129 research outputs found
Dynamic generation or removal of a scalar hair
We study dynamic processes through which the scalar hair of black holes is
generated or detached in a theory with a scalar field non-minimally coupled to
Gauss-Bonnet and Ricci scalar invariants. We concentrate on the nonlinear
temporal evolution of a far-from-equilibrium gravitational system. In our
simulations, we choose the initial spacetime to be either a bald Schwarzschild
or a scalarized spherically symmetric black hole. Succeeding continuous
accretion of the scalar field onto the original black hole, the final fate of
the system displays intriguing features, which depend on the initial
configurations, strengths of the perturbation, and specific metric parameters.
In addition to the scalarization process through which the bald black hole
addresses scalar hair, we observe the dynamical descalarization, which removes
scalar hair from an original hairy hole after continuous scalar field
accretion. We examine the temporal evolution of the scalar field, the metrics,
and the Misner-Sharp mass of the spacetime and exhibit rich phase structures
through nonlinear dynamical processes.Comment: 22 pages, 11 figure
Effect of Football Shoe Collar Type on Ankle Biomechanics and Dynamic Stability During Anterior and Lateral Single-Leg Jump Landings
In this study, we investigated the effects of football shoes with different collar heights on ankle biomechanics and dynamic postural stability. Fifteen healthy college football players performed anterior and lateral single-leg jump landings when wearing high collar, elastic collar, or low collar football shoes. The kinematics of lower limbs and ground reaction forces were collected by simultaneously using a stereo-photogrammetric system with markers (Vicon) and a force plate (Kistler). During the anterior single-leg jump landing, a high collar shoe resulted in a significantly smaller ankle dorsiflexion range of motion (ROM), compared to both elastic (p = 0.031, dz = 0.511) and low collar (p = 0.043, dz = 0.446) types, while also presenting lower total ankle sagittal ROM, compared to the low collar type (p = 0.023, dz = 0.756). Ankle joint stiffness was significantly greater for the high collar, compared to the elastic collar (p = 0.003, dz = 0.629) and low collar (p = 0.030, dz = 1.040). Medial-lateral stability was significantly improved with the high collar, compared to the low collar (p = 0.001, dz = 1.232). During the lateral single-leg jump landing, ankle inversion ROM (p = 0.028, dz = 0.615) and total ankle frontal ROM (p = 0.019, dz = 0.873) were significantly smaller for the high collar, compared to the elastic collar. The high collar also resulted in a significantly smaller total ankle sagittal ROM, compared to the low collar (p = 0.001, dz = 0.634). Therefore, the high collar shoe should be effective in decreasing the amount of ROM and increasing the dynamic stability, leading to high ankle joint stiffness due to differences in design and material characteristics of the collar types
Type I critical dynamical scalarization and descalarization in Einstein-Maxwell-scalar theory
We investigated the critical dynamical scalarization and descalarization of
black holes within the framework of the Einstein-Maxwell-scalar theory
featuring higher-order coupling functions. Both the critical scalarization and
descalarization displayed first-order phase transitions. When examining the
nonlinear dynamics near the threshold, we always observed critical solutions
that are linearly unstable static scalarized black holes. The critical
dynamical scalarization and descalarization share certain similarities with the
type I critical gravitational collapse. However, their initial configurations,
critical solutions, and final outcomes differ significantly. To provide further
insights into the dynamical results, we conducted a comparative analysis
involving static solutions and perturbative analysis.Comment: 38 pages, 12 figure
Nitrogen Doped Carbons Derived From Graphene Aerogel Templated Triazine-Based Conjugated Microporous Polymers for High-Performance Supercapacitors
Conjugated microporous polymers (CMPs) have attracted intensive attention owing to their permanent nanoporosity, large surface area and possibility for functionalization, however their application in energy storage suffers from poor conductivity and low hetero-atom content. Here, we demonstrate a hybrid of conjugated microporous polymers and graphene aerogel with improved conductivity. After treating at 800°C in NH3, the nitrogen content increases to 9.8%. The resulting microporous carbon exhibits a significant rise in supercapacitive performance up to 325 F g−1, 55% higher than pristine triazine-based CMPs, with energy density up to 12.95 Wh kg−1. Moreover, it has high stability with 99% retention after 10,000 cycles at 5 A g−1. The synergy of hierarchical porous structure, graphene-based conduction path and high percentage of hybridization with nitrogen ensures effective ion/electron transport and diffusion, making NH3-treated graphene aerogel/CMP hybrid a promising electrode material in high-performance supercapacitor
Nano-Subsidence Assisted Precise Integration of Patterned Two-Dimensional Materials for High-Performance Photodetector Arrays
The spatially precise integration of arrays of micro-patterned
two-dimensional (2D) crystals onto three-dimensionally structured Si/SiO
substrates represents an attractive strategy towards the low-cost
system-on-chip integration of extended functions in silicon microelectronics.
However, the reliable integration of the arrays of 2D materials on non-flat
surfaces has thus far proved extremely challenging due to their poor adhesion
to underlying substrates as ruled by weak van der Waals interactions. Here we
report on a novel fabrication method based on nano-subsidence which enables the
precise and reliable integration of the micro-patterned 2D materials/silicon
photodiode arrays exhibiting high uniformity. Our devices display peak
sensitivity as high as 0.35 A/W and external quantum efficiency (EQE) of ca.
90%, outperforming most commercial photodiodes. The nano-subsidence technique
opens a viable path to on-chip integrate 2D crystals onto silicon for
beyond-silicon microelectronics.Comment: 41 pages, 5 figures, with S
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