12,141 research outputs found
Linkage Between Poverty and Smoking in Philadelphia and Its Impact on Future Directions for Tobacco Control in the City.
Poverty is linked to negative health consequences and harmful health behaviors such as smoking. Despite this established correlation, few comparative studies have investigated the relationship between local poverty rates and smoking in urban settings through a Social Ecological Model framework. The authors sought to examine the linkage between local poverty rates in Philadelphia, Pennsylvania and adult smoking rates by scrutinizing existing patterns and potential mediating factors via publicly accessible data in established planning districts. The authors determined several individual, interpersonal, organizational, community, and environmental factors, varying across these districts, that impact smoking in Philadelphia. Poverty rates influence the resources, demographic makeup, and number of tobacco retailers a district has, which have downstream effects. The authors recommend that further investment is allocated to planning districts in order to mitigate the risk of smoking
On transport in quantum Hall systems with constrictions
Motivated by recent experimental findings, we study transport in a simple
phenomenological model of a quantum Hall edge system with a gate-voltage
controlled constriction lowering the local filling factor. The current
backscattered from the constriction is seen to arise from the matching of the
properties of the edge-current excitations in the constriction () and
bulk () regions. We develop a hydrodynamic theory for bosonic edge
modes inspired by this model, finding that a competition between two tunneling
process, related by a quasiparticle-quasihole symmetry, determines the fate of
the low-bias transmission conductance. In this way, we find satisfactory
explanations for many recent puzzling experimental results.Comment: 4 pages, 4 figure
Majorana Fermions and Non-Abelian Statistics in Three Dimensions
We show that three dimensional superconductors, described within a Bogoliubov
de Gennes framework can have zero energy bound states associated with pointlike
topological defects. The Majorana fermions associated with these modes have
non-Abelian exchange statistics, despite the fact that the braid group is
trivial in three dimensions. This can occur because the defects are associated
with an orientation that can undergo topologically nontrivial rotations. A new
feature of three dimensional systems is that there are "braidless" operations
in which it is possible to manipulate the groundstate associated with a set of
defects without moving or measuring them. To illustrate these effects we
analyze specific architectures involving topological insulators and
superconductors.Comment: 4 pages, 2 figures, published versio
High-Field Electrical Transport in Single-Wall Carbon Nanotubes
Using low-resistance electrical contacts, we have measured the intrinsic
high-field transport properties of metallic single-wall carbon nanotubes.
Individual nanotubes appear to be able to carry currents with a density
exceeding 10^9 A/cm^2. As the bias voltage is increased, the conductance drops
dramatically due to scattering of electrons. We show that the current-voltage
characteristics can be explained by considering optical or zone-boundary phonon
emission as the dominant scattering mechanism at high field.Comment: 4 pages, 3 eps figure
Quantum Hall line junction with impurities as a multi-slit Luttinger liquid interferometer
We report on quantum interference between a pair of counterpropagating
quantum Hall edge states that are separated by a high quality tunnel barrier.
Observed Aharonov-Bohm oscillations are analyzed in terms of resonant tunneling
between coupled Luttinger liquids that creates bound electronic states between
pairs of tunnel centers that act like interference slits. We place a lower
bound in the range of 20-40 m for the phase coherence length and directly
confirm the extended phase coherence of quantum Hall edge states.Comment: 4 pages, 3 figures, 1 tabl
Resonant Tunneling Between Quantum Hall Edge States
Resonant tunneling between fractional quantum Hall edge states is studied in
the Luttinger liquid picture. For the Laughlin parent states, the resonance
line shape is a universal function whose width scales to zero at zero
temperature. Extensive quantum Monte Carlo simulations are presented for which confirm this picture and provide a parameter-free prediction for the
line shape.Comment: 14 pages , revtex , IUCM93-00
Is there a renormalization of the 1D conductance in Luttinger Liquid model?
Properties of 1D transport strongly depend on the proper choice of boundary
conditions. It has been frequently stated that the Luttinger Liquid (LL)
conductance is renormalized by the interaction as . To
contest this result I develop a model of 1D LL wire with the interaction
switching off at the infinities. Its solution shows that there is no
renormalization of the universal conductance while the electrons have a free
behavior in the source and drain reservoirs.Comment: 5 pages, RevTex 2.0, attempted repair of tex error
Schemes for Parallel Quantum Computation Without Local Control of Qubits
Typical quantum computing schemes require transformations (gates) to be
targeted at specific elements (qubits). In many physical systems, direct
targeting is difficult to achieve; an alternative is to encode local gates into
globally applied transformations. Here we demonstrate the minimum physical
requirements for such an approach: a one-dimensional array composed of two
alternating 'types' of two-state system. Each system need be sensitive only to
the net state of its nearest neighbors, i.e. the number in state 1 minus the
number in state 2. Additionally, we show that all such arrays can perform quite
general parallel operations. A broad range of physical systems and interactions
are suitable: we highlight two potential implementations.Comment: 12 pages + 3 figures. Several small corrections mad
Quantum and Classical Binomial Distributions for the Charge Transmitted through Coherent Conductor
We discuss controversial results for the statistics of charge transport
through coherent conductors. Two distribution functions for the charge
transmitted was obtained previously, first by L.Levitov and G.Lesovik, [JETP
Letters Vol.55 p.555 (1992)] and the other initially by the same authors [ibid.
Vol.58 p.230 (1993)], and later the result was reproduced by several authors.
The latter distribution functions actually coincides with classical binomial
distribution (though obtained purely quantum mechanically) former (result of
1992) is different and we call it here quantum binomial distribution. The two
distribution function represent two opposite universal limits - one is purely
quantum, where interference is important, and the other is semiclassical, where
interference is smeared out. We show, that high order charge correlators,
determined by the either distribution functions, can all be measured in
different setups. The high order current correlators, starting the third order,
reveal (missed in previous studies) special oscillating frequency dependence on
the scale of the inverted time flight from the obstacle to the measuring point.
Depending on setup, the oscillating terms give substantially different
contributions.Comment: 4 pages; english versio
Dirac semimetal in three dimensions
In a Dirac semimetal, the conduction and valence bands contact only at
discrete (Dirac) points in the Brillouin zone (BZ) and disperse linearly in all
directions around these critical points. Including spin, the low energy
effective theory around each critical point is a four band Dirac Hamiltonian.
In two dimensions (2D), this situation is realized in graphene without
spin-orbit coupling. 3D Dirac points are predicted to exist at the phase
transition between a topological and a normal insulator in the presence of
inversion symmetry. Here we show that 3D Dirac points can also be protected by
crystallographic symmetries in particular space-groups and enumerate the
criteria necessary to identify these groups. This reveals the possibility of 3D
analogs to graphene. We provide a systematic approach for identifying such
materials and present ab initio calculations of metastable \beta-cristobalite
BiO_2 which exhibits Dirac points at the three symmetry related X points of the
BZ.Comment: 6 pages, 4 figure
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