4,596 research outputs found
Tuning a synthetic in vitro oscillator using control-theoretic tools
This paper demonstrates the effectiveness of simple control-theoretic tools in generating simulation-guided experiments on a synthetic in vitro oscillator. A theoretical analysis of the behavior of such system is motivated by high cost, time consuming experiments, together with the excessive number of tuning parameters. A simplified model of the synthetic oscillator is chosen to capture only its essential features. The model is analyzed using the small gain theorem and the theory of describing functions. Such analysis reveals what are the parameters that primarily determine when the system can admit stable oscillations. Experimental verification of the theoretical and numerical findings is carried out and confirms the predicted results regarding the role of production and degradation rates
The effect of heterogeneity on invasion in spatial epidemics: from theory to experimental evidence in a model system
Heterogeneity in host populations is an important factor affecting the ability of a pathogen to invade, yet the quantitative investigation of its effects on epidemic spread is still an open problem. In this paper, we test recent theoretical results, which extend the established âpercolation paradigmâ to the spread of a pathogen in discrete heterogeneous host populations. In particular, we test the hypothesis that the probability of epidemic invasion decreases when host heterogeneity is increased. We use replicated experimental microcosms, in which the ubiquitous pathogenic fungus Rhizoctonia solani grows through a population of discrete nutrient sites on a lattice, with nutrient sites representing hosts. The degree of host heterogeneity within different populations is adjusted by changing the proportion and the nutrient concentration of nutrient sites. The experimental data are analysed via Bayesian inference methods, estimating pathogen transmission parameters for each individual population. We find a significant, negative correlation between heterogeneity and the probability of pathogen invasion, thereby validating the theory. The value of the correlation is also in remarkably good agreement with the theoretical predictions. We briefly discuss how our results can be exploited in the design and implementation of disease control strategies
Supersymmetry Breaking from a Calabi-Yau Singularity
We conjecture a geometric criterion for determining whether supersymmetry is
spontaneously broken in certain string backgrounds. These backgrounds contain
wrapped branes at Calabi-Yau singularites with obstructions to deformation of
the complex structure. We motivate our conjecture with a particular example:
the quiver gauge theory corresponding to a cone over the first del
Pezzo surface, . This setup can be analyzed using ordinary supersymmetric
field theory methods, where we find that gaugino condensation drives a
deformation of the chiral ring which has no solutions. We expect this breaking
to be a general feature of any theory of branes at a singularity with a smaller
number of possible deformations than independent anomaly-free fractional
branes.Comment: 32 pages, 6 figures, latex, v2: minor changes, refs adde
Generation of ultrabright tunable polarization entanglement without spatial, spectral, or temporal constraints
The need for spatial and spectral filtering in the generation of polarization
entanglement is eliminated by combining two coherently-driven type-II
spontaneous parametric downconverters. The resulting ultrabright source emits
photon pairs that are polarization entangled over the entire spatial cone and
spectrum of emission. We detect a flux of 12 000 polarization-entangled
pairs/s per mW of pump power at 90% quantum-interference visibility, and the
source can be temperature tuned for 5 nm around frequency degeneracy. The
output state is actively controlled by precisely adjusting the relative phase
of the two coherent pumps.Comment: 10 pages, 5 figure
Complexity and anisotropy in host morphology make populations safer against epidemic outbreaks
One of the challenges in epidemiology is to account for the complex
morphological structure of hosts such as plant roots, crop fields, farms,
cells, animal habitats and social networks, when the transmission of infection
occurs between contiguous hosts. Morphological complexity brings an inherent
heterogeneity in populations and affects the dynamics of pathogen spread in
such systems. We have analysed the influence of realistically complex host
morphology on the threshold for invasion and epidemic outbreak in an SIR
(susceptible-infected-recovered) epidemiological model. We show that disorder
expressed in the host morphology and anisotropy reduces the probability of
epidemic outbreak and thus makes the system more resistant to epidemic
outbreaks. We obtain general analytical estimates for minimally safe bounds for
an invasion threshold and then illustrate their validity by considering an
example of host data for branching hosts (salamander retinal ganglion cells).
Several spatial arrangements of hosts with different degrees of heterogeneity
have been considered in order to analyse separately the role of shape
complexity and anisotropy in the host population. The estimates for invasion
threshold are linked to morphological characteristics of the hosts that can be
used for determining the threshold for invasion in practical applications.Comment: 21 pages, 8 figure
Tuning a synthetic in vitro oscillator using control-theoretic tools
This paper demonstrates the effectiveness of simple control-theoretic tools in generating simulation-guided experiments on a synthetic in vitro oscillator. A theoretical analysis of the behavior of such system is motivated by high cost, time consuming experiments, together with the excessive number of tuning parameters. A simplified model of the synthetic oscillator is chosen to capture only its essential features. The model is analyzed using the small gain theorem and the theory of describing functions. Such analysis reveals what are the parameters that primarily determine when the system can admit stable oscillations. Experimental verification of the theoretical and numerical findings is carried out and confirms the predicted results regarding the role of production and degradation rates
Metropolitan quantum key distribution with silicon photonics
Photonic integrated circuits (PICs) provide a compact and stable platform for
quantum photonics. Here we demonstrate a silicon photonics quantum key
distribution (QKD) transmitter in the first high-speed polarization-based QKD
field tests. The systems reach composable secret key rates of 950 kbps in a
local test (on a 103.6-m fiber with a total emulated loss of 9.2 dB) and 106
kbps in an intercity metropolitan test (on a 43-km fiber with 16.4 dB loss).
Our results represent the highest secret key generation rate for
polarization-based QKD experiments at a standard telecom wavelength and
demonstrate PICs as a promising, scalable resource for future formation of
metropolitan quantum-secure communications networks
Exceptional Collections and del Pezzo Gauge Theories
Stacks of D3-branes placed at the tip of a cone over a del Pezzo surface
provide a way of geometrically engineering a small but rich class of
gauge/gravity dualities. We develop tools for understanding the resulting
quiver gauge theories using exceptional collections. We prove two important
results for a general quiver gauge theory: 1) we show the ordering of the nodes
can be determined up to cyclic permutation and 2) we derive a simple formula
for the ranks of the gauge groups (at the conformal point) in terms of the
numbers of bifundamentals. We also provide a detailed analysis of four node
quivers, examining when precisely mutations of the exceptional collection are
related to Seiberg duality.Comment: 26 pages, 1 figure; v2 footnote 2 amended; v3 ref adde
Brane Tilings and Exceptional Collections
Both brane tilings and exceptional collections are useful tools for
describing the low energy gauge theory on a stack of D3-branes probing a
Calabi-Yau singularity. We provide a dictionary that translates between these
two heretofore unconnected languages. Given a brane tiling, we compute an
exceptional collection of line bundles associated to the base of the
non-compact Calabi-Yau threefold. Given an exceptional collection, we derive
the periodic quiver of the gauge theory which is the graph theoretic dual of
the brane tiling. Our results give new insight to the construction of quiver
theories and their relation to geometry.Comment: 46 pages, 37 figures, JHEP3; v2: reference added, figure 13 correcte
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