54,429 research outputs found
Asymptotic iteration method for eigenvalue problems
An asymptotic interation method for solving second-order homogeneous linear
differential equations of the form y'' = lambda(x) y' + s(x) y is introduced,
where lambda(x) \neq 0 and s(x) are C-infinity functions. Applications to
Schroedinger type problems, including some with highly singular potentials, are
presented.Comment: 14 page
Limits on entanglement in rotationally-invariant scattering of spin systems
This paper investigates the dynamical generation of entanglement in
scattering systems, in particular two spin systems that interact via
rotationally-invariant scattering. The spin degrees of freedom of the in-states
are assumed to be in unentangled, pure states, as defined by the entropy of
entanglement. Because of the restriction of rotationally-symmetric
interactions, perfectly-entangling S-matrices, i.e. those that lead to a
maximally entangled out-state, only exist for a certain class of separable
in-states. Using Clebsch-Gordan coefficients for the rotation group, the
scattering phases that determine the S-matrix are determined for the case of
spin systems with , 1, and 3/2.Comment: 6 pages, no figures; v.2: sections added, edited for clarity,
conclusions and calculation unchanged, typos corrected; v.3: new abstrct,
revised first two sections, added reference
Perturbation expansions for a class of singular potentials
Harrell's modified perturbation theory [Ann. Phys. 105, 379-406 (1977)] is
applied and extended to obtain non-power perturbation expansions for a class of
singular Hamiltonians H = -D^2 + x^2 + A/x^2 + lambda/x^alpha, (A\geq 0, alpha
> 2), known as generalized spiked harmonic oscillators. The perturbation
expansions developed here are valid for small values of the coupling lambda >
0, and they extend the results which Harrell obtained for the spiked harmonic
oscillator A = 0. Formulas for the the excited-states are also developed.Comment: 23 page
General energy bounds for systems of bosons with soft cores
We study a bound system of N identical bosons interacting by model pair
potentials of the form V(r) = A sgn(p)r^p + B/r^2, A > 0, B >= 0. By using a
variational trial function and the `equivalent 2-body method', we find explicit
upper and lower bound formulas for the N-particle ground-state energy in
arbitrary spatial dimensions d > 2 for the two cases p = 2 and p = -1. It is
demonstrated that the upper bound can be systematically improved with the aid
of a special large-N limit in collective field theory
The relationship between Hippocampal asymmetry and working memory processing in combat-related PTSD: a monozygotic twin study
BACKGROUND: PTSD is associated with reduction in hippocampal volume and abnormalities in hippocampal function. Hippocampal asymmetry has received less attention, but potentially could indicate lateralised differences in vulnerability to trauma. The P300 event-related potential component reflects the immediate processing of significant environmental stimuli and has generators in several brain regions including the hippocampus. P300 amplitude is generally reduced in people with PTSD. METHODS: Our study examined hippocampal volume asymmetry and the relationship between hippocampal asymmetry and P300 amplitude in male monozygotic twins discordant for Vietnam combat exposure. Lateralised hippocampal volume and P300 data were obtained from 70 male participants, of whom 12 had PTSD. We were able to compare (1) combat veterans with current PTSD; (2) their non-combat-exposed co-twins; (3) combat veterans without current PTSD and (4) their non-combat-exposed co-twins. RESULTS: There were no significant differences between groups in hippocampal asymmetry. There were no group differences in performance of an auditory oddball target detection task or in P300 amplitude. There was a significant positive correlation between P300 amplitude and the magnitude of hippocampal asymmetry in participants with PTSD. CONCLUSIONS: These findings suggest that greater hippocampal asymmetry in PTSD is associated with a need to allocate more attentional resources when processing significant environmental stimuli.Timothy Hall, Cherrie Galletly, C.R. Clark, Melinda Veltmeyer, Linda J. Metzger, Mark W. Gilbertson, Scott P. Orr, Roger K. Pitman and Alexander McFarlan
Proof of Rounding by Quenched Disorder of First Order Transitions in Low-Dimensional Quantum Systems
We prove that for quantum lattice systems in d<=2 dimensions the addition of
quenched disorder rounds any first order phase transition in the corresponding
conjugate order parameter, both at positive temperatures and at T=0. For
systems with continuous symmetry the statement extends up to d<=4 dimensions.
This establishes for quantum systems the existence of the Imry-Ma phenomenon
which for classical systems was proven by Aizenman and Wehr. The extension of
the proof to quantum systems is achieved by carrying out the analysis at the
level of thermodynamic quantities rather than equilibrium states.Comment: This article presents the detailed derivation of results which were
announced in Phys. Rev. Lett. 103 (2009) 197201 (arXiv:0907.2419). v3
incorporates many corrections and improvements resulting from referee
comment
Variational analysis for a generalized spiked harmonic oscillator
A variational analysis is presented for the generalized spiked harmonic
oscillator Hamiltonian operator H, where H = -(d/dx)^2 + Bx^2+ A/x^2 +
lambda/x^alpha, and alpha and lambda are real positive parameters. The
formalism makes use of a basis provided by exact solutions of Schroedinger's
equation for the Gol'dman and Krivchenkov Hamiltonian (alpha = 2), and the
corresponding matrix elements that were previously found. For all the discrete
eigenvalues the method provides bounds which improve as the dimension of the
basis set is increased. Extension to the N-dimensional case in arbitrary
angular-momentum subspaces is also presented. By minimizing over the free
parameter A, we are able to reduce substantially the number of basis functions
needed for a given accuracy.Comment: 15 pages, 1 figur
Spiked oscillators: exact solution
A procedure to obtain the eigenenergies and eigenfunctions of a quantum
spiked oscillator is presented. The originality of the method lies in an
adequate use of asymptotic expansions of Wronskians of algebraic solutions of
the Schroedinger equation. The procedure is applied to three familiar examples
of spiked oscillators
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