Ratios of charged antiparticles-to-particles near mid-rapidity in Au + Au collisions at sqrt[s(NN)]=130 GeV

We have measured the ratios of antiparticles to particles for charged pions, kaons, and protons near mid-rapidity in central Au+Au collisions at sqrt[s(NN)] = 130 GeV. We observe / = 1.00+/-0.01(stat)+/-0.02(syst), / = 0.91+/-0.07(stat)+/-0.06(syst), and

/

= 0.60+/-0.04(stat)+/-0.06(syst). The / and

/

ratios give a consistent estimate of the baryo-chemical potential mu(B) of 45 MeV, a factor of 5-6 smaller than in central Pb+Pb collisions at sqrt[s(NN)] = 17.2 GeV.     

Ene reactions of olefins,part II. The addition of ethylene to propylene and to isobutene and the addition of propylene to propylene

The pyrolysis of ethylene–propylene and ethylene–isobutene mixtures has been studied in a static system over the temperature range of 682°–754° K and for initial pressures of each olefin of 33–300 torr. The following molecular ene reactions were observed and the rate constants measured: Using thermodynamic data, rate constants for the corresponding retro-ene decomposition reactions were calculated and compared to kinetic data reported for similar compounds. Other products were formed by radical chain processes, the main higher molecular weight ones being cyclopentene and 1-methylcyclopentene. A mechanism involving addition of allyl radicals is suggested for the formation of these products.     

Regioselective hydrothiolation of terminal acetylene catalyzed by magnetite (Fe3O4) nanoparticles

Herein, we report a new and solvent-free methodology for the preparation of vinyl thioethers from terminal alkynes and thiols, using magnetite (Fe₃O₄) nanoparticles as a recyclable catalyst. With this greener method, the desired vinyl thioethers were achieved in good yields and with good stereoselectivity. In addition, the catalyst was easily recovered using a simple external magnet and reused for further catalytic reactions without significant loss of activity up to the fifth cycle.     

Magnetization dynamics due to pure spin currents in magnetic double layers

The magnetization dynamics in magnetic double layers is affected by spin-pump and spin-sink effects. So far, only the spin pumping and its effect on the magnetic damping has been studied. However, due to conservation of angular momentum this spin current also leads to magnetic excitation of the layer dissipating this angular momentum. In this Letter we use time resolved magneto-optic Kerr effect to directly show the excitation due to the pure spin current. In particular, we observe magnetization dynamics due to transfer of angular momentum in magnetic double layers. In contrast to other experiments where a spin polarized charge current is passed through a nanomagnet, the effects discussed in this Letter are based on pure spin currents without net transfer of electric charge.     

System size, energy, pseudorapidity, and centrality dependence of elliptic flow

This Letter presents measurements of the elliptic flow of charged particles as a function of pseudorapidity and centrality from Cu-Cu collisions at 62.4 and 200 GeV using the PHOBOS detector at the Relativistic Heavy Ion Collider. The elliptic flow in Cu-Cu collisions is found to be significant even for the most central events. For comparison with the Au-Au results, it is found that the detailed way in which the collision geometry (eccentricity) is estimated is of critical importance when scaling out system-size effects. A new form of eccentricity, called the participant eccentricity, is introduced which yields a scaled elliptic flow in the Cu-Cu system that has the same relative magnitude and qualitative features as that in the Au-Au system.     

Formation of a spirodiazaselenurane and its corresponding azaselenonium derivatives from the oxidation of 2,2'-selenobis(benzamide). Structure, properties and glutathione peroxidase activity

The oxidation of 2,2'-selenobis(benzamide) with N-chlorosuccinimide or hydrogen peroxide afforded the corresponding stable azaselenonium chloride and hydroxide, respectively. Both structures were characterized by spectroscopic and X-ray crystallographic methods. Each contains a covalent N-Se bond, as well as a noncovalent interaction between the selenium atom and the carbonyl oxygen atom of the other amide moiety. The treatment of the azaselenonium chloride with an excess of potassium hydride in DMSO-d(6) afforded the corresponding spirodiazaselenurane species, which proved hydrolytically unstable, but was characterized by NMR spectroscopy. The azaselenonium chloride displayed significant glutathione peroxidase-like catalytic activity in an assay with benzyl thiol and either hydrogen peroxide or tert-butyl hydroperoxide.     

An Information Theoretic Approach to Symbolic Learning in Synthetic Languages

An important aspect of using entropy-based models and proposed “synthetic languages”, is the seemingly simple task of knowing how to identify the probabilistic symbols. If the system has discrete features, then this task may be trivial; however, for observed analog behaviors described by continuous values, this raises the question of how we should determine such symbols. This task of symbolization extends the concept of scalar and vector quantization to consider explicit linguistic properties. Unlike previous quantization algorithms where the aim is primarily data compression and fidelity, the goal in this case is to produce a symbolic output sequence which incorporates some linguistic properties and hence is useful in forming language-based models. Hence, in this paper, we present methods for symbolization which take into account such properties in the form of probabilistic constraints. In particular, we propose new symbolization algorithms which constrain the symbols to have a Zipf–Mandelbrot–Li distribution which approximates the behavior of language elements. We introduce a novel constrained EM algorithm which is shown to effectively learn to produce symbols which approximate a Zipfian distribution. We demonstrate the efficacy of the proposed approaches on some examples using real world data in different tasks, including the translation of animal behavior into a possible human language understandable equivalent.     

Application of Copper(I) Iodide/Diorganoyl Dichalcogenides to the Synthesis of 4‐Organochalcogen Isoquinolines by Regioselective C?N and C?Chalcogen Bond Formation

A copper‐catalyzed cyclization of (ortho‐alkynyl)benzaldimines with diorganoyl dichalcogenides allowed the synthesis of 4‐organochalcogen isoquinolines, whereas the presence of base in the reaction medium inhibited the product formation producing the undesirable isoquinoline without the organochalcogen atom at the 4‐position. The cyclization reaction was carried out by using CuI (20 %) as a catalyst with diorganoyl dichalcogenides (1.5 equiv) in the presence of DMF at 100 °C. Furthermore, the reaction did not require an argon atmosphere and was carried out in an open flask. The cyclization reaction tolerated a variety of functional groups both in ortho‐alkynylbenzaldimines and diorganoyl dichalcogenides, such as trifluoromethyl, chloro, fluorine, and methoxyl, to give the six‐membered heterocyclic ring exclusively through a 6‐endo‐dig cyclization process. The organochalcogen group present at the 4‐position of the isoquinoline ring was further subjected to a selective chalcogen–lithium exchange reaction followed by the addition of aldehydes to afford the desired secondary alcohols in good yields. The obtained isoquinolines also proved to be suitable substrates for the Suzuki and Sonogashira coupling conditions affording the corresponding products through C? C bond formation.     

Spaces to discuss mathematics: communities of practice on an online discussion board

In theories of learning that adopt a situated stance to knowledge the notion of identity is vital; how learners position themselves in relation to, and are mutually positioned by, the situation within which they are learning will have a strong bearing on the learning outcomes. One of the challenges for learning mathematics in school is that learners position themselves, and are positioned, as pupils rather than as mathematicians. This paper focuses on discussion boards designed for secondary school mathematics students, and we use Wenger's (1998) model of communities of practice, building on earlier work by the authors (Back and Pratt 2007; Pratt and Kelly 2007) in which ‘idealised communities’ are constructed and used, to consider a case study of one participant who engages in developing his identity as a mathematician doing mathematics, as well his identity as a learner and a teacher of mathematics.