Tetrad formulation of junction conditions in general relativity.
Junction conditions across internal boundaries for Ricci rotation coefficients and Riemann tensor components in arbitrary reference tetrad frame
Estabrook, F. B.↗
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Junction conditions in general relativity
Tetrad and dyadic formulations of junction conditions in general relativity obtained and used to solve Einstein field equations
RELATIVITY THEORY↗
Phosphorus diffusion conditions for shallow junction solar cells
Phosphorus diffusion conditions for shallow junction solar cells
Kautz, H. E.↗
Characteristics of a Josephson junction harmonic mixer with external pumping
Numerical calculations are carried out on harmonic mixing with an externally pumped Josephson junction. Bias conditions for optimum conversion efficiency are studied for a variety of junction parameters. The predicted noise temperature for harmonic mixing is compared with that for fundamental mixing at the same signal frequency.
Taur, Y.↗
In Situ Irradiation and Measurement of Triple Junction Solar Cells at Low Intensity, Low Temperature (LILT) Conditions
The performance of triple junction InGaP/(In)GaAs/Ge space solar cells was studied following high energy electron irradiation at low temperature. Cell characterization was carried out in situ at the irradiation temperature while using low intensity illumination, and, as such, these conditions reflect those found for deep space, solar powered missions that are far from the sun. Cell characterization consisted of I-V measurements and quantum efficiency measurements. The low temperature irradiations caused substantial degradation that differs in some ways from that seen after room temperature irradiations. The short circuit current degrades more at low temperature while the open circuit voltage degrades more at room temperature. A room temperature anneal after the low temperature irradiation produced a substantial recovery in the degradation. Following irradiation at both temperatures and an extended room temperature anneal, quantum efficiency measurement suggests that the bulk of the remaining damage is in the (In)GaAs sub-cell
Quantum Efficiency↗
Reflecting boundary conditions for graded p-n junctions
In a graded junction, the formalism for handling reflecting boundary conditions must be modified. Since a significant drift term is present, zero recombination velocity at the surface does not imply a zero excess carrier gradient but rather zero overall flux. A model for analyzing p-n junctions fabricated by implantation or diffusion is presented, assuming the dominant recombination mechanism in the graded region is Auger. The model enables optimization of diode design. By proper selection of parameters, mainly by reducing surface concentration or by increasing the steepness of the dopant profile, it is possible to drastically reduce the saturation current generated by the graded region.
Schacham, S. E.↗
A parametric study of three-dimensional separation at a wing/body junction for supersonic free-stream conditions
The problem of three-dimensional separation at a wing/body junction has been investigated numerically using a three-dimensional Navier-Stokes code which employs the MacCormack's time split finite volume technique. An algebraic grid generation technique is used for generating the grid at a wing/body junction. Specific computational results on velocity and pressure distribution in the separated flow region are compared with the experimental results. A parametric study of flow parameters such as Mach number and Reynolds number have been carried out to understand their effect in interaction flow field. The parametric study indicates a strong dependency of the number of vortices at the junction on Mach number and Reynolds number.
Lakshmanan, B.↗
Analysis of a Transonic Alternating Flow Phenomenon Observed During Ares Crew Launch Vehicle Wind Tunnel Tests
A transonic wind tunnel test of the Ares I-X Rigid Buffet Model (RBM) identified a Mach number regime where unusually large buffet loads are present. A subsequent investigation identified the cause of these loads to be an alternating flow phenomenon at the Crew Module-Service Module junction. The conical design of the Ares I-X Crew Module and the cylindrical design of the Service Module exposes the vehicle to unsteady pressure loads due to the sudden transition from separated to attached flow about the cone-cylinder junction with increasing Mach number. For locally transonic conditions at this junction, the flow randomly fluctuates back and forth between a subsonic separated flow and a supersonic attached flow. These fluctuations produce a square-wave like pattern in the pressure time histories which, upon integration result in large amplitude, impulsive buffet loads. Subsequent testing of the Ares I RBM found much lower buffet loads since the evolved Ares I design includes an ogive fairing that covers the Crew Module-Service Module junction, thereby making the vehicle less susceptible to the onset of alternating flow. An analysis of the alternating flow separation and attachment phenomenon indicates that the phenomenon is most severe at low angles of attack and exacerbated by the presence of vehicle protuberances. A launch vehicle may experience either a single or, at most, a few impulsive loads since it is constantly accelerating during ascent rather than dwelling at constant flow conditions in a wind tunnel. A comparison of a wind-tunnel-test-data-derived impulsive load to flight-test-data-derived load indicates a significant over-prediction in the magnitude and duration of the buffet load
Sekula, Martin K.↗
Diffraction by a symmetric material junction simulated with generalized sheet transistion conditions
When diffraction by a material discontinuity in a thick dielectric/ferrite slab is treated for the dual integral equation approach (a variation of the Weiner-Hopf method), the resulting solution displays unknown constants, characteristic of the incompleteness associated with the generalized transition conditions employed in modeling a thick slab. The constants can be shown to depend on the geometry and properties of the discontinuity. Their explicit determination by enforcing field continuity across the slab junction is treated. The field internal to the slab is determined by first expressing the field as an expansion of discrete and continuous eigenmodes valid in the exterior and interior slab region. The expansion or mode coefficients are then identified by recasting the Weiner-Hopf solution in a suitable form, enabling the solution constants to be numerically computed by matching the field expansions to the left and right of the slab discontinuity at a discrete set of points.
Ricoy, Mark A.↗
Instrumentation System Diagnoses a Thermocouple
An improved self-validating thermocouple (SVT) instrumentation system not only acquires readings from a thermocouple but is also capable of detecting deterioration and a variety of discrete faults in the thermocouple and its lead wires. Prime examples of detectable discrete faults and deterioration include open- and short-circuit conditions and debonding of the thermocouple junction from the object, the temperature of which one seeks to measure. Debonding is the most common cause of errors in thermocouple measurements, but most prior SVT instrumentation systems have not been capable of detecting debonding. The improved SVT instrumentation system includes power circuitry, a cold-junction compensator, signal-conditioning circuitry, pulse-width-modulation (PWM) thermocouple-excitation circuitry, an analog-to-digital converter (ADC), a digital data processor, and a universal serial bus (USB) interface. The system can operate in any of the following three modes: temperature measurement, thermocouple validation, and bonding/debonding detection. The software running in the processor includes components that implement statistical algorithms to evaluate the state of the thermocouple and the instrumentation system. When the power is first turned on, the user can elect to start a diagnosis/ monitoring sequence, in which the PWM is used to estimate the characteristic times corresponding to the correct configuration. The user also has the option of using previous diagnostic values, which are stored in an electrically erasable, programmable read-only memory so that they are available every time the power is turned on.
Perotti, Jose↗
Optimal singular control with applications to trajectory optimization
A comprehensive discussion of the problem of singular control is presented. Singular control enters an optimal trajectory when the so called switching function vanishes identically over a finite time interval. Using the concept of domain of maneuverability, the problem of optical switching is analyzed. Criteria for the optimal direction of switching are presented. The switching, or junction, between nonsingular and singular subarcs is examined in detail. Several theorems concerning the necessary, and also sufficient conditions for smooth junction are presented. The concepts of quasi-linear control and linearized control are introduced. They are designed for the purpose of obtaining approximate solution for the difficult Euler-Lagrange type of optimal control in the case where the control is nonlinear.
Vinh, N. X.↗
Vibration and wave propagation characteristics of multisegmented elastic beams
Closed form analytical solutions are derived for the vibration and wave propagation of multisegmented elastic beams. Each segment is modeled as a Timoshenko beam with possible inclusion of material viscosity, elastic foundation and axial forces. Solutions are obtained by using transfer matrix methods. According to these methods formal solutions are first constructed which relate the deflection, slope, moment and shear force of one end of the individual segment to those of the other. By satisfying appropriate continuity conditions at segment junctions, a global 4x4 matrix results which relates the deflection, slope, moment and shear force of one end of the beam to those of the other. If any boundary conditions are subsequently invoked on the ends of the beam one gets the appropriate characteristic equation for the natural frequencies. Furthermore, by invoking appropriate periodicity conditions the dispersion relation for a periodic system is obtained. A variety of numerical examples are included.
Nayfeh, Adnan H.↗
Conditions for parametric oscillations in an abrupt-junction non-overdriven varactor doubler.
Parametric oscillations of nonoverdriven abrupt junction varactor doubler
Grayzel, A. I.↗
Turbulence Measurements on a Wing-Fuselage Junction Model for CFD Validation
Current turbulence models, such as those employed in Reynolds-averaged Navier-Stokes CFD, are unable to reliably predict the onset and extent of the three-dimensional separated flow that typically occurs in wing fuselage junctions. To critically assess, as well as to improve upon, existing turbulence models, experimental validation-quality flow field data in the junction region is needed. To that end, NASA has developed a CFD validation experiment for a generic full-span wing-fuselage junction model at subsonic conditions. In this paper, we present and discuss sample results from this effort, with a focus on turbulence measurements in the separated corner flow of the wing-fuselage junction that were obtained with an internally mounted laser Doppler velocimetry (LDV) system. In addition, sample comparisons between the flow field measurements and representative CFD of our test case are presented and here, we highlight some of the key discrepancies.
Kegerise, Michael↗
Design of high efficiency HLE solar cells for space and terrestrial applications
A first-order analysis of HLE cells is presented for both beginning-of-life and end-of-life conditions. Based on this analysis and on experimentally observed values for material parameters. Design approaches for both space and terrestrial cells are presented. The approaches result in specification of doping levels, junction depths, and surface conditions. The proposed structures are projected to have both high V sub OC and high J sub SC.
Neugroschel, A.↗
Knee-ligament loading properties as influenced by gravity. I - Junction with bone of 3-G rodents
The effect of 3-G conditions on the bone-to-ligament junctions of the knee is studied in rats. Results following chronic 3-G centrifugation of rats show that their bone-to-ligament junctions exhibited a force-sustaining capacity (F) which was 95 + or - 12% of the value for the control group. However, F was actually 29 + or - 5% greater for centrifuged rats than for control rats of comparable size, as the experimental animals grew to smaller body mass. It is concluded that gravity determines part of the magnitude of F, and therefore this value will probably be weaker after development in a weightless environment.
Wunder, C. C.↗
Necessary conditions for joining optimal singular and nonsingular subarcs
Necessary conditions for optimality of junctions between singular and nonsingular subarcs for singular optimal control problems
Mc Daniel, J. P.↗
Safety monitoring system for radioisotope thermoelectric generators
System alerts personnel of hazards which may develop while they are performing tests on radioisotope thermoelectric generator (RTG). Remedial action is initiated to minimize damage. Five operating conditions are monitored: hot junction temperature, cold junction temperature, thermal shroud coolant flow, vacuum in test chamber, and alpha radiation.
Zoltan, A.↗