Chao Wang

Chinese Academy of Sciences, Peping, Beijing, China

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Publications (24)45.97 Total impact

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    ABSTRACT: An experimental demonstration of spectral imaging with measurement dimensions compressed has been performed. With the method of dual compressed sensing (CS) we derive, the spectral image of a colored object can be obtained with only a single point detector, and sub-sampling is achieved in both spatial and spectral domains. The performances of dual CS spectral imaging are analyzed, including the effects of dual modulation numbers and measurement noise on the imaging quality. Our scheme provides a stable, high-flux measurement approach of spectral imaging.
    No preview · Article · Apr 2016 · Optics Communications
  • Fu Zheng · Chao Wang · Zhi-Bin Sun · Guang-Jie Zhai
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    ABSTRACT: InGaAs/InP avalanche photodiodes (APD) are rarely used in a free-running regime for near-infrared single photon detection. In order to overcome the detrimental afterpulsing, we demonstrate a passive quenching active reset integrated circuit. Taking advantage of the inherent fast passive quenching process and active reset to reduce reset time, the integrated circuit is useful for reducing afterpulses and is also area-efficient. We investigate the free-running single photon detector's afterpulsing effect, de-trapping time, dark count rate, and photon detection efficiency, and also compare with gated regime operation. After correction for deadtime and afterpulse, we find that the passive quenching active reset free-running single photon detector's performance is consistent with gated operation.
    No preview · Article · Jan 2016 · Chinese Physics B
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    Preview · Article · Dec 2015 · Optics Express
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    ABSTRACT: InGaAs/InP avalanche photodiodes (APD) are usually employed as Geiger-mode single photon detector at near-infrared wavelength between 1.0 mu m and 1.7 mu m. In order to work in the free-running regime rather than gated regime, we demonstrate a feedback quenching integrated circuit to rapidly quench the avalanche and reset the APD. Because this IC is close to the APD, parasitic capacitance is largely reduced, thus reducing the quench-time, reset-time and also the afterpulsing probability. We investigated the free-running single photon detector's afterpulsing effect, de-trapping time, dark count rate and detection efficiency and also compared with gated regime operation. After corrected for deadtime and afterpulse, we found the free-running detector performance is comparable with gated regime.
    No preview · Article · Nov 2015 · Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment
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    ABSTRACT: We report an experimental demonstration of spectral imaging with a spectrometer without any scanning. The spatial resolution is provided by spatial light modulation based on the theory of compressed sensing. Objects with both continuous and discrete spectrum are used to demonstrate the performance of our system, which shows wide-spectrum and high efficient spectral imaging ability. The spatial and spectral resolutions of our imaging system are also discussed.
    No preview · Article · Oct 2015 · Optics Communications
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    ABSTRACT: In this paper, we present an innovative method of double balanced differential configuration, in which two adjacent single photon avalanche diodes (SPADs) from the same wafer are configured as the first balanced structure, and the output signal from the first balanced stage is subtracted by the attenuated gate driving signal as the second balanced stage. The compact device is cooled down to 236 K to be characterized. At a gate repetition rate of 400 MHz and a 1 550 nm laser repetition rate of 10 MHz, the maximum photon detection efficiency of 13.5% can be achieved. The dark count rate is about 10−4 ns−1 at photon detection efficiency of 10%. The afterpulsing probability decreases with time exponentially. It is shown that this configuration is effective to discriminate the ultra-weak avalanche signal in high speed gating rates.
    No preview · Article · Mar 2015 · Optoelectronics Letters
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    ABSTRACT: We experimentally demonstrated a spectral imaging scheme with dual compressed sensing. With the dimensions of spectral and spatial information both compressed, the spectral image of a colored object can be obtained with only a single point detector. The effect of spatial and spectral modulation numbers on the imaging quality is also analyzed. Our scheme provides a stable, highly consistent approach of spectral imaging.
    Full-text · Article · Feb 2015
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    ABSTRACT: Compressed sensing realizes the sub-sampling of the sparse signal but with high computational effort. For this, many hardware implementations based on Orthogonal Matching Pursuit (OMP) algorithm have been researched, avoiding the direct matrix inversion calculation by Cholesky or QR decomposition. However, the computational complexity is still high, and the reconstruction precision is poor, which is unfavorable for extension. In order to address this problem, a high performance hardware implementation was proposed in this paper which used Coordinate Rotation Digital Computer (CORDIC) method constituting a systolic array to perform QR decomposition. This hardware architecture improves systolic array module and corresponding scheduling processing module by adding delay units, and can recover an 8-sparse signal of column dimension 256 in the order of columns, with the speed nearly 13 times faster than the software. Meanwhile, since the mean square error has a boltzmann relationship with the sparsity of the signals, the hardware performs well when the sparsity is below 8. Moreover, the curve fittings for software and hardware match well further proves the reconstruction ability of this hardware architecture. Finally, based on this hardware structure, a single photon imaging system was constructed, showing that, it can significantly speed up the imaging speed.
    No preview · Article · Dec 2014 · Journal of Computational Information Systems
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    ABSTRACT: A single-photon imaging system based on compressed sensing has been developed to image objects under ultra-low illumination. With this system, we have successfully realized imaging at the single-photon level with a single-pixel avalanche photodiode without point-by-point raster scanning. From analysis of the signal-to-noise ratio in the measurement we find that our system has much higher sensitivity than conventional ones based on point-by-point raster scanning, while the measurement time is also reduced.
    No preview · Article · Oct 2014 · Physics Letters A
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    ABSTRACT: Protein disulfide isomerase (PDI) composed of four thioredoxin-like domains a, b, b', and a', is a key enzyme catalyzing oxidative protein folding in the endoplasmic reticulum. Large scale molecular dynamics simulations starting from the crystal structures of human PDI (hPDI) in the oxidized and reduced states were performed. The results indicate that hPDI adopts more compact conformations in solution than in the crystal structures, which are stabilized primarily by inter-domain interactions, including the salt bridges between domains a and b' observed for the first time. A prominent feature of the compact conformations is that the two catalytic domains a and a' can locate close enough for intra-molecular electron transfer, which was confirmed by the characterization of an intermediate with a disulfide between the two domains. Mutations, which disrupt the inter-domain interactions, lead to decreased reductase activity of hPDI. Our molecular dynamics simulations and biochemical experiments reveal the intrinsic conformational dynamics of hPDI and its biological impact.
    Full-text · Article · Aug 2014 · PLoS ONE
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    ABSTRACT: Conventional single-pixel cameras recover images only from the data recorded in one arm of the digital micromirror device, with the light reflected to the other direction not to be collected. Actually, the sampling in these two reflection orientations is correlated with each other, in view of which we propose a sampling concept of complementary compressive imaging, for the first time to our knowledge. We use this method in a telescopic system and acquire images of a target at about 2.0 km range with 20 cm resolution, with the variance of the noise decreasing by half. The influence of the sampling rate and the integration time of photomultiplier tubes on the image quality is also investigated experimentally. It is evident that this technique has advantages of large field of view over a long distance, high-resolution, high imaging speed, high-quality imaging capabilities, and needs fewer measurements in total than any single-arm sampling, thus can be used to improve the performance of all compressive imaging schemes and opens up possibilities for new applications in the remote-sensing area.
    Preview · Article · Jul 2014 · Scientific Reports
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    ABSTRACT: In most vertebrates, fully grown oocytes are arrested in meiotic prophase I and only resume the cell cycle upon external stimuli, such as hormones. The proper arrest and resumption of the meiotic cycle is critical for reproduction. A Galpha(S) signaling pathway essential for the arrest is conserved in organisms from Xenopus to mouse and human. A previous gene association study implicated that mutations of human ACSL6 may be related to premature ovarian failure. However, functional roles of ACSL6 in human infertility have yet to be reported. In the present study, we found that triacsin C, a potent and specific inhibitor for ACSL, triggers maturation in Xenopus and mouse oocytes in the absence of hormone, suggesting ACSL activity is required for the oocyte arrest. In Xenopus, acsl1b may fulfill a major role in the process, because inhibition of acsl1b by knocking down its RNA results in abnormal acceleration of oocyte maturation. Such abnormally matured eggs cannot support early embryonic development. Moreover, direct inhibition of protein palmitoylation, which lies downstream of ACSLs, also causes oocyte maturation. Furthermore, palmitoylation of Galpha(s), which is essential for its function, is inhibited when the ACSL activity is blocked by triacsin C in Xenopus. Thus, disruption of ACSL activity causes inhibition of the Galpha(s) signaling pathway in the oocytes, which may result in premature ovarian failure in human.
    No preview · Article · Jul 2012 · Biology of Reproduction
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    ABSTRACT: Aim: Human protein disulfide isomerase (hPDI) is a key enzyme and a redox-regulated chaperone responsible for oxidative protein folding in the endoplasmic reticulum. This work aims to reveal the molecular mechanism underlying the redox-regulated functions of hPDI by determining the crystal structures of hPDI in different redox states. Results: The structures of hPDI (abb'xa') in both the reduced and oxidized states showed that the four thioredoxin domains of a, b, b', and a' are arranged as a horseshoe shape with two CGHC active sites, respectively, in domains a and a' facing each other at the two ends. In reduced hPDI, domains a, b, and b' line up in the same plane, whereas domain a' twists ∼45° out. The two active sites are 27.6 Å apart. In oxidized hPDI, the four domains are differently organized to stay in the same plane, and the distance between the active sites increases to 40.3 Å. In contrast to the closed conformation of reduced hPDI, oxidized hPDI exists in an open state with more exposed hydrophobic areas and a larger cleft with potential for substrate binding. Innovation: This is the first report of the high-resolution structures of hPDI containing all four domains in both the reduced and the oxidized states. It reveals the redox-regulated structural dynamic properties of the protein. Conclusion: The redox-regulated open/closed conformational switch of hPDI endows the protein with versatile target-binding capacities for its enzymatic and chaperone functions.
    No preview · Article · Jun 2012 · Antioxidants & Redox Signaling
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    ABSTRACT: An imaging system based on single photon counting and compressive sensing (ISSPCCS) is developed to reconstruct a sparse image in absolute darkness. The single photon avalanche detector and spatial light modulator (SLM) of aluminum micro-mirrors are employed in the imaging system while the convex optimization is used in the reconstruction algorithm. The image of an object in the very dark light can be reconstructed from an under-sampling data set, but with very high SNR and robustness. Compared with the traditional single-pixel camera used a photomultiplier tube (PMT) as the detector, the ISSPCCS realizes photon counting imaging, and the count of photons not only carries fluctuations of light intensity, but also is more intuitive.
    Full-text · Article · Feb 2012
  • Chao Wang · Jiang Yu · Lin Huo · Lei Wang · Wei Feng · Chih-chen Wang
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    ABSTRACT: Protein-disulfide isomerase (PDI), with domains arranged as abb'xa'c, is a key enzyme and chaperone localized in the endoplasmic reticulum (ER) catalyzing oxidative folding and preventing misfolding/aggregation of proteins. It has been controversial whether the chaperone activity of PDI is redox-regulated, and the molecular basis is unclear. Here, we show that both the chaperone activity and the overall conformation of human PDI are redox-regulated. We further demonstrate that the conformational changes are triggered by the active site of domain a', and the minimum redox-regulated cassette is located in b'xa'. The structure of the reduced bb'xa' reveals for the first time that domain a' packs tightly with both domain b' and linker x to form one compact structural module. Oxidation of domain a' releases the compact conformation and exposes the shielded hydrophobic areas to facilitate its high chaperone activity. Thus, the study unequivocally provides mechanistic insights into the redox-regulated chaperone activity of human PDI.
    No preview · Article · Nov 2011 · Journal of Biological Chemistry
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    ABSTRACT: Cherenkov radiation is used to study the production of particles during collisions, cosmic rays detections and distinguishing between different types of neutrinos and electrons. The optical properties of water are very important to the research of Cherenkov Effect. Lambert-beer law is a method to study the attenuation of light through medium. In this paper, optical properties of water are investigated by use of a water attenuation performance test system. The system is composed of the light-emitting diode (LED) light source and the photon receiver models. The LED light source model provides a pulse light signal which frequency is 1 kHz and width is 100ns. In photon receiver model, a high sensitivity photomultiplier tube (PMT) is used to detect the photons across the water. Because the output voltage amplitude of PMT is weak which is from 80mv to 120mV, a low noise pre-amplifier is used to improve the detector precise. An effective detector maximum time window of PMT is 100ns for a long lifetime, so a peak holder circuit is used to hold the maximum peak amplitude of PMT for the induced photons signal before the digitalization. In order to reduce the noise of peak holder, a multi-pulse integration is used before the sampling of analog to digital converter. At last, the detector of photons from the light source to the PMT across the water is synchronized to the pulse width of the LED. In order to calculate the attenuation coefficient and attenuation length of water precisely, the attenuation properties of air-to-water boundary is considered in the calculation.
    No preview · Conference Paper · Jun 2011
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    ABSTRACT: Recent developments in three-dimension imaging, quantum cryptography, and time-resolved spectroscopy have stimulated interest in Linear-Mode and Geiger-Mode detecting avalanche photodiodes operating in the short wavelength. A linear-mode detector based on an InGaAs avalanche photodiode (APD) has been investigated for use at near infrared communication wavelengths. In the experiments of this paper, sine gate signals coupled with DC biased voltage were applied to two APDs with the same semiconductor material and structure for detecting the pulse light signal. As the avalanche signals were mixed with sine wave background, a transformer-based method was applied to eliminate the background noise and improve the detection sensitivity of light induced signal. In order to test the maximum detection sensitivity, the sine pulse was delayed by a delay module before being applied to laser source, thus the pulse light signal and the sine pulse coupled to the detector were synchronized. From the performance tests, the frequency response from 10MHz to 100MHz is tested and the suitable range of biased voltage was acquired. Detection sensitivity and photoelectric gain were investigated in detail at 1.55um infrared wavelengths. In a word, the linear-mode APD working in gate-mode and mutual-differencing method can be widely used in optical communication such as Non-line-of-sight communication, free space communication, fiber communication, deep space communication, and satellite optical network communication.
    No preview · Article · Jun 2011 · Proceedings of SPIE - The International Society for Optical Engineering
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    ABSTRACT: Protein disulfide isomerase (PDI), which consists of multiple domains arranged as abb'xa'c, is a key enzyme responsible for oxidative folding in the endoplasmic reticulum. In this work we focus on the conformational plasticity of this enzyme. Proteolysis of native human PDI (hPDI) by several proteases consistently targets sites in the C-terminal half of the molecule (x-linker and a' domain) leaving large fragments in which the N terminus is intact. Fluorescence studies on the W111F/W390F mutant of full-length PDI show that its fluorescence is dominated by Trp-347 in the x-linker which acts as an intrinsic reporter and indicates that this linker can move between "capped" and "uncapped" conformations in which it either occupies or exposes the major ligand binding site on the b' domain of hPDI. Studies with a range of constructs and mutants using intrinsic fluorescence, collision quenching, and extrinsic probe fluorescence (1-anilino-8-naphthalene sulfonate) show that the presence of the a' domain in full-length hPDI moderates the ability of the x-linker to generate the capped conformation (compared with shorter fragments) but does not abolish it. Hence, unlike yeast PDI, the major conformational plasticity of full-length hPDI concerns the mobility of the a' domain "arm" relative to the bb' "trunk" mediated by the x-linker. The chaperone and enzymatic activities of these constructs and mutants are consistent with the interpretation that the reversible interaction of the x-linker with the ligand binding site mediates access of protein substrates to this site.
    No preview · Article · Aug 2010 · Journal of Biological Chemistry
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    ABSTRACT: Single-photon detector based on an InGaAs avalanche photodiode is one of hot research on the quantum photon, and is one of the key technologies on quantum communication and quantum image. It is widely used in applications as high sensitive photon spectrum, high speed optic measurement and so on. A suitable delay and comparator with latch function circuit are used to prevent positive and negative transient pulses from influencing the detection of true photon induced avalanches. A dead time modulation feedback control circuit decreases the after-pulse. Especially, ECL difference circuit is the key of high speed single photon detector. In addition, the detector uses the hot tube fan-cooling method. From the performance test, the lowest temperature reaches -62°C, the minimum gate pulse width is 2ns (Full-Width-Half-Max, FWHM) and the dark counter rate is 2.5×10-6 ns-1 with a detection rate of 10MHz when the quantum efficiency is more than 10%.
    No preview · Article · May 2010 · Proceedings of SPIE - The International Society for Optical Engineering
  • Hao Yang · Chao Wang · Zhibin Sun · Song Cao · Guangjie Zhai · Ming Li
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    ABSTRACT: Kossel-line diffraction method is an important way to measure the structure of crystals. Colloidal crystal is one of the hotspots on the condensed physics research. The paper investigates the kinetics process of crystallization on several hundreds nanometer particles in aqueous. In order to obtain the diffraction image, a 473nm wavelength laser is used to irradiate samples, and then the Kossel-line image of sample is projected onto the translucent screen and recorded by IEEE 1394 charge coupled device (CCD) cameras. Especially, gravity convection effects can be eliminated under microgravity environment, therefore the research of growth mechanism of colloidal crystals in the space has great scientific significance. The crystallization processes of three kinds of colloidal solution are investigated in the temperature field and electric field by means of the shear-flow assisted. Finally, laser diffraction images and white conformation images can be analyzed for exploring the phase-change rule of colloidal crystals. Besides, parameters can be adjusted online by remote control function in order to improve the flexibility of experiments.
    No preview · Article · May 2010 · Proceedings of SPIE - The International Society for Optical Engineering

Publication Stats

163 Citations
45.97 Total Impact Points

Institutions

  • 2004-2016
    • Chinese Academy of Sciences
      • • National Laboratory of Biomacromolecules
      • • Center for Space Science and Applied Research
      • • Institute of Botany
      Peping, Beijing, China
  • 2015
    • Beijing Institute of Technology
      Peping, Beijing, China
  • 2012
    • Capital Medical University
      Peping, Beijing, China