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Emami, M., e O. Naserian. "New large sets of t-designs from t-homogeneous groups". Discrete Mathematics, Algorithms and Applications 10, n.º 04 (30 de julho de 2018): 1850051. http://dx.doi.org/10.1142/s1793830918500519.
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One of the most common direct methods for constructing [Formula: see text]-designs and large sets of [Formula: see text]-designs is assembling orbits obtained from the action of a permutation group [Formula: see text] on the set of all [Formula: see text]-subsets of a [Formula: see text]-set. It is well known that when G is a [Formula: see text]-homogeneous group, then each orbit is a [Formula: see text]-design. Therefore the problem is that how one could assemble these orbits to make [Formula: see text]-designs with the same index to construct a large set of [Formula: see text]-designs. The case where the orbit sizes are limited up to two values is already investigated. Here, we present a generalization of this method to assemble the set of orbits when the orbit sizes are limited up to three values. Meanwhile, as an example of this method, we construct the large sets [Formula: see text] for [Formula: see text] two of them are new.
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Zeng, Yunlin, Timothy D. Brandt, Gongjie Li, Trent J. Dupuy, Yiting Li, G. Mirek Brandt, Jay Farihi et al. "The Gliese 86 Binary System: A Warm Jupiter Formed in a Disk Truncated at ≈2 au". Astronomical Journal 164, n.º 5 (12 de outubro de 2022): 188. http://dx.doi.org/10.3847/1538-3881/ac8ff7.
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Abstract Gliese 86 is a nearby K dwarf hosting a giant planet on a ≈16 day orbit and an outer white dwarf companion on a ≈century-long orbit. In this study we combine radial velocity data (including new measurements spanning more than a decade) with high angular resolution imaging and absolute astrometry from Hipparcos and Gaia to measure the current orbits and masses of both companions. We then simulate the evolution of the Gl 86 system to constrain its primordial orbit when both stars were on the main sequence; the closest approach between the two stars was then about 9 au. Such a close separation limited the size of the protoplanetary disk of Gl 86 A and dynamically hindered the formation of the giant planet around it. Our measurements of Gl 86 B and Gl 86 Ab’s orbits reveal Gl 86 as a system in which giant planet formation took place in a disk truncated at ≈2 au. Such a disk would be just big enough to harbor the dust mass and total mass needed to assemble Gl 86 Ab’s core and envelope, assuming a high disk accretion rate and a low viscosity. Inefficient accretion of the disk onto Gl 86 Ab, however, would require a disk massive enough to approach the Toomre stability limit at its outer truncation radius. The orbital architecture of the Gl 86 system shows that giant planets can form even in severely truncated disks and provides an important benchmark for planet formation theory.
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Prentice, Andrew J. R. "Is Amalthea a Captured Trojan Asteroid of Jupiter?" Highlights of Astronomy 13 (2005): 901. http://dx.doi.org/10.1017/s1539299600017470.
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AbstractThe Galileo spacecraft has found Jupiter’s inner regular moon Amalthea to be a porous assemblage of rock and ice. This and other factors point to Amalthea having first condensed in a solar orbit.
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KHOUANE, Boulanouar, Nasreddine BELBEKRI e J. Eddine BENMANSOUR. "An Overview of Software-Defined Radio Technology in CubeSat Communications". Algerian Journal of Signals and Systems 8, n.º 2 (31 de dezembro de 2023): 55–58. http://dx.doi.org/10.51485/ajss.v8i2.189.
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Small satellites are becoming more popular because they are cost-effective, easy to assemble, and use commercially available parts. However, traditional ground stations that communicate with small satellites require a lot of hardware and are expensive to build. This makes it challenging to get the most out of small satellites' information. Software Defined Radios (SDRs) have been developed to reduce the cost of these ground stations by doing many of the tasks in software. Many universities and organizations are developing SDR ground stations to communicate with satellites in different orbits. Communication with satellites is critical to their development and operation. This paper proposes a ground station that uses SDR technology to communicate with one or more small satellites in Low Earth Orbit (LEO). The station is cost-effective, portable, and easily scaled, allowing it to acquire data from satellites.
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Simms, Steven R., e Kathleen M. Heath. "Site Structure of the Orbit Inn: An Application of Ethnoarchaeology". American Antiquity 55, n.º 4 (outubro de 1990): 797–813. http://dx.doi.org/10.2307/281251.
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One goal of ethnoarchaeology is to strengthen archaeological inferences about the past. A fifteenth-century hunter-gatherer, open site in Utah is used to examine ethnoarchaeological contributions toward determining the use of space, duration of occupation, assemblage composition, and site function. Comparisons between macrorefuse and microrefuse patterning suggest that (1) the distribution of macrorefuse can help identify locations of ephemeral structures and household activity areas; (2) the distribution of microrefuse in this intermittently occupied open site is useful for assessing assemblage composition; (3) determining the characteristics of macro- and microrefuse improves hypotheses about duration of occupation; and (4) interpretation of plant remains can be improved by considering site-formation processes. The study points to the need for a closer linkage between ethnoarchaeology and the archaeology of the past.
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Goatley, Christopher H. R., David R. Bellwood e Orpha Bellwood. "Fishes on coral reefs: changing roles over the past 240 million years". Paleobiology 36, n.º 3 (2010): 415–27. http://dx.doi.org/10.1666/09035.1.
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Key morphological traits reveal changes in functional morphospace occupation of reef fish assemblages over time. We used measurements of key functional attributes (i.e., lower jaw length and orbit diameter) of 208 fossil fish species from five geological periods to create bivariate plots of functional morphological traits through time. These plots were used to examine possible function and ecological characteristics of fossil reef fish assemblages throughout the Mesozoic and Cenozoic. A previously unknown trend of increasing orbit diameter over time became apparent. The Teleostei are the principal drivers of this change. The Eocene appears to mark a dramatic increase in two previously rare feeding modes in fishes: nocturnal feeding and high-precision benthic feeding. Interestingly, members of the Pycnodontiformes had relatively large eyes since the Triassic and appear to be the ecological precursors of their later teleost counterparts and may have been among the earliest nocturnal feeding fishes. Our results highlight potential changes in the roles of fishes on coral reefs through time.
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Díaz-Giménez, E., A. Zandivarez e G. A. Mamon. "Compact groups from semi-analytical models of galaxy formation – II. Different assembly channels". Monthly Notices of the Royal Astronomical Society 503, n.º 1 (24 de fevereiro de 2021): 394–405. http://dx.doi.org/10.1093/mnras/stab535.
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ABSTRACT We study the formation of over 6000 compact groups (CGs) of galaxies identified in mock redshift-space galaxy catalogues built from semi-analytical models of galaxy formation (SAMs) run on the Millennium Simulations. We select CGs of four members in our mock SDSS galaxy catalogues and, for each CG, we trace back in time the real-space positions of the most massive progenitors of their four galaxies. By analysing the evolution of the distance of the galaxy members to the centre of mass of the group, we identify four channels of CG formation. The classification of these assembly channels is performed with an automatic recipe inferred from a preliminary visual inspection and based on the orbit of the galaxy with the fewest number of orbits. Most CGs show late assembly, with the last galaxy arriving on its first or second passage, while only 10–20 per cent form by the gradual contraction of their orbits by dynamical friction, and only a few per cent forming early with little subsequent contraction. However, a SAM from a higher resolution simulation leads to earlier assembly. Assembly histories of CGs also depend on cosmological parameters. At similar resolution, CGs assemble later in SAMs built on parent cosmological simulations of high density parameter. Several observed properties of mock CGs correlate with their assembly history: early-assembling CGs are smaller, with shorter crossing times, and greater magnitude gaps between their brightest two members, and their brightest galaxies have smaller spatial offsets and are more passive.
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Mann, Arjan, Emily J. McDaniel, Emily R. McColville e Hillary C. Maddin. "Carbonodraco lundi gen et sp. nov., the oldest parareptile, from Linton, Ohio, and new insights into the early radiation of reptiles". Royal Society Open Science 6, n.º 11 (novembro de 2019): 191191. http://dx.doi.org/10.1098/rsos.191191.
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Redescription of the holotype specimen of Cephalerpeton ventriarmatum Moodie, 1912, from the Middle Pennsylvanian (Moscovian) Francis Creek Shale of Mazon Creek, Illinois, confirms that it is a basal eureptile with close postcranial similarities to other protorothyridids, such as Anthracodromeus and Paleothyris . The skull is long and lightly built, with large orbits and a dorsoventrally short mandible similar to most basal eureptiles. Two specimens referred previously to Cephalerpeton cf. C . ventriarmatum from the approximately coeval Linton, Ohio, locality differ significantly from the holotype in cranial and mandibular proportions and tooth morphology. This material and an additional Linton specimen compare favourably to ‘short-faced’ parareptiles, such as Colobomycter and Acleistorhinus , and justify recognition of an acleistorhinid parareptile in the Linton assemblage. The new binomen is thus the oldest known parareptile.
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Singh, M., e V. J. Rajesh. "Mineralogical characterization of Juventae Chasma, Mars: evidences from MRO-CRISM". ISPRS - International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences XL-8 (28 de novembro de 2014): 477–79. http://dx.doi.org/10.5194/isprsarchives-xl-8-477-2014.
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Juventae Chasma is a long depression associated with Valles Marineris and this study discusses the spectral observation made after analysing the Mars Reconnaissance Orbiter (MRO) Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) Full Resolution targeted (FRT) Images in the wavelength region of 1000–2600 nm. Observations reveal the presence of hydrous sulphates, pyroxenes (mafic minerals) and silica rich minerals, more likely opaline silica or glass. Hydrous mineral identified shows the absorption bands, which are more consistent with gypsum. Absorption bands at 2300–2350 nm, and 2500–2550 nm, which are characteristics of carbonates, have been also identified in the region. Presence of this mineral assemblage, confirmed by the observed spectral signatures ranging from volcanic to sedimentary origin, implies a relatively geologically active area, and a significant region in terms of aqueous activity.
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Li, Delun, Lou Zhong, Wei Zhu, Zhipeng Xu, Qirong Tang e Wenhao Zhan. "A Survey of Space Robotic Technologies for On-Orbit Assembly". Space: Science & Technology 2022 (1 de setembro de 2022): 1–13. http://dx.doi.org/10.34133/2022/9849170.
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The construction of large structures is one of the main development trends of the space exploration in the future, such as large space stations, large space solar power stations, and large space telescopes. It is one of important development tendency, which aims to make full use of space robots to assemble space structures autonomously in the aerospace industry. Considering that on-orbit assembly is an effective method to solve the problem of construction of large-scale spatial structures, it is necessary to motivate and facilitate the research of space robotics technologies for on-orbit assembly. Therefore, in this paper, the development status of space robot technology and the relevant space robot on-orbit assembly technology in recent decades are summarized. First, based on the space robot motion planning and assembly sequence planning, the development of space robot planning algorithms is introduced. For space robot assembly task, the space robot assembly method is summarized. From the control point of view, how to solve the vibration suppression and compliant assembly of on-orbit assembly is reviewed, which provides a reference for the autonomous intelligent assembly of space robots for large-scale structures in space. In order to simulate the space assembly scene on the ground, this paper introduces the development of ground verification experiments and provides ideas for the effective verification of space on-orbit assembly technology. In summary, though some of these problems have been satisfactorily solved in the past research, further research is still necessary in the future. Finally, it looks forward to the future research direction of space machine on-orbit assembly.
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Maiato, Helder, Paula Sampaio, Catarina L. Lemos, John Findlay, Mar Carmena, William C. Earnshaw e Claudio E. Sunkel. "MAST/Orbit has a role in microtubule–kinetochore attachment and is essential for chromosome alignment and maintenance of spindle bipolarity". Journal of Cell Biology 157, n.º 5 (28 de maio de 2002): 749–60. http://dx.doi.org/10.1083/jcb.200201101.
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Multiple asters (MAST)/Orbit is a member of a new family of nonmotor microtubule-associated proteins that has been previously shown to be required for the organization of the mitotic spindle. Here we provide evidence that MAST/Orbit is required for functional kinetochore attachment, chromosome congression, and the maintenance of spindle bipolarity. In vivo analysis of Drosophila mast mutant embryos undergoing early mitotic divisions revealed that chromosomes are unable to reach a stable metaphase alignment and that bipolar spindles collapse as centrosomes move progressively closer toward the cell center and eventually organize into a monopolar configuration. Similarly, soon after depletion of MAST/Orbit in Drosophila S2 cells by double-stranded RNA interference, cells are unable to form a metaphase plate and instead assemble monopolar spindles with chromosomes localized close to the center of the aster. In these cells, kinetochores either fail to achieve end-on attachment or are associated with short microtubules. Remarkably, when microtubule dynamics is suppressed in MAST-depleted cells, chromosomes localize at the periphery of the monopolar aster associated with the plus ends of well-defined microtubule bundles. Furthermore, in these cells, dynein and ZW10 accumulate at kinetochores and fail to transfer to microtubules. However, loss of MAST/Orbit does not affect the kinetochore localization of D-CLIP-190. Together, these results strongly support the conclusion that MAST/Orbit is required for microtubules to form functional attachments to kinetochores and to maintain spindle bipolarity.
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Ji, Jialong, Guoxi Liu, Zhongjian Fang e Fei Song. "Research on the application of ADN propulsion module for satellites". Journal of Physics: Conference Series 2217, n.º 1 (1 de abril de 2022): 012085. http://dx.doi.org/10.1088/1742-6596/2217/1/012085.
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Abstract The novel technology of the liquid Ammonium Dinitramide(ADN) propulsion is researched for its higher working performance and safer characteristics. Based on the safe performance, the design of ADN propulsion system for satellites is also presented in this paper. At the same time, the research on ADN propulsion system module is presented in this paper, including the developing processes method, the interface analysis, and the assemblage in satellites. Two examples are described here besides an ADN propulsion module applied in orbit. From the research we can know that ADN propulsion technology is fit for satellites, and the modularization of ADN propulsion system is a better developing mode for small satellites, which can simplify the developing process of propulsion system and crafts. In the end, the further application object and further work of ADN propulsion module for satellites is stated.
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Massana-Cid, Helena, Antonio Ortiz-Ambriz, Andrej Vilfan e Pietro Tierno. "Emergent collective colloidal currents generated via exchange dynamics in a broken dimer state". Science Advances 6, n.º 10 (março de 2020): eaaz2257. http://dx.doi.org/10.1126/sciadv.aaz2257.
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Controlling the flow of matter down to micrometer-scale confinement is of central importance in material and environmental sciences, with direct applications in nano and microfluidics, drug delivery, and biotechnology. Currents of microparticles are usually generated with external field gradients of different nature (e.g., electric, magnetic, optical, thermal, or chemical ones), which are difficult to control over spatially extended regions and samples. Here, we demonstrate a general strategy to assemble and transport polarizable microparticles in fluid media through combination of confinement and magnetic dipolar interactions. We use a homogeneous magnetic modulation to assemble dispersed particles into rotating dimeric state and frustrated binary lattices, and generate collective currents that arise from a novel, field-synchronized particle exchange process. These dynamic states are similar to cyclotron and skipping orbits in electronic and molecular systems, thus paving the way toward understanding and engineering similar processes at different length scales across condensed matter.
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Sun, Vivian Z., e Ralph E. Milliken. "Characterizing the Mineral Assemblages of Hot Spring Environments and Applications to Mars Orbital Data". Astrobiology 20, n.º 4 (1 de abril de 2020): 453–74. http://dx.doi.org/10.1089/ast.2018.2003.
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Buchy, Marie-Céline, Wolfgang Stinnesbeck, Eberhard Frey e Arturo H. Gonzalez Gonzalez. "First occurrence of the genus Dakosaurus (Crocodyliformes, Thalattosuchia) in the Late Jurassic of Mexico". Bulletin de la Société Géologique de France 178, n.º 5 (1 de setembro de 2007): 391–97. http://dx.doi.org/10.2113/gssgfbull.178.5.391.
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Abstract The fragmentary rostrum of a thalattosuchian is described. The specimen comes from the vicinity of the village of San Juan de los Dolores, next to Los Lirios, Coahuila, northeastern Mexico. Associated ammonites allow to assign the specimen to the Kimmeridgian section (Upper Jurassic) of the La Casita Formation. Because of its massiveness, its cranial architecture and the morphology of its teeth, the specimen is referred to the genus Dakosaurus, but is too incomplete for further determination. The genus is known by few specimens from the Late Jurassic of Europe and Argentina, and was until now unknown from North and Central America. It represents a new but expected element of the assemblage of marine reptiles populating the Mexican Gulf during the Late Jurassic. The specimen is one of the few members of the group preserving in 3 dimensions and visible, the preorbital portion of the rostrum, and especially of the nasopharyngeal canal; it confirms the existence of a large space possibly housing salt glands rostral to the orbits.
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Tikhonenko, Iliya S., Anton A. Smirnov e Natalia Ya Sotnikova. "First direct identification of the barlens vertical structure in galaxy models". Astronomy & Astrophysics 648 (abril de 2021): L4. http://dx.doi.org/10.1051/0004-6361/202140703.
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Applying spectral dynamics methods to one typical N-body model with a barlens, we dissect the modelled bar into separate components supported by completely different types of orbits. We identify at least four components: a narrow elongated bar, a boxy bar, and two components contributing to the barlens. We analyse the vertical structure of all components that make up the thick part of the bar, which has a boxy/peanut shape (B/P bulge). We show that the ‘peanut’ shape is mainly due to the orbits that assemble the boxy part of the face-on bar. We associate the X-shape with the narrow and elongated bar. The wider part of the barlens with square-like isophotes contributes to the boxy shape of the B/P bulge when we observe the galaxy edge-on. However, the part of the barlens with rounded isophotes in the face-on view is a rather flat structure in the vertical direction without any significant off-centre protrusions. Thus, for the first time, we demonstrate that the rounded face-on barlens cannot be entirely associated with the B/P bulge.
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Nugent, C. R., Nicole J. Tan e James M. Bauer. "FindPOTATOs: Minor Planet Observation Linking Software". Planetary Science Journal 6, n.º 1 (1 de janeiro de 2025): 18. https://doi.org/10.3847/psj/ad94eb.
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Abstract For minor planet observations to be archived and used by the scientific community, observations of individual objects must be linked together into groups called tracklets. This linking is nontrivial, as linking software must find real tracklets in noisy data within a reasonable amount of time. We describe FindPOTATOs, a linking software written in Python that can assemble minor planet tracklets. With the appropriate parameters, FindPOTATOs assembles tracklets for a variety of objects, including close-approaching near-Earth objects and trans-Neptunian objects. FindPOTATOs is ideal for processing data sets taken at small observatories, processing archival data, or finding tracklets of minor planets on unusual orbits. This paper describes the code structure, usage, and validation.
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Smith, Nadia, William L. Smith, Elisabeth Weisz e Henry E. Revercomb. "AIRS, IASI, and CrIS Retrieval Records at Climate Scales: An Investigation into the Propagation of Systematic Uncertainty". Journal of Applied Meteorology and Climatology 54, n.º 7 (julho de 2015): 1465–81. http://dx.doi.org/10.1175/jamc-d-14-0299.1.
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AbstractUncertainty requirements for climate observations are more stringent than for weather observations because of the scale dependency of natural variation. At present there is no space-based climate observing system, so weather observations have to be aggregated for the study of large-scale change. The management and minimization of uncertainty sources in weather observations are, therefore, a high priority. This work is a first attempt at investigating if a single long-term record can be assembled with temperature retrievals from three hyperspectral satellite sounders in polar orbit: the Atmospheric Infrared Sounder (AIRS) on Aqua in afternoon orbit since 2002, the Infrared Atmospheric Sounding Interferometer (IASI) on MetOp-A in morning orbit since 2006, and the Cross-track Infrared Sounder (CrIS) on board the Suomi National Polar-Orbiting Partnership in afternoon orbit since 2011. These instruments measure not only the vertical atmospheric structure but also atmospheric composition, thus providing coincident observations of many essential climate variables. Two main sources of known systematic differences, namely local sampling time (LST) and instrument type (i.e., interferometer vs grating spectrometer), are characterized. For a 5-yr record it is shown that differences among these temperature soundings are height dependent; a multi-instrument data record could be assembled from measurements of the stratosphere but this is not yet possible for the troposphere, where cloud effects are shown to be dominant and dependent on instrument type. Moreover, LST differences are limited to regional systematic effects in the lower troposphere and boundary layer. This research is a step toward the development of transparent and geophysically consistent methods with which to assemble weather measurements into climate observations.
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Incarbona, Alessandro, Jaume Dinarès-Turell, Enrico Di Stefano, Giuseppe Ippolito, Nicola Pelosi e Rodolfo Sprovieri. "Orbital variations in planktonic foraminifera assemblages from the Ionian Sea during the Middle Pleistocene Transition". Palaeogeography, Palaeoclimatology, Palaeoecology 369 (janeiro de 2013): 303–12. http://dx.doi.org/10.1016/j.palaeo.2012.10.039.
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Popova, Julia V., Gera A. Pavlova, Alyona V. Razuvaeva, Lyubov A. Yarinich, Evgeniya N. Andreyeva, Alina F. Anders, Yuliya A. Galimova et al. "Genetic Control of Kinetochore-Driven Microtubule Growth in Drosophila Mitosis". Cells 11, n.º 14 (6 de julho de 2022): 2127. http://dx.doi.org/10.3390/cells11142127.
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Centrosome-containing cells assemble their spindles exploiting three main classes of microtubules (MTs): MTs nucleated by the centrosomes, MTs generated near the chromosomes/kinetochores, and MTs nucleated within the spindle by the augmin-dependent pathway. Mammalian and Drosophila cells lacking the centrosomes generate MTs at kinetochores and eventually form functional bipolar spindles. However, the mechanisms underlying kinetochore-driven MT formation are poorly understood. One of the ways to elucidate these mechanisms is the analysis of spindle reassembly following MT depolymerization. Here, we used an RNA interference (RNAi)-based reverse genetics approach to dissect the process of kinetochore-driven MT regrowth (KDMTR) after colcemid-induced MT depolymerization. This MT depolymerization procedure allows a clear assessment of KDMTR, as colcemid disrupts centrosome-driven MT regrowth but not KDMTR. We examined KDMTR in normal Drosophila S2 cells and in S2 cells subjected to RNAi against conserved genes involved in mitotic spindle assembly: mast/orbit/chb (CLASP1), mei-38 (TPX2), mars (HURP), dgt6 (HAUS6), Eb1 (MAPRE1/EB1), Patronin (CAMSAP2), asp (ASPM), and Klp10A (KIF2A). RNAi-mediated depletion of Mast/Orbit, Mei-38, Mars, Dgt6, and Eb1 caused a significant delay in KDMTR, while loss of Patronin had a milder negative effect on this process. In contrast, Asp or Klp10A deficiency increased the rate of KDMTR. These results coupled with the analysis of GFP-tagged proteins (Mast/Orbit, Mei-38, Mars, Eb1, Patronin, and Asp) localization during KDMTR suggested a model for kinetochore-dependent spindle reassembly. We propose that kinetochores capture the plus ends of MTs nucleated in their vicinity and that these MTs elongate at kinetochores through the action of Mast/Orbit. The Asp protein binds the MT minus ends since the beginning of KDMTR, preventing excessive and disorganized MT regrowth. Mei-38, Mars, Dgt6, Eb1, and Patronin positively regulate polymerization, bundling, and stabilization of regrowing MTs until a bipolar spindle is reformed.
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Chapin, Samantha, Holly Everson, William Chapin e Erik Komendera. "Built On-Orbit Robotically Assembled Gigatruss (BORG): Ground Robotic Demonstration". Aerospace 11, n.º 6 (31 de maio de 2024): 447. http://dx.doi.org/10.3390/aerospace11060447.
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The next generation of large space infrastructure will require crucial advancements in current technology. Current methodologies focus on large deployable structures folded into cramped payload fairings or revolutionary assembly techniques requiring many moving components. Utilizing both in-space assembly and deployable concepts, a hybrid mixed assembly scheme was posed using smaller deployable units interspersed with rigid connecting elements to assemble these large architectures. The Built On-Orbit Robotically Assembled Gigatruss (BORG) structure allows for modularity in assembly and repair with the number of separate elements comprising the structure to be reduced, compared to strut-by-strut assembly. The following documents the process of constructing and running physical trials on a prototype BORG architecture. Additionally, a Semantic and Fiducial Aided Graph Simultaneous Localization and Mapping (SF-GraphSLAM) approach is taken to verify the relation of assembled and deployed truss elements to aid in error evaluation and state estimation. This technology demonstration stands as a proof of concept in verifying the viability of the BORG architecture as a method for large structure assembly.
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Gnedin, Oleg Y., e José L. Prieto. "Dynamical Evolution of Globular Clusters in Hierarchical Cosmology". Proceedings of the International Astronomical Union 3, S246 (setembro de 2007): 403–7. http://dx.doi.org/10.1017/s1743921308016049.
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AbstractWe probe the evolution of globular clusters that could form in giant molecular clouds within high-redshift galaxies. Numerical simulations demonstrate that the large and dense enough gas clouds assemble naturally in current hierarchical models of galaxy formation. These clouds are enriched with heavy elements from earlier stars and could produce star clusters in a similar way to nearby molecular clouds. The masses and sizes of the model clusters are in excellent agreement with the observations of young massive clusters. Do these model clusters evolve into globular clusters that we see in our and external galaxies? In order to study their dynamical evolution, we calculate the orbits of model clusters using the outputs of the cosmological simulation of a Milky Way-sized galaxy. We find that at present the orbits are isotropic in the inner 50 kpc of the Galaxy and preferentially radial at larger distances. All clusters located outside 10 kpc from the center formed in the now-disrupted satellite galaxies. The spatial distribution of model clusters is spheroidal, with a power-law density profile consistent with observations. The combination of two-body scattering, tidal shocks, and stellar evolution results in the evolution of the cluster mass function from an initial power law to the observed log-normal distribution.
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Beaufort, Luc, e Marie-Pierre Aubry. "Fluctuations in the composition of Late Miocene calcareous nannofossil assemblages as a response to orbital forcing". Paleoceanography 5, n.º 6 (dezembro de 1990): 845–65. http://dx.doi.org/10.1029/pa005i006p00845.
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Gupta, Shyam M. "Orbital frequencies in radiolarian assemblages of the central Indian Ocean: implications on the Indian summer monsoon". Palaeogeography, Palaeoclimatology, Palaeoecology 197, n.º 1-2 (agosto de 2003): 97–112. http://dx.doi.org/10.1016/s0031-0182(03)00388-2.
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Itaki, Takuya, Nozomi Komatsu e Isao Motoyama. "Orbital- and millennial-scale changes of radiolarian assemblages during the last 220 kyrs in the Japan Sea". Palaeogeography, Palaeoclimatology, Palaeoecology 247, n.º 1-2 (abril de 2007): 115–30. http://dx.doi.org/10.1016/j.palaeo.2006.11.025.
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Wu, Naiqin, D. D. Rousseau e Xiuping Liu. "Response of mollusk assemblages from the Luochuan loess section to orbital forcing since the last 250 ka". Chinese Science Bulletin 45, n.º 17 (setembro de 2000): 1617–22. http://dx.doi.org/10.1007/bf02886225.
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Kear, Benjamin P., Natalie I. Schroeder e Michael S. Y. Lee. "An archaic crested plesiosaur in opal from the Lower Cretaceous high-latitude deposits of Australia". Biology Letters 2, n.º 4 (30 de junho de 2006): 615–19. http://dx.doi.org/10.1098/rsbl.2006.0504.
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Umoonasaurus demoscyllus gen. et sp. nov. is a new small-bodied (approx. 2.5 m) pliosauroid plesiosaur from the Lower Cretaceous (Aptian–Albian) of southern Australia. It is represented by several partial skeletons (one with a near complete skull is the most complete opalized vertebrate fossil yet known), and is unique in having large crests on the skull midline and above the orbits. Umoonasaurus is surprisingly archaic despite its relatively late age (approx. 115 Myr ago)—being simultaneously the most basal (primitive) and last surviving rhomaleosaurid. Notably, it lacks the ‘pliosauromorph’ features (large head, short neck, gigantism) typically characterizing many more derived Jurassic rhomaleosaurids; thus, reinforcing the suspected convergent evolution of the ‘pliosauromorph’ hypercarnivore body plan. Umoonasaurus inhabited an Early Cretaceous high-latitude (approx. 70° S) inland seaway subject to seasonally near-freezing climatic conditions. This extreme environment supported a diverse range of plesiosaur taxa, suggesting that these marine reptiles might have possessed adaptations (e.g. heightened metabolic levels) to cope with cold-water temperatures. Indeed, survival of ancient endemic lineages such as Umoonasaurus is a common phenomenon in Australian Cretaceous vertebrate assemblages and might have been facilitated by isolation in low-temperature high-latitude regions.
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Henry, Emilie A., Kira T. Lawrence, Laura C. Peterson e Marci M. Robinson. "A comparison of orbital-resolution, Late Pleistocene Alkenone and foraminiferal assemblage-based sea surface temperature reconstructions from the Southwest Pacific". Quaternary Science Reviews 277 (fevereiro de 2022): 107345. http://dx.doi.org/10.1016/j.quascirev.2021.107345.
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Li, ZhenHua, Shuiquan Deng, Myung-Hwan Whangbo e Hong-Gang Luo. "Orbital projection technique to explore the materials genomes of optical susceptibilities". AIP Advances 12, n.º 5 (1 de maio de 2022): 055206. http://dx.doi.org/10.1063/5.0067891.
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The development in materials science and pharmaceutics shows that there exist some key materials genomes, i.e., certain groups of atoms with specific constituents and structures, which govern the property of a series of materials based on them. To pinpoint such materials, genomes are helpful to assemble functional units and synthesize new materials and, thus, have a profound meaning. In this work, we develop an innovative method based on the idea of projecting atomic orbitals’ wavefunction, which enables us to project every physical quantity into their orbital contribution and, thus, can be widely used to identify the materials genomes of various properties. Within this framework, we derive the expressions of the projected optical susceptibilities and exhibit a paradigm of studying the corresponding materials genomes of optical properties, especially the desired nonlinear optical materials.
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Kaplan, Hannah H., Ralph E. Milliken, David Fernández-Remolar, Ricardo Amils, Kevin Robertson e Andrew H. Knoll. "Orbital evidence for clay and acidic sulfate assemblages on Mars based on mineralogical analogs from Rio Tinto, Spain". Icarus 275 (setembro de 2016): 45–64. http://dx.doi.org/10.1016/j.icarus.2016.03.019.
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Brooks, Allan M., Syeda Sabrina e Kyle J. M. Bishop. "Shape-directed dynamics of active colloids powered by induced-charge electrophoresis". Proceedings of the National Academy of Sciences 115, n.º 6 (22 de janeiro de 2018): E1090—E1099. http://dx.doi.org/10.1073/pnas.1711610115.
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The symmetry and shape of colloidal particles can direct complex particle motions through fluid environments powered by simple energy inputs. The ability to rationally design or “program” the dynamics of such active colloids is an important step toward the realization of colloidal machines, in which components assemble spontaneously in space and time to perform dynamic (dissipative) functions such as actuation and transport. Here, we systematically investigate the dynamics of polarizable particles of different shapes moving in an oscillating electric field via induced-charge electrophoresis (ICEP). We consider particles from each point group in three dimensions (3D) and identify the different rotational and translational motions allowed by symmetry. We describe how the 3D shape of rigid particles can be tailored to achieve desired dynamics including oscillatory motions, helical trajectories, and complex periodic orbits. The methodology we develop is generally applicable to the design of shape-directed particle motions powered by other energy inputs.
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Britto, Marcelo R., Flávio C. T. Lima e Max H. Hidalgo. "Corydoras ortegai, a new species of corydoradine catfish from the lower río Putumayo in Peru (Ostariophysi: Siluriformes: Callichthyidae)". Neotropical Ichthyology 5, n.º 3 (setembro de 2007): 293–300. http://dx.doi.org/10.1590/s1679-62252007000300009.
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A new species of Corydoras, C. ortegai, is described from tributaries of the lower course of río Putumayo in Peru, close to the border with Brazil and Colombia. The new species seems to be related to Corydoras reynoldsi, C. weitzmani, C. panda, and C. tukano, all of which share a pattern composed of uniform light ground color on body, dark bar ("mask") across orbit, and one or two large rounded blotches midlaterally on trunk. Corydoras ortegai is easily distinguished from these species, except C. panda, mainly by the absence of a midlateral trunk blotch at the dorsal-fin level, and the rounded shape of the midlateral trunk blotch at the adipose-fin level. Corydoras ortegai differs from C. panda by its greater number of lateral body plates, lack of dorsal-fin blotch, scattered chromatophores surrounding midregion of cleithrum, caudal fin with series of small blotches restricted to rays, slenderer body, and narrower intercleithral area. Corydoras ortegai belongs to a putatively monophyletic assemblage of Corydoras that occurs mainly in the Western Amazon basin, C. tukano excepted. The occurrence of Corydoras tukano in the rio Tiquié (upper Negro basin) and its putative sister species, C. ortegai, in the western Amazon, together with similar distribution patterns shared by other groups of fishes, suggest a biogeographic relationship between these areas.
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Yao, Junjie, Xiamin Hao, Biyu Song, Yizhen Jia, Chenqiang Hua e Miao Zhou. "Multi-orbital topolectrical circuit for topological quantum states". Nano Futures 6, n.º 2 (6 de abril de 2022): 021001. http://dx.doi.org/10.1088/2399-1984/ac5cd2.
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Abstract Remarkable progress has been made in using electric circuits as a powerful platform to realize a plethora of exotic topological quantum states, even of higher orders and/or dimensions. So far the proposed circuits are restricted to a single-orbital tight-binding model with different lattices. Here, we introduce the concept of a multi-orbital topolectrical circuit and construct practical LC circuits to demonstrate its superiorities. As a proof of concept, we assemble two sets of inductors in one plaquette to simulate a (px, py )-orbital model within a two-dimensional hexagonal lattice. In the presence of spin–orbit coupling, as generated by mixing voltage degrees of freedom, a quantum spin Hall (QSH) state emerges with spin-resolved edge modes propagating along the boundary in the time domain. Implementation of negative impedance converters (NICs) with nonreciprocal links transforms the circuit into a quantum anomalous Hall (QAH) state. Remarkably, we demonstrate that QSH/QAH states can be reversibly switched by tuning the resistance of NIC, and an experimental observable-edge distance ratio is proposed to facilitate the phase transition detection. This work provides an exciting playground for exploring multi-orbital physics in topolectrical circuits, paving the way for future applications in nanoelectronics, telecommunications, signal processing and quantum computing.
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Pritchard, Adam C., e Sterling J. Nesbitt. "A bird-like skull in a Triassic diapsid reptile increases heterogeneity of the morphological and phylogenetic radiation of Diapsida". Royal Society Open Science 4, n.º 10 (outubro de 2017): 170499. http://dx.doi.org/10.1098/rsos.170499.
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The Triassic Period saw the first appearance of numerous amniote lineages (e.g. Lepidosauria, Archosauria, Mammalia) that defined Mesozoic ecosystems following the end Permian Mass Extinction, as well as the first major morphological diversification of crown-group reptiles. Unfortunately, much of our understanding of this event comes from the record of large-bodied reptiles (total body length > 1 m). Here we present a new species of drepanosaurid (small-bodied, chameleon-like diapsids) from the Upper Triassic Chinle Formation of New Mexico. Using reconstructions of micro-computed tomography data, we reveal the three-dimensional skull osteology of this clade for the first time. The skull presents many archaic anatomical traits unknown in Triassic crown-group reptiles (e.g. absence of bony support for the external ear), whereas other traits (e.g. toothless rostrum, anteriorly directed orbits, inflated endocranium) resemble derived avian theropods. A phylogenetic analysis of Permo-Triassic diapsids supports the hypothesis that drepanosaurs are an archaic lineage that originated in the Permian, far removed from crown-group Reptilia. The phylogenetic position of drepanosaurids indicates the presence of archaic Permian clades among Triassic small reptile assemblages and that morphological convergence produced a remarkably bird-like skull nearly 100 Myr before one is known to have emerged in Theropoda.
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Stramer, Brian, Severina Moreira, Tom Millard, Iwan Evans, Chieh-Yin Huang, Ola Sabet, Martin Milner, Graham Dunn, Paul Martin e Will Wood. "Clasp-mediated microtubule bundling regulates persistent motility and contact repulsion in Drosophila macrophages in vivo". Journal of Cell Biology 189, n.º 4 (10 de maio de 2010): 681–89. http://dx.doi.org/10.1083/jcb.200912134.
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Drosophila melanogaster macrophages are highly migratory cells that lend themselves beautifully to high resolution in vivo imaging experiments. By expressing fluorescent probes to reveal actin and microtubules, we can observe the dynamic interplay of these two cytoskeletal networks as macrophages migrate and interact with one another within a living organism. We show that before an episode of persistent motility, whether responding to developmental guidance or wound cues, macrophages assemble a polarized array of microtubules that bundle into a compass-like arm that appears to anticipate the direction of migration. Whenever cells collide with one another, their microtubule arms transiently align just before cell–cell repulsion, and we show that forcing depolymerization of microtubules by expression of Spastin leads to their defective polarity and failure to contact inhibit from one another. The same is true in orbit/clasp mutants, indicating a pivotal role for this microtubule-binding protein in the assembly and/or functioning of the microtubule arm during polarized migration and contact repulsion.
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Watabe, Mahito. "Eurasian and North American phylogeny of Turolian hipparionine horses (Perissodactyla, Mammalia) in China". Paleontological Society Special Publications 6 (1992): 305. http://dx.doi.org/10.1017/s2475262200008650.
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The late Miocene Chinese hipparions are morphologically diversified showing similarity to both western Old World's and North American forms. Two Chinese taxa that are phylogenetically related to western Old World's forms are Hipparion fossatum (= H. forstende) from Baode (Shanxi) and H. hippidiodus from Qingyang (Gansu) and Baode. The former is related to H. mediterraneum and the latter to H. urmiense - platygenys from the Turolian localities in the western Old World. H. fossatum and H. hippidiodus are associated with the “dorcadoides” (open-land) and “mixed” faunas in northern China. Hipparion fossatum that is characterized by POF located close to the orbit co-occurs with large and morphologically specialized form, H. dermatorhinum in Baode (Loc.30). H. hippidiodus with reduced POF is discovered with smaller H. coelophyes in Loc. 43, 44 (Baode) and Loc. 115 (Gansu).The hipparions associated with the “gaudryi” (forest) fauna are characterized by well defined and small POF located far from the orbit. Those forms are: H. platyodus from Loc. 70; H. ptychodus from Loc. 73; H. tylodus from Hsi-Liang in Yushe - Wuxiang basins; and H. sefvei from Loc. 12 at Xin-an in Henan province. H. coelophyes from Baode (Loc.43 & 44) and Qingyang (Loc. 115) also show similar facial morphology to the these forms, although it has small size and shallow POF. Those forms are similar in facial and dental morphology to Hipparion sensu stricto and some species of Cormohipparion in North America.The assemblages of Chinese hipparions are composed of two groups whose members are phylogenetically similar to the forms from both western part of Eurasia and North America. The “gaudryi” fauna is considered younger than the other two on the basis of faunal analyses. The similarity in hipparionine taxonomy between northern China and North America in the latest Miocene is an evidences for possible faunal interchange(s) occurred during that period, as suggested by taxonomic analyses on carnivores and proboscideans in eastern half of Eurasia and North America.
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Henry, T., e M. Holynska. "Investigation of long-term storage of space materials for future constellation missions: study of Braycote® 601 EF lubricant". IOP Conference Series: Materials Science and Engineering 1287, n.º 1 (1 de agosto de 2023): 012011. http://dx.doi.org/10.1088/1757-899x/1287/1/012011.
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Abstract The long-term storage (LTS) of space materials is becoming more and more critical for the next missions. For instance, for MTG (Meteosat Third Generation) mission, 5-year assemble, integration and testing (AIT) time on ground, up to 17.5-year storage for recurring models plus at least 8.5 years in orbit operation are planned. Hence, a good understanding of materials’ aging properties is desirable to ensure that materials’ specifications are still suitable after LTS, and, eventually, to anticipate the potential non-conformities. For this purpose, the European Space Research and Technology Centre (ESTEC) is investigating these problematics thanks to its wide capabilities from aging with environmental, climatic and vacuum chambers up to physico-chemical characterizations by numerous instruments such as microscopes, spectroscopes, thermal, mechanical or electrical analyzers. An overview is presented herein through the study of a fluorinated based grease lubricant named Braycote® 601EF widely used in mechanisms in space sector such as the US space shuttles actuator or the basic end effectors of The European Robotic Arm.
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Engrand, Cécile, Jean Duprat, Noémie Bardin, Emmanuel Dartois, Hugues Leroux, Eric Quirico, Karim Benzerara et al. "The asteroid-comet continuum from laboratory and space analyses of comet samples and micrometeorites". Proceedings of the International Astronomical Union 11, A29A (agosto de 2015): 253–56. http://dx.doi.org/10.1017/s1743921316002994.
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AbstractComets are probably the best archives of the nascent solar system, 4.5 Gyr ago, and their compositions reveal crucial clues on the structure and dynamics of the early protoplanetary disk. Anhydrous minerals (olivine and pyroxene) have been identified in cometary dust for a few decades. Surprisingly, samples from comet Wild2 returned by the Stardust mission in 2006 also contain high temperature mineral assemblages like chondrules and refractory inclusions, which are typical components of primitive meteorites (carbonaceous chondrites - CCs). A few Stardust samples have also preserved some organic matter of comet Wild 2 that share some similarities with CCs. Interplanetary dust falling on Earth originate from comets and asteroids in proportions to be further constrained. These cosmic dust particles mostly show similarities with CCs, which in turn only represent a few percent of meteorites recovered on Earth. At least two (rare) families of cosmic dust particles have shown strong evidences for a cometary origin: the chondritic porous interplanetary dust particles (CP-IDPs) collected in the terrestrial stratosphere by NASA, and the ultracarbonaceous Antarctic Micrometeorites (UCAMMs) collected from polar snow and ice by French and Japanese teams. Analyses of dust particles from the Jupiter family comet 67P/Churyumov-Gerasimenko by the dust analyzers on Rosetta orbiter (COSIMA, GIADA, MIDAS) suggest a relationship to interplanetary dust/micrometeorites. A growing number of evidences highlights the existence of a continuum between asteroids and comets, already in the early history of the solar system.
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Wang, Yao. "Comparison of Machine Learning Strategies in Hazardous Asteroids Prediction". Highlights in Science, Engineering and Technology 39 (1 de abril de 2023): 201–8. http://dx.doi.org/10.54097/hset.v39i.6527.
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The purpose of this study is to use multiple classification algorithm from machine learning to predict hazardous asteroids that orbit Earth. Seven models are Logistic Regression, K-Nearest Neighbor Classifier, Random Forest Classifier, Decision Tree Classifier, Multinomial Naïve Bayes Classifier, Gradient Boosting Classifier, and Voting Classifier. Confusion matrix is used to evaluate those models. Evaluation metrics include accuracy, precision, recall, and f1-score. The result shows that random forest classifier has the greatest overall performance with highest accuracy. Decision Tree classifier, Gradient Boosting classifier, and Voting classifier also perform well. Gradient Boosting classifier is capable of greatly reducing the risk of hazardous asteroid, which is, reduce the number of hazardous asteroids that is predicted as non-hazardous. Because of assumptions of some models like Logistic Regression, data used in the experiment do not follow them, so the overall performance of those models are not well. It would be better to select data for fitting the model. The result shows that combined classifiers perform better. Voting Classifier can be used to assemble those accurate models and get a more accurate result by offsetting disadvantages of each model.
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Flahaut, Jessica, Janice L. Bishop, Simone Silvestro, Dario Tedesco, Isabelle Daniel e Damien Loizeau. "The Italian Solfatara as an analog for Mars fumarolic alteration". American Mineralogist 104, n.º 11 (1 de novembro de 2019): 1565–77. http://dx.doi.org/10.2138/am-2019-6899.
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Abstract The first definitive evidence for continental vents on Mars is the in situ detection of amorphous silica-rich outcrops by the Mars Exploration Rover Spirit. These outcrops have been tentatively interpreted as the result of either acid sulfate leaching in fumarolic environments or direct precipitation from hot springs. Such environments represent prime targets for upcoming astrobiology missions but remain difficult to identify with certainty, especially from orbit. To contribute to the identification of fumaroles and hot spring deposits on Mars, we surveyed their characteristics at the analog site of the Solfatara volcanic crater in central Italy. Several techniques of mineral identification (VNIR spectroscopy, Raman spectroscopy, XRD) were used both in the field and in the laboratory on selected samples. The faulted crater walls showed evidence of acid leaching and alteration into the advanced argillic-alunitic facies, with colorful deposits containing alunite, jarosite, and/or hematite. Sublimates containing various Al and Fe hydroxyl-sulfates were observed around the active fumarole vents at 90 °C. One vent at 160 °C was characterized by different sublimates enriched in As and Hb sulfide species. Amorphous silica and alunite assemblages that are diagnostic of silicic alteration were also observed at the Fangaia mud pots inside the crater. A wide range of minerals was identified at the 665 m diameter Solfatara crater that is diagnostic of acid-steam heated alteration of a trachytic, porous bedrock. Importantly, this mineral diversity was captured at each site investigated with at least one of the techniques used, which lends confidence for the recognition of similar environments with the next-generation Mars rovers.
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Cavin, Lionel, e Paulo M. Brito. "A new Lepisosteidae (Actinopterygii, Ginglymodi) from the Cretaceous of the Kem Kem Beds, southern Morocco". Bulletin de la Société Géologique de France 172, n.º 5 (1 de setembro de 2001): 661–70. http://dx.doi.org/10.2113/172.5.661.
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Abstract Lepisosteids or gars constitute a very special neopterygian group, with seven living species in two genera: Lepisosteus and Atractosteus. They live in freshwaters from the eastern part of North America and Central America. A new lepisosteid, Oniichthys falipoui gen. nov., sp. nov., is described on the basis of two well preserved specimens. Although the type locality is unknown, information provided by the fossil collector, the type of preservation of the specimen, and the nature of the attached matrix indicate, with confidence, that it comes from the Kem Kem beds of southern Morocco (fig. 1). The Kem Kem beds are rich fossiliferous horizons, exposed along the face of an escarpment extending from the north of Erfoud town to the Kem Kem area. The age of these outcrops is still debatable being considered as ?Albian in age [Forey and Grande, 1998] or regarded as Cenomanian, due to their elasmobranch assemblage [Sereno et al., 1996]. Oniichthys falipoui shows several derived characters of gars such as an elongated ethmoid region, an upper jaw formed by a chain of tooth-bearing bones, a joint between the quadrate and the lower jaw lying far forward, in front of the orbit and a large splint-like quadratojugal overlying the horizontal branch of the preopercle. O. falipoui shares with the primitive gar, Obaichthys decoratus, from the ?Albian Santana Formation of Brazil, the presence of toothed maxillaries, although in the Moroccan taxon, the maxillaries are anteriorly fused with infraorbitals. This structure confirms that, at least, some of the "infraorbital chain" bones bear maxillary teeth, fused to them during ontogeny. Discussion of characters leads to regard O. falipoui as more derived than Obaichthys, and to place it as the sister-group of Lepisosteus-Atractosteus.
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Atria, Ana María, José Parada, Yanko Moreno, Sebastián Suárez, Ricardo Baggio e Octavio Peña. "Synthesis, crystal structure and magnetic properties of diaquabis(2,6-diamino-7H-purin-1-ium-κN 9)bis(4,4′-oxydibenzoato-κO)cobalt(II) dihydrate". Acta Crystallographica Section C Structural Chemistry 74, n.º 1 (1 de janeiro de 2018): 37–44. http://dx.doi.org/10.1107/s2053229617016916.
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The title mononuclear CoII complex, [Co(C5H7N6)2(C14H8O5)2(H2O)2]·2H2O, has been synthesized and its crystal structure determined by X-ray diffraction. The complex crystallizes in the triclinic space group P\overline{1}, with one formula unit per cell (Z = 1 and Z′ = 1 \over 2). It consists of a mononuclear unit with the CoII ion on an inversion centre coordinated by two 2,6-diamino-7H-purin-1-ium cations, two 4,4′-oxydibenzoate anions (in a nonbridging κO-monodentate coordination mode, which is less common for the anion in its CoII complexes) and two water molecules, defining an octahedral environment around the metal atom. There is a rich assortment of nonbonding interactions, among which a strong N+—H...O− bridge, with a short N...O distance of 2.5272 (18) Å, stands out, with the H atom ostensibly displaced away from its expected position at the donor side, towards the acceptor. The complex molecules assemble into a three-dimensional hydrogen-bonded network. A variable-temperature magnetic study between 2 and 300 K reveals an orbital contribution to the magnetic moment and a weak antiferromagnetic interaction between CoII centres as the temperature decreases. The model leads to the following values: A (crystal field strength) = 1.81, λ (spin-orbit coupling) = −59.9 cm−1, g (Landé factor) = 2.58 and zJ (exchange coupling) = −0.5 cm−1.
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Najita, Joan R., e Scott J. Kenyon. "Takeout and Delivery: Erasing the Dusty Signature of Late-stage Terrestrial Planet Formation". Astrophysical Journal 944, n.º 2 (1 de fevereiro de 2023): 125. http://dx.doi.org/10.3847/1538-4357/acac8f.
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Abstract The formation of planets like Earth is expected to conclude with a series of late-stage giant impacts that generate warm dusty debris, the most anticipated visible signpost of terrestrial planet formation in progress. While there is now evidence that Earth-sized terrestrial planets orbit a significant fraction of solar-type stars, the anticipated dusty debris signature of their formation is rarely detected. Here we discuss several ways in which our current ideas about terrestrial planet formation imply transport mechanisms capable of erasing the anticipated debris signature. A tenuous gas disk may be regenerated via takeout (i.e., the liberation of planetary atmospheres in giant impacts) or delivery (i.e., by asteroids and comets flung into the terrestrial planet region) at a level sufficient to remove the warm debris. The powerful stellar wind from a young star can also act, its delivered wind momentum producing a drag that removes warm debris. If such processes are efficient, terrestrial planets may assemble inconspicuously, with little publicity and hoopla accompanying their birth. Alternatively, the rarity of warm excesses may imply that terrestrial planets typically form very early, emerging fully formed from the nebular phase without undergoing late-stage giant impacts. In either case, the observable signposts of terrestrial planet formation appear more challenging to detect than previously assumed. We discuss observational tests of these ideas.
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Incarbona, Alessandro, Enrico Di Stefano, Rodolfo Sprovieri e Serena Ferraro. "The Uniqueness of Planktonic Ecosystems in the Mediterranean Sea: The Response to Orbital- and Suborbital-Climatic Forcing over the Last 130,000 Years". Open Geosciences 8, n.º 1 (1 de janeiro de 2016): 567–78. http://dx.doi.org/10.1515/geo-2016-0050.
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AbstractThe Mediterranean Sea is an ideal location to test the response of organisms to hydrological transformations driven by climate change. Here we review studies carried out on planktonic foraminifera and coccolithophores during the late Quaternary and attempt the comparison of data scattered in time and space. We highlight the prompt response of surface water ecosystems to both orbital- and suborbital-climatic variations.A markedly different spatial response was observed in calcareous plankton assemblages, possibly due to the influence of the North Atlantic climatic system in the western, central and northern areas and of the monsoon system in the easternmost and southern sites. Orbital-induced climatic dynamics led to productive surface waters in the northern, western and central Mediterranean Sea during the last glacial and to distinct deep chlorophyll maximum layers in the eastern Mediterranean Sea coinciding with bottom anoxia episodes. High-frequency planktonic modifications are well documented in the Sicily Channel and Alboran Sea and highlight the occurrence of different steps within a single stadial (cold phase)/interstadial (warm phase) oscillation.The review of planktonic organisms in the marine sedimentary archive casts light on the uniqueness of the Mediterranean Sea, especially in terms of climatic/oceanographic/biological interaction and influence of different climatic systems on distinct areas. Further research is needed in the eastern Mediterranean Sea where results are obscured by low-resolution sedimentary records and by a strong focus on sapropel deposition dynamics.
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Tan, Zhenlin, Wenting Wang, Jiaxin He, Yike Zhang, Vicente Rodriguez-Gomez, Jiaxin Han, Zhaozhou Li e Xiaohu Yang. "The Mass and Redshift Dependence of Halo Star Clustering". Astrophysical Journal 976, n.º 1 (1 de novembro de 2024): 19. http://dx.doi.org/10.3847/1538-4357/ad834a.
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Abstract We adopt the two-point correlation function (2PCF) as a statistical tool to quantify the spatial clustering of halo stars for galaxy systems spanning a wide range in host halo virial mass ( 11.25 < log 10 M 200 c / M ⊙ < 15 ) and redshifts (0 < z < 1.5) from the IllustrisTNG simulations. Consistent with a previous study, we identify clear correlations between the strength of the 2PCF signals and galaxy formation redshifts, but over a much wider mass range. We find that such correlations are slightly stronger at higher redshifts and get weakened with the increase of host halo mass. We demonstrate that the spatial clustering of halo stars is affected by two factors: (1) the clustering gets gradually weakened as time passes (phase mixing); (2) newly accreted stars at more recent times would increase the clustering. For more massive galaxy systems, they assemble late, and the newly accreted stars would increase the clustering. The late assembly of massive systems may also help to explain the weaker correlations between the 2PCF signals and the galaxy formation redshifts in massive halos, as their 2PCFs are affected more by recently accreted stars, while formation redshift characterizes mass accretion on a much longer timescale. We find that the orbits of satellite galaxies in more massive halos maintain larger radial anisotropy, reflecting the more active accretion state of their hosts while also contributing to their stronger mass loss rates.
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Wang, Xinyuan, Yongtao Shui, Chaozheng Wang, Dezheng Yin e Hongjuan Ji. "Analysis of the influence of clearance on bending stiffness of space deployable mechanism in the locked state". Journal of Physics: Conference Series 2419, n.º 1 (1 de janeiro de 2023): 012014. http://dx.doi.org/10.1088/1742-6596/2419/1/012014.
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Abstract The future space station, which can simulate the gravity environment by rotation, has attracted the attention of scholars in recent years. It is considered a feasible scheme to fold the mechanism on the ground and assemble it into an artificial gravity ring after entering orbit. The deployable mechanism used to attach the space station is required to be large-scale and sufficiently high stiffness after deployment to ensure the safety and accuracy of the payload. However, the clearance will significantly reduce the stiffness of the mechanism, which is in the locked state. In this paper, the deployable mechanism with enhanced bending and torsion resistance configuration will be taken as the research object. First, based on the classical hinge stiffness model, the hinge equivalent model and the sliding joint equivalent model are proposed. Then, the finite element model based on equivalent stiffness is analyzed, and the effectiveness of the finite element model is verified by comparing the experimental results. Finally, the finite element model was used to analyze the influence of the clearance of the pin hole, the clearance of the sliding fit, and the position of the clearance on the bending stiffness of the deployable mechanism. The results show that the clearance greatly reduces the stiffness of the mechanism under small loads and weakens the bearing performance of components. At the same time, the position of the clearance should be taken seriously in the mechanism design.
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Nesbitt, Sterling J., John M. Zawiskie e Robert M. Dawley. "The osteology and phylogenetic position of the loricatan (Archosauria: Pseudosuchia) Heptasuchus clarki, from the ?Mid-Upper Triassic, southeastern Big Horn Mountains, Central Wyoming (USA)". PeerJ 8 (27 de outubro de 2020): e10101. http://dx.doi.org/10.7717/peerj.10101.
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Loricatan pseudosuchians (known as “rauisuchians”) typically consist of poorly understood fragmentary remains known worldwide from the Middle Triassic to the end of the Triassic Period. Renewed interest and the discovery of more complete specimens recently revolutionized our understanding of the relationships of archosaurs, the origin of Crocodylomorpha, and the paleobiology of these animals. However, there are still few loricatans known from the Middle to early portion of the Late Triassic and the forms that occur during this time are largely known from southern Pangea or Europe. Heptasuchus clarki was the first formally recognized North American “rauisuchian” and was collected from a poorly sampled and disparately fossiliferous sequence of Triassic strata in North America. Exposed along the trend of the Casper Arch flanking the southeastern Big Horn Mountains, the type locality of Heptasuchus clarki occurs within a sequence of red beds above the Alcova Limestone and Crow Mountain formations within the Chugwater Group. The age of the type locality is poorly constrained to the Middle—early Late Triassic and is likely similar to or just older than that of the Popo Agie Formation assemblage from the western portion of Wyoming. The holotype consists of associated cranial elements found in situ, and the referred specimens consist of crania and postcrania. Thus, about 30% of the osteology of the taxon is preserved. All of the pseudosuchian elements collected at the locality appear to belong to Heptasuchus clarki and the taxon is not a chimera as previously hypothesized. Heptasuchus clarki is distinct from all other archosaurs by the presence of large, posteriorly directed flanges on the parabasisphenoid and a distinct, orbit-overhanging postfrontal. Our phylogenetic hypothesis posits a sister-taxon relationship between Heptasuchus clarki and the Ladinian-aged Batrachotomus kupferzellensis from current-day Germany within Loricata. These two taxa share a number of apomorphies from across the skull and their phylogenetic position further supports ‘rauisuchian’ paraphyly. A minimum of three individuals of Heptasuchus are present at the type locality suggesting that a group of individuals died together, similar to other aggregations of loricatans (e.g., Heptasuchus, Batrachotomus, Decuriasuchus, Postosuchus).
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Vaniman, David, Steve Chipera, Elizabeth Rampe, Thomas Bristow, David Blake, Johannes Meusburger, Tanya Peretyazhko et al. "Gypsum on Mars: A Detailed View at Gale Crater". Minerals 14, n.º 8 (12 de agosto de 2024): 815. http://dx.doi.org/10.3390/min14080815.
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Gypsum is a common mineral at Gale crater on Mars, currently being explored by the Mars Science Laboratory (MSL) rover, Curiosity. In this paper, we summarize the associations of gypsum with other sulfate minerals (bassanite, anhydrite, jarosite, starkeyite, and kieserite) from the lowest levels of the crater’s northern moat zone (Aeolis Palus) up through ~0.8 km of the stratigraphic section in the lower slopes of the sedimentary mound developed around the central peak, Aeolis Mons (informally, Mount Sharp). The analysis is based on results from the CheMin X-ray diffraction instrument on Curiosity, supplemented with information from the rover’s versatile instrument suite. Gypsum does not occur with the same frequency as less hydrous Ca-sulfates, likely, in most cases, because of its dehydration to bassanite and possibly to anhydrite. All three of these Ca-sulfate phases often occur together and, along with other sulfates, in mixed assemblages that are evidence of limited equilibration on a cold, dry planet. In almost all samples, at least one of the Ca-sulfate minerals is present, except for a very limited interval where jarosite is the major sulfate mineral, with the implication of more acidic groundwater at a much later time in Gale crater’s history. Although observations from orbit reveal a sulfate-rich surface, currently active dark basaltic dunes at Gale crater have only small amounts of a single sulfate mineral, anhydrite. Gale crater has provided the most complete mineralogical analysis of a site on Mars so far, but the data in hand show that Gale crater mineralogy is not a blueprint with planet-wide application. The concurrent study of Jezero crater by the Mars 2020 mission and comparisons to what is believed to be the most extensive deposit of gypsum on Mars, in the dune fields at the north polar ice cap, show significant diversity. Unraveling the stories of gypsum and other sulfates on Mars is just beginning.
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O’Shea, Mark, Allen Allison e Hinrich Kaiser. "The taxonomic history of the enigmatic Papuan snake genus Toxicocalamus (Elapidae: Hydrophiinae), with the description of a new species from the Managalas Plateau of Oro Province, Papua New Guinea, and a revised dichotomous key". Amphibia-Reptilia 39, n.º 4 (2018): 403–33. http://dx.doi.org/10.1163/15685381-20181052.
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Abstract We trace the taxonomic history of Toxicocalamus, a poorly known genus of primarily vermivorous snakes found only in New Guinea and associated island archipelagos. With only a relatively limited number of specimens to examine, and the distribution of those specimens across many natural history collections, it has been a difficult task to assemble a complete taxonomic assessment of this group. As a consequence, research on these snakes has undergone a series of fits and starts, and we here present the first comprehensive chronology of the genus, beginning with its original description by George Albert Boulenger in 1896. We also describe a new species from the northern versant of the Owen Stanley Range, Oro Province, Papua New Guinea, and we present a series of comparisons that include heretofore underused characteristics, including those of unusual scale patterns, skull details, and tail tip morphology. Defined by the smallest holotype in the genus, the new species is easily differentiated from all other Toxicocalamus by a combination of the following eidonomic characters: fused prefrontal-internasal scute; single preocular, separate, not fused with prefrontal; minute circular, counter-sunk naris in the centre of a large, undivided, nasal scute; paired postoculars; single anterior temporal and paired posterior temporals; six supralabials, with 3rd and 4th supralabial contacting the orbit; dorsal scales in 15-15-15 rows; 235 ventral scales, 35 paired subcaudal scales; paired cloacal scales preceded by paired precloacal scales; and a short, laterally slightly compressed, ‘Ultrocalamus-type’ tail, terminating in a short conical scale. Differences from congeners in skull morphology include a reduced anterior extent of the parasphenoid, termination of the palatine tooth row at the anterior level of the parasphenoid, extent and shape of the premaxilla, shape and size of the prootics, extent and shape of the exoccipitals and occipital condyles, and features of the atlas-axis complex. This is the fifteenth species in the genus Toxicocalamus.
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Nazarova, T., e T. Rudych. "THE POPULATION OF OLBIA IN THE FIRST CENTURIES AD BASED ON THE MATERIALS OF ANTHROPOLOGY". Archaeology and Early History of Ukraine 53, n.º 4 (12 de setembro de 2024): 163–77. https://doi.org/10.37445/adiu.2024.04.11.
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Anthropological materials date from the Greco-Roman period of Olbia (1st—3rd centuries AD). Most of the finds can be dated to the 1st—2nd centuries AD, there are the assemblages with a narrower dating — the 2nd century. The main part of the series consists of bone remains from the western part of the Olbia necropolis where, according to the researchers, wealthy people were buried. Several skeletons from the northern part of the Olvian necropolis were involved in analysis. The material comes from the burial structures of different types: earthen crypts, regular graves, niche graves. The material from earthen crypts which, most likely, were the family tombs is dominated in the series. The total series of male skulls is characterized by a long, narrow, mid-height cranium, which is dolichocranial in shape. The forehead is medium wide, the angle of inclination of the frontal bone is medium. The face is of medium height, narrow in absolute dimensions. According to the upper face index, it falls into the mesen category, but with a lepton tendency. The horizontal profiling of the face is sharp. The face is orthognathic. The orbits are medium in size and mesoconch in the orbital index. The nose is medium high, narrow. The bones of the nose protrude strongly, the bridge of the nose is high. The female series in the average appearance is characterized by a long, medium-wide skull. Its height is on the border of medium and significant values. The skull is mesocranial in shape. The frontal bone is medium wide, the angle of inclination belongs to the medium category. The face is medium high, medium wide, according to the index finger is mesen. Its horizontal profiling is sharp. The face is orthognathic. The orbits are medium-high, serose-wide, they are mesoconch-shaped according to the index. The nose is medium high, narrow. The bones of the nose protrude strongly. The bridge of the nose is high. Men’s and women’s series have been considered in the circle of chronologically close series of Europe. According to the results of intergroup analysis of the population, the male series of the first centuries AD from Olbia shows the closest statistical similarity to the Chersonesus series of the 1st—4th centuries AD. The male population of Olbia and Chersonesus show the maximum distance of the inhabitants of Northern Pontic antique cities from the Scythian and Sarmatian series. During the Roman Age Olbia and Chersonesus were in the zone of Roman influence, and Roman legions were periodically stationed there. Perhaps at that time there was an influx of immigrants from the Western Pontic region, which was reflected to a greater extent in the composition of the male part of the inhabitants of both Olbia and Chersonesus. Infiltration of Iranian-speaking people into the population of these cities, if it took place indeed, was not significant. Iranian influences on the formation of the population in the anthropological material are well recorded in the materials from the Bosporan cities. The total female series from Roman Olbia demonstrates the morphological and statistical similarity, first of all, with groups from the Late Scythian hill-forts of the Lower Dnieper: Zolota Balka, Mykolaivka-Kozatska (materials of the 2nd century BC — 2nd century AD), series from several Late Scythian burial grounds of the Crimea — Belyaus and Scythian Neapolis (Eastern burial ground). Among the Northern Pontic antique cities this series is statistically and morphologically closest to the sample from Chersonesus. Most likely, the female population of Roman Olbia and the Lower Dnieper Late Scythian hill-forts had a large extent common genetic basis. It is possible that during hard times for Olbia and the region there was a periodic outflow of population from Olbia to the hillforts or opposite. The population of the individual Late Scythian groups of the Crimea, as well as Late Scythian sites of the Lower Dnieper, was formed primarily from two components, Scythian and Hellenic. In our series from the necropolis of Olbia, deformed skulls are not recorded, and the Olbian groups are statistically very distant from the Early, Middle, and Late Sarmatians.