21,917 research outputs found
Generalized Background-Field Method
The graphical method discussed previously can be used to create new gauges
not reachable by the path-integral formalism. By this means a new gauge is
designed for more efficient two-loop QCD calculations. It is related to but
simpler than the ordinary background-field gauge, in that even the triple-gluon
vertices for internal lines contain only four terms, not the usual six. This
reduction simplifies the calculation inspite of the necessity to include other
vertices for compensation. Like the ordinary background-field gauge, this
generalized background-field gauge also preserves gauge invariance of the
external particles. As a check of the result and an illustration for the
reduction in labour, an explicit calculation of the two-loop QCD
-function is carried out in this new gauge. It results in a saving of
45% of computation compared to the ordinary background-field gauge.Comment: 17 pages, Latex, 18 figures in Postscrip
Direct measurement of penetration length in ultra-thin and/or mesoscopic superconducting structures
We describe a method for direct measurement of the magnetic penetration
length in thin (10 - 100 nm) superconducting structures having overall
dimensions in the range 1 to 100 micrometers. The method is applicable for
broadband magnetic fields from dc to MHz frequencies.Comment: Accepted by Journal of Applied P:hysics (Jun 2006).5 pages, 5 figure
Using Ontology Fingerprints to evaluate genome-wide association study results
We describe an approach to characterize genes or phenotypes via ontology fingerprints which are composed of Gene Ontology (GO) terms overrepresented among those PubMed abstracts linked to the genes or phenotypes. We then quantify the biological relevance between genes and phenotypes by comparing their ontology fingerprints to calculate a similarity score. We validated this approach by correctly identifying genes belong to their biological pathways with high accuracy, and applied this approach to evaluate GWA study by ranking genes associated with the lipid concentrations in plasma as well as to prioritize genes within linkage disequilibrium (LD) block. We found that the genes with highest scores were: ABCA1, LPL, and CETP for HDL; LDLR, APOE and APOB for LDL; and LPL, APOA1 and APOB for triglyceride. In addition, we identified some top ranked genes linking to lipid metabolism from the literature even in cases where such knowledge was not reflected in current annotation of these genes. These results demonstrate that ontology fingerprints can be used effectively to prioritize genes from GWA studies for experimental validation
Small-Recoil Approximation
In this review we discuss a technique to compute and to sum a class of
Feynman diagrams, and some of its applications. These are diagrams containing
one or more energetic particles that suffer very little recoil in their
interactions. When recoil is completely neglected, a decomposition formula can
be proven. This formula is a generalization of the well-known eikonal formula,
to non-abelian interactions. It expresses the amplitude as a sum of products of
irreducible amplitudes, with each irreducible amplitude being the amplitude to
emit one, or several mutually interacting, quasi-particles. For abelian
interaction a quasi-particle is nothing but the original boson, so this
decomposition formula reduces to the eikonal formula. In non-abelian situations
each quasi-particle can be made up of many bosons, though always with a total
quantum number identical to that of a single boson. This decomposition enables
certain amplitudes of all orders to be summed up into an exponential form, and
it allows subleading contributions of a certain kind, which is difficult to
reach in the usual way, to be computed. For bosonic emissions from a heavy
source with many constituents, a quasi-particle amplitude turns out to be an
amplitude in which all bosons are emitted from the same constituent. For
high-energy parton-parton scattering in the near-forward direction, the
quasi-particle turns out to be the Reggeon, and this formalism shows clearly
why gluons reggeize but photons do not. The ablility to compute subleading
terms in this formalism allows the BFKL-Pomeron amplitude to be extrapolated to
asymptotic energies, in a unitary way preserving the Froissart bound. We also
consider recoil corrections for abelian interactions in order to accommodate
the Landau-Pomeranchuk-Migdal effect.Comment: 21 pages with 4 figure
Genome-Wide Transposon Screen of a Pseudomonas syringae mexB Mutant Reveals the Substrates of Efflux Transporters.
Bacteria express numerous efflux transporters that confer resistance to diverse toxicants present in their environment. Due to a high level of functional redundancy of these transporters, it is difficult to identify those that are of most importance in conferring resistance to specific compounds. The resistance-nodulation-division (RND) protein family is one such example of redundant transporters that are widespread among Gram-negative bacteria. Within this family, the MexAB-OprM protein complex is highly expressed and conserved among Pseudomonas species. We exposed barcoded transposon mutant libraries in isogenic wild-type and ΔmexB backgrounds in P. syringae B728a to diverse toxic compounds in vitro to identify mutants with increased susceptibility to these compounds. Mutants with mutations in genes encoding both known and novel redundant transporters but with partially overlapping substrate specificities were observed in a ΔmexB background. Psyr_0228, an uncharacterized member of the major facilitator superfamily of transporters, preferentially contributes to tolerance of acridine orange and acriflavine. Another transporter located in the inner membrane, Psyr_0541, contributes to tolerance of acriflavine and berberine. The presence of multiple redundant, genomically encoded efflux transporters appears to enable bacterial strains to tolerate a diversity of environmental toxins. This genome-wide screen performed in a hypersusceptible mutant strain revealed numerous transporters that would otherwise be dispensable under these conditions. Bacterial strains such as P. syringae that likely encounter diverse toxins in their environment, such as in association with many different plant species, probably benefit from possessing multiple redundant transporters that enable versatility with respect to toleration of novel toxicants.IMPORTANCE Bacteria use protein pumps to remove toxic compounds from the cell interior, enabling survival in diverse environments. These protein pumps can be highly redundant, making their targeted examination difficult. In this study, we exposed mutant populations of Pseudomonas syringae to diverse toxicants to identify pumps that contributed to survival in those conditions. In parallel, we examined pump redundancy by testing mutants of a population lacking the primary efflux transporter responsible for toxin tolerance. We identified partial substrate overlap for redundant transporters, as well as several pumps that appeared more substrate specific. For bacteria that are found in diverse environments, having multiple, partially redundant efflux pumps likely allows flexibility in habitat colonization
Multiple Reggeon Exchange from Summing QCD Feynman Diagrams
Multiple reggeon exchange supplies subleading logs that may be used to
restore unitarity to the Low-Nussinov Pomeron, provided it can be proven that
the sum of Feynman diagrams to all orders gives rise to such multiple regge
exchanges. This question cannot be easily tackled in the usual way except for
very low-order diagrams, on account of delicate cancellations present in the
sum which necessitate individual Feynman diagrams to be computed to subleading
orders. Moreover, it is not clear that sums of high-order Feynman diagrams with
complicated criss-crossing of lines can lead to factorization implied by the
multi-regge scenario. Both of these difficulties can be overcome by using the
recently developed nonabelian cut diagrams. We are then able to show that the
sum of -channel-ladder diagrams to all orders does lead to such multiple
reggeon exchanges.Comment: uu-encoded latex file with 11 postscript figures (20 pages
Sustainable Growth and Ethics: a Study of Business Ethics in Vietnam Between Business Students and Working Adults
Sustainable growth is not only the ultimate goal of business corporations but also the primary target of local governments as well as regional and global economies. One of the cornerstones of sustainable growth is ethics. An ethical organizational culture provides support to achieve sustainable growth. Ethical leaders and employees have great potential for positive influence on decisions and behaviors that lead to sustainability. Ethical behavior, therefore, is expected of everyone in the modern workplace. As a result, companies devote many resources and training programs to make sure their employees live according to the high ethical standards. This study provides an analysis of Vietnamese business students’ level of ethical maturity based on gender, education, work experience, and ethics training. The results of data from 260 business students compared with 704 working adults in Vietnam demonstrate that students have a significantly higher level of ethical maturity. Furthermore, gender and work experience are significant factors in ethical maturity. While more educated respondents and those who had completed an ethics course did have a higher level of ethical maturity, the results were not statistically significant. Analysis of the results along with suggestions and implications are provided
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