12,595 research outputs found
Effective model of the electronic Griffiths phase
We present simple analytical arguments explaining the universal emergence of
electronic Griffiths phases as precursors of disorder-driven metal-insulator
transitions in correlated electronic systems. A simple effective model is
constructed and solved within Dynamical Mean Field Theory. It is shown to
capture all the qualitative and even quantitative aspects of such Griffiths
phases.Comment: 9 pages, 7 figures, one reference corrected; minor corrections
include
A long-range and long-life telemetry data-acquisition system for heart rate and multiple body temperatures from free-ranging animals
The system includes an implantable transmitter, external receiver-retransmitter collar, and a microprocessor-controlled demodulator. The size of the implant is suitable for animals with body weights of a few kilograms or more; further size reduction of the implant is possible. The ECG is sensed by electrodes designed for internal telemetry and to reduce movement artifacts. The R-wave characteristics are then specifically selected to trigger a short radio frequency pulse. Temperatures are sensed at desired locations by thermistors and then, based on a heartbeat counter, transmitted intermittently via pulse interval modulation. This modulation scheme includes first and last calibration intervals for a reference by ratios with the temperature intervals to achieve good accuracy even over long periods. Pulse duration and pulse sequencing are used to discriminate between heart rate and temperature pulses as well as RF interference
A non-resonant dark-side solution to the solar neutrino problem
We re-analyse spin-flavour precession solutions to the solar neutrino problem
in the light of the recent SNO CC result as well as the 1258--day
Super-Kamiokande data and the upper limit on solar anti-neutrinos. In a
self-consistent magneto-hydrodynamics approach the resulting scheme has only 3
effective parameters: , and the neutrino mixing angle
. We show how a rates-only analysis for fixed slightly
favours spin-flavour precession (SFP) solutions over oscillations (OSC). In
addition to the resonant solution (RSFP for short), there is a new non-resonant
solution (NRSFP) in the ``dark-side''. Both RSFP and NRSFP lead to flat recoil
energy spectra in excellent agreement with the latest SuperKamiokande data. We
also show that in the presence of a neutrino transition magnetic moment of
Bohr magneton, a magnetic field of 80 KGauss eliminates all large
mixing solutions other than the so-called LMA solution.Comment: 12 pages, 3 postscript figures, using elsart.cls. Published versio
Conductor-backed coplanar waveguide resonators of Y-Ba-Cu-O and Tl-Ba-Ca-Cu-O on LaAlO3
Conductor-backed coplanar waveguide (CBCPW) resonators operating at 10.8 GHz have been fabricated from Tl-Ba-Ca-O (TBCCO) and Y-Ba-Cu-O (YBCO) thin films on LaAlO3. The resonators consist of a coplanar waveguide (CPW) patterned on the superconducting film side of the LaAlO3 substrate with a gold ground plane coated on the opposite side. These resonators were tested in the temperature range from 14 to 106 K. At 77 K, the best of our TBCCO and YBCO resonators have an unloaded quality factor (Qo) 7 and 4 times, respectively, larger than that of a similar all-gold resonator. In this study, the Qo's of the TBCCO resonators were larger than those of their YBCO counterparts throughout the aforementioned temperature range
Measurements of complex permittivity of microwave substrates in the 20 to 300 K temperature range from 26.5 to 40.0 GHz
A knowledge of the dielectric properties of microwave substrates at low temperatures is useful in the design of superconducting microwave circuits. Results are reported for a study of the complex permittivity of sapphire (Al2O3), magnesium oxide (MgO), silicon oxide (SiO2), lanthanum aluminate (LaAlO3), and zirconium oxide (ZrO2), in the 20 to 300 Kelvin temperature range, at frequencies from 26.5 to 40.0 GHz. The values of the real and imaginary parts of the complex permittivity were obtained from the scattering parameters, which were measured using a HP-8510 automatic network analyzer. For these measurements, the samples were mounted on the cold head of a helium gas closed cycle refrigerator, in a specially designed vacuum chamber. An arrangement of wave guides, with mica windows, was used to connect the cooling system to the network analyzer. A decrease in the value of the real part of the complex permittivity of these substrates, with decreasing temperature, was observed. For MgO and Al2O3, the decrease from room temperature to 20 K was of 7 and 15 percent, respectively. For LaAlO3, it decreased by 14 percent, for ZrO2 by 15 percent, and for SiO2 by 2 percent, in the above mentioned temperature range
Kolmogorov condition near hyperbolic singularities of integrable Hamiltonian systems
In this paper we show that, if an integrable Hamiltonian system admits a
nondegenerate hyperbolic singularity then it will satisfy the Kolmogorov
condegeneracy condition near that singularity (under a mild additional
condition, which is trivial if the singularity contains a fixed point)Comment: revised version, 11p, accepted for publication in a sepecial volume
in Regular and Chaotic Dynamics in honor of Richard Cushma
Millimeter wave surface resistance of RBa2Cu3O(7-delta) (R=Y,Eu,Dy,Sm,Er) superconductors
The measurements are reported of the millimeter wave surface resistance R(sub s) at 58.6 GHz of bulk samples of RBa2Cu3O(7-delta) (R = Y,Eu,Dy,Sm,Er) and of YBa2Cu3O(7-delta) superconducting films, in the temperature range from 20 to 300 K. The bulk samples were prepared by cold pressing the powders of RBa2Cu3O(7-delta) into one in. disks. The powders were prepared by several sinterings in one atmosphere of oxygen at 925 C, with grindings between sinterings, to obtain the superconducting phase. The thin films were deposited on SrTiO3 and LaGaO3 substrates by pulsed laser ablation. Each sample was measured by replacing the end wall of a gold-plated Te sub 013 circular mode copper cavity with the sample and determining the cavity quality factor . From the difference in the Q-factor of the cavity, with and without the sample, the R(sub s) of the sample was determined
Mimicking diffuse supernova antineutrinos with the Sun as a source
Measuring the electron antineutrino component of the cosmic diffuse supernova
neutrino background (DSNB) is the next ambitious goal for low-energy neutrino
astronomy. The largest flux is expected in the lowest accessible energy bin.
However, for E < 15 MeV a possible signal can be mimicked by a solar electron
antineutrino flux that originates from the usual 8B neutrinos by spin-flavor
oscillations. We show that such an interpretation is possible within the
allowed range of neutrino electromagnetic transition moments and solar
turbulent field strengths and distributions. Therefore, an unambiguous
detection of the DSNB requires a significant number of events at E > 15 MeV.Comment: 4 pages, 1 figur
Combined model-free and model-sensitive reinforcement learning in non-human primates
Contemporary reinforcement learning (RL) theory suggests
that potential choices can be evaluated by strategies that may
or may not be sensitive to the computational structure of tasks.
A paradigmatic model-free (MF) strategy simply repeats actions
that have been rewarded in the past; by contrast, modelsensitive
(MS) strategies exploit richer information associated
with knowledge of task dynamics. MF and MS strategies should
typically be combined, because they have complementary statistical
and computational strengths; however, this tradeoff between
MF/MS RL has mostly only been demonstrated in humans,
often with only modest numbers of trials. We trained
rhesus monkeys to perform a two-stage decision task designed
to elicit and discriminate the use of MF and MS methods. A descriptive
analysis of choice behaviour revealed directly that the
structure of the task (of MS importance) and the reward history
(of MF and MS importance) significantly influenced both
choice and response vigour. A detailed, trial-by-trial computational
analysis confirmed that choices were made according to a
combination of strategies, with a dominant influence of a particular
form of model sensitivity that persisted over weeks of testing.
The residuals from this model necessitated development of a
new combined RL model which incorporates a particular credit
assignment weighting procedure. Finally, response vigor exhibited
a subtly different collection ofMFand MS influences. These
results provide new illumination onto RL behavioural processes
in non-human primates
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