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51.
YUYING WU HIROAKI IKEDA HIROFUMI YOSHIDA SHIGENOBU SHINOHARA 《International Journal of Communication Systems》1996,9(1):5-11
This paper describes two types of bidirectional addressed audio signal transmission systems where the square-wave frequency modulation (SWFM) and intensity modulation (IM) are used to obtain the optical SWFM signals generated from LEDs at 850 nm. The first one is an addressed audio signal transmission network of tree structure. The sender and auxiliary receiver in the centre are connected to four terminals, each consisting of a receiver and an auxiliary sender, through pairs of optical fibres and an optical splitter used as an optical signal distributor. The second one is a new type of full-duplex one-to-one communication system. The sender and auxiliary receiver in one terminal are connected to the receiver and auxiliary sender in the other terminal through an optical fibre and a pair of directional couplers. Although LEDs in the second system deliver optical SWFM signals at the same wavelength of 850 nm at the same time, the communications are satisfactory because there is no interference from one LED to the other. In both the first and second experimental systems, the audio signal, address, and SWFM carrier occupy 10 Hz to 20 kHz, 65 kHz to 710 kHz, and 6 MHz, respectively. The SNR and distortion were 62 dB and 0.4 per cent, respectively. 相似文献
52.
Brain activation has been used to understand brain-level events associated with cognitive tasks or physical tasks. As a quantitative measure for brain activation, we propose entropy in place of signal amplitude and beta value, which are widely used, but sometimes criticized for their limitations and shortcomings as such measures. To investigate the relevance of our proposition, we provided 22 subjects with physical stimuli through elbow extension-flexion motions by using our exoskeleton robot, measured brain activation in terms of entropy, signal amplitude, and beta value; and compared entropy with the other two. The results show that entropy is superior, in that its change appeared in limited, well established, motor areas, while signal amplitude and beta value changes appeared in a widespread fashion, contradicting the modularity theory. Entropy can predict increase in brain activation with task duration, while the other two cannot. When stimuli shifted from the rest state to the task state, entropy exhibited a similar increase as the other two did. Although entropy showed only a part of the phenomenon induced by task strength, it showed superiority by showing a decrease in brain activation that the other two did not show. Moreover, entropy was capable of identifying the physiologically important location. 相似文献
53.
Functional load (FL) quantifies the contributions by phonological contrasts to distinctions made across the lexicon. Previous research has linked particularly low values of FL to sound change. Here, we broaden the scope of enquiry into FL to its evolution at higher values also. We apply phylogenetic methods to examine the diachronic evolution of FL across 90 languages of the Pama–Nyungan (PN) family of Australia. We find a high degree of phylogenetic signal in FL, indicating that FL values covary closely with genealogical structure across the family. Though phylogenetic signals have been reported for phonological structures, such as phonotactics, their detection in measures of phonological function is novel. We also find a significant, negative correlation between the FL of vowel length and of the following consonant—that is, a time-depth historical trade-off dynamic, which we relate to known allophony in modern PN languages and compensatory sound changes in their past. The findings reveal a historical dynamic, similar to transphonologization, which we characterize as a flow of contrastiveness between subsystems of the phonology. Recurring across a language family that spans a whole continent and many millennia of time depth, our findings provide one of the most compelling examples yet of Sapir’s ‘drift’ hypothesis of non-accidental parallel development in historically related languages. 相似文献
54.
55.
Johanne Heitmann Solheim Boris Zimmermann Valeria Tafintseva Simona Dzurendov Volha Shapaval Achim Kohler 《Molecules (Basel, Switzerland)》2022,27(6)
Extended multiplicative signal correction (EMSC) is a widely used preprocessing technique in infrared spectroscopy. EMSC is a model-based method favored for its flexibility and versatility. The model can be extended by adding constituent spectra to explicitly model-known analytes or interferents. This paper addresses the use of constituent spectra and demonstrates common pitfalls. It clarifies the difference between analyte and interferent spectra, and the importance of orthogonality between model spectra. Different normalization approaches are discussed, and the importance of weighting in the EMSC is demonstrated. The paper illustrates how constituent analyte spectra can be estimated, and how they can be used to extract additional information from spectral features. It is shown that the EMSC parameters can be used in both regression tasks and segmentation tasks. 相似文献
56.
57.
Photonic generation of microwave signals using dual-wavelength single-longitudinal-mode fiber lasers
Photonic generation of microwave signals is demonstrated with a dual-wavelength single-longitudinal-mode erbium-doped fiber ring laser. Microwave signal with a frequency of 21.07 GHz is obtained by aligning the reflection band of a uniform fiber Bragg grating to the two transmission peaks within a fiber Bragg grating-based Fabry-Perot filter. Stable dual-wavelength single-longitudinal-mode operation is guaranteed by means of the combined filtering effect of a saturable absorber and the Fabry-Perot filter. This approach provides an effective solution to the photonic generation of high-frequency microwave signals. 相似文献
58.
Based on the Rayleigh diffraction integral and complex analytical signal representation, the free-space analytical propagation equation and its Fourier spectrum for ultrashort chirped pulsed Gaussian beams with constant diffraction length are derived. The effect of chirp parameter on the spatiotemporal and spectral properties is illustrated with analytical formulas and numerical calculation results. It is shown that the axial spectra of ultrashort chirped pulsed Gaussian beams become broadened with increasing chirp parameter. For single optical cycle, the transversal intensity distribution is affected by increasing chirp parameter, but almost not affected for several optical cycles. Moreover, the positive or negative sign of the chirp parameter has no effect on the spectral distribution and intensity distribution. 相似文献
59.
High-order curvilinear mesh generation technique based on an improved radius basic function approach
A high-order curvilinear hybrid mesh generation technique is developed for high-order numerical method (eg, discontinuous Galerkin method) applications to improve the accuracy for problems with curve boundary. The grid generation technique is based on an improved radius basic function (RBF) approach by which the straight-edge mesh is converted into high-order curve mesh. Firstly, an initial straight-edge mesh is prepared by traditional grid generation software. Then, high-order interpolation points are inserted into the mesh entities such as edges, faces, and cells according to the final demand of mesh order. To preserve the original geometry, the inserted points on solid wall are then projected onto the CAD model using an open source tool “Open Cascade.” Finally, other inserted points in the field near the solid wall are moved to appropriate positions by the improved RBF approach to avoid tangled cells. If we use the original RBF approach, then the inserted points on the edge and face entities normal to the solid boundary in the region of boundary layer will move to improper positions. To overcome this problem, a weighting based on the local grid aspect ratio between normal direction and tangential direction is introduced into the baseline RBF approach. Three typical configurations are tested to validate the mesh generator. Meanwhile, a third-order solution of subsonic flow over an analytical 3D body of revolution in the second International Workshop on High-Order CFD Methods is supplied by a discontinuous Galerkin solver. These numerical tests demonstrate the potential capability of present technique for high-order simulations of complex geometries. 相似文献
60.
Yannis Kallinderis Eleni M. Lymperopoulou Georgios Spyridonos Panagiotis Antonellis 《国际流体数值方法杂志》2019,91(2):63-96
Curved geometries and the corresponding near-surface fields typically require a large number of linear computational elements. High-order numerical solvers have been primarily used with low-order meshes. There is a need for curved, high-order computational elements. Typical near-surface meshes consist of hexahedral and/or prismatic elements. The present work studies the employment of quadratic meshes that are relatively coarse for field simulations. Directionally quadratic high-order elements are proposed for the near-surface field regions. The quadratic meshes are compared with the conventional low-order ones in terms of accuracy and efficiency. The cases considered include closed surface volume calculations, as well as computation of gradients of several analytic fields. A special method of adaptive local quadratic meshes is proposed and evaluated. Truncation error analysis for quadratic grids yields comparison with the conventional linear hexahedral/prismatic meshes, which are subject to typical distortions such as stretching, skewness, and torsion. 相似文献