Optimal Microstructures Drag Reducing Mechanism of Riblets

We consider an optimal shape design problem of periodically distributed three-dimensional microstructures on surfaces of swimming bodies in order to reduce their drag. Our model is restricted to the flow in the viscous sublayer of the boundary layer of a turbulent flow. The costs for the optimization problem are very high because the three-dimensional flow equations have to be solved several times. We avoid this problem by approximations: the microscopic optimization problem is reduced applying homogenization. Considering a special geometry (riblets) the resulting so-called macroscopic optimization problem can be additionally reduced to a two-dimensional problem. We analyze the drag reducing mechanism of riblets which are believed to be optimal structures. Therefore we perform direct simulations on the total rough channel for different shapes of microstructures: riblets and fully three-dimensional structures.     

Continuity of Drag and Domain Stability in the Low Mach Number Limits

We consider a mathematical model of a rigid body immersed in a viscous, compressible fluid moving with a velocity prescribed on the boundary of a large channel containing the body. We assume that the Mach number is proportional to a small parameter ε and that the general boundary of the body contains small asperities of amplitude proportional to ε ^α for a certain α?>?0 and suppose the Navier’s slip condition on this rough boundary. We show that time averages of the drag functional converge, as ε → 0, to the corresponding time averages of the drag for the limit system, whereas the limit system is turning out to be the incompressible Navier–Stokes system with no-slip condition on the smooth limit body.     

Macroporous monolithic chiral stationary phases for capillary electrochromatography: New chiral monomer derived from cinchona alkaloid with enhanced enantioselectivity

A new chiral monomer derived from cinchona alkaloid, namely O-9-(tert-butylcarbamoyl)-11-[2-(methacryloyloxy)ethylthio]-10,11-dihydroquinine 1, was employed for the preparation of enantioselective monolithic capillary columns by an in situ copolymerization with 2-hydroxyethyl methacrylate 2 (HEMA), ethylene dimethacrylate 3 (EDMA) in the presence of cyclohexanol and 1-dodecanol as porogens (UV or thermal initiation of azobisisobutyronitrile (AIBN) as radical initiator). The porous properties and the electrochromatographic behavior of the new chiral monoliths were comparatively evaluated with previously described analogs obtained from O-9-[2-(methacryloyloxy)ethylcarbamoyl]-10,11-dihydroquinidine 4 as chiral monomer. Despite close structural and physicochemical similarities of the both chiral monomers, the pore distribution profiles of the resulting monoliths were shifted typically towards larger pore diameters with the new monomer 1. Once more, it was confirmed that a low cross-linking (10 wt% related to total monomers) and a pore diameter of about 1 microm in the dry state provides the best electrochromatographic efficiency as a result of lower resistance to mass transfer (smaller C-term contribution to peak broadening) and more homogeneous flow profile (smaller A-term). Most importantly, as expected the new poly(1-co-HEMA-co-EDMA) monoliths showed enhanced enantioselectivities and in addition faster separations as compared to poly(4-co-HEMA-co-EDMA) analogs, which represents a significant improvement. Further, the elution order was reversed owing to the pseudoenantiomeric behavior of quinine- and quinidine-derived monomers. Fluorescence-labeled 9-fluorenylmethoxycarbonyl (FMOC), dansyl (DNS), 7-dimethylaminosulfonyl-1,3,2-benzoxadiazol-4-yl (DBD), carbazole-9-carbonyl (CC) amino acids could be separated with resolution values between 2 and 4 (with efficiencies typically between 100,000 and 200,000 plates/m) and fluorescence detection (variable wavelength fluorescence detector in-line with UV) yielding routinely a gain in detection sensitivities up to two orders of magnitude without specific optimization of the conditions with regards to fluorescence efficiency.     

Amyloid Aggregates Arise from Amino Acid Condensations under Prebiotic Conditions

Current theories on the origin of life reveal significant gaps in our understanding of the mechanisms that allowed simple chemical precursors to coalesce into the complex polymers that are needed to sustain life. The volcanic gas carbonyl sulfide (COS) is known to catalyze the condensation of amino acids under aqueous conditions, but the reported di‐, tri‐, and tetra‐peptides are too short to support a regular tertiary structure. Here, we demonstrate that alanine and valine, two of the proteinogenic amino acids believed to have been among the most abundant on a prebiotic earth, can polymerize into peptides and subsequently assemble into ordered amyloid fibers comprising a cross‐β‐sheet quaternary structure following COS‐activated continuous polymerization of as little as 1 mm amino acid. Furthermore, this spontaneous assembly is not limited to pure amino acids, since mixtures of glycine, alanine, aspartate, and valine yield similar structures.     

Analysis of benzo[a]pyrene diol epoxide-DNA adducts by capillary zone electrophoresis- electrospray ionization-mass spectrometry in conjunction with sample stacking

Benzo[a]pyrene diol epoxide (BPDE) was reacted in vitro with (2'-deoxy)nucleotides and with calf thymus DNA. The modified DNA was enzymatically hydrolyzed to the 5'-monophosphate nucleotides using deoxyribonuclease I (DNA-ase I), nuclease P1 and snake venom phosphodiesterase (SVP). Most of the unmodified nucleotides were removed using solid phase extraction (SPE) in a polystyrene divinylbenzene copolymer. Three adducts could be detected and identified using capillary zone electrophoresis(negative)-ion electrospray ionization-mass spectrometry (CZE-(-)-ESI-MS) in conjunction with sample stacking. This way, not only a BPDE-dGMP adduct [(M-H)(-) at m/z 648], a well-known nucleotide adduct, could be retrieved, but also a BPDE-dAMP [(M-H)(-) at m/z 632] and a BPDE-dCMP adduct [(M-H)(-) at m/z 608] could be detected for the first time. The presence of the prominent ion at m/z 195 (the deoxyribose-phosphate ion) in the three low-energy collision-activated decomposition (CAD) spectra indicated that the adducts were formed through base-alkylation. CZE-positive ion ESI-MS/MS experiments were performed to obtain further information on base-alkylation. The absence of the loss of NH(3) from the nucleobase in each CAD spectrum points to an alkylated exocyclic NH(2) position of the nucleobase. So, the three adducts could be identified as BPDE-N(2)-dGMP, BPDE-N(6)-dAMP and BPDE-N(4)-dCMP using CZE-ESI-MS and CZE-ESI-MS/MS.     

Aufnahme von Spurenmengen Antimon (Radioantimon) durch einige Metalloxidhydrat-Niederschläge

Zusammenfassung Mit trägerfreiem¹²⁵Sb bzw. trägerarmem¹²⁴Sb wurde die Aufnahme von Spurenmengen Antimon(III) durch Fe(III)-, Al-, Zr- und Ti-Oxidhydrat untersucht. Für die Aufnahme von Antimon durch Mitfällung wurde gefunden: ZrTi>Fe Al. Bei Mitfällung aus 1M-NaCl und bei pH 7 sind etwa folgende Metallionenmengen erforderlich, um Antimon zur Hälfte mitzufällen: Zr oder Ti 0,02 mMol/l, Fe 0,1 mMol/l bzw. Al 3 mMol/l. Bei Fe-, Zr- und Ti-Oxidhydrat beträgt die Radioantimonaufnahme durch Mitfällung das 5- bis 8fache der Aufnahme durch Sorption an vorgebildeten Niederschlägen. Bei Mitfällung überwiegt daher hier Einbau in das Innere des Niederschlags sehr stark gegenüber Adsorption an der Oberfläche. Versuche mit Radiostrontium (trägerarmem⁸⁵Sr) ergeben im Gegensatz hierzu, daß bei Fe-, Al- und Ti-Oxidhydrat Mitfällung und Sorption an vorgebildeten Niederschlägen zu ungefähr gleich starker Aufnahme führen. Ferner wurde die Abhängigkeit der Radioantimonaufnahme vom pH und von der NaCl-Konzentration der Lösungen ermittelt und daraus Schlüsse auf die Natur des Aufnahmeprozesses gezogen.

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Uptake of trace amounts of antimony (radioantimony) by precipitates of some hydrated metal oxides

Uptake of trace amounts of antimony(III) by the hydrated oxides of Fe(III), Al, Zr and Ti was investigated using carrier-free¹²⁵Sb or¹²⁴Sb of high specific activity. For uptake of antimony by coprecipitation, the following order was found: ZrTi>FeAl. The amounts of metal ions required to coprecipitate half of the antimony from 1M-NaCl at pH 7 are: Zr or Ti-0.02 mMol/l, Fe-0.1 mMol/l, Al-3 mMol/l. With the hydrated oxides of Fe, Zr and Ti, uptake of radioantimony by coprecipitation is 5 to 8 times as great as uptake by sorption on preformed precipitates. In coprecipitation, incorporation into the interior of these precipitates thus exceeds adsorption on the surfaces considerably. In contrast, experiments with radiostrontium (⁸⁵Sr of high specific activity) have shown that for the hydrated oxides of Fe, Al and Ti uptake by sorption on preformed precipitates is about equal to that by coprecipitation. Dependance of uptake of radioantimony upon pH and concentration of NaCl was also determined and conclusions regarding the nature of the processes responsible for uptake were drawn.

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Mit 7 Abbildungen

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FürE. B. (Univ.-Prof. Dr.Engelbert Broda) mit herzlichen Wünschen zum 60. Geburtstag.     

Ausführung und Probleme der fluorimetrischen Uranbestimmung

Zusammenfassung Die fluorimetrische Uranbestimmungsmethode wurde zur Analyse von Kohlenaschen, Gesteinsproben und Auslaugelösungen von Kohlenaschen herangezogen. Bei der verwendeten Arbeitsmethodik werden Stoffe, die die Fluoreszenz des Urans herabsetzen, durch Extraktion des Urans mit Äthylacetat unter Zugabe von Aluminiumnitrat als Aussalzmittel abgetrennt. Jedoch gelingt eine vollständige Entfernung solcher löschender Stoffe nicht in allen Fällen, so daß das Zugabeverfahren anzuwenden ist. Die Pillen (98% NaF, 2% LiF) werden mit Hilfe eines Mekerbrenners durchgeschmolzen. Die Fluoreszenzmessung erfolgt mit einem Galvanek-Morrison-Fluorimeter. Reproduzierbarkeit und Empfindlichkeit dieser Arbeitsmethodik werden diskutiert. Für die Bestimmung sehr kleiner Urangehalte kann eine Konzentrierung des Urans durch Eindampfen der Äthylacetatextrakte durchgeführt werden.Um Angaben über die Störung der Bestimmungen (Fluoreszenzlöschung) durch einzelne Elemente zu erhalten, wurde für eine Reihe von Elementen die Löschwirkung und die Extraktion durch Äthylacetat ermittelt.

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Summary The fluorimetric method of determining uranium was used in the analysis, of coal ashes, rock samples and leaching solutions from coal ashes. In the method employed, materials which decrease the fluorescence of the uranium are separated by extracting the uranium with ethyl acetate and adding aluminium nitrate as salting-out agent. However, such quenching materials are not completely removed in all cases so that the addition procedure must be employed. The pellets (98% NaF, 2% LiF) are thoroughly fused with the aid of a Meker burner. The measurement of the fluorescence is done in a Galvanek-Morrison Fluorimeter. The reproducibility and the sensitivity of this procedure are discussed. When very small quantities of uranium are to be determined, the uranium may be concentrated by evaporation of the ethyl acetate extracts.To obtain information regarding the interference in the determinations (quenching of the fluorescence) by individual elements, the quenching action and the extraction by ethyl acetate were measured for a series of elements.

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Résumé La méthode de dosage fluorimétrique de l'uranium a été appliquée à l'analyse des cendres de charbon, aux échantillons de minéraux et aux eauxmères de lavage des cendres de charbon. Avec le mode opératoire employé, les substances qui réduisent la fluorescence de l'uranium sont séparées par extraction de celui-ci par l'acétate d'éthyle et addition de nitrate d'aluminium comme sel de relargage. Cependant, une séparation complète de certaines substances supprimant la fluorescence ne réussit pas dans tous les cas, de sorte que le procédé doit être appliqué avec ces impuretés. On fond au bec Meker les pastilles (98% NaF, 2% LiF). On effectue ensuite la mesure de la fluorescence avec un fluorimètre «Galvanek-Morrison». On discute la reproductibilité et la sensibilité de ce procédé. Pour le dosage de très petites teneurs en uranium on peut procéder à une concentration de celui-ci par evaporation de l'extrait par l'acétate d'éthyle.Pour obtenir des indications sur l'interférence produite par des éléments individuels sur les dosages (extinction de la fluorescence), l'action destructrice et l'extraction à l'acétate d'éthyle ont été utilisées pour une série d'éléments.

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Gewidmet zur 100. Wiederkehr des Geburtstages vonFriedrich Emich.     

Einfluß von Zirkoniumionen auf die Sorption von trägerfreiem Radiophosphat (32P)

Die Sorption von trärgerfreiem Radiophosphat (³²P) aus sauren Lösungen durch verschiedene Materialien wird durch Zugabe von Zirkoniumionen stark beeinfluβit. Bei einigen Sorbentien, icie Diatomeenerde, Tonmineralen und Aktivkohle, tritt bei Zugabe kleiner Zirkoniummengen eine wesentliche Steigerung der Aufnahme von ³²P ein. Gröβere Mengen Zirkonium bewirken wieder eine Abnahme der Sorption. Bei Aluminiumoxid als Sorbens führt hingegen jede Zirkoniumzugabe zu einer Verringerung der Aufnahme von Radiophosphat. Die hier mitgeleilten Erscheinungen beruhen auf der Bildung löslicher Zirkonium-Phosphat-Komplexionen.     

The electrostatic potentials in an electron-cyclotron-resonance processing plasma

The axial distribution of the electrostatic potentials ofan electron-cyclotron resonance (ECR) processing plasma confined in a do magnetic mirror geometry was characterized. The potential profiles far argon and helium at 8.0x 10^–4 and 4.0 × 10^–4 Torr were measured using electron emissive probes. The experimental measurements were then compared with the predictions of a one-dimensional, electrostatic, particle-in-cell computer code which runs on a personal computer. The potential profiles as predicted by the code showed good agreement with the experimental measurements.     

Application of time-resolved resonance Raman spectroscopy to the study of rapid intramolecular radiationless transitions

It is shown that the decay rate γ₂ of the excited state of a molecule can be determined by measuring the decrease of the resonance Raman intensity on a time scale much longer than γ^?1₂, provided that the time needed for repopulation of the ground state, following rapid intramolecular radiationless transitions from the excited state to a molecular quasicontinuum, is itself much longer than γ^?1₂. Thus, it should be possible to avoid the use of ultrashort pulses in the study of very fast intramolecular decay process.