The use of invariants is an important tool for analysis of distributed and concurrent systems modeled by Petri nets. For a large practical system, the computation of desired invariants by the existing techniques is a time-consuming task. This paper proposes a theoretical foundation for simplified computation of desired invariants. We provide invariant-preserving Petri net reduction rules followed by the conditions for the existence of invariants in various well-structured nets. If an invariant exists, it can be found directly from the net structure using the formulas derived, or by applying the existing techniques on the reduced net. 相似文献
Bottom Ash, a power plan t waste material and De-Oiled Soya, an agriculture waste product were successfully utilized in removing trisodium 2-hydroxy-1-(4-sulphonato-1-naphthylazo)naphthalene-3,6-disulphonate--a water-soluble hazardous azo dye (Amaranth). The paper incorporates thermodynamic and kinetic studies for the adsorption of the dye on these two waste materials as adsorbents. Characterization of each adsorbent was carried out by I.R. and D.T.A. curves. Batch adsorption studies were made by measuring effects of pH, adsorbate concentration, sieve size, adsorbent dosage, contact time, temperature etc. Specific rate constants for the processes were calculated by kinetic measurements and a first order adsorption kinetics was observed in each case. Langmuir and Freundlich adsorption isotherms were applied to calculate thermodynamic parameters. The adsorption on Bottom Ash takes place via film diffusion process at lower concentrations and via particle diffusion process at higher concentrations, while in the case of De-Oiled Soya process only particle diffusion takes place in the entire concentration range. 相似文献
Sludge, soil and leachate samples collected from a chromium-contaminated tannery waste dumping site in Kanpur, India, were found to contain considerable amounts of Cr(VI), despite the fresh tannery sludge containing little or no Cr(VI). Literature reports suggested that dry Cr(III) precipitates could be converted to Cr(VI) when heated in the presence of oxygen. Also, Cr(III) in aqueous phase could be oxidized through interaction with manganese dioxide (MnO2) surface to Cr(VI). Measurement of manganese in the sludge samples collected from the site showed concentrations up to 0.6 mg/g. Based on equilibrium calculations, it was determined that both dry phase Cr(III) oxidation by atmospheric oxygen and aqueous phase Cr(III) oxidation by MnO2 surface were thermodynamically feasible. It was further suggested that in aqueous phase, manganese may act effectively as an electron transporter between Cr(III) and dissolved oxygen during Cr(III) oxidation, leading to regeneration of MnO2 solid phase. Further, as dissolved Cr(III) is oxidized, dissolution of Cr(OH3) will take place to maintain the equilibrium between the dissolved and solid phases of Cr(III). In the pH range of 3-10, and at oxygen partial pressure (P(O2)) of 10(-6) atm or higher, equilibrium conditions stipulate nearly complete conversion of Cr(III) to Cr(VI). At P(O2) of 10(-20) atm or lower, very little Cr(VI) is expected to be present under equilibrium conditions. In the intermediate P(O2) regions, incomplete dissolution of the Cr(OH3) solid phase and only partial conversion of chromium from +3 to the +6 oxidation state is expected, especially at lower pH values. 相似文献
Microreactors as a novel concept in chemical technology enable the introduction of new reaction procedures in chemistry, pharmaceutical industry, and molecular biology. These miniaturized reaction systems offer many exceptional technical advantages for a large number of applications. One major application is in the bulk synthesis of nanoparticles. Despite the availability of a plethora of nanoparticle synthesis processes, there exist many difficulties in controlling the shape, size, and purity of nanoparticles in large quantities in a safe and cost-effective manner. These difficulties have been the principal factors adversely limiting the applications of ceramic nanoparticles. Recent experiments have shown that to study the process of growth and formation of nanoparticles, a reactor having much smaller dimensions, namely a microreactor is more appropriate. These studies have also shown that a microchannel reactor provides control over the mean residence time and hence over the nanoparticle size and shape. This paper deals with the design, fabrication, and testing issues related to a high temperature, ceramic microreactor by investigating the use of reactive gas streams in arrays of microchannel reactors. These innovations offer the potential to overcome the barriers associated with synthesis of ceramic nanoparticles in large quantities. 相似文献
Novel and potent inhibitors of Plasmodium falciparum plasmepsin II were identified by post‐processing the results of a docking screening with BEAR, a recently reported procedure for the refinement and rescoring of docked ligands in virtual screening. FRET substrate degradation assays performed on the 30 most promising compounds resulted in 26 inhibitors with IC50 values ranging from 4.3 nM to 1.8 μM .
We present a method to determine the average device channel temperature of AlGaN/GaN metal–oxide–semiconductor heterostructure field effect transistors (MOSHFETs) in the time domain under continuous wave (CW) and periodic-pulsed RF (radiation frequency) operational conditions. The temporal profiles of microwave output power densities of GaN MOSHFETs were measured at 2 GHz under such conditions and used for determination of the average channel temperature. The measurement technique in this work is also being utilized to determine the thermal time constant of the devices. Analytical temporal solutions of temperature profile in MOSHFETs are provided to support the method. The analytical solutions can also apply to generic field effect transistors (FETs) with an arbitrary form of time-dependent heat input at the top surface of the wafer. It is found that the average channel temperature of GaN MOSHFETs on a 300 μm sapphire substrate with the output power of 10 W/mm can be over 400 °C in the CW mode while the average channel temperature of GaN MOSHFETs on a SiC substrate with the same thickness only reaches 50 °C under the same condition. The highest average channel temperature in a pulsed RF mode will vary with respect to the duty cycle of the pulse and type of the substrate. 相似文献
Balanites aegyptiaca (L.) Del. is a widely distributed xerophytic multipurpose tree. The mesocarp of the fruit of B. aegyptiaca has detergent properties due to the presence of saponins. The stability potential of this biosurfactant at varying pH, temperature, and salinity has not been explored so far. In the present study, the relative surface tensions of five different concentrations of the biosurfactant were studied at different temperatures, salinity, and under pH conditions. This study reveals that this biosurfactant retains its activity over a wide range of pH (3–11) and at high salinity (7% NaCl). It is a thermostable cationic surfactant; surfactant activity was recorded even at 100 °C with the lowest relative surface tension of 0.47. High oil displacement (18.00 mm) was observed when studied with petrol. This biosurfactant was found to have a high emulsification index (E24) of 70% with mustard oil. These results indicate that biosurfactant derived from B. aegyptiaca may find use in a wide range of sectors such as textile, food, cosmetics, oil recovery, and healthcare under a wide range of physical and chemical conditions. It offers an efficient, economically viable, and plant-derived alternative to synthetic detergents and adds a way to maintain a sustainable environment. 相似文献
The reactivity of coal and biomass has been evaluated by comparing the optical and chemical changes in feed material prior and after the co-gasification. The proximate, ultimate, GCV, low-pressure N2 sorption isotherm, micropetrography, SEM and EDX spectroscopy analyses are carried out to assess the reactivity of blends of high ash Indian coal and biomass. The relative changes in parameters like surface area, pore size, and pore volume have been correlated with reacted percentage area of coal macerals and cellulose-lignin cellular structures of biomass. The Optimas image processing software is being used to mark the reacted portion of organic constituents and calculated the reactivity percentage. The bottom ash of pure coal has shown the least reacted organic matters, indicating inefficiency of high ash coal due to a large amount of inorganic and inertinite contents that is resisting the oxidation. The reactivity percentage is determined by the petrographic and SEM images, and varies from 36.34 to 99.64% and 6.61–96.22%, respectively. It is summarised that the estimation of percentage alteration of macerals and other micro-organic constituents can be used as one of the practical approaches for the assessment of the reactivity of coal and biomass. The blending ratio 6:4 of coal and press mud has shown the highest reactivity (>99.64%). The values of petrographic and SEM reactivity have shown good correlations with the carbon contents, unreacted vitrinites, mineral matters and biomass remnants. These relations have been taken into account to formulate the proposed petrographic empirically calculated reactivity (RPEC). The focus has also been made to investigate the influence of feed composition on carbon conversion and heating value of the product gas. 相似文献