Small Orbit Research Articles

On the osteology of Tapejara wellnhoferi KELLNER 1989 and the first occurrence of a multiple specimen assemblage from the Santana Formation, Araripe Basin, NE-Brazil

The postcranial elements of two similar sized and juvenile individuals, along with a partial skull, are attributed to the Early Cretaceous pterosaur Tapejara wellnhoferi. The remains, recovered from a single concretion of the Romualdo Member, Santana Formation, NE-Brazil, represent the first account of multiple specimens having settled together and allow for a complete review of postcranial osteology in tapejarid pterosaurs. A comparison of long bone morphometrics indicates that all specimens attributed to the Tapejaridae for which these elements are known (i.e. Huaxiapterus, Sinopterus, Tapejara) display similar bivariate ratios, suggesting that Chinese and Brazilian taxa must have exhibited similar growth patterns. An unusual pneumatic configuration, whereby the humerus is pierced by both dorsally and ventrally located foramina, is observed within T. wellnhoferi, while the pneumatic system is inferred to have invaded the hindlimbs via the femur in all members of the Azhdarchoidea. The partial preservation of the endocranial cavity allows for a reconstruction of the tapejarid brain, where despite a small orbit with respect to skull size, the presence of large flocculi and ocular lobes indicate that Tapejara possessed both excellent balancing and visual systems as a consequence of its aerial lifestyle.

Planar oscillations of a vibrating dumbbell-like body in a central field of forces

The problem of planar motions of a dumbbell-like body of variable length in a central field of Newtonian attraction is considered both in the exact formulation and in satellite approximation. In the satellite approximation the true anomaly of the center of mass is used as an independent variable, which has allowed us to represent the equation of planar oscillations of the dumbbell in the form similar to the Beletskii equation. Some exact solutions to the inverse problem are given both in the complete formulation and in satellite approximation. Under an assumption of small orbit eccentricity and amplitude of the dumbbell vibrations the conditions of existence are found for families of almost periodic motions and splitting separatrices. The phenomena of alternation of regular and chaotic motions are established numerically, as well as chaos suppression with increasing frequency of vibrations. Using the method of averaging the stabilization of tangent equilibria is proved to be impossible.

Snare Technique for Enucleation of Eyes With Advanced Retinoblastoma

Retrospective analysis of surgical outcomes for enucleation in pediatric retinoblastoma stage 5B using the snare wire loop (n = 55) and standard curved enucleation scissors (n = 22) revealed that a statistically significant longer mean optic nerve length was obtained with the snare (13.35 mm) compared with scissors (11.05 mm; P = .005). Four scissor cases had prolonged bleeding and required thrombin (18.2%), but no snare cases had difficulty with hemostasis (P = .005). More crush artifact was seen with the snare than with scissors (P<.001), but this did not affect the ability to determine tumor involvement at the surgical margin. The enucleation snare should be considered a valuable surgical instrument in the small pediatric orbit since obtaining the longest optic nerve segment has prognostic implications in retinoblastoma.

INJECTION AND EXTRACTION SYSTEMS FOR THE MUON FFAG RING IN THE NEUTRINO FACTORY

Non-scaling FFAG (NS-FFAG) rings have been proposed as a solution for muon acceleration in the Neutrino Factory. In order to achieve small orbit excursion and small time of flight variation, lattices with a very compact cell structure and consequent short straight sections are required. The resulting geometry, combined with the large transverse emittance of the muon bunch, places very challenging constraints on the injection/extraction systems. The injection/extraction system requires a set of distributed kickers, a superconducting septum and increased aperture in some of the main ring magnets. A scheme for both injection and extraction for a FFAG with triplet geometry is presented. In addition, a solution for the required kicker magnets is proposed.

Spin-orbit interaction in curved graphene ribbons

We study the electronic properties of electrons in flat and curved zigzag graphene ribbons using a tight-binding model within the Slater Koster approximation. We find that curvature dramatically enhances the action of spin orbit effects in graphene ribbons and has a strong effect on the spin orientation of the edge states: whereas spins are normal to the surface in the case of flat ribbons, this is no longer the case in the case of curved ribbons. We find that for the edge states, the spin density lies always in the plane perpendicular to the ribbon axis, and deviate strongly from the normal to the ribbon, even for very small curvature and the small spin orbit coupling of carbon. We find that curvature results also in an effective second neighbor hopping that modifies the electronic properties of zigzag graphene ribbons. We discuss the implications of our finding in the spin Hall phase of curved graphene Ribbons.

Transiting exoplanets from the CoRoT space mission

In this paper, the CoRoT Exoplanet Science Team announces its 14th discovery. Herein, we discuss the observations and analyses that allowed us to derive the parameters of this system: a hot Jupiter with a mass of $7.6 \pm 0.6$ Jupiter masses orbiting a solar-type star (F9V) with a period of only 1.5 d, less than 5 stellar radii from its parent star. It is unusual for such a massive planet to have such a small orbit: only one other known exoplanet with a higher mass orbits with a shorter period.

Control Design Applied to a Micro Electro Mechanical System: MEMS Comb Drive

This paper presents the linear optimal control technique for reducing the chaotic movement of the micro-electro-mechanical Comb Drive system to a small periodic orbit. We analyze the non-linear dynamics in a micro-electro-mechanical Comb Drive and demonstrated that this model has a chaotic behavior. Chaos control problems consist of attempts to stabilize a chaotic system to an equilibrium point, a periodic orbit, or more general, about a given reference trajectory. This technique is applied in analyzes the nonlinear dynamics in an MEMS Comb drive. The simulation results show the identification by linear optimal control is very effective.

Analytical Theory of the Geodesic Acoustic Mode in the Small and Large Orbit Drift Width Limits and its Application in a Study of Plasma Shaping Effect

Analytical theories of the geodesic acoustic mode (GAM) are reviewed in the small-and large-orbit drift width limits, respectively. Different physics pictures in these two limits are displayed. As an example, these two analytical methods are employed to investigate the plasma shaping effect on the frequency and collisionless damping rate of the GAM.

Spontaneous persistent currents in a quantum spin Hall insulator

We present a new mechanism for dissipationless persistent charge current. Two dimensional topological insulators hold dissipationless spin currents in their edges so that, for a given spin orientation, a net charge current flows which is exactly compensated by the counter-flow of the opposite spin. Here we show that ferromagnetic order in the edge upgrades the spin currents into persistent charge currents, without applied fields. For that matter, we study an interacting graphene zigzag ribbon with spin-orbit coupling. We find three electronic phases with magnetic edges that carry currents reaching 0.4nA, comparable to persistent currents in metallic rings, for the small spin orbit coupling in graphene. One of the phases is a valley half-metal.

Plasma shaping effects on the geodesic acoustic mode in the large orbit drift width limit

Plasma shaping effects on the geodesic acoustic mode (GAM) are revisited analytically in the large orbit drift width limit. Comparing with results from the small orbit drift width expansion method [Z. Gao et al., Phys. Plasmas 15, 074502 (2008)] the behavior of the real frequency is almost the same but the effect on the damping rate is different due to the change of dominant resonant mechanism, from low order harmonic transit resonance to high order harmonic resonance, or equivalently, to the magnetic drift resonance. As a result, although the GAM frequency decreases with an increasing elongation κ by dependence of [2/(κ2+1)]1/2, the damping is weakened mildly in the large orbit drift width limit, which is quite different from the result in the low small orbit drift limit, where the damping is enhanced exponentially with the decrease in frequency. Also, in the large orbit drift width limit, the dependence of the GAM damping rate on inverse aspect ratio ε is analytically obtained for the first time. As ε increases, the frequency behaves as a weakly decreasing parabola function of ε, and the damping rate increases parabolically, but more rapidly than the frequency decreases. The GAM with longer radial wavelength is more easily damped by the finite aspect ratio effect. It is also found that the Shafranov shift gradient has the similar effect as the inverse aspect ratio.

Small [formula omitted] extremal black holes in special geometry

We provide an intrinsic classification of the large and small orbits for N = 2 , 4D extremal black holes on symmetric spaces which does not depend on the duality frame used for the charges or on the special coordinates. A coordinate independent formula for the fake superpotential W, which (at infinity) represents the black hole ADM mass, is given explicitly in terms of invariants of the N = 2 special geometry.

Neolamprologus longicaudatus, a New Cichlid Fish from the Zairean Coast of Lake Tanganyika

A new cichlid, Neolamprologus longicaudatus sp. nov. is described, based on three specimens from the north Zairean coast of Lake Tanganyika. Although similar to N. furcifer, N. christyi and N. buescheri in having an elongate body, strongly emarginate caudal fin, and vertical fins partly covered with scales, this species is distinguishable from them by its small orbit, light grayish-brown coloration of body, dorsal fin lacking a submarginal dark band, 37 longitudinal body scales, 8 gill rakers on lower limb of the 1st gill arch, and a long pointed snout.

Analysis of possible early orbit contingencies and recovery strategies for Herschel/Planck

Herschel and Planck, the ESA astronomy cornerstone missions, were successfully launched on 2009/5/14 from Kourou on Ariane 5. Herschel, the largest ever infrared telescope, and Planck, to study the cosmic microwave background radiation, were injected together into a nearly parabolic orbit. From there, they were manoeuvred to their operational orbits around the libration point L 2 of the Sun–Earth system: a halo type orbit for Herschel and a small amplitude Lissajous orbit for Planck. Essential to nominal orbit insertion was a correction manoeuvre to be performed within 2 days from launch, to correct for the launcher dispersion, but also other systematic deviations from the required transfer conditions. The present work focuses on the preparation of recovery strategies in case an under-performance of the launcher or a failure to execute the first correction manoeuvre on time had occurred. In a first stage, the limits for extending the nominal orbit design even after an under-performance of the launcher or a delay of the first orbit correction were studied. Furthermore, alternative strategies implying substantial changes to the nominal design were also analysed as a means to recover the science return in case of severe under-performance or failure of the first correction manoeuvre.

Identification of Force Coefficients in a Squeeze Film Damper With a Mechanical Seal: Large Contact Force

Squeeze film dampers (SFDs) aid to reduce excessive vibration levels due to rotor imbalance and to raise stability thresholds in rotor-bearing systems. SFDs commonly include end seals to increase their damping capability with a lesser lubricant flow. Seals also aid to reduce the occurrence of air ingestion/entrapment that severely reduces the damper forced performance. However, most conventional end seals do not completely eliminate lubricant side leakage, which limits their effectiveness to prevent air ingestion. A novel end seal arrangement incorporates a spring loaded, contacting mechanical seal that effectively prevents lubricant side leakage and air ingestion. The mechanically sealed damper is intended for use in power engines for unmanned aircraft vehicles. The test damper journal is 2.54 cm in length and 12.7 cm in diameter, with a radial clearance of 0.127 mm. Prior literature reports dynamic load tests on the seal-SFD and measurements of orbital motions to characterize the mechanical parameters of both the mechanical seal and squeeze film damper section. The test data to date include damper operation for a single contact load (90 N) closing the mechanical seal. Presently, measurements of damper dynamic load performance are conducted with a larger contact force (260 N). A nonlinear parameter identification method in the frequency domain determines simultaneously the squeeze film damping and inertia coefficients and the seal dry-friction force. The test results show that the system equivalent viscous damping coefficients are twice as large as those obtained earlier with the smaller contact force. On the other hand, as expected, the squeeze film damper coefficients are nearly identical for both test configurations. Predicted squeeze film damping coefficients, from an improved model that includes the flow in the damper feed and discharge grooves, correlate well with the test data for small and moderate orbit radii. The experimental fluid added mass coefficients are in par with the actual mass of the bearing housing and accurately predicted.

Extraordinary cranial specialization in a new genus of extinct duck (Aves: Anseriformes) from Kauai, Hawaiian Islands

Talpanas lippa is described as a new genus and species of waterfowl from Kauai, Hawaiian Islands, that is unlike any other known member of the order. It is characterized by a short, stout tarsometatarsus and a braincase that is shallow and wide relative to its length with very small orbits. In comparison with extant species, the optic foramen of Talpanas is remarkably small whereas the maxillo-mandibular foramen, which is the exit point of the trigeminal nerve, is grossly enlarged. Relative to skull length and foramen magnum area, the maxillo-mandibular foramen is one order of magnitude larger in cross-sectional area than that of extant Anseriformes. We conclude that Talpanas had reduced visual abilities, as reflected externally by its small orbits and optic foramen, and a grossly hypertrophied trigeminal foramen. Taken together, this suggests that Talpanas may have been more heavily reliant upon somatosensory (tactile) cues for foraging than any living species of bird. Pectoral elements are unknown, but the evident lack of keen eyesight suggests that the species was flightless, as were many other insular waterfowl.

Formation flying solar-sail gravity tractors in displaced orbit for towing near-Earth asteroids

Several methods of asteroid deflection have been proposed in literature and the gravitational tractor is a new method using gravitational coupling for near-Earth object orbit modification. One weak point of gravitational tractor is that the deflection capability is limited by the mass and propellant of the spacecraft. To enhance the deflection capability, formation flying solar sail gravitational tractor is proposed and its deflection capability is compared with that of a single solar sail gravitational tractor. The results show that the orbital deflection can be greatly increased by increasing the number of the sails. The formation flying solar sail gravitational tractor requires several sails to evolve on a small displaced orbit above the asteroid. Therefore, a proper control should be applied to guarantee that the gravitational tractor is stable and free of collisions. Two control strategies are investigated in this paper: a loose formation flying realized by a simple controller with only thrust modulation and a tight formation realized by the sliding-mode controller and equilibrium shaping method. The merits of the loose and tight formations are the simplicity and robustness of their controllers, respectively.

Homoclinic and heteroclinic orbits for the 0² or 0²𝑖𝜔 singularity in the presence of two reversibility symmetries

This paper is devoted to the study of the dynamics of reversible vector fields close to an equilibrium when a 0 2 0^2 or a 0 2 i ω 0^2i\omega resonance occurs in the presence of two symmetries of reversibility. In the presence of a unique reversibility symmetry the existence of a homoclinic connection to 0 is known for the 0 2 0^2 resonance whereas for the 0 2 i ω 0^2i\omega resonance there is generically no homoclinic connection to 0 but there is always a homoclinic connection to an exponentially small periodic orbit. In the presence of a second symmetry of reversibility, the situation is more degenerate. Indeed, because of the second symmetry the quadratic part of the normal forms vanishes, and so the dynamics of the normal forms is governed by the cubic part. For the 0 2 0^2 resonance we prove the existence of homoclinic connections to 0 and of heteroclinic orbits. For the 0 2 i ω 0^2i\omega resonance we prove that in most of the cases the second symmetry induces the existence of homoclinic connections to 0 and of heteroclinic orbits whereas with a unique symmetry there is generically no homoclinic connection to 0. Such a reversible vector field with two reversibility symmetries occurs for instance after center manifold reduction when studying 2-dimensional waves in NLS type systems with one-dimensional potential or when studying localized waves in nonlinear chains of coupled oscillators. It also occurs when studying localized buckling in rods with noncircular cross section.

Dynamics of dust grains with a vaporable icy mantle

We show the effects of solar gravity, electromagnetic radiation and solar wind on the motion of micrometre-sized interplanetary dust grains for initially small eccentric orbits and for heliocentric distances less than 10 au. The traditional approach is that the solar wind effect and the Poynting-Robertson (P-R) effect are simultaneously taken into account through the numerical factor 1 + ηA/C pr , which is multiplied by the P-R effect. In reality, solar wind corpusculae erode the surface of the interplanetary grain. As a consequence, the value of the solar electromagnetic radiation pressure term increases, as it is inversely proportional to the size of the grain. In addition, the radiation pressure efficiency also varies because of the changes to the optical properties of the grain. Both these physical processes are taken into account, and the secular evolution of orbital elements for a Gaussian sphere with a volatile icy coating exhibits a secular increase of the semimajor axis and eccentricity as well as the longitude of perihelion. These secular changes of orbital elements do not exist in the conventional approach for the P-R and solar wind effects. The conventional approach yields 10 4 yr for the lifetime of inspiralling toward the Sun, if the evolution starts from the initial values of the semimajor axis a in = 4 au and eccentricity e in = 0.2. The Gaussian sphere with a volatile icy coating exhibits a semimajor axis greater than 10 au for t > 3 x 10 2 yr for the same initial orbital elements.

IGR J18483–0311: a new intermediate supergiant fast X-ray transient

IGR J18483-0311 is a high-mass X-ray binary recently discovered by INTEGRAL. Its periodic fast X-ray transient activity and its position in the Corbet diagram - although ambiguous - led to the conclusion that the source was a likely Be/X-ray binary (BeXB), even if a supergiant fast X-ray transient (SFXT) nature could not be excluded. We aimed at identifying the companion star of IGR J18483-0311 to discriminate between the BeXB and the SFXT nature of the source. Optical and near-infrared photometry, as well as near-infrared spectroscopy of the companion star were performed to identify its spectral type. We also assembled and fitted its broad-band spectral energy distribution to derive its physical parameters. We show that the companion star of IGR J18483-0311 is an early-B supergiant, likely a B0.5Ia, and that its distance is about 3-4 kpc. The early-B supergiant nature of its companion star, as well as its fast X-ray transient activity point towards an SFXT nature of IGR J18483-0311. Nevertheless, the long duration and the periodicity of its outbursts, as well as its high level of quiescence, are consistent with IGR J18483-0311 being an intermediate SFXT, in between classical supergiant X-ray binaries (SGXBs) characterised by small and circular orbits, and classical SFXTs with large and eccentric orbits.

Preliminary study of residual orbit oscillation in BEPCII

BEPCII has two rings each with an injection system. The injection system of each ring consists of two kicker magnets and a septum magnet. The injection layout of two rings is the same. Both two kickers would kick the beam in horizontal plane. The betatron phase advance in the horizontal plane between two kickers is designed exactly 180° in order to reduce the perturbation to the circulating beams during injection. In fact, the residual orbit oscillation will originate because of the existence of a variety of errors. The Librea Electron BPM processor is used to acquire the beam position data in turn-by-turn mode and to analyze the residual orbit oscillation. According to the measurement results, minimization of the residual orbit oscillation can be done by adjusting the peak field strength and trigger timing delay of two kickers. With very small residual orbit oscillation the two beams can keep collision condition during the injection.