We present a new bound on the ultralight axion (ULA) dark matter mass m_{a}, using the Lyman-alpha forest to look for suppressed cosmic structure growth: a 95% lower limit m_{a}>2×10^{-20} eV. This ...strongly disfavors (>99.7% credibility) the canonical ULA with 10^{-22} eV<m_{a}<10^{-21} eV, motivated by the string axiverse and solutions to possible tensions in the cold dark matter model. We strengthen previous equivalent bounds by about an order of magnitude. We demonstrate the robustness of our results using an optimized emulator of improved hydrodynamical simulations.
Functionalization of flexible materials based on mesoscopic reconstruction is a key strategy in fabricating biocompatible flexible electronics. This work is to acquire new mesoscopic bioelectronic ...hybrid materials of silk fibroin (SF)‐Ag nanoclusters (AgNCs@BSA; BSA: bovine serum albumin), which enhance significantly the performance of silk memristors. It is to build AgNCs@BSA into SF mesoscopic networks by templated β‐crystallization. Atomic force microscopy potential probing indicates that AgNCs@BSA serve as electronic potential wells that change completely the transport behavior of charge particles within the SF films. This leads to significant enhancement in the switching speed (≈10 ns), very good switching stability, extremely low set/reset voltages (0.3/−0.18 V) of SF meso‐hybrid memristors, compared with the original and other organic memristors, and displays unique synapse characteristics and the capability of synapse learning. Classical density functional theory Poisson–Nernst–Planck simulations indicate that the enhanced performance is subject to the low potential paths interconnecting the AgNCs@BSA, which guide charges' transport (Ag+) and deposition in SF films.
A completely new materials engineering strategy, functionalized templated mesoscopic reconstruction, is introduced. The designed silk meso‐functional materials display significantly enhanced performance and gives rise to a new class of silk electronics (memristors and synaptic emulators). This progress represents a breakthrough in flexible materials and flexible electronics.
Power-electronic-based grid emulators (GEs) emerge as a favorable method for testing grid-code compliances of wind turbines (WTs), thanks to their full controllability and improved efficiency. To ...accommodate the increasing power and voltage levels of WTs, scalability becomes a critical requirement for the topologies of converter-based GEs. This paper identifies first the power rating of future GEs based on the system architecture and the evolution of WTs, followed by evaluating converter topologies of GEs for high scalability. Design considerations of power semiconductor devices, step-up transformers, dc chopper and dc capacitors are also discussed for existing and prospective GEs.
The Earth system is often modeled as a dynamical system in what has come to be known as Earth System Models. When used to study anthropogenically forced climate change, these models are forced in ...such a way that they are not in a statistically stationary state. Yet, statistical statements are still made about the Earth climate system using only a single trajectory by taking temporal averages. At each moment in time, one draws a sample from a different distribution, raising questions about the utility of temporal averages, in stark contrast to the utility of temporal averages in ergodic systems. This work follows in the tradition of using a toy model to examine properties present in the Earth climate system. We aim to examine how we can make meaningful statistical statements in non-stationary systems when only dealing with a single trajectory. We use the Lorenz equations with a time-varying parameter as a starting point for comparing ensemble averages to temporal averages. We find that, in so far as the control parameter induces a slow and smooth change in the dynamics, the resulting statistics of ensemble averages compare well to those of temporal averages.
•A Markov chain-based methodology for the study of non-stationary dynamical systems.•Evolution of statistics in Lorenz system with a time-varying parameter is studied.•Given slowly-varying parameters, temporal averages correspond to ensemble averages.•Extension of methodology to study statistics in a changing climate is discussed.
Surrogate modeling and uncertainty quantification tasks for PDE systems are most often considered as supervised learning problems where input and output data pairs are used for training. The ...construction of such emulators is by definition a small data problem which poses challenges to deep learning approaches that have been developed to operate in the big data regime. Even in cases where such models have been shown to have good predictive capability in high dimensions, they fail to address constraints in the data implied by the PDE model. This paper provides a methodology that incorporates the governing equations of the physical model in the loss/likelihood functions. The resulting physics-constrained, deep learning models are trained without any labeled data (e.g. employing only input data) and provide comparable predictive responses with data-driven models while obeying the constraints of the problem at hand. This work employs a convolutional encoder-decoder neural network approach as well as a conditional flow-based generative model for the solution of PDEs, surrogate model construction, and uncertainty quantification tasks. The methodology is posed as a minimization problem of the reverse Kullback-Leibler (KL) divergence between the model predictive density and the reference conditional density, where the later is defined as the Boltzmann-Gibbs distribution at a given inverse temperature with the underlying potential relating to the PDE system of interest. The generalization capability of these models to out-of-distribution input is considered. Quantification and interpretation of the predictive uncertainty is provided for a number of problems.
•Physics-constrained surrogates achieve comparable accuracy with data-driven ones without labeled data and generalize better.•Flow-based conditional generative model trained with reverse KL-divergence without labels captures the predictive uncertainty.•The developed models are used to solve PDEs, as surrogate models and for uncertainty propagation and calibration tasks.•Convolutional neural nets capture multiscale features of PDE solution fields much more effectively than fully-connected ones.
On August 17, 2017 the LIGO interferometers detected the gravitational wave (GW) signal (GW170817) from the coalescence of binary neutron stars. This signal was also simultaneously seen throughout ...the electromagnetic (EM) spectrum from radio waves to gamma rays. We point out that this simultaneous detection of GW and EM signals rules out a class of modified gravity theories, termed “dark matter emulators,” which dispense with the need for dark matter by making ordinary matter couple to a different metric from that of GW. We discuss other kinds of modified gravity theories which dispense with the need for dark matter and are still viable. This simultaneous observation also provides the first observational test of Einstein’s weak equivalence principle (WEP) between gravitons and photons. We estimate the Shapiro time delay due to the gravitational potential of the total dark matter distribution along the line of sight (complementary to the calculation by Abbott et al. Astrophys. J. Lett. 848, L13 (2017)) to be about 400 days. Using this estimate for the Shapiro delay and from the time difference of 1.7 seconds between the GW signal and gamma rays, we can constrain violations of the WEP using the parametrized post-Newtonian parameter γ, and it is given by |γGW−γEM|<9.8×10−8.
The adiabatic theorem, a corollary of the Schrödinger equation, manifests itself in a profoundly different way in non-Hermitian arrangements, resulting in counterintuitive state transfer schemes that ...have no counterpart in closed quantum systems. In particular, the dynamical encirclement of exceptional points (EPs) in parameter space has been shown to lead to a chiral phase accumulation, non-adiabatic jumps and topological mode conversion
. Recent theoretical studies, however, have shown that contrary to previously established demonstrations, this behaviour is not strictly a result of winding around a non-Hermitian degeneracy
. Instead, it seems to be mostly attributed to the non-trivial landscape of the Riemann surfaces, sometimes because of the presence of an EP in the vicinity
. Here, in an effort to bring this counterintuitive aspect of non-Hermitian systems to light and confirm this hypothesis, we provide a set of experiments to directly observe the field evolution and chiral state conversion in an EP-excluding cycle in a slowly varying non-Hermitian system. To do so, a versatile yet unique fibre-based photonic emulator is realized that utilizes the polarization degrees of freedom in a quasi-common-path single-ring arrangement. Our observations may open up new avenues for light manipulation and state conversion, as well as providing a foundation for understanding the intricacies of the adiabatic theorem in non-Hermitian systems.
We construct an emulator for the halo mass function over group and cluster mass scales for a range of cosmologies, including the effects of dynamical dark energy and massive neutrinos. The emulator ...is based on the recently completed Mira-Titan Universe suite of cosmological N-body simulations. The main set of simulations spans 111 cosmological models with 2.1 Gpc boxes. We extract halo catalogs in the redshift range z = 0.0, 2.0 and for masses . The emulator covers an eight-dimensional hypercube spanned by { , , , 8, h, ns, w0, wa}; spatial flatness is assumed. We obtain smooth halo mass functions by fitting piecewise second-order polynomials to the halo catalogs and employ Gaussian process regression to construct the emulator while keeping track of the statistical noise in the input halo catalogs and uncertainties in the regression process. For redshifts z 1, the typical emulator precision is better than 2% for and <10% for . For comparison, fitting functions using the traditional universal form for the halo mass function can be biased at up to 30% at for z = 0. Our emulator is publicly available at https://github.com/SebastianBocquet/MiraTitanHMFemulator.
•Investigation of three modeling techniques for PV characteristic generation.•Operation of experimental data to evaluate the investigated models for three module technologies.•Development of a PV ...model selection mechanism according to three criteria.•Design of PV emulator based on SMPS and PV characteristic generator.•Implementation of the control and the model selection mechanism on the designed emulator.
The increasing interest in the testing of photovoltaic systems and conversion components, resulted in the growth of PV emulators development, especially the power converter based ones. These emulators allow the characteristics reproduction of PV modules and panels in a well-controlled environment, by using different PV modeling methods. In this paper, three modeling techniques are investigated for three PV technologies (Amorphous, CdTe and Mono-Si). The investigation of the models is done using experimental data from Green Energy Park in Morocco according to proposed evaluation criteria. The criteria themselves are based on the coefficient of determination, the Root Mean Square Error and the required computational time. The analysis results in a mechanism allowing the selection of the best modeling approach for each PV module technology. Afterwards, simulation work is carried out in order to design the control scheme of the PV emulator power supply. Then, the control and modeling method selection mechanism based on module technologies is implemented experimentally on the designed PV emulator system. Hence, the PV emulator along with its control and modeling method is validated for an example of Amorphous technology module.
Summary
In this paper, grounded and floating decremental/incremental memristor emulators have been proposed by using an operational transconductance amplifier (OTA), current differencing buffered ...amplifier (CDBA), and a grounded capacitor. The proposed memristor emulators are simpler in design over most of the realizations of memristor emulators available in the literature. The proposed configurations of grounded and floating decremental memristor emulators can be easily converted into grounded and floating incremental memristor emulators. The pinched hysteresis loops obtained from proposed memristor emulators are maintained up to 1‐MHz frequency in both decremental and incremental configurations. Simulation results have been obtained using a Mentor Graphics Eldo simulation tool in 0.18‐μm complementary metal‐oxide semiconductor (CMOS) technology parameters. Analog filters have also been designed to verify the performance of proposed grounded and floating memristor emulators.
In this paper, groundedand floating decremental/incremental memristor emulators have been proposed by using operationaltransconductance amplifier (OTA), current differencing buffered amplifier (CDBA) and a grounded capacitor. The proposed memristor emulators are simpler in design over most of the realizations of memristor emulatorsavailable in the literature. The pinched hysteresis loops obtained from proposed memristor emulators aremaintained up to 1 MHz frequency. Analog filters have also been designed to verify the performance of proposed grounded and floating memristor emulators.
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