How AD Can Help Solve Differential-Algebraic Equations

A characteristic feature of differential-algebraic equations is that one needs to find derivatives of some of their equations with respect to time, as part of so called index reduction or regularisation, to prepare them for numerical solution. This is often done with the help of a computer algebra system. We show in two significant cases that it can be done efficiently by pure algorithmic differentiation. The first is the Dummy Derivatives method, here we give a mainly theoretical description, with tutorial examples. The second is the solution of a mechanical system directly from its Lagrangian formulation. Here we outline the theory and show several non-trivial examples of using the "Lagrangian facility" of the Nedialkov-Pryce initial-value solver DAETS, namely: a spring-mass-multipendulum system, a prescribed-trajectory control problem, and long-time integration of a model of the outer planets of the solar system, taken from the DETEST testing package for ODE solvers

Cloning, Heterologous Expression, and Characterization of a βκ-Carrageenase From Marine Bacterium Wenyingzhuangia funcanilytica: A Specific Enzyme for the Hybrid Carrageenan–Furcellaran

Carrageenan is a group of important food polysaccharides with high structural heterogeneity. Furcellaran is a typical hybrid carrageenan, which contains the structure consisted of alternative beta-carrageenan and kappa-carrageenan motifs. Although several furcellaran-hydrolyzing enzymes have been characterized, their specificity for the glycosidic linkage was still unclear. In this study, we cloned, expressed, and characterized a novel GH16_13 furcellaran-hydrolyzing enzyme Cgbk16A_Wf from the marine bacterium Wenyingzhuangia fucanilytica CZ1127. Cgbk16A_Wf exhibited its maximum activity at 50 degrees C and pH 6.0 and showed high thermal stability. The oligosaccharides in enzymatic products were identified by liquid chromatography coupled with high-resolution mass spectrometry (LC-HRMS) and nuclear magnetic resonance (NMR) spectroscopy. It was confirmed that Cgbk16A_Wf specifically cleaves the beta-1,4 linkages between beta-carrageenan and kappa-carrageenan motifs from non-reducing end to reducing end. Considering the structural heterogeneity of carrageenan and for the unambiguous indication of the specificity, we recommended to name the furcellaran-hydrolyzing activity represented by Cgbk16A as beta kappa-carrageenase instead of furcellaranase

Response of granite residual soil slopes under dry–wet cycles

Granite residual soil is widely distributed in the southern coastal areas of China, and the slopes of granite residual soil are prone to instability and failure under the alternating action of rainfall and drying, which will cause great disasters to human society. In order to study the response mechanism of granite residual soil slopes under the alternating action of rainfall–drying–static–rainfall (RDSR), this study conducted indoor scaling model tests to analyze the response during dry and wet cycles. This study presented the response process of the slope under the influence of dry and wet cycles and discussed the change laws of slope deformation, water content, and matric suction. The results show that, under the alternating action of rainfall–drying–static–rainfall, 1) the network cracks on the slope form a dominant channel for rainwater seepage, which is the main reason for the rapid decline in soil anti-sliding ability within a short time; 2) at a rainfall intensity of 1.7–2.4 mm/min, the erosion effect of rain on the slope is obviously stronger than that of osmotic erosion, and the surface erosion failure of the granite residual soil slope tends to occur without an obvious sliding surface; 3) after the loss of matric suction over a certain period, the phenomenon of channeling and loss failure on the slope serve as a sufficient condition for slope instability failure but is not a necessary condition. The above research results are expected to provide the basis and reference for preventing and controlling landslide hazards in granite residual soil slopes under similar conditions

The biomarkers of immune dysregulation and inflammation response in Parkinson disease

Parkinson’s disease (PD) is referring to the multi-systemic α-synucleinopathy with Lewy bodies deposited in midbrain. In ageing, the environmental and genetic factors work together and overactive major histocompatibility complex pathway to regulate immune reactions in central nerve system which resulting in neural degeneration, especially in dopaminergic neurons. As a series of biomarkers, the human leukocyte antigen genes with its related proteomics play cortical roles on the antigen presentation of major histocompatibility complex molecules to stimulate the differentiation of T lymphocytes and i-proteasome activities under their immune response to the PD-related environmental alteration and genetic variation. Furthermore, dopaminergic drugs change the biological characteristic of T lymphatic cells, affect the α-synuclein presentation pathway, and inhibit T lymphatic cells to release cytotoxicity in PD development. Taking together, the serum inflammatory factors and blood T cells are involved in the immune dysregulation of PD and inspected as the potential clinic biomarkers for PD prediction

Study on Current-Carrying Tribological Characteristics of C-Cu Sliding Electric Contacts under Different Water Content

Previous studies have often observed that moisture can promote the lubricity and wear resistance of carbon-metal contact pairs in purely mechanical conditions. However, the damage to pantograph carbon strips was found to be aggravated in rainfall conditions, leading to a much lower service life than anticipated. This suggests a novel influence mechanism of water on carbon-copper (C-Cu) contacts during current-carrying friction. In this paper, the influence mechanism of water on the current-carrying friction characteristics of carbon-copper contacts, including friction coefficient, wear loss, electrical contact resistance, and arc discharge characteristics, was studied under different current levels by controlling the water content of carbon sliders. The results show that the variation trend of current-carrying tribological parameters of C-Cu contacts with water content at 60–100 A is significantly different from that at 20–40 A, which is mainly the result of the competition of lubrication, cooling, and obstruction of current transmission by moisture. The abnormal wear of carbon sliders in the water environment occurs when the current is greater than 60 A, and the main reason for the abnormal wear is the intensification of discharge erosion. In addition, micro-crack propagation under high water content is an important factor in the deterioration of carbon strip properties

Multi-physics analysis of a novel circular pantograph catenary system for high-speed trains

PurposeIn high-speed trains, the energy is supplied from a high voltage catenary to the vehicle via a pantograph catenary system (PCS). Carbon pantograph strips must maintain continuous contact with the wire to ensure safety and reliability. The contact is often confined to a particular spot, resulting in excessive wear due to mechanical and thermal damage, exacerbated by the presence of an electric arc and associated electrochemical corrosion. The effectiveness and reliability of the PCS impacts on the performance and safety of HSTs, especially under high-speed conditions. To alleviate some of these adverse effects, this paper aims to propose a configuration where a circular PCS replaces the currently used pantograph strips.Design/methodology/approachTwo dynamic multi-physics models of a traditional PCS with a carbon strip and a novel PCS with a circular pantograph strip catenary system are established, and the electrical and mechanical characteristics of these two systems are compared. Moreover, a PCS experimental platform is designed to verify the validity and accuracy of the multi-physics model.FindingsA novel circular pantograph system is proposed in this paper to alleviate some of the shortcomings of the traditional PCS. Comparing with a traditional PCS, the circular PCS exhibits superior performance in both electromagnetic and thermal aspects.Originality/valueThe paper offers a new technical solution to the PCS and develops a dedicated multi-physics model for analysis and performance prediction with the aim to improve the performance of the PCS. The new system offers numerous benefits, such as less friction heat, better heat dispersion and improved catenary-tracking performance

An investigation into the characteristics of a novel rotatable pantograph catenary system for high-speed trains

High speed trains receive traction electrical energy from a high-voltage catenary via a pantograph catenary system (PCS). As the velocity of trains increases, the traditional PCSs face significant challenges, such as strong aero resistance under high-speed conditions, severe electrochemical corrosion caused by poor contact between the pantograph strip and the catenary, harmful wear both on the pantograph strip and the contact wire produced by high-speed sliding friction between them, etc. The effectiveness and reliability of the PCS has a direct impact on the performance and safety of the HTS power supply. In order to alleviate some of these bottleneck effects related to the operation of the currently used PCSs, especially under high-speed conditions, this paper proposes a novel configuration where rotatable pantograph rollers replace the currently used pantograph strips. As the sliding friction is now replaced by rotating friction, this has numerous benefits, such as less friction heat, better heat dispersion and improved catenary-tracking performance. Moreover, should the whole system be modularized, it could adapt to different levels of traction power through adjusting the number of rollers

Multiobjective Optimization of the Integrated Grounding System for High-Speed Trains by Balancing Train Body Current and Overvoltage

As a unique exit point for power supply systems of high-speed trains, the onboard grounding system plays a critical role in providing the path for returning the traction current to traction substations. The grounding system applies two grounding modes: the working grounding and the protective grounding, both of which share the power discharging channel, the steel rail. Current reflux normally appears between the working grounding point and the protective grounding point due to the wheel-rail coupling effect. The “train-rail” current reflux may result in the appearance of a “train body” (TB) current, which may cause the onboard partial temperature surging. Moreover, some operational conditions, such as raising pantographs or operating vacuum circuit breakers, may trigger TB overvoltage, which may threaten the safety of the onboard devices. In this article, a “rail-train” coupling grounding model is built to evaluate both the TB current and overvoltage based on the measured parameters. The particle swarm optimization (PSO) algorithm is adopted to optimize this model with the aim to achieve a satisfactory balance between the TB current and overvoltage. The main difficulties of this multivariable multiobjective task include that many grounding parameters are involved meanwhile restricting both TB current and overvoltage. Ultimately, optimal solutions are achieved, considering design demand

Multi-physics analysis and optimisation of high-speed train pantograph-catenary systems allowing for velocity skin effect

A pantograph-catenary system (PCS) - an essential component to supply a high-speed train (HST) - faces a variety of new challenges due to the continuously increasing train speeds. The HST traction system receives power via an electrical contact between the pantograph strip and the high-voltage contact wire. This electrical contact is subject to serious mechanical shocks and significant electrochemical corrosion, making the modelling of the dynamic processes complicated, especially under high-speed and heavy-load conditions. The damage to the PCS - which is particularly noticeable at the edges of the pantograph strip - may become severe as the speed of the train rises. Moreover, as the speed increases, the distribution of the electrical current in the strip becomes uneven due to the velocity skin effect (VSE). To assess the impact of the VSE on the performance of PCSs, a multi-physics model has been created and is reported in this study. The model has been validated through experiments and the main aspects of its functionality - such as the VSE, friction, and air convection - have been identified and analysed at different speeds. The impact of speed on the traction current and the behaviour of thermal sources have been explored. With the increasing speed, the phenomenon of current clustering at the trailing edge of the strip becomes quite dramatic, resulting in a thermal surge in the region of the strip with high current density. To mitigate the negative impact caused by VSE in the PCSs, an improved kriging optimisation methodology has been utilised to optimise the parameters of the PCS. Recommendations regarding the optimal design of the PCS are put forward to improve the current-carrying performance and reduce the local temperature rise in the strip.</p

3D modelling of an integrated grounding system for high-speed trains considering rail-train current reflux

The integrated grounding system for high-speed trains consists of two parts: on-board dynamic and fixed terrestrial grounding sub-systems. The on-board grounding sub-system contains working and protective grounding modes, both of which share the rails as the common path for discharging current. Current reflux occurs frequently, which can contribute to the circumflux in the ‘train body – grounding wheel set – rail’ circle, due to the dynamic coupling effects between grounding points. The path and value of the circumflux vary transiently because of the changing impedance between the grounding wheels and rail under the dynamic conditions. In our previous work, a 2D grounding model was built to evaluate the impact from the current reflux, but the lateral and vertical impedances of train bodies and rails were ignored. In practice – when the protective and working grounding is applied independently to rails on the left- and right-hand side separately – the current reflux can be restricted by benefitting from the impedance existing in train bodies and rails. It therefore becomes essential to build a 3D ‘train–rail’ coupling grounding model accounting for the full-dimension impedances, while different grounding distribution protocols is considered to improve the grounding performance