587 research outputs found
The nonlinear development of the relativistic two-stream instability
The two-stream instability has been mooted as an explanation for a range of
astrophysical applications from GRBs and pulsar glitches to cosmology. Using
the first nonlinear numerical simulations of relativistic multi-species
hydrodynamics we show that the onset and initial growth of the instability is
very well described by linear perturbation theory. In the later stages the
linear and nonlinear description match only qualitatively, and the instability
does not saturate even in the nonlinear case by purely ideal hydrodynamic
effects.Comment: 15 pages, 9 figure
High Level Review of Training Packages - Phase 1 report - An analysis of the current and future context in which Training Packages will need to operate
An analysis of the current and future context in which Training Pac kages will need to operat
Local magneto-shear instability in Newtonian gravity
The magneto-rotational instability (MRI) - which is due to an interplay
between a sheared background and the magnetic field - is commonly considered a
key ingredient for developing and sustaining turbulence in the outer envelope
of binary neutron star merger remnants. To assess whether (or not) the
instability is active and resolved, criteria originally derived in the
accretion disk literature - thus exploiting the symmetries of such systems -
are often used. In this paper we discuss the magneto-shear instability as a
truly local phenomenon, relaxing common symmetry assumptions on the background
on top of which the instability grows. This makes the discussion well-suited
for highly dynamical environments such as binary mergers. We find that -
although this is somewhat hidden in the usual derivation of the MRI dispersion
relation - the instability crucially depends on the assumed symmetries.
Relaxing the symmetry assumptions on the background we find that the role of
the magnetic field is significantly diminished, as it affects the modes' growth
but does not drive it. This suggests that we should not expect the standard
instability criteria to provide a faithful indication/diagnostic of what "is
actually going on" in mergers. We conclude by making contact with a suitable
filtering operation, as this is key to separating background and fluctuations
in highly dynamical systems.Comment: 15 pages, 1 figur
Estimating Lunar Pyroclastic Deposit Depth from Imaging Radar Data: Applications to Lunar Resource Assessment
Lunar pyroclastic deposits represent one of the primary anticipated sources of raw materials for future human settlements. These deposits are fine-grained volcanic debris layers produced by explosive volcanism contemporaneous with the early stage of mare infilling. There are several large regional pyroclastic units on the Moon (for example, the Aristarchus Plateau, Rima Bode, and Sulpicius Gallus formations), and numerous localized examples, which often occur as dark-halo deposits around endogenic craters (such as in the floor of Alphonsus Crater). Several regional pyroclastic deposits were studied with spectral reflectance techniques: the Aristarchus Plateau materials were found to be a relatively homogeneous blanket of iron-rich glasses. One such deposit was sampled at the Apollo 17 landing site, and was found to have ferrous oxide and titanium dioxide contents of 12 percent and 5 percent, respectively. While the areal extent of these deposits is relatively well defined from orbital photographs, their depths have been constrained only by a few studies of partially filled impact craters and by imaging radar data. A model for radar backscatter from mantled units applicable to both 70-cm and 12.6-cm wavelength radar data is presented. Depth estimates from such radar observations may be useful in planning future utilization of lunar pyroclastic deposits
THE EFFECT OF SHOE TYPE ON VARIOUS KINETIC AND KINEMATIC VARIABLES DURING STEP-UP AND STEP-DOWN MOTIONS
The purpose of this study was to examine the effect of shoe type on the biomechanical responses to a stepping task. Participants (n = 8) performed six two minute stepping trials at a stepping rate of 72 bpm; 3 trials in hiking boots and 3 trials in hiking shoes. Lower limb joint angles and moments were calculated using Visual 3D. No significant differences were found in step down peak ground reaction forces (GRF), ankle, knee, and hip range of motion (ROM), joint moments, joint flexion at step down contact, or toe clearance height between footwear conditions. Due to the lack of differences found between footwear conditions, the use of either a hiking shoe or boot may not result in an increased risk of injury, therefore leaving the choice of footwear to the hiker’s personal preference
Crustal failure during binary inspiral
We present the first fully relativistic calculations of the crustal strain
induced in a neutron star by a binary companion at the late stages of inspiral,
employing realistic equations of state for the fluid core and the solid crust.
We show that while the deep crust is likely to fail only shortly before
coalescence, there is a large variation in elastic strain, with the outermost
layers failing relatively early on in the inspiral. We discuss the significance
of the results for both electromagnetic and gravitational-wave astronomy.Comment: 5 pages, 3 eps figure
NF-κB and IKK as therapeutic targets in cancer
The transcription factor NF-κB and associated regulatory factors (including IκB kinase subunits and the IκB family member Bcl-3) are strongly implicated in a variety of hematologic and solid tumor malignancies. A role for NF-κB in cancer cells appears to involve regulation of cell proliferation, control of apoptosis, promotion of angiogenesis, and stimulation of invasion/metastasis. Consistent with a role for NF-κB in oncogenesis are observations that inhibition of NF-κB alone or in combination with cancer therapies leads to tumor cell death or growth inhibition. However, other experimental data indicate that NF-κB can play a tumor suppressor role in certain settings and that it can be important in promoting an apoptotic signal downstream of certain cancer therapy regimens. In order to appropriately move NF-κB inhibitors in the clinic, thorough approaches must be initiated to determine the molecular mechanisms that dictate the complexity of oncologic and therapeutic outcomes that are controlled by NF-κB
Tidal deformations of neutron stars: The role of stratification and elasticity
We discuss the response of neutron stars to the tidal interaction in a
compact binary system, as encoded in the Love number associated with the
induced deformation. This problem is of interest for gravitational-wave
astronomy as there may be a detectable imprint on the signal from the late
stages of binary coalescence. Previous work has focussed on simple barotropic
neutron star models, providing an understanding of the role of the stellar
compactness and overall density profile. We add realism to the discussion by
developing the framework required to model stars with varying composition and
an elastic crust. These effects are not expected to be significant for the next
generation of detectors but it is nevertheless useful to be able to quantify
them. Our results show that (perhaps surprisingly) internal stratification has
no impact whatsoever on the Love number. We also show that crust elasticity
provides a (predictably) small correction to existing models.Comment: 16 pages, RevTeX, 3 eps figure
Ammonium chloride ingestion attenuates exercise-induced mRNA levels in human muscle
Minimizing the decrease in intracellular pH during high-intensity exercise training promotes greater improvements in mitochondrial respiration. This raises the intriguing hypothesis that pH may affect the exercise-induced transcription of genes that regulate mitochondrial biogenesis. Eight males performed 10x2-min cycle intervals at 80% VO2speak intensity on two occasions separated by ~2 weeks. Participants ingested either ammonium chloride (ACID) or calcium carbonate (PLA) the day before and on the day of the exercise trial in a randomized, counterbalanced order, using a crossover design. Biopsies were taken from the vastus lateralis muscle before and after exercise. The mRNA level of peroxisome proliferator-activated receptor co-activator 1α (PGC-1α), citrate synthase, cytochome c and FOXO1 was elevated at rest following ACID (P<0.05). During the PLA condition, the mRNA content of mitochondrial- and glucose-regulating proteins was elevated immediately following exercise (P<0.05). In the early phase (0-2 h) of post-exercise recovery during ACID, PGC-1α, citrate synthase, cytochome C, FOXO1, GLUT4, and HKII mRNA levels were not different from resting levels (P>0.05); the difference in PGC-1α mRNA content 2 h post-exercise between ACID and PLA was not significant (P = 0.08). Thus, metabolic acidosis abolished the early post-exercise increase of PGC-1α mRNA and the mRNA of downstream mitochondrial and glucose-regulating proteins. These findings indicate that metabolic acidosis may affect mitochondrial biogenesis, with divergent responses in resting and post-exercise skeletal muscle
Numerical relativity with characteristic evolution, using six angular patches
The characteristic approach to numerical relativity is a useful tool in
evolving gravitational systems. In the past this has been implemented using two
patches of stereographic angular coordinates. In other applications, a
six-patch angular coordinate system has proved effective. Here we investigate
the use of a six-patch system in characteristic numerical relativity, by
comparing an existing two-patch implementation (using second-order finite
differencing throughout) with a new six-patch implementation (using either
second- or fourth-order finite differencing for the angular derivatives). We
compare these different codes by monitoring the Einstein constraint equations,
numerically evaluated independently from the evolution. We find that, compared
to the (second-order) two-patch code at equivalent resolutions, the errors of
the second-order six-patch code are smaller by a factor of about 2, and the
errors of the fourth-order six-patch code are smaller by a factor of nearly 50.Comment: 12 pages, 5 figures, submitted to CQG (special NFNR issue
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