1,151 research outputs found
Negative Electron-electron Drag Between Narrow Quantum Hall Channels
Momentum transfer due to Coulomb interaction between two parallel,
two-dimensional, narrow, and spatially separated layers, when a current
I_{drive} is driven through one layer, is studied in the presence of a
perpendicular magnetic field B. The current induced in the drag layer,
I_{drag}, is evaluated self-consistently with I_{drive} as a parameter.
I_{drag} can be positive or negative depending on the value of the filling
factor \nu of the highest occupied bulk Landau level (LL). For a fully occupied
LL, I_{drag} is negative, i.e., it flows opposite to I_{drive}, whereas it is
positive for a half-filled LL. When the circuit is opened in the drag layer, a
voltage \Delta V_{drag} develops in it; it is negative for a half-filled LL and
positive for a fully occupied LL. This positive \Delta V_{drag}, expressing a
negative Coulomb drag, results from energetically favored near-edge inter-LL
transitions that occur when the highest occupied bulk LL and the LL just above
it become degenerate.Comment: Text file in Latex/Revtex/preprint format, 7 separate PS figures,
Physical Review B, in pres
Frictional Coulomb drag in strong magnetic fields
A treatment of frictional Coulomb drag between two 2-dimensional electron
layers in a strong perpendicular magnetic field, within the independent
electron picture, is presented. Assuming fully resolved Landau levels, the
linear response theory expression for the transresistivity is
evaluated using diagrammatic techniques. The transresistivity is given by an
integral over energy and momentum transfer weighted by the product of the
screened interlayer interaction and the phase-space for scattering events. We
demonstrate, by a numerical analysis of the transresistivity, that for
well-resolved Landau levels the interplay between these two factors leads to
characteristic features in both the magnetic field- and the temperature
dependence of . Numerical results are compared with recent
experiments.Comment: RevTeX, 34 pages, 8 figures included in tex
Magneto-Coulomb drag: interplay of electron--electron interactions and Landau quantization
We use the Kubo formalism to calculate the transresistivity for
carriers in coupled quantum wells in a large perpendicular magnetic field .
We find that is enhanced by approximately 50--100 times over that
of the B=0 case in the interplateau regions of the integer quantum Hall effect.
The presence of both electron--electron interactions and Landau quantization
results in (i) a twin-peaked structure of in the inter-plateau
regions at low temperatures, and, (ii) for the chemical potential at the center
of a Landau level band, a peaked temperature dependence of .Comment: 4 pages, RevTeX, 4 PS figures in text using eps
Effects of CO2 on H2O band profiles and band strengths in mixed H2O:CO2 ices
H2O is the most abundant component of astrophysical ices. In most lines of
sight it is not possible to fit both the H2O 3 um stretching, the 6 um bending
and the 13 um libration band intensities with a single pure H2O spectrum.
Recent Spitzer observations have revealed CO2 ice in high abundances and it has
been suggested that CO2 mixed into H2O ice can affect relative strengths of the
3 um and 6 um bands. We used laboratory infrared transmission spectroscopy of
H2O:CO2 ice mixtures to investigate the effects of CO2 on H2O ice spectral
features at 15-135 K. We find that the H2O peak profiles and band strengths are
significantly different in H2O:CO2 ice mixtures compared to pure H2O ice. In
all H2O:CO2 mixtures, a strong free-OH stretching band appears around 2.73 um,
which can be used to put an upper limit on the CO2 concentration in the H2O
ice. The H2O bending mode profile also changes drastically with CO2
concentration; the broad pure H2O band gives way to two narrow bands as the CO2
concentration is increased. This makes it crucial to constrain the environment
of H2O ice to enable correct assignments of other species contributing to the
interstellar 6 um absorption band. The amount of CO2 present in the H2O ice of
B5:IRS1 is estimated by simultaneously comparing the H2O stretching and bending
regions and the CO2 bending mode to laboratory spectra of H2O, CO2, H2O:CO2 and
HCOOH.Comment: 12 pages, 11 figures, accepted by A&
Coulomb Drag at the Onset of Anderson Insulators
It is shown that the Coulomb drag between two identical layers in the
Anderson insulting state indicates a striking difference between the Mott and
Efros-Shklovskii (ES) insulators. In the former, the trans-resistance
is monotonically increasing with the localization length ; in the latter,
the presence of a Coulomb gap leads to an opposite result: is enhanced
with a decreasing , with the same exponential factor as the single layer
resistivity. This distinction reflects the relatively pronounced role of
excited density fluctuations in the ES state, implied by the enhancement in the
rate of hopping processes at low frequencies. The magnitude of drag is
estimated for typical experimental parameters in the different cases. It is
concluded that a measurement of drag can be used to distinguish between
interacting and non-interacting insulating state.Comment: 15 pages, revte
Correlations in Nuclear Arrhenius-Type Plots
Arrhenius-type plots for multifragmentation process, defined as the
transverse energy dependence of the single-fragment emission-probability,
-ln(p_{b}) vs 1/sqrt(E_{t}), have been studied by examining the relationship of
the parameters p_{b} and E_{t} to the intermediate-mass fragment multiplicity
. The linearity of these plots reflects the correlation of the fragment
multiplicity with the transverse energy. These plots may not provide thermal
scaling information about fragment production as previously suggested.Comment: 12 pages, Latex, 3 Postscript figures include
A statistical interpretation of the correlation between intermediate mass fragment multiplicity and transverse energy
Multifragment emission following Xe+Au collisions at 30, 40, 50 and 60 AMeV
has been studied with multidetector systems covering nearly 4-pi in solid
angle. The correlations of both the intermediate mass fragment and light
charged particle multiplicities with the transverse energy are explored. A
comparison is made with results from a similar system, Xe+Bi at 28 AMeV. The
experimental trends are compared to statistical model predictions.Comment: 7 pages, submitted to Phys. Rev.
Magnetoconductivity of quantum wires with elastic and inelastic scattering
We use a Boltzmann equation to determine the magnetoconductivity of quantum
wires. The presence of a confining potential in addition to the magnetic field
removes the degeneracy of the Landau levels and allows one to associate a group
velocity with each single-particle state. The distribution function describing
the occupation of these single-particle states satisfies a Boltzmann equation,
which may be solved exactly in the case of impurity scattering. In the case
where the electrons scatter against both phonons and impurities we solve
numerically - and in certain limits analytically - the integral equation for
the distribution function, and determine the conductivity as a function of
temperature and magnetic field. The magnetoconductivity exhibits a maximum at a
temperature, which depends on the relative strength of the impurity and
electron-phonon scattering, and shows oscillations when the Fermi energy or the
magnetic field is varied.Comment: 21 pages (revtex 3.0), 5 postscript figures available upon request at
[email protected] or [email protected]
Using Glycosylated Hemoglobin to Define the Metabolic Syndrome in United States Adults
OBJECTIVE- To compare the use of GHb and fasting plasma glucose (FPG) to define the metabolic syndrome (MetS). RESEARCH DESIGN AND METHODS- Data from the U.S. National Health and Nutrition Examination Survey 1999-2006 were used. MetS was defined using the consensus criteria in 2009. Raised blood glucose was defined as either FPG â„100 mg/dl (5.6 mmol/l) or GHb â„5.7%. RESULTS- In 2003-2006, there was 91.3% agreement between GHb and FPG when either was used to define MetS. The agreement was good irrespective of age, sex, race/ethnicity, BMI, and diabetes status (â„87.4%). Similar results were found in 1999-2002. Among subjects without diabetes, only the use of GHb alone, but not FPG, resulted in significant association with cardiovascular diseases (odds ratio 1.45, P = 0.005). CONCLUSIONS- Using GHb instead of FPG to define MetS is feasible. It also identifies individuals with increased cardiovascular risk. © 2010 by the American Diabetes Association.published_or_final_versionThe 5th International Symposium on Healthy Aging: Is Aging a Disease?, Hong Kong, 6-7 March, 2010. In Diabetes Care, 2010, v. 33 n. 8, p. 1856-185
Many-body correlations probed by plasmon-enhanced drag measurements in double quantum well structures
Electron drag measurements of electron-electron scattering rates performed
close to the Fermi temperature are reported. While evidence of an enhancement
due to plasmons, as was recently predicted [K. Flensberg and B. Y.-K. Hu, Phys.
Rev. Lett. 73, 3572 (1994)], is found, important differences with the
random-phase approximation based calculations are observed. Although static
correlation effects likely account for part of this difference, it is argued
that correlation-induced multiparticle excitations must be included to account
for the magnitude of the rates and observed density dependences.Comment: 4 pages, 3 figures, revtex Accepted in Phys. Rev.
- âŠ