967 research outputs found
Axiomatic Theories of Intermediate Phases (IP) and Ideal Stretched Exponential Relaxation (SER)
Minimalist theories of complex systems are broadly of two kinds: mean-field
and axiomatic. So far all theories of properties absent from simple systems and
intrinsic to complex systems, such as IP and SER, are axiomatic. SER is the
prototypical complex temporal property of glasses, discovered by Kohlrausch 150
years ago, and now observed almost universally in microscopically homogeneous,
complex non-equilibrium materials (strong network and fragile molecular
glasses, polymers and copolymers, even electronic glasses). The Scher-Lax trap
model (1973) is paradigmatic for electronic SER; for molecular SER Phillips
(3RCS 1995) identified two "magic" shape fractions \beta = 3/5 and 3/7, as
confirmed by many later experiments here reviewed. In the dielectric SER
frequency domain involving ion conduction, there are also special beta values
for fused salts and glasses, slightly, but distinguishably, different because
of the presence of a forcing electric field
Applicability of siberian placer mining technology to Alaska
The result of Perestroyka and Glasnost has been an awakening of potential for cooperation between East and West. Nowhere has that been better demonstrated than
between Alaska and Magadan Province, USSR.
This report summarizes a one year effort financed by ASTF, with participation
from several technical organizations, to establish contacts with the Siberian placer mining industry. The purpose of the project was to provide initial assessment of the Soviet technology for placer mining in permafrost. A ten day trip to Magadan province by an ASTF team and a similar length visit to Alaska by the Soviet mining group representing the All Union Scientific and Research Institute of Gold and Rare Metals, (VNII-I), Magadan are described. The report also reviews translated data on mining in permafrost and describes surface and underground placer mining technology developed by the Soviets. The report also lists relevant publications on Soviet mining research and state of the art Soviet mining technology and expertise
Absence of Persistent Magnetic Oscillations in Type-II Superconductors
We report on a numerical study intended to examine the possibility that
magnetic oscillations persist in type II superconductors beyond the point where
the pairing self-energy exceeds the normal state Landau level separation. Our
work is based on the self-consistent numerical solution for model
superconductors of the Bogoliubov-deGennes equations for the vortex lattice
state. In the regime where the pairing self-energy is smaller than the
cyclotron energy, magnetic oscillations resulting from Landau level
quantization are suppressed by the broadening of quasiparticle Landau levels
due to the non-uniform order parameter of the vortex lattice state, and by
splittings of the quasiparticle bands. Plausible arguments that the latter
effect can lead to a sign change of the fundamental harmonic of the magnetic
oscillations when the pairing self-energy is comparable to the cyclotron energy
are shown to be flawed. Our calculations indicate that magnetic oscillations
are strongly suppressed once the pairing self-energy exceeds the Landau level
separation.Comment: 7 pages, revtex, 7 postscript figure
Electrode Polarization Effects in Broadband Dielectric Spectroscopy
In the present work, we provide broadband dielectric spectra showing strong
electrode polarization effects for various materials, belonging to very
different material classes. This includes both ionic and electronic conductors
as, e.g., salt solutions, ionic liquids, human blood, and
colossal-dielectric-constant materials. These data are intended to provide a
broad data base enabling a critical test of the validity of phenomenological
and microscopic models for electrode polarization. In the present work, the
results are analyzed using a simple phenomenological equivalent-circuit
description, involving a distributed parallel RC circuit element for the
modeling of the weakly conducting regions close to the electrodes. Excellent
fits of the experimental data are achieved in this way, demonstrating the
universal applicability of this approach. In the investigated ionically
conducting materials, we find the universal appearance of a second dispersion
region due to electrode polarization, which is only revealed if measuring down
to sufficiently low frequencies. This indicates the presence of a second
charge-transport process in ionic conductors with blocking electrodes.Comment: 9 pages, 6 figures, experimental data are provided in electronic form
(see "Data Conservancy"
Resonant Raman scattering off neutral quantum dots
Resonant inelastic (Raman) light scattering off neutral GaAs quantum dots
which contain a mean number, N=42, of electron-hole pairs is computed. We find
Raman amplitudes corresponding to strongly collective final states
(charge-density excitations) of similar magnitude as the amplitudes related to
weakly collective or single-particle excitations. As a function of the incident
laser frequency or the magnetic field, they are rapidly varying amplitudes. It
is argued that strong Raman peaks should come out in the spin-density channels,
not related to valence-band mixing effects in the intermediate states.Comment: Accepted in Physical Review
Orbital and spin contributions to the -tensors in metal nanoparticles
We present a theoretical study of the mesoscopic fluctuations of -tensors
in a metal nanoparticle. The calculations were performed using a semi-realistic
tight-binding model, which contains both spin and orbital contributions to the
-tensors. The results depend on the product of the spin-orbit scattering
time and the mean-level spacing , but are
otherwise weakly affected by the specific shape of a {\it generic}
nanoparticle. We find that the spin contribution to the -tensors agrees with
Random Matrix Theory (RMT) predictions. On the other hand, in the strong
spin-orbit coupling limit , the
orbital contribution depends crucially on the space character of the
quasi-particle wavefunctions: it levels off at a small value for states of
character but is strongly enhanced for states of character. Our numerical
results demonstrate that when orbital coupling to the field is included, RMT
predictions overestimate the typical -factor of orbitals that have dominant
-character. This finding points to a possible source of the puzzling
discrepancy between theory and experiment.Comment: 21 pages, 6 figures; accepted for publication in Physical Review
Nonmonotonic inelastic tunneling spectra due to surface spin excitations in ferromagnetic junctions
The paper addresses inelastic spin-flip tunneling accompanied by surface spin
excitations (magnons) in ferromagnetic junctions. The inelastic tunneling
current is proportional to the magnon density of states which is
energy-independent for the surface waves and, for this reason, cannot account
for the bias-voltage dependence of the observed inelastic tunneling spectra.
This paper shows that the bias-voltage dependence of the tunneling spectra can
arise from the tunneling matrix elements of the electron-magnon interaction.
These matrix elements are derived from the Coulomb exchange interaction using
the itinerant-electron model of magnon-assisted tunneling. The results for the
inelastic tunneling spectra, based on the nonequilibrium Green's function
calculations, are presented for both parallel and antiparallel magnetizations
in the ferromagnetic leads.Comment: 9 pages, 4 figures, version as publishe
Magnetization relaxation in (Ga,Mn)As ferromagnetic semiconductors
We describe a theory of Mn local-moment magnetization relaxation due to p-d
kinetic-exchange coupling with the itinerant-spin subsystem in the
ferromagnetic semiconductor (Ga,Mn)As alloy. The theoretical Gilbert damping
coefficient implied by this mechanism is calculated as a function of Mn moment
density, hole concentration, and quasiparticle lifetime. Comparison with
experimental ferromagnetic resonance data suggests that in annealed strongly
metallic samples, p-d coupling contributes significantly to the damping rate of
the magnetization precession at low temperatures. By combining the theoretical
Gilbert coefficient with the values of the magnetic anisotropy energy, we
estimate that the typical critical current for spin-transfer magnetization
switching in all-semiconductor trilayer devices can be as low as .Comment: 4 pages, 2 figures, submitted to Rapid Communication
Increasing uptake of FIT colorectal screening : protocol for the TEMPO randomised controlled trial testing a suggested deadline and a planning tool
Funding: This study is supported by an Early Diagnosis Advisory Group (EDAG) Project Grant from Cancer Research UK (C9227/A27877 - Increasing uptake of faecal immunochemical test (FIT) bowel screening: trial of providing a suggested deadline for FIT kit return, PI KAR, Co-investigators: CMC, AM, GJH, RJCS) and by a Response Mode Grant from the Scottish Chief Scientist Office (HIPS/17/23 - Increasing uptake of bowel cancer screening: development of a FIT planning support tool, PI: KAR, Co-investigators: SM, REOC, RCOC, AI, RJCS, MK).Introduction Screening can reduce deaths from colorectal cancer (CRC). Despite high levels of public enthusiasm, participation rates in population CRC screening programmes internationally remain persistently below target levels. Simple behavioural interventions such as completion goals and planning tools may support participation among those inclined to be screened but who fail to act on their intentions. This study aims to evaluate the impact of: (a) a suggested deadline for return of the test; (b) a planning tool and (c) the combination of a deadline and planning tool on return of faecal immunochemical tests (FITs) for CRC screening. Methods and analysis A randomised controlled trial of 40 000 adults invited to participate in the Scottish Bowel Screening Programme will assess the individual and combined impact of the interventions. Trial delivery will be integrated into the existing CRC screening process. The Scottish Bowel Screening Programme mails FITs to people aged 50–74 with brief instructions for completion and return. Participants will be randomised to one of eight groups: (1) no intervention; (2) suggested deadline (1 week); (3) suggested deadline (2 weeks); (4) suggested deadline (4 weeks); (5) planning tool; (6) planning tool plus suggested deadline (1 week); (7) planning tool plus suggested deadline (2 weeks); (8) planning tool plus suggested deadline (4 weeks). The primary outcome is return of the correctly completed FIT at 3 months. To understand the cognitive and behavioural mechanisms and to explore the acceptability of both interventions, we will survey (n=2000) and interview (n=40) a subgroup of trial participants. Ethics and dissemination The study has been approved by the National Health Service South Central—Hampshire B Research Ethics Committee (ref. 19/SC/0369). The findings will be disseminated through conference presentations and publication in peer-reviewed journals. Participants can request a summary of the results. Trial registration number clinicaltrials.govNCT05408169.Publisher PDFPeer reviewe
Electronic excitations and the tunneling spectra of metallic nanograins
Tunneling-induced electronic excitations in a metallic nanograin are
classified in terms of {\em generations}: subspaces of excitations containing a
specific number of electron-hole pairs. This yields a hierarchy of populated
excited states of the nanograin that strongly depends on (a) the available
electronic energy levels; and (b) the ratio between the electronic relaxation
rate within the nano-grain and the bottleneck rate for tunneling transitions.
To study the response of the electronic energy level structure of the nanograin
to the excitations, and its signature in the tunneling spectrum, we propose a
microscopic mean-field theory. Two main features emerge when considering an Al
nanograin coated with Al oxide: (i) The electronic energy response fluctuates
strongly in the presence of disorder, from level to level and excitation to
excitation. Such fluctuations produce a dramatic sample dependence of the
tunneling spectra. On the other hand, for excitations that are energetically
accessible at low applied bias voltages, the magnitude of the response,
reflected in the renormalization of the single-electron energy levels, is
smaller than the average spacing between energy levels. (ii) If the tunneling
and electronic relaxation time scales are such as to admit a significant
non-equilibrium population of the excited nanoparticle states, it should be
possible to realize much higher spectral densities of resonances than have been
observed to date in such devices. These resonances arise from tunneling into
ground-state and excited electronic energy levels, as well as from charge
fluctuations present during tunneling.Comment: Submitted to the Physical Review
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