Modelling and autoresonant control design of ultrasonically assisted drilling applications

The target of the research is to employ the autoresonant control technique in order to maintain the nonlinear oscillation mode at resonance (i.e. ultrasonic vibration at the tip of a drill bit at a constant level) during vibro-impact process. Numerical simulations and experiments have been executed. A simplified Matlab-Simulink model which simulates the ultrasonically assisted machining process consists of two parts. The first part represents an ultrasonic transducer that contains a piezoelectric transducer and a 2-step concentrator (waveguide). The second part reflects the applied load to the ultrasonic transducer due to the vibro-impact process. Parameters of the numerical models have been established based on experimental measurements and the model validity has been confirmed through experiments performed on an electromechanical ultrasonic transducer. The model of the ultrasonic transducer together with the model of the applied load was supplemented with a model of the autoresonant control system. The autoresonant control intends to provide the possibility of self-tuning and self-adaptation mechanism for an ultrasonic transducer to maintain its resonant regime of oscillations automatically by means of positive feedback. This is done through a signal to be controlled (please refer to Figure 7.2 and Figure 7.3) transformation and amplification. In order to examine the effectiveness and the efficiency of the autoresonant control system, three control strategies have been employed depending on the attributes of the signals to be controlled . Mechanical feedback control uses a displacement signal at the end of the 2nd step of the ultrasonic transducer. The other two control strategies are current feedback control and power feedback control. Current feedback control employs the electrical current flowing through the piezoceramic rings (piezoelectric transducer) as the signal to be controlled while power feedback control takes into account both the electrical current and the power of the ultrasonic transducer. Comparison of the results of the ultrasonic vibrating system excitation with different control strategies is presented. It should be noted that during numerical simulation the tool effect is not considered due to the complexity of a drill bit creates during the Ultrasonically Assisted Drilling (UAD) process. An effective autoresonant control system was developed and manufactured for machining experiments. Experiments on Ultrasonically Assisted Drilling (UAD) have been performed to validate and compare with the numerical results. Two sizes of drill bits with diameters 3mm and 6mm were applied in combination with three autoresonant control strategies. These were executed during drilling aluminium alloys with one fixed rotational speed associated with several different feed rates. Vibration levels, control efforts, feed force reduction were monitored during experiments. Holes quality and surface finish examinations supplement analysis of the autoresonant control results. In addition, another interesting research on the investigation of the universal matchbox (transformer) has been carried out. Introducing a varying air gap between two ferrite cores allows the optimization of the ultrasonic vibrating system, in terms of the vibration level, effective matchbox inductance, voltage and current level, phase difference between voltage and current, supplied active power etc (more details please refer to Appendix I)

Professional development of sessional academic staff in Australian universities

Since the 1970s the use of sessional academics has intensified. Sessional academics perform a critical role within the university and make a strong contribution to the quality of teaching outcomes. However, the management of these staff and training and development programs for them are under-developed. Given the increasing number of sessional academics, and the contributions of sessional academics to university work, it is time to recognize how important sessional academics have become and to research how these sessional academics are supported in their duties. The research project identifies and explains training and development issues facing sessional academic staff. The review of literature highlights the increasing casualization of the academic workforce and a training deficit situation. The research design is a mixed method case study involving a group of ten sessional academics, two full-time academics and their managers at X University Y Campus'. It covers the stories of their differing experiences of professional development, and explores their concerns and feelings in detail. Documentary data are gathered and analyzed in order to triangulate data gathered from interviews. The documents form a valuable source of information about sessional academics' purported training and development opportunities. The study contributes to the literature about sessional academics' training and development opportunities and provides suggestions for a model for improved support and training for sessional academic staff If acted on, the suggestions and model will provide sessional academics opportunities to develop professionally, to improve their own practice and, indirectly, to improve the achievement of their students. The study has the potential not only to improve the skill level of sessional academic staff at the University studied, but also implies benefits to universities, students and our community.</p

Enriching Chinese-English Bilingual Education with Translanguaging: an Australian case-study

Abstract for presentation at ALAA2016/ALS2016 joint day

Aggregation and Dissolution of Silver Nanoparticles in Natural Surface Water

This study investigated aggregation and silver release of silver nanoparticles suspended in natural water in the absence and presence of artificial sun light. The influence of the capping layer was investigated using uncoated particles and particles coated with citrate or Tween 80. The experiments were conducted over 15 days in batch mode using a river water matrix. Silver release was monitored over this time while the aggregation state and morphological changes of the silver nanoparticles were tracked using dynamic light scattering and transmission electron microscopy. Results indicate sterically dispersed particles coated with Tween released silver quicker than did bare- and citrate-coated particles, which rapidly aggregated. A dissolved silver concentration of 40 μg/L was reached after just 6 h in the Tween-coated particle systems, accounting for ca. 3% of the total silver. Similar levels of dissolved silver were reached in the uncoated and citrate-coated systems at the end of the 15 days. Silver release was not significantly impacted by the artificial sun light; however, the light (and citrate) imparted significant morphological changes to the particles. Their impact was masked by aggregation, which seemed to be the controlling process in this study

DataSheet1_A New Technique to Quantify the Local Predictability of Extreme Events: The Backward Nonlinear Local Lyapunov Exponent Method.docx

Extreme weather events have a large impact on society, but are challenging to forecast accurately. In this study, we carried out a theoretical investigation of the local predictability of extreme weather events using the Lorenz model. We introduce a new method using the backward nonlinear local Lyapunov exponent to quantitatively estimate the local predictability limits of extreme events. The local predictability limits of extreme events on an individual orbit of a dynamical trajectory are broadly the same, whereas this is not the case if they are on different orbits. The specific structure of the Lorenz attractor is responsible for this phenomenon. Our results show that the local predictability limits of extreme events do not decrease or increase monotonically as the events increase in magnitude. This indicates that the magnitude of extreme events is not the only factor that affects the local predictability. The dynamical flow, initial error size, and structure of an attractor may also affect the local predictability. We also quantitatively compared the local predictability of extreme warm and cold events. This showed that the local predictability limits of extreme warm events are higher than extreme cold events at the same probability. A statistical analysis (i.e., the minimum, first quartile, median, third quartile, and maximum) also suggests that the extreme warm events have higher local predictability limits. In general, extreme warm events are more predictable than extreme cold events.</p

BBr₃‑Assisted Preparation of Aromatic Alkyl Bromides from Lignin and Lignin Model Compounds

For the first time, BBr3-assisted nucleophilic substitution was applied to a variety of β-O-4 and α-O-4 model compounds for the highly effective cleavage of different C–O bonds, including C–Oα‑OH, Cβ–O/Cα–O and CMe–O bonds (<0.5 h and >99% conversion for most cases). Without any pretreatment, the substitution proceeds at room temperature in the absence of any catalyst, or additive, selectively affording phenols and important organic synthesis reagents, aromatic alkyl bromides, in high to excellent yields (up to 98%). Preliminary studies also highlight the prospect of this method for the effective cleavage of different types of C–O bonds in real lignin. A total 14 wt % yield of aromatic alkyl bromide, 4-(1,2-dibromo-3-hydroxypropyl)­benzene-1,2-diol (10), has been obtained from an extracted lignin through this method

Developing students’ English language capability and advancing academic learning through translanguaging practices: a case study in higher education

Abstract for presentation at ALAA2016 conference

In Situ-Doped Sulfonated Schiff-Base Networks in SPEEK Composite Membranes with Enhanced Proton Conductivity

Sulfonated polyether ether ketone (SPEEK) has been widely investigated in proton exchange membrane fuel cells (PEMFCs) due to its excellent thermal stability, chemical stability, and low cost compared with Nafion. However, excessive degree of sulfonation will easily lead to the decrease in thermal stabilities and mechanical properties of SPEEK membranes, which limits the enhancement of proton conductivity. In this work, a series of Schiff-base networks (SNWs) with different contents are in situ synthesized in the SPEEK membrane by a Schiff-base co-condensation reaction, and then, the composite membranes are soaked in sulfonic acid for further improvement of proton conductivity. The highest doping amount of the SNW filler in SPEEK can reach 20 wt %. High loading and low leaching rate of H2SO4 are easily achieved owing to the similar size between sulfuric acid molecules and micropores in SNW. Moreover, abundant amino and imine groups in SNW networks contribute to the anchoring of H2SO4 into the pores by acid–base interactions. The proton conductivity of the SPEEK/S-SNW-15 composite membrane can reach 115.53 mS cm–1 at 80 °C and 100% RH. Meanwhile, the composite membrane also exhibits satisfied stability and mechanical property

Aggregation Kinetics and Dissolution of Coated Silver Nanoparticles

Determining the fate of manufactured nanomaterials in the environment is contingent upon understanding how stabilizing agents influence the stability of nanoparticles in aqueous systems. In this study, the aggregation and dissolution tendencies of uncoated silver nanoparticles and the same particles coated with three common coating agents, trisodium citrate, sodium dodecyl sulfate (SDS), and Tween 80 (Tween), were evaluated. Early stage aggregation kinetics of the uncoated and coated silver nanoparticles were assessed by dynamic light scattering over a range of electrolyte types (NaCl, NaNO3, and CaCl2) and concentrations that span those observed in natural waters. Although particle dissolution was observed, aggregation of all particle types was still consistent with classical Derjaguin–Landau–Verwey–Overbeek (DLVO) theory. The aggregation of citrate-coated particles and SDS-coated particles were very similar to that for the uncoated particles, as the critical coagulation concentrations (CCC) of the particles in different electrolytes were all approximately the same (40 mM NaCl, 30 mM NaNO3, and 2 mM CaCl2). The Tween-stabilized particles were significantly more stable than the other particles, however, and in NaNO3 aggregation was not observed up to an electrolyte concentration of 1 M. Differences in the rate of aggregation under diffusion-limited aggregation conditions at high electrolyte concentrations for the SDS and Tween-coated particles, in combination with the moderation of their electrophoretic mobilities, suggest SDS and Tween imparted steric interactions to the particles. The dissolution of the silver nanoparticles was inhibited by the SDS and Tween coatings, but not by the citrate coating, and in chloride-containing electrolytes a secondary precipitate of AgCl was observed bridging the individual particles. These results indicate that coating agents could significant influence the fate of silver nanoparticles in aquatic systems, and in some cases these stabilizers may completely prevent particle aggregation

Fabrication of a Superhydrophobic, Fire-Resistant, and Mechanical Robust Sponge upon Polyphenol Chemistry for Efficiently Absorbing Oils/Organic Solvents

In this study, a superhydrophobic, fire-resistant, and mechanical robust sponge was fabricated through a two-step polyphenol chemistry strategy for efficiently absorbing oils/organic solvents (<i>rapidness in absorption rate and large quantity in absorption capacity</i>). Specifically, the Fe^(III)–polyphenol complex is formed upon the metal–organic coordination between tannic acid (TA, a typical polyphenol) and Fe^(III) ions, which is spontaneously coated on the surface of the pristine melamine sponge. Then, free catechol groups in the polyphenol are applied for grafting 1-dodecanethiol, thus generating the superhydrophobic sponge. Several characterizations have confirmed the chemical/topological structures, superhydrophobicity, fire-resistant merits, and mechanical robust property of the sponge. As a result, this sponge exhibits excellent absorption capacities of oils/organic solvents up to 69–176 times its own weight, indicating promising sorbents for removing oily pollutants from water. Meanwhile, owing to the facile fabrication process and inexpensive/easy available raw materials, the large-scale production of this sponge will be convenient and cost-effective