Fixed‐order robust H∞ control and control‐oriented uncertainty set shaping for systems with ellipsoidal parametric uncertainty

In this paper, sufficient conditions for robust output feedback controller design for systems with ellipsoidal parametric uncertainty are given in terms of solutions to a set of linear matrix inequalities. A polynomial method is employed to design a fixed‐order controller that assigns closed‐loop poles within a given region of the complex plane and that satisfies an H_∞ performance specification. The main feature of the proposed method is that it can be extended easily for control‐oriented uncertainty set shaping using a standard input design approach. Consequently, the results can be extended to joint robust control/input design procedure whose controller structure and performance specifications are translated into the requirements on the input signal spectrum used in system identification. This way, model uncertainty set can be tuned for the robust control design procedure. The simulation results show the effectiveness of the proposed method. Copyright © 2010 John Wiley & Sons, Ltd.     

Hot Compression Behavior of AsCast Precipitation Hardening Stainless Steel

 High temperature deformation characteristics of a semiaustenitic grade of precipitation hardening stainless steels were investigated by conducting hot compression tests at temperatures of 900-1 100 ℃ and strain rates of 0001-1 s-1. Flow behavior of this alloy was investigated and it was realized that dynamic recrystallization (DRX) was responsible for flow softening. The correlation between critical strain for initiation of DRX and deformation parameters including temperature and strain rate, and therefore, Zener Hollomon parameter (Z) was studied. Metallographic observation was performed to determine the as deformed microstructure. Microstructural observation shows that recrystallized grain size increases with increasing the temperature and decreasing the strain rate. The activation energy required for DRX of the investigated steel was determined using correlations of flow stress versus temperature and strain rate. The calculated value of activation energy, 460 kJ/mol, is in accordance with other studies on stainless steels. The relationship between peak strain and Z parameter is proposed.     

Grafting of ion-imprinted polymers on the surface of silica gel particles through covalently surface-bound initiators: a selective sorbent for uranyl ion

A new ion imprinted polymer coated silica gel sorbent has been prepared using the radical "grafting from" polymerization method through surface-bound azo initiators for selective uranyl uptake. The introduction of azo initiator onto the silica surface was achieved by the reaction of surface amino groups with 4,4'-azobis(4-cyanopentanoic acid chloride). The grafting step was then carried out in a stirred solution of initiator-modified silica particles in the presence of uranyl ion and functional and cross-linking monomers. The prepared sorbent was characterized using FT-IR spectroscopy, scanning electron microscopy (SEM), elemental analysis (EA), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and BET adsorption isotherm analysis. The influence of the uranyl concentration, pH, and flow rate of solution on the grafted polymer affinity has been investigated. Maximum uptake of uranyl ion was observed at a pH 3.0. The rebinding behavior of the sorbent has been successfully described by the Langmuir-Freundlich isotherm. The dynamic column capacity of sorbent and enrichment factor for uranyl ion were 52.9 +/- 3.4 micromol g(-1) and 52, respectively. It was found that imprinting results in increased affinity of the sorbent toward uranyl ion over strong competitor metal ions such as Fe(III) and Th(IV). The sorbent was repeatedly used and regenerated for 3 months without any significant decrease in polymer binding affinities. Finally the sorbent was applied to the preconcentration and determination of uranyl ion in real water samples.     

Reaction pathway of NiAl/WC nanocomposite synthesized from mechanical activated NiAlWC powder system

In this work, the mechanism of WC formation during mechanical alloying and subsequent annealing of nickel, aluminum, tungsten, and graphite powder mixtures was investigated. X-ray diffraction was used to evaluate phase changes. Microstructural and morphological evaluations of the powders were examined by FESEM and TEM. The XRD results confirmed that phase changes occurred by increasing milling time. After 10?h of ball milling, NiAl and W₂C phases formed and new tungsten carbides were synthesized by increasing of milling time. After 40?h, W was consumed completely and WC, WC_1-x, W₂C carbides along with NiAl were produced. After heat treatment of 40?h milled powder, W₂C and WC_1-x phases disappeared and NiAl/WC nanocomposite was formed. The results confirmed that the WC formation was a gradual reaction controlled by atomic diffusion.     

Photocatalytic degradation and mineralization of dye pollutants from wastewater under visible light using synthetic CuO-VO2/TiO2 nanotubes/nanosheets

CuO-VO₂/TiO₂ as a new nanocomposite was synthesized through hydrothermal method and identified by various spectroscopic techniques including X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), energy dispersive X-ray analysis (EDX), UV–visible, differential reflectance spectroscopy (DRS), and Mott–Schottky. The presence of nanotubes/nanosheets in the synthesized nanocomposite was confirmed by HR-TEM. The anatase and rutile crystalline forms of TiO₂ were detected by Raman spectroscopy and X-ray diffraction (XRD). XPS analysis confirmed the presence of CuO and VO₂ in the nanocomposite. The surface area and the band-gap energy of the nanocomposite were determined via N₂ adsorption–desorption analysis and DRS. The presence of a p–n junction between TiO₂ (n-type) and CuO/VO₂ (p-type) was confirmed by the Mott–Schottky analysis. The photocatalytic activity of the nanocomposite against methylene blue (MB), methyl orange (MO), and cango red (CR) was studied under visible-light irradiation. The times of degradation for the decomposition of the dyes were 10–25 min. The rate constants of degradation for MB, MO, and CR were calculated as 0.34, 0.090, and 0.155 min^?1, respectively. The catalyst was recovered four times. In addition, the mineralization of the dyes was investigated by chemical oxygen demand (COD). The reaction was performed in the presence of different radical scavengers, and the ·OH was found to be the predominantly active species in the photodegradation of the dyes.

     

Reduced graphene oxide/Cu<Subscript>2</Subscript>O nanostructure composite films as an effective and stable hydrogen evolution photocathode for water splitting

An efficient photocathode consisting of reduced graphene oxide/Cu₂O/Cu (rGO/Cu₂O/Cu) has been successfully prepared in this work via a facile two step method, consisting of chemical oxidation of a copper foil in alkaline solution using (NH₄)₂S₂O₈ as the oxidizing agent, dipping the prepared samples in graphene oxide (GO) solution and calcination at vacuum to form a rGO layer onto Cu₂O/Cu photocathode, which acts as a protective layer. The products were composed of a thin Cu₂O layer topped with a thin rGO film as the protective coating. The chemical composition and rGO amount in the composite materials were easily controlled by changing the immersion time to enhance PEC performance. UV–Vis spectroscopy, Raman spectroscopy, XRD, SEM, TEM and FTIR spectroscopy were used in the optical and morphological characterization of the graphene oxide and prepared photocathodes. Distinct patches of GO film are formed on the Cu(OH)₂ nanostructure surface, as shown by SEM results. Linear sweep voltammetry and chronoamperometry analysis have been applied in the photoelectrochemical characterizations in the dark and under illumination conditions. Photocurrent density provided by rGO/Cu₂O/Cu photocathode ??2.54 mA cm^??2 is three times greater than that of bare Cu₂O/Cu photocathode ??0.82 mA cm^??2 at 0 V vs. RHE under illumination. Low photostability of 42% is exhibited by bare Cu₂O/Cu photocathode after 200 s irradiation whereas rGO/Cu₂O/Cu photocathode shows approximately 98% of the initial photocurrent density. Therefore, a strategy has been developed in this work for the synthesis of this new photocathode using Cu₂O/Cu as an effective photocathode for photoelectrochemical (PEC) water splitting.     

Cascade delta-sigma modulator with pseudo-differential comparator-based switched-capacitor gain stage

A low-power, multi-stage delta-sigma modulator with comparator-based switched-capacitor (CBSC) gain stages is presented. The presented design eliminates the need for operational amplifiers and replaces them by comparators with current sources at their outputs to alleviate the effects of continued technology scaling on analog and mixed-signal circuits. The proposed technique significantly reduces power consumption and can be applied to switched-capacitor delta-sigma modulators of arbitrary order. Based on the proposed methodology, a 2-1 cascade, single-bit, pseudo-differential switched-capacitor delta-sigma modulator is developed and achieves a SNDR of 76.8 dB with an oversampling ratio of 64 at a clock frequency of 8 MHz.     

Hardware design of a new genetic based disk scheduling method

Disk management is an increasingly important aspect of operating systems research and development because it has great effect on system performance. As the gap between processor and disk performance continues to increase in modern systems, access to mass storage is a common bottleneck that ultimately limits overall system performance. In this paper, we propose hardware architecture of a new genetic based real-time disk scheduling method. Also, to have a precise simulation, a neural network is proposed to simulate seek-time of disks. Simulation results showed the hardware implementation of proposed algorithm outperformed software implementation in term of execution time, and other related works in terms of number of tasks that miss deadlines and average seeks.     

Development of wear resistant pressing moulds for the production of diamond composites

In the powder metallurgical process, diamond material composites are produced by pressing and sintering of a mixture, consisting of diamond and metal powder like cobalt. Due to the high hardness of diamond, the surface of press die is easily damaged. To increase the life time of press dies, thin layers, deposited by PVD, has been employed. First, the standard tests, such as scratch test and pin-on-disc, were performed in order to characterize the adhesion and the tribology of the coatings. The results of standard tests were evaluated by 3D surface analyzer, SEM, and light microscope. Afterwards, PVD thin layers were deposited on the inner surface of the dies in order to analyze and compare their behavior during the compaction process. The results evidenced remarkable effect of thin PVD coatings on enhancing wear resistance of the press dies.     

Generalization of Maximum A Posteriori Amplitude Estimator Under Speech Presence Uncertainty for Speech Enhancement

In this paper, we focus on the estimation-based frequency-domain speech enhancement methods under speech presence uncertainty. Through the minimization of an average risk function, a generalization of maximum a posteriori spectral amplitude estimator is derived. By adjusting the cost parameters, we can control the error caused by noise falsely detected as speech. Our experimental results show that the proposed system can be a simple alternative to Abramson’s simultaneous detection and estimation approach for speech enhancement since it involves merely estimation under speech presence uncertainty and does not require any detector. Moreover, the proposed estimator takes advantage of a more straightforward implementation, since there is no need for the computation of Bessel functions.