Scattering of potassium atomic beams from various cleaved surfaces

Scattering of potassium atomic beams from cleaved surfaces of LiF, KCl and mica were studied. The observed spatial distributions follow the cosine distribution in most cases. At large incident angles the distributions from LiF and KCl deviate from the cosine and show apparent backscatterings. A simple model is proposed to interpret the backscattering in terms of macroscopic roughness of cleaved surfaces. The sticking coefficient S (t) is defined and the mass balance between the incident and outgoing atoms is examined. Mass balance holds within the limits of errors on the surfaces of LiF and KCl at temperatures above 400 K. On a mica surface deposition of potassium atoms is observed even at temperatures higher than room temperature. It is shown from the change of the sticking coefficient that the deposition does not proceed linearly in the initial period.     

Mammalian laryngseal air sacs add variability to the vocal tract impedance: physical and computational modeling

Cavities branching off the main vocal tract are ubiquitous in nonhumans. Mammalian air sacs exist in human relatives, including all four great apes, but only a substantially reduced version exists in humans. The present paper focuses on acoustical functions of the air sacs. The hypotheses are investigated on whether the air sacs affect amplitude of utterances and/or position of formants. A multilayer synthetic model of the vocal folds coupled with a vocal tract model was utilized. As an air sac model, four configurations were considered: open and closed uniform tube-like side branches, a rigid cavity, and an inflatable cavity. Results suggest that some air sac configurations can enhance the sound level. Furthermore, an air sac model introduces one or more additional resonance frequencies, shifting formants of the main vocal tract to some extent but not as strongly as previously suggested. In addition, dynamic range of vocalization can be extended by the air sacs. A new finding is also an increased variability of the vocal tract impedance, leading to strong nonlinear source-filter interaction effects. The experiments demonstrated that air-sac-like structures can destabilize the sound source. The results were validated by a transmission line computational model.     

10 kHz 40 W Ti:sapphire regenerative ring amplifier

A cryogenically cooled Ti:sapphire regenerative ring amplifier was developed as a laser for generating a laser-produced plasma light source. With a 10 kHz 180 W pump laser, the amplifier output is 40 W before compression and 26 W after compression. We believe it to be the current highest average-power output from a single stage Ti:sapphire amplifier. The effective focal length of the thermal lens is measured to be 2.2 m at 100 K for 180 W of pump power. With a 1 m focal length lens placed in the resonator, the effect of a thermal lens on the resonator mode is suppressed. High conversion efficiency is achieved for the whole pumping power range without any additional measures for thermal compensation.     

Amide–π interactions between formamide and benzene

High‐level ab initio calculations have been carried out using a formamide–benzene model system to evaluate amide–π interactions. The interaction energies were estimated as a sum of the CCSD(T) correlation contribution and the HF energy at the complete basis set limit, for the geometries of the model structures at the energy minimum obtained by potential energy surface (PES) scans. NH/π geometry in a face‐on configuration was found to be the most attractive among the various geometries considered, with interaction energy of ?3.75 kcal/mol. An interaction energy of ?2.08 kcal/mol was calculated for the stacked N/Center type geometry, where the nitrogen atom of formamide points directly toward the center of the aromatic ring. The weakest C?O/π geometry, where a carbonyl oxygen atom points toward the plane of the aromatic ring, was found to have energy minimum at an intermolecular distance of 3.67 Å from the PES, with a repulsive interaction energy less than 1 kcal/mol. However, if there are simultaneous attractive interactions with other parts of the molecule besides the amide group, the weak repulsion could be easily overcome, to give a C?O/π geometry interaction. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2009     

Photochemical ring opening of thymidine and thymine in the presence of primary amines

Irradiation of thymidine or thymine in the presence of tert- butylamine at 0 °C provided ping-opened photoadduct $\text{3}$ which on heating at 70 °C gave 1-tert-butylthymine ($\text{2}$) quantitatively. Synthetic application of this photoexchange reaction with amines has been described.     

Facile Dehydrogenation of alpha-Amino Acids Chelated to a Ruthenium(II) Ion: (alpha-Imino acidato)ruthenium(II) Complexes

(alpha-Imino acidato)ruthenium(II) complexes, [Ru(II){N(R(1))=C(R(2))CO(2)}L(2)](+) (R(1) = R(2) = Me or R(1) = R(2) = -(CH(2))(3)-; L = 2,2'-bipyridine (=bpy) or 1,10-phenanthroline (=phen)), were obtained by anodic oxidation at a constant potential of the corresponding (alpha-amino acidato)ruthenium(II) complexes, N-methylalaninato or prolinato complexes, in good to excellent yields. (alpha-Imino acidato)ruthenium(II) complexes are stable in neutral or acidic aqueous solution. The half-wave potentials of alpha-imino acidato complexes are 0.73-0.78 V (vs SCE), which are more positive than those of the corresponding alpha-amino acidato complexes, 0.55-0.59 V. The crystal structure of [Ru(pro-H(2))(bpy)(2)]ClO(4).3H(2)O (pro-H(2) = 1,2-didehydroprolinato) has been determined by single-crystal X-ray analysis. Crystallographic data: space group C2/c, a = 21.73(1) ?, b = 19.33(1) ?, c = 14.58(1) ?, beta = 114.91(5) degrees, Z = 8, R = 0.0352. The length of the C=N double bond of the alpha-imino acidate moiety is 1.294(5) ?, and Ru-N(imino nitrogen) = 2.042(3) ?. The chelate ring of the alpha-imino acidato ligand is planar.     

Physicochemical analyses of phase transition and dehydration processes of a new oral 1beta-methylcarbapenem antibiotic agent,CS-834

The characterizations of the anhydrate (A-form), monohydrate (B1-form), and dihydrate (B2-form) of CS-834 were investigated by powder X-ray diffraction, differential scanning calorimetry (DSC), thermogravimetry-differential thermal analysis (TG-DTA), infrared spectroscopy, and Karl Fischer moisture titration. The typical DSC curve of the B2-form showed five endothermic peaks at 35.0, 46.4, 56.2, 99.2, and 190.4 degrees C and an exothermic peak at 123.4 degrees C. In TG-DTA analysis, the three peaks at 35.0, 46.4, and 56.2 degrees C had a total weight loss of 7.3%, corresponding to the release of two water molecules. From morphological observation under thermomicroscopy, the endothermic peak at 99.2 degrees C was attributed to the melting of the dehydrous crystals (B0-form) and the exothermic peak at 123.4 degrees C to the recrystallization to the A-form crystals. The endothermic peak at 190.4 degrees C was due to the melting of the A-form crystals. After incubation for 6.0 h at 35, 50, 60, and 80 degrees C, the powder X-ray diffraction patterns of the B2-form indicated that it was converted into the A-form via the B1-form and B0-form. Thus CS-834 exists in homologous hydrous crystal forms in multiple-phase transformations with the dehydration of two water molecules.     

Facile Palladium catalyzed decarboxylative allylation of active methylene compounds under neutral conditions using allylic carbonates

Palladium catalyzed decarboxylative allylation of active methylene compounds proceeded under mild neutral conditions using allylic carbonates, which are much more reactive than allylic acetates or phenoxides used commonly in the reaction.     

Simplified treatment of cooligomerization kinetics

Equations for the degree of polymerization and the cooligomer composition in the styrene (A)–methyl methacrylate (B)–CCl₄(S) system were derived from the assumed reaction scheme by the use of some assumptions for simplification, and their appropriateness was examined. The chain transfer constants of the growing radicals of styrene (C_SA) and methyl methacrylate (C_SB) to CCl₄, which were estimated from the apparent chain transfer constants C_SAB in the cooligomerization system, agreed with the homooligomerization values. This means that the degree of the polymerization of the cooligomer can be expressed by the equation: where P_n is the degree of polymerization of the cooligomer and P_nO is that when no chain transfer agent (CCl₄) is added; r_A and r_B are the monomer reactivity ratios of monomers A and B in this system. The cooligomer composition deviated from the statistical steady-state composition on the low molecular weight side, and this deviation was explained by the equation: