19,445 research outputs found
Method and apparatus for securing to a spacecraft Patent
Method and apparatus for connecting two spacecraft with probe of one inserted in rocket engine nozzle of other spacecraf
Optical testing cryogenic thermal vacuum facility
The construction of a turnkey cryogenic vacuum test facility was recently completed. The facility will be used to measure and record the surface profile of large diameter and 540 kg optics under simulated space conditions. The vacuum test chamber is a vertical stainless steel cylinder with a 3.5 diameter and a 7 m tangent length. The chamber was designed to maximize optical testing quality by minimizing the vibrations between the laser interferometer and the test specimen. This was accomplished by designing the chamber for a high natural frequency and vibration isolating the chamber. An optical test specimen is mounted on a movable presentation stage. During thermal vacuum testing, the specimen may be positioned to + or - 0.00025 cm accuracy with a fine adjustment mechanism. The chamber is evacuated by a close coupled Roots-type blower and rotary vane pump package and two cryopumps. The chamber is equipped with an optically dense gaseous nitrogen cooled thermal shroud. The thermal shroud is used to cool or warm the optical test specimen at a controlled rate. A control system is provided to automatically evacuate the chamber and cooldown the test specimen to the selected control temperature
Modeling Grain Boundaries using a Phase Field Technique
We propose a two dimensional frame-invariant phase field model of grain
impingement and coarsening. One dimensional analytical solutions for a stable
grain boundary in a bicrystal are obtained, and equilibrium energies are
computed. We are able to calculate the rotation rate for a free grain between
two grains of fixed orientation. For a particular choice of functional
dependencies in the model the grain boundary energy takes the same analytic
form as the microscopic (dislocation) model of Read and Shockley.Comment: 4 pages, 2 figure
A simulation model for wind energy storage systems. Volume 2: Operation manual
A comprehensive computer program (SIMWEST) developed for the modeling of wind energy/storage systems utilizing any combination of five types of storage (pumped hydro, battery, thermal, flywheel, and pneumatic) is described. Features of the program include: a precompiler which generates computer models (in FORTRAN) of complex wind source/storage/application systems, from user specifications using the respective library components; a program which provides the techno-economic system analysis with the respective I/O the integration of system dynamics, and the iteration for conveyance of variables; and capability to evaluate economic feasibility as well as general performance of wind energy systems. The SIMWEST operation manual is presented and the usage of the SIMWEST program and the design of the library components are described. A number of example simulations intended to familiarize the user with the program's operation is given along with a listing of each SIMWEST library subroutine
A simulation model for wind energy storage systems. Volume 1: Technical report
A comprehensive computer program for the modeling of wind energy and storage systems utilizing any combination of five types of storage (pumped hydro, battery, thermal, flywheel and pneumatic) was developed. The level of detail of Simulation Model for Wind Energy Storage (SIMWEST) is consistent with a role of evaluating the economic feasibility as well as the general performance of wind energy systems. The software package consists of two basic programs and a library of system, environmental, and load components. The first program is a precompiler which generates computer models (in FORTRAN) of complex wind source storage application systems, from user specifications using the respective library components. The second program provides the techno-economic system analysis with the respective I/O, the integration of systems dynamics, and the iteration for conveyance of variables. SIMWEST program, as described, runs on the UNIVAC 1100 series computers
Irreversible thermodynamics of creep in crystalline solids
We develop an irreversible thermodynamics framework for the description of
creep deformation in crystalline solids by mechanisms that involve vacancy
diffusion and lattice site generation and annihilation. The material undergoing
the creep deformation is treated as a non-hydrostatically stressed
multi-component solid medium with non-conserved lattice sites and
inhomogeneities handled by employing gradient thermodynamics. Phase fields
describe microstructure evolution which gives rise to redistribution of vacancy
sinks and sources in the material during the creep process. We derive a general
expression for the entropy production rate and use it to identify of the
relevant fluxes and driving forces and to formulate phenomenological relations
among them taking into account symmetry properties of the material. As a simple
application, we analyze a one-dimensional model of a bicrystal in which the
grain boundary acts as a sink and source of vacancies. The kinetic equations of
the model describe a creep deformation process accompanied by grain boundary
migration and relative rigid translations of the grains. They also demonstrate
the effect of grain boundary migration induced by a vacancy concentration
gradient across the boundary
Transition region and chromospheric signatures of impulsive heating events. II. Modeling
Results from the Solar Maximum Mission showed a close connection between the hard X-ray (HXR) and transition
region (TR) emission in solar flares. Analogously, the modern combination of RHESSI and IRIS data can inform
the details of heating processes in ways that were never before possible. We study a small event that was observed
with RHESSI, IRIS, SDO, and Hinode, allowing us to strongly constrain the heating and hydrodynamical properties
of the flare, with detailed observations presented in a previous paper. Long duration redshifts of TR lines observed
in this event, as well as many other events, are fundamentally incompatible with chromospheric condensation on a
single loop. We combine RHESSI and IRIS data to measure the energy partition among the many magnetic strands
that comprise the flare. Using that observationally determined energy partition, we show that a proper
multithreaded model can reproduce these redshifts in magnitude, duration, and line intensity, while simultaneously
being well constrained by the observed density, temperature, and emission measure. We comment on the
implications for both RHESSI and IRIS observations of flares in general, namely that: (1) a single loop model is
inconsistent with long duration redshifts, among other observables; (2) the average time between energization of
strands is less than 10 s, which implies that for a HXR burst lasting 10 minutes, there were at least 60 strands
within a single IRIS pixel located on the flare ribbon; (3) the majority of these strands were explosively heated with
an energy distribution well described by a power law of slope »-1.6; (4) the multi-stranded model reproduces the
observed line profiles, peak temperatures, differential emission measure distributions, and densities
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