Arrays and New Antenna Topologies for Increasing THz Power Generation Using Photomixers

Power limitations in CW THz generation imposed by conventional photomixers (“antenna emitters”, AEs) are the major drawbacks on THz generation. From the antenna point of view, two different strategies are proposed to increase the generated power: optimized arrays and lenses arrangements and the use of new dielectric horn antennas. Then, using multiple small lenses, one per each single element, instead of a large one, bigger than the array, makes the generated power much higher. In addition, horn antennas etched in the substrate are considered in order to reduce the energy distribution scattering. Finally, some manufacturing issues are discussed.     

Growth of carbon nanotube forests between a bi-metallic catalyst layer and a SiO2 substrate to form a self-assembled carbon–metal heterostructure

A special nanostructure was formed by the growth of carbon nanotubes (CNTs) between a substrate and a thin bi-metallic catalyst layer using a thermal chemical vapor deposition process. The catalyst layer is composed of adjacently disposed Cr and Ni phases formed prior to CNT growth. The Cr/Ni layer serves as a bi-metallic catalyst layer, which is pushed away from the substrate as a thin and continuous nanomembrane with the growth of CNTs. The self-assembled CNT–catalyst heterostructure possesses a smooth surface (RMS = 2.9 nm) with a metallic shine. Directly interlinked to the Cr/Ni layer, dense and vertically aligned multi-walled CNTs are found. Compared to conventional CNT films, the structure has significant advantages for CNT integration. From technology point of view, the structure allows further processing without impact on the CNTs as well as transfer of pristine vertically aligned CNTs to arbitrary substrates. Moreover, the as-grown CNT films provide an interface ideal for further electrical, thermal and mechanical contacting of CNT films. We present structural investigations of this special CNT–metal heterostructure. Furthermore, we discuss possible interface mechanisms during catalyst layer formation and CNT growth.     

Occurrence of pharmaceuticals and personal care products in german fish tissue: a national study

German Environment Specimen Bank (GESB) fish tissue samples, collected from 14 different GESB locations, were analyzed for 15 pharmaceuticals, 2 pharmaceutical metabolites, and 12 personal care products. Only 2 pharmaceuticals, diphenhydramine and desmethylsertraline, were measured above MDL. Diphenhydramine (0.04-0.07 ng g(-1) ww) and desmethylsertraline (1.65-3.28 ng g(-1) ww) were measured at 4 and 2 locations, respectively. The maximum concentrations of galaxolide (HHCB) (447 ng g(-1) ww) and tonalide (AHTN) (15 ng g(-1) ww) were measured at the Rehlingen sampling site in the Saar River. A significant decrease in HHCB and AHTN fish tissue concentrations was observed from 1995 to 2008 at select GESB sampling sites (r(2) = 0.69-0.89 for galaxolide and 0.89-0.97 for tonalide with p < 0.003). Galaxolide and tonalide fish tissue concentrations in Germany were ～19× and ～28× lower, respectively, as compared to fish tissue concentrations measured in a United States nationwide PPCP study conducted in 2006. Proximity of the sampling locations to the upstream wastewater treatment plant discharging point and mean annual flow at the sampling location were found to significantly predict galaxolide and tonalide fish tissue concentrations (HHCB: r(2) = 0.79, p = 0.021 and AHTN: r(2) = 0.81, p = 0.037) in Germany.     

Growth and disparities in Europe: Insights from a spatial growth model*

This paper provides a spatial neoclassical growth model for a system of N regional economies. Regional output growth is determined by interregional fixed capital relocations which depend on initial factor endowments as well as a region's relative location in space. The dynamics of the model are captured by a Taylor approximation, which provides a testable spatial econometric model specification that is applied for European regions on the NUTS 2 level. Both theoretical and empirical results show how relatively high human capital endowments are beneficial to growth if found within one region, but disadvantageous if found in neighbouring regions. Este artículo proporciona un modelo de crecimiento neo‐clásico espacial para un sistema de N economías regionales. El crecimiento del producto regional viene determinado por deslocalizaciones interregionales de capital fijo que dependen de la dotación de factores inicial, así como de la relativa localización espacial de una región. Las dinámicas del modelo son capturadas mediante una aproximación de Taylor, que proporciona una especificación comprobable de modelo econométrico espacial que se aplica a regiones europeas a nivel NUTS 2. Tanto los resultados teoréticos como los empíricos muestran como las dotaciones relativamente elevadas de capital humano son ventajosas para el crecimiento cuando se concentran en una región, pero una desventaja si se encuentran en regiones vecinas.      

Numerische Untersuchungen zur Pfropfenbildung in offenen Profilen in Abhängigkeit des Einbringverfahrens

Numerical studies of soil plugging in profiles with open cross‐section with respect to the installation method. Bracing and soil plugging can occur during installation of open‐ended piles. Especially, soil plugging in open‐ended steel piles plays an important role regarding the calculation of axial bearing capacity. Until today, it is hard to predict whether or not a soil plug forms inside the installed profile. Only little experimental data is available regarding soil plugging. In this paper numerical studies regarding the simulation of the penetration process of steel and open‐ended piles are presented. By investigation of the horizontal stresses and the void ratio distribution inside the pile it will be concluded whether or not a soil plug is formed with respect to the installation method. Furthermore, it is possible to gain further insight into the mechanism of soil plugging inside open‐ended piles.     

Tetranuclear yttrium and gadolinium 2-acetylcyclopentanoate clusters: Synthesis and their use as spin-coating precursors for metal oxide film formation for field-effect transistor fabrication

Lanthanide clusters [Ln_4(μ_3-OH)_2(η~2-accp)_4((μ-O)-η~2-accp)_6](Ln = Y(4),Gd(5); accp = 2-acetylcyclopentanoate) are accessible by treatment of [M(NO_3)_3·6 H_2 O](M = Y(1),Gd(2)) with 3 equiv. of Haccp(3) in presence of NaOH. The molecular structures of 4 and 5 in the solid-state are discussed. The thermal behavior of 4 and 5 was studied by TG under Ar and O_2, showing multistep decomposition processes. Additionally, DSC studies were carried out under an atmosphere of O_2. PXRD measurements of the TG residues confirm the formation of Ln_2 O_3.Spin-coating experiments were carried out with 4 and 5 for Ln_2 O_3 film deposition on silicon substrates. The layers are smooth, close and are of thicknesses of 18.87±1.13 nm and 25.59 ± 4.55 nm for Ln = Y and Gd, which was evidenced by SEM and EDX studies. Field-effect transistors were successfully fabricated by deposition of carbon nanotubes on top of the Y_2 O_3 films and formation of palladium contacts by a lift-off procedure. An on/off ratio of more than 4 orders of magnitude is achieved without considerable leakage currents. These results demonstrate the potential use of spin-coated Y_2 O_3 as a gate dielectric in electronic devices.     

Combining spectroscopic and potentiometric approaches to characterize competitive binding to humic substances

In an area that contains high concentrations of natural organic matter, it is expected that it plays an important role on the behavior of rare earth elements (REE), like europium, and of trivalent actinides. Competitive interactions with H+, inorganic species, major cations, e.g. Ca(II) or Mg(II), could influence these metals transport and bioavailability. Competitive experiments between cations, which can bind differently to humic substances and Eu3+, will bring an improved understanding of the competitive mechanisms. The aim of this study is to acquire data for Eu(III)/Cu(II) and Eu(III)/Ca(II) competitive binding to a sedimentary originated humic acid (Gorleben, Germany). The NICA-Donnan parameters for Ca2+, Cu2+, and Eu3+ obtained from competitive binding experiments using Ca2+ or Cu2+ ion selective electrodes were used to model time-resolved laser fluorescence spectroscopy (TRLFS) measurements. Eu3+ and CU2+ are in direct competition for the same type of sites, whereas Ca2+ has an indirect influence through electrostatic binding.