46,259 research outputs found
Dual-Species Plasmas Illustrate MHD Flows
Plasma loops created in the laboratory strongly resemble structures observed in the solar corona. For example, both solar coronal loops and experimental loops exhibit remarkably uniform axial cross sections. A magnetohydrodynamic theory that was proposed to explain this phenomenon predicts that a plasma loop whose axial magnetic field is constricted at both footpoints will experience bulk flows into the loop from both ends. To test this theory, dual-species plasma loops were formed by supplying a different neutral gas to each of the two footpoints. Optical filters were then used to separately image the motion of different sections of the plasma. Bulk flows were, in fact, observed
Doubly heavy hadrons and the domain of validity of doubly heavy diquark--anti-quark symmetry
In the limit of heavy quark masses going to infinity, a symmetry is known to
emerge in QCD relating properties of hadrons with two heavy quarks to analogous
states with one heavy anti-quark. A key question is whether the charm mass is
heavy enough so that this symmetry is manifest in at least an approximate
manner. The issue is crucial in attempting to understand the recent reports by
the SELEX Collaboration of doubly charmed baryons. We argue on very general
grounds that the charm quark mass is substantially too light for the symmetry
to emerge automatically via colour coulombic interactions. However, the
symmetry could emerge approximately depending on the dynamical details.Comment: 9 page
Random Walk Access Times on Partially-Disordered Complex Networks: an Effective Medium Theory
An analytic effective medium theory is constructed to study the mean access
times for random walks on hybrid disordered structures formed by embedding
complex networks into regular lattices, considering transition rates that
are different for steps across lattice bonds from the rates across network
shortcuts. The theory is developed for structures with arbitrary shortcut
distributions and applied to a class of partially-disordered traversal enhanced
networks in which shortcuts of fixed length are distributed randomly with
finite probability. Numerical simulations are found to be in excellent
agreement with predictions of the effective medium theory on all aspects
addressed by the latter. Access times for random walks on these partially
disordered structures are compared to those on small-world networks, which on
average appear to provide the most effective means of decreasing access times
uniformly across the network.Comment: 12 pages, 8 figures; added new results and discussion; added appendix
on numerical procedures. To appear in PR
Considerations concerning fatigue life of metal matrix composites
Since metal matrix composites (MMC) are composed from two very distinct materials each having their own physical and mechanical properties, it is feasible that the fatigue resistance depends on the strength of the weaker constituent. Based on this assumption, isothermal fatigue lives of several MMC's were analyzed utilizing a fatigue life diagram approach. For each MMC, the fatigue life diagram was quantified using the mechanical properties of its constituents. The fatigue life regions controlled by fiber fracture and matrix were also quantitatively defined
Preliminary results on two-dimensional interferometry of HL Tau
Preliminary two-dimensional speckle interferometry results of HL Tau were found to be qualitatively similar to those found with one-dimensional slit scanning techniques; results consist of a resolved component (approximately 0.7 arcsec in size) and an unresolved component. Researchers are currently reducing the rest of the data (taken on three different telescopes and at three different wavelengths) and are also exploring other high resolution methods like the shift and add technique and selecting only the very best images for processing. The availability of even better two-dimensional arrays within the next couple of years promises to make speckle interferometry and other high resolution techniques very powerful and exiting tools for probing a variety of objects in the subarcsec regime
ROBUSTNESS OF NON-PARAMETRIC MEASUREMENT OF EFFICIENCY AND RISK AVERSION
This paper examines the performance of a risk-adjusted non-parametric approach to measuring efficiency and risk aversion. Prior work is extended to the case where agent behavior is motivated by expected utility maximization. Results indicate the approach significantly outperforms traditional efficiency measurement methods when applied to risk averse agents.Risk and Uncertainty,
Accurate nine-decade temperature-compensated logarithmic amplifier
Transistor-driven temperature-stable amplifier with logarithmic operating characteristics permits presentation of the entire range of the reactor without range switching. This circuit is capable of monitoring ion chamber currents over spans of 8 or 9 decades and is used in nuclear reactor instrumentation. Application is found in materials under ultrahigh vacuum
Understanding practitioner professionalism in Aboriginal and Torres Strait Islander health: lessons from student and registrar placements at an urban Aboriginal and Torres Strait Islander primary health care service
Aboriginal and Torres Strait Islander peoples continue to be pathologised in medical curriculum, leaving graduates feeling unequipped to effectively work cross-culturally. These factors create barriers to culturally safe health care for Aboriginal and Torres Strait Islander peoples.
In this pilot pre-post study, we followed the learning experiences of 7 medical students and 4 medical registrars undertaking clinical placements at an urban Aboriginal and Torres Strait Islander primary health care service in 2014. Through analysis and comparison of pre- and post-placement responses to a paper-based case study of a fictitious Aboriginal patient, we identified four learning principles for medical professionalism: student exposure to nuanced, complex and positive representations of Aboriginal peoples; positive practitioner role modelling; interpersonal skills that build trust and minimise patient-practitioner relational power imbalances; and, knowledge, understanding and skills for providing patient centred, holistic care. Though not exhaustive, these principles can increase the capacity of practitioners to foster culturally safe and optimal health care for Aboriginal peoples. Furthermore, competence and effectiveness in Aboriginal health contexts is an essential component of medical professionalism
Symmetric Rotating Wave Approximation for the Generalized Single-Mode Spin-Boson System
The single-mode spin-boson model exhibits behavior not included in the
rotating wave approximation (RWA) in the ultra and deep-strong coupling
regimes, where counter-rotating contributions become important. We introduce a
symmetric rotating wave approximation that treats rotating and counter-rotating
terms equally, preserves the invariances of the Hamiltonian with respect to its
parameters, and reproduces several qualitative features of the spin-boson
spectrum not present in the original rotating wave approximation both
off-resonance and at deep strong coupling. The symmetric rotating wave
approximation allows for the treatment of certain ultra and deep-strong
coupling regimes with similar accuracy and mathematical simplicity as does the
RWA in the weak coupling regime. Additionally, we symmetrize the generalized
form of the rotating wave approximation to obtain the same qualitative
correspondence with the addition of improved quantitative agreement with the
exact numerical results. The method is readily extended to higher accuracy if
needed. Finally, we introduce the two-photon parity operator for the two-photon
Rabi Hamiltonian and obtain its generalized symmetric rotating wave
approximation. The existence of this operator reveals a parity symmetry similar
to that in the Rabi Hamiltonian as well as another symmetry that is unique to
the two-photon case, providing insight into the mathematical structure of the
two-photon spectrum, significantly simplifying the numerics, and revealing some
interesting dynamical properties.Comment: 11 pages, 5 figure
Anisotropic Hc2 of K0.8Fe1.76Se2 determined up to 60 T
The anisotropic upper critical field, Hc2(T), curves for K0.8Fe1.76Se2 are
determined over a wide range of temperatures down to 1.5 K and magnetic fields
up to 60 T. Anisotropic initial slopes of Hc2 ~ -1.4 T/K and -4.6 T/K for
magnetic field applied along c-axis and ab-plane, respectively, were observed.
Whereas the c-axis Hc2|c(T) increases quasi-linearly with decreasing
temperature, the ab-plane Hc2|ab(T) shows a flattening, starting near 25 K
above 30 T. This leads to a non-monotonic temperature dependence of the
anisotropy parameter \gamma= Hc2|ab/Hc2|c. The anisotropy parameter is ~ 2 near
Tc ~ 32 K and rises to a maximum \gamma ~ 3.6 around 27 K. For lower
temperatures, \gamma decreases with T in a linear fashion, dropping to \gamma ~
2.5 by T ~ 18 K. Despite the apparent differences between the K0.8Fe1.76Se2 and
(Ba0.55K0.45)Fe2As2 or Ba(Fe0.926Co0.074)2As2, in terms of the magnetic state
and proximity to an insulating state, the Hc2(T) curves are remarkably similar.Comment: slightly modified version, accepted to PRB, Rapid Communication
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