Showing papers by "Sandia National Laboratories published in 1968"

PATRICIA—Practical Algorithm To Retrieve Information Coded in Alphanumeric

Abstract: PATRICIA is an algorithm which provides a flexible means of storing, indexing, and retrieving information in a large file, which is economical of index space and of reindexing time. It does not require rearrangement of text or index as new material is added. It requires a minimum restriction of format of text and of keys; it is extremely flexible in the variety of keys it will respond to. It retrieves information in response to keys furnished by the user with a quantity of computation which has a bound which depends linearly on the length of keys and the number of their proper occurrences and is otherwise independent of the size of the library. It has been implemented in several variations as FORTRAN programs for the CDC-3600, utilizing disk file storage of text. It has been applied to several large information-retrieval problems and will be applied to others.

On a theory of heat conduction involving two temperatures

Abstract: In dieser Arbeit entwickeln wir eine neue Theorie der Warmeleitung. Diese Theorie, in der zwei Temperaturen auftreten, beseitigt einige Pathologien der klassischen Theorie.

A criterion for the time dependence of dynamic fracture

Abstract: Dynamic fracture is a time-dependent phenomena in which the spall stress depends on the stress pulse duration. It is shown that the empirical relation between the spall stress and the square root of the stress gradient is equivalent to a simple impulse criterion. A more general criterion based on the concept of cumulative damage is proposed, and good agreement is obtained between calculated and observed values of the spall layer thickness in aluminum.

A note on non-simple heat conduction

Abstract: In einem nicht-einfachen Material kann die Warmeubertragung durch zwei Temperaturen geregelt werden; die eine regelt die Strahlung, die andere die Leitung. In dieser Arbeit zeigen wir unter Benutzung fruherer Ergebnisse, dass bei stationaren Bedingungen die Differenz der beiden Temperaturen proportional zur Strahlungsdichte ist.

Photo-Ionization Cross Sections of the Elements Helium to Xenon

Abstract: The quantity $\ensuremath{-}\mathcal{r}(V(\mathcal{r})$ calculated by Herman and Skillman, using the Hartree-Fock-Slater approach, is approximated by a series of straight lines. With such a potential the radial Schr\"odinger equation is exactly solvable with Whittaker functions. The bound-state eigenvalue equation is found and is used to adjust the parameters of the straight lines so that the model eigenvalues and those of Herman and Skillman are in reasonable agreement. With the discrete and continuum orbitals of the model, the photo-ionization cross section for all the shells of the elements helium-xenon are computed.

Effects of Electron-Electron Interactions on Nuclear Spin-Lattice Relaxation Rates and Knight Shifts in Alkali and Noble Metals

Abstract: Nuclear-magnetic-resonance data for the alkali and noble metals are discussed in terms of Moriya's theory of exchange-enhanced spin-lattice relaxation rates. The available evidence suggests that the relaxation-rate enhancement resulting from collective electron effects is \ensuremath{\sim}20% smaller in lithium and sodium than predicted by the theory for the case of a $\ensuremath{\delta}$-function-potential electron-electron interaction. This small disparity is attributed to a nonzero interaction range whose magnitude is estimated to be less than an atomic radius. During the course of this study, low-temperature Knight-shift and spin-lattice relaxation data have been obtained for $^{39}\mathrm{K}$, $^{85}\mathrm{Rb}$, $^{87}\mathrm{Rb}$, and $^{133}\mathrm{Cs}$ in the respective metals. The results suggest that the exchange enhancements of the conduction-electron spin susceptibilities in these metals are comparable to those in lithium and sodium. Similar conclusions apply in the case of the noble metals.

Pressure Dependence of the Magnetic Transitions in Fe-Rh Alloys

Abstract: The pressure coefficients of the Curie temperature $\ensuremath{\theta}$ and the first-order transition temperature ${T}_{0}$ have been measured for two binary and three ternary alloys containing Fe and Rh. The coefficients are constant with pressure for all the alloys up to 25 kbars. The existence of a triple point in the $P\ensuremath{-}T$ plane is demonstrated for these alloys. At pressures above the critical pressure, there is no ferromagnetic state, only antiferromagnetic and paramagnetic, consistent with Hargitai's theory that Rh atoms have no moment in the antiferromagnetic state. The pressure data and Kouvel's field-dependence data are used for comparison with the ratio of volume change to magnetization change as predicted from thermodynamics. Exchange inversion is discussed and ruled out as an acceptable model for the magnetic behavior. The effects of heat treatment on ${T}_{0}$ and $\frac{d{T}_{0}}{\mathrm{dP}}$ and the relationship between ${T}_{0}$ and $\frac{d{T}_{0}}{\mathrm{dP}}$ are also discussed.

Temperature and Pressure Dependence of the Dielectric Constants of the Thallous Halides

Abstract: The effects of temperature (76-400\ifmmode^\circ\else\textdegree\fi{}K) and hydrostatic pressure (up to 20 kbar) on the static dielectric constants of single crystal TlCl and TlBr and polycrystalline TlI were investigated. TlCl and TlBr have the CsCl structure, whereas TlI transforms from an orthorhombic structure to the CsCl structure at 4.8 kbar and 300\ifmmode^\circ\else\textdegree\fi{}K. In all cases, the dielectric constant $\ensuremath{\epsilon}$ decreases with both increasing temperature (at low temperatures) and increasing pressure. At 1 bar and 293\ifmmode^\circ\else\textdegree\fi{}K, ${(\frac{\ensuremath{\partial}\mathrm{ln}\ensuremath{\epsilon}}{\ensuremath{\partial}T})}_{P}$ and ${(\frac{\ensuremath{\partial}\mathrm{ln}\ensuremath{\epsilon}}{\ensuremath{\partial}P})}_{T}$ (in units of ${10}^{\ensuremath{-}4}$\ifmmode^\circ\else\textdegree\fi{}${\mathrm{K}}^{\ensuremath{-}1}$ and ${10}^{\ensuremath{-}2}$ ${\mathrm{kbar}}^{\ensuremath{-}1}$) are -3.94 and -1.81, -3.70 and -1.77, -0.68 and -0.65 for TlCl, TlBr, and TlI (orthorhombic), respectively. For TlI (cubic) the corresponding values at 3 kbar and 293\ifmmode^\circ\else\textdegree\fi{}K are -4.04 and -1.47. At the orthorhombic \ensuremath{\rightarrow} cubic transition, $\ensuremath{\epsilon}$ of TlI increases by 35%, but this change is found to be entirely due to the change in volume, the total polarizability per molecule being independent of crystal structure. The temperature dependence of $\ensuremath{\epsilon}$ is separated into volume-dependent and volume-independent contributions. For the thallous halides the latter contribution, which is determined by anharmonic lattice effects, is large and determines the sign of ${(\frac{\ensuremath{\partial}\mathrm{ln}\ensuremath{\epsilon}}{\ensuremath{\partial}T})}_{P}$. On the basis of Szigeti's theory and the assumption that the optical dielectric constant ${\ensuremath{\epsilon}}_{\mathrm{op}}$ is a unique function of volume, it is found that anharmonicities in the potential energy and nonlinearities in the dipole moment account for 30-40% of the lattice contribution to $\ensuremath{\epsilon}$ of the thallous halides. The effective charge ratio $\frac{{e}^{*}}{e}$ at room temperature is 0.96 for TlCl and 0.95 for TlBr. At low temperatures, $\ensuremath{\epsilon}$ of TlCl and TlBr obeys a Curie-Weiss law $\ensuremath{\epsilon}=\frac{c}{(T\ensuremath{-}{T}_{0})}$ with ${T}_{0}$ negative. At high temperatures (g300\ifmmode^\circ\else\textdegree\fi{}K) the dielectric constant and dielectric loss are predominantly determined by the formation and transport of lattice defects. The activation energies calculated from the results agree well with values obtained from ionic-conductivity measurements.

Effect of Pressure on the Metal-Nonmetal Transition and Conductivity of Fe 3 O 4

Abstract: It was recently suggested that the metal-nonmetal transition which occurs in ${\mathrm{Fe}}_{3}$${\mathrm{O}}_{4}$ at \ensuremath{\simeq}120\ifmmode^\circ\else\textdegree\fi{}K may be of the Mott-Wigner type. Present results on the effects of pressure on the transition temperature and the conductivity of the low-temperature phase are consistent with such a model. ${\mathrm{Fe}}_{3}$${\mathrm{O}}_{4}$ may thus be the first material in which such a transition has been observed.

Triplet Exciton Phosphorescence in Crystalline Anthracene

Abstract: Long-lived triplet excitons in anthracene crystals were detected by simultaneous observation of both their weak red phosphorescence and the delayed blue fluorescence which results from exciton-exciton interaction. Absorption and emission spectra at room temperature show that the interacting excitons are free, i.e., they correspond to the electronic excitation levels of the pure crystal. Decay curves obey the anticipated bimolecular-interaction kinetic equations. The triplet radiative lifetime is about 60 sec. In contrast to the results at room temperature, the low-temperature behavior is dominated by exciton-tapping effects. The interaction between free and shallowly trapped excitons is much more efficient in yielding delayed blue fluorescence than is the free-free interaction which is dominant at room temperature.

Finite element solution to dynamic stability of bars.

Abstract: treated in Ref. 1. Note that for this low-frequency mode, \I/N = 1 in (6), and the correcting series is proportional to the Mach number Mb. The series converges rather slowly, but since Mb ~ 0(10~), the deviation from spatial uniformity is indeed quite small. Thus, as Oberg emphasized, the nonacoustic instability is, in fact, a special form of acoustic oscillation. The main point of the remarks here is simply that by means of a thorough analysis giving Eq. (7), one obtains the useful results for frequency and growth constant, valid for any grain configuration and subject only to the weak constraint that the meanflow Mach number is small. Similar formulas can be obtained also for gas and liquid rockets. The principal difference from the solid rocket arises from the influence of combustion within the chamber and not merely at the boundary.

Epoxy polymers. II. Macrostructure

Abstract: A variety of measurements indicate that thermosetting epoxy polymers contain closely packed floccules and an interstitial liquid similar to the starting materials. The fioccules are thought to be of colloidal origin and appear to be ordered with respect to each other in a three-dimensional array.

Nonlinear analysis of shells of revolution by the matrix displacement method.

Abstract: Matrix displacement method for nonlinear elastic analysis of shells of revolution under symmetrical and asymmetrical loadings

Calculation of the Self-Consistent Phonon Spectrum of hcp He 4

Abstract: A numerical computation is carried out of the phonon spectrum of hcp ${\mathrm{He}}^{4}$ with the self-consistent phonon theory. Dispersion curves in symmetry directions are compared with recent measurements using the inelastic-neutron-scattering technique. The computed anisotropy of the sound velocity is also compared with recent experimental results on acoustic propagation in oriented single crystals.

Controlled Recovery of Payloads at Large Glide Distances, Using the Para-Foil

Abstract: Recent progress of Sandia Laboratory in the development of a small guidance and control system and by the University of Notre Dame on the Para-Foil has indicated that the design of a system capable of recovering a 150-Ib payload from altitudes greater than 300,000 ft and ranges of from three to five times the deployment height (60,000 ft) is quite feasible. The Para-Foil is a completely nonrigid, self-inflating flying wing, capable of being packed and deployed like a conventional parachute and able to glide large distances. The guidance package is an electromechanical control system employing a direction-finding antenna to control the direction of the Para-Foil's glide path with respect to a ground or shipboard transmitter. The recovery system design program includes such parameters as size and weight of the recovery unit, size of the payload (W/S wing loading), glide ratio and wind structure, and flare-out capabilities in the recovery area. The full-scale recovery program includes numerous packing, deployment, and glide tests. These tests demonstrated successful deployment, excellent gliding performance (JL/D = 3.88) and dynamic flight stability, and very low impact velocities during the final recovery phases. Recent guidance and control tests also demonstrated excellent response in maneuverability of the Para-Foil. This paper summarizes the design program and the results of full-scale deployment and guided recovery flight tests and demonstrates the potential of the Para-Foil for use in many space-age recovery programs.

Vaporization of Lead Zirconate-Lead Titanate Materials: II, Hot-Pressed Compositions at Near Theoretical Density*

Abstract: The vaporization of lead monoxide from lead zirconate-lead titanate materials was studied by thermogravimetric techniques in vacuum with hot-pressed pellets of near theoretical density. The initial step of the complex, two-step vaporization observed in cold-pressed pellets in an earlier investigation is absent. The rate-determining step for both the porous, cold-pressed, and pore-free, hot-pressed materials is the bulk diffusion of lead across a thickening lead-depleted layer at the surface of the pellet and results in a parabolic time dependence. Although parabolic rate constants are slightly lower overall for the dense materials, the activation energies for the weight loss process remain approximately 38.5 and 35 kcal/mole for the pure and Bi-doped Pb(Zr0.65Ti0.35)O3 compositions, respectively. Vaporization mechanisms and rates were unchanged under nitrogen or oxygen pressures up to 50 torr at 1000°C. Alumina Knudsen cells were used to study the equilibrium vapor above a powdered, hot-pressed Pb(Zr0.65.Ti0.35)O3 composition. Mass spectrometric analysis of the vapor at 950°C showed that the vapor species and their relative abundances were the same as the equilibrium vapor species above pure lead monoxide. Continuous weight loss data from these cells gave an apparent vapor pressure that was 2% of the vapor pressure of pure lead monoxide at a given temperature, but gave the same second law enthalpy of vaporization. The overall vaporization process can be represented by the reversible equilibria: the diffusion of Pb2+ and O2- to the surface through a lead-depleted region whose phases and compositions are determined by the subsolidus phase relations in the PbO-ZrO2-TiO2 ternary system, the reaction at or near the surface to form PbO, and the subsequent vaporization of PbO.

The Plate Impact Configuration for Determining Mechanical Properties of Materials at High Strain Rates

Abstract: A review of the latest free surface motion and stress measuring instrumentation is presented along with a description of the plate impact one-dimensional strain configuration for determining mechanical properties under stress wave propagation conditions. A discussion is included of results of some other investigators who have used this configuration to determine dynamic yield stress and the degree of strain rate sensitivity.