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[IEEE 2017 IEEE Global Communications Conference (GLOBECOM 2017) - Singapore (2017.12.4-2017.12.8)] GLOBECOM 2017 - 2017 IEEE Global Communications Conference - Polar Decomposition Based Hybrid Beamforming Design for mmWave Massive MIMO Systems
摘要： This paper considers hybrid beamforming (HBF) for the point-to-point (P2P) millimeter wave (mmWave) massive MIMO systems. The optimal hybrid precoding and combining matrices that maximizes the system capacity can be obtained based on the singular value decomposition (SVD) of the channel matrix. Then, the optimal unconstrained hybrid digital and analog precoders (combiners) are designed according to the polar decomposition of the optimal hybrid precoding (combining) matrix. Considering the actual hardware constraints, we propose a joint transmitter and receiver HBF algorithm based upon polar decomposition. In this algorithm, the hybrid analog constrained precoding and combining matrices can be derived without having to incur an excessive computational complexity of an iterative approach. Simulation results show that the proposed algorithm can approach the performance of optimal unconstrained precoding, and is insensitive to the accuracy of the channel state information (CSI).
关键词： spectral efficiency,polar decomposition,massive MIMO,Hybrid beamforming,millimeter wave
更新于2025-09-09 09:28:46
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[IEEE 2017 IEEE Nuclear Science Symposium and Medical Imaging Conference (NSS/MIC) - Atlanta, GA (2017.10.21-2017.10.28)] 2017 IEEE Nuclear Science Symposium and Medical Imaging Conference (NSS/MIC) - Application of Deep Leaming in Multi-Material Decomposition of Spectral CT
摘要： Multi-material decomposition (MMD) is an important application of spectral Computed Tomography (CT). However, traditional image-domain material decomposition algorithms are based on pixel-wise usually, affected by noise and artifact easily. In order to enlarge the receptive field instead of considering the neighborhood of pixel only, we adopt deep learning technique to solve the multi-material decomposition problem. We build a convolutional neural network (CNN) to solve the MMD problem. Then we simulate some reconstruction images of spectral CT to train the network. After training, the CNN method can reduce the MSE by 1~2 orders in the test samples, comparing to the results of solving linear equations. As the conclusion, we think CNN shows its effectiveness to solve MMD problem, and has some irreplaceable advantages, but there still remains many researches to survey.
关键词： deep learning,spectral CT,CNN,multi-material decomposition
更新于2025-09-09 09:28:46
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[IEEE 2017 IEEE Nuclear Science Symposium and Medical Imaging Conference (NSS/MIC) - Atlanta, GA (2017.10.21-2017.10.28)] 2017 IEEE Nuclear Science Symposium and Medical Imaging Conference (NSS/MIC) - Deep residual learning in CT physics: scatter correction for spectral CT
摘要： Recently, spectral CT has been drawing a lot of attention in a variety of clinical applications primarily due to its capability of providing quantitative information about material properties. The quantitative integrity of the reconstructed data depends on the accuracy of the data corrections applied to the measurements. Scatter correction is a particularly sensitive correction in spectral CT as it depends on system effects as well as the object being imaged and any residual scatter is amplified during the non-linear material decomposition. An accurate way of removing scatter is subtracting the scatter estimated by Monte Carlo simulation. However, to get sufficiently good scatter estimates, extremely large numbers of photons are required, which may lead to unexpectedly high computational costs. Other approaches model scatter as a convolution operation using kernels derived using empirical methods. These techniques have been found to be insufficient in spectral CT due to their inability to sufficiently capture object dependence. In this work, we develop a deep residual learning framework to address both issues of computation simplicity and object dependency. A deep convolution neural network is trained to determine the scatter distribution from the projection content in training sets. In test cases of a digital anthropomorphic phantom and real water phantom, we demonstrate that with much lower computing costs, the proposed network provides sufficiently accurate scatter estimation.
关键词： convolutional neural network,deep residual learning,Monte Carlo simulation,scatter correction,spectral CT
更新于2025-09-09 09:28:46
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Implications of spectral-hole burning on the manipulation of spatial Goos–H?nchen shift in an atomic cell
摘要： We present a new scheme to report on Goos–H?nchen (GH) shift experienced by the Gaussian light beam incident at the plane optical interface filled with four-level sodium atomic medium in the spectral-hole burning region with and without Doppler broadening effect. Theoretical atomic density-matrix formalism is employed to obtain the susceptibility of atomic medium while the stationary-phase-theory is used to compute the GH shift in the reflected and transmitted probe beams subjected to control fields. A steep normal slope of dispersion is observed with a maximum and zero probability of transmission and reflection coefficients, respectively, at the regions of the spectral holes burning. In the normal dispersion spectrum at the region of spectral-hole burning, positive and negative GH shift is observed, respectively, in the transmitted and reflected light beams. However, at anomalous dispersive regions negative GH shift in the transmission beam and positive GH shift in the reflection beam is observed. The reflection and transmission coefficients as well as the spatial GH shift are the functions of probe detuning, collective phase of control fields and inverse Doppler broadening effect in the spectral-hole burning region. The study is expected to be useful for optoelectronic devices and optical-clocking applications.
关键词： Doppler broadening medium,Density-matrix formalism,Spectral hole burning,Spatial Goos–H?nchen shift,Stationary-phase-theory
更新于2025-09-09 09:28:46
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Retrieving vertical ozone profiles from measurements of global spectral irradiance
摘要： A new method is presented to determine vertical ozone profiles from measurements of spectral global (direct Sun plus upper hemisphere) irradiance in the ultraviolet. The method is similar to the widely used Umkehr technique, which inverts measurements of zenith sky radiance. The procedure was applied to measurements of a high-resolution spectroradiometer installed near the centre of the Greenland ice sheet. Retrieved profiles were validated with balloon-sonde observations and ozone profiles from the space-borne Microwave Limb Sounder (MLS). Depending on altitude, the bias between retrieval results presented in this paper and MLS observations ranges between ?5 and +3 %. The magnitude of this bias is comparable, if not smaller, to values reported in the literature for the standard Dobson Umkehr method. Total ozone columns (TOCs) calculated from the retrieved profiles agree to within 0.7±2.0 % (±1σ) with TOCs measured by the Ozone Monitoring Instrument on board the Aura satellite. The new method is called the “Global-Umkehr” method.
关键词： atmospheric composition,spectral irradiance,ozone profiles,UV monitoring,Umkehr technique
更新于2025-09-09 09:28:46
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Sensing coated iron-oxide nanoparticles with spectral induced polarization (SIP): Experiments in natural sand packed flow-through columns
摘要： The development of nanoparticle-based soil remediation techniques is hindered by the lack of accurate in situ nanoparticle (NP) monitoring and characterization methods. Spectral induced polarization (SIP), a non-invasive geophysical technique, offers a promising approach to detect and quantify NPs in porous media. However, its successful implementation as a monitoring tool requires an understanding of the polarization mechanisms, the governing NP-associated SIP responses and their dependence on the stabilizing coatings that are typically used for NPs deployed in environmental applications. Herein, we present SIP responses (0.1-10,000 Hz) measured during injection of a poloxamer-coated super-paramagnetic iron-oxide nanoparticle (SPION) suspension in flow-through columns packed with natural sand from the Borden Aquifer. An advective-dispersive transport model is fitted to outflow SPION concentration measurements to compute average concentrations over the SIP spatial response domain (within the columns). The average SPION concentrations are compared with the real and imaginary components of the complex conductivity. Excellent correspondence is found between the average SPION concentrations the columns and the imaginary conductivity values, suggesting that NP-mediated polarization (that is, charge storage) increases proportionally with increasing SPION concentration. Our results support the possibility of SIP monitoring of spatial and temporal NP distributions, which can be immediately deployed in bench-scale studies with the prospect of future real-world field applications.
关键词： Maxwell-Wagner polarization,relaxation time,super paramagnetic iron-oxide nanoparticles (SPIONs),Spectral induced polarization (SIP),chargeability
更新于2025-09-09 09:28:46
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Aerosol retrieval from multiangle, multispectral photopolarimetric measurements: importance of spectral range and angular resolution
摘要： We investigated the importance of spectral range and angular resolution for aerosol retrieval from multiangle photopolarimetric measurements over land. For this purpose, we use an extensive set of simulated measurements for different spectral ranges and angular resolutions and subsets of real measurements of the airborne Research Scanning Polarimeter (RSP) carried out during the PODEX and SEAC4RS campaigns over the continental USA. Aerosol retrievals performed from RSP measurements show good agreement with ground-based AERONET measurements for aerosol optical depth (AOD), single scattering albedo (SSA) and refractive index. Furthermore, we found that inclusion of shortwave infrared bands (1590 and/or 2250 nm) significantly improves the retrieval of AOD, SSA and coarse mode microphysical properties. However, accuracies of the retrieved aerosol properties do not improve significantly when more than five viewing angles are used in the retrieval.
关键词： spectral range,aerosol retrieval,angular resolution,AERONET,multiangle photopolarimetric measurements,RSP
更新于2025-09-09 09:28:46
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Metrological Analysis of an Optoelectronic Monitoring System for Profilograms of Shells of Rotation
摘要： Metrological analysis of optoelectronic monitoring systems for pro? lograms of shells of rotation was conducted. The optoelectronic systems that execute various methods for searching for the center of a part are examined. A mathematical model of a shell of rotation speci? ed by the pro? logram is considered. The dependence of absolute methodological error on this coef? cient is derived from the modeling results, and conclusions are drawn regarding the feasibility of applying one or another system, depending on the required accuracy and speed.
关键词： spectral analysis,pro? logram,monitoring system,geometric parameters,shell of rotation,method of center of gravity search
更新于2025-09-09 09:28:46
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[ACM Press SIGGRAPH Asia 2018 Posters - Tokyo, Japan (2018.12.04-2018.12.07)] SIGGRAPH Asia 2018 Posters on - SA '18 - Spectral rendering of fluorescence using importance sampling
摘要： Spectral rendering is necessary for rendering a scene with fluorescence, because fluorescence is a strongly wavelength dependent phenomenon. We propose a method for rendering fluorescence under global illumination environment efficiently by using importance sampling of wavelength considering both spectra of fluorescent materials and light sources.
关键词： global illumination,spectral rendering,importance sampling,Fluorescence
更新于2025-09-09 09:28:46
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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) - Robust Heart Rate Estimation During Physical Exercise Using Photoplethysmographic Signals
摘要： A method for estimating heart rate (HR) from photoplethysmographic (PPG) signal, during physical exercise, is presented in this paper. Accurate and reliable estimation of HR from PPG during intensive physical activity is challenging because intense motion artifacts can easily mask the true HR. If PPG signal is contaminated by intense motion artifacts, the highest peak of PPG spectrum is shifted from true HR due to motion artifacts. The proposed method employs a simple technique using spectral estimation and median filtering for HR estimation from intensely motion artifacts corrupted PPG signal. Experimental result for a database of 12 subjects recorded during fast running showed that the average absolute estimation error was 1.31 beats/minute.
关键词： spectral estimation,heart rate estimation,photoplethysmographic signals,motion artifacts,median filtering,physical exercise
更新于2025-09-09 09:28:46