153 research outputs found
Impact of energetic particle orbits on long range frequency chirping of BGK modes
Long range frequency chirping of Bernstein-Greene-Kruskal modes, whose
existence is determined by the fast particles, is investigated in cases where
these particles do not move freely and their motion is bounded to restricted
orbits. An equilibrium oscillating potential, which creates different orbit
topologies of energetic particles, is included into the bump-on-tail
instability problem of a plasma wave. With respect to fast particles dynamics,
the extended model captures the range of particles motion (trapped/passing)
with energy and thus represents a more realistic 1D picture of the long range
sweeping events observed for weakly damped modes, e.g. global Alfven
eigenmodes, in tokamaks. The Poisson equation is solved numerically along with
bounce averaging the Vlasov equation in the adiabatic regime. We demonstrate
that the shape and the saturation amplitude of the nonlinear mode structure
depends not only on the amount of deviation from the initial eigenfrequency but
also on the initial energy of the resonant electrons in the equilibrium
potential. Similarly, the results reveal that the resonant electrons following
different equilibrium orbits in the electrostatic potential lead to different
rates of frequency evolution. As compared to the previous model [Breizman B.N.
2010 Nucl. Fusion 50 084014], it is shown that the frequency sweeps with lower
rates. The additional physics included in the model enables a more complete 1D
description of the range of phenomena observed in experiments.Comment: Submitted to Nuclear Fusion 25/01/201
Dynamic interaction of plates in an inhomogeneous transversely isotropic space weakened by a crack
The problem of axisymmetric vibration of a flat thin rigid circular plate located inside a vertically exponentially graded, transversely isotropic material of infinite extent is addressed by means of a displacement potential method. The contact condition on one side of the foundation is assumed to be the perfect adhesion with the media but known to be faced by a penny-shaped crack at the other side as it occurs in anchors. The mixed boundary value problem is formulated with the aid of Hankel integral transforms and is written in the form of a set of singular integral equations. The analytical procedure for the special case of vertical movement of the rigid plate results in a closed form solution. The solution is pursued numerically for the general elastodynamic case. The physical quantities, such as contact stress on the plate and the stress and displacement fields in the non-homogeneous medium are obtained for different materials
Detection of lensing substructure using ALMA observations of the dusty galaxy SDP.81
We study the abundance of substructure in the matter density near galaxies
using ALMA Science Verification observations of the strong lensing system
SDP.81. We present a method to measure the abundance of subhalos around
galaxies using interferometric observations of gravitational lenses. Using
simulated ALMA observations, we explore the effects of various systematics,
including antenna phase errors and source priors, and show how such errors may
be measured or marginalized. We apply our formalism to ALMA observations of
SDP.81. We find evidence for the presence of a
subhalo near one of the images, with a significance of in a joint
fit to data from bands 6 and 7; the effect of the subhalo is also detected in
both bands individually. We also derive constraints on the abundance of dark
matter subhalos down to , pushing down to the
mass regime of the smallest detected satellites in the Local Group, where there
are significant discrepancies between the observed population of luminous
galaxies and predicted dark matter subhalos. We find hints of additional
substructure, warranting further study using the full SDP.81 dataset
(including, for example, the spectroscopic imaging of the lensed carbon
monoxide emission). We compare the results of this search to the predictions of
CDM halos, and find that given current uncertainties in the host halo
properties of SDP.81, our measurements of substructure are consistent with
theoretical expectations. Observations of larger samples of gravitational
lenses with ALMA should be able to improve the constraints on the abundance of
galactic substructure.Comment: 18 pages, 13 figures, Comments are welcom
ALMA observations of atomic carbon in z~4 dusty star-forming galaxies
We present ALMA [CI]() (rest frequency 492 GHz) observations for a
sample of 13 strongly-lensed dusty star-forming galaxies originally discovered
at 1.4mm in a blank-field survey by the South Pole Telescope. We compare these
new data with available [CI] observations from the literature, allowing a study
of the ISM properties of extreme dusty star-forming galaxies spanning
a redshift range . Using the [CI] line as a tracer of the molecular
ISM, we find a mean molecular gas mass for SPT-DSFGs of
M. This is in tension with gas masses derived via low- CO
and dust masses; bringing the estimates into accordance requires either (a) an
elevated CO-to-H conversion factor for our sample of and a gas-to-dust ratio , or (b) an high carbon abundance . Using observations of a range of additional atomic
and molecular lines (including [CI], [CII], and multiple transitions of CO), we
use a modern Photodissociation Region code (3D-PDR) to assess the physical
conditions (including the density, UV radiation field strength, and gas
temperature) within the ISM of the DSFGs in our sample. We find that the ISM
within our DSFGs is characterised by dense gas permeated by strong UV fields.
We note that previous efforts to characterise PDR regions in DSFGs may have
significantly underestimated the density of the ISM. Combined, our analysis
suggests that the ISM of extreme dusty starbursts at high redshift consists of
dense, carbon-rich gas not directly comparable to the ISM of starbursts in the
local Universe.Comment: 21 pages, 12 figures. Accepted for publication in MNRA
Coating mechanisms of single-walled carbon nanotube by linear polyether surfactants: insights from computer simulations
The noncovalent coating of carbon-based nanomaterials, such as carbon nanotubes, has important applications in nanotechnology and nanomedicine. The molecular modeling of this process can clarify its mechanism and provide a tool for the design of novel materials. In this paper, the coating mechanism of single-walled carbon nanotubes (SWCNT) in aqueous solutions by 1,2-dimethoxyethane oxide (DME), 1,2-dimethoxypropane oxide (DMP), poly(ethylene oxide) (PEO), poly(propylene oxide) (PPO) pentamers, and L64 triblock copolymer chains have been studied using molecular dynamics (MD) simulations. The results suggest a preferential binding to the SWCNT surface of the DMP molecules with respect to DME mainly driven by their difference in hydrophobicity. For the longer pentamers, it depends by the chain conformation. PPO isomers with radius of gyration larger than PEO pentamers bind more tightly than those with more compact conformation. In the case of the L64 triblock copolymer, the coating of the SWCNT surface produces a shell of PPO blocks with the PEO chains protruding into bulk water as expected from the so-called nonwrapping binding mechanism of SWCNT. In addition, the polymer coating, in qualitative agreement with experimental evidence on the poor capability of the L64 to disperse SWCNT, do not prevent the formation of CNT aggregates
The Burden of Statin Therapy based on ACC/AHA and NCEP ATP-III Guidelines: An Iranian Survey of Non-Communicable Diseases Risk Factors
To compare the burden of statin therapy according to the Third Adult Treatment Panel (ATP-III) and the American College of Cardiology/American Heart Association (ACC/AHA) guidelines the Survey of Risk Factors of Non-Communicable Disease (SuRFNCD)-2011of Iran was used. A survey analysis associated with sex and age categorization was run. Of total 3496 persons (1322 men) aged 40-70 years, based on the ACC/AHA guidelines, about 46.5 were eligible to receive moderate- to high-intensity statin therapy. Based on the ATP-III guidelines, 17.0 were considered as needing statin drugs. Among adults aged <60 years, the proportion of those who were eligible for statin therapy was higher (38.3) according to the ACC/AHA guidelines compared to the ATP-III guidelines (15.2), a difference more prominent in adults aged �60 years (85.2 versus 25.0). Agreement between the two guidelines was low (kappa: 0.32). Compared to the ATP-III guidelines, the ACC/AHA guidelines increase the number of adults eligible for statin therapy in an Iraninan population from 2.5 million to 7.0 million people according to the 2011 census, specifically in those aged � 60 years, a finding in agreement with those of studies from different countries. © 2018 The Author(s)
Sub-kiloparsec Imaging of Cool Molecular Gas in Two Strongly Lensed Dusty, Star-Forming Galaxies
We present spatially-resolved imaging obtained with the Australia Telescope
Compact Array (ATCA) of three CO lines in two high-redshift gravitationally
lensed dusty star-forming galaxies, discovered by the South Pole Telescope.
Strong lensing allows us to probe the structure and dynamics of the molecular
gas in these two objects, at z=2.78 and z=5.66, with effective source-plane
resolution of less than 1kpc. We model the lensed emission from multiple CO
transitions and the dust continuum in a consistent manner, finding that the
cold molecular gas as traced by low-J CO always has a larger half-light radius
than the 870um dust continuum emission. This size difference leads to up to 50%
differences in the magnification factor for the cold gas compared to dust. In
the z=2.78 galaxy, these CO observations confirm that the background source is
undergoing a major merger, while the velocity field of the other source is more
complex. We use the ATCA CO observations and comparable resolution Atacama
Large Millimeter/submillimeter Array dust continuum imaging of the same objects
to constrain the CO-H_2 conversion factor with three different procedures,
finding good agreement between the methods and values consistent with those
found for rapidly star-forming systems. We discuss these galaxies in the
context of the star formation - gas mass surface density relation, noting that
the change in emitting area with observed CO transition must be accounted for
when comparing high-redshift galaxies to their lower redshift counterparts.Comment: 14 pages, 7 figures; accepted for publication in Ap
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