Bound-Preserving Discontinuous Galerkin Methods with Modified Patankar Time Integrations for Chemical Reacting Flows

In this paper,we develop bound-preserving discontinuous Galerkin(DG)methods for chemical reactive flows.There are several difficulties in constructing suitable numerical schemes.First of all,the density and internal energy are positive,and the mass fraction of each species is between 0 and 1.Second,due to the rapid reaction rate,the system may contain stiff sources,and the strong-stability-preserving explicit Runge-Kutta method may result in limited time-step sizes.To obtain physically relevant numerical approximations,we apply the bound-preserving technique to the DG methods.Though traditional positivity-preserving techniques can successfully yield positive density,internal energy,and mass fractions,they may not enforce the upper bound 1 of the mass fractions.To solve this problem,we need to(i)make sure the numerical fluxes in the equations of the mass fractions are consistent with that in the equation of the density;(ii)choose conservative time integrations,such that the summation of the mass fractions is preserved.With the above two conditions,the positive mass fractions have summation 1,and then,they are all between 0 and 1.For time discretization,we apply the modified Runge-Kutta/multi-step Patankar methods,which are explicit for the flux while implicit for the source.Such methods can handle stiff sources with relatively large time steps,preserve the positivity of the target variables,and keep the summation of the mass fractions to be 1.Finally,it is not straightforward to combine the bound-preserving DG methods and the Patankar time integrations.The positivity-preserving technique for DG methods requires positive numerical approximations at the cell interfaces,while Patankar methods can keep the positivity of the pre-selected point values of the target variables.To match the degree of freedom,we use polynomials on rectangular meshes for problems in two space dimensions.To evolve in time,we first read the polynomials at the Gaussian points.Then,suitable slope limiters can be applied to enforce the positivity of the solutions at those points,which can be preserved by the Patankar methods,leading to positive updated numerical cell averages.In addition,we use another slope limiter to get positive solutions used for the bound-preserving technique for the flux.Numerical examples are given to demonstrate the good performance of the proposed schemes.

Electrochemical Degradation of Indigocarmine Dye at Ni/Graphite Modified Electrode in Aqueous Solution

Nickel Graphite modified electrode (Ni/GME) was prepared by electrochemical method and degradation of Indigocarmine (IC) dye was carried out. An investigation between the efficiency of degradation by graphite electrode and the Ni/graphite modified electrode has been carried out. The different effects of concentration, current density and temperature on the rate of degradation were studied. This study shows that the rate of the degradation is more for Ni doped modified graphite electrode. UV-Visible spectra before and after degradation of the dye solution were observed. The thin film formation of Ni or encapsulated in graphite rod is observed by scanning electron microscopy and energy dispersive X-ray spectroscopy (SEM & EDAX). The instantaneous current effectiveness values of different experimental conditions are evaluated. The anodic oxidation by Ni/ graphite modified electrode showed the complete degradation of aqueous solution indigocarmine, which is confirmed by UV-Visible and chemical oxygen demand (COD) measurements. The dye is converted into CO2, H2O and simpler inorganic salts. The results observed for reuse of modified electrodes indicate that the Ni/graphite modified electrode would be a promising anode for electrochemical degradation of indigocarmine. This method can be applied for the remediation of waste water containing organics, cost-effective and simple.

A Glassy Carbon Electrode Modified with Cellulose Nanofibrils from Ammophila arenaria for the Sensitive Detection of L-Trytophan

L-tryptophan is an essential amino acid for human health. Nanofibrillated cellulose (NFC) from marram grass (Ammophila arenaria) extracted from plants harvested in the center of Tunisia was used for the first time for the modification of a glassy carbon electrode (GCE), for the sensitive detection of L-tryptophan (Trp). After spectroscopic and morphological characterization of the extracted NFC, the GC electrode modification was monitored through cyclic voltammetry. The NFC-modified electrode exhibited good analytical performance in detecting Trp with a wide linear range between 7.5 × 10−4 mM and 10−2 mM, a detection limit of 0.2 µM, and a high sensitivity of 140.0 µA∙mM−1. Additionally, the NFC/GCE showed a good reproducibility, good selectivity versus other amino acids, uric acid, ascorbic acid, and good applicability to the detection of Trp in urine samples.

Chemically Modified Chitosan Beads as Molecularly Imprinted Polymer Matrix for Adsorptive Separation of Proteins

In a phosphate buffer, a hemoglobin (Hb)-imprinted polymer complex was prepared using maleic anhydride (MAH) modified chitosan beads as matrix, acrylamide (AM) as functional monomer, N,N-methylenebisacrylamide (MBA) as cross-linker and potassiumpersulfate (KPS) / sodium hydrogen sulfite (NaHSO3) as initiators. Langmuir analysis showed that an equal class of adsorption was formed in the molecular imprinting polymer (MIP), and the MIP has high adsorption capacity and selectivity for the imprinted molecule. The MIP can be reused and the recovery was approximately 100% at low concentration.

Performance improvement in polymeric thin film transistors using chemically modified both silver bottom contacts and dielectric surfaces

An efficient interface modification is introduced to improve the performance of polymeric thin film transistors. This efficient interface modification is first achieved by 4-fluorothiophenol（4-FTP） self-assembled monolayers（SAM） to chemically treat the silver source–drain（S/D） contacts while the silicon oxide（SiO2） dielectric interface is further primed by either hexamethyldisilazane（HMDS） or octyltrichlorosilane（OTS-C8）. Results show that contact resistance is the dominant factor that limits the field effect mobility of the PTDPPTFT4 transistors. With proper surface modification applied to both the dielectric surface and the bottom contacts, the field effect mobilities of the bottom-gate bottom-contact PTDPPTFT4 transistors were significantly improved from 0.15 cm^2·V^-1·s^-1 to 0.91 cm^2·V^-1·s^-1.

Highly dispersed Pd nanoparticles on chemically modified graphene with aminophenyl groups for formic acid oxidation

A novel electrode material based on chemically modified graphene （CMG） with aminophenyl groups is covalently functionalized by a nucleophilic ring-opening reaction between the epoxy groups of graphene oxide and the aminophenyl groups of p-phenylenediamine. Palladium nanoparticles with an average diameter of 4.2 nm are deposited on the CMG by a liquid-phase borohydride reduction. The electrocatalytic activity and stability of the Pd/CMG composite towards formic acid oxidation are found to be higher than those of reduced graphene oxide and commercial carbon materials such as Vulcan XC-72 supported Pd electrocatalysts.

A Novel Method of the Preparation ofChemically Modified Electrodes

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Electrochemical Behavior of Eu^（3＋） on Eastman AQ－29D Chemically Modified Electrode

The electrochemical behaviors of Eu3+ on Eastman AQ-29D/glassy carbon(GC) chemically modified electrode(CME) were studied. It was found that the reduction-oxidation process of Eu3+ is in a semi-infinite condition in 0.1 mol/L NaCIO4 supporting electrolyte(pH 4.4). The calibration curve was linear over the range 1.0×10-7 to 1.0×105 mol/L of Eu3+.The charge transport apparent diffusion coefficient of Eu3+ in the polymer film was determined to be(3.2±1.1)×10-11cm2/s by chronocoulometry.

The UV-VIS Studies of C_(60) Chemically Modified Polystyrene Film

The opticai properties of C,, chemicaiiy modified poiystyrene(C,, -PS copolymer) and the parent polystyrene (PS) films have been investigated.Addition of bulky C,, moiety, a special functional group, to the polystyrene by anovel organometallic reaction modified considerably the optical property of theparent polystyrene. The lattice periodicity of pure PS film is subject to someperturbation or distortion in varying degrees due to the covalent attachInent of bulkyC,, moiety to the polymer backbone. C,,-PS copolymer possesses a new energy ba-ndstructure with indirect forbidden band when compared with the parent PS.

Removal of astrazon golden yellow 7GL from colored wastewater using chemically modified clay

Chemically modified clay(CMC) was used as an adsorbent for the removal of Astrazon Golden Yellow 7GL(AGY-7GL), which is a basic dye from wastewater. For this purpose, the chemically modified clay was first characterized by determining zero point of charge(p Hzpc), and using BET, SEM and FTIR. Then effects of operational parameters on adsorption of AGY-7GL were studied in a batch system. The effect of various parameters such as contact time(0-180 min), pH(2-8), temperature(293-323 K), CMC concentration(0.075-0.5 mg/L) and initial AGY-7GL concentration(75-250 mg/L) were investigated on the adsorption efficiency and capacity adsorption of CMC for the removal of AGY-7GL. Thermodynamic and kinetic parameters were calculated from the results of the adsorption experiment. The evaluation of kinetic models shows that this data best fits the pseudo-second-order model. It is determined that the adsorption equilibrium data works very well with the nonlinear Freundlich isotherm model. Thermodynamic parameters such as ?H^0(19.0 k J/mol), ?G^0(-28.8 k J/mol) and ?S^0(0.148 k J/mol) were also determined. According to the experimental results, it is concluded that CMC could be used as an alternative low cost potential adsorbent for the removal of AGY-7GL from wastewater.

Contactless Raman Spectroscopy-Based Monitoring of Physical States of Silyl-Modified Polymers during Cross-Linking

Cross-linking of silyl-modified polymers occurs at the alkoxysilane groups attached to the ends of polymer chains by hydrolysis and polycondensation mechanisms in the presence of moisture. During these reactions, three different physical states can be identified (viscous, skin effect and cross-linked state). Knowledge of the evolution of these states at each reaction time is essential to determine the open time for the adhe-sive industry and is generally obtained by a manual method. Automation of this moni-toring could avoid operator error and could be used for very long cross linking reac-tions or to screen a large number of catalysts. Thus, a contactless micro process tech-nology was developed to correlate these physical states with an optical technology, Raman spectroscopy, by monitoring the decrease in intensity of the Si-OCH3 groups during chemical reactions. This online characterization method can also be used to compare the efficiencies of several catalysts for the cross-linking of silyl-modified polymers, using a minimum amount of chemical materials.

Fabrication of Chemically-Modified Electrode Containing 1:12 Phosphomolybdic Anions by Sol-Gel Technique and Its Electrocatalytic Reduction of BrO_3 ^-Anions

A novel chedrically-modified electrode containing 1:12 phosphomolybdic anions wasachieved on the surface of platinum electrode by the sol-gel technique. The electrode exhibits ahigh catalytic activity towards the electroreduction of BrO3- anions.

Study of the electrochemical properties of a transition metallic ions modified electrode in acidic VOSO_4 solution

Graphite material was used as the electrode for an all-vanadium redox flow battery, and the electrode was modified by transition metallic ions to enhance its electrochemical behavior. An porous graphite composite electrode has high specific surface area and high current density. The electrode modified by transition metallic ions has improved catalysis behavior that can catalyze the V（Ⅱ）-V（Ⅴ） redox reaction showed by cyclic voltammograms. This article studied the impedance of the modified electrode by electrochemical impedance spectroscopy （EIS）, and approved that the electrode modified by Co^2＋ and Mn^2＋ has a lower charge transfer resistance than the non-modified electrode. The effect of average particle size distribution is at lower frequencies that the slope of Warburg impedance is reduced by large particle size distribution. The voltage efficiency of the Co^2＋ modified electrode test cell is 81.5%, which is higher than that of the non-modified electrode.

Modified Augmented Lagrange Multiplier Methods for Large-Scale Chemical Process Optimization

Chemical process optimization can be described as large-scale nonlinear constrained minimization. The modified augmented Lagrange multiplier methods (MALMM) for large-scale nonlinear constrained minimization are studied in this paper. The Lagrange function contains the penalty terms on equality and inequality constraints and the methods can be applied to solve a series of bound constrained sub-problems instead of a series of unconstrained sub-problems. The steps of the methods are examined in full detail. Numerical experiments are made for a variety of problems, from small to very large-scale, which show the stability and effectiveness of the methods in large-scale problems.

Treatment of Wet FGD Wastewater by a Modified Chemical Precipitation Method Using a Solid Powder Reagent

This research focused on developing a modified chemical precipitation (MCP) method for treating wet flue gas desulfurization (FGD) waste water by adding a solid powder reagent directly. Simulated wet FGD wastewater was treated by MCP method in simulation experiments. Optimization experiments were carried out with the help of response surface methodology (RSM) and central composite design (CCD) to evaluate the effects and the interactions of experimental variables, including reagent dosage, temperature and pH value. The optimal reagent dosage, temperature and pH value were 3018.0 mg/L, 40.5 °C and 5.7, respectively. The RSM was demonstrated as an appropriate approach for the optimization of wet FGD wastewater treatment with the MCP method. A comparative study between the MCP method and the traditional chemical precipitation (TCP) method on raw wet FGD wastewater treatment was conducted. Results indicate that the MCP had less reagent dosage and variety than the TCP method had. Thus, the MCP method had a lower cost. © 2017, Tianjin University and Springer-Verlag Berlin Heidelberg.

Cyclic Voltammetric Responses of Nitrate Reductase on Chemical Modified Electrodes

Electrochemistry of nitrate reductases (NR) incorporated into 2-aminoethanethiol self-assembled on the gold electrode and polyacrylamide cast on the pyrolytic graphite electrode was examined. NR on chemical modified electrode showed electrochemical cyclic voltammetric responses in phosphate buffers.

Electrochemical Behavior and Its Electrocatalytic Activity of A P-Mo Heteropolyanion Modified ITO Electrode

s: A new method for the preparation of an organic-inorganic composite film of the heteropolyanion has been developed by modifying P(Mo2O7)6-7 to the indium tin oxide (ITO) electrode surface. The modified electrode displayed a strong catalytic activity towards the reduction of IO3-. In the range of 1.0?0-6~5?0-4mol/L, the catalytic current was linear proportional to the IO3- concentration.

Fretting Wear Behavior of Medium Carbon Steel Modified by Low Temperature Gas Multi-component Thermo-chemical Treatment

The introduction of surface engineering is expected to be an effective strategy against fretting damage. A large number of studies show that the low gas multi-component （such as carbon, nitrogen, sulphur and oxygen, etc） thermo-chemical treatment（LTGMTT） can overcome the brittleness of nitriding process, and upgrade the surface hardness and improve the wear resistance and fatigue properties of the work-pieces significantly. However, there are few reports on the anti-fretting properties of the LTGMTT modified layer up to now, which limits the applications of fretting. So this paper discusses the fretting wear behavior of modified layer on the surface of LZ50 （0.48%C） steel prepared by low temperature gas multi-component thermo-chemical treatment （LTGMTT） technology. The fretting wear tests of the modified layer flat specimens and its substrate （LZ50 steel） against 52100 steel balls with diameter of 40 mm are carried out under normal load of 150 N and displacement amplitudes varied from 2 μm to 40 μm. Characterization of the modified layer and dynamic analyses in combination with microscopic examinations were performed through the means of scanning electron microscope（SEM）, optical microscope（OM）, X-ray diffraction（XRD） and surface profilometer. The experimental results showed that the modified layer with a total thickness of 60 μm was consisted of three parts, i.e., loose layer, compound layer and diffusion layer. Compared with the substrate, the range of the mixed fretting regime（MFR） of the LTGMTT modified layer diminished, and the slip regime（SR） of the modified layer shifted to the direction of smaller displacement amplitude. The coefficient of friction（COF） of the modified layer was lower than that of the substrate in the initial stage. For the modified layer, the damage in partial slip regime（PSR） was very slight. The fretting wear mechanism of the modified layer both in MFR and SR was abrasive wear and delamination. The modified layer presented better wear resistance than the substrate in PSR and MFR; however, in SR, the wear resistance of the modified layer decreased with the increase of the displacement amplitudes. The experimental results can provide some experimental bases for promoting industrial application of LTGMTT modified layer in anti-fretting wear.

Electrochemical Determination of Trace Amounts of Lead (Ⅱ) and Cadmium (Ⅱ) at a Calix[6]arene Modified Carbon Paste Electrode

An electrochemical method for the simultaneous determination of lead(II) and Cadmium(II) with a calix[6]arene modified carbon paste electrode (CPE) has been developed. Pb2+ and Cd2+ were accumulated at the surface of the modified electrode via formation of chemical complexes with calix[6]arene, and reduced at 1.40 V. During the following anodic potential sweep, reduced lead and cadmium were oxidized, and two well-defined striping peaks appeared at about ?0.60 V and ?0.84 V. Compared with a bare carbon paste electrode, the calix[6]arene modified CPE greatly improves the sensitivity of determining lead and cadmium. The stripping peak currents change linearly with the concentration of Pb2+ 3.0×10?8–8.0×10?6 mol·L?1 and with that of Cd2+ 6.0×10?8–1.0×10?5 mol ·L?1. The detection limits of Pb2+ and Cd2+ are found to be 8.0×10?9 mol·L?1 and 2.0×10?8 mol·L?1, respectively. The modified carbon paste electrode was applied to determine trace levels of lead and cadmium in water samples. Comparing with that of atomic absorption spectrometry, the results suggests that the calix[6]arene modified CPE has great potential for the practical sample analysis. Key words lead(II) - cadmium(II) - calix[6]arene - differential pulse stripping voltammetry - chemically modified electrode CLC number O 657.15 Foundation item: Supported by the National Natural Science Foundation of China (60171023)Biography: JI Xiao-bo (1980-), male, Master, research direction: electroanalytical chemistry.

Electrochemical Behaviour of Europium-Ferrocene Derivative Complex Chemi cally Modified Electrodes

Electrochemical behaviours of Europium-ferrocene derivative complex chemically modified electrodes were studied in the paper. Various factors which affect the voltammetry of the thin film modified electrodes, and the charge transport process of the thin film electrode were discussed. Size of the hydrated anion (counter ion), concentration of the electrolyte, swelling property of the film in the solvent and thickness of the film have significant effects on the voltammetry of the thin film electrode. Electrochemical behaviours of europium-ferrocene derivative compelx chemically modified electrode were studied in an aqueous solution. When scan ning between 0-0.8 V (vs. SCE), experimental results indicate that the chemically modified electrode has good stability and reproducibility. The apparent rate constant of electrode reaction is deteminedd to be 6.7×10-1 s-1.