Angular Momentum Increases Research Articles

Strong gravitational lensing by Kerr and Kerr-Newman black holes

We study the strong gravitational lensing due to the Kerr black holes with angular momentum $a$ and the Kerr-Newman black holes with additional charge $Q$. We first derive the analytical expressions of the deflection angles of light rays that particularly diverge as they travel near the photon sphere. In this strong deflection limit, the light rays can circle around the black hole multiple times before reaching the observer, giving relativistic images. The obtained analytical expressions are then applied to compute the angular positions and the magnifications of relativistic images due to the supermassive galactic black holes. In this work, we focus on the outermost image with reference to the optical axis. We find that its angular separation from the one closest to the optical axis and the magnification increase in angular momentum $a$ of the black holes for light rays with direct orbits. Additionally, the effects of the charge $Q$ of black holes also increase the angular separation of the outermost image from the others and the magnification for both direct and retrograde orbits. The potentially increasing observability of the relativistic images from the effects of angular momentum and charge of the black holes will be discussed.

A note on Jacobi-type transitions in finite nuclei

The Jacobi-type transitions (JTTs) in nuclei and their connections with excite-state quantum phase transitions (ESQPTs) have been investigated within the framework of the interacting boson model (IBM) by both the semiclassical analysis and quantal calculations. The results indicate that the quadrupole deformation of a transitional system may change from γ rigid to γ soft as the angular momentum increases. This change may in turn drive the JTTs to occur around the saddle point of the corresponding classical potential, where the precursors of ESQPT can be also identified even for a realistic boson number. A further comparison between the experimental data and the model predictions confirms that the JTT phenomena may widely occur in the rare-earth isotopes associated with the 1st-order quantum phase transitions.

Biomechanics of In-Stance Balancing Responses Following Outward-Directed Perturbation to the Pelvis During Very Slow Treadmill Walking Show Complex and Well-Orchestrated Reaction of Central Nervous System.

Multiple strategies may be used when counteracting loss of balance during walking. Placing the foot onto a new location is not efficient when walking speed is very low. Instead medio-lateral displacement of center-of-pressure, rotation of body segments to produce a lateral ground-reaction-force, and pronounced braking of movement in the plane of progression is used. It is, however, presently not known in what way these in-stance balancing strategies are interrelated. Twelve healthy subjects walked very slowly on an instrumented treadmill and received outward-directed pushes to the waist. We created experimental conditions where the use of stepping strategy to recover balance following an outward push was minimized by appropriately selecting the amplitude and timing of perturbation. Our experimental results showed that in the first part of the response the principal strategy used to counteract the effect of a perturbing push was a short but substantial increase in lateral ground-reaction-force. Concomitant slowing of the movement and related anterior displacement of center-of-pressure enabled lateral displacement of center-of-pressure which was, together with a short but substantial increase in vertical ground-reaction-force, instrumental in reducing the inevitable increase of whole-body angular momentum in the frontal plane. However, anterior displacement of center-of-pressure and increased vertical ground-reaction-force also induced an increase in whole-body angular momentum in the sagittal plane. In the second part of the response the lateral ground-reaction-force was decreased with respect to unperturbed walking thus allowing for a decrease of whole-body angular momentum in the frontal plane. Additionally, an increase in anterior ground-reaction-force in the second part of the response propelled the center-of-mass in the direction of movement, thus re-synchronizing it with the frontal plane component of the center-of-mass as well as decreasing whole-body angular momentum in the sagittal plane. The results of this study show that use of in-stance balancing strategies counteracts the effect a perturbing push imposed on the center-of-mass, re-synchronizes the movement of center-of-mass in sagittal and frontal planes to the values seen in unperturbed walking and maintains control of whole-body angular momentum in both frontal and sagittal planes.

On the angular momentum history of galactic discs

ABSTRACT The stellar mass, size, and rotational velocity of galactic discs all grow from redshift ∼2 to the present by amounts that are estimated from observationally derived scaling relations. The product of these three quantities, the angular momentum of stellar discs, is then estimated to grow by a remarkably large factor, between ∼20 and ∼50, whereas other evidences suggest a more moderate increase. This requires that the specific angular momentum of the accreted gas should systematically increase with time while remaining corotational with the disc over most of the last ∼10 Gyr. Thus, the baryonic gas vorticity of the circumgalactic medium appears to emerge as a major driver in galaxy evolution, and this Letter is meant to attract attention on the sheer size of the angular momentum increase and on the need to explore to which extent this can be observed in nature and/or in simulations.

Angular Momentum Distribution in Galaxies and Inner Haloes Profile

In this paper, we extend the Romanowsky and Fall (2012) results concerning the stellar angular momentum to the mass range 103 ≲ M*/M⊙ ≲ 1012, and using this result, we calculate the inner slope, α of haloes density profiles in terms of Vrot, by using a previous model of Del Popolo, taking into account the interactions between dark matter and baryons through dynamical friction. Using the McConnachie sample, and that of Romanowsky and Fall, based only on observations, we show that in the quoted sample the rotationally supported galaxies, and the pressure supported ones are divided by a break atM* ≃ 107.8M⊙. Then we show that the slope α flattens monotonically, from α ≃ − 1 to α ≃ 0. The flattening is due to the increase of specific angular momentum moving fromMilkyWay-type galaxies to disk dwarf galaxies. Since at M* < 107.8M⊙, non-rotational supported galaxies start to dominate, the inner slope steepens again. The paper also extends the main result of Del Popolo (2016) to morphologies different from spheroids, and disks, taking into account the different morphologies delimited by the quoted ones. We finally compared our results with Di Cintio SPH simulations. The two models differ mainly at stellar masses smaller than M* ≲ 107.8M⊙. In our model the inner slope is flatter than in simulations. This imply that even finding a cored, α ≃ 0.4, profile in dSphs with masses slightly smaller than ≃106M⊙ will not imply necessarily a problem for the ΛCDM mode, as predicted by some simulations. To check which one of the two model was better describing data in this region, we used the LITTLE THINGS data, and compared the two models through a χ2, finding that our model gives a better description of the data.

Dynamics of particles near brane-world black hole

In this paper, we have explored the behavior of dynamics of neutral test particles near the brane-world black hole (BH). We have discussed the stability/instability near the circular orbits with the help of extremal and nonextremal BH. In this consideration, we investigate the last stable circular orbit [Formula: see text] that decreases with the increase of black hole parameters and concluded that the circular orbits are stable at [Formula: see text]. The effective potential vanishes at horizon in extremal BH. In case of nonextremal BH, the angular momentum decreases, whereas energy increases with the increase in dark parameter [Formula: see text]. Moreover, we find the conditions for the naked singularity and also express the effective potential that increases with the increase of angular momentum. Finally, the center-of-mass energy (CME) is constructed by the collision of particles in the vicinity of brane-world black hole and observed that the CME decreases with the increase of black hole parameters.

Mirror nuclei of 1n/2n halo systems as 1p/2p emitters

Background: The advent of radioactive ion beams has helped considerably to explore exotic decay modes like proton radioactivity in extremely proton-rich nuclei lying on or beyond the proton drip line. Recently, an experimental study was reported on the structural properties of proton-rich nucleus $^{11}\mathrm{O}$. Interestingly, $^{11}\mathrm{O}$ is the mirror nucleus of the widely studied $2n$ halo system $^{11}\mathrm{Li}$. In addition, $^{11}\mathrm{O}$ formed in the experiment was identified through its decay by $2p$ emission. A similar kind of interdependence between neutron halo and its mirror counterpart for $2p$ emission was reported [Charity, Elson, Komarov, Sobotka, Manfredi, and Shane, J. Phys.: Conf. Series 420, 012073 (2013)].Purpose: To study and analyze whether the mirror nuclei of known $1n$/$2n$ halo systems are $1p$/$2p$ emitters.Method: The preference for the mirror nuclei of $1n$/$2n$ halo systems for $1p$/$2p$ emission over the other ($2p$/$1p$ emission) is studied by $Q$-value systematics and potential energy minimization using a cluster-core model. The half-lives of the mirror nuclei of neutron halo systems were determined using a recently proposed empirical formula [Sreeja and Balasubramaniam, Eur. Phys. J. A 54, 106 (2018); Sreeja and Balasubramaniam, Eur. Phys. J. A 55, 33 (2019)].Results: Among the mirror nuclei of $1n$ halo systems, $^{11}\mathrm{N}$ (the mirror of $^{11}\mathrm{Be}$) and $^{15}\mathrm{F}$ (the mirror of $^{15}\mathrm{C}$) were found to have a preference for $1p$ emission over $2p$ emission by $Q$-value systematics. The potential energy surface analysis supported the result where both $^{11}\mathrm{N}$ and $^{15}\mathrm{F}$ were found to be ground-state $1p$ emitters. The trend got changed with an increase in angular momentum where the minimum in potential shifted from $1p$ to $2p$ cluster. Moreover, the half-life calculation matches with the result obtained from $Q$-value systematics.Conclusion: For the $2n$ halo systems, all the studies made indicate that the respective mirror nuclei have a preference for $2p$ emission. A similar conclusion cannot be drawn for the mirror nuclei of $1n$ halo systems except for $^{11}\mathrm{N}$ and $^{15}\mathrm{F}$, which were found to be ground-state $1p$ emitters. All the remaining mirror nuclei of $1n$ halo systems prefers $2p$ emission as favorable decay mode than the expected $1p$ emission. The empirical formula can be used as a good tool to evaluate half-life values of proton emitters provided the $Q$ values are known with desirable accuracy.

On the peripheral intensification of two-dimensional vortices in smaller-scale randomly forcing flow

The evolution of a monopolar vortex embedded in the field of smaller-scale randomly forced vorticity is examined using fully nonlinear two-dimensional simulations at large Reynolds numbers. The vortex is considered to be compact if its angular momentum decreases with the radius on the scale comparable to the radius of maximum azimuthal velocity. The energy decays without forcing, while the vortex remains compact despite its viscous spreading. This scenario dramatically changes in the strong forcing regime, characterized by the substantial growth of the vortex energy due to the increase in velocity and angular momentum at the vortex periphery so that ultimately, the vortex transforms into a noncompact structure. The maximum of angular momentum redistribution is found to be proportional to the enstrophy of smaller-scale vorticity field. The results have important implications for better understanding the fate of vortices and physical mechanisms of energy transfer.

Fano's Propensity Rule in Angle-Resolved Attosecond Pump-Probe Photoionization.

In a seminal article, Fano predicts that absorption of light occurs preferably with increase of angular momentum. We generalize Fano's propensity rule to laser-assisted photoionization, consisting of absorption of an extreme-ultraviolet photon followed by absorption or emission of an infrared photon. The predicted asymmetry between absorption and emission leads to incomplete quantum interference in attosecond photoelectron interferometry. It explains both the angular dependence of the photoionization time delays and the delay dependence of the photoelectron angular distributions. Our theory is verified by experimental results in Ar in the 20-40eV range.

A study on in-cylinder flow field of a 125cc motorcycle engine at low engine speeds

The in-cylinder flow characteristics of a four-stroke, four-valve, pent-roof small engine of motorcycle at engine speeds from 2000 rpm to 4000 rpm were studied using computational fluid dynamics (CFD). The aim of this study was to investigate the in-cylinder flow characteristics of small engines, including tumble, swirl, turbulent kinetic energy (TKE), angular momentum, in-cylinder air mass, turbulent velocity, turbulent length scale, and air flow pattern (in both intake and compression strokes) under motoring conditions. The engine geometry was created using SolidWorks, then was exported and analyzed using CONVERGE, a commercial CFD method. Grid independence analysis was carried out for this small engine and the turbulence model was observed using the renormalized group (RNG) k-ɛ model. The pressure boundary conditions were used to define the fluid pressure at the intake and exhaust of the port. The results showed that the increase in the engine speed caused the swirl flow in the small engine to be irregularly shaped. The swirl flow had a tendency to be stable and almost constant in the beginning of the compression stroke and increased at the end of compression stroke. However, the increase of in engine speed had no significant effect on the increase in tumble ratio, especially during the intake stroke. There was an increase in tumble ratio due to the increase in engine speed at the end of compression stroke, but only a marginal increase. The increase in engine speed had no significant effect on the increase in angular momentum, TKE, or turbulent velocity from the early intake stroke until the middle of the intake stroke. However, the angular momentum increased due to the increase in engine speed from the middle of the intake stroke to the end of compression stroke, and the angular momentum achieved the biggest increase when the engine speed rose from 3000 to 4000 rpm by 10 % at the end of the intake stroke. The increase in engine speed caused an increase of TKE and turbulent velocity from the middle of intake stroke until the end of compression stroke. Moreover, the biggest increase of TKE and turbulent velocity occurred when the engine speed rose from 3000 to 4000 rpm at the middle of intake stroke around 50 % and 25 %, respectively. Turbulent length scales appeared to be insensitive to increasing engine speed, especially in the intake stroke until 490 °CA. From that point, the value of the turbulent length scale increased as engine speed increased. The biggest increase in the turbulent length scales occurred when the intake valve was almost closed (around 20 %) and the engine speed was within two specific ranges (2000 to 3000 rpm and 3000 to 4000 rpm). Regarding the effect of engine speed, there were no significant effects upon the accumulated air mass in the small engine. The increase in engine speed caused an increase of turbulence in the combustion chamber during the late stages of the compression stroke. The increase in turbulence enhanced the mixing of air and fuel and made the mixture more homogeneous. Moreover, the increase in turbulence directly increased the flame propagation speed. Further research is recommended using a new design with several types of intake ports as well as combinations of different intake ports and some type of piston face, so that changes in air flow characteristics in small engines can be analyzed. Finally, this study is expected to help decrease the number of experiments necessary to obtain optimized systems in small engines.

Effect of Vector Correlations in Rotational-Translational Exchange on the Optical Anisotropy of Gaseous Molecular Complexes

A model for the formation of rotationally nonequilibrated ensembles of gaseous molecular complexes is developed taking into account the vector dynamics of translational-rotational exchange and its manifestation as anisotropic light absorption and emission. The proposed model is used to calculate the optical anisotropy of an ensemble of molecular complexes as a function of the change of partial angular momenta and the ratio of moments of inertia of the starting fragments and the resulting complexes. The increase of additional angular momentum due to moments induced during rotational-translational exchange is shown to be capable of causing both a decrease and increase of anisotropy depending on the shape of the complex inertia ellipsoids.

The interior volume calculation for an axially symmetric black hole

Since an axially symmetric metric is much more complicated than a spherically symmetric metric, the largest hypersurface that corresponds to the interior volume of a black hole proposed by Christodoulou and Rovelli, cannot be found easily. Analogous to a Schwarzschild black hole, the particular hypersurface at constant r in a Kerr black hole has been selected directly. Using the extrinsic curvature of the hypersurface, we investigate how the hypersurface deviates from the largest hypersurface as the black hole angular momentum increases. It is shown that the hypersurface is very close to the largest hypersurface and the spinning of spacetime has pretty limited influence. Therefore, the hypersurface can be regarded as the largest hypersurface approximately in a Kerr black hole. So the volume of the hypersurface can be regarded as the interior volume of a Kerr black hole. Subsequently, we also calculate the interior volume of a Kerr–Newman black hole.

Propagation properties of chirped Airy hollow Gaussian wave packets in a harmonic potential

Abstract Based on the analytical expression obtained by solving the ( 3 + 1 ) D Schrodinger-like equation, the spatiotemporal propagation properties of the chirped Airy hollow Gaussian (CAiHG) wave packets in harmonic potential are described and discussed in detail. Results show that the folds on the isosurfaces of the CAiHG wave packets deepen with the temporal chirp parameter β increasing. The wave rings of the CAiHG wave packets can be eliminated as the distribution factor increases, which lead to the stretch of the intensity distribution along the T axis. Moreover, in HGB-like condition, with the increase of the potential width parameter, the Poynting vector and the angular momentum increase and distribute more evenly while their distributions gradually become hollow as the propagation distance increases. Besides, the quantity of the main peaks of the gradient force is exactly proportional to the potential width parameter. As the beam orders increase, the secondary peaks gradually increase while the main peaks are opposite. When β ≤ 0 , the gradient force rapidly decreases while the gradient force decreases first and then increases when β > 0 .

Angular momentum of dwarf galaxies

Mass and specific angular momentum are two fundamental physical parameters of galaxies. We present measurements of the baryonic mass and specific angular momentum of 11 void dwarf galaxies derived from neutral hydrogen (H{\sc i}) synthesis data. Rotation curves were measured using 3D and 2D tilted ring fitting routines, and the derived curves generally overlap within the error bars, except in the central regions where, as expected, the 3D routines give steeper curves. The specific angular momentum of void dwarfs is found to be high compared to an extrapolation of the trends seen for higher mass bulge-less spirals, but comparable to that of other dwarf irregular galaxies that lie outside of voids. As such, our data show no evidence for a dependence of the specific angular momentum on the large scale environment. Combining our data with the data from the literature, we find a baryonic threshold of $\sim 10^{9.1}~M_{\odot}$ for this increase in specific angular momentum. Interestingly, this threshold is very similar to the mass threshold below which the galaxy discs start to become systematically thicker. This provides qualitative support to the suggestion that the thickening of the discs, as well as the increase in specific angular momentum, are both results of a common physical mechanism, such as feedback from star formation. Quantitatively, however, the amount of star formation observed in our dwarfs appears insufficient to produce the observed increase in specific angular momentum. It is hence likely that other processes, such as cold accretion of high angular momentum gas, also play a role in increasing the specific angular momentum.

Properties of strong and weak propellers from MHD simulations

The propeller regime has been studied using axisymmetric numerical simulations, where matter accretes from a thin turbulent disk and interacts with a rotating magnetized star. A wide range of propeller strengths has been studied, from very strong (where the magnetosphere rotates much more rapidly than the inner disk) to very weak (where the magnetosphere rotates only slightly faster than the inner disk). We observed, that in all propellers, the disk-magnetosphere interaction is a strongly non-stationary process. However, the time-averaged characteristics of propeller outflows depend almost entirely on the fastness parameter, ωs, which is the ratio of the stellar angular velocity to the inner disk’s Keplerian velocity. The relative amount of matter ejected into the wind (the efficiency of the propeller) and its velocity, energy and angular momentum increase with ωs. In addition, qualitative differences were observed between the strong and weak propellers: in the strong propellers, matter is accelerated above the escape velocity, forming large-scale outflows that consist of conically-shaped winds and a magnetic (Poynting flux) jet. In the weak propellers, matter flows into a widely-opened, conically-shaped wind with sub- or super-escape velocities that may partly fall back to the disk at some distance from the star. Stars spin down and a star-disk systems lose energy and angular momentum, which flow into winds and jets. Simulations were performed in dimensionless form for stars with magnetospheres of 5−7 stellar radii. Results of the simulations can be applied to different types of magnetized stars, including Classical T Tauri stars (CTTSs), cataclysmic variables (CVs), and accreting millisecond pulsars (MSPs).

Microscopic analysis of homogeneous electron gas by considering dipole–dipole interaction

Implying perturbation theory, the impact of the dipole–dipole interaction (DDI) on the thermodynamic properties of a homogeneous electron gas at zero temperature is investigated. Through the second quantization formalism, the analytic expressions for the ground state energy and the DDI energy are obtained. In this paper, the DDI energy has similarities with the previous works done by others. We show that its general behavior depends on density and the total angular momentum. Especially, it is found that the DDI energy has a highly state-dependent behavior. With the growth of density, the magnitude of DDI energy, which is found to be the summation of all energy contributions of the states with even and odd total angular momenta, grows linearly. It is also found that for the states with even and odd total angular momenta, the DDI energy contributions are corresponding to the positive and negative values, respectively. In particular, an increase of total angular momentum leads to decline in the magnitude of energy contribution. Therefore, the dipole–dipole interaction reveals distinct characteristics in comparison with central-like interactions.

A systematic study of band structure and electromagnetic properties of neutron rich odd mass Eu isotopes in the projected shell model framework

The positive and negative parity rotational band structure of the neutron rich odd mass Eu isotopes with neutron numbers ranging from 90 to 96 are investigated up to the high angular momentum. In the theoretical analysis of energy spectra, transition energies and electromagnetic transition probabilities we employ the projected shell model. The calculations successfully describe the formation of the ground and excited band structures from the single particle and multi quasiparticle configurations. Calculated excitation energy spectra, transition energies, exact quantum mechanically calculated B(E2) and B(M1) transition probabilities are compared with experimental data wherever available and a reasonably good agreement is obtained with the observed data. The change in deformation in the ground state band with the increase in angular momentum and the increase in neutron number has also been established.

Three-dimensional Hydrodynamical Simulations of Mass Transfer in Binary Systems by a Free Wind

Abstract A large fraction of stars in binary systems are expected to undergo mass and angular momentum exchange at some point in their evolution, which can drastically alter the chemical and dynamical properties and fates of the systems. Interaction by stellar wind is an important process in wide binaries. However, the details of wind mass transfer are still not well understood. We perform three-dimensional hydrodynamical simulations of wind mass transfer in binary systems to explore mass-accretion efficiencies and geometries of mass outflows, for a range of mass ratios from 0.05 to 1.0. In particular, we focus on the case of a free wind, in which some physical mechanism accelerates the expelled wind material balancing the gravity of the mass-losing star with the wind velocity comparable to the orbital velocity of the system. We find that the mass-accretion efficiency and accreted specific angular momentum increase with the mass ratio of the system. For an adiabatic wind, we obtain that the accretion efficiency onto the secondary star varies from about 0.1% to 8% for mass ratios between 0.05 and 1.0.

When is high Reynolds number shear flow not turbulent?

Rotating flow in which the angular velocity decreases outward while the angular momentum increases is known as ‘quasi-Keplerian’. Despite the general tendency of shear flow to break down into turbulence, this type of flow seems to maintain stability at very large Reynolds number, even when nonlinearly perturbed, a behaviour that strongly influences our understanding of astrophysical accretion discs. Investigating these flows in the laboratory is difficult because secondary Ekman flows, caused by the retaining Couette cylinders, can become turbulent on their own. A recent high Reynolds number numerical study by Lopez &amp; Avila (J. Fluid Mech., vol. 817, 2017, pp. 21–34) reconciles apparently discrepant laboratory experiments by confirming that this secondary flow recedes toward the axial boundaries of the container as the Reynolds number is increased, a result that enhances our understanding of nonlinear quasi-Keplerian flow stability.

Boundary-layer turbulence in experiments on quasi-Keplerian flows

Most flows in nature and engineering are turbulent because of their large velocities and spatial scales. Laboratory experiments on rotating quasi-Keplerian flows, for which the angular velocity decreases radially but the angular momentum increases, are however laminar at Reynolds numbers exceeding one million. This is in apparent contradiction to direct numerical simulations showing that in these experiments turbulence transition is triggered by the axial boundaries. We here show numerically that as the Reynolds number increases, turbulence becomes progressively confined to the boundary layers and the flow in the bulk fully relaminarizes. Our findings support that turbulence is unlikely to occur in isothermal constant-density quasi-Keplerian flows.