Non-equilibrium processes in heavy-ion collisions at relativistic energies

We use transport theory to describe the inclusive cross sections for protons and pions produced in collisions between two identical heavy ions at an energy of 800 MeV per particle. In addition to the nucleonic we take the Δ-degree of freedom into account. Thus we consider a two-component system whose distributions in transverse momentum and rapidity we describe by two coupled Fokker-Planck equations. These transport equations contain the one-nucleon knock-out process as initial condition. In the limit of large interaction times they lead to thermal equilibrium (fireball) distributions. For light nuclei the interaction time is not large enough for equilibrium to be reached. A recent experiment for two colliding carbon nuclei at 800 MeV per nucleon shows evidence of nonequilibrium effects. We compare our calculations with experimental data for ¹²C on ¹²C and Ne on NaF at 800 MeV/N.     

Rheologische Untersuchungen im System Wasser-Ton-Email-Elektrolyt

Zusammenfassung Mit einem Haake-Rotationsviskosimeter wurde die Viskosität verschiedener wäßriger Tonsuspensionen ohne und mit Elektrolytzusatz untersucht. Sämtliche untersuchten Tone zeichneten sich durch eine mehr oder weniger starke Elektrolytabhängigkeit aus. Die beiden Bestandteile eines Elektrolyten, Kation und Anion, wirken rheologisch entgegengesetzt. Kationen erhöhen, Anionen dagegen senken die Viskosität. Die Wirksamkeit der Kationen konnte mathematisch als eine Funktion der Polarisierungskraft formuliert werden. Von der Polarisierungskraft ist die Hydrathüllendicke, und von dieser wiederum die Abschirmung der Kationenladung abhängig. Die Polarisierungskraft ist außerdem ein Maß für die Basizität der Kationen. Somit können alle im Zusammenhang mit der Elektrolytabhängigkeit auftretenden rheologischen Erscheinungen an Tonsuspensionen auf eine einzige Größe, die Polarisierungskraft, zurückgeführt und durch sie erklärt werden.Die Kenntnis von den rheologischen Eigenschaften der Tone ermöglicht es, auch das Fließverhalten von tonhaltigen Emailschlickern zu verstehen und dasselbe in gewünschter Weise zu verändern. Reine Email-Wasser-Suspensionen sind thixotrop (besser 'pseudothixotrop), angerührte Ton-Wasser-Suspensionen dagegen rheopex (besser 'pseudo-rheopex). Durch Überlagerung beider Systeme erhält man ein strukturviskoses System. Hierzu sind etwa 30–40 Gew.-% Tonzusatz erforderlich. Man kann die Tonmenge erheblich senken, wenn die strukturviskose Verknüpfung der Tonteilchen untereinander durch Kationen, insbesondere Alkalikationen, bewerkstelligt wird. Die Kationen erzeugen die Viskosität, die Anionen beeinflussen die Fließgrenze.Die Tone wurden durch zwei rheologische Kenngrößen, den _r - und den-Wert, klassifiziert. Diese Größen charakterisieren eindeutig das Fließ- und Elektrolytverhalten kaolinitischer Tonsuspensionen und ermöglichen es, aus natürlichen Tonen Gemische mit gezielten rheologischen Eigenschaften herzustellen.

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Summary The rheological behaviour of aqueos suspensions of several natural clays was studied by means of a Haake Rotovisko rotating viscometer. The viscosity of clay suspensions depends on electrolytes. The two constituents of electrolytes, cation and anions, produce contrary rheological effects. Cations increase, but anions lower viscosity. The cation effectiveness was mathematically formulated as a function of polarization capacity. The connexion is the following: cation effectiveness is dependent on cation charge screening. Cation charge screening is based on solvation hull thickness. Solvation hull thickness depends on polarization capacity. Besides this polarization capacity is a criterion for the electropositive charakter of cations. So it is possible to explain the rheological behaviour of aqueous clay suspensions and to reduce the rheological effects to the polarization capacity of cations.The knowledge of the rheological clay properties makes it possible to understand the flow behaviour of clay containing enamel suspensions and to vary it in a different manner. Mere enamel water suspensions are thixotropic, on the contrary clay water suspensions are rheopexic. As a result of overlapping of both systems, a structure-viscous system is obtained. This needs an amount of 30–40% of clay. However, the amount of clay may be descreased, if cations with low polarization capacities, especially alkali cations, are added.Clays are classified by two characteristic rheological numbers, the _r - and the-value. Both values characterize flow- and electrolytic properties of kaolinitic clay suspensions and allow to produce mixtures from natural clays with special rheological properties.

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Herrn Professor Dr. K.Hansen zum 60. Geburtstag gewidmet

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Herrn Dr.H. Kyri danke ich für sein beständiges Interesse an dieser Arbeit und für ideenreiche Diskussionen. Besonderen Dank schulde ich FrauB. Schultes für ihre unermüdliche und hilfreiche Mitarbeit.     

Preparation,stoichiometry and magnetic properties of Cu y Cr2Se4−z Br x spinels with 0.5≲x≲2

The chemical composition of Cu _y Cr₂Se_4?z Br _x spinels depends strongly on the preparation parameters. Spinels with 0.8?y?1.2, 0.5?x?2, and 0?z?x?0.2 have been prepared. Whereas the lattice constanta _o of these spinels differs only by less than approximately 0.6%, their Curie temperatureT _c depends sensitively on the spinel composition. For Cu_1.1Cr₂Se_3.4Br_o.46,a _o=1.0410 nm andT _c=310 K were found to compared witha ₀=1.0447 nm andT _c=84 K of CuCr₂Se₂Br₂.     

Über die Spannungskorrektur von Halbwellenpotentialen

Zusammenfassung Es wird eine neue Methode zur Bestimmung des Widerstandswertes einer polarographischen Anordnung gegeben und ihre Brauchbarkeit belegt.     

New combinatorial approach for the investigation of kinetics and temperature dependence of surface reactions in thin organic films

In this paper we present a new, simple, and reproducible method for the rapid determination of the temperature dependence of solution phase surface reactions of organic thin films on solid supports. Instead of estimating the extent of reaction for many separate samples for many different temperatures sequentially, we exploit in our new high throughput combinatorial approach surface reactions carried out under a thermal gradient followed by position-resolved contact angle (CA) measurements. The reaction kinetics, activation energies, and entropies are, thus, accessible on the basis of measurements on a very limited set of samples that differ in reaction times. The kinetics and temperature dependence of surface reactions of the previously studied alkaline hydrolysis of 11,11'-dithiobis(N-hydroxysuccinimidylundecanoate) (NHS-C10) self-assembled monolayers (SAMs) on gold, as well as the ester hydrolysis in SAMs of the novel disulfide 11,11-dithiobis(tert-butylundecanoate) (t-Bu-C10), were investigated in detail using the conventional sequential and the new combinatorial approach. The reaction kinetics, corresponding apparent rate constants k, and activation energies Ea, as well as activation entropies deltaS double dagger, determined according to both approaches agree well with each other to within the experimental error. Hence, these parameters can be quantitatively determined using the described combinatorial approach. A comparison of the reactions of the two model systems indicated that the transition state is tighter for the acid-catalyzed ester hydrolysis in SAMs of the novel disulfide t-Bu-C10 compared to the hydrolysis of the ester groups in SAMs of NHS-C10 on gold.     

Sensitive and specific quantification of the anticancer agent ZD1839 (Gefitinib) in plasma by on-column focusing capillary liquid chromatography-tandem mass spectrometry

The development of an on-column focusing gradient capillary LC method coupled to tandem mass spectrometry (quadrupole-linear ion trap) for the quantitative determination of the anticancer agent ZD1839 (Gefitinib, Iressa) in blood plasma is described. Plasma samples (0.2 ml) were extracted with methyl tert-butyl ether. The analytes of interest, ZD1839 and the internal standard [(2)H8]ZD1839 (ZD1839-d8) were eluted on a 50 mm x 1 mm, 5 microm particle size, capillary ODS Hypersil column using an aqueous ammonium acetate gradient at 40 microl/min. Mass spectrometric detection was performed by a Q-Trap tandem mass spectrometer with electrospray positive ionisation, and monitored in the multiple reaction monitoring transitions 447 >128 and 455 >136, respectively. The limit of quantification of ZD18395 was 0.1 ng/ml. The method proved to be robust, allowing quantification of ZD1839 with sufficient precision, accuracy and sensitivity.     

Hierarchically structured monolithic silicalite-1 consisting of crystallized nanoparticles and its performance in the Beckmann rearrangement of cyclohexanone oxime

In this study, we present a synthetic pathway for the fabrication of self-supporting zeolite monoliths consisting of crystallized nanoparticles. A resorcinol-formaldehyde-based organic aerogel is used as a template, and silicalite-1 is used as the zeolite example. The silicalite-1 monoliths obtained consist of individual well-defined zeolite nanocrystals with sizes of 30-40 nm. The monoliths exhibit a high mechanical stability and have hierarchical porosity, with micropores within the zeolite particles, a mesopore system formed by the packing of the nanoparticles, and a macropore system on the monolith level. Such monolithic zeolites show high selectivity typically above 80% to epsilon-caprolactam combined with a high rate of reaction of 0.46 g(caprolactame)/(g(catalyst).h) in the Beckmann rearrangement of cyclohexanone oxime.     

Charge propagation in "ion channel sensors" based on protein-modified electrodes and redox marker ions

The mechanism of charge propagation in "ion channel sensors" (ICSs) consisting of gold electrodes modified with a layer of charged proteins and highly charged redox-active marker ions in solution was investigated by electrochemical techniques, QCM and AFM. The study is based on seven proteins (concanavalin A, cytochrome c, glucose oxidase, lysozyme, thyroglobulin, catalase, aldolase, and EF1-ATPase) in combination with seven electroactive marker ions ([Fe(CN)6]3-, [Fe(CN)6]4-, [Ru(NH3)6]3+, mono-, di-, and trimeric viologens), as well as a series of suppressor and enhancer ions leading to the following general statements: (i) electrostatic binding of charged marker ions to the domains of the protein is a prerequisite for an electrochemical current and (ii) charge propagation through the layer consists of electron hopping along surface-confined marker ions into the pores between adsorbed proteins. It is further shown that (iii) marker ions and suppressor ions with identical charge compete for oppositely charged sites on the protein domain, (iv) electrostatically bound multilayers of marker or enhancer ions with alternating charge form on a charged protein domain, and (v) self-exchange and exergonic ET catalysis between adsorbed marker ions and marker ions in solution take place. In addition to fundamental insight into the mechanism of charge propagation, valuable information for the design, optimization, and tailoring of new biosensors based on the ICS concept is demonstrated by the current findings.     

Gas-phase dissociation of oligoribonucleotides and their analogs studied by electrospray ionization tandem mass spectrometry

Oligoribonucleotides (RNA) and modified oligonucleotides were subjected to low-energy collision-induced dissociation in a hybrid quadrupole time-of-flight mass spectrometer to investigate their fragmentation pathways. Only very restricted data are available on gas-phase dissociation of oligoribonucleotides and their analogs and the fundamental mechanistic aspects still need to be defined to develop mass spectrometry-based protocols for sequence identification. Such methods are needed, because chemically modified oligonucleotides can not be submitted to standard sequencing protocols. In contrast to the dissociation of DNA, dissociation of RNA was found to be independent of nucleobase loss and it is characterized by cleavage of the 5'-P-O bond, resulting in the formation of c- and their complementary y-type ions. To evaluate the influence of different 2'-substituents, several modified tetraribonucleotides were analyzed. Oligoribonucleotides incorporating a 2'-methoxy-ribose or a 2'-fluoro-ribose show fragmentation that does not exhibit any preferred dissociation pathway because all different types of fragment ions are generated with comparable abundance. To analyze the role of the nucleobases in the fragmentation of the phosphodiester backbone, an oligonucleotide lacking the nucleobase at one position has been studied. Experiments indicated that the dissociation mechanism of RNA is not influenced by the nucleobase, thus, supporting a mechanism where dissociation is initiated by formation of an intramolecular cyclic transition state with the 2'-hydroxyl proton bridged to the 5'-phosphate oxygen.