Numerical evaluation of the effects of friction and geometric nonlinearities on the energy release rate in three- and four-point bend end-notched flexure tests

Nonlinear finite element analyses are used to examine the effects of friction and geometric nonlinearities on the energy release rate in three- and four-point bend end-notched flexure tests. Energy release rates are first determined by a recently developed direct energy balance approach. It is shown that the finite diameter loading rollers that are typically used in practical test set-ups cause both tests to be inherently nonlinear. The effect of these nonlinearities on the energy release rate is shown to be larger in the four point than the three point test and to increase with increasing roller diameter, increasing coefficient of friction along the crack plane, and decreasing supporting span length. For the four point test, the effect of these nonlinearities is also shown to increase with increasing ratio of inner to outer span length. Next, energy release rates at the onset of crack advance are determined by a simulated compliance calibration technique. This “perceived toughness” is compared with predictions of the “true toughness” given by the direct energy balance approach at the same load. It is shown that perceived toughnesses from this simulated compliance calibration procedure are larger than previously reported results that were obtained in a similar fashion using linear theory. In addition, the perceived toughness is shown to strongly depend upon the range used for fitting the load versus deflection data to obtain compliance. These findings are used to make some general recommendations regarding use of the two test methods and their associated data reduction techniques.     

A bending specimen for constant energy release rate under controlled displacement conditions

A bending specimen that gives a constant energy release rate (independent on the crack length) under controlled displacement conditions is developed. It is assumed that engineering beam theory is applicable, i.e. that among other things, small deformations and linear elastic isotropic material can be assumed.A specific geometry is analyzed numerically by use of the finite element method and experimentally by manufacturing a specimen with the actual geometry in PMMA (polymethylmetacrylate) and then determining the specimen stiffness for different crack lengths.It is found that the geometry considered gives a constant energy release rate under controlled displacement conditions.     

Software release management for component‐based software

Software release management is the process through which software is made available to and obtained by its users. Until now, this process has been relatively straightforward. However, the emergence of component‐based software is complicating software release management. Increasingly, software is constructed via the assembly of pre‐existing, independently produced, and independently released components. Both developers and users of such software are affected by these complications. Developers need to accurately document the complex and changing dependencies among the components constituting the software. Users must be involved in locating, retrieving, and assembling components in order to appropriately bring the software into their particular environment. In this paper, we introduce the problem of release management for component‐based software and discuss SRM, a prototype software release management tool we have developed that supports both developers and users in the software release management process. Copyright © 2002 John Wiley & Sons, Ltd.     

会展建筑中的大空间排烟系统分析

通过对会展建筑中的大空间展厅的火灾情形、排烟量及排烟方式的分析,得出了一个适合此类建筑的排烟系统设计的经济合理的参考方案.     

转炉煤气无气柜回收

针对转炉煤气回收系统改造期间煤气平衡困难的现状，在分析了原回收系统中气柜作用的基础上，提出了无气柜回收方式．通过增加PLC控制系统及用于控制压力上限的放散管等少量必要设施并充分利用现有设施，确定了压力上、下限等相关技术参数，解决了安全问题．实现了转炉煤气的无气柜方式回收．     

压水堆核电厂冷却剂碘同位素活度比值131I/133I与燃料完整性关系研究

压水堆核电厂正常运行期间燃料元件破损会造成一回路裂变产物活度升高,碘同位素活度比值131I/133I是行业内最常用的判断燃料破损情况的指标之一。本文介绍了压水堆正常运行期间冷却剂131I和133I的产生来源和迁移过程,建立模型估算了燃料完整、小破口和大破口情况下131I/133I范围,并通过在运CPR1000型压水堆核电厂的运行监测数据对计算模型进行了验证,两者符合得较好。     

pH-sensitive sodium alginate/calcined hydrotalcite hybrid beads for controlled release of diclofenac sodium

Objective: The aim of this study was to prepare pH-sensitive sodium alginate/calcined hydrotalcite (SA/CHT) hybrid bead with improved the burst release effect of the drug.

Materials and methods: A series of pH-sensitive SA/CHT hybrid beads were prepared by using Ca²⁺ cross-linking in the presence of diclofenac sodium (DS) and SA. The structure and drug loading of the beads were characterized by Fourier transform infrared spectroscopy and X-ray diffraction. The swelling and the drug release of the fabricated beads were investigated by the pH of test medium and CHT content.

Result: The formed positively charged hydrotalcite layers were adsorbed on the negatively charged SA polymer chains through electrostatic interaction and act as inorganic cross-linkers in the three-dimensional network. Compared to pure SA beads, the incorporation of CHT enhanced the drug encapsulation efficiency, improved the swelling behaviors and slowed the drug release from the hybrid beads.

Discussion and conclusions: The electrostatic interaction between hydrotalcite and SA has restricted the movability of the SA polymer chains, and then slowed down swelling and dissolution rates in aqueous solutions. The results provided a simple method to moderate drug release and matrix degradation of the SA beads.     

Neuronal ApoE Regulates the Cell-to-Cell Transmission of α-Synuclein

The presence of protein inclusions, called Lewy bodies (LBs) and Lewy neurites (LNs), in the brain is the main feature of Parkinson’s disease (PD). Recent evidence that the prion-like propagation of α-synuclein (α-syn), as a major component of LBs and LNs, plays an important role in the progression of PD has gained much attention, although the molecular mechanism remains unclear. In this study, we evaluated whether neuronal ApoE regulates the cell-to-cell transmission of α-syn and explored its molecular mechanism using in vitro and in vivo model systems. We demonstrate that neuronal ApoE deficiency attenuates both α-syn uptake and release by downregulating LRP-1 and LDLR expression and enhancing chaperone-mediated autophagy activity, respectively, thereby contributing to α-syn propagation. In addition, we observed that α-syn propagation was attenuated in ApoE knockout mice injected with pre-formed mouse α-syn fibrils. This study will help our understanding of the molecular mechanisms underlying α-syn propagation.     

Macro- and Nanoscale Effect of Ethanol on Bovine Serum Albumin Gelation and Naproxen Release

We report extended ethanol-induced gelation procedures of bovine serum albumin (BSA) at 37 °C and investigate the release behavior of a spin-labeled naproxen derivative (SL-NPX) from these hydrogels. The macroscopic mechanical properties of these gels during formation were studied using rheology, while a nanoscopic, more molecular view was obtained by analyzing the secondary structure of the protein during gelation via infrared (ATR-IR) spectroscopy. To evaluate the potential use of BSA hydrogels in controlled drug delivery, SL-NPX-BSA interaction was investigated in detail by continuous-wave electron paramagnetic resonance (CW EPR) spectroscopy, which provides information on the interaction of the small drug molecules and the hydrogel. In addition to CW EPR spectroscopy, dynamic light scattering (DLS), which provides insight into the size and nature of released components, was applied to characterize the combined influence of incubation time, ethanol, SL-drug, and BSA concentration on release behavior. It was found that the alteration of initial drug loading percentage, hydrogel incubation time as well as BSA and alcohol concentrations affect and thus tune the release rate of SL-NPX from BSA hydrogels. These results lead to the conclusion that BSA hydrogels as controlled release systems offer a remarkable fine-tuning capability for pharmaceutical applications due to the variety of gelation parameters.