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Search Results: 1 - 10 of 2206 matches for " Holger Seidlitz "
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Dimensioning of Punctiform Metal-Composite Joints: A Section-Force Related Failure Criterion  [PDF]
Holger Seidlitz, Lars Ulke-Winter, Colin Gerstenberger, Lothar Kroll
Open Journal of Composite Materials (OJCM) , 2014, DOI: 10.4236/ojcm.2014.43018
Abstract:

Reliable line production processes and simulation tools play a central role for the structural integration of thermoplastic composites in advanced lightweight constructions. Provided that material-adapted joining technologies are available, they can be applied in heavy-duty multi-material designs (MMD). A load-adapted approach was implemented into the new fully automatic and fault-tolerant thermo mechanical flow drill joining (FDJ) concept. With this method it is possible to manufacture reproducible high strength FRP/metal-joints within short cycle times and without use of extra joining elements for the first time. The analysis of FDJ joints requires a simplified model of the joint to enable efficient numerical simulations. The present work introduces a strategy in modeling a finite-element based analogous-approach for FDJ-joints with glass fiber reinforced polypropylene and high-strength steel. Combined with a newly developed section-force related failure criterion, it is possible to predict the fundamental failure behavior in multi-axial stress states. The functionality of the holistic approach is illustrated by a demonstrator that represents a part of a car body-in-white structure. The comparison of simulated and experimentally determined failure loads proves the applicability for several combined load cases.

Advanced Welding Technology for Highly Stressable Multi-Material Designs with Fiber-Reinforced Plastics and Metals  [PDF]
Holger Seidlitz, Sebastian Fritzsche, Marcello Ambrosio, Alexander Kloshek
Open Journal of Composite Materials (OJCM) , 2017, DOI: 10.4236/ojcm.2017.73010
Abstract: Organic sheets made out of fiber-reinforced thermoplastics are able to make a crucial contribution to increase the lightweight potential of a design. They show high specific strength- and stiffness properties, good damping characteristics and recycling capabilities, while being able to show a higher energy absorption capacity than comparable metal constructions. Nowadays, multi-material designs are an established way in the automotive industry to combine the benefits of metal and fiber-reinforced plastics. Currently used technologies for the joining of organic sheets and metals in large-scale production are mechanical joining technologies and adhesive technologies. Both techniques require large overlapping areas that are not required in the design of the part. Additionally, mechanical joining is usually combined with “fiber-destroying” pre-drilling and punching processes. This will disturb the force flux at the joining location by causing unwanted fiber- and inter-fiber failure and inducing critical notch stresses. Therefore, the multi-material design with fiber-reinforced thermoplastics and metals needs optimized joining techniques that don’t interrupt the force flux, so that higher loads can be induced and the full benefit of the FRP material can be used. This article focuses on the characterization of a new joining technology, based on the Cold Metal Transfer (CMT) welding process that allows joining of organic sheets and metals in a load path optimized way, with short cycle times. This is achieved by redirecting the fibers around the joining area by the insertion of a thin metal pin. The path of the fibers will be similar to paths of fibers inside structures found in nature, e.g. a knothole inside of a tree. As a result of the bionic fiber design of the joint, high joining strengths can be achieved. The increase of the joint strength compared to blind riveting was performed and proven with stainless steel and orthotropic reinforced composites in shear-tests based on the DIN EN ISO 14273. Every specimen joined with the new CMT Pin joining technology showed a higher strength than specimens joined with one blind rivet.
Influence on persistence and adherence with oral bisphosphonates on fracture rates in osteoporosis
Ariane H er, Cornelia Seidlitz, Holger Gothe, Guido Schiffhorst, Melvin Olson, et al
Patient Preference and Adherence , 2009, DOI: http://dx.doi.org/10.2147/PPA.S4673
Abstract: fluence on persistence and adherence with oral bisphosphonates on fracture rates in osteoporosis Original Research (4900) Total Article Views Authors: Ariane H er, Cornelia Seidlitz, Holger Gothe, Guido Schiffhorst, Melvin Olson, et al Published Date December 2008 Volume 2009:3 Pages 25 - 30 DOI: http://dx.doi.org/10.2147/PPA.S4673 Ariane H er1, Cornelia Seidlitz1, Holger Gothe1, Guido Schiffhorst1, Melvin Olson2, Peyman Hadji3, Bertram H ussler1 1IGES Institut, Friedrichstrasse 180, D-10117 Berlin, Germany; 2Novartis Pharma AG; 3Department of Gynaecology, University hospital of Giessen and Marburg GmbH, Marburg, Germany Background and Aim: Oral bisphosphonates have been shown to reduce the risk of fractures in patients with osteoporosis. It can be assumed that the clinical effectiveness of oral bisphosphonates depends on persistence with therapy. Methods: The influence of persistence with and adherence to oral bisphosphonates on fracture risk in a real-life setting was investigated. Data from 4451 patients with a defined index prescription of bisphosphonates were included. Fracture rates within 180, 360, and 720 days after index prescription were compared between persistent and non-persistent patients. In an extended Cox regression model applying multiple event analysis, the influence of adherence was analyzed. Persistence was defined as the duration of continuous therapy; adherence was measured in terms of the medication possession ratio (MPR). Results: In patients with a fracture before index prescription, fracture rates were reduced by 29% (p = 0.025) comparing persistent and non-persistent patients within 180 days after the index prescription and by 45% (p < 0.001) within 360 days. The extended Cox regression model showed that good adherence (MPR ≥ 0.8) reduced fracture risk by about 39% (HR 0.61, 95% CI 0.47–0.78; p < 0.01). Conclusions: In patients with osteoporosis-related fractures, good persistence and adherence to oral bisphosphonates reduced fracture risk significantly.
Influence on persistence and adherence with oral bisphosphonates on fracture rates in osteoporosis
Ariane Höer,Cornelia Seidlitz,Holger Gothe,Guido Schiffhorst
Patient Preference and Adherence , 2008,
Abstract: Ariane H er1, Cornelia Seidlitz1, Holger Gothe1, Guido Schiffhorst1, Melvin Olson2, Peyman Hadji3, Bertram H ussler11IGES Institut, Friedrichstrasse 180, D-10117 Berlin, Germany; 2Novartis Pharma AG; 3Department of Gynaecology, University hospital of Giessen and Marburg GmbH, Marburg, GermanyBackground and Aim: Oral bisphosphonates have been shown to reduce the risk of fractures in patients with osteoporosis. It can be assumed that the clinical effectiveness of oral bisphosphonates depends on persistence with therapy.Methods: The influence of persistence with and adherence to oral bisphosphonates on fracture risk in a real-life setting was investigated. Data from 4451 patients with a defined index prescription of bisphosphonates were included. Fracture rates within 180, 360, and 720 days after index prescription were compared between persistent and non-persistent patients. In an extended Cox regression model applying multiple event analysis, the influence of adherence was analyzed. Persistence was defined as the duration of continuous therapy; adherence was measured in terms of the medication possession ratio (MPR).Results: In patients with a fracture before index prescription, fracture rates were reduced by 29% (p = 0.025) comparing persistent and non-persistent patients within 180 days after the index prescription and by 45% (p < 0.001) within 360 days. The extended Cox regression model showed that good adherence (MPR ≥ 0.8) reduced fracture risk by about 39% (HR 0.61, 95% CI 0.47–0.78; p < 0.01).Conclusions: In patients with osteoporosis-related fractures, good persistence and adherence to oral bisphosphonates reduced fracture risk significantly.Keywords: compliance, fracture risk, oral bisphosphonates, persistence
Large sets of consecutive Maass forms and fluctuations in the Weyl remainder
Holger Then
Mathematics , 2012,
Abstract: We explore an algorithm which systematically finds all discrete eigenvalues of an analytic eigenvalue problem. The algorithm is more simple and elementary as could be expected before. It consists of Hejhal's identity, linearisation, and Turing bounds. Using the algorithm, we compute more than one hundredsixty thousand consecutive eigenvalues of the Laplacian on the modular surface, and investigate the asymptotic and statistic properties of the fluctuations in the Weyl remainder. We summarize the findings in two conjectures. One is on the maximum size of the Weyl remainder, and the other is on the distribution of a suitably scaled version of the Weyl remainder.
Screening for hypoglycemia at the bedside in the neonatal intensive care unit (NICU) with the Abbott PCx glucose meter
Cynthia Balion, Vijaylaxmi Grey, Afisi Ismaila, Susan Blatz, Wendy Seidlitz
BMC Pediatrics , 2006, DOI: 10.1186/1471-2431-6-28
Abstract: In this prospective study, all patients in the neonatal intensive care unit who had a plasma glucose test ordered were eligible to participate. Demographic information, sample collection information (nine variables) and a recent hematocrit value were recorded for each sample. Glucose measurements were taken at the bedside on the glucose meter (RN PCx) as well as in the laboratory on both the glucose meter (LAB PCx) and the laboratory analyzer (PG). Data were analyzed by simple and mixed-effects regression analysis and by analysis of a receiver operator characteristics (ROC) curve.There were 475 samples analyzed from 132 patients. RN PCx values were higher than PG values (mean = 4.9%), while LAB PCx results were lower (mean = -5.2%) than PG values. Only 31% of the difference between RN PCx – PG and 46% of the difference for LAB PCx – PG could be accounted for by the variables tested. The largest proportion of variance between PCx and PG measurements was explained by hematocrit (about 30%) with a greater effect seen at glucose concentrations ≤4.0 mmol/L (≤72 mg/dL)(48% and 40% for RN PCx and LAB PCx, respectively). The ROC analysis showed that for detection of all cases of hypoglycemia (PG < 2.6 mmol/L)(PG < 47 mg/dL) the PCx screening cut off value would need to be set at 3.8 mmol/L (68 mg/dL) requiring 20% of all samples to have confirmatory analysis by the laboratory method.The large difference between glucose results obtained by PCx glucose meter compared to the laboratory analyzer can be explained in part by hematocrit and low glucose concentration. These results emphasize that the glucose meter is useful only as a screening device for neonatal hypoglycemia and that a screening cut off value must be established.Adaptation to the extra-uterine environment requires the newborn to establish glucose regulation and this transition usually takes place smoothly. However, some infants such as those that are small or large for gestational age, discordant twins, those with
Glutamate Signaling in Healthy and Diseased Bone
Robert W. Cowan,Eric P. Seidlitz,Gurmit Singh
Frontiers in Endocrinology , 2012, DOI: 10.3389/fendo.2012.00089
Abstract: Bone relies on multiple extracellular signaling systems to maintain homeostasis of its normal structure and functions. The amino acid glutamate is a fundamental extracellular messenger molecule in many tissues, and is used in bone for both neural and non-neural signaling. This review focuses on the non-neural interactions, and examines the evolutionarily ancient glutamate signaling system in the context of its application to normal bone functioning and discusses recent findings on the role of glutamate signaling as they pertain to maintaining healthy bone structure. The underlying mechanisms of glutamate signaling and the many roles glutamate plays in modulating bone physiology are featured, including those involved in osteoclast and osteoblast differentiation and mature cell functions. Moreover, the relevance of glutamate signaling systems in diseases that affect bone, such as cancer and rheumatoid arthritis, is discussed, and will highlight how the glutamate system may be exploited as a viable therapeutic target. We will identify novel areas of research where knowledge of glutamate communication mechanisms may aid in our understanding of the complex nature of bone homeostasis. By uncovering the contributions of glutamate in maintaining healthy bone, the reader will discover how this complex molecular signaling system may advance our capacity to treat bone pathologies.
The colour-magnitude relation of Globular Clusters in Centaurus and Hydra - Constraints on star cluster self-enrichment with a link to massive Milky Way GCs
J. Fensch,S. Mieske,J. Mueller-Seidlitz,M. Hilker
Physics , 2014, DOI: 10.1051/0004-6361/201423971
Abstract: We investigate the colour-magnitude relation of metal-poor globular clusters, the 'blue tilt', in the Hydra and Centaurus galaxy clusters and constrain the primordial conditions for star cluster self-enrichment. We analyse U,I photometry for about 2500 globular clusters in the central regions of Hydra and Centaurus, based on FORS1@VLT data. We convert the measured colour-magnitude relations into mass-metallicity space and obtain a scaling of Z \propto M^{0.27 \pm 0.05} for Centaurus GCs and Z \propto M^{0.40 \pm 0.06} for Hydra GCs, consistent with results in other environments. We find that the GC mass-metallicity relation already sets in at present-day masses of a few 10^5 solar masses and is well established in the luminosity range of massive MW clusters like omega Centauri. We compare the mass-metallicity relation with predictions from the star cluster self-enrichment model by Bailin & Harris (2009). For this we include effects of dynamical and stellar evolution and a physically well motivated primordial mass-radius scaling. The self-enrichment model reproduces the observed relations well for average primordial half-light radii r_h ~ 1-1.5 pc, star formation efficiencies f_* ~ 0.3-0.4, and pre-enrichment levels of [Fe/H] ~ -1.7 dex. Within the self-enrichment scenario, the observed blue tilt implies a correlation between GC mass and width of the stellar metallicity distribution. We find that this implied correlation matches the trend of width with GC mass measured in Galactic GCs, including extreme cases like omega Cen and M54. We conclude that 1. A primordial star cluster mass-radius relation provides a significant improvement to the self-enrichment model fits. 2. Broadenend metallicity distributions as found in some massive MW globular clusters may have arisen naturally from self-enrichment processes, without the need of a dwarf galaxy progenitor.
Multiple quantum products in toric varieties
Holger Spielberg
International Journal of Mathematics and Mathematical Sciences , 2002, DOI: 10.1155/s0161171202107022
Abstract: We generalize the author's formula for Gromov-Witten invariants of symplectic toric manifolds (1999) to those needed to compute the quantum product of more than two classes directly, that is, involving the pullback of the Poincaré dual of the point class in the Deligne-Mumford spaces ℳ¯0,m.
On the Beurling algebras ?derivations and extensions
Holger Steiniger
International Journal of Mathematics and Mathematical Sciences , 2004, DOI: 10.1155/s0161171204309270
Abstract: Based on a description of the squares of cofinite primary ideals of Aα
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