Spherical Zone Research Articles

The Indentation Behavior of Closed-Cell Al Foam under the Flat-End Cylindrical Indenter

The indentation response of the closed-cell Al foam under the flat-end cylindrical indenter is examined by use the finite element method. The MSC/Marc finite element package is used to model the indentation response of the foam panels, and the Al foam was defined in MSC/Marc as the homogeneous, elasto-plastic material. The simulation result reveals that the deformation was found to be almost totally restricted to a spherical cap-shape compacted zone under the indenter, and the shape of the deformation zone is similar to the observed phenomenon from the indentation test.

Spherical interpolation using the partition of unity method: An efficient and flexible algorithm

An efficient and flexible algorithm for the spherical interpolation of large scattered data sets is proposed. It is based on a partition of unity method on the sphere and uses spherical radial basis functions as local approximants. This technique exploits a suitable partition of the sphere into a number of spherical zones, the construction of a certain number of cells such that the sphere is contained in the union of the cells, with some mild overlap among the cells, and finally the employment of an optimized spherical zone searching procedure. Some numerical experiments show the good accuracy of the spherical partition of unity method and the high efficiency of the algorithm.

Yield of singlet oxygen from optically pumped CCl4 solution of fullerenes

Boiling occurs in a solution of oxygen and fullerenes in CCl4 upon optical pumping of C60 upon the fast appearance of incandescent fullerenes in cold solvent. Upon single-photon absorption, a spherical zone of the critical state of CCl4 is formed within 5 ns (with a diameter of 22–25 nm, P cr ∼ 45 atm, and T cr ∼ 556 K). This spherical zone (gas-bubble nucleus) expands to a diameter of ∼100–400 nm for 2–5 ns. If the external pressure (natural or artificial) is rapidly released, the bubble accelerates and emerges into a vacuum chamber within 0.7–25 μs (the length of the passage is 0.1–5 cm depending on the construction of the singlet oxygen generator). We note that singlet oxygen appears 50 ns after the absorption of a photon by fullerene (i.e., inside of the almost formed gas bubble that only begins to emerge from the liquid to a low-pressure gas region).

Dual‐slot antennas for microwave tissue heating: Parametric design analysis and experimental validation

Design and validate an efficient dual-slot coaxial microwave ablation antenna that produces an approximately spherical heating pattern to match the shape of most abdominal and pulmonary tumor targets. A dual-slot antenna geometry was utilized for this study. Permutations of the antenna geometry using proximal and distal slot widths from 1 to 10 mm separated by 1-20 mm were analyzed using finite-element electromagnetic simulations. From this series, the most optimal antenna geometry was selected using a two-term sigmoidal objective function to minimize antenna reflection coefficient and maximize the diameter-to-length aspect ratio of heat generation. Sensitivities to variations in tissue properties and insertion depth were also evaluated in numerical models. The most optimal dual-slot geometry of the parametric analysis was then fabricated from semirigid coaxial cable. Antenna reflection coefficients at various insertion depths were recorded in ex vivo bovine livers and compared to numerical results. Ablation zones were then created by applying 50 W for 2-10 min in simulations and ex vivo livers. Mean zone diameter, length, aspect ratio, and reflection coefficients before and after heating were then compared to a conventional monopole antenna using ANOVA with post-hoc t-tests. Statistical significance was indicated for P <0.05. Antenna performance was highly sensitive to dual-slot geometry. The best-performing designs utilized a proximal slot width of 1 mm, distal slot width of 4 mm +/- 1 mm and separation of 8 mm +/- 1 mm. These designs were characterized by an active choking mechanism that focused heating to the distal tip of the antenna. A dual-band resonance was observed in the most optimal design, with a minimum reflection coefficient of -20.9 dB at 2.45 and 1.25 GHz. Total operating bandwidth was greater than 1 GHz, but the desired heating pattern was achieved only near 2.45 GHz. As a result, antenna performance was robust to changes in insertion depth and variations in relative permittivity of the surrounding tissue medium. In both simulations and ex vivo liver, the dual-slot antenna created ablations greater in diameter than a coaxial monopole (35 mm +/- 2 mm versus 31 mm +/- 2 mm; P<0.05), while also shorter in length (49 mm +/- 2 mm versus 60 mm +/- 6 mm; P < 0.001) after 10 min. Similar results were obtained after 2 and 5 min as well. Dual-slot antennas can produce more spherical ablation zones while retaining low reflection coefficients. These benefits are obtained without adding to the antenna diameter. Further evaluation for clinical microwave ablation appears warranted.

Guest Editorial Foreword to the Special Issue of the XII Symposium on Virtual and Augmented Reality

The special issue of the JIS (SBC Journal on 3D Inter- active Systems) acknowledging the best papers of the XII Symposium on Virtual and Augmented Reality (SVR 2010) was an important opportunity to present excellent papers in the Virtual and Augmented Reality field. The SVR is for more than 12 years the most important event on Virtual and Augmented Reality in Brazil, which is being conduct by academic professionals members of the Brazilian Computer Society (SBC) that is supporting the conference for so many years. Since this is the first special issue of JIS, we had selected papers to be included in the journal that fits the expectations of the readers. These papers were selected among the 10 best papers presented at the SVR 2010, and they come from different sub-areas of the Virtual and Augmented Reality. The development introduced in the papers present important new proposals and algorithms that might be used by several readers of the journal. The paper Exploring the Design of Transitional Hybrid User Interfaces authored by Daniela Trevisan, Felipe Carvalho, Alberto Raposo, Carla Freitas and Luciana Nedel, is about a discussion on how hybrid user interfaces should be managed in order to improve the feeling of immersion of the user in a virtual reality system. The second paper Expression Cloning Based on Anthropo- metric Proportions and Deformations by Motion of Spherical Influence Zones authored by Roberto C. Vieira, Creto Augusto Vidal, and Joaquim B. Cavalcante-Neto presented methods of mapping human facial expressions to virtual characters. This works was based on anthropometric proportions and geometric manipulations by moving influence zones of model with similar characteristics. The third paper Extending Brazilian DTV Middleware to Incorporate 3D Technologies authored by Daniel F. L. Souza, Liliane S. Machado, Tatiana A. Tavares explains how properly support for 3D content can be integrated on the new Brazilian Digital Television. The paper presents strategies and examples to prove their proposal. We would like to thank all the authors of this process that had to extend and adapted their papers as requested by both the submission and the reviewing process.

Expression Cloning Based on Anthropometric Proportions and Deformations by Motion of Spherical Influence Zones

Virtual tridimensional creatures are active actors in many types of applications nowadays, such as virtual reality, games and computer animation. The virtual actors encountered in those applications are very diverse, but usually have humanlike behavior and facial expressions. This paper deals with the mapping of facial expressions between virtual characters, based on anthropometric proportions and geometric manipulations by moving influence zones. Facial proportions of a base model is used to transfer expressions to any other model with similar global characteristics (if the base model is a human, for instance, the other models need to have two eyes, one nose and one mouth). With this solution, it is possible to insert new virtual characters in real-time applications without having to go through the tedious process of customizing the characters’ emotions.

Internal structure of the electrodeposited nanocrystalline Al–Mg alloy dendrites

Porous nanocrystalline supersaturated face centered cubic (fcc)-Al(Mg) dendrites with globular morphology were produced via electrodeposition. The cross-section of the globules revealed compact–disperse–compact structure along the growth direction. Initially compact globules formed due to high potential (or current density) which decreased eventually resulting in disperse-entity growth. Overlapping spherical diffusion zone formation over the disperse-entities was attributed as a reason for the compact growth at later stages. The internal structure of the globules was explained by the global potential (E)–time curve and the estimated local current densities ahead of deposit front. A growth mechanism for globular morphology was proposed using the results presented.

Effect of Nb Addition on Cu Precipitation in Ferritic Stainless Steel

Formations of Cu-rich precipitate in 18%Cr-1.5%Cu stainless steels without and with 0.5%Nb have been examined mainly using transmission electron microscopy. The specimens solution-treated at 1250°C were isothermally transformed at various temperatures between 500 and 850°C. Fine spherical Cu-rich solute zones were nucleated in the steels in the beginning of aging. These Cu-rich zones exhibited bcc structure and then transformed into 9R structure with twins during aging. The spherical 9R-Cu particles changed into rod-shaped fcc-Cu particles after prolonged aging. Laves phase of Fe 2 Nb type started to form in the Nb-added steel almost after finishing nucleation and growth of Cu particles. Addition of Nb in the steel delayed the nucleation of the Cu-rich zones due to slow diffusion of Nb atoms in ferrite.

Étude du comportement mécanique d'un matériau à structure duplex par la méthode des éléments finis

The microstructural design concept of bio-ceramics is based on relatively large (10–100 μm) spherical zones dispersed in a ceramic matrix. These zones contain variable fractions of ZrO 2 particles. On cooling from the fabrication temperature they expand relative to the matrix either completely during cooling or at first partially and then continue by stress induction. Compressive stresses are developing within and radially around zones. Tensile hoop stresses are created tangentially around the zones. The objective of these spherical zones is to preserve stress of rupture of the matrix at a high value and to support the deviation and the cracks bifurcation. The reinforcement in these materials is related to the interaction between the stress field in crack face and the residual stress fields around the spherical zones. In this article, we propose a study of the stress field around spherical inclusions using the finite elements method. These results are compared with those found analytically.

Undrained shear strengths of clay around an advancing cone

Strength anisotropy of clay is significantly associated with the orientation of principal strain. Mobilized undrained shear strength will vary with the orientation of the principal stresses because cone penetration imposes large rotations of the principal stresses in the surrounding soil. The objective of this paper is to investigate the undrained failure modes around an advancing cone. In this study, strain softening behavior is not considered. The strain field of the soil obtained using the strain path method shows that the principal strain conditions of the soil around an advancing cone can be simplified into the following zones: spherical expansion strain zone, plane strain shearing zone, cylindrical expansion shearing zone, cylindrical expansion zone, and transition zone. The mobilized undrained shear strength of clay in various strain states can be determined by employing the anisotropic strength criterion and the associated flow rule. The result shows that the ratio of the equivalent undrained strength mobilized in the vicinity of the cone tip over the undrained shear strength obtained from a Ko-consolidated undrained compression triaxial test is found to range from 0.88 to 1.07 when the strength anisotropy ratio ranges from 0.4 to 0.9.

Complex chemistry simulations of spark ignition in turbulent sprays

Three-dimensional DNS of two-phase flows with the point-source approximation and with complex chemistry for n-heptane has been used to extract physical information on the structure of igniting kernels following localised heat deposition in turbulent monodisperse sprays. Consistent with experiment, small sparks fail to ignite and sprays ignite later than premixed gaseous mixtures. Reaction rates are intense in spherical zones near droplets and much lower in the interdroplet spacing, resulting in a highly wrinkled flame surface. The propagation of these reaction zones was observed. The flame shows a locally non-premixed character, with reactions proceeding at a wide range of mixture fractions, which increases as evaporation progresses. The distribution of various chemical species is presented. The results constitute a database for model validation and physical analysis.

Fast and accurate interpolation of large scattered data sets on the sphere

In this paper a new efficient algorithm for spherical interpolation of large scattered data sets is presented. The solution method is local and involves a modified spherical Shepard’s interpolant, which uses zonal basis functions as local approximants. The associated algorithm is implemented and optimized by applying a nearest neighbour searching procedure on the sphere. Specifically, this technique is mainly based on the partition of the sphere in a suitable number of spherical zones, the construction of spherical caps as local neighbourhoods for each node, and finally the employment of a spherical zone searching procedure. Computational cost and storage requirements of the spherical algorithm are analyzed. Moreover, several numerical results show the good accuracy of the method and the high efficiency of the proposed algorithm.

1271: Usefulness of New Perfusion Electrode (Cool Wet Tip Electrode®) in Radiofrequency Ablation of Hepatic Tumors Compared with Cool-Tip Electrode

To illustrate the spectrum of percutaneous radiogequency ablation (RFA) using new perfusion electrode [cool-wet tip electrode® (CWT), RF Medical, Seoul, Korea] for hepatic lesions with varying location and pathologic condition. CWT is a variation of cool tip electrode (CT) with two side holes in active tip. A side hole is 0.02 mm in diameter for leaking normal saline at the rate of 1.6 mL/min each. CWT with 2 cm and 3 cm active tip produces large ablating zone up to 3.0 cm and 4.5 cm in diameter, respectively. So it can ablate 0.5 - 0.8 cm apart from the tip of electrode and produce a spherical zone rather than elliptical. It is useful to ablate a hard mass such as recurred hepatocellular carcinoma after transarterial chemoembolizations or calcified metastasis, exophytic mass, and mass broadly attached to the diaphragm. Imaging Findings or Procedure Details: Between January 2008 and August 2008, 104 nodules in 79 patients were ablated by CWT. We will describe the experiences of RFA using CWT in hepatic tumors with suitable indications, technique, advantages and limitations compared with RFA using existing CE. We also ablated an explanted bullock's liver as ex vivo study to compare the exact size of ablated zone. RFA using CWT showed better performance in terms of creating a larger and spherical ablating zone than that using CT. CWT was useful in ablation of variable hepatic tumors which is difficult to ablate by CT.

An Optimal Sliding Choke Antenna for Hepatic Microwave Ablation

Microwave ablation (MWA) is a minimally invasive technique increasingly used for thermal therapy of liver tumors. Effective MWA requires efficient interstitial antennas that destroy tumors and a margin of healthy tissue, in situ, while minimizing damage to the rest of the organ. Previously, we presented a method for optimizing MWA antenna designs by coupling finite element method models of antennas with a real-coded, multiobjective genetic algorithm. We utilized this procedure to optimize the design of a minimally invasive choke antenna that can be used to create near-spherical ablation zones of adjustable size (radius 1-2 cm) by adjusting treatment durations and a sliding structure of the antenna. Computational results were validated with experiments in ex vivo bovine liver. The optimization procedure yielded antennas with reflection coefficients below -30 dB, which were capable of creating spherical ablation zones up to 2 cm in radius using 100 W input power at 2.45 GHz with treatment durations under 2 min.

Microstructure and mechanical properties of spray-deposited Al–Zn–Mg–Cu alloy processed through hot rolling and heat treatment

In this study, Al–10.8Zn–2.8Mg–1.9Cu alloy was synthesized by the spray atomization and deposition technique. Microstructure and mechanical properties of the spray-deposited alloy processed through hot rolling and heat treatment were investigated by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction and tensile test. The results indicate that the microstructure of the spray-deposited alloy is mainly composed of the Al matrix and the Mg(ZnCu) 2 compounds. The fragmentation of the Mg(ZnCu) 2 phases in the alloy has been regarded as one of the main feature during hot rolling. After solution treating, the microstructure is found to be composed of the Al matrix and a spot of Al 7Cu 2Fe, Al 9FeNi compounds. The spray-deposited Al–Zn–Mg–Cu alloy in the T6 temper displays superior strength due to the presence of two types of coherent GP zones (spherical GPI zones and thin platelet GPII zones).

Shallow water equations on a rotating attracting sphere 2. Simple stationary waves and sound characteristics

This paper studies a model of shallow water on a rotating attracting sphere that describes large-scale motions of the planetary atmospheric gases and World ocean water. The propagation of sound perturbations on an equilibrium state is studied. The system of equations for bicharacteristics is integrated in elliptic functions. A description of simple stationary waves is given. It is proved that there exist two types of solutions (supercritical and subcritical) describing gas motion in a spherical zone, so that one of the boundary parallels is a source and the other is a sink. The obtained solutions are interpreted as large-scale circulating cells in the atmosphere.

Pile Bearing Capacity Factors and Soil Crushabiity

The existence of large magnitude stresses at the tip of a bearing pile is a well known phenomenon leading to crushing of soil grains and thus affecting pile behavior. Classical foundation design calculations which assume that the soil fails in shear and neglect volume change can be safely used where stress levels or particle strengths prevent crushing, however in the case of weak grains or high foundation stresses consideration should be given to the effects of grain crushing and the resulting volumetric compression. Model pile tests have been carried out in two skeletal carbonate sands and a standard silica sand with the aim of examining the variation of skin friction and end bearing capacities with degree of penetration. The mobilization of the strength of crushable soils requires a much higher strain level while at the same time the end bearing pressure on the model piles exceeded 10MPa inducing considerable particle breakage. The peak skin friction for all sands occurred at a settlement normalized by pile diameter, S∕D, of less than 0.1. At this point the carbonate sands generally had lower skin friction values than the silica sand. Further displacement caused a rapid decrease in skin friction for all three materials. At higher lateral stresses the less crushable Toyoura silica sand generated higher skin frictions. Samples of Chiibishi sand were sectioned and photographed. It was observed that a spherical plastic zone was formed at the base of the pile which expanded with increasing S∕D and a degraded layer of broken particles developed around the pile as S∕D increased. Large values of the Marsal particle breakage factor were restricted to a zone extending outwards to one pile radius. An end bearing capacity modification factor has been proposed to adapt the conventional bearing capacity equation for soil crushability. This modification factor is a function of soil compressibility and degree of penetration. The factor was shown to decrease with increasing soil compressibility and increase with normalized penetration S∕D.

Design of objective lens with reflective spherical Fresnel zone plate

An objective lens composed of a spherical Fresnel zone plate mirror and aspheric mirrors is designed. The Fresnel zone plate with a spherical shape is analyzed, and the method to approximately replace the aspherical mirror with spherical Fresnel zone plate is deduced. The objective lens is designed with a single spherical Fresnel zone plate mirror and three aspherical mirrors. Under the condition of 100 × magnification, 2.5 Fresnel number and 120° field angle, the modulation transfer function can reach above 40% at 0.6 line pairs/mm on the magnification side, and the distortion is less than 2.2%. This method can provide a reference for the application of Fresnel zone plate in visible light imaging, and has a bright future with the continuous development of the fabrication technique of Fresnel devices.

A Basis Illumination Approach to BRDF Measurement

Realistic descriptions of surface reflectance have long been a topic of interest in both computer vision and computer graphics research. In this paper, we describe a novel high speed approach for the acquisition of bidirectional reflectance distribution functions (BRDFs). We develop a new theory for directly measuring BRDFs in a basis representation by projecting incident light as a sequence of basis functions from a spherical zone of directions. We derive an orthonormal basis over spherical zones that is ideally suited for this task. BRDF values outside the zonal directions are extrapolated by re-projecting the zonal measurements into a spherical harmonics basis, or by fitting analytical reflection models to the data. For specular materials, we experiment with alternative basis acquisition approaches such as compressive sensing with a random subset of the higher order orthonormal zonal basis functions, as well as measuring the response to basis defined by an analytical model as a way of optically fitting the BRDF to such a representation. We verify this approach with a compact optical setup that requires no moving parts and only a small number of image measurements. Using this approach, a BRDF can be measured in just a few minutes.

Octadecylsilane hybrid silicas prepared by the sol–gel method: Morphological and textural aspects

A series of octadecylsilane-modified silicas was prepared by the sol–gel method through the hydrolysis and cocondensation of tetraethylorthosilicate (TEOS) with octadecyltriethoxysilane (ODS). The ODS:TEOS ratio was varied between 0:100 and 100:0. The resulting carbon content was between 2.5 and 53.4%. In the case of pure ODS, the resulting silica presented 68.6% of C. Hybrid silicas were characterized by scanning electron microscopy, energy dispersive X-ray spectroscopy, and 29Si nuclear magnetic resonance spectroscopy. Spheres of ca. 0.5–1.0 μm were obtained in the case of hydrolysis of pure TEOS. The combination of ODS:TEOS ratio yielded systems combining spherical and lamellar patterns zones. Monitoring the particle growth, it seems that spherical particles grow around lamellar zones, these latter concentrating the organosilicon moieties. The degree of cross-linking of ODS moieties was shown to be dependent on the ODS addition time and stirring speed.