Untersuchung von Pektin und Cellulosederivten

Ohne Zusammenfassung     

Mechanism of thermolysis of tetramethylammonium μ-chlorobis(triethylaluminate)

The thermolysis of tetramethylammonium μ-chlorobis(triethylaluminate) has been investigated. In addition to the previously reported products, [Me₄N][ClAlEt₃] and (AlEt₃)₂, Me₃N · AlEt₃ is formed simultaneously in lesser amounts. A mechanism for the observed thermolysis reactions is presented which predicts formation of methyl chloride as a transient species which undergoes further reaction with (AlEt₃)₂ to ultimately produce methane and ethylene. The experimentally observed methane/ethylene ratio supports the proposed mechanism.     

Tertiary phosphine complexes of cyclopentadienylmolybdenum carbonyl halides. Stereoselective syntheses and isomer separations

Pure cis and trans isomers of CpMo(CO)₂(L)X (Cp = η⁵-C₅H₅, L = PPh₃ or PBu₃, X = Br, or I) have been separated by chromatography and characterized by infrared and proton NMR spectroscopy. The reactions of trans-CpMo(CO)₂(L)CH₃ with HgX₂ (X = Cl, Br, I, SCN) afford cis-CpMo(CO)₂(L)X in high yield. Both linkage isomers are obtained in the reaction with Hg(SCN)₂, L = PPh₃. The mercuric halides react with CpMo(CO)₂(L)COCH₃ to form the metalmetal bonded derivatives trans-CpMo(CO)₂(L)HgX. Reactions of CpMo(CO)₂(L)CH₃ or CpMo(CO)₂(L)COCH₃ with bromine or iodine yield the halide complexes CpMo(CO)₂(L)X (X = Br and I, respectively), the product mixtures containing high proportions of the trans isomers.     

Spin twists, domain walls, and the cluster spin-glass phase of weakly doped cuprates

We examine the role of spin twists in the formation of domain walls, often called stripes, by focusing on the spin textures found in the cluster spin glass phases of and . To this end, we derive improved analytic expressions for the spin distortions produced by a frustrating bond, both near the core region of the bond and in the far field, and then derive an improved expression for interaction energies between such bonds. We critique our analytical theory by comparison to numerical solutions of this problem and find excellent agreement. By looking at collections of small numbers of such bonds localized in some region of a lattice, we demonstrate the stability of small “clusters” of spins, each cluster having its own orientation of its antiferromagnetic order parameter. Then, we display a domain wall corresponding to spin twists between clusters of locally ordered spins showing how spin twists can serve as a mechanism for stripe formation. Since the charges are localized in this model, we emphasize that these domain walls are produced in a situation for which no kinetic energy is present in the problem. Received 10 January 2000     

Relaxation Limit for Aw-Rascle System

We study the relaxation limit for the Aw-Rascle system of traffic flow. For this we apply the theory of invariant regions and the compensated compactness method to get global existence of Cauchy problem for a particular Aw-Rascle system with source, where the source is the relaxation term, and we show the convergence of this solutions to the equilibrium state.     

Ruthenium vinylidene and carbyne complexes containing a multifunctional tridentate ligand with a PNN donor set

The neutral, octahedral ruthenium vinylidene complexes mer,trans-[(PNN)Cl₂Ru(CCHR)] (PNN = N-(2-diphenylphosphinobenzylidene)-2-(2-pyridyl)ethylamine; R = Ph, 1a; R = ^tBu, 1b) are reported. An X-ray crystallographic study of 1a confirms the tridentate, meridional coordination mode of the PNN ligand. Compounds 1a and 1b undergo regioselective electrophilic addition with HBF₄ · Et₂O at C_β of the vinylidene ligand at low temperatures, and are cleanly and quantitatively converted to the ruthenium carbynes mer,trans-[(PNN)Cl₂Ru(CCH₂R)][BF₄] (R = Ph, 2a; R = ^tBu, 2b). Carbynes 2a and 2b are stable only at low temperatures (<−50 °C). Complex 1a undergoes ligand substitution with L to yield mer,trans-[(PNN)Cl₂Ru(L)] (L = MeCN, 3a; L = CO, 3b).     

Coherent Dynamics of Direct-Current-Driven Quantum-Dot-Array with Two Time-Dependent Embedded Impurities

The coherent dynamics of dc-driven quantum-dot array with two embedded time-dependent impurities is investigated, the exact crossings and avoided crossings in the quasienergies are associated with the evolution dynamics of the electron by the introduction of the envelope lines of the site＇s maximum returning probability. Through a perturbative scheme, the time-dependent Hamiltonian is replaced by an equivalent static one, whose structure reveals the new quantum tunnelling mechanism in the time-periodic driving system and sheds light on the alternative interpretation of dynamic localization and delocalization.     

干空气和冷冻水联产除湿空调节能特性研究

本文提出了一种将转轮除湿和再生式蒸发冷却相结合来实现干空气和冷冻水联产的除湿空调系统,以各组成部件为基础,建立了该系统的计算模型,并对其节能特性进行了分析.结果表明,ARI夏季工况下,干空气和冷冻水联产空调的热力COP在1左右,电力COP可达9.03,相应电力消耗和CO2排量比常规空调减少72.69%之多.存在使系统具有较好性能结构的再生温度范围.可以通过改变干空气比来调节潜/显热处理能力,进而实现无能量浪费地提供全部所需冷量.     

Multimode-diode-pumped gas (alkali-vapor) laser

We report what we believe to be the first demonstration of a multimode-diode-pumped gas laser: Rb vapor operating on the 795 nm D1 resonance transition. Peak output of approximately 1 W was obtained using a volume-Bragg-grating stabilized pump diode array. The laser's output radiance exceeded the pump radiance by a factor greater than 2000. Power scaling (by pumping with larger diode arrays) is therefore possible.