New procedure to calculate the Hansen solubility parameters of polymers

The simplest experimental method to determine the Hansen solubility parameters (HSPs) for a polymer is to evaluate whether or not it dissolves in selected solvents. Those solvents dissolving the polymer will have HSPs closer to those of the polymer than those that do not. A computer program or graphical method can then be used to find the HSP for the polymer. In this work, an improved method for calculating the HSP of polymers, based on the Nelder–Mead optimization algorithm, is presented. The results of this program fit the data very well. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 31–36, 2007     

Oxygen evolution during the formation and sintering of nickel-manganese oxide spinels for thermistor applications

Nickel-manganese spinel, prepared from 20 wt % NiO and 80 wt % Mn₂O₃, forms at 950°C by the intermediate formation of Mn₃O₄ with evolution of oxygen, determined by mass-spectrometric evolved gas analysis. On heating to higher temperatures, further oxygen is evolved resulting in pore formation and bloating of pressed sintered samples and anomalies in their densification and electrical properties. Thermodynamic considerations and X-ray diffraction intensity measurements suggest that all the Mn²⁺ is located in the tetrahedral spinel sites, this cation configuration remaining unchanged by higher-temperature treatments such as sintering.     

Alternative fuel and gasoline in an SI engine: A comparative study of performance and emissions characteristics

The strict regulation of environmental laws, the price of oil and its restricted resources, has made engine manufacturers use other energy resources instead of oil and its products. Despite the fact that nowadays alternative fuels are not currently widely used in vehicular applications, using these kinds of fuels will be definitely inevitable in the future. In this paper, a computer code is developed in Matlab environment and then its results are validated with experimental data. This simulated engine model could be used as an powerful tool to investigate the performance and emission of a given SI engine fueled by alternative fuels including hydrogen, propane, methane, ethanol and methanol. Also, the superior of alternative fuels is shown by comparing the performance and emissions of alternative fueled engines to those in conventional fueled engines. Eventually, it is concluded that volumetric efficiency of the engine working on hydrogen is the lowest (28% less that gasoline fueled engine), gasoline produce more power than the all being tested alternative fuels and BSFC of methanol is 91% higher than that of gasoline while BSFC of hydrogen is 63% less than gasoline.     

Prediction of the Brisance of Energetic Materials

The brisance parameter can be used to show the shattering power of an energetic compound and the speed to reach its peak pressure. It determines the effectiveness with which an explosive can fragment a shell. Nowadays, the sand test or sand crushing test is the preferred method for brisance measurements but there is no reliable method for the prediction of the brisance parameter. In this paper, a method for the prediction of the brisance through sand test for pure and mixed energetic materials as well as aluminized explosives is reported. It is based on the molecular structure of the desired compound and once the conclusion is established any experimental data is redundant. The calculated brisance relative to 2,4,6‐trinitrotoluene (=100) shows good agreement with the measured values.     

Group contribution model for determination of molecular diffusivity of non-electrolyte organic compounds in air at ambient conditions

Determination of diffusion coefficients of pure compounds in air is of great interest for modeling of air pollution control processes. In this communication, a Group Contribution (GC) method is applied to represent/predict the molecular diffusivity of chemical compounds in air at 298.15 K and atmospheric pressure. 4661 compounds from various chemical families have been investigated to propose a comprehensive and predictive model. The final model is resulted from coupling the Artificial Neural Network (ANN) with group contributions. Using this dedicated model, we obtain satisfactory results quantified by the following statistical results: Squared Correlation Coefficient=0.995, Standard Deviation Error=0.02, and Average Absolute Deviation=1.4% for the calculated/predicted properties from existing experimental values.     

Fe3O4@MCM-41@NH-SO3H: an Efficient Magnetically Reusable Nano-Catalyst for the Formylation of Amines and Alcohols

Silicon - In this article the preparation of Fe3O4@MCM-41@NH-SO3H, a new sulfonated magnetic mesoporous nanocomposite, is reported. The introduced catalyst is structurally based on MCM-41 as the...     

Robust non-aggressive three-axis attitude control of spacecraft: dynamic sliding mode approach

Conventional sliding mode control (SMC) has been extensively applied in controlling spacecrafts because of its appealing characteristics such as robustness and a simple design procedure. Several methods such as second-order sliding modes and discontinuous controllers are applied for the SMC implementation. However, the main problems of these methods are convergence and error tracking in a finite amount of time. This paper combines an improved dynamic sliding mode controller and model predictive controller for spacecrafts to solve the chattering phenomenon in traditional sliding mode control. To this aim, this paper develops dynamic sliding mode control for spacecraft’s applications to omit the chattering issue. The proposed approach shows robust attitude tracking by a set of reaction wheels and stabilizes the spacecraft subject to disturbances and uncertainties. The proposed method improves the performance of the SMC for spacecraft by avoiding chattering. A set of simulation results are provided that show the advantages and improvements of this approach (in some sense) compared to SMC approaches.     

Nickel‐Catalyzed Reductive Benzylation of Aldehydes with Benzyl Halides and Pseudohalides

The reductive benzylation of aromatic and aliphatic aldehydes with benzylic halides is reported using a nickel/zinc catalyst system. In addition to benzylic halides, the first report on the addition of benzylic triflates, acetates, tosylates and tritylates to aldehydes is also presented. By this new method a range of alcohols was synthesized efficiently from aldehydes and benzylic substrates at room temperature in moderate to high yields. The mild reaction conditions and good functional group tolerance make this nickel‐catalyzed process synthetically useful for the synthesis of diverse benzylic alcohols.

     

Low-voltage and low-power Ku-band CMOS LNA using capacitive feedback

Analog Integrated Circuits and Signal Processing - An ultra-wideband (12–18 GHz) low-noise amplifier (LNA) using a 65 nm CMOS technology is proposed, in which a...