Biomedical subjects

Xiaodong Zeng

Publications and source records attributed to Xiaodong Zeng.

5 recordsLinked to original sources

PubMed2005

Asymmetrical prism for beam shaping of laser diode stacks.

A beam-shaping scheme for a laser diode stack to obtain a flattop output intensity profile is proposed. The shaping element consists of an asymmetrical glass prism. The large divergence-angle compression in the direction perpendicular to the junction plane and the small divergence-angle expansion in the parallel direction are performed simultaneously by a single shaping element. The transformation characteristics are presented, and the optimization performance is investigated based on the ray-tracing method. Analysis shows that a flattop intensity profile can be obtained. This beam-shaping system can be fabricated easily and has a large alignment tolerance.

Journal Article↗

PubMed2005

Ecological dynamic model of grassland and its practical verification.

Based on the physico-biophysical considerations, mathematical analysis and some approximate formulations generally adopted in meteorology and ecology, an ecological dynamic model of grassland is developed. The model consists of three interactive variables, i.e. the biomass of living grass, the biomass of wilted grass, and the soil wetness. The major biophysical processes are represented in parameterization formulas, and the model parameters can be determined inversely by using the observational climatological and ecological data. Some major parameters are adjusted by this method to fit the data (although incomplete) in the Inner Mongolia grassland, and other secondary parameters are estimated through sensitivity studies. The model results are well agreed with reality, e.g., (i) the maintenance of grassland requires a minimum amount of annual precipitation (approximately 300 mm); (ii) there is a significant relationship between the annual precipitation and the biomass of living grass; and (iii) the overgrazing will eventually result in desertification. A specific emphasis is put on the shading effect of the wilted grass accumulated on the soil surface. It effectively reduces the soil surface temperature and the evaporation, hence benefits the maintenance of grassland and the reduction of water loss in the soil.

Biomass↗

PubMed2004

Far-field expression of a high-power laser diode.

Based on the off-axis theory, a model for describing the far field with the bipeak structure of a high-power laser diode is proposed. The computed results agree well with the measured far-field data of practical devices. A minimum overall error criterion for fitting the theoretical model with the measured data is also given. The results show that the overall error of this model is less than 5% for popular laser diodes. This model has a simple mathematical structure and can be easily used to design the beam-shaping system and to analyze the propagation properties when the laser beam passes through an optic system.

Journal Article↗

PubMed2003

Coupling light from a laser diode into a multimode fiber.

A parabolalike fiber end to couple the light from a high-power laser diode into a multimode fiber is presented. The formula for the coupling efficiency of such a system is given, and numerical evaluation shows that the theoretical coupling efficiency can be as high as 92% without an antireflection coating on the fiber's end face. This beam-shaping system can be fabricated easily and has a large alignment tolerance.

Journal Article↗

PubMed2002

Strain measurement in a concrete beam by use of the Brillouin-scattering-based distributed fiber sensor with single-mode fibers embedded in glass fiber reinforced polymer rods and bonded to steel reinforcing bars.

The strain measurement of a 1.65-m reinforced concrete beam by use of a distributed fiber strain sensor with a 50-cm spatial resolution and 5-cm readout resolution is reported. The strain-measurement accuracy is +/-15 microepsilon (microm/m) according to the system calibration in the laboratory environment with non-uniform-distributed strain and +/-5 microepsilon with uniform strain distribution. The strain distribution has been measured for one-point and two-point loading patterns for optical fibers embedded in pultruded glass fiber reinforced polymer (GFRP) rods and those bonded to steel reinforcing bars. In the one-point loading case, the strain deviations are +/-7 and +/-15 microepsilon for fibers embedded in the GFRP rods and fibers bonded to steel reinforcing bars, respectively, whereas the strain deviation is +/-20 microepsilon for the two-point loading case.

Journal Article↗