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 T=0KT=0 K

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 $T^{J}$, which is one or two orders of magnitude smaller than $T^{d}$, the direct transmission for elastic currents. Our theory is in excellent agreement with experimental data, yielding estimated values of $T^{J}$ which are of the order of $T^{d}$ / $T^{J}$ ~ 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

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