Showing papers by "Ye Xu published in 2009"

Aptamer-based microfluidic device for enrichment, sorting, and detection of multiple cancer cells.

Abstract: The ability to diagnose cancer based on the detection of rare cancer cells in blood or other bodily fluids is a significant challenge. To address this challenge, we have developed a microfluidic device that can simultaneously sort, enrich, and then detect multiple types of cancer cells from a complex sample. The device, which is made from poly(dimethylsiloxane) (PDMS), implements cell-affinity chromatography based on the selective cell-capture of immobilized DNA-aptamers and yields a 135-fold enrichment of rare cells in a single run. This enrichment is achieved because the height of the channel is on the order of a cell diameter. The sorted cells grow at the comparable rate as cultured cells and are 96% pure based on flow cytometry determination. Thus, by using our aptamer based device, cell capture is achieved simply and inexpensively, with no sample pretreatment before cell analysis. Enrichment and detection of multiple rare cancer cells can be used to detect cancers at the early stages, diagnose metast...

Enrichment of cancer cells using aptamers immobilized on a microfluidic channel.

Abstract: This work describes the development and investigation of an aptamer modified microfluidic device that captures rare cells to achieve a rapid assay without pretreatment of cells. To accomplish this, aptamers are first immobilized on the surface of a poly(dimethylsiloxane) microchannel, followed by pumping a mixture of cells through the device. This process permits the use of optical microscopy to measure the cell-surface density from which we calculate the percentage of cells captured as a function of cell and aptamer concentration, flow velocity, and incubation time. This aptamer-based device was demonstrated to capture target cells with >97% purity and >80% efficiency. Since the cell capture assay is completed within minutes and requires no pretreatment of cells, the device promises to play a key role in the early detection and diagnosis of cancer where rare diseased cells can first be enriched and then captured for detection.

Trigonometric Parallaxes of Massive Star-Forming Regions. II. Cep A and NGC 7538

Abstract: We report trigonometric parallaxes for the sources NGC 7538 and Cep A, corresponding to distances of 2.65+(0.12)(-0.11) and 0.70+(0.04)(-0.04) kpc, respectively. The distance to NGC 7538 is considerably smaller than its kinematic distance and places it in the Perseus spiral arm. The distance to Cep A is also smaller than its kinematic distance and places it in the "Local" arm or spur. Combining the distance and proper motions with observed radial velocities gives the location and full space motion of the star-forming regions. We find significant deviations from circular galactic orbits for these sources: both sources show large peculiar motions (greater than 10 km s(-1)) counter to galactic rotation and NGC 7538 has a comparable peculiar motion toward the Galactic center.

Trigonometric parallaxes of massive star-forming regions. i. s 252 & g232.6+1.0

Abstract: We are conducting a large program with the NRAO Very Long Baseline Array (VLBA) to measure trigonometric parallaxes of massive star-forming regions across the Milky Way. Here we report measurement of the parallax and proper motion of methanol masers in S 252 and G232.6+1.0. The parallax of S 252 is 0.476 +/- 0.006 mas (2.10+(0.027)(-0.026) kpc), placing it in the Perseus spiral arm. The parallax of G232.6+1.0 is 0.596 +/- 0.035 mas (1.68+-(0.11)(0.09) kpc), placing it between the Carina-Sagittarius and Perseus arms, possibly in a Local ( Orion) spur of the Carina-Sagittarius arm. For both sources, kinematic distances are significantly greater than their parallax distances. Our parallaxes and proper motions yield full space motions accurate to approximate to 1 km s(-1). Both sources orbit the Galaxy similar to 13 km s(-1) slower than circular rotation.

Trigonometric Parallaxes of Massive Star Forming Regions: III. G59.7+0.1 and W 51 IRS2

Abstract: We report trigonometric parallaxes for G59.7+0.1 and W 51 IRS2, corresponding to distances of 2.16+(0.10)(-0.09) kpc and 5.1+(2.9)(-1.4) kpc, respectively. The distance to G59.7+0.1 is smaller than its near kinematic distance and places it between the Carina-Sagittarius and Perseus spiral arms, probably in the Local (Orion) spur. The distance to W 51 IRS2, while subject to significant uncertainty, is close to its kinematic distance and places it near the tangent point of the Carina-Sagittarius arm. It also agrees well with a recent estimate based on O-type star spectro/photometry. Combining the distances and proper motions with observed radial velocities gives the full space motions of the star-forming regions. We find modest deviations of 5-10 km s(-1) from circular Galactic orbits for these sources, both counter to Galactic rotation and toward the Galactic center.

Trigonometric parallaxes of massive star-forming regions. v. g23.01–0.41 and g23.44–0.18

Abstract: We report trigonometric parallaxes for the massive star-forming regions G23.01-0.41 and G23.44-0.18, corresponding to distances of 4.59+(0.38)(-0.33) kpc and 5.88+(1.37)(-0.93) kpc, respectively. The distance to G23.01-0.41 is smaller than its near kinematic distance assuming a standard model of the Milky Way and less than half of its far kinematic distance, which has usually been assumed. This places it in the Crux-Scutum spiral arm. The distance to G23.44-0.18 is close to its near kinematic distance and most likely places it in the Norma spiral arm near the end of the Galactic bar. Combining the distance and proper motions with observed radial velocities gives the location and full space motion of the star-forming regions. We find large deviations from circular Galactic orbits for these sources: both sources show peculiar motions of 20-30 km s(-1) counter to Galactic rotation and toward the Galactic center. These large peculiar motions might be the result of gravitational perturbations from the Galactic bar.

Trigonometric parallaxes of massive star-forming regions. iv. g35.20-0.74 and g35.20-1.74

Abstract: We report trigonometric parallaxes for the high-mass star-forming regions G35.20-0.74 and G35.20-1.74, corresponding to distances of 2.19+(0.24)(-0.20) kpc and 3.27+(0.56)(-0.42) kpc, respectively. The distances to both sources are close to their near kinematic distances and place them in the Carina-Sagittarius spiral arm. Combining the distances and proper motions with observed radial velocities gives the locations and full space motions of the star-forming regions. Assuming a standard model of the Galaxy, G35.20-0.74 and G35.20-1.74 have peculiar motions of approximate to 13 km s(-1) and approximate to 16 km s(-1) counter to Galactic rotation and approximate to 9 km s(-1) toward the North Galactic Pole.

Lateral Flow Immunoassay Using Europium Chelate-Loaded Silica Nanoparticles as Labels

Abstract: Background: Despite their ease of use, lateral flow immunoassays (LFIAs) often suffer from poor quantitative discrimination and low analytical sensitivity. We explored the use of a novel class of europium chelate-loaded silica nanoparticles as labels to overcome these limitations. Methods: Antibodies were covalently conjugated onto europium chelate-loaded silica nanoparticles with dextran as a linker. The resulting conjugates were used as labels in LFIA for detection of hepatitis B surface antigen (HBsAg). We performed quantification with a digital camera and Adobe Photoshop software. We also used 286 clinical samples to compare the proposed method with a quantitative ELISA. Results: A detection limit of 0.03 μg/L was achieved, which was 100 times lower than the colloidal gold-based LFIAs and lower than ELISA. A precise quantitative dose-response curve was obtained, and the linear measurement range was 0.05–3.13 μg/L, within which the CVs were 2.3%–10.4%. Regression analysis of LFIA on ELISA results gave: log (LFIA) = −0.14 log (ELISA) + 1.03 μg/L with r = 0.99 for the quantification of HBsAg in 35 positive serum samples. Complete agreement was observed for the qualitative comparison of 286 clinical samples assayed with LFIA and ELISA. Conclusions: Europium chelate-loaded silica nanoparticle labels have great potential to improve LFIAs, making them useful not only for simple screening applications but also for more sensitive and quantitative immunoassays.

Absolute positions of 6.7-GHz methanol masers

Abstract: The ATCA, MERLIN and VLA interferometers were used to measure the absolute positions of 35 6.7-GHz methanol masers to subarcsecond or higher accuracy. Our measurements represent essential preparatory data for Very Long Baseline Interferometry, which can provide accurate parallax and proper motion determinations of the star-forming regions harboring the masers. Our data also allow associations to be established with infrared sources at different wavelengths. Our findings support the view that the 6.7 GHz masers are associated with the earliest phases of high-mass star formation.

Temperature evolution of structure and bonding of formic acid and formate on fully oxidized and highly reduced CeO2(111)

Abstract: Adsorption of formate on oxide surfaces plays a role in water-gas shift (WGS) and other reactions related to H2 production and CO2 utilization. CeO2 is of particular interest because its reducibility affects the redox of organic molecules. In this work, the adsorption and thermal evolution of formic acid and formate on highly ordered films of fully oxidized CeO2(111) and highly reduced CeOx(111) surfaces have been studied using reflection absorption infrared spectroscopy (RAIRS) under ultra-high vacuum conditions, and the experimental results are combined with density functional theory (DFT) calculations to probe the identity, symmetry, and bonding of the surface intermediates. Disordered ice, ordered α-polymorph and molecular formic acid bonded through the carbonyl are observed at low temperatures. By 250 K, desorption and deprotonation lead to formate coexisting with hydroxyl on CeO2(111), identified to be a bridging bidentate formate species that is coordinated to Ce cations in nearly C2v symmetry and interacting strongly with neighboring H. Changes in the spectra at higher temperatures are consistent with additional tilting of the formate, resulting in Cs(2) or lower symmetry. This change in bonding is caused primarily by interaction with oxygen vacancies introduced by water desorption at 300 K. On reduced CeOx, multiple low-symmetry formate states exist likewise due to interactions with oxygen vacancies. Isotopic studies demonstrate that the formyl hydrogen does not contribute to H incorporated in hydroxyl on the surface, and that both formate oxygen atoms may exchange with lattice oxygen at 400 K. The combined experimental and theoretical results thus provide important insights on the surface reaction pathways of formic acid on ceria.

Spectral Energy Distributions of 6.7 GHz Methanol Masers

Abstract: Context. The 6.7 GHz maser transition of methanol has been found exclusively towards massive star forming regions. A majority of the masers have been found to lack the presence of any associated radio continuum. This could be due to the maser emission originating prior to the formation of an H ii region around the central star, or from the central object being too cool to produce a H ii region. Aims. One way to distinguish between the two scenarios is to determine and model the spectral energy distributions (SEDs) of the masers. Methods. We observed a sample of 20 6.7 GHz methanol masers selected from the blind Arecibo survey, from centimeter to submillimeter wavelengths. We combined our observations with existing data from various Galactic plane surveys to determine SEDs from centimeter to near-infrared wavelengths. Results. We find that 70% of the masers do not have any associated radio continuum, with the rest of the sources being associated with hypercompact and ultracompact H ii regions. Modeling the SEDs shows them to be consistent with rapidly accreting massive

Trigonometric Parallaxes of 6.7 GHz Methanol Masers

Abstract: Emission from the 6.7 GHz methanol maser transition is very strong, is relatively stable, has small internal motions, and is observed toward numerous massive star-forming regions in the Galaxy. Our goal is to perform high-precision astrometry using this maser transition to obtain accurate distances to their host regions. Eight strong masers were observed during five epochs of VLBI observations with the European VLBI Network between 2006 June, and 2008 March. We report trigonometric parallaxes for five star-forming regions, with accuracies as good as $\sim22 \mathrm{\mu}$as. Distances to these sources are $2.57^{+0.34}_{-0.27}$ kpc for ON 1, $0.776^{+0.104}_{-0.083}$ kpc for L 1206, $0.929^{+0.034}_{-0.033}$ kpc for L 1287, $2.38^{+0.13}_{-0.12}$ kpc for NGC 281-W, and $1.59^{+0.07}_{-0.06}$ kpc for S 255. The distances and proper motions yield the full space motions of the star-forming regions hosting the masers, and we find that these regions lag circular rotation on average by $\sim$17 km s$^{-1}$, a value comparable to those found recently by similar studies.

A Search for Infall Evidence in EGOs I: the Northern Sample

Abstract: We report the first systematic survey of molecular lines (including HCO+ (1-0) and 12CO, 13CO, C18O (1-0) lines at 3 mm band) towards a new sample of 88 massive young stellar object (MYSO) candidates associated with ongoing outflows (known as extended green objects or EGOs) identified from the Spitzer GLIMPSE survey in the northern hemisphere with the PMO-13.7 m radio telescope. By analyzing the asymmetries of the optically thick line HCO+ for 69 of 72 EGOs with HCO+ detection, we found 29 sources with blue asymmetric profiles and 19 sources with red asymmetric profiles. This results in a blue excess of 0.14, seen as a signature of collapsing cores in the observed EGO sample. The relatively small blue excess measured in our full sample due to that the observed EGOs are mostly dominated by outflows and at an earlier evolutionary phase associated with IRDCs and 6.7 GHz methanol masers. The physical properties of clouds surrounding EGOs derived from CO lines are similar to those of massive clumps wherein the massive star forming cores associated with EGOs possibly embedded. The infall velocities and mass infall rates derived for 20 infall candidates are also consistent with the typical values found in MYSOs. Thus our observations further support the speculation of Cyganowski et al. (2008) that EGOs trace a population with ongoing outflow activity and active rapid accretion stage of massive protostellar evolution from a statistical view, although there maybe have limitations due to single-pointing survey with a large beam.

A multiwavelength study of the massive star-forming region IRAS 22506+5944

Abstract: We present a multi-line study of the massive star-forming region IRAS 22506+5944. A new 6.7 GHz methanol maser was detected. (12)CO, (13)CO, C(18)O and HCO(+) J = 1 - 0 transition observations reveal a star-formation complex consisting mainly of two cores. The dominant core has a mass of more than 200 M(circle dot), while the other one is only about 35 M(circle dot). Both cores are obviously at different evolutionary stages. A (12)CO energetic bipolar outflow was detected with an outflow mass of about 1.5 M(circle dot).

A multiwavelength study of massive star-forming region IRAS 22506+5944

Abstract: We present a multi-line study of the massive star-forming region IRAS 22506+5944. A new 6.7 GHz methanol maser was detected. 12CO, 13CO, C18O and HCO+ J = 1-0 transition observations reveal a star formation complex consisting mainly of two cores. The dominant core has a mass of more than 200 solar mass, while another one only about 35 solar mass. Both cores are obviously at different evolutionary stages. A 12CO energetic bipolar outflow was detected with an outflow mass of about 15 solar mass.

Recent advances in heterogeneous catalysis enabled by first-principles methods

Abstract: The development of the catalytic science since its advent in the early 19th century1 laid the foundation for the tremendous growth of the petroleum and chemical industries in the 20th century, one of the factors directly responsible for the substantial increase in the standards of living in the indu...

Mapping the Milky Way structure with methanol and water masers

Abstract: We review recent VLBA and VERA results in measuring trigonometric parallaxes of methanol and water maser sources. The derived source distances are typically accurate to 5-10%, and in a few cases even better. Proper motions are measured with typical uncertainties of a few kilometer per second. The VLBA data observed so far allow one to precisely locate portions of the Perseus Arm, the Local Spur and Carina-Sagittarius Arm. VERA and VLBA observations support the presence of an Outer Arm extending from the 2nd to the 3rd quadrant of the Milky Way. Derived peculiar motions suggest that the observed maser sources orbit slower than the Galaxy spins.

Applying Bayesian Neural Network to determine neutrino incoming direction in reactor neutrino experiments and supernova explosion location by scintillator detectors

Abstract: In the paper, it is discussed by using Monte-Carlo simulation that the Bayesian Neural Network (BNN) is applied to determine neutrino incoming direction in reactor neutrino experiments and supernova explosion location by scintillator detectors. As a result, compared to the method in ref. [1], the uncertainty on the measurement of the neutrino direction using BNN is significantly improved. The uncertainty on the measurement of the reactor neutrino direction is about 1.0° at the 68.3% C.L., and the one in the case of supernova neutrino is about 0.6° at the 68.3% C.L. . Compared to the method in ref. [1], the uncertainty attainable by using BNN reduces by a factor of about 20. And compared to the Super-Kamiokande experiment (SK), it reduces by a factor of about 8.

Application of Bayesian Neural Networks in High Energy Physics Experiments

Abstract: Some applications of Bayesian neural networks (BNN) in the high energy physics experiments are described in the present paper. They are the applications of BNN to particle identification in the second generation of BEijing Spectrometer experiment (BESII), event identification and event reconstruction in reactor neutrino experiments and supernova location in scintillator detector experiments, respectively. Compared to traditional method, better results are obtained in those experiments using BNN. So we believe that BNN can be also well applied to other fields in other experiments for the high energy physics.

Improving Application of Bayesian Neural Networks to Discriminate Neutrino Events from Backgrounds in Reactor Neutrino Experiments

Abstract: The application of Bayesian Neural Networks(BNN) to discriminate neutrino events from backgrounds in reactor neutrino experiments has been described in Ref.\cite{key-1}. In the paper, BNN are also used to identify neutrino events in reactor neutrino experiments, but the numbers of photoelectrons received by PMTs are used as inputs to BNN in the paper, not the reconstructed energy and position of events. The samples of neutrino events and three major backgrounds from the Monte-Carlo simulation of a toy detector are generated in the signal region. Compared to the BNN method in Ref.\cite{key-1}, more $^{8}$He/$^{9}$Li background and uncorrelated background in the signal region can be rejected by the BNN method in the paper, but more fast neutron background events in the signal region are unidentified using the BNN method in the paper. The uncorrelated background to signal ratio and the $^{8}$He/$^{9}$Li background to signal ratio are significantly improved using the BNN method in the paper in comparison with the BNN method in Ref.\cite{key-1}. But the fast neutron background to signal ratio in the signal region is a bit larger than the one in Ref.\cite{key-1}.

Improving application of Bayesian Neural Networks to discriminate neutrino events from backgrounds in reactor neutrino experiments

Abstract: The application of Bayesian Neural Networks (BNN) to discriminate neutrino events from backgrounds in reactor neutrino experiments has been described in ref. [1]. In the paper, BNN are also used to identify neutrino events in reactor neutrino experiments, but the numbers of photoelectrons received by PMTs are used as inputs to BNN in the paper, not the reconstructed energy and position of events. The samples of neutrino events and three major backgrounds from the Monte-Carlo simulation of a toy detector are generated in the signal region. Compared to the BNN method in [1], more 8He/9Li background and uncorrelated background in the signal region can be rejected by the BNN method in the paper, but more fast neutron background events in the signal region are unidentified using the BNN method in the paper. The uncorrelated background to signal ratio and the 8He/9Li background to signal ratio are significantly improved using the BNN method in the paper in comparison with the BNN method in ref. [1]. But the fast neutron background to signal ratio in the signal region is a bit larger than the one in ref. [1].

Discrimination between neutrino events and backgrounds using pulse shape information in reactor neutrino experiments

Abstract: The application of Bayesian neural networks (BNN) to discriminate neutrino events from backgrounds in reactor neutrino experiments has been described in Xu et al. (2008) [1] and Xu et al. (2009) [2] . In the present paper, the pulse shape information for a fast signal of a neutrino event or a background event is used as a part of inputs to BNN to discriminate neutrino events from backgrounds. The numbers of photoelectrons received by PMTs and the delay time for a delayed signal are used as the other part of inputs to BNN (Xu et al., 2009) [2] . As a result, compared to Xu et al. (2009) [2] , the identification efficiency of fast neutron background events is significantly improved using the BNN in the present paper. The other identification efficiencies are consistent with those in Xu et al. (2009) [2] .