906 research outputs found
Plant pathogens as biological agents for the control of weeds
Weed control is by far the most pervasive and costly need in agriculture, both in underdevel oped as well as in technologically advanced production systems. In 1994, losses due to weeds in U.S. agricultureâincluding herbi cide costs and yield lossesâamounted to over $ 15 billion, and about 96% of the more than 21 million acres of row crops grown in Iowa received at least one chemical herbicide appli cation. Pesticide use statistics reveal that more herbicides are used than any other class of pesticide. Despite the extensive use of herbi cides, certain weed species continue to cause problems in agriculture, and current control strategies for some of these are inadequate. Among these weeds are johnsongrass (Sor ghum halapense), the morning glorys (Ipomoea spp.), nutsedges (Cyperus esculentus), shattercane (Sorghum bicolor), and velvetleaf (Abutillon theophrasti)
Assessing residual reasoning ability in overtly non-communicative patients using fMRI
It is now well established that some patients who are diagnosed as being in a vegetative state or a minimally conscious state show reliable signs of volition that may only be detected by measuring neural responses. A pertinent question is whether these patients are also capable of logical thought. Here, we validate an fMRI paradigm that can detect the neural fingerprint of reasoning processes and moreover, can confirm whether a participant derives logical answers. We demonstrate the efficacy of this approach in a physically non-communicative patient who had been shown to engage in mental imagery in response to simple audi- tory instructions. Our results demonstrate that this individual retains a remarkable capacity for higher cogni- tion, engaging in the reasoning task and deducing logical answers. We suggest that this approach is suitable for detecting residual reasoning ability using neural responses and could readily be adapted to assess other aspects of cognition
Inertial modes of neutron stars with the superfluid core
We investigate the modal properties of inertial modes of rotating neutron
stars with the core filled with neutron and proton superfluids, taking account
of entrainment effects between the superfluids. In this paper, the entrainment
effects are modeled by introducing a parameter so that no entrainment
state is realized at . We find that inertial modes of rotating neutron
stars with the superfluid core are split into two families, which we call
ordinary fluid inertial modes (-mode) and superfluid inertial modes
(-mode). The two superfluids in the core counter-move for the -modes.
For the -modes, is only weakly
dependent on the entrainment parameter , where and are
the angular frequency of rotation and the oscillation frequency observed in the
corotating frame of the star, respectively. For the -modes, on the other
hand, almost linearly increases as increases. Avoided
crossings as functions of are therefore quite common between - and
-modes. We find that some of the -modes that are unstable against the
gravitational radiation reaction at become stable when is
larger than , the value of which depends on the mode. Since the
radiation driven instability associated with the current multipole radiation is
quite weak for the inertial modes and the mutual friction damping in the
superfluid core is strong, the instability caused by the inertial modes will be
easily suppressed unless the entrainment parameter is extremely small
and the mutual friction damping is sufficiently weak.Comment: 19 pages, 20 figures. To appear in MNRA
Constraining the physics of the r-mode instability in neutron stars with X-ray and UV observations
Rapidly rotating Neutron Stars in Low Mass X-ray Binaries (LMXBs) may be an
interesting source of Gravitational Waves (GWs). In particular, several modes
of stellar oscillation may be driven unstable by GW emission, and this can lead
to a detectable signal. Here we illustrate how current X-ray and ultra-violet
(UV) observations can constrain the physics of the r-mode instability. We show
that the core temperatures inferred from the data would place many systems well
inside the unstable region predicted by standard physical models. However, this
is at odds with theoretical expectations. We discuss different mechanisms that
could be at work in the stellar interior, and we show how they can modify the
instability window and make it consistent with the inferred temperatures.Comment: Submitted to MNRA
Remote Sensing D/H Ratios in Methane Ice: Temperature-Dependent Absorption Coefficients of CH3D in Methane Ice and in Nitrogen Ice
The existence of strong absorption bands of singly deuterated methane (CH3D)
at wavelengths where normal methane (CH4) absorbs comparatively weakly could
enable remote measurement of D/H ratios in methane ice on outer solar system
bodies. We performed laboratory transmission spectroscopy experiments,
recording spectra at wavelengths from 1 to 6 \mum to study CH3D bands at 2.47,
2.87, and 4.56 \mum, wavelengths where ordinary methane absorption is weak. We
report temperature-dependent absorption coefficients of these bands when the
CH3D is diluted in CH4 ice and also when it is dissolved in N2 ice, and
describe how these absorption coefficients can be combined with data from the
literature to simulate arbitrary D/H ratio absorption coefficients for CH4 ice
and for CH4 in N2 ice. We anticipate these results motivating new telescopic
observations to measure D/H ratios in CH4 ice on Triton, Pluto, Eris, and
Makemake.Comment: 17 pages, 7 figure
The r-modes in accreting neutron stars with magneto-viscous boundary layers
We explore the dynamics of the r-modes in accreting neutron stars in two
ways. First, we explore how dissipation in the magneto-viscous boundary layer
(MVBL) at the crust-core interface governs the damping of r-mode perturbations
in the fluid interior. Two models are considered: one assuming an
ordinary-fluid interior, the other taking the core to consist of superfluid
neutrons, type II superconducting protons, and normal electrons. We show,
within our approximations, that no solution to the magnetohydrodynamic
equations exists in the superfluid model when both the neutron and proton
vortices are pinned. However, if just one species of vortex is pinned, we can
find solutions. When the neutron vortices are pinned and the proton vortices
are unpinned there is much more dissipation than in the ordinary-fluid model,
unless the pinning is weak. When the proton vortices are pinned and the neutron
vortices are unpinned the dissipation is comparable or slightly less than that
for the ordinary-fluid model, even when the pinning is strong. We also find in
the superfluid model that relatively weak radial magnetic fields ~ 10^9 G (10^8
K / T)^2 greatly affect the MVBL, though the effects of mutual friction tend to
counteract the magnetic effects. Second, we evolve our two models in time,
accounting for accretion, and explore how the magnetic field strength, the
r-mode saturation amplitude, and the accretion rate affect the cyclic evolution
of these stars. If the r-modes control the spin cycles of accreting neutron
stars we find that magnetic fields can affect the clustering of the spin
frequencies of low mass x-ray binaries (LMXBs) and the fraction of these that
are currently emitting gravitational waves.Comment: 19 pages, 8 eps figures, RevTeX; corrected minor typos and added a
referenc
Gravitational field and equations of motion of spinning compact binaries to 2.5 post-Newtonian order
We derive spin-orbit coupling effects on the gravitational field and
equations of motion of compact binaries in the 2.5 post-Newtonian approximation
to general relativity, one PN order beyond where spin effects first appear. Our
method is based on that of Blanchet, Faye, and Ponsot, who use a post-Newtonian
metric valid for general (continuous) fluids and represent pointlike compact
objects with a delta-function stress-energy tensor, regularizing divergent
terms by taking the Hadamard finite part. To obtain post-Newtonian spin
effects, we use a different delta-function stress-energy tensor introduced by
Bailey and Israel. In a future paper we will use the 2.5PN equations of motion
for spinning bodies to derive the gravitational-wave luminosity and phase
evolution of binary inspirals, which will be useful in constructing matched
filters for signal analysis. The gravitational field derived here may help in
posing initial data for numerical evolutions of binary black hole mergers.Comment: 18 pages, no figur
r-modes in Relativistic Superfluid Stars
We discuss the modal properties of the -modes of relativistic superfluid
neutron stars, taking account of the entrainment effects between superfluids.
In this paper, the neutron stars are assumed to be filled with neutron and
proton superfluids and the strength of the entrainment effects between the
superfluids are represented by a single parameter . We find that the
basic properties of the -modes in a relativistic superfluid star are very
similar to those found for a Newtonian superfluid star. The -modes of a
relativistic superfluid star are split into two families, ordinary fluid-like
-modes (-mode) and superfluid-like -modes (-mode). The two
superfluids counter-move for the -modes, while they co-move for the
-modes. For the -modes, the quantity is
almost independent of the entrainment parameter , where and
are the azimuthal wave number and the oscillation frequency observed by an
inertial observer at spatial infinity, respectively. For the -modes, on
the other hand, almost linearly increases with increasing . It
is also found that the radiation driven instability due to the -modes is
much weaker than that of the -modes because the matter current associated
with the axial parity perturbations almost completely vanishes.Comment: 14 pages, 4 figures. To appear in Physical Review
TSPO: kaleidoscopic 18-kDa amid biochemical pharmacology, control and targeting of mitochondria
The 18-kDa translocator protein (TSPO) localizes in the outer mitochondrial membrane (OMM) of cells and is readily up-regulated under various pathological conditions such as cancer, inflammation, mechanical lesions and neurological diseases. Able to bind with high affinity synthetic and endogenous ligands, its core biochemical function resides in the translocation of cholesterol into the mitochondria influencing the subsequent steps of (neuro-)steroid synthesis and systemic endocrine regulation. Over the years, however, TSPO has also been linked to core cellular processes such as apoptosis and autophagy. It interacts and forms complexes with other mitochondrial proteins such as the voltage-dependent anion channel (VDAC) via which signalling and regulatory transduction of these core cellular events may be influenced. Despite nearly 40 years of study, the precise functional role of TSPO beyond cholesterol trafficking remains elusive even though the recent breakthroughs on its high-resolution crystal structure and contribution to quality-control signalling of mitochondria. All this along with a captivating pharmacological profile provides novel opportunities to investigate and understand the significance of this highly conserved protein as well as contribute the development of specific therapeutics as presented and discussed in the present review
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