Volume 11 (2011): Issue 2 (January 2011)

Consider a linear regression model where some or all of the observations of the dependent variable have been either rounded or interval-censored and only the resulting interval is available. Given a linear estimator β of the vector of regression parameters, we consider its possibilistic generalization for the model with rounded/censored data, which is called the OLS-set in the special case β = Ordinary Least Squares. We derive a geometric characterization of the set: we show that it is a zonotope in the parameter space. We show that even for models with a small number of regression parameters and a small number of observations, the combinatorial complexity of the polyhedron can be high. We therefore derive simple bounds on the OLS-set. These bounds allow to quantify the worst-case impact of rounding/censoring on the estimator β. This approach is illustrated by an example. We also observe that the method can be used for quantification of the rounding/censoring effect in advance, before the experiment is made, and hence can provide information on the choice of measurement precision when the experiment is being planned.

The present paper discusses the stability studies carried out on a small number of torque transducers over the years with capacities ranging from 10 Nm to 1000 Nm. The torque transducers have been calibrated using the torque standard machine based on the written standard calibration procedure. The study reveals that the uncertainty of measurement of torque transducers has been varying appreciably and it is more for lower range. Besides, the deviation from their average values has also been studied and found to be varying through the years.

Nowadays, analysis of electromyography (EMG) signal using wavelet transform is one of the most powerful signal processing tools. It is widely used in the EMG recognition system. In this study, we have investigated usefulness of extraction of the EMG features from multiple-level wavelet decomposition of the EMG signal. Different levels of various mother wavelets were used to obtain the useful resolution components from the EMG signal. Optimal EMG resolution component (sub-signal) was selected and then the reconstruction of the useful information signal was done. Noise and unwanted EMG parts were eliminated throughout this process. The estimated EMG signal that is an effective EMG part was extracted with the popular features, i.e. mean absolute value and root mean square, in order to improve quality of class separability. Two criteria used in the evaluation are the ratio of a Euclidean distance to a standard deviation and the scatter graph. The results show that only the EMG features extracted from reconstructed EMG signals of the first-level and the second-level detail coefficients yield the improvement of class separability in feature space. It will ensure that the result of pattern classification accuracy will be as high as possible. Optimal wavelet decomposition is obtained using the seventh order of Daubechies wavelet and the forth-level wavelet decomposition.

As a kind of smart material, MR (magneto-rheological) fluid is dramatically influenced by the external magnetic field and can change from the liquid state to semi-solid state in several milliseconds. In this paper, the effect of different volume of MRF on its shear performance is proposed. A set of testing systems, including the plate-on-plate MRF shearing test rig, is built up to measure the relationship between the produced shear torque and the added volume of MRF in different current. The variation of magnetic flux density in the shear gap is measured by teslameter and simulated before and after MRF is added. The results validate the effect of volume on the shear torque experimentally.

Computing the efficiency of flat-plate collector is vital in solar thermal system testing. This paper presents the design of ZigBee enabled data acquisition system for instantaneous flat-plate collector efficiency calculation. It involves measurement of parameters like inlet and outlet fluid temperatures, ambient temperature and solar radiation intensity. The designed system has a base station and a sensor node. ZigBee wireless communication protocol is used for communication between the base station and the sensor node for wireless data acquisition. The wireless sensor node which is mounted over the collector plate includes the necessary sensors and associated signal-conditioners. An application program has been developed on LabVIEW platform for data acquisition, processing and analysis and is executed in base station PC. Instantaneous flat-plate collector efficiency is computed and reported.

Recent techniques of radiofrequency (RF) probes and preamplifiers in Magnetic Resonance Imaging (MRI) developments almost reached the physical limits of signal to noise ratio (SNR). More improvements in speed accelerations of data acquisition are very difficult to achieve. One exception, called RF phased array coils, is recently being developed very progressively. The approach is conceptually similar to phased array used in radar techniques; hence it is usually called MRI phased array coils. It is necessary to ensure independence of the individual coil channels in the array by the coil and preamp decoupling and the coil geometry optimization to get maximum benefits from this technique. Thus, the qualitative design and method for optimization of geometric properties of the coil elements in phased arrays, with aim to increase SNR, minimize the G-factor and to limit noise correlation, are proposed in this paper. By the finite element method (FEM) simulations, we obtained the sensitivity maps and inductances of the coils. The introduced program primarily calculates the Sensitivity Encoding (SENSE) G-factor along with other parameters that can be derived from sensitivity maps. By the proposed optimization algorithm, the program is capable to calculate the optimal values of the geometric coil parameters in a relatively small number of iterations.

Continuously growing technologies and increasing quality requirements have exerted thrust to the metrological institutes to maintain a high level of calibration and measurement capabilities. Force, being very vital in various engineering and non - engineering applications, is measured by force transducers. Deviations in the values observed and mentioned in the calibration certificate for force transducers may primarily be due to the creep, time loading effect and temperature effect if not properly compensated. Beside these factors, machine interaction, parasitic components etc. pertaining to the quality of the force standard machine used for calibration also contribute to the deviations. An attempt has been made by National Physical Laboratory, India (NPLI) to automate the 50 kN dead weight force machine to minimize the influence of factors other than the factors related to the machine itself. The calibration of force transducers is carried out as per the standard calibration procedure based on standard ISO 376-2004 using the automated 50 kN dead weight force machine (cmc ± 0.003% (k=2)) under similar conditions both in manual mode and automatic mode. The metrological characterization shows improved metrological results for the force transducers when the 50 kN dead weight force machine is used in automatic mode as compared to the manual mode.