Rigidity of codimension two indefinite spheres

We describe all isometric immersions f:S _n ^s S _s ⁿ +2/S _s ⁿ n–s4, whenever the set of totally geodesic points does not disconnect S _s ⁿ , where S _n ^s denotes the complete n-dimensional indefinite Riemannian space form of constant positive curvature 1 and signature s.     

Generalized solutions of a class of nuclear-space-valued stochastic evolution equations

Generalized solutions are defined for stochastic evolution equations of the formdY _t =A ^* Y _t dt + dZ _t on the nuclear triplel(R ^d ) L²(R ^d ) l(R ^d ), whereA does not mapl(R ^d ) into itself. One case which is treated in detail involvesA = –(–) ^/2 ,0 < < 2. This example arises as the Langevin equation for the fluctuation limit of a system of particles migrating according to a symmetric stable process and undergoing critical branching in a random medium.The research of D. A. Dawson was supported by the Natural Sciences and Engineering Research Council of Canada. L. G. Gorostiza's research was supported in part by CONACyT Grants PCEXCNA-040319 and 140102 G203-006, Mexico.     

Divisible modules and space of divisibility of an integral domain

Sunto Se A è un modulo divisibile su un dominio d'integrità R e Q è il campo delle frazioni di R, sia R_A Q il massimo sopraanello di R tale che A possa essere dotato della struttura di R_A-modulo. La struttura di R_A riflette quella di A. Se A è un modulo divisibile semplice di torsione, cioè è divisibile di torsione e non ha sottomoduli divisibili propri non nulli, R_A è analiticamente irriducibile. Se C e D sono due moduli divisibili semplici, diciamo C equivalente a D se R_C=R_D. Se d-Space (R) è un insieme di rappresentanti delle classi di equivalenza degli R-moduli divisibili semplici, d-Space (R) puó essere dotato di una struttura di spazio di Hausdorff zero-dimensionale; lo spazio topologico d-Space (R) (da noi chiamato lo spazio di divisibilità di R) contiene un sottospazio chiuso omeomorfo alla superficie di Riemann astratta di R dotata della patch topology.

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Lavoro eseguito con il contribute del Ministero délia Pubblica Istruzione     

Stationary axisymmetric solutions in the vacuum Jordan-Brans-Dicke theory

It is shown that any stationary axisymmetric solution to the vacuum field equations of the Jordan-Brans-Dicke (JBD) theory may be obtained from a composition of any stationary axisymmetric vacuum Einstein spacetime with the Weyl class of metrics. Thus, generating solution techniques can be used to obtain any stationary axisymmetric JBD vacuum solution. In this manner, C. B. G. McIntosh's results concerning this topic are improved upon.     

Self-assembled peptide tubelets with 7 A pores

Here we report the preparation and structural characteristics of self-assembling peptide tubelets composed of 32-membered rings formed of alternating alpha-amino acids and cis-3-aminocyclohexanecarboxylic acids. The tubelets possess a partial hydrophobic core environment, provided by the projection of the cyclohexane C2 methylene moiety into the lumen, and a Van der Waals pore diameter of about 7 A.     

A comparative study of several HPLC methods for determining free amino acid profiles in honey

A study of the viability of three derivatizing reagents for obtaining amino acid profiles in honey through high performance liquid chromatography (HPLC) is presented. A method using diode array detection based on a reaction with diethyl ethoxymethylene malonate (DEMM) and two other methods using fluorescence detection based on derivatization with fluorenylmethyl chloroformate (FMOC-Cl) and 6-aminoquinolyl-N-hydroxysuccinimidyl carbamate (AQC) have been developed. The three methods yield detection limits close to the ppb level, but vary in relation to other analytical characteristics. The use of methyl chloroformate derivatives allows the profile to be obtained with the greatest sensitivity within a short time frame. On applying such methods to honey samples of diverse botanical origin, we observe that the proline values obtained are always lower than those found using the official spectrophotometric method, thereby underlining the advisability of using HPLC methods to reduce uncertainty in these results.     

Gas chromatographic/mass spectrometric determination of vinyl acetate levels in air

The determination of vinyl acetate at parts per 10⁹ by volume (ppbv) levels in air by gas chromatography/mass spectrometry (GC/MS) was achieved by optimizing the GC conditions and choosing specific extraction solvents that are sufficiently pure. The ideal solvent should not give rise to fragment ions at m/z 43, in order to rule out any possible interference during the monitoring of the same vinyl acetate ion. Traces of acetone and butan-2-one in solvents suitable for this GC/MS determination may also mislead the detection of vinyl acetate. A 440 μl volume of a mixture of tetrachloroethylene containing 9% acetonitrile allowed the recovery of more than 90% of the ester with a detection limit of 1.5 ppbv in air together with a good linearity of response.     

Reactions of organomercury fulminates with acetylene derivatives

Organomercury fulminates react with acetylene derivatives to give unstable 3-(organomercurio)isoxazoles, which isomerize to 2-cyanoenolates. These are hydrolyzed with hydrochloric acid to the corresponding enols and are cleaved by water at the double bond. With monosubstituted acetylenes, substitution at the free position by the organomercury residue is predominant.     

Asymmetry and magnetism in bis(oximato)-bridged heterobimetallic compounds: a computational approach

A density functional study of exchange coupling was carried out for a series of heterobinuclear oximato-bridged transition metal complexes. Model calculations were used to examine the influence of the electronic configuration of the metal atoms on the coupling constants. This analysis was complemented by a study of the variation of the coupling constant with the most usual structural distortions within this family of compounds. The influence of the nature of the terminal ligands as well as that of the symmetry on the bridge were also investigated.