16,875 research outputs found
Multi-fluid simulations of chromospheric magnetic reconnection in a weakly ionized reacting plasma
We present results from the first self-consistent multi-fluid simulations of
chromospheric magnetic reconnection in a weakly ionized reacting plasma. We
simulate two dimensional magnetic reconnection in a Harris current sheet with a
numerical model which includes ion-neutral scattering collisions, ionization,
recombination, optically thin radiative loss, collisional heating, and thermal
conduction. In the resulting tearing mode reconnection the neutral and ion
fluids become decoupled upstream from the reconnection site, creating an excess
of ions in the reconnection region and therefore an ionization imbalance. Ion
recombination in the reconnection region, combined with Alfv\'{e}nic outflows,
quickly removes ions from the reconnection site, leading to a fast reconnection
rate independent of Lundquist number. In addition to allowing fast
reconnection, we find that these non-equilibria partial ionization effects lead
to the onset of the nonlinear secondary tearing instability at lower values of
the Lundquist number than has been found in fully ionized plasmas.These
simulations provide evidence that magnetic reconnection in the chromosphere
could be responsible for jet-like transient phenomena such as spicules and
chromospheric jets.Comment: 8 Figures, 32 pages tota
First-Principles Calculation of Electric Field Gradients and Hyperfine Couplings in YBa2Cu3O7
The local electronic structure of YBa2Cu3O7 has been calculated using
first-principles cluster methods. Several clusters embedded in an appropriate
background potential have been investigated. The electric field gradients at
the copper and oxygen sites are determined and compared to previous theoretical
calculations and experiments. Spin polarized calculations with different spin
multiplicities have enabled a detailed study of the spin density distribution
to be made and a simultaneous determination of magnetic hyperfine coupling
parameters. The contributions from on-site and transferred hyperfine fields
have been disentangled with the conclusion that the transferred spin densities
essentially are due to nearest neighbour copper ions only with marginal
influence of ions further away. This implies that the variant temperature
dependencies of the planar copper and oxygen NMR spin-lattice relaxation rates
are only compatible with commensurate antiferromagnetic correlations. The
theoretical hyperfine parameters are compared with those derived from
experimental data.Comment: 14 pages, 12 figures, accepted to appear in EPJ
Off-diagonal disorder in the Anderson model of localization
We examine the localization properties of the Anderson Hamiltonian with
additional off-diagonal disorder using the transfer-matrix method and
finite-size scaling. We compute the localization lengths and study the
metal-insulator transition (MIT) as a function of diagonal disorder, as well as
its energy dependence. Furthermore we investigate the different influence of
odd and even system sizes on the localization properties in quasi
one-dimensional systems. Applying the finite-size scaling approach in
conjunction with a nonlinear fitting procedure yields the critical parameters
of the MIT. In three dimensions, we find that the resulting critical exponent
of the localization length agrees with the exponent for the Anderson model with
pure diagonal disorder.Comment: 12 pages including 4 EPS figures, accepted for publication in phys.
stat. sol. (b
Selective Dynamic Nuclear Spin Polarization in Spin-Blocked Double-Dot
We study the mechanism of dynamical nuclear spin polarization by hyperfine
interaction in spin-blocked double quantum dot system. We calculate the
hyperfine transition rates and solve the master equations for the nuclear
spins. Specifically, we incorporate the effects of the nuclear quadrupole
coupling due to the doping-induced local lattice distortion and strain. Our
results show that nuclear quadrupole coupling induced by the 5% indium
substitution can be used to explain the recent experimental observation of
missing arsenic NMR signal in the spin-blocked double dots.Comment: 4 pages, 3 figure
Detoxification in rehabilitation in England: effective continuity of care or unhappy bedfellows?
There is evidence that residential detoxification alone does not provide satisfactory treatment outcomes and that outcomes are significantly enhanced when clients completing residential detoxification attend rehabilitation services (Gossop, Marsden, Stewart, & Rolfe, 1999; Ghodse, Reynolds, Baldacchino, et al., 2002). One way of increasing the likelihood of this continuity of treatment is by providing detoxification and rehabilitation within the same treatment facility to prevent drop-out, while the client awaits a rehabilitation bed or in the transition process. However, there is little research evidence available on the facilities that offer both medical detoxification and residential rehabilitation. The current study compares self-reported treatment provision in 87 residential rehabilitation services in England, 34 of whom (39.1%) reported that they offered detoxification services within their treatment programmes. Although there were no differences in self-reported treatment philosophies, residential rehabilitation services that offered detoxification were typically of shorter duration overall, had significantly more beds and reported offering more group work than residential rehabilitation services that did not offer detoxification. Outcomes were also different, with twice as many clients discharged on disciplinary grounds from residential rehabilitation services without detoxification facilities. The paper questions the UK classification of residential drug treatment services as either detoxification or rehabilitation and suggests the need for greater research focus on the aims, processes and outcomes of this group of treatment providers
Weak localization and spin splitting in inversion layers on p-type InAs
We report on the magnetoconductivity of quasi two-dimensional electron
systems in inversion layers on p-type InAs single crystals. In low magnetic
fields pronounced features of weak localization and antilocalization are
observed. They are almost perfectly described by the theory of Iordanskii,
Lyanda-Geller and Pikus. This allows us to determine the spin splitting and the
Rashba parameter of the ground electric subband as a function of the electron
density.Comment: Accepted for publication in Phys. Rev. B, 4 page
Self-regulated fueling of galaxy centers: Evidence for star formation feedback
Using new, high-resolution interferometric observations of the CO and HCN molecules, we directly compare the molecular and ionized components of the interstellar medium in the center of the nearby spiral galaxy IC 342, on spatial scales of 10 pc. The morphology of the tracers suggests that the molecular gas flow caused by a large-scale stellar bar has been strongly affected by the mechanical feedback from recent star formation activity within the central 100 pc in the nucleus of the galaxy. Possibly, stellar winds and/or supernova shocks originating in the nuclear star cluster have compressed, and likely pushed outward, the infalling molecular gas, thus significantly reducing the gas supply to the central 10 pc. Although our analysis currently lacks kinematic confirmation due to the face-on orientation of IC 342, the described scenario is supported by the generally observed repetitive nature of star formation in the nuclear star clusters of late-type spiral galaxies
Whole Device Modeling of the FuZE Sheared-Flow-Stabilized Z Pinch
The FuZE sheared-flow-stabilized Z pinch at Zap Energy is simulated using
whole-device modeling employing an axisymmetric resistive magnetohydrodynamic
formulation implemented within the discontinuous Galerkin WARPXM framework.
Simulations show formation of Z pinches with densities of approximately 10^22
m^-3 and total DD fusion neutron rate of 10^7 per {\mu}s for approximately 2
{\mu}s. Simulation-derived synthetic diagnostics show peak currents and
voltages within 10% and total yield within approximately 30% of experiment for
similar plasma mass. The simulations provide insight into the plasma dynamics
in the experiment and enable a predictive capability for exploring design
changes on devices built at Zap Energy.Comment: 8 pages, 9 figures, IAEA FEC 202
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