Radial Fluctuations Research Articles

Solid Flow Mapping at the Bottom Section of a Pilot-Plant Scale Riser with the Help of a Radioactive Particle Tracking Technique

Solid phase velocity measurements are performed at the bottom section of a pilot plant scale cold-flow circulating fluidized bed riser with Geldart group B solids using a radioactive particle tracking technique. Experiments are performed at different gas velocities and solid fluxes to evaluate the effect of gas velocity and solid flux on solid phase velocity in the bottom section of the riser. Different flow quantities such as mean velocity, root-mean-square velocities, and granular temperature are calculated and presented at different heights. Solid motion is seen to occur in the axial direction primarily. It is observed that axial velocity fluctuation increases with the height where radial solid velocity fluctuation decreases. Both gas–solid and solid–solid interactions are vital in determining the solid flow field. Gas–solid interaction is critical in the axial direction, while solid–solid interaction is important in the radial direction.

Effect of the radial gap size on the deterministic flow in a centrifugal pump due to impeller-tongue interactions

The research on the flow in centrifugal pumps is quite broad and covers most of the relevant issues. However, most of the studies are focused on the steady behaviors and less literature is available for the dynamic interactions. Unsteady mechanisms for energy transfer and sources of impeller-tongue interaction can be identified in centrifugal pumps using the deterministic decomposition of the flow. Probably, the most important effect to be considered is the radial gap or spacing between the impeller exit diameter and the volute tongue radial location. The numerical dataset of a full 3D URANS model in a centrifugal pump has been employed to study in detail the effect of the radial gap size in the unsteady fluctuations of the velocity field within the pump, using the deterministic analysis as the main novelty. The numerical model developed by the authors has been already tested towards the prediction of the unsteady pressure field inside the volute, at the impeller exit. The new results presented here allow to see the impact of both geometrical and operating parameters on the flow discharge and momentum exchange. In particular, four different radial gaps (23.2%, 17.0%, 11.4% and 8.8% of the impeller diameter) operated at five different flow rates (from 20% to 160% of the nominal rate) have been numerically resolved and analyzed. The deterministic analysis reveals the major impact of the radial clearance on the blade-to-blade flow patterns within the impeller, especially at low flow rates. Unsteady viscous interaction induces radial velocity fluctuations that can be as high as a 40% of the time-averaged value. Moreover, this non-linear term can be perceived up to 1.5 times higher in the case of radial gap reductions from 23.2% to 8.8% of the impeller diameter. There is not a prevailing effect of the radial gap on that velocity component, and a pure temporal term dependence is found. On the contrary, the influence of the gap on the tangential component, responsible for the unsteady evolution of the impeller torque, is found to be the key parameter. Therefore, the fluctuations of the flow blockage are found to be the consequence of the impeller flow patterns and the fluctuations of the torque are to be assigned to the radial gap influence. All the post-processing routines have provided a precise picture of all the classic unsteady mechanisms involved: jet-wake pattern interaction, acoustic wave propagations and recirculating cells at off-design conditions. Hence, deterministic analysis is a useful tool to analyze the flow inside centrifugal pumps and it envisages the introduction of deterministic flow variables as objective functions for design optimization algorithms.

Heating up Peccei-Quinn scale

We discuss production of QCD axion dark matter in a novel scenario, which assumes time-varying scale of Peccei-Quinn symmetry breaking. The latter decreases as the Universe's temperature at early times and eventually stabilises at a large constant value. Such behavior is caused by the portal interaction between the complex field carrying Peccei-Quinn charge and a Higgs-like scalar, which is in thermal equilibrium with primordial plasma. In this scenario, axions are efficiently produced during the parametric resonance decay of thecomplex Peccei-Quinn field, relaxing to the minimum of its potential in the radiation-dominated stage. Notably, this process is not affected by the Universe's expansion rate and allows to generate the required abundance of dark matter independently of an axion mass. Phenomenological constraints on the model parameter space dependon the number density of radial field fluctuations, which are also generically excited along with axions, and the rate of their thermalization in the primordial plasma.For the ratio of radial field and axion particles number densities larger than ∼ 0.01 at the end of parametric resonance decay, the combination of cosmological and astrophysical observations with the CAST limit confinesthe Peccei-Quinn scale to a narrow range of values ∼ 108 GeV, —this paves the way for ruling out our scenario with the near future searches for axions.

A new electromagnetic probe array diagnostic for analyzing electrostatic and magnetic fluctuations in EAST plasmas

A novel electromagnetic probe array (EMPA) diagnostic, which consists of a magnetic probe array and an electrostatic probe array, has recently been developed on EAST. The EMPA is fixed near the first wall at horizontal port P. The magnetic probe array of the EMPA consists of 24 identical magnetic probes, each of them capable of measuring toroidal, poloidal and radial magnetic fluctuations simultaneously, providing additional toroidal magnetic fluctuation measurements compared with the regular magnetic probes on EAST. With a higher sampling rate and self-resonant frequency, the EMPA magnetic probes can provide higher frequency magnetic fluctuation measurements. The magnetic probe array of the EMPA is composed of two parallel layers of magnetic probes with a radial distance of 63 mm, and each layer of magnetic probes is arranged in four poloidal rows and three toroidal columns. The compact arrangement of the EMPA magnetic probe array largely improves the toroidal mode number measurement ability from to and also improves the high poloidal wave number measurement ability of magnetic fluctuations compared with the regular high frequency magnetic probes on EAST. The electrostatic probe array of the EMPA consists of two sets of four-tip probes and a single-tip probe array with three poloidal rows and four toroidal columns. It complements the electrostatic parameter measurements behind the main limiter and near the first wall in EAST. The engineering details of the EMPA diagnostic, including the mechanical system, the electrical system, the acquisition and control system, and the effective area calibration, are presented. The preliminary applications of the EMPA in L-mode and H-mode discharges on EAST have demonstrated that the EMPA works well for providing information on the magnetic and electrostatic fluctuations and can contribute to deeper physical analysis in future EAST experiments.

Departures from perfect isomorph behavior in Lennard-Jones fluids and solids.

Isomorphs are lines on a fluid or solid phase diagram along which the microstructure is invariant on affine density scaling of the molecular coordinates. Only inverse power (IP) and hard sphere potential systems are perfectly isomorphic. This work provides new theoretical tools and criteria to determine the extent of deviation from perfect isomorphicity for other pair potentials using the Lennard-Jones (LJ) system as a test case. A simple prescription for predicting isomorphs in the fluid range using the freezing line as a reference is shown to be quite accurate for the LJ system. The shear viscosity and self-diffusion coefficient scale well are calculated using this method, which enables comments on the physical significance of the correlations found previously in the literature to be made. The virial-potential energy fluctuation and the concept of an effective IPL system and exponent, n', are investigated, particularly with reference to the LJ freezing and melting lines. It is shown that the exponent, n', converges to the value 12 at a high temperature as ∼T-1/2, where T is the temperature. Analytic expressions are derived for the density, temperature, and radius derivatives of the radial distribution function along an isomorph that can be used in molecular simulation. The variance of the radial distribution function and radial fluctuation function are shown to be isomorph invariant.

Boundary-value-problem examination of the stability of a symmetrical rotor partially filled with a viscous incompressible fluid

Instabilities in a rotor system partially filled with a fluid can have an exponentially increasing amplitude, and this can cause catastrophic damage. Numerous theoretical models have been proposed, and numerous experiments have been conducted to investigate the mechanisms of this phenomenon. However, the explanation of the existence of the first unstable region induced by a viscous incompressible fluid is unclear, and only one solving method, a standard finite difference procedure, was proposed in 1991 for solving the instabilities in a system containing a symmetric rotor partially filled with a viscous incompressible fluid. To better understand the mechanisms of the instability induced by the viscous fluid, based on the linearized two-dimensional Navier–Stokes equations, this system's differential equations are transferred to solve the characteristic equations with boundary conditions. A Matlab boundary value problem (BVP) solver bvp5c proposed in 2008 is an efficient tool to solve this problem by uncoupling the boundary conditions with unknown initial guess. Applying this approach to a rotor system allows the instability regions to be obtained. In this study, first, the radial and tangential velocities and pressure fluctuations along the radial direction of a disk filled with fluid were examined. Then, parametric analysis of the effect of the Reynolds number R e c r, filling ratio H, damping ratio C, and mass ratio m on the system's stability was conducted. Using this calculation method allowed the first exploration of some new laws regarding the instabilities. These results will benefit the further understanding of the existence of the first unstable region of a rotor partially filled with a viscous incompressible fluid.

Expansion-enhanced super-resolution radial fluctuations enable nanoscale molecular profiling of pathology specimens

Expansion microscopy physically enlarges biological specimens to achieve nanoscale resolution using diffraction-limited microscopy systems1. However, optimal performance is usually reached using laser-based systems (for example, confocal microscopy), restricting its broad applicability in clinical pathology, as most centres have access only to light-emitting diode (LED)-based widefield systems. As a possible alternative, a computational method for image resolution enhancement, namely, super-resolution radial fluctuations (SRRF)2,3, has recently been developed. However, this method has not been explored in pathology specimens to date, because on its own, it does not achieve sufficient resolution for routine clinical use. Here, we report expansion-enhanced super-resolution radial fluctuations (ExSRRF), a simple, robust, scalable and accessible workflow that provides a resolution of up to 25 nm using LED-based widefield microscopy. ExSRRF enables molecular profiling of subcellular structures from archival formalin-fixed paraffin-embedded tissues in complex clinical and experimental specimens, including ischaemic, degenerative, neoplastic, genetic and immune-mediated disorders. Furthermore, as examples of its potential application to experimental and clinical pathology, we show that ExSRRF can be used to identify and quantify classical features of endoplasmic reticulum stress in the murine ischaemic kidney and diagnostic ultrastructural features in human kidney biopsies.

Effect of louver baffle on the stability and separation performance of the gas-solid separation fluidized bed

Bed density stability is often the dominant factor restricting the efficiency of coal beneficiation in gas-solid separation fluidized beds (GSSFB). Here, in order to improve the fluidization quality, a louver baffle was introduced into a conventional GSSFB, converting it into a so-called louver baffle separation fluidized bed (LBSFB). The influence of the louver baffle on the fluidization characteristics and coal separation efficiency of the GSSFB were investigated using a combination of experiments and numerical simulations. The minimum fluidized gas velocity, pressure drop, and cross section density of the bed were measured when baffle was placed at two different positions (H=40 mm and H=80 mm). Meanwhile, the evolution of bubble generation and particle flow were simulated when the baffle was placed at H= 40 mm and the operating gas velocity was 7.52 cm/s. The results showed that the use of a single guide baffle could effectively break up the bubbles in the bed, inhibit bubble growth and particle backmixing, and restore the uniform distribution of the updraft. When the louver baffle was installed at a height of H = 40 mm and the superficial gas velocity was 7.52 cm/s, the standard deviation of radial density fluctuation in the bed was reduced to 0.028 g/cm3, which is more than 35% lower than that of the conventional GSSFB, and that of the axial density fluctuation was reduced to 0.146 g/cm3. Under these conditions, the separation of 6–13 mm raw coal in a LBSFB resulted in a clean coal yield of 69.97% and a probable error, E, value of 0.082 g/cm3

Effect of Packing Structure Evolution on the Flow Characteristics in a Binary Composite Packed Bed Based on DEM-CFD Method

The evolution of mesoscale structures of particle packing in binary composite packed beds and their effects on flow characteristics and wall effects were investigated using the discrete element method (DEM) and computational fluid dynamics (CFD). The DEM model was used to build a series of randomly mixed packing structures of particles in accordance with the dynamic change of mass ratio between particles in two size ranges, which were then confirmed by the findings of an X-ray tomography (CT) scan. The results show that the packing structure of b25s75 was conducive to reducing the influence of wall effect in packed bed reactors. For b25s75, the dimensionless distance of radial porosity fluctuation from the wall is 0.3705, which is the smallest among the five packing models, indicating that this structure plays a suppressive role on the wall effect. In addition, the uniformity of velocity and temperature distributions in both the radial and axial directions of different packing structures were compared. The standard deviations of radial relative velocity distributions in the packed beds of b100, b75s25, b25s75 and s100 are 0.28, 0.178, 0.139 and 0.156, respectively, indicating that the stacking mode of b25s75 can make the fluid flow and the gas–solid interactions more uniform.

Elemental Fluctuation in Gd3Al2Ga3O12:Ce Crystals Imposed by Li+ and Mg2+ Co-Doping: The Impact on Defects, Luminescence, and Scintillation Properties

This research revealed the response of Ga and Al sublattices to the incorporation of mismatching substituents in Gd3Al2Ga3O12:Ce single crystals. Incompatible in size and charge, Li+ and Mg2+ substituents violated configurational entropy. This led to lattice distortion and triggered structural rearrangements. The radial fluctuation of the Ga and Al elements was proven by multi-elemental energy-dispersive X-ray spectroscopy mapping and elemental composition analysis. Further evidence was observed by the shift of the exciton creation energy toward higher energy in the vacuum ultraviolet excitation spectra recorded with synchrotron radiation. In the Li+ and Mg2+ co-doped samples, the crystal core was depleted with Ga atoms and enriched with Al elements. The crystal rim showed the opposite behavior. The change in thermoluminescence peak positions revealed a different mechanism for the formation of localized traps. As a result, Li+ co-doping slightly improved the light yield value, but at the same time decelerated the scintillation decay time. On the contrary, Mg2+ co-doping markedly diminished scintillation parameters.

Hydrodynamic and rheological characteristics of a pseudoplastic fluid through a rotating cylinder

The fully developed turbulent flow of pseudoplastic ( ) and Newtonian fluids in an isothermal axially rotating cylinder has been carried out using a large eddy simulation (LES) with an extended Smagorinsky model. The simulation Reynolds number of the present predictions has been assumed to be at various rotation rates This investigation seeks to assess the influence of the centrifugal force induced by the swirl on the mean flow quantities, turbulent statistics, and instantaneous turbulence structure to describe the rheological behavior and the turbulence features. The predicted results indicate that with increasing rotation rate, the pseudoplastic fluid tends to behave like a liquid when approaching the pipe center due to the lower apparent fluid viscosity in the logarithmic region as the pipe wall rotates. Moreover, the reduction in the pseudoplastic apparent viscosity in the core region induces a pronounced increase in the axial velocity profile further away from the pipe wall toward the core region. It is interesting to note that the growth of the centrifugal force induced by the swirl driven by the rotating pipe wall results in an apparent attenuation in turbulence intensities of the axial velocity fluctuation and, consequently, in the kinetic energy of turbulent fluctuations and the turbulent Reynolds shear stress of the axial-radial velocity fluctuations, as the pipe wall rotates. Moreover, the increased rotation rate leads also to a noticeable increase in the Root mean square (RMS) of the radial and tangential fluctuations. It can be said that the transport mechanism of turbulence intensities from the axial components to the other ones exhibits a marked increase with increasing pipe wall rotation.

Design of Double Staggered Parallel Bearingless Motor Drive System

To make bearingless motors (BMs) more competitive, it is imperative to reduce the cost while ensuring high performance. In this article, the driving system of the BM is optimized from the perspectives of the inverter topology and the control strategy. A dual-hybrid vector control driving scheme of the BM based on the double staggered parallel topology is proposed for the control performance and cost. Meanwhile, the levitation/torque stagger phase shift is adopted to lower the root-mean-square value of the dc-link current. The proposed driving scheme is compared with the traditional vector scheme based on a full-bridge topology on a bearingless pump system. It turns out that the two driving schemes are similar in current, speed, and rotor radial displacement fluctuation. The proposed scheme shows the advantages of simpler system structure and lower cost, so it is deemed as an attractive driving scheme for the BM.

Dendroclimatic studies of aspen growth in Moscow

This article presents the results of studying aspen (Populus tremula L.) growth in urbanized environment of Moscow metropolis with the help of dendrochronology method. Four significant correlation coefficients for data of two aspen chronologies and the group of forty-eight meteoparameters of current calendar year and the calendar year which was previous to the year of tree ring formation were established by the dendroclimatic method. According to the results of correlation calculation it was established that correlations sustainable for both considered chronologies as well as biologically interpretable ones between radial growth fluctuations and climatic data fluctuations are absent. It is due to the fact that the aspen trees on considered plots are in the conditions near the optimum zone and the factors, which are limiting radial growth size, change from year to year. One year one factor has strong deviation from optimal for species parameters, and another year it will be another factor. In this case the correlation analysis gives results about the lack of correlation, but it does not mean that climatic factors have no impact on tree ring formation. The absence of correlation, for instance, to the temperatures observed in May of the current year is important as this is a period of great cambium activity and assimilation biomass forming. So, the increase in temperature of this month, probably predicted with global warming, will not have a negative effect on aspen growth in the conditions of the studied stands.

Tracking the super resolved structure of mitochondria using red emissive carbon nanodots as a fluorescent biomarker.

Herein, we report new red emissive highly photostable and water-soluble carbon nanodots (TPP CNDs) to visualize mitochondrial dynamics using super-resolution radial fluctuations (SRRF) microscopy. The TPP CNDs were synthesized in a one-step method, using 3-(carboxypropyl)triphenylphosphonium bromide (TPP) and o-phenylenediamine (OPDA) as precursors. The obtained crystal structure, NMR, and mass data suggested the presence of [3-(1H-benzimidazol-2-yl)propyl](triphenyl)phosphonium bromide (C28H26N2P+Br-) as a molecular fluorophore (MF) on the surface of the TPP CNDs. The TPP CNDs showed better photostability than the commercially available MitoTracker™ Green and were highly capable for long-term imaging of mitochondrial fission during hyperglycemic conditions and structural changes upon an antidiabetic drug treatment, without altering their fluorescence nature.

Numerical study on uniformity of atmospheric helium gas dielectric barrier discharge on non-smooth surface regulated by sinusoidal clipping voltage

In practical applications of dielectric barrier discharges under atmospheric pressure, plasma usually acts on non-smooth surfaces. The electric field distortion and uneven surface charge distribution caused by its surface morphology will create an adverse effect on the uniformity and stability of the discharge. In this paper, we establish a simulation model of atmospheric pressure helium dielectric barrier discharge on a wavy lower dielectric plate, and use a sinusoidal clipping voltage to regulate the discharge uniformity. The results show that the discharge uniformity is improved compared with the unclipped case, and the discharge mode is changed from columnar mode to quasi-uniform mode. This can be attributed to the incomplete discharge dissipation caused by the reduction of air gap voltage; the subsequent electron backflow process neutralizes the the residual space electrons with the surface charge, which limits the accumulation of surface charges. With the increase of clipping ratio, the surface charge distribution becomes more uniform, and the radial fluctuation of electric field distribution weakens. In addition, the discharge efficiency is improved in a certain clipping range. This study reveals the mechanism of clipping voltage influence on non-smooth surface discharge, and provides a new idea for regulating the uniformity of dielectric barrier discharge.

Numerical investigations of turbulent heat transfer enhancement in circular tubes via modified internal profiles

Convective heat transfer enhancement in turbulent pipe flows via patterned surface textures is studied numerically via large eddy simulation (LES). The Reynolds and Prandtl numbers of the flow are 90,000 and 0.836, respectively. The patterned surface textures consist of ellipsoidal inward-facing elements, a wire coil, and spiral corrugations. The governing equations are solved on three-dimensional grids with the finite volume method using second-order temporal and spatial schemes. The mean Nusselt number and friction factor are calculated in each textured pipe and compared to an untextured baseline configuration. The inward-facing ellipsoidal elements showed the best performance yielding 22 − 42 % heat transfer enhancement with 41 − 97 % pressure loss penalty. The mechanisms driving convective heat transfer enhancement are examined via order-of-magnitude analysis of the first and second laws of thermodynamics. An effective convective mixing parameter is defined to reflect the interplay between the radial turbulence and local thermal gradients. The best enhancement technique yields 46% larger effective convective mixing with 26% lower turbulent kinetic energy compared to the least efficient case. The analysis shows that high heat transfer enhancement is promoted by inducing strong radial turbulent fluctuations in high-temperature-gradient regions while keeping other regions undisturbed. • Heat transfer enhancement via surface textures is studied via large eddy simulation. • Inward ellipsoids yield 22% higher heat transfer rate and 41% larger pressure drop. • The process driving heat transfer enhancement is explained via total energy budgets. • Near-wall radial fluctuations contribute the most towards enhancing heat transfer. • Axial vortices yield the best heat transfer enhancement and low entropy generation.

Pedestal fluctuation measurements with charge exchange imaging at the DIII-D tokamak

A new high radial resolution 2D multichannel Charge eXchange Imaging (CXI) diagnostic is under development for deployment at DIII-D. The diagnostic system will measure low-to-intermediate radial wavenumber carbon density fluctuations by observing the n = 8 - 7 (λ = 529.06 nm) C-VI emission line, resulting from charge exchange collisions between heating neutral beam atoms and the intrinsic carbon ion density. The new CXI diagnostic will provide measurements with ΔR ∼ 0.4 cm to access higher kr instabilities (kr < 8cm-1) predicted to arise in the steep-gradient region of the H-mode pedestal. The CXI system will feature 60 fiber bundles in a 12 × 5 arrangement, with each bundle consisting of four 1mm fibers. A custom optical system has been designed to filter and image incoming signals onto an 8 × 8 avalanche photodiode array. Additionally, a novel electronics suite has been designed and commissioned to amplify and digitize the relatively low-intensity carbon signal at a 2MHz bandwidth. Forward modeling results of the active C-VI emission suggest sufficient signal to noise ratios to resolve turbulent fluctuations. Prototype measurements demonstrate the ability to perform high frequency pedestal measurements.

Analysis of particle dispersion in a turbulent flow considering particle rotation

Non-spherical particles exist widely in natural and industrial fluid systems and the motions of non-spherical particles are significantly different from that of spherical particles. In this paper, a simplified model of non-spherical particles considering particle drag correction, lift, and rotation was established. Based on the Eulerian–Lagrangian simulation, the dispersion characteristics of spherical and non-spherical particles with different Stokes numbers in a high-speed turbulent jet were analyzed and compared considering the effect of particle rotation. The results show that, the differences in particle dispersion and radial velocity fluctuation between non-spherical particles and spherical particles in the jet are significant, especially when Stokes number is large. Moreover, the effects of different type of forces on the dispersion of non-spherical particles and spherical particles were compared in detail, which revealed that the change of the Magnus force caused by the increase in the angular velocity of non-spherical particles plays a dominant role in the differences of particle dispersion.

Super‐Resolution Near‐Infrared Fluorescence Microscopy of Single‐Walled Carbon Nanotubes Using Deep Learning

Single‐walled carbon nanotubes (SWCNTs) have unique optical and physical properties, with numerous biomedical imaging and sensing applications, owing to their near‐infrared (nIR) fluorescence which overlaps with the biological transparency window. However, their longer emission wavelengths compared to emitters in the visible range result in a lower resolution due to the diffraction limit. Moreover, the elongated high‐aspect‐ratio structure of SWCNTs poses an additional challenge on super‐resolution techniques that assume point emitters. Utilizing the advantages of deep learning and convolutional neural networks, along with the super‐resolution radial fluctuation (SRRF) algorithm for network training, a fast, parameter‐free, computational method is offered for enhancing the spatial resolution of nIR fluorescence images of SWCNTs. An average improvement of 22% in the resolution and 47% in signal‐to‐noise ratio (SNR) compared to the original images is shown, whereas SRRF leads to only 24% SNR improvement. The approach is demonstrated for a variety of SWCNT densities and length distributions, and a wide range of imaging conditions with challenging SNRs, including real‐time videos, without compromising the temporal resolution. The results open the path for accelerated and accessible super‐resolution of nIR fluorescent SWCNTs images, further advancing their applicability as nanoscale optical probes.

Investigation of flow behaviors in a fluidized bed reactor with binary mixture of Geldart-A and B particles

Flow dynamics in bubbling and turbulent fluidized beds containing both Geldart-A and B particles were investigated in this research. The numerical model was validated against experimental data, with a 6.16% average deviation. Results show that binary mixture segregation is enhanced as superficial gas velocity decreases. A larger flotsam packing ratio promotes homogeneous flotsam distribution; Second, bed density decreases with increasing bed height or superficial gas velocity. As the flotsam packing ratio decreases from 81.10 to 10.70%, bed density reaches the maximum at 41.50%, indicating the most severe volume contraction; Third, when the flotsam packing ratio decreases, the local mixing index's variances between upper and lower sections in dense phase first increases, then decreases, with stronger radial fluctuation detected; Fourth, as superficial gas velocity or flotsam packing ratio increases, the full mixing height ratio improves; Finally, multivariate correlations for dense phase bed expansion are established, yielding a 3.94% average error. • A modified EMMS drag model was adopted to examine flow features in a bidisperse fluidized bed. • The quantified impacts of superficial gas velocity and packing state on flow are obtained. • Multivariate correlations for dense phase bed expansion were fitted with high accuracy.