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  • 1
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    Magnification relations of quad lenses and applications on Einstein crosses (2016)
    Oxford University Press
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    Publication Date: 2016-07-30
    Description: In this work, we mainly study the magnification relations of quad lens models for cusp, fold and cross configurations. By dividing and ray-tracing in different image regions, we numerically derive the positions and magnifications of the four images for a point source lying inside of the astroid caustic. Then, based on the magnifications, we calculate the signed cusp and fold relations for the singular isothermal elliptical lenses. The signed fold relation map has positive and negative regions, and the positive region is usually larger than the negative region as has been confirmed before. It can also explain that for many observed fold image pairs, the fluxes of the Fermat minimum images are apt to be larger than those of the saddle images. We define a new quantity cross relation R cross which describes the magnification discrepancy between two minimum images and two saddle images. Distance ratio d sadd / d mini is also defined as the ratio of the distance of two saddle images to that of two minimum images. We calculate the cross relations and distance ratios for nine observed Einstein crosses. In theory, for most of the quad lens models, the cross relations decrease as the distance ratios increase. In observation, the cross relations of the nine samples do not agree with the quad lens models very well, nevertheless, the cross relations of the nine samples do not give obvious evidence for anomalous flux ratio as the cusp and fold types do. Then, we discuss several reasons for the disagreement, and expect good consistencies for more precise observations and better lens models in the future.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 2
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    Cusp summations and cusp relations of simple quad lenses (2015)
    Oxford University Press
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    Publication Date: 2015-03-29
    Description: We review five often used quad lens models, each of which has analytical solutions and can produce four images at most. Each lens model has two parameters, including one that describes the intensity of non-dimensional mass density, and the other one that describes the deviation from the circular lens. In our recent work, we have found that the cusp and the fold summations are not equal to 0, when a point source infinitely approaches a cusp or a fold from inner side of the caustic. Based on the magnification invariant theory, which states that the sum of signed magnifications of the total images of a given source is a constant, we calculate the cusp summations for the five lens models. We find that the cusp summations are always larger than 0 for source on the major cusps, while can be larger or smaller than 0 for source on the minor cusps. We also find that if these lenses tend to the circular lens, the major and minor cusp summations will have infinite values, and with positive and negative signs, respectively. The cusp summations do not change significantly if the sources are slightly deviated from the cusps. In addition, through the magnification invariants, we also derive the analytical signed cusp relations on the axes for three lens models. We find that both on the major and the minor axes the larger the lenses deviated from the circular lens, the larger the signed cusp relations. The major cusp relations are usually larger than the absolute minor cusp relations, but for some lens models with very large deviation from circular lens, the minor cusp relations can be larger than the major cusp relations.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 3
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    Neuronal activity promotes oligodendrogenesis and adaptive myelination in the mammalian brain (2014)
    American Association for the Advancement of Science (AAAS)
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    Publication Date: 2014-04-15
    Description: Myelination of the central nervous system requires the generation of functionally mature oligodendrocytes from oligodendrocyte precursor cells (OPCs). Electrically active neurons may influence OPC function and selectively instruct myelination of an active neural circuit. In this work, we use optogenetic stimulation of the premotor cortex in awake, behaving mice to demonstrate that neuronal activity elicits a mitogenic response of neural progenitor cells and OPCs, promotes oligodendrogenesis, and increases myelination within the deep layers of the premotor cortex and subcortical white matter. We further show that this neuronal activity-regulated oligodendrogenesis and myelination is associated with improved motor function of the corresponding limb. Oligodendrogenesis and myelination appear necessary for the observed functional improvement, as epigenetic blockade of oligodendrocyte differentiation and myelin changes prevents the activity-regulated behavioral improvement.〈br /〉〈br /〉〈a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4096908/" target="_blank"〉〈img src="https://static.pubmed.gov/portal/portal3rc.fcgi/4089621/img/3977009" border="0"〉〈/a〉   〈a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4096908/" target="_blank"〉This paper as free author manuscript - peer-reviewed and accepted for publication〈/a〉〈br /〉〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Gibson, Erin M -- Purger, David -- Mount, Christopher W -- Goldstein, Andrea K -- Lin, Grant L -- Wood, Lauren S -- Inema, Ingrid -- Miller, Sarah E -- Bieri, Gregor -- Zuchero, J Bradley -- Barres, Ben A -- Woo, Pamelyn J -- Vogel, Hannes -- Monje, Michelle -- 1S10RR02678001/RR/NCRR NIH HHS/ -- K08 NS070926/NS/NINDS NIH HHS/ -- K08NS070926/NS/NINDS NIH HHS/ -- R01 EY10257/EY/NEI NIH HHS/ -- T32 MH020016/MH/NIMH NIH HHS/ -- UL1 RR025744/RR/NCRR NIH HHS/ -- Howard Hughes Medical Institute/ -- New York, N.Y. -- Science. 2014 May 2;344(6183):1252304. doi: 10.1126/science.1252304. Epub 2014 Apr 10.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Departments of Neurology, Neurosurgery, and Pediatrics, Institute for Stem Cell Biology and Regenerative Medicine, Stanford University School of Medicine, Stanford, CA 94305, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/24727982" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Antigens, Thy-1/genetics ; Behavior, Animal/physiology ; *Cell Differentiation ; Cell Lineage ; Cell Proliferation ; Corpus Callosum/cytology/physiology ; Mice ; Mice, Mutant Strains ; Motor Activity/physiology ; Motor Cortex/cytology/*physiology ; Myelin Sheath/*metabolism ; Nerve Fibers, Myelinated/*metabolism ; Neural Stem Cells/*physiology ; Neurons/*physiology ; Oligodendroglia/*cytology ; Rhodopsin/genetics
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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