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排序方式: 共有701条查询结果,搜索用时 15 毫秒
51.
The present study reports the preparation and application of a novel biopolymer-based composite hydrogel (BCH) for removal of synthetic dye rhodamine 6G (Rh6G). BCH was prepared from biopolymer chitosan and acrylic acid monomer, in the presence of initiator (K2S2O8) and cross-linker thiourea using microwave irradiation. Synthesized chitosan-based composite hydrogel was characterized by using analytical techniques including Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), derivative thermogravimetric analysis (DTA) and differential thermal analysis (DTG). The stability of the adsorbent was demonstrated from its water uptake capacity. The dynamics of water sorption study showed the Fickian behavior. The investigations were continued to assess the adsorption potential of BCH for removal of Rh6G from aqueous solution. The effect of process parameters affecting the adsorption of rhodamine 6G (Rh6G), such as adsorbent dose, initial concentration of pollutant, contact time and pH of the solution was evaluated. Removal efficiency of chitosan-based composite hydrogel (BCH) was found to be 87.31% at pH 7 for BCH dose of 1 g/L after 8 h. The obtained data were fitted to adsorption isotherms and kinetics models. The adsorption equilibrium isotherm and kinetics studies indicated that the pseudo-second-order model and the Freundlich model well described the adsorption equilibrium of Rh6G on BCH. 相似文献
52.
S. Neupane G. Kaganas R. Valenzuela L. Kumari X. W. Wang W. Z. Li 《Journal of Materials Science》2011,46(14):4803-4811
We report the synthesis of ruthenium dioxide (RuO2) nanostructures by thermal evaporation of RuO2 powder. RuO2 nanostructures of different shapes were synthesized at various concentration, flow rate, and pressure of oxygen. At a constant
pressure of 3 torr of flowing oxygen, polygonal prism-like RuO2 nanorods with flat tips were grown at an O2 flow rate of 100 sccm; club-shaped nanorods with obelisk tip were formed at 300 and 600 sccm, and hollow rods with square
tip were formed at 1800 sccm. A mixture of O2 and Ar at a total flow rate of 600 sccm led to the formation of short club-shaped nanorods indicating the suppression effect
of Ar on the growth of nanorods. The pressure also had a significant effect on the formation of RuO2 nanostructures, at a fixed flow rate of 600 sccm of O2, a pressure of 3 torr resulted in the growth of club-shaped RuO2 nanorods, while high pressures of 380 and 760 torr resulted in the formation of both linear club-shaped and pine tree-like
hierarchical RuO2 nanorods. X-ray diffraction and transmission electron microscopy analysis indicated the formation of tetragonal phase of
RuO2 with high crystallinity. A density functional calculation on RuO2, RuO3, and RuO4 was performed to help to explain the experimental results. 相似文献
53.
Siba Prasada Panigrahi Sasmita Kumari Padhy Santanu Kumar Nayak 《International Journal of Adaptive Control and Signal Processing》2010,24(1):41-50
This paper addresses the exhaustive computational complexity of the maximum‐a‐posteriori equalizer and the inefficiency of the conventional decision feedback equalizer (DFE) algorithm in iterative equalization, especially when the higher‐level modulation is used with severely distorted Inter Symbol Interference channels. The new method proposed here improves the bit error rate (BER) performance by computing the extra metric rn+1 using the feedback symbols from previous iteration and combining it with a priori information of the symbols. After each iteration, the hard‐detected symbols are saved in the memory as a priori data for next iteration. We verified the proposed algorithm for Binary Phase Shift Keying and 8‐phase shift keying modulation. The promising simulation results show that the BER performance given by the proposed low complexity DFE algorithm improved dramatically throughout the iterations when the conventional DFE has only insignificant improvement in the process of iterative equalization. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
54.
Conoidal shells are very popular roofing units owing to their aesthetic elegance and stiffness. Many parts of the globe, which were earlier assumed to be seismologically stable, are now being considered as earthquake prone. Hence the necessity to build light structures using composites has become very important. In this paper an eight-noded isoparametric shell element is applied for analyzing the bending behavior of delaminated composite conoidal shells under a uniformly distributed load with different practical boundary conditions. To ensure compatibility of deformation and equilibrium of forces and moments at the delamination crack front, a multipoint constraint algorithm is incorporated, which leads to an unsymmetrical stiffness matrix. This formulation is validated through the solution of benchmark problems. Lamination, curvature, and extent of delamination area are varied to compare the performances of delaminated conoidal shells against those with no damage. The results are carefully observed, and a set of conclusions is presented at the end of the paper. 相似文献
55.
Polycrystalline sample of (Na0.5Bi0.5)ZrO3 was prepared using a high-temperature solid-state reaction technique. XRD analysis indicated the formation of a single-phase
orthorhombic structure. Dielectric study revealed the diffuse phase transition at 425 °C. AC impedance plots were used as
tools to analyse the electrical behaviour of the sample as a function of frequency at different temperatures. The ac impedance
studies revealed the presence of grain boundary effect at and above 350 °C. Complex impedance analysis indicated non-Debye
type dielectric relaxation and negative temperature coefficient of resistance (NTCR) character of (Na0.5Bi0.5)ZrO3. AC conductivity data were used to evaluate the density of states at Fermi level and activation energy of the compound. DC
electrical and thermal conductivities of grain and grain boundary have been assessed. 相似文献
56.
Sharma H. Kumari Kiran Singh L. S. Choudhary R. N. P. 《Bulletin of Materials Science》2002,25(2):133-136
The polycrystalline samples of Ca4Bi2Ti4Nb6O30 (herein designated CBTN) were synthesized by the conventional ceramic method. Preliminary X-ray structural study of the compound
showed the formation of a single phase solid solution having orthorhombic structure in the paraelectric phase. Measurements
of the dielectric constant (ε) and dielectric loss (tan δ) as a function of temperature (−180–200°C) at 1 kHz and 10 kHz and
also as a function of frequency (102 Hz to 104 Hz) at five different temperatures [−180°C, −40°C, − 10°C 26°C (room temperature) and 75°C] have shown a dielectric anomaly
and a phase transition at − 13 ±1°C in CBTN. 相似文献
57.
We consider a RAKE receiver for coherent binary orthogonal signaling employing predetection maximal-ratio combining (MRC), in which the tap weights are estimated by adding two matched filtered outputs using the two reference signals. The weight estimation errors here are not independent of the additive channel noise, and therefore do not fit into the Gaussian error model for MRC. Instead of analyzing the distribution of the weight estimation errors, we find the characteristic function of the decision variable, and from it we obtain a formula for the symbol error probability 相似文献
58.
Consider a Rake receiver for coherent binary antipodal signaling with: 1) a delayed received signal configuration; 2) weight estimation by matched filtering using the reference signal along with the decisions of the previous M symbol intervals; and 3) predetection maximal-ratio combining (MRC). The weight estimation errors here are not independent of the additive noise, and do not fit into the Gaussian weighting error model for MRC. Here we analyze the error performance of the receiver by obtaining the conditional symbol error probability, conditioned on past decisions, from the characteristic function of the decision variable, and getting the unconditional error probability (UEP) for a block of M consecutive symbols using a Markov model of the decision process. The channel is Rayleigh fading with independent and identically distributed branch gains. Results show that the error performance of the Gaussian distributed weighting error model is a bound for that of multiple symbol weight estimation by matched filtering, and the steady state UEP decreases with increase of M, but the amount of decrease reduces as M increases. 相似文献
59.
Fe3BO6 can be an ideal compound for devising functional magnetic and dielectric properties in a single material for multiple applications such as electrodes, gas sensors, or medical tools. Useful to tailor such properties, here we report on a self-controlled Fe3BO6 growth in a specific shape of nanorods from a supercooled liquid precursor (an inorganic polymeric liquid or glass) of an initial composition (100 − x)B2O3 − xFe2O3, x = 40–50 mol%. B2O3 as a strong glass former co-bridges the Fe3+ ions in oxygen polygons primarily in a 2-D interconnected polymer network so that it dictates preferably a 1-D directional growth on the reaction Fe3+ species in form of a compound Fe3BO6, a favorable phase to nucleate and grow when annealing a precursor at 500–800 °C in ambient air. Distinct nanorods with a diameter ∼200 nm and 40–100 μm length have been formed on 10–15 min annealing a sample in microwave at moderate temperature 550 °C. A bonded surface B2O3 layer (15–25 nm thickness) has grown on the Fe3BO6 of the nanorods in situ in a specific structure. XPS bands in the Fe3+, B3+ and O2− species confer this model structure. A local BO3 → BO4 conversion has incurred in the boroxol (B3O4.5)n, n → ∞, rings in the surface layer, showing three distinct IR bands at 1035, 1215 and 1425 cm−1. 相似文献
60.
Cryptanalysis and improvement of ‘a robust smart‐card‐based remote user password authentication scheme’ 下载免费PDF全文
Saru Kumari Muhammad Khurram Khan 《International Journal of Communication Systems》2014,27(12):3939-3955
With the use of smart card in user authentication mechanisms, the concept of two‐factor authentication came into existence. This was a forward move towards more secure and reliable user authentication systems. It elevated the security level by requiring a user to possess something in addition to know something. In 2010, Sood et al. and Song independently examined a smart‐card‐based authentication scheme proposed by Xu et al. They showed that in the scheme of Xu et al., an internal user of the system can turn hostile to impersonate other users of the system. Both of them also proposed schemes to improve the scheme of Xu et al. Recently, Chen et al. identified some security problems in the improved schemes proposed by Sood et al. and Song. To fix these problems, Chen et al. presented another scheme, which they claimed to provide mutual authentication and withstand lost smart card attack. Undoubtedly, in their scheme, a user can also verify the legitimacy of server, but we find that the scheme fails to resist impersonation attacks and privileged insider attack. We also show that the scheme does not provide important features such as user anonymity, confidentiality to air messages, and revocation of lost/stolen smart card. Besides, the scheme defies the very purpose of two‐factor security. Furthermore, an attacker can guess a user's password from his or her lost/stolen smart card. To meet these challenges, we propose a user authentication method with user anonymity. We show through analysis and comparison that the proposed scheme exhibits enhanced efficiency in contrast to related schemes, including the scheme of Chen et al. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献