Excess Velocity Research Articles

Rotationally Driven Ultraviolet Emission of Red Giant Stars

Abstract Main-sequence stars exhibit a clear rotation-activity relationship, in which rapidly rotating stars drive strong chromospheric/coronal ultraviolet and X-ray emission. While the vast majority of red giant stars are inactive, a few percent exhibit strong ultraviolet emission. Here we use a sample of 133 red giant stars observed by Sloan Digital Sky Survey APOGEE and Galaxy Evolution Explorer to demonstrate an empirical relationship between near-UV (NUV) excess and rotational velocity ( ). Beyond this simple relationship, we find that NUV excess also correlates with rotation period and with Rossby number in a manner that shares broadly similar trends to those found in M dwarfs, including activity saturation among rapid rotators. Our data also suggest that the most extremely rapidly rotating giants may exhibit so-called supersaturation, which could be caused by centrifugal stripping of these stars rotating at a high fraction of breakup speed. As an example application of our empirical rotation-activity relation, we demonstrate that the NUV emission observed from a recently reported system comprising a red giant with a black hole companion is fully consistent with arising from the rapidly rotating red giant in that system. Most fundamentally, our findings suggest a common origin of chromospheric activity in rotation and convection for cool stars from main sequence to red giant stages of evolution.

Titan aerogravity-assist maneuvers for Saturn/Enceladus missions

Mission analysis using aerogravity-assist (AGA) maneuver at Titan is presented in this paper. Considering Saturn arrival, Titan encounter, and different post-AGA orbits, the analysis uses vector diagrams to illustrate the relations among all conditions as well as design constraints. The analysis focuses on Enceladus mission concept and also present a summary result for Cassini-type Saturn system missions. Turn angles using AGA maneuver at Titan are quantified via numerical simulation, showing that 25-deg AGA turn angles are achievable with a Titan inbound excess velocity (V∞, IN) of 10–20 km/s. Results show that for an Enceladus mission, V∞, IN of 10 km/s is the minimum velocity required for AGA maneuver to achieve an outbound transfer orbit directly to Enceladus; the corresponding peak g-load is less than 6 g, peak heat rate less than 200 W/cm2, and total heat load of around 25 kJ/cm2. For a Cassini-type Saturn mission, a minimum V∞, IN of 5 km/s can be used for Titan AGA. The results showed are for V∞, IN of 6 km/s; and the corresponding peak g-load, peak heat rate, and total heat load are 1.5 g, 20 W/cm2, and 5 kJ/cm2 respectively.

High-speed stars: Galactic hitchhikers

Context.The search for stars born in the very early stages of the Milky Way star formation history is of paramount importance in the study of the early Universe since their chemistry carries irreplaceable information on the conditions in which early star formation and galaxy buildup took place. The search for these objects has generally taken the form of expensive surveys for faint extremely metal-poor stars, the most obvious but not the only candidates to a very early formation.Aims.Thanks toGaiaDR2 radial velocities and proper motions, we identified 72 bright cool stars displaying heliocentric transverse velocities in excess of 500 km s−1. These objects are most likely members of extreme outer-halo populations, either formed in the early Milky Way build-up or accreted from since-destroyed self-gravitating stellar systems.Methods.We analysed low-resolution FORS spectra of the 72 stars in the sample and derived the abundances of a few elements. Despite the large uncertainties on the radial velocity determination, we derived reliable orbital parameters for these objects.Results.The stars analysed are mainly slightly metal poor, with a few very metal-poor stars. Their chemical composition is much more homogeneous than expected. All the stars have very eccentric halo orbits, some extending well beyond the expected dimension of the Milky Way.Conclusions.These stars can be the result of a disrupted small galaxy or they could have been globular cluster members. Age estimates suggest that some of them are evolved blue stragglers, now on the subgiant or asymptotic giant branches.

Mixing and segregation behavior in an air dense medium fluidized bed with binary mixtures for dry coal beneficiation

Particle mixing and segregation behavior in an Air Dense Medium Fluidized Bed with binary mixtures of solid particles were investigated for dry coal beneficiation. Magnetite mixed with coal/gangue/sand particles belonging to Geldart B/D group were tested individually for the bed density adjustment. The effects of operating parameters including particle density ratio, particle size ratio, mixture composition, superficial gas velocity, and fluidized bed height on the mixing and segregation pattern were examined. The results demonstrated that the segregation becomes more severe with increasing density difference of binary mixtures. An increase in particle size ratio may also lead to partial segregation. Mixing and segregation of binary systems are almost independent of lower excess gas velocity and initial bed height when it is over 15 cm. Moreover, a mixing index was employed to evaluate the mixing and segregation performance, and the criteria for good mixing to achieve the bed density adjustment were identified.

Quantification of Solid Mixing in Bubbling Fluidized Beds via Two-Fluid Model Simulations

The influence of particle density and fluidization velocity on the mixing behavior of Geldart B particles was investigated in bubbling fluidized beds for various operating conditions using a two-fluid model approach. The simulation results proved that the predicted solid flow pattern for a wide range of Geldart B particles differs from particles of Geldart B/D classification at identical fluidization numbers. Quantitative analysis of the predicted solid velocity variances revealed that the solid axial dispersion rate is higher than the lateral one. In detail, a Peclet number of 1.54 and 3.92 was predicted for axial and lateral mixings, respectively. Also, the solid dispersion and diffusion coefficients were linearly correlated with the excess gas velocity for a range of particle properties. Finally, the characteristic global particle mixing times were computed. Thereby, the characteristic mixing time can be correlated with the particle Froude number, expanded bed height, and solid dispersion coefficient with high accuracy.

Investigation of fluidized bed behaviour using electrical capacitance tomography

AbstractThe temporal and cross‐sectional distributions of particles in a 127 mm diameter fluidized bed have been obtained using a new generation, high‐speed electrical capacitance tomography. Two planes of eight electrodes were used and mounted at 160 and 660 mm from the gas distributor which was a 3 mm thick porous plastic plate (maximum pore size of 50‐70 μm). 3 mm diameter, nearly‐spherical polyethylene granules made up the bed. Experiments at sampling frequencies of 200‐2000 cross‐sections per second and gas superficial velocities from just below the minimum fluidization to 83% above minimum fluidization velocities were used. The time series of the cross‐sectional average void fractions have been examined both directly and in amplitude and frequency space. The last two used probability density functions and power spectral densities. The information gathered shows that the fluidized bed was operating in the slugging mode, which is not surprising given the size of the particles. It has been found that an increase in the excess gas velocity above the minimum fluidization velocity resulted in an increase in the mean void fraction, an increase in the length and velocity of the slug bubbles as well as the bed height, and a slight decrease in the slug frequency. The results are presented in a level of detail suitable for comparison with later numerical simulation.

Development of a High-Speed Two-Disc Tribometer for Evaluation of Traction and Scuffing of Lubricated Contacts

This article describes the development of a high-speed, two-disc tribometer to conduct traction and scuffing tests emulating typical aerospace and automotive gear contacts. This tribometer is capable of achieving rolling velocities in excess of 50 m/s at sliding ratios and contact pressures representative of gear tooth contacts at elevated oil supply temperatures. A methodology to remove bearing drag from the traction torque measurements is presented as well as a noncontact surface temperature measurement system to quantify the surface bulk temperatures. Traction curve and scuffing test protocols representative of aerospace and automotive gear contact conditions are devised. Example traction curves and scuffing tests are presented to demonstrate the capabilities of the tribometer.

Experimental evaluation of the convection heat transfer coefficient of large particles moving freely in a fluidized bed reactor

Heat transfer is a key aspect in the performance of fluidized bed reactors. In particular, the dense phase heat transfer coefficient, which determines the heat exchanged between the bed and fuel particles, is of special relevance. This work presents a study on the heat transfer that occur when introducing pelletized particles of dry ice in a fluidized bed. The convection heat transfer coefficient is experimentally evaluated by means of the sublimation of dry ice particles using a novel methodology, which consists in a measurement system based on a macro-TGA fluidized bed and the corresponding evaluation of the acquired data. The system is capable of measuring the real time mass of the fluidized bed, which is a direct measure of the mass loss of the dry ice particles. The evaluation of such measurements allows to determine the convection heat transfer coefficient between the dry ice particles and the bed. Fixed and fluidized bed regimes, varying the excess gas velocity from -0.03 m/s up to 0.35 m/s, were tested for two different bed materials, namely Ballotini glass beads and alumina. The results of the sublimation and heat transfer coefficients are in good agreement with values reported in the literature, confirming the reliability of the experimental and postprocessing methodologies. In general, higher gas velocities enhance the dry ice particles mixing in the bed up to a limit in which the sublimation and convection heat transfer coefficients do not further increase. Additionally, the influence of the buoyancy behaviour of the dry ice particles in the bed on the convection heat transfer coefficient is discussed. The convection heat transfer coefficient decreases substantially if the dry ice particles present a flotsam behaviour and the gas velocity is not sufficiently high to ensure a proper circulation of the particles in the whole bed.

On the alignment of velocity and magnetic fields within magnetosheath jets

Abstract. Jets in the subsolar magnetosheath are localized enhancements in dynamic pressure that are able to propagate all the way from the bow shock to the magnetopause. Due to their excess velocity with respect to their environment, they push slower ambient plasma out of their way, creating a vortical plasma motion in and around them. Simulations and case study results suggest that jets also modify the magnetic field in the magnetosheath on their passage, aligning it more with their velocity. Based on Magnetospheric Multiscale (MMS) jet observations and corresponding superposed epoch analyses of the angles ϕ between the velocity and magnetic fields, we can confirm that this suggestion is correct. However, while the alignment is more significant for faster than for slower jets, and for jets observed close to the bow shock, the overall effect is small: typically, reductions in ϕ of around 10∘ are observed at jet core regions, where the jets' velocities are largest. Furthermore, time series of ϕ pertaining to individual jets significantly deviate from the superposed epoch analysis results. They usually exhibit large variations over the entire range of ϕ: 0 to 90∘. This variability is commonly somewhat larger within jets than outside them, masking the systematic decrease in ϕ at core regions of individual jets.

Ultrasonic studies on ternary liquid mixtures of some 1-alkanols with meta methoxy phenol and n hexane at 313 K

Abstract The thermo-physical parameters like density (ρ), ultrasonic velocity (U) and viscosity (η) have been experimentally measured for the Ternary Liquid Mixtures of Meta Methoxy Phenol (MMP) in n Hexane with 1 alkanols such as 1 propanol or 1 butanol or 1 pentanol at constant temperature 313 K and fixed frequency of 2 MHz. The thermodynamic and acoustical parameters such as adiabatic compressibility(β), absorption coefficient (α/f2), internal pressure(πi), cohesive energy(CE), free volume(Vf), free length(Lf), acoustic impedance(z), available volume(Va), viscous relaxation time, ∆G value, Lenard Jones potential, Degree of intermolecular interaction(χ) and K value were calculated from the experimental data. The various excess properties including excess acoustic impedance(ZE), excess free length(Lf)E, excess adiabatic compressibility(βE), excess free volume(VfE), excess ultrasonic velocity (UE) and excess internal pressure(πiE) were also computed from the calculated values. The values of UE, ZE, and LfE for each mixture have been fitted to the Redlich –Kister polynomial equation. The variation of these parameters with respect to different concentration at constant temperature for the three systems namely MMP+ 1 Propanol+n Hexane, MMP+ 1 Butanol+n Hexane and MMP+ 1 Pentanol+n Hexane have been discussed in the light of molecular interaction. Further, theoretical studies like Van Dael Ideal Mixing Relation, Impedance Dependant Relation, Junjie's and Nomoto's relation are validated with respect to experimental velocities at 313 K for all the different concentrations ranging from 0.001 M to 0.01 M of all the three systems and the Chi-square test for the goodness of fit is applied to check the validity of the theories.

Drag-based aerodynamic braking system for the Hyperloop: a numerical study

The Hyperloop promises to revolutionize the transport infrastructure of the 21st century by reducing travel time and allowing people to reach transonic speed on land. It carries with it the hope of a sustainable transportation system during an era of global energy crisis. Overall passenger safety in a high-speed pod necessitates a reliable braking system. This paper introduces the possibility of utilizing aerodynamic drag in the Hyperloop, anticipated to operate at high Mach and low Reynolds flow regime, to attenuate the speed of the pod. Numerical analysis was conducted to investigate the effect of incorporating an aerodynamic brake at different pod velocities (100, 135, and 150 m/s) and deployment angles (30°, 45°, 60°, and 90°). A detailed comparison between the proposed aerodynamic braking system (AeBS) and existing braking systems for the Hyperloop has been presented in this paper. The results demonstrate an increase in drag value of the pod by 3.4 times using a single 0.15 m2brake plate. When the brake plate was fully deployed at a pod velocity in excess of 112 m/s, the aerodynamic drag-based braking systems was shown to be more effective than the contemporary eddy current braking system.

An Ultrasonic Study on Acoustical and Excess Properties of Ternary Liquid Mixtures of 2-Bromoanisole + 1-Butanol + n-Hexane at Different Temperatures 303K, 308K and 313K and a Frequency 2MHz

The behaviour of liquid mixture of 2-Bromoanisole, 1-Butanol and n-Hexane as a function of temperature and composition has been investigated by measuring ultrasonic velocity in conjunction with density and viscosity at 303K, 308K and 318K for frequency 2 MHz using ultrasonic interferometer. With the help of the measured values ultrasonic velocity (u), viscosity (η) and density (ρ), the acoustical parameters like acoustic impedance, adiabatic compressibility, free length, free volume and internal pressure have been calculated. In order to know the molecular interaction between the components in the ternary liquid mixture, nature and strength of molecular interaction in the components of the ternary mixture, the actual values of acoustical parameters were computed in to their excess properties. Excess ultrasonic velocity (UE), excess acoustic impedance (ZE), excess intermolecular free length (LEf) excess adiabatic compressibility (βE), excess free volume (VfE) and excess internal pressure have been calculated for the ternary liquid mixtures containing 2-bromoanisole, 1-butanol in n-hexane at various temperatures 303K, 308K and 313K at fixed frequency 2MHz, for different concentrations ranges from 0.001M to 0.01M and fitted to the Redlich-Kister polynomial equation. The computed excess values of excess ultrasonic velocity, excess acoustic impedance, excess intermolecular free length, excess adiabatic compressibility, excess free volume and excess internal pressure were plotted against the concentration of ternary liquid of the mixture at different temperatures 303K, 308K and 313K at a fixed frequency of 2MHz. A good agreement has been found between the experimental and calculated values of the ultrasonic velocity. The strength and the nature of the interactions between like and unlike molecules have been discussed in terms of dipole-dipole, dipole-induced dipole, and induced dipole-induced dipole interaction through hydrogen bonding. The present study aims to evolve the impact of ultrasonic sound over the molecular interaction of ternary liquid mixture consisting of 2-bromoanisole, 1-butanol in n-hexane mixture at different temperature 303K, 308K and 313K.

Back Surface Recombination Velocity Dependent of Absorption Coefficient as Applied to Determine Base Optimum Thickness of an n+/p/p+ Silicon Solar Cell

The monochromatic absorption coefficient of silicon, inducing the light penetration depth into the base of the solar cell, is used to determine the optimum thickness necessary for the production of a large photocurrent. The absorption-generation-diffusion and recombination (bulk and surface) phenomena are taken into account in the excess minority carrier continuity equation. The solution of this equation gives the photocurrent according to absorption and electronic parameters. Then from the obtained short circuit photocurrent expression, excess minority carrier back surface recombination velocity is determined, function of the monochromatic absorption coefficient at a given wavelength. This latter plotted versus base thickness yields the optimum thickness of an n+-p-p+ solar cell, for each wavelength, which is in the range close to the energy band gap of the silicon material. This study provides a tool for improvement solar cell manufacture processes, through the mathematical relationship obtained from the thickness limit according to the absorption coefficient that allows base width optimization.

Studies On Molecular Interactions In Ternary Liquid Mixture Of Ortho Methoxy Phenol And 1 Propanol In n- Hexane At Various Temperatures Using Ultrasonic Technique

The thermo-physical parameters like density (ρ), ultrasonic velocity (U) and viscosity (η) have been experimentally measured for the Ternary Liquid Mixture of Ortho Methoxy Phenol (OMP)and 1 propanol in n hexaneat different temperatures viz. 303 K, 308 K, 313 K. The thermodynamic and acoustical parameters such as adiabatic compressibility(β), Rao (R), absorption coefficient (α/f2), internal pressure(πi), cohesive energy(CE), free volume(Vf), free length(Lf), acoustic impedance(z), available volume(Va), viscous relaxation time and Lenard Jones potential were calculated from the experimental data. The various excess properties including excess Ultrasonic velocity, excess acoustic impedance, excess free length, excess adiabatic compressibility, excess free volume and excess internal pressure were also computed. The variation of these parameters with respect to concentration and temperatures have been discussed in the light of molecular interaction

Ultrasonic Investigation of Liquid -Liquids Interactions In 2-Nitroanisole, 1-Pentanol In n-Hexane at Various Temperatures

With the help of the measured values ultrasonic velocity (u), viscosity(η) and density (ρ), the excess properties, ultrasonic velocity (UE), excess acoustic impedance (ZE), excess intermolecular free length (LEf) excess adiabatic compressibility(βE), excess free volume(VfE) and excess internal pressure have been calculated for the ternary liquid mixtures containing 2-Nitroanisole, 1- Pentanol in n-Hexane at various temperatures viz., 303, 308 and 313K at a constant frequency 2 MHz for different concentrations ranges from 0.001M to 0.01M and fitted to the Redlich-Kister polynomial equation. The excess ultrasonic velocity, excess acoustic impedance, excess intermolecular free length, excess adiabatic compressibility, excess free volume and excess internal pressure were plotted against the concentration of the mixture at different temperatures. A good agreement has been found between the experimental and calculated values of the ultrasonic velocity. The strength and the nature of the interactions between like and unlike molecules have been discussed

Three-Impulse Return Orbit Design and Characteristic Analysis for Manned Lunar Missions

Return orbit design and characteristic analysis are very important issues in manned lunar missions. In this paper, a three-impulse return orbit scheme is studied. First, a convenient method based on the conical surface of the hyperbolic excess velocity is proposed, which can effectively perform an approximate analysis of the velocity increment characteristic. Second, a serial orbit design strategy is presented to determine the entire return orbit from the lunar parking orbit to the intended landing site. In the initial design, a three-segment orbit patched method based on the pseudo-perilune parameters is applied. Backward and forward calculations are conducted in the hybrid orbit model and the patched-conic model respectively, with the perilune of the lunar escape orbit as the dividing point. In the accurate design, a two-segment orbit patched method is employed in the high-fidelity model. Finally, numerical simulations are used to verify the effectiveness and feasibility of the orbit design strategy. According to many simulation results achieved by this strategy, the characteristics of fixed-point return window and velocity increment are further analyzed.

The Land-Sea Breeze of the Red Sea: Observations, Simulations, and Relationships to Regional Moisture Transport.

Unique in situ observations of atmospheric conditions over the Red Sea and the coastal Arabian Peninsula are examined to study the dynamics and regional impacts of the local land‐sea breeze cycle (LSBC). During a 26‐month data record spanning 2008–2011, observed LSBC events occurred year‐round, frequently exhibiting cross‐shore wind velocities in excess of 8 m/s. Observed onshore and offshore features of both the land‐ and sea‐breeze phases of the cycle are presented, and their seasonal modulation is considered. Weather Research and Forecasting climate downscaling simulations and satellite measurements are used to extend the analysis. In the model, the amplitude of the LSBC is significantly larger in the vicinity of the steeper terrain elements encircling the basin, suggesting an enhancement by the associated slope winds. Observed and simulated conditions also reflected distinct gravity‐current characteristics of the intrinsic moist marine air mass during both phases of the LSBC. Specifically, the advance and retreat of marine air mass was directly tied to the development of internal boundary layers onshore and offshore throughout the period of study. Convergence in the lateral moisture flux resulting from this air mass ascending the coastal topography (sea‐breeze phase) as well as colliding with air masses from the opposing coastline (land‐breeze phase) further resulted in cumulous cloud formation and precipitation.

Control program for noncoplanar heliocentric flight to Venus of non-perfectly reflecting solar sail spacecraft

A noncoplanar controlled heliocentric flight to Venus of a spacecraft with a non-perfectly reflecting solar sail is considered. The aim of the heliocentric flight is to get a spacecraft into Hill sphere of Venus with zero hyperbolic excess velocity. An algorithm has been developed for applying the locally optimal control laws for the fastest change of the osculating elements. Solar sail orientation is controlled by thin-film control elements arranged along the solar sail surface perimeter. The flight trajectory, the control program and the required width and area of thin-film control elements are obtained as a result of motion simulation.

Comparative thermo-acoustic study of ternary mixture of polar and nonpolar solvents with benzene and ethanol system

The study of liquid mixtures containing polar or nonpolar components finds wide application in industrial and technological processes. The ultrasonic velocity (u) and density (ρ) of the ternary mixtures 1,2 propane-di-ol (polar) + ethanol + benzene (system I) and n-hexane (nonpolar) + ethanol + benzene (system II) as well as of pure components have been measured at 303 K temperature and at 2 MHz frequency. The ultrasonic velocity is measured using ultrasonic interferometry technique, and density is measured using relative density bottle. From these measured data, the excess acoustic parameters: excess ultrasonic velocity (uE), excess density (ρE), excess adiabatic compressibility (βE), excess intermolecular free length ( $$L_{\text{f}}^{\text{E}}$$ ), excess molar volume ( $$V_{\text{m}}^{\text{E}}$$ ) and excess acoustic impedance (ZE), have been calculated using standard relations. The variations in sign and values of excess acoustic parameters of the two systems help us to know the interaction and structural arrangement of the liquid mixture. The values of uE and ZE for system I show that the interaction changes from strong to weak interaction with increasing concentration and for system II it has dispersive-type interaction. There is an opposite trend in the values of ρE, βE, L f E and V m E for systems I and II. System I has smaller molar volume difference compared to system II, but relatively stronger Hp–π interaction gives it a compact structure. However, system II is more compressible due to dispersive-type interaction. Our work helps to understand the effect of the molecular interaction on behavior of liquid mixture of polar and nonpolar solvents in π-system clearly and concisely.

Deep space exploration orbit design departing from circumlunar orbit of lunar base

A design method for a new kind of deep space mission which departs from a circumlunar orbit of the lunar base is presented in this paper. The difference between this kind of deep space mission and the traditional one is well analyzed. The method of patched conics is employed to divide the mission trajectory into four independent parts. The independent selenocentric segment is designed using a Lambert Problem based method, while the geocentric trajectory from a certain point in three-dimensional space to a fixed excess velocity vector is determined analytically. Then the combination of these segments is optimized via genetic algorithm by minimizing the total velocity increasement. Finally, typically numerical simulations are demonstrated to verify the effectiveness of the proposed method.