CLL = (L,L; 0, 0) measurements and a structure due to a P partial wave in the pp system

Measurements of C_LL of pp elastic scattering near θ_c.m. = 90° at thirteen energies between 300 and 800 MeV are reported. These, together with previous values of C_NN, are used to extract values of two quantities, $\text{?}{}_{\mathrm{<mtext>s</mtext>}}$ and $\text{?}{}_{\mathrm{<mtext>t</mtext>}}$, which contain only spin-singlet and only coupled spin-triplet partial waves, respectively. The $\text{?}{}_{\mathrm{<mtext>s</mtext>}}$ curve, which is not dependent on C_LL, exhibits the behavior expected for the previously conjectured ¹D₂ resonance. The $\text{?}{}_{\mathrm{<mtext>t</mtext>}}$ curve also exhibits a resonance-like behavior, which could be due either to the ³P₀ or the ³P₂ partial wave.     

On the decays π0→νν′

Phenomenological aspects of π⁰→νν′ are considered. From the existing experimental information, we deduce an upper limit $\text{Γ(π}{}^0\text{→νν′)}\text{Γ(π}{}^0\text{→}\text{all}\text{)}\text{< 2.4 × 10}{}^{\mathrm{?5}}\text{(90\%}\text{c.l.}\text{)}$. Possible mechanisms which can give rise to this process are discussed. Branching ratios of the order of 10^?6 for decays into the known neutrinos (ν_e, ν_μ) are found possible. Rates comparable to the experimental limit for decays into final states involving additional neutrinos (massive or massless) cannot be ruled out.     

On greedy algorithms for series parallel graphs

This note describes some sufficient conditions for the maximum or minimum of a weighted flow (the weights are on paths, and are derived from weights on the edges of the path), of given volume in a series parallel graph to be found by a greedy algorithm.     

Mixed state ultrasonic attenuation in clean niobium near Hc2

Both longitudinal and shear ultrasonic attenuations and magnetization were measured as a function of magnetic field in the mixed state of two niobium single crystal samples with residual resistivity ratios of 68 and 2665 respectively. Particular attention was paid to the behavior of the attenuation at fields near H_c2. The higher purity sample showed marked frequency dependence of normalized attenuation at frequencies from 10 to 110 MHz. The other sample showed qualitatively similar but less pronounced frequency dependence at frequencies ranging from 10 to 435 MHz. Frequency dependence in both samples was in qualitative agreement with the theoretical results of Cerdeira and Houghton[1]. The attenuation changes near H_c2 at the lowest experimental frequencies were compared quantitatively with the frequency independent theoretical results of Houghton and Maki[2]. Agreement in the less pure sample was within a factor of two of the Houghton-Maki results at both 4·2 and 1·4 K. Quantitative comparison to theory for the purer sample must be qualified by the large observed frequency dependence. However, agreement between theory and experiment was excellent at 4·2 K. At 1·4 K in the purer sample, the theoretical predictions differed from experimental results by factors from two to six for various configurations of magnetic field and ultrasonic propagation and polarization directions. Houghton-Maki predictions of the dependence of ultrasonic attenuation on the geometry of magnetic field and ultrasonic propagation and polarization direction were also examined.     

The plasma in high-current pseudospark switches

The discharge behavior and the erosion rate of pseudospark switches for high currents (50-150 kA) and pulse lengths of several microseconds were investigated for different electrode materials. A capacitor discharge (3.3 μF) without any load was used at a maximum voltage of 30 kV. Side-on optical investigations were performed either with a streak camera or a fast shutter camera. Using metal electrodes, the discharge ignites on axis, then widens up radially and burns homogeneously at the edge of the central apertures. After about 500 ns, a stable anode spot is observed on the plane electrode surface (at currents exceeding 45 kA), the location of which is statistical. The discharge is transformed to a metal vapor are discharge and the erosion rate increases by more than one order of magnitude. With semiconductor electrodes (i.e., silicon carbide), a different discharge behavior is observed, After ignition on axis, the discharge burns homogeneously on the whole carbide surface. No contraction to a small area occurs in comparison to metal electrodes. The reignition of later current half cycles starts at the triple point metal-carbide-gas. Then the discharge again spreads homogeneously over the total carbide surface. The erosion rate is about two magnitudes lower in comparison to metals. We assume that the current is conducted in a thin surface sheath which is heated to more than 2000 K     

A labeling study of π-cycloheptatrienetricarbonylchromium(0)

Peaks of different intensities in the mass spectra of π-toluenetricarbonylchromium and π-cycloheptatrienetricarbonylchromium were studied by deuterium labeling of the latter compound. Incomplete hydrogen randomization in cycloheptatriene ligands preceding different reactions was observed, in contrast to the results for cycloheptatriene itself.