459 research outputs found
Application of a Novel Stability Control System for Coordination of Power Flow Control Devices in the Future GB Transmission System
With increasing large-scale renewable energy sources in the UK and the need for adequate transmission capacity to accommodate the upcoming renewable generations, more state-of-the-art power flow control devices such as embedded High Voltage DC (HVDC) links will soon be commissioned in the GB HV transmission system to provide the additional capacity. An operational stability control system is required to ensure the coordinated control of power flow control devices in order to achieve better dynamic performance and stability. The focus of this paper is to demonstrate the capability of a multi-variable controller for the coordinated control using a non-parametric sampled regulator control design method. This method is practical for applications in large power systems since the complexity of the controller design does not increase with the size and dynamic of the power system. Also, this design method is demonstrated in two power system applications in this paper
Prediction by Promoter Logic in Bacterial Quorum Sensing
Quorum-sensing systems mediate chemical communication between bacterial cells, coordinating cell-density-dependent processes like biofilm formation and virulence-factor expression. In the proteobacterial LuxI/LuxR quorum sensing paradigm, a signaling molecule generated by an enzyme (LuxI) diffuses between cells and allosterically stimulates a transcriptional regulator (LuxR) to activate its cognate promoter (pR). By expressing either LuxI or LuxR in positive feedback from pR, these versatile systems can generate smooth (monostable) or abrupt (bistable) density-dependent responses to suit the ecological context. Here we combine theory and experiment to demonstrate that the promoter logic of pR – its measured activity as a function of LuxI and LuxR levels – contains all the biochemical information required to quantitatively predict the responses of such feedback loops. The interplay of promoter logic with feedback topology underlies the versatility of the LuxI/LuxR paradigm: LuxR and LuxI positive-feedback systems show dramatically different responses, while a dual positive/negative-feedback system displays synchronized oscillations. These results highlight the dual utility of promoter logic: to probe microscopic parameters and predict macroscopic phenotype
Runs, Panics and Bubbles: Diamond-Dybvig and Morris-Shin Reconsidered
The basic two-noncooperative-equilibrium-point model of Diamond and Dybvig is considered along with the work of Morris and Shin utilizing the possibility of outside noise to select a unique equilibrium point. Both of these approaches are essentially nondynamic. We add an explicit replicator dynamic from evolutionary game theory to provide for a sensitivity analysis that encompasses both models and contains the results of both depending on parameter settings
Switchable Genetic Oscillator Operating in Quasi-Stable Mode
Ring topologies of repressing genes have qualitatively different long-term
dynamics if the number of genes is odd (they oscillate) or even (they exhibit
bistability). However, these attractors may not fully explain the observed
behavior in transient and stochastic environments such as the cell. We show
here that even repressilators possess quasi-stable, travelling-wave periodic
solutions that are reachable, long-lived and robust to parameter changes. These
solutions underlie the sustained oscillations observed in even rings in the
stochastic regime, even if these circuits are expected to behave as switches.
The existence of such solutions can also be exploited for control purposes:
operation of the system around the quasi-stable orbit allows us to turn on and
off the oscillations reliably and on demand. We illustrate these ideas with a
simple protocol based on optical interference that can induce oscillations
robustly both in the stochastic and deterministic regimes.Comment: 24 pages, 5 main figure
Iterative Random Forests to detect predictive and stable high-order interactions
Genomics has revolutionized biology, enabling the interrogation of whole
transcriptomes, genome-wide binding sites for proteins, and many other
molecular processes. However, individual genomic assays measure elements that
interact in vivo as components of larger molecular machines. Understanding how
these high-order interactions drive gene expression presents a substantial
statistical challenge. Building on Random Forests (RF), Random Intersection
Trees (RITs), and through extensive, biologically inspired simulations, we
developed the iterative Random Forest algorithm (iRF). iRF trains a
feature-weighted ensemble of decision trees to detect stable, high-order
interactions with same order of computational cost as RF. We demonstrate the
utility of iRF for high-order interaction discovery in two prediction problems:
enhancer activity in the early Drosophila embryo and alternative splicing of
primary transcripts in human derived cell lines. In Drosophila, among the 20
pairwise transcription factor interactions iRF identifies as stable (returned
in more than half of bootstrap replicates), 80% have been previously reported
as physical interactions. Moreover, novel third-order interactions, e.g.
between Zelda (Zld), Giant (Gt), and Twist (Twi), suggest high-order
relationships that are candidates for follow-up experiments. In human-derived
cells, iRF re-discovered a central role of H3K36me3 in chromatin-mediated
splicing regulation, and identified novel 5th and 6th order interactions,
indicative of multi-valent nucleosomes with specific roles in splicing
regulation. By decoupling the order of interactions from the computational cost
of identification, iRF opens new avenues of inquiry into the molecular
mechanisms underlying genome biology
Convex searches for discrete-time Zames-Falb multipliers
In this paper we develop and analyse convex searches for Zames--Falb
multipliers. We present two different approaches: Infinite Impulse Response
(IIR) and Finite Impulse Response (FIR) multipliers. The set of FIR multipliers
is complete in that any IIR multipliers can be phase-substituted by an
arbitrarily large order FIR multiplier. We show that searches in discrete-time
for FIR multipliers are effective even for large orders. As expected, the
numerical results provide the best -stability results in the
literature for slope-restricted nonlinearities. Finally, we demonstrate that
the discrete-time search can provide an effective method to find suitable
continuous-time multipliers.Comment: 12 page
Coupling between feedback loops in autoregulatory networks affects bistability range, open-loop gain and switching times
Biochemical regulatory networks governing diverse cellular processes such as stress-response,
differentiation and cell cycle often contain coupled feedback loops. We aim at understanding
how features of feedback architecture, such as the number of loops, the sign of the loops and
the type of their coupling, affect network dynamical performance. Specifically, we investigate
how bistability range, maximum open-loop gain and switching times of a network with
transcriptional positive feedback are affected by additive or multiplicative coupling with
another positive- or negative-feedback loop. We show that a network's bistability range is
positively correlated with its maximum open-loop gain and that both quantities depend on the
sign of the feedback loops and the type of feedback coupling. Moreover, we find that the
addition of positive feedback could decrease the bistability range if we control the basal level
in the signal-response curves of the two systems. Furthermore, the addition of negative
feedback has the capacity to increase the bistability range if its dissociation constant is much
lower than that of the positive feedback. We also find that the addition of a positive feedback to
a bistable network increases the robustness of its bistability range, whereas the addition of a
negative feedback decreases it. Finally, we show that the switching time for a transition from a
high to a low steady state increases with the effective fold change in gene regulation. In
summary, we show that the effect of coupled feedback loops on the bistability range and
switching times depends on the underlying mechanistic details
- …