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21.
22.
Nanocrystalline samples of Pb1−yLay(Ti1−xMnx)(1−y/4)O3 (PLMT) (y=0.06, x=0, 0.04, 0.07 and 0.10) were prepared by mechanical activation process (i.e., ball milling) followed by some annealing. The formation of single phase tetragonal crystal structure is confirmed by high-resolution X-ray diffraction study and by High resolution transmission electron micrographs (HRTEM), nano-scale compounds. The electrical behavior (i.e., impedance (Z) and electrical modulus (M)) of PLMT ceramics was studied by impedance spectroscopy technique in high temperature range. This study was carried out by means of the simultaneous analysis of the complex impedance (Z?) and electrical modulus (M*) functions in a wide frequency range (1 kHz-1 MHz). Impedance analysis has shown the grain and grain boundary contributions by an equivalent circuit model. Modulus analysis has provided vast information on charge transport processes. The simultaneous representation of the imaginary part of impedance and electric modulus (Z″, M″) vs. frequency revealed the localization of relaxation. The activation energy obtained from relaxation data may be attributed to oxygen ion vacancies. 相似文献
23.
The ferroelectric lead germanate (Pb5Ge3O11) and its isomorphous compounds are important because of their uses as pyroelectric and electro-optic devices. Comparison
of inter-planar d-spacings of Pb5Ge3−x
Si
x
O11 (x=0, 0.3, 0.7 and 1.00) suggests that there is no change in basic structure of Pb5Ge3−x
Si
x
O11 when Si is substituted for Ge in small quantity (x<1). The dielectric properties of the Si-substituted compounds have been studied as a function of temperature (30 to 200°C).
The ferroelectric-paraelectric phase transition has been observed at 185°C. The Si doping causes (a) Curie point to shift
towards low temperature, (b) peak value of the dielectric constant to decrease and (c) phase transition diffuse. The fast
increase in dielectric constant of pure Pb5Ge3O11 with temperature (beyond transition temperature) may be attributed to the development of space charge polarization in the
system. 相似文献
24.
Jiankun Shao Rishav Choudhary David F. Davidson Ronald K. Hanson Samuel Barak Subith Vasu 《Proceedings of the Combustion Institute》2019,37(4):4555-4562
The need for more efficient power cycles has attracted interest in super-critical CO2 (sCO2) cycles. However, the effects of high CO2 dilution on auto-ignition at extremely high pressures has not been studied in depth. As part of the effort to understand oxy-fuel combustion with massive CO2 dilution, we have measured shock tube ignition delay times (IDT) for methane/O2/CO2 mixtures and hydrogen/O2/CO2 mixtures using sidewall pressure and OH* emission near 306?nm. Ignition delay time was measured in two different facilities behind reflected shock waves over a range of temperatures, 1045–1578?K, in different pressures and mixture regimes, i.e., CH4/O2/CO2 mixtures at 27–286 atm and H2/O2/CO2 mixtures at 37–311 atm. The measured data were compared with the predictions of two recent kinetics models. Fair agreement was found between model and experiment over most of the operating conditions studied. For those conditions where kinetic models fail, the current ignition delay time measurements provide useful target data for development and validation of the mechanisms. 相似文献
25.
Séan J. Cassady Rishav Choudhary Vivek Boddapati Nicolas H. Pinkowski David F. Davidson Ronald K. Hanson 《国际化学动力学杂志》2020,52(11):725-738
The pyrolysis of propane plays an important role in determining the combustion properties of natural gas mixtures and offers insight into the cracking patterns of larger fuels. This work investigates propane pyrolysis behind reflected shock waves with a multiwavelength laser-absorption speciation technique. Nine laser wavelengths, sensitive to key pyrolysis species, were used to measure absorbance time histories during the decomposition of 2% propane in argon between 1022 and 1467 K, 3.7-4.3 atm. Absorbance models were developed at each diagnostic wavelength to interrogate common initial conditions, and time histories of all major species are reported at 1250, 1290, 1330, 1370, and 1410 K. Nearly complete carbon recovery observed at lower temperatures enabled the inference of hydrogen formation from atomic conservation, while decaying carbon recovery at high temperatures suggests the formation of allene and 1-butene. The results show systematically faster pyrolysis than predicted by kinetic modeling and motivate further study into the kinetics of propane pyrolysis. 相似文献
26.
Satyan Choudhary Alfred J. Crosby 《Journal of polymer science. Part A, Polymer chemistry》2018,56(23):1545-1551
Evaporative self-assembly (ESA), based on the “coffee-ring” effect, is a versatile technique for assembling particle solutions into mesoscale patterns and structures on different substrates. ESA works with a wide variety of organic and inorganic materials, where the solution is a combination of volatile solvent and nonvolatile solute. Modified ESA methods, such as “stop-and-go flow coating,” use a programmed meniscus “stick–slip” motion to create mesoscale assemblies with controlled shape, size, and architecture. However, current methods are not scalable for increased production volumes or patterning large surface areas. We demonstrate a new ESA method, where an oscillating blade controls the meniscus depinning and drives the evaporative assembly of solutes at the pinned meniscus. Results show that oscillation frequency and substrate speed control time/distance intervals between successive meniscus depinning, and the assembly dimensions depend on solution concentration, oscillation frequency, substrate speed, and meniscus height. We report the mechanism of the meniscus depinning and the control over assembly cross-sectional dimensions. This advance provides a scalable ESA method with faster processing times and maintained advantages. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 1545–1551 相似文献
27.
Suchismita Mohanty R. N. P. Choudhary B. N. Parida R. Padhee 《Applied Physics A: Materials Science & Processing》2014,116(4):1833-1840
Using a standard high-temperature solid-state reaction technique, polycrystalline samples of (Bi1?x , Na x ) (Fe1?x , Ta x ) O3 (x = 0.0, 0.5) were prepared. The formation of the desired materials was confirmed by X-ray diffraction. The surface texture of the prepared materials recorded by scanning electron microscope exhibits a uniform grain distribution with small voids suggesting the formation of high-density pellet samples. The impedance and dielectric properties of the materials were investigated as a function of temperature and frequency. The relative dielectric constant and loss tangent of BiFeO3 decrease on addition of NaTaO3 (x = 0.5). The effect of addition of NaTaO3 on grain and grain boundary contributions in the resistive and capacitive components of BiFeO3 was studied using complex impedance spectroscopy. The value of activation energy due to both grain and grain boundary of both the samples is nearly same. The nature of variation of dc conductivity confirms the Arrhenius behavior of the materials. Study of frequency dependence of ac conductivity suggests that the materials obey Jonscher’s universal power law and the presence of ionic conductivity. 相似文献
28.
Ajay M. Sorty Kamlesh K. Meena Khushboo Choudhary Utkarsh M. Bitla P. S. Minhas K. K. Krishnani 《Applied biochemistry and biotechnology》2016,180(5):872-882
Halotolerant bacteria associated with Psoralea corylifolia L., a luxuriantly growing annual weed in salinity-affected semi-arid regions of western Maharashtra, India were evaluated for their plant growth-promoting activity in wheat. A total of 79 bacteria associated with different parts viz., root, shoot and nodule endophytes, rhizosphere, rhizoplane, and leaf epiphytes, were isolated and grouped based on their habitat. Twelve bacteria isolated for their potential in plant growth promotion were further selected for in vitro studies. Molecular identification showed the presence of the genera Bacillus, Pantoea, Marinobacterium, Acinetobacter, Enterobacter, Pseudomonas, Rhizobium, and Sinorhizobium (LC027447-53; LC027455; LC027457, LC027459, and LC128410). The phylogenetic studies along with carbon source utilization profiles using the Biolog® indicated the presence of novel species and the in planta studies revealed promising results under salinity stress. Whereas the nodule endophytes had minute plant growth-promoting (PGP) activity, the cell free culture filtrates of these strains enhanced seed germination of wheat (Triticum aestivum L). The maximum vigor index was monitored in isolate Y7 (Enterobacter sp strain NIASMVII). Indole acetic acid (IAA) production by the isolates ranged between 0.22 and 25.58 μg mL?1. This signifies the need of exploration of their individual metabolites for developing next-generation bio-inoculants through co-inoculation with other compatible microbes. This study has potential in utilization of the weed-associated microbiome in terms of alleviation of salinity stress in crop plants. 相似文献
29.
The curing behaviour of diglycidyl ether of bisphenol-A (DGEBA) was investigated by the dynamic differential scanning calorimetry
using varying molar ratios of aromatic imide-amines and 4,4′-diaminodiphenylsulfone (DDS). The imide-amines were prepared
by reacting 1 mole of naphthalene 1,4,5,8-tetracarboxylic dianhydride (N) and 4,4′-oxodiphthalic anhydride (O) with 2.5 moles
of 4,4′-diaminodiphenyl ether (E) or 4,4′-diaminodiphenyl methane (M) or 4,4′-diaminodiphenylsulfone (S) and designated as
NE/OE or NM/OM or NS/OS. The mixture of the imide-amines and DDS at ratio of 0:1, 0.25:0.75, 0.5:0.5, 0.75:0.25 and 1:0 were
used to investigate the curing behaviour of DGEBA.
A single exotherm was observed on curing with mixture of imide-amines and DDS. This clearly shows that the two amines act
as co-curing agents. Curing temperatures were higher with imide-amines having sulfone linkage irrespective of anhydride. Curing
of DGEBA with mixture of imide-amines and or DDS resulted in a decrease in characteristic curing temperatures. The thermal
stability of the isothermally cured resins was also evaluated using dynamic thermogravimetry in a nitrogen atmosphere. The
char yield was higher in case of resins cured imide-amines based on N and E. The activation energy of decomposition and integral
procedural decomposition temperature were also calculated from the TG data. 相似文献
30.
Choudhary MI Siddiqui ZA Musharraf SG Nawaz SA Atta-Ur-Rahman 《Natural product research》2005,19(4):311-317
The microbial transformation of prednisone (17alpha,21-dihydroxy-pregna-1,4-diene-3,11,20-trione) (1) by Cunninghamella elegans afforded two metabolites, 17alpha,21-dihydroxy-5alpha-pregn-1-ene-3,11,20-trione (2) and 17alpha,20S,21-trihydroxy-5alpha-pregn-1-ene-3,11-dione (3), while the fermentation of 1 with Fusarium lini, Rhizopus stolonifer and Curvularia lunata afforded a metabolite 1,4-pregnadiene-17alpha,20S,21-triol-3,11-dione (4). Compound 3 was found to be a new metabolite. Their structures were elucidated on the basis of spectroscopic techniques. Compound 3 showed inhibitory activity against lipoxygenase enzyme. 相似文献