Supported zirconocene catalyst for preventing reactor fouling in ethylene polymerization

The commercial interest of metallocene complexes for olefin polymerization has led to additional efforts to prepare suitable metallocene complexes efficiently and economically. Ethylene polymerization was carried out with a series of heterogeneous catalysts which were prepared in various Zr/silica ratios by immobilization of Ind₂ZrCl₂ preactivated with methylaluminoxane (MAO) on silica. This method to form the catalyst system resulted in a polymerization catalyst with reduced fouling tendencies and improved reactor operability. Polymerization of ethylene was conducted in Buchi reactors in a slurry phase under mild pressure. Some of the physical properties of the obtained polymers were also determined. Copyright © 2005 Society of Chemical Industry     

Chitosan‐modified nanoclay–poly(AMPS) nanocomposite hydrogels with improved gel strength

BACKGROUND: Making (nano)composite structures is one of the efficient approaches for strengthening hydrogels extended in recent years. The present paper deals with the synthesis and properties of novel nanocomposite hydrogels based on 2‐acrylamido‐2‐methylpropane‐1‐sulfonic acid (AMPS). Initially, a bio‐modified clay, chitosan‐intercalated montmorillonite (chitoMMT), was prepared. Then, this was incorporated into the polymerization of AMPS in the presence of a macro‐crosslinker, i.e. poly(ethylene glycol) dimethacrylate, to yield super‐swelling nanocomposite hydrogels. The swelling capacity as well as some structural, rheological and thermomechanical properties of the hydrogels were studied and compared with those of the clay‐free counterpart. RESULTS: ChitoMMT exhibited no toxicity, which was confirmed using cell‐culture testing. A chitoMMT content of ca 6% was found to be the most favourable content of the bio‐modified clay for achieving a product with improved properties (i.e. the highest gel content, the highest gel strength and optimal thermal stability). Based on a dynamic mechanical thermal analysis study, an increased glass transition temperature (98.2 °C) and improved rubbery modulus (up to 238% higher than that of the clay‐free counterpart) were recorded. Thermogravimetric analysis verified that the thermal stability of nanocomposite samples was higher than that of clay‐free samples. CONCLUSION: Owing to the non‐toxicity of the incorporated chitoMMT, the strengthened hydrogels may be considered as potential candidates for bio‐applications. Copyright © 2009 Society of Chemical Industry     

Effects of pressure and carbon dioxide,hydrogen and nitrogen concentration on laminar burning velocities and NO formation of methane-air mixtures

We studied the effects of increasing pressure and adding carbon dioxide, hydrogen and nitrogen to Methane-air mixture on premixed laminar burning velocity and NO formation in experimentally and numerically methods. Equivalence ratio was considered within 0.7 to 1.3 for initial pressure between 0.1 to 0.5 MPa and initial temperature was separately considered 298 K. Mole fractions of carbon dioxide, hydrogen and nitrogen were regarded in mixture from 0 to 0.2. Heat flux method was used for measurement of burning velocities of Methane-air mixtures diluted with CO₂ and N₂. Experimental results were compared to the calculations using a detailed chemical kinetic scheme (GRI-MECH 3.0). The results in atmosphere pressure for Methane-air mixture were calculated and compared with the results of literature. Results were in good agreement with published data in the literature. Then, by adding carbon dioxide and nitrogen to Methaneair mixture, we witnessed that laminar burning velocity was decreased, whereas by increasing hydrogen, the laminar burning velocity was increased. Finally, the results showed that by increasing the pressure, the premixed laminar burning velocity decreased for all mixtures, and NO formation indicates considerable increase, whereas the laminar flame thickness decreases.     

A Method for Fabrication of Polycarbonate-Based Bioactive Platforms

Surface-based assays have been used extensively for the functional and structural analysis of biomolecules such as DNA or proteins. These experiments are established by the analysis of binding between acceptor molecules and immobilized receptors on a platform. Site-specific printing of receptor molecules on gold, glass, or polycarbonate (PC) surfaces is conventionally performed by the chemical derivatization of a surface, priming it to covalently bind to subsequently deposited receptor molecules. Unlike conventional methods, we have developed a new fabrication method for bioactive PC surfaces by directly molding PC granules doped with receptor molecules. PC-based receptor molecules were synthesized and commercially available PC granules were doped with these synthesized molecules. In our proof-of-concept study, PC doped with dye 1 (Fig. 1) was used as the receptor molecule. Using an aluminum mold and a hot press machine, PC-based objects were manufactured through compression molding using doped PC granules. Affinity analysis was evaluated by monitoring the localization of a monoclonal antibody elicited against dye 1 to the surface of the molded platforms by fluorescence microscopy. The results illustrated effective binding of an anti-dye 1 monoclonal antibody to the surface, substantiating successful display of assemblies of molecular receptors on the surface through compression molding. Although conventional surface functionalization methods impose limited applications and alter desired opto-mechanical properties of the polymer, our investigation provides a versatile means for the fabrication of bioactive PC-based platforms. It can also be used for engineering and imbedding receptor arrays within three-dimensional objects with applications to the production of opto-medical devices or biosensors.     

Global sensitivity analysis of certain and uncertain factors for a circular tunnel under seismic action

There are many certain and uncertain design factors which have unrevealed rational effects on the generation of tensile damage and the stability of the circular tunnels during seismic actions. In this research paper, we have dedicated three certain and four uncertain design factors to quantify their rational effects using numerical simulations and the Sobol’s sensitivity indices. Main effects and interaction effects between the design factors have been determined supporting on variance-based global sensitivity analysis. The results detected that the concrete modulus of elasticity for the tunnel lining has the greatest effect on the tensile damage generation in the tunnel lining during the seismic action. In the other direction, the interactions between the concrete density and both of concrete modulus of elasticity and tunnel diameter have appreciable effects on the tensile damage. Furthermore, the tunnel diameter has the deciding effect on the stability of the tunnel structure. While the interaction between the tunnel diameter and concrete density has appreciable effect on the stability process. It is worthy to mention that Sobol’s sensitivity indices manifested strong efficiency in detecting the roles of each design factor in cooperation with the numerical simulations explaining the responses of the circular tunnel during seismic actions.     

Superabsorbent polymers achieved by surface cross linking of poly(sodium acrylate) using microwave method

Surface cross linking is a post-treatment process for superabsorbent polymers (SAPs) leading to an increase in the absorbency under load (AUL). This process is typically carried out through conventional heating method. In the current study, for the first time, microwave method was used for surface treatment process of SAPs based on poly(sodium acrylate). Diglycidyl materials such as 1,4-butanediol diglycidyl ether (BDDGE), polyethylene diglycidyl ether (PEGDGE), and ethylene glycol diglycidyl ether (EGDGE) were utilized as surface cross-linking agents. Also, N,N-Dimethylaniline was used as a catalyst for surface treatment of poly(sodium acrylate) SAP with diglycidyl materials as the external cross linkers. The results showed that surface treatment time can be reduced from 1 to 3 h in the conventional heating to a few minutes by microwave method. The use of catalyst in surface treatment solution resulted in higher AULs. The AULs of SAPs were increased from 14 g/g for unmodified SAP to 17.5, 19 and 20.7 g/g after surface treatment for surface-treated SAPs with BDDGE, PEGDGE and EGDGE, respectively. These results present the microwave method as an effective alternative candidate for thermal surface treatment of SAP which can have economic benefits from the viewpoint of time and energy consumption industrially.

     

Application of transfer functions to model water injection in hydrocarbon reservoir

Water flooding is one of the most economical methods to increase oil recovery. In order to improve the ultimate oil recovery during waterflooding, it is essential to provide an accurate forecast of reservoir performance. Hence, various methods have been utilized to simulate reservoirs. Although grid-based simulation is the most common and accurate method, time-consuming computation and the demand for large quantities of data restrict the use of this method. Sometimes, a quick overview of reservoir performance is sufficient or all required data are not accessible. Therefore, in this study a fast simulator is introduced to provide a quick overview with the minimum amount of data.A new method is presented to forecast the performance of water injection based on Transfer Function (TF). In this approach, it is assumed that a reservoir consists of a combination of TFs. The order and arrangement of TFs are chosen based on the physical conditions of the reservoir which are ascertained by examining several cases. The selected arrangement and orders can be extended to any other reservoirs. Injection and production rates act as input and output signals to these TFs, respectively. After analyzing input and output signals, the unknown parameters of TFs are calculated. Subsequently, it is possible to predict reservoir performance.Four different cases are employed to validate the derived equation. The results reveal a good agreement with those obtained from the common grid-based simulators. In addition, it has been demonstrated that the TF parameters depend on the characteristics and the pattern of different sections of the reservoir.This approach is a quick way to forecast waterflooding performance and can be a new window for the future of fast simulators. It provides the prediction with higher certainty in comparison with the other fast simulators. Furthermore, the only requirements for the method are injection and production rates. The analytical solution of the method enables its utilization in finding optimum rates for water injection in a short period of time. The method also presents some key parameters such as well connectivity. The use of the model is limited to situations when a rapid estimation is looked for and/or adequate data is not accessible.     

An analytical formulation as an alternative to FEM software giving strain and stress distributions for the three-dimensional solution of extrusion problems

A new improved analytical method based on the upper bound theorem is presented for the solution of extrusion problems. This method has been formulated in such a way as to eliminate the deficiencies in the previous works in order to enable it as a powerful analytical tool as an alternative to finite element software. The proposed formulation is a general method of solution, which could be used for the analysis of many bulk forming processes. However, in this paper, the forward extrusion of a square section from a round billet has been presented as an example. Kinematically admissible velocity fields were computed which gave a more physically realistic material flow patterns as compared to previous works. The distribution of strain and stress as well as the results for the effect of process parameters on the extrusion load and die geometry was also given. These results were compared with FEM data to observe the accuracy and effectiveness of the present method. For the extrusion of square sections from round billets, detailed analysis of strain distribution on the exit section was carried out using the components of the power due to internal deformation, interface friction, and velocity discontinuities at the entry and exit surfaces. Comparison with experimental data was made, and verification of the theoretical results was carried out. The improvement of the results computed using the present method was shown by comparison with the previous works.     

In Vitro Monitoring of Magnesium-Based Implants Degradation by Surface Analysis and Optical Spectroscopy

Magnesium (Mg)-based degradable alloys have attracted substantial attention for tissue engineering applications due to their biodegradability and potential for avoiding secondary removal surgeries. However, insufficient data in the existing literature regarding Mg’s corrosion and gas formation after implantation have delayed its wide clinical application. Since the surface properties of degradable materials constantly change after contact with body fluid, monitoring the behaviour of Mg in phantoms or buffer solutions could provide some information about its physicochemical surface changes over time. Through surface analysis and spectroscopic analysis, we aimed to investigate the structural and functional properties of degradable disks. Since bubble formation may lead to inflammation and change pH, monitoring components related to acidosis near the cells is essential. To study the bubble formation in cell culture media, we used a newly developed Mg alloy (based on Mg, zinc, and calcium), pure Mg, and commercially available grade 2 Titanium (Ti) disks in Dulbecco’s Modified Eagle Medium (DMEM) solution to observe their behaviour over ten days of immersion. Using surface analysis and the information from near-infrared spectroscopy (NIRS), we concluded on the conditions associated with the medical risks of Mg alloy disintegration. NIRS is used to investigate the degradation behaviour of Mg-based disks in the cell culture media, which is correlated with the surface analysis where possible.     

基于Encore XP!(R)的多电压系统架构的全新电源监督与定序方案

目前,绝大多数电子系统(例如通讯/电子通讯服务器、家庭娱乐产品、个人计算机和外围设备以及数码相机和可携式摄像机、蜂窝电话和便携式媒体播放器)的设计都是基于多电压总线架构.在这些系统中,为了确保精确地控制向系统处理器和其他IC传输的电能,连续监控和调节启动过程、稳定状态操作、待机和省电模式阶段的系统电压至关重要.