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Electron bombardment produced clustered displacements, paired vacancies and interstitial atoms in Si, discussing possible mechanism for developing defects
It has been suggested that intersecting supernova remnants (SNRs) contribute to the production of gas at about 1 million K which is apparently observed in the interstellar medium. This suggestion is evaluated through a fairly detailed numerical simulation that is used to investigate the large-scale three-dimensional behavior of a test section of the gaseous galactic disk under the influence of evolving and interacting SNRs. Models for a noninteracting 'isolated' SNR and the ambient medium are discussed, pairs of interacting remnants are examined along with the mechanism by which their central cavities can become connected, and the evolution of larger aggregates of SNRs is analyzed. Results are presented for a sequence of simulations having the same values of supernova blast energy, ambient ion density, and isolated SNR lifetime, but different supernova rates per unit volume. These results show that SNR intersections can quickly generate large volumes, or 'tunnels', of very hot gas from a cold starting medium under conservative and reasonable assumptions, the most important of which are that SNRs can be treated as spheres and mass motions can be treated implicitly.
Sun-sensor optical system uses four pairs of pentaprisms to simplify alinement and reduce mechanical-stability requirements. Cross-shaped windows in field stop enhance sensitivity of signal detectors to changes in angular position. Two virtual images viewed by telescopes mark position and orientation of occulter panel. Reflector vertex, point source and corresponding virtual image are all equally spaced along a straight line.
A study on the elastic behavior of interface cracks in adhesively bonded lap-shear joints is presented. The problem is investigated by using a recently developed method of analysis based on conservation laws in elasticity for nonhomogeneous solids and fundamental relationships in fracture mechanics of dissimilar materials. The formulation leads to a pair of linear algebraic equations in mixed-mode stress intensity factors. Singular crack-tip stress intensity solutions are determined directly by information extracted from the far field. Stress intensity factors and associated energy release rates are obtained for various cases of interest. Fundamental nature of the interfacial flaw behavior in lap-shear adhesive joints is examined in detail.
Fiber-optic transducer offers several advantages over mechanical linkages. Angular position of rotary valve measured by pair of optical-fiber deflectometers. Measurement device sensitive, immune to electromagnetic interference, and does not wear out since fibers do not make contact with valve. Device more rugged than linear or rotary variable-differential transformers it replaces.
This report is the final report of a NASA Phase I SBIR contract, with some revisions to remove company proprietary data. The Shock Boundary Layer Interaction (SBLI) phenomena in a supersonic inlet involve mutual interaction of oblique shocks with boundary layers, forcing the boundary layer to separate from the inlet wall. To improve the inlet efficiency, it is desired to prevent or delay shock-induced boundary layer separation. In this effort, Innovative Technology Applications Company (ITAC), LLC and the University of Notre Dame (UND) jointly investigated the use of dielectric-barrier-discharge (DBD) plasma actuators for control of SBLI in a supersonic inlet. The research investigated the potential for DBD plasma actuators to suppress flow separation caused by a shock in a turbulent boundary layer. The research involved both numerical and experimental investigations of plasma flow control for a few different SBLI configurations: (a) a 12 wedge flow test case at Mach 1.5 (numerical and experimental), (b) an impinging shock test case at Mach 1.5 using an airfoil as a shock generator (numerical and experimental), and (c) a Mach 2.0 nozzle flow case in a simulated 15 X 15 cm wind tunnel with a shock generator (numerical). Numerical studies were performed for all three test cases to examine the feasibility of plasma flow control concepts. These results were used to guide the wind tunnel experiments conducted on the Mach 1.5 12 degree wedge flow (case a) and the Mach 1.5 impinging shock test case (case b) which were at similar flow conditions as the corresponding numerical studies to obtain experimental evidence of plasma control effects for SBLI control. The experiments also generated data that were used in validating the numerical studies for the baseline cases (without plasma actuators). The experiments were conducted in a Mach 1.5 test section in the University of Notre Dame Hessert Laboratory. The simulation results from cases a and b indicated that multiple spanwise actuators in series and at a voltage of 75 kVp-p could fully suppress the flow separation downstream of the shock. The simulation results from case c showed that the streamwise plasma actuators are highly effective in creating pairs of counter-rotating vortices, much like the mechanical vortex generators, and could also potentially have beneficial effects for SBLI control. However, to achieve these effects, the positioning and the quantity of the DBD actuators used must be optimized. The wind tunnel experiments mapped the baseline flow with good agreement to the numerical simulations. The experimental results were conducted with spanwise actuators for cases a and b, but were limited by the inability to generate a sufficiently high voltage due to arcing in the wind-tunnel test-section. The static pressure in the tunnel was lower than the static pressure in an inlet at flight conditions, promoting arching and degrading the actuator performance.
An operator can rapidly and automatically produce coded electrical signals by manipulating mechanical thumb wheel switches so as to instruct a service center to connect any number of telephone lines to the console thus enabling the operator to listen and/or talk over several lines simultaneously. The system includes an on-site console having several mechanically operated thumb wheel switches to which the desired lines to be connected can be dialed in. Electrical coded signals are fed to a number of banks of line AND gates representing units, tens and hundreds, a group of channel gates, and a command gate. These signals are gated out in a controlled manner to an encoder which generates tones that are transmitted over a single line to a communication service center.
The results of tests with five different vortex generators in an open circuit wind tunnel are reported. The tests were performed to enhance the data base on heat transfer effects of an isolated longitudinal vortex in a turbulent boundary layer and the effects of embedded vortex pairs. A heated plate was set in the boundary layer downstream of a tripping mechanism and measurements were made of the free stream and surface temperatures using thermocouples. A four-hole cobra probe assayed the velocity profiles. Trials revealed that vortex pairs with scales larger than the boundary layer thickness induce significant changes in the Stanton number. A 15 percent Stanton number increase was produced by isolated vortices, which swept cool free stream fluid into the near-wall region.
The hard X-ray spectrum of AGNs is nonthermal, probably arising from an electron-positron pair cascade, with some emission reflected off relatively cold matter. There has been interest in models on which protons are accelerated and create relativistic electrons on interaction with a local radiation field. It is shown here that a sufficient column density of protons can lead to runaway pair production: photons generated by the relativistic pairs are the targets for the protons to produce more pairs. This can produce X-ray fluxes with the characteristics observed in AGN. The model predicts the maximum ratio of luminosity to source size as well as their spectrum in the early phases. The same mechanism may also be able to create the knots of synchrotron-radiating pair plasma seen in sources such as 3C273.
Using the concept of intercepting orbits from a pair of Space Station serviced free flyers, a class of impact and shock wave experiments pertinent to planetary science can be performed. One proposed free flying vehicle is an impactor dispensor, and the second is the impact laboratory. How collision is achieved by utilizing essentially twice orbital velocity is demonstrated. The impactor dispensor contains a series of small flyer plates or other projectiles which are launched into the trajectory of the impactor laboratory at appropriate positions. The impactor laboratory is a large impact tank similar to those in terrestrial gun laboratories, except that it contains a supply of targets and instrumentation such as high speed cameras, flash X-ray apparatus and digital recorders. Shock and isentropic pressures of up to 20 Mbar are achievable with such a system which provides 15 km/sec impact velocities for precisely oriented projectiles.
Using the concept of intercepting orbits from a pair of Space Station serviced free flyers, a class of impact and shock wave experiments pertinent to planetary science can be performed. One proposed free flying vehicle is an impactor dispensor, and the second is the impact laboratory. How collision is achieved by utilizing essentially twice orbital velocity is demonstrated. The impactor dispensor contains a series of small flyer plates or other projectiles which are launched into the trajectory of the impactor laboratory at appropriate positions. The impactor laboratory is a large impact tank similar to those in terrestrial gun laboratories, except that it contains a supply of targets and instrumentation such as high speed cameras, flash X-ray apparatus, and digital recorders. Shock and isentropic pressures of up to 20 Mbar are achievable with such a system which provides 15 km/sec impact velocities for precisely oriented projectiles.
An electromagnetic attachment mechanism for use as an end effector of a remote manipulator system. A pair of electromagnets 15A,15B, each with a U-shaped magnetic core with a pull-in coil 34 and two holding coils 35,36 are mounted by a spring suspension system 38,47 on a base plate 25 of the mechanism housing 30 with end pole pieces 21,22 adapted to move through openings in the base plate when the attractive force of the electromagnets is exerted on a strike plate 65 of a grapple fixture 20 affixed to a target object 14. The pole pieces are spaced by an air gap from the strike plate when the mechanism first contacts the grapple fixture. An individual control circuit and power source is provided for the pull-in coil and one holding coil of each electromagnet. A back-up control circuit connected to the two power sources and a third power source is provided for the remaining holding coils. When energized, the pull-in coils overcome the suspension system and air gap and are automatically de-energized when the pole pieces move to grapple and impose a preload force across the grapple interface. A battery back-up 89A,89B is a redundant power source for each electromagnet in each individual control circuit and is automatically connected upon failure of the primary power source. A centerline mounted camera 31 and video monitor 70 are used in cooperation with a target pattern 19 on the reflective surface 67 of the strike plate to effect targeting and alignment.
Spectroscopic instruments currently being proposed may possess polarimetric capabilities which sould be nurtured and enhanced to permit characterization of basic emission mechanisms which are impossible using other techniques. Compton scattering and pair production detected the polarization of high energy (E is greater than 50 keV) protons in laboratory experiments. The polarization properties of a detection system consisting of 19 germanium crystals in a closed packed array are examined and the advantages of such a detector over Thompson scattering are discussed. The possiblity of using pair production to detect polarization of high energy gamma rays, and the associated modulation factors are discussed. The central difficulty involved in using pair production polarimeters in astrophysical applications is that the typical opening of the electron or positron direction with respect to the incident photon aircitron is small, of order E/sq mc. Multiple scattering in the material used to convert the photons to an electron positron pair causes deviations in the direction of the electron and positron.
An analytical solution is developed for the determination of the stresses and displacements in a unidirectional fiber-reinforced composite containing an arbitrary number of broken fibers as well as longitudinal yielding and splitting of the matrix. The solution is developed using a materials-modeling approach which is based on a shear-lag stress transfer mechanism. The equilibrium equation in the axial direction gives a pair of integral equations which are solved numerically. Excellent agreement is shown to exist between the solution and experimental results for notched unidirectional boron/aluminum laminates without splitting. For brittle matrix composites (i.e. epoxy) equally good results are indicated for both matrix yielding and splitting. For yielding without splitting the fracture strength depends on crack length while for large splitting it is crack length independent.
An analytical solution is developed for the determination of the stresses and displacements in a unidirectional fiber-reinforced composite containing an arbitrary number of broken fibers as well as longitudinal yielding and splitting of the matrix. The solution is developed using a 'materials-modeling' approach which is based on a shear-lag stress transfer mechanism. The equilibrium equation in the axial direction gives a pair of integral equations which are solved numerically. Excellent agreement is shown to exist between the solution and experimental results for notched unidirectional boron/aluminum laminates without splitting. For brittle matrix composites (i.e., epoxy) equally good results are indicated for both matrix yielding and splitting. For yielding without splitting the fracture strength is found to depend on crack length while for large splitting it is crack length independent.
Conservation laws of elasticity for nonhomogeneous materials were developed and were used to study the crack behavior in adhesively bonded lap shear joints. By using these laws and the fundamental relationships in fracture mechanics of interface cracks, the problem is reduced to a pair of linear algebraic equations, and stress intensity solutions can be determined directly by information extracted from the far field. The numerical results obtained show that: (1) in the lap-shear joint with a given adherend, the opening-mode stress intensity factor, (K sub 1) is always larger than that of the shearing-mode (K sub 2); (2) (K sub 1) is not sensitive to adherent thickness abut (K sub 2) increases rapidly with increasing thickness; and (3) (K sub 1) and (K sub 2) increase simultaneously as the interfacial crack length increases.
A payload retention device for grappling and retaining a payload in docked position on a supporting structure in the cargo bay of a space vehicle is presented. The device comprises a two-fault tolerant electromagnetic grappling system comprising electromagnets for attracting and grappling a grapple strike plate affixed to the payload when in proximity thereto and an electromechanical latching assembly comprising a pair of independent latching subassemblies. Each subassembly comprises a set of latching pawls which are driven into latching and unlatching positions relative to a grappled payload by a pair of gearmotors, each equipped with a ratchet clutch drive mechanism which is two-fault tolerant with respect to latching such that only one gearmotor of the four needs to be operational to effect a latch of the payload but is single fault tolerant with respect to release of a latched payload. Sensors are included for automatically sensing the magnetic grappling of a payload and for automatically de-energizing the gearmotors of the latching subassemblies when a latch condition is achieved.
In this talk we present a model for analyzing space-based entanglement distribution links. In particular, we analyze deterministic entanglement distribution links relevant to quantum communication applications where all communication nodes must be synchronized with deterministic photon arrival times. The focus is on systems operating within practical limitations set by current technology. The architectures studied in this work are based on all-photonic links with probabilistic (memory-less) entanglement swapping used to signal the success of the entanglement distribution without destroying the entangled state. An end-to-end link model is described which accounts for satellite orbital mechanics as well as the physical effects of entangled photon pair sources, space-to-ground atmospheric channels, two-photon interference, pointing and tracking, and photon counting detectors with and without photon number resolution (this is joint work with Robert Manning, Ian Nemitz, and Bryan Welch).