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Effects of two-photon absorption on pseudo-random bit sequence operating at high speed
摘要： The effect of two-photon absorption (TPA) on all-optical logic operation in quantum-dot semiconductor optical amplifier (QD-SOA) has been carried out. We model the rate equation with the TPA effect for the logic XOR gate, AND gate, and, for pseudo-random bit sequence (PRBS) generation. The simulated results indicate that the TPA induced pumping increases the output Q-factor (quality). The results show that the quality of the output depends on the input pulse width and the speed of operation. The PRBS system can operate at 250 and 320 Gb/s but an increase in pulse width decreases the output Q-factor.
关键词： quantum-dot semiconductor optical amplifier,pseudorandom bit sequence,optical logic,Q factor,Two-photon absorption
更新于2025-09-23 15:23:52
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Ordered Sequence Detection and Barrier Signal Design for Digital Pulse Interval Modulation in Optical Wireless Communications
摘要： This paper proposes an ordered sequence detection (OSD) for digital pulse interval modulation (DPIM) in optical wireless communications. Leveraging the sparsity of DPIM sequences, OSD shows comparable performance to the optimal maximum likelihood sequence detection (MLSD) with much lower complexity. Compared with the widely adopted sample-by-sample optimal threshold detection (OTD), it considerably improves the bit error rate (BER) performance by mitigating error propagation. Moreover, this paper proposes a barrier signal-aided digital pulse interval modulation (BDPIM), where the last of every K symbols is allocated with more power as an inserted barrier signal. BDPIM with OSD (BDPIM-OSD) can limit the error propagation between two adjacent barriers. To reduce the storing delay when using OSD to detect extremely large packets, we propose BDPIM with a combination of OTD and OSD (BDPIM-OTD-OSD), within which long sequences are cut into pieces and separately detected. Approximate upper bounds of the average BER performance of DPIM-OTD, DPIM-OSD, BDPIM-OSD and BDPIM-OTD-OSD are analyzed. Simulations are conducted to corroborate our analysis. Optimal parameter settings are also investigated in uncoded and coded systems by simulations. Simulation results show that the proposed OSD and BDPIM bring significant improvement in uncoded and coded systems over various channels.
关键词： signal design,error propagation,bit error rate,ordered sequence detection,Digital pulse interval modulation
更新于2025-09-23 15:23:52
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Enhanced Active Power balancing capability of Grid connected Solar PV fed Cascaded H-bridge Converter
摘要： Cascaded H-bridge converter is a promising solution for next generation large scale PV system having both active and reactive power exchange capacity. However, one challenge with this converter is unbalanced power generation among the clusters or cells due to variation in radiation level, temperature, dusting on PV cells etc. In order to inject balanced power to the grid, in this paper, a controlled exchange of reactive power is proposed so that the converter can work with unbalanced power generation within the clusters. Magnitude of reactive power exchange is derived and necessary conditions discussed. Additionally, the magnitude of zero voltage is derived taking into account both active and reactive power exchange with the grid. By exchanging reactive power, the converter can also be used during low voltage ride through (LVRT) condition. This paper introduces a novel representation of unbalanced power generation using barycentric coordinate system which helps to identify regions in the power plane which require the exchange of reactive power. The proposed method is verified through computer simulation and in a laboratory prototype.
关键词： Maximum Power point tracking (MPPT),Active power,Zero sequence voltage,Reactive power,Solar Photovoltaic,Cascaded H-bridge multilevel converter(CHB)
更新于2025-09-23 15:23:52
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Fast Padé Transform for increasing the signal to noise ratio of spectra provided by STEAM pulse sequence
摘要： BACKGROUND/OBJECTIVE: There are two routine pulse-sequences for single voxel spectroscopy (SVS), point resolved spectroscopy (PRESS) and stimulated echo acquisition mode (STEAM). Although STEAM has several advantages in comparison to PRESS, signal/noise ratio (SNR) superiority of PRESS makes it the first choice for SVS. Application of Fast Padé transform (FPT) instead of Fast Furrier transform (FFT) might increase the SNR of the signal produced by STEAM pulse-sequence and therefore allows the benefits of its advantages. We aimed to evaluate and compare the noise root mean square (RMS) and SNR provided by STEAM pulse-sequence using both FPT and FFT. MATERIALS AND METHOD: A gelatin-based phantom was constructed in a 19-cm acrylic cylinder. The phantom had two normal/tumoral parts. The SVS was performed using a 3T MRI scanner. STEAM pulse-sequence were used with the following parameters: TR = 2000 ms, TM = 10 ms, and three TEs of 20, 135 and 270 ms with two data-points of 1024 and 512 and voxel-size of 1 cm3. The raw data were extracted and processed using both FFT and FPT estimators to produce the spectrum. The noise RMS and SNR of Cho and Cr metabolites were assessed. RESULTS: According to the results, noise RMS of spectra provided by FPT were decreased between 3619.01–14252.94% in comparison to FFT (p < 0.00001). The SNR of Cr1 and Cho peaks of the spectra provided by FPT were increased more than 96.80 and 97.18, respectively (0.00006 < p < 0.02). DISCUSSION: The difference of noise RMS’s provided by FPT are thousands percent less than FFT. This enormous decrease in noise provides a good increase of SNR. While the range of Cr1 and Cho SNR by FFT are between 41.55–120.32 the range of SNRs of these peaks provided by FPT are between 1719.99–9744.79, which implies a significant difference between the efficiency of FPT and FFT. CONCLUSION: This study showed that application of FPT in comparison to FFT can increase the spectra SNR and so that its usage can be helpful during the application of STEAM pulse-sequence which results in lower SNR in comparison to PRESS pulse-sequence. Thus, we should make use of the advantages of STEAM pulse-sequence.
关键词： Magnetic resonance spectroscopy,signal to noise ratio,STEAM pulse sequence,Fast Padé Transform,Fast Furrier Transform
更新于2025-09-23 15:22:29
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Long-term photometric observations of pre-main sequence objects in the field of North America/Pelican Nebula
摘要： To broaden the search and study stars in the early evolutionary phase, we investigated a sample of 17 pre-main sequence objects previously detected as either Hα emission-line pre-main sequence stars or T Tauri variables located in the field of the North America/Pelican Nebula complex. Johnson-Cousins B, V, Rc, Ic magnitudes and mean color indices for the program stars are determined from more than 12 400 measurements from archive photographic plates and from CCD data collected at 7 observatories covering the period of almost 60 years from 1954 up to 2013. We complemented previously rare insights on the photometry of the program stars and presented their photometric history, which for almost all program stars is the first long term photometric monitoring on a timescale of 6 decades. Eight program stars are found to be classical T Tauri stars of variability type II, while 6 program stars are weak-line T Tauri stars of variability type I. For the first time, periodicity is found for three stars: V1716 Cyg indicates a 4.15 day period, V2051 Cyg indicates a 384 day period, and V521 Cyg a period of 503 days.
关键词： stars: pre-main sequence,stars: variables: general
更新于2025-09-23 15:22:29
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Physical properties of the jet from DG Tauri on sub-arcsecond scales with HST/STIS
摘要： Context. Stellar jets are believed to play a key role in star formation, but the question of how they originate is still being debated. Aims. We derive the physical properties at the base of the jet from DG Tau both along and across the flow and as a function of velocity. Methods. We analysed seven optical spectra of the DG Tau jet, taken with the Hubble Space Telescope Imaging Spectrograph. The spectra were obtained by placing a long-slit parallel to the jet axis and stepping it across the jet width. The resulting position-velocity diagrams in optical forbidden emission lines allowed access to plasma conditions via calculation of emission line ratios. In this way, we produced a 3D map (2D in space and 1D in velocity) of the jet's physical parameters i.e. electron density ne, hydrogen ionisation fraction xe, and total hydrogen density nH. The method used is a new version of the BE-technique. Results. A fundamental improvement is that the new diagnostic method allows us to overcome the upper density limit of the standard [S ii] diagnostics. As a result, we find at the base of the jet high electron density, ne ～ 105, and very low ionisation, xe ～ 0.02?0.05, which combine to give a total density up to nH ～ 3 × 106. This analysis confirms previous reports of variations in plasma parameters along the jet, (i.e. decrease in density by several orders of magnitude, increase of xe from 0.05 to a plateau at 0.7 downstream at 2'' from the star). Furthermore, a spatial coincidence is revealed between sharp gradients in the total density and supersonic velocity jumps. This strongly suggests that the emission is caused by shock excitation. No evidence was found of variations in the parameters across the jet, within a given velocity interval. The position-velocity diagrams indicate the presence of both fast accelerating gas and slower, less collimated material. We derive the mass outflow rate, ˙Mj, in the blue-shifted lobe in different velocity channels, that contribute to a total of ˙Mj ～ 8 ± 4× 10?9 M☉ yr?1. We estimate that a symmetric bipolar jet would transport at the low and intermediate velocities probed by rotation measurements, an angular momentum flux of ˙Lj ～ 2.9 ± 1.5 × 10?6 M☉ yr?1 AU km s?1. We discuss implications of these findings for jet launch theories. Conclusions. The derived properties of the DG Tau jet are demonstrated to be consistent with magneto-centrifugal theory. However, non-stationary modelling is required in order to explain all of the features revealed at high resolution.
关键词： ISM: jets and outflows,Herbig-Haro objects,stars: pre-main sequence,stars: formation
更新于2025-09-23 15:22:29
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An efficient pixel clustering-based method for mining spatial sequential patterns from serial remote sensing images
摘要： The accumulation of serial remote sensing images provides plentiful data for discovering sequential spatial patterns in various fields such as agricultural monitoring, urban development, and vegetation cover. Otherwise, traditional sequential pattern-mining algorithms cannot be directly or efficiently applied to remote sensing images. In this study, we propose a pixel clustering-based method to improve the efficiency of mining spatial sequential patterns from raster serial remote sensing images (SRSI). Firstly, the images are compressed by using the Run-Length coding schema. Then, pixels with identical sequences are clustered by means of the Run-length code-based spatial overlay operation. Finally, a pruning strategy is proposed, to extend the prefixSpan algorithm to skip unnecessary database scanning when mining from pixel groups. The experimental results indicate that the method presented in this paper could extract spatial sequential patterns from SRSI efficiently. Although accurate support rates for the patterns may not be obtained, our method could ensure that all patterns are extracted with a lower time cost.
关键词： Sequence mining,Spatial sequential pattern,Pixels cluster,Serial remote sensing images
更新于2025-09-23 15:22:29
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[IEEE 2018 25th IEEE International Conference on Image Processing (ICIP) - Athens, Greece (2018.10.7-2018.10.10)] 2018 25th IEEE International Conference on Image Processing (ICIP) - A Machine Learning Approach to Accurate Sequence-Level Rate Control Scheme for Video Coding
摘要： In this paper, we propose a two-pass encoding framework to handle the problem of sequence-level rate control. We consider the sequence-level encoding parameter constant rate factor (CRF) as the factor to be adjusted. The proposed framework mainly has two key contributions. First, we provide a second order model to characterize the relationship between the bitrate and CRF. The proposed second order model outperforms the traditional linear model significantly. Second, we adopt a shallow neural network to train the relationship between the content-dependent features with the second-order model parameters. The proposed neural network is quite simple but able to estimate the model parameters accurately. We implement the proposed algorithm under tensorflow. Experimental results show that our proposed method obviously outperforms the state-of-the-art method.
关键词： sequence-level,constant rate factor,video coding,Rate control,Machine learning,second order model
更新于2025-09-23 15:21:21
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The <i>Gaia</i> DR2 view of the Gamma Velorum cluster: resolving the 6D structure
摘要： Gaia-ESO Survey observations of the young Gamma Velorum cluster led to the discovery of two kinematically distinct populations, Gamma Vel A and B, respectively, with population B extended over several square degrees in the Vela OB2 association. Using the Gaia DR2 data for a sample of high-probability cluster members, we find that the two populations differ not only kinematically, but are also located at different distances along the line of sight, with the main cluster Gamma Vel A being closer. A combined fit of the two populations yields (cid:36)A = 2.895 0.011 mas 11.5 pc and 383.4+2.5+15.3 and 0.091 14.2 pc, respectively, showing that Gamma Vel A is closer than Gamma Vel B by 38 pc. We find that the two clusters are nearly coeval, and that Gamma Vel B is expanding. We suggest that Gamma Vel A and B are two independent clusters located along the same line of sight.
关键词： open clusters and associations: individual: Gamma Velorum,stars: late-type,stars: pre-main sequence,stars: distances,stars: kinematics and dynamics
更新于2025-09-23 15:21:21
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[IEEE 2018 IEEE 5G World Forum (5GWF) - Silicon Valley, CA, USA (2018.7.9-2018.7.11)] 2018 IEEE 5G World Forum (5GWF) - 5G New Radio Physical Random Access Preamble Design
摘要： To cope with the stringent requirements imposed on the random access (RA) procedure by the use cases envisioned for 5G NR, we propose an RA preamble design based on cyclically delay-Doppler shifted ??-sequences. In contrast to the legacy 4G LTE RA preambles based on Zadoff-Chu (ZC) sequences, the proposed design is very robust against frequency uncertainties originating from wireless channel propagation and local oscillator imperfections. Simulation results show that the proposed ??-sequence based preambles deliver good performance even under harsh transmission conditions, while ZC based preambles fail. Further advantages of adopting ??-sequence based preambles in 5G NR include random access channel (RACH) capacity enhancement, support for low-power devices and low complexity implementation.
关键词： preamble,??-sequence,New Radio (NR),random access,5G,ZC sequence,RACH
更新于2025-09-23 15:21:01