Enhanced cohesion of photo-oxygenated fullerene films: A new opportunity for lithography

The irradiation of sublimed fullerene (C₆₀ and C₇₀) thin films with ultraviolet light in an oxygen-rich ambient has been found to lead to a substantially increased cohesive energy in the fullerene solid. The decreased solubility and lower vapor pressure of the phototransformed material enables wet (organic solvents) or dry (thermal or photon-induced sublimation) development of photo-defined negative images. One micrometer wide lines with good edge definition are demonstrated. X-ray, infrared, optical absorption, and high performance liquid chromatography reveal that photo-oxygenated C₆₀ retains its fcc crystal structure but with a substantial fraction of the C₆₀ molecules modified with carbonyl (C=O) bonds.     

Dispersion energy between closed-shell and half-closed-shell molecules.an ab inito calculation from a perturbation procedure on LiHe

A perturbation procedure previously used for closed-shell molecules is generalized to the case of the interaction between closed-shell and half-closed-shell molecules In particular, the use of different denominators is considered and special attention is paid to the effect of small basis sets for LiHe.     

Ab initio calculation of the intermolecular energy between two hydrogen molecules near the van der Waals minimum

The interaction energy between two hydrogen molecules near the van der Waals minimum is computed as the sum of the SCF interaction energy of the supermolecule and the so-called Hartree-Fock dispersion energy. The most stable configuration is the perpendicular planar one (T configuration), this configuration being stable through the first order term. The energy averaged over the four configurations is in agreement with the available experimental data. The perturbative polarization energy is negligible near the van der Waals minimum but it seems that the charge transfer energy must be taken into account.     

Effect of ionic charge on energy contributions to the interaction of an ion with a polar molecule: ab initio calculations for MH2O (M = Mg, Mg, Mg, Ca, Ca, Ca)

For MH₂O (M = Mg, Mg⁺, Mg²⁺, Ca, Ca⁺, Ca²⁺) various energy contributions (first-order, induction and charge-transfer, dispersion) are compared. Near the minimum, stability due to the first-order energy decreases and that due to dispersion increases from M²⁺ to M⁰. For M²⁺, dispersion represents only 1–7% of the total energy; it may reach 25% with M⁺ and is largely responsible for stability of the neutral complex.     

Loudness predicts prominence: fundamental frequency lends little

We explored a database covering seven dialects of British and Irish English and three different styles of speech to find acoustic correlates of prominence. We built classifiers, trained the classifiers on human prominence/nonprominence judgments, and then evaluated how well they behaved. The classifiers operate on 452 ms windows centered on syllables, using different acoustic measures. By comparing the performance of classifiers based on different measures, we can learn how prominence is expressed in speech. Contrary to textbooks and common assumption, fundamental frequency (f0) played a minor role in distinguishing prominent syllables from the rest of the utterance. Instead, speakers primarily marked prominence with patterns of loudness and duration. Two other acoustic measures that we examined also played a minor role, comparable to f0. All dialects and speaking styles studied here share a common definition of prominence. The result is robust to differences in labeling practice and the dialect of the labeler.     

Rhythm measures and dimensions of durational variation in speech

Patterns of durational variation were examined by applying 15 previously published rhythm measures to a large corpus of speech from five languages. In order to achieve consistent segmentation across all languages, an automatic speech recognition system was developed to divide the waveforms into consonantal and vocalic regions. The resulting duration measurements rest strictly on acoustic criteria. Machine classification showed that rhythm measures could separate languages at rates above chance. Within-language variability in rhythm measures, however, was large and comparable to that between languages. Therefore, different languages could not be identified reliably from single paragraphs. In experiments separating pairs of languages, a rhythm measure that was relatively successful at separating one pair often performed very poorly on another pair: there was no broadly successful rhythm measure. Separation of all five languages at once required a combination of three rhythm measures. Many triplets were about equally effective, but the confusion patterns between languages varied with the choice of rhythm measures.     

What marks the beat of speech?

Which acoustic properties of the speech signal differ between rhythmically prominent syllables and non-prominent ones? A production experiment was conducted to identify these acoustic properties. Subjects read out repetitive text to a metronome, trying to match stressed syllables to its beat. The analysis searched for the function of the speech signal that best predicts the timing of the metronome ticks. The most important factor in this function is found to be the contrast in loudness between a syllable and its neighbors. The prominence of a syllable can be deduced from the specific loudness in an (approximately) 360 ms window centered on the syllable in question relative to an (approximately) 800-ms-wide symmetric window.     

All valence-electrons calculations on purines and pyrimidines

An iterative extended Hückel calculation (IEHC) has been performed for the purine and pyrimidine bases of the nucleic acids. The results presented concern the electron distribution and the dipole moments, the atomic orbital populations and the hybridization ratios, the energies of the molecular orbitals and the ionization potentials. In particular, the relative orders of the dipole moments and of the -ionization potentials are correctly reproduced but their absolute values are too great.

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Zusammenfassung Die Purin- und Pyrimidinbasen der NukleinsÄuren wurden mit einer IEHC-NÄherung berechnet. Es werden die Elektronenverteilungen, die Dipolmomente, die AO-Population, die Hybridisierungskonstanten, die MO-Energien und die Ionisationspotentiale angegeben. Die Reihenfolge der Dipolmomente und -Ionisationspotentiale wird richtig erhalten.

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Résumé La méthode de Hückel étendue itérative a été utilisée pour l'étude de la structure électronique des bases puriques et pyrimidiques des acides nucléiques. Les résultats présentés concernent la distribution des charges électriques et les valeurs des moments dipolaires, les populations des orbitales atomiques et les constantes d'hybridation, les énergies des orbitales moléculaires et les valeurs des potentiels d'ionisation. En particulier, les valeurs des moments dipolaires et des potentiels d'ionisation tout en étant dans le bon ordre relatif sont trop élevées en valeur absolue.

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This work was supported by grant No. GM-12229 of the U.S. Public Health Service (National Institute of General Medical Sciences).