Numerical study on the cavity dynamics for vertical water entries of twin spheres

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.

Roles of host proteases in the entry of SARS-CoV-2

The spike protein(S)of SARS-CoV-2 is responsible for viral attachment and entry,thus a major factor for host suscep-tibility,tissue tropism,virulence and pathogenicity.The S is divided with S1 and S2 region,and the S1 contains the receptor-binding domain(RBD),while the S2 contains the hydrophobic fusion domain for the entry into the host cell.Numerous host proteases have been implicated in the activation of SARS-CoV-2 S through various c leavage sites.In this article,we review host proteases including furin,trypsin,transmembrane protease serine 2(TMPRSS2)and cathepsins in the activation of SARS-CoV-2 S.Many betacoronaviruses including SARS-CoV-2 have polybasic residues at the S1/S2 site which is subjected to the cleavage by furin.The S1/S2 cleavage facilitates more assessable RBD to the receptor ACE2,and the binding triggers further conformational changes and exposure of the S2'site to proteases such as type Il transmembrane serine proteases(TTPRs)including TMPRSS2.In the presence of TMPRSS2 on the target cells,SARS-CoV-2 can utilize a direct entry route by fusion of the viral envelope to the cellular membrane.In the absence of TMPRSS2,SARS-CoV-2 enter target cells via endosomes where multiple cathepsins cleave the S for the successful entry.Additional host proteases involved in the cleavage of the S were discussed.This article also includes roles of 3C-like protease inhibitors which have inhibitory activity against cathepsin L in the entry of SARS-CoV-2,and discussed the dual roles of such inhibitors in virus replication.

Application of Thermodynamic Database to Corrosion of ZrO_(2) Containing Submerged Entry Nozzle in Steel Continuous Casting Process

The CALPHAD thermodynamic databases are very useful to analyze the complex chemical reactions happening in high temperature material process.The FactSage thermodynamic database can be used to calculate complex phase diagrams and equilibrium phases involving refractories in industrial process.In this study,the FactSage thermodynamic database relevant to ZrO_(2)-based refractories was reviewed and the application of the database to understanding the corrosion of continuous casting nozzle refractories in steelmaking was presented.

Experimental observation on water entry of a sphere in regular wave

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.

Ca^(2+)-induced myelin pathology precedes axonal spheroid formation and is mediated in part by store-operated Ca^(2+)entry after spinal cord injury

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.

Eye-shaped keyboard for dual-hand text entry in virtual reality

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.

切顶沿空留巷充填体—矸石协同承载机理及控制技术研究

针对深部沿空留巷顶底板移近量大、充填体大变形破坏失稳等问题,采用数值模拟和现场实践相结合的方法,分析了传统沿空留巷和切顶卸压协同承载沿空留巷围岩应力演化规律和变形特征,揭示了切顶沿空留巷充填体—矸石协同承载机理。在此基础上,以朱庄煤矿Ⅲ635工作面沿空留巷为工程背景,提出了一种巷旁充填体—矸石组合结构体协同承载的切顶卸压沿空留巷技术,建立充填体—矸石协同支撑顶板力学模型、推导出顶板挠度方程,并进行工程应用。数值模拟结果表明:采用切顶卸压协同承载沿空留巷技术后,实体煤帮和充填体的垂直应力峰值分别降低了28.3%、44.4%,巷道顶底板移近量降低了58.2%。现场应用结果表明:采用该技术后,顶底板和两帮移近量分别为382.9、253.6 mm,工作面支架平均支撑力下降了45.3%,有效控制了巷道变形。可为类似条件下沿空留巷围岩控制提供参考。

跨介质航行器入水流固耦合特性研究综述

本文综述了跨介质航行器入水问题的研究进展,特别关注了入水流固耦合特性、弹性体结构入水冲击以及高速入水现象。入水过程涉及复杂的流体动力学现象,包括空泡形成、冲击载荷以及与航行体动力学特性的相互作用,这些因素都对航行器的设计和性能产生重大影响。本文讨论了跨介质航行器的基本概念,其具有独特的战略应用价值。入水过程中的关键挑战包括处理巨大的冲击载荷和复杂的流体动力学特性,这要求对航行器的形状、入水速度和入水姿态进行精密控制以优化性能。针对不同形状的航行体如何影响冲击响应和空泡动态,详细介绍了通过高速摄影和传感器技术在不同条件下进行的入水试验,这些试验帮助研究学者观察并分析了入水过程中的空泡形成、流体喷射以及随后的空泡闭合等现象。随着计算技术的进步,人们开始使用仿真技术研究多相流动和航行体结构的相互作用。总之,跨介质航行器的入水研究是一个多学科交叉的研究。通过深入理解入水过程中的物理现象和力学响应,可以为未来航行器的设计和操作提供科学依据,推动海空一体化航行器技术的发展。

贵州沿空留巷支护技术的分析与改进

针对贵州某煤矿沿空留巷在原有支护条件下,靠上帮一侧顶板以及下帮底角的岩层变形破坏较严重的情况,对巷道支护方式进行改进。利用数值模拟软件,对改进支护后的巷道围岩变形破坏情况进行分析。研究发现:改进支护后的巷道围岩变形破坏情况得到明显改善,改进后的支护方式能够较好地阻滞巷道上帮一侧顶板和下帮底角的岩层严重变形破坏,从而保持巷道围岩的完整性和稳定性,研究可为类似条件矿井沿空留巷的支护方式提供参考。

多层坚硬顶板特厚煤层综放工作面小煤柱护巷技术

为研究小煤柱护巷巷道的稳定性及其阻隔同层位邻近采空区灾害的特征,以大同矿区石炭系坚硬顶板特厚煤层开采为工程背景,采用理论分析、实验研究、数值模拟等研究方法,从小煤柱护巷巷道的稳定性和其是否具有阻隔同层位邻近采空区有害气体能力2个角度,综合分析小煤柱的合理尺寸及其在不同采动阶段渗透率的演化特征。针对同忻煤矿石炭系煤层8210工作面沿空掘巷小煤柱开采具体的开采条件,建立了双关键层采场内外应力场叠加的力学模型,推导出双关键层条件下沿空掘巷小煤柱合理尺寸的计算关系式,理论确定8210工作面小煤柱合理尺寸为6.0 m;应用DJG–Ⅱ型煤岩渗流测试装备,研究不同采动阶段小煤柱渗透率演化特征,试验确定在第3采动阶段小煤柱渗透率较初始渗透率增大了23倍,该阶段小煤柱基本失去了阻隔邻近采空区有害气体的能力。根据理论研究结果,现场选取6 m小煤柱进行工业性试验;根据试验研究结果,开采试验过程中对小煤柱进行了改性降透措施,在小煤柱表面及顶板距煤柱帮1500 mm范围内喷射厚层混凝土(100 mm)。实践表明:工作面回采过程中小煤柱护巷的回采巷道发生了一定的变形量,但是巷道变形在安全可控范围之内,巷道稳定,可实现安全回采;开采过程中8210工作面上隅角CH4气体浓度远低于邻近8305工作面采空区CH4气体浓度,表明小煤柱经过改性降透后具备了阻隔同层位邻近采空区有害气体的能力;开采实践也进一步验证了理论和试验研究成果的合理性和科学性。研究成果可以为类似条件下小煤柱护巷技术的推广应用提供参考。

空心弹高速入水机理及特性数值模拟研究

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。

民机典型机身框段垂直入水冲击特性研究

为了研究民机典型机身框段垂直入水冲击特性,采用入水冲击试验系统开展不同高度下的圆柱体入水冲击试验,研究其入水冲击响应;基于LS-DYNA任意拉格朗日-欧拉(arbitrary Lagrange-Euler,ALE)方法建立流体域均匀网格及局部加密网格模型,通过对比圆柱体入水冲击试验结果验证网格收敛性及流体域模型;基于验证的流体域模型及机身框段模型,研究机身框段在6.02 m/s速度下的入水冲击特性,并分析与刚性地面冲击特性的差异性以及不同入水冲击速度下的机身框段冲击响应特性。结果表明:ALE方法在结构入水冲击方面具有较高的模拟精度,且采用局部加密网格时可以极大减少流体域模型网格数量和入水冲击计算时间。机身框段入水冲击时的失效模式与刚性地面冲击时的失效模式较为一致,但机身框段结构整体变形程度减小,客舱地板横梁变形程度增大;机身框仍是吸能最多的部件,但水也吸收了大量的冲击能量,使得地板导轨处的加速度始终小于刚性地面冲击时的加速度;随着机身框段入水冲击速度的增大,机身框发生弯折和上翘的程度加剧。

深部沿空巷道锚固围岩破坏失稳能量驱动机理

深部沿空巷道受侧向顶板断裂所产生的动载影响,锚固围岩易产生大变形,甚至破坏失稳。以山东省孙村煤矿31120工作面上平巷为工程背景,首先采用YTJ20型岩层探测记录仪获得了锚固顶板裂隙发育规律及以脆性张裂破坏为主的破坏方式。然后,通过相似材料模拟试验方法获得了深部沿空巷道侧向顶板前期、过渡期和后期3个运动阶段典型特征,并分析了不同阶段锚固围岩破裂演化及能量释放规律;其中过渡期运动阶段锚固围岩内部应力、变形量急剧增大,裂隙发育明显,能量释放显著,对沿空巷道锚固围岩稳定性影响最大。最后,构建了侧向顶板断裂运动下沿空巷道结构力学模型,给出了锚固围岩输入能量与可抵抗能量定量计算方法,揭示了侧向顶板断裂诱发锚固围岩破坏失稳能量驱动机理,并定义了失稳能量判据,即当作用在沿空巷道锚固围岩上的能量大于锚固围岩可抵抗能量时,将发生破坏失稳。进一步地,提出了锚固围岩失稳风险等级划分方法和相应地控制技术,计算结果表明,31120工作面沿空巷道锚固围岩失稳风险等级为中风险。采取加强支护措施后,沿空巷道顶底板及两帮移近量分别减小35.47%和35.71%,锚索受力减小23.43%,变形速度明显降低,锚固围岩能量积聚程度减小。

谈谈语言组合整体观对词典释义的促进作用——以《现代汉语词典》对“方便、活泛、口子、有”等条目修订为例

辞书编纂理念决定辞书编纂水平,辞书编修要以先进的语言学理论做指导。文章以《现代汉语词典》对“方便、活泛、口子、有”等条目的修订为例,讨论如何通过具体的释义和括注来解决一个组合的整体意义和各组成成分意义之间的关系问题,从而说明词汇语义学中的“组合整体观”对词典释义的促进作用。

入水速度对冰孔约束下圆柱体倾斜入水过程的影响分析

针对极地环境下超空泡圆柱体入水问题,基于雷诺平均方程引入流体体积模型,结合重叠网格技术建立了冰孔约束下圆柱体入水数值仿真方法。在此基础上,开展不同入水速度下圆柱体穿越冰孔入水过程仿真,分析了圆柱体入水过程中的空泡演化与载荷特性。研究结果表明:冰孔约束限制了孔内水域的流动,进而改变了表面喷溅的状态及空泡壁的形态,以至延迟了空泡表面闭合时间。随着入水速度的增大,冰孔约束对空泡形态的限制作用基本一致,圆柱体头部出现了更大范围的高压区域,且呈现出非对称分布;冰孔约束增大了圆柱体入水冲击载荷,使得圆柱体水下速度加快衰减,并促使圆柱体偏转角度大于无冰工况。研究结果可为极地超空泡武器入水稳定性提供参考。

火星探测器进入过程防热层温度测量方法

火星探测器进入过程中的防热层烧蚀温度是防热结构设计和气动热环境辨识的关键参数之一。为了满足防热层温度在轨测量的需求,提出采用柱塞式结构大底分层测温探头和U形结构背罩测温探头,与电缆和多通道温度变换器共同组成温度传感器进行在轨测温的方法。设计内容包括测温探头热电偶元件选取、结构形式和安装方式,以及信号集中放大变换和自动冷端补偿等。开展全量程标定和风洞专项试验验证,证明所设计的温度传感器可以实现1300℃以下烧蚀温度变化全过程测量,测量精度达到0.28%。该温度传感器已在我国首次火星探测任务“天问一号”探测器的着陆巡视器上成功应用,可为进/再入航天器烧蚀温度在轨测量的实施提供借鉴和参考。

跨国公司东道国和母国制度距离对企业创新绩效的影响——基于上市公司数据的实证分析

基于制度理论和行为者能动性视角,研究跨国公司东道国和母国制度距离如何对企业创新绩效产生不对称的影响,并考察企业政治关联和海外进入模式的调节作用。研究发现,正向制度距离对企业创新绩效产生正向影响,而负向制度距离越大,越不利于企业创新绩效提高;与没有政治关联的企业相比,企业具有政治关联则使得正向制度距离与企业创新绩效之间的正相关关系降低,并削弱了负向制度距离对企业创新绩效的负向影响;此外,企业选择跨国并购或绿地新建的进入模式也会调节制度距离方向与企业创新绩效之间的关系。研究结论不仅丰富了制度距离视角下企业创新绩效的研究,而且为政府制定相关政策和企业国际化决策提供了有益的实践启示。

高速跨介质入水多相流动与流固耦合特性研究综述

高速跨介质入水问题广泛存在于海洋工程、航空航天等领域,入水多相流动与流固耦合作用机理是该领域的研究热点,对于跨介质航行器的载荷预报、弹道稳定性评估、结构强度校核以及安全性设计等具有重要意义。本文围绕高速跨介质入水所涉及的基础关键力学问题,重点论述了高速跨介质多相流动与空泡演化、冲击载荷与降载方法、运动稳定性与流固耦合响应、流固耦合数值研究方法等方面的研究现状,并针对目前仍存在的问题提出了建议,旨在为高速跨介质入水的相关研究与设计等提供参考。

外资进入与女性就业——基于就业率和性别工资差距的双重视角

在中国性别就业差异逐渐扩大的背景下,探讨吸引和利用外商直接投资能否为提高女性就业比例和缩小性别工资差距提供新的动力,对实现中国劳动力市场性别平等、共享对外开放成果至关重要。基于1998~2021年中国省际面板数据和中国家庭收入调查数据库,从就业率和性别工资差距的双重视角出发,实证分析外资进入对中国女性就业的影响及其机制,并考察外资进入速度的调节效应。研究结果表明,外资进入能够提高女性就业率和缩小性别工资差距。异质性分析表明,以独资方式进入的外商直接投资和来自欧美国家的外商直接投资更有助于提高女性就业率和缩小性别工资差距;同时,外资进入对女性就业的积极作用在私营内资企业、高性别平等化地区、东部地区以及第三产业中影响更大。影响机制结果表明,增加市场竞争程度和促进技术进步是外资进入能够提高女性就业率和缩小性别工资差距的主要渠道。从调节效应上看,过快的外资进入速度减缓了外资进入对提高女性就业率和缩小性别工资差距的积极影响。因此,应通过完善市场竞争机制、提高企业技术水平、合理把控外资进入速度等措施,充分发挥外资进入对提高女性就业率和缩小性别工资差距的重要作用。研究结果为促进女性共享对外开放成果和经济可持续发展提供了新思路。

ADAFT:SDN大规模流表的适应性深度聚合存储架构

为解决软件定义网络(SDN)数据平面中的三态内容可寻址存储器(TCAM)资源紧张问题,提出了一种基于内容表项树的SDN流表深度聚合方法,进而构建一种SDN大规模流表的适应性深度聚合存储架构ADAFT。该架构放宽了聚合表项之间的汉明距离要求,构建内容表项树聚合动作集不同的流表项,显著提高了流表聚合程度。设计了一种TCAM装载率感知的内容表项树动态限高机制,以降低流表查找开销。同时,提出了一种TCAM装载率感知的表项聚合适应性选择策略,以均衡流表聚合程度和查找开销。实验结果表明,ADAFT架构的流表压缩率明显高于现有方法,最高可达65.74%。