Small Radius Of Curvature Research Articles

Performance Improvement of Collision Warning System on Curved Road Based on Intervehicle Communication

The vehicle on-board sensor based Advanced Driver Assistant System possesses limitations on a small road with a small radius of curvature because of the sensor’s inability to operate in nondetectable domains. This study suggests an Improved Cooperative Collision Warning System (ICCWS) that considers the curvature of the road and is based on intervehicle communication. To predict the radius of curvature of the road, the Arc Relative Distance (ARD), the real relative distance to a preceding vehicle on a curved road has been used. The risk of collision with the preceding vehicle is decided by calculating an index of the risk of collision on a curved road using the computed ARD. The effects of ICCWS, proposed through this simulation, have been reviewed, and the improvement in performance in following a preceding vehicle has been analyzed quantitatively via comparative analysis with the conventional forward collision warning system. Accordingly, if the estimating algorithm for curvature developed in this study is applied to a real system, the performance of following a preceding vehicle can be improved without any specific changes to the system.

Effect of flow rate on the characteristics of repetitive microsecond-pulse gliding discharges

Gliding discharges driven by microsecond-pulse power supply can generate non-thermal plasmas with high energy and high power density at atmospheric pressure. However, the flowing air significantly influences the characteristics of the microsecond-pulse gliding discharges in a repetitive mode. In this paper, in order to obtain the characteristics of the microsecond-pulse gliding discharges in a needle-to-needle gap, a microsecond-pulse power supply with an output voltage up to 30 kV, a pulse width 8 s, and a pulse repetition frequencies 1 Hz 3000 Hz is used to investigate the electrical characteristics of gliding discharges by analyzing the voltage-current waveforms and obtaining the discharge images. Experimental results show that there are three typical discharge modes in the microsecond-pulse gliding discharges as the applied voltage increases, i.e. corona discharge, diffuse discharge, and gliding-like discharge. Both voltage-current waveforms and the discharge images at different discharge modes have significantly different behaviors. Corona discharge only exists near the positive electrode with a small radius of curvature. Diffuse discharges behave as the overlapped plasma channels bridge the entire gap. The channel of diffuse discharge is full of gap, which starts from the positive electrode, spreads in all directions, and ends at the negative electrode. Gliding-like discharge behaves as a continuous spark channeling, showing a continuous spark, which is discharging strongly and influenced by flow rates. Furthermore, both pulse repetition frequency (PRF) and flow rate remarkably affects the characteristics of microsecond-pulse gliding discharges. When the flow rate is small (2 L/min), the spark channels of gliding-like discharge gradually concentrate with the increase of the PRF. However, when the flow rate is larger (16 L/min), the spark channels of gliding-like discharge behave dispersively when the PRF increases. In our opinion, different characteristics of microsecond-pulse gliding discharge at different flow rates are closely related to the memory effect of the residual particles in the discharges and the state of the air flow. When the flow rate is small (2 L/min), the air flow is stable, and the discharge is generated in a laminar flow state. In this case, the memory effect of particles in repetitive microsecond-pulse gliding discharges dominates the formation of the discharges. These particles could enhance the electric field strength for the next pulse. Because the time interval between two pulses at high PRF is shorter than that at low PRF, there are fewer particles leaving the air gap at high PRF. Thus, memory effect is more significant at high PRF. As a result, the channel of spark discharge concentrates with the increase of the PRF. When the flow rate increases to 16 L/min, the calculated Reynolds number increases to 2864, indicating the transition from laminar state to turbulence state. The residual particles are more likely to escape from the gap. Thus, memory effect slightly affects the characteristics of the microsecond-pulse gliding discharges. In this case, the state of the air flow dominates the formation of the discharge. The spark channels spread towards the top in the direction of the gas flow, making the region of the spark channels gradually disperse as the PRF increases.

Focusing performance of hard X-ray single Kinoform lens

Nowadays, X-ray nanoprobe plays an important role in many research fields, ranging from materials science to geophysics and environmental science, to biophysics and protein crystallography. Refractive lenses, mirrors, and Laue lenses, can all focus X-rays into a spot with a size of less than 50 nm. To design a refractive lens at fixed wavelengths, absorption in the lens material can be significantly reduced by removing 2πup phase-shifting regions. This permits short focal length devices to be fabricated with small radii of curvatures at the lens apex. This feature allows one to obtain a high efficiency X-ray focusing. The reduced absorption loss also enables optics with a larger aperture, and hence improving the resolution for focusing. Since the single Kinoform lens can focus hard X-ray into a spot on a nanoscale efficiently, it has very important application prospect in X-ray nano-microscopy and nano-spectroscopy. We present a theoretical analysis of optical properties of the single Kinoform lens. Using Fermat's principle of least time, an exact solution of the single Kinoform lens figure is derived. The X-ray diffraction theory is reviewed. The complex amplitude transmittance function of the X-ray single Kinoform lens is derived. According to Fourier optics and optical diffraction theory, we set up the physical model of X-ray single Kinoform lens focusing. Employing this physical model, we study how the focusing performance of hard X-ray single Kinoform lens is influenced by the material, the photon energy, the number of steps and the vertex radius of curvature. We find that diamond single Kinoform lens can achieve a smaller focusing beam size with higher intensity gain than Al and Si single Kinoform lens. The single Kinoform lens designed at a certain photon energy can also focus other photon energies with different lateral beam sizes, axial beam sizes, intensity gains and focusing distances. The numbers of steps of a single Kinoform lens can be lessened with the thickness of step increasing, while the single Kinoform lens keeps good focusing performance. To improve the focusing performance further, reducing the vertex radius of curvature is proposed. Following these rules, a single Kinoform lens is optimally designed to focus 30 keV hard X-ray down to a lateral size of 14 nm (full-width at half-maximum, FWHM) and an axial size of 62 μm (FWHM) with an intensity gain of four orders of magnitude and transmittance of 30%.

Design and Research of Multiple Fiber Tows Placement Control System

In view that present traditional composites forming technologies are difficult to guarantee the processing quality of complex components such as components with small curvature radius or with concave-convex surface. this paper used the fiber placement technology, and in order to achieve the single independent and overall joint movement control of each fiber tows ,it adopted the mainstream open control mode of a PC machine combined with a programmable multi-axis motion controller . At the same time, it introduced a feedback system to realize the accurate pressure control of multiple fiber tows, so as to ensure the quality of fiber placement.

Сто років формулі Піка для визначення початкової напруженості коронного розряду

This article is dedicated to the memory of well-known electrical engineer Frank William Peek, Junior, who estimated the corona inception electric field on the surface of electrodes with a small radius of curvature which allows for corona discharge inception and also known as the “Peek’s law”. Analyzing Peek’s first publications dated 1911–1915, we have seen that he has elaborated and summarized the laws, which describe the phenomenon of corona discharge in gas on the wires of power transmission line. In particular, Peek presented the final version of the half-empirical formula in 1915, which allows estimating the voltage under which a corona appears on high-voltage wires, as well as estimating the power loss caused by this phenomenon. Attention has been drawn to the unrenowned facts related to Peek’s discovery of the formula. It has been discovered that the scientist was using the mean-value method when working on the formula. Also, attention has been drawn to the reasons of difference in indices (coefficients) in Peek’s formula, which can be seen in literature and publications of different authors in our country, as well as other countries. Based on the results of the research of Peek’s successors, it has been shown that all new charts repeat his formula and differ from it only by the value of numeric coefficients and, sometimes, the exponent in the denominator. Three ways of using his formula have been summarized; its direct application in electric power industry has been shown.

Study on stiffness of elastohydrodynamic line contact

The stiffness of oil film, contact body and the resultant stiffness of elastohydrodynamic line contacts with various radii of curvature, loads and entrainment velocities are studied based on the numerical analysis of oil film thickness and elastic deformation. It is found that the elastohydrodynamic contact stiffness is close to the Hertzian contact stiffness in the cases of high loads, low speeds and small radii of curvature. The critical conditions in which the elastohydrodynamic stiffness can be approximated by the Hertzian stiffness are investigated and verified by the dynamic simulation of the valve train in a diesel engine.

Chemical reaction and mixing inside a coalesced droplet after a head-on collision

We investigated the phenomena of a chemical reaction inside a coalesced droplet after a direct (head-on) collision. A droplet containing an alkaline solution collided with a droplet containing a pH indicator on a surface with a wettability gradient. We used a high-speed camera to observe the color-changing reaction inside the coalesced droplet. Compared with a traditional dye-mixing test, the chemical reaction inside the coalesced droplet facilitated the mixing of two counter-reactive fluids and was more than 100 times as efficient as for unreactive fluids mixing inside the coalesced droplet. Instead of mere mixing, a chemical reaction inside a coalesced droplet is valuable for applications in a digital microfluidic open system. In droplet coalescence, the characteristics of the fluids and the ratio of volumes of two droplets caused a varied profile of the droplet coalescence, especially the neck curvature that affects the shape of the material interface between the two droplets at an initial phase. We observed the evolution of the chemical reaction with a varying radius of neck curvature inside the coalesced droplet. For the case of a small radius of neck curvature, the small interfacial area between two reactive fluids accumulated an intense heat of reaction and induced a rapid growth of the fingers. For the case of a large radius of neck curvature, the growth of fingers was slight and the interface was uniform across the large interfacial area. Our work illustrates a correlation between the rate of chemical reaction and the profile of a coalesced droplet, which is a significant reference in droplet-based microfluidic systems for biochemical applications.

Investigation and improvement of 3D rolling process for 3D surface parts

3D rolling is a novel forming process for manufacturing 3D surface parts by employing a pair of forming rolls as a forming tool. By controlling the nonuniform distribution of roll gap of the forming rolls, residual stress of the sheet metal makes the sheet metal bend in the transverse and longitudinal directions simultaneously. As the roll adjusting radius is much larger than the target transverse curvature radius of the forming surface, the forming roll could rotate around its axis easily, which is suitable for producing 3D surface parts including the wide sheet metal with relatively small transversal curvature radius. In this paper, different roll adjusting radii are investigated for 3D surface parts, and the 3D rolling process has been improved to increase the length of effectively forming region of the forming parts and improve the utilization rate of sheet metal. Finite element analysis models are established; spherical and saddle surfaces are simulated. The corresponding experimental results are obtained. The dimensional accuracy of the forming part is measured, and the differences of the forming processes are analyzed by comparing the simulated results. The comparison and analysis of the forming results show the feasibility of the improved method of 3D rolling process for 3D surface parts.

Distribution of Electric Field for EMU's Post Insulators Based on the Finite Element Method

Compared with power system, post insulators used in High-speed Electric Multiple Unit (EMU) have unique features such as limited space, low number of sheds and complex pantograph, which produces high electric field at some part of post insulators. When the insulators electric field exceeds a numerical value, it will produce corona discharge and reduce the reliability of High-speed EMU. At the same time, a distinct discharge phenomenon has been observed on the surface of the small curvature radius for pantograph. For guiding optimization of electric field for post insulators and pantograph, a simplified model of post insulators as well as the pantograph is established to calculate the distribution of potential and electric field based on ANSYS. Because the applied voltage cycle is far less than the relaxation time of the dielectric, electrostatic field module can be used in the ANSYS Simulation. By simulating, the maximum electric field is occurred at the pantograph angle and some measures should be taken to reduce the electric field to assure the reliability of the EMU. The potential would decrease along the axis of the post insulator and the first umbrella bear the largest voltage drop.

Extending microcontact printing for patterning of thick polymer layers: semi-drying of inks and contact mechanisms

We investigate the applicability of the microcontact printing technique for the patterning of polymeric etch-resistant layers with thicknesses in the order of micrometers. In contrast to small molecular materials such as thiols and silane coupling agents typically used in microcontact printing, the patterning of thick layers requires tuning of the rheological properties of an ink film to prevent pattern deformation and attain high-quality transfer. By evaluating the swelling rate of a microcontact stamp material (i.e. poly(dimethylsiloxane) (PDMS)) and the evaporation rate of solvents, we find an optimal ink formulation to attain the desired semi-dried state for the printing of polymer layers. In polymer films with solid content below the optimal limit, split- or wrinkle-type deformations were found depending on the adhesion force and deformability of ink films, while overly-dried polymer films failed to be transferred. These phenomena are in qualitative agreement with deformation curves obtained from colloidal probe microscopy measurements that successfully revealed the deformability and adhesion of semi-dried polymer films. Further investigation of the effects of stamp stiffness on pattern formation reveals that a pattern region in which the thickness profile has a small curvature radius failed to be transferred when a stiffer PDMS stamp was used. This type of defect is thought to be caused by incomplete contact between the film and substrate due to a semi-circular cap structure of the polymer film and insufficient deformation of the stamp. Herein, a detailed contacting mechanism for high-quality patterning is discussed on the basis of the Hertz contact model. Using the developed etch-resistant ink and optimized printing process conditions, a finely defined etched structure for a silicon substrate is obtained.

Graded metal carbon protein binding films prepared by hybrid cathodic arc — Glow discharge plasma assisted chemical vapor deposition

Graded composite layers containing metal and plasma polymer components were deposited using a cathodic arc in conjunction with plasma immersion ion implantation. Using a bias potential throughout, pure metal was deposited initially using the cathodic arc alone and then acetylene was added to the process to increase the fraction of the plasma polymerized carbon film. To test adhesion, the substrate and film were strongly deformed by folding the substrate inward and outward with a small radius of curvature. Strong adhesion between the metal surface and the deposited layers was achieved by the use of the graded layers as inferred from the SEM observations of the deformation region. Strong adhesion of biologically active protein molecules to the surface of the graded layer was confirmed by detergent washing and colorimetric enzyme activity assays. These characteristics suggest that the coatings may be suitable for cardiovascular stent applications.

A comparison between characteristics of atmospheric-pressure plasma jets sustained by nanosecond- and microsecond-pulse generators in helium

Power source is an important parameter that can affect the characteristics of atmospheric-pressure plasma jets (APPJs), because it can play a key role on the discharge characteristics and ionization process of APPJs. In this paper, the characteristics of helium APPJs sustained by both nanosecond-pulse and microsecond-pulse generators are compared from the aspects of plume length, discharge current, consumption power, energy, and optical emission spectrum. Experimental results showed that the pulsed APPJ was initiated near the high-voltage electrode with a small curvature radius, and then the stable helium APPJ could be observed when the applied voltage increased. Moreover, the discharge current of the nanosecond-pulse APPJ was larger than that of the microsecond-pulse APPJ. Furthermore, although the nanosecond-pulse generator consumed less energy than the microsecond-pulse generator, longer plume length, larger instantaneous power per pulse and stronger spectral line intensity could be obtained in the nanosecond-pulse excitation case. In addition, some discussion indicated that the rise time of the applied voltage could play a prominent role on the generation of APPJs.

Spots on electrodes and images of a gap during pulsed discharges in an inhomogeneous electric field at elevated pressures of air, nitrogen and argon

Pulsed discharge in a nonuniform electric field accompanied by the appearance of bright spots due to explosive electron emission on electrodes has been investigated. The experiments were carried out using three experimental setups, a voltage pulse duration at a matched load of 2 ns, 40 ns, and 130 ns, respectively. Data on the formation of electrode spots during diffuse discharges in tube-plate or needle-plate gap configurations filled with gases at elevated pressures (air, nitrogen and argon) were obtained. It was found that in the air and other gases, bright spots arise on the flat electrode, and on the negative polarity of the electrode with a small radius of curvature, during the direction change of the current through the gap and the increase of the voltage pulse duration. It was shown that at the positive polarity of the electrode with a small radius of curvature, bright spots on the flat electrode arise due to the participation of the dynamic displacement current in the gap conductance.

Impact of layup rate on the quality of fiber steering/cut-restart in automated fiber placement processes

AbstractDeveloping reliable processes is one of the key elements in producing high-quality composite components using an automated fiber placement (AFP) process. In this study, both simulation and experimental studies were carried out to investigate fiber steering and cut/restart under different processing parameters, such as layup rate and compaction pressure, during the AFP process. First, fiber paths were designed using curved fiber axes with different radii. Fiber placement trials were then conducted to investigate the quality of the steered fiber paths. Furthermore, a series of sinusoidal fiber paths were fiber placed and investigated. Moreover, a six-ply laminate with cut-outs in it was manufactured in the cut/restart trials. The accuracy of the fiber cut/restart was compared at different layup rates for both one- and bi-directional layups. Experimental results show that it was possible to layup steered fiber paths with small radii of curvature (minimum 114 mm) designed for this study when the proper process condition was used. It was observed from the cut/restart trials that the quality of tow cut was independent of layup speed; however, the accuracy of tow restart was related to the layup speed. The faster the layup speed, the less accurate was the tow restart.

Diffusion and seed shape: intertwined parameters in the synthesis of branched metal nanostructures.

Branched nanocrystals display interesting optical and catalytic properties on account of their high surface areas and tips with small radii of curvatures. However, many synthetic routes toward branched nanocrystals result in inhomogeneous samples on account of asymmetric branching. Seed-mediated coreduction is a recently developed route to symmetrically branched nanocrystals where the symmetry of the seeds is transferred to the final stellated morphologies. Here, general guidelines to stellated nanocrystals are outlined by surveying coreduction of Au and Pd precursors in the presence of a variety of shape-controlled Au seeds to achieve Au/Pd nanostructures. Single-crystalline, twinned, and anisotropic seeds were analyzed to expand the classes of stellated nanostructures synthetically accessible. Significantly, single-crystalline Au seeds adopt {100}-terminated intermediates prior to branching, regardless of initial seed shape. We compared these results with those obtained with shape-controlled Pd seeds, and seed composition was identified as an important synthetic parameter, with Pd seeds being more resistant to shape changes during overgrowth. This difference is attributed to the greater diffusion rate of Au atoms on Au seeds compared to Au atoms on Pd seeds. These results provide guidelines for the seeded synthesis of symmetrically branched nanocrystals and architecturally defined bimetallic nanostructures in general.

Scale effects of round-crested weir flow

ABSTRACTScale effects of round-crested weir flow originate from viscosity and surface tension. No general weir flow equation accounting for these is available in the literature. In this work an equation is developed accounting for scale effects. Given the lack of knowledge on the laminar boundary layer development for these flows, detailed two-dimensional and integral laminar boundary layer solutions were obtained, from which an analytical solution results. The surface tension effect is included by allowing for high streamline curvature effects, as is typical for flow over very small weir models. The developments were used to successfully predict the discharge characteristics of circular weirs of small crest radius of curvature. The research indicates a minimum of R=0.01 m. Provided that 0.01 m<R<0.30 m, a minimum overflow head of 0.04 m keeps the discharge curve free from significant scale effects. The equations are also applied to the broad-crested weir using a flow analogy for the separation bubble.

Laser Direct Writing of Thick Hybrid Polymers for Microfluidic Chips

This work presents patterning of thick (10–50 µm) hybrid polymer structures of ORMOCER® by laser direct writing. ORMOCER® combine polymer-like fabrication processes with glass-like surface chemistry that is beneficial for many bio-microfluidic applications. ORMOCER® is liquid before exposure, so patterning is done by contact-free lithography, such as proximity exposure. With laser direct writing, we obtained higher resolution patterns, with smaller radius of curvature (~2–4 µm), compared to proximity exposure (~10–20 µm). Process parameters were studied to find the optimal dose for different exposure conditions and ORMOCER® layer thicknesses. Two fluidic devices were successfully fabricated: a directional wetting device (fluidic diode) and an electrophoresis chip. The fluidic diode chip operation depends on the sharp corner geometry and water contact angle, and both have been successfully tailored to obtain diodicity. Electrophoresis chips were used to separate of two fluorescent dyes, rhodamine 123 and fluorescein. The electrophoresis chip also made use of ORMOCER® to ORMOCER® bonding.

Stabilization and structure of n-heptane tribrachial flames in axisymmetric laminar jets

A set of tribrachial flames of n-heptane/air is simulated with finite rate chemistry and detailed transport in a realistic laminar jet configuration for which experimental data are available. The flames differ by the temperature of the unburnt mixture and stabilization height, which controls the mixture fraction gradient ahead of the flame front. The simulations reproduce the lift-off heights in the experiments, showing that the flame stabilizes further downstream as the unburnt temperature decreases. For the lowest unburnt temperature, resulting in a weak mixture fraction gradient at the tribrachial point, positive stretch along the rich premixed wing leads to an increase in the rate of chemical reaction in the whole flame. The tribrachial flame burning velocity exceeds that in the unstretched, one-dimensional flame. For the highest temperature, the flame stabilizes closest to the nozzle. Large flame tilt, large mixture fraction gradient, and small radius of curvature lead to a reduction in the heat release rate and the flame propagates slower than its one-dimensional counterpart. The observed behavior is explained with a detailed analysis of the flame geometry, differential diffusion effects, flame stretch, and transport of heat and mass from the burnt gases to the flame front.

Initial stage of breakdown of a point-plane gap filled with high-pressure nitrogen and SF6

The initial stage of breakdown of sulfur hexafluoride (SF6) and nitrogen in a nonuniform electric field at high pressures is studied. High voltage pulses with amplitudes of up to 350 kV have been applied across the discharge gap with the “point-plane” geometry of the electrodes. Experimental results on the dynamics of light emission from different zones of the discharge gap can be explained by generation of an ionization wave, which started from a potential electrode with a small radius of curvature. It is found that the speed of the ionization wave front in nitrogen and SF6 is higher in the second half of the discharge gap as compared to the first one. It is shown that the speed of ionization wave front decreases as SF6 and nitrogen pressure increases. The average speed of ionization wave front is shown to be ∼2 cm/ns in SF6 under a pressure of 0.25 MPa and ∼3.6 cm/ns in nitrogen under a pressure of 0.3 MPa under the negative polarity of high-voltage pulses when bridging a discharge gap of about 13 mm.

Metal Nanoridges in Hollow Si-Loaded Plasmonic Waveguides for Optimal Mode Properties and Ultra-Compact Photonic Devices

To achieve subwavelength mode confinement, we propose a hybrid plasmonic waveguide consisting of a metal nanoridge embedded in a silica-covered hollow silicon ridge waveguide on a metal substrate. The mode confinement, propagation length, and figure of merit are optimized by controlling the geometry of the waveguide. At the optimal figure of merit, the normalized mode area of 3.0 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> (λ <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /4) is achieved while retaining a propagation length of 163.0 μm at the telecom wavelength of 1550 nm. The coupling strength of a directional coupler composed of two such waveguides is analyzed to examine the degree of integration of photonic integrated circuits. A strong dependence on the coupling length makes the proposed structure very favorable for use in various plasmonic devices. Furthermore, transmission through a 90° bend (studied to examine the compactness of the proposed waveguide), is observed to be 80% at the small radius of curvature of 0.7 μm.