Neutrons produced by 1.22 GeV antiproton interactions with nuclei

Inclusive neutron energy spectra were measured by time of flight using 1.22 GeV antiprotons from LEAR, CERN, as projectiles and targets from natural Al, Cu, Ag, Ho, Ta, Au, Pb, Bi, U. The sum of two Maxwellian distributions was fitted to the spectra obtained at several forward and backward angles yielding neutron multiplicities M_i and slope or temperature parameters T _i for the low-energy (evaporative, i=1) and high-energy (pre-equilibrium,i=2) parts, respectively. M ₁ increases with A, proportional to the nuclear volume, and M ₂ is growing with A , proportional to the nuclear radius. The T parameters are nearly independent of A. The results are compared with previous multiplicity measurements with a neutron detector, intranuclear cascade calculations and neutron spectra from stopped antiproton annihilation on nuclei. With the measured proton spectra also the ratio of emitted neutrons to protons was determined for Au. Received: 25 February 2000 / Accepted: 19 May 2000     

X‐Ray Photoelectron Spectral Studies on Planar NiS4 and NiS2P2 Chromophores. Single Crystal X‐Ray Structural Study on [1, 4‐Bis(diphenylphosphino‐k,P, P')butane](piperidinecarbodithioato‐S,S')‐Nickel(II) Perchlorate

X‐ray photoelectron spectral study was made on the complexes Ni(nmedtc)₂( 1 ), [Ni(nmedtc)(PPh₃)₂]ClO₄( 2 ), [Ni‐(nmedtc)(dppe)]BPh₄( 3 ) (where nmedtc = N‐methyl, N‐ethanoldithiocarbamate, dppe = 1, 2‐bis(diphenylphosphino)ethane). The nickel 2p_3/2 binding energy values for chelated and free phosphine complexes are 854.0 and 854.1 eV which are significantly different from Ni2p_3/2 BE value of NiS₄ chromophore, indicating the relative dearth of electron density on Ni in NiS₂P₂ chromophores. The presence of two phosphine groups in NiS₂P₂ chromophore alleviates the electron density on the metal atom. More electron density is being pulled away from the metal atom in chelates than in the PPh₃ analogue. This observation is in line with solution studies by cyclic voltammetry. A one‐electron reduction potential was observed to be the minimum for NiS₂P₂ chromophores compared to the others. Also the crystal structure of the complex [Ni(pipdtc)(1, 4‐dppb)]ClO₄ (pipdtc^‐ = piperidinecarbodithioato anion, 1, 4‐dppb = bis(diphenylphosphino)butane) prepared by the reaction between Ni(pipdtc)₂, NiCl₂�6₂2O, and 1, 4‐dppb in CH₃CN‐CH₃OH is reported.     

Defect interaction and solid electrolyte transition in AgI-based materials

The first-order phase transition that leads to the superionic phase in AgI-based materials is studied by dc-conductivity measurements and a free energy model. By properly adjusting the model parameters, an abrupt change of disordering concentration, Δη?, is predicted at a transition temperature, T_t. The temperature dependence of the dc-conductivity, σ(T), is well fitted to the η?(T) equilibrium configuration obtained from the trial free energy function. The reported comparative study was done using an AgI–KI modified sample. The model also predicts a transition temperature, T_c for a continuous phase transition (Δη? = 0).     

Synthesis of fluorinated 1,2,4-oxadiazin-6-ones through ANRORC rearrangement of 1,2,4-oxadiazoles

The reaction of 3-ethoxycarbonyl-5-perfluoroalkyl-1,2,4-oxadiazoles with hydroxylamines has been investigated, evidencing the possibility of competitive reaction paths. Nucleophilic addition of hydroxylamine to the electrophilic C(5) of the 1,2,4-oxadiazole ring, followed by ring-opening and ring-closure with enlargement, leads to high yield and in very mild experimental conditions to the formation of 5-hydroxyamino-3-perfluoroalkyl-6H-1,2,4-oxadiazin-6-ones, one of these presenting water gelation ability. In turn, reactions with N-methylhydroxylamine lead the exclusive formation of 4-perfluoroacylamino-2-methyl-2H-1,2,5-oxadiazol-3-ones through the well known Boulton-Katritzky rearrangement.     

Determination of sulfonamide residues in water samples by in-line solid-phase extraction-capillary electrophoresis

An in-line solid-phase extraction-capillary electrophoresis method with UV–vis detection was developed for the monitoring of residues of five sulfonamides (sulfadoxin, sulfadimethoxine, sulfamerazine, sulfachloropyridazine and sulfamethoxazole) in tap, bottled mineral and river waters. For this purpose an analyte concentrator was constructed, based on the introduction of a small portion of a solid-phase extraction sorbent into the electrophoretic capillary to carry out an in-line concentration step, improving sensitivity. A detailed study was carried out to optimize parameters affecting the in-line solid-phase extraction process, such as the design of the concentrator device, type of sorbent and conditions of elution and injection. The proposed method is simple for the environmental monitoring of these antibiotic residues in waters, allowing the direct injection of the samples without any off-line pretreatment and achieving limits of detection between 0.3 and 0.6 μg/L. Recoveries ranging 52.2–109.2% and relative standard deviations below 13.4% were obtained.     

Representation systems and undergraduate proof production: A comment on Weber

Weber (2009) suggested that counterexamples can be generated by a syntactic proof production, apparently contradicting our earlier assertion (Alcock & Inglis, 2008). Here we point out that this ostensible difference is the result of Weber working with theoretical definitions that differ slightly from ours. We defend our approach by arguing that Weber’s relies upon an as yet unspecific metric for gauging the amount of work conducted in each representation system, and that it does not recognize an important asymmetry between the status of representation systems in the context of undergraduate mathematics.     

Parallelization of the integral equation formulation of the polarizable continuum model for higher-order response functions

We present a parallel implementation of the integral equation formalism of the polarizable continuum model for Hartree-Fock and density functional theory calculations of energies and linear, quadratic, and cubic response functions. The contributions to the free energy of the solute due to the polarizable continuum have been implemented using a master-slave approach with load balancing to ensure good scalability also on parallel machines with a slow interconnect. We demonstrate the good scaling behavior of the code through calculations of Hartree-Fock energies and linear, quadratic, and cubic response function for a modest-sized sample molecule. We also explore the behavior of the parallelization of the integral equation formulation of the polarizable continuum model code when used in conjunction with a recent scheme for the storage of two-electron integrals in the memory of the different slaves in order to achieve superlinear scaling in the parallel calculations.     

Five-to-six membered ring-rearrangements in the reaction of 5-perfluoroalkyl-1,2,4-oxadiazoles with hydrazine and methylhydrazine

The hydrazinolysis reaction of 5-perfluoroalkyl-1,2,4-oxadiazoles with hydrazine or methylhydrazine as bidentate nucleophiles has been investigated. The reaction occurred through the addition of the bidentate nucleophile to the C(5)-N(4) double bond of the 1,2,4-oxadiazole followed by ring-opening and ring-closure (ANRORC) involving the second nucleophilic site of the reagent. This ring-closure step could involve either the original C(3) of the 1,2,4-oxadiazole (giving a five-to-five membered ring rearrangement) or an additional electrophilic center linked to it (exploiting a five-to-six membered ring rearrangement). An alternative initial nucleophilic attack may involve the additional electrophilic center linked at C(3), that is the carbonyl group, leading to the formation of the hydrazones which undergo the Boulton-Katritzky rearrangement (BKR). The chosen reaction path is a function of the used nucleophile and of the nature of the substituent at C(3). At variance with previous hypotheses, when methylhydrazine was used, the observed regiochemistry always showed the preferred initial attack by the less hindered NH(2) end of the nucleophile on C(5). Moreover, new spectroscopic evidence allowed the assignment of correct structures to the products formed by reaction of 5-perfluoroalkyl-3-phenyl-1,2,4-oxadiazoles with methylhydrazine.     

Yukawa Couplings in Heterotic Compactification

We present a practical, algebraic method for efficiently calculating the Yukawa couplings of a large class of heterotic compactifications on Calabi-Yau three-folds with non-standard embeddings. Our methodology covers all of, though is not restricted to, the recently classified positive monads over favourable complete intersection Calabi-Yau three-folds. Since the algorithm is based on manipulating polynomials it can be easily implemented on a computer. This makes the automated investigation of Yukawa couplings for large classes of smooth heterotic compactifications a viable possibility.     

Interesting Reactivity in the Thermolysis and Photolysis of 2,3-Diphenyl-1-naphthol

Abstract  2,3-Diphenyl-1-naphthol (1) undergoes two unexpected reactions under different conditions. Compound (1) was heated in DMSO-d₆ and underwent a Pummerer type thermal reaction to give two isomeric products, 1-(methylthio)methoxy-2,3-diphenyl naphthol-d₅ which crystallized in the space group with a = 7.1610(9) ?, b = 11.2795(15) ?, c = 12.8905(17) ?, α = 114.049(2)°, β = 96.589(2)°, and γ = 102.945(2)°, and 2-(methylthio)methyl-2,3-diphenyl 1(2H)-naphthalenone-d₅ which crystallized in the space group with a = 8.5981(5) ?, b = 10.4374(6) ?, c = 11.1078(6) ?, α = 78.748(2)°, β = 67.709(2)°, and γ = 83.184(2)°. Photolysis (254 nm) of (1) resulted in 2,2′,3,3′-tetraphenyl-1,1′-bi-2-naphthol which crystallized in the space group P2₁/c with a = 26.3616(11) ?, b = 10.1707(4) ?, c = 23.3376(9) ?, and β = 99.034(2)°. Graphical Abstract  When 2,3-diphenyl-1-naphthol was heated in DMSO-d₆ two unexpected isomers, 1-(methylthio)methoxy-2,3-diphenyl naphthol-d₅ and the racemate 2-(methylthio)methyl-2,3-diphenyl 1(2H)-naphthalenone-d₅ were produced. Photolysis in THF at 254 nm led to the unexpected product 2,2′,3,3′-tetraphenyl-1,1′-bi-2-naphthol. All structures were elucidated by X-ray crystallography.