9,458 research outputs found
Direct and Indirect Detection of Neutralino Dark Matter and Collider Signatures in an Model with Two Intermediate Scales
We investigate the detectability of neutralino Dark Matter via direct and
indirect searches as well as collider signatures of an model with two
intermediate scales. We compare the direct Dark Matter detection cross section
and the muon flux due to neutralino annihilation in the Sun that we obtain in
this model with mSUGRA predictions and with the sensitivity of current and
future experiments. In both cases, we find that the detectability improves as
the model deviates more from mSUGRA. In order to study collider signatures, we
choose two benchmark points that represent the main phenomenological features
of the model: a lower value of and reduced third generation sfermion
masses due to extra Yukawa coupling contributions in the Renormalization Group
Equations, and increased first and second generation slepton masses due to new
gaugino loop contributions. We show that measurements at the LHC can
distinguish this model from mSUGRA in both cases, by counting events containing
leptonically decaying bosons, heavy neutral Higgs bosons, or like--sign
lepton pairs.Comment: 21 pages, 16 figure
Fluxon Dynamics of a Long Josephson Junction with Two-gap Superconductors
We investigate the phase dynamics of a long Josephson junction (LJJ) with
two-gap superconductors. In this junction, two channels for tunneling between
the adjacent superconductor (S) layers as well as one interband channel within
each S layer are available for a Cooper pair. Due to the interplay between the
conventional and interband Josephson effects, the LJJ can exhibit unusual phase
dynamics. Accounting for excitation of a stable 2-phase texture arising
from the interband Josephson effect, we find that the critical current between
the S layers may become both spatially and temporally modulated. The spatial
critical current modulation behaves as either a potential well or barrier,
depending on the symmetry of superconducting order parameter, and modifies the
Josephson vortex trajectories. We find that these changes in phase dynamics
result in emission of electromagnetic waves as the Josephson vortex passes
through the region of the 2-phase texture. We discuss the effects of this
radiation emission on the current-voltage characteristics of the junction.Comment: 14 pages, 6 figure
Does Antarctic Krill Employ Body Shrinkage as an Overwintering Strategy?
To determine if Antarctic krill employ body shrinkage as one of its overwintering mechanisms in the field, Euphausia superba and Euphausia crystallorophias were collected during fall and winter in and around Marguerite Bay through US Southern Ocean GLOBEC field programs during fall and winter 2001 and 2002. The relationships between the body length and weight of both krill species were exponentially correlated with no significant differences between the two species (p\u3e0.05). The ratio between eye diameter and body length of individual krill was examined in an expectation that it could be used as an indicator of the body shrinkage as previously suggested by Shin and Nicol (2002). These ratios were significantly different between the two krill species. Especially, E. crystallorophias had bigger eyes than E. superba. In both krill species, eye diameters were highly correlated with body lengths (regression coefficients â„ 0.70). For E. crystallorophias, no significant differences of the ratio of eye diameter/body length were detected between fall and winter. Even though the ratios for E. superba were seasonally varied, it was not clear whether body shrinkage was an actual and critical overwintering mechanism for the krill population found in this study area. These results suggest that some individuals of E. superba might experience the body shrinkage during a part of their life, but this morphological index alone (eye diameter/body length) may be insufficient to unambiguously separate the shrunk krill from the non-shrunk ones in the field-collected animals
Effects of Resonant Cavity on Macroscopic Quantum Tunneling of Fluxon in Long Josephson Junctions
We investigate the effects of high-Q_c resonant cavity on macroscopic quantum
tunneling (MQT) of fluxon both from a metastable state to continuum and from
one degenerate ground-state of a double-well potential to the other. By using a
set of two coupled perturbed sine-Gordon equations, we describe the tunneling
processes in linear long Josephson junctions (LJJs) and find that MQT in the
resonant cavity increases due to potential renomalization, induced by the
interaction between the fluxon and cavity.Enhancement of the MQT rate in the
weak-coupling regime is estimated by using the experimantally accessible range
of the model parameters. The tunneling rate from the metastable state is found
to increase weakly with increasing junction-cavity interaction strength.
However, the energy splitting between the two degenerate ground-states of the
double-well potential increases significantly with increasing both the
interaction strength and frequency of the resonant cavity mode. Finally, we
discuss how the resonant cavity may be used to tune the property of Josephson
vortex quantum bits.Comment: Accepted for publication in Phy. Rev.
Monoclinic and Correlated Metal Phase in VO_2 as Evidence of the Mott Transition: Coherent Phonon Analysis
In femtosecond pump-probe measurements, the appearance of coherent phonon
oscillations at 4.5 THz and 6.0 THz indicating the rutile metal phase of VO_2
does not occur simultaneously with the first-order metal-insulator transition
(MIT) near 68^oC. The monoclinic and correlated metal(MCM) phase between the
MIT and the structural phase transition (SPT) is generated by a photo-assisted
hole excitation which is evidence of the Mott transition. The SPT between the
MCM phase and the rutile metal phase occurs due to subsequent Joule heating.
The MCM phase can be regarded as an intermediate non-equilibrium state.Comment: 4 pages, 2 figure
Nanotextured Morphology of Poly(methyl methacrylate) and Ultraviolet Curable Poly(urethane acrylate) Blends via Phase Separation
Domain structures of spin-coated immiscible poly(methyl methacrylate) (PMMA) and ultraviolet (UV) curable poly(urethane acrylate) (PUA) blends were studied using atomic force microscopy (AFM). Spin casting the PMMA/PUA blends in propylene glycol monomethyl ether acetate (PGMEA) was accompanied with phase separation, and PUA was subsequently cross-linked under UV radiation. Selective dissolution of PMMA in the phase-separated films was feasible using tetrahydrofuran (THF) solvent after the UV curing process, because the cured PUA material is highly stable against THF. Morphology of phase-separated structure, including domain size and height, could be controlled by varying total concentration of the blended solution, and various nanoscale features such as island-like and hole-like structures were achieved by changing weight ratio of the two immiscible polymers
Elevated intracellular cAMP exacerbates vulnerability to oxidative stress in optic nerve head astrocytes.
Glaucoma is characterized by a progressive loss of retinal ganglion cells and their axons, but the underlying biological basis for the accompanying neurodegeneration is not known. Accumulating evidence indicates that structural and functional abnormalities of astrocytes within the optic nerve head (ONH) have a role. However, whether the activation of cyclic adenosine 3',5'-monophosphate (cAMP) signaling pathway is associated with astrocyte dysfunction in the ONH remains unknown. We report here that the cAMP/protein kinase A (PKA) pathway is critical to ONH astrocyte dysfunction, leading to caspase-3 activation and cell death via the AKT/Bim/Bax signaling pathway. Furthermore, elevated intracellular cAMP exacerbates vulnerability to oxidative stress in ONH astrocytes, and this may contribute to axonal damage in glaucomatous neurodegeneration. Inhibition of intracellular cAMP/PKA signaling activation protects ONH astrocytes by increasing AKT phosphorylation against oxidative stress. These results strongly indicate that activation of cAMP/PKA pathway has an important role in astrocyte dysfunction, and suggest that modulating cAMP/PKA pathway has therapeutic potential for glaucomatous ONH degeneration
Properties of Central Caustics in Planetary Microlensing
To maximize the number of planet detections, current microlensing follow-up
observations are focusing on high-magnification events which have a higher
chance of being perturbed by central caustics. In this paper, we investigate
the properties of central caustics and the perturbations induced by them. We
derive analytic expressions of the location, size, and shape of the central
caustic as a function of the star-planet separation, , and the planet/star
mass ratio, , under the planetary perturbative approximation and compare the
results with those based on numerical computations. While it has been known
that the size of the planetary caustic is \propto \sqrt{q}, we find from this
work that the dependence of the size of the central caustic on is linear,
i.e., \propto q, implying that the central caustic shrinks much more rapidly
with the decrease of compared to the planetary caustic. The central-caustic
size depends also on the star-planet separation. If the size of the caustic is
defined as the separation between the two cusps on the star-planet axis
(horizontal width), we find that the dependence of the central-caustic size on
the separation is \propto (s+1/s). While the size of the central caustic
depends both on and q, its shape defined as the vertical/horizontal width
ratio, R_c, is solely dependent on the planetary separation and we derive an
analytic relation between R_c and s. Due to the smaller size of the central
caustic combined with much more rapid decrease of its size with the decrease of
q, the effect of finite source size on the perturbation induced by the central
caustic is much more severe than the effect on the perturbation induced by the
planetary caustic. Abridged.Comment: 5 pages, 4 figures, ApJ accepte
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