A no-tension elastic–plastic model and optimized back-analysis technique for modeling nonlinear mechanical behavior of rock mass in tunneling

In this paper, we present a no-tension elastic–plastic model and an optimized back-analysis technique for stability analysis of underground tunnels. A set of constitutive equations is presented to simulate the no-tension behavior and plastic yielding of jointed rock masses which yield according to the Drucker–Prager yield criterion and permits no-tension. A nonlinear 2-D finite element model is consequently formulated for the prediction of the behavior of the excavated rock mass. As for the model parameters, the genetic algorithm technique is employed to find the optimal rock mass properties by minimizing the discrepancy between the predicted results and field measurement. The nonlinear finite element model coupling with the genetic algorithm optimized back-analysis technique is then applied to a synthetic example of a deep tunnel in yielding rock. The results show that the forward and back-analysis system is capable of estimating the model parameters with stable and good convergence and give reasonable predictions. Numerical experiments are also carried out to check the influences of position and numbers of measurements to the reliability of the back-analysis results. Furthermore, the sensitivity analysis of the genetic algorithms optimization procedure is discussed in terms of identification of geo-material properties.     

A NUMERICAL SCHEME FOR NON-FOURIER HEAT CONDUCTION,PART II: TWO-DIMENSIONAL PROBLEM FORMULATION AND VERIFICATION

A flux-splitting algorithm based on the Godunov numerical scheme developed for the solution of the one-dimensional non-Fourier heat conduction equation by Yeung and Lam [1] is extended for the investigation of thermal wave propagation in rectangular media. The derivation of the solution method and the stability criteria are presented in detail. Physical problems subjected to various boundary conditions (e.g., first, second, and third kinds) can be studied with the numerical scheme. A comparison of the exact solution with the one calculated by the proposed procedure is presented to confirm the validity of the numerical procedure. The numerical scheme is applicable for the study of short-pulse heating in advanced materials, microstructures, thin films, semiconductor devices, and superconductors.     

Distance learning in advanced military education: Analysis of joint operations course in the Taiwan military

High-ranking officers require advanced military education in war tactics for future combat. However, line officers rarely have time to take such courses on campus. The conventional solution to this problem used to take the inefficient correspondence courses. Whereas Internet technologies progress, online course is the current trend for military training. However, the question is what distance learning methodology best suits such a proprietary learning purpose.This study presents a sequential process of developing distance learning courses in advanced military education. Further, the Petri-Net analytical approach is adopted to discover the essential interaction requirements of advanced military education delivered via Internet. This study developed a systematic method for designing e-learning systems according to specific requirements of target courses. The proposed approach starts by comparing on-campus programs with the existing e-learning systems to identify the steps required to transform the program into an e-learning system. After first outlining the pedagogy of the on-campus program, its proposed teaching flow through the Internet is then sketched. Finally, the Petri-Net model was used for in-depth analysis of the stages affecting the learning curve of the line office taking e-learning courses. The example of a “Joint Operations” AME course elaborated the presented approach. An e-learning system prototype was also designed accordingly. Lastly, an experiment was conducted to verify the efficiency of the presented approach.     

Performance of DS SS system under on-off wideband jamming

A performance analysis of a direct sequence spread spectrum (DS SS) system under a periodic on-off wideband jammer is presented. Closed-form results of system bit error rate (BER) are derived for all possible cases of jammer duty cycle     

A single-layer PDMS-on-silicon hybrid microactuator with multi-axis out-of-plane motion capabilities-part II: fabrication and characterization

This paper reports on fabrication and characterization of a new electrostatic microactuator that achieves out-of-plane multi-axis motion with a single silicon device layer. The multi-axis motion with the simple actuator design is possible by incorporating a three-dimensional (3-D) polydimethylsiloxane (PDMS) microstructure. This paper develops a new device processing method named "Soft-Lithographic Lift-Off and Grafting (SLLOG)" to fabricate the previously designed PDMS-on-silicon hybrid actuator structure. SLLOG is a low-temperature (less than 150/spl deg/C) process that allows replica molded PDMS microstructures to be integrated in silicon micromachined device patterns. The fabricated actuator is characterized using laser vibrometry. The experimental results demonstrate actuation motions achieved in three independent axes with fast dynamic response reaching a bandwidth of about 5 kHz. The fabricated PDMS-on-silicon actuator yields a vertical displacement up to 5 /spl mu/m and rotational motions with a 0.6-/spl deg/ tilting angle at a 40-V peak-to-peak ac actuation voltage.     

The effect of oxidants on 2-MIB concentration with the presence of cyanobacteria.

In this study, the effect of three oxidants, sodium hypochlorite, potassium permanganate, and ozone, were tested for the removal of 2-MIB with presence of cyanobacteria. Algae in water samples from the source water of Feng-Shen waterworks (FSW), Taiwan were cultivated at 30 degrees C with continuous light at an intensity between 2,500 and 3,400 lux. During the cultivating process, water samples were analyzed for nutrients, light absorbance at 665 nm (A665), and 2-MIB concentration. The 2-MIB concentrations within the incubated samples increased to as high as 1,000 ng/L to 2,000 ng/L, although no extra nutrients were added to the raw water. After 2 to 3 days incubation, the intracellular 2-MIB concentration was as high as 70% of the total 2-MIB in the samples. The algae that developed were mainly cyanobateria, and more than 90% belonged to the Genus Oscillatorias. An almost 100% removal of both 2-MIB and geosmin in the raw water was observed after ozonation for 10 minutes at a dosing rate of 0.91 mg/l-min. Chlorine and permanganate were much less effective, both removing only about 11% of the 2-MIB within 60 minutes at oxidant concentration of 10 mg/l. Oxidation of the cultivated samples showed that chlorine and permanganate may damage algae cells causing them to release intracellular 2-MIB. During the 60 minutes of reaction time, the total 2-MIB concentrations (intracellular plus dissolved) varied by no more than 10%, however, the ratios between dissolved and total 2-MIB concentrations increased. Two effects of ozonation on the 2-MIB concentration in the cultivated samples were observed when the algae were young, namely 2-MIB release from damaged cells and 2-MIB oxidization. The rates of 2-MIB release and 2-MIB destruction were similar. However, old algae cells were more easily damaged. As a result, intracellular 2-MIB was released faster, and the soluble 2-MIB was destroyed more quickly by ozonation.     

A pilot study of the marginal adaptation and surface morphology of glass-cermet cements

This study investigated changes in the marginal adaptation and surface morphology of Ketac-Silver and Chelon-Silver glass-current cements over time. Dispersalloy amalgam was used as a control. Contralateral pairs of carious primary molars were restored with the test materials and amalgam. Clinical evaluations were scheduled at 12, 18, and 24 months after placement. Gold-plated replicas of the restorations were observed with scanning electron microscopy. Fractures and cracks in the surface of the Dispersalloy and Chelon-Silver increased the surface roughness; however, the damage was superficial and self-limiting in the Dispersalloy restorations, while in Chelon-Silver the fractures caused the material to break down in layers. A substantial quantity of pores, usually smaller than 50 microns in diameter, were observed throughout the surface of the Chelon-Silver restorations. The pores in the surface of Ketac-Silver were fewer and smaller. The incidence of cavomarginal breakdown increased with time. Chelon-Silver restorations had a higher rate of cavomarginal breakdown than did Ketac-Silver and Dispersalloy restorations up to 18 months. However, there was no statistically significant difference in the marginal adaptation of the three groups at 24 months.     

The elastic analysis of a dent on pressurised pipe

The elastic analysis of a dent on a pressurised cylinder is investigated. The predetermined shapes of the dent are grouped into three categories according to the physical geometry of the dent width, namely the local dent, the short dent, and the long dent. The induced bending stresses associated with the dent are evaluated using Sanders's non-linear shell theory. The geometry of the dent is treated as an initial geometric imperfection and incorporated in the expressions of strain. The non-linear cylindrical shell equations thus obtained are linearised and then solved by a Fourier series expansion technique. Comparison of theoretical results with the finite element approach is made for a pipe of assumed dimensions and pressure. Good agreement of the results is observed. The analytical approach of this paper is suitable for pipe or cylinder with a dent depth of up to five times the wall thickness.     

On the J-intergral blunting line applied to linear amorphous polymers

Summary The development of crazes of linear amorphous polymers competes with the occurrence of general yielding in the plastic zone in tensile deformation. For toughened semi-ductile linear amorphous polymers, general yielding in the plastic zone is suppressed by the development of crazes. This suppresion prevents the crack tip from being blunt. Therefore it is recommended that the blunting line be neglected for the evaluation of Jic. For semi-ductile linear amorphous polymers, general yielding in the plastic zone takes place and blunts the crack tip. Thus the blunting line cannot be neglected for the evaluation of Jic.