Density Contours Research Articles

Velocity gradient in Kelvin-Helmholtz instability for supersonic fluid

Two-dimensional numerical calculations using weighted essentially non-oscillatory schemes （WENO） scheme were performed to study velocity gradient in the Kelvin-Helmholtz （KH） instability for supersonic fluid. It is found that the velocity gradient has a stabilization effect on the KH instability for supersonic fluid, and the linear growth rate empirical formula with velocity gradient stabilization effect is deduced. The empirical formula with velocity gradient stabilization effect agrees well will the simulation results. The sharp density contour is obtained, which indicates that the WENO finite difference scheme has good capturing ability in interface deformation. The evolution of KH vortex is influenced by the velocity gradient. When the density gradient is fixed, it is found that the larger the velocity gradient the smaller the transverse scale of the KH vortex.

The Mechanism of Generation of May 12, 2008 MS8.0 Wenchuan Earthquake

AbstractIn this paper, the 3‐D finite element method combined with discontinuous deformation analysis (DDA + FEM) is used with the constraints of 3‐D tectonic blocks of Qinghai‐Tibet Plateau and neighboring areas to study the gestation mechanism of the Wenchuan earthquake on 12 May 2008. The topography on both sides of the Longmen Shan fault zone, the remarkable change in thickness of the crust and its layers, and the influence of a stronger crust in the Sichuan Basin and Ordos block on the eastern side of the fault zone are taken into consideration. With the GPS data as constraints on the boundary, the calculated velocity and stress fields agree with the GPS measurements and the focal mechanisms. On this basis, the distribution of risk factors on the boundary faults of tectonic blocks, which characterize overall influences of shear stress and normal stress on fault plane etc., is calculated numerically. The results show that the sections with high risk factors coincide with the areas where most of the MS > 7.0 earthquakes have occurred in recent decades, including the MS=8.0 Wenchuan earthquake in 2008. Trial computation of situations of two different structures on both east and west side of the Longmen Shan fault zone show that significant changes of the topography on both sides, the thickness and the layers of the crust, and the physical properties played important roles in the gestation mechanism of theWenchuan earthquake. The calculated distribution maps of strain intensity show that the eastern edges of Qinghai‐Tibet Plateau are close to the strain intensity steep change zone. Of the zones with steep change in strain intensity in eastern edge of the plateau, Longmen Shan fault zone shows the steepest change. The intensity contour on the east side of the fault zone decay faster than the west side. In addition, the calculated strain energy density contours show that the Longmen Shan fault zone is located a high strain energy density band with the same width and direction as the fault in the upper and middle crust. In the upper crust, low strain energy density is found on both sides of the fault. In the middle crust, the strain energy density decreases from west to east: the western side has high strain energy density, the eastern side has low strain energy density. Our results show that under strong subduction of the Indian plate, constraints of 3D tectonic blocks in the Qinghai‐Tibetan Plateau and influence of special tectonic environment on the western and eastern sides of the Longmen Shan fault zone, the seismic fault area, where the Wenchuan earthquake occurred, had accumulated sufficient strain energy. It indicates that the area is in a mechanically unstable state.

Numerical study of flow field visualizations over a payload shroud at transonic speeds

The article presents a flow field visualization study on a typical payload shroud at transonic Mach numbers range. The numerical simulation over the heat shield is carried out by solving axisymmetric, turbulent, compressible, Reynolds-averaged Navier—Stokes equations. The closure of these equations is achieved using the Baldwin—Lomax turbulence model. The density contour plots are obtained at Mach number 0.80, 0.90, 0.95, and 1.0. The transonic flow field features over the heat shield are captured and compared with the schlieren pictures, and good matching between them is exhibited. The movement of the terminal shock is found to be a non-linear function of freestream Mach number. The location of the shock on the heat shield is also confirmed with the flight data. The numerical studies have shown that the reliable estimation of the transonic flow field can be made in conjunction with the flow visualization technique.

Exact potential-density pairs for flattened dark haloes

Cosmological simulations suggest that dark matter haloes are not spherical, but typically moderately to strongly triaxial systems. We investigate methods to convert spherical potential-density pairs into axisymmetric ones, in which the basic characteristics of the density profile (such as the slope at small and large radii) are retained. We achieve this goal by replacing the spherical radius r by an oblate radius m in the expression of the gravitational potential. We extend and formalize the approach pioneered by Miyamoto & Nagai (1975) to be applicable to arbitrary potential-density pairs. Unfortunately, an asymptotic study demonstrates that, at large radii, such models always show a R^(-3) disc superposed on a smooth roughly spherical density distribution. As a result, this recipe cannot be used to construct simple flattened potential-density pairs for dynamical systems such as dark matter haloes. Therefore we apply a modification of our original recipe that cures the problem of the discy behaviour. An asymptotic analysis now shows that the density distribution has the desired asymptotic behaviour at large radii (if the density falls less rapidly than r^(-4)). We also show that the flattening procedure does not alter the shape of the density distribution at small radii: while the inner density contours are flattened, the slope of the density profile is unaltered. We apply this recipe to construct a set of flattened dark matter haloes based on the realistic spherical halo models by Dehnen & McLaughlin (2005). This example illustrates that the method works fine for modest flattening values, whereas stronger flattening values lead to peanut-shaped density distributions.

EM 3D contour maps provide protein assembly at the nanoscale within the neuronal porosome complex.

The neuronal porosome complex, the secretory machinery at the plasma membrane of nerve terminals, is a 12-17-nm cup-shaped lipoprotein structure possessing a central plug. Since the porosome is a membrane associated, multi-protein complex measuring >650 kD, it has precluded generation of 3D crystals for x-ray diffraction studies, nor structural analysis at the atomic level using solution magnetic resonance spectroscopy. These limitations were partially overcome in the current studies, furthering our understanding of the porosome structure. Using atomic force microscopy, electron microscopy and electron density and 3D contour mapping, finally provides at the nanoscale, the structure and assembly of proteins within the neuronal porosome complex. Results from this study demonstrate a set of eight protein units lining the porosome cup, each connected via spoke-like elements to a central plug region within the structure. The isolation of intact porosomes for near-atomic resolution using cryo-electron diffraction measurements, is finally possible.

Investigations of the CN/Cu(1 1 1) system using density functional theory

The geometry, CN–CN interaction and surface bond strength and structure of the CN–Cu(1 1 1) system has been investigated using LCAO-DFT. The lowest energy adsorption sites for perpendicularly oriented, C down CN has been shown to be threefold with a slight preference for the fcc site. The binding energies for the two and threefold sites have been shown to lie in the range 1.441–1.574 eV. Studies of the electron density contours have shown an enhancement of charge in the σ-bond and a depletion of charge in the π-bond for binding in the fcc, hcp and twofold sites. A similar charge distribution is seen for CN groups bound in tilted orientations though at lower binding energies. For both the perpendicular and tilted orientations the Cu atoms closest to the C atom are seen to undergo nominal out of plane displacements of −0.02 to 0.08 Ǻ accompanied by an internal repolarization of their charge. An estimate of the lateral interaction strength of between 8.3% and 9.6% of the CN-surface binding energy for each high symmetry binding position has been obtained for perpendicular bound CN. The estimated energy differences due to lateral effects estimated with DFT are energetically comparable to the reported energy differences between perpendicular and parallel adsorption structures for CN. Thus, very subtle effects that may be beyond the accuracy of DFT may determine the actual geometry in this system, which should not be addressed without also considering lateral interactions via unit cell size.

Electronic and magnetic properties of digitally Ti doped InP: A first principles study

AbstractUsing the full‐potential linearized augmented plane wave method within the generalized gradient approximation, we study the electronic and the magnetic properties of digitally Ti doped InP. It is quite interesting that digitally Ti‐doped InP system shows half metallic ferromagnetism even though both bulk zinc blende TiP and InP are paramagnetic. We also investigate the electronic and the magnetic properties as a function of spacer layer thickness. Their properties such as exchange coupling constant and atomic projected density of states are more or less independent of the InP thickness. Spin density contour maps indicate that the spin‐polarization is confined within the TiP plane. The system may show a highly anisotropic property in spin‐polarized transport. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Sequential and global optimization in powder injection molding processing

The work is focused on the overall optimization associated to powder injection molding (PIM). The PIM process includes four main stages, from the mixture of the powders and binders to the final sintering stage. Injection and sintering stages are considered to be the most important for optimization, as they mostly affect the final quality of the produced components. The injection stage shapes the green parts but initiates powders segregation that will be inherited and amplified by the sintering stage to finally appear in the resulting products. One first introduces an optimization loop based on the surfaces response method to minimize the powder segregation. Then the results are transferred to a sintering optimization loop applied through an experimentally calibrated thermo-mechanical creep model to predict the shrinkage and density contours on the final parts. The overall optimization combines both optimizers based on the developed simulation tools to provide a realistic way to improve the PIM process design accounting the different processing stages.

Helices of Boron−Nitrogen Hexagons and Decagons. A Theoretical Study

Ab initio self-consistent field molecular orbital and density functional theory calculations have been performed on a series of helical boron-nitrogen structures comprised of fused hexagons and larger polygons. The presence of an even number N of rings in the boron-nitrogen [N]helicenes leads to the possibility of angular isomers. The electronic structure and stability of three isomeric nonhydrogenated boron-nitrogen helices were investigated at the HF/6-31G(d) and the B3LYP/6-31G(d) levels of theory. According to this study some of the initially assumed regular helical structures are unstable; two types of the isomeric structures convert to characteristically different equilibrium geometries. Electron density contours were calculated in order to interpret the existing bonding patterns.

Quantum vortices within the complex quantum Hamilton–Jacobi formalism

Quantum vortices are investigated in the framework of the quantum Hamilton-Jacobi formalism. A quantum vortex forms around a node in the wave function in the complex space, and the quantized circulation integral originates from the discontinuity in the real part of the complex action. Although the quantum momentum field displays hyperbolic flow around a node, the corresponding Polya vector field displays circular flow. It is shown that the Polya vector field of the quantum momentum function is parallel to contours of the probability density. A nonstationary state constructed from eigenstates of the harmonic oscillator is used to illustrate the formation of a transient excited state quantum vortex, and the coupled harmonic oscillator is used to illustrate quantization of the circulation integral in the multidimensional complex space. This study not only analyzes the formation of quantum vortices but also demonstrates the local structures for the quantum momentum field and for the Polya vector field near a node of the wave function.

A Suprime-Cam study of the stellar population of the Ursa Major I dwarf spheroidal galaxy

We present deep and wide V , I CCD photometry of the Ursa Major I (UMa I) dwarf spheroidal galaxy (dSph) in the Local Group. The images of the galaxy were taken with the Subaru/Suprime-Cam wide field camera, covering a field of 34´ $\times$ 27´ located at the centre of the galaxy. The colour-magnitude diagram (CMD) of the UMa I dSph shows a steep and narrow red giant branch (RGB), blue and red horizontal branch (HB), and main sequence (MS) stars. A well-defined main sequence turn-off (MSTO) is found to be located at $V_{0,\rm MSTO}$ ~ 23.5 mag. The distance modulus is derived as $(m-M)_0$ = 19.93 ± 0.1 (corresponding to a distance D = 96.8 ± 4 kpc) from the V -band magnitude of the horizontal branch ($V_{0,\rm HB}$ = 20.45 ± 0.02). The mean metallicity of the RGB stars is estimated by the $V-I$ colour as [Fe/H] ~ -2.0. The turn-off age estimated by overlaying the theoretical isochrones reveals that most of stars in the UMa I dSph are formed at a very early epoch (~12 Gyr ago). The isopleth map of stellar number density of the UMa I dSph, based upon the resolved star counts of MS, RGB, HB stars as well as blue stragglers (BS), shows that the morphology of the UMa I dSph is quite irregular and distorted, suggesting that the galaxy is in a process of disruption. The very old and metal-poor nature of the stellar population implies that the star formation history of this newly discoverd faint dSph may have been different from other well-known “classical” dSphs, which show significant stellar populations of intermediate age. The stellar population of the UMa I dSph closely resembles that of Galactic old metal-poor globular clusters, but its size is typical of Galactic dSphs ( r e = 188 [pc], $r_{1/2}$ = 300 [pc]), and the shape of its spatial density contours suggests that it is undergoing tidal disruption. These characteristics of stellar population and spatial distribution of the faint galaxies help us to understand how they formed and evolved, and give a hint to the nature of the building blocks of hierarchical galaxy formation.

First-principles study of the mechanical properties of NiAl microalloyed by M (Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd)

Structural, electronic and elastic properties for NiAl with 4d alloying elements M (Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd) have been studied using the first-principles pseudopotential density functional method within a generalized gradient approximation. From the elastic constants, C11, C12, C44, bulk modulus B0, Young's modulus E, the shear modulus G, the ratios of shear modulus to bulk modulus G/B0, negative Cauchy pressure parameter (C12 − C44) and Poisson's ratio ν calculated after structural full relaxation, M (Tc, Ru, Rh, Pd) alloying addition in NiAl has been shown to increase the stiffness of NiAl and improve its ductility. The density of states and charge density contour involving alloying additions of Ru were further investigated to clarify the electronic causes of the alloying additions.

Theoretical Study on the Structure and Stability of Some Unusual Boron−Nitrogen Helices

Ab initio self-consistent field molecular orbital and density functional theory calculations have been performed on a series of helical structures comprised of boron-nitrogen analogues of extended helicenes, with helically arranged N fused benzene rings, and alternating N benzene units fused to N - 1 cyclobutadiene rings as reference structures. The electronic structure and stability of boron-nitrogen analogues of angular [N]helicenes, [N]phenylenes (N = 5, 6, 7, 12), and [N]methylenylnaphthalenes (N = 6) were investigated at the HF/6-31G(d) and the B3LYP/6-31G(d) levels of theory. The presence of an even number N of rings in the boron-nitrogen [N]helicenes leads to the possibility of angular isomers. Electron density contours were calculated in order to interpret the existing bonding patterns. These structures may provide supramolecular building blocks and macromolecular "springs" with unusual electronic properties.

Human neural stem cells migrate along the nigrostriatal pathway in a primate model of Parkinson's disease

Although evidence of damage-directed neural stem cell (NSC) migration has been well-documented in the rodent, to our knowledge it has never been confirmed or quantified using human NSC (hNSC) in an adult non-human primate modeling a human neurodegenerative disease state. In this report, we attempt to provide that confirmation, potentially advancing basic stem cell concepts toward clinical relevance. hNSCs were implanted into the caudate nucleus (bilaterally) and substantia nigra (unilaterally) of 7, adult St. Kitts African green monkeys ( Chlorocebus sabaeus) with previous exposure to systemic 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), a neurotoxin that disrupts the dopaminergic nigrostriatal pathway. A detailed quantitative analysis of hNSC migration patterns at two time points (4 and 7 months) following transplantation was performed. Density contour mapping of hNSCs along the dorsal–ventral and medial–lateral axes of the brain suggested that > 80% of hNSCs migrated from the point of implantation to and along the impaired nigrostriatal pathway. Although 2/3 of hNSCs were transplanted within the caudate, < 1% of 3 × 10 6 total injected donor cells were identified at this site. The migrating hNSC did not appear to be pursuing a neuronal lineage. In the striatum and nigrostriatal pathway, but not in the substantia nigra, some hNSCs were found to have taken a glial lineage. The property of neural stem cells to align themselves along a neural pathway rendered dysfunctional by a given disease is potentially a valuable clinical tool.

Prediction of Dislocation Cores in Aluminum from Density Functional Theory

The strain field of isolated screw and edge dislocation cores in aluminum are calculated using density-functional theory and a flexible boundary condition method. Nye tensor density contours and differential displacement fields are used to accurately bound Shockley partial separation distances. Our results of 5-7.5 A (screw) and 7.0-9.5 A (edge) eliminate uncertainties resulting from the wide range of previous results based on Peierls-Nabarro and atomistic methods. Favorable agreement of the predicted cores with limited experimental measurements demonstrates the need for quantum mechanical treatment of dislocation cores.

Sequential and global optimization in powder injection molding processing

The work is focused on the overall optimization associated to powder injection molding (PIM). The PIM process includes four main stages, from the mixture of the powders and binders to the final sintering stage. Injection and sintering stages are considered to be the most important for optimization, as they mostly affect the final quality of the produced components. The injection stage shapes the green parts but initiates powders segregation that will be inherited and amplified by the sintering stage to finally appear in the resulting products. One first introduces an optimization loop based on the surfaces response method to minimize the powder segregation. Then the results are transferred to a sintering optimization loop applied through an experimentally calibrated thermo-mechanical creep model to predict the shrinkage and density contours on the final parts. The overall optimization combines both optimizers based on the developed simulation tools to provide a realistic way to improve the PIM process des...

Spatial distribution of the wave field of the surface modes sustaining filamentary discharges

The study presents the electrodynamical description of surface-wave-sustained discharges contracted in filamentary structures. The results are for the spatial distribution of the wave field and for the wave propagation characteristics obtained from a two-dimensional model developed for describing surface-wave behavior in plasmas with an arbitrary distribution of the plasma density. In accordance with the experimental observations of filamentary discharges, the plasma density distribution considered is completed by cylindrically shaped gas-discharge channels extended along the discharge length and positioned in the out-of-center region of the discharge, equidistantly in an azimuthal direction. Due to the two-dimensional inhomogeneity of the plasma density of the filamentary structure, the eigen surface mode of the structure is a hybrid wave, with all—six—field components. For identification of its behavior, the surface wave properties in the limiting cases of a plasma ring and a single filament—both radially inhomogeneous—are involved in the discussions. The presentation of the results is for filamentary structures with a decreasing number of filaments (from 10 to 2) starting with the plasma ring, the latter supporting propagation of an azimuthally symmetric wave. Due to the resonance absorption of the surface waves, always present because of the smooth variation of the plasma density, the contours of the critical density are those guiding the surface wave propagation. Decreasing number of filaments in the structure leads to localization of the amplitudes of the wave-field components around the filaments. By analogy with the spatial distribution of the wave field in the plasma ring, the strong resonance enhancement of the wave-field components is along that part of the contour of the critical density which is far off the center of the filamentary structure. The analysis of the spatial distribution of the field components of the filamentary structure shows that the hybrid wave is an eigenmode of the whole structure, i.e., the wave field does not appear as a superposition of fields of eigenmodes of the separated filaments completing it. It is stressed that the spatial distribution of the field components of the eigen hybrid mode of the filamentary structure has an azimuthally symmetric background field.

An ion thruster internal discharge chamber electrostatic probe diagnostic technique using a high-speed probe positioning system

Extensive resources have been allocated to diagnose and minimize lifetime-limiting factors in gridded ion thrusters. While most of this effort has focused on grid erosion, results from wear tests indicate that discharge cathode erosion may also play an important role in limiting the lifetime of ring-cusp ion thrusters proposed for future large flagship missions. The detailed characterization of the near-cathode discharge plasma is essential for mitigating discharge cathode erosion. However, severe difficulty is encountered when attempting to measure internal discharge plasma parameters during thruster operation with conventional probing techniques. These difficulties stem from the high-voltage, high-density discharge cathode plume, which is a hostile environment for probes. A method for interrogating the discharge chamber plasma of a working ion thruster over a two-dimensional grid is demonstrated. The high-speed axial reciprocating probe positioning system is used to minimize thruster perturbation during probe insertion and to reduce heating of the probe. Electrostatic probe measurements from a symmetric double Langmuir probe are presented over a two-dimensional spatial array in the near-discharge cathode assembly region of a 30-cm-diameter ring-cusp ion thruster. Electron temperatures, 2-5 eV, and number density contours, with a maximum of 8 x 10(12) cm(-3) on centerline, are measured. These data provide detailed electron temperature and number density contours which, when combined with plasma potential measurements, may shed light on discharge cathode erosion processes and the effect of thruster operating conditions on erosion rates.

Integrated Sensing and Processing Acoustic Resonance Spectrometry (ISP-ARS) for Sample Classification

This research introduces a novel process analytical technique, integrated sensing and processing acoustic resonance spectrometry (ISP-ARS), and compares ISP-ARS with conventional full-spectrum ARS for the characterization of solid fuel premixes used in a new pill safe designed to protect narcotics. In ISP-ARS, the acoustic excitation waveform is the analog implementation of the chemometric weight function, encoded for this work on an MP3 player and used to distinguish between fuel samples, sparing post-collection multivariate computation. In effect, the detector directly outputs the sample identity. Repeated measurements of batches of similar fuel mixtures over time produce an automatic projection of similar spectra into corresponding three-dimensional probability density contours, thus, forming the analyte classification directly. For the characterization of ten different fuel mixtures, full spectral ARS resulted in a median intermixture distance in multidimensional standard deviations (MSDs) of 185.1, while ISP-ARS resulted in a median MSD distance of 81.3. The median cross-validation MSD was 1.41 for the ARS and 1.58 for the ISP-ARS. Distances in MSDs greater than three are considered separable, and MSDs less than three are indistinguishable. The classification procedure correctly identified all samples for both analytical techniques. ISP-ARS is an effective, simpler, and more rapid alternative to full spectrum ARS that can be implemented with a commercial MP3 player and used as an inexpensive spectrometric sensor for dynamic data-driven application simulations (DDDAS) and process analytical applications.

Computational modeling of environmental plutonyl mono-, di- and tricarbonate complexes with Ca counterions: Structures and spectra: [formula omitted], PuO 2(CO 3) 2Ca, and PuO 2(CO 3) 3Ca 3

We have computed the structures, and select vibrational spectra, electron density and molecular orbital contour plots of plutonium(VI) complexes of environmental importance such as [PuO 2(CO 3) 2] 2− and [PuO 2(CO 3) 3] 4−. We show that Ca 2+ is efficacious in gas-phase modeling of electronic and spectroscopic properties of multiply charged plutonyl di and tricarbonate anions through complexes such as PuO 2(CO 3) 2Ca and [PuO 2(CO 3) 3Ca 3] 2+.