Segmented Flow Research Articles

Learning Monocular Depth in Dynamic Scenes via Instance-Aware Projection Consistency

We present an end-to-end joint training framework that explicitly models 6-DoF motion of multiple dynamic objects, ego-motion, and depth in a monocular camera setup without supervision. Our technical contributions are three-fold. First, we highlight the fundamental difference between inverse and forward projection while modeling the individual motion of each rigid object, and propose a geometrically correct projection pipeline using a neural forward projection module. Second, we design a unified instance-aware photometric and geometric consistency loss that holistically imposes self-supervisory signals for every background and object region. Lastly, we introduce a general-purpose auto-annotation scheme using any off-the-shelf instance segmentation and optical flow models to produce video instance segmentation maps that will be utilized as input to our training pipeline. These proposed elements are validated in a detailed ablation study. Through extensive experiments conducted on the KITTI and Cityscapes dataset, our framework is shown to outperform the state-of-the-art depth and motion estimation methods. Our code, dataset, and models are publicly available.

Tuning the gas-liquid-solid segmented flow for enhanced heterogeneous photosynthesis of Azo- compounds

Difficult handling the solid catalysts remains one of the pain points in the continuous flow photochemistry. In this work, the gas–liquid-solid segmented flow was employed in the photocatalytic production of azo- compounds (azoxybenzene and azobenzene) from nitrobenzene using graphitic carbon nitride (g-C3N4) as solid catalyst. Compared with the batch reactor, the photocatalytic reaction rate was greatly improved in the microreactor, and the reaction time was shortened from 180 min of the batch to 7.5 min for near-full conversion of nitrobenzene. The effects of various reaction parameters (temperature, light source power, catalyst content) in the continuous system were examined, and the reaction kinetic was found in first order. The photocatalytic reaction performance was very sensitive to the gas–liquid-solid segmented flow conditions, which needed to be carefully tuned. With the help of high-speed camera and micro particle image velocimetry (µ-PIV) techniques, it was identified that the increasing inert gas fraction resulted in more stable segmented flow with shorter liquid segments, favoring the reaction rate. With a high gas fraction, the intensity of recirculation in the liquid segments was strengthened by the increasing total flow rate, enhancing the local mass transfer, thereby benefiting the photocatalytic reaction. Overall, the continuous microreactor reached 5.6 times higher productivity per volume (26.1 mmol/h*L) of azo- compounds than the batch reactor under the same conditions. The successful photosynthesis of azo- compounds demonstrated the great potential of the presented gas–liquid-solid segmented flow, and the findings of this work provide useful guidance on its future application in other heterogeneously catalyzed reactions.

Evaluation of fracture closure and its contribution to total production for a well with non-planar asymmetrical vertical fracture based on bottom-hole pressure

Hydraulic-fracturing is an important well-stimulation technique, the fracture closure is inevitable during production. The existing pressure transient analysis models either ignore the length of fracture-closure segment that causes the explained fracture half-length to be smaller, or only use the fracture conductivity to evaluate fracture closure. To fully evaluate fracture closure and provide a reference for oilfield engineers determining whether need measures to improve the well performance, meanwhile considering the non-planar asymmetrical fracture is common met in low-permeability reservoirs, this paper proposes to use two parameters (flowrate proportion and conductivity of fracture-closure segment) to comprehensively evaluate fracture closure, and hence develops double-segment non-planar asymmetrical fracture model (DPAFM). Planar asymmetrical fracture model is simplified case of proposed model. The semi-analytical solution is obtained by using finite difference method (FDM) and Gonzalez-Chavez and Cinco-Ley (2006) model is used to verify the solution. The results of this work show that (a) The example of actual well simulation proves the model is more suitable for the actual field data, and the model established is better matched than the saphir software; (b) The proposed model can obtain production proportion and conductivity of fracture-closure segment to comprehensively evaluate fracture closure; (c) There are four typical flow regimes for the DPAFM, including bilinear flow, interference linear flow, formation linear flow, pseudo-radial flow. The interference linear flow regime with ‘V-shape’ characteristic is unique; (d) Conventional explanation thinks the ‘V-shape’ characteristic represents the secondary fracture developed (e.g., OFFN, TLFN and MOFN). However, this paper gives another possibility that the ‘V-shape’ reflects fracture closure. The findings of this study can help for better understanding of illustrating the practicability of proposed methodology in evaluating the fracture closure and reservoir parameters. This research provides guidance for technicians to formulate the next step to increase production plan and helps the oilfield engineers determine whether take measures to improve the well performance. • We present a double-segment non-planar asymmetrical fracture model (DPAFM) considering the effect of conditions inside fracture. • We provide an additional explanation about ‘V-shape’ characteristic on the pressure derivative curve besides the complex fracture geometries. • The field cases illustrate the practicability of proposed methodology in evaluating the reservoir parameters, fracture closure, fracture segment flow rate and fracture propagation.

Three-dimensional gradient and spin-echo readout for time-encoded pseudo-continuous arterial spin labeling: Influence of segmentation factor and flow compensation.

PurposeTo monitor the complete passage of the labeled blood through the vascular tree into tissue and improve the quantification of ASL maps, we evaluated the effect of 3D gradient and spin‐echo (GRASE) readout segments on temporal SNR (tSNR) and image blurriness for time‐encoded pseudo‐continuous arterial spin labeling and the effect of flow‐compensation gradients on the presence of intravascular signal.MethodsFifteen volunteers were scanned using time‐encoded pCASL with 2D EPI and single‐segment, two‐segments, and three‐segments 3D‐GRASE readouts with first‐order flow compensation (FC) gradients. Two‐segments 3D‐GRASE scans were acquired with 25%, 50%, 75%, and 100% of full first‐order FC. Temporal SNR was assessed, and cerebral blood flow and arterial blood volume were quantified for all readout strategies.ResultsFor single‐segment 3D GRASE, tSNR was comparable to 2D EPI for perfusion signal but worse for the arterial signal. Two‐segments and three‐segments 3D GRASE resulted in higher tSNR than 2D EPI for perfusion and arterial signal. The arterial signal was not well visualized for 3D‐GRASE data without FC. Visualization of the intravascular signal at postlabeling delays of 660 ms and 1060 ms was restored with FC. Adequate visualization of the intravascular signal was achieved from 75% of FC gradient strength at a postlabeling delay of 660 ms. For a postlabeling delay of 1060 ms, full‐FC gradients were the best option to depict intravascular signal.ConclusionSegmented GRASE provided higher effective tSNR compared with 2D‐EPI and single‐segment GRASE. Flow compensation with GRASE readout should be carefully controlled when applying for time‐encoded pCASL to visualize intravascular signal.

Kinetic Simulation of Segmented Plasma Flow Meter Response in the Ionospheric Plasma

AbstractA relatively simple design of a segmented flow meter is presented for measuring in situ plasma flow velocities and other space plasma parameters. The response of the flow meter to space environment is simulated for plasma conditions representative of the ionosphere at mid and low latitudes using a Particle in cell code. A synthetic data set consisting of ion currents collected by several segments of the flow meter, and the physical parameters for which they were calculated, is then used to construct a solution library from which inference models can be constructed, using radial basis function and neural network regressions. Simulation results show that with such a flow meter, it should be possible to infer plasma flow velocities in the direction perpendicular to the ram direction, with uncertainties of ±45 m/s or less. Models can also be constructed to infer plasma densities, with a maximum relative error of 23%. This work is presented as a first assessment and proof of concept for an original design of a simple and robust flow meter.

A NIR laser induced self-healing PDMS/Gold nanoparticles conductive elastomer for wearable sensor

Self-healing conductive elastomers have been widely used in smart electronic devices, such as wearable sensors. However, nano fillers hinder the flow of polymer segments, which make the development of conductive elastomer with rapid repair and high ductility a challenge. In this work, thioctic acid (TA) was grafted onto amino-modified polysiloxane (PDMS-NH2) by dehydration condensation of amino group and carboxyl group. By introducing gold nanoparticles, a dynamic network based on S-Au interaction was constructed. The dynamic gold cross-linking could effectively dissipate the energy exerted by external force and improve the extensibility of conductive elastomer. In addition, S-Au interaction had a good optothermal effect, so that the elastomer rapidly healed under NIR irradiation, and the repair efficiency reached 92%. We further evaluated the performance of the conductive elastomer as a strain sensor. The sample could accurately monitor the bending of human joints and small muscle state changes. This kind of self-healable conductive elastomer based on dynamic S-Au interaction has great potential in the fields of interpersonal interaction and health monitoring.

Gas–Liquid Two-Phase Flow and Heat Transfer without Phase Change in Microfluidic Heat Exchanger

This work presents an experimental study of the possibility of intensifying in microfluidic heat exchangers (MFHE) by creating a two-phase segmented flow (gas–liquid). Measurements of convective heat transfer were carried out using an MFHE, consisting of six channels 1 × 1 mm. Experimental studies have shown that segmented flow makes it possible to increase the Nusselt number of a laminar flow in MFHE up to 1.67 and reduce thermal resistance up to 1.7 times compared to single-phase flow. At the same time, it was found that the intensification of heat exchange by a two-phase flow is observed only for the range of the volume fraction of gas from 10 to 30%. In addition, the calculation of the thermal performance criterion, including both thermal and hydraulic parameters (friction factor), also confirmed the promise of using the Taylor segmented flow as a method for single-phase heat transfer intensifying in microchannels.

Comparative evaluation of color Doppler and conventional digital subtraction angiography in arterial disease

Introduction: Peripheral Arterial Occlusive Disease (PAOD) leads to narrowing and hardening of arteries which leads to increased risk of lower extremity amputation. Hence, the accuracy of non-invasive diagnostic methods such as Color Doppler (CD) needs to be assessed in comparison to the conventional digital subtraction angiography (CDSA). Objective: To compare color Doppler and conventional digital subtraction arteriography in patients of infragenicular arterial disease. To evaluate and correlate the findings of CD with arteriography as the gold standard, in PAOD of the lower extremities in supra-genicular part and to define whether color Doppler, is an alternative or an adjunct to DSA. Methods: In this study 60 patients suspected of lower limb PAD aged between 40 and 70 years were included. All these patients with symptoms suggestive of PAOD underwent color Doppler study of lower limb arterial system. Afterward, 55 patients of PAOD formed the subjects and their affected lower limbs evaluated by CD and arteriography, for localization and grading of lesion in the arteries, into normal/insignificant stenosis and occlusion. The sensitivity, specificity, and positive and negative predictive values of CD as compared to CDSA in arterial disease were calculated. Results were analyzed by two way contingency tables, using calculator, and SSP software. Results: As compared to conventional digital subtraction angiography, Doppler assessment was more sensitive specific with greater diagnostic accuracy. Conclusion: CD is better than conventional digital subtraction angiography in diagnosis of Grade 1 &2 cases, with better assessment of soft plaques, segmental flow and recanalization in PAD and CD performed well compared with conventional digital subtraction angiography. Hence color Doppler can be an alternative to conventional digital subtraction angiography in diagnosing peripheral arterial occlusive diseases in supragenicular part of lower limb arteries.

Method for Reproducible Shipboard Segmented Flow Analysis Ammonium Measurement Using an In-House Reference Material for Quality Control

Ammonium is a fundamental nutrient for phytoplankton growth in seawater and is a key component of the microbial loop. Ammonium measured in parallel with other nutrients is crucial in understanding the small temporal scale changes in oceanographic ecology. Despite the importance of measuring ammonium at sea, owing to its lability, there is no consensus on the best method. The lack of availability of certified reference materials for ammonium in seawater also makes it difficult to assess the accuracy and reproducibility of ammonium measurements. In this study we present a modified segmented flow analysis method using ortho-phthaldialdehyde (OPA) with fluorescence detection to measure ammonium at sea together with four other macro-nutrients (nitrate, nitrite, silicate and phosphate) in near real time. An in-house ammonium quality control (QC) material was produced to improve the accuracy and repeatability of the measurement at sea. The QC was prepared following two different methods and stored in two types of containers. The suitability of the in-house QC’s as a reference material were assessed onboard the RV Investigator in 2018 during two oceanographic voyages, including one on the repeat SR03 CLIVAR transect. This paper describes the production and assessment of the in-house QC for ammonium in seawater, providing groundwork for creating a short-term stable ammonium reference material for sea going voyages. The uncertainty of this method of ammonium measurement was found to be 0.10 μmol/L at ammonium concentration of 1.0 μmol/L. Results show that preparation of the QC inside a laminar flow cabinet and directly into 10 mL polypropylene sample tubes just prior to the commencement of the voyage improved its stability.

Continuous synthesis of monodisperse silica microspheres over 1 μm size

This study presents a robust and scalable method for synthesizing continuously the silica microspheres via the Stober method. Owing to the superb mixing accessible with gas-liquid segmented flow in coiled microtube, satisfactory morphology and mono-dispersity of silica spheres was obtained. The continuous method was firstly optimized through investigating the effects of various operation parameters on the morphology, particle size, size distribution and chemical structure of silica spheres. Without the surfactant, the size of silica spheres was limited < 850 nm due to the partial blockage of microchannel when synthesizing larger silica spheres. The addition of surfactant migrated the clogging issue, enabling the reliable synthesis of microspheres with diameters over 1 μm within a four times shorter residence time (30 min). Moreover, the mono-dispersity of silica microspheres could be further improved by increasing the gas/liquid ratio in segmented flow due to the more intensified mixing in liquid segments, as verified in visual flow field investigation.

Effect of wettability on hydrodynamics and mass transfer in small capillaries

The wettability of the reactor wall has a significant effect on the interfacial liquid–liquid mass transfer rates in segmented flow. This work quantitatively demonstrates the importance of choosing the right material of construction of flow reactors to achieve the desired mass transfer performance. Glass and PTFE capillaries of identical diameter were used to study the effect of hydrophilic and hydrophobic surfaces on the hydrodynamics and mass transfer of the system. It was observed that for the overall mass transfer coefficient (kLa) changed by two orders of magnitude depending on the wettability of the continuous phase. The observations indicated that it is essential to achieve complete wetting of the capillary walls by the continuous phase for significant mass transfer enhancement. The observations are discussed on the basis of film thickness and slip velocity at the wall as well as the slip velocity at liquid–liquid interface. Predictions of the mass transfer coefficient using a model based on the interfacial and fluid properties showed excellent match with the experiments thereby allowing us to explore the effects of wettability on the overall mass transfer coefficient in greater detail.

Direct observations of tribological behavior in cutting with textured cutting tools

As widely reported in the literature, the micro-texturing technique has a significant potential to improve the performance of cutting tools by reducing cutting forces, friction, temperature, and tool wear, and further, by improving tribological behavior at the tool-chip and tool-workpiece interface. However, it is also known that the effects of textures on the cutting tool surface strongly depend on the texture geometry and dimensions, and that the application of indiscriminate surface textures to cutting tools often results in adverse effects on cutting performance, indicating that an improved understanding of surface phenomena is required to further develop textured cutting tools. This paper summarizes recent advances in tool surface texturing in metal cutting fields, and continues to describe how the textured surface of a cutting tool influences the deformation fields of the workpiece material, including both primary and secondary shear zones, by means of direct in-situ observation using particle image velocimetry analysis to understand the behavior in the vicinity of the textured surfaces during the cutting process. The experimental results with the textured cutting tool reveal that the effect of the grooved rake face on the cutting force differs depending on the relative position of the microgroove with respect to the undeformed chip thickness. The friction condition and where the texture is located determine the performance of the surface texture. The link between the interface friction and chip flow mode is discussed, and it is demonstrated that surface textures can alter the chip flow mode from a segmented flow with redundant deformation to a steadier homogeneous flow with lower cutting energy.

Cu-catalyzed aerobic oxidation of diphenyl sulfide to diphenyl sulfoxide within a segmented flow regime: Modeling of a consecutive reaction network and reactor characterization

A continuous flow homogeneous Cu-catalyzed aerobic oxidation of diphenyl sulfide to diphenyl sulfoxide was investigated. The protocol utilized copper sulfate pentahydrate as catalyst, pyridine as ligand, molecular oxygen as oxidant, 2,2,6,6-tetramethyl-1-piperidinyl oxidanyl (TEMPO) as co-oxidant, and methanol as solvent. The continuous flow reactor system was characterized through a residence time distribution (RTD) study, showing that the flow reactor could be modeled as a plug flow reactor. The hydrodynamics of the system were simulated using computational fluid dynamics (CFD). The liquid slug length, bubble length and bubble frequency from the simulation closely corresponded to the experimentally-observed values. The volumetric mass transfer coefficient (kLa) was estimated by applying Higbie’s penetration model for micro-scale diffusion. A reaction profiling approach was applied within continuous flow to generate experimental data to fit a consecutive reaction network for the monooxidation of diphenyl sulfide to the diphenyl sulfoxide and then the subsequent overoxidation to the diphenyl sulfone. The reaction network comprised of four kinetic parameters (A1, Ea1, A2 and Ea2). Three out of four of the fitting parameters could be estimated with less than 7% uncertainty and the fitted model closely correspond to the experimental data, with R2 = 0.994. The fit-for-purpose model was then used to explore the experimental design space in silico. The models were successfully validated in a scale-out experiment which was operated over 4 h collection time to give 72% conversion and 65% sulfoxide yield, corresponding to a selectivity of 91% and a throughput of 0.61 g·h−1.

Circumferential trabecular meshwork cell density in the human eye

The cells residing in the trabecular meshwork (TM) fulfill important roles in the maintenance of the tissue and the regulation of intraocular pressure (IOP). Here we examine (i) TM cell distribution along the circumference of the human eye, (ii) differences in TM cell density between regions of high and low outflow, and (iii) whether TM cell distribution in eyes from donors with primary open angle glaucoma (POAG) differs from that of normal eyes. Toward this end, the TM cell density from 12 radial segments around the circumference of the TM of human donor eyes (n = 6) with and without POAG was determined using histochemical methods. Areas of high, median, and low outflow were mapped in a different set of human donor eyes that were perfused in organ culture, and TM cell densities in these areas were determined in normal (n = 11) and POAG eyes (n = 6).Our analysis of 1380 tissue sections taken from the first set of six eyes shows that the average TM cell density of these six eyes ranges from 15.5 to 23.7 cells/100 μm and is negatively correlated to the maximum IOP recorded for each donor eye (R2 = 0.91). Considerable differences in TM cell density exist among sections taken from the same segment of an individual eye (average standard deviation = 2.35 cells/100 μm). Less variability is observed among the segment averages across the eye's circumference (average standard deviation = 1.03 cells/100 μm). Variations in cell density are similar between normal and POAG eyes and are not correlated with the anatomic position of examined segments (p = 0.745). The analysis of the second set of eyes shows that TM regions of high outflow display a TM cell density similar to regions of median or low outflow in both normal and POAG eyes. Together these findings demonstrate that (i) statistically significant differences in TM cell density exist along the circumference of each eye (ii) TM cellularity is not correlated with segmental flow and (iii) eyes with POAG, while displaying reduced TM cellularity, do not exhibit higher TM cell variability than normal eyes. Finally, statistical analysis of sections and segments indicates that measurements from 12 sections taken from 2 segments provide a reliable and cost-effective estimate of a human eye's TM cell density.

Boundary Observer Design for Stochastic Phase Transition Models of Nonequilibrium Traffic Flow

State estimate of traffic flow of a freeway segment is considered by using the method of boundary observer design. The observer control and measurements are all located at the boundaries. The nonequilibrium traffic flow dynamics are modeled as a Markov jump linear hyperbolic system with phase transitions. Based on the Lyapunov techniques, the sufficient conditions of matrix inequalities are derived for the exponentially mean-square static as well as the dynamic boundary observer design. Using real traffic data of vehicle trajectories from the Next Generation Simulation (NGSIM) project, the developed stochastic phase transition model of the nonequilibrium traffic flow is calibrated. Moreover, the simulation results illustrate the effectiveness of the boundary observer design for traffic estimation.

Process Intensification Approach Using Microreactors for Synthesizing Nanomaterials-A Critical Review.

Nanomaterials have found many applications due to their unique properties such as high surface-to-volume ratio, density, strength, and many more. This review focuses on the recent developments on the synthesis of nanomaterials using process intensification. The review covers the designing of microreactors, design principles, and fundamental mechanisms involved in process intensification using microreactors for synthesizing nanomaterials. The microfluidics technology operates in continuous mode as well as the segmented flow of gas–liquid combinations. Various examples from the literature are discussed in detail highlighting the advantages and disadvantages of microfluidics technology for nanomaterial synthesis.

Numerical modeling of segmented flow in coiled flow inverter: Hydrodynamics and mass transfer studies

A novel CFD modeling approach was developed to investigate the hydrodynamics and mass transfer in a gas–liquid slug flowing through microscale coil and coiled flow inverter channels. One straight slug model was formulated by adding a virtual centrifugal body force. The model was validated in terms of the helicity and secondary flow magnitude. The secondary flow magnitude was shown to be a power function of the Dean number, and a new correlation was proposed. The mass transfer across the interface was compared to that obtained in previous studies. The new model described the temporal and spatial distribution of species in the slug reasonably well. The volumetric mass transfer coefficient kLa in the coil was found to be 1.5 times higher than that in the straight channel, and the enhancement in kLa reached a maximum at a modified Dean number of 1.2.

Analysis of the impact of the labyrinth seal geometric parameters on the leakage

This paper includes results of experimental research and CFD calculations concerning gas flow in segments of straight through labyrinth seals of fixed length and varying number of teeth. Relation between the number of teeth and the leakage is analyzed in this paper. Authors determined the range of teeth number for which the minimum leakage was achieved. They focused particularly on the analysis of geometry with maximum number of teeth which fell within the range of the minimum leakage. For this geometry they examined the relation between the thickness of the teeth and the distribution of gas pressure and velocity along the seal and the leakage size. Data presented in this paper indicate that the teeth thickness has a significant impact on the flow parameters.

Modeling fluid outflow from a channel consisting of three different segments

The topic of the article is modeling fluid outflow from a channel consisting of three different segments. The subject of research is the outflow of fluid from a channel consisting of three different sections. The article discusses the parameters of the fluid flow in the channel segments of the converging flow section, the section of a constant radius and expanding flow section. Research methods are based on Newton's rheological law; the continuity equation and the Navier-Stokes equation, which are the basic equations of fluid flow; and on the method of mathematical modeling and analytical method of solution. Expressions of hydrodynamic parameters for each segment, with a successively located converging section, a section of a constant radius, and expanding flow sections, are determined in the article by analytical method. Analytical expressions are obtained for the pressure and average flow rate of the fluid in the channel where there are converging rectilinear inlet flow area, cylindrical average area, and expanding rectilinear outlet flow area. The solutions obtained make it possible to determine the flow parameters in the zone of the vibration baffle of pipeline transport of such a geometry that damps vibrations caused by the flow; in the transition sections of the channels of hydraulic drives and in other channels of the fluid flow, which are set to improve the hydrodynamic parameters of the flow.

In Search of the Origins of Financial Fluctuations: The Inelastic Markets Hypothesis

We develop a framework to theoretically and empirically analyze the fluctuations of the aggregate stock market. Households allocate capital to institutions, which are fairly constrained, for example operating with a mandate to maintain a fixed equity share or with moderate scope for variation in response to changing market conditions. As a result, the price elasticity of demand of the aggregate stock market is small, and flows in and out of the stock market have large impacts on prices. Using the recent method of granular instrumental variables, we find that investing $1 in the stock market increases the market's aggregate value by about $5. We also develop a new measure of capital flows into the market, consistent with our theory. We relate it to prices, macroeconomic variables, and survey expectations of returns. We analyze how key parts of macro-finance change if markets are inelastic. We show how general equilibrium models and pricing kernels can be generalized to incorporate flows, which makes them amenable to use in more realistic macroeconomic models and to policy analysis. Our framework allows us to give a dynamic economic structure to old and recent datasets comprising holdings and flows in various segments of the market. The mystery of apparently random movements of the stock market, hard to link to fundamentals, is replaced by the more manageable problem of understanding the determinants of flows in inelastic markets. We delineate a research agenda that can explore a number of questions raised by this analysis, and might lead to a more concrete understanding of the origins of financial fluctuations across markets.