1,527 research outputs found
Vortices and the entrainment transition in the 2D Kuramoto model
We study synchronization in the two-dimensional lattice of coupled phase
oscillators with random intrinsic frequencies. When the coupling is larger
than a threshold , there is a macroscopic cluster of
frequency-synchronized oscillators. We explain why the macroscopic cluster
disappears at . We view the system in terms of vortices, since cluster
boundaries are delineated by the motion of these topological defects. In the
entrained phase (), vortices move in fixed paths around clusters, while
in the unentrained phase (), vortices sometimes wander off. These
deviant vortices are responsible for the disappearance of the macroscopic
cluster. The regularity of vortex motion is determined by whether clusters
behave as single effective oscillators. The unentrained phase is also
characterized by time-dependent cluster structure and the presence of chaos.
Thus, the entrainment transition is actually an order-chaos transition. We
present an analytical argument for the scaling for small
lattices, where is the threshold for phase-locking. By also deriving the
scaling , we thus show that for small , in
agreement with numerics. In addition, we show how to use the linearized model
to predict where vortices are generated.Comment: 11 pages, 8 figure
Universality in the one-dimensional chain of phase-coupled oscillators
We apply a recently developed renormalization group (RG) method to study
synchronization in a one-dimensional chain of phase-coupled oscillators in the
regime of weak randomness. The RG predicts how oscillators with randomly
distributed frequencies and couplings form frequency-synchronized clusters.
Although the RG was originally intended for strong randomness, i.e. for
distributions with long tails, we find good agreement with numerical
simulations even in the regime of weak randomness. We use the RG flow to derive
how the correlation length scales with the width of the coupling distribution
in the limit of large coupling. This leads to the identification of a
universality class of distributions with the same critical exponent . We
also find universal scaling for small coupling. Finally, we show that the RG
flow is characterized by a universal approach to the unsynchronized fixed
point, which provides physical insight into low-frequency clusters.Comment: 14 pages, 10 figure
Single-cell zeroth-order protein degradation enhances the robustness of synthetic oscillator
In Escherichia coli, protein degradation in synthetic circuits is commonly achieved by the ssrA-tagged degradation system. In this work, we show that the degradation kinetics for the green fluorescent protein fused with the native ssrA tag in each cell exhibits the zeroth-order limit of the Michaelis–Menten kinetics, rather than the commonly assumed first-order. When measured in a population, the wide distribution of protein levels in the cells distorts the true kinetics and results in a first-order protein degradation kinetics as a population average. Using the synthetic gene-metabolic oscillator constructed previously, we demonstrated theoretically that the zeroth-order kinetics significantly enlarges the parameter space for oscillation and thus enhances the robustness of the design under parametric uncertainty
Implementing Badhwar-O'Neill Galactic Cosmic Ray Model for the Analysis of Space Radiation Exposure
For the analysis of radiation risks to astronauts and planning exploratory space missions, accurate energy spectrum of galactic cosmic radiation (GCR) is necessary. Characterization of the ionizing radiation environment is challenging because the interplanetary plasma and radiation fields are modulated by solar disturbances and the radiation doses received by astronauts in interplanetary space are likewise influenced. A model of the BadhwarO'Neill 2011 (BO11) GCR environment, which is represented by GCR deceleration potential theta, has been derived by utilizing all of the GCR measurements from balloons, satellites, and the newer NASA Advanced Composition Explorer (ACE). In the BO11 model, the solar modulation level is derived from the mean international sunspot numbers with timedelay, which has been calibrated with actual flight instrument measurements to produce better GCR flux data fit during solar minima. GCR fluxes provided by the BO11 model were compared with various spacecraft measurements at 1 AU, and further comparisons were made for the tissue equivalent proportional counters measurements at low Earth orbits using the highcharge and energy transport (HZETRN) code and various GCR models. For the comparison of the absorbed dose and dose equivalent calculations with the measurements by Radiation Assessment Detector (RAD) at Gale crater on Mars, the intensities and energies of GCR entering the heliosphere were calculated by using the BO11 model, which accounts for timedependent attenuation of the local interstellar spectrum of each element. The BO11 model, which has emphasized for the last 24 solar minima, showed in relatively good agreement with the RAD data for the first 200 sols, but it was resulted in to be less well during near the solar maximum of solar cycle 24 due to subtleties in the changing heliospheric conditions. By performing the error analysis of the BO11 model and the optimization in reducing overall uncertainty, the resultant BO13 model corrects the fit at solar maxima as well as being accurate at solar minima. The BO13 model is implemented to the NASA Space Cancer Risk model for the assessment of radiation risks. Overall cumulative probability distribution of solar modulation parameters represents the percentile rank of the average interplanetary GCR environment, and the probabilistic radiation risks can be assessed for various levels of GCR environment to support mission design and operational planning for future manned space exploration missions
The Role of Federated Learning in a Wireless World with Foundation Models
Foundation models (FMs) are general-purpose artificial intelligence (AI)
models that have recently enabled multiple brand-new generative AI
applications. The rapid advances in FMs serve as an important contextual
backdrop for the vision of next-generation wireless networks, where federated
learning (FL) is a key enabler of distributed network intelligence. Currently,
the exploration of the interplay between FMs and FL is still in its nascent
stage. Naturally, FMs are capable of boosting the performance of FL, and FL
could also leverage decentralized data and computing resources to assist in the
training of FMs. However, the exceptionally high requirements that FMs have for
computing resources, storage, and communication overhead would pose critical
challenges to FL-enabled wireless networks. In this article, we explore the
extent to which FMs are suitable for FL over wireless networks, including a
broad overview of research challenges and opportunities. In particular, we
discuss multiple new paradigms for realizing future intelligent networks that
integrate FMs and FL. We also consolidate several broad research directions
associated with these paradigms.Comment: 8 pages, 5 figures, 1 tabl
Towards Quantum Belief Propagation for LDPC Decoding in Wireless Networks
We present Quantum Belief Propagation (QBP), a Quantum Annealing (QA) based
decoder design for Low Density Parity Check (LDPC) error control codes, which
have found many useful applications in Wi-Fi, satellite communications, mobile
cellular systems, and data storage systems. QBP reduces the LDPC decoding to a
discrete optimization problem, then embeds that reduced design onto quantum
annealing hardware. QBP's embedding design can support LDPC codes of block
length up to 420 bits on real state-of-the-art QA hardware with 2,048 qubits.
We evaluate performance on real quantum annealer hardware, performing
sensitivity analyses on a variety of parameter settings. Our design achieves a
bit error rate of in 20 s and a 1,500 byte frame error rate of
in 50 s at SNR 9 dB over a Gaussian noise wireless channel.
Further experiments measure performance over real-world wireless channels,
requiring 30 s to achieve a 1,500 byte 99.99 frame delivery rate at
SNR 15-20 dB. QBP achieves a performance improvement over an FPGA based soft
belief propagation LDPC decoder, by reaching a bit error rate of and
a frame error rate of at an SNR 2.5--3.5 dB lower. In terms of
limitations, QBP currently cannot realize practical protocol-sized
( Wi-Fi, WiMax) LDPC codes on current QA processors. Our
further studies in this work present future cost, throughput, and QA hardware
trend considerations
A 3D-Hybrid-Shot Spiral Sequence for Hyperpolarized C Imaging
Purpose: Hyperpolarized imaging experiments have conflicting requirements of
high spatial, temporal, and spectral resolution. Spectral-Spatial RF excitation
has been shown to form an attractive magnetization-efficient method for
hyperpolarized imaging, but the optimum readout strategy is not yet known.
Methods: In this work we propose a novel 3D hybrid-shot spiral sequence which
features two constant density regions that permit the retrospective
reconstruction of either high spatial or high temporal resolution images post
hoc, (adaptive spatiotemporal imaging) allowing greater flexibility in
acquisition and reconstruction.
Results: We have implemented this sequence, both via simulation and on a
pre-clinical scanner, to demonstrate its feasibility, in both a 1H phantom and
with hyperpolarized 13C pyruvate in vivo. Conclusion: This sequence forms an
attractive method for acquiring hyperpolarized imaging datasets, providing
adaptive spatiotemporal imaging to ameliorate the conflict of spatial and
temporal resolution, with significant potential for clinical translation
Multiscale Computations on Neural Networks: From the Individual Neuron Interactions to the Macroscopic-Level Analysis
We show how the Equation-Free approach for multi-scale computations can be
exploited to systematically study the dynamics of neural interactions on a
random regular connected graph under a pairwise representation perspective.
Using an individual-based microscopic simulator as a black box coarse-grained
timestepper and with the aid of simulated annealing we compute the
coarse-grained equilibrium bifurcation diagram and analyze the stability of the
stationary states sidestepping the necessity of obtaining explicit closures at
the macroscopic level. We also exploit the scheme to perform a rare-events
analysis by estimating an effective Fokker-Planck describing the evolving
probability density function of the corresponding coarse-grained observables
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