Constraints on nucleon decay via invisible modes from the Sudbury Neutrino Observatory

Data from the Sudbury Neutrino Observatory have been used to constrain the lifetime for nucleon decay to "invisible" modes, such as n-->3nu. The analysis was based on a search for gamma rays from the deexcitation of the residual nucleus that would result from the disappearance of either a proton or neutron from 16O. A limit of tau(inv)>2 x 10(29) yr is obtained at 90% confidence for either neutron- or proton-decay modes. This is about an order of magnitude more stringent than previous constraints on invisible proton-decay modes and 400 times more stringent than similar neutron modes.     

Preferential Site Occupation in the Quasi‐Ternary Channel Compounds TlCr5S8–ySey (1 ≤ y ≤ 7) Introducing Anisotropic Variations of Interatomic Interactions: A Systematical Study of their Crystal Structures

The results of single crystal X‐ray investigations of the quasi‐ternary channel compounds TlCr₅S_8–ySe_y (1 ≤ y ≤ 7) show a linear increase of the unit cell volume with increasing Se content as expected for a solid solution. The successive occupation of the four distinct chalcogene sites by Se, however occurs in a nonlinear way. During the substitution the two sites X1 and X2 are strongly preferred by the Se atoms. For site X3 no significant preference is observed and site X4 is clearly less favoured by the Se atoms. This unusual behaviour can be interpreted on the basis of the different polarizabilities of the constituting atoms. The occupation of X1 and X2 by Se gives the strongest covalent bonding interactions, especially between Tl and Se thus being the driving force for the high preference of Se for these two sites. The preferential occupation of the four crystallographically independent chalcogene sites leads to an unexpected and spectacular dependence of the unit cell parameters and of the interatomic distances as function of the Se content. The a axis shows a negative deviation from linearity, whereas the c axis exhibits a positive one. The monoclinic angle β passes a maximum at y = 5, and finally drops to a value comparable with that obtained for the pure sulfide. A detailed analysis demonstrates that the series can be divided into the two different regions 0 ≤ y ≤ 4 and 5 ≤ y ≤ 8, both characterized by a linear variation of the lattice parameters as well as of the interatomic distances.     

Generators of matrix algebras in dimension 2 and 3

Let K be an algebraically closed field of characteristic zero and consider a set of 2×2 or 3×3 matrices. Using a theorem of Shemesh, we give conditions for when the matrices in the set generate the full matrix algebra.     

Tuning of Water and Hydroxide Content of Intercalated Ruddlesden-Popper-type Oxides in the PrSr(3)Co(1.5)Fe(1.5)O(10-δ) System

A series of hydration experiments of the Ruddlesden-Popper phase PrSr(3)Co(1.5)Fe(1.5)O(10-δ) with varying levels of oxygen nonstoichiometry were performed with the goal to clarify phase formation and underlying mechanisms and driving forces. The hydration reaction is most intense for partly reduced samples with a vacancy concentration corresponding to δ ≈ 1. Fully oxidized samples show little or no tendency toward hydration. Presence of oxygen vacancies acts as a prerequisite for hydration. Probably, the basicity of the materials owing to A-site cations is another contributing factor to the hydration ability. Under CO(2) free conditions pure hydrates and oxide hydroxides are formed. In CO(2)-containing atmosphere, additional carbonate anions are easily incorporated into the hydrate, probably at the expense of hydroxyl groups. The I-centered PrSr(3)Co(1.5)Fe(1.5)O(8)(OH)(2)·1H(2)O achieves a highly expanded c-axis upon the topochemical insertion reactions. In situ powder synchrotron X-ray diffraction (SXRD) shows that the hydrate converts to an oxide hydroxide, PrSr(3)Co(1.5)Fe(1.5)O(8)(OH)(2), at 70 °C with a primitive orthorhombic unit cell. Upon heating above 170 °C, an I-centered product is formed for which further dehydroxylation occurs at around 400-500 °C. Rietveld refinement of SXRD data shows that the absorbed water molecules fill the tetrahedral voids of the [AO](RS) rock salt layer of the monoclinic hydrate.     

Influence of precursors chemistry on ALD growth of cobalt-molybdenum oxide films

Cobalt molybdenum compounds are important catalytic materials in many processes, e.g. in splitting of ammonia to form CO free hydrogen fuel. We here report on deposition of such cobalt molybdenum oxides by atomic layer deposition (ALD) using different types of metal precursors CoCp(2) (Cp = cyclopentadienyl), Co(thd)(2) (Hthd = 2,2,6,6-tetramethylheptan-3,5-dione), Mo(CO)(6) and oxygen precursors O(3), H(2)O, and (O(3) + H(2)O). The growth dynamics have been investigated using quartz crystal microbalance (QCM) methods. It is evident that mixing of the different precursor chemistries affect the growth patterns. When water is introduced to the reactions, a surface controlled mechanism takes place which guides the deposited stoichiometry towards the CoMoO(4) phase over a wide range of cobalt rich pulsed compositions. This is a rare example of how surface chemistry can control stoichiometry of depositions in ALD. The deposited films have been investigated by X-ray diffraction, Raman spectroscopy and atomic force microscopy. The catalytic activity of selected films have been characterized by temperature programmed ammonia decomposition, proving the films to be catalytically active and lowering the decomposition temperature by some 200 °C.     

Watching the Methanol-to-Olefin Process with Time- and Space-Resolved High-Energy Operando X-ray Diffraction

The movement of reactants in a large methanol-to-olefin reactor bed was visualized by fast scanning synchrotron X-ray diffraction. Changes in the structure of the catalyst showed the formation of reaction intermediates and coke, which can be tracked along the reactor bed. The observations lead to a new model for the progress of the reaction and explain the role of methanol in coke formation.     

Well-Posedness of A Compressible Gas-Liquid Model for Deepwater Oil Well Operations

The main purpose of this paper is two-fold: (i) to generalize an existence result for a compressible gas-liquid model with a friction term recently published by Friis and Evje [SIAM J. Appl. Math., 71 (2011), pp. 2014–2047]; (ii) to derive a uniqueness result for the same model. A main ingredient in the existence part is the observation that we can consider weaker assumptions on the initial liquid and gas mass, and still obtain an existence result. Compared to the above mentioned work, we rely on a more refined application of the estimates provided by the basic energy estimate. Concerning the uniqueness result, we borrow ideas from Fang and Zhang [Nonlinear Anal. TMA, 58 (2004), pp. 719–731] and derive a stability result under appropriate constraints on parameters that determine rate of decay toward zero at the boundary for gas and liquid masses, and growth rate of masses associated with the friction term and viscous coefficient.     

Zur Bestimmung des Schwefels in Eisen und Stahl

Ohne Zusammenfassung     

Generic 2×2 matrices with involution

Procesi has given a linear basis for the ring ofm generic 2×2 matrices. We do the same for the ring ofm generic 2×2 matrices with transpose involution.