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31.
In this paper the stability of motion of a symmetric satellite-gyrostat, with Visco-elastic square plate attached to it, around the center of mass in a circular orbit under a central gravitational field is studied. The gyrostat has a rotor oriented inside it such that the rotor becomes dynamically as well as statically stable with respect to the whole system. A study of the stability of this system has been done by using the method of separation of motion and averaging. Furthermore, we have solved the problem where there is no rotor. 相似文献
32.
Nazar Mohammad Ranjha Ikram Ullah Khan Shahzad Naseem 《Journal of Sol-Gel Science and Technology》2009,50(3):281-289
Flurbiprofen loaded PCL/PVP blend microspheres were prepared by o/w solvent evaporation method using various concentrations
of gelatin as emulsifying agent. Microsphere recovery decreased with a decrease in the concentration of the emulsifier in
the dispersion. Encapsulation efficiency and drug loading of microspheres increased with decrease in concentration of emulsifying
agent. Hydration rate, encapsulation efficiency and drug loading of microspheres increased with increase in concentration
of PVP. Rheological properties showed free flowing nature of microspheres. SEM (Scanning electron microscope) revealed microspheres
were discrete, spherical and became porous with decrease in concentration of emulsifying agent but smooth with higher concentration
of emulsifying agent. FTIR (Fourier transform infrared spectroscopy) spectra of pure and encapsulated flurbiprofen in all
formulation showed no significant difference in characteristic peaks, suggesting stability of flurbiprofen during encapsulation
process. X-RD (X-ray powder diffractometry) of pure flurbiprofen shows sharp peaks, which decreases on encapsulation, indicating
dispersion at molecular level and hence decrease in the crystallinity of drug in microspheres. Microspheres showed an enteric
nature at pH 1.2 and a sustained release pattern at pH 6.8. Rapid drug release was observed in microspheres with higher concentration
of PVP (polyvinylpyrrolidone), PVP acts as channeling agent. Formulation with low concentration of emulsifying agent also
showed a fast release due to porous structure. Drug release kinetics followed zero order at pH 1.2 while at pH 6.8 Higuchi
model was best fitted and was found non fickian. 相似文献
33.
Suzuki-Miyaura cross-coupling reactions of tetrabromo-p-benzoquinone provide a convenient approach to tetraaryl-p-benzoquinones. 相似文献
34.
Herein, we propose a scheme for the realization of two-dimensional atomic localization in aλ-type three-level atomic medium such that the atom interacts with the two orthogonal standing-wave fields and a probe field. Because of the spatially dependent atom-field interaction, the information about the position of the atom can be obtained by monitoring the probe transmission spectra of the weak probe field for the first time. A single and double sharp localized peaks are observed in the one-wavelength domain. We have theoretically archived high-resolution and high-precision atomic localization within a region smaller thanλ/25×λ/25. The results may have potential applications in the field of nano-lithography and advance laser cooling technology. 相似文献
35.
We have theoretically investigated two-dimensional atom localization using the absorption spectra of birefringence beams of light in a single wavelength domain.The atom localization is controlled and modified through tunneling effect in a conductive chiral atomic medium with absorption spectra of birefringent beams.The significant localization peaks are investigated in the left and right circularly polarized beam.Single and double localized peaks are observed in different quadrants with minimum uncertainty and significant probability.The localized probability is modified by controlling birefringence and tunneling conditions.These results may be useful for the capability of optical microscopy and atom imaging. 相似文献
36.
The kinetic theory of plasma has been employed to compute the test-charge potential distributions accounting for quantization effects in magnetized electron-positron-ion (EPI) plasmas. In this regard, the degenerate positrons and electrons are assumed to follow the Fermi-Dirac distribution, while inertial ions are modelled by Maxwellian velocity distribution. By solving the Fourier-transformed Vlasov–Poisson equations, a modified dielectric function and electrostatic potential is obtained. By imposing various constraints on the test-charge speed, the potential profile has been analysed in terms of Debye–Hückel (DH), far-field (FF), and wake-field (WF) potentials. It has been found that the amplitude of DH and FF potentials increases by the inclusion of quantization effects, and it becomes the opposite for the WF potential profile. Furthermore, the variation of positron concentration significantly affects the DH, FF, and WF potentials. The present findings are important to understand the shielding phenomenon in degenerate multi-species plasmas. 相似文献
37.
Rasheed AhmadKhera Rasheed Ahmad Ihsan Ullah Obaid‐Ur‐Rahman Abid Olumide Fatunsin Muhammad Sher Alexander Villinger Peter Langer 《Helvetica chimica acta》2010,93(9):1705-1715
2‐Aryl‐2,3‐dihydro‐4H‐pyran‐4‐ones were prepared in one step by cyclocondensation of 1,3‐diketone dianions with aldehydes. The use of HCl (10%) for the aqueous workup proved to be very important to avoid elimination reactions of the 5‐aryl‐5‐hydroxy 1,3‐diones formed as intermediates. The TiCl4‐mediated cyclization of a 2‐aryl‐2,3‐dihydro‐4H‐pyran‐4‐one with 1,3‐silyloxybuta‐1,3‐diene resulted in cleavage of the pyranone moiety and formation of a highly functionalized benzene derivative. 相似文献
38.
Tris(2‐aminoethyl)amine‐based ferrocene‐terminated dendrimers as burning rate catalysts for ammonium perchlorate‐based propellant decomposition 下载免费PDF全文
Zain‐ul‐Abdin Li Wang Haojie Yu Rizwan Ullah Khan Raja Summe Ullah Muhammad Haroon 《应用有机金属化学》2018,32(4)
Ferrocene‐based derivatives show potential application as burning rate catalysts (BRCs) for solid composite propellants. However, migration problems of simple ferrocene‐based derivatives limit their application as BRCs in solid composite propellants. To overcome the migration problems of ferrocene‐based BRCs and to enhance the burning rate of ammonium perchlorate (AP)‐based propellants, zero‐ to second‐generation tris(2‐aminoethyl)amine‐based ferrocene‐terminated dendrimers (G0, G1 and G2) were synthesized. The structures of G0, G1 and G2 were confirmed using 1H NMR, Fourier transform infrared and UV–visible spectroscopies. The electrochemical behavior of G0, G1 and G2 was investigated using cyclic voltammetry. It was found that G0, G1 and G2 showed redox behavior due to the presence of ferrocene and this redox behavior was diffusion controlled over the investigated scan range. The burning rate catalytic effect of G0, G1 and G2 on thermal decomposition of AP was investigated using thermogravimetry and differential thermogravimetry. G0, G1 and G2 showed good catalytic effect on the thermal decomposition of AP. Anti‐migration studies showed that migration of G0, G1 and G2 was much slower than that of 2,2‐bis(ethylferrocenyl)propane (catocene) and ferrocene. 相似文献
39.
Islam Ullah Khan Tehseen Aman Muhammad Asif Iqbal Asrar Ahmad Kazi 《Mikrochimica acta》2000,134(1-2):27-31
Fluoxetine hydrochloride reacts with benzoyl peroxide and potassium iodide, after heating for 1 min at 30 °C, to give a blue
colour having maximum absorbance at 570 nm. The reaction is selective for fluoxetine with 0.01 mg/mL as visual limit of quantitation
and provides a basis for a new spectrophotometric determination. The colour reaction obeys Beer’s law from 0.1 mg/10 mL to
2.0 mg/10 mL of fluoxetine and the relative standard deviation is 0.68%. The qualitative assessment of tolerable amounts of
other drugs is also studied.
Received September 21, 1998. Revision September 10, 1999. 相似文献
40.
Nazakat Ullah 《Pramana》1993,41(2):171-174
A formulation is developed to derive exact analytic expressions for electron-electron correlation and density of electrons
in momentum space using hydrogenic wave functions. It is shown that for large atoms the expression for density of electrons
has a simple form. 相似文献