PubMed Health⌕ Search

Biomedical subjects

X J Wang

Publications and source records attributed to X J Wang.

At least 37 records · Page 2Linked to original sources
PubMed2004

Uncertainty analysis of parameters for modeling the transfer and fate of benzo(a)pyrene in Tianjin wastewater irrigated areas.

A Monte Carlo simulation for uncertainty analysis of three key parameters (local coal consumption rate Q(1L), dry deposition velocity of aerosol particulate Kp and biodegradation rate of benzo(a)pyrene in soil and sediment K(R3)) was conducted in this study. Results of the simulation indicate that the three parameters were influenced by uncertainty and that all equilibrium concentrations in the four bulk compartments and various sub-compartments were log-normally distributed. However, the results also indicated that among the six primary transfer fluxes, erosion associated with solids in soil and deposition associated with solids in water, along with output from sewers were also log-normally distributed, while deposition from air to soil and biodegradation in soil and sediment followed normal distributions. The effect of uncertainty on the model results of the three key parameters was derived using a comparison of upper and lower of confidence interval boundaries at the 95% level of confidence. The results reveal that uncertainty in the key parameters had a more significant influence on equilibrium concentrations of the chemical in the bulk compartments of soil and sediment than on concentrations in the other two bulk compartments, various sub-compartments and the six predominant transfer fluxes.

Benzo(a)pyrene↗
PubMed2004

Evaluation of factors influencing root-induced changes of copper fractionation in rhizosphere of a calcareous soil.

Major factors influencing the root-induced copper fractionation changes within the rhizosphere of maize, wheat, pea, and soybean seedlings were evaluated using a contaminated calcareous soil. The effects of acidification, alkalization, and introduction of root exudates were investigated by addition of acid, alkaline and root exudates from solution cultures, prior to incubation and copper fractionation. Raw and sterilized soils were compared for changes of copper fractionation in the rhizosphere using rhizoboxes with maize, wheat, pea and soybean seedlings. The results indicated that the general trend in considerable changes was similar among the plant species studied. The rhizosphere experienced a depletion of carbonate associated and organic bound copper along with an accumulation of exchangeable and Fe-Mn oxide bound copper. The resulting significant influence of root exudates on copper fractionation appears to have been produced through complexation rather than acidification or alkalization. The increase in exchangeable copper in rhizosphere was strengthened by microorganisms.

Copper↗
PubMed2003

First ultraviolet high-gain harmonic-generation free-electron laser.

We report the first experimental results on a high-gain harmonic-generation (HGHG) free-electron laser (FEL) operating in the ultraviolet. An 800 nm seed from a Ti:sapphire laser has been used to produce saturated amplified radiation at the 266 nm third harmonic. The results confirm the predictions for HGHG FEL operation: stable central wavelength, narrow bandwidth, and small pulse-energy fluctuation.

Journal Article↗
PubMed2003

Medium scale spatial structures of Polycyclic Aromatic Hydrocarbons in the topsoil of Tianjin area.

The spatial distribution patterns of Polycyclic Aromatic Hydrocarbons (PAHs) in soil are important to regional environmental assessment. In this paper, the spatial structural features of sixteen prior PAH compounds in the topsoil of Tianjin area, as well as soil properties, were studied. Results shown that medium scale spatial autocorrelations were well revealed. Spherical models with sills could be used to fit all experimental variograms. The spatial structures of PAHs contents demonstrated significant anisotropy. Air precipitation caused by the combustion of coal was the key factor in the formation of the spatial structural patterns of PAHs in the topsoil of Tianjin area.

China↗
PubMed2002

Surface-roughness wakefield measurements at brookhaven accelerator test facility.

An experiment has been carried out at the Brookhaven Accelerator Test Facility to investigate the effect of a surface-roughness wakefield in narrow beam tubes with artificially created bumps. The measurements show that the synchronous modes decay significantly due to the randomization of the roughness pattern. It is pointed out that this decay mechanism has not been investigated in the previous experiment at DESY and the investigators' conclusion does not apply for surface-roughness wakefields in real surfaces.

Journal Article↗
PubMed2002

Fundamental and harmonic microbunching in a high-gain self-amplified spontaneous-emission free-electron laser.

Electron beam microbunching in both the fundamental and second harmonic in a high-gain self-amplified spontaneous emission free-electron laser (SASE FEL) was experimentally characterized using coherent transition radiation. The microbunching factors for both modes (b(1) and b(2)) approach unity, an indication of FEL saturation. These measurements are compared to the predictions of FEL simulations. The simultaneous capture of the microbunching and SASE radiation for individual micropulses correlate the longitudinal electron beam structure with the FEL gain.

Journal Article↗
PubMed2002

Modeling for point-non-point source effluent trading: perspective of non-point sources regulation in China.

In the past decades, little abatement efforts have been implemented on China's non-point source water pollution, and studies aiming at non-point sources regulation were also rare. Watershed abatement trading between point and non-point sources may serve as a cost-effective way to deal with the problem. The inherent uncertainty of non-point emissions, however, could affect the feasibility and outcome of point-non-point effluent trading. The purpose of this paper is to model the watershed point-non-point abatement trading incorporating the uncertainty of non-point source emissions, and to examine its impacts on trading equilibrium and trading ratio. The uncertainties of non-point emissions were taken into consideration by setting an acceptable probability by which the watershed emission constraints were achieved. Using the watershed optimization model, the optimal abatement allocation and trading ratio were explicitly illustrated. It was found that they were affected significantly by the variances of non-point emissions, the reliability requirement assigned to the non-point abatement, and the marginal abatement costs of point and non-point sources. Since the variances of non-point emissions may increase or decrease at the abatement level, the impacts of these factors were discussed in different circumstances. Based on the illumination of the trading model, future directions and implications of point-non-point trading in China were discussed.

Journal Article↗
PubMed2002

Experimental characterization of nonlinear harmonic radiation from a visible self-amplified spontaneous emission free-electron laser at saturation.

Nonlinear harmonic radiation was observed using the VISA self-amplified, spontaneous emission (SASE) free-electron laser (FEL) at saturation. The gain lengths, spectra, and energies of the three lowest SASE FEL modes were experimentally characterized. The measured nonlinear harmonic gain lengths and center spectral wavelengths decrease with harmonic number, n, which is consistent with nonlinear harmonic theory. Both the second and third nonlinear harmonics energies are about 1% of the fundamental energy. These experimental results demonstrate for the first time the feasibility of using nonlinear harmonic SASE FEL radiation to produce coherent, femtosecond x rays.

Journal Article↗
PubMed2002

Changes of biophysical behavior of k562 cells for p16 gene transfer.

p16 gene was transferred into human erythroleukemia cell line K562 that had been subjected to p16 deletion. The changes of biophysical behavior of K562 cells after gene transfer were studied with the micropipette technique. The micropipette data were analyzed with a standard solid viscoelastic model. In comparison to untransfected control K562 cells and the cells transfected with an empty vector, the p16-transfected K562 cells showed an increase in the elastic element K(1), which is inversely proportional to the maximum deformation over a long period of time, whereas the viscous element mu and the other elastic element K(2) showed no significant difference. The results indicate that K562 cells became more rigid after p16 transfer. The p16-transfected K562 cells also had a higher surface charge density. This study contributes to our knowledge about the suppression effect of p16 gene on tumor cell migration and about its use in gene therapy.

Biophysical Phenomena↗
PubMed2001

Inducible expression of transforming growth factor beta1 in papillomas causes rapid metastasis.

Transforming growth factor beta1 (TGF-beta1) acts as a tumor suppressor at early stages of carcinogenesis, however, it has also been suggested to promote tumor progression at late stages. To determine at which stage and by what mechanisms this functional switch occurs, we have generated gene-switch-TGF-beta1 mice in which TGF-beta1 transgene expression can be induced in skin tumors at specific stages. These mice were exposed to a chemical carcinogenesis protocol, which allows tumorigenesis to develop in progressive stages from benign papillomas to malignant carcinomas. Remarkably, TGF-beta1 transgene induction in papillomas rapidly induced metastasis. This function is in sharp contrast to its tumor suppressive effect when TGF-beta1 transgene expression was induced early in the protocol. Transgenic papillomas exhibited down-regulation of TGF-beta receptors and their signal transducer, the Smads, and loss of the invasion suppressor E-cadherin/catenin complex in the cell membrane. These molecules were lost only in malignant carcinomas in control mice at a much later stage. Furthermore, transgenic papillomas exhibited elevated expression of matrix metalloproteinases and increased angiogenesis. Our study suggests that TGF-beta1 overexpression may directly induce tumor metastasis by initiating events necessary for invasion. Down-regulation of TGF-beta signaling components in tumor epithelia selectively abolishes growth inhibition, thus, switching the role of TGF-beta1 to a metastasis promoter.

Animals↗
PubMed2001

Loss of presenilin 1 is associated with enhanced beta-catenin signaling and skin tumorigenesis.

Presenilin 1 (PS1) is required for the proteolytic processing of Notch and the beta-amyloid precursor protein (APP), molecules that play pivotal roles in cell-fate determination during development and Alzheimer's disease pathogenesis, respectively. In addition, PS1 interacts with beta-catenin and promotes its turnover through independent mechanisms. Consistent with this activity, we report here that PS1 is important in controlling epidermal cell proliferation in vivo. PS1 knockout mice that are rescued through neuronal expression of human PS1 transgene develop spontaneous skin cancers. PS1-null keratinocytes exhibit higher cytosolic beta-catenin and beta-catenin/lymphoid enhancer factor-1/T cell factor (beta-catenin/LEF)-mediated signaling. This effect can be reversed by reintroducing wild-type PS1, but not a PS1 mutant active in Notch processing but defective in beta-catenin binding. Nuclear beta-catenin protein can be detected in tumors. Elevated beta-catenin/LEF signaling is correlated with activation of its downstream target cyclin D1 and accelerated entry from G(1) into S phase of the cell cycle. This report demonstrates a function of PS1 in adult tissues, and our analysis suggests that deregulation of beta-catenin pathway contributes to the skin tumor phenotype.

Animals↗
PubMed2001

NAD(P)H:quinone oxidoreductase 1 deficiency and increased susceptibility to 7,12-dimethylbenz[a]-anthracene-induced carcinogenesis in mouse skin.

BACKGROUND: The phase II enzyme NAD(P)H :quinone oxidoreductase 1 (NQO1) catalyzes quinone detoxification, protecting cells from redox cycling, oxidative stress, mutagenicity, and cytotoxicity induced by quinones and its precursors. We have used NQO1(-/-) C57BL/6 mice to show that NQO1 protects them from skin cancer induced by the polycyclic aromatic hydrocarbon benzo[a]pyrene. Herein, we used NQO1(-/-) mice to investigate whether NQO1 also protects them against 7,12-dimethylbenz[a]anthracene (DMBA), where methyl substituents diminish primary quinone formation. METHODS: Dorsal skin of NQO1(-/-) or wild-type C57BL/6 mice was shaved. When tested as a complete carcinogen, DMBA (500 or 750 microg in 100 microL of acetone) alone was applied to the shaved area. When tested as a tumor initiator, DMBA (200 or 400 nmol in 100 microL of acetone) was applied to the shaved area; 1 week later, twice-weekly applications of phorbol 12-myristate 13-acetate (PMA)-10 microg dissolved in 200 microL of acetone-to the same area began and were continued for 20 weeks. Tumor development was monitored in all mice (12-15 per group). All statistical tests were two-sided. RESULTS: When DMBA (750 microg) was tested as a complete carcinogen, about 50% of the DMBA-treated NQO1(-/-) mice but no DMBA-treated wild-type mouse developed skin tumors. When DMBA (both concentrations) was used as a tumor initiator, NQO1(-/-) mice developed larger tumors at a greater frequency than their wild-type littermates. Twenty-three weeks after the first PMA treatment in the tumor initiator test, all 30 NQO1(-/-) mice given 400 nmol of DMBA had developed skin tumors, compared with 33% (10 of 30) of treated wild-type mice (P<.001). CONCLUSIONS: NQO1(-/-) mice are more susceptible to DMBA-induced skin cancer than are their wild-type littermates, suggesting that NQO1 may protect cells from DMBA carcinogenesis.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed2001

EGF-dependent translocation of green fluorescent protein-tagged PLC-gamma1 to the plasma membrane and endosomes.

Growth factor-dependent translocation of phospholipase C-gamma1 (PLC-gamma1) was investigated using a green fluorescent protein-tagged PLC-gamma1 (PLC-gamma1-GFP) expressed in human epidermoid carcinoma A-431 cells. In the absence of growth factors, PLC-gamma1-GFP was present throughout the cytoplasm of A-431 cells. Treatment of the cells with epidermal growth factor (EGF) produced a very rapid redistribution of PLC-gamma1-GFP to the plasma membrane in a nonuniform manner. This translocation to the plasma membrane was insensitive to an inhibitor of phosphatidylinositol 3-kinase and was independent of cell adhesion. However, the translocation was disrupted by an agent which depolymerizes the actin cytoskeleton. At later times following the addition of EGF, PLC-gamma1-GFP appeared associated with intracellular vesicles. Stimulation of A-431 cells by Texas red-conjugated EGF for more than 10 min resulted in punctate intracellular PLC-gamma1-GFP distribution that colocalized with Texas red-conjugated EGF. This suggests that PLC-gamma1 is translocated to endosomes after EGF treatment, probably by associating with the internalized and autophosphorylated EGF receptor. Fractionation studies demonstrated that the EGF-induced plasma membrane-localized PLC-gamma1 is concentrated in caveolae microdomains. Disruption of caveolae with methyl-beta-cyclodextrin resulted in the ablation of EGF-induced, but not bradykinin-induced, mobilization of intracellular Ca(2+). This treatment, however, only partially decreased PLC-gamma1 membrane translocation.

Caveolae↗
PubMed2001

Characterization of a high-gain harmonic-generation free-electron laser at saturation.

We report on an experimental investigation characterizing the output of a high-gain harmonic-generation (HGHG) free-electron laser (FEL) at saturation. A seed CO2 laser at a wavelength of 10.6 microm was used to generate amplified FEL output at 5.3 microm. Measurement of the frequency spectrum, pulse duration, and correlation length of the 5.3 microm output verified that the light is longitudinally coherent. Investigation of the electron energy distribution and output harmonic energies provides evidence for saturated HGHG FEL operation.

Journal Article↗
PubMed2001

Modeling translocation of particles on one-dimensional polymer lattices.

We introduce a general random walk model that is an extension of the random walk model proposed by Berg. The model can be used to describe a particle's translocation along a polymeric lattice with a nonuniform distribution of obstacles. These obstacles are representative of DNA-bound proteins, of drugs, and of a DNA packing environment. Using this model in the bacteriophage replication process, we show the effects of random obstacles on an ATP-driven particle's translocation along single-stranded DNA. The principal finding is that the average statistical time of the translocation process decreases with the increase of an obstacle's strength. We also find an interesting relation between the average statistical time and the DNA chain length. Our results can be used to explain some physiological phenomena. They show the usefulness of our model in an analysis of the effect of random obstacles on particles' translocation along one-dimensional polymer lattices.

Adenosine Triphosphate↗
PubMed2001

Elements involved in the regulation of the StAR gene.

The steroidogenic acute regulatory protein (StAR) mediates the transfer of cholesterol from the outer to the inner mitochondrial membrane, the regulated step in steroidogenesis. A most interesting facet of this protein is the manner in which its expression is acutely regulated. In this regard, a number of studies have concentrated on the search for consensus cis regulatory elements within its promoter, and, more importantly, on whether these elements are involved in its expression. This short review will summarize some of the findings that have been reported concerning the nature of how the expression of this gene is regulated.

Animals↗
PubMed2001

Exponential gain and saturation of a self-amplified spontaneous emission free-electron laser.

Self-amplified spontaneous emission in a free-electron laser has been proposed for the generation of very high brightness coherent x-rays. This process involves passing a high-energy, high-charge, short-pulse, low-energy-spread, and low-emittance electron beam through the periodic magnetic field of a long series of high-quality undulator magnets. The radiation produced grows exponentially in intensity until it reaches a saturation point. We report on the demonstration of self-amplified spontaneous emission gain, exponential growth, and saturation at visible (530 nanometers) and ultraviolet (385 nanometers) wavelengths. Good agreement between theory and simulation indicates that scaling to much shorter wavelengths may be possible. These results confirm the physics behind the self-amplified spontaneous emission process and forward the development of an operational x-ray free-electron laser.

Journal Article↗