Berechnung von Streumassenradien aus unverschmierten und spaltverschmierten Röntgen-Kleinwinkelstreukurven

Zusammenfassung Die Röntgen-Kleinwinkelstreukurve von Partikeln wird bei äquidistanten Werten des Streuwinkels registriert. Der Streumassenradius der Partikel wird durch gewichtete Summation der Intensitätswerte bestimmt. Dieser Parameter kann sowohl aus der vorher entschmierten als auch aus der mit unendlich langem Primärstrahl verschmierten Streukurve erhalten werden. An einem Beispiel wird gezeigt, daß die gewichtete Summation von nur fünf Intensitätswerten ausreicht, um den Streumassenradius mit einem Abbruchfehler von weniger als einem Prozent zu bestimmen — vorausgesetzt, die Partikel sind nahezu isometrisch und ohne Hohlräume.

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Calculation of radii of gyration from desmeared and smeared small-angle X-ray scattering curves

The small-angle X-ray scattering curve of particles is recorded at equidistant values of the scattering angle. The radius of gyration of the particles is determined by weighted summation of the intensity values. This parameter may be obtained either from a previously desmeared scattering curve as well as directly from data smeared by an infinitely long primary beam. An example is given, showing that a weighted summation of only five intensity values is sufficient to determine the radius of gyration at a truncation error smaller than one percent, provided that the particles are nearly isometric and without hollows.

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Mit 1 Abbildung     

Verhalten der Dicarba-closo-dodecaborane bei der Caprolactampolymerisatior

Ohne Zusammenfassung     

Luminescent Symmetrically and Unsymmetrically Substituted Diboranes(4)

A series of 4-(dimethylamino)phenyl and pentafluorophenyl-substituted 1,2-bis(dimethylamino)diboranes(4) of type A , benzo-fused cyclic 1,4-diaza-2,3-diborinanes of type B , and 1,2-diduryldiboranes(4) of type C were synthesized and structurally characterized. Spectroscopic studies revealed that the substitution pattern is a decisive factor for the observation of fluorescence in most of the derivatives A to C . For diboranes(4) of type A , unsymmetrical substitution with electron-donating and -withdrawing groups at the boron centers is crucial to invoke fluorescence, albeit weak. Substitution at the boron atoms of 1,4-diaza-2,3-diborinane species B leads to a modified skeletal structure. Finally, the grafting of 4-(dimethylamino)phenyl groups to diboranes(4) of type C results in extraordinary Stokes shifts in nonpolar solvents.     

Catalytic efficiency of iron(III) oxides in decomposition of hydrogen peroxide: competition between the surface area and crystallinity of nanoparticles

Various iron(III) oxide catalysts were prepared by controlled decomposition of a narrow layer (ca. 1 mm) of iron(II) oxalate dihydrate, FeC(2)O(4).2H(2)O, in air at the minimum conversion temperature of 175 degrees C. This thermally induced solid-state process allows for simple synthesis of amorphous Fe(2)O(3) nanoparticles and their controlled one-step crystallization to hematite (alpha-Fe(2)O(3)). Thus, nanopowders differing in surface area and particle crystallinity can be produced depending on the reaction time. The phase composition of iron(III) oxides was monitored by XRD and (57)Fe M?ssbauer spectroscopy including in-field measurements, providing information on the relative contents of amorphous and crystalline phases. The gradual changes in particle size and surface area accompanying crystallization were evaluated by HRTEM and BET analysis, respectively. The catalytic efficiency of the synthesized nanoparticles was tested by tracking the decomposition of hydrogen peroxide. The obtained kinetic data gave an unconventional nonmonotone dependence of the rate constant on the surface area of the samples. The amorphous nanopowder with the largest surface area of 401 m(2) g(-1) revealed the lowest catalytic efficiency, while the highest efficiency was achieved with the sample having a significantly lower surface area, 337 m(2) g(-1), exhibiting a prevailing content of crystalline alpha-Fe(2)O(3) phase. The obtained rate constant, 26.4 x 10(-3) min(-1) (g/L)(-1), is currently the highest value published. The observed rare catalytic phenomenon, where the particle crystallinity prevails over the surface area effects, is discussed with respect to other processes of heterogeneous catalysis.     

利用强场多光子电离技术实现对多原子分子离子振动量子态的光学操控

利用飞秒光电子影像技术研究了碘甲烷分子在飞秒强激光场作用下的多光子电离动力学,在实验上实现了运用飞秒强场多光子电离技术对多原子分子离子的振动量子态进行光学操控.提高了飞秒激光的强度,从1.6×1013W/cm2提高到2.5×1013W/cm2.在增大的激光强度范围内,发现了新的能量组分,并对此进行归属.通过采集光电离的光电子影像可以得到强场电离后光电子的动能分布和角度分布两方面的信息,前期的研究主要侧重于讨论光电子动能随光强的变化,重点讨论了光电子角度分布随光强的变化,通过观察光电子角度分布的变化趋势对振动量子态调控机理进一步认识.     

A hybrid approach for predicting the distribution of vibro-acoustic energy in complex built-up structures

Finding the distribution of vibro-acoustic energy in complex built-up structures in the mid-to-high frequency regime is a difficult task. In particular, structures with large variation of local wavelengths and/or characteristic scales pose a challenge referred to as the mid-frequency problem. Standard numerical methods such as the finite element method (FEM) scale with the local wavelength and quickly become too large even for modern computer architectures. High frequency techniques, such as statistical energy analysis (SEA), often miss important information such as dominant resonance behavior due to stiff or small scale parts of the structure. Hybrid methods circumvent this problem by coupling FEM/BEM and SEA models in a given built-up structure. In the approach adopted here, the whole system is split into a number of subsystems that are treated by either FEM or SEA depending on the local wavelength. Subsystems with relative long wavelengths are modeled using FEM. Making a diffuse field assumption for the wave fields in the short wave length components, the coupling between subsystems can be reduced to a weighted random field correlation function. The approach presented results in an SEA-like set of linear equations that can be solved for the mean energies in the short wavelength subsystems.