854 research outputs found
Planetary Stability Zones in Hierarchical Triple Star Systems
A symplectic integrator algorithm suitable for hierarchical triple systems is
formulated and tested. The positions of the stars are followed in hierarchical
Jacobi coordinates, whilst the planets are referenced purely to their primary.
The algorithm is fast, accurate and easily generalised to incorporate
collisions. There are five distinct cases -- circumtriple orbits, circumbinary
orbits and circumstellar orbits around each of the stars in the hierarchical
triple -- which require a different formulation of the symplectic integration
algorithm. As an application, a survey of the stability zones for planets in
hierarchical triples is presented, with the case of a single planet orbiting
the inner binary considered in detail. Fits to the inner and outer edges of the
stability zone are computed. Considering the hierarchical triple as two
decoupled binary systems, the earlier work of Holman & Wiegert on binaries is
shown to be applicable to triples, except in the cases of high eccentricities
and close or massive stars. Application to triple stars with good data in the
multiple star catalogue suggests that more than 50 per cent are unable to
support circumbinary planets, as the stable zone is almost non-existent.Comment: 16 pages, MNRAS, in pres
A New Superintegrable Hamiltonian
We identify a new superintegrable Hamiltonian in 3 degrees of freedom,
obtained as a reduction of pure Keplerian motion in 6 dimensions. The new
Hamiltonian is a generalization of the Keplerian one, and has the familiar 1/r
potential with three barrier terms preventing the particle crossing the
principal planes. In 3 degrees of freedom, there are 5 functionally independent
integrals of motion, and all bound, classical trajectories are closed and
strictly periodic. The generalisation of the Laplace-Runge-Lenz vector is
identified and shown to provide functionally independent isolating integrals.
They are quartic in the momenta and do not arise from separability of the
Hamilton-Jacobi equation. A formulation of the system in action-angle variables
is presented.Comment: 11 pages, 4 figures, submitted to The Journal of Mathematical Physic
Nickel hydrogen bipolar battery electrode design
The preferred approach of the NASA development effort in nickel hydrogen battery design utilizes a bipolar plate stacking arrangement to obtain the required voltage-capacity configuration. In a bipolar stack, component designs must take into account not only the typical design considerations such as voltage, capacity and gas management, but also conductivity to the bipolar (i.e., intercell) plate. The nickel and hydrogen electrode development specifically relevant to bipolar cell operation is discussed. Nickel oxide electrodes, having variable type grids and in thicknesses up to .085 inch are being fabricated and characterized to provide a data base. A selection will be made based upon a system level tradeoff. Negative (hydrpogen) electrodes are being screened to select a high performance electrode which can function as a bipolar electrode. Present nickel hydrogen negative electrodes are not capable of conducting current through their cross-section. An electrode was tested which exhibits low charge and discharge polarization voltages and at the same time is conductive. Test data is presented
HD 98800: A most unusual debris disc
The dynamics of planetesimals in the circumbinary debris disc of the
quadruple star system HD 98800 are investigated. Evolving a spherical shell of
test particles from a million years ago to the present day indicates that both
coplanar and retrograde warped discs could exist, as well as a high inclination
halo of material. Significant gaps are seen in the discs, as well as unexpected
regions of stability due to the retrograde nature of the stellar orbits.
Despite a viewing angle almost perpendicular to the direction of the warp of
the planetesimal disc it is still intersected by the line of sight for
eccentricities of the outer orbit of 0.5 or less.Comment: MNRAS, in pres
High Inclination Planets in Multistellar Systems
The Kozai mechanism often destabilises high inclination orbits. It couples
changes in the eccentricity and inclination, and drives high inclination,
circular orbits to low inclination, eccentric orbits. In a recent study of the
dynamics of planetesimals in the quadruple star system HD98800 (Verrier & Evans
2008), there were significant numbers of stable particles in circumbinary polar
orbits about the inner binary pair which are apparently able to evade the Kozai
instability. Here, we isolate this feature and investigate the dynamics through
numerical and analytical models. The results show that the Kozai mechanism of
the outer star is disrupted by a nodal libration induced by the inner binary
pair on a shorter timescale. By empirically modelling the period of the
libration, a criteria for determining the high inclination stability limits in
general triple systems is derived. The nodal libration feature is interesting
and, although effecting inclination and node only, shows many parallels to the
Kozai mechanism. This raises the possibility that high inclination planets and
asteroids may be able to survive in multistellar systems.Comment: MNRAS, submitte
Crack Detectability in Vertical Axis Cooling Pumps During Operation
The problem which is faced in this paper is the analysis of the effects of a transverse propagating crack on the vibrational behaviour of a vertical axis cooling pump. The crack is assumed to develop in a section between the impeller and a seal, which prevents the hot water to flow upwards along the rotor shaft. The pressurized seal is fed with an injection of cold water. Crack initiation may be due to a thermal striping phenomenon. Afterwards, crack growth could be driven by a combination of thermal and mechanical loads, causing alternate cyclic stress in the shaft. Cracking instances of this type have been reported worldwide in several machines of similar design. In this paper, the fact is emphasized that the crack behavior is likely to be influenced by the thermal field and by the water pressure in the cracked area. A dynamical lineshaft model, integrated by an original representation of the crack, has been developed to investigate the possible vibratory symptoms related to a crack propagation. The vibrations are generally measured in correspondence of a rigid coupling which connects the motor shaft to the pump shaft, in position which is rather far away from crack. 1x rev., 2x rev and 3x rev. vibration components, which are generally displayed by the machine condition monitoring system and are the most significative symptoms of the presence of a transverse crack in a rotating shaft, are calculated
Superintegrability of the Caged Anisotropic Oscillator
We study "the Caged Anisotropic Harmonic Oscillator", which is a new example
of a superintegrable, or accidentally degenerate Hamiltonian. The potential is
that of the harmonic oscillator with rational frequency ratio (l:m:n), but
additionally with barrier terms describing repulsive forces from the principal
planes. This confines the classical motion to a sector bounded by the principal
planes, or cage. In 3 degrees, there are five isolating integrals of motion,
ensuring that all bound trajectories are closed and strictly periodic. Three of
the integrals are quadratic in the momenta, the remaining two are polynomials
of order 2(l+m-1) and 2(l+n-1). In the quantum problem, the eigenstates are
multiply degenerate, exhibiting multiple copies of the fundamental pattern of
the symmetry group SU(3).Comment: Submitted to the Journal of Mathematical Physic
Rurality as a predictor of perinatal mental health and well‐being in an Australian cohort
Objective
Perinatal emotional well-being is more than the presence or absence of depressive and anxiety disorders; it encompasses a wide range of factors that contribute to emotional well-being. This study compares perinatal well-being between women living in metropolitan and rural regions.
Design
Prospective, longitudinal cohort.
Participants/setting
Eight hundred and six women from Victoria and Western Australia recruited before 20 weeks of pregnancy and followed up to 12 months postpartum.
Main outcome measures
Rurality was assessed using the Modified Monash Model (MM Model) with 578 in metropolitan cities MM1, 185 in regional and large rural towns MM2-MM3 and 43 in rural to remote MM4-MM7. The Structured Clinical Interview for DSM-IV (SCID-IV) was administered at recruitment to assess depression, and symptoms of depression and anxiety were measured using the Edinburgh Post-natal Depression Scale and the State and Trait Anxiety Scale, respectively. Other measures included stressful events, diet, exercise, partner support, parenting and sleep.
Results
The prevalence of depressive disorders did not differ across rurality. There was also no difference in breastfeeding cessation, exercise, sleep or partner support. Women living in rural communities and who also had depression reported significantly higher parenting stress than metropolitan women and lower access to parenting activities.
Conclusions
Our study suggests while many of the challenges of the perinatal period were shared between women in all areas, there were important differences in parenting stress and access to activities. Furthermore, these findings suggest that guidelines and interventions designed for perinatal mental health should consider rurality
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