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191.
The crystallization behaviour of Fe 70.8 Nb 3.7 Cu 1 Al 2.7 Mn 0.7 Si 13.5 B 7.6 alloy prepared in the form of amorphous ribbons by melt-spinning technique was studied using differential scanning calorimetry and the temperature variation in resistivity. An X-ray diffaction and transmission electron microscopy study showed the formation of f-Fe(Si, Al) and/or Fe 3 (Si, Al) nanoparticles after the first stage of crystallization. The activation energy for this nanophase formation was 68 kcal mol m1 . The brittleness of the alloy increased with the formation of nanoparticles after heat treatment. Superior soft magnetic properties were achieved when the material was heat treated at 790 K for 15 min. The particle size at the optimum heat treatment condition for superior soft magnetic properties was found to be 6.0 -0.5 nm which was less compared than for the Fe-Nb-Cu-Si-B system. The observed coercivity value at the optimum heat treatment condition was found to be 0.32 A m m1 (approximately 4 mOe). The presence of Al in the alloy reduced the particle size and the magnetic anisotropy energy of the system, which resulted in superior soft magnetic properties of the heat-treated materials. 相似文献
192.
Tarak Nath Burai Debashis Panda E Siva Subramaniam Iyer Anindya Datta 《Journal of luminescence》2012,132(11):2929-2936
The rate and extent of photoinduced electron transfer change significantly as a result of confinement in nanovolumes. Study of such processes is an active area of research in physical chemistry. The effect is most interesting when the molecules that participate in PET are charged. In the present article, the modulation of PET has been studied for two anionic fluorophores: Lucifer Yellow CH and chlorin p6 with Methylviologen dication. PET, manifested in the quenching of fluorescence of the fluorophores, has been modulated by incorporating the molecules in organized assemblies like micelles, reverse micelles and supramolecular hosts. The dynamics of the process has been monitored in the femtosecond to nanosecond timescale. The modulation of the electron transfer has been found to be occurring mainly due to the disruption of contact ion pairs formed between the fluorophores and the quencher. 相似文献
193.
194.
Band‐selective excited ultrahigh resolution PSYCHE‐TOCSY: fast screening of organic molecules and complex mixtures
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Jagadeesh Bharatam 《Magnetic resonance in chemistry : MRC》2016,54(4):308-314
Precise assignments of 1H atomic sites and establishment of their through‐bond COSY or TOCSY connectivity are crucial for molecular structural characterization by using 1H NMR spectroscopy. However, this exercise is often hampered by signal overlap, primarily because of 1H–1H scalar coupling multiplets, even at typical high magnetic fields. The recent developments in homodecoupling strategies for effectively suppressing the coupling multiplets into nice singlets (pure‐shift), particularly, Morris's advanced broadband pure‐shift yielded by chirp excitation (PSYCHE) decoupling and ultrahigh resolution PSYCHE‐TOCSY schemes, have shown new possibilities for unambiguous structural elucidation of complex organic molecules. The superior broadband PSYCHE‐TOCSY exhibits enhanced performance over the earlier TOCSY methods, which however warrants prolonged experimental times due to the requirement of large number of dwell increments along the indirect dimension. Herein, we present fast and band‐selective analog of the broadband PSYCHE‐TOCSY, which is useful for analyzing complex organic molecules that exhibit characteristic yet crowded spectral regions. The simple pulse scheme relies on band‐selective excitation (BSE) followed by PSYCHE homodecoupling in the indirect dimension. The BSE‐PSYCHE‐TOCSY has been exemplified for Estradiol and a complex carbohydrate mixture comprised of six constituents of closely comparable molecular weights. The experimental times are greatly reduced viz., ~20 fold for Estradiol and ~10 fold for carbohydrate mixture, with respect to the broadband PSYCHE‐TOCSY. Furthermore, unlike the earlier homonuclear band‐selective decoupling, the BSE‐PSYCHE‐decoupling provides fully decoupled pure‐shift spectra for all the individual chemical sites within the excited band. The BSE‐PSYCHE‐TOCSY is expected to have significant potential for quick screening of complex organic molecules and mixtures at ultrahigh resolution. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
195.
Reactivity and Operational Stability of N‐Tailed TAMLs through Kinetic Studies of the Catalyzed Oxidation of Orange II by H2O2: Synthesis and X‐ray Structure of an N‐Phenyl TAML
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Genoa R. Warner Matthew R. Mills Clarissa Enslin Shantanu Pattanayak Chakadola Panda Tamas Kumar Panda Prof. Sayam Sen Gupta Prof. Alexander D. Ryabov Prof. Terrence J. Collins 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(16):6226-6233
The catalytic activity of the N‐tailed (“biuret”) TAML (tetraamido macrocyclic ligand) activators [Fe{4‐XC6H3‐1,2‐( N COCMe2 N CO)2NR}Cl]2? ( 3 ; N atoms in boldface are coordinated to the central iron atom; the same nomenclature is used in for compounds 1 and 2 below), [X, R=H, Me ( a ); NO2, Me ( b ); H, Ph ( c )] in the oxidative bleaching of Orange II dye by H2O2 in aqueous solution is mechanistically compared with the previously investigated activator [Fe{4‐XC6H3‐1,2‐( N COCMe2 N CO)2CMe2}OH2]? ( 1 ) and the more aggressive analogue [Fe(Me2C{CON(1,2‐C6H3‐4‐X) N CO}2)OH2]? ( 2 ). Catalysis by 3 of the reaction between H2O2 and Orange II (S) occurs according to the rate law found generally for TAML activators (v=kIkII[FeIII][S][H2O2]/(kI[H2O2]+kII[S]) and the rate constants kI and kII at pH 7 both decrease within the series 3 b > 3 a > 3 c . The pH dependency of kI and kII was investigated for 3 a . As with all TAML activators studied to‐date, bell‐shaped profiles were found for both rate constants. For kI, the maximal activity was found at pH 10.7 marking it as having similar reactivity to 1 a . For kII, the broad bell pH profile exhibits a maximum at pH about 10.5. The condition kI?kII holds across the entire pH range studied. Activator 3 b exhibits pronounced activity in neutral to slightly basic aqueous solutions making it worthy of consideration on a technical performance basis for water treatment. The rate constants ki for suicidal inactivation of the active forms of complexes 3 a – c were calculated using the general formula ln([S0]/[S∞])=(kII/ki)[FeIII]; here [FeIII], [S0], and [S∞] are the total catalyst concentration and substrate concentration at time zero and infinity, respectively. The synthesis and X‐ray characterization of 3 c are also described. 相似文献
196.
Frontispiece: Rhodium Enalcarbenoids: Direct Synthesis of Indoles by Rhodium(II)‐Catalyzed [4+2] Benzannulation of Pyrroles
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197.
Lower bounds on the scalar dissipation rate in rectilinear flows are found for three sets of constraints. The bounding dissipation rates provide upper bound estimates of the scalar concentration variance. One of the lower bounds on the dissipation rate is close to the dissipation rate assessed from detailed numerical simulation. This proximity enables a simplified model of concentration variance. For a pulse input of solute, the predictions of concentration variance by the simplified model are in agreement with the results of detailed simulation. The large-time bimodality of the concentration variance and its rate of decay observed in the detailed numerical simulations is predicted by the simplified model. 相似文献
198.
Nonlinear dynamics of a pipe conveying pulsating fluid with parametric and internal resonances 总被引:1,自引:0,他引:1
In this paper, the nonlinear planar vibration of a pipe conveying pulsatile fluid subjected to principal parametric resonance
in the presence of internal resonance is investigated. The pipe is hinged to two immovable supports at both ends and conveys
fluid at a velocity with a harmonically varying component over a constant mean velocity. The geometric cubic nonlinearity
in the equation of motion is due to stretching effect of the pipe. The natural frequency of the second mode is approximately
three times the natural frequency of the first mode for a range of mean flow velocity, resulting in a three-to-one internal
resonance. The analysis is done using the method of multiple scales (MMS) by directly attacking the governing nonlinear integral-partial-differential
equations and the associated boundary conditions. The resulting set of first-order ordinary differential equations governing
the modulation of amplitude and phase is analyzed numerically for principal parametric resonance of first mode. Stability,
bifurcation, and response behavior of the pipe are investigated. The results show new zones of instability due to the presence
of internal resonance. A wide array of dynamical behavior is observed, illustrating the influence of internal resonance. 相似文献
199.
R. K. Nath S. Dasgupta S. Ghosh A. Mitra A. K. Panda 《Journal of Dispersion Science and Technology》2013,34(11):1447-1455
The binding behavior of acidic capsular polysaccharide (SPS), isolated from Klebsiella serotype K43, with oppositely charged dyes and surfactants have been studied by way of absorbance and emission spectroscopic measurements. Each repeating unit of the SPS consists of three D-mannose, one D-galactose, and one D-glucuronic acid residue. The anionic polysaccharide exhibited chromotropic character and induced strong metachromasy in the cationic dye, pinacyanol chloride (PCYN) through the formation of a 1:1 stoichiometric complex. Evaluation of thermodynamic parameters, viz., changes in free energy (ΔG), enthalpy (ΔH), and entropy (ΔS), for the formation of dye-polymer complex and studies on the effect of different cosolvents were also evaluated to shed light on the binding nature as well as the extent of stability of the dye-polymer complex. Fluorescence of the cationic dye acridine orange (AO) was quenched with the progressive addition of SPS, which was found to be of Stern-Volmer type. Cationic surfactants in their pure form as well as in the mixed state with nonionic surfactant (Tween-20), replaced the dye bound to the polymer matrices; thus the original band intensities of the dyes could be reverted. Such studies revealed the involvement of both electrostatic as well as hydrophobic interactions between the dye-polymer as well as surfactant-polymer aggregates. 相似文献
200.
Siva S. Panda 《合成通讯》2013,43(5):729-735
A simple and efficient procedure for the synthesis of 2-arylbenzimidazoles through a one-pot condensation of o-phenylenediamines with aryl aldehydes in water is described. Short reaction time, large-scale synthesis, easy and quick isolation of the product, and excellent yield are the main advantages of this procedure. 相似文献