Pressure measurements in laboratory-scale blast wave flow fields

The present study examines the effects that temporal and spatial averagings due to finite size and finite response time of pressure transducers have on the pressure measurements in blast wave flow fields generated by milligram charges of silver azide. In such applications, the characteristic time and length scales of the physical process are of the same order of magnitude as the temporal and spatial characteristics of the transducer. The measured pressure values will then be spatially and temporally averaged, and important parameters for the assessment of blast effects may not be properly represented in the measured trace. In this study, face-on and side-on pressure transducer setups are considered. In the experiments, face-on and side-on readings at the same distance from the charge as well as time-resolved optical visualization of the whole flow field are obtained simultaneously for the same explosive event. The procedure of data extraction from the experimental pressure traces is revisited and discussed in detail. In the numerical modeling part of the study, numerical blast flow fields are generated using an Euler flow solver. A numerical pressure transducer model is developed to qualitatively simulate the averaging effects. The experimental and numerical data show that the results of pressure measurements in experiments with small charges must be used with great caution. The effective averaging of the pressure signal may lead to a significant underestimation of blast wave intensities. The side-on setup is especially prone to this effect. The face-on setup provides results close to those obtained from optical records only if the pressure transducer is sufficiently remote from the charge.     

An experimental study on micro-EDM in low-resistivity deionized water using short voltage pulses

Deionized water has been used as dielectric fluid for micro-electrical discharge machining (micro-EDM) because it gives higher material removal rate and lower tool wear than hydrocarbon oil. Moreover, it is a relatively low-cost and eco-friendly substance. Therefore, deionized water tends to be more favorable for micro-EDM. However, it causes weak electrochemical reaction during micro-EDM due to its slight conductivity. This leads to the unanticipated additional material removal from the workpiece which affects the machining shape and quality. The study in this paper aims to suppress the electrochemical reaction in die-sinking micro-EDM using deionized water by employing short voltage pulse. Experiments were carried out to fabricate micro-holes using the developed nanosecond pulse circuit. Different pulse parameters were applied to identify the main factor affecting the electrochemical reaction rate. Machining gap was found to be thinner and workpiece surface adjacent to the rim of micro-holes were found to be free of defects caused by material dissolution when pulse duration reached a critical value. Moreover, the influence of pulse parameters on material removal rate and machined shape was also investigated. Besides, energy-dispersive X-ray spectroscopy analysis showed that the machined surface using deionized water was less affected from material migration during micro-EDM process in comparison to hydrocarbon oil.     

Retardation of High-Temperature Fuel Ash Corrosion of Fireside Boiler Tubes via Nanoparticles

The high-temperature corrosion rate of boiler tubes was studied as a function of inhibitor concentration, time, and temperature in the absence and presence of fuel ash. Samples of steel tubes were taken from boilers that operate in Northern Baghdad Station for Electric Power Generation. Fuel ash was collected from the boiler combustion chamber, as well. Normal and nano-MgO were used as a corrosion inhibitor in different mixing ratios. A weight loss technique was used to evaluate the corrosion rates, while scanning electron microscopy was used to study the surface morphology. It was seen that corrosion rates increased with both time and temperature, and decreased with the addition of inhibitors. The maximum inhibitor efficiency was 81 %, obtained via using nano-MgO at mixing weight ratio 2:1, 600 °C, and 10 h. The Presence of fuel ash had harmful effects on the steel surface.     

An experimental investigation on the effects of exponential window and impact force level on harmonic reduction in impact-synchronous modal analysis

A novel method called Impact-synchronous modal analysis (ISMA) was proposed previously which allows modal testing to be performed during operation. This technique focuses on signal processing of the upstream data to provide cleaner Frequency response function (FRF) estimation prior to modal extraction. Two important parameters, i.e., windowing function and impact force level were identified and their effect on the effectiveness of this technique were experimentally investigated. When performing modal testing during running condition, the cyclic loads signals are dominant in the measured response for the entire time history. Exponential window is effectively in minimizing leakage and attenuating signals of non-synchronous running speed, its harmonics and noises to zero at the end of each time record window block. Besides, with the information of the calculated cyclic force, suitable amount of impact force to be applied on the system could be decided prior to performing ISMA. Maximum allowable impact force could be determined from nonlinearity test using coherence function. By applying higher impact forces than the cyclic loads along with an ideal decay rate in ISMA, harmonic reduction is significantly achieved in FRF estimation. Subsequently, the dynamic characteristics of the system are successfully extracted from a cleaner FRF and the results obtained are comparable with Experimental modal analysis (EMA).     

Formulation and characterisation of nanosuspension of herbal extracts for enhanced antiradical potential

Nanotechnology is a promising technique to increase the bioavailability of herbal medicines. This paper presents the nanosuspension approach for increasing the aqueous solubility and thereby bioactivity of important herbal extracts. Nanosuspensions of the seeds of three plants extract (Silybum marianum, Elettaria cardamomum and Coriandrum sativum) were prepared by using polyvinyl alcohol (1.5% w/v) as a stabiliser. Prepared nanoparticles were characterised by scanning electron microscope. Activity of nanosuspension formulation was assessed by using four in vitro antioxidant assays. S. marianum, E. cardamomum and C. sativum particle size was observed to fall in range of 446.1 ± 112.6, 456.63 ± 339.2 and 432.1 ± 172.8 nm, respectively, most of the particles were having spherical shape and smooth topology. These synthesised nanoparticles were found to be more effective against quenching free radical than their crude extracts and standards [butylated hydroxyl toluene and ascorbic acid]. C. sativum nanosuspension showed most free radical scavenging potential against 2,2-diphenyl-1-picrylhdrazyl (DPPH) and superoxide free radical scavenging assays (IC₅₀ 0.59 ± 0.01 and 0.81 ± 0.11 mg/ml). S. marianum nanosuspension was found to be most effective against DPPH radicals scavenging (IC₅₀ 0.34 ± 0.02 mg/ml). It was concluded that nanosuspension of herbal medicines potentiates the antioxidant potential.     

Schulze and ranked-pairs voting are fixed-parameter tractable to bribe,manipulate, and control

Schulze and ranked-pairs elections have received much attention recently, and the former has quickly become a quite widely used election system. For many cases these systems have been proven resistant to bribery, control, or manipulation, with ranked pairs being particularly praised for being NP-hard for all three of those. Nonetheless, the present paper shows that with respect to the number of candidates, Schulze and ranked-pairs elections are fixed-parameter tractable to bribe, control, and manipulate: we obtain uniform, polynomial-time algorithms whose running times’ degrees do not depend on the number of candidates. We also provide such algorithms for some weighted variants of these problems.     

Assessment of organic acid-rich bio-sap to generate electricity

The study has focused on electricity generation from organic acid-rich bio-substrate like star fruit (Averrhoa carambola). The sap of star fruit was selected as an electrolyte due to the presence of significant amounts of organic acids such as citric acid and ascorbic acid. To preserve the sap, 2% phenol by volume was used to reduce the growth of microorganisms, and the addition of phenol did not affect the initial pH. It was observed that due to an increase in the electrode surface area, reaction rate and current generation had been amplified. Internal resistance also decreased rapidly because of the large electrode surface area. Furthermore, internal resistance was the significant barrier in electricity generation, which was also successfully controlled by the baffle flow agitation system. Moreover, the baffle flow agitation system reduces the formation of dead zones and increases the total dissolved solids inside the electrochemical cell compartments during operation.