Elliptical Cross Section Research Articles

TOPOLOGICAL STUDY OF TORSIONAL SPINE MAGNETIC RECONNECTION AT NULL POINT

The spine is an isolated field line which approaches the null (or recedes from it), so called torsional spine reconnection occurs when field lines in the vicinity of the fan rotate, with current becoming concentrated along the spine so that nearby field lines undergo rotational slippage. In of these region, the spine and fan are perpendicular and there is no flux transfer across spine or fan. The geometry of the current layers within which torsional spine reconnection occur is strongly dependent on the symmetry of the magnetic field. Torsional spine reconnection occurs in a narrow tube around the spine, with elliptical crosssection when the fan eigenvalues are different. The eccentricity of the ellipse increases as the degree of asymmetry increases, with the short axis of the ellipse being along the strong field direction. The spatiotemporal peak current, and the peak reconnection rate attained, are found not to depend strongly on the degree of asymmetry.

Study on the effect of jet cross section shape on molten fuel fragmentation behavior with simulant experiments

In this study, melt-jets with elliptical cross sections are employed with different melt temperature, water temperature, penetration velocity and water depth to explore the influence of the jet cross-sectional shape on melt-jet fragmentation behavior. When free fall distance is larger than 40 cm, the jet cross-sectional shape has no obvious influence on the fragmentation behavior in the current experimental conditions. When water temperature or melt temperature increases, the fragmentation becomes more complete with higher debris bed sphericity and smaller debris bed porosity. When melt penetration velocity is higher, smaller particles can be produced, but it has no obvious effect on debris bed porosity and sphericity. Water depth which is larger than 40 cm has no obvious effect on the fragmentation behavior. Weber number theory can be used to predict the mass median diameter of debris bed, and Stephan number (St) to predict the trend of debris bed porosity and sphericity. The jet breakup length model proposed by Epstein and Fauske (2001) is much better to predict jet breakup length.

Assessing the height, width and other parameters of elliptical yarn cross-section through the thickness of orthogonal fabrics

This research focuses to assess the height, width, and other parameters of the elliptical yarn cross-section of woven fabrics through the new methodology. Hence this research studies the Elliptical Cross-Section of the yarn through the orthogonal fabric. Because in orthogonal fabric, the weft series stay straight. The samples of orthogonal weaves are produced using different counts of weft yarns. The thicknesses of orthogonal fabrics are estimated. The method of calculating the height of yarn from the thickness of the orthogonal fabric is evolved. The height of different counts of weft yarns used in weaving the orthogonal fabrics is calculated. From the height of the yarn, the width of the yarn is calculated. The height and width of the yarn are compared with the diameter. The comparison shows that the cross-section of the yarn remains elliptical in the fabric. The equations for calculating the flattening and bulging percentages are derived. It is observed that these two percentages are equal. It shows that when the yarn cross-section becomes elliptical in the fabric, the amount of flattening makes the yarn get bulge to the same amount in its width. The constant of height and constant of width are also derived. These constants are equated with the constants of diameter. The study also derived the equation to calculate the height and width of the elliptical cross-section of the given yarn count using the constants. The height, width, and diameter of different yarn counts are compared. The increase/decrease in flattening percentage between the coarser-finer yarns, single–2 ply yarns, and single-folded yarns are examined. It is suggested that the height and width of yarn assessed from the thickness are used to assess the other specifications viz. crimp percentage, cover percentage, and GSM of the fabrics.

Research on the penetration characteristics of elliptical cross-section projectile into semi-infinite metal targets

To better understand the penetration characteristics of the elliptical cross-section projectile (ECSP) into metal targets, a series penetration experiments of projectiles with different shape cross-section to semi-infinite aluminum target were carried out. The shape ratios of typical ECSPs were 1.25 and 1.56, respectively, and another was circular cross-section projectile (CCSP) which has the same cross-section area in accordance with ECSP. In the penetration experiments, the projectiles were launched with striking velocities ranged from 400 m/s to 1000 m/s, and strain sensors were arranged on the impact surface of the aluminum target to catch the dynamic response during the penetration process. Then, characteristics of cracks on the impact surface of targets, penetration depths and penetration trajectory were measured after the penetration experiments. The results indicated that the dynamic response and damage behavior of targets showed obvious asymmetry under the penetration of ECSPs. Strain data had a decreasing trend from the major axis to the minor axis of the ellipse, and the length and number of cracks of the ECSP were larger than that of the CCSP. Besides, a theoretical model was developed to explain the asymmetric deformation and failure behavior of targets based on the conformal mapping theory and the strain path method. Calculation results showed that the asymmetric deformation of targets was directly caused by the displacement boundary conditions of the ellipse.

Performance improvement of single-junction photovoltaic systems using a new design of a heat pipe-based heat sink: Experimental study

A newly integrated single-junction PV-heat pipe system with an innovative heat sink design comprised of an elliptical cross-section area and varied aspect ratios is proposed and experimentally investigated. Unlike the prior systems, the proposed one fits the requirements for practical applications, such as adequate cooling efficiency, ease in manufacturing, reliability, low operating and maintenance costs, noiseless and powerless operation, and so increases total system efficiency. Several experiments were carried out indoors to examine the effect of using four working fluids (Pure water, Ethanol, Methanol, and Ethylene Glycol based water solution (50 % by volume), four distinct charging ratios (50, 60, 70, and 80 %), and different heat loads to mimic the absorbed energy due to incident solar irradiance received by the solar cell. The results showed that the heat pipe with an elliptical cross-section area performed better than the one with a circular cross-section area with more than 300 W/m2 increase in heat absorbed rate at 50 ℃ oil temperature and more than 2700 W/m2 increase in heat absorbed rate at 90 ℃ oil temperature. Furthermore, when compared to other working fluids and charging ratios, the heat pipe filled with Ethanol as the working fluid and a charge ratio of 70 % performs better for all operating temperatures tested and aspect ratio. The reduction in PV module temperature ranging from 9 to 16.36 ℃ depends on the working fluid, charging ratio and the operating temperature. While the increase in the PV module output power ranging from 4 to 8.18 % at the different working fluids, charging ratios and operating temperatures.

Investigation of the dynamic behavior of three-layer cylindrical shells of elliptical form under internal axisymmetric pulse loading

The results of the assessment of the dynamic behavior of three-layer cylindrical shells of circular and elliptical cross-sections under internal impulse loading are given. The finite-element method was used to calculate the indicators of the stress-strain state (SSS) of such structures by the NASTRAN software complex. The values normal deflections and normal stresses of circular and three elliptical forms of intersection of cylindrical structures are determined. A comparative analysis of the values of these indicators with the results of the dynamic behavior of uneven cylindrical shells was performed.
 The shape and curvature of the cross section of three-layer cylindrical thin-walled composite shells significantly affect their SSS under dynamic impulse loading.
 Replacing the circular shape of the cross section of a cylindrical structure with an elliptical one and increasing the ratio of the semiaxes of the elliptical section leads to an increase in normal deflections and normal stresses of the middle surface of the structure.

Impact of elasticity of polymer filler of three-layer cylindrical structure of elliptical section on its behavior under internal impulse loading

The impact of the elasticity of the polymer filler of a three-layer cylindrical structure of normal elliptical cross-section on its stress-strain state under internal impulse loading was studied. Determined values and distribution of normal deflections and stresses in sections S1 and S2. The finite-element method of calculating the stress-strain state (SSS) of such a structure by the software-calculation complex Fimap with NX Nastran was applied. Conclusions were made regarding the sufficient expediency of considering the elasticity of the filler when optimizing the design of such structures.
 Increasing the elasticity of the polymer filler increases the strength and monolithicity of the layered structure. The use of this method ensures efficiency and is appropriate when the ratio of elasticity of the materials of the layers and filler is Е1.3 /Еt ≤50.

Morphology of Shear-Induced Polymer Cylindrites Revealed by 3D Optical Imaging.

Two-photon confocal laser microscopy was used to obtain three-dimensional (3D) images of the morphology of poly(lactic acid) after shear-induced crystallization. The necessary fluorescence contrast was achieved by doping the polymer with Nile Red. The dye gets partially rejected from the growing crystalline aggregates during their formation, thus creating a renderable high-low fluorescence boundary outlining the shape of the aggregates. Parallel-plate melt-shearing and pulling a glass fiber through the melt were used as the two methods to achieve shear-induced crystallization. This study focuses on the shape of the resulting cylindrites, i.e., large-diameter shish-kebabs. The first 3D images of polymer cylindrites show that, if far from boundaries, they are circular cylinders, highly regular after fiber pull, but less so after parallel-plate shear. In the latter case, the cylindrite reveals the trajectory of the foreign particle that had nucleated its growth. Interestingly, lateral growth of the cylindrites was found to accelerate toward the sample surface when approaching it, giving the cylindrite an elliptical cross section. Furthermore and surprisingly, in the case of fiber pull, a row of spherulites is nucleated at the polymer-substrate interface nearest to the fiber, aligned along the fiber axis and appearing ahead of the rest of the space-filling spherulites. Both the phenomena, elliptical cylindrites and row of spherulites, are attributed to negative pressure buildup peaking at the cylindrite growth front and at the nearby film surface caused by crystallization-induced volume contraction. The pressure and flow distribution in the system is confirmed by numerical simulation. The results illustrate the value of 3D imaging of crystalline morphology in polymer science and polymer processing industry.

Impact of process-induced ellipticity on the RESET process of cylindrical phase change memory devices

Phase change memory (PCM) is one of the promising candidates for the next-generation high-speed non-volatile memory which exhibits excellent scalability. The cylindrical-type PCM devices entering the nano-scale regime should show their tolerance to the variation in the manufacturing process. However, it is highly challenging to fabricate cylindrical-type nano-scale devices ideally with circular cross-sections. In general, the degree of variation in circular cross-section is dictated by a geometrical parameter called aspect ratio (AR). In this study, the impact of variation in AR of heater (ARheater) and active material, Ge2Sb2Te5 (ARGST) on the RESET programming of the mushroom-type cylindrical PCM device is systematically investigated by using 3D TCAD simulations. The simulation results reveal that the RESET current (IRESET) of the reference device (100 nm heater diameter) consisting of elliptical cross-sections increases significantly to ∼67% when ARheater = 2 and 1 ≤ ARGST ≤ 2, whereas for the scaled-down devices of 20 nm and 10 nm heater diameter with elliptical cross-sections, the IRESET increases to ∼35% and ∼38% when ARheater = 2 and ARGST = 1, and further IRESET increases to ∼54% and ∼63% when ARheater = 2 and ARGST = 2 leading to high-power RESET programming. In the case of the reference device, the ARGST did not play any significant role on IRESET. However, in the scaled-down devices, both ARheater and ARGST significantly affect the IRESET. Furthermore, the device employing a vertically-oriented elliptical heater and horizontally-oriented elliptical GST (where ARheater = 2 and ARGST = 0.5) shows the peculiar re-amorphization among all the cases considered in this study. Hence, the miniaturized cylindrical PCM devices comprising elliptical cross-sections due to process-induced variability require an accurate understanding of the programming characteristics for reliable modeling and simulations.

Experimental Investigation on the Response of Elliptical CFT Columns Subjected to Lateral Impact Loading

This study reports an experimental investigation on the impact behavior of elliptical concrete-filled steel tubular (CFT) columns subjected to lateral loading. A total of five CFT columns, including one circular cross-section and four elliptical cross-sections, were tested using a horizontal-impact-testing system. The influences of the impact velocity, the impact times, and the cross-section geometry on the dynamic response of the elliptical CFT columns were analyzed. The experimental results have shown that the specimens withstood the global displacements without the buckling of the steel tubes. The strain rates of the steel tubes in this paper were small. The impact velocity had significant influences on the impact load-time histories and energy absorption. Meanwhile, the impact times had little influence on the impact force and displacement at the same impact velocity. Circular CFT columns have the highest ductility and impact-energy-absorption capacity. Based on the finite element analysis software ABAQUS, the finite element models of the elliptical CFT columns under impact loads were established. The simulation results were in good agreement with the experimental results. Finally, the mechanical mechanism of the elliptical CFT columns under lateral impact was analyzed by the finite element model.

Role of particle local curvature in cellular wrapping.

Cellular uptake through membranes plays an important role in adsorbing nutrients and fighting infection and can be used for nanomedicine developments. Endocytosis is one of the pathways of cellular uptake which associate with elastic deformation of the membrane wrapping around the foreign particle. The deformability of the membrane is strongly regulated by the presence of a cortical cytoskeleton placed underneath the membrane. It is shown that shape and orientation of the particles influence on their internalization. Here, we study the role of particle local curvature in cellular uptake by investigating the wrapping of an elastic membrane around a long cylindrical object with an elliptical cross-section. The membrane itself is adhered to a substrate mimicking the cytoskeleton. Membrane wrapping proceeds differently whether the initial contact occurs at the target's highly curved part (vertical) or along its long side (horizontal). We obtain a wrapping phase diagram as a function of the membrane-cytoskeleton and the membrane-target adhesion energy, which includes three distinct regimes (unwrapped, partially wrapped and fully wrapped), separated by two phase transitions. We also provide analytical expressions for the boundaries between the different regimes which confirm that the transitions strongly depend on the orientation and aspect ratio of the nanowire.

Low-Loss Flexible Polarization-Maintaining Hollow Waveguide for Linearly Polarized 100 GHz Radiation Transmission and Subwavelength Imaging

Terahertz imaging has been developed rapidly in recent years. However, conventional terahertz imaging systems are often bulky due to the free space propagation. Various subwavelength sized probes have been developed to realize high resolution. However the tiny probes often suffer from high loss. A flexible metallic polarization-maintaining (PM) hollow waveguides with elliptical cross section is investigated and fabricated. The waveguide is used for transmitting linearly polarized terahertz (THz) radiation and flexible imaging. Bore size of the waveguide is on the order of wavelength. Transmission loss is as low as 0.92 dB/m. High birefringence of 0.08 and measured polarization ratio of 97.2% are achieved by the waveguide at 100 GHz. Moreover, a scanning 100 GHz imaging system is established by using the waveguide as a flexible probe. The PM capability of the fabricated waveguide brings benefits compared to conventional non-PM circular waveguide. The linearly polarized fundamental modes are easily excited and can be propagated through the fabricated waveguides to one meter away with polarization maintenance, which results in compressing of output beam and realizes a high resolution. A resolution better than λ/3 is achieved. It is further experimentally verified that the waveguide is robust to bending and twisting deformation, and maintained the imaging quality during flexible imaging. A subwavelength bore-sized single-polarization single-mode waveguide is also fabricated to simultaneously achieve high horizontal and vertical resolutions. The discussed waveguide is easy to fabricate and may find important applications in THz microscopy and flexible polarization imaging.

A micro gas chromatography column fabricated by ultrafast laser-assisted chemical etching

A novel micro gas chromatography column (μGCC) with straight-sided elliptic microchannel cross sections was prepared by ultrafast laser-assisted chemical etching inside a glass substrate. The straight-sided elliptic cross sections resulted in a uniform distribution of the flow velocity field. This uniform distribution and the use of a microchannel with a consistent composition led to a uniform stationary phase coating. Upon the separation of a test mixture of C7–C11 alkanes, highly symmetrical chromatographic peaks were obtained. The tailing factors of the chromatographic peaks ranged from 0.95 to 1.05, which satisfies the relevant provisions of Pharmacopoeia of the People's Republic of China (ChP). The test results show that the improvement of the tailing factors is mainly due to the optimization of the cross-section structure rather than the optimization of the test conditions. Notably, due to the simple preparation processes and the low cost of the glass substrate, the total manufacturing cost of this novel μGCC is low.

Numerical investigation and entropy generation for flow boiling evaporation in U-bend tube heat exchanger with elliptical and circular cross-sections

• Entropy generation for flow boiling in a U-bend tube heat exchanger with the elliptical and circular cross-section. • Effect of mass velocities on entropy generation for flow boiling a in a U-bend tube heat exchanger. • Local entropy generation for flow boiling along the Length of the U-bend tube heat exchanger. • Effect of the bend on the flow pattern in the U-bend tube heat exchanger with an elliptical and circular cross-section. This paper presents the numerical analysis of entropy generation of two-phase flow boiling in a U-bend tube heat exchanger with the elliptical and circular cross-sections of the same hydraulic diameter for oriented downward flow. The entropy generation criterion due to pressure drop and heat transfer irreversibilities was utilized to measure the quality of energy transfer in the heat exchanger. For the purpose of comparison, the same geometrical parameters were used. The computations were implemented using computational fluid dynamics code for the operating parameters such as mass velocities ranging from 100 to 500 kg/m 2 s with respect to vapour qualities from 0.1 to 0.9 and a constant uniform heat flux of 10 kW/m 2 imposed on the tube’s outer surface. The results reveal that the U-bend tube heat exchanger with the elliptical cross-section performs better than the circular cross-section due to the lower entropy generations obtained in the elliptical cross-section compared to the circular cross-section. The effect of bend on liquid and vapour phase distribution in circular and elliptical cross-sections was illustrated by the flow pattern, just before and after the bend. The flow patterns formed after the bend were quite different from the ones formed before the bend. For the elliptical and circular cross-sections, the flow patterns were observed to be almost the same with the fluids taking the shape of the cross-section. The numerical calculations were validated and found to be consistent with what was found in the open literature.

Reduced Plasma Frequency Calculation Based on Particle-in-Cell Simulations

We propose a scheme to calculate the reduced plasma frequency of a cylindrical-shaped electron beam flowing inside of a cylindrical tunnel, based on results obtained from Particle-in-cell (PIC) simulations. In PIC simulations, we modulate the electron beam using two parallel, non-intercepting, closely-spaced grids which are electrically connected together by a single-tone sinusoidal voltage source. The electron energy and the beam current distributions along the length of the tunnel are monitored after the system is operating at steady-state. We build a system matrix describing the beam's dynamics, estimated by fitting a 2x2 matrix that best agrees with the first order differential equations that govern the physics-based system. Results are compared with the theoretical Branch and Mihran model, which is typically used to compute the plasma frequency reduction factor in such systems. Our method shows excellent agreement with the theoretical model, however, it is also general. Our method can be potentially utilized to determine the reduced plasma frequencies of electron beams propagating in differently-shaped beam tunnels, where no theoretical model yet exists, such as the case of a cylindrical or elliptical electron beam propagating inside of a metallic beam tunnel of cylindrical, square, or elliptical cross-section. It can be applied also to electron beams composed of multiple streams.

Photoacoustic waves of a fluidic elliptic cylinder: Analytic solution and finite element method study

In this study, we focused on the photoacoustic wave production of a fluidic elliptic cylinder for modelling blood vessels, where the consideration of the elliptic cross section can be important for some diagnosis of vascular diseases. First, under the condition of optically-thin absorption, the analytic solution based on the photoacoustic Helmholtz equation in elliptic cylinder coordinates by using Mathieu functions was derived. Then, the finite element method (FEM) model was established to verify the analytic solution. In addition to photoacoustic waves and corresponding photoacoustic power spectra, both near- and far-field photoacoustic amplitude angular distributions were compared. The results revealed that the angular dependent photoacoustic power spectra are critical indicators of the ellipse shape variation. This finding can provide a considerable insight into the photoacoustic diagnosis of the blood vessel changes not only in terms of sizes but also shapes.

An analytical method for the solution of earthquake-induced hydrodynamic forces and wave forces on multiple vertical cylinders with arbitrary smooth sections

Analytical methods are developed to investigate the interaction of water with multiple cylinders with arbitrary smooth cross-sections subjected to horizontal ground motion and incident linear waves. Based on the boundary conditions of the seafloor and the water surface, the three-dimensional Laplace equation was transformed into the two-dimensional (2D) Helmholtz equation. Based on the condition that the coefficient function of the cylinder surface can be expanded into a Fourier series, radiation theory and diffraction theory are extended to solve earthquake-induced hydrodynamic forces and wave forces on multiple cylinders. The proposed analytical solution consists of the high-order scattered wave pressures due to diffracted waves. The present method was verified using two double cylinder arrays with elliptical and round-ended cross-sections. Finally, this method was extended to multiple scattering analysis for the interaction of water under earthquake and wave loads.

On the use of twisting technique to enhance the performance of helically coiled heat exchangers

This paper introduces an idea to enhance the thermal performance of helically coiled heat exchangers by integrating the effect of using a tube with an elliptical cross section shape with the effect of tube twisting. Numerical simulations showed that the combination of these two effects resulted in disrupting the growth of hydrodynamic and thermal boundary layers leading to better distributions of temperature, velocity, and turbulent kinetic energy compared with the untwisted model with a circular cross section. The Nusselt number was found to be increased significantly by decreasing the aspect ratio of the elliptical tube shape along with increasing the number of tube twisting turns. The average Nusselt number was increased by 29.24% when using aspect ratio of 0.3 with a twist ratio of 0.0327 m. The enhancement in the thermal performance is accompanied with an increase in the pressure drop due to the increased turbulence levels. Findings of this research reveal that this technique is promising in raising the performance of helically coiled heat exchangers. Detailed analysis provided may be useful for future researches on this topic.

Virial relations for elongated plasmas in a tokamak and their potential use in magnetic diagnostics

Virial relations are traditionally considered as providing the diamagnetic parameter, poloidal beta βp, and internal inductance ℓi through the integrals determined by the plasma shape and poloidal magnetic field at the plasma–vacuum interface. This gives rise to discussions of their potential applications for diagnostic purposes. Recently, this concept was analyzed in the numerical study of Bongard et al. [Phys. Plasmas 23, 072508 (2016)]. Here, we analytically calculate three main virial integrals (traditionally denoted as S1, S2, and S3) for the plasma with elliptical cross section. The results are expressed through the plasma elongation, its radial derivative, and a similar derivative Δ′ of the Shafranov shift, all taken at the plasma boundary. The geometry of magnetic surfaces inside is not constrained, which guaranties the applicability of the results in a wide area. It is shown that S1 must be a constant, S3 weakly depends on ℓi, and only S2 is a sensitive function of the plasma state through Δ′. This makes S2 the quantity most suitable for diagnostics, while independence of S1 on the plasma shape, βp, and ℓi can be good for calibrations. The difficulties of inferring ℓi from the measured S3 are now shown explicitly.

Stark-localization as a probe of nanostructure geometry

It is a central tenet of quantum mechanics that spatial resolution is limited by the wave nature of particles. Energies of stationary states reflect delocalized wave functions and cannot be ascribed to any single point. Yet, electrons confined in nanostructures become localized against the boundary by strong electric fields. Energies then reflect the local curvature of the nanostructure surface rather than entire volume. We propose using spectroscopy of Stark-localized states to map nanostructure surface curvature. By varying field direction, local curvatures are extracted from absorption spectra. Moreover, the required field strength is shown to be feasible experimentally. We use nanowires with elliptic cross section as a detailed benchmark providing quantitative error estimates and practical guide lines.