28,177 research outputs found
Coefficients and terms of the liquid drop model and mass formula
The coefficients of different combinations of terms of the liquid drop model
have been determined by a least square fitting procedure to the experimental
atomic masses. The nuclear masses can also be reproduced using a Coulomb radius
taking into account the increase of the ratio with increasing
mass, the fitted surface energy coefficient remaining around 18 MeV
Electron spin interferometry using a semiconductor ring structure
A ring structure fabricated from GaAs is used to achieve interference of the
net spin polarization of conduction band electrons. Optically polarized spins
are split into two packets by passing through two arms of the ring in the
diffusive transport regime. Optical pumping with circularly polarized light on
one arm establishes dynamic nuclear polarization which acts as a local
effective magnetic field on electron spins due to the hyperfine interaction.
This local field causes one spin packet to precess faster than the other,
thereby controlling the spin interference when the two packets are combined.Comment: 4 pages, 2 figure
Study of advanced rotary combustion engines for commuter aircraft
Performance, weight, size, and maintenance data for advanced rotary aircraft engines suitable for comparative commuter aircraft system evaluation studies of alternate engine candidates are provided. These are turbocharged, turbocompounded, direct injected, stratified charge rotary engines. Hypothetical engines were defined (an RC4-74 at 895 kW and an RC6-87 at 1490 kW) based on the technologies and design approaches used in the highly advanced engine of a study of advanced general aviation rotary engines. The data covers the size range of shaft power from 597 kW (800 hp) to 1865 kW (2500 hp) and is in the form of drawings, tables, curves and written text. These include data on internal geometry and configuration, installation information, turbocharging and turbocompounding arrangements, design features and technologies, engine cooling, fuels, scaling for weight size BSFC and heat rejection for varying horsepower, engine operating and performance data, and TBO and maintenance requirements. The basic combustion system was developed and demonstrated; however the projected power densities and performance efficiencies require increases in engine internal pressures, thermal loading, and rotative speed
Surface tension in a compressible liquid-drop model: Effects on nuclear density and neutron skin thickness
We examine whether or not the surface tension acts to increase the nucleon
density in the nuclear interior within a compressible liquid-drop model. We
find that it depends on the density dependence of the surface tension, which
may in turn be deduced from the neutron skin thickness of stable nuclei.Comment: 4 pages, 1 figure, to be published in Physical Review
Antiferromagnetic s-d exchange coupling in GaMnAs
Measurements of coherent electron spin dynamics in
Ga(1-x)Mn(x)As/Al(0.4)Ga(0.6)As quantum wells with 0.0006% < x < 0.03% show an
antiferromagnetic (negative) exchange bewteen s-like conduction band electrons
and electrons localized in the d-shell of the Mn2+ impurities. The magnitude of
the s-d exchange parameter, N0 alpha, varies as a function of well width
indicative of a large and negative contribution due to kinetic exchange. In the
limit of no quantum confinement, N0 alpha extrapolates to -0.09 +/- 0.03 eV
indicating that antiferromagnetic s-d exchange is a bulk property of GaMnAs.
Measurements of the polarization-resolved photoluminescence show strong
discrepancy from a simple model of the exchange enhanced Zeeman splitting,
indicative of additional complexity in the exchange split valence band.Comment: 5 pages, 4 figures and one action figur
Large N lattice QCD and its extended strong-weak connection to the hypersphere
We calculate an effective Polyakov line action of QCD at large Nc and large
Nf from a combined lattice strong coupling and hopping expansion working to
second order in both, where the order is defined by the number of windings in
the Polyakov line. We compare with the action, truncated at the same order, of
continuum QCD on S^1 x S^d at weak coupling from one loop perturbation theory,
and find that a large Nc correspondence of equations of motion found in
\cite{Hollowood:2012nr} at leading order, can be extended to the next order.
Throughout the paper, we review the background necessary for computing higher
order corrections to the lattice effective action, in order to make higher
order comparisons more straightforward.Comment: 33 pages, 7 figure
Optoelectronic control of spin dynamics at near-THz frequencies in magnetically doped quantum wells
We use time-resolved Kerr rotation to demonstrate the optical and electronic
tuning of both the electronic and local moment (Mn) spin dynamics in
electrically gated parabolic quantum wells derived from II-VI diluted magnetic
semiconductors. By changing either the electrical bias or the laser energy, the
electron spin precession frequency is varied from 0.1 to 0.8 THz at a magnetic
field of 3 T and at a temperature of 5 K. The corresponding range of the
electrically-tuned effective electron g-factor is an order of magnitude larger
compared with similar nonmagnetic III-V parabolic quantum wells. Additionally,
we demonstrate that such structures allow electrical modulation of local moment
dynamics in the solid state, which is manifested as changes in the amplitude
and lifetime of the Mn spin precession signal under electrical bias. The large
variation of electron and Mn-ion spin dynamics is explained by changes in
magnitude of the sp−d exchange overlap.Comment: 4 pages, 3 figure
Open timelike curves violate Heisenberg's uncertainty principle
Toy models for quantum evolution in the presence of closed timelike curves
(CTCs) have gained attention in the recent literature due to the strange
effects they predict. The circuits that give rise to these effects appear quite
abstract and contrived, as they require non-trivial interactions between the
future and past which lead to infinitely recursive equations. We consider the
special case in which there is no interaction inside the CTC, referred to as an
open timelike curve (OTC), for which the only local effect is to increase the
time elapsed by a clock carried by the system. Remarkably, circuits with access
to OTCs are shown to violate Heisenberg's uncertainty principle, allowing
perfect state discrimination and perfect cloning of coherent states. The model
is extended to wave-packets and smoothly recovers standard quantum mechanics in
an appropriate physical limit. The analogy with general relativistic
time-dilation suggests that OTCs provide a novel alternative to existing
proposals for the behaviour of quantum systems under gravity
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