An estimation of the penetration rate of rotary drills using the Specific Rock Mass Drillability index

The main purpose of the present study was to provide a practical,convenient drillability prediction model based on rock mass characteristics,geological sampling from blast holes,and drill operational f...     

Fatigue Crack Initiation and Propagation in Piles of Integral Abutment Bridges

Abstract: A new continuum damage modeling approach of “successive initiation” is used to determine the location of a thermomechanical fatigue crack initiation and the propagation path and rate in piles of integral abutment bridges. A global‐local modeling approach is introduced to determine the critical location in the pile where a crack is initiated using a 3‐dimensional nonlinear finite element model and to implement “successive initiation.” A simulated case study is used to showcase the multistep procedure. The results indicate that for a pile subjected to the maximum stress, the first fatigue‐induced crack initiates in the tip of the flange at the element immediately below the abutment. Several other cracks at different locations form in the flange of the pile while the initial crack continues to propagate in the flange to the web. The crack propagation rate increases as more cracks initiate in the flange. The propagation rate decreases when the crack reaches the web. Based on the case study presented, a crack could initiate in the pile in as little as 6 years, but it may take about 20 years for it to reach the web; however, final failure of the pile may not take place for several decades. The method can also be used as a guide in bridge foundation inspection and in the determination of the remaining life of an existing bridge.     

Adaptive control of cold rolling system in electrical strips production system with online-offline predictors

One of the main concerns of strips producers is to measure strip thickness accurately as it is produced. Correct modelling of the sensitivity of output variables to input variables in a rolling mill model is one of the keys to obtaining more accurate data. An adaptive control system that uses an artificial neural network (ANN) creates a model of the process directly from measurement data. Using the model, the control system can predict how the process will react to control actions. The creation of the model and the computation of the control strategy are carried out automatically by the control system. The proportional–integral–derivative controller is used in this method to increase accuracy of final estimated variables and to increase accuracy of control of the system. To determine the correct tuning for thickness control, three control parameters are considered: the roll gap, and front and back tensions. A predictive model is used, based on the sensitivity equations of the process, where the sensitivity factors are computed by differentiating a previously trained neural network. Results of a case study in a real plant show that this online-offline model is effective in reducing thickness variations in produced strips.     

A successive parameter estimation algorithm for chirplet signal decomposition

In ultrasonic imaging systems, the patterns of detected echoes correspond to the shape, size, and orientation of the reflectors and the physical properties of the propagation path. However, these echoes often are overlapped due to closely spaced reflectors and/or microstructure scattering. The decomposition of these echoes is a major and challenging problem. Therefore, signal modeling and parameter estimation of the nonstationary ultrasonic echoes is critical for image analysis, target detection, and object recognition. In this paper, a successive parameter estimation algorithm based on the chirplet transform is presented. The chirplet transform is used not only as a means for time-frequency representation, but also to estimate the echo parameters, including the amplitude, time-of-arrival, center frequency, bandwidth, phase, and chirp rate. Furthermore, noise performance analysis using the Cramer Rao lower bounds demonstrates that the parameter estimator based on the chirplet transform is a minimum variance and unbiased estimator for signal-to-noise ratio (SNR) as low as 2.5 dB. To demonstrate the superior time-frequency and parameter estimation performance of the chirplet decomposition, ultrasonic flaw echoes embedded in grain scattering, and multiple interfering chirplets emitted by a large, brown bat have been analyzed. It has been shown that the chirplet signal decomposition algorithm performs robustly, yields accurate echo estimation, and results in SNR enhancements. Numerical and analytical results show that the algorithm is efficient and successful in high-fidelity signal representation.     

Status of biodiesel research and development in Pakistan

Performance of biodiesel in engines is well established and biodiesel is currently adjudged as a low carbon fuel with the most potential of replacing fossil fuels. The fossil fuel sources are dwindling in Pakistan resulting in importation of about 8.1 million tonnes at approximately US$ 9.4 billion per annum. In the ambit of this justification, augmenting the energy scarce resources in Pakistan through intense harnessing of the varied biodiesel sources can adequately address the deficiency and can ensure energy security. Towards this end, the progress attained in biodiesel related researches in Pakistan are evaluated and presented with the view of highlighting ways of achieving the target set by the Government. A feedstock that drew less attention is spent triglycerides, and the little work reported by some organizations appeared promising. Now the onus is upon organizations such as the Alternative Energy Development Board and Pakistan State Oil to harness the research results from several indigenous Universities and develop a full-scale biodiesel economy in Pakistan.     

Simulation of erosive smoothing in the abrasive jet micro-machining of glass

Abrasive jet micro-machining (AJM) is a promising technique to machine micro-features in brittle and ductile materials. However, the roughness of micro-channels machined using AJM is generally greater than that from other methods of micro-machining such as wet etching. Previous investigators have suggested that the surface roughness resulting from AJM can be reduced by post-blasting with abrasive particles at a relatively low kinetic energy. This approach was investigated in the present work by measuring the roughness reduction of a reference unmasked channel in borosilicate glass as a function of post-blasting particle size, velocity, dose, and impact angle. Post-blasting the reference channels reduced the roughness by up to 60%. It was observed that post-blasting at shallower angles was more efficient, probably due to the increased amount of edge chipping as opposed to cratering, which contributed to the enhanced removal of profile peaks, leaving a smoother surface. Moreover, post-blasting with smaller particles ultimately resulted in smoother surfaces, but at the penalty of requiring a relatively large particle dose, and consequently a significantly increased channel depth, before reaching the steady-state roughness. Hence, finishing with smaller particles until reaching the steady-state roughness may not be practical when a shallow channel is desired. A previously developed numerical model was modified and used to simulate the post-blasting process leading to the creation of smooth channels as a function of particle size, velocity, dose, impact angle, and target material properties. The model simulated both crater formation (due to growth of lateral cracks) and the chipping of facet edges. Comparisons with centerline roughness measurements for channels in borosilicate glass showed that the model can predict the transient roughness reduction with post-blasting particle dose with a 7% average error.     

Effect of ultrasound radiation on the size and size distribution of synthesized copper particles

The effect of ultrasound radiation on the size and size distribution of synthesized copper particles was investigated under various concentrations of ethylene glycol (E.G.) as a capping agent. Monodispersed copper particles were produced by the reduction of an aqueous copper (II) sulfate solution at the presence of hydrazine monohydrate. X-ray diffraction and scanning electron microscopy analysis revealed that the morphology, size, and size distribution of produced particles were influenced by the reducing agent injection rate, capping agent concentration, and sonication. Increasing the injection rate of reducing agent to an amount higher than a critical value decreases the size of copper particles and also converts the monodispersed particles to polydispersed particles. Results of using a sonifier at the reduction stage revealed that finer monodispersed copper particles can be achieved at higher injection rates related to the critical value. Increasing the concentration of E.G. as a capping agent decreases the size of copper particles, while applying ultrasound radiation along with increasing the concentration of E.G. increases the size of copper particles. Morphology of particles varies by the concentration and type of the capping agent. Higher reducing agent injection rates and the application of a sonifier at the instance of reduction result in smaller spherical particles at various capping agent concentrations.     

Isotropic fading vector broadcast Channels:The scalar upper bound and loss in degrees of freedom

We propose a scalar upper bound on the capacity region of the isotropic fading vector broadcast channel in terms of the capacity region of a scalar fading broadcast channel. The scalar upper bound is applicable to the broad class of isotropic fading broadcast channels regardless of the distribution of the users' channel magnitudes, the distribution of the additive noise experienced by each user, or the amount of channel knowledge available at the receiver. Using this upper bound, we prove the optimality of the Alamouti scheme in a broadcast setting, extend the recent results on the capacity of nondegraded, fading scalar broadcast channels to nondegraded fading vector broadcast channels, and determine the capacity region of a fading vector Gaussian broadcast channel with channel magnitude feedback. We also provide an example of a Rayleigh-fading broadcast channel with no channel state information available to the receiver (CSIR), where the bound on the capacity region obtained by a naive application of the scalar upper bound is provably loose, because it fails to account for the additional loss in degrees of freedom due to lack of channel knowledge at the receiver. A tighter upper bound is obtained by separately accounting for the loss in degrees of freedom due to lack of CSIR before applying the scalar upper bound.     

Synthesis and characterization of alumina flakes/polymer composites

Alumina flakes were prepared by solution combustion method and milled to provide powder. XRD and SEM data exhibited microsized flakes with 100 nm thickness and nanosized grains. Then the powders were dispersed in polystyrene (PS) and poly methyl methacrylate (PMMA) matrixes and thin sheets of composites were produced by solution method. Mechanical properties of the composites were characterized using tensile test and their fracture surfaces, elemental composition and hydrophobic property were tested by SEM, EDX and contact angle techniques, respectively. The results exhibited better mechanical properties compared to pure polymer samples i.e. the elastic modulus in PMMA and PS composites, were increased about 107 and 109%, respectively. In addition the composite surfaces became more hydrophobic than pure polymer systems. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Nanospikes on Customized 3D-Printed Titanium Implant Surface Inhibits Bacterial Colonization

Additive manufacturing has opened the door to patient-tailored orthopedic implants, which can significantly minimize implant failures associated with prosthesis-to-bone mismatch. Success of an implant also depends on the choice of implant materials, effective osseointegration, implant quality, and the mechanical properties together with its capability to limit infection due to bacterial contamination. Herein, nanospikes are created on 3D-printed titanium-alloyed implant surfaces, which can kill bacteria to minimize any implant-associated infections. For the first time, orthopedic implants with a fracture to the proximal phalanx are fabricated using selective laser melting (SLM) followed by a heat-treatment step and the hydrothermal process. It is showed in the results that by optimizing SLM parameters, dimensionally consistent parts can be produced and tensile properties of the 3D-printed implants can be significantly improved via a simple cyclic heat-treatment process compared to the traditionally manufactured implants. Nanospikes similar to those present on dragonfly wings fabricated on 3D-printed implants surface are able to kill above 90% of adhering bacteria by rupturing the membranes upon contact. These results indicate that fabrication of patient-specific 3D-printed implants with inherent bactericidal properties has the potential to eliminate postsurgical infections and possible implant failures.