Excess Velocity Research Articles

Innovative Method Using Magnetic Particle Tracking to Measure Solids Circulation in a Spouted Fluidized Bed

We describe an innovative method for measuring particle motion inside spouted fluidized beds. The method uses a magnetic tracer particle, which follows the bulk particle flow and is continuously tracked by multiple magnetic field detectors located outside the bed. We analyze signals from the detectors to determine the tracer position at each instant in time. From statistical analysis of the tracer trajectory, characteristic measures of the bulk particle flow, such as the average recirculation frequency, can be determined as a function of operating conditions. For experiments with a range of particle sizes and densities in a 3.9-cm-diameter spouted bed, we find that average solids recirculation rates correlate with excess velocity (superficial minus minimum spouting velocity), particle density, and bed depth.

Friction velocity and aerodynamic roughness of conventional and undercutter tillage within the Columbia Plateau, USA

Friction velocity ( u * ) and aerodynamic roughness ( z o ) at the soil–plant–atmosphere interface affect wind erosion, but no attempts have been made to quantify these parameters as affected by tillage systems within the Columbia Plateau region of the Pacific Northwest United States. Wind velocity profiles above adjacent field plots (>2 ha), with plots subject to conventional or undercutter tillage during the summer fallow phase of a winter wheat–summer fallow rotation, were measured over 50 high wind events (wind velocities in excess of 6.4 m s −1 at a height of 3 m) during 2005 and 2006 near Lind, Washington to determine u * and z o of tillage treatments. Wheat stubble plots were subject to either conventional (disks) or undercutter (wide V-shaped blades) tillage in spring and then periodically rodweeded prior to sowing winter wheat in late summer. Prior to sowing, u * for conventional and undercutter tillage respectively averaged 0.36 and 0.46 m s −1 in 2005 and 0.38 and 0.40 m s −1 in 2006 while z o for conventional and undercutter tillage respectively averaged 2 and 7 mm in 2005 and 2 and 4 mm in 2006. The aerodynamically rougher surface of undercutter tillage was predicted to suppress vertical dust flux; this was collaborated with observations in the field where undercutter tillage reduced dust flux as compared with conventional disk tillage. Undercutter tillage, therefore, appears to be an effective management practice to roughen the surface and thereby suppress dust emissions from agricultural land subject to summer fallow within the Columbia Plateau.

Grain boundary diffusion patterns under nonequilibrium and migration of grain boundaries in nanoctructure materials

In this work, the model of grain boundary diffusion from a permanent source along nonequilibrium migratory grain boundaries is considered. Grain boundary nonequilibrium is characterized by a value of boundary excess energy up to which relaxation goes. It is shown increasing excess energy and migration velocity of nonequilibrium boundaries lead to increasing diffusant volume penetrating into a sample during annealing time.

The Structure of AGNs from X-Ray Absorption Variability

AbstractWe present new evidence of X-ray absorption variability on time scales from a few hours to a few days for several nearby bright AGNs. The observed NH variations imply that the X-ray absorber is made of clouds eclipsing the X-ray source with velocities in excess of 103 km s−1, and densities, sizes and distances from the central black hole typical of BLR clouds. We conclude that the variable X-ray absorption is due to the same clouds emitting the broad emission lines in the optical/UV. We then concentrate on the two highest signal-to-noise spectra of eclipses, discovered in two long observations of NGC 1365 and Mrk 766, and we show that the obscuring clouds have a cometary shape, with a high density head followed by a tail with decreasing NH. Our results show that X-ray time resolved spectroscopy can be a powerful way to directly measure the physical and geometrical properties of BLR clouds.

Ultrasonic and spectroscopic investigations of charge-transfer complexes in ternary liquid mixtures

Charge-transfer complexes formed between iodine ( σ-acceptor) and pyrrole, thiophene and pyridine ( π as well as n-electron donors) have been studied spectrophotometric and ultrasonic techniques at 303.15 K in dimethyl sulphoxide medium. The measured values of ultrasonic velocity, density and viscosity and the derived acoustical parameters such as adiabatic compressibility ( κ), free length ( L f), internal pressure ( π i), molar volume ( V m) and available volume ( V a) have been used to study the molecular interactions and the complexes of heterocyclic aromatic compounds. The excess thermodynamic parameters like excess velocity ( u E), excess adiabatic compressibility ( κ E), excess free length ( L f E), excess molar volume ( V m E) and excess available volume ( V a E) have been computed and the sign and magnitude of these parameters indicate the strength of interactions and the formation of charge-transfer complex. The formation constants of the charge-transfer complexes were determined by the Benesi–Hildebrand equations (optical method) and compared with those obtained from Kannappan method (ultrasonic method). The formation constants of complexes of iodine with aromatic compounds depend on the structure of the donor and acceptor molecules.

Faint Lyman-break galaxies as a crucial test for galaxy formation models

It has recently been shown that galaxy formation models within the LambdaCDM cosmology predict that, compared to the observed population, small galaxies (with stellar masses < 10^{11} M_sun) form too early, are too passive since z ~ 3 and host too old stellar populations at z=0. We then expect an overproduction of small galaxies at z > 4 that should be visible as an excess of faint Lyman-break galaxies. To check whether this excess is present, we use the MORGANA galaxy formation model and GRASIL spectro-photometric + radiative transfer code to generate mock catalogues of deep fields observed with HST-ACS. We add observational noise and the effect of Lyman-alpha emission, and perform color-color selections to identify Lyman-break galaxies. The resulting mock candidates have plausible properties that closely resemble those of observed galaxies. We are able to reproduce the evolution of the bright tail of the luminosity function of Lyman-break galaxies (with a possible underestimate of the number of the brightest i-dropouts), but uncertainties and degeneracies in dust absorption parameters do not allow to give strong constraints to the model. Besides, our model shows a clear excess with respect to observations of faint Lyman-break galaxies, especially of z_{850} ~ 27 V-dropouts at z ~ 5. We quantify the properties of these "excess" galaxies and discuss the implications: these galaxies are hosted in dark matter halos with circular velocities in excess of 100 km s^{-1}, and their suppression may require a deep re-thinking of stellar feedback processes taking place in galaxy formation.

Velocity and concentration measurements in initial region of submerged round jets in stagnant environment and in coflow

Velocity and concentration fields are measured in submerged round jets in a stagnant environment and in coflow using laser Doppler anemometry and laser-induced fluorescence. Measurements are made in the initial region within distances of 40 jet exit diameter at jet Reynolds number between 1000 and 5000 and coflow-to-jet velocity ratio from 0 to 0.43. Different behaviors of jet spreading and dilution are found in jets at three different ranges of Reynolds number in which the jets are classified as initially laminar, transitional or turbulent. In the zone of established flow, the jet centerline velocity and concentration decay with downstream distance at different rates in the three groups of jets. For jets in coflow, axial development of normalized forms of centerline mean excess velocity and mean concentration at different velocity ratios can be reasonably well collapsed onto universal trends through the use of momentum length scale. Turbulence properties inside a jet are increased by the presence of a strong coflow. Inside the zone of flow establishment, some strange features are observed on jet turbulence properties. The length of zone of flow establishment increases from the turbulent jets, to the transition jets and to the laminar jets. The zone lengths for concentration are shorter than those for velocity by one to two jet exit diameters. Both lengths are shortened further in the presence of a coflow. For jets a stagnant environment and in the strong jet flow region of jets in coflow, jet widths increase linearly with downstream distance in transitional and turbulent jets. Self-similarity of radial profiles of mean velocity or excess velocity, mean concentration, turbulence intensities and concentration fluctuation level is explored in the zone of established flow.

Morphology and density structure of post-CME current sheets

<i>Context. <i/>Eruption of a coronal mass ejection (CME) drags and “opens” the coronal magnetic field, presumably leading to the formation of a large-scale current sheet and field relaxation by magnetic reconnection.<i>Aims. <i/>We analyze the physical characteristics of ray-like coronal features formed in the aftermath of CMEs, to confirm whether interpreting this phenomenon in terms of a reconnecting current sheet is consistent with observations. <i>Methods. <i/>The study focuses on measurements of the ray width, density excess, and coronal velocity field as a function of the radial distance.<i>Results. <i/> The morphology of the rays implies that they are produced by Petschek-like reconnection in the large-scale current sheet formed in the wake of CME. The hypothesis is supported by the flow pattern, often showing outflows along the ray, and sometimes also inflows into the ray. The inferred inflow velocities range from 3 to 30 km s<sup>-1<sup/>, and are consistent with the narrow opening-angle of rays, which add up to a few degrees. The density of rays is an order of magnitude higher than in the ambient corona. The density-excess measurements are compared with the results of the analytical model in which the Petschek-like reconnection geometry is applied to the vertical current sheet, taking into account the decrease in the external coronal density and magnetic field with height.<i>Conclusions. <i/>The model results are consistent with the observations, revealing that the main cause of the density excess in rays is a transport of the dense plasma from lower to higher heights by the reconnection outflow.

Momentum transport in electron-dominated NSTX spherical torus plasmas

The National Spherical Torus Experiment (NSTX) operates between 0.35 and 0.55 T, which, when coupled to up to 7 MW of neutral beam injection, leads to central rotation velocities in excess of 300 km s−1 and E × B shearing rates up to 1 MHz. This level of E × B shear can be up to a factor of five greater than typical linear growth rates of long-wavelength ion (e.g. ITG) modes, at least partially suppressing these instabilities. Evidence for this turbulence suppression is that the inferred diffusive ion thermal flux in NSTX H-modes is often at the neoclassical level, and thus these plasmas operate in an electron-dominated transport regime. Analysis of experiments using n = 3 magnetic fields to change plasma rotation indicate that local rotation shear influences local transport coefficients, most notably the ion thermal diffusivity, in a manner consistent with suppression of the low-k turbulence by this rotation shear. The value of the effective momentum diffusivity, as inferred from steady-state momentum balance, is found to be larger than the neoclassical value. Results of perturbative experiments indicate inward pinch velocities of up to 40 m s−1 and perturbative momentum diffusivities of up to 4 m2 s−1, which are larger by a factor of several than those values inferred from steady-state analysis. The inferred pinch velocity values are consistent with values based on theories in which low-k turbulence drives the inward momentum pinch. Thus, in NSTX while the neoclassical ion energy transport effects can be relatively high and dominate the ion energy transport, the neoclassical momentum transport effects are near zero, meaning that transport of momentum is dominated by any low-k turbulence that exists.

INERTIAL ALFVÉN WAVE ACCELERATION OF SOLAR FLARE ELECTRONS

The possibility that electrons could be accelerated by inertial Alfven waves to hard X-ray-emitting energies in the low solar corona during flares is investigated theoretically. This investigation is prompted in part by recent microwave observations indicating that the coronal magnetic field is strong enough that the Alfven velocity cA above active regions could be of the order of a tenth of the speed of light or more; electrons can be accelerated to velocities in excess of cA on collisionless timescales via reflection by a single inertial Alfven wave pulse. It is shown that the fraction of particles accelerated is a sensitive function of the initial electron temperature and the transverse length scale δx of the shear Alfven wave pulse; under typical pre-flare coronal conditions, a significant fraction of the electron population can be accelerated if δx is of the order of a few meters or less.

Wide-Beam X-Ray Source Target Thermal Management Simulation Using Inner Jet Cooling

A wide-beam area X-ray source has been proposed as a practical replacement for synchrotron sources in clinical DEI applications. Due to a wide X-ray illumination area, a decrease in X-ray flux is expected and thus high electron beam currents up to 3A are considered. To ensure the target performance without deterioration, melting, cracking, or even evaporation, an active cooling system is required for the target block in order to remove the heat and allow for sufficient scanning time. In this study, jet cooling of the target back is investigated for a prototype proof-of-principle target. The prototype target was simulated with the transient k-ɛ turbulence multiphysics model in ANSYS CFX. The simulations were conducted at a heat flux of 1.8×107 W/m2, consistent with values anticipated for a full scale target. The simulation results show that the target temperature exceeds the copper melting point in 2 seconds at inlet velocities below 2 m/s. Also, critical heat flux calculations show that a 1.5 m/s inlet velocity at atmospheric pressure is a lower limit for prevention of target burnout using water as a coolant. Inlet velocities in excess of 2 m/s allows for steady-state operation while satisfying all thermal design constraints.

Advancements in the Development of a Plasma-Driven Electromagnetic Launcher

The institute for advanced technology (IAT) is developing a plasma-driven railgun to launch low-mass projectiles of 5-10 g to a velocity in excess of 7 km/s. Accomplishing this goal requires overcoming the problem of bore ablation, which has been linked to an observed velocity ceiling of about 6 km/s in plasma-armature launchers. Bore ablation is a direct consequence of the intense heat radiated by plasma armatures. Controlling bore ablation requires a coordinated approach that includes magnetic augmentation to reduce power dissipation in the plasma, high-purity alumina insulators to raise the ablation resistance of the bore, and pre-acceleration to prevent ablation of the bore materials at low velocity. This paper describes the consequences of excessive bore ablation, the rationale for the IAT experiment, and results obtained from the hardware that has been designed and tested to date.

The Kinematics of Kepler’s Supernova Remnant as Revealed byChandra

I have determined the expansion of the supernova remnant of SN 1604 (Kepler's supernova) based on archival Chandra ACIS-S observations made in 2000 and 2006. The measurements were done in several distinct energy bands, and were made for the remnant as a whole, and for six individual sectors. The average expansion parameter indicates that the remnant expands on average as r ∝ t0.5, but there are significant differences in different parts of the remnant: the bright northwestern part expands as r ∝ t0.35, whereas the rest of the remnant's expansion shows an expansion r ∝ t0.6. The latter is consistent with an explosion in which the outer part of the ejecta has a negative power law slope for density (ρ ∝ v−n) of n = 7, or with an exponential density profile [ρ ∝ exp (− v/ve) ]. The expansion parameter in the southern region, in conjunction with the shock radius, indicates a rather low value (<5 × 1050 erg) for the explosion energy of SN 1604 for a distance of 4 kpc. A higher explosion energy is consistent with the results if the distance is larger. The filament in the eastern part of the remnant, which is dominated by X-ray synchrotron radiation, seems to mark a region with a fast shock speed r ∝ t0.7, corresponding to a shock velocity of v = 4200 km s−1, for a distance to SN 1604 of 4 kpc. This is consistent with the idea that X-ray synchrotron emission requires shock velocities in excess of ~2000 km s−1. The X-ray-based expansion measurements reported are consistent with results based on optical and radio measurements but disagree with previous X-ray measurements based on ROSAT and Einstein observations.

Preface

An elusive goal of the hypervelocity impact community has been the evaluation of the ballistic response of space hardware to impact velocities ranging from 8 to 11 km/s using projectiles with known properties. The design, development, and use, during the 1960s, of a three-stage, light-gas gun at McGill University is reviewed. The developers of this gun claim that they were able to launch cylindrical, 12.7-mm-diameter Lexan disks with masses of 1.5 and 1.1 g to velocities of 9.6 and 10.5 km/s, respectively. This paper presents the results of an internally funded program at the University of Dayton Research Institute (UDRI) to duplicate the published performance of the McGill University launcher. A support structure and various components of a third stage which used an 8.1-mm-diameter launch tube were added to the UDRI 75/30-mm, two-stage, light-gas gun, making the arrangement of the components similar to the one used by McGill University. Work on the development of the UDRI three-stage, light-gas gun is a continuing effort, with the goal of successfully launching small diameter (∼3 mm or less) aluminum spheres to velocities in excess of 9 km/s. To date, the highest projectile velocity achieved with the UDRI three-stage, light-gas gun has been 8.65 km/s.

Controls on the height and spacing of eolian ripples and transverse dunes: A numerical modeling investigation

Ripples and transverse dunes in areas of abundant sand supply increase in height and spacing as a function of time, grain size, and excess shear velocity. How and why each of these factors influence ripple and transverse dune size, however, is not precisely known. In this paper, the controls on the height and spacing of ripples and transverse dunes in areas of abundant sand supply are investigated using a numerical model for the formation of eolian bedforms from an initially flat surface. This bedform evolution model combines the basic elements of Werner's [Werner, B.T., 1995. Eolian dunes: Computer simulations and attractor interpretation. Geology 23, 1107–1110.] cellular automaton model of dune formation with a model for boundary layer flow over complex topography. Particular attention is paid to the relationship between bed shear stress and slope on the windward (stoss) side of evolving bedforms. Nonlinear boundary layer model results indicate that bed shear stresses on stoss slopes increase with increasing slope angle up to approximately 20°, then decrease with increasing slope angle as backpressure effects become limiting. In the bedform evolution model, the linear boundary layer flow model of Jackson and Hunt [Jackson, P.S., Hunt, J.C.R., 1975. Turbulent wind flow over a low hill. Quarterly Journal of the Royal Meteorological Society 101, 929–955.], generalized to 3D, is modified to include the nonlinear relationship between bed shear stress and slope. Bed shear stresses predicted by the modified Jackson and Hunt flow model are then used to predict rates of erosion and deposition iteratively through time within a mass-conservative framework similar to Werner [Werner, B.T., 1995. Eolian dunes: Computer simulations and attractor interpretation. Geology 23, 1107–1110.]. Beginning with a flat bed, the model forms ripples that grow in height and spacing until a dynamic steady-state condition is achieved in which bedforms migrate downwind without further growth. The steady-state ripple spacing predicted by this model is approximately 3000 times greater than the aerodynamic roughness length of the initially flat surface, which is a function of grain size and excess shear velocity. Once steady-state ripples form, they become the dominant roughness element of the surface. The increase in roughness associated with ripple formation triggers the same bedform instability that created ripples, causing dunes to form at a larger scale. In this way, the numerical model of this paper suggests that ripples and dunes are genetically linked. Transverse dunes in this model have a steady-state height and spacing that is controlled by the effective roughness length of the rippled surface, which is shown to be on the order of 500 times greater than the original roughness length, but varies significantly with the details of ripple morphology. The model predictions for ripple and dune spacing and their controlling variables are consistent with field measurements from the published literature. The model of this paper provides a preliminary process-based understanding of the granulometric control of ripples and dunes in areas of abundant sand supply and unidirectional prevailing winds, and it argues for a genetic linkage between ripples and dunes via a scaling relationship between eolian bedform size and the aerodynamic roughness length.

DMSP/GPS observations of intense ion upflow in the midnight polar ionosphere associated with the SED plume during a super geomagnetic storm

We report observations from the GPS TEC and DMSP F‐15 satellite showing that a very strong upward field‐aligned (FA) plasma velocity and flux at F‐region heights in the auroral zone/polar cap boundary during a passage of the polar tongue of ionization (TOI) full of storm‐enhanced density (SED) materials occurred in the event of the super geomagnetic storm on Nov. 20, 2003. The upward FA ion velocities in excess of 460 m/s are obtained from observations of the DMSP F‐15 satellite. With enhancements of the plasma density caused by the TOI, FA ion fluxes are estimated to about 1.2 × 1014 ions m−2s−1, which are comparable to those observed by the ground‐based radar in the polar cusp. Therefore, during the super geomagnetic storm a s SED can cause a TOI plume at F region altitudes, which leads to a strong upward ion flux reaching 1–2 orders of magnitude larger than that of the typical flux at midnight auroral zone/polar cap boundary. Through estimations of the influence of those upflow ions associated with SED plumes on the development of the super storm, our result suggests that the midnight auroral zone/polar cap boundary becomes an important source to directly provide rich O+ to the ring current during super geomagnetic storms.

Molecular Interaction Studies in Ternary Liquid Mixtures of Quinoline at Varying Temperatures

Density r, Viscosity η, and ultrasonic velocity u, have been measured in pure Quinoline, o-cresol, m-cresol, p-cresol and methanol and in their ternary liquid mixtures with quinoline and methanol as common components at 303.15, 308.15, 313.15 and 318.15K over the entire range of composition. From these experimental data, various thermo-acoustic parameters such as excess molar volume VmE, excess ultrasonic velocity uE, viscosity deviation Δη and excess Gibb’s free energy of activation for viscous flow ΔG*E have been calculated. The deviation/excess parameters were plotted against the mole fraction of quinoline over the whole composition range. The observed negative and positive values of deviaiton/excess thermo-acoustic parameters were explained on the basis of intermolecular interactions present in these mixtures.

Impact of thin aluminum sheets with aluminum spheres up to 9 km/s

The results of further development of the University of Dayton Research Institute (UDRI), three-stage, light-gas gun and impact test data are presented. We have successfully launched 2.38-mm-diameter aluminum spheres to velocities in excess of 9 km/s with no damage to the launcher components. The results of several tests in which 2.38-mm-diameter aluminum spheres impacted thin aluminum sheets at velocities up to 9.10 km/s are presented. Quantitative data obtained from these tests were used to extend previously established relationships to velocities which are typical of the collisions of orbital debris with spacecraft. These test results include: bumper-sheet hole diameter as a function of impact velocity; determination of the fragmentation-initiation-threshold velocity for spheres impacting very thin sheets; and continued demonstration of the “scalability” of the test results using the bumper-thickness-to-projectile-diameter ratio ( t / D ) as the scaling factor.

Storm-Time Strong Field-Aligned Ion Upflow in Region of the SED Plume

We report the observations from the GPS TEC and DMSP F-13 satellites showing that very strong upward field-aligned (FA) ion velocity and flux in the outer region of the storm-enhanced density (SED) occurred in the event of the geomagnetic storm on 29–31 May 2003. By a method of coordinate transformation, upward FA ion velocities in excess of 250 m/s are obtained from the observations of the DMSP F-13 satellite. Further, an FA ion flux is estimated to be about 4.5 × 1013 ions/m2s in the dusk sector. The estimated FA ion velocity and flux provide a powerful direct proof to support the scenario that there is a strong coupling of particles between the ionosphere and plasmasphere in the region of the SED plume. In the process, FA ion flux transports from the ionosphere to the plasmasphere in the region of the SED plume. Therefore, the plume of SED in the ionosphere provides an important source to the enhanced density of O+ in the storm-time plasmasphere.

Polishing the diastolic dysfunction measurement stick

Diastolic heart failure currently accounts for more than 50% of all heart failure cases in Western societies.1 Because of normal left ventricular (LV) systolic function, diastolic heart failure is mainly attributed to diastolic LV dysfunction evident from slow LV relaxation and high diastolic LV stiffness.2,3 High diastolic LV stiffness is the most important cause of the repetitive heart failure episodes occurring in these patients,4 while high arterial elastance,5 atrial remodelling,6 and impaired chronotropic7 or vasomotor8 responses are additional contributors. Because of the pathophysiological importance of diastolic LV dysfunction, all previous diagnostic guidelines for diastolic heart failure considered evidence of diastolic LV dysfunction to be essential for the diagnosis.9–11 The recently updated diagnostic guidelines for diastolic heart failure provided by the Echocardiography and Heart Failure Associations of the European Society of Cardiology12 continued to adhere to this principle and required three conditions to be simultaneously satisfied for the diagnosis of diastolic heart failure: (i) signs or symptoms of fluid congestion; (ii) a normal systolic LV function evident from a LV ejection fraction (EF) >50% and a LV end-diastolic volume index <97 mL/m2, and (iii) evidence of diastolic LV dysfunction. The latter can be acquired by cardiac catheterization, by Doppler echocardiography, and by biomarkers such as brain natriuretic peptide (BNP) and NT-proBNP. A pulmonary capillary wedge pressure larger than 12 mmHg, an LV end-diastolic pressure (LVEDP) larger than 16 mmHg, and a ratio of mitral early diastolic flow velocity over tissue Doppler mitral annular lengthening velocity (E/E′) in excess of 15 provide stand-alone evidence of diastolic LV dysfunction. An E/E′ ratio ranging from 8 to 15 (E/E′ 8–15), BNP larger than 200 pg/mL, and NT-proBNP larger than 220 pg/mL require additional investigations to establish presence of diastolic …