Microscopic vision system with all-in-focus and depth images

In this paper, a high-speed digital processed microscopic observational system for telemicrooperation is proposed with a dynamic focusing system and a high-speed digital-processing system using the depth from focus criterion. In our previous work [10], we proposed a system that could simultaneously obtain an all-in-focus image as well as the depth of an object. In reality, in a microoperation, it is not easy to obtain good visibility of objects with a microscope focused at a shallow depth, especially in microsurgery and DNA studies, among other procedures. In this sense, the all-in-focus image, which keeps an in-focus texture over the entire object, is useful for observing microenvironments with the microscope. However, one drawback of the all-in-focus image is that there is no information about the objects depth. It is also important to obtain a depth map and show the 3D microenvironments at any view angle in real time to actuate the microobjects. Our earlier system with a dynamic focusing lens and a smart sensor could obtain the all-in-focus image and the depth in 2 s. To realize real-time microoperation, a system that could process at least 30 frames per second (60 times faster than the previous system) would be required. This paper briefly reviews the depth from focus criterion to Simultaneously achieve the all-in-focus image and the reconstruction of 3D microenvironments. After discussing the problem inherent in our earlier system, a frame-rate system constructed with a high-speed video camera and FPGA (field programmable gate array) hardware is discussed. To adapt this system for use with the microscope, new criteria to solve the ghost problem in reconstructing the all-in-focus image are proposed. Finally, microobservation shows the validity of this system.Received: 12 August 2001, Accepted: 17 July 2002, Published online: 12 November 2003 Correspondence to: Kohtaro Ohba     

Control of Underactuated Manipulators using Fuzzy Logic Based Switching Controller

This paper introduces a new concept for designing a fuzzy logic based switching controller in order to control underactuated manipulators. The proposed controller employs elemental controllers, which are designed in advance. Parameters of both antecedent and consequent parts of a fuzzy indexer are optimized by using evolutionary computation, which is performed off-line. Design parameters of the fuzzy indexer are encoded into chromosomes, i.e., the shapes of the Gaussian membership functions and corresponding switching indices of the consequent part are evolved to minimize the angular position errors. Such parameters are trained for different initial configurations of the manipulator and the common rule base is extracted. Then, these trained fuzzy rules can be brought into the online operations of underactuated manipulators. 2-DOF underactuated manipulator is taken into consideration so as to illustrate the design procedure. Computer simulation results show that the new methodology is effective in designing controllers for underactuated robot manipulators.     

Fabrication of hexagonal GaN on the surface of β-Ga2O3 single crystal by nitridation with NH3

The fabrication of GaN on the surface of a bulk β-Ga₂O₃ single crystal by nitridation with NH₃ was investigated for the purpose of using it as a substrate for GaN epitaxial growth. A β-Ga₂O₃ single crystal was prepared using a floating zone furnace with double ellipsoidal mirrors, and its polished (100) plane was nitridated in NH₃ atmosphere at 850 °C for 5 h. It was found that hexagonal GaN with preferred in-plane orientation was produced on the surface of β-Ga₂O₃, and the thickness of nitride layers was approximately 50 nm. High resolution transmission electron microscopic observation indicated that the synthesized GaN was composed of the aggregation with single crystalline GaN particles, whose size ranged from ∼ 5 nm to ∼ 50 nm, and dislocation or defect was not observed in a GaN particle. This method could be expected as a new route to fabricate a substrate for epitaxial growth of III-nitride materials instead of using a bulk GaN single crystal.     

Molecular beam epitaxy of c-plane wurtzite GaN on nitridized a-plane β-Ga2O3

Epitaxial growth of GaN on β-Ga₂O₃ single crystal substrates by the molecular beam epitaxy technique is demonstrated for the first time. Standard and in-plane X-ray diffraction evidence the growth of c-plane wurtzite GaN on a-plane β-Ga₂O₃, the epitaxial relationship being 0 1 0_Ga2O3 1 1 2¯ 0_GaN and 0 0 1_Ga2O31¯ 1 0 0_GaN. Epitaxial growth without any buffer layer is achieved after an effective surface nitridation under NH₃ gas.     

Technical application of fracture mechanics to thin-walled structures

This paper reviews recent developments in the application of fracture mechanics to such structures as welded steel tanks, ships, and thin-wall pressure vessels, with particular attention to Japanese work. It describes methods for estimating critical crack size and safe working conditions, taking into account such fabrication variables as angular distortion, welding residual stress, prestrain, plate curvature and stress concentration. Whilst most of the paper is devoted to a consideration of the conditions for crack instability, it also discusses crack arrest and gives experimental results for the effect of thickness on both initiation and arrest.     

Dielectric dispersion in a disordered nitrite compound: AgNo2·NH3

A pronounced dielectric dispersion was observed along the a- and c-axes in a disordered nitrite compound of AgNO₂·NH3. The activation energy of 0.32 eV was found for the dielectric relaxation time both along the a-axis and along the c-axis. Phase transition was not observed down to liquid helium temperature.     

A note on brittle crack deceleration in a structural steel

The deceleration of a brittle crack in a steel is attributed to plastic deformation developed around the crack. The investigation shows that a ductile fibrous crack stops suddenly, but a brittle cleavage crack does sluggishly.

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Résumé La décélération d'une fissure fragile dans un acier est attribuée à la déformation plastique qui se développe autour de cette fissure.L'étude montre qu'une fissure fibreuse et ductile s'arrête brutalement tandis qu'une fissure fragile et de clivage s'arrête lentement.

     

Nonaqueous titrimetric analysis of sulfuric and alkylbenzene sulfonic acids in detergent intermediates

A single differential nonaqueous titration method is presented for the analysis of sulfuric and alkylbenzene sulfonic acids in a detergent intermediate material. The organic and sulfuric acids in the sample were quantitatively titrated potentiometrically with standard cyclohexylamine solution. With certain specified sample compositions, approximate sulfuric acid determinations may be made without sample weighing or the use of standardized titrant. The titration is based upon the ratio of the first and second end points of the differential titration curve. Because of its simplicity, the latter method adaption is especially useful for routine control type analyses.