Spherical Filter Research Articles

Effect of oxides composition on the mechanical properties of non‐sintered spherical filters from waste steel slag

AbstractNon‐sintered spherical filters (NSSFs) from the waste steel slag for bottom filtration process are regarded as promising materials for sustainable development with economical benefits due to saving natural resource pebbles. To further optimize the preparation process, the influence mechanism of the main oxides on characteristics are comprehensively examined in this work. CaO in the raw materials makes it easier to release active components from the resulting glass body structure, while the expansion stress of Ca(OH)2 crystals precipitated under highly basic circumstances needs special consideration. SiO2 can positively contribute to the properties due to its adequate participation in the hydration reaction and the micro‐aggregate effect. Al3+ tends to combine and form a stable tetrahedral structure, which is conducive to liquid viscosity and the hindrance of hydration reaction of the active substance. Under the 6% mass ratio of MgO, NSSFs exhibit relatively excellent in physical properties. Specifically, the stimulation and promotion effect of MgO on hydration reaction is superior to the negative effect of excessive product Mg(OH)2 on expansion stress. Fe2O3 particles convert the structure in NSSFs to a dense state by the filling effect and serving as nucleation sites to promote the formation of hydration products.

Spherical convolutions on molecular graphs for protein model quality assessment

Processing information on three-dimensional (3D) objects requires methods stable to rigid-body transformations, in particular rotations, of the input data. In image processing tasks, convolutional neural networks achieve this property using rotation-equivariant operations. However, contrary to images, graphs generally have irregular topology. This makes it challenging to define a rotation-equivariant convolution operation on these structures. In this work, we propose spherical graph convolutional network that processes 3D models of proteins represented as molecular graphs. In a protein molecule, individual amino acids have common topological elements. This allows us to unambiguously associate each amino acid with a local coordinate system and construct rotation-equivariant spherical filters that operate on angular information between graph nodes. Within the framework of the protein model quality assessment problem, we demonstrate that the proposed spherical convolution method significantly improves the quality of model assessment compared to the standard message-passing approach. It is also comparable to state-of-the-art methods, as we demonstrate on critical assessment of structure prediction benchmarks. The proposed technique operates only on geometric features of protein 3D models. This makes it universal and applicable to any other geometric-learning task where the graph structure allows constructing local coordinate systems. The method is available at https://team.inria.fr/nano-d/software/s-gcn/.

Experimental study of seepage flow properties with biofilm development in porous media with different filter morphologies

Biofilm growth can impact seepage flow properties in the porous media, thereby affecting the performance of the infiltration systems. To better understand and characterize the biofilm distribution and its effect on seepage flow fields in the porous media with different morphologies, two-dimensional transparent flow cells were developed using X-ray images of zeolite, gravel, and ceramsite columns to study the effect of biofilm development and the pore structure on seepage flow properties. The results revealed that the filter morphology and biofilm growth significantly impacted the seepage flow field in porous media. With biofilm growth, a preferential flow pathway was more likely to be formed in angular filter cells (zeolite-shaped cells) than spherical filter cells (ceramsite-shaped cells). It was also found that microbial growth rate was closely related to seepage flowrate in 2D porous media cells. The biofilm grew faster in the areas with higher seepage flowrate. The biofilm accumulation did not seem to affect the location of the preferential seepage flow, probably due to the high permeability of the biofilm in the large pore throats. Although the water head loss of ceramsite-shaped cells was larger than that of two others due to its relatively smaller size of pore throat, the ceramsite-shaped cells presented small dead zone and short-circuiting, which means that ceramiste filter media had higher hydraulic efficiency.

Heterogeneous Spatial Quality for Omnidirectional Video

Heterogeneous spatial quality in 360-degree videos is characterized by regions of high and low quality appearing in the same video chunk. Encoding quality-varying omnidirectional videos enables bandwidth waste optimization without compromising the quality inside the client's viewport. Heterogeneous spatial quality has been implemented using either the concept of tiling or Facebook's offset projection. In this paper, we study the preparation of heterogeneous 360-degree videos with three main contributions. We propose two novel approaches that prepare heterogeneous quality versions of a 360-degree video based on two video decomposition techniques: the Gaussian pyramid and the Laplace pyramid. We also introduce a spherical filter for omnidirectional videos which allows to further reduce the video bit-rate by exploring the spherical properties of the 360-degree videos. We compare the performance of the proposed three methods to tiling and the offset projection in representative scenarios of heterogeneous spatial quality in 360-degree videos and highlight the key trade-off between bit-rate and video quality to consider when implementing these approaches.

Investigation on optical path of laser detection of multiple thermal fluids and suppression of high-temperature stray radiation interference

The on-line detection of the component content of multiple thermal fluids (MTFs) has a crucial impact on heavy oil recovery. A long absorption path-length is an indispensable condition for on-line laser detection system (MTFs-OLDS). Therefore, an open-path reflectarray gas cell was presented based on multi-reflection absorption spectroscopy model. The off-axis optical receiver with extinction threads and spherical filter cavity was designed to suppress the thermal radiation emitted from high temperature injection tube internal wall. The effect of detecting deviations on receiving efficiency and the effectiveness of stray radiation suppression structure were analyzed by Monte Carlo ray tracing method. The results show that the proposed absorption path-length is enhanced 22 times, when the optical window material is fused silica and the reflector mirror coating is silver. The increases of beam divergence angle and alignment error have a reduction role of receiving efficiency. Extinction ratio of extinction threads is improved with base length and hemline length decrease. After adding the filter cavity in the dewar baffle, the point source transmittance (PST) of off-axis optical receiver can be reduced to 1.21 × 10−7 at the off-field angle 5° of incident stray light. The conclusion indicates the PST of the optical receiver of MTFs-OLDS is less than the maximum allowable value, and the level of stray radiation suppression is dramatically improved.

Numerical and Experimental Study of Bubble Dynamics in Contact with a Solid Surface

A complex numerical and experimental method is proposed for studying 3D dynamics of a bubble contacting with a surface in the presence of an acoustic field. The numerical approach is based on the boundary element method for potential flows, which is most efficient for solving the problems in a 3D formulation. The use of heterogeneous computer architectures consisting of central graphic processors and becoming more and more popular makes it possible to increase the scale of the problem and sufficiently reduce the calculation time. The mesh destabilization problems are solved using a spherical filter. To describe the contact line dynamics, a semi-empirical law of motion is used. The experimental method is based on high-speed recording and optical microscopy. An air bubble contacts with the inner surface of an experimental cell made from acrylic glass and filled with distilled water. The acoustic field in the cell generated by a disk-shaped acoustic radiator is measured using a hydrophone. The behavior of the bubble contacting with a hydrophillic surface is considered for the cases of a fixed or moving contact line. The shape and volume oscillations of the bubble are investigated. The results of numerical simulations agree qualitatively with the experimental data.

A Finite Element Galerkin High Order Filter for the Spherical Limited Area Model

Two dimensional finite element method with quadrilateral basis functions was applied to the spherical high order filter on the spherical surface limited area domain. The basis function consists of four shape functions which are defined on separate four grid boxes sharing the same gridpoint. With the basis functions, the first order derivative was expressed as an algebraic equation associated with nine point stencil. As the theory depicts, the convergence rate of the error for the spherical Laplacian operator was found to be fourth order, while it was the second order for the spherical Laplacian operator. The accuracy of the new high order filter was shown to be almost the same as those of Fourier finite element high order filter. The two-dimension finite element high order filter was incorporated in the weather research and forecasting (WRF) model as a hyper viscosity. The effect of the high order filter was compared with the built-in viscosity scheme of the WRF model. It was revealed that the high order filter performed better than the built in viscosity scheme did in providing a sharper cutoff of small scale disturbances without affecting the large scale field. Simulation of the tropical cyclone track and intensity with the high order filter showed a forecast performance comparable to the built in viscosity scheme. However, the predicted amount and spatial distribution of the rainfall for the simulation with the high order filter was closer to the observed values than the case of built in viscosity scheme.

Constriction size distributions of granular filters: a numerical study

The retention capability of granular filters is controlled by the narrow constrictions connecting the voids within the filter. The theoretical justification for empirical filter rules used in practice includes consideration of an idealised soil fabric in which constrictions form between co-planar combinations of spherical filter particles. This idealised fabric has not been confirmed by experimental or numerical observations of real constrictions. This paper reports the results of direct, particle-scale measurement of the constriction size distribution (CSD) within virtual samples of granular filters created using the discrete-element method (DEM). A previously proposed analytical method that predicts the full CSD using inscribed circles to estimate constriction sizes is found to poorly predict the CSD for widely graded filters due to an over-idealisation of the soil fabric. The DEM data generated are used to explore quantitatively the influence of the coefficient of uniformity, particle size distribution and relative density of the filter on the CSD. For a given relative density CSDs form a narrow band of similarly shaped curves when normalised by characteristic filter diameters. This lends support to the practical use of characteristic diameters to assess filter retention capability.

(Continuous) Phase Modulation on the Hypersphere

We introduce phase modulation on the hypersphere (PMH) for load-modulated multiple-input multiple-output (MIMO) transmitters with a single central power amplifier. In PMH, the peak to average ratio of the sum power before pulse shaping is 1; thus, the central power amplifier of load-modulated MIMO transmitters does not require any back-off. We derive the capacity of PMH on an additive white Gaussian noise channel and show that the input signal should be uniformly distributed on a hypersphere. The mutual information of uniformly distributed PMH input is derived in an uplink multiple-access independent identically distributed Gaussian MIMO channel using the replica method from statistical physics. Furthermore, discrete PMH is introduced using spherical codes and also generalizing minimum shift keying from the complex unit circle to the hypersphere. We investigate different pulse shaping methods for PMH including a novel spherical filtering. Using spherical pulse shaping, the signal stays on the hypersphere. Various filters are investigated, and a tradeoff between spectral shape and peak-to-average-sum-power ratio (PASPR) is found. For as few as four antennas, good spectral properties (similar to root-raised cosine pulses) can be achieved at very low PASPR. Both former and latter further improve with increasing the number of antennas.

Efficient and Accurate Spherical Kernel Integrals Using Isotropic Decomposition

Spherical filtering is fundamental to many problems in image synthesis, such as computing the reflected light over a surface or anti-aliasing mirror reflections over a pixel. This operation is challenging since the profile of spherical filters (e.g., the view-evaluated BRDF or the geometry-warped pixel footprint, mentioned before) typically exhibits both spatial and rotational variation at each pixel, precluding precomputed solutions. We accelerate complex spherical filtering tasks using isotropic spherical decomposition (ISD), decomposing spherical filters into a linear combination of simpler isotropic kernels. Our general ISD is flexible to the choice of the isotropic kernels, and we demonstrate practical realizations of ISD on several problems in rendering: shading and prefiltering with spatially varying BRDFs, anti-aliasing-environment-mapped mirror reflections, and filtering of noisy reflectance data. Compared to previous basis-space rendering solutions, our shading solution generates ground-truth-quality results at interactive rates, avoiding costly reconstruction and large approximation errors.

Adsorption Removal of Phosphorus from Wastewater by Steel Slag Filter Material

Spherical steel slag filter material with high porosity, large specific surface area was made by using steel slag as the main raw material, adding binder and pore forming agent. The influences of PH, phosphorus concentration and adsorption time on the adsorption effect of steel slag filter material were investigated. The adsorption characteristics of steel slag filter on phosphorus were studied based on adsorption isotherm model and adsorption kinetics model. Adsorption results were used to fit Langmuir and Freundlish formula. The correlation of Freundlish model was significant and the correlation coefficient was 0.92907.

Attitude Estimation Based on the Spherical Simplex Transformation Modified Unscented Kalman Filter

An antenna attitude estimation algorithm is proposed to improve the antenna pointing accuracy for the satellite communication on-the-move. The extrapolated angular acceleration is adopted to improve the performance of the time response. The states of the system are modified according to the modification rules. The spherical simplex transformation unscented Kalman filter is used to improve the precision of the estimated attitude and decrease the calculation of the unscented Kalman filter. The experiment results show that the proposed algorithm can improve the instantaneity of the estimated attitude and the precision of the antenna pointing, which meets the requirement of the antenna pointing.

Preparation of Compound Clinoptilolite Filter Material and Performance of Ammonia Nitrogen Removal

This experiment use natural clinoptilolite powder as main materials to prepare the large specific surface and high porosity spherical compound filter material by adding adhesive and pore-forming agent etc.This compound filter material has favourable effect when treating sanitary wastewater. The static adsorption test showed that the absorption ratio of ammonia-nitrogen is 58.5% when the compound filter material dosage was 100g/L, NH4+-N concentration was 100mg/L and the contact time was 40min.The cure fitting of the adsorption isotherm of NH4+-N on the compound filter material could be well described by the Langmuir formula and R2 (the coefficient of determination) is 0.99216. At the stably running phase, when the average concentrations of influent NH3-N was 35mg/L, the average removal ratio and concentration of effluent NH4+-N reached 83.51% and 5.81mg/L which could meet the first degree of national wastewater discharge standard (GB 8978-1996).

Adsorption Performance of Ammonia onto Compound Clinoptilolite Filter Material

In order to combine the microbial metabolism characteristics in biological aerated filter (BAF) with the adsorption and ion-exchange ability of natural clinoptilolite to treat sanitary wastewater, the experiment use clinoptilolite powder as main materials to prepare the large specific surface and high porosity spherical compound filter material by adding adhesive and pore-forming agent etc and get better effect on sanitary wastewater treatment.The static adsorption test showed that the adsorb ratios of ammonia-nitrogen is 58.5% when the compound filter material dosage was 100g/L, NH3-N concentration was 100mg/L and the contact time was 40min.The cure fitting of the adsorption isotherm of NH3-N on the compound filter material could be well described by the Langmuir formula and the coefficient of determination is 0.99216.

The Experimental Study of Ammonia Removal in Compound Clinoptilolite Biological Aerated Filter (BAF)

The experiment use clinoptilolite powder as main materials to prepare the large specific surface and high porosity spherical compound filter material.Experimental results indicate that compound filter material is used as filter medium in biological aerated filter for wastewater treatment，in the early 5 days the average removal rate of NH3-N was 58.5% in biological aerated filter when the average influent NH3-N concentration was 37 mg/L. At the stably running phase, the average removal ratio and concentration of effluent NH3-N reached 83.51% and 5.81mg/L, when the average concentrations of influent NH3-N was 35mg/L which could meet the first order discharging index of Integrated Wastewater Discharge Standard (GB 8978-1996).

The Preparation of Composite Zeolite Filter

Using natural-zeolite as main raw material, prepare spherical composite zeolite filter material by adding adhesive, pore-forming agent, etc. By measuring cylinder compressive strength apparent porosity and adsorption capacity of ammonia and doing orthogonal experiment, the optimal process combination is C3A1B3, namely ω zeolite powder : ω adhesive : ω pore-forming agent =55%：35%：10%, activation temperature is 150°C, activation time is 3h.The end product’s packing density is 674Kg/m3, cylinder compressive strength is 4.32MPa, and apparent porosity is 59.02%.

The Performance Test of Composite Zeolite Filter

Use natural zeolite to prepare spherical composite zeolite filter material. With range analysis, the composite zeolite filter material’s packing density is 674Kg/m3, cylinder compressive strength is 4.32MPa, and apparent porosity is 59.02%. Compared with ceramsite, composite zeolite filter whose surface roughness has larger specific surface area and higher porosity. At the start of biofilm formation and stability of the operational phase, composite zeolite filter Biological Aerated Filter (BAF)’s ammonia removal is better than ceramsite BAF, and its Biofilm biomass is higher, thus more proper to be the carrier of BAF.

The impact of anisotropy from finite light traveltime on detecting ionized bubbles in redshifted 21-cm maps

The detection of ionized bubbles around quasars in redshifted 21-cm maps is possibly one of the most direct future probes of reionization. We consider two models for the growth of spherical ionized bubbles to study the apparent shapes of the bubbles in redshifted 21-cm maps, taking into account the finite light traveltime (FLTT) across the bubble. In both models, the bubble has a period of rapid growth beyond which its radius either saturates or grows slowly. We find that the FLTT, whose effect is particularly pronounced for large bubbles, causes the bubble’s image to continue to grow well after its actual growth is over. There are two distinct FLTT distortions in the bubble’s image: (i) its apparent centre is shifted along the line of sight (LOS) towards the observer from the quasar and (ii) it is anisotropic along the LOS. The bubble initially appears elongated along the LOS. This is reversed in the later stages of growth where the bubble appears compressed. The FLTT distortions are expected to have an impact on matched filter bubble detection where it is most convenient to use a spherical template for the filter. We find that the best matched spherical filter gives a reasonably good estimate of the size and the shift in the centre of the anisotropic image. The mismatch between the spherical filter and the anisotropic image causes a degradation in the signal-to-noise ratio relative to that of a spherical bubble. The degradation is in the range 10–20 per cent during the period of rapid growth when the image appears elongated and is less than 10 per cent in the later stages when the image appears compressed. We conclude that a spherical filter is adequate for bubble detection. The FLTT distortions do not affect the lower limits for bubble detection with 1000 h of GMRT observations. The smallest spherical filter for which a detection is possible has comoving radii 24 and 33 Mpc for 3σ and 5σ detections, respectively, assuming a neutral fraction 0.6 at z∼ 8.

Structure change of Typhoon Nari (2007) in the weakening stage

The structure of Typhoon Nari (11th 2007) was investigated based on the field observations and the numerical simulation with the Weather Research and Forecasting (WRF) model. The observations were carried out using the wind profiler and dual Doppler radar at Haenam Weather Observatory and Jeju Island, which were analyzed along with the Quick Scatterometer (QuikSCAT) dataset. The simulation data were obtained from the 60 hours run of the WRF model to get the detailed structure, intensity, and track of the typhoon during the period from 0000 UTC 14 September 2007 to 1200 UTC 16 September. The TC initialization for the numerical simulation was performed with the use of the 3D balanced bogus vortex and spherical high-order filter proposed by Kwon and Cheong (2010) to provide accurate forecasts of the track and intensity. The horizontal wind fields at the surface, the tangential and radial winds, were analyzed using the QuikSCAT data and the model results. The vertical wind structure was investigated using the dual-Doppler and wind profiler data in combination with the model simulation results. The structure change of Typhoon Nari during the weakening stage was analyzed based on the simulations. Compared to the mature stage, in the weakening stage the Typhoon Nari was found to have stronger asymmetric component, and it exhibited stronger vertical tilt but with reduced vertical extent. It was shown that the strong uppertropospheric outflow loses its strength gradually in the weakening stage, but the height of maximum outflow layer was remained unchanged due to the environmental forcing by the upper-troposphere jet. Comparison of the observation and model simulation revealed that a weak outflow was formed in the mid-troposphere in addition to the primary outflow in the upper troposphere.

Transformation properties of dynamic subgrid-scale models in a frame of reference undergoing rotation

Theoretical consideration is presented for the transformation properties of the subgrid-scale (SGS) models for the SGS stress tensor in a non-inertial frame of reference undergoing rotation. As was previously shown (Speziale, C.G., Geophys. Astrophys. Fluid Dynamics 33, 199 (1985)), an extra correction term is yielded for the SGS stress tensor in the transformation of a rotating frame relative to an inertial framing. We derived the exact expression for the correction term for the spherical Gaussian filter function. Certain transformation rules are imposed on the SGS stress by the derived correction term, namely the SGS stress is not indifferent to a frame rotation, but the divergence of the SGS stress is frame indifferent. Conformity of the modelled SGS stress tensor estimated using the previous dynamic SGS models (the dynamic Smagorinsky, dynamic mixed and nonlinear models) with these transformation rules is examined. It is shown that values for certain model parameters contained in the mixed models can be theoretically determined by imposing these rules. We have conducted the a priori and a postepriori numerical assessments of the SGS models in decaying homogeneous turbulence which is subjected to rotation. All of the previous dynamic models were found to violate the rules except for the nonlinear model. The nonlinear model is form invariant, but the result obtained using the nonlinear model showed significant deviation from the DNS data. Failure of previous models was attributable to insufficient accuracy in approximating the modified cross term in the decomposition of the SGS stress tensor. A dynamic mixed model is proposed to eliminate the truncation error for the modelled correction term, in which multilevel filtering of the velocity field was utilized. The proposed model obeyed the transformation rules when the level of the multifiltering operation was large. It was shown that the defiltered model is derived in the limit of the infinite level of multifiltering and that the defiltered model is form invariant.