Measurement of the glottal impedance with a mechanical model

An approximate but realistic model of the human larynx was constructed to gain better knowledge of the complex glottal impedance and its dependence on glottal width, flow, and frequency. The glottal width was adjustable from 0 to 3 mm, the flow from 0 to 500 cm3/s. The model was fitted into a system of tubes, through which compressed air could be conducted. Supraglottally, a broadband signal was fed into the tube, and, with a two-microphone directional coupler, the complex glottal impedance at a given reference plane was directly determined as a function of frequency. Since the calculated impedance is sensitively dependent on the definition of the position of the reference plane, it is difficult to obtain quantitative statements about the frequency dependence. Nevertheless, in the presence of flow, it is possible to achieve reliable results by analysis of the relative position of the measured curves. On the one hand, the glottal inductance decreases linearly with increasing flow velocity; on the other hand, it diminishes nonlinearly with decreasing frequency. Finally, some difficulties in the definition of glottal impedance are pointed out.     

Multiple-walled BN nanotubes obtained with a mechanical alloying technique

An experimental method to obtain multiple-walled nanotubes of BN using low energy is presented. The method is based on the use of mechanical alloying techniques with elemental boron powders and nitrogen gas mixed in an autoclave at room temperature. The chemical and structural characteristics of the multiple-walled nanotubes were obtained using different techniques, such as X-ray diffraction, transmission electron microscopy, EELS microanalysis, high-resolution electron microscopy images and theoretical simulations based on the multisliced approach of the electron diffraction theory. This investigation clearly illustrates the production of multiple-wall BN nanotubes at room temperature. These results open up a new kind of synthesis method with low expense and important perspectives for use in large-quantity production. PACS 61.16.Bg; 79.60.Jv; 61.46.1w; 61.50.Ah     

Effect and minimization of errors in in situ ground impedance measurements

The transfer function method is a procedure to measure the surface impedance of grounds in situ. In this article, the influence of measurement errors on the predicted surface impedance is investigated numerically. Even small errors in the range of accuracy of common measurement equipment can lead to significant errors in the impedance. This is especially true for errors in the transfer function at frequencies below about 500 Hz and for highly reflecting grounds. To a lesser degree, errors in the measurement geometry contribute to the uncertainty of the estimated impedance. To minimize these effects, an improved geometry is suggested for the frequency range 100-400 Hz significantly reducing the average error. However, even with this optimized geometry the average error for high impedance grounds, like compacted silt, in this frequency range will be around 50%. Therefore, the use of the transfer function method cannot be recommended in this case unless the requirements in accuracy are very low for a specific application or particular favourable measurement conditions are given.     

机械阻抗测量的一种新方法

本文介绍了一种新的机械阻抗测量方法－声强法，由定义出发将机械阻抗表为功率流和加速度响应谱的函数，应用结构声强技术测量功率流，声强法不需要测量作用力信号，可以用于测量任意结构中的各类机械阻抗，实验结果表明，声强获得的测量值与直接获得的测量值相近，声强法能较准确地测量一维和二维匀质结构中机械阻抗。     

Optical properties of hydroxyapatite obtained by mechanical alloying

Calcium phosphate based bioceramics, mainly in the form of hydroxyapatite (HA), have been in use in medicine and dentistry for the last 20 years. Applications include coatings of orthopaedic and dental implants, alveolar ridge augmentation, maxillofacial surgery, otolaryngology, and scaffolds for bone growth and as powders in total hip and knee surgery. These materials exhibit several problems of handling and fabrication, which can be overcome by mixing with a suitable binder. In this paper, mechanical alloying has been used successfully to produce nanocrystalline powders of HA using five different experimental procedures. The milled HA were studied by X-ray powder diffraction, infrared and Raman scattering spectroscopy. For four different procedures, HA was obtained after a couple of hours of milling (on an average, 20 h of milling depending on the reaction procedure). The XRD patterns indicate that the grain size is within the range of 29-103 nm. This milling process, used to produce HA, presents the advantage that melting is not necessary and the powder obtained is nanocrystalline with extraordinary mechanical properties. The material can be compacted and transformed in solid ceramic samples. The high efficiency of the process opens a way to produce commercial amount of nanocrystalline HA. Due to the nanocrystalline character of this powder, their mechanical properties have changed and for this reason a pressure of 1 GPa is enough to shape the sample into any geometry.     

Flow aeroacoustic damping using coupled mechanical electrical impedance in lined pipeline

We report a new noise-damping concept which utilizes a coupled mechanical–electrical acoustic impedance to attenuate an aeroacoustic wave propagating in a moving gas confined by a cylindrical pipeline. An electrical damper is incorporated to the mechanical impedance, either through the piezoelectric, electrostatic, or electro-magnetic principles.Our numerical study shows the advantage of the proposed methodology on wave attenuation. With the development of the micro-electro-mechanical system and material engineering, the proposed configuration may be promising for noise reduction.     

Compensation for pixel-mismatch errors in shift-multiplexed holographic data storage

To read out correct data from shift-multiplexed holographic data storage, we propose a novel method of pixel matching by use of a tiny plane-parallel refraction plate placed in the path of converging readout beams. Tilting the refraction plate produces a shift in the lateral position of the readout beam incident upon the holographic storage disk, leading to compensation for pixel-mismatch errors by an improvement in bit-error rate of 3 orders of magnitude.     

The mechanical point impedance of the human head, with and without skin penetration

The fact that a titanium screw can be implanted into the mastoid portion of the human skull, at the same time establishing a permanent, reaction-free skin penetration, has made it possible to attach a new bone conduction hearing aid directly to the skull. To understand and improve this new method of bone stimulation, the mechanical point impedance of the titanium screw-skull system was measured. The conventional point impedance of the skin-covered mastoid portion of the temporal bone was also measured and the difference in magnitude between the two impedances was calculated. An impedance head (Brüel & Kjaer 8001) and an FFT analyzer (Hewlett-Packard 5423) were used for mechanical point impedance measurements. Seven patients have been investigated. The magnitude of the impedance for the screw-skull system was found to be generally between 10 and 30 dB higher than that for the conventional skin-covered mastoid bone. One conclusion is that the conventional point impedance of the skin-covered mastoid portion of the human skull is essentially due to the properties of the skin and subcutaneous soft tissue. Another conclusion is that a much lower stimulation velocity is needed, with skin penetration, to produce a given hearing sensation.     

The inversion of NMR log data sets with different measurement errors.

We present a composite-data processing method which simultaneously processes two or more data sets with different measurement errors. We examine the role of the noise level of the data in the singular value decomposition inversion process, the criteria for a proper cutoff, and its effect on the uncertainty of the solution. Examples of processed logs using the composite-data processing method are presented and discussed. The possible usefulness of the apparent T(1)/T(2) ratio extracted from the logs is illustrated.     

Magnetocaloric properties of amorphous GdNiAl obtained by mechanical grinding

An amorphous GdNiAl sample was prepared by mechanical grinding performed on a crystallised intermetallic. The treatment changes greatly the ferromagnetic behaviour of this compound; its Curie temperature decreases from 57 K (unmilled sample) to 29 K (milled sample). Specific heat and magnetisation measurements reveal that amorphous GdNiAl exhibits an interesting magnetocaloric effect; for an applied magnetic field of 5 T a change of 8.9 J/kgK is observed at 36 K for the isothermal magnetic entropy. PACS 75.30.Sg; 65.40.+g; 75.50.Kj     

Investigation of errors in the Kramers-Kronig analysis of reflectance data

To date all estimates of the errors introduced by application of Kramers-Kronig analysis to reflectance data have been based solely on experimental values. This paper presents an investigation based on an analytical model, whereby the reliability of the method can be calculated exactly. It is shown that the errors in? ₂ due to the “unmeasured region” can be reduced to acceptable values. The method of fitting the results to known optical constants gives errors in? ₂ of the order of 0.05 or less for the most commonly used extrapolation procedure, and 0.01 or less for more refined approximations. This corresponds to a precision in the reflectance determination of the order of 0.5% and 0.1% respectively.     

Internal consistency of NMR data obtained in partially aligned biomacromolecules

A method of testing structure-related NMR data prior to structure calculations is presented. The test is applicable to second rank tensor interactions (dipolar coupling, anisotropic chemical shielding, and quadrupolar interaction) observed in partially aligned samples of biomacromolecules. The method utilizes the fact that only limited number of frequencies corresponding to the mentioned interactions can be measured independently in a rigid fragment of the macromolecule. Additional values can be predicted as linear combinations of the set of independent frequencies. Internal consistency of sufficiently large sets of frequencies measured in individual molecular fragments is tested by comparing the experimental data with their predicted values. The method requires only knowledge of local geometry (i.e., definition of the interaction tensors in the local coordinate frames of the fragments). No information about the alignment or shape of the molecule is required. The test is best suited for planar fragments. Application to peptide bonds and nucleic acid bases is demonstrated.     

Dynamical properties of Cr-Fe amorphous powders obtained from mechanical milling

Mössbauer measurements have been performed in situ in the temperature range of 25 to 550°C for three Cr-Fe samples: Cr₇₂Fe₂₈ crystalline alloy (I), as-milled amorphous Cr₆₅Fe₃₅ powders made by mechanical grinding (II) and the same powder annealed at 420°C for 2 h (III). The temperature dependence of isomer shifts for samples I and III follows the variation predicted by the second-order Doppler effect, while for the sample II a deviation has been observed. The Debye temperatures have been determined to be 420, 400 and 380 K for sample I, III and II, respectively. A linear dependence onT ^3/2 of quadrupole splitting of the annealed powder is observed.     

Crack detection by measurement of mechanical impedance of a rotor-bearing system

Measurements were done to determine the influence of a transverse crack on the mobility of a rotor-bearing system. The results show that the mobility changes substantially due to the presence of crack and follows definite trends with the crack depth and direction of force application. The significant changes in mobility were observed at the natural frequency and at the running frequency of the rotor system. Good agreement between the experimental results and numerical simulations has been observed. The measurement of mobility has been suggested for crack detection and condition monitoring of rotor-bearing systems.     

On the use of multichannel data acquisition of impedance spectra

Impedance spectroscopy is a powerful technique for electrical and electrochemical characterisation of ionic conductors and other electroceramics. Thus, one might tempted to use multichannel data acquisition to allow the utilisation of expensive LCR meters for simultaneous measurements. This work shows results for YSZ and strontium titanate ceramics, obtained with a multi-channel data acquisition system, to demonstrate the limitations of this approach and the applicability of some corrections. Impedance spectra are affected under multi-channel conditions, mainly in the high frequency contributions, and this is approximately described by a stray capacitance. The bulk contribution of the spectra is most affected. Contributions of internal interfaces (e.g. grain boundaries) are relatively well characterised, mainly after the proposed corrections. The characterisation of electrode processes is not affected. Paper presented at the 9th EuroConference on Ionics, Ixia, Rhodes, Greece, Sept. 15–21, 2002.     

Inverse scattering for surface impedance from phase-less far field data

We present a numerical comparison of a regularized Newton-type method and a direct method for reconstructing the surface impedance function of a three dimensional acoustic scatterer with known shape from the full far field pattern for scattering of one incident time-harmonic plane wave. Furthermore, we propose a modification of the Newton-type algorithm to recover a real-valued surface impedance from phase-less far field data. Numerical reconstructions illustrate the feasibility of the methods.     

Automated measurement of ac impedance data: Acquisition and analysis

A set of algorithms (the IONICS systems) for the acquisition and analysis of ac impedance data in superionic conductivity research using an IBM PC compatible computer, have been developed and tested extensively. The algorithms can be used for acquiring ac impedance data at different frequencies as a function of temperature. The furnace can also be controlled simultaneously. The data can then be graphically displayed and numerically fitted with the appropriate curves, i.e., straight lines on Arrhenius plots and arcs of circles complex impedence plots. This paper describes the IONICS system, which consists of three modules ACQUIRE, ANALYSE and GENERATE.