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排序方式: 共有622条查询结果,搜索用时 15 毫秒
611.
A series of samples consisting of spinel Fe3O4 nanoparticles with controlled particle sizes and increasing concentration has been obtained through ‘mild’ ball milling (BM) experiments by using an organic carrier liquid. We have succeeded in producing quite narrow particle size distributions with mean values d7–10 nm by an appropriate choice of the milling time for each concentration. The method proved to be practical to tailor the final particle size without formation of undesirable phases. All samples showed superparamagnetic behavior at room temperature, with transition to a blocked state at TB10–20 K. The mean value and distribution width of the size distributions for the three samples studied were obtained from M(H) cycles recorded at T>TB showing good agreement with X-ray diffraction and electron microscopy results. The effect of increasing interparticle interactions was to shift TB upwards, as inferred from magnetization measurements. Mössbauer spectra at low temperatures showed no evidence of enhanced spin disorder. 相似文献
612.
We show that for all n-mode Gaussian states of continuous variable systems, the entanglement shared among n parties exhibits the fundamental monogamy property. The monogamy inequality is proven by introducing the Gaussian tangle, an entanglement monotone under Gaussian local operations and classical communication, which is defined in terms of the squared negativity in complete analogy with the case of n-qubit systems. Our results elucidate the structure of quantum correlations in many-body harmonic lattice systems. 相似文献
613.
We demonstrate the existence of general constraints on distributed quantum correlations, which impose a trade-off on bipartite and multipartite entanglement at once. For all N-mode Gaussian states under permutation invariance, we establish exactly a monogamy inequality, stronger than the traditional one, that by recursion defines a proper measure of genuine N-partite entanglement. Strong monogamy holds as well for subsystems of arbitrary size, and the emerging multipartite entanglement measure is found to be scale invariant. We unveil its operational connection with the optimal fidelity of continuous variable teleportation networks. 相似文献
614.
Toimil P Daviña R Sabín J Prieto G Sarmiento F 《Journal of colloid and interface science》2012,367(1):193-198
The influence of La(3+) on the colloidal stability of liposomes made up by two zwitterionic phospholipids, 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and 1-palmitoyl-2-[16-fluoropalmitoyl-phosphatidylcholine (F-DPPC), in aqueous media has been investigated by dynamic light scattering and electrophoretic mobility. The critical aggregation concentration (c.a.c.) of La(3+) for F-DPPC and DPPC liposomes were experimentally obtained, and the results were compared with theoretical predictions using the Derjaguin-Landau-Verwey-Overbeek theory. In order to evaluate the influence of the state of the bilayer on the stability of liposomes, all experiments were performed at temperatures below and above the chain-melting phase-transition temperature of lipids (transition temperature of lipids). Changes in the size of both types of liposomes and high values of polydispersity in the presence of La(3+) showed that these ions induce aggregation of liposomes at 25 °C and at 60 °C. At 25 °C, when the bilayer of F-DPPC liposomes is interdigited, DPPC liposomes are more resistant to aggregation than the liposomes formed with F-DPPC. However, this difference disappears at 60 °C, when both bilayers have the same conformation. The experimental results also indicate that the c.a.c. is higher at 60 °C than at 25 °C for both types of liposomes. In fact, it has been observed by dynamic light scattering measurements that aggregation of liposomes at 25 °C can be prevented by increasing the solution temperature for La(3+) concentrations near to the c.a.c. Moreover, the behavior of these liposomes in the presence of the ion was studied at temperatures above and below the transition temperature of the phospholipids. 相似文献
615.
Pérez-Estrada S Joseph-Nathan P Jiménez-Vázquez HA Medina-López ME Ayala-Mata F Zepeda LG 《The Journal of organic chemistry》2012,77(4):1640-1652
Benzoyl-S,O-acetals 1a and 1b were used as chiral auxiliaries to achieve the diastereoselective preparation of both enantiomers of 2-methoxy-2-phenylpent-3-ynoic acids (MPPAs). The latter were condensed with several chiral secondary alcohols and some primary amines to evaluate their potential as chiral derivatizing agents (CDAs). The (1)H NMR spectra of the corresponding esters and amides showed strong consistency with the absolute configuration of the carbinol and amine moieties, whose observed ΔδL(1) and ΔδL(2) values were in the ranges of 0.1-0.4 and 0.02-0.12 ppm, respectively. 相似文献
616.
Roberto Benzi Sergio Ciliberto Cristophe Baudet Gerardo Ruiz Chavarria 《Physica D: Nonlinear Phenomena》1995,80(4):385-398
In this paper we investigate the scaling properties of three-dimensional isotropic and homogeneous turbulence. We analyze a new form of scaling (extended self-similarity) recently introduced in the literature. We found that anomalous scaling of the velocity structure functions is clearly detectable even at a moderate and low Reynolds number and it extends over a much wider range of scales with respect to the inertial range. 相似文献
617.
We study Taylor diffusion for the case when the diffusion transverse to the bulk motion is a persistent random walk on a one-dimensional lattice. This is mapped onto a Markovian walk where each lattice site has two internal states. For such a model we find the effective diffusion coefficient which depends on the rate of transition among internal states of the lattice. The Markovian limit is recovered in the limit of infinite rate of transitions among internal states; the initial conditions have no role in the leading-order time-dependent term of the effective dispersion, but a strong effect on the constant term. We derive a continuum limit of the problem presented and study the asymptotic behavior of such limit. 相似文献
618.
Gerardo A. Gonzalez de la Cruz C.E.T.Gonçalves da Silva 《Solid State Communications》1977,21(7):621-624
We apply the Cluster-Bethe-lattice method to calculate the local density of one-magnon states for a binary substitutional ferromagnetic alloy. Short range order effects for the alloy are included. Simple clusters of one atom and one atom plus its nearest neighbors are studied. We show that, for the latter type of cluster, there are localized excitations the energies of which fall outside the continuum of excitations. 相似文献
619.
620.
Norma A. Cortez Gerardo Aguirre Miguel Parra-Hake Ratnasamy Somanathan 《Tetrahedron: Asymmetry》2013,24(20):1297-1302
The synthesis of (R)-tembamide and (R)-aegeline via asymmetric transfer hydrogenation involving enantioenriched monosulfonamide–RhCp1 complex in aqueous sodium formate as hydride donor is described. 相似文献