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61.
Harutyunyan AR Awasthi N Jiang A Setyawan W Mora E Tokune T Bolton K Curtarolo S 《Physical review letters》2008,100(19):195502
Fe nanoclusters are becoming the standard catalysts for growing single-walled carbon nanotubes via chemical vapor decomposition. Contrary to the Gibbs-Thompson model, we find that the reduction of the catalyst size requires an increase of the minimum temperature necessary for the growth. We address this phenomenon in terms of solubility of C in Fe nanoclusters and, by using first-principles calculations, we devise a simple model to predict the behavior of the phases competing for stability in Fe-C nanoclusters at low temperature. We show that, as a function of particle size, there are three scenarios compatible with steady state growth, limited growth, and no growth of single-walled carbon nanotubes, corresponding to unaffected, reduced, and no solubility of C in the particles. 相似文献
62.
Recently, it was argued that the binegativity might be a good quantifier of entanglement for two-qubit states. Like the concurrence and the negativity, the binegativity is also analytically computable quantifier for all two qubits. Based on numerical evidence, it was conjectured that it is a PPT (positive partial transposition) monotone and thus fulfills the criterion to be a good measure of entanglement. In this work, we investigate its behavior under noisy channels which indicate that the binegativity is decreasing monotonically with respect to increasing noise. We also find that the binegativity is closely connected to the negativity and has closed analytical form for arbitrary two qubits. Our study supports the conjecture that the binegativity is a monotone. 相似文献
63.
K
β-to-K
α X-ray intensity ratios of Fe and Ni in pure metals and in Fe
x
Ni1−x
alloys (x=0.20, 0.50, 0.58) exhibiting similar crystalline structure have been measured following excitation by 59.54 keV γ-rays from a 241Am point source, to understand as to why the properties of permalloy Fe0.2Ni0.8 is distinct from other alloy compositions. It is observed that the valence electronic structure of Fe0.2Ni0.8 alloy is totally different from other alloys which may be attributed to its special magnetic properties. 相似文献
64.
Conjugate polymers provide the possibility of exploiting both the chemical and physical attributes of the polymers for membrane-based gas separation. The presence of delocalized π electrons provides high chain stiffness with low packing density, thus making the membrane a rigid structure that favors facilitated transport. Historically, the polymeric membranes were constrained by the tradeoff relationship between gas permeability and gas selectivity. So, different methods were investigated to prepare the membranes that can overcome the limitation. In recent years, electroconductive polymeric membranes have gained attention with their enhanced transportation properties combining the separation behavior depending on both molecular size discrimination as well as the facilitated transport. They offer better selectivity toward polar gases such as CO2 because of the increased solubility. This review is aimed to provide a literature survey on gas separation using conjugate polymers such as polyaniline, polypyrrole, and some derivatives of polythiophenes. It contains various methods used by different researchers to enhance the gas separation properties of the membranes with improved mechanical and thermal stability such as changing the morphology and membrane preparation methods. In addition, it provides the pros and cons of various factors affecting the conjugate polymer membrane performance. The major challenges and future work that can be done in improving the transportation properties through the membrane to achieve viable membranes are also discussed so that they can be used for commercial and practical applications in the future. 相似文献
65.
[reaction: see text] Palladium(0)-catalyzed cross-coupling reactions between tris(dihydropyranyl)indium 1 and aryl halides 2 have been investigated. Aryl iodides and electron-deficient aryl bromides couple efficiently with the in situ-generated indium reagents in the presence of 1-5 mol % Cl(2)Pd(PPh(3))(2) to produce substituted dihydropyrans 3 with minimal (<10%) dimer (4) formation. Organoindium reagents derived from D-glucal also undergo cross couplings with aryl iodides to produce C-aryl glycals. 相似文献
66.
The first example of ionic liquid-promoted one-pot oxidative conjugate hydrocyanation of Baylis-Hillman adducts with trimethylsilyl cyanide (TMSCN) is reported. The oxidation of Baylis-Hillman adducts with IBX/[bmim]Br or isomerization-oxidation with NaNO3/[Hmim]HSO4 systems affords β-ketomethylene compounds or [E]-cinnamaldehydes, respectively. These α,β-unsaturated carbonyl compounds undergo Michael addition with TMSCN in the same vessel to afford the corresponding thermodynamically more stable β-cyanated products. Thermodynamically less stable 1,2-addition products were not formed. The present regioselective reactions are promoted by ionic liquids, which can be recycled easily for further use without any loss of efficiency. 相似文献
67.
A Awasthi S S Chauhan M Parent Jean-Marie Proth 《The Journal of the Operational Research Society》2010,61(7):1159-1167
Partitioning of large networks is vital for decentralized management and control.This paper presents two algorithms called ‘Hierarchical Recursive Progression-1’ (HRP-1) and ‘Hierarchical Recursive Progression-2’ (HRP-2) for partitioning of large networks into subnetworks of limited size with very few interconnections between them. In other words, we are trying to maximize the internal nodes and minimize the external connections of the subnetworks. The restriction on the size and the external connections is obtained by comparison against a user-defined value for the size of the subnetwork and for external connections via a term called density. The density of a subnetwork is defined as the ratio of the number of external connections and the size of the subnetwork. The two algorithms presented in the paper are based on the principle of subnetwork clustering. At the start of the algorithms,the number of subnetworks is equal to the total number of nodes of the network with each subnetwork containing a single node. Later, subnetworks are merged at various runs of the algorithm to form new subnetworks using connectivity,density and size criteria. The algorithms terminate when all the subnetworks satisfy a user-defined size and density limit. The difference between the algorithms HRP-1 and HRP-2 lies in the definition of density of subnetworks and the way through which the subnetworks are grouped at consecutive iterations of the algorithm. Note that the number of nodes inside the subnetworks never violates the size limit, thereby ensuring even distribution of load on the partitions obtained. Finally, the two algorithms are compared and tested on randomly generated graphs and a part of Paris road Network. 相似文献
68.
An expeditious and concise method has been described for the synthesis of ailanthoidol through convergent route starting from vanillin. The protocol involving intramolecular Wittig as a key reaction afforded ailanthoidol in overall high yield. 相似文献
69.
Chiranjeev Sharma NeupaneSatish Kumar Awasthi 《Tetrahedron letters》2012,53(45):6067-6070
Tricyclohexane triperoxide (TCTP) was synthesized as a main by-product of tetraoxane synthesis and was characterized by spectroscopic techniques viz. 1H NMR, 13C NMR, FT-IR and Raman. The single crystal X-ray structure revealed the inclusion of solvent in 1:1 stoichiometric ratio involving a unique trifurcated C(sp3)-H?O hydrogen bonding imparting remarkable symmetry to the molecule. The thermal stability of single crystal was determined by TG-DTA and DSC. 相似文献
70.
Santosh Kumar Rai Meena Sharma Madhu Jain Abhishek Awasthi Dharmendra Kumar Purshottam Narayanan Kuttanpillai Nair Ashok Kumar Sharma 《Applied biochemistry and biotechnology》2010,162(7):1929-1937
An efficient in vitro process for rapid production of cloned plants of Uraria picta has been developed employing nodal stem segments taken from field-grown plants. Explants showed bud-break followed by regeneration
of shoots with restricted growth within 12 days on modified Murashige and Skoog’s medium supplemented with 0.25 mg l–1 each of 6-benzylaminopurine and indole-3-acetic acid and 25 mg l-1 adenine sulfate. Normal growth of shoots with good proliferation rate was achieved by reducing the concentrations of 6-benzylaminopurine
and indole-3-acetic acid to 0.1 mg l-1 each and incorporating 0.5 mg l-1 gibberellic acid in the medium in which, on an average, 19.6 shoots per explant were produced. Further, during successive
subcultures, increased concentrations of adenine sulfate (50 mg l-l) and gibberellic acid (2 mg l-l) along with the addition of 20 mg l-l
dl-tryptophan were found conducive to control the problem of necrosis of shoots. In this treatment, several “crops” of shoots
were obtained from single culture by repeated subculturing of basal portion of stalk in long-term. Isolated shoots rooted
100% in 0.25 mg l-1 indole-3-butyric acid. In vitro-raised plants after hardening in inorganic salt solution grew normally in soil and came to
flowering. Genetic fidelity of in vitro-raised plants was ascertained by rapid amplified polymorphic DNA (RAPD) markers. Also,
quantitative estimation of two isoflavonones in their root extracts further confirmed true-to-type nature of plantlets. 相似文献