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Series of measurements on the thermal expansion coefficients of several aerospace alloys and standard materials establish relationships between related alloys that would aid in predicting their thermal expansion reliability. Thermal expansion data are also necessary for the reduction of electrical resistivity measurements of those same materials.
A series of ceramic compositions based on variations in the crystal-glass ratio of a mullite body were developed. The thermal expansion of these compositions varies from 3.7 to 5.0 x 10 to the -6th/deg C to 800 C. The materials are particularly useful for applications involving silicon, in that an identical thermal expansion is available. The high-temperature creep data for the lower-expansion compositions are inferior as a result of their higher glass contents. Raw material sources and fabrication procedures for specific compositions are given.
The field line resonance expansion is studied with a magnetohydrodynamic (MHD) model applicable to earth's magnetotail. Using a Frobenius series solution, this expansion is found to be inconsistent. The inconsistency is seen by evaluating the terms in the model equations that the expansion neglects as small. Their effect is to provide a solution more singular than that determined by the expansion procedure. A tentative alternative expansion procedure, retaining these neglected terms approximately, yields a nonsingular solution, suggesting that resonant mode conversion rather than field line resonance is the appropriate phenomenon.
A method for iterative reanalysis in automated structural design is presented for a finite-element analysis using the direct stiffness approach. A basic feature of the method is that the generalized stiffness and inertia matrices are expressed as functions of structural design parameters, and these generalized matrices are expanded in Taylor series about the initial design. Only the linear terms are retained in the expansions. The method is approximate because it uses static condensation, modal reduction, and the linear Taylor series expansions. The exact linear representation of the expansions of the generalized matrices is also described and a basis for the present method is established. Results of applications of the present method to the recalculation of the natural frequencies of two simple platelike structural models are presented and compared with results obtained by using a commonly applied analysis procedure used as a reference. In general, the results are in good agreement. A comparison of the computer times required for the use of the present method and the reference method indicated that the present method required substantially less time for reanalysis. Although the results presented are for relatively small-order problems, the present method will become more efficient relative to the reference method as the problem size increases. An extension of the present method to static reanalysis is described, ana a basis for unifying the static and dynamic reanalysis procedures is presented.
The radial dynamics of the nighttime plasma sheet during substorms is examined. The spatial dependence of plasma sheet variations at different radial distances is studied on the basis of simultaneous recordings from two closely spaced satellites. The simultaneous measurements of the plasma sheet behavior earthward and tailward of r = 15 earth radii confirm substorm models which predict a thinning of the near-earth plasma sheet before the formation of an X-type neutral line, followed by a thickening on the earthward side and a further thinning on the tailward side. Temporal correlations between the plasma sheet variations and substorm development on the ground are studied by obtaining accurate timing of individual substorm expansion onsets. In particular, during multiple onset storms, the near-earth plasma sheet is found to experience a series of multiple expansions and contractions, which usually occur in a one-to-one relationship with ground Pi 2 bursts and are well correlated with auroral zone and low-altitude magnetic disturbances.
The toughness and coefficient of thermal expansion of a series of functionalized graphene sheet - epoxy nanocomposites are investigated. Functionalized graphene sheets are produced by splitting graphite oxide into single graphene sheets through a rapid thermal expansion process. These graphene sheets contain approx. 10% oxygen due to the presence of hydroxide, epoxide, and carboxyl functional groups which assist in chemical bond formation with the epoxy matrix. Intrinsic surface functionality is used to graft alkyl amine chains on the graphene sheets, and the addition of excess hardener insures covalent bonding between the epoxide matrix and graphene sheets. Considerable improvement in the epoxy dimensional stability is obtained. An increase in nanocomposite toughness is observed in some cases.
Recursive generation of expansion coefficients of time-dependent f and g series in two-body problem, using algebraic recurrence formulas
This software translates MAPGEN (Europa and APGEN) domains to ASPEN, and the resulting domain can be used to perform planning for the Mars Exploration Rover (MER). In other words, this is a conversion of two distinct planning languages (both declarative and procedural) to a third (declarative) planning language in order to solve the problem of faithful translation from mixed-domain representations into the ASPEN Modeling Language. The MAPGEN planning system is an example of a hybrid procedural/declarative system where the advantages of each are leveraged to produce an effective planner/scheduler for MER tactical planning. The adaptation of the planning system (ASPEN) was investigated, and, with some translation, much of the procedural knowledge encoding is amenable to declarative knowledge encoding. The approach was to compose translators from the core languages used for adapting MAGPEN, which consists of Europa and APGEN. Europa is a constraint- based planner/scheduler where domains are encoded using a declarative model. APGEN is also constraint-based, in that it tracks constraints on resources and states and other variables. Domains are encoded in both constraints and code snippets that execute according to a forward sweep through the plan. Europa and APGEN communicate to each other using proxy activities in APGEN that represent constraints and/or tokens in Europa. The composition of a translator from Europa to ASPEN was fairly straightforward, as ASPEN is also a declarative planning system, and the specific uses of Europa for the MER domain matched ASPEN s native encoding fairly closely. On the other hand, translating from APGEN to ASPEN was considerably more involved. On the surface, the types of activities and resources one encodes in APGEN appear to match oneto- one to the activities, state variables, and resources in ASPEN. But, when looking into the definitions of how resources are profiled and activities are expanded, one sees code snippets that access various information available during planning for the moment in time being planned to decide at the time what the appropriate profile or expansion is. APGEN is actually a forward (in time) sweeping discrete event simulator, where the model is composed of code snippets that are artfully interleaved by the engine to produce a plan/schedule. To solve this problem, representative code is simulated as a declarative series of task expansions. Predominantly, three types of procedural models were translated: loops, if statements, and code blocks. Loops and if statements were handled using controlled task expansion, and code blocks were handled using constraint networks that maintained the generation of results based on what the order of execution would be for a procedural representation. One advantage with respect to performance for MAPGEN is the use of APGEN s GUI. This GUI is written in C++ and Motif, and performs very well for large plans.
This paper presents simulation predictions of novel over-the-rotor acoustic liner configurations compared with experimental data. This is a follow on to the investigation on the effect of grazing flow on grooved over-the-rotor casing treatments. The purpose of this modeling investigation stems from the determination that traditional liner modeling techniques are inadequate for nontraditional internal liner cavity geometries. A series of these expansion chamber type liner design concepts were previously developed by Glenn Research Center and tested using the Langley Research Center Normal Incidence Tube. The measured normalized impedance and absorption coefficient is compared with that obtained from the COMSOL Multiphysics® simulation. Additionally, using a parametric case study, another series of simulations were conducted to determine what additional benefits, if any, this genre of liner has to offer the acoustics community. A total of 53 permutations of this concept was investigated. The results indicate that with longer internal fins, the resonance is sifted to lower frequencies.
Under certain conditions the normalized autocorrelation function ρ(τ) of stationary random noise may be expanded as a power series about the point τ = 0. This paper indicates that the coefficients of the expansion are rather simply related to the average rate of occurrence of zeros in the noise function and its derivatives. The expansion of academic interest in providing another perspective of the relationships among the noise function, its power spectrum, and its autocorrelation function. It may also be of practical interest in providing a quick means of estimating the normalized autocorrelation function from a noise record over the range of τ in which the power series converges rapidly. The class of noise spectrum for which convergent series expansion is not possible is of interest in pointing up necessary physical characteristics of noise signals which have such spectra.
Lorentz invariant method for obtaining motion equations from Einstein gravitational field equations, assuming metric tensor and field functions expansion into power series
Hansen planetary theory basic function, discussing perturbations expansion into trigonometric series
Continuing development and expansion of a series of P-channel MOSFET circuits in flight data systems is reported. Using hybrid thick film techniques, these circuits evolved into bugs with more than 1000 transistors on a chip. A proposed data system for Helios satellite will have approximately 130 bugs and a semiconductor count of more than 100,000, will weigh less than 1 N and use less than 1.2 W.
A modified stepwise regression is applied to flight data from a light research air-plane operating at high angles at attack. The well-known phenomenon referred to as buckling or porpoising is analyzed and modeled using both power series and spline expansions of the aerodynamic force and moment coefficients associated with the longitudinal equations of motion.
Sensors used to monitor bioreactor conditions directly often perform poorly in the face of adverse nonphysiological conditions. One way to circumvent this is to use a remote sensor block. However, such a configuration usually causes a significant time lag between measurements and the actual state values. Here, the problem of implementing feedback control strategies for such systems, described by nonlinear equations, is addressed. The problem is posed as an optimal control problem with a linear quadratic performance index. The linear control law so obtained is used to implement feedback. A global linearization technique as well as an expansion using Taylor series is used to linearize the nonlinear system, and the feedback is subsequently implemented.
The fractal and marginal fractal regimes in surface geometry are studied. The basic notions of fractal geometry are applied to a small surface patch in a developed sea, corresponding to the equilibrium wave number spectrum. Topothesy, outer and inner boundaries of the fractal range, and a cascade pattern in surface geometry are discussed. Theoretical predictions of whitecap and foam coverage are presented. A fractal decomposition for a surface patch is developed based on the Karhunen-Loeve expansion. The resulting series formalizes the cascade process of constructing realization of a Gaussian random patch. The implications of the research for microwave remote sensing signatures are considered.
The performance of a carrier phase locked loop (PLL) driven by a periodic Doppler input is studied. By expanding the Doppler input into a Fourier series and applying the linearized PLL approximations, it is easy to show that, for periodic frequency disturbances, the resulting steady state phase error is also periodic. Compared to the method of expanding frequency excursion into a power series, the Fourier expansion method can be used to predict the maximum phase error excursion for a periodic Doppler input. For systems with a large Doppler rate fluctuation, such as an optical transponder aboard an Earth orbiting spacecraft, the method can be applied to test whether a lower order tracking loop can provide satisfactory tracking and thereby save the effect of a higher order loop design.
Polyimides are finding increased applications in microelectronics due to their high thermal stability, good chemical resistance, good adhesion, low moisture absorption, good mechanical properties, and low coefficient of thermal expansion (CTE). Four series of random copolyimides were synthesized and characterized for potential application as encapsulants, stress-relief layers, and interlevel dielectrics. Several candidates exhibited good combinations of physical and mechanical properties with inherent viscosities from 1.21 to 1.42 dL/g, T(sub g)'s ranging from 251 to 277 C, 10% weight loss temperatures between 503 and 527 C, and CTEs ranging from 33 to 39 ppm/deg C. Mechanical properties at room temperature for the best candidates included tensile strengths of 17.8-21.3 ksi, moduli between 388 and 506 ksi, and elongations of 11-43%. Moisture absorption for these copolyimides ranged between 0.85 and 1.38 wt %.