Eine rechnergesteuerte Schnellmethode zur Bestimmung von Harnstoff in Milcherzeugnissen: Magermilchpulver unterschiedlicher Provenienz

Zusammenfassung Es wurde die enzymatische Harnstoff-Bestimmung in Sprühmagermilchpulvern auf ein rechnergesteuertes photometrisches Analysensystem übertragen. Die einfach zu handhabende Probenvorbereitung verleiht dem Analysensystem einen hohen Grad an Rationalität. Die flüssigen Proben wurden direkt oder nach Ultrafiltration für die Harnstoff-Bestimmung eingesetzt. Die Wiederholbarkeit bei der Probenvorbereitung ausgedrückt als Variationskoeffizient betrug im Mittel 0,69%, die Standardabweichung bei aufeinanderfolgenden Testansätzen 0,115–0,135 bei einem durchschnittlichen Gehalt von 5,4–5,5 mg Harnstoff/100 ml Magermilch. Die Methode wurde an einem umfangreichen Probenmaterial von 147 Magermilchpulvern, die nach saisonalen (Januar bis Oktober) Kriterien ausgewählt wurden, erprobt. Es wurde auf diese Weise ein breiter Überblick über die jahreszeitabhängigen Harnstoffgehalte in Sprühmagermilchpulvern unterschiedlicher Herkunft erhalten. Die Harnstoffgehalte sind von Februar bis Mai nahezu konstant (0,25–0,26%), steigen von Juni bis Oktober aber auf Werte von 0,32% an.

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A rapid computer aided method for the determination of urea in dairy products — skim milk powder

Summary The enzymatic determination of urea in spray-dried skim milk powders was transferred to a computer aided photometric analysing system. Sample preparation is optimal using ultrafiltration, but the direct use of a milk sample is also possible with this system. The precision including sample preparation as coefficient of variation was about 0.69%, the standard deviation of the assay was 0.115–0.135 at an average content of 5.4–5.5 mg urea per 100 ml skim milk. The method was tested on 147 spray-dried skim milk powders, which were of varying origin and collected at different times of the year (Jan.-Oct.). In this way a representative survey for the urea content of a great number of skim milk powders was possible. It was also shown, that the urea content is highly affected by season. It is very constant from February to May (0.25–0.26%), and rises from June to October up to nearly 0.32%.

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Herrn Professor Dr. Dr. Andreas Lembke, Institut für Virusforschung und experimentelle Medizin, D-2420 Eutin-Siebek zum 75. Geburtstag gewidmet.     

Zur statistik des einbaus einer als regler in polyamid 12 verwendeten aliphatischen dicarbonsäure

As hard blocks in polyether block amides, polyamides are used whose length is intensively regulated by dicarboxylic acids. Since, with regard to melting and crystallization behaviour, this acid constitutes an interfering structural unit in the chain, and in the case of a completely converted product each chain contains one acid molecule, it is essential to know where in the chain incorporation will occur. As opposed to monofunctional chain regulators which always form a chain end, a bifunctional chain regulator can a priori also be randomly incorporated into the inner part of the chain. This leads to a far greater interference than occurs if the chain regulator molecule and the chain end, which acts as an interfering unit in any case, coincide with each other. By means of adipic acid-regulated oligoamides based on lauryl lactam, the incorporation of the chain regulator was examined by NMR spectroscopy and compared with model calculations. This resulted in a close match only if it was presupposed that the incorporation was carried out randomly with the same degree of probability at any point whatsoever between two lauryl lactam structural units or at the chain end. Further calculations illustrate the effects of the incorporation of the chain regulator on the size of the amorphous portion.     

New Strategy for Optimizing Water Application under Trickle Irrigation

The determination of water application parameters for creating an optimal soil moisture profile represents a complex nonlinear optimization problem which renders traditional optimization into a cumbersome procedure. For this reason, an alternative methodology is proposed which combines a numerical subsurface flow model and artificial neural networks (ANN) for solving the problem in two, fully separate steps. The first step employs the flow model for calculating a large number of wetting profiles (output), obtained from a systematic variation of both water application and initial soil moisture (input). The resulting matrix of corresponding input/output values is used for training the ANN. The second step, the application of the fully trained ANN, then provides the irrigation parameters which range from a specified initial soil moisture to a desired crop-specific soil moisture profile. In order to avoid substantial disadvantages associated with the common feedforward backpropagation approach, a self-organizing topological feature map is implemented to perform this task. After a comprehensive sensitivity analysis, the new methodology is applied to the outcome of an irrigation experiment. The convincing results recommend the new methodology as a positive contribution towards an improved irrigation efficiency.     

Towards processible poly(pyrrol-2-ylsquaraines)

Summary In an attempt to produce a processible poly(pyrrol-2-ylsquaraine) by forming a copolymer of poly(pyrrol-2-ylsquaraine) with polymethylmethacrylate, two synthetic routes were utilised. The first included forming the polysquaraine and then polymerising the attached methacrylate groups to form the desired product and the second proceeded via the preformed methacrylate polymer, containing N-alkylpyrrole side chains, which was then condensed with squaric acid. Difficulties arose in the first route when the polysquaraine product was found to be insoluble, hence preventing any further polymerisation but partial solubility during the second procedure did allow bissquaraines to be formed and, as a consequence, the resultant product exhibited fluorescent properties. Yet the desired processible poly(pyrrol-2-ylsquaraine) was not achieved. Received: 30 October 1997/Revised version: 22 January 1998/Accepted: 23 January 1998     

Microstructural analysis of residual projectiles—A new method to explain penetration mechanisms

In the present work it is shown that metallographic analysis can supply a lot of detailed information about metallurgical events which happen during the penetration of metallic projectiles into armor steel. With the help of these findings models of penetration processes are derived. The deformation, fracture, and phase transformation processes of projectiles are investigated, which consist of tungsten, a tool steel, and a tungsten heavy metal, respectively. These were shot into armor steel at velocities between 1000m/s and 2000 m/s. The extensively deformed tungsten and the brittle steel form two opposite poles; between those the heavy metal takes a mid position. The more ductile a material is, the sooner its penetration approaches the piercing of a liquid jet. On the other hand, in a brittle material quick rupture is followed by turbulent motion and friction welding of the fragments. In this case extensive deformation is observed only in the skin layer of a fragment and in shear bands. Special attention is drawn to features which are characteristic for ballistic piercing processes,e.g., molten films and adiabatic shear deformation. Formerly Research Scientist at the Hochschule der Bundeswehr in Hamburg, West Germany, and thereafter at an institute in France doing military research     

Low temperature fabrication of magnesium phosphate cement scaffolds by 3D powder printing

Synthetic bone replacement materials are of great interest because they offer certain advantages compared with organic bone grafts. Biodegradability and preoperative manufacturing of patient specific implants are further desirable features in various clinical situations. Both can be realised by 3D powder printing. In this study, we introduce powder-printed magnesium ammonium phosphate (struvite) structures, accompanied by a neutral setting reaction by printing farringtonite (Mg₃(PO₄)₂) powder with ammonium phosphate solution as binder. Suitable powders were obtained after sintering at 1100°C for 5 h following 20–40 min dry grinding in a ball mill. Depending on the post-treatment of the samples, compressive strengths were found to be in the range 2–7 MPa. Cytocompatibility was demonstrated in vitro using the human osteoblastic cell line MG63.     

APC的InfraStruXure~(英飞)设计 为思科亚太区NSITE提供强有力支撑

英飞集成系统实际给我们提供了一种方案:目前,我们可以根据现在的需求而选择40kW的功率,当我们的业务增长时,英飞集成系统可以轻松升级以适应我们的需要。"