3D numerical simulation of drilling residual stresses

Drilling can affect the integrity of the surface of a mechanical component and reduce its fatigue life. Thus, drilling parameters such as lubrication or drilling velocity must be optimized to ensure a satisfactory residual mechanical state of the hole surfaces. Unfortunately, experimental tests are time consuming and it is not easy to observe the cutting process because of the confinement of the drill zone. The literature does not exhibit any numerical simulation capable of simulating 3D thermomechanical phenomena in the drill zone for large depth holes. Therefore, residual stresses cannot be easily simulated by means of the sole drilling parameters. The aim of this article is to propose a new numerical approach to compute drilling residual stresses for large-depth holes. A first simulation is developed to simulate heat transfer by means of a 3D thermoviscoplastic simulation in a new Rigid-ALE framework allowing the use of large calculation time steps. Then, a time interpolation and a spatial projection are implemented to rebuild the Lagrangian thermal history of the machined component. Finally, a thermo-elastoplastic simulation is carried out to compute residual stresses in the final workpiece. In this paper, the method is applied to a 316L austenitic stainless steel in the case of an unlubricated hole. The computed residual stresses are compared to experimental measurements.     

The stress concentration near a rigid line inclusion in a prestressed, elastic material. Part II.: Implications on shear band nucleation, growth and energy release rate

The full-field and asymptotic solutions derived in Part I of this article (for a lamellar rigid inclusion, embedded in a uniformly prestressed, incompressible and orthotropic elastic sheet, subject to a far-field deformation increment) are employed to analyse shear band formation, as promoted by the near-tip stress singularity. Since these solutions involve the prestress as a parameter, stress and deformation fields can be investigated near the boundary of ellipticity loss (but still within the elliptic range). In the vicinity of this boundary, the incremental stress and displacement fields evidence localized deformations with patterns organized into shear bands, evidencing inclinations corresponding to those predicted at ellipticity loss. These localized deformation patterns are shown to explain experimental results on highly deformed soft materials containing thin, stiff inclusions. Finally, the incremental energy release rate and incremental J-integral are derived, related to a reduction (or growth) of the stiffener. It is shown that this is always positive (or negative), but tends to zero approaching the Ellipticity boundary, which implies that reduction of the lamellar inclusion dies out and, simultaneously, shear bands develop.     

Simple,Efficient, and Convenient One‐Pot Synthesis of Imidazole Derivatives in the Presence of Nanosilica‐supported Imidazolium Ionic Liquid as a Catalyst

An efficient and simple synthesis of 2,4,5‐trisubstituted imidazoles is achieved by three‐component cyclocondensation of benzil, aldehyde, and ammonium acetate by using nanosilica‐supported imidazolium ionic liquid as a catalyst under solvent‐free conditions. The key advantages of this process are high to excellent yields, short reaction time, easy work‐up, and the reusability of the catalyst.     

Study on the green click-chemistry synthesis of 4-trifluoroacetyl-1,2,3-triazoles

A metal-free and solvent free click-chemistry procedure has been revealed for the synthesis of 4-trifluoroacetyl-1,2,3-triazoles from corresponding azides and alkyne with high yield and selectivity. The pure products could be easily obtained via crystallization of the reaction mixture (standing for 1 day). Among the 4-trifluoroacetyl-1,2,3-triazoles, 3ba showed the best anticancer activity against HepG2 cell with IC₅₀ of 0.0267?μmol/ml. This method has the advantages of less pollution, low cost, simple treatment and more efficiency.     

Liquidation risk in insurance under contemporary regulatory frameworks

In traditional research in insurance and finance, a firm is subject to immediate liquidation when its asset value process drops to an absorbing low barrier. This treatment greatly simplifies research but largely ignores the complexity of the liquidation procedure in the real world. In banking and finance, many researchers have taken into account the features of Chapter 7 liquidation and Chapter 11 reorganization of the U.S. Bankruptcy Code. Also, there have been similar discussions in insurance regulation, but few works have been done to achieve a quantitative understanding of the liquidation risk in insurance under contemporary regulatory frameworks. In this paper, we quantify the rehabilitation proceeding in insurance, which is akin to Chapter 11 reorganization of the U.S. Bankruptcy Code, and we conduct a probabilistic analysis of the liquidation risk of an insurance company having the option of rehabilitation. In doing so, we construct a three-barrier model to describe the solvent and insolvent states in which the surplus process follows different time-homogeneous diffusions. We derive analytical expressions for the liquidation probability and the Laplace transform of the liquidation time with a fixed grace period and then extend the study to the case with independent exponentially distributed grace periods. If further restricted to the constant elasticity of variance (CEV) framework, the obtained formulas become completely explicit.     

Solvent generated liquid-liquid chromatography with nonaqueous ternary systems

Summary It is demonstrated that highly stable and reproducible LLC-columns can be prepared by generating the stationary phase dynamically by the mobile phase. It is shown that such a solvent generated liquid-liquid chromatography can be realized if two conditions are fulfilled: one phase of a liquid-liquid system must be used as mobile phase and the solid support must be better wetted by the other phase of the system. This general principle of solvent generated LLC was investigated for nonaqueous ternary liquid-liquid systems. The liquid-liquid retention mechanism was verified by correlation of chromatographic and partition data. It is shown that significant changes in the retention characteristics occur when going from the liquid-solid to the liquid-liquid retention mode for systems having the same qualitative composition.Presented at the 14th International Symposium on Chromatography London, September, 13–17, 1982.     

TheT 1 state ofp-nitroaniline and related molecules: A CNDO/S study

The nature of the lowest energy triplet state (T ₁) ofp-nitroaniline (PNA), N,N-dimethyl-p-nitroaniline (DMPNA) and nitrobenzene (NB) is reexamined using the semiempirical CNDO/S-CI method with selected parameter options. The present results indicate that in the case of theunperturbed molecules the short-axis polarized * n() triplet largely localized at the acceptor end of the molecule may lie lower in energy than the triplet manifold counterpart of the intense intramolecular charge-transferD ⁺ A ^–singlet excitation. Computations suggest, however, that polar solvents strongly stabilize the PNA and DMPNA * charge-transfer triplet relative to other excitations, whereas specific solvent hydrogen-bonded interactions stabilize the * n() triplet of NB below those of * character. These assignments allow a rationalization of phosphorescence lifetime data,T _n T ₁ absorption measurements and relative photochemical behavior.     

Residual methods for the large-scale matrix pth root and some related problems

The problem of finding the pth root of a matrix has received special attention in the last few years. Standard approaches for this problem include and combine some variations of Newton’s method, which in turn involve matrix factorizations that, in general, are not suitable for large-scale problems. Motivated by some recently developed low-cost iterative schemes for nonlinear problems, we consider and analyze specialized residual methods that only require a few matrix-matrix products per iteration, and hence are suitable for the large-scale case. As a by-product we also discuss the advantages of residual methods for general nonlinear problems whose variables separate. Preliminary and encouraging numerical results are presented for computing pth roots of large-scale symmetric and positive definite matrices, for different values of p.     

溶剂对TNS与ANS荧光光谱的影响

研究了两种光谱探针TNS与ANS在不同溶剂中的荧光光谱,为此类荧光探针的应用奠定了一定的基础。结果表明溶剂对TNS与ANS荧光光谱的影响是一般溶剂效应与特殊溶剂效应共同作用的结果。     

Goodness-of-fit inference for the Cox–Aalen additive–multiplicative regression model

The Cox–Aalen additive–multiplicative intensity model of Scheike and Zhang (Scand. J. Statist. 29, 2002) is considered. We study goodness-of-fit tests based on the stratified martingale residual process. Asymptotic distribution of the process is derived and the Kolmogorov–Smirnov type test is constructed. Several ways of overcoming the problem of complexity of the limiting distribution are discussed. The results are accompanied by a small Monte Carlo study.