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791.
U. Chakravarty P. A. Naik B. S. Rao V. Arora H. Singhal G. M. Bhalerao A. K. Sinha P. Tiwari P. D. Gupta 《Applied physics. B, Lasers and optics》2011,103(3):571-577
A comparative experimental study of the X-ray emission in the water-window spectral region has been performed using carbon
nanofibers (CNFs) of different sizes and graphite plate targets, irradiated with ultra-short (Ti:sapphire) laser pulses. More
than an order of magnitude enhancement in the X-ray yield is observed from CNFs of 60-nm diameter with respect to graphite
targets. The X-ray emission from CNFs of 160-nm diameter was also high. The integrated X-ray yield of these carbon-based targets
scales with the laser intensity (I
L) as IL ~ 1.3-1.4I_{\mathrm{L}}^{\sim 1.3-1.4} in the intensity range of 4×1016–4×1017 W/cm2. The effect of the laser pulse duration on the X-ray emission from the CNFs was also studied by varying the pulse duration
from 45 fs up to 3 ps at a constant fluence of 2×104 J/cm2. The optimum laser pulse duration for maximum X-ray emission increases with the diameter of the CNFs used. The results are
explained from physical considerations of heating and hydrodynamic expansion of the CNF plasma in which resonance field enhancement
takes place while passing through two times the critical density. The results add to the efforts towards achieving an efficient
low-cost water-window X-ray source for microscopy. 相似文献
792.
Aneeta Kharkwal Shailesh N. Sharma Kiran Jain Leena Arora Parul Chawla A. K. Singh S. Chand 《Colloid and polymer science》2013,291(11):2607-2617
CuInS2 (CIS) particles were directly synthesized in P3HT matrix with different concentrations ratio of P3HT and CIS (1:2, 1:4, and 1:8) by decomposition of copper indium xanthate (CIX). Here, copper indium xanthate and P3HT were mixed homogeneously in o-dichlorobenzene (DCB), which induced the formation of the CIS nanoparticles by the thermal decomposition of the precursor compound in situ at temperatures as low as 110 °C. The effects of the precursor concentration on the size of the CIS nanoparticles was studied by microstructure investigations (TEM, AFM, XRD) and UV–vis measurements show that these CIS composites possess a direct bandgap energy higher than 1.45 eV depending on the concentration of P3HT. PL quenching of P3HT polymer (i.e., higher accessible fraction of fluorophores) was found to be more for in situ rather than ex situ conditions for comparable CIX concentrations or particle size. This can be attributed to the fact that in in situ synthesis, P3HT act as surface directing template for CIS nanoparticles which is not so in the case of ex situ synthesis. Due to this, the polymeric stabilization of the CIS nanocomposites is better realized for in situ synthesis as compared to ex situ synthesis. 相似文献
793.
Manoj Kumar Neha Sikri Sulekha Chahal Jitender Sharma Bhavna Sharma Poonam Yadav Monika Bhardwaj Divya Vashishth Pooja Kadyan Sudhir Kumar Kataria Sunita Dalal 《Molecules (Basel, Switzerland)》2021,26(13)
Urease is an enzyme that plays a significant role in the hydrolysis of urea into carbonic acid and ammonia via the carbamic acid formation. The resultant increase in pH leads to the onset of various pathologies such as gastric cancer, urolithiasis, hepatic coma, hepatic encephalopathy, duodenal ulcers and peptic ulcers. Urease inhibitors can reduce the urea hydrolysis rate and development of various diseases. The Cinnamomum genus is used in a large number of traditional medicines. It is well established that stem bark of Cinnamomum cassia exhibits antiulcerogenic potential. The present study evaluated the inhibitory effect of seven extracts of Cinnamomum camphora, Cinnamomum verum and two pure compounds Camphene and Cuminaldehyde on urease enzyme. Kinetic studies of potential inhibitors were carried out. Methanol extract (IC50 980 µg/mL) of C. camphora and a monoterpene Camphene (IC50 0.147 µg/mL) possess significant inhibitory activity. The Lineweaver Burk plot analysis suggested the competitive inhibition by methanol extract, hexane fraction and Camphene. The Gas Chromatography-Mass Spectroscopy (GC–MS) analysis of hexane fraction revealed the contribution of various terpenes. The present study targets terpenes as a new class of inhibitors that have potential therapeutic value for further development as novel drugs. 相似文献
794.
Mrityunjaya Asthana Neha SharmaRitush Kumar Jay Bahadur SinghRadhey M. Singh 《Tetrahedron letters》2014
I2-catalyzed base-free reactions of 3-homoallylquinoline-2-thiones have been described for the synthesis of tetracyclic quinolines, tetrahydrofuro [2′,4′:4,6]thiopyrano[2,3-b]quinolines in excellent yields. Similarly, I2-catalyzed reactions could proceed to tricyclic quinolines from hydroxyl group protected 3-homoallylquinoline-2-thiones. However, deprotection of group in tricyclic quinoline with HI again transformed into tetracyclic quinoline. The sulfonium salt intermediate has been proposed to explain these reactions. 相似文献
795.
Alex Nazzaro Brandon Lu Nicholas Sawyer Andrew M. Watkins Paramjit S. Arora 《Angewandte Chemie (International ed. in English)》2023,62(41):e202303943
Mimics of protein secondary and tertiary structure offer rationally-designed inhibitors of biomolecular interactions. β-Sheet mimics have a storied history in bioorganic chemistry and are typically designed with synthetic or natural turn segments. We hypothesized that replacement of terminal inter-β-strand hydrogen bonds with hydrogen bond surrogates (HBS) may lead to conformationally-defined macrocyclic β-sheets without the requirement for natural or synthetic β-turns, thereby providing a minimal mimic of a protein β-sheet. To access turn-less antiparallel β-sheet mimics, we developed a facile solid phase synthesis protocol. We surveyed a dataset of protein β-sheets for naturally observed interstrand side chain interactions. This bioinformatics survey highlighted an over-abundance of aromatic–aromatic, cation-π and ionic interactions in β-sheets. In correspondence with natural β-sheets, we find that minimal HBS mimics show robust β-sheet formation when specific amino acid residue pairings are incorporated. In isolated β-sheets, aromatic interactions endow superior conformational stability over ionic or cation-π interactions. Circular dichroism and NMR spectroscopies, along with high-resolution X-ray crystallography, support our design principles. 相似文献
796.
Effect of pyrolysis temperature and operating temperature on the performance of nanoporous carbon membranes 总被引:1,自引:0,他引:1
Clare J. Anderson Steven J. Pas Gaurav Arora Sandra E. Kentish Anita J. Hill Stanley I. Sandler Geoff W. Stevens 《Journal of membrane science》2008,322(1):19-27
Technology designed to capture and store carbon dioxide (CO2) will play a significant role in the near-term reduction of CO2 emissions and is considered necessary to slow global warming. Nanoporous carbon (NPC) membranes show promise as a new generation of gas separation membranes suitable for CO2 capture.We have made supported NPC membranes from polyfurfuryl alcohol (PFA) at various pyrolysis temperatures. Positron annihilation lifetime spectrometry (PALS) and wide angle X-ray diffraction (WAXD) results indicate that the pore size decreases whilst the porosity increases with increasing pyrolysis temperature. The membrane performance results support these findings with a significant increase in permeance being seen with increasing pyrolysis temperature, which relates to the increase in porosity.Mixed gas performance measurements also show an increase in CH4 permeance as the operating temperature is increased from 35 to 200 °C, which can be related to an increase in the rate of diffusion. However, the selectivity decreases with increasing operating temperature due to the smaller changes in the CO2 permeance. These smaller changes in CO2 permeance can be related to the stronger adsorption of this gas on the carbon surface at lower operating temperatures. Interestingly, regardless of the original pyrolysis temperature, the selectivity at higher operating temperatures is similar, whereas the permeance remains related to this pyrolysis temperature. 相似文献
797.
Postharvest residues for southern pine species have not previously been quantified to compare volumes produced from both thinnings
and clearcut volumes. A John Deere 1490 Slash Bundler bundled postharvest residues following a first thinning of a 14-year-old
stand, a second thinning of a 25-year-old stand, and a clearcut of a naturally regenerated mature stand of 54 years of age.
Regardless of stand type, nearly one-fifth of merchantable volume harvested was collected as postharvest residue. Initial
bundle moisture contents were 127.3, 81.1, and 49.4% dry basis (db) for the first and second thinnings and mature stands,
respectively. Bundle needles content was found to significantly influence the relative moisture contents of the bundles by
stand type due to the high moisture content of needles compared to other bundle components. Bundles were stored outside and
exposed to very hot and dry conditions and dried very rapidly to lowest moisture contents of 22.8, 14.5, and 13.5% (db) for
first and second thinnings and mature stands, respectively. Response to moderating temperatures and higher precipitation resulted
in rapid moisture content increase to 69.9, 46.2, and 38.1% (db) for the first and second thinnings and mature stand bundles
by the end of the study. Temperature and precipitation and bundle percentage needles content all significantly influenced
the rapid moisture content variations observed over the study periods. 相似文献
798.
799.
Jaimy KB Safeena VP Ghosh S Hebalkar NY Warrier KG 《Dalton transactions (Cambridge, England : 2003)》2012,41(16):4824-4832
Visible light sensitive Fe(3+) and Ce(4+) co-doped nano TiO(2) photocatalyst has been prepared by a modified aqueous sol-gel method and the activity has been measured in terms of degradation of MB dye. Both dopants shifted the absorption profile of TiO(2) to the visible region and improved activity. Fe(3+) ions trapped the charge carriers due to the stable electronic configuration and improved their separation. Ce(4+) ions, which were mainly located at the grain boundaries, cause dislocations by bending the valence and conduction bands of TiO(2) and prevent the recombination of photoexcited electrons and holes. The co-doped TiO(2) compositions exhibited higher photocatalytic activity than that of pure titania and commercially available Degussa P25 under visible light by utilising the individual and synergistic contributions of Fe(3+) and Ce(4+) dopants, respectively. 相似文献
800.
Myung Han Lee Kolin C. Hribar Teresa Brugarolas Neha P. Kamat Jason A. Burdick Daeyeon Lee 《Advanced functional materials》2012,22(1):131-138
The generation of near‐infrared (NIR)‐sensitive microcapsules is presented and it is demonstrated that the release properties of these microcapsules can be tailored by controlling their morphology. A biocompatible polymer, poly(DL‐lactic‐co‐glycolic)acid (PLGA) is used to form hollow microcapsules from monodisperse water‐in‐oil‐in‐water (W/O/W) double emulsions. Both the composition of PLGA and the oil phase of W/O/W double emulsions significantly affect the morphology of the subsequently formed microcapsules. PLGA microcapsules with vastly different morphologies, from spherical to “snowman‐like” capsules, are obtained due to changes in the solvent quality of the oil phase during solvent removal. The adhesiveness of the PLGA‐laden interface plays a critical role in the formation of snowman‐like microcapsules. NIR‐sensitive PLGA microcapsules are designed to have responsive properties by incorporating Au nanorods into the microcapsule shell, which enables the triggered release of encapsulated materials. The effect of capsule morphology on the NIR responsiveness and release properties of PLGA microcapsules is demonstrated. 相似文献