A new model for permeability impairment due to asphaltene deposition0 تومان
The existing theoretical and empirical models to describe asphaltene deposition in porous media do not consider the complicated structure of pore network. Permeability reduction due to asphaltene deposition has been mainly attributed to pore volume shrinkage (porosity reduction). However, asphaltene particles can also block pore throats which will lead to severe permeability reduction even when a large fraction of total pore volume still remains intact. Thus, there is a need for permeability models that are explicitly function of pore/hydraulic connectivity. This paper provides a review of the existing models and examines a permeability model that explain permeability impairment due to asphaltene deposition. In this study, we propose a new permeability model based on Critical Path Analysis (CPA) which is a function of average coordination number (average number of available/connected neighbor pores). Furthermore, experimental data in the literature related to limestone, sandstone and carbonate (dolomite) samples are utilized to understand combined effects of surface deposition and interconnectivity loss due to pore blockage on permeability reduction. We observed that surface deposition is the dominant mechanism in the limestone samples studied here owing to large pore throat size compared to the particle size. In the sandstone samples, both the surface deposition and pore throat plugging mechanisms contribute fairly the same in the observed permeability reduction. For the carbonate (dolomite) samples, the pore blockage is the dominant mechanism, which results in rapid sharp decrease of the permeability. It is expected that the outcome of this work improves prediction of the asphaltene deposition in the near wellbore region.
Carbon electrodes for capacitive technologies0 تومان
An overview of capacitive technologies based on carbon materials (energy storage in electrical double-layer capacitors (EDLCs), capacitive deionization (CDI), energy harvesting, capacitive actuation, and potential controlled chromatography) is presented. The review reveals the role of carbon for these scientific and industrial purposes with disclosing the benefits and limitations of various nanostructured carbons for a certain application. A special attention is placed on the electrical double-layer (EDL) formation mechanisms affected by the porous texture of carbon and the electrode architecture. The importance of a careful selection of the electrolytic solution for the EDL formation inside the intraparticle pores of carbon electrodes is also enlightened.
Characterization of activated sludge settling properties with a sludge collapse-acceleration stage0 تومان
The sedimentability of the activated sludge can be affected by the presence of a large variety of coagulants and polymers from a previous physical-chemical process. In this paper, the activated sludge settling process in industrial wastewater treatment plants where the sludge does not settle in a conventional way is studied. The two observed constant hindered settling velocity stages and the instant the intermediate sludge acceleration period occurs are described. A variation of the Richardson and Zaki model is used to characterize the two stages of constant settling velocity. The concentration of suspended solids, where a sudden decrease of hindered settling velocity was observed, is calculated. Finally, a new hypothesis to explain the processes triggering the collapse of the initial homogeneous sludge structure and the existence of an acceleration period is formulated.
Clathrate hydrate formation in NaCl and MgCl2 brines at low pressure conditions0 تومان
Hydrate-based desalination (HBD) has been developed to obtain fresh water from seawater in an economic and environmental sustainable manner. As a low-pressure hydrate former for the HBD process, chlorodifluoromethane (R22) hydrates were formed in the pressure range of 1–6 bar under brine environments, aqueous NaCl and MgCl2 solutions. Synchrotron X-ray diffraction and Raman spectroscopy measurements revealed that the R22 hydrates formed with NaCl and MgCl2 show structure I and enclathration of R22 molecules into the large cages. These results also confirmed that the salt ions cannot be encaged in the gas hydrate framework, reflecting the ion exclusion behavior for HBD above the eutectic of water and hydrated salts. The formation kinetics of R22 clathrate hydrate in the presence of salts show that both the initial growth rate and pressure drop of the R22 hydrates heavily depend on the salinity of aqueous solutions. A new theoretical approach adopting the transient time-dependent apparent rate constant of hydrate formation with salts was proposed to predict the formation kinetics of R22 hydrates under brine environments, which was in good agreements with the experimental results. These results provide good information for separating ionic compounds from aqueous solutions by hydrate-based separation processes.
Decolorization performance of TiO2/Zr catalysts supported on Nanostructured material including Carbon0 تومان
A composite of Zr-doped TiO2 and carboxylic multiwall carbon nano tube (MWCNT-COOH) as a support was successfully synthesized by using Sol-Gel method. Increasing specific surface area of TiO2/Zr nano photocatalyst (NPC), perform by padding the catalyst on substrate of (MWCNT-COOH). The porous structure of catalyst with high specific surface area obtained via calcination phase by removed carbonaceous structure.TiO2 with Zr as dopant lead to high photo catalyst activity and decreasing BG energy. Decolorization ability of NPCs monitored by using UV–Vis spectrophotometer. Padding of TiO2 on MWCNT- COOH as substrate cause high specific area and the best photocatalytic activity. Properties of support and catalyst were characterized by SEM, TEM, XRD, FT-IR and BET. For photocatalytic applications, the band gap of the synthesized semiconductors was determined. The TOC analysis has perform for proving the Decolorization of Acid Red 88 as a Azo dye. TiO2/Zr/MWCNT-COOH was the best performance.
Design and Synthesis of Natural Polymer Derived From Wheat Starch0 تومان
This reaction, first part of the synthesis starch octenyl succinic anhydride were synthesised by addition of 2-octenyl succinic anhydride aqueos solution to suspension modified wheat starch. After this part a certain amount of aluminum sulfate was added to starch octenyl succinic anhydride slurry.The results of SEM and FT-IR,27ALNMR, HNMR confirmed the fotmation of ester group and the cross-link with AL3+.Aluminum octenyl succinic anhydride (ASO) with starch. ASO is a unique, hydrophobically modified natural polymer, used in cosmetics and food industry.
Electrochemical Behavior of Conductive Cotton Textile: Effect of Conducting Particles0 تومان
In this study, a electrochemical sensor based on smart textile was fabricated. The smart conductive textiles was prepared using coating of a cotton fabric by different four conductive particles include single and multi- wall carbon nanotube, graphene oxide and silver nanoparticles and their conductivity properties was compared together. The scanning electron microscope was used to observation of surface morphology of the fabric samples. The coated fabric by silver nanoparticles has highest conductivity in compared with carbon coated fabrics. The performance of Ag coated fabric was evaluated as a working electrode.
Enhanced electrochemical performance of hyperbranched poly0 تومان
We report a facile route for the synthesis of hyperbranched polyamido-graphenes (HBP(A-G)) as non-metallic high capacity electrodes for charge storage in supercapacitors. HBP(A-G) were synthesized by Michael addition of polyamines, ethylene diamine (EDA), diethylene triamine (DETA), triethylene tetraamine (TETA), to acrylamide grafted graphene oxide, followed by reduction in situ. A 3D network of stiff graphene sheets connected by flexible polyamine chain was formed. Hyperbranching increased d-spacing and BET surface area of graphene stacks, which enhanced accessibility of sites for ion storage, and prevented restacking. HBP(A-G) electrodes displayed electric double layer capacitance behaviour with excellent specific capacitance. The charge storage capacity of the electrodes increased with an increase in the amine chain length. Specific capacitance of electrodes containing HBP(TETA-G) was found to be 269 F g-1 in a symmetric two electrode electrochemical cell, using 1 M H2SO4 electrolyte at a current density of 1 A g-1 for voltage range of 0- 1 V. An increase in the length of amine chains improved ion mobility, lowered equivalent distributed resistance and time constant of the electrodes.
Fabrication of an Electrochemical Biosensor for early detection of Colorectal cancer based on miRNA hybridyzation method0 تومان
For the detection of DNA hybridization, a new electrochemical biosensor was developed on the basis of the interaction of Doxirubicine (DOX) with 22-mer oligonucleotides (from human Colorectal cancer) a simple biosensing design to yield an ultrasensitive electrochemical biosensor for cancer biomarker detection on Screen Printed Gold Electrodes (SPGE) without use of any modification on electrode surface perhaps direct detection with the help of electroactive label (DOX) and MicroRNA92a (miRNA) as an biomarker selected for being up-regulated in Colorectal cancer. The biosensor was assembled in two stages the immobilization of the probe that was modified on an SPGE and second stage of target hybridization of completely match strand electroactive label DOX has been used after hybridization process which is an intercalator with our miRNA strands as an redox indicator for amplifying the electrochemical signal of miRNA 92a. For conformation electrochemical techniques including Cyclic Voltammetery (CV) and Differential Pulse Voltammetery (DPV). were used and hybridization was observed successfully .The final biosensor provided a sensitive detection of miRNA 92a with good selectivity.
Impacts of Magnetic Water on Some Mechanical Properties of Normal and High-Strength Concrete0 تومان
One of the most important points which have been considered by scholars and those involved in concrete technology science is improvement of various concrete features. For achieving this goal, in two recent decades, very widespread studies have been performed and one of their most important studies is using magnetic water technology in concrete. By using this technology, the physical structure of water could be changed so that the number of molecules in a molecular association is reduced from 14 to 5 or 6 molecules and as a result, the water surface tension is decreased. Using magnetic water in concrete mixture causes consistency and reduction of water to cement ratio of concrete and also increasing of its durability and strength. In the present study, the impact of magnetic water on mechanical properties of normal concretes and high strength concretes such as consistency and compressive strength has been investigated. The tests results indicate that using magnetic water in concrete mixture increases its compressive strength by 17% and 465 respectively. Also, it accelerates the cement hydration reaction and increases concrete slump.
In Vitro Biocompatibility of a Compliant, Blood Compatible, and Biodegradable Nanofibrous Scaffold for Vascular Tissue Engineering0 تومان
A vascular scaffold must not only support appropriate structural integrity until neotissue can form, but also closely mimic the strength and compliance of native blood vessels. Hemocompatibility is also clearly a crucial factor to raise success of the engineered construct since the vascular scaffold comes in contact with blood. The degradation profile of the scaffold is another important criterion to consider for successful applications in tissue engineering of load-bearing structures like blood vessel tissues. A tissue-engineered vascular graft requires complete scaffold degradation with well-defined cellular organization and tissue remodeling. To cover all these required features, we carried out the blend electrospinning to fabricate nanofibers of poly(L-lactide acid-co-poly ε-caprolactone) (PLCL), a biodegradable and compliant polymer, gelatin (Gel), a biodegradable and commercially available natural biopolymer possessing many integrin binding sites (such as RGD) for cell adhesion, and Tecophilic (TP), a hydrophilic, elastic and hemocompatible polyether-based thermoplastic aliphatic polyurethane, with a weight ratio of 60:20:20 (PGT;60/20/20) resulted in creation of a compliant, hemocompatible and biodegradable scaffold. The nanofibrous structure of the scaffold was visualized using a scanning electron microscope (SEM). The surface characterization of scaffold was carried out using ATR-FTIR spectroscopic analysis. For evaluating the potential of electrospun PGT;60/20/20 scaffold as a substrate for vascular regeneration, we cultured human aortic smooth muscle cells (SMCs) on the scaffold and studied the biocompatibility of the structure by performing the proliferation assay and cell morphology assessment. SEM images demonstrated that electrospun PGT;60/20/20 nanofibers were successfully produced with a fiber diameter of 459±198 nm which revealed a significant reduction compared to fiber diameter of electrospun pure PLCL and pure TP. ATR-FTIR analysis confirms the presence of all components within the fibers. Comparing the behavior of SMCs on PGT;60/20/20 scaffolds with that on electrospun PLCL and TP scaffolds confirmed the potential use of PGT;60/20/20 nanofibers in blood vessel tissue engineering.
Increasing of Concrete Endurance in Acidic and Sulfate Environments Using Calcareous Materials0 تومان
In the present study, replacement of normal concrete aggregates with calcareous and silica aggregates and concrete endurance against acidic corrosion has been investigated. For this purpose, a number of concrete samples were built and placed in sulfate sodium and magnesium solutions. Then, in various time intervals, changes of weight, dimension and strength of samples have been assessed and the obtained results on the samples and solutions were considered as basis of judgment. Regarding the results of performed tests, it is observed that the samples built with calcareous aggregates have higher endurance and strength in acidic and corrosive environments. Regarding the statistical analyses, the calcareous samples showed more than 53% endurance improvement in acidic and corrosiveenvironments. So, using calcareous aggregates is an applied suggestion for raising the concreteendurance.
Investigation of adsorption of aromatic dyes by carbon nanotubes: A DFT study of NMR parameters0 تومان
In this study, the adsorption of aromatic dyes on the surface of carbon nanotubes was investigated by quantum mechanical calculations. Exploring a novel sensor for detection of toxic aromatic compounds, interaction of pristine single-walled carbon nanotubes (5, 0) zigzag CNT (SWCNT) was investigated using the density functional theory (DFT) within the local density approximation. It was found that the pristine CNT can effectively interact with aromatic dyes. So that their electronic and structural properties are changed upon exposure to aromatic compounds. In the most stable configuration, the binding energy is negative (Ead= -3.922 kcal/mol) and suggesting that the absorption reaction is possible. The impacts of the estereoelectronic effect associated with donor-acceptor electron delocalizations on the structural and electronic properties and reactivity of zigzag open-end single wall carbon nanotubes (SWCNTs) as nano adsorbents in interaction with aromatic dyes was studied based on the DFT calculations. The total electronic energy, orbital energies, density of state (DOS), LUMO-HOMO energy bond gaps, Adsorption energies (EAd) were calculated. Moreover, Nuclear Magnetic Resonance (NMR) shielding tensors were calculated by using the Gauge Independent Atomic Orbital (GIAO) method in order to determination of intramolecular interactions and chemical properties of molecules.
Investigation of Lithium Complex Hydrides Li2MH5 (M = B, Al) as Hydrogen Storage materials; A theoretical study0 تومان
Lithium complex hydrides Li2MH5 (M= B, Al) in are potential hydrogen storage material because of their high capacity of (10, 6.5 wt. % respectively) H2. However, their high thermodynamic stability is unfavorable for dehydrogenation processes. Understanding the bonding nature of Al-H, B-H and Li-H are essential for predicting their dehydrogenation mechanism and then improving their dehydrogenation performance. Quadrupolar parameters of nuclei can be used as a tool to understand the electronic structure of compounds. In this work thecharge density distribution in Li2AlH5 and Li2BH5 was compared. Thus using calculated Nuclear Quadrupole Coupling Constants (NQCC) of 2H nuclei, the electronic structure of Li2AlH5 and Li2BH5 was studied. The results show that between two proposed dehydrogenation mechanisms for Li2MH5, hetro phase dehydrogenation is preferred than partial dissociation to LiMH4. Furthermore easier condition for hetro phase dehydrogenation is expected in Li2AlH5. The electric field gradient (EFG) of quadrupolar nuclei were calculated to obtain NQCC parameters. All calculations performed using Gaussian 03 at MP2/6-311G** level of theory. The selected level and basis set give the rather acceptable qualitative NQCCs of hydrogen atoms.
Magnetic graphitic carbon nitride polymers: Solvothermal synthesis as macroscopic samples (nano structure)0 تومان
In order to prepare C3N4 as macroscopic sample, two synthesis attempts of the graphitic variety were carried out. The first consists on the condensation of melamine and cyanuric chloride (P D130 MPa, T D250±C) with triethylamine acting as solvent in supercritical conditions. The second one consists on the pyrolysis of melamine (P D2.5 GPa, T D800±C) in presence of hydrazine. The two routes led to a graphite-like carbon nitride; nevertheless, the first product is poorly crystallized and contains a larger amount of hydrogen as NHx due to a partial condensation .the sample was studied with UV/VIS and IR and C NMR.
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