Heterodimers based on CoPt3-Au nanocrystals with tunable domain size

We describe an approach to synthesize colloidal nanocrystal heterodimers composed of CoPt(3) and Au. The growth is based on the nucleation of gold domains on preformed CoPt(3) nanocrystals. It is a highly versatile methodology which allows us to tune independently the size of the two domains in each dimer by varying several reaction parameters. The statistical analysis of the distribution of the domain sizes in the dimers and the compositional mapping achieved by dark field imaging and energy dispersive spectroscopy confirm that the two domains in each dimer are indeed made of CoPt(3) and Au, respectively. Structural characterization by high-resolution transmission electron microscopy shows that the two domains, both having cubic fcc Bravais lattice, can share a common {111}, {100}, or {110} facet, depending on the size of the initial CoPt(3) seeds. The magnetization measurements evidence a ferromagnetic CoPt(3) phase with a relatively low anisotropy as a consequence of their disordered crystalline structure, regardless of the presence of a Au tip. We believe that this prototype of nanocrystal dimer, which can be manipulated under air, can find several applications in nanoscience, as the Au section can be exploited as the preferential anchor point for various molecules, while the CoPt(3) domain can be used for magnetic detection.     

Solvent response and dielectric relaxation in supercooled butyronitrile

We have measured the dynamics of solvation of a triplet state probe, quinoxaline, in the glass-forming dipolar liquid butyronitrile near its glass transition temperature T(g)=95 K. The Stokes shift correlation function displays a relaxation time dispersion of considerable magnitude and the optical linewidth changes along the solvation coordinate in a nonmonotonic fashion. These features are characteristic of solvation in viscous solvents and clearly indicate heterogeneous dynamics, i.e., spatially distinct solvent response times. Using the dielectric relaxation data of viscous butyronitrile as input, a microscopic model of dipolar solvation captures the relaxation time, the relaxation dispersion, and the amplitude of the dynamical Stokes shift remarkably well.     

Bianchi V cosmological model in Palatini <Emphasis Type="Italic">f</Emphasis>(<Emphasis Type="Italic">R</Emphasis>) gravity

We apply the dynamical systems approach to investigate the spatially homogeneous and anisotropic Bianchi type V models for the Palatini version of f(R) gravity. In particular, we examine the existence of equilibrium points along with their exact solutions and stability properties for two different forms of f(R). Moreover, the evolution of shear and spatial curvature by performing the phase space analysis are studied and also the phases of evolution from anisotropic universe to the stable de-Sitter flat universe are discussed.     

Strong lensing of a regular black hole with an electrodynamics source

In this paper we have investigated the gravitational lensing phenomenon in the strong field regime for a regular, charged, static black holes with non-linear electrodynamics source. We have obtained the angle of deflection and compared it to a Schwarzschild black hole and Reissner Nordström black hole with similar properties. We have also done a graphical study of the relativistic image positions and magnifications. We hope that this method may be useful in the detection of non-luminous bodies like this current black hole.     

QM/MM study of the interaction between zigzag SnC nanotube and small toxic gas molecules

Adsorptions of small toxic molecules such as CO, N₂, HCN, SO₂, H₂CO, and NH₃ on a single‐walled (6,0) SnC nanotube (SnCNT) are investigated using Quantum Mechanics/Molecular Mechanics (QM/MM) methodology. The calculations are carried out at the B3LYP/6‐311++G(d,p)//LANL2DZ:UFF level of theory. The high layer of the model consists of a pyrene‐type ring on the nanotube surface as the adsorption site, where one gas molecule is allowed to interact. Conversely, for the adsorption of the two molecules, a larger site like a coronene ring is used for the high layer. Adsorption energy, Gibbs free energy change, Mulliken charge transfer, and total electron‐density maps are computed in each case. The adsorption strength of the gas molecule on the SnCNT surface is also analyzed from the density of states projected to different atoms (PDOS) of the nanotube–adsorbate complexes. The adsorptions of CO and N₂ on the (6,0) SnCNT surface require to cross potential barriers, and the corresponding transition structures are identified by ONIOM‐IRC calculations. For the remaining four molecules, the processes of adsorption are predicted to be barrier‐less. The calculations for the adsorption of H₂CO on (5,0) and (7,0) SnCNT surfaces are extended to study the effect of the size of the nanotube. Results for the adsorption of a single molecule on (6,0) SnCNT using B3LYP functional are compared with those obtained from a dispersion corrected functional such as M06‐2X. © 2015 Wiley Periodicals, Inc.     

Three‐dimensional coherent diffractive imaging on non‐periodic specimens at the ESRF beamline ID10

The progress of tomographic coherent diffractive imaging with hard X‐rays at the ID10 beamline of the European Synchrotron Radiation Facility is presented. The performance of the instrument is demonstrated by imaging a cluster of Fe₂P magnetic nanorods at 59 nm 3D resolution by phasing a diffraction volume measured at 8 keV photon energy. The result obtained shows progress in three‐dimensional imaging of non‐crystalline samples in air with hard X‐rays.     

Band-edge ultrafast pump-probe spectroscopy of core/shell CdSe/CdS rods: assessing electron delocalization by effective mass calculations

CdSe/CdS dot/rods nanocrystals show interesting physical properties related to the band-alignment at the hetero-interface, which controls the band-edge electron delocalization over the rods. Here the differential transmission spectra of CdSe/CdS nanorod samples with different core sizes have been measured using excitation resonant to the core transition. The photo bleaching ratio between dot and rod transitions increases with the dot size, indicating a trend towards electron localization. This trend has been further quantified by performing effective mass calculations in which the conduction band misalignment was varied in order to reproduce the observed bleaching feature ratio. The best agreement was found for negligible conduction band misalignment for small dots of around 2.3 nm in diameter, and about -0.1 eV misalignment was estimated for the larger dots, above 3.5 nm in diameter. This shows that the band misalignment might be dependent on the geometry of the system, and we argue that this might be related to different strain developed at the hetero-interface.     

Synthesis, structural characterization and catalytic activity of a multifunctional enzyme mimetic oxoperoxovanadium(V) complex

The synthesis and structural characterization of a novel oxoperoxovanadium(V) complex [VO(O(2))(PAH)(phen)] containing the ligands 2-phenylacetohydroxamic acid (PAHH) and 1,10-phenanthroline (phen) has been accomplished. The oxoperoxovanadium(V) complex was found to mimic both vanadate-dependent haloperoxidase (VHPO) activity as well as nuclease activity through effective interaction with DNA. The complex is the first example of a structurally characterized stable oxoperoxovanadium(V) complex with a coordinated bi-dentate hydroximate moiety (-CONHO(-)) from 2-phenylacetohydroximate (PAH). The oxoperoxovanadium(V) complex has been used as catalyst for the peroxidative bromination reaction of some unsaturated alcohols (e.g. 4-pentene-1-ol, 1-octene-3-ol and 9-decene-1-ol) in the presence of H(2)O(2) and KBr. The catalytic products have been characterized by GC-MS analysis and spectrophotometric methods. The DNA binding of this complex has been established with CT DNA whereas the DNA cleavage was demonstrated with plasmid DNA. The interactions of the complex with DNA have been monitored by electronic absorption and fluorescence emission spectroscopy. Viscometric measurements suggest that the compound is a DNA intercalator. The nuclease activity of this complex was confirmed by gel electrophoresis studies.     

About the fastest growth of the Order Parameter in models of percolation

The growth of the average size 〈_smax〉$〈s_{max}〉$ of the largest component at the percolation threshold _pc(N)$p_c\left(N\right)$ on a graph of size N$N$ has been defined as 〈_smax(_pc(N),N)〉∼N^χ$〈s_{max}(p_c\left(N\right),N)〉\sim N^{\chi }$. Here we argue that the precise value of the ‘growth exponent’ χ$\chi$ indicates the nature of percolation transition; χ<1$\chi <1$ or χ=1$\chi =1$ determines if the transition is continuous or discontinuous. We show that a related exponent η=1−χ$\eta =1-\chi$ which describes how the average maximal jump sizes in the Order Parameter decays on increasing the system size, is the single exponent that describes the finite-size scaling of a number of distributions related to the fastest growth of the Order Parameter in these problems. Excellent quality scaling analysis are presented for the two single peak distributions corresponding to the Order Parameters at the two ends of the maximal jump, the bimodal distribution constructed by the weighted average of these distributions and for the distribution of the maximal jump in the Order Parameter.