A new instrument for the measurement of low dynamic torque†

The instrument has been fabricated using ‘Velodyne’as one of its components applying the principle of a speed control system. The applications of the instrument for the measurement of viscosities of liquids, frictional torque of small bearings and performance characteristics of miniature size electrical motors have been explained and the results of the tests conducted are provided.     

Synthesis of polyaniline nanostructures with controlled morphology by a two-phase strategy

Polyaniline nanostructures with tubular, spherical, polyhedral, dendritic and belt-like morphologies were synthesized by simply tuning the preparation conditions in a two-phase medium. SEM, FTIR and UV–vis were applied for the characterization of the products. The results showed that the polarity of the organic solvents, the amount of ammonium peroxydisulfate (APS) and the concentration of the acetic acid influenced the morphologies of the polyaniline nanostructures. The difference in the polyaniline morphologies was attributed to the difference in the relative rate of interfacial nucleation to aqueous nucleation. The route reported here is expected to be applied for the controlled synthesis of various polymer nanostructures.     

Simulation of Radial Electric Field and Internal Transport Barrier Formation in Small Size Divertor Tokamak Plasma Edge

The simulation of the radial electric field shear, which is responsible for L-H transition by means B2SOLPS0.5.2D transport code, gives the dependence of this shear on plasma parameters. Also, as result of uni-directional neutral beam heating, internal transport barrier is formed and ion radial heat flux q _ir starts to decrease. Furthermore, the dependence of radial electric field shear on ion temperature gradient ITG has also investigated.     

Tetrapyrazinoporphyrazines with different number of peripheral pyridyl rings: Synthesis,photophysical and photochemical properties

Zinc tetrapyrazinoporphyrazines comprising different numbers of pyridin-2-yl and tert-butylsulfanyl substituents were prepared by the statistical condensation of two precursors – 5,6-bis(tert-butylsulfanyl)pyrazine-2,3-dicarbonitrile (A) and 5,6-dipyridin-2-yl-pyrazine-2,3-dicarbonitrile (B). The ensuing zinc tetrapyrazinoporphyrazines were chromatographically separated on silica column and characterized. Adjacent (AABB) and opposite (ABAB) isomers were not separated. The prepared zinc tetrapyrazinoporphyrazines did not differ in their Q-band position but the B-band position was shifted hypsochromically for compounds bearing more pyridyl units; in addition, a weak band at 450–520 nm decreased with increasing number of pyridyl substituents. Singlet oxygen quantum yields (Φ_Δ in the range 0.69–0.53) decreased with increasing number of pyridyl units on the macrocyclic core, while fluorescence quantum yields showed the reverse tendency (Φ_F in the range 0.22–0.26).     

An investigation of the amount of lead in blood of Tehran citizens in 1980–1981

A simple atomic absorption method for lead analysis is described; more than 830 samples of inhabitants on the basis to their age, sex, occupation and residential locations were collected for a period of one year (March 1980‐February 1981) and the results of analysis are given.     

Sub-optimal automatic generation control of interconnected power system using constrained feedback control strategy

This paper presents sub-optimal AGC regulator designs for a 2-area interconnected power system using constrained feedback control strategy. The power system with identical thermal plants consisting of non-reheat thermal turbines interconnected via parallel AC/DC links is considered for the investigations. The formulation of optimal AGC problem involves solution of non-linear matrix equations, which requires an appropriate computational technique to yield a solution with high speed and accuracy. The implementation of optimal AGC regulator requires monitoring of all the state variables of the system or state reconstruction, which may be undesirable from cost and complexity considerations. Due to these limitations of optimal AGC regulators, sub-optimal AGC regulators are designed based on the constrained feedback control strategy using the feedback of system states which are accessible and available for measurement. Different structures of state cost weighting matrix ‘Q’ are also considered in the study. The power system dynamic performance is analyzed based on time response plots achieved with the implementation of designed optimal and sub-optimal AGC regulators in the wake of 1% load disturbance in one of the areas.     

Tuning the thermal properties of borosilicate glass ceramic seals for solid oxide fuel cells

In this paper, a series of Sr–Ba–borosilicate glass-ceramics (10–40 mole% B₂O₃) were prepared to investigate the effect of borate content on the thermal properties as well as volatilization behavior. For crystallized samples with increasing borate contents, the dilatometric softening points decrease, from 702 to 660 °C, as do the coefficients of thermal expansion, from 9.5 to 7.5 × 10^?6 K^?1. In addition, the weight loss from these materials, in wet forming gas at 780 °C for 28 days, decreases by a factor of two as the borate content increases from 10 to 40 mole%. The borate-containing phase, SrB₂O₄, forms with increasing borate content. The significant improvement in stability against volatility can be attributed to the formation of SrB₂O₄, which is consistent with the results of thermochemical calculations. These results therefore indicate one way to design sealing compositions to use B₂O₃ to tailor thermal properties without sacrificing thermal stability.     

Limitation of Na-H codoping in achieving device-quality p-type ZnO

Na-H in-situ codoping in single crystalline ZnO films was carried out by plasma assisted molecular beam epitaxy. It is found that Na-H codoping dramatically enhances the formation of substitutional Na (Na_Zn) in ZnO lattice due to the unchanged Fermi level. The annealing temperature needed to kick out H, however, is very high, which would concurrently result in a notable decrease of Na concentration to its solution limit in ZnO, namely, in the range of 10¹⁷ cm⁻³. Our results suggest that Na-H codoping method has a limited effect on enhancing the p-type conductivity of ZnO.     

Sintering of oxide nuclear fuel: Plastic flow mechanism

A theoretical approach to solving the sintering problem of nuclear oxide fuels is described. We are proposing a new physical sintering model: the main mechanism for oxide nuclear shrinkage is the plastic flow of the matter under internal stress and capillary forces.