932 research outputs found
Transport in the metallic regime of Mn doped III-V Semiconductors
The standard model of Mn doping in GaAs is subjected to a coherent potential
approximation (CPA) treatment. Transport coefficients are evaluated within the
linear response Kubo formalism. Both normal (NHE) and anomalous contributions
(AHE) to the Hall effect are examined. We use a simple model density of states
to describe the undoped valence band. The CPA bandstructure evolves into a spin
split band caused by the exchange scattering with Mn dopants. This gives
rise to a strong magnetoresistance, which decreases sharply with temperature.
The temperature () dependence of the resistance is due to spin disorder
scattering (increasing with ), CPA bandstructure renormalization and charged
impurity scattering (decreasing with ). The calculated transport
coefficients are discussed in relation to experiment, with a view of assessing
the overall trends and deciding whether the model describes the right physics.
This does indeed appear to be case, bearing in mind that the hopping limit
needs to be treated separately, as it cannot be described within the band CPA.Comment: submitted to Phys. Rev.
Hall conductivity in the presence of spin-orbit interaction and disorder
Starting from the Kubo formula, we expand the Hall conductivity using a
cumulant approach which converges quickly at high temperatures (k_BT > energy
differences of initial and final scattering states) and can be extended to low
temperatures. The theory can deal with the sign, the ordinary and the anomalous
contributions to the Hall effect. When applied to include the spin-orbit
interaction to first order, we recover what is essentially the
Karplus-Luttinger result for the anomalous Hall effect. Contact is made to the
Chazalviel and Nozieres-Lewiner formulae. A side-jump type formula is obtained
by using an exact application of linear response. We show that there exists an
exact rigid Hall current which is not a Fermi level property. We introduce a
relationship between mass and diffusivity which allows us to generalize the
theory to strong disorder and even introduce a mobility edge. The formalism
provides a systematic and practical way of analyzing both ordinary and
anomalous contributions to the Hall conduction including the changes of sign,
and in the presence of serious disorder. As a byproduct of the method, we show
that the anomalous Hall coefficient can vary with resistance to the power n,
with 1 <= n <= 2 depending on the degree of coherence.Comment: Accepted for publication in Physical Review
Unexpected transcellular protein crossover occurs during canonical DNA transfection.
Transfection of DNA has been invaluable for biological sciences, yet the effects upon membrane homeostasis are far from negligible. Here, we demonstrate that Neuro2A cells transfected using Lipofectamine LTX with the fluorescently coupled Botulinum serotype A holoenzyme (EGFP-LcA) cDNA express this SNAP25 protease that can, once translated, escape the transfected host cytosol and become endocytosed into untransfected cells, without its innate binding and translocation domains. Fluorescent readouts revealed moderate transfection rates (30–50%) while immunoblotting revealed a surprisingly total enzymatic cleavage of SNAP25; the transgenic protein acted beyond the confines of its host cell. Using intracellular dyes, no important cytotoxic effects were observed from reagent treatment alone, which excluded the possibility of membrane ruptures, though noticeably, intracellular acidic organelles were redistributed towards the plasma membrane. This drastic, yet frequently unobserved, change in protein permeability and endosomal trafficking following reagent treatment highlights important concerns for all studies using transient transfection
Impact of mash feeding versus pellets on propionic/butyric acid levels and on total Escherichia coli load in the gastrointestinal tract of growing pigs
Feed characteristics may influence
the bacterial community composition and metabolic
activities in the pig gastrointestinal tract, known to be
associated with positive effects on the gut. Use of mash
feed is associated with reduced Salmonella excretion,
but little is known of its effect on the Escherichia coli
population or of the mechanism of action. Our objectives
were to assess the effect of feed texture combined
with feed particle size on VFA profiles and levels,
total E. coli count, and the presence of genes encoding
virulence factors of pathogenic E. coli strains in the
digestive tract along with their impact on pig performance
of fattening pigs. Pigs (n = 840) on a commercial
farm received mash or pellet diets of different particle
sizes during the fattening period. Caecal and colon contents
from 164 pigs were sampled at the slaughterhouse
for enumeration of E. coli by quantitative PCR (qPCR)
and for VFA quantification by capillary gas chromatography.
The yccT gene was used to enumerate total E.
coli. Improved pig performances associated with pellet
texture and a 500-μm size were observed. Caecal (P =
0.02) and colon (P < 0.01) propionic acid concentrations
were lower for pigs receiving pellet rather than
mash feed. Similarly, caecal (P = 0.01) and colon (P <
0.001) butyric acid concentrations were also lower for
pigs receiving pellet rather than mash feed, as determined
by capillary gas chromatography. Moreover,
caecal (P = 0.03) and colon (P < 0.001) butyric acid
concentrations were higher for pigs receiving a feed
with a 1,250-μm particle size rather than a 500-μm
particle size. On the other hand, total caecal and colon
E. coli levels were higher for pigs receiving pellet feed
than for those receiving mash feed. For total E. coli
enumeration, caecal (P < 0.01) and colon (P < 0.01)
yccT gene copies were higher for pigs receiving pellet
rather than mash feed. No effect of particle size on
fatty acid concentrations or on E. coli numbers was
observed. Virulence gene quantification revealed no
trend. Taken together, results showed that mash feed
is associated with lower growth performance but with
favorable intestinal changes linked to VFA levels and E.
coli reduction in the intestine
An improved method for statistical studies of the internal kinematics of HII regions: the case of M 83
We present the integrated Halpha emission line profile for 157 HII regions in
the central 3.4' x 3.4' of the galaxy M 83 (NGC 5236). Using the Fabry-Perot
interferometer GHaFaS, on the 4.2 m William Herschel on La Palma, we show the
importance of a good characterization of the instrumental response function for
the study of line profile shapes. The luminosity-velocity dispersion relation
is also studied, and in the log(L)-log(sigma) plane we do not find a linear
relation, but an upper envelope with equation log(L)=0.9 *log(sigma)+38.1. For
the adopted distance of 4.5 Mpc, the upper envelope appears at the luminosity
L=10^38.5 ergs, in full agreement with previous studies of other galaxies,
reinforcing the idea of using HII regions as standard candles.Comment: 13 pages, 9 figures, accepted for publication in MNRA
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