Small Separation Distances Research Articles

Performance Comparison of Alternative Indoor 5G Micro-Operator Deployments in 3.6-GHz and 26-GHz Bands

The fifth generation (5G) networks will provide local high-quality wireless services, especially within indoor areas. New local 5G network operator models, such as the recently introduced micro-operators, are increasingly important for vertical specific service delivery. The emergence of 5G micro-operator networks in spatially confined areas depends on local spectrum availability. In this paper, we investigate the performance of local 5G indoor micro-operator networks in the 3.6-GHz and 26-GHz bands. We consider two uncoordinated time-division duplex networks in adjacent buildings sharing the same channel with different base station antenna configurations and deployment densities. We evaluate the resulting performance of the victim network via system simulations. We have observed that the center frequency does not significantly impact the downlink performance unless the network is noise-limited. However, the uplink performance in 26-GHz band is affected by higher coupling losses between the base stations and mobile terminals. Our results indicate that beamforming and wider bandwidths help to improve the performance in 26-GHz band. More importantly, two indoor micro-operators can successfully coexist with a very small separation distance in the 26-GHz band, while in the 3.6-GHz band, a considerably larger isolation between the networks is required, for example, in the form of a much larger separation distance.

Stable and contact‐free time stepping for dense rigid particle suspensions

SummaryWe consider suspensions of rigid bodies in a two‐dimensional viscous fluid. Even with high‐fidelity numerical methods, unphysical contact between particles occurs because of spatial and temporal discretization errors. We extend a time stepping method that avoids overlap by imposing a minimum separation distance between all pairs of bodies. In its original form, the method discretizes interactions between different particles explicitly. Therefore, to avoid stiffness, a large minimum separation distance is used. In this paper, we introduce a new implicit time stepping method that is able to simulate dense suspensions with large time step sizes and a small minimum separation distance. The method is tested on various unbounded and bounded flows, and rheological properties of the resulting suspensions are computed.

Direct Laser Annealing of Surface‐Enhanced Raman Scattering Substrates

A laser‐annealing technique for the fabrication of surface‐enhanced Raman scattering (SERS) substrates consisting of closely packed gold nanoparticles (AuNPs) with high densities and small separation distances is reported. Laser annealing enables strongly localized interaction between the laser spot and the colloidal AuNPs within the irradiation area. Multiple stages of the alternative spin‐coating of colloidal AuNPs and laser‐annealing processes enable filling of the gaps between the AuNPs by newly produced ones in the subsequent stages. Thus, both the fill factor and the distribution density of the AuNPs are increased largely with increasing the number of fabrication stages, which favors the improvement of the SERS performance. In contrast, the conventional furnace or hot‐plate annealing heats the substrate and the colloidal film simultaneously, and the melted AuNPs tend to aggregate to form larger ones with large separation distance. Thus, compared with the SERS effective by furnace‐annealed substrates, laser‐annealed substrates supply a further enhancement factor larger than 3.7. Thus, laser annealing is proved as a more effective approach for the fabrication of SERS substrates through annealing colloidal AuNPs.

Dipole states and coherent interaction in surface-acoustic-wave\xa0coupled phononic resonators

Manipulation of mechanical motion at the micro-scale has been attracting continuous attention, leading to the successful implementation of various strategies with potential impact on classical and quantum information processing. We propose an approach based on the interplay between a pair of localised mechanical resonators and travelling surface acoustic waves (SAW). We demonstrate the existence of a two-sided interaction, allowing the use of SAW to trigger and control the resonator oscillation, and to manipulate the elastic energy distribution on the substrate through resonator coupling. Observation of the vectorial structure of the resonator motion reveals the existence of two coupling regimes, a dipole-dipole-like interaction at small separation distance versus a surface-mediated mechanical coupling at larger separation. These results illustrate the potential of this platform for coherent control of mechanical vibration at a resonator level, and reciprocally for manipulating SAW propagation using sub-wavelength elements.

A Miniaturized Dual-Band Dual-Polarized Band-Notched Slot Antenna Array With High Isolation for Base Station Applications

In this article, a miniaturized dual-band dual-polarized slot antenna array is proposed for base station applications. It consists of two closely located $1 \times 4$ subarrays for the digital cellular system (DCS) and wideband code division multiple access (WCDMA) operations. The band-notched slot antenna (BNSA) is designed and adopted as the subarray element with radiation-suppression characteristic at notch frequencies. The notch frequency for one subarray is designed at the center operating frequency of the other subarray. As a result, the radiation from DCS subarray could be effectively suppressed within the WCDMA band and vice versa, resulting in high isolation between two subarrays with a small separation distance. By using the artificial magnetic conductor (AMC) reflector, the array height could be reduced by half, as compared with the perfect electric conductor (PEC) counterpart. In addition, a four-way unequal power divider is designed for the array's beam-pattern synthesis. For the demonstration, the proposed array is fabricated and measured. The measurement results show that the dual-band array achieves the impedance bandwidths of 1.65-1.88 and 1.89-2.22 GHz, the isolations over 25 dB, the realized boresight gains of 12.2-12.8 and 12.3-13.2 dBi, and the sidelobe levels below -18 dB. The results indicate that the proposed array is a promising candidate for base-station applications.

Electrochemically Enhanced Dissolution of Silica and Alumina in Alkaline Environments.

Dissolution of mineral surfaces at asymmetric solid-liquid-solid interfaces in aqueous solutions occurs in technologically relevant processes, such as chemical/mechanical polishing (CMP) for semiconductor fabrication, formation and corrosion of structural materials, and crystallization of materials relevant to heterogeneous catalysis or drug delivery. In some such processes, materials at confined interfaces exhibit dissolution rates that are orders of magnitude larger than dissolution rates of isolated surfaces. Here, the dissolution of silica and alumina in close proximity to a charged gold surface or mica in alkaline solutions of pH 10-11 is shown to depend on the difference in electrostatic potentials of the surfaces, as determined from measurements conducted using a custom-built electrochemical pressure cell and a surface forces apparatus (SFA). The enhanced dissolution is proposed to result from overlap of the electrostatic double layers between the dissimilar charged surfaces at small intersurface separation distances (<1 Debye length). A semiquantitative model shows that overlap of the electric double layers can change the magnitude and direction of the electric field at the surface with the less negative potential, which results in an increase in the rate of dissolution of that surface. When the surface electrochemical properties were changed, the dissolution rates of silica and alumina were increased by up to 2 orders of magnitude over the dissolution rates of isolated compositionally similar surfaces under otherwise identical conditions. The results provide new insights on dissolution processes that occur at solid-liquid-solid interfaces and yield design criteria for controlling dissolution through electrochemical modification, with relevance to diverse technologies.

Short-path-length corrections to Djordjevic-Gyulassy-Levai-Vitev energy loss

We compute the correction to the energy loss of a hard parton due to short separation distances between the creation of the particle and the in-medium scattering center that stimulates bremsstrahlung radiation, to first order in opacity. In deriving the result we make full use of the large formation time assumption, which results in a significant reduction of the number of diagrams contributing to the small separation distance correction. An asymptotic analysis of our small separation distance correction term finds that the correction dominates at large $\sim 100$ GeV parent parton energies; scales like $L$ with the size of the system for small $L$, but like $L^0$ at larger $L$; and breaks color triviality. An extensive numerical investigation of the correction term confirms the aforementioned analytic findings, reveals that the correction term does not go to zero for large $L$, finds that the correction is sensitive to the mass of the parent parton, and shows a crucial dependence of the energy loss on a proper treatment of the physics of separation distances on the order of the Debye screening length. However, an examination of the large formation time approximation shows that it is violated for much of the phase space of the emitted radiation, implying a need to investigate the sensitivity of jet quenching results from relaxing this approximation. Our result constitutes an important step toward understanding partonic energy loss in small colliding systems.

Theory of Surface Forces in Multivalent Electrolytes.

Aqueous electrolyte solutions containing multivalent ions exhibit various intriguing properties, including attraction between like-charged colloidal particles, which results from strong ion–ion correlations. In contrast, the classical Derjaguin–Landau–Verwey–Overbeek theory of colloidal stability, based on the Poisson–Boltzmann mean-field theory, always predicts a repulsive electrostatic contribution to the disjoining pressure. Here, we formulate a general theory of surface forces, which predicts that the contribution to the disjoining pressure resulting from ion–ion correlations is always attractive and can readily dominate over entropic-induced repulsions for solutions containing multivalent ions, leading to the phenomenon of like-charge attraction. Ion-specific short-range hydration interactions, as well as surface charge regulation, are shown to play an important role at smaller separation distances but do not fundamentally change these trends. The theory is able to predict the experimentally observed strong cohesive forces reported in cement pastes, which result from strong ion–ion correlations involving the divalent calcium ion.

Three dimensional numerical simulation of drops suspended in a channel under uniform electric field

Abstract In this paper, numerical study of emulsion of drops in a channel under uniform electric field is investigated. The electric field is created by imposing an electric potential difference across the channel walls. The leaky dielectric model developed by Taylor is used to compute the electric force. The electric conductivity ratio σ r = σ i σ o and electric permittivity ratio e r = e i e o are used to study oblate and prolate drops The interaction of drop-to-wall and drop-to-drop are investigated by changing the dimensionless numbers. Oblate drops and prolate drops with σ r e r , are always attracted to the walls, but prolate drops with σ r > e r , are attracted by or repelled from the walls depending on the initial distance and electric properties. Drop-to-drop interaction depends on the initial configuration of drops. Drop pairs that are placed at an angle relative to the direction of the electric field, are always attracted towards each other. If they have an initial separation distance in the direction of the electric field, they are attracted to the walls or towards each other depending on their separation distance. Prolate drops with σ r > e r , obtain a different configuration in their final state. They may stick together or have a small separation distance, depending on their electric properties. Increasing the electric capillary number, changes the vertical and horizontal separation distance of drop pairs at steady state configuration. It also decreases the time required to reach steady state configuration. The behavior of emulsion of drops is studied by considering oblate drops, prolate drops with σ r e r and prolate drops with σ r > e r . All drops form fiber chains in the direction of the electric field that will break in stronger Poiseuille flow. Oblate drops either settle on the walls or migrate to the channel center line, but prolate drops form chains of fibers that sometimes extend between the walls. Presence of drops will change the well-known parabolic velocity profile especially for prolate drops that are suspended in the channel. The channel flow rate is also studied for different emulsion of drops and electric field. At a constant electric field and pressure gradient, the channel flow rate for oblate emulsion is higher than prolate ones. As the electric field strength increases, the channel flow rate will also increase for oblate emulsions.

Numerical modeling of the dynamics of bubble oscillations subjected to fast variations in the ambient pressure with a coupled level set and volume of fluid method.

A numerical method for modeling and understanding the dynamics of bubble oscillations subjected to fast variations in the ambient pressure is proposed under low Mach number conditions. In the present work, the method uses a single-fluid continuum formalism of weakly compressible axisymmetric Navier-Stokes equations for the numerical simulation of liquid-gas flows with surface tension and adopts the interface capturing approach based on a coupled level set and volume of fluid (CLSVOF) method for describing the moving and deformed interfaces. To demonstrate the efficacy of the proposed method, first, the numerical results of the radial oscillations of a spherical gas bubble are tested with the numerical solutions of Rayleigh-Plesset equation. Then, the numerical method is applied to reproduce the growth and subsequent collapse of a bubble in an infinite liquid medium observed in experiments. Finally, the numerical simulation of the interaction of two oscillating bubbles at small separation distance is evaluated in response to a moderate step change in the ambient pressure. It is shown that two deformable bubbles undergo coupled radial and oscillatory translational motions which eventually results in the bubbles' attraction and coalescence caused by the secondary Bjerknes forces. The numerical predictions show very good accuracy with the experimental and numerical results reported in the literature.

Capillary bridges between unequal-sized spherical particles: Rupture distances and capillary forces

This study focuses on capillary bridges between unequal-sized spherical particles in the pendular regime where the capillary bridge surface is axisymmetric. An analytical theory as well as closed-form expressions have been developed for the rupture distance and the capillary force. These expressions have been validated with a very large dataset of numerical solutions of the governing Young-Laplace equation, generated through a high-resolution integration method.For small capillary bridge volumes and contact angles smaller than 20∘, it has been shown that the meridional profile of the capillary bridge between unequal-sized particles can be accurately described by part of ellipses and that the contact radii for the large and the small particle are approximately equal. Contrary to the widely used toroidal approximation, the developed analytical theory takes into account the governing Young-Laplace equation, according to which the capillary force is constant along the capillary bridge. The analytical theory rigorously shows that expressions developed for cases with equal-sized particles can be directly employed in cases with unequal-sized particles by the use of the Derjaguin radius when the capillary bridge volume is small. Expressions for the rupture distance and the capillary force have also been derived analytically.For large capillary bridge volumes the use of the Derjaguin radius is not sufficient to accurately describe the properties of capillary bridges between particles with unequal sizes. By curve-fitting to the large dataset of numerical solutions of the Young-Laplace equation, a closed-form expression for the rupture distance has been developed, that accounts for the influence of the particle size ratio and that is accurate over a wide range of capillary bridge volumes. Expressions in the literature for the capillary force between unequal-sized spherical particles have been rigorously evaluated. With the new expression for the rupture distance, an improved closed-form expression for the capillary force has been formulated that is accurate for a wide range of small and large capillary bridge volumes (more specifically, when the ratio of the capillary bridge volume to the cubic root of the Derjaguin radius is smaller than 0.5) and separation distances, for contact angles smaller than 40∘.

Molecular dynamics simulations of Lennard-Jones systems confined between suspended nanoscale graphene sheets.

The distribution of particles interacting with Lennard-Jones potentials and confined between parallel graphene sheets is investigated by molecular dynamics simulations. For small separation distances, the particles are densely localized in the central region between the graphene sheets. However, two high-density layers appear as the separation distance increases. The particle distribution also depends on the temperature, tensile force of the graphene sheets, and the initial configuration, and various configurations are observed for large separation. For example, an argon cluster initially located between the graphene sheets changes shape, and a bridge between the parallel walls is formed at low temperature. In contrast to the Lennard-Jones system sandwiched between rigid walls, the flexibility of the graphene sheets strongly affects the distribution of particles in the direction perpendicular to the graphene sheets.

Interaction potential of two spherical macroparticles at constant surface potentials

Electrostatic interaction between two spherical macroparticles at constant charges of the particles and constant surface potentials is studied. The interaction potential of two spherical macroparticles as a function of surface separation distance L is calculated using capacitance and potential coefficients. At small separation distances, the capacitance coefficients are defined by Russell’s asymptotical formulae; at large distances, the potential coefficients are calculated by approximate formulae obtained in this paper and, at intermediate distances, the capacitance and potential coefficients are found by smoothly joining the asymptotical and approximate formulae. A comparison of the data obtained in this paper with those of the previous papers is performed. It has been established that this technique provides the rather high precision in the interaction potential calculation for all interparticle distances.

Center of Mass Motion of Short-Range Correlated Nucleon Pairs studied via the A(e,e^{'}pp) Reaction.

Short-range correlated (SRC) nucleon pairs are a vital part of the nucleus, accounting for almost all nucleons with momentum greater than the Fermi momentum (k_{F}). A fundamental characteristic of SRC pairs is having large relative momenta as compared to k_{F}, and smaller center of mass (c.m.) which indicates a small separation distance between the nucleons in the pair. Determining the c.m. momentum distribution of SRC pairs is essential for understanding their formation process. We report here on the extraction of the c.m. motion of proton-proton (pp) SRC pairs in carbon and, for the first time in heavier and ansymetric nuclei: aluminum, iron, and lead, from measurements of the A(e,e^{'}pp) reaction. We find that the pair c.m. motion for these nuclei can be described by a three-dimensional Gaussian with a narrow width ranging from 140 to 170 MeV/c, approximately consistent with the sum of two mean-field nucleon momenta. Comparison with calculations appears to show that the SRC pairs are formed from mean-field nucleons in specific quantum states.

Velocity Spectra and Coherence Estimates in the Marine Atmospheric Boundary Layer

Two years of continuous sonic anemometer measurements conducted in 2007 and 2008 at the FINO1 platform are used to investigate the characteristics of the single- and two-point velocity spectra in relation to the atmospheric stability in the marine atmospheric boundary layer. The goals are to reveal the limits of current turbulence models for the estimation of wind loads on offshore structures, and to propose a refined description of turbulence at altitudes where Monin–Obukhov similarity theory may be limited. Using local similarity theory, a composite spectrum model, combining a pointed and a blunt model, is proposed to describe the turbulence spectrum for unstable, neutral and stable conditions. Such a model captures the $$-1$$ power law followed by the velocity spectra at an intermediate frequency range in the marine atmospheric boundary layer. For the Monin–Obukhov similarity parameter $$\zeta < 0.3$$ , the Davenport coherence model captures the vertical coherence of the horizontal velocity components well. A two-parameter exponential decay function is found more appropriate for modelling the coherence of the vertical velocity component. Under increasingly stable conditions, the size of the eddies in the vertical coordinate reduces, such that smaller separation distances than that covered in the present dataset may be required to study the coherence with sufficient accuracy.

Controlling Selective Doping and Energy Transfer between Transition Metal and Rare Earth Ions in Nanostructured Glassy Solids

AbstractSelective doping of optically active ions into the nanocrystalline phase(s) of glass ceramics is of interest for photoluminescence (PL) applications to control the energy transfer (ET) processes between dopants on the nanometer length scale. Here, the focus is on explaining the essential knowledge of the distribution of two groups of active ions: transition metal (Ni2+ and Cr3+) and rare earth (Yb3+ and Er3+) ions, which are doped into i) single‐phase Ga2O3 and ii) dual‐phase Ga2O3 and YF3 nanocrystals (NCs). These NCs are obtained by thermally crystallizing ternary silicate‐ and quinary fluorosilicate‐based glasses, respectively. It is found that the two types of active ions can successfully be doped into Ga2O3 NCs, resulting in enhanced ET between the dopants because of the small separation distance of, e.g., &lt;10 Å, whereas ET is significantly suppressed when Ga2O3 and YF3 NCs are coprecipitated. In this case, the studied rare earth ions have a high propensity for being selectively doped in YF3 NCs. The studied transition‐metal ions can always be found in Ga2O3 NCs irrespective of the presence of the fluoride phase. The selective doping and the ET between the two types of active ions can be controlled simultaneously on annealing. This may allow for the achievement of diverse PL properties, such as ultrabroadband near‐infrared and upconversion‐mediated Stokes emissions.

Electrostatic formation of polymer particle stabilised liquid marbles and metastable droplets – Effect of latex shell conductivity

HypothesisParticle cohesion and conductivity affects the electrostatically driven transport of particles to a suspended water droplet. The conditions at which liquid marbles and particle stabilised liquid droplets form are a function of these parameters. ExperimentParticle beds placed below an earthed pendent water drop had a negative potential applied, thus inducing an opposing positive charge on the liquid, which results in particle transfer and eventual coating of the liquid drop. Experiments where both the particle bed was constantly moved slowly toward the droplet, and the particle bed remained at a fixed, small separation distance were completed. These enabled the investigation of a number of variables that influence successful aggregate formation, including separation distance between the droplet and particle bed, coating mechanism and kinetics of the transfer process. FindingsMonodisperse polystyrene core particles with polypyrrole shells of various cohesiveness and conductivity were observed to behave differently in the presence of the applied potential, where the least cohesive and conductive sample (polystyrene) required the smallest separation distance, i.e. the greatest field strength for particle transfer. Increasing conductivity of the particle shell decreases the field strength required for particle transfer, and thus an increase was observed in separation distance at which particles were observed to move to the air-water interface. The transfer kinetics followed the same trend where the least conductive and cohesive sample was the slowest to coat the air-water interface, and vice-versa. Since an increase in cohesion hinders particle transfer, it is concluded that particle conductivity is of greater importance in the electrostatic aggregation process.

Numerical study of turbulent annular impinging jet flow and heat transfer from a flat surface

This paper presents the results of a numerical investigation of fluid flow and heat transfer due to a turbulent annular jet impingement on an isothermally heated flat surface. Annular impinging jets enhance the heat transfer and spread it more uniformly over the impingement surface compared to the round impinging jet, and have one noteworthy characteristic of forming a reverse stagnation flow. A parametric numerical study for turbulent annular jet impingement is conducted for various blockage ratios (0.4–0.8) and non-dimensional jet exit-to-target plate separation distances (0.5–4.0) at a wide range of jet exit Reynolds number (5000–25,000). The numerical computation on a highly refined mesh is performed using the ANSYS Fluent commercial code and the computational process is validated against other published experimental data on similar flow and geometric configuration. In order to choose an appropriate turbulence model for the computations, the performance of few different turbulence models is evaluated based on the comparison against experimental Nusselt number distribution on the flat surface. The Realizable k-ε model was chosen over the other turbulence model in this study. There are two different distinguished critical jet-to-target plate distance for a specific blockage ratio and jet exit Reynolds number, that generates three different flow patterns. When the separation distance is large, the impinging annular jet flow patterns, defined as flow pattern-1, is comparable/similar to the flow patterns of conventional impinging round jet. For intermediate separation distance, a doughnut-shaped recirculation region develops just downstream of the annular nozzle exit and a reverse stagnation flow occurs near the domain axis and the impingement surface, which is defined as the flow pattern-2. For small separation distance, the flow diverges more to the outer side of the annular slot and a reverse stagnation flow develops, which influences the heat transfer rate on the impingement plate. This is designated as flow pattern-3. The separation distances at which the transition from one flow pattern to the other occurs are designated as Hc1 and Hc2. These critical distances are determined for each combination of the blockage ratio and the Reynolds number considered. Additionally, the heat transfer processes are analyzed and the average Nusselt number as a function of the blockage ratio and Reynolds number is calculated and presented.

Effect of propylene glycol ether fuelling on the different physico-chemical properties of the emitted particulate matters: Implications of the soot reactivity

The research work presented here focuses on the particulate matter (PM) number concentration and its physico-chemical properties from the combustion of di and tri-propylene glycol methyl ether/diesel blends (D20 and T20 respectively). Exhaust PM were characterised using a Scanning Transmission electron microscopy equipped with energy dispersive X-ray spectroscopy (S/TEM-EDX) to quantify the nanostructure, morphology and elemental composition of the agglomerates, Raman spectroscopy (RS) to further examine the particulate graphite like structure and thermo-gravimetric analyser (TGA) to analyse the oxidative reactivity. The increase in the fuel oxygen content reduces both, exhaust PM levels and NOx emissions. TGA analysis confirms that the oxygenated blends enhance the particulates oxidative reactivity and increase their volatile fraction in the following order T20 > D20 > Diesel. EDX analysis shows that the combustion of both D20 and T20 lowers the PM carbon fraction and ash precipitations but increases its oxygen functional groups in the same order. Furthermore, a notable reduction in the primary particles size was recorded, whose carbon layers were found to be more tortuous than diesel, but no significant modification was shown in their length. Unconventionally, smaller separation distance was seen between the carbon layers, and higher graphitisation order was seen from the RS analysis. It was finally concluded that concerning the nanoscale parameters, the initial curvature of the carbon layers present a stronger influence in dictating the particles reactivity compared to the graphitisation order or the initial length and separation distance of the carbon layers. As for the macroscale, primary particle size and the portion of oxygen in the particle could be another possible reason for the better soot reactivity seen from the propylene glycol ethers combustion. The significance of the reduced exhaust particles’ level and modified PM’s physical and elemental properties can improve Diesel Particulate Filter (DPF) regeneration and allows engine calibration that can favour NOx emissions reduction (i.e. lower NOx – PM trade-off lines).

Influences of the separation distance, ship speed and channel dimension on ship maneuverability in a confined waterway

Ship maneuvering in the confined inland waterway is investigated using the system-based method, where a nonlinear transient hydrodynamic model is adopted and confinement models are implemented to account for the influence of the channel bank and bottom. The maneuvering model is validated using the turning circle test, and the confinement model is validated using the experimental data. The separation distance, ship speed, and channel width are then varied to investigate their influences on ship maneuverability. With smaller separation distances and higher speeds near the bank, the ship's trajectory deviates more from the original course and the bow is repelled with a larger yaw angle, which increase the difficulty of maneuvering. Smaller channel widths induce higher advancing resistances on the ship. The minimum distance to the bank are extracted and studied. It is suggested to navigate the ship in the middle of the channel and with a reasonable speed in the restricted waterway.