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531.
Hui Gao Marie-Christine Jones Pankaj Tewari Maxime Ranger Jean-Christophe Leroux 《Journal of polymer science. Part A, Polymer chemistry》2007,45(12):2425-2435
Amphiphilic star-shaped polymers were synthesized by atom transfer radical polymerization (ATRP). Four-, 5-, and 6-arm ATRP initiators were prepared and used to polymerize glycidylmethacrylate. The resulting polymers were hydrolyzed to yield poly(glycerolmethacrylate)s (PGOHMAs), and then partially esterified with lauroyl or stearoyl chloride (40–60 mol % vs. hydroxyl groups). Alkylated PGOHMAs were found to assemble into 20–60 nm aggregates in dichloromethane (DCM) above a critical concentration. Particle size essentially depended on the branching degree of the polymer. The micelles were extremely efficient in extracting Congo red from water into DCM, with the highest incorporations (97 mg/g) obtained for the 6-arm polymer modified with stearoyl chloride (60 mol %). The entrapment efficiency for the latter was further improved in alkaline solution. The high level of incorporation achieved for these amphiphilic multiarm polymers suggests that such reverse micelles could be potentially useful as drug delivery systems and nanoreactors in catalytic organic reactions or for water purification. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2425–2435, 2007 相似文献
532.
Pankaj Sharma Jose Luis Arias Jaime Vasquez Valente Gomez Rene Guiterrez 《中国化学会会志》2007,54(3):681-684
Homogeneous hydroformylation of 1‐pentene under synthesis gas experimental conditions was studied using RhClCO(PPh3)2 complex with different triarylstibines. Three different stibine ligands SbR3 [where R = 2,4,6‐mesityl (TMS), 2‐furyl (TFS), 2‐N,N‐dimethylbenzylamine (TDMBAS)], have been tested. It is interesting to note that 2:1 addition of these stibine ligands to the RhClCO(PPh3)2 complex catalyst increases the aldehydes yields with an appreciable n:iso ratio. The catalytic activity of the system shows a TDMBAS > TMS > TFS pattern which indicates that not only basicity of the ligand alone is playing a role in the activity but the steric effect is also very important, and it is combination of these two factors that contributes to the resulting catalytical activity. The maximum yield of aldehydes obtained were 98.7% with n/iso = 1.4 when RhClCO(PPh3)2 + TFS system was used and 93.7% with n/iso = 2.43 when TDMBAS ligand was studied. 相似文献
533.
Pankaj K. Agarwal Ferran Hurtado Godfried T. Toussaint Joan Trias 《Discrete Applied Mathematics》2008,156(1):42-54
Given a set S of n?3 points in the plane (not all on a line) it is well known that it is always possible to polygonize S, i.e., construct a simple polygon P such that the vertices of P are precisely the given points in S. For example, the shortest circuit through S is a simple polygon. In 1994, Grünbaum showed that an analogous theorem holds in R3. More precisely, if S is a set of n?4 points in R3 (not all of which are coplanar) then it is always possible to polyhedronize S, i.e., construct a simple (sphere-like) polyhedron P such that the vertices of P are precisely the given points in S. Grünbaum's constructive proof may yield Schönhardt polyhedra that cannot be triangulated. In this paper several alternative algorithms are proposed for constructing such polyhedra induced by a set of points, which may always be triangulated, and which enjoy several other useful properties as well. Such properties include polyhedra that are star-shaped, have Hamiltonian skeletons, and admit efficient point-location queries. We show that polyhedronizations with a variety of such useful properties can be computed efficiently in O(nlogn) time. Furthermore, we show that a tetrahedralized, xy-monotonic, polyhedronization of S may be computed in time O(n1+ε), for any ε>0. 相似文献
534.
Pankaj Kumar S. C. Jain Vikram Kumar Suresh Chand R. P. Tandon 《The European physical journal. E, Soft matter》2009,28(4):361-368
Current-voltage (J -Vcharacteristics of poly(3-hexylthiophene) (P3HT) are studied at different temperatures upto high voltages ∼ 20 V in the hole-only
device configuration. The characteristics are studied in the temperature range 310-210K. In the intermediate voltage range
the J -V characteristics follow J
V
l+1 , where l > 1 . As the voltage increases to high values J still varies as a power law i.e. as Vm, but contrary to the literature result m becomes < 2 . This behavior is explained theoretically in terms of non-zero injection Schottky barriers. The complete analytical
expressions for the actual trap filled limit voltage (V′
TFL) and J -V curves beyond V′
TFL are presented. 相似文献
535.
Satyendra Singh Pankaj Srivastava Abhay Mishra 《Physica E: Low-dimensional Systems and Nanostructures》2009,42(1):46-50
The structural stability and electronic properties of four different shapes of GaSb nanowire have been studied by ab-initio method using the generalized gradient approximations. The different structures were two atom linear wire, two atom zigzag wire, four atom square wire and six atom hexagonal wire. The geometry optimization and the stability of all nanowires were investigated. We explore the minimum energy atomic configuration for all the considered shapes. We find that four atom square wire configuration has greater stability in comparison to other shapes. The analysis of density of states and band structures of optimized nanowires predicts that semiconducting nanowires may be metallic or semiconducting. The behavior entirely depends upon the geometrical structure. 相似文献
536.
Das Pankaj Konwar Dilip Sengupta Pinaki Dutta Dipak K 《Transition Metal Chemistry》2000,25(4):426-429
Rhodium(I) carbonyl complexes [Rh(CO)2ClL] where L = Ph3PO, Ph3PS and Ph3PSe, were synthesized and characterized by elemental analysis, i.r. and by 1H-, 13C- and 31P-n.m.r. spectroscopy. The vBD;(CO) band frequencies in the complexes follow the order: Ph3PO > Ph3PS > Ph3PSe, in keeping with the hard/soft nature of the interactions. The complexes undergo oxidative additions with electrophiles
such as MeI, PhCH2Cl and I2 to give, e.g. [Rh(CO)(COMe)ClIL] which react with PPh3 to give trans-[Rh(CO)Cl(PPh3)2]. The catalytic activity of the [Rh(CO)2ClL] complexes in carbonylation of MeOH is higher than that of the well-known [Rh(CO)2I2]− species.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
537.
Bansal V Poddar P Ahmad A Sastry M 《Journal of the American Chemical Society》2006,128(36):11958-11963
The syntheses of inorganic materials by biological systems is characterized by processes that occur close to ambient temperatures, pressures, and neutral pH, as is exemplified by biosilicification and biomineralization processes in nature. Conversely, laboratory-based syntheses of oxide materials often require extremes of temperature and pressure. We have shown here the extracellular, room-temperature biosynthesis of 4-5 nm ternary oxide nanoparticles such as barium titanate (BT) using a fungus-mediated approach. The tetragonality as well as a lowered Curie transition temperature in sub-10 nm particles was established, and the ferroelectricity in these particles was shown using Kelvin probe microscopy. 相似文献
538.
La0.5Sr0.5CoO3-yttria-stabilized zirconia (LSCO-YSZ) composite cathode for solid oxide fuel cell (SOFC) has been fabricated by wet impregnation method. Nitrate precursors of La, Sr, and Co have been impregnated into the pre-sintered porous YSZ matrix, which is converted into LSCO phase after calcination at 850 °C in the presence of glycine as confirmed from X-ray diffraction. LSCO of 5, 7, and 10 wt% impregnated porous YSZ have been electrochemically characterized using 2-probe AC conductivity method. Maximum ionic conductivity of 0.27 S/cm at 800 °C and activation energy of 0.15 eV between 600 and 800 °C have been observed for 10 wt% LSCO-YSZ cathode. Area-specific resistance of 1.01 Ω cm2 at 800 °C is estimated for the electrolyte-supported half-cell (10 wt% LSCO-YSZ/YSZ). After testing the LSCO-YSZ cathode matrix, the electrolyte-supported full cell (10 wt% LSCO-YSZ/YSZ/NiO-YSZ) has been tested and produced maximum power density 51.12 mW/cm2 (109.38 mA/cm2) at 800 °C. The electrolyte-supported full cell exhibited 6 Ω cm2 electrode polarization at 800 °C in H2, which is in higher side leading to low performance. LSCO-YSZ/YSZ/NiO-YSZ SOFC found to give stable performance up to 2 h and scanning electron microscopy analysis has been carried out before and after cell testing to assess the morphological changes. 相似文献
539.
Table of Contents
Transport in Porous Media 相似文献540.
Pankaj?SehgalEmail author Hidekazu?Doe Manu?Sharma Daniel?E.?Otzen 《Colloid and polymer science》2004,282(7):677-683
Solubilization of different zwitterionic phospholipid vesicles structures such as L--phosphatidylcholine (PC) and 1,2-didecanoyl-sn-glycero-3-phosphocholine (DPC) have been studied in aqueous bulk by using zwitterionic surfactant dimethylhexadecylammoniopropanesulfonate (HPS). This has been done by studying the aggregation of HPS in pure water and in the presence of 7–36 M of fixed concentrations of each lipid with the help of pyrene fluorescence intensity (I
1/I
3) measurements. The fluorescence measurements showed that HPS monomers undergo two kinds of aggregation process, which were identified by the three breaks in a plot of pyrene fluorescence versus HPS concentration. The first two breaks, C
1 and C
2, indicate the onset and completion of vesicle solubilization respectively, upon incorporation of HPS monomers into the vesicles and led to solubilization in the form of mixed micelles. This process was not clearly visible at low lipid concentration. We evaluated the partition coefficient (K), which defines the degree of partitioning of surfactant monomers into the vesicles with respect to the aqueous medium. A high K value of HPS-lipid aggregates indicates the stronger interactions between surfactant and lipid vesicles. The K values evaluated for PC and DPC are quite close to each other, which indicates that K values were independent of phospholipid chain length. 相似文献