Memory effects in combining isotope ratio monitoring with isotope dilution mass spectrometry

Combining isotope ratio monitoring with isotope dilution techniques provides very accurate results in the quantitative analysis of volatile organic chemical compounds by gas chromatography/mass spectrometry (GC/MS). However, this method requires that spikes highly enriched in (13)C be used. This may lead to memory effects which will be investigated in more detail. They occur when the component of the mixture to be investigated exhibits an isotope ratio which is different from that of the component eluted earlier from the column during the chromatographic separation process. A residue of this component, which is shown in the gas chromatogram as tailing, falsifies the result of the isotope ratio measurement. This also leads to false amount-of-substance measurement results. Memory effects can be avoided by using spikes of low (13)C content, by adjusting the composition of the reference solution to that of the sample, or by ensuring effective sample preparation, thus separating disturbing mixture components prior to the measurement. Copyright 1999 John Wiley & Sons, Ltd.     

Control of Nanospaces with Molecular Devices

Cavitands and capsules define nanoliter spaces for recognition, isolation and reactions of small molecules. These systems are usually self-assembled and factors such as solvent size, stoichiometry, and packing factors determine what goes into the spaces. Here we examine two switching devices to control what and when guests get in and out of these hosts: bipyridyl-metal chelation and azobenzene photoisomerization. The effects are reversible by treatment with conventional chelating agents and brief heating, respectively. Accordingly, it is possible to trigger reactions that take place within a cylindrical capsule by light, even though the reaction process is not photochemical by nature. Likewise the presence of metals can regulate reactions without acting as direct catalysts.     

Structure and properties of an eight-coordinate Mn(II) complex that demonstrates a high water relaxivity

An air-stable eight-coordinate (8C) Mn(II)N(8) complex has been synthesized utilizing an N(4) imidazole/imine ligand. The 8C dodecahedral geometry is structurally robust as the Mn complex is stable to air, NO(g), and potential coordinating anions. The structural, spectroscopic and water relaxivity properties of this complex are reported.     

Remote points and the like in pointfree topology

A point p of β, where X is a Tychonoff space, is called a remote point if for any nowhere dense D ⊆, X, p ∉ cl_βx D. A subset S of X is called round if whenever the closure in βX of a zero-set of X contains S, then it is a neighborhood of S. The purpose of this paper is to study these notions in the pointfree context. In the process, we introduce N-homomorphisms and show how the Stone extension of an N-homomorphism transfers remote points back and forth.      

Enhancement of radiosensitivity of oral carcinoma cells by iodinated chlorin p6 copper complex in combination with synchrotron X‐ray radiation

The combination of synchrotron X‐ray radiation and metal‐based radiosensitizer is a novel form of photon activation therapy which offers the advantage of treating malignant tumors with greater efficacy and higher precision than conventional radiation therapy. In this study the anticancer cytotoxic efficacy of a new chlorophyll derivative, iodinated chlorin p₆ copper complex (ICp₆‐Cu), combined with synchrotron X‐ray radiation (8–10 keV) in two human oral cancer cell lines is explored. Pre‐treatment of cells with 20 µM and 30 µM ICp₆‐Cu for 3 h was found to enhance the X‐ray‐induced cytotoxicity with sensitization enhancement ratios of 1.8 and 2.8, respectively. ICp₆‐Cu localized in cytoplasm, mainly in lysosomes and endoplasmic reticulum, and did not cause any cytotoxicity alone. The radiosensitization effect of ICp₆‐Cu accompanied a significant increase in the level of reactive oxygen species, damage to lysosomes, inhibition of repair of radiation‐induced DNA double‐strand breaks, increase in cell death and no significant effect on cell cycle progression. These results demonstrate that ICp₆‐Cu is a potential agent for synchrotron photon activation therapy of cancer.     

Exact piezothermoelastic solution of simply-supported orthotropic circular cylindrical panel in cylindrical bending

Summary This work presents an exact piezothermoelastic solution of infinitely long, simply supported, cylindrically orthotropic, piezoelectric, radially polarised, circular cylindrical shell panel in cylindrical bending under thermal and electrostatic excitation. The general solution of the governing differential equations is obtained by separation of variables. The displacements, electric potential and temperature are expanded in appropriate Fourier series in the circumferential coordinate to satisfy the boundary conditions at the simply-supported longitudinal edges. The governing equations reduce to Euler-Cauchy type of ordinary differential equations. Their general solution involves six constants for each Fourier component. These are solved from the algebraic equations obtained by satisfying the boundary conditions at the lateral surfaces. The solution of the inverse problem of inferring the applied temperature field from the given measured distribution of electrical potential difference between the lateral surfaces of the shell has also been presented. Numerical results are presented for typical thermal and electrostatic loadings for various values of radius to thickness ratio.     

Axisymmetric static and dynamic buckling of laminated thick truncated conical cap

Axisymmetric buckling analysis is presented for moderately thick laminated shallow, truncated conical caps under transverse load. Buckling under uniformly distributed loads and ring loads applied statically or as step function loads is considered. Marguerre-type, first-order shear deformation shallow shell theory is formulated in terms of transverse deflection w, the rotation ψ of the normal to the mid-surface and the stress function Φ. The governing equations are solved by the orthogonal point collocation method. Truncated conical caps with a circular opening, which is either free or plugged by a rigid central mass, have been analysed for clamped and simple supports with movable and immovable edge conditions. Typical numerical results are presented illustrating the effect of various parameters.