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 A rainfall threshold-based extreme rainfall alert (ERA) service was launched in 2009 and superseded in 2011 by the surface water flood risk assessment (SWFRA).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 SrTiO3_3 substrates

Mono- and multilayer FeSe thin films grown on SrTiO$_\mathrm{3}$ and BiTiO$_\mathrm{3}$ 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 ($e$-$ph$) interaction between the FeSe electrons and oxygen phonons in the substrates that is peaked in the forward scattering (small ${\bf q}$) 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