An Asymmetric Cone Model for Halo Coronal Mass Ejections

Due to projection effects, coronagraphic observations cannot uniquely determine parameters relevant to the geoeffectiveness of CMEs, such as the true propagation speed, width, or source location. The Cone Model for Coronal Mass Ejections (CMEs) has been studied in this respect and it could be used to obtain these parameters. There are evidences that some CMEs initiate from a flux-rope topology. It seems that these CMEs should be elongated along the flux-rope axis and the cross section of the cone base should be rather elliptical than circular. In the present paper we applied an asymmetric cone model to get the real space parameters of frontsided halo CMEs (HCMEs) recorded by SOHO/LASCO coronagraphs in 2002. The cone model parameters are generated through a fitting procedure to the projected speeds measured at different position angles on the plane of the sky. We consider models with the apex of the cone located at the center and surface of the Sun. The results are compared to the standard symmetric cone model

Electrical transport and magnetic properties of nanostructured La0.67Ca0.33MnO3

Nanostructured La0.67Ca0.33MnO3 (NS-LCMO) was formed by pulsed-laser deposition on the surface of porous Al2O3. The resistance peak temperature (Tp) of the NS-LCMO increases with increasing average thickness of the films, while their Curie temperatures (Tc) remain unchanged. The coercive field of the samples increases with decreasing film thickness and its temperature dependence can be well described by Hc(T) = Hc(0)[1-(T/TB)1/2]. A large magnetoresistance and strong memory effect were observed for the NS-LCMO. The results are discussed in terms of the size effect, Coulomb blockade and magnetic tunneling effect. This work also demonstrates a new way to get nanostructured manganites

Ab Initio Molecular Dynamics Simulation of Liquid Ga_xAs_{1-x} Alloys

We report the results of ab initio molecular dynamics simulations of liquid Ga_xAs_{1-x} alloys at five different concentrations, at a temperature of 1600 K, just above the melting point of GaAs. The liquid is predicted to be metallic at all concentrations between x = 0.2 and x = 0.8, with a weak resistivity maximum near x = 0.5, consistent with the Faber-Ziman expression. The electronic density of states is finite at the Fermi energy for all concentrations; there is, however, a significant pseudogap especially in the As-rich samples. The Ga-rich density of states more closely resembles that of a free-electron metal. The partial structure factors show only a weak indication of chemical short-range order. There is also some residue of the covalent bonding found in the solid, which shows up in the bond-angle distribution functions of the liquid state. Finally, the atomic diffusion coefficients at 1600K are calculated to be 2.1 \times 10^{-4} cm^2/sec for Ga ions in Ga_{0.8}As_{0.2} and 1.7 \times 10^{-4} cm^2/sec for As ions in Ga_{0.2}As_{0.8}.Comment: 29 pages, 10 eps figures, accepted for publication in Phys. Rev.

Prediction Space Weather Using an Asymmetric Cone Model for Halo CMEs

Halo coronal mass ejections (HCMEs) are responsible of the most severe geomagnetic storms. A prediction of their geoeffectiveness and travel time to Earth's vicinity is crucial to forecast space weather. Unfortunately coronagraphic observations are subjected to projection effects and do not provide true characteristics of CMEs. Recently, Michalek (2006, {\it Solar Phys.}, {\bf237}, 101) developed an asymmetric cone model to obtain the space speed, width and source location of HCMEs. We applied this technique to obtain the parameters of all front-sided HCMEs observed by the SOHO/LASCO experiment during a period from the beginning of 2001 until the end of 2002 (solar cycle 23). These parameters were applied for the space weather forecast. Our study determined that the space speeds are strongly correlated with the travel times of HCMEs within Earth's vicinity and with the magnitudes related to geomagnetic disturbances

Influence of the starting composition on the structural and superconducting properties of MgB2 phase

We report the preparation of Mg$_{1-x}$B$_{2}$ (0$\le$x$\le$0.5) compounds with the nominal compositions. Single phase MgB$_{2}$ was obtained for x=0 sample. For 0$<$x$\le$0.5, MgB$_{4}$ coexists with "MgB$_{2}$" and the amount of MgB$_{4}$ increases with x. With the increase of x, the lattice parameter ${\it c}$ of "MgB$_{2}$" increases and the lattice parameter ${\it a}$ decreases, correspondingly T$_{c}$ of Mg$_{1-x}$B$_{2}$ decreases. The results were discussed in terms of the presence of Mg vacancies or B interstitials in the MgB$_{2}$ structure. This work is helpful to the understanding of the MgB$_{2}$ films with different T$_{c}$, as well as the Mg site doping effect for MgB$_{2}$.Comment: 11 pages, 4 figure

Direct Measurements of the Branching Fractions for D0→K−e+νeD^0 \to K^-e^+\nu_e and D0→π−e+νeD^0 \to \pi^-e^+\nu_e and Determinations of the Form Factors f+K(0)f_{+}^{K}(0) and f+π(0)f^{\pi}_{+}(0)

The absolute branching fractions for the decays $D^0 \to K^-e ^+\nu_e$ and $D^0 \to \pi^-e^+\nu_e$ are determined using $7584\pm 198 \pm 341$ singly tagged $\bar D^0$ sample from the data collected around 3.773 GeV with the BES-II detector at the BEPC. In the system recoiling against the singly tagged $\bar D^0$ meson, $104.0\pm 10.9$ events for $D^0 \to K^-e ^+\nu_e$ and $9.0 \pm 3.6$ events for $D^0 \to \pi^-e^+\nu_e$ decays are observed. Those yield the absolute branching fractions to be $BF(D^0 \to K^-e^+\nu_e)=(3.82 \pm 0.40\pm 0.27)$ and $BF(D^0 \to \pi^-e^+\nu_e)=(0.33 \pm 0.13\pm 0.03)$. The vector form factors are determined to be $|f^K_+(0)| = 0.78 \pm 0.04 \pm 0.03$ and $|f^{\pi}_+(0)| = 0.73 \pm 0.14 \pm 0.06$. The ratio of the two form factors is measured to be $|f^{\pi}_+(0)/f^K_+(0)|= 0.93 \pm 0.19 \pm 0.07$.Comment: 6 pages, 5 figure

A probabilistic method for the operation of three-phase unbalanced active distribution networks

YesThis paper proposes a probabilistic multi-objective optimization method for the operation of three-phase distribution networks incorporating active network management (ANM) schemes including coordinated voltage control and adaptive power factor control. The proposed probabilistic method incorporates detailed modelling of three-phase distribution network components and considers different operational objectives. The method simultaneously minimizes the total energy losses of the lines from the point of view of distribution network operators (DNOs) and maximizes the energy generated by photovoltaic (PV) cells considering ANM schemes and network constraints. Uncertainties related to intermittent generation of PVs and load demands are modelled by probability density functions (PDFs). Monte Carlo simulation method is employed to use the generated PDFs. The problem is solved using ɛ-constraint approach and fuzzy satisfying method is used to select the best solution from the Pareto optimal set. The effectiveness of the proposed probabilistic method is demonstrated with IEEE 13- and 34- bus test feeders

Comparison of Soil Respiration in Typical Conventional and New Alternative Cereal Cropping Systems on the North China Plain

We monitored soil respiration (Rs), soil temperature (T) and volumetric water content (VWC%) over four years in one typical conventional and four alternative cropping systems to understand Rs in different cropping systems with their respective management practices and environmental conditions. The control was conventional double-cropping system (winter wheat and summer maize in one year - Con. W/M). Four alternative cropping systems were designed with optimum water and N management, i.e. optimized winter wheat and summer maize (Opt. W/M), three harvests every two years (first year, winter wheat and summer maize or soybean; second year, fallow then spring maize - W/M-M and W/S-M), and single spring maize per year (M). Our results show that Rs responded mainly to the seasonal variation in T but was also greatly affected by straw return, root growth and soil moisture changes under different cropping systems. The mean seasonal CO2 emissions in Con. W/M were 16.8 and 15.1 Mg CO2 ha(-1) for summer maize and winter wheat, respectively, without straw return. They increased significantly by 26 and 35% in Opt. W/M, respectively, with straw return. Under the new alternative cropping systems with straw return, W/M-M showed similar Rs to Opt. W/M, but total CO2 emissions of W/S-M decreased sharply relative to Opt. W/M when soybean was planted to replace summer maize. Total CO2 emissions expressed as the complete rotation cycles of W/S-M, Con. W/M and M treatments were not significantly different. Seasonal CO2 emissions were significantly correlated with the sum of carbon inputs of straw return from the previous season and the aboveground biomass in the current season, which explained 60% of seasonal CO2 emissions. T and VWC% explained up to 65% of Rs using the exponential-power and double exponential models, and the impacts of tillage and straw return must therefore be considered for accurate modeling of Rs in this geographical region