Biomedical subjects

Xudong Zhang

Publications and source records attributed to Xudong Zhang.

At least 19 recordsLinked to original sources

PubMed2006

Spectroscopic properties and thermal stability of Er3+ -doped TeO2-B2O3-Nb2O5-ZnO glass for potential WDM amplifier.

A series of novel 70TeO2-(15-x)B2O3-xNb2O5-15ZnO-1wt.% Er2O3 (TBN x=0, 3, 6, 9, 12 and 15 mol%) tellurite glasses were prepared. The thermal stability, absorption spectra, emission spectra, and the lifetime of the (4)I(13/2) level of Er(3+) ions were measured and investigated. Three Judd-Ofelt intensity parameters Omega(t) (t=2, 4 and 6) (Omega(2)=(5.42-6.76)x10(-20)cm(2); Omega(4)=(1.37-1.73)x10(-20)cm(2); Omega(6)=(0.70-0.94)x10(-20)cm(2)) of Er(3+) ions were calculated by Judd-Ofelt theory. It is found that the Omega(6) first increases with the increase of Nb2O5 content from 0 to 6 mol% and then decreases, which is mainly affected by the number of non-bridging oxygen ions of the glass network. The high peak of stimulated emission cross-section (sigma(e)(peak)=(0.77-0.91)x10(-20)cm(2)) of Er(3+): (4)I(13/2)-->(4)I(15/2) transition were obtained according to McCumber theory and broad full width at half maximum (FWHM=65-73 nm) of the (4)I(13/2)-->(4)I(15/2) transition of Er(3+) ions were measured. The results indicate that these new TBN glasses can be used as a candidate host material for potential broadband optical amplifiers.

Absorption↗

PubMed2006

Spectroscopic properties of Er(3+)/Yb(3+) co-doped Bi(2)O(3)-B(2)O(3)-GeO(2) glasses.

Er(3+)/Yb(3+) co-doped 60Bi(2)O(3)-(40 - x)B(2)O(3)-xGeO(2) (BBG; x=0, 5, 10, 15 mol%) glasses that are suitable for fiber lasers, amplifiers have been fabricated and characterized. The absorption spectra, emission spectra, and lifetime of the (4)I(13/2) level and quantum efficiency of Er(3+):(4)I(13/2) --> (4)I(15/2) transition were measured and calculated. With the substitution of GeO(2) for B(2)O(3), both Delta lambda(eff) and sigma(e) decrease from 75 to 71 nm and 9.88 to 8.12 x 10(-21) cm(2), respectively. The measured lifetime of the (4)I(13/2) level and quantum efficiency of Er(3+):(4)I(13/2) --> (4)I(15/2) transition increase from 1.18 to 1.5 ms and 36.2% to 43.2%, respectively. The emission spectra of Er(3+):(4)I(13/2) --> (4)I(15/2) transition was also analyzed using a peak-fit routine, and an equivalent four-level system was proposed to estimate the stark splitting for the (4)I(15/2) and (4)I(13/2) levels of Er(3+) in the BBG glasses. The results indicate that the (4)I(13/2) --> (4)I(15/2) emission of Er(3+) can be exhibit a considerable broadening due to a significant enhance the peak A, and D emission.

Bismuth↗

PubMed2006

Enhancement of viability of fat grafts in nude mice by endothelial progenitor cells.

BACKGROUND: A recent discovery showed that endothelial progenitor cells (EPCs) could augment collateral vessel growth to ischemic tissues. OBJECTIVE: The objective was to demonstrate the effects of EPCs on the vasculogenesis and survival of free transplanted fat tissues in nude mice. METHODS: EPCs from human donors were cultured in vitro for 7 days. Human fat tissues were injected subcutaneously into the scalps of 20 6-week-old nude male mice. EPCs stained with CM-DiI were mixed with the transplanted fat tissues and injected into the mice. EBM-2 medium was used as control group. The animals were euthanized 15 weeks after the procedure. Graft volume were measured, and histologic evaluation was performed. The central part of fat tissues was histologically evaluated 15 weeks after the fat injection. RESULTS: The survival volume of the experimental group was significantly greater than that of the control group (p< .05). Less cyst formation and fibrosis was obtained in the experimental group. Histologic evaluation of the central part of fat tissues 15 weeks after the fat injection showed that capillary densities increased markedly in the experimental group mice. CONCLUSION: The results indicate that EPCs have the ability to enhance the survival and the quality of the transplanted fat tissues.

Adipose Tissue↗

PubMed2006

[Effects of specific microbial biocides on N transformation in soil with glucose amendment].

In an incubation test of soil with glucose amendment, two kinds of nitrogenous fertilizer and three kinds of specific microbial biocides were applied, and the contents of soil NH(4+)-N, NO3(-)-N, glucosamine and muramic acid were measured to differentiate the relative contribution and timing characteristics of soil microbes in nitrogen immobilization. The results showed that penicillin and streptomycin decreased the transformation rate of NH(4+)-N markedly, with more significant effects than actidione. The amount ratio of glucosamine to muramic acid after applying penicillin and streptomycin rapidly increased first, and tended to equilibrium then. With the application of actidione, the transformation rate of NO3(-)-N decreased continuously, and the synthesis of glucosamine was inhibited, while penicillin and streptomycin had no significant effects on them. At the early stage of incubation, bacteria could rapidly immobilize both NH(4+)-N and NO3(-)-N, with NH(4+)-N preferred, while at the later stage of incubation, fungi were the dominant contributor to nitrogen transformation, and had much stronger ability of utilizing NO3(-)-N than bacteria.

Anti-Bacterial Agents↗

PubMed2005

Psychophysics of reading with a limited number of pixels: towards the rehabilitation of reading ability with visual prosthesis.

Psychophysics of reading with limited numbers of pixels has received increasing attention as the envisioned visual prosthesis offers a possibility to restore some useful reading ability to the blind through the pixelized vision it generates. This paper systematically studied how several important parameters of pixelized vision affect reading performance. A closed-circuit television reading platform with digital image processing capacities was developed to convert images of printed text into pixelized patterns made up of discrete dots. Reading rates in six normally sighted subjects were measured under different combinations of pixel number, window width, and angular subtense of pixel array. The results showed that reading is possible with as few as 6 x 6 binary pixels, at 15 words/min. It was also found that for a given array of pixels, maximum reading rates occur at a specific medium window width, due to a tradeoff between window width and character sampling resolution. It was also observed that pixelized reading exhibits more significant scale dependence than normal vision. Reading rates were decreased by increasing the angular subtense of the pixel array while keeping other parameters fixed. We hope these results will be helpful to the design of visual prosthesis for the rehabilitation of reading abilities.

Adult↗

PubMed2005

A 3D canted antiferromagnetic porous metal-organic framework with anatase topology through assembly of an analogue of polyoxometalate.

The unique porous metal-organic framework {KCo3(C6H4O7)(C6H5O7)(H2O)2.8H2O}8 (1), which exhibits an unprecedented infinite 3D (3,6)-connected decorated anatase net, has been obtained by hydrothermal reaction. Upon dehydration, the compound retains crystallinity and exhibits a type I N2 sorption isotherm, characteristic of a microporous solid with apparent Langmuir surface area 939 m2/g and pore volume 0.31 cm3/g. Magnetic measurements for both 1 and dehydrated 1 show the spin-canted antiferromagnetic state below 5 K and a magnetic hysteresis loop at 2 K. Thus, dehydrated 1 represents the first metal-organic framework for which microporosity and a spin-canted antiferromagnetic state coexist, which demonstrates that the self-assembly of organo-polymetal clusters and metal ions can provide a potential route to magnetic porous metal-organic frameworks.

Journal Article↗

PubMed2005

A gas chromatographic/mass spectrometric method for tracing the microbial conversion of glucose into amino sugars in soil.

Amino sugars in soils are heterogeneous and have been used as microbial residue biomarkers to investigate the microbial contribution to soil organic matter. However, it is not clear what the available carbon source is and how glucose is utilized for the synthesis of soil amino sugars. This paper presents a new gas chromatography/mass spectrometry (GC/MS) approach for the identification of 13C incorporation into three amino sugars, D-glucosamine, D-galactosamine, and muramic acid, in soil incubated with U-13C-glucose. Method evaluation showed that the chemical ionization (CI) mode was suitable for all these amino sugars, but that electron impact (EI) mode was applicable only to glucosamine and galactosamine. The 13C conversion rate was estimated based on the abundance ratio of the ions corresponding to the masses of the ions F+n and F (where n is the skeleton carbon number in the fragment ions F of the amino sugars) and calculated as atom percentage excess. The reproducibility of the method was excellent and clearly adequate for the present purpose. In addition, the new approach is highly accurate as tested with mixtures of U-13C-glucose and natural glucose.

Amino Sugars↗

PubMed2005

Development and evaluation of an optimization-based model for power-grip posture prediction.

An optimization-based model for power-grip posture prediction was proposed. The model was based on the premise that the hand prehensile configuration in a power grip best conforms to the object shape. This premise was embodied by an optimization procedure that minimized the sum of distances from the finger joints to the object surface. The model was evaluated against data from an experiment that measured the grasp postures of 28 subjects having diverse anthropometry. The intra- and inter-person variabilities in grip postures were empirically assessed and used as benchmark values for model evaluation. The evaluation showed that the root-mean-square (RMS) values of angle differences between the predicted and measured postures had a 13.7 degrees grand mean (across all joints, subjects, and two cylindrical handles grasped), whereas the RMS values of the inter- and intra-person variabilities in measured postures had grand means of 13.0 degrees and 4.4 degrees , respectively. The model can be readily generalized to the prediction of postures in power-grasping objects of different shapes, and adapted for testing alternative prehensile strategies or performance criteria.

Adult↗

PubMed2005

A normative database of thumb circumduction in vivo: center of rotation and range of motion.

This article reports a systematic research effort aimed at establishing a normative database of thumb circumduction range of motion (ROM) and related kinematic characteristics in vivo while examining the effects of anthropometry, gender, and direction of rotation. Twenty-eight (14 men, 14 women) anthropometrically diverse participants performed maximum voluntary thumb circumductions as the trajectories of the surface markers placed on their thumb landmarks were recorded by an optoelectronic motion capture system. A globographic representation method was employed to model the measured marker trajectories, determining the center of rotation and central reference axes for thumb circumduction. Thumb ROM was quantified using (a) the joint sinuses expressing the thumb orientation change with respect to the reference axes and (b) cone volumes circumscribed by the thumb at the distal phalangeal, interphalangeal, and metacarpophalangeal levels. Data analyses resulted in statistical summaries of the derived kinematic and ROM measures with significant effects identified and regression equations predicting the cone volumes. Potential applications of this research include ergonomic design of hand-operated controls or devices and evaluation of thumb impairments or disorders.

Aged↗

PubMed2005

[Effects of salinity stress on poplars seedling growth and soil enzyme activity].

A pot culture experiment with two clones of poplars (P1 and P2) showed that soil salinity had a definite inhibitory effect on the establishment and growth of seedlings. The survival rate, seedling height and weight, and root weight were all declined with increasing soil salinity. When the salinity was 0.2%, 0.4%, 0.6% and 0.8%, the shoot growth of P1 and P2 decreased by 23.24%, 48.56%, 70.76% and 83.33%, and 71.77%, 83.25%, 86.28% and 91.39%, respectively, in comparing with the control. Regressive analyses showed that soil salinity had a linear relationship with chlorophyll content, and a binomial relationship with leaf proline content. The activities of soil beta-glucosidase and L-asparaginase were decreased with increasing soil salinity. When the salinity was 0.2%, 0.4%, 0.6% and 0.8%, the beta-glucosidase activity in P1 and P2 soils decreased by 10.96%, 20.07%, 30.96% and 37.44%, and 11.21%, 18.94%, 34.89% and 41.31%, respectively. The salinity tolerance of P1 was better than that of P2.

Asparaginase↗

PubMed2005

[Research advances in ecosystem flux].

To develop the long-term localized observation and investigation on ecosystem flux is of great importance. On the basis of generalizing the concepts and connotations of ecosystem flux, this paper introduced the construction and development histories of Global Flux Networks, Regional Flux Networks (Ameri-Flux, Euro-Flux and Asia-Flux) and China-Flux, as well as the main methodologies, including micrometeorological methods (such as eddy correlation method, mass balance method, energy balance method and air dynamic method)and chamber methods (static and dynamic chamber methods), and their basic operation principles. The research achievements, approaches and advances of CO2, N2O, CH4, and heat fluxes in forest ecosystem, farmland ecosystem, grassland ecosystem and water ecosystem were also summarized. In accordance with the realities and necessities of ecosystem flux research in China, some suggestions and prospects were put forward.

Air Pollutants↗

PubMed2004

Quantitative analysis of finger motion coordination in hand manipulative and gestic acts.

This article reports an experimental study that aimed to quantitatively analyze motion coordination patterns across digits 2-5 (index to little finger), and examine the kinematic synergies during manipulative and gestic acts. Twenty-eight subjects (14 males and 14 females) performed two types of tasks, both right-handed: (1) cylinder-grasping that involved concurrent voluntary flexion of digits 2-5, and (2) voluntary flexion of individual fingers from digit 2 to 5 (i.e., one at a time). A five-camera opto-electronic motion capture system measured trajectories of 21 miniature reflective markers strategically placed on the dorsal surface landmarks of the hand. Joint angular profiles for 12 involved flexion-extension degrees of freedom (DOF's) were derived from the measured coordinates of surface markers. Principal components analysis (PCA) was used to examine the temporal covariation between joint angles. A mathematical modeling procedure, based on hyperbolic tangent functions, characterized the sigmoidal shaped angular profiles with four kinematically meaningful parameters. The PCA results showed that for all the movement trials (n = 280), two principal components accounted for at least 98% of the variance. The angular profiles (n = 2464) were accurately characterized, with the mean (+/-SD) coefficient of determination (R2) and root-mean-square-error (RMSE) being 0.95 (+/-0.12) and 1.03 degrees (+/-0.82 degrees ), respectively. The resulting parameters which quantified both the spatial and temporal aspects of angular profiles revealed stereotypical patterns including a predominant (87% of all trials) proximal-to-distal flexion sequence and characteristic interdependence--involuntary joint flexion induced by the voluntarily flexed joint. The principal components' weights and the kinematic parameters also exhibited qualitatively similar variation patterns. Motor control interpretations and new insights regarding the underlying synergistic mechanisms, particularly in relation to previous findings on force synergies, are discussed.

Biomechanical Phenomena↗

PubMed2004

[Effects of lower limit of subsurface drip irrigation on tomato growth and its yield in plastic tunnel].

A subsurface drip irrigation experiment was conducted in a plastic tunnel to study the effects of different lower limits of subsurface drip irrigation on tomato growth and its yield. The lower limits of subsurface drip irrigation were expressed by soil water suctions detected by tensiometers placed in 30 cm soil layer. The designed values of soil water suction in this experiment were 10, 16, 25, 40 and 63 kPa, respectively. The results showed that the height and biomass of tomato plant decreased significantly with increasing lower limits of subsurface drip irrigation. Parabolic regression curves were suitable to simulate the relationships of stem diameter of tomato plant, yield, and water use efficiency (WUE) with lower limits of subsurface drip irrigation. The relationship between the ratio of stem diameter to plant height of tomato and lower limit could be simulated by three-dimensional multinomial regression curve. The growth of tomato root and shoot and their ratio R/S) varied under different lowerlimits of subsurface drip irrigation. The tomato plant grew well, RI/S was favorable, and the yield and WUE were higher when soil water suction was in the range of 25- 33 kPa. When this range was served as the criteria for subsurface drip irrigation, the soil water content at the beginning of irrigation should be lower, and the irrigation frequency should be fewer than that of conventional irrigation. This range of soil water suction was in favor of improving the WUE and decreasing labor cost for tomato cultivation in plastic tunnel.

Biomass↗

PubMed2004

[Effects of illumination, carbon source and reducing power on N2O emission from maize and soybean seedlings].

The closed chamber measurement of N2O emission from soybean and maize seedlings showed that there were two peaks (10:30 and 14:30) of N2O flux at the daytime. There was a correlation between N2O emission and illumination. The variation of illumination had a significant influence on N2O flux from soybean and maize seedlings. There was a positive correlation between N2O emission and illumination when the illumination was below 11,345 Lx (for soybean, R2 = 0.7332) or 2,000 Lx (for maize, R2 = 0.8711), and a negative correlation when the illumination was over 11,345 Lx (for soybean, R2 = 0.7755) or 20,000 Lx (for maize, R2 = 0.8972). Addition of carbon source (glucose) and NADH (reducing power) decreased N2O flux.

Carbon↗

PubMed2003

Model-guided derivation of lumbar vertebral kinematics in vivo reveals the difference between external marker-defined and internal segmental rotations.

This study investigated whether the external marker-defined spine inter-segmental rotation is different from the internal vertebral rotation, and explored how to estimate the latter from limited surface measurement. A kinematic model was first created to elucidate analytically the relation between the external and internal rotations. A novel approach guided by the model was proposed for deriving vertebral centers of rotation (CORs) from measured planar trajectories of skin-surface markers. The approach involved a recursive procedure for establishing local (anatomical) coordinate systems, and an optimization routine that identified the maximum-likelihood circles best fitting the marker trajectories in local coordinate systems. An experiment with 10 subjects (5 males and 5 females) was conducted to test the approach along with the model. Skin-surface markers were strategically placed over individual spinous processes and other body landmarks, and recorded by an opto-electronic system while sagittally symmetric load-lifting movements were being performed. For the majority (89%) of measured motions, the COR locations for lumbar vertebrae (L2-L5) were derived successfully: solutions resulting from the optimization routine met a convergence criterion governed by the model, and were in agreement with existing data from radiographic or cadaveric studies. Empirical results confirmed the differences between the external marker-defined inter-segmental motions and corresponding internal vertebral rotations (1.1-5.8 degrees on average, all statistically significant). The study demonstrated the necessity and viability of quantifying internal vertebral kinematics when utilizing non-invasive marker-based measurement for spine-related clinical diagnosis and biomechanical modeling.

Adult↗

PubMed2003

Determining finger segmental centers of rotation in flexion-extension based on surface marker measurement.

This paper describes the development of a novel algorithm for deriving finger segmental center of rotation (COR) locations during flexion-extension from measured surface marker motions in vivo. The algorithm employs an optimization routine minimizing the time-variance of the internal link lengths, and incorporates an empirically quantifiable relationship between the local movement of a surface marker around a joint (termed "surface marker excursion") and the joint flexion-extension. The latter relationship constrains and simplifies the optimization routine to make it computationally tractable. To empirically investigate this relationship and test the proposed algorithm, an experiment was conducted, in which hand cylinder-grasping movements were performed by 24 subjects (12 males and 12 females). Spherical retro-reflective markers were placed at various surface landmarks on the dorsal aspect of each subject's right (grasping) hand, and were measured during the movements by an opto-electronic system. Analysis of experimental data revealed a highly linear relationship between the "surface marker excursion" and the marker-defined flexion-extension angle: the average R(2) in linear regression ranged from 0.89 to 0.97. The algorithm successfully determined the CORs of the distal interphalangeal, proximal interphalangeal, and metacarpophalangeal joints of digits 2-5 during measured motions. The derived CORs appeared plausible as examined in terms of the physical locations relative to surface marker trajectories and the congruency across different joints and individuals.

Adult↗

PubMed2003

Effects of load and speed on lumbar vertebral kinematics during lifting motions.

This experimental study investigated the effects of load magnitude and movement speed on lumbar vertebral kinematics during lifting task performance. Ten participants performed sagittally symmetric lifting movements with systematically varied load using either a normal or a faster-than-normal speed. Skin-surface markers were strategically placed over the participants' spinous processes and other landmarks representing major body joints and were recorded during the movements by a motion capture system. The center of rotation (COR) locations and segmental movement profiles for lumbar vertebrae L2 to L5 were derived and analyzed. Results suggested that (a) the COR locations and vertebral angular displacement were not significantly affected by the speed or load variation; (b) a faster speed tended to shorten the time to complete the acceleration for all the lumbar vertebrae considered; and (c) the load increase incurred a tendency for the L5 to complete the primary displacement in a briefer time while enduring greater peak acceleration and velocity. The findings lead to a better understanding of the relation between lifting dynamics and spinal motion. Potential applications of this research include the development of more accurate biomechanical models and software tools for depicting spinal motions and quantifying low-back stress.

Adult↗

PubMed2003

[Characteristics and environmental significance of soil dissolved organic matter].

Soil is a complex ecosystem with multi-interface. A numerous studies on soil dissolved organic matter (DOM) were carried out, and proved that DOM was one of the most active chemical components in the environment. Increasing attention has been paid on the study of soil DOM, especially in recent years, and the study has become an interdisciplinary focus in the fields of soil science, ecology, and environmental science due to the important roles of DOM in the biogeochemical cycles of carbon, nitrogen, phosphorus, sulfur, etc. In addition, DOM has significant effects on pedogenesis, growth and metabolism of soil microorganisms, decomposition and transformation of soil organic matter, and transport of pollutants in soils. The recent literatures about extraction methods, origin, composition, contents and controlling factors, bioavailability, and environmental significance of DOM were therefore reviewed, and future research aspects on this topic were also proposed.

Environmental Monitoring↗