87 research outputs found
Enhanced magnetocaloric effect in frustrated magnetic molecules with icosahedral symmetry
We investigate the magnetocaloric properties of certain antiferromagnetic
spin systems that have already been or very likely can be synthesized as
magnetic molecules. It turns out that the special geometric frustration which
is present in antiferromagnets that consist of corner-sharing triangles leads
to an enhanced magnetocaloric effect with high cooling rates in the vicinity of
the saturation field. These findings are compared with the behavior of a simple
unfrustrated spin ring as well as with the properties of the icosahedron. To
our surprise, also for the icosahedron large cooling rates can be achieved but
due to a different kind of geometric frustration.Comment: 5 pages, 8 figures, more information at
http://obelix.physik.uni-osnabrueck.de/~schnack
Novel Simulation-Inspired Roller Spreading Strategies for Fine and Highly Cohesive Metal Powders
When fine powders are to be used in powder bed metal additive manufacturing
(AM), a roller is typically utilized for spreading. However, the cohesive
nature of fine metal powder still presents challenges, resulting in low density
and/or inconsistent layers under sub-standard spreading conditions. Here,
through computational parameter studies with an integrated discrete
element-finite element (DEM-FEM) framework, we explore roller-based strategies
that are predicted to achieve highly cohesive powder layers. The exemplary
feedstock is a Ti-6Al-4V 0-20 um powder, that is emulated using a
self-similarity approach based on experimental calibration. The computational
studies explore novel roller kinematics including counter-rotation as well as
angular and transverse oscillation applied to standard rigid rollers as well as
coated rollers with compliant or non-adhesive surfaces. The results indicate
that most of these approaches allow to successfully spread highly cohesive
powders with high packing fraction (between 50%-60% in a single layer) and
layer uniformity provided that the angular/oscillatory, relative to the
transverse velocity, as well as the surface friction of the roller are
sufficiently high. Critically, these spreading approaches are shown to be very
robust with respect to varying substrate conditions (simulated by means of a
decrease in surface energy), which are likely to occur in LBPF or BJ, where
substrate characteristics are the result of a complex multi-physics (i.e.,
powder melting or binder infiltration) process. In particular, the combination
of the identified roller kinematics with compliant surface coatings, which are
known to reduce the risk of tool damage and particle streaking in the layers,
is recommended for future experimental investigation
Adakite-like granitoids of Songkultau: A relic of juvenile Cambrian arc in Kyrgyz Tien Shan
The early Paleozoic Terskey Suture zone, located in the southern part of the Northern Tien Shan domain in Kyrgyzstan, comprises tectonic slivers of dismembered ophiolites and associated primitive volcanics and deep-marine sediments. In the Lake Songkul area, early-middle Cambrian pillow basalts are crosscut by the Songkultau intrusion of coarse-grained gneissose quartz diorites and tonalites with geochemical characteristics typical for high-SiO2 adakites (SiO2 ​> ​56 ​wt.%, Al2O3 ​> ​15 ​wt.%, Na2O ​> ​3.5 ​wt.% and high Sr/Y and La/Yb ratios). The Songkultau granitoids have positive initial εNd (+3.8 to +6.4) and εHf (+12.3 to +13.5) values indicating derivation from sources with MORB-like isotopic signature. Volcanic formations, surrounding the Songkultau intrusion, have geochemical affinities varying from ocean floor to island arc series. This rock assemblage is interpreted as a relic of an early-middle Cambrian primitive arc where the adakite-like granitoids were derived from partial melting of young and hot subducted oceanic crust. An age of 505 ​Ma, obtained for the Songkultau intrusion, shows that hot subduction under the Northern Tien Shan continued until middle Cambrian. The primitive arc complexes were obducted onto the Northern Tien Shan domain, where the Andean type continental magmatic arc developed in Cambrian and Ordovician. Formation of the Andean type arc was accompanied by uplift, erosion and deposition of coarse clastic sediments. A depositional age of ca. 470 Ma, obtained for the gravellites in the Lake Songkul area, is in agreement with the timing of deposition for lower Ordovician conglomerates elsewhere in the Northern Tien Shan, and corresponds to the main phase of the Andean type magmatism. The Songkultau adakites in association with surrounding ocean floor and island arc formations constitute a relic of a primitive Cambrian arc and represent a juvenile domain of substantial size identified so far within the predominantly crustal-derived terranes of Tien Shan. On a regional scale this primitive arc can be compared with juvenile Cambrian arcs of Kazakhstan, Gorny Altai and Mongolia.©2020 China University of Geosciences (Beijing) and Peking University. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/)
Spatial Mapping of Powder Layer Density for Metal Additive Manufacturing via X-ray Microscopy
Uniform powder spreading is a requisite for creating consistent, high-quality
components via powder bed additive manufacturing (AM), wherein layer density
and uniformity are complex functions of powder characteristics, spreading
kinematics, and mechanical boundary conditions. High spatial variation in
particle packing density, driven by the stochastic nature of the spreading
process, impedes optical interrogation of these layer attributes. Thus, we
present transmission X-ray imaging as a method for directly mapping the
effective depth of powder layers at process-relevant scale and resolution.
Specifically, we study layers of nominal 50-250 micrometer thickness, created
by spreading a selection of commercially obtained Ti-6Al-4V, 316 SS, and
Al-10Si-Mg powders into precision-depth templates. We find that powder layer
packing fraction may be predicted from a combination of the relative thickness
of the layer as compared to mean particle size, and flowability assessed by
macroscale powder angle of repose. Power spectral density analysis is
introduced as a tool for quantification of defect severity as a function of
morphology, and enables separate consideration of layer uniformity and
sparsity. Finally, spreading is studied using multi-layer templates, providing
insight into how particles interact with both previously deposited material and
abrupt changes in boundary condition. Experimental results are additionally
compared to a purpose-built discrete element method (DEM) powder spreading
simulation framework, clarifying the competing role of adhesive and
gravitational forces in layer uniformity and density, as well as particle
motion within the powder bed during spreading
Spatially Resolved Ultraviolet Spectroscopy of the Great Dimming of Betelgeuse
The bright supergiant, Betelgeuse (Alpha Orionis, HD 39801) experienced a
visual dimming during 2019 December and the first quarter of 2020 reaching an
historic minimum 2020 February 713. During 2019 September-November, prior to
the optical dimming event, the photosphere was expanding. At the same time,
spatially resolved ultraviolet spectra using the Hubble Space Telescope/Space
Telescope Imaging Spectrograph revealed a substantial increase in the
ultraviolet spectrum and Mg II line emission from the chromosphere over the
southern hemisphere of the star. Moreover, the temperature and electron density
inferred from the spectrum and C II diagnostics also increased in this
hemisphere. These changes happened prior to the Great Dimming Event. Variations
in the Mg II k-line profiles suggest material moved outwards in response to the
passage of a pulse or acoustic shock from 2019 September through 2019 November.
It appears that this extraordinary outflow of material from the star, likely
initiated by convective photospheric elements, was enhanced by the coincidence
with the outward motions in this phase of the 400 day pulsation cycle.
These ultraviolet observations appear to provide the connecting link between
the known large convective cells in the photosphere and the mass ejection event
that cooled to form the dust cloud in the southern hemisphere imaged in 2019
December, and led to the exceptional optical dimming of Betelgeuse in 2020
February.Comment: 11 pages, 8 figures, Astrophysical Journal, accepte
A broadly cross-reactive monoclonal antibody against hepatitis E virus capsid antigen
To generate a hepatitis E virus (HEV) genotype 3 (HEV-3)–specific monoclonal antibody (mAb), the Escherichia coli–expressed carboxy-terminal part of its capsid protein was used to immunise BALB/c mice. The immunisation resulted in the induction of HEV-specific antibodies of high titre. The mAb G117-AA4 of IgG1 isotype was obtained showing a strong reactivity with the homologous E. coli, but also yeast-expressed capsid protein of HEV-3. The mAb strongly cross-reacted with ratHEV capsid protein derivatives produced in both expression systems and weaker with an E. coli–expressed batHEV capsid protein fragment. In addition, the mAb reacted with capsid protein derivatives of genotypes HEV-2 and HEV-4 and common vole hepatitis E virus (cvHEV), produced by the cell-free synthesis in Chinese hamster ovary (CHO) and Spodoptera frugiperda (Sf21) cell lysates. Western blot and line blot reactivity of the mAb with capsid protein derivatives of HEV-1 to HEV-4, cvHEV, ratHEV and batHEV suggested a linear epitope. Use of truncated derivatives of ratHEV capsid protein in ELISA, Western blot, and a Pepscan analysis allowed to map the epitope within a partially surface-exposed region with the amino acid sequence LYTSV. The mAb was also shown to bind to human patient–derived HEV-3 from infected cell culture and to hare HEV-3 and camel HEV-7 capsid proteins from transfected cells by immunofluorescence assay. The novel mAb may serve as a useful tool for further investigations on the pathogenesis of HEV infections and might be used for diagnostic purposes.
Key points
• The antibody showed cross-reactivity with capsid proteins of different hepeviruses.
• The linear epitope of the antibody was mapped in a partially surface-exposed region.
• The antibody detected native HEV-3 antigen in infected mammalian cells
Uniformity of rotavirus strain nomenclature proposed by the Rotavirus Classification Working Group (RCWG)
In April 2008, a nucleotide-sequence-based, complete genome classification system was developed for group A rotaviruses (RVs). This system assigns a specific genotype to each of the 11 genome segments of a particular RV strain according to established nucleotide percent cutoff values. Using this approach, the genome of individual RV strains are given the complete descriptor of Gx-P[x]-Ix-Rx-Cx-Mx-Ax-Nx-Tx-Ex-Hx. The Rotavirus Classification Working Group (RCWG) was formed by scientists in the field to maintain, evaluate and develop the RV genotype classification system, in particular to aid in the designation of new genotypes. Since its conception, the group has ratified 51 new genotypes: as of April 2011, new genotypes for VP7 (G20-G27), VP4 (P[28]-P[35]), VP6 (I12-I16), VP1 (R5-R9), VP2 (C6-C9), VP3 (M7-M8), NSP1 (A15-A16), NSP2 (N6-N9), NSP3 (T8-T12), NSP4 (E12-E14) and NSP5/6 (H7-H11) have been defined for RV strains recovered from humans, cows, pigs, horses, mice, South American camelids (guanaco), chickens, turkeys, pheasants, bats and a sugar glider. With increasing numbers of complete RV genome sequences becoming available, a standardized RV strain nomenclature system is needed, and the RCWG proposes that individual RV strains are named as follows: RV group/species of origin/country of identification/common name/year of identification/G- and P-type. In collaboration with the National Center for Biotechnology Information (NCBI), the RCWG is also working on developing a RV-specific resource for the deposition of nucleotide sequences. This resource will provide useful information regarding RV strains, including, but not limited to, the individual gene genotypes and epidemiological and clinical information. Together, the proposed nomenclature system and the NCBI RV resource will offer highly useful tools for investigators to search for, retrieve, and analyze the ever-growing volume of RV genomic data.Fil: Matthijnssens, Jelle. Katholikie Universiteit Leuven; BélgicaFil: Ciarlet, Max. Novartis Vaccines & Diagnostics; Estados UnidosFil: McDonald, Sarah M.. National Institute Of Allegry & Infectious Diseases (niaid) ; National Institutes Of Health;Fil: Attoui, Houssam. Animal Health Trust.; Reino UnidoFil: Bányai, Krisztián. Hungarian Academy of Sciences; HungrÃaFil: Brister, J. Rodney. National Library Of Medicine; Estados UnidosFil: Buesa, Javier. Universidad de Valencia; EspañaFil: Esona, Mathew D.. Centers for Disease Control and Prevention; Estados UnidosFil: Estes, Mary K.. Baylor College of Medicine; Estados UnidosFil: Gentsch, Jon R.. Centers for Disease Control and Prevention; Estados UnidosFil: Iturriza Gómara, Miren. Health Protection Agency; Reino UnidoFil: Johne, Reimar. Federal Institute for Risk Assessment; AlemaniaFil: Kirkwood, Carl D.. Royal Children's Hospital; AustraliaFil: Martella, Vito. Università degli Studi di Bari; ItaliaFil: Mertens, Peter P. C.. Animal Health Trust.; Reino UnidoFil: Nakagomi, Osamu. Nagasaki University; JapónFil: Parreño, Gladys Viviana. Consejo Nacional de Investigaciones CientÃficas y Técnicas; Argentina. Instituto Nacional de TecnologÃa Agropecuaria. Centro de Investigación en Ciencias Veterinarias y Agronómicas. Instituto de VirologÃa; ArgentinaFil: Rahman, Mustafizur. International Centre For Diarrhoeal Disease Research; BangladeshFil: Ruggeri, Franco M.. Istituto Superiore Di Sanita; ItaliaFil: Saif, Linda J.. Ohio State University; Estados UnidosFil: Santos, Norma. Universidade Federal do Rio de Janeiro; BrasilFil: Steyer, Andrej. University of Ljubljan; EsloveniaFil: Taniguchi, Koki. Fujita Health University School of Medicine; JapónFil: Patton, John T.. National Institute Of Allegry & Infectious Diseases (niaid) ; National Institutes Of Health;Fil: Desselberger, Ulrich. University of Cambridge; Estados UnidosFil: van Ranst, Marc. Katholikie Universiteit Leuven; Bélgic
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