Validation of the thermomechanical microstructural model for closed-die forging

The objective of the paper is the assessment of the predictive ability of the thermomechanical-microstructural model for the closed-die forging process. The model combines the rigid-plastic flow formulation with the finite element solution of the Fourier equation with the closed-form equations describing processes of recrystallization and grain growth. Experimental validation of the mechanical and thermal components of the model is presented in earlier publications; present work focuses on the microstructural part. Experiment includes closed-die forging of the carbon-manganese steel samples and the measurements of the grain size on the cross-sections of the forgings after the deformation. Spherical samples, which involve significant inhomogeneity of the strain and the temperature fields, have been chosen for a presentation of the results.     

A mechanism of solar cell degradation in high intensity,high temperature space missions

The behavior of standard space photovoltaic assemblies in a high intensity, high temperature environment (HIHT) is addressed. Experimentally, an HIHT environment, typical for missions to the inner planets of the solar system such as Mercury, characterized by temperatures of 500K and 11 solar constant irradiance in the ultraviolet region below 400 nm, was simulated in a vacuum. Independently of the triple junction cell technology used, module degradation up to 20% in power was observed during several hundred hours of test. Electroluminescence analysis identified discrete top cell shunts close to the cell edge, in particular around the frontside contact pads. Cross‐sectional transmission electron microscopy performed on several degraded cells revealed an etched contact pad metallization/cap layer interface and more importantly, several 100‐nm large, oriented Cu₃P inclusions at the shunted locations. A chemical degradation mechanism is proposed. Short wavelength ultraviolet light interacting with polysiloxanes used as module encapsulant produces hydrogen and methyl radicals. With these building blocks, an organic acid can be formed on external reaction surfaces such as the Ag busbars that simultaneously serve as a source of oxygen. Cu traces present in the Ag segregate to the surface and are transported by this acid to the contact pad of the cell in the liquid phase. An adapted cell design was developed to prevent this degradation mechanism believed to be of relevance for all HIHT space environments. A several hundred micrometer‐wide rim composed of the outermost cell area is electrically separated from the inner cell area and provides a barrier against environmental attack. None of the photovoltaic assemblies featuring this mesa cell design showed any fill factor‐induced power degradation any more. Copyright © 2011 John Wiley & Sons, Ltd.     

The accuracy of a solid packing fraction model in recognizing zones of different dendritic structures

A front tracking method on a fixed control-volume grid, based on assumed dendrite tip kinetics, is applied to discuss the accuracy of a numerical model where the coherency solid fraction is used in the identification of diverse dendritic regions developing within a mushy zone during binary alloy solidification driven by diffusion and thermo-solutal buoyancy forces. It is shown that this critical value of a solid volume fraction is not constant but changes with time and along the border separating the regions.     

An atypical approach identifies TYR234 as the key base catalyst in chondroitin AC lyase

Chondroitin AC lyase from Flavobacterium heparinum catalyses the degradation of chondroitin by an anionic E1cb elimination mechanism that involves proton abstraction from C5 of glucuronic acid. The lyase also carries out efficient proton transfer to a sugar nitronate anion, which was designed originally as an inhibitor of the enzyme, with a second-order rate constant of kcat/Km=2.7x10(6) M(-1) s(-); this is very similar to that of the natural chondroitin substrate (kcat/Km=1.3x10(6) M(-1) s(-1)). Studies with this nitronate should therefore provide insight into the proton-transfer step (general base catalysis) within this mechanism. Indeed, the Tyr234Phe mutant of the enzyme was essentially inactive with the natural substrate and correspondingly did not catalyse proton transfer to the nitronate, thereby implicating this residue as the general base catalyst. Parallel studies designed to identify the acid catalyst were carried out by using a substrate with a 2,4-dinitrophenol leaving group that needs no acid assistance for departure. These results are consistent with Tyr234 also playing the role of acid catalyst. Not only do these studies confirm the suspected role of Tyr234, but also they validate a new methodology for identification of acid/base catalysts in lyases and epimerases of this type. In addition a structural and mechanistic rationale is provided for different active-site acid/base configurations in syn and anti lyases.     

The possibility of employing a calculable four-electrodeconductance cell to substitute for the secondary standards ofelectrolytic conductivity

It appears that a four-electrode conductance cell designed and used according to the van der Pauw method can be applied for the absolute determination of the electrolytic conductivity of solutions with an accuracy comparable with that of the secondary standards for this quantity. Therefore there may be a possibility of avoiding the use of those standards in some cases. The results of the experimental investigation of a prototype model of the cell of this type, carried out by the authors, are consistent with the theoretical considerations and computer modeling. An absolute determination of electrolytic conductivity has been made for 0.01 and 0.1 M KCl solutions, with an overall uncertainty lower than 0.4%     

Empirical Analysis of Construction Enterprise Information Systems: Assessing System Integration, Critical Factors, and Benefits

Attaining higher levels of system integration is seen as the primary goal of construction enterprise information systems (CEIS). Increased system integration resulting from CEIS implementation is expected to lead to numerous benefits. These benefits encompass information technology infrastructure and strategic, operational, organizational, and managerial aspects of the firm. By adopting CEIS, firms seek tangible and intangible benefits, such as cost reduction, improved productivity, enhanced efficiency, and business growth. Through the use of statistical analysis, this study quantifies the critical success factors that impact CEIS integration and the ensuing benefits. Furthermore, it analyzes the effects of system integration on CEIS induced benefits. It also investigates the impact of CEIS strategy on CEIS induced benefits and identifies the relationship between CEIS strategy and system integration. Finally, it assesses the effects of CEIS induced benefits on user satisfaction and provides a CEIS implementation guide map for construction firms.     

Minimizing the Distortion of Steel Profiles by Controlled Cooling

A complex thermomechanical model is introduced for the simulation of the transient fields of temperature and stresses during the quenching of steel products. The material behaviour is an extension of the classical J₂‐plasticity theory with the extension of temperature and phase fraction dependent yield criteria. The coupling effects, i.e., dissipation of mechanical energy, transformation induced plasticity (TRIP), and phase transformation enthalpy, are considered. The model is used for the determination of the optimal cooling or quenching for reducing the distortion in the long steel profiles. The simulation results are presented in order to investigate the effects of material properties, boundary conditions, profile size and geometry. In the simulations, L‐, T‐ and U‐profiles made of steel C45 and steel C80 are considered. It is demonstrated that with a higher cooling rate in the mass lumped regions of the profiles, the distortion can be reduced.     

两种新颖的胶版印刷纸表面掉毛掉粉的评价方法

掉毛和掉粉是胶版印刷过程中最为棘手的问题之一,由于纸张表面粘结不牢固,细小纤维或粉尘在印刷过程中脱落下来,黏附在印版或橡皮布上导致印刷图像恶化,清洗它们的过程费钱费时.本文介绍了两种测量纸张表面掉毛掉粉的新方法,即利用计算机图像获取和分析系统,先获取细小纤维和颗粒脱落的数字图像,通过统计和分析图像,预测纸张掉毛掉粉趋势.其与传统的IGT(拉毛强度测试)方法相比,简便可靠,对生产实践具有更好的指导意义.