Eine Methode der Phosphors?urebestimmung

Ohne Zusammenfassung(Aus dem Universitätslaboratorium von Prof. Naumann zu Giessen.)     

Kondo anomalies of heat conductivity and Lorenz ratio in normal state (La,Ce) Al2

The thermal conductivity of LaAl₂ and of two dilute (La, Ce)Al₂ alloys was measured in the normal state between 0.4 and 8 K. From the lattice conductivity of LaAl₂ a high dislocation densityN _d caused by the arc melting process can be inferred. After annealingN _d is reduced by an order of magnitude. For the (La, Ce)Al₂ samples minima are observed at 5 K in theW ^e ·T vs.T curves (W ^e =electronic thermal resistivity). Below 1 K the quantityW ^e ·T is linear in (— lnT). The electronic Lorenz ratioL ^e (T)=ρ(T)/W ^e (T) ·T shows a maximum at 2 K with a value 23% aboveL ^e (0). It is for the first time that this Kondo anomaly is established in its full temperature dependence.     

Nuclear inelastic scattering and Mössbauer spectroscopy as local probes for ligand binding modes and electronic properties in proteins: vibrational behavior of a ferriheme center inside a β-barrel protein

In this work, we present a study of the influence of the protein matrix on its ability to tune the binding of small ligands such as NO, cyanide (CN(-)), and histamine to the ferric heme iron center in the NO-storage and -transport protein Nitrophorin 2 (NP2) from the salivary glands of the blood-sucking insect Rhodnius prolixus. Conventional M?ssbauer spectroscopy shows a diamagnetic ground state of the NP2-NO complex and Type I and II electronic ground states of the NP2-CN(-) and NP2-histamine complex, respectively. The change in the vibrational signature of the protein upon ligand binding has been monitored by Nuclear Inelastic Scattering (NIS), also called Nuclear Resonant Vibrational Spectroscopy (NRVS). The NIS data thus obtained have also been calculated by quantum mechanical (QM) density functional theory (DFT) coupled with molecular mechanics (MM) methods. The calculations presented here show that the heme ruffling in NP2 is a consequence of the interaction with the protein matrix. Structure optimizations of the heme and its ligands with DFT retain the characteristic saddling and ruffling only if the protein matrix is taken into account. Furthermore, simulations of the NIS data by QM/MM calculations suggest that the pH dependence of the binding of NO, but not of CN(-) and histamine, might be a consequence of the protonation state of the heme carboxyls.     

Influence of interparticle interactions on the kinetics of self-assembly and mechanical strength of nanoparticulate aggregates

Computer simulations based on Discrete Element Method have been performed in order to investigate the influence of interparticle interactions on the kinetics of self-assembly and the mechanical strength of nanoparticle aggregates.Three different systems have been considered.In the first system the interaction between particles has been simulated using the JKR (Johnson,Kendall and Roberts) contact theory,while in the second and third systems the interaction between particles has been simulated using van der Waals and electrostatic forces respectively.In order to compare the mechanical behaviour of the three systems,the magnitude of the maximum attractive force between particles has been kept the same in all cases.However,the relationship between force and separation distance differs from case to case and thus,the range of the interparticle force.The results clearly indicate that as the range of the interparticle force increases,the self-assembly process is faster and the work required to produce the mechanical failure of the assemblies increases by more than one order of magnitude.     

The electronic thermal conductivity of superconductors with paramagnetic impurities

We have measured the thermal conductivitiesK _s in the superconducting state andK _n in the normal state of (La_1–x RE_x) Al₂ single crystals (RE: Gd, Ce;x0.005) between 0.4 and 8 K. The lattice conductivity is small in the superconducting state above 0.5T _c and in the normal state and is independent of annealing. Annealing does, however, strongly depress the ratioK _s ^e /K _n ^e of the electronic thermal conductivities. We also report on a theory of the electronic thermal conductivity which describes the experimental results quantitatively. Interaction effects between impurities show up for the samples with the highest RE-concentration.Work performed within the research program of the Sonderforschungsbereich 125 Aachen/Jülich/Köln     

Structure of polymer-stabilized magnetic fluids: small-angle neutron scattering and mean-field lattice modeling

Small-angle neutron scattering and mean-field lattice modeling were used to characterize a class of water-based magnetic fluids tailored specifically to extract soluble organic compounds from water. The fluids consist of a suspension of approximately 7 nm magnetite (Fe3O4) nanoparticles coated with a bifunctional polymer layer comprised of an outer hydrophilic poly(ethylene oxide) (PEO) region for colloidal stability and an inner hydrophobic poly(propylene oxide) (PPO) region for solubilization of organic compounds. The inner region of the polymer shell is increasingly depleted of water as the fraction of PPO side chains increases. The incorporation of PPO side chains also leads to a small increase in interparticle attraction. The lattice model predicted a shell structure similar to that of a PEO-PPO-PEO triblock copolymer (Pluronic) micelle, with equivalent levels of hydration but with more PEO present in the PPO-rich regions, as the side chains grafted to the surface are less able to segregate than when in free micellar systems.     

JT-60U装置温度分布剖面不变性的实验研究

在一系列H模放电条件下，建立了一个旨在研究等离子体温度分布剖面不变性的数据库。介绍了数据库建立过程中要解决的关键问题和所用软件，对等离子体温度分布剖面不变性及芯部约束与边缘参数的关系进行了研究。