Some comments on the parameter choices for S.C.M.O. calculations on five membered heteroatomic π-electron systems

It has been reported [1] that the usual semi-empirical S.C.M.O. treatments of heteroatomic -electron systems yield unexpected dependencies of charge distribution on the _core terms involving the heteroatoms. Other workers [2] have claimed that the most usual choices of parameters yield chemically unreasonable charge densities in furan and pyrrole. It is shown here that the first effect is related to the relative magnitudes of the diagonal elements of the Fock matrix and that the second depends very strongly on the nonnearest neighbor F matrix elements but can be overcome with certain parameter choices by the inclusion of non-nearest neighbor _core terms in the calculations.

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Zusammenfassung Bei den üblichen semiempirischen SCMO-Rechnungen an Heteroaromaten ergeben sich unerwartete Abhängigkeiten der Ladungsverteilung von den _Rumpf-Termen [1]. Die gebräuchlichste Parameterwahl führt zu chemisch unverständlichen Ladungsverteilungen bei Furan und Pyrrol [2]. Es wird gezeigt, daß der erste Effekt mit der relativen Größe der Diagonalelemente der Fockmatrix zusammenhängt; der zweite Effekt hängt sehr stark von den Nichtnachbarelementen ab: Bei Einschluß von Nichtnachbar- _Rumpf-Termen und entsprechender Parameterwahl erhält man befriedigende Ladungsverteilungen.

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Résumé Il a été indiqué [1] que le traitement semi-empirique S.C.M.O. habituel des systèmes d'électrons dans les hétérocycles comporte des relations in attendues entre la distribution de charge et les termes _coeur impliquant les hétéroatomes. D'autres chercheurs [2] ont affirmé que les choix les plus communs de paramètres fournissent des densités de charge dans le furane et le pyrrole déraisonnables sur le plan chimique. On montre ici que le premier effet est lié aux grandeurs relatives des éléments diagonaux de la matrice de Fock et que le second effet dépend fortement des éléments non immédiatement voisins de cette matrice, mais peut être annulé avec certains choix de paramètres par introduction des termes non voisins _coeur dans les calculs.

     

Morphology of uniaxially oriented poly(ethylene terephthalate)

The morphological character of uniaxially oriented poly(ethylene terephthalate) (PET) films was investigated as a function of draw ratio. Dynamic mechanical, infrared, and crystallite-size measurements were made on the samples. In addition, selective degradation experiments and molecular weight determinations were employed. The dynamic mechanical measurements indicated a sharp decrease in irregular folds for draw ratios of 3.0 and higher, which also coincided with the essentially complete disappearence of regular folds (from the 988 cm^?1 band in the infrared spectra) in unannealed samples. Infrared studies of drawn samples annealed under different conditions gave evidence in support of a structure in which the chains are stretched out. Apparent crystallite-size measurements showed a sudden increase in length of the crystals in the direction of the draw beyond a draw ratio of 3.0. Molecular weight measurements showed a large increase in average chain length in the residue after selective degradation of amorphous material and folds; undrawn and slightly drawn samples gave a much lower M _n. Based on these observations, it is postulated that for higher draw ratios and present drawing conditions, the crystals are of the straight chain type, somewhat similar to the fringed-micelle crystal concept.     

The reaction π−p → K0Σ0 up to 2375 MeV/c

Differential cross-section and polarization measurements for the reaction π^?p → K⁰Σ⁰ are presented from 1395 to 2375 MeV/c incident beam momentum. The polarization data from an earlier experiment, from thershold to 1334 MeV/c, have been re-analysed by an improved method leading to a substantial reduction in the errors.     

A New Procedure for the Distribution of Periodicals

The magazine and newspaper wholesaler or distributor faces the problem of allocating copies of each new issue of each periodical among the retail outlets that sell that particular title. A large distributor will typically distribute over 150 new issues each week, with some issues being sent to more than 1000 retail outlets. This paper describes the development of a new distribution procedure which was undertaken for a major distributor.     

1H NMR spectra of E and Z pyridine-2-carbaldehyde 2′-pyridylhydrazone and related compounds

Proton magnetic resonance spectra at 100 MHz are reported for the E- and Z-isomers of pyridine-2-carbaldehyd 2′- pyridylhydrazone in carbon tetrachloride, d₆-dimethylsulphoxide and d₆-benzene solutions, and for various monomethylated derivatives in d₆-dimethylsulphoxide. The spectral parameters obtained by analysis with the help of LAOCOON 3 are discussed in terms of solvent effects and the chemical shift changes consequent upon isomerisation are evaluated. Some conclusions are reached concerning the preferred conformations of the E- and Z-isomers of pyridine-2-carbaldehyde 2′-pyridylhydrazone.     

Measurement of charged-particle multiplicities in gluon and quark jets in pp collisions at square root of s = 1.8 TeV

We report the first largely model independent measurement of charged particle multiplicities in quark and gluon jets, Nq and Ng, produced at the Fermilab Tevatron in pp collisions with a center-of-mass energy of 1.8 TeV and recorded by the Collider Detector at Fermilab. The measurements are made for jets with average energies of 41 and 53 GeV by counting charged particle tracks in cones with opening angles of theta(c) = 0.28, 0.36, and 0.47 rad around the jet axis. The corresponding jet hardness Q = Ejet theta c varies in the range from 12 to 25 GeV. At Q = 19.2 GeV, the ratio of multiplicities r = Ng/Nq is found to be 1.64+/-0.17, where statistical and systematic uncertainties are added in quadrature. The results are in agreement with resummed perturbative QCD calculations.     

The cochlear amplifier as a standing wave: "squirting" waves between rows of outer hair cells?

This paper draws attention to symmetric Lloyd-Redwood (SLR) waves-known in ultrasonics as "squirting" waves-and points out that their distinctive properties make them well-suited for carrying positive feedback between rows of outer hair cells. This could result in standing-wave resonance-in essence a narrow-band cochlear amplifier. Based on known physical properties of the cochlea, such an amplifier can be readily tuned to match the full 10-octave range of human hearing. SLR waves propagate in a thin liquid layer enclosed between two thin compliant plates or a single such plate and a rigid wall, conditions found in the subtectorial space of the cochlea, and rely on the mass of the inter-plate fluid interacting with the stiffness of the plates to provide low phase velocity and high dispersion. The first property means SLR wavelengths can be as short as the distance between rows of outer hair cells, allowing standing wave formation; the second permits wide-range tuning using only an order-of-magnitude variation in cochlear physical properties, most importantly the inter-row spacing. Viscous drag at the two surfaces potentially limits SLR wave propagation at low frequencies, but this can perhaps be overcome by invoking hydrophobic effects.     

Search for pair production of scalar top quarks in R-parity violating decay modes in pp collisions at square root of s=1.8 TeV

We present the results of a search for pair production of scalar top quarks (t(1)) in an R-parity violating supersymmetry scenario in 106 pb(-1) of pp collisions at square root of s=1.8 TeV collected by the Collider Detector at Fermilab. In this mode each t(1) decays into a tau lepton and a b quark. We search for events with two tau's, one decaying leptonically (e or mu) and one decaying hadronically, and two jets. No candidate events pass our final selection criteria. We set a 95% confidence level lower limit on the t(1) mass at 122 GeV/c(2) for Br(t(1)-->tau b)=1.     

Mode dependent vibrational autoionization of Rydberg states of NO2. II. Comparing the symmetric stretching and bending vibrations

Triple-resonance excitation and high-resolution photoelectron spectroscopy are combined to characterize the mode selectivity of vibrational autoionization of the high Rydberg states of NO2. Photoelectron spectra and vibrational branching fractions are reported for autoionizing Rydberg states converging to the NO2+ X 1Sigmag +(110) state, that is, with one quantum in the symmetric stretch, nu1, and one quantum in the bending vibration, nu2. These results indicate that autoionization proceeds most efficiently through the loss of one quantum from the symmetric stretch rather than from the bending vibration. The implications of this result are discussed in terms of the autoionization mechanism.     

Synthesis of methanesulfonyl chloride (MSC) from methane and sulfuryl chloride

Methane is transformed selectively to methanesulfonyl chloride at low temperature by liquid-phase reaction of methane with SO(2)Cl(2) in the presence of a free radical initiator and a promoter using 100% H(2)SO(4) as the solvent.