9,257 research outputs found
Why P/OF should look for evidences of over-dense structures in solar flare hard X-ray sources
White-light and hard X-ray (HXR) observations of two white-light flares (WLFs) show that if the radiative losses in the optical continuum are powered by fast electrons directly heating the WLF source, then the column density constraints imposed by the finite range of the electrons requires that the WLF consist of an over-dense region in the chromosphere, with density exceeding 10 to the 14th power/cu cm. Thus, we recommend that P/OF search for evidences of over-dense structures in HXR images obtained simultaneously with optical observations of flares
Production of pseudoscalar Higgs-bosons in collisions
We investigate the production of a pseudoscalar Higgs-boson using the
reaction at an collider with center of
mass energy of 500 GeV. Supersymmetric contributions are included and provide a
substantial enhancement to the cross section for most values of the symmetry
breaking parameters. We find that, despite the penalty incurred in converting
one of the beams into a source of backscattered photons, the
process is a promising channel for the detection of the .Comment: 9 pages RevTex + 2 Postscript figures tar.gzip.uuencode
Weak Localization Thickness Measurements of Si:P Delta-Layers
We report on our results for the characterization of Si:P delta-layers grown
by low temperature molecular beam epitaxy. Our data shows that the effective
thickness of a delta-layer can be obtained through a weak localization analysis
of electrical transport measurements performed in perpendicular and parallel
magnetic fields. An estimate of the diffusivity of phosphorous in silicon is
obtained by applying this method to several samples annealed at 850 Celsius for
intervals of zero to 15 minutes. With further refinements, this may prove to be
the most precise method of measuring delta-layer widths developed to date,
including that of Secondary Ion Mass Spectrometry analysis
Do About Half the Top Quarks at FNAL Come From Gluino Decays?
We argue that it is possible to make a consistent picture of FNAL data
including the production and decay of gluinos and squarks. The additional cross
section is several pb, about the size of that for Standard Model (SM) top quark
pair production. If the stop squark mass is small enough, about half of the top
quarks decay to stop squarks, and the loss of SM top quark pair production rate
is compensated by the supersymmetric processes. This behavior is consistent
with the reported top quark decay rates in various modes and other aspects of
the data, and suggests several other possible decay signatures. This picture
can be tested easily with more data, perhaps even with the data in hand, and
demonstrates the potential power of a hadron collider to determine
supersymmetric parameters. It also has implications for the top mass
measurement and the interpretation of the LEP excess.Comment: 18 pages, including 4 Postscript figures, uses epsf.tex, also
available at http://www.hep.anl.gov/theory/mrenna
Some applications of quasi-velocities in optimal control
In this paper we study optimal control problems for nonholonomic systems
defined on Lie algebroids by using quasi-velocities. We consider both
kinematic, i.e. systems whose cost functional depends only on position and
velocities, and dynamic optimal control problems, i.e. systems whose cost
functional depends also on accelerations. The formulation of the problem
directly at the level of Lie algebroids turns out to be the correct framework
to explain in detail similar results appeared recently (Maruskin and Bloch,
2007). We also provide several examples to illustrate our construction.Comment: Revtex 4.1, 20 pages. To appear in Int. J. Geom. Meth. Modern Physic
Transport in an inhomogeneous interacting one--dimensional system
Transport through a one--dimensional wire of interacting electrons connected
to semi--infinite leads is investigated using a bosonization approach. An
incident electron is transmitted as a sequence of partial charges. The dc
conductance is found to be entirely determined by the properties of the leads.
The dynamic nonlocal conductivity is rigorously expressed in terms of the
transmission. For abrupt variations of the interaction parameters at the
junctions the central wire acts as a Fabry--Perot resonator. When one of the
connected wires has a tendency towards superconducting order, partial Andreev
reflection of an incident electron occurs.Comment: 11 pages, RevTeX 3.0, 1 postscript figure, everything in a uuencoded
fil
Objective User Engagement With Mental Health Apps: Systematic Search and Panel-Based Usage Analysis.
BACKGROUND: Understanding patterns of real-world usage of mental health apps is key to maximizing their potential to increase public self-management of care. Although developer-led studies have published results on the use of mental health apps in real-world settings, no study yet has systematically examined usage patterns of a large sample of mental health apps relying on independently collected data.
OBJECTIVE: Our aim is to present real-world objective data on user engagement with popular mental health apps.
METHODS: A systematic engine search was conducted using Google Play to identify Android apps with 10,000 installs or more targeting anxiety, depression, or emotional well-being. Coding of apps included primary incorporated techniques and mental health focus. Behavioral data on real-world usage were obtained from a panel that provides aggregated nonpersonal information on user engagement with mobile apps.
RESULTS: In total, 93 apps met the inclusion criteria (installs: median 100,000, IQR 90,000). The median percentage of daily active users (open rate) was 4.0% (IQR 4.7%) with a difference between trackers (median 6.3%, IQR 10.2%) and peer-support apps (median 17.0%) versus breathing exercise apps (median 1.6%, IQR 1.6%; all z≥3.42, all P
CONCLUSIONS: Although the number of app installs and daily active minutes of use may seem high, only a small portion of users actually used the apps for a long period of time. More studies using different datasets are needed to understand this phenomenon and the ways in which users self-manage their condition in real-world settings
Josephson current through a Luttinger liquid
We study the Josephson effect through a one-dimensional system of interacting
electrons, connected to two superconductors by tunnel junctions. The
interactions are treated in the framework of the one-channel Luttinger model.
At zero temperature, the Josephson critical current is found to decay
algebraically with increasing distance between the junctions. The exponent is
proportional to the strength of the Coulomb interaction. If the Luttinger
liquid has a finite size, the Josephson current depends on the total number of
electrons modulo 4. These parity effects are studied for the ring, coupled
capacitively to a gate-voltage and threaded by a magnetic flux. The Josephson
current changes continuously as a function of the gate voltage and {\em
stepwise} as a function of the magnetic flux. The electron-electron interaction
introduces {\em qualitatively} new features compared to the non-interacting
case.Comment: 8 pages REVTEX , 4 figures available upon reques
Experiments on the Fermi to Tomonaga-Luttinger liquid transition in quasi-1D systems
We present experimental results on the tunneling into the edge of a two
dimensional electron gas (2DEG) obtained with GaAs/AlGaAs cleaved edge
overgrown structures. The electronic properties of the edge of these systems
can be described by a one-dimensional chiral Tomonaga-Luttinger liquid when the
filling factor of the 2DEG is very small. Here we focus on the region where the
Tomonaga-Luttinger liquid breaks down to form a standard Fermi liquid close to
and show that we recover a universal curve, which describes all
existing data.Comment: 5 pages, localisation 2002, conference proceeding
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