Large Moment Of Inertia Research Articles

Radio Pulse Search and X-Ray Monitoring of SAX J1808.4−3658: What Causes Its Orbital Evolution?

Abstract The accreting millisecond X-ray pulsar SAX J1808.4−3658 shows a peculiar orbital evolution that proceeds at a very fast pace. It is important to identify the underlying mechanism responsible for this behavior because it can help to understand how this system evolves and which physical processes (such as mass loss or spin–orbit coupling) are occurring in the binary. It has also been suggested that, when in quiescence, SAX J1808.4−3658 turns on as a radio pulsar, a circumstance that might provide a link between accreting millisecond pulsars and black-widow (BW) radio pulsars. In this work, we report the results of a deep radio pulsation search at 2 GHz using the Green Bank Telescope in 2014 August and an X-ray study of the 2015 outburst with Chandra, Swift XRT, and INTEGRAL. In quiescence, we detect no radio pulsations and place the strongest limit to date on the pulsed radio flux density of any accreting millisecond pulsar. We also find that the orbit of SAX J1808.4−3658 continues evolving at a fast pace. We compare the orbital evolution of SAX J1808.4−3658 to that of several other accreting and nonaccreting binaries, including BWs, redbacks, cataclysmic variables, black holes, and neutron stars in low-mass X-ray binaries. We discuss two possible scenarios: either the neutron star has a large moment of inertia and is ablating the donor, generating mass loss with an efficiency of 40%, or the donor star has a strong magnetic field of at least 1 kG and is undergoing quasi-cyclic variations due to spin–orbit coupling.

Closed-loop control for global coverage and equatorial hovering about an asteroid

The purpose of this work is to develop a simple control law to implement stable orbits about a small rotating celestial body to achieve global coverage as well as fixed-body hovering on the equatorial plane. The celestial body is assumed to be rotating about a principal axis, with constant rotational velocity along the largest moment of inertia. A simple three dimensional closed-loop guidance law function of position and velocity is defined and analyzed, enabling the determination of the guidance constants to assure convergence to any desired circular orbit about the irregular celestial body, controlling independently five orbital parameters: inclination, right ascension of the ascending node, orbital radius, orbital rate and equatorial longitude. Representative numerical results are presented for an Eros type asteroid.

True polar wander of Enceladus from topographic data

Many objects in the solar system are suspected to have experienced reorientation of their spin axes. As their rotation rates are slow and their shapes are nearly spherical, the formation of mass anomalies, by either endogenic or exogenic processes, can change objects’ moments of inertia. Therefore, the objects reorient to align their largest moment of inertia with their spin axis. Such a phenomenon is called True Polar Wander (TPW).Here we report the discovery of a global series of topographic lows on Saturn's satellite Enceladus that we interpret to show that this synchronously locked moon has undergone TPW by ∼55° about the tidal axis. We use improved topographic data from the spherical harmonic expansion of Cassini limb and stereogrammetric measurements to characterize regional topography over the surface of Enceladus. We identify a group of nearly antipodal basins orthogonal to a basin chain tracing a non-equatorial circumglobal belt across Enceladus' surface. We argue that the belt and the antipodal regions are fossil remnants of earlier equator and poles, respectively. We argue that these lows arise from isostasic compensation and that their pattern reflects spatial variations in internal dynamics of the ice shell. Our hypothesis is consistent with a variety of geological features visible in Cassini images.

Axial segregation of granular mixtures as the rotational stabilization of the radial core

We use the concept of rotational stability to explain the axial segregation of granular mixture inside a rotating horizontal container. We consider the core of radially segregated granular mixture as a dissipative rotating rigid body. The geometric constraints imposed by the container and the minimization of the rotational kinetic energy favor the deformation of the radial core from prolate to oblate configurations, which has larger moment of inertia. Axial segregation is the regime when the oblates pierce the sheath made of the larger grains. The thickness of the oblate is limited by the axial diffusion. This model naturally and parsimoniously accounts for several salient features of axial segregation, such as the location of first formation, scaling with container diameter, inversion, coarsening and transient oscillation of the axial bands.

Observation of high-spin bands with large moments of inertia inXe124

High-spin states in Xe124 have been populated using the Se80(Ca48,4n) reaction at a beam energy of 207 MeV and high-multiplicity, γ-ray coincidence events were measured using the Gammasphere spectrometer. Six high-spin bands with large moments of inertia, similar to those observed in neighboring nuclei, have been observed. The experimental results are compared with calculations within the framework of the cranked Nilsson-Strutinsky model. It is suggested that the configurations of the bands involve excitations of protons across the Z=50 shell gap coupled to neutrons within the N=50-82 shell or excited across the N=82 shell closure.

The effect of tidal torques on the structure and evolution of rotating stars

The tide is a very important physical factor which can affect significantly the structure and evolution of stars. Tidal coefficients in three theoretical models have been explored in this paper. Basing on the equations of angular momentum transport and chemical elements mixing, we can investigate the effect of tidal coefficients on the structure and mixing of chemical elements. It is shown that the tidal coefficient is related to stellar masses, metal abundances, and evolutionary stages. The tidal coefficient E 2 increases with stellar mass but decreases metal abundance and evolutionary time. The bigger tidal coefficient is, the higher efficiency of processes which the orbital angular momentum transforms into the spin angular momentum will be. Furthermore, angular momentum transports efficiently inside the star. Tidal torques can enhance the helium and nitrogen at the stellar surface and enlarge the convective core which can cause the star to shift toward high luminosity. Comparing model M1 with M3, we find that rotational mixing induced by tidal torque can reduce the opacity, and radiative temperature gradient but it can inhibit the hydrodynamic effects of centrifugal force which can increase the radiative temperature gradient. Therefore, tidally induced rotational mixing can decrease the convective core. Furthermore, rotational mixing induced by tidal torque can increase both the number density of hydrogen in stellar core and the efficiency of nuclear reactions. This physical process may increase central temperatures and cause the star to expand greatly. The star will have a large moment of inertia. It is of significance to investigate the tidal mixing in close binary systems.

Bone Functionality and Division II Male and Female Collegiate Athletes from Multiple Sports

Participation in athletics is a risk factor for stress fracture however athletes are also viewed as icons of health, specifically bone health. Bone adaptation may vary depending on the type of loading; high or low impact sport. Are the tibiae of athletes involved in high impact sports (volleyball and soccer) functionally adapted compared to runners and swimmers? PURPOSE: To determine if Division II collegiate athletes had functionally adapted tibia (sufficient strength relative to body size) and whether functional adaptation can be determined from both the 25% and 50% tibial site. METHODS: No single variable indicates bone strength (Jepsen, 2013) and therefore cortical area (Ct.Ar), cortical bone mineral density (cBMD), moment of inertia (J) and bone strength (Strength-strain Index) were measured in 73 athletes (46 females and 27 males (age: 20.2 ± 1.7 yrs, body fat % 16.9 ± 7.5)) and 19 college student controls (8 females and 11 males (age: 23.3 ± 2.3 yrs, body fat % 21.1 ± 7.7)) using peripheral quantitative computed tomography (pQCT) at 25% and 50% of tibial length. Bone functionality was assessed by plotting bone strength vs loading (body weight x tibial length) and robustness (total area/length) vs loading. Based on the residuals from the regression, an athlete’s individual functionality was determined and two groups were formed (functionally adapted (FA) and under adapted (UA)). Student’s t-test detected differences. RESULTS: Height, weight, % body fat and tibial length were similar between the FA and UA groups. However, the FA female group had stronger (27%), more robust bones (23%), with larger moments of inertia (J) (33%) than the female UA group. Male FA group had similar cortical area and cBMD (P<0.05) as the male UA group but they had more robust (23%) stronger (26%) bones with larger J (32%). Both the 25% and 50% sites resulted in similar FA and UA groups and differences. Interestingly the FA and UA groups were comprised of athletes from all teams yet a majority of swimmers were found in the UA female group. CONCLUSIONS: Bone functional adaptation cannot be determined by anthropometric variables. FA groups had robust tibiae at the 25% and 50% site and larger J, allowing them to withstand the bending and torsional loads in sports. Determining bone functionality using the 25% or 50% site of the tibia yielded similar results.

Option selection in whole-body rotation movements in gymnastics

Abstract When a gymnast performs a somersault, the linear and angular momentum along with a particular control of inertia during the flight phase constrain the possibilities for action. Given the complexity and dynamic nature of the human moving system, one could argue that there exist a particular amount of stable coordination states when performing somersaults. The goal of this study was to explore the manifold of movement options and coordination states along with their differentiating parameters for a single somersault in gymnastics based on a simple mathematical model reflecting gymnast’s rotation behavior during the flight phase. Biomechanical parameters determining rotation behavior during a somersault were systematically varied with regard to a particular set of biomechanical constraints defining a successful somersault performance. Batch simulations revealed that from 10229760 simulation cycles only 655346 (approximately 6.41%) led to successful somersault performance. A subsequent analysis of the movement option landscape for the optimum angular momentum revealed ten coordination states for a single somersault that could be clearly distinguished based on the simulation parameters. Taken the results together, it becomes apparent that it may be most advisable to perform a single somersault with a larger moment of inertia when achieving the tucked position, a longer duration to achieve the tucked position, a longer duration of staying tucked, and an intermediate moment of inertia during landing. This strategy comprises the largest amount of movement options associated with an upright landing and thus the highest probability of success when performing a single somersault.

Inertial Motions of a Rigid Body with a Cavity Filled with a Viscous Liquid

We study inertial motions of the coupled system, \({\mathscr{S}}\), constituted by a rigid body containing a cavity entirely filled with a viscous liquid. We show that for arbitrary initial data having only finite kinetic energy, every corresponding weak solution (a la Leray–Hopf) converges, as time goes to infinity, to a uniform rotation, unless two central moments of inertia of \({\mathscr{S}}\) coincide and are strictly greater than the third one. This corroborates a famous “conjecture” of N.Ye. Zhukovskii in several physically relevant cases. Moreover, we show that, in a known range of initial data, this rotation may only occur along the central axis of inertia of \({\mathscr{S}}\) with the larger moment of inertia. We also provide necessary and sufficient conditions for the rigorous nonlinear stability of permanent rotations, which improve and/or generalize results previously given by other authors under different types of approximation. Finally, we present results obtained by a targeted numerical simulation that, on the one hand, complement the analytical findings, whereas, on the other hand, point out new features that the analysis is yet not able to catch, and, as such, lay the foundation for interesting and challenging future investigation.

Observation of high-spin bands with large moments of inertia in Xe 124

Observation of high-spin bands with large moments of inertia in Xe 124

Improvement of DC Motor Velocity Estimation Using a Feedforward Neural Network

This paper proposes a method for improving the DC motor velocity estimations and the estimations obtained from the state observer, when the system operates with large moments of inertia. First, the state observer for estimating velocity and DC motor position, is designed. Then, the variable structure controller is formed using estimated position and velocity values. State observer and designed controller are implemented in default system control logic. Dependences between estimated velocities and moments of inertia are established and presented by experimental results. It is noted that velocity time responses of the designed controller are not as expected when the system operates with large moments of inertia on the motor shaft. The feedforward neural network is empirically designed and implemented in control logic with purpose to solve poor velocity estimations and to improve overall system performances. It is experimentally shown that an artificial network improves estimation quality of the observer and overall control of the system for different input signals.

Superfluidity of helium-4 around a Mg11 cluster

We present results for 4He solvation of a Mg11 cluster obtained with path integral Monte Carlo simulations. Using a pair-wise additive model for the helium-cluster interaction, we calculate energies, 4He densities and the superfluid response of 4He to a rotation of the Mg11 cluster which has symmetric top symmetry. We find a significant superfluid fraction in the first 4He solvation layer around both axes of the cluster well before 4He covers the whole cluster. Based on the superfluid fraction, we estimate that Mg11 in a large 4He nanodroplet would have an effective rotational constant between 60% and 70% of the gas phase rotational constant for rotation about the axis with larger moment of inertia. The dependence of the effective rotational constants on 4He cluster size N is similar to that of previously studied molecules with much larger gas phase rotational constants, with an initial decrease and a turn-around (at N = 13) when part of the 4He density becomes superfluid.

The spin–orbit resonant problem including core–mantle gravitational coupling

In this work, we numerically study an improved model of the spin–orbit resonances with applications in the exoplanetary dynamics. While in the classical model the planetary rotation is characterized by the motion of the whole planet around the axis with the largest moment of inertia, the model which we revisit here considers differential rotation and gravitational coupling between distinct internal layers of the planet. We have prepared a numerical code with the equations of motion of differential rotation of an inner core and an outer mantle. We apply the model to the exoplanet Kepler-10b. Supposing a terrestrial-like interior structure for the planet, numerical exploration of the rotational phase space shows that the effects of the gravitational forces of the external layers of the planet on the rotation of a solid inner core may be not negligible.

Closed-Loop Control of Close Orbits Around Asteroids

The purpose of this work is to develop a simple control law to perform orbit transfer about a small rotating celestial body. The celestial body is assumed to be rotating about a principal axis, with constant rotational velocity along the largest moment of inertia. An analysis of the spacecraft natural trajectories is performed in the body-fixed coordinate system. A three-dimensional closed-loop guidance law is defined and analyzed, enabling the determination of the guidance constants to assure convergence to any desired orbit about the irregular celestial body. The particular case of synchronous orbits is further studied, enabling determination of the required guidance constants to implement stable synchronous orbits. Numerical results are presented for representative cases.

A SURVEY FOR Hα PULSAR BOW SHOCKS

We report on a survey for Hα bow shock emission around nearby γ-detected energetic pulsars. This survey adds three Balmer-dominated neutron star bow shocks to the six previously confirmed examples. In addition to the shock around Fermi pulsar PSR J1741−2054, we now report Hα structures around two additional γ-ray pulsars, PSR J2030+4415 and PSR J1509−5850. These are the first known examples of Hα nebulae with pre-ionization halos. With new measurements, we show that a simple analytic model can account for the angular size and flux of the bow shocks' apices. The latter, in particular, provides a new pulsar probe and indicates large moments of inertia and smaller distances than previously assumed in several cases. In particular, we show that the re-measured PSR J0437−4715 shock flux implies I = (1.7 ± 0.2) × 1045/(fH isin i) g cm2. We also derive a distance d ≈ 0.72 kpc for the γ-ray only pulsar PSR J2030+4415 and revised distances for PSRs J1959+2048 (1.4 kpc) and J2555+6535 (∼1 kpc), smaller than the conventional DM-estimated values. Finally, we report upper limits for 94 additional LAT pulsars. An estimate of the survey sensitivity indicates that for a warm neutral medium filling factor ϕWNM ∼ 0.3 there should be a total of approximately nine Hα bow shocks in our LAT-targeted survey; given that seven such objects are now known, a much larger ϕWNM seems problematic.

Transverse wobbling: A collective mode in odd-Atriaxial nuclei

The wobbling motion of a triaxial rotor coupled to a high-j quasiparticle is treated semiclassi- cally. Longitudinal and transverse coupling regimes can be distinguished depending on, respectively, whether the quasiparticle angular momentum is oriented parallel or perpendicular to the rotor axis with the largest moment of inertia. Simple analytical expressions for the wobbling frequency and the electromagnetic E2 and M1 transition probabilities are derived assuming rigid alignment of the quasiparticle with one of the rotor axes and harmonic oscillations (HFA). Transverse wobbling is characterized by a decrease of the wobbling frequency with increasing angular momentum. Two examples for transverse wobbling, 163Lu and 135Pr, are studied in the framework of the full triax- ial particle-rotor model and the HFA. The signature of transverse wobbling, decreasing wobbling frequency and enhanced E2 inter-band transitions, is found in agreement with experiment.

SMISMO 밸브 구조를 채용한 유압식 굴삭기의 평탄화 작업을 위한 휴리스틱 접근

SMISMO valve configuration is now starting to draw attention of the researchers of the construction equipment industry to increase the fuel efficiency of their equipment like excavators and wheel-loaders. An open-loop control strategy for grading operation of hydraulic excavator systems using SMISMO valve configuration is investigated in this paper. Tabor`s algorithm for 1 d.o.f. SMISMO system under the assumption of quasi-static operation is revealed as not adequate for multi d.o.f. system with large moment of inertia even though the motion of the system is slow. New parameters are proposed in this paper. It modifies Tabor`s open-loop control strategy for the grading operation of hydraulic excavators using SMISMO valve configuration. A simulation-based parameter tuning method is also proposed. It uses GA (Genetic Algorithm) to find the best parameter values. Simulation study for a practical hydraulic excavator shows the validity of the proposed open-loop control strategy.

On the formation of elliptic stones due to periodic water waves

On the beaches of the oceans may be found amongst many stones with irregular shapes also stones that are nearly perfect ellipsoids. In this work, two grinding processes in the surf for stones of ellipsoidal shape are described mathematically on the basis of simple physical models. The first process is the abrasion of material perpendicular to the shortest axis of the stone sliding on the sand of the beach. The model explains the experimental fact that oblong stones with small b/a-ratios as a rule are slim stones with a small c/a-ratio. The second process is connected with a rolling motion around the axis of the largest moment of inertia, which leads to an effective grinding on a surface strip perpendicular to the ab-plane. The corresponding calculation yields a criterion for the form stability of the ellipsoid. The obtained result is virtually identical with the experimentally observed maximum of the error distribution function for the b/a-ratio.

Self-Tuning Fuzzy Adaptive PID Pitch Control of Wind Power Systems

A large variable speed constant frequency (VSCF) wind power system usually adopts the variable pitch control technology to ensure the output power is steady to ensure the safety of the wind power system above the rated wind speed. But the strong nonlinear and large moment of inertia of wind turbine result in the difficulty of variable pitch control, both simple fuzzy control and conventional PID control can not achieve a good control effect. Concerning this issue, variable pitch control algorithm is proposed based on self-tuning fuzzy adaptive PID control strategy. According to the dynamic model of VSCF, a simulation model of wind turbine control system is built in this paper with Matlab/Simulink. When the wind speed is random variable above the rated speed, the simulation results show that the proposed control strategy can keep the output power of the system around the rated power.

Ontogeny of locomotion and head movement of the African spurred tortoise (Geochelone sulcata)

The aim of this research is to describe the changes of head and neck kinematics as they relate to the growth of the African spurred tortoise (Geochelone sulcata). The basics of tortoise locomotion have been described previously. These studies, however, have not investigated locomotor changes in head kinematics due to body size. Infra‐red motion capture was used to obtain detailed kinematics of the head, limbs, and carapace on six live tortoises ranging in body mass from 10.8 to 66.2 kg. The results of the study showed that while there is no correlation between body size and stride duration (p = 0.198) or duty factor (p = 0.109), there is a significant positive correlation between size of tortoise and stride length (p = 0.016). To assess head stability, we compared the average magnitude of the maximum positive and negative differences between the rotational acceleration of the head and body in the sagittal plane. Head instability, regardless of body size, increases as stride average linear velocity increases (all p &lt; 0.004). This rate of head instability increase with stride velocity was less marked in the larger tortoises compared to smaller tortoises (p = 0.017). Thus, larger tortoises maintain a more constant head stability. Our data do not differentiate increases in muscle mass, larger moment of inertia because of increased head mass, or other possible control factors as the source of this increase in head stability.