Non-linear model for FET differential amplifier

A simple formula is presented for the relationship between an input differential voltage and the corresponding output differential current of an FET differential amplifier. Also, a closed-form expression is derived for the output signal of a differential amplifier excited by a multi-sinusoidal input signal.     

On structural,optical and dielectric properties of zinc aluminate nanoparticles

Zinc aluminate nanoparticles with average particle size of 40 nm were synthesized using a sol–gel combustion method. X-ray diffractometry result was analysed by Rietveld refinement method to establish the phase purity of the material. Different stages of phase formation of the material during the synthesis were investigated using differential scanning calorimetry and differential thermogravimetric analysis. Particle size was determined with transmission electron microscopy and the optical bandgap of the nanoparticles was determined by absorption spectroscopy in the ultraviolet-visible range. Dielectric permittivity and a.c. conductivity of the material were measured for frequencies from 100 kHz to 8 MHz in the temperature range of 30–120°C. The presence of Maxwell–Wagner type interfacial polarization was found to exist in the material and hopping of electron by means of quantum mechanical tunneling is attributed as the reason for the observed a.c. conductivity.     

The influence of time elapsed after milking and lactation stage on the lactoperoxidase system of milk in Sahiwal cattle and Nili‐Ravi buffaloes

The effects of time elapsed after milking and lactation stage were assessed on the lactoperoxidase (LP) enzyme activity and concentrations of thiocyanate in Sahiwal cattle (N = 15) and Nili‐Ravi buffaloes (N = 15). The LP activity and thiocyanate concentrations decreased as the time elapsed after milking (P < 0.05) but the concentration of these components increased as the lactation advanced. The LP enzyme activity was sufficient until 12 h post milking but the thiocyanate concentration after 8 h decreased to an insufficient level to activate the LP System, hence additional thiocyanate would be beneficial from external sources. No difference was noted regarding the LPS activity in cattle and buffaloes at the time of collection and subsequently after storage. However, at the end of lactation, the thiocyanate concentration was lower in buffaloes than that in cattle. (P < 0.05).     

烟酰胺抑制人皮黑素细胞的适宜浓度研究

研究了烟酰胺对酪氨酸酶活性、人皮黑素细胞的增殖率、细胞周期动力学和黑素合成的影响。结果显示：烟酰胺体外抑制酪氨酸酶活性不明显；随浓度增加、作用时间的延长，烟酰胺抑制黑素细胞的增殖作用明显；0．25g／L烟酰胺加入24h后，细胞增殖指数明显下降，细胞多处于G0-G1期，S期细胞数量也显减少。实验发现：0．25g／L以上的烟酰胺均可以抑制黑素细胞中黑素合成，其中0．25g／L的烟酰胺可抑制黑素合成且对细胞损伤作用最小。故推荐0．25g／L的烟酰胺为安全、有效作用浓度。     

TOCOPHEROLS AND PHOSPHOLIPIDS ENHANCE THE OXIDATIVE STABILITY OF BORAGE AND EVENING PRIMROSE TRIACYLGLYCEROLS

The effect of individual phospholipids and tocopherols as well as their combinations on the oxidative stability of borage and evening primrose triacylglycerols (TAG) was investigated. Based on conjugated dienes (CD) and 2-thiobarbituric acid reactive substances (TBARS) formed in borage and evening primrose TAG, the antioxidant effectiveness of phosphatidylcholine (PC), was higher than that of phosphotidylethanolamine (PE) in borage TAG while the reverse was observed for evening primrose TAG. Meanwhile, a synergistic effect between tocopherols and phospholipids in both borage and evening primrose TAG was noted. The most effective combination in borage TAG was that of PC and α-tocopherol, while PE with α-tocopherol exerted the best effects in evening primrose TAG. Therefore, the antioxidant effectiveness of phospholipids may vary depending on their fatty acid composition, nature of the functional groups and the chemical composition of the lipid system in which they are examined. The results also demonstrate the importance of minor components of vegetable oils on their oxidative stability.