Journal articles on the topic 'Spatial mode interference'
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1
Leuthold, J., R. Hess, J. Eckner, P. A. Besse, and H. Melchior. "Spatial mode filters realized with multimode interference couplers." Optics Letters 21, no. 11 (June 1, 1996): 836. http://dx.doi.org/10.1364/ol.21.000836.
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Slagmolen, B. J. J., D. A. Shaddock, M. B. Gray, and D. E. McClelland. "Frequency stability of spatial mode interference (tilt) locking." IEEE Journal of Quantum Electronics 38, no. 11 (November 2002): 1521–28. http://dx.doi.org/10.1109/jqe.2002.804267.
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Ottaway, D. J., M. B. Gray, D. A. Shaddock, C. Hollitt, P. J. Veitch, J. Munch, and D. E. McClelland. "Stabilization of injection-locked lasers using spatial mode interference." IEEE Journal of Quantum Electronics 37, no. 5 (May 2001): 653–57. http://dx.doi.org/10.1109/3.918577.
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Chow, Jong H., Glenn de Vine, Malcolm B. Gray, and David E. McClelland. "Measurement of Gouy phase evolution by use of spatial mode interference." Optics Letters 29, no. 20 (October 15, 2004): 2339. http://dx.doi.org/10.1364/ol.29.002339.
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Karpeev, S. V., V. V. Podlipnov, and A. M. Algubili. "An interference scheme for generating inhomogeneously polarized laser radiation using a spatial light modulator." Computer Optics 44, no. 2 (April 2020): 214–18. http://dx.doi.org/10.18287/2412-6179-co-698.
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An optical system for converting linearly polarized laser beams into cylindrical vector beams is developed and experimentally investigated. The scheme is based on the coherent addition of mode beams using a Mach-Zehnder interferometer. The simplicity and versatility of the optical setup is achieved through the use of different sections in the area of the spatial light modulator for the si-multaneous generation of two spatially separated given mode beams. Each of the beams then propagates in one of the arms of the interferometer and undergoes the necessary polarization-phase transformations to obtain a cylindrical vector beam after the addition of mode beams.
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FUCHS, ARMIN, J. A. SCOTT KELSO, and HERMANN HAKEN. "PHASE TRANSITIONS IN THE HUMAN BRAIN: SPATIAL MODE DYNAMICS." International Journal of Bifurcation and Chaos 02, no. 04 (December 1992): 917–39. http://dx.doi.org/10.1142/s0218127492000537.
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Pattern formation and switching between self-organized states are often associated with instabilities in open, nonequilibrium systems. We describe an experiment which shows that systematically changing a control parameter induces qualitative changes in sensorimotor coordination and brain activity, as registered by a 37-SQUID (Superconducting Quantum Interference Device) array. Near the instability point, predicted features of nonequilibrium phase transitions (critical slowing down, fluctuation enhancement) are observed in both the psychophysical data and the brain signals obtained from single SQUID sensors. Further analysis reveals that activity from the entire array displays spatial patterns evolving in time. Such spatiotemporal patterns are characterized by the dynamics of only a few coherent spatial modes.
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Chanthawong, Narin, Satoru Takahashi, Kiyoshi Takamasu, and Hirokazu Matsumoto. "High-Accuracy Calibration of CMM Using Temporal-Coherence Fiber Interferometer with Fast-Repetition Comb Laser." Key Engineering Materials 625 (August 2014): 66–72. http://dx.doi.org/10.4028/www.scientific.net/kem.625.66.
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A coordinate measuring machine (CMM) is a measuring system with the means to move probing system and capability to determine spatial coordinates on working surface. CMM is used in many industry fields from few micrometers of work pieces to a 5-meter truck. The verification method of CMM is done following international standard. The artifacts for calibrated reference length are the end standards, such as gauge block and step gauge, or laser interferometer for large size CMM. The current laser interferometer is operated by continuous laser and interference fringe counting. One constraint of continuous laser is an incremental measurement. The measurement path cannot be interrupted during the measurement period. We developed a new absolute interferometer system from a short-pulse mode-locked fiber laser. A Fabry–Pérot etalon (FPE) is used to select high-frequency parts of repetition-frequency modes of the mode-locked comb laser at the wavelength of 1.55 μm. The 5-GHz repetition-modified laser beam, which is realized by a new fiber-type FPE, is transmitted to a fiber-type Michelson interferometer. The interference fringes exhibit a temporal coherence interference and can be used for measuring spatial positioning. The temporal coherence between different pairs of modified pulse trains is referred to as absolute length standards. The performance of CMM was determined directly from different positions of two interference fringe patterns.
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Yang, Weiguo. "Single-SectionFabry-Perot Mode-Locked Semiconductor Lasers." Advances in OptoElectronics 2011 (March 2, 2011): 1–11. http://dx.doi.org/10.1155/2011/780373.
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We present a review of the theoretical models and experimental verification of the single-section Fabry-Perot mode-locked semiconductor lasers based on multiple-spatial-mode (MSM) coupling. The mode-locked operation at the repetition rates of 40 GHz and higher and the pulse width of a few picoseconds are confirmed by the intensity autocorrelation, the fast photo detection and RF spectrum, and the optical spectral interference measurement of ultrafast pulse. The spatial mode coupling theory of single-section Fabry-Perot mode-locked semiconductor lasers is also reviewed, and the results are compared with the experimental observations. The small signal modulation response of these lasers, which exhibits high-frequency responses well beyond the relaxation oscillation resonance limit, is also modeled theoretically, and the simulation is verified by the experimental measurements.
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Zhao, Xiaoyu, Zhenhua Xu, Ming Feng, Qun Li, Peiwen Zhang, Jia You, Song Gao, and Baoshu Yin. "Satellite Investigation of Semidiurnal Internal Tides in the Sulu-Sulawesi Seas." Remote Sensing 13, no. 13 (June 28, 2021): 2530. http://dx.doi.org/10.3390/rs13132530.
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The mode-1 semidiurnal internal tides that emanate from multiple sources in the Sulu-Sulawesi Seas are investigated using multi-satellite altimeter data from 1993–2020. A practical plane-wave analysis method is used to separately extract multiple coherent internal tides, with the nontidal noise in the internal tide field further removed by a two-dimensional (2-D) spatial band-pass filter. The complex radiation pathways and interference patterns of the internal tides are revealed, showing a spatial contrast between the Sulu Sea and the Sulawesi Sea. The mode-1 semidiurnal internal tides in the Sulawesi Sea are effectively generated from both the Sulu and Sangihe Island chains, forming a spatially inhomogeneous interference pattern in the deep basin. A cylindrical internal tidal wave pattern from the Sibutu passage is confirmed for the first time, which modulates the interference pattern. The interference field can be reproduced by a line source model. A weak reflected internal tidal beam off the Sulawesi slope is revealed. In contrast, the Sulu Island chain is the sole energetic internal tide source in the Sulu Sea, thus featuring a relatively consistent wave and energy flux field in the basin. These energetic semidiurnal internal tidal beams contribute to the frequent occurrence of internal solitary waves (ISWs) in the study area. On the basis of the 28-year consistent satellite measurements, the northward semidiurnal tidal energy flux from the Sulu Island chain is 0.46 GW, about 25% of the southward energy flux. For M2, the altimetric estimated energy fluxes from the Sulu Island chain are about 80% of those from numerical simulations. The total semidiurnal tidal energy flux from the Sulu and Sangihe Island chains into the Sulawesi Sea is about 2.7 GW.
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Ou, Zhi Long, Yong Qin Yu, Jia Rong Zheng, Ji Shun Wang, Xue Chen, Pei Guang Yan, and Chen Lin Du. "In-Fiber Mach-Zehnder Interferometer Fabricated by Femtosecond Laser." Advanced Materials Research 658 (January 2013): 232–36. http://dx.doi.org/10.4028/www.scientific.net/amr.658.232.
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We have demonstrated several MZIs based on two spaced 3-dB LPFGs with different interference lengths in conventional SMFs fabricated in air by femtosecond laser pulses with the duration of 200 fs and the repetition rate of 250 kHz. Experimental results show that the average fringe spatial period increases with the resonance wavelength, while decreases with the interference length in approximately inverse proportion. The dominant cladding mode interfering with core mode has been calculated. The MZI sensitivity on temperature, refractive index and strain with a length of 16mm has also been investigated.
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LUO, XIANGANG, YUEGUANG LV, CHUNLEI DU, JUNXIAN MA, HAO WANG, HAIYING LI, GAIRONG YANG, and HANMIN YAO. "SPATIAL DISTRIBUTION OF SURFACE PLASMON POLARITON FROM METALLIC NANOSTRUCTURES." Modern Physics Letters B 19, no. 12 (May 30, 2005): 599–606. http://dx.doi.org/10.1142/s0217984905008578.
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The spatial distribution of the interference of surface plasmon polariton (SPP) on metallic nanostructures has been studied. The results show that the transmission of electromagnetic radiation is remarkably enhanced for frequencies close to the surface plasmon band and the interference of SPP can redistribute the illumination light into subwavelength-scale spatial distribution with high intensity, which beats the Rayleigh diffraction limit. For an appropriate thickness, the transmission of an unperforated structure can be larger than that of holes or slits systems with the same periodicity and thickness when the coupled surface plasmon wave mode is excited. With the help of the interference of the horizontal plasmon excited by Bragg resonance due to the periodicity in the horizontal direction, the vertical plasmons, excited in z direction via Fabry–Perot cavity resonance in different grooves, are correlated, so the transmission is increased via the tunneling process. The properties of transparency for light but impenetrability for gas and liquid will be of importance for device applications. The information on near-field distribution from perforated metallic structures is important for understanding the underlying physics, as well as for optimizing photonic crystals for possible applications.
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Shaddock, D. A., M. B. Gray, and D. E. McClelland. "Frequency locking a laser to an optical cavity by use of spatial mode interference." Optics Letters 24, no. 21 (November 1, 1999): 1499. http://dx.doi.org/10.1364/ol.24.001499.
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Zhang, Bo, Fenghua Li, Zhenglin Li, Yanjun Zhang, and Jingyan Wang. "Transverse horizontal spatial coherence in shallow water." MATEC Web of Conferences 283 (2019): 02001. http://dx.doi.org/10.1051/matecconf/201928302001.
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Since the advent of large-aperture array processing, more and more attention has been paid to the sound field correlation, which has fundamental limit to the array gain of spatial coherent signal processing. The two dominant mechanisms that degrade the spatial coherence are normal modes (or multi-paths) interference and the environmental variability caused by several relevant oceanographic processes. In the present study, the transverse horizontal spatial coherence of explosive signals has been studied experimentally by a bottom-mounted array in the Northern South China Sea. And the effects of normal mode interference on the transverse horizontal spatial coherence have been analyzed numerically. Expressed in terms of wavelengths, the coherence length is shown to be larger than 170λ/185λ at acoustic frequency 508-640Hz/80-101Hz in shallow water. It is much greater than Carey’s shallow-water result 30λ estimated from array signal gain after assuming a specific functional form for the coherence (The Journal of the Acoustical Society of America 104, 831 (1998)). It, however, is consistent with Rouseff’s modelling result of a coherence length larger than 100λ (The Journal of the Acoustical Society of America 138, 2256 (2015)). Both Carey and Rouseff argue that the transverse horizontal spatial coherence length depends only weakly on range, in direct. In the present study, however, the coherence length is shown to depend highly on source-receiver range, and it fluctuates synchronously with the sound-field intensity while range varies.
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Al-Salehi, Abdul Rahman, Ijaz Mansoor Qureshi, Aqdas Naveed Malik, Wasim Khan, and Abdul Basit. "Dual-function radar–communications: information transmission during FDA radar listening mode." International Journal of Microwave and Wireless Technologies 12, no. 1 (July 22, 2019): 1–12. http://dx.doi.org/10.1017/s1759078719000990.
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AbstractWe investigate the frequency diverse array (FDA) for joint radar and communication systems. The basic idea is to use the transmitter/receiver modules of the radar system for communication purpose during listening mode as a secondary function. The radar will be performing its routine functions during the active mode as a primary function. An FDA at the transmitter side will be used to produce an orthogonal frequency division multiplexed signal, which is proposed for the communication system. The directivity of the radar antenna, FDA in this case, provides an additional advantage to mitigate the interferences other than the Direction of Interest (DoI). The proposed technique allows two beampatterns to be transmitted sequentially from the same FDA structure. Due to the communication signal transmission in the mainlobe of the second beampattern, the bit error rate achieved in the mainlobe is better than the existing techniques using the sidelobe transmission for communications. At the receiver, both incoming signals of radar and communication will share a different spatial angle. Simulation results indicate the novelty of the idea to suppress the interferences in terms of DoI. Furthermore, we analyzed the signal-to-interference ratio and Cramer–Rao lower bounds for angle and range estimation for the proposed technique.
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Zullo, R., A. Giorgini, S. Avino, P. Malara, P. De Natale, and G. Gagliardi. "Laser-frequency locking to a whispering-gallery-mode cavity by spatial interference of scattered light." Optics Letters 41, no. 3 (February 1, 2016): 650. http://dx.doi.org/10.1364/ol.41.000650.
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Maalouf, Elsa, and Carlos Torres-Verdín. "Interpretation of borehole flexural measurements in high-angle wells using 3D spatial sensitivity functions." GEOPHYSICS 83, no. 6 (November 1, 2018): D217—D229. http://dx.doi.org/10.1190/geo2017-0808.1.
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Undulating wells are routinely drilled to improve reservoir exposure across hydrocarbon-bearing zones. Although conventional acoustic-log interpretation methods are reliable in vertical wells, they often yield inaccurate results when applied to high-angle or horizontal wells due to azimuthal asymmetry, spatial averaging effects, and wave-mode interference. Three-dimensional finite-difference and finite-element algorithms are typically used to quantify the aforementioned effects on acoustic logs, but they are extremely demanding on the central processing unit’s (CPU) time and memory. We develop a fast algorithm to simulate flexural slownesses acquired in high-angle wells using 3D linear spatial sensitivity functions. Spatial sensitivity functions quantify the variation of phase slowness measured by the sonic tool due to spatial perturbations of elastic properties. First, we construct 3D frequency-dependent sensitivity functions of flexural modes using the product of 1D axial, radial, and azimuthal sensitivity functions obtained from first-order approximations. Then, we simulate frequency-domain flexural logs acquired with wireline tools and dipole sources in isotropic and vertical transversely isotropic (VTI) formations penetrated by high-angle wells. For the examined examples, simulated flexural logs exhibit root-mean-square errors less than [Formula: see text] when compared with those calculated with a 3D time-domain finite-difference (3D-TDFD) algorithm. We found that in isotropic formations with layers thinner than the length of the receiver array, flexural slownesses acquired separately with cross dipoles are different because of geometric asymmetry, whereas in VTI formations we observed differences between cross-dipole slownesses because of effective anisotropy. Furthermore, the flexural logs are affected by spatial averaging introduced by the acoustic wireline tool, especially in the vicinity of layer boundaries. Three-dimensional sensitivity functions reduce the computation time of the flexural logs from an average of 15 h of CPU time per depth (using 3D-TDFD methods) to less than 3 min. The fast simulation algorithm disregards wave reflections, wave-mode conversion, and wave-mode interference occurring at layer boundaries.
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Gao, Dangli, Dan Wang, Xiangyu Zhang, Xiaojuan Feng, Hong Xin, Sining Yun, and Dongping Tian. "Spatial control of upconversion emission in a single fluoride microcrystal via the excitation mode and native interference effect." Journal of Materials Chemistry C 6, no. 3 (2018): 622–29. http://dx.doi.org/10.1039/c7tc05032a.
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Doblas, Ana, Charity Hayes-Rounds, Rohan Isaac, and Felio Perez. "Single-Shot 3D Topography of Transmissive and Reflective Samples with a Dual-Mode Telecentric-Based Digital Holographic Microscope." Sensors 22, no. 10 (May 17, 2022): 3793. http://dx.doi.org/10.3390/s22103793.
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Common path DHM systems are the most robust DHM systems as they are based on self-interference and are thus less prone to external fluctuations. A common issue amongst these DHM systems is that the two replicas of the sample’s information overlay due to self-interference, making them only suitable for imaging sparse samples. This overlay has restricted the use of common-path DHM systems in material science. The overlay can be overcome by limiting the sample’s field of view to occupy only half of the imaging field of view or by using an optical spatial filter. In this work, we have implemented optical spatial filtering in a common-path DHM system using a Fresnel biprism. We have analyzed the optimal pinhole size by evaluating the frequency content of the reconstructed phase images of a star target. We have also measured the accuracy of the system and the sensitivity to noise for different pinhole sizes. Finally, we have proposed the first dual-mode common-path DHM system using a Fresnel biprism. The performance of the dual-model DHM system has been evaluated experimentally using transmissive and reflective microscopic samples.
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Elsas, Robbe, Jeroen Hoebeke, Dries Van Leemput, Adnan Shahid, Glenn Daneels, Jeroen Famaey, and Eli De Poorter. "Intra-Network Interference Robustness: An Empirical Evaluation of IEEE 802.15.4-2015 SUN-OFDM." Electronics 9, no. 10 (October 15, 2020): 1691. http://dx.doi.org/10.3390/electronics9101691.
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While IEEE 802.15.4 and its Time Slotted Channel Hopping (TSCH) medium access mode were developed as a wireless substitute for reliable process monitoring in industrial environments, most deployments use a single/static physical layer (PHY) configuration. Instead of limiting all links to the throughput and reliability of a single Modulation and Coding Scheme (MCS), you can dynamically re-configure the PHY of link endpoints according to the context. However, such modulation diversity causes links to coincide in time/frequency space, resulting in poor reliability if left unchecked. Nonetheless, to some level, intentional spatial overlap improves resource efficiency while partially preserving the benefits of modulation diversity. Hence, we measured the mutual interference robustness of certain Smart Utility Network (SUN) Orthogonal Frequency Division Multiplexing (OFDM) configurations, as a first step towards combining spatial re-use and modulation diversity. This paper discusses the packet reception performance of those PHY configurations in terms of Signal to Interference Ratio (SIR) and time-overlap percentage between interference and targeted parts of useful transmissions. In summary, we found SUN-OFDM O3 MCS1 and O4 MCS2 performed best. Consequently, one should consider them when developing TSCH scheduling mechanisms in the search for resource efficient ubiquitous connectivity through modulation diversity and spatial re-use.
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Zhang, Shizhao, and Shengchun Piao. "Broadband Sound Intensity Interference Frequency Periodicity and Pulse Source Localization." Journal of Marine Science and Engineering 9, no. 2 (February 15, 2021): 200. http://dx.doi.org/10.3390/jmse9020200.
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In order to analyze the frequency periodicity characteristics of acoustic field interference and realize acoustic source ranging (ASR), the normal mode model is used to analyze the interference characteristics of the broadband acoustic field under the condition of horizontally layered medium; the broadband received signal field when the broadband pulse signal passes through the acoustic field is also simulated. The variation of interference patterns with frequency is analyzed, and their spatial interference characteristics and mechanisms are analyzed. Based on the interference theory, the relation between the acoustic source range and the frequency periodicity of the broadband acoustic intensity interference is derived. Simulation and experimental results show that this relation can accurately estimate the far-field acoustic source range, and the estimation accuracy and real-time performance are greatly improved compared with previous methods. Besides, simulation shows that the method combined with multiple-receiver ranging obtains high-precision direction of arrival (DOA) estimation as well as ASR. The relation between acoustic source position and broadband acoustic field interference frequency periodicity can be used to improve far-field ASR and DOA estimation, which is of great value for oceanography, marine engineering, and marine military. In addition, this relation can also be extended to that between the modal interference frequency periodicity and other related parameters in other physical fields for parameter inversion.
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Zhang, Ke, Yang Wei, Jin Zhang, He Ma, Xinhe Yang, Gaotian Lu, Kenan Zhang, Qunqing Li, Kaili Jiang, and Shoushan Fan. "Electrical control of spatial resolution in mixed-dimensional heterostructured photodetectors." Proceedings of the National Academy of Sciences 116, no. 14 (March 19, 2019): 6586–93. http://dx.doi.org/10.1073/pnas.1817229116.
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Low-dimensional nanomaterials, such as one-dimensional (1D) nanomaterials and layered 2D materials, have exhibited significance for their respective unique electronic and optoelectronic properties. Here we show that a mixed-dimensional heterostructure with building blocks from multiple dimensions will present a synergistic effect on photodetection. A carbon nanotube (CNT)–WSe2–graphene photodetector is representative on this issue. Its spatial resolution can be electrically switched between high-resolution mode (HRM) and low-resolution mode (LRM) revealed by scanning photocurrent microscopy (SPCM). The reconfigurable spatial resolution can be attributed to the asymmetric geometry and the gate-tunable Fermi levels of these low-dimensional materials. Significantly, an interference fringe with 334 nm in period was successfully discriminated by the device working at HRM, confirming the efficient electrical control. Electrical control of spatial resolution in CNT–WSe2–graphene devices reveals the potential of the mixed-dimensional architectures in future nanoelectronics and nano-optoelectronics.
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Liu, Yunpeng, Teng Zhang, Jian Su, Tao Jing, Min Lin, Pei Li, and Xingpeng Yan. "Reconstruction resolution enhancement of EPISM based holographic stereogram with hogel spatial multiplexing." Chinese Physics B 31, no. 4 (March 1, 2022): 044201. http://dx.doi.org/10.1088/1674-1056/ac306f.
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We investigate how the splicing mode of a holographic element (hogel) affects the reconstruction of a 3D scene to improve the reconstruction resolution of a holographic stereogram fabricated using the effective perspective image segmentation and mosaicking method (EPISM). First, the effect of hogel spatial multiplexing on holographic recording and reconstruction is studied based on the mechanism of recording interference fringes in the holographic recording medium. Second, combined with the influence of multiple exposures on the hologram’s diffraction efficiency, the diffraction efficiency of the holographic stereogram is analyzed in the spatial multiplexing mode. The holographic stereogram is then regarded as a special optical imaging system. The theory of spatial bandwidth product is adopted to describe the comprehensive resolution of the holographic stereogram, which explains why hogel spatial multiplexing can significantly improve the reconstruction resolution of a holographic stereogram. Compared with the traditional printing method under the same parameters in optical experiments, hogel spatial multiplexing has a lower diffraction efficiency but a higher quality of reconstructed image, consistent with the theoretical analysis.
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Peng, Meiping, Bo Li, Zhongjiang Yan, and Mao Yang. "A Spatial Group-Based Multi-User Full-Duplex OFDMA MAC Protocol for the Next-Generation WLAN." Sensors 20, no. 14 (July 9, 2020): 3826. http://dx.doi.org/10.3390/s20143826.
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The Wireless Local Area Network (WLAN) has become a dominant piece of technology to carry wireless traffic for Internet of Things (IoT). The next-generation high-density WLAN scenario is very suitable for the development trend of the industrial wireless sensor network. However, in the high-density deployed WLAN scenarios, the access efficiency is low due to severe collisions, and the interference is diffused due to the scattered locations of the parallel access stations (STAs), which results in low area throughput, i.e., low spatial reuse gain. A spatial group-based multi-user full-duplex orthogonal frequency division multiple access (OFDMA) (GFDO) multiple access control (MAC) protocol is proposed. Firstly, the STAs in the network are divided into several spatial groups according to the neighbor channel sensing ability. Secondly, a two-level buffer state report (BSR) information collection mechanism based on P-probability is designed. Initially, intra-group STAs report their BSR information to the group header using low transmission power. After that, group headers report both their BSR information collected from their members and inter-group interference information to the access point (AP). Finally, AP schedules two spatial groups without mutual interference to carry on multi-user full duplex transmission on the subchannels in cascading mode. The closed-form formulas are theoretically derived, including the number of uplink STAs successfully collected by AP, the network throughput and area throughput under saturated traffic. The simulation results show that the theoretical analysis coincide with the simulation results. The system throughput of the GFDO protocol is 16.8% higher than that of EnFD-OMAX protocol.
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Nomerotski, Andrei, Michael Keach, Paul Stankus, Peter Svihra, and Stephen Vintskevich. "Counting of Hong-Ou-Mandel Bunched Optical Photons Using a Fast Pixel Camera." Sensors 20, no. 12 (June 19, 2020): 3475. http://dx.doi.org/10.3390/s20123475.
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The uses of a silicon-pixel camera with very good time resolution (∼nanosecond) for detecting multiple, bunched optical photons is explored. We present characteristics of the camera and describe experiments proving its counting capabilities. We use a spontaneous parametric down-conversion source to generate correlated photon pairs, and exploit the Hong-Ou-Mandel (HOM) interference effect in a fiber-coupled beam splitter to bunch the pair onto the same output fiber. It is shown that the time and spatial resolution of the camera enables independent detection of two photons emerging simultaneously from a single spatial mode.
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Zhang, Yao, Ben Yang, Atif Ghafoor, Yang Zhang, Yu-Fan Zhang, Rui-Pu Wang, Jin-Long Yang, Yi Luo, Zhen-Chao Dong, and J. G. Hou. "Visually constructing the chemical structure of a single molecule by scanning Raman picoscopy." National Science Review 6, no. 6 (November 1, 2019): 1169–75. http://dx.doi.org/10.1093/nsr/nwz180.
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Abstract The strong spatial confinement of a nanocavity plasmonic field has made it possible to visualize the inner structure of a single molecule and even to distinguish its vibrational modes in real space. With such ever-improved spatial resolution, it is anticipated that full vibrational imaging of a molecule could be achieved to reveal molecular structural details. Here we demonstrate full Raman images of individual vibrational modes at the ångström level for a single Mg-porphine molecule, revealing distinct characteristics of each vibrational mode in real space. Furthermore, by exploiting the underlying interference effect and Raman fingerprint database, we propose a new methodology for structural determination, which we have called ‘scanning Raman picoscopy’, to show how such ultrahigh-resolution spectromicroscopic vibrational images can be used to visually assemble the chemical structure of a single molecule through a simple Lego-like building process.
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Hu, Ping, Hong-Wei Wu, Wen-Jun Sun, Nong Zhou, Xue Chen, Yong-Qiang Yang, and Zong-Qiang Sheng. "Observation of localized acoustic skyrmions." Applied Physics Letters 122, no. 2 (January 9, 2023): 022201. http://dx.doi.org/10.1063/5.0131777.
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Recently, acoustic skyrmions have been explored by tailoring velocity vectorial near-field distributions based on the interference of multiple spoof surface acoustic waves, providing new dimensions for advanced sound information processing, transport, and data storage. Here, we theoretically investigate and experimentally demonstrate that a deep-subwavelength spiral metastructure can also generate the acoustic skyrmion configuration. Analyzing the resonant response of the metastructure and observing the spatial profile of the velocity field, we find that the localized skyrmionic modes correspond to eigenmodes of the spiral structure. Thus, the skyrmionic modes do not require carefully tailored external excitation condition and they have multiple resonating frequencies unlike the single skyrmionic mode realized by the interference of multiple waves. We also demonstrate that the topological protected skyrmions supported by the subwavelength metastructure is robust against structure deformations and existence of structure defects. The real-space acoustic skyrmion topology may open new avenues for designing ultra-compact and robust acoustic devices, such as acoustic sensors, acoustic tweezers, and acoustic antennas.
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Lee, K., J. Jung, and J. H. Lee. "Optical fiber polarization-entangled photon pair source using intermodal spontaneous four-wave mixing in the visible spectral band." Laser Physics Letters 20, no. 1 (December 13, 2022): 015101. http://dx.doi.org/10.1088/1612-202x/aca757.
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Abstract The theoretical and experimental investigation results of the generation of the polarization-entangled photon pairs operating at visible wavelengths are reported. The generation of polarization-entangled photon pairs was based on intermodal spontaneous four-wave mixing (IM-SFWM) using standard step-index few-mode fiber. It was shown theoretically that several combinations of IM-SFWM processes could occur depending on spatial modes of a pump beam. A polarization-entangled photon pair source based on Sagnac loop incorporating a segment of few-mode fiber were then experimentally created. A two-photon interference fringe visibility of our implemented photon pair source were 91.7% and 88.8% in H/V bases and D/A bases, respectively. A quantum state tomography was also conducted to reconstruct the density matrix of the generated state with a fidelity to a maximum entangled state of 93.1%.
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Xu, Guojun, Weihua Zhang, Min Zhu, Jizhou Guo, Yanqun Wu, and Jiahua Zhu. "Research on Underwater Acoustic Target Depth Classification Based on Modal Filtering Characteristics of Long Horizontal Line Array." International Journal of Acoustics and Vibration 27, no. 1 (March 29, 2022): 3–9. http://dx.doi.org/10.20855/ijav.2022.27.11820.
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Considering the problem of depth classification of underwater acoustic targets in shallow water, a classification method based on modal filtering characteristics of long horizontal line array(HLA) beamforming in a negative thermocline environment was proposed. Based on normal mode theory, the spatial filtering characteristics of long HLA are studied by beamforming, and it was found that this characteristic can filter a normal mode. In the negative thermocline environment, the acoustic fields excited by deep and shallow sources and received by deep receivers are controlled by different modes. Surface reflection bottom reflection (SRBR) mode and non-surface reflection bottom reflection (NSRBR) mode show different interference structures in range-spectrum. Based on the characteristics of modal filtering and sound field classification, a depth classification method for shallow water acoustic targets in a negative thermocline environment is established. Numerical results show that the proposed method is robust and can effectively distinguish the acoustic source targets above or below the thermocline (surface and underwater targets) without knowing the specific acoustic environment parameters in advance.
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Брюшинин, М. А., В. В. Куликов, И. А. Соколов, Е. Н. Савченков, Н. И. Буримов, С. М. Шандаров, А. Р. Ахматханов, М. А. Чувакова, and В. Я. Шур. "Нестационарная фотоэдс в периодически поляризованном кристалле MgO : LiNbO-=SUB=-3-=/SUB=-." Физика твердого тела 65, no. 2 (2023): 207. http://dx.doi.org/10.21883/ftt.2023.02.54291.519.
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The diffusion mode of the non-steady-state photo-EMF excitation is investigated in periodically poled MgO:LiNbO₃ crystal at light wavelength λ=457 nm. The signal excitation is carried out along the polar axis of the crystal; the dependencies of the signal amplitude versus the phase modulation frequency, intensity and spatial frequency of the interference pattern are studied in this geometry. The analysis of these dependencies allows determining the photoelectric parameters of the material – the type, value and relaxation time of the photoconductivity, as well as the diffusion length of charge carriers.
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Gkonis, Panagiotis K., and Dimitra I. Kaklamani. "Reduced Complexity BER Calculations in Large Scale Spatial Multiplexing Multi-User MIMO Orientations in Frequency Selective Fading Environments." Electronics 8, no. 7 (June 26, 2019): 727. http://dx.doi.org/10.3390/electronics8070727.
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In this article, a computationally-efficient approach is presented for Bit Error Rate (BER) calculations in multi-user Multiple Input Multiple Output (MIMO) frequency selective fading environments, operating in spatial multiplexing transmission mode. To this end, theoretical expressions for the equivalent Signal to Interference plus Noise Ratio (SINR) per active user and transmission mode, as well as mean BER, are derived. The key idea is that all parameters related to BER calculations can be expressed as sums of identically distributed random variables (RVs). Hence, computational burden can be reduced, since summation formulas take into account the parameters of a standalone RV along with the correlation of an arbitrary pair of RVs. As results indicate, the proposed approach can accurately estimate mean BER in multiuser MIMO orientations with increased reception diversity order, for arbitrary number of transmit/receive antennas, a modulation scheme, and a number of resolvable multi-path components.
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Buczkowski, T., D. Janusek, H. Zavala-Fernandez, M. Skrok, M. Kania, and A. Liebert. "Influence of Mobile Phones on the Quality of ECG Signal Acquired by Medical Devices." Measurement Science Review 13, no. 5 (October 1, 2013): 231–36. http://dx.doi.org/10.2478/msr-2013-0035.
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Abstract Health aspects of the use of radiating devices, like mobile phones, are still a public concern. Stand-alone electrocardiographic systems and those built-in, more sophisticated, medical devices have become a standard tool used in everyday medical practice. GSM mobile phones might be a potential source of electromagnetic interference (EMI) which may affect reliability of medical appliances. Risk of such event is particularly high in places remote from GSM base stations in which the signal received by GSM mobile phone is weak. In such locations an increase in power of transmitted radio signal is necessary to enhance quality of the communication. In consequence, the risk of interference of electronic devices increases because of the high level of EMI. In the present paper the spatial, temporal, and spectral characteristics of the interference have been examined. The influence of GSM mobile phone on multilead ECG recordings was studied. It was observed that the electrocardiographic system was vulnerable to the interference generated by the GSM mobile phone working with maximum transmit power and in DTX mode when the device was placed in a distance shorter than 7.5 cm from the ECG electrode located on the surface of the chest. Negligible EMI was encountered at any longer distance.
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Li, Xiaoji, Leiming Sun, Jiemei Huang, and Fanze Zeng. "Research on Orbital Angular Momentum Recognition Technology Based on a Convolutional Neural Network." Sensors 23, no. 2 (January 14, 2023): 971. http://dx.doi.org/10.3390/s23020971.
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In underwater wireless optical communication (UWOC), a vortex beam carrying orbital angular momentum has a spatial spiral phase distribution, which provides spatial freedom for UWOC and, as a new information modulation dimension resource, it can greatly improve channel capacity and spectral efficiency. In a case of the disturbance of a vortex beam by ocean turbulence, where a Laguerre–Gaussian (LG) beam carrying orbital angular momentum (OAM) is damaged by turbulence and distortion, which affects OAM pattern recognition, and the phase feature of the phase map not only has spiral wavefront but also phase singularity feature, the convolutional neural network (CNN) model can effectively extract the information of the distorted OAM phase map to realize the recognition of dual-mode OAM and single-mode OAM. The phase map of the Laguerre–Gaussian beam passing through ocean turbulence was used as a dataset to simulate and analyze the OAM recognition effect during turbulence caused by different temperature ratios and salinity. The results showed that, during strong turbulence Cn2=1.0×10−13K2m−2/3, when different ω = −1.75, the recognition rate of dual-mode OAM (ℓ = ±1~±5, ±1~±6, ±1~±7, ±1~±8, ±1~±9, ±1~±10) had higher recognition rates of 100%, 100%, 100%, 100%, 98.89%, and 98.67% and single-mode OAM (ℓ = 1~5, 1~6, 1~7, 1~8, 1~9, 1~10) had higher recognition rates of 93.33%, 92.77%, 92.33%, 90%, 87.78%, and 84%, respectively. With the increase in ω, the recognition accuracy of the CNN model will gradually decrease, and in a fixed case, the dual-mode OAM has stronger anti-interference ability than single-mode OAM. These results may provide a reference for optical communication technologies that implement high-capacity OAM.
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Nguyen, Le Van, Ba Cao Nguyen, Xuan Nam Tran, and Le The Dung. "Closed-Form Expression for the Symbol Error Probability in Full-Duplex Spatial Modulation Relay System and Its Application in Optimal Power Allocation." Sensors 19, no. 24 (December 6, 2019): 5390. http://dx.doi.org/10.3390/s19245390.
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Full-duplex (FD) communication and spatial modulation (SM) are two promising techniques to achieve high spectral efficiency. Recent works in the literature have investigated the possibility of combining the FD mode with SM in the relay system to benefit their advantages. In this paper, we analyze the performance of the FD-SM decode-and-forward (DF) relay system and derive the closed-form expression for the symbol error probability (SEP). To tackle the residual self-interference (RSI) due to the FD mode at the relay, we propose a simple yet effective power allocation algorithm to compensate for the RSI impact and improve the system SEP performance. Both numerical and simulation results confirm the accuracy of the derived SEP expression and the efficacy of the proposed optimal power allocation.
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He, Xianwen, Gaoqi Dou, and Jun Gao. "Individual Channel Estimation in a Diamond Relay Network Using Relay-Assisted Training." International Journal of Digital Multimedia Broadcasting 2017 (2017): 1–8. http://dx.doi.org/10.1155/2017/1320689.
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We consider the training design and channel estimation in the amplify-and-forward (AF) diamond relay network. Our strategy is to transmit the source training in time-multiplexing (TM) mode while each relay node superimposes its own relay training over the amplified received data signal without bandwidth expansion. The principal challenge is to obtain accurate channel state information (CSI) of second-hop link due to the multiaccess interference (MAI) and cooperative data interference (CDI). To maintain the orthogonality between data and training, a modified relay-assisted training scheme is proposed to migrate the CDI, where some of the cooperative data at the relay are discarded to accommodate relay training. Meanwhile, a couple of optimal zero-correlation zone (ZCZ) relay-assisted sequences are designed to avoid MAI. At the destination node, the received signals from the two relay nodes are combined to achieve spatial diversity and enhanced data reliability. The simulation results are presented to validate the performance of the proposed schemes.
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Jia, Hao, Ting Zhou, Xin Fu, Jianfeng Ding, Lei Zhang, and Lin Yang. "Integrated five-port non-blocking optical router based on mode-selective property." Nanophotonics 7, no. 5 (May 24, 2018): 853–58. http://dx.doi.org/10.1515/nanoph-2018-0010.
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AbstractIn this paper, we propose and demonstrate a five-port optical router based on mode-selective property. It utilizes different combinations of four spatial modes at input and output ports as labels to distinguish its 20 routing paths. It can direct signals from the source port to the destination port intelligently without power consumption and additional switching time to realize various path steering. The proposed architecture is constructed by asymmetric directional coupler based mode-multiplexers/de-multiplexers, multimode interference based waveguide crossings and single-mode interconnect waveguides. The broad optical bandwidths of these constituents make the device suitable to combine with wavelength division multiplexing signal transmission, which can effectively increase the data throughput. Measurement results show that the insertion loss of its 20 routing paths are lower than 8.5 dB and the optical signal-to-noise ratios are larger than 16.3 dB at 1525–1565 nm. To characterize its routing functionality, a 40-Gbps data transmission with bit-error-rate (BER) measurement is implemented. The power penalties for the error-free switching (BER<10−9) are 1.0 dB and 0.8 dB at 1545 nm and 1565 nm, respectively.
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Cosoli, Simone. "Implementation of the Listen-Before-Talk Mode for SeaSonde High-Frequency Ocean Radars." Journal of Marine Science and Engineering 8, no. 1 (January 19, 2020): 57. http://dx.doi.org/10.3390/jmse8010057.
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The International Telecommunication Union (ITU) Resolution 612, in combination with Report ITU-R M2.234 (11/2011) and Recommendation ITU-R M.1874-1 (02/2013), regulates the use of the radiolocation services between 3 and 50 MHz to support high frequency oceanographic radar (HFR) operations. The operational frame for HFR systems include: band sharing capabilities, such as synchronization of the signal modulation; pulse shaping and multiple levels of filtering, to reduce out-of-band interferences; low radiated power; directional transmission antenna, to reduce emission over land. Resolution 612 also aims at reducing the use of spectral bands, either through the application of existing band-sharing capabilities, the reduction of the spectral leakage to neighboring frequency bands, or the development and implementation of listen-before-talk (LBT) capabilities. While the LBT mode is operational and commonly used at several phased-array HFR installations, the implementation to commercial direction-finding systems does not appear to be available yet. In this paper, a proof-of-concept is provided for the implementation of the LBT mode for commercial SeaSonde HFRs deployed in Australia, with potential for applications in other networks and installations elsewhere. Potential critical aspects for systems operated under this configuration are also pointed out. Both the receiver and the transmitter antennas may lose efficiency if the frequency offset from the resonant frequency or calibration pattern are too large. Radial resolution clearly degrades when a dynamical adaptation of the bandwidth is performed, which results in non-homogeneous spatial resolution and reduction of the quality of the data. A recommendation would be to perform the LBT-adapt scans after a full measurement cycle (1-h or 3-h, depending on the system configuration) is concluded. Mutual cross-interference from clock offsets between two HFR systems may bias the frequency scans when the site computers controlling data acquisitions are not properly time-synchronized.
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Banerjee, Santanu, D. P. Boyle, A. Maan, R. Majeski, R. Kaita, D. Smith, M. von Hellermann, C. Hansen, W. Capecchi, and D. Elliott. "Feasibility study of a high spatial and time resolution beam emission spectroscopy diagnostic for localized density fluctuation measurements in Lithium Tokamak eXperiment-β (LTX-β)." Review of Scientific Instruments 93, no. 11 (November 1, 2022): 113523. http://dx.doi.org/10.1063/5.0101834.
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Trapped electron mode (TEM) is the main source of turbulence predicted for the unique operation regime of a flat temperature profile under low-recycling conditions in the LTX-β tokamak, while ion temperature gradient driven turbulence may also occur with gas fueling from the edge. To investigate mainly TEM scale density fluctuations, a high spatial and time resolution 2D beam emission spectroscopy (BES) diagnostic is being developed. Apart from spatially localized density turbulence measurement, BES can provide turbulence flow and flow shear dynamics. This BES system will be realized using an avalanche photodiode-based camera and narrow band interference filter. The system can acquire data at 2 MHz. Simulations with the Simulation of Spectra (SOS) code indicate that a high signal to noise ratio can be achieved with the proposed system. This will enable sampling the density fluctuations at this high time resolution. The design considerations and system optimization using the SOS code are presented.
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Babalola, Oluwaseyi Paul, and Vipin Balyan. "WiFi Fingerprinting Indoor Localization Based on Dynamic Mode Decomposition Feature Selection with Hidden Markov Model." Sensors 21, no. 20 (October 13, 2021): 6778. http://dx.doi.org/10.3390/s21206778.
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Over the years, WiFi received signal strength indicator (RSSI) measurements have been widely implemented for determining the location of a user’s position in an indoor environment, where the GPS signal might not be received. This method utilizes a huge RSSI dataset collected from numerous access points (APs). The WiFi RSSI measurements are nonlinear with distance and are largely influenced by interference in the indoor environment. Therefore, machine learning (ML) techniques such as a hidden Markov model (HMM) are generally utilized to efficiently identify a trend of RSSI values, which corresponds to locations around a region of interest. Similar to other ML tools, the performance and computing cost of the HMM are dependent on the feature dimension since a large quantity of RSSI measurements are required for the learning process. Hence, this article introduces a feature extraction method based on dynamic mode decomposition (DMD) for the HMM to effectively model WiFi fingerprint indoor localization. The DMD is adopted since it decomposes RSSIs to meaningful spatial and temporal forms over a given time. Here, the mode forms are analytically reconstructed to produce low-dimensional feature vectors, which are used with the HMM. The localization performance of the proposed HMM-DMD is compared with other well-known ML algorithms for WiFi fingerprinting localization using simulations. The results show that the HMM-DMD algorithm yields a significant localization performance improvement, accuracy, and reasonable processing time in comparison with the state-of-the-art algorithms.
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You, Zhiwei, Peifen Xu, Jing Qian, Lianpeng Cao, Yanan Du, and Qiang Fu. "Frequency-Bessel Transform Based Microtremor Survey Method and Its Engineering Application." International Journal of Environmental Research and Public Health 19, no. 20 (October 18, 2022): 13484. http://dx.doi.org/10.3390/ijerph192013484.
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The development and utilization of urban underground space depend heavily on an understanding of urban geological conditions. The microtremor survey method is essential in urban geological surveys due to its quickness, convenience, non-destructiveness, and interference resistance. Since only the fundamental dispersion curves of Rayleigh waves can be obtained by utilizing the spatial autocorrelation method, the inversion results have multiple solutions. To improve the accuracy of the microtremor survey, this study employed the frequency-Bessel transform to extract the fundamental and higher modes of dispersion information of Rayleigh waves from the microtremor data array and verified the effectiveness of this method by synthesizing theoretical microtremor signals. Additionally, taking into account the order identification challenges brought on by mode jumps or missing modes in the dispersion curve, this study processed a multi-mode dispersion curve based on the newly proposed inversion objective function coupled with a genetic algorithm to obtain a shallow surface S-wave velocity structure. Compared to the traditional inversion objective function, the new function presented in this study could address mode misidentification more effectively and improved the accuracy of inversion calculations. Finally, the applicability and dependability of the frequency-Bessel-transform-based microtremor survey method were evaluated in a practical engineering case.
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Lee, Yishi. "Deconvolution filter for parameter estimation of composite stress wave propagating in the wooden cylindrical structure." Journal of the Acoustical Society of America 151, no. 4 (April 2022): A136. http://dx.doi.org/10.1121/10.0010901.
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Through-transmission using the embedded waveguide technique in the cross-section plane of cylindrical structure produces radial and Rayleigh modes. These two modes propagate in the heart and shell regions of the plane, allowing a comprehensive characterization of the material. The significant spatial difference generates a distinct temporal separation between the two modes for large cylindrical structures, allowing direct mode characterization. For cylindrical structures with smaller diameters, the pronounced multi-path interference produces an erroneous energy response that hinders the accurate mode characterization. In this so-called multiple-input-single-output (MISO) system, the arrival time and amplitude estimations are an underdetermined problem. This work presents a novel decomposition filter design consisting of three steps. (1) Gabor’s wavelet transforms the stress wave signal in the time-frequency domain; (2) The approximation of the inverse point-spread-function (PSF) response via a series of frequency polynomials generates a set of optimal coefficients; (3) Derive the inverse deconvolution kernel via the dual derivative operator from the obtained optimal coefficients in step 2. This presentation will demonstrate the algorithmic formulation with numerical and empirical validations. Its broader impact will enhance the parametric estimation of the diagnostic stress wave for material characterization.
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Yang, Chong, Yu Fu, Jianmin Yuan, Min Guo, Keyu Yan, Huan Liu, Hong Miao, and Changchun Zhu. "Damage Identification by Using a Self-Synchronizing Multipoint Laser Doppler Vibrometer." Shock and Vibration 2015 (2015): 1–9. http://dx.doi.org/10.1155/2015/476054.
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The vibration-based damage identification method extracts the damage location and severity information from the change of modal properties, such as natural frequency and mode shape. Its performance and accuracy depends on the measurement precision. Laser Doppler vibrometer (LDV) provides a noncontact vibration measurement of high quality, but usually it can only do sampling on a single point. Scanning LDV is normally used to obtain the mode shape with a longer scanning time. In this paper, a damage detection technique is proposed using a self-synchronizing multipoint LDV. Multiple laser beams with various frequency shifts are projected on different points of the object, reflected and interfered with a common reference beam. The interference signal containing synchronized temporal vibration information of multiple spatial points is captured by a single photodetector and can be retrieved in a very short period. Experiments are conducted to measure the natural frequencies and mode shapes of pre- and postcrack cantilever beams. Mode shape curvature is calculated by numerical interpolation and windowed Fourier analysis. The results show that the artificial crack can be identified precisely from the change of natural frequencies and the difference of mode shape curvature squares.
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Horton, Matthew J., Oluwafemi S. Ojambati, Rohit Chikkaraddy, William M. Deacon, Nuttawut Kongsuwan, Angela Demetriadou, Ortwin Hess, and Jeremy J. Baumberg. "Nanoscopy through a plasmonic nanolens." Proceedings of the National Academy of Sciences 117, no. 5 (January 15, 2020): 2275–81. http://dx.doi.org/10.1073/pnas.1914713117.
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Plasmonics now delivers sensors capable of detecting single molecules. The emission enhancements and nanometer-scale optical confinement achieved by these metallic nanostructures vastly increase spectroscopic sensitivity, enabling real-time tracking. However, the interaction of light with such nanostructures typically loses all information about the spatial location of molecules within a plasmonic hot spot. Here, we show that ultrathin plasmonic nanogaps support complete mode sets which strongly influence the far-field emission patterns of embedded emitters and allow the reconstruction of dipole positions with 1-nm precision. Emitters in different locations radiate spots, rings, and askew halo images, arising from interference of 2 radiating antenna modes differently coupling light out of the nanogap, highlighting the imaging potential of these plasmonic “crystal balls.” Emitters at the center are now found to live indefinitely, because they radiate so rapidly.
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Buijsman, Maarten C., Sonya Legg, and Jody Klymak. "Double-Ridge Internal Tide Interference and Its Effect on Dissipation in Luzon Strait." Journal of Physical Oceanography 42, no. 8 (August 1, 2012): 1337–56. http://dx.doi.org/10.1175/jpo-d-11-0210.1.
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Abstract Luzon Strait between Taiwan and the Philippines features two parallel north–south-oriented ridges. The barotropic tides that propagate over these ridges cause strong internal waves and dissipation. The energy dissipation mechanisms and the role of the baroclinic wave fields in this dissipation are investigated using numerical simulations with the Massachusetts Institute of Technology general circulation model (MITgcm). The model is integrated over two-dimensional configurations along a zonal transect at 20.6°N for a maximum duration of a spring–neap cycle. Nearly all dissipation occurs at the steep ridge crests due to high-mode turbulent lee waves with horizontal scales of several kilometers and vertical scales of hundreds of meters. The spatial structure and timing of the predicted velocities and dissipation agree with observations and confirm the existence of these lee waves. The lee wave strength is greatly affected by the internal waves generated at the other ridge. When semidiurnal barotropic tides are dominant, the internal wave beams from both ridges nearly superpose after one surface reflection. The remotely generated internal waves from both ridges are therefore in phase with each other and the barotropic tides at the ridges. The barotropic-to-baroclinic energy conversion, energy flux divergence, ridge top velocities, and dissipation are stronger compared to the sum of the single east ridge and single west ridge cases. When diurnal tides are dominant, the wave fields are more out of phase and the conversion, divergence, and dissipation are less than or equal to the single ridge cases combined.
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Moore, Steven Ian, Michael G. Ruppert, and Yuen Kuan Yong. "Multimodal cantilevers with novel piezoelectric layer topology for sensitivity enhancement." Beilstein Journal of Nanotechnology 8 (February 6, 2017): 358–71. http://dx.doi.org/10.3762/bjnano.8.38.
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Self-sensing techniques for atomic force microscope (AFM) cantilevers have several advantageous characteristics compared to the optical beam deflection method. The possibility of down scaling, parallelization of cantilever arrays and the absence of optical interference associated imaging artifacts have led to an increased research interest in these methods. However, for multifrequency AFM, the optimization of the transducer layout on the cantilever for higher order modes has not been addressed. To fully utilize an integrated piezoelectric transducer, this work alters the layout of the piezoelectric layer to maximize both the deflection of the cantilever and measured piezoelectric charge response for a given mode with respect to the spatial distribution of the strain. On a prototype cantilever design, significant increases in actuator and sensor sensitivities were achieved for the first four modes without any substantial increase in sensor noise. The transduction mechanism is specifically targeted at multifrequency AFM and has the potential to provide higher resolution imaging on higher order modes.
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Torres, Luis M., Francisco J. Cañete, and Luis Díez. "Matched Filtering for MIMO Coherent Optical Communications with Mode-Dependent Loss Channels." Sensors 22, no. 3 (January 21, 2022): 798. http://dx.doi.org/10.3390/s22030798.
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The use of digital signal processors (DSP) to equalize coherent optical communication systems based on spatial division multiplexing (SDM) techniques is widespread in current optical receivers. However, most of DSP implementation approaches found in the literature assume a negligible mode-dependent loss (MDL). This paper is focused on the linear multiple-input multiple-output (MIMO) receiver designed to optimize the minimum mean square error (MMSE) for a coherent SDM optical communication system, without previous assumptions on receiver oversampling or analog front-end realizations. The influence of the roll-off factor of a generic pulse-amplitude modulation (PAM) transmitter on system performance is studied as well. As a main result of the proposed approach, the ability of a simple match filter (MF) based MIMO receiver to completely eliminate inter-symbol interference (ISI) and crosstalk for SDM systems under the assumption of negligible MDL is demonstrated. The performance of the linear MIMO fractionally-spaced equalizer (FSE) receiver for an SDM system with a MDL-impaired channel is then evaluated by numerical simulations using novel system performance indicators, in the form of signal to noise and distortion ratio (SNDR) loss, with respect to the case without MDL. System performance improvements by increasing the transmitter roll-off factor are also quantified.
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Zhao, Zhongxiang, Matthew H. Alford, James B. Girton, Luc Rainville, and Harper L. Simmons. "Global Observations of Open-Ocean Mode-1 M2 Internal Tides." Journal of Physical Oceanography 46, no. 6 (June 2016): 1657–84. http://dx.doi.org/10.1175/jpo-d-15-0105.1.
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AbstractA global map of open-ocean mode-1 M2 internal tides is constructed using sea surface height (SSH) measurements from multiple satellite altimeters during 1992–2012, representing a 20-yr coherent internal tide field. A two-dimensional plane wave fit method is employed to 1) suppress mesoscale contamination by extracting internal tides with both spatial and temporal coherence and 2) separately resolve multiple internal tidal waves. Global maps of amplitude, phase, energy, and flux of mode-1 M2 internal tides are presented. The M2 internal tides are mainly generated over topographic features, including continental slopes, midocean ridges, and seamounts. Internal tidal beams of 100–300 km width are observed to propagate hundreds to thousands of kilometers. Multiwave interference of some degree is widespread because of the M2 internal tide’s numerous generation sites and long-range propagation. The M2 internal tide propagates across the critical latitudes for parametric subharmonic instability (28.8°S/N) with little energy loss, consistent with the 2006 Internal Waves across the Pacific (IWAP) field measurements. In the eastern Pacific Ocean, the M2 internal tide loses significant energy in propagating across the equator; in contrast, little energy loss is observed in the equatorial zones of the Atlantic, Indian, and western Pacific Oceans. Global integration of the satellite observations yields a total energy of 36 PJ (1 PJ = 1015 J) for all the coherent mode-1 M2 internal tides. Finally, satellite observed M2 internal tides compare favorably with field mooring measurements and a global eddy-resolving numerical model.
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Martin, Nadine, Klaus Schwamborn, Henning Urlaub, Boyi Gan, Jun-Lin Guan, and Anne Dejean. "Spatial Interplay between PIASy and FIP200 in the Regulation of Signal Transduction and Transcriptional Activity." Molecular and Cellular Biology 28, no. 8 (February 19, 2008): 2771–81. http://dx.doi.org/10.1128/mcb.01210-07.
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ABSTRACT The members of the protein inhibitor of activated STAT (PIAS) family of proteins are implicated in fundamental cellular processes, including transcriptional regulation, either through action as E3 SUMO ligases or through SUMO-independent effects. We report here the identification of FIP200 (focal adhesion kinase family-interacting protein of 200 kDa) as a new PIASy-interacting protein. We show that the interaction depends on the integrity of the RING finger of PIASy and the carboxy terminus of FIP200. Both in vitro and in vivo sumoylation assays failed to reveal any sumoylation of FIP200, suggesting that FIP200 is not a bona fide SUMO substrate. Immunofluorescence microscopy and subcellular fractionation, either upon forced PIASy expression or in the absence of PIASy, revealed that interaction with PIASy redistributes FIP200 from the cytoplasm to the nucleus, correlating with abrogation of FIP200 regulation of TSC/S6K signaling. Conversely, FIP200 enhances the transcriptional activation of the p21 promoter by PIASy whereas PIASy transcription activity is severely reduced upon FIP200 depletion by RNA interference. Chromatin immunoprecipitation analysis demonstrates that endogenous PIASy and FIP200 are corecruited to the p21 promoter. Altogether, these results provide the first evidence for the existence of a close—spatially controlled—mode of regulation of FIP200 and PIASy nucleocytoplasmic functions.
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Wang, Zhiren, Wen Chen, Danan Dong, Chenglong Zhang, Yu Peng, and Zhengqi Zheng. "An Advanced Multipath Mitigation Method Based on Trend Surface Analysis." Remote Sensing 12, no. 21 (November 2, 2020): 3601. http://dx.doi.org/10.3390/rs12213601.
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Among various ways to eliminate the multipath effect in high-precision global navigation satellite system positioning, the multipath hemispherical map (MHM) is a typical multipath correction method based on spatial domain repeatability, which is suitable for not only static environments, but also some dynamic carriers, such as ships and aircraft. So, it has notable advantages and is widely used. The MHM method divides the sky into grids according to the azimuth and elevation angles of satellite, and calculates the average of the residuals within the grid points as its multipath calibration value. It is easy to implement, but it will inevitably lead to excessive or insufficient multipath correction in the grid. The trend surface analysis-based multipath hemispherical map (T-MHM) method makes up for this deficiency by performing trend surface analysis on the multipath spatial changes within the grid points. However, the effectiveness of T-MHM is limited and less capable of resisting noise interference due to the multicollinearity between the independent variables caused by the special spatial distribution of multipath sampling and the overfitting problem caused by ignoring the multipath anisotropy. Thus, we proposed an improved multipath elimination method named AT-MHM (advanced trend surface analysis-based multipath hemispherical model), which cautiously judges the occurrence of the above problems and gives corresponding solutions. This was extended to double-difference mode, which expands the scope of application. The performance of AT-MHM in GPS pseudorange multipath mitigation was verified on geodetic receiver and low-cost receiver in a strong multipath environment with high occlusion.
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Alford, Matthew H., Michael C. Gregg, and Mark A. Merrifield. "Structure, Propagation, and Mixing of Energetic Baroclinic Tides in Mamala Bay, Oahu, Hawaii." Journal of Physical Oceanography 36, no. 6 (June 1, 2006): 997–1018. http://dx.doi.org/10.1175/jpo2877.1.
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Abstract Large semidiurnal vertical displacements (≈100 m) and strong baroclinic currents (≈0.5 m s−1; several times as large as barotropic currents) dominate motions in Mamala Bay, outside the mouth of Pearl Harbor, Hawaii. During September 2002, the authors sought to characterize them with a 2-month McLane moored profiler deployment and a 4-day intensive survey with a towed CTD/ADCP and the Research Vessel (R/V) Revelle hydrographic sonar. Spatial maps and time series of turbulent dissipation rate ε, diapycnal diffusivity Kρ, isopycnal displacement η, velocity u, energy E, and energy flux F are presented. Dissipation rate peaks in the lower 150 m during rising isopycnals and high strain and shows a factor-of-50 spring–neap modulation. The largest Kρ values, in the western bay near a submarine ridge, exceed 10−3 m2 s−1. The M2 phases of η and u increase toward the west, implying a westward phase velocity cp ≈ 1 m s−1 and horizontal wavelength ≈60 km, consistent with theoretical mode-1 values. These phases vary strongly (≈±45°) in time relative to astronomical forcing, implying remotely generated signals. Energy and energy flux peak 1–3 days after spring tide, supporting this interpretation. The group velocity, computed as the ratio F/E, is near ≈1 m s−1, also in agreement with theoretical mode-1 values. Spatial maps of energy flux agree well with results from the Princeton Ocean Model, indicating converging fluxes in the western bay from waves generated to the east and west. The observations indicate a time-varying interference pattern between these waves that is modulated by background stratification between their sources and Mamala Bay.
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Garambois, S., C. Voisin, M. A. Romero Guzman, D. Brito, B. Guillier, and A. Réfloch. "Analysis of ballistic waves in seismic noise monitoring of water table variations in a water field site: added value from numerical modelling to data understanding." Geophysical Journal International 219, no. 3 (September 2, 2019): 1636–47. http://dx.doi.org/10.1093/gji/ggz391.
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SUMMARY Passive seismic interferometry allows to track continuously the weak seismic velocity changes in any medium by correlating the ambient seismic noise between two points to reconstruct the Green’s function. The ballistic surface waves of the reconstructed Green’s functions are used to monitor the changes of water table induced by a controlled experiment in the Crépieux-Charmy (France) exploitation field. Viscoelastic numerical modelling of the monitoring experiment reproduces quite satisfactorily the sensitivity of the surface waves to the water table previously observed with seismic noise data. This numerical approach points out that this sensitivity is controlled by mode mixing of Rayleigh waves. It also made it possible to identify the refracted P wave and to extract its anticorrelated sensitivity to water table variations. Depending on the offset between receivers, it was observed numerically that the interferences between the different waves (with different velocities) composing the seismic wavefield slightly affect the quantitative sensitivity to water table changes. This suggests the use of an optimal spatial and temporal observation window for which wave interference is minor and does not blur the quantitative response to water table variations. We were thus able to determine the relationship between velocity and water table variations for all waves involved. From numerical computations, we identify a weak signal-to-noise ratio phase in the noise correlograms, with a anticorrelated sensitivity to the water table: the reconstructed refracted waves.