Reactant adsorption in differential pulse polarography: Effects of adsorptive depletion of reactant,non-linear adsorption isotherms and uncompensated resistance

Digital simulation techniques are applied to the diagnosis of the ways in which the peak currents and wave shapes of differential pulse polarograms are affected by the adsorption of reactants or products. The changes in the polarograms introduced by the items mentioned in the title are examined and their magnitudes calculated and compared with experimental polarograms. Some implications of the results in analytical applications of differential pulse polarography are described.     

Electroorganic chemistry—XI : The stereochemistry of electroreduction of cyclic ketones

Cyclic ketones were electrolytically reduced in isopropanol and in H₂SO₄H₂OMeOH. It was found that, in isopropanol the stereoisomer ratios of the products were approximately equal to the thermodynamic relative stabilities, whereas in H₂SO₄H₂OMeOH the thermodynamically unstable epimeric alcohols formed were more than that anticipated from the relative stabilities. The mechanism of this electroreduction involving the stereoselective adsorption and electron transfer is discussed.     

Voiceless affricate/fricative distinction by frication duration and amplitude rise slope

Previous psychophysical studies have shown that the perceptual distinction between voiceless fricatives and affricates in consonant-vowel syllables depends primarily on frication duration, whereas amplitude rise slope was suggested as the cue in automatic classification experiments. The effects of both cues on the manner of articulation between /integral of/ and /t integral of/ were investigated. Subjects performed a forced-choice task (/integral of/ or /t integral of) in response to edited waveforms of Japanese fricatives /integral of i/, /integral of u/, and /integral of a/. We found that frication duration, onset slope, and the interaction between duration and onset slope influenced the perceptual distinction. That is, the percent of /integral of/ responses increased with an increase in frication duration (experiments 1-3). The percent of /integral of/ responses also increased with a decrease in slope steepness (experiment 3), and the relative importance between slope portions was not even but weighted at onset (experiments 1 and 2). There was an interaction between the two cues of frication duration and steepness. The relative importance of the slope cue was maximum at a frication duration of 150 ms (experiment 3). It is concluded that the frication duration and amplitude rise slope at frication onset are acoustic cues that discriminate between /integral of/ and /t integral of/, and that the two cues interact with each other.     

Synthesis of novel pentafluorosulfanylfurans. Two retro-Diels-Alder approaches

The first examples of furan substituted with an SF5 group are reported. 3-pentafluorosulfanylfurans were prepared from their respective 2-pentafluorosulfanyl-5-cyano-7-oxabicyclo[2.2.1]hept-2-ene precursors via retro-Diels-Alder reactions. Also, a tandem cycloaddition/retrocycloaddition reaction between 4-phenyloxazole and 1-pentafluorosulfanylhex-1-yne was used to prepare 3-pentafluorosulfanyl-4-butylfuran. [reaction: see text].     

Anomalous High Pressure Properties in Fullerene Superconductors

Abstract

Correlations among lattice parameter, external pressure, and critical temperature T_c has been surveyed on fullerene superconductors with a wide range of lattice parameters and various valence states. The observed value of dT_c/dP for Na₂Rb_0.5Cs_0.5C₆₀ and Li₃CsC₆₀, having small interfullerene separations, is about a few times lager than that of K₃C₆₀. In contrast, small dT_c/dP values are found in fullerides with expanded unit cells, such as (NH₃)_xNaAA^?C₆₀ (A, A^? = K, Rb and Cs) and A₃Ba₃C₆₀. Interestingly, the chemical and physical pressure effects on T_c are considerably different in these fullerides with large interfullerene spacings. Our results suggest that the pressure dependence is scaled by an interfullerene distance when the interfullerene distances is small, but that this scaling fails when the unit cell is expanded.     

Electronic Properties of Ba-Intercalated Fullerides

Abstract

Raman spectra have been measured on Ba_xC₆₀ binary systems for x=3, 4 and 6. The pentagonal pinch Ag(2) mode exhibits a softening in an approximately proportional manner to the formal valence of C₆₀ molecule. This result suggests that the valence of C₆₀ in Ba doped systems are understood by the naive ionic crystal model based on Ba²⁺. The broader Raman peaks in superconducting Ba₄C₆₀ indicates that the electron-phonon interaction is considerably large comparing to those for Ba₃C₆₀ and Ba₆C₆₀.     

Laser micro-machining using near-field optics

Solid immersion lenses (SIL) facilitate high numerical aperture (NA) and consequent sub-wavelength diffraction limited focusing in near-field optics based systems. Such systems are in commercial and research use for various applications including near-field scanning optical microscopy, ultra-high-density magneto-optic data storage and near-field nanolithography. Here, we present a novel manufacturing method using SIL-based near-field optics for laser-induced patterning on silicon wafers. The near-field effect of SILs was investigated by using hemispherical lenses made of three different materials (BK7, Sapphire, LaSFN9) to superfocus an incident Q-switched, 532 nm Nd:YAG laser beam transmitted through a focusing objective. This optical arrangement achieved a laser-processed feature resolution near the diffraction limit in air. Results of experiments that were conducted at various processing conditions to investigate the effects of varying incident laser power (with peak pulse power less than 1 W), pulse width, number of pulses and size of SIL on processed feature size and resolution are presented. Experimental results are compared with numerical simulations using the simplified model.     

Dissolution kinetics of K-alum crystals as judged from the measurements of surface undersaturations

The normal dissolution rates, the slopes and the average velocities of dissolution steps of etch pits on the (111) face of a K-alum crystal, originating from dislocations with Burgers vector 110, were measured in relation to the surface undersaturations. From the mutual relations, it was shown that the dissolution was controlled by both diffusion and surface kinetic processes, although the contribution of the latter process was smaller than in the case of growth. It was also demonstrated that the normal dissolution rate was always larger than the growth rate. This is attributed to the fact that the slopes of growth hillocks are invariably smaller than those of etch pits.