فصلنامه پیک نور علوم
سال دوم شماره 1 (پیاپی 5، بهار 1387)

Persistent photoconductivity (ppc) has been investigated in detail in a bulk CdTe(Sb) Semiconductor. The relaxation of ppc in CdTe(Sb) is found to follow a power_law, Ippc (t)= t –α, in temperature region 110K< T < 295 K, The parameter α as a function of temperature is obtaind. However, the ppc is observed only above 90K, that is contrast to previous reported results on most materials which exhibit PPC effects predominantly at low temperatures. Apossible mechanism is the presence of random local potential fluctuations in the sample, which strongly influence the carrier transport properties. Such fluctuations could be induced either by the compositional fluctuations or the impurity potential.

Vavsar area covers an area of 2413 hectares situated in 53°37΄35˝ - 53°4345˝ longitude and 36°540˝-36°1013˝ latitude. The vegetation of Vavsar area was studied, using the Braun-Blanquet (Zygmatist) School. Based on the analysis of phytosociological data and by using AFC and CAH methods, 8 associations were recognized. The Following associations constitute the major part of the area: Astragalo caspici-Onobrychidetum cornutae, Stachyetum laxae, Fagetum orientalis, Querco macrantherae-Fagetum orientalis. The distribution of plant associations in the protected areas is mainly affected by topographic features, including altitude, slop and exposure as well as edaphic factors, such as soil depth and texture. In general, these factors operate in the establishment of plant communities in the different elevation zones and slopes.

Due to high antagonistic activity of Trichoderma viride and Gliocladium virens, isolates T.v.Mo from T.viride and isolates Torbat I and G.v.pro from G. virens were selected and their efficacy was studied on Rhizoctonia solani (caused sugar beet damping-off) in invitro conditions. Antagonistic ability of Trichoderma and Gliocladium isolates was investigated as dual culture on PDA in concomitant and sequential cultures, 48 and 96 hours after R. solani culturing and it was found that all isolates inhibit R. solani mycelial growth. Isolate T.v.Mo in experiment 1 and 2, and isolate Torbat I in all 3 experiments stopped its mycelial growth and sporulated on it. Volatile metabolites of antagonistic isolates had significant inhibitory effect on mycelial growth of the pathogen, among which G.v.pro isolate with inhibition percent of 85.55% had the best effect. In investigation of inhibitory effect of 5 concentrations (10-% 15-% 20-% 25-% 30-%) of culture filtrates of antagonistic isolates in reduction of R. solani mycelial growth, it was found that none of the isolates at the mentioned concentrations had any effect on R. solani mycelial growth. Microscopic observations showed that these isolates coiled around, penetrated and degenerated hyphae of R. solani, stopped its growth and finally lysed it.

In this paper, using paraformaldehyde and formic acid as reagent in solution phase benzylic oximes with high yields have been converted to the corresponding carbonyl compounds and non benzylic oximes showed no reaction to this reagents. Also, these reactions have been examined in solvent- free conditions which led to the regeneration of carbonyl compounds.

In this work, first, copolymer of butyl acrylate/vinyl acetate (ButAc-co- VAC) was prepared by emulsion polymerization in aqueous medium. In the second step, aniline was polymerized in the copolymer matrix by chemical oxidation polymerization. Polymerization of aniline was carried out in the presece of p-toluene sulfonic acid (PTSA) as do pant. Ammonium per sulfate was used as an initiator. Purified composite material of Polyaniline/ (BuA-VAc) was dissolved in dichlorometane by using mechanical mixer. The films was prepared by casting method. The four-point conductivity measurements showd that the blend conductivity is 2.8 S. cm−1. Cyclic voltammograms (CV) revealed that the blend materials are electroactive. It was shown that the electrical activity of polyaniline was transfered successfully to the blend. Amount of conductivity compared with various do pant ions. The mechanical properties of the films indicated that the blend could be considered as an elastomer.

One of the most important aims in composite industry is to improve the properties of composite materials. In this research the effects of adding polypropylene Fiber and also the nano silica particles to epoxy resin using hand lay-up technique have been studied. It was found that increasing the polypropylene fiber with lower amount of glass fiber with increasing amount of nano silica up the 0.4 phr improved the impact properties of composites, but these properties showed a decreasing trend when adding over 0.4 phr nano silica. However, the same trend was observed when tensile strength and tensile modulus were determined: In case of bending tests, increasing the amount of polypropylene fiber increased the bending strength and modulus. But by adding nano silica particles a reverse effect was observed.

The most common process for production of phosphoric acid in the World, is wet process phosphoric acid (WPPA). Because the acid is produces from this process in the production of industrial grade and food grade contains many impurities, must be purified. Therefore, the purification process contains coagulation, discoloration with charcoal, sulfate precipitation, filtration, extraction with solvent and ion exchange process. Florine is eliminated by precipitation in the form sodium flour silicate. Arsenic is precipitated in form of cupper arsenide. Lead, iron and aluminous is precipitated by glacial acetic acid. Sulfate is precipitated by barium soluble salt.The selective solvent is used for extraction is three n-butyl phosphate (TBP). The result is obtained in laboratory is in accord with the above process.