Muon diffusion and electronic magnetism in Y2_2Ti2_2O7_7

We report a $\mu$SR study in a Y$_2$Ti$_2$O$_7$ single crystal. We observe slow local field fluctuations at low temperature which become faster as the temperature is increased. Our analysis suggests that muon diffusion is present in this system and becomes small below 40 K and therefore incoherent. A surprisingly strong electronic magnetic signal is observed with features typical for muons thermally diffusing towards magnetic traps below $\approx 100$ K and released from them above this temperature. We attribute the traps to Ti$^{3+}$ defects in the diluted limit. Our observations are highly relevant to the persistent spin dynamics debate on $R_2$Ti$_2$O$_7$ pyrochlores and their crystal quality

Hierarchical Action Classification with Network Pruning

Research on human action classification has made significant progresses in the past few years. Most deep learning methods focus on improving performance by adding more network components. We propose, however, to better utilize auxiliary mechanisms, including hierarchical classification, network pruning, and skeleton-based preprocessing, to boost the model robustness and performance. We test the effectiveness of our method on four commonly used testing datasets: NTU RGB+D 60, NTU RGB+D 120, Northwestern-UCLA Multiview Action 3D, and UTD Multimodal Human Action Dataset. Our experiments show that our method can achieve either comparable or better performance on all four datasets. In particular, our method sets up a new baseline for NTU 120, the largest dataset among the four. We also analyze our method with extensive comparisons and ablation studies

A receptor-like kinase mutant with absent endodermal diffusion barrier displays selective nutrient homeostasis defects

We thank the Genomic Technologies Facility (GTF) and the Central Imaging Facility (CIF) of the University of Lausanne for expert technical support. We thank Valérie Dénervaud Tendon, Guillaume Germion, Deborah Mühlemann, and Kayo Konishi for technical assistance and John Danku and Véronique Vacchina for ICP-MS analysis. This work was funded by grants from the Swiss National Science Foundation (SNSF), the European Research Council (ERC) to NG and a Human Frontiers Science Program (HFSP) grant to JT and NG. GL and CM were supported by the Agropolis foundation (Rhizopolis) and the Agence Nationale de la Recherche (HydroRoot; ANR-11-BSV6-018). MB was supported by a EMBO long-term postdoctoral fellowship, JEMV by a Marie Curie IEF fellowship and TK by the Japan Society for the Promotion of Sciences (JSPS).Peer reviewedPublisher PD

Additive Manufacturing of Metallic Materials: A Review

In this review article, the latest developments of the four most common additive manufacturing methods for metallic materials are reviewed, including powder bed fusion, direct energy deposition, binder jetting, and sheet lamination. In addition to the process principles, the microstructures and mechanical properties of AM-fabricated parts are comprehensively compared and evaluated. Finally, several future research directions are suggested

Cell Biology of Cheating - Mechanisms of Chromosome Segregation During Female Meiosis

Karyotype, chromosome number and composition, is a basic characteristic of species and its changes are frequently associated with speciation. Karyotype conversion, from mostly telocentric (centromere terminal) to mostly metacentric (centromere internal), typically reflects fixation of Robertsonian (Rb) fusions, a common chromosomal rearrangement that joins two telocentric chromosomes at their centromeres to create one metacentric. Fixation of Rb fusions can be explained by meiotic drive: biased chromosome segregation during female meiosis. However, there is no mechanistic explanation of why fusions preferentially segregate to the egg in some populations, leading to fixation and karyotype change, while other populations preferentially eliminate the fusions and maintain a telocentric karyotype. Using laboratory models and wild mice, we show that differences in centromere strength predict the direction of drive. Stronger centromeres, with higher kinetochore protein levels and altered interactions with spindle microtubules, are preferentially retained in the egg. Rb fusions preferentially segregate to the polar body in laboratory mouse strains when the fusion centromeres are weaker than those of telocentrics. Conversely, fusion centromeres are stronger relative to telocentrics in natural house mouse populations that have changed karyotype by accumulating metacentric fusions. Preferential chromosome segregation is predicted to depend on spindle asymmetry. We show that meiosis I (MI) spindles are asymmetric, with more stable microtubules (MTs) oriented towards the cortex. Based on our observations we propose a model in which a signal from the cortex induces MT asymmetry. We exploit Rb fusions to study mechanisms of meiotic chromosome segregation when erroneous kinetochore-MT attachments are recognized and destabilized. Improper attachments typically lack tension between kinetochores and are positioned off-center on the spindle. Low tension is a widely accepted mechanism for recognizing errors, but whether chromosome position regulates MT attachments is unknown. We show that proximity to spindle poles destabilizes kinetochore-MTs, and that stable attachments are restored by inhibiting Aurora A kinase at spindle poles. During the correction of attachment errors, kinetochore MTs detach near spindle poles to allow formation of correct attachments. We propose that chromosome position on the spindle provides spatial cues for the fidelity of meiotic cell division

Elevated intracellular cAMP exacerbates vulnerability to oxidative stress in optic nerve head astrocytes.

Glaucoma is characterized by a progressive loss of retinal ganglion cells and their axons, but the underlying biological basis for the accompanying neurodegeneration is not known. Accumulating evidence indicates that structural and functional abnormalities of astrocytes within the optic nerve head (ONH) have a role. However, whether the activation of cyclic adenosine 3',5'-monophosphate (cAMP) signaling pathway is associated with astrocyte dysfunction in the ONH remains unknown. We report here that the cAMP/protein kinase A (PKA) pathway is critical to ONH astrocyte dysfunction, leading to caspase-3 activation and cell death via the AKT/Bim/Bax signaling pathway. Furthermore, elevated intracellular cAMP exacerbates vulnerability to oxidative stress in ONH astrocytes, and this may contribute to axonal damage in glaucomatous neurodegeneration. Inhibition of intracellular cAMP/PKA signaling activation protects ONH astrocytes by increasing AKT phosphorylation against oxidative stress. These results strongly indicate that activation of cAMP/PKA pathway has an important role in astrocyte dysfunction, and suggest that modulating cAMP/PKA pathway has therapeutic potential for glaucomatous ONH degeneration

Controlling the shape and topology of two-component colloidal membranes

Changes in the geometry and topology of self-assembled membranes underlie diverse processes across cellular biology and engineering. Similar to lipid bilayers, monolayer colloidal membranes have in-plane fluid-like dynamics and out-of-plane bending elasticity. Their open edges and micron length scale provide a tractable system to study the equilibrium energetics and dynamic pathways of membrane assembly and reconfiguration. Here, we find that doping colloidal membranes with short miscible rods transforms disk-shaped membranes into saddle-shaped surfaces with complex edge structures. The saddle-shaped membranes are well-approximated by Enneper's minimal surfaces. Theoretical modeling demonstrates that their formation is driven by increasing positive Gaussian modulus, which in turn is controlled by the fraction of short rods. Further coalescence of saddle-shaped surfaces leads to diverse topologically distinct structures, including catenoids, tri-noids, four-noids, and higher order structures. At long time scales, we observe the formation of a system-spanning, sponge-like phase. The unique features of colloidal membranes reveal the topological transformations that accompany coalescence pathways in real time. We enhance the functionality of these membranes by making their shape responsive to external stimuli. Our results demonstrate a novel pathway towards control of thin elastic sheets' shape and topology -- a pathway driven by the emergent elasticity induced by compositional heterogeneity.Comment: 15 pages, 9 figure