Space vector based modulation scheme for reducing capacitor RMS current in three-level diode-clamped inverter

The DC capacitor is an important component in a voltage source inverter.The RMS current flowing through the capacitor determines the capacitor size and losses. The losses, in turn, influence the capacitor life. This paper proposes a space vector based modulation strategy for reducing the capacitor RMS current in a three-level diode-clamped inverter. An analytical closed-form expression is derived for the DC capacitor RMS current with the proposed PWM strategy. The analytical expression is validated through simulations and also experimentally. Theoretical and experimental results are presented, comparing the proposed strategy with conventional space vector PWM (CSVPWM). It is shown that the proposed strategy reduces the capacitor RMS current significantly at high modulation indices and high power factors. (C) 2014 Elsevier B.V. All rights reserved.

Selective and Sensitive Turn-on Chemosensor for Arsenite Ion at the ppb Level in Aqueous Media Applicable in Cell Staining

A newly designed and structurally characterized cell permeable diformyl-p-cresol based receptor (HL) selectively senses the AsO33- ion up to ca. 4.1 ppb in aqueous media over the other competitive ions at biological pH through an intermolecular H-bonding induced CHEF (chelationenhanced fluorescence) process, established by detailed experimental and theoretical studies. This biofriendly probe is highly competent in recognizing the existence of AsO33- ions in a living organism by developing an image under a fluorescence microscope and useful to estimate the amount of arsenite ions in various water samples.

AN OPTIMUM SHRINKAGE ESTIMATOR BASED ON MINIMUM-PROBABILITY-OF-ERROR CRITERION AND APPLICATION TO SIGNAL DENOISING

We address the problem of designing an optimal pointwise shrinkage estimator in the transform domain, based on the minimum probability of error (MPE) criterion. We assume an additive model for the noise corrupting the clean signal. The proposed formulation is general in the sense that it can handle various noise distributions. We consider various noise distributions (Gaussian, Student's-t, and Laplacian) and compare the denoising performance of the estimator obtained with the mean-squared error (MSE)-based estimators. The MSE optimization is carried out using an unbiased estimator of the MSE, namely Stein's Unbiased Risk Estimate (SURE). Experimental results show that the MPE estimator outperforms the SURE estimator in terms of SNR of the denoised output, for low (0 -10 dB) and medium values (10 - 20 dB) of the input SNR.

Histone H3K9 acetylation level modulates gene expression and may affect parasite growth in human malaria parasite Plasmodium falciparum

Three-dimensional positioning of the nuclear genome plays an important role in the epigenetic regulation of genes. Although nucleographic domain compartmentalization in the regulation of epigenetic state and gene expression is well established in higher organisms, it remains poorly understood in the pathogenic parasite Plasmodium falciparum. In the present study, we report that two histone tail modifications, H3K9Ac and H3K14Ac, are differentially distributed in the parasite nucleus. We find colocalization of active gene promoters such as Tu1 (tubulin-1 expressed in the asexual stages) with H3K9Ac marks at the nuclear periphery. By contrast, asexual stage inactive gene promoters such as Pfg27 (gametocyte marker) and Pfs28 (ookinete marker) occupy H3K9Ac devoid zones at the nuclear periphery. The histone H3K9 is predominantly acetylated by the PCAF/GCN5 class of lysine acetyltransferases, which is well characterized in the parasite. Interestingly, embelin, a specific inhibitor of PCAF/GCN5 family histone acetyltransferase, selectively decreases total H3K9Ac acetylation levels (but not H3K14Ac levels) around the var gene promoters, leading to the downregulation of var gene expression, suggesting interplay among histone acetylation status, as well as subnuclear compartmentalization of different genes and their activation in the parasites. Finally, we found that embelin inhibited parasitic growth at the low micromolar range, raising the possibility of using histone acetyltransferases as a target for antimalarial therapy.

Poly(vinylidene fluoride)-Based Flexible and Lightweight Materials for Attenuating Microwave Radiations

Two unique materials were developed, like graphene oxide (GO) sheets covalently grafted on to barium titanate (BT) nanoparticles and cobalt nanowires (Co-NWs), to attenuate the electromagnetic (EM) radiations in poly(vinylidene fluoride) (PVDF)-based composites. The rationale behind using either a ferroelectric or a ferromagnetic material in combination with intrinsically conducting nanoparticles (multiwall carbon nanotubes, CNTs), is to induce both electrical and magnetic dipoles in the system. Two key properties, namely, enhanced dielectric constant and magnetic permeability, were determined. PVDF/BT-GO composites exhibited higher dielectric constant compared to PVDF/BT and PVDF/GO composites. Co-NWs, which were synthesized by electrodeposition, exhibited saturation magnetization (M-s) of 40 emu/g and coercivity (Hc) of 300 G. Three phase hybrid composites were prepared by mixing CNTs with either BT-GO or Co-NWs in PVDF by solution blending. These nanoparticles showed high electrical conductivity and significant attenuation of EM radiations both in the X-band and in the Ku-band frequency. In addition, BT-GO/CNT and Co-NWs/CNT particles also enhanced the thermal conductivity of PVDF by ca. 8.7- and 9.3-fold in striking contrast to neat PVDF. This study open new avenues to design flexible and lightweight electromagnetic interference shielding materials by careful selection of functional nanoparticles

A 5th and 7th order harmonic suppression scheme using capacitive filtering for 2-level VSI fed IM drive

In this paper, a 5th and 7th harmonic suppression technique for a 2-level VSI fed IM drive, by using capacitive filtering is proposed. A capacitor fed 2-level inverter is used on an open-end winding induction motor to suppress all 5th and 7th order harmonics. A PWM scheme that maintains the capacitor voltage, while suppressing the harmonics is also proposed. The proposed scheme is valid for the entire modulation range, including overmodulation and six-step mode of operation of the main inverter.

Amorphous W-S-N thin films: The atomic structure behind ultra-low friction

Amorphous W-S-N in the form of thin films has been identified experimentally as an ultra-low friction material, enabling easy sliding by the formation of a WS2 tribofilm. However, the atomic-level structure and bonding arrangements in amorphous W-S-N, which give such optimum conditions for WS2 formation and ultra-low friction, are not known. In this study, amorphous thin films with up to 37 at.% N are deposited, and experimental as well as state-of-the-art ab initio techniques are employed to reveal the complex structure of W-S-N at the atomic level. Excellent agreement between experimental and calculated coordination numbers and bond distances is demonstrated. Furthermore, the simulated structures are found to contain N bonded in molecular form, i.e. N-2, which is experimentally confirmed by near edge X-ray absorption fine structure and X-ray photoelectron spectroscopy analysis. Such N-2 units are located in cages in the material, where they are coordinated mainly by S atoms. Thus this ultra-low friction material is shown to be a complex amorphous network of W, S and N atoms, with easy access to W and S for continuous formation of WS2 in the contact region, and with the possibility of swift removal of excess nitrogen present as N-2 molecules. (C) 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Interpreting the upper level structure of the Madden-Julian oscillation

The nonlinear response of a spherical shallow water model to an imposed heat source in the presence of realistic zonal mean zonal winds is investigated numerically. The solutions exhibit elongated, meridionally tilted ridges and troughs indicative of a poleward dispersion of wave activity. As the speed of the jets is increased, the equatorial Kelvin wave is unaffected but the global Rossby wave train coalesces to form a compact, amplified quadrupole structure that bears a striking resemblance to the observed upper level structure of the Madden-Julian oscillation. In the presence of strong subtropical westerly jets, the advection of planetary vorticity by the meridional flow and relative vorticity by the zonally averaged background flow conspire to create the distinctive quadrupole configuration of flanking Rossby waves.

Validation of polyvinylidene fluoride nasal sensor to assess nasal obstruction in comparison with subjective technique

Objective: The aim of this study is to validate the applicability of the PolyVinyliDene Fluoride (PVDF) nasal sensor to assess the nasal airflow, in healthy subjects and patients with nasal obstruction and to correlate the results with the score of Visual Analogue Scale (VAS). Methods: PVDF nasal sensor and VAS measurements were carried out in 50 subjects (25-healthy subjects and 25 patients). The VAS score of nasal obstruction and peak-to-peak amplitude (Vp-p) of nasal cycle measured by PVDF nasal sensors were analyzed for right nostril (RN) and left nostril (LN) in both the groups. Spearman's rho correlation was calculated. The relationship between PVDF nasal sensor measurements and severity of nasal obstruction (VAS score) were assessed by ANOVA. Results: In healthy group, the measurement of nasal airflow by PVDF nasal sensor for RN and LN were found to be 51.14 +/- 5.87% and 48.85 +/- 5.87%, respectively. In patient group, PVDF nasal sensor indicated lesser nasal airflow in the blocked nostrils (RN: 23.33 +/- 10.54% and LN: 32.24 +/- 11.54%). Moderate correlation was observed in healthy group (r = 0.710, p < 0.001 for RN and r = 0.651, p < 0.001 for LN), and moderate to strong correlation in patient group (r = 0.751, p < 0.01 for RN and r = 0.885, p < 0.0001 for LN). Conclusion: PVDF nasal sensor method is a newly developed technique for measuring the nasal airflow. Moderate to strong correlation was observed between PVDF nasal sensor data and VAS scores for nasal obstruction. In our present study, PVDF nasal sensor technique successfully differentiated between healthy subjects and patients with nasal obstruction. Additionally, it can also assess severity of nasal obstruction in comparison with VAS. Thus, we propose that the PVDF nasal sensor technique could be used as a new diagnostic method to evaluate nasal obstruction in routine clinical practice. (C) 2015 Elsevier Inc. All rights reserved.

ADAPTATION OF MW LEVEL NATURAL GAS LEAN BURN ENGINE FOR PRODUCER GAS OPERATION A GRID CONNECTED POWER PLANT

Availability of producer gas engines at MW being limited necessitates to adapt engine from natural gas operation. The present work focus on the development of necessary kit for adapting a 12 cylinder lean burn turbo-charged natural gas engine rated at 900 kWe (Waukesha make VHP5904LTD) to operate on producer and set up an appropriate capacity biomass gasification system for grid linked power generation in Thailand. The overall plant configuration had fuel processing, drying, reactor, cooling and cleaning system, water treatment, engine generator and power evacuation. The overall project is designed for evacuation of 1.5 MWe power to the state grid and had 2 gasification system with the above configuration and 3 engines. Two gasification system each designed for about 1100 kg/hr of woody biomass was connected to the engine using a producer gas carburetor for the necessary Air to fuel ratio control. In the use of PG to fuel IC engines, it has been recognized that the engine response will differ as compared to the response with conventional fueled operation due to the differences in the thermo-physical properties of PG. On fuelling a conventional engine with PG, power de-rating can be expected due to the lower calorific value (LCV), lower adiabatic flame temperature (AFT) and the lower than unity product to reactant more ratio. Further the A/F ratio for producer gas is about 1/10th that of natural gas and requires a different carburetor for engine operation. The research involved in developing a carburetor for varying load conditions. The patented carburetor is based on area ratio control, consisting of a zero pressure regulator and a separate gas and air line along with a mixing zone. The 95 litre engine at 1000 rpm has an electrical efficiency of 33.5 % with a heat input of 2.62 MW. Each engine had two carburetors designed for producer gas flow each capable of handling about 1200 m3/hr in order to provide similar engine heat input at a lower conversion efficiency. Cold flow studies simulating the engine carburetion system results showed that the A/F was maintained in the range of 1.3 +/- 0.1 over the entire flow range. Initially, the gasification system was tested using woody biomass and the gas composition was found to be CO 15 +/- 1.5 % H-2 22 +/- 2% CH4 2.2 +/- 0.5 CO2 11.25 +/- 1.4 % and rest N-2, with the calorific value in the range of 5.0 MJ/kg. After initial trials on the engine to fine tune the control system and adjust various engine operating parameter a peak load of 800 kWe was achieved, while a stable operating conditions was found to be at 750 kWe which is nearly 85 % of the natural gas rating. The specific fuel consumption was found to be 0.9 kg of biomass per kWh.

Seventeen-Level Inverter Formed by Cascading Flying Capacitor and Floating Capacitor H-Bridges

A multilevel inverter for generating 17 voltage levels using a three-level flying capacitor inverter and cascaded H-bridge modules with floating capacitors has been proposed. Various aspects of the proposed inverter like capacitor voltage balancing have been presented in the present paper. Experimental results are presented to study the performance of the proposed converter. The stability of the capacitor balancing algorithm has been verified both during transients and steady-state operation. All the capacitors in this circuit can be balanced instantaneously by using one of the pole voltage combinations. Another advantage of this topology is its ability to generate all the voltages from a single dc-link power supply which enables back-to-back operation of converter. Also, the proposed inverter can be operated at all load power factors and modulation indices. Additional advantage is, if one of the H-bridges fail, the inverter can still be operated at full load with reduced number of levels. This configuration has very low dv/dt and common-mode voltage variation.

Parametric Studies on Saltwater Intrusion into Coastal Aquifers for Anticipate Sea Level Rise

Saltwater intrusion into coastal aquifers is a global issue, exacerbated by increasing demands for freshwater in coastal regions. This study investigates into the parametric analysis on saltwater intrusion in a conceptual, coastal, unconfined aquifer considering wide range of freshwater draft and anticipated sea level rise. The saltwater intrusion under various circumstances is simulated through parametric studies using MODFLOW, MT3DMS and SEAWAT. The MODFLOW is used to simulate the groundwater flow system under changing hydro-dynamics in coastal aquifer. To simulate solute transport MT3DMS and SEAWAT is used. The saltwater intrusion process has direct bearing on hydraulic conductivity and inversely related to porosity. It may also be noted that increase in recharge rate considered in the study does not have much influence on saltwater intrusion. Effect of freshwater draft at locations beyond half of the width of the aquifer considered has marginal effect and hence can be considered as safe zone for freshwater withdrawals. Due to the climate change effect, the anticipated rise in sea level of 0.88 m over a century is considered in the investigation. This causes increase in salinity intrusion by about 25%. The combined effect of sea level rise and freshwater draft (C) 2015 The Authors. Published by Elsevier B.V.

Polyvinylidene fluoride based lightweight and corrosion resistant electromagnetic shielding materials

Various NixCo1-x alloys (with x varying from 0-60 wt%, Ni: nickel, Co: cobalt) were prepared by vacuum arc melting and mixed with polyvinylidene fluoride (PVDF) to design lightweight, flexible and corrosion resistant materials that can attenuate electromagnetic radiation. The saturation magnetization scaled with the fraction of Co in the alloy. Two key properties such as high-magnetic permeability and high-electrical conductivity were targeted. While the former was achieved using a Ni-Co alloy, multiwalled carbon nanotubes (CNTs) in the composites accomplished the latter. A unique approach was adopted to prepare the composites wherein PVDF powder along with CNTs and Ni-Co flakes were made into a paste, using a solvent, followed by hot pressing. Interestingly, CNTs facilitated in uniform dispersion of the Ni-Co alloy in PVDF, as manifested from synergistic improvement in the electrical conductivity. A significant improvement in the shielding effectiveness (41 dB, >99.99% attenuation) was achieved with the addition of 50 wt% of Ni40Co60 alloy and 3 wt% CNTs. Intriguingly, due to the unique processing technique adopted here, the flexibility of the composites was retained and more interestingly, the composites were resistant to corrosion as compared to only Ni-Co alloy.

Panchromatic Borane-aza-BODIPY Conjugate: Synthesis, Intriguing Optical Properties, and Selective Fluorescent Sensing of Fluoride Anions

A new triarylborane-aza-BODIPY conjugate is reported. The compound consists of two blue emissive dimesitylarylborane moieties and a near-infrared (NIR) emissive aza-BOIDPY core and shows panchromatic absorption spanning approximately 300-800 nm. DFT computational studies suggest limited electronic communication between the individual fluorophore units. Hence, the partial energy transfer from blue fluorophore triarylborane to NIR chromophore aza-BODIPY unit leads to a broad dual-emissive feature covering a large part of visible and NIR region. Furthermore, the broadband emissive compound can act as a selective sensor for fluoride anion as a result of fluorescence quenching response in both visible and NIR spectral regions.

Simultaneous perturbation methods for adaptive labor staffing in service systems

We consider the problem of optimizing the workforce of a service system. Adapting the staffing levels in such systems is non-trivial due to large variations in workload and the large number of system parameters do not allow for a brute force search. Further, because these parameters change on a weekly basis, the optimization should not take longer than a few hours. Our aim is to find the optimum staffing levels from a discrete high-dimensional parameter set, that minimizes the long run average of the single-stage cost function, while adhering to the constraints relating to queue stability and service-level agreement (SLA) compliance. The single-stage cost function balances the conflicting objectives of utilizing workers better and attaining the target SLAs. We formulate this problem as a constrained parameterized Markov cost process parameterized by the (discrete) staffing levels. We propose novel simultaneous perturbation stochastic approximation (SPSA)-based algorithms for solving the above problem. The algorithms include both first-order as well as second-order methods and incorporate SPSA-based gradient/Hessian estimates for primal descent, while performing dual ascent for the Lagrange multipliers. Both algorithms are online and update the staffing levels in an incremental fashion. Further, they involve a certain generalized smooth projection operator, which is essential to project the continuous-valued worker parameter tuned by our algorithms onto the discrete set. The smoothness is necessary to ensure that the underlying transition dynamics of the constrained Markov cost process is itself smooth (as a function of the continuous-valued parameter): a critical requirement to prove the convergence of both algorithms. We validate our algorithms via performance simulations based on data from five real-life service systems. For the sake of comparison, we also implement a scatter search based algorithm using state-of-the-art optimization tool-kit OptQuest. From the experiments, we observe that both our algorithms converge empirically and consistently outperform OptQuest in most of the settings considered. This finding coupled with the computational advantage of our algorithms make them amenable for adaptive labor staffing in real-life service systems.