8,353 research outputs found
Incommensurate spin correlations in highly oxidized cobaltates LaSrCoO
We observe quasi-static incommensurate magnetic peaks in neutron scattering
experiments on layered cobalt oxides La2-xSrxCoO4 with high Co oxidation states
that have been reported to be paramagnetic. This enables us to measure the
magnetic excitations in this highly hole-doped incommensurate regime and
compare our results with those found in the low-doped incommensurate regime
that exhibit hourglass magnetic spectra. The hourglass shape of magnetic
excitations completely disappears given a high Sr doping. Moreover, broad
low-energy excitations are found, which are not centered at the incommensurate
magnetic peak positions but around the quarter-integer values that are
typically exhibited by excitations in the checkerboard charge ordered phase.
Our findings suggest that the strong inter-site exchange interactions in the
undoped islands are critical for the emergence of hourglass spectra in the
incommensurate magnetic phases of La2-xSrxCoO4.Comment: http://www.nature.com/articles/srep25117
Tomato chocolate spot virus, a member of a new torradovirus species that causes a necrosis-associated disease of tomato in Guatemala
Tomatoes in Guatemala have been affected by a new disease, locally known as âmancha de chocolateâ (chocolate spot). The disease is characterized by distinct necrotic spots on leaves, stems and petioles that eventually expand and cause a dieback of apical tissues. Samples from symptomatic plants tested negative for infection by tomato spotted wilt virus, tobacco streak virus, tobacco etch virus and other known tomato-infecting viruses. A virus-like agent was sap-transmitted from diseased tissue to Nicotiana benthamiana and, when graft-transmitted to tomato, this agent induced chocolate spot symptoms. This virus-like agent also was sap-transmitted to Datura stramonium and Nicotiana glutinosa, but not to a range of non-solanaceous indicator plants. Icosahedral virions ~28â30Â nm in diameter were purified from symptomatic N. benthamiana plants. When rub-inoculated onto leaves of N. benthamiana plants, these virions induced symptoms indistinguishable from those in N. benthamiana plants infected with the sap-transmissible virus associated with chocolate spot disease. Tomatoes inoculated with sap or grafted with shoots from N. benthamiana plants infected with purified virions developed typical chocolate spot symptoms, consistent with this virus being the causal agent of the disease. Analysis of nucleic acids associated with purified virions of the chocolate-spot-associated virus, revealed a genome composed of two single-stranded RNAs of ~7.5 and ~5.1Â kb. Sequence analysis of these RNAs revealed a genome organization similar to recently described torradoviruses, a new group of picorna-like viruses causing necrosis-associated diseases of tomatoes in Europe [tomato torrado virus (ToTV)] and Mexico [tomato apex necrosis virus (ToANV) and tomato marchitez virus (ToMarV)]. Thus, the ~7.5Â kb and ~5.1Â kb RNAs of the chocolate-spot-associated virus corresponded to the torradovirus RNA1 and RNA2, respectively; however, sequence comparisons revealed 64â83% identities with RNA1 and RNA2 sequences of ToTV, ToANV and ToMarV. Together, these results indicate that the chocolate-spot-associated virus is a member of a distinct torradovirus species and, thus, another member of the recently established genus Torradovirus in the family Secoviridae. The name tomato chocolate spot virus is proposed
Prevalence of Tidal Interactions among Local Seyfert Galaxies: The Control Experiment
We test whether there is a relation between the observed tidal interactions
and Seyfert activity by imaging in HI twenty inactive galaxies at the same
spatial resolution and detection threshold as the Seyfert sample. This control
sample of inactive galaxies were closely matched in Hubble type, range in size
and inclination, and have roughly comparable galaxy optical luminosity to the
Seyfert galaxies. We find that only ~15% of the galaxies in our control sample
are disturbed in HI, whereas the remaining ~85% show no disturbances whatsoever
in HI. Even at a spatial resolution of ~10 kpc, none of the latter galaxies
show appreciable HI disturbances reminiscent of tidal features.
In a companion paper (Kuo et al. 2008), we report results from the first
systematic imaging survey of Seyfert galaxies in atomic hydrogen (HI) gas. We
find that only ~28% of the eighteen Seyfert galaxies in that sample are visibly
disturbed in optical starlight. By contrast, ~94% of the same Seyfert galaxies
are disturbed spatially and usually also kinematically in HI gas on galactic
scales of >~20 kpc. In at least ~67% and up to perhaps ~94% of cases, the
observed disturbances can be traced to tidal interactions with neighboring
galaxies detected also in HI. The dramatic contrast between the observed
prevalence of HI disturbances in the Seyfert and control samples implicates
tidal interactions in initiating events that lead to luminous Seyfert activity
in a large fraction of local disk galaxies.Comment: 38 pages, 27 figures, Accepted for publication in ApJ. Changes from
previous version: The title of the previous version of this paper appeared in
Astroph was incorrect. It has been replaced with the correct on
Continuity of Local Time: An applied perspective
Continuity of local time for Brownian motion ranks among the most notable
mathematical results in the theory of stochastic processes. This article
addresses its implications from the point of view of applications. In
particular an extension of previous results on an explicit role of continuity
of (natural) local time is obtained for applications to recent classes of
problems in physics, biology and finance involving discontinuities in a
dispersion coefficient. The main theorem and its corollary provide physical
principles that relate macro scale continuity of deterministic quantities to
micro scale continuity of the (stochastic) local time.Comment: To appear in: "The fascination of Probability, Statistics and Their
Applications. In honour of Ole E. Barndorff-Nielsen on his 80th birthday
The MSW Effect in Quantum Field Theory
We show in detail the general relationship between the Schr\"{o}dinger
equation approach to calculating the MSW effect and the quantum field
theoretical S-matrix approach. We show the precise form a generic neutrino
propagator must have to allow a physically meaningful ``oscillation
probability'' to be decoupled from neutrino production fluxes and detection
cross-sections, and explicitly list the conditions---not realized in cases of
current experimental interest---in which the field theory approach would be
useful.Comment: 20 page REVTeX file, submitted to Phys. Rev.
Long-range interactions in the effective low energy Hamiltonian of Sr2IrO4: a core level resonant inelastic x-ray scattering study
We have investigated the electronic structure of Sr2IrO4 using core level
resonant inelastic x-ray scattering. The experimental spectra can be well
reproduced using ab initio density functional theory based multiplet ligand
field theory calculations, thereby validating these calculations. We found that
the low-energy, effective Ir t2g orbitals are practically degenerate in energy.
We uncovered that covalency in Sr2IrO4, and generally in iridates, is very
large with substantial oxygen ligand hole character in the Ir t2g Wannier
orbitals. This has far reaching consequences, as not only the onsite
crystal-field energies are determined by the long range crystal-structure, but,
more significantly, magnetic exchange interactions will have long range
distance dependent anisotropies in the spin direction. These findings set
constraints and show pathways for the design of d^5 materials that can host
compass-like magnetic interactions
Choosing among Partition Models in Bayesian Phylogenetics
Bayesian phylogenetic analyses often depend on Bayes factors (BFs) to determine the optimal way to partition the data. The marginal likelihoods used to compute BFs, in turn, are most commonly estimated using the harmonic mean (HM) method, which has been shown to be inaccurate. We describe a new more accurate method for estimating the marginal likelihood of a model and compare it with the HM method on both simulated and empirical data. The new method generalizes our previously described stepping-stone (SS) approach by making use of a reference distribution parameterized using samples from the posterior distribution. This avoids one challenging aspect of the original SS method, namely the need to sample from distributions that are close (in the KullbackâLeibler sense) to the prior. We specifically address the choice of partition models and find that using the HM method can lead to a strong preference for an overpartitioned model. In contrast to the HM method and the original SS method, we show using simulated data that the generalized SS method is strikingly more precise (repeatable BF values of the same data and partition model) and yields BF values that are much more reasonable than those produced by the HM method. Comparisons of HM and generalized SS methods on an empirical data set demonstrate that the generalized SS method tends to choose simpler partition schemes that are more in line with expectation based on inferred patterns of molecular evolution. The generalized SS method shares with thermodynamic integration the need to sample from a series of distributions in addition to the posterior. Such dedicated path-based Markov chain Monte Carlo analyses appear to be a cost of estimating marginal likelihoods accurately
Annealing-Induced Full Amorphization in a Multicomponent Metallic Film
We present direct experimental evidence that controllable amorphization and nanocrystallization during annealing of metastable films could serve as a precursor for exciting nanomaterials. The interesting discovery is that certain sputtered crystalline films become completely amorphous when annealed in the temperature range between the glass temperature and the crystallization temperature. Unlike other metallic glassy materials that exhibit annealing-induced devitrification, our good glass-forming films are transformed into various nanoscale and amorphous structures due to the annealing process. The formation of an amorphous phase gives rise to notable alterations in the electrical and mechanical properties of the film
A Contribution by Ice Nuclei to Global Warming
Ice nuclei (IN) significantly affect clouds via supercooled droplets, that in turn modulate atmospheric radiation and thus climate change. Since the IN effect is relatively strong in stratiform clouds but weak in convective ones, the overall effect depends on the ratio of stratiform to convective cloud amount. In this paper, 10 years of TRMM (Tropical Rainfall Measuring Mission) satellite data are analyzed to confirm that stratiform precipitation fraction increases with increasing latitude, which implies that the IN effect is stronger at higher latitudes. To quantitatively evaluate the IN effect versus latitude, large-scale forcing data from ten field campaigns are used to drive a CRM (cloud-resolving model) to generate longterm cloud simulations. As revealed in the simulations, the increase in the net downward radiative flux at the TOA (top of the atmosphere) from doubling the current IN concentrations is larger at higher latitude, which is attributed to the meridional tendency in the stratiform precipitation fraction. Surface warming from doubling the IN concentrations, based on the radiative balance of the globe, is compared with that from anthropogenic COZ . It is found that the former effect is stronger than the latter in middle and high latitudes but not in the Tropics. With regard to the impact of IN on global warming, there are two factors to consider: the radiative effect from increasing the IN concentration and the increase in IN concentration itself. The former relies on cloud ensembles and thus varies mainly with latitude. In contrast, the latter relies on IN sources (e.g., the land surface distribution) and thus varies not only with latitude but also longitude. Global desertification and industrialization provide clues on the geographic variation of the increase in IN concentration since pre-industrial times. Thus, their effect on global warming can be inferred and then be compared with observations. A general match in geographic and seasonal variations between the inferred and observed warming suggests that IN may have contributed positively to global warming over the past decades, especially in middle and high latitudes
On the Evolution of the Neutrino State inside the Sun
We reexamine the conventional physical description of the neutrino evolution
inside the Sun. We point out that the traditional resonance condition has
physical meaning only in the limit of small values of the neutrino mixing
angle, theta<<1. For large values of theta, the resonance condition specifies
neither the point of the maximal violation of adiabaticity in the nonadiabatic
case, nor the point where the flavor conversion occurs at the maximal rate in
the adiabatic case. The corresponding correct conditions, valid for all values
of theta including theta>pi/4, are presented. An adiabaticity condition valid
for all values of theta is also described. The results of accurate numerical
computations of the level jumping probability in the Sun are presented. These
calculations cover a wide range of Delta m^2, from the vacuum oscillation
region to the region where the standard exponential approximation is good. A
convenient empirical parametrization of these results in terms of elementary
functions is given. The matter effects in the so-called "quasi-vacuum
oscillation regime" are discussed. Finally, it is shown how the known
analytical results for the exponential, 1/x, and linear matter distributions
can be simply obtained from the formula for the hyperbolic tangent profile. An
explicit formula for the jumping probability for the distribution N_e ~
(coth(x/l) +- 1) is obtained.Comment: 34 pages, 8 figure
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