bluuebunny/crossref_metadata_2025 huggingface dataset:
Six genes as potential diagnosis and prognosis biomarkers for hepatocellular carcinoma through data mining
Authors: Zhang Yaqiong , Wang Yong , Liu Huaidong , Li Bo
Published: December 2018

Hepatocellular carcinoma (HCC) is one of the most common malignant tumors and the third of cancer mortality worldwide. Although the study of HCC has made great progress, the molecular mechanism and signal pathways of HCC are not yet clear. Therefore, it is necessary to investigate the early diagnosis and prognosis biomarkers for HCC. The aim of this study is to screen the relevant genes and study the association of gene expression with the survival status of HCC patients using bioinformatics approaches, in the hope of establishing marker genes for diagnosis and prognosis of HCC. The gene expression data and corresponding clinical information of HCC samples were downloaded from the The Cancer Genome Atlas database. We performed to study the relationship between gene expression and prognosis of HCC and screen significantly relevant genes associated with prognosis of HCC by analyzing survival and function enrichment of genes. In this study, we collected 421 samples with gene expression data, including 371 tumor samples and 50 normal samples. By using single factor Cox regression analysis, we screened 1,197 genes significantly associated with survival time in the modeling data containing 117 samples and also searched six genes as the best markers to predict living status of HCC patients. Besides, we established score system of survival risk of HCC. Our study recognized six genes (PGBD3, PGM5P3‐AS1, RNF5, UTP11, BAG6, and KCND2) to be significantly associated with diagnosis and prognosis of HCC, providing novel targets for studying potential mechanism about the progression of HCC.
On the independence number of graphs related to a polarity
Authors: Mattheus Sam , Pavese Francesco , Storme Leo
Published: December 2018

We investigate the independence number of two graphs constructed from a polarity of . For the first graph under consideration, the Erdős‐Rényi graph , we provide an improvement on the known lower bounds on its independence number. In the second part of the paper, we consider the Erdős‐Rényi hypergraph of triangles . We determine the exact magnitude of the independence number of , even. This solves a problem posed by Mubayi and Williford [On the independence number of the ErdŐs‐RÉnyi and projective norm graphs and a related hypergraph, J. Graph Theory, 56 (2007), pp. 113‐127, Open Problem 3].
Tooth development and replacement in the Atlantic Cutlassfish, Trichiurus lepturus, with comparisons to other Scombroidei
Authors: Bemis Katherine E. , Burke Samantha M. , St. John Carl A. , Hilton Eric J. , Bemis William E.
Published: December 2018

Atlantic Cutlassfish, Trichiurus lepturus, have large, barbed, premaxillary and dentary fangs, and sharp dagger‐shaped teeth in their oral jaws. Functional teeth firmly ankylose to the dentigerous bones. We used dry skeletons, histology, SEM, and micro‐CT scanning to study 92 specimens of T. lepturus from the western North Atlantic to describe its dentition and tooth replacement. We identified three modes of intraosseous tooth replacement in T. lepturus depending on the location of the tooth in the jaw. Mode 1 relates to replacement of premaxillary fangs, in which new tooth germs enter the lingual surface of the premaxilla, develop horizontally, and rotate into position. We suggest that growth of large fangs in the premaxilla is accommodated by this horizontal development. Mode 2 occurs for dentary fangs: new tooth germs enter the labial surface of the dentary, develop vertically, and erupt into position. Mode 3 describes replacement of lateral teeth, in which new tooth germs enter a trench along the crest of the dentigerous bone, develop vertically, and erupt into position. Such distinct modes of tooth replacement in a teleostean species are unknown. We compared modes of replacement in T. lepturus to 20 species of scombroids to explore the phylogenetic distribution of these three replacement modes. Alternate tooth replacement (in which new teeth erupt between two functional teeth), ankylosis, and intraosseous tooth development are plesiomorphic to Bluefish + other Scombroidei. Our study highlights the complexity and variability of intraosseous tooth replacement. Within tooth replacement systems, key variables include sites of formation of tooth germs, points of entry of tooth germs into dentigerous bones, coupling of tooth germ migration and bone erosion, whether teeth develop horizontally or immediately beneath the tooth to be replaced, and how tooth eruption and ankylosis occur. Developmentally different tooth replacement processes can yield remarkably similar dentitions.
Development of an HIV‐1 integrase genotyping assay for HIV‐1 subtype AE
Authors: Liu Yang , Margot Nicolas , Kitrinos Kathryn M. , Callebaut Christian
Published: December 2018

An human immunodeficiency virus (HIV)‐1 integrase (IN) genotyping assay was developed to evaluate clinical samples from patients infected with HIV‐1 subtype AE, a subtype highly prevalent in Asia. The HIV‐1 IN gene was amplified from plasma‐derived HIV‐1 viral RNA via reverse transcription polymerase chain reaction followed by population sequencing. Assay sensitivity was also evaluated using serially diluted plasma samples. The genotyping assay successfully amplified the IN gene from patient plasma samples with HIV‐1 RNA as low as 500 copies/mL. This assay is suitable for IN genotyping to identify IN drug resistance mutations in HIV‐1 patients harboring subtype AE virus.
Genetic algorithms applied to the design of robust biquadratic filters
Authors: Lovay Mónica A. , Romero Eduardo A. , Peretti Gabriela M.
Published: December 2018

This work presents a design methodology for discrete active RC biquadratic filters based on genetic algorithm (GA). The main difference with other methods is the consideration of the passive sensitivities during the optimization process. The GA delivers the values of resistors and capacitors (from E series) that comply with the desired specifications and minimize at the same time the sensitivities. This characteristic leads to filters that exhibit low deviations in their functional parameters, despite drifts in the values of passive components. Additionally, the method allows the designer to establish the gain in the passband. In this way, it overcomes the problem of low gain values observed in some of the solutions given by other authors. The paper presents an evaluation campaign that considers 12 designs for showing the robustness of the method. This study analyses the results delivered by the GA at transfer function level using MATLAB. Subsequent evaluations validate these results by using SPICE simulations. Following these procedures, it is observed a proper matching between the behaviors of the filters predicted by the GA and the simulated ones. The performance comparison with other heuristics (solving the same problem) shows that our proposal is well suited for the design of active filters. The stochastic nature of the GA allows obtaining different design alternatives in each run. This feature gives the designer the possibility to choose between several options that are more appropriate for a particular design problem. The paper also provides a simple guideline for dealing with the results from the iterative executions of the GA. The design method requires tools that are usual to find in the industry. Practitioners can straightforwardly implement it, even those that are nonspecialists in heuristics.
Simultaneous determination of five phthalate esters and bisphenol A in milk by packed‐nanofiber solid‐phase extraction coupled with gas chromatography and mass spectrometry
Authors: Tang Zigang , Han Qing , Xie Li , Chu Lanling , Wang Yu , Sun Ying , Kang Xuejun
Published: December 2018

A novel polystyrene/pyridine composite nanofiber was synthesized and utilized as the sorbent material for the solid‐phase extraction of bisphenol A and five common phthalate esters in milk. The method of extraction integrated extraction and preconcentration of target analytes into a single step. Bisphenol A and five common phthalate esters were selected as target compounds for the development and evaluation of the method. The effects of operating parameters for nanofiber‐based solid‐phase extraction, such as selection and amount of sorbent, the volume fraction of perchlorate (precipitate protein), desorption solvent, volume of desorption solvent, and effect of salt addition were optimized. Under optimal conditions, higher extraction recoveries (89.6–118.0%) of the six compounds in milk spiked at three levels were obtained, and the satisfied relative standard deviation were ranged from 0.6 to 10.9%. The detection limits and quantification limits of the method ranged from 0.01 to 0.06 μg/L and 0.05 to 0.53 μg/L, respectively. Matrix effects were also verified and well controlled in the range of 91.3–109.3%. The new method gave better performance metrics than Chinese standard method and other published methods. Thus, the proposed method may be applied to the analysis of the phthalate esters and bisphenol A in complex matrixes.
Fabrication of boron‐rich multiple monolithic fibers for the solid‐phase microextraction of carbamate pesticide residues in complex samples
Authors: Wu Jiangyi , Mei Meng , Huang Xiaojia
Published: December 2018

To enrich carbamate pesticides from complex matrices, an adsorbent based on poly (vinylboronic anhydride pyridine complex‐co‐ethylenedimethacrylate) monolith was fabricated and utilized as the extraction phase of multiple monolithic fiber solid‐phase microextraction. Due to the abundant boron atoms in the monolith, the B–N coordination interaction between adsorbent and analytes play a key role in the efficient extraction of analytes. Under the optimized conditions, the monolithic fibers were combined with high‐performance liquid chromatography for the quantify trace levels of carbamate pesticides in environmental water and orange juice samples. For water sample, the limit of detection and limit of quantification were in the range of 0.017–0.29 and 0.057–0.96 μg/L, respectively. The related values in orange juice samples were 0.038–0.39 and 0.12–1.36 μg/kg, respectively. Besides, the proposed method also exhibits wide linearity, satisfactory coefficients of determination, and good precision. The introduced approach was successfully applied to determine trace target analytes in real‐life samples. The spiked recoveries with different fortified concentrations were in the range of 80.4–117% for water samples and 83.7–119% for fruit juice samples. The relative standard deviations were below 10%. The results evidence that the suggested method was convenient, reliable, and eco‐friendly for the monitoring of trace levels of carbamate pesticides in complex samples such as waters and juices.
SNP‐SNP and SNP‐environment interactions of potentially functional HOTAIR SNPs modify the risk of hepatocellular carcinoma
Authors: Zhang Junguo , Liu Li , Lin Zhifeng , Ji Xiaohui , Pi Lucheng , Lin Xinqi , Tian Nana , Liu Guiyan , Liu Qing , Lin Ziqiang , Chen Sidong , Yu Xinfa , Gao Yanhui
Published: December 2018

HOX transcript antisense intergenic RNA (HOTAIR) has been widely regarded as a functional lncRNA contributing to multiple cancers. However, few studies have examined the effect of single nucleotide polymorphisms (SNPs) in HOTAIR on the occurrence and development of hepatocellular carcinoma (HCC). In this study, three potentially functional HOTAIR SNPs (rs17105613, rs12427129, and rs3816153) were selected using bioinformatic tools. A case‐control study including 1262 cases and 1559 controls was conducted to explore the association of HOTAIR SNPs with the risk of HCC in a Southern Chinese population. We found that SNPs rs12427129 and rs3816153 were associated with the risk of HCC in dominant genetic models (CC: CT + TT, adjusted odds ratio (OR) = 0.72, 95% confidence interval (CI) = 0.57–0.90 and GG: GT + TT, adjusted OR = 1.30, 95%CI = 1.08–1.57). Additionally, SNP–environment interactions for rs12427129, rs3816153, and HBsAg status were found to enhance the risk of HCC, with FDR‐P as an additive interaction equal to 0.0006 and 0.0144, respectively. In multifactor dimensionality reduction (MDR) analysis, the three‐factor model (HBsAg status, rs12427129 and rs3816153) yielded the highest test accuracy of 77.74% (permutation P < 0.001). Interestingly, the effect of rs12427129 and rs3816153 on the risk of HCC could be modified by HBsAg status, while the rs12427129 CT/TT genotype could antagonize the detrimental effect of rs3816153 GT/TT genotype on HCC. Our findings suggest that rs12427129 and rs3816153, including their SNP‐SNP and SNP‐environment interaction with HBsAg status, potentially play important roles on the susceptibility to HCC.
Mechanics with non‐Leibniz derivatives
Authors: Kobelev Vladimir
Published: December 2018

The non‐Leibniz Hamiltonian and Lagrangian formalism for the certain class of dissipative systems is introduced in this article. The formalism is based on the generalized differentiation κ‐operator with a non‐zero Leibniz defect. The Leibniz defect of the introduced operator linearly depends on one scaling parameter. In a special case, if the Leibniz defect vanishes, the κ‐operator reduces to the common differentiation operator. The new operator allows the formulation of the variational principles and corresponding equations of Lagrange and Hamiltonian types for dissipative systems. The solutions of some generalized dynamical equations are provided in closed form.
Christian Otto Mohr und Friedrich Hebbel – Söhne aus Wesselburen in Dithmarschen
Authors: Gaul Lothar
Published: December 2018

Der Artikel zeigt die Parallelität im Leben zweier bedeutender Söhne aus Dithmarschen auf. Christian Otto Mohr, Sohn des Kirchspielvogts Mohr in Wesselburen wurde einer der Väter der graphischen Statik, bekannt als Professor für Mechanik in Stuttgart und Dresden. Friedrich Hebbel war der Sohn des Gärtners des Vogtes Mohr und wurde mit dessen Förderung zu Deutschlands bekanntestem Dramatiker.
On a modification of the EVEN‐IRA algorithm for the solution of T‐even polynomial eigenvalue problems
Authors: Faßbender Heike , Saltenberger Philip
Published: December 2018

We discuss the numerical solution of T‐even n × n polynomial eigenvalue problems and show how a small portion of the spectrum can be obtained using just 𝒪(n3) arithmetic operations. For that purpose, we apply the EVEN‐IRA algorithm proposed in [1] to a special structure‐preserving linearization. In this particular situation, the Arnolid iteration as a main part of the EVEN‐IRA algorithm can be realized very efficiently.
Teaching Vision‐based Control for Autonomous Driving with Lego Mindstorms EV3, Raspberry Pi and Simulink
Authors: Otto Svenja , Schmitt Alexander , Dücker Daniel , Seifried Robert
Published: December 2018

Lego Mindstorms is a popular platform to teach robotics in schools and colleges. Basic mechanical properties as well as programming concepts can be taught to students of various ages. However, there are limitations, for example the lack of a camera for vision‐based control which is fundamental for autonomous applications like self‐driving cars. Within the framework of a summer school, we solve this limitation by adding a webcam and a Raspberry Pi to the platform. The class is designed to teach undergraduate students mechanical principles, vision‐based control and basic programming concepts in a project‐based setting.
Higher‐order surface FEM for incompr. Navier‐Stokes flows on manifolds
Authors: Fries Thomas‐Peter
Published: December 2018

Stationary and instationary Stokes and Navier‐Stokes flows are considered on curved surfaces in three dimensions. A stabilized, mixed, higher‐order surface FEM with individual element orders is used for the approximation of the geometry, velocities, pressure, and Lagrange multiplier to enforce tangential velocities. Benchmark test cases are proposed and higher‐order convergence rates are confirmed.
Damage and failure mechanisms of ductile metals in biaxial experiments with non‐proportional loading paths
Authors: Zistl Moritz , Gerke Steffen , Brünig Michael
Published: December 2018

The paper deals with an experimental series of the biaxial X0‐specimen to study the loading path dependence of ductile damage and fracture under non‐proportional loading. The damage and fracture behavior of ductile metals depend on the stress state, consequently the material deterioration has to be studied experimentally to develop and validate the corresponding material model. Experimentally the specimen surfaces have been monitored by digital image correlation (DIC) while the fracture surfaces have been analyzed by scanning electron microscopy (SEM). The experimental results based on proportional and non‐proportional loading paths clearly show that damage and fracture processes are affected by the loading history.
Optimal parameters for a family of flux‐correction methods strongly reducing overshoot in unsteady flow computation
Authors: Niessner Herbert
Published: December 2018

Flux‐correction allows to reduce or even remove overshoot occuring when Lax‐Wendroff methods are used to calculate one‐dimensional flow. There is a whole family of methods [3] depending on two parameters, whose optimal values are derived. One controls the amount of diffusion to reduce overshoot, the other determines removal of this diffusion as far as overshoot does not reappear, thus largely retaining accuracy of the employed Lax‐Wendroff method.
Stability of a second‐order method for phase change in porous media flow
Authors: Alvarez Mario , Gomez‐Vargas Bryan , Ruiz Baier Ricardo , Woodfield James
Published: December 2018

We analyse the stability of a second‐order finite element scheme for the primal formulation of a Brinkman‐Boussinesq model where the solidification process influences the drag and the viscosity. The problem is written in terms of velocity, temperature, and pressure, and we produce numerical approximations to the flow observed in heated cavities and near ice sheets.
Using magnetic fluids to model convection of planetary or stellar interiors in laboratory scale
Authors: Szabo Peter S. B. , Früh Wolf‐Gerrit
Published: December 2018

Baroclininc flow induced via thermomagnetic convection is investigated as a potential model of convection of planetary interiors at a laboratory scale. To reproduce a central force field, a permanent magnet is used that acts on a magnetic fluid contained in a spherical shell. In addition to maintaining the inner sphere and outer shell at different temperatures, the system is rotating around its central axis. Results suggest that magnetic fluids reproduce the essential qualitative character of the baroclinic flows and may be a useful tool to investigate convective flow in planetary interiors. To quantify the effect of magnetic forcing, a parameter ΘM was developed which represents the equivalent to the thermal Rossby number.
Coupled Simulations Involving Light‐weight Structures within Turbulent Flows: A Complementary Experimental and Numerical Application
Authors: De Nayer Guillaume , Wood Jens Nikolas , Breuer Michael , Apostolatos Andreas , Wüchner Roland
Published: December 2018

Due to their easy‐to‐shape and light‐weight characteristics, membranous structures are common in modern civil engineering. As all outside buildings they are exposed to wind loads and consequently undergo fluid‐structure interactions (FSI). In order to dimension these membranous constructions and to avoid the damage of the material by FSI, numerical and experimental investigations are necessary. The current paper presents the simulation part of complementary experimental and numerical investigations relying on an advanced numerical simulation methodology.
Robust Blind Image Fusion for Misaligned Hyperspectral Imaging Data
Authors: Bungert Leon , Ehrhardt Matthias J. , Reisenhofer Rafael
Published: December 2018

The low spatial resolution of hyperspectral imaging can be significantly improved by fusing the hyperspectral image with a high resolution photograph. In most practical cases, however, the exact alignment between the fused images is not known a priori. In this work, we study how including a blind deconvolution approach in the mathematical model can help resolve translational misalignments. In particular, we investigate the influence of different initialization strategies. The efficiency of the proposed model is validated by numerical experiments using both simulated and real remote sensing data.
Noncooperative Model Predictive Control for Affine‐Quadratic Games
Authors: Stieler Marleen , Baumann Michael H. , Grüne Lars
Published: December 2018

Nash strategies are a natural solution concept in noncooperative game theory because of their ‘stable’ nature: If the other players stick to the Nash strategy it is never beneficial for one player to unilaterally change his or her strategy. In this sense, Nash strategies are the only reliable strategies.

The idea to perform and analyze Model Predictive Control (MPC) based on Nash strategies instead of optimal control sequences is appealing because it allows for a systematic handling of noncooperative games, which are played in a receding horizon manner. In this paper we extend existence and uniqueness results on Nash equilibria for affine‐quadratic games. For this class of games we moreover state sufficient conditions that guarantee trajectory convergence of the MPC closed loop.
An analytical approach to the accurate modeling of visco‐elastic materials with stochastic microstructure
Authors: Junker Philipp , Nagel Jan
Published: December 2018

This paper presents a mathematically accurate and numerically very fast procedure to compute both expectation and variance (and standard deviation) of the stresses in a visco‐elastic material with stochastically fluctuating elastic properties. The stochastic material properties turn the evolution equation for the viscous strain components into a stochastic ordinary differential equation (ODE). We solve this ODE analytically for arbitrary loading cases which allows for a separation of deterministic and stochastic contributions. As a consequence, we are able to present precise formulas for the expectation and variance of the stresses. Material point simulations for various loading cases and varying viscosities are compared to Monte‐Carlo results which prove the reliability of our approach.
Efficient analysis of stress concentrations in laminated composite structures with geometric discontinuities
Authors: Schnabel Jan Eike , Mittelstedt Christian
Published: December 2018

A semi‐analytical analysis method for displacements, strains and stresses in laminated composite plates with local reinforcement by patches/doublers is presented. The analysis approach is based on a “global” solution provided by the Classical Laminate Plate Theory (CLPT). Further, a “local” model is introduced which discretizes each laminate ply into several mathematical layers. For each of these mathematical layers an additional displacement field is postulated. These additional displacement fields capture the localized phenomena close to the free edge of the patch and in the plate‐doubler junction but decay rapidly with increasing distance from these locations, i.e. the CLPT solution is recovered. The model shows excellent agreement with FE analyses for different plate‐doubler lay‐ups with the benefit of highly reduced computational costs.
An anisotropic continuum damage model for concrete based on biaxial experiments
Authors: Michalski Alexander , Brünig Michael
Published: December 2018

The paper deals with an anisotropic continuum damage model to describe the brittle damage and fracture behavior of plain concrete. Due to the stress state dependence of damage and fracture, multiaxial experiments have to be analyzed to make sure the model is able to simulate the observed physical phenomena. Therefore, simulations with a two‐dimensional version of the proposed model have been carried out based on the experimental data from existing literature. These simulations show a dependence of the model parameters on the stress state.
Validation of Bredt's formulas by the method of asymptotic splitting
Authors: Schmidrathner Christian
Published: December 2018

The equations describing torsion of prismatic bars with thin‐walled closed cross sections, known as Bredt's formulas, are verified using the method of asymptotic splitting. In particular, the strong formulation of the Saint Venant problem of a straight beam is expanded asymptotically. At first, well‐known technical assumptions of the shear stress distribution are validated. Further, the influence of a transverse force acting on the beam is considered. This shear force causes a deformation of the cross section and therefore an adaption of Bredt's formulas. Two distinct formulations of the shear center, called the kinematic and the energetic shear center, are obtained. The latter are verified in numerical experiments.
Enhanced Assumed Strain Methods for Implicit Gradient‐Enhanced Damage‐Plasticity
Authors: Neuner Matthias , Schreter Magdalena , Hofstetter Günter
Published: December 2018

The combination of plasticity theory and continuum damage mechanics facilitates the description of hardening and softening material behavior, accumulation of inelastic strains, and stiffness degradation due to damage. For regularizing softening material behavior in finite element simulations, the enrichment of the constitutive relations by means of a nonlocal counterpart of an internal strain‐like thermodynamic state variable, implicitly defined as the solution of a higher order PDE, is a suitable approach in order to obtain mesh‐insensitive results [1]. However, for plasticity models assuming dilatant plastic flow, such as commonly employed for cohesive‐frictional materials like concrete or rock, spurious locking phenomena due to kinematic constraints can arise in conjunction with low order finite elements. This issue was observed and discussed in [2] for simple (local) linear‐elastic perfectly plastic material models. As a remedy, specific enhanced assumed strain (EAS) methods to enrich the normal strain rate field were proposed and assessed. The present contribution demonstrates the formulation of these EAS methods combined with the fully coupled displacement‐nonlocal damage framework, and shows an application to mode II failure employing a gradient‐enhanced damage‐plasticity model for concrete. The insensitivity of the presented approach with respect to the finite element mesh is discussed.
On the rate‐depentent regularization for damage modeling
Authors: Langenfeld Kai , Junker Philipp , Mosler Jörn
Published: December 2018

A model framework for the analysis of isotropic quasi‐brittle damage, was recently presented in [1]. Within this paper, the model in [1] is significantly improved. To be more precise, and in contrast to [1], the novel model: (i) eliminates unnecessary model parameters, (ii) can be better interpreted from a physics point of view, (iii) can capture a fully softened state (zero stresses) and (iv) is characterized by a very simple evolution equation which (v) can be integrated fully implicitly and (vi) the resulting time discrete evolution equation can be solved analytically providing a numerically efficient closed form solution, cf. [2].
Funnel control for nonlinear systems with higher relative degree
Authors: Berger Thomas , Lê Huy Hoàng , Reis Timo
Published: December 2018

We consider tracking control for nonlinear multi‐input, multi‐output systems which have arbitrary strict relative degree and input‐to‐state stable internal dynamics. For a given reference signal, our aim is to design a controller which achieves that the tracking error evolves within a prespecified performance funnel around the reference signal. To this end, we introduce a new controller which involves the first r−1 derivatives of the tracking error, where r is the strict relative degree of the system.
Mixed Eulerian–Lagrangian description in the statics of a flexible belt with tension and bending hanging on two pulleys
Authors: Scheidl Jakob , Vetyukov Yury , Oborin Evgenii , Krommer Michael , Schmidrathner Christian
Published: December 2018

Studying the mechanics of thin, axially moving strings, beams or plates (e.g.: belt drives, cable cars, …) at mixed Eulerian–Lagrangian description, which features the transformation of material coordinates to spatial ones, is more appropriate than the classical material (Lagrangian) one, see [1, 2]. Aiming at testing a newly proposed non‐material finite element formulation we study the statics of a looped belt as a rod hanging in contact with two pulleys. Numerical experiments demonstrate rapid mesh convergence as well as correspondence to semi‐analytical results and conventional Lagrangian finite element solutions.
Discontinuous approximation of flow in porous media with adsorption
Authors: Bürger Raimund , Kenettinkara Sudarshan Kumar , Ruiz‐Baier Ricardo , Torres Héctor
Published: December 2018

Polymer flooding in petroleum reservoir engineering can be described by a Brinkman‐based model of flow in porous media coupled to a non‐strictly hyperbolic system of conservation laws for multiple components that form the aqueous phase. The coupled flow‐transport problem is discretized by coupling an H(div)‐conforming discontinuous Galerkin (DG) method for the Brinkman flow problem with a classical DG method for the transport equations.
Periodic solutions of measure differential inclusions
Authors: Paschkowski Manuela , Arnold Martin
Published: December 2018

When modelling mechanical systems with contact and impact forces the most important characteristic is the occurrence of velocity jumps during the impacts. Even for simple applications like the bouncing ball [3] or the impact oscillator [1] this nonsmooth effect may arise infinitely often during a finite time. A suitable setting, whose solution space includes such strongly nonsmooth functions, are the measure differential inclusions (MDI) [7]. The mentioned framework is used to prove existence of periodic solutions for the impact oscillator independent of initial values or system parameters.
Numerical and Experimental Analyses of the Effect of Negative Stress Triaxialities on Ductile Damage and Failure
Authors: Schmidt Marco , Gerke Steffen , Brünig Michael
Published: December 2018

The paper deals with an experimental and corresponding numerical series of the biaxial Z‐specimen, which is made of an aluminum alloy, to investigate the effect of negative stress triaxialities on ductile damage and failure, which are stress‐state‐dependent. Therefore, the continuum model contains a stress‐state‐dependent damage condition and a stress‐state‐dependent damage rule to describe the damage and failure mechanisms. In the experimental evaluation, in addition to force‐displacement curves, optical investigations such as digital image correlation (DIC) and scanning electron microscopy (SEM) were used. The results showed that with compression‐shear load fracture occurs at greater negative triaxialities than previously known. Therefore a new function for the cut‐off value of stress triaxiality is proposed.
Numerical models for the prediction of the behavior of a flexible slender shaped membrane in interaction with free surface flow under the influence of a moving flotsam
Authors: Makaremi Masouleh M. , Wozniak G.
Published: December 2018

The motivation for this work is the great need of applying light structures for the protection of coastal areas from detrimental effects of rapid water runoff. In case of windy or stormy weather conditions, light structures are extremely vulnerable to be attacked by floating debris and even tree trunks. To meet the safety criteria, speculation of this impulsive force on light structures gains in importance on account of the massive deformation of membrane. This matter provides the incentive to investigate an impact phenomenon numerically. The analysis was first performed within a standalone Abaqus standard environment, where the effect of fluid domain on the flexible structure was executed on structure by user subroutine of DLOAD, which was updated in each iteration based on new deformed shape. This model was extended by a partitioned strategy which makes it possible for fluid and structure domains to be interconnected powerfully. The impact of free surface water flow on the membrane was executed using the finite volume solver of Star CCM+, which behaves in response to displacements of the structures. On account of added mass effects, the implicit coupling algorithm between fluid and solid regions was implemented.
Examining errors and correction techniques for SPH
Authors: Fürstenau Jan‐Philipp , Weißenfels Christian , Wriggers Peter
Published: December 2018

Despite its popularity, it is well known that the SPH method in its original form is not even zeroth order consistent [5]. This inconsistency results from the SPH‐ansatz function, the so‐called kernel, only depending on the chosen smoothing length, ignoring the current particle distribution. For the examination the heat conduction equation was chosen. Heat conduction test cases have the advantage, that their particle distribution can remain constant during the whole simulation. In this work the resulting errors are highlighted and the influence of common correction techniques of zeroth order are compared.
Determining angular velocities of fast rotating objects based on motion blur to control an optomechanical derotator
Authors: Altmann Bettina , Pape Christian , Reithmeier Eduard
Published: December 2018

Investigations of machine components are important for a faultless functioning of the machine. Ideally, the components are investigated during operation. Thus, a realistic performance of the machine can be analyzed. However, measurements of fast rotating machine components can be quite challenging especially under bad illumination conditions leading to the necessity of high exposure times. In case high‐speed cameras reach their limits due to motion blur resulting of high exposure times or high velocities, an optomechanical image derotator can still lead to sufficient results. This is due to its operating principle consisting of a rotating reflector assembly inspired by a Abbe‐Koenig‐prism which optically eliminates the rotational movement. To generate a stationary image, the optomechanical image derotator containing the reflector assembly has to rotate exactly half as fast as the rotating object. Therefore, the angular velocity of the object has to be determined. A common way for this is the use of rotary encoders although not every machine can be equipped with such sensors. A flexible solution for this is to identify the angular position and thereby the velocity with a high speed camera capturing images of the rotating object. Using image processing algorithms the marker can be detected and thus the velocity can be calculated from the image data. However, due to high rotational velocities and long exposure times motion blur of the marker can occur. Generally, motion blur can be treated as an artifact since it impedes the image analysis. However, motion blur can be used to determine the velocity of the rotating objects in knowing the shutter speed as well as the length of the streaking of a blurred object. This work presents an approach which determines the rotational velocity from image blur for different velocities. The resulting information will be used as the input source for a velocity control of the derotator. Furthermore it will be discussed whether the velocity information is precise enough to control the derotator leading to a resting image of the rotating object.
Sequential solution of parameter identification and optimal control problems for robotic systems
Authors: Runge Margareta , Flaßkamp Kathrin , Büskens Christof
Published: December 2018

Nowadays Parameter Identification Problems (PIP) are one of the main tasks in many engineering applications. For example, a model for the dynamic behavior of a robotic system has to be found. Before we can work with a system, e.g. solve an optimal control problem (OCP) to optimally perform an assigned task, we have to identify unknown parameters within the system model. In general, system identification is a one‐time job before system operation, but often there remain inaccuracies or the system changes over time, e.g. due to wear. Thus, the model has to be adapted during the process. This paper presents an algorithm where PIPs and OCPs are sequentially solved in order to obtain online parameter updates. First numerical results for an idealized two‐link robot are presented.
An Overview of Isogeometric Boundary Element Methods for Acoustic and Electromagnetic Scattering Problems
Authors: Dölz Jürgen , Kurz Stefan , Schöps Sebastian , Wolf Felix
Published: December 2018

We introduce the concept of isogeometric boundary element methods, by first reviewing the required trace spaces and then constructing a conforming spline discretisation. We highlight how to use this approach to solve Dirichlet problems induced by the Helmholtz‐ and electric wave equation, and conclude by presenting numerical examples.
A Numerical Study of the Robustness of Transcription Methods for Parameter Identification Problems
Authors: Schäfer Kai , Flaßkamp Kathrin , Büskens Christof
Published: December 2018

In this work, we apply transcription methods known from optimal control to nonlinear dynamic parameter identification problems. We analyze and compare the methods with the help of an application example from robotics. More specifically, we investigate their robustness against varying initial parameters and show numerically, that an increasing number of variables leads to a more robust optimization behavior and qualitatively better solutions.
A revised taxonomy for the competence oriented description of learning outcomes for study programs in engineering sciences
Authors: Mittermeier Franziska , Ullmann Rupert , Müller Gerhard
Published: December 2018

The modularisation of study programs due to the Bologna Process leads to a growing number of selection choices and an increasing flexibility in the individual curriculum design. Therefore an appropriate description of the learning outcomes of the individual modules is crucial for ensuring consistent personal curricula and the continuous acquisition of competences. At the Technische Universität München, learning outcomes are currently described in continuous texts using Bloom's taxonomy. Although this taxonomy is commonly accepted, in practical applications there are problems regarding a clear description of the acquired competences in engineering sciences. Thus, we extended Anderson's and Krathwohl's revision of Bloom's taxonomy for the explicit application to engineering studies. In the reformulation we expressed the stage of qualification via a breakdown into quantified levels of knowledge (know what), skills (know how), and competences (know why). Furthermore, we introduced a tabular description instead of a continuous text. This allows for a systematic storage and analysis in a database. Therefore besides an appropriate and clear description of learning outcomes, the new system delivers access to various possibilities: First, the new taxonomy facilitates the detection of conflicts between learning outcomes of different modules using a web‐based tool for the analysis of module interfaces. Furthermore, the level system eases competence orientated examination via adapting questions to the respective qualification level addressed in the module description. Finally, the new system simplifies the recognition of credits, which becomes more important due to the increasing mobility of students.
Nitsche's method for form‐finding of multipatch isogeometric membrane analysis
Authors: Apostolatos Andreas , Bletzinger Kai‐Uwe , Wüchner Roland
Published: December 2018

Membranes constitute an important category of thin‐walled and in particular tensile structures [1], for which in contrast to shells their structural rigidity is obtained by means of prestress rather than relying on bending stiffness. In particular, the structures considered in this study act in pure membrane state and have no bending stiffness. A big challenge of such structures is finding the shape of static equilibrium. This is not a trivial task since not every shape under any prestress distribution or loading condition renders a static equilibrium configuration. This is even more prominent when prestressed cables are attached to the structure. To overcome this problem for general tensile structures, various types of form‐finding methods were developed [2, 3]. In this study, the Updated Reference Strategy (URS) [4, 5] is presented in combination with multipatch isogeometric analysis [6] as discretization method. The enforcement of the continuity constraints along the common patch interfaces [7] is realized using a Nitsche‐type method [8] while the results are evaluated and compared with the Penalty‐based approach [9].
The Particle Finite Element Method for the modelling and simulation of solid body interactions
Authors: Schewe Markus , Menzel Andreas
Published: December 2018

Both simulation and, in particular, the underlying algorithmic treatment of effects such as fracture or abrasive wear are generally very complex in nature and thus computationally expensive. The Particle Finite Element Method (PFEM) according to [1] constitutes a promising compromise between physical accuracy and computational efficiency. The PFEM allows the separation of material within a repeated remeshing and shape detection step. Such applications of the PFEM may be incorporated in simulations of fracture and cutting. The methods used in PFEM can be adapted to the task of identifying contact areas and meshing the contact zone between solid bodies. Therefore, PFEM offers a good framework to combine both, the contact between solid bodies and the separation of material, in order to develop a simulation framework for abrasive wear.
Modeling of Electromechanically Induced Phase Transitions in Lead Zirconate Titanate (PZT) Based on the Condensed Method
Authors: Uckermann Philip , Lange Stephan , Ricoeur Andreas
Published: December 2018

This research is about determining the effects of phase transitions in lead zirconate titanate. Transformations between tetragonal and rhombohedral phases have been implemented using an adapted evolution law. Predictions concering polycrystalline material behavior are made by the condensed method. Stresses and strains under electric loads are considered to investigate upcoming effects near the morphotropic phase boundary. An interpretation concerning actuator applications will be provided.
New thoughts on the anti plane shear problem
Authors: Voss Jendrik , Neff Patrizio , Baaser Herbert
Published: December 2018

We reconsider anti‐plane shear deformations of the form ϕ(x) = (x1, x2, x3 + u(x1, x2)) based on prior work of Knowles and relate the existence of anti‐plane shear deformations to fundamental constitutive concepts of elasticity theory like polyconvexity, rank‐one convexity and tension‐compression symmetry. In addition, we provide finite‐element simulations to visualize our theoretical findings.
Sensitivity analysis of a non‐local, gradient enhanced damage model
Authors: Guhr Fabian , Barthold Franz‐Joseph , Menzel Andreas , Sprave Leon , Liedmann Jan
Published: December 2018

The sensitivities for a non‐local, gradient enhanced damage model are analysed. To model the damage accumulation, a non‐local, gradient enhanced damage model is proposed. Contrary to other approaches, where a local variable is coupled to a non‐local one, see e.g. [1–3], solely a non‐local variable is introduced which is calculated simultaneously with the displacements for each node point. By means of a variational approach, the stiffness matrix as well as the sensitivities, see [4], can be calculated for implementation into the finite element method (FEM) and the minimisation, using sequential quadratic programming (SQP). The framework allows to optimise given geometries with respect to the damage evolution either directly with the damage as the objective function, or indirectly by choosing the damage as a constraint at every finite element node.
Viscoelasticity of cross‐linked actin network embedded in cytosol
Authors: Wiegold Tillmann , Klinge Sandra , Aygün Serhat , Gilbert Robert P. , Holzapfel Gerhard A.
Published: December 2018

An eukaryotic cell is a complex system including various components with different structures and roles. The current contribution deals with the microscopic and macroscopic simulations of a cell if two of its components are considered: cytosol and actin network. At the microscopic level, the actin is modeled by the Holzapfel‐Ogden model, including an extension for viscous effects. The model provides a relationship between the stretch of a single polymer chain and the applied tension force. This relationship includes the influence of the physical length of a single chain, its end‐to‐end distance and the stretch modulus. The viscous effects occurring due to deviatoric changes are modeled corresponding to a spring and a dashpot of the generalized Maxwell model. The cytosol is modeled by a large strain viscous model from the FEAP program. Finally, the effective behavior of the cell cytoplasm is simulated by using the multiscale finite element method. This method has been chosen since it is suitable for simulating nonlinear heterogeneous materials with a zero‐ratio of the characteristic lengths of scales. The selected numerical example deals with the effective material behavior for a tension test with two holding phases.
Modeling and simulation of curing processes using time‐adaptive, high‐order time integration
Authors: Leistner Chris , Abliz Dilmurat , Ziegmann Gerhard , Hartmann Stefan
Published: December 2018

Nowadays, epoxy resins are extensive applied as a matrix in fiber‐reinforced materials. However, its production process is very sensitive to temperature control. High process temperatures substantially accelerate the exothermic production process, which can lead to combustion. Therefore, a constitutive model of the matrix material must be provided first. Second, initial boundary value problems need to be treated by time‐adaptive, high‐order time integration schemes within finite elements in order to obtain precise and reliable results within an appropriate calculation time.
A new insight into the J‐, M‐, and L‐integrals of dislocations
Authors: Agiasofitou Eleni , Lazar Markus
Published: December 2018

The explicit formulas of the J‐, M‐, and L‐integrals of straight (screw and edge) dislocations in isotropic materials are presented. The obtained results reveal the physical interpretation and significance of the M‐, and L‐integrals for straight dislocations. The M‐integral between two straight dislocations (per unit length) is equal to half the interaction energy of the two dislocations (per unit length) depending on the distance and on the angle, plus twice the corresponding pre‐logarithmic energy factor. The L3‐integral between two straight dislocations is the z‐component of the configurational vector moment or the rotational moment (torque) about the z‐axis caused by the interaction between the two dislocations.
Multi‐Disciplinary Design Optimization of Missile Fin Configuration
Authors: Rašuo Boško , Vidanović Nenad , Kastratović Gordana
Published: December 2018

The aim of the paper is to establish and demonstrate the significant capacity and performances of a well predictive numerical environment, developed for multidisciplinary design optimization purposes, which presents one more contribution in cases of fluid‐structure interaction numerical modelling. Numerical modelling of fluid‐structure interaction was conducted through closely coupled aerodynamic and structural computational domains, with very good overall computational reliability and accuracy. The developed algorithm enabled an increased number of feasible optimal geometries of fin, while its special feature was the overall improvement of the missile initial geometry.