344 research outputs found
Aerodynamic Interference on Finned Slender Body
Aerodynamic interference can occur between high-speed slender bodies when in close proximity. A complex flowfield develops where shock and expansion waves from a generator body impinge upon the adjacent receiver body and modify its aerodynamic characteristics in comparison to the isolated case. The aim of this research is to quantify and understand the multibody interference effects that arise between a finned slender body and a second disturbance generator body. A parametric wind tunnel study was performed in which the effects of the receiver incidence and axial stagger were considered. Computational fluid dynamic simulations showed good agreement with the measurements, and these were used in the interpretation of the experimental results. The overall interference loads for a given multibody configuration were found to be a complex function of the pressure footprints from the compression and expansion waves emanating from the generator body as well as the flow pitch induced by the generator shockwave. These induced interference loads change sign as the shock impingement location moves aft over the receiver and in some cases cause the receiver body to become statically unstable. Overall, the observed interference effects can modify the subsequent body trajectories and may increase the likelihood of a collision
Azaphosphatrane Organocatalysts in Confined Space: Cage Effect in CO2 Conversion
International audienceThe endohedral functionalization of a molecular cage by an azaphosphatrane unit has allowed for the creation of highly engineered catalytic cavities for efficient conversion of CO2 into cyclic carbonates. Strong structure/activity/stability correlations have been demonstrated by careful adjustment of the size, shape, and electronic properties of the hemicryptophane host
Comparison of Magnetic Field Structures on Different Scales in and around the Filamentary Dark Cloud GF 9
New visible polarization data combined with existing IR and FIR polarization
data are used to study how the magnetic field threading the filamentary
molecular cloud GF 9 connects to larger structures in its general environment.
We find that when both visible and NIR polarization data are plotted as a
function of extinction, there is no evidence for a plateau or a saturation
effect in the polarization at Av ~ 1.3 as seen in dark clouds in Taurus. This
lack of saturation effect suggests that even in the denser parts of GF 9 we are
still probing the magnetic field. The visible polarization is smooth and has a
well-defined orientation. The IR data are also well defined but with a
different direction, and the FIR data in the core region are well defined and
with yet another direction, but are randomly distributed in the filament
region. On the scale of a few times the mean radial dimension of the molecular
cloud, it is as if the magnetic field were `blind' to the spatial distribution
of the filaments while on smaller scales within the cloud, in the core region
near the IRAS point source PSC 20503+6006, polarimetry shows a rotation of the
magnetic field lines in these denser phases. Hence, in spite of the fact that
the spatial resolution is not the same in the visible/NIR and in the FIR data,
all the data put together indicate that the field direction changes with the
spatial scale. Finally, the Chandrasekhar and Fermi method is used to evaluate
the magnetic field strength, indicating that the core region is approximately
magnetically critical. A global interpretation of the results is that in the
core region an original poloidal field could have been twisted by a rotating
elongated (core+envelope) structure. There is no evidence for turbulence and
ambipolar diffusion does not seem to be effective at the present time.Comment: 33 pages, 6 tables, 8 figures, Accepted by Ap
Bioengineered embryoids mimic post-implantation development in vitro.
The difficulty of studying post-implantation development in mammals has sparked a flurry of activity to develop in vitro models, termed embryoids, based on self-organizing pluripotent stem cells. Previous approaches to derive embryoids either lack the physiological morphology and signaling interactions, or are unconducive to model post-gastrulation development. Here, we report a bioengineering-inspired approach aimed at addressing this gap. We employ a high-throughput cell aggregation approach to simultaneously coax mouse embryonic stem cells into hundreds of uniform epiblast-like aggregates in a solid matrix-free manner. When co-cultured with mouse trophoblast stem cell aggregates, the resulting hybrid structures initiate gastrulation-like events and undergo axial morphogenesis to yield structures, termed EpiTS embryoids, with a pronounced anterior development, including brain-like regions. We identify the presence of an epithelium in EPI aggregates as the major determinant for the axial morphogenesis and anterior development seen in EpiTS embryoids. Our results demonstrate the potential of EpiTS embryoids to study peri-gastrulation development in vitro
Pregnancy outcomes in anti-NMDA receptor encephalitis: Case series
To report the effects of anti-NMDA receptor (NMDAR) encephalitis in pregnant patients and their babies.We studied a retrospective cohort of patients who developed anti-NMDAR encephalitis during pregnancy or became pregnant while recovering from the encephalitis. In addition, we reviewed the English literature between 2010 and 2019 related to this topic.We studied 11 patients; 6 developed anti-NMDAR encephalitis during pregnancy, and 5 became pregnant while recovering. There were no obstetrical complications, but 6 (55%) babies were premature. Ten newborns were healthy, and 1 (9%) developed transient respiratory distress. Nine infants had assessable follow-up (median 18 months; range, 7-96 months), and all showed normal development. We identified 21 cases in the English literature. Obstetrical complications occurred in 7 (33%) pregnancies. Two patients died of septic shock (1 baby successfully delivered), another 2 had miscarriages, and in 2, the pregnancy was terminated. Sixteen babies (76%) were delivered, 9 (56%) premature. At birth, 13/16 (81%) newborns were healthy, 2/16 (13%) had transient neurologic or respiratory symptoms, and 1 (6%) died of brain edema. Follow-up (median 12 months; range, 6-36 months) was reported for 8 children: 7 (88%) showed normal development and behavior, and 1 (13%) cortical dysplasia. Immunotherapy was used during pregnancy in 7 (64%) of our patients and 18 (86%) of the reported cases, including rituximab in 4 cases, without adverse effects.Patients who develop anti-NMDAR encephalitis during pregnancy or become pregnant during recovery often have obstetrical complications, but most of the newborns are healthy and appear to have normal development.Copyright © 2020 The Author(s). Published by Wolters Kluwer Health, Inc. on behalf of the American Academy of Neurology
Paraneoplastic cerebellar ataxia and antibodies to metabotropic glutamate receptor 2
To report the presence of a new neuronal surface antibody against the metabotropic glutamate receptor 2 antibody (mGluR2-Ab) in 2 patients with paraneoplastic cerebellar ataxia.mGluR2-Abs were initially characterized by immunohistochemistry on the rat brain and confirmed by immunofluorescence on HEK293 cells transfected with mGluR2. Additional studies included analysis of potential cross-reactivity with other mGluRs, expression of mGluR2 in patients' tumors, and the effects of mGluR2-Abs on cultures of rat hippocampal neurons.Patient 1 was a 78-year-old woman with progressive cerebellar ataxia with an initial relapsing-remitting course who developed a small-cell tumor of unknown origin. Patient 2 was a 3-year-old girl who presented a steroid-responsive acute cerebellitis preceding the diagnosis of an alveolar rhabdomyosarcoma. Patients' serum and CSF showed a characteristic immunostaining of the hippocampus and cerebellum in rat brain sections and immunolabeled the cell surface of live rat hippocampal neurons. HEK293 cells transfected with mGluR1, 2, 3, and 5 confirmed that patients' antibodies only recognized mGluR2. mGluR2-Abs were not detected in 160 controls, 120 with paraneoplastic, autoimmune, or degenerative ataxias, and 40 with autoimmune encephalitis and antibodies against mGluR5 or unknown antigens. Expression of mGluR2 in tumors was confirmed by immunohistochemistry using a commercial mGluR2-Ab. Incubation of live rat hippocampal neurons with CSF of patient 2 did not modify the density of surface mGluR2 clusters.mGluR2-Abs are a novel biomarker of paraneoplastic cerebellar ataxia. The potential pathogenic effect of the antibodies is not mediated by downregulation or internalization of neuronal surface mGluR2.Copyright © 2019 The Author(s). Published by Wolters Kluwer Health, Inc. on behalf of the American Academy of Neurology
Analyse rĂ©trospective de lâadaptation Ă la sĂ©cheresse chez le douglas
For a number of years in certain regions of France the Douglas-fir trees (Pseudotsuga menziesii [Mirb.] Franco) have presented symptoms of withering which have been attributed to drought. Our results show that the hydraulic function of the wood plays a part in the resistance of the Douglas-fir to dry conditions. Narrower cellular conduits, and therefore a greater wood density, contribute to the survival of trees confronted with a period of a marked water deficit. This idea is confirmed by the existence of significant relationships between wood density and hydraulic properties of wood in which the raw sap circulates, and also by the relationships found between the ecological preferences of specimens in their area of origin and the density of their wood in regions of France where they have been introduced. Those coming from dry regions have a tendency to develop wood with characteristics similar to that of trees which have survived drought. While the relationship between wood density and survival has been demonstrated, the differences in the nature of this relationship between different sites show that the mechanisms involved are complex and to a large extent still not understood.Le douglas (Pseudotsuga menziesii [Mirb.] Franco) prĂ©sente depuis quelques annĂ©es dans certaines rĂ©gions de France des symptĂŽmes de dĂ©pĂ©rissement que nous attribuons Ă la sĂ©cheresse. Nos rĂ©sultats montrent que le fonctionnement hydraulique du bois joue un rĂŽle dans la rĂ©sistance du douglas Ă la sĂ©cheresse: des conduits cellulaires plus Ă©troits, c'est-Ă -dire une densitĂ© plus Ă©levĂ©e, favoriseraient la survie d'arbres confrontĂ©s Ă un Ă©pisode de dĂ©ficit en eau marquĂ©. Cette idĂ©e est renforcĂ©e par l'existence de relations significatives entre densitĂ© du bois et propriĂ©tĂ©s hydrauliques du bois dans lequel circule la sĂšve brute, et par les relations trouvĂ©es entre prĂ©fĂ©rences Ă©cologiques de provenances dans leur aire d'origine et densitĂ© de leur bois dans les rĂ©gions d'introduction en France: les provenances issues de rĂ©gions sĂšches ont tendance Ă dĂ©velopper un bois possĂ©dant des caractĂ©ristiques proches de celles des survivants Ă la sĂ©cheresse. Si la relation densitĂ© du boisâsurvie a bien Ă©tĂ© mise en Ă©vidence, des diffĂ©rences entre sites dans la nature de cette relation montrent que les mĂ©canismes impliquĂ©s sont complexes et encore largement incompris.Seit einigen Jahren zeigt die Douglasie (Pseudotsuga menziesii [Mirb.] Franco) in verschiedenen Regionen Frankreichs Absterbeerscheinungen, die wir der Trockenheit zuschreiben. Unsere Untersuchungen belegen, dass das Leitsystem des Holzes bei der Resistenz der Douglasie gegenĂŒber Trockenheit eine Rolle spielt: Engere GefĂ€sse, d.h. eine höhere Holzdichte, wĂŒrden das Ăberleben der BĂ€ume in Perioden mit ausgeprĂ€gtem Wassermangel begĂŒnstigen. Diese Idee wird durch signifikante ZusammenhĂ€nge zwischen der Holzdichte und den hydraulischen Eigenschaften des Splintholzes sowie durch die gefundenen Beziehungen zwischen den ökologischen Vorlieben der Provenienzen in ihrer Herkunftsregion und der Dichte ihres Holzes in den Regionen Frankreichs, in denen sie eingebracht wurden, belegt: HerkĂŒnfte aus trockenen Regionen haben die Tendenz, ein Holz zu entwickeln, das Ă€hnliche Eigenschaften zeigt wie dasjenige von BĂ€umen, die Trockenperioden ĂŒberlebten. Die Beziehung HolzdichteâĂberleben konnte zwar klar herausgestellt werden, jedoch zeigen die Unterschiede zwischen den Standorten, dass die Wirkungsmechanismen komplex sind und grösstenteils noch nicht verstanden werden.EstaciĂłn Experimental Agropecuaria BarilocheFil: Rozenberg, Philippe. INRA. Biologie intĂ©grĂ©e pour la valorisation de la diversitĂ© des arbres et de la forĂȘt; FranciaFil: Sergent, Anne Sophie. Instituto Nacional de TecnologĂa Agropecuaria (INTA). EstaciĂłn Experimental Agropecuaria Bariloche. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Instituto de Investigaciones Forestales y Agropecuarias Bariloche; ArgentinaFil: Dalla Salda, Guillermina. Instituto Nacional de TecnologĂa Agropecuaria (INTA). EstaciĂłn Experimental Agropecuaria Bariloche. Ărea de Recursos Forestales. Grupo de EcologĂa Forestal; ArgentinaFil: Martinez Meier, Alejandro. Instituto Nacional de TecnologĂa Agropecuaria (INTA). EstaciĂłn Experimental Agropecuaria Bariloche. Ărea de Recursos Forestales. Grupo de EcologĂa Forestal; ArgentinaFil: Marin, Sara. INRA. Biologie intĂ©grĂ©e pour la valorisation de la diversitĂ© des arbres et de la forĂȘt; FranciaFil: Ruiz Diaz, Manuela. INRA. Biologie intĂ©grĂ©e pour la valorisation de la diversitĂ© des arbres et de la forĂȘt; FranciaFil: Bastien, Jean-Charles. INRA. Biologie intĂ©grĂ©e pour la valorisation de la diversitĂ© des arbres et de la forĂȘt; FranciaFil: Sanchez, Leopoldo. INRA. Biologie intĂ©grĂ©e pour la valorisation de la diversitĂ© des arbres et de la forĂȘt; FranciaFil: BrĂ©da, Nathalie. INRA. Biologie intĂ©grĂ©e pour la valorisation de la diversitĂ© des arbres et de la forĂȘt; Franci
Pressure-induced dimerization and valence bond crystal formation in the Kitaev-Heisenberg magnet alpha-RuCl3
Magnetization and high-resolution x-ray diffraction measurements of the
Kitaev-Heisenberg material alpha-RuCl3 reveal a pressure-induced
crystallographic and magnetic phase transition at a hydrostatic pressure of
p=0.2 GPa. This structural transition into a triclinic phase is characterized
by a very strong dimerization of the Ru-Ru bonds, accompanied by a collapse of
the magnetic susceptibility. Ab initio quantum-chemistry calculations disclose
a pressure-induced enhancement of the direct 4d-4d bonding on particular Ru-Ru
links, causing a sharp increase of the antiferromagnetic exchange interactions.
These combined experimental and computational data show that the Kitaev spin
liquid phase in alpha-RuCl3 strongly competes with the crystallization of spin
singlets into a valence bond solid
Learning to control a BMI-driven wheelchair for people with severe tetraplegia
Mind-controlled wheelchairs are an intriguing assistive mobility solution applicable in complete paralysis. Despite technical progress in brain-machine interface (BMI) technology, its translation remains elusive. The primary objective of this study is to probe the hypothesis that BMI skill acquisition by end-users is fundamental to control a non-invasive brain-actuated intelligent wheelchair in real-world settings. Here, we show that three tetraplegic spinal cord injury users could be trained to operate a non-invasive, self-paced thought-controlled wheelchair and execute complex navigation tasks. However, only the two users exhibiting increasing decoding performance and feature discriminancy, as well as significant neuroplasticity changes and improved BMI command latency, achieved high navigation performance. Additionally, we show that dexterous, continuous control of robots is possible through low-degree of freedom, discrete and uncertain control channels like a motor imagery BMI, by blending human and artificial intelligence through shared-control methodologies. We posit that subject learning and shared-control are the key-components paving the way for translational non-invasive BMI
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