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Yu Luo

Publications and source records attributed to Yu Luo.

At least 163 records · Page 9Linked to original sources
arXiv2021

Observation of topological edge states in thermal diffusion

The topological band theory predicts that bulk materials with nontrivial topological phases support topological edge states. This phenomenon is universal for various wave systems and has been widely observed for electromagnetic and acoustic waves. Here, we extend the notion of band topology from wave to diffusion dynamics. Unlike the wave systems that are usually Hermitian, the diffusion systems are anti-Hermitian with purely imaginary eigenvalues corresponding to decay rates. Via direct probe of the temperature diffusion, we experimentally retrieve the Hamiltonian of a thermal lattice, and observe the emergence of topological edge decays within the gap of bulk decays. Our results show that such edge states exhibit robust decay rates, which are topologically protected against disorders. This work constitutes a thermal analogue of topological insulators and paves the way to exploring defect-immune heat dissipation.

cond-mat.mes-hall↗
arXiv2021

Cosmic Web-Halo Connection Between Twin Universes

Both simulation and observational data have shown that the spin and shape of dark matter halos are correlated with their nearby large-scale environment. As structure formation on different scales is strongly coupled, it is trick to disentangle the formation of halo with the large-scale environment, making it difficult to infer which is the driving force for the correlation between halo spin/shape with the large-scale structure. In this paper, we use N-body simulation to produce twin Universes that share the same initial conditions on small scales but different on large scales. This is achieved by changing the random seeds for the phase of those k modes smaller than a given scale in the initial conditions. In this way, we are able to disentangle the formation of halo and large-scale structure, making it possible to investigate how halo spin and shape correspond to the change of environment on large scales. We identify matching halo pairs in the twin simulations as those sharing the maximum number of identical particles within each other. Using these matched halo pairs, we study the cross match of halo spin and their correlation with the large-scale structure. It is found that when the large-scale environment changes (eigenvector) between the twin simulations, the halo spin has to rotate accordingly, although not significantly, to maintain the universal correlation seen in each simulation. Our results suggest that the large-scale structure is the main factor to drive the correlation between halo properties and their environment.

astro-ph.CO↗
arXiv2021

Bayesian inference for continuous-time hidden Markov models with an unknown number of states

We consider the modeling of data generated by a latent continuous-time Markov jump process with a state space of finite but unknown dimensions. Typically in such models, the number of states has to be pre-specified, and Bayesian inference for a fixed number of states has not been studied until recently. In addition, although approaches to address the problem for discrete-time models have been developed, no method has been successfully implemented for the continuous-time case. We focus on reversible jump Markov chain Monte Carlo which allows the trans-dimensional move among different numbers of states in order to perform Bayesian inference for the unknown number of states. Specifically, we propose an efficient split-combine move which can facilitate the exploration of the parameter space, and demonstrate that it can be implemented effectively at scale. Subsequently, we extend this algorithm to the context of model-based clustering, allowing numbers of states and clusters both determined during the analysis. The model formulation, inference methodology, and associated algorithm are illustrated by simulation studies. Finally, We apply this method to real data from a Canadian healthcare system in Quebec.

stat.ME↗
arXiv2021

Bayesian Clustering for Continuous-Time Hidden Markov Models

We develop clustering procedures for longitudinal trajectories based on a continuous-time hidden Markov model (CTHMM) and a generalized linear observation model. Specifically in this paper, we carry out finite and infinite mixture model-based clustering for a CTHMM and achieve inference using Markov chain Monte Carlo (MCMC). For a finite mixture model with prior on the number of components, we implement reversible-jump MCMC to facilitate the trans-dimensional move between different number of clusters. For a Dirichlet process mixture model, we utilize restricted Gibbs sampling split-merge proposals to expedite the MCMC algorithm. We employ proposed algorithms to the simulated data as well as a real data example, and the results demonstrate the desired performance of the new sampler.

stat.ME↗
arXiv2021

A Robust Tube-Based Smooth-MPC for Robot Manipulator Planning

Model Predictive Control (MPC) has shown the great performance of target optimization and constraint satisfaction. However, the heavy computation of the Optimal Control Problem (OCP) at each triggering instant brings the serious delay from state sampling to the control signals, which limits the applications of MPC in resource-limited robot manipulator systems over complicated tasks. In this paper, we propose a novel robust tube-based smooth-MPC strategy for nonlinear robot manipulator planning systems with disturbances and constraints. Based on piecewise linearization and state prediction, our control strategy improves the smoothness and optimizes the delay of the control process. By deducing the deviation of the real system states and the nominal system states, we can predict the next real state set at the current instant. And by using this state set as the initial condition, we can solve the next OCP ahead and store the optimal controls based on the nominal system states, which eliminates the delay. Furthermore, we linearize the nonlinear system with a given upper bound of error, reducing the complexity of the OCP and improving the response speed. Based on the theoretical framework of tube MPC, we prove that the control strategy is recursively feasible and closed-loop stable with the constraints and disturbances. Numerical simulations have verified the efficacy of the designed approach compared with the conventional MPC.

cs.RO↗
arXiv2021

Adaptive Deconvolution-based stereo matching Net for Local Stereo Matching

In deep learning-based local stereo matching methods, larger image patches usually bring better stereo matching accuracy. However, it is unrealistic to increase the size of the image patch size without restriction. Arbitrarily extending the patch size will change the local stereo matching method into the global stereo matching method, and the matching accuracy will be saturated. We simplified the existing Siamese convolutional network by reducing the number of network parameters and propose an efficient CNN based structure, namely Adaptive Deconvolution-based disparity matching Net (ADSM net) by adding deconvolution layers to learn how to enlarge the size of input feature map for the following convolution layers. Experimental results on the KITTI 2012 and 2015 datasets demonstrate that the proposed method can achieve a good trade-off between accuracy and complexity.

cs.CV↗
arXiv2020

Surface Dyakonov-Cherenkov Radiation

Recent advances in engineered material technologies (e.g., photonic crystals, metamaterials, plasmonics, etc) provide valuable tools to control Cherenkov radiation. In all these approaches, however, the designed materials interact only with the particle velocity to affect Cherenkov radiation, while the influence of the particle trajectory is generally negligible. Here, we report on surface Dyakonov-Cherenkov radiation, i.e. the emission of directional Dyakonov surface waves from a swift charged particle moving atop a birefringent crystal. This new type of Cherenkov radiation is highly susceptible to both the particle velocity and trajectory, e.g. we observe a sharp radiation enhancement when the particle trajectory falls in the vicinity of a particular direction. Moreover, close to the Cherenkov threshold, such a radiation enhancement can be orders of magnitude higher than that obtained in traditional Cherenkov detectors. These distinct properties allow us to determine simultaneously the magnitude and direction of particle velocities on a compact platform. The surface Dyakonov-Cherenkov radiation studied in this work not only adds a new degree of freedom for particle identification, but also provides an all-dielectric route to construct compact Cherenkov detectors with enhanced sensitivity.

physics.optics↗
arXiv2020

The specific star formation rate function at different mass scales and quenching: A comparison between cosmological models and SDSS

We present the eddington bias corrected Specific Star Formation Rate Function (sSFRF) at different stellar mass scales from a sub-sample of the Sloan Digital Sky Survey Data Release DR7 (SDSS), which is considered complete both in terms of stellar mass (${\rm M_{\star}}$) and star formation rate (SFR). The above enable us to study qualitatively and quantitatively quenching, the distribution of passive/star-forming galaxies and perform comparisons with the predictions from state-of-the-art cosmological models, within the same ${\rm M_{\star}}$ and SFR limits. We find that at the low mass end (${\rm M_{\star}} = 10^{9.5} - 10^{10} \, {\rm M_{\odot}}$) the sSFRF is mostly dominated by star-forming objects. However, moving to the two more massive bins (${\rm M_{\star}} = 10^{10} - 10^{10.5} \, {\rm M_{\odot}}$ and ${\rm M_{\star}} = 10^{10.5} - 10^{11} \, {\rm M_{\odot}}$) a bi-modality with two peaks emerges. One peak represents the star-forming population, while the other describes a rising passive population. The bi-modal form of the sSFRFs is not reproduced by a range of cosmological simulations (e.g. Illustris, EAGLE, Mufasa, IllustrisTNG) which instead generate mostly the star-forming population, while a bi-modality emerges in others (e.g. L-Galaxies, Shark, Simba). Our findings reflect the need for the employed quenching schemes in state-of-the-art models to be reconsidered, involving prescriptions that allow "quenched galaxies" to retain a small level of SF activity (sSFR $=$ ${\rm 10^{-11} {\rm yr^{-1}}}$-${\rm 10^{-12} {\rm yr^{-1}}}$) and generate an adequate passive population/bi-modality even at intermediate masses (${\rm M_{\star}} = 10^{10} - 10^{10.5} \, {\rm M_{\odot}}$).

astro-ph.GA↗
arXiv2020

The formation of blue cluster in local Universe

It is well known from the Butcher-Oemler effect that galaxies in dense environment are mostly red with little star formation and the fraction of blue galaxies in galaxy groups/clusters also declines rapidly with redshifts. A recent work by Hashimoto et al. reported a local 'blue cluster' with high fraction of blue galaxies ($\sim 0.57$), higher than the model predictions. They ascribed this blue cluster to the feeding of gas along a filamentary structure around the cluster. In this work we use group catalog from the Sloan Digital Sky Survey Data Release 7 (SDSS DR7) and the state-of-art of semi-analytic model (SAM) to investigate the formation of blue clusters in local Universe. In total, we find four blue clusters with halo mass $\sim 10^{14}M_{\odot}$ at $0.02 < z < 0.082$, while only the one found by Hashimoto et al. is in a filamentary structure. The SAM predicts that blue clusters have later formation time and most blue satellite galaxies are recently accreted. We conclude that the formation of blue clusters is mainly governed by newly accreted blue satellites, rather than the effect of large-scale environment.

astro-ph.GA↗
arXiv2020

What has quenched the massive spiral galaxies?

Quenched massive spiral galaxies have attracted great attention recently, as more data is available to constrain their environment and cold gas content. However, the quenching mechanism is still uncertain, as it depends on the mass range and baryon budget of the galaxy. In this letter, we report the identification of a rare population of very massive, quenched spiral galaxies with stellar mass $\gtrsim10^{11}{\rm~M_\odot}$ and halo mass $\gtrsim10^{13}{\rm~M_\odot}$ from the Sloan Digital Sky Survey at redshift $z\sim0.1$. Our CO observations using the IRAM-30m telescope show that these galaxies contain only a small amount of molecular gas. Similar galaxies are also seen in the state-of-the-art semi-analytical models and hydro-dynamical simulations. It is found from these theoretical models that these quenched spiral galaxies harbor massive black holes, suggesting that feedback from the central black holes has quenched these spiral galaxies. This quenching mechanism seems to challenge the popular scenario of the co-evolution between massive black holes and massive bulges.

astro-ph.GA↗
arXiv2020

The parameter-free Finger-Of-God model and its application to 21cm intensity mapping

Using the galaxy catalog built from ELUCID N-body simulation and the semi-analytical galaxy formation model, we have built a mock HI intensity mapping map. We have implemented the Finger-of-God (FoG) effect in the map by considering the galaxy HI gas velocity dispersion. By comparing the HI power spectrum in the redshift space with the measurement from IllustrisTNG simulation, we have found that such FoG effect can explain the discrepancy between current mock map built from N-body simulation and Illustris TNG simulation. Then we built a parameter-free FoG model and a shot-noise model to calculate the HI power spectrum. We found that our model can accurately fit both the monopole and quadrupole moments of the HI matter power spectrum. Our method of building the mock HI intensity map and the parameter-free FoG model will be widely useful for the up-coming 21cm intensity mapping experiments, such as CHIME, Tianlai, BINGO, FAST and SKA. It is also crucial for us to study the non-linear effects in 21cm intensity mapping.

astro-ph.CO↗
arXiv2020

Effect of He on the Order-Disorder Transition in Ni3Al under Irradiation

The order-disorder transition in Ni-Al alloys under irradiation represents an interplay between various re-ordering processes and disordering due to thermal spikes generated by incident high energy particles. Typically, ordering in enabled by diffusion of thermally-generated vacancies, and can only take place at temperatures where they are mobile and in sufficiently high concentration. Here, in-situ transmission electron micrographs reveal that the presence of He, usually considered to be a deleterious immiscible atom in this material, promotes reordering in Ni3Al at temperatures where vacancies are not effective ordering agents. A rate-theory model is presented, that quantitatively explains this behavior, based on parameters extracted from atomistic simulations. These calculations show that the V2He complex is an effective agent through its high stability and mobility. It is surmised that immiscible atoms may stabilize reordering agents in other materials undergoing driven processes, and preserve ordered phases at temperature where the driven processes would otherwise lead to disorder.

cond-mat.mtrl-sci↗
arXiv2020

Controlling Cherenkov threshold with nonlocality

Cherenkov radiation is generally believed to be threshold-free in hyperbolic metamaterials owing to the extremely large photonic density of states in classical local framework. While recent advances in nonlocal and quantum effects extend our understanding of light-matter interactions in metallic nanostructures, the influence of nonlocality on threshold-free Cherenkov radiation still remains elusive. Here we theoretically demonstrate that the nonlocality provides an indispensable way to flexibly engineer Cherenkov thresholds in metallodielectric layered structures. Particularly, the nonlocality results in a lower-bound velocity cutoff, whose value is comparable to the electron Fermi velocity. Surprisingly, this lower-bound threshold can be significantly smaller than the classically predicted one if the metamaterial works around epsilon-near-zero frequencies. The capability to control Cherenkov thresholds opens numerous prospects for practical applications of Cherenkov radiation, in particular, for integrated free-electron radiation sources.

physics.app-ph↗
arXiv2020

Quantifying quantum non-Markovianity based on quantum coherence via skew information

Based on the nonincreasing property of quantum coherence via skew information under incoherent completely positive and trace-preserving maps, we propose a non-Markovianity measure for open quantum processes. As applications, by applying the proposed measure to some typical noisy channels, we find that it is equivalent to the three previous measures of non-Markovianity for phase damping and amplitude damping channels, i.e., the measures based on the quantum trace distance, dynamical divisibility, and quantum mutual information. For the random unitary channel, it is equivalent to the non-Markovianity measure based on $l_1$ norm of coherence for a class of output states and it is incompletely equivalent to the measure based on dynamical divisibility. We also use the modified Tsallis relative $α$ entropy of coherence to detect the non-Markovianity of dynamics of quantum open systems, the results show that the modified Tsallis relative $α$ entropy of coherence are more comfortable than the original Tsallis relative $α$ entropy of coherence for small $α$.

quant-ph↗
arXiv2019

Practical Issues of Energy Harvesting and Data Transmissions in Sustainable IoT

The sustainable Internet of Things (IoT) is becoming a promising solution for the green living and smart industries. In this article, we investigate the practical issues in the radio energy harvesting and data communication systems through extensive field experiments. A number of important characteristics of energy harvesting circuits and communication modules have been studied, including the non-linear energy consumption of the communication system relative to the transmission power, the wake-up time associated with the payload, and the varying system power during consecutive packet transmissions. In order to improve the efficiency of energy harvest and energy utilization, we propose a new model to accurately describe the energy harvesting process and the power consumption for sustainable IoT devices. Experiments are performed using commercial IoT devices and RF energy harvesters to verify the accuracy of the proposed model. The experiment results show that the new model matches the performance of sustainable IoT devices very well in the real scenario.

eess.SP↗
arXiv2019

Dunkl-Supersymmetric Orthogonal functions associated with classical orthogonal polynomials

We consider the eigenvalue problem associated with the Dunkl-type differential operator (in which the reflection operator R is involved) L = dx R + v(x), (v(-x) = -v(x)), in the context of supersymmetric quantum mechanical models. By solving this eigenvalue problem with the help of known exactly solvable potentials, we construct several classes of functions satisfying certain orthogonality relations. We call them the Dunkl-supersymmetric (Dunkl-SUSY) orthogonal functions. These functions can be expressed in terms of the classical orthogonal polynomials (COPs). The key feature of these functions is that they appear by pairs, i.e., Qn(x) and Qn(-x) are both the eigenfunctions of L. A general formulation of the Dunkl-SUSY orthogonal polynomials is also presented.

math-ph↗
arXiv2019

A metamaterial-free fluid-flow cloak

The model of ideal fluid flow around a cylindrical obstacle exhibits a long-established physical picture where originally straight streamlines will be deflected over the whole space by the obstacle. As inspired by transformation optics and metamaterials, recent theories have proposed the concept of fluid cloaking able to recover the straight streamlines as if the obstacle does not exist. However, such a cloak, similar to all previous transformation-optics-based devices, relies on complex metamaterials, being difficult to implement. Here we deploy the theory of scattering cancellation and report on the experimental realization of a fluid-flow cloak without metamaterials. This cloak is realized by engineering the geometry of the fluid channel, which effectively cancels the dipole-like scattering of the obstacle. The cloaking effect is demonstrated via direct observation of the recovered straight streamlines in the fluid flow with injected dyes. Our work sheds new light on conventional fluid control and may find applications in microfluidic devices.

physics.app-ph↗