2,406 research outputs found
Far-infrared spectra of lateral quantum dot molecules
We study effects of electron-electron interactions and confinement potential
on the magneto-optical absorption spectrum in the far-infrared range of lateral
quantum dot molecules. We calculate far-infrared (FIR) spectra for three
different quantum dot molecule confinement potentials. We use accurate exact
diagonalization technique for two interacting electrons and calculate
dipole-transitions between two-body levels with perturbation theory. We
conclude that the two-electron FIR spectra directly reflect the symmetry of the
confinement potential and interactions cause only small shifts in the spectra.
These predictions could be tested in experiments with nonparabolic quantum dots
by changing the number of confined electrons. We also calculate FIR spectra for
up to six noninteracting electrons and observe some additional features in the
spectrum.Comment: For better quality Figs download manuscript from
http://www.fyslab.hut.fi/~mma/FIR/Helle_qdmfir.ps.g
Bispectrum as Baryon Acoustic Oscillation Interferometer
The galaxy bispectrum, measuring excess clustering of galaxy triplets, offers
a probe of dark energy via baryon acoustic oscillations (BAOs). However up to
now it has been severely underused due to the combinatorically explosive number
of triangles. Here we exploit interference in the bispectrum to identify
triangles that amplify BAOs. This approach reduces the computational cost of
estimating covariance matrices, offers an improvement in BAO constraints
equivalent to lengthening BOSS by 30%, and simplifies adding bispectrum BAO
information to future large-scale redshift survey analyses.Comment: 6 pages, 3 figures; revised to match published versio
Spin-wave interference in three-dimensional rolled-up ferromagnetic microtubes
We have investigated spin-wave excitations in rolled-up Permalloy microtubes
using microwave absorption spectroscopy. We find a series of quantized
azimuthal modes which arise from the constructive interference of Damon-Eshbach
type spin waves propagating around the circumference of the microtubes, forming
a spin-wave resonator. The mode spectrum can be tailored by the tube's radius
and number of rolled-up layers.Comment: 12 pages, 4 figure
Control of many electron states in semiconductor quantum dots by non-Abelian vector potentials
Adiabatic time evolution of degenerate eigenstates of a quantum system
provides a means for controlling electronic states since mixing between
degenerate levels generates a matrix Berry phase. In the presence of spin-orbit
coupling in n-type semiconductor quantum dots the electron Hamiltonian is
invariant under time reversal operation and the many body groundstate may be
doubly degenerate. This double degeneracy can generate non-Abelian vector
potentials when odd number of electrons are present. We find that the
antisymmetry of many electron wavefunction has no effect on the matrix Berry
phase. We have derived equations that allow one to investigate the effect of
electron correlations by expressing the non-Abelian vector potentials for many
electron system in terms of single electron non-Abelian vector potentials.Comment: minor changes included, accepted in Phys. Rev.
Microstrip superconducting quantum interference device amplifiers with submicron Josephson junctions: enhanced gain at gigahertz frequencies
We present measurements of an amplifier based on a dc superconducting quantum
interference device (SQUID) with submicron Al-AlOx-Al Josephson junctions. The
small junction size reduces their self-capacitance and allows for the use of
relatively large resistive shunts while maintaining nonhysteretic operation.
This leads to an enhancement of the SQUID transfer function compared to SQUIDs
with micron-scale junctions. The device layout is modified from that of a
conventional SQUID to allow for coupling signals into the amplifier with a
substantial mutual inductance for a relatively short microstrip coil.
Measurements at 310 mK exhibit gain of 32 dB at 1.55 GHz.Comment: Version with high resolution figures at:
http://physics.syr.edu/~bplourde/bltp-publications.ht
Strategic Networking for Online Success
The growth of online social networks and the decreasing effectiveness of traditional marketing have lead to a large interest in social networks. For an appropriate application of new marketing approaches marketers have to understand the impact of interactions and relationships among network members on their individual outcome and network popularity in order to use online social networks effectively in marketing. In this study we analyze networking behavior of music artists for promoting their music. Our sample consists of a set of 480 music artists who actively operate online social networks for personal success on two independent online social network platforms at the same time. Personal network information on both platforms is tracked monthly over a period of six months. Applying a count data approach we relate well-established egocentric network measures to online success. Our results indicate that online success is determined by the social network structure and networking activities of the music artists rather than by their outside popularity. Most importantly, the drivers of online success are not limited to the size of the of the artist’s personal network. The findings of our study provide several insights into the use of personal online social networks for marketing products and services
Gold standard program for heavy smokers in a real-life setting
Background: High-intensity smoking cessation programs generally lead to more continuous abstinence, however, lower rates of success have been reported among heavy smokers. The aim was to evaluate continuous abstinence among heavy smokers during the intensive 6-week Gold Standard Program (GSP) and to identify modifiable factors associated with continuous abstinence. Methods: In this nationwide clinical study based on 36,550 smokers attending an intensive cessation program in Denmark. Heavy smoking was defined as ≥7 points in the Fagerström Nicotine Dependency Test, smoking ≥20 cigarettes daily or ≥20 pack-years. Results: Overall, 28% had a Fagerström score ≥7 points, 58% smoked ≥20 cigarettes daily and 68% smoked ≥20 pack-years. Continuous abstinence was 33% in responders (6-months response rate: 78%); however, abstinence was approximately 1–6% lower in the heavy smokers than the overall population. Attending GSP with an individual format (vs. group/other, OR 1.23–1.44); in a hospital setting (vs. pharmacy/municipality services, OR 1.05–1.11); and being compliant (attending the planned meetings OR 4.36–4.89) were associated with abstinence. Abstinence decreased in a dose-dependent manner with increasing smoking severity. Conclusions: Abstinence after GSP was 1–6% lower in the heavy smokers than in the overall study population. Modifiable factors may be used for small improvements in continued abstinence. However attempts to improve compliance seemed especially promising
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