24,939 research outputs found
Angular Momentum Distribution Function of the Laughlin Droplet
We have evaluated the angular-momentum distribution functions for finite
numbers of electrons in Laughlin states. For very small numbers of electrons
the angular-momentum state occupation numbers have been evaluated exactly while
for larger numbers of electrons they have been obtained from Monte-Carlo
estimates of the one-particle density matrix. An exact relationship, valid for
any number of electrons, has been derived for the ratio of the occupation
numbers of the two outermost orbitals of the Laughlin droplet and is used to
test the accuracy of the MC calculations. We compare the occupation numbers
near the outer edges of the droplets with predictions based on the chiral
Luttinger liquid picture of Laughlin state edges and discuss the surprisingly
large oscillations in occupation numbers which occur for angular momenta far
from the edge.Comment: 11 pages of RevTeX, 2 figures available on request. IUCM93-00
Spam - solutions and their problems
We analyze the success of filtering as a solution to the spam problem when used alone or concurrently with sender and/or receiver pricing. We find that filters alone may exacerbate the spam problem if the spammer attempts to evade them by sending multiple variants of the message to each consumer. Sender and receiver prices can effectively reduce or eliminating spam, either on their own or when used together with filtering. Finally, we discuss the impli- cations for social welfare of using the different spam controls.Spam; filtering; email; receiver pricing; sender pricing
Existence Advertising, Price Competition, and Asymmetric Market Structure
We examine a two stage duopoly game in which firms advertise their existence to consumers in stage 1 and compete in prices in stage 2. Whenever the advertising technology generates positive overlap in customer bases the equilib- rium for the stage 1 game is asymmetric in that one firm chooses to remain small in comparison to its competitor. For a specific random advertising technology we show that one firm will always be half as large as the other. No equilibrium in pure price strategies exists in the stage 2 game and as long as there is some overlap in customer bases the mixed strategy equilibrium is far from the Bertrand equilibrium.Existence advertising; price dispersion; Bertrand paradox; information; duopoly
Streda-like formula in spin Hall effect
A generalized Streda formula is derived for the spin transport in spin-orbit
coupled systems. As compared with the original Streda formula for charge
transport, there is an extra contribution of the spin Hall conductance whenever
the spin is not conserved. For recently studied systems with quantum spin Hall
effect in which the z-component spin is conserved, this extra contribution
vanishes and the quantized value of spin Hall conductivity can be reproduced in
the present approach. However, as spin is not conserved in general, this extra
contribution can not be neglected, and the quantization is not exact.Comment: 4 pages, no figur
Numerical Tests of the Chiral Luttinger Liquid Theory for Fractional Hall Edges
We report on microscopic numerical studies which support the chiral Luttinger
liquid theory of the fractional Hall edge proposed by Wen. Our calculations are
based in part on newly proposed and accurate many-body trial wavefunctions for
the low-energy edge excitations of fractional incompressible states.Comment: 12 pages + 1 figure, Revte
Technology development: A partnership that makes sense
Discussed here is an approach to how academic institutions, government entities, and industrial organizations can work effectively to utilize their relative strengths to more effectively meet common goals. The discussion relates to the University of Houston-Clear Lake (UHCL) Research Institute for Computing and Information Systems (RICIS) Program to bring about this type of triad in the Clear Lake area. It is concluded that the interfaces among these groups must remain independent to maintain a healthy counterbalance to their respective entities. However, each entity can and must understand the entire mechanism to exploit each interface to the fullest. Only through such cooperation can the continued technical success of the NASA/Clear Lake area be assured
Can we evaluate population screening strategies in UK general practice? A pilot randomised controlled trial comparing postal and opportunistic screening for genital chlamydial infection
STUDY OBJECTIVE: To assess whether opportunistic and postal screening strategies for Chlamydia trachomatis can be compared with usual care in a randomised trial in general practice
DESIGN: Feasibility study for a randomised controlled trial.
SETTING: Three West of Scotland general medical practices: one rural, one urban/deprived and one urban/affluent.
PARTICIPANTS: 600 women aged 16-30 years, 200 from each of three participating practices selected at random from a sample of West of Scotland practices that had expressed interest in the study. The women could opt out of the study. Those who did not were randomly assigned to one of three groups: postal screening, opportunistic screening or usual care.
MAIN RESULTS: 38% (85/221) of the approached practices expressed interest in the study. Data were collected successfully from the 3 participating practices, although intensive support was required. There were considerable workload implications for staff, both in relation to implementing the screening strategies and managing the research process.
124 of the 600 women opted out of the study. During the four-month study period, 55% (81/146) of the control group attended their practice but none was offered screening. 59% (80/136) women in the opportunistic group attended their practice of whom 55% (44/80) were offered screening. Of those, 64% (28/44) accepted, representing 21% of the opportunistic group. 48% (59/124) of the postal group returned samples.
CONCLUSION: A randomised controlled trial comparing postal and opportunistic screening for chlamydial infection in general practice is feasible, though resource intensive. There may be problems with generalising from screening trials in which patients may opt out from the offer of screening
A novel platform for two-dimensional chiral topological superconductivity
We show that the surface of an -wave superconductor decorated with a
two-dimensional lattice of magnetic impurities can exhibit chiral topological
superconductivity. If impurities order ferromagnetically and the
superconducting surface supports a sufficiently strong Rashba-type spin-orbit
coupling, Shiba sub-gap states at impurity locations can hybridize into
Bogoliubov bands with non-vanishing, sometimes large, Chern number . This
topological superconductor supports chiral Majorana edge modes. We
construct phase diagrams for model two-dimensional superconductors, accessing
the dilute and dense magnetic impurity limits analytically and the intermediate
regime numerically. To address potential experimental systems, we identify
stable configurations of ferromagnetic iron atoms on the Pb (111) surface and
conclude that ferromagnetic adatoms on Pb surfaces can provide a versatile
platform for two-dimensional topological superconductivity
Collective excitations in double-layer quantum Hall systems
We study the collective excitation spectra of double-layer quantum-Hall
systems using the single mode approximation. The double-layer in-phase density
excitations are similar to those of a single-layer system. For out-of-phase
density excitations, however, both inter-Landau-level and intra-Landau-level
double-layer modes have finite dipole oscillator strengths. The oscillator
strengths at long wavelengths for the latter transitions are shifted upward by
interactions by identical amounts proportional to the interlayer Coulomb
coupling. The intra-Landau-level out-of-phase mode has a gap when the ground
state is incompressible except in the presence of spontaneous inter-layer
coherence. We compare our results with predictions based on the
Chern-Simons-Landau-Ginzburg theory for double-layer quantum Hall systems.Comment: RevTeX, 21 page
- …