Search

The modular multilevel converter-based high voltage direct current transmission (MMC-HVDC) technology has become an effective integrating method for large-capacity offshore wind farms. However, if AC side faults occur between the MMC and the wind farm, conventional current differential protection might not detect the enlarge fault current at the wind farm and the MMC. In the worst case, MMC blocking may occur and can cause relay refusal. Therefore, a novel singular value decomposition (SVD) based pilot protection is proposed to address this problem. A Hankel matrix is established for the short-circuit current at each end of the AC line and can rapidly detects the singularity of the signal and its derivative. The SVD method only uses a short time window which enables the detection of the fault features before MMC blocking occurs. A detailed model of an offshore wind farm connected to the MMC-HVDC system is established in the real-time digital simulator (RTDS). A protection device compliant with industry standards is used to implement the SVD-based protection algorithm. Hardware-in- loop dynamic experimental tests are conducted to verify the performance of the proposed protection method. The experimental results demonstrate that the SVD-based protection method has excellent performance during various fault scenarios.

With the integration of the large-scale wind farms, the conventional pilot protection is facing new challenges. It suffers from the performance degradation can even refuse operation for some extreme faut scenarios. To address this problem, this paper presents a novel pilot protection based on cosine similarity. The protection setting calculation and industrial application testing is investigated. The functional structure is described and the logic of the cosine similarity based protection is evaluated under different fault scenarios. Compared with the conventional differential protection, application of the proposed protection can greatly improve the relay performance. The proposed protection is embedded into an industry relay device, the standard hardware-in-loop tests are carried out using the real time digital simulator (RTDS) before the industrial application. Now the protection device based on cosine similarity is installed in the wind farms and put into operation in Inner Mongolia.

The wettability of graphene is critical for numerous applications but is very sensitive to its surface cleanness. Herein, by clarifying the impact of intrinsic contamination, i.e., amorphous carbon, which is formed on the graphene surface during the high-temperature chemical vapor deposition (CVD) process, the hydrophilic nature of clean graphene grown on single-crystal Cu(111) substrate was confirmed by both experimental and theoretical studies, with an average water contact angle of ∼23°. Furthermore, the wettability of as-transferred graphene was proven to be highly dependent on its intrinsic cleanness, because of which the hydrophilic, clean graphene exhibited improved performance when utilized for cell culture and cryoelectron microscopy imaging. This work not only validates the intrinsic hydrophilic nature of graphene but also provides a new insight in developing advanced bioapplications using CVD-grown clean graphene films.

Cryo-electron microscopy (cryo-EM) has emerged as a vital tool to reveal the native structure of beam-sensitive biomolecules and materials. Yet high-resolution cryo-EM analysis is still limited by the poorly controlled specimen preparation and urgently demands a robust supporting film material to prepare desirable samples. Here, we developed a bilayer Janus graphene membrane with the top-layer graphene being functionalized to interact with target molecules on the surface, while the bottom layer being kept intact to reinforce its mechanical steadiness. The ultraclean and atomically thin bilayer Janus membrane prepared by our protocol on one hand generates almost no extra noise and on the other hand reduces the specimen motion during cryo-EM imaging, thus allowing the atomic-resolution characterization of surface functional groups. Using such Janus membranes in cryo-EM specimen preparation, we were able to directly image the lithium dendrite and reconstruct macromolecules at near-atomic resolution. Our results demonstrate the bilayer Janus design as a promising supporting material for high-resolution cryo-EM and EM imaging.

The laser-induced breakdown spectroscopy (LIBS) analysis method displays significant matrix effects which greatly hinder the application of this technology. Even if the concentration of a certain element is constant, the physical properties and composition of the sample will affect the element signal. In order to further deepen the understanding of matrix effects, in this paper, the effect of matrix effects (Al matrix and Fe matrix) on the quantitative analysis of Si, Mn, Cr and Cu under different laser defocusing amounts and spectrometer delays is researched. This study found that the matrix effects have different degrees of effect on the analysis line under different experimental parameters. Moreover, the effect of the matrix effects can be reduced by adjusting the laser defocus amount and spectrometer delay. In addition, taking the spectrum generated by the pure sample as the matrix background and subtracting the intensity value of the matrix background at the analysis line can reduce the interference of the matrix effects. After deducting the matrix background, the determination coefficient of mixed quantitative analysis of the three elements Si, Cu, and Cr in Al and Fe matrixes can reach more than 0.99. Besides, for the Mn 257.6 nm, which is severely interfered by the spectrum of the Al matrix and Fe matrix, respectively, the determination coefficient of the mixed quantitative analysis can reach 0.9855.

As an alternative to satellite communications, multi-hop relay networks can be deployed for maritime long-distance communications. Distinct from terrestrial environment, marine radio signals are affected by many factors, e.g., weather conditions, evaporation ducting, and ship rocking caused by waves. To ensure the data transmission reliability, the block Markov superposition transmission (BMST) codes, which are easily configurable and have predictable performance, are applied in this study. Meanwhile, the physical-layer network coding (PNC) scheme with spatial modulation (SM) is adopted to improve the spectrum utilization. For the BMST-SM-PNC system, we propose an iterative algorithm, which utilizes the channel observations and the a priori information from BMST decoder, to compute the soft information corresponding to the XORed bits constructed by the relay node. The results indicate that the proposed scheme outperforms the convolutional coded SM-PNC over fast-fading Rician channels. Especially, the performance can be easily improved in high spatial correlation maritime channel by increasing the memory m.

Formation of graphene wrinkle arrays can periodically alter the electrical properties and chemical reactivity of graphene, which is promising for numerous applications. However, large-area fabrication of graphene wrinkle arrays remains unachievable with a high density and defined orientations, especially on rigid substrates. Herein, relying on the understanding of the formation mechanism of transfer-related graphene wrinkles, the graphene wrinkle arrays are fabricated without altering the crystalline orientation of entire graphene films. The choice of the transfer medium that has poor wettability on the corrugated surface of graphene is proven to be the key for the formation of wrinkles. This work provides a deep understanding of formation process of transfer-related graphene wrinkles and opens up a new way for periodically modifying the surface properties of graphene for potential applications, including direct growth of AlN epilayers and deep ultraviolet light emitting diodes.

Contamination commonly observed on the graphene surface is detrimental to its excellent properties and strongly hinders its application. It is still a great challenge to produce large-area clean graphene film in a low-cost manner. Herein, we demonstrate a facile and scalable chemical vapor deposition approach to synthesize meter-sized samples of superclean graphene with an average cleanness of 99 %, relying on the weak oxidizing ability of CO to etch away the intrinsic contamination, i.e., amorphous carbon. Remarkably, the elimination of amorphous carbon enables a significant reduction of polymer residues in the transfer of graphene films and the fabrication of graphene-based devices and promises strongly enhanced electrical and optical properties of graphene. The facile synthesis of large-area superclean graphene would open the pathway for both fundamental research and industrial applications of graphene, where a clean surface is highly needed.

Although single-particle cryogenic electron microscopy (cryo-EM) has been applied extensively for elucidating many crucial biological mechanisms at the molecular level, this technique still faces critical challenges, the major one of which is to prepare the high-quality cryo-EM specimen. Aiming to achieve a more reproducible and efficient cryo-EM specimen preparation, novel supporting films including graphene-based two-dimensional materials have been explored in recent years. Here we report a robust and simple method to fabricate EM grids coated with single- or few-layer reduced graphene oxide (RGO) membrane in large batch for high-resolution cryo-EM structural determination. The RGO membrane has decreased interlayer space and enhanced electrical conductivity in comparison to regular graphene oxide (GO) membrane. Moreover, we found that the RGO supporting film exhibited nice particle-absorption ability, thus avoiding the air-water interface problem. More importantly, we found that the RGO supporting film is particularly useful in cryo-EM reconstruction of sub-100 kDa biomolecules at near-atomic resolution, as exemplified by the study of RBD-ACE2 complex and other small protein molecules. We envision that the RGO membranes can be used as a robust graphene-based supporting film in cryo-EM specimen preparation.

This paper describes how the maximum blur radius affects the depth results by depth from the defocus (DFD) method based on liquid crystal (LC) lens. Boundary frequency is determined by the maximum blur radius. It is found that if the maximum blur radius used in the calculation is larger than the real value, the depth resolution obtained is reduced; on the other hand, if one smaller than the real value is used, the depth resolution in the middle range of the scene is increased, but errors occur in the near and far planes. Using the maximum blur radius close to the real one results in the best depth results.

The fast development of high-resolution electron microscopy (EM) demands a background-noise-free substrate to support the specimens, where atomically thin graphene membranes can serve as an ideal candidate. Yet the preparation of robust and ultraclean graphene EM grids remains challenging. Here we present a polymer- and transfer-free direct-etching method for batch fabrication of robust ultraclean graphene grids through membrane tension modulation. Loading samples on such graphene grids enables the detection of single metal atoms and atomic-resolution imaging of the iron core of ferritin molecules at both room- and cryo-temperature. The same kind of hydrophilic graphene grid allows the formation of ultrathin vitrified ice layer embedded most protein particles at the graphene-water interface, which facilitates cryo-EM 3D reconstruction of archaea 20S proteasomes at a record high resolution of ~2.36 Å. Our results demonstrate the significant improvements in image quality using the graphene grids and expand the scope of EM imaging., High-resolution electron microscopy requires robust and noise-free substrates to support the specimens. Here, the authors present a polymer- and transfer-free direct-etching method for fabrication of graphene grids with ultraclean surfaces and demonstrate cryo-EM at record high resolution.

This paper proposes a novel refocusing method that can effectively, digitally refocus objects on the arbitrary plane of the three-dimensional scene from the all-in-focus intensity and depth image pair with a liquid crystal (LC) lens camera. LC lens imaging system combines the transient prosperity of LC lens and the image process to simultaneously obtain the large depth of field intensity and depth image. The LC lens imaging system captured a set of constant magnification images with different focused distances between the two LC lens states’ switching. Then the depth information will be calculated with the far- and near-focused images, and the large depth of field intensity will be fused from the sets of images.

The method of double-pulse laser-induced breakdown spectroscopy is usually employed to enhance the spectral signal intensity. However, in this study, double-pulse laser-induced breakdown spectroscopy is adopted to investigate the effect of the self-absorption reduction of the spectrum. This research explored that the influence of the change of the gas environment generated by the first laser beam on the self-absorption effect of the plasma spectrum by the second laser beam. Especially despite the different combinations of laser energy, for the three elements of Cu, Mn and Ni, the weakest spectral self-absorption effect can be obtained when the double-pulse delays are around 80 μs, 100 μs, and 110 μs, respectively. In addition, this paper also found that when the energy of the first laser beam is unchanged, the spectral self-absorption effect has a strong correlation with the double-pulse delay, and has a weak correlation with the change of the second laser energy.

In this study, non-orthogonal multiple access (NOMA)-based coordinated direct and relay transmission (CDRT) is considered, where a base station ( BS ) directly communicates with two cell-centre users (CCUs) while communicating with a cell-edge user (CEU) via a relay. A novel dynamic scheme is proposed, in which the CCU close to the BS will act as a relay to assist the CEU in the second phase if it can obtain the prior information of the CEU in advance, otherwise it will switch to the receiving mode. To evaluate the system performance of the proposed scheme, the closed-form expressions of the outage probability, diversity order and ergodic sum rate (SR) are, respectively, derived. Simulation results demonstrate that the proposed scheme attains greater diversity order for the CEU as well as superior outage performance without performance loss of the ergodic SR, compared with conventional one in NOMA-based CDRT. In addition, a suboptimal power allocation (SPA) for this dynamic scheme is put forward, for which the closed-form expression is also obtained. It is also indicated that the presented SPA for dynamic scheme achieves near-optimal ergodic SR performance at high SNR region.

The technique of micro-laser-induced breakdown spectroscopy (μLIBS) usually refers to analyzing the surface of the sample using a compact focused laser beam in the optical microscope range. Compared to conventional laser-induced breakdown spectroscopy (LIBS), it can provide more abundant form, structure, and content information on a smaller, less sample condition. Hence, the application field is very wide. In this paper, the basic status of μLIBS in the selection of laser source and the structure of optical path system is introduced, and its application in metal, semiconductor, animal and plant fields is reviewed. The existing problems and potential development direction is pointed out.

The wettability of graphene remains controversial owing to its high sensitivity to the surroundings, which is reflected by the wide range of reported water contact angle (WCA). Specifically, the surface contamination and underlying substrate would strongly alter the intrinsic wettability of graphene. Here, we investigate the intrinsic wettability of graphene by measuring WCA on suspended, superclean graphene membrane using environmental scanning electron microscope. An extremely low WCA with an average value ∼ 30o was observed, confirming the hydrophilic nature of pristine graphene. This high hydrophilicity originates from the charge transfer between graphene and water molecules through H-π interaction. Our work provides a deep understanding of the water-graphene interaction and opens up a new way for measuring the surface properties of 2D materials. This article is protected by copyright. All rights reserved.

A polar code-based overlapping transmission scheme to improve channel utilisation for Internet of Vehicles is presented. In the presented scheme, different relay nodes (RNs) are allowed to send their packets to the destination node (DN) in the same time slot and frequency band. The signals from RNs to DN are overlapped and hence non-orthogonal. However, the information in the overlapped signals can be recovered by the proposed decoding algorithm. Numerical results show that the decoding algorithm performs well on information recovery in the presented transmission scheme.

Graphene exhibits properties of atomic thickness, high transparency, and high carrier mobility, which is highly desirable for a flexible transparent conductive material. However, the electronic properties of large-area chemical vapor deposition grown graphene film suffer from insulated polymer contaminations introduced by the transfer process and the easily cracked nature. Here, we report a preparation method of a transfer-medium-free large-area nanofiber-reinforced graphene (a-PAN/G) film simply by annealing the electrostatically spun polyacrylonitrile (PAN) nanofibers on the graphene film. The film could be free-standing on water and suspended in air with high transparency and enhanced electrical and mechanical properties compared to that of a monolayer graphene film. The flexible transparent a-PAN/G films were demonstrated as active materials for sensitive pressure sensors. The obtained pressure sensors demonstrate high sensitivity (44.5 kPa-1 within 1.2 kPa), low operating voltage (0.01-0.5 V), and excellent stability for 5500 loading-unloading cycles, revealing promising potential applications in wearable electronics.

In this paper, a multiple-input multiple-output (MIMO) amplify-and-forward (AF) relay system with direct link is investigated, where simultaneous wireless information and power transfer (SWIPT) technique is applied at the multiple-antenna relay node which splits the received signal into two parts, one portion is used for information decoding (ID) and the other portion is adopted for energy harvesting (EH). By considering power splitting (PS) scheme of SWIPT, the relay node consumes the harvested energy to forward the ID signal to the destination. We design the precoding matrixes of the source and relay nodes to derive the achievable rate. Finally, the analytical results are validated by the simulations.

In this paper, a multiple-input multiple-output (MIMO) two-way amplify-and-forward (AF) relay system is investigated, where simultaneous wireless information and power transfer (SWIPT) technique is applied at the massive-antenna relay node which splits the received signal into two parts, one portion is used for information decoding (ID) and the other portion is adopted for energy harvesting (EH). By considering power splitting (PS) scheme of SWIPT, the relay node consumes the harvested energy to forward the ID signal to two users. When the number of relay antennas approaches to infinity, the deterministic sum-rate of the relay system is analyzed. The close-form expression of optimal PS factor is derived. Finally, the analytical results are validated by the simulations.

In the micro-laser-induced breakdown spectroscopy field, when the laser ablated crater on the surface of the sample is less than 10 μm, it is difficult to detect the plasma emission line because of short lifetime of excited plasma, and simultaneous quantitative analysis of multiple elements is rarely reported. In this paper, a picosecond LIBS micro-area analysis scheme is proposed. Compared with the femtosecond laser micro-area analysis system, this scheme is more mature and reliable, and is more beneficial to engineering applications. In addition, in this study, the effect of the number of laser pulses on the crater morphology was studied. It was observed that a certain crater depth would have an enhancement effect on the signal, and by controlling the laser energy, a crater less than the diffraction limit was obtained. Moreover, a multielement simultaneous analysis on a set of molybdenum-copper stainless steel samples containing 40%-70% iron was performed when the ablated crater had an outer diameter of approximately 5 μm and an inner diameter of approximately 3 μm. By accumulating spectral intensity, background removal, and abnormal point processing, the calibration results for the eight elements of Mn, Cr, Ni, Cu, Ti, V, Nb and Al were not less than 0.95 using the basic calibration method. Among them, the calibration results for Ni, Cu, V, Nb, Al elements are all higher than 0.99 and the detection limits of the obtained elements range from 0.04% to 1.8%.

Flow fields play an important role in performance enhancement of a Proton Exchange Membrane Fuel Cells (PEMFCs). However, the weak mass transport ability of the conventional parallel flow field seriously affects the cell performance, especially at high current density. In this work, a series of S-shaped flow fields are designed and experimentally verified. The effects of key design parameters, such as the S radius (R) and the S length (H), on the cell performance are investigated in detail by recording the polarization curves under different cathode relative humidity (RH) levels and stoichiometric ratios. The results indicate that the small R and large H are beneficial to the promotion of cell performance owing to the increased turbulence and decreased liquid water content in the cell, which is also proved by the electrochemical impedance spectroscopy (EIS). However, the pressure drop significantly increases at the same time, which affects the output ability of the cell. Considering the net output capacity and the processing processing possibility, the cell with the S radius of 17.4 mm and the S length of 40 mm exhibited the peak power density of 1.02 W cm−2, with 15% higher than the CPFF (870 W cm−2).

Mycobacterium tuberculosis (MTB) infection remains a serious infectious disease worldwide, causing 8.8 million new infections and 1.45 million deaths in 2010 [1]. The emergence of drug-resistant strains of MTB poses a significant threat to the control of the disease globally. Multidrugresistant MTB (MDR-TB), defined as being resistant to at least rifampicin (RMP) and isoniazid (INH), and extensively drug-resistant TB (XDR-TB), defined as being additionally resistant to any fluoroquinolone and one injectable secondline drug, are associated with higher treatment failure rates. China is the second largest nation in terms of the number of the MTB infection, and 9.3% of the cases are MDR-TB [2]. MDR-TB arises from spontaneous chromosomal mutations at low frequency, but clinical MDR-TB largely occurs as a result of man-made selection during disease treatment of these genetic alterations through erratic drug supply, suboptimal physician prescription, and poor patient adherence [3]. S315T/M mutation in katG and mutations in the promoter region of inhA operon are the main mechanisms of INH resistance [4,5]. Mutations at positions 516, 526, and 531 in rpoB are the most frequent mutations in RMP-resistant MTB strains [6]. Since the transmission of the selected MDR-TB strains causes a large number of MDR-TB cases [7,8], the need for rapid, reliable, and cost-effective drug susceptibility testing (DST) is urgent. Polymerase chain reaction (PCR) followed by ligase detection reaction (LDR) method has been widely used to detect various single nucleotide polymorphisms and drug-resistant mutations with high sensitivity and low cost [9–12]. In the present study, we established a PCR-LDR assay for the simultaneous detection of the mutations related to MDR-TB, and evaluated its performance using isolates and clinical samples. Here, a total of 120 MTB isolates obtained from pulmonary TB patients at The Third Hospital of Changzhou, during July, 2011 and March, 2012 were collected and subjected to DST for RMP and INH in the BACTEC MGIT 960 instrument with medium, and DST supplement (Becton Dickinson and Company, Sparks, USA) as recommended by the manufacturer. All the 120 MTB isolates were detected by phenotypic DST, PCR-LDR, and DNA sequencing. The specific primers and probes (Supplementary Tables S1 and S2) for both wild type and mutant type targeting codon 315 of the katG gene, codon 15 of the inhA promoter region, codons 516, 526, and 531 of rpoB. All the primers and probes were synthesized by Invitrogen (Shanghai, China). Genome DNA of MTB was extracted by a commercial kit (Fosun Diagnostics, Shanghai, China) according to manufacturer’s instruction. All isolates were detected by both the PCR-LDR assay and sequencing. The multiplex PCR-LDR method was the same as described in previous studies [11,12]. The amplifications and LDR were performed in a PE 9600 thermal cycler (Life Technology, Foster City, USA). The LDR products were electrophoresed on an ABI 377 DNA Sequencer (Life Technology) for 30 min. Results were analyzed using the GeneMapper software (Life Technology). Meanwhile, the PCR products of rpoB and inhA promoter region were purified and sequenced by Life Technology. The results of phenotypic DST, PCR-LDR, and DNA sequencing were summarized in Table 1. Phenotypic DST of MTB isolates indicated that 26 (21.7%) at low level (1 mg/ ml) and 11 (9.2%) at high level (10 mg/ml) resistance to INH, while 17 (14.2%) at low-level and 9 (7.5%) at highlevel resistance to RMP. Among them, 13 (10.8%) were resistant to both INH and RMP at low level, or MDR. PCR-LDR assays for the detection of MDR-TB were carried out on 120 isolates. The S315M in katG was detected in 16 (13.3%) of 120 isolates. No S315T mutation in katG and G15T mutation in the promoter region of inhAwas detected. The D516V/G, H526Y/D, S531/L/W mutations in rpoB were detected in 1 (0.8%), 3 (2.5%), and 8 (6.7%) of 120 isolates, respectively. The typical results of PCR-LDR were shown in Fig. 1 and Supplementary Fig. S1. Acta Biochim Biophys Sin 2014, 46: 78–81 |a The Author 2013. Published by ABBS Editorial Office in association with Oxford University Press on behalf of the Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences. DOI: 10.1093/abbs/gmt119. Advance Access Publication 11 November 2013

Contamination is a major concern in surface and interface technologies. Given that graphene is a 2D monolayer material with an extremely large surface area, surface contamination may seriously degrade its intrinsic properties and strongly hinder its applicability in surface and interfacial regions. However, large-scale and facile treatment methods for producing clean graphene films that preserve its excellent properties have not yet been achieved. Herein, an efficient postgrowth treatment method for selectively removing surface contamination to achieve a large-area superclean graphene surface is reported. The as-obtained superclean graphene, with surface cleanness exceeding 99%, can be transferred to dielectric substrates with significantly reduced polymer residues, yielding ultrahigh carrier mobility of 500 000 cm2 V-1 s-1 and low contact resistance of 118 Ω µm. The successful removal of contamination is enabled by the strong adhesive force of the activated-carbon-based lint roller on graphene contaminants.

Achieving high expression levels of recombinant human serum albumin (HSA) for purification is a solution for the large amount of plasma-derived HSA needed in therapeutic applications. Here, we employed phiC31 integrase system and chicken hypersensitive site-4 (cHS4) insulators to construct a HSA expression vector for high-level HSA expression. The phiC31 integrase system mediated efficient transgene integration in bovine mammary epithelial cells (bMECs). A preferred pseudo attP site, which had 38 % identity with the 39 bp wild-type attP sequence, was detected in six out of 55 bMEC colonies. Addition of the cHS4 insulator to the phiC31 integrase system resulted in 8-20-fold increases of HSA expression compared with that of using integrase alone. Moreover, the reverse-oriented cHS4 insulator in the phiC31 integrase system provided the optimal level of HSA expression in bMECs.

This paper presents a method for the automatic adjustment of the laser defocusing amount in micro-laser-induced breakdown spectroscopy. A microscopic optical imaging system consisting of a CCD camera and a 20× objective lens was adopted to realize the method. The real-time auto-focusing of the system was achieved by detecting the effective pixels of the light spot generated by the laser pointer. The focusing accuracy of the method could achieve 3 μm. The element concentrations of Mn and Ni in low-alloy steels were analyzed at a crater diameter of about 35 μm using the presented method. After using the presented method, the determination coefficients of Mn and Ni both exceeded 0.997, with the root-mean-square errors being 0.0133 and 0.0395, respectively. Scanning analysis was performed on the inclined plane and the curved surface by means of focusing control and non-focusing control. Ten characteristic spectral lines of Fe were selected as the analysis lines. With the focusing control, the average relative standard deviations obtained on the inclined plane and curved surface were both less than 5%, and much less than the values without focusing control, 14.6% and 40.39%.

This paper reports on the laser notching technology in C70S6 steel for fracture splitting connecting rod using a Nd:YAG pulsed laser. The effects of process parameters on starting notch (SN) dimension and morphology were investigated by both finite element method (FEM) simulations and physical experiments for various process parameters. Optical microscopy and the scanning electron microscope (SEM) were used for the measurement of SN dimension and the observation of SN morphology in the experiment. The results were compared with the predictions. It was found that the FEM simulations results showed good consistency with the experiments, which indicates that the finite element model is feasible and reliable. Based on the principal findings from the two methods, optimum ranges of process parameters for different fracture splitting connecting rods were predicted, which are a flexibly adjusting notch depth, a curvature radius less than 0.08 mm and an opening angle within the range 18–26°. The results indicate that the predicting ranges are suitable for making good SNs, which has also been proved by the fracture splitting experiments.

Heterostructures based on graphene and other 2D atomic crystals exhibit fascinating properties and intriguing potential in flexible optoelectronics, where graphene films function as transparent electrodes and other building blocks are used as photoactive materials. However, large-scale production of such heterostructures with superior performance is still in early stages. Herein, for the first time, the preparation of a submeter-sized, vertically stacked heterojunction of lead iodide (PbI2 )/graphene on a flexible polyethylene terephthalate (PET) film by vapor deposition of PbI2 on graphene/PET substrate at a temperature lower than 200 °C is demonstrated. This film is subsequently used to fabricate bendable graphene/PbI2 /graphene sandwiched photodetectors, which exhibit high responsivity (45 A W-1 cm-2 ), fast response (35 µs rise, 20 µs decay), and high-resolution imaging capability (1 µm). This study may pave a facile pathway for scalable production of high-performance flexible devices.

Corrugation is a ubiquitous phenomenon for graphene grown on metal substrates by chemical vapor deposition, which greatly affects the electrical, mechanical, and chemical properties. Recent years have witnessed great progress in controlled growth of large graphene single crystals; however, the issue of surface roughness is far from being addressed. Here, the corrugation at the interface of copper (Cu) and graphene, including Cu step bunches (CuSB) and graphene wrinkles, are investigated and ascribed to the anisotropic strain relaxation. It is found that the corrugation is strongly dependent on Cu crystallographic orientations, specifically, the packed density and anisotropic atomic configuration. Dense Cu step bunches are prone to form on loose packed faces due to the instability of surface dynamics. On an anisotropic Cu crystal surface, Cu step bunches and graphene wrinkles are formed in two perpendicular directions to release the anisotropic interfacial stress, as revealed by morphology imaging and vibrational analysis. Cu(111) is a suitable crystal face for growth of ultraflat graphene with roughness as low as 0.20 nm. It is believed the findings will contribute to clarifying the interplay between graphene and Cu crystal faces, and reducing surface roughness of graphene by engineering the crystallographic orientation of Cu substrates.

Using Physical Layer Network Coding in Two-way Relay Channels, different carrier frequency in Multiple Access phase will cause serious performance loss of wireless communication systems. Joint Physical-layer Network Coding and Channel Coding can improve system performance and reduce facility complexity to a large extant. However, a great majority of these designs only consider synchronization at present. This paper proposes joint design of PNC and LDPC with complete frequency offset of single-node and average frequency offset of two-node in condition of carrier frequency offsets. We design two corresponding frequency offset filters and reanalyze their useful signal part and noise distribution. Simulation results indicate that two proposed joint PNC and LDPC with carrier frequency offsets have a great performance compared with traditional Physical-layer Network Coding.

Based on the assumption that the user nodes and relay node are equipped with multiple antennas, we propose the minimum mean squared error (MMSE) pre-equalization scheme to address the interference elimination issue for two-way AF MIMO relay systems. Compared to the zero-forcing (ZF) equalization and MMSE equalization, it is proved that MMSE pre-equalization scheme has the lowest noise power in MIMO system. Therefore, MMSE pre-equalization is adopted at transmit node in both multiple access phase and broadcast phase. The performance of the proposed scheme is demonstrated by numerical simulations.

In order to plug water channeling of fractured tight oil reservoir, a new type of copolymer as the main agent is used for deep profile control and oil displacement. This copolymer is synthesized with modified cellulose and acrylamide, which has relatively lower viscosity and can meet the requirements of injection into the formation. And it has good performance of shear resistance, which can migrate into the deep formation and maintain the good performance. And a gel, which is consisting of the copolymer and cross-linking agent, has a good performance under formation conditions. The gel strength and gelation time can be controlled to meet the requirements of construction. Oilfield construction shows that the way of multistage alternating injection of the profile control and oil displacement agent and formation water can push the gel into the deep formation and can plug the water channeling of fractures to improve the sweep efficiency with a wider range. After construction, the oil production is increased from 1.13 t/d to 4 t/d and the water cut is decreased from 98.16 % to 91.54 %. The results of laboratory experiment and field test show that the developed profile control and oil displacement agent and the way of multistage alternating injection are suitable for EOR of the fractured tight oil reservoirs.

With the development of optical communication technology, all-optical network is promising in next generation networks. Characterized by good transparency, wavelength routing, compatibility and scalability, all-optical network has become the most promising candidate for future high-capacity network. And reconfigurable optical add/drop multiplexer (ROADM) has been regarded as one of the key equipments of the intelligent WDM optical communication network. In this paper, we compare several design methods of ROADM, and introduce the design and implementation of ROADM based on fiber Bragg grating (FBG) and optical switch (OSW). We also propose the new idea of FBGs OSW composed OSW and FBG collimator, which is the integration package of FBGs and collimator. Benefited from the filter characteristics of FBGs and the selectivity of OSW, the performance of ROADM can be optimized. In addition, the ROADM has been tested and analyzed.

Quantum key can be theoretically demonstrated to be secure and now commercially available. The bit rate of the quantum key distribution is much lower than that for "one-time pad" needs. The practical bit limitation of the quantum key distribution system is analyzed to explain necessity for bit amplification. The method of bit amplification is also introduced in this paper.

A new type of CATV network management system developed by universal MCU, which supports SNMP, is proposed in this paper. From the point of view in both hardware and software, the function and method of every modules inside the system, which include communications in the physical layer, protocol process, data process, and etc, are analyzed. In our design, the management system takes IP MAN as data transmission channel and every controlled object in the management structure has a SNMP agent. In the SNMP agent developed, there are four function modules, including physical layer communication module, protocol process module, internal data process module and MIB management module. In the paper, the structure and function of every module are designed and demonstrated while the related hardware circuit, software flow as well as the experimental results are tested. Furthermore, by introducing RTOS into the software programming, the universal MCU procedure can conducts such multi-thread management as fast Ethernet controller driving, TCP/IP process, serial port signal monitoring and so on, which greatly improves efficiency of CPU.