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At least 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

A program to compute three-dimensional subsonic unsteady aerodynamic characteristics using the doublet lattic method, L216 (DUBFLX). Volume 1: Engineering and usage

The program input presented consists of configuration geometry, aerodynamic parameters, and modal data; output includes element geometry, pressure difference distributions, integrated aerodynamic coefficients, stability derivatives, generalized aerodynamic forces, and aerodynamic influence coefficient matrices. Optionally, modal data may be input on magnetic file (tape or disk), and certain geometric and aerodynamic output may be saved for subsequent use.

Richard, M.↗
NASA NTRS2011

A Treatise on Equivalent-Plate Stiffnesses for Stiffened Laminated-Composite Plates and Plate-Like Lattices

A survey of studies conducted since 1914 on the use of equivalent-plate stiffnesses in modeling the overall, stiffness-critical response of stiffened plates and shells is presented. Two detailed, comprehensive derivations of first-approximation equivalent-plate stiffnesses are also presented that are based on the Reissner-Mindlin-type, first-order transverse-shear deformation theory for anisotropic plates. Equivalent-plate stiffness expressions, and a corresponding symbolic manipulation computer program, are also presented for several different stiffener configurations. These expressions are very general and exhibit the full range of anisotropies permitted by the Reissner-Mindlin-type, first-order transverse-shear deformation theory for anisotropic plates. The expressions presented in the present study were also compared with available, previously published results. For the most part, the previously published results are for special cases of the general expressions presented herein and are almost in complete agreement. Analysis is also presented that extends the use of the equivalent-plate stiffness expressions to sandwich plates.

Nemeth, Michael P.↗
NASA NTRS1978

Continuum models for beam-like and plate-like lattice structures

A simple, rational approach is presented for developing continuum models for large repetitive beam-like and plate-like lattices with arbitrary configurations subjected to static, thermal and dynamic loadings. The continuum models for these structures are shear flexible beams and plates. They account for local effects in the repeating element of the actual structure and are characterized by their thermoelastic strain and kinetic energies from which the equations of motion and constitutive relations can be derived. The procedure for developing the expressions for thermoelastic strain and kinetic energies of the continuum involves introducing basic assumptions regarding the variation of the temperature, displacement and strain components in one or two directions (for plate-like and beam-like lattices) and obtaining effective thermoelastic and dynamic coefficients of the continuum in terms of material properties and geometry of the original lattice structure. The high accuracy of the continuum models developed is demonstrated by means of numerical examples.

Noor, A. K.↗
NASA NTRS1976

Computer simulation of screw dislocation in aluminum

The atomic structure in a 110 screw dislocation core for aluminum is obtained by computer simulation. The lattice statics technique is employed since it entails no artificially imposed elastic boundary around the defect. The interatomic potential has no adjustable parameters and was derived from pseudopotential theory. The resulting atomic displacements were allowed to relax in all three dimensions.

Esterling, D. M.↗
NASA NTRS1978

Modified lattice-statics approach to dislocation calculations. I - Formalism

A modified lattice-statics method to calculate the atomic displacements associated with a screw dislocation is outlined. The model incorporates an anharmonic region wherein the forces are derived from a pair potential. Appropriate energy and force expressions are derived. The modifications necessary for the implementation of the conjugate-gradient function minimization method are also derived.

Esterling, D. M.↗
NASA NTRS1990

Parametric analysis of swept-wing geometry with sheared wing tips

A computational parameter study is presented of potential reductions in induced drag and increases in lateral-directional stability due to sheared wing tips attached to an untwisted wing of moderate sweep and aspect ratio. Sheared tips are swept and tapered wing-tip devices mounted in the plane of the wing. The induced-drag results are obtained using an inviscid, incompressible surface-panel method that models the nonlinear effects due to the deflected and rolled-up wake behind the lifting surface. The induced-drag results with planar sheared tips are compared to straight-tapered tip extensions and nonplanar winglet geometries. The lateral-directional static-stability characteristics of the wing with sheared tips are estimated using a quasi-vortex-lattice method. For certain combinations of sheared-tip sweep and taper, both the induced efficiency of the wing and the relevant static-stability derivatives are predicted to increase compared to the wing with a straight-tapered tip modification.

Fremaux, C. M.↗
NASA NTRS1994

Q-derivatives, coherent states and squeezing

We show that the q-deformation of the Weyl-Heisenberg (q-WH) algebra naturally arises in discretized systems, coherent states, squeezed states and systems with periodic potential on the lattice. We incorporate the q-WH algebra into the theory of (entire) analytical functions, with applications to theta and Bloch functions.

Celeghini, E.↗
NASA NTRS1995

High Temperature Superconductivity in Praseodymium Doped (0%, 2%, 4%) in Melt-Textured Y(1-x)Pr(x)Ba2Cu3O(7-delta) Systems

A study of the magnetic and structural properties of the alloy Y(1-x)Pr(x)Ba2Cu3O(7-delta) of 0%, 2%, and 4% doping of praseodymium is presented. The resulting oxides of the alloy series are a high-temperature superconductor Y-Ba-Cu-O, which has an orthorhombic superconducting crystal-lattice. Magnetic relaxation studies have been performed on the Y-Pr-Ba-CuO bulk samples for field orientation parallel to the c-axis, using a vibrating sample magnetometer. Relaxation was measured at several temperatures to obtain the irreversible magnetization curves used for the Bean model. Magnetization current densities were derived from the relaxation data. Field and temperature dependence of the logarithmic flux-creep relaxation was measured in critical state. The data indicates that the effective activation energy U(eff) increases with increasing T between 77 K and 86 K. Also, the data shows that U(eff)(T) and superconducting transition temperature, Tc, decreased as the lattice parameters increased with increasing Pr ion concentration, x, for the corresponding Y(1-x)Pr(x)Ba(x)Cu3O(7-delta) oxides. One contribution to Tc decrease in this sampling is suspected to be due to the larger ionic radius of the Pr(3+) ion. The upper critical field (H(sub c2)) was measured in the presence of magnetic field parallel to the c axis. A linear temperature dependence with H(sub c2) was obtained.

James, Claudell↗
NASA NTRS1972

Calculation of body-centered-cubic lattice sums with an application to ferromagnetism.

The lattice sums for the bcc lattice are recalculated using the method of Flax and Raich to obtain more general expressions, valid for all temperatures, in terms of a Langevin function and its derivatives. Formulas are presented which enable easy numerical evaluation. A comparison with well-known low-temperature expansions and with the results of direct numerical integration demonstrates the validity at low temperatures of the more general expressions calculated here.

Wintucky, E. G.↗
NASA NTRS2000

Protein Crystals Grow Purer in Space: Physics of Phenomena

This presentation will summarize the quantitative experimental and theoretical results obtained by B.R. Thomas, P.G. Vekilov, D.C. Carter, A.M. Holmes, W.K. Widierow and the Author, the team with expertise in physics, biochemistry, crystallography and engineering. Impurities inhomogeneously trapped by a growing crystal - e.g., producing sectorial structure and/or striations - may induce macroscopic internal stress in it if an impurity molecule has slightly (less than 10%) different shape or volume than the regular one(s) they replace. We tested for the first time plasticity and measured Young modulus E of the triclinic, not cross-linked lysozyme by triple point bending technique. Triclinic lysozyme crystals are purely elastic with E similar or equal to 1/5 (raised dot) 10 (exp 9) partial derivative yn/sq cm. The strength limit, sigma (sub c) similar or equal to 10 (exp -3)E similar or equal to Epsilon (sub c), where sigma (sub c) and epsilon (sub c) are critical stress and strain, respectively. Scaling E and sigma (sub c) with the lattice spacing suggests similar binding stiffness in inorganic and biomolecular crystals. The inhomogeneous internal stress may be resolved in these brittle crystals either by cracking or by creation of misoriented mosaic blocks during, not after growth. If each impurity molecule induces in the lattice elementary strain epsilon (sub 0) similar or equal to 3 (raised dot) 10 (exp -2) (this is maximal elementary strain that can arise at the supersaturation DELTA mu/kT similar or equal to 2 and macroscopic molecular concentration difference between subsequent macrolayers or growth sectors is partial derivativeC similar or equal to 5 (raised dot) 10 (exp -3), the internal strain epsilon similar or equal to epsilon (sub 0) partial derivative C similar or equal to 10 (exp -4). Mosaic misorientation resolving such strain is approximately 30 arcsec. Tenfold increase of impurity concentration may cause cracking. Estimates of stress in an isometric sectorial crystal show that lysozyme crystals can tolerate the stress till the size of 0.5mm. Dissolving mosaic lysozyme crystal shows that the mosaicity, indeed, is absent below that size.

Chernov, Alex A.↗
NASA NTRS1992

Extension theorems for homogenization on lattice structures

When applying homogenization techniques to problems involving lattice structures, it is necessary to extend certain functions defined on a perforated domain to a simply connected domain. This paper provides general extension operators which preserve bounds on derivatives of order l. Only the special case of honeycomb structures is considered.

Miller, Robert E.↗
NASA NTRS1981

The unsteady suction analogy and applications

A method of the unsteady suction analogy is developed using the unsteady quasi-vortex-lattice method which accurately predicts unsteady leading-edge and side-edge suction forces, and applies to any reduced frequencies. The importance of vortex lag is demonstrated, and damping derivatives, including roll and pitch damping derivatives with reduced frequencies and angles of attack are accurately predicted. Agreement of predicted pitch stiffness derivatives, however, is found to depend on the Reynolds number, possible aeroelastic effect, and the degree of edge-separated vortex flow on the model. Applications to the prediction of longitudinal dynamic stability derivatives for slender wings at high angles of attack are also presented.

Lan, C. E.↗
NASA NTRS1998

Silicate Mineralogy of the Dust in the Inner Coma of Comet C/1995 01 (Hale-Bopp) Pre- and Post-Perihelion

We present 7.6 - 13.3 microns infrared (IR) spectrophotometry (R approx. = 180 - 350) of the 10 microns silicate emission from dust in the inner coma (i.e., within a diameter of 3in.) of comet C/1995 O1 (Hale-Bopp) at four temporal epochs from 1996 October through 1997 June during Hale-Bopp s approach to, arrival at, and recession from perihelion. The HIFOGS spectra at large heliocentric distances exhibit strong emission peaks from 9.9 - 10.1 microns and at 11.2 microns. The HIFOGS spectra of Hale-Bopp taken 1996 October 07 - 14 UT are identical in shape to the ISO SWS spectrum at 2.8 AU obtained on 1996 October 06 UT. Magnesium-rich olivine was unambiguously identified due to presence of the expected 11.2 microns peak along with the matching far-IR 18 microns, 23 microns, and 33 microns peaks in the ISO SWS spectrum. In contrast, to large heliocentric distances, we find that the silicate feature at small heliocentric distances (tau(sub lambda) less than or = 1.7 AU) exhibits strong peaks at 9.3 microns, 9.9 - 10.1 microns, and 11.2 microns, and weak at 10.5 microns and 11.8 microns. We will show that the dramatic increase of the 9.3 microns and 10.0 microns peaks close to perihelion leads to the hypothesis that there are two crystalline grain components with significantly different temperatures. The hotter mineral species (including olivines) radiate over a large range of heliocentric distances at detectable leve!s. The cooler mineral species (pyroxenes) radiate on the Wien side of the blackbody, too faint to detect in the mid-infrared spectra, until close to the sun when this species radiates on the Reyleigh-Jeans tail and becomes apparent. Decomposition of the observed silicate emission features into mineral components through comparison of the height and shape of the silicate feature ("Flux/cont") derived from the cometary spectra, to optical extinctions (Qext) derived from laboratory measurements of terrestrial silicate minerals and interplanetary dust particles (IDPs) is successful for a combination of warm grains (consisting of olivines, amorphous olivines, amorphous pyroxenes, and layer-lattice silicates) and cool grains (crystalline pyroxenes).

Wooden, Diane H.↗
NASA NTRS2010

The Lattice and Thermal Radiation Conductivity of Thermal Barrier Coatings: Models and Experiments

The lattice and radiation conductivity of ZrO2-Y2O3 thermal barrier coatings was evaluated using a laser heat flux approach. A diffusion model has been established to correlate the coating apparent thermal conductivity to the lattice and radiation conductivity. The radiation conductivity component can be expressed as a function of temperature, coating material scattering, and absorption properties. High temperature scattering and absorption of the coating systems can be also derived based on the testing results using the modeling approach. A comparison has been made for the gray and nongray coating models in the plasma-sprayed thermal barrier coatings. The model prediction is found to have a good agreement with experimental observations.

Zhu, Dongming↗
NASA NTRS2015

Water Distribution in the Continental and Oceanic Upper Mantle

Nominally anhydrous minerals such as olivine, pyroxene and garnet can accommodate tens to hundreds of ppm H2O in the form of hydrogen bonded to structural oxygen in lattice defects. Although in seemingly small amounts, this water can significantly alter chemical and physical properties of the minerals and rocks. Water in particular can modify their rheological properties and its distribution in the mantle derives from melting and metasomatic processes and lithology repartition (pyroxenite vs peridotite). These effects will be examined here using Fourier transform infrared spectrometry (FTIR) water analyses on minerals from mantle xenoliths from cratons, plume-influenced cratons and oceanic settings. In particular, our results on xenoliths from three different cratons will be compared. Each craton has a different water distribution and only the mantle root of Kaapvaal has evidence for dry olivine at its base. This challenges the link between olivine water content and survival of Archean cratonic mantle, and questions whether xenoliths are representative of the whole cratonic mantle. We will also present our latest data on Hawaii and Tanzanian craton xenoliths which both suggest the intriguing result that mantle lithosphere is not enriched in water when it interacts with melts from deep mantle upwellings (plumes).

Peslier, Anne H.↗
NASA NTRS2002

Microscopic Foundation and Simulation of Coupled Carrier-Temperature Diffusions in Semiconductor Lasers

A typical semiconductor-based optoelectronic device, such as a diode laser, consists of three subsystems: an optical field, an electron-hole plasma (EHP), and a host crystal lattice. The physics of such a device involves the interplay of optical, electrical and thermal processes. A proper description of such a device requires that all three processes are treated on equal footing and in a self-consistent fashion. Furthermore, since a semiconductor laser has intrinsic spatial inhomogeneity, such a self-consistency naturally leads to a set of partial differential equations in space and time. There is a significant lacking of research interest and results on the transport aspects of optical devices in the literature with only a few exceptions. Even the most important carrier diffusion coefficient has not been properly derived and studied so far for optically excited plasma, while most of the work adopted results from electronics community where heavily doped semiconductors with mainly one type of carriers are dealt with. The corresponding transport equation for plasma energy or temperature has received even less attention. In this talk we describe our recent results on such a self-consistent derivation of temperature and carrier-density diffusion equations coupled with the lasing process. Starting from the microscopic semiconductor Bloch equations (SBEs) including the Boltzmann transport terms in the distribution function equations for electrons and holes, we derived a closed set of diffusion equations for carrier densities and temperatures with self-consistent coupling to Maxwell's equation and to an effective optical polarization equation. The coherent many-body effects are included within the screened Hartree-Fock approximation, while scatterings are treated within the second Born approximation including both the in- and out-scatterings. Microscopic expressions for electron-hole (e-h) and carrier-LO (c-LO) phonon scatterings are directly used to derive the momentum and energy relaxation rates. These rates expressed as functions of temperatures and densities lead to microscopic expressions for self- and mutual-diffusion coefficients in the coupled density-temperature diffusion equations. Approximations for reducing the general two-component description of the electron-hole plasma (EHP) to a single-component one are discussed. In particular, we show that a special single-component reduction is possible when e-h scattering dominates over c-LO phonon scattering. The ambipolar diffusion approximation is also discussed and we show that the ambipolar diffusion coefficients are independent of e-h scattering, even though the diffusion coefficients of individual components depend sensitively on the e-h scattering rates. Our discussions lead to new perspectives into the roles played in the single-component reduction by the electron-hole correlation in momentum space induced by scatterings and the electron-hole correlation in real space via internal static electrical field. Finally, the theory is completed by coupling the diffusion equations to the lattice temperature equation and to the effective optical polarization which in turn couples to the laser field. The equations derived above are implemented in various limiting cases to a typical diode laser to study the consequences of nonlinear diffusion and the cross diffusion terms on laser behavior, especially the dynamic behavior of a diode laser under modulation. Detailed results will be presented by comparing with the standard rate equation results.

Li, J.↗
NASA NTRS1987

Ginzburg-Landau theory for the solid-liquid interface of bcc elements

Consideration is given to a simple order-parameter theory for the interfacial tension of body-centered-cubic solids in which the principal order parameter is the amplitude of the density wave at the smallest nonzero reciprocal-lattice vector of the solid. The parameters included in the theory are fitted to the measured heat of fusion, melting temperature, and solid-liquid density difference, and to the liquid structure factor and its temperature derivative at freezing. Good agreement is found with experiment for Na and Fe and the calculated anisotropy of the surface tension among different crystal faces is of the order of 2 percent. On the basis of various assumptions about the universal behavior of bcc crystals at melting, the formalism predicts that the surface tension is proportional to the heat of fusion per surface atom.

Shih, W. H.↗
NASA NTRS1990

Estimate of loads during wing-vortex interactions by Munk's transverse-flow method

The inviscid, incompressible interaction of a wing with a vortex is studied by use of Munk's transverse-flow method. The method assumes that the loading on the wing is such that the local circulatory flow of the vortex is turned so that the wing and its vortex wake act as a barrier to the flow. This permits the analysis to be carried out by mapping the transverse flowfield into the flow about a circle to find the vorticity distribution in the wake. Closed-form expressions are then derived for the bound circulation in the wind and for the lift and rolling moment induced by the vortex on the encountering wing. Comparisons of the loads predicted by these relationships with those of vortex-lattice theory for a flat wing of a rectangular planform indicate that they accurately represent the various parameters when the aspect ratio of the encountering wing is less than about two. When flat rectangular wings of higher aspect ratios are considered, some sort of correction is needed. Examples are then presented to illustrate some applications of the results.

Rossow, Vernon J.↗