Dual Z-source inverter with three-level reduced common-mode switching

This paper presents the design of a dual Z-source inverter that can be used with either a single dc source or two isolated dc sources. Unlike traditional inverters, the integration of a properly designed Z-source network and semiconductor switches to the proposed dual inverter allows buck-boost power conversion to be performed over a wide modulation range, with three-level output waveforms generated. The connection of an additional transformer to the inverter ac output also allows all generic wye-or delta-connected loads with three-wire or four-wire configuration to be supplied by the inverter. Modulationwise, the dual inverter can be controlled using a carefully designed carrier-based pulsewidth-modulation (PWM) scheme that will always ensure balanced voltage boosting of the Z-source network while simultaneously achieving reduced common-mode switching. Because of the omission of dead-time delays in the dual-inverter PWM scheme, its switched common-mode voltage can be completely eliminated, unlike in traditional inverters, where narrow common-mode spikes are still generated. Under semiconductor failure conditions, the presented PWM schemes can easily be modified to allow the inverter to operate without interruption, and for cases where two isolated sources are used, zero common-mode voltage can still be ensured. These theoretical findings, together with the inverter practicality, have been confirmed in simulations both using PSIM with Matlab/Simulink coupler and experimentally using a laboratory-implemented inverter prototype.

Electrical insulation of high voltage inductor with co-axial electrode at floating voltage

Inductive fault current limiters (FCLs) have several advantages, such as significant current limitation, immediate triggering and relatively low losses. Despite these advantages, saturated core FCLs have not been commercialized due to its large size and associated high costs. A major remaining challenge is to reduce the footprint of the device. In this paper, a solution to reduce the overall footprint is proposed and discussed. In arrangements of windings on a core in reactors such as FCLs, the core is conventionally grounded. The electrical insulation distance between high voltage winding and core can be reduced if the core is left at floating potential. This paper shows the results of the investigation carried out on the insulation of such a coil-core assembly. Two experiments were conducted. In the first, the behavior of the apparatus under high voltage conditions was assessed by performing power frequency and lightning impulse tests. In the second experiment, a low voltage test was conducted during which voltages of different frequencies and pulses with varying rise times were applied. A finite element simulation was also carried out for comparison and further investigation

Art spaces, public space, and the link to community development

Recent literature credits community art spaces with both enhancing social interaction and engagement and generating economic revitalization. This article argues that the ability of art spaces to realize these outcomes is linked to their role as public spaces and that their community development potential can be expanded with greater attention to this role. An analysis of the public space characteristics is useful because it encourages consideration of sometimes overlooked issues, particularly the effect of the physical environment on outcomes related to community development. I examine the relationship between public space and community development at various types of art spaces including artist cooperatives, ethnic-specific art spaces, and city-sponsored art centers in central city and suburban locations. This study shows that through their programming and other activities, art spaces serve various public space roles related to community development. However, the ability of many to perform as public spaces is hindered by facility design issues and poor physical connections in their surrounding area. This article concludes with proposals for enhancing the community development role of the art spaces through their function as public spaces.

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.

Regulation of microRNA-1288 in colorectal cancer : altered expression and its clinicopathological significance

We aim to examine the miR-1288 expression in cancer cell lines and a large cohort of patients with colorectal cancer. Two colon cancer cell lines (SW480 and SW48) and one normal colonic epithelial cell line (FHC) were recruited. The miRNA expressions of miR-1288 were tested on these cell lines by using quantitative real-time polymerase chain reaction (qRT-PCR). An exogenous miR-1288 (mimic) was used to detect cell proliferation and cell cycle changes in SW480 using MTT calorimetric assay and flow cytometry, respectively. In addition, tissues from 122 patients with surgical resection of colorectum (82 adenocarcinomas, 20 adenomas, and 20 non-neoplastic tissues) were tested for miR-1288 expression by qRT-PCR. The colon cancer cell lines showed reduced expression of miR-1288 compared to normal colonic epithelial cell line. Over expression of miR-1288 in SW480 cell line showed increased cell proliferation and increased G2-M phase cells. In tissues, reduced miR-1288 expression was noted in majority of colorectal adenocarcinoma compared to colorectal adenoma and non-neoplastic tissues. Reduced or absent expression of miR-1288 was noted in 76% (n = 62/82) of the cancers. The expression levels of miR-1288 were higher in distal colorectal adenocarcinomas (P = 0.013) and in cancers of lower T staging (P = 0.033). To conclude, alternation of miR-1288 expression is important in the progression of colorectal cancer. The differential regulation of miR-1288 was found to be related to cancer location and pathological staging in colorectal cancers.

Reactive Oxygen Species and Reactive Nitrogen Species in Epigenetic Modifications

For the normal homeostasis of a cell, there must be a balance between radical oxygen species/radical nitrogen species (ROS/RNS) production and the neutralization of these species by antioxidant scavenging. In times of stress, this balance is not maintained, and the result is oxidative stress. This stress can affect many pathways in the body and result in pathological consequences. Recent evidence suggests that ROS/RNS can affect the epigenetic regulation of genes by affecting the function of histone and DNA modifying enzymes, thus affecting phenotypic changes within the cellular environment. In the following chapter, we provide a broad overview of how oxidative stress induced by ROS/RNS can affect epigenetics, and using lung disease as our model we link the connection between these processes.

Functional role for senataxin, defective in ataxia oculomotor apraxia type 2, in transcriptional regulation

Ataxia oculomotor apraxia type 2 (AOA2) is an autosomal recessive neurodegenerative disorder characterized by cerebellar ataxia and oculomotor apraxia. The gene mutated in AOA2, SETX, encodes senataxin, a putative DNA/RNA helicase which shares high homology to the yeast Sen1p protein and has been shown to play a role in the response to oxidative stress. To investigate further the function of senataxin, we identified novel senataxin-interacting proteins, the majority of which are involved in transcription and RNA processing, including RNA polymerase II. Binding of RNA polymerase II to candidate genes was significantly reduced in senataxin deficient cells and this was accompanied by decreased transcription of these genes, suggesting a role for senataxin in the regulation/modulation of transcription. RNA polymerase II-dependent transcription termination was defective in cells depleted of senataxin in keeping with the observed interaction of senataxin with poly(A) binding proteins 1 and 2. Splicing efficiency of specific mRNAs and alternate splice-site selection of both endogenous genes and artificial minigenes were altered in senataxin depleted cells. These data suggest that senataxin, similar to its yeast homolog Sen1p, plays a role in coordinating transcriptional events, in addition to its role in DNA repair.

Characterization of a DC-driven microplasma between a capillary tube and water surface

A microplasma generated between a stainless-steel capillary and water surface in ambient air with flowing argon as working gas appears as a bright spot at the tube orifice and expands to form a larger footprint on the water surface, and the dimensions of the bell-shaped microplasma are all below 1 mm. The electron density of the microplasma is estimated to be ranging from 5.32 × 109 cm−3 to 2.02 × 1014 cm−3 for the different operating conditions, which is desirable for generating abundant amounts of reactive species. A computational technique is adopted to fit the experimental emission from the N2 second positive system with simulation results. It is concluded that the vibrational temperature (more than 2000 K) is more than twice the gas temperature (more than 800 K), which indicates the non-equilibrium state of the microplasma. Both temperatures showed dependence on the discharge parameters (i.e., gas flow and discharge current). Such a plasma device could be arranged in arrays for applications utilizing plasmainduced liquid chemistry.

A three-level flying-capacitor rectifier based supercapacitor direct integration scheme for distributed generation systems

Supercapacitors are increasingly used as short term energy storage elements in distributed generation systems. The traditional approach in integrating them to the main system is the use of interfacing dc-dc converters which introduce additional costs and power losses. This paper therefore, presents a novel direct integration scheme for supercapacitors and thereby eliminates associated costs and power losses of interfacing converters. The idea is simply to replace ordinary capacitors of three-level flying-capacitor rectifiers with supercapacitors and operate them under variable voltage conditions. An analysis on the reduction of power losses by the proposed system is presented. Furthermore, supercapacitor sizing and implementation issues such as effects of the variable voltage operation and resistive behavior of supercapacitors at high frequencies are also discussed. Simulation results are presented to verify the efficacy of the proposed system in suppressing short term power fluctuations in wind generation system.

In search of the missing link in CSR : an analysis of the government influence

Research on corporate social responsibility (CSR) has not differentiated the varying degree of government influence in its multiple roles on different types of CSR. However, different il1fluences resulting from the different roles he govemment plays in the CSR arena an shape different CSR behavior. This paper examines the efficacy of the govemment influence on four types of corporate social responsibilities: legal, economic, philanthropic and ethical. We argue that the govemment influence on firms' CSR disposition varies in intensizv and salience depending on the level of interdependency between the government and the firm and the deployable strategies available to the govemment. We have identified the strongest link between the government as mandator and legal CSR and weakest link between the govemment as endorser and ethical CSR. We provide implications for government policy makers and future studies in this area.

Mitigation of harmonics of DFIGs in DC-Microgrids

During the last few years, there has been an increased attention paid on the developments of DC microgrids (DCMGs) and their applications. For economical and more flexible wind power generation, doubly fed induction generator (DFIG) is regarded as a most commonly used generator in wind farms. This paper presents a configuration and operation method for a DCMG connected with DFIGs, in which the controller of the DFIG is designed for maximum power point tracking (MPPT). The generation of harmonics and their effects on the generator in this configuration are analyzed and a harmonic compensation method is proposed. Furthermore, the simulation results are presented to show that the DFIG can be operated effectively in DCMGs and harmonic currents can be reduced.

A statistical approach to quantify the impact on voltage quality caused by PV generators

A probabilistic method is proposed to evaluate voltage quality of grid-connected photovoltaic (PV) power systems. The random behavior of solar irradiation is described in statistical terms and the resulting voltage fluctuation probability distribution is then derived. Reactive power capabilities of the PV generators are then analyzed and their operation under constant power factor mode is examined. By utilizing the reactive power capability of the PV-generators to the full, it is shown that network voltage quality can be greatly enhanced.

Investigation of corona sources in high voltage power lines

This paper describes the results of experiments made in the vicinity of EHV overhead lines to investigate sources of clouds of charged particles using simultaneously-recording arrays of electric field meters to measure direct electric fields produced under ion clouds. E-field measurements, made at one metre above ground level, are correlated with wind speed and direction, and with measurements from ionisation counters and audible corona effects to identify possible positions of sources of corona on adjacent power lines. Measurements made in dry conditions on EHV lines in flat remote locations with no adjacent buildings or large vegetation indicate the presence of discrete ion sources associated with high stress points on some types of line hardware such as connectors and conductor spacers. Faulty line components such as insulators and line fittings are also found to be a possible source of ion clouds.

An analysis on the possibility of using capacitors of a three-level capacitor clamped inverter as power smoothing elements for wind power systems

This paper presents a new direct integration scheme for supercapacitors that are used to mitigate short term power fluctuations in wind power systems. The idea is to replace ordinary capacitors of a 3-level flying capacitor inverter by supercapacitors and operate them under variable voltage conditions. This approach eliminates the need of interfacing dc-dc converters for supercapacitor integration and thus considerably improves the overall efficiency. However, the major problem of this unique system is the change of supercapacitor voltages. An analysis on the effects of these voltage variations are presented. A space vector modulation method, built from the scratch, is proposed to generate undistorted current even in the presence of dynamic changes in supercapacitor voltages. A supercapacitor voltage equalisation algorithm is also proposed. Furthermore, resistive behavior of supercapacitors at high frequencies and the need for a low pass filter are highlighted. Simulation results are presented to verify the efficacy of the proposed system in suppressing short term wind power fluctuations.

Beliefs about infant regulation, early infant behaviors and maternal postnatal depressive symptoms

Background: Young infants may have irregular sleeping and feeding patterns. Such regulation difficulties are known correlates of maternal depressive symptoms. Parental beliefs regarding their role in regulating infant behaviours also may play a role. We investigated the association of depressive symptoms with infant feeding/sleeping behaviours, parent regulation beliefs, and the interaction of the two. Method: In 2006, 272 mothers of infants aged up to 24 weeks completed a questionnaire about infant behaviour and regulation beliefs. Participants were recruited from general medical practices and child health clinics in Brisbane, Australia. Depressive symptomology was measured using the Edinburgh Postnatal Depression Scale (EPDS). Other measures were adapted from the ALSPAC study. Results: Regression analyses were run controlling for partner support, other support, life events, and a range of demographic variables. Maternal depressive symptoms were associated with infant sleeping and feeding problems but not regulation beliefs. The most important infant predictor was sleep behaviours with feeding behaviours accounting for little additional variance. An interaction between regulation beliefs and sleep behaviours was found. Mothers with high regulation beliefs were more susceptible to postnatal depressive symptoms when infant sleep behaviours were problematic. Conclusion: Mothers of young infants who expect greater control are more susceptible to depressive symptoms when their infant presents challenging sleep behaviour.