Disturbed State Model for Porous Saturated Materials

The widely used Terzaghi theory for deformation or consolidation in porous materials is based on the effective stress, a rather fictitious quantity, carried by the soil skeleton through the particle contact area, which is assumed to be negligible. This note presents a new generalized model based on the disturbed state concept, in which the average or weighted stress carried by the soil skeleton and fluid is defined on the basis of the change in contact area during deformation, that can be proportional to quantities such as the void ratio. A simple problem is solved in which the predictions from the proposed model and Terzaghi theory are compared. The proposed model has potential application as a general procedure for deformation in porous materials.     

A study of CaO (Fe2O3)1−x (Al2O3)x system

The members of the ferrite series CF_1?1A_x and with O ? × ? 0.8 have been studied by x-ray diffraction and Mössbauer spectroscopic techniques. The observed Mössbauer parameters are explained in the light of the following model, which is supported by the x-ray data. For non-zero x, the two phases CF and CA co-exist such that Al and Fe are distributed in these, respectively. With increase in x, the CF phase decreases and the CA phase increases.     

A three-dimensional model of droplet impact and solidification

A three-dimensional model has been developed to simulate the fluid dynamics, heat transfer and phase-change that occur when a molten metal droplet falls onto a flat substrate. The model is an extension of one developed by Bussmann et al. [Phys. Fluids 11 (1999) 1406] and combines a fixed-grid control volume discretization of the fluid flow and energy equations with a volume-tracking algorithm to track the droplet free surface, and an improved fixed velocity method to track the solidification front. Surface tension is modeled as a volume force acting on fluid near the free surface. Contact angles are applied as a boundary condition at liquid-solid contact lines. The energy equations in both the liquid and solid portions of the droplet are solved using the Enthalpy method. Heat transfer within the substrate is by conduction alone. Thermal contact resistance at the droplet-substrate interface is included in the model. We studied the deposition of tin droplets on a stainless steel surface using both experiments and numerical simulations. The results of two different scenarios are presented: the normal impact of a 2.7 mm tin droplet at 1 m/s, and of the oblique impact of a 2.2 mm tin droplet at 2.35 m/s onto a surface inclined at 45° to the horizontal. Images obtained from numerical model were compared with experimental photographs and found to agree well.     

Maternal mortality in Fiji

The spontaneous behaviour at late pregnancy was measured as motor activity by Supermex in SHN mice, which have a rather high still-birth rate. The activities during both light and dark phases as well as during the total period were significantly higher in mice with still-birth than those with normal delivery. Meanwhile, in normal delivery group, there was little correlation between the spontaneous activity and the reproductive parameters, except for litter size or total pup weight. These results strongly suggest that calmness, especially at late pregnancy is prerequisite for normal delivery and that reproduction itself after delivery was not markedly affected by the behaviour of mother at late pregnancy.     

Melt strength of calcium carbonate filled polypropylene melts

This paper investigates the extensional rheology (through melt strength measurement) of calcium carbonate (CaCO₃) filled polypropylene (PP) melts. Different concentrations of CaCO₃ filled PP were produced by mixing two master batches of pure PP and 70 wt% CaCO₃ filled PP in required proportions in a counter‐rotating twin‐screw extruder. It was found that the melt strength of the CaCO₃–PP melts was independent of CaCO₃ concentrations up to 25 vol%. Further increase in CaCO₃ concentration led to a severe reduction of melt strength. © 2002 Society of Chemical Industry     

Analysis of a predictor—regulator system

A high-performance control system called “predictor—regulator” is proposed, its governing laws are derived, and it is applied to simulated processes to evaluate its characteristics, and to real processes to demonstrate its feasibility. The proposed system is made up of a two-loop configuration[4]: a fast auxiliary loop consisting of a controller and a simple lag element, and a main loop provided with another controller operating on the process. Both the controllers are conventional PID type commercial controllers. Theoretical study reveals that, by suitable choice of the compensator parameters, the control arrangement could result in remarkably superior performance. While, for the key loads, both steady state and transient errors become practically zero with the aid of only two P-controllers, inclusion of integral action aids in achieving control against secondary (unmeasured) disturbances also. The design and performance of the regulator system are evaluated via simulation. Several practical aspects of the control problem are examined, and criteria for choosing the auxiliary lag, the modes of control, and the controller settings are established. Applicability of the technique to a wide range of processes (e.g. complex higher order and dead time processes) is also discussed. The results obtained confirm that the control approach could match combined feedforward—feedback regulation in its performance, and classical feedback in design simplicity and ease of implementation.     

The extrusion force and the mean strain rate during the extrusion of strain rate sensitive materials

The force required to extrude a strain rate sensitive material under conditions of homogeneous deformation is calculated by the uniform work method. The force is shown to be a strong function of the rate sensitivity of the material. A new definition of the mean strain rate during extrusion is proposed, which is particularly appropriate to rate sensitive materials. For extrusion ratios of 40 to 160 and a power law strain rate sensitivity of 0.2, the present method leads to extrusion pressures 30 to 60 pct higher than when no account is taken of the rate sensitivity of the flow stress in the die zone. In an appendix, a design for a constant true strain rate (CTSR) die is described, which permits experiments to be carried out without the necessity for rate sensitivity corrections.     

Implementation and test results of a generalized self-tuningexcitation controller

A self-tuning excitation controller performing the functions of AVR (automatic voltage regulation) and stabilization, and an interactive man-machine interface have been implemented using two microcomputers. The general setup of the hardware and software are described. Results of experimental tests on a physical model of a power system are also presented. The results demonstrate the effectiveness of the adaptive controller