Quadrilateral Cross Section Research Articles

An individual ZnO microwire homojunction LED with ultraviolet electroluminescence spectrally purified using Pt nanoparticles cladding

Low-dimensional ultraviolet light sources are enormous significance due to their wide range of potential applications, ranging from bioscience and high-resolution biological imaging, environmental conservation to public hygiene. Nevertheless, developing energy-efficient and cost-efficient light sources still remains serious challenges. In this study, p-type ZnO microwires with Sb-incorporation (ZnO:Sb MWs) were synthesized individually. The p-type conductivity was proofed using an individual MW based back-gated field-effect transistor; while the ZnO:Sb MWs with quadrilateral cross-section exhibited stimulated emission resonant in well-defined Fabry-Perot mode on the benefit of single-crystalline quality and atomically smooth side facets. The newly synthesized ZnO:Sb MW was further used to fabricate homojunction light-emitting device by employing n-type ZnO film as electron-transporting layer. A strong ultraviolet emissions peaking at around 378.5 nm was achieved upon forward biased electrically, but illustrating much broader electroluminescence (EL) linewidth. Introducing Pt nanoparticles (PtNPs) with desired plasmons, the light-out intensity is significantly enhanced. Particularly, the broad EL profiles narrowed to about 16.6 nm at high injection regime, achieving electron-holes radiative recombination in the ZnO:Sb MWs active region. The results exhibit a prominent progress achieving high-quality ZnO nano/microstructures with genuine p-type conductivity, which has great hopes for its future applications and development in ZnO homojunction optoelectronic devices.

A Novel Design Method of Heat Sink with Conjugate Heat Transfer by Free-Shape Channel Modeling

Heat sink is an indispensable and even hard-core device which ensures the reliability and lifespan of most electronic equipment. Geometry factor plays a crucial role in the heat sink design. This paper proposes a novel geometric modeling method for heat sink with conjugate heat transfer properties, which involves parametric design of the flow passage patterns and cross-sections. Two assumed serpentine cooling plates with round and quadrilateral cross-sections are utilized to validate the proposed method respectively. During modeling, the fixed geometry dimensions are divided into several degrees of freedom to promote the flexibility of geometry factor with regard to heat sink design. The Bernstein-Bézier function is utilized to define these degrees of freedom. The numerical simulations based on the orthogonal experimental design are carried out, and then the results are analyzed and compared. The experimental results revealed that the optimised design can be obtained by adjusting the relevant control coefficients, which further improves the performance of cooling plate effectively. This paper guides the heat sink design and provides an insight into the structure problems from the perspective of geometry parameterization.

A semi-analytical FE method for the 3D bending analysis of nonhomogeneous orthotropic toroidal shells

Based on Reissner's mixed variational theorem (RMVT), the authors develop a semi-analytical finite element (FE) method for a three-dimensional (3D) bending analysis of nonhomogeneous orthotropic, complete and incomplete toroidal shells subjected to uniformly-distributed loads. In this formulation, the toroidal shell is divided into several finite annular prisms (FAPs) with quadrilateral cross-sections, where trigonometric functions and serendipity polynomials are used to interpolate the circumferential direction and meridian-radial surface variations in the primary field variables of each individual prism, respectively. The material properties of the toroidal shell are considered to be nonhomogeneous orthotropic over the meridian-radial surface, such that homogeneous isotropic toroidal shells, laminated cross-ply toroidal shells, and single- and bi-directional functionally graded toroidal shells can be included as special cases in this work. Implementation of the current FAP methods shows that their solutions converge rapidly, and the convergent FAP solutions closely agree with the 3D elasticity solutions available in the literature.

General non-uniform quadrilateral cross-sections for thin-walled FG sandwich beams

The paper aims at introducing an analysis of thin-walled functionally graded sandwich beams for general non-uniform quadrilateral cross-sections. Generally, the materials are assumed to be graded through the thickness following a predefined shape while Poisson's ratio kept as a constant due to its less domination. The cross-section linearly varies from one end to another end of the beam. In order to relax the difficulties in modeling as well as capturing the behaviors of thin-walled functionally graded beams, a higher-order approach has been applied including warping, coupling distortions as well as Poisson's distortion. A multi-separated beam on each edge of the cross-section which is an application of the so-called beam-frame-modal method is adopted. Subsequently, the effects of these major importance along with anisotropy of materials are then fully considered. As a consequence, the analysis is able to extensively applied to closed-section beam-shells with different curvatures. In order to illustrate the accuracy and computational efficiency of the method, various examples have been conducted in which the results obtained from finite element package as ABAQUS are employed.
 Keywords:
 quadrilateral cross-section; thin-walled FG beam; higher-order coupling; beam frame modal.

Bending Property of Honeycombed 3D Woven Composites with Quadrilateral Cross Section

The delamination resistance and damage tolerance of traditional honeycomb composites are poor. To overcome these defects, 3D (three-dimensional) integrated woven composites of honeycomb structure were designed, and then manufactured using the vacuum assisted resin transfer molding process (VARTM), based on the 3D self-prepared fabrics used as reinforcements. The load-displacement curves, maximum bending load-velocity curves, and bar chart of energy absorption were determined experimentally and calculated by finite element simulation. The results showed good agreement between experimental and finite element simulation data. The correctness of the model was verified, so the model can be used to predict the mechanical properties of 3D integrated woven composites of honeycomb structure with quadrilateral cross section.

Zamana Bağlı Kavite Akışı Aeroakustiğinin Büyük Girdap Simülasyonu ile Sayısal Olarak İncelenmesi

Flow along a cavity is of special interest for researchers due to the occurrence of free shear layer flow and related high levels of sound and pressure forces. In this study, turbulent flow along an open cavity at a low inlet Mach number (Ma = 0.034) is modelled by Large Eddy Simulations (LES). The velocity profiles at various stations inside the open cavity are compared to available experimental data. It is found that LES results agree with experimental data and detects the transient pressure change in the flow field satisfactorily. Transient pressure data in the flow field is evaluated in acoustic analogy. The noise generated by the cavity is compared with the established Rossiter modes and is found to be reasonable. To create an effect on the sound pressure levels (SPL), a small obstacle with quadrilateral cross section is immersed in the shear layer at three different locations. This causes that the SPL peaks are reduced compared to the case without any obstacle. Thus, cavity-induced noise form specific frequencies are redistributed to high frequency broadband noise as a result of this passive flow control method.

Wavelength-Tunable Waveguide Emissions from Electrically Driven Single ZnO/ZnO:Ga Superlattice Microwires

Because of the superlattice structures comprising periodic and alternating crystalline layers, one-dimensional photon crystals can be employed to expand immense versatility and practicality of modulating the electronic and photonic propagation behaviors, as well as optical properties. In this work, individual superlattice microwires (MWs) comprising ZnO and Ga-doped ZnO (ZnO/ZnO:Ga) layers were successfully synthesized. Wavelength-tunable multipeak emissions can be realized from electrically driven single superlattice MW-based emission devices, with the dominant wavelengths tuned from ultraviolet to visible spectral regions. To illustrate the multipeak character, single superlattice MWs were selected to construct fluorescent emitters, and the emission wavelength could be tuned from 518 to 562 nm, which is dominated by Ga incorporation. Especially, by introducing Au quasiparticle film decoration, emission characteristics can further be modulated, such as the red shift of the emission wavelengths, and the multipeaks were strongly modified and split into more and narrower subbands. In particular, electrically pumped exciton-polariton emission was realized from heterojunction diodes composed of single ZnO/ZnO:Ga superlattice MWs and p-GaN layers in the blue-ultraviolet spectral regions. With the aid of localized surface plasmons from Au nanoparticles, which deposited on the superlattice MW, significant improvement of emission characteristics, such as enhancement of output efficiencies, blue shift of the dominant emission wavelengths, and narrowing of the spectral linewidth, can be achieved. The multipeak emission characteristics would be originated from the typical optical cavity modes, but not the Fabry-Perot mode optical cavity formed by the bilateral sides of the wire. The resonant modes are likely attributed to the coupled optical microcavities, which formed along the axial direction of the wire; thus, the emitted photons can be propagated and selected longitudinally. Therefore, the novel ZnO/ZnO:Ga superlattice MWs with a quadrilateral cross section can provide a potential platform to construct multicolor emitters and low-threshold exciton-polariton diodes and lasers.

One-dimensional analysis of thin-walled beams with diaphragms and its application to optimization for stiffness reinforcement

This paper presents a method to analyze thin-walled beams with quadrilateral cross sections reinforced with diaphragms using a one-dimensional higher-order beam theory. The effect of a diaphragm is reflected focusing on the increase of static stiffness. The deformations on the beam-interfacing boundary of a thin diaphragm are described by using deformation modes of the beam cross section while the deformations inside the diaphragm are approximated in the form of complete cubic polynomials. By using the principle of minimum potential energy, its stiffness that significantly affects distortional deformation of a thin-walled beam can be considered in the one-dimensional beam analysis. It is shown that the accuracy of the resulting one-dimensional analysis is comparable with that by a shell element based analysis. As a means to demonstrate the usefulness of the present approach for design, position optimization problems of diaphragms for stiffness reinforcement of an automotive side frame are solved.

Quadrangular-CNT-Fe3O4-C composite based on quadrilateral carbon nanotubes as anode materials for high performance lithium-ion batteries

A q-CNT-Fe3O4-C composite was synthesized via the homogeneous precipitation of FeOOH nanoparticles on quadrangular carbon nanotubes (q-CNT) substrates. The q-CNT multi-walled carbon nanotube featured one closed end and an open end with a quadrilateral cross section, and the nanotubes were prepared by using co-carbonization method. The FeOOH nanoparticles were encapsulated by amorphous carbon via a hydrothermal treatment and high-temperature calcination of glucose. TEM showed that diameter of the q-CNT was 100 nm and the tube thickness was 20 nm. The outer wall of the q-CNT was attached to Fe3O4 with sizes ranging from 80 to 100 nm via a layer of an amorphous carbon coating. It delivered a specific capacity of 1031.5 mAh g−1 after 100 cycles at a current density of 200 mA g−1. After 60 cycles, it showed a high specific capacity of 485.6 mAh g−1 even at 2000 mA g−1. CV and EIS results further suggested that the q-CNT-Fe3O4-C composite exhibited lithium ion uptake/release reversibility and a rapid high current charge/discharge capability. The excellent rate performances of the q-CNT-Fe3O4-C composite can be attributed to the superior electronic transport properties of the quadrilateral CNT with one open end and the synergistic effects of the hybrid components.

Higher order analysis of thin-walled beams with axially varying quadrilateral cross sections

A thin-walled beam finite element with a varying quadrilateral cross section is formulated based on a higher order beam theory. For the calculation of distortions, the beam frame approach, which models the cross section by using two-dimensional Euler beams, is used. Distortions induced by the Poisson’s effect and warpings are analytically derived. Three-dimensional displacements at an arbitrary point of a present beam element can be described by interpolating three-dimensional displacements at the end sections. Straight and curved thin-walled beams with varying cross sections are solved to show the validity of the proposed approach.

Buckling and longitudinal cracks in electromagnetically accelerated hollow cylinders

Hollow cylindrical Al-6061 T6 projectiles, driven in a coilgun system, suffer radial compression and buckle into quadrilateral or pentagonal cross sections. In some cases, the projectiles fail by developing longitudinal cracks in the compressed region. Simulations of the coilgun-projectile system, using Johnson–Cook and Bao–Wierzbicki failure models, reproduce buckling and formation of longitudinal cracks via localization of plastic strain and high temperatures around the bends of the buckled geometry. Failed specimens were micro-graphically investigated and the cause of failure attributed to synergistic effect of buckled geometry and localized high temperature zones.

Analysis of a shell of revolution subjected to axisymmetric loading taking into account geometric nonlinearity on the basis of the mixed finite element method

An algorithm is presented to obtain the deformation matrix for the annular finite element with a quadrilateral cross-section. The displacement and strain increments are taken as nodal unknowns. For numerical realization of the algorithm, we take the functional obtained using the principle of equal works for the internal and external forces at a step of loading. A newly developed version of approximating the unknown quantities allowed us to solve the problem of taking into account the finite element displacement as a rigid body.

Fully Coupled 10-Degree-of-Freedom Beam Theory for Piecewise Straight Thin-Walled Beams with General Quadrilateral Cross Sections

A fully coupled 10-degree-of-freedom (DOF) beam theory is developed for the analysis of thin-walled closed piecewise straight beams of general quadrilateral cross sections. The developed beam theory can predict the structural response of arbitrarily shaped thin-walled quadrilateral sectioned beams that are curved or connected to each other through a number of angled joints. For accurate prediction, the local effects by four beam sectional deformations such as torsional warping, torsional distortion, bending warping, and bending distortion must be taken into account in addition to the structural responses by standard six translational and rotational DOFs of the Timoshenko beam theory. When two straight beams of general quadrilateral sections meet at an angle, all 10 DOF deformations become fully coupled. Furthermore, it is not easy to derive the exact interface conditions at the angled joint because 10 DOFs have different physical behavior. For the analysis of the beam system in consideration, the section deformation patterns corresponding to all of the 10 DOFs are presented. In particular, the cross-sectional shape functions for bending distortion and bending warping for general quadrilateral sections are derived for the first time. Then, a systematic method to match 10 DOFs of two straight quadrilateral beams meeting at a joint of an arbitrary angle is developed. Several numerical case studies are considered to check the validity of the developed beam analysis.

Preparation and Optical Properties of Prism-Shaped GaN Nanorods

Large quantities of prism-shaped GaN nanorods were prepared by a thermal CVD reaction between Ga and NH3 on LaAlO3 crystal substrates. The distinct morphology of the GaN nanorods lies in their prism-like out shape and most of them have a quadrilateral cross section. The Raman spectrum of the GaN nanorods shows two additional bands at 255 and 419 cm-1. Moreover, a large red shift of A1(LO) phonon has been observed compared with that of bulk GaN crystals. Room-temperature photoluminescence measurement reveals a broad emission ranging from 2.5 to 3.5 eV with some fine structures, which are believed to be associated with the defect levels.

Vibration of Thick Circular Disks and Shells of Revolution

A fully numerical and consistent method using the three-dimensional theory of elasticity is presented in this paper to study the free vibrations of an axially symmetric solid. The solid is defined in the cylindrical coordinates r,θ,z by a quadrilateral cross section in the r-z plane bounded by four straight and/or curved edges. The cross section is then mapped using the natural coordinates (ξ,η) to simplify the mathematics of the problem. The displacement fields are expressed in terms of the product of two simple algebraic polynomials in ξ and η, respectively. Boundary conditions are enforced in the later part of the solution by simply controlling coefficients of the polynomials. The procedure setup in this paper is such that it was possible to investigate the free axisymmetric and asymmetric vibrations of a wide range of problems, namely; circular disks, cylinders, cones, and spheres with considerable success. The numerical cases include circular disks of uniform as well as varying thickness, conical/cylindrical shells and finally a spherical shell of uniform thickness. Convergence study is also done to examine the accuracy of the results rendered by the present method. The results are compared with the finite element method using the eight-node isoparametric element for the solids of revolution and published data by other researchers.

End Effects of Thin-Walled Beams with General Quadrilateral Cross Sections

End effects due to sectional deformations of thin-walled beams with closed cross section are analysed by a one-dimensional theory. In particular, end effects associated with warping (out of plane m otion) and distortion (in plane motion) are investigated. The exact solutions as a vector form are newly derived to reveal slowly-decaying nature of the end effects in a thin-walled beam loaded by a couple. Several examples of thin-walled beams under various loading conditions indicate that the local end effect zone due to warping and distortion is approximately ten times the typical beam width.

Analysis of Thin-Walled Closed Beams With General Quadrilateral Cross Sections

This paper deals with the one-dimensional static and dynamic analysis of thin-walled closed beams with general quadrilateral cross sections. The coupled deformations of distortion as well as torsion and warping are investigated in this work. A new approach to determine the functions describing section deformations is proposed. In particular, the present distortion function satisfies all the necessary continuity conditions unlike Vlasov's distortion function. Based on these section deformation functions, a one-dimensional theory dealing with the coupled deformations is presented. The actual numerical work is carried out using two-node C0 finite element formulation. The present one-dimensional results for some static and free-vibration problems are compared with the existing and the plate finite element results.

Germanium dioxide whiskers synthesized by laser ablation

We obtained germanium dioxide (GeO2) whiskers in bulk quantity by ablating a germanium target at 820 °C with a pulsed KrF excimer laser in an argon atmosphere. Most of the GeO2 whiskers were smooth and straight with hexagonal or triangular, or quadrilateral cross sections while some of them had a bamboo-shoot-shaped form. Results of scanning electron microscopy, transmission electron microscopy, and x-ray diffraction showed that the whiskers are hexagonal crystalline GeO2.

Sound suppressor exhaust structure

A sound suppressor exhaust structure (10) for a jet engine. The exhaust structure has a nozzle body (12) having a generally cylindrical forward intake opening (14) to accomodate an aft end of a jet engine, and a generally quadrilateral aft exit opening (16). An openable sound suppression chamber is situated aft of the exit opening and is formed by two opposing enclosure structures (18, 20) each having a major surface (22, 24) and each hingedly attached in a clamshell manner to the nozzle body (12). The opening enclosure structures (18, 20) are indefinitely movable between an open and a closed configuration such that, when the enclosure structures (18, 20) are closed, a chamber having a generally quadrilateral cross section is defined and situated aft of the exit opening. Each enclosure structure (18, 20) has a major surface (22, 24) through which are substantially uniformly disposed a plurality of small apertures (38) such that from about 15 % to about 25 % per square foot of each major surface is void and from about 45 to 65 apertures are provided per square foot. The apertures (38) here defined are small and tightly spaced to thereby beneficially result in agressive noise suppression as well as structural light weight.

Optimum design of yokeless permanent magnets

This paper discusses the selection of the design parameters and the optimum geometry of yokeless permanent magnets that generate a uniform field H0 within an arbitrary closed cavity. The optimum design minimizes the volume of magnetic material and it is determined by the geometry of the cavity, the magnitude of intensity H0, and a characteristic point F that controls the configuration of the magnetostatic potential as well as the flux of the magnetic induction. The optimization procedure is applied to a two-dimensional magnet with a quadrilateral cross section.