Experimental study of the effect of non-circular flow geometry on the critical heat flux

An experimental study of the effect of flow geometry (circular, rectangular, triangular, and dumb-bell shaped) on the critical heat flux (CHF) was performed using R-134a as a coolant. The CHF is affected by the following geometric parameters: hydraulic-equivalent diameter, heated length, gap size, channel shape, and curvature. It may also be affected by the thermal conductivity of the wall material and wall thickness. The effect of flow geometry on CHF is influenced by flow parameters. The effect of these parameters on CHF was examined, and recommendations for predicting the CHF in non-circular geometries have been made.     

A time-varying sliding surface for robust position control of a DCmotor drive

In this paper, a new variable-structure position control law for a DC motor is proposed. The algorithm, based on a time-varying switching line, guarantees the existence of a sliding mode from the beginning of the shaft motion. Indeed, the surface is initially designed to pass through the initial representative point and subsequently moved toward a predetermined desired surface via shifting. By this means, the reaching phase is eliminated and the motor behavior is insensitive to unknown mechanical configuration changes. The algorithm has been tested in simulation and the experiment has been performed using a low-cost 16-bit microcontroller. Then, an advanced test bed is used in order to evaluate the tracking properties and the robustness capacities of the variable-structure control law with variations of the mechanical configuration     

Design techniques for orthogonal Modulated filterbanks based on a compact representation

This paper presents a method to design perfect reconstruction orthogonal modulated filterbanks having a very large number of subbands. At first, using the angular parameterization of the underlying lattice structure, the problem is formulated as an unconstrained optimization problem. Then, it is shown for two different optimization criteria (the minimization of the out-of-band energy and the maximization of the time-frequency localization) that the optimized lattice coefficients can be interpolated in two different ways. A first characterization takes advantage of the fact that the angles related to successive polyphase components of the prototype filter have a smooth behavior. A new parameterization, named compact representation, is therefore introduced, which shows that a linear increase of the number of parameters with respect to the number of subbands can be avoided with practically no loss of accuracy. A second observation concerns the also smooth behavior of each angular parameter when considering an increasing number of subbands. The efficiency of the two approaches is illustrated by the design of filterbanks with a large number of subbands going from 32 up to 4096, including prototype filters up to a length of 32 768.     

Fuzzy logic applied to speed control of a stepping motor drive

Nowadays, thanks to the development of microprocessors, stepping motors are widely used in robotics and in the numerical control of machine tools where they have to perform high-precision positioning operations. Nevertheless, the variations of the mechanical configuration of the drive, which are common to these two applications, can lead to a loss of synchronism for high stepping rates. Moreover, the classical open-loop speed control is weak and a closed-loop control becomes necessary. In this paper, the fuzzy logic principle is applied to control the speed of a stepping motor drive with feedback. An advanced test bed is used in order to evaluate the tracking properties and the robustness capacities of the fuzzy logic controller when variations of the mechanical configuration occur. The experiment has been performed using a low-cost 16 bit microcontroller in order to verify the design performance     

Do nasal ciliary changes reflect bronchial changes? An ultrastructural study

Ciliary dyskinesia is characterized by recurrent respiratory tract infections secondary to abnormal ciliary structure and function. The diagnosis of ciliary dyskinesia is based on the detection of axonemal ultrastructural abnormalities (AUA) is respiratory mucosa samples. In most cases, the diagnosis of AUA is made on samples obtained from nasal ciliated cells with little discomfort to the patient. However, no studies have been performed in the same patient to confirm whether nasal samples reflect bronchial ciliary changes. To answer this question and to determine whether it is necessary to sample bronchial cells for the diagnosis of ciliary dyskinesia, we investigated 12 patients (between the age of 5 and 63 yr) with chronic sputum production. The presence of situs inversus, bronchiectasis, chronic sinusitis, and sterility was investigated to determine an inherited disorder. Two groups were established: Group 1 = six patients with an inherited disorder and Group 2 = six patients without evidence of an inherited disorder. Samples were obtained by brushing or biopsy of nasal and bronchial mucosa and were processed for transmission electron microscopy. In Group 1, the mean AUA was 65.2 +/- 11.4%. The following predominant axonemal defects were found: absence of dynein arms (DA) (four patients), central complex abnormalities (CC) (one patient), and various AUA (one patient). Nasal and bronchial samples correlated significantly for total AUA (r' = 1, p < 0.01) and for outer DA defects (r' = 0.96, p < 0.05). A good but not significant correlation was found for inner DA (r' = 0.83) and peripheral microtubule (PM) defects (r' = 0.71). In Group 2, the mean AUA was 9.6 +/- 2.3%.(ABSTRACT TRUNCATED AT 250 WORDS)     

Electrochemical aspects of the H2SO4SO2 thermoelectrochemical cycle for hydrogen production

Oxidation of SO₂ has been studied on electrode surfaces in sulfuric acid solutions as a function of acid concentration and temperature. The majority of work was conducted on platinum electrodes of high surface area. Some of the limitations of the reaction have been determined. The reaction is highly irreversible; however, the final product is sulfuric acid, apparently produced via a dithionate intermediate. The reaction rate at constant potential vs a hydrogen electrode in the same solution is strongly dependent on sulfuric acid concentration. Temperature has little effect on the rate. The reaction is not “catalytic” in the normal electrochemical sense: for example, adsorbing metals (e.g. Pt) show rates similar to those on non-adsorbing metals (e.g. Au). Carbons, graphites and carbides are inactive. In some potential and SO₂ partial pressure ranges, the process has a very low SO₂ reaction order. This can ensure relatively uniform hydrogen current density in a practical system, at high SO₂ conversion rates. The limiting steps in engineered SO₂-depolarized hydrogen production cells are reviewed.     

Analysis, design, and implementation of two-channel linear-phasefilter banks: a new approach

The problem of designing two-channel perfect-reconstruction FIR filter banks with linear-phase analysis and synthesis filters is revisited. Based on a new algebraic formulation, all the possible factorized forms for this two-band filter bank are derived. We thus obtain complete and canonical solutions for the filter banks, composed of odd-order symmetric and antisymmetric filters (type-A systems) and for those built with symmetric even order filters (type-B systems). A strong characteristic of these new cascade structures, which, until now, had not been identified, is related to a defectivity property. Taking this into account is the key issue to cover all the FIR solutions and to design cascade structures being robust to the quantization of their parameters. Design examples are provided that illustrate our method