Density Contours Research Articles

Comparison of BES measurements of ion-scale turbulence with direct gyro-kinetic simulations of MAST L-mode plasmas

Observations of ion-scale (kyρi ⩽ 1) density turbulence of relative amplitude ≳0.2% are available on the Mega Amp Spherical Tokamak (MAST) using a 2D (8 radial × 4 poloidal channel) imaging beam emission spectroscopy diagnostic. Spatial and temporal characteristics of this turbulence, i.e., amplitudes, correlation times, radial and perpendicular correlation lengths and apparent phase velocities of the density contours, are determined by means of correlation analysis. For a low-density, L-mode discharge with strong equilibrium flow shear exhibiting an internal transport barrier in the ion channel, the observed turbulence characteristics are compared with synthetic density turbulence data generated from global, non-linear, gyro-kinetic simulations using the particle-in-cell code NEMORB. This validation exercise highlights the need to include increasingly sophisticated physics, e.g., kinetic treatment of trapped electrons, equilibrium flow shear and collisions, to reproduce most of the characteristics of the observed turbulence. Even so, significant discrepancies remain: an underprediction by the simulations of the turbulence amplitude and heat flux at plasma periphery and the finding that the correlation times of the numerically simulated turbulence are typically two orders of magnitude longer than those measured in MAST. Comparison of these correlation times with various linear timescales suggests that, while the measured turbulence is strong and may be ‘critically balanced’, the simulated turbulence is weak.

Electronic band structure and specific features of AA- and AB-stacking of carbon nitride (C3N4): DFT calculation

The state-of-the-art all-electron full potential linear augmented plane wave based on density functional theory was applied for calculating the structural, electronic band structure, effective mass, density of state, and valence electron charge density of AA- and AB-stacking of carbon nitride (C3N4). Calculations were performed using four schemes, namely local density approximation (LDA-CA) by Ceperley–Alder, generalized gradient approximation developed by Perdew Burke and Ernzerhof (GGA-PBE), Engel–Vosko generalized gradient approximation (EV-GGA) and the recently developed modified Becke–Johnson (mBJ) potentials. The calculated band structure and total density of states verify the semiconducting nature of the two configurations with band gap of about 2.589 eV and 2.990 eV for AA- and AB-stacking of C3N4. The effective mass ratio of electron, heavy hole and light hole were calculated for both AA- and AB-stacking. The upper valence band in AB-stacking is much flatter as compared to AA-stacking, and elucidates a dramatic increase in the effective mass ratio of heavy holes which cause a reduction in group velocity of the wave packet and consequently decrease the mobility of the charge carrier. The partial density of state shows the variation in the orbital state and its strength as one moves from AA- to AB-stacking. The strong hybridization among the orbitals of both stacking (AA- and AB-) shows covalent nature of the bonds. The calculated valence electron charge density contour shows the prevailing covalent nature of C and N bonds with negligible percentage (8.08%) of ionicity.

Dangling bond modulating the electronic and magnetic properties of zigzag SiGe nanoribbon

First-principles nonmagnetic calculations reveal a metallic character in zigzag SiGe nanoribbons (ZSiGeNRs) regardless of their width. The partial DOS projected onto the Si and Ge atoms of ZSiGeNR shows that a sharp peak at the Fermi level is derived from the edge Si and Ge atoms. The charge density contours show the Si–Ge bond is covalent bond, while for the Si–H bond and Ge–H bond, the valence charges are strongly accumulated around H atoms due to their stronger 1s potential and the higher electronegativity of 2.20 than that of 1.90 for Si atom and 2.01 for Ge atom, so that a significant charge transformation from Si or Ge atoms to H atoms and thus an ionic binding feature. Spin–polarization calculations show that the band structures of ZSiGeNR are modified by the dangling bonds. Compared with perfect ZSiGeNR which is a ferrimagnetic semiconductor, the bands of the ZSiGeNRs with bare Si edge, bare Ge edge, and bare Si and Ge edges shift up and nearly flat extra bands appear at the Fermi level. The ZSiGeNR with bare Si edge or bare Ge edge is a ferrimagnetic metal, while ZSiGeNR with bare Si and Ge edges is a nonmagnetic metal.

Thermoelectric properties, electronic structure and optoelectronic properties of anisotropic Ba2Tl2CuO6 single crystal from DFT approach

First principle calculation was performed for the electronic structure, electronic charge density, Fermi surface, optical and thermoelectric properties of Ba2Tl2CuO6 compound. From the electronic band structure the two overlapping bands and the density of state at Fermi level (29.2states/Ryd-cell) confirms the superconducting behavior. Colors of the Fermi surface elucidate speed of electrons and strength of the superconductivity as well. The bonding nature was investigated using the calculated charge density contour plot, it shows mixed ionic-covalent nature of Cu3O and Tl3O while Ba3O shows dominant ionic nature with small covalency. The optical properties were calculated and discussed in details. The calculated uniaxial anisotropy value (0.7913) clarifies a considerable anisotropy between two dominant tensor components of dielectric function. Moreover the evaluation of Seebeck coefficient and thermal conductivity conform that the compound is much suitable for thermoelectric applications.

Optimal rank-based tests for Common Principal Components

This paper provides optimal testing procedures for the m-sample null hypothesis of Common Principal Components (CPC) under possibly non Gaussian and heterogenous elliptical densities. We first establish, under very mild assumptions that do not require finite moments of order four, the local asymptotic normality (LAN) of the model. Based on that result, we show that the pseudo-Gaussian test proposed in Hallin et al. (2010a) is locally and asymptotically optimal under Gaussian densities. We also show how to compute its local powers and asymptotic relative efficiencies (AREs). A numerical evaluation of those AREs, ho wever, reveals that, while remain- ing valid, this test is poorly efficient away from the Gaussian. Moreover, it still requires finite moments of order four. We therefore propose rank-based proc edures that remain valid under any possibly heterogenous m-tuple of elliptical densities, irrespective of any moment assumptions--in elliptical families, indeed, principal components naturally can be based on the scatter matrices characterizing the density contours, hence do not require finite variances. Those rank-based tests are not only validity-robust in the sense that they survive arbitrary elliptical populationdensities: we show that they also are efficiency-robust, in the sense that their local powers do not deteriorate under non-Gaussian alternatives. In the homogeneous case, the normal-score version of our tests uniformly dominates, in the Pitman sens e, the optimal pseudo-Gaussian test. Theoretical results are obtained via a nonstandard application of Le Cam's methodology in the context of curved LAN experiments. The finite-sample properties of the proposed tests are investigated through simulations.

Numerical Investigation of Combined Top and Lateral Blowing in a Peirce-Smith Converter

Abstract Typical current operation of lateral-blown Peirce-Smith converters (PSCs) has the common phenomenon of splashing and slopping due to air injection. The splashing and wave motion in these converters cause metal losses and potential production lost time due to intermittent cleaning of the converter mouth and thus reduced process throughput. Understanding of the effect of combined top and lateral blowing could possibly lead to alternative technology advancement for increased process efficiency. In this study, computational fluid dynamics (CFD) simulations of conventional common practice (lateral blowing) and combined (top and lateral blowing) in a PSC were carried out, and results of flow variables (bath velocity, turbulence kinetic energy, etc.) were compared. The two-dimensional (2-D) and three-dimensional (3-D) simulations of the three-phase system (air–matte–slag) were executed utilizing a commercial CFD numerical software code, ANSYS FLUENT 14.0. These simulations were performed employing the volume of fluid and realizable turbulence models to account for multiphase and turbulent nature of the flow, respectively. Upon completion of the simulations, the results of the models were analysed and compared by means of density contour plots, velocity vector plots, turbulent kinetic energy vector plots, average turbulent kinetic energy, turbulent intensity contour plots and average matte bulk velocity. It was found that both blowing configuration and slag layer thickness have significant effects on mixing propagation, wave formation and splashing in the PSC as the results showed wave formation and splashing significantly being reduced by employing combined top- and lateral-blowing configurations.

First principle study of the electronic structure, Fermi surface, electronic charge density and optical properties of ThCu5In and ThCu5Sn single crystals

The electronic structure, Fermi surface, electronic charge density and optical properties of ThCu5In and ThCu5Sn single crystals are studied. The calculations are based on the full potential-linearized augmented plane wave (FPLAPW) method. The exchange and correlation potential is treated by the local density approximation (LDA) and generalized-gradient approximation (GGA), in addition the Engel–Vosko (EV-GGA) formalism was also applied. The DFT calculations show that these compounds have metallic origin. The contribution of different bands was analyzed from total and partial density of states curves. The values of the density of states at Fermi energy (N(EF)) for ThCu5In (ThCu5Sn) is 1.75 (1.63) states/eV unit cell. The bare electronic specific heat coefficient (γ) is found to be equal to 0.30 and 0.28mJ/mol-K2 for ThCu5In and ThCu5Sn, respectively. The Fermi surface of ThCu5In/ThCu5Sn is composed of three/four bands crossing along the R–Γ direction. The bonding features are analyzed by using the electronic charge density contour in the (101) crystallographic plane and it shows the covalent character of Cu–Cu and Sn/In–Cu bonds. The optical properties were also calculated and analyzed.

The potential energy surface of singlet cyclobutadiene and substituted analogs: a coupled-cluster study

Coupled-cluster investigations (CCSD/cc-pVDZ and CCSD/cc-pVQZ//CCSD/cc-pVDZ) of singlet cyclobutadiene and fifteen-substituted analogs were conducted. A local minimum with a square frame does not exist on their potential surfaces. The well-known rectangular D2h minimum, the square D4h transition state, and two additional stationary points were found on cyclobutadiene’s potential surface. This included a transition state with a rhombic carbon ring and C2h symmetry, separating two equivalent puckered C2v local minima. The predicted barriers were 19.7 and 19.8 kcal/mol at the CCSD/cc-pVDZ and CCSD/cc-pVQZ//CCSD/cc-pVDZ levels, respectively. The relative strain energies of rectangular D2h cyclobutadiene and all fifteen-substituted analogs were obtained from isodesmic reactions. Progressive substitution with methyl or BH2 groups continuously lowers ring strain while increasing substitution with fluorines or trifluoromethyl groups steadily increases ring strain. C4(BH2)4 is 16.6 and 13.3 kcal/mol less strained than cyclobutadiene while C4F4 is 17.7 and 21.5 kcal/mol more strained at the levels above. Cyclobutadiene is more strained than both cyclopropene and cyclobutene by 12.2 and 37.0 kcal/mol, respectively. Electron density contours indicate that fluorine substitution raised the electron density especially in the short C=C ring bonds above/below the ring plane (π-electrons) but not in the ring plane (σ-electrons). BH2-substitutions lower the ring π-electron density with little effect in the ring plane. Methyl substituents have little effect on electron densities. All rings retain a strong bond alternation tendency (rectangular) whether substituted with electron-donating or -attracting groups. One-bond coupling constants and the percent p-character in ring C-to-C and C-to-substituent bonds are described.

Multivariate approach to change detection from fraction images

Detection of changes in remotely sensed digital images acquired on different dates are commonly highly influenced by radiometric differences and registration problems. Using fraction images obtained from the linear model of spectral mixing, the radiometric problems can be minimized and interpretation of changes in land cover is simplified. This note explores an algorithm for detecting changes between fraction images, which provides a probabilistic threshold, from which pixels that have undergone change can be identified and classified. The technique requires multivariate normality for the differences of fractions and is based on the fact that the contours of constant density are defined by χ2 values, according the choice of probability level. To include spatial information, morphological operations were performed on the binary images created by the algorithm. Results obtained using synthetic images with high noise levels showed kappa values above 0.87 and a detection rate of approximately 80%, when a low level of significance and morphological filters were used. The experiment using a real pair of images (Landsat-TM), in turn, has successfully identified mining areas and deforestation regions.

Ultra soft pseudo potential investigation of fundamental physical properties of CaXO3 (X=Sn and Hf) distorted perovskites: A reference study to the perfect perovskites

The structural, electronic and optical properties of CaXO3 distorted perovskites compounds have been investigated by employing the Vanderbilt Ultra Soft Pseudo Potential (US-PP) using the plane wave method (PW) within density functional theory (DFT) and the local density approximation LDA. The studies of the dependence with pressure of enthalpies have confirmed the excellent mechanical stability of these materials. We have found that these compounds have a direct band gaps (G–G). The (110) charge density contour show that these distorted compounds exhibit a zig zag electronic short chains in contrast of ideal perovskites presenting a perfectly aligned chains. Elastic–electronic correlation was established between Cij individual elastic constant and the bonding-anti bonding chemical bonds. After that, some above properties were studied under hydrostatic pressure effect. CaSnO3 perovskite was very sensitive towards pressure than CaHfO3. The reflectivity maximum of these materials occurs in the ultra-violet energy ranges, which indicate that these perovskites can serve in some technological applications. Optical anisotropy shows that the compound CaSnO3 is considered as more anisotropic than CaHfO3. Furthermore, anisotropy maximum was found to be according to [010] and [100] directions for CaHfO3 and CaSnO3, respectively.

An improved approach for predicting the density of azido compounds

In this paper, a total of 30 azido compounds were optimised with the B3LYP method of density functional theory using six basis sets (3-21G, 6-31G, 6-31G*, 6-31G**, 6-31+G** and 6-311G*) and semi-empirical PM3 and AM1 methods. The molar volumes based on the isoelectron density contour were evaluated using a Monte Carlo integration scheme (model 1) and the integral equation formalism polarised continuum model (model 2). The densities were predicted subsequently. Excellent linear correlations were found between the results obtained with the two models, and different methods had little effect on the densities calculated using model 2. Quantitative relationships were established with the calculated and experimental densities of 25 azido compounds in the training set, and were used to predict the densities of five azido compounds in the testing set. The results obtained agree well with the experimental data, and model 2 gives a better result than model 1, with root mean square errors being 0.02 and 0.03 g cm− 3, respectively. Therefore, model 2 is a more reliable and convenient model to predict the densities of azido compounds. This approach is believed to be applicable to other kinds of compounds too.

Density of electronic states and dispersion of optical functions of defect chalcopyrite CdGa2X4 (X = S, Se): DFT study

A density functional theory (DFT) based on full potential linear augmented plane wave (FPLAPW) was used for calculating the electronic structure, charge density and optical properties of CdGa2X4 (X=S, Se) compounds. Local density approximation (LDA), generalized gradient approximation (GGA), Engle Vasko generalized gradient approximation (EVGGA) and recently modified Becke–Johnson (mBJ) were applied to calculate the band structure, total and partial density of states. The investigation of band structures and density of states of CdGa2X4 (X=S, Se) elucidate that mBJ potential show close agreement to the experimental results. The mBJ potential was selected for further explanation of optical properties of CdGa2X4 (X=S, Se). The study of electronic charge density contours shows that change in the bond lengths and bond nature affect the band gap of the compounds. The two non-zero dielectric tensor components and its derivatives show considerable anisotropy between the perpendicular and parallel components. The present work provide accurate information about the combination (hybridization) of orbital, formation of bands and dispersion of non-zero tensor components of CdGa2X4 (X=S, Se).

First-principles study of the electronic structure, charge density, Fermi surface and optical properties of zintl phases compounds Sr2ZnA2 (A=P, As and Sb)

We present first-principles calculations of the electronic structure, Fermi surface, electronic charge density and optical properties of Sr2ZnA2 (A=P, As and Sb) based on density-functional theory using the local density approximation (LDA), generalized-gradient approximation (GGA) and the Engel–Vosko GGA formalism (EV-GGA). Additionally, modified Becke–Johnson (mBJ) is also used to improve the band splitting results. The calculated band structure and density of states show that Sr2ZnA2 compounds are metallic. The total DOS at Fermi level N(EF) is 72.92, 73.06 and 33.47 states/eV and the bare electronic specific heat coefficient (γ) is 12.64, 5.805 and 12.67mJ/mol-K2 for Sr2ZnP2, Sr2ZnAs2 and Sr2ZnSb2, respectively. The Fermi surface of Sr2ZnA2 compounds is composed of two bands crossing along the Γ−A direction of Brillouin zone. There exists a strong hybridization between Zn-p/s and Sb-d, Sb-p and Sr-d and also between Sr-s and Sr-p states. The bonding features are analyzed by using the electronic charge density contour in the (101) crystallographic plane. We found that Sr forms an ionic bond with Zn, whereas Zn forms a strong covalent interaction with P/As/Sb atoms. For further insight information about the electronic structure, the optical properties are derived and analyzed.

Theoretical study of photophysical properties of 1,4-dihydropyrrolo[3,2-b]pyrrole-cored branched molecules with thienylenevinylene arms toward broad absorption spectra for solar cells

A series of oligo(thienylenevinylene) derivatives with 1,4-dihydropyrrolo[3,2-b]pyrrole as core has been investigated at the PBE0/6-31G(d) and the TD-PBE0/6-31+G(d,p) levels to design materials with high performances such as broad absorption spectra and higher balance transfer property. The results show that position and amount of arm affect the electronic density contours of frontier molecular orbitals significantly. The molecule with four arms owns the narrowest energy gap and the largest maximum absorption wavelength, and the molecule with two arms in positions a and c has the broadest absorption region among the designed molecules. Calculated reorganization energies of the designed molecules indicate that the molecules with two arms can be good potential ambipolar transport materials under proper operating conditions.

Sol–gel synthesis, crystal structure, electronic properties and magnetic studies of B2+xAsxCo4−3xO7 (0.0 ≤ x ≤ 0.75) composites

Synthesis of B2+xAsxCo4−3xO7 (S1–S4: x = 0.0, 0.25, 0.50 and 0.75) composite oxides were performed by sol–gel method. The powder X-ray diffraction pattern and Reitveld refinement results revels that the samples are formed monoclinic phase with Z = 2 and space group P21/m. Average crystallite size of the samples determined by Scherrer’s relation are found to be ~28–50 nm. The observed and calculated density values are determined and compared. Thermogram shows no phase transition in the range of 50–1,000 °C. The scanning electron micrographs show the morphology of the samples which are observed, the crystallites are rod like shape. The purity and the quantitative analysis were examined by the energy dispersive X-ray. The B–O and Co–O bonds of different sites show marginal variation in the samples, the circular valence charge density contour map of the Co and O in S1–S4 show partial covalent nature of Co–O. Based on the plane-wave density functional theory calculations on crystal structure for band structure and density of states of sample S1–S4 using CASTEP programme package show all the samples are conductor with no band gap. The magnetic moment plot in the range ±10 kG indicates the weak ferromagnetic behavior of the samples. The electron paramagnetic resonance line shapes of all four (S1–S4) samples are isotropic, Diffuse reflectance spectra of sample S1–S4 at room temperature show the band around 273 nm is ligand to metal (O2− → Co2+) charge transfer transition and d–d transition around 570 nm, respectively.

Comparative foraging behaviour of sympatric Humboldt and Magellanic Penguins reveals species-specific and sex-specific strategies

How closely related marine organisms mitigate competition for resources while foraging at sea is not well understood, particularly the relative importance of interspecific and intraspecific mitigation strategies. Using location and time—depth data, we investigated species-specific and sex-specific foraging areas and diving behaviour of the closely related Humboldt (Spheniscus humboldti) and Magellanic (S. magellanicus) Penguins breeding in sympatry at Islotes Puñihuil in southern Chile during the chick-rearing period. The average duration of foraging trips was <20 h and did not differ significantly between species or between sexes of each species. Magellanic Penguins made significantly deeper and longer dives than Humboldt Penguins. Males of both species made significantly longer dives than females. Total distance travelled per foraging trip was significantly greater for males than for females, and females made more direct trips (less sinuous) than males. Foraging effort was concentrated in waters up to 15 km to the west and south-west of the colony. The overlap in density contours was lower between species than between sexes within a species. In general, dive characteristics and foraging areas differed more between Magellanic and Humboldt Penguins than between the sexes of each species. In contrast to the findings of studies of flying seabirds, the foraging behaviour of these penguins differs more between species than between sexes.

Numerical and experimental study of steam‐water two‐phase flow through steam jet pump

ABSTRACTThe Steam Jet Pump (SJP) is the most suitable pump for pumping radioactive and hazardous liquids because of its mechanical simplicity, no maintenance, low cost, easy construction, no leakage, simple control, and so on. The only problem with the SJP is the complexity in the transport phenomena involved in it. In this study, the void fraction in the mixing section has been measured experimentally through gamma‐ray densitometry technique, and the flow through the SJP was simulated numerically. The reported numerical study of the SJP is very limited because of the complexity of the problem. In this work, three‐dimensional steady state numerical simulations of the SJP were carried out using the Shah Direct‐Contact Condensation (DCC) model developed previously. The experimental and Computational Fluid Dynamics (CFD) results of void fraction have been compared at different steam inlet pressure, and it was found that they match closely with each other. The transport phenomena in the SJP were explained using the CFD results of condensation heat transfer coefficient, steam plume shape, radial temperature distributions, and contours of static pressure and steam density. This study helps in validating the Shah direct‐contact condensation model and providing valuable information about the transport phenomena occurring within the mixing section of the SJP. © 2013 Curtin University of Technology and John Wiley &amp; Sons, Ltd.

Directional recording of swell from distant storms

Almost fifteen years ago in the pages of this Journal, one of us presented power spectra of ocean waves and swell off Pendeen and Perranporth in north Cornwall (Barber & Ursell 1948). The outstanding feature of these spectra is the successive shift of peaks toward higher frequencies. This is the expected behaviour of dispersive wave trains from rather well-defined sources. Storms generate a broad spectrum of frequencies; the low frequencies are associated with the largest group velocity and accordingly are the first to arrive at distant stations. The time rate of increase in the frequency of peaks determines the distance and time of origin. In this way Barber & Ursell were able to identify the dispersive arrivals with a low pressure area in the North Atlantic, a tropical storm off Florida, and a storm off Cape Horn, at distances of 1200, 2800, and 6000 miles, respectively, from the Cornish stations. The measurements were consistent with the simple classical result that each frequency,/, is propagated with its appropriate group velocity, V = g/(47[/*). The present study is in a sense a refinement to the work of Barber & Ursell. The frequency resolution and sensitivity have each been increased by an order of m agnitude, and this makes it possible to detect and resolve meteorological sources that have previously been out of reach. The antipodal swell from the Indian Ocean is a case in point

Gag (Mycteroperca microlepis) space-use correlations with landscape structure and environmental conditions

To explore variation in space use under different environmental conditions, we acoustically tagged gag (Mycteroperca microlepis) established on experimental artificial reefs in the Gulf of Mexico and used an acoustic positioning array to record animal positions during the winters of 2007 and 2008. From side-scan sonar imagery, we created a categorical habitat map of the hard- and sand-bottom habitats surrounding the reef. We recorded water conditions using an Acoustic Doppler Current Profiler. Correlations between gag space use (distance from the reef, distance from the seafloor, and travel speed) and environmental conditions (bottom type, time of day, lunar phase, and water temperature, speed and flow direction) showed gag typically using space near, but not directly at the reef. The 50% and 95% kernel density contours fell within 17 and 39m of the reef, respectively, though gag spent the most time about 10m from the reef. All individuals made occasional excursions beyond their primary space-use areas. Gag spent 86% of the time within 2.5m of the seafloor, with periods of frequent or extended movement up to 9m from the seafloor, usually near the reef. On average, gag moved about 25% farther from the reef during the day; correlations with other environmental conditions were weak or unclear. In all cases, variation in space-use among individuals or of particular individuals over time was greater than the variability explained by changing environmental conditions.

Counter effects of meridional flows and magnetic fields in stationary axisymmetric self-gravitating barotropes under the ideal MHD approximation: clear examples – toroidal configurations

We obtain the general forms for the current density and the vorticity from the integrability conditions of the basic equations which govern the stationary states of axisymmetric magnetized self-gravitating barotropic objects with meridional flows under the ideal magnetohydrodynamics (MHD) approximation. As seen from the stationary condition equations for such bodies, the presence of the meridional flows and that of the poloidal magnetic fields act oppositely on the internal structures. The different actions of these two physical quantities, the meridional flows and the poloidal magnetic fields, could be clearly seen through stationary structures of the toroidal gaseous configurations around central point masses in the framework of Newtonian gravity because the effects of the two physical quantities can be seen in an amplified way for toroidal systems compared to those for spheroidal stars. The meridional flows make the structures more compact, i.e. the widths of toroids thinner, while the poloidal magnetic fields are apt to elongate the density contours in a certain direction depending on the situation. Therefore, the simultaneous presence of the internal flows and the magnetic fields would work as if there were no such different actions within and around the stationary gaseous objects such as axisymmetric magnetized toroids with internal motions around central compact objects under the ideal MHD approximation, although these two quantities might exist in real systems.