16,034 research outputs found
Tunable conductance of magnetic nanowires with structured domain walls
We show that in a magnetic nanowire with double magnetic domain walls,
quantum interference results in spin-split quasistationary states localized
mainly between the domain walls. Spin-flip-assisted transmission through the
domain structure increases strongly when these size-quantized states are tuned
on resonance with the Fermi energy, e.g. upon varying the distance between the
domain walls which results in resonance-type peaks of the wire conductance.
This novel phenomena is shown to be utilizable to manipulate the spin density
in the domain vicinity. The domain walls parameters are readily controllable
and the predicted effect is hence exploitable in spintronic devices.Comment: 4 pages with 4 figure
Ferromagnetic tunneling junctions at low voltages: elastic versus inelastic scattering at
In this paper we analyze different contributions to the magnetoresistance of
magnetic tunneling junctions at low voltages. A substantial fraction of the
resistance drop with voltage can be ascribed to variations of the density of
states and the barrier transmission with the bias. However, we found that the
anomaly observed at zero bias and the magnetoresistance behavior at very small
voltages, point to the contribution of inelastic magnon-assisted tunneling. The
latter is described by a transfer parameter , which is one or two orders
of magnitude smaller than , the direct transmission for elastic
currents. Our theory is in excellent agreement with experimental data, yielding
estimated values of which are of the order of / ~ 40.Comment: 13 pages, 4 figures (in postscript format). PACS numbers: 72.25.-b,
73.23.-b, 72.10.D
The Epeak-Eiso plane of long Gamma Ray Bursts and selection effects
We study the distribution of long Gamma Ray Bursts in the Ep-Eiso and in the
Ep,obs-Fluence planes through an updated sample of 76 bursts, with measured
redshift and spectral parameters, detected up to September 2007. We confirm the
existence of a strong rest frame correlation Ep ~ Eiso^0.54+-0.01. Contrary to
previous studies, no sign of evolution with redshift of the Ep-Eiso correlation
(either its slope and normalisation) is found. The 76 bursts define a strong
Ep,obs-Fluence correlation in the observer frame (Ep,obs ~ F^0.32+-0.05) with
redshifts evenly distributed along this correlation. We study possible
instrumental selection effects in the observer frame Ep,obs-Fluence plane. In
particular, we concentrate on the minimum peak flux necessary to trigger a
given GRB detector (trigger threshold) and the minimum fluence a burst must
have to determine the value of Ep,obs (spectral analysis threshold). We find
that the latter dominates in the Ep,obs-Fluence plane over the former. Our
analysis shows, however, that these instrumental selection effects do not
dominate for bursts detected before the launch of the Swift satellite, while
the spectral analysis threshold is the dominant truncation effect of the Swift
GRB sample (27 out of 76 events). This suggests that the Ep,obs-Fluence
correlation defined by the pre--Swift sample could be affected by other, still
not understood, selection effects. Besides we caution about the conclusions on
the existence of the Ep,obs-Fluence correlation based on our Swift sample
alone.Comment: To appear in MNRA
Snake orbits and related magnetic edge states
We study the electron motion near magnetic field steps at which the strength
and/or sign of the magnetic field changes. The energy spectrum for such systems
is found and the electron states (bound and scattered) are compared with their
corresponding classical paths. Several classical properties as the velocity
parallel to the edge, the oscillation frequency perpendicular to the edge and
the extent of the states are compared with their quantum mechanical
counterpart. A class of magnetic edge states is found which do not have a
classical counterpart.Comment: 8 pages, 10 figure
Spectral analysis of Swift long GRBs with known redshift
We study the spectral and energetics properties of 47 long-duration gamma-ray
bursts (GRBs) with known redshift, all of them detected by the Swift satellite.
Due to the narrow energy range (15-150 keV) of the Swift-BAT detector, the
spectral fitting is reliable only for fitting models with 2 or 3 parameters. As
high uncertainty and correlation among the errors is expected, a careful
analysis of the errors is necessary. We fit both the power law (PL, 2
parameters) and cut--off power law (CPL, 3 parameters) models to the
time-integrated spectra of the 47 bursts, and present the corresponding
parameters, their uncertainties, and the correlations among the uncertainties.
The CPL model is reliable only for 29 bursts for which we estimate the nuf_nu
peak energy Epk. For these GRBs, we calculate the energy fluence and the rest-
frame isotropic-equivalent radiated energy, Eiso, as well as the propagated
uncertainties and correlations among them. We explore the distribution of our
homogeneous sample of GRBs on the rest-frame diagram E'pk vs Eiso. We confirm a
significant correlation between these two quantities (the "Amati" relation) and
we verify that, within the uncertainty limits, no outliers are present. We also
fit the spectra to a Band model with the high energy power law index frozen to
-2.3, obtaining a rather good agreement with the "Amati" relation of non-Swift
GRBs.Comment: 16 pages. To appear in MNRAS. Minor changes were introduced in this
last versio
OB Stars in the Solar Neighborhood I: Analysis of their Spatial Distribution
We present a newly-developed, three-dimensional spatial classification
method, designed to analyze the spatial distribution of early type stars within
the 1 kpc sphere around the Sun. We propose a distribution model formed by two
intersecting disks -the Gould Belt (GB) and the Local Galactic Disk (LGD)-
defined by their fundamental geometric parameters. Then, using a sample of
about 550 stars of spectral types earlier than B6 and luminosity classes
between III and V, with precise photometric distances of less than 1 kpc, we
estimate for some spectral groups the parameters of our model, as well as
single membership probabilities of GB and LGD stars, thus drawing a picture of
the spatial distribution of young stars in the vicinity of the Sun.Comment: 28 pages including 9 Postscript figures, one of them in color.
Accepted for publication in The Astronomical Journal, 30 January 200
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The role of consumption in material reduction opportunities: the impact of product lifetime in supplying the UK steel demand
Most of the products purchased in the UK are manufactured in other countries. As a result, worldwide greenhouse gases (GHG) emissions released to manufacture all products purchased in the UK are significantly higher than the UK territorial emissions. More than one half of global industrial emissions result from the use of steel, cement, paper, plastics, and aluminium. In this paper, the UK consumption of products that embody these five materials is estimated. For steel, which is the most widely used among these five materials, consumption and accumulation patterns are examined across four product categories. The impact of steel product lifetime extension is examined for the UK as one option for material demand reduction at the consumption stage of the supply chain. Different levels of steel product lifetimes are simulated for the UK in 2050 and their impacts are examined in terms of UK steel production, implicit steel imports, and global carbon dioxide emissions. Steel product lifetime extension promotes a reduction in the need for steel imports, by reducing the demand for new steel, which leads to lower carbon dioxide emissions required to supply the UK steel demand. The results demonstrate the criticality of a focus on the consumption stage, since any interventions made towards demand reduction of end-use goods leads to material reduction across the supply chain
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