Second harmonic generation in optical fibers

We describe second harmonic generation in silica based optical fibers as a function of time and the preliminary explanations published so far in the literature. The latter deal essentially with the electromagnetic aspect of the phenomenon. By a different way of analysis (closer to material science), we emphasize on the structural defects active in this non-linear property.     

针对工业应用的汽车通信网络

从家庭住屋到大型住宅楼、办公楼及工厂,建筑物自动化是越来越发展的一个极重要方面。受需要增强安全性和提高能源效率这两项21世纪最重要优先任务的推动,建筑物和工业厂房中运行的系统变得越来越复杂,互连程度也不断提高。     

A comparison between thermosonics and thermography for delamination detection in polymer matrix laminates

Over recent decades, industry has used more and more frequently composite laminates. If many Non-Destructive Testing (NDT) methods have already been developed to test such structures, detecting defects in polymer matrix laminates remains difficult. After a short overview of the main existing NDT methods, this paper focuses on two techniques which appear to be very promising: thermosonics and infra-red (IR) thermography. For thermosonics tests, an ultrasonic horn mechanically loads the sample, while an IR camera records the defect heating. For thermography tests, the heating is due to an optical wave. If minor improvements on the test device are presented for thermosonics tests, IR thermography tests are achieved with a CO₂ laser as excitation source, which is a very innovative approach. This paper provides many experimental results obtained from an aeronautical carbon-epoxy plate with a central delamination. It is shown that both methods are very suitable for detecting such a defect, even if each method has its own advantages. Finally, some improvements to further optimize the thermography tests are proposed in conclusion.     

Milk yield loss in response to feed restriction is associated with mammary epithelial cell exfoliation in dairy cows

In dairy cows, feed restriction is known to decrease milk yield by reducing the number of mammary epithelial cells (MEC) in the udder through a shift in the MEC proliferation–apoptosis balance, by reducing the metabolic activity of MEC, or both. The exfoliation of MEC from the mammary epithelium into milk is another process that may participate in regulating the number of MEC during feed restriction. The aim of the present study was to clarify the mechanisms that underlie the milk yield loss induced by feed restriction. Nineteen Holstein dairy cows producing 40.0 ± 0.7 kg/d at 77 ± 5 d in milk were divided into a control group (n = 9) and a feed-restricted group (n = 10). Ad libitum dry matter intake (DMI) was recorded during a pre-experimental period of 2 wk. For 29 d (period 1), cows were fed either 100 (control) or 80% (feed-restricted) of their ad libitum DMI measured during the pre-experimental period. Then, all cows were fed ad libitum for 35 d (period 2). Milk production and DMI were recorded daily. Blood and milk samples were collected once during the pre-experimental period; on d 5, 9, and 27 of period 1; and on d 5, 9, and 30 of period 2. Mammary epithelial cells were purified from milk using an immunomagnetic method to determine the rate of MEC exfoliation. Mammary tissue samples were collected by biopsy at the end of each period to analyze the rates of cell proliferation and apoptosis and the expression of genes involved in synthesizing constituents of milk. Feed restriction decreased milk yield by 3 kg/d but had no effect on rates of proliferation and apoptosis in the mammary tissue or on the expression of genes involved in milk synthesis. The daily MEC exfoliation rate was 65% greater in feed-restricted cows than in control cows. These effects in feed-restricted cows were associated with reduced insulin-like growth factor-1 and cortisol plasma concentrations. When all cows returned to ad libitum feeding, no significant difference on milk yield or MEC exfoliation rate was observed between feed-restricted and control cows, but refeeding increased prolactin release during milking. These results show that the exfoliation process may play a role in regulating the number of MEC in the udders of dairy cows during feed restriction without any carryover effect on their milk production.     

An FPGA implementation of HW/SW codesign architecture for H.263 video coding

In this paper, we present an efficient HW/SW codesign architecture for H.263 video encoder and its FPGA implementation. Each module of the encoder is investigated to find which approach between HW and SW is better to achieve real-time processing speed as well as flexibility. The hardware portions include the Discrete Cosine Transform (DCT), inverse DCT (IDCT), quantization (Q) and inverse quantization (IQ). Remaining parts were realized in software executed by the NIOS II softcore processor. This paper also introduces efficient design methods for HW and SW modules. In hardware, an efficient architecture for the 2-D DCT/IDCT is suggested to reduce the chip size. A NIOS II Custom instruction logic is used to implement Q/IQ. Software optimization technique is also explored by using the fast block-matching algorithm for motion estimation (ME). The whole design is described in VHDL language, verified in simulations and implemented in Stratix II EP2S60 FPGA. Finally, the encoder has been tested on the Altera NIOS II development board and can work up to 120 MHz. Implementation results show that when HW/SW codesign is used, a 15.8-16.5 times improvement in coding speed is obtained compared to the software based solution.     

Identification and understanding of fouling in low-pressure membrane (MF/UF) filtration by natural organic matter (NOM)

An understanding of natural organic matter (NOM) as a membrane foulant and the behavior of NOM components in low-pressure membrane fouling are needed to provide a basis for appropriate selection and operation of membrane technology for drinking water treatment. Fouling by NOM was investigated by employing several innovative chemical and morphological analyses.

Source (feed) waters with a high hydrophilic (HPI) fraction content of NOM resulted in significant flux decline. Macromolecules of a relatively hydrophilic character (e.g. polysaccharides) were effectively rejected by low-pressure membranes, suggesting that macromolecular compounds and/or colloidal organic matter in the hydrophilic NOM fraction may be a problematic foulant of low-pressure membranes. Moreover, the significant organic fouling that is contributed by polysaccharides and/or proteins in macromolecular and/or colloidal forms depends on molecular shape (structure) as well as size (i.e. molecular weight). More significant flux decline was observed in microfiltration (MF) compared to ultrafiltration (UF) membrane filtration. MF membrane fouling may be caused by pore blockage associated with large (macromolecular) hydrophilic molecules and/or organic colloids. In the case of UF membranes, the flux decline may be caused by sequential or simultaneous processes of surface (gel layer) coverage during filtration. Morphological analyses support the notion that membrane roughness may be considered as a more important factor in membrane fouling by controlling interaction between molecules and the membrane surface, compared to the hydrophobic/hydrophilic character of membranes. Membrane fouling mechanisms are not only a function of membrane type (MF versus UF) but also depend on source (feed) water characteristics.     

Transferts thermiques entre un serpentin et des fluides newtoniens ou non—newtoniens agités par une turbine à pales inclinées dans une cuve

The present work deals with the heat transfer from a hélicoïdal worm to newtonian or non-newtonian liquids, which and stirred by a 4 pitched blade-turbine in a cylindrical tank. The effective viscosity of the pseudoplastic liquids is determined by the Metzner-Otto model combined with the Ellis rheological equation. The heat transfer in the newtonian fluids in a turbulent system is most precisely represented by the following equations: (a) (b) In the case of non-newtonian fluids and of downward pumping, the following equation enables to obtain a very precise evaluation of the heat-transfer coefficient in a transitional flow.