34,021 research outputs found
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
Altruism and Voluntary Provision of Public Goods.
We study how people's predisposition towards altruism, as measured by tools developed by psychologists, affects their behaviour in a voluntary contributions public good environment. Earlier experiments provide evidence against the strong free rider hypothesis; however, contributions to the public good decrease with repetition. We investigate whether a high level of contributions can be sustained in groups of subjects who have been pre-selected on the basis of their altruistic inclinations. In the first stage of the experiment, each subject responds to a psychology questionnaire that measures various dimensions of one's personality. The subjects are then matched in groups according to their altruism scores, and engage in a voluntary contribution game. We consider whether the levels and dynamics of group contributions differ significantly between the groups with altruists and non-altruists. We find that subjects' altruism has a weak but positive effect on group behaviour in the public good game.PUBLIC OWNERSHIP ; BEHAVIOUR ; GAMES
Part of the D - dimensional Spiked harmonic oscillator spectra
The pseudoperturbative shifted - l expansion technique PSLET [5,20] is
generalized for states with arbitrary number of nodal zeros. Interdimensional
degeneracies, emerging from the isomorphism between angular momentum and
dimensionality of the central force Schrodinger equation, are used to construct
part of the D - dimensional spiked harmonic oscillator bound - states. PSLET
results are found to compare excellenly with those from direct numerical
integration and generalized variational methods [1,2].Comment: Latex file, 20 pages, to appear in J. Phys. A: Math. & Ge
Quantum fluctuations of a vortex in an optical lattice
Using a variational ansatz for the wave function of the Bose-Einstein
condensate, we develop a quantum theory of vortices and quadrupole modes in a
one-dimensional optical lattice. We study the coupling between the quadrupole
modes and Kelvin modes, which turns out to be formally analogous to the theory
of parametric processes in quantum optics. This leads to the possibility of
squeezing vortices. We solve the quantum multimode problem for the Kelvin modes
and quadrupole modes numerically and find properties that cannot be explained
with a simple linear-response theory.Comment: final version, minor change
An in situ instrument for planar O2 optode measurements at benthic interfaces
A new in situ instrument for two‐dimensional mapping of oxygen in coastal sediments is presented. The measuring principle is described, and potential mechanical disturbances, solute and particle smearing associated with the measurements, and calibration routines are evaluated. The first in situ measurements obtained in two different benthic communities are presented. In a shallow photosynthetic sediment (1 m of water depth), an extensive horizontal and temporal variation in the O2 distribution caused by benthic photosynthesis and irrigating fauna was resolved. Repetitive planar optode measurements performed along a transect in central Øresund, Denmark (17 m of water depth) revealed a positive correlation between the apparent O2 penetration depths (OP) measured with a lateral distance <5.0 mm, whereas OP measured with a larger horizontal distance (up to 50 m) were not correlated. Consequently, the OP varied in patches with a characteristic size of 5.0 mm. The instrument described is a powerful new tool for in situ characterization of spatiotemporal variations in O2 distributions within benthic communities. The instrument can be adapted for use at full ocean depths, e.g., on deep‐sea landers or remote operating vehicles
Recommended from our members
Performing Euroscepticism: the UK press and Cameron’s Bloomberg speech
Magnetic properties of -FeCr alloy as calculated with the charge and spin self-consistent KKR(CPA) method
Magnetic properties of a FeCr alloy calculated with
the charge and spin self- consistent Korringa-Kohn-Rostoker (KKR) and combined
with coherent potential approximation (KKR-CPA) methods are reported.
Non-magnetic state as well as various magnetic orderings were considered, i.e.
ferromagnetic (FM) and more complex anti-parallel (called APM) arrangements for
selected sublattices, as follows from the symmetry analysis. It has been shown
that the Stoner criterion applied to non-magnetic density of states at the
Fermi energy, is satisfied for Fe atoms situated on all five lattice
sites, while it is not fulfilled for all Cr atoms. In FM and APM states, the
values of magnetic moments on Fe atoms occupying various sites are dispersed
between 0 and 2.5 , and they are proportional to the number of Fe atoms
in the nearest-neighbor shell. Magnetic moments of Cr atoms havin much smaller
values were found to be coupled antiparallel to those of Fe atoms. The average
value of the magnetic moment per atom was found to be that
is by a factor of 4 larger than the experimental value found for a
FeCr sample. Conversely, admitting an anti-
parallel ordering (APM model) on atoms situated on C and D sites, according to
the group theory and symmetry analysis results, yielded a substantial reduction
of to 0.20 $\mu_B$. Further diminution of to 0.15 ,
which is very close to the experimental value of 0.14 , has been
achieved with the KKR-CPA calculations by considering a chemical disorder on
sites B, C and D
- …