AIM:To investigate the morphological characteristics of retinal vessels in patients with different severity of diabetic retinopathy(DR)and in patients with or without diabetic macular edema(DME).METHODS:The 239 eyes o...AIM:To investigate the morphological characteristics of retinal vessels in patients with different severity of diabetic retinopathy(DR)and in patients with or without diabetic macular edema(DME).METHODS:The 239 eyes of DR patients and 100 eyes of healthy individuals were recruited for the study.The severity of DR patients was graded as mild,moderate and severe non-proliferative diabetic retinopathy(NPDR)according to the international clinical diabetic retinopathy(ICDR)disease severity scale classification,and retinal vascular morphology was quantitatively analyzed in ultra-wide field images using RU-net and transfer learning methods.The presence of DME was determined by optical coherence tomography(OCT),and differences in vascular morphological characteristics were compared between patients with and without DME.RESULTS:Retinal vessel segmentation using RU-net and transfer learning system had an accuracy of 99%and a Dice metric of 0.76.Compared with the healthy group,the DR group had smaller vessel angles(33.68±3.01 vs 37.78±1.60),smaller fractal dimension(Df)values(1.33±0.05 vs 1.41±0.03),less vessel density(1.12±0.44 vs 2.09±0.36)and fewer vascular branches(206.1±88.8 vs 396.5±91.3),all P<0.001.As the severity of DR increased,Df values decreased,P=0.031.No significant difference between the DME and non-DME groups were observed in vascular morphological characteristics.CONCLUSION:In this study,an artificial intelligence retinal vessel segmentation system is used with 99%accuracy,thus providing with relatively satisfactory performance in the evaluation of quantitative vascular morphology.DR patients have a tendency of vascular occlusion and dropout.The presence of DME does not compromise the integral retinal vascular pattern.展开更多
As a promising ultra-wide bandgap semiconductor, gallium oxide(Ga_2O_3) has attracted increasing attention in recent years. The high theoretical breakdown electrical field(8 MV/cm), ultra-wide bandgap(~ 4.8 eV) and l...As a promising ultra-wide bandgap semiconductor, gallium oxide(Ga_2O_3) has attracted increasing attention in recent years. The high theoretical breakdown electrical field(8 MV/cm), ultra-wide bandgap(~ 4.8 eV) and large Baliga's figure of merit(BFOM) of Ga_2O_3 make it a potential candidate material for next generation high-power electronics, including diode and field effect transistor(FET). In this paper, we introduce the basic physical properties of Ga_2O_3 single crystal, and review the recent research process of Ga_2O_3 based field effect transistors. Furthermore, various structures of FETs have been summarized and compared, and the potential of Ga_2O_3 is preliminary revealed. Finally, the prospect of the Ga_2O_3 based FET for power electronics application is analyzed.展开更多
AIM: To evaluate the fractal feature of the retinal vasculature of normal eyes on a stereographic projected and montaged ultra-wide field(UWF) fluorescein angiography(FA).METHODS: Prospective, observational, cross-sec...AIM: To evaluate the fractal feature of the retinal vasculature of normal eyes on a stereographic projected and montaged ultra-wide field(UWF) fluorescein angiography(FA).METHODS: Prospective, observational, cross-sectional study. Totally 59 eyes of 31 normal subjects were imaged using the Optos 200 Tx. Images obtained at different gaze angles stereographically projected and montaged. The early-phase UWF FA frames were processed to segment the retinal vasculature and the results were exported as binary masks. The fractal dimension(FD) was calculated using the box-counting method.RESULTS: The global FD for the entire retina was 1.6±0.04, with no difference between males and females(1.59±0.04 vs 1.61±0.04, P=0.084) or between right and left eyes(1.6±0.04 vs 1.6±0.05, P=0.61). FD was nonuniformly distributed among four quadrants(P<0.001) and decreased as the distance from the fovea increased(P<0.001). A negative association was observed between FD and age(R=-0.37, P=0.006), and this relationship was observed in the posterior and mid-peripheral retina(P<0.05) but absent in far-periphery(P>0.05).CONCLUSION: Fractal geometry is non-uniformly distributed across the retina in normal eyes and decreases from the fovea to the far-periphery. Subjects with an older age tend to have a smaller FD, however, the FD in the farperiphery does not appear to be influenced by age.展开更多
In this paper, a compact coplanar epsilon.negative(ENG) antenna is proposed with ultra.wide operation band and small size of 18×11.5 mm2. The proposed antenna is designed based on a coplanar.waveguide(CPW) feedin...In this paper, a compact coplanar epsilon.negative(ENG) antenna is proposed with ultra.wide operation band and small size of 18×11.5 mm2. The proposed antenna is designed based on a coplanar.waveguide(CPW) feeding antenna, and thus the via.free structure is employed to realize the ENG unit cell, which is convenient to tune the frequency of zeroth.order resonance(ZOR) and extends the ZOR bandwidth. The high.order resonant frequencies are achieved and mainly determined by the separate slots that are located between the radiating patch and the ground plane. Adding the left.handed inductance between the radiating patch and ground has slight impact on the high.order resonant frequencies, and then the ultra.wide band is achieved by merging the ZOR bandwidth with the high.order resonant bandwidths. The ground plane primarily works as a matching network for the proposed antenna. Although it generates a low.frequency resonance, the performance is undesirable due to the impedance mismatching. The measured results show that the reflection coefficient, |S11| <.10 d B, is in a wide frequency range from 5.25 to 13 GHz, which covers the upper operation band of UWB communication. Also, the antenna contains relatively stable gains and omni.directional radiation patterns.展开更多
To tackle challenges such as interference and poor accuracy of indoor positioning systems,a novel scheme based on ultra-wide bandwidth(UWB)technology is proposed.First,we illustrate a distance measuring method between...To tackle challenges such as interference and poor accuracy of indoor positioning systems,a novel scheme based on ultra-wide bandwidth(UWB)technology is proposed.First,we illustrate a distance measuring method between two UWB devices.Then,a Taylor series expansion algorithm is developed to detect coordinates of the mobile node using the location of anchor nodes and the distance between them.Simulation results show that the observation error under our strategy is within 15 cm,which is superior to existing algorithms.The final experimental data in the hardware system mainly composed of STM32 and DW1000 also confirms the performance of the proposed scheme.展开更多
As one of the ultra-wide bandgap {UWBG)semiconducting materials,gallium oxide has attractive properties with a wide bandgap of about 4.8 eV and a high breakdown field of about 8 MWcm,which offers an alternative platfo...As one of the ultra-wide bandgap {UWBG)semiconducting materials,gallium oxide has attractive properties with a wide bandgap of about 4.8 eV and a high breakdown field of about 8 MWcm,which offers an alternative platform for various applications such as high performance power switches,RF amplifiers,solar blind photodetectors,and harsh environment signal processing.展开更多
The modern landmine's electronic fuse is susceptible to strong interference or can even be damaged by the ultra-wide band electromagnetic pulse(UWB-EMP). The finite-difference time-domain(FDTD) method in lossy me...The modern landmine's electronic fuse is susceptible to strong interference or can even be damaged by the ultra-wide band electromagnetic pulse(UWB-EMP). The finite-difference time-domain(FDTD) method in lossy media with cylindrical coordinates is used to study the interactions of the UWB-EMP with the landmine. First, the coupling of UWB-EMP into the landmine shielding shell through an aperture is numerically simulated. Second, the coupled electromagnetic field of mine shells made of different shielding materials and with apertures of different sizes is plotted. Third, the aperture coupling laws of UWB-EMP into shells are analyzed and categorized. Such an algorithm is capable of effectively preventing ladder similar errors, and consequently improving the calculation precision, and in addition to adopting the message passing interface(MPI) parallel method to divide the total calculating range into more sub-ranges, the overall calculating efficiency is greatly increased. These calculations are surely a constructive reference for modern landmine design against electromagnetic damage.展开更多
AIM: To evaluate the value of ultra-wide field(UWF) imaging in the management of traumatic retinopathy under the condition of corneal scar or fixed small pupil after complicated ocular trauma. METHODS: Twenty-eigh...AIM: To evaluate the value of ultra-wide field(UWF) imaging in the management of traumatic retinopathy under the condition of corneal scar or fixed small pupil after complicated ocular trauma. METHODS: Twenty-eight patients(28 eyes) with complicated ocular trauma were enrolled in the study from June 2016 to May 2017, including 19 males and 9 females with age ranged from 11 to 64(43.42±12.62)y. All patients were treated with secondary vitrectomy after emergency operation for wound repair of open ocular trauma. Direct ophthalmoscopy and 45-degree fundus photography were taken at each time point of follow up for comparison of findings with UWF images. Routine eye examination including visual acuity, intraocular pressure, slit lamp examination were performed and analyzed as well.RESULTS: Among the 28 traumatized eyes, the positive rate for identification of traumatic retinopathed was 32.1%(9 cases), 14.9%(5 cases), and 85.7%(24 cases) with direct ophthalmoscopy, 45-degree fundus photography, and UWF imaging, respectively. The detective rate of UWF imaging under the condition of corneal scar or fixed small pupil was statistically greater than that of 45-degree fundus photography and direct ophthalmoscopy(Bonferroni correction, P〈0.001). UWF image was obtained in 19 eyes with opaque corneal scar, otherwise their fundus could not be seen by conventional methods. The additional findings of traumatic retinopathies by UWF imaging included periretinal membranes or pre-retinal proliferating strip, retinal holes, hemorrhage in the vitreous or sub-retinal space.CONCLUSION: UWF imaging is superior to traditional fundus photography in the evaluation of traumatic retinopathies under the condition of corneal scar or fixed small pupil after complicated ocular trauma.展开更多
To realize effective utilization of renewable energy sources,a novel polymorphic topology with hybrid control strategy based LLC resonant converter was analyzed and designed in this paper.By combining the merits of a ...To realize effective utilization of renewable energy sources,a novel polymorphic topology with hybrid control strategy based LLC resonant converter was analyzed and designed in this paper.By combining the merits of a full bridge LLC resonant converter,three-level half bridge LLC resonant converter,and variable frequency control mode,the converter realizes an intelligent estimation of input voltage by automatically changing its internal cir-cuit topology.Under this control strategy,different input voltages determine different operation modes.This is achieved in full bridge LLC mode when the input voltage is low.If the input voltage rises to a certain level,it operates in three-level half bridge LLC mode.These switches are digital and entirely carried out by the DSP(Digi-tal Signal Processor),which means that an auxiliary circuit is unnecessary,where a simple strategy of software modification can be utilized.Experimental results of a 500W prototype with 100V~600V input voltage and full load efficiency of up to 92%are developed to verify feasibility and practicability.This type of converter is suitable for applications with an ultra-wide input voltage range,such as wind turbines,photovoltaic generators,bioenergy,and other renewable energy sources.展开更多
Theoretical calculations predict transition frequencies in the terahertz range for the field-effect transistors based on carbon nanotubes, and this shows their suitability for being used in high frequency applications...Theoretical calculations predict transition frequencies in the terahertz range for the field-effect transistors based on carbon nanotubes, and this shows their suitability for being used in high frequency applications. In this paper, we have designed a field-effect transistor based on carbon nanotube with high transition frequency suitable for ultra-wide band applications. We did this by optimizing nanotube diameter, gate insulator thickness and dielectric constant. As a result, we achieved the transition frequency about 7.45 THz. The environment of open source software FETToy is used to simulate the device. Also a suitable model for calculating the transition frequency is presented.展开更多
The evaluation of System Performance of UWB (ultra-wide band) jointing in MC (multi-carrier) signaling in correlated environments is presented in the report. The correlated Nakagami-m statistical distribution for the ...The evaluation of System Performance of UWB (ultra-wide band) jointing in MC (multi-carrier) signaling in correlated environments is presented in the report. The correlated Nakagami-m statistical distribution for the multipath fading model is assumed in this scenario. In fact to establish the model for analyzing in this article is using MC-CDMA (multi-carrier code-division multiple-access) system characterization combined with a UWB scheme. The average BER (bit error rate) is calculated and compared to a special case of previously published results. Studied results from this paper can be implied to approve the system performance for a UWB system combined with a MC-CDMA wireless communication system. It is worth noting that the Nakagami-m distributed fading parameter significantly dominates UWB system performance when it cooperates with MC signaling under a fading environment. Finally, it is worthy of noting that when the SNR (signal-to-noise ratio) at system’s receiver reaches a preset high threshold value, the parameter of power decay ratio effect could be not included.展开更多
The paper presents a fully integrated ultra-wide band(UWB)low noise amplifier(LNA)for 3-10 GHz applications.It employs self-biased resistive-feedback and current-reused technique to achieve wide input matching and low...The paper presents a fully integrated ultra-wide band(UWB)low noise amplifier(LNA)for 3-10 GHz applications.It employs self-biased resistive-feedback and current-reused technique to achieve wide input matching and low power characteristics.An improved biased architecture is adopted in the second stage to attain a better gain-compensation performance.The design is verified with TSMC standard 1 P6 M 0.18μm RF CMOS process.The measurement results show that the parasitic problem of the transistors at high frequencies is solved.A high and flat S21 of 9.7±1.5 dB and the lowest NF 3.5 dB are achieved in the desired frequency band.The power consumption is only 7.5 mA under 1.6 V supply.The proposed LNA achieves broadband flat gain,low noise,and high linearity performance simultaneously,allowing it to be used in 3-10 GHz UWB applications.展开更多
The Peak to Average power Ratio (PAR) of a Multi-Band Orthogonal Frequency-Division Multiplexing (MB-OFDM) Ultra-Wide Band (UWB) signals can be substantially larger than that of single carrier or carrier-less ultra-wi...The Peak to Average power Ratio (PAR) of a Multi-Band Orthogonal Frequency-Division Multiplexing (MB-OFDM) Ultra-Wide Band (UWB) signals can be substantially larger than that of single carrier or carrier-less ultra-wideband signals. In this letter, a novel PAR reduction scheme for the MB-OFDM UWB system based on spreading and interleaving is proposed. By spreading the coded bits over each subcarrier in corresponding band and interleaving the spread symbols across all bands, the PAR statistics of the MB-OFDM signals can be improved and the PAR is reduced obviously. In the PAR reduction scheme, there is no loss in transmission data rate or Bit Error Rate (BER) performance decreasing. Since the spreading and interleaving operation are implemented by unitary Hadamard sequences and used for an approach to provide the robustness of the UWB system to narrowband interference, there is no additional implementation burden. Simulation results show that the investigated scheme gives the PAR reduction of 3dB compared with that of the original MB-OFDM signals.展开更多
To solve the precision self-positioning problem for mobile robot,a positioning program based on ultra-wideband technology was proposed. Ultra-wideband pulse has very high bandwidth; ranging accuracy can achieve centim...To solve the precision self-positioning problem for mobile robot,a positioning program based on ultra-wideband technology was proposed. Ultra-wideband pulse has very high bandwidth; ranging accuracy can achieve centimeter-level theoretically. The mobile robot obtained the distance to the reference node by sending ultra-wideband pulse. According to the geometric relations among the references and the robot,establish equations to calculate the position coordinates. Then Kalman filter algorithm was applied for mobile robot tracking. Simulation results show that robot positioning and tracking based on ultra-wideband technology can achieve indoor and outdoor seamless docking.展开更多
Ultra-wideband (UWB) is one of the recent topics that received a great concern from academia and industry. However, UWB found many difficulties to be standardized due to the overlay working that made UWB an important ...Ultra-wideband (UWB) is one of the recent topics that received a great concern from academia and industry. However, UWB found many difficulties to be standardized due to the overlay working that made UWB an important potential interference source to many licensed and unlicensed spectrum throughout the band 3.1 to 10.6 GHz. This paper demonstrates the design of integrated triple band notched for UWB Microstrip antenna. We simulated UWB short range systems which require low power and these are built using inexpensive digital components. We proposed a compact triple band notched CPW (Co-planar Waveguide) fed Micro strip Antenna (MSA) for UWB. This band-notched antenna has rejection characteristics at 3.2 GHz (for Wi-MAX band 3.16 to 3.32 GHz), at 5.5 GHz (for WLAN 2 band—5.3 to 5.72 GHz) and at 7.9 GHz (for ITU band 7.72 GHz to 8.13 GHz). The simulation was done using IE3D simulator.展开更多
This work designs a new system(1-x)Na_(0.5)Bi_(0.5+y)TiO_(3-x)NaTaO_(3)with a nonstoichiometric bismuth ratio,which is used as dielectrics of ceramics capacitors.Phase structure evolution of(1-x)Na_(0.5)Bi_(0.5+y)TiO_...This work designs a new system(1-x)Na_(0.5)Bi_(0.5+y)TiO_(3-x)NaTaO_(3)with a nonstoichiometric bismuth ratio,which is used as dielectrics of ceramics capacitors.Phase structure evolution of(1-x)Na_(0.5)Bi_(0.5+y)TiO_(3-x)NaTaO_(3)is characterized using XRD,Raman and TEM.Dielectric and resistant properties of(1-x)Na_(0.5)Bi_(0.5+y)TiO_(3-x)NaTaO_(3)are investigated with increasing concentration of NaTaO_(3).With these in-vestigations,the structure and defect chemistry of(1-x)Na_(0.5)Bi_(0.5+y)TiO_(3-x)NaTaO_(3)are rationalized and their respective impact on capacitor properties are elucidated.The optimized composition 0.8Na_(0.5)Bi_(0.51)TiO_(3)-0.2NaTaO_(3)possesses an ultra-wide operating temperature range(-92e398C),in which both stable permittivity and low dielectric loss is obtained.Furthermore,the fabrication of multilayer ceramics capacitors(MLCC)based on 0.8Na_(0.5)Bi_(0.51)TiO_(3)-0.2NaTaO_(3)dielectrics is investigated.With the addition of sintering aids,0.8Na_(0.5)Bi_(0.51)TiO_(3)-0.2NaTaO_(3)could be co-fired with Ag at 910℃in air,and the low temperature co-fired ceramic(LTCC)capacitors maintain good temperature stability of permittivity and low dielectric loss in-100-352℃.Therefore,our work provides a new route for pre-paring ultra-wide operating temperature capacitors at low manufacturing costs.展开更多
A novel technique is proposed for the generation of ultra-wide and flat optical frequency comb(OFC)based on serially cascading three stages of electro absorption modulators(EAMs)through sinusoidal radio frequency(RF)s...A novel technique is proposed for the generation of ultra-wide and flat optical frequency comb(OFC)based on serially cascading three stages of electro absorption modulators(EAMs)through sinusoidal radio frequency(RF)signals by setting frequencies at f GHz,f/2 GHz and f/4 GHz.Here,the first stage acts as subcarrier generator,the second stage acts as subcarrier doubler,and the third stage acts as subcarrier quadrupler.In addition,a higher number of subcarriers can easily be generated by adjusting the driving sinusoidal RF signal.In this paper,cascading three stages of EAMs driven by50 GHz,25 GHz and 12.5 GHz clock sources,we obtain 272 subcarriers with spacing of 2.5 GHz and power deviation within 1 d B.Theoretical analysis of serially cascaded EAMs for subcarrier generation is also investigated.Principal analysis and simulation of this technique are demonstrated.展开更多
Narrow bandpass filters(NBPFs)play important roles in optics,such as quantum communication,spectrometer,and wavelength division multiplexing.However,the stopband and restraint ability of traditional NBPFs is limited.I...Narrow bandpass filters(NBPFs)play important roles in optics,such as quantum communication,spectrometer,and wavelength division multiplexing.However,the stopband and restraint ability of traditional NBPFs is limited.In this article,a coupled Tamm plasmon polaritons(TPPs)induced transmission theory has been proposed to design high-efficiency NBPFs with ultra-wide deep stopbands.An NBPF at 1.55 μm has been experimentally demonstrated with full width at half maximum(FWHM)of 10 nm and stopband ranging from 0.2 to 25 μm which is 62 times wider than that of traditional ones.Furthermore,the restraint depth of the stopband reaches 0.03%,which is only 1/20 of a traditional filter with the same FWHM.Its advantage in restraining ambient light over traditional ones has also been demonstrated with an InGaAs infrared detector.It provides a very powerful way to capture specific narrowband optical signals from ultra-wide strong ambient light,especially useful for daytime quantum communications.展开更多
The Ultra-WideBand(UWB) technique, which offers good energy efficiency, flexible data rate, and high ranging accuracy, has recently been recognized as a revived wireless technology for short distance communication.Thi...The Ultra-WideBand(UWB) technique, which offers good energy efficiency, flexible data rate, and high ranging accuracy, has recently been recognized as a revived wireless technology for short distance communication.This paper presents a brief overview of two UWB techniques, covering Impulse-Radio UWB(IR-UWB) and FrequencyModulation UWB(FM-UWB) methods. The link margin enhancement technique, Very-WideBand(VWB), and power consumption reducing technique, chirp UWB, are also introduced. Then, several potential applications of IR-UWB with transceiver architectures are addressed, including high data rate proximity communication and secure wireless connectivity. With fine-ranging and energy-efficient communication features, the UWB wireless technology is highly promising for secure mobile Internet of Things(IoT) applications.展开更多
基金Supported by Zhejiang Medical Health Science and Technology Project(No.2023KY490).
文摘AIM:To investigate the morphological characteristics of retinal vessels in patients with different severity of diabetic retinopathy(DR)and in patients with or without diabetic macular edema(DME).METHODS:The 239 eyes of DR patients and 100 eyes of healthy individuals were recruited for the study.The severity of DR patients was graded as mild,moderate and severe non-proliferative diabetic retinopathy(NPDR)according to the international clinical diabetic retinopathy(ICDR)disease severity scale classification,and retinal vascular morphology was quantitatively analyzed in ultra-wide field images using RU-net and transfer learning methods.The presence of DME was determined by optical coherence tomography(OCT),and differences in vascular morphological characteristics were compared between patients with and without DME.RESULTS:Retinal vessel segmentation using RU-net and transfer learning system had an accuracy of 99%and a Dice metric of 0.76.Compared with the healthy group,the DR group had smaller vessel angles(33.68±3.01 vs 37.78±1.60),smaller fractal dimension(Df)values(1.33±0.05 vs 1.41±0.03),less vessel density(1.12±0.44 vs 2.09±0.36)and fewer vascular branches(206.1±88.8 vs 396.5±91.3),all P<0.001.As the severity of DR increased,Df values decreased,P=0.031.No significant difference between the DME and non-DME groups were observed in vascular morphological characteristics.CONCLUSION:In this study,an artificial intelligence retinal vessel segmentation system is used with 99%accuracy,thus providing with relatively satisfactory performance in the evaluation of quantitative vascular morphology.DR patients have a tendency of vascular occlusion and dropout.The presence of DME does not compromise the integral retinal vascular pattern.
基金supported by the National Natural Science Foundation of China(Nos.61521064,61522408,61574169,6 1334007,61474136,61574166)the Ministry of Science andTechnology of China(Nos.2016YFA0201803,2016YFA0203800,2017YFB0405603)+2 种基金the Key Research Program of Frontier Sciences of Chinese Academy of Sciences(Nos.QYZDB-SSWJSC048,QYZDY-SSW-JSC001)the Beijing Municipal Science and Technology Project(No.Z171100002017011)the Opening Project of the Key Laboratory of Microelectronic Devices&Integration Technology,Institute of Microelectronics of Chinese Academy of Sciences
文摘As a promising ultra-wide bandgap semiconductor, gallium oxide(Ga_2O_3) has attracted increasing attention in recent years. The high theoretical breakdown electrical field(8 MV/cm), ultra-wide bandgap(~ 4.8 eV) and large Baliga's figure of merit(BFOM) of Ga_2O_3 make it a potential candidate material for next generation high-power electronics, including diode and field effect transistor(FET). In this paper, we introduce the basic physical properties of Ga_2O_3 single crystal, and review the recent research process of Ga_2O_3 based field effect transistors. Furthermore, various structures of FETs have been summarized and compared, and the potential of Ga_2O_3 is preliminary revealed. Finally, the prospect of the Ga_2O_3 based FET for power electronics application is analyzed.
文摘AIM: To evaluate the fractal feature of the retinal vasculature of normal eyes on a stereographic projected and montaged ultra-wide field(UWF) fluorescein angiography(FA).METHODS: Prospective, observational, cross-sectional study. Totally 59 eyes of 31 normal subjects were imaged using the Optos 200 Tx. Images obtained at different gaze angles stereographically projected and montaged. The early-phase UWF FA frames were processed to segment the retinal vasculature and the results were exported as binary masks. The fractal dimension(FD) was calculated using the box-counting method.RESULTS: The global FD for the entire retina was 1.6±0.04, with no difference between males and females(1.59±0.04 vs 1.61±0.04, P=0.084) or between right and left eyes(1.6±0.04 vs 1.6±0.05, P=0.61). FD was nonuniformly distributed among four quadrants(P<0.001) and decreased as the distance from the fovea increased(P<0.001). A negative association was observed between FD and age(R=-0.37, P=0.006), and this relationship was observed in the posterior and mid-peripheral retina(P<0.05) but absent in far-periphery(P>0.05).CONCLUSION: Fractal geometry is non-uniformly distributed across the retina in normal eyes and decreases from the fovea to the far-periphery. Subjects with an older age tend to have a smaller FD, however, the FD in the farperiphery does not appear to be influenced by age.
基金supported by the National Natural Science Foundation of China (NNSF) under Grant 61531016National Natural Science Foundation of China (NNSF) under Grant 61271090+1 种基金Sichuan province science and technology support project under Grant 2016GZ0059Sichuan province science and technology support project under Grant 2017GZ0110
文摘In this paper, a compact coplanar epsilon.negative(ENG) antenna is proposed with ultra.wide operation band and small size of 18×11.5 mm2. The proposed antenna is designed based on a coplanar.waveguide(CPW) feeding antenna, and thus the via.free structure is employed to realize the ENG unit cell, which is convenient to tune the frequency of zeroth.order resonance(ZOR) and extends the ZOR bandwidth. The high.order resonant frequencies are achieved and mainly determined by the separate slots that are located between the radiating patch and the ground plane. Adding the left.handed inductance between the radiating patch and ground has slight impact on the high.order resonant frequencies, and then the ultra.wide band is achieved by merging the ZOR bandwidth with the high.order resonant bandwidths. The ground plane primarily works as a matching network for the proposed antenna. Although it generates a low.frequency resonance, the performance is undesirable due to the impedance mismatching. The measured results show that the reflection coefficient, |S11| <.10 d B, is in a wide frequency range from 5.25 to 13 GHz, which covers the upper operation band of UWB communication. Also, the antenna contains relatively stable gains and omni.directional radiation patterns.
基金National Key Research and Development Program of China,No.2018YFC0604404.
文摘To tackle challenges such as interference and poor accuracy of indoor positioning systems,a novel scheme based on ultra-wide bandwidth(UWB)technology is proposed.First,we illustrate a distance measuring method between two UWB devices.Then,a Taylor series expansion algorithm is developed to detect coordinates of the mobile node using the location of anchor nodes and the distance between them.Simulation results show that the observation error under our strategy is within 15 cm,which is superior to existing algorithms.The final experimental data in the hardware system mainly composed of STM32 and DW1000 also confirms the performance of the proposed scheme.
文摘As one of the ultra-wide bandgap {UWBG)semiconducting materials,gallium oxide has attractive properties with a wide bandgap of about 4.8 eV and a high breakdown field of about 8 MWcm,which offers an alternative platform for various applications such as high performance power switches,RF amplifiers,solar blind photodetectors,and harsh environment signal processing.
基金Project supported by the Postdoctoral Science Foundation of China(Grant No.2014M552610)
文摘The modern landmine's electronic fuse is susceptible to strong interference or can even be damaged by the ultra-wide band electromagnetic pulse(UWB-EMP). The finite-difference time-domain(FDTD) method in lossy media with cylindrical coordinates is used to study the interactions of the UWB-EMP with the landmine. First, the coupling of UWB-EMP into the landmine shielding shell through an aperture is numerically simulated. Second, the coupled electromagnetic field of mine shells made of different shielding materials and with apertures of different sizes is plotted. Third, the aperture coupling laws of UWB-EMP into shells are analyzed and categorized. Such an algorithm is capable of effectively preventing ladder similar errors, and consequently improving the calculation precision, and in addition to adopting the message passing interface(MPI) parallel method to divide the total calculating range into more sub-ranges, the overall calculating efficiency is greatly increased. These calculations are surely a constructive reference for modern landmine design against electromagnetic damage.
基金Supported by Sichuan Province Scientific Research Project of Institutions of Higher Education (No.2017ZRQN-108)
文摘AIM: To evaluate the value of ultra-wide field(UWF) imaging in the management of traumatic retinopathy under the condition of corneal scar or fixed small pupil after complicated ocular trauma. METHODS: Twenty-eight patients(28 eyes) with complicated ocular trauma were enrolled in the study from June 2016 to May 2017, including 19 males and 9 females with age ranged from 11 to 64(43.42±12.62)y. All patients were treated with secondary vitrectomy after emergency operation for wound repair of open ocular trauma. Direct ophthalmoscopy and 45-degree fundus photography were taken at each time point of follow up for comparison of findings with UWF images. Routine eye examination including visual acuity, intraocular pressure, slit lamp examination were performed and analyzed as well.RESULTS: Among the 28 traumatized eyes, the positive rate for identification of traumatic retinopathed was 32.1%(9 cases), 14.9%(5 cases), and 85.7%(24 cases) with direct ophthalmoscopy, 45-degree fundus photography, and UWF imaging, respectively. The detective rate of UWF imaging under the condition of corneal scar or fixed small pupil was statistically greater than that of 45-degree fundus photography and direct ophthalmoscopy(Bonferroni correction, P〈0.001). UWF image was obtained in 19 eyes with opaque corneal scar, otherwise their fundus could not be seen by conventional methods. The additional findings of traumatic retinopathies by UWF imaging included periretinal membranes or pre-retinal proliferating strip, retinal holes, hemorrhage in the vitreous or sub-retinal space.CONCLUSION: UWF imaging is superior to traditional fundus photography in the evaluation of traumatic retinopathies under the condition of corneal scar or fixed small pupil after complicated ocular trauma.
文摘To realize effective utilization of renewable energy sources,a novel polymorphic topology with hybrid control strategy based LLC resonant converter was analyzed and designed in this paper.By combining the merits of a full bridge LLC resonant converter,three-level half bridge LLC resonant converter,and variable frequency control mode,the converter realizes an intelligent estimation of input voltage by automatically changing its internal cir-cuit topology.Under this control strategy,different input voltages determine different operation modes.This is achieved in full bridge LLC mode when the input voltage is low.If the input voltage rises to a certain level,it operates in three-level half bridge LLC mode.These switches are digital and entirely carried out by the DSP(Digi-tal Signal Processor),which means that an auxiliary circuit is unnecessary,where a simple strategy of software modification can be utilized.Experimental results of a 500W prototype with 100V~600V input voltage and full load efficiency of up to 92%are developed to verify feasibility and practicability.This type of converter is suitable for applications with an ultra-wide input voltage range,such as wind turbines,photovoltaic generators,bioenergy,and other renewable energy sources.
文摘Theoretical calculations predict transition frequencies in the terahertz range for the field-effect transistors based on carbon nanotubes, and this shows their suitability for being used in high frequency applications. In this paper, we have designed a field-effect transistor based on carbon nanotube with high transition frequency suitable for ultra-wide band applications. We did this by optimizing nanotube diameter, gate insulator thickness and dielectric constant. As a result, we achieved the transition frequency about 7.45 THz. The environment of open source software FETToy is used to simulate the device. Also a suitable model for calculating the transition frequency is presented.
文摘The evaluation of System Performance of UWB (ultra-wide band) jointing in MC (multi-carrier) signaling in correlated environments is presented in the report. The correlated Nakagami-m statistical distribution for the multipath fading model is assumed in this scenario. In fact to establish the model for analyzing in this article is using MC-CDMA (multi-carrier code-division multiple-access) system characterization combined with a UWB scheme. The average BER (bit error rate) is calculated and compared to a special case of previously published results. Studied results from this paper can be implied to approve the system performance for a UWB system combined with a MC-CDMA wireless communication system. It is worth noting that the Nakagami-m distributed fading parameter significantly dominates UWB system performance when it cooperates with MC signaling under a fading environment. Finally, it is worthy of noting that when the SNR (signal-to-noise ratio) at system’s receiver reaches a preset high threshold value, the parameter of power decay ratio effect could be not included.
基金Supported by the National Natural Science Foundation of China(No.61534003,61874024,61871116)
文摘The paper presents a fully integrated ultra-wide band(UWB)low noise amplifier(LNA)for 3-10 GHz applications.It employs self-biased resistive-feedback and current-reused technique to achieve wide input matching and low power characteristics.An improved biased architecture is adopted in the second stage to attain a better gain-compensation performance.The design is verified with TSMC standard 1 P6 M 0.18μm RF CMOS process.The measurement results show that the parasitic problem of the transistors at high frequencies is solved.A high and flat S21 of 9.7±1.5 dB and the lowest NF 3.5 dB are achieved in the desired frequency band.The power consumption is only 7.5 mA under 1.6 V supply.The proposed LNA achieves broadband flat gain,low noise,and high linearity performance simultaneously,allowing it to be used in 3-10 GHz UWB applications.
基金Supported by the National 863 High Technology Research Program of China (N0.2005AA123320)Universities Natural Science Research Project of Jiangsu Province (No.05KJB510101).
文摘The Peak to Average power Ratio (PAR) of a Multi-Band Orthogonal Frequency-Division Multiplexing (MB-OFDM) Ultra-Wide Band (UWB) signals can be substantially larger than that of single carrier or carrier-less ultra-wideband signals. In this letter, a novel PAR reduction scheme for the MB-OFDM UWB system based on spreading and interleaving is proposed. By spreading the coded bits over each subcarrier in corresponding band and interleaving the spread symbols across all bands, the PAR statistics of the MB-OFDM signals can be improved and the PAR is reduced obviously. In the PAR reduction scheme, there is no loss in transmission data rate or Bit Error Rate (BER) performance decreasing. Since the spreading and interleaving operation are implemented by unitary Hadamard sequences and used for an approach to provide the robustness of the UWB system to narrowband interference, there is no additional implementation burden. Simulation results show that the investigated scheme gives the PAR reduction of 3dB compared with that of the original MB-OFDM signals.
基金High Technology Research and Development Program(863program) of China (No.2007AA041604)
文摘To solve the precision self-positioning problem for mobile robot,a positioning program based on ultra-wideband technology was proposed. Ultra-wideband pulse has very high bandwidth; ranging accuracy can achieve centimeter-level theoretically. The mobile robot obtained the distance to the reference node by sending ultra-wideband pulse. According to the geometric relations among the references and the robot,establish equations to calculate the position coordinates. Then Kalman filter algorithm was applied for mobile robot tracking. Simulation results show that robot positioning and tracking based on ultra-wideband technology can achieve indoor and outdoor seamless docking.
文摘Ultra-wideband (UWB) is one of the recent topics that received a great concern from academia and industry. However, UWB found many difficulties to be standardized due to the overlay working that made UWB an important potential interference source to many licensed and unlicensed spectrum throughout the band 3.1 to 10.6 GHz. This paper demonstrates the design of integrated triple band notched for UWB Microstrip antenna. We simulated UWB short range systems which require low power and these are built using inexpensive digital components. We proposed a compact triple band notched CPW (Co-planar Waveguide) fed Micro strip Antenna (MSA) for UWB. This band-notched antenna has rejection characteristics at 3.2 GHz (for Wi-MAX band 3.16 to 3.32 GHz), at 5.5 GHz (for WLAN 2 band—5.3 to 5.72 GHz) and at 7.9 GHz (for ITU band 7.72 GHz to 8.13 GHz). The simulation was done using IE3D simulator.
基金supported by National Natural Science Foundation of China(51972265,52272121)the Innovation Capability Support Program of Shaanxi(Program No.2021KJXX-30)the German Ministry of Education and Research(BMBF)for funding the Young Investigator Group HTL-NBT within the program“NanoMatFutur”(Grant No.03XP0146).
文摘This work designs a new system(1-x)Na_(0.5)Bi_(0.5+y)TiO_(3-x)NaTaO_(3)with a nonstoichiometric bismuth ratio,which is used as dielectrics of ceramics capacitors.Phase structure evolution of(1-x)Na_(0.5)Bi_(0.5+y)TiO_(3-x)NaTaO_(3)is characterized using XRD,Raman and TEM.Dielectric and resistant properties of(1-x)Na_(0.5)Bi_(0.5+y)TiO_(3-x)NaTaO_(3)are investigated with increasing concentration of NaTaO_(3).With these in-vestigations,the structure and defect chemistry of(1-x)Na_(0.5)Bi_(0.5+y)TiO_(3-x)NaTaO_(3)are rationalized and their respective impact on capacitor properties are elucidated.The optimized composition 0.8Na_(0.5)Bi_(0.51)TiO_(3)-0.2NaTaO_(3)possesses an ultra-wide operating temperature range(-92e398C),in which both stable permittivity and low dielectric loss is obtained.Furthermore,the fabrication of multilayer ceramics capacitors(MLCC)based on 0.8Na_(0.5)Bi_(0.51)TiO_(3)-0.2NaTaO_(3)dielectrics is investigated.With the addition of sintering aids,0.8Na_(0.5)Bi_(0.51)TiO_(3)-0.2NaTaO_(3)could be co-fired with Ag at 910℃in air,and the low temperature co-fired ceramic(LTCC)capacitors maintain good temperature stability of permittivity and low dielectric loss in-100-352℃.Therefore,our work provides a new route for pre-paring ultra-wide operating temperature capacitors at low manufacturing costs.
文摘A novel technique is proposed for the generation of ultra-wide and flat optical frequency comb(OFC)based on serially cascading three stages of electro absorption modulators(EAMs)through sinusoidal radio frequency(RF)signals by setting frequencies at f GHz,f/2 GHz and f/4 GHz.Here,the first stage acts as subcarrier generator,the second stage acts as subcarrier doubler,and the third stage acts as subcarrier quadrupler.In addition,a higher number of subcarriers can easily be generated by adjusting the driving sinusoidal RF signal.In this paper,cascading three stages of EAMs driven by50 GHz,25 GHz and 12.5 GHz clock sources,we obtain 272 subcarriers with spacing of 2.5 GHz and power deviation within 1 d B.Theoretical analysis of serially cascaded EAMs for subcarrier generation is also investigated.Principal analysis and simulation of this technique are demonstrated.
基金This work was funded by the National Natural Science Foundation of China(NSFC)(No.11874376)Shanghai Science and Technology Foundations(Nos.19DZ2293400,19ZR1465900,and 21WZ2504800)+3 种基金Shanghai Municipal Science and Technology Major Project(No.2019SHZDZX01)the Chinese Academy of Sciences President’s International Fellowship Initiative(Nos.2020VTA0009,2020PT0020,and 2021PT0007)And thanks to the support of Soft Matter Nanofab(No.SMN180827)Analytical Instrumentation Center(No.#SPST-AIC10112914)(SPST,ShanghaiTech University).
文摘Narrow bandpass filters(NBPFs)play important roles in optics,such as quantum communication,spectrometer,and wavelength division multiplexing.However,the stopband and restraint ability of traditional NBPFs is limited.In this article,a coupled Tamm plasmon polaritons(TPPs)induced transmission theory has been proposed to design high-efficiency NBPFs with ultra-wide deep stopbands.An NBPF at 1.55 μm has been experimentally demonstrated with full width at half maximum(FWHM)of 10 nm and stopband ranging from 0.2 to 25 μm which is 62 times wider than that of traditional ones.Furthermore,the restraint depth of the stopband reaches 0.03%,which is only 1/20 of a traditional filter with the same FWHM.Its advantage in restraining ambient light over traditional ones has also been demonstrated with an InGaAs infrared detector.It provides a very powerful way to capture specific narrowband optical signals from ultra-wide strong ambient light,especially useful for daytime quantum communications.
基金supported in part by the National Natural Science Foundation of China (No. 61774092)。
文摘The Ultra-WideBand(UWB) technique, which offers good energy efficiency, flexible data rate, and high ranging accuracy, has recently been recognized as a revived wireless technology for short distance communication.This paper presents a brief overview of two UWB techniques, covering Impulse-Radio UWB(IR-UWB) and FrequencyModulation UWB(FM-UWB) methods. The link margin enhancement technique, Very-WideBand(VWB), and power consumption reducing technique, chirp UWB, are also introduced. Then, several potential applications of IR-UWB with transceiver architectures are addressed, including high data rate proximity communication and secure wireless connectivity. With fine-ranging and energy-efficient communication features, the UWB wireless technology is highly promising for secure mobile Internet of Things(IoT) applications.