The role of elastic scattering analysis in studies of anodic oxidation

Résumé L'analyse par diffusion élastique peut détecter de microquantités à condition qu'elles soient concentrées dans des films minces. En outre, la méthode peut directement fournir des indications sur l'emplacement des éléments. Ces caractéristiques ont été mises à profit pour apporter un instrument utile à l'étude des processus d'oxydation.      

Ultra-low energy elastic scattering in a system of three He atoms

Differential Faddeev equations in total angular momentum representation are used for the first time to investigate ultra-low energy elastic scattering of a helium atom on a helium dimer. Six potential models of interatomic interaction are investigated. The results improve and extend the Faddeev equations based results known in literature. The employed method can be applied to investigation of different elastic and inelastic processes in three- and four-atomic weakly bounded systems below three-body threshold.     

Effective potential energy curves of H2 molecule evolving in a strong time‐dependent magnetic field

Evolution of hydrogen molecule, starting initially from its field‐free ground state, in a time‐dependent (TD) magnetic field of order 10¹¹ G is presented in a parallel internuclear axis and magnetic field‐axis configuration. Effective potential energy curves (EPECs), in terms of exchange and correlation energy, of the hydrogen molecule as a function of TD magnetic‐field strength, are analyzed through TD density functional computations based on a quantum fluid dynamics approach. The numerical computations are performed for internuclear separation R ranging from 0.1 to 14.0 a.u. The EPECs exhibit field‐dependent significant potential‐well minima both at large internuclear separations and at short internuclear separations with a considerable increase in the exchange and correlation energy of the hydrogen molecule. The results, when compared with the time‐independent (TI) studies involving static TI magnetic fields, reveal TD behavior of field‐dependent crossovers between different spin‐states of hydrogen molecule as indicated by the TI investigations in static magnetic fields. Besides this, present work reveals interesting dynamics in the TD total‐electronic charge‐density distribution of the hydrogen molecule. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Ultracold O2 + O2 collisions in a magnetic field: on the role of the potential energy surface

The collision dynamics of (17)O(2)((3)Σ(g)(-)) + (17)O(2)((3)Σ(g)(-)) in the presence of a magnetic field is studied within the close-coupling formalism in the range between 10 nK and 50 mK. A recent global ab initio potential energy surface (PES) is employed and its effect on the dynamics is analyzed and compared with previous calculations where an experimentally derived PES was used [T. V. Tscherbul et al., New J. Phys 134, 055021 (2009)]. Compared to the results using the older PES, magnetic-field dependence of the low-field-seeking state in the ultracold regime is characterized by a very large background scattering length, a(bg), and cross sections exhibit broader and more pronounced Feshbach resonances. The marked resonance structure is somewhat surprising considering the influence of inelastic scattering but it can be explained by resorting to the analytical van der Waals theory, where the short-range amplitude of the entrance channel wavefunction is enhanced by the large a(bg). This strong sensitivity to the short range of the ab initio PES persists up to relatively high energies (10 mK). After this study and despite quantitative predictions are very difficult, it can be concluded that the ratio between elastic and spin relaxation scattering is generally small, except for magnetic fields which are either low or close to an asymmetric Fano-type resonance. Some general trends found here, such as a large density of quasibound states and a propensity toward large scattering lengths, could be also characteristic of other anisotropic molecule-molecule systems.     

Liquid crystal electrohydrodynamics in the presence of a magnetic field: the dynamic scattering transition

We have studied electrohydrodynamic convection in the nematic liquid crystal MMBA in the conduction regime in the presence of a competing magnetic field. This field substantially alters the behaviour of the system, causing a metastable surface deformation and travelling waves. The magnetic field also alters the transition between the two dynamic scattering modes so that both states retain anisotropic ordering. A scaling relation is found describing this hysteretic transition. We report the existence of a stable mixed state of DSM 1 and DSM 2.     

Liquid crystal electrohydrodynamics in the presence of a magnetic field: the dynamic scattering transition

We have studied electrohydrodynamic convection in the nematic liquid crystal MMBA in the conduction regime in the presence of a competing magnetic field. This field substantially alters the behaviour of the system, causing a metastable surface deformation and travelling waves. The magnetic field also alters the transition between the two dynamic scattering modes so that both states retain anisotropic ordering. A scaling relation is found describing this hysteretic transition. We report the existence of a stable mixed state of DSM 1 and DSM 2.     

Measurements of light scattering changes induced by a strong optical field in solutions of tRNA

Changes in light scattering induced by a strong laser beam, as predicted theoretically by Kielich, were measured for unfractionated yeast transfer ribonucleic acid (tRNA) solutions. The vertically polarized electric field of a strong laser pulse (λ = 1060nm) amounted to 4.5 × 10³ esu cgs; its duration was 10 nsec. A weak incident laser beam (λ = 630nm) was also polarized vertically and the vertical and horizontal intensity components of the light scattered through 90° at the latter wavelength were measured. These measurements together with previous results from measurements of Rayleigh light scattering and light scattering in a magnetic field permitted evaluation of the tensor of third-order polarizability (c = 3 × 10^?30 esu cgs, c = ?373 × 10^?30 esu cgs) and the anisotropy of the third-order polarizability components with its sign (δ_c = +56 × 10^?2, δ_c = +0.25 × 10^?2 for tRNA monomer and aggregate, respectively). The new method described may be useful for studies of macromolecules and macromolecular complexes of biological importance.     

Novel highly elastic magnetic materials for dampers and seals: part II. Material behavior in a magnetic field

The combination of polymers with magnetic particles displays novel and often enhanced properties compared to the traditional materials. They can open up possibilities for new technological applications. The magnetic field sensitive elastomers represent a new type of composites consisting of small particles, usually from nanometer range to micron range, dispersed in a highly elastic polymeric matrix. In this paper, we show that in the presence of built‐in magnetic particles it is possible to tune the elastic modulus by an external magnetic field. We propose a phenomenological equation to describe the effect of the external magnetic field on the elastic modulus. We demonstrate the engineering potential of new materials on the examples of two devices. The first one is a new type of seals fundamentally different from those used before. In the simplest case, the sealing assembly includes a magnetoelastic strip and a permanent magnet. They attract due to the magnetic forces. This ensures that due to high elasticity of the proposed composites and good adhesion properties, the strip of magnetoelastic will adopt the shape of the surface to be sealed, this fact leading to an excellent sealing. Another straightforward application of the magnetic composites is based on their magnetic field dependent elastic modulus. Namely, we demonstrate in this paper the possible application of these materials as adjustable vibration dampers. Copyright © 2007 John Wiley & Sons, Ltd.     

Efficient method for quantum calculations of molecule-molecule scattering properties in a magnetic field

We show that the cross sections for molecule-molecule collisions in the presence of an external field can be computed efficiently using a total angular momentum basis, defined either in the body-fixed frame or in the space-fixed coordinate system. This method allows for computations with much larger basis sets than previously possible. We present calculations for (15)NH-(15)NH collisions in a magnetic field. Our results support the conclusion of the previous study that the evaporative cooling of rotationally ground (15)NH molecules in a magnetic trap has a prospect of success.     

Permanent magnet assembly producing a strong tilted homogeneous magnetic field: towards magic angle field spinning NMR and MRI

We introduce a cylindrical permanent magnet design that generates a homogeneous and strong magnetic field having an arbitrary inclination with respect to the axis of the cylinder. The analytical theory of 3 D magnetostatics has been applied to this problem, and a hybrid magnet structure has been designed. This structure contains two magnets producing a longitudinal and transverse component for the magnetic field, whose amplitudes and homogeneities can be fully controlled by design. A simple prototype has been constructed using inexpensive small cube magnets, and its magnetic field has been mapped using Hall and NMR probe sensors. This magnet can, in principle, be used for magic angle field spinning NMR and MRI experiments allowing for metabolic chemical shift profiling in small living animals.     

Calculation of the electric hypershielding at the nuclei of molecules in a strong magnetic field

The third-rank electric hypershielding at the nuclei of 14 small molecules has been evaluated at the Hartree-Fock level of accuracy, by a pointwise procedure for the geometrical derivatives of magnetic susceptibilities and by a straightforward use of its definition within the Rayleigh-Schrodinger perturbation theory. The connection between these two quantities is provided by the Hellmann-Feynman theorem. The magnetically induced hypershielding at the nuclei accounts for distortion of molecular geometry caused by strong magnetic fields and for related changes of magnetic susceptibility. In homonuclear diatomics H(2), N(2), and F(2), a field along the bond direction squeezes the electron cloud toward the center, determining shorter but stronger bond. It is shown that constraints for rotational and translational invariances and hypervirial theorems provide a natural criterion for Hartree-Fock quality of computed nuclear electric hypershielding.     

Capture and recombination of charge carriers in a strong electric field in quasi-one-dimensional crystals with scattering centers

The asymmetric random walk method is used to find the time dependence of the density of free charge carriers in a chain containing traps and neutral barriers, assuming a strong electric field. Fluctuations in the density of defects are taken into account exactly. The kinetics of the density decay has two stages: fast exponential decay at small times and slow decay (-[ln(t) + const]t^-, where a l is a combination of the parameters of the system) at long times. It is also shown that in the presence of barrier defects the asymptotic forms of the decrease in the number of charge carriers due to capture by traps and due to germinal recombination are the same.Institute of Theoretical Physics, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 27, No. 2, pp. 129–133, March–April, 1991. Original article submitted May 21, 1990.     

The aggregation of ferrocolloids in a magnetic field

The structure of chain aggregates forming in a low-concentration monodisperse ferrocolloid in a uniform permanent magnetic field was studied. The configuration integral of a flexible fluctuating chain of arbitrary length was calculated using the matrix method of coordinate system rotation with allowance made for the dipole-dipole interaction of the magnetic moments of nearest ferroparticles. The equilibrium distribution over aggregate chain lengths was determined from the condition of minimum of the free energy functional. It was shown that, even for infinitely diluted ferrofluids, an increase in the strength of external magnetic field led to a noticeable lengthening of chain aggregates at strong interparticle magnetodipole interaction. This results in faster (compared to Langevins law) growth of the magnetization of a system in weak and intermediate fields.Translated from Kolloidnyi Zhurnal, Vol. 66, No. 6, 2004, pp. 766–774.Original Russian Text Copyright © 2004 by Ivanov.     

The role of avoided crossings in the dynamics of strong laser field — matter interactions

The structure of quasi-energy surfaces, i.e. of quasi-energies as functions of external parameters like the laser frequency, laser intensity, atomic distances etc., is discussed and avoided crossings are traced to the existence of diabolical points at the origin of doublecone structures. The notion of non-contractable closed loops produces non-trivial Berry-phases. We then consider the interaction of atomic or molecular systems with relatively short smooth pulses and find that avoided crossings and, hence, diabolical points essentially, dominate non-adiabatic effects; away from avoided crossings the system evolves adiabatically in Floquet states, phases picked up during this motion lead to a new interference phenomenon which we study numerically in an appropriately simplified model. A scenario for the measurement of Berry phases is proposed which is linked to this interference in an essential manner; its eventual feasibility stems from the fact that at least two external parameters can be freely tuned in laser-atom (molecule) systems.     

Synchronous multielement detection by forward scattering in a transverse magnetic field (SYNFO)

Forward scattering in a transverse magnetic field is a sensitive method for the detection of low concentrations of elements. It has a large dynamic range in comparison to atomic absorption spectroscopy and is a “zero-method”. The application for $\text{syn}$chronous multielement detection by $\text{for}$ward scattering (SYNFO) is described. A continuous light source and a vidicon camera as detection system are used. In contrast to emission spectroscopy the spectra are easy to identify because they only consist of the few resonance lines.Different light sources were tested and detection limits and dynamic ranges of resonance lines of Tl, Fe, Pb, Zn, and Cd in a wavelength range between 260 and 335 nm were synchronously determined.     

The role of energy transfer processes in surface (enhanced) inelastic light scattering

Surface (enhanced) light scattering is treated as an efficient energy transfer between excited electronic states of the adsorbate and the metal, follow     

A parallel acquisition charged particle energy analyser using a magnetic field

A new form of charged particle energy analyser is proposed. It is broadly based on the 180° magnetic spectrograph, but is intended to detect charged particles moving out of the dispersion plane with a helical motion. The analyser has the capability to acquire charged particle energy spectra over a large energy range, similar to those acquired in Auger electron spectroscopy, ca. 2500 eV and large angular range, up to 90°, in parallel. These conditions are more favourable for surface analysis by electron spectroscopy at high vacuum, where for example an electron energy resolution of 0.2% to 0.5% is typical. Expressions showing how the landing positions of the charged particles on the detector vary as a function of energy and polar take off angle are determined as well as the conditions for optimum energy resolution at a range of polar take off angles. The equations reveal that in general, the device obtains the highest resolution at angles of revolution greater than 180°. The design is simple and could be easily put into practice using available material and technologies and be used to analyse the energies of electrons emitted from a sample placed in a scanning electron microscope. It can be made to function with a primary electron beam of any desired energy and could fit in to the small space between the sample and the end of an electron column. However, the device is difficult to retrofit into existing SEMs and ideally an SEM column needs to be designed to work in association with the analyser. The direction of the magnetic field of the analyser is coincident with the axis of the electron gun so that the primary beam is little influenced by the magnetic field and symmetry can be maintained in the primary beam electron column. Because the device is intended to acquire electron spectra in parallel, any movement of the primary beam on the sample because of a ramping field in the analyser is avoided. The field of view and the effect of the analyser upon the operation of the SEM are discussed. Spectra including elastic and Auger peaks reveal an energy resolution of ~4 eV at 900‐eV electron energy. Copyright © 2016 John Wiley & Sons, Ltd.     

Study of the nmr spectra of mono- and oligosaccharides in the region of a strong magnetic field

Conclusions An investigation of the NMR spectra of mono- and oligosaccharides in the region of a strong magnetic field permits a judgment of the conformational and configurational changes in the structure of monosaccharides, as well as the order and conformation of the bonds between monosaceharide residues in oligosaccharides.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1854–1856, August, 1969.