Investigation of the microstructure and thermo-mechanical properties of functionally graded materials fabricated by the vibrating centrifugal solid particle method

In this research, SiC/Al A413.1 functionally graded materials (FGMs) were fabricated by the vibrating centrifugal solid particle method (VCSPM), and the effects of the SiC particles on the microstructure and thermo-mechanical properties of an A413.1 aluminium alloy were investigated. The benefits of a vibration during centrifugal casting of FGMs are illustrated. After designing and fabricating the centrifugal casting machine, cylindrical FGM specimens were produced using the centrifugal solid particle method (CSPM) and VCSPM. This study used SiC particles with an average particle size from 50 to 62 μm as reinforcements to fabricate A413.1-10 wt% SiC functionally gradient composites at three annular mould speeds (900–1500 and 2100 rpm) and with or without a vibration of the mould. The Brinell hardness was measured; the yield strength (YS), ultimate tensile strength (UTS) and Young’s modulus (E) were determined by tensile testing; the density was determined by the Archimedes method; and the thermal expansion coefficients were measured with a dilatometer. A comparison of the samples produced by the conventional method and VCSPM shows a significant reduction in the porosity and an increase in the distribution gradient of the reinforcing particles for the VCSPM case. It can be concluded that in both processes, the mechanical and thermal properties improved in most cases by moving from the inner radius to the outer radius because of the movement of particles towards the outer radius from the centrifugal force. The results also show that the use of a vibration dramatically increased the rate and speed of migration of gas bubbles towards the inner radius, and the mechanical properties (hardness, YS, UTS and E) improved by moving from the inner to outer radius due to an increase in the percentage of silicon carbide particles. Upon increasing the velocity and using the VCSPM, the slope of these changes becomes steeper than those for the vibration-free mode and at low rotation speeds.

Director Fluctuations in Two-Dimensional Liquid Crystal Disclinations

We present analytical calculations of the energies and eigenfunctions of all normal modes of excitation of charge +1 two-dimensional splay (bend) disclinations confined to an annular region with inner radius R1 and outer radius R2 and with perpendicular (tangential) boundary conditions on the region’s inner and outer perimeters. Defects such as these appear in islands in smectic-C films and can in principle be created in bolaamphiphilic nematic films. Under perpendicular boundary conditions on the two surfaces and when the ratio β=Ks/Kb of the splay to bend 2D Frank constants is less than one, the splay configuration is stable for all values μ=R2/R1. When β>1, the splay configuration is stable only for μ less than a critical value μc(β), becoming unstable to a “spiral” mixed splay-bend configuration for μ>μc. The same behavior occurs in trapped bend defects with tangential boundary conditions but with Ks and Kb interchanged. By calculating free energies, we verify that the transition from a splay or bend configuration to a mixed one is continuous. We discuss the differences between our calculations that yield expressions for experimentally observable excitation energies and other calculations that produce the same critical points and spiral configurations as ours but not the same excitation energies. We also calculate measurable correlation functions and associated decay times of angular fluctuations.

Effect of central and peripheral cone- and rod-specific stimulation on the pupillary light reflex

Purpose To assess the effect of central and peripheral stimulation on the pupillary light reflex. The aim was to detect possible differences between cone- and rod-driven reactions. Methods Relative maximal pupil constriction amplitude (relMCA) and latency to constriction onset (latency) to cone- and rod-specific stimuli of 30 healthy participants (24 ± 5 years (standard deviation)) were measured using chromatic pupil campimetry. Cone- and rod-specific stimuli had different intensities and wavelengths according to the Standards in Pupillography. Five filled circles with radii of 3°, 5°, 10°, 20° and 40° and four rings with a constant outer radius of 40° and inner radii of 3°, 5°, 10° and 20° were used as stimuli. Results For cone-and rod-specific stimuli, relMCA increased with the stimulus area for both, circles and rings. However, increasing the area of a cone-specific ring by minimizing its inner radius with constant outer radius increased relMCA significantly stronger than the same did for a rod-specific ring. For cones and rods, a circle stimulus with a radius of 40° created a lower relMCA than the summation of the relMCAs to the corresponding ring and circle stimuli which combined create a 40° circle-stimulus. Latency was longer for rods than for cones. It decreased with increasing stimulus area for circle stimuli while it stayed nearly constant with increasing ring stimulus area for cone- and rod-specific stimuli. Conclusion The effect of central stimulation on relMCA is more dominant for cone-specific stimuli than for rod-specific stimuli while latency dynamics are similar for both conditions.

Improved prediction method for ground surface thawing settlement caused by the melting of tunnel horizontal frozen wall

With the rapid development of urban subway tunnel, artificial ground freezing technology is becoming more and more mature. With the natural thawing of horizontal frozen wall, thawing settlement will occur on stratum due to the thawing of frozen soil and the consolidation of thawed soil, which will inevitably bring adverse impact on the surrounding environment of subway tunnel. Therefore, the establishment of a reasonable ground surface thawing settlement prediction method will provide a favorable theoretical support for predicting the ground surface deformation in advance and taking active thawing settlement control measures. In the paper, the time functions of ground surface thawing settlement and consolidation settlement of tunnel horizontal frozen wall are established based on the stochastic medium theory during natural thawing period, and the calculation methods of thawing front radius, inner radius of thawing shrinkage region and inner radius of consolidation region are proposed. The results show that the cumulative ground surface thawing settlement is larger than that of Cai et al. after considering the consolidation of the thawed soil, which fully indicates that the ground surface settlement caused by the drainage and consolidation of the thawed soil cannot be ignored. In addition, the thawing displacement rate of frozen soil is greater than the consolidation displacement rate of thawed soil during the natural thawing and the thawed soil will be consolidated at a lower settlement rate for a long time after the natural thawing period.

Spherical micro-hole grid for high-resolution retarding field analyzer

A wide-acceptance-angle spherical grid composed of numerous micro cylindrical holes was developed to be used for the retarding grid of a display-type retarding field analyzer (RFA) and to enhance the energy resolution (E/ΔE). Each cylindrical hole with a diameter of 50 µm and a depth of 80 µm is directed to the spherical center. The inner radius of the spherical grid is 40 mm. The holed area corresponds to an acceptance angle of ±52°. The E/ΔE of an RFA equipped with the developed holed grid was estimated to be 2000 from a measured Au 4f photoemission spectrum. A clear photoelectron hologram was observed in the Mo 4p core-level region of MoS2, indicating that the RFA with the holed grid is effective for photoelectron holography.

Nodal Sets of Steklov Eigenfunctions near the Boundary: Inner Radius Estimates

We show that Steklov eigenfunctions in a bounded Lipschitz domain have wavelength dense nodal sets near the boundary, in contrast to what can happen deep inside the domain. Conversely, in a 2D Lipschitz domain $\Omega $, we prove that any nodal domain of a Steklov eigenfunction contains a half-ball centered at $\partial \Omega $ of radius $c_{\Omega }/{\lambda }$.

Sound absorption based on Micro-perforated panels and Acoustic Black Hole principle

Acoustic black holes (ABHs) have been so far investigated mainly for bending wave ma-nipulation in mechanical structures such as beams or plates. The investigations on ABHs for sound wave manipulation, referred to as Sonic black holes (SBHs) are scarce. Existing SBH structure for sound reduction in air is typically formed by putting a set of rings inside a duct wall with decreasing inner radius according to a power law. As such, the structure is very complex and difficult to be practically realized, which hampers the practical application of SBHs for sound reduction. This study explores the possibilities of achieving SBH effects using other types of structural configurations. In particular, micro-perforated panels are proposed to be introduced into the conventional SBH structure, and the simulation results show that the new formed SBH structure is simpler in configuration in terms of number of rings and more efficient in terms of sound energy trapping and dissipation.

Configuration of a Monopulse Antenna Assembly for Small Diameter Flight Vehicle Applications

In this letter, configuration of a monopulse direction-finding (DF) antenna assembly is presented which can be applied for small diameter flight vehicle applications. The assembly consists of five antennas which consist of four radome mounted antennas and a slot fed cavity antenna. All antennas are located inside of a tangent ogive radome of 1.52 λc inner radius where λc corresponds to the wavelength of the center frequency. To verify the DF performance of the antenna assembly, sum (Σ) and delta (Δ)-patterns are measured and its Δ/Σ monopulse curves are presented.

A study on an incompressible polymeric pressurized vessel subjected to bulk degradation

To study the mechanical behavior of an incompressible polymeric degradable vessel subjected to the neo-Hookean constitutive model, two solution frameworks are introduced. One is combining a recently developed semi-analytical method and the [Formula: see text]-family time approximation (hybrid method). The other is the Standard Galerkin Finite Element Method (SGFEM), which is implemented by providing a script in the FlexPDE commercial software. A deformation-induced evolution law is used to study the dependence of material properties upon time and position in the polymeric vessel during bulk degradation. The convergence of the two proposed methods on degradable vessel responses under the axisymmetric plane-strain conditions is seen. Although the hybrid method, unlike the SGFEM, is implemented as an iteration-based algorithm, it uses highly acceptable central processing unit time because it can directly solve differential equations without converting variables. The FlexPDE method is much easier to extend to more complex case studies because the hybrid method is based on an analytical approach. It is found that less pressure is required to maintain the incompressibility of the material during the degradation. The material response to incompressibility decreases more sharply in the inner radius of the vessel. Initially, the hoop stress decreases in the inner radius but eventually reaches more than its virgin value.

Electron-LO-phonon Intrasubband Scattering Rates in a Hollow Cylinder Under the Influence of a Uniform Axial Applied Magnetic Field

Scattering rates arising from the interactions of electrons with bulk longitudinal optical (LO) phonon modes in a hollow cylinder are calculated as functions of the inner radius and the uniform axial applied magnetic field. Now, the specific nature of electron-phonon interactions mainly depends on the character of the energy spectrum of electrons. As is well known, in cylindrical quantum wires, the application of a parallel magnetic field lifts the double degeneracy of the non-zero azimuthal quantum number states; m≠0; irrespective of all electron's radial quantum number l states. In fact, this Zeeman splitting is such that the m < 0 electron's energy subbands initially decrease with the increase of the parallel applied magnetic field. In a solid cylinder, the lowest-order; {l = 1; m = 0} subband is always the ground state. In a hollow cylinder, however, as the axial applied magnetic field is increased, the electron's energy subbands take turns at becoming the ground state; following the sequence {m=0,-1,-2...-N} of azimuthal quantum numbers. Furthermore, in a hollow cylinder, in general, the electron's energy separations between any two subbands are less than the LO phonon energy except for exceptionally high magnetic fields, and some highest-order quantum number states. In view of this, the discussion of the energy relaxation here is focused mainly on intrasubband scattering of electrons and only within the lowest-order {l = 1; m = 0} electron's energy subband. The intrasubband scattering rates are found to be characterized by shallow minima in their variations with the inner radius, again, for a fixed outer radius. This feature is a consequence of a balance between two seemingly conflicting effects of the electron's confinement by the inner and outer walls of the hollow cylinder. First; increased confinement of the charge carriers generally leads to the enhancement of the rates. Second; the presence of a hole in a hollow cylinder leads to a significant suppression of the scattering rates. The intrasubband scattering rates also show a somewhat parabolic increase in their variations with the applied magnetic field; an increase which is more pronounced in a relatively thick hollow cylinder.