12,356 research outputs found
Sheaves on Toric Varieties for Physics
In this paper we give an inherently toric description of a special class of
sheaves (known as equivariant sheaves) over toric varieties, due in part to A.
A. Klyachko. We apply this technology to heterotic compactifications, in
particular to the (0,2) models of Distler, Kachru, and also discuss how
knowledge of equivariant sheaves can be used to reconstruct information about
an entire moduli space of sheaves. Many results relevant to heterotic
compactifications previously known only to mathematicians are collected here --
for example, results concerning whether the restriction of a stable sheaf to a
Calabi-Yau hypersurface remains stable are stated. We also describe
substructure in the Kahler cone, in which moduli spaces of sheaves are
independent of Kahler class only within any one subcone. We study F theory
compactifications in light of this fact, and also discuss how it can be seen in
the context of equivariant sheaves on toric varieties. Finally we briefly
speculate on the application of these results to (0,2) mirror symmetry.Comment: 83 pages, LaTeX, 4 figures, must run LaTeX 3 times, numerous minor
cosmetic upgrade
Physical Results from Unphysical Simulations
We calculate various properties of pseudoscalar mesons in partially quenched
QCD using chiral perturbation theory through next-to-leading order. Our results
can be used to extrapolate to QCD from partially quenched simulations, as long
as the latter use three light dynamical quarks. In other words, one can use
unphysical simulations to extract physical quantities - in this case the quark
masses, meson decay constants, and the Gasser-Leutwyler parameters L_4-L_8. Our
proposal for determining L_7 makes explicit use of an unphysical (yet
measurable) effect of partially quenched theories, namely the double-pole that
appears in certain two-point correlation functions. Most of our calculations
are done for sea quarks having up to three different masses, except for our
result for L_7, which is derived for degenerate sea quarks.Comment: 26 pages, 12 figures (discussion on discretization errors at end of
sec. IV clarified; minor improvements in presentation; results unchanged
Why human color vision cannot reliably detect cerebrospinal fluid xanthochromia
Background - Visual assessment of cerebrospinal fluid (CSF) for xanthochromia ( yellow color) is practiced by the majority of laboratories worldwide as a means of diagnosing intracranical bleeds.Methods - Colorimetric and spectrophotometric analysis of CSF samples for recognizing the presence of bilirubin either in low concentrations or in the presence of hemolysed blood.Results - The experiments provide the physiological and colorimetric basis for abandoning visual assessment of CSF for xanthochromia.Conclusion - We strongly recommend relying on spectrophotometry as the analytical method of choice
Staggered fermion matrix elements using smeared operators
We investigate the use of two kinds of staggered fermion operators, smeared
and unsmeared. The smeared operators extend over a hypercube, and tend to
have smaller perturbative corrections than the corresponding unsmeared
operators. We use these operators to calculate kaon weak matrix elements on
quenched ensembles at , 6.2 and 6.4. Extrapolating to the continuum
limit, we find . The
systematic error is dominated by the uncertainty in the matching between
lattice and continuum operators due to the truncation of perturbation theory at
one-loop. We do not include any estimate of the errors due to quenching or to
the use of degenerate and quarks. For the
electromagnetic penguin operators we find
and . We also use the ratio of unsmeared to
smeared operators to make a partially non-perturbative estimate of the
renormalization of the quark mass for staggered fermions. We find that tadpole
improved perturbation theory works well if the coupling is chosen to be
\alpha_\MSbar(q^*=1/a).Comment: 22 pages, 1 figure, uses eps
D-branes, B fields, and Ext groups
In this paper we extend previous work on calculating massless boundary Ramond
sector spectra of open strings to include cases with nonzero flat B fields. In
such cases, D-branes are no longer well-modelled precisely by sheaves, but
rather they are replaced by `twisted' sheaves, reflecting the fact that gauge
transformations of the B field act as affine translations of the Chan-Paton
factors. As in previous work, we find that the massless boundary Ramond sector
states are counted by Ext groups -- this time, Ext groups of twisted sheaves.
As before, the computation of BRST cohomology relies on physically realizing
some spectral sequences. Subtleties that cropped up in previous work also
appear here.Comment: 23 pages, LaTeX; v2: typos fixed; v3: reference adde
GLSM realizations of maps and intersections of Grassmannians and Pfaffians
In this paper we give gauged linear sigma model (GLSM) realizations of a
number of geometries not previously presented in GLSMs. We begin by describing
GLSM realizations of maps including Veronese and Segre embeddings, which can be
applied to give GLSMs explicitly describing constructions such as the
intersection of one hypersurface with the image under some map of another. We
also discuss GLSMs for intersections of Grassmannians and Pfaffians with one
another, and with their images under various maps, which sometimes form exotic
constructions of Calabi-Yaus, as well as GLSMs for other exotic Calabi-Yau
constructions of Kanazawa. Much of this paper focuses on a specific set of
examples of GLSMs for intersections of Grassmannians G(2,N) with themselves
after a linear rotation, including the Calabi-Yau case N=5. One phase of the
GLSM realizes an intersection of two Grassmannians, the other phase realizes an
intersection of two Pfaffians. The GLSM has two nonabelian factors in its gauge
group, and we consider dualities in those factors. In both the original GLSM
and a double-dual, one geometric phase is realized perturbatively (as the
critical locus of a superpotential), and the other via quantum effects.
Dualizing on a single gauge group factor yields a model in which each geometry
is realized through a simultaneous combination of perturbative and quantum
effects.Comment: LaTeX, 50 pages; v2: typos fixed and a few comments on other
dualities adde
Spectrophotometry for cerebrospinal fluid pigment analysis
The use of spectrophotometry for the analysis of the cerebrospinal fluid (CSF) is reviewed. The clinically relevant CSF pigments--oxyhemoglobin and bilirubin--are introduced and discussed with regard to clinical differential diagnosis and potentially confounding variables (the four T's: traumatic tap, timing, total protein, and total bilirubin). The practical laboratory aspects of spectrophotometry and automated techniques are presented in the context of analytical and clinical specificity and sensitivity. The perceptual limitations of human color vision are highlighted and the use of visual assessment of the CSF is discouraged in light of recent evidence from a national audit in the United Kingdom. Finally, future perspectives including the need for longitudinal CSF profiling and routine spectrophotometric calibration are outlined
SENSE-project: : environmental assessment for the fruit juice industry (III)
The SENSE research project proposes a set of Key Environmental Performance Indicators (KEPI) to measure the environmental impact of the fruit juice production. The Blueprint Roadmap summarizes the policy context for the SENSE-tool and identifies opportunities and synergies between SENSE and other initiatives.Non peer reviewe
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