H*(10) and neutron spectra around linacs

Neutron spectrum and ambient dose equivalent has been measured around two 10 MV linear accelerators. Measurements were carried out in Mevatron and Primus model linacs, both made by Siemens. Main differences between those models are the beam collimator and the vault room. Here, Bonner sphere spectrometer with a passive thermal neutron detector has been utilized to measure the neutron spectrum inside the vault. Using an active detector the neutron spectrum was measured at the vault’s door of both accelerators. With a neutron area monitor the dose equivalent was measured by the door at both vault doors. Neutron strength, total fluence rate and ambient dose equivalent were compared, from this was found that shielding conditions are better in the Primus model.     

A composition formula in the rank two free group

Using the fundamental group of a punctured torus, a free group of rank two, and the fact that the natural eipmorphism from onto has as kernel the group of inner automorphisms of , we describe representatives of the conjugacy classes of generating pairs of and give explicit relations between them.

     

On the Construction of K-Operators in Field Theories as Sections Along Legendre Maps

The time-evolution K-operator (or relative Hamiltonian vector field) in mechanics is a powerful tool which can be geometrically defined as a vector field along the Legendre map. It has been extensively used by several authors for studying the structure and properties of the dynamical systems (mainly the nonregular ones), such as the relation between the Lagrangian and Hamiltonian formalisms, constraints, and higher-order mechanics. This paper is devoted to defining a generalization of this operator for field theories, in a covariant formulation. In order to do this, we use sections along maps, in particular multivector fields (skew-symmetric contravariant tensor fields of order greater than 1), jet fields and connection forms along the Legendre map. As a relevant result, we use these geometrical objects to obtain the solutions of the Lagrangian and Hamiltonian field equations, and the equivalence among them (specially for nonregular field theories).     

On an integral inequality and related summability results

We introduce the class E _p ^q of functions satisfying a new integral reverse inequality and we study the relationships with the classical Gehring and Muckenhaupt classes. In our main result, we prove higher integrability properties that generalize and improve the results obtained in [7] and [1].     

EPR studies of ion pairing in nematic butyl p-(p-ethoxyphenoxy carbonyl)—phenyl carbonate

The potassium salt of tetracyanoethylene (KTCNE) has been dissolved in nematic butyl p-(p-ethoxyphenoxy carbonyl)—phenyl carbonate by itself and in the presence of the ionophores 18-crown-6, dibenzo-18-crown-6, cryptand 222, nonactin, and valinomycin. The EPR spectra obtained from the ionophore containing solutions indicate the following equilibrium IK⁺ + TCNE^? ? (IK⁺ — TCNE^?). Here I represents the ionophore and (IK⁺ — TCNE^?) represents an ionophore complexed loose ion pair. A similar equilibrium occurs in the absence of the ionophore. In general for the (IK⁺— TCNE^?) ion pair, the degree of orientational ordering and the magnitude of its temperature dependence decrease as the molecular weight of I increases.     

Volumes of mixing ofn-alkanenitriles withn-alkanes: Interpretation through the Prigogine-Flory-Patterson theory

We present in this work the results of measurements of excess volumes of mixing V ^E at 30°C over the whole composition range for sixteen mixtures of n-hexanenitrile, n-octanenitrile, n-decanenitrile, and n-dodecanenitrile mixed individually with n-heptane, n-decane, n-tridecane, and n-hexadecane. The experimental values of V ^E show a regular pattern of behavior for the four sets of binary systems. In each group of mixtures for a given n-alkanenitrile, the magnitude of V ^E decreases as the n-alkane chain-length decreases. For mixtures containing a common n-alkane, V ^E decreases with increasing n-alkanenitrile chain-length. In order to explain the observed behavior, we have used the Prigogine-Flory-Patterson theory, which divides V ^E into three different contributions. The agreement between the theoretical and experimental V ^E is reasonable for the systems studied.     

Determination of the relative stereochemistry of flexible organic compounds by Ab initio methods: conformational analysis and Boltzmann-averaged GIAO 13C NMR chemical shifts

Ab initio calculations at the Hartree-Fock level with full-geometry optimization using the 6-31G(d) basis set, and GIAO (gauge including atomic orbitals) (13)C NMR chemical shifts, are presented here as a support in the study of the stereochemistry of low-polar organic compounds having an open-chain structure. Four linear stereoisomers, fragments of a natural product previously characterized by experimental (13)C NMR spectra, which possesses three stereogenic centers, 11 carbon atoms, and 38 atoms in total, were considered. Conformational searches, by empirical force-field molecular dynamics, pointed out the existence of 8-13 relevant conformers per stereoisomer. Thermochemical calculations at the ab initio level in the harmonic approximation of the vibrational modes, allowed the evaluation, at 298.15 K, of the standard Gibbs free energy of the conformers. The (13)C NMR chemical shift of a given carbon atom in each stereoisomer was considered as the average chemical shift value of the same atom in the different conformers. The averages were obtained by the Boltzmann distribution, using the relative standard free energies as weighting factors. Computed parameters related to linear correlation plots of experimental (13)C chemical shifts versus the corresponding computed average data allowed us to distinguish among the four stereoisomers.     

Hydrogen bonding, solvation, and hydrolysis of cisplatin: a theoretical study

Density functional calculations on a range of hydrogen bonded clusters of cisplatin are reported. A systematic search of 1:1 cisplatin:water complexes reveals only three stable minima, which contain a number of common, recurring interactions, such as an N-H...O-H...Cl bridging mode. Expanding these clusters by adding water molecules leads to a model of the first solvation shell of cisplatin, which contains the above motifs along with several strong water-water interactions. The strengths of such interactions are rationalized on the basis of electrostatic potentials, and quantified by use of Atoms in Molecules properties. This analysis also allows us to estimate cisplatin's position on Abraham's hydrogen bond acidity and basicity scales, indicating that cisplatin is a strong donor and acceptor of hydrogen bonds due to the dominance of hard, electrostatic interactions. The effects of this explicit solvation on the barrier to hydrolysis, and hence activation, of cisplatin are explored, indicating a slightly higher barrier than in the gas phase, leading to better agreement with experiment than either gas phase or continuum solvation calculations.     

Liquid–liquid phase behaviour,liquid–liquid density,and interfacial tension of multicomponent systems at 298 K

Experimental liquid–liquid phase diagrams are presented for the multicomponent systems isooctane–benzene–(80 mass% methanol + 20 mass% water)–5 mass% isobutyl alcohol (2-methyl-1-propanol) and isooctane–benzene–(80 mass% methanol + 20 mass% water)–15 mass% isobutyl alcohol, at 298.15 K. The density and interfacial tension of conjugate phases of concentration located in the isothermal binodal have been determined at 298.15 K for the partially miscible systems: isooctane–benzene–methanol, isooctane–benzene–(80 mass% methanol + 20 mass% water), isooctane–benzene–(80 mass% methanol + 20 mass% water)–5 mass% isobutyl alcohol, and isooctane–benzene–(80 mass% methanol + 20 mass% water)–15 mass% isobutyl alcohol. The experimental tie-line data define the binodal or coexistence curve of the two studied multicomponent systems and depending on the initial isobutyl alcohol concentration the liquid–liquid phase diagram is either of type II, with low alcohol concentration, or type I, with high concentration of alcohol, which is a clear indication that the solubility of the partially miscible systems is greatly enhanced via the co-solvency phenomenon. It is observed that both the density of each conjugate phase and the interfacial tension of each tie-line are valuable indicators of the degree of solubility of the multicomponent systems. Furthermore the experimental tie-lines data were correlated with the NRTL and UNIQUAC solution models with satisfactory quantitative results.