Showing papers by "Technische Universität Darmstadt published in 2003"

Light Scattering from Small Particles

Abstract: In the laser Doppler and phase Doppler techniques a part of the incident laser light is imaged by the particles onto the detectors. It is this scattered light which carries information about the particle velocity and its properties and thus, the light scattered from small particles plays a central role in the basic physics of these measurement techniques. In recognition of this, the following chapter is devoted to the fundamentals of elastic light scattering from small particles. The simplest case of a homogeneous and isotropic sphere is considered.

Continuous Lattices and Domains

Abstract: Information content and programming semantics are just two of the applications of the mathematical concepts of order, continuity and domains. The authors develop the mathematical foundations of partially ordered sets with completeness properties of various degrees, in particular directed complete ordered sets and complete lattices. Uniquely, they focus on partially ordered sets that have an extra order relation, modelling the notion that one element 'finitely approximates' another, something closely related to intrinsic topologies linking order and topology. Extensive use is made of topological ideas, both by defining useful topologies on the structures themselves and by developing close connections with numerous aspects of topology. The theory so developed not only has applications to computer science but also within mathematics to such areas as analysis, the spectral theory of algebras and the theory of computability. This authoritative, comprehensive account of the subject will be essential for all those working in the area.

Model-driven development: a metamodeling foundation

Abstract: Metamodeling is an essential foundation for MDD, but there's little consensus on the precise form it should take and role it should play. The authors analyze the underlying motivation for MDD and then derive a concrete set of requirements that a supporting infrastructure should satisfy. They discuss why the traditional "language definition" interpretation of metamodeling isn't a sufficient foundation and explain how it can be extended to unlock MDD's full potential.

Iterated local search

Abstract: This is a survey of "Iterated Local Search", a general purpose metaheuristic for finding good solutions of combinatorial optimization problems. It is based on building a sequence of (locally optimal) solutions by: (1) perturbing the current solution; (2) applying local search to that modified solution. At a high level, the method is simple, yet it allows for a detailed use of problem-specific properties. After giving a general framework, we cover the uses of Iterated Local Search on a number of well studied problems.

R-Boundedness, Fourier Multipliers, and Problems of Elliptic and Parabolic Type

Abstract: Introduction Notations and conventions $\mathcal R$-Boundedness and Sectorial Operators: Sectorial operators The classes ${\mathcal{BIP}}(X)$ and $\mathcal H^\infty(X)$ $\mathcal R$-bounded families of operators $\mathcal R$-sectorial operators and maximal $L_p$-regularity Elliptic and Parabolic Boundary Value Problems: Elliptic differential operators in $L_p(\mathbb{R}^n E)$ Elliptic problems in a half space: General Banach spaces Elliptic problems in a half space: Banach spaces of class $\mathcal{HT}$ Elliptic and parabolic problems in domains Notes References.

AttrakDiff: Ein Fragebogen zur Messung wahrgenommener hedonischer und pragmatischer Qualität

Abstract: Die Evaluation interaktiver Produkte ist eine wichtige Aktivitat im Rahmen benutzerzentrierter Gestaltung. Eine Evaluationstechnik, die sich meist auf die Nutzungsqualitat oder „Gebrauchstauglichkeit“ eines Produkts konzentriert, stellen Fragebogen dar. Zur Zeit werden allerdings weitere, sogenannte „hedonische“ Qualitatsaspekte diskutiert. Diese beruhen auf den menschlichen Bedurfnissen nach Stimulation und Identitat, wahrend bei Gebrauchstauglichkeit (bzw. „pragmatischer Qualitat“) der Bedarf zur kontrollierten Manipulation der Umwelt im Vordergrund steht. In diesem Beitrag wird der „AttrakDiff 2“ Fragebogen vorgestellt, der sowohl wahrgenommene pragmatische als auch hedonische Qualitat zu messen vermag. Ergebnisse zur Reliabilitat und Validitat werden vorgestellt und diskutiert. AttrakDiff 2 stellt einen ersten Beitrag zur Messung von Qualitatsaspekten dar, die uber die reine Gebrauchstauglichkeit hinausgehen.

Processing techniques for functionally graded materials

Abstract: An overview of the achievements of the German priority program “Functionally Graded Materials (FGM)” in the field of processing techniques is given. Established powder processes and techniques involving metal melts are described, and recent developments in the field of graded polymer processing are considered. The importance of modeling of gradient formation, sintering and drying for the production of defect-free parts with predictable gradients in microstructure is discussed, and examples of a successful application of numerical simulations to the processing of functionally graded materials are given.

Multi-level partition of unity implicits

Abstract: We present a new shape representation, the multi-level partition of unity implicit surface, that allows us to construct surface models from very large sets of points. There are three key ingredients to our approach: 1) piecewise quadratic functions that capture the local shape of the surface, 2) weighting functions (the partitions of unity) that blend together these local shape functions, and 3) an octree subdivision method that adapts to variations in the complexity of the local shape.Our approach gives us considerable flexibility in the choice of local shape functions, and in particular we can accurately represent sharp features such as edges and corners by selecting appropriate shape functions. An error-controlled subdivision leads to an adaptive approximation whose time and memory consumption depends on the required accuracy. Due to the separation of local approximation and local blending, the representation is not global and can be created and evaluated rapidly. Because our surfaces are described using implicit functions, operations such as shape blending, offsets, deformations and CSG are simple to perform.

Light-emitting field-effect transistor based on a tetracene thin film.

Abstract: We report the first organic light-emitting field-effect transistor. The device structure comprises interdigitated gold source and drain electrodes on a $\mathrm{S}\mathrm{i}/\mathrm{S}\mathrm{i}{\mathrm{O}}_{\mathrm{2}}$ substrate. A polycrystalline tetracene thin film is vacuum sublimated on the substrate forming the active layer of the device. Both holes and electrons are injected from the gold contacts into this layer leading to electroluminescence from the tetracene. The output characteristics, transfer characteristics, and the optical emission properties of the device are reported. A possible mechanism for electron injection is suggested.

Diversity and abundance of Crenarchaeota in terrestrial habitats studied by 16S RNA surveys and real time PCR

Abstract: Novel phylogenetic lineages of as yet uncultivated crenarchaeota have been frequently detected in low to moderate-temperature, marine and terrestrial environments. In order to gain a more comprehensive view on the distribution and diversity of Crenarchaeota in moderate habitats, we have studied 18 different terrestrial and freshwater samples by 16S rDNA-based phylogenetic surveys. In seven different soil samples of diverse geographic areas in Europe (forest, grassland, ruderal) and Asia (permafrost, ruderal) as well as in two microbial mats, we have consistently found one particular lineage of crenarchaeota. The diversity of Crenarchaeota in freshwater sediments was considerably higher with respresentative 16S rDNA sequences distributed over four different groups within the moderate crenarchaeota. Systematic analysis of a 16S rDNA universal library from a sandy ecosystem containing 800 clones exclusively revealed the presence of the soil-specific crenarchaeotal cluster. With primers specific for non-thermophilic crenarchaeota we established a rapid method to quantify archaeal 16S rDNA in real time PCR. The relative abundance of crenarchaeotal rDNA was 0.5-3% in the bulk soil sample and only 0.16% in the rhizosphere of the sandy ecosystem. A nearby agricultural setting yielded a relative abundance of 0.17% crenarchaeotal rDNA. In total our data suggest that soil crenarchaeota represent a stable and specific component of the microbiota in terrestrial habitats.

Costs, Commitment and Compliance: The Impact of EU Democratic Conditionality on Latvia, Slovakia and Turkey

Abstract: ‘Democratic conditionality’ is the core strategy of the EU to induce candidate states to comply with its human rights and democracy standards. How does it work and when is it effective? This article reports findings of a comparative study of ‘hard cases’: Slovakia under Meciar; Turkey; and Latvia. We argue that EU democratic conditionality is a strategy of ‘reinforcement by reward’ which works through intergovernmental material bargaining. Its efficacy depends on the candidate governments’ domestic political costs of compliance. By contrast, social influence and transnational mobilization have proved ineffective.

On the origin of binding energy shifts of core levels of supported gold nanoparticles and dependence of pretreatment and material synthesis

Abstract: X-ray photoelectron spectroscopy (XPS) investigations of supported nanoparticles smaller than 10 nm show a significant shift of the electron binding energy of core levels compared with the bulk values. In this work, such shifts were examined at differently supported and prepared gold nanoparticles for the 4f electron level. Special attention was paid to the influence of reducing pretreatment in hydrogen and, moreover, the influence of different oxide supports. Surprisingly, in most cases, lower binding energies than the Au 4f7/2of 84.0 eV were observed depending on the oxidic support as well as the pretreatment conditions. The origin of these differences of the core level values are discussed in terms of different models like electron transfer from the support to the particles, size and geometric effects. It seems that especially geometric factors like the particle shape play an important role.

Origin of the threshold voltage instability in SiO 2 /HfO 2 dual layer gate dielectrics

Abstract: The magnitude of the V/sub T/ instability in conventional MOSFETs and MOS capacitors with SiO/sub 2//HfO/sub 2/ dual-layer gate dielectrics is shown to depend strongly on the details of the measurement sequence used. By applying time-resolved measurements (capacitance-time traces and charge-pumping measurements), it is demonstrated that this behavior is caused by the fast charging and discharging of preexisting defects near the SiO/sub 2//HfO/sub 2/ interface and in the bulk of the HfO/sub 2/ layer. Based on these results, a simple defect model is proposed that can explain the complex behavior of the V/sub T/ instability in terms of structural defects as follows. 1) A defect band in the HfO/sub 2/ layer is located in energy above the Si conduction band edge. 2) The defect band shifts rapidly in energy with respect to the Fermi level in the Si substrate as the gate bias is varied. 3) The rapid energy shifts allows for efficient charging and discharging of the defects near the SiO/sub 2//HfO/sub 2/ interface by tunneling.

Gradual shifts in sites of free-auxin production during leaf-primordium development and their role in vascular differentiation and leaf morphogenesis in Arabidopsis

Abstract: The major regulatory shoot signal is auxin, whose synthesis in young leaves has been a mystery To test the leaf-venation hypothesis [R Aloni (2001) J Plant Growth Regul 20: 22–34], the patterns of free-auxin production, movement and accumulation in developing leaf primordia of DR5::GUS-transformed Arabidopsis thaliana (L) Heynh were visualized DR5::GUS expression was regarded to reflect sites of free auxin, while immunolocalization with specific monoclonal antibodies indicated total auxin distribution The mRNA expression of key enzymes involved in the synthesis, conjugate hydrolysis, accumulation and basipetal transport of auxin, namely indole-3-glycerol-phosphate-synthase, nitrilase, IAA-amino acid hydrolase, chalcone synthase and PIN1 as an essential component of the basipetal IAA carrier, was investigated by reverse transcription–polymerase chain reaction Near the shoot apex, stipules were the earliest sites of high free-auxin production During early stages of primordium development, leaf apical dominance was evident from strong β-glucuronidase activity in the elongating tip, possibly suppressing the production of free auxin in the leaf tissues below it Hydathodes, which develop in the tip and later in the lobes, were apparently primary sites of high free-auxin production, the latter supported by auxin-conjugate hydrolysis, auxin retention by the chalcone synthase-dependent action of flavonoids and also by the PIN1-component of the carrier-mediated basipetal transport Trichomes and mesophyll cells were secondary sites of free-auxin production During primordium development there are gradual shifts in sites and concentrations of free-auxin production occurring first in the tip of a leaf primordium, then progressing basipetally along the margins, and finally appearing also in the central regions of the lamina This developmental pattern of free-auxin production is suggested to control the basipetal maturation sequence of leaf development and vascular differentiation in Arabidopsis leaves Electronic Supplementary Material is available if you access this article at http://dxdoiorg/101007/s00425-002-0937-8 On that page (frame on the left side), a link takes you directly to the supplementary material

Conquering aspects with Caesar

Abstract: Join point interception (JPI), is considered an important cornerstone of aspect-oriented languages. However, we claim that JPI alone does not suffice for a modular structuring of aspects. We propose CAESAR, a model for aspect-oriented programming with a higher-level module concept on top of JPI, which enables reuse and componentization of aspects, allows us to use aspects polymorphically, and introduces a novel concept for dynamic aspect deployment.

Identification of Active Sites in Gold-Catalyzed Hydrogenation of Acrolein

Abstract: The active sites of supported gold catalysts, favoring the adsorption of C=O groups of acrolein and subsequent reaction to allyl alcohol, have been identified as edges of gold nanoparticles. After our recent finding that this reaction preferentially occurs on single crystalline particles rather than multiply twinned ones, this paper reports on a new approach to distinguish different features of the gold particle morphology. Elucidation of the active site issue cannot be simply done by varying the size of gold particles, since the effects of faceting and multiply twinned particles may interfere. Therefore, modification of the gold particle surface by indium has been used to vary the active site characteristics of a suitable catalyst, and a selective decoration of gold particle faces has been observed, leaving edges free. This is in contradiction to theoretical predictions, suggesting a preferred occupation of the low-coordinated edges of the gold particles. On the bimetallic catalyst, the desired allyl alcohol is the main product (selectivity 63%; temperature 593 K, total pressure p(total) = 2 MPa). From the experimentally proven correlation between surface structure and catalytic behavior, the edges of single crystalline gold particles have been identified as active sites for the preferred C=O hydrogenation.

Shock waves, dead zones and particle-free regions in rapid granular free-surface flows

Abstract: Shock waves, dead zones and particle-free regions form when a thin surface avalanche of granular material flows around an obstacle or over a change in the bed topography. Understanding and modelling these flows is of considerable practical interest for industrial processes, as well as for the design of defences to protect buildings, structures and people from snow avalanches, debris flows and rockfalls. These flow phenomena also yield useful constitutive information that can be used to improve existing avalanche models. In this paper a simple hydraulic theory, first suggested in the Russian literature, is generalized to model quasi-two-dimensional flows around obstacles. Exact and numerical solutions are then compared with laboratory experiments. These indicate that the theory is adequate to quantitatively describe the formation of normal shocks, oblique shocks, dead zones and granular vacua. Such features are generated by the flow around a pyramidal obstacle, which is typical of some of the defensive structures in use today.

Synthesis of cubic zirconium and hafnium nitride having Th3P4 structure.

Abstract: High-pressure synthesis is a powerful method for the preparation of novel materials with high elastic moduli and hardness. Additionally, such materials may exhibit interesting thermal, optoelectronic, semiconductuing, magnetic or superconducting properties. Here, we report on the high-pressure synthesis of zirconium and hafnium nitrides with the stoichiometry M3N4, where M = Zr, Hf. Synthesis experiments were performed in a laser-heated diamond anvil cell at pressures up to 18 GPa and temperatures up to 3,000 K. We observed formation of cubic Zr3N4 and Hf3N4 (c-M3N4) with a Th3P4-structure, where M-cations are eightfold coordinated by N anions. The c-M3N4 phases are the first binary nitrides with such a high coordination number. Both compounds exhibit high bulk moduli around 250 GPa, which indicates high hardness. Moreover, the new nitrides, c-Zr3N4 and c-Hf3N4, may be the first members of a larger group of transition metal and/or lanthanide nitrides with interesting ferromagnetic or superconducting behaviour.

Acidobacteria form a coherent but highly diverse group within the bacterial domain: evidence from environmental genomics.

Abstract: Summary Acidobacteria have been established as a novel phy- lum of Bacteria that is consistently detected in many different habitats around the globe by 16S rDNA- based molecular surveys. The phylogenetic diversity, ubiquity and abundance of this group, particularly in soil habitats, suggest an important ecological role and extensive metabolic versatility. However, the genetic and physiological information about Acido- bacteria is scarce. In order to gain insight into genome structure, evolution and diversity of these microorganisms we have initiated an environmental genomic approach by constructing large insert librar- ies directly from DNA of a calcerous grassland soil. Genomic fragments of Acidobacteria were identified with specific 16S rDNA probes and sequence analy- ses of six independently identified clones were per- formed, representing in total more than 210 000 bp. The 16S rRNA genes of the genomic fragments dif- fered between 2.3% and 19.9% and were placed into two different subgroups of Acidobacteria (groups III and V). Although partial co-linearity was found between genomic fragments, the gene content around the rRNA operons was generally not conserved. Phy- logenetic reconstructions with orthologues that were encoded on two of the six genomic fragments (PurF, PurL, PurB and formamidopyrimidine-DNA glycosy- lase) confirmed the coherence of the acidobacterial phylum. One genomic fragment harboured a cluster of eight genes which was syntenic and highly homol- ogous to genomic regions in Rhodopseudomonas palustris and Bradyrhizobium japonicum , including a conserved two-component system. Phylogenetic analysis of the putative response regulator confirmed that this similarity between Rhizobiales and Acido- bacteria might be due to a horizontal gene transfer. In total, our data give first insight into the genome con- tent and diversity of the ubiquitously distributed but poorly characterized phylum of Acidobacteria. Fur- thermore they support the phylogenetic inferences made from 16S rRNA gene libraries, suggesting that Acidobacteria form a broad group in the same sense and with a similar diversity as that of many well-stud- ied bacterial phyla.

Modelling of compound semiconductors: analytical bond-order potential for gallium, nitrogen and gallium nitride

Abstract: An analytical bond-order potential for GaN is presented that describes a wide range of structural properties of GaN as well as bonding and structure of the pure constituents. For the systematic fit of the potential parameters reference data are taken from total-energy calculations within the density functional theory if not available from experiments. Although long-range interactions are not explicitly included in the potential, the present model provides a good fit to different structural geometries including defects and high-pressure phases of GaN.

The Super-FRS project at GSI

Abstract: The GSI projectile fragment separator FRS has demonstrated with many pioneering experiments the research potential of in-flight separators at relativistic energies. Although the present facility has contributed much to the progress in the field of nuclear structure physics, major improvements are desirable in the future. The characteristics of the proposed next-generation facility at GSI, the Super-FRS, will be presented and compared to other projects. The Super-FRS is a large-acceptance superconducting fragment separator followed by different experimental branches including a combination with a new storage-cooler ring system. This system consists of a collector ring (CR) and a new experimental storage ring (NESR) which allow precision mass and lifetime measurements as well as in-ring reaction studies. The NESR can be operated in combination with an electron ring to measure electron scattering with exotic nuclei. This electron heavy-ion collider will open up new fields for nuclear structure research.