Positronium annihilation data and actual free-volume distribution in polymers

Determination of the size distribution of free-volume holes in solids, in particular, polymers, is an important physicochemical problem. The positron annihilation technique has been proposed for this purpose. The central point in this technique is the quantitative interpretation of data, especially, for substances with a high specific surface area. A developed free-volume system in open-pore membrane materials, such as poly(trimethylsilylpropyne) PTMSP and the spirocyclically bound benzodioxane polymer PIM-1, and polymeric sorbents (hypercrosslinked polystyrenes) makes it possible for the first time to compare the sorption characteristics and positron annihilation data on the character of size distribution of nanopores in these polymers. In combination with the results of mathematical simulation of the structure and radiothermoluminescence measurements, the array of data indicate the structural inhomogeneity of the test amorphous materials. It was shown that this inhomogeneity in relation to the positron annihilation technique is expressed in the insufficiency of the representation of the orthopositronium decay curve by one component that takes into account the Gaussian lifetime distribution (symmetrical pore size distribution) and in the necessity of use of several decay components. The feasibility of revealing a nonrandom character of pore size distribution gives the positron annihilation technique an advantage over other approaches (inverse gas chromatography, ¹²⁹Xe NMR) to investigation of nanopores in polymers.     

Porphyrin-based nanoporous network polymers

Network polymers exhibiting large surfaces areas (900-1000 m2g-1) are prepared by the highly efficient dibenzodioxane forming reaction between meso-tetrakis(pentafluorophenyl)porphyrin and a rigid bis(catechol) monomer.     

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.     

Search for doubly charged Higgs bosons decaying to dileptons in pp collisions at square root of s=1.96 TeV

We present the results of a search for doubly charged Higgs bosons (H+/-+/-) decaying to dileptons (ll(')) using approximately 240 pb(-1) of pp collision data collected by the CDF II experiment at the Fermilab Tevatron. In our search region, given by same-sign ll(') mass m(ll('))>80 GeV/c(2) (100 GeV/c(2) for ee channel), we observe no evidence for H+/-+/- production. We set limits on sigma(pp -->H++H---->l(+)l('+)l(-)l('-)) as a function of the mass of the H+/-+/- and the chirality of its couplings. Assuming exclusive same-sign dilepton decays, we derive lower mass limits on H(+/-+/-)(L) of 133, 136, and 115 GeV/c(2) in the ee, mumu, and emu channels, respectively, and a lower mass limit of 113 GeV/c(2) on H(+/-+/-)(R) in the mumu channel, all at the 95% confidence level.