1,929 research outputs found
First Experiences Integrating PC Distributed I/O Into Argonne's ATLAS Control System
First Experiences Integrating PC Distributed I/O Into Argonne's ATLAS Control
System The roots of ATLAS (Argonne Tandem-Linac Accelerator System) date back
to the early 1960s. Located at the Argonne National Laboratory, the accelerator
has been designated a National User Facility, which focuses primarily on
heavy-ion nuclear physics. Like the accelerator it services, the control system
has been in a constant state of evolution. The present real-time portion of the
control system is based on the commercial product Vsystem [1]. While Vsystem
has always been capable of distributed I/O processing, the latest offering of
this product provides for the use of relatively inexpensive PC hardware and
software. This paper reviews the status of the ATLAS control system, and
describes first experiences with PC distributed I/O.Comment: ICALEPCS 2001 Conference, PSN WEAP027, 3 pages, 1 figur
Composite Reflective/Absorptive IR-Blocking Filters Embedded in Metamaterial Antireflection Coated Silicon
Infrared (IR) blocking filters are crucial for controlling the radiative
loading on cryogenic systems and for optimizing the sensitivity of bolometric
detectors in the far-IR. We present a new IR filter approach based on a
combination of patterned frequency selective structures on silicon and a thin
(50 thick) absorptive composite based on powdered reststrahlen
absorbing materials. For a 300 K blackbody, this combination reflects
50\% of the incoming light and blocks \textgreater 99.8\% of the total
power with negligible thermal gradients and excellent low frequency
transmission. This allows for a reduction in the IR thermal loading to
negligible levels in a single cold filter. These composite filters are
fabricated on silicon substrates which provide excellent thermal transport
laterally through the filter and ensure that the entire area of the absorptive
filter stays near the bath temperature. A metamaterial antireflection coating
cut into these substrates reduces in-band reflections to below 1\%, and the
in-band absorption of the powder mix is below 1\% for signal bands below 750
GHz. This type of filter can be directly incorporated into silicon refractive
optical elements
The Relational Database Aspects of Argonne's ATLAS Control System
The Relational Database Aspects of Argonnes ATLAS Control System Argonnes
ATLAS (Argonne Tandem Linac Accelerator System) control system comprises two
separate database concepts. The first is the distributed real-time database
structure provided by the commercial product Vsystem [1]. The second is a more
static relational database archiving system designed by ATLAS personnel using
Oracle Rdb [2] and Paradox [3] software. The configuration of the ATLAS
facility has presented a unique opportunity to construct a control system
relational database that is capable of storing and retrieving complete archived
tune-up configurations for the entire accelerator. This capability has been a
major factor in allowing the facility to adhere to a rigorous operating
schedule. Most recently, a Web-based operator interface to the control systems
Oracle Rdb database has been installed. This paper explains the history of the
ATLAS database systems, how they interact with each other, the design of the
new Web-based operator interface, and future plans.Comment: ICALEPCS 2001 Conference, PSN WEAP066, 3 pages, 3 figure
Structural diversity in the type IV pili of multidrug-resistant Acinetobacter
Acinetobacter baumannii is a Gram-negative coccobacillus found primarily in hospital settings that has recently emerged as a source of hospital-acquired infections. A. baumannii expresses a variety of virulence factors, including type IV pili, bacterial extracellular appendages often essential for attachment to host cells. Here, we report the high resolution structures of the major pilin subunit, PilA, from three Acinetobacter strains, demonstrating thatA. baumannii subsets produce morphologically distinct type IV pilin glycoproteins. We examine the consequences of this heterogeneity for protein folding and assembly as well as host-cell adhesion by Acinetobacter. Comparisons of genomic and structural data with pilin proteins from other species of soil gammaproteobacteria suggest that these structural differences stem from evolutionary pressure that has resulted in three distinct classes of type IVa pilins, each found in multiple species
Global Diffusion in a Realistic Three-Dimensional Time-Dependent Nonturbulent Fluid Flow
We introduce and study the first model of an experimentally realizable
three-dimensional time-dependent nonturbulent fluid flow to display the
phenomenon of global diffusion of passive-scalar particles at arbitrarily small
values of the nonintegrable perturbation. This type of chaotic advection,
termed {\it resonance-induced diffusion\/}, is generic for a large class of
flows.Comment: 4 pages, uuencoded compressed postscript file, to appear in Phys.
Rev. Lett. Also available on the WWW from http://formentor.uib.es/~julyan/,
or on paper by reques
Study of the microstructure resulting from brazed aluminium materials used in heat exchangers
Re-solidification of AA4343 cladding after brazing as well as the related precipitation in the modified AA3003 core material have been investigated. Analysis of the re-solidified material showed that partial dissolution of the core alloy occurs in both the brazing joints and away of them. Far from the brazing joints, the dissolution is, however, limited and diffusion of silicon from the liquid into the core material leads to solid-state precipitation in the so-called “band of dense precipitates” (BDP). On the contrary, the dissolution is enhanced in the brazing joint to such an extent that no BDP could be observed. The intermetallic phases present in the resolidified areas as well as in the core material have been analyzed and found to be mainly cubic alpha-Al(Mn,Fe)Si. These results were then compared to predictions made with available phase diagram information
Application of powder metallurgy techniques to produce improved bearing elements for liquid rocket engines
The objective was to apply powder metallurgy techniques for the production of improved bearing elements, specifically balls and races, for advanced cryogenic turbopump bearings. The materials and fabrication techniques evaluated were judged on the basis of their ability to improve fatigue life, wear resistance, and corrosion resistance of Space Shuttle Main Engine (SSME) propellant bearings over the currently used 440C. An extensive list of candidate bearing alloys in five different categories was considered: tool/die steels, through hardened stainless steels, cobalt-base alloys, and gear steels. Testing of alloys for final consideration included hardness, rolling contact fatigue, cross cylinder wear, elevated temperature wear, room and cryogenic fracture toughness, stress corrosion cracking, and five-ball (rolling-sliding element) testing. Results of the program indicated two alloys that showed promise for improved bearing elements. These alloys were MRC-2001 and X-405. 57mm bearings were fabricated from the MRC-2001 alloy for further actual hardware rig testing by NASA-MSFC
Conservation Laws and Energy Transformations in a Class of Common Physics Problems
We analyze a category of problems that is of interest in many physical situations, including those encountered in introductory physics classes: systems with two well-delineated parts that exchange energy, eventually reaching a shared equilibrium with a loss of mechanical or electrical energy. Such systems can be constrained by a constant of the system (e.g., mass, charge, momentum, or angular momentum) that uniquely determines the mechanical or electrical energy of the equilibrium state, regardless of the dissipation mechanism. A representative example would be a perfectly inelastic collision between two objects in one dimension, for which momentum conservation requires that some of the initial kinetic energy is dissipated by conversion to thermal or other forms as the two objects reach a common final velocity. We discuss how this feature manifests in a suite of four well-known and disparate problems that all share a common mathematical formalism. These examples, in which the energy dissipated during the process can be difficult to solve directly from dissipation rates, can be approached by students in a first-year physics class by considering conservation laws and can therefore be useful for teaching about energy transformations and conserved quantities. We then illustrate how to extend this method by applying it to a final example
A simulation toolkit for electroluminescence assessment in rare event experiments
A good understanding of electroluminescence is a prerequisite when optimising
double-phase noble gas detectors for Dark Matter searches and high-pressure
xenon TPCs for neutrinoless double beta decay detection.
A simulation toolkit for calculating the emission of light through electron
impact on neon, argon, krypton and xenon has been developed using the Magboltz
and Garfield programs. Calculated excitation and electroluminescence
efficiencies, electroluminescence yield and associated statistical fluctuations
are presented as a function of electric field. Good agreement with experiment
and with Monte Carlo simulations has been obtained
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