28,108 research outputs found
Convoluted fabric for full-pressure gloves
Fabric, made of nylon ripstop coated with Neoprene, provides expansive and contractive mobility along posterior surface of glove fingers allowing maximum digital dexterity and tactility
Taber Vibration Isolator for Vacuum and Cryogenic Applications
We present a procedure for the design and construction of a passive,
multipole, mechanical high-stop vibration isolator. The isolator, consisting of
a stack of metal disks connected by thin wires, attenuates frequencies in the
kilohertz range, and is suited to both vacuum and cryogenic environments. We
derive an approximate analytical model and compare its predictions for the
frequencies of the normal modes to those of a finite element analysis. The
analytical model is exact for the modes involving only motion along and
rotation about the longitudinal axis, and it gives a good approximate
description of the transverse modes. These results show that the high-frequency
behavior of a multi-stage isolator is well characterized by the natural
frequencies of a single stage. From the single-stage frequency formulae, we
derive relationships among the various geometrical parameters of the isolator
to guarantee equal attenuation in all degrees of freedom. We then derive
expressions for the attenuation attainable with a given isolator length, and
find that the most important limiting factor is the elastic limit of the spring
wire material. For our application, which requires attenuations of 250 dB at 1
kHz, our model specifies a six-stage design using brass disks of approximately
2 cm in both radius and thickness, connected by 3 cm steel wires of diameters
ranging from 25 to 75 microns. We describe the construction of this isolator in
detail, and compare measurements of the natural frequencies of a single stage
with calculations from the analytical model and the finite element package. For
translations along and rotations about the longitudinal axes, all three results
are in agreement to within 10% accuracy.Comment: 11 pages, 13 figures, REVTe
Analytical and experimental study of reentrant stream crossed-field amplifiers Final report
Computer simulation and noise measurements of reentrant stream crossed-field amplifier
In an expanding universe, what doesn't expand?
The expansion of the universe is often viewed as a uniform stretching of
space that would affect compact objects, atoms and stars, as well as the
separation of galaxies. One usually hears that bound systems do not take part
in the general expansion, but a much more subtle question is whether bound
systems expand partially. In this paper, a very definitive answer is given for
a very simple system: a classical "atom" bound by electrical attraction. With a
mathemical description appropriate for undergraduate physics majors, we show
that this bound system either completely follows the cosmological expansion, or
-- after initial transients -- completely ignores it. This "all or nothing"
behavior can be understood with techniques of junior-level mechanics. Lastly,
the simple description is shown to be a justifiable approximation of the
relativistically correct formulation of the problem.Comment: 8 pages, 9 eps figure
Phenolic cutter for machining foam insulation
Pre-pregged fiber glass is an efficient abrasive for machining polystyrene and polyurethane foams. It bonds easily to any cutter base made of aluminum, steel, or phenolic, is inexpensive, and is readily available
Design considerations and test facilities for accelerated radiation effects testing
Test design parameters for accelerated dose rate radiation effects tests for spacecraft parts and subsystems used in long term mission (years) are detailed. A facility for use in long term accelerated and unaccelerated testing is described
A guideline for heavy ion radiation testing for Single Event Upset (SEU)
A guideline for heavy ion radiation testing for single event upset was prepared to assist new experimenters in preparing and directing tests. How to estimate parts vulnerability and select an irradiation facility is described. A broad brush description of JPL equipment is given, certain necessary pre-test procedures are outlined and the roles and testing guidelines for on-site test personnel are indicated. Detailed descriptions of equipment needed to interface with JPL test crew and equipment are not provided, nor does it meet the more generalized and broader requirements of a MIL-STD document. A detailed equipment description is available upon request, and a MIL-STD document is in the early stages of preparation
The periodic standing-wave approximation: eigenspectral computations for linear gravity and nonlinear toy models
The periodic standing wave approach to binary inspiral assumes rigid rotation
of gravitational fields and hence helically symmetric solutions. To exploit the
symmetry, numerical computations must solve for ``helical scalars,'' fields
that are functions only of corotating coordinates, the labels on the helical
Killing trajectories. Here we present the formalism for describing linearized
general relativity in terms of helical scalars and we present solutions to the
mixed partial differential equations of the linearized gravity problem (and to
a toy nonlinear problem) using the adapted coordinates and numerical techniques
previously developed for scalar periodic standing wave computations. We argue
that the formalism developed may suffice for periodic standing wave
computations for post-Minkowskian computations and for full general relativity.Comment: 21 pages, 10 figures, RevTe
The use of satellites in non-goestationary orbits for unloading geostationary communication satellite traffic peaks. Volume 2: Technical report
The part of the geostationary (GEO) orbital arc used for United States domestic fixed, communications service is rapidly becoming filled with satellites. One of the factors currently limiting its utilization is that communications satellites must be designed to have sufficient capacity to handle peak traffic leads, and thus are under utilized most of the time. A solution is to use satellites in suitable non-geostationary orbits to unload the traffic peaks. Three different designs for a non-geostationary orbit communications satellite system are presented for the 1995 time frame. The economic performance is analyzed and compared with geostationary satellites for two classes of service, trunking and customer premise service. The result is that the larger payload of the non-geostationary satellite offsets the burdens of increased complexity and worse radiation environment to give improved economic performance. Depending on ground terminal configuration, the improved economic performance of the space segment may be offset by increased ground terminal expenses
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