Methoden und Anwendungen der statistischen Prozeß- und Qualitätskontrolle im chemischen Betrieb

Methodology and applications of statistical process and quality control in chemical plant. Statistical process and quality control, known respectively as SPC and SQC, presently command considerably attention. Originating with buyers of chemical products, the vocabulary and methodology of this area of expertise are increasingly entering the chemical plant. Appropriate use of these techniques is considered in the present article. A brief presentation of the philosophy of quality assurance in production using the methods of SPC and SQC is followed by a terse explanation of the goals and techniques of SPC/SQC. The applicability of the methods to process engineering is a special problem. Questions of the necessary adaptation and introduction into the conventional procedures of process control are discussed. Instrumentalization of plant with digital process controllers provides a framework for implementation of integrated solutions of such quality assurance systems in production. This is explained with the aid of examples.     

On the kinetics of the chlorination of titanium dioxide in the presence of solid carbon

Metallurgical and Materials Transactions B - The influence of solid carbon on the chlorination of TiO2 with Cl2 and CO-CO2-Cl2 gas mixtures was investigated gravimetrically using rutile and...     

Mechanical properties of electron-beam-melted AlSi12 surface layers

The melting parameters for an AlSi12 alloy, which lead to surface-melted layers with constant melting depth and smooth surface have been discovered using the electron beam melting technique. The main mechanical properties of the melted layer were determined with different testing methods, which were adapted for this specific use. Examination under quasistatic stresses showed an increase of the hardness of 60% compared with the base material. The tensile strength increased in the melted layer by about 50%, whereas the elongation was not reduced drastically. Examination under fatigue stress resulted in a reduced fatigue strength of the surface-melted samples. The reason for this was crack initiation at pores at the boundary of melted layer and base material. For a poreless melted AlSi12 alloy, however, the same fatigue strength as for the base material was found.     

Diverticulitis of the cecum

Ten patients with diverticulitis of the cecum are reported upon herein. The disease is difficult to distinguish preoperatively from that of appendicitis and may be difficult to distinguish intraoperatively from carcinoma of the cecum. The diverticula are usually solitary and may be of the true or false variety. A review of the literature is presented, and the difficulties of diagnosis and treatment are discussed. We advocate local resection of the diverticulum, when possible, and a right hemicolectomy when the diagnosis is in doubt or when local resection or invagination would jeopardize the ileocecal valve or the blood supply to the intestine. With more awareness of diverticulitis of the cecum, intraoperative diagnosis may be made easier and the treatment simplified.     

Zur frühzeitigen Erkennung gefährlicher Reaktionszustände in chemischen Reaktoren

Detection of hazardous states of chemical reactors in early stages of runaway . Safe operation of chemical reactors with strongly exothermic reactions requires the availability of measurement devices which are able to detect hazardous reactions in early stages. Only then can one adopt adequate countermeasures and thus avoid such dangerous situations. This paper attempts to show that modern control theory provides model-based state reconstruction methods for the solution of this detection problem. A mathematical model serves as a source of a-priori information on process behaviour in order to reconstruct the whole state vector of the plant from those quantities which are easy to measure. A knowledge of the whole state allows predictive calculation of the reaction and hence early detection of hazardous states. The possibilities of such a concept for the safe operation of strongly exothermic reactions are illustrated by the example of a simple batch process.     

Global metabolic profiling of Escherichia coli cultures: an evaluation of methods for quenching and extraction of intracellular metabolites

Metabolomics and systems biology require the acquisition of reproducible, robust, reliable, and homogeneous biological data sets. Therefore, we developed and validated standard operating procedures (SOPs) for quenching and efficient extraction of metabolites from Escherichia coli to determine the best methods to approach global analysis of the metabolome. E. coli was grown in chemostat culture so that cellular metabolism could be held in reproducible, steady-state conditions under a range of precisely defined growth conditions, thus enabling sufficient replication of samples. The metabolome profiles were generated using gas chromatography/time-of-flight mass spectrometry (GC/TOF-MS). We employed univariate and multivariate statistical analyses to determine the most suitable method. This investigation indicates that 60% cold (-48 degrees C) methanol solution is the most appropriate method to quench metabolism, and we recommend 100% methanol, also at -48 degrees C, with multiple freeze-thaw cycles for the extraction of metabolites. However, complementary extractions would be necessary for coverage of the entire complement of metabolites as detected by GC/TOF-MS. Finally, the observation that metabolite leakage was significant and measurable whichever quenching method is used indicates that methods should be incorporated into the experiment to facilitate the accurate quantification of intracellular metabolites.     

Online coupling of gas chromatography to nuclear magnetic resonance spectroscopy: method for the analysis of volatile stereoisomers

The identification of volatile cis/trans-stereoisomers was accomplished by employing a hyphenated GC-NMR system. The chromatographic and spectroscopic conditions were optimized with respect to the (1)H NMR detection. A special processing technique was developed to handle the recorded NMR spectra in the gas phase with very low sample amounts. The processed stopped-flow (1)H NMR spectra of the investigated chromatographic peaks unequivocally revealed the structure of the corresponding compounds.     

Helicoverpa zea CYP6B8 and CYP321A1: different molecular solutions to the problem of metabolizing plant toxins and insecticides

Under continual exposure to naturally occurring plant toxins and synthetic insecticides, insects have evolved cytochrome P450 monooxygenases (P450s) capable of metabolizing a wide range of structurally different compounds. Two such P450s, CYP6B8 and CYP321A1, expressed in Helicoverpa zea (a lepidopteran) in response to plant allelochemicals and plant signaling molecules metabolize these compounds with varying efficiencies. While sequence alignments of these proteins indicate highly divergent substrate recognition sites (SRSs), homology models developed for them indicate that the two active site cavities have essentially the same volume with distinct shapes dictated by side-chain differences in SRS1 and SRS5. CYP6B8 has a narrower active site cavity extending from substrate access channel pw2a with a very narrow access to the ferryl oxygen atom. This predicted shape suggests that bulkier molecules bind further from the ferryl oxygen at positions that are not as effectively metabolized. In contrast, CYP321A1 is predicted to have a more spacious cavity allowing larger molecules to access the heme-bound oxygen. The metabolic profiles for several plant toxins (xanthotoxin, angelicin) and insecticides (cypermethrin, aldrin and diazinon) correlate well with these predictive models. The absence of Thr in the I helix of CYP321A1 and hydroxyl groups on many of its substrates suggests that this insect P450 mediates oxygen activation by a mechanism different from that employed by CYP107A1 and CYP158A1, which are two bacterial P450s also lacking Thr in their I helix, and most other P450s that contain Thr in their I helix.