Dense Stream Research Articles

Transient Glimpses: Unveiling Occluded Backgrounds through the Spike Camera

The de-occlusion problem, involving extracting clear background images by removing foreground occlusions, holds significant practical importance but poses considerable challenges. Most current research predominantly focuses on generating discrete images from calibrated camera arrays, but this approach often struggles with dense occlusions and fast motions due to limited perspectives and motion blur. To overcome these limitations, an effective solution requires the integration of multi-view visual information. The spike camera, as an innovative neuromorphic sensor, shows promise with its ultra-high temporal resolution and dynamic range. In this study, we propose a novel approach that utilizes a single spike camera for continuous multi-view imaging to address occlusion removal. By rapidly moving the spike camera, we capture a dense stream of spikes from occluded scenes. Our model, SpkOccNet, processes these spikes by integrating multi-view spatial-temporal information via long-short-window feature extractor (LSW) and employs a novel cross-view mutual attention-based module (CVA) for effective fusion and refinement. Additionally, to facilitate research in occlusion removal, we introduce the S-OCC dataset, which consists of real-world spike-based data. Experimental results demonstrate the efficiency and generalization capabilities of our model in effectively removing dense occlusions across diverse scenes. Public project page: https://github.com/Leozhangjiyuan/SpikeDeOcclusion.

Experimental study of a dense stream of particles impacting on an inclined surface

We present measurements of the impact process of gravity-driven flows of particles against inclined surfaces for a range of particle loadings in the four-way coupled regime. These were investigated with particle image velocimetry (PIV) for a range of particle curtain thicknesses, volume fractions, velocities and mass flow rates using a series of hoppers of various aperture sizes, following impact on a steel plate at a range of angles from 15° to 75°. In addition, micro-shadowgraphy was used to provide new details of the region of impact, providing the first direct evidence of the formation of layer of particles that slide along the surface for sufficiently high particle volume fractions. Statistical measurements of particle impact and rebound velocities, together with rebound angle and coefficient of restitution, were obtained from the PIV analysis, which revealed that an increase in particle loading leads to increase in the probability that a layer of particles at the surface is formed at the point of impact. This layer acts to absorb energy for all impact angles, thereby influencing the rebound processes. For impact angles close to the normal direction the layer also increases the range of rebound angles, while it causes particles to slide along the surface as a chute-like flow for large inclination angles.

Portable platform for leukocyte extraction from blood using sheath-free microfluidic DLD.

Leukocyte count is routinely performed for diagnostic purposes and is rapidly emerging as a significant biomarker for a wide array of diseases. Additionally, leukocytes have demonstrated considerable promise in novel cell-based immunotherapies. However, the direct retrieval of leukocytes from whole blood is a significant challenge due to their low abundance compared to erythrocytes. Here, we introduce a microfluidic-based platform that isolates and recovers leukocytes from diluted whole blood in a single step. Our platform utilizes a novel, sheathless method to initially sediment and focus blood cells into a dense stream while flowing through a tubing before entering the microfluidic device. A hexagonal-shaped structure, patterned at the device's inlet, directs all the blood cells against the channel's outer walls. The focused cells are then separated based on their size using the deterministic lateral displacement (DLD) microfluidic technique. We evaluated various parameters that could influence leukocyte separation, including different focusing structures (assessed both computationally and experimentally), the orientation of the tubing-chip interface, the effects of blood sample hematocrit (dilution), and flow rate. Our device demonstrated the ability to isolate leukocytes from diluted blood with a separation efficiency of 100%, a recovery rate of 76%, and a purity of 80%, while maintaining a cell viability of 98%. The device operates for over 30 min at a flow rate of 2 μL min-1. Furthermore, we developed a handheld pressure controller to drive fluid flow, enhancing the operability of our platform outside of central laboratories and enabling near-patient testing. Our platform can be integrated with downstream cell-based assays and analytical methods that require high leukocyte purity (80%), ranging from cell counting to diagnostics and cell culture applications.

Scalable Data Concentrator with Baseline Interconnection Network for Triggerless Data Acquisition Systems

Triggerless data acquisition systems (DAQs) require that the data stream is transmitted from multiple links and into the processing node. The short input data words must be concentrated and packed into the longer bit vectors the output interface (e.g., PCI Express) uses. In that process, the unneeded data must be eliminated, and a dense stream of useful DAQ data must be created. Additionally, the time order of the data should be preserved. This paper presents a new solution using the Baseline Network with Reversed Outputs (BNRO) for high-speed data routing. A thorough analysis of the network’s operation enabled increased scalability compared to the previously published concentrator based on an 8 × 8 network. The solution may be scaled by adding additional layers to the BNRO network while minimizing resource consumption. Simulations were performed for four and five layers (16 and 32 inputs). The FPGA implementation and tests in the actual hardware were successfully performed for 16 inputs. The pipeline registers may be added in each layer independently, shortening the critical path and increasing the maximum acceptable clock frequency.

CFFR-Net: A channel-wise features fusion and recalibration network for surgical instruments segmentation

Surgical instrument segmentation plays a crucial role in robot-assisted surgery by furnishing essential information about instrument location and orientation. This information not only enhances surgical planning but also augments the precision and safety of procedures. Despite promising strides in recent research on surgical instrument segmentation, accuracy still faces obstacles due to local feature processing limitations, surgical environment complexity, and instrument morphological variability. To address these challenges, we introduced the channel-wise features fusion and recalibration network (CFFR-Net). This network utilizes a dual-stream mechanism, combining a context-guided block and dense block for feature extraction. The context-guided block captures a variety of contextual information by using different dilation rates. Additionally, CFFR-Net employs a fusion mechanism that harmonizes context-guided and dense streams. This integration, along with the inclusion of Squeeze-and-Excitation attention, enhances both the precision and robustness of semantic instrument segmentation.We performed experiments using two publicly available datasets for surgical instrument segmentation: the Kvasir-instrument and Endovis2017 datasets. The results of these experiments were highly encouraging, as our proposed model exhibited remarkable performance on both datasets compared to the state-of-the-art methods. On the Kvasir-instrument set, our model achieved a Dice score of 95.84% and mean intersection over union (mIOU) value of 92.40%. Similarly, on the Endovis2017 set, it obtained a Dice score of 95.47% and mIOU value of 93.02%.

Establishing the conditions for the formation of a near-wall layer of solid granular fill of a rotating drum

This paper reports the assessment of the influence of dynamic motion parameters on the formation and disappearance at the cylindrical surface of the chamber of the rotating drum of the near-wall layer of non-loose granular fill. Based on the results of experimental visualization of the flow, the effect of solidity on the behavior of granular fill was revealed. The hydrodynamic effect of fill quasi-liquefaction under the action of solidity has been established, which involves the occurrence of a connecting interaction between adjacent layers and the surface of the chamber. Conversion of shear circulation flow to homogeneous dense clustered stream with slipping and rolling without relative movement of particles was detected. The hydrodynamic characteristics of circulation flow transition to the near-wall layer mode during rotation acceleration have been defined. Such a transition is implemented by smoothly increasing the thickness of the layer when the rest of the fill is circulated at the bottom of the chamber. The effect of the rheological hysteresis of the movement of the rotating chamber fill, caused by quasi-liquefaction of non-loose granular environment, has been established. The effect implies exceeding the speed limit ωfl in the formation of a near-wall layer, at rotation acceleration, above the boundary ωdl of the layer disappearance when the rotation slows down. The manifestation of hysteresis mainly increases with an increase in Reynolds number. The intensity of increased hysteresis manifestation increases with a decrease in the degree of filling the chamber. The value of the Froud number for the ωfl and ωdl boundaries increases with the increase in Re. It has been established that at the relative particle size of the dispersed fill ψdc≈(0.065–1.04)·10‑3 and Re=30–500, Fr=1–2.9, for the ωfl boundary, and Fr=0.5–1.4, for the ωdl boundary. The Fr value for the ωfl limit was found to exceed this value for the ωdl boundary by 1.6–2.1 times. The established effects make it possible to substantiate the rational parameters for the grinding process in drum-roll mills

Concept to recognize crisis of organizational and institutional separation by Artificial Intelligence System

The sphere of anti-crisis management is highlighted in relation to the open variety of organizational and institutional separations that are typical for the higher forms of industrial and post-industrial economies. This article shows the typicity and relevance of critical management situations associated with the emergence of crises. Furthermore, it justifies the objective orientation to a dense (not sparse) stream of crisis situations requiring identification, ranking, and classification. A strict management interpretation of the separation crisis is given through an assessment of the nature of the dynamics of the separation state indexes. Also, the document presents a generalized typological classification of crises. This article shows the necessity of using a high-level Artificial Intelligence System for this purpose, an indispensable component of which is the classification component.

Applicability of the VisiSize D30 shadowgraph system for cloud microphysical measurements

Abstract. A commercial shadowgraph system, the Oxford Lasers VisiSize D30, originally designed to characterize industrial and agricultural sprays, was tested with respect to its application for measuring cloud microphysical properties such as droplet size distribution and number concentration. A laboratory experiment with a dense stream of polydisperse cloud-like droplets indicated a strong dependence of the depth of field, and thus also the sample volume, on particle size. This relationship was determined and a suitable correction method was developed to improve estimations of droplet number concentration and size distribution. The spatial homogeneity of the detection probability inside the sample volume and the minimum droplet diameter providing uniform detection were examined. A second experiment with monodisperse droplets produced by a Flow Focusing Monodisperse Aerosol Generator (FMAG) verified the sizing accuracy and demonstrated reasonable agreement between the instruments. Effects of collisions and the evaporation of droplets produced by the FMAG were observed. Finally, when the instrument was applied to sample atmospheric clouds at a mountain-based observatory, it performed reliably during a 3-week-long field experiment. Based on the laboratory and field tests, recommendations concerning the use of the instrument for cloud droplet measurements were formulated.

Oort cloud Ecology

We simulate the formation and evolution of Oort clouds around the 200 nearest stars (within ∼16 pc according to theGaiaDR2) database. This study is performed by numerically integrating the planets and minor bodies in orbit around the parent star and in the Galactic potential. The calculations start 1 Gyr ago and continue for 100 Myr into the future. In this time frame, we simulate how asteroids (and planets) are ejected from the vicinity of the stars and settle in an Oort cloud and how they escape the local stellar gravity to form tidal streams. A fraction of 0.0098 to 0.026 of the asteroids remain bound to their parent star. The orbits of these asteroids isotropize and circularize because of the influence of the Galactic tidal field and eventually form an Oort cloud between ∼104and ∼2 × 105au. We estimate that ≲6% of the nearby stars may have a planet in their Oort cloud. The majority of asteroids (and some of the planets) become unbound from their parent star to become free floating in the Galactic potential. These interstellar asteroids remain in a similar orbit around the Galactic center to their host star, forming dense streams of rogue interstellar asteroids and planets. The Solar System occasionally passes through such tidal streams, potentially giving rise to occasional close encounters with objects in this stream. Two recently discovered sources, 1I/(2017 Q3) ’Oumuamua and 2I/(2019 Q4) Borisov, may be such objects. Although the direction from which an individual object originated cannot easily be traced back to the original host, multiple such objects coming from the same source might help to identify their origin. Currently, the Solar System is in the bow or wake of the tidal stream of approximately ten of the nearby stars, which might contribute considerably to the interaction rate. Overall, we estimate that the local density of such leftovers from the planet-formation process contributes to a local density of 1.2 × 1014per pc−3, or ≳0.1 of the interstellar visitors originate from the obliterated debris disks of such nearby stars.

Toward Global Stochastic River Flood Modeling

AbstractGlobal flood models integrate flood maps of constant probability in space, ignoring the correlation between sites and thus potentially misestimating the risk posed by extreme events. Stochastic flood models alleviate this issue through the simulation of flood events with a realistic spatial structure, yet their proliferation at large scales has historically been inhibited by data quality and computer availability. In this paper, we show, for the first time, the efficacy of modeled river discharge reanalyses in the characterization of flood spatial dependence in the absence of a dense stream gauge network. While global hydrological models may show poor correspondence with absolute observed river flows, we find that the rate at which they can simulate the joint occurrence of relative flow exceedances at two given locations is broadly similar to when a gauge‐based statistical model is used. Evidenced over the United States, flood events simulated using observed gauge data from the U.S. Geological Survey versus those generated using modeled streamflows have similar (i) distributions of site‐to‐site correlation strength, (ii) relationships between event size and return period, and, importantly, (iii) loss distributions when incorporated into a continental‐scale flood risk model. Extremal dependence is generally quantified less accurately on larger rivers, in arid climates, in mountainous terrain, and for the rarest high‐magnitude events. However, local‐scale errors are shown to broadly cancel each other out when combined, producing an unbiased flood spatial dependence model. These findings suggest that building accurate stochastic flood models worldwide may no longer be a distant aspiration.

Mapping legal authority for terrestrial conservation corridors along streams.

Wildlife corridors aim to promote species’ persistence by connecting habitat patches across fragmented landscapes. Their implementation is limited by patterns of land ownership and complicated by differences in the jurisdictional and regulatory authorities under which lands are managed. Terrestrial corridor conservation requires coordination across jurisdictions and sectors subject to site‐specific overlapping sources of legal authority. Mapping spatial patterns of legal authority concurrent with habitat condition can illustrate opportunities to build or leverage capacity for connectivity conservation. Streamside areas provide pragmatic opportunities to leverage existing policy mechanisms for riverine and terrestrial habitat connectivity across boundaries. Conservation planners and practitioners can make use of these opportunities by harmonizing actions for multiple conservation outcomes. We formulated an integrative, data‐driven method for mapping multiple sources of legal authority weighted by capacity for coordinating terrestrial habitat conservation along streams. We generated a map of capacity to coordinate streamside corridor protections across a wildlife habitat gap to demonstrate this approach. We combined values representing coordination capacity and naturalness to generate an integrated legal‐ecological resistance map for connectivity modeling. We then computed least‐cost corridors across the integrated map, masking the terrestrial landscape to focus on streamside areas. Streamside least‐cost corridors in the integrated, local‐scale model diverged (∼25 km) from national‐scale least‐cost corridors based on naturalness. Spatial categories comparing legal‐ and naturalness‐based resistance values by stream reach highlighted potential locations for building or leveraging existing capacity through spatial coordination of policy mechanisms or restoration actions. Agencies or nongovernmental organizations intending to restore or maintain habitat connectivity across fragmented landscapes can use this approach to inform spatial prioritization and build coordination capacity. Article impact statement: Combined mapping of legal authority and habitat condition reveals capacity to coordinate actions along streams for clean water and wildlife.

Heating of the real polar cap of radio pulsars

ABSTRACT The heating of the real polar cap surface of radio pulsars by the bombardment of ultra-relativistic charges is studied. The real polar cap is a significantly smaller area within or close by the conventional polar cap, which is encircled by the last open field lines of the dipolar field $\vec{B}_\mathrm{ d}$. It is surrounded by those field lines of the small-scale local surface field $\vec{B}_\mathrm{ s}$ that join the last open field lines of $\vec{B}_\mathrm{ d}$ in a height of ∼105 cm above the cap. As the ratio of radii of the conventional and real polar cap Rdip/Rpc ∼ 10, flux conservation requires Bs/Bd ∼ 100. For rotational periods P ∼ 0.5 s, Bs ∼ 1014 G creates a strong electric potential gap that forms the inner accelerating region (IAR) in which charges gain kinetic energies ∼3 × 1014 eV. This sets an upper limit for the energy that backflowing charges can release as heat in the surface layers of the real polar cap. Within the IAR, which is flown through with a dense stream of extremely energetic charges, no stable atmosphere of hydrogen can survive. Therefore, we consider the polar cap as a solidified ‘naked’ surface consisting of fully ionized iron ions. We discuss the physical situation at the real polar cap, calculate its surface temperatures Ts as functions of Bs and P, and compare the results with X-ray observations of radio pulsars.

Human Activities and Climate Variability Affecting Inland Water Surface Area in a High Latitude River Basin

Spatiotemporal changes in the surface area of inland water bodies have important implications in regional water resources, flood control, and drought hazard prediction. Although inland water bodies have been investigated intensively, few studies have looked at the effect of human activities and climate variability on surface area of inland waters at a larger scale over time and space. In this study, we used MODIS (MOD13Q1) images to determine water surface area extent at 250 m spatial resolution. We then applied this algorithm with MOD13Q1 images taken at 16-day intervals from 2000 to 2018 to a large river basin in China’s northeast high latitude region with dense stream network and abundant wetlands to investigate spatiotemporal distribution and dynamics of inland water bodies. The study identified 209 ponds, lakes, and reservoirs with an average total surface area of 2080 km2 in the past 19 years. The total water surface area fluctuated largely from 942 km2 to 5169 km2, corresponding to rainfall intensity and flood. We found that the total water surface area in this high latitude river basin showed an increasing trend during the study period, while the annual precipitation amount in the river basin also had an increasing trend concurrently. Precipitation and irrigation significantly contributed to the monthly change of water surface area, which reached the highest during June and August. The increase of water surface area was significant in the lower basin floodplain region, where agricultural irrigation using groundwater for rice production has progressed. Four nationally important wetland preserves (Zhalong, Xianghai, Momoge, and Chagan Lake) in the river basin made up nearly 50% of the basin’s total water surface area, of which Zhalong, Xianghai, and Momoge are designated by The Ramsar Convention as wetland sites of international importance. Seasonally, these water bodies reached their maximal surface area in August, when both the monsoon weather and agricultural discharge prevailed. This study demonstrates that water surface area in a high latitude river basin is affected by both human activities and climate variation, implying that high latitude regions will likely experience more changes in surface water distribution as global climate change continues and agriculture becomes intensified.

Study of changes of vessel’s speed in ice conditions on the Northern Sea Route

Based on archive information of automatic identification system (AIS), studies of changes in the commercial speed of large-capacity ice-class vessels Arc7 along the route in the Kara Sea on the Northern Sea Route are carried out. To plan maritime traffic in the Arctic seas, it is necessary to have objective data on the influence of various factors on speed and time of transition. To ensure the safety of Arctic shipping, it is necessary to have objective data on the effect of ice on speed and maneuverability of vessels. It was proposed to use a geographic information system (GIS), the layers of which include data on the speeds and routes of vessels of various capacities and data on monitoring ice conditions. Detailed attention was paid to the route in the Kara Sea, as it the main entrance to the Northern Sea Route from the west, the movement of vessels was studied during the winter navigation period under the most severe ice conditions (March) and during the summer navigation period for clean water (September). It was found that in the dense stream of ships in summer navigation, the speed of ships varies slightly and depends on the density and intensity of traffic, and in winter navigation, the speed of ships has dramatic changes as ships go along the route with a large lateral deviation from the route. Research is performed at the Arctic Faculty of Admiral Makarov State University of Maritime and Inland Shipping. In future, all obtained relationships can be used for modeling the maritime traffic on the Northern Sea Route with an increase in the number of large-capacity vessels with Arc7 ice-class.

Investigating the jamming of particles in a three-dimensional fluid-driven flow via coupled CFD–DEM simulations

The clogging of a dense stream of particles when passing through an orifice occurs ubiquitously in both natural and industrial fields. Since most of the jamming phenomena lead to the negative effects, studying and preventing jamming is of great importance. There are two typical types of jamming due to different types of driving force: (a) gravity-driven jamming and (b) fluid-driven jamming. Among these two types of jamming, the fluid-driven jamming occurs in fluid-driven particle flows, and the initial solid concentration, the fluid velocity, and the orifice-particle size ratio has been demonstrated to have effects on the occurrence of this jamming. Although the individual influence of the initial solid concentration and orifice-particle size ratio on jamming has been studied, the coupled effects of these two factors on jamming are little known. In addition, the complex effects of the fluid velocity on jamming have not been fully discussed. To address these problems, this work performs a three-dimensional simulation of the fluid-driven jamming using the coupled Computational Fluid Dynamics–Discrete Element Method (CFD–DEM) model. At first, the jamming probability under different initial conditions is studied. The jamming probability is displayed on the solid concentration–orifice size ratio plane to illustrate the coupled effects of these two factors on jamming. The simulation results show that the critical solid concentration, at which the jamming probability increases to 1, increases with the orifice-particle size ratio. This is because an orifice with a larger orifice size ratio has a greater particle discharge capacity, which allows more particles to pass through without jamming. Then, we reveal the influence of fluid velocity over a wide range on the fluid-driven jamming type, jamming probability and shape of the jamming dome. To the author’s knowledge, this is the first time that the shape of the jamming dome has been related to the fluid velocity. The jamming dome formed in the higher-speed flow has a greater curvature due to the greater fluid drag acting on the particles.

Numerical investigation of coal particle stream ignition in oxy-atmosphere

The ignition of a stream of coal particles under oxy-fuel atmosphere is studied numerically in a laminar flow. Devolatilization of coal particles is modeled with the chemical percolation devolatilization (CPD) method coupled with a detailed chemistry model for homogeneous reactions. The particle and gas phase interactions are modeled with a fully coupled Euler-Lagrange code. A parametric study is performed to investigate the influence of particle number density, gas temperature, and velocity on ignition. We found that increasing particle number density delays the onset of ignition. Delayed ignition in denser streams is due to the lower gas temperature, which is caused by the higher energy required for particle heating. In addition, increasing particle number density leads to a more continuous and narrower flame front. Particle heating and ignition induce velocity variations in the gas phase through the coupling with particles. In the denser stream, velocity variations become significant and compromise the validity of a constant velocity assumption that is usually made in computing ignition delay time from the observed ignition location. It is also found that high particle slip velocities lead to a locally low volatile concentration and low temperature, and consequently increase ignition delay time.

A New Method of Selective Laser Cladding

A new approach to selective laser cladding using conical laser beams has been elaborated. The initial round laser beam is divided into two or more circular beams with regulated distribution of the laser power between them. The circular beams are converted into conical beams that are focused separately on the surface and on different areas of the deposited material for their efficient heating. The delivery of laser energy into the powder stream is very effective because it provides a complete uniform absorption of laser energy in a dense powder stream (104–106 cm–3). Under wire deposition, substrate heating reduces residual stresses due to temperature gradients and compensates for heat loss from the deposition zone by thermal conduction. The required power density for melt contact formation is significantly reduced.

Non-axisymmetric line-driven disc winds – I. Disc perturbations

We study mass outflows driven from accretion discs by radiation pressure due to spectral lines. To investigate non-axisymmetric effects, we use the Athena++ code and develop a new module to account for radiation pressure driving. In 2D, our new simulations are consistent with previous 2D axisymmetric solutions by Proga et al. who used the Zeus 2D code. Specifically, we find that the disc winds are time dependent, characterized by a dense stream confined to $\sim 45^{\circ}$ relative to the disc midplane and bounded on the polar side by a less dense, fast stream. Introducing a vertical, $\phi$-dependent, subsonic velocity perturbation in the disc midplane does not change the overall character of the solution but global outflow properties such as the mass, momentum and kinetic energy fluxes are altered by up to 100%. Non-axisymmetric density structures develop and persist mainly at the base of the wind. They are relatively small, and their densities can be a few times higher that the azimuthal average. The structure of the non-axisymmetric and axisymmetric solutions differ also in other ways. Perhaps most importantly from the observational point of view are the differences in the so called clumping factors, that serve as a proxy for emissivity due to two body processes. In particular, the spatially averaged clumping factor over the entire fast stream, while it is of a comparable value in both solutions, it varies about 10 times faster in the non-axisymmetric case.

Dense underflow into a lake or reservoir—Sub-critical flow.

Steady two-dimensional flow of a dense stream down a slight embankment into a lake or a reservoir is considered. The inflowing water is separated from the ambient lake water by a density interface. This work follows on from earlier work in which the flows down a steep incline with a relatively high flow rate were considered. Here, the flow is slow and the entry angle is small, resulting in waves on the interface. The fluid is assumed to be of finite depth and the incoming channel makes an angle α to the horizontal. Limiting flows are found when the fluid separates at a stagnation point or alternatively when the waves reach maximum steepness. The regions in parameter space where such solutions are obtained are delineated for different flow conditions.

Investigation of tungsten surface changes after interaction with dense plasma streams compared with the results given by a simple 1D model

AbstractIn this work, plasma–target interactions on tungsten samples, carried out in a Mather-type plasma focus PF-1000 device, were investigated. The experimental results have been compared to 1D model computer simulations. Samples were studied by means of scanning electron microscopy, focused ion beam microscopy and precise measurements of weight loss. Additionally, simulations based on the numerical solution of a 1D heat conductivity equation were carried out. The samples exhibited relatively high resistance to the generated plasma streams. The practical work indicated a loss of about 1.54 mg per plasma focus discharge. The computer model calculations gave a weight loss one magnitude greater. An attempt to explain this discrepancy is given in the paper.