2,305 research outputs found
Double- Order in a Frustrated Random Spin System
We use the three-dimensional Heisenberg model with site randomness as an
effective model of the compound Sr(FeMn)O. The model consists
of two types of ions that correspond to Fe and Mn ions. The nearest-neighbor
interactions in the ab-plane are antiferromagnetic. The nearest-neighbor
interactions along the c-axis between Fe ions are assumed to be
antiferromagnetic, whereas other interactions are assumed to be ferromagnetic.
From Monte Carlo simulations, we confirm the existence of the
double- ordered phase characterized by two wave numbers,
and . We also identify the spin ordering pattern in
the double- ordered phase.Comment: 5pages, 3figure
Nonthermal Emission Associated with Strong AGN Outbursts at the Centers of Galaxy Clusters
Recently, strong AGN outbursts at the centers of galaxy clusters have been
found. Using a simple model, we study particle acceleration around a shock
excited by an outburst and estimate nonthermal emission from the accelerated
particles. We show that emission from secondary electrons is consistent with
the radio observations of the minihalo in the Perseus cluster, if there was a
strong AGN outburst >~10^8 yrs ago with an energy of ~1.8x10^62 erg. The
validity of our model depends on the frequency of the large outbursts. We also
estimate gamma-ray emission from the accelerated particles and show that it
could be detected with GLAST.Comment: Accepted for publication in ApJ
Non-Stationary Dark Energy Around a Black Hole
Numerical simulations of the accretion of test scalar fields with
non-standard kinetic terms (of the k-essence type) onto a Schwarzschild black
hole are performed. We find a full dynamical solution for the spherical
accretion of a Dirac-Born-Infeld type scalar field. The simulations show that
the accretion eventually settles down to a well known stationary solution. This
particular analytical steady state solution maintains two separate horizons.
The standard horizon is for the usual particles propagating with the limiting
speed of light, while the other sonic horizon is for the k-essence
perturbations propagating with the speed of sound around this accreting
background. For the case where the k-essence perturbations propagate
superluminally, we show that one can send signals from within a black hole
during the approach to the stationary solution. We also find that a ghost
condensate model settles down to a stationary solution during the accretion
process.Comment: 8 pages, 10 figure
Speed of Sound in the Mass Varying Neutrinos Scenario
We discuss about the speed of sound squared in the Mass Varying Neutrinos
scenario (MaVaNs). Recently, it was argued that the MaVaNs has a catastrophic
instability which is the emergence of an imaginary speed of sound at the
non-relativistic limit of neutrinos. As the result of this instability, the
neutrino-acceleron fluid cannot act as the dark energy. However, it is found
that the speed of sound squared in the neutrino-acceleron fluid could be
positive in our model. We examine the speed of sound in two cases of the scalar
potential. One is the small fractional power-law potential and another is the
logarithmic one. The power-law potential model with the right-handed neutrinos
gives a stable one.Comment: 17 pages, References added, minor modification
Scalable Spatial Super-Resolution using Entangled Photons
N00N states -- maximally path-entangled states of N photons -- exhibit
spatial interference patterns sharper than any classical interference pattern.
This is known as super-resolution. However, even with perfectly efficient
number-resolving detectors, the detection efficiency of all previously
demonstrated methods to measure such interference decreases exponentially with
the number of photons in the N00N state, often leading to the conclusion that
N00N states are unsuitable for spatial measurements. Here, we create spatial
super-resolution fringes with two-, three-, and four-photon N00N states, and
demonstrate a scalable implementation of the so-called ``optical centroid
measurement'' which provides an in-principle perfect detection efficiency.
Moreover, we compare the N00N-state interference to the corresponding classical
super-resolution interference. Although both provide the same increase in
spatial frequency, the visibility of the classical fringes decreases
exponentially with the number of detected photons, while the visibility of our
experimentally measured N00N-state super-resolution fringes remains
approximately constant with N. Our implementation of the optical centroid
measurement is a scalable method to measure high photon-number quantum
interference, an essential step forward for quantum-enhanced measurements,
overcoming what was believed to be a fundamental challenge to quantum
metrology
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The olfactory basis of orchid pollination by mosquitoes.
Mosquitoes are important vectors of disease and require sources of carbohydrates for reproduction and survival. Unlike host-related behaviors of mosquitoes, comparatively less is understood about the mechanisms involved in nectar-feeding decisions, or how this sensory information is processed in the mosquito brain. Here we show that Aedes spp. mosquitoes, including Aedes aegypti, are effective pollinators of the Platanthera obtusata orchid, and demonstrate this mutualism is mediated by the orchid's scent and the balance of excitation and inhibition in the mosquito's antennal lobe (AL). The P. obtusata orchid emits an attractive, nonanal-rich scent, whereas related Platanthera species-not visited by mosquitoes-emit scents dominated by lilac aldehyde. Calcium imaging experiments in the mosquito AL revealed that nonanal and lilac aldehyde each respectively activate the LC2 and AM2 glomerulus, and remarkably, the AM2 glomerulus is also sensitive to N,N-diethyl-meta-toluamide (DEET), a mosquito repellent. Lateral inhibition between these 2 glomeruli reflects the level of attraction to the orchid scents. Whereas the enriched nonanal scent of P. obtusata activates the LC2 and suppresses AM2, the high level of lilac aldehyde in the other orchid scents inverts this pattern of glomerular activity, and behavioral attraction is lost. These results demonstrate the ecological importance of mosquitoes beyond operating as disease vectors and open the door toward understanding the neural basis of mosquito nectar-seeking behaviors
Mechanism and scalability of tip vortex cavitation suppression by water and polymer injection
Tip vortex cavitation (TVC) is typically the first form of cavitation observed in propellers; therefore a delay in its onset is sought. TVC suppression via mass injection in the core of the vortex was studied with an elliptical plan-form hydrofoil NACA-66 modified in a recirculating water tunnel with known nuclei distribution. The solutions injected were water and Polyox WSR 301 solution with concentration ranging from 10 to 500pmm. It was observed that TVC was suppressed in all cases where mass was injected. Higher polymer concentration solutions and higher flux rate provided a drop in cavitation desinence of 1.8 Water injection at the lowest flux rate provided the smallest drop in cavitation desinence, 0.03. A saturation effect for the TVC suppression was also observed for both the polymer concentration (125ppm) and volume flux rate (Qjet / Qcore = 0.48). The mechanisms and scalability that lead to TVC suppression via mass injection will be investigated.http://deepblue.lib.umich.edu/bitstream/2027.42/84320/1/CAV2009-final149.pd
Chandra Observations of A Galactic Supernova Remnant Vela Jr.: A New Sample of Thin Filaments Emitting Synchrotron X-Rays
A galactic supernova remnant (SNR) Vela Jr. (RX J0852.04622, G266.61.2)
shows sharp filamentary structure on the north-western edge of the remnant in
the hard X-ray band. The filaments are so smooth and located on the most outer
side of the remnant. We measured the averaged scale width of the filaments
( and ) with excellent spatial resolution of {\it Chandra}, which are
in the order of the size of the point spread function of {\it Chandra} on the
upstream side and 49.5 (36.0--88.8) arcsec on the downstream side,
respectively. The spectra of the filaments are very hard and have no line-like
structure, and were well reproduced with an absorbed power-law model with
2.67 (2.55--2.77), or a {\tt SRCUT} model with = 4.3
(3.4--5.3) Hz under the assumption of . These results
imply that the hard X-rays are synchrotron radiation emitted by accelerated
electrons, as mentioned previously. Using a correlation between a function
and the SNR age, we estimated the
distance and the age of Vela Jr.: the estimated distance and age are 0.33
(0.26--0.50) kpc and 660 (420--1400) years, respectively. These results are
consistent with previous reports, implying that --age relation may be
a useful tool to estimate the distance and the age of synchrotron X-ray
emitting SNRs.Comment: 19 pages, 8 figures, ApJ, in pres
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