Breit-Wigner formulas for the scattering phase and the total scattering cross-section in the semi-classical limit

In this paper we prove results in resonance scattering for the Schrödinger operatorP _v=–h ²+V, V being a smooth, short range potential onR ⁿ . More precisely, for energy near a trapping energy level ₀ for the classical system defined by the Hamiltonianp(x,)= ²+V(x), we prove that the scattering phase and the scattering cross sections associated to (P _v, P₀) have the Breit-Wigner form (Lorentzian line shape) in the limith0.     

Synthesis and intramolecular cyclization of bisthiadiazinylmethane derivatives

Bisthiadiazinylmethane derivatives obtained from 1,2,6-thiadiazine 1,1-dioxides and formaldehyde, undergo unusual intramolecular cyclizations to thiadiazino [4,3-g] [2,1,3] benzothiadiazine tetraoxides. The structures of the newly synthesized compounds are discussed on the basis of ¹H and ¹³C-NMR data and X-ray analysis.     

Conductive polyethylene-carbon black composites by elongational-flow injection molding Part 3. Study of the structure and morphology

The morphology and structure of high molecular weight linear polyethylene (M _w 450000) filled with carbon black and processed using molds that introduce an elongational flow component during injection molding has been examined using electron microscopy and x-ray diffraction techniques. The study of fracture surfaces reveals the display of shish-kebabs oriented along the injection direction with segregated longitudinal channels of carbon black particles. Molecular and lamellar changes in orientation are, furthermore, studied across the thickness of the moldings. It is shown that addition of carbon black particles to injection-molded polyethylene induces significant changes in lamellar orientation. Thus, while lamellar overgrowth proceeds perpendicular to the fiber axes within carbon free channels, lamellae grow randomly within carbon-enriched regions where flow is less pronounced.     

The preparation of 4-oxo-N-aryl-4H-1-benzopyran-2-acetamides by the condensation/cyclization of trilithiated acetoacetanilides with lithiated methyl salicylates

Several acetoacetanilides were trilithiated in excess lithium diisopropylamide, and the resulting polylithiated intermediates were regioselectively condensed with lithiated methyl salicylates followed by acid cyclization to substituted 4-oxo-N-aryl-4H-1-benzopyran-2-acetamides (benzopyranone-2-acetamides).     

Fluoroquinolone Antimicrobials: Singlet Oxygen, Superoxide and Phototoxicity

The fluoroquinolone antibacterial agents possess photo-sensitizing properties that lead to phototoxic responses in both human and animal subjects. The phototoxicity order reported in humans is: fleroxacin > lomefloxacin, pefloxacin > ciprofloxacin ? enoxacin, norfloxacin and ofloxacin. Studies both in vivo and in vitro have related this phototoxicity to the generation of reactive oxygen species including hydrogen peroxide and the hydroxyl radical. We determined the quantum yields of singlet oxygen generation (φ_Δ,) by detection of the singlet oxygen (¹O₂) luminescence at 1270 tun for several fluoroquinolones, naphthyridines and other structurally related compounds. All the fluoroquinolones examined have low φ_Δ values ranging from 0.06 to 0.09 in phosphate buffer at pD 7.5. We also determined the ¹O₂ quenching constants for these compounds and their values were on the order of 10⁶M^?1 s¹, except for lomefloxacin whose rate constant was 1.8 × 10⁷M^?1 s^?1. The φ_Δ values were significantly decreased in a solvent of lower polarity such as methanol (0.007 ≤φ_Δ≤ 0.02). The production of ¹O₂ by these antibiotics did not correlate with the order reported for their phototoxicity. We also measured the photogeneration (λ > 300 nm) of superoxide by these antibacterials in dimethylsulfoxide using electron paramagnetic resonance and the spin trap 5,5-dimethyl-l-pyrroiine N-oxide. Although there is not a one-to-one correspondence between the relative rates of superoxide generation and the phototoxicity ranking of the fluoroquinolones, the more phototoxic compounds tended to produce superoxide at a faster rate. Nevertheless, the magnitudes of the observed differences do not appear sufficient to explain the range of fluoroquinolone phototoxicity potencies in human and animal subjects in general and the high activity of fleroxacin and lomefloxacin in particular. For these latter drugs the photoinduced loss of the F₈ atom as fluoride and the concomitant generation of a highly reactive carbene at C-8 provide a more plausible mechanism for their potent phototoxic and photocarcinogenic properties.     

Stress development during drying of calcium carbonate suspensions containing carboxymethylcellulose and latex particles

Stress development during drying of coatings produced from aqueous dispersions of calcium carbonate particles in the presence and absence of organic binders was studied using a controlled-environment stress apparatus that simultaneously monitored drying stress, weight loss, and relative humidity. Specifically, the influence of two organic binders on drying stress evolution was investigated: (1) carboxymethylcellulose, a water-soluble viscosifying aid, and (2) a styrene-butadiene latex emulsion of varying glass transition temperature. The stress histories exhibited three distinct regions. First, a period of stress rise was observed, which reflected the capillary tension exerted by the liquid on the particle network. Second, a maximum stress was observed. Third, it was followed by a period of either stress decay or rise depending on the organic species present. Significant differences in stress histories were observed between coatings containing soluble and nonsoluble binders. Maximum drying stresses (sigmamax) of 0.2-0.5 MPa were observed for coatings produced from pure calcium carbonate or calcium carbonate-latex suspensions, whereas coatings with carboxymethylcellulose exhibited substantially higher sigmamax values of 1-2 MPa. Upon drying, these coatings were quite hygroscopic, such that cyclic variations in relative humidity induced large cyclic changes in residual stress.     

Some rules forS(-2k) dipole sums?

Stieltjes conditions and the ratio test provide necessary but not sufficient conditions onS(-2k) dipole sums. If the dipole sums are accurate the associated [n, n –1] Padé approximant provides a better representation of (), the frequency-dependent dipole polarizability, than a truncated series expression and, in addition, should bound () below. It is shown how constraints on the dipole sums effect the form of the [2,1] Padé approximant and an additional constraint is derived that ensures the analyticity of the approximant on 0 < ₁. There then follows a discussion of the reliability of available literature dipole sum values for small molecules containing H, C, N and O.     

on the existence of organometallic palladium(IV) complexes

The reactions of palladium(II) compounds of the type Cl₂PdL₂ with bromobis(pentafluorophenyl)thallium(III) has been reexamined. The reported preparation of the organo palladium(IV) complex Cl₂Pd(C₆F₅)₂(PPh₃)₂ could not be repeated, and instead mixtures of binuclear palladium(II) compounds, Cl₂Pd(C₆F₅)₂L₂, and mononuclear palladium(II) compounds were obtained. The binuclear are transformed into the mononuclear complexes on addition of an excess of ligand L.The chlorine bridging atoms of the binuclear complexes can be replaced by other halogens or pseudohalogens by treatment with salts of the MX type (X = Br, I, SCN).