6,598 research outputs found
Development of hydrogen resistant alloys
The most hostile operating environments in the O2/H2 Space Shuttle Main Engine are gaseous hydrogen and hydrogen/water vapor. After years of evaluating commercially available alloys, only a few high strength alloys have been found that perform satisfactorily in these environments. This paper describes the evaluation of various compositions of the Fe-Ni-Co system with elemental additions of Cr, Cb, Ti and Al. After processing, notched tensile specimens were tested in 5000 psi hydrogen at room temperature as the prime screening test. The H2/air ratio was used as the selection/rejection criteria
Material technology
Advanced high pressure O2/H2 propulsion systems as exemplified by the Space Shuttle Main Engine (SSME) create challenging operating environments for materials. Many components operate in either hydrogen or hydrogen-steam environments which may significantly degrade the performance of common alloys. The objective of the materials technology projects is to develop and evaluate candidate materials for application in advanced high pressure O2/H2 propulsion systems. These new and improved materials are to improve the durability or performance of the SSME or derivative engine. The program includes projects on the following topics: (1) Hydrogen Resistant Alloys; (2) High Pressure O2 Ignition and Burning; (3) Improved Turbine Blades; (4) Improved Turbine Disk Material; (5) Impact Reactivity in High Pressure O2; and Fiber Reinforced Superalloys
Dynamic temporal behaviour of the keyboard action on the Hammond organ and its perceptual significance
Relativistic ionization-rescattering with tailored laser pulses
The interaction of relativistically strong tailored laser pulses with an
atomic system is considered. Due to a special tailoring of the laser pulse, the
suppression of the relativistic drift of the ionized electron and a dramatic
enhancement of the rescattering probability is shown to be achievable. The high
harmonic generation rate in the relativistic regime is calculated and shown to
be increased by several orders of magnitude compared to the case of
conventional laser pulses. The energies of the revisiting electron at the
atomic core can approach the MeV domain, thus rendering hard x-ray harmonics
and nuclear reactions with single atoms feasible
Light scattering and phase behavior of Lysozyme-PEG mixtures
Measurements of liquid-liquid phase transition temperatures (cloud points) of
mixtures of a protein (lysozyme) and a polymer, poly(ethylene glycol) (PEG)
show that the addition of low molecular weight PEG stabilizes the mixture
whereas high molecular weight PEG was destabilizing. We demonstrate that this
behavior is inconsistent with an entropic depletion interaction between
lysozyme and PEG and suggest that an energetic attraction between lysozyme and
PEG is responsible. In order to independently characterize the lysozyme/PEG
interactions, light scattering experiments on the same mixtures were performed
to measure second and third virial coefficients. These measurements indicate
that PEG induces repulsion between lysozyme molecules, contrary to the
depletion prediction. Furthermore, it is shown that third virial terms must be
included in the mixture's free energy in order to qualitatively capture our
cloud point and light scattering data. The light scattering results were
consistent with the cloud point measurements and indicate that attractions do
exist between lysozyme and PEG.Comment: 5 pages, 2 figures, 1 tabl
Columnar and lamellar phases in attractive colloidal systems
In colloidal suspensions, the competition between attractive and repulsive
interactions gives rise to a rich and complex phenomenology. Here, we study the
equilibrium phase diagram of a model system using a DLVO interaction potential
by means of molecular dynamics simulations and a thermodynamical approach. As a
result, we find tubular and lamellar phases at low volume fraction. Such
phases, extremely relevant for designing new materials, may be not easily
observed in the experiments because of the long relaxation times and the
presence of defects.Comment: 5 pages, 5 figure
Fruit Quality And Consumption By Songbirds During Autumn Migration
Seasonal fruits are an important food resource for small songbirds during autumn migration in southern New England. Therefore, conservation and management of important stopover sites used by migrating birds requires knowledge about nutritional requirements of songbirds and nutritional composition of commonly consumed fruits. We measured nutrient composition and energy density of nine common fruits on Block Island, Rhode Island, and conducted a field experiment to estimate consumption rates of three of these fruits by birds during autumn migration. Most common fruits on Block Island contained primarily carbohydrates (41.3–91.2% dry weight), and little protein (2.6–8.6%) and fat (0.9–3.7%), although three contained more fat: Myrica pennsylvanica (50.3%), Viburnum dentatum (41.3%), and Parthenocissus quinquefolia (23.6%). Bird consumption of high-fat, high-energy V. dentatum fruit and high-carbohydrate, low-energy Phytolacca americana fruit was greater than consumption of Aronia melanocarpa, a high-carbohydrate, low-energy fruit. We estimated that migratory birds on Block Island must eat up to four times their body mass in fruit wet weight each day to satisfy their energy requirements when eating low-energy fruits such as P. americana, and they cannot satisfy their protein requirements when eating only certain high-energy fruits such as V. dentatum. Our results suggest that many migratory birds must eat both fruits and insects to meet their dietary needs. Thus, shrubland habitat at important migratory stopover sites such as Block Island should be managed so that it contains a variety of preferred fruit-bearing shrubs and an adequate abundance of insects
Octupole strength in the neutron-rich calcium isotopes
Low-lying excited states of the neutron-rich calcium isotopes Ca
have been studied via -ray spectroscopy following inverse-kinematics
proton scattering on a liquid hydrogen target using the GRETINA -ray
tracking array. The energies and strengths of the octupole states in these
isotopes are remarkably constant, indicating that these states are dominated by
proton excitations.Comment: 15 pages, 3 figure
Theory and simulation of short-range models of globular protein solutions
We report theoretical and simulation studies of phase coexistence in model
globular protein solutions, based on short-range, central, pair potential
representations of the interaction among macro-particles. After reviewing our
previous investigations of hard-core Yukawa and generalised Lennard-Jones
potentials, we report more recent results obtained within a DLVO-like
description of lysozyme solutions in water and added salt. We show that a
one-parameter fit of this model based on Static Light Scattering and
Self-Interaction Chromatography data in the dilute protein regime, yields
demixing and crystallization curves in good agreement with experimental
protein-rich/protein-poor and solubility envelopes. The dependence of cloud and
solubility points temperature of the model on the ionic strength is also
investigated. Our findings highlight the minimal assumptions on the properties
of the microscopic interaction sufficient for a satisfactory reproduction of
the phase diagram topology of globular protein solutions.Comment: 17 pages, 8 figures, Proc. of Conference "Structural Arrest
Transitions in Colloidal Systems with Short-Range Attractions", Messina
(ITALY) 17-20 December 200
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