Effects of Manganese Substitution in the Nd_(2)Co_(17-x)Mn_(x) Compounds on Structural and Magnetic Properties

The structural and magnetic properties of the Nd_(2)Co_(17-x)Mn_(x)(x≤14)compounds have been investigated by means of x-ray diffraction and magnetization measurements.The Nd_(2)Co_(17-x)Mn_(x)(x≤14)compounds have a rhombohedral Th2Zn17-type structure.The unit-cell volume increases with increasing x.The Curie temperature and the saturation magnetization of these compounds show a marvelous drop with increasing x.The spin reorientation is observed at about 190 K in the Nd_(2)Co_(15)Mn_(2) compound.

Recovery of Collided RFID Tags With Frequency Drift on Physical Layer

In a passive ultra-high frequency(UHF)radio frequency identification(RFID)system,the recovery of collided tag signals on a physical layer can enhance identification efficiency.However,frequency drift is very common in UHF RFID systems,and will have an influence on the recovery on the physical layer.To address the problem of recovery with the frequency drift,this paper adopts a radial basis function(RBF)network to separate the collision signals,and decode the signals via FM0 to recovery collided RFID tags.Numerical results show that the method in this paper has better performance of symbol error rate(SER)and separation efficiency compared to conventional methods when frequency drift occurs.

10 Gb/s classical secure key distribution based on temporal steganography and private chaotic phase scrambling

Secure distribution of high-speed digital encryption/decryption keys over a classical fiber channel is strongly pursued for realizing perfect secrecy communication systems.However,it is still challenging to achieve a secret key rate in the order of tens of gigabits per second to be comparable with the bit rate of commercial fiber-optic systems.In this paper,we propose and experimentally demonstrate a novel solution for high-speed secure key distribution based on temporal steganography and private chaotic phase scrambling in the classical physical layer.The encryption key is temporally concealed into the background noise in the time domain and randomly phase scrambled bit-by-bit by a private chaotic signal,which provides two layers of enhanced security to guarantee the privacy of key distribution while providing a high secret key rate.We experimentally achieved a record classical secret key rate of 10 Gb/s with a bit error rate lower than the hard-decision forward error correction(HD-FEC)over a 40 km standard single mode fiber.The proposed solution holds great promise for achieving high-speed key distribution in the classical fiber channel by combining steganographic transmission and chaotic scrambling.

多次雷电冲击对氧化锌避雷器阀片性能的影响(英文)

A lightning arrester is used for electrical equipment protection against damage due to lightning strikes.One example of protected electrical equipment is electrical power transformer.If there is no lightning arrester installed to the transformer,when a lightning strike happens,it may receive a very high lightning overvoltage,which is certainly resulted in the transformer damage at its insulation.Usually,a lightning arrester specification data attached to a lightning arrester contains the rating data of the lightning arrester current and voltage.In the use of lightning arrester,the possibility of receiving multiple lightning strikes is not taken into account sometimes.In fact,in some places,the number of multiple strikes in short duration is quiet high in number.This condition makes the lightning arrester being stroked by multiple lightning strikes.Therefore,it may change the lightning arrester's properties,and then the arrester may not be able to provide good electrical equipment protection against lightning strike anymore.This condition will result in great loss to electrical companies and electrical consumers.Therefore,this research studied the effect of applying multiple lightning strikes to ZnO lightning arrester block.Every time a group of lightning impulse current is applied to the ZnO lightning arrester block,it is followed by the measuring of its 50 Hz voltage and current characteristic. The changing in the ZnO lightning arrester block 50 Hz characteristic then can be analyzed.It was found that by applying more numbers of lightning strikes which made the arrester becoming worse,even though,actually,the lightning impulse peak current was still under the rating of the lightning arrester current.In this case for a 5 kA,24 kV lightning arrester,even though the lightning impulse peak current flowing through the ZnO lightning arrester block was still 2500 A,the lightning arrester ZnO block had already been damaged.Having been damaged,an alternating current flowing through the damaged ZnO block was about 10000 times as much current flowing to the good one.The maximum of impulse energy absorbed by a ZnO block recorded was 334.7 J/cm^3.The damaged ZnO block should be replaced by a good one.

Capture-aware Bayesian RFID Tag Estimate for Large-scale Identification

Dynamic framed slotted Aloha algorithm is one of popular passive radio frequency identification(RFID) tag anticollision algorithms. In the algorithm, a frame length requires dynamical adjustment to achieve higher identification efficiency.Generally, the adjustment of the frame length is not only related to the number of tags, but also to the occurrence probability of capture effect. Existing algorithms could estimate both the number of tags and the probability of capture effect. Under large-scale RFID tag identification, however, the number of tags would be much larger than an initial frame length. In this scenario, the existing algorithm's estimation errors would substantially increase. In this paper, we propose a novel algorithm called capture-aware Bayesian estimate, which adopts Bayesian rules to accurately estimate the number and the probability simultaneously. From numerical results, the proposed algorithm adapts well to the large-scale RFID tag identification. It has lower estimation errors than the existing algorithms. Further,the identification efficiency from the proposed estimate is also higher than the existing algorithms.

Region-based multisensor image fusion method

Image fusion should consider the priori knowledge of the source images to be fused, such as the characteristics of the images and the goal of image fusion, that is to say, the knowledge about the input data and the application plays a crucial role. This paper is concerned on multiresolution （MR） image fusion. Considering the characteristics of the multisensor （SAR and FLIR etc） and the goal of fusion, which is to achieve one image in possession of the contours feature and the target region feature. It seems more meaningful to combine features rather than pixels. A multisensor image fusion scheme based on K-means duster and steerable pyramid is presented. K-means cluster is used to segment out objects in FLIR images. The steerable pyramid is a multiresolution analysis method, which has a good property to extract contours information at different scales, Comparisons are made with the relevant existing techniques in the literature. The paper concludes with some examples to illustrate the efficiency of the proposed scheme.

Mask-based denoising scheme for ghost imaging

Ghost imaging(GI)is thought of as a promising imaging method in many areas.However,the main drawback of GI is the huge measurement data and low signal-to-noise ratio.In this paper,we propose a novel mask-based denoising scheme to improve the reconstruction quality of GI.We first design a mask through the maximum between-class variance(OTSU)method and construct the measurement matrix with speckle patterns.Then,the correlated noise in GI can be effectively suppressed by employing the mask.From the simulation and experimental results,we can conclude that our method has the ability to improve the imaging quality compared with traditional GI method.

Anomalous thermal expansion of Gd_2Fe_(15.5)Cr_(1.5) compound

The structure and magnetic properties of Gd2Fe15.5Cr1.5 compound were investigated by means of X-ray diffraction and magnetization measurements.The Gd2Fe15.5Cr1.5 compound had a rhombohedral Th2Zn17-type structure.The Curie temperature of Gd2Fe15.5Cr1.5 compound was about 570 K.This value was about 60 K higher than that of the mother compound Gd2Fe17.Negative thermal expansion was found in Gd2Fe15.5Cr1.5 compound in a broad temperature range 294-572 K by X-ray dilatometry.The coefficient of the average thermal expansion was =-3.87×10-6 K-1 in 294-512 K,and-1.58×10-5 in 512-572 K.The magnetostriction deformations from 294 to 532 K were calculated by means of the differences between the experimental values of the lattice parameters and corresponding values extrapolated from the paramagnetic range.The result showed that the spontaneous volume magnetostrictive deformation ωS decreased linearly from 4.73×10-3 to 0.11×10-3 with the temperature increasing from 294 to 532 K.The analysis showed that the ωS mainly came from the contribution of the spontaneous linear magnetostrictive λc along the c axis.

Hybrid-integrated chalcogenide photonics

High-quality photonic materials are critical for promoting integrated photonic devices with broad bandwidths,high efficiencies,and flexibilities for high-volume chip-scale fabrication.Recently,we designed a home-developed chalcogenide glass(ChG)-Ge_(25)Sb_(10)S_(65)(GeSbS)for optical information processing chips and systems,which featured an ultrabroad transmission window,a high Kerr nonlinearity and photoelastic coefficient,and compatibility with the photonic hybrid integration technology of silicon photonics.Chip-integrated GeSbS microresonators and microresonator arrays with high quality factors and lithographically controlled fine structures were fabricated using a modified nanofabrication process.Moreover,considering the high Kerr nonlinearity and photoelastic effect of ChGs,we realised a novel ChG hybrid integrated chip,inspired by recent advances in integrated soliton microcombs and acousto-optic(AO)modulators.

On-chip chalcogenide microresonators with low-threshold parametric oscillation

Chalcogenide glass (ChG) is an attractive material for highly efficient nonlinear photonics,which can cover an ultrabroadband wavelength window from the near-visible to the footprint infrared region. However,it remains a challenge to implement highly-efficient and low-threshold optical parametric processes in chip-scale ChG devices due to thermal and light-induced instabilities as well as a high-loss factor in ChG films. Here,we develop a systematic fabrication process for high-performance photonic-chip-integrated ChG devices,by which planarintegrated ChG microresonators with an intrinsic quality (Q) factor above 1 million are demonstrated. In particular,an in situ light-induced annealing method is introduced to overcome the longstanding instability underlying ChG film. In high-Q ChG microresonators,optical parametric oscillations with threshold power as low as 5.4 mW are demonstrated for the first time,to our best knowledge. Our results would contribute to efforts of making efficient and low-threshold optical microcombs not only in the near-infrared as presented but more promisingly in the midinfrared range.

Microbubble resonators combined with a digital optical frequency comb for high-precision air-coupled ultrasound detectors

Fast and sensitive air-coupled ultrasound detection is essential for many applications such as radar,ultrasound imaging,and defect detection.Here we present a novel approach based on a digital optical frequency comb(DOFC)technique combined with high-Q optical microbubble resonators(MBRs).DOFC enables precise spectroscopy on resonators that can trace the ultrasound pressure with its resonant frequency shift with femtometer resolution and sub-microsecond response time.The noise equivalent pressure of air-coupled ultrasound as low as 4.4 m Pa∕pHz is achieved by combining a high-Q(~3×10~7)MBR with the DOFC method.Moreover,it can observe multi-resonance peaks from multiple MBRs to directly monitor the precise spatial location of the ultrasonic source.This approach has a potential to be applied in 3 D air-coupled photoacoustic and ultrasonic imaging.

Ultra-sharp silicon multimode waveguide bends based on double free-form curves

Mode-division multiplexing(MDM)can greatly improve the capacity of information transmission.The multimode waveguide bend(MWB)with small size and high performance is of great significance for the on-chip MDM integrated system.In this paper,an MWB with high performance based on double free-form curves(DFFCs)is proposed and realized.The DFFC is a combination of a series of arcs optimized by the inverse design method.The fabrication of this MWB only needs one-step lithography and plasma etching and has a large fabrication tolerance.MWBs with effective radii of 6μm and 10μm are designed to support three modes and four modes,respectively.The proposed method gives the best overall performance considering both the effective bending radius and the transmission efficiency.The fabricated MWB with four mode channels has low excess losses and crosstalks below-21 dB in the wavelength range from 1520 to 1580 nm.It is expected that this design can play an important role in promoting the dense integration of multimode transmission systems.