Oscillating magnetic field current drive in a spherical plasma device

The continuous steady-state current drive in a spherical argon plasma by transverse oscillating magnetic field (OMF) is investigated. The experimental results reveal that a rotating magnetic field is generated, and its amplitude depends linearly on the external steady vertical magnetic field. It has been shown that steady toroidal currents of up to about 400 A can be driven by a 490 kHz OMF with an input power of 1.4 kW. The generation of steady toroidal magnetic fields directed oppositely in the upper and lower hemispheres have been recorded. The measurements of time-varying magnetic fields unveil a strong nonlinear effect of the frequency-doubled field harmonics generation. The electron number density and temperature of up to 6.2×1018 m-3 and 12 eV have been obtained. The observed effects validate the existing theory of the OMF current drive in spherical plasmas.

Evaluation of resonant damping techniques for Z-source current-type inverter

For the renewable energy sources whose outputs vary continuously, a Z-source current-type inverter has been proposed as a possible buck-boost alternative for grid-interfacing. With a unique X-shaped LC network connected between its dc power source and inverter topology, Z-source current-type inverter is however expected to suffer from compounded resonant complications in addition to those associated with its second-order output filter. To improve its damping performance, this paper proposes the careful integration of Posicast or three-step compensators before the inverter pulse-width modulator for damping triggered resonant oscillations. In total, two compensators are needed for wave-shaping the inverter boost factor and modulation ratio, and they can conveniently be implemented using first-in first-out stacks and embedded timers of modern digital signal processors widely used in motion control applications. Both techniques are found to damp resonance of ac filter well, but for cases of transiting from current-buck to boost state, three-step technique is less effective due to the sudden intermediate discharging interval introduced by its non-monotonic stepping (unlike the monotonic stepping of Posicast damping). These findings have been confirmed both in simulations and experiments using an implemented laboratory prototype.

Robust control scheme for a microgrid with PFC capacitor connected

Capacitors are widely used for power-factor correction (PFC) in power systems. When a PFC capacitor is installed with a certain load in a microgrid, it may be in parallel with the filter capacitor of the inverter interfacing the utility grid and the local distributed-generation unit and, thus, change the effective filter capacitance. Another complication is the possibility of occurrence of resonance in the microgrid. This paper conducts an in-depth investigation of the effective shunt-filter-capacitance variation and resonance phenomena in a microgrid due to a connection of a PFC capacitor. To compensate the capacitance-parameter variation, an Hinfin controller is designed for the voltage-source- inverter voltage control. By properly choosing the weighting functions, the synthesized Hinfin controller would exhibit high gains at the vicinity of the line frequency, similar to traditional high- performance P+ resonant controller and, thus, would possess nearly zero steady-state error. However, with the robust Hinfin controller, it will be possible to explicitly specify the degree of robustness in face of parameter variations. Furthermore, a thorough investigation is carried out to study the performance of inner current-loop feedback variables under resonance conditions. It reveals that filter-inductor current feedback is more effective in damping the resonance. This resonance can be further attenuated by employing the dual-inverter microgrid conditioner and controlling the series inverter as a virtual resistor affecting only harmonic components without interference with the fundamental power flow. And finally, the study in this paper has been tested experimentally using an experimental microgrid prototype.

A high frequency, low voltage stackable full bridge module for modular multilevel cascade converter (MMCC) research

A new small full bridge module for MMCC research is presented. Each full bridge converter cell is a single small (65 × 30 mm) multilayer PCB with two low voltage high current (22 V, 40 A) integrated half bridge ICs and the necessary isolated control signals and auxiliary power supply (2500 V isolation). All devices are surface mount, minimising cell height (4 mm) and parasitic inductance. Each converter cell can be physically stacked with PCB connectors propagating the control signals and inter-cell power connections. Many cells can be trivially stacked to create a large multilevel converter leg with isolated auxiliary power and control signals. Any of the MMCC family members is then easily formed. With a change in placement of stacking connector, a parallel connection of bridges is also possible. Operation of a nine level parallel full bridge is demonstrated at 12 V and 384 kHz switching frequency delivering a 30 W 2 kHz sinewave into a resistive load. A number of new applications for this novel module aside from MMCC development are listed.

miR-126 in human cancers : clinical roles and current perspectives

miR-126 has been implicated in the processes of inflammation and angiogenesis. Through these processes, miR-126 is implicated in cancer biology, but its role there has not been well reviewed. The aim of this review is to examine the molecular mechanisms and clinicopathological significance of miR-126 in human cancers. miR-126 was shown to have roles in cancers of the gastrointestinal tract, genital tracts, breast, thyroid, lung and some other cancers. Its expression was suppressed in most of the cancers studied. The molecular mechanisms that are known to cause aberrant expression of miR-126 include alterations in gene sequence, epigenetic modification and alteration of dicer abundance. miR-126 can inhibit progression of some cancers via negative control of proliferation, migration, invasion, and cell survival. In some instances, however, miR-126 supports cancer progression via promotion of blood vessel formation. Downregulation of miR-126 induces cancer cell proliferation, migration, and invasion via targeting specific oncogenes. Also, reduced levels of miR-126 are a significant predictor of poor survival of patients in many cancers. In addition, miR-126 can alter a multitude of cellular mechanisms in cancer pathogenesis via suppressing gene translation of numerous validated targets such as PI3K, KRAS, EGFL7, CRK, ADAM9, HOXA9, IRS-1, SOX-2, SLC7A5 and VEGF. To conclude, miR-126 is commonly down-regulated in cancer, most likely due to its ability to inhibit cancer cell growth, adhesion, migration, and invasion through suppressing a range of important gene targets. Understanding these mechanisms by which miR-126 is involved with cancer pathogenesis will be useful in the development of therapeutic targets for the management of patients with cancer.

Signet-ring cell carcinoma of colorectum : current perspectives and molecular biology

PURPOSE Colorectal signet-ring cell carcinoma (SRCC) is rare, and very little detailed information on the molecular biology of the disease is available. METHODS The literature on the clinical, pathological and, in particular, the molecular biology of this rare entity was critically reviewed. The reviewed articles take into account a total of 1,817 cases of SRCC, but only 143 cases have molecular data available. The characteristics of two patients with colorectal SRCC were also discussed. RESULTS Colorectal SRCC mostly occurs in younger patients, is larger and has different site predilection compared with conventional colorectal adenocarcinoma. It can occur as one of the synchronous cancers in the colorectum. The cancer is usually diagnosed at advanced stages because of the late manifestation of symptoms, and aggressive treatment strategy is required. Limited reports in the literature have shown that the variant of colorectal cancer demonstrated a different pattern of genetic alterations of common growth kinase-related oncogenes (K-ras, BRAF), tumour suppressor genes (p53, p16), gene methylation and cell adhesion-related genes related to the Wingless signalling pathway (E-cadherin and beta-catenin) from conventional colorectal adenocarcinoma. Colorectal SRCC also showed high expression of mucin-related genes and genes related to the gastrointestinal system. There was also a higher prevalence of microsatellite instability-high tumours and low Cox-2 expression in colorectal SRCC as opposed to conventional adenocarcinoma. CONCLUSIONS Colorectal SRCC has unique molecular pathological features. The unique molecular profiles in SRCC may provide molecular-based improvements to patient management in colorectal SRCC.

Thermal effect of plasmon oscillations on the tunnel current in gold nanoisland thin film at low laser intensity

The effect of plasmon oscillations on the DC tunnel current in a gold nanoisland thin film (GNITF) is investigated using low intensity P~1W/cm2 continuous wave lasers. While DC voltages (1–150 V) were applied to the GNITF, it was irradiated with lasers at different wavelengths (k¼473, 532, and 633 nm). Because of plasmon oscillations, the tunnel current increased. It is found that the tunnel current enhancement is mainly due to the thermal effect of plasmon oscillations rather than other plasmonic effects. The results are highly relevant to applications of plasmonic effects in opto-electronic devices.

Effect of ion current density on the properties of vacuum arc-deposited TiN coatings

The influence of ion current density on the thickness of coatings deposited in a vacuum arc setup has been investigated to optimize the coating porosity. A planar probe was used to measure the ion current density distribution across plasma flux. A current density from 20 to 50 A/m2 was obtained, depending on the probe position relative to the substrate center. TiN coatings were deposited onto the cutting inserts placed at different locations on the substrate, and SEM was used to characterize the surfaces of the coatings. It was found that lowdensity coatings were formed at the decreased ion current density. A quantitative dependence of the coating thickness on the ion current density in the range of 20-50 A/m2 were obtained for the films deposited at substrate bias of 200 V and nitrogen pressure 0.1 Pa, and the coating porosity was calculated. The coated cutting inserts were tested by lathe machining of the martensitic stainless steel AISI 431. The results may be useful for controlling ion flux distribution over large industrial-scale substrates.

Effect of broadcast baiting on abundance patterns of red imported fire ants (Hymenoptera: Formicidae) and key local ant genera at long-term monitoring sites in Brisbane, Australia

In 2001, the red imported fire ant (Solenopsis invicta Buren) was identified in Brisbane, Australia. An eradication program involving broadcast bait treatment with two insect growth regulators and a metabolic inhibitor began in September of that year and is currently ongoing. To gauge the impacts of these treatments on local ant populations, we examined long-term monitoring data and quantified abundance patterns of S. invicta and common local ant genera using a linear mixed-effects model. For S. invicta, presence in pitfalls reduced over time to zero on every site. Significantly higher numbers of S. invicta workers were collected on high-density polygyne sites, which took longer to disinfest compared with monogyne and low-density polygyne sites. For local ants, nine genus groups of the 10 most common genera analyzed either increased in abundance or showed no significant trend. Five of these genus groups were significantly less abundant at the start of monitoring on high-density polygyne sites compared with monogyne and low-density polygyne sites. The genus Pheidole significantly reduced in abundance over time, suggesting that it was affected by treatment efforts. These results demonstrate that the treatment regime used at the time successfully removed S. invicta from these sites in Brisbane, and that most local ant genera were not seriously impacted by the treatment. These results have important implications for current and future prophylactic treatment efforts, and suggest that native ants remain in treated areas to provide some biological resistance to S. invicta.

Doubly Fed Induction Generator for wind energy generation using nine-switch power converter

A Three-Phase Nine-Switch Converter (NSC) topology for Doubly Fed Induction Generator in wind energy generation is proposed in this paper. This converter topology was used in various applications such as Hybrid Electric Vehicles and Uninterruptable Power Supplies. In this paper, Nine-Switch Converter is introduced in Doubly Fed Induction Generator in renewable energy application for the first time. It replaces the conventional Back-to-Back Pulse Width Modulated voltage source converter (VSC) which composed of twelve switches in many DFIG applications. Reduction in number of switches is the most beneficial in terms of cost and power switching losses. The operation principle of Nine-Switch Converter using SPWM method is discussed. The resulting NSC performance of rotor side current control, active power and reactive control are compared with Back-to Back voltage source converter performance. DC link voltage regulation using front end converter is also presented. Finally the simulation results of DFIG performances using NSC and Back-to-Back VSC are analyzed and compared.

Reduction and adsorption of Pb2+ in aqueous solution by nano zero-valent iron : a SEM, TEM and XPS study

This study reports the synthesis, characterization and application of nano zero-valent iron (nZVI). The nZVI was produced by a reduction method and compared with commercial available ZVI powder for Pb2+ removal from aqueous phase. Comparing with commercial ZVI, the laboratory made nZVI powder has a much higher specific surface area. XRD patterns have revealed zero valent iron phases in two ZVI materials. Different morphologies have been observed using SEM and TEM techniques. EDX spectrums revealed even distribution of Pb on surface after reaction. The XPS analysis has confirmed that immobilized lead was present in its zero-valent and bivalent forms. ‘Core-shell’ structure of prepared ZVI was revealed based on combination of XRD and XPS characterizations. In addition, comparing with Fluka ZVI, this lab made nZVI has much higher reactivity towards Pb2+ and within just 15 mins 99.9% removal can be reached. This synthesized nano ZVI material has shown great potential for heavy metal immobilization from waste water.

Dispersion of zero valent iron nanoparticles onto bentonites and the decolourization of orange II

Nano Zero valent iron (Fe0) were reported as an effective material for azo dye removal, however, similar to other nano-materials, ultra-fine powder has a strong tendency to agglomerate into larger particles, resulting in an adverse effect on both effective surface area and catalyst performance. Here we report nano sized Fe0 particles dispersed onto the surface of natural bentonites. X-ray diffraction was used to study the sample phases. Scanning electron microscopy and transmission electron microscopy were applied to study the morphology and morphological changes. Spherical individual Fe0 particles were observed after dispersion onto bentonites, and these samples were used for orange II (OII) decolourization with wide working pH range. Higher reactivity is attributed to good dispersion of Fe0 particles on clay minerals’ surface. This study is significant for providing novel modified clay based catalyst materials for the decolourization of azo dye contaminants from wastewater.

Mode switching DFIG for low voltage ride through

With the rapid development of world-wide wind energy generation using doubly fed induction generations (DFIGs), low voltage ride through (LVRT) has become a great concern. This paper focuses on a unique topology of DFIG called IG connection mode to help the DFIG ride through grid faults smoothly. Transient analysis of IG connection mode is carried out to derive the generator currents. With this analysis, the control strategy for IG connection mode DFIG was developed. From the simulation results, it is clearly visible that IG mode could work in both normal and low grid voltage conditions. Simulation results clearly show that the DFIG with the proposed mode switching control could smoothly ride through low voltage grid faults while satisfying grid code requirements.

Design of mode switching scheme for low-voltage ride-through of doubly fed induction generators

A mode switching doubly fed induction generator (MSDFIG) scheme is proposed for the purpose of achieving low-voltage ride-through for wind turbines. The MSDFIG operates as a doubly fed induction generator (DFIG) under normal condition but upon the detection of a low-voltage incident, the generator is to smoothly transfer to operate under the induction generator mode through the switching in of a set of stator-side crowbar. The MSDFIG automatically reverts back to the DFIG mode when network voltage recovers. A new strategy on the control of the crowbar resistance is included. Analysis shows that the proposed MSDFIG scheme can ride through the complete low-voltage and voltage recovery stages. Effectiveness of the scheme is demonstrated through simulation and experiment studies.

Cascaded multilevel converter based bidirectional inductive power transfer (BIPT) system

A typical low power IPT system employs an H-Bridge converter with a simple control strategy to generate a high frequency current from DC power supply. This paper proposes a cascaded multilevel converter for bidirectional IPT (BIPT) systems, which is suitable for low to medium power applications as well as for situations such as PV cells where several individual DC sources are to be utilized. A novel modulation strategy is proposed for the multilevel converter with the aim of minimizing switching losses. Series - Series (SS) compensation circuit is adopted for the IPT system and a mathematical model is presented to minimize the coil losses of the system under varying output power. Theoretical results presented in comparison to the simulations to demonstrate the applicability of the proposed concept and the validity of the developed model. The experimental results show the feasibility of the proposed phase shift modulation.