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71.
Several neotropical leaf-beetles of the genus Platyphora ingest and specifically metabolize plant acquired pyrrolizidine alkaloids (PAs) of the lycopsamine type (e.g., rinderine or intermedine) and enrich the processed alkaloids in their exocrine defensive secretions. In contrast to the related palaearctic leaf beetles of the genus Oreina, which absorb and store only the non-toxic alkaloid N-oxides, Platyphora sequesters PAs exclusively as protoxic tertiary amines. In this study, the ability of P. boucardi larvae to accumulate PAs was investigated. Tracer studies with [14C]rinderine and its N-oxide revealed that P. boucardi larvae, like adult beetles, utilize the two alkaloidal forms with the same efficiency, but accumulate the alkaloid as a tertiary amine exclusively. Ingested rinderine is rapidly epimerized to intermedine, which is localized in the hemolymph and all other tissues; it is also detected on the larval surface. Like adults, larvae are able to synthesize their own alkaloid esters (beetle PAs) from orally administered [14C]retronecine and endogenous aliphatic 2-hydroxy acids. These retronecine esters show the same tissue distribution as intermedine. A long-term feeding experiment lasting for almost four months revealed that retronecine esters synthesized from [14C]retronecine in the larvae are transferred from larvae via pupae into the exocrine glands of adult beetles. Pupae contain ca. 45% of the labeled retronecine originally ingested, metabolized, and stored by larvae; ca. 12% of larval radioactivity could be recovered from the defensive secretions of adults sampled successively over two and a half months. Almost all of this radioactivity is found in the insect-made retronecine esters that are highly enriched in the defensive secretions, i.e., more than 200-fold higher concentration compared to pupae. 相似文献
72.
R. Kree T. Yasseri A.K. Hartmann 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》2009,267(8-9):1407-1411
We present a continuum theory and a Monte Carlo model of self-organized surface pattern formation by ion-beam sputtering including effects of beam profiles. Recently, it has turned out that such secondary ion-beam parameters may have a strong influence on the types of emerging patterns. We first discuss several cases, for which beam profiles lead to random parameters in the theory of pattern formation. Subsequently we study the evolution of the averaged height profile in continuum theory and find that the typical Bradley–Harper scenario of dependence of ripple patterns on the angle of incidence can be changed qualitatively. Beam profiles are implemented in Monte Carlo simulations, where we find generic effects on pattern formation. Finally, we demonstrate that realistic beam profiles, taken from experiments, may lead to qualitative changes of surface patterns. 相似文献
73.
74.
Synchronization of processes is one of the major performance bottlenecks in a distributed system. The synchronization is usually achieved via message passing. There are two basic types of overhead in such a synchronization: the rate of message exchange, and the blocking probabilities of processes. In this paper we consider two processes synchronizing via message passing and study their performance behavior on the basis of the above-mentioned overheads. A number of protocols for message exchange are analyzed. The model gives rise to a three-dimensional Markov chain. An algorithm to solve the model and numerical results are presented to compare the various protocols. 相似文献
75.
Vinyl Polymerization Initiated by Reducing Compounds of Transition Metals. VII. Polymerization of Methyl Methacrylate in the Presence of Molybdenum(III) Chloride/Sulfoxide Systems The polymerization of methyl methacrylate initiated by the molybdenum(III) chloride/dimethyl sulfoxide redox system was carried out at 70° in 1, 4-dioxane. The rate of polymerization can be described by the equation Rp = k · [MoCl3]0,5 · [DMSO]0,5 · [MMA]1,0. The overall activation energy was estimated to be 36.0 kJ/mol. It was found that diethyl, dipropyl, dibutyl, diphenyl and dibenzyl sulfoxides could also initiate the polymerization of methyl methacrylate in the presence of molybdenum(III) chloride, whereas vanadium(II) chloride, vanadium(III) chloride, titanium(III) chloride and chromium(II) acetate are inactive in combination with sulfoxides. 相似文献
76.
Kirsten Bobzin Nazlim Bagcivan Arnold Gillner Claudia Hartmann Jens Holtkamp Walter Michaeli Fritz Klaiber Maximilian Sch?ngart Sebastian Thei? 《Production Engineering》2011,5(4):415-422
Molding of micro structures by injection molding leads to special requirements for the molds e.g. regarding wear resistance
and low release forces of the molded components. At the same time it is not allowed to affect the replication precision. Physical
vapor deposition (PVD) is one of the promising technologies for applying coatings with adapted properties like high hardness,
low roughness, low Young’s modulus and less adhesion to the melt of polymers. Physical vapor deposition technology allows
the deposition of thin films on micro structures. Therefore, the influence of these PVD layers on the contour accuracy of
the replicated micro structures has to be investigated. For this purpose injection mold inserts were laser structured with
micro structures of different sizes and afterwards coated with two different coatings, which were deposited by a magnetron
sputter ion plating PVD technology. After deposition, the coatings were analyzed by techniques regarding hardness, Young’s
modulus and morphology. The geometries of the micro structures were analyzed by scanning electron microscopy before and after
coating. Afterwards, the coated mold inserts were used for injection molding experiments. During the injection molding process,
a conventional and a variothermal temperature control of the molds were used. The molded parts were analyzed regarding roughness,
structure height and structure width by means of laser microscopy. 相似文献
77.
R. Kree T. Yasseri A.K. Hartmann 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》2009,267(8-9):1403-1406
We present a new Monte Carlo model and a new continuum theory of surface pattern formation due to “surfactant sputtering”, i.e. erosion by ion beam sputtering including a submonolayer coverage of additional, co-sputtered surfactant atoms. This setup, which has been realized in recent experiments in a controlled way leads to a number of interesting possibilities to modify pattern forming processing conditions. We will present three simple scenarios, which illustrate some potential applications of the method. In all three cases, simple Bradley–Harper type ripples appear in the absence of surfactant, whereas new, interesting structures emerge during surfactant sputtering. 相似文献
78.
X-ray powder diffraction, microscopy, thermal analysis and electron probe microanalysis were used to characterize a ZrO2-MgO inert matrix containing CeO2 as a homolog for PuO2 and Er2O3 as a burnable poison. The synthesis was carried out using a precipitation method. A large composition range of MgO to ZrO2 was evaluated to determine phases present, phase mixing, phase composition, microstructure and thermal properties. It was found that most compositions of the material consist of two phases: MgO (periclase) and ZrO2 (cubic zirconia). The zirconia phase incorporates 5% (wt/wt) MgO and up to 14% and 12% (wt/wt) CeO2 and Er2O3, respectively. The MgO phase remains pure, which will enable it to retain its heat transfer and solubility properties and will improve the overall thermal conductivity and reprocessing component of the inert matrix fuel. The results with Ce will be used as the basis of future studies with actinides. 相似文献
79.
Georg Schitter Andreas J. Steiner Gerit Pototschnig Elisabeth Scheucher Martin Thonhofer Chris A. Tarling Prof. Stephen G. Withers Katrin Fantur Prof. Eduard Paschke Prof. Don J. Mahuran Brigitte A. Rigat Prof. Michael B. Tropak Carina Illaszewicz Prof. Robert Saf Prof. Arnold E. Stütz Prof. Tanja M. Wrodnigg 《Chembiochem : a European journal of chemical biology》2010,11(14):2026-2033
A collection of new reversible glycosidase inhibitors of the iminoalditol type featuring N‐substituents containing perfluorinated regions has been prepared for evaluation of physicochemical, biochemical and diagnostic properties. The vast variety of feasible oligofluoro moieties allows for modular approaches to customised structures according to the intended applications, which are influenced by the fluorine content as well as the distance of the fluorous moiety from the ring nitrogen. The first examples, in particular in the D ‐galacto series, exhibited excellent inhibitory activities. A preliminary screen with two human cell lines showed that, at subinhibitory concentrations, they are powerful pharmacological chaperones enhancing the activities of the catalytically handicapped lysosomal D ‐galactosidase mutants associated with GM1 gangliosidosis and Morquio B disease. 相似文献
80.
Douglas E. Burkes J. Rory Kennedy Thomas Hartmann Cynthia A. Papesch 《Nuclear Engineering and Design》2009,239(12):2747-2753
Metallic fuel alloys consisting of uranium, plutonium, and zirconium with minor additions of americium and neptunium are under evaluation for potential use to transmute long-lived transuranic actinide isotopes in fast reactors. The current irradiation test series design, designated AFC2, includes minor additions of rare earth elements to simulate expected fission product carry-over from the electrochemical molten salt reprocessing technique. The metal fuel alloys have been fabricated by an arc casting technique. The as-cast fuel alloys have been investigated for phase and thermal properties, specifically, enthalpies of transition, transition temperatures, and room temperature phase characteristics. Results and observations related to these characteristics for the “fresh” fuel alloys are provided. The alloy compositions are based on a U-20Pu-3Am-2Np-15Zr alloy, along with additions of 1 and 1.5 wt% RE (at the expense of U) where RE denotes rare earth alloy of cerium, lanthanum, praseodymium and neodymium. Phase behavior and associated transitions have been compared to available U-Pu-Zr ternary diagrams with acceptable agreement. Enthalpies of transition were deconvoluted from heating and cooling thermal traces for relatively reliable values. The rare earth additions to the base alloy have a minimal influence on the room temperature phases present, but the room temperature phases present slightly impacted the enthalpies of transition and transition temperatures. 相似文献