Field-portable, high-speed GC/TOFMS

This work is focused on developing a fast gas chromatograph, time-of-flight mass spectrometer (GC/TOFMS) for man-portable field use. The goal is to achieve a total system solution for meeting performance, size, weight, power, cost, and ruggedness requirements for a laboratory in the field. The core technology will also be adaptable to specific applications including real-time point detection for hazardous chemical releases (e.g., chemical weapons), for biological agent signature identification, and for mobile monitoring platforms (e.g., air, ship, truck). Previously we presented results of a feasibility demonstration for a 30-lb field-portable TOFMS system. In this work we present recent progress in integrating a low-power, high-speed GC and show the capability for accurately recording fast GC transients for targeted compound detection using a quadrupole ion trap, time-of-flight instrument (QitTof).     

An improved method FO the determination of90Sr in large samples of seawater

The determination of⁹⁰Sr in large sample of seawater by its daughter product⁹⁰Y by means of solvent extraction with bis-2-ethylhexyl-phosphoric acid (HDEHP) ini n-heptane leads to²³⁴Th contamination. Two methods are described by which the²³⁸U daughter product²³⁴Th is separated from the Y³⁺ samples, either by a cation exchanger procedure or by a co-recipitation with Zr₃(PO₄)₄.     

Polymer networks by molecular dynamics simulation: Formation, thermal, structural and mechanical properties

A molecular dynamics simulation method is presented and used in the study of the formation of polymer networks. We study the formation of networks representing the methylene repeating units as united atoms. The network formation is accomplished by cross-linking polymer chains with dedicated functional end groups. The simulations reveal that during the cross-linking process, initially branched molecules are formed before the gel point; approaching the gel point, larger branched entities are formed through integration of smaller branched molecules, and at the gel point a network spanning the simulation box is obtained; beyond the gel point the network continues to grow through the addition of the remaining molecules of the sol phase onto the gel (the network); the final completion of the reaction occurs by intra-network connection of dangling ends onto unsaturated cross-linkers. The conformational properties of the strands in the undeformed network are found to be very similar with the conformational properties of the chains before cross-linking. The uniaxial deformation of the formed networks is investigated and the modulus determined from the stress-strain curves shows reciprocal scaling with the precursor chain length for networks formed from sufficiently large precursor chains (N ≥ 20).     

Atomlessr-maximal sets

We focus on % MathType!End!2!1!(A), the filter of supersets ofA in the structure of the computably enumerable sets under the inclusion relation, whereA is an atomlessr-maximal set. We answer a long-standing question by showing that there are infinitely many pairwise non-isomorphic filters of this type. Research partially supported NSF Grants DMS-96-3465 (Cholak) and DMS-95-00983 (Nies). The authors would like to thank Mike Stob for his help and interest.     

Some Isoperimetric Inequalities in Electrochemistry and Hele Shaw Flows

Isoperimetric inequalities are applied to a moving-boundaryproblem for doubly-connected domains. This problem occurs forexample in electrochemistry, in which case the domains in questionare the electrolyte of an electrolytic cell. The two electrodessurrounding the electrolyte are assumed to grow or dissolve,at different rates in general, by electrochemical reaction.We obtain optimal estimates showing, for example, that the leastchange in volume of each electrode always occurs in sphericalsymmetry.     

Undecidable fragments of elementary theories

We introduce a general framework to prove undecidability of fragments. This is applied to fragments of theories arising in algebra and recursion theory. For instance, the V3V-theories of the class of finite distributive lattices and of the p.o. of recursively enumerable many-one degrees are shown to be undecidable.Presented by S. Burris.