7,705 research outputs found
Large-scale electric fields resulting from magnetic reconnection in the corona
The method of Forbes and Priest (2-D model) is applied to the large two-ribbon flare of July 29, 1973, for which both detailed H observations and magnetic data are available. For this flare the ribbons were long, nearly straight, and parallel to each other, and the 2-D model for the coronal field geometry may be adequate. The temporal profile E(t) is calculated and indicates that reconnection sets in at the beginning of the decay phase. From this time the electric field grows rapidly to a maximum value of about 2 V/cm within just a few minutes. Thereafter it decreases monotonically with time
Magnetic field re-arrangement after prominence eruption
It has long been known that magnetic reconnection plays a fundamental role in a variety of solar events. Although mainly invoked in flare problems, large scale loops interconnecting active regions, evolving coronal hole boundaries, the solar magnetic cycle itself, provide different evidence of phenomena which involve magnetic reconnection. A further example might be given by the magnetic field rearrangement which occurs after the eruption of a prominence. Since most often a prominence reforms after its disappearance and may be observed at about the same position it occupied before erupting, the magnetic field has to undergo a temporary disruption of relax back, via reconnection, to a configuration similar to the previous one. The above sequence of events is best observable in the case of two ribbon (2-R) flares but most probably is associated with all filament eruptions. Even if the explanation of the magnetic field rearrangement after 2-R flares in terms of reconnection is generally accepted, the lack of a 3-dimensional model capable of describing the field reconfiguration, has prevented, up to now, a thorough analysis of its topology as traced by H alpha/x ray loops. A numerical technique is presented which enables oneto predict and visualize the reconnected configuration, at any time, and therefore allows one to make a significant comparison of observations and model predictions throughout the whole process
Effect of Vinyl and Silicon Monomers on Mechanical and Degradation Properties of Bio-Degradable Jute-Biopol® Composite
Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.Composites of jute fabrics (Hessian cloth) and Biopol® were prepared by compression molding process. Three types of Biopol® (3-hydroxbutyrate-co-3-hydroxyvalarate) such as D300G, D400G and D600G, depending on the concentration of 3-hydroxyvalarate (3HV) in 3-hydroxbutyrate (3HB) were taken for this purpose. Mechanical properties such as tensile strength (TS), bending strength (BS), elongation at break (Eb) and impact strength (IS) of the jute-Biopol® composites were studied. It was found that the composite with D400G produced higher mechanical properties in comparison to the other two types of Biopol®. To increase mechanical properties as well as interfacial adhesion between fiber and matrix, 2-ethyl hydroxy acrylate (EHA), vinyl tri-methoxy silane (VMS) and 3-methacryloxypropyl tri-methoxy silane (MPS) were taken as coupling agents. Enhanced mechanical properties of the composites were obtained by using these coupling agents. Biopol® D400G composites showed the highest mechanical properties. Among the coupling agents EHA depicts the highest increase of mechanical properties such as tensile strength (80%), bending strength (81%), elongation at break (33%) and impact strength (130%) compared pure Biopol. SEM investigations demonstrate that the coupling agents improve the interfacial adhesion between fiber and matrix. The surface of the silanized jute was characterized by FTIR and found the deposition of silane on jute fiber was observed. Soil degradation test proved that the composite prepared with EHA treated jute exhibits better degradation properties in comparison to pure Biopol®
Are there sterile neutrinos at the eV scale?
New predictions for the anti-neutrino flux emitted by nuclear reactors
suggest that reactor experiments may have measured a deficit in the
anti-neutrino flux, which can be interpreted in terms of oscillations between
the known active neutrinos and new sterile states. Motivated by this
observation, we perform a re-analysis of global short-baseline neutrino
oscillation data in a framework with one or two sterile neutrinos. While one
sterile neutrino is still not sufficient to reconcile the signals suggested by
reactor experiments and by the LSND and MiniBooNE experiments with null results
from other searches, we find that, with the new reactor flux prediction, the
global fit improves considerably when the existence of two sterile neutrinos is
assumed.Comment: 5 pages, 5 figures, v2: reference and acknowledgements adde
Intercomparison of numerical models of flaring coronal loops
The proposed Benchmark Problem consists of an infinitesimal magnetic flux tube containing a low-beta plasma. The field strength is assumed to be so large that the plasma can move only along the flux tube, whose shape remains invariant with time (i.e., the fluid motion is essentially one-dimensional). The flux tube cross section is taken to be constant over its entire length. In planar view the flux tube has a semi-circular shape, symmetric about its midpoint s = s sub max and intersecting the chromosphere-corona interface (CCI) perpendicularly at each foot point. The arc length from the loop apex to the CCI is 10,000 km. The flux tube extends an additional 2000 km below the CCI to include the chromosphere, which initially has a uniform temperature of 8000 K. The temperature at the top of the loop was fixed initially at 2 X 1 million K. The plasma is assumed to be a perfect gas (gamma = 5/3), consisting of pure hydrogen which is considered to be fully ionized at all temperatures. For simplicity, moreover, the electron and ion temperatures are taken to be everywhere equal at all times (corresponding to an artificially enhanced electron-ion collisional coupling). While there was more-or-less unanimous agreement as to certain global properties of the system behavior (peak temperature reached, thermal-wave time scales, etc.), no two groups could claim satisfactory accord when a more detailed comparison of solutions was attempted
Magnetism and superconductivity at LAO/STO-interfaces: the role of Ti 3d interface electrons
Ferromagnetism and superconductivity are in most cases adverse. However,
recent experiments reveal that they coexist at interfaces of LaAlO3 and SrTiO3.
We analyze the magnetic state within density functional theory and provide
evidence that magnetism is not an intrinsic property of the two-dimensional
electron liquid at the interface. We demonstrate that the robust ferromagnetic
state is induced by the oxygen vacancies in SrTiO3- or in the LaAlO3-layer.
This allows for the notion that areas with increased density of oxygen
vacancies produce ferromagnetic puddles and account for the previous
observation of a superparamagnetic behavior in the superconducting state.Comment: 5 pages, 4 figures, to appear in Physical Review B (Rapid
Communications
Interface hole-doping in cuprate-titanate superlattices
The electronic structure of interfaces between YBaCuO and
SrTiO is studied using local spin density approximation (LSDA) with
intra-atomic Coulomb repulsion (LSDA+U). We find a metallic state in
cuprate/titanate heterostructures with the hole carriers concentrated
substantially in the CuO-layers and in the first interface TiO and SrO
planes. This effective interface doping appears due to the polarity of
interfaces, caused by the first incomplete copper oxide unit cell.
Interface-induced high pre-doping of CuO-layers is a key mechanism
controlling the superconducting properties in engineered field-effect devices
realized on the basis of cuprate/titanate superlattices.Comment: 5 pages, 5 figure
On the estimation of time dependent lift of a European Starling during flapping
We study the role of unsteady lift in the context of flapping wings in birds'
flight. Both aerodynamicists and biologists attempt to address this subject,
yet it seems that the contribution of the unsteady lift still holds many open
questions. The current study deals with the estimation of unsteady aerodynamic
forces on a freely flying bird through analysis of wingbeat kinematics and near
wake flow measurements using time resolved particle image velocimetry. The
aerodynamic forces are obtained through unsteady thin airfoil theory and lift
calculation using the momentum equation for viscous flows. The unsteady lift is
comprised of circulatory and non-circulatory components. Both are presented
over wingbeat cycles. Using long sampling data, several wingbeat cycles have
been analyzed in order to cover the downstroke and upstroke phases. It appears
that the lift varies over the wingbeat cycle emphasizing its contribution to
the total lift and its role in power estimations. It is suggested that the
circulatory lift component cannot assumed to be negligible and should be
considered when estimating lift or power of birds in flapping motion
Beam-Based Alignment of the NuMI Target Station Components at FNAL
The Neutrinos at the Main Injector (NuMI) facility is a conventional
horn-focused neutrino beam which produces muon neutrinos from a beam of mesons
directed into a long evacuated decay volume. The relative alignment of the
primary proton beam, target, and focusing horns affects the neutrino energy
spectrum delivered to experiments. This paper describes a check of the
alignment of these components using the proton beam.Comment: higher resolution figures available on Fermilab Preprint Server (see
SPIRES entry), accepted for publication in Nucl. Instr. and Meth.
Impact of DM direct searches and the LHC analyses on branon phenomenology
Dark Matter direct detection experiments are able to exclude interesting
parameter space regions of particle models which predict an important amount of
thermal relics. We use recent data to constrain the branon model and to compute
the region that is favored by CDMS measurements. Within this work, we also
update present colliders constraints with new studies coming from the LHC.
Despite the present low luminosity, it is remarkable that for heavy branons,
CMS and ATLAS measurements are already more constraining than previous analyses
performed with TEVATRON and LEP data.Comment: 17 pages, 2 figure
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