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Experimental observation of chiral phonons in monolayer WSe2
Chirality characterizes an object that is not identical to its mirror image. In condensed matter physics, Fermions have been demonstrated to obtain chirality through structural and time-reversal symmetry breaking. These systems display unconventional electronic transport phenomena such as the quantum Hall effect and Weyl semimetals. However, for bosonic collective excitations in atomic lattices, chirality was only theoretically predicted and has never been observed. We experimentally show that phonons can exhibit intrinsic chirality in monolayer tungsten diselenide, whose lattice breaks the inversion symmetry and enables inequivalent electronic K and -K valley states. The time-reversal symmetry is also broken when we selectively excite the valley polarized holes by circularly polarized light. Brillouin-zone-boundary phonons are then optically created by the indirect infrared absorption through the hole-phonon interactions. The unidirectional intervalley transfer of holes ensures that only the phonon modes in one valley are excited. We found that such photons are chiral through the transient infrared circular dichroism, which proves the valley phonons responsible to the indirect absorption has non-zero pseudo-angular momentum. From the spectrum we further deduce the energy transferred to the phonons that agrees with both the first principle calculation and the double-resonance Raman spectroscopy. The chiral phonons have significant implications for electron-phonon coupling in solids, lattice-driven topological states, and energy efficient information processing
NeuroQuantify -- An Image Analysis Software for Detection and Quantification of Neurons and Neurites using Deep Learning
The segmentation of cells and neurites in microscopy images of neuronal
networks provides valuable quantitative information about neuron growth and
neuronal differentiation, including the number of cells, neurites, neurite
length and neurite orientation. This information is essential for assessing the
development of neuronal networks in response to extracellular stimuli, which is
useful for studying neuronal structures, for example, the study of
neurodegenerative diseases and pharmaceuticals. However, automatic and accurate
analysis of neuronal structures from phase contrast images has remained
challenging. To address this, we have developed NeuroQuantify, an open-source
software that uses deep learning to efficiently and quickly segment cells and
neurites in phase contrast microscopy images. NeuroQuantify offers several key
features: (i) automatic detection of cells and neurites; (ii) post-processing
of the images for the quantitative neurite length measurement based on
segmentation of phase contrast microscopy images, and (iii) identification of
neurite orientations. The user-friendly NeuroQuantify software can be installed
and freely downloaded from GitHub
https://github.com/StanleyZ0528/neural-image-segmentation
From elastomers to thermoplasts β Precise control of isotactic propylene structure and properties and the role of different structural elements in its mechanical behaviour
Studies of polypropylene with different degrees of isotacticity have shown a way of the rational design of material with predetermined mechanical properties starting from the synthesis stage already β controlled introducement of stereodefects will allow the smooth adjustment of the Young's modulus and elasticity in the range from plastic to elastomer materials. It was also revealed that modern theoretical models of the elasticity can be successfully applied not only for the description of the mechanical behaviour of polymers, but also for better understanding of the mechanism of elasticity in them. While in the low crystalline materials deformation has Gaussian nature, in the materials of the intermediate crystallinity (30β40%) percolation takes place, and the cross-linking network becomes harder, manifesting the switch to the thermotropic behaviour of the material. Simultaneously the divide between cross- and slip-links becomes substantial, as an extensibility grows sharply
Factors affecting faculty use of learning technologies: Implications for models of technology adoption
This study examines factors associated with the use of learning technologies by higher education faculty. In an online survey in a UK university, 114 faculty respondents completed a measure of Internet self-efficacy, and reported on their use of learning technologies along with barriers to their adoption. Principal components analysis suggested two main barriers to adoption: structural constraints within the University and perceived usefulness of the tools. Regression analyses indicated both these variables, along with Internet self-efficacy, were associated with use of online learning technology. These findings are more consistent with models of technology engagement that recognize facilitating or inhibiting conditions (unified theory of acceptance and use of technology; decomposed theory of planned behavior) than the classic technology acceptance model (TAM). Practical implications for higher education institutions are that while faculty training and digital literacy initiatives may have roles to play, structural factors (e.g., provision of resources and technical support) must also be addressed for optimal uptake of learning technologies
Extreme Technicolor & The Walking Critical Temperature
We map the phase diagram of gauge theories of fundamental interactions in the
flavor-temperature plane using chiral perturbation theory to estimate the
relation between the pion decaying constant and the critical temperature above
which chiral symmetry is restored. We then investigate the impact of our
results on models of dynamical electroweak symmetry breaking and therefore on
the electroweak early universe phase transition.Comment: RevTeX, 18 pages, 3 figure
Enhanced cellular uptake of aminosilane-coated superparamagnetic iron oxide nanoparticles in mammalian cell lines
Role of micropipes in the formation of pores at foreign polytype boundaries in SiC crystals
The role of micropipes in pore formation in SiC crystals with foreign polytype inclusions is studied by means of synchrotron phase sensitive radiography, optical and scanning electron microscopies, and color photoluminescence. The pores at the inclusion boundaries are revealed, and their shapes and locations are analyzed. It is found that the pores arise due to the attraction of micropipes by the foreign polytype interfaces, followed by micropipe coalescence. The observed pores have tubular or slit shapes. Tubular pores nucleate at the inclusion corners, where the inclusion-associated stresses are concentrated. Slit pores spread between them and follow the shape of the inclusion boundaries. We explain the observations within a two-dimensional model of elastic interaction between micropipes and inclusion boundaries, which accounts for free surfaces of micropipes.open119sciescopu
Magnetism and its microscopic origin in iron-based high-temperature superconductors
High-temperature superconductivity in the iron-based materials emerges from,
or sometimes coexists with, their metallic or insulating parent compound
states. This is surprising since these undoped states display dramatically
different antiferromagnetic (AF) spin arrangements and Nel
temperatures. Although there is general consensus that magnetic interactions
are important for superconductivity, much is still unknown concerning the
microscopic origin of the magnetic states. In this review, progress in this
area is summarized, focusing on recent experimental and theoretical results and
discussing their microscopic implications. It is concluded that the parent
compounds are in a state that is more complex than implied by a simple Fermi
surface nesting scenario, and a dual description including both itinerant and
localized degrees of freedom is needed to properly describe these fascinating
materials.Comment: 14 pages, 4 figures, Review article, accepted for publication in
Nature Physic
Spin State Disproportionation in Insulating Ferromagnetic LaCoO3 Epitaxial Thin Films
The origin of insulating ferromagnetism in epitaxial LaCoO3 films under
tensile strain remains elusive despite extensive research efforts have been
devoted. Surprisingly, the spin state of its Co ions, the main parameter of its
ferromagnetism, is still to be determined. Here, we have systematically
investigated the spin state in epitaxial LaCoO3 thin films to clarify the
mechanism of strain induced ferromagnetism using element-specific x-ray
absorption spectroscopy and dichroism. Combining with the configuration
interaction cluster calculations, we unambiguously demonstrate that Co3+ in
LaCoO3 films under compressive strain (on LaAlO3 substrate) are practically a
low spin state, whereas Co3+ in LaCoO3 films under tensile strain (on SrTiO3
substrate) have mixed high spin and low spin states with a ratio close to 1:3.
From the identification of this spin state ratio, we infer that the dark strips
observed by high-resolution scanning transmission electron microscopy indicate
the position of Co3+ high spin state, i.e., an observation of a spin state
disproportionation in tensile-strained LaCoO3 films. This consequently explains
the nature of ferromagnetism in LaCoO3 films
Versatility of MicroRNA Biogenesis
MicroRNAs (miRNAs) are short single-stranded RNA molecules that regulate gene expression. MiRNAs originate from large primary (pri) and precursor (pre) transcripts that undergo various processing steps along their biogenesis pathway till they reach their mature and functional form. It is not clear, however, whether all miRNAs are processed similarly. Here we show that the ratio between pre-miRNA and mature miRNA forms varies between different miRNAs. Moreover, over-expression of several factors involved in miRNA biogenesis, including Exportin-5, Drosha, NF90a, NF45 and KSRP, displayed bidirectional effects on pre/mature miRNA ratios, suggesting their intricate biogenesis sensitivity. In an attempt to identify additional factors that might explain the versatility in miRNA biogenesis we have analyzed the contribution of two hnRNP family members, hnRNPH1 and hnRNPR. Knock-down or over-expression of these genes suggested that hnRNPR inhibits, whereas hnRNPH1 facilitates, miRNA processing. Overall, our results emphasize that miRNA biogenesis is versatile
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