Particle Radius Research Articles

Effect of titanium nitride inclusions on the mechanical properties of direct laser deposited Inconel 718

Additive manufacturing (AM) of metal is attractive for its ability to fabricate complex and tailored structures. However, unusual thermal history during the manufacturing process creates unique microstructures, which leads to non-uniform mechanical behavior. In this paper, we report the room temperature and high temperature mechanical properties of Inconel 718 fabricated by laser-based directed energy deposition. Surprisingly, failure strain at all tested temperatures exhibited noticeable scatter, which is attributed to the formation of titanium nitride (TiN) inclusions. While heat treatment was conducted on AM Inconel 718 to minimize the influence of the inhomogeneous as-built microstructure, it resulted in significant increase in the volume fraction, number density, and maximum particle radius of the TiN inclusions. Consequently, dispersion of mechanical properties became more severe. Experimental investigation (strain mapping, fractography, and X-ray microscopy) supported by finite element analysis implies that premature failure of AM Inconel 718 is mainly due to transgranular cracks of the TiN inclusions that propagates into the matrix.

Estimation of carbon dust particle lifetime in a radio-frequency thermal plasma

A carbon dust particle in a collisionless thermal plasma is studied under the assumption of the drifting Maxwellian distribution with a time varying velocity caused by the oscillatory radio-frequency (RF) field. The dust particle potential decreases while its fluctuation increases with the increasing RF field strength or the decreasing frequency even taken into account the thermionic current. As the thermionic current is increased by changing the dust particle surface temperature, the resultant increasing dust particle potential can vary from negative to positive, and the fluctuation of the dust particle potential increases first and then decreases. When the dust particle heating and mass loss processes are considered, it is found that the fluctuation of the total energy flux to the dust particle is mainly determined by the electron energy flux, which causes the stair-like increase of the dust particle surface temperature in heating process and the stair-like decrease of the dust particle radius in the mass loss process. With the increasing RF field strength or decreasing frequency, the increase of the total energy flux to the dust particle leads to the decrease of the dust particle lifetime. The results mean that the presence of the RF field can shorten the dust particle lifetime or reduce the dust particle survivability in RF plasma, by compared with in the absence of the RF field.

Numerical Investigation on the Performance of IT-SOEC with Double-Layer Composite Electrode

The double-layer composite electrode has attracted increasing attention in the field of intermediate-temperature solid oxide electrolysis cells (IT-SOEC). To investigate the effects of the cathode diffusion layer (CDL) and cathode functional layer (CFL) structure on performance, a three-dimensional multi-scale IT-SOEC unit model is developed. The model comprehensively considers the detailed mass transfer, electrochemical reaction and heat transfer processes. Meanwhile, percolation theory is adopted to preserve the structural characteristics and material properties of the composite electrode. The mesostructure model and the macroscopic model are coupled in the solution. The effects of the porosity of the CDL, the electrode particle size and the composition of the composite electrode in the CFL on the mass transport process and electrolysis performance of the IT-SOEC unit are analyzed. The results show that the appropriate mass flux and energy consumption in the electrode are obtained with a CDL porosity in the range of 0.3–0.5. The decrease in the electrode particle size is conducive to the improvement of the electrolysis reaction rate. The maximum reaction rate in the CFL increases by 32.64% when the radius of the electrode particle is reduced from 0.5 μm to 0.3 μm. The excellent performance can be obtained when the volume fractions of the electrode phase and electrolyte phase in the CFL tend to be uniform. This study will provide guidance for the performance optimization of IT-SOEC and further promote the development of IT-SOEC hydrogen production technology in engineering applications.

DISJOINING PRESSURE IN THIN SPHERICAL LIQUID FILMS AND VAPOR LAYERS WITH MOLECULAR CORRELATIONS INCLUDED

Based on the expression for a grand thermodynamic potential as a molecular density functional, disjoining pressures in thin liquid films around nanosized wettable spherical particles and in thin vapor layers around nonwettable particles are calculated depending the degree of lyophilicity, film thickness and particle size. A characteristic feature of the approach is the full consideration of hard-sphere molecular correlations according to the fundamental measure theory in the density functional method and finding the complete dependence of the grand thermodynamic potential of the system on stable droplet or bubble size. Although the obtained results show a qualitative agreement between the new calculated disjoining pressure dependences and those obtained by us earlier in the framework of a simpler gradient method of the molecular density functional, the new results differ significantly quantitatively. It is confirmed that the disjoining pressure in the liquid film around nanosized lyophilic particle grows with the particle radius and lyophilicity.

Diffusiophoresis of hydrophobic spherical particles in a solution of general electrolyte

The present article deals with the diffusiophoresis of hydrophobic rigid colloids bearing arbitrary ζ-potential. We derived the generic expression for the diffusiophoretic velocity of such a colloid exposed in an externally applied concentration gradient of the general electrolyte solution. The derived expression takes into account the relaxation effect and is applicable for all values of surface ζ-potential and hydrodynamic slip length at large κa (κa≥ca.50), where κ−1 is the thickness of the electric double layer and a is the particle radius. We further derived several closed-form expressions for particle velocity derived under various electrostatic and hydrodynamic conditions when the particle is exposed in an applied concentration gradient of binary symmetric (e.g., z:z), asymmetric (1:2, 2:1, 3:1, 1:3), and a mixed electrolyte (mixture of 1:1 and 2:1 electrolytes). The results for diffusiophoretic velocity are further illustrated graphically to indicate the mutual interaction of chemiphoresis, induced electrophoresis due to unequal mobilities of cations and anions of the electrolyte, and the mechanism by which the sufficiently charged particle migrates opposite to the direction of the applied concentration gradient. The impact of hydrophobicity is further discussed.

Search for Ultraheavy Dark Matter from Observations of Dwarf Spheroidal Galaxies with VERITAS

Dark matter is a key piece of the current cosmological scenario, with weakly interacting massive particles (WIMPs) a leading dark matter candidate. WIMPs have not been detected in their conventional parameter space (100 GeV ≲M χ ≲ 100 TeV), a mass range accessible with current Imaging Atmospheric Cherenkov Telescopes. As ultraheavy dark matter (UHDM; M χ ≳ 100 TeV) has been suggested as an underexplored alternative to the WIMP paradigm, we search for an indirect dark matter annihilation signal in a higher mass range (up to 30 PeV) with the VERITAS γ-ray observatory. With 216 hr of observations of four dwarf spheroidal galaxies, we perform an unbinned likelihood analysis. We find no evidence of a γ-ray signal from UHDM annihilation above the background fluctuation for any individual dwarf galaxy nor for a joint-fit analysis, and consequently constrain the velocity-weighted annihilation cross section of UHDM for dark matter particle masses between 1 TeV and 30 PeV. We additionally set constraints on the allowed radius of a composite UHDM particle.

Lower bound on the time-to-mass ratio of closed circular motions around spinning and charged naked singularities

It has recently been conjectured that circular trajectories (geodesic as well as non-geodesic) around central compact objects are characterized by the time-to-mass universal lower bound T_{infty }/M>{{mathcal {C}}}, where {T_{infty },M} are respectively the orbital period as measured by flat-space asymptotic observers and the mass of the central compact object, and mathcal{C}=O(1) is a dimensionless constant of order unity. In the present paper we prove that this dimensionless bound is respected by circular orbits around central naked singularities. Intriguingly, it is explicitly proved that the orbital-time-to-mass ratio T_{infty }/M around a central super-spinning singularity remains finite even in the rrightarrow 0 limit of circular orbits with infinitesimally small radial coordinates (which are characterized by a diverging time-to-radius ratio, T_{infty }/rrightarrow infty ). In particular, we reveal the fact that the shortest orbital period around a super-spinning naked singularity is given by the dimensionless relation T_{infty }/M=2pi . In addition, we explore the functional behavior of the time-to-mass ratio of circular trajectories around super-charged (non-vacuum) naked singularities and prove that the dimensionless ratio T_{infty }/M(r) is bounded from below, where M(r) is the gravitational mass contained within the orbital radius of the test particle.

Slow Rotation of a Soft Colloidal Sphere Normal to Two Plane Walls

The creeping flow of a viscous fluid around a soft colloidal sphere rotating about a diameter normal to two planar walls at an arbitrary position between them is theoretically investigated in the steady limit of small Reynolds numbers. The fluid velocity outside the particle consists of the general solutions of the Stokes equation in circular cylindrical and spherical coordinates, while the fluid velocity inside the porous surface layer of the particle is expressed by the general solution of the Brinkman equation in spherical coordinates. The boundary conditions are implemented first on the planar walls by means of the Hankel transforms and then at the particle and hard-core surfaces by a collocation technique. The torque exerted on the particle by the fluid is calculated as a function of the ratio of the core-to-particle radii, ratio of the particle radius to the flow penetration length of the porous layer, and relative particle-to-wall spacings over the entire range. The wall effect on the rotating soft particle can be significant. The hydrodynamic torque exerted on the confined soft sphere increases as the relative particle-to-wall spacings decrease and stays finite even when the soft sphere contacts the plane walls. It is smaller than the torque on a hard sphere (or soft one with a reduced thickness or penetration length of the porous layer), holding the other parameters constant. For a given relative wall-to-wall spacing, this torque is minimal when the particle is situated midway between the walls and rises as it locates closer to either wall.

The Hemispheric Asymmetry of Gravity Wave Impact on the Polar Mesospheric Cloud, Based on the Aeronomy of Ice in the Mesosphere Satellite

In this research, we analyze the gravity wave (GW) energy density, ice water content (IWC), particle radius, and cloud albedo data of 16 polar mesospheric cloud (PMC) seasons in the Northern Hemisphere (NH) from 2007 to 2014 and Southern Hemisphere (SH) from 2007/2008 to 2014/2015, based on observations from the Cloud Imaging and Particle Size and Solar Occultation For Ice Experiment instruments. The influence of GW activity on the formation of PMCs is studied by hemispheric contrast. In the NH, the GW flux generally starts to increase significantly around the summer solstice during the 8 PMC seasons. In 6/8 of these seasons, the IWC is positively correlated with the variation of GW. When the GW activity is enhanced to reach the maximum, the IWC will start to increase and reach the peak within 0–23 days. In comparison, in the SH, the GW peaks around 55 days after the solstice. The timing of PMC appearance also varies, with the IWC starting to grow 20 days after the solstice and the GW increasing in 55 days after the solstice. In particular, the IWC starts even earlier than the solstice in the seasons of 2012/2013 and 2013/2014.

Research on longitudinal vibration suppression of underwater vehicle shafting based on particle damping

A particle damper is applied to suppress the longitudinal vibration of underwater vehicle shafting in order to reduce vibration level and improve silence and stealth of underwater vehicles. The model of rubber-coated steel particle damper was established with discrete element method and PFC3D simulation software, the damping energy consumption law of collision and friction between particle and damper and between particle and particle investigated, the effects of particle radius, mass filling ratio, cavity length, excitation frequency, excitation amplitude, rotating speed and both stacking and motion states of particles on the system vibration suppression were discussed, and the bench test was carried out to verify the law. It revealed the mechanism of longitudinal vibration suppression of particle damping, established the intrinsic relationship between of total energy consumption of particle and vibration of system, and put forward the evaluating method of longitudinal vibration suppression effect by total energy consumption of particle and vibration reduction ratio. The research results show that the mechanical model of particle damper is reasonable and the simulation data is reliable; the rotating speed, mass filling ratio and cavity length have significant effects on the total energy consumption of particle and vibration reduction ratio.

Optimal hybrid renewable energy generation planning based on BSG-starcraft radius particle swarm optimization

Optimal hybrid renewable energy generation planning based on BSG-starcraft radius particle swarm optimization

Effect of the Distribution Characteristics of TiC Phases Particles on the Strengthening in Nickel Matrix

Molecular dynamics (MD) was used to simulate the effect of TiC particles distribution on the tribological behavior of the reinforced composites. The mechanical properties, friction coefficient, number of wear atoms, stress and temperature, and microscopic deformation behavior of TiC/Ni composites during nano-friction were systematically investigated by MD to reveal the effect of TiC distribution on the friction removal mechanism of the material. It was found that the larger the radius of the TiC particles, or the shallower the depth of the TiC particles, the easier it was to generate stress concentrations around the TiC particles, forming a high dislocation density region and promoting the nucleation of dislocations. This leads to severe friction hardening, reducing the atomic number of abrasive chips and reducing the friction coefficient by approximately 6% for every 1 nm reduction in depth, thus improving the anti-wear capacity. However, when the radius of the TiC particles increases and the thickness from the surface deepens, the elastic recovery in material deformation is weakened. We also found that the presence of the TiC particles during the friction process changes the stress state inside the workpiece, putting the TiC particles and the surrounding nickel atoms into a high-temperature state and increasing the concentrated temperature by 30 K for every 1 nm increase in depth. Nevertheless, the workpiece atoms below the TiC particles invariably exist in a low-temperature state, which has a great insulation effect and improves the high-temperature performance of the material. The insight into the wear characteristics of TiC particles distribution provides the basis for a wide range of TiC/Ni applications.

Light scattering of a uniform uniaxial anisotropic sphere by an on-axis high-order Bessel vortex beam.

Analytical solutions to the scattering of a uniform uniaxial anisotropic sphere illuminated by an on-axis high-order Bessel vortex beam (HOBVB) are investigated. Using the vector wave theory, the expansion coefficients of the incident HOBVB in terms of the spherical vector wave functions (SVWFs) are obtained. According to the orthogonality of the associated Legendre function and exponential function, more concise expressions of the expansion coefficients are derived. It can reinterpret the incident HOBVB faster compared with the expansion coefficients of double integral forms. The internal fields of a uniform uniaxial anisotropic sphere are proposed in the integrating form of the SVWFs by introducing the Fourier transform. The differences of scattering characteristics of a uniaxial anisotropic sphere illuminated by a zero-order Bessel beam, Gaussian beam, and HOBVB are exhibited. Influences of the topological charge, conical angle, and particle size parameters on the angle distributions of the radar cross section are analyzed in detail. The scattering and extinction efficiencies varied with the particle radius, conical angle, permeability, and dielectric anisotropy are also discussed. The results provide insights into the scattering and light-matter interactions and may find important applications in optical propagation and optical micromanipulation of biological and anisotropic complex particles.

An integrated modeling approach to predict critical flow rate for fines migration initiation in sandstone reservoirs and water-bearing formations

Fines migration causes formation damage in sandstone reservoirs and water-bearing subsurface formations. Several factors affect fines migration such as composition and salinity of permeating brine, flow rate, and system pH. Electrostatic forces of van der Waals attraction and electric double layer repulsion, gravitational force and hydrodynamic force all contribute to fines detachment and migration under certain conditions. The current research presents a new integrated model of electrostatic, gravitational, and hydrodynamic forces to estimate the critical injection rate of NaCl brine for fines migration initiation in subsurface formations.The DLVO modeling approach was modified by considering electrostatic, hydrodynamic, and gravitational forces. Parameters such as injection brine salinity, average fine particle size, and zeta potential of sand-brine systems were used, and effective forces were quantified. A microscopic force and torque balance approach was applied to model hydrodynamic forces to modify the DLVO model. The developed models were validated with experimental results.The profiles of injection velocity versus fine particle radius were generated and the models predicted critical flow rates of 0.9, 2.6, and 3.8 cc/min for 0.15 M, 0.2 M, and 0.25 M NaCl, respectively. For model validation, the coreflood experiments were performed on Berea sandstone core samples under given salinities and critical flow rates were determined. Comparable experimental results were obtained with critical flow rates of 1, 3, and 4 cc/min for 0.15 M, 0.2 M, and 0.25 M NaCl, respectively. In addition, sensitivity analysis assesses the impact of different forces on the fines migration phenomenon.Formation damage caused by fines migration is a well-documented problem in sandstone reservoirs and water-bearing formations. Regulating the injection/ permeating fluid rate and salinity can avoid fines migration and associated permeability impairment. Our study presents a novel approach incorporating electrostatic, gravitational, and hydrodynamic forces to accurately predict fines mobilization in fine-containing subsurface formations.

What in particle morphology determines the DLVO interaction energy between hematite particles in electrolyte solutions?

The experimental stability of hematite particles (radius: ∼74 nm) dispersed in solutions of varying salinity deviates considerably from predictions based on the Derjaguin–Landau–Verwey–Overbeek (DLVO) theory. For untreated hematite particles, at pH = 6 and 10, the theoretical values could be matched to the experimental ones by modifying the particle radius used in calculations from 74 to 13 nm. For particles heat-treated at 350 °C for 1 h, the theoretical values at pH = 10 could also be matched to the experimental ones by modifying the particle radius to 7 nm. Atomic force microscopy measurements revealed that the radius of curvature for surface protrusions on the hematite particles was 14 nm on average for the untreated particles at pH = 6 and 10, which almost equals the aforementioned modified particle radius. For the heat-treated hematite particles at pH = 10, the average radius of curvature was 9 nm, which also matched the corresponding modified particle radius. Therefore, we argue that the interaction energy between hematite particles is governed by not the overall particle radius but the curvature radius for surface protrusions. This could account for the discrepancy between theory and experiment regarding the salinity-dependent stability ratio of these particle dispersions.

Metasurface supporting quasi-BIC for optical trapping and Raman-spectroscopy of biological nanoparticles.

Optical trapping combined with Raman spectroscopy have opened new possibilities for analyzing biological nanoparticles. Conventional optical tweezers have proven successful for trapping of a single or a few particles. However, the method is slow and cannot be used for the smallest particles. Thus, it is not adapted to analyze a large number of nanoparticles, which is necessary to get statistically valid data. Here, we propose quasi-bound states in the continuum (quasi-BICs) in a silicon nitride (Si3N4) metasurface to trap smaller particles and many simultaneously. The quasi-BIC metasurface contains multiple zones with high field-enhancement ('hotspots') at a wavelength of 785 nm, where a single nanoparticle can be trapped at each hotspot. We numerically investigate the optical trapping of a type of biological nanoparticles, namely extracellular vesicles (EVs), and study how their presence influences the resonance behavior of the quasi-BIC. It is found that perturbation theory and a semi-analytical expression give good estimates for the resonance wavelength and minimum of the potential well, as a function of the particle radius. This wavelength is slightly shifted relative to the resonance of the metasurface without trapped particles. The simulations show that the Q-factor can be increased by using a thin metasurface. The thickness of the layer and the asymmetry of the unit cell can thus be used to get a high Q-factor. Our findings show the tight fabrication tolerances necessary to make the metasurface. If these can be overcome, the proposed metasurface can be used for a lab-on-a-chip for mass-analysis of biological nanoparticles.

Monte Carlo analysis of focused Gaussian beam in scattering media: Curvature correction and Mie scattering

We introduce curvature correction into the Monte Carlo (MC) technique to determine the suitable photon-step size and initial photon distribution in the focusing lens aperture, that can account for the effects of the radius of curvature on the axial intensity profile of a focused Gaussian beam that is propagated through a scattering medium. The scattering anisotropy of the medium is determined via the Mie scattering theory for given values of the scattering particle radius, density, and phase distribution values while optical ray tracing is used to determine the occurrence of scattering events. We evaluate the performance of the modified MC technique for random and periodic media by examining the axial intensity profiles of the propagating focused beam. Relative to the predictions of the scalar diffraction theory, curvature correction improves the accuracy of the MC results with decreasing step size s and increasing number of steps Ns. In the absence of scattering, the axial beam distribution approaches that of the scalar diffraction theory for a given numerical aperture (NA≤0.5), s, and Ns based on the Linfoot’s image quality criteria of fidelity, correlation quality and structural content.

Scheme of non-contact manipulation: Acoustic radiation force on spherical particle in a spherical shell structure

A theoretical solution of the acoustic radiation force of an arbitrary beam on spherical particles in a spherical shell structure is presented. Taking the bladder and urinary calculus as the background, the finite element simulation of specific parameters was carried out to verify the accuracy and feasibility of the theoretical solution. The variation law of the acoustic radiation force on the particles with the particle radius, incident wave spectrum, viscosity coefficient of the medium inside the spherical shell structure, and distance from the center of the particle to the center of the spherical shell structure is studied. This scheme provides a design idea and theoretical basis for the non-contact manipulation of particles inside the spherical shell structure, and has a wide range of application scenarios in industrial applications and life sciences.

Satellite characterization of global stratospheric sulfate aerosols released by Tonga volcano

Large volcanic eruptions create an enhanced layer of sulfate aerosols in the stratosphere. These sulfuric acid droplets persist for many months, altering the climate and stratospheric chemistry. Sulfate aerosols scatter sunlight back to space, cooling the surface of the Earth and absorb outgoing thermal radiation, heating the stratosphere. The calculation of the climate impact of sulfate aerosols depends on their physical properties such as droplet size and chemical composition. These properties are not well known, and this uncertainty contributes to the errors in climate model predictions. Here we derive the first empirical formula that predicts the composition of stratospheric sulfate aerosols from volcanic eruptions from the air temperature and water vapor pressure. Measurements of atmospheric infrared transmittance of the Hunga Tonga-Hunga Ha'apai sulfate aerosol plume by the Atmospheric Chemistry Experiment (ACE) satellite were analyzed to determine composition (weight percent of sulfuric acid) and median particle radius. These data are supplemented by measurements of the Raikoke and Nabro eruptions. Our analysis allows the properties of volcanic aerosols in the stratosphere to be predicted reliably in atmospheric models.

A computer simulation study of extended DLVO interactions between calcite nanoparticles and real rough surfaces

The interaction energy between calcite nanoparticles and real rough surfaces in calcium carbonate supersaturated solutions was numerically calculated according to the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory and the surface element integration method. Three different surfaces, namely polished stainless steel, plasma-treated stainless steel, and fluorine-doped diamond-like carbon film, were prepared by mechanical polishing, plasma sputtering and film deposition, and characterized by atomic force microscopy. These images were then used as inputs in numerical simulations, where particle radius, solution concentration, surface electric potential, and surface tension components were varied. A total of 4052 simulations were performed. It was obtained that smaller particles interact more strongly with the surface and therefore are more attracted or repelled by the surface than larger ones. The effect of surface roughness on the particle interaction, however, depends on the physicochemical properties of the system and, therefore, a given surface may change its fouling behavior when the set of experimental conditions is changed. The effect of particle size on particle-surface interaction was found to be dependent on the relative sizes of the particle and the typical roughness features of the surface. A new local roughness metric – the minimum distance between the south pole of the particle and the rough substrate – can be used to predict the contact energy. These results may be important to engineer better antifouling surfaces for a wide range of applications, such as oil and gas exploitation and water treatment and desalination.