- 标题
- 摘要
- 关键词
- 实验方案
- 产品
-
Block-based Optical Color Image Encryption Based on Double Random Phase Encoding
摘要： This paper investigates and presents a block-based opto-color cipher using double random phase encoding (DRPE) with different block sizes. The color plainimage is divided into equal-sized blocks and then converted to an optical signal by an optical emitter. The obtained optical signal is encrypted by employing the DRPE technique, which applies two types of phase modulation, time, and Fourier domains. Finally, the optical color cipherimage is, upon detection, converted to digital format by a charge-coupled device digital camera. Experiments and security analysis show that the proposed block-based optical color image cipher using DRPE with increased block size is secure, effective, and including a good immunity to channel noise.
关键词： Fourier domain,optical color image,DRPE,time domain,and image encryption
更新于2025-09-23 15:22:29
-
Spectral versus Time-Domain OCT in Detecting Preoperative Epiretinal Membranes that Accompany Macular Holes
摘要： Purpose: To compare the sensitivities of spectral-domain optical coherence tomography (SD-OCT) versus time-domain OCT (TD-OCT) in identifying epiretinal membranes (ERM) preoperatively in patients who underwent surgery for full-thickness macular holes (FTMH). Methods: This is an interventional retrospective case series of 59 eyes diagnosed with FTMHs who underwent 25-G pars plana vitrectomy with internal limiting membrane peeling between 2009 and 2015. Preoperative OCTs were obtained by SD-OCT (Spectralis, Heidelberg, Germany) or TD-OCT (Stratus, Carl Zeiss Meditec, Dublin, CA, USA). Volume scans were reviewed for ERM accompanying the FTMH. This was compared to indocyanine green-negative staining and intraoperative findings of ERM as the gold standard. Results: Baseline characteristics between the SD-OCT and TD-OCT groups were comparable. Mean duration of postoperative follow-up was 41.4 weeks (±49.0). Of 59 eyes, 33 (55.9%) exhibited an ERM intraoperatively. Four ERMs (SD-OCT group) compared to 12 (TD-OCT group) were not visualized on preoperative OCT (p = 0.003). Sensitivity and specificity of SD-OCT in ERM detection was 79% and 100% compared to 14% and 91% for TD-OCT. Visual acuity improved in both arms (0.5 and 0.3 logMAR units in SD-OCT and TD-OCT, respectively (p = 0.002, 0.0002). Conclusions: We found that SD-OCT was superior to TD-OCT in identifying the presence of ERM preoperatively in patients who underwent macular hole surgery. Since ERMs may decrease the chance of successful pharmacologic vitreolysis, we recommend using SD-OCT over TD-OCT in the evaluation of patients with FTMH to more accurately identify ERMs and allow more comprehensive treatment decisions (pharmacologic versus surgical).
关键词： Epiretinal membrane,Spectral-domain optical coherence tomography,Macular hole,Time-domain optical coherence tomography
更新于2025-09-23 15:22:29
-
[IEEE IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Valencia (2018.7.22-2018.7.27)] IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Focusing of Spaceborne Bistatic SAR Data Based on Time-Domain Perturbation
摘要： Spaceborne bistatic synthetic aperture radar (BiSAR) system with an inclined geosynchronous (GEO) illuminator and a low-earth-orbit (LEO) receiver is capable of providing higher signal-to-noise ratio (SNR), finer resolution and vast area of surveillance. However, spatial-variant characteristics of the echo signal caused by the complex bistatic formation raise technical challenges in data focusing. To address the issue, an improved chirp scaling (CS) algorithm based on time-domain perturbation is proposed. Firstly, the signal model of GEO-LEO bistatic SAR is derived based on the geometry. Then, two-dimension (2-D) perturbation functions are employed to correct the spatial-variant characteristics of the echo signal. Finally, the phase compensation functions are generated to compensate for the residual phase. The proposed algorithm is able to implement wide-swath and high-resolution imaging. Simulation results of point targets show the validity of the presented method.
关键词： chirp scaling,spatial-variant,imaging,bistatic SAR,time-domain perturbation
更新于2025-09-23 15:22:29
-
Soft-Output Detection Methods for Sparse Millimeter Wave MIMO Systems with Low-Precision ADCs
摘要： In this paper, we propose computationally-efficient yet near-optimal soft-output detection methods for coded millimeter wave (mmWave) multiple-input multiple-output (MIMO) systems with low-precision analog-to-digital converters (ADCs). The underlying idea of the proposed methods is to construct an extremely sparse inter-symbol-interference (ISI) channel model by jointly exploiting the delay-domain sparsity in mmWave channels and a high quantization noise caused by low-precision ADCs. Then we harness this sparse channel model to create a trellis diagram with a reduced number of states and a factor graph with very sparse edge connections, which are used for computationally-efficient soft-output detection methods. Using the reduced trellis diagram, we present a soft-output detection method that computes the log-likelihood ratios (LLRs) of coded bits by optimally combining the quantized received signals obtained from multiple receive antennas using a forward-and-backward algorithm. To reduce the computational complexity further, we also present a low-complexity detection method using the sparse factor graph to compute the LLRs in an iterative fashion based on a belief propagation algorithm. Simulations results demonstrate that the proposed soft-output detection methods provide significant frame-error-rates gains compared to the existing frequency-domain equalization techniques in a coded mmWave MIMO system using one or two bit ADCs.
关键词： soft-output detection,time-domain equalization,low-precision analog-to-digital converter (ADC),multiple-input-multiple-output (MIMO),Millimeter wave communications
更新于2025-09-23 15:22:29
-
Dual-prism based terahertz time-domain attenuated total reflection spectroscopy and its application to characterise the hydration state of L-threonine in solution
摘要： To investigate the hydration state of amino acids, terahertz time-domain attenuated total internal reflection (THz TD-ATR) spectroscopy is often adopted to measure the complex permittivity. However, the classical THz TD-ATR spectroscopy system has only a single ATR prism and requires prism cleaning for different measuring modes, increasing the time consumed and easily introducing errors due to the changing environment. To accelerate the measurements and avoid the influence of environmental fluctuations, in this paper, we designed and built a dual-prism based THz TD-ATR spectroscopy: two ATR prisms with and without samples setting on the optical rail can be sequentially switched to optical systems for easily and rapidly collecting both sample and reference ATR spectra. According to the measurements of deionised water, the dual-prism based THz TD-ATR spectroscopy system can measure the sample complex permittivity rapidly and with high accuracy. The complex permittivity of L-threonine in aqueous solution is measured and analysed via the proposed system, and the hydration numbers of L-threonine solutions in different concentrations are quantitatively characterised. It is believed that the dual-prism based THz TD-ATR technique is a powerful tool for quickly and accurately investigating the hydration of amino acids.
关键词： Terahertz spectroscopy,Complex permittivity,Time-domain attenuated total internal reflection,Amino acid hydration
更新于2025-09-23 15:22:29
-
[IEEE 2018 International Symposium on Electronics and Telecommunications (ISETC) - Timisoara, Romania (2018.11.8-2018.11.9)] 2018 International Symposium on Electronics and Telecommunications (ISETC) - Investigation of Wave Propagation in a Plasma Antenna using 3D FDTD
摘要： The advancement of computer technology has led numerical methods to obtain a widespread usage. One of the most frequently used numerical methods in recent years is finite difference time domain method (FDTD). The behaviour of electromagnetic waves at the boundaries of the problem space has been studied by using perfectly matched layer (PML) type boundary conditions in FDTD.On the other hand, the majority of the substances in the universe are plasma. Plasma is a well known reconfigurable medium with different dielectric and conductive properties. Operating frequency of a plasma antenna is investigated in this paper. The field distributions around the plasma antenna have been evaluated using three dimensional FDTD. It has been shown that the plasma antenna can operate with characteristics similar to a wire antenna. C/C++ and MATLAB programming environments are used for simulations.
关键词： Finite Difference Time Domain,perfectly matched layer,plasma antenna
更新于2025-09-23 15:22:29
-
Topology optimization of flextensional piezoelectric actuators with active control law
摘要： This work deals with the concept of Topology Optimization Method (TOM) applied to the design of a flextensional piezoelectric actuator (FPEA) targeting vibration attenuation of its dynamic response. On these actuators the piezoceramic shape is usually fixed and it is more advantageous to optimize the host structure topology. The flextensional actuator is formed by two piezo-ceramic layers that act as a sensor and an actuator coupled with a constant gain active velocity feedback control law (AVFC). The optimization procedure is fully described and implemented, with no simplification for the piezo-ceramic AVFC introduced to the model acts by modifying the damping matrix according to the measurements of the state variables of the system in time-domain. The dynamic equation analyzed throughout the response for the rectangular four-noded finite element (FE) analysis is obtained by the Newmark’s time-integration method, which is applied to the physical equation and to the adjoint equation needed for the sensitivity analysis. A gradient-based optimization method is applied to minimize the response signal energy of the FPEA under a transient mechanical load. Results are obtained for different control gain values to evaluate their influence on the final topology. The optimized host structure material topology for the nc-nodes model is compared with the collapsed nodes (c-nodes) model. In addition, the nc-nodes model is useful to future developments that intends to provide an external circuit to this FPEA structure aiming to intensify the AVFC damping effect.
关键词： Topology Optimization Method,Time domain transient analysis,Flextensional Piezoactuator,Active control law,Non-collapsed piezoelectric nodes
更新于2025-09-23 15:22:29
-
Design of Real-Time Slope Monitoring system using Time-Domain Reflectometry with Wireless Sensor Network
摘要： Slope monitoring systems using WSN is an efficient technique to track slope movements or failures. Instability in slope contributes greatly in hazards caused to lives and property in mining areas and operations. Electronic instrumentation like wire-line extensometers, piezometers, total stations etc. are used for sensing the slope stability. The available wireless monitoring systems like SSR, LiDAR, Laser monitoring techniques are more expensive. In order to overcome this, efficient and economically feasible measurement systems for slope monitoring are needed. This paper presents the design, development and field implementation of an online, cost-effective wireless system for real-time slope monitoring which gives visible warning of a possible slope failure. The system is designed on Arduino board as a platform with RF module (ZigBee) for wireless communication. Additionally, using python the database and GUI are implemented. The experimental field TDR data is also verified with the total station monitoring system.
关键词： ZigBee,slope monitoring,time domain reflectometry (TDR),Coaxial cable,wireless sensor network (WSN)
更新于2025-09-23 15:22:29
-
[IEEE 2018 20th International Conference on Transparent Optical Networks (ICTON) - Bucharest (2018.7.1-2018.7.5)] 2018 20th International Conference on Transparent Optical Networks (ICTON) - Transforming the Fiber-Optic Network into a Dense and Ultrasensitive Seismic Sensor Array
摘要： We show a technology capable of performing position-resolved measurement of nanostrain perturbations along a conventional optical fiber cable, with meter-scale resolution. This technology can be deployed in already existing networks to achieve a dense and ultrasensitive seismic sensor array. Applications ranging from seismic protection to chemical sensing are explored.
关键词： seismology,distributed fiber optics sensors,Rayleigh scattering,optical time domain reflectometry,distributed acoustic sensors
更新于2025-09-23 15:22:29
-
[IEEE 2018 41st International Conference on Telecommunications and Signal Processing (TSP) - Athens, Greece (2018.7.4-2018.7.6)] 2018 41st International Conference on Telecommunications and Signal Processing (TSP) - Experimental Verification of the Optimum Diagonal Loading Level for Adaptive Matched Filtering with ?-OTDR System
摘要： Recently, a temporal adaptive matched filtering technique has been proposed to reduce the background noise in phase-sensitive optical time domain reflectometry (φ-OTDR) systems deployed for fibre optic distributed acoustic sensing (DAS) applications. This technique utilizes noise covariance matrix inversion which is estimated from signal-free assumed training samples. The detection performance degradation due to desired signal presence in the training data and the ill-conditioning of the matrix because of the limited training data are conventionally avoided by adding some amount of white noise on the diagonal elements of the covariance matrix. In this paper, the optimum level for this diagonal loading (DL) is investigated for DAS applications and verified with real φ-OTDR data. The optimum DL level which has been analytically proven in beamforming applications is shown to be applicable in the temporal domain noise filtering for DAS applications. The experimental results validate that the optimum DL value is negative.
关键词： diagonal loading,phase-sensitive optical time domain reflectometry (OTDR),distributed vibration sensors,optimum filtering.,Adaptive matched filter
更新于2025-09-23 15:22:29