Effective Radius Of Curvature Research Articles

Use of Friction Pendulum System for Seismic Isolation of Museum Artifacts: Mathematical Modeling and Parametric Study

ABSTRACT
 Earthquakes seriously threaten precious artifacts in museums worldwide. Many historical pieces of inestimable importance that are considered the common heritage of humanity have been damaged by earthquakes. Robust measures must be put in place to protect museum artifacts from the perils associated with seismic risks. Seismic isolation devices like spherically shaped bearings are one of the best options to prevent seismic damage of museum artifacts thanks to achieving a long period under low weights. Therefore, the objective of this research is to assess the effectiveness of friction pendulum-type isolators, one of the spherically shaped bearings, in seismic isolation of museum artifacts and to identify the appropriate design parameters. In this study, a non-isolated single-degree-of-freedom model and a 2-degree-of-freedom model isolated with a single friction pendulum bearing inside a building were established for a museum artifact. A parametric study was conducted using the root mean square and the maximum accelerations and displacements of the isolated mass at different values of friction coefficient and effective radius of curvature, as well as the maximum displacement of the friction pendulum system. Afterward, the non-isolated and isolated mass responses were compared in the time domain based on selected parameters obtained from the parametric study. The behavior of the isolator was analyzed, and its effectiveness was evaluated.

Higgs phases at non-zero density from holography

We show how Higgs phases at non-zero density can be described using a simple analytic method for gauge theories possessing a holographic dual. We introduce co-dimension one branes in a bottom-up gravity dual that are sources of form flux, such that the effective curvature radius is changed when the brane is crossed. This mimics the expected flow produced by color branes nucleating in a top-down model.

4H-SiC Trench Gate Lateral MOSFET With Dual Source Trenches for Improved Performance and Reliability

The SiC trench gate lateral MOSFET featuring dual source trenches is proposed in this work. 2D numerical simulations by TCAD are conducted to study the performance and the reliability of the proposed structure and the conventional ones. With the trench gate, the device specific ON-resistance is reduced by more than 50% compared to that of the planar gate device. The device with proposed dual source trenches can also prevent the Pwell punch through problem that occurs in conventional lateral LMOS. As a result, a blocking voltage over 1200V can be achieved with the proposed structure. The proposed devices have two types of configurations. Compared with the configuration of double shallow trenches, the configuration of deep and shallow trenches can mitigate the curvature effect near the P+ source region by increasing the effective curvature radius. As a result, the RESURF doping and epi thickness windows are both expanded by <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.5{\times }$ </tex-math></inline-formula> . Furthermore, as the deep source trenches push the electric field away from the gate trench, the off-state oxide field is effectively reduced to below 3MV/cm. Thus, the long-term reliability is substantially improved. In addition, the deep and shallow source trench configuration provides the enhanced screen effect and hence lowers the gate charge by 50%. Faster switching can be achieved with this structure.

Mechanics of shape-locking-governed R2G adhesion with shape memory polymers

Shape memory polymers (SMPs), with unique properties such as tunable elastic modulus, temporary shape locking and shape recovery upon external stimulation, are emerging as a new class of smart materials with switchable adhesion capabilities. A prominent feature of the adhesion between SMP and a spherical indenter is the so-called R2G adhesion, defined as making contact in the rubbery state to a certain indentation depth followed by detachment in the glassy state. While it has been demonstrated that the R2G adhesion with SMPs can achieve orders of magnitude higher adhesive strength compared to conventional elastic adhesive systems with similar geometrical and adhesion parameters, the fundamental mechanics of R2G adhesion and why it leads to such tremendous adhesion enhancement remain largely mysterious at this point. Here, combined experimental testing, theoretical analysis, and finite element analysis (FEA) based on a thermomechanical constitutive model of SMP are performed to investigate the mechanics of R2G adhesion with a rigid spherical indenter. It is shown that the orders of magnitude enhancement of R2G adhesion over conventional elastic adhesion systems is mostly governed by the shape locking effect during the transition from the rubbery to glassy states. The shape locking effect freezes the deformed configuration of the SMP substrate, resulting in nearly conformal contact between the spherical indenter and the glassy-state SMP substrate, thus greatly increases the effective radius of curvature of the contact surface. Our experimental measurements and FEA simulations demonstrate that the net effect of shape locking leads to a pull-off force of a sphere nearly the same as that of a flat punch on an elastic half-space with the same contact radius. An explicit expression of the pull-off force for R2G adhesion is proposed based on flat-punch adhesion. Our results from combined experimentation, modeling and simulations reveal the fundamental mechanics of R2G adhesion. Such understanding provides guidance for the design of SMP smart adhesives.

Robotic scanning free-space measurement system for electromagnetic performance evaluation of curved radar absorbing structures

Radar absorbing structures are manufactured for stealth missions and total quality inspection applies to evaluate their performances before assembly to stealth weapon systems. This study adopted a six-axis robot arm to move a target specimen in a scanning free-space measurement system for electromagnetic performance evaluation. The six-axis robot arm completely enables the system to maintain the specimen at the focal point of the antenna and solves the issue of curvature effect on the return loss results of the curved specimens, faced in the two- and three-axis scanning free-space measurement systems. The six-axis robotic scanning free-space measurement system uses a RobotStudio to extract the position and orientation of each target point on the specimen to be evaluated and uses a robotic scanning algorithm to transform all the points into a scan path. The system was verified by variable and constant curvature radar absorbing structure specimens with frequency selective surfaces. Return losses ( S 11s) of the nonsymmetrical cambered airfoil specimen and S-shaped double curvature specimen that could not be accurately evaluated with a three-axis stage-based scanning free-space measurement system were measured by the six-axis robotic scanning free-space measurement system. All the specimen results adhere to the theoretical parameters of the specimen. The transition region results of the S-shaped specimen were studied using effective radius of curvature. Finally, the inspected results of the S-shaped specimen were curvature compensated to check the effect of negative and positive curvature on the specimen resonance frequency performance.

Risk‐based seismic design of base‐isolated structures with single surface friction sliders

AbstractChoosing friction pendulum isolators to avoid problems with device displacement capacity or boundary wall collision is a critical part of the seismic design of base isolation systems. This paper developed a probabilistic method to quantify the risk of failure in single friction pendulum bearing (FPB) devices. This was done by calibrating a demand‐intensity model for FPBs from numerical analysis for several device property combinations. These properties encompassed the dynamic friction coefficient and effective radius of curvature—key parameters impacting these FPB devices’ seismic response. Through this demand‐intensity model, a closed‐form and relatively simple approach to quantify the mean annual frequency of exceeding a given device displacement threshold, or risk of failure, was proposed. By applying this simplified method to several case study structures and comparing it with a more extensive assessment involving multiple stripe analysis (MSA) using hazard‐consistent ground motions, the proposed simplified approach could provide very accurate estimates of displacement‐based failure risk in FPB devices under the assumption of no non‐linear behaviour in the superstructure. This proposed approach implies that structural engineers can now quickly assess the actual failure rates of different FPB device combinations used in practice to give a more uniform level of safety or reliability when designing and assessing FPB‐isolated systems. It is also arguably much simpler, direct and accurate than currently available code‐based approaches.

Influence of anisotropic ocean turbulence on effective radius of curvature of partially coherent Hermite–Gaussian beam

Based on the extended Huygens–Fresnel principle and Wigner distribution function (WDF), the influence of anisotropic ocean turbulence on effective radius of curvature (ERC) for partially coherent Hermite–Gaussian (PCHG) beams is studied in detail. Our numerical results show that the beam orders and the anisotropic ocean turbulence factors have a certain influence on ERC of PCHG beams propagating in anisotropic ocean turbulence. Besides, ocean turbulence parameters and beam initial parameters would exert different influence on ERC of PCHG beams propagating in anisotropic ocean turbulence. In addition, Rayleigh range of PCHG beams propagating in anisotropic ocean turbulence decreases with increasing anisotropic ocean turbulence factors. These findings may be used for anisotropic ocean optical communications of PCHG beams.

Qualitative evidence of the flexoelectric effect in a single multi-wall carbon nanotube by nanorobotic manipulation

The flexoelectric effect corresponds to the linear variation of the electric polarization of a material subjected to a strain gradient (i.e., during its mechanical bending). Unlike piezoelectricity, it also exists in non-centrosymmetric materials. Furthermore, due to the gradient term, its magnitude can increase as the size of the system decreases. Thanks to this effect, nanoscale systems could be used to harvest thermal vibration energy to power a microdevice. These could be multi-wall carbon nanotubes since they are known to bend easily in an elastic manner. However, it is very challenging to experimentally measure the flexoelectric behavior of a single multi-wall carbon nanotube due to its small size (less than 50 nm in diameter), to the low level of induced charges, and to the need to vary the imposed stress. To progress in this direction, a six-degree-of-freedom robot with a fiber tip is used inside a dual-beam microscope to pick up few single carbon nanotubes from a tangle and connect them to the fiber tip. After ion-soldering the two tips, each carbon nanotube is dynamically bent several times while monitoring the brightness of the bending area and its effective radius of curvature. This allowed us to demonstrate qualitatively the flexoelectric effect at the level of a single multi-wall carbon nanotube.

Frontal plane roll-over analysis of prosthetic feet

In prosthetic walking mediolateral balance is compromised due to the lack of active ankle control, by moments of force, in the prosthetic limb. Active control is reduced to the hip strategy, and passive mechanical stability depends on the curvature of the prosthetic foot under load. Mediolateral roll-over curvatures of prosthetic feet are largely unknown. In this study we determined the mediolateral roll-over characteristics of various prosthetic feet and foot-shoe combinations. Characteristics were determined by means of an inverted pendulum-like apparatus. The relationship between the centre of pressure (CoP) and the shank angle was measured and converted to roll-over shape and effective radius of curvature. Further, hysteresis (i.e., lagging in CoP displacement due to material compliance or slip) at vertical shank angle was determined from the hysteresis curve. Passive mechanical stability varied widely, though all measured foot-shoe combinations were relatively compliant. Mediolateral motion of the CoP ranged between 4 mm and 40 mm, thereby remaining well within each foot’s physical width. Derived roll-over radii of curvature are also small, with an average of 102 mm. Hysteresis ranges between 20% and 115% of total CoP displacement and becomes more pronounced when adding a shoe. This may be due to slipping of the foot core in its cosmetic cover, or the foot in the shoe. Slip may be disadvantageous for balance control by limiting mediolateral travel of the CoP. It may therefore be clinically relevant to eliminate mediolateral slip in prosthetic foot design.

Propagation properties of partially coherent quasi-rectangular beams in a turbulent atmosphere

A class of random, wide-sense stationary optical beams with uniform correlations, named the partially coherent quasi-rectangular beam, is introduced theoretically. Based on the extended Huygens-Fresnel principle, the analytical expressions for the cross-spectral density (CSD), effective radius of curvature, and beam wander of the beam in the non-Kolmogorov turbulence are derived. It is found that the position of maximum intensity of the partially coherent quasi-rectangular beams shifts farther from the axis at intermediate distance, the shift in the turbulence is depressed compared to that in free space. As the effective radius of curvature decreases from infinity to a constant with the increase of the coherence length, it always takes a higher value than that in free-space propagation when the other parameters are fixed. In addition, the beam wander can be reduced by picking a relative small initial beam width, short coherence length, or long wavelength. These results are of importance for optical systems operating through long-range turbulent channels in which a beam must have a range-dependent tilt, e.g. on travelling around an obstacle on the axis.

Characteristics of partial discharge and AC electrical tree in XLPE and MgO/XLPE nanocomposites

In order to investigate the effect of nano-doping on partial discharge (PD) and electrical tree growth in cross-linked polyethylene (XLPE), samples of 0.5 wt% magnesium oxide MgO/XLPE were prepared and an AC experiment was carried out. A color-coded diagram for PD signal was developed to describe the PD activity during the whole process of treeing. The results show that the PD intensity in positive half cycle of voltage (PHC) is larger than that in negative half cycle of voltage (NHC), and the PD magnitude in MgO/XLPE is lower than that in XLPE. Moreover, the tree length and morphology in MgO/XLPE are similar to those in XLPE. Furthermore, a finite element simulation based on the bipolar charge transport model was applied to investigate the effect of space charge on PD under AC voltage. Simulation results suggest that the characteristics of PD and tree growth may be associated with the accumulated charge around the needle tip. The distribution of negative charges in NHC would be wider than that of positive charges in PHC, which would weaken the electric field in NHC and lead to the less PD in NHC. Moreover, the range of charge shield in MgO/XLPE may be larger and is equivalent to increasing the effective radius of curvature of needle tip, which would lead to smaller electric field and lower PD magnitude in MgO/XLPE. However, the addition of nano-MgO reduces the crystallinity of material based on the differential scanning calorimetry (DSC) result. Hence, although the PD magnitude in MgO/XLPE is lower, the MgO/XLPE researched in this paper does not show significant resistance to AC tree growth.

Simple Universal Kelvin Equation Valid in Critical Point Vicinity, External-Internal State Correction, and their Application in Understanding of Oxygen Capillary Evaporation and Condensation in Mesoporous Silica MCM-41

A new simple universal form of the Kelvin equation, which can be used near the gas-liquid phase transition critical point, and the correction of the pressure and density for gas phase fluid outside the porous medium are taken into account for the oxygen meniscus effective curvature radius calculation at the phase equilibrium in mesoporous silica MCM-41, on the basis of the capillary evaporation and condensation experimental data.

Simple universal Kelvin equation valid in critical point vicinity, external-internal state correction, and their application in understanding of normal pentane capillary evaporation and condensation in mesoporous silica MCM-41

A new simple universal form of the Kelvin equation, which can be used near the gas-liquid phase transition critical point, and the correction of the pressure and density for gas phase fluid outside the porous medium are used for the normal pentane meniscus effective curvature radius calculation at the phase equilibrium in mesoporous silica MCM-41, on the basis of the capillary evaporation and condensation experimental data. Normal pentane is suggested as a promising fluid for characterizing the porosity that can be used even at room temperature.

Propagation properties of partially coherent crescent-like beams under maritime environment.

Based on the extended Huygens-Fresnel principle, the analytical expressions for the intensity distribution, effective radius of curvature, beam wander, Strehl ratio, and the power in the bucket of a partially coherent crescent-like (PCCL) beam under the maritime environment are derived. The propagation properties of the PCCL beams through the maritime environment are investigated in detail. Numerical results indicate that, for the maritime environment, the propagation properties and beam quality of a PCCL beam are closely related to its initial beam parameters and the turbulence parameters. Comparative analyses are performed for the new models under the marine turbulence and the terrestrial turbulence. It turns out that the marine turbulence influences the beam width and the beam wander more than the terrestrial turbulence does. Also, the beam quality of the PCCL beams in marine turbulence can be improved by choosing a large beam width, high coherence length, or short wavelength. The PCCL beams have a range-dependent tilt, which can be useful for some practical applications, such as traveling around an obstacle. The results are of significance for over-the-sea communication systems.

Selection of CVD Diamond Crystals for X-ray Monochromator Applications Using X-ray Diffraction Imaging

A set of 20 single crystal diamond plates synthesized using chemical vapor deposition (CVD) was studied using X-ray diffraction imaging to determine their applicability as side-bounce (single-reflection) Laue monochromators for synchrotron radiation. The crystal plates were of optical grade (as provided by the supplier) with (001) nominal surface orientation. High dislocation density was found for all samples. Distortions in the crystal lattice were quantified for low-index Laue reflections of interests using rocking curve topography. Maps of effective radius of curvature in the scattering plane were calculated using spline interpolation of the rocking curve peak position across the studied plates. For several selected plates, nearly flat regions with large effective radius of curvature were found ( R 0 ≳ 30 - 70 m, some regions as large as 1 × 4 mm 2 ). The average width of the rocking curve for these regions was found to be about 150 μ rad (r.m.s.). These observations suggest that the selected CVD diamond plates could be used as intermediate-bandwidth monochromators refocusing the radiation source to a specific location downstream with close to 1:1 distance ratio.

Roll-over analysis of a new design carbon fiber prosthetic foot

Many researchers adopted the quasi static roll over testing in the calculation of a prototype prosthetic feet roll over shape. In this work, the prototype of a new carbon fiber prosthetic foot was tested for roll over characteristic. An inverted pendulum like apparatus has been built to achieve the required test, and the prosthesis roll over shape calculated. Roll over characteristics were estimated as: effective radius of curvature about 202mm, center of curvature of 26.55mm, and the forward travel against shank angle was plotted.

Second-order statistical properties of a J0-correlated Schell-model beam in a turbulent atmosphere

We derive the analytical expressions for the second-order moments of the Wigner distribution function of a J0-correlated Schell-model (JCSM) beam propagating in a turbulent atmosphere. With the help of the second-order moments, we explore the second-order statistical properties (i.e., the M2-factor, the effective radius of curvature and the Rayleigh range) of a JCSM beam propagating in a turbulent atmosphere for different turbulence parameters and beam parameters. It is found that the statistical properties of the JCSM beam are closely related to the initial beam parameters and turbulence parameters, and we can mitigate the negative effect of the turbulence by choosing suitable initial beam parameters. Our results will be useful for long distance free-space optical communications.

Simple Universal Kelvin Equation Valid in Critical Point Vicinity, External-Internal State Correction, and their Application in Argon Capillary Condensation in Mesoporous Silica MCM-41

A new simple universal form of the Kelvin equation, which can be used near the gas-liquid phase transition critical point, and the correction of the pressure and density for gas phase fluid outside the porous medium are taken into account for the argon meniscus effective curvature radius calculation at the phase equilibrium in mesoporous silica MCM-41 on the basis of the capillary condensation experimental data.

Simple Universal Kelvin Equation Valid in the Critical Point Vicinity, External-Internal State Correction, and their Application to Nitrogen Capillary Condensation in Mesoporous Silica SBA-15

A new simple universal form of the Kelvin equation, which can be used near the gas-liquid critical point and the correction of the pressure for vapor outside the porous medium are used for the N2 meniscus effective curvature radius calculation at the phase equilibrium in mesoporous silica SBA-15, on the basis of the capillary condensation experimental data.

Effective Radius of Curvature and Rayleigh Length of Partially-Coherent Array Beams Passing Through Oceanic Turbulence

Based on the spatial power spectrum of the refractive index of ocean water, we derive analytical expressions for the effective radius of curvature and Rayleigh length of partially-coherent Hermite–Gaussian linear array (PCHGA) beams propagating through oceanic turbulence. In addition, we discuss theoretically and analyze numerically the influence of oceanic turbulence and array parameters. The effective radius of curvature and Rayleigh length of PCHGA beams increase with the relative strength of temperature and salinity fluctuations, the rate of dissipation of turbulent kinetic energy per unit mass of fluid, the array beam number, beam order, and relative separation distance, but decrease with the increase in the rate of dissipation of the mean-square temperature. The analysis provided here will help to understand the propagation of array beams through ocean turbulence.