150,711 research outputs found
Efficient implementation of real-time programs under the VAX/VMS operating system
Techniques for writing efficient real-time programs under the VAX/VMS oprating system are presented. Basic operations are presented for executing at real-time priority and for avoiding needlless processing delays. A highly efficient technique for accessing physical devices by mapping to the input/output space and accessing the device registrs directly is described. To illustrate the application of the technique, examples are included of different uses of the technique on three devices in the Langley Avionics Integration Research Lab (AIRLAB): the KW11-K dual programmable real-time clock, the Parallel Communications Link (PCL11-B) communication system, and the Datacom Synchronization Network. Timing data are included to demonstrate the performance improvements realized with these applications of the technique
ASSIST: User's manual
Semi-Markov models can be used to compute the reliability of virtually any fault-tolerant system. However, the process of delineating all of the states and transitions in a model of a complex system can be devastingly tedious and error-prone. The ASSIST program allows the user to describe the semi-Markov model in a high-level language. Instead of specifying the individual states of the model, the user specifies the rules governing the behavior of the system and these are used by ASSIST to automatically generate the model. The ASSIST program is described and illustrated by examples
Viscous flow of the Cu47-Ti34-Zr11-Ni8 glass forming alloy
The viscosity of the Cu47-Ti34-Zr11-Ni8 glass forming alloy was determined by beam bending experiments and by a noncontact oscillating drop technique. These viscosity data can be described with the Vogel-Fulcher-Tammann relation. Using the strong/fragile classification of glasses, Cu47-Ti34-Zr11-Ni8 is more fragile than the strong Zr-Ti-Cu-Ni-Be metallic glass formers
Brazing process using'al-Si filler alloy reliably bonds aluminum parts
Brazing process employs an aluminum-silicon filler alloy for diffusion bonding of aluminum parts in a vacuum or inert gas atmosphere. This process is carried out at temperatures substantially below those required in conventional process and produces bonds of greater strength and reliability
High Efficiency Large Area Polysilicon Solar Cells
Large area (100 sq cm) polysilicon solar cells having efficiencies of up to 14.1% (100 mW/sq cm, 25 C) were fabricated and a detailed analysis was performed to identify the efficiency loss mechanisms. The 1-5 characteristics of the best cell were dominated by recombination in the quasi-neutral base due to the combination of minority carrier diffusion length and base resistivity. An analysis of the microstructural defects present in the material and their effect on the electrical properties is presented
Imaging and quantum efficiency measurement of chromium emitters in diamond
We present direct imaging of the emission pattern of individual
chromium-based single photon emitters in diamond and measure their quantum
efficiency. By imaging the excited state transition dipole intensity
distribution in the back focal plane of high numerical aperture objective, we
determined that the emission dipole is oriented nearly orthogonal to the
diamond-air interface. Employing ion implantation techniques, the emitters were
engineered with various proximities from the diamond-air interface. By
comparing the decay rates from the single chromium emitters at different depths
in the diamond crystal, an average quantum efficiency of 28% was measured.Comment: 11 pages and 4 figure
Analysis of ZDDP content and thermal decomposition in motor oils using NAA and NMR
Zinc dialkyldithiophosphates (ZDDPs) are one of the most common anti-wear
additives present in commercially-available motor oils. The ZDDP concentrations
of motor oils are most commonly determined using inductively coupled plasma
atomic emission spectroscopy (ICP-AES). As part of an undergraduate research
project, we have determined the Zn concentrations of eight
commercially-available motor oils and one oil additive using neutron activation
analysis (NAA), which has potential for greater accuracy and less sensitivity
to matrix effects as compared to ICP-AES. The 31P nuclear magnetic resonance
(31P-NMR) spectra were also obtained for several oil additive samples which
have been heated to various temperatures in order to study the thermal
decomposition of ZDDPs.Comment: Manuscript has been accepted for publication in Physics Procedia as
part of the proceedings of the 23rd International Conference on Application
of Accelerators in Research and Industry (CAARI 2014
The quiescent progenitors of four Type II-P/L supernovae
We present Large Binocular Telescope difference imaging data for the final
years of four Type II-P/L supernovae progenitors. For all four, we find no
significant evidence for stochastic or steady variability in the U, B, V, or
R-bands. Our limits constrain variability to no more than roughly 5-10% of the
expected R-band luminosities of the progenitors. These limits are comparable to
the observed variability of red supergiants in the Magellanic Clouds. Based on
these four events, the probability of a Type II-P/L progenitor having an
extended outburst after Oxygen ignition is <37% at 90% confidence. Our
observations cannot exclude short outbursts in which the progenitor returns to
within ~10% of its quiescent flux on the time scale of months with no dust
formation.Comment: 9 pages, 8 figures, 1 table. Accepted to MNRA
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