传输/反射法测量复介电常数的若干问题

研究了传输／反射法测量线性材料复介电常数εr的厚度谐振、多值性等问题，得到了解决这些问题的有效方法。通过改进NRW传输／反射法，由散射参数直接得到了归一化特性阻抗与传播常数，从而可以把已有的三个确定复介电常数的方程用到NRW传输／反射法中。联合应用这三个方程解决了上述问题，这使得人们可以用传输／反射法对任意厚度的样品在任意频率上进行复介电常数的稳定测量。用波导取样器与同轴线取样器分别得到的实验结果证明了此方法的有效性与可实现性。     

In vivo Cellular Uptake,Degradation, and Biocompatibility of Polyelectrolyte Microcapsules

Polyelectrolyte microcapsules are made by layer‐by‐layer (LbL) coating of a sacrificial template, followed by decomposition of the template, to produce hollow microcapsules. In this paper, we report on the in vivo cellular uptake, degradation and biocompatibility of polyelectrolyte microcapsules produced from alternating dextran sulphate and poly‐L‐arginine layers on a template of calcium carbonate microparticles. We show that a moderate tissue reaction is observed after subcutaneous injection of polyelectrolyte microcapsules in mice. Within sixteen days after subcutaneous injection, most of the microcapsules are internalized by the cells and start to get degraded. The number of polyelectrolyte layers determines the stability of the microcapsules after cellular uptake.     

Ultrahydrophobic PMMA micro- and nano-textured surfaces fabricated by optical lithography and plasma etching for X-ray diffraction studies

Polymeric (PMMA) ultrahydrophobic surfaces with contact angles up to about 170° have been fabricated and used in the context of synchrotron radiation experiments on biological droplets. The different microfabrication processes included either an optical lithography phase followed by a plasma texturing one or a single step deep reactive ion etch attack.The drying of several biological solution droplets has been monitored. Room temperature evaporation experiments (lysozyme, lactalbumin, cytochrome C, doxorubicin and synthesized peptides) finally result in the formation of easily detachable hollow residuals because of the low interaction between the ultrahydrophobic substrate and the aqueous droplet while pilot experiments (bovine insulin) in a sitting-drop environment bring to the formation of well defined crystals. Recent results about in situ X-ray diffraction experiments by SAXS & WAXS (Small and Wide Angle X-ray Scattering) μ-beam techniques confirm that the presence of such surfaces influences the formation of crystal or fibril structures. These substrates represent indeed a suitable support to study biological and inorganic droplets in a near contact-free environment exploiting the homogeneous evaporation rate induced by the ultrahydrophobicity of the system.     

Novel Low‐Power High‐dB Range CMOS Pseudo‐Exponential Cells

In this paper, novel CMOS pseudo‐exponential circuits operating in a class‐AB mode are presented. The pseudo‐exponential approximation employed is based on second order equations. Such terms are derived in a straightforward way from the inherent nonlinear currents of class‐AB transconductors. The cells are appropriate to be integrated in portable equipment due to their compactness and very low power consumption. Measurement results from a fabricated prototype in a 0.5 μm technology reveal a range of 45 dB with errors lower than ±0.5 dB, a power consumption of 100 μW, and an area of 0.01 mm².     

燃煤飞灰的显微颗粒类型与显微结构特征

利用光学显微镜和扫描电子显微镜对不同燃煤煤种和锅炉类型电厂飞灰进行观察研究,建立了燃煤飞灰微颗粒的系统分类方案,并揭示出各类颗粒的显微结构特征,首先根据物质成分将飞灰分出硅铝质,铁质,钙质和炭粒4个组,然后根据微观形貌和内部结构分出16种显微颗粒类型。研究发现空心微珠和子母珠是飞灰中普遍存在的显微颗粒类型,不仅广泛分布于不同粒级的硅铝质颗粒中,而且常见于钙质和铁质颗粒中,发现并命名了多孔微珠这一新的显微颗粒类型;在多种颗粒中广泛分布的次级细小灰球的发现,为飞灰显微结构的成因研究提供了科学依据。     

In situ study of the formation of silicide phases in amorphous Co-Si mixed layers

We investigate Co silicide phase formation when extra Si is added within an as deposited 50 nm Co film. The addition of Si is investigated for both the Co/SiO₂ and Co/Si(1 0 0) system. A series of 10 Co-Si mixed films with a Si content varying from 21 to 59 at.% was prepared and investigated during annealing with in situ X-ray diffraction. The oxide system is used as reference system to identify phases that initially crystallize in an amorphous mixture of a given composition. Multiple phases can nucleate, and the temperature of crystallization depends on the Co-Si atomic ratio. Upon heating of the Co(Si)/Si system, the first reaction is a similar crystallization reaction of the Co(Si) mixture. Once the first phase is formed, one has the normal system of a silicide phase in contact with an unlimited amount of Si from the substrate, and the sequential phase formation towards CoSi₂ is established. For deposited layers of composition ranging from 48%Si to 52%Si, the CoSi is the first phase to form and increasing the amount of Si leads to a remarkable improvement of the thermal stability of CoSi on Si(1 0 0). CoSi₂ nucleation was extensively delayed by 150 °C compared to the reaction observed from a pure Co film on Si(1 0 0). Electron backscatter diffraction measurements reveal that in this range, the gradual Si increase systematically leads to bigger CoSi grains (up to 20 μm). This shows that the grain size of the CoSi precursor strongly affects the nucleation of the following CoSi₂ phase. Laser-light scattering measurements suggest that adding more than 42%Si reduces the roughness of the CoSi₂ layer.     

Optical micro-structures fabricated on top of optical fibers by means of two-photon photopolymerization

In this work we report, for the first time to our knowledge, the possibility to fabricate various structures, with good optical proprieties, on the top of optical fibers, using the two-photon lithography (TPL) technique. We show the convenience of this approach to quickly create generic 3D shapes using a single set-up by contrast to past shape-dependent methods. A set of different structures are fabricated and characterized to demonstrate the versatility of this approach and their high optical quality.     

A new decoder for the optimum recovery of nonadditive watermarks

Watermark detection, i.e., the detection of an invisible signal hidden within an image for copyright protection or data authentication, has classically been tackled by means of correlation-based techniques. Nevertheless, when watermark embedding does not obey an additive rule, or when the features the watermark is superimposed on do not follow a Gaussian pdf, correlation-based decoding is not the optimum choice. A new decoding algorithm is presented here which is optimum for nonadditive watermarks embedded in the magnitude of a set of full-frame DFT coefficients of the host image. By relying on statistical decision theory, the structure of the optimum is derived according to the Neyman-Pearson criterion, thus permitting to minimize the missed detection probability subject to a given false detection rate. The validity of the optimum decoder has been tested thoroughly to assess the improvement it permits to achieve from a robustness perspective. The results we obtained confirm the superiority of the novel algorithm with respect to classical correlation-based decoding.     

BaTiO_3纤维/PUIPN_s纳米复合体系导电性能研究

用红外光谱跟踪确定了同步互穿聚合物网络的形成工艺 ,并制成其梯次化复合涂层 ,TEM检测表明两相间的相畴尺寸在纳米级范围内 ;在此基础上 ,以钛酸钡超细纤维对此网络体系进行复合 ,确定偶联剂的加入量及复合工艺 ,测量了不同复合量下材料的电阻率 ,并考察了其伏安特性。此工作可为拓展此类材料的应用领域提供有价值的参考数据。     

Physical study of the dissipated power area in high electron mobility transistors for thermal modelling

The hot area in power transistors due to the power dissipation is determined from a 2D-hydrodynamic model. The power is calculated everywhere in the device from the knowledge of the physical quantities (current density, electric field). The hot area is determined accurately to be coupled to a thermal modelling giving the temperature everywhere in the device [J. Park, M.-W Shin, C.-C. Lee, Thermal modeling and measurement of GaN-based HFET devices, IEEE Electron Device Lett. 24(7) (2003) 424-426 [1]; J.-C Jacquet, R. Aubry, H. Gérard, E. Delos, N. Rolland, Y. Cordier, A. Bussutil, M. Rousseau, S.L. Delage, Analytical transport model of AlGaN/GaN HEMT based on electrical and thermal measurement, 12th GAAS Symposium, Amsterdam, 2004, pp. 235-238 [2].]. The method is applied to HEMTs (high electron mobility transistors) based on GaAs or GaN. It is shown that the hot area depends on the bias conditions and on the transistor gate recess topology.