3,769 research outputs found
Third edge for a graphene nanoribbon: A tight-binding model calculation
The electronic and transport properties of an extended linear defect embedded
in a zigzag nanoribbon of realistic width are studied, within a tight binding
model approach. Our results suggest that such defect profoundly modify the
properties of the nanoribbon, introducing new conductance quantization values
and modifying the conductance quantization thresholds. The linear defect along
the nanoribbon behaves as an effective third edge of the system, which shows a
metallic behavior, giving rise to new conduction pathways that could be used in
nanoscale circuitry as a quantum wire.Comment: 6 pages, 6 figures. Two new figures and a few references adde
Equity of Inpatient Health Care in Rural Tanzania:\ud A Population- and Facility-Based Survey
To explore the equity of utilization of inpatient health care at rural Tanzanian health centers through the use of a short wealth questionnaire.Methods: Patients admitted to four rural health centers in the Kigoma Region of Tanzania from May 2008 to May 2009 were surveyed about their illness, asset ownership and demographics. Principal component analysis was used to compare the wealth of the inpatients to the wealth of the region’s general population, using data from a previous population-based survey. Among inpatients, 15.3% were characterized as the most poor, 19.6% were characterized as very poor, 16.5% were characterized as poor, 18.9% were characterized as less poor, and 29.7% were characterized as the least poor. The wealth distribution of all inpatients (p < 0.0001), obstetric inpatients (p < 0.0001), other inpatients (p < 0.0001), and fee-exempt inpatients (p < 0.001) were significantly different than the wealth distribution in the community population, with poorer patients underrepresented among inpatients. The wealth distribution of pediatric inpatients (p = 0.2242) did not significantly differ from the population at large. The findings indicated that while current Tanzanian health financing policies may have improved access to health care for children under five, additional policies are needed to further close the equity gap, especially for obstetric inpatients.\u
Noise properties of two single electron transistors coupled by a nanomechanical resonator
We analyze the noise properties of two single electron transistors (SETs)
coupled via a shared voltage gate consisting of a nanomechanical resonator.
Working in the regime where the resonator can be treated as a classical system,
we find that the SETs act on the resonator like two independent heat baths. The
coupling to the resonator generates positive correlations in the currents
flowing through each of the SETs as well as between the two currents. In the
regime where the dynamics of the resonator is dominated by the back-action of
the SETs, these positive correlations can lead to parametrically large
enhancements of the low frequency current noise. These noise properties can be
understood in terms of the effects on the SET currents of fluctuations in the
state of a resonator in thermal equilibrium which persist for times of order
the resonator damping time.Comment: Accepted for publication in Phys. Rev.
Viscoelasticity and metastability limit in supercooled liquids
A supercooled liquid is said to have a kinetic spinodal if a temperature Tsp
exists below which the liquid relaxation time exceeds the crystal nucleation
time. We revisit classical nucleation theory taking into account the
viscoelastic response of the liquid to the formation of crystal nuclei and find
that the kinetic spinodal is strongly influenced by elastic effects. We
introduce a dimensionless parameter \lambda, which is essentially the ratio
between the infinite frequency shear modulus and the enthalpy of fusion of the
crystal. In systems where \lambda is larger than a critical value \lambda_c the
metastability limit is totally suppressed, independently of the surface
tension. On the other hand, if \lambda < \lambda_c a kinetic spinodal is
present and the time needed to experimentally observe it scales as
exp[\omega/(\lambda_c-\lambda)^2], where \omega is roughly the ratio between
surface tension and enthalpy of fusion
-Scale Decoupling of the Mechanical Relaxation and Diverging Shear Wave Propagation Lengthscale in Triphenylphosphite
We have performed depolarized Impulsive Stimulated Scattering experiments to
observe shear acoustic phonons in supercooled triphenylphosphite (TPP) from
10 - 500 MHz. These measurements, in tandem with previously performed
longitudinal and shear measurements, permit further analyses of the relaxation
dynamics of TPP within the framework of the mode coupling theory (MCT). Our
results provide evidence of coupling between the shear and
longitudinal degrees of freedom up to a decoupling temperature = 231 K. A
lower bound length scale of shear wave propagation in liquids verified the
exponent predicted by theory in the vicinity of the decoupling temperature
Austerity, political control and supplier selection in English local government: implications for autonomy in multi-level systems
Analysis of 60,000 contracts awarded by English councils between 2015-19 reveals that austerity constraints are a key predictor of councils outsourcing services to for-profit suppliers, regardless of their political control. Conservative Party-controlled councils are also more likely to contract with for-profit suppliers, although we found no link between Labour-controlled councils and not-for-profit suppliers, nor evidence that political or budgetary factors influence whether councils contract with providers based in their own region. We argue that centrally imposed funding cuts, and a belief that for-profit suppliers represent a cheaper option, could be overriding Labour Party councils’ ideological preference for not-for-profit providers
Nano-wires with surface disorder: Giant localization lengths and quantum-to-classical crossover
We investigate electronic quantum transport through nano-wires with one-sided
surface roughness. A magnetic field perpendicular to the scattering region is
shown to lead to exponentially diverging localization lengths in the
quantum-to-classical crossover regime. This effect can be quantitatively
accounted for by tunneling between the regular and the chaotic components of
the underlying mixed classical phase space.Comment: 4 pages, 3 figures; final version (including added references
A nearly closed ballistic billiard with random boundary transmission
A variety of mesoscopic systems can be represented as a billiard with a
random coupling to the exterior at the boundary. Examples include quantum dots
with multiple leads, quantum corrals with different kinds of atoms forming the
boundary, and optical cavities with random surface refractive index. The
specific example we study is a circular (integrable) billiard with no internal
impurities weakly coupled to the exterior by a large number of leads with one
channel open in each lead. We construct a supersymmetric nonlinear
-model by averaging over the random coupling strengths between bound
states and channels. The resulting theory can be used to evaluate the
statistical properties of any physically measurable quantity in a billiard. As
an illustration, we present results for the local density of states.Comment: 5 pages, 1 figur
Human Resource Development for Health in Indonesia: Challenges of Achieving the Millennium Development Goals
The development of Human Resources for Health (HRH) is one of the keys to achieving The Millennium Development Goals (MDG). Providing and ensuring the best health care service in every region of Indonesia has long been a major concern. Several challenges faced by HRH development are a shortage of professionals, uneven distribution of professionals between regions, a variety of settings (urban and rural), and management of the health workforce under a decentralization system
Local and chain dynamics in miscible polymer blends: A Monte Carlo simulation study
Local chain structure and local environment play an important role in the
dynamics of polymer chains in miscible blends. In general, the friction
coefficients that describe the segmental dynamics of the two components in a
blend differ from each other and from those of the pure melts. In this work, we
investigate polymer blend dynamics with Monte Carlo simulations of a
generalized bond-fluctuation model, where differences in the interaction
energies between non-bonded nearest neighbors distinguish the two components of
a blend. Simulations employing only local moves and respecting a non-bond
crossing condition were carried out for blends with a range of compositions,
densities, and chain lengths. The blends investigated here have long-chain
dynamics in the crossover region between Rouse and entangled behavior. In order
to investigate the scaling of the self-diffusion coefficients, characteristic
chain lengths are calculated from the packing length of the
chains. These are combined with a local mobility determined from the
acceptance rate and the effective bond length to yield characteristic
self-diffusion coefficients . We find that the
data for both melts and blends collapse onto a common line in a graph of
reduced diffusion coefficients as a function of reduced chain
length . The composition dependence of dynamic properties is
investigated in detail for melts and blends with chains of length twenty at
three different densities. For these blends, we calculate friction coefficients
from the local mobilities and consider their composition and pressure
dependence. The friction coefficients determined in this way show many of the
characteristics observed in experiments on miscible blends.Comment: 12 pages, 13 figures, editorial change
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