Irregular-shaped Objects Research Articles

Mineralogy and petrography of amoeboid olivine aggregates from the reduced CV3 chondrites Efremovka, Leoville and Vigarano: Products of nebular condensation, accretion and annealing

Abstract— Amoeboid olivine aggregates (AOAs) from the reduced CV chondrites Efremovka, Leoville and Vigarano are irregularly‐shaped objects, up to 5 mm in size, composed of forsteritic olivine (Fa<10) and a refractory, Ca, Al‐rich component. The AOAs are depleted in moderately volatile elements (Mn, Cr, Na, K), Fe, Ni‐metal and sulfides and contain no low‐Ca pyroxene. The refractory component consists of fine‐grained calcium‐aluminum‐rich inclusions (CAIs) composed of Al‐diopside, anorthite (An100), and magnesium‐rich spinel (∼1 wt% FeO) or fine‐grained intergrowths of these minerals; secondary nepheline and sodalite are very minor. This indicates that AOAs from the reduced CV chondrites are more pristine than those from the oxidized CV chondrites Allende and Mokoia. Although AOAs from the reduced CV chondrites show evidence for high‐temperature nebular annealing (e.g., forsterite grain boundaries form 120° triple junctions) and possibly a minor degree of melting of Al‐diopside‐anorthite materials, none of the AOAs studied appear to have experienced extensive (>50%) melting. We infer that AOAs are aggregates of high‐temperature nebular condensates, which formed in CAI‐forming regions, and that they were absent from chondrule‐forming regions at the time of chondrule formation. The absence of low‐Ca pyroxene and depletion in moderately volatile elements (Mn, Cr, Na, K) suggest that AOAs were either removed from CAI‐forming regions prior to condensation of these elements and low‐Ca pyroxene or gas‐solid condensation of low‐Ca‐pyroxene was kinetically inhibited.

THE xyzr ALGORITHM SPECIALIZED FOR EIGENVIBRATION PROBLEM OF BORED AND LAMINATED OBJECTS

We can determine elastic properties of an object from its eigenvibration frequencies, as long as a numerical calculation algorithm is available for the eigenvibration frequencies. The xyz algorithm developed by Visscheret al. [1] is an extremely versatile method applicable even for anisotropic, inhomogeneous, and irregular-shaped objects, with the exception of bored and laminated systems. I examined the characteristics and performance of the originalxyz algorithm, and succeeded in developing the xyzr algorithm for bored and laminated sphere and cylinder. The accuracy and convergency of the xyzr algorithm are examined by comparison with analytical solutions; the method is accurate enough for us to develop a new experimental technique to obtain the elastic properties of soft materials accommodated in a solid container.

A Method to Assess Spatial Coordinates in Art and Archaeological Objects: Application of Tomography to a Dolmen

A method to determine the values of spatial coordinates of bodies, specifically adapted to study art and archaeological objects, was developed and tested on a dolmen made of granite in north-west Spain.This method, based on geometric principles, comprises an easy-to-assemble rigid structure as a physical support, and software based on the algorithms discussed below, which together provide a rapid and inexpensive means of assessing coordinates. One of the main features of this procedure is the ability to quantify the accuracy of the coordinates being calculated according to the quality of the input measurements. The simplicity of obtaining data means that the method can even be performed upon rough and irregular-shaped objects, and in zones where other instruments are difficult to handle; for example, the interior of dolmens or small cavities.A demonstration of the method was performed upon an upright stone of a megalith in north-west Spain (Axeitos Dolmen, La Coruña). The coordinates of many points of measurement surrounding the object, combined with parameters from ultrasonic signals, were used to achieve three-dimensional tomography. Considering the experimental errors produced by different operators, the accuracy achieved when estimating the coordinates was better than 1cm. The tomograms obtained have been employed to assist in the evaluation of damage to this megalith.

Onion-Like Nanoscale Structures and Fullerene-Type Cages Formed by Electron Irradiation of Turbostratic Bx.C1-x (x<0.2)

ABSTRACTFlakes of CVD grown BxC1-x, (x<0.2) films were exposed to intense electron irradiation (flux density up to ∼100 A/cm2) in a 300 kV high resolution electron microscope equipped with a field emission gun. The starting flakes revealed a turbostratic BxC1-x structure. The composition of the starting materials and irradiated products was determined by using electron energy loss spectroscopy (EELS). Depending on the electron dose applied, irradiation of the turbostratic material led to formation of soap-bubble-like irregularly-shaped objects (linear dimensions of ∼2–5 nm), onion- and semi-onion-like structures (d∼10nm), nested fullerenes (3–14 shells) and elementary fullerene-type cages (d∼0.7 nm). It is thought that these curled and closed nanostructures arise from a continuous bending of the hexagonal Bx C1-x sheets under electron irradiation. Finally, some possible structural models of BxC1-x fullerenes are considered.

Contactless mass determination of arbitrarily shaped dielectric objects [using resonant cavities

Microwave resonant cavities have been studied as possible sensors for rapid determination of the mass or weight of perturbing dielectric objects of given permittivity and density, but of arbitrary shape, inserted into the cavity. Tracking the coordinates of the peak of the resonant curve with and without the object, i.e. measuring shift of resonant frequency and change in the cavity Q-factor, provides information that together with a calibration equation is sufficient for the object mass or weight determination. During the calibration procedure, the parameters of the empty cavity, as well as the permittivity and the specific gravity of the object material must be known. The measurement technique does not, in principle, require any contact between the object and the measuring system, and measurements can be rapid and reasonably accurate. Basic principles of the shape-independent measurements are presented, and experimental results are given for common plastic objects of irregular shapes measured in resonant cavities operating at 640 MHz and 1.7, 2.5 and 3.2 GHz.

Acoustic measurements of scattering by objects of irregular shape

Although many scatterers in nature are irregular in shape, the data on the scattering of sound by asymmetrical bodies is relatively limited. Our understanding of the scattering of underwater sound by nonregular shaped targets is therefore significantly less developed than that due to scattering by scatterers of symmetry. In the present work, measurements are reported on the backscattering from irregularly shaped solid elastic particles in both the time and frequency domains. Backscatter data have been collected for a variety of irregularly shaped particles at varying orientations. These observations show a number of characteristics which are comparable with scattering by targets of symmetry, particularly the property of the scattered echo being significantly longer in duration than the insonifying pulse. This pulse elongation for symmetrical targets is normally interpreted using resonance scattering theory, RST, as arising from radiation due to surface eigen waves on the body of the scatterer. In the present work the interpretation of the scattering by irregular shaped targets has been guided by resonance scattering studies, and an understanding of the response formulated within this framework.

A new two-dimensional phase unwrapping algorithm for MRI images.

The phase of an image obtained with many magnetic resonance imaging techniques is related to some physical variable of interest. This phase needs to be unwrapped, which is complicated by the presence of noise and multiple objects of irregular shape. A new two-dimensional phase unwrapping algorithm is presented, along with simulation results.

Observations on resonant cavity perturbation by dielectric objects

Microwave resonators can be used as sensors for sorting dielectric objects. Differences in volume or mass can be distinguished among objects of irregular shape but of uniform dielectric properties. Moisture content, or other permittivity-dependent qualities can also be distinguished independent of mass or volume when objects are of uniform shape. Fundamental principles of the shape-independent and size-independent measurements are discussed, and experimental results are presented. >

Computation of electromagnetic field scattered by three-dimensional permeable objects

A surface integral equation is derived for electromagnetic scattering by highly conducting permeable objects of irregular shapes and solved, numerically, using the method of moments. The analysis make uses of the impedance boundary condition to simplify the formulation and reduce the computation time and memory requirements associated with the method of moments. Results for the induced voltage across a receiving loop antenna are presented. The computed and exact theoretical results for spherical objects are in good agreement. >

Orientation estimation of 3D surface patches

Orientation estimation of a surface patch is an essential step in an automatic inspection job or a 3D template matching scheme for object recognition. Two main problems of the estimation are non-uniform surface sampling and self-occlusion. To solve these problems, we propose to use a 3D spherical window to extract the correct patch and to use closed contours on the surface patch for matching. 3D resampling on a contour is simple and uniform for all viewing directions. Orientation estimation based on the resampled contours is reasonably accurate and can be computed at high speed. However, better accuracy is obtained if more surface patches are used to compute an object orientation first, and the patch orientation is then deduced from the model of the object. The method is designed mainly for irregular-shaped objects.

Microwave Resonator Techniques for Sorting Dielectric Objects

ABSTRACTMicrowave resonators have been found to be sensitive devices for sorting dielectric objects of irregular shapes according to their volumes, for detecting voids inside objects of similar shape or for determining moisture content in objects of varying volumes. Fundamental principles of operation as well as experimental results are discussed in the paper.

Using a Spread Sheet Program to Model the Interaction of Low-Frequency Electric Fields with Inhomogeneous, Irregularly Shaped Objects

This paper describes the use of an ordinary business spread sheet program to calculate, using a two-stage finite difference method, the electric fields and current densities produced inside irregularly shaped models of the upper arm and forearm. The limb interiors are inhomogeneous, being represented as realistic cross-sections of bone and muscle.A spread sheet forms a two-dimensional array. Each cell of the sheet can correspond to a physical element of space. Equations entered into the cells then represent the relationships among the potentials of the corresponding spatial elements.The model is validated for a two-layer, lossy dielectric cylinder. Good agreement is obtained between the numerical and analytical solutions in this case except near the boundaries of the outer layer. The electric field within the limb depends on the shape and orientation of the limb relative to the applied field. The flow of current around the less conductive bones in the forearm can be observed.

Scattering from arbitrarily-shaped objects with impedance boundary conditions

A numerical method is developed to determine the electromagnetic field scattered by homogeneous imperfectly conducting and impedance objects of irregular shape. An integral equation for the induced surface currents on the body surface is derived and solved numerically by the method of moments. Numerical results are given for a sphere with different surface impedances and for lossy finite circular and elliptic cylinders. The results are compared with the Mie series solution for spheres and with the integral equation formulation of bodies of revolution for the finite circular cylinder.

Measurement of intracranial tissue volume using computed tomographic images and a personal computer.

A software package called MacMeasure was developed previously to measure the size of intracellular structures by means of photomicrographs. We have expanded the application of this program to computed tomographic (CT) images. Using three objects of irregular shape and unequal size (phantoms), we compared volumetric determinations made with a CT mainframe computer and a widely available personal computer. The phantom objects were scanned in a GE CT/T 9800 scanner with serial, nonoverlapping slices 3.0 mm in thickness. The image data were first measured directly from the magnetic archive tape with the CT control terminal. Hard copies of the CT scans were then measured with a Macintosh SE computer and a digitizing tablet with a crosshair cursor driven by the MacMeasure software package. A third method of measuring volume was by tracing individual CT images onto paper (hard copies). The tracings were then cut out, weighed, and converted to surface area by dividing the weights by a weight/surface area standard (26.37 mg = 25 cm2) calibrated to the CT image scale (5.0 cm). The total surface area value was then converted to volume by multiplying by a single CT slice thickness (0.3 cm). Finally, the phantom objects were placed in water-filled graduated cylinders to determine their volume by fluid displacement. The technique using MacMeasure and the personal computer provides an accurate means of determining surface area and volumes using hard copies of CT images. It avoids occupying costly CT computer time and is the most rapid method of volume measurement of the three techniques tested (CT mainframe = 6.0 hours, trace/weigh = 3.5 hours, and PC = 1.25 hours).(ABSTRACT TRUNCATED AT 250 WORDS)

Depolarization of the scattered radiation fields by conducting objects of irregular shape above rough land and sea: Full wave solutions

The full wave approach to problems of scattering by rough surfaces has been applied to the problem of depolarization of the scattered radiation fields by objects of finite conductivity and irregular shape. In the analysis, complete expansions are employed, exact boundary conditions are imposed, and a variable coordinate system that conforms with the local features of the irregular surface is used. The full wave solutions are expressed in forms that can be readily compared with earlier solutions, and they can be used to reconcile the differences and bridge the wide gap between these solutions. Thus the full wave solutions for the backscatter cross section are shown to reduce to the physical optics solutions when the high‐frequency, stationary phase approximations are used. Similarly, for slightly rough surfaces the full wave expressions reduce to the perturbational solutions for the backscatter cross section. The full wave solutions are shown to be consistent with the duality reciprocity and realizability relationships in electromagnetic theory. These solutions are invariant to coordinate transformations. Since upward and downward scattering are considered in the analysis, multiple scattering and shadowing effects are taken into account in a self‐consistent manner. Thus the total scattered field varies continuously as the observer moves across a shadow boundary, and there is no need to introduce transition terms derived from other theories. The full wave approach can be applied to deterministic, periodic, and random rough surfaces. It can also be used to determine the scattering by finite scatterers in the presence of rough land or sea.

An approximate method for scattering in elastodynamics — The born approximation I: the general formulation

A formulation for the scattering of elastic waves by inhomogeneities embedded in an infinite space is presented and an approximate solution procedure in the spirit of Born approximation is introduced. The Born approximation has been a valuable tool in quantum mechanics. It is based on the integral representation of the field equations which are conventionally derived as partial differential equations, and consists of an iterative solution of these integral equations. The principal motivation for this work is the need of studying waves scattered by objects of irregular shapes. The analysis is for the cavity (lined and unlined) and for rigid inclusion (fixed and movable) cases. Both the near and far field solutions and the solution for the global motion of rigid inclusions are presented.

Absorption microphotometry of irregular-shaped objects.

A new microphotometric method (mainly for the evaluation of microchemical color reactions) which uses measurements at two wave lengths (developed byOrnstein and, independently, by the author) is presented in a form which greatly reduces the computational labor (for an illustration, see Table 3).

A Simple Method of Measuring the Surface Area of Small Objects of Irregular Shape

A Simple Method of Measuring the Surface Area of Small Objects of Irregular Shape