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Abstract: This work studies structural and various electrical properties of polycrystalline La0.7Sr0.25 Na0.05 Mn0.9Ti0.1O3 (LSNMTi), which were prepared by standard solid state reaction technique. The formation of a single phase rhombohedral structure of the composition was confirmed by the X-ray diffraction study. The electrical behavior of sintered pellets investigated by impedance spectra has shown frequency dependent behavior. Both conductivity and electric modulus formalisms have been used to study the relaxation dynamics of charge carriers. The variation of ac conductivity with frequency at different temperatures obeys the universal Jonscher׳s power law (σ ac αw). [Copyright &y& Elsevier]

The charge carrier's dynamics of La 0.7 (Sr 5/6 Na 1/6) 0.3 Mn 0.7 Ti 0.3 O 3 (LSNMTO) ceramic is conducted using the temperature and frequency dependences of the electrical conductivity and their scaling formalisms. The structural study indicates that LSNMTO crystallizes in a rhombohedral R 3 ‾ c perovskite structure with no detectible secondary phases. A phase transition from the high-temperature metallic behavior to the low-temperature semiconductor nature is observed from the electrical conductivity curve at T S-M = 415 K. Further, it is observed that the cation-anion-cation and the cation-cation interactions are present in the material, and play important role in governing the electrical behaviors of LSNMTO. From 200 K to 415 K, the Non-adiabatic Small Polaron Hopping is the predominant conduction process, although the Mott-Variable Range Hopping mechanism governs the conductivity at low temperatures. In the intermediate temperature range, the dynamic of the charge carriers is explained using the Shklovskii Efros model. The frequency-activated conductivity obeyed the universal laws (double-Jonscher and Jonscher laws). At high frequencies, the dispersion of the conductivity spectra is attributed to the presence of hopping and tunneling conduction processes. The Time-Temperature Superposition Principle (TTSP) is obeyed over a large temperature range from 160 K to 350 K. Below 160 K, the deviation from the TTSP is attributed to the coexistence of hopping and tunneling conduction mechanisms. Deviations from the Summerfield scaling and shifts of the isotherms to higher values on decreasing the temperature are due to the local structural disorder in LSNMTO. Therefore, the structural particularities of LSNMTO can result in diverse conduction pathways giving an increase to the deviations from the Summerfield scaling. The studied ceramic exhibits a very motivating maximum negative temperature coefficient of resistance NTCR = −13.36% which is significantly elevated as compared to previously investigated compounds. [ABSTRACT FROM AUTHOR]

Two-year-old Norway spruce (Picea abies (L.) Karst) seedlings were exposed to traffic emissions along roadsides with three different traffic densities and speed limits; highway, street and a quiet local road. The responses of the exposed seedlings as a host plant and those of spruce shoot aphid (Cinara pilicornis Hartig) were studied. The concentrations of soluble N and free amino acids, defence chemicals (total phenolics, monoterpenes) were analysed, and aphid growth and reproduction were studied. Along the highway, street and at the local roadcontrol site, the atmospheric concentrations of black carbon (BC) and oxides of N (NOx) were measured for 1 week during the experiment. The BC data indicate deposition of organic particulate compounds along the highway and street. The NOx concentrationsalong the highway and street showed great diurnal variation, but theaverage NOx concentrations were relatively low. Thus, no changes in N metabolism or growth of the exposed Norway spruce seedlings were found. Along the street, the concentrations of many individual free amino acids, such as proline, as well as total amino acid concentrations, were lower than at the associated control site. Correspondingly, there was also no increase in spruce shoot aphid mean relative growth rate. The aphid reproduction, however, increased along the highway and is suggested to be due to more conducive microclimatic conditions at the exposure site or lack of natural enemies. No changes in defence chemicals (total phenolics, monoterpenes) in relation to the traffic exposure were found. Instead, the microclimatic conditions(temperature, solar irradiation) seemed to affect the concentration of total phenolics. [ABSTRACT FROM AUTHOR]

The effects of motor vehicle exhaust gas on Norway spruce seedlings (Picea abies (L.) Karst) and plant/insect interaction of spruce shootaphid (Cinara pilicornis Hartig) was studied. The exhaust gas concentrations in the fumigation chambers were monitored and controlled by measuring the concentration of nitrogen oxides (NOx) with a computer aided feedback system. The concentrations of major exhaustgas components (black carbon [BC], fine particles, VOCs and carbonylcompounds) in the chamber air were also measured. Reponses of Norwayspruce seedlings to a 2 and 3-week exhaust gas exposure and subsequent performance of spruce shoot aphid were studied using realistic exposure regimes; 50, 100 and 200 ppb NOx. The feedback control system based on NOx concentrations proved an adequate and practical means for controlling the concentration of exhaust gasesand studying plant responses in controlled environment chambers. Theexhaust exposure resulted in increased concentrations of proline, glutamine, threonine, aspartic acid, glycine and phenylalanine and decreased concentration of arginine, serine, alanine and glycine in youngneedles. No changes in soluble N concentrations were observed. The results are interpreted as a stress response rather than use of NOx as a nitrogen source. No changes in total phenolics and onlytransient changes in some individual terpene concentrations were detected. The exhaust gas exposure stressed the exposed seedlings, but had no significant effect on N metabolism or the production of defencechemicals. Aphid performance was not significantly affected. SolubleN, secondary metabolism and aphid performance were not sensitive to exhaust gas exposure during shoot elongation in Norway spruce. [ABSTRACT FROM AUTHOR]