SEARCH · Engineering Papers

Results for “excited state methods”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 181 records · Page 10

All sources NASA NTRS DOE OSTI

NASA NTRS1999

Energy Levels of C IV: The Polarization Method

In a previous publication [Can. J. Phys. 75, 11 (1997)] we calculated the generalized polarizabilities up to multipole order 3 as well as certain higher-order hyperpolarizabilities for two-electron atoms and ions of Z=2-6 and 10. In this paper we apply some of these results to calculate excited-state energies in three times ionized (lithium-like) carbon. For states with angular momentum L greater than or equal to 3 accurate results are obtained using an asymptotic polarizability expansion that includes nonadiabatic effects. Comparison is made with recent optical measurements, and a critical discussion of the correct form of the expansion is given. In addition, the possibility of very accurate measurements of the fine-structure splitting encourages us to present a table of such splittings to very high accuracy. An appendix contains similar results for lithium-like oxygen and neon ions.

Bhatia, A. K.↗

NASA NTRS1983

The low-lying 2-sigma-minus states of OH

The configuration-interaction method is used to determine the electronic wave functions of the two lowest 2-sigma-minus states of OH using four different atomic orbital basis sets. Potential energy curves, transition moments, oscillator strengths, and photodissociation cross sections are obtained. Electronic transition dipole moments connecting the excited 1 2-sigma-minus and 2(D)2-sigma-minus states with each other and with the ground chi-2-pi state are presented as functions of internuclear distance. The theoretical absorption oscillator strengths for the D-2-sigma-minus(v prime = 0) from chi-2-pi(v double prime = 0) transition are in good agreement with the empirical value derived from astronomical measurement. The photodissociation cross sections for absorption from the v prime = 0, 1, and 2 levels of the ground state into the continuum of the 1 2-sigma-minus state are calculated, and the interstellar and cometary photodissociation rates are derived.

Van Dishoeck, E. F.↗

NASA NTRS1989

Vibration signature analysis of multistage gear transmission

An analysis is presented for multistage multimesh gear transmission systems. The analysis predicts the overall system dynamics and the transmissibility to the gear box or the enclosed structure. The modal synthesis approach of the analysis treats the uncoupled lateral/torsional model characteristics of each stage or component independently. The vibration signature analysis evaluates the global dynamics coupling in the system. The method synthesizes the interaction of each modal component or stage with the nonlinear gear mesh dynamics and the modal support geometry characteristics. The analysis simulates transient and steady state vibration events to determine the resulting torque variations, speeds, changes, rotor imbalances, and support gear box motion excitations. A vibration signature analysis examines the overall dynamic characteristics of the system, and the individual model component responses. The gear box vibration analysis also examines the spectral characteristics of the support system.

Choy, F. K.↗

NASA NTRS1989

Vibration signature analysis of multistage gear transmission

Choy, F. K.↗

NASA NTRS1993

Theoretical Study of the Electronic Spectra of a Polycyclic Aromatic Hydrocarbon, Naphthalene, and its Derivatives

In order to preselect possible candidates for the origin of diffuse interstellar bands observed, semiempirical quantum mechanical method INDO/S was applied to the optical spectra of neutral, cationic, and anionic states of naphthalene and its hydrogen abstraction and addition derivatives. Comparison with experiment shows that the spectra of naphthalene and its ions were reliably predicted. The configuration interaction calculations with single-electron excitations provided reasonable excited state wavefunctions compared to ab initio calculations that included higher excitations. The degree of similarity of the predicted spectra of the hydrogen abstraction and derivatives to those of naphthalene and ions depends largely on the similarity of the it electron configurations. For the hydrogen addition derivatives, very little resemblance of the predicted spectra to naphthalene was found because of the disruption of the aromatic conjugation system. The relevance of these calculations to astrophysical issues is discussed within the context of these polycyclic aromatic hydrocarbon models. Comparing the calculated electronic energies to the Diffuse Interstellar Bands (DIBs), a list of possible candidates of naphthalene derivatives is established which provides selected candidates for a definitive test through laboratory studies.

Du, Ping↗

NASA NTRS1995

Model checking

Automatic formal verification methods for finite-state systems, also known as model-checking, successfully reduce labor costs since they are mostly automatic. Model checkers explicitly or implicitly enumerate the reachable state space of a system, whose behavior is described implicitly, perhaps by a program or a collection of finite automata. Simple properties, such as mutual exclusion or absence of deadlock, can be checked by inspecting individual states. More complex properties, such as lack of starvation, require search for cycles in the state graph with particular properties. Specifications to be checked may consist of built-in properties, such as deadlock or 'unspecified receptions' of messages, another program or implicit description, to be compared with a simulation, bisimulation, or language inclusion relation, or an assertion in one of several temporal logics. Finite-state verification tools are beginning to have a significant impact in commercial designs. There are many success stories of verification tools finding bugs in protocols or hardware controllers. In some cases, these tools have been incorporated into design methodology. Research in finite-state verification has been advancing rapidly, and is showing no signs of slowing down. Recent results include probabilistic algorithms for verification, exploitation of symmetry and independent events, and the use symbolic representations for Boolean functions and systems of linear inequalities. One of the most exciting areas for further research is the combination of model-checking with theorem-proving methods.

Dill, David L.↗

NASA NTRS1988

Evaluation of materials for tunable vibronic lasers

Three techniques (peak single-pass gain, fluoresence band narrowing, and lifetime shortening) for determining the effects of stimulated emission on the spectra of solid-state vibronic laser materials have been compared. The methods were employed to determine the pump energy density and population inversion at threshold, the stimulated emission cross section, and the gain coefficient for two potential vibronic laser materials. An effective shortening of the fluorescence lifetime is predicted at high excitation levels, with a distinct threshold where stimulated emission processes become important.

Kliewer, Michael L.↗

NASA NTRS1966

Radiative corrections to the energies of atoms and molecules.

Approximation method using sum rules for energy shift in atomic system due to interaction of electrons with vacuum electromagnetic field applied to hydrogen, helium and lithium atom ground states and hydrogen molecule

HYDROGEN ATOM↗

NASA NTRS1974

Ion-molecule reactions and vibrational deactivation of H2/+/ ions in mixtures of hydrogen and helium

Use of ion cyclotron resonance methods to measure the thermal energy rate constants for a number of ion-molecule reactions involving hydrogen and hydrogen-helium mixtures. Assuming that the distribution of initial vibrational states in the H2(+) ion is a near-Franck-Condon distribution, the occurrence of collisional deactivation of vibrationally excited H2(+) ions by He atoms is identified, and an approximate rate constant for the deactivation process and its dependence on vibrational energy are given.

Theard, L. P.↗

NASA NTRS1984

Radiative lifetimes of the second negative system of O2(+)

The dipole moment of the A2Pi(u)-X2Pi(g) transition of O2(+) is calculated as a function of internuclear distance using ab initio methods. The band absorption oscillator strengths and band transition probabilities of the second negative system are derived and the resulting lifetimes are compared with experimental data. The high-lying v double prime levels of the ground state may decay into low-lying v prime levels of the excited state. The corresponding radiative lifetimes are calculated.

Wetmore, R. W.↗

NASA NTRS1998

Optical model methods of predicting nuclide production from spallation reactions

Quantum mechanical optical model methods for calculating isotope production cross sections from the spallation of heavy nuclei by high-energy protons are developed from a modified abrasion-ablation collision formalism. The abrasion step is treated quantum-mechanically as a knockout process which leaves the residual prefragment nucleus in an excited state. In ablation the prefragment deexcites to produce the final fragment. The excitation energies of the prefragments are estimated from a combination of liquid drop and frictional-spectator interaction considerations. Estimates of elemental and isotopic production cross sections are in good agreement with recently published cross section measurements.

NASA Discipline Radiation Health↗

NASA NTRS2016

Extracting Damping Ratio from Dynamic Data and Numerical Solutions

There are many ways to extract damping parameters from data or models. This Technical Memorandum provides a quick reference for some of the more common approaches used in dynamics analysis. Described are six methods of extracting damping from data: the half-power method, logarithmic decrement (decay rate) method, an autocorrelation/power spectral density fitting method, a frequency response fitting method, a random decrement fitting method, and a newly developed half-quadratic gain method. Additionally, state-space models and finite element method modeling tools, such as COMSOL Multiphysics (COMSOL), provide a theoretical damping via complex frequency. Each method has its advantages which are briefly noted. There are also likely many other advanced techniques in extracting damping within the operational modal analysis discipline, where an input excitation is unknown; however, these approaches discussed here are objective, direct, and can be implemented in a consistent manner.

Casiano, M. J.↗

NASA NTRS1997

Numerical Modeling of Tidal Effects in Polytropic Accretion Disks

A two-dimensional time-dependent hybrid Fourier-Chebyshev method of collocation is developed and used for the study of tidal effects in accretion disks, under the assumptions of a polytropic equation of state and a standard alpha viscosity prescription. Under the influence of the m = 1 azimuthal component of the tidal potential, viscous oscillations in the outer disk excite an m = 1 eccentric instability in the disk. While the m = 2 azimuthal component of the tidal potential excites a Papaloizou-Pringle instability in the inner disk (a saturated m = 2 azimuthal mode), with an elliptic pattern rotating at about a fraction (approx. = 1/3) of the local Keplerian velocity in the inner disk. The period of the elliptic mode corresponds well to the periods of the short-period oscillations observed in cataclysmic variables. In cold disks (r(Omega)/c(sub s) = M approx. = 40) we also find a critical value of the viscosity parameter (alpha approx. = 0.01), below which shock dissipation dominates and is balanced by the wave amplification due to the wave action conservation. In this case the double spiral shock propagates all the way to the inner boundary with a Mach number M(sub s) approx. = 1.3.

Godon, Patrick↗

NASA NTRS2007

System and Method for Detecting Cracks and their Location

A system and method are provided for detecting cracks and their location in a structure. A circuit coupled to a structure has capacitive strain sensors coupled sequentially and in parallel to one another. When excited by a variable magnetic field, the circuit has a resonant frequency that is different for unstrained and strained states. In terms of strained states, the resonant frequency is indicative of a region of the circuit that is experiencing strain induced by strain in a region of the structure in proximity to the region of the circuit. An inductor is electrically coupled to one end of each circuit. A magnetic field response recorder wirelessly transmits the variable magnetic field to the inductor and senses the resonant frequency of the circuit so-excited by the variable magnetic field.

Woodward, Stanley E.↗

NASA NTRS1975

Theory of photoelectron thermalization and transport in the ionosphere

A new theoretical approach for calculating the equilibrium photoelectron flux energy and pitch angle distribution in the ionosphere is presented. Photoelectron transport, secondary electron production, and energy degradation by the excitation of the discrete energy states of the neutral atmospheric constituents and by continuous energy transfer to the ambient thermal electron gas are included in a manner consistent with the Boltzmann equation which constitutes the foundation of the theory. A difference equation, suitable for numerical solution, is given, and a numerical method for the solution of this equation is discussed in detail.

Mantas, G. P.↗

NASA NTRS1975

Electron impact excitation of zinc vapor at 40 eV

The first set of normalized differential and integral cross sections for elastic scattering and excitation involving the four lowest states of zinc is presented, taking into account tests in which the impact energy was 40 eV. In the tests an electron beam was scattered by a zinc target beam. The zinc beam was produced by heating a tantalum crucible containing zinc. An electron-bombardment method was used in heating the crucible.

Williams, W.↗

NASA NTRS1991

Absolute cascade-free cross-sections for the 2S to 2P transition in Zn(+) using electron-energy-loss and merged-beams methods

Absolute cascade-free excitation cross-sections in an ion have been measured for the resonance 2S to 2P transition in Zn(+) using electron-energy-loss and merged electron-ion beams methods. Measurements were carried out at electron energies of below threshold to 6 times threshold. Comparisons are made with 2-, 5-, and 15-state close-coupling and distorted-wave theories. There is good agreement between experiment and the 15-state close-coupling cross-sections over the energy range of the calculations.

Smith, Steven J.↗

NASA NTRS1974

Temperature dependence of vibrational relaxation in the HF, DF, HF-CO2, and DF-CO2 systems

The laser excited fluorescence method has been employed to determine rate constants for V to V, R and V to R, T relaxation HF (nu = 1) and DF(nu = 1) by CO2 over the temperature range from 295 to 670 K. The self-deactivation rates for HF(nu = 1) and DF(nu = 1) by ground state molecules and the rate of V to V, R transfer from HF(nu = 1) and DF(nu = 1) to the CO2 (00/0/1) state exhibit a marked decrease with increasing temperature. The results provide additional evidence for the conversion of the large vibrational energy defects of the present systems into rotational motion of the hydrogen halide under the influence of a sizable attractive intermolecular potential well.

Lucht, R. A.↗