Articoli di riviste sul tema "Couple orbital de rotation"
Segui questo link per vedere altri tipi di pubblicazioni sul tema: Couple orbital de rotation.
Cita una fonte nei formati APA, MLA, Chicago, Harvard e in molti altri stili
Vedi i top-50 articoli di riviste per l'attività di ricerca sul tema "Couple orbital de rotation".
Accanto a ogni fonte nell'elenco di riferimenti c'è un pulsante "Aggiungi alla bibliografia". Premilo e genereremo automaticamente la citazione bibliografica dell'opera scelta nello stile citazionale di cui hai bisogno: APA, MLA, Harvard, Chicago, Vancouver ecc.
Puoi anche scaricare il testo completo della pubblicazione scientifica nel formato .pdf e leggere online l'abstract (il sommario) dell'opera se è presente nei metadati.
Vedi gli articoli di riviste di molte aree scientifiche e compila una bibliografia corretta.
1
Bolmont, E., F. Gallet, S. Mathis, C. Charbonnel, L. Amard e Y. Alibert. "Tidal dissipation in rotating low-mass stars and implications for the orbital evolution of close-in massive planets". Astronomy & Astrophysics 604 (agosto 2017): A113. http://dx.doi.org/10.1051/0004-6361/201730662.
Abstract (sommario):
Observations of hot-Jupiter exoplanets suggest that their orbital period distribution depends on the metallicity of the host stars. We investigate here whether the impact of the stellar metallicity on the evolution of the tidal dissipation inside the convective envelope of rotating stars and its resulting effect on the planetary migration might be a possible explanation for this observed statistical trend. We use a frequency-averaged tidal dissipation formalism coupled to an orbital evolution code and to rotating stellar evolution models in order to estimate the effect of a change of stellar metallicity on the evolution of close-in planets. We consider here two different stellar masses: 0.4 M⊙ and 1.0 M⊙ evolving from the early pre-main sequence phase up to the red-giant branch. We show that the metallicity of a star has a strong effect on the stellar parameters, which in turn strongly influence the tidal dissipation in the convective region. While on the pre-main sequence, the dissipation of a metal-poor Sun-like star is higher than the dissipation of a metal-rich Sun-like star; on the main sequence it is the opposite. However, for the 0.4 M⊙ star, the dependence of the dissipation with metallicity is much less visible. Using an orbital evolution model, we show that changing the metallicity leads to different orbital evolutions (e.g., planets migrate farther out from an initially fast-rotating metal-rich star). Using this model, we qualitatively reproduced the observational trends of the population of hot Jupiters with the metallicity of their host stars. However, more steps are needed to improve our model to try to quantitatively fit our results to the observations. Specifically, we need to improve the treatment of the rotation evolution in the orbital evolution model, and ultimately we need to consistently couple the orbital model to the stellar evolution model.
2
Pezzotti, C., P. Eggenberger, G. Buldgen, G. Meynet, V. Bourrier e C. Mordasini. "Revisiting Kepler-444". Astronomy & Astrophysics 650 (giugno 2021): A108. http://dx.doi.org/10.1051/0004-6361/202039652.
Abstract (sommario):
Context. Kepler-444 is one of the oldest planetary systems known thus far. Its peculiar configuration consisting of five sub-Earth-sized planets orbiting the companion to a binary stellar system makes its early history puzzling. Moreover, observations of HI-Lyα variations raise many questions about the potential presence of escaping atmospheres today. Aims. We aim to study the orbital evolution of Kepler-444-d and Kepler-444-e and the impact of atmospheric evaporation on Kepler-444-e. Methods. Rotating stellar models of Kepler-444-A were computed with the Geneva stellar evolution code and coupled to an orbital evolution code, accounting for the effects of dynamical, equilibrium tides and atmospheric evaporation. The impacts of multiple stellar rotational histories and X-ray and extreme ultraviolet (XUV) luminosity evolutionary tracks are explored. Results. Using detailed rotating stellar models able to reproduce the rotation rate of Kepler-444-A, we find that its observed rotation rate is perfectly in line with what is expected for this old K0-type star, indicating that there is no reason for it to be exceptionally active as would be required to explain the observed HI-Lyα variations from a stellar origin. We show that given the low planetary mass (~0.03 M⊕) and relatively large orbital distance (~0.06 AU) of Kepler-444-d and e, dynamical tides negligibly affect their orbits, regardless of the stellar rotational history considered. We point out instead how remarkable the impact is of the stellar rotational history on the estimation of the lifetime mass loss for Kepler-444-e. We show that, even in the case of an extremely slow rotating star, it seems unlikely that such a planet could retain a fraction of the initial water-ice content if we assume that it formed with a Ganymede-like composition.
3
Daley, Thomas M., e Dale Cox. "Orbital vibrator seismic source for simultaneous P‐ and S‐wave crosswell acquisition". GEOPHYSICS 66, n. 5 (settembre 2001): 1471–80. http://dx.doi.org/10.1190/1.1487092.
Abstract (sommario):
A recently developed borehole seismic source, the orbital vibrator, was successfully deployed in a crosswell survey in a fractured basalt aquifer. This seismic source uses a rotating eccentric mass to generate seismic energy. Source sweeps with clockwise and counter‐clockwise rotations are recorded at each source location. Because this source generates circularly polarized waves, unique processing algorithms are used to decompose the recordings into two equivalent linearly oscillating, orthogonally oriented seismic sources. The orbital vibrator therefore generates P‐ and S‐waves simultaneously for all azimuths. A coordinate rotation based on P‐wave particle motion is used to align the source components from various depths. In a field experiment, both P‐ and S‐wave arrivals were recorded using fluid‐coupled hydrophone sensors. The processed field data show clear separation of P‐ and S‐wave arrivals for in‐line and crossline source components, respectively. A tensor convolutional description of the decomposition process allows for extension to multicomponent sensors.
4
Lindh, Grant D., Taylor J. Mach e T. Daniel Crawford. "The optimized orbital coupled cluster doubles method and optical rotation". Chemical Physics 401 (giugno 2012): 125–29. http://dx.doi.org/10.1016/j.chemphys.2011.11.002.
5
Li, Liang, e Yiqiu Mao. "On Dynamics of Double-Diffusive Convection in a Rotating Couple-Stress Fluid Layer". Mathematics 12, n. 7 (28 marzo 2024): 1017. http://dx.doi.org/10.3390/math12071017.
Abstract (sommario):
The current article focuses on the examination of nonlinear instability and dynamic transitions in a double-diffusive rotating couple-stress fluid layer. The analysis was based on the newly developed dynamic transition theory by T. Ma and S. Wang. Through a comprehensive linear spectrum analysis and investigation of the principle of exchange of stability (PES) as the thermal Rayleigh number crosses a threshold, the nonlinear orbital changes during the transition were rigorously elucidated utilizing reduction methods. For both single real and complex eigenvalue crossings, local pitch-fork and Hopf bifurcations were discovered, and directions of these bifurcations were identified along with transition types. Furthermore, nondimensional transition numbers that signify crucial factors during the transition were calculated and the orbital structures were illustrated. Numerical studies were performed to validate the theoretical results, revealing the relations between key parameters in the system and the types of transition. The findings indicated that the presence of couple stress and a slow diffusion rate of solvent and temperature led to smoother nonlinear transitions during convection.
6
Yeomans, D. K. "Cometary Orbital Dynamics and Astrometry". International Astronomical Union Colloquium 116, n. 1 (1989): 3–17. http://dx.doi.org/10.1017/s0252921100109613.
Abstract (sommario):
AbstractComets are the only large solar system bodies where nongravitational forces directly affect their dynamic motions. Their approach to within a few AU of the Sun initiates the vaporization of nucleus ices, and the resulting rocket-like effects either add to or subtract from the comet’s orbital energy; the sign of the energy change depends upon the comet’s rotation direction and its spin pole orientation. The cometary outgassing phenomena have generally been modeled by assuming a rapidly rotating nucleus of water ice that outgasses symmetrically with respect to perihelion. Although this nongravitational acceleration model has been quite successful in providing accurate orbits and ephemerides, several comets exhibit water production rates and visual light curves that are noticeably asymmetric with respect to perihelion. New asymmetric models are being developed that attempt to represent more closely the cometary outgassing phenomena. For the same comet, derived nongravitational parameters can differ widely, depending upon which model is used to fit the astrometric data. The uncertainties in the data and in the nongravitational acceleration model prevent realistic extrapolations of these objects’ motion beyond a few hundred years, particularly if close planetary encounters are involved. Accurate orbits, ephemerides and efforts to model the nongravitational effects ultimately depend upon the quality of the astrometric data. Using a combination of long-focus telescopes, charge coupled device (CCD) detectors, microdensitometer reductions and modern star catalogs, cometary astrometric data can be generated that are accurate to the sub arcsecond level. While occultation, spacecraft, and radar observations can provide powerful astrometric data when available, it is still the ground-based optical observations that must provide the vast majority of data for cometary astrometry in the foreseeable future.
7
Gallet, F., E. Bolmont, J. Bouvier, S. Mathis e C. Charbonnel. "Planetary tidal interactions and the rotational evolution of low-mass stars". Astronomy & Astrophysics 619 (novembre 2018): A80. http://dx.doi.org/10.1051/0004-6361/201833576.
Abstract (sommario):
Context. The surface angular velocity evolution of low-mass stars is now globally understood and the main physical mechanisms involved in it are observationally quite constrained. However, while the general behaviour of these mechanisms is grasped, their theoretical description is still under ongoing work. This is the case, for instance, about the description of the physical process that extracts angular momentum from the radiative core, which could be described by several theoretical candidates. Additionally, recent observations showed anomalies in the rotation period distribution of open cluster, main sequence, early K-type stars that cannot be reproduced by current angular momentum evolution models. Aims. In this work, we study the parameter space of star-planet system’s configurations to investigate if including the tidal star-planet interaction in angular momentum evolution models could reproduce the anomalies of this rotation period distribution. Methods. To study this effect, we use a parametric angular momentum evolution model that allows for core-envelope decoupling and angular momentum extraction by magnetized stellar wind that we coupled to an orbital evolution code where we take into account the torque due to the tides raised on the star by the planet. We explore different stellar and planetary configurations (stellar mass from 0.5 to 1.0 M⊙ and planetary mass from 10 M⊕ to 13 Mjup) to study their effect on the planetary orbital and stellar rotational evolution. Results. The stellar angular momentum is the most impacted by the star-planet interaction when the planet is engulfed during the early main sequence phase. Thus, if a close-in Jupiter-mass planet is initially located at around 50% of the stellar corotation radius, a kink in the rotational period distribution opens around late and early K-type stars during the early main sequence phase. Conclusions. Tidal star-planet interactions can create a kink in the rotation period distribution of low-mass stars, which could possibly account for unexpected scatter seen in the rotational period distribution of young stellar clusters.
8
Felker, Peter M. "Nuclear-orbital/configuration-interaction study of coupled translation-rotation states in (H2)2@C70". Journal of Chemical Physics 138, n. 4 (28 gennaio 2013): 044309. http://dx.doi.org/10.1063/1.4776262.
9
Borre, C. C., D. Baade, A. Pigulski, D. Panoglou, A. Weiss, Th Rivinius, G. Handler et al. "Short-term variability and mass loss in Be stars". Astronomy & Astrophysics 635 (marzo 2020): A140. http://dx.doi.org/10.1051/0004-6361/201937062.
Abstract (sommario):
Context. Be stars are physically complex systems that continue to challenge theory to understand their rapid rotation, complex variability, and decretion disks. γ Cassiopeiae (γ Cas) is one such star but is even more curious because of its unexplained hard thermal X-ray emission. Aims. We aim to examine the optical variability of γ Cas and thereby to shed more light on its puzzling behaviour. Methods. We analysed 321 archival Hα spectra from 2006 to 2017 to search for frequencies corresponding to the 203.5 day orbit of the companion. Space photometry from the SMEI satellite from 2003 to 2011 and the BRITE-Constellation of nano-satellites from 2015 to 2019 were investigated in the period range from a couple of hours to a few days. Results. The orbital period of the companion of 203.5 days is confirmed with independent measurements from the structure of the Hα line emission. A strong blue versus red asymmetry in the amplitude distribution across the Hα emission line could hint at a spiral structure in the decretion disk. With the space photometry, the known frequency of 0.82 d−1 is confirmed in data from the early 2000s. A higher frequency of 2.48 d−1 is present in the data from 2015 to 2019 and possibly in the early 2000s as well. A third frequency at 1.25 d−1 is proposed to exist in both SMEI and BRITE data. Seemingly, only a non-radial pulsation interpretation can explain all three variations. The two higher frequencies are incompatible with rotation.
10
Belokonov, I. V., I. A. Timbai, P. N. Nikolaev e U. M. Orazbaeva. "Analysis of SamSat-218D nanosatelite motion acording to trajectory measurements". VESTNIK of Samara University. Aerospace and Mechanical Engineering 18, n. 4 (21 gennaio 2020): 18–28. http://dx.doi.org/10.18287/2541-7533-2019-18-4-18-28.
Abstract (sommario):
The motion of the SamSat-218D nanosatellite is analyzed by trajectory measurements. Special features of nanosatellite behavior in low orbits were experimentally confirmed. These features are due to both the influence of the atmosphere and the nanosatellites’ inherent mass-inertia characteristics: the orbital lifetime of nanosatellites is shorter, whereas angular acceleration generated by the aerodynamic moment couple is much higher than that of satellites with large sizes and masses. Variation of the ballistic coefficient in time is estimated from known trajectory measurements and information on the average density of the atmosphere at the points of trajectory measurements. The ballistic coefficient of the SamSat-218D nanosatellite having the shape of a rectangular parallelepiped depends on the spatial angle of attack and the angle of proper rotation. The ratio of the maximum value of the ballistic coefficient to the minimum value is 4.75. This made it possible to evaluate the nature of possible motion relative to the nanosatellite center of mass by the behavior of the ballistic coefficient. The most probable motion relative to the center of mass of the SamSat-218D nanosatellite is the transient motion between different equilibrium positions, due to commensurate aerodynamic and gravitational moments and insignificant angular velocities.
11
Ahuir, Jérémy, Antoine Strugarek, Allan Sacha Brun, Stéphane Mathis, Emeline Bolmont, Mansour Benbakoura, Victor Réville e Christophe Le Poncin-Lafitte. "Could star-planet magnetic interactions lead to planet migration and influence stellar rotation?" Proceedings of the International Astronomical Union 15, S354 (giugno 2019): 295–99. http://dx.doi.org/10.1017/s1743921319009992.
Abstract (sommario):
AbstractThe distribution of hot Jupiters, for which star-planet interactions can be significant, questions the evolution of exosystems. We aim to follow the orbital evolution of a planet along the rotational and structural evolution of the host star by taking into account the coupled effects of tidal and magnetic torques from ab initio prescriptions. It allows us to better understand the evolution of star-planet systems and to explain some properties of the distribution of observed close-in planets. To this end we use a numerical model of a coplanar circular star-planet system taking into account stellar structural changes, wind braking and star-planet interactions, called ESPEM (Benbakoura et al. (2019)). We find that depending on the initial configuration of the system, magnetic effects can dominate tidal effects during the various phases of the evolution, leading to an important migration of the planet and to significant changes on the rotational evolution of the star. Both kinds of interactions thus have to be taken into account to predict the evolution of compact star-planet systems.
12
Makarov, Valeri V., e Alexey Goldin. "Chaotic Capture of a Retrograde Moon by Venus and the Reversal of Its Spin". Universe 10, n. 1 (28 dicembre 2023): 15. http://dx.doi.org/10.3390/universe10010015.
Abstract (sommario):
Planets are surrounded by fractal surfaces (traditionally called Hill spheres), separating the inner zones of long-term stable orbital motion of their satellites from the outer space where the gravitational pull from the Sun takes over. Through this surface, external minor bodies in trajectories loosely co-orbital to a planet can be stochastically captured by the planet without any assistance from external perturbative forces, and can become moons chaotically orbiting the planet for extended periods of time. Using state-of-the-art orbital integrators, we simulate such capture events for Venus, resulting in long-term attachment phases by reversing the forward integration of a moon initially attached to the planet and escaping it after an extended period of time. Chaotic capture of a retrograde moon from a prograde heliocentric orbit appears to be more probable because the Hill sphere is almost four times larger in area for a retrograde orbit than for a prograde orbit. Simulated capture trajectories include cases with attachment phases up to 860,000 years for prograde moons and up to 370,000 years for retrograde moons. Although the probability of a long-term chaotic capture from a single encounter is generally low, the high density of co-orbital bodies in the primordial protoplanetary disk makes this outcome possible, if not probable. The early Venus was surrounded by a dusty gaseous disk of its own, which, coupled with the tidal dissipation of the kinetic energy in the moon and the planet, could shrink the initial orbit and stabilize the captured body within the Hill surface. The tidal torque from the moon, for which we use the historical name Neith, gradually brakes the prograde rotation of Venus, and then reverses it, while the orbit continues to decay. Neith eventually reaches the Roche radius and disintegrates, probably depositing most of its material on Venus’ surface. Our calculations show that surface density values of about 0.06 kg m−2 for the debris disk may be sufficient to stabilize the initial chaotic orbit of Neith and to bring it down within several radii of Venus, where tidal dissipation becomes more efficient.
13
Pogonin, Alexander E., Ivan Yu Kurochkin, Alexey V. Eroshin, Maksim N. Zavalishin e Yuriy A. Zhabanov. "Comprehensive Study of Equilibrium Structure of Trans-Azobenzene: Gas Electron Diffraction and Quantum Chemical Calculations". Physchem 4, n. 2 (8 maggio 2024): 131–46. http://dx.doi.org/10.3390/physchem4020010.
Abstract (sommario):
The geometrical re parameters of trans-azobenzene (E-AB) free molecule were refined by gas electron diffraction (GED) method using available experimental data obtained previously by S. Konaka and coworkers. Structural analysis was carried out by various techniques. First of all, these included the widely used molecular orbital constrained gas electron diffraction method and regularization method. The results of the refinements using different models were also compared—a semirigid model, three variants of one-dimensional dynamic models, and a two-dimensional pseudoconformer model. Several descriptions have been used due to the fact that E-AB has a shallow potential energy surface along the rotation coordinates of phenyl groups. Despite this, it turned out that the semirigid model is suitable for use for E-AB and allows good agreement with experimental data to be achieved. According to the results of GED structural analysis, coupled with the results of DLPNO-CCSD(T0) calculations, E-AB has a planar structure. Based only on GED data, it is impossible to unambiguously determine the rotational angle of the phenyl group due to the facts that (i) with rotation over a wide range of angles, the bonded distances in the molecule change insignificantly and (ii) potential function in a structural analysis within a dynamic model is not determined with the necessary accuracy. This work also examines the sensitivity of the GED method to structural changes caused by trans-cis isomerization. The paper also analyzes the applicability of different variants of density functional theory (DFT) calculations in GED structural analysis using E-AB as an example. There are not enough similar methodological works in the literature. This experimental and methodological information is especially important and relevant for planning and implementing GED experiments and corresponding processing of the results for azobenzene derivatives, in which the conformer and isomeric diversity are even more complicated due to the presence of different substituents.
14
Ivanova, G. A., e V. S. Khoroshilov. "On control of spacecraft orientation to the ground data acquisition station". Kosmičeskaâ tehnika. Raketnoe vooruženie 2023, n. 1 (12 maggio 2023): 41–47. http://dx.doi.org/10.33136/stma2023.01.041.
Abstract (sommario):
The article dwells on the spacecraft attitude control to point the onboard antenna to the ground data acquisition station during the communication session. Antenna is fixed relative to the spacecraft body. Pur-pose of the antenna is to receive the flight task aboard the spacecraft and to downlink the telemetry infor-mation. When orbiting, the spacecraft position relative to the ground data acquisition station changes contin-uously. It is due to the diurnal rotation of the Earth, spacecraft orbital motion and angular motion of the spacecraft relative to the center of mass under the impact of the disturbing and control moments. To tilt the spacecraft uses reaction wheels, installed in axes of coordinate system coupled with spacecraft center of mass. Electromagnets are used to unload the reaction wheels. The reaction wheels control law is suggested, which tilts the spacecraft to point the antenna to the ground data acquisition station. Mathematical model of the spacecraft dynamics relative to center of mass is given, using the suggested reaction wheels control law. The following external disturbing moments, acting on the spacecraft in flight, are taken into consideration: gravitational, magnetic, aerodynamic moments and solar radiation moment of forces. Dipole model of the magnetic field of the Earth is used to calculate the magnetic moments. Software was developed and space-craft dynamics was simulated on the personal computer with the specified initial data. Simulation initial con-ditions correspond to the attitude control mode of the spacecraft relative to the orbital coordinate system with the specified accuracy. Simulation results verify the applicability of the suggested reaction wheel control law. Key words: electrical axis of the antenna, mathematical model, coordinate system, transformation matrix, vector.
15
Modesto, Leonardo, Tian Zhou e Qiang Li. "Geometric Origin of the Galaxies’ Dark Side". Universe 10, n. 1 (29 dicembre 2023): 19. http://dx.doi.org/10.3390/universe10010019.
Abstract (sommario):
We show that Einstein’s conformal gravity can explain, simply, and on the geometric ground, galactic rotation curves, without the need to introduce any modification in both the gravitational as well as in the matter sector of the theory. The geometry of each galaxy is described by a metric obtained, making a singular rescaling of Schwarzschild’s spacetime. The new exact solution, asymptotically anti-de Sitter, manifests an unattainable singularity at infinity that cannot be reached in finite proper time; namely, the spacetime is geodetically complete. It deserves to be noticed that, in this paper, we have a different opinion from the usual one. Indeed, instead of making the metric singularity-free, we make it apparently but harmlessly even more singular than Schwarzschild’s. Finally, it is crucial to point out that Weyl’s conformal symmetry is spontaneously broken into the new singular vacuum rather than the asymptotically flat Schwarzschild’s one. The metric is unique according to the null energy condition, the zero acceleration for photons in the Newtonian regime, and the homogeneity of the Universe at large scales. Once the matter is conformally coupled to gravity, the orbital velocity for a probe star in the galaxy turns out to be asymptotically constant consistent with the observations and the Tully–Fisher relation. Therefore, we compare our model with a sample of 175 galaxies and show that our velocity profile very well interpolates the galactic rotation curves after a proper choice of the only free parameter in the metric. The mass-to-luminosity ratios of galaxies turn out to be close to 1, consistent with the absence of dark matter.
16
Tassiopoulou, Styliani, Georgia Koukiou e Vassilis Anastassopoulos. "Revealing Coupled Periodicities in Sunspot Time Series Using Bispectrum—An Inverse Problem". Applied Sciences 14, n. 3 (5 febbraio 2024): 1318. http://dx.doi.org/10.3390/app14031318.
Abstract (sommario):
Sunspot daily time series have been available for almost two centuries providing vast and complicated information about the behavior of our star and especially the interaction of the motion of the planets and other possible interstellar phenomena and their effects on the surface of the Sun. The main result obtained from the sunspot time series analysis is the imprint of various periodicities, such as the planets’ orbital periods and the planetary synodic periods on the sunspots signature. A detailed spectrum representation is achieved by means of a periodogram and a virtual extension of the time length segments with zeroed samples for longer representations. Furthermore, the dependence or coupling of these periodicities is explored by means of a bispectrum. We establish the exact interdependencies of the periodic phenomena on the sunspot time series. Specific couplings are explored that are proved to be the key issues for the coupled periodicities on the sunspot time series. In this work, contrary to what has been presented in the literature, all periodic phenomena are limited within the time period of an 11-year cycle as well as the periodicities of the orbits of the planets. The main findings are the observed strong coupling of the Mercury, Venus, and Mars periodicities, as well as synodic periodicities with all other periodicities that appear on the sunspot series. Simultaneously, the rotation of the Sun around itself (25.6 to 33.5 days) provides an extensive coupling of all recorded periodicities. Finally, there is strong evidence of the existence of a quadratic mechanism, which couples all the recorded periodicities, but in such a way that only frequency pairs that sum up to specific periods are coupled. The justification for this kind of coupling is left open to the scientific community.
17
Idini, Benjamin, e David J. Stevenson. "The Lost Meaning of Jupiter’s High-degree Love Numbers". Planetary Science Journal 3, n. 1 (1 gennaio 2022): 11. http://dx.doi.org/10.3847/psj/ac4248.
Abstract (sommario):
Abstract NASA’s Juno mission recently reported Jupiter’s high-degree (degree ℓ, azimuthal order m = 4, 2) Love number k 42 = 1.289 ± 0.063 (1σ), an order of magnitude above the hydrostatic k 42 obtained in a nonrotating Jupiter model. After numerically modeling rotation, the hydrostatic k 42 = 1.743 ± 0.002 is still 7σ away from the observation, raising doubts about our understanding of Jupiter’s tidal response. Here, we use first-order perturbation theory to explain the hydrostatic k 42 result analytically. We use a simple Jupiter equation of state (n = 1 polytrope) to obtain the fractional change in k 42 when comparing a rotating model with a nonrotating model. Our analytical result shows that the hydrostatic k 42 is dominated by the tidal response at ℓ = m = 2 coupled into the spherical harmonic ℓ, m = 4, 2 by the planet’s oblate figure. The ℓ = 4 normalization in k 42 introduces an orbital factor (a/s)2 into k 42, where a is the satellite semimajor axis and s is Jupiter’s average radius. As a result, different Galilean satellites produce a different k 42. We conclude that high-degree tesseral Love numbers (ℓ > m, m ≥ 2) are dominated by lower-degree Love numbers and thus provide little additional information about interior structure, at least when they are primarily hydrostatic. Our results entail important implications for a future interpretation of the currently observed Juno k 42. After including the coupling from the well-understood ℓ = 2 dynamical tides (Δk 2 ≈ −4%), Jupiter’s hydrostatic k 42 requires an unknown dynamical effect to produce a fractional correction Δk 42 ≈ −11% in order to fit Juno’s observation within 3σ. Future work is required to explain the required Δk 42.
18
Mbarki, Mohammed, Marc Oettinghaus e Gerhard Raabe. "Quantum-chemical Ab Initio Calculations on the Donor–Acceptor Complex Pyridine–Borabenzene (C5H5N–BC5H5)". Australian Journal of Chemistry 67, n. 2 (2014): 266. http://dx.doi.org/10.1071/ch13407.
Abstract (sommario):
The adduct of borabenzene (C5H5B) and pyridine (C5H5N) was studied by means of quantum-chemical ab initio and time-dependent density functional theory calculations at different levels of theory. In the fully optimized structure (MP2/6-311++G**) of the free donor–acceptor complex (C2), the C–B–C angle amounts to 120.6°. The planes of the two aromatic rings enclose a torsion angle of ~40° with a barrier to rotation about the B–N bond of less than 3 kcal mol–1 (1 kcal mol–1 = 4.186 kJ mol–1). The highest computational level applied in this study (complete basis set limit, coupled cluster with single and double excitations (CCSD)) results in an energy associated with the reaction of borabenzene with pyridine of –52.2 kcal mol–1. Natural bond orbital analyses were performed to study the bond between the borabenzene and the pyridine unit of the adduct. The UV-vis spectrum of the adduct was calculated employing time-dependent density functional theory methods and the symmetry-adapted cluster-configuration interaction method. Our calculated electronic excitation spectrum of the pyridine adduct as well as its spectrum of the normal modes qualitatively reproduce the characteristic features of the IR and the UV-vis spectra described by experimentalists and thus allows assignment of the observed absorption bands, which in part agree with those by other authors.
19
Mbarki, M., M. Oettinghaus e G. Raabe. "Corrigendum to: Quantum-chemical Ab Initio Calculations on the Donor–Acceptor Complex Pyridine–Borabenzene (C5H5N–BC5H5)". Australian Journal of Chemistry 69, n. 5 (2016): 583. http://dx.doi.org/10.1071/ch13407_co.
Abstract (sommario):
The adduct of borabenzene (C5H5B) and pyridine (C5H5N) was studied by means of quantum-chemical ab initio and time-dependent density functional theory calculations at different levels of theory. In the fully optimized structure (MP2/6-311++G**) of the free donor–acceptor complex (C2), the C–B–C angle amounts to 120.6°. The planes of the two aromatic rings enclose a torsion angle of ~40° with a barrier to rotation about the B–N bond of less than 3kcalmol–1 (1kcalmol–1=4.186kJmol–1). The highest computational level applied in this study (complete basis set limit, coupled cluster with single and double excitations (CCSD)) results in an energy associated with the reaction of borabenzene with pyridine of –52.2kcalmol–1. Natural bond orbital analyses were performed to study the bond between the borabenzene and the pyridine unit of the adduct. The UV-vis spectrum of the adduct was calculated employing time-dependent density functional theory methods and the symmetry-adapted cluster-configuration interaction method. Our calculated electronic excitation spectrum of the pyridine adduct as well as its spectrum of the normal modes qualitatively reproduce the characteristic features of the IR and the UV-vis spectra described by experimentalists and thus allows assignment of the observed absorption bands, which in part agree with those by other authors.
20
Berdeu, Anthony, Maud Langlois e Frédéric Vachier. "First observation of a quadruple asteroid". Astronomy & Astrophysics 658 (febbraio 2022): L4. http://dx.doi.org/10.1051/0004-6361/202142623.
Abstract (sommario):
Context. Extreme adaptive optics systems, such as the Spectro-Polarimetric High-contrast Exoplanet REsearch facility (SPHERE), push forward the limits in high contrast and high resolution in direct imaging. The main objectives of these instruments are exoplanet detection and characterisation. Aims. We aim to increase the contrast limits to detect new satellites orbiting known asteroids. We use cutting-edge data reduction techniques and data processing algorithms that are essential to best analyse the raw data provided by the instruments and increase their performances. Doing so, the unequalled performances of SPHERE also make it a unique tool to resolve and study asteroids in the solar system, expanding the domain of its main science targets. Methods. We applied a newly developed data reduction pipeline for integral field spectrographs on archival SPHERE data of a resolved asteroid, (130) Elektra. It was coupled with a dedicated point spread function reconstruction algorithm to model the asteroid halo. Following the halo removal, the moon signal could be extracted more accurately. The moon positions were fitted at three epochs and were used to derive the orbital parameters via a genetic-based algorithm. Results. We announce the discovery of S/2014 (130) 2, a third moon orbiting (130) Elektra, making it the first quadruple asteroid ever found. It is identified in three different epochs, 9, 30, and 31 Dec. 2014, at a respective angular separation of 258 mas (333 km), 229 mas (327 km), and 319 mas (457 km). We estimate that this moon has a period of 0.679 ± 0.001 day and a semi-major axis of 344 ± 5 km, with an eccentricity of 0.33 ± 0.05 and an inclination of 38° ±19° compared to the primary rotation axis. With a relative magnitude to the primary of 10.5 ± 0.5, its size is estimated to be 1.6 ± 0.4 km. Conclusions. The orbital parameters of S/2014 (130) 2 are poorly constrained due to the unfavourable configurations of the available fragmentary data. Additional observations are needed to better estimate its orbit and to suggest a formation model. This new detection nonetheless shows that dedicated data reduction and processing algorithms modelling the physics of the instruments can push their contrast limits further.
21
Heller, René. "Formation of hot Jupiters through disk migration and evolving stellar tides". Astronomy & Astrophysics 628 (agosto 2019): A42. http://dx.doi.org/10.1051/0004-6361/201833486.
Abstract (sommario):
Since the discovery of Jupiter-sized planets in extremely close orbits around Sun-like stars, several mechanisms have been proposed to produce these “hot Jupiters”. Here we address their pile-up at 0.05 AU observed in stellar radial velocity surveys, their long-term orbital stability in the presence of stellar tides, and their occurrence rate of 1.2 ± 0.38% in one framework. We calculate the combined torques on the planet from the stellar dynamical tide and from the protoplanetary disk in the type-II migration regime. The disk is modeled as a 2D nonisothermal viscous disk parameterized to reproduce the minimum-mass solar nebula. We simulate an inner disk cavity at various radial positions near the star and simulate stellar rotation periods according to observations of young star clusters. The planet is on a circular orbit in the disk midplane and in the equatorial plane of the star. We show that the two torques can add up to zero beyond the corotation radius around young, solar-type stars and stop inward migration. Monte Carlo simulations with plausible variations of our nominal parameterization of the star-disk-planet model predict hot-Jupiter survival rates between about 3% (for an α disk viscosity of 10−1) and 15% (for α = 10−3) against consumption by the star. Once the protoplanetary disk has been fully accreted, the surviving hot Jupiters are pushed outward from their tidal migration barrier and pile up at about 0.05 AU, as we demonstrate using a numerical implementation of a stellar dynamical tide model coupled with stellar evolution tracks. Orbital decay is negligible on a one-billion-year timescale due to the contraction of highly dissipative convective envelopes in young Sun-like stars. We find that the higher pile-up efficiency around metal-rich stars can at least partly explain the observed positive correlation between stellar metallicity and hot-Jupiter occurrence rate. Combined with the observed hot-Jupiter occurrence rate, our results for the survival rate imply that ≲8% (α = 10−3) to ≲43% (α = 10−1) of sun-like stars initially encounter an inwardly migrating hot Jupiter. Our scenario reconciles models and observations of young spinning stars with the observed hot-Jupiter pile up and hot-Jupiter occurrence rates.
22
Noack, L., K. G. Kislyakova, C. P. Johnstone, M. Güdel e L. Fossati. "Interior heating and outgassing of Proxima Centauri b: Identifying critical parameters". Astronomy & Astrophysics 651 (luglio 2021): A103. http://dx.doi.org/10.1051/0004-6361/202040176.
Abstract (sommario):
Context. Since the discovery of a potentially low-mass exoplanet around our nearest neighbour star Proxima Centauri, several works have investigated the likelihood of a shielding atmosphere and therefore the potential surface habitability of Proxima Cen b. However, outgassing processes are influenced by several different (unknown) factors such as the actual planet mass, mantle and core composition, and different heating mechanisms in the interior. Aims. We aim to identify the critical parameters that influence the mantle and surface evolution of the planet over time, as well as to potentially constrain the time-dependent input of volatiles from mantle into the atmosphere. Methods. To study the coupled star–planet evolution, we analysed the heating produced in the interior of Proxima Cen b due to induction heating, which strongly varies with both depth and latitude. We calculated different rotation evolutionary tracks for Proxima Centauri and investigated the change in its rotation period and magnetic field strength. Unlike the Sun, Proxima Centauri possesses a very strong magnetic field of at least a few hundred Gauss, which was likely even stronger in the past. We applied an interior structure model for varying planet masses (derived from the unknown inclination of observation of the Proxima Centauri system) and iron weight fractions, that is, different core sizes, in the range of observed Fe-Mg variations in the stellar spectrum. We used a mantle convection model to study the thermal evolution and outgassing efficiency of Proxima Cen b. For unknown planetary parameters such as initial conditions, we chose randomly selected values. We took heating in the interior due to variable radioactive heat sources and induction heating into account and compared the heating efficiency to tidal heating. Results. Our results show that induction heating may have been significant in the past, leading to local temperature increases of several hundreds of Kelvin. This early heating leads to an earlier depletion of the interior and volatile outgassing compared to if the planet had not been subject to induction heating. We show that induction heating has an impact comparable to tidal heating when assuming latest estimates on its eccentricity. Furthermore, we find that the planet mass (linked to the planetary orbital inclination) has a first-order influence on the efficiency of outgassing from the interior.
23
Casaretto, Nicolas, Sébastien Pillet, El-Eulmi Bendeif, Dominik Schaniel, Anna K. E. Gallien, Peter Klüfers e Theo Woike. "Photocrystallography and IR spectroscopy of light-induced linkage NO isomers in [RuBr(NO)2(PCyp3)2]BF4". Acta Crystallographica Section B Structural Science, Crystal Engineering and Materials 71, n. 6 (1 dicembre 2015): 788–97. http://dx.doi.org/10.1107/s2052520615018132.
Abstract (sommario):
One single photo-induced linkage NO isomer (PLI) is detected and characterized in the dinitrosyl pentacoordinated compound [RuBr(NO)2(PCyp3)2]BF4 by a combination of photocrystallographic and IR analysis. In the ground state, the molecule adopts a trigonal–bipyramidal structure with the two NO ligands almost linear with angles Ru—N1—O1 = 168.92 (16), Ru—N2—O2 = 166.64 (16)°, and exactly equal distances of Ru—N = 1.7838 (17) and O—N = 1.158 (2) Å. After light irradiation of 405 nm at T = 10 K, the angle of Ru—N2—O2 changes to 114.2 (6)° by rotation of the O atom towards the Br ligand with increased distances of Ru—N2 = 1.992 (6) and N2—O2 = 1.184 (8) Å, forming a bent κN bonded configuration. Using IR spectroscopy, the optimal wavelength and maximum population of 39 (1)% of the PLI is determined. In the ground state (GS), the two symmetric νs(NO) and asymmetric νas(NO) vibrations are measured at 1820 and 1778 cm−1, respectively. Upon photo-irradiation, the detection of only one new vibrational ν(NO) stretching band at 1655 cm−1, assigned to the antisymmetric coupled vibration mode and shifted to lower wavenumbers by −123 cm−1, supports the photocrystallographic result. These experimental results are supported by additional DFT calculations, which reproduce the structural parameters and vibrational properties of both the ground state and the photo-induced linkage isomer well. Especially the experimentally characterized molecular structure of the PLI state corresponds to an energy minimum in the calculations; the stabilization of the bent κN bonded configuration of the PLI state originates from specific intramolecular orbital overlap.
24
Liew, S., M. Poole, J. Kenton-Smith, S. Tan e Barry L. Eppley. "Orbital and Globe Rotation". Journal of Craniofacial Surgery 10, n. 6 (novembre 1999): 526. http://dx.doi.org/10.1097/00001665-199911000-00013.
25
Sbitnev, Valeriy. "Quaternion Algebra on 4D Superfluid Quantum Space-Time: Can Dark Matter Be a Manifestation of the Superfluid Ether?" Universe 7, n. 2 (31 gennaio 2021): 32. http://dx.doi.org/10.3390/universe7020032.
Abstract (sommario):
Quaternions are a natural framework of 4D space-time, where the unit element relates to time, and three others relate to 3D space. We define a quaternion set of differential torsion operators (shifts with rotations) that act to the energy-momentum tensor written on the same quaternion basis. It results in the equations of gravity-torsion (gravitomagnetic) fields that are similar to Maxwell’s equations. These equations are parent equations, generating the following equations: (a) equations of the transverse gravity-torsion waves; (b) the vorticity equation describing vortices orbital speed of which grows monotonically in the vortex core but far from it, it goes to a permanent level; (c) the modified Navier–Stokes equation leading to the Schrödinger equation in the nonrelativistic limit and to the Dirac equation in the relativistic limit. The Ginsburg–Landau theory of superfluidity resulting from the Schrödinger equation shows the emergence of coupled proton-antiproton pairs forming the Bose–Einstein condensate. In the final part of the article, we describe Samokhvalov’s experiment with rotating nonelectric, nonferromagnetic massive disks in a vacuum. It demonstrates an unknown force transferring the rotational moment from the driving disk to a driven one. It can be a manifestation of the dark matter. For studying this phenomenon, we propose a neutron interference experiment that is like the Aharonov–Bohm one.
26
Luo, Jian Guo, e Mao Yan He. "Cubic Hybrid Mechanism Based on S[T] Output Base and P/R Input Base". Advanced Materials Research 430-432 (gennaio 2012): 1725–28. http://dx.doi.org/10.4028/www.scientific.net/amr.430-432.1725.
Abstract (sommario):
Based on the flexibility of single couple of serial mechanism and the stability of multi couples of parallel mechanism, a new type of S[T] output base of hybrid mechanism presented, component of sphere joint run through the tiger joint, this component still the output one with the capability of rotate in three dimensional space. Add serial branch including three translation couple P or/and rotation couple R to the new type of S[T] output base, put these members on one cubic frame, twenty seven configurations obtained with 3-DOF(degree of freedom) allow of three dimensional rotation, twenty seven configurations belong to three conditions obtained with 4-DOF allow of three dimensional rotation and one dimensional translation, nine configurations belong to three conditions obtained with 5-DOF allow of three dimensional rotation and two dimensional translation, one configuration obtained with 6-DOF allow of three dimensional rotation and three dimensional translation, all those sixty four configurations have no more than six translation couple or rotation couple, and the sum of two kind of couple is equal to six. Developing new type of hybrid manipulator based on the hybrid cubic mechanism constructed with S[T] output base and P/R input base will be possible in theory and useful.
27
Mennickent, R. E. "Long photometric cycles in hot algols". Serbian Astronomical Journal, n. 194 (2017): 1–21. http://dx.doi.org/10.2298/saj1794001m.
Abstract (sommario):
We summarize the development of the field of Double Periodic Variables (DPVs, Mennickent et al. 2003) during the last fourteen years, placing these objects in the context of intermediate-mass close interacting binaries similar to ? Persei (Algol) and ? Lyrae (Sheliak) which are generally called Algols. DPVs show enigmatic long photometric cycles lasting on average about 33 times the orbital period, and have physical properties resembling, in some aspects, ? Lyrae. About 200 of these objects have been found in the Galaxy and the Magellanic Clouds. Light curve models and orbitally resolved spectroscopy indicate that DPVs are semi-detached interacting binaries consisting of a near main-sequence B-type star accreting matter from a cooler giant and surrounded by an optically thick disc. This disc contributes a significant fraction of the system luminosity and its luminosity is larger than expected from the phenomenon of mass accretion alone. In some systems, an optically thin disc component is observed in well developed Balmer emission lines. The optically thick disc shows bright zones up to tens percent hotter than the disc, probably indicating shocks resulting from the gas and disc stream dynamics. We conjecture that a hotspot wind might be one of the channels for a mild systemic mass loss, since evidence for jets, winds or general mass loss has been found in ? Lyrae, AUMon, HD170582, OGLE05155332-6925581 and V393 Sco. Also, theoretical work by Van Rensbergen et al. (2008) and Deschamps et al. (2013) suggests that hotspot could drive mass loss from Algols. We give special consideration to the recently published hypothesis for the long-cycle, consisting of variable mass transfer driven by a magnetic dynamo (Schleicher and Mennickent 2017). The Applegate (1992) mechanism should modify cyclically the equatorial radius of the chromospherically active donor producing cycles of enhanced mass loss through the inner Lagrangian point. Chromospheric emission in V393 Sco, an optically thicker hotspot in the high-state of HD170582 and evidence for magnetic fields in many Algols are observational facts supporting this picture. One of the open questions for this scenario is why, among the Algols showing evidence for magnetic fields, the DPV long-cycle is present only under some combinations of stellar parameters, particularly those including the B-type gainers. Other open questions are what are the descendants of these interesting binaries, how much mass contain the discs around the likely rapidly rotating gainers, and the role played by the outflows through the Lagrangian L2 and L3 points reported in a couple of systems.
28
Jermyn, Adam S., Jamie Tayar e Jim Fuller. "Differential rotation in convective envelopes: constraints from eclipsing binaries". Monthly Notices of the Royal Astronomical Society 491, n. 1 (26 ottobre 2019): 690–707. http://dx.doi.org/10.1093/mnras/stz2983.
Abstract (sommario):
ABSTRACT Over time, tides synchronize the rotation periods of stars in a binary system to the orbital period. However, if the star exhibits differential rotation, then only a portion of it can rotate at the orbital period, so the rotation period at the surface may not match the orbital period. The difference between the rotation and orbital periods can therefore be used to infer the extent of the differential rotation. We use a simple parametrization of differential rotation in stars with convective envelopes in circular orbits to predict the difference between the surface rotation period and the orbital period. Comparing this parametrization to observed eclipsing binary systems, we find that in the surface convection zones of stars in short-period binaries there is very little radial differential rotation, with |r∂rln Ω| < 0.02. This holds even for longer orbital periods, though it is harder to say which systems are synchronized at long periods, and larger differential rotation is degenerate with asynchronous rotation.
29
Verma, Anish, e Krzysztof Starosta. "Collective and single-particle degrees of freedom in rotating nuclei". Canadian Journal of Chemistry 96, n. 2 (febbraio 2018): 158–67. http://dx.doi.org/10.1139/cjc-2017-0275.
Abstract (sommario):
In 1937, Hermann Jahn and Edward Teller published their research describing a mechanism of symmetry breaking in nonlinear polyatomic molecules resulting in a lifting of orbital degeneracy of an electronic state (Proc. R. Soc. London, Ser. A 1937, 161, 220), yielding insight into molecular structure. The impact of symmetry breaking on the energy and structure of quantum states is not unique to molecules and may be applied to nuclei, involving degenerate nucleon states as opposed to electronic states. Reinhard and Otten showed that the nuclear Jahn–Teller effect provides a mechanism applicable to describe the commonly observed collective quadrupole surface motion (Nucl. Phys. A 1984, 420, 173). To take into account single-particle effects, it is important to properly model the valence nucleons, especially those occupying large angular momenta orbitals near the Fermi level. In this work, a model has been developed in which two valence nucleons of the same kind are coupled to an axially symmetric quadrupole deformed rotor of the D2 symmetry and interact through the nuclear delta force. To test this model, the band of the lowest-energy state at a given spin for 126Ce is reproduced. The resultant wavefunctions are then used to calculate the g factor, reduced electric quadrupole transition probability, and spectroscopic quadrupole moment all as a function of spin. This method lays the groundwork to explore higher order symmetries following the multipole expansion.
30
Mehta, C. B., e M. Singh. "Compressible Analysis of Bénard Convection of Magneto Rotatory Couple-Stress Fluid". International Journal of Applied Mechanics and Engineering 23, n. 1 (1 febbraio 2018): 91–105. http://dx.doi.org/10.1515/ijame-2018-0006.
Abstract (sommario):
AbstractThermal Instability (Benard’s Convection) in the presence of uniform rotation and uniform magnetic field (separately) is studied. Using the linearized stability theory and normal mode analyses the dispersion relation is obtained in each case. In the case of rotatory Benard’s stationary convection compressibility and rotation postpone the onset of convection whereas the couple-stress have duel character onset of convection depending on rotation parameter. While in the absence of rotation couple-stress always postpones the onset of convection. On the other hand, magnetic field on thermal instability problem on couple-stress fluid for stationary convection couple-stress parameter and magnetic field postpones the onset of convection. The effect of compressibility also postpones the onset of convection in both cases as rotation and magnetic field. Graphs have been plotted by giving numerical values to the parameters to depict the stationary characteristics. Further, the magnetic field and rotation are found to introduce oscillatory modes which were non-existent in their absence and then the principle of exchange of stability is valid. The sufficient conditions for non-existence of overstability are also obtained.
31
Mehta, Chander Bhan. "Magneto-rotatory compressible couple-stress fluid heated from below in porous medium". Studia Geotechnica et Mechanica 38, n. 1 (1 marzo 2016): 55–63. http://dx.doi.org/10.1515/sgem-2016-0006.
Abstract (sommario):
Abstract The study is aimed at analysing thermal convection in a compressible couple stress fluid in a porous medium in the presence of rotation and magnetic field. After linearizing the relevant equations, the perturbation equations are analysed in terms of normal modes. A dispersion relation governing the effects of rotation, magnetic field, couple stress parameter and medium permeability have been examined. For a stationary convection, the rotation postpones the onset of convection in a couple stress fluid heated from below in a porous medium in the presence of a magnetic field. Whereas, the magnetic field and couple stress postpones and hastens the onset of convection in the presence of rotation and the medium permeability hastens and postpones the onset of convection with conditions on Taylor number. Further the oscillatory modes are introduced due to the presence of rotation and the magnetic field which were non-existent in their absence, and hence the principle of exchange stands valid. The sufficient conditions for nonexistence of over stability are also obtained.
32
Kumar, Pardeep. "Magneto-Rotatory Convection in Couple-Stress Fluid". WSEAS TRANSACTIONS ON FLUID MECHANICS 18 (6 ottobre 2023): 58–65. http://dx.doi.org/10.37394/232013.2023.18.6.
Abstract (sommario):
Background: Thermal convection is the most convective instability when crystals are produced from a single element like silicon and the thermal instability of a fluid layer heated from below plays an important role in geophysics, oceanography, atmospheric physics, etc. The flow through porous media is of considerable interest for petroleum engineers, for geophysical fluid dynamicists and has importance in chemical technology and industry. Many of the flow problems in fluids with couple-stresses indicate some possible experiments, that could be used for determining the material constants, and the results are found to differ from those of Newtonian fluid. Keeping this in view, the present work was to study the effect of a uniform vertical magnetic field on the couple-stress fluid heated from below in the presence of a uniform vertical rotation through permeable media. Methodology: The present problem is studied using the linearized stability theory, Boussinesq approximation, normal mode analysis, and the dispersion relation is obtained. Results: The stationary convection, stability of the system, and oscillatory modes are discussed. In the case of stationary convection, the rotation postpones the onset of convection. The magnetic field and couple-stress may hasten the onset of convection in the presence of rotation while in the absence of rotation; they always postpone the onset of convection. The medium permeability hastens the onset of convection in the absence of rotation while in the presence of rotation, it may postpone the onset of convection. The rotation and magnetic field are found to introduce oscillatory modes in the system which was non-existent in their absence. A sufficient condition for the non-existence of overstability is also obtained.
33
Rahul e Naveen Sharma. "On a Couple-Stress Rivlin-Ericksen Ferromagnetic Fluid Heated from Below with Varying Gravity, Rotation, Magnetic Field and Suspended Particles Flowing Through a Porous Medium". International Journal of Applied Mechanics and Engineering 27, n. 2 (1 giugno 2022): 177–98. http://dx.doi.org/10.2478/ijame-2022-0027.
Abstract (sommario):
Abstract The thermal instability of a couple-stress Rivlin-Ericksen ferromagnetic fluid with varying gravity field, suspended particles, rotation and magnetic field flowing through a porous medium is investigated. The dispersion relation has been developed and solved analytically using the normal mode approach and linear stability theory. The effect of suspended particles, rotation, couple stress, permeability and magnetic field on the fluid layer has been investigated. For stationary conventions, it is found that suspended particles always have a destabilizing effect for λ>0 and a stabilizing effect for λ<0 and couple-stress, magnetic field and permeability of the medium have a stabilizing effect on the thermal instability under certain conditions. In the absence of the rotation couple-stress has a stabilizing effect if λ >0 and a destabilizing effect if λ<0. Rotation has a stabilizing effect if λ >0 and a destabilizing effect if λ<0. In the absence of rotation permeability has a stabilizing effect if λ<0 and a destabilizing effect if λ>0. Magnetisation always has a stabilizing effect (λ>0 or λ<0).
34
Fernandes, Rafael M., e Jörn W. F. Venderbos. "Nematicity with a twist: Rotational symmetry breaking in a moiré superlattice". Science Advances 6, n. 32 (agosto 2020): eaba8834. http://dx.doi.org/10.1126/sciadv.aba8834.
Abstract (sommario):
Motivated by recent reports of nematic order in twisted bilayer graphene (TBG), we investigate the impact of the triangular moiré superlattice degrees of freedom on nematicity. In TBG, the nematic order parameter is not Ising like, as in tetragonal crystals, but has a three-state Potts character related to the threefold rotational symmetry (C3z) of the moiré superlattice. We find that, even in the presence of static strain that explicitly breaks the C3z symmetry, the system can still undergo a nematic-flop phase transition that spontaneously breaks in-plane twofold rotations. Moreover, elastic fluctuations, manifested as acoustic phonons, mediate a nemato-orbital coupling that ties the nematic director orientation to certain soft directions in momentum space, rendering the Potts-nematic transition mean field and first order. In contrast to the case of rigid crystals, the Fermi surface hot spots associated with these soft directions are maximally coupled to low-energy nematic fluctuations in the moiré superlattice case.
35
Kagan, Yan Y. "Double-couple earthquake source: symmetry and rotation". Geophysical Journal International 194, n. 2 (16 maggio 2013): 1167–79. http://dx.doi.org/10.1093/gji/ggt156.
36
Kagan, Yan Y. "Simplified algorithms for calculating double-couple rotation". Geophysical Journal International 171, n. 1 (ottobre 2007): 411–18. http://dx.doi.org/10.1111/j.1365-246x.2007.03538.x.
37
Pan, Qiaoyun, Weiyu Lv, Li Deng, Sumei Huang e Aixi Chen. "Cooling a Rotating Mirror Coupled to a Single Laguerre–Gaussian Cavity Mode Using Parametric Interactions". Nanomaterials 12, n. 20 (21 ottobre 2022): 3701. http://dx.doi.org/10.3390/nano12203701.
Abstract (sommario):
We study the cooling of a rotating mirror coupled to a Laguerre–Gaussian (L–G) cavity mode, which is assisted by an optical parametric amplifier (OPA). It is shown that the presence of the OPA can significantly lower the temperature of the rotating mirror, which is very critical in the application of quantum physics. We also find that the increase in angular momentum has an influence on the cooling of the rotating mirror. Our results may provide a potential application in the determination of the orbital angular momentum of light fields and precision measurement.
38
Schroeder, Paul. "Central Body Rotation Drives Orbital Revolutions". Journal of Geoscience and Environment Protection 06, n. 12 (2018): 70–84. http://dx.doi.org/10.4236/gep.2018.612005.
39
Kumar, Pardeep, Roshan Lal e Poonam Sharma. "Effect Of Rotation On Thermal Instability In Couple-Stress Elastico-Viscous Fluid". Zeitschrift für Naturforschung A 59, n. 7-8 (1 agosto 2004): 407–11. http://dx.doi.org/10.1515/zna-2004-7-803.
Abstract (sommario):
The thermal instability of a layer of a couple-stress fluid acted on by a uniform rotation is considered. Following the linearized stability theory and normal mode analysis, the dispersion relation is obtained. For stationary convection it is found that rotation has a stabilizing effect, whereas the couple-stress has both stabilizing and destabilizing effects. It is found that the presence of rotation introduces oscillatory modes in the system. A sufficient condition for the non-existence of overstability is also obtained.
40
Volostnikov, V. G. "Orbital angular momentum of the spiral beams". Computer Optics 43, n. 3 (giugno 2019): 504–6. http://dx.doi.org/10.18287/2412-6179-2019-43-3-504-506.
Abstract (sommario):
At first sight, any rotation generates some angular momentum (it is true for a solid body). But these characteristics (rotation and orbital angular momentum) are rather different for optics and mechanics. In optics there are the situation when the rotation is important. On the other hand, there are the cases where the nonzero orbital angular momentum is necessary. The main goal of this article is to investigate a relationship between a rotation under propagation of spiral beam and its angular momentum. It can be done the following conclusion: there is no any relation between rotation under propagation of spiral beam and its OAM.
41
Kumar, Pardeep. "Stability Analysis in Couple-Stress Rotatory Fluid". WSEAS TRANSACTIONS ON HEAT AND MASS TRANSFER 16 (29 giugno 2021): 49–58. http://dx.doi.org/10.37394/232012.2021.16.8.
Abstract (sommario):
The aim of the present research was to study the effect of uniform rotation on the layer of a couple-stress fluid heated from below in porous medium. Following the linearized stability theory, Boussinesq approximation and normal mode analysis, the dispersion relation is obtained. The stationary convection, stability of the system and oscillatory modes are discussed. For the case of stationary convection, it is found that rotation has a stabilizing effect, whereas the couple-stress parameter and medium permeability have both stabilizing and destabilizing effects on the system. It is found that the presence of rotation introduces oscillatory modes in the system which were non-existent in its absence. A sufficient condition for the non-existent of overstability is also obtained.
42
Zoghbi, Jean-Paul A. "Quantization of Planetary Systems and its Dependency on Stellar Rotation". Publications of the Astronomical Society of Australia 28, n. 3 (2011): 177–201. http://dx.doi.org/10.1071/as09062.
Abstract (sommario):
AbstractWith the discovery of now more than 500 exoplanets, we present a statistical analysis of the planetary orbital periods and their relationship to the rotation periods of their parent stars. We test whether the structural variables of planetary orbits, i.e. planetary angular momentum and orbital period, are ‘quantized’ in integer or half-integer multiples of the parent star's rotation period. The Solar System is first shown to exhibit quantized planetary orbits that correlate with the Sun's rotation period. The analysis is then expanded over 443 exoplanets to statistically validate this quantization and its association with stellar rotation. The results imply that the exoplanetary orbital periods are highly correlated with the parent star's rotation periods and follow a discrete half-integer relationship with orbital ranks n = 0.5, 1.0, 1.5, 2.0, 2.5, etc. The probability of obtaining these results by pure chance is p < 0.024. We discuss various mechanisms that could justify this planetary quantization, such as the hybrid gravitational instability models of planet formation, along with possible physical mechanisms such as the inner disc's magnetospheric truncation, tidal dissipation, and resonance trapping. In conclusion, we statistically demonstrate that a quantized orbital structure should emerge from the formation processes of planetary systems and that this orbital quantization is highly dependent on the parent star's rotation period.
43
Kumar, Pardeep, e Mahinder Singh. "Rotatory Thermosolutal Convection in a Couple-Stress Fluid". Zeitschrift für Naturforschung A 64, n. 7-8 (1 agosto 2009): 448–54. http://dx.doi.org/10.1515/zna-2009-7-807.
Abstract (sommario):
AbstractThe thermosolutal instability of couple-stress fluid in the presence of uniform vertical rotation is considered. Following the linearized stability theory and normal mode analysis, the dispersion is obtained. For the case of stationary convection, the stable solute gradient and rotation have stabilizing effects on the system, whereas the couple-stress has both stabilizing and destabilizing effects. The dispersion relation is also analyzed numerically. The stable solute gradient and the rotation introduce oscillatory modes in the system, which did not occur in their absence. The sufficient conditions for the non-existence of overstability are also obtained.
44
Lanza, A. F. "Orbital period modulation in hot Jupiter systems". Monthly Notices of the Royal Astronomical Society 497, n. 3 (27 luglio 2020): 3911–24. http://dx.doi.org/10.1093/mnras/staa2186.
Abstract (sommario):
ABSTRACT We introduce a model for the orbital period modulation in systems with close-by giant planets based on a spin–orbit coupling that transfers angular momentum from the orbit to the rotation of the planet and vice versa. The coupling is produced by a permanent non-axisymmetric gravitational quadrupole moment assumed to be present in the solid core of the planet. We investigate two regimes of internal planetary rotation, that is, when the planet rotates rigidly and when the rotation of its deep interior is time-dependent as a consequence of a vacillating or intermittent convection in its outer shell. The model is applied to a sample of very hot Jupiters predicting maximum transit-time deviations from a constant-period ephemeris of approximately 50 s in the case of rigid rotation. The transit time variations of WASP-12, currently the only system showing evidence of a non-constant period, cannot be explained by assuming rigid rotation, but can be modelled in the time-dependent internal rotation regime, thus providing an alternative to their interpretation in terms of a tidal decay of the planet orbit.
45
Clement, Maurice J. "Pulsation in Rapidly Rotating Stars". Symposium - International Astronomical Union 162 (1994): 117–27. http://dx.doi.org/10.1017/s0074180900214691.
Abstract (sommario):
The line-profile variables observed on the upper main sequence have been interpreted by some astronomers to be the manifestation of nonaxisymmetric oscillations. More specifically, most of these variables can be modelled by prograde or corotating equatorial waves. In the absence of rotation, these waves have surface velocity distributions which are given simply by spherical harmonics. Unfortunately, the corresponding velocity fields in the presence of rotation are much more difficult to calculate. In this paper, I will summarize what is known about the effect of rapid rotation on the normal mode eigenfunctions of main sequence stars. The principal conclusions are as follows: Low-order, axisymmetric modes couple very strongly to rotation and their velocity distributions are very much different from those of their zero-rotation counterparts. On the other hand, higher-order (shorter wavelength), nonaxisymmetric modes couple only weakly to rotation and, therefore, retain many of the spherical harmonic properties that they possess in the absence of rotation.
46
Kagan, Y. Y. "3-D rotation of double-couple earthquake sources". Geophysical Journal International 106, n. 3 (settembre 1991): 709–16. http://dx.doi.org/10.1111/j.1365-246x.1991.tb06343.x.
47
Murakami, Masahiro, Yasufumi Miyamoto, Munehiro Hasegawa, Ippei Usui e Takanori Matsuda. "Torque control by metal-orbital interactions". Pure and Applied Chemistry 78, n. 2 (1 gennaio 2006): 415–23. http://dx.doi.org/10.1351/pac200678020415.
Abstract (sommario):
The silyl substituent of 3-silylcyclobutene prefers inward rotation rather than outward rotation during a thermal ring-opening reaction, giving the Z-isomer predominantly. This intriguing behavior was explained by assuming electron-accepting interactions between the low-lying σ*-orbital of the silicon-carbon linkage and the highest occupied molecular orbital (HOMO) of the opening cyclobutene system, which are possible only in the inward transition state. On the basis of this finding, a novel method for the stereoselective synthesis of functionalized 1,3-butadiene derivatives from cyclobutenones was developed. Boryl substituents exhibit even stronger preference for inward rotation than silyl substituents as a result of electron delocalization from the cyclobutene HOMO into the vacant p-orbital of boron at the inward transition state.
48
Stark, Alexander, Jürgen Oberst e Hauke Hussmann. "Mercury’s resonant rotation from secular orbital elements". Celestial Mechanics and Dynamical Astronomy 123, n. 3 (21 luglio 2015): 263–77. http://dx.doi.org/10.1007/s10569-015-9633-4.
49
Madáč, Kamil, e Andrej Madáč. "Orbital Radii and Rotation of Celestial Bodies". Acta Mechanica Slovaca 17, n. 4 (31 ottobre 2013): 48–51. http://dx.doi.org/10.21496/ams.2013.045.
50
Stanly, W., e R. Vasanthakumari. "Effect of rotation on dusty couple-stress fluid with hydromagnetic field heated below through porous medium". World Journal of Engineering 15, n. 1 (12 febbraio 2018): 148–55. http://dx.doi.org/10.1108/wje-12-2016-0158.
Abstract (sommario):
Purpose The purpose of this paper is used to study the combined effect of solute gradient and magnetic field on dusty couple-stress fluid in the presence of rotation through a porous medium. Design/methodology/approach The perturbation technique (experimental method) is applied in this study. Findings For the case of stationary convection, solute gradient and rotation have stabilizing effect, whereas destabilizing effect is found in dust particles in the system. Couple stress and medium permeability both have dual character to its stabilizing effect in the absence of magnetic field and rotation. Magnetic field succeeded in establishing a stabilizing effect in the absence of rotation. Originality/value The results are discussed by allowing one variable to vary and keeping other variables constant, as well as by drawing graphs.