1,721,025 research outputs found
Waypoint-Based ZEM/ZEV Feedback Guidance: Applications To Low-Thrust Interplanetary Transfer and Orbit Raising
Full text linkLow-thrust guided trajectories for space missions are extremely important for fuel-efficient autonomous space travel. The goal of this paper is to design an optimized, waypoint-based, closed-loop solution for low-thrust, long duration orbit transfers. The Zero-Effort-Miss/Zero-Effort-Velocity (ZEM/ZEV) feedback guidance algorithm which has been demonstrated to exhibit great potential for autonomous onboard implementation is applied in a waypoint fashion. Generally, ZEM/ZEV is derived by solving an optimal guidance problem under well-defined assumptions, where the gravitational acceleration is either constant or time-dependent and the thrust/acceleration command is unlimited. If gravity is not constant, the target state is generally achieved in a suboptimal fashion. A way to improve the performances is to divide total trajectory into many segments, and determining with a rigorous optimization method near-optimal waypoints to connect the different segments. Here we consider two possible scenarios, i.e. 1) a low-thrust transfer Earth-Mars and 2) a low-thrust orbit raising from LEO to GEO. For both cases, open-loop energy and fuel-optimal trajectories generated by L. Ferrella and F. Topputo are considered as reference trajectories where a set of arbitrary points are targeted by the ZEM/ZEV guidance in a sequential fashion. An initial parametric study is conducted to evaluate guidance performances as function of the number of the selected waypoints. Subsequently, a global optimization problem, parametrized with the position of the points on the trajectory is solved using a genetic algorithm to determine the minimum set of waypoints necessary for close-to-fuel-optimal waypoint space guidance. The optimization results are compared with the parametric analysis for both scenarios to show that the proposed approach is feasible in achieving quasi-optimal performances even for challenging cases where 500 revolutions are required for low-thrust orbit raising in the Earth gravitational field. Finally, the proposed waypoint-based guidance algorithm is simulated in a more realistic scenarios including perturbing acceleration to verify the robustness of the system via a Monte Carlo analysis
Next‐generation sequencing analysis of root canal microbiota associated with a severe endodontic‐periodontal lesion
No full textA patient with an unusual endo‐periodontal lesion, without coronal decay or damage, likely caused by a deep periodontal lesion with subsequent endodontic bacterial migration, required medical care. Next‐generation sequencing (NGS) was used to assess the endodontic microbiota in vestibular and palatal canals after tooth extraction, evidencing a predominant population (Fusobacterium nucleatum) in one endodontic canal, and a mixed bacterial population with six major populations almost equally distributed in the other endodontic canal (F. nucleatum, Porphyromonas gingivalis, P. endodontis, Parvimonas, Peptostreptococcus stomatis, Prevotella multiformis). These data could suggest different, separated ecologic niches in the same endodontic system, with potentially different pathogenicity levels, clinical manifestations and prognoses for every single canal of the same tooth
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
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
Prevalence of pathogens related to bovine respiratory disease before and after transportation in beef steers: Preliminary results
Full text linkBovine respiratory disease (BRD) is a serious health and economic problem in the beef industry, which is often associated with transportation and caused by different pathogens. The prevalence of bovine herpesvirus type 1 (BoHV-1), bovine adenovirus (BAdV), bovine viral diarrhea virus (BVDV), bovine coronavirus (BCoV), bovine respiratory syncytial virus (BRSV), bovine parainfluenza virus (BPiV), Pasteurella multocida, Mannheimia haemolytica, Histophilus somni, Mycoplasma bovis, in the nasal microbiota of beef steers before and after the same long-distance journey from France to southern Italy was documented. Fifty-six Limousine animals of three different shipments, travelling on three different days from February to April, were included. Prior to shipment (T0) and four days after arrival (T1), two DNS/animal were collected and tested by Real Time quantitative PCR (qPCR). Univariate logistic regression was carried out, considering time and day as fixed factors and the outcome of qPCR for each pathogen as a dependent categorical dichotomous variable (positive/negative, 1/0). The fact that the number of H. somni positive animals were found to be higher in the third shipment than the first and second one, indicating that this pathogen was already present before loading, is relevant. The prevalence of BCoV, BRSV, M. haemolytica, M. bovis, P. multocida was higher at T1 than T0, suggesting that other factors, such as stress and the epidemiological status of the arrival farm, played a role. The tested animals were not treated before and after transport, and our results are in agreement with the current literature, supporting the hypothesis that the prevalence of pathogens related to BRD would increase after travelling, with an increased risk of pathogens shedding
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
Molecular detection and characterization of Carnivore chaphamaparvovirus 1 in dogs
No full textCanine chaphamaparvovirus (CaChPV) is a newly recognised parvovirus discovered by metagenomic analysis during an outbreak of diarrhoea in dogs in Colorado, USA, in 2017 and more recently detected in diarrhoeic dogs in China. Whether the virus plays a role as canine pathogen and whether it is distributed elsewhere, in other geographical areas, is not known. We performed a case-control study to investigate the possible association of CaChPV with enteritis in dogs. CaChPV DNA was detected both in the stools of diarrhoeic dogs (1.9 %, 3/155) and of healthy animals (1.6 %, 2/120). All the CaChPV-infected dogs with diarrhea were mixed infected with other enteric viruses such as canine parvovirus (formerly CPV-2), canine bufavirus (CBuV) and canine coronavirus (CCoV), whilst none of the asymptomatic CaChPV positive animals resulted co-infected. The nearly full-length genome and the partial capsid protein (VP) gene of three canine strains, Te/36OVUD/19/ITA, Te/37OVUD/19/ITA and Te/70OVUD/19/ITA, were reconstructed. Upon phylogenetic analyses based on the NS1 and VP aa sequences, the Italian CaChPV strains tightly clustered with the American reference viruses. Distinctive residues could be mapped to the deduced variable regions of the VP of canine and feline chaphamaparvoviruses, considered as important markers of host range and pathogenicity for parvoviruses
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