Chaos in stimulated Raman scattering

Coherent state technique and maximal Lyapunov exponent method are used for the study of deterministic chaos in a system governing stimulated Raman scattering. The influence of the external pumping on dynamics of the system is investigated. Phase portraits and FFT spectra are presented.The author would like to express his sincere thanks to prof. J. Peina for his comments and stimulating discussions.     

Direct C−H Borylation of Arenes Catalyzed by Saturated Hydride-Boryl-Iridium-POP Complexes: Kinetic Analysis of the Elemental Steps

The saturated trihydride IrH₃{κ³-P,O,P-[xant(PiPr₂)₂]} ( 1 ; xant(PiPr₂)₂=9,9-dimethyl-4,5-bis(diisopropylphosphino)xanthene) activates the B−H bond of two molecules of pinacolborane (HBpin) to give H₂, the hydride-boryl derivatives IrH₂(Bpin){κ³-P,O,P-[xant(PiPr₂)₂]} ( 2 ) and IrH(Bpin)₂{κ³-P,O,P-[xant(PiPr₂)₂]} ( 3 ) in a sequential manner. Complex 3 activates a C−H bond of two molecules of benzene to form PhBpin and regenerates 2 and 1 , also in a sequential manner. Thus, complexes 1 , 2 , and 3 define two cycles for the catalytic direct C−H borylation of arenes with HBpin, which have dihydride 2 as a common intermediate. C−H bond activation of the arenes is the rate-determining step of both cycles, as the C−H oxidative addition to 3 is faster than to 2 . The results from a kinetic study of the reactions of 1 and 2 with HBpin support a cooperative function of the hydride ligands in the B−H bond activation. The addition of the boron atom of the borane to a hydride facilitates the coordination of the B−H bond through the formation of κ¹- and κ²-dihydrideborate intermediates.     

A new concept in lightning parameters measurement

Nowadays the electrical activity measured in tall objects has been widely characterized, but the collected data of lightning rods installed in buildings do not amount to enough to obtain reliable statistics. The measures stored at relatively few points are not representative of the different types of installations. Furthermore, the protection model applied for lightning air terminal installations is based on theoretical models. This paper describes the design of a micro-station to measure some lightning parameters in real lightning air terminal installations correlated to the nature of emplacement instead of triggering lightning or choosing points with a high number of lightning impacts.     

C-branched chiral (racemic) macrocyclic amino acids: structure of their Ni(II), Zn(II) and Cu(II) complexes

A new procedure for the synthesis of macrocyclic embedded bis-α-amino acids and their use as cation-ligands is described. These compounds are able to form stable Cu(II), Zn(II) and Ni(II) complexes as long as they have a flexible tether between the two nitrogen atoms. For a given macrocycle, the X-ray diffraction studies revealed diastereomerically pure complexes having different geometries depending on the metal ion.     

Existence and regularity properties of non-isotropic singular elliptic equations

We establish existence and sharp regularity results for solutions to singular elliptic equations of the order u ^−β , 0 < β < 1, with gradient dependence and involving a forcing term λ f(x, u). Our approach is based on a singularly perturbed technique. We show that if the forcing parameter λ > 0 is large enough, our solution is positive. For λ small solutions vanish on a nontrivial set and therefore they exhibit free boundaries. We also establish regularity results for the free boundary and study the asymptotic behavior of the problem as b\searrow 0{\beta\searrow 0} and b\nearrow 1{\beta\nearrow 1}. In the former, we show that our solutions u _β converge to a C ^1,1 function which is a solution to an obstacle type problem. When b\nearrow 1{\beta\nearrow 1} we recover the Alt-Caffarelli theory.     

Zur Kinetik der Polymerisation von Aethylen mit löslichen Ziegler-Natta-Katalysatoren

Zusammenfassung Die Geschwindigkeit der Aethylenpolymerisation bei konstantem Druck, in Toluol, unter Verwendung von Katalysator-Systemen der allgemeinen Zusammensetzung Cp₂TiRCl/RAlCl₂ (C_p=Cyclopentadienyl; R, R=Alkyl) wurde gemessen. Gleiche Geschwindigkeit bei Al/Ti=1,2 und 2,0 beweist einen 1:1 Komplex als katalytisch aktive Spezies.Durch Variieren von R (am Ti) und R (am Al) konnten die Einflüsse dieser Gruppen auf die Polymerisationsgeschwindigkeit getrennt untersucht werden.Zwei Abbruchsreaktionen wurden festgestellt, von denen die eine mit Reduktion Ti(IV)Ti(III) gekoppelt und die andere vermutlich der langsamen Bildung eines inaktiven Komplexes aus einer Titan- und zwei Aluminiumeinheiten zuzuschreiben ist.

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Summary Rates of ethylene uptake at constant pressure in toluene, with the use of catalytic systems of the general composition Cp₂TiRCl/RAlCl₂ (Cp=cyclopentadienyl: R,R=alkyl) have been measured. Equality of the observed rates at Al/Ti=1.2 and 2.0 shows the 1:1 complex to be the active species. On varying R (on Ti) and R (on Al) the influence of these substituents on the rate of polymerization could be determined. Two termination reactions have been observed. The first is due to the reduction Ti(IV)Ti(III), and the second is attributed to the slow formation of an inactive complex including 1 Ti(IV) and 2 Al-alkyls.

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Mit 6 Abbildungen und 1 Tabelle

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Herrn Prof. Dr.J.W.Breitenbach zum 60. Geburtstag gewidmet.     

Synthesis of alkyl α- and β-<Emphasis Type="SmallCaps">d</Emphasis>-glucopyranoside-based chiral crown ethers and their application as enantioselective phase-transfer catalysts

Chiral monoaza-15-crown-5-type lariat ethers annelated to alkyl 4,6-O-benzylidene-α- and β-d-glucopyranosides have been synthesized. These macrocycles generated significant asymmetric induction as phase-transfer catalysts in a few two-phase reactions. The catalytic effect of the lariat ethers with methoxy, ethoxy, and i-propoxy substituents on C-1 of the sugar unit in both α and β positions was compared. In liquid–liquid two-phase reactions, the nature and position of the substituents did not have much effect. The α-anomers were somewhat more efficient in terms of enantioselectivity than the β forms. In asymmetric Darzens condensations, in the epoxidation of trans-chalcone, in the Michael addition of β-nitrostyrene and diethyl acetamidomalonate, and in the reaction of 2-benzylidene-1,3-indandione with diethyl bromomalonate, maximum enantioselectivities of 73, 94, 78, and 72%, respectively, were obtained in presence of glucopyranoside-based lariat ethers as catalysts.     

A new combined electrothermal-hollow cathode atom and emission source

A new radiation source based on the FANES-method has been developed in order to achieve an intensity enhancement of the radiation produced. Investigations carried out with this new source are controlled by a computer system connected with a multichannel spectrometer having a wavelength modulated background corrector. First results show that the combination of the two sources increases the emission intensity of spectral lines.