2,158 research outputs found
A New S-S' Pair Creation Rate Expression Improving Upon Zener Curves for I-E Plots
To simplify phenomenology modeling used for charge density wave
(CDW)transport, we apply a wavefunctional formulation of tunneling Hamiltonians
to a physical transport problem characterized by a perturbed washboard
potential. To do so, we consider tunneing between states that are
wavefunctionals of a scalar quantum field. I-E curves that match Zener curves -
used to fit data experimentally with wavefunctionals congruent with the false
vacuum hypothesis. This has a very strong convergence with electron-positron
pair production representations.The similarities in plot behavior of the
current values after the threshold electric field values argue in favor of the
Bardeen pinning gap paradigm proposed for quasi-one-dimensional metallic
transport problems.Comment: 22 pages,6 figures, and extensive editing of certain segments.Paper
has been revised due to acceptance by World press scientific MPLB journal.
This is word version of file which has been submitted to MPLBs editor for
final proofing. Due for publication perhaps in mid spring to early summer
200
An open question: Are topological arguments helpful in setting initial conditions for transport problems in condensed matter physics?
The tunneling Hamiltonian is a proven method to treat particle tunneling
between different states represented as wavefunctions in many-body physics. Our
problem is how to apply a wave functional formulation of tunneling Hamiltonians
to a driven sine-Gordon system. We apply a generalization of the tunneling
Hamiltonian to charge density wave (CDW) transport problems in which we
consider tunneling between states that are wavefunctionals of a scalar quantum
field. We present derived I-E curves that match Zenier curves used to fit data
experimentally with wavefunctionals congruent with the false vacuum hypothesis.
THe open question is whether the coefficients picked in both the
wavefunctionals and the magnitude of the coefficents of the driven sine Gordon
physical system should be picked by topological charge arguements that in
principle appear to assign values that have a tie in with the false vacuum
hypothesis first presented by Sidney ColemanComment: 17 pages, 4 figures (1a to 2b) on two pages. Specific emphasis on if
or not topological arguements a la Trodden, Su et al add to formulation of
condensed matter transport problem
Impulsive cylindrical gravitational wave: one possible radiative form emitted from cosmic strings and corresponding electromagnetic response
The cosmic strings(CSs) may be one important source of gravitational
waves(GWs), and it has been intensively studied due to its special properties
such as the cylindrical symmetry. The CSs would generate not only usual
continuous GW, but also impulsive GW that brings more concentrated energy and
consists of different GW components broadly covering low-, intermediate- and
high-frequency bands simultaneously. These features might underlie interesting
electromagnetic(EM) response to these GWs generated by the CSs. In this paper,
with novel results and effects, we firstly calculate the analytical solutions
of perturbed EM fields caused by interaction between impulsive cylindrical GWs
(would be one of possible forms emitted from CSs) and background celestial high
magnetic fields or widespread cosmological background magnetic fields, by using
rigorous Einstein - Rosen metric. Results show: perturbed EM fields are also in
the impulsive form accordant to the GW pulse, and asymptotic behaviors of the
perturbed EM fields are fully consistent with the asymptotic behaviors of the
energy density, energy flux density and Riemann curvature tensor of
corresponding impulsive cylindrical GWs. The analytical solutions naturally
give rise to the accumulation effect which is proportional to the term of
distance^1/2, and based on it, we for the first time predict potentially
observable effects in region of the Earth caused by the EM response to GWs from
the CSs.Comment: 34 pages, 12 figure
The Influence of Magnetic Field Geometry on the Evolution of Black Hole Accretion Flows: Similar Disks, Drastically Different Jets
Because the magneto-rotational instability is capable of exponentially
amplifying weak preexisting magnetic fields, it might be hoped that the
character of the magnetic field in accretion disks is independent of the nature
of the seed field. However, the divergence-free nature of magnetic fields in
highly conducting fluids ensures that their large-scale topology is preserved,
no matter how greatly the field intensity is changed. By performing global
two-dimensional and three-dimensional general relativistic magnetohydrodynamic
disk simulations with several different topologies for the initial magnetic
field, we explore the degree to which the character of the flows around black
holes depends on the initial topology. We find that while the qualitative
properties of the accretion flow are nearly independent of field topology,
jet-launching is very sensitive to it: a sense of vertical field consistent for
at least an inner disk inflow time is essential to the support of strong jets.Comment: 42 pages; 17 figures; Accepted for publication in ApJ (some new
discussion and 2 new figures
Perceived life expectancy among dialysis recipients: a scoping review
Rationale & Objective: Greater prognostic understanding is associated with higher quality care at the end of life. We undertook a scoping review to explore how long dialysis recipients expect to live. Study Design: Scoping Review Setting and Study Population: People with kidney failure over 18 years old. Search Strategy & Sources: Studies were identified by searching Medline, Embase, APA PsycINFO, HMIC and ProQuest Database for terms related to âlife expectancyâ, âself -estimatedâ and âend stage kidney diseaseâ. Data Extraction: Search strategies yielded 349 unique, potentially eligible studies, with 8 meeting the inclusion criteria after screening. Results: Significant mismatches between dialysis recipients and their healthcare provider estimations of prognosis were reported, with patients predicting significantly higher life expectancies than healthcare professionals and almost no agreement between patient and nephrologist estimates of one-year survival. Documented cognitive impairment did not affect 1- or 5-year prognosis estimates, neither did gender, age, time on dialysis or discussing perceived life expectancy. Dialysis recipients who thought they were on the transplant-list or self-identified as black had higher perceived life expectancy: people who were 75 years or older, or with fair/ poor self-reported health status had lower. Those with lower perceived life expectancy preferred care focusing on relieving pain and discomfort: people who thought they had a higher chance of survival were significantly more likely to prefer life-extending care. Limitations: There is a marked paucity of research in this area with most studies conducted in North American cohorts. Conclusions: Optimistic patient prognostic expectations persist in dialysis recipients. Given the effects of perceived life expectancy on treatment choices and subsequent quality of life, it is important that transparent discussions regarding prognosis are conducted with people receiving dialysis and their families
Why do people choose nephrology? Identifying positive motivators to aid recruitment and retention
Increasing concerns about recruitment and retention of junior doctors have led to renewed interest in how and when trainees choose their specialties. To our knowledge, no study has yet reported what attracts UK applicants to nephrology nor how clinicians develop vocational interests or make occupational choices. With this in mind, we sought to explore the motivation behind current nephrologist's career choices in the UK. We interviewed 11 nephrologists using a semi-structured face-to-face approach and used interpretative phenomenological analysis to conduct and analyse the interviews. We found role models were pivotal in encouraging specialization in nephrology, particularly those encountered in early postgraduate training. The diversity, diagnostic challenge and cross-specialty knowledge was highlighted as well as the ability to 'make a difference to patients' lives'. Nephrologists enjoyed the challenge of managing very sick, acutely unwell patients as well as the holistic continuity of long-term care offered to dialysis patients and their families. Academic and procedural components were attractive motivators to the specialty and the flexibility to have multiple interests was noted, with many nephrologists having 'portfolio' careers. Based on these results, we suggest strategies the specialty can use to aid policy decision making, promote recruitment and improve educational experiences within current training programmes
Where is the Radiation Edge in Magnetized Black Hole Accretion discs?
General Relativistic (GR) Magnetohydrodynamic (MHD) simulations of black hole
accretion find significant magnetic stresses near and inside the innermost
stable circular orbit (ISCO), suggesting that such flows could radiate in a
manner noticeably different from the prediction of the standard model, which
assumes that there are no stresses in that region. We provide estimates of how
phenomenologically interesting parameters like the ``radiation edge", the
innermost ring of the disc from which substantial thermal radiation escapes to
infinity, may be altered by stresses near the ISCO. These estimates are based
on data from a large number of three-dimensional GRMHD simulations combined
with GR ray-tracing. For slowly spinning black holes (), the radiation
edge lies well inside where the standard model predicts, particularly when the
system is viewed at high inclination. For more rapidly spinning black holes,
the contrast is smaller. At fixed total luminosity, the characteristic
temperature of the accretion flow increases between a factor of over
that predicted by the standard model, whilst at fixed mass accretion rate,
there is a corresponding enhancement of the accretion luminosity which may be
anywhere from tens of percent to order unity. When all these considerations are
combined, we find that, for fixed black hole mass, luminosity, and inclination
angle, our uncertainty in the characteristic temperature of the radiation
reaching distant observers due to uncertainty in dissipation profile (around a
factor of 3) is {\it greater} than the uncertainty due to a complete lack of
knowledge of the black hole's spin (around a factor of 2) and furthermore that
spin estimates based on the stress-free inner boundary condition provide an
upper limit to .Comment: 20 pages, 17 figures, accepted by MNRAS; major changes to original,
including entirely new sections discussing characteristic temperature of
black hole accretion flows and implications for measurements of black hole
spin, along with substantially expanded conclusio
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