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81.
Praveen Khatri 《Journal of Physics and Chemistry of Solids》2009,70(2):385-29
Polycrystalline sample of Ca3Nb2O8 was prepared by a high-temperature solid-state reaction technique. X-ray diffraction (XRD) analysis confirms the formation of single-phase compound of hexagonal (rhombohedral) crystal structure at room temperature. Scanning electron micrograph of the material showed uniform grain distribution on the surface of the sample. Detailed studies of dielectric properties of the compound, studied in a wide frequency range (102-106 Hz) at different temperatures (25-500 °C), exhibit a dielectric anomaly suggesting phase transition of ferroelectric-paraelectric and structural type at 300 °C. Electrical properties of the material were analyzed using a complex impedance technique. The Nyquists plot showed the presence of bulk effect in the material in the studied temperature range. Studies of electrical conductivity over a wide temperature range suggest that the compound has negative temperature coefficient of resistance behavior. 相似文献
82.
Berchmans S Nirmal RG Prabaharan G Madhu S Yegnaraman V 《Journal of colloid and interface science》2006,303(2):604-610
The layer-by-layer assembly of silver nanoclusters with 3,3'-dithiodipropionic acid (DTDPA) as spacers was prepared through self-assembly on a gold foil and has been characterized by cyclic voltammetric and AFM techniques. The DTDPA molecules acting as spacers between the layers of silver serve as molecular interconnects for the four layers prepared in this work. The organization of layers was found to decrease with an increase in the number of layers. The layer-by-layer assembly of silver clusters motivated us to prepare silver nanowires stabilized by the bifunctional molecules DTDPA through template synthesis using cellulose nitrate membranes. The nanostructures formed by this method were characterized by SEM, TEM, AFM, FTIR, CV, and photoluminescence studies. It is observed that the DTDPA molecules, instead of forming molecular interconnects, protect the structures by self-assembling themselves along the edges of the nanostructures. The concept of self-assembly protecting the nanostructures is demonstrated in this work. 相似文献
83.
Bulk Ge7Se93?xSbx (21 ? x ? 32) glasses are prepared by melt quenching method and electrical switching studies have been undertaken on these samples to elucidate the type of switching and the composition and thickness dependence of switching voltages. On the basis of the compressibility and atomic radii, it has been previously observed that Se-based glasses exhibit memory switching behavior. However, the present results indicate that Ge7Se93?xSbx glasses exhibit threshold type electrical switching with high switching voltages. Further, these samples are found to show fluctuations in the current–voltage (I–V) characteristics. The observed threshold behavior of Ge7Se93?xSbx glasses has been understood on the basis of larger atomic radii and lesser compressibilities of Sb and Ge. Further, the high switching voltages and fluctuations in the I–V characteristics of Ge–Se–Sb samples can be attributed to the high resistance of the samples and the difference in thermal conductivities of different structural units constituting the local structure of these glasses. The switching voltages of Ge7Se93?xSbx glasses have been found to decrease with the increase in the Sb concentration. The observed composition dependence of switching voltages has been understood on the basis of higher metallicity of the Sb additive and also in the light of the Chemically Ordered Network (CON) model. Further, the thickness dependence of switching voltages has been studied to reassert the mechanism of switching. 相似文献
84.
Kandula Madhu Kumar Reddy Sarva Santhisudha Gundluru Mohan Kotha Peddanna Chippada Appa Rao 《Phosphorus, sulfur, and silicon and the related elements》2016,191(6):933-938
A one pot three-component nano Gd2O3 catalyzed neat reaction of 2-morpholinoethanamine and dimethylphosphite with various salicylaldehydes under microwave irradiation afforded a series of new α-aminophosphonates in high yields. The synthesized compounds were characterized by FT-IR, (1H, 13C, 31P)-NMR, and mass spectral methods. The antioxidant activity of these compounds was evaluated against DPPH, NO, and H2O2 methods and found that the compound Dimethyl (2-hydroxy-5-nitrophenyl) (2-morpholinoethylamino) methylphosphonate (4h) has higher antioxidant activity than the corresponding standards. 相似文献
85.
Li H Chiang WS Fratini E Ridi F Bausi F Baglioni P Tyagi M Chen SH 《J Phys Condens Matter》2012,24(6):064108
The influence of a new comb-shaped polycarboxylate-based superplasticizer (CSSP) on the hydration kinetics and transport properties of aged cement pastes has been investigated by high-resolution quasi-elastic neutron scattering (QENS) and low temperature differential scanning calorimetry (LT-DSC). A new method of analysis of QENS spectra is proposed. By applying the refined method we were able to access to four independent physical parameters including the self-diffusion coefficient of the hydration water confined in the cement paste. Mean squared displacement (MSD) of the hydrogen atom for mobile water molecules displays a dynamic crossover temperature in agreement with DSC data. The experimental results indicate that CSSP polymer added into cement paste moderates the hydration process and decreases the dynamic crossover temperature of the hydration water. 相似文献
86.
Using first-principles calculations, we demonstrate the existence of anisotropic ferromagnetic interactions in Co embedded graphene nanoribbons (GNRs). Spin polarization of the edge states is found to alter significantly compared to the metal-free cases. Our findings can all be well-justified as the output of the interplay between the development of an induced spin polarization in the neighborhood of the Co atoms and the maintaining of the polarization picture of the Co-free GNR. Based on our results, we propose an efficient pathway for graphene-based spintronics applications. 相似文献
87.
Synthesis, spectral, electrochemical, and anion binding properties of 3,5-bis(dipyrromethanyl) boron-dipyrromethenes 总被引:1,自引:0,他引:1
Four new boron-dipyrromethenes (BODIPYs) containing dipyrromethanyl substituents at 3,5-positions, bis(3,5-dipyrromethanyl) BODIPYs 5-8, were synthesized by treating their corresponding 3,5-diformyl BODIPYs 1-4 with excess pyrrole under mild acid catalyzed reaction conditions. The compounds 5-8 are stable and freely soluble in common organic solvents. One-dimensional, two-dimensional NMR, high resolution mass spectrometry (HRMS), absorption, fluorescence, and electrochemical techniques were used to characterize the compounds. The spectral and electrochemical studies indicated that dipyrromethanyl groups at 3,5-positions of BODIPY are less electron deficient compared to formyl groups at the same positions. The anion binding studies indicated that bis(3,5-dipyrromethanyl) BODIPY compounds containing four pyrrole NH groups showed preferential binding with F(-) ion over other anions, as confirmed by using NMR, fluorescence, and electrochemical studies. 相似文献
88.
R. S. Sathyapriya Suma Nair V. Kamesh R. K. Prabhath Madhu Nair R. Acharya D. D. Rao 《Journal of Radioanalytical and Nuclear Chemistry》2012,294(3):387-390
A study was conducted to estimate the thorium concentration in locally grown vegetables in high background radiation area (HBRA) of southern coastal regions of India. Locally grown vegetables were collected from HBRA of southern coastal regions of India. Thorium concentration was quantified using instrumental neutron activation analysis. The samples were irradiated at CIRUS reactor and counted using a 40% relative efficiency HPGe detector coupled to MCA. The annual intake of thorium was evaluated using the consumption data provided by National Nutrition Monitoring Board. The daily intake of 232Th from the four food categories (green leafy vegetables, others vegetables, roots and tubers, and fruits) ranged between 0.27 and 5.352?mBq?d?1. The annual internal dose due to ingestion of thorium from these food categories was 46.8?×?10?8 for female and 58.6?×?10?8?Sv?y?1 for male. 相似文献
89.
90.
Madhu Santosh Ku Mutyala Deepika Bandhanadham Vijaya Rohini Pendyala 《Acta Mechanica Sinica》2009,25(1):1-12
Advances in the field of micro electro mechanical systems and their uses now offer unique opportunities in the design of ultrasensitive analytical tools. The analytical community continues to search for cost-effective, reliable, and even portable analytical techniques that can give reliable and fast response results for a variety of chemicals and biomolecules. Microcantilevers (MCLs) have emerged as a unique platform for label-free chem-sensor or bioassay. Several electronic designs, including piezoresistive, piezoelectric, and capacitive approaches, have been applied to measure the bending or frequency change of the MCLs upon exposure to chemicals. This review summarizes mechanical, fabrication, and electronics approaches to increase the sensitivity of MCL sensors. 相似文献