Robust control of a class of non-linear systems and applications to robotics

This paper addresses the problems of designing and analysing a set of stable and robust controls for nonlinear systems whose equations are representative of mechanical systems such as robot manipulators. When applied to robotics, this theoretical analysis proves that most of the control schemes which are used in practice or proposed in the literature, ranging from the simplest PD control to more complex controls such as adaptive controls or controls based on the so-called ‘computed torque method’, are liable to perform equally well if the manipulator is perfectly rigid and ideal sensors are used. Consequently, it appears that the main justification for using elaborate schemes is to avoid the need for including large constant control gains when high performance is demanded. At this stage, the analysis suggests the possibility of using more flexible non-linear control gains as a way of improving all schemes.     

Stress-wave attenuation in thin structures by ultrasonic through-transmission

The steady-state amplitude of the output of an ultrasonic through-transmission measurement is analyzed and the result is given in closed form. Provided that the product of the input and output transduction ratios, the specimen-transducer reflection coefficient, the specimen-transducer phase-shift parameter, and the material phase velocity are known, this analysis gives a means for determining the through-thickness attenuation of an individual thin sample. Multiple stress-wave reflections are taken into account, and so signal echoes do not represent a difficulty. An example is presented for a graphite fiber epoxy composite (Hercules AS/3501-6). Thus, the technique provides a direct method for continuous or intermittent monitoring of through-thickness attenuation of plate structures which may be subject to service structural degradation.     

Pulse broadening in multimode graded-index fibres

A closed-form expression is obtained for pulse broadening in graded-index fibres with k2(r)=1?r2+?2r4+?+?nr2n. Pulse broadening for k2(r)=1?r2+0.615r4+70r6 and r<0.1 is 12 times smaller than for square-law fibres if material dispersion is neglected.     

Momentum of photons in dielectrics

A confusion is sometimes made in the literature between the mass-carrying momentum of a photon, which is inversely proportional to the refractive index of the medium in which it propagates, and the momentum taken up by an absorber located in a fluid, which is directly proportional to the refractive index of the fluid. The distinction between these two momenta is clarified by considering an artificial dielectric.     

CRAPE DRYING : FROM SAMPLE BEHAVIOUR TO THE DRIER PROJECT

A drier project necessitates the efficient formulation of the behaviour of product samples. When the temperature gap is great, the drying rate must make explicit the influence of the thnc air parameters : temperature, moisture, velocity. The case of the grape demonsnates that the adimensional expression formulated by Van Meel and Keey. must be completed in order to be adjusted to experiments.

The hot air drier model composed of the equations of conservation and thin layer drying rate can sometimes be simplified into a form of analytic integral equation around the drying rate. W e drying can be considered generally as adiabatic.

Two examples of grape driers are presented and show the value of simplified tools for the project. In a tunnel drier with a high air temperature one can speak of the celerity of a drying front which progress along the trolleys. In a short drier connected to an agricultural solar collector, the integration of the drying rate takes into account the variation of the meteorological data.     

Apparent total alpha1-antitrypsin deficiency: report of a case

A 29-year-old female, with chronic renal failure and chronic bilateral emphysema, was admitted with severe uremia and septicemia secondary to multiple abscesses in the right kidney. Her condition improved after right nephrectomy. Pulmonary function studies showed marked obstructive and restrictive lung disease consistent witht the diagnosis of primary emphysema. On biochemical and histological examination, the liver was found to be normal. Alpha1-antitrypsin could not be demonstrated in the patient's serum at normal pH by any of the known techniques, but protein molecules with alpha1-antitrypsin antigencity were found at pH 4.8; this suggests a pH-dependent structural difference in alpha1-antitrypsin protein. Starch gel electrophoresis gave a multibanding pattern not previously described. A new form of apparent total alpha-1-antitrypsin deficiency is postulated.