The Fracture of Concrete due to Erosive Wear by High Velocity Water Flow

Wear and erosion of concrete structures by high velocity water flow is a basic aspect of the durability of marine and water constructions. The mechanism of concrete failure in such constructions is not well understood. Using high velocity water jets for simulating the loading, the authors observed the general behavior of the material during failure and investigated the influence of water velocity and exposure time. The results show that the interface between hardened cement paste and aggregate grains plays the main role in the fracture process. The basic mechanism of material failure is the generation and propagation of cracks at this interface. It is found that a critical loading intensity, which is characterized by a threshold velocity and a threshold exposure time, must be achieved in order to induce the erosion process. Through mass removal measurements, a mathematical relation between both parameters and the erosion intensity is found. Using a computer program for simulating the hydrodynamics inside a crack, the water pressure and flow velocities in a model crack were calculated.     

Mechanism of surface modification of the Ti-6Al-4V alloy using a gas tungsten arc heat source

The surface modification of a Ti-6Al-4V alloy using a gas tungsten arc, as a heat source, was studied. The experimental results show that the titanium alloy surface can be melted and nitrided using pure nitrogen or a nitrogen/argon mixture shielding atmosphere. The resolidified surfaces are 0.9 to 1.2-mm thick and contain titanium nitride dendrites, α-titanium, and α″-titanium (martensite). The average dendrite arm spacing is influenced by the electrode speed. Small titanium nitride dendrites are homogeneously distributed in the resolidified surfaces. The microstructure and phase constitution in the resolidified surfaces were determined and analyzed, and the mechanism of the formation of titanium nitrides is discussed. The results show that the nitriding kinetics obey parabolic laws and are, therefore, controlled by nitrogen diffusion. The nitrogen-concentration depth profiles, calculated using Fick’s second law of diffusion, are compared to experimental nitrogen depth profiles, showing satisfactory agreement.     

3D finite element modeling of the thermally induced residual stress in the hybrid laser/arc welding of lap joint

In this study, a three-dimensional (3D) finite element model is developed to investigate thermally induced stress field during hybrid laser–gas tungsten arc welding (GTAW) process. In the hybrid welding case, we focus on the GTAW process sharing common molten pool with laser beam and playing an augment role in the hybrid welding system. An experiment-based thermal analysis is performed to obtain the temperature history, which then is applied to the mechanical (stress) analysis. A modified material model is used to consider the influence of face-to-face contact between the top and bottom metal sheets in the thermo-mechanical analysis of welding lap joints. Results show that the normal stress components prevail in the weld zone during hybrid welding process, and maximum thermal stress exceeding the yield point of material exists at the heat affected zone (HAZ) near the weld pool. Increasing the welding speed causes the penetration and width of weld bead to decrease, and the thermal stress concentration at the welded joint is also reduced accordingly. After welding and cooling down, longitudinal tensile stress (SZ) and transverse compressive stress (SX) are retained in the formed weld, and the higher longitudinal compressive stress exists around the weld bead. In addition, a series of experiments are performed to validate the numerical results, and a qualitative agreement is achieved. Compared to the welded joint obtained by GTAW and laser welding alone, the residual stress concentration in the weld joint obtained by hybrid laser–GTAW is the minimal one.     

FCO sampling of digital video using perfect reconstruction filterbanks

Three-dimensional nonseparable perfect reconstruction filter banks using three-dimensional nonseparable sampling by two, FCO, are proposed. Filter structures are derived and applied to digital video. Separation into two bands is obtained, and it is shown to perform better from the perceptual point of view than interlaced sequences resulting from the quincunx sampling of a progressively scanned signal in time-vertical dimensions.     

Biguanide Pharmaceutical Formulations and the Applications of Bile Acid-Based Nano Delivery in Chronic Medical Conditions

Biguanides, particularly the widely prescribed drug metformin, have been marketed for many decades and have well-established absorption profiles. They are commonly administered via the oral route and, despite variation in oral uptake, remain commonly prescribed for diabetes mellitus, typically type 2. Studies over the last decade have focused on the design and development of advanced oral delivery dosage forms using bio nano technologies and novel drug carrier systems. Such studies have demonstrated significantly enhanced delivery and safety of biguanides using nanocapsules. Enhanced delivery and safety have widened the potential applications of biguanides not only in diabetes but also in other disorders. Hence, this review aimed to explore biguanides’ pharmacokinetics, pharmacodynamics, and pharmaceutical applications in diabetes, as well as in other disorders.