We report a wavelength-switchable fiber ring laser that includes a Bragg grating-based acoustooptic superlattice modulator. Wavelength switching of the laser emission is achieved by controlling the peak reflectivity of the different reflection bands that appear on both sides of the Bragg wavelength when a longitudinal acoustic wave propagates along the grating. 相似文献
We describe a novel microfluidic perfusion system for high-resolution microscopes. Its modular design allows pre-coating of
the coverslip surface with reagents, biomolecules, or cells. A poly(dimethylsiloxane) (PDMS) layer is cast in a special molding
station, using masters made by photolithography and dry etching of silicon or by photoresist patterning on glass or silicon.
This channel system can be reused while the coverslip is exchanged between experiments. As normal fluidic connectors are used,
the link to external, computer-programmable syringe pumps is standardized and various fluidic channel networks can be used
in the same setup. The system can house hydrogel microvalves and microelectrodes close to the imaging area to control the
influx of reaction partners. We present a range of applications, including single-molecule analysis by fluorescence correlation
spectroscopy (FCS), manipulation of single molecules for nanostructuring by hydrodynamic flow fields or the action of motor
proteins, generation of concentration gradients, trapping and stretching of live cells using optical fibers precisely mounted
in the PDMS layer, and the integration of microelectrodes for actuation and sensing. 相似文献
The present paper tries to contribute to quantifying the relationship between the amount of corrosion and cover cracking. The variables studied were: cover/diameter (c/ø), proportions of cement, w/c, cast position of the bar, transverse reinforcement and corrosion rate. The corrosion is accelerated by applying constant currents causing the rebar to act as an anode. The results indicate that the cracking process develops in two steps: generation and propagation. Radius losses of about 15–50 μm are necessary to generate the first visible crack (<0.1 mm width). The propagation follows a behaviour of the type: w (crack width in mm)=a+bx (radius loss in μm). 相似文献
In this paper, analytical functions for the estimation of the temperature-dependent behaviors of poorly and highly dispersed graphene oxide reinforced nanocomposite (GORNC) materials are studied in the framework of a machine learning-based approach. The validity of the presented models is shown comparing the results achieved from this modeling with those reported in the open literature. Also, the application of the obtained functions in solving the thermal buckling problem of beams constructed from such nanocomposites is demonstrated based on an energy-based method incorporated with a shear deformable beam hypothesis. The verification of the results indicates that the presented mechanical model can approximate the buckling behaviors of nanocomposite beams with remarkable precision. It can be realized from the results that the temperature plays an indispensable role in the determination of the buckling load which can be endured by the nanocomposite structure.
Standard numerical optimization methods become very computational time consuming when dealing with synthesis of array antenna excitation laws, especially when number of elements exceeds a few tenths. Array antenna designer needs a fast and efficient synthesis tool, since the design phase implies several reoptimizations within the definition phase, in order to satisfy tradeoffs on antagonistic requirements : performances, size, cost,… We propose the use of an efficient, from the computational time point of view, and secured, from the convergence point of view, synthesis method illustrated by two examples. The optimized solution satisfies a sta-tionarity condition, which leads to steady solutions in frequency but also with regard to errors (manufacturing, …). Based on analytical calculus performed before any numerical resolution and together with the use of fast Fourier transform algorithms, this method leads to reduced optimization times (in the order of a minute) for arrays of some tenths up to some hundred feeds, computations being performed on a pc. Two theoretical applications are presented and for each of them a computed example is also shown; moreover possible extensions are considered. 相似文献
During the last decades, the term "anhedonia", conceptualized as a incapacity to experience pleasure, have become associated with conditions as different as schizophrenia and depression. This paper deals with the conceptual and historial frames in which anhedonia was first constructed, and shows that the sources for the current fuzziness of this concept include neglect of the fact that anhedonia is conceptually parasitical upon the notion of pleasure, that it has been rather superficially conceptualized as the reduction or abolition in a "putative" function which itself is unlikely to be unitary in nature, and that it has never been quite specified whether the mechanism concerns a deficit in brain signal or not. 相似文献
In this paper, a novel three-dimensional (3-D) space-vector algorithm for four-leg multilevel converters is presented. It can be applied to active power filters or neutral-current compensator applications for mitigating harmonics and zero-sequence components using abc coordinates (referred from now on this paper as natural coordinates). This technique greatly simplifies the selection of the 3-D region where a given voltage vector is supposed to be found. Compared to a three-level modulation algorithm for three-leg multilevel converters, this algorithm does not increase its complexity and the calculations of the active vectors with the corresponding switching time that generate the reference voltage vector. In addition, the low-computational cost of the proposed algorithm is always the same and it is independent of the number of levels of the converter. 相似文献
The ??digital fabrication?? revolution being lived today, both in knowledge creation and in technological developments will become more than a simple formal exploration in architecture and design, or a set of tools exclusive to advanced industries. New tools and processes are becoming more accessible to the masses and are being shared all over the world through Internet platforms, with an open source philosophy, both in software and hardware. The collective mind that is being empowered everyday will define the future of production in the life of mankind and its relation with the environment. The role of architects, engineers, designers and many other professionals, will be reshaped and reconfigured to fit into new models of production and creation. These will need to be supported by new manufacturing platforms, knowledge generating and sharing know-how. 相似文献
Ca3Co4?xCuxO9 polycrystalline thermoelectric ceramics with small amounts of Cu have been synthesized by the classical solid state method. X-ray diffraction data have shown that all the Cu has been incorporated into the Ca3Co4O9 structure and no Cu-containing secondary phases have been produced. Apparent density measurements have shown that all samples are very similar, with densities around 75 % of the theoretical one. Electrical resistivity decreases when Cu content increases until x = 0.03 while Seebeck coefficient remains practically constant for all samples. The improvement in resistivity leads to higher power factor values than the obtained for the undoped samples. 相似文献