Eigenvalues of the Boltzmann collision operator for binary gases: Mass dependence

Eigenvalues of the Boltzmann collision operator are calculated versus mass ratio with two different methods. One method involves the expansion of the eigenfunctions in speed polynomials, whereas with the second method the eigenfunctions are evaluated at discrete points based on a particular gaussian quadrature rule. The discrete ordinate method proved to be superior provided the mass ratio was neither too large nor too small. The approach of the eigenvalues to the continuum boundary was also studied for several mass ratios.     

Eigenvalues of the boltzmann collision operator for binary gases: Relaxation of anisotropic distributions

The time eigenvalues of the Boltzmann collision operator for the hard-sphere cross section are calculated with a discrete ordinate method. The anisotropic part of the collision operator is considered in the present work. The approach to equilibrium of a gas initially non-maxwellian and anisotropic is considered.     

Surface holography with LEED electrons

The present status of surface holography using low energy electron diffraction intensities is described. It is shown that diffuse intensity distributions appearing with disordered adsorption on a crystalline substrate can be interpreted in a holographic sense by the single adatom acting as a beam splitter for the primary electron beam. We demonstrate that intensities taken at many energies need to enter the reconstruction integral in order to retrieve well resolved atomic images. We also show that the method can be extended to use also discrete superstructure spot intensities instead of diffuse maps, so opening the field to ordered superstructures. The power and applicability of the method is discussed.     

Interreflection errors in Fourier transform spectroscopy: a preliminary appraisal

The presence of systematic ordinate errors in Fourier transform spectroscopy (FTS) is discussed, largely in terms of interreflection effects between the various interfaces of a two-beam interferometer and its adjacent optical components. Seven distinct categories of interreflection are specified and some consequences are noted. Certain types of optical filter are described which can be used diagnostically to distinguish between ordinate errors arising from interreflections and the intrinsic ordinate errors. The latter are those that remain when the interreflection effects have been removed by optical modifications. A strategy for achieving this is suggested. Finally, a theoretical model is being considered as a general way of handling a complicated problem.     

Effective one-dimensional dipole moment function for the OH stretching overtone spectra of simple acids and alcohols

To gain insight on the absorption intensities, as well as the direction of the transition moment for the OH stretching vibration in alcohols and acids, we performed detailed analyses for nitric acid, acetic acid, methanol, tert-butyl alcohol, water, and OH radical. We obtained both the potential energy surface and the dipole moment function (DMF) by the B3LYP method and performed quantum mechanical vibrational calculation using the grid variational method based on the local mode model. In this work, we employed the sum rule of the absorption intensities for the one-dimensional (1-D) vibrational Hamiltonian to construct an effective 1-D DMF, which is responsible for the total sum of the overtone intensities. The direction of this effective DMF was found to be tilted away from the OH bond by about 30 degrees for the polyatomic molecules. The nonlinearity of the DMFs in the directions parallel and perpendicular to the OH bond is discussed to rationalize the tilting. Furthermore, we analyzed the effective 1-D DMFs with the vibrational wave function expansion method and derived the effective portion of the 1-D DMF that is responsible for the overtone transition moment.     

Optical study of the adsorption and surface condensation of vapours in the vicinity of saturation on a smooth surface

Polymolecular adsorption of the vapours of a number of liquids near the saturation point on a smooth glass surface has been measured by the optical micropolarization method. It is shown that for polar liquids (water, alcohols, nitrobenzene) the adsorption isotherm intersects the saturation ordinate and can be represented only by an exponential, but not a power relation. On the contrary, for non-polar liquids, such as carbon tetrachloride and benzene, the isotherm apparently has the saturation ordinate as its asymplote. Therefore in the case of polar liquids, contrary to non-polar, no gradual transition from the adsorbed layer to the volume is possible, this transition taking the form of a jump similar to a phase transformation of the first kind. The data given favour the idea that this transition is due to the difference in the structures between which gradual transition is impossible.     

Amplification of Electronic Circular Dichroism—A Tool to Follow Self-Assembly of Chiral Molecular Capsules

Electronic circular dichroism (ECD) can be used to study various aspects of self-assembly (definition of stoichiometric ratios, chirality amplification during self-assembly, host-guest complexation). In this work, we show that ECD is a valuable tool for monitoring the self-assembly of chiral peptide-based capsules. By analyzing the signs, intensities, and temperature dependences of ECD bands, the effects of the non-specific processes can be separated from the restriction of intramolecular motion (RIM) caused by discrete self-assembly. Analysis of experimental and theoretical ECD spectra show that the differences between assembled and non-assembled species originate from induction of inherently chiral conformation and restriction of conformational freedom that leads to amplification of ECD signals during self-assembly of discrete species.     

Quantitative EPMA of element depth distribution

A new model for the ionization depth distribution function has been proposed. Within the framework of this model full electron flux is considered to be divided into two fluxes propagating in forward and backward directions through a sample. The intensities of these fluxes can be derived on the basis of simple assumptions of electron-solid interactions. The approach can be effectively applied to a system with an arbitrary form of depth concentration profile. The obtained results are in reasonable agreement with Monte Carlo simulations and experimental results. Some mathematical techniques have been presented for quantitative analysis of thin films on substrates and element depth distribution.     

Identifying the Crystalline Orientation of Black Phosphorus Using Angle‐Resolved Polarized Raman Spectroscopy

An optical anisotropic nature of black phosphorus (BP) is revealed by angle‐resolved polarized Raman spectroscopy (ARPRS), and for the first time, an all‐optical method was realized to identify the crystal orientation of BP sheets, that is, the zigzag and armchair directions. We found that Raman intensities of A_g¹, B_2g, and A_g² modes of BP not only depend on the polarization angle α, but also relate to the sample rotation angle θ. Furthermore, their intensities reach the local maximum or minimum values when the crystalline orientation is along with the polarization direction of scattered light (e_s). Combining with the angle‐resolved conductance, it is confirmed that A_g² mode intensity achieves a relative larger (or smaller) local maximum under parallel polarization configuration when armchair (or zigzag) direction is parallel to e_s. Therefore, ARPRS can be used as a rapid, precise, and nondestructive method to identify the crystalline orientation of BP layers.     

Fourier transform Raman spectroscopy of Syncrude sweet blend distillation fractions derived from Athabasca bitumen

The C-H stretching region in FT-Raman spectra of Syncrude sweet blend (SSB) and three distillation fractions (naphtha, light gas oil and heavy gas oil) was analyzed in detail in this investigation. The frequencies and intensities of the 11 aliphatic and three aromatic C-H bands used to fit the spectrum of SSB were equal to the averages (weighted sums) of the corresponding quantities in the spectra of the fractions. The additivity of the spectra, thought to be a consequence of the large number of discrete compounds contained in each fraction, makes it possible to estimate the composition of other SSB samples using the spectra of the fractions reported in this work. In the aromatic C-H region, total intensities can be used to calculate the distribution of aromatics among the distillation fractions; these data also permit calculation of the fractional aromaticity (per cent aromatic carbon) for SSB and each fraction, with accuracies comparable to those obtained using NMR spectroscopy.     

Stark control of a chiral fluoroethylene derivative

Hydrogen dissociation is an unwanted competing pathway if a torsional motion around the C═C double bond in a chiral fluoroethylene derivative, namely (4-methylcyclohexylidene) fluoromethane (4MCF), is to be achieved. We show that the excited state H-dissociation can be drastically diminished on time scales long enough to initiate a torsion around the C═C double bond using the nonresonant dynamic Stark effect. Potential energy curves, dipoles, and polarizabilities for the regarded one-dimensional reaction coordinate are calculated within the CASSCF method. The influence of the excitation and the laser control field is then simulated using wave packet dynamics.     

In-plane and out-of-plane diffraction of H2 from Ru(001)

H(2) diffraction from the Ru(001) surface has been measured for incident energies E(i) = 78-150 meV and incident angles Θ(i) = 22.1-64.1°. In-plane and out-of-plane angular distributions were measured for incidence along [110] and [100] directions. Out-of-plane diffraction channels were found to be predominant for the explored experimental conditions regardless of the incidence direction. An analysis of diffraction intensities reveals that diffraction out of the scattering plane is enhanced for high incidence angles. Diffractive transitions with wavevector change in the surface plane and transversal to the incidence direction ΔK(⊥) were observed to be favored among the out-of-plane diffractive transitions. These features could be reproduced by model calculations of diffraction intensities performed using a three-dimensional soft potential. This suggests that a kinematic effect is responsible for the large out-of-plane intensities observed in experiment, more than any other features of the six-dimensional H(2)-surface interaction potential.     

Ordered complex structures formed by paramagnetic particles via self-assembly under an ac/dc combined magnetic field

We apply ac and dc magnetic fields simultaneously in orthogonal directions to each other to a solution, in which paramagnetic microparticles are dispersed, and show that complex secondary structures composed of oscillating chain clusters, that is, long linear clusters interconnected by T-, L-, and criss-cross-junctions, are self-assembled. Disklike clusters are formed at some junctions and the number of disklike clusters increases as the frequency of the ac magnetic field increases. We finally show that the angle between long linear clusters can be altered by changing the ratio of the intensities of the ac and dc magnetic fields.     

Eine methode zur qualitativen und quantitativen infrarotspektroskopischen analyse von metall-tetramethylendithiocarbamidat-gemischen ohne vorhergehende auftrennung

A method for the direct i.r. analysis of metal-tetramethylenedithiocarbamate mixtures without preceding separation is proposed. Because of the remarkable shifts of the M-S-stretching vibrations and the small losses of energy by stray light, the region beyond 400 cm^-1 is the most useful for a determination in potassium bromide. Model analyses with standard mixtures of Pb(II)- and Hg(II)-TMDTC, and Fe(III)-, Co(III)- and Ni(II)-TMDTC are described. The method' can be used for the determination of trace amounts of heavy metals in aqueous solutions after complexation with Na-TMDTC and extraction with chloroform. The detection limit for application of the 13-mm standard KBr method and a routine spectrometer (without ordinate expansion) is about 10 μg of metal.     

Functional selectivity in GPCR modulator screening

In high throughput screening systems, a single concentration of a new compound is tested in a biological system to detect direct effects (agonists) or effects on other ligands (antagonists). In this latter case, the chemical context of the assay is defined by a balance of maximal sensitivity (limited agonist concentration) and maximal window to observe effect (sizable agonist concentration to induce measurable effect). For allosteric modulators, there are other factors that should be considered in high throughput screening environments. Specifically, the saturable aspect of allosteric effect can dissociate the observed ordinate change in response (% inhibition) and potency of effect (concentration at which a given ordinate % effect is obtained). Also, the specter of probe dependence can be important in systems where the physiologically relevant agonist cannot be used for screening (i.e. HIV-1 entry). Finally, the interactive nature of allosteric systems can cause complex relationships between the chemical context of an assay and potency of allosteric modulator. For example, in cases where the efficacy of an agonist is reduced but the affinity is increased by a modulator, it may be more beneficial to have higher concentrations of agonist in the screening assay to optimize sensitivity to modulators. This must be balanced for allosteric potentiators with the need to retain a window to observe increased agonist effect.     

Calibration-Free Laser-Induced Breakdown Spectroscopy: State of the art

The aim of this paper is offering a critical review of Calibration-Free Laser-Induced Breakdown Spectroscopy (CF-LIBS), the approach of multi-elemental quantitative analysis of LIBS spectra, based on the measurement of line intensities and plasma properties (plasma electron density and temperature) and on the assumption of a Boltzmann population of excited levels, which does not require the use of calibration curves or matrix-matched standards. The first part of this review focuses on the applications of the CF-LIBS method. Quantitative results reported in the literature, obtained in the analysis of various materials and in a wide range of experimental conditions, are summarized, with a special emphasis on the departure from nominal composition values. The second part is a discussion of the simplifying assumptions which lie at the basis of the CF-LIBS algorithm (stoichiometric ablation and complete atomization, thermal equilibrium, homogeneous plasma, thin radiation, detection of all elements). The inspection of the literature suggests that the CF-LIBS method is more accurate in analyzing metallic alloys rather than dielectrics. However, the full exploitation of the method seems to be still far to come, especially for the lack of a complete characterization of the effects of experimental constraints. However, some general directions can be suggested to help the analyst in designing LIBS measurements in a way which is more suited for CF-LIBS analysis.     

He-N2O偶极矩面及振转跃迁强度的理论研究

用超分子MP4方法和大基组(aug-cc-pVTZ)及键函数得到He-N₂O体系的分子间从头算势能面及偶极矩面,用离散变量表象方法计算了⁴He-N₂O及³He-N₂O体系的振转能级,并进一步计算得到其振转跃迁强度,计算结果很好地解释了实验现象.     

Methodology for the qualitative screening of parallel arrays of potential Am ligands using a photographic film

A screening method for parallel Am³⁺ ligand libraries is presented. The method makes use of α-radiation in combination with a photographic film to detect the complexed Am³⁺. After screening and development of the film spots of varying intensities are obtained. The intensities of the spots correspond with the amount of complexed Am³⁺. This allows a fast discrimination between the Am³⁺ complexation efficiencies of ligands from large libraries. Depending on the exposure time of the film, activities as small as 5 Bq ²⁴¹Am can be detected. Using internal standards a semi-quantitative assessment can be performed.     

Filling factor of a paramagnetic sample in a rectangular cavity: theory and application

A computational method is presented for calculating the filling factor of an electron paramagnetic resonance (EPR) tube in a rectangular TE102 cavity. The algorithm employs the conventional finite element method. In addition to the filling factor, the algorithm allows to calculate the quality factor and the reflection coefficient of the loaded cavity. This method allows calculating very accurately the EPR signal intensities from which the spin concentration of paramagnetic samples can be determined. A comparison between the predicted EPR signal intensities to several experimental results was found to be satisfactory. The method also allows optimizing the EPR tube dimensions and its glass quality to improve measurement sensitivity.