Synthesis and structural characterization of Zn(O3PCH2OH), a new microporous zinc phosphonate

Zn(O3PCH2OH) (1) has been formed by reaction of zinc acetate with diethyl hydroxymethylphosphonate. The acidity of the zinc solution effects hydrolysis of the phosphonate to produce phosphonic acid in situ. 1 crystallizes in the trigonal spacegroup R3, with a = 15.9701(2) A, c = 7.783(2) A, and Z = 18. The compound has channels in the [001] direction, formed by phosphonate groups bridging the octahedral coordinated zinc atoms. The zinc atoms are coordinated by the three oxygens of the phosphonate group and the oxygen of the hydroxy group.     

Temperature dependent characteristics of La2O2S: Ln [Ln=Eu, Tb] with various Ln concentrations over 5-60 °C

This research is aimed at developing an optical sensor for remotely measuring human skin temperature in electromagnetically hostile environments, such as within a magnetic resonance imaging (MRI) scanner. In this feasibility study, various concentrations of europium-doped lanthanum oxysulphide (La₂O₂S: Eu—0.1-15 mol% (m/o)) and terbium-doped lanthanum oxysulphide (La₂O₂S: Tb—0.005-50 m/o) have been investigated in terms of crystallinity, photoluminescent (PL) spectral and decay time characteristics. For both phosphors, X-ray diffraction (XRD) has shown that as dopancy increases, the (1 0 0) and (0 0 2) reflections merge and there is a reduction in the c-axis parameter as well as the crystallite size. Photoluminescent characterisation (337 nm excitation) has also shown a dependency to dopant concentration through variance of peak intensity. Temperature dependent decay time measurements were carried out over a low temperature range 5-60 °C. Optimum brightness of these temperature dependent lines is achieved at concentrations of 1 and 10 m/o for La₂O₂S: Eu and La₂O₂S: Tb respectively. However, optimum temperature dependency is achieved at lower concentration for La₂O₂S: Eu, specifically at 0.1 m/o. In comparison to conventional phosphor temperature dependent characteristic, La₂O₂S: Tb showed an increase in decay time with respect to temperature for concentrations above 2 m/o.     

Synthesis and novel reactivity of halomethyldimethylsulfonium salts

Iodomethyl-, chloromethyl-, and fluoromethyldimethylsulfonium salts, 4b-d, have been synthesized and are observed to be highly reactive molecules that exhibit extraordinary diversity with respect to the nature of their reactivity, undergoing facile direct substitution (S(N)2) reactions, but also being highly susceptible to electron-transfer reactions. Cyclic voltametry experiments indicated that the iodomethyldimethylsulfonium compound, 4b, is a potent electron acceptor, even surpassing the reactivity of perfluoro-n-alkyl iodides in that capacity. The iodo- and chloromethyldimethylsulfonium salts, 4b,c, as well as the analogous iodomethyltrimethylammonium salt, 3a, are shown to be reactive SET acceptors.     

Electron capture rates on nuclei and implications for stellar core collapse

Supernova simulations to date have assumed that during core collapse electron captures occur dominantly on free protons, while captures on heavy nuclei are Pauli blocked and are ignored. We have calculated rates for electron capture on nuclei with mass numbers A=65-112 for the temperatures and densities appropriate for core collapse. We find that these rates are large enough so that, in contrast to previous assumptions, electron capture on nuclei dominates over capture on free protons. This leads to significant changes in core collapse simulations.     

Simulation of the spherically symmetric stellar core collapse, bounce, and postbounce evolution of a star of 13 solar masses with boltzmann neutrino transport, and its implications for the supernova mechanism

With exact three-flavor Boltzmann neutrino transport, we simulate the stellar core collapse, bounce, and postbounce evolution of a 13M star in spherical symmetry, the Newtonian limit, without invoking convection. In the absence of convection, prior spherically symmetric models, which implemented approximations to Boltzmann transport, failed to produce explosions. We consider exact transport to determine if these failures were due to the transport approximations made and to answer remaining fundamental questions in supernova theory. The model presented here is the first in a sequence of models beginning with different progenitors. In this model, a supernova explosion is not obtained.     

Michael addition of phosphorus derivatives on tetraethyl ethylidenediphosphonate

Nucleophilic phosphorus add to tetraethyl ethylidene diphosphonate in protic solvent to yield the product of the Michael reaction. This reaction appeared to be reversible at a temperature upper than 160 °C. To avoid this reverse reaction, alkylation in α position of the two phosphonate functions by activated elecrophile is reported.     

Neutrino-induced nucleosynthesis of A>64 nuclei: the nu p process

We present a new nucleosynthesis process that we denote as the nu p process, which occurs in supernovae (and possibly gamma-ray bursts) when strong neutrino fluxes create proton-rich ejecta. In this process, antineutrino absorptions in the proton-rich environment produce neutrons that are immediately captured by neutron-deficient nuclei. This allows for the nucleosynthesis of nuclei with mass numbers A>64, , making this process a possible candidate to explain the origin of the solar abundances of (92,94)Mo and (96,98)Ru. This process also offers a natural explanation for the large abundance of Sr seen in a hyper-metal-poor star.     

Lead Analysis in Soils and Sediments at the Saginaw Field and Stream Club

Samples from the Saginaw Field and Stream Club in Saginaw County, Michigan, were collected to determine whether lead levels at the club shooting ranges pose a threat to the environment. Flame atomic absorption spectroscopy (AAS) was used to determine lead levels in soil and sediment samples digested for total lead as well as soluble lead. Lead was present at levels exceeding 10,000 mg/kg in some surface soil samples. In general, lead was pervasive at the site in both metallic and soluble forms. Each of the shooting ranges contains areas where lead occurs at concentrations significantly in excess of the Michigan Department of Environmental Quality criteria and therefore poses a potential risk to the human users of the land as well as to the native wildlife.     

Effects of inelastic neutrino-nucleus scattering on supernova dynamics and radiated neutrino spectra

Based on the shell model for Gamow-Teller and the random phase approximation for forbidden transitions, we calculate cross sections for inelastic neutrino-nucleus scattering (INNS) under supernova (SN) conditions, assuming a matter composition given by nuclear statistical equilibrium. The cross sections are incorporated into state-of-the-art stellar core-collapse simulations with detailed energy-dependent neutrino transport. While no significant effect on the SN dynamics is observed, INNS increases the neutrino opacities noticeably and strongly reduces the high-energy tail of the neutrino spectrum emitted in the neutrino burst at shock breakout. Relatedly the expected event rates for the observation of such neutrinos by earthbound detectors are reduced by up to about 60%.