1,722,857 research outputs found
Analysis of ballistic capture in Sun–planet models
No full textAnalysis of ballistic capture orbits in Sun–planet systems is conducted in this paper. This mechanism utilizes purely gravitational forces, and may occur in non-Keplerian regimes. Ballistic capture orbits are generated by proper manipulation of sets of initial conditions that satisfy a simple definition of stability. Six Sun–planet systems are considered, including the inner planets, Jupiter, and Saturn. The role of planets orbital eccentricity, their true anomaly, and mass ratios is investigated. Moreover, the influence of the post-capture orbit in terms of inclination and orientation is also assessed. Analyses are performed from qualitative and quantitative perspective. The quality of capture orbits is measured by means of the stability index, whereas the capture ratio gives information on their statistical occurrence. Some underlying principles on the selection of the dynamical model, the initial true anomaly, and inclination are obtained. These provide a reference for practical cases
Capability of satellite-aided ballistic capture
Full text linkIn this paper we study a special instance of ballistic capture dynamics: the case in which the capture orbit about a planet experiences a close passage to one or more of its natural satellites. The capability of the satellites in improving ballistic capture is assessed. The dynamical framework considers at least the gravitational attractions of the Sun, the planet, and its satellites, all acting on a massless particle. The effect of the satellites is introduced explicitly by modifying a previously developed method, which relies on three-dimensional stable sets and n-body dynamics with precise ephemeris. Once a stability criterium is defined, initial conditions defined over a computational grid are integrated forward and backward. This allows us to classify orbits into different sets. Ballistic capture orbits with prescribed features are generated by manipulating these sets. Two indices, namely the hyperbolic velocity and the stability index, are used to assess the performance of pre- and post-capture portions, respectively. A Pareto frontier is used to extract orbits of practical interest. Case studies are performed in the context of Earth and Jupiter environments. Comparing to the situation with no moons, the satellite-aided ballistic capture can evidently increase the pre-capture energy and post-capture stability, so making it possible to have permanent capture of a particle at zero-cost. This is a desirable feature in mission design
Mars orbit insertion via ballistic capture and aerobraking
Full text linkA novel Mars orbit insertion strategy that combines ballistic capture and aerobraking is presented. Mars ballistic capture orbits that neglect the aerodynamics are first generated, and are distilled from properly computed stable and unstable sets by using a pre-established method. A small periapsis maneuver is implemented at the first close encounter to better submit a post-capture orbit to the aerobraking process. An adhoc patching point marks the transition from ballistic capture to aerobraking, from which an exponential model simulating the Martian atmosphere and a box-wing satellite configuration are considered. A series of apoapsis trim maneuvers are then computed by targeting a prescribed pericenter dynamic pressure. The aerobraking duration is then estimated using a simplified two-body model. Yaw angle tuning cancels the inclination deflections owing to out-of-plane perturbation from the Sun. A philosophy combining in-plane and out-of-plane dynamics is proposed to simultaneously achieve the required semi-major axis and inclination. Numerical simulations indicate that the developed method is more efficient in terms of the fuel consumption, insertion safety, and flexibility when compared with other state-of-the-art insertion strategies
The Neutrophil/Lymphocyte Ratio Could Predict Noninvasive Mechanical Ventilation Failure in Patients with Acute Exacerbation of Chronic Obstructive Pulmonary Disease: A Retrospective Observational Study [Corrigendum]
No full textSun W, Luo Z, Jin J, Cao Z, Ma Y. Int J Chron Obstruct Pulmon Dis. 2021;16:2267–2277.
The authors have advised the author list on page 2267 is incorrect. The text “Yingmin Ma2” should read “Yingmin Ma1,2”.
The authors apologize for this error
Multilayer ferroelectret-based energy harvesting insole
Full text linkThis paper reports a flexible energy harvesting insole made of multilayer ferroelectrets, and demonstrates that this insole can power a wireless signal transmission. We have previously studied the energy harvesting characteristics of single and 10-layer ferroelectrets under compressive forces with quantified amplitudes and frequencies. In this work, we fabricate a flexible insole using multilayer ferroelectrets, and increase the number of layers from 10 up to 80, then use this insole to harvest energy from footsteps. We use this insole to power a commercial ZigBee wireless transmitter, and successfully demonstrate that an 8-bit data transmission can be solely powered by the energy harvested from this insole for every 3 to 4 footsteps. It confirms the anticipation from our previous work that the multilayer ferroelectrets are capable of powering the start-up and transmission of a low-power chipset, and shows a potential of using this energy harvesting insole in wearable applications
An electromechanical model of ferroelectret for energy harvesting
Full text linkFerroelectret is a cellular polymer foam that is able to convert compressive and bending forces into electrical signals, which 10 can be used for both sensing and energy harvesting. In the past several research groups have proposed theoretical models that 11 relate the output voltage of the ferroelectret to its mechanical deformation. This is particularly useful for sensing applications 12 where the signal-to-noise ratio is important. However, for energy harvesting applications, a theoretical model needs to include 13 both the voltage across a resistive load and the duration of the electrical signal as energy is an integral of power over time. In 14 this work, we propose a theoretical model that explains the behaviour of a ferroelectret when used as an energy harvester. This 15 model can be used to predict the energy output of a ferroelectret by knowing its parameters, and therefore optimize the harvester 16 design for specific energy harvesting application
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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