866 research outputs found
Solvable model of a polymer in random media with long ranged disorder correlations
We present an exactly solvable model of a Gaussian (flexible) polymer chain
in a quenched random medium. This is the case when the random medium obeys very
long range quadratic correlations. The model is solved in spatial
dimensions using the replica method, and practically all the physical
properties of the chain can be found. In particular the difference between the
behavior of a chain that is free to move and a chain with one end fixed is
elucidated. The interesting finding is that a chain that is free to move in a
quadratically correlated random potential behaves like a free chain with , where is the end to end distance and is the length of the
chain, whereas for a chain anchored at one end . The exact
results are found to agree with an alternative numerical solution in
dimensions. The crossover from long ranged to short ranged correlations of the
disorder is also explored.Comment: REVTeX, 28 pages, 12 figures in eps forma
Coupled dynamics of voltage and calcium in paced cardiac cells
We investigate numerically and analytically the coupled dynamics of
transmembrane voltage and intracellular calcium cycling in paced cardiac cells
using a detailed physiological model and its reduction to a three-dimensional
discrete map. The results provide a theoretical framework to interpret various
experimentally observed modes of instability ranging from electromechanically
concordant and discordant alternans to quasiperiodic oscillations of voltage
and calcium
Micro water harvesting for climate change mitigation: Trade-offs between health and poverty reduction in Northern Ethiopia
Proton-counting radiography for proton therapy: a proof of principle using CMOS APS technology
Despite the early recognition of the potential of proton imaging to assist proton therapy (Cormack 1963 J. Appl. Phys. 34 2722), the modality is still removed from clinical practice, with various approaches in development. For proton-counting radiography applications such as computed tomography (CT), the water-equivalent-path-length that each proton has travelled through an imaged object must be inferred. Typically, scintillator-based technology has been used in various energy/range telescope designs. Here we propose a very different alternative of using radiation-hard CMOS active pixel sensor technology. The ability of such a sensor to resolve the passage of individual protons in a therapy beam has not been previously shown. Here, such capability is demonstrated using a 36 MeV cyclotron beam (University of Birmingham Cyclotron, Birmingham, UK) and a 200 MeV clinical radiotherapy beam (iThemba LABS, Cape Town, SA). The feasibility of tracking individual protons through multiple CMOS layers is also demonstrated using a two-layer stack of sensors. The chief advantages of this solution are the spatial discrimination of events intrinsic to pixelated sensors, combined with the potential provision of information on both the range and residual energy of a proton. The challenges in developing a practical system are discussed
High Density Fabrication Process for Single Flux Quantum Circuits
We implemented, optimized and fully tested over multiple runs a
superconducting Josephson junction fabrication process tailored for the
integrated digital circuits that are used for control and readout of
superconducting qubits operating at millikelvin temperatures. This process was
optimized for highly energy efficient single flux quantum (ERSFQ) circuits with
the critical currents reduced by factor of ~10 as compared to those operated at
4.2 K. Specifically, it implemented Josephson junctions with 10 uA unit
critical current fabricated with a 10 uA/um2 critical current density. In order
to circumvent the substantial size increase of the SFQ circuit inductors, we
employed a NbN high kinetic inductance layer (HKIL) with a 8.5 pH/sq sheet
inductance. Similarly, to maintain the small size of junction resistive shunts,
we used a non-superconducting PdAu alloy with a 4.0 ohm/sq sheet resistance.
For integration with quantum circuits in a multi-chip module, 5 and 10 um
height bump processes were also optimized. To keep the fabrication process in
check, we developed and thoroughly tested a comprehensive Process Control
Monitor chip set.Comment: 10 pages, 5 figures, 1 tabl
Nutritional Status of Adolescent Girls from Rural Communities of Tigray, Northern Ethiopia
Background: Addressing the nutritional needs of adolescents could be an important step towards breaking the vicious cycle of intergenerational malnutrition.Objective: Assess nutritional status of rural adolescent girls.Design: Cross-sectional.Methods: Anthropometric and socio-demographic information from 211 adolescent girls representing 650 randomly selected households from thirteen communities in Tigray was used in data analysis. Height-for-age and BMI-for-age were compared to the 2007 WHO growth reference. Data were analyzed using SAS, Version 9.1.Results: None of the households reported access to adolescent micronutrient supplementation. The girls were shorter and thinner than the 2007 WHO reference population. The cross-sectional prevalence of stunting and thinness were 26.5% and 58.3%, respectively. Lack of latrine facilities was significantly associated with stunting (p = 0.0033) andthinness (
Localization of a polymer in random media: Relation to the localization of a quantum particle
In this paper we consider in detail the connection between the problem of a
polymer in a random medium and that of a quantum particle in a random
potential. We are interested in a system of finite volume where the polymer is
known to be {\it localized} inside a low minimum of the potential. We show how
the end-to-end distance of a polymer which is free to move can be obtained from
the density of states of the quantum particle using extreme value statistics.
We give a physical interpretation to the recently discovered one-step
replica-symmetry-breaking solution for the polymer (Phys. Rev. E{\bf 61}, 1729
(2000)) in terms of the statistics of localized tail states. Numerical
solutions of the variational equations for chains of different length are
performed and compared with quenched averages computed directly by using the
eigenfunctions and eigenenergies of the Schr\"odinger equation for a particle
in a one-dimensional random potential. The quantities investigated are the
radius of gyration of a free gaussian chain, its mean square distance from the
origin and the end-to-end distance of a tethered chain. The probability
distribution for the position of the chain is also investigated. The glassiness
of the system is explained and is estimated from the variance of the measured
quantities.Comment: RevTex, 44 pages, 13 figure
Technology-dependent rehabilitation involving action observation and movement imagery for adults with stroke: can it work? Feasibility of self-led therapy for upper limb rehabilitation after stroke
Background. Motor (re)learning via technology-dependent therapy has the potential to complement traditional therapies available to older adults living with stroke after hospital discharge and increase therapy dose. To date, little is known about the feasibility of technology-dependent therapy in a home setting for this population. Objective. To develop a technology-dependent therapy that provides mental and physical training for older adults with stroke and assess feasibility. Specifically we ask, "Can it work"? Design. Single group repeated measures. Methods. 13 participants, aged 18 years and over, were recruited over a six-month period. All participants had mild upper limb impairment following a stoke and were no longer receiving intensive rehabilitation. All participants received 18 days of technology-dependent therapy in their own home. Information was gathered on recruitment and retention, usability, and suitability of outcome measures. Results. 11 participants completed the study. The recruitment rate (number recruited/number canvassed; 10.7%) suggests 1907 participants would need to be canvassed to recruit the necessary sample size (n=204) for a definitive trial designed to provide 90% power at 5% level of significance to detect a clinically meaningful difference of 5.7 points on the Action Research Arm Test. The usability of the application was rated as exceptional on the System Usability Scale. Effectiveness cannot be determined from this study; however, there was a trend for improvement in measures of upper limb function and emotional well-being. Limitations. The study was limited by a relatively small sample size and lack of control group. Conclusions. This study demonstrated proof of concept of a technology-dependent therapy for upper limb rehabilitation following stroke. The data suggest a definitive trial is feasible, additional strategies to improve recruitment should be considered. Outcome measures aligned with the residual motor function of participants are required
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