1,721,081 research outputs found
Astrocyte dysfunction drives abnormal resting-state functional connectivity in depression
No full textMajor depressive disorder (MDD) is a devastating mental disorder that affects up to 17% of the population worldwide. Even though brain-wide network-level abnormalities in MDD patients via resting-state functional MRI (rsfMRI) exist, the mechanisms underlying such network changes are unknown despite their immense potential for depression diagnosis and management. Here, we show that the astrocytic calcium deficient mice, inositol 1,4,5-trisphosphate-type-2 receptor knockout mice (Itpr2-/- mice), display abnormal rsfMRI functional connectivity (rsFC) in depression-related networks, especially decreased rsFC in mPFC-related pathways. We further uncover rsFC decreases in MDD patients highly consistent with those of Itpr2-/- mice, especially in mPFC-related pathways. Optogenetic activation of mPFC astrocytes partially enhances rsFC in depression-related networks in both Itpr2-/- and wild-type mice. Optogenetic activation of the mPFC neurons or mPFC-striatum pathway rescues disrupted rsFC and depressive-like behaviors in Itpr2-/- mice. Our results identify the previously unknown role of astrocyte dysfunction in driving rsFC abnormalities in depression
Over 240 resonances on a metasurface-pixelated silicon wafer in an octave-spanning terahertz range
No full textMetasurfaces hold tremendous promise for various innovative sensing applications, thanks to their remarkable ability to manipulate light. A recent significant advancement in this research direction is using quasi-BIC (bound states in the continuum) metasurfaces for mid-infrared molecular sensing, which relies on creating a series of nearly uniformly spaced, sharp resonances on a single device. Although many studies have highlighted the potential of adopting this method in the terahertz (THz) regime, experimental demonstration is lacking. In this work, the first experimental demonstration of such frequency comb-like, quasi-BIC resonances on a single device is presented in the THz regime. By pixelating a 6-inch Si wafer with 25 different metasurfaces that possess both high-order quasi-BIC modes and a geometric scaling, a set of 241 sharp resonances ranging from 350 to 750 GHz is produced based on numerical simulation. By using a high-resolution vector network analyzer, 140 peaks that fall into the detection range from 500 to 750 GHz are confirmed experimentally, and their frequencies match well with the simulated results. By experimentally demonstrating frequency comb-like, quasi-BIC THz resonances on a single device, this work shows a new path for metasurface-based sensing in the THz regime.</p
Directional conversion of a THz propagating wave into surface waves in deformable metagratings
No full textControllable conversion between propagating light waves and surface waves (SWs) has recently attracted significant research interests. This paper demonstrates, via numerical simulation, for the first time all-dielectric SW converters that possess a tunable and directional SW conversion efficiency. The SW converters contain multiple metagratings of Si pillars embedded in a deformable substrate. In the analysis, an infinitely large, bi-periodic metagrating under the illumination of linearly polarized light is considered first. The SW conversion efficiency of this metagrating can be modulated between 4.3% and 51.0% for incident light frequency at 0.8 THz by stretching the deformable substrate along the direction of SW propagation. Subsequently, two SW converters under circularly polarized light illumination are analyzed, where a similar level of efficiency modulation is retained in finite-sized metagratings. In these converters, only the metagrating channels along the stretch direction have a strong SW conversion efficiency, which can reach 40.4% after normalization against the effective grating area. The directivity, a parameter defined here to reveal the energy contrast among the output channels, reaches 38.6 in one of the converters. Due to its high tunability, high directivity and compact size, the SW converters may be used as tunable optical sensors and light couplers in the THz regime
Floodplain hydrodynamics and connectivity in a natural compound channel during unsteady flow events
No full textThis study investigates the hydrodynamics features and the floodplain connectivity of a natural compound channel under unsteady flood conditions using a two-dimensional shallow water equation model and a Lagrangian particle tracking method. Two flood events in 2019 in the middle reach of the Ganjiang River in China were simulated. The results show that during the rising stage, flow first passed through the low-lying areas of the floodplain. The floodplain discharge ratio increased almost linearly with the depth ratio between the floodplain and main channel when the floodplain was not fully inundated. When the floodplain was fully inundated, a second linear relationship was found between the floodplain discharge ratio and depth ratio. During the falling stage, flow first moved back to the low-lying floodplain and main channel before fully receding from the floodplain. The sequence of peak velocity, discharge and stage in unsteady flow lee to higher velocities, lower depths, and shorter residence times during the rising limb compared to those in the falling limb at the same discharge. The threshold discharge for floodplain inundation was during the rising stage larger than during the falling stage. The shortest particle residence time was observed at the flood peak, while the residence time in the rising stage was longer than in the falling stage. The particle travel distance was similar at different stages. The exchange flux between the river and floodplain increased with inflow discharge following a power law relationship. The ratio of exchange flux to inflow discharge also increased with inflow discharge up to an upper limit of 65.5 %. Particle residence time was negatively correlated with discharge following a power law with a lower limit of 2630 s, while particle travel distance is positively correlated with discharge following a power law with an upper limit of 2325 m. These findings shed light on the complex hydrodynamic processes and connectivity patterns in natural compound channels during unsteady flood conditions
The effect of natural and engineered hydraulic conditions on river-floodplain connectivity using hydrodynamic modeling and particle tracking analysis
Full text linkHydraulic conditions and water resources management projects can significantly alter river-floodplain connectivity, which in turn can alter hydrologic and biogeochemical processes in river corridors. In this study, the hydrodynamics of river-floodplain connectivity under different flood conditions and the effect of the Nanchang Water Resources Project Group (NWRPG) in the middle branch of the Ganjang River were investigated using a combination of two-dimensional hydrodynamic simulations and particle tracking. The hydrodynamic model was calibrated and validated using data from several gauging stations and field measurements. Floods in the Ganjang River can be limited to the river itself (“River Flood”, flood with normal lake level) or further extended to the Poyang Lake (“Lake Flood”, flood with high lake level). The results show that compared with “River Flood” scenarios, “Lake Flood” scenarios increased the water level flooding a larger area. The flow velocity decreased and the residence time (RT) of particles increased. The particle travel distance (PTD) of “River Flood” was larger than that of “Lake Flood”. The larger the flood, the greater the transboundary flux between the river and the floodplain, and the shorter the RT and PTD. The effect of NWRPG was the permanent flooding of part of the river floodplain, causing some habitat loss. Due to the increase in discharge, the implementation of the NWRPG results in a shorter RT with a smaller standard deviation, which has little effect on the PTD distribution. These findings can facilitate river connectivity restoration efforts in the Ganjang River and also provide a reference for assessing the impact of barrage projects
Deep-subwavelength gap modes in all-dielectric metasurfaces for high-efficiency and large-angle wavefront bending
No full textAll-dielectric, phase-gradient metasurfaces manipulate light via a judiciously designed planar distribution of high and low refractive indices. In the established design approaches, the high-index elements play a dominant role, while the electromagnetic field existing between these elements is routinely viewed as either an incidental by-product or detrimental crosstalk. Here we propose an alternative approach that concentrates on exploring the low-index materials for wavefront shaping. In our Si metasurface, the low-index air gap between adjacent Si fins is judiciously tuned, while the high-index Si fins only have a single size across the whole metasurface. These gap modes provide the full 2π phase coverage, as well as high and relatively uniform transmission, at the deep-subwavelength scale. These characteristics are ideal for mapping a steep phase gradient, consequently suitable for high-efficiency and large-angle wavefront bending. This light manipulation capability is exemplified with numerical simulation in PW-SW (freely propagating wave to surface wave) conversion, where the wavefront is deflected by an angle of 90°. In the gap-mode meta-converters, the average unit size can be only 1/60 of free-space wavelength, an order of magnitude smaller than that of conventional all-dielectric metasurfaces. Their conversion efficiency can reach 68%, the highest value reported for any all-dielectric gradient metasurface THz converter
Effect of bank slope and ambient groundwater discharge on hyporheic transport and biogeochemical reactions in a compound channel
No full textAs floodplains are inundated during floods in a compound channel, solutes in the surface water column reach the hyporheic zone and react with solutes upwelled from the groundwater. These biogeochemical reactive processes, such as aerobic respiration, nitrification, and denitrification, need more clarification. In this study, a 3D hydrodynamic model combined with a 2D groundwater and biogeochemical model was used to examine the influence of bank slope angle and ambient groundwater discharge on these processes. A denitrification zone was found under the interface between the main channel and the floodplain when the bank slope angle was 90°, while lower angles extended that zone horizontally. In addition, a lower bank angle decreased N entry into the streambed and enhanced nitrogen removal. A decrease in ambient groundwater had a negative impact on both aerobic respiration and denitrification. When the ambient groundwater discharge reached below abput 0.9 m/d, nitrification was dominant in the model domain, and the hyporheic zone turned into a NO3 source. The greatest removal efficiency, equal to 0.8, was attained at a discharge rate
of 0.5 m/d for ambient groundwater and a bank slope angle of 30°. The hyporheic zone should lose its ability to remove N when ambient groundwater discharges exceed 0.25 m/d and removal efficiency fluctuates by 0. In conclusion, our findings indicate that bank slope angle and ambient groundwater discharge have a substantial impact on solute transport and biogeochemical activities in the hyporheic zone of a compound channel
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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