In this study, a three dimensional(3D) numerical model of six-degrees-of-freedom(6DOF) is applied to simulate the water entries of twin spheres side-by-side at different lateral distances and time intervals.The turbul...In this study, a three dimensional(3D) numerical model of six-degrees-of-freedom(6DOF) is applied to simulate the water entries of twin spheres side-by-side at different lateral distances and time intervals.The turbulence structure is described using the shear-stress transport k-ω(SST k-ω) model, and the volume of fluid(VOF) method is used to track the complex air-liquid interface. The motion of spheres during water entry is simulated using an independent overset grid. The numerical model is verified by comparing the cavity evolution results from simulations and experiments. Numerical results reveal that the time interval between the twin water entries evidently affects cavity expansion and contraction behaviors in the radial direction. However, this influence is significantly weakened by increasing the lateral distance between the two spheres. In synchronous water entries, pressure is reduced on the midline of two cavities during surface closure, which is directly related to the cavity volume. The evolution of vortexes inside the two cavities is analyzed using a velocity vector field, which is affected by the lateral distance and time interval of water entries.展开更多
This paper presents a novel experiment to observe the whole water entry process of a free-falling sphere into a regular wave.A time-accurate synchronizing system modulates the moment elaborately to ensure the sphere i...This paper presents a novel experiment to observe the whole water entry process of a free-falling sphere into a regular wave.A time-accurate synchronizing system modulates the moment elaborately to ensure the sphere impacting onto the water surface at the desirable wave phase.Four high-speed cameras focus locally to measure the high-precision size of the cavity evolution.Meanwhile,the aggregated field view of the camera array covers both the splash above the free surface and the entire cavity in the wave.The detailed methodologies are described and verified for the hardware set-up and the image post-processing.The theoretical maximum deviation is 1.7%on the space scale.The integral morphology of the cavity is captured precisely in the coordinate system during the sphere penetrates through the water at four representative wave phases and the still water.The result shows that the horizontal velocity of the fluid particle in the wave impels the cavity and changes the shape distinctly.Notably,the wave motion causes the cavity to pinch offearlier at the wave trough phase and later at the wave crest phase than in the still water.The wave motion influences the falling process of the sphere slightly in the present parameters.展开更多
The formation of axonal spheroid is a common feature following spinal cord injury.To further understand the source of Ca^(2+)that mediates axonal spheroid formation,we used our previously characterized ex vivo mouse s...The formation of axonal spheroid is a common feature following spinal cord injury.To further understand the source of Ca^(2+)that mediates axonal spheroid formation,we used our previously characterized ex vivo mouse spinal cord model that allows precise perturbation of extracellular Ca^(2+).We performed twophoton excitation imaging of spinal cords isolated from Thy1YFP+transgenic mice and applied the lipophilic dye,Nile red,to record dynamic changes in dorsal column axons and their myelin sheaths respectively.We selectively released Ca^(2+)from internal stores using the Ca^(2+)ionophore ionomycin in the presence or absence of external Ca^(2+).We reported that ionomycin dose-dependently induces pathological changes in myelin and pronounced axonal spheroid formation in the presence of normal 2 m M Ca^(2+)artificial cerebrospinal fluid.In contrast,removal of external Ca^(2+)significantly decreased ionomycin-induced myelin and axonal spheroid formation at 2 hours but not at 1 hour after treatment.Using mice that express a neuron-specific Ca^(2+)indicator in spinal cord axons,we confirmed that ionomycin induced significant increases in intra-axonal Ca^(2+),but not in the absence of external Ca^(2+).Periaxonal swelling and the resultant disruption in the axo-myelinic interface often precedes and is negatively correlated with axonal spheroid formation.Pretreatment with YM58483(500 n M),a well-established blocker of store-operated Ca^(2+)entry,significantly decreased myelin injury and axonal spheroid formation.Collectively,these data reveal that ionomycin-induced depletion of internal Ca^(2+)stores and subsequent external Ca^(2+)entry through store-operated Ca^(2+)entry contributes to pathological changes in myelin and axonal spheroid formation,providing new targets to protect central myelinated fibers.展开更多
We propose an eye-shaped keyboard for high-speed text entry in virtual reality (VR), having the shape of dual eyes with characters arranged along the curved eyelids, which ensures low density and short spacing of the ...We propose an eye-shaped keyboard for high-speed text entry in virtual reality (VR), having the shape of dual eyes with characters arranged along the curved eyelids, which ensures low density and short spacing of the keys. The eye-shaped keyboard references the QWERTY key sequence, allowing the users to benefit from their experience using the QWERTY keyboard. The user interacts with an eye-shaped keyboard using rays controlled with both the hands. A character can be entered in one step by moving the rays from the inner eye regions to regions of the characters. A high-speed auto-complete system was designed for the eye-shaped keyboard. We conducted a pilot study to determine the optimal parameters, and a user study to compare our eye-shaped keyboard with the QWERTY and circular keyboards. For beginners, the eye-shaped keyboard performed significantly more efficiently and accurately with less task load and hand movement than the circular keyboard. Compared with the QWERTY keyboard, the eye-shaped keyboard is more accurate and significantly reduces hand translation while maintaining similar efficiency. Finally, to evaluate the potential of eye-shaped keyboards, we conducted another user study. In this study, the participants were asked to type continuously for three days using the proposed eye-shaped keyboard, with two sessions per day. In each session, participants were asked to type for 20min, and then their typing performance was tested. The eye-shaped keyboard was proven to be efficient and promising, with an average speed of 19.89 words per minute (WPM) and mean uncorrected error rate of 1.939%. The maximum speed reached 24.97 WPM after six sessions and continued to increase.展开更多
为分析空心弹高速入水的机理及其特性,基于雷诺时均Navier-Stokes方程、VOF(volume of fluid)多相流模型、Realizable k-ε湍流模型,引入Schnerr-Sauer空化模型和重叠网格技术对空心弹高速入水进行数值模拟研究,获得了通孔孔径和头部形...为分析空心弹高速入水的机理及其特性,基于雷诺时均Navier-Stokes方程、VOF(volume of fluid)多相流模型、Realizable k-ε湍流模型,引入Schnerr-Sauer空化模型和重叠网格技术对空心弹高速入水进行数值模拟研究,获得了通孔孔径和头部形状对空心弹的空化特性、空泡形态和入水运动特性的影响规律。研究显示数值计算的空泡形态和入水速度、位移曲线与实验结果吻合较好,验证了数值模拟方法的可行性。结果表明:当通孔孔径不同时,通孔孔径越大,空化现象越明显,通孔射流越长,但对空泡半径的影响不大;通孔孔径越小,空泡闭合时间越早,与水面碰撞产生的阻力系数峰值越高,空心弹入水稳定后其阻力系数也越大;无量纲直径在0.575~0.600之间时,空心弹的运动最为稳定。当头部锥角不同时,头部锥角越大,空泡直径越大,空化现象出现得越晚,但空化生成的速度更快;随着头部锥角的增大,阻力系数变大,空心弹的速度衰减变快,相同时间运动的距离较短;头部锥角越大,俯仰角的变化越小,空心弹的运动越稳定。展开更多
基金China Academy of Launch Vehicle Technology(Grant No.CALT-2022-03)Science and Technology on Underwater Information and Control Laboratory(Grant No.2021-JCJQ-LB-030-05).
文摘In this study, a three dimensional(3D) numerical model of six-degrees-of-freedom(6DOF) is applied to simulate the water entries of twin spheres side-by-side at different lateral distances and time intervals.The turbulence structure is described using the shear-stress transport k-ω(SST k-ω) model, and the volume of fluid(VOF) method is used to track the complex air-liquid interface. The motion of spheres during water entry is simulated using an independent overset grid. The numerical model is verified by comparing the cavity evolution results from simulations and experiments. Numerical results reveal that the time interval between the twin water entries evidently affects cavity expansion and contraction behaviors in the radial direction. However, this influence is significantly weakened by increasing the lateral distance between the two spheres. In synchronous water entries, pressure is reduced on the midline of two cavities during surface closure, which is directly related to the cavity volume. The evolution of vortexes inside the two cavities is analyzed using a velocity vector field, which is affected by the lateral distance and time interval of water entries.
基金sponsored by the National Natural Sci-ence Foundation of China(Grant Nos.12102262,U22136010 and 11632012).
文摘This paper presents a novel experiment to observe the whole water entry process of a free-falling sphere into a regular wave.A time-accurate synchronizing system modulates the moment elaborately to ensure the sphere impacting onto the water surface at the desirable wave phase.Four high-speed cameras focus locally to measure the high-precision size of the cavity evolution.Meanwhile,the aggregated field view of the camera array covers both the splash above the free surface and the entire cavity in the wave.The detailed methodologies are described and verified for the hardware set-up and the image post-processing.The theoretical maximum deviation is 1.7%on the space scale.The integral morphology of the cavity is captured precisely in the coordinate system during the sphere penetrates through the water at four representative wave phases and the still water.The result shows that the horizontal velocity of the fluid particle in the wave impels the cavity and changes the shape distinctly.Notably,the wave motion causes the cavity to pinch offearlier at the wave trough phase and later at the wave crest phase than in the still water.The wave motion influences the falling process of the sphere slightly in the present parameters.
文摘The formation of axonal spheroid is a common feature following spinal cord injury.To further understand the source of Ca^(2+)that mediates axonal spheroid formation,we used our previously characterized ex vivo mouse spinal cord model that allows precise perturbation of extracellular Ca^(2+).We performed twophoton excitation imaging of spinal cords isolated from Thy1YFP+transgenic mice and applied the lipophilic dye,Nile red,to record dynamic changes in dorsal column axons and their myelin sheaths respectively.We selectively released Ca^(2+)from internal stores using the Ca^(2+)ionophore ionomycin in the presence or absence of external Ca^(2+).We reported that ionomycin dose-dependently induces pathological changes in myelin and pronounced axonal spheroid formation in the presence of normal 2 m M Ca^(2+)artificial cerebrospinal fluid.In contrast,removal of external Ca^(2+)significantly decreased ionomycin-induced myelin and axonal spheroid formation at 2 hours but not at 1 hour after treatment.Using mice that express a neuron-specific Ca^(2+)indicator in spinal cord axons,we confirmed that ionomycin induced significant increases in intra-axonal Ca^(2+),but not in the absence of external Ca^(2+).Periaxonal swelling and the resultant disruption in the axo-myelinic interface often precedes and is negatively correlated with axonal spheroid formation.Pretreatment with YM58483(500 n M),a well-established blocker of store-operated Ca^(2+)entry,significantly decreased myelin injury and axonal spheroid formation.Collectively,these data reveal that ionomycin-induced depletion of internal Ca^(2+)stores and subsequent external Ca^(2+)entry through store-operated Ca^(2+)entry contributes to pathological changes in myelin and axonal spheroid formation,providing new targets to protect central myelinated fibers.
文摘We propose an eye-shaped keyboard for high-speed text entry in virtual reality (VR), having the shape of dual eyes with characters arranged along the curved eyelids, which ensures low density and short spacing of the keys. The eye-shaped keyboard references the QWERTY key sequence, allowing the users to benefit from their experience using the QWERTY keyboard. The user interacts with an eye-shaped keyboard using rays controlled with both the hands. A character can be entered in one step by moving the rays from the inner eye regions to regions of the characters. A high-speed auto-complete system was designed for the eye-shaped keyboard. We conducted a pilot study to determine the optimal parameters, and a user study to compare our eye-shaped keyboard with the QWERTY and circular keyboards. For beginners, the eye-shaped keyboard performed significantly more efficiently and accurately with less task load and hand movement than the circular keyboard. Compared with the QWERTY keyboard, the eye-shaped keyboard is more accurate and significantly reduces hand translation while maintaining similar efficiency. Finally, to evaluate the potential of eye-shaped keyboards, we conducted another user study. In this study, the participants were asked to type continuously for three days using the proposed eye-shaped keyboard, with two sessions per day. In each session, participants were asked to type for 20min, and then their typing performance was tested. The eye-shaped keyboard was proven to be efficient and promising, with an average speed of 19.89 words per minute (WPM) and mean uncorrected error rate of 1.939%. The maximum speed reached 24.97 WPM after six sessions and continued to increase.
文摘为分析空心弹高速入水的机理及其特性,基于雷诺时均Navier-Stokes方程、VOF(volume of fluid)多相流模型、Realizable k-ε湍流模型,引入Schnerr-Sauer空化模型和重叠网格技术对空心弹高速入水进行数值模拟研究,获得了通孔孔径和头部形状对空心弹的空化特性、空泡形态和入水运动特性的影响规律。研究显示数值计算的空泡形态和入水速度、位移曲线与实验结果吻合较好,验证了数值模拟方法的可行性。结果表明:当通孔孔径不同时,通孔孔径越大,空化现象越明显,通孔射流越长,但对空泡半径的影响不大;通孔孔径越小,空泡闭合时间越早,与水面碰撞产生的阻力系数峰值越高,空心弹入水稳定后其阻力系数也越大;无量纲直径在0.575~0.600之间时,空心弹的运动最为稳定。当头部锥角不同时,头部锥角越大,空泡直径越大,空化现象出现得越晚,但空化生成的速度更快;随着头部锥角的增大,阻力系数变大,空心弹的速度衰减变快,相同时间运动的距离较短;头部锥角越大,俯仰角的变化越小,空心弹的运动越稳定。
