Hydrogenation of a Magnesium–Mg<Subscript>2</Subscript>Yb Alloy

A possibility for hydrogenation of a two-phase magnesium alloy containing intermetallic compound Mg₂Yb by hydrogen and ammonia is found to yield hydride phases MgH₂ and MgYbH_3.5 in various temperature schedules. The use of ammonia in the range 350–500°C leads to the formation of magnesium and ytterbium nitrides.     

Beyond the corey reaction: one-step diolefination of cyclic ketones

The reactivities of the cyclic ketones cycloheptanone, cyclodecanone, and cycloundecanone with dimethylsulfoxonium methylide generated from trimethylsulfoxonium iodide and base (NaH) were studied in diglyme at 130 degrees C. Oxiranes, which primarily form via the Corey reaction, lead to ring expansions to give oxetanes and oxacyclopentanes when an excess of dimethylsulfoxonium methylide is used. The Corey reaction is suppressed in the presence of excess of base, and 1,3-terminal dienes form instead (we term this reaction the Yurchenko diolefination). Our mechanistic proposal involves the deprotonation of the betaine that forms after the attack of dimethylsulfoxonium methylide on the carbonyl group of the ketone. The key step of the diolefination reaction involves a [2,3]-sigmatropic rearrangement of the ylide to a gamma-unsaturated sulfoxide with a barrier of 9.9 kcal/mol (DeltaH298, MP2/cc-pVDZ, for the cycloheptane derivative). The elimination of sulfenic acid from the gamma-unsaturated sulfoxide in the terminal step of the diolefination is associated with a higher barrier (17.3 kcal/mol) but is strongly accelerated in the presence of base. The reactivity of cyclic ketones in the Yurchenko reaction depends on the ring size; medium-sized cyclodecanone is less reactive than either cycloheptanone or cyclododecanone.     

Suppression of high-p{T} neutral pion production in central Pb+Pb collisions at sqrt[S{NN}]=17.3 GeV relative to p+C and p+Pb collisions

Neutral pion transverse momentum spectra were measured in p+C and p+Pb collisions at sqrt[S{NN}]=17.4 GeV at midrapidity (2.3 less than or approximately equal eta{lab} less than or approximately equal 3.0) over the range 0.7 less than or approximately equal p{T} less than or approximately equal 3.5 GeV/c. The spectra are compared to pi{0} spectra measured in Pb+Pb collisions at sqrt[S{NN}]=17.3 GeV in the same experiment. For a wide range of Pb+Pb centralities (N{part} less than or approximately equal 300), the yield of pi{0}'s with p{T} greater than or approximately equal 2 GeV/c is larger than or consistent with the p+C or p+Pb yields scaled with the number of nucleon-nucleon collisions (N{coll}), while for central Pb+Pb collisions with N{part}greater than or approximately equal 350, the pi{0} yield is suppressed.     

A study of the behavior of 2-chlorvinyldichloroarisine in soils

The conversion of 2-chlorvinyldichloroarisine ClCH=CHAsCl₂ (lewisite, I) in various soil samples is studied by IR spectroscopy. At the initial stage of the process, the rate and character of lewisite conversion are primarily determined by the presence of free surface hydroxyl groups in the sample (which manifest themselves as narrow intense absorption bands at 3700 and 3620 cm⁻¹), being nearly independent of the content of physically adsorbed water (a wide band at 3430 cm⁻¹). In sandy soils, which contain only a small concentration of hydroxyls, if any, lewisite experiences no noticeable decomposition, at least over a period of five days. By contrast, in clayey soils, possessing a high sorbability, the concentration of hydroxyls, highly reactive species, is large enough to completely hydrolyze lewisite into 2-chlorovinylarsonous acid ClCH=CHAs(OH)₂ and then 2-chlorovinylarsineoxide ClCH=CHAsO within several hours.     

New large grain,highly crystalline,transparent glass–ceramics

Two main reasons assure the transparency in the visible of some glass–ceramics (TGC): their crystal sizes are much smaller than the wavelength of light or the difference between the refractive index of glass matrix and crystal phase is small. The majority of traditional TGC have nano-size crystals and small to moderate crystallized volume fraction, usually between 3% and 70%. In this article we present a new type of transparent glass–ceramics having large (micrometric) grain size and very high crystallized volume fraction, which reaches up to 97%. Their high transparency mainly results from simultaneous variations of the glass matrix and crystal compositions during crystallization, which considerably decreases the difference between the respective refractive indexes, and this factor prevails, regardless of crystal size. Preliminary tests of their optical properties indicate that this new family of TGC can be further developed by doping with transition metals and rare-earths.     

Size Dependences of the Magnetic Properties of Superconducting Lead–Porous Glass Nanostructures

Superconducting structures Pb–PG formed by filling a porous glass matrix with the lead from melt under pressure have been investigated. Samples with characteristic pore structure diameters of d ≈ 7, 3, and 2 nm have been studied. It has been found that the critical temperature of the superconducting transition in the samples under study is similar to the corresponding value T_c ≈ 7.2 K for bulk lead. At the same time, it has been observed that the critical magnetic field of the nanocomposites, which attains H_c(T = 0 K) ≈ 165 kOe for Pb–PG (3 nm), exceeds several times the value H_c(0) = 803 Oe for bulk lead. The low-temperature magnetic- field dependences of magnetic moment M(H) contain quasi-periodic flux jumps, which vanish with a decrease in the lead nanostructure diameter. A qualitative model of the observed effects is considered.