On the complexity of purely complex μ computation and relatedproblems in multidimensional systems

In this paper, the following robust control problems are shown to be NP-hard: given a purely complex uncertainty structure Δ, determine if: 1) μ_Δ(M)<1, for a given rational matrix M; 2) ∥M(·)∥_μ<1, for a given rational transfer matrix M(s); and 3) inf(Q∈H^∞)∥F(T,Q)∥_μ<1, for a given linear fractional transformation F(T,Q) with rational coefficients. In other words, purely complex μ computation, analysis, and synthesis problems are NP-hard. It is also shown that checking stability and computing the H^∞ norm of a multidimensional system, are NP-hard problems. Therefore, it is rather unlikely to find nonconservative polynomial time algorithms for solving the problems in complete generality     

Effective electrodeposition of poly(3,4-ethylenedioxythiophene)-based organic coating on metallic food packaging for active corrosion protection

Journal of Applied Electrochemistry - Modern technologies continuously need special materials with specific properties to adopt the desired application. Recently, numerous researches have been...     

Tailoring Cu/Al2O3 catalysts for the catalytic pyrolysis of tomato waste

In this study, pyrolysis of tomato waste has been performed in fixed bed tubular reactor at 500 °C, both in absence and presence of Cu/Al₂O₃ catalyst. The influences of heating rate, catalyst preparation method and catalyst loading on bio-oil yields and properties were examined. According to pyrolysis experiments, the highest bio-oil yield was obtained as 30.31% with a heating rate of 100 °C/min, 5% Cu/Al₂O₃ catalyst loading ratio and co-precipitation method. Results showed that the catalysts have strong positive effect on bio-oil yields. Bio-oil quality obtained from fast catalytic pyrolysis was more favorable than that obtained from non-catalytic and slow catalytic pyrolysis.     

On L1 optimal control

It is shown that the problem of minimizing the effect of the worst disturbance on the output, where the signals have finite one norms, is equivalent to the same problem with bounded disturbances. The following situations provide the motivation to study such a problem. (1) Disturbances are generated by a fixed bounded-input, bounded-output (BIBO) stable, linear time-invariant (LTI) system with unknown initial conditions and zero input. (The output of this fixed system is the disturbance input to the original control system). (2) Disturbances are generated by an unknown BIBO stable LTI system whose fixed input consists of the unit impulse (this is the dual of (1)). In both of these situations, the disturbances will have a finite one norm     

Application of economical models for dye removal from aqueous solutions: cash flow,cost–benefit,and alternative selection methods

Although there are numerous adsorption studies performed by using various adsorbents, there is no deterministic knowledge about selection of appropriate adsorbent type from present alternatives. In order to evaluate the advantages of the selected adsorbent species mathematically, researchers may use economical models such as cash flow diagrams, cost–benefit analyses, and alternative selection methods. In spite of the fact that these models have been used in many other engineering branches they are rarely applied in environmental research. In this study we have aimed to investigate usability of the mentioned economical models in adsorption of reactive azo dyes from aqueous solutions. Activated ash, a waste material, and commercial granular activated carbon were decided to be adsorbent alternatives. By applying economical models appropriate adsorbent type was selected considering both adsorption efficiencies and economical conditions. Although similar tendencies were monitored in cash flow diagrams; considering the amount of expenses activated ash exhibited remarkable advantages compared to granular activated carbon. Furthermore, results of cost–benefit analyses showed that activated ash has been advantageous when total costs and profits were evaluated together. Results of this study suggest usage of these economical models even in adsorption studies in order to provide accurate information on the selection of appropriate adsorbent type. These methods enable evaluation of economical conditions, which is generally neglected, together with the obtained removal efficiencies.     

Design and optimization of high-speed resonant cavity enhancedSchottky photodiodes

Resonant cavity enhanced (RCE) photodiodes (PD's) are promising candidates for applications in optical communications and interconnects where high-speed high-efficiency photodetection is desirable. In RCE structures, the electrical properties of the photodetector remain mostly unchanged; however, the presence of the microcavity causes wavelength selectivity accompanied by a drastic increase of the optical field at the resonant wavelengths. The enhanced optical field allows to maintain a high efficiency for faster transit-time limited PD's with thinner absorption regions. The combination of an RCE detection scheme with Schottky PD's allows for the fabrication of high-performance photodetectors with relatively simple material structures and fabrication processes. In top-illuminated RCE Schottky PD's, a semitransparent Schottky contact can also serve as the top reflector of the resonant cavity. We present theoretical and experimental results on spectral and high-speed properties of GaAs-AlAs-InGaAs RCE Schottky PD's designed for 900-nm wavelength     

Biosorption of copper (II) from aqueous solutions by wheat shell

The adsorption capacity of wheat shell for copper (II) was studied at various pH (2-7), agitation speeds (50-250 rpm) and initial metal ion concentrations (Co, from 10 to 250 mg.L⁻¹). Maximum biosorption of copper onto wheat shell occurred at 240 rpm agitation speed and at pH between 5 and 6. The biosorption values of copper (11) were increased with increasing pH from 2 to 5 and decreased with increasing copper/wheat shell (x/m) ratios from 0.83 to 10.84 mgCu(II).g⁻¹ wheat shell. The biosorption efficiencies at these x/m ratios were 99% and 52%, respectively, at the end of the 120 min contact time (t). The equilibrium isotherms and kinetics were obtained from batch adsorption experiments at 298 K. It was observed that wheat shell was a suitable biosorbent for removing Cu(II) from aqueous solutions.     

Organic semiconductor-based photonic crystals for solar cell arrays: band gap and optical properties

Photonic crystals (PCs) hold great potential for designing new optical devices because of the possibility of the manipulation of light with PCs. There has been an increase in research on tuning the optical properties of PCs to design devices. We design organic semiconductor-based PC structures and calculate optical properties using the plane wave expansion method and finite-difference time-domain method in an air background for a hexagonal lattice. We showed the possibility of the solar cell arrays for a 2D PC cavity on an organic semiconductor base infiltrated with a nematic liquid crystal. E7 type has been used as a nematic liquid crystal and 4,4′-Bis[4-(diphenylamino) styryl]biphenyl as an organic semiconductor material.     

Quantifying effects of ramp metering on freeway safety

This study presents a real-time crash prediction model and uses this model to investigate the effect of the local traffic-responsive ramp metering strategy on freeway safety. Safety benefits of ramp metering are quantified in terms of the reduced crash potential estimated by the real-time crash prediction model. Driver responses to ramp metering and the consequent traffic flow changes were observed using a microscopic traffic simulation model and crash potential was estimated for a 14.8 km section of I-880 in Hayward, California and a hypothetical isolated on-ramp network. The results showed that ramp metering reduced crash potential by 5-37% compared to the no-control case. It was found that safety benefits of local ramp metering strategy were only restricted to the freeway sections in the vicinity of the ramp, and were highly dependent on the existing traffic conditions and the spatial extent over which the evaluation was conducted. The results provide some insight into how a local ramp metering strategy can be modified to improve safety (by reducing total crash potential) on longer stretch of freeways over a wide range of traffic conditions.