Evidence for the Aging of Wax Deposits in Crude Oils by Ostwald Ripening

The ageing of wax deposits is known to occur in paraffinic waxes forming in pipelines and storage tanks. It is characterized by a hardening of the deposit and an increase in paraffin content. A mechanism for the ageing of deposits, based on diffusion caused by temperature-concentration gradients within the wax, has been previously proposed. This work presents evidence indicating Ostwald Ripening to be another ageing mechanism of wax deposits. Rheology of paraffinic crudes, kept isothermally at temperatures in the neighborhood of the pour point, shows a kinetic of hardening of the oil samples. The X-ray diffraction and Cross Polar Microscopy indicate this phenomenon to be caused by an increase of the crystallites size with time. The DSC measurements support the idea that recrystallization takes place in the wax sample. The evidence gathered shows another ageing mechanism based on the recryztallization of the paraffins, such as Ostwald Ripening, to be responsible for the ageing of wax deposits besides the diffusion mechanism previously proposed     

Placing underground pressure pipes by machine

A machine system has been patented in the German Democratic Republic which links a digger and pipe placing unit for installing and connecting PVC pressure pipes underground with the minimum of soil displacement. The authors are engineers working at the Academy of Building, Institute for Civil Engineering, Leipzig.     

4-Methylimidazol in Caramel und caramelgef?rbten Lebensmitteln

Zusammenfassung Es wird eine spezifische und kochempfindliche Methode zur Bestimmung von 4-Methylimidazol (4-MeI) in Caramel und caramelgefärbten Lebensmitteln beschrieben. Nach der Extraktion wird 4-MeI gaschromatographisch mit einem stickstoffspezifischen elektrochemischen Detektor (Hall) bestimmt. Als weniger spezifische Alternative kann ein thermoionischer Detektor eingesetzt werden. Bei Zusätzen von 5–200 mg 4-MeI/kg Karamel beträgt die Wiederfindungsrate 90–94%.Die Nachweisgrenze der Methode liegt unterhalb 0,1 mg 4-MeI/kg Caramel; in karamelgefärbten Lebensmitteln können weniger als 0,01 mg/kg nachgewiesen werden.

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4-methylimidazole in caramel and caramel-colored foodsDetermination by gas-liquid-chromatography with nitrogen-specific detectors

Summary A specific and highly sensitive method for the determination of 4-methylimidazole (4-MeI) in caramel and caramel-colored foods is described. After extraction the amount of 4-MeI is determined by gas-liquid chromatography with a nitrogen-specific electrochemical detector (Hall). As a less specific alternative a thermoionic detector can be used. With additions in the range of 5–200 mg 4-MeI/kg caramel, recoveries of 90–94% are obtained.The limit of detection is <0.1 mg 4-Mel/kg caramel; in caramel-colored foods less than 0.01 mg/kg can be detected.

     

Technology of braze welding absorber tubes to copper foil in solar collectors by the GTA method

The classification of aluminium alloys on the basis of main alloy elements and usability for heat treatment is presented. The essential problems occurring in welding of aluminium and its alloys are mentioned. The most advanced methods of joining these materials are described. Results of investigations into the possibility of joining of thin walled elements of aluminium alloys by low heat input arc welding methods, plasma arc welding and hybrid laser+MIG welding are also presented.     

Supramolecular assembly/reassembly processes: molecular motors and dynamers operating at surfaces

Among the many significant advances within the field of supramolecular chemistry over the past decades, the development of the so-called "dynamers" features a direct relevance to materials science. Defined as "combinatorial dynamic polymers", dynamers are constitutional dynamic systems and materials resulting from the application of the principles of supramolecular chemistry to polymer science. Like supramolecular materials in general, dynamers are reversible dynamic multifunctional architectures, capable of modifying their constitution by exchanging, recombining, incorporating components. They may exhibit a variety of novel properties and behave as adaptive materials. In this review we focus on the design of responsive switchable monolayers, i.e. monolayers capable to undergo significant changes in their physical or chemical properties as a result of external stimuli. Scanning tunneling microscopy studies provide direct evidence with a sub-nanometre resolution, on the formation and dynamic response of these self-assembled systems featuring controlled geometries and properties.     

Changes in the Cell Wall Proteome of Leaves in Response to High Temperature Stress in Brachypodium distachyon

High temperature stress leads to complex changes to plant functionality, which affects, i.a., the cell wall structure and the cell wall protein composition. In this study, the qualitative and quantitative changes in the cell wall proteome of Brachypodium distachyon leaves in response to high (40 °C) temperature stress were characterised. Using a proteomic analysis, 1533 non-redundant proteins were identified from which 338 cell wall proteins were distinguished. At a high temperature, we identified 46 differentially abundant proteins, and of these, 4 were over-accumulated and 42 were under-accumulated. The most significant changes were observed in the proteins acting on the cell wall polysaccharides, specifically, 2 over- and 12 under-accumulated proteins. Based on the qualitative analysis, one cell wall protein was identified that was uniquely present at 40 °C but was absent in the control and 24 proteins that were present in the control but were absent at 40 °C. Overall, the changes in the cell wall proteome at 40 °C suggest a lower protease activity, lignification and an expansion of the cell wall. These results offer a new insight into the changes in the cell wall proteome in response to high temperature.