Optical Diagnostics of Anode Surface Temperature in Vacuum Interrupters with Different CuCr Compositions

The requirements for contact material in vacuum interrupters are demanding because the arc medium is formed by electrode evaporation during the operation. Copper chromium alloy (CuCr) is widely used as contact material. Different compositions could result in a different rate of successful interruption. This work compares vacuum arc properties for two CuCr compositions - 75/25 and 50/50 weight percent. The contact surface temperature is measured during and after the vacuum arc with an AC current flow at 2kA magnitude. Quantitative characterization of the contact surface temperature was obtained with near-infrared spectroscopy using Planck curve fitting and spectrally filtered high-speed photography. Evaluation of the anode surface temperature has shown a slower surface cooling for CuCr 50/50 compared to 75/25. Despite this, CuCr 75/25 has experienced higher temperature with dispersion in a larger area during the arcing time, in a successful current interruption

Correction: Analysis of the transient response of a dual-fed RC transmission line

This is an Erratum for Analysis of the transient response of a dual-fed RC transmission line. PLoS One 10(3):e0116993-1-e0116993-11 Article number 2 2015. DOI: http://doi.org/10.1371/journal.pone.0116993.The transient analysis of a uniform transmission line of finite length is considered in this paper. For the first time this paper provides an analytical expression for the time-domain response of an RC transmission line, which is stimulated by a step function that is fed into both ends of the transmission line. In particular, we find an analytical expression for the step response at the center of the transmission line, in order to determine the worst-case rise time. This is of interest, for example, in large charge-coupled device (CCD) arrays, where long polysilicon lines are dual-fed in order to mitigate degradation in rise time. The analytical expressions for the RC transmission line are supported by computer-simulated lumped RC models.Mohsen Dorraki, Gregory K. Cambrell, Derek Abbot

Downregulation of Caspase 8 in a group of Iranian breast cancer patients – A pilot study

Acknowledgments Author contributions: MA performed related laboratory work, helped with sample collection, analysed the data and drafted the manuscript. ND and FAJ helped with sample collection and laboratory work. ASF and MG confirmed the diagnosis and provided the appropriate specimens. AP conceived and designed the study, supervised the project and edited the manuscript. The authors would like to thank the research council of Mashhad University of Medical Sciences, Mashhad, Iran for the financial support (Grant Number: 940936).Peer reviewedPublisher PD

Parameter identification using moment of velocity

Many physical systems can be adequately modelled using a second-order approximation. Thus, the problem of system identification often reduces to the problem of estimating the position of a single pair of complex–conjugate poles. This paper presents a convenient but approximate technique for the estimation of the position of a single pair of complex–conjugate poles, using the moment of velocity (MoV). The MoV is a Hilbert transform based signal processing tool that addresses the shortcomings of instantaneous frequency. We demonstrate that the MoV can be employed for parameter identification of a dynamical system. We estimate the damping coefficient and oscillation frequency via MoV of the impulse response.M. Dorraki, M.S. Islam, A. Allison and D. Abbot

The development of tumour vascular networks

The growth of solid tumours relies on an ever-increasing supply of oxygen and nutrients that are delivered via vascular networks. Tumour vasculature includes endothelial cell lined angiogenesis and the less common cancer cell lined vasculogenic mimicry (VM). To study and compare the development of vascular networks formed during angiogenesis and VM (represented here by breast cancer and pancreatic cancer cell lines) a number of in vitro assays were utilised. From live cell imaging, we performed a large-scale automated extraction of network parameters and identified properties not previously reported. We show that for both angiogenesis and VM, the characteristic network path length reduces over time; however, only endothelial cells increase network clustering coefficients thus maintaining small-world network properties as they develop. When compared to angiogenesis, the VM network efficiency is improved by decreasing the number of edges and vertices, and also by increasing edge length. Furthermore, our results demonstrate that angiogenic and VM networks appear to display similar properties to road traffic networks and are also subject to the well-known Braess paradox. This quantitative measurement framework opens up new avenues to potentially evaluate the impact of anti-cancer drugs and anti-vascular therapies

Hip osteoarthritis: A novel network analysis of subchondral trabecular bone structures

Hip osteoarthritis (HOA) is a degenerative joint disease that leads to the progressive destruction of subchondral bone and cartilage at the hip joint. Development of effective treatments for HOA remains an open problem, primarily due to the lack of knowledge of its pathogenesis and a typically late-stage diagnosis.We describe a novel network analysis methodology for microcomputed tomography (micro-CT) images of human trabecular bone.We explored differences between the trabecular bone microstructure of femoral heads with and without HOA. Large-scale automated extraction of the network formed by trabecular bone revealed significant network properties not previously reported for bone. Profound differences were discovered, particularly in the proximal third of the femoral head, where HOA networks demonstrated elevated numbers of edges, vertices, and graph components. When further differentiating healthy joint and HOA networks, the latter showed fewer small-world network properties, due to decreased clustering coefficient and increased characteristic path length. Furthermore,we found that HOA networks had reduced length of edges, indicating the formation of compressed trabecular structures. In order to assess our network approach,we developed a deep learningmodel for classifying HOA and control cases, and we fed it with two separate inputs: (i) micro-CT images of the trabecular bone, and (ii) the network extracted from them. The model with plain micro-CT images achieves 74.6% overall accuracy while the trained model with extracted networks attains 96.5% accuracy. We anticipate our findings to be a starting point for a novel description of bone microstructure in HOA, by considering the phenomenon from a graph theory viewpoint.Mohsen Dorraki, Dzenita Muratovic, Anahita Fouladzadeh, Johan W. Verjans, Andrew Allison, David M. Findlay and Derek Abbot

Investigation on Fault Current Making in Medium Voltage Switchgear in Air

Closing a switch under a fault condition could result in extensive electrical contact wear and a possible switch failure. A load break switch (LBS), as one of the critical components in medium voltage (MV) power grids, should be able to be closed under short circuit currents of thousands of amperes. The dielectric breakdown between closing contacts creates a pre-strike arc before the contacts touch. Part of the short circuit current flows through the pre-strike arc, and the rest passes through the contacts when sliding through each other. The dissipated energy in the switching arc is partly absorbed by the electrical contact surfaces, increasing their temperature to melting and evaporation points. This increase may result in switch failure because of contacts welding when molten contact surfaces are closed. Depending on the dielectric strength of the insulation gas, the prestrike arcing time could be different. SF6 has been the most efficient insulation gas because of its high dielectric strength and thermal properties. However, it should be replaced because it is one of the most potent greenhouse gases. This PhD thesis focuses on making operations in air MV-LBS. A synthetic test circuit for making short-circuit current and a model switch are designed based on standards. Different measurement methods are employed to investigate the switch degradation and failure in short-circuit making operations. Arc emission spectroscopy is performed to characterize the pre-strike arc properties at different closing speeds. The arc dynamic motion concluded from the spatially resolved temperature profiles at different times shows that the arc gets stabilized after a few hundred microseconds in the middle of the switch between contacts. Based on the derived temperature profiles, an indirect way of estimating the arc voltage has been proposed, which was in agreement with the corrected direct measurements. Furthermore, electrical characterization of the making is performed at different stages of the operation. For the model switch, higher dissipated arc energies at the same current level result in higher contact mass loss, while an increase in the closing speed over proportionally reduces the contact degradation. The destructive energy of the pre-strike arc causing contacts degradation is measured to be at least one order of magnitude higher than the energy dissipation by ohmic loss when the current flows between sliding contacts in the closed position. Therefore, it can be concluded that the most destructive impact of making operation occurs at the first half-cycle of the short circuit current where the prestrike arc exists. The results of short circuit current making tests with one half-cycle could be extended to the test conditions according to IEC 62271-103 standard, where the minimum duration of short circuit current flow should be 0.2 s

A Mathematical and Engineering Approach to the Investigation of C-Reactive Protein as a Cancer Biomarker and the Evolution of Cancer Networks

Although medical intervention has been successful at least for some pathologies, cancer remains one of the greatest killers in the world, mainly in western countries. As a valuable tool in the fight against cancer, mathematical modelling has recently been added to the research field. The mathematical modelling of cancer provides an exact framework for understanding cancer evolution and for testing biological hypotheses. By translating biological complexity and translating biological components of cancer development into mathematical terms, the modelling process describes cancer-related phenomena as a complex set of interactions with the emerging outcome predicted by mathematical investigation that defines the field of mathematical oncology. In fact, this field is characterized by two key features: i) that mathematical models can be applied to develop a quantitative understanding cancer, and ii) that biology proposes new mathematical challenges, which motivate enhanced mathematical tools. Therefore, this PhD thesis investigates a mathematical approach to cancer, and the research include a number of sub-projects. Specifically, investigations of the behaviour of Creactive protein (CRP) as a cancer biomarker and evolution of cancer vascular networks is carried out. The first part of this thesis considers the role of biomarkers such as CRP in cancer prognosis starting with a comprehensive literature review on CRP. We then provide a prescription for CRP data sampling in clinical trials. Also, we investigate CRP forecasting and prediction via deep learning and ARIMA approaches. The remainder of the thesis concerns the use of graph theory in cancer vascular networks. This can split into two types: angiogenesis and vascular mimicry. We first review mathematical and computational models for angiogenesis. Then, we investigate the networks formed by pancreatic and breast cancers and endothelial cells, by applying graph theory to experimental cell growth data.Thesis (Ph.D.) -- University of Adelaide, School of Electrical & Mechanical Engineering, 202

Optical investigation on pre-strike arc characteristics in medium-voltage load break switches

Medium voltage load break switches (MV-LBS) should pass fault current while closing and be able to re-open for the next operation. Replacing SF6 as a high impact greenhouse insulating gas with air, makes the switch design more challenging because of the higher pre-strike arcing time and energy dissipation between contacts which leads to more contact surface erosion and an even higher possibility of welding. In this paper, a synthetic test circuit is used to emulate stresses applied to MV-LBS during the making of short-circuit currents. Since there are difficulties in accurate direct measurement of arc voltage because of the inherent response of the measurement system, an alternative method using optical emission spectroscopy (OES) is proposed. OES measures the pre-strike arc temperature distribution profile close to the cathode surface at a test voltage of 18 kV and a making current of 17 kA. The arc electrical characterization is achieved using the obtained spectroscopy results, Lowke's model and thermal air plasma transport properties. A maximum arc temperature of 12 500 K while the arc moves from the lower part of the cathode to the center, arc voltage of 30–58 V, and dissipated energy of 79–87 J are calculated for the pre-strike arc considering the impact of copper evaporated from the contact surfaces. Different arc behavior is observed in closing the contacts compared to free-burning arcs, which indicates gas flow blowing the arc caused by the contact movement. This investigation could be used for a better understanding of switching behavior and efficient control of the operation

Spectroscopic Investigation of Metal Content in Prestrike Arc During Making Operation in a Low-Current Model Switch

Energy dissipation during prestrike arc is the critical factor for electrical contacts erosion and welding in medium voltage load break switches. Using air-filled devices as an alternative to SF₆ makes the switch environmentally friendly, but leads to a more challenging process due to a higher prestrike arcing time between contacts. Therefore, understanding the erosion process of electrical contacts is crucial to improve the switch lifetime. Determination of contacts surface evaporation by optical emission spectroscopy is one of the most precise methods to investigate the prestrike arc interface with the contacts. In this article, the temporal and spatial profiles of copper and tungsten emitted species during prestrike arc are presented. For this purpose, a circuit consisting of a synthetic dc high voltage part is used to initiate the arc. The temporal evolution of CuI, CuII, and WI shows evaporation of the cathode and the anode surfaces during the prestrike arc, and the spatial profiles show an inhomogeneous distribution of the vapors alongside the arc root