Minimum value assured by a method to determine gold in alloys by using laser-induced breakdown spectroscopy and partial least-squares calibration model

A procedure for estimating the minimum value assured by an analytical method has been developed. It is applied to the determination of gold in jewellery alloys by means of a recently proposed spectroscopy technique. The laser-induced breakdown spectroscopic data of 17 gold alloys, with gold concentration ranging between 50 and 100% were used as calibration set for carrying out the partial least-squares regression (PLS). Ninety alloys, with known gold concentration, were used to evaluate the method’s accuracy. Finally, the minimum guaranteed value of the gold content was analysed, taking into account the values for gold hallmark in Spanish regulations.     

Atomistic understanding of the C·T mismatched DNA base pair tautomerization via the DPT: QM and QTAIM computational approaches

It was established that the cytosine·thymine (C·T) mismatched DNA base pair with cis‐oriented N1H glycosidic bonds has propeller‐like structure (|N3C4C4N3| = 38.4°), which is stabilized by three specific intermolecular interactions–two antiparallel N4H…O4 (5.19 kcal mol^?1) and N3H…N3 (6.33 kcal mol^?1) H‐bonds and a van der Waals (vdW) contact O2…O2 (0.32 kcal mol^?1). The C·T base mispair is thermodynamically stable structure (ΔG_int = ?1.54 kcal mol^?1) and even slightly more stable than the A·T Watson–Crick DNA base pair (ΔG_int = ?1.43 kcal mol^?1) at the room temperature. It was shown that the C·T ? C*·T* tautomerization via the double proton transfer (DPT) is assisted by the O2…O2 vdW contact along the entire range of the intrinsic reaction coordinate (IRC). The positive value of the Grunenberg's compliance constants (31.186, 30.265, and 22.166 Å/mdyn for the C·T, C*·T*, and TS_{C·T ? C*·T*}, respectively) proves that the O2…O2 vdW contact is a stabilizing interaction. Based on the sweeps of the H‐bond energies, it was found that the N4H…O4/O4H…N4, and N3H…N3 H‐bonds in the C·T and C*·T* base pairs are anticooperative and weaken each other, whereas the middle N3H…N3 H‐bond and the O2…O2 vdW contact are cooperative and mutually reinforce each other. It was found that the tautomerization of the C·T base mispair through the DPT is concerted and asynchronous reaction that proceeds via the TS_{C·T ? C*·T*} stabilized by the loosened N4? H? O4 covalent bridge, N3H…N3 H‐bond (9.67 kcal mol^?1) and O2…O2 vdW contact (0.41 kcal mol^?1). The nine key points, describing the evolution of the C·T ? C*·T* tautomerization via the DPT, were detected and completely investigated along the IRC. The C*·T* mispair was revealed to be the dynamically unstable structure with a lifetime 2.13·× 10^?13 s. In this case, as for the A·T Watson–Crick DNA base pair, activates the mechanism of the quantum protection of the C·T DNA base mispair from its spontaneous mutagenic tautomerization through the DPT. © 2013 Wiley Periodicals, Inc.     

An Improved Computational Strategy to Estimate Residual Stresses from Crack Compliance Data

The successive cracking (crack compliance) method is a destructive technique aimed at determination of residual stresses in various structural members. The laboratory measurements performed during extension of a crack are followed by a computational analysis. We propose a modification of the numerical approach in order to simplify the method and improve its accuracy. The basic idea of the proposed modification is to approximate plastic strains rather than the residual stresses directly. Furthermore, we use the goal oriented adaptive finite element method that generates optimal meshes for evaluation of strains at specific points.     

ENVIRONMENTAL COMPLIANCE AND OPTIMAL OIL AND GAS EXPLOITATION

This paper examines the impacts of environmental regulations on firms in the oil and gas industry. A model is developed using optimal control theory, which extends the existing models by incorporating the environmental compliance costs into the exploration and production stages. An approach for measuring the cumulative impacts of these regulations on the firm's exploration and production is presented. The results indicate that rising environmental compliance costs lead to reductions in investment and production, and the alteration of investment and production profiles. This implies that less resources will be developed and associated economic benefit will decline. Therefore, it is vital for policy makers to consider carefully whether the perceived environmental benefits derived from these regulations justify associated compliance costs.     

Crack-compliance method for assessing residual stress due to loading/unloading history: Numerical and experimental analysis

The understanding of how materials fail is still today a fundamental research problem for scientist and engineers. The main concern is the assessment of the necessary conditions to propagate a crack that will eventually lead to failure. Nevertheless, this kind of analysis tends to be more complicated, when a prior loading history in the material is taken into consideration and it will be extremely important to recognize all the factors involved in this process. In this work, a numerical simulation and experimental evaluation of the induction of residual stresses, which change the crack initiation conditions, in a modified compact tensile specimen is presented. Several analyses were carried out; an initial evaluation (numerical and experimental) was performed in a specimen without a crack and this was used for the estimation of a residual stress field produced by an overload; three more cases were simulated and a crack was introduced in each specimen (1 mm, 5 mm and 10 mm long, respectively). The overload was then applied to set up a residual stress field into the component; furthermore, in each case the Crack Compliance Method (CCM) was applied to measure the induced residual stress field. By performing this numerical simulation, the accuracy of the CCM can be evaluated and later corroborated by experimental procedure. On the other hand, elastic-plastic finite element analysis was utilized for the residual stress estimation. The analyses were based on the mechanical properties of a biocompatible material (AISI 316L). The obtained results provided significant data about diverse factors, like; the manner in which a residual stress field could modify the crack initiation conditions, the convenient set up for the induction of a beneficial residual stresses field, as well as useful information that can be applied for the experimental implementation in this research. Finally, some beneficial aspects of residual stresses are discussed.     

考虑非概率可靠性的结构柔顺度拓扑优化设计

实际工程中广泛存在的不确定性可能对结构拓扑设计产生重要影响。基于不确定性的多椭球凸模型描述及非概率可靠性指标的定义,建立了材料体积约束和不确定参数范围约束下、结构柔顺度极小极大化为目标的非概率可靠性拓扑优化数学模型。结合移动渐进线方法,基于单循环策略实现该连续Minimax优化问题的求解。经典算例尺寸优化设计结果说明了...     

Numerical analysis of a contact problem including bone remodeling

In this work, a contact problem between an elastic body and a deformable obstacle is numerically studied. The bone remodeling of the material is also taken into account in the model and the contact is modeled using the normal compliance contact condition. The variational problem is written as a nonlinear variational equation for the displacement field, coupled with a first-order ordinary differential equation to describe the physiological process of bone remodeling. An existence and uniqueness result of weak solutions is stated. Then, fully discrete approximations are introduced based on the finite element method to approximate the spatial variable and an Euler scheme to discretize the time derivatives. Error estimates are obtained, from which the linear convergence of the algorithm is derived under suitable regularity conditions. Finally, some 2D numerical results are presented to demonstrate the behavior of the solution.     

基于扩展多尺度有限元法的含液闭孔材料拓扑优化

基于扩展多尺度有限元方法,提出了含液闭孔结构多尺度拓扑优化方法。该多尺度优化方法旨在研究含液闭孔胞元布局对整体含液闭孔结构力学性能的影响。首先针对含液闭孔结构的整体结构柔顺性问题,采用类似SIMP模型对结构的宏观粗网格等效刚度阵进行插值,建立含液闭孔结构柔顺性的拓扑优化列式;其次,针对含液闭孔材料能够利用胞体内部液体腔体积增量产生变形的特性,提出含液闭孔材料柔性机构的概念,并以结构指定位置方向输出位移为目标,建立液体体积膨胀作用下的含液闭孔柔性机构多尺度拓扑优化数学模型。本文基于自主软件平台SiPESC完成了程序研发,并通过数值算例验证了所提出的拓扑优化方法的有效性。     

Screw theoretic view on dynamics of spatially compliant beam

Beams with spatial compliance can be deformed as bending in a plane, twisting, and extending. In terms of the screw theory on rigid body motions, the concept of ＂deflection screw＂ is introduced, a spatial compliant beam theory via the deflection screw is proposed, and the spatial compliance of such a beam system is presented and analysed based on the material theory and fundamental kinematic assumptions. To study the dynamics of the spatially compliant beam, the potential energy and the kinetic energy of the beam are discussed by using the screw theory to obtain the Lagrangian. The Rayleigh-Ritz method is used to compute the vibrational frequencies based on discussions of boundary conditions and shape functions. The eigenfrequencies of the beam with spatial compliance are compared with those of individual deformation cases, pure bending, extension, or torsion. Finally, dynamics of a robot with two spatial compliant links and perpendicular joints is studied using the spatial compliant beam theory. Coupling between the joint rigid body motions and the deformations of spatial compliant links can easily be found in dynamic simulation. The study shows the effectiveness of using the screw theory to deal with the problems of dynamic modeling and analysis of mechanisms with spatially compliant links.