Interaction between transmission control protocol （TCP） and random early detection （RED） gateway in the Internet congestion control system has been modelled as a discrete-time dynamic system which exhibits complex...Interaction between transmission control protocol （TCP） and random early detection （RED） gateway in the Internet congestion control system has been modelled as a discrete-time dynamic system which exhibits complex bifurcating and chaotic behaviours. In this paper, a hybrid control strategy using both state feedback and parameter perturbation is employed to control the bifurcation and stabilize the chaotic orbits embedded in this discrete-time dynamic system of TCP/RED. Theoretical analysis and numerical simulations show that the bifurcation is delayed and the chaotic orbits are stabilized to a fixed point, which reliably achieves a stable average queue size in an extended range of parameters and even completely eliminates the chaotic behaviour in a particular range of parameters. Therefore it is possible to decrease the sensitivity of RED to parameters. By using the hybrid strategy, we may improve the stability and performance of TCP/RED congestion control system significantly.展开更多
5G is a new generation of mobile networking that aims to achieve unparalleled speed and performance. To accomplish this, three technologies, Device-to-Device communication (D2D), multi-access edge computing (MEC) and ...5G is a new generation of mobile networking that aims to achieve unparalleled speed and performance. To accomplish this, three technologies, Device-to-Device communication (D2D), multi-access edge computing (MEC) and network function virtualization (NFV) with ClickOS, have been a significant part of 5G, and this paper mainly discusses them. D2D enables direct communication between devices without the relay of base station. In 5G, a two-tier cellular network composed of traditional cellular network system and D2D is an efficient method for realizing high-speed communication. MEC unloads work from end devices and clouds platforms to widespread nodes, and connects the nodes together with outside devices and third-party providers, in order to diminish the overloading effect on any device caused by enormous applications and improve users’ quality of experience (QoE). There is also a NFV method in order to fulfill the 5G requirements. In this part, an optimized virtual machine for middle-boxes named ClickOS is introduced, and it is evaluated in several aspects. Some middle boxes are being implemented in the ClickOS and proved to have outstanding performances.展开更多
SnO2 nanotwists on thin film and SnO2 short nanowires on nanorods have been grown on single silicon substrates by using Au-Ag alloying catalyst assisted carbothermal evaporation of SnO2 and active carbon powders. The ...SnO2 nanotwists on thin film and SnO2 short nanowires on nanorods have been grown on single silicon substrates by using Au-Ag alloying catalyst assisted carbothermal evaporation of SnO2 and active carbon powders. The morphology and the structure of the prepared nanostructures are determined on the basis of field-emission scanning electron microscopy （FESEM）, transmission electron microscopy （TEM）, selected area electronic diffraction （SAED）, high-resolution transmission electron microscopy （HRTEM）, x-ray diffraction （XRD）, Raman and photoluminescence （PL） spectra analysis. The new peaks at 356, 450, and 489 nm in the measured PL spectra of two kinds of SnO2 nanostructures are observed, implying that more luminescence centres exist in these SnO2 nanostructures due to nanocrystals and defects. The growth mechanism of these nanostructures belongs to the vapour liquid-solid （VLS） mechanism.展开更多
Thermal conduetances between Cu and graphene covered carbon nanotubes （gCNTs） are calculated by molecular dynamics simulations. The results show that the thermal conductance is about ten times larger than that of Cu...Thermal conduetances between Cu and graphene covered carbon nanotubes （gCNTs） are calculated by molecular dynamics simulations. The results show that the thermal conductance is about ten times larger than that of Cu- CNT interface. The enhanced thermal conductance is due to the larger contact area introduced by the graphene layer and the stronger thermal transfer ability of the Cu-gCNT interface. From the linear increasing thermal conductance with the increasing total contact area, an effective contact area of such an interface can be defined.展开更多
Photocatalytic seawater splitting is an attractive way for producing green hydrogen.Significant progresses have been made recently in catalytic efficiencies,but the activity of catalysts can only maintain stable for a...Photocatalytic seawater splitting is an attractive way for producing green hydrogen.Significant progresses have been made recently in catalytic efficiencies,but the activity of catalysts can only maintain stable for about 10 h.Here,we develop a vacancy-engineered Ag_(3)PO_(4)/CdS porous microreactor chip photocatalyst,operating in seawater with a performance stability exceeding 300 h.This is achieved by the establishment of both catalytic selectivity for impurity ions and tailored interactions between vacancies and sulfur species.Efficient transport of carriers with strong redox ability is ensured by forming a heterojunction within a space charge region,where the visualization of potential distribution confirms the key design concept of our chip.Moreover,the separation of oxidation and reduction reactions in space inhibits the reverse recombination,making the chip capable of working at atmospheric pressure.Consequently,in the presence of Pt co-catalysts,a high solar-to-hydrogen efficiency of 0.81%can be achieved in the whole durability test.When using a fully solar-driven 256 cm2 hydrogen production prototype,a H_(2) evolution rate of 68.01 mmol h−1 m−2 can be achieved under outdoor insolation.Our findings provide a novel approach to achieve high selectivity,and demonstrate an efficient and scalable prototype suitable for practical solar H_(2) production.展开更多
This paper presents a source localization algorithm based on the source signal's time-difference-of-arrival(TDOA) for asynchronous wireless sensor network.To obtain synchronization among anchors,all anchors broadc...This paper presents a source localization algorithm based on the source signal's time-difference-of-arrival(TDOA) for asynchronous wireless sensor network.To obtain synchronization among anchors,all anchors broadcast signals periodically,the clock offsets and skews of anchor pairs can be estimated using broadcasting signal's time-of-arrivals(TOA) at anchors.A kalman filter is adopted to improve the accuracy of clock offsets and track the clock drifts due to random fluctuations.Once the source transmits signal,the TOAs at anchors are stamped respectively and source's TDOA error due to clock offset and skew of anchor pair can be mitigated by a compensation operation.Based on a Gaussian noise model,maximum likelihood estimation(MLE) for the source position is obtained.Performance issues are addressed by evaluating the Cramer-Rao lower bound and the selection of broadcasting period.The proposed algorithm is simple and effective,which has close performance with synchronous TDOA algorithm.展开更多
The effect of phosphorus passivation on 4H-SiC（0001） silicon （Si） dangling bonds is investigated using ab initio atomistic thermodynamic calculations. Phosphorus passivation commences with chemisorption of phospho...The effect of phosphorus passivation on 4H-SiC（0001） silicon （Si） dangling bonds is investigated using ab initio atomistic thermodynamic calculations. Phosphorus passivation commences with chemisorption of phosphorus atoms at high-symmetry coordinated sites. To determine the most stable structure during the passivation process of phosphorus, a surface phase diagram of phosphorus adsorption on SiC （0001） surface is constructed over a coverage range of 1/9-1 monolayer （ML）. The calculated results indicate that the 1/3 ML configuration is most energetically favorable in a reasonable environment. At this coverage, the total electron density of states demonstrates that phosphorus may effectively reduce the interface state density near the conduction band by removing 4H-SiC （0001） Si dangling bonds. It provides an atomic level insight into how phosphorus is able to reduce the near interface traps.展开更多
The time and efficiency of charge collection are the key factors of monolithic active pixel sensor devices for minimum ionizing particles tracking detection.In this paper,3D models of pixels with different resistivity...The time and efficiency of charge collection are the key factors of monolithic active pixel sensor devices for minimum ionizing particles tracking detection.In this paper,3D models of pixels with different resistivity epitaxial layers(epi-layers) are built and simulated using Synopsys-Sentaurus.The basic characteristics of detectors are evaluated,including electric potential,electric field,and depleted region.Results indicate that the high resistivity (HR) epi-layer is a better choice.Further,simulation results show that the key collection performance is significantly improved owing to a wider and stronger electric field in the N type HR epi-layer.展开更多
We report on the design,fabrication,and characterization of a micro plane-plane geometry CMOS device,which has a heat emitter and a heat receiver,capable of studying the near-field radiative heat transfer at a 550nm g...We report on the design,fabrication,and characterization of a micro plane-plane geometry CMOS device,which has a heat emitter and a heat receiver,capable of studying the near-field radiative heat transfer at a 550nm gap.Under high vacuum conditions,the heat emitter is heated by supplying driving currents and heated again after removing the heat receiver.The heating power difference between the two kinds of heating experiments indicates the existence of a proximity effect in the heat transfer between the emitter and the receiver.Our experiments pave the way towards overcoming the construction difficulty of plane-plane geometry with a nanometer gap.展开更多
Zr_(0.9)Mg_(0.1)O_(2−δ) nanofibers and ZrO_(2) nanofibers are synthesized using electrospinning and the calcination technique.The nanofibers are characterized using x-ray diffraction(XRD),a field emission scanning el...Zr_(0.9)Mg_(0.1)O_(2−δ) nanofibers and ZrO_(2) nanofibers are synthesized using electrospinning and the calcination technique.The nanofibers are characterized using x-ray diffraction(XRD),a field emission scanning electron microscope(FE-SEM),and a Brunauer–Emmett–Teller(BET)surface analyzer.The humidity sensing properties of Zr_(0.9)Mg_(0.1)O_(2−δ) nanofiber sensors are analyzed and compared with those of ZrO_(2) nanofiber sensors.The Zr_(0.9)Mg_(0.1)O_(2−δ) nanofiber humidity sensors exhibit a broader humidity range of 11–97%relative humidity(RH),good linearity,small humidity hysteresis,and rapid response and recovery times.The complex impedance plots of the Zr_(0.9)Mg_(0.1)O_(2−δ) sensor at different RHs are drawn,and the humidity sensing mechanism is discussed via an equivalent circuit.展开更多
When clock frequencies exceed gigahertz, the skin depth in analog and digital circuits greatly decreases. The irregular shape of the cross section of the interconnect plays an increasingly important role in interconne...When clock frequencies exceed gigahertz, the skin depth in analog and digital circuits greatly decreases. The irregular shape of the cross section of the interconnect plays an increasingly important role in interconnect parasitic extraction. However, existing methods only focus on the rough surface of the interconnect, while ignoring other irregular shapes, such as the trapezoidal cross section. In this work, a new simulation method is proposed for irregular interconnects, which is applicable to arbitrary irregular shapes and to a wide range of frequencies. The method involves generating a mesh information file firstly, and then extracting the frequency-dependent resistance based on a numerical solution of scalar wave modeling by using the method of moments. The singularity extraction method is used to calculate the self-inductors. The data from experiments verify the accuracy of our proposed method.展开更多
Self-aligned-gate heterostructure field-effect transistor（HFET） is fabricated using a wet-etching method.Titanium nitride（TiN） is one kind of thermal stable material which can be used as the gate electrode.A Ti/Au...Self-aligned-gate heterostructure field-effect transistor（HFET） is fabricated using a wet-etching method.Titanium nitride（TiN） is one kind of thermal stable material which can be used as the gate electrode.A Ti/Au cap layer is fixed on the gate and acts as an etching mask.Then the T-shaped gate is automatically formed through over-etching the TiN layer in 30% H2O2 solution at 95 ℃.After treating the ohmic region with an inductively coupled plasma（ICP） method,an Al layer is sputtered as an ohmic electrode.The ohmic contact resistance is approximately 0.3 Ω·mm after annealing at a low-temperature of 575 ℃ in N2 ambient for 1 min.The TiN gate leakage current is only 10^-8 A after the low-temperature ohmic process.The access region length of the self-aligned-gate（SAG） HFET was reduced from 2 μm to 0.3 μm compared with that of the gate-first HFET.The output current density and transconductance of the device which has the same gate length and width are also increased.展开更多
Conventional wavelength modulation spectroscopy(WMS)is vulnerable to the influence of low-frequency noise.Accuracy of the method highly depends on the performance of the costly lock-in amplifier.In this article,we rep...Conventional wavelength modulation spectroscopy(WMS)is vulnerable to the influence of low-frequency noise.Accuracy of the method highly depends on the performance of the costly lock-in amplifier.In this article,we report a new and effective method for reconstructing second-harmonic signals through WMS based on fast Fourier transform(FFT).This method is less disturbed by low-frequency noise because it does not use a low-frequency ramp wave.Formulation and detection procedures were presented.The discrete second-harmonic waveform can be obtained by continuously changing the DC signal and FFT analysis in this method.Second-harmonic waveforms acquired by the two means are generally consistent.The experimental study validates the obtained gas concentration from 5% to 30%,showing a good linear relationship by the proposed method.The maximum relative error on concentration extraction is 2.87%;as for conventional WMS,this value is 4.50%.The developed measurement method may have potential in computed tomography.展开更多
A novel and efficient speckle noise reduction algorithm based on Bayesian wavelet shrinkage using cycle spinning is proposed. First, the sub-band decompositions of non-logarithmically transformed SAR images are shown....A novel and efficient speckle noise reduction algorithm based on Bayesian wavelet shrinkage using cycle spinning is proposed. First, the sub-band decompositions of non-logarithmically transformed SAR images are shown. Then, a Bayesian wavelet shrinkage factor is applied to the decomposed data to estimate noise-free wavelet coefficients. The method is based on the Mixture Gaussian Distributed （MGD） modeling of sub-band coefficients. Finally, multi-resolution wavelet coefficients are reconstructed by wavelet-threshold using cycle spinning. Experimental results show that the proposed despeclding algorithm is possible to achieve an excellent balance between suppresses speckle effectively and preserves as many image details and sharpness as possible. The new method indicated its higher performance than the other speckle noise reduction techniques and minimizing the effect of pseudo-Gibbs phenomena.展开更多
A method of single channel speech enhancement is proposed by de-noising using stationary wavelet transform. The approach developed herein processes multi-resolution wavelet coefficients individually and then recovery ...A method of single channel speech enhancement is proposed by de-noising using stationary wavelet transform. The approach developed herein processes multi-resolution wavelet coefficients individually and then recovery signal is reconstructed. The time invariant characteristics of stationary wavelet transform is particularly useful in speech de-noising. Experimental results show that the proposed speech enhancement by de-noising algorithm is possible to achieve an excellent balance between suppresses noise effectively and preserves as many target characteristics of original signal as possible. This de-noising algorithm offers a superior performance to speech signal noise suppress.展开更多
A theoretical model and mathematical description for silicon micromachined elec- trostatic or capacitive ultrasonic imaging transducers have been developed. Ac- cording to the model the basic performance parameters of...A theoretical model and mathematical description for silicon micromachined elec- trostatic or capacitive ultrasonic imaging transducers have been developed. Ac- cording to the model the basic performance parameters of such a transducer, such as natural frequencies, eigenfunctions, resonance and anti-resonance frequencies, and the mechanical impedance of the diaphragm can be predicted from the ge- ometry of the transducer and property parameters of materials used. The paper reveals that this type of transducers has two basic operation modes, correspond- ing to the resonance of a mass-spring oscillator comprised of the diaphragm and the air cushion, and the first-order bending mode of the diaphragm itself respec- tively, and presents an optimal method for extending the bandwidth by making the two modes coupled, and thereby provides a theoretical basis for the optimal de- sign.展开更多
The purpose of this study is to present an application of a novel enhancement technique for enhancing medical images generated from X-rays. The method presented in this study is based on a nonlinear partial differenti...The purpose of this study is to present an application of a novel enhancement technique for enhancing medical images generated from X-rays. The method presented in this study is based on a nonlinear partial differential equation （PDE） model, Kramer＇s PDE model. The usefulness of this method is investigated by experimental results. We apply this method to a medical X-ray image. For comparison, the X-ray image is also processed using classic Perona-Malik PDE model and Catte PDE model. Although the Perona-Malik model and Catte PDE model could also enhance the image, the quality of the enhanced images is considerably inferior compared with the enhanced image using Kramer＇s PDE model. The study suggests that the Kramer＇s PDE model is capable of enhancing medical X-ray images, which will make the X-ray images more reliable.展开更多
The repeatable bipolar resistive switching phenomenon is observed in amorphous Al2O3 prepared by metalorganic chemical vapor deposition on ITO glass, with ITO as the bottom electrode and Ag as the top electrode. The c...The repeatable bipolar resistive switching phenomenon is observed in amorphous Al2O3 prepared by metalorganic chemical vapor deposition on ITO glass, with ITO as the bottom electrode and Ag as the top electrode. The crystal structure, morphology, composition and optical properties of Al2O3 thin films are investigated by x-ray diffraction, x-ray photoelectron spectroscopy, atomic force microscopy and ultraviolet-visible-infrared spectroscopy, respectively. The electronic character of Ag/Al2O3/ITO structure is tested by an Agilent B1500A. The device shows a typical bipolar resistive switching behavior under the dc voltage sweep mode at room temperature. The variation ratio between HRS and LRS is larger than nearly three orders of magnitude, which indicates the good potential of this structure in future resistive random access memory （ReRAM） applications. Based on the conductive filament model, the high electric field is considered the main reason for the resistive switching according to our measurements.展开更多
Due to undesirable interference via unintended coupling paths, switching converters may exhibit complex intermittency, which appears as a form of bifurcation undergoing regular operation, subharmonics, and chaos order...Due to undesirable interference via unintended coupling paths, switching converters may exhibit complex intermittency, which appears as a form of bifurcation undergoing regular operation, subharmonics, and chaos orderly and repeatedly for a long period of time. Such intermittent operation, being an unwanted operating state, should normally be avoided in power converters. This paper expounds the mechanism and conditions for the emergence of intermittency in a common current-mode controlled Boost converter. It is found that interference at frequencies near the switching frequency or its rational multiples may induce intermittent operation. The strengths and frequencies of the interfering signals determine the type and period of intermittency. The problem is analyzed by transforming the time-bifurcation analysis to a conventional parameter-bifurcation analysis. Based on this transformation, intermittency can be investigated from the bifurcation control viewpoint. Furthermore, the critical circuit parameter conditions for the emergence of intermittency can be predicted and compared with those from circuit simulation.展开更多
Due to wide input fluctuation with line frequency of 50 Hz, power-factor-correction （PFC） Boost converters tend to exhibit fast-scale instability over time domain. The traditional remedy is to impose slope compensat...Due to wide input fluctuation with line frequency of 50 Hz, power-factor-correction （PFC） Boost converters tend to exhibit fast-scale instability over time domain. The traditional remedy is to impose slope compensation so as to weaken or eliminate this instability. A theoretical principle on the implementation of slope compensation signal is still lacking. Empirical design will induce over compensation frequently, resulting in a large decrease of power factor. In order to tackle this issue, by constructing the discrete-time iterative map of the PFC Boost converter from the viewpoint of bifurcation control theory of nonlinear systems, consequently, the criterion of critical stability for the PFC circuit can be established. Based on this stability criterion, appropriate design of slope compensation can be achieved. Our work indicates that 3 main circuit parameters （i.e. switching cycle, output reference voltage and inductor） determine the effective amplitude design of the slope compensation signal. The results, validated by a large quantity of analytical and numerical studies, show that appropriate slope compensation can be effective in weakening （or controlling） fast-scale bifurcation while maintaining a rather high input power factor.展开更多
基金Project supported by the National Natural Science Foundation of China (Grant No 70571017)
文摘Interaction between transmission control protocol （TCP） and random early detection （RED） gateway in the Internet congestion control system has been modelled as a discrete-time dynamic system which exhibits complex bifurcating and chaotic behaviours. In this paper, a hybrid control strategy using both state feedback and parameter perturbation is employed to control the bifurcation and stabilize the chaotic orbits embedded in this discrete-time dynamic system of TCP/RED. Theoretical analysis and numerical simulations show that the bifurcation is delayed and the chaotic orbits are stabilized to a fixed point, which reliably achieves a stable average queue size in an extended range of parameters and even completely eliminates the chaotic behaviour in a particular range of parameters. Therefore it is possible to decrease the sensitivity of RED to parameters. By using the hybrid strategy, we may improve the stability and performance of TCP/RED congestion control system significantly.
文摘5G is a new generation of mobile networking that aims to achieve unparalleled speed and performance. To accomplish this, three technologies, Device-to-Device communication (D2D), multi-access edge computing (MEC) and network function virtualization (NFV) with ClickOS, have been a significant part of 5G, and this paper mainly discusses them. D2D enables direct communication between devices without the relay of base station. In 5G, a two-tier cellular network composed of traditional cellular network system and D2D is an efficient method for realizing high-speed communication. MEC unloads work from end devices and clouds platforms to widespread nodes, and connects the nodes together with outside devices and third-party providers, in order to diminish the overloading effect on any device caused by enormous applications and improve users’ quality of experience (QoE). There is also a NFV method in order to fulfill the 5G requirements. In this part, an optimized virtual machine for middle-boxes named ClickOS is introduced, and it is evaluated in several aspects. Some middle boxes are being implemented in the ClickOS and proved to have outstanding performances.
基金Project supported by the Fund of Shenzhen Key Lab of Micro-nano Photonic Information Technology,China (Grant No 2000811)the National Natural Science Foundation of China (Grant No 10704050)Fok Ying Tung Educational Foundation (Grant No 114009)
文摘SnO2 nanotwists on thin film and SnO2 short nanowires on nanorods have been grown on single silicon substrates by using Au-Ag alloying catalyst assisted carbothermal evaporation of SnO2 and active carbon powders. The morphology and the structure of the prepared nanostructures are determined on the basis of field-emission scanning electron microscopy （FESEM）, transmission electron microscopy （TEM）, selected area electronic diffraction （SAED）, high-resolution transmission electron microscopy （HRTEM）, x-ray diffraction （XRD）, Raman and photoluminescence （PL） spectra analysis. The new peaks at 356, 450, and 489 nm in the measured PL spectra of two kinds of SnO2 nanostructures are observed, implying that more luminescence centres exist in these SnO2 nanostructures due to nanocrystals and defects. The growth mechanism of these nanostructures belongs to the vapour liquid-solid （VLS） mechanism.
基金Supported by the National National Science Foundation of China under Grant No 61131004the Fundamental Research Funds for the Central Universities under Grant No DUT14LAB11
文摘Thermal conduetances between Cu and graphene covered carbon nanotubes （gCNTs） are calculated by molecular dynamics simulations. The results show that the thermal conductance is about ten times larger than that of Cu- CNT interface. The enhanced thermal conductance is due to the larger contact area introduced by the graphene layer and the stronger thermal transfer ability of the Cu-gCNT interface. From the linear increasing thermal conductance with the increasing total contact area, an effective contact area of such an interface can be defined.
基金support from the Industry-University Cooperation Project of Fujian Province(2023H6003)F.L.gratefully acknowledges financial support from the Fuzhou Fuzhi Photocatalysis Research Center+1 种基金Q.C.gratefully acknowledges financial support from the National Natural Science Foundation of China(22022205,22372193)the CAS Project for Young Scientists in Basic Research(YSBR-054).
文摘Photocatalytic seawater splitting is an attractive way for producing green hydrogen.Significant progresses have been made recently in catalytic efficiencies,but the activity of catalysts can only maintain stable for about 10 h.Here,we develop a vacancy-engineered Ag_(3)PO_(4)/CdS porous microreactor chip photocatalyst,operating in seawater with a performance stability exceeding 300 h.This is achieved by the establishment of both catalytic selectivity for impurity ions and tailored interactions between vacancies and sulfur species.Efficient transport of carriers with strong redox ability is ensured by forming a heterojunction within a space charge region,where the visualization of potential distribution confirms the key design concept of our chip.Moreover,the separation of oxidation and reduction reactions in space inhibits the reverse recombination,making the chip capable of working at atmospheric pressure.Consequently,in the presence of Pt co-catalysts,a high solar-to-hydrogen efficiency of 0.81%can be achieved in the whole durability test.When using a fully solar-driven 256 cm2 hydrogen production prototype,a H_(2) evolution rate of 68.01 mmol h−1 m−2 can be achieved under outdoor insolation.Our findings provide a novel approach to achieve high selectivity,and demonstrate an efficient and scalable prototype suitable for practical solar H_(2) production.
基金supported by the National Natural Science Foundation of China under Grant No.61571452 and No.61201331
文摘This paper presents a source localization algorithm based on the source signal's time-difference-of-arrival(TDOA) for asynchronous wireless sensor network.To obtain synchronization among anchors,all anchors broadcast signals periodically,the clock offsets and skews of anchor pairs can be estimated using broadcasting signal's time-of-arrivals(TOA) at anchors.A kalman filter is adopted to improve the accuracy of clock offsets and track the clock drifts due to random fluctuations.Once the source transmits signal,the TOAs at anchors are stamped respectively and source's TDOA error due to clock offset and skew of anchor pair can be mitigated by a compensation operation.Based on a Gaussian noise model,maximum likelihood estimation(MLE) for the source position is obtained.Performance issues are addressed by evaluating the Cramer-Rao lower bound and the selection of broadcasting period.The proposed algorithm is simple and effective,which has close performance with synchronous TDOA algorithm.
基金Project supported by the National High Technology Research and Development Program of China(Grant No.2014AA052401)the National Natural Science Foundation of China(Grant No.61474013)the National Grid Science&Technology Project,China(Grant No.5455DW150006)
文摘The effect of phosphorus passivation on 4H-SiC（0001） silicon （Si） dangling bonds is investigated using ab initio atomistic thermodynamic calculations. Phosphorus passivation commences with chemisorption of phosphorus atoms at high-symmetry coordinated sites. To determine the most stable structure during the passivation process of phosphorus, a surface phase diagram of phosphorus adsorption on SiC （0001） surface is constructed over a coverage range of 1/9-1 monolayer （ML）. The calculated results indicate that the 1/3 ML configuration is most energetically favorable in a reasonable environment. At this coverage, the total electron density of states demonstrates that phosphorus may effectively reduce the interface state density near the conduction band by removing 4H-SiC （0001） Si dangling bonds. It provides an atomic level insight into how phosphorus is able to reduce the near interface traps.
基金supported by the France-China Particle Physics Laboratory(FCPPL)the China Scholarship Council(CSC)grant.
文摘The time and efficiency of charge collection are the key factors of monolithic active pixel sensor devices for minimum ionizing particles tracking detection.In this paper,3D models of pixels with different resistivity epitaxial layers(epi-layers) are built and simulated using Synopsys-Sentaurus.The basic characteristics of detectors are evaluated,including electric potential,electric field,and depleted region.Results indicate that the high resistivity (HR) epi-layer is a better choice.Further,simulation results show that the key collection performance is significantly improved owing to a wider and stronger electric field in the N type HR epi-layer.
基金Supported by the National Natural Science Foundation of China under Grant Nos 60806038 and 61131004the National High Technology Research and Development Program of China under Grant Nos 2006AA040102 and 2006AA040106.
文摘We report on the design,fabrication,and characterization of a micro plane-plane geometry CMOS device,which has a heat emitter and a heat receiver,capable of studying the near-field radiative heat transfer at a 550nm gap.Under high vacuum conditions,the heat emitter is heated by supplying driving currents and heated again after removing the heat receiver.The heating power difference between the two kinds of heating experiments indicates the existence of a proximity effect in the heat transfer between the emitter and the receiver.Our experiments pave the way towards overcoming the construction difficulty of plane-plane geometry with a nanometer gap.
基金Supported by the National Natural Science Foundation of China under Grant Nos 61176068,61131004.
文摘Zr_(0.9)Mg_(0.1)O_(2−δ) nanofibers and ZrO_(2) nanofibers are synthesized using electrospinning and the calcination technique.The nanofibers are characterized using x-ray diffraction(XRD),a field emission scanning electron microscope(FE-SEM),and a Brunauer–Emmett–Teller(BET)surface analyzer.The humidity sensing properties of Zr_(0.9)Mg_(0.1)O_(2−δ) nanofiber sensors are analyzed and compared with those of ZrO_(2) nanofiber sensors.The Zr_(0.9)Mg_(0.1)O_(2−δ) nanofiber humidity sensors exhibit a broader humidity range of 11–97%relative humidity(RH),good linearity,small humidity hysteresis,and rapid response and recovery times.The complex impedance plots of the Zr_(0.9)Mg_(0.1)O_(2−δ) sensor at different RHs are drawn,and the humidity sensing mechanism is discussed via an equivalent circuit.
文摘When clock frequencies exceed gigahertz, the skin depth in analog and digital circuits greatly decreases. The irregular shape of the cross section of the interconnect plays an increasingly important role in interconnect parasitic extraction. However, existing methods only focus on the rough surface of the interconnect, while ignoring other irregular shapes, such as the trapezoidal cross section. In this work, a new simulation method is proposed for irregular interconnects, which is applicable to arbitrary irregular shapes and to a wide range of frequencies. The method involves generating a mesh information file firstly, and then extracting the frequency-dependent resistance based on a numerical solution of scalar wave modeling by using the method of moments. The singularity extraction method is used to calculate the self-inductors. The data from experiments verify the accuracy of our proposed method.
文摘Self-aligned-gate heterostructure field-effect transistor（HFET） is fabricated using a wet-etching method.Titanium nitride（TiN） is one kind of thermal stable material which can be used as the gate electrode.A Ti/Au cap layer is fixed on the gate and acts as an etching mask.Then the T-shaped gate is automatically formed through over-etching the TiN layer in 30% H2O2 solution at 95 ℃.After treating the ohmic region with an inductively coupled plasma（ICP） method,an Al layer is sputtered as an ohmic electrode.The ohmic contact resistance is approximately 0.3 Ω·mm after annealing at a low-temperature of 575 ℃ in N2 ambient for 1 min.The TiN gate leakage current is only 10^-8 A after the low-temperature ohmic process.The access region length of the self-aligned-gate（SAG） HFET was reduced from 2 μm to 0.3 μm compared with that of the gate-first HFET.The output current density and transconductance of the device which has the same gate length and width are also increased.
基金supported in part by the National Natural Science Foundation of China(Nos.61411130312 and 61308053)Guangdong Provincial Key Laboratory of Semiconductor Micro Display(No.2020B121202003)Foshan Science and Technology Bureau。
文摘Conventional wavelength modulation spectroscopy(WMS)is vulnerable to the influence of low-frequency noise.Accuracy of the method highly depends on the performance of the costly lock-in amplifier.In this article,we report a new and effective method for reconstructing second-harmonic signals through WMS based on fast Fourier transform(FFT).This method is less disturbed by low-frequency noise because it does not use a low-frequency ramp wave.Formulation and detection procedures were presented.The discrete second-harmonic waveform can be obtained by continuously changing the DC signal and FFT analysis in this method.Second-harmonic waveforms acquired by the two means are generally consistent.The experimental study validates the obtained gas concentration from 5% to 30%,showing a good linear relationship by the proposed method.The maximum relative error on concentration extraction is 2.87%;as for conventional WMS,this value is 4.50%.The developed measurement method may have potential in computed tomography.
基金Supported by the Education Foundation of Anhui Province (No.2005kj058)
文摘A novel and efficient speckle noise reduction algorithm based on Bayesian wavelet shrinkage using cycle spinning is proposed. First, the sub-band decompositions of non-logarithmically transformed SAR images are shown. Then, a Bayesian wavelet shrinkage factor is applied to the decomposed data to estimate noise-free wavelet coefficients. The method is based on the Mixture Gaussian Distributed （MGD） modeling of sub-band coefficients. Finally, multi-resolution wavelet coefficients are reconstructed by wavelet-threshold using cycle spinning. Experimental results show that the proposed despeclding algorithm is possible to achieve an excellent balance between suppresses speckle effectively and preserves as many image details and sharpness as possible. The new method indicated its higher performance than the other speckle noise reduction techniques and minimizing the effect of pseudo-Gibbs phenomena.
基金Supported by the Education Foundation of Anhui Province (No.2002kj003)
文摘A method of single channel speech enhancement is proposed by de-noising using stationary wavelet transform. The approach developed herein processes multi-resolution wavelet coefficients individually and then recovery signal is reconstructed. The time invariant characteristics of stationary wavelet transform is particularly useful in speech de-noising. Experimental results show that the proposed speech enhancement by de-noising algorithm is possible to achieve an excellent balance between suppresses noise effectively and preserves as many target characteristics of original signal as possible. This de-noising algorithm offers a superior performance to speech signal noise suppress.
基金Supported by the National Natural Science Foundation of China (Grant Nos. 60374044 and 69974001)
文摘A theoretical model and mathematical description for silicon micromachined elec- trostatic or capacitive ultrasonic imaging transducers have been developed. Ac- cording to the model the basic performance parameters of such a transducer, such as natural frequencies, eigenfunctions, resonance and anti-resonance frequencies, and the mechanical impedance of the diaphragm can be predicted from the ge- ometry of the transducer and property parameters of materials used. The paper reveals that this type of transducers has two basic operation modes, correspond- ing to the resonance of a mass-spring oscillator comprised of the diaphragm and the air cushion, and the first-order bending mode of the diaphragm itself respec- tively, and presents an optimal method for extending the bandwidth by making the two modes coupled, and thereby provides a theoretical basis for the optimal de- sign.
文摘The purpose of this study is to present an application of a novel enhancement technique for enhancing medical images generated from X-rays. The method presented in this study is based on a nonlinear partial differential equation （PDE） model, Kramer＇s PDE model. The usefulness of this method is investigated by experimental results. We apply this method to a medical X-ray image. For comparison, the X-ray image is also processed using classic Perona-Malik PDE model and Catte PDE model. Although the Perona-Malik model and Catte PDE model could also enhance the image, the quality of the enhanced images is considerably inferior compared with the enhanced image using Kramer＇s PDE model. The study suggests that the Kramer＇s PDE model is capable of enhancing medical X-ray images, which will make the X-ray images more reliable.
基金Supported by the National Natural Science Foundation of China under Grant Nos 61107028 and 61131004, and the Fundamental Research Funds for the Central Universities under Grant No DUT12JB11.
文摘The repeatable bipolar resistive switching phenomenon is observed in amorphous Al2O3 prepared by metalorganic chemical vapor deposition on ITO glass, with ITO as the bottom electrode and Ag as the top electrode. The crystal structure, morphology, composition and optical properties of Al2O3 thin films are investigated by x-ray diffraction, x-ray photoelectron spectroscopy, atomic force microscopy and ultraviolet-visible-infrared spectroscopy, respectively. The electronic character of Ag/Al2O3/ITO structure is tested by an Agilent B1500A. The device shows a typical bipolar resistive switching behavior under the dc voltage sweep mode at room temperature. The variation ratio between HRS and LRS is larger than nearly three orders of magnitude, which indicates the good potential of this structure in future resistive random access memory （ReRAM） applications. Based on the conductive filament model, the high electric field is considered the main reason for the resistive switching according to our measurements.
基金the National Natural Science Foundation of China (Grant Nos. 60402001 and 60672023)the Science and Technological Fund of Anhui Province for Outstanding Youth (Grant No. 08040106807)
文摘Due to undesirable interference via unintended coupling paths, switching converters may exhibit complex intermittency, which appears as a form of bifurcation undergoing regular operation, subharmonics, and chaos orderly and repeatedly for a long period of time. Such intermittent operation, being an unwanted operating state, should normally be avoided in power converters. This paper expounds the mechanism and conditions for the emergence of intermittency in a common current-mode controlled Boost converter. It is found that interference at frequencies near the switching frequency or its rational multiples may induce intermittent operation. The strengths and frequencies of the interfering signals determine the type and period of intermittency. The problem is analyzed by transforming the time-bifurcation analysis to a conventional parameter-bifurcation analysis. Based on this transformation, intermittency can be investigated from the bifurcation control viewpoint. Furthermore, the critical circuit parameter conditions for the emergence of intermittency can be predicted and compared with those from circuit simulation.
基金Supported by the National Natural Science Foundation of China (Grant Nos. 60402001, 60672023)the Science and Technological Fund of Anhui Province for Outstanding Youth (Grant No. 08040106807)
文摘Due to wide input fluctuation with line frequency of 50 Hz, power-factor-correction （PFC） Boost converters tend to exhibit fast-scale instability over time domain. The traditional remedy is to impose slope compensation so as to weaken or eliminate this instability. A theoretical principle on the implementation of slope compensation signal is still lacking. Empirical design will induce over compensation frequently, resulting in a large decrease of power factor. In order to tackle this issue, by constructing the discrete-time iterative map of the PFC Boost converter from the viewpoint of bifurcation control theory of nonlinear systems, consequently, the criterion of critical stability for the PFC circuit can be established. Based on this stability criterion, appropriate design of slope compensation can be achieved. Our work indicates that 3 main circuit parameters （i.e. switching cycle, output reference voltage and inductor） determine the effective amplitude design of the slope compensation signal. The results, validated by a large quantity of analytical and numerical studies, show that appropriate slope compensation can be effective in weakening （or controlling） fast-scale bifurcation while maintaining a rather high input power factor.
