2,201 research outputs found
The effects of growth factors on multicellular spheroids formed by chick embryonic retinal cells
Retinal cells from chick embryos aged 7.5 days of gestation were cultured for two months in a non-adherent suspension culture dish to study the effects of growth factors and co-culture with retinal pigment epithelial cells on their differentiation. Dissociated retinal cells became cellular aggregates (multicellular spheroids) within a day, and rosettes were formed in the spheroids after 2 days. Ultrastructurally, neurons of the rosettes developed connecting cilia, ellipsoids (accumulation of mitochondria), and external limiting membrane, indicative of their differentiation into photoreceptor cells. Epidermal growth factor enhanced the expression of rhodopsin by rosette-forming neurons, while basic fibroblast growth factor induced the growth of Mueller cells at 4 weeks, and their transdifferentiation into lens-epithelial-like cells at 8 weeks. Co-culture of retinal cells with retinal pigment epithelial cells enhanced the formation of rosettes in spheroids. Multicellular spheroids formed in a dish for suspension culture would provide a convenient in vitro system to examine differentiation and transdifferentiation of the retina.</p
Phonon-glass electron-crystal thermoelectric clathrates: Experiments and theory
Type-I clathrate compounds have attracted a great deal of interest in
connection with the search for efficient thermoelectric materials. These
compounds constitute networked cages consisting of nano-scale
tetrakaidecahedrons (14 hedrons) and dodecahedrons (12 hedrons), in which the
group 1 or 2 elements in the periodic table are encaged as the so-called
rattling guest atom. It is remarkable that, though these compounds have
crystalline cubic-structure, they exhibit glass-like phonon thermal
conductivity over the whole temperature range depending on the states of
rattling guest atoms in the tetrakaidecahedron. In addition, these compounds
show unusual glass-like specific heats and THz-frequency phonon dynamics,
providing a remarkable broad peak almost identical to those observed in
topologically disordered amorphous materials or structural glasses, the
so-called Boson peak. An efficient thermoelectric effect is realized in
compounds showing these glass-like characteristics. This decade, a number of
experimental works dealing with type-I clathrate compounds have been published.
These are diffraction experiments, thermal and spectroscopic experiments in
addition to those based on heat and electronic transport. These form the raw
materials for this article based on advances this decade. The subject of this
article involves interesting phenomena from the viewpoint of not only physics
but also from the view point of the practical problem of elaborating efficient
thermoelectric materials. This review presents a survey of a wide range of
experimental investigations of type-I clathrate compounds, together with a
review of theoretical interpretations of the peculiar thermal and dynamic
properties observed in these materials.Comment: 51pages, 43 figure
siEDM: an efficient string index and search algorithm for edit distance with moves
Although several self-indexes for highly repetitive text collections exist,
developing an index and search algorithm with editing operations remains a
challenge. Edit distance with moves (EDM) is a string-to-string distance
measure that includes substring moves in addition to ordinal editing operations
to turn one string into another. Although the problem of computing EDM is
intractable, it has a wide range of potential applications, especially in
approximate string retrieval. Despite the importance of computing EDM, there
has been no efficient method for indexing and searching large text collections
based on the EDM measure. We propose the first algorithm, named string index
for edit distance with moves (siEDM), for indexing and searching strings with
EDM. The siEDM algorithm builds an index structure by leveraging the idea
behind the edit sensitive parsing (ESP), an efficient algorithm enabling
approximately computing EDM with guarantees of upper and lower bounds for the
exact EDM. siEDM efficiently prunes the space for searching query strings by
the proposed method, which enables fast query searches with the same guarantee
as ESP. We experimentally tested the ability of siEDM to index and search
strings on benchmark datasets, and we showed siEDM's efficiency.Comment: 23 page
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