Solid state transformations of Au-Cu-Pt alloys studied by in-situ X-ray synchrotron radiation and DSC

Seven alloys of the ternary Au-Cu-Pt system, containing 75 or 76.5 wt.% Au with 0–15 wt.% Pt and heat-treated to a fully ordered condition, are examined using in-situ synchrotron radiation to determine transformation temperatures and phases formed, and to investigate mechanisms of ordering and disordering. These experiments are complemented by differential scanning calorimetry. Diffraction data show that the alloys can be separated into three groups according to their stable low-temperature ordered phase(s), namely L1₀, L1₂, or the two combined. Platinum increases transformation temperatures in comparison with binary AuCu, two-phase ordered alloys showing the highest transformation temperatures. Details of the evolution of the X-ray diffraction peak structures upon heating and cooling point to significant differences between mechanisms of disordering and ordering: whereas ordering visibly proceeds at significant undercooling by nucleation and growth, disordering appears, from the visible shifts in peak position, to progress in more homogeneous fashion within the alloy.     

Assembly and Characterizations of Bifunctional Fluorescent and Magnetic Microneedles With One Decade Length Tunability

This report presents the fabrication of bifunctional magnetic and fluorescent microneedles (µNDs) made of a ternary mixture of magnetic nanoparticles (NPs), quantum dots (QDs), and polyelectrolyte. The assembly relies on the electrostatic complexation of negatively charged NPs with positively charged polymer strands and is controlled by the charge ratio between the nanoparticle building blocks and the polymer mortar. The resulting 1D objects can be actuated using an external magnetic field and can be imaged using fluorescence microscopy, thanks to the fluorescent and superparamagnetic properties inherited from their NP constituents. Using a combination of core and surface characterizations and a state‐of‐the‐art image analysis algorithm, the dependence of the brightness and length on the ternary composition is thoroughly investigated. In particular, statistics on hundreds of µNDs with a range of compositions show that the µNDs have a log‐lormal length distribution and that their mean length can be robustly tuned in the 5–50 µm range to match the relevant length scales of various applications in micromixing, bioassays or biomechanics.     

SR3: secure resilient reputation-based routing

In this paper, we propose SR3 (which means secure resilient reputation-based routing), a secure and resilient algorithm for convergecast routing in wireless sensor networks. SR3 uses lightweight cryptographic primitives to achieve data confidentiality and unforgeability. Security of SR3 has been proven formally using two verification tools: CryptoVerif and Scyther. We made simulations to show the resiliency of SR3 against various scenarios, where we mixed selective forwarding, blackhole, wormhole, and Sybil attacks. We compared our solution to several routing algorithms of the literature. Our results show that the resiliency accomplished by SR3 is drastically better than the one achieved by those protocols, especially when the network is sparse. Moreover, unlike previous solutions, SR3 self-adapts after compromised nodes suddenly change their behavior.     

Facteur de couplage phase-amplitude des diodes lasers avec absorbant saturable

The phase-amplitude coupling factor (α-factor) is one of the fundamental parameters of semiconductor lasers. We show that this factor can be evaluated by time-resolved spectroscopic measurements in pulsed regime. Experiments are carried out with injectionseeded single-mode GaAs lasers whose active stripe includes regions of saturable absorption made by ion implantation. We show that the measured pulse downchirp is proportional to pulse energy. The downchirp amplitude is found to approach four laser cavity intermode spacings at the highest energies. Correspondingly, the ±-values can be five times higher than those reported to date in litterature. High a-values are confirmed in pulse compression experiments. Several mechanisms are proposed to interprete these new results.     

Polarization control in a vertical cavity surface emitting laser submitted to optical feedback

We study experimentally and theoretically two polarization effects in a vertical cavity surface emitting laser submitted to optical feedback. In a first experiment, we obtain flips between two linearly polarized laser modes up to a frequency of 50 MHz using an external cavity with a polarizer. In a second experiment, polarization self modulation is demonstrated up to a frequency of 2.6 GHz, using a quarter wave plate instead. Numerical calculations, based on a four levels model for the active medium, show a good agreement with the experiments.     

Models for Audiovisual Fusion in a Noisy-Vowel Recognition Task

This paper presents a study of models for audiovisual (AV) fusion in a noisy-vowel recognition task. We progressively elaborate audiovisual models in order to respect the major principle demonstrated by human subjects in speech perception experiments (the synergy principle): audiovisual identification should always be more efficient than auditory-alone or visual-alone identification. We first recall that the efficiency of audiovisual speech recognition systems depends on the level at which they fuse sound and image: four AV architectures are presented, and two are selected for the following of the study. Secondly, we show the importance of providing a contextual input linked to the Signal-to-Noise Ratio (SNR) in the fusion process. Then we propose an original approach using an efficient nonlinear dimension reduction algorithm (curvilinear components analysis) in order to increase the performances of the two AV architectures. Furthermore, we show that this approach allows an easy and efficient estimation of the reliability of the audio sensor in relation to SNR, that this estimation can be used to control the AV fusion process, and that it significantly improves the AV performances. Hence, altogether, nonlinear dimension reduction, context estimation and control of the fusion process enable us to respect the synergy criterion for the two most used architectures.     

卫星高光谱红外大气探测的正演模拟研究

利用精确的红外大气辐射传输计算模型KCARTA,模拟计算了光谱分辨率、通道光谱响应函数、光谱定标精度、大气倾斜路径和表面发射率对高光谱观测亮温的影响.正演计算的结果表明：1）提高光谱分辨率明显增加了可探测的大气亮温;2）各种内、外部因素的变化对高光谱仪器将产生远较低光谱仪器更大的观测亮温差.本研究可为我国高光谱大气探测仪器的设计以及高光谱大气探测反演算法研究的开展提供科学的参考依据.     

Paraxial approximation effect on a dielectric interface analysis

We are presenting a fast new method of analysing a dielectric interface which is assumed to be cylindrically symmetrical. It is based on a multimode Gaussian beam development. Then two different cases are considered and we show the kind of results we can expect from this process. Finally, we explain in detail the relationships between the paraxial approximation and further justified simplifications which lead to an important calculation time decrease.