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A new type of global operator to be used in evaluating matrix elements of two-particle delta functions is introduced. It is based, like the Trivedi one-particle operator, on the Poisson equation and is easier to apply than the method of Hiller, Sucher and Feinberg. After a test in the helium isoelectronic sequence, the new method is applied successfully to the interesting problem of hyperfine structure in muonic helium.
The analysis, design, and on-orbit tuning of robust controllers require more information about the plant than simply a nominal estimate of the plant transfer function. Information is also required concerning the uncertainty in the nominal estimate, or more generally, the identification of a model set within which the true plant is known to lie. The identification methodology that was developed and experimentally demonstrated makes use of a simple but useful characterization of the model uncertainty based on the output error. This is a characterization of the additive uncertainty in the plant model, which has found considerable use in many robust control analysis and synthesis techniques. The identification process is initiated by a stochastic input u which is applied to the plant p giving rise to the output. Spectral estimation (h = P sub uy/P sub uu) is used as an estimate of p and the model order is estimated using the produce moment matrix (PMM) method. A parametric model unit direction vector p is then determined by curve fitting the spectral estimate to a rational transfer function. The additive uncertainty delta sub m = p - unit direction vector p is then estimated by the cross spectral estimate delta = P sub ue/P sub uu where e = y - unit direction vectory y is the output error, and unit direction vector y = unit direction vector pu is the computed output of the parametric model subjected to the actual input u. The experimental results demonstrate the curve fitting algorithm produces the reduced-order plant model which minimizes the additive uncertainty. The nominal transfer function estimate unit direction vector p and the estimate delta of the additive uncertainty delta sub m are subsequently available to be used for optimization of robust controller performance and stability.
The computation of a steady 3D viscous flow past a slender delta wing-body configuration with trailing edge control surfaces is presented. For the numerical simulation, a cell centered finite volume Navier-Stokes zonal method was used and, besides the standard nonplanar zonal interfacing techniques, a new zonal capability, called a 'virtual zone', was implemented. This capability enables the end caps of the wings or flaps to be gridded and interfaced with the rest of the flowfield in a natural and straightforward manner. The computational results for 0-, 10-, and 24-deg angles-of-attack were found to agree with experimental results qualitively and quantitatively.
The external thermal insulation systems for the Space Shuttle solid rocket boosters and the Air Force Titan IV payload fairings were in jeopardy due to EPA regulatory problems, endangering the flight status of both vehicles. The Marshall Convergent Coating (MCC-1) Development Team was formed in February 1994 to develop and implement an EPA-compliant external thermal insulation system for both systems. MCC-1 made use of a process known as Convergent Spray Technology (CST), a solventless, sprayable process that eliminated the environmentally hazardous chemicals involved with the old methods. Implemented in record time, the new insulation was so successful that it was selected for two additional flight vehicles, Boeing's Sea Launch and Delta TV. The activity also led to commercial spin-off pilot projects. The team continues today to share data between the various production sites, resolve production issues, expand the material's use, and consider potential improvements for the future.
The generalization of a class of low-dissipative high order filter finite difference schemes for long time wave propagation of shock/turbulence/combustion compressible viscous gas dynamic flows to compressible MHD equations for structured curvilinear grids has been developed. The new scheme consists of a divergence free preserving high order spatial base scheme with a filter approach which can be divergence-free preserving depending on the type of filter operator being used, the method of applying the filter step, and the type of flow problem to be considered. Several variants of the filter approach that cater to different flow types are proposed. These filters provide a natural and efficient way for the minimization of the divergence of the magnetic field (Delta * B) numerical error in the sense that no standard divergence cleaning is required. Performance evaluation of these variants, and the key role that the proper treatment of their corresponding numerical boundary conditions can play will be illustrated. Many levels of grid refinement and detailed comparison with several commonly used compressible MHD shock-capturing schemes will be sought. For certain MHD 2-D test problems, divergence free preservation of the magnetic fields of these filter schemes has been achieved.
Human behavior often consists of a series of distinct activities, each characterized by a unique pattern of interaction with the visual environment. This is true even in a restricted domain, such as a piloting an aircraft, where activities with distinct visual signatures might be things like communicating, navigating, and monitoring. We propose a novel analysis method for gaze-tracking data, to perform blind discovery of these hypothetical activities. The method is in some respects similar to recurrence analysis, but here we compare not individual fixations, but groups of fixations aggregated over a fixed time interval. The duration of this interval is a parameter that we will refer to as delta. We assume that the environment has been divided into a set of N different areas-of-interest (AOIs). For a given interval of time of duration delta, we compute the proportion of time spent fixating each AOI, resulting in an N-dimensional vector. These proportions can be converted to integer counts by multiplying by delta divided by the average fixation duration (another parameter that we fix at 280 milliseconds). We compare different intervals by computing the chi-square statistic. The p-value associated with the statistic is the likelihood of observing the data under the hypothesis that the data in the two intervals were generated by a single process with a single set of probabilities governing the fixation of each AOI. The method has been applied to approximately 100 hours of eye movement data collected from pilots in a high-fidelity B747 flight simulator, and the results have been compared to synthetic data in which the each activity is represented as first-order Markov process with random probabilities assigned to the AOIs. Randomly-generated synthetic activities can require thousands of fixations to be discriminated with statistical significance, while the human data can be clustered using averaging windows of some 10's of seconds, suggesting that the actual activities are much more narrowly focused than random Markov models.
The objective of CAM is to develop, test, and analyze thin film membrane materials for separation and purification of carbon dioxide (CO2) from mixtures of gases, such as those found in the Martian atmosphere. The membranes are targeted toward In Situ Resource Utilization (ISRU) applications that will operate in extraterrestrial environments and support future unmanned and human space missions. A primary application is the Sabatier Electrolysis process that uses Mars atmosphere CO2 as raw material for producing water, oxygen, and methane for rocket fuel and habitat support. Other applications include use as an inlet filter to collect and concentrate Mars atmospheric argon and nitrogen gases for habitat pressurization, and to remove CO2 from breathing gases in Closed Environment Life Support Systems (CELSS). CAM membrane materials include crystalline faujasite (FAU) zeolite and rubbery polymers such as silicone rubber (PDMS) that have been shown in the literature and via molecular simulation to favor adsorption and permeation of CO2 over nitrogen and argon. Pure gas permeation tests using commercial PDMS membranes have shown that both CO2 permeance and the separation factor relative to other gases increase as the temperature decreases, and low (Delta)P(Sub CO2) favors higher separation factors. The ideal CO2/N2 separation factor increases from 7.5 to 17.5 as temperature decreases from 22 C to -30 C. For gas mixtures containing CO2, N2, and Ar, plasticization decreased the separation factors from 4.5 to 6 over the same temperature range. We currently synthesize and test our own Na(+) FAU zeolite membranes using standard formulations and secondary growth methods on porous alumina. Preliminary tests with a Na(+) FAU membrane at 22 C show a He/SF6 ideal separation factor of 62, exceeding the Knudsen diffusion selectivity by an order of magnitude. This shows that the membrane is relatively free from large defects and associated non-selective (viscous flow) transport mechanisms. The Membrane Test Facility (MTF) has been developed to measure membrane permeance over a wide range of temperature and pressure. The facility uses two volume compartments separated by the membrane that are instrumented to measure temperature, delta pressure across the membrane, and gas composition. A thermal shroud supports and encloses the membrane, and provides temperature control. Methods were developed to determine membrane permeance using the first order decay of the pressure difference between the sealed compartments, using the total pressure for pure gases, and partial pressure of each species in gas mixtures. The technique provides an end-to-end measurement of gas permeance that includes concentration polarization effects. Experiments have shown that in addition to membrane permeance properties, the geometry and design of associated structures play an important role in how membrane systems will function on Mars.
Computational simulation of the vertical tail buffet problem is accomplished using a delta wing-vertical tail configuration. Flow conditions are selected such that the wing primary-vortex cores experience vortex breakdown and the resulting flow interacts with the vertical tail. This multidisciplinary problem is solved successively using three sets of equations for the fluid flow, aeroelastic deflections and grid displacements. For the fluid dynamics part, the unsteady, compressible, full Navier-Stokes equations are solved accurately in time using an implicit, upwind, flux-difference splitting, finite-volume scheme. For the aeroelastic part, the aeroelastic equation for bending vibrations is solved accurately in time using the Galerkin method and the four-stage Runge-Kutta scheme. The grid for the fluid dynamics computations is updated every few time steps using a third set of interpolation equations. The computational application includes a delta wing of aspect ratio 1 and a rectangular vertical tail of aspect ratio 2, which is placed at 0.5 root-chord length downstream of the wing trailing edge. The wing angle of attack is 35 deg and the flow Mach number and Reynolds number are 0.4 and 10,000, respectively.
The development of large area multiwire proportional chambers, to be used as high resolution spatial detectors in cosmic ray experiments is described. A readout system was developed which uses a directly coupled, lumped element delay-line whose characteristics are independent of the MWPC design. A complete analysis of the delay-line and the readout electronic system shows that a spatial resolution of about 0.1 mm can be reached with the MWPC operating in the strictly proportional region. This was confirmed by measurements with a small MWPC and Fe-55 X-rays. A simplified analysis was carried out to estimate the theoretical limit of spatial resolution due to delta-rays, spread of the discharge along the anode wire, and inclined trajectories. To calculate the gas gain of MWPC's of different geometrical configurations a method was developed which is based on the knowledge of the first Townsend coefficient of the chamber gas.
Two Voyager spacecraft are currently engaged in exploration of the outer solar system with Voyager 2 scheduled to conduct the first close-up investigation of the planet Uranus during the period November 4, 1985 through March 3, 1986. Flight engineering for the Voyager project has the objectives of delivering a functioning spacecraft containing observing sequences to the right places at the right times. Due to the changing environment as the mission has progressed outward from Jupiter to Saturn to Uranus (and on to Neptune), this engineering task has included the development of significant new capabilities. The paper utilizes the case-study method to examine some new spacecraft capabilities in three subsystems: data, attitude and articulation control, and power. The implementation of a new navigational data-type, delta DOR, is also reviewed. An overview is given of the Voyager sequencing process for the cruise and encounter phases with a case study focusing on late updating of part of the near encounter sequence. The prospective mission to Neptune is previewed.
An experimental investigation was conducted in a water tunnel to identify the effects of apex blowing on two delta-wing models undergoing constant pitch-rate motion. One wing was of 60-degree sweep and the other was of 76-degree sweep. Flow visualization methods were utilized to determine vortex burst locations for a wide range of pitch-up (nose up) and plunge (nose down) rates, apex jet strengths, and blowing directions. Results indicate that blowing along the 60-degree wing vortex core or along the 76-degree wing centerline results in a notable improvement in vortex behavior under both static and dynamic conditions. The results are most dramatic during dynamic plunging (nose down) conditions, where blowing resulted in the reformation of vortices with significant length.
Two techniques for characterizing fatigue delamination in double cantilever beams, the delamination growth onset method and the delamination growth and arrest method, are evaluated. Two glass/epoxy systems, S2/SP250 and S2/CE9000, were tested at R = 0.1 and R = 0.5. The values of the strain energy release rate threshold Delta G(Ith) for no onset of delamination growth until one million cycles were compared with the values of Delta G(I) at delamination arrest. The values at arrest were consistently higher because fiber bridging occurred in the tests. Normalizing Delta G(I) by the mode I value of interlaminar fracture toughness G(Ir) at the corresponding delta A gave values of Delta G(I)/G(Ir) at delamination arrest which were closer to the threshold values obtained from the Delta G-N technique. However, this normalization did not represent a generic materials characterization technique and did not allow for delamination onset predictions.
This paper investigates the development and use of semi-analytic methods for propellant depot orbit selection in cyclic, coplanar, Keplerian GSO missions. The cyclic depot transfer strategy which allows for non-optimum (e.g. non-Hohmann) transfer, is constrained by resonance requirements allowing for descent rendezvous/refueling with fuel depots positioned during the ascent phase of the mission. The mission benefit using this transfer technique allows an improvement in propulsion system efficiency which can lead to approximately 43 percent reduction in initial launch mass when compared to traditional methods, but with the trade-off of longer mission timelines. A family of potential transfers is identified with an 'optimum' selection not based on conventional delta V minimization. The results of this analysis include reduced transfer times and greater potential initial launch mass savings over previous work.
An assessment of the plasticity-induced crack-closure concept is made, in light of some of the questions that have been raised on the validity of the concept, and the assumptions that have been made concerning crack-dp damage below the crack-opening stress. The impact of using other crack-tip parameters, such as the cyclic crack-tip displacement, to model crack-growth rate behavior was studied. Crack-growth simulations, using a crack-closure model, showed a close relation between traditional Delta K eff, and the cyclic crack-tip displacement (Delta eff) for an aluminum alloy and a steel. Evaluations of the cyclic hysteresis energy demonstrated that the cyclic plastic damage below the crack-opening stress was negligible in the Paris crack-growth regime. Some of the standard and newly proposed remote measurement methods to determine the 'effective' crack-tip driving parameter were evaluated on middle-crack tension specimens. A potential source of the Kmax effect on crack-growth rates was studied on an aluminum alloy. Results showed that the ratio of Kmax to Kc had a strong effect on crack-growth rates at high stress ratios and at low stress ratios for very high stress levels. The crack-closure concept and the traditional crack-growth rate equations were able to correlate and predict crack-growth rates under these extreme conditions.
A new tool was developed to predict the boundary layer quantities required by several physics-based predictive/analytic methods that assess damaged Orbiter tile. This new tool, the Boundary Layer Property Prediction (BLPROP) tool, supplies boundary layer values used in correlations that determine boundary layer transition onset and surface heating-rate augmentation/attenuation factors inside tile gouges (i.e. cavities). BLPROP interpolates through a database of computed solutions and provides boundary layer and wall data (delta, theta, Re(sub theta)/M(sub e), Re(sub theta)/M(sub e), Re(sub theta), P(sub w), and q(sub w)) based on user input surface location and free stream conditions. Surface locations are limited to the Orbiter s windward surface. Constructed using predictions from an inviscid w/boundary-layer method and benchmark viscous CFD, the computed database covers the hypersonic continuum flight regime based on two reference flight trajectories. First-order one-dimensional Lagrange interpolation accounts for Mach number and angle-of-attack variations, whereas non-dimensional normalization accounts for differences between the reference and input Reynolds number. Employing the same computational methods used to construct the database, solutions at other trajectory points taken from previous STS flights were computed: these results validate the BLPROP algorithm. Percentage differences between interpolated and computed values are presented and are used to establish the level of uncertainty of the new tool.
New methods for integrating systems of stiff, nonlinear, first order, ordinary differential equations are developed by casting the differential equations into integral form. Nonlinear recursive relations are obtained that allow the solution to a system of equations at time t plus delta t to be obtained in terms of the solution at time t in explicit and implicit forms. Examples of accuracy obtained with the new technique are given by considering systems of nonlinear, first order equations which arise in the study of unified models of viscoplastic behaviors, the spread of the AIDS virus, and predator-prey populations. In general, the new implicit algorithm is unconditionally stable, and has a Jacobian of smaller dimension than that which is acquired by current implicit methods, such as the Euler backward difference algorithm; yet, it gives superior accuracy. The asymptotic explicit and implicit algorithms are suitable for solutions that are of the growing and decaying exponential kinds, respectively, whilst the implicit Euler-Maclaurin algorithm is superior when the solution oscillates, i.e., when there are regions in which both growing and decaying exponential solutions exist.
The author has identified the following significant results. Of the four change detection techniques (post classification comparison, delta data, spectral/temporal, and layered spectral temporal), the post classification comparison was selected for further development. This was based upon test performances of the four change detection method, straightforwardness of the procedures, and the output products desired. A standardized modified, supervised classification procedure for analyzing the Texas coastal zone data was compiled. This procedure was developed in order that all quadrangles in the study are would be classified using similar analysis techniques to allow for meaningful comparisons and evaluations of the classifications.
The intercontinental clock synchronization capabilities of Very Long Baseline Interferometry (VLBI) and the Navigation Technology Satellite (NTS) were compared in May 1978 by using both methods to synchronize the cesium clocks at the NASA Deep Space Net complexes at Madrid, Spain, and Goldstone, California. The VLBI experiments used the Wideband VLBI Data Acquisition System. The Navigation Technology Satellites were used with NTS Timing Receivers developed by the Goddard Space Flight Center. The two methods agreed at about the one-half microsecond level. The VLBI system also obtained long-term stability information on the HP5061A004 cesium standards by measuring delta T/T over four 3- to 4-day intervals, obtaining stability estimates of (1 + or - 1)x10 to the -13th power for the combined timing systems.