54 research outputs found
Superpotentials for M-theory on a G_2 holonomy manifold and Triality symmetry
For -theory on the holonomy manifold given by the cone on {\bf
S^3}\x {\bf S^3} we consider the superpotential generated by membrane
instantons and study its transformations properties, especially under monodromy
transformations and triality symmetry. We find that the latter symmetry is,
essentially, even a symmetry of the superpotential. As in Seiberg/Witten
theory, where a flat bundle given by the periods of an universal elliptic curve
over the -plane occurs, here a flat bundle related to the Heisenberg group
appears and the relevant universal object over the moduli space is related to
hyperbolic geometry.Comment: 58 pages, latex; references adde
Deuteron distribution in nuclei and the Levinger's factor
We compute the distribution of quasideuterons in doubly closed shell nuclei.
The ground states of O and Ca are described in coupling
using a realistic hamiltonian including the Argonne and the
Urbana IX models of two-- and three--nucleon potentials, respectively. The
nuclear wave function contains central and tensor correlations, and correlated
basis functions theory is used to evaluate the distribution of neutron-proton
pairs, having the deuteron quantum numbers, as a function of their total
momentum. By computing the number of deuteron--like pairs we are able to
extract the Levinger's factor and compare to both the available experimental
data and the predictions of the local density approximation, based on nuclear
matter estimates. The agreement with the experiments is excellent, whereas the
local density approximation is shown to sizably overestimate the Levinger's
factor in the region of the medium nuclei.Comment: 26 pages, 8 figures, typeset using REVTe
Heavy quarkonium: progress, puzzles, and opportunities
A golden age for heavy quarkonium physics dawned a decade ago, initiated by
the confluence of exciting advances in quantum chromodynamics (QCD) and an
explosion of related experimental activity. The early years of this period were
chronicled in the Quarkonium Working Group (QWG) CERN Yellow Report (YR) in
2004, which presented a comprehensive review of the status of the field at that
time and provided specific recommendations for further progress. However, the
broad spectrum of subsequent breakthroughs, surprises, and continuing puzzles
could only be partially anticipated. Since the release of the YR, the BESII
program concluded only to give birth to BESIII; the -factories and CLEO-c
flourished; quarkonium production and polarization measurements at HERA and the
Tevatron matured; and heavy-ion collisions at RHIC have opened a window on the
deconfinement regime. All these experiments leave legacies of quality,
precision, and unsolved mysteries for quarkonium physics, and therefore beg for
continuing investigations. The plethora of newly-found quarkonium-like states
unleashed a flood of theoretical investigations into new forms of matter such
as quark-gluon hybrids, mesonic molecules, and tetraquarks. Measurements of the
spectroscopy, decays, production, and in-medium behavior of c\bar{c}, b\bar{b},
and b\bar{c} bound states have been shown to validate some theoretical
approaches to QCD and highlight lack of quantitative success for others. The
intriguing details of quarkonium suppression in heavy-ion collisions that have
emerged from RHIC have elevated the importance of separating hot- and
cold-nuclear-matter effects in quark-gluon plasma studies. This review
systematically addresses all these matters and concludes by prioritizing
directions for ongoing and future efforts.Comment: 182 pages, 112 figures. Editors: N. Brambilla, S. Eidelman, B. K.
Heltsley, R. Vogt. Section Coordinators: G. T. Bodwin, E. Eichten, A. D.
Frawley, A. B. Meyer, R. E. Mitchell, V. Papadimitriou, P. Petreczky, A. A.
Petrov, P. Robbe, A. Vair
spectroscopy
In the framework of potential models for heavy quarkonium the mass spectrum
for the system () is considered. Spin-dependent splittings, taking
into account a change of a constant for effective Coulomb interaction between
the quarks, and widths of radiative transitions between the () levels
are calculated. In the framework of QCD sum rules, masses of the lightest
vector and pseudoscalar states are estimated, scaling relation
for leptonic constants of heavy quarkonia is derived, and the leptonic constant
is evaluated.Comment: IHEP 94-51, LATEX, 39 page
Large expert-curated database for benchmarking document similarity detection in biomedical literature search
Document recommendation systems for locating relevant literature have mostly relied on methods developed a decade ago. This is largely due to the lack of a large offline gold-standard benchmark of relevant documents that cover a variety of research fields such that newly developed literature search techniques can be compared, improved and translated into practice. To overcome this bottleneck, we have established the RElevant LIterature SearcH consortium consisting of more than 1500 scientists from 84 countries, who have collectively annotated the relevance of over 180 000 PubMed-listed articles with regard to their respective seed (input) article/s. The majority of annotations were contributed by highly experienced, original authors of the seed articles. The collected data cover 76% of all unique PubMed Medical Subject Headings descriptors. No systematic biases were observed across different experience levels, research fields or time spent on annotations. More importantly, annotations of the same document pairs contributed by different scientists were highly concordant. We further show that the three representative baseline methods used to generate recommended articles for evaluation (Okapi Best Matching 25, Term Frequency-Inverse Document Frequency and PubMed Related Articles) had similar overall performances. Additionally, we found that these methods each tend to produce distinct collections of recommended articles, suggesting that a hybrid method may be required to completely capture all relevant articles. The established database server located at https://relishdb.ict.griffith.edu.au is freely available for the downloading of annotation data and the blind testing of new methods. We expect that this benchmark will be useful for stimulating the development of new powerful techniques for title and title/abstract-based search engines for relevant articles in biomedical research.Peer reviewe
The nuclear collective motion
Current developments in nuclear structure are discussed from a theoretical perspective. First, the progress in theoretical modeling of nuclei is reviewed. This is followed by the discussion of nuclear time scales, nuclear collective modes, and nuclear deformations. Some perspectives on nuclear structure research far from stability are given. Finally, interdisciplinary aspects of the nuclear many-body problem are outlined
The effects of judicial campaign activity on the legitimacy of courts: A survey-based experiment
The purpose of this article is to investigate the consequences of judicial campaign activity for the perceived legitimacy of the Pennsylvania judiciary. The authors find that politicized campaign ads do detract from court support, although they find practically no difference between traditional campaign ads (e.g., presenting endorsements from groups) and strong attack ads. But this finding must be understood within the context of the 2007 Pennsylvania election increasing court support for all respondents, even those exposed to the most politicized ad content. Being exposed to politicized ads seems to retard the benefits of elections but does not eliminate them. © 2011 University of Utah.Articl
Synthesis of ferrocenyl-1,2-diketones and related compounds:Crystal and molecular structures of 1,2-diferrocenylethanedione and 1-ferrocenyl-2-(4-biphenylyl) ethanedione
Ferrocenyl-1,2-diketones FcCOCOR, 3, [Fc = (C5H5)Fe(C5H4)] can be prepared by oxidation of acylferrocenes FcCOCH2R or, more efficiently, by oxidation of the isomeric ketones FcCH2COR, 2. The ketones 2 are in turn readily synthesized from the salt (FcCH2PPh3)+I- via the acylated salts [FcCH(COR)PPh3]+I-. The haloacylferocenes FcCOCClxH3-x (x = 1, 2, 3, of which the x = 2 example is synthetically equivalent to a diketone) are synthesized by Friedel-Crafts acylation of ferrocene using CClxH3-xCOCl/AlCl3, but the reaction proceeds via two parallel pathways, one giving the normal acyl derivatives FcCOCClxH3-x and the other giving the reduced products FcCOCClx-1H4-x. Two diketones FcCOCOFc 3b and FcCOCOC6H4Ph 3c have been structurally characterised by single-crystal X-ray diffraction.</p
Synthesis of ferrocenyl-1,2-diketones and related compounds:Crystal and molecular structures of 1,2-diferrocenylethanedione and 1-ferrocenyl-2-(4-biphenylyl) ethanedione
Ferrocenyl-1,2-diketones FcCOCOR, 3, [Fc = (C5H5)Fe(C5H4)] can be prepared by oxidation of acylferrocenes FcCOCH2R or, more efficiently, by oxidation of the isomeric ketones FcCH2COR, 2. The ketones 2 are in turn readily synthesized from the salt (FcCH2PPh3)+I- via the acylated salts [FcCH(COR)PPh3]+I-. The haloacylferocenes FcCOCClxH3-x (x = 1, 2, 3, of which the x = 2 example is synthetically equivalent to a diketone) are synthesized by Friedel-Crafts acylation of ferrocene using CClxH3-xCOCl/AlCl3, but the reaction proceeds via two parallel pathways, one giving the normal acyl derivatives FcCOCClxH3-x and the other giving the reduced products FcCOCClx-1H4-x. Two diketones FcCOCOFc 3b and FcCOCOC6H4Ph 3c have been structurally characterised by single-crystal X-ray diffraction.</p
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