41,007 research outputs found
Observation of narrow-band noise accompanying the breakdown of insulating states in high Landau levels
Recent magnetotransport experiments on high mobility two-dimensional electron
systems have revealed many-body electron states unique to high Landau levels.
Among these are re-entrant integer quantum Hall states which undergo sharp
transitions to conduction above some threshold field. Here we report that these
transitions are often accompanied by narrow- and broad-band noise with
frequencies which are strongly dependent on the magnitude of the applied dc
current.Comment: 4 pages, 3 figure
Metastable Resistance Anisotropy Orientation of Two-Dimensional Electrons in High Landau Levels
In half-filled high Landau levels, two-dimensional electron systems possess
collective phases which exhibit a strongly anisotropic resistivity tensor. A
weak, but as yet unknown, rotational symmetry-breaking potential native to the
host semiconductor structure is necessary to orient these phases in macroscopic
samples. Making use of the known external symmetry-breaking effect of an
in-plane magnetic field, we find that the native potential can have two
orthogonal local minima. It is possible to initialize the system in the higher
minimum and then observe its relaxation toward equilibrium.Comment: 5 pages, 3 figures. Figure references corrected. Version accepted for
publication in Physical Review Letter
Study of a signal processor employing a synthetic phase isolator
Evaluation of signal data processor employing synthetic phase isolator techniqu
A controlled study of community-based exercise training in patients with moderate COPD.
BackgroundThe effectiveness of clinic-based pulmonary rehabilitation in advanced COPD is well established, but few data exist for less severe patients treated in alternative settings. The purpose of this study was to investigate whether a novel, community-based exercise program (CBE) was feasible and effective for patients with moderate COPD.MethodsNineteen patients with moderate COPD (mean FEV1 62%) and self-reported exercise impairment were randomized to 12-weeks of progressive endurance and strength training at a local health club under the guidance of a certified personal trainer, or to continuation of unsupervised habitual physical activity. Outcomes assessed at baseline and 12 weeks included session compliance, intensity adherence, treadmill endurance time, muscle strength, dyspnea, and health status.ResultsCompliance was 94% and adherence was 83%. Comparisons between CBE and control groups yielded the following mean (SEM) differences in favor of CBE: endurance time 134 (74) seconds versus -59 (49) seconds (P=0.041) and TDI 5.1 (0.8) versus -0.2 (0.5) (P<0.001). The CBE group increased muscle strength (weight lifted) by 11.8 kilograms per subject per week of training (P<0.001). SGRQ was not significantly changed.ConclusionsWe demonstrated the feasibility and effectiveness of a novel community-based exercise program involving health clubs and personal trainers for patients with moderate COPD.Trial registrationClinicalTrials.gov Identifier NCT01985529
A Method for the Study of Human Factors in Aircraft Operations
A method for the study of human factors in the aviation environment is described. A conceptual framework is provided within which pilot and other human errors in aircraft operations may be studied with the intent of finding out how, and why, they occurred. An information processing model of human behavior serves as the basis for the acquisition and interpretation of information relating to occurrences which involve human error. A systematic method of collecting such data is presented and discussed. The classification of the data is outlined
New Physics in High Landau Levels
Recent magneto-transport experiments on ultra-high mobility 2D electron
systems in GaAs/AlGaAs heterostructures have revealed the existence of whole
new classes of correlated many-electron states in highly excited Landau levels.
These new states, which appear only at extremely low temperatures, are
distinctly different from the familiar fractional quantum Hall liquids of the
lowest Landau level. Prominent among the recent findings are the discoveries of
giant anisotropies in the resistivity near half filling of the third and higher
Landau levels and the observation of re- entrant integer quantum Hall states in
the flanks of these same levels. This contribution will survey the present
status of this emerging field.Comment: 8 pages, 9 figures. To be published in the Proceedings of the 13th
International Conference on the Electronic Properties of Two-Dimensional
System
Reply to Simon's Comment on "Evidence for an Anisotropic State of Two-Dimensional Electrons in High Landau Levels"
We recently reported [PRL 82, 394 (1999)] large transport anisotropies in a
two-dimensional electron gas in high Landau levels. These observations were
made utilizing both square and Hall bar sample geometries. Simon recently
commented [cond-mat/9903086] that a classical calculation of the current flow
in the sample shows a magnification of an underlying anisotropy when using a
square sample. In this reply we present more recent data obtained with a very
high mobility sample, and reiterate that, with or without magnification, an
anisotropic state develops in high Landau levels at very low temperatures.Comment: 1 page, 1 figur
Spin 1 inversion: a Majorana tensor force for deuteron alpha scattering
We demonstrate, for the first time, successful S-matrix to potential
inversion for spin one projectiles with non-diagonal yielding a
interaction. The method is a generalization of the
iterative-perturbative, IP, method. We present a test case indicating the
degree of uniqueness of the potential. The method is adapted, using established
procedures, into direct observable to potential inversion, fitting ,
, , and for d + alpha scattering over
a range of energies near 10 MeV. The interaction which we find is
very different from that proposed elsewhere, both real and imaginary parts
being very different for odd and even parity channels.Comment: 7 pages Revtex, 4 ps figure
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