9,397 research outputs found
Robustness and modular design of the Drosophila segment polarity network
Biomolecular networks have to perform their functions robustly. A robust
function may have preferences in the topological structures of the underlying
network. We carried out an exhaustive computational analysis on network
topologies in relation to a patterning function in Drosophila embryogenesis. We
found that while the vast majority of topologies can either not perform the
required function or only do so very fragilely, a small fraction of topologies
emerges as particularly robust for the function. The topology adopted by
Drosophila, that of the segment polarity network, is a top ranking one among
all topologies with no direct autoregulation. Furthermore, we found that all
robust topologies are modular--each being a combination of three kinds of
modules. These modules can be traced back to three sub-functions of the
patterning function and their combinations provide a combinatorial variability
for the robust topologies. Our results suggest that the requirement of
functional robustness drastically reduces the choices of viable topology to a
limited set of modular combinations among which nature optimizes its choice
under evolutionary and other biological constraints.Comment: Supplementary Information and Synopsis available at
http://www.ucsf.edu/tanglab
Effect of polymer concentration and length of hydrophobic end block on the unimer-micelle transition broadness in amphiphilic ABA symmetric triblock copolymer solutions
The effects of the length of each hydrophobic end block N_{st} and polymer
concentration \bar{\phi}_{P} on the transition broadness in amphiphilic ABA
symmetric triblock copolymer solutions are studied using the self-consistent
field lattice model. When the system is cooled, micelles are observed, i.e.,the
homogenous solution (unimer)-micelle transition occurs. When N_{st} is
increased, at fixed \bar{\phi}_{P}, micelles occur at higher temperature, and
the temperature-dependent range of micellar aggregation and half-width of
specific heat peak for unimer-micelle transition increase monotonously.
Compared with associative polymers, it is found that the magnitude of the
transition broadness is determined by the ratio of hydrophobic to hydrophilic
blocks, instead of chain length. When \bar{\phi}_{P} is decreased, given a
large N_{st}, the temperature-dependent range of micellar aggregation and
half-width of specific heat peak initially decease, and then remain nearly
constant. It is shown that the transition broadness is concerned with the
changes of the relative magnitudes of the eductions of nonstickers and solvents
from micellar cores.Comment: 8 pages, 4 figure
The effect of asymmetry of the coil block on self-assembly in ABC coil-rod-coil triblock copolymers
Using the self-consistent field approach, the effect of asymmetry of the coil
block on the microphase separation is focused in ABC coil-rod-coil triblock
copolymers. For different fractions of the rod block , some stable
structures are observed, i.e., lamellae, cylinders, gyroid, and core-shell
hexagonal lattice, and the phase diagrams are constructed. The calculated
results show that the effect of the coil block fraction is
dependent on . When , the effect of asymmetry of
the coil block is similar to that of the ABC flexible triblock copolymers; When
, the self-assembly of ABC coil-rod-coil triblock copolymers
behaves like rod-coil diblock copolymers under some condition. When continues to increase, the effect of asymmetry of the coil block reduces.
For , under the symmetrical and rather asymmetrical
conditions, an increase in the interaction parameter between different
components leads to different transitions between cylinders and lamellae. The
results indicate some remarkable effect of the chain architecture on
self-assembly, and can provide the guidance for the design and synthesis of
copolymer materials.Comment: 9 pages, 3 figure
Multi-Context Attention for Human Pose Estimation
In this paper, we propose to incorporate convolutional neural networks with a
multi-context attention mechanism into an end-to-end framework for human pose
estimation. We adopt stacked hourglass networks to generate attention maps from
features at multiple resolutions with various semantics. The Conditional Random
Field (CRF) is utilized to model the correlations among neighboring regions in
the attention map. We further combine the holistic attention model, which
focuses on the global consistency of the full human body, and the body part
attention model, which focuses on the detailed description for different body
parts. Hence our model has the ability to focus on different granularity from
local salient regions to global semantic-consistent spaces. Additionally, we
design novel Hourglass Residual Units (HRUs) to increase the receptive field of
the network. These units are extensions of residual units with a side branch
incorporating filters with larger receptive fields, hence features with various
scales are learned and combined within the HRUs. The effectiveness of the
proposed multi-context attention mechanism and the hourglass residual units is
evaluated on two widely used human pose estimation benchmarks. Our approach
outperforms all existing methods on both benchmarks over all the body parts.Comment: The first two authors contribute equally to this wor
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