Simulations and experiments on active vibration control of a plate with integrated piezoceramics

A frequency domain model on the basis of a rectangular plate with symmetrically integrated piezo-elements is extended to time domain suitable to use for on-line active vibration control simulations. Electromechanical effects of piezoceramic elements such as mass, stiffness and actuation are included in the model. The model is coupled to a control simulator comprising both Feedforward and Feedback algorithms. Simulations are made using the model to investigate some important aspects that may be encountered in practice such as system identification and control performance for different configurations. Finally, both controllers are implemented in DSP boards and experiments are carried out. Results demonstrate the representativeness of the system model and the efficiency of the algorithms for a SISO system. It is noted that the model developed in this paper is accurate and flexible enough to represent the real system in a control situation. The whole on-line simulation process is capable of reproducing reliable results to guide implementation of controllers.     

Intrinsic properties of the optical coupling between axisymmetric Gaussian beams

On the basis of the overlap integral method, an approximate analytical model is derived to estimate the coupled optical power between axisymmetric Gaussian beams when transverse, axial, and angular misalignments simultaneously exist in three dimensions. Seven optical properties are derived from a detailed analysis of the model. Because the model is an approximate analytical solution to the overlap integral method, the existence of each property is also investigated by a numerical solution. Results show that all seven properties are intrinsic to the optical coupling phenomenon between Gaussian beams. Because numerous single-mode device-to-fiber coupling systems can be well described by use of Gaussian beams, the seven properties provide a solid basis to develop model-based algorithms for single-mode device-to-fiber alignment automation.     

Influence of smoothing window length on electromyogram amplitudeestimates

A systematic, experimental study of the influence of smoothing window length on the signal-to-noise ratio (SNR) of electromyogram (EMG) amplitude estimates is described. Surface EMG waveforms were sampled during nonfatiguing, constant-force, constant-angle contractions of the biceps or triceps muscles, over the range of 10%-75% maximum voluntary contraction. EMG amplitude estimates were computed with eight different EMG processor schemes using smoothing length durations spanning 2.45-500 ms. An SNR was computed from each amplitude estimate (deviations about the mean value of the estimate were considered as noise). Over these window lengths, average ± standard deviation SNR's ranged from 1.4±0.28 to 16.2±5.4 for unwhitened single-channel EMG processing and from 3.2±0.7 to 37.3±14.2 for whitened, multiple-channel EMG processing (results pooled across contraction level). It was found that SNR increased with window length in a square root fashion. The shape of this relationship was consistent with classic theoretical predictions, however none of the processors achieved the absolute performance level predicted by the theory. These results are useful in selecting the length of the smoothing window in traditional surface EMG studies. In addition, this study should contribute to the development of EMG processors which dynamically tune the smoothing window length when the EMG amplitude is time varying     

Model-based far-field alignment algorithm for Gaussian beamlike single-mode optical devices

Single-mode device-to-fiber alignment automation is usually achieved with a classical mathematical optimization approach. We present a different approach, which is based on the identification of particular intrinsic characteristics of the coupled optical power and on estimating residual axial, transverse, and angular misalignments in the far field. Such a model-based approach is based on the physical nature of the optical coupling phenomenon and can replace or be complementary to already known automated alignment methods. An alignment algorithm is described and validated experimentally using two single-mode fibers as Gaussian beam emitter and receiver.     

Experimental investigation of the intrinsic properties of the optical coupling between axisymmetric Gaussian beams

Continuing a previous analytical and numerical work, an experimental investigation of seven intrinsic properties of the optical coupling between axisymmetric Gaussian beams is presented. In this study, two single-mode fibers are used as the receiver and the emitter and a five-axis nanopositioning system is used to investigate optical coupling properties by moving one fiber relative to the other. Experiments demonstrate the existence of sufficiently accurate hyperbolic, parabolic, and linear trends for the optical coupling phenomenon, which can be useful for developing model-based alignment algorithms.     

One- and two-dimensional single-mode differential fiber-optic displacement sensor for submillimeter measurements

Using the overlap integral method and the Gaussian approximation for the single-mode fiber-optic field, the working principle of one- and two-dimensional differential fiber-optic displacement sensors for submillimeter measurements is demonstrated. The sensors consist of one emitting fiber and two or three receiving fibers, respectively, for the one- and two-dimensional sensors. Sensor responses are intrinsically linear over a wide range of travels. Moreover, for the two-dimensional sensor, each axis of displacement can be measured independently. Sensor responses are simulated experimentally using a highly precise robot. Linearity, travel, and sensitivity are characterized for the different gap distance between the emitting and receiving fibers. A design chart that includes nonlinearity error, travel, sensitivity, and gap is finally proposed.     

Frame loads accuracy assessment of semianalytical multibody dynamic simulation methods of a recreational vehicle

The design of a vehicle frame is largely dependent on the loads applied on the suspension and heavy parts mounting points. These loads can either be estimated through full analytical multibody dynamic simulations, or from semi-analytical simulations in which tire and road sub-models are not included and external vehicle loads, recorded during field testing, are used as inputs to the wheel hubs. Several semi-analytical methods exist, with various modeling architectures, yet, it is unclear how one method over another improves frame loads prediction accuracy.

This study shows that a semi-analytical method that constrains the vehicle frame center of gravity movement along a recorded trajectory, using a control algorithm, leads to an accuracy within 1% for predicting frame loads, when compared to reference loads from a full analytical model. The control algorithm computes six degrees of freedom forces and moments applied at the vehicle center of gravity to closely follow the recorded vehicle trajectory. It is also shown that modeling the flexibility of the suspension arms and controlling wheel hub angular velocity both contribute in improving frame loads accuracy, while an acquisition frequency of 200 Hz appears to be sufficient to capture load dynamics for several maneuvers. Knowledge of these loads helps engineers perform appropriate dimensioning of vehicle structural components therefore ensuring their reliability under various driving conditions.

     

Critique des fondements épistémologiques des approches spirituelles en psychologie.

The aim of the present article is to expose a rather disconcerting aspect of psychology which is, the coexistence within it of both a scientific and a spiritual discourse. First, a clear definition of spirituality is presented. This will enable us to explain how problematic this concept is for science generally and for psychology in particular. Secondly, we will present three psychological approaches that fit our previous definition of spirituality: integrationism, logotherapy and the transpersonal approach. Starting from our previous discussion and critic of spirituality, we will see how, each in their own may, these three approaches fall in contradiction with the established facts and method of modern science. (PsycINFO Database Record (c) 2010 APA, all rights reserved)