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In this chapter, to investigate the tensile behavior of CNTs, finite element models of single-walled carbon nanotubes (SWCNTs) in perfect and doped modes for common types of carbon nanotube (CNT) configuration, i.e., the armchair, zigzag, and chiral models, were generated using a commercial finite element software (MSC Marc). To create the computational models, nodes were placed at the locations of carbon atoms and the bonds between them were modeled using three-dimensional elastic generalized beam elements. Doped models were simulated by three different heteroatoms including silicon, nitrogen, and boron separately with the doping concentration ranging from 0 to 5%. Young’s moduli of all models were obtained and compared with the perfect structures. The results indicated that Young’s modulus of chiral SWCNTs is larger than the moduli of the armchair and zigzag SWCNTs in all models and incorporating the silicon and boron atoms into CNT led to a linear reduction in Young’s modulus which was most significant for silicon and less noticeable for boron. Regarding nitrogen doping, a different trend was observed that was a negligible and less conspicuous increment in the value of Young’s modulus by increasing the percentage of doping. Besides, this behavior was the same for all armchair, zigzag, and chiral configurations with the same dopant atom. The investigations also revealed that the structural irregularity and ripples, which are induced by dopant atoms, are a key factor which influences the tensile behavior of CNTs. Our results for Young’s modulus of doped CNTs are in good agreement with recent investigations.
This Encyclopedia covers the entire science of continuum mechanics including the mechanics of materials and fluids. The encyclopedia comprises mathematical definitions for continuum mechanical modeling, fundamental physical concepts, mechanical modeling methodology, numerical approaches and many fundamental applications. The modelling and analytical techniques are powerful tools in mechanical civil and areospsace engineering, plus in related fields of plasticity, viscoelasticity and rheology. Tensor-based and reference-frame-independent, continuum mechanics has recently found applications in geophysics and materials.
The wide range of factors contributing to wind resource assessment accuracy in complex terrain
(2022)
Background:
Glaucoma, a characteristic type of optic nerve degeneration in the posterior pole of the eye, is a common cause of irreversible vision loss and the second leading cause of blindness worldwide. As an optic neuropathy, glaucoma is identified by increasing degeneration of retinal ganglion cells (RGCs), with consequential vision loss. Current treatments only postpone the development of retinal degeneration, and there are as yet no treatments available for this disability. Recent studies have shown that replacing lost or damaged RGCs with healthy RGCs or RGC precursors, supported by appropriately designed bio-material scaffolds, could facilitate the development and enhancement of connections to ganglion cells and optic nerve axons. The consequence may be an improved retinal regeneration. This technique could also offer the possibility for retinal regeneration in treating other forms of optic nerve ailments through RGC replacement.
Methods:
In this brief review, we describe the innovations and recent developments in retinal regenerative medicine such as retinal organoids and gene therapy which are specific to glaucoma treatment and focus on the selection of appropriate bio-engineering principles, biomaterials and cell therapies that are presently employed in this growing research area.
Results:
Identification of optimal sources of cells, improving cell survival, functional integration upon transplantation, and developing techniques to deliver cells into the retinal space without provoking immune responses are the main challenges in retinal cell replacement therapies.
Conclusion:
The restoration of visual function in glaucoma patients by the RGC replacement therapies requires appropriate protocols and biotechnology methods. Tissue-engineered scaffolds, the generation of retinal organoids, and gene therapy may help to overcome some of the challenges in the generation of clinically safe RGCs.
Social work across the world has been shaped by prevailing political systems, their influence on the welfare system and hence the social work profession. This thesis examines how the social work profession evolved in South Africa focusing on the political transition from Apartheid to democracy. Particular interests of the research are the development of South African social workers professionalism regarding professional conduct and professional identity. Moreover, it brings out the manifold changes the profession had to undergo in the political transition and consequently the issues the social work profession deals with today.
For an efficient operation of a low voltage PMSM an optimized voltage usage is very important. Because of the relation between the low voltage and the high currents in this type of machine, a large voltage reserve is needed to compensate the influence of parameter mismatches and to guarantee a stable current control. As the power is limited by the low voltage in this type of hybrid drive systems, optimizing the voltage usage is also required to maximize the power and the torque availability. This paper describes a closed loop flux control to maximize the voltage usage. The controller feedback is used to estimate and maximize the available torque for each operating point.
For a low voltage IPMSM used in a hybrid drive system of a consumer car, it is of the highest importance to design a torque controller circuit that produces an accurate torque at the shaft. The accurate torque is needed to distribute the load between the combustion engine, or the manual break, and the electrical drive. As the capacitance of the batteries used in this type of car is usually very small, the control of the batteris state of charge and its output current is quite critical. Therefore, a precise torque control is elementary. Temperature changes have a large impact on the IPMSM internal parameters. Especially the permanent magnet flux and the stator resistance are affected by temperature changes. There are techniques to observe and calculate the temperature variation of these parameters. This contribution describes a method to handle the influence of temperature variation on the actual torque at the shaft, by correcting the current commands of the open loop controller.
High‑cell‑density cultivation of Vibrio natriegens in a low‑chloride chemically defined medium
(2023)
Future electricity flows and their impact on the power distribution grid on a decentralized level
(2022)
This paper explores the influence of French cultural standards and dimensions on the corporate culture, the management style and the international development of the French petroleum company Total by using empirical methods. Due to its important degree of internationalisation, Total projects a considerably internationalised outward appearance, in which French national cultural influences are hardly recognisable. On the other hand, the internal processes and structures of the company are significantly more influenced by French cultural characteristics and standards. Qualitative individual interviews of employees from the middle management of Total provide the basis for the empirical examination. The results of these interviews confirm the findings of analytical studies, complement them with broader views and provide clear indications for the influence of national culture on the type of communication, hierarchical structure, as well as work organisation and decision making processes within the company.
In recent years, machine learning methods have taken a
firm place in society and their use continues to grow. The challenge
here is their little to almost non-existent interpretability. The aim of this
paper is to uncover the possibilities of interpreting machine learning. The
novel mechanisms and procedures of the emerging field of interpretable
machine learning are presented. In a two-part analysis, intrinsically
interpretable machine learning methods and established post-hoc interpretation
methods are examined in more detail. The focus is on their
functionality, properties and boundary conditions. Finally, a use case
will be used as an example to demonstrate how post-hoc interpretation
methods can contribute to the explainability of an image classifier and
systematically provide new insights into a model.
Inside the “Sandbox”
(2022)
Interpretable neural networks based on continuous-valued logic and multicriteria decision operators
(2020)
Application and machine learning methods for dynamic load point controls of electric vehicles (xEVs)
(2020)
From the customer's perspective, the appeal of electric vehicles depends on the simplicity and ease of their use, such as flexible access to electric power from the grid to recharge the batteries of their vehicles. Therefore, the expansion of charging infrastructure will be an important part of electric mobility. The related charging infrastructure is a big challenge for the load capacity of the grid connection without additional intelligent charge management: if the control of the charging process is not implemented, it is necessary to ensure the total of the maximum output of all xEVs at the grid connection point, which requires huge costs. This paper proposes to build a prediction module for forecasting dynamic charging load using machine learning (ML) techniques. The module will be integrated into a real charge management concept with optimization procedures for controlling the dynamic load point. The value of load forecasting through practical load data of a car park were taken to illustrate the proposed methods. The prediction performance of different ML methods under the same data condition (e.g., holiday data) are compared and evaluated.
In this presentation the actual state of the ongoing investigations of spray painting processes are summarized. Already at the end of the last century, first experimental and numerical work was done aiming to estimate the film thickness distribution and the transfer efficiency of spray painting processes of complex workpieces. First successful numerical simulations basically used the classical Euler-Langrange approach, in case of electrostatically supported atomizers extended by the necessary models for the charging of droplets and the interaction between charged droplets and electrical fields. Measured droplet size distributions and velocities near the atomizers have been applied as inlet conditions for the simulations.
Effects of Reusing Polyamide 12 Powder on the Mechanical Properties of Additively Manufactured Parts
(2022)
This paper describes the modelling, simulation and energy management of a fuel cell hybrid heavy-duty truck. For this purpose, a longitudinal dynamic model of a 26t truck was set up and the load requirement for the drive train was determined based on a driving cycle. To meet this load requirement as efficiently and dynamically as possible three different energy management strategies were implemented, tested and the impact on the overall system was analysed. In addition, the behaviour of the hybrid system with the various energy management strategies with different battery capacity is shown and analysed.
Application of Induction Thermography for Detection of Near Surface Defects in Steel Products
(2020)
Infusion stands are a central tool in health care. They are mainly found in hospitals, are
usually in use for many years, sometimes carry enormous loads (e.g. irrigation solutions,
perfusors), are also used by mobility-impaired persons to support walking, promote mobility
and self-determination during ongoing infusion therapy, and must be stored in sufficient
numbers. The weaknesses of the existing design of infusion stands are well known to users.
Nevertheless, for decades there has been no further development or adaptation to new,
changed requirements, let alone to new technical possibilities. In the short term, it makes
sense to further develop the existing infusion stand models in an evolutionary manner in
order to quickly produce an improvement in the functions and to mitigate the greatest
weaknesses. In this respect, the project team has shown in the context of technical
developments that there are very simple, but in terms of functionality, safety and data
protection very worthwhile adaptations that can and should be taken up by the industry. The
redesign of the basic element alone brings so much improvement for the use of this aid that
an industrialization in several senses – for the individual and society – would be more than
promising. With this research project, the project group would like to give an impulse for the
participatory involvement of users in assistive technology research. The user groups can
participate in different phases of the product development; at least the products should be
evaluated regularly in their application by the users.
The objective of this study is to investigate the influence of veneering technique (hand-layering vs. milling) on the fracture resistance of bi-layer implant-supported zirconia-based hybrid-abutment crowns. Mandibular molar copings were anatomically designed and milled. Copings were then veneered by hand-layering (HL) (n = 20) and milling using the Cad-On technique (LD) (n = 20). Crowns were cemented to zirconia hybrid-abutments. Ten samples of each group acted as a control while the remaining ten samples were subjected to fatigue in a chewing simulator. Crowns were loaded between 50 and 100 N for 1.2 million cycles under simultaneous temperature fluctuation between 5 and 55 °C. Crowns were then subjected to static load a to fracture test. Data were statistically analysed using the one-way ANOVA. Randomly selected crowns from each group were observed under scanning electron microscopy to view fractured surfaces. Study results indicate that during fatigue, LD crowns had a 100% survival rate; while HL crowns had a 50% failure rate. Fracture resistance of LD crowns was statistically significantly higher than that of HL crowns at the baseline and after fatigue (p ≤ 0.05). However, fatigue did not cause a statistically significant reduction in fracture resistance in both LD and HL groups (p > 0.05). Copings fractured in the LD crowns only and the fracture path was different in both LD and HL groups. According to the results, it was concluded that milled veneer implant-supported hybrid-abutment crowns exhibit significantly higher fracture resistance, and better withstand clinical masticatory loads in the posterior region compared to the hand-layered technique. Also, fatigue application and artificial aging caused no significant strength reduction in both techniques. Clinical significance: Different veneering techniques and materials (hand-layering or milling) act differently to clinical forces and environment and may be prone to early chipping during service. Therefore, practitioners are urged to consider the appropriate veneering protocol for posterior implant-supported hybrid-abutment restorations.
Our current mobility paradigm increasingly faces economic, ecological, and social limits in urban areas. The aim of this paper is to analyse if a fleet of shared autonomous electric vehicles (AEVs) can meet these challenges while satisfying the current requirements of privately-owned internal combustion engine vehicles (ICEVs). Therefore, analytical models have been developed to simulate and investigate the impacts of mobility behaviour in Berlin and Stuttgart (Germany). The collected data were used to calculate the fleet size, the energy consumption, the emission of particulate matter, nitrogen oxides, and the carbon footprint of different shared AEVs in comparison with privately owned ICEVs. The approach shows that the system of a shared AEV fleet could lower externalities (accident avoidance, traffic jams, free spaces, parking costs and lifetime losses) in cities and generate cost benefits for customers.
HElmar-LiMo 2040
(2023)
Approach to denoising of interfered 4-channel FMCW radar data using Convolutional Neural Network
(2023)
Approach to denoising of interfered 4-channel FMCW radar data using Convolutional Neural Network
(2023)
TCP Usage Guidance in the Internet of Things (IoT), draft-ietf-lwig-tcp-constrained-node-networks-13
(2020)
This document provides guidance on how to implement and use the Transmission Control Protocol (TCP) in Constrained-Node Networks(CNNs), which are a characteristic of the Internet of Things (IoT).Such environments require a lightweight TCP implementation and may not make use of optional functionality. This document explains a number of known and deployed techniques to simplify a TCP stack as well as corresponding tradeoffs. The objective is to help embedded
developers with decisions on which TCP features to use.
OAFuser: Online Adaptive Extended Object Tracking and Fusion using automotive Radar Detections
(2020)
This paper presents the Online Adaptive Fuser: OAFuser, a novel method for online adaptive estimation of motion and measurement uncertainties for efficient tracking and fusion by applying a system of several estimators for ongoing noise along with the conventional state and state covariance estimation. In our system, process and measurement noises are estimated with steady-state filters to obtain combined measurement noise and process noise estimators for all sensors in order to obtain state estimation with a linear Minimum Mean Square Error (MMSE) estimator and accelerating the system’s performance. The proposed adaptive tracking and fusion system was tested based on high fidelity simulation data and several real-world scenarios for automotive radar, where ground truth data is available for evaluation. We demonstrate the proposed method’s accuracy and efficiency in a challenging, highly dynamic scenario where our system is benchmarked with Multiple Model filter in terms of error statistics and run time performance.
Hot isostatic pressing can be utilized to reduce the anisotropic mechanical properties of Al–Si–Mg alloys fabricated by laser powder-bed fusion (L-PBF). The implementation of post processing densification processes can open up new fields of application by meeting high quality requirements defined by aircraft and automotive industries. A gas pressure of 75 MPa during hot isostatic pressing lowers the critical cooling rate required to achieve a supersaturated solid solution. Direct aging uses this pressure related effect during heat treatment in modern hot isostatic presses, which offer advanced cooling capabilities, thereby avoiding the necessity of a separate solution annealing step for Al–Si–Mg cast alloys. Hot isostatic pressing, followed by rapid quenching, was applied to both sand cast as well as laser powder-bed fused Al–Si–Mg aluminum alloys. It was shown that the critical cooling rate required to achieve a supersaturated solid solution is significantly higher for additively manufactured, age-hardenable aluminum alloys than it is for comparable sand cast material. The application of hot isostatic pressing can be combined with heat treatment, consisting of solution annealing, quenching and direct aging, in order to achieve both a dense material with a small number of preferred locations for the initiation of fatigue cracks and a high material strength.
Comparing multidimensional sensor data from vehicle fleets with methods of sequential data mining
(2020)
A matter of reality
(2018)
Due to the increasing relevance of data, more and more data from various sources is accumulated for a variety of purposes. At the same time, however, there is a shortage of data in areas where it is urgently needed. Particularly in the field of machine learning, there is a lack of good and usable training data. Therefore, this research paper is concerned with the virtual data acquisition for the training of neural networks. For this purpose, first an application was developed that aims to generate virtual, automatically labeled data. Subsequently, a neural network was trained on the generated virtual data and tested on real data.
A matter of reality
(2018)
Due to the increasing relevance of data, more and more data from various sources is accumulated for a variety of purposes. At the same time, however, there is a shortage of data in areas where it is urgently needed. Particularly in the field of machine learning, there is a lack of good and usable training data. Therefore, this research paper is concerned with the virtual data acquisition for the training of neural networks. For this purpose, first an application was developed that aims to generate virtual, automatically labeled data. Subsequently, a neural network was trained on the generated virtual data and tested on real data.
An optimal control problem for equations with p-structure and its finite element discretization
(2022)
Laser powder-bed fusion (LPBF) has significantly gained in importance and has become one of the major fabrication techniques within metal additive manufacturing. The fast cooling rates achieved in LPBF due to a relatively small melt pool on a much larger component or substrate, acting as heat sink, result in fine-grained microstructures and high oversaturation of alloying elements in the α-aluminum. Al-Si-Mg alloys thus can be effectively precipitation hardened. Moreover, the solidified material undergoes an intrinsic heat treatment, whilst the layers above are irradiated and the elevated temperature in the built chamber starts the clustering process of alloying elements directly after a scan track is fabricated. These silicon-magnesium clusters were observed with atom probe tomography in as-built samples. Similar beneficial clustering behavior at higher temperatures is known from the direct-aging approach in cast samples, whereby the artificial aging is performed immediately after solution annealing and quenching. Transferring this approach to LPBF samples as a possible post-heat treatment revealed that even after direct aging, the outstanding hardness of the as-built condition could, at best, be met, but for most instances it was significantly lower. Our investigations showed that LPBF Al-Si-Mg exhibited a high dependency on the quenching rate, which is significantly more pronounced than in cast reference samples, requiring two to three times higher quenching rate after solution annealing to yield similar hardness results. This suggests that due to the finer microstructure and the shorter diffusion path in Al-Si-Mg fabricated by LPBF, it is more challenging to achieve a metastable oversaturation necessary for precipitation hardening. This may be especially problematic in larger components.
Laser powder bed fusion has become one of the major techniques within metal additive manufacturing, especially when delicate structures and high geometric accuracy are concerned. Lately, the awareness of the material-specific macroscopic anisotropy has risen and led to widespread investigations on the static mechanical strength. However, little is known about the fracture behavior of the layer-wise fabricated metal components and their affinity of crack propagation between consecutive layers, which is particularly important for aluminium–silicon alloys containing embrittled zones in double-irradiated areas. A recent study indicated that there is a significant drop in fracture toughness in case the crack growth direction is parallel to the layering. To investigate this matter further and to shed light on the fracture toughness behavior in the range of a 0°–45° angle offset between the crack growth direction relative to the layering, notched samples with varying polar angles were subjected to mode I fracture toughness testing. Our results indicate that the fracture toughness is an almost-stable characteristic up to a mismatch of about 20° between the crack propagation path and the layering, at which point the fracture toughness decreases by up to 10%.