2,186 research outputs found
Confined One Dimensional Harmonic Oscillator as a Two-Mode System
The one-dimensional harmonic oscillator in a box problem is possibly the
simplest example of a two-mode system. This system has two exactly solvable
limits, the harmonic oscillator and a particle in a (one-dimensional) box. Each
of the two limits has a characteristic spectral structure describing the two
different excitation modes of the system. Near each of these limits, one can
use perturbation theory to achieve an accurate description of the eigenstates.
Away from the exact limits, however, one has to carry out a matrix
diagonalization because the basis-state mixing that occurs is typically too
large to be reproduced in any other way. An alternative to casting the problem
in terms of one or the other basis set consists of using an "oblique" basis
that uses both sets. Through a study of this alternative in this
one-dimensional problem, we are able to illustrate practical solutions and
infer the applicability of the concept for more complex systems, such as in the
study of complex nuclei where oblique-basis calculations have been successful.
Keywords: one-dimensional harmonic oscillator, particle in a box, exactly
solvable models, two-mode system, oblique basis states, perturbation theory,
coherent states, adiabatic mixing.Comment: 11 pages and 9 figures; Submitted to American Journal of Physic
Local Single- and Two-Phase Heat Transfer from an Impinging Cross-Shaped Jet
Local single- and two-phase heat transfer distributions are measured under a confined impinging jet issuing from a cross-shaped orifice. Spatially resolved temperature maps and convection coefficients resulting from the impinging flow are obtained via infrared imaging of a thin-foil heat source. The cooling patterns in single- and two-phase operation are explained by an accompanying numerical investigation of the fluid flow issuing from the orifice; computed velocity magnitudes and turbulence intensities are presented. In single-phase operation, the coolest surface temperatures correspond to areas with high liquid velocities. High velocities and developing turbulence are also shown to increase convective heat transfer along the diagonal outflow directions from the impinging jet. During two-phase transport, boiling preferentially begins in regions of low velocity, providing enhanced heat transfer in the areas least affected by the impingement. The cross-shaped orifice achieves local heat transfer coefficients that exceed the stagnation-point value of a circular jet of equivalent open orifice area by up to 1.5 times, while resulting in an increased pressure drop only 1.1 times higher than that of the circular jet
Efimov states and their Fano resonances in a neutron-rich nucleus
Asymmetric resonances in elastic n+C scattering are attributed to
Efimov states of such neutron-rich nuclei, that is, three-body bound states of
the n+n+C system when none of the pairs is bound or some of them only
weakly bound. By fitting to the general resonance shape described by Fano, we
extract resonance position, width, and the "Fano profile index". While Efimov
states have been discussed extensively in many areas of physics, there is only
one very recent experimental observation in trimers of cesium atoms. The
conjunction that we present of the Efimov and Fano phenomena may lead to
experimental realization in nuclei.Comment: 4 double-column pages, 3 figure
A Tomographic-PIV Investigation of Vapor-Induced Flow Structures in Confined Jet Impingement Boiling
Tomographic particle image velocimetry (PIV) is used to study the effect of confinement gap height on the liquid flow characteristics in jet impingement boiling. This first application of tomographic PIV to flow boiling is significant given the complexity of confined two-phase jet impingement. A jet of subcooled wa- ter at a Reynolds number of 5,0 0 0 impinges onto a circular heat source undergoing boiling heat transfer at a constant heat input. Confinement gap heights of 8, 4, and 2 jet diameters are investigated. A visual hull method is used to reconstruct the time-varying regions of the vapor in the flow. The vapor motion is found to govern the liquid flow pattern and turbulence generation in the confinement gap. Time-averaged velocities and regions of turbulent kinetic energy in the liquid are highest for a confinement gap height of 8 jet diameters, with lower velocity magnitude and turbulence being observed for the smaller spac- ings. Coherent vortical structures identified with the λ2 -criterion are found to occur most frequently near the moving vapor interface. The most intense regions of turbulent kinetic energy do not coincide with the location of coherent structures within the flow. Irrotational velocity fluctuations in the liquid phase caused by vapor bubble pinch-offare the primary cause of the high turbulent kinetic energy measured in these regions. At a gap height of H / d = 2 the vapor plume is constrained as it grows from the heat source, causing bulk flow oscillations in the downstream region of the confinement gap
Algebraic characterization of X-states in quantum information
A class of two-qubit states called X-states are increasingly being used to
discuss entanglement and other quantum correlations in the field of quantum
information. Maximally entangled Bell states and "Werner" states are subsets of
them. Apart from being so named because their density matrix looks like the
letter X, there is not as yet any characterization of them. The su(2) X su(2) X
u(1) subalgebra of the full su(4) algebra of two qubits is pointed out as the
underlying invariance of this class of states. X-states are a seven-parameter
family associated with this subalgebra of seven operators. This recognition
provides a route to preparing such states and also a convenient algebraic
procedure for analytically calculating their properties. At the same time, it
points to other groups of seven-parameter states that, while not at first sight
appearing similar, are also invariant under the same subalgebra. And it opens
the way to analyzing invariant states of other subalgebras in bipartite
systems.Comment: 4 pages, 1 figur
SASE FEL Storage Ring
We explore the possibility of operating a SASE FEL with a Storage Ring. We
use a semi-analytical model to obtain the evolution inside the undulator by
taking into account the interplay on the laser dynamics due to the induced
energy spread and to the radiation damping. We obtain the Renieri's limit for
the stationary output power and discuss the possibility of including in our
model the effect of the beam instabilities.Comment: 5 page
Anomalous Elasticity of Polymer Cholesterics
We show that polymer cholesterics have much longer pitches than comparable
short molecule cholesterics, due to their anomalous elasticity. The pitch
of a chiral mixture with concentration near the racemic (non-chiral)
concentration diverges like with (for short molecule cholesterics ). The short molecule law is
recovered for polymers of finite molecular length once the pitch is
longer than a length that diverges like with . Our predictions could be tested by measurements of the pitch in DNA.Comment: 12 pages, Plain TeX, (1 postscript figure, compressed, uuencoded and
appended to paper), minor corrections, IASSNS-HEP-94/4
Pair creation: back-reactions and damping
We solve the quantum Vlasov equation for fermions and bosons, incorporating
spontaneous pair creation in the presence of back-reactions and collisions.
Pair creation is initiated by an external impulse field and the source term is
non-Markovian. A simultaneous solution of Maxwell's equation in the presence of
feedback yields an internal current and electric field that exhibit plasma
oscillations with a period tau_pl. Allowing for collisions, these oscillations
are damped on a time-scale, tau_r, determined by the collision frequency.
Plasma oscillations cannot affect the early stages of the formation of a
quark-gluon plasma unless tau_r >> tau_pl and tau_pl approx. 1/Lambda_QCD
approx 1 fm/c.Comment: 16 pages, 6 figure, REVTEX, epsfig.st
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