19,742 research outputs found
Supersymmetry and the AdS Higgs Phenomenon
We examine the AdS Higgs phenomenon for spin-1 fields, and demonstrate that
graviphotons pick up a dynamically generated mass in AdS_4, once matter
boundary conditions are relaxed. We perform an explicit one-loop calculation of
the graviphoton mass, and compare this result with the mass generated for the
graviton in AdS. In this manner, we obtain a condition for unbroken
supersymmetry. With this condition, we examine both N=2 and N=4 gauged
supergravities coupled to matter multiplets, and find that for both cases the
ratio between dynamically generated graviton and graviphoton masses is
consistent with unbroken supersymmetry.Comment: 12 pages, JHEP forma
Local optical field variation in the neighborhood of a semiconductor micrograting
The local optical field of a semiconductor micrograting (GaAs, 10x10 micro m)
is recorded in the middle field region using an optical scanning probe in
collection mode at constant height. The recorded image shows the micro-grating
with high contrast and a displaced diffraction image. The finite penetration
depth of the light leads to a reduced edge resolution in the direction to the
illuminating beam direction while the edge contrast in perpendicular direction
remains high (~100nm). We use the discrete dipole model to calculate the local
optical field to show how the displacement of the diffraction image increases
with increasing distance from the surface.Comment: 12 pages, 3 figure
Helium recombination spectra as temperature diagnostics for planetary nebulae
Electron temperatures derived from the \ion{He}{1} recombination line ratios,
designated (\ion{He}{1}), are presented for 48 planetary nebulae
(PNe). We study the effect that temperature fluctuations inside nebulae have on
the (\ion{He}{1}) value. We show that a comparison between (\ion{He}{1}) and the electron temperature derived from the Balmer jump of
the \ion{H}{1} recombination spectrum, designated (\ion{H}{1}),
provides an opportunity to discriminate between the paradigms of a chemically
homogeneous plasma with temperature and density variations, and a two-abundance
nebular model with hydrogen-deficient material embedded in diffuse gas of a
``normal'' chemical composition (i.e. solar), as the possible causes of
the dichotomy between the abundances that are deduced from collisionally
excited lines to those deduced from recombination lines. We find that (\ion{He}{1}) values are significantly lower than (\ion{H}{1})
values, with an average difference of (\ion{H}{1})-(\ion{He}{1}) K. The result is consistent with the expectation of
the two-abundance nebular model but is opposite to the prediction of the
scenarios of temperature fluctuations and/or density inhomogeneities. From the
observed difference between (\ion{He}{1}) and (\ion{H}{1}), we estimate that the filling factor ofhydrogen-deficient
components has a typical value of . In spite of its small mass, the
existence of hydrogen-deficient inclusions may potentially have a profound
effect in enhancing the intensities of \ion{He}{1} recombination lines and
thereby lead to apparently overestimated helium abundances for PNe.Comment: 27 pages, 7 figures, accepted for publication in MNRA
Decomposition Methods for Large Scale LP Decoding
When binary linear error-correcting codes are used over symmetric channels, a
relaxed version of the maximum likelihood decoding problem can be stated as a
linear program (LP). This LP decoder can be used to decode error-correcting
codes at bit-error-rates comparable to state-of-the-art belief propagation (BP)
decoders, but with significantly stronger theoretical guarantees. However, LP
decoding when implemented with standard LP solvers does not easily scale to the
block lengths of modern error correcting codes. In this paper we draw on
decomposition methods from optimization theory, specifically the Alternating
Directions Method of Multipliers (ADMM), to develop efficient distributed
algorithms for LP decoding.
The key enabling technical result is a "two-slice" characterization of the
geometry of the parity polytope, which is the convex hull of all codewords of a
single parity check code. This new characterization simplifies the
representation of points in the polytope. Using this simplification, we develop
an efficient algorithm for Euclidean norm projection onto the parity polytope.
This projection is required by ADMM and allows us to use LP decoding, with all
its theoretical guarantees, to decode large-scale error correcting codes
efficiently.
We present numerical results for LDPC codes of lengths more than 1000. The
waterfall region of LP decoding is seen to initiate at a slightly higher
signal-to-noise ratio than for sum-product BP, however an error floor is not
observed for LP decoding, which is not the case for BP. Our implementation of
LP decoding using ADMM executes as fast as our baseline sum-product BP decoder,
is fully parallelizable, and can be seen to implement a type of message-passing
with a particularly simple schedule.Comment: 35 pages, 11 figures. An early version of this work appeared at the
49th Annual Allerton Conference, September 2011. This version to appear in
IEEE Transactions on Information Theor
Non-diagonal Charged Lepton Yukawa Matrix: Effects on Neutrino Mixing in Supersymmetry
Generally the diagonalization of the mass matrix of the charged leptons is a
part of the neutrino UPMNS matrix. However, usually this contribution is
ignored by assuming a diagonal mass matrix for charged leptons. In this letter
we test this common assumption in the context of neutrino physics. Our
analytical and numerical results for two supersymmetric models reveal that such
a simplification is not justified. Especially for the solar and reactor mixing
angles important modifications are found.Comment: 22 pages 8 figure
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5 S,15 S-Dihydroperoxyeicosatetraenoic Acid (5,15-diHpETE) as a Lipoxin Intermediate: Reactivity and Kinetics with Human Leukocyte 5-Lipoxygenase, Platelet 12-Lipoxygenase, and Reticulocyte 15-Lipoxygenase-1.
The reaction of 5 S,15 S-dihydroperoxyeicosatetraenoic acid (5,15-diHpETE) with human 5-lipoxygenase (LOX), human platelet 12-LOX, and human reticulocyte 15-LOX-1 was investigated to determine the reactivity and relative rates of producing lipoxins (LXs). 5-LOX does not react with 5,15-diHpETE, although it can produce LXA4 when 15-HpETE is the substrate. In contrast, both 12-LOX and 15-LOX-1 react with 5,15-diHpETE, forming specifically LXB4. For 12-LOX and 5,15-diHpETE, the kinetic parameters are kcat = 0.17 s-1 and kcat/ KM = 0.011 μM-1 s-1 [106- and 1600-fold lower than those for 12-LOX oxygenation of arachidonic acid (AA), respectively]. On the other hand, for 15-LOX-1 the equivalent parameters are kcat = 4.6 s-1 and kcat/ KM = 0.21 μM-1 s-1 (3-fold higher and similar to those for 12-HpETE formation by 15-LOX-1 from AA, respectively). This contrasts with the complete lack of reaction of 15-LOX-2 with 5,15-diHpETE [Green, A. R., et al. (2016) Biochemistry 55, 2832-2840]. Our data indicate that 12-LOX is markedly inferior to 15-LOX-1 in catalyzing the production of LXB4 from 5,15-diHpETE. Platelet aggregation was inhibited by the addition of 5,15-diHpETE, with an IC50 of 1.3 μM; however, LXB4 did not significantly inhibit collagen-mediated platelet activation up to 10 μM. In summary, LXB4 is the primary product of 12-LOX and 15-LOX-1 catalysis, if 5,15-diHpETE is the substrate, with 15-LOX-1 being 20-fold more efficient than 12-LOX. LXA4 is the primary product with 5-LOX but only if 15-HpETE is the substrate. Approximately equal proportions of LXA4 and LXB4 are produced by 12-LOX but only if LTA4 is the substrate, as described previously [Sheppard, K. A., et al. (1992) Biochim. Biophys. Acta 1133, 223-234]
Disks in a narrow channel jammed by gravity and centrifuge: profiles of pressure, mass density and entropy density
This work investigates jammed granular matter under conditions that produce
heterogeneous mass distributions on a mesoscopic scale. We consider a system of
identical disks that are confined to a narrow channel, open at one end and
closed off at the other end. The disks are jammed by the local pressure in a
gravitational field or centrifuge. All surfaces are hard and frictionless. We
calculate the profiles of pressure, mass density, and entropy density on a
mesoscopic length scale under the assumption that the jammed states are
produced by random agitations of uniform intensity along the channel. These
profiles exhibit trends and features governed by the balancing of
position-dependent forces and potential energies. The analysis employs a method
of configurational statistics that uses interlinking two-disk tiles as the
fundamental degrees of freedom. Configurational statistics weighs the
probabilities of tiles according to competing potential energies associated
with gravity and centrifugation. Amendments account for the effects of the
marginal stability of some tiles due to competing forces.Comment: 20 pages, 10 figure
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