A random-sampling high dimensional model representation neural network for building potential energy surfaces

We combine the high dimensional model representation (HDMR) idea of Rabitz and co-workers [J. Phys. Chem. 110, 2474 (2006)] with neural network (NN) fits to obtain an effective means of building multidimensional potentials. We verify that it is possible to determine an accurate many-dimensional potential by doing low dimensional fits. The final potential is a sum of terms each of which depends on a subset of the coordinates. This form facilitates quantum dynamics calculations. We use NNs to represent HDMR component functions that minimize error mode term by mode term. This NN procedure makes it possible to construct high-order component functions which in turn enable us to determine a good potential. It is shown that the number of available potential points determines the order of the HDMR which should be used.     

Polar solvation and solvation dynamics in supercritical CHF3: Results from experiment and simulation

Solvation dynamics of the probe trans-4-(dimethylamino)-4'-cyanostilbene (DCS) have been measured in supercritical fluoroform at 310 K (1.04 Tc) and solvent densities over the range 1.4-2.0 rho(c) using optical Kerr-gated emission spectroscopy. Steady-state measurements and computer simulations of this and the related system coumarin 153 (C153) in fluoroform are used to help interpret the observed dynamics. The solvent contribution to the Stokes shift of DCS is estimated to be 2300 +/- 400 cm(-1) and nearly density independent over the range (0.7-2.0)rho(c). Spectral response functions are bimodal and can be fit to biexponential functions having time constants of approximately 0.5 ps (85%) and 3-10 ps (15%) over the observable range ((1.4-2.0)rho(c)). Computer simulations based on a 2-site model of fluoroform and assuming an electrostatic solvation mechanism appear to properly account for the magnitude and weak density dependence of the Stokes shifts but predict much faster solvation than is observed. Possible reasons for the discrepancy are discussed.     

Is the future universe singular: Dark matter versus modified gravity?

The fundamental problem of the occurrence/removal of finite-time future singularity in the universe evolution for coupled Dark Energy (DE) is addressed. It is demonstrated the existence of the (instable or local minimum) de Sitter space solution which may cure the Type II or Type IV future singularity for DE coupled with DM as the result of tuning the initial conditions. In case of phantom DE, the corresponding coupling may help to resolve the coincidence problem but not the Big Rip (Type I) singularity issue. We show that modified gravity of special form or inhomogeneous DE fluid may offer the universal scenario to cure the Type I, II, III or IV future singularity of coupled (fluid or scalar) DE evolution.     

Influence of Cholesterol on Molecular Motions in Spin-Labeled Lipid Bilayers Observed by Stimulated ESE

Electron spin echo (ESE) study was performed for spin-labeled lipids 1-palmitoyl-2-stearoyl-(5-d)-sn-glycero-3-phosphocholine in 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine phospholipid bilayer. Recently (Isaev and Dzuba in J Phys Chem B 112:13285–13291, 2008), three-pulse stimulated ESE was shown to be sensitive to two types of orientational motion of spin labels in phospholipid bilayers at low temperatures (~100–150 K). The first one is fast stochastic libration, with correlation time on the nanosecond time scale. The second one is slow rotational motion, developing on the accessible for measurements microsecond time scale in a small range of reorientation angles, ~0.1°–1°. These two types of motions may be easily discriminated by dependences of the echo decay rates on the time delays between the pulses. The presence of cholesterol in lipid bilayers is found to suppress remarkably rotational motions, while on the contrary stochastic librations seem to become somewhat enhanced. These results evidence that cholesterol increases the long-time stability of lipid orientations in the bilayer, with simultaneous increase of fast fluctuations of these orientations. The former may be related to the known condensing effect of cholesterol and to raft formations, while the latter to the ordering effect.     

Spatial light modulator as a reconfigurable intracavity dispersive element for tunable lasers

An improved approach for narrow-band wavelength selection in tunable lasers is described. To provide the tunability, a reconfigurable diffractive optical element (DOE) based on a programmable spatial light modulator (PSLM) is applied. With a proper choice of the phase transfer function of the PSLM, the device can be used as a dispersive intra-cavity component for precise tuning within the lasing spectral band of a solid-state dye laser. The suggested design allows avoiding the mechanical movement of any cavity components. The tunability performance and simulation are demonstrated using the Fourier optics method.     

A theoretical-spectroscopy, ab initio-based study of the electronic ground state of SbH3

For the stibine isotopologue , we report improved theoretical calculations of the vibrational energies below 8000 cm⁻¹ and simulations of the rovibrational spectrum in the 0-8000 cm⁻¹ region. The calculations are based on a refined ab initio potential energy surface and on a new dipole moment surface obtained at the coupled cluster CCSD(T) level. The theoretical results are compared with the available experimental data in order to validate the ab initio surfaces and the TROVE computational method [Yurchenko SN, Thiel W, Jensen P. J Mol Spectrosc 2007;245:126-40] for calculating rovibrational energies and simulating rovibrational spectra of arbitrary molecules in isolated electronic states. A number of predicted vibrational energies of are provided in order to stimulate new experimental investigations of stibine. The local-mode character of the vibrations in stibine is demonstrated through an analysis of the results in terms of local-mode theory.     

Control of octahedral tilts and magnetic properties of perovskite oxide heterostructures by substrate symmetry

Perovskite transition-metal oxides are networks of corner-sharing octahedra whose tilts and distortions are known to affect their electronic and magnetic properties. We report calculations on a model interfacial structure which avoids chemical influences and show that the symmetry mismatch imposes an interfacial layer with distortion modes that do not exist in either bulk material, creating new interface properties driven by symmetry alone. Depending on the resistance of the octahedra to deformation, the interface layer can be as small as one unit cell or extend deep into the thin film.     

Quality control of coatings with the help of local electrochemical analysis

Local electrochemical analysis with a pressed-on electrochemical cell is suggested for the estimation of the quality of coatings protecting the surface of materials, for the detection of different defects and for the control of the thickness and composition of coatings. The suggested local electrochemical analysis allows the determination of the throwing power of the electrolytes used in electrodepositions. Received: 8 December 1997 / Accepted: 21 August 1998