682 research outputs found
Conditioning the soil microbiome through plant–soil feedbacks suppresses an aboveground insect pest
Plant science
Measuring proper motions of isolated neutron stars with Chandra
The excellent spatial resolution of the Chandra observatory offers the
unprecedented possibility to measure proper motions at X-ray wavelength with
relatively high accuracy using as reference the background of extragalactic or
remote galactic X-ray sources. We took advantage of this capability to
constrain the proper motion of RX J0806.4-4123 and RX J0420.0-5022, two X-ray
bright and radio quiet isolated neutron stars (INSs) discovered by ROSAT and
lacking an optical counterpart. In this paper, we present results from a
preliminary analysis from which we derive 2 sigma upper limits of 76 mas/yr and
138 mas/yr on the proper motions of RX J0806.4-4123 and RX J0420.0-5022
respectively. We use these values together with those of other ROSAT discovered
INSs to constrain the origin, distance and evolutionary status of this
particular group of objects. We find that the tangential velocities of radio
quiet ROSAT neutron stars are probably consistent with those of 'normal'
pulsars. Their distribution on the sky and, for those having accurate proper
motion vectors, their possible birth places, all point to a local population,
probably created in the part of the Gould Belt nearest to the earth.Comment: 8 pages, 3 figures, to appear in Astrophysics and Space Science, in
the proceedings of "Isolated Neutron Stars: from the Interior to the
Surface", edited by D. Page, R. Turolla and S. Zan
The Effective Field Theory of Inflation
We study the effective field theory of inflation, i.e. the most general
theory describing the fluctuations around a quasi de Sitter background, in the
case of single field models. The scalar mode can be eaten by the metric by
going to unitary gauge. In this gauge, the most general theory is built with
the lowest dimension operators invariant under spatial diffeomorphisms, like
g^{00} and K_{mu nu}, the extrinsic curvature of constant time surfaces. This
approach allows us to characterize all the possible high energy corrections to
simple slow-roll inflation, whose sizes are constrained by experiments. Also,
it describes in a common language all single field models, including those with
a small speed of sound and Ghost Inflation, and it makes explicit the
implications of having a quasi de Sitter background. The non-linear realization
of time diffeomorphisms forces correlation among different observables, like a
reduced speed of sound and an enhanced level of non-Gaussianity.Comment: 26 pages. v2: minor corrections, JHEP published versio
An Assessment of the Use of Chimpanzees in Hepatitis C Research Past, Present and Future: 2. Alternative Replacement Methods
The use of chimpanzees in hepatitis C virus (HCV) research was examined in the report associated with this paper (1: Validity of the Chimpanzee Model), in which it was concluded that claims of past necessity of chimpanzee use were exaggerated, and that claims of current and future indispensability were unjustifiable. Furthermore, given the serious scientific and ethical issues surrounding chimpanzee experimentation, it was proposed that it must now be considered redundant — particularly in light of the demonstrable contribution of alternative methods to past and current scientific progress, and the future promise that these methods hold. This paper builds on this evidence, by examining the development of alternative approaches to the investigation of HCV, and by reviewing examples of how these methods have contributed, and are continuing to contribute substantially, to progress in this field. It augments the argument against chimpanzee use by demonstrating the comprehensive nature of these methods and the valuable data they deliver. The entire life-cycle of HCV can now be investigated in a human (and much more relevant) context, without recourse to chimpanzee use. This also includes the testing of new therapies and vaccines. Consequently, there is no sound argument against the changes in public policy that propose a move away from chimpanzee use in US laboratories
A Search for Fast Radio Bursts with the GBNCC Pulsar Survey
We report on a search for Fast Radio Bursts (FRBs) with the Green Bank
Northern Celestial Cap (GBNCC) Pulsar Survey at 350 MHz. Pointings amounting to
a total on-sky time of 61 days were searched to a DM of 3000 pc cm while
the rest (23 days; 29% of the total time) were searched to a DM of 500 pc
cm. No FRBs were detected in the pointings observed through May 2016. We
estimate a 95% confidence upper limit on the FRB rate of FRBs
sky day above a peak flux density of 0.63 Jy at 350 MHz for an
intrinsic pulse width of 5 ms. We place constraints on the spectral index
by running simulations for different astrophysical scenarios and
cumulative flux density distributions. The non-detection with GBNCC is
consistent with the 1.4-GHz rate reported for the Parkes surveys for in the absence of scattering and free-free absorption and in the presence of scattering, for a Euclidean flux distribution. The
constraints imply that FRBs exhibit either a flat spectrum or a spectral
turnover at frequencies above 400 MHz. These constraints also allow estimation
of the number of bursts that can be detected with current and upcoming surveys.
We predict that CHIME may detect anywhere from several to 50 FRBs a day
(depending on model assumptions), making it well suited for interesting
constraints on spectral index, the log -log slope and pulse profile
evolution across its bandwidth (400-800 MHz).Comment: 18 pages, 10 figures, Accepted for publication in Ap
Pulsar-wind nebulae and magnetar outflows: observations at radio, X-ray, and gamma-ray wavelengths
We review observations of several classes of neutron-star-powered outflows:
pulsar-wind nebulae (PWNe) inside shell supernova remnants (SNRs), PWNe
interacting directly with interstellar medium (ISM), and magnetar-powered
outflows. We describe radio, X-ray, and gamma-ray observations of PWNe,
focusing first on integrated spectral-energy distributions (SEDs) and global
spectral properties. High-resolution X-ray imaging of PWNe shows a bewildering
array of morphologies, with jets, trails, and other structures. Several of the
23 so far identified magnetars show evidence for continuous or sporadic
emission of material, sometimes associated with giant flares, and a few
possible "magnetar-wind nebulae" have been recently identified.Comment: 61 pages, 44 figures (reduced in quality for size reasons). Published
in Space Science Reviews, "Jets and Winds in Pulsar Wind Nebulae, Gamma-ray
Bursts and Blazars: Physics of Extreme Energy Release
Pion, kaon, proton and anti-proton transverse momentum distributions from p+p and d+Au collisions at GeV
Identified mid-rapidity particle spectra of , , and
from 200 GeV p+p and d+Au collisions are reported. A
time-of-flight detector based on multi-gap resistive plate chamber technology
is used for particle identification. The particle-species dependence of the
Cronin effect is observed to be significantly smaller than that at lower
energies. The ratio of the nuclear modification factor () between
protons and charged hadrons () in the transverse momentum
range GeV/c is measured to be
(stat)(syst) in minimum-bias collisions and shows little
centrality dependence. The yield ratio of in minimum-bias d+Au
collisions is found to be a factor of 2 lower than that in Au+Au collisions,
indicating that the Cronin effect alone is not enough to account for the
relative baryon enhancement observed in heavy ion collisions at RHIC.Comment: 6 pages, 4 figures, 1 table. We extended the pion spectra from
transverse momentum 1.8 GeV/c to 3. GeV/
Demonstration of the temporal matter-wave Talbot effect for trapped matter waves
We demonstrate the temporal Talbot effect for trapped matter waves using
ultracold atoms in an optical lattice. We investigate the phase evolution of an
array of essentially non-interacting matter waves and observe matter-wave
collapse and revival in the form of a Talbot interference pattern. By using
long expansion times, we image momentum space with sub-recoil resolution,
allowing us to observe fractional Talbot fringes up to 10th order.Comment: 17 pages, 7 figure
Azimuthal anisotropy and correlations in p+p, d+Au and Au+Au collisions at 200 GeV
We present the first measurement of directed flow () at RHIC. is
found to be consistent with zero at pseudorapidities from -1.2 to 1.2,
then rises to the level of a couple of percent over the range . The latter observation is similar to data from NA49 if the SPS rapidities
are shifted by the difference in beam rapidity between RHIC and SPS.
Back-to-back jets emitted out-of-plane are found to be suppressed more if
compared to those emitted in-plane, which is consistent with {\it jet
quenching}. Using the scalar product method, we systematically compared
azimuthal correlations from p+p, d+Au and Au+Au collisions. Flow and non-flow
from these three different collision systems are discussed.Comment: Quark Matter 2004 proceeding, 4 pages, 3 figure
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