Restricted Configuration Research Articles

Theoretical study on photochemical behavior of trans-2-[4′-(dimethylamino)styryl]benzothiazole

Photochemistry of trans-2-[4′-(dimethylamino)styryl]benzothiazole ( t-DMASBT) has been examined theoretically. Ground state calculations are performed by density functional theory (DFT) method. For excited-state calculations restricted configuration interaction singles (RCIS) combined with time dependent DFT (TDDFT) approach was used. Theoretical calculations predicted the existence of two ground state conformers and the photophysics of both the conformers are nearly identical. With torsional rotation of dimethylamino group, the energies of S 1 and S 2 states increase, but that of S 3 state decreases. In contrary to an earlier report [J. Photochem. Photobiol. A: Chem. 195 (2008) 368–377], the calculation predicted at the perpendicular geometry the HOMO is localized on dimethylamino and, HOMO and LUMO are decoupled. Excitation from HOMO to LUMO at perpendicular geometry results in twisted intramolecular charge transfer (TICT) state. Avoided crossing of S 3 and S 1 states causes a barrier for formation of TICT state from locally excited state. Potential energy surface of isomerization constructed by TDDFT method suggests that the photoisomers are formed through phantom state in a nonradiative way, not by a radiative way from cis and trans isomers as proposed earlier by Saha et al. [J. Photochem. Photobiol. A: Chem. 199 (2008) 179–187].

Feasibility studies for the alignment of the Thirty Meter Telescope

The Alignment and Phasing System (APS) of the Thirty Meter Telescope (TMT) is an instrument that will be responsible for aligning the primary, secondary, and tertiary mirrors of TMT. The telescope and APS are modeled with a ray tracing simulation program. Various sets of initial conditions and alignment procedures are simulated, and results are compared to the image quality specifications for the telescope. A key factor in alignment quality is the rotation of the flat tertiary mirror (M3), which rotates to serve the science instruments. The procedures that use only APS measurements yield unacceptably large image diameters, while procedures that use measurements from APS and another WFS at a different location result in telescope alignments that produce acceptable image diameters at the 90% confidence level. These two-sensor procedures can separate M3 errors from errors on other mirrors better than APS-only procedures. However, APS-only procedures should be adequate for the restricted configurations of instruments available at first light. In general, APS-only procedures should also be capable of maintaining the alignment produced initially by the more complex two-sensor procedures.

Identifying Cochlear Implant Channels with Poor Electrode-Neuron Interface: Partial Tripolar, Single-Channel Thresholds and Psychophysical Tuning Curves

The goal of this study was to evaluate the ability of a threshold measure, made with a restricted electrode configuration, to identify channels exhibiting relatively poor spatial selectivity. With a restricted electrode configuration, channel-to-channel variability in threshold may reflect variations in the interface between the electrodes and auditory neurons (i.e., nerve survival, electrode placement, and tissue impedance). These variations in the electrode-neuron interface should also be reflected in psychophysical tuning curve (PTC) measurements. Specifically, it is hypothesized that high single-channel thresholds obtained with the spatially focused partial tripolar (pTP) electrode configuration are predictive of wide or tip-shifted PTCs. Data were collected from five cochlear implant listeners implanted with the HiRes90k cochlear implant (Advanced Bionics Corp., Sylmar, CA). Single-channel thresholds and most comfortable listening levels were obtained for stimuli that varied in presumed electrical field size by using the pTP configuration for which a fraction of current (sigma) from a center-active electrode returns through two neighboring electrodes and the remainder through a distant indifferent electrode. Forward-masked PTCs were obtained for channels with the highest, lowest, and median tripolar (sigma = 1 or 0.9) thresholds. The probe channel and level were fixed and presented with either the monopolar (sigma = 0) or a more focused pTP (sigma > or = 0.55) configuration. The masker channel and level were varied, whereas the configuration was fixed to sigma = 0.5. A standard, three-interval, two-alternative forced choice procedure was used for thresholds and masked levels. Single-channel threshold and variability in threshold across channels systematically increased as the compensating current, sigma, increased and the presumed electrical field became more focused. Across subjects, channels with the highest single-channel thresholds, when measured with a narrow, pTP stimulus, had significantly broader PTCs than the lowest threshold channels. In two subjects, the tips of the tuning curves were shifted away from the probe channel. Tuning curves were also wider for the monopolar probes than with pTP probes for both the highest and lowest threshold channels. These results suggest that single-channel thresholds measured with a restricted stimulus can be used to identify cochlear implant channels with poor spatial selectivity. Channels having wide or tip-shifted tuning characteristics would likely not deliver the appropriate spectral information to the intended auditory neurons, leading to suboptimal perception. As a clinical tool, quick identification of impaired channels could lead to patient-specific mapping strategies and result in improved speech and music perception.

Comparative Theoretical Study of Rotamerism and Excited State Intramolecular Proton Transfer of 2-(2′-Hydroxyphenyl)benzimidazole, 2-(2′-Hydroxyphenyl)imidazo[4,5-b]pyridine, 2-(2′-Hydroxyphenyl)imidazo[4,5-c] pyridine and 8-(2′-Hydroxyphenyl)purine

The effect of nitrogen substitution in the benzene ring of 2-(2'-hydroxyphenyl)benzimidazole (HPBI) on the photophysics and rotamerization were examined theoretically by a comparative study of HPBI with 2-(2'-hydroxyphenyl)imidazo[4,5-b]pyridine (HPIP-b), 2-(2'-hydroxyphenyl)imidazo[4,5-c]pyridine (HPIP-c), and 8-(2'-hydroxyphenyl)purine (HPP). Density functional theory (DFT) was used for ground state calculations. Restricted configuration interaction singles (RCIS) combined time dependent DFT (TDDFT) was used for excited state calculations. The calculations reveal in the ground state all of the molecules have two stable rotameric forms, but their relative population is strongly affected by nitrogen substitution. The excitation and emission bands have been calculated theoretically for the rotamers and tautomers. Fluorescence emission and excitation spectra were recorded for HPBI in dioxane and compared with the theoretical results. Theoretical excitation and emission data are in good agreement with the available experimental data. The potential energy surface simulated for the proton transfer processes reflect that it is not favorable in S(0) state, but it is feasible in S(1) state in all of the molecules. Except in HPIP-b, HPIP-b', and HPP', in all other nitrogen substituted molecules, the energy difference between the keto and enol form along the excited state proton transfer coordinates decreases compared to that in HPBI. The study also reveals that torsional relaxation of tautomer to twisted state competes with radiative transitions and leads to fluorescence quenching. Nitrogen substitution enhances this torsional induced nonradiative process and it follows the order HPBI < HPIP-b < HPIP-c < HPP.

Four-lepton LHC events from MSSM Higgs boson decays into neutralino and chargino pairs

Heavy neutral Higgs boson production and decay into neutralino and chargino pairs is studied at the Large Hadron Collider in the context of the minimal supersymmetric standard model. Higgs boson decays into the heavier neutralino and chargino states, i.e., H0,A0?X20,X30,X20,X40,X30,X30,X30,X40,X40X40 as well as H0,A0?1±X2,X2+X2? (all leading to four-lepton plus missing transverse energy final states), is found to improve the possibilities of discovering such Higgs states beyond those previously identified by considering H0,A0?X20X20 decays only. In particular, H0,A0 bosons with quite heavy masses, approaching ~ 800 GeV in the so-called `decoupling region' where no clear SM signatures for the heavier MSSM Higgs bosons are known to exist, can now be discerned, for suitable but not particularly restrictive configurations of the low energy supersymmetric parameters. The high MA discovery reach for the H0 and A0 may thus be greatly extended. Full event-generator level simulations, including realistic detector effects and analyses of all significant backgrounds, are performed to delineate the potential H0,A0 discovery regions. The wedgebox plot technique is also utilized to further analyze the 4? plus missing transverse energy signal and background events. This study marks the first thorough and reasonably complete analysis of this important class of MSSM Higgs boson signature modes. In fact, this is the first time discovery regions including all possible neutralino and chargino decay modes of the Higgs bosons have ever been mapped out.

Restricted active space spin-flip configuration interaction approach: theory, implementation and examples

A new formulation of the spin-flip (SF) method is presented. The electronic wave function is specified by the definition of an active space and through alpha-to-beta excitations from a Hartree-Fock reference. The method belongs to the restricted active space (RAS) family, where the CI expansion is restricted by classifying the molecular orbitals in three subspaces. Properties such as spin completeness, variationality, size consistency, size intensivity, and orbital invariance are discussed. The implementation and applications use a particular truncation of the wave function, with the inclusion of hole and particle contributions such that for fixed active space size, the number of amplitudes is linear in molecular size. This approach is used to investigate single and double bond-breaking, the singlet-triplet gap of linear acenes, electronic transitions in three Ni(II) octahedral complexes, the low-lying states of the 2,5-didehydrometaxylylene (DDMX) tetraradical and the ground state multiplicity of 28 non-Kekulé structures. The results suggest that this approach can provide a quite well balanced description of nearly degenerate electronic states at moderate computational cost.

D314 STUDY ON P-Q CURVES OF COOLING FANS FOR THERMAL DESIGN OF ELECTRONIC EQUIPMENT : EFFECTS OF OPENING POSITION LOCATED IN FRONT OF A FAN(Components-3)

This paper describes the relationship between fan performance and configuration factors such as flow inlet porosity of an electronic enclosure, or flow obstacles which imitate high-density packages and restricted flow area configurations for a development of a fan performance prediction model. We focus on an electronic enclosure or an obstacle in front of the fan individually as factors which have dominant effects to the fan. First, we installed an enclosure model in front of the test fan and measured its P-Q curves while operating it in an enclosure. Secondly, we installed a perforated plate in front of the fan as an obstacle and investigated the P-Q curve changes as affected by the position and distance between the adjacent area and the fan. When the perforated plate was located in front of the fan, the P-Q curves were adversely affected, and the flow rate was determined by the open area ratio in front of the fan.

Two component calculations of Pt2 with relativistic effective core potential including spin‐orbit operator

AbstractThe Kramers restricted two‐component ab initio calculations were performed for the eight lowest electronic states of Pt2 using the relativistic effective core potential with the spin‐orbit operator at the multireference first‐order configuration interaction level of theory employing two‐component molecular spinors as one‐electron basis. The dominant role of the spin‐orbit effects are mainly accounted for by using two‐component spinors as one‐electron wave function, and the importance of the dynamic and the nondynamic electron correlation effects are shown by employing configuration interaction and coupled cluster methods to obtain reliable spectroscopic data for this molecule. The two‐component molecular spinors were generated from Kramers restricted Hartree–Fock calculations for the average configuration and used in the multireference Kramers restricted configuration interaction method to account for nondynamic correlation effect. Effect of dynamic correlations was investigated with the Kramers restricted coupled‐cluster (KRCC) method. Spectroscopic constants calculated at the KRCC level are in good agreement with the most recent experimental values. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009

MODELING THE GROUND STATE GEOMETRY AND ESTIMATING THE CHARGE TRANSFER TRANSITION ENERGY OF THE TOLUENE–ICl MOLECULAR COMPLEX BY AB INITIO AND DFT METHODS

Out of several plausible isomeric structures of the toluene–ICl charge transfer (CT) complex, the most feasible one was determined by a detailed ab initio and DFT study at the HF, B3LYP, and mPW1PW91 levels using 6-31++G(d, p) basis set. Potential energy surface scans were performed with six possible structures ( I and Cl facing the o-, m-, and p-carbon atoms of toluene separately); the structures at the local minima of the surfaces were subjected to frequency calculation and the ones having no negative frequency were accepted as the real structure in the ground state. These structures were then subjected to full optimization. It was observed that the I – Cl bond, with its I atom oriented toward the aromatic ring, stands vertically above a C -atom at the ortho or para positions, being inclined at about 9° to the line perpendicular to the aromatic ring. Complexation increases the I – Cl bond length. After correction for basis set superposition error through a counterpoise calculation, we conclude from the binding energy that the preferred structure is the one with ICl above the ortho C atom. The calculated binding energy closely matches the experimental free energy of complexation. The electronic CT transition energy (hν CT ) with this structure in the ground state was calculated in vacuo by the restricted configuration interaction singlets method and in carbontetrachloride medium by the time dependent density functional theory method under the polarizable continuum model. The value of hν CT obtained from the ground-to-excited state transition electric dipole moments of the complex, is close to (somewhat underestimated) the reported experimental value.

Emergent antegrade endovascular stent placement in a patient with perforated Stanford B dissection via right axillary artery

We present a case of a ruptured chronic Stanford B dissection of the aorta which was successfully treated with a tapered endoprosthesis using the right axillary artery for access. Challenges to endovascular strategies for thoracic aortic pathology include relatively restricted endoprosthesis configurations and problems associated with endovascular access. Especially in younger patients the right axillary artery should be considered as a possible and safe access for antegrade stent placement.

Extracting continuum information fromΨ(t)in time-dependent wave-packet calculations

The theory of measurement projection operators in grid-based time-dependent wave-packet calculations involving electronic continua in atoms and molecules is discussed. A hierarchy of projection operators relevant in their individual restricted configuration spaces is presented. At asymptotically large distances from the scattering or interaction center the projection operators involve plane waves only. To reach this asymptotic regime, however, large propagation times and large boxes may be required. At somewhat smaller distances from the scattering center, the projection operators are expressed in terms of analytical single-center Coulomb scattering waves with incoming wave boundary conditions. If propagation of the wave packet to these asymptotic regimes is impeded, the projection operators involve the exact scattering states which are not readily available in the wave-packet calculation and hence must be supplied by an additional, typically very demanding, calculation. The present approach suggests an exact way of analyzing the timely problem of the one-electron continuum in nonperturbative calculations. A key feature is that the propagated wave packet includes every interaction of the full Hamiltonian. The practicality of the proposed method is illustrated by the nontrivial example of strong-field ionization of the molecular hydrogen ion. Finally, the extension of the presented ideas to single and double ionization of two-electron systems is discussed.

Dynamics of dissolved polymer chains in isotropic turbulence

Polymers are remarkable molecules that have relaxation times that can span 15 orders of magnitude. The very longest of the relaxation times for high molecular weight polymers are sufficiently long to overlap with fluid mechanical times scales; under those circumstances, polymers can influence the flow. A well-known example that is still not fully understood is polymer drag reduction. It has been known since Toms (1949 Proc. 1st Int. Congress on Rheology 2 135–41) that parts per million (mass basis) concentrations of polymers can reduce the drag on a solid surface by as much as 80%. Understanding the mechanism of drag reduction requires an understanding of the dynamics of the dissolved polymer chain in response to local fluctuations in the turbulent flow field. We investigate this by using Brownian dynamics simulations of bead-spring models of polymers immersed in a turbulent solvent that is separately computed using direct numerical simulations. We observe that polymer chains with parameters that are effective for drag reduction generally remain stretched for long periods of time and only occasionally relax. The relatively restricted configuration space they sample makes it reasonable to represent their behavior with simpler dumbbell models. We also study the spatial structure of the polymer stresses using a Lagrangian strategy. The results explain the need for relatively high spatial resolution for numerical simulations of polymer flows.

Investigation of the structure, the optical properties, and the photophysics of some indolocarbazoles having terminal aromatic rings

Structures, optical properties, and photophysics of ladder indolo[3,2- b]carbazoles substituted symmetrically by phenylene and thiophene rings have been investigated theoretically and experimentally. The ground state optimized structures were obtained using the density functional theory (DFT) as approximated by the B3LYP functional and employing the 6-31G ∗ basis set. All derivatives were found nonplanar in their electronic ground states. The character and the energy of the singlet–singlet electronic transitions have been investigated by applying the time-dependent density functional theory (TDDFT) to the correspondingly optimized-ground-state geometries. The ab initio restricted configuration interaction (singles) method (RCIS/6-31G ∗) was adopted to obtain the first singlet excited-state structures (S 1) of the molecule. TDDFT calculations performed on the S 1 optimized geometries was used to obtain emission energies. UV–vis and fluorescence spectroscopies were analyzed in conjunction with theoretical calculations. The computed excitation and emission energies were found in reasonable agreement with the experimental absorption and fluorescence spectra. Finally, the photophysical behavior of the indolocarbazoles have been studied by means of steady state and time resolved fluorescence. The overall data have allowed the determination of the rate constants for the radiative and nonradiative decay processes. Both theoretical and experimental data show that the replacement of phenylene rings by thiophene units induces a red shift in the absorption and fluorescence spectra. This behavior is interpreted in terms of the electron donor properties of the thiophene ring. On the other hand, the change of the substitutional pattern, from 2,8 to 3,9, causes a significant hypsochromic shift of the absorption and fluorescence bands.

Exact Removal of the Center-of-Mass Spurious States from Level Densities

We give recursive formulae for the exact removal of the contribution of the center-of-mass spurious states from the fixed-spin and parity nuclear level density found in shell-model calculations, provided the total level density for restricted configurations is known. The method is valid for a large class of problems using a harmonic oscillator basis. Using our earlier methods based on statistical spectroscopy that utilize the centroids and widths for a restricted class of fixed-spin configurations, such as Nvariant Planck's over 2piomega excitations, one can calculate very accurately level densities free of spurious states. The approach is applicable to other fermion and boson systems trapped by an oscillator potential.

Threshold and channel interaction in cochlear implant users: Evaluation of the tripolar electrode configuration

The efficacy of cochlear implants is limited by spatial and temporal interactions among channels. This study explores the spatially restricted tripolar electrode configuration and compares it to bipolar and monopolar stimulation. Measures of threshold and channel interaction were obtained from nine subjects implanted with the Clarion HiFocus-I electrode array. Stimuli were biphasic pulses delivered at 1020 pulses/s. Threshold increased from monopolar to bipolar to tripolar stimulation and was most variable across channels with the tripolar configuration. Channel interaction, quantified by the shift in threshold between single- and two-channel stimulation, occurred for all three configurations but was largest for the monopolar and simultaneous conditions. The threshold shifts with simultaneous tripolar stimulation were slightly smaller than with bipolar and were not as strongly affected by the timing of the two channel stimulation as was monopolar. The subjects' performances on clinical speech tests were correlated with channel-to-channel variability in tripolar threshold, such that greater variability was related to poorer performance. The data suggest that tripolar channels with high thresholds may reveal cochlear regions of low neuron survival or poor electrode placement.

Geometry and Control of Human Eye Movements

In this paper, we study the human oculomotor system as a simple mechanical control system. It is a well known physiological fact that all eye movements obey Listing's law, which states that eye orientations form a subset consisting of rotation matrices for which the axes are orthogonal to the normal gaze direction. First, we discuss the geometry of this restricted configuration space (referred to as the Listing space). Then we formulate the system as a simple mechanical control system with a holonomic constraint. We propose a realistic model with musculotendon complexes and address the question of controlling the gaze. As an example, an optimal energy control problem is formulated and numerically solved

Optical and Photophysical Properties of Indolocarbazole Derivatives

We present a study of the optical and photophysical properties of five ladder indolo[3,2-b]carbazoles, namely, M1, M2, M3, M4, and M5. The ground-state optimized structures were obtained by B3LYP/6-31G* density functional theory (DFT) calculations, whereas the optimization (relaxation) of the first singlet excited electronic state (S1) was performed using the restricted configuration interaction (singles) (RCIS/6-31G*) approach. The excitation to the S1 state does not cause important changes in the geometrical parameters of the compounds, as corroborated by the small Stokes shifts. The excitation and emission energies have been obtained by employing the time-dependent density functional theory (TDDFT). For all the compounds, excitation to the S1 state is weakly allowed, whereas the S2 <-- S0 electronic transition of each oligomer possesses a much larger oscillator strength. The absorption and fluorescence spectra of the compounds have been recorded in chloroform. A reasonable agreement is obtained between TDDFT vertical transition energies and the (0,0) absorption and fluorescence bands. On one hand, the pattern of the aliphatic side chains does not affect the absorption and fluorescence maxima of the compounds. On the other hand, the replacement of aliphatic chains by phenyl or thiophene rings induces hypsochromic shifts in the absorption and fluorescence spectra. Finally, the fluorescence quantum yield and lifetime of the compounds in chloroform have been obtained. From these data, the radiative and nonradiative rate constants of the deactivation of the S1 state have been determined.

Noise-enhanced Fisher information in parallel arrays of sensors with saturation

This paper investigates stochastic resonance in parallel arrays of uncoupled saturating devices. The Fisher information is used to demonstrate the possibility of noise improved parameter estimation for arbitrary parametric signals. Especially, it is shown that improvement by noise always occurs in these arrays, for any configuration of the input signal, even in optimal configuration. The results contribute to establish stochastic resonance in parallel uncoupled arrays as a general mechanism of enhancement by noise, which can occur in wide classes of nonlinearities and for various information processing tasks. It can supplement other mechanisms of stochastic resonance that take place in isolated nonlinearities but generally in restricted configurations of the input signal.

Patient-specific bronchoscopy visualization through BRDF estimation and disocclusion correction

This paper presents an image-based method for virtual bronchoscope with photo-realistic rendering. The technique is based on recovering bidirectional reflectance distribution function (BRDF) parameters in an environment where the choice of viewing positions, directions, and illumination conditions are restricted. Video images of bronchoscopy examinations are combined with patient-specific three-dimensional (3-D) computed tomography data through two-dimensional (2-D)/3-D registration and shading model parameters are then recovered by exploiting the restricted lighting configurations imposed by the bronchoscope. With the proposed technique, the recovered BRDF is used to predict the expected shading intensity, allowing a texture map independent of lighting conditions to be extracted from each video frame. To correct for disocclusion artefacts, statistical texture synthesis was used to recreate the missing areas. New views not present in the original bronchoscopy video are rendered by evaluating the BRDF with different viewing and illumination parameters. This allows free navigation of the acquired 3-D model with enhanced photo-realism. To assess the practical value of the proposed technique, a detailed visual scoring that involves both real and rendered bronchoscope images is conducted.

Ab initio calculation of P, T-odd interaction constant in BaF: a restricted active space configuration interaction approach

A fully relativistic restricted active space (RAS) configuration interaction (CI) approach is employed to compute the P, T-odd interaction constant Wd of the ground 2Σ state of BaF. The present calculation estimates Wd = −0.352 × 1025 Hz/e-cm. We also report the dipole moment μe of the ground state of BaF which is in good agreement with experiment.