Experimental and numerical analysis of a carousel stirrer for reverberation chambers
The paper analyzes the performance of a reverberation chamber equipped by a “carousel” stirring system. The working volume is positioned inside the stirrer rotating volume. More precisely, the carousel consists of several vertical strips that rotate around a central axis and having a total diameter as large as possible compared to chamber dimensions. An FDTD code, optimized for reverberation chamber simulations and tested with experimental results, is used to analyze the chamber performance as function of strip number and width. The proposed setup increases the working volume and improves the reverberation chamber behavior with respect to a traditional setup. Moreover, it needs just one motor to control the stirrer, and it does not require more complex mechanical part. All simulations are compared to measurements showing a good agreement.
A mechanical mode-stirred reverberation chamber inspired by chaotic cavities
A multivariate approach to the calculation of field-field correlation matrices is used to estimate the number of uncorrelated positions in a mode-stirred reverberation chamber (RC) inspired by chaotic cavities. The growth of the number of independent stirrer configurations is found to increase more rapidly with frequency than in a conventional RC. This is ascribed to the regular geometry forming the baseline cavity (screened room) of an RC, responsible for localizing energy and preserving regular (bouncing ball) modes. Smooth wall deformations are introduced in order to create underlying wave dynamical instability and then destroy survived regular modes. Numerical full-wave simulations are performed for a reverberation chamber with corner hemispheres and wall spherical caps. Field sampling is performed by moving a mechanical “carousel” stirrer. It is found that a wave-chaotic RC has improved performances in terms of lowest usable frequencies and number of uncorrelated cavity realizations of mechanical stirrers.
Electrophysiological evidence that a subset of midbrain dopamine neurons integrate the reward signal induced by electrical stimulation of the posterior mesencephalon
This study was aimed at determining whether midbrain dopamine (DA) neurons are trans-synaptically activated by rewarding electrical stimulation applied near the midline in the posterior mesencephalon (PM), and in the affirmative, whether the increase in firing was proportional to the rewarding effectiveness of the stimulation. Experiments were performed on male Long-Evans rats trained to lever press to obtain 400 ms trains of cathodal rectangular pulses. Following the training period, curves relating the rates of responding to the stimulation frequencies were determined at two current intensities and reward thresholds were calculated for each animal. Each animal was then anesthetized with urethane (1.2 g/kg, i.p.) and firing rate of DA neurons were recorded before, during, and after each of 50 trains (1 train/3 s) of stimulation to the PM using stimulation parameters that either sustained near threshold responding (rewarding), or failed to sustain responding (non-rewarding), in the behavioral tests. A total of 24 DA cells were recorded from 13 behaviorally trained animals, and of these, 17 (71%) responded to rewarding stimulation by an increase in firing, five (21%) were unresponsive and two (8%) were inhibited. In 12 of the 17 cells that were activated, the increase in firing was proportional to the rewarding effectiveness of the stimulation rather than the total strength of the stimulation. These results provide evidence that a subset of midbrain DA neurons are trans-synaptically activated by rewarding PM stimulation and constitute a second, or subsequent, stage of the reward-relevant pathway that integrates the PM reward signal.