Simulations of the Boundary Layer Between a White Dwarf and its Accretion Disk

Using a 2.5D time-dependent axisymmetric numerical code we recently developed, we solve the full compressible Navier-Stokes equations (including an alpha-viscosity prescription) to determine the structure of the boundary layer between the white dwarf and the accretion disk in non-magnetic cataclysmic varia ble systems. In this preliminary work, our numerical approach does not include radiation. In the energy equation, we either take the dissipation function (Phi) into account or we assumed that the energy is instantly radiated away (Phi). For a slowly rotating non magnetized accreting white dwarf, the accretion disk e xtends all the way to the stellar surface. There, the matter impacts and spread s towards the poles as new matter continuously piles up behind it. We carried out numerical simulations for different values of the alpha viscosity parameter (alpha), corresponding to different mass accretion rates. In the high viscosity cases (alpha=0.1), the spreading boundary layer sets off a gravity wave in the s urface matter. The accretion flow moves supersonically over the cusp making it s usceptible to the rapid development of gravity wave and/or Kelvin-Helmholtz shea ring instabilities. This BL is optically thick and extends more than 30 degrees to either side of the disk plane after only 3/4 of a Keplerian rotation period (19s). In the low viscosity cases (alpha=0.001), the spreading boundary layer does not set off gravity waves and it is optically thin.Comment: final version, ApJ, in pres

A Survey of Far Ultraviolet Spectroscopic Explorer Observations of Cataclysmic Variables

During its lifetime, the Far Ultraviolet Spectroscopic Explorer (FUSE) was used to observe 99 cataclysmic variables in 211 separate observations. Here, we present a survey of the moderate resolution (R\simeq10,000), far-ultraviolet (905 - 1188 {\deg}A), time-averaged FUSE spectra of cataclysmic variables (CVs). The FUSE spectra are morphologically diverse. They show contributions from the accretion disk, the disk chromosphere, disk outflows, and the white dwarf, but the relative contribution of each component varies widely as a function of CV subtype, orbital period and evolutionary state, inclination, mass accretion rate, and magnetic field strength of the white dwarf. The data reveal information about the structure, temperature, density and mass flow rates of the disk and disk winds, the temperature of the white dwarf and the effects of ongoing accretion on its structure, and the long-term response of the systems to disk outbursts. The complete atlas of time-averaged FUSE spectra of CVs are available at the Multimission Archive at Space Telescope Science Institute as a High Level Science Product.Comment: ApJS, in press. The extra panels in the figure sets for Figures 1 and 2 are included at the end of the manuscrip

An Exploratory Study of RFID Implementation in the Supply Chain

The purpose of this paper is to investigate the barriers and motivations for adopting radio frequency identification (RFID), the level of RFID implementation, the processes RFID is utilized in, and issues in the deployment of RFID. A survey instrument was developed based on a literature review. The survey was then distributed to the members of the Association for Operations Management Rhode Island and Boston chapters. The results were then analyzed. It was found that the majority of the surveyed firms are not considering RFID implementation. Lack of a business case and lack of understanding were cited as their main concerns. For firms considering RFID implementation and firms that had implemented RFID, better inventory management, obtaining competitive advantage, and cost reduction were the three most important motivations for adopting RFID. Financial concerns and the lack of a business case were the most prevalent issues. In addition, product tracking (pallets, cases, and items) in shipping was the most cited RFID application. It was also found that considering firms are facing less pressure from customers to adopt RFID and reported a much higher degree of apprehension regarding potential issues than implementing firms reported for actual difficulties faced. One of the limitations is the small sample size (n = 49) which may limit the generalizability of the results. By identifying barriers, motivations, and issues in the implementation of RFID, this study further educates practitioners on the challenges and opportunities of RFID, as well as providing direction to academicians for further research on this area