Showing papers by "Sandia National Laboratories published in 1969"
TL;DR: In this paper, a thermodynamische Theorie of nichteinfachen, elastischen Stoffen wird gezeigt, dass Substanzen vom Grade hoher als eins vorkommen konnen; vorausgesetzt, man das eventuelle Vorhandensein zweier verschiedener Temperaturen in Betracht zieht.
Abstract: Diese Arbeit behandelt eine thermodynamische Theorie von nichteinfachen, elastischen Stoffen Es wird gezeigt, dass Substanzen vom Grade hoher als eins vorkommen konnen; vorausgesetzt, dass man das eventuelle Vorhandensein zweier verschiedener Temperaturen in Betracht zieht
349 citations
TL;DR: In this article, a straight line approximation of the one-electron Schrodinger equation was made, leading to an exactly solvable one-Electron Schroda equation for the elements Be-Ar.
Abstract: The quantity $\ensuremath{-}rV(r)$ for ions, formed by removing a $1s$ electron from the neutral atom, is computed by the approach of Herman and Skillman. A straight-line approximation of $\ensuremath{-}rV(r)$ is made, leading to an exactly solvable one-electron Schr\"odinger equation. The discrete and continuum orbitals are used to compute Auger $\mathrm{KLL}$ and $\mathrm{KLM}$ transition rates, radiative rates, and fluorescence yields for the elements Be-Ar. Comparison with experimental $K$-shell fluorescence yields indicates the calculations are 25% too high for Mg and Al and within 5% for Ar. Comparison of the individual Auger transition intensities for F, Ne, Na, and Mg indicates differences of 50%. This 50% difference between calculated and measured individual Auger transition intensities persists up to Ar, where the sum of the individual intensities is in better than 7% agreement with that derived from the fluorescence yield and $K$-state width.
221 citations
01 May 1969
TL;DR: In this article, the effect of light scattering properties on the orientation of the ceramic polar axis (electrical poling direction) has been investigated and shown to be independent of the magnitude of electrical poling (ferroelectric remanence state).
Abstract: Thin polished plates of hot-pressed rhombohedral lead zirconate-lead titanate ceramics possess one of two types of electro-optic properties depending on the nominal grain diameter. In poled coarse-grained ceramics the electrooptic effect of importance for devices is the dependence of the light scattering properties on the orientation of the ceramic polar axis (electrical poling direction). The light scattering properties are essentially independent of the magnitude of electrical poling (ferroelectric remanence state). Poled fine-grained ceramics are birefringent, and their light transmission characteristics are similar to those of optically uniaxial crystals. These materials exhibit orthotropic symmetry with respect to the optic axis, which coincides with the ceramic polar axis. The fine-grained ceramic electrooptic effect of primary importance for devices is the dependence of the effective birefringence on the magnitude of electrical poling as well as on the intensity of the applied biasing electric field. Retardation of a ceramic plate can be varied incrementally by partial switching or continuously by application of a nonswitching bias field. Both coarse- and fine-grained ceramics have the property that localized areas as small as 25 µ by 25 µ can be poled or switched independently without affecting the light transmission characteristics of the surrounding area. The locally switched areas are stable with time, but they can be "erased" by switching them back to their original orientation. Each locally switched area can function as a light shutter, valve, or spectral filter depending on the ceramic material, the switching mode, and the characteristics of the incident light.
117 citations
TL;DR: In this paper, a finite-difference method and a nonlinear overrelaxation method are investigated for solving the viscous shock layer at the stagnation point of a blunt body.
Abstract: A finite-difference method and a nonlinear overrelaxation method are investigated for solving the viscous shock layer at the stagnation point of a blunt body. An air gas model is employed with finite reaction rates and accurate thermodynamic and transport properties. For a body with a 1-in. nose radius and at a velocity of 20 kfps, the present results at 100, 150, 200, and 250 kft show that boundary-layer theory with the inviscid edge flow in chemical equilibrium is appropriate for some altitude below 150 kft. When the altitude is 250 kft, the effects of shock slip must be included in the viscous shock-layer solution. For this case, the air is only slightly dissociated and ionized. The present results, with a seven-species air model, are in general agreement with the diatomic air model results of Cheng and Chung.
105 citations
TL;DR: In this article, it was shown that detailed information about rare-earth properties can be derived from an analysis of the NMR data, showing that the relationship between the Knight shift and the rare earth paramagnetic susceptibility is shown.
Abstract: The temperature dependences, signs, and magnitudes of the phosphorus, arsenic, antimony, and bismuth nuclear-magnetic-resonance (NMR) Knight shifts in the NaCl-type rare-earth group-$\mathrm{V}A$ intermetallic compounds have been studied in detail for the temperature range of 1.5-600\ifmmode^\circ\else\textdegree\fi{}K. The Knight shifts in the nonmagnetic compounds, such as LaP, were found to be temperature-independent. For most of the magnetic compounds, such as GdP, the temperature-dependent part of the Knight shift was found to obey a Curie-Weiss law. However, for the praseodymium, samarium, and thulium compounds, the effect of the sixfold cubic crystal-field interaction on the rare-earth ion could not be neglected. An analysis, showing the relationship between the Knight shift and the rare-earth $4f$ paramagnetic susceptibility ${\ensuremath{\chi}}_{f}(T)$, is presented. In this manner, it is shown that detailed information about ${\ensuremath{\chi}}_{f}(T)$ can be derived from an analysis of the NMR data. Furthermore, it is shown that the hyperfine field at the nonmagnetic site in these compounds arises from the spin component S of the total angular momentum J of the rare-earth ion, and not from the magnetization at the rare-earth site. The $s\ensuremath{-}f$ exchange energies $\ensuremath{\Gamma}$ for these compounds were calculated using the uniform conduction-electron spin-polarization model for the Knight shift. For the rare-earth Group-$\mathrm{V}A$ intermetallic compounds, $\ensuremath{\Gamma}$ was found to be negative (antiferromagnetic) and relatively constant (\ensuremath{\simeq} -0.3 eV) for all of these compounds. Comparisons are made for the $s\ensuremath{-}f$ exchange energies for all of the various rare-earth intermetallic compounds for which NMR measurements are available. It is again found that $\ensuremath{\Gamma}$ is negative and relatively constant in magnitude. For all of these compounds, the total hyperfine field per unit spin $S$ is found to be of the order of -50 kOe. No explanation for this phenomenon is advanced. It is shown that a consistent analysis of the Knight-shift data in terms of the Ruderman-Kittel-Kasuya-Yosida theory is probably impossible. The NMR linewidths $\ensuremath{\delta}H$ in the nonmagnetic compounds were found to be in agreement with the calculated dipolar contribution, while for the magnetic compounds, the NMR linewidth $\ensuremath{\delta}H$ was found to be due to the presence of demagnetization fields arising from the nonspherical shape of the particles in the powdered samples.
85 citations
TL;DR: In this article, a specialized form of Reissner's variational principle is developed which is suitable for anisotropic incompressible and nearly-incompressible thermoelasticity.
84 citations
TL;DR: In this paper, the authors measured the resistivity, temperature, and injection level dependences of the minority carrier lifetime in neutron irradiated p- and n-type silicon, and compared the predictions of two alternate models for recombination at defect clusters.
Abstract: Measurements are reported which provide extensive data on the resistivity, temperature, and injection level dependences of the minority carrier lifetime in neutron irradiated p- and n-type silicon. The lifetime damage constants are observed to be quite dependent on the injected minority carrier density, in both conductivity types, over the temperature range from 76°K to 300°K. The low injection level damage constants have been measured and found to be dependent on material resistivity in p-type silicon, but only slightly dependent on resistivity in n-type silicon. The results of the experimental studies are compared to the predictions of two alternate models for recombination at defect clusters. For defect clusters of approximately 250 A radius, as expected from range calculations, these comparisons indicate that each contains a relatively small number of deep defects (30 - 40). The defects are individually characterized by a deep donor level near Ev + 0.35 eV and a deep acceptor level near Ec - 0.50 eV. Since these levels correspond approximately to the known energy levels of the silicon divacancy, it is suggested that the divacancy may be the active recombination center within the defect clusters.
77 citations
TL;DR: In this paper, an empirical equation is developed for the prediction of total penetration distance of a projectile in many natural earth targets, based on approximately 160 full-scale penetration tests into a variety of targets, including rock, gypsite, permafrost, ice, desert alluvium, silt, sand and saturated clay.
Abstract: An empirical equation is developed for the prediction of total penetration distance of a projectile in many natural earth targets. Development of this equation was based on approximately 160 full-scale penetration tests into a variety of targets, including rock, gypsite, permafrost, ice, desert alluvium, silt, sand and saturated clay. The parameters considered in the development (other than target materials) were (1) projectile weights from 222 to 5,750 lb, (2) projectile diameters from 3.1 to 18 in., (3) impact velocities from 78 to 1,077 fps, and (4) 11 projectile nose shapes. The equation fits 91% of the data within 20% and fits 98.5% of the data within 25%. The necessary tables of nose-performance coefficients and soil constants are presented for practical engineering usage.
72 citations
69 citations
TL;DR: Twenty-nine integer linear programming problems, raging from very simple to apparently rather difficult, are introduced and the results of running these problems on four different computer codes, involving five distinct algorithms are presented.
Abstract: In this report, twenty-nine integer linear programming problems, raging from very simple to apparently rather difficult, are introduced. The results of running these problems on four different computer codes, involving five distinct algorithms, are presented as both time and iteration data. A brief description of the codes used is also included.
66 citations
TL;DR: In this article, the dynamic yield behavior of Ferrovac E iron was studied over a temperature range of 76-573°K and it was concluded that the motion of twinning dislocations is the mechanism of dynamic yielding of iron.
TL;DR: In this paper, the authors show that the limited coherence of the primary electrons necessitates the use of statistical methods in characterizing LEED beam profiles, which can be used to characterize the adsorption sites and the nature and distribution of mistakes in the periodicity of surface structures.
TL;DR: The ferroelectric field effect has been observed in a semiconducting thin film of n-type tin oxide deposited on a lead zirconate-titanate ceramic substrate as mentioned in this paper.
Abstract: The ferroelectric field effect has been observed in a semiconducting thin film of n-type tin oxide deposited on a ferroelectric lead zirconate-titanate ceramic substrate. The semiconductor was deposited by electron gun evaporation onto a thermally depolarized (randomly oriented) substrate which permitted the carrier concentration of the film to be enhanced or depleted depending on the direction of polarization of the substrate. Typical average resistivity values of 200-A films are approximately 0.1 Ω.cm for the depoled state, 0.01 Ω.cm for the enhanced state, and 100-1000 Ω.cm for the depleted state. "On"-"off" ratios as high as 1.7 \times 10^{5} have been observed in a single device. The transition from enhancement to depletion is quasi-continuous due to the small size and random orientation of the individual crystallites in the ceramic. Conductance measurements during this transition have yielded field effect mobilities in the range 7-10 cm2/V.s; and maximum average carrier densities in the range 0.5-1.0 × 1020carriers/cm 3 . The tin oxide-ceramic devices described here suffer from the long-term drift that is characteristic of many field effect devices. The resistivity of a device stored in the depleted state will decrease from 3 to 4 orders of magnitude in times between 104-105minutes.
TL;DR: In this paper, it was shown that diffusion of singlet excitons cannot explain the time dependence of the fluorescence intensity in tetracene-doped anthracene crystals; however, the predictions of a long-range energy transfer mechanism can be made to agree with experimental results.
Abstract: It is shown that diffusion of singlet excitons cannot explain the time dependence of the fluorescence intensity in tetracene-doped anthracene crystals; however, the predictions of a long-range energy-transfer mechanism can be made to agree with experimental results.
TL;DR: In contrast to the strong temperature dependence of the $71}\mathrm{Ga}$ Knight shift, only a weak temperature dependence was observed in the Au${Al, Ga, and In} Knight shift.
Abstract: Measurements of the $^{197}\mathrm{Au}$ Knight shift in Au${\mathrm{Al}}_{2}$, Au${\mathrm{Ga}}_{2}$, and Au${\mathrm{In}}_{2}$ are reported. In contrast to the strong temperature dependence of the $^{71}\mathrm{Ga}$ Knight shift, only a weak temperature dependence of the $^{197}\mathrm{Au}$ Knight shift in Au${\mathrm{Ga}}_{2}$ is observed. Electronic energy-band calculations for these compounds yield differences which provide an improved model for interpreting these and other experimental results.
TL;DR: In this paper, it was shown that vanadium spin susceptibility can be described by a virtual bound model in which the impurity susceptibility, resonance shift, and nuclear-spin relaxation rates are enhanced by local Coulomb interactions.
Abstract: The low-temperature (1-4\ifmmode^\circ\else\textdegree\fi{}K) magnetic properties of dilute (0.1-10 at.%) $\mathrm{Au}\mathrm{V}$ alloys have been studied by means of pulsed-NMR techniques. The previously reported $^{51}\mathrm{V}$ line-shape anomaly for vanadium concentrations near 1 at.% is shown to result from a large reduction in the vanadium spin susceptibility for vanadium impurities that are nearest neighbors to each other. The observed change in the $^{51}\mathrm{V}$ resonance shift from a negative value (-1.5%) at low vanadium concentrations to a positive value (+0.6%) at high concentrations is consistent with the expected variation in the ratio of "nonmagnetic" to "magnetic" vanadium concentrations. The nuclear resonances are severely broadened as a result of oscillatory spindensity disturbances associated with $d$-resonance scattering of the host conduction electrons. There is no indication, however, that the field-induced impurity magnetization gives rise to significant long-range negative-definite spin polarizations in the host metal as suggested recently. This conclusion is supported by the absence of positive $^{109}\mathrm{Ag}$ resonance shifts in ternary $Au(\mathrm{Ag})\mathrm{V}$ alloys containing up to 20 at.% silver. In general, our measurements suggest that "magnetic" as well as "nonmagnetic" vanadium sites can be described by a virtual bound $d$-state model in which the impurity susceptibility, resonance shift, and nuclear-spin relaxation rates are enhanced by local Coulomb interactions. The two types of vanadium sites are distinguished by different enhancement factors, or, equivalently, different spin-fluctuation frequencies. The $^{51}\mathrm{V}$ spin-lattice relaxation rates ${{T}_{1}}^{\ensuremath{-}1}$ are directly proportional to the absolute temperature over the entire composition range. In the infinite-dilution limit ${T}_{1}T\ensuremath{\approx}17$ msec\ifmmode^\circ\else\textdegree\fi{}K, while at high concentrations ${T}_{1}T$ approaches the metallic vanadium value. An analysis of the infinite-dilution $^{51}\mathrm{V}$ shift and relaxation-rate data indicates that the impurity-site spin susceptibility accounts for most of the measured bulk susceptibility.
TL;DR: In this paper, a large-defection response is monitored using a high-speed streak camera, and dynamic-strain measurements are obtained with the elastic-plastic structural computer program DEPROSS.
Abstract: Clamped circular plates are impulsively loaded with sheet explosive, and the resulting large-defection response is monitored using a high-speed streak camera, and dynamic-strain measurements. Dynamic and final-plate deflections as well as strain-time histories of various locations on the plates are compared to deflections and strains obtained with the elastic-plastic structural computer program DEPROSS. It is shown that DEPROSS adequately computes the dynamic response of this highly nonlinear biaxial-stress problem.
TL;DR: The Sandia Laboratories Hermes II has produced a 170 kA beam of electrons at energies of 12 million volts for times of 100 ns as mentioned in this paper, which is the state-of-the-art performance.
Abstract: Pulsed power technology has grown rapidly during the last decade. Particular credit is due to research efforts at United Kingdom Atomic Weapons Research Establishment (AWRE). The largest machine presently in operation is the Sandia Laboratories Hermes II which has produced a 170 kA beam of electrons at energies of 12 million volts for times of 100 ns. This paper reviews the design and performance of the Hermes II and includes data from Hermes I, a prototype.
TL;DR: In this article, it was shown that instantaneous values of positions and velocities do not determine the solution uniquely for the two-body electrodynamics problem in the case of one-dimensional motion.
Abstract: The two-body problem of classical electrodynamics can be formulated in terms of action at a distance by using the retarded Li\'enard-Wiechert potentials (or a combination of retarded and advanced potentials). The resulting equations of motion in the retarded case, for example, form a complicated functional delay-differential system. For such equations in the case of one-dimensional motion, as shown in an earlier paper, one can specify rather arbitrary past histories of the particles, and then solve for the future trajectories. Yet it is often assumed or asserted that unique trajectories would be determined by the specification of Newtonian initial data (the positions and velocities of the particles at some instant). Simple examples of delay-differential equations should lead one to doubt this. For example, even if the values of $x$ and all its derivatives are given at ${t}_{0}$, the equation ${x}^{\ensuremath{'}}(t)=ax(t)+bx(t\ensuremath{-}\ensuremath{\tau})$, with $\ensuremath{\tau}g0$ and $b\ensuremath{
e}0$, still has infinitely many solutions valid for all $t$. Nevertheless, under certain special conditions for the electrodynamic equations it is found that instantaneous values of positions and velocities do indeed determine the solution uniquely. The case treated in this paper involves two charges of like sign moving on the $x$ axis, assumed to have been subject only to their mutual retarded electrodynamic interaction for all time in the past. The similar questions of existence and uniqueness for a more general model, e.g., three-dimensional motion or half-retarded and half-advanced interactions, or even for charges with opposite signs remain open.
TL;DR: A review of the recent results obtained in the study of binary transition metal hydrides can be found in this article, where the distinct and unusual properties of these hydride, their preparation and their kinetic, thermodynamic, and structural properties are discussed.
Abstract: The purpose of this report is to review some of the recent results obtained in the study of binary transition metal hydrides. In addition to published work, previously unpublished data from the Sandia Laboratories is included. Subjects covered are the distinct and unusual properties of these hydrides, their preparation, and their kinetic, thermodynamic, and structural properties.
TL;DR: In this article, the details of the martensite reaction have been investigated by thin foil electron microscopy techniques in high purity Ti-Cr binary alloys containing 2.4-5.9 at.
TL;DR: In this paper, the joint continuuity of monotonic functions is studied and the authors propose a joint continuity model for monotone functions, which they call Joint Continuity of Monotonic Functions (JCLF).
Abstract: (1969). Joint Continuity of Monotonic Functions. The American Mathematical Monthly: Vol. 76, No. 1, pp. 74-76.
TL;DR: A very simple numerical procedure is developed which is easily programmed and which uses reliable subroutines and is capable of handling a large class of problems.
Abstract: A new technique based upon an invariant imbedding-Ricatti transformation approach is presented for the calculation of eigenvalues ofSturm-Liouville type systems of differential equations.
A very simple numerical procedure is developed which is easily programmed and which uses reliable subroutines. The method is capable of handling a large class of problems. Included among these are problems in which the eigenvalues appears in a non-linear fashion, cases in which the eigenvalue occurs in the boundary condition, and equations which have singularities.
The numerical computations are generally well-conditioned and very accurate results were obtained.
Es wird eine neue Technik, basierend auf einer Methode, welche invariante Einbettung (Invariant Imbedding) mit derRicatti-Transformation kombiniert, dargestellt zum Zwecke der Berechnung der Eigenwerte von Differentialgleichungssystemen, welche vomSturm-Liouville-Typ sind.
Eine sehr einfache numerische Prozedur ist entwickelt worden, die leicht zu programmieren ist und verlaβliche Unterprogramme benutzt. Dieses Verfahren vermag eine umfangreiche Klasse von Problemen zu handhaben. Unter ihnen sind solche inbegriffen, bei denen der Eigenwert in einer nichtlinearen Form auftritt; auch Falle, wo der Eigenwert in der Randbedingung vorkommt; und schlieβlich auch Gleichungen, die Singularitaten aufweisen.
Es sei betont, daβ die hier von uns behandelten numerischen Berechnungen im allgemeinen stabil sind und sehr genaue Ergebnisse hervorzubringen vermogen.
TL;DR: Ferroelectric lead zirconate-titanate ceramics appear promising for use as electrically controlled retarders because both conventional electrooptic and nonvolatile incremental retardation changes can be induced in areas as small as 25 µ on a side as mentioned in this paper.
Abstract: Ferroelectric lead zirconate-titanate ceramics appear promising for use as electrically controlled retarders because both conventional electrooptic and nonvolatile incremental retardation changes can be induced in areas as small as 25 µ on a side. One particular composition, Pb 0.97 La 0.02 Zr 0.65 Ti 0.35 O 3 , has so far proved superior to all other rhombohedral lead zirconate-titanates when judged by either the conventional electrooptic retardation variation with applied bias voltage, or the nonvolatile incremental retardation change with remanent polarization state of the ceramic. Furthermore, this same lanthanum-doped composition exhibits a marked decrease in undesirable light scattering when compared with extensive data on the same composition with bismuth doping. Scattering also decreases with increasing wavelength λ, and the ceramic transmittance is greater than 85 percent for 3 µ<λ<8 µ with sample thickness less than 50 µ. This increased transmittance now makes feasible the construction of multistage ceramic electrooptic systems.
TL;DR: Variation of the angle of incidence (AoI) offers a simple experimental method of increasing the number of unknown optical parameters that can be determined from ellipsometric measurements on a complex reflecting structure as discussed by the authors.
TL;DR: In this paper, the phonon frequencies were calculated for aluminum from a theory based on Coulomb interactions among the ions, Born-Mayer repulsion between nearest-neighbor ion cores, and a local pseudopotential interaction between ions and conduction electrons.
Abstract: The phonon frequencies were calculated for aluminum from a theory based on Coulomb interactions among the ions, Born-Mayer repulsion between nearest-neighbor ion cores, and a local pseudopotential interaction between ions and conduction electrons. For both a Harrison modified point-ion potential and a local Heine-Abarenkov potential, the parameters of the theory were determined to give the best over-all fit to the measured phonon dispersion curves. For the two pseudopotentials so determined, the Born-Mayer repulsion was found to be negligible, the screened form factors ${w}_{q}$ are the same for $0\ensuremath{\le}q\ensuremath{\le}1.8{k}_{F}$ and are in good agreement with Fermi-surface data, and the calculated phonon frequencies are the same. The calculated frequencies depend sensitively on $|{w}_{q}|$ for $0\ensuremath{\le}q\ensuremath{\le}2{k}_{F}$, and also depend strongly on some average of $|{w}_{q}|$ for larger $q$.
TL;DR: The observation of neutrons produced by irradiation of polycrystalline LiD targets with a high-power laser was reported in this paper, where single pulses from a mode-locked ε-nd−nd+3$-doped glass laser were amplified up to energies of 25 J. Pulse widths were 2-3 psec.
Abstract: The observation of neutrons produced by irradiation of polycrystalline LiD targets with a high-power laser is reported. Single pulses from a mode-locked ${\mathrm{Nd}}^{+3}$-doped glass laser were amplified up to energies of 25 J. Pulse widths were 2-3 psec as measured by the two-photon fluorescence technique. The analyses of these experiments yield a somewhat higher rate of neutron production than the similar experiments recently reported by Basov et al..
TL;DR: The lasing transition in boat-grown cadmium-doped GaAs is similar to that previously found in GaAs: Zn. as discussed by the authors showed that the three excited states of this transition lie at energies of 1.484, 1.486, and 1.507 eV, respectively.
Abstract: The lasing transition in boat-grown cadmium-doped GaAs is similar to that previously found in GaAs:Zn. In cadmium-doped GaAs, the three excited states of this transition (${C}^{\ensuremath{'}}$, ${B}^{\ensuremath{'}}$, and ${A}^{\ensuremath{'}}$) lie at energies of 1.484, 1.486, and 1.507 eV, respectively. In addition, there is a broad-band emission peak centered at 1.37 eV. All of these peaks move to lower energies with decreasing excitation intensity. 1.5-MeV electron irradiation causes exponential decreases in the broad-band and near-band-edge intensities with increasing electron fluence for fluences greater than ${10}^{16}$ $\frac{e}{{\mathrm{cm}}^{2}}$. Isochronal annealing of the irradiated material in the temperature range 50-190\ifmmode^\circ\else\textdegree\fi{}C causes increases in the emission centered about 1.37 eV, but the emission is modified and appears as two peaks (Cd 0, and Cd 1) at 1.369 and 1.337 eV. The temperature dependence of the intensity of the peaks indicate that Cd 1 is a phonon replica of Cd 0. The development of the structure is interpreted as occurring when Ga vacancies migrate and form localized modes that weaken the coupling of the Cd 0 defect to the lattice. Diminution of intensity and loss of structure are observed in the temperature range 190-240\ifmmode^\circ\else\textdegree\fi{}C and result from a decrease in the number of centers giving rise to localized modes. The killer center which degrades the luminesence is believed to be the As vacancy which anneals out at about 240\ifmmode^\circ\else\textdegree\fi{}C. The energy shift of the lasing transition and of the broad-band emission are interpreted to indicate that both bands are the emission envelopes of unresolved donor-acceptor pair transitions. The lasing transition arises from the recombination of holes localized at neutral Cd acceptors, with electrons localized at donors, possibly Si; whereas the broad-band emission is due to pair annihilation involving the same donor and Cd in a different charge state.
TL;DR: In this article, the dynamic stability behavior of thin circular cylindrical shells subjected to a supersonic flow field is investigated theoretically and compared with existing experimental data, combined effects of axisymmetric initial geometric imperfections, radial edge constraint, and prestability deformations are considered.
Abstract: : Recent wind tunnel results indicate that the existing cylindrical shell aeroelastic stability theories are generally nonconservative. Therefore, some type of destabilizing mechanism is needed in the present theory to enhance correlation with experiment. In the paper, the dynamic stability behavior of thin circular cylindrical shells subjected to a supersonic flow field is investigated theoretically and compared with existing experimental data. Combined effects of axisymmetric initial geometric imperfections, radial edge constraint, and prestability deformations are considered. The cylinder's motion is described with nonlinear Donnell type shell equations coupled with a linear 'piston theory' aerodynamic approximation. A modal type approach employing Galerkin's approximate technique is used to investigate the dynamic stability about the shell's deformed middle surface. Prestability deformations alone have been shown to have very little influence on the aeroelastic stability behavior of very thin shells. However, with the inclusion of initial imperfections, the combined effect is destabilizing. The resulting aeroelastic stability boundaries correlate quite well with existing experimental data. (Author)