2,088 research outputs found
Optimal cellular mobility for synchronization arising from the gradual recovery of intercellular interactions
Cell movement and intercellular signaling occur simultaneously during the
development of tissues, but little is known about how movement affects
signaling. Previous theoretical studies have shown that faster moving cells
favor synchronization across a population of locally coupled genetic
oscillators. An important assumption in these studies is that cells can
immediately interact with their new neighbors after arriving at a new location.
However, intercellular interactions in cellular systems may need some time to
become fully established. How movement affects synchronization in this
situation has not been examined. Here we develop a coupled phase oscillator
model in which we consider cell movement and the gradual recovery of
intercellular coupling experienced by a cell after movement, characterized by a
moving rate and a coupling recovery rate respectively. We find (1) an optimal
moving rate for synchronization, and (2) a critical moving rate above which
achieving synchronization is not possible. These results indicate that the
extent to which movement enhances synchrony is limited by a gradual recovery of
coupling. These findings suggest that the ratio of time scales of movement and
signaling recovery is critical for information transfer between moving cells.Comment: 18 single column pages + 1 table + 5 figures + Supporting Informatio
Electrode current distributions in MGD CHANNELS
Current distribution to and electric field behavior of segmented electrodes in linear magnetogasdynamic generato
Nonlinearity arising from noncooperative transcription factor binding enhances negative feedback and promotes genetic oscillations
We study the effects of multiple binding sites in the promoter of a genetic
oscillator. We evaluate the regulatory function of a promoter with multiple
binding sites in the absence of cooperative binding, and consider different
hypotheses for how the number of bound repressors affects transcription rate.
Effective Hill exponents of the resulting regulatory functions reveal an
increase in the nonlinearity of the feedback with the number of binding sites.
We identify optimal configurations that maximize the nonlinearity of the
feedback. We use a generic model of a biochemical oscillator to show that this
increased nonlinearity is reflected in enhanced oscillations, with larger
amplitudes over wider oscillatory ranges. Although the study is motivated by
genetic oscillations in the zebrafish segmentation clock, our findings may
reveal a general principle for gene regulation.Comment: 11 pages, 8 figure
Synchronization in the presence of distributed delays
We study systems of identical coupled oscillators introducing a distribution
of delay times in the coupling. For arbitrary network topologies, we show that
the frequency and stability of the fully synchronized states depend only on the
mean of the delay distribution. However, synchronization dynamics is sensitive
to the shape of the distribution. In the presence of coupling delays, the
synchronization rate can be maximal for a specific value of the coupling
strength.Comment: 6 pages, 3 figure
Delayed coupling theory of vertebrate segmentation
Rhythmic and sequential subdivision of the elongating vertebrate embryonic
body axis into morphological somites is controlled by an oscillating
multicellular genetic network termed the segmentation clock. This clock
operates in the presomitic mesoderm (PSM), generating dynamic stripe patterns
of oscillatory gene-expression across the field of PSM cells. How these spatial
patterns, the clock's collective period, and the underlying cellular-level
interactions are related is not understood. A theory encompassing temporal and
spatial domains of local and collective aspects of the system is essential to
tackle these questions. Our delayed coupling theory achieves this by
representing the PSM as an array of phase oscillators, combining four key
elements: a frequency profile of oscillators slowing across the PSM; coupling
between neighboring oscillators; delay in coupling; and a moving boundary
describing embryonic axis elongation. This theory predicts that the
segmentation clock's collective period depends on delayed coupling. We derive
an expression for pattern wavelength across the PSM and show how this can be
used to fit dynamic wildtype gene-expression patterns, revealing the
quantitative values of parameters controlling spatial and temporal organization
of the oscillators in the system. Our theory can be used to analyze
experimental perturbations, thereby identifying roles of genes involved in
segmentation.Comment: published online 10 December 2008, Adv. Online Pub. HFSP Journal
(free access
Energy Conversion Research
Contains report on one research project.U. S. Air Force (Research and Technology Division) under Contract AF33(615)-3489 with the Air Force Aero Propulsion Laboratory, Wright-Patterson Air Force Base, Ohi
Burh: Improvement of Suffix Trees
The wireless machine learning solution to model checking is defined not only by the understanding of interrupts, but also by the typical need for voice- over-IP. Given the trends in linear-time archetypes, electrical engineers famously note the analysis of thin clients. Burh, our new algorithm for the UNIVAC computer, is the solution to all of these challenges
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