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The limited per-pixel bandwidth of most microscopy methods requires compromises between field of view, sampling density and imaging speed. This limitation constrains studies involving complex motion or fast cellular signaling, and presents a major bottleneck for high-throughput structural imaging. Here, we combine high-speed intensified camera technology with a versatile, reconfigurable and dramatically improved Swept, Confocally Aligned Planar Excitation (SCAPE) microscope design that can achieve high-resolution volumetric imaging at over 300 volumes per second and over 1.2 GHz pixel rates. We demonstrate near-isotropic sampling in freely moving Caenorhabditis elegans, and analyze real-time blood flow and calcium dynamics in the beating zebrafish heart. The same system also permits high-throughput structural imaging of mounted, intact, cleared and expanded samples. SCAPE 2.0’s significantly lower photodamage compared to point-scanning techniques is also confirmed. Our results demonstrate that SCAPE 2.0 is a powerful, yet accessible imaging platform for myriad emerging high-speed dynamic and high-throughput volumetric microscopy applications.

Super-resolution optoacoustic imaging of microvascular structures deep in mammalian tissues has so far been impeded by strong absorption from densely-packed red blood cells. Here we devised 5 µm biocompatible dichloromethane-based microdroplets exhibiting several orders of magnitude higher optical absorption than red blood cells at near-infrared wavelengths, thus enabling single-particle detection in vivo. We demonstrate non-invasive three-dimensional microangiography of the mouse brain beyond the acoustic diffraction limit (<20 µm resolution). Blood flow velocity quantification in microvascular networks and light fluence mapping was also accomplished. In mice affected by acute ischemic stroke, the multi-parametric multi-scale observations enabled by super-resolution and spectroscopic optoacoustic imaging revealed significant differences in microvascular density, flow and oxygen saturation in ipsi- and contra-lateral brain hemispheres. Given the sensitivity of optoacoustics to functional, metabolic and molecular events in living tissues, the new approach paves the way for non-invasive microscopic observations with unrivaled resolution, contrast and speed. Optoacoustic super-resolution at millimeter-scale depths has been impeded by the strong background absorption from blood cells. Here, the authors use dichloromethane microdroplets with high optical absorption and demonstrate 3D microangiography of the mouse brain via optoacoustic localization.

The tailward high‐speed flows, in which various kinetic processes and magnetic structures can be embedded, are usually produced by the magnetic reconnection in the Earth's magnetotail. Here, using high‐resolution measurements from the Magnetospheric Multiscale (MMS) mission, we report an intense current in the tailward high‐speed flow. The current density can reach ∼180 nA/m2 and is primarily carried by electrons. Taking advantage of the First‐Order Taylor Expansion (FOTE) method, we reveal that such an intense current is associated with a ribbon‐like magnetic structure. A large electric field, reaching ∼90 mV/m, is also observed at the magnetic structure. The Hall term dominates the electric field, however, the contribution from the pressure gradient term and the electron inertial term is nonnegligible and can lead to strong energy conversion (E  ⋅   J > 2 nW/m3) through the synergistic action with the intense current. This study improves the understanding of the current behaviors and energy conversion associated with magnetic structures in the Earth's magnetotail. Plain Language Summary As products of the magnetotail magnetic reconnection, the earthward and tailward high‐speed flows can be usually observed as associated with a variety of kinetic processes and magnetic structures. Here, for the first time, we report an electron‐carried intense current associated with a ribbon‐like magnetic structure in the tailward high‐speed flow, by using high‐resolution MMS data and the First‐Order Taylor Expansion (FOTE) method. Encountering a large electric field with a nonnegligible contribution from the pressure gradient term and electron inertial term, such intense current leads to a strong energy conversion at the ribbon‐like magnetic structure. This study shed light on how the intense current is associated with the ribbon‐like magnetic structure and how the strong energy conversion is driven at such a structure, which complements the knowledge of the energy conversion process in the Earth's magnetotail. Key Points An electron‐carried intense current (J > 180 nA/m2) is observed in association with a ribbon‐like structure in the tailward high‐speed flow A large electric field, with nonnegligible contribution from pressure gradient and electron inertial term, is observed at such a structure The intense current and large electric field work together to drive a strong energy conversion (E ⋅  J > 2 nW/m3) at this structure

In Earth’s low atmosphere, hurricanes are destructive due to their great size, strong spiral winds with shears, and intense rain/precipitation. However, disturbances resembling hurricanes have not been detected in Earth’s upper atmosphere. Here, we report a long-lasting space hurricane in the polar ionosphere and magnetosphere during low solar and otherwise low geomagnetic activity. This hurricane shows strong circular horizontal plasma flow with shears, a nearly zero-flow center, and a coincident cyclone-shaped aurora caused by strong electron precipitation associated with intense upward magnetic field-aligned currents. Near the center, precipitating electrons were substantially accelerated to ~10 keV. The hurricane imparted large energy and momentum deposition into the ionosphere despite otherwise extremely quiet conditions. The observations and simulations reveal that the space hurricane is generated by steady high-latitude lobe magnetic reconnection and current continuity during a several hour period of northward interplanetary magnetic field and very low solar wind density and speed. Hurricanes in the Earth’s low atmosphere are known, but not detected in the upper atmosphere earlier. Here, the authors show a long-lasting hurricane in the polar ionosphere and magnetosphere with large energy and momentum deposition despite otherwise extremely quiet conditions.

The science of cities aims to model urban phenomena as aggregate properties that are functions of a system’s variables. Following this line of research, this study seeks to combine two well-known approaches in network and transportation science: (i) The macroscopic fundamental diagram (MFD), which examines the characteristics of urban traffic flow at the network level, including the relationship between flow, density, and speed. (ii) Percolation theory, which investigates the topological and dynamical aspects of complex networks, including traffic networks. Combining these two approaches, we find that the maximum number of congested clusters and the maximum MFD flow occur at the same moment, precluding network percolation (i.e. traffic collapse). These insights describe the transition of the average network flow from the uncongested phase to the congested phase in parallel with the percolation transition from sporadic congested links to a large, congested cluster of links. These results can help to better understand network resilience and the mechanisms behind the propagation of traffic congestion and the resulting traffic collapse. This study analyzes the way car traffic networks collapse by connecting classical traffic flow descriptors with percolation theory: The maximum average car traffic flow in a network and the maximum number of congested clusters occur at the same moment, precluding the network percolation.

This study focuses on assessing pedestrian walking characteristics on sidewalks. The fundamental relationships of flow - speed - density were investigated and analysed in Samawah city. The video recording method was implemented to observe pedestrian characteristics such as flow and speed at four survey sites. These data were used to develop mathematical models that figure the aforementioned relationships. To obtain the best fitting of each relationship, the coefficient of determination R2 was calculated. The results of this study were compared with the other research outputs. Finally, the level of service boundaries for pedestrians' movements on sidewalks were defined.

When a ballistic missile re-enters the atmosphere at hypersonic speed, the warhead and the incoming flow have a violent effect, resulting in a rapid increase in the air temperature of the surrounding flow field, and the persistent high temperature will make the optical window of the ballistic laser fuzes appear ablation phenomenon, which seriously affects the ranging accuracy of the laser detection system. In this paper, the optical window of the laser fuze is taken as the research object, quartz glass is chosen as the optical window material, and the thermal response of the optical window of the laser fuze detection system is numerically simulated according to the heat flux density parameter of the ballistic missile when it re-enters the atmosphere. The simulation results show that the quartz glass as the optical window has good ablation resistance and thermal insulation performance.

Owing to its mathematical elegance and empirical accuracy, the speed-density model is critical in solving macroscopic traffic problems. This study developed an improved general-logistic-based speed-density model, which is a new method in macroscopic traffic flow theory. This article extensively discusses the properties of the general-logistic-based speed-density model. The physical meanings and values of all the parameters were determined based on the effect of heavy vehicles and the method for the linear and nonlinear regression analysis. The accuracy and versatility of the developed model were also found to be excellent based on the field data and relative error.

Nominally zero-pressure-gradient fully developed flat-plate turbulent boundary layers with heated and unheated isothermal walls at supercritical pressures are studied by solving the full compressible Navier–Stokes equations using direct numerical simulation. With a heated isothermal wall, the wall temperature sets such that the flow temperature varies through the pseudo-critical temperature, and thus pseudo-boiling phenomena occur within the boundary layers. The pseudo-boiling process induces strongly nonlinear real-fluid effects in the flow and interacts with near-wall turbulence. The peculiar abrupt density variations through the pseudo-boiling process induce significant near-wall density fluctuations $\\sqrt{\\overline{\\unicode[STIX]{x1D70C}^{\\prime }\\unicode[STIX]{x1D70C}^{\\prime }}}/\\overline{\\unicode[STIX]{x1D70C}}\\approx 0.4{-}1.0$ within the heated transcritical turbulent boundary layers. The large near-wall density fluctuations induce a turbulent mass flux $\\unicode[STIX]{x1D70C}^{\\prime }u_{i}^{\\prime }$ , and the turbulent mass flux amplifies the Favre-averaged velocity fluctuations $u_{i}^{\\prime \\prime }$ in the near-wall predominant structures of streamwise low-speed streaks that are associated with the ejection (where $u^{\\prime \\prime }<0$ and $v^{\\prime \\prime }>0$ ), while reducing the velocity fluctuations in the high-speed streaks associated with the sweep ( $u^{\\prime \\prime }>0$ and $v^{\\prime \\prime }<0$ ). Although the near-wall low-speed and high-speed streak structures dominate the Reynolds-shear-stress generation, the energized Favre-averaged velocity fluctuations in the low-speed streaks enhance both the mean-density- and density-fluctuation-related Reynolds shear stresses ( $-\\overline{\\unicode[STIX]{x1D70C}}\\overline{u^{\\prime \\prime }v^{\\prime \\prime }}$ and $-\\overline{\\unicode[STIX]{x1D70C}^{\\prime }u^{\\prime \\prime }v^{\\prime \\prime }}$ ) in the ejection event and, as a result, alter the Reynolds-shear-stress profile. The large density fluctuations also alter the near-wall viscous-stress profile and induce a near-wall convective flux $-\\overline{\\unicode[STIX]{x1D70C}}\\widetilde{u}\\widetilde{v}$ (due to non-zero $\\widetilde{v}$ ). The changes in the contributions in the stress-balance equation result in a failure of existing velocity transformations to collapse to the universal law of the wall. The large density fluctuations also greatly contribute to the turbulent kinetic energy budget, and especially the mass flux contribution term becomes noticeable as one of the main positive terms. The unheated non-transcritical turbulent boundary layers show a negligible contribution of the real-fluid effects, and the turbulence statistics agree well with the statistics of an incompressible constant-property turbulent boundary layer with a perfect-gas law.

We present a theoretical asymptotic solution for high-speed transient flow through microporous media in this work by addressing the inertia effect in the high-pressure-difference pulse-decay process. The capillaric model is adopted, in which a bundle of straight circular tubes with a high length–radius ratio is used to represent the internal flow paths of microporous media so that the flow is described by a simplified incompressible Navier–Stokes equation based on the mean density, capturing the major characteristics of mass flow rate. By order-of-magnitude analysis and asymptotic perturbation, the inertial solution with its dimensionless criterion for the high-pressure-difference pulse-decay process is derived. To be compared with experimental data, the theoretical solution involves all three related effects, including the inertia effect, the slippage effect and the compressibility effect. A self-built experimental platform is therefore established to measure the permeability of microporous media by both pulse-decay and steady-state methods to validate the theoretical solution. The results indicate that the relative difference between two methods is less than 30 % even for permeability at as low as $48.2$ nD $(10^{-21}\\,{\\rm m}^2)$, and the present theoretical solution can accurately capture the inertia effect in the high-pressure-difference pulse-decay process, which significantly accelerates the measurements for ultra-low-permeability samples.