. Content analysis was undertaken both manually and electronically, utilising NVivo 10.
Results: Response rate was 12% (n=11). Over fifteen days, a total of 123 hours and 58 minutes of observations were recorded in 11 separate pharmacies of 11 individual pharmacists. The sample was evenly split by gender (female n=6; male n=5) and pharmacy ownership (independent n=5; multiple n=6). Employment statuses included employee pharmacists (n=6), owners (n=4) and a locum (n=1). Average period of registration as a pharmacist was 19 years (range 5-39 years). Average prescriptions busyness of pharmacies ranged from 2,600 â 24,000 items dispensed per month. Two key themes were: âInterruptions and task-switchingâ and âdistractions and multi-tasking.â All observed pharmacistsâ work was dominated by interruptions, task-switches, distractions and multi-tasking, often to manage a barrage of conflicting demands. These practices were observed to be part of a deep-rooted culture in the community setting. Directional work maps illustrated the extent and direction of task switching employed by pharmacists.
Conclusions: In this study pharmacistsâ working practices were permeated by interruptions and multi-tasking. These practices are inefficient and potentially reduce patient safety in terms of dispensing accuracy
Rapid, diffusional shuttling of poly(A) RNA between nuclear speckles and the nucleoplasm
Speckles are nuclear bodies that contain pre-mRNA splicing factors and polyadenylated RNA. Because nuclear poly(A) RNA consists of both mRNA transcripts and nucleus-restricted RNAs, we tested whether poly(A) RNA in speckles is dynamic or rather an immobile, perhaps structural, component. Fluorescein-labeled oligo(dT) was introduced into HeLa cells stably expressing a red fluorescent protein chimera of the splicing factor SC35 and allowed to hybridize. Fluorescence correlation spectroscopy (FCS) showed that the mobility of the tagged poly(A) RNA was virtually identical in both speckles and at random nucleoplasmic sites. This same result was observed in photoactivation-tracking studies in which caged fluorescein-labeled oligo(dT) was used as hybridization probe, and the rate of movement away from either a speckle or nucleoplasmic site was monitored using digital imaging microscopy after photoactivation. Furthermore, the tagged poly(A) RNA was observed to rapidly distribute throughout the entire nucleoplasm and other speckles, regardless of whether the tracking observations were initiated in a speckle or the nucleoplasm. Finally, in both FCS and photoactivation-tracking studies, a temperature reduction from 37 to 22°C had no discernible effect on the behavior of poly(A) RNA in either speckles or the nucleoplasm, strongly suggesting that its movement in and out of speckles does not require metabolic energy. © 2006 by The American Society for Cell Biology
Theoretical Study of Cubic Structures Based on Fullerene Carbon Clusters: CC and (C
We study a new hypothetical form of solid carbon \csc, with a unit cell which
is composed of the \cs \ fullerene cluster and an additional single carbon atom
arranged in the zincblende structure. Using {\it ab initio} calculations, we
show that this new form of solid carbon has lower energy than hyperdiamond, the
recently proposed form composed of \cs \ units in the diamond structure. To
understand the bonding character of of these cluster-based solids, we analyze
the electronic structure of \csc \ and of hyperdiamond and compare them to the
electronic states of crystalline cubic diamond.Comment: 15 pages, latex, no figure
N=2 Supersymmetric Scalar-Tensor Couplings
We determine the general coupling of a system of scalars and antisymmetric
tensors, with at most two derivatives and undeformed gauge transformations, for
both rigid and local N=2 supersymmetry in four-dimensional spacetime. Our
results cover interactions of hyper, tensor and double-tensor multiplets and
apply among others to Calabi-Yau threefold compactifications of Type II
supergravities. As an example, we give the complete Lagrangian and
supersymmetry transformation rules of the double-tensor multiplet dual to the
universal hypermultiplet.Comment: 23 pages, LaTeX2e with amsmath.sty; v2: corrected typos and added
referenc
Electronic Structure of Transition-Metal Dicyanamides Me[N(CN)] (Me = Mn, Fe, Co, Ni, Cu)
The electronic structure of Me[N(CN)] (Me=Mn, Fe, Co, Ni, Cu)
molecular magnets has been investigated using x-ray emission spectroscopy (XES)
and x-ray photoelectron spectroscopy (XPS) as well as theoretical
density-functional-based methods. Both theory and experiments show that the top
of the valence band is dominated by Me 3d bands, while a strong hybridization
between C 2p and N 2p states determines the valence band electronic structure
away from the top. The 2p contributions from non-equivalent nitrogen sites have
been identified using resonant inelastic x-ray scattering spectroscopy with the
excitation energy tuned near the N 1s threshold. The binding energy of the Me
3d bands and the hybridization between N 2p and Me 3d states both increase in
going across the row from Me = Mn to Me = Cu. Localization of the Cu 3d states
also leads to weak screening of Cu 2p and 3s states, which accounts for shifts
in the core 2p and 3s spectra of the transition metal atoms. Calculations
indicate that the ground-state magnetic ordering, which varies across the
series is largely dependent on the occupation of the metal 3d shell and that
structural differences in the superexchange pathways for different compounds
play a secondary role.Comment: 20 pages, 11 figures, 2 table
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