323,188 research outputs found
Safe picosatellite release from a small satellite carrier
No full textThe Berlin Infrared Optical System satellite, which is scheduled for launch in 2016, will carry onboard a picosatellite and release it through a spring mechanism. After separation, it will perform proximity maneuvers in formation with the picosatellite solely based on optical navigation. Therefore, it is necessary to keep the distance of the two spacecraft within certain boundaries. This is especially challenging because the employed standard spring mechanism is designed to impart a separation velocity to the picosatellite. A maneuver strategy is developed in the framework of relative orbital elements. The goal is to prevent loss of formation while mitigating collision risk. The main design driver is the performance uncertainty of the release mechanism. The analyzed strategy consists of two maneuvers: the separation itself, and a drift-reduction maneuver of the Berlin Infrared Optical System satellite after 1.5 revolutions. The selected maneuver parameters are validated in a Monte Carlo simulation. It is demonstrated that both the risk of formation evaporation (separation of more than 50 km) as well as the eventuality of a residual drift toward the carrier are below 0.1%. In the latter case, formation safety is guaranteed by a passive safety achieved through a proper relative eccentricity/inclination vector separation
Safe Release of a Picosatellite from a Small Satellite Carrier in Low Earth Orbit
No full textThe BIROS satellite, which is scheduled for launch in 2015 into a low Earth
orbit, will carry onboard a picosatellite and subsequently release it through a spring mechanism with a fixed velocity. In the frame of the AVANTI experiment, the BIROS satellite will perform proximity maneuvers in a mid-range formation with the picosatellite, based solely on optical navigation through its onboard camera. Therefore it is necessary to keep the relative distance of the two spacecraft within certain limits. This is contradicted by the fact, that the spring mechanism is designed to create a large and safe separation between the two spacecraft.
In this paper a maneuver strategy is developed in the framework of relative orbital elements. The goal is to avoid any risk of collision on one side and to mitigate the possibility of formation evaporation on the other side. Main design drivers are several uncertainties—most prominently the performance uncertainty of the release mechanism. The analyzed strategy consists of two maneuvers: the separation itself and a drift reduction maneuver of the BIROS satellite after 1.5 revolutions. Afterwards a third maneuver is to be performed to minimize the residual drift, estimated through an orbit determination with radar tracking.
The selected maneuver parameters are validated in a Monte Carlo simulation. It is demonstrated that the risk of formation evaporation is below 0.1% as well as the eventuality of a residual drift towards the carrier. In the latter case formation safety is guaranteed by a passive safety achieved through a proper relative eccentricity/inclination vector separation
Catalogvs Bibliothecae Miscellaneae Olim Coeptae A Wilh. Ernesto Tentzelio, Consiliario Et Historiographo Saxonico, Avctae Vero A Christiano Wahrmvthio, S. S. Caes. Rom. Germ. Reg. Polon. Et Borvss. Maiest. Ac Sereniss. Elect. Et Dvc. Saxon. Nvmismat. Scvlpt. Et Fabricatore Privileg. Cvivs Pars Prima, Avctionis Lege, Plvs Licitantibvs Parata Pecvnia, In Cvria Saxo-Gothana, D. XXI. Et Seqv. Aprilis MDCCXXXIIX. ... Distrahenda
No full textVorlageform des Erscheinungsvermerks: Impr. Arnstadii, Litteris Schillianis. Prostat Gothae Apvd Avctorem
Selective Removal of the Tert-butoxycarbonyl Group From Secondary-amines - Znbr2 As the Deprotecting Reagent
No full textZnBr2 in dichloromethane is a convenient reagent for mild and selective removal of the tert-butoxycarbonyl group from secondary amines. Among the available protections for the amino function, the tert-butoxy-carbonyl (t-Boc) group remains the most popular, owing to the convenience of its introduction and removal.1 There are several deprotecting conditions, adjustable to different chemical environments, but generally protic media or strong Lewis acids2 are recommended. We report here a new deprotecting reagent, ZnBr2 in dichloromethane, which removes t-Boc and is compatible with acidic sensitive functionalities, as exemplified for allylsilane 1 (scheme 1). When a carboxyethyl function (1a) was used as the nitrogen masking group, the expected heterocyclization to adduct 2a occurred in presence of ZnBr23, but if the t-Boc (1b) was present, in the same conditions the secondary amine 2b was obtained. © 1989, Taylor & Francis Group, LLC. All rights reserved
Diffusive author(s), cohesive author: Analysis of S/N (1994)
No full textThis study indicates the ways in which various aspects of the author(s) are brought forth in Dumb type’s performance art, the S/N production. Previous research has suggested a non-hierarchical organization of Dumb type and the absence of a “privileged author” in Dumb type’s collaborative work, S/N. However, the results that I have investigated from member’s interviews on the creative process of S/N along with my analysis of the recorded images of S/N, indicate a different aspect of the author(s). First, S/N was created through, so to speak, the collective ideas of the members of Dumb type. Further, S/N has at least nine quotations from previous performances, installations, and printed writings, besides the work-in-progress technique. Explicating one of the “author functions” as given by Michel Foucault, each text has plural subjects of the author. However, it has been revealed from members’ interviews that Teiji Furuhashi had a decision-making role in selecting the members’ ideas within the performance. Since then, S/N has had plural subjects of creation; however, Furuhashi is one of the subjects of creation along with the “privileged author.” S/N has plural authors (diffusive authors) yet at the same time, it has a “privileged author,” Teiji Furuhashi (cohesive author)
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe 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
NFκB activation and stimulation of chemokine production in normal human macrophages by the gadolinium-based magnetic resonance contrast agent Omniscan: possible role in the pathogenesis of nephrogenic systemic fibrosis.
No full textNephrogenic systemic fibrosis (NSF) is a generalised fibrotic disorder occurring in certain individuals with renal insufficiency exposed to gadolinium-based contrast agents (GdBCA) for MRI. Histopathological examination of affected tissues shows increased numbers of activated macrophages. To elucidate the mechanisms responsible for macrophage activation, the effects of the GdBCA Omniscan on normal human macrophage global gene expression, chemokine production and nuclear factor κB (NFκB) activation was examined. Normal human monocyte-derived macrophages were incubated with Omniscan (50 mM) and their gene expression analysed by microarrays and real-time PCR. Macrophage chemokine production was assayed by multiplex ELISA. NFκB activation was assessed by NFκB nuclear localisation and quantitation of intracellular levels of inducible nitric oxide synthase (iNOS) protein. A specific cell-permeable NFκB peptide inhibitor was used to abrogate NFκB stimulation of chemokine and iNOS protein levels. CCL8/MCP-2 in affected skin of patients with NSF was examined by indirect immunofluorescence. Omniscan caused a profound change in the transcriptome of differentiated human normal macrophages in vitro, including a large increase in the expression of genes encoding CC and CXC chemokines. It induced rapid nuclear localisation of NFκB and stimulation of iNOS protein levels and chemokine production which were blocked by an NFκB inhibitory peptide. CCL8/MCP-2, the most upregulated chemokine following in vitro macrophage exposure to Omniscan, was strongly increased in NSF-affected skin. The GdBCA Omniscan induces potent stimulation of macrophage gene expression, NFκB activation and increased NFκB-mediated production of CC and CXC chemokines and iNOS. These alterations may play a crucial role in the pathogenesis of NSF
1,3-diastereocontrol With Bromoallenes - Synthesis of Enantiomerically Pure Beta-branched Alpha-amino-acids
No full textBromoallenes 3a and 3b derived from (D)-Serine undergo S(N)2' alkylation with organo copper reagents to give alkynyl amino alcohol derivatives. These compounds can be further transformed into blanched enantiomerically enriched alpha-amino acids as, for example (L)-Isolcucine and (L)-Alloisoleucine
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