A Metric for an Evans-Vigier Field

In this paper we present an example of a specific metric which geometrizes explicitly a light-like four-vector potential field (Evans-Vigier field). We define the concepts of semilocal and complete geometrization and show that a light-like vector field has the same geometrical structure as a gravitational Kerr field. With this background in mind we discuss a theoretical proposition that a rotating body generates, besides a special gravitational field, a magnetic-type gauge field which might be identified with a geometrized Evans-Vigier field. We finally present a discussion which inform us that a classical Evans-Vigier field represents a novel type of field because we cannot identify it with any of the known electromagnetic fields.     

Composite membranes based on gellan and poly(N-vinylimidazole). Synthesis and characterization

Composite membranes based on gellan and poly(N-vinylimidazole) were prepared by using the method of solvent evaporation. In acid medium ionic interactions are established and evidenced by measurements of FTIR spectroscopy. The properties of these membranes were investigated by using elemental analysis, thermogravimetric analysis, atomic force microscopy and dynamic swelling experiments. The thermic behavior of the membranes depends on the nature of interactions and swelling degree is highly dependent on pH and composition. The properties of these membranes suggest potential applications in the field of biodegradable materials or as supports for drugs in view of their controlled release.     

3-center-4-electron bonding in [(silox)2Mo=NtBu]2(mu-Hg) controls reactivity while frontier orbitals permit a dimolybdenum pi-bond energy estimate

Na/Hg reduction of (silox)2Cl2Mo=NtBu (3) afforded C2h [(silox)2Mo=NtBu]2(mu-Hg) (12-Hg), which consists of two distorted trigonal monoprisms with Hg at the each apex (d(MoHg) = 2.6810(5) A). Calculations reveal 3c4e bonding in the linear MoHgMo linkage that renders 12-Hg susceptible to nucleophilic cleavage. Exposure to PMe3 and pyridine rapidly (<5 min) affords (silox)2(tBuN)MoLn (L = PMe3, n = 1 (1-PMe3); py, n = 2 (1-py2)), while poorer nucleophiles (L = C2H4, 2-butyne) yield adducts (e.g., 1-C2H4 and 1-C2Me2) after prolonged heating. The HOMO and LUMO of 12-Hg are "stretched" pi and pi* orbitals from which four states arise: 1Ag (GS), 3Bu, 1Bu, and 1Ag. DeltaE = E(1Bu) - E(3Bu) = 2K, where K is the exchange energy. Magnetic studies indicate E(3Bu) - E(1Ag) approximately 550 cm-1 (calcd 1744 cm-1), and a UV-vis absorption at 10 000 cm-1 is assigned to 1Ag --> 1Bu, permitting K to be evaluated as 4725 cm-1. With the pi --> pi* transition in Schrock's [Mo(NAr)(CH2tBu)(OC6F5)]2 (4) assigned at 528 nm, this estimation places its pi-bond energy as {E(pi2 --> pi1pi*1 in 4) - E(1Ag --> 1Bu in 12-Hg)} + E(1Ag --> 3Bu in 12-Hg) = 27 kcal/mol.     

Poly(1,3,4-oxadiazole-imide)s containing dimethylsilane groups

New poly(1,3,4-oxadiazole-imide)s containing dimethylsilane units have been prepared by solution polycondensation reaction of an aromatic dianhydride incorporating dimethylsilane group, namely bis(3,4-dicarboxyphenyl)dimethylsilane dianhydride, with different aromatic diamines having preformed 1,3,4-oxadiazole ring, such as 2,5-bis(p-aminophenyl)-1,3,4-oxadiazole, 2,5-bis[p-(4-aminophenoxy)phenyl]-1,3,4-oxadiazole, 2,5-bis[p-(3-aminophenoxy)phenyl]-1,3,4-oxadiazole, 2-(4-fluorophenyl)-5-(3,5-diaminophenyl)-1,3,4-oxadiazole, and 2-(4-dimethylaminophenyl)-5-(3,5-diaminophenyl)-1,3,4-oxadiazole. The polymers were easily soluble in polar organic solvents, such as N-methylpyrrolidinone, N,N-dimethylformamide, and pyridine, as well as in less polar organic solvents, such as tetrahydrofuran and chloroform. Very thin coatings deposited on silicon wafers exhibited smooth, pinhole-free surface in atomic force microscopy investigations. The polymers showed high thermal stability with decomposition temperature being above 415 °C.They exhibited a glass transition in the temperature range of 202-282 °C, with reasonable interval between glass transition and decomposition temperature. Solutions of the polymers in N,N-dimethylformamide exhibited fluorescence, having maximum emission wavelength in the range of 353-428 nm.     

Comparative performance of INAA and other spectroscopy techniques in the elemental analysis of stainless steel materials

Samples of high alloy Stainless Steel SS 1 were analyzed by instrumental neutron activation analysis (INAA) at 5 research institutes in 4 European countries within the frame of an Inter-Laboratory Comparison (ILC) exercise aiming at checking if the results were independent of the standardization methods, and if INAA was accurate enough to contribute to certification. The mean element concentration values yielded by INAA were also compared with mean values obtained by atomic emission spectroscopy techniques at other laboratories that took part in the International Proficiency Testing organized by KIMAB Institute of Sweden, producer of the SS 1. The performances of the nuclear and atomic techniques were compared in terms of the z-score values calculated for 11 element concentrations evaluated by the two analytical ways. Finally, consideration is given to the ways in which highest accuracy and precision can be ensured for certifying stainless steels as CRMs.     

Density functional theory study of indirect nuclear spin-spin coupling constants with spin-orbit corrections

This work outlines the calculation of indirect nuclear spin-spin coupling constants with spin-orbit corrections using density functional response theory. The nonrelativistic indirect nuclear spin-spin couplings are evaluated using the linear response method, whereas the relativistic spin-orbit corrections are computed using quadratic response theory. The formalism is applied to the homologous systems H2X (X=O,S,Se,Te) and XH4 (X=C,Si,Ge,Sn,Pb) to calculate the indirect nuclear spin-spin coupling constants between the protons. The results confirm that spin-orbit corrections are important for compounds of the H2X series, for which the electronic structure allows for an efficient coupling between the nuclei mediated by the spin-orbit interaction, whereas in the case of the XH4 series the opposite situation is encountered and the spin-orbit corrections are negligible for all compounds of this series. In addition we analyze the performance of the density functional theory in the calculations of nonrelativistic indirect nuclear spin-spin coupling constants.     

Cyclodextrins in Polymer Synthesis: Photoinitiated Free‐Radical Polymerization of N‐Isopropylacrylamide in Water Initiated by a Methylated β‐Cyclodextrin/2‐Hydroxy‐2‐methyl‐1‐phenylpropan‐1‐one Host/Guest Complex

Methylated β‐cyclodextrin (Me‐β‐CD) was used to complex a free‐radical photoinitiator, 2‐hydroxy‐2‐methyl‐1‐phenylpropan‐1‐one ( 1 ), yielding the water‐soluble 1 : 1 host/guest complex 1 a . The structure of complex 1 a was verified by means of IR, UV/vis and ¹H NMR spectroscopy. The influence of Me‐β‐CD as the host on the photopolymerization kinetics of N‐isopropylacrylamide was studied. Compared to the photopolymerization carried out under nearly identical conditions but without cyclodextrin, an increase in the polymerization rate was registered in the presence of complex 1 a .