Injection-seeding and self-injection-seeding of gain-switched Fabry-Pérot laser diodes

We present a simple model which allows us to predict the spectral behaviour of gain-switched Fabry-Pérot (F-P) laser diodes submitted to a weak quasi-monochromatic cw (or pulsed) injection signal. Different experiments are reported for illustration, some of them being new. The model describes the competition between the injection-driven field and the spontaneousnoise driven field during pulse build-up. The relative amplitudes of the two fields are evaluated at the gains-witching time as well as the spectral content of the injection-driven field. Different types of modal selection are found depending on the injection conditions. In the case of cw injection, there is a wide range of injection frequencies leading to single-mode emission, but two-mode lasing is also predicted for lasers exhibiting strong intrinsic chirp. These results are confirmed in experiments carried out on a 1.5 μm Fabry-Pérot laser driven by different cw dfb injection lasers. In the case of pulsed injection, the laser behaviours are similar but the model also shows the influence of the pulsed-injection arrival time on the mode selection process. This is experimentally illustrated in the case of a pulsed 1.3 μm laser operated in self-injection, the injected signal resulting from a weak spectrally-filtered optical feedback.     

Design of Polymer Coatings in Automotive Engines

Driven by economical and ecological reasons, thermoplastics based coatings were more and more used in automotive engines. Two design concepts, flame spraying and serigraphy PEEK coatings on light metal substrate, were introduced in this paper. The friction and wear behavior of PEEK based coatings were investigated systematically. Coatings with different crystallinities can be obtained when cooling speed is controlled. Among three sprayed coatings considered with different crystallinities, the one with highest crystallinity exhibits best friction and wear behavior under dry sliding condition. Under lubricated sliding condition, however, the amorphous coating gives lower friction coefficient. The micron particles such as SiC,MoS2 and graphite in composite coatings can improve significantly the coating wear resistance and have a impact on coating friction behavior.     

Nonlocal Image and Movie Denoising

Neighborhood filters are nonlocal image and movie filters which reduce the noise by averaging similar pixels. The first object of the paper is to present a unified theory of these filters and reliable criteria to compare them to other filter classes. A CCD noise model will be presented justifying the involvement of neighborhood filters. A classification of neighborhood filters will be proposed, including classical image and movie denoising methods and discussing further a recently introduced neighborhood filter, NL-means. In order to compare denoising methods three principles will be discussed. The first principle, “method noise”, specifies that only noise must be removed from an image. A second principle will be introduced, “noise to noise”, according to which a denoising method must transform a white noise into a white noise. Contrarily to “method noise”, this principle, which characterizes artifact-free methods, eliminates any subjectivity and can be checked by mathematical arguments and Fourier analysis. “Noise to noise” will be proven to rule out most denoising methods, with the exception of neighborhood filters. This is why a third and new comparison principle, the “statistical optimality”, is needed and will be introduced to compare the performance of all neighborhood filters. The three principles will be applied to compare ten different image and movie denoising methods. It will be first shown that only wavelet thresholding methods and NL-means give an acceptable method noise. Second, that neighborhood filters are the only ones to satisfy the “noise to noise” principle. Third, that among them NL-means is closest to statistical optimality. A particular attention will be paid to the application of the statistical optimality criterion for movie denoising methods. It will be pointed out that current movie denoising methods are motion compensated neighborhood filters. This amounts to say that they are neighborhood filters and that the ideal neighborhood of a pixel is its trajectory. Unfortunately the aperture problem makes it impossible to estimate ground true trajectories. It will be demonstrated that computing trajectories and restricting the neighborhood to them is harmful for denoising purposes and that space-time NL-means preserves more movie details.     

On Straight Line Segment Detection

In this paper we propose a comprehensive method for detecting straight line segments in any digital image, accurately controlling both false positive and false negative detections. Based on Helmholtz principle, the proposed method is parameterless. At the core of the work lies a new way to interpret binary sequences in terms of unions of segments, for which a dynamic programming implementation is given. The proposed algorithm is extensively tested on synthetic and real images and compared with the state of the art.

Influence of risk expectation on haptically cued corrective manoeuvres during near lane departure

Some driving devices are designed to prevent road departures. One such device, motor priming (MP), provides small pulses to the steering wheel towards the lane centre, without correcting the trajectory itself. Compared with the other lane departure warning systems, its higher efficacy has been demonstrated; it is hypothesised that this relies on the action of haptic cues at the sensorimotor level (Navarro, J., Mars, F., and Hoc, J.M., 2007. Lateral control assistance for car drivers: a comparison of motor priming and warning systems. Human Factors, 49 (5), 950-960). The way in which corrective manoeuvres, primed by MP, can be influenced by processes that operate at higher levels of cognitive control, such as risk evaluation, is an issue. Results showed that MP improved all indicators of steering efficiency, starting with reaction times. Risk expectation and situation analysis did not influence reaction times but came into play soon after the corrective manoeuvre was initiated. Thus, although MP triggered the response at the sensorimotor level, higher levels of cognition (symbolic control) quickly modulated the execution of the corrective manoeuvre. PRACTITIONER SUMMARY: This paper showed that corrective manoeuvres following directional pulses on the steering wheel (motor priming) are modulated by risk expectation. The conclusion may be of interest for designers of haptics-based automation such as lane departure warning and lane keeping assistance systems.     

束流真空管道中放电现象的实验研究

目前正在欧洲核子中心(CERN)建造的LHC(Large Hadron Collider)是世界上最大的加速器,它是一个具有高能量(7 TeV)大流强(0.53 A)的质子加速器.在它的直线节真空系统中,绝大部分的真空盒内表面将被镀上NEG薄膜.这样在又细又长的真空盒里,当有束流通过时,NEG薄膜不仅可以作为分布式吸气剂泵使用,而且NEG薄膜还具有降低二次电子发射系数的作用,因此了解NEG薄膜的性能是很重要的.     

Mixing Two Bibliography Style Languages

This article reports a twofold experience. On the one hand, we show that some concepts related to xml can be used to define a language for formatting a bibliography section put at the end of a printed work. On the second hand, we show that this new language can be used jointly with the bibliography style language of BIBT_EX in the new version of MlBIBT_EX. This should ease the transition between the “old” bibliography style language and the “new” one.     

Copper metallization influence on power MOS reliability

This work presents the influence of copper when it is introduced in very small quantities into the metallization. The techniques implemented for the characterization are those commonly available in the industry: the characterization method, which will be presented, can be used to highlight problems of copper diffusion on finished devices.