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- 摘要
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- 实验方案
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Caracterización y simulación de ruido en las imágenes de PET reconstruidas con OSEM: desarrollo de un método para la generación de imágenes sintéticas
摘要： Introduction: The goals of the study are to characterize imaging properties in 2D PET images reconstructed with the iterative algorithm ordered-subset expectation maximization (OSEM) and to propose a new method for the generation of synthetic images. Material and methods: The noise is analyzed in terms of its magnitude, spatial correlation, and spectral distribution through standard deviation, autocorrelation function, and noise power spectrum (NPS), respectively. Their variations with position and activity level are also analyzed. This noise analysis is based on phantom images acquired from 18F uniform distributions. Experimental recovery coefficients of hot spheres in different backgrounds are employed to study the spatial resolution of the system through point spread function (PSF). The NPS and PSF functions provide the baseline for the proposed simulation method: convolution with PSF as kernel and noise addition from NPS. Results: The noise spectral analysis shows that the main contribution is of random nature. It is also proven that attenuation correction does not alter noise texture but it modifies its magnitude. Finally, synthetic images of 2 phantoms, one of them an anatomical brain, are quantitatively compared with experimental images showing a good agreement in terms of pixel values and pixel correlations. Thus, the contrast to noise ratio for the biggest sphere in the NEMA IEC phantom is 10.7 for the synthetic image and 8.8 for the experimental image. Conclusions: The properties of the analyzed OSEM-PET images can be described by NPS and PSF functions. Synthetic images, even anatomical ones, are successfully generated by the proposed method based on the NPS and PSF.
关键词： PET,Autocorrelation function,OSEM,Iterative reconstruction,Noise power spectrum,Point spread function
更新于2025-09-23 15:22:29
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[IEEE 2019 International Conference on Robotics and Automation in Industry (ICRAI) - Rawalpindi, Pakistan (2019.10.21-2019.10.22)] 2019 International Conference on Robotics and Automation in Industry (ICRAI) - Low Cost 2D Laser Scanner Based Indoor Mapping and Classification System
摘要： Although the field of automatic speaker or speech recognition has been extensively studied over the past decades, the lack of robustness has remained a major challenge. Feature warping is a promising approach and its effectiveness significantly depends on the relative positions of each of the features in a sliding window. However, the relative positions are changed due to the non-linear effect of noise. Aiming at the problem, this paper takes the advantage of ranking feature, which is obtained directly by sorting a feature sequence in descending order, to propose a method. It first labels the central frame in a sliding window as speech or noise dominant (‘‘reliable’’ or ‘‘unreliable’’). In the unreliable case, the ranking of the central frame is estimated. Subsequently, the estimated ranking is mapped to a warped feature using a desired target distribution for recognition experiments. Through the theoretical analysis and experimental results, it is found that autocorrelation of a ranking sequence is larger than that of the corresponding feature sequence. What is more, rank correlation is not easily influenced by abnormal data or data that are highly variable. Thus, this paper deals with a ranking sequence rather than a feature sequence. The proposed feature enhancement approach is evaluated in an open-set speaker recognition system. The experimental results show that it outperforms missing data method based on linear interpolation and feature warping in terms of recognition performance in all noise conditions. Furthermore, the method proposed here is a feature-based method, which may be combined with other technologies, such as model-based, scores-based, to enhance the robustness of speaker or speech recognition system.
关键词： Robustness,ranking feature,rank correlation,open-set speaker recognition,autocorrelation,feature warping,missing data method
更新于2025-09-23 15:21:01
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Photon statistics and dynamics of nanolasers subject to intensity feedback
摘要： Using a fully stochastic numerical scheme, we theoretically investigate the behavior of a nanolaser in the lasing transition region under the influence of intensity feedback. Studying the input-output curves as well as the second-order correlations for different feedback fractions, we obtain an insight into the role played by the fraction of photons reinjected into the cavity. Our results reveal that the transition shrinks and moves to lower pump values with the feedback strength, and irregular pulses can be generated when the feedback is sufficiently large. The interpretation of the observation is strengthened through the comparison with the temporal traces of the emitted photons and with the radio-frequency power spectra. These results provide insight into the physics of nanolasers as well as validating the use of the second-order autocorrelation as a sufficient tool for interpretation of the dynamics. This confirmation offers a solid basis for the reliance on autocorrelations in experiments studying the effects of feedback in nanodevices.
关键词： nanolasers,stochastic simulation,intensity feedback,photon statistics,autocorrelation
更新于2025-09-23 15:19:57
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Stray light autocorrelation for the measurement of ultrashort laser pulses
摘要： Ultrashort laser pulses in the femtosecond range are of growing interest in medicine and micro material processing for industrial applications. The most interesting parameter is the pulse duration, which can only be measured by optical autocorrelation methods incorporating an optically nonlinear medium. Established methods mostly use monocrystalline beta barium borate (BBO) in transmission, exhibiting a high nonlinear conversion efficiency. However, this material is brittle, expensive and sophisticated in adjustment due to the necessary non-collinear phase matching. Since fiber-based high energy femtosecond laser systems become more and more achievable, the conversion efficiency of the nonlinear medium should no longer be seen as the restricting factor. Therefore, this research work discusses the suitability of several nonlinear media with differing translucency. Quartz, ammonium dihydrogen phosphate (ADP) and aluminum nitride (AlN) were compared in a standard autocorrelation setup and a novel versatile setup measuring frequency-doubled stray light. Best results were achieved with AlN, which appears to be a suitable and promising alternative material to BBO, reducing the expenses by two to three orders of magnitude.
关键词： autocorrelation,Stray light autocorrelation,aluminum nitride,ultrashort laser pulses
更新于2025-09-19 17:13:59
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Temporal profile measurements of ultrafast pulsed laser systems
摘要： Ultrafast pulsed lasers can be used to measure the phenomena occurring at femtosecond (fs) (10?15 s) time scale which include photo synthesis, protein collapsing and sub-atomic vibrations. In normal course, the temporal pro?le of the nanosecond (ns) pulsed lasers can be estimated by using the standard detectors because the recombination time of the electron-hole pair is of the order of ns. Nevertheless, the electronic equipment and the standard detectors are insuf?cient to measure the temporal pro?le of the ultrafast pulsed lasers. In the present investigation, we compare various techniques to measure the temporal pro?le of the ultrafast lasers which is followed by the details of the experimental con?guration of an autocorrelation technique. The temporal pro?le of the ultrafast pulsed lasers has shown various pulse width values in the experimental set-up when recorded at different con?gurations.
关键词： Second harmonic generation,Nonlinear optics,Autocorrelation measurement,Ultrafast spectroscopy,Ultrafast pulses
更新于2025-09-16 10:30:52
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[IEEE OCEANS 2019 - Marseille - Marseille, France (2019.6.17-2019.6.20)] OCEANS 2019 - Marseille - Extracting the interference components of normal modes in a shallow water waveguide using modified autocorrelation warping transform <sup>*</sup>
摘要： In underwater acoustic signal processing, current attention is on interference components of normal modes which can provide a means to estimate source range or depth. In this paper, we propose a modi?ed warping transform for the autocorrelation function of received signal. Through deducing the expression of the horizontal wavenumber in shallow water waveguide, the proposed warping transform is valid in most shallow water waveguide, not only in an ideal waveguide. Since we warped the autocorrelation function of received signal, we have no need to estimate the arrival time of signal. Note that the phase of the warped function is related to source range. We propose a method based on the proposed warping transform to estimate source range. Simulation results present the effectiveness of the warping transform and the passive source range estimation method.
关键词： autocorrelation function,warping transform,range estimation,interference components of normal modes
更新于2025-09-12 10:27:22
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Ytterbium-doped fiber laser as pulsed source of narrowband amplified spontaneous emission
摘要： We report random noise pulsed regime of an ytterbium-doped fiber laser arranged in common Fabry-Perot configuration. We show that the laser output obeys the photon statistics inherent to narrowband amplified spontaneous emission and that the noise pulsing is properly addressed in terms of probability density and autocorrelation functions. Our novel approach reveals, in particular, that the regime’s coherence time dramatically shortens, from few ns to tens ps, with increasing laser power.
关键词： narrowband amplified spontaneous emission,coherence time,photon statistics,probability density,ytterbium-doped fiber laser,autocorrelation functions,random noise pulsed regime
更新于2025-09-11 14:15:04
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Directional, Horizontal Inhomogeneities of Cloud Optical Thickness Fields Retrieved from Ground-Based and Airborne Spectral Imaging
摘要： Clouds exhibit significant horizontal inhomogeneities of their optical and microphysical properties, which complicate their realistic representation in weather and climate models. In order to investigate the directional, horizontal structure of cloud inhomogeneities, two-dimensional (2D) horizontal fields of optical thickness of subtropical cirrus and Arctic stratus with a spatial resolution of <10 m are investigated. The cloud optical thickness fields were derived from downward (transmitted) solar spectral radiance measurements from the ground beneath four cirrus clouds, and upward (reflected) radiances measured from aircraft above ten Arctic stratus clouds. The data were collected during the two major field campaigns Clouds, Aerosol, Radiation, and tuRbulence in the trade wInd regime over BArbados (CARRIBA) and VERtical Distribution of Ice in Arctic clouds (VERDI). Scalar one-dimensional (1D) and 2D autocorrelation functions, as well as power spectral densities are derived from the retrieved τ fields. Decorrelation lengths and scale breaks are identified and used to characterize the size range of the inhomogeneities and their influence on three-dimensional (3D) radiative effects. These studies reveal that there are considerable directional cloud inhomogeneities along and across the prevailing cloud structures. Therefore it is not sufficient to quantify horizontal cloud inhomogeneities by scalar 1D inhomogeneity parameters; 2D parameters are necessarily required.
关键词： power spectral densities,spectral imaging,autocorrelation functions,scale breaks,cloud optical thickness,decorrelation lengths,horizontal inhomogeneities,3D radiative effects
更新于2025-09-10 09:29:36
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[IEEE 2018 40th Annual International Conference of the IEEE Engineering in Medicine and Biology Society (EMBC) - Honolulu, HI (2018.7.18-2018.7.21)] 2018 40th Annual International Conference of the IEEE Engineering in Medicine and Biology Society (EMBC) - A 5-ms Error, 22-μA Photoplethysmography Sensor using Current Integration Circuit and Correlated Double Sampling
摘要： This paper presents a low-power Photoplethysmography (PPG) sensing method. The PPG is commonly used in recent wearable devices to detect cardiovascular information including heartbeat. The heartbeat is useful for physical activity and stress monitoring. However, the PPG circuit consumes large power because it consists of LED and photodiode. To reduce its power consumption without accuracy degradation, a cooperative design of circuits and algorithms is proposed in this work. A straightforward way to reduce the power is intermittent driving of LED, but there is a disadvantage that the signal is contaminated by a noise while circuit switching. To overcome this problem, we introduce correlated double sampling (CDS) method, which samples an integration circuit output twice with short intervals after the LED turns on and uses the difference of these voltage. Furthermore, an up-conversion method using linear interpolation, and an error correction using autocorrelation are introduced. The proposed PPG sensor, which consists of the LED, the photodiode, the current integration circuit, a CMOS switch, an A/D converter, and an MCU, is prototyped. It is evaluated by actual measurement with 22-year-old subject. The measurement results show that 22-μA total current consumption is achieved with 5-ms mean absolute error.
关键词： wearable devices,low-power,heartbeat monitoring,Photoplethysmography (PPG),autocorrelation,correlated double sampling (CDS)
更新于2025-09-04 15:30:14
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[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 - Effect of a Thin DRY Snow Layer on the Lake ICE Thickness Measurement using Wideband Autocorrelation Radiometry
摘要： Wideband autocorrelation radiometry (WiBAR) is a new method to remotely sense the microwave propagation time τdelay of multi-path microwave emission of low loss layered surfaces such as dry snowpack and freshwater lake ice pack. The microwave propagation time τdelay through the pack yields a measure of its vertical extent; thus, this technique is a direct measurement of depth. However, the presence of a different low loss layer on the lake ice pack such as dry snow pack introduces another multi-path interference, which can effect the lake ice pack thickness measurement. We present a simple geophysical forward model for the multipath interference phenomenon and derive the WiBAR system requirements needed to correctly measure the ice pack thickness. An X-band instrument fabricated from commercial-off-the-shelf (COTS) components are used to measure the thickness freshwater lake ice at the University of Michigan Biological Station. Ice thickness retrieval is demonstrated from nadir to 73.9?.
关键词： Snowpack,autocorrelation,icepack,microwave radiometry,remote sensing
更新于2025-09-04 15:30:14