Distributed Multicircular Circumnavigation Control for UAVs with Desired Angular Spacing

This paper addresses a multicircular circumnavigation control for UAVs with desired angular spacing around a nonstationary target.By defining a coordinated error relative to neighboring angular spacing,under the premise that target information is perfectly accessible by all nodes,a centralized circular enclosing control strategy is derived for multiple UAVs connected by an undirected graph to allow for formation behaviors concerning the moving target.Besides,to avoid the requirement of target’s states being accessible for each UAV,fixed-time distributed observers are introduced to acquire the state estimates in a fixed-time sense,and the upper boundary of settling time can be determined offline irrespective of initial properties,greatly releasing the burdensome communication traffic.Then,with the aid of fixed-time distributed observers,a distributed circular circumnavigation controller is derived to force all UAVs to collaboratively evolve along the preset circles while keeping a desired angular spacing.It is inferred from Lyapunov stability that all errors are demonstrated to be convergent.Simulations are offered to verify the utility of proposed protocol.

Elliptical encirclement control capable of reinforcing performances for UAVs around a dynamic target

Most researches associated with target encircling control are focused on moving along a circular orbit under an ideal environment free from external disturbances.However,elliptical encirclement with a time-varying observation radius,may permit a more flexible and high-efficacy enclosing solution,whilst the non-orthogonal property between axial and tangential speed components,non-ignorable environmental perturbations,and strict assignment requirements empower elliptical encircling control to be more challenging,and the relevant investigations are still open.Following this line,an appointed-time elliptical encircling control rule capable of reinforcing circumnavigation performances is developed to enable Unmanned Aerial Vehicles(UAVs)to move along a specified elliptical path within a predetermined reaching time.The remarkable merits of the designed strategy are that the relative distance controlling error can be guaranteed to evolve within specified regions with a designer-specified convergence behavior.Meanwhile,wind perturbations can be online counteracted based on an unknown system dynamics estimator(USDE)with only one regulating parameter and high computational efficiency.Lyapunov tool demonstrates that all involved error variables are ultimately limited,and simulations are implemented to confirm the usability of the suggested control algorithm.

Pressure effects in AlAs/Inx Ga1-xAs/GaAs resonant tunnelling diodes for application in micromachined sensors

This paper reports the current-voltage characteristics of [001]-oriented AlAs/InxGa1-xAs/GaAs resonant tunnelling diodes （RTDs） as a function of uniaxial external stress applied parallel to the [110] and the [1^-10] orientations, and the output characteristics of the GaAs pressure sensor based on the pressure effect on the RTDs. Under [110] stress, the resonance peak voltages of the RTDs shift to more positive voltages. For [1^-10] stress, the peaks shift toward more negative voltages. The resonance peak voltage is linearly dependent on the [110] and [1^-0] stresses and the linear sensitivities are up to 0.69 mV/MPa, -0.69 mV/MPa respectively. For the pressure sensor, the linear sensitivity is up to 0.37 mV/kPa.

A Novel Method for Heightening Sensitivity of Prism Coupler-Based SPR Sensor

We present a novel method for heightening the sensitivity of a prism coupler-based surface plasmon resonance(SPR)sensor.The method is based on the total reflection prism made of BK7 glass combined with the Kretschmann geometry of theattenuated total reflection(ATR)method.Compared to the conventional methods of prism coupler-based SPR,the novel method provides higher sensitivity to the measurement system.Theoretical simulations show that the detection sensitivity to the refractive index(RI)of the sensor based on the novel approach has a strong dependence on the thickness of the metal layer.The RI resolution of the sensor is predicted to be 8×10^(-7)refractive index units(RIU)under the condition of optimum metal film thickness.This novel method can leave out a precision angle rotation device in the angle modulation and it is unnecessary to adjust the acceptance angle of the light detector.The principal advantage of this method over other methods of light intensity modulation based on prism coupler-based SPR is high sensitivity,expediency to measure and application of long distances.

Graphene-based heterojunction for enhanced photodetectors

Graphene has high light transmittance of 97.7% and ultrafast carrier mobility, which means it has attracted widespread attention in two-dimensional materials. However, the optical absorptivity of single-layer graphene is only 2.3%, and the corresponding photoresponsivity is difficult to produce at normal light irradiation. And the low on–off ratio resulting from the zero bandgap makes it unsuitable for many electronic devices, hindering potential development. The graphene-based heterojunction composed of graphene and other materials has outstanding optical and electrical properties, which can mutually modify the defects of both the graphene and material making it then suitable for optoelectronic devices. In this review,the advantages of graphene-based heterojunctions in the enhancement of the performance of photodetectors are reviewed.Firstly, we focus on the photocurrent generation mechanism of a graphene-based heterojunction photodetector, especially photovoltaic, photoconduction and photogating effects. Secondly, the classification of graphene-based heterojunctions in different directions is summarized. Meanwhile, the latest research progress of graphene-transition metal dichalcogenide(TMD) heterojunction photodetectors with excellent performance in graphene-based heterostructures is introduced. Finally,the difficulties faced by the existing technologies of graphene-based photodetectors are discussed, and further prospects are proposed.

Pressure effect study on the Ⅰ-Ⅴ property of the GaAs-based resonant tunnelling structure by photoluminescence measurement

This paper discusses the I-V property of the GaAs-based resonant tunnelling structure （RTS） under external uniaxial pressure by photoluminescence studies. Compressive pressure parallel to the [110] direction, whose value is determined by Hooke＇s law, is imposed on the sample by a helix micrometer. With the increase of the applied external uniaxial compressive pressure, the blue shift and splitting of the luminescence peaks were observed, which have some influence on the I-V curve of RTS from the point of view of the energy gap, and the splitting became more apparent with applied pressure. Full width at half maximum broadening could also be observed.

A Novel Method for Enhancing Goos-Hǎnchen Shift in Total Internal Reflection

Due to the tiny shift in order of optical wavelength for Goos-Hǎnchen （GH） shift, it is very difficult to directly measure and apply the GH shift. We develop a new method for enhancing GH shift of both TE and TM polarized waves. The method is based on a total reflection prism made of BK9 glass combined with a precise measurement of the resulting spatial displacement with a one-dimensional charge coupled device （CCD）. Measurements are performed to examine the validity of the method. Experimental and theoretical results indicate the feasibility of the method with an enhancement in optical wavelenghth shift at millimetre scale. The method is advantageous to application the GH shift in the optical domain, and is also meaningful for measuring even smaller changes in the refractive index of a liquid.

Fabrication and magnetic properties of NiFe_2O_4 nanorods

NiFe2O4 nanorods have been successfully synthesized via thermal treatment of the rod-like precursor fabricated by Ni-doped （x-FeOOH, which was enwrapped by the complex of citric acid and Niz~. The morphology evolution during the calcination of the precursor nanorods was investigated with transmission electron microscopy （TEM）, and the phase and the magnetic properties of samples were analyzed through X-ray diffraction （XRD） and vibrating sample magnetometer （VSM）. The results indicated that the diameter of the NiFe204 nanorods obtained ranged between 30 and 50 nm, and the length ranged between 2 and 3 um. As the calcination temperature was up to 600℃, the coercivity, saturation magnetization, and remanent magnetization of the samples were 36.1 kA.m^-1, 27.2 A.m2.kg^-1, and 5.3 A.m2.kg^-1, respectively. The NiFe2O4 nanorods prepared have higher shape anisotropy and superior magnetic properties than those with irregular shapes.

Effect of Cu addition on corrosion resistance and shape memory effect of Fe-14Mn-5Si-9Cr-5Ni alloy

The modification of Fe-14Mn-5Si-9Cr-5Ni shape memory alloys(SMAs) by copper addition was carried out, aiming at further enhancing its corrosion resistance. The results of electrochemical potentiodynamic measurement and immersion test show that copper can remarkably improve the corrosion resistance in Cl- solution. Otherwise, it is found that copper cannot markedly affect the mechanical properties nor the shape memory effect(SME). As for the effects of copper on Fe-Mn-Si based alloys, the austenite strengthening is one of the key factors to improve SME.

Corrosion and mechanical properties of hot-extruded AZ31 magnesium alloys

AZ31 magnesium alloys were hot-extruded at 573 K and 623 K with extrusion ratio(λ) of 20,35 and 50.The corrosion and mechanical behavior of hot-extruded AZ31 were studied by galvanic tests and tensile tests.The microstructures of the studied AZ31 alloys were also investigated with optical microscope.The results show that,compared with the as-cast AZ31 alloy,the corrosion potentials of all hot-extruded AZ31 alloys are increased by 60 mV.Moreover,at the extrusion temperature of 623 K,the galvanic current of AZ31 alloy decreases with increasing extrusion and the galvanic corrosion resistance is increased by 10%with the extrusion ratio of 50.In addition,the tensile strength and elongation of the extruded alloys are significantly enhanced by about 20%and 140%,respectively.The improvement of corrosion resistance and obvious increasing of mechanical properties of AZ31 alloys by hot-extrusion are ascribed to grain refinement and microstructural modification together with the homogeneous distribution of intermetallic phases throughout the matrix.

Attitude Optimization Algorithm of GFIMU with Installation Errors

Taking the accelerometer installation errors into consideration, the attitude optimization algorithm of Gyro Free Inertial Meastement Unit （GFIMU） is studied in the high spinning condition in this paper. A ten-accelerometer configuration is designed so as to establish a mathematical model to acquire the angular speeds in the case of installation errors. Precision of the algorithm is evaluated by using damping GaussNewton method. A large amotmt of sinmlation results show that ff the accelertlmter＇s angleinstallation errors main-tain small （〈5°）, the errors of attitude angles can be limited within ±1°. Hence, the algorithm has a great applicable value in engineering.

Study on Echo Time-Delay Estimation of Pulsed Laser Fuze

Pulse laser range detector is to measure the distance by estimating the time delay between the emitting pulse and echo pulse.In this paper,a mathematical model for the target echo signal of laser fuze has been established;in accordance with this model,the formulas for echo time-delay estimation and for amplitude estimation based on least squares criterion have been deduced.It is argued and simulated that the resolution of echo time-delay estimation could be improved through multi-reference correlation approach.Experiments illustrate that the approach enables pulsed laser fuze to perform high-precision ranging under a low signal-to-noise ratio condition.

Effect of thermal processing on microstructure and mechanical properties of AZ80 magnesium alloy

The influences of deformation temperature and deformation degree on the microstructure and mechanical properties of AZ80 magnesium alloy were investigated by the adoption of isothermal plain strain compression experiment.The results show that thermal compression processing can refine the grain size and the tensile strength of all the deformed AZ80 magnesium alloys is increased to the maximum of 320 MPa.With the increasing of deformation temperature,the tensile strength decreases;with the increasing of the deformation degree,the tensile strength increases significantly in the temperature range of 200-300℃and becomes stable at temperature higher than 300℃.During the compression processing of AZ80 magnesium alloys,at lower temperature (<300℃),dynamic recrystallization is incomplete and a certain hardening effect is preserved,which makes great effect of deformation degree on the properties.At higher temperature(>300℃),dynamic recrystallization is complete and refined grain strengthening is dominant,leading to little effect of deformation degree on mechanical properties.

Comparison between photoluminescence spectroscopy and photoreflectance spectroscopy in CuGaSe_2 epilayer

Photoluminescence （PL） spectroscopy and photoreflectance （PR） spectroscopy are very useful techniques for studying the properties of materials. In this paper, the same material of Cu-rich metal-organic vapour phase epitaxy （MOVPE） grown CuGaSe2 layer is investigated in a temperature range from 20 to 300 K to compare these two techniques. Both PL and PR spectra appear red shifted, less intense and broadened. The temperature dependence of interband transitions is studied by using the Manoogian Leclerc equation. The values of the band gap energy at T=0K and the effective phonon temperature are estimated. The temperature dependences of intensities and broadenings of PL and PR spectral lines are also analysed. Based on the results of the comparison, the features and applications of the PL and PR can be shown in detail.

Research on the Key Technology of LTCC Pressure Sensor

This article introduces the fabrication technology processes of the capacitive pressure sensor based on the low temperature co-fired ceramic （LTCC） material. Filling the cavity with different materials as a sacrificial layer is mainly discussed, and two different materials are chosen in the fabrication. It is found that the cavity filled with polyimide expands largely during sintering, while carbon ESL49000 material filled is more preferable to keep the cavity flat. Finally, the structure leaving without an air evacuation channel is designed and tested in a built-up pressure environment, the frequency measured decreases approximately linearly with the pressure applied, which proves the design leaving no air evacuation channel advisable.

Temperature dependence of biaxial strain and its influence on phonon and band gap of GaN thin film

Hexagonal GaN epilayer grown on sapphire substrate by metal organic chemical vapour deposition （MOCVD） is studied using Raman scattering and photoluminescence in a temperature range from 100K to 873 K. The model of strain （stress） induced by the different lattice parameters and thermal coefficients of epilayer and substrate as a function of temperature is set up. The frequency and the linewidth of E2^high mode in a GaN layer are modelled by a theory with considering the thermal expansion of the lattice, a symmetric decay of the optical phonons, and the strain （stress） in the layer. The temperature-dependent energy shift of free exeiton A is determined by using Varshni empirical relation, and the effect of strain （stress） is also investigated. We find that the strain in the film leads to a decreasing shift of the phonon frequency and an about 10meV-inereasing shift of the energy in a temperature range from 100 K to 823 K.

Withdrawal of Chinese Physics Letters 28 (2011) 107301 "High-Efficiency Graphene Photo Sensor Using a Transparent Electrode" by LIU Tao and HUANG Zheng

The authors withdraw the research paper“High-Efficiency Graphene Photo Sensor Using a Transparent Electrode”,which was published in Chinese Physics Letters 28(10),107301(2011),due to the major mistakes in management and experiment,which led to the authors adopting inappropriate data published without sufficient examination and permission processes.

High-Efficiency Graphene Photo Sensor Using a Transparent Electrode

We report the first implementation of transparent electrodes in bottom-gate graphene transistors used for photo detection.Compared to conventional nontransparent electrodes,the transparent electrodes allow photons to transmit through to the graphene beneath,providing an enlarged absorption area and thereby giving rise to an enhancement of photocurrent generation.The devices are fabricated with an asymmetric metallization scheme and the experimental results show that the maximum photocurrent density using the transparent electrodes(ITO and Pd/ITO)is over two times higher than that using the nontransparent electrodes(Ti and Pd),indicating a significant enhancement in the performance of graphene photo sensors.

Collective Excitation and Quantum Depletion of a Bose-Einstein Condensate in a Periodic Array of Quantum Wells

With the help of a set of exact closed-form solutions to the stationary Gross–Pitaevskii （GP） equation, we calculate the collective excitation and quantum depletion of a weakly interacting Bose gas in the presence of a periodic array of quantum wells. The excitation spectrum （Bogoliubov spectrum） is obtained from the solution of the linearized time-dependent GP equation, which develops energy bands hωj（ p） periodic in quasi-momentum space. Moreover, we calculate the excitation strengths Zj（ p） relative to the density operator and then the dynamic structure factor S（ p,ω）. Accordingly, the analytical expressions of quantum depletion of the system are obtained. We find that the quantum depletion is enhanced when the interatomic interactions become larger and the potential is sufficiently deep. The conditions for the possible experimental realization of our scenario are also proposed.