Unified power quality conditioner based on a three-level NPC inverter using fuzzy control techniques for all voltage disturbances compensation

This paper presents a novel and efficient control scheme for unified power quality conditioner (UPQC) based on three-level neutral point clamped (NPC) inverter using fuzzy logic techniques. The proposed UPQC is capable of mitigating source current harmonics and compensate all voltage disturbances such as voltage sags, swells, unbalances and harmonics. It is designed by the integration of series and shunt active filters (AFs) sharing a common DC bus capacitor. The DC voltage is maintained constant using proportional integral voltage controller. The synchronous reference frame (SRF) theory is used to get the reference signals for shunt active power filters (APFs) and the power reactive theory (p-q theory) for series APFs. The shunt and series APF reference signals derived from the control algorithm and sensed signals are injected in two controllers to generate switching signals. To improve the UPQC capability, fuzzy logic techniques are introduced to control the series APF. The performances of the proposed UPQC system are evaluated in terms of power factor correction, mitigation of voltage or current harmonics and all other voltage disturbances compensation using Matlab-Simulink software and SimPowerSystem toolbox. The simulation results illustrate the performance of the proposed UPQC at the common connection point of the nonlinear load to improve the power energy quality.     

Electro activated water mechanism on Escherichia coli and Enterococcus faecalis and optimization of operating parameters

In this study, the efficacy of electro activated water (EAW) and its mechanism on Escherichia coli and Enterococcus faecalis were investigated. The effects of different operating parameters of EAW on inactivation of bacteria were evaluated by response surface methodology (RSM). The interaction of free chlorine concentration and treatment time at 25 °C had a synergetic effect on E. coli and E. faecalis inactivation. The increase in crystal violet uptake showed the deterioration of cell membrane permeability. The release of 260 nm absorbing materials from both bacteria increased after EAW treatment. Protein degeneration increased with deformation of E. coli and E. faecalis cell membranes, which in turn was followed by the release of proteins together with other intracellular components such as DNA, RNA, potassium, and phosphate.

Practical applications

An electrode module was setup to produce EAW from a mixture of salt and tap water. Freshly prepared EAW was added to the bacterial pellets, mixing thoroughly and immediately initiating a timer. The mixtures were set at different treatment times. The effects of three operating parameters (treatment time, free chlorine concentration (FCC) and temperature) on bacteria inactivation were investigated using Response surface methodology. Crystal violet uptake assay, 260 nm release study and FT‐IR spectroscopy analysis were conducted to determine the mechanism of action of EAW.     

Experimental Investigation of a Bubbly Two-Phase Flow in an Open Capillary Channel under Microgravity Conditions

The study of a bubbly laminar two-phase flow in an open capillary channel under microgravity conditions was conducted aboard the sounding rocket, Texus-45. The channel geometry, the liquid (FC-72) and the experimental conditions were chosen based on an analysis for application toward liquid management in space. The channel consists of two parallel plates that were b = 25 mm wide and separated by a distance of a = 10 mm. The flow along the length l = 80 mm is bounded by a free surface on one side and a plate on the opposite side. Bubbles are injected at the inlet of the capillary channel via six capillary tubes. The features of the gas injection were chosen with regard to the required bubble size, the injection frequency, and the gas and liquid flow rates. Different liquid and gas flow rates were tested leading to a volumetric quality ranging between 0.07 and 0.11. The experimental results show the interaction among bubbles and with the liquid free surface.     

Texture analysis of raw and cooked tubers of short‐duration lines of cassava by multivariate and fractional conversion techniques

BACKGROUND: Cassava tubers are mainly consumed after boiling in water. Their cooking quality depends on the variety, maturity, growing conditions and physicochemical and starch properties. In this study the textural and gelatinisation characteristics of ten short‐duration lines of cassava were assessed. Textural changes due to cooking were modelled by fractional conversion techniques and correlated with gelatinisation and physicochemical properties by principal component analysis. RESULTS: There was a significant variation (P < 0.05) in the textural properties of tubers and the thermal and pasting properties of flours among varieties. The degree of cooking and relative firmness of tubers were modelled by a linear equation. The thermal softening behaviour was modelled by a dual‐mechanism first‐order kinetic model with rate constant values ranging from 0.106 to 0.190 min^?1. About 69.21% of the total variation in texture profile, gelatinisation and physicochemical parameters could be explained by the first three principal components. CONCLUSION: The results indicated that the textural and gelatinisation properties varied considerably among different varieties. However, the interaction between the components of the tubers and the structural make‐up of the tuber tissues played a more important role than the physicochemical and functional properties. Copyright © 2008 Society of Chemical Industry     

Case study of surge avoidance design for centrifugal compressor systems during emergency shut-down (ESD)

Compression systems with centrifugal compressors are widely used in gas involving processes. Surge protection system design is crucial in avoiding any damage in abnormal circumstances such as emergency shutdown (ESD), start-up, coast-down operation, and normal shutdown. We analyzed four cases of existing centrifugal compressor systems, three CO₂ compression systems and one off-gas compression system, to study the surge protection availability during ESD. All compression systems were working well at normal operating condition, but some systems could not avoid surge during ESD. To check the surge cases, the surge criteria flowchart was suggested and surge analysis through dynamic simulation was done using a commercial process simulator. To avoid a surge during ESD, a sensitivity analysis was done while considering the following process parameters: pre-stroke time, anti-surge valve (ASV) type, capacity, and stroke time. We optimized ASV design using response surface method with two selected parameters from the sensitivity study, ASV capacity and stroke time. Finally, the installation of the hot gas recycle system was analyzed to avoid surge occurrence.     

Multi-layer atom chips for atom tunneling experiments near the chip surface

This paper describes the design and fabrication of an atom chip to be used in ultra-high-vacuum cells for cold-atom tunneling experiments. A fabrication process was developed to pattern micrometer- and nanometer-scale copper wires onto a single chip. The wires, with fabricated widths down to 200 nm, can sustain current densities of more than 7.5 × 10⁷ A/cm². Partially suspended wires, developed in order to reduce the Casimir–Polder force between atoms and surface, were also fabricated and tested. Extensive measurements for variable wire width show that the sustainable currents are sufficiently large to allow chip-based atom tunneling experiments. Such chips may allow the realization of an atom transistor.     

Decreased Serum Levels of Sphingomyelins and Ceramides in Sickle Cell Disease Patients

Limited data are available on the serum levels of different sphingomyelin (CerPCho) and ceramide (CER) species in sickle‐cell disease (SCD). This study was aimed at identifying the levels of C16–C24 CerPCho and C16–C24 CER in serum obtained from SCD patients and controls. Circulating levels of neutral sphingomyelinase (N‐SMase) activity, ceramide‐1‐phosphate (C1P), and sphingosine‐1‐phosphate (S1P) were also determined. Blood was collected from 35 hemoglobin (Hb)A volunteers and 45 homozygous HbSS patients. Serum levels of C16–C24 CerPCho and C16–C24 CER were determined by an optimized multiple reaction monitoring (MRM) method using ultrafast liquid chromatography (UFLC) coupled with tandem mass spectrometry (MS/MS). Serum activity of N‐SMase was assayed by standard kit methods, and C1P and S1P levels were determined by enzyme‐linked immunosorbent assay. A significant decrease was observed in the serum levels of C18–C24 CerPCho in patients with SCD compared to controls. No significant difference was found in C16 CerPCho levels between the two groups. Very‐long‐chain C22–C24 CER were significantly decreased in SCD, while long‐chain C16–C20 CER levels showed no significant difference between SCD patients and controls. Significant positive correlation was found between the serum total cholesterol levels and C18–C24 CerPCho and C22–C24 CER in SCD patients. Patients with SCD had significantly elevated serum activity of N‐SMase as well as increased circulating levels of C1P and S1P compared to controls. The decrease in serum levels of C18–C24 CerPCho in patients with SCD was accompanied by decreased levels of C22–C24 CER. Future studies are needed to understand the role of decreased CerPCho and CER in the pathophysiology of SCD.     

Abstractive Text Summarization based on Improved Semantic Graph Approach

The goal of abstractive summarization of multi-documents is to automatically produce a condensed version of the document text and maintain the significant information. Most of the graph-based extractive methods represent sentence as bag of words and utilize content similarity measure, which might fail to detect semantically equivalent redundant sentences. On other hand, graph based abstractive method depends on domain expert to build a semantic graph from manually created ontology, which requires time and effort. This work presents a semantic graph approach with improved ranking algorithm for abstractive summarization of multi-documents. The semantic graph is built from the source documents in a manner that the graph nodes denote the predicate argument structures (PASs)—the semantic structure of sentence, which is automatically identified by using semantic role labeling; while graph edges represent similarity weight, which is computed from PASs semantic similarity. In order to reflect the impact of both document and document set on PASs, the edge of semantic graph is further augmented with PAS-to-document and PAS-to-document set relationships. The important graph nodes (PASs) are ranked using the improved graph ranking algorithm. The redundant PASs are reduced by using maximal marginal relevance for re-ranking the PASs and finally summary sentences are generated from the top ranked PASs using language generation. Experiment of this research is accomplished using DUC-2002, a standard dataset for document summarization. Experimental findings signify that the proposed approach shows superior performance than other summarization approaches.