Spectral Energies Research Articles

Computer Classification of State in Healthy Preterm Neonates

Nineteen electroencephalographic (EEG) sleep measures describing four physiologic aspects of sleep behavior (i.e. sleep continuity, EEG spectra, body and eye movements, and autonomic measures) were derived from visual and computer analyses of 71 24-channel, 3-hour EEG sleep recordings on 52 healthy preterm neonates from 28-36.5 weeks postconceptional age (PCA). Forty-eight subjects were neurodevelopmentally normal up to 2 years of age. Four electrographic states that comprise tracé discontinu of the preterm neonate were defined in terms of increasing seconds of EEG quiescence per minute. A regression analysis was performed after transformations of nonlinear data sets representing the 19 EEG sleep measures, with the four sleep states as outcome variables. Postconceptional age was also included in these analyses as the 20th explanatory variable. Four measures best defined the EEG sleep states, explaining 75% of the variance: decreasing rapid eye movements per minute, decreasing numbers of spontaneous arousals per minute, increasing spectral theta energies, and decreasing facial movements per minute. Other cerebral and noncerebral measures, including total spectral EEG energies, spectral EEG energies in three bandwidths (i.e. delta, alpha, beta), cardiac and respiratory measures, and body movements, did not contribute as significantly to the prediction. Inclusion of PCA into the regression equation with the four EEG measures, selected by the analysis procedure, indicated that its contribution to state prediction was also small; the effect of PCA on state was found to be explained by the four EEG sleep measures.

Electron impact ionization of tetramethylsilane (TMS)

We studied the electron impact ionization of tetramethylsilane (TMS), Si(CH 3) 4, which is utilized in plasma polymerization applications, using various mass spectrometric techniques. Absolute partial cross-sections for the formation of the parent ion and 15 fragment ions were measured in a high resolution double-focusing sector field mass spectrometer from threshold to 90 eV. Complementary measurements of mass spectral cracking patterns of TMS were also carried out using two quadrupole mass spectrometers. Dissociative ionization of TMS was found to be the dominant process. The Si(CH 3) 3 + ion is by far the most abundant fragment ion with a maximum cross-section of about 1 × 10 −15cm 2. In contrast, the maximum parent ionization cross-section is less than 2% of that value. On the basis of the measured partial ionization cross-sections, mass spectral cracking patterns and appearance energies of the various ionic products, we propose a collision-induced decomposition scheme for the TMS molecule. Three major decomposition channels were identified which all involve the total or partial removal of a methyl group. The agreement of our measured absolute partial ionization cross-sections with earlier data obtained by a different technique is generally poor.

Prediction of lower developmental performances of healthy neonates by neonatal EEG-sleep measures

Previous neurophysiologic studies from our laboratory have demonstrated altered EEG-sleep behavior at conceptional term ages in healthy preterm infant compared with a term cohort. Developmental assessments at 12 and 24 months of age of 16 children in each cohort were compared using MANOVA. Differences were detected on MANOVA between each cohort on Bayley mental and motor performance scores, while social skills (Vineland) and temperament (Carey) were similar. Healthy preterm infants had lower scores at 12 months of age ( P < .0001) and 24 months ( P < .04) than term infants before adjustment for prematurity. No group differences were observed after adjustment. For the combined cohort of 32 healthy neonates, specific neonatal EEG-sleep measures were included as predictor variables in regression analyses with Bayley mental scores as outcome variables. Lower Bayley mental scores at 12 and 24 months were associated with higher spectral EEG correlations, lower spectral EEG energies in the beta frequency ranges, fewer arousals per minute, lower rapid eye movements per minute, and shorter sleep latencies from awake state to active sleep. Significant associations were observed before adjustment for prematurity at both 12 and 24 months, and after adjustment at 12 months of age for lower spectral beta EEG energies. Lower socioeconomic class also correlated with lower developmental scores. Even in the absence of major neonatal illnesses, brain adaptation to prematurity influences later developmental outcome. Adjustment for “age equivalency” may be required up to at least 24 months of age even in a healthy preterm population.

High-Resolution Rovibrational Absorption Spectrum of CO2−N2O

The rovibrational absorption spectrum of the weakly bound cluster CO2−N2O has been observed in the region of the ν3 CO2 asymmetric stretch (∼2350 cm-1). Clusters were formed by supersonic expansion of a mixture of N2O:CO2 in a 4:1 ratio using He carrier gas. Approximately 340 lines have been assigned. Both parallel and perpendicular transitions were observed. The ground state rotational constants A, B, and C are 0.294 924(12), 0.058 004(6), and 0.048 400(6) cm-1, respectively. The quartic centrifugal distortion constants are Dj = 5.03(17) × 10-7 cm-1, Djk = −3.92(9) × 10-6 cm-1, Dk = 1.26(2) × 10-5 cm-1, δj = 1.61(92) × 10-8 cm-1, and δk = 1.77(80) × 10-6 cm-1. Ab initio calculations for several CO2−N2O equilibrium structures have been done on the Hartree−Fock self-consistent field level using a 6-311g* basis set. Møller−Plesset MP2 and MP3 calculations were carried out for the two possible slipped parallel configurations of the dimer. The planar slipped parallel geometry with the oxygen atom of N2O nearest the CO2 monomer was found to be the most stable structure. The spectral constants and stabilization energies were compared to those of the CO2 and N2O homodimers. A planar slipped parallel geometry is observed with the O of N2O nearly over the C of CO2. Rcm and θ are 3.4701 Å and 60.1°, respectively, assuming the CO2 and N2O are parallel to each other.

Maturational trends of EEG-sleep measures in the healthy preterm neonate

Five physiologic groupings of 45 EEG-sleep measures were acquired from serial 24-channel EEG-sleep recordings (i.e., sleep architecture, continuity, EEG spectral, phasic, and autonomic measures), utilizing 129 studies on 56 healthy preterm infants from 28 to 43 weeks postconceptional age (PCA) who were neurodevelopmentally normal on follow-up. Regression analyses chose the least number of measures that best reflected maturation. Four of 45 variables (i.e., spectral α energy during quiet sleep, total spectral EEG energy, arousal number during active sleep, and percentage of EEG discontinuity) most significantly explained brain maturation in neonates <36 weeks PCA. Three of 45 variables (i.e., spectral θ and β energies during active sleep and spectral α energy during quiet sleep) were most representative after 36 weeks PCA. Spectral EEG energies were the strongest indicators of maturation compared with other measures, particularly in near-term neonates.

Deep level electronic structure of ZnSe/GaAs heterostructures

We performed 1—2 keVcathodoluminescence measurements and He-Ne and HeCd excited photoluminescence studies of ZnSe/GaAs( 100) heterostructures grown by molecular beam epitaxy. Our goal was to investigate the deep level electronic structure and its connection with the heterojunction band offsets. We observed novel deep level emission features at 0.8, 0.98, 1.14, and 1.3 eV which are characteristic of the ZnSe overlayer and independent in energy of overlayer thickness. The corresponding deep levels lie far below those of the near-bandedge features commonly used to characterize the ZnSe crystal quality. The relative intensity and spatial distribution of the deep level emission was found to be strongly affected by the Zn/Se atomic flux ratio employed during ZnSe growth. The same flux ratio has been shown to influence both the quality of the ZnSe overlayer and the band offset in ZnSe/GaAs heterojunctions. In heterostructures fabricated in Se-rich growth conditions, that minimize the valence band offset and the concentration of Se vacancies, the dominant deep level emission is at 1.3 eV. For heterostructures fabricated in Zn-rich growth conditions, emission by multiple levels at 0.88,0.98, and 1.14 eV dominates. The spectral energies and intensities of deep level transitions reported here provide a characteristic indicator of ZnSe epilayer stoichiometry and near-interface defect densities.

Shake-up satellite structure of transition metal auger spectra: L 2,3M 4,5M 4,5 spectra of the 4d metals

Core hole Auger spectra of transition and noble metals have been relatively little studied because they are usually very broad, and because they provide little direct valence band information. Narrow and simple L 2,3M 4,5M 4,5 spectra of the 4d metals have been recently reported, however. Study of spectral peak energies has produced considerable information regarding ground and excited state electronic structure of these metals. Comparison of the spectra with atomic theoretical ones indicates that, whereas the L 2,3M 4,5M 4,5 spectra of In, Sn and Sb manifest atomic nature, in such open shell metals as Ag and Pd, these spectra evince intrinsic satellite structures below those of the Auger transitions proper. The L 2 and L 3 satellites, in contrast to those of the 3d LMM spectra, have the same form (within experimental error) and do not seem to involve L 2L 3X Coster-Kronig transitions, most of which are energetically forbidden. On the basis of the experimental systematics of the 4d spectra and the interpretation of 3d LMM spectra, we have identified these satellites as arising from shake-up involving spectator valence band holes. To our knowledge, such shake-up features have not been directly observed before in transition metals.

Spectral properties and numerical modelling of a critically phase-matched nanosecond LiB3O5 Optical Parametric Oscillator

We report on the spectral properties and numerical modelling of a singly resonant Optical Parametric Oscillator (OPO) of Lithium-triBOrate (LBO). The OPO is pumped by the second, third or fourth harmonic of an injection-seeded,Q-switched Nd:YAG laser. The measured OPO parameters are the tuning range, the threshold, the spectral linewidth, the efficiency and the output power. For the LBO-OPO critical type-I phase-matching (xy-plane) provides a wide tuning range and optimum values of the effective nonlinear coefficient. Pumped, for example, by the 355nm third harmonic the spectral range extends from 414 nm to 2.47 µm. With a 15 mm long crystal the OPO generates a total output-pulse energy of 77 mJ with an efficiency of 45%. For 266 nm pump radiation the signal wave is in the near ultraviolet at 307–325 nm. If pumped at 532 nm the OPO generates simultaneously two pairs of signal and idler waves in the infrared (0.707–2.15 µm). The pulse-energy fluctuations of the two pairs are correlated. If, however, the OPO is injection-seeded at one of the signal waves the two wavelength pairs are anti-correlated. The observed wavelength tuning as well as the measured spectral line-widths, threshold energies and efficiencies are in agreement with the values predicted by computer simulation.

Temporal masking in automatic speech recognition

It is reasonable to expect that relevant features for speech recognition should be the features that are well heard. Therefore the successful extraction of such relevant acoustic features must respect properties of the auditory periphery. To examine its temporal properties full masking (detection) and partial masking (loudness matching) experimental paradigms are used. The results of these masking experiments suggested a model consisting of a combination of linear and nonlinear components. Hence a recently introduced RelAtive SpecTrAl (RASTA) engineering technique for speech feature extraction [Hermansky etal., Proc. Int. Conf. Acoustic, Speech, and Signal Process. (1993)] has been introduced, which employs linear temporal filtering of critical-band spectral energies done between two static nonlinearities and which has been successful as a feature extraction technique in automatic speech recognition. A correspondence between the results of the experiments and the behavior of the RASTA model has been found. Possible modifications of the RASTA technique to incorporate additional details of the experimental results will be discussed.

Multisphere Neutron Spectroscopy Measurements at the Los Alamos National Laboratory Plutonium Facility

Multisphere neutron spectroscopy methods are applied to measure representative working fields within the Los Alamos National Laboratory (LANL) Plutonium Facility. This facility hosts dynamic processes, which include the fabrication of {sup 238}Pu heat sources for radioisotope generators used to power space equipment and a variety of plutonium research programs that involve recovery, hydrofluorination, and metal production. Neutron fluence per unit lethargy, as a function of neutron energy measured for locations throughout this facility, are described. Dosimeter/remmeter response functions [e.g., determined for a 22.8-cm-diameter neutron rem detector (NRD), an Anderson/Braun-type neutron ``Snoopy`` monitor, track-etch CR-39, BDI-100 bubble detectors, and Kodak type A nuclear track emulsion film, (NTA)] are folded into these spectra to calculate absolute response values of counts, tracks, or bubbles per unit-dose equivalent. The relative response values per unit- dose equivalent for bare and albedo {sup 6}LiF-based thermoluminescent dosimeters (TLDs) are also calculated to estimate response scenarios encountered with use of the LANL-TLD. These results are further compared to more conventional methods of estimating neutron spectral energies such as the ``9-to-3 ratio`` method.

Theoretical Studies of Xanthates, Dixanthogen, Metal Xanthates, and Related Compounds

Ab initio molecular orbital techniques have been used to calculate a number of properties of the xanthate anion, (OH)CS -1 2, and related molecules, to assist in the characterization of xanthate collector species formed on sulfide mineral surfaces during froth flotation. Calculated geometries for xanthate and dithiocarbamate ions and for dixanthogen are in good agreement with experiment. For metal xanthate complexes, calculated bond lengths and angles within the xanthate moiety agree well with experiment and help us to understand observed changes in C-S and C-O stretching frequencies upon complexation. Calculated energies of frontier molecular orbitals are consistent with available experimental photoemission, electron transmission, and X-ray absorption spectral data. The highest energy occupied molecular orbitals are of S 3 p nonbonding and II-bonding types, whereas the lowest energy empty orbitals are of C-S II* and C-S σ* types (or S-S σ* type in dixanthogen). X-ray absorption spectral energies are calculated at both C and S edges for many of the compounds studied. 13C NMR may also prove valuable for species characterization in these systems, and our calculations show that at least the nearest-neighbor geometry about C can be determined from the 13C NMR shielding tensor. Preliminary studies also indicate that trends in UV spectral energies for different xanthate complexes can be calculated semiquantitatively. The molecular orbital calculations facilitate the interpretation of spectral data in terms of the geometric and electronic structures of the species involved.

Quantum spectra and classical orbits in the pairing model: A simple connection.

We derive a qualitative and quantitative connection between the quantal spectral distribution and energies and actions of classical orbits in the symmetric pairing model.

Pseudospectral full configuration interaction

A pseudospectral formulation of the full configuration interaction method is presented in this paper. This represents the first application of the pseudospectral approximation to configuration interaction expansions. It is shown that a formal scaling advantage of n, the number of molecular orbital basis functions, is achieved. The spectral and pseudospectral total energies obtained for a series of first-row atoms and ions are compared. The relative operation counts of the spectral and pseudospectral methods are also discussed in this paper. Finally, two hybrid spectral/pseudospectral approximations that vastly improve the accuracy of the pseudospectral total energies are presented.

EEG markers of early Alzheimer's disease in computer selected tonic REM sleep

All night sleep/wake EEGs were examined for diagnostic sensitive to early Alzheimer's diesease (AD) using computer automated techniques. Thirty-nine AD patients and 43 normal controls underwent 9 h of EEG recording in the sleep laboratory. All-night EEGs were screened for ideal, low artifact tonic REM sleep using autoregressive and power spectral techniques. The frequency spectral during tonic REM sleep revealed a significant shift towards slower wave formeds in AD vs. control subjects. Beta (> 12 Hz0 was reduced adn theta and delta (2–8 Hz) increased in AD compared to control groups. This frequency shift was demonstrated by several analytic techniques, including binned spectral energies and unique zones in the frequency spectra. Discriminant analyses using optimal binned EEG variables correctly classified 74% of AD and 98% of control subjects, and unique zone scores correctly classified 92% of AD and 95% of control subjects, indicating that these sleep EEG changes are apparently predictive of AD status.

Dynamic pulmonary imaging: performance properties of a digital fluoroscopy system.

The physical characteristics of dynamic pulmonary imaging with digital fluoroscopy, which differ from those in DSA equipment, have been determined. The spectral distributions and mean energies were calculated and corresponding exposures with varying high voltage and copper filtration (60-100 kVp, 0-2.83 mm Cu) were measured. The utilization of 90-100 kVp with a filter consisting of 1.39 mm Cu and 3 mm Al minimized disturbing skeletal artifacts and reduced the radiation exposure by a factor of approximately 5 in comparison with imaging at 60 kVp without copper filtration. Simultaneously, the measured signal decreased by about 25%. The mean energy of this spectrum exceeded that of 140 kVp chest imaging. The dynamic pulmonary imaging method produces logarithmically transformed x-ray transmittance values linearly related (r = -0.999) to water thickness between 7-10.5 cm, which is equivalent to the normal range of the chest in pediatric patients. A good linear correlation (r = 0.933,N = 92) was obtained when the change in transmitted radiation was compared with tidal volume measured in a rabbit model using a pneumotachometer. The results indicate that the method is applicable for quantitative measurements of pulmonary ventilation. Changes in tidal ventilation can be measured with this noninvasive x-ray imaging technique.

A model for eddy diffusivity in a stable boundary layer

Expressions for the vertical and the lateral diffusivity coefficients were derived from the Local Similarity Theory and the Statistical Diffusion Theory. For such, the spectral density energies for the turbulent velocities were used. The expressions here derived are compared with the diffusivity coefficients for momentum and heat suggested by Sorbjan (from the Minnesota experiments) and Nieuwstadt (from the Cabauw experiments). This comparison allows us to conclude that turbulence is equally efficient in transporting momentum, heat and contaminants in an ideally stable boundary layer.

The application of zero-range potentials to the electronic properties of footballene, C 60

We have used the experimental value of the first special transition from molecular beam studies of C 60 to determine the one parameter in a semi-empirical method that couples zero-range potentials with the free electron method. The method then allows the estimation of three other spectral transition energies and the relative spacing of five photoionization peaks. These results an excellent qualitative match and even a reasonable quantitative match of the nine transitions with the theoretical values. The one fitted parameter is the strength of the zero-range potential. All other semi-empirical quantities entering the calculation are geometric in nature. Because of the high sphericity of the molecule, two electron integrals are easily calculated within the model, and we obtain estimates of 0.83 eV for the 1T lu to 3T lu splitting, 1.9 eV for the electron affinity, and 11.2 eV for the second ionization potential. Variations in the charge distribution lead to the conclusion that, inclusing the σ electrons, there are 60 bonds with order 1.321 and 30 with order 1.359. The success of the treatment strongly suggests that simple geometry dominates much of the physics of C 60.

Ab initio calculation of Ti NMR shieldings for titanium oxides and halides

Titanium NMR shielding constants have been calculated using ab initio coupled Hartree-Fock perturbation theory and polarized double-zeta basis sets for TiF 4, TiF 6 2−, TiCI 4, Ti(OH) 4, Ti(OH 2) 6 4+, Ti(OH) 4O, and Ti(OH) 3O −. In all cases the calculations were performed at Hartree-Fuck energy-optimized geometries. For Ti(OH) 4 a S 4-symmetry geometry with nonlinear ∠ TiOH was employed. Relative shieldings are in reasonable agreement with experiment for TiF 6 2−, TiCI 4, and Ti(OR) 4, where R = H or alkyl. Ti(OH 2) 6 4+ is predicted to be more highly shielded than Ti(OH) 4 by about 340 ppm. The five-coordinate complex Ti(OH) 4O, whose calculated structure matches well that measured by extended X-ray absorption fine structure in K 2O · TiO 2 · SiO 2 glass, is actually deshielded compared to Ti(OH) 4 by about 40 ppm. X-ray absorption-near-edge spectral energies have also been calculated for TiF 4, TiCI 4, Ti(OH) 4, and Ti(OH) 4O using an equivalent ionic core virtual-orbital method and the observed reduction in term energy for the five-coordinate species compared to Ti(OH) 4 has been reproduced. Replacement of the H atoms in Ti(OH) 4 by point charges has only a slight effect upon σ Ti, suggesting a possible means of incorporating second-neighbor effects in NMR calculations for condensed phases.

Tungsten(V) binuclear thiocomplexes with diethyldithiocarbamate. Synthesis, spectral, thermal and kinetic studies

We report the synthesis, using reactions in different solvents, and the study of di-μ-sulfido-bis(sulfido N,N-diethyldithiocarbamate) dy-tungsten(V) adducts with pyridine or substituted pyridines, with formula assigned as W 2S 4(diethyldtc) 2B 2, where dtc=dithiocarbamate; B=pyridine (Py), 3-methylpyridine (3-MP), 4-methylpyridine (4-MP), 3,5-dimethylpyridine (3,4-DMP), 3-aminopyridine (3-AP) and 4-aminopyridine (4-AP). The complexes obtained have been identified by IR and electronic spectra, magnetic susceptibility measurements and analytical data. We have also studied the thermal behaviour and kinetic parameters, by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), of the thermal decomposition of these adducts in the solid state. From the DSC curves, the activation energies and pre-exponential Arrhenius factors for the endothermic process corresponding to the loss of two moles of coordinated base were calculated. We have also deduced the mechanism of the reaction using a new non-isothermal kinetic method. The effects of steric hindrance and the inductive effects exercised by the functional groups, amino and methyl of the pyridine, in the formation of the adducts are discussed. The relationship between the basicity of the pyridines, IR and electronic spectral data and activation energies has also been explored.

Calculation of the inner shell excitation spectra and estimation of the electron scattering and dissociative attachment resonance energies of SF 6, SO 2, SF 2O, SF 2O 2, SF 4, SF 4O and S 2F 10

We have calculated the S inner shell excitation spectra of SF 6, SO 2, SF 2O, SF 2O 2, SF 4, SF 4O and S 2F 10 using ab initio methods within the equivalent ionic core virtual orbital model. For SF 4 we have taken energy differences between initial and final states of the core excited molecules at both the SCF and SCF-CI levels, while for the other molecules we have used only a Koopmans' theorem level approach. Trends in inner shell spectral energies for the whole series of molecules are adequately reproduced at the Koopmans' theorem level and quantitative agreement with experiment is obtained for SF 4 at the Δ E SCF-CI level. Direct SCF calculations of the vertical electron affinities of the neutral molecules SO 2, SF 4 and SF 2O 2 allow us to evaluate a stabilization energy, connecting the term energy of a given unoccupied orbital in inner shell excitation spectra and the energy of the cross-section maximum it produces in electron scattering or dissociative electron attachment. Using this stabilization energy plus experimental inner shell term energies we can correctly reproduce trends in the energies of dissociative electron attachment within this series. For SF 4 and SF 2O 2 we have also calculated both inner shell spectral intensities (within the dipole approximation) and orbital electron density plots to more fully characterize the empty orbitals. The lowest energy empty orbital of core ionized SF 2O 2 is both SO π* and SF σ* in character and is consequently less stable than the LUMO of SF 4 which has onlySF σ* character.