Transition Velocity Research Articles

The evolution of hot Jupiters revealed by the age distribution of their host stars.

The unexpected discovery of hot Jupiters challenged the classical theory of planet formation inspired by our solar system. Until now, the origin and evolution of hot Jupiters are still uncertain. Determining their age distribution and temporal evolution can provide more clues into the mechanism of their formation and subsequent evolution. Using a sample of 383 giant planets around Sun-like stars collected from the kinematic catalogs of the Planets Across Space and Time project, we find that hot Jupiters are preferentially hosted by relatively younger stars in the Galactic thin disk. We subsequently find that the frequency of hot Jupiters declines with age as [Formula: see text]. In contrast, the frequency of warm/cold Jupiters shows no significant dependence on age. Such a trend is expected from the tidal evolution of hot Jupiters' orbits, and our result offers supporting evidence using a large sample. We also perform a joint analysis on the planet frequencies in the stellar age-metallicity plane. The result suggests that the frequencies of hot Jupiters and warm/cold Jupiters, after removing the age dependence are both correlated with stellar metallicities as [Formula: see text] and [Formula: see text], respectively. Moreover, we show that the above correlations can explain the bulk of the discrepancy in hot Jupiter frequencies inferred from the transit and radial velocity (RV) surveys, given that RV targets tend to be more metal-rich and younger than transits.

Can Cold Jupiters Sculpt the Edge-of-the-multis?

Compact systems of multiple close-in super-Earths/sub-Neptunes (compact multis) are a ubiquitous outcome of planet formation. It was recently discovered that the outer edges of compact multis are located at smaller orbital periods than expected from geometric and detection biases alone, suggesting some truncation or transition in the outer architectures. Here we test whether this edge-of-the-multis might be explained in any part by distant giant planets in the outer regions (≳1 au) of the systems. We investigate the dynamical stability of observed compact multis in the presence of hypothetical giant (≳0.5 M Jup) perturbing planets. We identify what parameters would be required for hypothetical perturbing planets if they were responsible for dynamically sculpting the outer edges of compact multis. Edge-sculpting perturbers are generally in the range of P ∼ 100–500 days for the average compact multi, with most between P ∼ 200 and 300 days. Given the relatively close separation, we explore the detectability of the hypothetical edge-sculpting perturbing planets, finding that they would be readily detectable in transit and radial velocity data. We compare to observational constraints and find it unlikely that dynamical sculpting from distant giant planets contributes significantly to the edge-of-the-multis. However, this conclusion could be strengthened in future work by a more thorough analysis of the detection yields of the perturbing planets.

Effects of projectile parameters on the momentum transfer and projectile melting during hypervelocity impact

The effects of projectile/target impedance matching and projectile shape on energy, momentum transfer and projectile melting during collisions are investigated by numerical simulation. By comparing the computation results with the experimental results, the correctness of the calculation and the statistical method of momentum transfer coefficient is verified. Different shapes of aluminum, copper and heavy tungsten alloy projectiles striking aluminum, basalt, and pumice target for impacts up to 10 km/s are simulated. The influence mechanism of the shape of the projectile and projectile/target density on the momentum transfer was obtained. With an increase in projectile density and length-diameter ratio, the energy transfer time between the projectile and targets is prolonged. The projectile decelerates slowly, resulting in a larger cratering depth. The energy consumed by the projectile in the excavation stage increased, resulting in lower mass-velocity of ejecta and momentum transfer coefficient. The numerical simulation results demonstrated that for different projectile/target combinations, the higher the wave impedance of the projectile, the higher the initial phase transition velocity and the smaller the mass of phase transition. The results can provide theoretical guidance for kinetic impactor design and material selection.

Insights into protective performance of CoCrNi medium entropy alloy coating subjected to supersonic micro-ballistic impact

Medium- and high-entropy alloys (MEAs and HEAs) coatings have attracted increasing attention owing to their exceptional mechanical properties and potential applications in structures protective from supersonic microparticle impact. However, there are no experimental insights into their protective performance. In this study, we fabricated high-quality amorphous CoCrNi MEA coatings with a thickness of 4.5 μm on the rigid and flexible substrates through ion beam-assisted deposition. Based on nanoindentation and laser-induced supersonic microparticle impact experiments, the mechanical properties and protective performance of the CoCrNi MEA coating were characterized and compared with those of the aluminum and copper coating. The results show that the CoCrNi MEA coating exhibits a high hardness of 9.7 GPa and an elastic modulus of 146.8 GPa. Under the supersonic impact, the CoCrNi MEA coating shows high coefficient of restitution, low rebound-to-fracture transition velocity, and small impact-mode ratios. The impact-mode ratios of the CoCrNi MEA coating subjected to microparticles of different materials further indicate that the CoCrNi MEA coating can efficiently withstand the high-velocity impact of most metallic particles except tungsten ones. Our work provides direct experimental insights into the excellent impact resistance of CoCrNi MEA coatings, which holds a great promise for improving the reliability and durability of equipment subjected to high-speed collisions of solid particles entrained within the air such as ice and sand dust.

Destinations and Pathways of the Indonesian Throughflow Water in the Indian Ocean

Abstract Passage of the Indonesian Throughflow (ITF) water through the Indian Ocean constitutes an essential section of the upper limb of the global ocean conveyor belt. Although existing studies have identified a major exit of the ITF water to the Atlantic Ocean through the Agulhas Current system, our knowledge regarding other possible destinations and primary pathways remains limited. This study applies the Connectivity Modeling System (CMS) particle tracking algorithm to seven model-based ocean current datasets. The results reveal a robust return path of the ITF water to the Pacific Ocean. The partition ratio between the Atlantic and Pacific routes is 1.60 ± 0.54 to 1, with the uncertainty representing interdataset spread. The average transit time across the Indian Ocean is 10–20 years to the Atlantic and 15–30 years to the Pacific. The “transit velocity” is devised to describe the three-dimensional pathways in a quantitative sense. Its distribution demonstrates that the recirculation structures in the southwestern subtropical Indian Ocean favor the exit to the Atlantic, while the Antarctic Circumpolar Current in the Southern Ocean serves as the primary corridor to the Pacific. Our analysis also suggests the vital impact of vertical motions. In idealized tracing experiments inhibiting vertical currents and turbulent mixing, more water tends to linger over the Indian Ocean or return to the Pacific. Turbulence mixing also contributes to vertical motions but only slightly affects the destinations and pathways of ITF water.

Updated Planetary Mass Constraints of the Young V1298 Tau System Using MAROON-X

The early K-type T-Tauri star, V1298 Tau (V = 10 mag, age ≈ 20–30 Myr) hosts four transiting planets with radii ranging from 4.9 to 9.6 R ⊕. The three inner planets have orbital periods of ≈8–24 days while the outer planet’s period is poorly constrained by single transits observed with K2 and the Transiting Exoplanet Survey Satellite (TESS). Planets b, c, and d are proto–sub-Neptunes that may be undergoing significant mass loss. Depending on the stellar activity and planet masses, they are expected to evolve into super-Earths/sub-Neptunes that bound the radius valley. Here we present results of a joint transit and radial velocity (RV) modeling analysis, which includes recently obtained TESS photometry and MAROON-X RV measurements. Assuming circular orbits, we obtain a low-significance (≈2σ) RV detection of planet c, implying a mass of and a conservative 2σ upper limit of <39 M ⊕. For planets b and d, we derive 2σ upper limits of M b < 159 M ⊕ and M d < 41 M ⊕, respectively. For planet e, plausible discrete periods of P e > 55.4 days are ruled out at the 3σ level while seven solutions with 43.3 < P e/d < 55.4 are consistent with the most probable 46.768131 ± 000076 days solution within 3σ. Adopting the most probable solution yields a 2.6σ RV detection with a mass of 0.66 ± 0.26 M Jup. Comparing the updated mass and radius constraints with planetary evolution and interior structure models shows that planets b, d, and e are consistent with predictions for young gas-rich planets and that planet c is consistent with having a water-rich core with a substantial (∼5% by mass) H2 envelope.

The study of phase transition of MoS2 regulated by H+

The mixed-phase MoS2 (1T/2H MoS2) with heterostructure exhibited high catalytic activity. The specific ratios of 1T/2H could exhibit optimal performance in various applications. Therefore, more methods need be developed for synthesizing 1T/2H mixed-phase MoS2. Herein, a viable route was studied for the phase transition of 1T/2H MoS2 regulated by H+. Briefly, the commercially available bulk MoS2 was used to obtain 1T/2H MoS2 via chemical intercalation of Li+. Then the residual Li+ around 1T/2H MoS2 was replaced by H+ in acidic electrolytes, owing to the extremely higher charge-to-volume ratio of H+. Thus, the thermodynamically unstable 1T phase lost the protection of residual Li+ and could be re-transforming into the relatively stable 2H phase. The change of the 2H/(2H+1T) ratio was measured using novel extinction spectroscopy, which provides a rapid identification method in comparison with x-ray photoelectron spectroscopy (XPS). The experimental results revealed that the concentration of H+ influenced the phase transition velocity of MoS2. In particular, the phase transition from 1T to 2H phase in the H+ solution was faster at the beginning, and the higher the H+ concentration in an acidic solution, the faster the increase in 2H content. For an instant, the ratio of the 2H phase was increased by 7.08% in an acidic solution (CH + = 2.00 M) after 1 h, which was several times greater than the case in the distilled water. This finding provides a promising method to easily obtain different ratios of 1T/2H MoS2, which is beneficial for further development of catalytic performance especially in energy generation and storage.

Transport effects in biochip sensors with redox cycling amplification

We report a study of transport effects on a microfluidic sensor-chip in which electrochemical sensing is amplified by redox cycling using an interdigitated electrode array (IDA). A full three-dimensional simulation-based model and a simple one-dimensional model for the transition velocity between the two regimes is presented. These models indicate that there exist two dominant regimes: one which is limited by redox cycling diffusion—a unique feature of IDAs— and another which is limited by convection and has dominant flow effects. The transition velocity between the two sensing regimes was found to be vflow[mmsec]=0.335L[μm]+0.04 which is similar to the prediction of vflow∝1L, obtained from the one-dimensional model.

Study of the thickness of the liquid film formed by a round water jet impinging on a curved cylindrical wall

An experimental setup has been established to investigate the thickness profiles of the liquid film formed by an oblique round water jet impinging on curved walls. The influence of the jet velocity, jet angle, and radius of curvature of the curved wall on the thickness profile of the liquid film has been investigated. Both on the flat and curved walls, as the jet velocity increases, the mode of the liquid film transitions from laminar to turbulent, and the thickness of the liquid film decreases first and then increases along the flow direction. The transition velocity range for the curved walls with the radius of curvature R = 30 mm is 19.1–25.08 m/s (Re = 10 946–14 373). Both on the flat and curved walls, the thicknesses of the liquid film increase in the downstream part of the liquid film while decreasing in the upstream part, as the jet angle increases. The laminar and turbulent thickness prediction models of liquid film on flat walls were extended to curved walls by replacing the distance away from a stagnation point with the radius of curvature. Predictions obtained by the present models agree well with measurements. Errors of the film thickness between the predictions and measurements along the centerline are mainly less than 20%, and the correlation coefficients (σc) are mainly located in 0.85–0.99.

A novel dynamic dry friction model for applications in mechanical dynamical systems

This work presents a novel continuously differentiable, dynamic dry friction model, with dependence on normal contact force, slip velocity, and static and dynamic coefficients of friction. The state-of-the-art, Brown and McPhee friction model depends on transitional velocity, which is an empirical parameter. A limitation with this model is that there is no generic approach to select the optimal value for the transitional velocity for a certain application. The simulation results presented in this work highlight the sensitivity of friction force with transitional velocity in Brown and McPhee’s model to obtain smooth solutions, which are supportive in control system applications. It is because control systems require jitter-free signals in order to save costs on low-pass filters. The proposed model overcomes such empirical dependence on transition velocity through a combination of an iterative methodology and an empirical parameterization. In this article, a comprehensive analysis of the proposed friction model and the contributing parameters is carried out. The algorithm to implement the proposed friction model is elaborated. The proposed friction model is then simulated and compared against Brown and McPhee’s model. using a stick-slip benchmark problem. Furthermore, the proposed force model is applied to two spatial multibody systems formulated using index 0 tangent space differential-algebraic equations. The results demonstrate how the proposed friction model can be employed in dynamical mechanical systems. The independence on transitional velocity in the proposed friction model is observed to be effective for obtaining smooth solutions that make it suitable for control system applications.

Impact dynamics of droplets on the well-designed wrinkled surfaces: Enhancement of bounding ability

Designing the nanostructured substrates with efficiently executing self-cleaning functions such as anti-icing, anti-fogging, anti-flaming, and anti-corrosion is always a hot scientific research topic and plays an essential role in practical applications. Herein, a novel substrate decorated with wrinkled structures is investigated. Results show that it has a large improvement in the reduction of contact time compared with the smooth substrate, and could affect the critical velocity of transition between retraction rebound and non-reaction transition. Effects of geometrical parameters of the wrinkled structures on droplet rebounding ability are detailed discussed, such as angles, intervals, and arrangement gradient. Most importantly, a well-designed substrate decorated with wrinkled structures and two confinement walls is proposed, which is found that the contact time could be largely reduced due to the limitation of spreading behaviors of the impacting droplets resulting from the heavy restriction effect of the confined walls. The findings of this work are expected to provide potential implications for many multidisciplinary fields, such as aerospace engineering, industrial manufacturing, interfacial heat transfer, environment, energy storage, and so forth.

Correlation between RF signal first-arrival and minimum spectral transit time in cancellous bone

Measurement of the singular ultrasound velocity of a homogeneous sample may be calculated by division of its thickness and propagation transit time, generally utilizing a detection criterion of an RF signal’s first-arrival. A porous composite sample composed of two materials of differing ultrasound velocity will however exhibit a range of transit times. Ultrasound transit time spectroscopy (UTTS) considers propagation of an array of sonic-rays, with minima and maxima values ranging from entire higher and lower velocity materials, respectively. The aim of this Technical Note is to test the hypothesis that conventional RF signal transit time measurement correlates with the minimum spectral transit time, utilizing previously obtained experimental data from human cancellous bone samples. Linear regression yielded a coefficient of determination (R2) of 94%. The authors consider a practical consequence of the hypothesis is that information on the variability of transit time within a heterogeneous test sample may be better assessed by UTTS than conventional RF first-arrival transit time measurement. Noting the fundamental relationships between transit time, velocity, and elasticity of a test sample, there is further potential for UTTS to describe both velocity and elasticity spectroscopies within a wide range of structurally complex composites.

Experimental and Numerical Analysis of the Effect of Rheological Models on Measurements of Shear-Thinning Fluid Flow in Smooth Pipes

The aim of this research is to investigate the effects of rheological models of shear-thinning fluids and their estimated parameters on the predictions of laminar, transitional, and turbulent flow. The investigation was carried out through experimental and computational fluid dynamics (CFD) studies in horizontal pipes (diameters of 19.1 mm and 76.2 mm). Six turbulent models using Reynolds averaged Navier–Stokes equations in CFD_ANSYS Fluent 19.0 were examined in a 3D simulation followed by comparison studies between numerical and experimental results. Regarding results of laminar regions in power-law rheology models, Metzner and Reed presented the best fit for the pressure loss and transitional velocity. For the turbulent region, correlations observed by Wilson and Thomas as well as Dodge and Matzner had good agreement with the experimental results. For Herschel–Bulkley fluids, pressure losses and transitional regions based on a yielded region were examined and compared to the experimental results and the modified Slatter Reynolds number, where the results provided good estimation. For both pipe diameters, the Slatter model was the best fit for pressure losses of Herschel–Bulkley fluids in the turbulent regime. Furthermore, when comparing k-omega and k-epsilon turbulence models to the power-law behaviour, numerical studies delivered the most accurate results with fluids that have a higher behaviour index. However, the error percentage significantly increased at a higher shear rate in the Herschel–Bulkley fluids with a greater yield stress effect. Moreover, the modified Herschel–Bulkley viscosity function by Papanastasiou was implemented in the current CFD study. This function was numerically stabilized, devoid of discontinuity at a low strain rate, and more effective in transitional regions.

Sound velocities of natural goethite across α–ɛ phase transformation under dynamic compression

Goethite (α-FeOOH), a vital water- and hydrogen-bearing natural mineral, is extensively distributed on the Earth's surface and probably in the lower mantle. Laboratory measurements of its phase transition and sound velocities provide crucial data for a more rational understanding of the deep-water transportation and physical properties of the Earth's interior. Herein, the Hugoniot equation of state and sound velocities of natural goethite up to around 15 GPa are measured by dynamic compression. The discontinuities pertinent to the density and sound velocities of goethite are observed at 7.1 (2) GPa, in which a solid–solid phase transition occurs from α- (Pbnm) to ɛ-FeOOH (P21nm). Through this structural phase transition, the longitudinal and shear wave velocities in order, enhance by about 5% and 12%. We suggest that changes in the sound velocity due to the FeOOH phase transition may contribute to the discontinuity in the subduction zones.

Investigation of mechanical and insulation properties of Sorel cement binding light concrete

In this study, some mechanical and insulation properties of light concrete with Sorel cement were investigated by using Sorel cement, which is an alternative to cements used in the market. In addition, samples were produced by substituting some additives separately into the Sorel cement mixtures in order to evaluate the waste materials in the inactive state and to improve some of the mechanical and insulation properties of the Sorel cemented samples. In this study the flexural and compressive strengths, thermal conductivity, thermal resistance, ultrasound transition velocity, unit weight, water absorption and apparent porosity, bulk expansion, alkali silica reaction (ASR), surface area analysis (BET) and microstructures of samples were investigated. The reference samples were Sorel cement (SC), the other samples were made of mixtures of SC, pumice (P), air-entraining additive (AEA), Afşin Elbistan fly ash (AEFA), wood and corncob shavings (WS, CS). According to the findings, it can be said that while the flexural and compressive strength of the lightweight aggregate samples decreased compared to the reference sample, there were improvements in heat and sound insulation properties. The determined values differed according to the type and ratio of lightweight aggregates. It was observed that the increase in the ambient temperature of the SC samples had a positive effect on the flexural and compressive strength values up to 100 °C, while it caused a decrease in the strength values after a certain temperature. It was seen that the strength values of SC samples kept in water decreased due to the cracks formed. The results showed that the samples produced with Sorel cement had high strength. Sample strengths produced with pumice used as aggregate are higher than those with wood chips and corncob sawdust. It was determined that Sorel cement could not be used together with AEFA because the samples were shattered. No incompatibility was observed with AEA and WS additives either; however, the strength value was low in those with CS added.

Turbulent fluidization and transition velocity of Geldart B granules in a spout–fluidized bed reactor

Turbulent fluidization and transition velocity of Geldart B granules in a spout–fluidized bed reactor

MP05-07 VALIDATING THE THEORY OF PHASE TRANSITION FROM CALCIUM OXALATE DIHYDRATE TO MONOHYDRATE IN THE STONE FORMATION: THE FIRST ARTIFICIAL IN VIVO EXPERIMENT

You have accessJournal of UrologyCME1 Apr 2023MP05-07 VALIDATING THE THEORY OF PHASE TRANSITION FROM CALCIUM OXALATE DIHYDRATE TO MONOHYDRATE IN THE STONE FORMATION: THE FIRST ARTIFICIAL IN VIVO EXPERIMENT Mihoko Maruyama, Uta Michibata, Yutaro Tanaka, Hiroshi Yoshikawa, Kazufumi Takano, Rie Tajiri, Kazumi Taguchi, Shuzo Hamamoto, Atsushi Okada, Takahiro Yasui, Shigeyoshi Usami, Masayuki Imanishi, Masashi Yoshimura, and Yusuke Mori Mihoko MaruyamaMihoko Maruyama More articles by this author , Uta MichibataUta Michibata More articles by this author , Yutaro TanakaYutaro Tanaka More articles by this author , Hiroshi YoshikawaHiroshi Yoshikawa More articles by this author , Kazufumi TakanoKazufumi Takano More articles by this author , Rie TajiriRie Tajiri More articles by this author , Kazumi TaguchiKazumi Taguchi More articles by this author , Shuzo HamamotoShuzo Hamamoto More articles by this author , Atsushi OkadaAtsushi Okada More articles by this author , Takahiro YasuiTakahiro Yasui More articles by this author , Shigeyoshi UsamiShigeyoshi Usami More articles by this author , Masayuki ImanishiMasayuki Imanishi More articles by this author , Masashi YoshimuraMasashi Yoshimura More articles by this author , and Yusuke MoriYusuke Mori More articles by this author View All Author Informationhttps://doi.org/10.1097/JU.0000000000003216.07AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookLinked InTwitterEmail Abstract INTRODUCTION AND OBJECTIVE: We have previously reported that the phase transition phenomenon of calcium oxalate (CaOx) makes urinary stones harder. Knowing phase transition velocity helps estimate the change of the patient's stone hardness over time. It affects the decision-making of the fragmentation treatment methods. However, the mechanism of the phase transition has not been clarified. Therefore, we stimulated the phase transition of CaOx dihydrate (COD) stone to CaOx monohydrate (COM), and observed the time course of the internal and surface structure. METHODS: A urinary stone mainly composed of COD, in which the phase transition has not progressed much, was stored in a vial containing CaOx supersaturated solution at 37oC with gentle shaking. We picked up the stone from the solution every week and observed the phase transition process from COD to COM. X-ray micro-CT and scanning electron microscopy were introduced. After completing the phase transition observation, a thin section of the stone was prepared. Then, the phase identification was performed in more detail using polarizing microscopy and Raman microscopy. RESULTS: The dissolution of the COD crystal surface and nucleation of COM crystals co-occurred. The inside of the COD stone underwent a phase transition to COM. After the transition, we found typical mosaic and concentric structures of COM (Figure 1). The extent of the transition from COD to COM strongly depended on the area. An area where crystal defects, cracks, and crystal boundaries exist, transited fast (∼10 μm/h); a few millimeter size COD crystals almost turned into COM structures in only two weeks. The transition ratio was faster than that in the human body. CONCLUSIONS: We have succeeded in the world's first artificial urinary stone phase transition experiment. Once the phase transition starts, rapid progress possibly occurs. Further, transformation velocity strongly depends on COD crystal structure and aggregation state. Our observation showed experimental phase transition of a natural urinary stone is faster than that in the human body, and indicated a potential mechanism enabled to slow down the phase transition of crystals in vivo, which could be useful to prevent stone formation. Source of Funding: JSPS KAKENHI Grant Numbers (JP19K22965, JP20K21658, JP22H00302, JP22H01971) © 2023 by American Urological Association Education and Research, Inc.FiguresReferencesRelatedDetails Volume 209Issue Supplement 4April 2023Page: e46 Advertisement Copyright & Permissions© 2023 by American Urological Association Education and Research, Inc.MetricsAuthor Information Mihoko Maruyama More articles by this author Uta Michibata More articles by this author Yutaro Tanaka More articles by this author Hiroshi Yoshikawa More articles by this author Kazufumi Takano More articles by this author Rie Tajiri More articles by this author Kazumi Taguchi More articles by this author Shuzo Hamamoto More articles by this author Atsushi Okada More articles by this author Takahiro Yasui More articles by this author Shigeyoshi Usami More articles by this author Masayuki Imanishi More articles by this author Masashi Yoshimura More articles by this author Yusuke Mori More articles by this author Expand All Advertisement PDF downloadLoading ...

Recruit-aged adults may preferentially weight task goals over deleterious cost functions during short duration loaded and imposed gait tasks

Optimal motor control that is stable and adaptable to perturbation is reflected in the temporal arrangement and regulation of gait variability. Load carriage and forced-marching are common military relevant perturbations to gait that have been implicated in the high incidence of musculoskeletal injuries in military populations. We investigated the interactive effects of load magnitude and locomotion pattern on motor variability, stride regulation and spatiotemporal complexity during gait in recruit-aged adults. We further investigated the influences of sex and task duration. Healthy adults executed trials of running and forced-marching with and without loads at 10% above their gait transition velocity. Spatiotemporal parameters were analyzed using a goal equivalent manifold approach. With load and forced-marching, individuals used a greater array of motor solutions to execute the task goal (maintain velocity). Stride-to-stride regulation became stricter as the task progressed. Participants exhibited optimal spatiotemporal complexity with significant but not meaningful differences between sexes. With the introduction of load carriage and forced-marching, individuals relied on a strategy that maximizes and regulates motor solutions that achieve the task goal of velocity specifically but compete with other task functions. The appended cost penalties may have deleterious effects during prolonged execution, potentially increasing the risk of musculoskeletal injuries.

Effect of Jet Velocity on the Formation of Moderate or Intense Low-Oxygen Dilution Combustion of Pulverized Coal.

Moderate or intense low-oxygen dilution (MILD) combustion of pulverized coal is regarded as a new combustion technology with great potential due to its advantages of reducing NO x emission and improving the uniformity of heat flux in the furnace. Increasing the jet velocity has been proved to be an important technical means to achieve MILD oxy-coal combustion, especially without a high level of preheat, but the transition mechanism of coal combustion modes with the increase of jet velocity is not clear enough. In this work, a high-velocity coal-laden jet combustion system on the basis of a flat-flame burner was designed to study the effect of jet velocity on the formation of MILD combustion of pulverized coal. The combustion mode transition of the pulverized coal jet is revealed by analyzing the flame structure, temperature, radiation, and reaction intensity through a variety of optical measurement methods. Theoretical criteria for combustion mode were applied to predict the formation of MILD combustion and were validated by the experimental data. In the environment with an ambient temperature of 1600 °C, the transition velocity of the coal jet into the MILD combustion regime is about 50 m/s and about 100 m/s at 5 and 15% O2 molar fraction, respectively. The dilution effect, jet entrainment, and turbulent mixing in the high-velocity jet, as the key factors to achieve an MILD combustion regime, were analyzed theoretically and experimentally. The dilution effect inherent in the jet significantly reduces the reactant concentration and ultimately reduces the reaction intensity and flame brightness while the entrainment of the jet promotes the radial dispersion of particles and the flame uniformity, which is dominant at lower jet velocities. Strong turbulent mixing promotes the ignition and volatile combustion, which is dominant at higher jet velocities.

Comparisons of Detection Paradigm of Planet: Transit and Radial Velocity

The transit and radial velocity method are two most widely used approach in exoplanet detection. This paper compares the advantages and disadvantages of two methods based on the characteristics of planets they found and different calculation results. Different distribution of parameters brings the preference for two methods. In detail, the radial velocity method discovered more gigantic planets while still have most planets with smaller size like that of the transit method. The minimum and maximum of orbital period are all relatively lower for transit method. Significant difference in the composition of planets found by two method occurs when combining mass and radius to compare density distribution. More Super-Earth planets seem to appear in transit data compared to radial velocity method in the same radius range. These patterns are closely related to the characteristics of observation condition. The various data processing method also affects the resulting parameters. This paper attempts to reach the calculation for transit and radial velocity method with basic fitting models, which will be compared with calculations of the same planets from previous researches. These results shed light on guiding further exploration of planet detections.