Nonzero Intensities Research Articles

Infrared Spectra of Protonated Water Clusters, H+(H2O)4, in Eigen and Zundel Forms Studied by Vibrational Quasi-Degenerate Perturbation Theory

The infrared spectrum of H+(H2O)4 recently observed in a wide spectral range has shown a series of bands in a range of 1700-2500 cm-1, which can not be understood by the standard harmonic normal mode analysis. Here, we theoretically investigate the origin of these bands with a focus on (1) the possibility of coexistence of multiple isomers in the Eigen [H3O+(H2O)3] and Zundel [H5O2+(H2O)2] forms and (2) the effect of anharmonic coupling that gives rise to nonzero intensities for overtones and combination bands. Anharmonic vibrational calculations are carried out for the Eigen and Zundel clusters by the second-order vibrational quasi-degenerate perturbation theory (VQDPT2) based on optimized coordinates. The anharmonic potential energy surface and the dipole moment surfaces are generated by a multiresolution approach combining one-dimensional (1D) grid potential functions derived from CCSD(T)-F12, 2D and 3D grid potential functions derived from B3LYP for important coupling terms, and a quartic force field derived from B3LYP for less important terms. The spectrum calculated for the Eigen cluster is in excellent agreement with the experiment, assigning the bands in the range of 1700-2500 cm-1 to overtones and combination bands of a H3O+ moiety in line with recent reports [ J. Phys. Chem. A 2015 , 119 , 9425 ; Science 2016 , 354 , 1131 ]. On the other hand, characteristic OH stretching bands of the Zundel cluster is found to be absent in the experimental spectrum. We therefore conclude that the experimental spectrum originates solely from the Eigen cluster. Nonetheless, the present calculation for the Eigen cluster poorly reproduces a band observed at 1765 cm-1. A possible nature of this band is discussed.

Nonlinear spike-and-slab sparse coding for interpretable image encoding.

Sparse coding is a popular approach to model natural images but has faced two main challenges: modelling low-level image components (such as edge-like structures and their occlusions) and modelling varying pixel intensities. Traditionally, images are modelled as a sparse linear superposition of dictionary elements, where the probabilistic view of this problem is that the coefficients follow a Laplace or Cauchy prior distribution. We propose a novel model that instead uses a spike-and-slab prior and nonlinear combination of components. With the prior, our model can easily represent exact zeros for e.g. the absence of an image component, such as an edge, and a distribution over non-zero pixel intensities. With the nonlinearity (the nonlinear max combination rule), the idea is to target occlusions; dictionary elements correspond to image components that can occlude each other. There are major consequences of the model assumptions made by both (non)linear approaches, thus the main goal of this paper is to isolate and highlight differences between them. Parameter optimization is analytically and computationally intractable in our model, thus as a main contribution we design an exact Gibbs sampler for efficient inference which we can apply to higher dimensional data using latent variable preselection. Results on natural and artificial occlusion-rich data with controlled forms of sparse structure show that our model can extract a sparse set of edge-like components that closely match the generating process, which we refer to as interpretable components. Furthermore, the sparseness of the solution closely follows the ground-truth number of components/edges in the images. The linear model did not learn such edge-like components with any level of sparsity. This suggests that our model can adaptively well-approximate and characterize the meaningful generation process.

Iterative 3D projection reconstruction of 23 Na data with an 1 H MRI constraint

To increase the signal-to-noise ratio (SNR) and to reduce artifacts in non-proton magnetic resonance imaging (MRI) by incorporation of a priori information from (1) H MR data in an iterative reconstruction. An iterative reconstruction algorithm for 3D projection reconstruction (3DPR) is presented that combines prior anatomical knowledge and image sparsity under a total variation (TV) constraint. A binary mask (BM) is used as an anatomical constraint to penalize non-zero signal intensities outside the object. The BM&TV method is evaluated in simulations and in MR measurements in volunteers. In simulated BM&TV brain data, the artifact level was reduced by 20% while structures were well preserved compared to gridding. SNR maps showed a spatially dependent SNR gain over gridding reconstruction, which was up to 100% for simulated data. Undersampled 3DPR (23) Na MRI of the human brain revealed an SNR increase of 29 ± 7%. Small anatomical structures were reproduced with a mean contrast loss of 14%, whereas in TV-regularized iterative reconstructions a loss of 66% was found. The BM&TV algorithm allows reconstructing images with increased SNR and reduced artifact level compared to gridding and performs superior to an iterative reconstruction using an unspecific TV constraint only.

Nonparaxial propagation of an elegant Laguerre-Gaussian beam orthogonal to the optical axis of a uniaxial crystal

Analytical expressions of the nonparaxial propagation of even and odd elegant Laguerre-Gaussian beams orthogonal to the optical axis of a uniaxial crystal are derived. The intensity distributions of even and odd elegant Laguerre-Gaussian beams and their three components propagating in uniaxial crystals orthogonal to the optical axis are illustrated by numerical examples. Even though one of the two transversal components of even and odd elegant Laguerre-Gaussian beams in the input plane is set to be zero, this transversal and the longitudinal components have nonzero intensities and cannot be neglected upon propagation inside the uniaxial crystal. The evolution laws of even and odd elegant Laguerre-Gaussian beams propagating in uniaxial crystals orthogonal to the optical axis are also demonstrated. The intensity distributions of even and odd elegant Laguerre-Gaussian beams can be modulated by the uniaxial crystal, which is beneficial to the some applications involving in the special beam profile.

Downscaling of Short-Term Precipitation from Regional Climate Models for Sustainable Urban Planning

A framework for downscaling precipitation from RCM projections to the high resolutions in time and space required in the urban hydrological climate change impact assessment is outlined and demonstrated. The basic approach is that of Delta Change, developed for both continuous and event-based applications. In both cases, Delta Change Factors (DCFs) are calculated which represent the expected future change of some key precipitation statistics. In the continuous case, short-term precipitation from climate projections are analysed in order to estimate DCFs associated with different percentiles in the frequency distribution of non-zero intensities. The DCFs may then be applied to an observed time series, producing a realisation of a future time series. The event-based case involves downscaling of Intensity-Duration-Frequency (IDF) curves based on extreme value analysis of annual maxima using the Gumbel distribution. The resulting DCFs are expressed as a function of duration and frequency (i.e., return period) and may be used to estimate future design storms. The applications are demonstrated in case studies focusing on the expected changes in short-term precipitation statistics until 2100 in the cities of Linz (Austria) and Wuppertal (Germany). The downscaling framework is implemented in the climate service developed within the EU-project SUDPLAN.

IONIS: Approximate atomic photoionization intensities

A program to compute relative atomic photoionization cross sections is presented. The code applies the output of the multiconfiguration Dirac–Fock method for atoms in the single active electron scheme, by computing the overlap of the bound electron states in the initial and final states. The contribution from the single-particle ionization matrix elements is assumed to be the same for each final state. This method gives rather accurate relative ionization probabilities provided the single-electron ionization matrix elements do not depend strongly on energy in the region considered. The method is especially suited for open shell atoms where electronic correlation in the ionic states is large. Program summary Program title: IONIS Catalogue identifier: AEKK_v1_0 Program summary URL: http://cpc.cs.qub.ac.uk/summaries/AEKK_v1_0.html Program obtainable from: CPC Program Library, Queenʼs University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 1149 No. of bytes in distributed program, including test data, etc.: 12 877 Distribution format: tar.gz Programming language: Fortran 95 Computer: Workstations Operating system: GNU/Linux, Unix Classification: 2.2, 2.5 Nature of problem: Photoionization intensities for atoms. Solution method: The code applies the output of the multiconfiguration Dirac–Fock codes Grasp92 [1] or Grasp2K [2], to compute approximate photoionization intensities. The intensity is computed within the one-electron transition approximation and by assuming that the sum of the single-particle ionization probabilities is the same for all final ionic states. Restrictions: The program gives nonzero intensities for those transitions where only one electron is removed from the initial configuration(s). Shake-type many-electron transitions are not computed. The ionized shell must be closed in the initial state. Running time: Few seconds for a large problem with a few thousand configurations.

Control of dipolar relaxation in external fields

We study dipolar relaxation in both ultra-cold thermal and Bose-condensed chromium atom gases. We show three different ways to control dipolar relaxation, making use of either a static magnetic field, an oscillatory magnetic field, or an optical lattice to reduce the dimensionality of the gas from 3D to 2D. Although dipolar relaxation generally increases as a function of a static magnetic field intensity, we find a range of non-zero magnetic field intensities where dipolar relaxation is strongly reduced. We use this resonant reduction to accurately determine the S=6 scattering length of chromium atoms: $a_6 = 103 \pm 4 a_0$. We compare this new measurement to another new determination of $a_6$, which we perform by analysing the precise spectroscopy of a Feshbach resonance in d-wave collisions, yielding $a_6 = 102.5 \pm 0.4 a_0$. These two measurements provide by far the most precise determination of $a_6$ to date. We then show that, although dipolar interactions are long-range interactions, dipolar relaxation only involves the incoming partial wave $l=0$ for large enough magnetic field intensities, which has interesting consequences on the stability of dipolar Fermi gases. We then study ultra-cold chromium gases in a 1D optical lattice resulting in a collection of independent 2D gases. We show that dipolar relaxation is modified when the atoms collide in reduced dimensionality at low magnetic field intensities, and that the corresponding dipolar relaxation rate parameter is reduced by a factor up to 7 compared to the 3D case. Finally, we study dipolar relaxation in presence of radio-frequency (rf) oscillating magnetic fields, and we show that both the output channel energy and the transition amplitude can be controlled by means of rf frequency and Rabi frequency.

Reduction of peak-locking errors produced by Gaussian sub-pixel interpolation in cross-correlation digital particle image velocimetry

Cross-correlation, whether by a direct or spectral calculation, remains the most common analysis method for digital particle image velocimetry. Gaussian sub-pixel interpolation likewise remains a common method for achieving measurement resolution at fractional pixel displacements. Specific to the use of Gaussian sub-pixel interpolation, the particular form of the cross-correlation function is shown to affect the peak-locking or mean-bias error that increases the probability of the measurement occurring at integer pixel displacements. The main effect is from nonzero mean image intensities that cause a shift in the amplitude of the cross-correlation function away from zero and introduce a bias error into the Gaussian interpolation formula. A simple, but not universal, method of reducing this error is to use the covariance function, often calculated in a single step after calculation of the cross-correlation function. This effectively shifts the amplitude back toward zero and reduces the bias that originates in the interpolation formula. Examples are shown using synthetic particle image simulations and experimental water jet PIV images from the 2003 PIV Challenge.

Stochastic resonance in the mechanoelectrical transduction of hair cells

In transducing mechanical stimuli into electrical signals, at least some hair cells in vertebrate auditory and vestibular systems respond optimally to weak periodic signals at natural, nonzero noise intensities. We understand this stochastic resonance by constructing a faithful mechanical model reflecting the hair cell geometry and described by a nonlinear stochastic differential equation. This Langevin description elucidates the mechanism of hair cell stochastic resonance while supporting the hypothesis that noise plays a functional role in hearing.

Excited State Properties of C6H6 and C6D6 Studied by Feynman Path Integral−ab Initio Simulations

The Feynman path integral Monte Carlo formalism has been combined with an ab initio configuration interaction approach in order to analyze the excited singlet states of the benzene isomers C6H6 and C6D6 under the conditions of thermal equilibrium. Electronic transition energies PIĒT and oscillator strength PIfosc, which have been sampled over large sets of nuclear configurations, are compared with single-configuration results ET, fosc. The latter set of quantities has been derived for the D6h energy minimum of benzene. The present quantum Monte Carlo simulations lead to a simple physical picture for the nonzero intensities of the transitions to the two lowest excited singlet states of the two benzene isomers. Under D6h conditions, the transitions to the 1B2u and 1B1u states are dipole-forbidden. The influence of the nuclear degrees of freedom on the excited-state properties of the two π rings up to room temperature is quantum driven. The quantum fluctuations of the nuclei on a potential energy surface wi...

Two-dimensional fluorescence correlation spectroscopy with modulated excitation.

Overlap of multiple states or multiple species in a chemical system often creates a congested fluorescence spectrum that is difficult to interpret. The resolution of component spectra is essential for the understanding of the structure and dynamics of such multicomponent systems. In this paper, two-dimensional fluorescence correlation spectroscopy (2D FCS) is presented for the dissection of component spectra using the time correlation function. In 2D FCS, the time response of fluorescence intensity is collected at various wavelengths upon an external perturbation. The time correlation function is evaluated between wavelengths. A two-dimensional fluorescence correlation spectrum, or a plot of the correlation intensity as a function of two wavelength axes, resolves the overall spectrum into component spectra. The characteristics of the two-dimensional time correlation function are demonstrated in the frequency domain fluorescence spectroscopy in which the sinusoidally modulated excitation provides the external perturbation. Using 2D FCS, fine vibronic structures of the component fluorescence emission spectra were completely resolved from a strongly overlapped one-dimensional mixture spectrum. The existence of multiple microenvironments of a probe molecule in a biological system is evidenced by nonzero asynchronous correlation intensities. The corresponding spectra are retrieved from correlation analysis. Unlike traditional resolution methods in fluorescence spectroscopy based on statistical fitting of fluorescence decays, 2D FCS can resolve species whose fluorescence decays are linked by the rate constants in chemical reactions and species displaying multiexponential decay kinetics.

Phase-space four stability in the cascaded parametric down-conversion

Four-photon correlated states in the scheme of two sequential parametric down-conversion processes coupled with the χ (3)-nonlinear self-phase modulation of the cavity modes are considered. The generation regimes of the modes are semiclassically analyzed. Above threshold bistable generation regime with two stable branches, which have definite nonzero intensities, as distinct from the most semiclassically bistable schemes is observed. Phase-space multistability of the cavity modes is investigated by the Wigner functions calculated on the quantum-jump simulations.

MAPPIT 2: Second Generation High-resolution Imaging at the AAT

AbstractInterferometric methods have been used at a number of observatories to improve the spatial resolution of large optical telescopes, approaching and in some cases reaching the diffraction limit. The principal methods used have been speckle interferometry and non-redundant masking (NRM). The MAPPIT (Masked APerture Plane Interference Telescope) instrument has been used for NRM observations at the 3·9 m Anglo-Australian Telescope. This paper describes a proposed instrument, MAPPIT 2, which would use a Shack-Hartmann wavefront sensor in parallel with an interferometer performing NRM or one-dimensional speckle interferometry. The inclusion of the data from the wavefront sensor will enhance the sensitivity of the instrument, especially for the imaging of relatively complex objects (those giving more than a few resolution elements with non-zero intensities). Limiting the instantaneous spatial resolution to one dimension allows available CCD detectors to operate with 100% duty cycle. Observations at a number of position angles allow two-dimensional images to be obtained.

New operational regimes of a CO2 laser with an intracavity saturable absorber

New operational regimes were achieved experimentally in a CO2 laser containing CH3OH vapour as an intracavity saturable absorber. In these regimes the time dependences of the intensities could be interpreted on the basis of heteroclinic orbits in the phase space around two, three, or more fixed unstable points with nonzero intensities.

Cosmic-Ray Transport and Acceleration. II. Cosmic Rays in Moving Cold Media with Application to Diffusive Shock Wave Acceleration

view Abstract Citations (69) References (26) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Cosmic-Ray Transport and Acceleration. II. Cosmic Rays in Moving Cold Media with Application to Diffusive Shock Wave Acceleration Schlickeiser, Reinhard Abstract We discuss the transport and acceleration of cosmic rays in a cold background medium that moves with the nonrelativistic (U/V much less than 1) bulk speed U(z) parallel to the ordered uniform magnetic field B0 = B0eZ with superposed Alfén plasma waves propagating parallel and/or antiparallel to B0. For a power-law dependence 1(K||)∝ K||-q, 1 < q < 4 of the power spectrum of magnetic irregularities on the parallel Alfvénic wavenumber K||, we calculate the respective Fokker-Planck coefficients Dμμ, Dμp, Dpp, and the implied transport parameters as the spatial diffusion coefficient κ(z, p), the momentum diffusion coefficient α2(z, p), and the rate of adiabatic deceleration α1(z, p) whose general relation to the Fokker-Planck coefficients has been established by Schlickeiser. A detailed discussion of the influence of the Alfvén wave's polarization state and propagation direction on the results is provided. The main results are the following: 1. Waves of only one polarization state (left-hand or right-hand) propagating in one or both directions lead to a whole resonance gap interval where Dμμ = Dμp = Dpp = 0, implying infinitely large spatial and momentum diffusion coefficients. 2. With waves of both polarization states traveling in only one direction (either forward [parallel] to B0 or backward [antiparallel] to B0 in the fluid's rest frame), a resonance gap occurs at one point in μ-space leading to an infinitely large spatial diffusion coefficient for q ≥ 2. Only in this unphysical case (κ = ∞!) the cosmic- ray transport equation is of first order in momentum. 3. With waves of both polarization states traveling with equal or different but nonzero intensities in both directions, no resonance gaps occur, and the full transport equation (κ ≠ # 0, α1 ≠ 0, α2 ≠ 0) results. 4. In the case of right-hand and left-hand waves propagating with equal intensity in both directions, the mean free path of particles and the cosmic-ray anisotropy are calculated for different values of the power spectrum spectral index q. Unlike earlier work, finite expressions result for q ≥ 2. For q ≥ 2, the anisotropy and the mean free path are enhanced by a factor (V/U)q-2 as compared to the case q <2. The anisotropy consists of two parts: one contribution results from the momentum gradient of the isotropic distribution function (Compton-Getting effect), the second contribution is related to pitch-angle scattering and the spatial gradient of the isotropic distribution function. Within the confines of quasi-linear theory the cosmic-ray transport equations contains spatial diffusion and convection as well as momentum diffusion and convection terms. The widely used transport equation without momentum diffusion can be reproduced only in the unrealistic case of waves moving only in one direction, but this case would imply an infinitely large spatial diffusion coefficient for q ≥ 2 due to a resonance gap at μR = (U±VA)/V. Finally, two astrophysical applications of the derived transport equation are considered: (i) cosmic-ray transport and acceleration in the dynamical interstellar medium, and (ii) steady diffusive acceleration of energetic particles at astrophysical shock waves. In the latter case the full transport equation is solved analytically for a special spatial variation of the spatial diffusion coefficient but for any given velocity pattern. It is shown that the resulting particle momentum spectrum is an infinite superposition of power-law spectra approaching a single power law at momenta large compared to the injection momentum. Publication: The Astrophysical Journal Pub Date: January 1989 DOI: 10.1086/167010 Bibcode: 1989ApJ...336..264S Keywords: COSMIC RAYS: GENERAL; PARTICLE ACCELERATION; PLASMAS; POLARIZATION; SHOCK WAVES; WAVE MOTIONS full text sources ADS | Related Materials (1) Part 1: 1989ApJ...336..243S

Quantum and quasiclassical lasing regimes

The Scully-Lamb quantum-mechanical laser theory is generalized to the case of active atoms situated in superposed upper and lower active states. In this case, a laser emits a field of nonzero average intensity. If there is no interference between the active levels of the active atoms, a state of the field may be found for which the average quantum-mechanical intensity is zero. An investigation is made of pumping in a molecular oscillator and in gas lasers. It is shown in which cases pumping causes interference between the active levels of the active atoms. An interference experiment which can distinguish between fields having zero and nonzero average intensities is discussed.

Macroscopic Quantum Fluctuations and First-Order Phase Transition in a Laser

A homogeneously broadened two-mode ring laser has two metastable states in which one or the other mode intensity is zero. Quantum fluctuations cause the system to switch spontaneously, and at random times, between these states. The probability distribution of the light intensity of one laser mode has been measured, and found to exhibit two completely resolved peaks at zero and nonzero intensities, as predicted. This confirms the existence of a first-order laser phase transition.

Spin density and bonding in the CoCl4 2? ion in Cs3CoCl5. Part 1. Magnetic structure factors from polarised neutron diffraction

The magnetic structure factors of 101 unique hkl reflections of Cs3CoCl5 have been measured at 4.2 K with a magnetic field of 4.6 T along the crystal c axis. A further 110 unique reflections with a magnetic field of 1.5 T along the a axis have also been obtained. A statistical analysis of the errors in the data sets has been made so that the reliability of their interpretation in models of chemical interest may be assessed. Ten of the c-data reflections, all based on low nuclear structure factors, were rejected on statistical grounds. The major sources of error in the data were found to be extinction and multiple scattering, with counting statistics and machine instability playing a lesser role. The two data sets agree well, no reflection exceeding 3σ from its scaled value. Using a free-ion Co2+ magnetic form factor, the data are reproduced to within 5% by a single spherical model of spin occupation 3d2.4x0.6, where x represents orbitals much more diffuse than Co2+ 3d functions. That is, the data indicate that ca. 80% of the spin is located in Co2+ 3d-like orbitals and 20% is in more diffuse orbitals, whether cobalt-centred or delocalised onto the chlorine ligand atoms. Covalence is indicated by the non-zero intensities of the l-odd data. Small, but statistically significant deviations from the above model are expected to be correlated with, for example, the concentration of the Co2+ 3d spin into the t2 orbitals and the details of the distribution of the diffuse ‘x’ population.

Semiclassical theory of optical rotation near resonance absorption

A recently presented technique is used to derive expressions for the dynamical polarizability α and the optical rotation parameter β which do not diverge at resonant absorption frequencies and nonzero light intensities. The effective α and β are intensity dependent but yield the usual divergent forms in the limit of zero intensity.

ChemInform Abstract: PLATINUM(I) COMPLEXES, CRYSTAL STRUCTURE OF BIS(TETRA‐N‐PROPYLAMMONIUM)BIS(CARBONYLDICHLOROPLATINATE(I))

Chemischer InformationsdienstVolume 6, Issue 43 Organoelement Compounds ChemInform Abstract: PLATINUM(I) COMPLEXES, CRYSTAL STRUCTURE OF BIS(TETRA-N-PROPYLAMMONIUM)BIS(CARBONYLDICHLOROPLATINATE(I)) ANTHONY MODINOS, ANTHONY MODINOSSearch for more papers by this authorPETER WOODWARD, PETER WOODWARDSearch for more papers by this author ANTHONY MODINOS, ANTHONY MODINOSSearch for more papers by this authorPETER WOODWARD, PETER WOODWARDSearch for more papers by this author First published: October 28, 1975 https://doi.org/10.1002/chin.197543415AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume6, Issue43October 28, 1975 RelatedInformation