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991.
992.
Nanotubes are important "building block" materials for nanotechnology, but a synthesis process for short (sub-100-nm) solid-state nanotubes with structural order and monodisperse diameter has remained elusive. To achieve this goal, it is critical to possess a definitive mechanistic framework for control over nanotube dimensions and structure. Here we employ solution-phase and solid-state characterization tools to elucidate such a mechanism, particularly that governing the formation of short ( approximately 20 nm), ordered, monodisperse (3.3 nm diameter), aluminum-germanium-hydroxide ("aluminogermanate") nanotubes in aqueous solution. Dynamic light scattering (DLS), vibrational spectroscopy, and electron microscopy show that pH-control of chemical speciation in the aluminogermanate precursor solution is important for producing nanotubes. A combination of DLS, UV-vis spectroscopy, and synthesis variations is then used to study the nanotube growth process as a function of temperature and time, revealing the initial condensation of amorphous nanoparticles of size approximately 6 nm and their transformation into ordered aluminogermanate nanotubes. The main kinetic trends in the experimental data can be well reproduced by a two-step mathematical model. From these investigations, the central phenomena underlying the mechanism are enumerated as: (1) the generation (via pH control) of a precursor solution containing aluminate and germanate precursors chemically bonded to each other, (2) the formation of amorphous nanoscale ( approximately 6 nm) condensates via temperature control, and (3) the self-assembly of short nanotubes from the amorphous nanoscale condensates. This mechanism provides a model for controlled low-temperature (<373 K) assembly of short, monodisperse, structurally ordered nanotube objects. 相似文献
993.
Venkatesh G Ramanathan S Nair NK Mansor SM Sattar MA Khan MA Navaratnam V 《Biomedical chromatography : BMC》2007,21(5):484-490
A simple and sensitive RP-HPLC-UV method was developed and validated for simultaneous determination of atenolol and propranolol and subsequently applied to investigate the effect of dimethyl sulfoxide in rat in situ intestinal permeability studies. Atenolol (400 microm) and propranolol (100 microm) were perfused in the small intestine of anaesthetized (pentobarbitone sodium 60 mg/kg, i.p.) male Sprague-Dawley rats either in the presence (1, 3 and 5%) or in the absence of dimethyl sulfoxide. There was no significant alteration (p > 0.05) in the permeability of atenolol and propranolol, which indicated there was no effect of various concentrations of dimethyl sulfoxide (1-5%) on the membrane integrity of the rat intestinal tissues. The analytical method was validated on a C(4) column with a mobile phase comprising ammonium acetate buffer (pH 3.5, 0.02 m) and acetonitrile in the ratio of 30:70 (v/v) at a flow rate of 1.0 mL/min. The validated method was found to be accurate and precise and stability studies were carried out at different storage conditions and both analytes were found to be stable. These findings are applicable for determining the absorbability of water-insoluble drugs and new chemical entities for the purpose of classifying them in the biopharmaceutical classification system. 相似文献
994.
The onset of steady, cellular convection in a horizontal fluid layer heated from below is considered taking into account the possibility of radiative heat transfer in addition to conduction and convection. The radiation is found to have a stabilizing effect even in the presence of surface tension. The effect of surface viscosity and surface deflexion are also discussed. The coupling between the surface tension and buoyancy becomes weaker as the radiative heat transfer rate is increased. 相似文献
995.
Direct determination of curvatures of bent plates using a double-glass-plate shearing interferometer
A single-exposure reflective moiré technique for the direct recording of curvature contours of laterally loaded plates is
proposed. The specular reflection of a coherent, collimated beam of light by the loaded specimen is collected by a field lens
and focussed onto a shearing interferometer. The shearing interferometer consists of two thin, identical plane-parallel glass
plates, placed successively in the optical path near the focal plane and aligned at 45 deg to the optical axis. The two plates
shear the narrow convergent beam from the lens twice optically, producing three sets of images—superposing one over the other—at
the image plane. Curvature fringes result in the region overlapped by all three images. 相似文献
996.
In this paper, three dimensional momentum and continuity equations and three dimensional energy equations are solved simultaneously to obtain pressure, velocity and temperature field in the fluid of a hydrodynamic circular journal bearing. Solutions of these equations are obtained by using the powerful numerical technique, finite element method. For a range of values of eccentricity ratios, the static performance characteristics in terms of the load capacity, attitude angle, end leakage and the power loss are computed and the results are presented.
相似文献
Untersuchung des Strömungs- und Temperaturverhaltens eines Wellenlagers
Zusammenfassung In der Arbeit werden die dreidimensionalen Impuls-, Kontinuitäts- und Energiegleichungen gleichzeitig gelöst, um die Druck-, Geschwindigkeits- und Temperaturverteilung im Fluid eines hydrodynamischen Wellenlagers zu erhalten. Die Lösung wird mit Hilfe des wirksamen Werkzeugs der Finiten Elemente gewonnen. Für einen gewissen Bereich des Exzentrizitätsverhältnisses sind die statischen Betriebscharakteristiken als Funktion der Belastung, des Anstiegswinkels, der Leckage und des Reibungsdruckverlustes berechnet und dargestellt worden.
相似文献
997.
L. Venkatramana K. Sreenivasulu K. Sivakumar K. Dayananda Reddy 《Journal of Thermal Analysis and Calorimetry》2014,115(2):1829-1834
Densities (ρ) of pure liquids and their mixtures have been measured at 303.15 and 313.15 K and atmospheric pressure over the entire composition range for the binary mixtures of benzylalcohol with 1-propanol, 1-butanol, 1-pentanol, and 1-hexanol by using Rudolph Research Analytical digital densitometer (DDM-2911 model). Further, the ultrasonic sound velocities for the above said mixtures were also measured at 303.15 and 313.15 K. The measured density data were used to compute excess molar volumes (V E) and these were compared with the values obtained by Hwang equation. Isentropic compressibility (κ S) and excess isentropic compressibilities (κ S E ) were evaluated from experimental sound velocity and density data. Moreover, the experimental sound velocities were analyzed in terms of theoretic models namely, collision factor theory and free length theory. The experimental results were discussed in terms of intermolecular interactions between component molecules. 相似文献
998.
Kishore Kumar Nair Weqar A. Siddiqi Rajesh Kumar Ram Niwas Robin Gogoi Chitra Srivastava Madhuban Gopal 《Journal of separation science》2014,37(9-10):1126-1133
In order to identify the most suitable method for the estimation of nanosulfur for studying its residue dynamics, the present work was taken up. HPLC and GC methods were explored for its analysis. A comparative study of the existing analytical methods for the quality control of nanosulfur was undertaken. UV spectrophotometry and HPLC methods were superior with lower LOD when compared to GC–MS, which was not satisfactory due to breakage of catenated S20 into S6 and S8. The method has been validated by analyzing various nanosulfur formulations of known concentrations. The recovery of the UV and HPLC methods ranged from 80.71 to 109.51% and 82.31 to 109.84%, respectively. The LOD of UV, GC–MS, and HPLC is 4, 20, and 1 ppm, respectively. The retention time of sulfur was 13.77 (HPLC), 2.89 (ultra high performance liquid chromatography), and 12.715 + 21.524 min (GC–MS). The method was successfully utilized for estimating sulfur in natural samples such as water from a sulfur hot spring and wastewater. The method has been validated by following the method recommended by the American Society for Testing and Materials. The HPLC method emerged as the best analytical method for the estimation of elemental sulfur. 相似文献
999.
Unearthing the Mechanism of Prebiotic Nitrile Bond Reduction in Hydrogen Cyanide through a Curious Association of Two Molecular Radical Anions
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Ambar Banerjee Gaurab Ganguly Ravi Tripathi Dr. Nisanth N. Nair Dr. Ankan Paul 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(21):6348-6357
HCN is clearly associated with the prebiotic chemical evolution of life. It has been known for decades that the radiolysis of HCN solutions produces sugars, amino acids and nucleobases. Remarkably, recent experimental studies have shown that the photolytic reduction of aqueous HCN by a photoredox reagent [Cu(CN)3]2? specifically yields sugars, which are the essential building blocks of RNA. Although a mechanistic understanding of such reductions with solvated electrons is poor, the general consensus is that they involve neutral free radicals. We show herein through the use of electronic structure studies and molecular simulations that the reduction of the nitrile bond of HCN is initiated through the formation of a molecular dipole‐bound anion from the photoredox reagent. Our theoretical studies show how HCN binds to the photoexcited reagent and then extracts an electron from the reagent and is ultimately detached as a dipole‐bound anion. The dipole‐bound anionic form of [HCN]? can easily convert into a solvated valence‐bound form of [HCN]?. After the formation of solvated [HCN]?, an extraordinary chemical event ensues through a counter‐intuitive coupling of two valence‐bound anions to form a solvated molecular dianionic intermediate, [HCN]22?. Finally, a proton‐coupled electron transfer occurs within the dianionic entity to complete the reduction. This mechanistic scenario is applicable to the reduction of other prebiotic nitrile species and avoids neutral radical‐based pathways, thereby preventing the proliferation of reactive species and preserving chemical selectivity. Furthermore, we show how such similar nitrile reduction pathways operate to yield the sugar precursors. 相似文献
1000.
Vijayashree Chandrashekar Chandrika Chandrashekar Rajath Shivakumar Sourav Bhattacharya Arijit Das Bhaskar Gouda Subbaramiah Sundara Rajan 《Applied biochemistry and biotechnology》2014,173(5):1135-1144
Acrylamide finds diverse industrial applications but is considered an environmental threat because of its neurotoxic, carcinogenic, and teratogenic effects. Certain bacteria enzymatically degrade acrylamide to acrylic acid and ammonia. The present investigation was carried out to isolate and identify an acrylamide-degrading bacterium from industrial effluent. Bacterial growth and extent of acrylamide degradation in the presence of different acrylamide concentrations, nutrients, varied range of pH, and temperature were analyzed. Among the eight acrylamide-degrading isolates, isolate BAC-6 demonstrated the highest degradation, and based upon the partial 16S rDNA sequencing, it was identified as Pseudomonas aeruginosa. P. aeruginosa BAC-6 grew over a wide range of acrylamide concentrations, but the highest degradation was recorded at 500 mg/L concentration with concomitant cell growth. Among the carbon supplements, mannitol supported the highest growth and degradation. Maximum degradation was reported at neutral pH. A mesophilic temperature range (25–40 °C) facilitated conducive bacterial growth followed by degradation. The highest degradation and bacterial growth were observed at 30 and 35 °C, respectively. Thus, it could be inferred from the present investigation that cultural conditions strongly affected the degradation potential of P. aeruginosa BAC-6 and advocated the utilization of the isolate in bioremediation of sites polluted with acrylamide. 相似文献