499 research outputs found
Multi-Object Analysis of Volume, Pose, and Shape Using Statistical Discrimination
One goal of statistical shape analysis is the discrimination between two populations of objects. Whereas traditional shape analysis was mostly concerned with studying single objects, analysis of multi-object complexes presents new challenges related to alignment and relative object pose. In this paper, we present a methodology for discriminant analysis of sets multiple shapes. Shapes are represented by sampled medial manifolds including normals to the boundary. Non-Euclidean metrics that describe geodesic distance between sets of sampled representations are used for shape alignment and discrimination. Our choice of discriminant method is the distance weighted discriminant (DWD) because of its generalization ability in high dimensional, low sample size settings. Using an unbiased, soft discrimination score we can associate a statistical hypothesis test with the discrimination results. Furthermore, localization and nature significant differences between populations can be visualized via the average best discriminating axis
Continuous-variable quantum teleportation of entanglement
Entangled coherent states can be used to determine the entanglement fidelity
for a device that is designed to teleport coherent states. This entanglement
fidelity is universal, in that the calculation is independent of the use of
entangled coherent states and applies generally to the teleportation of
entanglement using coherent states. The average fidelity is shown to be a poor
indicator of the capability of teleporting entanglement; i.e., very high
average fidelity for the quantum teleportation apparatus can still result in
low entanglement fidelity for one mode of the two-mode entangled coherent
state.Comment: 5 pages, 1 figure, published versio
Coulomb blockade of strongly coupled quantum dots studied via bosonization of a channel with a finite barrier
A pair of quantum dots, coupled through a point contact, can exhibit Coulomb
blockade effects that reflect an oscillatory term in the dots' total energy
whose value depends on whether the total number of electrons on the dots is
even or odd. The effective energy associated with this even-odd alternation is
reduced, relative to the bare Coulomb blockade energy for uncoupled dots, by a
factor (1-f) that decreases as the interdot coupling is increased. When the
transmission coefficient for interdot electronic motion is independent of
energy and the same for all channels within the point contact (which are
assumed uncoupled), the factor (1-f) takes on a universal value determined
solely by the number of channels and the dimensionless conductance g of each
individual channel.
This paper studies corrections to the universal value of (1-f) that result
when the transmission coefficent varies over energy scales of the size of the
bare Coulomb blockade energy. We consider a model in which the point contact is
described by a single orbital channel containing a parabolic barrier potential,
and we calculate the leading correction to (1-f) for one-channel (spin-split)
and two-channel (spin-degenerate) point contacts in the limit where the single
orbital channel is almost completely open. By generalizing a previously used
bosonization technique, we find that, for a given value of the dimensionless
conductance g, the value of (1-f) is increased relative to its value for a
zero-thickness barrier, but the absolute value of the increase is small in the
region where our calculations apply.Comment: 13 pages, 3 Postscript figure
Cigarette pack messages about toxic chemicals: A randomised clinical trial
Background The USA can require tobacco companies to disclose information about harmful and potentially harmful chemicals in cigarette smoke, but the impact of these messages is uncertain. We sought to assess the effect of placing messages about toxic chemicals on smokers' cigarette packs. Methods Participants were 719 adult cigarette smokers from California, USA, recruited from September 2016 through March 2017. We randomly assigned smokers to receive either factual messages about chemicals in cigarette smoke and their health harms (intervention) or messages about not littering cigarette butts (control) on the side of their cigarette packs for 3 weeks. The primary trial outcome was intention to quit smoking. Results In intent-to-treat analyses, smokers whose packs had chemical messages did not have higher intentions to quit smoking at the end of the trial than those whose packs had control messages (P=0.56). Compared with control messages, chemical messages led to higher awareness of the chemicals (28% vs 15%, P<0.001) and health harms (60% vs 52%, P=0.02) featured in the messages. In addition, chemical messages led to greater negative affect, thinking about the chemicals in cigarettes and the harms of smoking, conversations about the messages and forgoing a cigarette (all P<0.05). Discussion Chemical messages on cigarette packs did not lead to higher intentions to quit among smokers in our trial. However, chemical messages informed smokers of chemicals in cigarettes and harms of smoking, which directly supports their implementation and would be critical to defending the messages against cigarette company legal challenges. Trial registration number NCT02785484
Public Understanding of Cigarette Smoke Chemicals: Longitudinal Study of US Adults and Adolescents
Introduction: The US Food and Drug Administration has increased communication efforts that aim to raise public awareness of the harmful constituents (ie, chemicals) in cigarette smoke. We sought to investigate whether the public's awareness of these chemicals has increased in light of such efforts. Methods: Participants were national probability samples of 11 322 US adults and adolescents recruited in 2014-2015 (wave 1) and 2016-2017 (wave 2). Cross-sectional telephone surveys assessed awareness of 24 cigarette smoke chemicals at both timepoints. Results: The proportion of US adults aware of cigarette smoke chemicals did not differ between waves 1 and 2 (25% and 26%, p =. 19). In contrast, awareness of chemicals among adolescents fell from 28% to 22% (p <. 001), mostly due to lower awareness of carbon monoxide, arsenic, benzene, and four other chemicals. Belief that most of the harmful chemicals in cigarette smoke come from burning the cigarette also fell from waves 1 to 2 (adults: 31% vs. 26%; adolescents: 47% vs. 41%, both ps <. 05). Participants were more likely to be aware of cigarette smoke chemicals if they had been exposed to anti-smoking campaign advertisements (p <. 05) or had previously sought chemical information (p <. 05). Cigarette smoke chemical awareness did not differ between smokers and nonsmokers. Conclusion: Awareness of cigarette smoke chemicals remains low and unchanged among adults and decreased somewhat among adolescents. The association of chemical awareness with information exposure via campaigns and information seeking behavior is promising. More concerted communication efforts may be needed to increase public awareness of cigarette smoke chemicals, which could potentially discourage smoking. Implications: Awareness of the toxic chemicals in cigarette smoke may contribute to quitting. The US Food and Drug Administration is making efforts to increase public awareness of these chemicals. Two national surveys (2014-2017) found that chemical awareness was low among adults and adolescents. Although awareness did not change among adults, awareness among adolescents dropped over time. In addition, exposure to anti-smoking campaigns and chemical information seeking behavior were associated with higher awareness of chemicals in cigarette smoke. Campaigns and other efforts may be needed to increase awareness of cigarette smoke chemicals
Numerical study of the thermoelectric power factor in ultra-thin Si nanowires
Low dimensional structures have demonstrated improved thermoelectric (TE)
performance because of a drastic reduction in their thermal conductivity,
{\kappa}l. This has been observed for a variety of materials, even for
traditionally poor thermoelectrics such as silicon. Other than the reduction in
{\kappa}l, further improvements in the TE figure of merit ZT could potentially
originate from the thermoelectric power factor. In this work, we couple the
ballistic (Landauer) and diffusive linearized Boltzmann electron transport
theory to the atomistic sp3d5s*-spin-orbit-coupled tight-binding (TB)
electronic structure model. We calculate the room temperature electrical
conductivity, Seebeck coefficient, and power factor of narrow 1D Si nanowires
(NWs). We describe the numerical formulation of coupling TB to those transport
formalisms, the approximations involved, and explain the differences in the
conclusions obtained from each model. We investigate the effects of cross
section size, transport orientation and confinement orientation, and the
influence of the different scattering mechanisms. We show that such methodology
can provide robust results for structures including thousands of atoms in the
simulation domain and extending to length scales beyond 10nm, and point towards
insightful design directions using the length scale and geometry as a design
degree of freedom. We find that the effect of low dimensionality on the
thermoelectric power factor of Si NWs can be observed at diameters below ~7nm,
and that quantum confinement and different transport orientations offer the
possibility for power factor optimization.Comment: 42 pages, 14 figures; Journal of Computational Electronics, 201
Kondo effect in coupled quantum dots: a Non-crossing approximation study
The out-of-equilibrium transport properties of a double quantum dot system in
the Kondo regime are studied theoretically by means of a two-impurity Anderson
Hamiltonian with inter-impurity hopping. The Hamiltonian, formulated in
slave-boson language, is solved by means of a generalization of the
non-crossing approximation (NCA) to the present problem. We provide benchmark
calculations of the predictions of the NCA for the linear and nonlinear
transport properties of coupled quantum dots in the Kondo regime. We give a
series of predictions that can be observed experimentally in linear and
nonlinear transport measurements through coupled quantum dots. Importantly, it
is demonstrated that measurements of the differential conductance , for the appropriate values of voltages and inter-dot tunneling
couplings, can give a direct observation of the coherent superposition between
the many-body Kondo states of each dot. This coherence can be also detected in
the linear transport through the system: the curve linear conductance vs
temperature is non-monotonic, with a maximum at a temperature
characterizing quantum coherence between both Kondo states.Comment: 20 pages, 17 figure
Electric current circuits in astrophysics
Cosmic magnetic structures have in common that they are anchored
in a dynamo, that an external driver converts kinetic energy into internal
magnetic energy, that this magnetic energy is transported as Poynting fl ux across the magnetically dominated structure, and that the magnetic energy
is released in the form of particle acceleration, heating, bulk motion,
MHD waves, and radiation. The investigation of the electric current system is
particularly illuminating as to the course of events and the physics involved.
We demonstrate this for the radio pulsar wind, the solar flare, and terrestrial
magnetic storms
Evidence for muon neutrino oscillation in an accelerator-based experiment
We present results for muon neutrino oscillation in the KEK to Kamioka (K2K)
long-baseline neutrino oscillation experiment. K2K uses an accelerator-produced
muon neutrino beam with a mean energy of 1.3 GeV directed at the
Super-Kamiokande detector. We observed the energy dependent disappearance of
muon neutrino, which we presume have oscillated to tau neutrino. The
probability that we would observe these results if there is no neutrino
oscillation is 0.0050% (4.0 sigma).Comment: 5 pages, 4 figure
Search for the standard model Higgs boson decaying into two photons in pp collisions at sqrt(s)=7 TeV
A search for a Higgs boson decaying into two photons is described. The
analysis is performed using a dataset recorded by the CMS experiment at the LHC
from pp collisions at a centre-of-mass energy of 7 TeV, which corresponds to an
integrated luminosity of 4.8 inverse femtobarns. Limits are set on the cross
section of the standard model Higgs boson decaying to two photons. The expected
exclusion limit at 95% confidence level is between 1.4 and 2.4 times the
standard model cross section in the mass range between 110 and 150 GeV. The
analysis of the data excludes, at 95% confidence level, the standard model
Higgs boson decaying into two photons in the mass range 128 to 132 GeV. The
largest excess of events above the expected standard model background is
observed for a Higgs boson mass hypothesis of 124 GeV with a local significance
of 3.1 sigma. The global significance of observing an excess with a local
significance greater than 3.1 sigma anywhere in the search range 110-150 GeV is
estimated to be 1.8 sigma. More data are required to ascertain the origin of
this excess.Comment: Submitted to Physics Letters
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