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101.
Structural and dielectric properties of sodium-potassium niobate (Na1?x KxNbO3) (0.250?≤?x?≤?0.350) ceramics, prepared by the solid-state reaction method were investigated. Observed dielectric properties show a strong compositional dependence, at all the measured temperatures (from room temperature to 150°C) and frequencies (from 1 to 1000?kHz). In the prepared compositions, the lowest values of dielectric permittivity, loss tangent and electrical conductivity were found, and an anomaly in the shifting pattern of X-ray diffraction (XRD) peaks and change in the slope of a/c vs. x plot were observed at x?=?0.315. The observed structural and dielectric anomaly gives a morphotropic phase boundary-like indication, in Na1?xKxNbO3 system, at x?=?0.315. 相似文献
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103.
Ultra-Compact Objects (ucos) have been found tobe interesting astrophysical entities. The existence ofsuch a possible stable object has been discussed byconsidering the stability of Tolman's type VII solution which is one of the few physicallyrelevant exact solutions of Einstein's field equationsfor a static and spherically symmetric massdistribution. A distinctive feature of this solutionamong the others is that the surface density alsodrops to zero (i.e., the continuity of density, and therespective derivative of the metric parameter() is also assured at the surface of theconfiguration). The stability analysis of this solution,according to the variational method [20], as well as thebinding-energy criteria of fluid spheres shows that theconfiguration remains stable at least up to a central redshift, z0 5.09, and surfaceredshift, za 0.78 (i.e. up to a u mass/size) value 0.3428), thereby confirmingthe existence of an ultracompact object (uco) thatcorresponds to a mass to size ratio (u M/a) 1/3. 相似文献
104.
Bioguided Isolation and Antiproliferative Activity of Constituents from Smilax korthalsii A.D.C. Leaves
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Abdulmumeen A. Hamid Olapeju O. Aiyelaagbe Arvind S. Negi Suaib Luqman Fatima Kaneez 《中国化学会会志》2016,63(7):562-571
Ethyl acetate extract of Smilax korthalsii A.D.C. leaves exhibited antiproliferative activity on leukaemia carcinoma K562, hepatic liver cancer cells WRL and colorectal carcinoma with IC50 of 125.20, 46.10 and 160.00 μM respectively. Isolation of the bioactive ethyl acetate extract of Smilax korthalsii A.D.C. leaves gave eight compounds; 3β‐hydroxyspirost‐5‐ene (diosgenin), 1 , β‐sitosterol, 2 , lup‐5,11,20‐trien‐23‐ol, 3 , uneicos‐9‐enoic acid, 4 , ethylheptadecan‐17‐oic‐9‐enoate, 5 , cis‐octadec‐9‐enoic acid, 6 , hexadec9‐enoic acid, 7 and 11‐methyltridec‐12‐en‐1‐ol, 8 . The isolated compounds were tested against four human cancer cell lines: leukaemia carcinoma, K‐562; hepatic liver cancer cells, WRL; colorectal carcinoma, COLO; and breast carcinoma, MCF‐7 using the MTT assay. Diosgenin 1 exhibited significant antiproliferative activity against all four cell lines (IC50; K562=6.25, WRL=14.34, COLO=38.00, MCF‐7=12.40 μM), while compounds 3, 6 and 7 inhibited the growth of K‐562 at 20, 50 and 100 μM concentrations with IC50 of 90.20, 75.92 and 50.72 μM respectively. Other isolated compounds also showed cytotoxic properties against K‐562, WRL and COLO, but showed low inhibition of MCF‐7. 相似文献
105.
Shubhandra Tripathi Gaurava Srivastava Aastha Singh A. P. Prakasham Arvind S. Negi Ashok Sharma 《Journal of computer-aided molecular design》2018,32(4):559-572
Colchicine site inhibitors are microtubule destabilizers having promising role in cancer therapeutics. In the current study, four such indanone derivatives (t1, t9, t14 and t17) with 3,4,5-trimethoxyphenyl fragment (ring A) and showing significant microtubule destabilization property have been explored. The interaction mechanism and conformational modes triggered by binding of these indanone derivatives and combretastatin at colchicine binding site (CBS) of αβ-tubulin dimer were studied using molecular dynamics (MD) simulation, principle component analysis and free energy landscape analysis. In the MD results, t1 showed binding similar to colchicine interacting in the deep hydrophobic core at the CBS. While t9, t14 and t17 showed binding conformation similar to combretastatin, with ring A superficially binding at the CBS. Results demonstrated that ring A played a vital role in binding via hydrophobic interactions and got anchored between the S8 and S9 sheets, H8 helix and T7 loop at the CBS. Conformational modes study revealed that twisting and bending conformational motions (as found in the apo system) were nearly absent in the ligand bound systems. Absence of twisting motion might causes loss of lateral contacts in microtubule, thus promoting microtubule destabilization. This study provides detailed account of microtubule destabilization mechanism by indanone ligands and combretastatin, and would be helpful for designing microtubule destabilizers with higher activity. 相似文献
106.
Negi AS Sengupta K Sood AK 《Langmuir : the ACS journal of surfaces and colloids》2005,21(25):11623-11627
We have studied clustering of colloidal particles under the influence of an ac electric field as a function of frequency. The field was applied in a direction perpendicular to the confining walls. Two regimes are observed, a low frequency regime where the clusters are isotropic with a local triangular order, as reported earlier in the literature, and a new high-frequency regime where the clusters are highly elongated (anisotropic) with no local order. The crossover from one regime to the other occurs at a critical frequency, f(c). The threshold field for the cluster formation, E(th), increases with frequency in both the regimes. An increase in the particle size leads to a reduction in both E(th) and f(c). We present evidence to show that the elongated structures seen at high frequency are related to the field inhomogeneities at imperfections on the conducting surface. We also propose a possible mechanism based on hydrodynamic flow considerations to explain the formation of these clusters. 相似文献
107.
A. N. Shaikh B. S. Negi S. Sadasivan 《Journal of Radioanalytical and Nuclear Chemistry》2002,253(2):231-234
Forty brands of tobacco used in Indian cigarettes, 20 brands of bidis (tobacco rolled in wrapper leaves), 15 brands of chewing tobacco and 15 brands of snuff tobacco were analyzed by nuclear and allied techniques. The elements measured into tobacco can be grouped into seven categories from less than 1 ppm to 5% by weight. Concentration level varied from 0.5-5% for (Ca, K, Cl), 400-1500 ppm (Fe), 200-600 ppm (Na), 100-300 ppm (Ti, Mn, Br and Sr), 10-100 ppm (Cu, Zn and Rb), 1-10 ppm (Cr, Ni, Pb and La) and less than 1 ppm (As, Co, Cd, Sb, Hg and Eu). Among the above elements Cr, Ni, As, Cd, Pb, Hg and Sb are considered toxic. The percentage transfer of the elements from cigarette tobacco to smoke particles during smoking was also estimated using a smoking machine and collecting the smoke particles on a filter paper. The results show that Br, Cr, Sb and Zn have high percentage transfer from tobacco to its smoke of the order of 2-15%. Out of these Sb has the highest 15%. Cobalt, Fe and Sc have lowest percentage of transfer of the order of less than 1%. The percent transfer of these elements from tobacco to tobacco smoke is higher in case of bidis (1.5-3.0 times) as compared to cigarettes. In cigarettes also non-filter cigarettes have higher transfer (2-3 times) as compared to filter tip cigarettes. 相似文献
108.
Masa-Aki Kakimoto Yuvraj Singh Negi Yoshio Imai 《Journal of polymer science. Part A, Polymer chemistry》1986,24(7):1511-1517
Polycondensation of 2,5-bis(4-chloroformyl)-3,4-diphenylthiophene ( I ) with various bisphenols afforded tetraphenylthiophene-containing aromatic polyesters by the interfacial or solution polycondensation method. Polyamide–esters were obtained from I and aminophenols by means of the interfacial technique. These polymers had inherent viscosities of 0.4–0.8 dL/g. All the polymers were readily soluble in various organic solvents, and could be cast into transparent and flexible films. Their glass transition temperatures were in the range of 235–335°C. These polymers did not lose weight below 400°C in either air or nitrogen. 相似文献
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