Showing papers by "Leibniz University of Hanover published in 2002"

Ecological responses to recent climate change.

Abstract: There is now ample evidence of the ecological impacts of recent climate change, from polar terrestrial to tropical marine environments. The responses of both flora and fauna span an array of ecosystems and organizational hierarchies, from the species to the community levels. Despite continued uncertainty as to community and ecosystem trajectories under global change, our review exposes a coherent pattern of ecological change across systems. Although we are only at an early stage in the projected trends of global warming, ecological responses to recent climate change are already clearly visible.

Understanding Relationship Marketing Outcomes An Integration of Relational Benefits and Relationship Quality

Abstract: The importance of developing and maintaining enduring relationships with customers of service businesses is generally accepted in the marketing literature. A key challenge for researchers is to identify and understand how managerially controlled antecedent variables influence important relationship marketing outcomes (e.g., customer loyalty and word-of-mouth communication). Relational benefits, which have a focus on the benefits consumers receive apart from the core service, and relationship quality, which focuses on the overall nature of the relationship, represent two approaches to understanding customer loyalty and word of mouth. This article integrates these two concepts by positioning customer satisfaction and commitment as relationship quality dimensions that partially mediate the relationship between three relational benefits (confidence benefits, social benefits, and special treatment benefits) and the two outcome variables. The results provide support for the model and indicate that the concepts ...

Absorption and Emission of Hexagonal InN. Evidence of Narrow Fundamental Band Gap.

Abstract: (a) Ioffe Physico-Technical Institute, Russian Academy of Science, Polytekhnicheskaya 26, 194021 St. Petersburg, Russia (b) Institut für Festkörpertheorie and Theoretische Optik, Friedrich-Schiller-Universität Jena, Max-Wien-Platz 1, D-07743 Jena, Germany (c) Department of Electronics and Information Science, Kyoto Institute of Technology, Matsugasaki, Sakyo-ku, Kyoto 606-8585, Japan (d) Institute of Solid State and Semiconductor Physics, Belarus Academy of Sciences, Brovki 17, 220072 Minsk, Belarus (e) LfI, University of Hannover, Schneiderberg 32, D-30167 Hannover, Germany

EDUTELLA: a P2P networking infrastructure based on RDF

Abstract: Metadata for the World Wide Web is important, but metadata for Peer-to-Peer (P2P) networks is absolutely crucial. In this paper we discuss the open source project Edutella which builds upon metadata standards defined for the WWW and aims to provide an RDF-based metadata infrastructure for P2P applications, building on the recently announced JXTA Framework. We describe the goals and main services this infrastructure will provide and the architecture to connect Edutella Peers based on exchange of RDF metadata. As the query service is one of the core services of Edutella, upon which other services are built, we specify in detail the Edutella Common Data Model (ECDM) as basis for the Edutella query exchange language (RDF-QEL-i) and format implementing distributed queries over the Edutella network. Finally, we shortly discuss registration and mediation services, and introduce the prototype and application scenario for our current Edutella aware peers.

Bubble‐Size distributions and flow fields in bubble columns

Abstract: Bubble-size distributions and flow fields in bubble columns are calculated numerically. The population balance is simplified and reduced to a balance equation for the average bubble volume. Models developed predict the rate of bubble breakup and coalescence based on physical principles. The flow fields are numerically calculated for bubble columns with cylindrical cross sections using the Euler-Euler method. The newly derived balance equations for the average bubble volumes are implemented into a commercial CFD code. The solutions of the balance equation for high superficial gas velocities result mainly in two fractions: one for the fraction with small and the other for the fraction with large bubble diameters. Both are considered pseudocontinuous phases, in addition to the liquid phase. The calculated flow fields are characterized by several large-scale vortices. The local volume fractions of gas and liquid are locally inhomogeneous and highly time-dependent. The time-averaged flow field is axisymmetric and stationary. The calculated volume fractions, velocities, and bubble-size distributions agree well with existing and previously published experimental results for bubble columns up to 0.3 m in diameter.

Band Gap of Hexagonal InN and InGaN Alloys

Abstract: A survey of most recent studies of optical absorption, photoluminescence, photoluminescence excitation, and photomodulated reflectance spectra of single-crystalline hexagonal InN layers is presented. The samples studied were undoped n-type InN with electron concentrations between 6 × 10 18 and 4 × 10 19 cm -3 . It has been found that hexagonal InN is a narrow-gap semiconductor with a band gap of about 0.7 eV, which is much lower than the band gap cited in the literature. We also describe optical investigations of In-rich In x Ga 1-x N alloy layers (0.36 < x < 1) which have shown that the bowing parameter of b ∼ 2.5 eV allows one to reconcile our results and the literature data for the band gap of In x Ga 1-x N alloys over the entire composition region. Special attention is paid to the effects of post-growth treatment of InN crystals. It is shown that annealing in vacuum leads to a decrease in electron concentration and considerable homogenization of the optical characteristics of InN samples. At the same time, annealing in an oxygen atmosphere leads to formation of optically transparent alloys of InN-In 2 O 3 type, the band gap of which reaches approximately 2 eV at an oxygen concentration of about 20%. It is evident from photoluminescence spectra that the samples saturated partially by oxygen still contain fragments of InN of mesoscopic size.

Biocompatibility of Dental Casting Alloys

Abstract: Most cast dental restorations are made from alloys or commercially pure titanium (cpTi). Many orthodontic appliances are also fabricated from metallic materials. It has been documented in vitro and in vivo that metallic dental devices release metal ions, mainly due to corrosion. Those metallic components may be locally and systemically distributed and could play a role in the etiology of oral and systemic pathological conditions. The quality and quantity of the released cations depend upon the type of alloy and various corrosion parameters. No general correlation has been observed between alloy nobility and corrosion. However, it has been documented that some Ni-based alloys, such as beryllium-containing Ni alloys, exhibit increased corrosion, specifically at low pH. Further, microparticles are abraded from metallic restorations due to wear. In sufficient quantities, released metal ions-particularly Cu, Ni, Be, and abraded microparticles-can also induce inflammation of the adjacent periodontal tissues and the oral mucosa. While there is also some in vitro evidence that the immune response can be altered by various metal ions, the role of these ions in oral inflammatory diseases such as gingivitis and periodontitis is unknown. Allergic reactions due to metallic dental restorations have been documented. Ni has especially been identified as being highly allergenic. Interestingly, from 34% to 65.5% of the patients who are allergic to Ni are also allergic to Pd. Further, Pd allergy always occurrs with Ni sensitivity. In contrast, no study has been published which supports the hypothesis that dental metallic materials are mutagenic/genotoxic or might be a carcinogenic hazard to man. Taken together, very contradictory data have been documented regarding the local and systemic effects of dental casting alloys and metallic ions released from them. Therefore, it is of critical importance to elucidate the release of cations from metallic dental restorations in the oral environment and to determine the biological interactions of released metal components with oral and systemic tissues.

Micro-optical realization of arrays of selectively addressable dipole traps: a scalable configuration for quantum computation with atomic qubits.

Abstract: We experimentally demonstrate novel structures for the realization of registers of atomic qubits: We trap neutral atoms in one- and two-dimensional arrays of far-detuned dipole traps obtained by focusing a red-detuned laser beam with a microfabricated array of microlenses. We are able to selectively address individual trap sites due to their large lateral separation of $125\text{ }\ensuremath{\mu}\mathrm{m}$. We initialize and read out different internal states for the individual sites. We also create two interleaved sets of trap arrays with adjustable separation, as required for many proposed implementations of quantum gate operations.

Spatial information retrieval and geographical ontologies an overview of the SPIRIT project

Abstract: A large proportion of the resources available on the world-wide web refer to information that may be regarded as geographically located. Thus most activities and enterprises take place in one or more places on the Earth's surface and there is a wealth of survey data, images, maps and reports that relate to specific places or regions. Despite the prevalence of geographical context, existing web search facilities are poorly adapted to help people find information that relates to a particular location. When the name of a place is typed into a typical search engine, web pages that include that name in their text will be retrieved, but it is likely that many resources that are also associated with the place may not be retrieved. Thus resources relating to places that are inside the specified place may not be found, nor may be places that are nearby or that are equivalent but referred to by another name. Specification of geographical context frequently requires the use of spatial relationships concerning distance or containment for example, yet such terminology cannot be understood by existing search engines. Here we provide a brief survey of existing facilities for geographical information retrieval on the web, before describing a set of tools and techniques that are being developed in the project SPIRIT : Spatially-Aware Information Retrieval on the Internet (funded by European Commission Framework V Project IST-2001-35047).

Menacing mold: the molecular biology of Aspergillus fumigatus.

Abstract: Infections with mold pathogens have emerged as an increasing risk faced by patients under sustained immunosuppression. Species of the Aspergillus family account for most of these infections, and in particular Aspergillus fumigatus may be regarded as the most important airborne pathogenic fungus. The improvement in transplant medicine and the therapy of hematological malignancies is often complicated by the threat of invasive aspergillosis. Specific diagnostic methods are still limited as are the possibilities of therapeutic intervention, leading to the disappointing fact that invasive aspergillosis is still associated with a high mortality rate that ranges from 30% to 90%. In recent years considerable progress has been made in understanding the genetics of A. fumigatus, and molecular techniques for the manipulation of the fungus have been developed. Molecular genetics offers not only approaches for the detailed characterization of gene products that appear to be key components of the infection process but also selection strategies that combine classical genetics and molecular biology to identify virulence determinants of A. fumigatus. Moreover, these methods have a major impact on the development of novel strategies leading to the identification of antimycotic drugs. This review summarizes the current knowledge on the biology, molecular genetics, and genomics of A. fumigatus.

The Timing of New Technology Adoption: Theoretical Models and Empirical Evidence

Abstract: This paper surveys the theoretical literature on the timing of new technology adoption. It presents the state of the art as it falls into two major categories, depending on whether the particular model deals with uncertainty regarding the arrival and value of a new technology and/or strategic interaction in the product market. Empirical evidence is reviewed, and recommendations are given for future research.

Teachers' Gender Stereotypes as Determinants of Teacher Perceptions in Elementary School Mathematics

Abstract: This study analyzes the hypothesized biasing effect of teachers' gender stereotypes on their impressions of their students' competence and effort in mathematics. 48 teachers participated in the study and responded to the questionnaires concerning perceptions of about 300 of their third and fourth grade students. In general, teacher perceptions were consistent with stereotypes of gender differences: Boys have more developmental resources in mathematics. Furthermore, this bias in teacher perceptions of their students' resources in math is linked to the teacher's own category — based, gender role stereotypic beliefs regarding the general distribution of math talent between boys and girls. The finding is moderated by the student's performance level: It only holds for average and low achieving but not for high achieving boys and girls. In this way, students' performance level is an essential mediator-variable in the transmission of teachers' gender stereotypes.

Challenge of mixed insulating liquids for use in high-voltage transformers.1. Investigation of mixed liquids

Abstract: The aim of this work is to present results of investigations into mixtures of two insulating liquids, recently proposed as alternatives to mineral oil. The mixtures are a combination of the widely available mineral oil and a specific amount of ester liquid, which has similar electrical properties combined with fewer environmental risks but high hygroscopicity. The water saturation limit of esters is more than 40 times larger than that of mineral oils. Esters absorb water vapor from the air in larger quantities than mineral oil, and this hygroscopicity reduces the moisture content in solid insulation due to diffusion from the solid into the liquid, while the dielectric properties of ester liquids are only slightly changed . Although the life of an oil in service depends primarily on its initial quality, service conditions need to be considered also. The investigations have therefore been carried out on unaged mixed liquids as well as on specimens under severe ageing conditions. Pure liquids have also been investigated to provide baseline data for comparison purposes. The first part of the investigation compares the properties of the mixed liquids with those of pure liquids. The second part of the investigation, will evaluate the compatibility of the mixed liquids with insulating papers used in high-voltage transformers.

In-situ microscopy: Online process monitoring of mammalian cell cultures

Abstract: The in-situ microscope is a system developed to acquire images of mammalian cells directly inside a bioreactor (in-situ) duringa fermentation process. It requires only minimal operator intervention and it is well suited for either batch or long-termperfusion fermentation runs. The system fits into a 25 mm standard port and has a retractable housing, similar to the industry standard InTrac. Therefore, it can be cleaned and serviced without interruption of the process or risking contamination. A sampling zone inside the bioreactor encloses adefined volume of culture and an image sequence is taken. The height of the sampling zone is set by the control program and canbe adjusted during the cultivation to accommodate a wide range of change in cell density. The system has an infinity correctedoptical train and uses a progressive scan CCD camera to acquirehigh quality images. Process relevant information like cell density is extracted fromthe images by digital image processing software, currently in development for mammalian cells (CHO, BHK). The first version ofthe software will be able to estimate the cell density, cellsize distribution and to give information of the degree of aggregation (single and double cells, cell clusters).

Alveolar bone grafting in patients with complete clefts: a comparative study between secondary and tertiary bone grafting.

Abstract: Objective: This investigation evaluated the results of alveolar bone grafting in patients with complete clefts, comparing secondary alveolar bone grafting (during the mixed stage of dentition) versus tertiary bone grafting (after completion of the second stage of dentition). Design: This was a retrospective study. Of 140 osteoplasties, which all were operated according to the same standardized surgical technique, a clinical and roentgenological follow-up investigation was carried out in a collective of 85 osteoplasties. Clinically we searched for oronasal fistulae, assessed the periodontal status, determined the extent of the gingival attachment in the area of the osteoplasty, and searched for vertical growth disturbances in the area of the osteoplasty. Roentgenologically the height of the alveolar bone in the former clefted area was ascertained. Setting: Records were obtained from a clinical and radiological study of the Department of Oral and Maxillofacial Surgery of the Medical University of H...

Perceptual audio coding using adaptive pre- and post-filters and lossless compression

Abstract: This paper proposes a versatile perceptual audio coding method that achieves high compression ratios and is capable of low encoding/decoding delay. It accommodates a variety of source signals (including both music and speech) with different sampling rates. It is based on separating irrelevance and redundancy reductions into independent functional units. This contrasts traditional audio coding where both are integrated within the same subband decomposition. The separation allows for the independent optimization of the irrelevance and redundancy reduction units. For both reductions, we rely on adaptive filtering and predictive coding as much as possible to minimize the delay. A psycho-acoustically controlled adaptive linear filter is used for the irrelevance reduction, and the redundancy reduction is carried out by a predictive lossless coding scheme, which is termed weighted cascaded least mean squared (WCLMS) method. Experiments are carried out on a database of moderate size which contains mono-signals of different sampling rates and varying nature (music, speech, or mixed). They show that the proposed WCLMS lossless coder outperforms other competing lossless coders in terms of compression ratios and delay, as applied to the pre-filtered signal. Moreover, a subjective listening test of the combined pre-filter/lossless coder and a state-of-the-art perceptual audio coder (PAC) shows that the new method achieves a comparable compression ratio and audio quality with a lower delay.

Metropolitan Innovation Systems: A Comparison between Barcelona, Stockholm, and Vienna:

Abstract: This article uses data from the European Regional Innovation Survey to provide insights into the innovative activity and innovation networking of the most important innovation actors, namely manufacturing firms, producer service firms, and research institutes. The innovation capacities of the metropolitan innovation systems differ markedly. In respect to cooperation partners, vertical relationships predominate. Only in Stockholm do research institutes play a significant role in assisting innovation processes in manufacturing firms. Spatial proximity of cooperation partners is very important, confirming the concept of territorially based systems of innovation. At the same time, the actors surveyed cooperate intensively with cooperation partners outside the region.

Cervical tooth wear and sensitivity: erosion, softening and rehardening of dentine; effects of pH, time and ultrasonication

Abstract: Background Cervical dentine wear is commonly observed and may be associated with dentine hypersensitivity. Erosion is thought to play a part in both conditions but compared to enamel has been little studied in dentine. Aim The aims of these studies in vitro were to: (i) determine the effects of citric acid on dentine at different pH values and over time; (ii) measure the depth of dentine demineralisation or softening using ultrasonication; (iii) determine whether softened dentine can be remineralised or rehardened using artificial saliva. Methods Groups of flat dentine specimens prepared from unerupted human third molar teeth were: (a) exposed to citric acid at pH 3.2 for periods up to 4 h with mineral water as control; (b) exposed to citric acid at pH 2.54, 3.2, 4.5, 5.5 and 6.0 for 2 h and then subjected to ultrasonication stepwise up to 480 s; (c) exposed to citric acid at pH 2.54, 3.2, and 4.5, placed into artificial saliva for 24 h and then subjected to ultrasonication as in (b). Loss of dentine was measured by profilometry, after, each phase of erosion, ultrasonication and immersion in artificial saliva. Results Depth of erosion significantly increased non-linearly with time and significantly decreased with increasing pH. Ultrasonication had minimal albeit significant effects on control specimens. Removal of softened dentine increased with ultrasonication time. Depth of softening significantly increased with increasing erosion time to 2 h, plateauing at 2 microm. Depth of softening increased to 2 microm from pH 2.54 to pH 3.2 and decreased at higher pH values thereafter. 24 h in artificial saliva provided no protection to the soften zone against ultrasonicaion. Citric acid at all pH values and exposure times removed the dentine smear layer to expose tubules. Ultrasonication did not remove the smear layer on control specimens but removed all deposits formed after exposure to artificial saliva. Conclusion It is concluded that dentine is susceptible to erosion even at relatively high pH, the tubule system is readily exposed and dentine, unlike enamel, shows little propensity to remineralise.

Sulfate reduction is increased in transgenic Arabidopsis thaliana expressing 5'-adenylylsulfate reductase from Pseudomonas aeruginosa.

Abstract: The two-electron reduction of sulfate to sulfite in plants is mediated by 5'-adenylylsulfate (APS) reductase, an enzyme theorized to be a control point for cysteine synthesis. The hypothesis was tested by expression in Arabidopsis thaliana under transcriptional control of the CaMV 35S promoter of the APS reductase from Pseudomonas aeruginosa (PaAPR) fused with the rbcS transit peptide for localization of the protein to plastids. PaAPR was chosen for the experiment because it is a highly stable enzyme compared with the endogenous APS reductase of A. thaliana, and because PaAPR is catalytically active in combination with the plant thioredoxins m and f indicating that it would likely be catalytically active in plastids. The results indicate that sulfate reduction and O-acetylserine (OAS) production together limit cysteine synthesis. Transgenic A. thaliana lines expressing PaAPR accumulated sulfite, thiosulfate, cysteine, gamma-glutamylcysteine, and glutathione. Sulfite and thiosulfate increased more than did cysteine, gamma-glutamylcysteine and glutathione. Thiosulfate accumulation was most pronounced in flowers. Feeding of OAS to the PaAPR-expressing plants caused cysteine and glutathione to increase more rapidly than in comparably treated wild type. Both wild-type and transgenic plants accumulated sulfite and thiosulfate in response to OAS feeding. The PaAPR-expressing plants were slightly chlorotic and stunted compared with wild type. An attempt to uncover the source of thiosulfate, which is not thought to be an intermediate of sulfate reduction, revealed that purified beta-mercaptopyruvate sulfurtransferase is able to form thiosulfate from sulfite and beta-mercaptopyruvate, suggesting that this class of enzymes could form thiosulfate in vivo in the presence of excess sulfite.

Temperature Dependence of Water Retention Curves for Wettable and Water-Repellent Soils

Abstract: The capillary pressure (ψ) in unsaturated porous media is known to be a function of temperature (T). Temperature affects the surface tension (α) of the pore water, but possibly also the angle of contact (y). Because information on the temperature dependence of (γ) in porous media is rare, we conducted experiments with three wettable soils and their hydrophobic counterparts. The objectives were (i) to determine the temperature dependence of the water retention curve (WRC) for wettable and water-repellent soils, (ii) to assess temperature effects on the apparent contact angle γ A derived from those WRCs, and (iii) to evaluate two models (Philip-de Vries and Grant-Salehzadeh) that describe temperature effects on (. Columns packed with natural or hydrophobized soil materials were first water saturated, then drained at 5, 20, and 38°C, and rewetted again to saturation. Capillary pressure and water content, 0, at five depths in the columns were measured continuously. The observations were used to determine the change in γ A with T, as well as a parameter β 0 that describes the change in ( with T. It was found that the Philip-de Vries model did not adequately describe the observed relation between ( and T. A mean value for β 0 of -457 K was measured, whereas the Philip-de Vries model predicts a value of -766 K. Our results seem to confirm the Grant-Salezahdeh model that predicts a temperature effect on γ A . For the sand and the silt we studied, we found a decrease in γ A between 1.0 to 8.5°, when the temperature was increased from 5 to 38°C. Both β 0 and γ A were only weak functions of 0. Furthermore, it seemed that for the humic soil under study, surfactants, i.e., the dissolution of soil organic matter, may compound the contact angle effect of the soil solids.

Generation of an entangled four-photon W state

Abstract: We present a scheme to produce an entangled four-photon W state by using linear optical elements. The symmetrical setup of linear optical elements consists of four beam splitters, four polarization beam splitters, and four mirrors. A photon Einstein-Podolsky-Rosen pair and two single photons are required as the input modes. The projection on the W state can be made by a four-photon coincidence measurement. Further, we show that by means of a horizontally oriented polarizer in front of one detector, the W state of three photons can be generated.