The determination of phenol in urine by enzymatic hydrolysis/headspace gas chromatography

Summary A new method has been developed for the determination of phenol in urine in which the phenol conjugates are hydrolysed enzymatically and the liberated phenol is analysed by headspace chromatography. The results compare favourably with those obtained by the method of van Haaften and Sie in which acid hydrolysis is carried out in a heated GC precolumn. The enzymatic hydrolysis headspace technique appears to be very reliable and does not suffer from the disadvantages of precolumn acid hydrolysis.Since this paper was submitted, we have found a report on the enzymatic hydrolysis of phenyl glucuronide in urine followed by gas chromatographic analysis which seems to have been overlooked by later workers. The paper is by H. Desoille, T. F. Gandenzi-Britto and M. Philbert in Archives des Maladies Professionelles, de Medecine du Travail et de Securite Sociale (Paris),30 (3), 129 (1969).     

Identification of archaeal proteins that affect the exosome function in vitro

Background  

The archaeal exosome is formed by a hexameric RNase PH ring and three RNA binding subunits and has been shown to bind and degrade RNA in vitro. Despite extensive studies on the eukaryotic exosome and on the proteins interacting with this complex, little information is yet available on the identification and function of archaeal exosome regulatory factors.     

High precision delta(17)O isotope measurements of oxygen from silicates and other oxides: method and applications

The use of infrared laser-assisted fluorination to release oxygen from milligram quantities of silicates or other oxide mineral grains is a well-established technique. However, relatively few studies have reported the optimisation of this procedure for oxygen-17 isotope measurements. We describe here details of an analytical system using infrared (10 μm) laser-assisted fluorination, in conjunction with a dual inlet mass spectrometer of high resolving power ( approximately 250) to provide (17)O and (18)O oxygen isotope measurements from 0.5-2 mg of silicates or other oxide mineral grains. Respective precisions (1) of typically 0.08 and 0.04 per thousand are obtained for the complete analytical procedure. Departures from the mass-dependent oxygen isotope fractionation line are quantified by Delta(17)O; our precision (1) of such measurements on individual samples is shown to be +/-0.024 per thousand. In turn, this permits the offset between parallel, mass-dependent fractionation lines to be characterised to substantially greater precision than has been possible hitherto. Application of this system to investigate the (17)O versus (18)O relationship for numerous terrestrial whole-rock and mineral samples, of diverse geological origins and age, indicates that the complete data set may be described by a single, mass-dependent fractionation line of slope 0.5244+/- 0.00038 (standard error). Copyright 1999 John Wiley & Sons, Ltd.     

A NEW FINITE ELEMENT APPROXIMATION OF A STATE-CONSTRAINED OPTIMAL CONTROL PROBLEM

In this paper, we study numerical methods for an optimal control problem with pointwise state constraints. The traditional approaches often need to deal with the deltasingularity in the dual equation, which causes many difficulties in its theoretical analysis and numerical approximation. In our new approach we reformulate the state-constrained optimal control as a constrained minimization problems only involving the state, whose optimality condition is characterized by a fourth order elliptic variational inequality. Then direct numerical algorithms （nonconforming finite element approximation） are proposed for the inequality, and error estimates of the finite element approximation are derived. Numerical experiments illustrate the effectiveness of the new approach.     

Virtual modes and the surface boundary condition in underwater acoustics

An explicit expression for the contribution of continuous normal modes to the acoustic pressure field in shallow water is derived under the assumption of constant sound speed in the bottom. An approximate evaluation of the resulting integral leads to a summation over “virtual” modes. These virtual modes are similar to the trapped modes except that their amplitudes decay with range. Their contribution is important in certain situations, for example at short ranges and where there may be few or no trapped modes. The validity of the “pressure release” boundary condition at the surface is investigated. This approximate boundary condition is justified by allowing for energy leakage into the air and examining the virtual mode contribution to the normal mode expression. These virtual modes converge identically to the usual trapped mode expression in the limit of zero air density.     

Coupled perturbed modes and internal solitary waves

Coupled perturbed mode theory combines conventional coupled modes and perturbation theory. The theory is used to directly calculate mode coupling in a range-dependent shallow water problem involving propagation through continental shelf internal solitary waves. The solitary waves considered are thermocline depressions, separating well-mixed upper and lower layers. The method is fast and accurate. Results highlight mode coupling associated with internal solitary waves, and mode capture or loss to and from the discrete mode spectrum.     

On subalgebras which survive contraction

We prove the following theorem: if a subalgebraB of an algebraG is spanned by root vectors, then ifX is a regular element ofG, the limit {ie160-1} Ad exptX(B) exists and is isomorphic toB, i.e.B survives contraction withX. The algebraSL(2C) is considered as an example. In particular it is shown thatSL(2C) itself survives and applications to relativistic scattering theory are indicated.Research supported in part by the Air Force Office of Scientific Research, Office of Aerospace Research, under Grant No. AF-AFOSR-232-66.On leave of absence from the Central Research Institute for Physics. Address after September 15, 1967: Central Research Institute for Physics, Budapest, Hungary.N.A.T.O. post-doctoral fellow.