Characterization of a Cohesive Soil Bed using a Cone Pressuremeter

A new cone pressuremeter has been developed at the University of Engineering and Technology, Lahore-Pakistan. The new device is called the Akbar Pressuremeter (APMT). This paper is based on the APMT testing of a cohesive soil deposit comprised of low plastic lean clay (CL) to sandy silty clay (CL-ML). The APMT testing, using a full-displacement technique, standard penetration tests and undisturbed samples, was carried out at two locations. The soil strength and type were determined using the undisturbed samples. The applied pressure-cavity strain curves of the APMT tests performed at different levels were analysed to determine soil strength and stiffness. The undrained shear strength of the undisturbed samples was determined in the laboratory by unconfined compression tests. This paper provides a comparison of the parameters interpreted from the pressuremeter and those determined from other field and laboratory methods.     

Simulation of Stimulated Raman Scattering

Stimulated Raman scattering (SRS) with ordinary (O-mode) wave at phase space (x, v) is investigated. For this purpose Vlasov equation is solved with one simulation method. Evolution of distribution function for an early time and a later time is presented. Initial distribution function has Gaussian shape, that is important in plasma heating, but as the time passed, this function due to the perturbation extends over space and velocity. In this situation, the behavior of distribution function has an important role in instability rate. Then instability rate for SRS is obtained and these results are showed in some special times and special cells. Density fluctuations affect instability rate and there is no remarkable damping at early times. At later times instability rate reduces sensitively which is in accordance to electron plasma wave damping and then heating the electrons. Also with increase in frequency of the incident wave, the instability rate due to saturation decreases sensitively.     

Gas-phase driven nano-machined TiO2 ceramics

A simple, inexpensive gas phase reaction termed as “nanocarving process” converts TiO₂ grains into arrays of single crystal nanofibers by selective and anisotropic etching. This process is conducted by exposing dense polycrystalline TiO₂ to a H₂/N₂ environment at 700 °C. The dimensions of nanofibers are around 20 nm in diameter and 1 μm in length. The preferred crystallographic orientation for the nanocarving process is the <001> direction. Nanoparticles composed of Fe and Ni were observed on the surface of TiO₂ that formed nanofiber tips. Sintering parameters before the nanocarving treatment play a critical role in the formation of nanofibers. As sintering temperature and time increased, the rate of nanofiber generation decreased. Moreover, it was observed that by varying the heat treatment conditions, it is possible to create other structures like nanowhiskers and nanofilaments. Nanowhiskers were formed by reoxidation of nanofiber-formed TiO₂ over 600 °C. Nano-filaments were generated by heat treating sintered TiO₂ in N₂-carrying water vapor at 700 °C.     

Microstructure, permeability and rheological behavior of lost foam refractory coatings

The effect of microstructure on rheology and permeability of three commercial lost foam refractory coatings available on the market called samples I, II, and III, respectively was investigated in this study. Thermal gravimetric/differential thermal analysis (TG/DTA) method was used for detailed analysis of the organic components and to determine the thermal stability of the coatings. Particle shape and size and particle size distribution (PSD) were obtained by optical microscopy and morphological studies were carried out by scanning electron microscopy (SEM). Also the scanning electron microscopy energy dispersive X-ray analysis (SEM/EDXA) technique was used for elemental analysis of refractory particles. To determine the crystalline structure of the samples, X-ray diffraction (XRD) analysis was carried out. Permeability measurements were conducted with a modified apparatus originally used for determining the permeability of casting sand. Finally the rheological behavior of the samples was investigated using a rotating coaxial rheometer to provide the flow curve for coating suspensions. The studies revealed that coating I has the highest permeability, which can be due to its large mean particle size and wide particle size distribution (PSD). Furthermore it was found that the investigated refractory coatings behave as non-Newtonian fluids with shear thinning behavior. All coatings exhibited yield stresses, indicate that they behave as Bingham-type pseudoplastic fluids.     

Nonlinear stress analysis of offshore pipelines during pickup operations

This paper presents a method of analyzing the stresses in a submarine pipeline as it is picked up off the sea floor by barge davits. A nonlinear large-deflection analysis is used and the pipeline is modeled as a series of finite beam segments from the ocean bottom on up. The governing equations are derived and the pipeline configuration satisfying known boundary conditions is determined by an initial-value approach using an iterativetype technique. Boundary conditions at the mudline are identified by modeling the pipeline resting on the ocean bed as a semi-infinite tensioned beam on an elastic foundation. The effects of a nonlinear stress-strain curve for the pipe material are included and both Ramberg-Osgood and Hutchinson formulations are considered. With the technique suggested, any given pickup procedure can be analyzed or a reliable procedure can be developed based on a given allowable pipe stress level and any desired improvement in the final configuration and/or stress levels may be achieved by a variation of the parameters involved. A practical example is examined to demonstrate the applicability of the analysis presented, which should provide a useful tool in either judging or developing a pickup procedure.     

Novel Structural Modulation in Ceramic Sensors Via Redox Processing in Gas Buffers

High selectivity, enhanced sensitivity, short response time, and long shelf-life are some of the key features sought in the solid-state ceramic-based chemical sensors. As the sensing mechanism and catalytic activity are predominantly surface-dominated, benign surface features in terms of small grain size, large surface area, high aspect ratio and, open and connected porosity, are required to realize a successful material. In order to incorporate these morphological features, a technique based on rigorous thermodynamic consideration of the metal/metal oxide coexistence is described. By modulating the oxygen partial pressure across the equilibrium M/MO proximity line, formation and growth of new oxide surface on an atomic/submolecular level under conditions of "oxygen deprivation," with exotic morphological features, has been achieved in potential sensor materials. This paper describes the methodology and discusses the results obtained in the case of potential semiconducting ceramic oxide-based carbon monoxide and hydrogen sensors with enhanced characteristics.     

Distance transform algorithm for measuring nanofiber diameter

This paper describes a new distance transform method used for measuring fiber diameter in electrospun nanofiber webs. In this algorithm, the effect of intersection is eliminated, which brings more accuracy to the measurement. The method is tested by a series of simulated images with known characteristics as well as some real webs obtained from electrospinning of PVA. Our method is compared with the distance transform method. The results obtained by our method were significantly better than the distance transform, indicating that the new method could successfully be used to measure electrospun fiber diameter.