21,614 research outputs found
Relics of Supersymmetry in Ordinary 1-flavor QCD: Hairpin Diagrams and Scalar-Pseudoscalar Degeneracy
The large- orientifold planar equivalence between SUSY
Yang-Mills theory and ordinary 1-flavor QCD suggests that low-energy
quark-gluon dynamics in QCD should be constrained by the supersymmetry of the
parent theory. One SUSY relic expected from orientifold equivalence is the
approximate degeneracy of the scalar and pseudoscalar mesons in 1-flavor QCD.
Here we study the role of the annihilation (hairpin) contributions
to the meson correlators. These annihilation terms induce mass shifts of
opposite sign in the scalar and pseudoscalar channels, making degeneracy
plausible. Calculations of valence and hairpin correlators in quenched lattice
QCD are consistent with approximate degeneracy, although the errors on the
scalar hairpin are large. We also study the role of annihilation in
the 1- and 2-flavor Nambu-Jona Lasinio model, where annihilation terms arise
from the chiral field determinant representing the axial U(1) anomaly.
Scalar-pseudoscalar degeneracy for the 1-flavor case reduces to a constraint on
the relative size of the anomalous and non-anomalous 4-fermion couplings.Comment: 17 pages, 3 figure
Transport phenomenology for a holon-spinon fluid
We propose that the normal-state transport in the cuprate superconductors can
be understood in terms of a two-fluid model of spinons and holons. In our
scenario, the resistivity is determined by the properties of the holons while
magnetotransport involves the recombination of holons and spinons to form
physical electrons. Our model implies that the Hall transport time is a measure
of the electron lifetime, which is shorter than the longitudinal transport
time. This agrees with our analysis of the normal-state data. We predict a
strong increase in linewidth with increasing temperature in photoemission. Our
model also suggests that the AC Hall effect is controlled by the transport
time.Comment: 4 pages, 1 postscript figure. Uses RevTeX, epsf, multico
Computing equilibrium states of cholesteric liquid crystals in elliptical channels with deflation algorithms
We study the problem of a cholesteric liquid crystal confined to an
elliptical channel. The system is geometrically frustrated because the
cholesteric prefers to adopt a uniform rate of twist deformation, but the
elliptical domain precludes this. The frustration is resolved by deformation of
the layers or introduction of defects, leading to a particularly rich family of
equilibrium configurations. To identify the solution set, we adapt and apply a
new family of algorithms, known as deflation methods, that iteratively modify
the free energy extremisation problem by removing previously known solutions. A
second algorithm, deflated continuation, is used to track solution branches as
a function of the aspect ratio of the ellipse and preferred pitch of the
cholesteric.Comment: 9 pages, 6 figure
Developmental and tissue-specific expression of the Q5k gene
Expression of the Q5k gene was examined by
northern blot analysis and polymerase chain reaction
(PCR) in the AKR mouse and various cell lines, each of
the H-2k haplotype. Our results show that Q5k mRNA is
present during the whole postimplantational development
of the AKR embryo/fetus (gestation day 6 to 15). In the
juvenile mouse (week 2 to 4) transcription of the Q5k
gene persisted in all organs examined. In contrast, in the
adult animal expression of the Q5k gene was limited to
the thymus and uterus of the pregnant mouse. Upon malignant
transformation, the amount of Q5k-specific mRNA
increased dramatically in thymus and could also be
observed in the spleen of thymoma bearing animals. Expression
of the Q5k gene was also detectable in several
transformed mouse cell lines. Mitogen stimulation or
treatment with cytokines induced Q5k expression in
primary spleen cell cultures. A possible explanation for
the tissue-restricted expression in the adult AKR mouse
is discussed
Complex microwave conductivity of PrCeCuO thin films using a cavity perturbation method
We report a study of the microwave conductivity of electron-doped
PrCeCuO superconducting thin films using a
cavity perturbation technique. The relative frequency shifts obtained for the
samples placed at a maximum electric field location in the cavity are treated
using the high conductivity limit presented recently by Peligrad
Using two resonance modes, TE (16.5 GHz) and TE
(13 GHz) of the same cavity, only one adjustable parameter is needed
to link the frequency shifts of an empty cavity to the ones of a cavity loaded
with a perfect conductor. Moreover, by studying different sample
configurations, we can relate the substrate effects on the frequency shifts to
a scaling factor. These procedures allow us to extract the temperature
dependence of the complex penetration depth and the complex microwave
conductivity of two films with different quality. Our data confirm that all the
physical properties of the superconducting state are consistent with an order
parameter with lines of nodes. Moreover, we demonstrate the high sensitivity of
these properties on the quality of the films
Fractionally charged Wilson loops as a probe of -dependence in sigma models: Instantons vs. large N
The behavior of Wilson loops with fractional charge is used to study the
-dependence of the free energy density for the
, , and sigma models in two spacetime dimensions. The
function is extracted from the area law for a Wilson loop of
charge . For , is smooth in the region
and well-described by a dilute instanton gas throughout the
range . For and the energy exhibits a clear cusp
and evidence for discrete, degenerate vacua at , as expected from
large arguments. For the -dependence is in good quantitative
agreement with the leading order large prediction
throughout the range .Comment: 16 pages, 10 figure
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Human gut Bacteroides capture vitamin B12 via cell surface-exposed lipoproteins.
Human gut Bacteroides use surface-exposed lipoproteins to bind and metabolize complex polysaccharides. Although vitamins and other nutrients are also essential for commensal fitness, much less is known about how commensal bacteria compete with each other or the host for these critical resources. Unlike in Escherichia coli, transport loci for vitamin B12 (cobalamin) and other corrinoids in human gut Bacteroides are replete with conserved genes encoding proteins whose functions are unknown. Here we report that one of these proteins, BtuG, is a surface-exposed lipoprotein that is essential for efficient B12 transport in B. thetaiotaomicron. BtuG binds B12 with femtomolar affinity and can remove B12 from intrinsic factor, a critical B12 transport protein in humans. Our studies suggest that Bacteroides use surface-exposed lipoproteins not only for capturing polysaccharides, but also to acquire key vitamins in the gut
Creative and collaborative strategies for social enterprises in the Philippines
Social entrepreneurs are a bold lot. As Bill Drayton, author of Leading Social Entrepreneurs Changing the World, puts it: “Social entrepreneurs are not content to give a fish or teach how to fish. They will not rest until they have revolutionized the fishing industry.” This quotation captures how these driven individuals have created social value through innovative ideas that often challenge conventions. Their vehicle for this is the social enterprise
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