排序方式: 共有23条查询结果,搜索用时 46 毫秒
1.
Broadly tunable phase-stable single-frequency terahertz radiation is generated with an optical heterodyne photomixer. The photomixer is excited by two near-infrared CW diode lasers that are phase locked to the stabilized optical frequency comb of a femtosecond titanium:sapphire laser. The terahertz radiation emitted by the photomixer is downconverted into RF frequencies with a waveguide harmonic mixer and measurement-limited linewidths at the Hertz level are demonstrated. 相似文献
2.
Both polymeric and fibrous drag-reducing additives can be used to suppress the torque of agitators operating in a turbulent regime. Unlike the tubular flow, the influence of the fibrous additive is stronger than that of the polymer but their combined action seems to be additive. The action of the drag-reducing additives is further enhanced by the presence of a second phase (gaseous or liquid) in the stirred tank. In aerated tanks, the torque on the shaft of the agitator is not only reduced by more than 70% but also the flooding point is shifted to higher gas rates. An application of this phenomenon to fermentation tanks and similar technologies has been suggested. 相似文献
3.
Drábik M. Gáliková L. Varshney K. G. Quraishi M. A. 《Journal of Thermal Analysis and Calorimetry》2004,76(1):91-96
The applicability of MDF synthesis procedure, the coincidence of the interfacial cross-linking and the moisture resistance
of MDF-related mixes based on two industrial Portland cements (CEM I, CEM II) and poly-P are reported. The knowledge of the
moisture resistance of synthesized material is of paramount importance; two independent experimental methods confirmed that
the moisture resistance of MDF cements based on CEM I (or CEM II) with 5% of poly-P achieves sufficient levels at 50% RH and
at ambient values of RH. The results of thermal analysis are directly related to the former knowledge on the appearance and
role of cross-links in the interfacial zone of MDF cements.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
4.
Ishtiaque Ahamad Rajendra Prasad Mumtaz Ahmad Quraishi 《Journal of Solid State Electrochemistry》2010,14(11):2095-2105
The present study examines the effect of fexofenadine, an antihistamine drug, on corrosion inhibition of mild steel in molar
hydrochloric acid solution using different techniques under the influence of various experimental conditions. Results revealed
that fexofenadine is an effective inhibitor and percent inhibition efficiency increased with its concentration; reaching a
maximum value of 97% at a concentration of 3.0 × 10−4 M. Fourier-transform infrared spectroscopy (FTIR) observations of steel surface confirmed the protective role of the studied
drug. Polarization studies showed that fexofenadine is a mixed-type inhibitor. The adsorption of the inhibitor on mild steel
surface obeyed the Langmuir adsorption isotherm with free energy of adsorption (∆G°ads) of −40 kJ mol−1. Energy gaps for the interactions between mild steel surface and fexofenadine molecule were found to be close to each other
showing that fexofenadine has the capacity to behave as both electron donor and electron acceptor. The results obtained from
the different corrosion evaluation techniques are in good agreement. 相似文献
5.
Proni G Pescitelli G Huang X Quraishi NQ Nakanishi K Berova N 《Chemical communications (Cambridge, England)》2002,(15):1590-1591
A circular dichroic (CD) excition chirality method based on host-guest chiral recognition has been developed to determine the absolute configuration of carboxylic acids with an alpha-stereogenic center; an amide C = O-->Zn coordination, identified by infrared spectroscopy and computations, is involved in this complexation. 相似文献
6.
Jan Brauer Elisabeth Quraishi Lisa Marie Kammer Prof. Till Opatz 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(72):18168-18174
A simple visible light photochemical, nickel-catalyzed synthesis of ketones from carboxylic acid-derived precursors is presented. Hantzsch ester (HE) functions as a cheap, green and strong photoreductant to facilitate radical generation and also engages in the Ni-catalytic cycle to restore the reactive species. With this dual role, HE allows for the coupling of a large variety of radicals (1°,2°, benzylic, α-oxy & α-amino) with aroyl and alkanoyl moieties, a new feature in reactions of this type. With both precursors deriving from abundant carboxylic acids, this protocol is a welcome addition to the organic chemistry toolbox. The reaction proceeds under mild conditions without the need for toxic metal reagents or bases and shows a wide scope, including pharmaceuticals and complex molecular architectures. 相似文献
7.
Ambrish Singh Ishtiaque Ahamad V. K. Singh Mumtaz Ahamed Quraishi 《Journal of Solid State Electrochemistry》2011,15(6):1087-1097
The inhibition of the corrosion of mild steel in hydrochloric acid solution by the seed extract of Karanj (Pongamia pinnata) has been studied using weight loss, electrochemical impedance spectroscopy, potentiodynamic polarization, and linear polarization
techniques. Inhibition was found to increase with increasing concentration of the extract. The effect of temperature, immersion
time, and acid concentration on the corrosion behavior of mild steel in 1 M HCl with addition of extract was also studied.
The adsorption of the extract on the mild steel surface obeyed the Langmuir adsorption isotherm. Values of inhibition efficiency
calculated from weight loss, potentiodynamic polarization, and electrochemical impedance spectroscopy are in good agreement.
Polarization curves showed that Karanj (P. pinnata) seed extract behaves as a mixed-type inhibitor in hydrochloric acid. The activation energy as well as other thermodynamic
parameters for the inhibition process was calculated. The adsorbed film on mild steel surface containing Karanj (P. pinnata) seed extract inhibitor was also measured by Fourier transform infrared spectroscopy. The results obtained showed that the
seed extract of Karanj (P. pinnata) could serve as an effective inhibitor of the corrosion of mild steel in hydrochloric acid media. 相似文献
8.
Sowmya Ramkumar D. Nalini Mumtaz A. Quraishi Eno E. Ebenso Chandrabhan Verma 《Journal of heterocyclic chemistry》2020,57(1):103-119
In the present study, four imidazoline (IDZ) and four isoxazolines (ISO) heterocyclics differing in the nature of methoxy (-OCH3) and aromatic (phenyl and naphthyl) moieties are synthesized, characterized and evaluated as corrosion inhibitors for mild steel in acidic solution of 1 M HCl. Results showed that imidazoline based heterocyclic compounds are better corrosion inhibitors than isoxazoline based heterocyclics and both classes of compounds showed inhibition efficiency of more than 85% at 20 mgL−1 concentration. Results further showed that inhibitors containing methoxy, phenyl, and naphthyl moieties showed higher protection efficiency as compared to the inhibitors without these moieties. PDP Study revealed that investigated IDZs and ISOs acted as mixed type inhibitors and their adsorption on the metallic surface followed the Langmuir adsorption isotherm model. All the experimental results were corroborated by density function theory (DFT) based quantum chemical calculations. Numerous DFT based indices calculated for neutral as well as protonated forms of the IDZs and ISOs in order to get better insight about metal-IDZs/ISOs interactions. Outcomes of the DFT analysis showed that protonated (cationic) form of the all the inhibitors are more strongly adsorbed on the metallic surface as compared to their neutral form. 相似文献
9.
Ambrish Singh J. N. Avyaya Eno. E. Ebenso M. A. Quraishi 《Research on Chemical Intermediates》2013,39(2):537-551
The inhibition ability of Dapsone’s Schiff’s base with salicylaldehyde (1:2) for mild steel corrosion in 1 M HCl solution at 308 K was studied by means of potentiodynamic polarization, electrochemical impedance spectroscopy techniques, and gravimetric analysis. Results showed that Dapsone salicylaldehyde performed well as a good inhibitor for mild steel in 1 M HCl solution with maximum inhibition efficiency of 95 % at 500 ppm. The adsorption isotherm of the inhibitor followed the Langmuir adsorption. The value of free energy of adsorption showed that it is a spontaneous process and followed typical physical adsorption. 相似文献
10.