Showing papers by "Jian Chen published in 2012"

Performance of a novel LED lamp arrangement to reduce SNR fluctuation for multi-user visible light communication systems

Abstract: This paper investigates the performance of our recently proposed LED lamp arrangement to reduce the SNR fluctuation from different locations in the room for multi-user visible light communications. The LED lamp arrangement consists of 4 LED lamps positioned in the corners and 12 LED lamps spread evenly on a circle. Our studies show that the SNR fluctuation under such a LED lamp arrangement is reduced from 14.5 dB to 0.9 dB, which guarantees that users can obtain almost identical communication quality, regardless of their locations. After time domain zero-forcing (ZF) equalization, the BER performances and channel capacities of 100-Mbit/s and 200-Mbit/s bipolar on-off-keying (OOK) signal with most significant inter-symbol interference (ISI) are very close to that of the channel without any ISI caused by this LED lamp arrangement.

Performance of dimming control scheme in visible light communication system

Abstract: We investigate the performance of visible light communication (VLC) system with a pulse width modulation (PWM) dimming control scheme. Under this scheme, the communication quality in terms of number of transmitted bits and bit error rate (BER) of less than 10(-3) should be guaranteed. However, for on-off-keying (OOK) signal, the required data rate becomes 10 times as high as the original data rate when the duty cycle of dimming control signal is 0.1. To make the dimming control scheme easy to be implemented in VLC system, we propose the variable M-QAM OFDM VLC system, where M is adjusted according to the brightness of LED light in terms of duty cycle. The results show that with different duty cycles the required data rates are not higher than the original value and less LED lamp power is required to guarantee the communication quality, which makes the dimming control system that satisfies both communication and illumination requirements easy to be implemented and power-saving.

Integrated Microgrid Laboratory System

Abstract: The paper presents an integrated microgrid laboratory system with a flexible and reliable multimicrogrid structure; it contains multiple distributed generation systems and energy storage systems and integrates with a diesel generator that serves as a back-up power source and flywheel energy storage for fast balancing to provide uninterruptible power-supply services in cooperation with the diesel generator. The microgrid system, by adopting the master-slave control strategy, can be transited flexibly between grid-connected and islanded modes and can be disconnected from the utility when a fault occurs or the power quality falls below specified standards. The developed bi-directional inverter which is applied in the system plays an important role. The small microgrids of this system are intended to operate separately or in the form of one large microgrid with a certain switch status. Furthermore, experiments on control, protection, and other technologies have been carried out. The results show that the operation conditions meet the related IEEE Standard 1547 and power quality requirements. The integrated microgrid laboratory system is able to operate stably and reliably under different conditions, including mode transition and fault events.

A Superconducting Magnet System for Whole-Body Metabolism Imaging

Abstract: A 9.4 Tesla superconducting magnet is designed and fabricated with a warm bore of 800 mm for neuroscience research. The superconducting magnet will be made of a NbTi Wire-in-Channel (WIC) conductor with a higher ratio of copper to non-copper, which thus sustains the high stresses. It is cooled to operate temperature at 4.2 K liquid helium. The cryostat system is cooled through GM cryocoolers, some used to cool the radiation shield, and the others realize the re-condensed liquid helium. The MRI magnet system has a high level of stored energy, about 134 MJ, and a relatively-lower nominal current, about 212.5 A. The magnet will be operated in a persistent current mode with a superconducting switch. The WIC wires are employed to meet the cryostability criteria to avoid any risks from quench. The protection circuit with the subdivision of the coil reduces the terminate voltage and hot-spot temperature. In the paper, the specifications of magnet system will be presented.

RRM1 and ERCC1 expression in peripheral blood versus tumor tissue in gemcitabine/carboplatin-treated advanced non-small cell lung cancer.

Abstract: To comparatively evaluate the prognostic or predictive value of ribonucleotide reductase M1 (RRM1) and excision repair cross-complementation 1 (ERCC1) gene expression in peripheral blood versus tumor tissue from patients with advanced non-small cell lung cancer (NSCLC) treated by gemcitabine/platinum chemotherapy. A total of 49 patients with advanced NSCLC receiving gemcitabine plus carboplatin chemotherapy were studied. RRM1 and ERCC1 mRNA levels in the peripheral blood and tumor tissue were determined by real-time fluorescent quantitative PCR. The relationships between gene expression and clinical and pathological factors, response to chemotherapy as well as prognosis, were evaluated. RRM1 expression in peripheral blood and tumor tissue, but not ERCC1 expression, was found to be positively correlated (r = 0.332, 0.258; P = 0.020, 0.073; respectively). RRM1 and ERCC1 expression levels were nearly synchronous in both peripheral blood (r = 0.351; P = 0.013) and tumor tissue (r = 0.634; P < 0.001). Neither was correlated with clinical and pathological factors. Patients with low RRM1 expression in peripheral blood or low RRM1 or ERCC1 expression in tumor tissue experienced better response to chemotherapy (50.0 vs. 16.0%, 50.0 vs. 16.0%, and 54.2 vs. 12.0%; P = 0.012, 0.012, and 0.003; respectively), longer median survival (18.5 vs. 13.0 months, 18.5 vs. 12.0 months, and 19.8 vs. 12.5 months; P = 0.043, 0.014 and 0.007; respectively), and longer progression-free survival (6.0 vs. 4.0 months, 7.8 vs. 3.9 months, and 5.8 vs. 3.8 months; P = 0.044, 0.016, and 0.008; respectively). Cox multivariate regression analysis showed that ERCC1 expression in tumor tissue was independent indicator for overall survival. Advanced NSCLC patients with low RRM1 mRNA expression both in peripheral blood and in tumor tissue could benefit from gemcitabine/carboplatin chemotherapy. ERCC1 mRNA expression in tumor tissue may be a predictive and prognostic indicator in advanced NSCLC patients receiving gemcitabine/carboplatin chemotherapy.

XRCC1 Arg399Gln and clinical outcome of platinum-based treatment for advanced non-small cell lung cancer: a meta-analysis in 17 studies

Abstract: Objective: XRCC1 polymorphism is a research hotpot in individual treatment for non-small cell lung cancer (NSCLC) To obtain the association between XRCC1 polymorphism and clinical outcome of platinum-based treatment for NSCLC, a meta-analysis was conducted Methods: Databases including PubMed, Embase, Cochrane, and Chinese National Knowledge Infrastructure (CNKI) were searched for publications that met the inclusion criteria A fixed effect model was used to estimate pooled odds ratio (OR) and hazard ratio (HR) with 95% confidence interval (CI) for the association between XRCC1 Arg399Gln and response or survival of platinum-based treatment for advanced NSCLC A chi-squared-based Q-test was used to test the heterogeneity hypothesis Egger’s test was used to check publication bias Results: Seventeen published case-control studies that focus on the association between XRCC1 Arg399Gln and response or survival of platinum-based treatment for advanced NSCLC in 2 256 subjects were included in this meta-analysis, of whom 522 were AA genotypes (232% frequency), 916 AG genotypes (406% frequency), and 818 GG genotypes (362% frequency) The overall response rate (ORR) was 452% (110/243) for AA genotype patients, 299% for AG genotype (73/244), and 307% for GG genotype (124/403) The heterogeneity test did not show any heterogeneity and the Egger’s test did not reveal an obvious publication bias among the included studies The meta-analysis indicated that AA genotype patients presented higher response rates toward platinum drug treatment compared with G model (GG+GA) patients (GG vs AA model: OR=0489, 95% CI 0266–0900, P=0021; AG vs AA model: OR=0608, 95% CI 0392–0941, P=0026; GA+AA vs GG model: OR=1259, 95% CI 0931–1701, P=0135; GG+GA vs AA model: OR=0455, 95% CI 0313–0663, P=00001) However, no evidence validates XRCC1 associates with the survival following platinum drug therapy Conclusions: Our meta-analysis suggested that XRCC1 Arg399Gln is related with the sensitivity of NSCLC patients to platinum-based treatment AA genotype patients present more desirable curative effectiveness compared with other patients

Character and fabrication of Al/Al2O3/Al tunnel junctions for qubit application

Abstract: The superconductive Josephson junction is the key device for superconducting quantum computation. We have fabricated Al/ Al2O3/Al tunnel junctions using a double angle evaporation method based on a suspended shadow mask. The Al2O3 junction barrier has been formed by introducing pure oxygen into the chamber during the fabrication process. We have adjusted exposure conditions by changing either the oxygen pressure or the oxidizing time during the formation of tunnel barriers to control the critical current density Jc and the junction specific resistance Rc . Measurements of the leakage in Al/Al2O3/Al tunnel junctions show that the devices are suitable for qubit applications.

A simple Fourier transform spectrometer for terahertz applications

Abstract: A simple Fourier transform spectrometer was designed and constructed for the measurement of detectors, sources, passive devices and materials in the terahertz (THz) range. It can be operated at frequencies between 0.3 and 1.5 THz, using a 50-μm-thick Mylar-film beam splitter. The spectral range can be changed by altering the thickness of the beam splitter. The highest frequency resolution is 750 MHz. We studied the properties of heterodyne detectors including superconductor mixers and semiconductor harmonic mixers, direct detectors including an InSb semiconductor bolometer, superconducting tunnel junctions and the Golay cell, and sources including Gunn oscillators and a microwave source with its multipliers, as well as various materials and passive devices including Si wafers and metal mesh filters.

Terahertz detectors based on superconducting hot electron bolometers

Abstract: Low noise terahertz (THz) heterodyne detectors based on superconducting niobium nitride (NbN) hot electron bolometers (HEBs) have been studied. The HEB consists of a planar antenna and an NbN bridge connecting across the antennas inner terminals on a high-resistivity Si substrate. The double sideband noise temperatures at 4.2 K without corrections have been characterized from 0.65 to 3.1 THz. The excess quantum noise factor β of about 4 has been obtained, which agrees well with the calculated value. Allan variance of the HEB has been measured, and Allan time up to 20 s is obtained using a microwave feedback method. Also, the intermediate frequency gain bandwidth (GBW) was measured using two different methods, resulting in same GBW value of about 3.5 GHz.

Simultaneous measurement of local longitudinal and transverse wave velocities, attenuation, density, and thickness of films by using point-focus ultrasonic spectroscopy

Abstract: This paper presents an ultrasonic technique for simultaneous determination of the complete set of acoustical and geometrical properties of a film or a thin layer in a stratified material embedded between two known materials using point-focus ultrasonic spectroscopy, which provides a high lateral resolution. The theoretical model of the two-dimensional spectrum Rt(θ,ω) of the stratified material is calculated as a function of six parameters of the unknown layer: longitudinal and transverse velocities cl, ct, attenuation αl, αt, density ρ, and thickness h, which fully determined the properties of the film. The experimental spectrum Re(θ,ω) can be measured by V(z,t) technique. A two-step algorithm is presented to decompose the searching process of parameters from one six-dimensional to two three-dimensional spaces. The sensitivity of the two-dimensional spectrum to individual properties and its stability against experimental noise are studied. The full set properties of a 250 μm thick stainless steel film an...

Angular measurement of acoustic reflection coefficients by the inversion of V(z, t) data with high frequency time-resolved acoustic microscopy.

Abstract: For inspection of mechanical properties and integrity of critical components such as integrated circuits or composite materials by acoustic methodology, it is imperative to evaluate their acoustic reflection coefficients, which are in close correlation with the elastic properties, thickness, density, and attenuation and interface adhesion of these layered structures. An experimental method based on angular spectrum to evaluate the acoustic coefficient as a function of the incident angle, θ, and frequency, ω, is presented with high frequency time-resolved acoustic microscopy. In order to achieve a high spatial resolution for evaluation of thin plates with thicknesses about one or two wavelengths, a point focusing transducer with a nominal center frequency of 25 MHz is adopted. By measuring the V(z, t) data in pulse mode, the reflection coefficient, R(θ, ω), can be reconstructed from its two-dimensional spectrum. It brings simplicity to experimental setup and measurement procedure since only single translation of the transducer in the vertical direction is competent for incident angle and frequency acquisition. It overcomes the disadvantages of the conventional methods requiring the spectroscopy for frequency scanning and/or ultrasonic goniometer for angular scanning. Two substrates of aluminum and Plexiglas and four stainless plates with various thicknesses of 100 μm, 150 μm, 200 μm, and 250 μm were applied. The acoustic reflection coefficients are consistent with the corresponding theoretical calculations. It opened the way of non-destructive methodology to evaluate the elastic and geometrical properties of very thin multi-layers structures simultaneously.

Performance of variable M-QAM OFDM visible light communication system with dimming control

Abstract: We investigate the performance of VLC system with pulse width modulation (PWM) dimming control. Under this scheme the communication quality in terms of correctly-received bits could remain the same by applying variable M-QAM OFDM.

Fast scanning mode and its realization in a scanning acoustic microscope.

Abstract: The scanning speed of the two-dimensional stage dominates the efficiency of mechanical scanning measurement systems. This paper focused on a detailed scanning time analysis of conventional raster and spiral scan modes and then proposed two fast alternative scanning modes. Performed on a self-developed scanning acoustic microscope (SAM), the measured images obtained by using the conventional scan mode and fast scan modes are compared. The total scanning time is reduced by 29% of the two proposed fast scan modes. It will offer a better solution for high speed scanning without sacrificing the system stability, and will not introduce additional difficulties to the configuration of scanning measurement systems. They can be easily applied to the mechanical scanning measuring systems with different driving actuators such as piezoelectric, linear motor, dc motor, and so on. The proposed fast raster and square spiral scan modes are realized in SAM, but not specially designed for it. Therefore, they have universal adaptability and can be applied to other scanning measurement systems with two-dimensional mechanical scanning stages, such as atomic force microscope or scanning tunneling microscope.

Detection system for improving stability of high sensitivity terahertz mixer and detection method

Abstract: The invention discloses a detection system for improving the stability of a high sensitivity terahertz mixer, which comprises a terahertz frequency band local oscillator signal source, a beam splitter, a silicon lens, a mixer, a coaxial three-way joint, a direct current blocker, an isolator, a low-temperature low-noise amplifier, a normal temperature intermediate-frequency amplifier, a band-pass filter, a device for converting an intermediate frequency power into a direct current voltage, a computer, a direct current bias power supply, a bias deice, a microwave source and a low temperature dewar. The invention also discloses a detection method for improving the stability of the high sensitivity terahertz mixer. In the invention, a feedback circuit is used to control a microwave power further lower than a terahertz power so as to compensate the instability of a terahertz local oscillator power; and by taking the HEB (Hot Electron Bolometer) mixer as an example, the Allen time of the mixer is prolonged to about 10 seconds from about 1 second and the temperature resolution is improved by 30 percent.

Spectral dependence of ultra-low dark count superconducting single photon detector for the evaluation of broadband parametric fluorescence

Abstract: Superconducting nanowire single photon detectors (SNSPD) have unique characteristics of ultra low dark counts and wide spectrum sensitivity. These natures are indispensable for the evaluation of ultra-broadband parametric fluorescence, which are used for the quantum optical coherence tomography and novel optical non-linear experiments. Here we report the spectral dependence of the detection efficiency of a meander type SNSPD device, having reduced strip width of 50 nm, over a wide spectrum range up to near infra-red wavelength. The fiber coupled, meander type device was fabricated using 6 nm thick Niobium nitride (NbN) nanowires of reduced strip width, 50 nm, patterned over a MgO substrate with active area of 10 x 10 μm 2 . A maximum efficiency of 32% at 500 nm, 30% at 600 nm, 16% at 800 nm, 10% at 1000 nm, and 1% at 1550 nm with the normalized bias current of 0.95 (bias 37 μA ) was observed at 4.2 K. The salient feature of the device is, it exhibits a very low dark count rate (DCR) of only 2 Hz at the standard operating bias of 37 μA and ultra low DCR of 0.01Hz at 34 μA. Moreover, at this reduced bias with 0.01Hz DCR, the detection efficiency is not appreciably decreased in the visible region (32% at 500 nm and 30% at 600 nm) and an order decrease is observed (0.1%) at 1550 nm. The noise equivalent power (NEP) is of the order 10 -19 WHz-1/2 in the visible region and 10 -17 WHz - 1/2 in the near IR region. Ultra-broad band parametric fluorescence of band width from 791 nm to 1610 nm generated by a quasi-phase matched (QPM) device was successfully detected with this SSPD.

User-oriented visible light communication system with dimming control scheme

Abstract: Our recent progresses in visible light communication (VLC) systems are reviewed. The methods to improve performances of VLC system for single user and multi-user are described. The principle and performance under dimming control scheme are also studied.

Phase estimation in coherent optical fiber communication systems with advanced modulation formats

Abstract: The performance of decision-aided maximum likelihood (DA ML) phase estimation is investigated for different modulation formats, and Gardner-timing-based frequency offset estimation is demonstrated which achieves an estimation range of ±0.5 times the system symbol rate.

Landau-Zener-St"uckelberg Interference of Microwave Dressed States in a Superconducting Phase Qubit

Abstract: National Laboratory of Solid State Microstructures,School of Physics, Nanjing University, Nanjing 210093, China(Dated: November 2, 2010)Dressed state[1], the eignstate of a combined system of light and matter, has been proposed asfundamental concept to interpret quantum interaction between photons and atoms or molecules.Recently, this picture has been extended to describe the hybrid system of photons and super-conducting circuits[2{4]. Here, we present the rst observation of Landau-Zener-Stuc kelberg (LZS)interference[5] of the dressed states arising from an arti cial atom, a superconducting phase qubit[6],interacting with a microwave eld. The LZS interference fringes, which depend on the sweep rate,the frequency and power of the microwave, and the initial state of the qubit, agree with the theoret-ical prediction quantitatively. The LZS interferometry between the microwave dressed qubit statesalso enables us to control the quantum states of a tetrapartite solid-state system with ease andprecision, demonstrating the feasibility of implementing ecient multipartite quantum logic gateswith this unique approach.

Preparation method of high-temperature superconductive Josephson bicrystal junction

Abstract: The invention discloses a preparation method of a high-temperature superconductive Josephson bicrystal junction Microbridge etching for the high-temperature superconductive Josephson bicrystal junction is carried out through combination of an acid etching process and an ion etching process, so that not only is the problem of serious sideetching caused by a super-thick film when only the acid etching process is adopted solved, but also the problem of long-term super-high temperature when only the ion etching process is adopted is avoided Meanwhile, the film is properly thinned by using the ion etching process after etching is finished so that the weak connection performance at a microbridge crystal boundary is further improved, a favorable superconductive Josephson effect of the junction is ensured, and the nonlinearity of the junction is improved A current and voltage relation curve of a T1BaCaCuO bicrystal junction is measured under the condition of liquid nitrogen by using a four-electrode method, and the critical current Ic is about 200muA when the temperature is 60K; an obvious Shapiro step appears after 210G microwave irradiation is added; and a 210G frequency mixing experiment is carried out to obtain 14th subharmonic frequency mixing intermediate frequency output, and therefore, the preparation method has favorable application and development prospects

Extraordinary Transmission through Fractal-Featured Metallic and Superconducting Films at Terahertz Frequency

Abstract: We report on fractal-featured square and ring-shaped apertures with a Sierpinski carpet pattern (SCP) on metallic and superconducting NbN films. Multiple extraordinary terahertz (THz) transmission peaks are studied in the transmission spectra using both THz time-domain spectroscopy and numerical simulation. The characteristic transmission peaks are found to be associated with the interaction of surface plasmon polaritons (SPPs) and localized surface plasmons (LSPs) for ring-shaped apertures. The effect of LSPs is less remarkable in the square apertures. For the superconducting NbN film, when the temperature is slightly lower than the critical transition temperature Tc, the peak magnitude of SPP resonances is most prominent due to the non-monotonic temperature dependence of kinetic inductance. These results provide a new way to design compact and efficient THz devices.

Compound manipulation of micro-particles using a single device:Ultrasonic trapping, transporting, and rotating

Abstract: Ultrasonic manipulation is widely used as a noncontact technology and recently small particles rotating on a vibrating substrate has been observed. In this report,a novel methodology which compounds the procedures of ultrasonic trapping, transporting and rotating micro-particles in fluid using a single device is investigated. Irregular micro-particles in a standing wave field experience both acoustic radiation force and torque, which drive the particles to pressure nodes and keep them in a balance posture. A prototype device has also been built according to this theory, which six phase-controlled piezoelectric transducers whose sound beam axes are arranged with an angle of 60 deg in the x-y plane are used to generate ultrasonic standing waves with arbitrary node. The transducers are divided to two groups, so the wave field can be rotated by switching between the two groups. The synthesized sound field is scanned using a needle hydrophone and 200 μm irregular SiO2 particles are used to perform the compound...

Decision-aided carrier phase estimation for coherent optical communication systems

Abstract: We review the performance of decision-aided maximum likelihood (DA ML) phase estimation and its adaptive counterpart in different modulation formats.