Characterization of cocoa butters and other vegetable fats by pyrolysis-mass spectrometry

Pyrolysis Mass Spectrometry (Py-MS) was used for the discrimination of cocoa butters from other vegetable fats. Mass spectra ranging from 50 amu to 250 amu were analyzed by principal component analysis (PCA) and with neural nets. The application of neural nets leads to a good discrimination between the two classes. Detailed analysis of the nets revealed that only the first 60 masses were used within the net. The use of PCA requires a careful selection of the number of masses included in the calculation. Canonical variance analysis was applied to determine the significant masses. Optimal performance of PCA was observed only using the first 22 significant masses. Most of these masses were different from the ones used by the neural net. It seems that the mass spectra obtained by Py-MS contain sufficient information for the discrimination of pure cocoa butter from other vegetable fats, but none of the methods seems to be able to extract all information available. Neural net provides a very robust method for this task and no prior data selection was necessary. Received: 13 May 1996 / Revised: 7 August 1996 / Accepted: 7 August 1996     

Über die Synthese von 4-Amino-2H-imidazolen aus Imidazolin-Δ3-thionen-(5)

Zusammenfassung 2,4,5-substituierte 4-Alkylamino-2H-imidazole entstehen mit guten Ausbeuten aus 2-Methyl-2,4-diaryl-imidazolin-³-thionen-(5) durch Umsetzung mit prim. bzw. sek. aliphatischen oder heterocyclischen Aminen in Benzol bei Rückflußtemperatur.

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2.4.5-substituted 4-alkylamino-2H-imidazoles are formed in good yields by the reaction of 2-methyl-2.4-diaryl-³-imidazoline-5-thiones with prim. or sec. aliphatic or heterocyclic amines in boiling benzene.

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55. Mitt.:F. Asinger, E.-Chr. Witte undW. Schäfer, Ann. Chem., im Druck.

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Teil der DissertationG. Kriebel, Techn. Hochschule Aachen, 1965.     

Determination of transition curves of high-Tc superconductors by phase contrast microscopy

A new method which allows the detection of the superconducting phase transition of high-T_c superconductors (HTSC) on a microscopic scale is reported. Micro-size holes in thin foils of superconducting material are examined in a transmission electron microscope at varying temperatures. The superconducting transition induces small changes in the image intensity within the holes, which can be detected by using electronic image analysis. Superconducting transition curves are then obtained for various types of high-T_c superconductors and for given values of the applied magnetic field.     

Si/SiO2-templated formation of ultraflat metal surfaces on glass, polymer, and solder supports: their use as substrates for self-assembled monolayers

This paper describes the use of several methods of template stripping (TS) to produce ultraflat films of silver, gold, palladium, and platinum on both rigid and polymeric mechanical supports: a composite of glass and ultraviolet (UV)-curable adhesive (optical adhesive, OA), solder, a composite of poly(dimethyl siloxane) (PDMS) and OA, and bare OA. Silicon supporting its native oxide layer (Si/SiO2) serves as a template for both mechanical template stripping (mTS), in which the metal film is mechanically cleaved from the template, and chemical template stripping (cTS), in which the film-template composite is immersed in a solution of thiols, and the formation of the SAM on the metal film causes the film to separate from the template. Films formed on all supports have lower root-mean-square (rms) roughness (as measured by atomic force microscopy, AFM) than films used as-deposited (AS-DEP) by electron-beam evaporation. Monolayers of n-dodecanethiolate formed by the mTS and cTS methods are effectively indistinguishable by scanning tunneling microscopy (STM); molecularly resolved images could be obtained using both types of surfaces. The metal surfaces, before being cleaved, are completely protected from contact with the atmosphere. This protection allows metal surfaces intended to support SAMs to be prepared in large batch lots, stored, and then used as needed. Template stripping thus eliminates the requirement for evaporation of the film immediately before use and is a significant extension and simplification of the technology of SAMs and other areas of materials science requiring clean metal surfaces.     

A study of the feasibility of active shock isolation

Summary The subject matter of this paper is a pilot study of the feasibility of active shock isolation. Whereas conventional shock isolation systems use passive elements such as springs and dashpots, this study is concerned with investigating the advantages of using active elements, e. g., servo or force generators, in addition to passive elements. In actuality the excitation function of the isolating system is not known. The case considered here is a one-degree-of-freedom system, where the complete input is known, and the objective is to find a control to optimize the active isolator performance and compare it with an optimally tuned linear passive isolator. The maesure of performance is the ratio of the magnitudes of the maximum absolute acceleration of the protected equipment to the maximum acceleration of the shock-excited environment. Two numerical methods of solution, dynamic and linear programming, are considered and their relative merits assessed.

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Übersicht In der vorliegenden Arbeit werden Brauchbarkeit und Zweckmäßigkeit einer aktiven Stoßdämpfung untersucht. Während die üblichen Dämpfer meist nicht-regelbare, passive Dämpfungsglieder besitzen, soll hier untersucht werden, ob die Verwendung zusätzlicher aktiver, servogesteuerter Dämpfungsglieder Vorteile bringt. In der Praxis ist die Eingangsfunktion bei Erregungsbeginn nicht bekannt. Hier soll jedoch die Eingangsfunktion bei Erregungsbeginn als bekannt angenommen werden. Der Dämpfer besitze einen Freiheitsgrad. Es soll die optimale Arbeitsweise des aktiven Stoßdämpfers gesucht und mit einer optimal abgestimmten passiven Anlage verglichen werden. Als Maß für die Wirksamkeit des Dämpfers wird das Verhältnis der maximalen absoluten Beschleunigung der Schwingermasse zur maximalen Erregerbeschleunigung betrachtet. Zwei numerische Verfahren, dynamisches und lineares Programmieren, werden zur Lösung verwendet und ihre Vor- und Nachteile diskutiert.

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Abbreviated version of a Ph. D. thesis from a research project directed by Prof. I. Fluegge-Lotz in the Division of Engineering Mechanics, Stanford, University, Stanford, California, U.S.A. A microfilm copy of the dissertation is obtainable from the University of Michigan, Ann Arbor, Michigan.     

Zum Reaktionsverhalten von Imidazolin-Δ3-thionen-(5)

Zusammenfassung Imidazolin-³-thione-(5) sind zyklische Thioamide, die auch als Thiolimide (5-Mercapto-2H-imidazole) reagieren können. Die Reaktionsmöglichkeiten des exozyklisch gebundenen S-Atoms werden am Beispiel des 2-Methyl1-2,4-diphenyl-imidazolin-³-thion-(5) demonstriert. Vom Thiolimid-Tautomeren leiten sich Cd- und Cu-Salze, S-Alkyl- und S-Acylderivate sowie das Bis-[2H-imidazol-5-yl]-disulfid ab. Aus dem Thioamid entsteht mit H₂O₂ in Methanol das S-Oxid, das sich durch Acetylierung und nachfolgende Hydrolyse in das Disulfid überführen läßt. In höherer Ausbeute entsteht das Disulfid direkt aus dem Imidazolin-³-thion-(5) durch Behandeln mitAc ₂O und H₂O₂ in Gegenwart von Pyridin. Disulfid oder Imidazolin-³-thion-(5) ergeben mit SO₂Cl₂ 5-Chlor-2H-imidazol, welches mit Aminen zu 5-Amino-2H-imidazolen ungesetzt werden kann. Aus der reduktiven Entschwefelung von Imidazolin-³-thion mit LiAlH₄ resultieren unter Ringöffnung Gemische zweier isomerer Diamine.

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³-Imidazoline-5-thiones are cyclic thioamides which can react also as thiol imides (5-mercapto-2H-imidazoles). The reactions of the exocyclic S atom are demonstrated with 2-methyl-2.4-diphenyl-³-imidazoline-5-thione.Derivatives of the tautomer thiolimide are cadmium and copper salts, S-alkyl and S-acyl derivatives and the bis-[2H-imidazol-5-yl]-disulphide. Oxidation of the thioamide in methanolic solution with H₂O₂ gives the corresponding disulphide. Better yields of the disulphide are obtained when ³-imidazoline-5-thione is treated simultaneously withAc ₂O, H₂O₂ and pyridine. Reaction of the disulphide or of the ³-imidazoline-5-thione with SO₂Cl₂ gives 5-chloro-2H-imidazole, which can be converted to 5-amino-2H-imidazoles with amines. Desulphurization of the ³-imidazoline-5-thione under reducing conditions (LiAlH₄) causes ring opening to yield a mixture of two isomeric diamines.

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Teil der DissertationA. Wegerhoff, T. H. Aachen (1964).

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Teil der DissertationG. Kriebel, T. H. Aachen (1965).     

Effects of lipopolysaccharide-induced inflammation on expression of growth-associated genes by corticospinal neurons

Background  

Inflammation around cell bodies of primary sensory neurons and retinal ganglion cells enhances expression of neuronal growth-associated genes and stimulates axonal regeneration. We have asked if inflammation would have similar effects on corticospinal neurons, which normally show little response to spinal cord injury. Lipopolysaccharide (LPS) was applied onto the pial surface of the motor cortex of adult rats with or without concomitant injury of the corticospinal tract at C4. Inflammation around corticospinal tract cell bodies in the motor cortex was assessed by immunohistochemistry for OX42 (a microglia and macrophage marker). Expression of growth-associated genes c-jun, ATF3, SCG10 and GAP-43 was investigated by immunohistochemistry or in situ hybridisation.     

Influence of defects on the electrical characteristics of mercury-drop junctions: self-assembled monolayers of n-alkanethiolates on rough and smooth silver

This paper compares the structural and electrical characteristics of self-assembled monolayers (SAMs) of n-alkanethiolates, SCn (n = 10, 12, 14), on two types of silver substrates: one used as-deposited (AS-DEP) by an electron-beam evaporator, and one prepared using the method of template-stripping. Atomic force microscopy showed that the template-stripped (TS) silver surfaces were smoother and had larger grains than the AS-DEP surfaces, and reflectance-absorbance infrared spectroscopy showed that SAMs formed on TS substrates were more crystalline than SAMs formed on AS-DEP substrates. The range of current densities, J (A/cm2), measured through mercury-drop junctions incorporating a given SAM on AS-DEP silver was, on average, several orders of magnitude larger than the range of J measured through the same SAM on TS silver, and the AS-DEP junctions failed, on average, 3.5 times more often within five current density-voltage (J-V) scans than did TS junctions (depending on the length of the alkyl chains of the molecules in the SAM). The apparent log-normal distribution of J through the TS junctions suggests that, in these cases, it is the variability in the effective thickness of the insulating layer (the distance the electron travels between electrodes) that results in the uncertainty in J. The parameter describing the decay of current density with the thickness of the insulating layer, beta, was either 0.57 A-1 at V = +0.5 V (calculated using the log-mean of the distribution of values of J) or 0.64 A-1 (calculated using the peak of the distribution of values of J) for the TS junctions; the latter is probably the more accurate. The mechanisms of failure of the junctions, and the degree and sources of uncertainty in current density, are discussed with respect to a variety of defects that occur within Hg-drop junctions incorporating SAMs on silver.