913 resultados para Geometric mixture


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Corneal and anterior segment imaging techniques have become a crucial tool in the clinical practice of ophthalmology, with a great variety of applications, such as corneal curvature and pachymetric analysis, detection of ectatic corneal conditions, anatomical study of the anterior segment prior to phakic intraocular lens implantation, or densitometric analysis of the crystalline lens. From the Placido-based systems that allow only a characterization of the geometry of the anterior corneal surface to the Scheimpflug photography-based systems that provide a characterization of the cornea, anterior chamber, and crystalline lens, there is a great variety of devices with the capability of analyzing different anatomical parameters with very high precision. To date, Scheimpflug photography-based systems are the devices providing the more complete analysis of the anterior segment in a non-invasive way. More developments are required in anterior segment imaging technologies in order to improve the analysis of the crystalline lens structure as well as the ocular structures behind the iris in a non-invasive way when the pupil is not dilated.

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During grasping and intelligent robotic manipulation tasks, the camera position relative to the scene changes dramatically because the robot is moving to adapt its path and correctly grasp objects. This is because the camera is mounted at the robot effector. For this reason, in this type of environment, a visual recognition system must be implemented to recognize and “automatically and autonomously” obtain the positions of objects in the scene. Furthermore, in industrial environments, all objects that are manipulated by robots are made of the same material and cannot be differentiated by features such as texture or color. In this work, first, a study and analysis of 3D recognition descriptors has been completed for application in these environments. Second, a visual recognition system designed from specific distributed client-server architecture has been proposed to be applied in the recognition process of industrial objects without these appearance features. Our system has been implemented to overcome problems of recognition when the objects can only be recognized by geometric shape and the simplicity of shapes could create ambiguity. Finally, some real tests are performed and illustrated to verify the satisfactory performance of the proposed system.

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Basalts from the base of a small seamount on ~1.5-m.y.-old crust west of the East Pacific Rise (EPR) at 9°N are intermediate in chemical and isotopic composition between light-rare-earth-element-depleted tholeiite (normal midocean ridge basalt (MORB)) and alkali basalt. Like oceanic alkali basalt, these rocks contain significantly more Ba, K, P, Sr, Ti, U, and Zr than normal MORB. Since the absolute abundances of these elements are still well below alkali basalt levels, the label transitional is adopted for these basalts. A series of fractionated MORB also occurs in this area, northwest of the Siqueiros Fracture Zone - Transform Fault. The normal tholeiites are either olivine-plagioclase or plagioclase-clinopyroxene phyric, while the transitional basalts are spinel-olivine phyric. Fractional crystallization quantitatively accounts for the chemical variability of the tholeiitic series but not for the transitional basalts. The tholeiitic series probably evolved in a crustal magma chamber ~4 km below the crest of the East Pacific Rise. 143Nd/144Nd and other chemical data suggest that the large-ion-lithophile-enriched transitional basalts may represent a hybrid of normal MORB and Siqueiros area alkali basalt. Incompatible element plots of K, P, and U indicate possible derivation of the transitional basalts by magma mixing. Magma mixing of unfractionated normal MORB and Siqueiros alkali basalt has been quantified. Derivation of the transitional basalts from a 1:1 mixture is supported by all available chemical data, including Cr, Cu, Nd, Ni, Sm, Sr, U, and V. This magma mixing apparently occurred at ?<~30 km depth within a few tens of kilometers from the EPR axis. These Siqueiros area EPR transitional basalts are compared with Mid-Atlantic Ridge (MAR) transitional basalts from the Iceland and Azores areas. The Siqueiros area basalts reflect a profound chemical and isotopic heterogeneity in the upper mantle, similar to that found along the MAR. Unlike the MAR, the EPR shows no evidence of plumelike bulges and associated large-scale outpourings of nonnormal MORB resulting from these mantle heterogeneities. Siqueiros alkali basalt and MORB, as well as transitional basalt and MORB, were recovered from single dredge hauls. Such close spatial and temporal proximity of the inferred mantle sources places severe constraints on geometric and physicochemical upper mantle models.

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Federal Highway Administration, Traffic Systems Division, Washington, D.C.

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Federal Highway Administration, Environmental Division, Washington, D.C.

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Federal Highway Administration, Environmental Division, Washington, D.C.

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Federal Highway Administration, Environmental Division, Washington, D.C.

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Federal Highway Administration, Office of Program and Policy Planning, Washington, D.C.

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Mode of access: Internet.

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Federal Highway Administration, Office of Research and Development, Washington, D.C.

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Mode of access: Internet.