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Hot dry rock (HDR) is a kind of clean energy with significant potential. Since the 1970s, the United States, Japan, France, Australia, and other countries have attempted to conduct several HDR development research projects to extract thermal energy by breaking through key technologies. However, up to now, the development of HDR is still in the research, development, and demonstration stage. An HDR exploration borehole (with 236 °C at a depth of 3705 m) was drilled into Triassic granite in the Gonghe Basin in northwest China in 2017. Subsequently, China Geological Survey (CGS) launched the HDR resources exploration and production demonstration project in 2019. After three years of efforts, a sequence of significant technological breakthroughs have been made, including the genetic model of deep heat sources, directional drilling and well completion in high-temperature hard rock, large-scale reservoir stimulation, reservoir characterization, and productivity evaluation, reservoir connectivity and flow circulation, efficient thermoelectric conversion, monitoring, and geological risk assessment, etc. Then the whole-process technological system for HDR exploration and production has been preliminarily established accordingly. The first power generation test was completed in November 2021. The results of this project will provide scientific support for HDR development and utilization in the future.©2022 China Geology Editorial Office.

Electrically tunable metasurfaces with pixel-level phase control are good candidates for dynamic manipulation of the beam direction in the terahertz band, which is a critical and highly desired technique for next generation communications. Yet the complex biasing, limited aperture and cross talk hinders its progress. In this study, we propose a magnetic-field-globally controlled metasurface for beam switching. The metasurface is composed of a bi-layer silicon metagrating on a magneto-optical substrate InSb. The beam direction is governed by two physical processes: the magnetically-controlled polarization and the polarization-controlled diffraction. By utilizing the circular dichroism and Faraday rotation effects in InSb, the metasurface can operate at two frequency bands. The beam is switched among four directions by properly choosing the magnetic field biasing and the frequency. This study offers a promising solution for beam management using magnetic field biasing and in a global manner. [ABSTRACT FROM AUTHOR]

Manipulating terahertz (THz) polarization in an efficient and broadband manner is of great significance to facilitating THz applications, including communications, imaging, defense, and homeland security. In this work, a dispersion compensation scheme is proposed for high‐efficiency and ultra‐broadband THz polarization manipulation using an anisotropic dielectric‐metal hybrid metadevice. The operating bandwidth is broadened by dispersion compensation, where the dielectric grating provides an artificial birefringence with a phase dispersion of positive slope and the metallic grating provides a phase dispersion of negative slope. Experimental results show that the device achieves two ultra‐broadband dispersion compensation, corresponding to the achromatic quarter‐wave plate in the lower frequency band (QWP: 0.5–2.0 THz, PCR >0.95) and the achromatic half‐wave plate in the higher frequency band (HWP: 1.0–2.1 THz, PCR >0.9), respectively. Theoretically, the bandwidth of QWP can be further improved to 2.6 THz by optimizing the grating dispersion, which brings huge application space to cover most of the THz radiation. This hybrid metadevice configuration offers a versatile platform for engineering electromagnetic waves, and the strategy of phase compensation can be generalized to extend the bandwidth of the metadevice in imaging and communications. [ABSTRACT FROM AUTHOR]

Broadband terahertz (THz) chirality and wavefront manipulation play important roles in wireless communication, imaging, and radar systems. In this work, by integrating liquid crystal (LC) into a dielectric metasurface, the gradient phase distribution from the Si metasurface and the tunable birefringent phase shift from LC are engineered to perform an active spin‐decoupled beam steering with the strong spin asymmetric transmission. By using geometric symmetry analysis, the relationships between the symmetry breaking and the optical chirality of the metadevice are revealed under different LC orientations, and both the simulations and experiments further verify the dependence of this chirality on spin‐decoupled beam steering with different spin states. The results show that with the orientation changes of the LC by driving the different magnetic fields, the circular dichroism of the device at the 0° deflection angle is ≈100% dynamically modulated and even flipped in the broadband range of 0.8–1.3 THz. With these changes in THz chirality, a tunable spin‐decoupled beam steering occurs in the range of 25°‐45°. This work shows that tunable LC anisotropy leads to more complex symmetry breaking in this structure, and results in more functions than conventional spin‐decoupled wavefront manipulations, which expands the scope of THz chiral metadevice and its applications. [ABSTRACT FROM AUTHOR]

Controlling terahertz (THz) waves, especially the polarization state and deflection angle, is important in THz application systems. But most of conventional THz metasurfaces have limitations in efficiency and working bandwidth. Although Pancharatnam-Berry (P-B) metasurfaces shows excellent manipulation for the circular polarized (CP) waves (or called photonic spin states) without phase dispersion, there is still challenge in active controlling. Here, we developed a magnetically tunable gyrotropic P-B metasurface by combining the gyroelectric semiconductor InSb and the P-B elements, which obtain two important effects: One is the active photonic spin Hall effect, which controls the conversion between two CP states and the deflection in space. A broadband working frequency of 1.02∼1.7 THz is obtained with the sweeping deflection angle from 36.6° to 83.5° and the highest efficiency of over 70%. The other is photonic spin filter effect, which reflects one CP state but absorb the other orthogonal CP state, realizing nonreciprocal absorption with the isolation of 24 dB. This active, high efficiency and broadband P-B metasurface opens a new way in manipulation of the THz wave propagation and polarization states in both space and frequency domains. [ABSTRACT FROM AUTHOR]

The Faraday rotation effect of both the La: yttrium iron garnet (YIG) film and the YIG metasurface were experimentally and numerically investigated in the terahertz (THz) region. A THz magneto-optic polarization measurement system was used to observe the transmission, resonance, and magneto-optical effect of the La:YIG film and YIG metasurface. The THz artificial chirality and resonance localization of the helical metasurface generate the superchiral THz field, which enhances the THz magneto-optical effect of the YIG film. The results show that the Faraday effect of the YIG metasurface is about three times that of the pure YIG film, whose differential rotation angle increases from 8° to over 24°. This work achieves more sensitively active polarization control of THz waves, which is of great significance for THz polarization conversion, sensing, and non-reciprocal transmission. [ABSTRACT FROM AUTHOR]

The terahertz (THz) resonance, chirality, and polarization conversion properties of a double-layer chiral metasurface have been experimentally investigated by THz time domain spectroscopy system and polarization detection method. The special symmetric geometry of each unit cell with its adjacent cells makes a strong chiral electromagnetic response in this metasurface, which leads to a strong polarization conversion effect. Moreover, compared with the traditional THz transmission resonance sensing for film thickness, the polarization sensing characterized by polarization elliptical angle (PEA) and polarization rotation angle (PRA) shows a better Q factor and figure of merit (FoM). The results show that the Q factors of the PEA and PRA reach 43.8 and 49.1 when the interval film is 20 μm, while the Q factor of THz resonance sensing is only 10.6. And these PEA and PRA can play a complementary role to obtain a double-parameter sensing method with a higher FoM, over 4 times than that of resonance sensing. This chiral metasurface and its polarization sensing method provide new ideas for the development of high-efficiency THz polarization manipulation, and open a window to the high sensitive sensing by using THz polarization spectroscopy. [ABSTRACT FROM AUTHOR]

While the terahertz regime has proved to be a promising solution for wireless big-data transmission, the lack of available functional devices working in this band seriously constrain the wide engineering applications. In this paper, the silver nanorods in polyvinyl alcohol (PVA) film are developed for enhancing and accelerating THz all-optical modulation. The modulation depth can reach 80% under 0.6W/cm2, and the speed can reach 3kHz which is much faster than our previous research. It has been attributed to the plasmonic hot carriers' effect of the silver nanorods, which makes the photoexcited electrons more easily jump out of the barrier and assemble in the heterostructure between PVA and silicon. Moreover, the photoelectronic response is proved to be related to the plasmonic absorption of the pumping light, which means the modulation speed is decided by the color of the pump light. This experiment phenomenon provides a way to build color-selective terahertz all-optical modulators. Considering its capability for broadband, efficient, and fast modulation of THz waves, this low-cost and conveniently fabricated device could be broadly applied in polymer related THz devices. [ABSTRACT FROM AUTHOR]

In this paper, a novel flight control scheme is proposed by using the variable domain fuzzy control method. The proposed control strategy can improve control performance of near-space hypersonic vehicles (NHV) despite uncertainties and external disturbances. The control accuracy and anti-interference velocity are improved, and the calculated quantity is decreased by the change of fuzzy domain. To overcome the chattering phenomenon, the dynamic adaptive terminal slidingmode control (TSMC) strategy is raised. The control law is designed by an intermediate auxiliary systems, step-by-step. Additionally, the Lyapunov method is used to prove that the tracking errors are converged in finite time. [ABSTRACT FROM AUTHOR]

Coupled dielectric-metal gratings are investigated for broadband terahertz (THz) wave polarization conversion and asymmetric transmission by the experiments and numerical simulations, which are composed of the subwavelength Si grating and metallic wire grating layers. The dielectric grating layer with a large artificial birefringence and low dispersion is employed as a phase engineered waveplate, and the metal wire grating arranged with a 45° angle to the dielectric grating is utilized as a high-efficiency polarizer. Due to the subwavelength integration, this coupled grating presents a local resonance coupling mechanism between dielectric and metal gratings, which greatly enhances the polarization rotation and expands the bandwidth, not a simple combination with dielectric and metallic gratings. The results demonstrate that a broadband asymmetric transmission with an extinction ratio of 30dB from 0.2 to 1.2 THz is achieved and the highest transmission of 90% can be obtained. It provides a simple way towards practical applications for THz artificial dispersion materials, polarization control and asymmetric transmission. [ABSTRACT FROM AUTHOR]

Recent research work on magneto-optical micro- structure devices in terahertz (THz) regime has been reviewed. Some magneto-optical materials responding at THz frequency range were introduced. Based on these magneto-optical materials, MO microstructures devices were reviewed, including magnetic photonic crystals, magneto-plasmonics, and magneto-metasurface all in the submillimetre scale. These devices can realize several functions of isolating, modulation, sensing, and directional beam scanning. Moreover, the necessary conditions of forming THz nonreciprocal transmission in magneto-optical microstructure devices were concluded, and the tunability of these devices was also analysed, which strongly depends on the magneto-optical property of material and the symmetry of structure. The unique magneto-optical effects make it play an irreplaceable role in the high performance THz applications of communication, imaging, and sensing systems. [ABSTRACT FROM PUBLISHER]

In this paper, a T-S fuzzy model of the NSV (Nearspace Vehicle) kinematic model is established based on fuzzy approximation theory, and a new fuzzy robust tracking control law is designed in reference to the feedforward control of the linear system. In order to account for a case in which no augmented matrix is introduced, the control law is designed as a compound form of feedback and feedforward, and the gains of feedback and feedforward are solved by LMI (Linear Matrix Inequalities). The strategy is applied to the anti-interference control of NSV attitudes, and the convergence of tracking errors is analyzed according to the Lyapunov method. Simulation results based on the NSV demonstrate the validity of the proposed method. [ABSTRACT FROM AUTHOR]

An extraordinary optical transmission effect in a complementary metallic disk and hole array has been experimentally and numerically investigated in the terahertz (THz) regime, which shows a high transmission peak despite having zero effective aperture in the direction of light propagation. The results confirm that this effect is contributed not only by the surface plasmon excited on metallic disk and hole but also the resonance in the dielectric rod between them. Moreover, an optically pumped THz wave modulation with 40% amplitude modulation depth has been demonstrated in this device using a 532-nm laser with only 150 mW/mm2 power density. This novel plasmonic structure with high $Q$ transmission peak shows great promising applications in the THz modulation, filtering, and sensing. [ABSTRACT FROM PUBLISHER]

Terahertz (THz) silicon photonic column (PC) array has been designed and fabricated, and its resonance effect has been experimentally and numerically investigated. Using this resonance effect, the refractive index sensing for liquids has been demonstrated in this device by the theoretical model calculation, numerical simulation, and experimental measurement. Moreover, resonance dependence on different incident angles in this device has also been shown. These results confirm that this THz PC array can be used as a THz refractive index sensor with high sensitivity and robustness. This sensing strategy shows that the structured surface of this device is compatible for liquid monitoring and easy to couple and transmit THz waves, and therefore can be more easily implemented in liquid refractive index sensing. [ABSTRACT FROM PUBLISHER]

We determine the 2003 M6.2 and M6.1 Dayao earthquake sequence location and velocity structure of the hypocenter area by the simultaneous inversion of hypocenter location and velocity structure. The distribution of the M6.2 earthquake sequences shows the shape of a ‘V’ along the depth, which corresponds to the reversing triangle shape of low-velocity structure, namely, the after-shocks of M6.2 are distributed along the transitional zones of high- and low-velocity structure. The zones of rupture of M6.2 and M6.1 are located on the southeast side of the reversing triangle shape of low-velocity structure. The mainshock of M6.2 ruptures downwards and the mainshock of M6.1 ruptures upwards along the transitional zones of high- and low-velocity structure. The velocity structure at the depth of 6 km shows that there is the quadrant of high- and low-velocity structure and the aftershocks of M6.2 and M6.1 are distributed along the northwest transitional zones of high- and low-velocity structure. The value of low-velocity structure at the southeast side of M6.2 is higher than the value of the low-velocity structure at the northwest side, which is disadvantageous to rupture southeastward for M6.2 and is advantageous to accumulate the energy for the occurrence of M6.1. Copyright © 2009 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Based on 43 Harvard CMT solutions in Yunnan region, GPS observations from 1999 to 2004 by China Crustal Movement Observatory Network, and results from SKS splitting and Pn fast wave anisotropy, we obtained the average directions of principle stress fields at different depths by average angle method. Then we further analyzed the coupling difference between geodynamic parameters in different tectonic blocks. Then we built five three-dimensional finite element models to simulate the crustal velocity field in Sichuan-Yunnan region and stratified stress–strain fields in different tectonic blocks. In order to implement the numerical simulation, we constrained the FEA model boundaries with GPS observations, and determined the possible flow patterns at the top of upper mantle by SKS anisotropic splitting data. Based on the simulated kinematic pattern and stress–strain fields, we analyzed the geodynamic environment in the deep part of the area, and found that the difference between lateral stress fields in different tectonic blocks is the main reason why the boundaries of tectonic blocks and their neighborhood are so active areas and capable of generating strong earthquakes. Copyright © 2009 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Generally, fuzzy approximation models require some human knowledge and experience. Operator's experience is involved in the mathematics of fuzzy theory as a collection of heuristic rules. The main goal of this paper is to present a new method for identifying unknown nonlinear dynamics such as Rössler system without any human knowledge. Instead of heuristic rules, the presented method uses the input-output data pairs to identify the Rössler chaotic system. The training algorithm is a modified Levenberg-Marquardt (L-M) method, which can adjust the parameters of each linear polynomial and fuzzy membership functions on line, and do not rely on experts' experience excessively. Finally, it is applied to training Rössler chaotic system fuzzy identification. Comparing this method with the standard L-M method, the convergence speed is accelerated. The simulation results demonstrate the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

The training of neural networks using the extended Kalman filter (EKF) algorithm is plagued by the drawback of high computational complexity and storage requirement that may become prohibitive even for networks of moderate size. In this paper, we present a local EKF training and pruning approach that can solve this problem. In particular, the by-products obtained along with the local EKF training can be utilized to measure the importance of the network weights. Comparing with the original global approach, the proposed local EKF training and pruning approach results in a much lower computational complexity and storage requirement. Hence, it is more practical in solving real world problems. The performance of the proposed algorithm is demonstrated on one medium- and one large-scale problems, namely, sunspot data prediction and handwritten digit recognition. [ABSTRACT FROM AUTHOR]