1,721,491 research outputs found
Cartesian trajectory planning of space robots using a multi-objective optimization
No full textCartesian trajectory planning of a free-floating space robot is impacted by dynamic singularities due to the inverse kinematics equations. Although various methods have been proposed to avoid the singularities, very few of them are suitable for the trajectory planning of a high degree-of-freedom (DOF) space robot in the Cartesian space. In this paper, a method of combining Damped Least Squares (DLS) and feedback compensation is developed to avoid such singularities. The trajectories of the end-effector are parametrized with Bézier curves, which are simple and make it easy to limit the joint velocities. Moreover, because of certain missions, such as communication and observation, base attitude disturbance and moving time are considered to establish a cost function and the trajectory planning is transformed into a multi-objective optimization. Chaotic particle swarm optimization (CPSO) is employed to solve the optimization, which can improve the premature phenomenon of particle swarm optimization (PSO). Simulation results are presented for the trajectory planning of a 6 DOF space robot and demonstrate the effectiveness of the proposed method
Minimum Residual Vibrations for Flexible Satellites with Frequency Uncertainty
Full text linkThe resonant frequencies will be excited if satellites perform a rapidly maneuver, which will increase the vibration settling time. In order to reduce the maneuver time and the residual vibration after maneuver, a set of shaped angular acceleration profiles are presented, and their analytical solutions are derived by minimizing the time integral of the squared magnitude of the difference between angular acceleration and its mean value subject to that the magnitude of the residual vibrations at several frequencies surrounding the natural frequency are zero. Then, suitable frequency points, where the residual vibrations are constrained to be zero, are chosen to minimize the acceleration time subject to both the residual vibration magnitude limit and the angular acceleration magnitude limit. Finally, three sets of simulations are presented to demonstrate that the shaped angular acceleration profiles can reduce the residual vibration under the frequency uncertainty
Attenuated expression of gelsolin in association with induction of aquaporin-1 and nitric oxide synthase in dysfunctional hearts of aging mice exposed to endotoxin
No full textSepsis triggered by endotoxinemia may impair cardiac function. A decline in tolerance to septic shock occurs with aging. This study addressed the hypothesis that aging negatively impairs expression of gelsolin, and axerts the regulatory effects on the water channel protein aquaporin-1 (AQP-1) and endotoxin-inducible nitric oxide synthase (iNOS). We explored whether the age-related gene changes are associated with the cardiac dysfunction induced by endotoxic stress exposure. Male mice at young (∼ 3-month) and old (∼ 12-month) ages received intraperitoneal injections of saline or lipopolysaccharide (LPS, 30mg/Kg). Cardiac performance and morphology were analyzed by echocardiography at baseline and 2 and 24 h after injection. At the end of treatment, the animals were sacrificed, and cardiac tissues were collected for assessing expression of gelsolin, AQP-1, iNOS, and transcription-3 (STAT3). LPS administration led to a decreased contractility while increasing cardiac dimensions in both young and old mice. LPS also markedly induced expression of gelsolin in both animal groups. However, compared to young mice, old mice showed compromised induction of gelsolin and cardiac performance in response to endotoxin. Meanwhile, the LPS-exposed old animals exhibited higher levels of AQP-1, iNOS, and phosphorylated STAT3. Gelsolin-null mice had increased expression of glycosylated AQP-1 and STAT3 phosphorylation as well as cardiac dysfunction. Thus, endotoxin administration induces expression of gelsolin, AQP-1 and pro-inflammatory genes, such as iNOS. Our data suggest that changed expression of gelsolin, AQP-1 and iNOS may contribute to dysfunction of hearts in aged subjects with septic endotoxinemia. Copyright © by BIOLIFE, s.a.s
Observer-based fixed-time tracking control for space robots in task space
No full textThe problem of task-space tracking control of a free-floating space robot is addressed in this paper. Based on a fixed-time extended state observer (FXESO), a fixed-time position and attitude control (FXPAC) method is developed. The attitude of the end-effector is represented in modified Rodrigues parameters (MRPs). The FXESO provides the estimation of the joint velocity and the lumped disturbance for the control system. Based on the backstepping technique and a power integrator, the FXPAC method is designed. This control scheme can guarantee tracking errors converging to a neighborhood of the origin within a fixed time in the presence of the external disturbance. Moreover, since the inverse of the generalized Jacobian matrix is involved in the controller, it is necessary to consider dynamic singularities. To handle these singularities, a method of combining the singularity separation and damped reciprocal (SSDR) is applied to the space robot. Numerical simulations are presented to demonstrate the effectiveness of the proposed method
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
Pestalotiopsis licualacola K. Geng, Y.
No full textPestalotiopsis licualacola K. Geng, Y. Song, K.D. Hyde & Yong Wang bis, sp. nov. (Fig. 2) MycoBank MB 803183 Type: — CHINA. Hainan Province: Xinglong County, Tropical Botanical Garden, living leaves of Licuala grandis, 8 March 2012, HGUP 4057, K. Geng, HGUPd4057, holotype! Differs from related Pestalotiopsis and Pestalosphaeria species mainly by its noticeably narrower, fusiform conidia with mostly a single apical appendage. Colonies on PDA attaining 7 cm diam. after 7 days at 25° C, with edge undulate, whitish, aerial mycelium on surface, fruiting bodies black, concentric; reverse of culture yellow to pale brown. Conidiophores most often indistinct. Conidiogenous cells discrete, hyaline, simple, filiform, 4–10 µm long. Conidia 16–20 × 3–5 µm (x = 17.4 × 3.9 µm), fusiform, straight to slightly curved, 4-septate, smooth, greyish brown; basal cell conical, hyaline, thin-walled, 2–4 µm long (x = 2.4 µm); with three median cells, dark brown, concolorous, septa and periclinal walls darker than the rest of the cell, together 9.5–12 µm long (x = 11 µm); second cell from base 2.7–4.2 µm (x = 3.6 µm); third cell 2.4–4 µm (x = 3.3 µm); fourth cell 2.5–3.8 µm (x = 3.2 µm); apical cell hyaline, conic to subcylindrical, 1.8–3.6 µm (x = 2.4 µm); with 1–3 tubular apical appendages (mostly 1) without knobs, arising from the apex of the apical cell, 4–9.5 µm long (x = 6.6 µm); basal appendage filiform, short. Etymology: —In reference to the host, Licuala grandis, from which this fungus was first isolated.Published as part of Geng, Kun, Zhang, Bin, Song, Yu, Hyde, Kevin D., Kang, Ji-Chuan & Wang, Yong, 2013, A new species of Pestalotiopsis from leaf spots of Licuala grandis from Hainan, China, pp. 49-54 in Phytotaxa 88 (3) on pages 51-52, DOI: 10.11646/phytotaxa.88.3.2, http://zenodo.org/record/507190
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
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
- …
