An unconditionally stable explicit algorithm for structural dynamics

This paper presents an unconditionally stable explicit algorithm for the direct integration of the structural dynamic equations of motion. The algorithm is restricted to a diagonal mass matrix and positive definite symmetric stiffness and damping matrices. The algorithm is based on splitting the stiffness and damping matrices into strictly lower and upper trangular form. Unconditional stability is proven, but only for the undamped case and a completely symmetric splitting of the stiffness matrix. An alternate splitting method is also presented and numerical examples indicate superior performance over the symmetric splitting, but only a conditional stability. A spring-mass-dashpot model is used to illustrate the algorithm.     

Laser microwave double-resonance experiment on trapped 113Cd+ ions

The possibility of using Cd⁺ ions as a microwave frequency standard whose light source is an all-solid state UV laser system is presented. The ground-state hyperfine splitting of trapped ¹¹³Cd⁺ ions is measured using an RF trap technique. The transition is detected using a laser microwave double-resonance method in the presence of He buffer gas. The splitting is determined to be 15 199 862 858(2) Hz. The preciseness of the value was improved over that in previous data by seven orders of magnitude. A light source of 214.5 nm is being developed by the authors for optical pumping and laser-cooling of Cd⁺ ions whose fundamental oscillator is based on diode lasers     

New processes for recovery of acetic acid from waste water

This paper addresses an industrially important problem of acetic acid recovery from a waste water stream via reactive distillation. The presence of a three-phase regime on the column stages due to a liquid–liquid phase split between aqueous and organic phases is a typical characteristic of this process. A modern modeling approach is presented to detect the existence of potential phase splitting in this column. A good agreement of a phase splitting model with the literature data has been shown. A theoretical study for the recovery of acetic acid from its 30 wt% aqueous solution by esterification with n-butanol is presented. Alternate column structures were investigated and two structures rendering theoretically close to 100% conversion of acetic acid were identified. The dynamic simulations were performed on proposed structures to see transient responses wrt. to common process disturbances. The work was originally presented at the PRES-2006 (27–31 August) conference in Prague, Czech Republic.     

PVU and wave-particle splitting schemes for Euler equations of gas dynamics

A new way of flux-splitting, termed as the wave-particle splitting is presented for developing upwind methods for solving Euler equations of gas dynamics. Based on this splitting, two new upwind methods termed as Acoustic Flux Vector Splitting (AFVS) and Acoustic Flux Difference Splitting (AFDS) methods are developed. A new Boltzmann scheme, which closely resembles the wave-particle splitting, is developed using the kinetic theory of gases. This method, termed as Peculiar Velocity based Upwind (PVU) method, uses the concept of peculiar velocity for upwinding. A special feature of all these methods is that the unidirectional and multidirectional parts of the flux vector are treated separately. Extensive computations done using these schemes demonstrate the soundness of the ideas.     

Analysis of a buffer strip laminate with fiber and matrix damage and interlaminar debonding

A shear lag solution for a hybrid buffer strip laminate containing initial damage in the form of a rectilinear notch, matrix splitting and interlaminar debonding is presented. The model is a unidirectional monolayer with two symmetric constraint layers that represent angle plies. The intent of the analysis is to estimate the remote strain required to propagate the initial damage and/or to fail the laminate catastrophically. The analytical solution has a set of integral equations in which material and geometric parameters appear explicitly. Some typical results are presented for a graphite/epoxy panel having either high strength and low modulus or low strength and low modulus buffer strips. Matrix damage, angle plies, and interlaminar debonding are shown to affect the damage tolerance capability of buffer strip laminates.     

Flux difference splitting for the Euler equations in generalised coordinates using a local parameterisation of the equation of state

An efficient algorithm based on flux difference splitting is presented for the solution of the three-dimensional Euler equations of gas dynamics in a generalised coordinate system with a general equation of state. The scheme is based on solving linearised Riemann problems approximately and in more than one dimension incorporates operator splitting. The algorithm uses a local parameterisation of the equation of state and as a consequence requires only one function evaluation in each computational cell. The scheme has good shock capturing properties and the advantage of using body-fitted meshes. Numerical results are shown for Mach 8 flow of equilibrium air past a circular cylinder.This work forms part of the research programme for the Institute of Computational Fluid Dynamics at the Universities of Oxford and Reading and was funded by AWRE, Aldermaston under Contract No. NSN/13B/2A88719.     

A splitting algorithm for simulation-based optimization problems with categorical variables

In the design of complex products, some product components can only be chosen from a finite set of options. Each option then corresponds to a multidimensional point representing the specifications of the chosen components. A splitting algorithm that explores the resulting discrete search space and is suitable for optimization problems with simulation-based objective functions is presented. The splitting rule is based on the representation of a convex relaxation of the search space in terms of a minimum spanning tree and adopts ideas from multilevel coordinate search. The objective function is underestimated on its domain by a convex quadratic function. The main motivation is the aim to find—for a vehicle and environment specification—a configuration of the tyres such that the energy losses caused by them are minimized. Numerical tests on a set of optimization problems are presented to compare the performance of the algorithm developed with that of other existing algorithms.     

Approximate Riemann solutions of the two-dimensional shallow-water equations

A finite-difference scheme based on flux difference splitting is presented for the solution of the two-dimensional shallow-water equations of ideal fluid flow. A linearised problem, analogous to that of Riemann for gasdynamics, is defined and a scheme, based on numerical characteristic decomposition, is presented for obtaining approximate solutions to the linearised problem. The method of upwind differencing is used for the resulting scalar problems, together with a flux limiter for obtaining a second-order scheme which avoids non-physical, spurious oscillations. An extension to the two-dimensional equations with source terms, is included. The scheme is applied to a dam-break problem with cylindrical symmetry.     

Experimental research on the critical conditions and critical equation of chip splitting when turning a C45E4 disc workpiece symmetrically with a high-speed steel double-edged turning tool

Chip splitting is a natural chip separation phenomenon that can significantly reduce cutting energy consumption. To reveal its occurrence mechanisms, a method for obtaining its critical conditions through cutting experiments and establishing its critical equation is proposed in this paper. Based on previous research results regarding the relationship between chip removal interference and chip splitting, the control variables that affect chip splitting are identified by analyzing a geometric model of the cutting process. A total of 366 experiments on turning a C45E4 disc workpiece with a high-speed steel double-edged turning tool based on the dichotomy method were conducted and 51 experimental data on chip splitting critical conditions were obtained. According to these experimental data, a critical equation expressed by a finite-degree polynomial with a cutting thickness equal to the other control variables was fitted. By analyzing the critical surface, it was determined that chip splitting followed a law in which the smaller the cutting thickness and the larger the absolute value of the negative rake angle, edge angle, and edge inclination of the tool, the more likely chip splitting was to occur. Through a verification experiment, it was determined that the derived critical equation could accurately predict the occurrence of 95.24% of chip splitting. It was also determined that the occurrence of chip splitting led to a cliff-like drop in the specific total cutting force with a maximum drop of 51.23%. This research lays a foundation for the rational utilization of chip splitting in tool structure parameter design and cutting parameter energy saving optimization.The full text can be downloaded at https://link.springer.com/article/10.1007/s40436-021-00378-7     

EPR of Graphite and Fullerenes

Analysis of the EPR results for graphite and fullerenes has led to the development of a model for the g-factor in follerene based on the analogy between graphite and fullerene. Pressure dependence of g-factor in C₆₀ powder confirms the validity of this model. ¹³C hyperfine splitting of_a0.36 mT in pristine fullerene is also reported. The g-factors of C₆₀^-1 and C₆₀^-3 in a solution and in a different K°C₆₀ fullerides are presented. C₆₀⁺ⁿ states should be described by the spectroscopic splitting factor larger than that of a free spin.     

光电催化分解水用可见光响应型氧化物光阳极的改性研究进展

光电催化分解水是绿色制氢的重要途径之一。由于水氧化反应在热力学和动力学上极难发生, 因而制备高效光阳极成为光电催化分解水的瓶颈问题。为满足未来商业化应用需求(太阳能制氢转换效率>10%), 研制高效光阳极成为亟待解决的关键难题。研究表明, 具有价格低廉、吸光性良好、毒性小且光电化学稳定性高等突出优点的可见光响应型氧化物: WO₃、α-Fe₂O₃和BiVO₄,是目前光电催化分解水用光阳极的理想材料。在过去几十年里, 围绕该类氧化物光阳极的研究已取得显著成果。本文重点论述了高效光电催化分解水制氢用WO₃、α-Fe₂O₃和BiVO₄光阳极改性的研究进展。另外, 文中简述了此类可见光响应型氧化物光阳极在无偏压光电催化分解水中的研究现状, 并提出其存在的问题及未来发展方向。     

A finite fracture mechanics formulation to predict fibre kinking and splitting in CFRP under combined longitudinal compression and in-plane shear

An analytical model to predict fibre kinking and splitting in CFRP under combined longitudinal compression and in-plane shear is presented. The model is based on the fracture mechanics of microcracks and split formation between the fibres during kink-band formation or splitting. A simple criterion which can readily be used in design is derived from the model. The predictions from this criterion are compared with experimental data and numerical results available in the literature, and are found to be in good agreement.     

Lot Splitting Under Learning Effects with Minimal Revenue Requirements and Multiple Lot Types

The lot splitting problem in the presence of learning is addressed. This work is an extension of an approach proposed for splitting in the case of a single item. We address the issue of a minimal revenue requirement from partial deliveries until a predetermined time. This is achieved by imposing a constraint on what is originally an unconstrained optimization problem. When sublots of different items are involved, the optimal splitting decisions have to be combined with the sequencing of the deliveries. Numerical examples are presented to demonstrate the proposed approach.     

Influence of mix proportions and curing conditions on tensile splitting strength of high strength concretes

The effect of the composition of high strength concretes with low water to binder ratio and silica fume on the development of splitting tensile strength was studied. A statistical approach was employed to develop formulation which could adequately describe the relations between splitting tensile strength and the concrete composition, when cured in two different regimes: water curing at 20°C and sealed curing at 30°C. Autogenous shrinkage was induced in the second type of curing but was largely eliminated in the first one. The relations were presented as nomograms which could be used as a basis for mix design. The correlation between tensile splitting strength and compressive strength could not be described in terms of a simple linear relation with a characteristic constant. For the range of variables studied, the ratio between tensile and compressive strength varied over a large range of 0.08 to 0.12. As a result, the relations developed here for tensile strength are quite different in nature than those for compressive strength in a previous study. Analysis of the data suggest that tensile strength is sensitive to effects which induce autogenous shrinkage to a much greater extent than compressive strength. It is proposed that this may be the main reason for the different trends observed for the relations between the composition of the low water/binder ratio concretes and their compressive and tensile strength.     

Blister delamination analysis in fibre reinforced plastics using beam-column theory with an energy release rate criterion

A theoretical analysis is presented for the crack propagation of a layered fibre reinforced plastic strip in compression, in the presence of a blister. Account is taken of a resin rich layer at the delaminating edge and of an initial deflection in the blister geometry. A typical set of design curves is given which shows the influence of blister length, applied strain and resin stiffness on loads required for splitting.     

A Splitting Algorithm For Identifying Qualitative Variables Related To A Dichotomous Dependent Variable

A splitting algorithm based on Shannon measure of mutual information is presented. The algorithm is designed to select individual levels of qualitative variables that are significantly related to a skewed dichotomous dependent variable. The use of this technique in conjunction with a grouping algorithm based on similar principles is illustrated with an actual application.     

Self-Supported Transition-Metal-Based Electrocatalysts for Hydrogen and Oxygen Evolution

Electrochemical water splitting is a promising technology for sustainable conversion, storage, and transport of hydrogen energy. Searching for earth-abundant hydrogen/oxygen evolution reaction (HER/OER) electrocatalysts with high activity and durability to replace noble-metal-based catalysts plays paramount importance in the scalable application of water electrolysis. A freestanding electrode architecture is highly attractive as compared to the conventional coated powdery form because of enhanced kinetics and stability. Herein, recent progress in developing transition-metal-based HER/OER electrocatalytic materials is reviewed with selected examples of chalcogenides, phosphides, carbides, nitrides, alloys, phosphates, oxides, hydroxides, and oxyhydroxides. Focusing on self-supported electrodes, the latest advances in their structural design, controllable synthesis, mechanistic understanding, and strategies for performance enhancement are presented. Remaining challenges and future perspectives for the further development of self-supported electrocatalysts are also discussed.     

Measurement of fracture toughness by nanoindentation methods: Recent advances and future challenges

In this paper, we describe recent advances and developments for the measurement of fracture toughness at small scales by the use of nanoindentation-based methods including techniques based on micro-cantilever, beam bending and micro-pillar splitting. A critical comparison of the techniques is made by testing a selected group of bulk and thin film materials. For pillar splitting, cohesive zone finite element simulations are used to validate a simple relationship between the critical load at failure, the pillar radius, and the fracture toughness for a range of material properties and coating/substrate combinations. The minimum pillar diameter required for nucleation and growth of a crack during indentation is also estimated. An analysis of pillar splitting for a film on a dissimilar substrate material shows that the critical load for splitting is relatively insensitive to the substrate compliance for a large range of material properties. Experimental results from a selected group of materials show good agreement between single cantilever and pillar splitting methods, while a discrepancy of ∼25% is found between the pillar splitting technique and double-cantilever testing. It is concluded that both the micro-cantilever and pillar splitting techniques are valuable methods for micro-scale assessment of fracture toughness of brittle ceramics, provided the underlying assumptions can be validated. Although the pillar splitting method has some advantages because of the simplicity of sample preparation and testing, it is not applicable to most metals because their higher toughness prevents splitting, and in this case, micro-cantilever bend testing is preferred.     

对称复合板冷轧变形模式的上限分析

应用上限法建立了对称复合板冷轧变形模式的数学模型,在此基础上对软复层复合板在不同条件下冷轧时的变形模式进行了计算,给出了相关计算曲线。计算结果表明,依过程参数的不同,软复层复合板冷轧时存在比例变形、界面撕开及不稳定变形三种可能的变形模式。加工率越大、界面结合强度越高、基体材料的相对强度和复合板轧后的相对厚度越小,则均匀变形区越大,界面撕开区越小。不稳定变形区仅在基体材料的相对厚度和相对强度足够大时才存在。      

Nonlinear fracture mechanics and plasticity of the split cylinder test

The split cylinder test is subjected to an analysis combining nonlinear fracture mechanics and plasticity. The fictitious crack model is applied for the analysis of splitting tensile fracture, and the Mohr-Coulomb yield criterion is adopted for modelling the compressive crushing/sliding failure. Two models are presented, a simple semi-analytical model based on analytical solutions for the crack propagation in a rectangular prismatic body, and a finite element model including plasticity in bulk material as well as crack propagation in interface elements. A numerical study applying these models demonstrates the influence of varying geometry or constitutive properties. For a split cylinder test in load control it is shown how the ultimate load is either plasticity dominated or fracture mechanics dominated. The transition between the two modes is related to changes in geometry or constitutive properties. This implies that the linear elastic interpretation of the ultimate splitting force in term of the uniaxial tensile strength of the material is only valid for special situations, e.g. for very large cylinders. Furthermore, the numerical analysis suggests that the split cylinder test is not well suited for determining the tensile strength of early age or fibre reinforced concrete.