Non-uniform Gap Research Articles

Study of atmospheric-pressure glow discharge plasma jets based on analysis of electric field

To achieve an atmospheric-pressure glow discharge (APGD) in a long electrode gap and generate large-diameter atmospheric-pressure glow discharge plasma jets (APGDPJs), an electrode, adopting the mode of a dielectric barrier discharge with a non-uniform dielectric thickness, was used. For the analysis of the electric field profile of the electrode, the strong electric field areas that could easily generate discharge could initially be formed in the non-uniform gap. Additionally, the distribution of the electric field with high intensity in the short gap and low intensity in the long gap was not likely to result in a filament discharge. Experiments indicate that the electrode could not only achieve APGD in the discharge gap by using air and nitrogen, but also generate stable nitrogen APGDPJs with a diameter of 3.5 mm. This was a relatively large diameter achieved for a glow discharge nitrogen plasma jet device.

Topographic viscous fingering: fluid-fluid displacement in a channel of non-uniform gap width.

We consider the displacement of one fluid by a second immiscible fluid through a long, thin permeable channel whose thickness and permeability decrease away from the axis of the channel. We build a model that illustrates how the shape of the fluid-fluid interface evolves in time. We find that if the injected fluid is of the same viscosity as the original fluid, then the cross-channel variations in permeability and thickness tend to focus the flow along the centre of the channel. If the viscosity of the injected fluid is smaller than the original fluid, then this flow focusing intensifies, leading to very poor sweep of the original fluid in the system, with the injected fluid bypassing much of the channel. We also show that if the viscosity ratio of the injected fluid to the original fluid is sufficiently large, then a blunt nose may develop at the leading edge of the injected fluid, whereas the remainder of the fluid-fluid interface becomes stretched out along the edges of the channel. This leads to a much more efficient sweep of the original fluid from the channel. We generalize the model to illustrate how buoyancy forces and capillary pressure affect the evolution of the system and compare our model predictions with some simple laboratory experiments. This partial stabilization of a fluid interface in a channel of non-uniform width represents a generalization of the classical Saffman-Taylor instability, and our nonlinear solutions for the evolution of the interface highlight the importance of cross-channel variations in permeability and thickness in modelling flow in channelled reservoirs.This article is part of the themed issue 'Energy and the subsurface'.

Study of Flexoelectricity in Graphene Composite Structures

ABSTRACTThis paper introduces the theoretical and experimental investigation of flexoelectric behavior in a graphene composite structure consisting of multilayer CVD-graphene deposited on an ALD-platinum catalyst layer deposited on top of n-silicon substrate. The polarization induced by varying the radius of curvature from 200–1500 mm by applying bending stresses was investigated experimentally. Meanwhile, due to the cluster-growth nature of the ALD-platinum catalyst layer, a strong correlation was observed between the resulting number of graphene layers and the Pt catalyst layer thickness, which subsequently had a strong impact on the induced polarization. A polarization current of up to 7.4 mA was detected when the composite structure was bent through a 600-mm radius of curvature. Residual stresses at the interface of the different layers were estimated experimentally in the order of 85–217 MPa. The effect of thermally-induced stresses, residual stresses at the interface layers, thickness of graphene layers, and radius of curvature were investigated theoretically using the finite element method (FEM) and first-principle analyses. Theoretically, it was confirmed that non-uniform strain results in an appreciable non-uniform graphene band gap opening, in addition to non-uniform change of the band structure across the surface and thickness which results in increasing the potential energy difference between the graphene layers. FEM confirmed that thermally induced strains could further enhance the power output of the device by inducing a flexoelectric current combined with the thermionic response. This is verified by estimating a lattice displacement up to 0.31 Å in response to 2-mW heat flux, which corresponds to an appreciable graphene band opening and a potential energy difference across the graphene layers in the order of 1.23 eV, as estimated by the tight binding model.

Atmospheric-pressure glow plasma synthesis of plasmonic and photoluminescent zinc oxide nanocrystals

In this paper, we present a large-volume (non-micro) atmospheric pressure glow plasma capable of rapid, large-scale zinc oxide nanocrystal synthesis and deposition (up to 400 μg/min), whereas in the majority of the literature, nanoparticles are synthesized using micro-scale or filamentary plasmas. The reactor is an RF dielectric barrier discharge with a non-uniform gap spacing. This design encourages pre-ionization during the plasma breakdown, making the discharge uniform over a large volume. The produced zinc oxide nanocrystals typically have diameters ranging from 4 to 15 nm and exhibit photoluminescence at ≈550 nm and localized surface plasmon resonance at ≈1900 cm−1 due to oxygen vacancies. The particle size can be tuned to a degree by varying the gas temperature and the precursor mixing ratio.

Graphene-metal-semiconductor composite structure for multimodal energy conversion

In this paper we present a new approach to enhance the energy conversion efficiency of metal-semiconductor junction by integrating CVD-grown graphene on top of Pt/Si junction. Flexoelectric behavior can be observed and further modulated in the fabricated composite structure as a result of the mismatch in the mechanical and thermal properties and the residual stresses at the interface of the structural layers induced from the thin-film deposition processes. Moreover, graphene layer acts as an antireflection coating to the metal-semiconductor structure, therefore, upon exposure to a heat flux or infrared radiation, the thermionic behavior can also be observed by forming a carrier-free layer as a result of charge transfer from graphene to metal. Therefore, we suggest that due to the heterogeneous composite nature of the proposed structure, both thermionic and flexoelectric energy conversion behaviors can work in conjunction upon exposure to heat flux or IR radiation increasing the overall efficiency of the device. The polarization induced by varying the radius of curvature from 600 to 2000mm by applying bending stresses was investigated experimentally. Meanwhile, due to the cluster-growth nature of the ALD-platinum catalyst layer, a strong correlation was observed between the resulting graphene layer thickness and the Pt catalyst layer thickness, which subsequently had a strong impact on the induced polarization. A polarization current of up to 7.4mA was detected when the composite structure was bent through a 600-mm radius of curvature. Residual stresses at the interface of the different layers were estimated experimentally in the order of 85–217MPa. The effect of thermally induced stresses, residual stresses at the interface layers, thickness of graphene layer, and radius of curvature were investigated theoretically using multi-scale FEM and first-principle calculations using tight binding method. Theoretically, it was confirmed that non-uniform strain results in non-uniform appreciable graphene band gap opening (in the order of 0.6–1.02eV), in addition to non-uniform change of the band structure across the width and thickness. Both effects eventually resulted in net polarization. FEM confirmed that thermo-mechanically induced strains could further enhance the power output of the device by inducing a flexoelectric current combined with the thermionic response. This is verified by estimating a graphene lattice distortion in the order of 0.31Å in response to 2-mW heat flux, which corresponds to approximately 12.6% distortion in the graphene lattice parameter. Controlling the film residual stresses at interface between the layers can further modulate the mismatch and maximum lattice distortion.

A NEW METHOD OF DRIVING WIRE DIPOLE ANTENNAS TO MULTIBAND OPERATION VIA NON-UNIFORM EBG LATTICES FOR EMPLOYMENT TO WIRELESS COMMUNICATION APPLICATIONS

In this paper, a novel approach is attained to the design of low profile antenna structures with wire dipoles and multiband operation. The aim is achieved by utilization of non-uniform Electromagnetic Band Gap (EBG) lattices as reflectors, and this potential comes to be added to the total of special capabilities of this type of Artificial Magnetic Conductors (AMC). It is proved that a properly designed EBG of this type can resonate at more than one frequency and is capable to drive, inside these bands, the dipole to higher order modes of operation besides its basic one. The resulting hybrid radiator apart from its multiband operation exhibits high gain that reaches the value of 9.6 dB, satisfactory Mean Effective Gain (MEG) and very low correlation coefficients, much less than 0.1, between the signals at the input of the dipoles in the case that the radiator is configured as an antenna array. The study of these quantities was performed using the signal characteristics of a real mobile communication environment along with the hybrid antenna properties of operation. The presented analytical results show that the designed radiators are competitive to the classical microstrip ones and can be effectively used in modern wireless communication networks, incorporated either into stationary or into mobile units.

Proposal of a Wireless Power Transfer Technique for Low-Power Multireceiver Applications

In this paper, we proposed and verified the feasibility of a unique wireless power transfer structure called a rail transformer to drive multiple low-power devices such as electronic shelf label (ESL) devices. The rail transformer is composed of a rectangular, circular-shaped transmitting yoke and two transmitting coils to provide wireless power. Multiple receiving yokes coupled with receiving coils are installed across the elongated edge of the transmitting yoke. It can be driven by low-frequency ac power at 50/60 Hz. In our prototype, the transmitting yoke is 900 mm long and 15 mm wide. We obtained the minimal induced wireless power, and the voltage was $\sim 61$ mW and 3.5 V, which is sufficient to drive a typical ESL device. By designing a nonuniform gap thickness between the transmitting and the receiving yokes at the specific locations, we improved the uniformity of the induced power for multiple ESL devices.

Shape error prediction and compensation of three-dimensional surface in flexibly-reconfigurable roll forming

The Flexibly-reconfigurable roll forming (FRRF) scheme as one of the advanced continuous roll forming processes consists of upper and lower flexible rollers that can be controlled by each reconfigurable punch module. The shape error in the FRRF process often results in undesirable changes in the shape of the deformed surface and brings about a deviation in the precision of the deformed product. This study considers the changes in the shape error of a deformed configuration by controlling the non-uniform gap between both flexible rollers in the transverse direction. A Non-uniform rational B-spline (NURBS) type control methodology is introduced based on the transverse target curve and the thickness reduction ratio. The function for the transverse target curve is reconstructed by using a NURBS curve, and the function of the reduction ratios of the thickness is assumed to have linear increments. Finite element simulations are conducted for the FRRF process with the AA5052-H32 sheet material by applying NURBS-type control methodology for both flexible rollers. The transverse shape error of the three-dimensional surface is predicted by using a numerical approach, and its results are experimentally verified. A Reverse displacement compensation (RDC) method is adopted to compensate the transverse shape error of the deformed surface. Consequently, the proposed RDC method is validated as a suitable approach to address the transverse shape error. This method contributes to further developing capabilities to modify the profiles of the upper and lower flexible rollers in the flexibly-reconfigurable roll forming process for various 3D surface parts.

The shape analysis of three-dimensional flexible rolling method

A new forming method, three-dimensional flexible rolling, is proposed for three-dimensional surface parts, which can form the parts effectively with the dieless characteristics. In this study, the shape of bending rolls is circle and the bending radii of upper and lower rolls are different; therefore, the roll gap is non-uniform. Because of the roll gap, an uneven compression appears at the transversal direction, which leads to a non-uniform elongation in feeding direction. The parts bend in two directions at the same time, and the three-dimensional surface shape is obtained. The forming rules of flexible rolling are proposed to analyze the relationship between the pressure ratio and the deformation extent of double-curved surface. The function between the non-uniform roll gap and the bending radius is deduced from the theory of invariable volume. An experimental device is developed to do the forming experiments. The feasibility of the device and the advantage of the method have been validated through numbers of experiments. Typical three-dimensional surface parts such as the convex and saddle parts have been completed for researching and analyzing. Some fine numerical simulation results of flexible rolling have been obtained. Finally, the simulation results are compared with the actual results to analyze the shape and illustrate the forming effect.

Hybrid antenna arrays with non-uniform Electromagnetic Band Gap lattices for wireless communication networks

A method to design hybrid antenna configurations with very low profile, suitable for smart and Multiple Input–Multiple Output antenna systems is proposed. The antennas are incorporated with novel Electromagnetic Band Gap (EBG) surfaces with non-similar cells. These non-uniform EBG surfaces have been properly designed to cause focusing, of the incident waves, thus enhancing the characteristics of operation of antenna elements positioned in close proximity to the surface and also to increase the isolation between them. Theoretical analysis of the reflection mechanism of this type of lattices as well as the prediction of the resulting performance of the antenna is presented. All these considerations are validated with implementation and simulation of the hybrid structures inside the Universal Mobile Telecommunications System frequency band. The results show that increment of the gain and isolation between the antenna elements can be obtained. Moreover, results for the correlation coefficient between the elements, for Gaussian distribution of the incoming waves have been received and the tolerance of the antennas to the variation of the polarization characteristics of the incoming waves has been investigated. A Genetic Algorithm has been constructed and applied to find the proper geometry of the hybrid antennas in order the correlation coefficient to be minimized and get almost independent from the polarization of incident waves.

The VIMOS Public Extragalactic Redshift Survey (VIPERS)

[Abridged] Non-uniform sampling and gaps in sky coverage are common in galaxy redshift surveys, but these effects can degrade galaxy counts-in-cells and density estimates. We carry out a comparison of methods that aim to fill the gaps to correct for the systematic effects. Our study is motivated by the analysis of the VIMOS Extragalactic Redshift Survey (VIPERS), a flux-limited survey (i<22.5) based on one-pass observations with VIMOS, with gaps covering 25% of the surveyed area and a mean sampling rate of 35%. Our findings are applicable to other surveys with similar observing strategies. We compare 1) two algorithms based on photometric redshift, that assign redshifts to galaxies based on the spectroscopic redshifts of the nearest neighbours, 2) two Bayesian methods, the Wiener filter and the Poisson-Lognormal filter. Using galaxy mock catalogues we quantify the accuracy of the counts-in-cells measurements on scales of R=5 and 8 Mpc/h after applying each of these methods. We also study how they perform to account for spectroscopic redshift error and inhomogeneous and sparse sampling rate. We find that in VIPERS the errors in counts-in-cells measurements on R<10 Mpc/h scales are dominated by the sparseness of the sample. All methods underpredict by 20-35% the counts at high densities. This systematic bias is of the same order as random errors. No method outperforms the others. Random and systematic errors decrease for larger cells. We show that it is possible to separate the lowest and highest densities on scales of 5 Mpc/h at redshifts 0.5<z<1.1, over a large volume such as in VIPERS survey. This is vital for the characterisation of cosmic variance and rare populations (e.g, brightest galaxies) in environmental studies at these redshifts.

Evaluation of the sealing capability of implants to titanium and zirconia abutments against Porphyromonas gingivalis, Prevotella intermedia, and Fusobacterium nucleatum under different screw torque values

When evaluating long-term implant success, clinicians have always been concerned with the gap at the implant-abutment junction, where bacteria can accumulate and cause marginal bone loss. However, little information regarding bacterial leakage at the implant-abutment junction, or microgap, is available. The purpose of this study was to evaluate sealing at 2 different implant-abutment interfaces under different screw torque values. Twenty sterile zirconia abutments and 20 sterile titanium abutments were screwed into 40 sterile implants and placed in test tubes. The ability of a bacterial mixture of Prevotella intermedia, Porphyromonas gingivalis, and Fusobacterium nucleatum to leak through an implant-titanium abutment seal under 20 and 35 Ncm torque values and an implant-zirconia abutment seal under 20 and 35 Ncm torque values was evaluated daily until leakage was noted. Once a unit demonstrated leakage, a specimen was plated. After 4 days, the number of colonies on each plate was counted with an electronic colony counter. Plating was used to verify whether or not bacterial leakage occurred and when leakage first occurred. The implant-abutment units were removed and rinsed with phosphate buffered saline solution and evaluated with a stereomicroscope. The marginal gap between the implant and the abutment was measured and correlated with the amount of bacterial leakage. The data were analyzed with ANOVA. Bacterial leakage was noted in all specimens, regardless of material or screw torque value. With titanium abutments, changing the screw torque value from 20 to 35 Ncm did not significantly affect the amount of bacterial leakage. However, with zirconia abutments, changing the screw torque value from 20 to 35 Ncm was statistically significant (P<.017). Overall, the marginal gap noted was larger at the zirconia-abutment interface (5.25 ±1.99 μm) than the titanium-abutment interface (12.38 ±3.73 μm), irrespective of the screw torque value. Stereomicroscopy revealed a nonuniform marginal gap in all specimens. The results of this study showed that, over time, bacteria will leak through the implant-abutment microgap at the implant-abutment interface. Implants with a titanium abutment demonstrate a smaller microgap than implants with a zirconia abutment. Tightening the zirconia abutment screw from 20 to 35 Ncm decreases the size of the microgap, which suggests a more intimate fit between the implant and the abutment.

Flow Mode Magnetorheological Dampers with an Eccentric Gap

This paper analyzes flow mode magnetorheological (MR) dampers with an eccentric annular gap (i.e., a nonuniform annular gap). To this end, an MR damper analysis for an eccentric annular gap is constructed based on approximating the eccentric annular gap using a rectangular duct with a variable gap, as well as a Bingham-plastic constitutive model of the MR fluid. Performance of flow mode MR dampers with an eccentric gap was assessed analytically using both field-dependent damping force and damping coefficient, which is the ratio of equivalent viscous field-on damping to field-off damping. In addition, damper capabilities of flow mode MR dampers with an eccentric gap were compared to a concentric gap (i.e., uniform annular gap).

大気圧Air/CO2混合ガス不平等電界ギャップのELF-ULF帯域での交流火花破壊特性

大気圧Air/CO2混合ガス不平等電界ギャップのELF-ULF帯域での交流火花破壊特性

Research of Bearing Crown Roller-Raceway by Non-Uniform Interelectrode Gap Electrochemical Mechanical Machining

Electrochemical mechanical machining (ECMM) is introduced to the manufacture of bearing crown roller-raceway in consideration of the very problems appearing in traditional machining methods. Firstly, numerical model on the non-uniform interelectrode gap ECMM is established and anode crown shapes under different cathode shapes are analyzed. Afterwards, according to the requirement of anode crown related cathode shape is formed through numerical simulation. In the end, the crown of bearing roller-raceway is machined by practical concave cathode with improved surface quality and certain crown face.

A particle trapping chip using the wide and uniform slit formed by a deformable membrane with air bubble plugs

We present a high-efficient particle trapping chip, where a wide and uniform slit is formed by a deformable membrane barrier with air bubble plugs. The previous particle trapping methods based on membrane barriers resulted in low trapping efficiency due to the non-uniform slit gap between the membrane and the substrate, especially at the side walls of rectangular channel. In the present method, the air bubble plugs remained in the extended microchannel during sample filling process, block the particle passage at the both side ends of the membrane, thus all particles flow through the uniform slit gap. Therefore, high-efficient particle trapping without particle loss can be achieved. The present particle trapping chip was composed of three layers: pneumatic (top), membrane and channel (bottom) layers. The membrane was deformed by the pneumatic pressure applied from the top layer. In the experimental study using 10.3 μm-diameter polystyrene beads, the membrane barrier with the air bubble plugs successfully trapped the injected beads with the trapping efficiency of 100% at the flow rate of 10 μl/min, while the barrier without the air bubble plugs showed low efficiency of 20%. At the increased flow rate of 20 μl/min, beads were still trapped with trapping efficiency over 98% in the present device. By using a mixture of 5.7 and 10.3 μm-diameter beads, we also verified the present method was capable to trap and release the beads selectively according to their size with the release efficiency of 95.1%. The present simple and effective particle trapping device is applicable for the high-efficient bioparticle isolation and recovery in the micro total analysis system.

Prediction of Boiling-Induced Natural-Circulation Flow in Engineered Cooling Channels

Boiling-induced natural-circulation flow in various engineered cooling channels is modeled and solved by considering the conservation of mass, momentum, and energy in the two-phase mixture, along with the two-phase friction drop and void fraction. The model is applied to estimate the induced mass flow rates through a uniform annular gap and a nonuniform annular gap between the reactor vessel and insulation under the in-vessel corium retention-external reactor vessel cooling conditions, and in the engineered corium cooling system of an ex-vessel core catcher during a severe accident. Dependence of the induced flow rate on various system parameters including the channel gap size, inlet diameter, inlet subcooling, and wall heat flux has been identified numerically. Results of the present study provide useful information for enhancing the design of engineered cooling channels to assure long-term cooling and retention of corium under severe accident conditions.

Comparison of various contact algorithms for poroelastic tissues

Capabilities of the commercial finite element package ABAQUS in simulating frictionless contact between two saturated porous structures were evaluated and compared with those of an open source code, FEBio. In ABAQUS, both the default contact implementation and another algorithm based on an iterative approach requiring script programming were considered. Test simulations included a patch test of two cylindrical slabs in a gapless contact and confined compression conditions; a confined compression test of a porous cylindrical slab with a spherical porous indenter; and finally two unconfined compression tests of soft tissues mimicking diarthrodial joints. The patch test showed almost identical results for all algorithms. On the contrary, the confined and unconfined compression tests demonstrated large differences related to distinct physical and boundary conditions considered in each of the three contact algorithms investigated in this study. In general, contact with non-uniform gaps between fluid-filled porous structures could be effectively simulated with either ABAQUS or FEBio. The user should be aware of the parameter definitions, assumptions and limitations in each case, and take into consideration the physics and boundary conditions of the problem of interest when searching for the most appropriate model.

Streamer propagation in non-uniform gaps at ambient atmospheric air pressures

AbstractThe streamer propagation in point-plane, non-uniform gaps under high applied electric fields, prior to the impact of primary streamer on cathode, is analyzed. The configuration used is an anode hyperboloid with 50-μm radius of curvature, and a flat plate as the cathode. The applied voltage is 130-kV direct current, and an initial electron is assumed to exist close to the anode in ambient air. The geometry used is a two-dimensional axisymmetry with a gap of 5 cm between the anode and the cathode. It is shown that the streamer is formed on the anode tip as expected, and midway toward the cathode, it separates into two streamers, the primary streamer that continues its propagation toward the cathode, and the branched streamer expanding radially toward the outer boundaries. The qualitative behavior of the discharge is analyzed in terms of streamer speeds, radial and axial electric fields, charged particle densities, and conductive currents. A branched streamer plasma structure was observed along the path of the primary plasma structure expanding radially outwards.

Thermal simulation of sodium heated once through steam generator for a fast reactor

In typical sodium cooled fast reactors, steam generators (SG) transports heat from hot liquid sodium to high pressure feed water. Feed water gets heated and converted to superheated steam and is used to roll the turbine. In SG, tubes are in triangular pitch pattern and shell in cylindrical shape, making some non-uniform gap at periphery allowing sodium to by-pass resulting radial thermal difference. Estimation of this thermal difference is very important in order to design a provision to accommodate the maximum differential thermal expansion among tubes and shell and to resist maximum thermal cycles faced by SG in its design life. A detailed three-dimensional thermal analysis of a sector model of SG with 30 m long tube is performed by combining a commercial Computational Fluid Dynamic code with in-house one-dimensional code DESOPT. The analysis is also validated with in-house experimental test facility results. From the analysis, the radial and axial temperature distributions and the differential temperature between tubes and shell are estimated for commercial fast breeder reactors SG for normal operation and typical plugged tube conditions and the results are highlighted in this paper. The results would form input for the estimation of differential thermal expansion of shell and tubes of SG and design of tube-sheets.