1,447 research outputs found
A Model for the Voltage Steps in the Breakdown of the Integer Quantum Hall Effect
In samples used to maintain the US resistance standard the breakdown of the
dissipationless integer quantum Hall effect occurs as a series of dissipative
voltage steps. A mechanism for this type of breakdown is proposed, based on the
generation of magneto-excitons when the quantum Hall fluid flows past an
ionised impurity above a critical velocity. The calculated generation rate
gives a voltage step height in good agreement with measurements on both
electron and hole gases. We also compare this model to a hydrodynamic
description of breakdown.Comment: 4 pages including 3 figure
Polygonal excitations of spinning and levitating droplets
The shape of a weightless spinning liquid droplet is governed by the balance
between the surface tension and centrifugal forces. The axisymmetric shape for
slow rotation becomes unstable to a non-axisymmetric distortion above a
critical angular velocity, beyond which the droplet progresses through a series
of 2-lobed shapes. Theory predicts the existence of a family of 3- and 4-lobed
equilibrium shapes at higher angular velocity. We investigate the formation of
a triangular-shaped magnetically levitated water droplet, driven to rotate by
the Lorentz force on an ionic current within the droplet. We also study
equatorial traveling waves which give the droplet 3, 4 and 5-fold symmetry.Comment: Supplementary information at
http://www.nottingham.ac.uk/~ppzlev/Drople
Shape oscillations of a charged diamagnetically-levitated droplet
We investigate the effect of electrical charge on the normal mode frequencies
of electrically-charged diamagnetically levitated water droplets with radii
4.5-7.5 mm using diamagnetic levitation. This technique allows us to levitate
almost spherical droplets and therefore to directly compare the measured
vibrational frequencies of the first seven modes of the charged droplet with
theoretical values calculated by Lord Rayleigh, for which we find good
agreement
Cytogenetic studies of early myeloid progenitor compartments in Ph<SUP>1</SUP>- positive chronic myeloid leukemia. II. Long-term culture reveals the persistence of Ph<SUP>1</SUP>-negative progenitors in treated as well as newly diagnosed patients
We recently showed that long-term marrow cultures can be used to demonstrate the presence of Philadelphia (Ph1) negative progenitors in patients with newly diagnosed Ph1-positive chronic myeloid leukemia (CML). We now report results for 6 chronic phase patients studied 5-83 mo postdiagnosis and an additional 3 newly diagnosed patients. Marrow metaphases were exclusively Ph1-positive. Clonogenic assays revealed a minor population of Ph1-negative progenitors in 3 cases (1 treated, 2 untreated). Long-term marrow culture adherent layers contained Ph1- negative progenitors in 6 cases (3 treated, 3 untreated). Whenever this occurred, the Ph1-negative population had become the only one detectable within 3-4 wk, and this was always associated with a rapid decline of the Ph1-positive population. For 2 of the 3 cases where Ph1- negative progenitors were not detected, there was a similar rapid decline in the Ph1-positive population in culture. In the other case, Ph1-positive progenitors were maintained at levels typically seen in normal long-term marrow cultures. These results suggest that chromosomally normal stem cells may persist for a considerable period in the marrow of some, but perhaps not all, patients with CML, even in the face of maintenance chemotherapy. In addition, they provide new evidence of heterogeneity in this disease, as shown by the variable ability of Ph1-positive progenitor populations to be maintained in vitro
Validation of magnetophonon spectroscopy as a tool for analyzing hot-electron effects in devices
It is shown that very high precision hot-electron magnetophonon experiments made on n+n−n+-GaAs sandwich device structures which are customized for magnetoresistance measurements can be very accurately modeled by a new Monte Carlo technique. The latter takes account of the Landau quantization and device architecture as well as material parameters. It is proposed that this combination of experiment and modeling yields a quantitative tool for the direct analysis of spatially localized very nonequilibrium electron distributions in small devices and low dimensional structures
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