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931.
Thermal instability in an electrically conducting two component Boussinesq fluid-saturated-porous medium has been investigated, in the presence of Soret coefficient. The porous medium is confined between two horizontal surfaces, and subjected to a constant vertical magnetic field. Flow in the porous medium is characterized by generalized Darcy model, which includes the time derivative term. Performing linear and non-linear stability analysis, the effect of magnetic field on the stability of flow through porous medium has been investigated. The normal mode method is used in linear stability analysis, while a weak non-linear analysis based on a minimal representation of double Fourier series method is used in non-linear analysis. The critical Rayleigh number, wave number for stationary and oscillatory modes, and frequency of oscillations are obtained analytically using linear theory. Effects of various parameters on stationary, oscillatory and finite amplitude convection, rate of heat and mass transfer have been obtained analytically and presented graphically. 相似文献
932.
Thalidomide treats multiple myeloma and protracts life-span of patient, but its bioavailability is limited as it is poorly water soluble. Thalidomide nano-flakes are produced to improve the drug dissolution rate. Two nanoflake production methods are utilized for a comparative study: a supercritical antisolvent (SAS) method and a supercritical antisolvent with enhanced mass transfer (SAS-EM). SAS-EM utilizes ultrasonication to improve dispersion upon injection within the supercritical carbon dioxide. Comparative study of SAS and SAS-EM thalidomide confirmed that the application of ultrasonication improved the micro/nano particles produced by SAS. The effects of ultrasound power on the formation of thalidomide particles are examined. The particle size and morphology were characterized by SEM. The thalidomide nano-flakes produced by SAS-EM were smaller than the particles produced by SAS. Dissolution rates of the produced particles, evaluated by HPLC, demonstrated an increase in the thalidomide dissolution rate for the SAS-EM produced particles. The polymorphs and crystallinity of thalidomide particles (flakes) were observed by FTIR and XRD. In this research, the supercritical processing significantly modified the crystal formation of thalidomide from an original state of a β-polymorph to the amorphous state α-polymorph after supercritical processing. 相似文献
933.
934.
S. K. Maurya Y. K. Gupta Saibal Ray Debabrata Deb 《The European Physical Journal C - Particles and Fields》2017,77(1):45
In the present study we search for a new stellar model with spherically symmetric matter and a charged distribution in a general relativistic framework. The model represents a compact star of embedding class 1. The solutions obtained here are general in nature, having the following two features: first of all, the metric becomes flat and also the expressions for the pressure, energy density, and electric charge become zero in all the cases if we consider the constant \(A=0\), which shows that our solutions represent the so-called ‘electromagnetic mass model’ [17], and, secondly, the metric function \(\nu (r)\), for the limit n tending to infinity, converts to \(\nu (r)=C{r}^{2}+ ln~B\), which is the same as considered by Maurya et al. [11]. We have investigated several physical aspects of the model and find that all the features are acceptable within the requirements of contemporary theoretical studies and observational evidence. 相似文献
935.
In this paper, we investigate the time-varying interconnectedness of international Real Estate Investment Trusts (REITs) markets using daily REIT prices in twelve major REIT countries since the Global Financial Crisis. We construct dynamic total, net total and net pairwise return and volatility connectedness measures to better understand systemic risk and the transmission of shocks across REIT markets. Our findings show that that REIT market interdependence is dynamic and increases significantly during times of heightened uncertainty, including the COVID-19 pandemic. We also find that the US REIT market along with major European REITs are generally sources of shocks to Asian-Pacific REIT markets. Furthermore, US REITs appear to dominate European REITs. These findings highlight that portfolio diversification opportunities decline during times of market uncertainty. 相似文献
936.
N. Sinha Sahas B. K. Singh K. Kumar N. Singh M. K. Gupta G. C. Budakoti B. Kumar 《Crystal Research and Technology》2009,44(2):167-172
Single crystals of L‐histidine tetrafluoroborate (C6H10N3O2BF4 , L‐HFB) were grown by solution growth method using two different temperature profiles: conventional, in which the growth temperature was kept constant at 30°C and rapid, in which it was increased in steps of 1 K per day while keeping the other growth conditions same. Crystals grew in nearly 30 and 10 days in the two methods, respectively. The crystals were transparent and showing its characteristic morphology. Both types of crystals were characterized by XRD for their structural comparison. Surface morphology and growth features of the crystals were studied by SEM. Features of two dimensional layer growth steps, rectangular etch pits, slip lines and bands, etc. were observed. The presence of various functional groups and their bonding were studied by FTIR in the range 4000‐400 cm‐1. Thermal stability of the crystals was determined by thermo‐gravimetric and differential thermal analysis. The generation of green light due to second harmonic generation for fundamental λ =1064 nm has been confirmed in both cases. Dielectric constant measurement was carried out in the range 20Hz‐2MHz. In the UV‐Vis studies, high transmittance and a shorter ‘lower cut off' value (232 nm) were observed. The effect of rapid growth on the structural, morphological and optical properties of the crystals were studied and compared to those of crystals grown in conventional way. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
937.
Varsha R. Mehto Akanksha Mehto Dhirendra Kumar Gupta Rajendra Kumar Pandey 《中国化学会会志》2016,63(11):935-946
This paper presents our results on the successful fabrication of HCl‐doped polyaniline (PANI)/ZnO nanocomposites via an electrochemical synthesis route. Different weight percents of ZnO nanoparticles were uniformly dispersed in the PANI matrix. The interaction between the dispersed ZnO nanoparticle and PANI was studied using X‐ray diffraction, ultraviolet–visible absorption spectroscopy, photoluminescence (PL) spectroscopy, X‐ray photoelectron spectroscopy, atomic force microscopy, thermogravimetry, and transmission electron microscopy. It is shown that the doping state of the PANI/ZnO nanocomposite is highly improved as compared to that of PANI. The dispersed PANI/ZnO nanocomposites exhibit enhanced PL behavior and thermal stability. 相似文献
938.
In this article, we have reported electron impact total ionisation cross sections for the bio-molecules pyridine, pyrimidine, n-propylamine, urea, formamide and N-methylformamide from ionisation threshold to 2000 eV. The present calculations are based on the spherical complex optical potential formalism and complex scattering potential ionisation contribution method. The results obtained for pyridine and pyrimidine are compared with available theoretical and experimental results and are found to be in excellent agreement with existing data. The ionisation cross sections for other molecules are reported for the first time. An interesting relation between the peak of inelastic and ionisation cross sections with target parameters is also reported. It was found that both the cross sections at their maximum depend linearly with these parameters, confirming the consistency of the values reported here. 相似文献
939.
Andriy Fedorov Jacob Fluckiger Gregory D. Ayers Xia Li Sandeep N. Gupta Clare Tempany Robert Mulkern Thomas E. Yankeelov Fiona M. Fennessy 《Magnetic resonance imaging》2014
Multi-parametric Magnetic Resonance Imaging, and specifically Dynamic Contrast Enhanced (DCE) MRI, play increasingly important roles in detection and staging of prostate cancer (PCa). One of the actively investigated approaches to DCE MRI analysis involves pharmacokinetic (PK) modeling to extract quantitative parameters that may be related to microvascular properties of the tissue. It is well-known that the prescribed arterial blood plasma concentration (or Arterial Input Function, AIF) input can have significant effects on the parameters estimated by PK modeling. The purpose of our study was to investigate such effects in DCE MRI data acquired in a typical clinical PCa setting. First, we investigated how the choice of a semi-automated or fully automated image-based individualized AIF (iAIF) estimation method affects the PK parameter values; and second, we examined the use of method-specific averaged AIF (cohort-based, or cAIF) as a means to attenuate the differences between the two AIF estimation methods. 相似文献
940.
Anamika Bajpai Kashi Nath Prasad Priyanka Mishra Rakesh Kumar Gupta Aloukick K. Singh Bal Krishna Ojha 《Magnetic resonance imaging》2014