Showing papers by "Leibniz University of Hanover published in 2004"

Computational Contact Mechanics

Abstract: This paper describes modern techniques used to solve contact problems within Computational Mechanics. On the basis of a continuum description of contact, the mathematical structure of the contact formulation for finite element methods is derived. Emphasis is also placed on the constitutive behavior at the contact interface for normal and tangential (frictional) contact. Furthermore, different discretization schemes currently applied to solve engineering problems are formulated for small and finite strain problems. These include isoparametric interpolations, node-to-segment discretizations and also mortar and Nitsche techniques. Furthermore, several algorithms related to spatial contact search and fulfillment of the inequality constraints at the contact interface are discussed. Here, especially the penalty and Lagrange multiplier schemes are considered and also SQP- and linear-programming methods are reviewed. Keywords: contact mechanics; friction; penalty method; Lagrange multiplier method; contact algorithms; finite element method; finite deformations; discretization methods

Reasoning and Ontologies for Personalized E-Learning in the Semantic Web.

Abstract: The challenge of the semantic web is the provision of distributed information with well-defined meaning, understandable for different parties. Particularly, applications should be able to provide individually optimized access to information by taking the individual needs and requirements of the users into account. In this paper we propose a framework for personalized e-Learning in the semantic web and show how the semantic web resource description formats can be utilized for automatic generation of hypertext structures from distributed metadata. Ontologies and metadata for three types of resources (domain, user, and observation) are investigated. We investigate a logic-based approach to educational hypermedia using TRIPLE, a rule and query language for the semantic web.

Detector description and performance for the first coincidence observations between LIGO and GEO

Abstract: For 17 days in August and September 2002, the LIGO and GEO interferometer gravitational wave detectors were operated in coincidence to produce their first data for scientific analysis. Although the detectors were still far from their design sensitivity levels, the data can be used to place better upper limits on the flux of gravitational waves incident on the earth than previous direct measurements. This paper describes the instruments and the data in some detail, as a companion to analysis papers based on the first data.

Susceptibility of some electronic equipment to HPEM threats

Abstract: In this paper, an overview of the susceptibility of a large number of different electronic devices like computer networks, computer systems, microprocessor boards, microcontrollers, and other basic integrated circuits (ICs) to different threats like electromagnetic pulse (EMP), ultrawideband (UWB), and high-power microwave pulses (HPM) is given. The presented data will include a comparison of the HPM and UWB susceptibility of some devices and a deeper look into the destruction effects in ICs. Therefore, the ICs were opened and the destruction effects were investigated. A norm based approach to describe the threat of different pulses to electronic devices gives a theoretical explanation for the measured susceptibility data.

Personalization in distributed e-learning environments

Abstract: Personalized support for learners becomes even more important, when e-Learning takes place in open and dynamic learning and information networks. This paper shows how to realize personalized learning support in distributed learning environments based on Semantic Web technologies. Our approach fills the existing gap between current adaptive educational systems with well-established personalization functionality, and open, dynamic learning repository networks. We propose a service-based architecture for establishing personalized e-Learning, where personalization functionality is provided by various web-services. A Personal Learning Assistant integrates personalization services and other supporting services, and provides the personalized access to learning resources in an e-Learning network.

Evaluation of quality of life after laparoscopic surgery: evidence-based guidelines of the European Association for Endoscopic Surgery.

Abstract: Measuring health-related quality of life (QoL) after surgery is essential for decision making by patients, surgeons, and payers. The aim of this consensus conference was twofold. First, it was to determine for which diseases endoscopic surgery results in better postoperative QoL than open surgery. Second, it was to recommend QoL instruments for clinical research. An expert panel selected 12 conditions in which QoL and endoscopic surgery are important. For each condition, studies comparing endoscopic and open surgery in terms of QoL were identified. The expert panel reached consensus on the relative benefits of endoscopic surgery and recommended generic and disease-specific QoL instruments for use in clinical research. Randomized trials indicate that QoL improves earlier after endoscopic than open surgery for gastroesophageal reflux disease (GERD), cholecystolithiasis, colorectal cancer, inguinal hernia, obesity (gastric bypass), and uterine disorders that require hysterectomy. For spleen, prostate, malignant kidney, benign colorectal, and benign non-GERD esophageal diseases, evidence from nonrandomized trials supports the use of laparoscopic surgery. However, many studies failed to collect long-term results, used nonvalidated questionnaires, or measured QoL components only incompletely. The following QoL instruments can be recommended: for benign esophageal and gallbladder disease, the GIQLI or the QOLRAD together with SF-36 or the PGWB; for obesity surgery, the IWQOL-Lite with the SF-36; for colorectal cancer, the FACT-C or the EORTC QLQ-C30/CR38; for inguinal and renal surgery, the VAS for pain with the SF-36 (or the EORTC QLQ-C30 in case of malignancy); and after hysterectomy, the SF-36 together with an evaluation of urinary and sexual function. Laparoscopic surgery provides better postoperative QoL in many clinical situations. Researchers would improve the quality of future studies by using validated QoL instruments such as those recommended here.

What makes mavens tick? exploring the motives of market mavens initiation of information diffusion

Abstract: With growing competition and the increasing complexity of commercial information, interpersonal communication continues to be important to marketers. Market mavens, those consumers with general product knowledge that act as disseminators of product information, play a central role in influencing others’ purchase decisions. Previous research, which has focused on mavens’ demographics and media consumption, has neglected the motives that drive these consumer communicators. From a survey of 326 consumers, we explore how those respondents ranked high on the maven scale differ in terms of their motivations to engage in word‐of‐mouth behavior from those scoring lower on the maven scale. Our results indicate that market mavens, compared with moderate and non‐mavens, are motivated to a greater extent by a sense of obligation to share information, a desire to help others, and feelings of pleasure associated with informing others about products. The relationship between initial information diffusion, maven group, and the investigated motivations are also explored. Implications for marketers targeting mavens are offered.

Dynamics of F=2 spinor Bose-Einstein condensates.

Abstract: We experimentally investigate and analyze the rich dynamics in $F=2$ spinor Bose-Einstein condensates of $^{87}\mathrm{R}\mathrm{b}$. An interplay between mean-field driven spin dynamics and hyperfine-changing losses in addition to interactions with the thermal component is observed. In particular, we measure conversion rates in the range of ${10}^{\ensuremath{-}12}\text{ }\text{ }{\mathrm{c}\mathrm{m}}^{3}\text{ }{\mathrm{s}}^{\ensuremath{-}1}$ for spin-changing collisions within the $F=2$ manifold and spin-dependent loss rates in the range of ${10}^{\ensuremath{-}13}\text{ }\text{ }{\mathrm{c}\mathrm{m}}^{3}\text{ }{\mathrm{s}}^{\ensuremath{-}1}$ for hyperfine-changing collisions. We observe polar behavior in the $F=2$ ground state of $^{87}\mathrm{R}\mathrm{b}$, while we find the $F=1$ ground state to be ferromagnetic. We further see a magnetization for condensates prepared with nonzero total spin.

Apoplastic binding of aluminum is involved in silicon-induced amelioration of aluminum toxicity in maize.

Abstract: The alleviating effect of silicon (Si) supply on aluminum (Al) toxicity was suggested to be based on ex or in planta mechanisms. In our experiments with the Al-sensitive maize (Zea mays) cultivar Lixis, Si treatment but not Si pretreatment ameliorated Al-induced root injury as revealed by less root-growth inhibition and callose formation. Si treatment did not affect monomeric Al concentrations in the nutrient solution, suggesting an in planta effect of Si on Al resistance. A fractionated analysis of Si and Al in the 1-cm root apices revealed that more than 85% of the root-tip Al was bound in the cell wall. Al contents in the apoplastic sap, the symplastic sap, and the cell wall did not differ between −Si and +Si plants. Si did not affect the Al-induced exudation of organic acid anions and phenols from the root apices. However, Al treatment greatly enhanced Si accumulation in the cell wall fraction, reducing the mobility of apoplastic Al. From our data we conclude that Si treatment leads to the formation of hydroxyaluminumsilicates in the apoplast of the root apex, thus detoxifying Al.

Cosmogenic nuclide evidence for low weathering and denudation in the wet, tropical highlands of Sri Lanka

Abstract: [1] Some of the lowest weathering and erosion rates in any mountain range in the world have been measured using cosmogenic nuclides in the steep, humid, tropical highlands of Sri Lanka. The total preanthropogenic denudation rates were measured in creek sediments and soil samples from unperturbed rain forest sites, bedrock from mountain crests, and bedrock from inselbergs. Denudation rates are in the range of 5–30 t km−2 yr−1 (2–11 mm ky−1). These rates average denudation over the last 50–250 ky. Weathering exports in rivers draining the mountainous Central Highlands show that silicate weathering rates are also low, varying from 5 to 20 t km−2 yr−1 today (2–7 mm ky−1), but they represent a significant fraction of the total denudation. All these observations run contrary to the conventional geomorphologic and geochemical wisdom that would predict rapid erosion for highlands of high relief, temperatures, and precipitation. We speculate that the high relief in Sri Lanka represents the remnant of a geomorphic block that was uplifted during rifting at 130 Ma or even earlier and that was reduced to the interior of the island by rapid receding of escarpments after continental breakup. It is possible that throughout this history, hillslopes, where not exposing bare bedrock, were protected by thick weathered profiles. Such clay-rich layers would inhibit silicate weathering by shielding bedrock from weathering agents. In the absence of landscape rejuvenation, physical erosion rates are low, and fresh mineral surfaces are not being supplied. The observation that wet, steep, tropical highlands can have low rates of rock weathering and erosion has some potentially profound implications for the long-term controls of atmospheric CO2 budgets: High temperature and precipitation, which are much invoked though controversial agents for silicate dissolution and CO2 drawdown, become ineffective in promoting weathering in areas that are not tectonically active.

LES Study of the Energy Imbalance Problem with Eddy Covariance Fluxes

Abstract: The spatial representativeness of heat fluxes on the basis of single-tower measurements, and the mechanism of the so-called energy imbalance problem, are investigated through numerical experiments using large-eddy simulation (LES). LES experiments are done for the daytime atmospheric boundary layer heated over a flat surface, as a best-case scenario completely free of sensor errors and the uncertainties of field conditions. Imbalance is defined as the deviation of the `turbulent' heat flux at a grid point from the horizontally averaged `total' heat flux. Both the theoretical and numerical results of the present study suggest the limitation of single-tower measurements and the necessity of horizontally-distributed observation networks. The temporally averaged `turbulent' flux based on a point measurement systematically underestimates the `total' flux (negative imbalance). This is attributed to local advection effects caused by the existence of turbulent organized structures (TOS), whose time scale is much longer than that of thermal plumes. The temporal and spatial change of TOS patterns causes low-frequency trends in the velocity and temperature data resulting in large scatter of the flux estimates. The influences of geostrophic wind speed, averaging time, observation height, computational domain size and resolution on tower-measured fluxes are also discussed. Finally, it is suggested that a weak inhomogenity in surface heating may reduce the negative bias of flux estimates.

Creativity and Openness: Further Validation of Two Creative Product Measures

Abstract: This study sought to further validate two measures of creative imagination, and studied their relation to other creativity and personality measures. 151 college students completed the Urban and Jellen (1996) Test of Creative Thinking-Drawing Production (TCT-DP), an inventory of past creative accomplishments, a Thematic Apperception Test (TAT) story, and scales for creative personality and the 5-factor model. 86 of these participants also created autophotographic essays depicting themselves, scored for individuality/richness by consensual assessments. TCT-DP protocols were scored according to the manual, and also consensually assessed by teams of artist- and psychologist-judges. Factorial validity and relations to consensual assessments supported convergent and discriminant validity of the TCT-DP. The TCT-DP also correlated significantly with other creative products-the individuality of photo essays and rated creativity of TAT stories. Photo individuality correlated with past creative accomplishments in se...

Intra- and perioperative complications of the LeFort I osteotomy: a prospective evaluation of 1000 patients.

Abstract: The LeFort I osteotomy has become a routine procedure in elective orthognathic surgery. The authors report the occurrence of intra- or perioperative complications in a series of 1000 consecutive LeFort I osteotomies performed within a 20-year period. In total, 64 (6.4%) patients experienced complications. Anatomical complications affected 26 (2.6%), patients, including 16 (1.6%) with a deviation of the nasal septum and 10 (1.0%) with non-union of the osteotomy gap. Extensive bleeding that required blood transfusion occurred in 11 (1.1%) patients exclusively after bimaxillary corrections; in 1 patient a ligation of the external carotid artery became necessary. Significant infections such as abscesses or maxillary sinusitis occurred in 11 (1.1%) patients. No patient experienced an osteomyelitis. Ischemic complications affected 10 (1.0%) patients, including 2 (0.2%) who experienced an aseptic necrosis of the alveolar process and 8 (0.8%) who, under critical revision, were affected by retractions of the gingiva. Five (0.5%) patients experienced an insufficient fixation of the osteosynthesis material. The risk and the extent of complications was enhanced in patients with anatomical irregularities (eg, in patients with craniofacial dysplasias, orofacial clefts, or vascular anomalies). The risk of ischemic complications was enhanced in extensive dislocations or transversal segmentation of the maxilla. The authors conclude that patients with major anatomical irregularities should be informed about an enhanced risk of Le-Fort I osteotomies. Preoperative planning avoiding transversal segmentation or extensive dislocations of the maxilla should reduce the occurrence of complications. For healthy individuals, the risk of complications with the LeFort I osteotomy is considered low.

Symmetry of steady periodic surface water waves with vorticity

Abstract: For large classes of vorticities we prove that a steady periodic gravity water wave with a monotonic profile between crests and troughs must be symmetric. The analysis uses sharp maximum principles for elliptic partial differential equations.

Electron transport and back reaction in nanocrystalline TiO2 films prepared by hydrothermal crystallization

Abstract: The electron transport and back reaction in nanocrystalline TiO2 films prepared at low temperature using a new hydrothermal crystallization method on conductive glass and plastic substrates have been investigated by intensity modulated photocurrent spectroscopy (IMPS) and intensity modulated photovoltage spectroscopy (IMVS). The hydrothermal method enables the preparation of crack-free TiO2 thick films and at the same time enhances the electron transport compared to films prepared by low-temperature sintering, providing a path towards efficient photoelectrode materials for flexible dye-sensitized solar cells. UV/ozone treatment of the films enables the removal of residual organics left from the hydrothermal preparation process. Since these organics represent surface states that mediate the back reaction of electrons, the electron lifetime is increased by their removal, while the electron transport is not enhanced significantly. High-temperature sintering of the hydrothermally prepared films leads to both ...

Setting upper limits on the strength of periodic gravitational waves from PSR J1939+2134 using the first science data from the GEO 600 and LIGO detectors

Abstract: Data collected by the GEO 600 and LIGO interferometric gravitational wave detectors during their first observational science run were searched for continuous gravitational waves from the pulsar J1939+2134 at twice its rotation frequency. Two independent analysis methods were used and are demonstrated in this paper: a frequency domain method and a time domain method. Both achieve consistent null results, placing new upper limits on the strength of the pulsar’s gravitational wave emission. A model emission mechanism is used to interpret the limits as a constraint on the pulsar’s equatorial ellipticity.

Analysis of LIGO data for gravitational waves from binary neutron stars

Abstract: We report on a search for gravitational waves from coalescing compact binary systems in the Milky Way and the Magellanic Clouds. The analysis uses data taken by two of the three LIGO interferometers during the first LIGO science run and illustrates a method of setting upper limits on inspiral event rates using interferometer data. The analysis pipeline is described with particular attention to data selection and coincidence between the two interferometers. We establish an observational upper limit of R<1.7x10^(2) per year per Milky Way Equivalent Galaxy (MWEG), with 90% confidence, on the coalescence rate of binary systems in which each component has a mass in the range 1-3 M☉.

Water potential and aggregate size effects on contact angle and surface energy

Abstract: Soil wettability affects hydrological processes like infiltration, percolation, preferential flow, and surface runoff. Wettability is related to the soil-water contact angle, which in turn depends on the solid surface free energy. Little is known, however, about contact angles and their dependence on soil water potential. The main objective of this study was therefore to investigate the dynamics of contact angle due to variation of the water potential. Aggregate fractions of 2- to 4-, 1- to 2-, and <1-mm diameter and corresponding homogenized material of a subcritical water repellent Orthic Luvisol were studied at water potentials of -1000, -154, -30, and -0.14 MPa. Wettability was assessed in terms of the advandng contact angle by the capillary rise method (CRM). Additionally, we calculated the surface free energy. Results showed, that the contact angle increased as water potential increased to a specific level. It was found for several soil samples, that above this water potential level, the contact angle decreased again. The change of contact angle due to variation of water potential reached nearly 90° for one sample. Contact angles of homogenized fractions were slightly larger than those measured for the aggregate surfaces. Surface free energy was consistently between 55 and 65 mJ m -2 with relative contributions of the dispersion and polar components to surface free energy of approximately 1/3 and 2/3, respectively. We conclude, that the assessment and physical description of the specific water potential for which a surface becomes wettable is a key factor for a better understanding of soil wetting.

2D mapping of cluttered indoor environments by means of 3D perception

Abstract: This paper presents a combination of a 3D laser sensor and a line-base SLAM algorithm which together produce 2D line maps of highly cluttered indoor environments. The key of the described method is the replacement of commonly used 2D laser range sensors by 3D perception. A straightforward algorithm extracts a virtual 2D scan that also contains partially occluded walls. These virtual scans are used as input for SLAM using line segments as features. The paper presents the used algorithms and experimental results that were made in a former industrial bakery. The focus lies on scenes that are known to be problematic for pure 2D systems. The results demonstrate that mapping indoor environments can be made robust with respect to both, poor odometry and clutter.

The multi-protein family of Arabidopsis sulphotransferases and their relatives in other plant species

Abstract: All members of the sulphotransferase (SOT, EC 2.8.2.-) protein family use 39-phosphoadenosine 59-phosphosulphate (PAPS) as the sulphuryl donor and transfer the sulphonate group to an appropriate hydroxyl group of several classes of substrates. These enzymes have highly conserved domains and can be found in eubacteria and eukaryotes. In mammals, sulphate conjugation catalysed by SOTs constitutes an important reaction in the transformation of xenobiotics, and in the modulation of the biological activity of steroid hormones and neurotransmitters. In plants, sulphateconjugation reactions seem to play an important role in plant growth, development, and adaptation to stress. To date only a few plant SOTs have been characterized in detail. The flavonol 3- and 49-SOTs from Flaveria species (Asteraceae), which catalyse the sulphonation of flavonol aglycones and flavonol 3-sulphates, respectively, were the first plant SOTs for which cDNA clones were isolated. The plasma membrane associated gallic acid SOT of Mimosa pudica L. pulvini cells may be intrinsic to signalling events that modify the seismonastic response. In Brassica napus L. a SOT catalyses the O-sulphonation of brassinosteroids and thereby abolishes specifically the biological activity of 24-epibrassinolide. The fully sequenced genome of Arabidopsis thaliana Heynh. contains in total 18 genes that are likely to encode SOT proteins based on sequence similarities of the translated products with an average identity of 51.1%. So far only one SOT from A. thaliana (At5g07000) was functionally characterized: the protein was shown to catalyse the sulphonation of 12hydroxyjasmonate and thereby inactivate excess jasmonic acid in plants. The substrates and, therefore, the physiological roles of SOTs are very diverse. By using the numerous informative databases and methods available for the model plant A. thaliana, the elucidation of the functional role of the SOT protein family will be accelerated.

Large Eddy Simulation of the Ocean Mixed Layer: The Effects of Wave Breaking and Langmuir Circulation

Abstract: Large eddy simulation (LES) of the ocean mixed layer was performed in which both wave breaking and Langmuir circulation are realized. Wave breaking was represented by random forcing consistent with the observed near-surface turbulence, and Langmuir circulation was realized by the Craig–Leibovich vortex force. High- resolution simulations were carried out using parallel computing with or without each contribution, wave breaking and Langmuir circulation, with an aim to clarify their respective roles in the ocean mixed layer. The effects of wave breaking were found to be mainly limited to the near-surface zone of the upper few meters. Langmuir circulations below it are not significantly modified, although they become somewhat weakened and less coherent. Under the influence of wave breaking, however, the turbulence production in the upper-ocean mixed layer becomes dominated by the turbulent kinetic energy flux, contrary to the case of the atmospheric boundary layer where it is dominated by shear prod...

Molecular characterization and isolation of the F/f gene for femaleness in cucumber ( Cucumis sativus L.)

Abstract: The biological processes leading to sex expression in plants are of tremendous practical significance for fruit production of many agricultural and horticultural crops. Sex-expression studies in cucumber showed that the different sex types are determined by three major genes: M/m, F/f and A/a. The M/m gene in the dominant condition suppresses stamina development and thus leads to female flowers. The F/f gene in the dominant condition shifts the monoecious sex pattern downwards and promotes femaleness by causing a higher level of ethylene in the plant. To investigate the molecular character of the gene F/f, we used nearly isogenic gynoecious ( MMFF) and monoecious ( MMff) lines (NIL) produced by our own backcross programme. Our investigations confirmed the result of other groups that an additional genomic ACC synthase (key enzyme of ethylene biosynthesis) sequence ( CsACS1G) should exist in gynoecious genotypes. A linkage was also verified between the F/f locus and the CsACS1G sequence with our plant material. After the exploration of different Southern hybridization patterns originating from different CsACS1 probes, a restriction map of the CsACS1 locus was constructed. By using this restriction map, the duplication of the CsACS1 gene and following mutation of the CsACS1G gene could be explained. The promoter regions of the genes CsACS1G and CsACS1 were amplified in a splinkerette PCR and sequenced. An exclusive amplification of the new isolated sequence ( CsACS1G) in gynoecious ( MMFF) and sub-gynoecious ( MMFf) genotypes confirmed that the isolated gene is the dominant F allele.

PeerTrust: Automated Trust Negotiation for Peers on the Semantic Web

Abstract: Researchers have recently begun to develop and investigate policy languages to describe trust and security requirements on the Semantic Web. Such policies will be one component of a run-time system that can negotiate to establish trust on the Semantic Web. In this paper, we show how to express different kinds of access control policies and control their use at run time using PeerTrust, a new approach to trust establishment. We show how to use distributed logic programs as the basis for PeerTrust’s simple yet expressive policy and trust negotiation language, built upon the rule layer of the Semantic Web layer cake. We describe the PeerTrust language based upon distributed logic programs, and compare it to other approaches to implementing policies and trust negotiation. Through examples, we show how PeerTrust can be used to support delegation, policy protection and negotiation strategies in the ELENA distributed eLearning environment. Finally, we discuss related work and identify areas for further research.

No Registration Needed: How to Use Declarative Policies and Negotiation to Access Sensitive Resources on the Semantic Web

Abstract: Gaining access to sensitive resources on the Web usually involves an explicit registration step, where the client has to provide a predetermined set of information to the server. The registration process yields a login/password combination, a cookie, or something similar that can be used to access the sensitive resources. In this paper we show how an explicit registration step can be avoided on the Semantic Web by using appropriate semantic annotations, rule-oriented access control policies, and automated trust negotiation. After presenting the PeerTrust language for policies and trust negotiation, we describe our implementation of implicit registration and authentication that runs under the Java-based MINERVA Prolog engine. The implementation includes a PeerTrust policy applet and evaluator, facilities to import local metadata, policies and credentials, and secure communication channels between all parties.