26,133 research outputs found
Origin of the transient unpulsed radio emission from the PSR B1259-63 binary system
We discuss the interpretation of transient, unpulsed radio emission detected
from the unique pulsar/Be-star binary system PSR B1259-63. Extensive monitoring
of the 1994 and 1997 periastron passages has shown that the source flares over
a 100-day interval around periastron, varying on time-scales as short as a day
and peaking at 60 mJy (~100 times the apastron flux density) at 1.4 GHz.
Interpreting the emission as synchrotron radiation, we show that (i) the
observed variations in flux density are too large to be caused by the shock
interaction between the pulsar wind and an isotropic, radiatively driven,
Be-star wind, and (ii) the radio emitting electrons do not originate from the
pulsar wind. We argue instead that the radio electrons originate from the
circumstellar disk of the Be star and are accelerated at two epochs, one before
and one after periastron, when the pulsar passes through the disk. A simple
model incorporating two epochs of impulsive acceleration followed by
synchrotron cooling reproduces the essential features of the radio light curve
and spectrum and is consistent with the system geometry inferred from pulsed
radio data.Comment: To be published in Astrophysical Journal Letters 7 pages, 1
postscript figur
Polydimethylsiloxane based microfluidic diode
In this paper, we present a novel elastomer-based microfluidic device for rectifying flow. The device is analogous to an electronic diode in function since it allows flow in one direction and stops flow in the opposing direction. The device is planar, in-line and can be replica molded via standard soft lithography techniques. The fabrication process is outlined in detail and follows a simple procedure that requires only photolithography and one replica molding step. Several geometries of devices are presented along with their flow versus pressure characteristics. A brief discussion of the device behavior is presented along with possible uses for the device
Surface water flood warnings in England: overview, Assessment and recommendations based on survey responses and workshops
Following extensive surface water flooding (SWF) in England in summer 2007, progress has been made in improving the management and prediction of this type of flooding. A rainfall threshold-based extreme rainfall alert (ERA) service was launched in 2009 and superseded in 2011 by the surface water flood risk assessment (SWFRA). Through survey responses from local authorities (LAs) and the outcome of workshops with a range of flood professionals, this paper examines the understanding, benefits, limitations and ways to improve the current SWF warning service. The current SWFRA alerts are perceived as useful by district and county LAs, although their understanding of them is limited. The majority of LAs take action upon receipt of SWFRA alerts, and their reactiveness to alerts appears to have increased over the years and as SWFRA superseded ERA. This is a positive development towards increased resilience to SWF. The main drawback of the current service is its broad spatial resolution. Alternatives for providing localised SWF forecast and warnings were analysed, and a two-tier national-local approach, with pre-simulated scenario-based local SWF forecasting and warning systems, was deemed most appropriate by flood professionals given current monetary, human and technological resources
Aspects of electron-phonon interactions with strong forward scattering in FeSe Thin Films on SrTiO substrates
Mono- and multilayer FeSe thin films grown on SrTiO and
BiTiO substrates exhibit a greatly enhanced superconductivity over
that found in bulk FeSe. A number of proposals have been advanced for the
mechanism of this enhancement. One possibility is the introduction of a
cross-interface electron-phonon (-) interaction between the FeSe
electrons and oxygen phonons in the substrates that is peaked in the forward
scattering (small ) direction due to the two-dimensional nature of the
interface system. Motivated by this, we explore the consequences of such an
interaction on the superconducting state and electronic structure of a
two-dimensional system using Migdal-Eliashberg theory. This interaction
produces not only deviations from the expectations of conventional
phonon-mediated pairing but also replica structures in the spectral function
and density of states, as probed by angle-resolved photoemission spectroscopy,
scanning tunneling microscopy/spectroscopy, and quasi-particle interference
imaging. We also discuss the applicability of Migdal-Eliashberg theory for a
situation where the \ep interaction is peaked at small momentum transfer and in
the FeSe/STO system
Electronic structure and magnetic properties of Li_2ZrCuO_4 - a spin 1/2 Heisenberg system in vicinity to a quantum critical point
Based on density functional calculations, we present a detailed theoretical
study of the electronic structure and the magnetic properties of the quasi-one
dimensional chain cuprate Li_2ZrCuO_4 (Li_2CuZrO_4). For the relevant ratio of
the next-nearest neighbor exchange J_2 to the nearest neighbor exchange J_1 we
find alpha = -J_2/J_1 = 0.22\pm0.02 which is very close to the critical point
at 1/4. Owing this vicinity to a ferromagnetic-helical critical point, we study
in detail the influence of structural peculiarities such as the reported Li
disorder and the non-planar chain geometry on the magnetic interactions
combining the results of LDA based tight-binding models with LDA+U derived
exchange parameters. Our investigation is complemented by an exact
diagonalization study of a multi-band Hubbard model for finite clusters
predicting a strong temperature dependence of the optical conductivity for
Li_2ZrCuO_4
Automated data acquisition and reduction system for torsional braid analyzer
Automated Data Acquisition and Reduction System (ADAR) evaluates damping coefficient and relative rigidity by storing four successive peaks of waveform and time period between two successive peaks. Damping coefficient and relative rigidity are then calculated and plotted against temperature or time in real time
Quiet Clean Short-haul Experimental Engine (QCSEE) Under-The-Wing (UTW) composite nacelle subsystem test report
The element and subcomponent testing conducted to verify the under the wing composite nacelle design is reported. This composite nacelle consists of an inlet, outer cowl doors, inner cowl doors, and a variable fan nozzle. The element tests provided the mechanical properties used in the nacelle design. The subcomponent tests verified that the critical panel and joint areas of the nacelle had adequate structural integrity
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