Conical Region Research Articles

Two-wind interactions in binaries with two orbiting giant stars

ABSTRACT Some red giant envelopes present spiral structures (seen either in dust-scattered stellar continuum or in molecular line emission), the most striking example probably being AFGL 3068. This object has been modeled (both analytically and numerically) in terms of a wind ejected from a star in orbit around a binary companion. We revisit both analytical models and 3D simulations of a wind from an orbiting red giant star, and extend the numerical simulations to the case of a binary with two red giants with strong winds. We find that most two-wind models on the orbital plane show a ‘double spiral’ structure close to the binary source, and that these two arms merge into a single spiral structure at larger distances. However, for the case of a binary with two identical winds, the two spiral arms are still present at large distances from the binary source. We also find that for models of two (not identical) dynamically important winds, a region close to the orbital plane has material from both winds. Also, an approximately conical region centered on the orbital axis is filled exclusively by the wind with larger momentum rate. These two structures lead to morphologies reminiscent of the so-called ‘hour glass’ planetary nebulae. Finally, we find that increasing wind velocity disparities lead to the formation of clumpy structures along the spiral arms. Observations of ‘clumpy spirals’ are therefore likely to indicate the presence of two strong winds from the stars in the central binary system.

Mitigating exhalation puffs during oxygen therapy for respiratory disease.

We investigate the dispersal of exhalations corresponding to a patient experiencing shortness of breath while being treated for a respiratory disease with oxygen therapy. Respiration through a nasal cannula and a simple O2 mask is studied using a supine manikin equipped with a controllable mechanical lung by measuring aerosol density and flow with direct imaging. Exhalation puffs are observed to travel 0.35 ± 0.02 m upward while wearing a nasal cannula, and 0.29 ± 0.02 m laterally through a simple O2 mask, posing a higher direct exposure risk to caregivers. The aerosol-laden air flows were found to concentrate in narrow conical regions through both devices at several times their concentration level compared with a uniform spreading at the same distance. We test a mitigation strategy by placing a surgical mask loosely over the tested devices. The mask is demonstrated to alleviate exposure by deflecting the exhalations from being launched directly above a supine patient. The surgical mask is found to essentially eliminate the concentrated aerosol regions above the patient over the entire oxygenation rates used in treatment in both devices.

Study on the particle interaction in a hydrocyclone classifier with multi-component feed blend at a high solids content

In mineral processing circuits, the feed to hydrocyclone consists of different density particle system at varying degrees of liberation and sizes, leading to a multi-component system. These different density components' interaction affects the separation in the hydrocyclones, particularly at high feed solids concentrations. In this work, an attempt is made to account for bi-component particle interaction in a hydrocyclone at different feed solids concentrations (10–50 wt%). For classification experiments, pure silica and pure magnetite components were utilized as a ratio of 1:1 in the feed mixture. Customized orthogonal array experiments were carried out using three-spigot and pressure level for 3″ and 4″ hydrocyclones. Components' grade efficiency curves and the performance parameters (d50; Rf; Rs;α;β) were estimated and analysed using the Whiten Equation. The cut-size and beta parameter of the mixture and individual components witnessed to increase with increasing feed solids concentration. Suspension rheology and hindered settling rate studies were carried out to understand the influence of the fine and coarse particle interaction on the performance of the hydrocyclone processing bi-component mixture at different feed solids concentrations. The enhanced viscous flow at the conical region attributes the crowding effect and the dense medium effect near apex zone, and consequential coarse and fines inflections are observed. The lighter particle displacement in the presence of heavier component is further supported by the locus of maximum volume fraction and equilibrium position from the numerical analysis.

Photo-dissociation mechanism of trifluoroacetyl chloride in the gas phase: AIMS dynamic simulations.

In this article, the structures and energies of CF3COCl in the low-lying electronic states have been determined by SA-2-CAS(8,7)/6-31G* and SA-2-MSPT2(8,7)/6-31G* calculations, which include equilibrium geometries, transition states, and three minimum-energy conical intersections (CI-1, CI-2, and CI-3) between S0 and S1 states. The AIMS method was used to carry out non-adiabatic dynamic simulations with the ab initio calculation performed at the SA-2-CAS(8,7)/6-31G* level. Upon irradiation to the S1 state, CF3COCl first relaxes to S1 minimum and then overcomes the ∼10 kcal/mol (TSS1_CCl) or ∼30 kcal/mol (TSS1_CO) barrier to the conical intersection region CI-1 or CI-3 (minor), with the S1 → S0 transition probability of 63:1. After non-adiabatic transition to the S0 state through CI-1, trajectories mainly distribute to three different reaction pathways, with one going back to S0 minimum through shortening of the C-Cl bond, the other forming CF3CO and Cl radicals by continuous elongation of the C-Cl distance, and another dissociating into CF3 + CO + Cl and running into the CI-3 region through elongation of C-C and C-Cl distances. Moreover, we found that the trajectories would recross to the S1 state with the recrossing probability of 13.9% through the CI-3 region due to the extremely sloped topographic character of CI-3. On the basis of time evolution of wavefunctions simulated here, the product ratio of CF3 + CO + Cl and CF3CO + Cl is 53.5%:18.4%, which is consistent with the experimental value of 3:1. We further explain the photo-dissociation wavelength dependence of CF3COCl, and the product ratio of CF3 + CO + Cl increases with the increase in total energy.

Virtual implantation technique to estimate endoprosthetic contact of percutaneous osseointegrated devices in the tibia

Percutaneous osseointegrated (OI) devices have an endoprosthesis attached to the residual bone of an amputated limb, then pass permanently through the skin to be connected to the distal prosthetic componentry outside of the body. Whether the bone-anchoring region of current OI endoprostheses are cylindrical, and/or conical, they require intimate bone-endoprosthesis contact to promote stabilizing bone attachment. However, removing too much cortical bone to achieve more contact leads to thinner and, subsequently, weaker cortical walls. Endoprostheses need to be designed to balance these factors, namely maximizing the contact, while minimizing the volume of bone removed. In this study, 27 human tibias were used to develop and validate a virtual implantation method. Then, 40 additional tibias were virtually implanted with mock cylindrical and conical bone-anchoring regions at seven residual limb lengths to measure resultant bone-endoprosthesis contact and bone removal. The ratio of bone-endoprosthesis contact to bone volume removed showed the conical geometry had more contact area per volume bone removed for all amputation levels (p ≤ 0.001). In both mock devices, cortical penetration of the endoprosthesis at 20% residual length occurred in 74% of cases evaluated, indicating that alternative endoprosthesis geometries may be needed for clinical success in that region of bone.

"On-The-Fly" Non-Adiabatic Dynamics Simulations on Photoinduced Ring-Closing Reaction of a Nucleoside-Based Diarylethene Photoswitch.

Nucleoside-based diarylethenes are emerging as an especial class of photochromic compounds that have potential applications in regulating biological systems using noninvasive light with high spatio-temporal resolution. However, relevant microscopic photochromic mechanisms at atomic level of these novel diarylethenes remain to be explored. Herein, we have employed static electronic structure calculations (MS-CASPT2//M06-2X, MS-CASPT2//SA-CASSCF) in combination with non-adiabatic dynamics simulations to explore the related photoinduced ring-closing reaction of a typical nucleoside-based diarylethene photoswitch, namely, PS-IV. Upon excitation with UV light, the open form PS-IV can be excited to a spectroscopically bright S1 state. After that, the molecule relaxes to the conical intersection region within 150 fs according to the barrierless relaxed scan of the C1–C6 bond, which is followed by an immediate deactivation to the ground state. The conical intersection structure is very similar to the ground state transition state structure which connects the open and closed forms of PS-IV, and therefore plays a crucial role in the photochromism of PS-IV. Besides, after analyzing the hopping structures, we conclude that the ring closing reaction cannot complete in the S1 state alone since all the C1–C6 distances of the hopping structures are larger than 2.00 Å. Once hopping to the ground state, the molecules either return to the original open form of PS-IV or produce the closed form of PS-IV within 100 fs, and the ring closing quantum yield is estimated to be 56%. Our present work not only elucidates the ultrafast photoinduced pericyclic reaction of the nucleoside-based diarylethene PS-IV, but can also be helpful for the future design of novel nucleoside-based diarylethenes with better performance.

Relation between Ejection Mechanism and Ion Abundance in the Electric Double Layer of Droplets.

Charged droplets have been associated with distinct chemical reactivity. It is assumed that the composition of the surface layer plays a critical role in enhancing the reaction rates in the droplets relative to their bulk solution counterparts. We use atomistic modeling to relate the localization of ions in the surface layer to their ejection propensity. We find that ion ejection takes place via a two-stage process. First, a conical protrusion emerges as a result of a global droplet deformation that is insensitive to the locations of the single ions. The ions are subsequently ejected as they enter the conical regions. The study provides mechanistic insight into the ion-evaporation mechanism, which can be used to revise the commonly used ion-evaporation models. We argue that atomistic molecular dynamics simulations of minute nanodrops do not sufficiently distinguish the ion-evaporation mechanism from a Rayleigh fission. We explain mass spectrometry data on the charge state of small globular proteins and the existence of supercharged droplet states that have been detected in experiments.

A CFD study of gas and particle motion in an aerosol generator operated by desublimation process

In this work, a novel aerosol generator for submicron particles with a core-shell structure is presented. The operation process starts with the sublimation by heat of an organic material, copper phthalocyanine (CuPc), to form an under saturated gas flow. Then, the adiabatic expansion through a Laval nozzle is used to form a supersaturated free jet. Finally, by employing an active cooling and the injection of titanium dioxide (TiO2) core particles, on the free jet side, the aerosol formation is enabled by the desublimation process. The Euler–Lagrange CFD simulations of the gas and particle flow revealed the rotating backflow of the core particles inside the cooled expansion chamber. Hence, the core particles are transported into the conical free jet region emerging from the Laval nozzle where the highest supersaturation of CuPc occurs. In addition to the numerical simulations, the resulting structure and size of the generated particles were experimentally investigated by employing scanning mobility particle sizer and a scanning electron microscope analysis. The surface of modified TiO2 core particles showed a punctual coating with desublimated CuPc.

CFD and statistical approach to optimize the average air velocity and air volume fraction in an inert-particles spouted-bed reactor (IPSBR) system

Inert-particles spouted bed reactor (IPSBR) is characterized by intense mixing generated by the circular motion of the inert particles. The operating parameters play an important role in the performance of the IPSBR system, and therefore, parameter optimization is critical for the design and scale-up of this gas–liquid contact system. Computational fluid dynamics (CFD) provides detailed modeling of the system hydrodynamics, enabling the determination of the operating conditions that optimize the performance of this contact system. The present work optimizes the main IPSBR operating parameters, which include a feed-gas velocity in the range 0.5–1.5 m/s, orifice diameter in the range 0.001–0.005 m, gas head in the range 0.15–0.35 m, mixing-particle diameter in the range 0.009–0.0225 m, and mixing-particle to reactor volume fraction in the range 2.0–10.0 vol % (which represents 0.01–0.1 kg of mixing particles loading). The effects of these parameters on the average air velocity and average air volume fraction in the upper, middle, and conical regions of the reactor were studied. The specific distance for each region has been measured from the orifice point to be 50 mm for the conical region, 350 mm for the middle region and 550 mm for the upper rejoin. The selected factors were optimized to obtain the minimum air velocity distribution (maximum gas residence time) and the maximum air volume fraction (maximum interfacial area concentration) because these conditions will increase the gas holdup, the gas–liquid contact area, and the mass transfer coefficient among phases. Response surface methodology (RSM) was used to determine the optimum operating conditions. The regression analysis showed an excellent fit of the experimental data to a second-order polynomial model. The interaction between the process variables was evaluated using the obtained three-dimensional surface plots. The analysis revealed that under the optimized parameters of a feed-gas velocity of 1.5 m/s, orifice diameter of 0.001 m, gas head of 0.164 m, mixing-particle diameter of 0.0225 m, and mixing-particle loading of 0.02 kg, the minimum average air velocity and highest air volume fraction were observed throughout the reactor.

Electromagnetic field of the circular magnetic source in biconical section

The problem of axially-symmetric electromagnetic wave diffraction from the perfectly conducting biconical scatterer formed by the finite cone placed in the semi-infinite conical region is solved rigorously using the mode-matching and analytical regularization techniques. The problem is reduced to the infinite systems of linear algebraic equations (ISLAE) of the second kind. The obtained equations admit the reduction procedure and can be solved with a given accuracy for any geometrical parameters and frequency. The numerical examples of the solution are presented. The analysis of the source location influences on the far-field pattern for different geometrical parameters of the bicone is carried out.

Creation of large temperature anisotropies in a laboratory plasma

Ion temperature anisotropy in an expanding magnetized plasma is investigated using laser induced fluorescence. Parallel and perpendicular ion velocity distribution functions (IVDFs) were measured simultaneously with high spatial resolution in the expanding plasma. Large ion temperature anisotropies (T⊥i/T∥i∼10) are observed in a conical region at the periphery of the expanding plasma plume. A simple 2D Boris stepper model that incorporates the measured electric field structure is able to reproduce the gross features of the measured perpendicular IVDFs. A Nyquist stability analysis of the measured IVDFs suggests that multiple instabilities with k⊥ρi∼1 and k||ρi∼0.2 are likely to be excited in these plasmas.

Can supernova shells feed supermassive black holes in galactic nuclei?

Aims. We simulate shells created by supernovae expanding into the interstellar medium of the nuclear region of a galaxy, and analyze how the shell evolution is influenced by the supernova position relative to the galactic center, by the interstellar matter density, and by the combined gravitational pull of the nuclear star cluster and supermassive black hole (SMBH). Methods. We adopted simplified hydrodynamical simulations using the infinitesimally thin layer approximation in 3D (code RING) and determined whether and where the shell expansion may bring new gas into the inner parsec around the SMBH. Results. The simulations show that supernovae occurring within a conical region around the rotational axis of the galaxy can feed the central accretion disk surrounding the SMBH. For ambient densities between 103 and 105 cm−3, the average mass deposited into the central parsec by individual supernovae varies between 10 and 1000 solar masses depending on the ambient density and the spatial distribution of supernova events. Supernovae occurring in the aftermath of a starburst event near a galactic center can supply two to three orders of magnitude more mass into the central parsec, depending on the magnitude of the starburst. The deposited mass typically encounters and joins an accretion disk. The fate of that mass is then divided between the growth of the SMBH and an energetically driven outflow from the disk.

A Beam-Steerable Lens Antenna forKu-Band High-Power Microwave Applications

A beam-steerable lens antenna based on the concept of Risley prism is presented in this communication. The antenna is made up of a feed antenna and three transmit-array (T-A) lenses, including a stationary lens and two rotatable lenses. Beam steering is achieved by rotating the two rotatable lenses around the antenna axis independently. An antenna prototype has been successfully designed, simulated, fabricated, and measured in Ku -band. The results show that the beam of the antenna can be steered to any direction within a 91.2° conical region. During beam steering, the measured peak gain of the antenna reaches 38.1 dBi, the maximum aperture efficiency achieves 80.5%, and the gain variation is less than 1.7 dB. Moreover, the simulated results show that the power-handling capacity of this antenna could reach gigawatt level, which indicates application potentials of this antenna in high-power microwave (HPM) field.

Morphological characteristics of streamer region for long air gap positive discharge

Knowledge of leader corona is the basis for long spark discharge modelling, which is critical to understand the underlying physics of lightning flashes and dielectric breakdown of long air gap widely utilized in power systems. This paper presents an accurate observation of the leader corona. The morphology of the leader corona region during the discharge was obtained using a high-speed camera and an image-enhanced charge-coupled device camera. Statistical results showed that the morphology of the streamer region varied at different discharge sub-phases. The first corona was a conical region with the average apex angle of 118.91°; the leader corona region behaved as a cone with an average vertex angle of 75.87° during the leader propagation process; the streamer area in the final jump was a combination of a cylinder and a cone with the average vertex angle of 82.61°. Noting that the obtained cone apex angle of the leader corona during the leader propagation phase was significantly smaller than that in photographical reports, and the observation results were related to the selected temporal resolution of the optical image apparatus. The discussion on the effect of the single-frame exposure time on observation results found that the average vertex angle of the conical streamer region gradually decreased with the decrease of the single-frame exposure time, and eventually tended to a stable value of about 75.96°. For comparison purposes, discharge experiments under two gap-distances demonstrated that on the premise of stable leader, the statistical distribution characteristics of the leader corona vertex angle were consistent, indicating the universal applicability to the simulation researches. Finally, it is found that the distortion of the electric field caused by the space charge explained the variation of the streamer area during the discharge process.

Simulation of beam steering control in arrayed liquid prisms system based on electrowetting-on-dielectric

In this paper, an arrayed liquid prisms system based on electrowetting-on-dielectric (EWOD) is proposed to modulate the three-dimensional beam steering control. The relationships between beam steering control range, electrowetting contact angle, and liquid refractive index are derived. COMSOL is employed to demonstrate the beam steering control properties of the electrowetting-based arrayed liquid prisms when bias voltages are applied. The influence of contact angle, liquid refractive index, and interval between adjacent prisms are discussed. The results show that the beam steering control performance of the system will be greatly improved, and the range of beam steering angle is −20° to 20° by selecting optimum combinations of liquids and rational interval between adjacent prisms. The arrayed liquid prisms system can succeed to achieve continuous control of beam steering in a conical region with an apex angle of 40°, and the vertex of the circular cone is located at the 15.02 mm in the z-axis. The proposed system will promote the development of non-mechanical beam steering technology and have a wide range of applications.

Flow structures of over-expanded supersonic gaseous jets for deep-water propulsion

Supersonic gaseous jets with large ambient pressure are typically found in deep-water propulsion systems. The interactions between gas and water are turbulent, and the plume exhibits unstable bubbly interfaces. This work employed both experimental and numerical methods to obtain the flow structures of over-expanded gaseous jets driven by different pressure ratios in water. Direct measurements of the interfacial behaviour of submerged gaseous jets with pressurised water, were performed using high-speed digital photography. Numerical simulations were also conducted to characterise flow structures by the interplay of inertia and buoyancy forces. It was found that the interface of injection into water showed continuous fluctuations and strong mixing in the conical regions. The intermittent expansion-necking characteristics just beyond the nozzle exit, induced the pressure oscillation of the flow field near the wall, localised liquid water attack of the exit wall, and aggravated the over-expansion of nozzle working conditions. These periodic phenomena were attributed to Kelvin-Helmholtz (K–H) instabilities, driven by the large gradients of velocity and density in the shearing layers. The oscillation characteristics were assessed at different ambient pressures, providing theoretical support for the design of engineering devices working over a wide range of water depths.

Experimental study of surface roughness, dimensional accuracy and time of fabrication of parts produced by fused deposition modelling

Purpose This paper aims to focus on an experimental study of surface roughness, dimensional accuracy and time of fabrication of parts produced by fused deposition modelling (FDM) technique of additive manufacturing. The fabricated parts of acrylonitrile butadiene styrene (ABS) material have pyramidal and conical features. Influence of five process parameters of FDM, namely, layer thickness, wall print speed, build orientation, wall thickness and extrusion temperature is studied on response characteristics. Furthermore, regression models for responses are developed and significant process parameters are optimized. Design/methodology/approach Comprehensive experimental study is performed using response surface methodology. Analysis of variance is used to investigate the influence of process parameters on surface roughness, dimensional accuracy and time of fabrication in both outer pyramidal and inner conical regions of part. Furthermore, a multi-response optimization using desirability function is performed to minimize surface roughness, improve dimensional accuracy and minimize time of fabrication of parts. Findings It is found that layer thickness and build orientation are significant process parameters for surface roughness of parts. Surface roughness increases with increase in layer thickness, while it decreases initially and then increases with increase in build orientation. Layer thickness, wall print speed and build orientation are significant process parameters for dimensional accuracy of FDM parts. For the time of fabrication, layer thickness and build orientation are found as significant process parameters. Based on the analysis, statistical non-linear quadratic models are developed to predict surface roughness, dimensional accuracy and time of fabrication. Optimization of process parameters is also performed using desirability function. Research limitations/implications The present study is restricted to the parts of ABS material with pyramidal and conical features only fabricated on FDM machine with delta configuration. Originality/value From the critical review of literature it is found that some researchers have made to study the influence of few process parameters on surface roughness, dimensional accuracy and time of fabrication of simple geometrical parts. Also, regression models and optimization of process parameters has been performed for simple parts. The present work is focussed on studying all these aspects in complicated geometrical parts with pyramidal and conical features.

Numerical study of rheological behaviors of a compound droplet in a conical nozzle

The dynamics of compound droplets is more and more attractive because of their applications in a wide range of industrial and natural processes. This study aims to improve the understanding of dynamical rheological behaviors of a compound droplet moving in a nozzle with a conical shape in the downstream region via front-tracking-based simulations. The numerical results show that the compound droplet experiences three stages of deformation: the entrance stage (in front of the conical region), the transit stage (within the conical region), and the exit stage (in the exit of the nozzle). The droplet receives the maximum deformation in the axial direction during the transit stage, and the radially maximum deformation occurs during the exit stage. Because of the acceleration induced by the conical region, the inner droplet of the compound droplet can break up into smaller droplets during the exit stage. To reveal the transition between the finite deformation and the breakup, many parameters including the Capillary number Ca (varied in the range of 0.0125–1.6), the droplet size relative to the nozzle size R1/R0 (varied in the range of 0.2–0.9), the droplet radius ratio R21 (varied in the range of 0.3–0.8), the viscosity ratios μ21 and μ31 (varied in the range of 0.05–3.2), the interfacial tension ratio σ21 (varied in the range of 0.125–8.0), the conical angle α (varied in the range of 4°–34°) and the initial location of the inner droplet (i.e. the droplet eccentricity) are considered. From the finite deformation mode, the transition to the breakup mode of the inner droplet occurs when increasing any of Ca, R1/R0, R21 and α, or decreasing any of μ21 and σ21. The breakup mode is also enhanced when the inner droplet is initially located closer to the leading side of the outer droplet. However, varying μ31 induces no transition between these modes. The regime diagrams of these modes, based on these parameters, are also proposed.

Sediment Transport and Morphodynamics Induced by a Translating Monopolar Vortex

AbstractWe performed laboratory experiments to describe and quantify the transport of sediment and the changes in the bed due to a generic translating monopolar vortex. Experiments were performed inside a water‐filled, square tank with a particle bed on the bottom and a vertical plate attached perpendicular to one of the sidewalls. The tank was placed on top of a rotating table to create the vortex by changing its rotation rate. This change created a current inside the tank that separated at the edge of the vertical plate, with the shear layer rolling up into a vortex. Once the vortex was formed, the table was promptly stopped. Sediment particles are brought into suspension and captured by the vortex, forming a conical region that moves with the vortex until the sediment resettles in the bed, changing the original bed morphology. Three different measurement techniques were used to obtain information about the flow velocities, the sediment in suspension, and the net changes in the bed. Changes in the bed morphology occur along the trajectory of the vortex, where a region of erosion is followed by a region of deposition. The strength of a vortex is the main parameter governing the capture and suspension of particles with similar characteristics. A power law relationship is found between the vortex strength and the net displaced particle volume. Experiments were also performed without sediment to determine if the presence of sediment could affect the vortex dynamics. However, a definitive answer requires more experiments to obtain reliable statistics.

New insight into the photoinduced wavelength dependent decay mechanisms of the ferulic acid system on the excited states.

The ferulic acid (FA) is a kind of phenolic acid widely exists in nature plants. Apart from its medicinal values, the FA is also widely applied in cosmetic industry. Recently, it was found to have potential applications in commercial sunscreens for its strong photostability and photoprotection property from harmful UV rays. Such excellent property lies in the ultrafast decay process of the FA system when exposure to the UV light, but the underlying detailed relaxation pathway is still less clear-cut. In the current work, high-level ab initio electronic structure calculations and on-the-fly surface hopping dynamics simulations were employed to explore the photoinduced decay mechanism of the FA system both on the S1 and S3 states in the gas phase. The results provide a reasonable explanation for the wavelength dependent decay patterns of FA system. The S1 state decay pathway is driven by a re-emission process to dissipate excess energy. While for the S3 state deactivation process, the pathway is dominated by a non-adiabatic process driven by the internal conversion process through the conical intersection regions. A S3-S1-S0 two step decay pattern is proposed, and the pathways are mainly driven by a puckering distortion motion of the aromatic ring and a twisting motion around the bridging double bond. The calculation results contribute to a better understanding of detailed dynamics behavior of the FA deactivation process, and provide theoretical guidance for further design of efficient and environmentally friendly sunscreens.