Optimal Decentralized Regulation for a Class of Flow Networks

Optimal decentralized regulation is considered for a class of flow networks where, at each intersection, a selective switch links a single input–output pair at anytime. It is shown that a special case of the above is an urban traffic network with signalized intersection. We analyze first the traffic situation of an isolated intersection based on the point-queuing model of traffic and model the intersection dynamics via two states: either unsaturated or saturated. According to the different traffic characteristics of the two states, we design two intersection controllers and then combine them into one hybrid controller. This hybrid controller is extended to the multi-intersection case and becomes a decentralized hybrid intersection controller. A simulation study is given in this paper and it shows that this decentralized hybrid intersection control method can improve the performance of traffic networks and by extension the performance of more general flow networks.     

The gas-sensing potential of nanocrystalline SnO2 produced by a mechanochemical milling via centrifugal action

In this work, the synthesis of undoped nanocrystalline tin dioxide powders and the subsequent preparation of SnO₂ thick-films were studied. An initial mixture of SnCl₂ and Ca(OH)₂ was sealed in a vial for milling in an air atmosphere. Heat treatment of the milled powder resulted in the formation of tetragonal and orthorhombic SnO₂ phases, which was confirmed by X-ray diffraction (XRD) analysis. It was found that crystallite size could be controlled by varying the milling time, the rotation speed and the temperature used for the heat treatment. Crystallite sizes in the range 20 to 30 nm (determined by XRD measurements) were obtained. The total pore volume was 0.22 ml/g for a measured particle size of 37 m²/g. No contamination of the powder during milling was found. The response of the prepared thick-films to H₂S gas in the concentration range 0.5 to 10 ppm in air was investigated as a function of the preparation conditions. The advantage of mechanochemical synthesis of powder is its relative simplicity, low cost and possibility of obtaining isolated, unagglomerated nanosized grains. It is shown that chemical reactions, which usually occur in the vibratory mill to produce the SnO phase, can also be initiated during a short processing time in the centrifugal mill. Received: 25 July 2001 / Accepted: 4 September 2001 / Published online: 20 December 2001     

Excess capacitance of ZnO-Au varactors

Doped ZnO single crystals were deposited with gold and indium in 1×10^–8 Torr vacuum. The lithium-doped ZnO single crystals and the gold interface revealed not only a Schottky diode but also varactor characteristics. TheI-V andC-V characteristics of ZnO:Li-Au devices were determined in the 0–140 mV and 0–1.5 V ranges.The frequency dependence of ZnO:Li-Au varactors was investigated in the 6–550 kHz range and the value of the most efficient varactor frequency was found to be 50 kHz for the lithium-doped samples prepared.To bring further insight into the matter the concept of excess capacitance was introduced and 1/C ²=f(–V) curves were rearranged between 0–150 mV where Schottky characteristics are non-linear. The excess capacitance values of lithium-doped varactors were determined at four different frequencies and ranged from 26 pF at 50 kHz to 70 pF at 6kHz.Finally, the bulk donor concentrations of the single crystals were calculated from the modifiedC-V curves to beN _D= 3×10²⁰ m^–3. On the other hand, the bulk donor concentration determined from the non-modifiedC-V curves wasN _D=1.02×10²² m^–3.     

Simultaneous Determination of Anthocyanin and Ponceau 4R in Drink Powders by Derivative Spectrophotometry and Partial Least-Squares Multivariate Spectrophotometric Calibration

Summary.  Two methods for the simultaneous determination of anthocyanin and ponceau 4R in drink powders by second derivative spectrophotometry and by partial least-squares multivariate spectrophotometric calibration are described. The procedures do not require any separation step. The methods were applied to determine both colorants in commercial gelatin powders; the results obtained are compared. Received September 7, 2000. Accepted (revised) November 20, 2000     

Dynamic compensation temperature in the kinetic spin-2 Ising model in an oscillating magnetic field on alternate layers of a hexagonal lattice

Eigenstate bases are used to study electrical conductivity in graphene in the presence of short-range diagonal disorder and inter-valley scattering. For the first time, the behavior of graphene in a moderate and weak disorderd regime is presented. For disorder strength, W / t ≥  5, the density of states is flat. A connection is then established with the work of Abrahams et al. using Microscopic Renormalization Group (MRG) approach. For disorder strength, W / t = 5, results are in good agreement. For low disorder strength, W / t = 2, energy-resolved current matrix elements squared for different locations of the Fermi energy from the band centre is studied. Explicit dependence of the current matrix elements on Fermi energy is shown. It is found that states close to the band centre are more extended and fall off nearly as 1/E_l ² as one moves away from the band centre. Further studies on current matrix elements versus disorder strength suggests a cross-over from weakly localized to a very weakly localized system. Using the Kubo-Greenwood formula, conductivity and mobility is calculated. For low disorder strength, conductivity is in a good qualitative agreement with the experiments, even for the on-site disorder. The intensity plots of the eigenstates also reveal clear signatures of puddle formation for very small carrier concentration. We also make comparision with square lattice and find that graphene is more easily localized when subject to disorder.     

Optimal design of plastic structures under impulsive and dynamic pressure loading

Optimal design of a rigid-plastic stepped beam and circular plate is considered in the first part of the paper assuming the mode form of motion. The form of optimal mode is sought for which a structure of constant volume attains a minimum of local or mean deflection. It is assumed that the constant kinetic energy Ko is attained by the structure through impulsive loading. Differences between optimal static and dynamic solutions are discussed. Non-uniqueness of modes is demonstrated and significance of stable mode motions is emphasized. In the second part of the paper, an optimal design of a rigid-plastic stepped beam loaded by a uniform pressure over a time interval 0 ? t ? t₁ is considered assuming constant beam volume and looking for a design corresponding to minimum of local deflection. The solution presented is valid for moderate dynamic pressures when mode motion occurs during consecutive time intervals and no travelling plastic hinges exist.     

Surface characterization and H2S-sensing potential of iron molybdate particles produced by supercritical solvothermal method and subsequent oxidation

The mostly crystalline polymorph β-FeMoO₄ was prepared by solvothermal synthesis from organic precursors, followed by high temperature supercritical drying in an autoclave. Crystallization of the synthesized particles occurred during subsequent heat treatment at 350 °C, confirmed by X-ray diffraction pattern analysis. The presence of Fe³⁺ ions in the powder, both well-crystallized and amorphous after heat treatment at 500 °C, was confirmed by room temperature Mössbauer spectrum. Thick-film gas sensors were prepared by conventional hand coating of a paste, the Fe₂(MoO₄)₃ powder mixed with an α-terpineol-based solvent, over the Au electrodes. The response of the prepared sensors to H₂S gas in the low concentration range 1–10 ppm in air was investigated. Moderately fast response and recovery times were observed. The iron molybdate, produced at low temperature, may be successfully used in the preparation of a H₂S gas sensor.     

Solid–liquid interfacial energy of neopentylglycol solid solution in equilibrium with neopentylglycol–(D) camphor eutectic liquid

The grain boundary groove shapes for equilibrated solid neopentylglycol (NPG) solution (NPG–3 mol% D-camphor) in equilibrium with the NPG–DC eutectic liquid (NPG–36.1 mol% D-camphor) have been directly observed using a horizontal linear temperature gradient apparatus. From the observed grain boundary groove shapes, the Gibbs–Thomson coefficient (Г), solid–liquid interfacial energy (σ_SL) of NPG solid solution have been determined to be (7.5±0.7)×10^?8 K m and (8.1±1.2)×10^?3 J m^?2, respectively. The Gibbs–Thomson coefficient versus T_mΩ^1/3, where Ω is the volume per atom was also plotted by linear regression for some organic transparent materials and the average value of coefficient (τ) for nonmetallic materials was obtained to be 0.32 from graph of the Gibbs–Thomson coefficient versus T_mΩ^1/3. The grain boundary energy of solid NPG solution phase has been determined to be (14.6±2.3)×10^?3 J m^?2 from the observed grain boundary groove shapes. The ratio of thermal conductivity of equilibrated eutectic liquid to thermal conductivity of solid NPG solution was also measured to be 0.80.