Science in China Series E: Technological Sciences

The first HTS front-end subsystem for wireless base station in China was developed. This demonstration system, which aims at the application in GSM 1800 mobile communication base station, consists of a single RF path, i.e. one filter and one LNA, integrated with the pulse tube cooler. The subsystem works at a pass band of 1710–1785 MHz with a gain of 18 dB and at a temperature of 70 K. The accomplishment of such a demonstration subsystem can boost the development of HTS commercial subsystem.

Hydropower project may bring with it social-economic profits as well as side effects. The built dam and reservoir often cause some problems to the surrounding areas, among which the ecological and environmental effects caused by hydropower projects are always concerned by the public. In this article, we take the Ertan reservoir catchment as the research area and try to quantitatively analyze the variation of vegetation cover and soil erosion by remote sensing technique, and to comprehensively assess the evolvement and development trend of reservoir catchment. Soil erosion, land use/cover are used as ecological and environmental indicators which reflect the changes before, after and in the period of the construction of Ertan hydropower station. Supported by the multi-source remote sensing data (from satellite Landsat and CBERS) and DEM data, the land use/cover is interpreted through RS images which are classified both by unsupervised and supervised method, and the driving factors of the ecological changes are also analyzed. At the same time, the changes of soil loss are also monitored and analyzed during flood seasons of Ertan reservoir area before and after reservoir impoundment (1995, 2000 and 2005) using the revised universal soil loss equation (RUSLE). The results show that during the recent 13 years the arable land area has decreased obviously, and construction area and water surface have increased slightly. The increase of vegetation cover has some relations with the implementation of local ecological projects, i.e., de-farming to forestry and de-farming to pasture projects. At the same time, changes may also be caused by the climate adjustment in the reservoir area. In the ten years from 1995 to 2005, the high soil loss classes were transforming to lowly level classes continuously. All of these show that the soil loss of Ertan reservoir area is getting better.

In this study, the dynamic characteristic of a multi-sensor system made up of such sensors as are sensitive to several parameters is discussed, and the effect of cross-sensitivity on the precision of a measurement system is also discussed. A multi-sensor system is looked as a serial of a linear filter and a memoryless nonlinear system, i.e. Wiener system, and the subsequent information fusion system is regarded as a Hammerstein system, i.e. a serial of a memoryless nonlinear system and a linear filter. On the basis of static calibration, it is presented to determine the inverse filter in a Hammerstein system using blind deconvolution. In order to control the uncertainty of amplitude of signals recovered by blind deconvolution well, a regulation approach to regulating the inverse linear filter coefficient matrixes is presented according to the identity between inverse filter coefficient matrixes and static calibrating matrix. So the approximate inverse dynamic model of multi-sensor system is obtained, the degree of distortion of dynamic measurement result is reduced, the measurement precision is improved, and the need of practice can be reached. Simulation example and simulation result show that the recovered error of the inputs of sensor system, the frequency of which is 1/10 of sampling frequency, is 1/20 of the measurement results without dynamic compensation, and is one half of the measurement results with sole dynamic compensation, and the rapidity is improved 2 times. The dynamic compensation results of a metal oxide semiconductor methane sensor show that the dynamic measurement error is less than one half of that without dynamic compensation. So this method expands the bandwidth of multi-sensor system.

The representation of 1/f signal with wavelet transformation is explored. It is shown that a class of 1/f signal can be represented via wavelet synthetic formula and that a statistically self-similar property of signals may be characterized by the correlation functions of wavelet coefficients in the wavelet domain.

A new transient stability margin is proposed based on a new expression of dynamic security region (DSR) which is developed from the existing expression of DSR. Applications of the DSR based transient stability margin to contingency ranking and screening are discussed. Simulations in the 10-machine 39-bus New England system are performed to show the effectiveness of the proposed DSR based transient stability margin.

A novel scheme to compress optical pulses is proposed and demonstrated numerically, which is based on a nonlinear optical loop mirror constructed from dispersion decreasing fiber (DDF). We show that, in contrast to the conventional soliton-effect pulse compression in which compressed pulses are always accompanied by pedestals and frequency chirps owning to nonlinear effects, the proposed scheme can completely suppress pulse pedestals and frequency chirps. Unlike the adiabatic compression technique in which DDF length must increase exponentially with input pulsewidth, the proposed scheme does not require adiabatic condition and therefore can be used to compress long pulses by using reasonable fiber lengths. For input pulses with peak powers higher than a threshold value, the compressed pulses can propagate like fundamental solitons. Furthermore, the scheme is fairly insensitive to small variations in the loop length and is more robust to higher-order nonlinear effects and initial frequency chirps than the adiabatic compression technique.

The distribution of the neutron spectra in the thermal column hole of Xi’an pulse reactor was measured with the time-of-flight method. Compared with the thermal Maxwellian theory neutron spectra, the thermal neutron spectra measured is a little softer, and the average neutron energy of the experimental spectra is about 0.042±0.01 eV. The thermal neutron fluence rate at the front end of thermal column hole, measured with gold foil activation techniques, is about 1.18×105 cm−2 s−1. The standard uncertainty of the measured thermal neutron fluence is about 3%. The spectra-averaged cross section of 197Au(n, γ) determined by the experimental thermal neutron spectra is (92.8±0.93) ×10−24 cm2.

The role of atomic hydrogen and hydrogen-induced martensites in hydrogen embrittlement in slow strain rate tensile tests and hydrogen-induced delayed cracking (HIC) in sustained load tests for type 304 L stainless steel was quantitatively studied. The results indicated that hydrogen-induced martensites formed when hydrogen concentration C 0 exceeded 30 ppm, and increased with an increase in C 0, i.e. M(vol%)=62–82.5 exp (−C 0/102). The relative plasticity loss caused by the martensites increased linearly with increasing amount of the martensites, i.e. l δ(M), %=0.45 M (vol %)=27.9−37.1 exp(−C0/102). The plasticity loss caused by atomic hydrogen l δ(H) increased with an increase in C 0 and reached a saturation value l δ(H)max=40% when C 0>100 ppm. l δ(H) decreased with an increase in strain rate $$\dot \varepsilon $$ , i.e. l δ(H), $$\% = - 21.9 - 9.9\dot \varepsilon $$ , and was zero when $$\dot \varepsilon \geqslant \dot \varepsilon _c = 0.032/s$$ . HIC under sustained load was due to atomic hydrogen, and the threshold stress intensity for HIC decreased linearly with in C 0, i.e. K IH (Mpam1/2)=91.7−10.1 In C 0 (ppm). The fracture surface of HIC was dimple if K 1 was high or/and C 0 was low, otherwise it was quasi-cleavage. The boundary line between ductile and brittle fracture surface was K 1-54+25exp(−C 0/153)=0.