2,275 research outputs found
Symbiotic Cell Differentiation and Cooperative Growth in Multicellular Aggregates
As cells grow and divide under a given environment, they become crowded and
resources are limited, as seen in bacterial biofilms and multicellular
aggregates. These cells often show strong interactions through exchanging
chemicals, as in quorum sensing, to achieve mutualism. Here, to achieve stable
division of labor, three properties are required. First, isogenous cells
differentiate into several types. Second, this aggregate of distinct cell types
shows better growth than that of isolated cells, by achieving division of
labor. Third, this cell aggregate is robust in the number distribution of
differentiated cell types. We here address how cells acquire the ability of
cell differentiation and division of labor simultaneously, which is also
connected with the robustness of a cell society. For this purpose, we developed
a dynamical-systems model of cells consisting of chemical components with
intracellular catalytic reaction dynamics. The reactions convert external
nutrients into internal components for cellular growth, and the divided cells
interact via chemical diffusion. We found that cells sharing an identical
catalytic network spontaneously differentiate via induction from cell-cell
interactions, and then achieve division of labor, enabling a higher growth rate
than that in the unicellular case. This symbiotic differentiation emerged for a
class of reaction networks with limited resources and strong cell-cell
interactions. Then, robustness in the cell type distribution was achieved,
while instability of collective growth could emerge even among the cooperative
cells when the internal reserves of products were dominant. The present
mechanism is simple and general as a natural result of interacting cells with
resource limitation, and is consistent with the observed behaviors and forms of
several aggregates of unicellular organisms.Comment: 14 pages, 6 figure
Plasma polymerized high energy density dielectric films for capacitors
High energy density polymeric dielectric films were prepared by plasma polymerization of a variety of gaseous monomers. This technique gives thin, reproducible, pinhole free, conformable, adherent, and insoluble coatings and overcomes the processing problems found in the preparation of thin films with bulk polymers. Thus, devices are prepared completely in a vacuum environment. The plasma polymerized films prepared all showed dielectric strengths of greater than 1000 kV/cm and in some cases values of greater than 4000 kV/cm were observed. The dielectric loss of all films was generally less than 1% at frequencies below 10 kHz, but this value increased at higher frequencies. All films were self healing. The dielectric strength was a function of the polymerization technique, whereas the dielectric constant varied with the structure of the starting material. Because of the thin films used (thickness in the submicron range) surface smoothness of the metal electrodes was found to be critical in obtaining high dielectric strengths. High dielectric strength graft copolymers were also prepared. Plasma polymerized ethane was found to be thermally stable up to 150 C in the presence of air and 250 C in the absence of air. No glass transitions were observed for this material
Universal Transitions between Growth and Dormancy via Intermediate Complex Formation
A simple cell model consisting of a catalytic reaction network with
intermediate complex formation is numerically studied. As nutrients are
depleted, the transition from the exponential growth phase to the
growth-arrested dormant phase occurs along with hysteresis and a lag time for
growth recovery. This transition is caused by the accumulation of intermediate
complexes, leading to the jamming of reactions and the diversification of
components. These properties are generic in random reaction networks, as
supported by dynamical systems analyses of corresponding mean-field models.Comment: 6+6 pages, 3+6 figure
Linear Response Theory of Evolved Metabolic Systems
Predicting cellular metabolic states is a central problem in biophysics.
Conventional approaches, however, sensitively depend on the microscopic details
of individual metabolic systems. In this Letter, we derived a universal linear
relationship between the metabolic responses against nutrient conditions and
metabolic inhibition, with the aid of a microeconomic theory. The relationship
holds in arbitrary metabolic systems as long as the law of mass conservation
stands, as supported by extensive numerical calculations. It offers
quantitative predictions without prior knowledge of systems.Comment: 6+6 pages, 3+4 figures, 1 tabl
An investigation of children's peer trust across culture: is the composition of peer trust universal?
The components of children's trust in same-gender peers (trust beliefs, ascribed trustworthiness, and dyadic reciprocal trust) were examined in samples of 8- to 11-year-olds from the UK, Italy, and Japan. Trust was assessed by children's ratings of the extent to which same-gender classmates kept promises and kept secrets. Social relations analyses confirmed that children from each country showed significant: (a) actor variance demonstrating reliable individual differences in trust beliefs, (b) partner variance demonstrating reliable individual differences in ascribed trustworthiness, and (c ) relationship variance demonstrating unique relationships between interaction partners. Cultural differences in trust beliefs and ascribed trustworthiness also emerged and these differences were attributed to the tendency for children from cultures that value societal goals to share personal information with the peer group
Um modelo orientado a objetos para o cálculo da estimativa da área acessĂvel a solvente.
Estimativa da ASA. Descrição do método utilizado. Modelo orientado a objetos proposto.bitstream/CNPTIA/10655/1/doc46.pdfAcesso em: 29 maio 2008
The tambaqui (Colossoma macropomum) transcriptome at sex differentiation stage.
As females of tambaqui (Colossoma macropomum) are heavier than males at harvest, farming all-female populations would be more profitable. Unraveling the genetic and physiological mechanisms involved in sex determination and sex differentiation is then a fundamental objective in order to achieve sex control in this species. Therefore, we produced and assembled individual transcriptome libraries of juveniles sampled just prior to the gonadal sex differentiation in order to identify genes putatively related to testicular or ovarian differentiation in tambaqui
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