Polymerization of Methyl Methacrylate by Heat-Catalyst and Gamma-Irradiation Methods

Methyl methacrylate (MMA) was bulk-polymerized with 0 to 4% crosslinker (ethylene glycol dimethacrylate, EGDM, and trimethylol propane trimethacrylate, TMPTM), initiated with 0.05 to 5% catalyst (Vazo) at 65-75 C or 0.1 to 1 Mrad/hr gamma radiation at 20 C. Heat-catalyzed MMA conversion to polymer vs. time was obtained directly from polymer mass, which indicated that about 90% conversion had occurred at the exothermic peak temperature. The time to the exothermic peak temperature was used to determine sample polymerization time. The over-all polymerization rate varied with the half-power of initiator concentration. An Arrhenius plot of the initiator-time data gave an activation energy of 18 kcal/mole. A log-log relationship was found between crosslinker concentration and polymerization time over the 65-75 C temperature and 0.1-0.4% initiator range. The crosslinkers were found equally efficient in reducing polymerization time. Peak exothermie temperature varied directly with time, irrespective of the initiator and crosslinker concentrations or bath temperature except as they affected time. In the irradiation tests, the crosslinkers exhibited different data fits: log-log with EGDM and semilog for TMPTM. The time-dose rate equation for uncrosslinked MMA was analogous to that for heat-catalyzed polymerization. Molecular weight of uncrosslinked PMMA was determined as a function of temperature and catalyst concentration, and dose rate. Similar molecular weights were obtained for heat-catalyzed polymerization at 65 C and gamma irradiation at 20 C for numerically the same initiator concentration (%) and does rate (Mrad/hr)

Dynamic Mechanical Behavior of Black Cherry (Prunus Serotina EHRH.)

The dynamic mechanical properties of black cherry (Prunus serotina Ehrh.) have been investigated as a function of temperature at audio frequencies. Relaxation processes are evident near 200, 360, and 510 K. The process near 200 K was investigated as a function of initial moisture content (based on mass measurements prior to testing). At moisture contents greater than about 20%, the damping peak is centered near 185 K. This relaxation shifts with moisture content, and at moisture contents below 6%, the peak is centered near 225 K. The relaxation in the 360 K region is also associated with initial moisture content. For oven-dry black cherry specimens, the dynamic mechanical properties in the 360 K region are nearly temperature-independent. The relaxation near 510 K is believed to be associated with thermal degradation of wood constituents that are known to degrade in that temperature region

Some Physical Properties of Birch Carbonized in A Nitrogen Atmosphere

The dynamic mechanical properties, mass loss, and shrinkage data of birch carbonized in a nitrogen atmosphere to different temperatures from 473 to 973 K have been investigated. The dynamic elastic modulus data decreased as the heat treatment temperatures approached 673 K. Major mass loss and shrinkage accompanied the decrease in the modulus data. Treatments at higher temperatures (> 673 K) produced substantially less additional mass loss and shrinkage but produced increased rigidity in the char. The internal friction behavior of the char was complex

FCNC in left-right symmetric theories and constraints on the right-handed scale

We revise the limits on the FCNC higgses in manifestly left-right symmetric theories. It is shown that the combination of the Kobayashi-Maskawa CP-violation with the tree level $\Delta S=2$ higgs exchange gives very large contribution to the CP-violating $\epsilon$ parameter. It leads to the new strong constraint on the FCNC higgs mass, M>50- 100 TeV, enhanced by factor of the order $\sqrt{m_t/m_c}$. Being addressed to the supersymmetric left-right models, FCNC problem requires both right-handed scale and supersymmetric mass parameters be heavier than 50 TeV for $tan\beta\sim 1$. The most relaxed case corresponds to $tan\beta\sim 20- 30$ where right-handed scale can be of the order of few TeV.Comment: 11 pages, latex, 3 figure

Prospective surveillance of invasive group a streptococcal disease, Fiji, 2005-2007.

We undertook a prospective active surveillance study of invasive group A streptococcal (GAS) disease in Fiji over a 23-month period, 2005-2007. We identified 64 cases of invasive GAS disease, which represents an average annualized all-ages incidence of 9.9 cases/100,000 population per year (95% confidence interval [CI] 7.6-12.6). Rates were highest in those >65 years of age and in those <5 years, particularly in infants, for whom the incidence was 44.9/100,000 (95% CI 18.1-92.5). The case-fatality rate was 32% and was associated with increasing age and underlying coexisting disease, including diabetes and renal disease. Fifty-five of the GAS isolates underwent emm sequence typing; the types were highly diverse, with 38 different emm subtypes and no particular dominant type. Our data support the view that invasive GAS disease is common in developing countries and deserves increased public health attention

Expression of divIB of Bacillus subtilis during vegetative growth

Expression of the division initiation gene, divIB, of Bacillus subtilis vegetative growth was examined. lacZ fusion studies and transcription start point mapping have established that a sigma A promoter proximal to divIB is utilized in vivo. The -10 region of this promoter, which is located 93 bp upstream of the start codon, has been defined precisely by site-directed mutagenesis that destroys the promoter. Examination of transcripts by Northern (RNA) blotting has shown that there are at least two transcripts for divIB. The established proximal promoter was found to give rise to a very minor transcript which could not be convincingly demonstrated in wild-type cells but which became apparent upon insertion of a plasmid into the chromosome just upstream of this promoter. The major transcript for divIB originated from a site several kb upstream of the gene and is probably the same as the long polycistronic message also traversing the murD-spoVE-murG genes that was identified previously by others (A.D. Henriques, H. de Lencastre, and P.J. Piggot, Biochimie 74:735-748, 1992). Transcription from the proximal promoter alone, in an upstream-deletion mutant strain, provided sufficient DivIB for normal growth and division as well as sporulation

On the Hadronic Beam Model for Gamma-ray Production in Blazars

We consider, herein, a model for gamma-ray production in blazars in which a relativistic, highly-collimated electron-proton beam interacts with a dense, compact cloud as the jet propagates through the broad and perhaps narrow line regions (BLR and NLR) of active galactic nuclei (AGN). During the propagation of the beam through the cloud, the process of excitation of plasma waves becomes an important energy loss mechanism, especially for mildly relativistic proton beams. We compute the expected spectra of gamma-rays from the decay of neutral pions produced in hadronic collisions of the beam with the cloud, taking into account collisionless losses of the electron-proton beam. This model may explain the X-ray and TeV gamma-ray (both low and high emission states) of Mrk 421 as a result of synchrotron emission of secondary pairs from the decay of charged pions and gamma-ray emission from the decay of neutral pions for the plausible cloud parameters. However clouds can not be too hot and too dense. Otherwise the TeV gamma-rays can be attenuated by the bremsstrahlung radiation in the cloud and the secondary pairs are not able to efficiently produce synchrotron flares because of the dominant role of inverse Compton scattering. The non-variable $\gamma$-ray emission observed from Mrk 421 in the EGRET energy range cannot be described by the $\gamma$-rays from decay of neutral pions provided that the spectrum of protons in the beam is well described by a simple power law. These $\gamma$-rays might only be produced by secondary pairs scattering the soft non-variable X-rays which might originate in the inner part of the accretion disk.Comment: 14 pages,3 figures, latex, submitted to Ap

Supernova pointing with low- and high-energy neutrino detectors

A future galactic SN can be located several hours before the optical explosion through the MeV-neutrino burst, exploiting the directionality of $\nu$-$e$-scattering in a water Cherenkov detector such as Super-Kamiokande. We study the statistical efficiency of different methods for extracting the SN direction and identify a simple approach that is nearly optimal, yet independent of the exact SN neutrino spectra. We use this method to quantify the increase in the pointing accuracy by the addition of gadolinium to water, which tags neutrons from the inverse beta decay background. We also study the dependence of the pointing accuracy on neutrino mixing scenarios and initial spectra. We find that in the ``worst case'' scenario the pointing accuracy is $8^\circ$ at 95% C.L. in the absence of tagging, which improves to $3^\circ$ with a tagging efficiency of 95%. At a megaton detector, this accuracy can be as good as $0.6^\circ$. A TeV-neutrino burst is also expected to be emitted contemporaneously with the SN optical explosion, which may locate the SN to within a few tenths of a degree at a future km$^2$ high-energy neutrino telescope. If the SN is not seen in the electromagnetic spectrum, locating it in the sky through neutrinos is crucial for identifying the Earth matter effects on SN neutrino oscillations.Comment: 13 pages, 7 figures, Revtex4 format. The final version to be published in Phys. Rev. D. A few points in the original text are clarifie

Testing quark mass matrices with right-handed mixings

In the standard model, several forms of quark mass matrices which correspond to the choice of weak bases lead to the same left-handed mixings $V_L=V_{CKM}$, while the right-handed mixings $V_R$ are not observable quantities. Instead, in a left-right extension of the standard model, such forms are ansatze and give different right-handed mixings which are now observable quantities. We partially select the reliable forms of quark mass matrices by means of constraints on right-handed mixings in some left-right models, in particular on $V^R_{cb}$. Hermitian matrices are easily excluded.Comment: 12 pages RevTex, no figures. Minor corrections. Comment on SO(10) changed and one reference adde