Stream Formation Research Articles

Hydraulic tests of a random helical packing element

A large number of different packing elements are applied in the chemical, oil refining, petrochemical, food and other industries for implementing heat-and-mass transfer processes in columns. The advantage of packed columns consists in their high efficiency, low flow resistance and stable operation. The most important requirements for packing elements include their high specific surface area, large free volume proportion, ease of manufacture and low material consumption. However, few available packing elements meet all of the aforementioned requirements. In this work, we developed a helical packing element for implementing heat-and-mass transfer processes in distillation, absorption and extraction columns, as well as in cooling towers, and carried out a series of respective hydraulic tests. The novel packing element is characterized by a simple design, implying coiling a metal strip into a helix. Such a shape excludes the contact with neighbouring elements, which prevents blocking of the packing surface and formation of stagnant zones. A specific feature of this design consists in the smooth surface of the element, which prevents the formation of drops and streams, thus reducing the mass transfer efficiency. The film-like flow through the packing element ensures high mass transfer characteristics with minimum entrainment, thus contributing to the reduction of flow resistance. On the basis of experimental data, empirical equations were obtained for calculating the flow resistance of dry and wet packing patterns. A comparative analysis of the developed packing element with Pall Rings and Inzhekhim-2000 is provided. It is shown that the developed helical packing element is characterized by a large surface area, significant free volume and low flow resistance. In addition, the simple design of the element significantly reduces its production costs.

Distribution of suspended matter off the western coast of the crimea under impact of the strong winds of various directions

The mechanisms of formation and distribution of total suspended matter (tsm) off the West Coast of Crimea under the influence of strong winds of various directions were investigated on the base of satellite data of medium and high resolution. The maximum tsm reaching the values of 200 mg / l was is observed during strong southern winds. In this case, the zone of high tsm is located at the western shelf of the Crimea limited by a 50 m isobath. The wave impact on resuspension of bottom sediments and the erosion of clay cliffs located on the west coast of Crimea lead to the formation of a large amount of tsm. After the storm, a northern alongshore current transfers tsm to the north. During northeast winds, the highest tsm are observed not near the coast, but in the seaward part of the shelf between 30 and 50 m isobaths. It is likely that turbulent mixing during such winds resuspense bottom sediments in shallow areas, which are further transported from the coast due to the offshore winds. The wind surge in this case leads to the formation of a band of clean cold water near the coast. A specific feature of the action of the northern and northwestern storms is the formation of a longshore jet stream along the western coast. The current occurs at the front of the upwelling zone. The stream transports the suspended matter offshore southward. The concentration of the suspended matter in this case is also much lower than when exposed to the southern winds, but it can reach a value of 3 mg/l.

Statistical properties of substructures around Milky Way-sized haloes and their implications for the formation of stellar streams

Stellar streams originating in disrupted dwarf galaxies and star clusters are observed around the Milky Way and nearby galaxies. Such substructures are the important tracers that record how the host haloes have accreted progenitor galaxies. Based on the cosmological context, we investigate the relationship between structural properties of substructures such as length and thinness at $z=0$, and orbits of their progenitors. We model stellar components of a large sample of substructures around Milky Way-sized haloes by combining semi-analytic models with a high-resolution cosmological $N$-body simulation. Using the Particle Tagging method, we embed stellar components in progenitor haloes and trace phase-space distributions of the substructures down to $z=0$. We find that the length and thinness of substructures vary smoothly as the redshift when the host haloes accrete their progenitors. For substructures observed like streams at $z=0$, a large part of the progenitors is accreted by their host haloes at redshift $0.5\lesssim z\lesssim 2.5$. Substructures with progenitors out of this accretion redshift range are entirely or less disrupted by $z=0$ and cannot be observed as streams. We also find that the distributions of length and thinness of substructures vary smoothly as pericenter and apocenter of the progenitors. Substructures observed like streams tend to have the specific range of $10\ {\rm kpc} \lesssim r_{\rm peri}\lesssim100\ {\rm kpc}$ and $50\ {\rm kpc} \lesssim r_{\rm apo}\lesssim300\ {\rm kpc}$.

Towards a complete understanding of the Magellanic Stream Formation

The Magellanic Clouds (MCs) have lost most of their gas during their passage by the Milky Way, a property that has never been successfully modelled. Here, we use accurate and mesh-free hydrodynamic simulations to reproduce the Magellanic Stream and the MCs in the frame of a ‘ram-pressure plus collision’ model. This model reproduces many of the observed properties of the H i Stream including most of its density profile along its length and its dual filamentary structure. Besides this, ram-pressure combined with Kelvin–Helmholtz instabilities extracts amounts of ionized and H i gas consistent with those observed. The modelled scenario also reproduces the Magellanic Bridge, including the offset between young and old stars, and the collision between the Clouds, which is responsible of the very elongated morphology of the Small Magellanic Cloud along the line of sight. This model has solved most of the mysteries linked to the formation of the Magellanic Stream. The Leading Arm is not reproduced in the current model because it requires an alternative origin.

Conditions for Plasma Jet Formation in a Laminar Plasmatron

The laminar plasma jet is an effective tool of plasma technologies for material processing thanks to great values of bulk temperature and high penetration of a plasma stream. However, laminar stream formation in an axial jet plasmatron is connected with a number of difficulties caused by physical restrictions. Conditions of formation of a laminar stream at the exit from a plasmatron nozzle with interelectrode inserts are found when using the most widespread plasma-forming gases. With use of a method of universal characteristics of arc and heat-transfer model of arc of jet plasmatrons, calculation of characteristics of the arc compressed by walls of the discharge channel is carried out; the necessary arc compression ratio in the stable laminar stream mode and its extreme values taking into account the permissible thermal load on walls of the discharge channel in the arc stabilization zone are defined. It is shown that reduction of the diameter of the plasmatron discharge channel reducing diameter of the laminar plasma stream exhausting from a plasmatron nozzle reduces the permissible values of the arc compression ratio. Influence of the cooling mode of walls of the plasmatron arc channel formed by interelectrode inserts on the arc compression ratio at separate water cooling of each interelectrode insert and at their joint cooling is shown. All calculations were carried out for the values of gas consumption and discharge channel length meeting a basic condition of laminar stream formation of Re < 150. The arc current values necessary for a laminar plasma stream formation, depending on the discharge channel section and a plasma-forming gas consumption taking into account thermal properties of the gas environment, are determined. The method proposed in this article makes it possible to calculate an arc column temperature profile in the stabilization zone of a laminar plasmatron and can be used when developing plasmatrons with a stable laminar stream of set plasma-forming gas.

From Theory to Practice

Modern video streaming uses adaptive bitrate (ABR) algorithms that run inside video players and continually adjust the quality (i.e., bitrate) of the video segments that are downloaded and rendered to the user. To maximize the quality-of-experience (QoE) of the user, ABR algorithms must stream at a high bitrate with low rebuffering and low bitrate oscillations. Further, a good ABR algorithm is responsive to user and network events and can be used in demanding scenarios such as low-latency live streaming. Recent research papers provide an abundance of ABR algorithms but fall short on many of the above real-world requirements. We develop Sabre, an open-source publicly available simulation tool that enables fast and accurate simulation of adaptive streaming environments. We empirically validated Sabre to show that it accurately simulates real-world environments. We used Sabre to design and evaluate BOLA-E and DYNAMIC, two novel ABR algorithms. We also developed a FAST SWITCHING algorithm that can replace segments that have already been downloaded with higher-bitrate (thus, higher-quality) segments. The new algorithms provide higher QoE to the user in terms of higher bitrate, fewer rebuffers, and lesser bitrate oscillations. In addition, these algorithms react faster to user events such as startup and seek, and they respond more quickly to network events such as improvements in throughput. Further, they perform very well for live streams that require low latency, a challenging scenario for ABR algorithms. Overall, our algorithms offer superior video QoE and responsiveness for real-life adaptive video streaming, in comparison to the state-of-the-art. Importantly, all three algorithms presented in this article are now part of the official DASH reference player dash.js and are being used by video providers in production environments. While our evaluation and implementation are focused on the DASH environment, our algorithms are equally applicable to other adaptive streaming formats such as Apple HLS.

Neural crest streaming as an emergent property of tissue interactions during morphogenesis.

A fundamental question in embryo morphogenesis is how a complex pattern is established in seemingly uniform tissues. During vertebrate development, neural crest cells differentiate as a continuous mass of tissue along the neural tube and subsequently split into spatially distinct migratory streams to invade the rest of the embryo. How these streams are established is not well understood. Inhibitory signals surrounding the migratory streams led to the idea that position and size of streams are determined by a pre-pattern of such signals. While clear evidence for a pre-pattern in the cranial region is still lacking, all computational models of neural crest migration published so far have assumed a pre-pattern of negative signals that channel the neural crest into streams. Here we test the hypothesis that instead of following a pre-existing pattern, the cranial neural crest creates their own migratory pathway by interacting with the surrounding tissue. By combining theoretical modeling with experimentation, we show that streams emerge from the interaction of the hindbrain neural crest and the neighboring epibranchial placodal tissues, without the need for a pre-existing guidance cue. Our model suggests that the initial collective neural crest invasion is based on short-range repulsion and asymmetric attraction between neighboring tissues. The model provides a coherent explanation for the formation of cranial neural crest streams in concert with previously reported findings and our new in vivo observations. Our results point to a general mechanism of inducing collective invasion patterns.

ProIO: An event-based I/O stream format for protobuf messages

ProIO is a new event-oriented streaming data format which utilizes Google’s Protocol Buffers (protobuf) to be flexible and highly language-neutral. The ProIO concept is described here along with its software implementations. The performance of the ProIO concept for a dataset with Monte-Carlo event records used in high-energy physics was benchmarked and compared/contrasted with ROOT I/O. Various combinations of general-purpose compression and variable-length integer encoding available in protobuf were used to investigate the relationship between I/O performance and size-on-disk in a few key scenarios. Program summaryProgram Title: ProIOProgram Files doi:http://dx.doi.org/10.17632/mfxsg2d5x5.1Licensing provisions: BSD 3-clauseProgramming language: Python, Go, C++, JavaNature of problem: In high-energy and nuclear physics (HEP and NP), Google’s Protocol Buffers (protobufs) can be a useful tool for the persistence of data. However, protobufs are not well-suited for describing large, rich datasets. Additionally, features such as direct event access, lazy event decoding, general-purpose compression, and self-description are features that are important to HEP and NP, but that are missing from protobuf.Solution method: The solution adopted here is to describe and implement a streaming format for wrapping protobufs in an event structure. This solution requires small (typically less than 1000 lines of code) implementations of the format in the desired programming languages. With this approach, most of the I/O heavy lifting is done by the protobufs, and ProIO adds the necessary physics-oriented features.

Capturing the spatiotemporal dynamics of self-generated, task-initiated thoughts with EEG and fMRI

The temporal structure of self-generated cognition is a key attribute to the formation of a meaningful stream of consciousness. When at rest, our mind wanders from thought to thought in distinct mental states. Despite the marked importance of ongoing mental processes, it is challenging to capture and relate these states to specific cognitive contents. In this work, we employed ultra-high field functional magnetic resonance imaging (fMRI) and high-density electroencephalography (EEG) to study the ongoing thoughts of participants instructed to retrieve self-relevant past episodes for periods of 22sec. These task-initiated, participant-driven activity patterns were compared to a distinct condition where participants performed serial mental arithmetic operations, thereby shifting from self-related to self-unrelated thoughts. BOLD activity mapping revealed selective enhanced activity in temporal, parietal and occipital areas during the memory compared to the mental arithmetic condition, evincing their role in integrating the re-experienced past events into conscious representations during memory retrieval. Functional connectivity analysis showed that these regions were organized in two major subparts, previously associated to “scene-reconstruction” and “self-experience” subsystems. EEG microstate analysis allowed studying these participant-driven thoughts in the millisecond range by determining the temporal dynamics of brief periods of stable scalp potential fields. This analysis revealed selective modulation of occurrence and duration of specific microstates in the memory and in the mental arithmetic condition, respectively. EEG source analysis revealed similar spatial distributions of the sources of these microstates and the regions identified with fMRI. These findings imply a functional link between BOLD activity changes in regions related to a certain mental activity and the temporal dynamics of mentation, and support growing evidence that specific fMRI networks can be captured with EEG as repeatedly occurring brief periods of integrated coherent neuronal activity, lasting only fractions of seconds.

Increasing the Selectivity for Sulfur Formation in Biological Gas Desulfurization.

In the biotechnological desulfurization process under haloalkaline conditions, dihydrogen sulfide (H2S) is removed from sour gas and oxidized to elemental sulfur (S8) by sulfide-oxidizing bacteria. Besides S8, the byproducts sulfate (SO42–) and thiosulfate (S2O32–) are formed, which consume caustic and form a waste stream. The aim of this study was to increase selectivity toward S8 by a new process line-up for biological gas desulfurization, applying two bioreactors with different substrate conditions (i.e., sulfidic and microaerophilic), instead of one (i.e., microaerophilic). A 111-day continuous test, mimicking full scale operation, demonstrated that S8 formation was 96.6% on a molar H2S supply basis; selectivity for SO42– and S2O32– were 1.4 and 2.0% respectively. The selectivity for S8 formation in a control experiment with the conventional 1-bioreactor line-up was 75.6 mol %. At start-up, the new process line-up immediately achieved lower SO42– and S2O32– formations compared to the 1-bioreactor line-up. When the microbial community adapted over time, it was observed that SO42– formation further decreased. In addition, chemical formation of S2O32– was reduced due to biologically mediated removal of sulfide from the process solution in the anaerobic bioreactor. The increased selectivity for S8 formation will result in 90% reduction in caustic consumption and waste stream formation compared to the 1-bioreactor line-up.

Debris of Asteroid Disruptions Close to the Sun

The under-abundance of asteroids on orbits with small perihelion distances suggests that thermally-driven disruption may be an important process in the removal of rocky bodies in the Solar System. Here we report our study of how the debris streams arise from possible thermally-driven disruptions in the near-Sun region. We calculate that a small body with a diameter $\gtrsim0.5$ km can produce a sufficient amount of material to allow the detection of the debris at the Earth as meteor showers, and that bodies at such sizes thermally disrupt every $\sim2$ kyrs. We also find that objects from the inner parts of the asteroid belt are more likely to become Sun-approacher than those from the outer parts. We simulate the formation and evolution of the debris streams produced from a set of synthetic disrupting asteroids drawn from Granvik et al. (2016)'s near-Earth object population model, and find that they evolve 10--70 times faster than streams produced at ordinary solar distances. We compare the simulation results to a catalog of known meteor showers on Sun-approaching orbits. We show that there is a clear overabundance of Sun-approaching meteor showers, which is best explained by a combining effect of comet contamination and an extended disintegration phase that lasts up to a few kyrs. We suggest that a few asteroid-like Sun-approaching objects that brighten significantly at their perihelion passages could, in fact, be disrupting asteroids. An extended period of thermal disruption may also explain the widespread detection of transiting debris in exoplanetary systems. Data and codes that generate the figures and main results of this work are publicly available on 10.5281/zenodo.2547298 and https://github.com/Yeqzids/near-sun-disruptions.

Block stream characteristics in Southern Carpathians (Romania)

Block streams, as common features in the Southern Carpathians, are essential for understanding the evolution of alpine environments. Despite their widespread occurrence, they have frequently been omitted from previous inventories of periglacial landforms and from the general understanding of landscape development. This study evaluated the environmental controls on spatial distribution and dimensions of 2056 block streams for a better understanding of their evolution and climatic significance. Different lithology classes and topographic characteristics were assessed using standard least-square linear regression and one-way analysis of variance (ANOVA). The majority of the block streams belong to the linear morphological type, but six other types of morphologies were found (e.g. sinuous, curved, and braided). Bivariate and multivariate statistical analysis revealed a high density of landforms on southern slopes (59%), granite terrains (47%), and above 1750 m. Large features occur mainly on southern slopes and in areas with granites. Landform dimensions and spatial distribution are influenced to a certain degree by lithology, slope aspect, and elevation, making it difficult to identify a dominant factor. Block streams developed extensively at the end of the Pleistocene under permafrost conditions. Today, these features suggest inactivity, but during the cool episodes of the Holocene (e.g. Little Ice Age - LIA), the formation of block streams above 2100 m was re-initiated. Future absolute dating and monitoring of landform dynamics will support these findings.

Influence of backstreaming ions on spot size of 2 MeV electron beam

AbstractInfluence of backstreaming ions from the target on spot size of focused 2 MeV electron beam was considered. The 2D version of the particle-in-cell code KARAT was used to study the formation of the ions stream and dynamics of the electron beam. It was shown that light species emitted from the target can disrupt the beam. The emission of low-ionized states of tantalum cannot disrupt the beam during about 30 ns or longer. A few non-invasive techniques of mitigation of the beam disruption were considered. Final magnetic lens with fast variation of magnetic field of several hundred Ampere-turns per nanosecond is capable to stabilize initial spot size of the compressed beam at the target.

Роль озонового слоя в формировании зимнего струйного течения в средней атмосфере

Роль озонового слоя в формировании зимнего струйного течения в средней атмосфере

Error Sensitivity Analysis of DMB Transport Streams

In this paper, we examine the sensitivity of the digital multimedia broadcasting (DMB) MPEG-2 transport stream (TS) format to transmission errors. To find the sensitivity of different parts of TS packets to transmission errors, each TS packet is divided into four cells, i.e., the first three cells comprising 48 bytes each and the last cell is of 44 bytes length. Bit errors are then introduced into these different parts of the TS packets. The sensitivity of DMB videos to transmission errors and their locations is assessed in terms of the following measures: 1) Number of decoder crashes; 2) Number of decodable videos; 3) Total number of decodable frames; and 4) Objective perceptual video quality of the decoded videos. The structural similarity index and visual information fidelity criterion are used as objective perceptual quality metrics. Simulations are performed on seven different DMB videos using various bit error rates. The results show that the first cell of the TS packets is highly sensitive to bit errors compared to the subsequent three cells, both in terms of spatial and temporal video quality. Further, the sensitivity decreases from Cell 1 to Cell 4 of a DMB TS packet. The error sensitivity analysis reported in this paper may guide the development of more reliable transmission systems for future DMB systems and services. Specifically, the insights gained from this study may support designing better error control schemes that take the sensitivity of different parts of DMB TS packets into consideration.

Implementation of Data Conversion Interface Between Midas and DUT2014 Structural Model

DUT2014 is a computational program developed by our team for the elastic-plastic time history analysis of super high-rise building structures. The integrated platform code is open source, which has all the materials and elements for the structural analysis of super high-rise buildings. Moreover, the integrated platform has a new element state transition algorithm (STP), which greatly improves the computational efficiency of elastic-plastic time history analysis. Midas is a finite element analysis software, which has good elastic analysis function and non-linear analysis function, and it has good pre-processing function. Preprocessing of DUT2014 is a command stream format in text format, and its modeling function is relatively cumbersome. In order to realize the customization of DUT2014 modeling function, this paper decided to develop an interface program to transform Midas model data file to DUT2014 model data file. This paper establishes an interface program for converting Midas structured data model file into DUT2014 structured data model file by using Microsoft Visual C++ programming program. In order to verify the correctness of structural data model transformation, this paper will use interface program to transform three different scale structures, and then verify the accuracy of the interface by comparing the quality information, modal calculation results, elastic time history response and elastic-plastic time history response of the model before and after transformation.

Free-field evoked auditory brainstem responses in cochlear implant users.

The importance of binaural cues in auditory stream formation and sound source segregation is widely accepted. When treating one ear with a cochlear implant (CI) the peripheral auditory system gets partially replaced and processing delays get added potentially, thus important interaural time differences get altered. However, these effects are not fully understood, leaving a lack of systematic binaural fitting strategies with respect to an optimal binaural fusion. To get new insights into such alterations, we suggest a novel method of free-field auditory brainstem evoked responses (ABRs) analysis in CI users. This method does not bypass the technically induced intrinsic delays of the sound processor while leaving the whole electrode array active, thus the most natural way of stimulation is provided. We compared the ABRs collected of 12 CI users and 12 normal hearing listeners using two different stimuli (chirp, click) at four different intensities each. We analyzed the ABRs using the average of 2000 trials as well as a single trial analysis and found consistent results in the ABRs’ amplitudes and latencies, as well as in single trial relationships between both groups. This method provides a new perspective into the natural CI users’ ABRs and can be useful in future research regarding binaural interaction and fusion.

CHARACTERISTIC OF THE SOIL MOISTURE STATE BASED ON CARTOGRAPHIC METHODS AND SATELLITE SURVEY DATA

Problem Statement and Purpose. The article describe the features and directions of space imagery materials usage for determination of humidity and degradation of arable lands. The geomorphological smdies carried out by the method of relief plastics andmorphodynamic analysis based on space survey data made it possible to determine the areas of soil degradation, namely, their ovemioistening. Application of remote sensing materials of the Earth within the limits of the performed research allowed determination of soil moisture, soil degradation processes (washout of humus horizon, waterlogging, flooding). The object of the study is the soil cover of the territory of the Baryshevsky area of the Kiev region. The subject of the study is the soil humidity and its degradation. The research aimed to determination of the soil moisture content, areas of waterlogging and flooding based on materials of remote sensing of the Earth and applying the method of relief plastics with morphodynamic analysis.Data &amp; Methods. The geomorphological methods of investigation based on the digital terrain model and computer processing of space images was applied for determining the areas with different degrees of moisture that could lead to soil degradation. Moisture was determined by the methods of classification the Sentinel space images, as well as by using the normalized moisture index (NWI).Based on the relief plastics method, the elevations and depressions of the Earth's surface relief could be detected. The areas with elevation of the relief surface include watersheds, hills, ridges, but depressions could be observed in case of beams, valleys, lowlands, etc. Morphodynamic analysis allows us to see the direction of flows and transport of particles. The integration of the space images analysis and the relief plastics method with morphodynamic analysis make it possible to see a general picture of the direction of geochemical flows from elevated areas of streams formation to areas of accumulation of ground masses and moistureResults Applying of a complex methodology in the analysis of the territory allows us to determine the areas of demolition and accumulation of ground masses and water. The directions of surface demolition of the upper layer of soil and water to the lowered sections of the relief are shown. Thus, in the microcrops the soil moisture is higher depend on climatic conditions and could lead to accumulation and stagnation of water. The methods described above allow us to determine and predict the surface areas prone to waterlogging. The research results can be used for mapping of the structure of soil cover.

Experimental studies of heat dissipation by a stream of dressing products during dry dressing of conventional ceramic grinding wheels

Part of the energy required to perform the dressing process is converted into heat, which is generated by friction and elastic-plastic deformations occurring in the contact area of diamond grit and the grinding wheel. This heat is diffused by thermal conduction in the direction of the grinding wheel and the body of the dresser, electromagnetic radiation, convection and it is also transferred through the particle stream of dressing products. This article describes the assessment method and the results of the research on the amount of heat accumulated in the stream of the particles of the dressing products. In the presented method, the enthalpy of the stream was estimated based on the measurements of electrical voltage generated by the Peltier module set in a short distance from the point of stream formation, transversely to the direction of its movement. The method of determining the thermal-voltage characteristics of the module necessary to determine the amount of heat released by the particle stream is described. The research of enthalpy streams was carried out during dry dressing of conventional ceramic grinding wheels made of brown and white fused aluminum oxide and green silicon carbide. Dressing studies were performed with a single point diamond dresser using various feed values and dressing depths. Measurements of the Peltier module voltage were carried out simultaneously with measurements of the diamond grain temperature in the dresser and the power of dressing. On the basis of the obtained results, the correlation of the module voltage signals and the diamond temperature is evaluated. Furthermore the influence of dressing parameters and type of grinding wheel abrasive material on the magnitude of stream enthalpy and its share in dressing energy are also evaluated. The studies show that the module voltage remains in almost full, linear correlation (ρ > 0.95) with the diamond dresser temperature; the amount of heat carried by the stream constitutes a few percentage points (2%–5%) part of the dressing energy, and the amount of this share increases with the increase of the thermal conductivity of the grinding wheel material and dressing volume capacity.

Neuronal correlates of auditory streaming in the auditory cortex of behaving monkeys.

This study tested the hypothesis that spiking activity in the primary auditory cortex of monkeys is related to auditory stream formation. Evidence for this hypothesis was previously obtained in animals that were passively exposed to stimuli and in which differences in the streaming percept were confounded with differences between the stimuli. In this study, monkeys performed an operant task on sequences that were composed of light flashes and tones. The tones alternated between a high and a low frequency and could be perceived either as one auditory stream or two auditory streams. The flashes promoted either a one-stream percept or a two-stream percept. Comparison of different types of sequences revealed that the neuronal responses to the alternating tones were more similar when the flashes promoted auditory stream integration, and were more dissimilar when the flashes promoted auditory stream segregation. Thus our findings show that the spiking activity in the monkey primary auditory cortex is related to auditory stream formation.