Showing papers by "Zhen Li published in 2003"

Raman spectroscopy study of ZnO-based ceramic films fabricated by novel sol-gel process

Abstract: The ZnO-based ceramic films doped with different dopants were prepared by a novel sol–gel process. The phase composition of the films was determined via X-ray diffraction analysis. The influence of the dopants on the residual stress, carrier concentration and the secondary phases was studied by means of Raman spectroscopy. Raman spectra show that the E2 phonon frequency shifts 3–6 cm−1 to lower wavenumbers, whereas the A1(LO) mode shifts 3.2–6.1 cm−1 to higher wavenumbers when the films were doped with Bi2O3, Sb2O3, MnO, Cr2O3, Y2O3 and Al2O3, indicating that both the tensile residual stress and the free carrier concentration were increased with doping. The larger stress is considered to originate from the lattice distortion, which was caused by the substitution of the doping ions for Zn2+, and the lattice mismatch between the ZnO crystals and the interfacial phases. The secondary phases were affected markedly by both Y2O3 and Al2O3. The intensity and the position of Raman bands of Zn7Sb2O12 and ZnCr2O4 phases changed obviously. The films showed remarkable nonlinear voltage–current characteristics, but the nonlinear coefficient of the films decreased evidently as the addition of Y2O3 or Al2O3.

The variability of NDVI over northwest China and its relation to temperature and precipitation

Abstract: Land vegetation plays a major role in the global climate change through the carbon cycle, and climate change in turn affects vegetation growth and its photosynthetic activity. In arid and semi-arid areas, sparse vegetation cover characterizes environments. Thus quantitative temporal series analysis of vegetation distribution and its variations enables observing annual trends, and helps to find out the reason for environment variability. There are serious environmental problems, such as deforestation, soil erosion, salinization, and desert encroachment in northwestern China, its natural conditions are very delicate. In this paper, we build a time series of vegetation change by the NDVI (normalized difference vegetation index) covered northwest regions over 19 years (1982-2000), and analyze the time serial NDVI variability using three methods, which are simple differencing, slope map of NDVI, slope map of biomass. The correlation analysis between NDVI with the temperature and precipitation in northwestern China was carried out. The results showed that there was significant positive correlation between NDVI and precipitation but that temperature was not strongly correlated with NDVI in northwest China.

Anionic ring-opening polymerization of adipic anhydride initiated by potassium poly(ethylene glycol)ate

Abstract: Poly(adipic anhydride) (PAA) was prepared by the ring-opening polymerization of adipic anhydride (AA) initiated by potassium poly(ethylene glycol)ate. The effects of various factors, such as the amount of initiator, concentration of the monomer, reaction time and temperature, and polarity of the solvent on the polymerization were investigated. The crude polymerized product was a mixture of PAA homopolymer and poly(ethylene glycol)-poly(adipic anhydride) block copolymer, as confirmed by 1H-NMR and gel permeation chromatography. Chain-transfer reactions occurred intensively for the AA polymerization in both the nonpolar solvent toluene and the polar solvents CHCl3 and tetrahydrofuran, which predominantly determined the molecular weight and the monomer conversion for the polymerized product. The lower monomer conversion in toluene was ascribed to a lower livingness for the initiator in the nonpolar solvent when compared with other two, polar solvents.

Postfunctionalization strategy for developing polyphosphazene with a high loading of highly polar molecules in the side arms

Abstract: A new postfunctionalization strategy for developing polyphosphazene functionalized with a high density of highly polar molecules was explored, and the moiety loading was up to 0.84 per unit. A polyphosphazene with N,N-dialkyl-substituted aniline as side chains was first synthesized by a direct substituted reaction, and then post azo coupling of p-nitrobenzenediazonium fluoroborate toward the aniline groups afforded functionalized polyphosphazenes with highly polar molecules. The structural characterization was performed with 1H-NMR, IR, and ultraviolet–visible spectroscopy and gel permeation chromatography. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2989–2993, 2003

A new postfunctional method to synthesize C60‐containing polysiloxanes

Abstract: Two new C60-containing polysiloxanes were synthesized by a new postfunctional method. First, the predesigned amimo end-functionalized polysiloxane was prepared, and then the reactive macromolecular intermediate reacted with C60 molecules in chlorobenzene to yield the C60-containing polysiloxanes. Molecular structural characterization for the polymers was presented by 1H-NMR, IR, and ultraviolet-visible spectra. The polymers exhibited good solubility in common organic solvents and were air stable. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2068–2071, 2003

Frozen ground deformation monitoring using SAR interferometry

Abstract: The interferometric SAR technique has demonstrated its capability to measure ground deformation in wide range of application. The seasonal freeze/thaw transition will cause the deformation of ground surface, which is the main factor for engineering construction in permafrost region. China begins construction of Qinghai-Tibet railway in 2002. About 550 km of the railway will pass through permafrost areas. Thawing and temperature rising has a great influence on railway stability. In this study, five sciences SAR SLC images, including Tandem data, are used to produce multiple interferograms. Two typical methods for deformation detection are discussed. One is the InSAR measure with the high accurate DEM used to reduce the terrain effect, the other is differential InSAR. The data of deformation in experiment site are compared quantitatively with precise and accurate geodetic data derived from field measurement respectively. The analysis of precision and reliability of two methods showed that the InSAR measure with the high accurate DEM is the suitable technique for deformation monitoring using ERS-1/2 SAR data in Qinghai-Tibet Plateau. Additionally, an InSAR monitoring system of frozen ground deformation is proposed for the Qinghai-Tibet railway building.

Synthesis and Characterization of Biodegradable Poly(ester anhydride) Based on -Caprolactone and Adipic Anhydride Initiated by Potassium Poly(ethylene glycol)ate

Abstract: Novel biodegradable poly(ester anhydride) block copolymers based on -caprolactone (-CL) and adipic anhydride (AA) were prepared by sequential polymerization. -CL was first initiated by potassium poly(ethylene glycol)ate and polymerized into active chains (PCL-O-K+), which were then used to initiate the ring-opening polymerization of AA. The effects of the AA feed ratio, solvent polarity, monomer concentration, and temperature on sequential polymerization were investigated. The copolymers, obtained under different conditions, were characterized by Fourier transform infrared, 1H NMR, gel permeation chromatography (GPC), and differential scanning calorimetry (DSC). The GPC results showed that the weight-average molecular weights of the block copolymers were approximately 6.0 × 104. The DSC results indicated the immiscibility of the two components

Digital elevation model construction using ASTER stereo VNIR scene in Antarctic in-land ice sheet

Abstract: Digital elevation information of Antarctic in-land ice sheet is very important in research of ice flow ASTER (Advanced Spaceborne Thermal Emission and Reflectance Radiometer) is an imaging instrument on board Terra-the first Earth Observing System (EOS) satellite The ASTER Earth Observation Satellite offers nearly simultaneous capture of stereo images, minimizing temporal changes and sensor modeling errors Band 3 of the VNIR sensor includes two channels, a nadir looking scene and a backward looking scene This provides stereo coverage from which a DEM can be automatically extracted For the research region of Antarctic Grove Mountains, a pair of ASTER L1A stereo scene product acquired in December 27/sup th/ 2001 is used to extract digital elevation model Accuracy of the DEM is highly dependent on the source of the ground control points used Several field ground control points in this region are selected The final DEM result is compared to DEM surveyed in 2000 using GPS by Chinese surveyors, which indicates good accuracy and powerful usability of ASTER DEM construction in tough Antarctic in-land environment

Blue-ice domain discrimination using interferometric coherence in Antarctic Grove Mountains

Abstract: Discrimination of blue-ice domain is very important for meteorolite searching and Antarctic inland ice sheet evolvement research. Application of SAR interferometric coherence to blue-ice domain target discrimination is studied over polar inland ice. For the region of Grove Mountains in East Antarctica, interferometric coherence analysis is carried out for a pair of tandem ERS- 1/2 SLC full scenes acquired in February 1996. The investigation indicates significant differences in coherence between blue-ice and other ice sheet features, providing possibilities for target discrimination. The generated blue-ice domain map is compared to a reference blue-ice domain map extracted from TM image acquired in 1990. The final results indicates good consistency.

Extraction of vegetation parameters based on simulated annealing algorithm using polarimetric SAR interferometry data

Abstract: An inversion scheme of vegetation parameters based on a simulated annealing algorithm using polarimetric SAR interferometry (Pol-InSAR) data is presented. Comparing the result of inversion with field measurement, it indicates that the inversion algorithm can obtain the height of vegetation with good accuracy.