Low Rotation Rates Research Articles

Continuous extraction of α- and β-amylases from Zea mays malt in a PEG4000/CaCl 2 ATPS

In the present work, α- and β-amylase enzymes from Zea mays malt were recovered by continuous extraction in a PEG/CaCl 2 aqueous two-phase system (ATPS). The influences of the flux rate ( R Q), free area of vane ( A free) and vane rotation ( R V) on enzyme recovery were studied by optimization using response surface methodology (RSM). The protein content and enzyme activity were measured from time to time in the extract and refined fluxes. RSM curves showed a squared dependence of recovery index with the R Q, A free and R V. The best system for recovering the maize malt enzymes was with low vane rotation and flux rate and high free area of vane. α- and β-amylases were purified 130-fold in the salt-rich phase.

Analytic Models of the Infinite Porous Rotating Disk Electrode

The current generated from the electrochemical reaction in a porous rotating disk electrode (PRDE) is modeled analytically where the reactant transport is dominated by either advection or diffusion. When advection dominates, the concentration field of the reactant is found by assuming each fluid element behaves as a batch reactor and tracking them along their streamlines, utilizing the solution of the flow field in an infinite porous rotating disk by Joseph. The current is expressed in a simple algebraic form involving a dimensionless reaction time. The model accurately depicts the universal curve found from previous experiments and numerical simulations when the ratio of height to radius of the disk is less than about 0.25. The diffusion-dominated regime is modeled utilizing a boundary layer theory. The current is found as a function of the rotation rate, reaction rate, permeability, diffusion coefficients, kinematic viscosity, and geometry of the disk. The model coincides with the Levich equation at low rotation rates and shows excellent agreement with simulations and experiments regardless of the geometry of the disk. Combined, the two analytic models accurately describe the PRDE for the full range of its operation when the disk is sufficiently thin that the infinite disk assumption holds.

An Experimental Investigation into the Influence of Fillers on the Development of Normal Stresses and Stress Relaxation in Asphalt Mixtures Due to Torsion

This study documents the measurement of normal stresses and stress relaxation in sand-asphalt mixtures fabricated with different fillers and asphalts during torsion. Hydrated lime and limestone fillers and asphalts graded as PG64-22 and AC-30 (from Sinclair (Wyoming), Crown (Nevada), and Crown (Canada)) are used in the fabrication of the sand-asphalt mixtures. The specimens are tested in a torsional rheometer. The experimental results clearly show that the normal stresses that are developed are quite significant even for specimens tested at very low rotational rates. Also, asphalts from different sources show differences in peak normal stresses and in their relaxation pattern. The measurement of significant normal stresses is a reflection of the nonlinear character of the material and warrants the development of nonlinear constitutive models for describing their behavior.

Single and multiphase CFD approaches for modelling partially baffled stirred vessels: Comparison of experimental data with numerical predictions

Whilst the use of CFD to study mixing vessels is now common-place, there are still many specialised applications that are yet to be addressed. Here we present CFD and PIV results for a hydrodynamic study of a partially baffled vessel with a free surface. The standard k – ɛ and SSG Reynolds Stress turbulence models are used and the numerical predictions of the mean flow field are compared with experimental data for single phase modelling. At low rotation rates a flat free surface is observed and the flow is simulated using a single phase model, whilst at high rotation rates an Eulerian–Eulerian multiphase model is used to capture the free surface location, even under conditions when gas is drawn down to the impeller. It is shown that there are significant transient effects that mean many of the “rules of thumb” that have been developed for fully baffled vessels must be revisited. In particular such flows have central vortices that are unsteady and complex, transient flow-induced vortical structures generated by the impeller–baffle interactions and require a significant number of simulated agitator rotations before meaningful statistical analysis can be performed. Surprisingly, better agreement between CFD and experimental data was obtained using the k – ɛ than the SSG Reynolds stress model. The multiphase inhomogeneous approach used here with simplified physics assumptions gives good agreement for power consumption, and with PIV measurements with flat and deformed free surfaces, making this affordable method practical to avoid the erroneous modelling assumption of a flat free surface often made in such cases.

A material rigidity effect of a bimorph piezoelectric actuator

This paper presents the numerical modeling of a piezoelectric actuator used to avoid thelimitation of the lock-in region in a ring resonator. Ring resonators have proved suitable foruse as inertial sensors for navigation, guidance and attitude controls. However, theiraccuracy has been limited by the lock-in region due to frequency coupling between twocounter-propagating waves at low rotation rates. This coupling introduces no phasedifference, and no angular increment is detected. The problem can be overcome bymechanically dithering the ring resonator. Mechanically, the vibro-elastic bimorphpiezoelectric actuator has been used as a control but is influenced by piezoelectric rigidityeffects. To more accurately predict the dithering frequency of a mechanical dither,numerical modeling of a piezoelectric actuator includes the piezoelectric rigidity effect ofthe actuator, which occurs in both the static and dynamic behaviors of composite plateshaving piezoelectric layers symmetrically bonded to the top and bottom surfaces.Corrections were made to figures 1 and 2 on 13 June 2007. The corrected electronic version is identical to the print version

Vane rheology of cohesionless glass beads

The rheology of a single coarse granular powder has been studied with shear vane rotational viscometry. The torque required to maintain constant rotation of a vane tool in a loose bed of glass beads (with a mean particle size of 203 μm) is measured as a function of vane immersion depth and rotational speed. The resulting torque profiles exhibit both Coulombic behavior at low rotational rates and fluid-like, collisional behavior at high rotational rates. Analyzing vane shaft and end effects allows the flow dynamics at the cylindrical and top and bottom disk surfaces of vane rotation to be determined. Disk surfaces show a uniform torque profile consistent with Coulombic friction over most of the rotational rates studied. In contrast, cylindrical surfaces show both frictional and collisional torque contributions, with significant dynamic torque increases at deep immersion depths and fast vane rotation.

Torsional oscillations of slowly rotating relativistic stars

We study the effects of rotation on the torsional modes of oscillating relativistic stars with a solid crust. Earlier works in Newtonian theory provided estimates of the rotational corrections for the torsional modes and suggested that they should become CFS unstable, even for quite low rotation rates. In this work, we study the effect of rotation in the context of general relativity using elasticity theory and in the slow-rotation approximation. We find that the Newtonian picture does not change considerably. The inclusion of relativistic effects leads only to quantitative corrections. The degeneracy of modes for different values of $m$ is removed, and modes with $\ell=m$ are shifted towards zero frequencies and become secularly unstable at stellar rotational frequencies $\sim$ 20-30 Hz.

On the Behavior of the Porous Rotating Disk Electrode

The behavior of the current from a porous rotating disk electrode (PRDE) as a function of the rotation rate, electrode geometry, and porosity at large overpotentials is studied experimentally. The current shows a much richer behavior than the flat RDE, including a sigmoidal dependence on the rotation rate. At low rotation rates, the measured current is qualitatively similar to that of an RDE, with the current increasing with the square of the rotation rate. However, at a critical rotation rate, which we term the lower critical rotation rate and which depends on the radius, the thickness, and the porosity of the porous disk, the current increases much more rapidly than predicted by the Levich theory. At a larger, upper critical rotation rate, the current increases more slowly and then approaches a plateau. The plateau value greatly exceeds that predicted by Levich and is about 20 times greater than that for a flat electrode. The results are explained in terms of the angular velocity dependence of the ratio of the effective electrochemical reaction time to the residence time of the fluid in the porous disk. A theory is presented that collapses the data onto a universal curve.

High Pulling Rate Defect-Free Crystals with Axially Asymmetric Characteristics Due to Controlled Melt Convection

We reviewed experimental results of the variation of growth parameters bringing forth the axially asymmetric formation of vacancy-interstitial boundary and the increase of the critical growth rate V*, transition from interstitial to vacancy, of Czochralski-grown silicon crystals. Such results show that controlled melt convection for defect-free crystals can make the critical growth rate V* much higher like EMCZ. Some parameters can control interstitial oxygen concentration in the crystal effectively as well. From the cone-shaped shouldering test, asymmetric formation of {111} crystal facets was obtained at very low crucible rotation, which confirms asymmetric distributions of the melt temperature. Based on the results of two dimensional (2D) and three dimensional (3D) simulations, it is shown that the very low crucible rotation rate decreases radial temperature gradient and increases axial temperature gradient in the silicon melt.

Morphology and thermal conductivity of yttria-stabilized zirconia coatings

An electron beam directed vapor deposition method was used to grow 7 wt.% Y 2O 3–ZrO 2 (7YSZ) coatings and the effects of substrate rotation upon the coating porosity, morphology, texture, and thermal conductivity were explored. As the rotation rate was increased, the texture changed from 〈1 1 1〉 to 〈1 0 0〉. Under stationary deposition, the coatings were composed of straight columns, while low-frequency rotation resulted in wavy columns. Increases in rotation rate resulted in a gradual straightening and narrowing of the growth columns. The pore fraction slowly decreased as the rotation rate increased. The thermal conductivity was found to be inversely related to the pore fraction. The structural and thermal conductivity alterations are a result of changes to flux shadowing associated with specimen rotation in a gas jet-entrained vapor plume. The minimum thermal conductivity at a low rotation rate is 0.8 W/(m K), well below that of conventionally deposited coatings.

Humans can perceive heading without visual path information

It has previously been reported that humans can determine their direction of 3D translation (heading) from the 2D velocity field of retinal motion experienced during self-motion through a rigid environment, as is done by current computational models of visual heading estimation from optic flow. However, these claims were supported by studies that used stimuli that contained low rotational flow rates and/or additional visual cues beyond the velocity field or a task in which observers were asked to indicate their future trajectory of self-motion (path). Thus, previous conclusions about heading estimation have been confounded by the presence of other visual factors beyond the velocity field, by the use of a path-estimation task, or both. In particular, path estimation involves an exocentric computation with respect to an environmental reference, whereas heading estimation is an egocentric computation with respect to one's line of sight. Here, we use a heading-adjustment task to demonstrate that humans can precisely estimate their heading from the velocity field, independent of visual information about path, displacement, layout, or acceleration, with accuracy robust to rotation rates at least as high as 20 deg/s. Our findings show that instantaneous velocity-field information about heading is directly available for the visual control of locomotion and steering.

Parametric design consideration of a vibro-elastic bimorph piezoelectric converter for a ringlaser gyroscope

Gyroscopes have been used as suitable inertial instruments for navigation, guidance, andattitude controls. Their accuracy as very sensitive sensors is limited by the lock-in region(dead band) due to frequency coupling between two counter-propagating waves at lowrotation rates. This frequency coupling gives no phase difference, and no angular incrementis detected. The problem can be overcome by mechanically dithering the gyroscope.Mechanically, the vibro-elastic bimorph piezoelectric converter (hereinafter, dither) is usedfor feasible control.This paper presents the design considerations of the mechanical dither, taking mechanicaland piezoelectric parameters into account. Verification of the theoretical equations isperformed through FEM (finite-element method) applications.

Effect of Hydraulic Jump on Hydrodynamics and Heat Transfer in a Thin Liquid Film Flowing Over a Rotating Disk Analyzed by Integral Method

Flow and heat transfer in a liquid film flowing over the surface of a rotating disk was analyzed by integral technique. The integral analysis includes the prediction of the hydraulic jump and its effects on heat transfer. The results of this analysis are compared to the earlier results that did not include this effect. At low inlet Reynolds numbers and high Rossby numbers, corresponding to low film inertia and low rotation rates, respectively, a hydraulic jump appears on the disk surface. The location of the jump and the liquid film height at this location are predicted. A scaling analysis of the equations governing the film thickness provided a semi-empirical expression for these quantities that was found to be in very good agreement with numerical results. Heat transfer analysis shows that the Nusselt numbers for both constant disk surface temperature and constant disk surface heat flux boundary conditions are lowered in the vicinity of the hydraulic jump due to the thickened liquid film. This effect can be more pronounced for the constant heat flux case depending on the location of the hydraulic jump. The Nusselt number exhibits a turning point at the jump location and can have higher values downstream of the hydraulic jump compared to those obtained from the analysis that does not include the gravitational effects.

Amphetamine induced rotation in the assessment of lesions and grafts in the unilateral rat model of Parkinson's disease

In the unilateral rat model of Parkinson's disease (PD), amphetamine induced rotation is widely used as an index of both lesion deficits and of graft-derived recovery. We have analysed the time course of the rotational response in lesioned rats, and in rats with lesions and dopamine grafts. In lesioned rats, the rotation exhibited a typical dose-dependent response, with low rates of rotation in the first 10 min after injection, rising gradually to a maximum after 20–30 min. Grafted rats exhibited a peak of rotation in the first 10 min after injection, which then fell to a minimum after 30 min. We demonstrate that the response seen in grafted rats is both drug and dose-dependent and show that the rotational profile results from interaction of the grafted and intact striata which exhibit differential temporal responses to the amphetamine.

Polygons on a Rotating Fluid Surface

We report a novel and spectacular instability of a fluid surface in a rotating system. In a flow driven by rotating the bottom plate of a partially filled, stationary cylindrical container, the shape of the free surface can spontaneously break the axial symmetry and assume the form of a polygon rotating rigidly with a speed different from that of the plate. With water, we have observed polygons with up to 6 corners. It has been known for many years that such flows are prone to symmetry breaking, but apparently the polygonal surface shapes have never been observed. The creation of rotating internal waves in a similar setup was observed for much lower rotation rates, where the free surface remains essentially flat [J. M. Lopez, J. Fluid Mech. 502, 99 (2004). We speculate that the instability is caused by the strong azimuthal shear due to the stationary walls and that it is triggered by minute wobbling of the rotating plate.

Investigations of the catalytic properties of manganese oxides for the oxygen reduction reaction in alkaline media

The oxygen reduction reaction (ORR) was studied in KOH electrolyte on different manganese oxides, dispersed on a carbon powder (MnOx/C). The oxides were prepared by different methods, for producing MnO, Mn3O4 and MnO2 as major phases dispersed on the Vulcan XC-72 carbon. The oxides were characterized by XRD (X-ray diffraction) and in situ XANES (X-ray absorption near edge structure). The electrochemical measurements were made using cyclic voltammetry and steady state polarization curves carried out in an ultra-thin layer rotating ring/disk electrode. The results have shown lower activity for the ORR on the MnOx/C species compared to that on Pt/C, but higher activity compared to that of pure Vulcan carbon. Formation of HO2- involving 2e− per O2 molecule is the main path of the ORR in the studied MnOx/C catalysts but, at low overpotentials and rotation rates the number of electrons is raised to 4 due to the occurrence of a HO2- disproportionation reaction. Large differences of electrocatalytic activity were seen for the different oxide species, and these were related to the presence of a Mn(IV) phase and the occurrence of a mediation processes involving the reduction of Mn(IV) to Mn(III), followed by the electron transfer of Mn(III) to oxygen.

Asymmetric distributions of grown-in microdefects in Czochralski silicon

The axial temperature gradient in the CZ–Si melt near the crystal–melt interface was increased by controlling the crucible and crystal rotation rate. For the crystal grown under the increased temperature gradient in the melt with a very low crucible rotation rate, asymmetric distributions of grown-in microdefects were formed. This result has never been reported, and cannot be explained simply by any theory such as Voronkov's theory. In addition, it is shown that the shape of the crystal–melt interface is not the parameter determining the dominant type of point defects. Therefore, a new aspect of the formation behavior of point defects is discussed in terms of asymmetry of the melt temperature distributions.

On the flow stability in vertical rotating disc MOCVD reactors under a wide range of process parameters

A systematic study has been performed to investigate flow stability in vertical rotating disc MOCVD reactors under a wide range of process parameters, such as chamber pressure (10–1000 Torr), wafer carrier rotation rate (0–1500 rpm), growth temperature (500–1100 °C), isothermal reactor wall temperature (25–250 °C), total gas flow rate (10–350 slm), and varying concentrations of hydride and inert carrier gases (H 2, N 2, and NH 3). Quantitative flow stability maps have been developed based on extensive two-dimensional/three-dimensional numerical modeling for the entire domain of possible process parameters. It has been shown that all typical flow regime regions encountered in a rotating disc reactor (plug-flow, stagnation-flow, buoyancy-induced, and rotation-induced flow regimes) can be presented in a single “ P– ω ” (pressure vs. rotation rate) diagram, which also transparently captures the effects of all process parameters mentioned above on the flow stability in the rotating disc reactors. Two zones of buoyancy-driven flow with different asymptotic behavior for low and high rotation rate (weak and strong rotation dependence, respectively) have been identified. Moreover, a rotation rate range has been identified where transition between buoyancy-driven flow and rotationally driven flow occurs, which is also the range where the maximum pressure can be achieved in rotating disc reactors.

Steady rotating flows over a ridge

A model describing rotating single-layer flows over a parabolic ridge is investigated. A method of constructing steady solutions is introduced, and is used to extend previous results and determine exact regime diagrams describing the qualitative nature of the solution. Analytic expressions for the boundaries between transcritical flow and supercritical and subcritical flows are given as a function of obstacle height, Froude number of the upstream flow, and the flow inverse Burger number (a nondimensional number proportional to the square of the rotation rate). For fixed obstacle height, the nature of the supercritical transition is found to change as the rotation rate increases, with a hysteresis region like that in nonrotating flow being present only at lower rotation rates. At higher rotation rates, solutions with stationary jumps over the obstacle become stable, and abrupt transitions between supercritical and transcritical flow no longer occur. An exact analytic expression is also found for transcritical flow over the obstacle, which is closely related to the solutions for nonlinear inertia-gravity waves of limiting amplitude found by Shrira. For sufficiently high ridges in initially supercritical flow, a wave train of nonlinear inertia-gravity waves of limiting amplitude appears behind a downstream hydraulic jump.

An experimental study of fixed points and chaos in the motion of spheres in a Stokes flow

We present the results of an investigation of a novel dynamical system in which one, two or three solid spheres are free to move in a horizontal rotating cylinder which is completely filled with a highly viscous fluid. At low rotation rates, steady motion is found where the balls adopt stable equilibrium positions rotating adjacent to the rising wall at a speed which is in agreement with available theory. At higher cylinder speeds time-dependent motion sets in via Hopf bifurcations, and when one or two balls are present the motion is strictly periodic. Perhaps surprisingly, it is found that three balls are required to produce low-dimensional chaos.