Indirect carbon–carbon spin–spin couplings across one,two and three bonds in pyridine and diazine systems: experiment and theory

An excellent linear correlation is found between a large body of experimental spin–spin carbon–carbon couplings, J(CC), across one, two and three bonds in pyridine and diazine ring systems and the corresponding B3PW91/6‐311++G(d,p)//B3PW91/6‐311++G(d,p) computations. The correlation does not differ significantly from the simplest relationship possible, J(CC)_exp. = J(CC)_calcd., within a small and random spread of about 1 Hz. There are 276 experimental values considered, and 124 out of these are new and come from the present work. The aromatic carbon–carbon couplings vary from ?7.6 through +78.5 Hz. It is shown that the correlation provides a reliable tool for predictions of the signs of aromatic J(CC)'s even if the magnitudes of the latter are of the order of 1 Hz. It is demonstrated, for the first time, that the relatively weak ² J(CC) couplings, in the heteroaromatic systems studied, can bear either sign and span a considerable range of about 11 Hz. The character of the correlation indicates that rovibronic effects on aromatic J(CC)'s and those of nuclear motions on aromatic J(CC)'s are practically negligible. All of this is in a perfect agreement with our recent extensive studies on aromatic J(CC)'s in analogous benzene ring system. Substituent effects on the aromatic J(CC)'s turn out to be significant not only for ¹J(CC)'s but also for most of ³J(CC)'s and ² J(CC)'s, and the computation neatly reciprocates these trends. Copyright © 2008 John Wiley & Sons, Ltd.     

Ion Mobility Measurements of Carbon Tetrachloride

Abstract

The ion mobility and drift velocity of carbon tetrachloride have been measured at various ratios of E/P_o, ranging from 1.0 to 9 volts/ (cm-Torr). The technique employed for these measurements utilizes a polonium alpha particle source which serves both as the source for ionization as well as the means for producing a reference pulse from a solid state silicon barrier detector. The thermal electrons which are produced are readily captured by carbon tetrachloride and the resulting negative ion, assumed to be CC1₄ ^?, is detected by means of a proportional counter located at the end of the drift path. The zero field reduced mobility obtained for CC1₄ ^?was 0.42 cm²/(volt-sec). The nature of the ionic species is explained in terms of the quantum mechanical theory of ionic mobility as put forth by Dalgarno.     

Dispersive effects in the excitation of the ground-state rotational band of deformed nuclei by medium energy protons

The effects of long-range correlations on high-energy elastic and inelastic proton-nucleus scattering are investigated using a coupled-channel (CC) formalism where dispersive effects, i.e. virtual excitations and de-excitations of the nucleus during the scattering process, are taken into account. When treated to all orders, this CC approach is completely equivalent to the Glauber multiple scattering model, whereas it reduces to the DWIA when the coupling between channels is neglected. In ¹²C, we compare the results of the CC formalism where only a finite number of collective channels are explicitly treated with those obtained in a full Glauber calculation. This permits one to get a clear appreciation of the importance of the various sequential processes. In addition it sheds light on the influence of those channels which have been omitted. This CC approach is then applied to investigate the excitation of the ground-state rotational band in the deformed samarium isotopes, ¹⁵²Sm and ¹⁵⁴Sm, by l GeV protons. It appears that the elastic scattering on deformed nuclei is only weakly affected by dispersive corrections, at least for momentum transfer less than 2 fm^?1. In contrast, inelastic scattering to the ²⁺, 4⁺ and 6⁺ rotational states proceeds not only by direct transitions, but includes also crucial multi-step contributions which strongly affect the differential cross sections.     

High-intensity ultrasound pretreatment influence on whey protein isolate and its use on complex coacervation with kappa carrageenan: Evaluation of selected functional properties

The aim of this work was to evaluate the influence of high-intensity ultrasound (HIUS) treatment on whey protein isolate (WPI) molecular structure as a previous step for complex coacervation (CC) with kappa-carrageenan (KC) and its influence on CC functional properties. Protein suspension of WPI (1% w/w) was treated with an ultrasound probe (24 kHz, 2 and 4 min, at 50 and 100% amplitude), non HIUS pretreated WPI was used as a control. Coacervation was achieved by mixing WPI and KC dispersions (10 min). Time and amplitude of the sonication treatment had a direct effect on the molecular structure of the protein, FTIR-ATR analysis detected changes on pretreated WPI secondary structure (1600–1700 cm⁻¹) after sonication. CC electrostatic interactions were detected between WPI positive regions, KC sulfate group (1200–1260 cm⁻¹), and the anhydrous oxygen of the 3,6 anhydro-D-galactose (940–1066 cm⁻¹) with a partial negative charge. After ultrasound treatment, a progressive decrease in WPI particle size (nm) was detected. Rheology results showed pseudoplastic behavior for both, KC and CC, with a significant change on the viscosity level. Further, volume increment, stability, and expansion percentages of CC foams were improved using WPI sonicated. Besides, HIUS treatment had a positive effect on the emulsifying properties of the CC, increasing the time emulsion stability percentage. HIUS proved to be an efficient tool to improve functional properties in WPI-KC CC.     

Pressure dependence of electron scattering by DX centres in GaAs and AlGaAs

Abstract

The electron mobility of heavily n-dopped GaAs and AlGaAs increases rapidly with applied hydrostatic pressure as carriers are trapped at DX centres. This has been taken as evidence against the Chadi and Chang (CC) negative charge state model of the DX centre. We argue that DX^? centres are formed close to d⁺ centres in highly doped samples, and that the mobility data is in fact fully consistent with the CC model, when such dipole-like correlations are included.     

The effects of crystal field on Nd(su3+) in the laser host YVO(in4)

The behavior of Nd³⁺ in the laser host yttrium orthovanadate, YVO₄, has been investigated with respect to its absorption spectra By taking into consideration intermediate coupling, a new set of crystal field parameters is obtained which gives a lower rms deviation between observed and calculated energies for 25 of the 26 levels of the ⁴I term than that reported earlier using a pure Russell-Saunders basis. The computed g-factors are also in good accord with resonance results Vanous quantities including the nuclear hyperfine parameters have been calculated Nuclear properties which depend on the crystal field are predicted for both the isotopes of Nd     

Coupling the Lorentz Integral Transform (LIT) and the Coupled Cluster (CC) Methods: A Way Towards Continuum Spectra of “Not-So-Few-Body” Systems

Here we summarize how the LIT and CC methods can be coupled, in order to allow for ab initio calculations of reactions in medium mass nuclei. Results on ¹⁶O are reviewed and preliminary calculations on ⁴⁰Ca are presented.     

On electromagnetic fields in the Hamiltonian description of continua

The group theoretical structure of an infinite dimensional Hamiltonian formulation of continuum mechanics is studied using as an example the Maxwell-Vlasov system. In contrast to earlier works, electromagnetism and charged matter are coupled via Poisson brackets without using the vector potential. The charged matter is described on the group of canonical transformations on R⁶ and we show that its evolution arises from a symplectic structure, modified by the magnetic field. The configurations of the electromagnetic field must be constrained by the physical requirement of the Gauss law. With the energy-functional taken as a Hamiltonian this leads - even for relativistic particles - to the well-known equations of motion.     

Tensor interactions and polarization phenomena in heavy-ion scattering

Elastic and inelastic scattering of ⁷Li by ⁵⁸Ni at E_lab = 14.2 and 20.3 MeV is investigated theoretically, special emphasis being laid on polarization phenomena. A parameter-independent study shows second-rank tensor interactions to be the main origin of tensor analyzing powers for both elastic and inelastic scattering. Coupled-channel (CC) calculations using cluster-folding interactions which include the tensor terms are found to be successful in reproducing the data for cross sections and vector and tensor analyzing powers, when projectile excitation effects are sufficiently taken into account. Scattering of ⁶Li by ⁵⁸Ni at E_lab = 20.0 MeV is also investigated by the CC calculation, where successes similar to the ⁷Li case are obtained in understanding experimental data.     

The characteristics and properties of optimised amorphous silicon field effect transistors

A series of experiments aimed at improving the performance of amorphous silicon field effect transistors has been carried out. The dc and dynamic characteristics of the optimised devices are described. Stable devices capable of ON-currents of the order of 100 μA with OFF-currents ?10^?11 A can be fabricated which could, in principle, be used to address more than 1000 lines of a liquid crystal display. The properties of the highly conducting ON-state channel have also been studied. The field effect mobility, 0.3 cm² V^?1 s^?1 at room temperature, has an activation energy of 0.1 eV at the higher gate voltages. The possible reasons for the improvement in performance over earlier devices are discussed.     

Energy fluxes in helical magnetohydrodynamics and dynamo action

Renormalized viscosity, renormalized resistivity, and various energy fluxes are calculated for helical magnetohydrodynamics using perturbative field theory. The calculation is of firstorder in perturbation. Kinetic and magnetic helicities do not affect the renormalized parameters, but they induce an inverse cascade of magnetic energy. The sources for the large-scale magnetic field have been shown to be (1) energy flux from large-scale velocity field to large-scale magnetic field arising due to non-helical interactions and (2) inverse energy flux of magnetic energy caused by helical interactions. Based on our flux results, a primitive model for galactic dynamo has been constructed. Our calculations yield dynamo time-scale for a typical galaxy to be of the order of 10⁸ years. Our field-theoretic calculations also reveal that the flux of magnetic helicity is backward, consistent with the earlier observations based on absolute equilibrium theory.     

EPR of orthorhombic Gd3+-M+ complexes in SrF2

In this paper we report new results of EPR experiments on orthorhombic Gd³⁺-M⁺ complexes (M = Na, K, Rb and Ag) in SrF₂. Special attention is payed to the second degree crystal field parameters B⁰₂ and B²₂ and a comparison with earlier results on corresponding complexes in CaF₂ and BaF₂ is made. We conclude that the main contributions to these crystal field parameters are of electrostatic nature.     

Molecular states in highly-excited 12Be and 10Be

Molecular resonances having the ⁶He+⁶He and ⁴He+⁶He structures, which have recently been observed in the highly excited ¹²Be and ¹⁰Be, respectively, are studied by the microscopic coupled-channels (CC) calculation in which excitations of the soft-dipole and quadrupole modes of the colliding ⁶He nuclei are taken into account in the Goldhaber-Teller model. The CC calculation predicts several molecular-rotational bands in the energy range of the observed resonances and the energies and spins of the calculated resonances agree well with the experimental data.     

Bremsstrahlung by neutral atomic nitrogen

We show that the strong absorption resonances in bremsstrahlung by electrons in the field of neutral nitrogen atoms predicted in an earlier paper⁽¹⁾ are removed by the inclusion of configuration interaction in continuum wave functions.     

High field domains in n-PbTe at 80 K

In contrast to earlier publications our measurements show, that travelling high field domains are responsible for the electric instability in n-type PbTe at 80 K (V_d = 2?3 × 10⁷ cm/sec). A transverse magnetic field lowers the threshold field strength of this instability. This effect is attributed to the Hall field shorting at the cathode, which causes a higher local electric field at opposite corners of the sample.     

Biasing effects on thallium and silver chlorides with dc/ac voltage

Comparison was made between crystals of thallium chloride and silver chloride on their biasing effects with dc/ac voltage. Previous reports say that, although their electrical conductivities are similar, the dominant charge carriers in the former are the Cl⁻ ions while the Ag⁺ ions in the latter. The present dc/ac study demonstrates the following: for thallium chloride, although Cl⁻ conduction may be dominant under low bias field, Tl⁺ conduction supercedes Cl⁻ conduction when the bias field is enhanced. For silver chloride, Ag⁺ conduction is overwhelming within wide temperature range, to cause easy dielectric breakdown on dc biasing. Concerning the extrinsic conductivity seen at temperatures below 60 °C (thallium chloride) or below 150 °C (silver chloride), it is ascribed to grain-boundary related electron conduction, not to grain-boundary related Tl⁺ or Ag⁺ conduction as reported earlier.     

Properties of advanced coupled-cluster Green's function

ABSTRACT

We present an extension of the analysis previously applied to the retarded part of the coupled cluster (CC) Green's function to its advanced part. In analogy to our earlier studies for the retarded part, we demonstrate that the advanced CC Green's function is expressed in terms of connected diagrams only, which is a direct consequence of algebraic form of equations satisfied by CC amplitudes. We also demonstrate that ω-derivatives of the advanced CC Green's function can be calculated analytically and can be expressed in terms of connected diagrams only. We analyse the structure of connected diagrams and the role of intermediate operators which satisfy electron affinity equation-of-motion CC-type conditions.     

Theoretical study of Ti0 and Pb+ centers in alkali halide and alkaline earth fluoride type crystals

A theoretical study has been carried out on the hfi of Pb⁺ defects in KCl, CaF₂ and BaF₂ using an earlier developed crystal field model. Experimental results can be explained in the same way as was done for Tl⁰ in KCl. However some parameters seem to have a less physical meaning than in the case of Tl⁰. A new method is in progress using the ASW band structure procedure in order to estimate genuine solid state effects. Preliminary results are encouraging.     

Hall constants and magnetoresistance in aluminium single crystals,studied by means of helicon resonances

The Hall coefficient and the transverse magnetoresistance in aluminium single crystals were determined from measurements on standing helicon waves, in the three main crystallographic directions [100], [110] and [111]. The magnetic fields ranged from 1 to 7T and the temperature from 4.2 to 20 K. A Legendy-type theory with parameters adapted to the separation of the satellites as measured at high fields gave good fittings over the whole field range. The Hall coefficients, determined in this work, decrease with magnetic field as mentioned in earlier publications, but are generally lower than those published previously for comparable field ranges.The transverse magnetoresistance as a function of temperature was determined from a continuous recording of the helicon response at resonance. The temperature dependent part of the resistivity varies according to a T³ law for all fields. The field dependence is close to linear, but indications of quadratic and saturation behaviour are also present.     

Raman Spectrum of Crystalline Pyrimidine

In an earlier work¹we have investigated an oriented crystal of pyrimidine at liquid nitrogen temperature using polarized infrared radiation. The static field effect for an A₂ mode (16a) and correlation field splitting for fourteen fundamentals have been observed¹. This paper reports the Raman spectrum of crystalline pyrimidine at liquid nitrogen temperature.