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Transcranial imaging of functional cerebral hemodynamic changes in single blood vessels using in vivo photoacoustic microscopy
No full text[[abstract]]Optical imaging of changes in total hemoglobin concentration (HbT), cerebral blood volume (CBV), and hemoglobin oxygen saturation (SO2) provides a means to investigate brain hemodynamic regulation. However, high-resolution transcranial imaging remains challenging. In this study, we applied a novel functional photoacoustic microscopy technique to probe the responses of single cortical vessels to left forepaw electrical stimulation in mice with intact skulls. Functional changes in HbT, CBV, and SO2 in the superior sagittal sinus and different-sized arterioles from the anterior cerebral artery system were bilaterally imaged with unambiguous 36x65-mu m(2) spatial resolution. In addition, an early decrease of SO2 in single blood vessels during activation (i.e., 'the initial dip') was observed. Our results indicate that the initial dip occurred specifically in small arterioles of activated regions but not in large veins. This technique complements other existing imaging approaches for the investigation of the hemodynamic responses in single cerebral blood vessels.[[fileno]]2030143010034[[department]]電機工程學
Dual-frequency laser Doppler velocimeter for speckle noise reduction and coherence enhancement
Get PDF[[abstract]]We study the characteristics of a dual-frequency laser Doppler velocimeter (DF-LDV) based on an optically injected semiconductor laser. The laser operated in a period-one (P1) dynamical state with two optical frequencies separated by 11.25 GHz is used as the dual-frequency light source. With a microwave beat signal carried by the light, the DF-LDV possesses both the advantages of good directionality, high intensity, and high spatial resolution from the light and low speckle noise and good coherence from the microwave, respectively. By phase-locking the two frequency components with a microwave signal, the coherence of the dual-frequency light source can be further improved and the detection range can be much extended. In this paper, velocity resolutions of the DF-LDV with different amounts of speckle noise and at different detection ranges are experimentally measured and analyzed. Compared with the conventional single-frequency LDV (SF-LDV), the velocity resolution of the DF-LDV is improved by 8x10(3) times from 2.5 m/s to 0.31 mm/s for a target with a longitudinal velocity v(z) - 4 cm/s, a transverse velocity v(t) - 5 m/s, and at a detection range of 108 m.[[fileno]]2030181010019[[department]]電機工程學
Maintaining temporal coherence in video retargeting using mosaic-guided scaling
No full text[[abstract]]Video retargeting from a full-resolution video to a lower resolution display will inevitably cause information loss. Content-aware video retargeting techniques have been studied to avoid critical visual information loss while resizing a video. Maintaining the spatio-temporal coherence of a retargeted video is very critical on visual quality. Camera motions and object motions, however, usually make it difficult to maintain temporal coherence using existing schemes. In this paper, we propose the use of a panoramic mosaic to guide the scaling of corresponding regions of video frames in a video shot to ensure good temporal coherence. In the proposed method, after aligning video frames in a shot to a panoramic mosaic constructed for the shot, a global scaling map for these frames is derived from the panoramic mosaic. Subsequently, the local scaling maps of individual frames are derived from the global map and is further refined according to spatial coherence constraints. Our experimental results show that the proposed method can effectively maintain temporal coherence so as to achieve good visual quality even a video contains camera motions and object motions.[[fileno]]2030144010027[[department]]電機工程學
A synchronization scheme based on Gaussian pulses for cooperative MIMO OFDM systems
No full text[[abstract]]In this paper, we propose a novel preamble design of Gaussian pulses, along with a synchronization scheme, for cooperative MIMO OFDM systems. In our preamble design, the training signals of cooperating nodes are well separated from each other in both time domain and frequency domain to suppress their mutual interference in both domains, whereas they are only separated in either of the two domains in the state of the art. Accordingly, multiple propagation delays and carrier frequency offsets (CFOs) can be jointly estimated using the proposed synchronization scheme, while they are separately estimated in time domain and frequency domain in conventional synchronization schemes. We also design a proper correlation window size for the proposed synchronization scheme to effectively reduce computational complexity as well as to maintain satisfactory performance. Computer simulations verify the superiority of the proposed approach over existing synchronization schemes.[[fileno]]2030102030153[[department]]電機工程學
Coverage- extended cooperative geographic routing with optimal power allocation for wireless multihop networks
No full text[[abstract]]In time-varying flat-fading environments, time domain channel correlations are required for accurate channel estimation and interpolation. However, the correlation property, which depends on the Doppler spread, is hard to be extracted from corrupted channel responses within a short channel estimation interval. In this work, based on an approximate channel model via the Taylor expansion, we propose a joint channel and Doppler spread estimation scheme over time-varying flat-fading channels. It employs the expectation-maximization (EM) algorithm to iteratively attain the maximum-likelihood (ML) channel and Doppler spread estimates. Simulation results show that the proposed scheme achieves accurate performance of both channel estimation and Doppler spread estimation within a short estimation interval.[[fileno]]2030102030155[[department]]電機工程學
A credibility-based cooperative spectrum sensing technique for cognitive radio systems
No full text[[abstract]]Spectrum sensing is one of the major elements of cognitive radio applications. A single secondary user (SU) usually cannot provide robust sensing capability due to channel effects. In order to overcome this problem, cooperative spectrum sensing techniques have been proposed. Because conventional cooperative spectrum sensing schemes assumed that all sensing nodes have the same sensing reliability, the SUs were assigned identical false-alarm probability even though some of them suffer deep fading, which may degrade their detection performance. In this study, we propose an adaptive credibility-based cooperative spectrum sensing technique, which evaluates the sensing reliability of SUs based on previous sensing performance, and adjusts the probability of false alarm of each SU individually. Assigning a higher false alarm probability for a more reliable SU can result in better detection performance. To verify the effectiveness of the proposed cooperative spectrum sensing technique, both the false alarm probability and the detection probability are simulated under Rayleigh fading channels, and the results show that the proposed approach outperforms any conventional detection method in terms of detection performance.[[fileno]]2030102030161[[department]]電機工程學
Research of Digital Relays based on Real-Time Simulation Techniques
No full text[[abstract]]This paper presents works involving developments of a real-time simulation laboratory of digital relay systems used for transmission system protections, based on RT-Lab. These relay models are designed to facilitate the investigation and evaluation of the protection system. A practical 345KV 72.8 km transmission line of Taiwan Power system is constructed to verify operations of differential relays and distance relays. Dynamic responses under various fault scenarios are verified. Simulation results of these tests show that the developed relay models operate correctively for various events. Also, the program execution time can be significantly reduced in comparison with results obtained from off-line Matlab/Simulink simulations.[[fileno]]2030140030045[[department]]電機工程學
Distributed real-time simulation modeling and analysis of a micro-grid with renewable energy sources
No full text[[abstract]]Micro-grid is a new concept gained significant attentions due to the increasing distributed energy sources. Several micro-grid test beds in the forms of either hardware or software simulation have been developed around the world. In Taiwan, one 20KVA 3W3Ø micro-grid test bed has been conducted in National Tsing Hua University (NTHU). This micro-grid consists of various fundamental power system components, including two synchronous generators (SG), one fixed speed induction generator (FSIG), and one doubly-fed induction generator (DFIG). In this paper, simulation results of the NTHU micro-grid system in distributed real-time simulation platform OPAL-RT are reported. Dynamical modeling of various distributed generations (DG) will be studied. Control strategies for DGs are verified through simulations on two different scenarios: (1) transition from the grid-connected mode to the islanding mode, and (2) load variation in the islanding mode.[[fileno]]2030140030051[[department]]電機工程學
A Novel Low Gate-Count Serializer Topology with Multiplexer- Flip-Flops
No full text[[abstract]]This paper proposes Multiplexer-Flip-Flops (MUX-FFs) to be a high-throughput and low-cost solution for serial link transmitters. We also propose Multiplexer-Latches (MUX-Latches) that possess the logic function of combinational circuits and storing capacity of sequential circuits. Adopting the pipeline with MUX-FFs, which are composed of cascaded latches and MUX-Latches, many latch gates for sequencing can be removed. Analysis shows that an 8-to-1 serializer in the pipeline topology with MUX-FFs reduces 52% gate-count compared to the traditional pipeline topology. To verify the function of the proposed design, a chips is implemented with the proposed 8-to-1 serializer with MUX-FFs in 90 nm CMOS technology. The measured results show that the proposed serializer with MUX-FFs are bit-error-free (with BER <; 10-12), operating at up to 12 Gbit/s.[[fileno]]2030122030050[[department]]電機工程學
Design and Implementation of Multiple Maximum Power Point Trackers for Multi-String PV Panels in DC-Microgrid Applications
No full text[[abstract]]This paper presents design and implementation of multiple maximum power point trackers (MPPTs) with wide input voltage variation for dc distribution systems. The topology of the proposed MPPT combines buck and boost converters to accommodate PV input voltage from 0 V to 850 V. The control algorithm for tracking maximum power points is based on a “perturbation and observation” method. The proposed MPPT can on-line check the input configuration of PV-panel strings to determine the current for maximum power calculation. In the paper, operational principle, analysis and design of the proposed MPPT configuration and mode transition will be first presented. Flowcharts of the control algorithm include perturbation and observation method and on-line PV-panel string configuration check will be then explained. Experimental results obtained from three-string MPPTs with the maximum power of 10 kW have verified its performance and feasibility.[[fileno]]2030197030006[[department]]電機工程學