Improving the performance of industrial ethanol‐producing yeast by expressing the aspartyl protease on the cell surface

The yeasts used in fuel ethanol manufacture are unable to metabolize soluble proteins. The PEP4 gene, encoding a vacuolar aspartyl protease in Saccharomyces cerevisiae, was either secretively or cell‐surface anchored expressed in industrial ethanol‐producing S. cerevisiae. The obtained recombinant strains APA (expressing the protease secretively) and APB (expressing the protease on the cell wall) were studied under ethanol fermentation conditions in feed barley cultures. The effects of expression of the protease on product formation, growth and cell protein content were measured. The biomass yield of the wild‐type was clearly lower than that of the recombinant strains (0.578 ± 0.12 g biomass/g glucose for APA and 0.582 ± 0.08 g biomass/g glucose for APB). In addition, nearly 98–99% of the theoretical maximum level of ethanol yield was achieved (relative to the amount of substrate consumed) for the recombinant strains, while limiting the nitrogen source resulted in dissatisfactory fermentation for the wild‐type and more than 30 g/l residual sugar was detected at the end of fermentation. In addition, higher growth rate, viability and lower yields of byproducts such as glycerol and pyruvic acid for recombinant strains were observed. Expressing acid protease can be expected to lead to a significant increase in ethanol productivity. Copyright © 2010 John Wiley & Sons, Ltd.     

The finite element analysis of a fractured tibia applied by composite bone plates considering contact conditions and time-varying properties of curing tissues

This paper addresses the use of composite bone plates in healing long-bone fractures such as transverse fractures of the tibia using finite element analysis, that takes into consideration contact conditions and material property variations of calluses in relation to the healing period. For the time-varying properties of calluses in relation to the healing period, stepwise material properties were imposed on the callus part based on the time elapsed, and the loading conditions were coupled with the callus properties based on the length of the healing period. The strain distributions at the fracture site were calculated according to the stacking sequence of the bone plate and healing time. The analysis results showed that composite bone plates with stacking sequences of [0]_12T for the Kevlar/BCP composites generated the most appropriate strain distributions at the fracture site during the early healing process.     

Numerical simulation of critical current performance in Nb3Sn strand subjected to periodic bending deformation

In the ITER Engineering Design Activity (EDA), four NB₃Sn model coils were developed and successfully tested. However, it was revealed that the critical current of the conductor degraded with the increase of electromagnetic force. One of the explanations of this phenomenon is a strand bending caused by enormous electromagnetic force. The authors therefore developed a simulation code using the distributed circuit model to investigate dependency of the critical current performance on the periodic bending deformation. The simulation results were in good agreement with the experiments. The dependence of the critical current on the periodic transverse load, temperature, periodic load pitch, thickness of Ta barrier which prevents Cu stabilizer from being contaminated by Sn, twist pitch of the strand, and RRR of the bronze matrix was investigated using the developed code. The results showed that the critical current degraded less with decreasing the pitch of the transverse load and increasing the Ta barrier thickness. It suggests that the shorter cabling pitch and the larger bending stiffness prevent the critical current degradation. © 2010 Wiley Periodicals, Inc. Electr Eng Jpn, 171(3): 7–15, 2010; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20923     

Strain sensing behavior of electrically conductive fibers under large deformation

Electrically conductive fiber/yarn/fabric is one of the promising materials as flexible conductive sensors because of their sensitivity to strain, temperature and humidity. Aiming at developing of effective flexible sensors, this study investigates experimentally the strain sensing behavior of PPy (polypyrrole)-coated Lycra fibers, showing that the electrically resistance of the conductive fibers changes with the deformation of fibers. The variation in electrically resistance is mainly related to the micro-cracks appearing on the fiber surface during deformation. Then, the effects of the characteristic parameters of the micro-cracks are studied statistically by means of image processing functions in MATLAB, and the governing parameters are determined. Based on the results, a model is built to describe the variation of electrical resistance by the parameters of the micro-cracks. The analytical results are compared with the experimental results, showing an acceptable agreement.     

Theoretical analysis of geometrical and mechanical parameters in plain woven structures

An analytic solution for the estimation of structural parameters and initial tensile modulus of plain woven fabrics under uniaxial tensile loading in their linear elastic domain of deformation is presented. For this purpose, a new approach in straight line geometry with a parallel segment to the fabric plane and an inclined segment at the weave intersection in 3D form is proposed which leads to the theoretical estimation of all the structural parameters of plain woven fabrics with saw-tooth geometry. Defining and applying of JJ₂ Ratio in the model enable us to modify the geometrical model and estimate the value of structural parameters considering the history of samples influenced mainly by its manufacturing process. The strain energy method and Castigliano’s theorem are used for the mechanical analysis of the structure. The elasticity, bending, shearing, and compression rigidity of yarns are incorporated into the model. It has been shown that predicting the geometrical and mechanical parameters of woven fabrics before production are possible if and only if the crimp value of the fabrics can be estimated before their production. The proposed theory is validated and compared by applying into some experimental data and a previous model.     

基于局部应力应变法的大型港口起重机疲劳寿命估算

基于局部应力应变法理论较为详细地给出了疲劳寿命估算方法和思路，分析研究了动态数据采样与处理方法，并以实例计算说明了其可行性与实用性。     

Constitutive modeling for the dynamic recrystallization evolution of AZ80 magnesium alloy based on stress-strain data

In order to improve the understanding of the dynamic recrystallization (DRX) behaviors of as-cast AZ80 magnesium alloy, a series of isothermal upsetting experiments with height reduction 60% were performed at the temperatures of 523 K, 573 K, 623 K and 673 K, and the strain rates of 0.01 s⁻¹, 0.1 s⁻¹, 1 s⁻¹ and 10 s⁻¹ on a Gleeble 1500 thermo-mechanical simulator. Dependence of the flow stress on temperature and strain rate is described by means of the conventional hyperbolic sine equation. By regression analysis, the activation energy of DRX in the whole range of deformation temperature was determined to be Q = 215.82 kJ mol⁻¹. Based on dσ/d? versus σ curves and their processing results, the ?ow stress curves for AZ80 magnesium alloy were evaluated that they have some characteristic points including the critical strain for DRX initiation (?_c), the strain for peak stress (?_p), and the strain for maximum softening rate (?*), which means that the evolution of DRX can be expressed by the process variables. In order to characterize the evolution of DRX volume fraction, the modified Avrami type equation including ?_c and ?* as a function of the dimensionless parameter controlling the stored energy, Z/A, was evaluated and the effect of deformation conditions was described in detail. Finally, the theoretical prediction on the relationships between the DRX volume fractions and the deformation conditions were validated by the microstructure graphs.     

Considerations of rock dilation on modeling failure and deformation of hard rocks-a case study of the mine-by test tunnel in Canada

For the compressive stress-induced failure of tunnels at depth, rock fracturing process is often closely associated with the generation of surface parallel fractures in the initial stage, and shear failure is likely to occur in the final process during the formation of shear bands, breakouts or V-shaped notches close to the excavation boundaries. However, the perfectly elastoplastic, strain-softening and elasto-brittle-plastic models cannot reasonably describe the brittle failure of hard rock tunnels under high in-situ stress conditions. These approaches often underestimate the depth of failure and overestimate the lateral extent of failure near the excavation. Based on a practical case of the mine-by test tunnel at an underground research laboratory (URL) in Canada, the influence of rock mass dilation on the depth and extent of failure and deformation is investigated using a calibrated cohesion weakening and frictional strengthening (CWFS) model. It can be found that, when modeling brittle failure of rock masses, the calibrated CWFS model with a constant dilation angle can capture the depth and extent of stress-induced brittle failure in hard rocks at a low confinement if the stress path is correctly represented, as demonstrated by the failure shape observed in the tunnel. However, using a constant dilation angle cannot simulate the nonlinear deformation behavior near the excavation boundary accurately because the dependence of rock mass dilation on confinement and plastic shear strain is not considered. It is illustrated from the numerical simulations that the proposed plastic shear strain and confinement-dependent dilation angle model in combination with the calibrated CWFS model implemented in FLAC can reasonably reveal both rock mass failure and displacement distribution in vicinity of the excavation simultaneously. The simulation results are in good agreement with the field observations and displacement measurement data.     

High strain rate deformation and cracking of AA 2219 aluminium alloy welded propellant tank

Aluminium alloy AA 2219 (Al–6.6Cu–1Mn) is the candidate material for the fabrication of propellant storage tank of launch vehicle. Cold rolled sheets of 6.5 mm thickness are used to make the cylindrical shell, while sheets of 4.5 mm thickness are used for the construction of dome through petal forming technique. Petals, formed through cone rolling, treated to T87 temper condition are welded together by TIG welding to configure the dome. Such domes are joined to the cylindrical shell through a ring by TIG welding.The upper stage consists of two tanks, one oxidizer tank (liq. O₂) and other fuel tank (liq. H₂). After completing various developmental qualification tests, propellant flow rate test of one of the system was carried out. Almost all the liquid oxygen of the tank was removed and only a little quantity remained at the bottom. During one of the subsequent tests; when dry nitrogen gas was purged to evaporate the remaining liquid oxygen, the oxidizer tank dome catastrophically fractured with an audible sound. Fracture of oxidizer tank dome, placed at lower part of the system caused excessive deformation and subsequently it also caused fracture of fuel tank dome placed just over it.Detailed metallurgical investigations were carried out on the failed components and it was found that the tank failed under very high strain rate deformation. This paper brings out the details of the investigation carried out.