10,707 research outputs found
Nonlinear signaling on biological networks: the role of stochasticity and spectral clustering
Signal transduction within biological cells is governed by networks of
interacting proteins. Communication between these proteins is mediated by
signaling molecules which bind to receptors and induce stochastic transitions
between different conformational states. Signaling is typically a cooperative
process which requires the occurrence of multiple binding events so that
reaction rates have a nonlinear dependence on the amount of signaling molecule.
It is this nonlinearity that endows biological signaling networks with robust
switch-like properties which are critical to their biological function. In this
study, we investigate how the properties of these signaling systems depend on
the network architecture. Our main result is that these nonlinear networks
exhibit bistability where the network activity can switch between states that
correspond to a low and high activity level. We show that this bistable regime
emerges at a critical coupling strength that is determined by the spectral
structure of the network. In particular, the set of nodes that correspond to
large components of the leading eigenvector of the adjacency matrix determines
the onset of bistability. Above this transition, the eigenvectors of the
adjacency matrix determine a hierarchy of clusters, defined by its spectral
properties, which are activated sequentially with increasing network activity.
We argue further that the onset of bistability occurs either continuously or
discontinuously depending upon whether the leading eigenvector is localized or
delocalized. Finally, we show that at low network coupling stochastic
transitions to the active branch are also driven by the set of nodes that
contribute more strongly to the leading eigenvector.Comment: 30 pages, 12 figure
Sigma Model Corrections to the Confining Background
Sigma model () corrections to the confining string
background are obtained. The main result is that the Poincar\'e invariant
ansatz is maintained. Physical conditions for the dissapearance of the naked
singularity are discussed.Comment: LaTeX,12 page
Noise rectification in quasigeostrophic forced turbulence
We study the appearance of large scale mean motion sustained by stochastic
forcing on a rotating fluid (in the quasigeostrophic approximation) flowing
over topography. As in other noise rectification phenomena, the effect requires
nonlinearity and absence of detailed balance to occur. By application of an
analytical coarse graining procedure we identify the physical mechanism
producing such effect: It is a forcing coming from the small scales that
manifests in a change in the effective viscosity operator and in the effective
noise statistical properties.Comment: 4 pages revtex, including 5 figures. Related material at
http://www.imedea.uib.es/Nonlinear and http://www.imedea.uib.es/Oceanography
Figure 4 replaced by a slightly better on
Whose land of the free? Latina transgender immigrants in the United States
Transgender women from Latin America are driven to migrate to the United States in pursuit of a place where they can escape violence and discrimination. However, their experience in the United States continues to be one of oppression. Transgender Latina immigrants in the United States are the target of systematic oppression and interpersonal violence that affect their overall health and well-being. These experiences have led many transgender Latina immigrants to assume leadership roles and to organise social movements in demand for their human rights and dignity in the United States. Recommendations are provided for community leaders, policymakers, and academics
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