25,231 research outputs found
Effect of parallel magnetic field on the Zero Differential Resistance State
The non-linear zero-differential resistance state (ZDRS) that occurs for
highly mobile two-dimensional electron systems in response to a dc bias in the
presence of a strong magnetic field applied perpendicular to the electron plane
is suppressed and disappears gradually as the magnetic field is tilted away
from the perpendicular at fixed filling factor . Good agreement is found
with a model that considers the effect of the Zeeman splitting of Landau levels
enhanced by the in-plane component of the magnetic field.Comment: 4 pages, 4 figure
Three-body structure of low-lying 12Be states
We investigate to what extent a description of 12Be as a three-body system
made of an inert 10Be-core and two neutrons is able to reproduce the
experimental 12Be data. Three-body wave functions are obtained with the
hyperspherical adiabatic expansion method. We study the discrete spectrum of
12Be, the structure of the different states, the predominant transition
strengths, and the continuum energy spectrum after high energy fragmentation on
a light target. Two 0+, one 2+, one 1- and one 0- bound states are found where
the first four are known experimentally whereas the 0- is predicted as an
isomeric state. An effective neutron charge, reproducing the measured B(E1)
transition and the charge rms radius in 11Be, leads to a computed B(E1)
transition strength for 12Be in agreement with the experimental value. For the
E0 and E2 transitions the contributions from core excitations could be more
significant. The experimental 10Be-neutron continuum energy spectrum is also
well reproduced except in the energy region corresponding to the 3/2- resonance
in 11Be where core excitations contribute.Comment: 16 pages, 9 figures. Accepted for publication in Physical Review
Spheromak formation and sustainment studies at the sustained spheromak physics experiment using high-speed imaging and magnetic diagnostics
A high-speed imaging system with shutter speeds as fast as 2 ns and double frame capability has been used to directly image the formation and evolution of the sustained spheromak physics experiment (SSPX) [E. B. Hooper et al., Nucl. Fusion 39, 863 (1999)]. Reproducible plasma features have been identified with this diagnostic and divided into three groups, according to the stage in the discharge at which they occur: (i) breakdown and ejection, (ii) sustainment, and (iii) decay. During the first stage, plasma descends into the flux conserver shortly after breakdown and a transient plasma column is formed. The column then rapidly bends and simultaneously becomes too dim to photograph a few microseconds after formation. It is conjectured here that this rapid bending precedes the transfer of toroidal to poloidal flux. During sustainment, a stable plasma column different from the transient one is observed. It has been possible to measure the column diameter and compare it to CORSICA [A. Tarditi et al., Contrib. Plasma Phys. 36, 132 (1996)], a magnetohydrodynamic equilibrium reconstruction code which showed good agreement with the measurements. Elongation and velocity measurements were made of cathode patterns also seen during this stage, possibly caused by pressure gradients or E×B drifts. The patterns elongate in a toroidal-only direction which depends on the magnetic-field polarity. During the decay stage the column diameter expands as the current ramps down, until it eventually dissolves into filaments. With the use of magnetic probes inserted in the gun region, an X point which moved axially depending on current level and toroidal mode number was observed in all the stages of the SSPX plasma discharge
Cosmological Constant and Noncommutativity: A Newtonian point of view
We study a Newtonian cosmological model in the context of a noncommutative
space. It is shown that the trajectories of a test particle undergo
modifications such that it no longer satisfies the cosmological principle. For
the case of a positive cosmological constant, spiral trajectories are obtained
and corrections to the Hubble constant appear. It is also shown that, in the
limit of a strong noncommutative parameter, the model is closely related to a
particle in a G\"odel-type metric.Comment: 14 pages, 3 figures, Introduction was changed and references added.
Final version accepted for publication in JMPL
3D wedge filling and 2D random-bond wetting
Fluids adsorbed in 3D wedges are shown to exhibit two types of continuous
interfacial unbinding corresponding to critical and tricritical filling
respectively. Analytic solution of an effective interfacial model based on the
transfer-matrix formalism allows us to obtain the asymptotic probability
distribution functions for the interfacial height when criticality and
tricriticality are approached. Generalised random walk arguments show that, for
systems with short-ranged forces, the critical singularities at these
transitions are related to 2D complete and critical wetting with random bond
disorder respectively.Comment: 7 pages, 3 figures, accepted for publication in Europhysics Letter
Large Quantum Superpositions and Interference of Massive Nanometer-Sized Objects
We propose a method to prepare and verify spatial quantum superpositions of a
nanometer-sized object separated by distances of the order of its size. This
method provides unprecedented bounds for objective collapse models of the wave
function by merging techniques and insights from cavity quantum optomechanics
and matter wave interferometry. An analysis and simulation of the experiment is
performed taking into account standard sources of decoherence. We provide an
operational parameter regime using present day and planned technology.Comment: 4 pages, 2 figures, to appear in PR
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