High-Frequency Ultrasound for Assessment of Peri-Implant Bone Thickness

Purpose: The aim of this study was to evaluate the accuracy of high-frequency ultrasound (HFUS) for measurement of bone thickness surrounding dental implants. Methods: Eight porcine bone samples containing dental implants were scanned by a HFUS scanner and compared using cone-beam computed tomography (CBCT) and an optical scanner. Bone thickness was measured in the buccolingual region of dental implants in 10 points distributed between the platform and apical portion of the implant. Results: The mean measurement error for the ultrasound method was 0.11 mm, whereas CBCT showed a measurement error of 0.20 mm. For both devices, the maximal measurement error was 0.28 mm. Conclusion: Within the simulated limited conditions of this study, high-frequency ultrasound, with optical scanning used as a reference, presented higher accuracy in comparison to CBCT, and seems to be a promising tool for measuring peri-implant bone.

The SOI Micro-Accelerometer Fabricated by Sacrificial Process

This paper presents the fabricationof SOI micro-accelerometer by using the sacrificial process. The structure ofthe SOI micro-accelerometer is designed and analyzed by the finite element modeling.As for the fabrication issue, the problem of electrode metal layer to standagainst HF etching is first studied. Second, to prevent the over-etching of theBOX layer during structure releasing process, the etching rate of the BOX layeris carefully investigated and an optimal etching duration is obtained. Third,the adhesion phenomenon between comb fingers during releasing process isstudied and optimized finger geometry is proposed to solve such problem.Devices based on the sacrificial process is carried out successfully, themeasurement results show that the sensitivity of the accelerometer is about 35mV/g, with a maximal measurement error of 12mg, and a maximal nonlinear error of0.41% within 50g.

Remote Testing of the UHF Radiation Field Generated by Corona Discharge of the Transmission Lines

The UHF radiation field generated by corona discharge of the two 500kV AC transmission lines was tested. The influencing factors of radiation field, including climate, bundle conductors number and test distance, were analyzed. Test results indicate that the field continuously arranges from 200MHz to 700MHz, mainly from 200MHz to 500MHz. The maximal measurement distance is 300 meters. The climate and bundled conductors number affect the radiation field obviously. The discharge will become intense when the temperature and humidity increase and bundle conductors number decays. The peak values of the electric field strength which decay rapidly with the distance increasing, can arrive several hundreds uV/m. The test results rich the UHF radiation field data and offer references to testing and evaluating the electromagnetic interference generated by corona discharge of ultra-high voltage transmission lines.

Measurement and Analysis of Modulated Doublet Mode Response in Mock Bladed Disks

The steady-state response of spatially modulated doublet modes that occur in low count flexible bladed disks is investigated for the case in which the structure is driven by a harmonic traveling wave excitation source. Finite element simulation and modal testing of prototypical bladed disk structures demonstrate the presence of particular wavenumbers, beyond the base number of nodal diameters, which contaminate and distort the appearance of certain doublet modes. The manner in which the natural frequency and wavenumber content of such modes shift and split as functions of the number of blades and their span angle is discussed in the light of a companion perturbation analysis for rotationally periodic structures. Resonance conditions are established and verified through simultaneous measurements made with a spin test stand using sensors that are placed in the rotating (structure) and stationary (excitation) frames of reference. The traveling wave response components of a repeated frequency doublet mode are shown to propagate either in the same or opposite direction as the excitation source, depending on whether certain algebraic relationships between the excitation order, the base number of nodal diameters, and the contamination wavenumbers are satisfied. To the extent that such components can travel at different phase speeds and directions relative to one another, the placement of sensors on the structure can be optimized to best measure the response amplitude. Conversely, other placements can result in sub-maximal measurement of peak vibration amplitude over the structure.

The quantitative definition of cattle carcasses

The possibility of defining quantitatively the carcasses of cattle has been investigated and a procedure evolved, based upon "conformation", "finish", and "quality", which are the features appraised by beef-carcass graders. A series of ratios has been used to define "conformation" with respect to shape rather than to dimensional attributes. For example, length, "meatiness", and compactness, which are attributes of a hind leg, are described by a ratio of which the numerator is the "circumference" measurement at an anatomically fixed point whereas the denominator is a defined length measurement. The trade term "finish" is covered by a percentage assessment of the distribution of subcutaneous fat over the carcass whereas thickness of fat is the mean of two measurements of depth made at points fixed anatomically. The proportion of fat to lean is stated by a ratio of which the numerator is a maximal measurement of the depth of lean meat a t a defined situation and the denominator is the mean depth of subcutaneous fat. Attributes of "quality" are colour of fat, firmness of fat, "marbling", and colour of lean meat. A series of five defined colours has been used to classify colour in a sample of subcutaneous fat rendered by heat. Firmness of fat has been related to a series of iodine numbers of greater or lesser magnitude: firm, medium, soft, and oily fats were found to be classifiable by the reaction of the rendered substance to slight manual pressure exerted through a blunt probe. The degree of marbling was determined from the size relation of a petrol-ether extract to a sample portion of the carcass taken at a defined situation. Colour of lean meat was classified by reference to a series of defined colours which were given distinctive numbers. Quantitative figures from observations may he recorded for examination by statistical methods or they may be transposed as diagrammatic presentations which may be related to trade standards or to market types for the purpose of judging carcass competitions. The procedure may also be used to provide data from which a "fleshing index" can be determined. Examples of all three possibilities are stated. The procedure has been tested on three series of animals, from which measurement errors for individual carcasses were calculated and found to be satisfactorily low. However, it has not yet been adequately tested for the comparison of between-group differences in carcasses, principally because no animals suitable for such a test are likely to become available until experimental conditioning is undertaken. The procedure is, therefore, presented tentatively.