First-principles study of CoO films on MnO (1 1 1): Stability and interfacial structure

Based on the generalized gradient approximation, full potential linearized augmented plane-wave (FP-LAPW) calculations have been performed to study the stability and the interfacial structure of CoO/MnO (1 1 1). The surface energy, the strain energy and the binding energy are calculated and discussed. The calculations revealed that the CoO/MnO (1 1 1) is a stable interface structure. Also examined were the electronic properties and the atomic spin magnetic moments of the interface. It was found that the interface exhibited half-metallic property and the atomic magnetic moments were obviously weakened at the interface for metal atoms compared with the corresponding magnetic moments in bulk material.     

Evidences dominating the formation of ZnO nanostructures via in-situ study in an environmental scanning electron microscope

In order to well understand the growth mechanism of the diverse morphology of the ZnO nanostructures, in situ analysis of the formation of different ZnO nanostructures, such as nanowires, nanocombs, and nanosheets, has been conducted in an environmental scanning electron microscope (ESEM). It is found that both nanocombs and nanosheets grew in two-stage heating processes on parent nanowires. The difference is that the nanocombs were synthesized in extremely high pressure of zinc vapor via a self-catalyzed vapor-liquid-solid process, while the ZnO nanosheets were grown in relatively low pressure of zinc vapor. All the growth processes were revealed in real time imaging. It is demonstrated that the change in the growth environments can influence the thickness of the ZnO polycrystalline surface of the zinc powder, which alters the pressure of the zinc vapor and in turn determines the morphology of the final nanostructures.     

De–excitation of compound nuclei with A around 56: reduction of the emission barriers for protons and alpha particles

This paper contributes to the discussion on the phenomena of the enhanced emission of low–energetic charged particles during compound nuclei decay. The decay of compound nuclei ⁵²Fe, ⁵⁶Ni, and ⁵⁹Cu was studied. Energy spectra and emission angles of evaporated charged particles were measured in coincidence with gamma rays to determine the corresponding evaporation residue nucleus. Additionally, evaporation residue distributions were determined with the Munich rf recoil spectrometer. In this way, detailed channel–specific evaporation data were obtained for theoretical analysis. We extracted evaporation barriers and compared them with corresponding fusion barriers. The main result was revealed to be a lowering of the evaporation barrier for protons and alpha particles relative to the fusion barriers. But the observed effect is not as intensive as reported in recent studies. Received: 15 June 1998 / Revised version: 5 November 1998     

A new high-spin isomer in 145Sm

A new high-spin isomer in ¹⁴⁵Sm was observed by in-beam γ-ray spectroscopy with the reaction ¹²²Sn(²⁷Al,3np) at 127 MeV performed at the Nordball multi-detector array in Roskilde. The excitation energy of the isomer was determined to be E _x= 11147 keV, and using the generalized centroid-shift method its half-life was found to be T _1/2= (7.4 ± 1.0) ns. Received: 23 October 1998     

Punctuated evolution due to delayed carrying capacity

A new delay equation is introduced to describe the punctuated evolution of complex nonlinear systems. A detailed analytical and numerical investigation provides the classification of all possible types of solutions for the dynamics of a population in the four main regimes dominated respectively by: (i) gain and competition, (ii) gain and cooperation, (iii) loss and competition and (iv) loss and cooperation. Our delay equation may exhibit bistability in some parameter range, as well as a rich set of regimes, including monotonic decay to zero, smooth exponential growth, punctuated unlimited growth, punctuated growth or alternation to a stationary level, oscillatory approach to a stationary level, sustainable oscillations, finite-time singularities as well as finite-time death.     

Fabrication and characterization of CuO-core/TiO2-shell one-dimensional nanostructures

We have fabricated CuO-core/TiO₂-shell one-dimensional nanostructures by coating the CuO nanowires with MOCVD-TiO₂. The structure of the core/shell nanowires has been investigated by using scanning electron microscopy, transmission electron microscopy, and X-ray diffraction analysis techniques. The CuO-cores and the TiO₂-shells of the as-synthesized nanowires have been found to have crystalline monoclinic CuO and crystalline tetragonal anatase TiO₂ structures, respectively. The CuO-core/TiO₂-shell nanowires are winding and has rougher surface, whereas the CuO nanowires are straight and have smoother surface.Influence of the substrate temperature and the growth time on the structure such as the morphology, size, and crystallographic orientation of CuO nanowires synthesized by thermal oxidation of Cu foils have also been investigated. All the nanowires have only the CuO phase synthesized at 600 °C, whereas those synthesized at 400 °C have both CuO and Cu₂O phases. The highest density of CuO nanowires with long thin straight morphologies can be obtained at 600 °C. In addition, the growth mechanism of the CuO nanowires has been discussed.     

Synchrotron radiation assistant MOCVD deposition of ZnO films on Si substrate

The growth of ZnO film on Si(1 0 0) substrate has been studied with synchrotron radiation (SR) assisted MOCVD method. The diethylzinc (DEZn) and CO₂ are used as source materials, while Nitrogen is employed as a carrier gas for DEZn. With the assistance of SR the ZnO film can be deposited even at room temperature. XRD, SEM and photoluminescence (PL) studies show that the crystal quality of ZnO films grown with the assistance of SR is higher than that of those without SR assistance. The growth mechanism of ZnO film with the SR assistant MOCVD system is primarily discussed.     

Statistical properties of world investment networks

We have performed a detailed investigation on the world investment networks constructed from the Coordinated Portfolio Investment Survey (CPIS) data of the International Monetary Fund, ranging from 2001 to 2006. The distributions of degrees and node strengths are scale-free. The weight distributions can be well modeled by the Weibull distribution. The maximum flow spanning trees of the world investment networks possess two universal allometric scaling relations, independent of time and the investment type. The topological scaling exponent is 1.17±0.02 and the flow scaling exponent is 1.03±0.01.     

Multifractality in the random parameter model for multivariate time series

The Random Parameter model was proposed to explain the structure of the covariance matrix in problems where most, but not all, of the eigenvalues of the covariance matrix can be explained by Random Matrix Theory. In this article, we explore the scaling properties of the model, as observed in the multifractal structure of the simulated time series. We use the Wavelet Transform Modulus Maxima technique to obtain the multifractal spectrum dependence with the parameters of the model. The model shows a scaling structure compatible with the stylized facts for a reasonable choice of the parameter values.     

Multiresolution analysis of fluctuations in non-stationary time series through discrete wavelets

We illustrate the efficacy of a discrete wavelet based approach to characterize fluctuations in non-stationary time series. The present approach complements the multifractal detrended fluctuation analysis (MF-DFA) method and is quite accurate for small size data sets. As compared to polynomial fits in the MF-DFA, a single Daubechies wavelet is used here for detrending purposes. The natural, built-in variable window size in wavelet transforms makes this procedure well suited for non-stationary data. We illustrate the working of this method through the analysis of binomial multifractal model. For this model, our results compare well with those calculated analytically and obtained numerically through MF-DFA. To show the efficacy of this approach for finite data sets, we also do the above comparison for Gaussian white noise time series of different sizes. In addition, we analyze time series of three experimental data sets of tokamak plasma and also spin density fluctuations in 2D Ising model.