One-Dimensional Poisson Growth Models With Random and Asymmetric Growth

Suppose there is a Poisson process of points X _i on the line. Starting at time zero, a grain begins to grow from each point X _i , growing at rate A _i to the left and rate B _i to the right, with the pairs (A _i , B _i ) being i.i.d. A grain stops growing as soon as it touches another grain. When all growth stops, the line consists of covered intervals (made up of contiguous grains) separated by gaps. We show (i) a fraction 1/e of the line remains uncovered, (ii) the fraction of covered intervals which contain exactly k grains is (k–1)/k!, (iii) the length of a covered interval containing k grains has a gamma(k–1) distribution, (iv) the distribution of the grain sizes depends only on the distribution of the total growth rate A _i +B _i , and other results. Similar theorems are obtained for growth processes on a circle; in this case we need only assume the pairs (A _i , B _i ) are exchangeable. These results extend those of Daley, et al. (2000) who studied the case where A _i =B _i =1. Simulation results are given to illustrate the various theorems.     

Product ion studies of diastereomeric benzo[ghi]fluoranthene tetraols by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and post-source decay

The product ion formation characteristics of the four diastereomeric tetrahydroxy benzo[ghi]fluoranthene compounds formed by hydrolysis of the syn and anti diastereomers of trans-3,4-dihydroxy-5,5a-epoxy-3,4,5,5a-tetrahydrobenzo[ghi]fluoranthene are studied using matrix-assisted laser desorption/ionization and post-source decay (PSD) to determine a correlation between the fragmentation characteristics of these tetraols and the structures of the diol-epoxide diastereomers from which they are hydrolyzed. The tetraols formed by the trans ring opening of the diol epoxides during hydrolysis yield product ion spectra specific for the syn and anti configurations of their precursor diol epoxides. All four diastereomeric tetraols form product ions by the losses of one and/or two water molecules in varying proportions when lithium-cationized molecule ions (m/z 301) are selected for PSD product ion analysis. The differences in the PSD spectra of these four Li+-cationized molecules are rationalized in terms of a water loss mechanism that involves the 1,2 elimination of a hydrogen atom and hydroxyl group that are cis with respect to each other on adjacent carbons.     

Synthesis of bis N-heterocyclic carbenes,derivatives and metal complexes

A method for the synthesis and isolation of 1,1′-methylene-bis-(3-aryl-imidazol-2-ylidene) ligands, aryl = 2,6-diisopropyl-phenyl (DiPP), L^DiPP, mesityl (mes), L^mes, is reported, which provides synthetically useful quantities of high purity. Derivatisation of L^DiPP with chalcogenides gave the adducts L^DiPPE₂, E = S, Se, Te. Reaction of L^DiPP with [Pd(tmeda)Me₂], [Pt(μ-SMe₂)Me₂]₂, [Ir(1,5-COD)(μ-Cl)]₂/KPF₆ and [NiBr₂(dme)] gave [Pd(L^DiPP)Me₂] (1), [Pt(L^DiPP)Me₂] (2), [Ir(L^DiPP)(1,5-COD)](PF₆) (3) and [Ni(L^DiPP)Br₂] (4), respectively. The latter was reduced in the presence of CO to [Ni(L^DiPP)(CO)₂] (5). The structures of L^mes, L^DiPPTe₂, and 1–5 are also reported.     

Improved direct measurement of the parity-violation parameter Ab using a mass tag and momentum-weighted track charge

We present an improved direct measurement of the parity-violation parameter A(b) in the Z boson-b-quark coupling using a self-calibrating track-charge technique applied to a sample enriched in Z-->bb events via the topological reconstruction of the B hadron mass. Manipulation of the Stanford Linear Collider electron-beam polarization permits the measurement of A(b) to be made independently of other Z-pole coupling parameters. From the 1996-1998 sample of 400,000 hadronic Z decays, produced with an average beam polarization of 73.4%, we find A(b)=0.906+/-0.022(stat)+/-0.023(syst).     

Do intelligent configuration search techniques outperform random search for large molecules?

We compare three global configuration search methods on a scalable model problem to measure relative performance over a range of molecule sizes. Our model problem is a 2-D polymer composed of atoms connected by rigid rods in which all pairs of atoms interact via Lennard–Jones potentials. The global minimum energy can be calculated analytically. The search methods are all hybrids combining a global sampling algorithm with a local refinement technique. The sampling methods are simulated annealing (SA ), genetic algorithms (GA ), and random search. Each of these uses a conjugate gradient (CG ) routine to perform the local refinement. Both GA and SA perform progressively better relative to random search as the molecule size increases. We also test two other local refinement techniques in addition to CG , coupled to random search as the global method. These are simplex followed by CG and simplex followed by block-truncated Newton. For small problems, the addition of the intermediate simplex step improved the performance of the overall hybrid method. © 1992 John Wiley & Sons, Inc.     

Improved direct measurement of A(b) and A(c) at the Z(0) pole using a lepton tag

The parity violation parameters A(b) and A(c) of the Zb(b) and Zc(c) couplings have been measured directly, using the polar angle dependence of the polarized cross sections at the Z(0) pole. Bottom and charmed hadrons were tagged via their semileptonic decays. Both the electron and muon analyses take advantage of new multivariate techniques to increase the analyzing power. Based on the 1993-1998 SLD sample of 550,000 Z(0) decays produced with highly polarized electron beams, we measure A(b) = 0.919+/-0.030(stat)+/-0.024(syst), and A(c) = 0.583+/-0.055(stat)+/-0.055(syst).     

First symmetry tests in polarized Z0 decays to bbg

We have made the first direct symmetry tests in the decays of polarized Z0 bosons into fully identified bbg states, collected in the SLD experiment at SLAC. We searched for evidence of parity violation at the bbg vertex by studying the asymmetries in the b-quark polar- and azimuthal-angle distributions, and for evidence of T-odd, CP-even or CP-odd, final-state interactions by measuring angular correlations between the three-jet plane and the Z0 polarization. We found results consistent with standard model expectations and set 95% C. limits on anomalous contributions.     

Direct measurements of Ab and Ac using vertex and kaon charge tags at the SLAC detector

Exploiting the manipulation of the SLAC Linear Collider electron-beam polarization, we present precise direct measurements of the parity-violation parameters A(c) and A(b) in the Z-boson-c-quark and Z-boson-b-quark coupling. Quark-antiquark discrimination is accomplished via a unique algorithm that takes advantage of the precise SLAC Large Detector charge coupled device vertex detector, employing the net charge of displaced vertices as well as the charge of kaons that emanate from those vertices. From the 1996-1998 sample of 400 000 Z decays, produced with an average beam polarization of 73.4%, we find A(c)=0.673+/-0.029(stat)+/-0.023(syst) and A(b)=0.919+/-0.018(stat)+/-0.017(syst).