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"Flying machines."
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Planes
\"From early flight through jumbo jets, this board book, jam packed with more than 30 flying machines, will soar into the hands of your little ones.\"--Provided by publisher.
Book
A four-dimensional cousin of the Segre cubic
This note is devoted to a special Fano fourfold defined by a four-dimensional space of skew-symmetric forms in five variables. This fourfold appears to be closely related with the classical Segre cubic and its Cremona-Richmond configuration of planes. Among other exceptional properties, it is infinitesimally rigid and has Picard number six. We show how to construct it by blow-up and contraction, starting from a configuration of five planes in a four-dimensional quadric, compatibly with the symmetry group [S.sub.5]. From this construction, we are able to describe the Chow ring explicitly. Keywords: Fano manifold, Segre cubic, prehomogeneous space, small resolution, Grassmannian, rigidity, del Pezzo surface.
Journal Article
Flying machines
Provides information about flying machines throughout history and explains the science of flight and aerodynamics, in a book that includes five models for balsa wood and paper planes.
Book
Cloud chaser
Emery spends the summer building a flying machine with a new neighbor, an old man named Leon.
Book
Ship- and aircraft-based XCH.sub.4 over oceans as a new tool for satellite validation
Satellite-based estimations of dry-air column-averaged mixing ratios of methane (XCH.sub.4) contribute to a better understanding of changes in CH.sub.4 emission sources and variations in its atmospheric growth rates. High accuracy of the satellite measurements is required, and therefore, extensive validation is performed, mainly against the Total Carbon Column Observing Network (TCCON). However, validation opportunities at open-ocean areas outside the coastal regions are sparse. We propose a new approach to assess the accuracy of satellite-derived XCH.sub.4 trends and variations. We combine various ship and aircraft observations with the help of atmospheric chemistry models, mainly used for the stratospheric column, to derive observation-based XCH.sub.4 (obs. XCH.sub.4). Based on our previously developed approach for the application to XCO.sub.2, we investigated three different advancements, from a simple approach to more elaborate approaches (approaches 1, 2, and 3), to account for the higher tropospheric and stratospheric variability in CH.sub.4 as compared to CO.sub.2 . Between 2014 and 2018, at 20-40° N of the western Pacific, we discuss the uncertainties in the approaches and the derived obs. XCH.sub.4 within 10° by 20° latitude-longitude boxes. Uncertainties were 22 ppb (parts per billion) for approach 1, 20 ppb for approach 2, and 16 ppb for approach 3. We analyzed the consistency with the nearest TCCON stations and found agreement of approach 3 with Saga of 1±12 ppb and -1±11 ppb with Tsukuba for the northern and southern latitude box, respectively. Furthermore, we discuss the impact of the modeled stratospheric column on the derived obs. XCH.sub.4 by applying three different models in our approaches. Depending on the models, the difference can be more than 12 ppb (0.6 %), showing the importance for the appropriate choice. We show that our obs. XCH.sub.4 dataset accurately captures seasonal variations in CH.sub.4 over the ocean. Using different retrievals of the Greenhouse Gases Observing Satellite (GOSAT) from the National Institute for Environmental Studies (NIES), the RemoTeC full-physics retrieval operated at the Netherlands Institute for Space Research (SRON), and the full-physics retrieval of the University of Leicester (UoL-OCFP), we demonstrate the applicability of the dataset for satellite evaluation. The comparison with results of approach 3 revealed that NIES showed a difference of -0.04 ± 13 ppb and strong scatter at 20-30° N, while RemoTeC and OCFP have a rather systematic negative bias of -12.1 ± 8.1 and -10.3 ± 9.6 ppb. Our new approach to derive XCH.sub.4 reference datasets over the ocean can contribute to the validation of existing and upcoming satellite missions in future.
Journal Article
Probing local magnetic states in the van der Waals ferromagnet Fe.sub.4GeTe.sub.2 by a vector-field magnetic force microscope
In this study, we systematically investigate the magnetic domain structure of Fe.sub.4GeTe.sub.2 single crystals, employing a cryogenic vector-field magnetic force microscope to probe its temperature and magnetic field dependencies. The material undergoes a spin-reversal transition at around 110 K, leading to a gradual magnetization reorientation from in-plane to out-of-plane as temperature decreases. Our observations reveal a complex domain structure featuring striped shapes enclosed by wavy closed loops, exhibiting limited sensitivity to temperature variations without an external magnetic field. When subject to an out-of-plane magnetic field, the domain structure transforms into micrometric elongated striped shapes, gradually evolving into a more irregular pattern. Conversely, in in-plane measurements, the system displays an inhomogeneous distribution of micrometric bubble-like domains, progressively interconnecting into striped shapes. These distinctive responses are attributed to the interplay between small uniaxial and shape anisotropies within the material. Our findings contribute to a deeper understanding of the magnetic domain dynamics in van der Waals ferromagnetic materials, laying the groundwork for further investigations and potential applications in electronic devices.
Journal Article