Mass spectral behavior of the hydrolysis products of sesqui- and oxy-mustard type chemical warfare agents in atmospheric pressure chemical ionization

Bis(2-hydroxyethylthio)alkanes and bis(2-hydroxyethylthioalkyl)ethers are important biological and environmental degradation products of sulfur mustard analogs known as sesqui- and oxy-mustards. We used atmospheric pressure chemical ionization mass spectrometry (APCI MS) to acquire characteristic spectra of these compounds in positive and negative ionization modes. Positive APCI mass spectra exhibited [M + H](+); negative APCI MS generated [M + O(2)](-), [M - H](-), and [M - 3H](-); and both positive and negative APCI mass spectra contained fragment ions due to in-source collision-induced dissociation. Product ion scans confirmed the origin of fragment ions observed in single-stage MS. Although the spectra of these compounds were very similar, positive and negative APCI mass spectra of the oxy-mustard hydrolysis product, bis(2-hydroxyethylthiomethyl)ether, differed from the spectra of the other compounds in a manner that suggested a rearrangement to the sesqui-mustard hydrolysis product, bis(2-hydroxyethylthio)methane. We evaluated the [M + O(2)](-) adduct ion for quantification via liquid chromatography-MS/MS in the multiple-reaction monitoring (MRM) mode by constructing calibration curves from three precursor/product ion transitions for all the analytes. Analytical figures of merit generated from the calibration curves indicated the stability and suitability of these transitions for quantification at concentrations in the low ng/mL range. Thus, we are the first to propose a quantitative method predicated on the measurement of product ions generated from the superoxide adduct anion of the sesqui-and oxy-mustard hydrolysis products.     

Inverse semigroups on graphs

For each [directed] graph we construct an inverse semigroup. Our main application is a simple proof of the characterization of partially ordered sets ofJ-classes of finite semigroups, and some generalizations; our proof avoids using the inductive construction of the previous method by one of the authors [4]. For a connected graph in which each vertex has index at least two, our construction gives a congruence free inverse semigroup. In the final section we describe how a slight modification bf the construction yields the polycyclic monoids.     

Thermo-osmosis of sorbable gases in porous media : Part II. Cascades

The theoretical basis of mixture separation by thermo-osmosis has been developed for two different experimental arrangements. In the first of these two vessels are connected only by a membrane across which a temperature gradient is maintained. Expressions were obtained for the separation factor of binary mixtures in terms of heats of transport, for pressure and composition changes across the membrane, and for determining the heat of transport of each component. In the second arrangement the vessels are connected via the membrane and also by a capillary of appropriate geometry, so that in the steady state there is a constant circulation of each component of the mixture. Expressions have again been derived for the steady state separation factor, and pressure and composition differences for binary mixtures.     

Low distortion euclidean embeddings of trees

We consider the problem of embedding a certain finite metric space to the Euclidean space, trying to keep the bi-Lipschitz constant as small as possible. We introduce the notationc ₂(X, d) for the least distortion with which the metric space (X, d) may be embedded in a Euclidean space. It is known that if (X, d) is a metric space withn points, thenc ₂(X, d)≤0(logn) and the bound is tight. LetT be a tree withn vertices, andd be the metric induced by it. We show thatc ₂(T, d)≤0(log logn), that is we provide an embeddingf of its vertices to the Euclidean space, such thatd(x, y)≤‖f(x)−f(y) ‖≤c log lognd(x, y) for some constantc. Supported in part by grants from the Israeli Academy of Sciences and the US-Israel Binational Science Foundation. Supported in part by NSF under grants CCR-9215293 and by DIMACS, which is supported by NSF grant STC-91-19999 and by the New Jersey Commission on Science and Technology.     

A free boundary problem for a singular system of differential equations: An application to a model of tumor growth

In this paper we consider a free boundary problem for a nonlinear system of two ordinary differential equations, one of which is singular at some points, including the initial point . Because of the singularity at , the initial value problem has a one-parameter family of solutions. We prove that there exists a unique solution to the free boundary problem. The proof of existence employs two ``shooting' parameters. Analysis of the profiles of solutions of the initial value problem and tools such as comparison theorems and weak limits of solutions play an important role in the proof. The system considered here is motivated by a model in tumor growth, but the methods developed should be applicable to more general systems.

     

Framework for three-dimensional coherent diffraction imaging by focused beam x-ray Bragg ptychography

We present the framework for convergent beam Bragg ptychography, and, using simulations, we demonstrate that nanocrystals can be ptychographically reconstructed from highly convergent x-ray Bragg diffraction. The ptychographic iterative engine is extended to three dimensions and shown to successfully reconstruct a simulated nanocrystal using overlapping raster scans with a defocused curved beam, the diameter of which matches the crystal size. This object reconstruction strategy can serve as the basis for coherent diffraction imaging experiments at coherent scanning nanoprobe x-ray sources.     

Quantum symmetric derivatives

For , a one-parameter family of symmetric quantum derivatives is defined for each order of differentiation as are two families of Riemann symmetric quantum derivatives. For , symmetrization holds, that is, whenever the th Peano derivative exists at a point, all of these derivatives of order also exist at that point. The main result, desymmetrization, is that conversely, for , each symmetric quantum derivative is a.e. equivalent to the Peano derivative of the same order. For and , each th symmetric quantum derivative coincides with both corresponding th Riemann symmetric quantum derivatives, so, in particular, for and , both th Riemann symmetric quantum derivatives are a.e. equivalent to the Peano derivative.

     

Periodic behaviour for the evolutionary dam problem and related free boundary problems Evolutionary dam problem

The time dependent dam problem describing the seepage of a compressible or incompressible fluid in a porous dam is studied. We prove existence of solutions in a suitable weak sense, and uniqueness for rectangular dams. Existence or periodic solutions is established and questions ofstability and periodic behavior for large time are studied.     

Counting the number of solutions in combustion and reactive flow problems

Summary Computational methods and comparison theory enable, when combined, an enhanced capability for counting the number of solutions in combustion equations. Very good lower bounds for the last turning point reveal a stable high temperature explosion branch for very small positive exothermicity.