A control synthesis approach for time discrete event systems

In this paper, we introduce a control synthesis method for discrete event systems whose behavior is dependent on explicit values of time. Our goal is to control the occurrence dates of the controllable events so that the functioning of the system respects given specifications. The system to be controlled is modeled by a time Petri net. In a previous work we proposed a systematic method to build the timed automaton which models the exact behavior of a time Petri net. Furthermore, the forbidden behaviors of the system are modeled by forbidden timed automaton locations. This paper focuses on the control synthesis method, which consists in computing new firing conditions for the timed automaton transitions so that the forbidden locations are no longer reachable.     

Effects of storage on quality of carrot juices produced with lactofermentation and acidification

In this study, effects on the yield and the quality of product properties of carrot juice produced with lactofermentation and added citric acid, and with and without total enzymatic liquefaction (Pectinex Ultra SP-L) were investigated. Samples were stored at room temperature for 6 months and analytical changes which might occur were determined at day 0 and after 2, 4 and 6 months by quality control tests. In enzyme-treated samples, the yield and the quality of mineral incrementation were determined. Accordingly, ash and water-soluble dry matter contents were increased in the samples. Galacturonic acid formed after enzymatic breakdown of pectin in the raw material increased the total acidity of the samples. Sensorial tests of the product were also carried out. According to the test results, the products produced with enzyme treatment at day 0, after 2 and 4 months storages were found to be the ones mostly preferred. However the samples without enzyme treatment were preferred by the panelists after long-term (6 months) storage.     

The kinetics of heat-induced structural changes of beta-lactoglobulin

Heat-induced structural changes of beta-lactoglobulin were studied at temperatures ranging from 67.5 to 82.5 degrees C, and at pH 7.5. These changes were monitored by measurement of surface hydrophobicity, thiol availability, and protein solubility. Kinetic studies were conducted to quantitatively describe the contribution of hydrophobic and SH/SS interchange reactions to the thermal structural changes of beta-lactoglobulin. Results indicate that beta-lactoglobulin is sensitive to heat-induced interchange reactions with consequences for protein solubility. The extent of changes measured by the increase in surface hydrophobicity and the decrease in slow-reacting SH groups content could be described by a first-order fractional conversion model and were characterized by activation energy values of 233.9 +/- 8.6 and 148.2 +/- 6.7 kJ/mol, respectively. The break in the Arrhenius plot suggested in literature for beta-lactoglobulin denaturation was confirmed in this study only for the kinetics of exposed SH groups.     

Study of adsorption characteristics of long chain alkyl amine and petroleum sulfonate on silicates by electrokinetic potential,microflotation, FTIR,and AFM analyses

The long-chain alkyl amines and petroleum sulfonates are mostly used to remove unwanted minerals from feldspar ores in acidic pHs. In this study, their adsorption characteristics on pure albite and quartz were investigated by electrokinetic potential measurements, microflotation tests, Fourier transform infrared spectroscopy, and atomic force microscopy studies. According to the results, amine had strong influence on zeta potentials of both albite and quartz turning them positive and resulting over 90% flotation recovery at certain pH values. Petroleum sulfonate, on the other hand, was less effective in terms of both zeta potential values and flotation recovery responses of albite. Although albite and quartz had different zeta potentials and flotation recovery responses with each collector, they displayed similar adsorption bands of CH₂ group over fingerprint region and adsorption layers with different intensities after being treated with the collectors. However, the adsorption of each collector on the minerals was altered by rinsing with acetone indicating that the interaction of the collectors with albite and quartz surfaces were mostly by Coulombic forces and hydrogen bonding.     

Electrochemical degradation and toxicity reduction of C.I. Basic Red 29 solution and textile wastewater by using diamond anode

Electrochemical oxidation of Basic Red 29 (BR29) was studied in a bipolar trickle tower (BTT) reactor by using Raschig ring shaped boron-doped diamond (BDD) electrodes, which were originally employed by the present researchers, in a recirculated batch mode. The model solution was prepared with BR29 using distilled water. The effects of initial dye concentration, Na(2)SO(4) concentration as supporting electrolyte, current density, flow rate and initial pH on the removal efficiency were investigated, and practically, complete BR29 removal (over 99%) was obtained in all the studies. After optimum experimental conditions were determined, textile wastewater has also studied by monitoring the destruction of color and COD. With the textile wastewater, 97.2% of color and 91% of COD removal were, respectively, achieved at the current density of 1mA/cm(2). Microtox toxicity tests were performed in both BR29 solution and textile wastewater under optimum experimental conditions, and relatively good toxicity reductions were obtained with respect to the initial values. According to the results, BDD anode was seen to be a unique material for the degradation of BR29 and COD and also the reduction of toxicity simultaneously.     

Insights into the physico-chemical behavior of CoCl<Subscript>2</Subscript>/polyimide hybrid materials

Hybrid fluorinated polyimide materials have been obtained by incorporation of various quantities of cobalt(II) chloride (CoCl₂) into polyimide matrix. Polycondensation reaction of equimolar amounts of 4,4′-diamino-3′3′-dimethyldiphenylmethane and 2,2′-bis(3,4-dicarboxyphenyl) hexafluoropropane dianhydride has been carried out to produce in the first stage a polyamidic acid solution in which CoCl₂?×?6H₂O has been placed. Further thermal treatment of this system led to the corresponding imide structure filled with the halide salt. An exhaustive study was directed to the influence of Co²⁺ ions on the modified polyimide behavior as a function of its surroundings. To survey the functional properties of as-obtained Co²⁺-containing polyimide systems, several techniques such as FTIR, UV-vis and broadband dielectric spectroscopy, differential scanning calorimetry, and thermogravimetric and scanning electron microscopy were employed. A special concern was directed to the study of the optical properties induced by the addition of CoCl₂ into polymer solutions and films. The magnetic response of the polyimide was investigated in correlation with the salt quantity embedded in the PI film. The variation of the real and imaginary parts of the hybrid films’ dielectric permittivity was registered in a broad frequency and temperature range, from 10 to 10⁶ Hz and from ?130 to 230 °C, respectively.     

Encrustation Prevention in PVC Reactors

Poly(vinyl chloride) is one of the world's most important bulk thermoplastics. Approximately 15 million tons are produced annually. About 80% of this is made by the suspension process. Suspension polymerization of vinyl chloride is almost invariably accompanied by the formation of scale on the internal surfaces of the polymerization reactor, including moving surfaces such as those of the impeller. The formation of scale, or deposits of PVC, on the internal surfaces of reactors has always been a problem in the manufacture of PVC because of reduced heat transfer, large alteration of the agitation regime present in the reactor, and broken-off scale fragments that block transfer systems and contaminate the product. Therefore scale must be cleaned periodically. Until the early 1970s these deposits were removed manually; PVC workers were exposed to high levels of VCM and considerable production time was lost. The introduction of large reactors in 1975 made it practical to mechanize the cleaning. High-pressure water sprays are employed for this purpose. However, such devices remove only the slightly adherent sandy deposits. For strongly attached deposits, a thorough manual cleaning is necessary after a series of polymerization batches. Manual cleaning requires extensive safety measures to protect the workers from VCM vapor inside the reactor. In addition, such cleaning is costly and undesirable. In more recent years, methods have been developed to suppress or inhibit the formation of scale on the reactor walls. Proposed solutions in this field are sparese. The patient literature claims many chemical treatments to resuce reactor fouling. Many PVC producers have developed effective buildup-suppressant treatments, which significantly reduce the need for reactior cleaning. They vary from treatments to render the reactor wall hydrophilic and reduce the adsorption of VCM (e.g., application of a sulfonic acid polymer to the reactor surface [1]) to systems containing polymerization inhibitors and radical traps (e.g., organic dyes and phenolic resins). The most successful of these probably work by a combination of both mechanisms. In this paper the soultions are reviewed brifly and emphasis is given to suspension polymerization where the initiator is monomer soluble.     

Ab initio lattice dynamics of Ni2MnX (X = Sn, Sb) magnetic shape memory alloys

In this study, we present the results of first principles calculations of elastic constants and phonon properties of nickel-manganese based magnetic shape memory compounds Ni₂MnSn and Ni₂MnSb in stoichiometric composition. The plane wave basis sets and pseudopotential method within spin-polarized generalized gradient approximation (σ-GGA) scheme of the density functional theory is applied. In investigation of the phonon dispersion spectra, linear response technique of the Density Functional Perturbation Theory is used. Phonon softening is observed in dispersion spectra at the transverse acoustic mode (TA₂) in [ζ ζ 0] direction as an indication of the structural instability of these systems to shear deformation. The vibrational instability of Ni₂MnSb system is larger than that of Ni₂MnSn yielding negative phonon frequencies. This vibrational anomaly is also verified by the low shear modulus and large elastic anisotropy ratio. The minority spin Fermi surfaces of both systems exhibit strong nesting features.