7,062 research outputs found

    Mediators of mechanotransduction between bone cells

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    Mechanical forces are known to regulate the function of tissues in the body, including bone. Bone adapts to its mechanical environment by altering its shape and increasing its size in response to increases in mechanical load associated with exercise, and by decreasing its size in response to decreases in mechanical load associated with microgravity or prolonged bed rest. Changes in bone size and shape are produced by a cooperative action of two main types of the bone cells - osteoclasts that destroy bone and osteoblasts that build bone. These cell types come from different developmental origins, and vary greatly in their characteristics, such as size, shape, and expression of receptor subtypes, which potentially may affect their responses to mechanical stimuli. The objective of this study is to compare the responses of osteoclasts and osteoblasts to mechanical stimulation. This study has allowed us to conclude the following: 1. A mediator is released from a single source cell. 2. The response to the mediator changes with distance. 3. The value of the apparent diffusion coeficient increases with distance. 4. A plausible proposed mechanism is that ATP is released and degrades to ADP. 5. Future experiments are required to confim that ATP is the mediator as suggested

    Tests of star formation metrics in the low metallicity galaxy NGC 5253 using ALMA observations of H30α\alpha line emission

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    We use Atacama Large Millimeter/submillimeter Array (ALMA) observations of H30α\alpha (231.90 GHz) emission from the low metallicity dwarf galaxy NGC 5253 to measure the star formation rate (SFR) within the galaxy and to test the reliability of SFRs derived from other commonly-used metrics. The H30α\alpha emission, which originates mainly from the central starburst, yields a photoionizing photon production rate of (1.9±\pm0.3)×\times1052^{52} s1^{-1} and an SFR of 0.087±\pm0.013 M_\odot yr1^{-1} based on conversions that account for the low metallicity of the galaxy and for stellar rotation. Among the other star formation metrics we examined, the SFR calculated from the total infrared flux was statistically equivalent to the values from the H30α\alpha data. The SFR based on previously-published versions of the Hα\alpha flux that were extinction corrected using Paα\alpha and Paβ\beta lines were lower than but also statistically similar to the H30α\alpha value. The mid-infrared (22 μ\mum) flux density and the composite star formation tracer based on Hα\alpha and mid-infrared emission give SFRs that were significantly higher because the dust emission appears unusually hot compared to typical spiral galaxies. Conversely, the 70 and 160 μ\mum flux densities yielded SFR lower than the H30α\alpha value, although the SFRs from the 70 μ\mum and H30α\alpha data were within 1-2σ\sigma of each other. While further analysis on a broader range of galaxies are needed, these results are instructive of the best and worst methods to use when measuring SFR in low metallicity dwarf galaxies like NGC 5253.Comment: 14 pages, 5 figures, accepted for publication in MNRA

    U-Note: Capture the Class and Access it Everywhere

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    We present U-Note, an augmented teaching and learning system leveraging the advantages of paper while letting teachers and pupils benefit from the richness that digital media can bring to a lecture. U-Note provides automatic linking between the notes of the pupils' notebooks and various events that occurred during the class (such as opening digital documents, changing slides, writing text on an interactive whiteboard...). Pupils can thus explore their notes in conjunction with the digital documents that were presented by the teacher during the lesson. Additionally, they can also listen to what the teacher was saying when a given note was written. Finally, they can add their own comments and documents to their notebooks to extend their lecture notes. We interviewed teachers and deployed questionnaires to identify both teachers and pupils' habits: most of the teachers use (or would like to use) digital documents in their lectures but have problems in sharing these resources with their pupils. The results of this study also show that paper remains the primary medium used for knowledge keeping, sharing and editing by the pupils. Based on these observations, we designed U-Note, which is built on three modules. U-Teach captures the context of the class: audio recordings, the whiteboard contents, together with the web pages, videos and slideshows displayed during the lesson. U-Study binds pupils' paper notes (taken with an Anoto digital pen) with the data coming from U-Teach and lets pupils access the class materials at home, through their notebooks. U-Move lets pupils browse lecture materials on their smartphone when they are not in front of a computer

    The comfortable roller coaster -- on the shape of tracks with constant normal force

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    A particle that moves along a smooth track in a vertical plane is influenced by two forces: gravity and normal force. The force experienced by roller coaster riders is the normal force, so a natural question to ask is: what shape of the track gives a normal force of constant magnitude? Here we solve this problem. It turns out that the solution is related to the Kepler problem; the trajectories in velocity space are conic sections.Comment: 10 pages, 4 figure