检索结果-南通市图书馆

Multi-scale simulations of apatite-collagen composites： from molecules to materials

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Frontiers of Materials Science 2017年第1期11卷 1-12页

作者： dirk ZAHN Lehrstuhl for Theoretische Chemie/Computer Chemie Centrum Friedrich-Alexander Universitat Erlangen-Numberg Nagelsbachstraβe25 91052 Erlangen Germany

We review scale-bridging simulation studies for the exploration of atomic- to-meso scale processes that account for the unique structure and mechanic properties of apatite-protein composites. As the atomic structure and composition of such complex biocomposites only partially is known, the first part （i） of our modelling studies is dedicated to realistic crystal nucleation scenarios of inorganic-organic composites. Starting from the association of single ions, recent insights range from the mechanisms of motif formation, ripening reactions and the self-organization of nanocrystals, including their interplay with growth-controlling molecular moieties. On this basis, （ii） reliable building rules for unprejudiced scale-up models can be derived to model bulk materials. This is exemplified for （enamel-like） apatite-protein composites, encompassing up to 106 atom models to provide a realistic account of the 10 nm length scale, whilst model coarsening is used to reach pm length scales. On this basis, a series of deformation and fracture simulation studies were performed and helped to rationalize biocomposite hardness, plasticity, toughness, self-healing and fracture mechanisms. Complementing experimental work, these modelling studies provide particularly detailed insights into the relation of hierarchical composite structure and favorable mechanical properties.

关键词： biocomposites deformation fracture molecular simulation

The role of phosphorus in the metabolism of arsenate by a freshwater green alga, Chlorella vulgaris

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Journal of Environmental Sciences 2016年第11期28卷 169-178页

作者： Josh Baker dirk Wallschlager Trent University Environmental and Life Sciences Graduate Program 1600 West Bank Dr Peterborough ON K9L 0G2 Canada School of the Environment Department of Chemistry and Water Quality Centre Trent University 1600 West Bank Dr Peterborough ONK9L 0G2 Canada

A freshwater microalga, Chlorella vulgaris, was grown in the presence of varying phosphate concentrations（〈 10–500 μg/L P） and environmentally realistic concentrations of arsenate（As（Ⅴ））（5–50 μg/L As）. Arsenic speciation in the culture medium and total cellular arsenic were measured using AEC-ICP-MS and ICP-DRC-MS, respectively, to determine arsenic biotransformation and uptake in the various phosphorus scenarios. At high phosphate concentration in the culture medium, 〉 100 μg/L P, the uptake and biotransformation of As（Ⅴ） was minimal and dimethylarsonate（DMAs（Ⅴ）） was the dominant metabolite excreted by C. vulgaris, albeit at relatively low concentrations. At common environmental P concentrations, 0–50 μg/L P, the uptake and biotransformation of As（Ⅴ） increased. At these higher As-uptake levels, arsenite（As（Ⅲ）） was the predominant metabolite excreted from the cell. The concentrations of As（Ⅲ） in these low P conditions were much higher than the concentrations of methylated arsenicals observed at the various P concentrations studied. The switchover threshold between the（small） methylation and（large） reduction of As（Ⅴ） occurred around a cellular As concentration of 1 fg/cell. The observed nearly quantitative conversion of As（Ⅴ） to As（Ⅲ） under low phosphate conditions indicates the importance of As（Ⅴ） bio-reduction at common freshwater P concentrations. These findings on the influence of phosphorus on arsenic uptake, accumulation and excretion are discussed in relation to previously published research. The impact that the two scenarios of As（Ⅴ） metabolism, As（Ⅲ） excretion at high As（Ⅴ）-uptake and methylarsenical excretion at low As（Ⅴ）-uptake, have on freshwater arsenic speciation is discussed.

关键词： Arsenic Speciation Phosphorus Freshwater algae Toxicity Biotransformation

Structural pavement assessment in Germany

在线全文

学校读者我要写书评

暂无评论

Frontiers of Structural and Civil Engineering 2018年第2期12卷 183-191页

作者： Lutz PINKOFSKY dirk JANSEN Bundesanstalt fur Straflenwesen (Federal Highway Research Institute) BASt Bruederstrasse 53 51427 Bergisch Gladbach Germany

The aging structure as well as the considerable increase of heavy-traffic load on Germany＇s motorways and trunk roads encourages the use of innovative, sound and reliable methods for the structural assessment on network level as well as on project level. Essential elements for this are data, which allow a reliable assessment. For a holistic approach to structural pavement assessment performance orientated measurements will be necessary. In combination with functional parameters as well as write-down models, strategically motivated decision making processes will be useful combined with technically motivated decision processes. For the application at the network level, the available methods for performance orientated measurements are still challenging, as they are based either on testing drill-cores or on non- traffic speed methods. In recent years significant innovation steps have been made to bring traffic speed bearing capacity measurements and methods for evaluating pavement structures on the road. The paper summarizes the actual assessment procedures in Germany as well as the ongoing work on the development and implementation of new methods and techniques.

关键词： pavement assessment Germany structure system

Numerical modelling of a turbulent bluff-body flow with Reynolds stress turbulent models

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Progress in Natural Science:Materials International 2005年第5期15卷 458-462页

作者： dirk ROEKAERTS CJ2628 Delft Delft University of Technology Department of Applied Physics The Netherlands

Numerical modelling of a turbulent bluff-body flow has been performed using differential Reynolds stress models (DRSMs). To clarify the applicability of the existing DRSMs in this complex flow, several typical DRSMs, including LRR-IP model, JM model, SSG model, as well as a modified LRR-IP model, have been validated and evaluated. The performance difference between various DRSMs is quite significant. Most of the above mentioned DRSMs cannot provide overall satisfactory predictions for this challenging test case. Motivated by the deficiency of the existing approaches, a new modification of LRR-IP model has been proposed. A very significant improvement of the prediction of flow field is obtained.

关键词： bluff-body flow differential Reynolds stress models turbulent model.

Eosinophilic cholangitis is a potentially underdiagnosed etiology in indeterminate biliary stricture

在线全文

同方期刊数据库

学校读者我要写书评

暂无评论

World Journal of Gastroenterology 2017年第6期23卷 1044-1050页

作者： dirk Walter Sylvia hartmann Eva Herrmann Jan Peveling-Oberhag Wolf O Bechstein Stefan Zeuzem Martin-Leo Hansmann Mireen Friedrich-Rust Jorg G Albert Department of Internal Medicine I Johann Wolfgang Goethe-University Hospital Dr.Senckenberg Institute for Pathology Johann Wolfgang Goethe-University Hospital Institute of Biostatistics and Mathematical Modeling Johann Wolfgang Goethe-University Hospital Department for Gastroenterology Hepatology and EndocrinologyRobert-Bosch Hospital Department of General and Visceral Surgery Johann Wolfgang Goethe-University Hospital

To investigate presence and extent of eosinophilic cholangitis (EC) as well as IgG4-related disease in patients with indeterminate biliary stricture (IBS).METHODSAll patients with diagnosis of sclerosing cholangitis (SC) and histopathological samples such as biopsies or surgical specimens at University Hospital Frankfurt from 2005-2015 were included. Histopathological diagnoses as well as further clinical course were reviewed. Tissue samples of patients without definite diagnosis after complete diagnostic work-up were reviewed regarding presence of eosinophilic infiltration and IgG4 positive plasma cells. Eosinophilic infiltration was as well assessed in a control group of liver transplant donors and patients with primary sclerosing *** hundred and thirty-five patients with SC were included. In 10/135 (13.5%) patients, no potential cause of IBS could be identified after complete diagnostic work-up and further clinical course. After histopathological review, a post-hoc diagnosis of EC was established in three patients resulting in a prevalence of 2.2% (3/135) of all patients with SC as well as 30% (3/10) of patients, where no cause of IBS was identified. 2/3 patients with post-hoc diagnosis of EC underwent surgical resection with suspicion for malignancy. Diagnosis of IgG4-related cholangitis was observed in 7/135 patients (5.1%), whereas 3 cases were discovered in post-hoc analysis. 6/7 cases with IgG4-related cholangitis (85.7%) presented with eosinophilic infiltration in addition to IgG4 positive plasma cells. There was no patient with eosinophilic infiltration in the control group of liver transplant donors (n = 27) and patients with primary sclerosing cholangitis (n = 14).CONCLUSIONEC is an underdiagnosed benign etiology of SC and IBS, which has to be considered in differential diagnosis of IBS.

关键词： Indeterminate biliary stricture endoscopy endoscopic retrograde cholangiopancreatography eosinophilic cholangitis bile duct stenosis IgG4-related disease primary sclerosing cholangitis

Phosphorus release from vivianite and hydroxyapatite by organic and inorganic compounds

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Pedosphere 2020年第2期30卷 190-200页

作者： Stella GYPSER dirk FREESE Brandenburg University of Technology Cottbus-Senftenberg Faculty of EnvironmentProcess EngineeringBiotechnology and ChemistryDepartment of Soil Protection and RecultivationKonrad-Wachsmann-Allee 6Cottbus 03046Germany

Based on recent mining rates and the exhaustion of global phosphorus(P)reserves,there is a need to mobilize P already stored in soils,and its recovery from secondary resources such as Ca-and Fe-phosphates is *** Ca-phosphate hydroxyapatite forms a good fertilizer source,while vivianite is formed in waterlogged soils and *** sludge treatment,the formation of vivianite has been identified,being mainly ***-term P release from both hydroxyapatite and vivianite was studied using different inorganic(CaCl2 and CaSO4)and organic(citric and humic acid)reagents during batch *** CaCl2 and CaSO4 represent the soil solution,while citric and humic acids as organic constituents affect P availability in the rhizosphere and during the process of ***,the flow-through reactor(FTR)technique with an infinite sink was used to study the long-term P release *** cumulative P release was higher by organic acids than by inorganic *** cumulative P release rates were higher in the FTR with CaCl2 as compared to the batch *** infinite sink application caused a continuously high concentration gradient between the solid and liquid phases,leading to higher desorption rates as compared to the batch *** predominant amount of the total P released over time was available for a short *** inorganic anion exchange occurred at easily available binding sites,organic acids affected the more heavily available binding sites,which could be embedded within the mineral *** results showed that organic compounds,especially citric acid,play a superior role as compared to the inorganic constituents of the soil solution during the recovery of already stored P from the tertiary phosphates vivianite and hydroxyapatite.

关键词： anion exchange batch technique citric acid flow-through reactor humic acid ligand exchange phosphate phosphorus recovery

Utilization of fly ash from coal-fired power plants in China

在线全文

学校读者我要写书评

暂无评论

Journal of Zhejiang University-Science A(Applied Physics & Engineering) 2008年第5期9卷 681-687页

作者： Eva SELIC Jan-dirk HERBELL Waste Management Engineering Department of Mechanical Engineering University of Duisburg-Essen Duisburg 47057 Germany

The rapidly increasing demand for energy in China leads to the construction of new power plants all over the country. Coal, as the main fuel resource of those power plants, results in increasing problems with the disposal of solid residues from combustion and off gas cleaning. This investigation describes chances for the utilization of fly ash from coal-fired power plants in China. After briefly comparing the situation in China and Germany, the status of aluminum recycling from fly ash and the ad- vantages for using fly ash in concrete products are introduced. Chemical and physical analyses of Chinese fly ash samples, e.g., X-ray diffraction (XRD), ICP (Inductive Coupled Plasma) and particle size analysis, water requirement, etc. are presented. Rea- sonable amounts of aluminum were detected in the samples under investigation, but for recovery only sophisticated procedures are available up to now. Therefore, simpler techniques are suggested for the first steps in the utilization of Chinese fly ash.

关键词： Fly ash utilization Aluminum recycling Concrete Chemical and physical analyses

Crystal plasticity finite element simulations on extruded Mg-10Gd rod with texture gradient

在线全文

学校读者我要写书评

暂无评论

Journal of Magnesium and Alloys 2024年第8期12卷 3409-3430页

作者： Jaeseong Lee dirk Steglich Youngung Jeong Department of Materials Convergence and System Engineering Changwon National University25 Changwondaehak-roChangwonRepublic of Korea Helmholtz-Zentrum Hereon Institute of Material Systems ModelingD-21502 GeesthachtGermany School of Materials Science and Engineering Changwon National University25 Changwondaehak-roChangwonRepublic of Korea

The mechanical properties of an extruded Mg-10Gd sample, specifically designed for vascular stents, are crucial for predicting its behavior under service conditions. Achieving homogeneous stresses in the hoop direction, essential for characterizing vascular stents, poses challenges in experimental testing based on standard specimens featuring a reduced cross section. This study utilizes an elasto-visco-plastic self-consistent polycrystal model(ΔEVPSC) with the predominant twinning reorientation(PTR) scheme as a numerical tool, offering an alternative to mechanical testing. For verification, various mechanical experiments, such as uniaxial tension, compression, notched-bar tension, three-point bending, and C-ring compression tests, were conducted. The resulting force vs. displacement curves and textures were then compared with those based on the ΔEVPSC model. The computational model's significance is highlighted by simulation results demonstrating that the differential hardening along with a weak strength differential effect observed in the Mg-10Gd sample is a result of the interplay between micromechanical deformation mechanisms and deformation-induced texture evolution. Furthermore, the study highlights that incorporating the axisymmetric texture from the as-received material incorporating the measured texture gradient significantly improves predictive accuracy on the strength in the hoop direction. Ultimately, the findings suggest that the ΔEVPSC model can effectively predict the mechanical behavior resulting from loading scenarios that are impossible to realize experimentally, emphasizing its valuable contribution as a digital twin.

关键词： Crystal plasticity Texture Finite element C-ring Three-point bending

Hazard Rate Estimation for GNSS-Based Train Localization Using Model-Based Approach

在线全文

学校读者我要写书评

暂无评论

Chinese Journal of Electronics 2020年第1期29卷 49-56页

作者： LU Debiao TANG Dezhang SPIEGEL dirk Beijing Engineering Research Center of EMC and GNSS Technology for Rail Transportation School of Electronic and Information Engineering Beijing Jiaotong University Deutsche Bahn AG Bahntower

GNSS(Global navigation satellite system)has shown its ability on the non-safety relevant applications in various applications. In railway domain, safety is the utmost concern, GNSS-based train localization unit is the carrier of safe localization. EN 50126 standard specifies the electric and electronic system performance requirements as Reliability, availability, maintainability and safety(RAMS). Safety performance characteristic is based on the reliability and availability analysis *** formal method considering the risk identification and analysis is compulsory for the safety assessment. This paper provides the method for hazard analysis of the GNSS-based train localization function and further the hazard rate estimation of each hazard. The model-based approach using GNSS localization unit working principle is proposed to study railway localization behavior *** hazard for the localization unit is formally stated, real collected data on circular test track in Beijing is studied using the proposed method. The result shows that the safety requirement of the performance can be transformed into safety integrity properly, the risks of GNSS in train station environment conditions are presented.

关键词： Tolerable hazard rate GNSS Risk analysis Train localization