7,329 research outputs found
Helmet latching and attaching ring
A neck ring releasably secured to a pressurized garment carries an open-ended ring normally in the engagement position fitted into an annular groove and adapted to fit into a complementary annular groove formed in a helmet. Camming means formed on the inner surface at the end of the helmet engages the open-ended ring to retract the same and allow for one motion donning even when the garment is pressurized. A projection on the end of the split ring is engageable to physically retract the split ring
Hyperuniformity, quasi-long-range correlations, and void-space constraints in maximally random jammed particle packings. II. Anisotropy in particle shape
We extend the results from the first part of this series of two papers by
examining hyperuniformity in heterogeneous media composed of impenetrable
anisotropic inclusions. Specifically, we consider maximally random jammed
packings of hard ellipses and superdisks and show that these systems both
possess vanishing infinite-wavelength local-volume-fraction fluctuations and
quasi-long-range pair correlations. Our results suggest a strong generalization
of a conjecture by Torquato and Stillinger [Phys. Rev. E. 68, 041113 (2003)],
namely that all strictly jammed saturated packings of hard particles, including
those with size- and shape-distributions, are hyperuniform with signature
quasi-long-range correlations. We show that our arguments concerning the
constrained distribution of the void space in MRJ packings directly extend to
hard ellipse and superdisk packings, thereby providing a direct structural
explanation for the appearance of hyperuniformity and quasi-long-range
correlations in these systems. Additionally, we examine general heterogeneous
media with anisotropic inclusions and show for the first time that one can
decorate a periodic point pattern to obtain a hard-particle system that is not
hyperuniform with respect to local-volume-fraction fluctuations. This apparent
discrepancy can also be rationalized by appealing to the irregular distribution
of the void space arising from the anisotropic shapes of the particles. Our
work suggests the intriguing possibility that the MRJ states of hard particles
share certain universal features independent of the local properties of the
packings, including the packing fraction and average contact number per
particle.Comment: 29 pages, 9 figure
Black Holes and Naked Singularities in Low Energy Limit of String Gravity with Modulus Field
We show that the black hole solutions of the effective string theory action,
where one-loop effects that couple the moduli to gravity via a Gauss-Bonnet
term are taken into account, admit primary scalar hair. The requirement of
absence of naked singularities imposes an upper bound on the scalar charges.Comment: more details are added and some misprint are correcte
Neural Networks for Modeling and Control of Particle Accelerators
We describe some of the challenges of particle accelerator control, highlight
recent advances in neural network techniques, discuss some promising avenues
for incorporating neural networks into particle accelerator control systems,
and describe a neural network-based control system that is being developed for
resonance control of an RF electron gun at the Fermilab Accelerator Science and
Technology (FAST) facility, including initial experimental results from a
benchmark controller.Comment: 21 p
Walking a Tightrope: Unaccompanied migrant young people, transitions and futures
With the collaboration of Praxis Community Projects and Shpresa Programme, a series of photography workshops were conducted with young people from different backgrounds who have gone through similar experiences of migration. Many of these people came to the UK on their own as children, without their family. Their images narrate the difficult and continuous journey they make, and the life changing transitions that this journey entailed. It is a journey without a clear point of departure or arrival - or a clear sense of direction – but which brings multiple transformations and transitions along the way. People have to negotiate completely different cultural, social and political environments and, most importantly, the constraints of an exclusionary asylum system that has profound effects on their everyday lives. These young people often live with the terrifying uncertainty of not knowing what will happen to them or whether they will be returned to the country from which they have fled
Industrial Applications of Auger Surface Analysis
Scanning Auger microscopy is distinguished by its unique combination of surface selectivity, high spatial resolution, ease of identifying elements and quantifying composition, and ability to distinguish between chemical states. This paper describes several applications of scanning Auger microscopy, emphasizing the range of industrial research activities:
1. Electronic Materials. Contamination in an integrated circuit processing facility was identified and procedures for its removal determined. Causes for the delamination of printed circuit board foils were identified. Superlattice films were characterized and the deposition process evaluated.
2. Tribology. Analysis of surfaces in lubricated sliding contact revealed the effects of con tact kinematics and of molybdenum antifriction additives.
3. Corrosion. Early growth stages of phosphate coatings were found to be associated with a thin phosphate layer, not visible in SEM, interspersed with larger crystals. A corrosion layer on stainless steel/aluminum bimetal trim was shown to contain calcium carbonate and silicate deposits consistent with its galvanic protection mechanism.
4. Catalysis. Oxidation studies of Pd/ Rh alloys revealed varying surface compositions as a function of heat treatment temperature.
Several problems commonly encountered in Auger analysis are described and ways of minimizing or estimating their effects are discussed
A study of the phase transition in the usual statistical model for nuclear multifragmentation
We use a simplified model which is based on the same physics as inherent in
most statistical models for nuclear multifragmentation. The simplified model
allows exact calculations for thermodynamic properties of systems of large
number of particles. This enables us to study a phase transition in the model.
A first order phase transition can be tracked down. There are significant
differences between this phase transition and some other well-known cases
Rare isotope production in statistical multifragmentation
Producing rare isotopes through statistical multifragmentation is
investigated using the Mekjian method for exact solutions of the canonical
ensemble. Both the initial fragmentation and the the sequential decay are
modeled in such a way as to avoid Monte Carlo and thus provide yields for
arbitrarily scarce fragments. The importance of sequential decay, exact
particle-number conservation and the sensitivities to parameters such as
density and temperature are explored. Recent measurements of isotope ratios
from the fragmentation of different Sn isotopes are interpreted within this
picture.Comment: 10 eps figure
Develop and demonstrate manufacturing processes for fabricating graphite filament reinforced polymide (Gr/PI) composite structural elements
A study was conducted to assess the merits of using graphite/polyimide, NR-150B2 resin, for structural applications on advanced space launch vehicles. The program was divided into two phases: (1) Fabrication Process Development; and (2) Demonstration Components. The first phase of the program involved the selection of a graphite fiber, quality assurance of the NR-150B2 polyimide resin, and the quality assurance of the graphite/polyimide prepreg. In the second phase of the program, a limited number of components were fabricated before the NR-150B2 resin system was removed from the market by the supplier, Du Pont. The advancement of the NR-150B2 polyimide resin binder was found to vary significantly based on previous time and temperature history during the prepregging operation. Strength retention at 316C (600F) was found to be 50% that of room temperature strength. However, the composite would retain its initial strength after 200 hours exposure at 316C (600F). Basic chemistry studies are required for determining NR-150B2 resin binder quality assurance parameters. Graphite fibers are available that can withstand high temperature cure and postcure cycles
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