Biomedical subjects

Yanfei Wang

Publications and source records attributed to Yanfei Wang.

9 recordsLinked to original sources

PubMed2006

Regularized inversion method for retrieval of aerosol particle size distribution function in W(1,2) space.

A determination of the aerosol particle size distribution function by using the particle spectrum extinction equation is an ill-posed integral equation of the first kind. To overcome this, we must incorporate regularization techniques. Most of the literature focuses on the Phillips-Twomey regularization or its variations. However, there are drawbacks for some applications in which the real aerosol distributions have large oscillations in a Junge-type distribution. The reason for this is that the scale matrix based on the norm of the second differences in the Phillips-Twomey regularization is too ill- conditioned to filter the large perturbations induced by the small algebraic spectrum of the kernel matrix and the additive noise. Therefore we reexamine the aerosol particle size distribution function retrieval problem and solve it in W1,2 space. This setting is based on Sobolev's embedding theorem in which the approximate solution best simulates the true particle size distribution functions. For choosing the regularization parameters, we also develop an a posteriori parameter choice method, which is based on the discrepancy principle. Our numerical results are based on the remote sensing data measured by the CE318 sunphotometer in Jia Xiang County, Shan Dong Province, China, and are performed to show the feasibility of the proposed algorithms.

Journal Article↗

PubMed2006

Surface-enhanced Raman scattering on mercaptopyridine-capped CdS microclusters.

We obtained the high-quality Raman spectra of 4-mercaptopyridine (4-Mpy) adsorbed on CdS microclusters. The Raman signals were enhanced relative to the same molecules in solution. We compared the Raman spectra of 4-Mpy molecules adsorbed on CdS microclusters and Ag substrate. The difference of 4-Mpy molecules adsorbed on semiconductor and metal substrate was revealed. The results demonstrated that adsorbed species on semiconductor CdS can be detected by SERS spectroscopy.

Microscopy, Electron, Scanning↗

PubMed2006

Direct fast method for time-limited signal reconstruction.

We consider reconstruction of signals by a direct method for the solution of the discrete Fourier system. We note that the reconstruction of a time-limited signal can be simply realized by using only either the real part or the imaginary part of the discrete Fourier transform (DFT) matrix. Therefore, based on the study of the special structure of the real and imaginary parts of the discrete Fourier matrix, we propose a fast direct method for the signal reconstruction problem, which utilizes the numerically truncated singular value decomposition. The method enables us to recover the original signal in a stable way from the frequency information, which may be corrupted by noise and/or some missing data. The classical inverse Fourier transform cannot be applied directly in the latter situation. The pivotal point of the reconstruction is the explicit computation of the singular value decomposition of the real part of the DFT for any order. Numerical experiments for 1D and 2D signal reconstruction and image restoration are given.

Journal Article↗

PubMed2005

An intron-encoded protein assists RNA splicing of multiple similar introns of different bacterial genes.

Four group II introns were found in an unusually intron-rich dnaN gene (encoding the beta subunit of DNA polymerase III) of the cyanobacterium Trichodesmium erythraeum, and they have strong similarities to two introns of the RIR gene (encoding ribonucleotide reductase) of the same organism. Of these six introns, only the RIR-3 intron encodes a maturase protein and showed efficient RNA splicing when expressed in Escherichia coli cells. The other five introns do not encode a maturase protein and did not show RNA splicing in E. coli. But these maturase-less introns showed efficient RNA splicing when the RIR-3 intron-encoded maturase protein was co-expressed from a freestanding gene in the same cell. These findings demonstrated that an intron-encoded protein could function as a general maturase for multiple introns of different genes. Major implications may include an intron-mediated co-regulation of the different genes and a resemblance of the evolutionary origin of spliceosomal introns.

Alternative Splicing↗

PubMed2005

Classification of cancer cell lines using an automated two-dimensional liquid mapping method with hierarchical clustering techniques.

A two-dimensional liquid mapping method was used to map the protein expression of eight ovarian serous carcinoma cell lines and three immortalized ovarian surface epithelial cell lines. Maps were produced using pI as the separation parameter in the first dimension and hydrophobicity based upon reversed-phase HPLC separation in the second dimension. The method can be reproducibly used to produce protein expression maps over a pH range from 4.0 to 8.5. A dynamic programming method was used to correct for minor shifts in peaks during the HPLC gradient between sample runs. The resulting corrected maps can then be compared using hierarchical clustering to produce dendrograms indicating the relationship between different cell lines. It was found that several of the ovarian surface epithelial cell lines clustered together, whereas specific groups of serous carcinoma cell lines clustered with each other. Although there is limited information on the current biology of these cell lines, it was shown that the protein expression of certain cell lines is closely related to each other. Other cell lines, including one ovarian clear cell carcinoma cell line, two endometrioid carcinoma cell lines, and three breast epithelial cell lines, were also mapped for comparison to show that their protein profiles cluster differently than the serous samples and to study how they cluster relative to each other. In addition, comparisons can be made between proteins differentially expressed between cell lines that may serve as markers of ovarian serous carcinomas. The automation of the method allows reproducible comparison of many samples, and the use of differential analysis limits the number of proteins that might require further analysis by mass spectrometry techniques.

Adenocarcinoma, Clear Cell↗

PubMed2005

EP 80317, a ligand of the CD36 scavenger receptor, protects apolipoprotein E-deficient mice from developing atherosclerotic lesions.

CD36, a type B scavenger receptor expressed on macrophages, appears to play a major role in fatty streak formation through scavenging oxidatively modified lipoproteins in the arterial wall. We tested the hypothesis that EP 80317, a novel CD36 ligand derived from the growth hormone (GH)-releasing peptide family but devoided of any GH releasing activity, exerts anti-atherosclerotic effects in apolipoprotein E-deficient (apoE-/-) mice fed an atherogenic diet from 6 wk of age. Daily subcutaneous injections of EP 80317 (300 microg/kg) or vehicle were initiated at 6, 10, 12, or 14 wk until death at 18 wk. En face analyses of the entire aortic tree revealed a striking reduction (up to 51%) of lesion areas in EP 80317-treated apoE-/- mice compared with controls. Chronic treatment with EP 80317 (12 wk) is also associated with a 30% decrease in total plasma cholesterol, suggesting potential effects of this drug on cholesterol metabolism at the intestine/hepatic levels. EP 80317 exerts both preventive and curative effects on atherosclerotic lesion progression that were shown to be reversible after cessation of treatment. At the macrophage level, EP 80317 reduced oxidized low density lipoproteins internalization and up-regulated genes involved in cholesterol efflux, including peroxisome proliferator-activated receptor gamma (PPARgamma), liver x receptor alpha (LXRalpha), and the ATP binding cassette (ABC) transporters ABCA1 and ABCG1, supporting a role in regulating peripheral cholesterol trafficking. Importantly, the effects of EP 80317 were shown to be CD36 dependent, inasmuch as no anti-atherosclerotic or hypocholesterolemic effects were observed in apoE/CD36 double-deficient mice. In addition, long-term treatment of apoE/CD36 double-deficient mice with EP 80317 did not modulate the expression of genes of the PPARgamma-LXRalpha-ABC transporters pathway. Our results suggest that EP 80317, as a CD36 ligand, might be a prototype for a novel class of anti-atherosclerotic agents.

ATP Binding Cassette Transporter 1↗

PubMed2005

Optical properties of Ag/CdTe nanocomposite self-organized by electrostatic interaction.

Ag/CdTe nanocomposite was prepared via self-organization process by electrostatic interaction between positively charged CdTe quantum dots and negatively charged Ag nanoparticles and examined with respect to their optical properties. The positively charged CdTe quantum dots and negatively charged Ag nanoparticles were synthesized separately by modifying nanoparticles surface with cationic and anionic thiol compounds, respectively. The result showed that the mixing ratio of Ag nanoparticles to CdTe quantum dots is an important parameter for controlling resulting composites. The resulting solution is optically transparent if one component is in excess. Photoluminescence of CdTe quantum dots undergoes considerably quenching if CdTe nanocrystals are in excess and SERS spectra of BVPP absorbed on Ag colloid became stronger if Ag nanoparticles are in excess. Nevertheless, while the ratio is approximately 1, micrometer-sized solid composite is obtained with the elapse of 1h after mixing. SERS spectra for solid composite only exhibit the signals of the CdS nanocrystal which reflected that prolonged refluxing during the synthesis leads to a partial hydrolysis of the thiols and to the incorporation of the sulfur from the thiol molecules into the the growing nanoparticles to form mixed CdTe(S) nanocrystal, similar to CdTe/CdS core/shell structure. From the results, we conclude that optical properties of Ag/CdTe are dependent on the mixing ratio of both nanoparticles.

Cadmium Compounds↗

PubMed2003

Direct dynamics study of N-protonated diglycine surface-induced dissociation. Influence of collision energy.

A quantum mechanical and molecular mechanical (QM + MM) direct dynamics classical trajectory simulation is used to study energy transfer and fragmentation in the surface-induced dissociation (SID) of N-protonated diglycine, (gly)2H+. The peptide ion collides with the hydrogenated diamond [111] surface. The Austin Model 1 (AM1) semiempirical electronic structure theory is used for the (gly)2H+ intramolecular potential and molecular mechanical functions are used for the diamond surface potential and peptide/surface intermolecular potential. The simulations are performed at collision energies Ei of 30, 50, 70, and 100 eV and collision angle of 0 degrees (perpendicular to the surface). The percent energy transfer to the peptide ion is nearly independent of Ei, while energy transfer to the surface increases with increase in Ei. A smaller percent of the energy remains in peptide translation as Ei is increased. These trends in energy transfer are consistent with previous trajectory simulations of SID. At each Ei the most likely initial pathway leading to fragmentation is rupture of the +H3NCH2-CONHCH2COOH bond. Fragmentation occurs by two general mechanisms. One is the traditional Rice-Ramsperger-Kassel-Marcus (RRKM) model in which the peptide ion is activated by its collision with the surface, "bounces off", and then dissociates after undergoing intramolecular vibrational energy redistribution (IVR). The other mechanism is shattering in which the ion fragments as it collides with the surface. Shattering is the origin of the large increase in number of product channels with increase in Ei, i.e., 6 at 30 eV, but 59 at 100 eV. Shattering becomes the dominant dissociation mechanism at high Ei.

Energy Transfer↗

PubMed2002

Sugar transport through maltoporin of Escherichia coli: role of the greasy slide.

The lining of the maltodextrin-specific maltoporin (LamB) channel exhibits a string of aromatic residues, the greasy slide, part of which has been shown previously by crystallography to be involved in substrate binding. To probe the functional role of the greasy slide, alanine scanning mutagenesis has been performed on the six greasy slide residues and Y118 at the channel constriction. The mutants were characterized by an in vivo uptake assay and sugar-induced-current-noise analysis. Crystallographic analysis of the W74A mutant showed no perturbation of the structure. All mutants showed considerably decreased maltose uptake rates in vivo (<10% of the wild-type value), indicating the functional importance of the investigated residues. Substitutions at the channel center revealed appreciably increased (up to 100-fold) in vitro half-saturation concentrations for maltotriose and maltohexaose binding to the channel. Sugar association rates, however, were significantly affected also by the mutations at either end of the slide (W74A, W358A, and F227A), an effect which became most apparent upon nonsymmetrical sugar addition. The kinetic data are discussed on the basis of an asymmetric one-site two-barrier model, which suggests that, at low substrate concentrations, as are found under physiological conditions, only the heights of the extracellular and periplasmic barriers, which are reduced by the presence of the greasy slide, determine the efficiency of this facilitated diffusion channel.

Alanine↗