19,441 research outputs found
Transport of interacting electrons in arrays of quantum dots and diffusive wires
We develop a detailed theoretical investigation of the effect of Coulomb
interaction on electron transport in arrays of chaotic quantum dots and
diffusive metallic wires. Employing the real time path integral technique we
formulate a new Langevin-type of approach which exploits a direct relation
between shot noise and interaction effects in mesoscopic conductors. With the
aid of this approach we establish a general expression for the Fano factor of
1D quantum dot arrays and derive a complete formula for the interaction
correction to the current which embraces all perturbative results previously
obtained for various quasi-0D and quasi-1D disordered conductors and extends
these results to yet unexplored regimes.Comment: 12 pages, 2 figure
Dark and Baryonic Matter in Bright Spiral Galaxies: I.Near-infrared and Optical Broadband Surface Photometry of 30 Galaxies
We present photometrically calibrated images and surface photometry in the B,
V, R, J, H, and K-bands of 25, and in the g, r, and K-bands of 5 nearby bright
(Bo_T<12.5 mag) spiral galaxies with inclinations between 30-65 degrees
spanning the Hubble Sequence from Sa to Scd. Data are from The Ohio State
University Bright Spiral Galaxy Survey, the Two Micron All Sky Survey, and the
Sloan Digital Sky Survey Second Data Release. Radial surface brightness
profiles are extracted, and integrated magnitudes are measured from the
profiles. Axis ratios, position angles, and scale lengths are measured from the
near-infrared images. A 1-dimensional bulge/disk decomposition is performed on
the near-infrared images of galaxies with a non-negligible bulge component, and
an exponential disk is fit to the radial surface brightness profiles of the
remaining galaxies.Comment: 28 page
A Look At Three Different Scenarios for Bulge Formation
In this paper, we present three qualitatively different scenarios for bulge
formation: a secular evolution model in which bulges form after disks and
undergo several central starbursts, a primordial collapse model in which bulges
and disks form simultaneously, and an early bulge formation model in which
bulges form prior to disks. We normalize our models to the local z=0
observations of de Jong & van der Kruit (1994) and Peletier & Balcells (1996)
and make comparisons with high redshift observations. We consider model
predictions relating directly to bulge-to-disk properties. As expected, smaller
bulge-to-disk ratios and bluer bulge colors are predicted by the secular
evolution model at all redshifts, although uncertainties in the data are
currently too large to differentiate strongly between the models.Comment: 19 pages, 6 figures, accepted for publication in the Astrophysical
Journa
Field efficacy of new compounds to replace copper for scab control in organic apple production
Efficacy of compounds was investigated in field experiments in Denmark and the Netherlands according to EPPO guidelines. Some Yucca extracts and potassium bicarbonate had an efficacy similar to sulphur on leaves. Addition of sulphur to Yucca 1 and to potassium bicarbonate increased the level of efficacy to that of copper. This confirms results from earlier years. Although a dose increase resulted in better efficacy, this was more prominent for Yucca1 than for potassium bicarbonate
The evolution of the stellar populations in low surface brightness galaxies
We investigate the star formation history and chemical evolution of low
surface brightness (LSB) disk galaxies by modelling their observed
spectro-photometric and chemical properties using a galactic chemical and
photometric evolution model incorporating a detailed metallicity depen dent set
of stellar input data. For a large fraction of the LSB galaxies in our sample,
observed properties are best explained by models incorporating an exponentially
decreasing global star formation rate (SFR) ending at a present-day gas
fraction (M_{gas}/(M_{gas}+M_{stars}) = 0.5 for a galaxy age of 14 Gyr. For
some galaxies small amplitude star formation bursts are required to explain the
contribution of the young (5-50 Myr old) stellar population to the galaxy
integrated luminosity. This suggests that star formation has proceeded in a
stochastic manner.
The presence of an old stellar population in many late-type LSB galaxies
suggests that LSB galaxies roughly follow the same evolutionary history as HSB
galaxies, except at a much lower rate. In particular, our results imply that
LSB galaxies do not form late, nor have a delayed onset of star formation, but
simply evolve slowly.Comment: To be published in A&
Universality of Shot-Noise in Multiterminal Diffusive Conductors
We prove the universality of shot-noise in multiterminal diffusive conductors
of arbitrary shape and dimension for purely elastic scattering as well as for
hot electrons. Using a Boltzmann-Langevin approach we reduce the calculation of
shot-noise correlators to the solution of a diffusion equation. We show that
shot-noise in multiterminal conductors is a non-local quantity and that
exchange effects can occur without quantum phase coherence even at zero
electron temperature. Concrete numbers for shot-noise are given that can be
tested experimentally.Comment: 4 double-column pages, REVTeX, 1 eps figure embedded with eps
Quantum partition noise of photo-created electron-hole pairs
We show experimentally that even when no bias voltage is applied to a quantum
conductor, the electronic quantum partition noise can be investigated using GHz
radiofrequency irradiation of a reservoir. Using a Quantum Point Contact
configuration as the ballistic conductor we are able to make an accurate
determination of the partition noise Fano factor resulting from the
photo-assisted shot noise. Applying both voltage bias and rf irradiation we are
able to make a definitive quantitative test of the scattering theory of
photo-assisted shot noise.Comment: 4 pages, 4 figure
The cholesterol-raising diterpenes from coffee beans increase serum lipid transfer protein activity levels in humans
Cafestol and kahweolâditerpenes present in unfiltered coffeeâ strongly raise serum VLDL and LDL cholesterol and slightly reduce HDL cholesterol in humans. The mechanism of action is unknown. We determined whether the coffee diterpenes may affect lipoprotein metabolism via effects on lipid transfer proteins and lecithin:cholesterol acyltransferase in a randomized, double-blind cross-over study with 10 healthy male volunteers. Either cafestol (61â64 mg/day) or a mixture of cafestol (60 mg/day) and kahweol (48â54 mg/day) was given for 28 days. Serum activity levels of cholesterylester transfer protein, phospholipid transfer protein and lecithin:cholesterol acyltransferase were measured using exogenous substrate assays. Relative to baseline values, cafestol raised the mean (±S.D.) activity of cholesterylester transfer protein by 18±12% and of phospholipid transfer protein by 21±14% (both P<0.001). Relative to cafestol alone, kahweol had no significant additional effects. Lecithin:cholesterol acyltransferase activity was reduced by 11±12% by cafestol plus kahweol (P=0.02). It is concluded that the effects of coffee diterpenes on plasma lipoproteins may be connected with changes in serum activity levels of lipid transfer proteins
The Polytropic Equation of State of Interstellar Gas Clouds
Models are presented for the polytropic equation of state of
self-gravitating, quiescent interstellar gas clouds. A detailed analysis,
including chemistry, thermal balance, and radiative transfer, is performed for
the physical state of the gas as a function of density, metallicity, velocity
field, and background radiation field. It is found that the stiffness of the
equation of state strongly depends on all these physical parameters, and the
adiabatic index varies between 0.2-1.4. The implications for star formation, in
particular at high redshift and in starburst galaxies, and the initial stellar
mass function are discussed.Comment: Accepted by Ap
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