Preparation and characterization of a composite of silver iodide and synthetic zeolite ZSM5

A composite material made up of AgI and the potassium form of the synthetic zeolite ZSM5 has been prepared by treating the silver form of ZSM5 with potassium iodide. The composite has been characterised by X-ray powder diffractometry, IR and X-ray photoelectron spectroscopy, electron microsonde analyses and ac conductivity measurements. The Agl content in the composite material is 11.5%. On the basis of the conductivity data obtained for the composite material as well as for K-ZSM5, Ag-ZSM5, microcrystalline AgI and a physical mixture of AgI and K-ZSM5, it has been inferred that, in the composite material, AgI forms a thin conductive shell on the surface of the K-ZSM5 particles.     

UV absorption spectra and kinetics of the self reaction of CFCl2CH2O2 and CF2ClCH2O2 radicals in the gas phase at 298 K

The ultraviolet absorption spectra of the peroxy radicals derived from hydrochlorofluorocarbons 141b and 142b, (CFCl₂CH₂O₂ and CF₂ClCH₂O₂, respectively), and the kinetics of their self reactions have been studied in the gas phase at 298 K using a pulse radiolysis technique. Absorption cross sections were quantified over the wavelength range 220–300 nm. Measured absorption cross sections at 250 nm were indistinguishable within the experimental uncertainties (≈10%) and yield; Errors represent the sum of statistical uncertainty and our estimate of potential systematic errors. Our absorption cross section data were then used to derive the observed self reaction rate constants for reactions (1) and (2), defined as ?d[RO₂]/dt = 2k[RO₂]² (R = CFCl₂CH₂ or CF₂ClCH₂), of k_1obs = (4.36 ± 0.64) × 10^?12 and k_2obs = (4.13 ± 0.58) × 10^?12 cm³ molecule^?1 s^?1, quoted errors represent 2σ. These results are discussed with respect to previous studies of the absorption spectra and kinetics of peroxy radicals.     

ON THE DNA BENDING BY PSORALEN INTERSTRAND CROSSLINKING. A GEL ELECTROPHORETIC STUDY

Abstract— A synthetic, partially double stranded decadeoxyribonucleotide with cohesive ends, containing one potential psoralen photo-crosslinking site centrally positioned (5'-d(CGGGCTACCC) + 3'-d(CCGATGGGGC)), has been ligated to double stranded DNA oligomers, which were subsequently photoreacted with 4,5',8-trimethylpsoralen. It was found that psoralen DNA interstrand crosslinking does not significantly alter the electrophoretic mobility of these DNA molecules in polyacrylamide gels. Based on this, we conclude that any bends in the DNA helix that may be induced by psoralen DNA interstrand crosslinking must be significantly less than the 45^° proposed by Tomic et at. (1987) (Science, 238, 1722) and/or of a different nature than the DNA sequence dependent bends due to d(A)_n tracts.     

Electron-mediating Cu(A) centers in proteins: a comparative high field (1)H ENDOR study

High field (W-band, 95 GHz) pulsed electron-nuclear double resonance (ENDOR) measurements were carried out on a number of proteins that contain the mixed-valence, binuclear electron-mediating Cu(A) center. These include nitrous oxide reductase (N(2)OR), the recombinant water-soluble fragment of subunit II of Thermus thermophilus cytochrome c oxidase (COX) ba(3) (M160T9), its M160QT0 mutant, where the weak axial methionine ligand has been replaced by a glutamine, and the engineered "purple" azurin (purpAz). The three-dimensional (3-D) structures of these proteins, apart from the mutant, are known. The EPR spectra of all samples showed the presence of a mononuclear Cu(II) impurity with EPR characteristics of a type II copper. At W-band, the g( perpendicular) features of this center and of Cu(A) are well resolved, thus allowing us to obtain a clean Cu(A) ENDOR spectrum. The latter consists of two types of ENDOR signals. The first includes the signals of the four strongly coupled cysteine beta-protons, with isotropic hyperfine couplings, A(iso), in the 7-15 MHz range. The second group consists of weakly coupled protons with a primarily anisotropic character with A(zz) < 3 MHz. Orientation selective ENDOR spectra were collected for N(2)OR, M160QT0, and purpAz, and simulations of the cysteine beta-protons signals provided their isotropic and anisotropic hyperfine interactions. A linear correlation with a negative slope was found between the maximum A(iso) value of the beta-protons and the copper hyperfine interaction. Comparison of the best-fit anisotropic hyperfine parameters with those calculated from dipolar interactions extracted from the available 3-D structures sets limit to the sulfur spin densities. Similarly, the small coupling spectral region was simulated on the basis of the 3-D structures and compared with the experimental spectra. It was found that the width of the powder patterns of the weakly coupled protons recorded at g(perpendicular) is mainly determined by the histidine H(epsilon)(1) protons. Furthermore, the splitting in the outer wings of these powder patterns indicates differences in the positions of the imidazole rings relative to the Cu(2)S(2) core. Comparison of the spectral features of the weakly coupled protons of M160QT0 with those of the other investigated proteins shows that they are very similar to those of purpAz, where the Cu(A) center is the most symmetric, but the copper spin density and the H(epsilon)(1)-Cu distances are somewhat smaller. All proteins show the presence of a proton with a significantly negative A(iso) value which is assigned to an amide proton of one of the cysteines. The simulations of both strongly and weakly coupled protons, along with the known copper hyperfine couplings, were used to estimate and compare the spin density distribution in the various Cu(A) centers. The largest sulfur spin density was found in M160T9, and the lowest was found in purpAz. In addition, using the relation between the A(iso) values of the four cysteine beta-protons and the H-C-S-S dihedral angles, the relative contribution of the hyperconjugation mechanism to A(iso) was determined. The largest contribution was found for M160T9, and the lowest was found for purpAz. Possible correlations between the spin density distribution, structural features, and electron-transfer functionality are finally suggested.     

Liquid chromatography-mass spectrometry method to determine alcohol ethoxylates and alkylamine ethoxylates in soil interstitial water,ground water and surface water samples

Alcohol ethoxylates (AEs) and alkylamine ethoxylates (AMEs) are used as adjuvants in pesticide formulations. Analytical procedures for these compounds in environmental aqueous samples using LC-MS are presented. Sample preparation uses solid-phase extraction with Porapak Rdx cartridges. Detection limits and recoveries in ground water and surface water are, respectively, AEs: 16-60 ng/l, 35-93% and AMEs: 0.3-6 microg/l, 28-96%. The lower recoveries are obtained for the apolar surfactants. The procedure was employed on samples of ground water and soil interstitial water collected from farming areas. The individual AEs were detected at concentration levels ranging from 33 to 189 ng/l water.     

Contraction mappings in interval analysis

Under certain conditions, the contraction mapping fixed point theorem guarantees the convergence of the iterationx _i+1=f(x _i ) toward a fixed point of the functionf:R ⁿ →R ⁿ. When an interval extensionF off is used in a similar iteration scheme to obtain a sequence of interval vectors these conditions need not provide convergence to a degenerate interval vector representing the fixed point, even if the width of the initial interval vector is chosen arbitrarily small. We give a sufficient condition on the extensionF in order that the convergence is guaranteed. The centered form of Moore satisfies this condition.     

Afshar’s Experiment Does Not Show a Violation of Complementarity

A recent experiment performed by S. Afshar [first reported by M. Chown, New Sci. 183:30, 2004] is analyzed. It was claimed that this experiment could be interpreted as a demonstration of a violation of the principle of complementarity in quantum mechanics. Instead, it is shown here that it can be understood in terms of classical wave optics and the standard interpretation of quantum mechanics. Its performance is quantified and it is concluded that the experiment is suboptimal in the sense that it does not fully exhaust the limits imposed by quantum mechanics.     

Possible nature of oscillations in the time dependences of the internal friction and effective shear modulus in Al-Cu alloys

The conditions of the appearance of in-phase oscillations in the time dependences of the low-frequency internal friction and effective shear modulus G _eff in Al-0.01 wt% Cu and Al-0.001 wt % Cu alloys are studied. The in-phase oscillations are shown to appear in the alloys only when their dislocation-impurity structure is disturbed from equilibrium and the impurity concentration near a dislocation is optimum. This fact suggests that the in-phase oscillations are due to a collective character of dislocation-impurity interactions, which leads to a transfer of energy of translational dislocation motion to transverse dislocation vibrations in the main slip plane.     

The Bailey transform and false theta functions

An empirical exploration of five of Ramanujan's intriguing false theta function identities leads to unexpected instances of Bailey's transform which, in turn, lead to many new identities for both false and partial theta functions. 2000 Mathematics Subject Classification Primary—33D15, 11P83 Partially supported by National Science Foundation Grant DMS 0457003. Supported by the Australian Research Council.     

A new look at extensional rheology of low-density polyethylene

The nonlinear rheology of three selected commercial low-density polyethylenes (LDPE) is measured in uniaxial extensional flow. The measurements are performed using three different devices including an extensional viscosity fixture (EVF), a homemade filament stretching rheometer (DTU-FSR) and a commercial filament stretching rheometer (VADER-1000). We show that the measurements from the EVF are limited by a maximum Hencky strain of 4, while the two filament stretching rheometers are able to probe the nonlinear behavior at larger Hencky strain values where the steady state is reached. With the capability of the filament stretching rheometers, we show that LDPEs with quite different linear viscoelastic properties can have very similar steady extensional viscosity. This points to the potential for independently controlling shear and extensional rheology in certain rate ranges.