Modal control of beam flexural vibration

An active control system was developed to control the flexural vibrations of a beam with a modal filtering with only one secondary actuator. Segmented piezoelectric actuators and sensors were used for driving and sensing the bending beam vibrations. The primary actuator was fed by a broadband random disturbance signal in order to excite the first five modes of the structure. However, only the second to fifth modes were controlled. The control algorithm was implemented on a DSP board and the input and output signals were filtered using high order low pass filters. These filters, implemented on the DSP board avoid the degrading effect on the control performances of the higher order modes and which are not controlled. The modal filtering was achieved by computing. To this end, it is based on a previous identification procedure. This latter models, in one step, the dynamics of the structure and also the transfer function of the electronic circuits of the controller. The identified filtered modes were then used to compute the gain matrix using a LQR technique (linear quadratic regulator). Simulations of the active control were carried out and practical implementation of the control algorithms was performed. Experimental and simulation results were then compared and discussed.

Characterization of the mechanical nonlinear behavior of piezoelectric ceramics.

A characterization of the nonlinear behavior with high signal excitation in piezoceramic resonators was carried out. The behavior of power devices working at resonance, in which high strains are involved, is explained. A theoretical model previously described is used to explain the motional impedance variation proportional to the square of the motional current. This impedance increase DeltaZ is independent of the frequency and explains: the nonlinear elasticity that produces the A-F effect, the nonlinear mechanical losses that increase greatly close to the resonance, and the hysteresis phenomenon produced with frequency sweeps. Different methods for measuring the mechanical nonlinear coefficients of piezoceramics with high signal excitation are presented. An experimental method is proposed to measure the mechanical loss tangent and the compliance variations as a function of the mean square strain in the piezoceramic. This consists in measuring the maximum admittance and the series resonance frequency for downward frequencies. At this jumping point, the phase angle remains zero whatever the amplitude of the excitation. Two main coefficients characterizing the material mechanical nonlinearity are deduced. Experimental measurements were carried out to compare the nonlinearity of different ceramic materials in longitudinal and transverse mode.

A piezomotor using longitudinal actuators.

A new travelling wave type ultrasonic motor has been developed which uses longitudinal piezoelectric actuators to generate a progressive wave on the surface of a metallic ring. The rotor, which moves through frictional force, is pressed on this elastic plate. This paper deals with the motor construction and its characteristics. Theoretical modelling and experimental performances obtained with the motor prototypes are reported. A maximum of 0.8 Nm and a no-load rotation speed of 120 rpm have been obtained with a double rotor prototype. The results indicate that this piezomotor is proved to operate successfully at a mechanical output power of 4 W.

[Primary leiomyosarcoma of the pulmonary artery. Apropos of a case. Review of the literature]. / Léiomyosarcome primitif de l'artère pulmonaire. A propos d'un cas: revue de la littérature.

A 59-year-old woman hospitalised because of dyspnea and a heart murmur in a context of pyrexia was found to have evidence of obstruction of the pulmonary arterial system, clearly defined by ultrasonography, catheterisation and angiography and Imatron scan. The particular feature of this fifth reported case of pulmonary artery leiomyosarcoma is its documentation by transesophageal ultrasonography and tumor biopsy during catheterisation. Surgery with partial excision of the tumor was followed by survival for 6 months, bearing in mind the absence of chemo- or radiosensitivity of this type of tumor. Cases from the literature are reviewed.

Uptake and binding of serotonin by primary cultures of mouse astrocytes.

Primary cultures of glia contain a high glial fibrillary acidic protein level and exhibit important glutamine synthetase activity. They take up serotonin via a high affinity carrier-mediated system with a Km of micromolar range. The Km of this transport process does not vary during cell growth or maturation; however, during the last period of morphological change induced by dibutyryl cyclic AMP, an increase in Vmax is observed. Chlorimipramine, fluoxetine and fenfluramine at 10-4 M inhibit this uptake. 3H-5-HT still binds to partially purified astrocytic membranes on a single type of site. During growth, neither KD nor Bmax were modified. During the maturation period, KD decreased to about 50% of its control level. Methysergide inhibits that binding.

Benzodiazepine receptors on primary cultures of mouse astrocytes.

Benzodiazepines bind to glial membranes on a single type of site, with a high affinity (KD = 5 x 10(-9) M) on about 100 fmol of sites per mg protein. The number of binding sites is increased when the membranes are treated with Triton X-100. Antiepileptic drugs such as clonazepam and phenobarbital and hypnotic drugs such as Ro-11-3128 and Ro-11-6896 are able in pharmacological concentrations to displace [3H]flunitrazepam from its glial binding sites.

Effect of prostaglandins and dibutyryl cyclic AMP on the morphology of cells in primary astroglial cultures and on metabolic enzymes of GABA and glutamate metabolism.

Prostaglandins (PGE1) and dibutyryl cyclic AMP (dBc AMP) induce similar morphological changes in astrocytes obtained in primary cultures. PGE1 and dBc AMP increased 2 enzymes of GABA and glutamate metabolism, GABA-T and AAT, but did not modify GDH and GLN-S. Prostaglandins probably affect the cAMP content of glial cells and act in the same way as dBc AMP on glial cell differentiation.

Two forms of GABA transaminase in pig brain: purification and properties.

Two forms of GABA transaminase which could be distinguished by ion-exchange chromatography have been separated and purified in pig brain. The two forms have different Km values for alpha-ketoglutarate and show different degrees of inhibition by various salts. Although the two forms are separable, they have identical antigenic properties, pH optima, and NH2 terminal amino acid composition, and they appear to be of the same molecular size. The biological significance or the relationship between multiple forms of GABA transaminase is not yet understood.

Cyclic guanosine monophosphate in primary cultures of glial cells.

Cyclic GMP was found in primary cultures of glial cells obtained by dissociation of newborn mouse brain hemispheres. Its basal level (0.52 pmoles/mg cell protein) was as high as that found in adult mouse brain cortex but 10 times lower than in cerebellum. When glia were grown in the presence of dBcAMP, astrocytes changed their morphology; cGMP level increased and reached about 8 to 10 times the basal value. This increase was dose dependant with cAMP and was enhanced by the presence of 5mM Theophylline. Two hypothesis are discussed, either a direct action oc cAMP on glial cGMP metabolism or an indirect one on the protein activator of cGMP phosphodiesterase.

In vivo effects of noradrenaline and noradrenergic receptor agonists and antagonists on rat cerebellar cyclic GMP levels.

Cerebellar cyclic GMP levels can be altered by neurotransmitters and their receptor agonists and antagonists. In this study, we investigated the action of noradrenaline and certain drugs affecting alpha- and beta-adrenoceptors on rat cerebellaceptor agonists such as methoxamine and phenylephrine increased cGMP levels. alpha-Adrenoceptor antagonists such as phentolamine, phenoxybenzamine and ARC 239 decreased cGMP levels, whereas yohimbine and piperoxane which are known to act as presynaptic alpha-adrenoceptor antagonists had no effect. The action of clonidine which decreased cGMP levels at low doses was probably due to the fact that this adrenoceptor agonist inhibited the release of noradrenaline from adrenergic nerve terminals, since piperoxane injected prior to clonidine antagonized the effect of clonidine on cerebellar cGMP, and since pretreatment of the animals with 6-hydroxydopamine partially antagonized the effect of clonidine. Isoproterenol, a beta-noradrenergic agonist had no effect on cerebellar cGMP levels. Propranolol, a beta-noradrenergic antagonist decreased cGMP levels. Phenoxybenzamine or propranolol injected prior to noradrenaline decreased cerebellar cGMP.

Effect of fenfluramine administration on synaptosomal uptake of some neurotransmitters and on synaptosomal enzymes which metabolise GABA.

Fenfluramine has been considered to deplete neuronal 5-hydroxytryptamine (5-HT). This compound is able to reduce the synaptosomal uptake of 5-HT and other neurotransmitters such as GABA and glutamic acid (Glu). The effects of fenfluramine on these three compounds considered as neurotransmitters are different. The inhibition is of competitive type for 5-HT and non-competitive for GABA and Glu. Concerning the enzymes involved in GABA synthesis and degradation, Fenfluramine increases Glutamic acid decarboxylase activity and decreases GABA-trasaminase activity in synaptosomes. Decreased synaptosomal GABA levels could be attributed to a lower uptake. An enzymatic regulating system may be responsible in restoring the GABA level. A similar mechanism concerning serotonin has been previously suggested (Costa et al., 1971).

GABA metabolism in cultured glial cells.

GABA-transaminase has been characterized in cultured astrocytes. It is identical to the synaptosomal and perikaryal enzyme in terms of charge, molecular weight, and stability, but it differs in its affinity for GABA, which is much higher in the glial compartment. GABA-transaminase has been shown to be inducible by high GABA concentrations, which suggests that astrocytes have the possibility not only to transport GABA but also to metabolize the amino acid which is taken up.

Effect of L-glutamate and kainate on rat cerebellar cGMP levels in vivo.

L-glutamate and kainate administered intracerebroventricularly (i.c.v.) both produced dose-dependent increases in rat cerebellar cGMP. The increased cGMP produced by L-glutamate, but not that produced by kainate, could be completely abolished by the glutamate antagonist glutamate diethylester which had no effect alone. The data suggest that L-glutamate and kainate may be acting upon different sub-populations of glutamate receptors, both of which may be involved in the regulation of cerebellar cGMP levels.