42,315 research outputs found
Reinforcement of polymeric structures with asbestos fibrils
Investigation determines structural potential of asbestos fibrils. Methods are developed for dispersing macrofibers of the asbestos into colloidal-sized ultimate fibrils and incorporating these fibrils in matrices without causing reagglomeration
Development of a Straw Tube Chamber with Pickup-Pad Readout
We have developed a straw tube chamber with pickup-pad readout. The mechanism
for signal pickup, the size of the pickup signal, and the distribution of
signals among neighboring pads are discussed. We have tested a prototype
chamber in a beamtest at Brookhaven National laboratory and have measured
chamber efficiencies in excess of 99%.Comment: 7 pages, 8 figures, 2 tables. Talk presented at DPF '99 Meeting, UCL
The reinforcement of polymeric structures by asbestos fibrils Final report, 1 Apr. 1965 - 30 Apr. 1966
Dispersion techniques for asbestos fibril reinforcement of polymeric structures, and tensile strength data on reinforced composite
MeV oxygen ion implantation induced compositional intermixing in AlAs/GaAs superlattices
We present in this letter an investigation of compositional intermixing in AlAs/GaAs superlattices induced by 2 MeV oxygen ion implantation. The results are compared with implantation at 500 keV. In addition to Al intermixing in the direct lattice damage region by nuclear collision spikes, as is normally present in low-energy ion implantation, Al interdiffusion has also been found to take place in the subsurface region where MeV ion induced electronic spike damage dominates and a uniform strain field builds up due to defect generation and diffusion. Uniform compositional intermixing of the superlattices results after subsequent thermal annealing when Al interdiffusion is stimulated through recovery of the implantation-induced lattice strain field, the reconstruction and the redistribution of lattice defects, and annealing of lattice damage
Generalized Supersymmetric Perturbation Theory
Using the basic ingredient of supersymmetry, we develop a simple alternative
approach to perturbation theory in one-dimensional non-relativistic quantum
mechanics. The formulae for the energy shifts and wave functions do not involve
tedious calculations which appear in the available perturbation theories. The
model applicable in the same form to both the ground state and excited bound
states, unlike the recently introduced supersymmetric perturbation technique
which, together with other approaches based on logarithmic perturbation theory,
are involved within the more general framework of the present formalism.Comment: 13 pages article in LaTEX (uses standard article.sty). No Figures.
Sent to Ann. Physics (2004
Exploratory studies of contact angle hysteresis, wetting of solidified rare gases and surface properties of mercury Final report
Contact angle hysteresis, wetting of solidified rare gases, and surface properties of mercur
A Composite Genome Approach to Identify Phylogenetically Informative Data from Next-Generation Sequencing
We have developed a novel method to rapidly obtain homologous genomic data
for phylogenetics directly from next-generation sequencing reads without the
use of a reference genome. This software, called SISRS, avoids the time
consuming steps of de novo whole genome assembly, genome-genome alignment, and
annotation. For simulations SISRS is able to identify large numbers of loci
containing variable sites with phylogenetic signal. For genomic data from apes,
SISRS identified thousands of variable sites, from which we produced an
accurate phylogeny. Finally, we used SISRS to identify phylogenetic markers
that we used to estimate the phylogeny of placental mammals. We recovered
phylogenies from multiple datasets that were consistent with previous
conflicting estimates of the relationships among mammals. SISRS is open source
and freely available at https://github.com/rachelss/SISRS.Comment: 12 pages plus36 figures, 1 supplementary table, 3 supplementary
figure
Influence of substrate temperature on lattice strain field and phase transition in MeV oxygen ion implanted GaAs crystals
A detailed study of the influence of substrate temperature on the radiation-induced lattice strain field and crystalline-to-amorphous (c-a) phase transition in MeV oxygen ion implanted GaAs crystals has been made using channeling Rutherford backscattering spectroscopy, secondary ion mass spectrometry, and the x-ray rocking curve technique. A comparison has been made between the cases of room temperature (RT) and low temperature (LT) (about 100 K) implantation. A strong in situ dynamic annealing process is found in RT implantation at a moderate beam current, resulting in a uniform positive strain field in the implanted layer. LT implantation introduces a freeze-in effect which impedes the recombination and diffusion of initial radiation-created lattice damage and defects, and in turn drives more efficiently the c-a transition as well as strain saturation and relaxation. The results are interpreted with a spike damage model in which the defect production process is described in terms of the competition between defect generation by nuclear spikes and defects diffusion and recombination stimulated by electronic spikes. It is also suggested that the excess population of vacancies and their complexes is responsible for lattice spacing expansion in ion-implanted GaAs crystals
Attentional load and sensory competition in human vision: Modulation of fMRI responses by load fixation during task-irrelevant stimulation in the peripheral visual field.
Perceptual suppression of distractors may depend on both endogenous and exogenous factors, such as attentional load of the current task and sensory competition among simultaneous stimuli, respectively. We used functional magnetic resonance imaging (fMRI) to compare these two types of attentional effects and examine how they may interact in the human brain. We varied the attentional load of a visual monitoring task performed on a rapid stream at central fixation without altering the central stimuli themselves, while measuring the impact on fMRI responses to task-irrelevant peripheral checkerboards presented either unilaterally or bilaterally. Activations in visual cortex for irrelevant peripheral stimulation decreased with increasing attentional load at fixation. This relative decrease was present even in V1, but became larger for successive visual areas through to V4. Decreases in activation for contralateral peripheral checkerboards due to higher central load were more pronounced within retinotopic cortex corresponding to 'inner' peripheral locations relatively near the central targets than for more eccentric 'outer' locations, demonstrating a predominant suppression of nearby surround rather than strict 'tunnel vision' during higher task load at central fixation. Contralateral activations for peripheral stimulation in one hemifield were reduced by competition with concurrent stimulation in the other hemifield only in inferior parietal cortex, not in retinotopic areas of occipital visual cortex. In addition, central attentional load interacted with competition due to bilateral versus unilateral peripheral stimuli specifically in posterior parietal and fusiform regions. These results reveal that task-dependent attentional load, and interhemifield stimulus-competition, can produce distinct influences on the neural responses to peripheral visual stimuli within the human visual system. These distinct mechanisms in selective visual processing may be integrated within posterior parietal areas, rather than earlier occipital cortex
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