Showing papers by "Zhen Li published in 2001"

Aerosol properties at a midlatitude Northern Hemisphere continental site

Abstract: Measurements of chemical, physical, and optical properties of ambient aerosol particles were obtained at Bondville, Illinois. This research was completed to increase the spatial and temporal resolution of measured aerosol. Results from measurements describe (1) the physical and chemical characteristics of the aerosol and (2) the dependence of light scattering and backscattering on wavelength of light λ, controlled relative humidity RH, and aerosol particle chemical composition. Formulations for the hygroscopic growth factor f(RH), and backscatter ratio b, as functions of λ and RH and estimates of the upscatter fraction β¯, and Angstrom exponent a are also provided. For aerosol sampled at the site from January to December 1995, the mean gravimetric mass concentration for particles with aerodynamic diameter (dpa)≤1 μm had an arithmetic mean and standard deviation of 10.6±6.5 μg/m3, respectively. Ion chromatography (IC) speciated 53% of the total gravimetric mass for particles with dpa≤1 μm. Most of the IC-identified material (88.0±13.5%) consisted of NH4+ and SO42−. Material not identified with IC was primarily elemental and organic carbon. The total aerosol light-scattering coefficient at λ = 550 nm and RH≤40% was 51.6±43.2 Mm−1 for dpa≤10 μm and 42.0±34.9 Mm−1 for dpa≤1 μm. Mean values of f(RH = 82.5%, λ) for total scattering ranged between 1.4 and 1.5 and for back scattering between 1.1 and 1.2. Mean values of b(λ) ranged from 0.11 to 0.18 for RH<40% and from 0.09 to 0.14 for RH = 82.5%. Mean values of β¯ ranged from 0.21 to 0.30 depending on λ, RH, and the particle size distribution. Mean values of a ranged between 1.8 and 2.4 for RH<40% and 1.8 and 2.1 for RH = 82.5%. These measured properties are now available for use in models to reduce uncertainties when quantifying direct aerosol radiative forcing at a continental site influenced by aerosol with anthropogenic origin.

Synthesis of polyphosphazenes as potential photorefractive materials

Abstract: A new series of polyorganophosphazenes have been designed for potential photorefractive effect and synthesized via a nucleophilic substitution reaction of poly(dichlorophosphazene) with N -(6-Hydroxyhexanyl)carbazole ( HCZ ) as charge-transporting agent, N -(6-Hydroxyhexanyl)-3-(4-Nitrophenylazo)carbazole ( HNACZ ) as electro-optical chromophore. The component concentrations in the polymers can be controlled by different feed ratios between HCZ and HNACZ . The structural characterization for the high polymers was presented by 1 H-NMR, IR and UV–Visible spectra, gel permeation chromatograply (GPC) and differential scanning calorimetry (DSC).

SAR Interferometry coherence analysis for snow mapping

Abstract: For climatological and hydrological investigations, the areas covered by snow and their spatial variability are important parameters, particularly in alpine regions. A interferometric SAR technique not only can produce a high-resolution digital elevation models but also can detect the changes in the surface. By comparing four ERS-1/2 repeat pass SAR image in the Tibet Plateau test area, we find that the coherence measurements from the bare soil, bare rock and the short vegetation are significantly high, and lake and snow cover have very low coherence. On other way, the entire target may show very low coherence if there are great decorrelations due to other parameters, such as spatial baseline, rotation and temporal. We will demonstrate the method and result for snow mapping by using both backscattering and coherence measurements with repeat passes ERS-1 image data at the Kunlunshan Mountain, the Tibetan plateau (36/spl deg/03'N, 91/spl deg/00'E). An accuracy of better than 82% can be achieved if we consider the classification result from TM imagery as the ground truth. The results showed that the coherence measurements provide an effective way to map snow-covered area.

Synthesis and luminescence of polyphosphazenes with carbazolyl side chains

Abstract: Two new blue-light-emitting polyphosphazenes (1 and 2) containing carbazolyl groups as side chains were synthesized from a highly reactive macromolecular intermediate by a nucleophilic substitution reaction. Molecular structural characterization for the polymers was presented by 1H NMR, IR, and ultraviolet–visible spectra, gel permeation chromatography, and differential scanning calorimetry. The polymers exhibited excellent solubility in common organic solvents and were thermally stable. A fluorescence analysis of the two materials in tetrahydrofuran showed a strong blue light emitting. The quantum yields of the polyphosphazenes were 0.55 for 1 and 0.64 for 2, relative to quinoline (in 0.1 N H2SO4). An electroluminescent diode was fabricated, and a bright blue light was observed; the maximum external quantum efficiency was about 0.026% at an applied forward voltage of 23 V. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3428–3433, 2001

Retrieving dry snow density with SIR-C polarimetric SAR data

Abstract: For a given incidence angle at the snow surface, a greater snow density causes a greater change in the incidence angle at the snow-ground interface; for a given snow density, however, a larger incidence angle at the snow surface results in a greater change in the refractive angle in the snow layer, by comparing the difference of incidence angle at the snow-ground interface and the air-snow interface with different snow density. Algorithm for estimating dry snow density used backscattering measurements with polarimetric SAR at L-band frequency is developed based on simulation of the surface backscattering componentsσ g hh andσ g vv using the IEM model and regression analysis. The comparison of the estimated snow density from SAR L-band images with that from field measurements during the SIR-C/X-SAR overpass shows root means square error of 0.050 g/cm3. It shows that this algorithm can be accurately used to estimate dry snow density distribution.

The effect of poly(ethylene oxide) on the characteristics of Triton X-100/1-butanol/ n-octane/water reverse micelles

Abstract: Nonionic poly(oxyethylene) surfactant with about ten ethylene oxide units and 1-butanol have been studied in reverse micelles with one nonpolar solvent(n-octane) at different water contents in the presence and in the absence of poly (ethylene oxide) (PEO) using two absorption probes, methyl orange and methyl blue MB and one spin probe, 5-doxylstearic acid. The study has focused attention on the effect of the addition of PEO on the phase behavior of the system, the state of water in the reverse micelles, and the locus of PEO solubilized in reverse micelles. In the presence of PEO, some PEO segments may penetrate into the interface close to the palisade layer of the reverse micelles and then replace some water molecules, which results in a less close arrangement between the chains of surfactants as well as between alcohol molecules.

An analysis on the forearm bone mass density of rural female and the environmental risk factors

Abstract: The distribution of distal and proximal forearm bone mass densities (BMD) with age was discribed and the environmental risk factors of rural female analyzed A group of 1432 rural female aged 15 and over were sellected Their demographic characteristics, living and eating habit were obtained by standardized questionnaire The distal and proximal forearm bone mass density were measured by peripheral dual-energy X ray absorptionmetry (pDEXA) The results showed that the distal and proximal forearm BMDs were increased with age before age 25 and 30 respectively, and reached the peak value at age 30-35 The distal forearm bone density decreased significantly at age 40 while the proximal forearm BMD decreased at age 45 Bone loss rate of the two bone sites was increased significantly at age 50 and reached the peak value at age 55-60 Only the the density of proximal forearm bone, and the year of menopause was the main cause of low bone density Body weight was the positive factor for bone density at age less than 60 Height only positively affected the proximal forearm bone of those at age 30-45 More ever, drinking tea, parity and educational status may affect distal forearm bone in certain age group while parity, educational status, occupation and marital status were possible risk factors of proximal forearm BMD It is concluded that environmental risk factors of BMD varied with bone site and age The prevention of low BMD must rely on subject's age and bone site The surveillance of low bone density must put the emphasis on spony bone