The interaction of electron beams and electromagnetic fields in relativistic Cerenkov generators

A method of numerical analysis of linear and nonlinear nonstationary processes in relativistic Cerenkov generators based on periodic superdimensional waveguides is proposed. The main idea lies in considering a nonregular waveguide as a sequence of wave transformers and using a cross-section method. Configurations of eigenwave fields of periodic waveguides with a high-current relativistic electron beam are considered. The processes of generation development in a section of a relativistic multiwave generator are studied. We show that the system frequency is proved to be determined by the longitudinal resonances of surface waves and internal feedback.     

Two-photon absorption in two-dimensional conjugated quadrupolar chromophores

We present ultrafast z-scan measurements of the two-photon absorption (TPA) spectra of a pair of two-dimensionally conjugated quadrupolar donor/acceptor (D/A) chromophores. The all-donor substituted species displays a peak TPA cross section [sigma(2)=520+/-30 GM] that is more than twice that of the D-A species [sigma(2)=240+/-20 GM]. Unlike previous structure-property studies that have evaluated TPA behavior for D/A molecules through the comparison of dipolar and quadrupolar compounds, both molecules investigated herein are quadrupolar, ultimately providing a more consistent evaluation of the effects of donor and/or acceptor substitution on the TPA of conjugated chromophores.     

The effect of topical anesthesia on vocal fold motion

The objective of this study was to determine if topical anesthesia to the larynx and pharynx affects vocal fold motion during dynamic voice evaluation with transnasal flexible endoscopy. Transnasal dynamic laryngeal examinations of 10 patients with no voice complaints were evaluated by five blinded fellowship-trained laryngologists. Each patient was examined before and after application of topical anesthetic. Reviewers rated briskness of right and left vocal fold movement and longitudinal tension on a visual analogue scale. Statistical comparisons were made between individual subject scores before and after anesthetic application. Inter-rater reliability was also assessed. No statistical difference was observed between subject scores before and after anesthetic application. Average intraclass correlation coefficients were 0.643 and 0.591 for pre- and postanesthesia scores, respectively. Application of topical anesthesia to the larynx and pharynx does not affect vocal fold motion.     

Polyynes as a model for carbyne: synthesis, physical properties, and nonlinear optical response

With the Fritsch-Buttenberg-Wiechell rearrangement as a primary synthetic route, a series of conjugated, triisopropylsilyl end-capped polyynes containing 2-10 acetylene units has been assembled. In a few steps, significant quantities of the polyynes are made available, which allow for a thorough analysis of their structural, physical, and optical properties. Molecules in the series have been characterized in detail using (13)C NMR spectroscopy, differential scanning calorimetry, mass spectrometry, and, for four derivatives including octayne 6, X-ray crystallography. UV-vis spectroscopy of the polyynes 1-7 shows a consistent lowering of the HOMO-LUMO gap (E(g)) as a function of the number of acetylene units (n), fitting a power-law relationship of E(g) approximately n(-)(0.379)(+/-)(0.002). The third-order nonlinear optical (NLO) properties of the polyyne series have been examined, and the nonresonant molecular second hyperpolarizabilities (gamma) increase as a function of length according to the power-law gamma approximately n(4.28)(+/-)(0.13). This result exhibits an exponent that is larger than theoretically predicted for polyynes and higher than is observed for polyenes and polyenynes. The combined linear and nonlinear optical results confirm recent theoretical studies that suggest polyynes as model 1-D conjugated systems. On the basis of UV-vis spectroscopic analysis, the effective conjugation length for this series of polyynes is estimated to be ca. n = 32, providing insight into characteristics of carbyne.     

The surprising nonlinear optical properties of conjugated polyyne oligomers

Polyynes represent a unique class of conjugated organic compounds. The third-order nonlinear optical response of polyynes has been extensively modeled theoretically, and it is generally believed that the increase in molecular second hyperpolarizability (gamma) as a function of length for polyynes should be lower than that for polyenes. Experimental evidence to test this prediction, however, has been absent. We have synthesized conjugated polyynes that contain up to 20 consecutive sp-hybridized carbons, and we have determined their nonresonant gamma-values as a function of the number of acetylene repeat units (n). These gamma-values demonstrate a power-law behavior versus n(gamma approximately n(4.28+/-0.13)), with an exponent that is both larger than theoretically predicted for polyynes and substantially higher than that observed for polyenes or polyenynes. Furthermore, no saturation of the linear or nonlinear optical properties is observed.     

Vacuum moulding of a superplastic in two dimensions

A mathematical model is proposed for the process of vacuum superplasticforming. The model exploits the fact that in most industrialapplications the sheet aspect ratio (thickness/sheet width)is small. After an initial consideration of some of the moregeneral properties and the literature of superplastic materials,the elastic/plastic deformation of an internally-inflated thin-walledcylinder is examined. Plates of arbitrary geometry are thenconsidered. A quasisteady model in which the sheet moves througha sequence of steady states is developed. Some simplified closed-formsolutions are examined, but for general cases a system of nonlinearpartial differential equations must be solved numerically. Anefficient and accurate semi-explicit numerical scheme is proposedand a simplified stability analysis is presented; the methodis then used to compute properties of superplastic vacuum mouldedsheets in a number of practically motivated cases.     

Evolution of chemical bonding and electron density rearrangements during D3h → D3d reaction in monolayered TiS2: A QTAIM and ELF study

Monolayered titanium disulfide TiS₂, a prospective nanoelectronic material, was previously shown to be subject to an exothermic solid‐state D_3h–D_3d reaction that proceeds via a newly discovered transition state. Here, we study the reaction in detail using topological methods of quantum chemistry (quantum theory of atoms in molecules and electron localization function analysis) and show how electron density and chemical bonding between the atoms change in the course of the reaction. The reaction is shown to undergo a series of topological catastrophes, associated with elementary chemical events such as break and formation of bonds (including the unexpected formation of S? S bonding between sulfur layers), and rearrangement of electron density of outer valence and core shells. © 2014 Wiley Periodicals, Inc.     

On the possibility of phase transitions with the formation of SiO<Subscript>2</Subscript> peroxide forms in the earth mantle and their effect on mantle convection

Based on the hypothesis advanced by S. P. Gabuda that the SiO₂ molecule could undergo a transition from the linear form to the isomeric form with a ring-shaped (bent) structure, an idea is proposed that when the mantle substance melts, a phase transition of the bent SiO₂ form into the linear SiO₂ form can occur in the lower mantle. This phase transition might be of great importance for the lower-mantle convection processes and also for the rise of mantle plumes carrying both heat energy, and broad range of platinum group and rare elements to the Earth surface.     

Spontaneous dissociation of xenon tetroxide: phase and structural changes

XeO(4) is a noble gas compound remarkable for its high explosiveness in the crystalline state and spontaneous explosion at melting temperature. Both phenomena are studied by analyzing potential energy surfaces corresponding to elementary dissociation acts. It is shown that a spontaneous explosion of xenon tetroxide can be explained by a phase transition associated with structural T(d) → D(2h) change and be triggered by rearrangement of electron levels due to the Jahn-Teller effect.