Human chondrocytes in tridimensional culture.

peer reviewedCartilage was taken from the macroscopically normal part of human femoral heads immediately after orthopedic surgical operations for total prothesis consecutive to hip arthrosis. After clostridial collagenase digestion and repeated washings, chondrocytes (10(6) cells) were cultivated in a gyrotory shaker (100 rpm). Under these conditions, cells were kept in suspension and after 3 to 5 d formed a flaky aggregate which, on Day 10, became dense. These chondrocytes were morphologically differentiated: they had a round shape, were situated inside cavities, and were surrounded by a new matrix. Histochemical methods showed the presence of collagen and polysaccharides in cell cytoplasm and in intercellular matrix, and the immunofluorescence method using specific antisera (anticartilage proteoglycans and anti-type II collagen) showed that these two constituents were in intercellular matrix. The measurement of the amounts of proteoglycans (PG) released into culture medium and those present in chondrocyte aggregate (by a specific PG radioimmunoassay) showed a maximum production on Days 3 to 5 of culture, then the production decreased and stabilized (from Day 10 to the end of culture). The observed difference between the amounts of PG in aggregates after 20 d and those after 2 h of culture demonstrated that PG neosynthesis did occur during cultivation. This conclusion was supported by other results obtained by [14C]glucosamine incorporation in chondrocyte aggregates. Moreover, the aggregate fresh weight related to cell number (appreciated by DNA assay) increased significantly with culture duration. Three-dimensional chondrocyte culture represents an interesting model: chondrocytes were differentiated morphologically as well as biosynthetically and synthesized a new cartilage matrix

Strategies for two‐dimensional and three‐dimensional field computation in the design of permanent magnet motors

This study discusses strategies for the design of permanent magnet motors (PMMs) exploiting two-dimensional (2D) and 3D field models. Five most common methodologies are compared and errors arising from 2D classical models considered. Examples comparing 2D and 3D results are presented and discussed for two selected types of motors. An approach has been put forward which allows the accuracy of classical 2D models to be improved by introducing correction coefficients arising from preliminary 3D simulations. A possibility of employing quasi-3D models has also been explored for the design and analysis of PMMs with the stator and rotor lamination packets of different lengths. Comparative analysis of results has been provided arising from the 2D and 3D models for a classical and a double rotor PMM

Visual Stability and the Motion Aftereffect: A Psychophysical Study Revealing Spatial Updating

Eye movements create an ever-changing image of the world on the retina. In particular, frequent saccades call for a compensatory mechanism to transform the changing visual information into a stable percept. To this end, the brain presumably uses internal copies of motor commands. Electrophysiological recordings of visual neurons in the primate lateral intraparietal cortex, the frontal eye fields, and the superior colliculus suggest that the receptive fields (RFs) of special neurons shift towards their post-saccadic positions before the onset of a saccade. However, the perceptual consequences of these shifts remain controversial. We wanted to test in humans whether a remapping of motion adaptation occurs in visual perception

Soft-landing control of low-energy solenoid valve actuators

An automotive, fluid-control solenoid valve is composed of an electromagnetic reluctance actuator and a near-constant-force spring. Its motion profile is characterized by short closed-To-open transition times which demand fast switching, while valve lifetime improves by minimizing the impact velocity, i.e. a soft landing. In this paper, a cascaded position-and current-feedback control is designed and implemented on nonlinear, axisymmetric magnetostatic finite element simulations of a low-energy solenoid valve actuator. By applying the cascaded control, actuator performance is improved considerably, as a soft landing, a timely actuation, and an increased energy-efficient device have been obtained

General formulation of the magnetostatic field and temperature distribution in electrical machines using spectral element analysis

In this paper, a general approach to the description of the magnetic field and temperature distribution in electrical machines using the spectral element analysis is presented. In the spectral element method, higher order Legendre-Gauss-Lobatto polynomials are applied to describe the different fields. The magnetic flux distribution is derived using the magnetic vector potential, and nonlinear magnetic material is modeled based on its BH curve. The thermal model is based on the heat equation. The magnetic and thermal domains are coupled by the ohmic and iron losses, and the latter is computed using the loss separation model of Bertotti. The results are compared with the finite element method, and a good agreement is obtained for both the spatial magnetic flux density and the temperature distributions

High-order methods applied to nonlinear magnetostatic problems

This paper presents a comparison between two high-order modeling methods for solving magnetostatic problems under magnetic saturation, focused on the extraction of machine parameters. Two formulations are compared, the first is based on the Newton-Raphson approach, and the second successively iterates the local remanent magnetization and the incremental reluctivity of the nonlinear soft-magnetic material. The latter approach is more robust than the Newton-Raphson method, and uncovers useful properties for the fast and accurate calculation of incremental inductance. A novel estimate for the incremental inductance relying on a single additional computation is proposed to avoid multiple nonlinear simulations which are traditionally operated with finite difference linearization or spline interpolation techniques. Fast convergence and high accuracy of the presented methods are demonstrated for the force calculation, which demonstrates their applicability for the design and analysis of electromagnetic devices

Soft-landing control of low-energy solenoid valve actuators

\u3cp\u3eAn automotive, fluid-control solenoid valve is composed of an electromagnetic reluctance actuator and a near-constant-force spring. Its motion profile is characterized by short closed-To-open transition times which demand fast switching, while valve lifetime improves by minimizing the impact velocity, i.e. a soft landing. In this paper, a cascaded position-and current-feedback control is designed and implemented on nonlinear, axisymmetric magnetostatic finite element simulations of a low-energy solenoid valve actuator. By applying the cascaded control, actuator performance is improved considerably, as a soft landing, a timely actuation, and an increased energy-efficient device have been obtained.\u3c/p\u3