Hemispherical End Research Articles

Depolarization of light scattered by gold nanospheres and nanorods

According to the theory of light scattering by small randomly oriented particles, the intensity ratio I VH/I VV cannot exceed 1/3 (van de Hulst, 1957; Kerker, 1969; the subscripts V and H denote the vertical and horizontal polarizations with respect to the scattering plane). In this paper, it is shown that this statement is erroneous for metal particles with plasmon resonance. For aqueous dispersions of randomly oriented gold spheroids and cylinders with hemispherical ends, the spectral dependence of the depolarization is calculated theoretically in the Rayleigh approximation and using the rigorous T-matrix method. It is shown that the value of I VH/I VV in the scattering region of plasmon resonance (550–650 nm) becomes larger than 1/3 when the axial ratio of particles exceeds 2–2.5. To check this theory experimentally, gold nanospheres with particle diameters of 15, 27, and 45 nm (determined from data on dynamic light scattering) and nanorods with a thickness of about 15–20 nm and an axial ratio of 2.5–3.2 (found from the positions of the peaks of longitudinal resonance of absorption and scattering at an angle of 90°) were synthesized. For two samples of nanorods, the experimentally determined values of the depolarization of laser radiation (632.8 nm) scattered at an angle of 90° yielded I VH/I VV = 0.3 and 0.36, which is in good agreement with the theory.

物体情報および外界センサを用いない重力下の安定ピンチング法の検証

This paper shows that secure pinching under the gravity effect can be realized by a pair of robot fingers with hemispherical ends using a coordinated sensory-feedback signal constructed without any information of an object (e.g., center of mass, mass, length, object angle) . The proposed control signals which can be easily calculated from only encoder data of the finger angles and the finger physical parameters are adaptable to rigid objects with parallel or non-parallel flat surfaces. Numerical simulations and experimental results show that the closed-loop finger-object system finally falls into some stable state satisfying the force/torque balance, that is, into a force/torque equilibrium point. In other words, the results show that stable “blind grasping” under the situation of closing eyes and neither using any tactile sensor nor force-sensing can be actualized even by a pair of robot fingers like human pinching an object by means of the thumb and index finger, provided that preshaping of finger postures is fulfilled adequately.

Computing the flow past a cylinder with hemispherical ends

A novel application of a spectral element method with a Fourier expansion in the third dimension is used to compute the flow past a cylinder with hemispherical ends. This cylinder is useful as it is a sphere at the small length ratio limit, while approaching a straight circular cylinder as the length ratio is increased. Measurements of the Strouhal frequency and mean drag are presented, and results of a grid independence study show that 128 Fourier planes were required to resolve the flow to an accuracy better than 1%. With 64 planes, forces were predicted accurate to 2%, but Strouhal frequencies were over predicted by approximately 8%. The measured Strouhal frequencies provide useful benchmark data for future low Reynolds number studies of the flow past short cylinders.

A Generalized Wagner Method for Three-Dimensional Slamming

Impact between the water and ship, that is, slamming, can cause important global and local effects. A numerical method has been applied to predict water entry loads on three-dimensional bodies. The problem is solved as an initial value problem using the boundary element method. The Green second identity is used to represent the velocity potential as a distribution of Rankine sources and dipoles over the body surface and free surface. The problem is stepped up in time using the information from the boundary conditions. The kinematic free-surface condition is used to determine the intersection between the body surface and free surface at each time step. The exact body boundary condition is used, whereas the dynamic free-surface condition, φ = 0, is approximated on to a horizontal line and not on the exact free-surface profile. The approach presented by Zhao et al (1996) for two-dimensional water entry problems was extended to arbitrary three-dimensional bodies in this presented work. An idealized shape, which consists of cylindrical mid-body and hemispherical ends, was studied. The wetted body surface is calculated with great detail and is considered to be more important than the free-surface elevation away from the body. Drop tests have been carried out to verify and validate the numerical simulation. The effect of the angle between the free surface and the body surface has also been studied. The agreement between theory and experiments is good, and the effect of three-dimensionality is documented. The presented computational method is found to be robust for engineering use and computationally less demanding. The experimental results for vertical force have a strong oscillatory nature, and this has been analyzed using a simplified hydroelastic model. The hydroelastic model gives reasonable representation of the dynamic oscillations found in the vertical force. Reasons for the observed deviations between the numerical and the experimental results are documented. Recommendations for conducting drop tests with minimal dynamic effects are also presented.

Dynamic response of an elliptic plate to impact loading: Theory and experiment

The paper presents an analytical approach to investigating vibrations of an elliptic plate upon impact with an indenter having a hemispherical end. The approach is based on expanding the sought for functions to trigonometric series. The dynamic behaviour of the plate is described in terms of the Timoshenko-type theory that accounts for transverse shear strains and rotary inertia of the normal. Cases of impact in the plate focus and centre have been investigated. Theoretical results are in good agreement with experimental data obtained by using the dynamic wide-range strain measurement technique.

Measurement and modeling of residual stress in a welded Haynes ® 25 cylinder

An experimental and simulation study of residual stresses was made in the vicinity of a gas tungsten arc weld, used to join a hemispherical end cap to a cylinder. The capped cylinder is used in a satellite application and was fabricated from a Co-based Haynes ® 25 alloy. The cylinder was 34.7 mm in outer diameter and 3.3 mm in thickness. The experimental measurements were made by neutron diffraction and the simulation used the implicit Marc finite element code. The experimental resolution was limited to approximately 3 mm parallel to the axis of the cylinder (the weld was 6 mm in the same direction) and comparison over the same volume of the finite element prediction showed general agreement. Subject to the limited spatial resolution, the largest experimentally measured tensile residual stress was 180 MPa, located at the middle of the weld. However, the predictions suggest that there are regions in the weld where average tensile residual stresses as much as 400 MPa exist. One qualitative disparity between the model and the experiments was that the measurement included a larger degree of asymmetry on either side of the weld than predicted by the model.

Stress intensity factors of semi-elliptical surface cracks in pressure vessels by global-local finite element methodology

In the present study the problem of calculation of the stress intensity factors (SIF) of semi-elliptical cracks located in the stress concentration areas of a pressure vessel is numerically solved by advanced global-local finite element (FE) analysis. The common characteristic of the cases solved is that the stress field at the crack area varies along the axial, the circumferential, as well as, the through-the-thickness directions. SIF solutions for such problems are not available, neither analytically, nor numerically, as the currently existing solutions in the literature (numerical results, Newman–Raju empirical equations, weight function solutions, etc.) are only valid for uniform stress distribution along the axial and circumferential directions of the pressure vessel and allow variation only through-the-thickness. The crack locations considered are the intersection of the cylinder to a nozzle and the connection of the cylinder with its hemi-spherical ends. The stress intensity factors are presented in a suitable table format for various geometrical configurations of both the pressure vessel and the semi-elliptical crack, thus providing a useful tool for the fracture mechanics design of cracked pressure vessels. The modeling details of the sub-structuring methodology, employed in the analysis, are extensively discussed and the numerical approach is proven to be very efficient for the SIF calculation of pressure vessel semi-elliptical cracks.

The effect of the size, shape, and structure of metal nanoparticles on the dependence of their optical properties on the refractive index of a disperse medium

The effect of the size, shape, and structure of gold and silver nanoparticles on the dependence of their extinction and integral scattering spectra on the dielectric environment has been investigated. Calculations were performed using the Mie theory for spheres and nanoshells and the T-matrix method for chaotically oriented bispheres, spheroids, and s cylinders with hemispherical ends. The sensitivity of plasmon resonances to variations in the refractive index of the environment in the range 1.3–1.7 for particles of different equivolume size, as well as to variations in the thickness of the metal layer of nanoshells, was studied. For nanoparticles with an equivolume diameter of 15 nm, the maximal shifts of plasmon resonances due to variation in the refractive index of the environment are observed for bispheres and the shifts decrease in the series nanoshells, s cylinders or spheroids, and spheres. For particles 60 nm in diameter, the largest shifts of plasmon resonances occur for nanoshells and the shifts decrease in the series bispheres, s cylinders or spheroids, and spheres. All other conditions being the same, silver nanoparticles are more sensitive to the resonance tuning due to a change in the dielectric environment.

Identifying microstructural deformation mechanisms in snow using discrete-element modeling

AbstractA dynamic model of dry snow deformation is developed using a discrete-element technique to identify microstructural deformation mechanisms and simulate creep densification processes. The model employs grain-scale force models, explicit geometric representations of individual ice grains, and snow microstructure using assemblies of grains. Ice grains are randomly oriented cylinders of random length with hemispherical ends. Particle contacts are detected using a novel and efficient method based on the dilation operation in mathematical morphology. Grain-scale ice interaction algorithms, based on observed snow and ice microscale behavior, are developed and implemented in the model. These processes include grain contact sintering, grain boundary sliding and rotation at contacts, and grain contact deformation in tension, compression, shear, torsion and bending. Grain-scale contact force algorithms are temperature- and rate-dependent, with both elastic and viscous components. Grain bonds rupture when elastic stresses exceed ice tensile or shear strengths, after which intergranular friction and particle rearrangement control deformation until the snow compacts to its critical density. Simulations of creep settlement using 1000-grain model snow samples indicate the bulk viscosity of snow is controlled by the grain contact viscosity and area, grain packing and the increased number of frozen bonds that form during settlement. A linear relationship between contact viscosity and bulk snow viscosity at any specified density indicates that the linear model parameters can be accurately scaled, allowing simulations to be conducted for a broad range of dynamic and viscous creep deformation problems.

A new spectral resonance of metallic nanorods

The extinction, integrated scattering, and absorption spectra of gold and silver nanorods with random and regular orientation are studied. The calculations are performed for spheroids, circular cylinders, circular cylinders with hemispherical ends (T-matrix method), and rectangular prisms (discrete dipole approximation). A new quadrupole resonance is discovered that arises between the usual plasmon dipole resonances excited by a field longitudinal or transverse with respect to the symmetry axis. The new resonance can be excited only by a TM incident wave and is the greatest for orientation of the symmetry axis of the particle at an angle of 54° with respect to the light beam.

Design of Horizontal Vessels Operated as CSTR – Basic Mixing Tasks, RTD, Productivity

AbstractAgitator performance in standard vertical vessels with cylindrical shape, dished bottom and zero to four baffles has been the topic of numerous publications. In certain industries, however, horizontal cylindrical vessels with hemispherical ends, divided internally into multiple compartments, are preferred for continuous processes operating at high pressures. Use of standard correlations derived from vertical vessels may lead to incorrect performance predictions for these horizontal vessels, and hence unsatisfactory process results. A number of laboratory trials were undertaken to identify differences in behavior and potential means to improve design for horizontal vessels. Differences with respect to solids suspension, mixing time and residence time distribution were studied. CFD simulations were undertaken and validated against the experimental results.

Pseudolaminar Boundary Layer on a Blunt Body Subjected to a Heterogeneous Flow

The distributions of the velocities of air and solid particles in a pseudolaminar boundary layer developing on the surface of a cylinder with a hemispherical end face are experimentally investigated. The experiments reveal a significant rise of fluctuations of the particle velocity in the wall region of the boundary layer. Data are obtained on the decrease in the particle concentration in the vicinity of the model wall compared to its value in the external flow.

Stability on a manifold: concurrent control for secure grasp and manipulation of a rigid object by dual robot fingers

It is well known that three frictionless fingers suffice to immobilize any 2D object with triangular shape but four fingers are necessary for a parallelepiped. However, it has been recently shown that only two fingers are enough to realize secure grasp of a rigid object with parallel flat surfaces in a dynamic sense if finger ends have a hemispherical shape with appropriate radius and thereby roIlings are induced between finger ends and object surfaces. This paper focuses on the two problems: 1) realization of secure grasp of rigid objects with non-parallel flat surfaces (including triangular objects) by dual multi-degrees-of-freedom rigid fingers with hemispherical ends and 2) concurrent realization of secure grasp and orientation control of polygonal objects under the effect of gravity. It is shown that stable grasp is realized by a sensory feedback constructed on the basis of measurements of finger joint angles and angles of the object surfaces relative to finger links without knowing object kinematics and mass center. Further, it is shown that there exists an additional sensory feedback that can regulate orientation angle of the object simultaneously. Copyright©2003 IFAC

Dynamic force/torque balance of 2D polygonal objects by a pair of rolling contacts and sensory‐motor coordination

AbstractIt is well known that three frictionless fingers suffice to immobilize any 2D object with triangular shape but four fingers are necessary for a parallelepiped. However, it has been recently shown that only two fingers are enough to realize secure grasp of a rigid object with parallel flat surfaces in a dynamic sense if finger ends have a hemispherical shape with appropriate radius and thereby rollings are induced between finger ends and object surfaces. This paper focuses on the two problems: (1) dynamic force/torque balance of 2D polygonal objects under the effect of gravity force by means of a pair of rolling contacts and (2) concurrent realization of dynamically secure grasp and orientation control of 2D polygonal objects by using a pair of multi‐fingered hands with hemispherical ends and sensory feedback signals without knowing object kinematics and mass center. It is shown that the force/torque balance can be attained by controlling both the contact positions and inducing adequate forces in both normal and tangential directions at each of contact points indirectly through finger joints without knowing object mass center and other kinematic parameters. © 2003 Wiley Periodicals, Inc.

A stability theory of a manifold: concurrent realization of grasp and orientation control of an object by a pair of robot fingers

This paper is concerned with a stability theory of motion governed by Lagrange's equation for a pair of multi-degrees of freedom robot fingers with hemi-spherical finger ends grasping a rigid object under rolling contact constraints. When a pair of dual two d.o.f. fingers is used and motion of the overall fingers-object system is confined to a plane, it is shown that the total degree of freedom of the fingers-object system is redundant for realization of stable grasping though there arise four algebraic constraints. To resolve the redundancy problem without introducing any other extra and artificial performance index, a concept of stability of motion starting from a higher dimensional manifold to a lower-dimensional manifold, expressing a set of states of stable grasp with prescribed contact force, is introduced and thereby it is proved in a rigorous way that stable grasp in a dynamic sense is realized by a sensory feedback constructed by means of measurement data of finger joint angles and the rotational angle of the object. Further, it is shown that there exists an additional sensory feedback that realizes not only stable grasp but also orientation control of the object concurrently. Results of computer simulation based on Baumgarte's method are presented, which show the effectiveness of the proposed concept and analysis.

The Distribution of Phase Velocities of Heterogeneous Flow in the Neighborhood of the Stagnation Point of a Blunt Body

The paper gives the results of experimental investigation of the velocities of both phases of heterogeneous flow in the neighborhood of the stagnation point of a blunt body with a hemispherical end face. The distribution of the velocities of “pure” air, of incident particles, and of particles reflected from the body is measured. The resultant data are necessary for constructing mathematical models of flows of gas with solid particles which intensively interact both with the model surface and with one another.

Opening of carbon nanotubes by addition of oxygen

The opening of carbon nanotubes by the addition of oxygen to form C n O 6 has been modelled using the AM1 Hamiltonian and the program mopac 6.0. Three series of nanotubes based on C 60 were considered. The first series was based on pulling two hemispherical halves of C 60 apart along a fivefold axis and inserting additional carbon atoms between the hemispheres to form C 70, C 80, C 90 and C 100. The second series was obtained similarly by pulling C 60 apart along a threefold axis to form the D 3 h and D 3 isomers of C 78 and the D 3 d and D 3 isomers of C 96. The third series was based on the extension of C 60 along a twofold axis to form C 76 and C 92. There is a wide diversity in the bonding patterns in these nanotubes. In general, the hemispherical ends resemble C 60 with single bonds on pent–hex edges and double bonds on hex–hex edges, with the exception of C 80 in which there is significant double bond character on the pent–hex edges. The six-membered rings on the hemispherical ends have the normal Kekulé pattern of single and double bonds. In general, the distinction between single and double bonds is continued into the tube part of the structure but again there are some exceptions. For example, in C 70, D 3-C 78 and C 76 there are some six-membered rings with delocalised bonding. In C 90, D 3 h -C 78 and D 3 d -C 96 there are six-membered rings composed of six single bonds with six double bonds radiating out from the ring and these rings show significantly different chemical properties. Addition of oxygen occurs as near as possible to the end of the nanotube with the opening of a large hole leading into the interior of the structure. In the most favourable structures, a pair of oxygen atoms adds onto a hex–hex edge replacing the CC double bond by two CO ketone groups and the coalescence of two six-membered rings. Multiple additions may be of the same type leading to tris(diketone) structures with the coalescence of four six-membered rings into two different types of 18-membered rings. Alternatively, additional oxygen atoms may add onto pent–hex edges replacing the CC single bond with a COC ether linkage forming the mixed ether/ketones or the mixed ether/lactones which are generally the most stable types of structure.

Dynamic Stable Pinching by a Pair of Robot Fingers

This paper is concerned with a stability problem of pinching motion by a pair of robot fingers with hemispherical ends maintaining a grasp of a rigid object with two parallel flat surfaces and at the same time regulating its orientation. It is then shown that there exists a sensory feedback from measurement of finger joint angles and the rotational angle of the object to control inputs to joint actuators and this feedback connection from sensing to action realizes simultaneous grasp and orientation control of the object, provided that motion of the fingers-object system is confined to a plane. To discuss the stability of grasping together with orientation control in a rigorous sense, a new concept called “stability on a manifold” is intorduced and the convergence of a solution trajectory to a lower dimensional manifold subject to a prescribed grasping force together with a prescribed orientation of the object is proved.

Gaussian curvature and the equilibrium among bilayer cylinders, spheres, and discs.

In mixtures of cetyltrimethylammonium bromide (CTAB) and sodium perfluorooctanoate (FC(7)) in aqueous solution, novel bilayer cylinders with hemispherical end caps and open, flat discs coexist with spherical unilamellar vesicles, apparently at equilibrium. Such equilibrium among bilayer cylinders, spheres, and discs is only possible for systems with a spontaneous curvature, R(o), and a positive Gaussian curvature modulus, kappa. We have measured the size distributions of the spherical vesicles, cylinders, and discs by using cryo-electron microscopy; a simple analysis of this length distribution allows us to independently determine that the mean curvature modulus, kappa approximately 5 +/- 1 k(B)T and kappa approximately 2 +/- 1 k(B)T. This is one of the few situations in which R(o), kappa, and kappa can be determined from the same experiment. From a similar analysis of the disk size distribution, we find that the edges of the discs are likely stabilized by excess CTAB. The fraction of discs, spherical vesicles, and cylinders depends on the CTABFC(7) mole ratio: increasing CTAB favors discs, while decreasing CTAB favors cylinders. This control over aggregate shape with surfactant concentration may be useful for the design of templates for polymerization, mesoporous silicates, etc.

Electrophoretic Motion of a Circular Cylindrical Particle in a Circular Cylindrical Microchannel

This paper investigates the electrophoretic motion of a circular cylindrical particle with hemispherical ends in a circular cylindrical microchannel filled with an aqueous electrolyte solution. The influences of three parameters on the electrophoretic motion of the particle are considered: the ratio of the particle radius to the channel radius, a/b; the ratio of the axial length of the particle to its radius, L/a; and the ratio of the zeta potential of the channel to that of the particle, γ = ζw/ζp. It is assumed that the electrical double layers are thin, that is, κa → ∞. In the analysis, the liquid phase is divided into the inner region, which consists of the electrical double layers, and the outer region, which consists of the remainder of the liquid. A theoretical model governing the inner region and the outer region has been constructed, and a force balance on the particle surface is used to determine the particle velocity. The finite element method is employed to solve the resulting set of equations. It is found that the particle velocity in a microchannel decreases as a/b increases or as L/a increases. The particle velocity is also found to decrease linearly as γ increases. On the basis of these results, an analysis of the electrophoretic separation of particles in a microchannel is presented. It is found that circular cylindrical particles of the same zeta potential, in small circular cylindrical microchannels filled with an aqueous electrolyte solution, can be separated by size.