- 标题
- 摘要
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- 实验方案
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Thermal Deformation Analysis and Electron Beam Optics Simulation for a Thermionic Electron Gun Design
摘要： When the thermionic electron gun of the klystron operates, the structure around the cathode is subjected to thermal deformation due to the high operating temperature of the cathode. A thermal deformation analysis of the existing electron gun with 'cold' dimensions (dimension on fabrication) was done using the ANSYS code to get the 'hot' dimensions of the electron gun on operation. After that, the optics of the emitted electron beam were simulated using two codes (EGUN and CST-PS) for the two cases of the 'cold' dimension and the 'hot' dimension. We compared the beam trajectories of the above two cases to investigate the change in the physical quantities, which would have a strong effect on the klystron performance due to the thermal deformation. The thermal deformation was found to cause a perveance change as large as 15%. The scalloping behavior was also investigated with an applied magnetic field for the two cases of cold and hot dimensions.
关键词： EGUN code,CST code,Electron gun,ANSYS code,Klystron,Thermal deformation
更新于2025-09-23 15:23:52
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Performance Limits of FSO Based SAC-OCDMA System Under Weather Conditions
摘要： In this paper, the Spectral Amplitude Coding Optical Code Division Multiple Access (SAC-OCDMA) is investigated in Free Space Optics (FSO) using Zero Cross Correlation (ZCC) codes to evaluate its performance limits in terms of link range. The system is analyzed under clear, haze, moderate fog and dense fog weather conditions. This system has been evaluated numerically and by simulation analysis by maintaining the transmitted power at 10 dBm, for safety reason, according to International Telecommunication Union (ITU) and minimum acceptable BER of 10–9. The simulation results shown that the present system can transmit 622 Mbps/1 Gbps up to maximum link range of 1450 m/1100 m and 61 m/54 m under clear and dense fog conditions, respectively.
关键词： fog,haze,free space optic (FSO),spectral amplitude coding optical code division multiple access (SAC-OCDMA),zero cross-correlation (ZCC)
更新于2025-09-23 15:23:52
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[IEEE 2018 IEEE 3rd Optoelectronics Global Conference (OGC) - Shenzhen (2018.9.4-2018.9.7)] 2018 IEEE 3rd Optoelectronics Global Conference (OGC) - High Speed Novel Hybrid Modulation Technique of Visible Light Communication Based on Artificial Neural Network Equalizer
摘要： Visible light communication (VLC) which realizes data transmission and universal illumination simultaneously has attracted much attention recently. However, the transmission rate of the VLC remains low due to the low bandwidth performance and inter-symbol interference (ISI). Therefore, a hybrid approach using pulse amplitude modulation and pulse width modulation in conjunction with an artificial neural network (ANN) equalizer is proposed, which can theoretically increase the transmission rate by 4 times compared with the traditional way, and provide variable brightness to realize the integration of data transmission and illumination control. In addition, an artificial neural network equalizer is proposed to undo the effects of ISI, considering that the bandwidth of the LED is only 3MHz. Without the ANN equalizer, the maximum transmission rate of the proposed hybrid modulation link only reaches 36 Mbps under the condition of no signal processing; however, with the ANN equalizer, the transmission speed can up to 2.6 Gbps. The proposed system not only achieves a genuine combination of data transmission and control illumination levels, but also realizes a high data rate with less complexity.
关键词： code division multiple access,pulse amplitude modulation,visible light communication,artificial neural network equalizer
更新于2025-09-23 15:23:52
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Functional Diversity in the Retina Improves the Population Code
摘要： Within a given brain region, individual neurons exhibit a wide variety of different feature selectivities. Here, we investigated the impact of this extensive functional diversity on the population neural code. Our approach was to build optimal decoders to discriminate among stimuli using the spiking output of a real, measured neural population and compare its performance against a matched, homogeneous neural population with the same number of cells and spikes. Analyzing large populations of retinal ganglion cells, we found that the real, heterogeneous population can yield a discrimination error lower than the homogeneous population by several orders of magnitude and consequently can encode much more visual information. This effect increases with population size and with graded degrees of heterogeneity. We complemented these results with an analysis of coding based on the Chernoff distance, as well as derivations of inequalities on coding in certain limits, from which we can conclude that the beneficial effect of heterogeneity occurs over a broad set of conditions. Together, our results indicate that the presence of functional diversity in neural populations can enhance their coding fidelity appreciably. A noteworthy outcome of our study is that this effect can be extremely strong and should be taken into account when investigating design principles for neural circuits.
关键词： retina,neural coding,discrimination error,mutual information,functional diversity,Chernoff distance,population code,heterogeneity
更新于2025-09-23 15:23:52
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Performance Evaluation of Hybrid FSO-SACOCDMA System under Different Weather Conditions
摘要： Spectral amplitude coding optical code division multiple access (SACOCDMA) is a multiplexing technique, which provides faster speed, efficiency, security and unlimited bandwidth. It is widely preferred because of its ability to eliminate multiple access interference (MAI). Free space optics (FSO) provides a wireless link to transmit data securely at higher rates for last mile access. In this work, a 100 Gb/s hybrid FSO-SACOCDMA is designed using direct detection. The performance of FSO using SACOCDMA utilizing NZCC (New Zero Cross Correlation) code is evaluated under different weather conditions (clear weather, haze and fog) for ten users where each user carries 10 Gb/s. The results indicate that in clear weather FSO distance can be extended up to 13 km. Moreover, after using pre-amplifier in clear weather, FSO enhances the maximum distance to 35 km with acceptable signal to noise ratio and bit error rate. Using an amplifier in the link not only makes the quality of the signal better but it also increases the communication range.
关键词： spectral amplitude coding optical code division multiple access (SACOCDMA),free space optics (FSO),direct detection (DD),new zero cross correlation (NZCC)
更新于2025-09-23 15:23:52
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Rapid Identification of Functional Pyrrolysyl-tRNA Synthetases via Fluorescence-Activated Cell Sorting
摘要： The orthogonal pyrrolysyl-tRNA synthetase/tRNACUA pair and their variants have provided powerful tools for expanding the genetic code to allow for engineering of proteins with augmented structure and function not present in Nature. To expedite the discovery of novel pyrrolysyl-tRNA synthetase (PylRS) variants that can charge non-natural amino acids into proteins site-specifically, herein we report a streamlined protocol for rapid construction of the pyrrolysyl-tRNA synthetase library, selection of the functional PylRS mutants using fluorescence-activated cell sorting, and subsequent validation of the selected PylRS mutants through direct expression of the fluorescent protein reporter using a single bacterial strain. We expect that this protocol should be generally applicable to rapid identification of the functional PylRS mutants for charging a wide range of non-natural amino acids into proteins.
关键词： non-natural amino acids,flow cytometry,mutagenesis,amber codon suppression,genetic code expansion
更新于2025-09-23 15:23:52
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The joint weight enumerator of an LCD code and its dual
摘要： A binary linear code is called LCD if it intersects its dual trivially. We show that the coefficients of the joint weight enumerator of such a code with its dual satisfy linear constraints, leading to a new linear programming bound on the size of an LCD code of given length and minimum distance. In addition, we show that this polynomial is, in general, an invariant of a matrix group of dimension 4 and order 12. Also, we sketch a Gleason formula for this weight enumerator.
关键词： LCD code,Linear programming bounds,Linear binary code
更新于2025-09-23 15:22:29
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[IEEE 2018 IEEE 3rd Optoelectronics Global Conference (OGC) - Shenzhen (2018.9.4-2018.9.7)] 2018 IEEE 3rd Optoelectronics Global Conference (OGC) - Signal Quality Improvement in Optical PPM-CDMA Systems Based SIC Scheme
摘要： Optical pulse position modulation-code division multiple access (PPM-CDMA) system with an interference theoretically analyzed. Successive interference cancellation (SIC) scheme has the ability to suppress the overlapping between the users by subtracting the strongest one from the original received signals one by one until all users detected. Different optical codes have been used for the comparison purpose; results show that the system with SIC scheme using modified quadratic congruence codes has better performance than the system using modified prime code as signature codes. In addition, the system with SIC scheme significantly superior to the one without SIC scheme.
关键词： code division multiple access,optical communication,interference cancellation,pulse position modulation
更新于2025-09-23 15:22:29
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[IEEE 2018 International Conference on Current Trends towards Converging Technologies (ICCTCT) - Coimbatore (2018.3.1-2018.3.3)] 2018 International Conference on Current Trends towards Converging Technologies (ICCTCT) - Generation and Analyzation of Spectral Density for IRNSS SPS PRN Code
摘要： The Indian Regional Navigational Satellite System (IRNSS) satellites provide two services namely standard Positioning Service (SPS) and Restricted Service (RS). L5 and S are the frequency bands from which both the services are utilized. To transmit the navigational information in SPS downlink gold codes are used. Most of the GNSS will work on the principle of CDMA where PRN sequences are the heart of the system. In this paper Pseudo Random Noise (PRN) codes are generated for an SPS signal which is called as SPS PRN code. A CDMA signal is generated using these sequences by using BPSK modulation. The analysis is done based on a time domain signal basis and is used to derive the Power Spectral Density of a CDMA signal. The spectrum analyser optimal operating conditions are observed by using the analytical results. To generate these codes, the polynomials G1 & G2 are selected, which are similar to ones used by GPS C/A signal and are as per the pre-conditions provided in IRNSS_SPS_ICD_June 2014. This paper also covers the process of selection of codes to be computed and the properties of PN-sequence are also analysed. The Xilinx ISE test system and Mat lab apparatus were used for the simulation of SPS PRN codes and additionally the implementation of PRN code is done on FPGA hardware wherein positive results have been obtained. These obtained simulated test results are within the theoretical limits.
关键词： ISE SIMULATOR,FPGA,CDMA,CORRELATION,PRN CODE
更新于2025-09-23 15:22:29
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LSBs-based quantum color images watermarking algorithm in edge region
摘要： Based on the NEQR representation for quantum color and binary images, an enhanced quantum watermarking scheme is investigated through Gray code transform and least significant bit (LSB) steganography, which embeds a quantum binary image (i.e., watermark image) into the edge region of a quantum color image (i.e., carrier image) LSB and second LSB. The size of the carrier and watermark images are assumed to be 2n × 2n and 2n?1 × 2n?1, respectively. At first, the watermark image is resized into an appropriate size image with 4-qubit grayscale based on the nearest neighbor interpolation method, which is of the same size with the preselected edge region in carrier image. To enhance the security of the watermark image, the binary code of 4-qubit grayscale of watermark image is transformed into the corresponding Gray code, and one 3-Controlled-NOT gate is utilized to generate a quantum binary image |K 1(cid:2). To further scatter the watermark image qubits that are embedded into the LSB and second LSB of carrier image, the quantum image |K 1(cid:2) is employed to choose any two channels from the color image among the three channels of R, G and B (i.e., R, G or R, B channels would be chosen as the embedding channels). Furthermore, a quantum binary image |K 2(cid:2) is generated through XOR operation decided by the quantum image |K 1(cid:2), which is used to determine the embedding order of watermark image qubits. The extraction process is the inverse operation of embedding, which also needs the two quantum binary key images |K 1(cid:2) and |K 2(cid:2). Finally, the experiment results are simulated under the classical computer software MATLAB 2016(b), which illustrates that our investigated LSBs-based quantum watermarking has a better visual effect than some related works in terms of PSNR value.
关键词： Nearest neighbor interpolation,Gray code transform,Quantum watermarking,Least significant bit
更新于2025-09-23 15:21:21