Industrial applications of supercritical fluid chromatography: polymer analysis

Summary Polymers can be difficult to fully characterize by conventional chromatographic methods [i.e., gas chromatography (GC), high performance liquid chromatography (HPLC) and size exclusion chromatography (SEC)] due to temperature instability, detector incompatibility, nonvolatility, molecular weight considerations or insufficient chromatographic efficiency. Capillary supercritical fluid chromatography (SFC) offers several advantages for polymer analysis. Complex distributions can be resolved, low temperatures can be used and individual oligomers can be detected, allowing differences in molecular weight distributions to be quantitatively and qualitatively measured. In this paper, results will be shown for the analysis of various types of polymers demonstrating how changes in chromatographic parameters affect the analysis

---

Industrielle Anwendungen der Chromatographie mit überkritischen fluiden Phasen: Polymeranalyse

     

Reproducibility in capillary supercritical fluid chromatography: Comparison of injection techniques

An analysis of the precision obtained using commercially available microvalve injectors is reported for three modes of injection: conventional split; timed-split; and direct. Results from this study show that good precision (< 3% RSD for external standard and < 1% RSD for internal standard methods) can be obtained with capillary supercritical fluid chromatography (SFC). However, particular attention must be paid to the type of valve used, the orientation of the column relative to the valve, the mode of interfacing or connecting the column to the valve, and the type of pressure or density programming used for the analysis as all of these factors will affect the reproducibility.     

Charged hadron multiplicities and inclusive π− distributions in inelastic ep scattering

Electroproduction of hadrons is studied in the kinematic region W < 2.8 GeV and 0.3 < Q² < 1.4 GeV² using the DESY streamer chamber. Prong cross sections, charged-particle multiplicities and inclusive π^? distributions are presented. The average charged multiplicity is found to be independent of Q² in the Q² range studied here; however it is lower than in photoproduction. The fraction of forward π^? is found to be significantly less in electroproduction than in photoproduction. The 〈p_⊥²〉 for inclusive π^? is, for all x values, similar to that found in photoproduction.     

Determination of promethazine in human plasma by automated high-performance liquid chromatography with electrochemical detection and by gas chromatography-mass spectrometry

A highly specific and sensitive method using automated high-performance liquid chromatography with electrochemical detection (HPLC-ED) and a method using gas chromatography-mass spectrometry (GC-MS) have been developed for the quantitative determination of promethazine in plasma. The lowest detectable concentration by HPLC-ED is 0.1 ng/ml of plasma and by GC-MS 0.5 ng/ml of plasma. The HPLC-ED method incorporates a valve switching unit to prevent all of the electroactive impurities from entering the electrode compartment, thus maintaining the sensitivity of the detector for the analyses of large numbers of samples. The GC-MS method incorporates the highly specific selected-ion monitoring technique. Plasmas derived from healthy subjects each given a single 50-mg oral dose of promethazine were analyzed by both HPLC-ED and GC-MS. The two methods compare favorably with a correlation coefficient of 0.92 and a slope of 1.059. While both methods are suitable for studying single-dose pharmacokinetics of promethazine, the automated HPLC-ED method has a decided advantage in being more sensitive and suitable for unattended overnight analyses of the large number of samples encountered in pharmacokinetic studies. The specificity of the HPLC-ED method is demonstrated by comparison to the GC-MS analysis of biological samples.     

Anti-plane shear fields with discontinuous deformation gradients near the tip of a crack in finite elastostatics

Summary This paper reconsiders the problem of determining the elastostatic field near the tip of a crack in an all-round infinite body deformed by a Mode III loading at infinity to a state of anti-plane shear. The problem is treated for a class of incompressible, homogeneous, isotropic elastic materials whose constitutive laws permit a loss of ellipticity in the governing displacement equation of equilibrium at sufficiently severe shearing strains. The analysis represents a generalization of that reported in an earlier study and, as before, is carried out for the small-scale nonlinear crack problem, in which a crack of finite length is replaced by a semi-infinite one, and the nonlinear field far from the crack-tip is matched to the near field predicted by the linearized theory. The methods employed in the present paper are necessarily largely qualitative, since they apply to all materials in the class considered. The principal feature of the resulting elastic field is the presence of two symmetrically located curves issuing from the crack-tip and bearing discontinuities in displacement gradient and stress.The results communicated in this paper were obtained in the course of an investigation supported in part by Contract N00014-75-C-0196 with the Office of Naval Research in Washington, D.C.     

Vectorial Approach to Fast Correlation Attacks

A new, vectorial approach to fast correlation attacks on binary memoryless combiners is proposed. Instead of individual input sequences or their linear combinations, the new attack is targeting subsets of input sequences as a whole thus exploiting the full correlation between the chosen subset and the output sequence. In particular, the set of all the input sequences can be chosen as the target. The attack is based on a novel iterative probabilistic algorithm which is also applicable to general memoryless combiners over finite fields or finite rings. To illustrate the effectiveness of the introduced approach, experimental results obtained for random balanced combining functions are presentedMost of this work was done while he was with Rome CryptoDesign Center, Gemplus, Italy     

Remarks on bang-bang control in a Hilbert space

The control of a linear system, whose performance index is the sum of a linear term and a quadratic term, is considered. A necessary and sufficient condition is given for the optimal control to be bang-bang, and this is used to extend and clarify the results of Refs. 1–2. As an illustration, an application to an elliptic boundary-value problem is given.This research was supported by the SFB 72 of the DFG, West Germany.