Wirtschaft an der Grenze. Studien zum Wirtschaftsleben in römischen Militärlagern im Norden Britanniens

Die wichtigsten Quellen für die Erforschung des Wirtschaftsleben in den Militärlagern im Norden Britanniens sind die im Kastell Vindolanda gefundenen Holztäfelchen mit Texten aus dem Lageralltag von ca. 90-120 n. Chr. sowie die archäologischen Funde aus der Region. Nicht zuletzt aufgrund dieser Quellenlage wurde der Betrachtungszeitraum auf die Zeit von Agricola bis Hadrianus begrenzt. Es hat sich gezeigt, daß das Wirtschaftsleben in den römischen Militärlagern im Norden Britanniens dieser Epoche einerseits bürokratische Züge trägt, da Führungspersonen in Militär und Verwaltung im Rahmen redistributiver Strukturen viele Güter beschafften, die an die Soldaten gegen Abzüge vom Sold ausgegeben wurden. Andererseits stand diesem Verfahren eine beeindruckende Dynamik im Marktgeschehen gegenüber, die durch die Erfordernisse der Heeresversorgung und des individuellen Konsums der Soldaten entstand. Zu den Bereichen der Wirtschaftstätigkeit, in denen ein starker Einfluß der Bürokratie herrschte, zählten insbesondere die Versorgung mit den Grundnahrungsmitteln (v. a. Getreide, Bier). Hypothesen über ein militärisches Redistributivsystem für Olivenöl unter der Ägide des praefectus annonae wurden allerdings nicht bestätigt. Die Existenz einer zentralen Behörde für die Heeresversorgung im Reich für die Principatszeit nicht nachgewiesen werden. Es zeigte sich statt dessen eine in der Forschung bisher nicht so deutlich gesehene Verantwortung und Aktivität unterer militärischer Entscheidungsträger vor Ort. Die Märkte an der britannischen Grenze bieten eine sehr viel differenzierteres Bild als man es von Handelsplätzen am äußersten Rande der romanisierten Welt vielleicht erwartet hätte. Vor allem zeichneten sie sich durch ein breites Angebot an Waren aus, die über große Entfernungen heran transportiert worden waren (Wein, Oliven, mediterrane Fischcaucen, Pfeffer, Importkeramik). Im Bereich des Handwerks sind im Norden Britanniens durch archäologische Funde und die Tätigkeitsbezeichnungen von Handwerkern in den Texten aus Vindolanda vielfältige Zeugnisse eines Engagements der Militärs präsent.

Beschreibung von Oberflächenphänomenen durch relativistische Clusterrechnungen unter Verwendung eines Einbettungsverfahrens

For the theoretical investigation of local phenomena (adsorption at surfaces, defects or impurities within a crystal, etc.) one can assume that the effects caused by the local disturbance are only limited to the neighbouring particles. With this model, that is well-known as cluster-approximation, an infinite system can be simulated by a much smaller segment of the surface (Cluster). The size of this segment varies strongly for different systems. Calculations to the convergence of bond distance and binding energy of an adsorbed aluminum atom on an Al(100)-surface showed that more than 100 atoms are necessary to get a sufficient description of surface properties. However with a full-quantummechanical approach these system sizes cannot be calculated because of the effort in computer memory and processor speed. Therefore we developed an embedding procedure for the simulation of surfaces and solids, where the whole system is partitioned in several parts which itsself are treated differently: the internal part (cluster), which is located near the place of the adsorbate, is calculated completely self-consistently and is embedded into an environment, whereas the influence of the environment on the cluster enters as an additional, external potential to the relativistic Kohn-Sham-equations. The basis of the procedure represents the density functional theory. However this means that the choice of the electronic density of the environment constitutes the quality of the embedding procedure. The environment density was modelled in three different ways: atomic densities; of a large prepended calculation without embedding transferred densities; bulk-densities (copied). The embedding procedure was tested on the atomic adsorptions of 'Al on Al(100) and Cu on Cu(100). The result was that if the environment is choices appropriately for the Al-system one needs only 9 embedded atoms to reproduce the results of exact slab-calculations. For the Cu-system first calculations without embedding procedures were accomplished, with the result that already 60 atoms are sufficient as a surface-cluster. Using the embedding procedure the same values with only 25 atoms were obtained. This means a substantial improvement if one takes into consideration that the calculation time increased cubically with the number of atoms. With the embedding method Infinite systems can be treated by molecular methods. Additionally the program code was extended by the possibility to make molecular-dynamic simulations. Now it is possible apart from the past calculations of fixed cores to investigate also structures of small clusters and surfaces. A first application we made with the adsorption of Cu on Cu(100). We calculated the relaxed positions of the atoms that were located close to the adsorption site and afterwards made the full-quantummechanical calculation of this system. We did that procedure for different distances to the surface. Thus a realistic adsorption process could be examined for the first time. It should be remarked that when doing the Cu reference-calculations (without embedding) we begun to parallelize the entire program code. Only because of this aspect the investigations for the 100 atomic Cu surface-clusters were possible. Due to the good efficiency of both the parallelization and the developed embedding procedure we will be able to apply the combination in future. This will help to work on more these areas it will be possible to bring in results of full-relativistic molecular calculations, what will be very interesting especially for the regime of heavy systems.

Lithography-free micro- and nanostructuring based on conventional plasma etching

In now-a-days semiconductor and MEMS technologies the photolithography is the working horse for fabrication of functional devices. The conventional way (so called Top-Down approach) of microstructuring starts with photolithography, followed by patterning the structures using etching, especially dry etching. The requirements for smaller and hence faster devices lead to decrease of the feature size to the range of several nanometers. However, the production of devices in this scale range needs photolithography equipment, which must overcome the diffraction limit. Therefore, new photolithography techniques have been recently developed, but they are rather expensive and restricted to plane surfaces. Recently a new route has been presented - so-called Bottom-Up approach - where from a single atom or a molecule it is possible to obtain functional devices. This creates new field - Nanotechnology - where one speaks about structures with dimensions 1 - 100 nm, and which has the possibility to replace the conventional photolithography concerning its integral part - the self-assembly. However, this technique requires additional and special equipment and therefore is not yet widely applicable. This work presents a general scheme for the fabrication of silicon and silicon dioxide structures with lateral dimensions of less than 100 nm that avoids high-resolution photolithography processes. For the self-aligned formation of extremely small openings in silicon dioxide layers at in depth sharpened surface structures, the angle dependent etching rate distribution of silicon dioxide against plasma etching with a fluorocarbon gas (CHF3) was exploited. Subsequent anisotropic plasma etching of the silicon substrate material through the perforated silicon dioxide masking layer results in high aspect ratio trenches of approximately the same lateral dimensions. The latter can be reduced and precisely adjusted between 0 and 200 nm by thermal oxidation of the silicon structures owing to the volume expansion of silicon during the oxidation. On the basis of this a technology for the fabrication of SNOM calibration standards is presented. Additionally so-formed trenches were used as a template for CVD deposition of diamond resulting in high aspect ratio diamond knife. A lithography-free method for production of periodic and nonperiodic surface structures using the angular dependence of the etching rate is also presented. It combines the self-assembly of masking particles with the conventional plasma etching techniques known from microelectromechanical system technology. The method is generally applicable to bulk as well as layered materials. In this work, layers of glass spheres of different diameters were assembled on the sample surface forming a mask against plasma etching. Silicon surface structures with periodicity of 500 nm and feature dimensions of 20 nm were produced in this way. Thermal oxidation of the so structured silicon substrate offers the capability to vary the fill factor of the periodic structure owing to the volume expansion during oxidation but also to define silicon dioxide surface structures by selective plasma etching. Similar structures can be simply obtained by structuring silicon dioxide layers on silicon. The method offers a simple route for bridging the Nano- and Microtechnology and moreover, an uncomplicated way for photonic crystal fabrication.

Optical Characterization of Organic Gain Materials for UV-emitting Hybrid Complex Coupled VCSELs

In this thesis, optical gain measurement setup based on variable stripe length method is designed, implemented and improved. The setup is characterized using inorganic and organic samples. The optical gain of spiro-quaterphenyl is calculated and compared with measurements from the setup. Films with various thicknesses of spiro-quaterphenyl, methoxy-spiro-quaterphenyl and phenoxy-spiro-quaterphenyl are deposited by a vacuum vapor deposition technique forming asymmetric slab waveguides. The optical properties, laser emission threshold, optical gain and loss coefficient for these films are measured. Additionally, the photodegradation during pumping process is investigated.

Punching Shear Behavior of UHPC Flat Slabs

At the Institute of Structural Engineering of the Faculty of Civil Engineering, Kassel University, series tests of slab-column connection were carried out, subjected to concentrated punching load. The effects of steel fiber content, concrete compressive strength, tension reinforcement ratio, size effect, and yield stress of tension reinforcement were studied by testing a total of six UHPC slabs and one normal strength concrete slab. Based on experimental results; all the tested slabs failed in punching shear as a type of failure, except the UHPC slab without steel fiber which failed due to splitting of concrete cover. The post ultimate load-deformation behavior of UHPC slabs subjected to punching load shows harmonic behavior of three stages; first, drop of load-deflection curve after reaching maximum load, second, resistance of both steel fibers and tension reinforcement, and third, pure tension reinforcement resistance. The first shear crack of UHPC slabs starts to open at a load higher than that of normal strength concrete slabs. Typically, the diameter of the punching cone for UHPC slabs on the tension surface is larger than that of NSC slabs and the location of critical shear crack is far away from the face of the column. The angle of punching cone for NSC slabs is larger than that of UHPC slabs. For UHPC slabs, the critical perimeter is proposed and located at 2.5d from the face of the column. The final shape of the punching cone is completed after the tension reinforcement starts to yield and the column stub starts to penetrate through the slab. A numerical model using Finite Element Analysis (FEA) for UHPC slabs is presented. Also some variables effect on punching shear is demonstrated by a parametric study. A design equation for UHPC slabs under punching load is presented and shown to be applicable for a wide range of parametric variations; in the ranges between 40 mm to 300 mm in slab thickness, 0.1 % to 2.9 % in tension reinforcement ratio, 150 MPa to 250 MPa in compressive strength of concrete and 0.1 % to 2 % steel fiber content. The proposed design equation of UHPC slabs is modified to include HSC and NSC slabs without steel fiber, and it is checked with the test results from earlier researches.