44,894 research outputs found
Decoherence in QED at finite temperature
We consider a wave packet of a charged particle passing through a cavity
filled with photons at temperature T and investigate its localization and
interference properties. It is shown that the wave packet becomes localized and
the interference disappears with an exponential speed after a sufficiently long
path through the cavity.Comment: Latex, 10 page
Spatial imaging of Zn and other elements in Huanglongbing-affected grapefruit by synchrotron-based micro X-ray fluorescence investigation
Huanglongbing (HLB) is a highly destructive, fast-spreading disease of citrus, causing substantial economic losses to the citrus industry worldwide. Nutrient levels and their cellular distribution patterns in stems and leaves of grapefruit were analysed after graft-inoculation with lemon scions containing 'Candidatus Liberibacter asiaticus' (Las), the heat-tolerant Asian type of the HLB bacterium. After 12 months, affected plants showed typical HLB symptoms and significantly reduced Zn concentrations in leaves. Micro-XRF imaging of Zn and other nutrients showed that preferential localization of Zn to phloem tissues was observed in the stems and leaves collected from healthy grapefruit plants, but was absent from HLB-affected samples. Quantitative analysis by using standard references revealed that Zn concentration in the phloem of veins in healthy leaves was more than 10 times higher than that in HLB-affected leaves. No significant variation was observed in the distribution patterns of other elements such as Ca in stems and leaves of grapefruit plants with or without graft-inoculation of infected lemon scions. These results suggest that reduced phloem transport of Zn is an important factor contributing to HLB-induced Zn deficiency in grapefruit. Our report provides the first in situ, cellular level visualization of elemental variations within the tissues of HLB-affected citrus. © 2014 © The Author 2014. Published by Oxford University Press on behalf of the Society for Experimental Biology
The Triple Pulsar System PSR B1620-26 in M4
The millisecond pulsar PSR B1620-26, in the globular cluster M4, has a white
dwarf companion in a half-year orbit. Anomalously large variations in the
pulsar's apparent spin-down rate have suggested the presence of a second
companion in a much wider orbit. Using timing observations made on more than
seven hundred days spanning eleven years, we confirm this anomalous timing
behavior. We explicitly demonstrate, for the first time, that a timing model
consisting of the sum of two non-interacting Keplerian orbits can account for
the observed signal. Both circular and elliptical orbits are allowed, although
highly eccentric orbits require improbable orbital geometries.
The motion of the pulsar in the inner orbit is very nearly a Keplerian
ellipse, but the tidal effects of the outer companion cause variations in the
orbital elements. We have measured the change in the projected semi-major axis
of the orbit, which is dominated by precession-driven changes in the orbital
inclination. This measurement, along with limits on the rate of change of other
orbital elements, can be used to significantly restrict the properties of the
outer orbit. We find that the second companion most likely has a mass m~0.01
Msun --- it is almost certainly below the hydrogen burning limit (m<0.036 Msun,
95% confidence) --- and has a current distance from the binary of ~35 AU and
orbital period of order one hundred years. Circular (and near-circular) orbits
are allowed only if the pulsar magnetic field is ~3x10^9 G, an order of
magnitude higher than a typical millisecond pulsar field strength. In this
case, the companion has mass m~1.2x10^-3 Msun and orbital period ~62 years.Comment: 12 pages, 6 figures, 3 tables. Very minor clarifications and
rewording. Accepted for publication in the Astrophys.
Rectification from Radially-Distorted Scales
This paper introduces the first minimal solvers that jointly estimate lens
distortion and affine rectification from repetitions of rigidly transformed
coplanar local features. The proposed solvers incorporate lens distortion into
the camera model and extend accurate rectification to wide-angle images that
contain nearly any type of coplanar repeated content. We demonstrate a
principled approach to generating stable minimal solvers by the Grobner basis
method, which is accomplished by sampling feasible monomial bases to maximize
numerical stability. Synthetic and real-image experiments confirm that the
solvers give accurate rectifications from noisy measurements when used in a
RANSAC-based estimator. The proposed solvers demonstrate superior robustness to
noise compared to the state-of-the-art. The solvers work on scenes without
straight lines and, in general, relax the strong assumptions on scene content
made by the state-of-the-art. Accurate rectifications on imagery that was taken
with narrow focal length to near fish-eye lenses demonstrate the wide
applicability of the proposed method. The method is fully automated, and the
code is publicly available at https://github.com/prittjam/repeats.Comment: pre-prin
Inviscid dynamical structures near Couette flow
Consider inviscid fluids in a channel {-1<y<1}. For the Couette flow
v_0=(y,0), the vertical velocity of solutions to the linearized Euler equation
at v_0 decays in time. At the nonlinear level, such inviscid damping has not
been proved. First, we show that in any (vorticity) H^{s}(s<(3/2)) neighborhood
of Couette flow, there exist non-parallel steady flows with arbitrary minimal
horizontal period. This implies that nonlinear inviscid damping is not true in
any (vorticity) H^{s}(s<(3/2)) neighborhood of Couette flow and for any
horizontal period. Indeed, the long time behavior in such neighborhoods are
very rich, including nontrivial steady flows, stable and unstable manifolds of
nearby unstable shears. Second, in the (vorticity) H^{s}(s>(3/2)) neighborhood
of Couette, we show that there exist no non-parallel steadily travelling flows
v(x-ct,y), and no unstable shears. This suggests that the long time dynamics in
H^{s}(s>(3/2)) neighborhoods of Couette might be much simpler. Such contrasting
dynamics in H^{s} spaces with the critical power s=(3/2) is a truly nonlinear
phenomena, since the linear inviscid damping near Couette is true for any
initial vorticity in L^2
Distribution Substation Dynamic Reconfiguration and Reinforcement-Digital Twin Model
The proliferation of electric vehicles will increase demand and alter the load profiles on final distribution substations quicker than traditional reinforcement techniques can respond. As it is nontrivial to determine in advance, to street level granularity, where and when vehicles will charge, a more flexible approach to substation reinforcement is preferable to the existing rip-out-and-replace technique for an overloaded transformer. Distribution Substation Dynamic Reconfiguration (DSDR) combines reinforcement using parallel transformers with reconfiguration algorithms to flexibly operate the substation in the face of uncertain loading conditions, by dynamically switching transformers in and out of service. This paper presents a digital twin and a benchtop scale model of the DSDR substation for the development and evaluation of such algorithms, along with two algorithms for optimizing substation technical losses. Initial results show that on a single tested substation model, efficiency increased by 5.40% with Net-Zero Year 2050 load profiles versus traditional reinforcement
Superconductivity in an Einstein Solid AxV2Al20 (A = Al and Ga)
A cage compound AxV2Al20 (Al10V), that was called an Einstein solid by Caplin
and coworkers 40 years ago, is revisited to investigate the low-energy, local
vibrations of the A atoms and their influence on the electronic and
superconducting properties of the compound. Polycrystalline samples with A =
Al, Ga, Y, and La are studied through resistivity and heat capacity
measurements. Weak-coupling BCS superconductivity is observed below Tc = 1.49,
1.66, and 0.69 K for Ax = Al0.3, Ga0.2, and Y, respectively, but not above 0.4
K for Ax = La. Low-energy modes are detected only for A = Al and Ga, which are
approximately described by the Einstein model with Einstein temperatures of 24
and 8 K, respectively. A weak but significant coupling between the low-energy
modes, which are almost identical to those called rattling in recent study, and
conduction electrons manifests itself as anomalous enhancement in resistivity
at around low temperatures corresponding to the Einstein temperatures.Comment: 12 pages, 5 figures, to be published in J. Phys. Soc. Jp
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