arXiv subjects

Hao Wei

Publications and source records attributed to Hao Wei.

At least 73 records · Page 4Linked to original sources

arXiv2021

Effect of Redshift Distributions of Fast Radio Bursts on Cosmological Constraints

Nowadays, fast radio bursts (FRBs) have been a promising probe for astronomy and cosmology. However, it is not easy to identify the redshifts of FRBs to date. Thus, no sufficient actual FRBs with identified redshifts can be used to study cosmology currently. In the past years, one has to use the simulated FRBs with "known" redshifts instead. To simulate an FRB, one should randomly assign a redshift to it from a given redshift distribution. But the actual redshift distribution of FRBs is still unknown so far. Therefore, many redshift distributions have been assumed in the literature. In the present work, we study the effect of various redshift distributions on cosmological constraints, while they are treated equally. We find that different redshift distributions lead to different cosmological constraining abilities from the simulated FRBs. This result emphasizes the importance to find the actual redshift distribution of FRBs, and reminds us of the possible bias in the FRB simulations due to the redshift distributions.

astro-ph.CO↗

arXiv2020

CorDEL: A Contrastive Deep Learning Approach for Entity Linkage

Entity linkage (EL) is a critical problem in data cleaning and integration. In the past several decades, EL has typically been done by rule-based systems or traditional machine learning models with hand-curated features, both of which heavily depend on manual human inputs. With the ever-increasing growth of new data, deep learning (DL) based approaches have been proposed to alleviate the high cost of EL associated with the traditional models. Existing exploration of DL models for EL strictly follows the well-known twin-network architecture. However, we argue that the twin-network architecture is sub-optimal to EL, leading to inherent drawbacks of existing models. In order to address the drawbacks, we propose a novel and generic contrastive DL framework for EL. The proposed framework is able to capture both syntactic and semantic matching signals and pays attention to subtle but critical differences. Based on the framework, we develop a contrastive DL approach for EL, called CorDEL, with three powerful variants. We evaluate CorDEL with extensive experiments conducted on both public benchmark datasets and a real-world dataset. CorDEL outperforms previous state-of-the-art models by 5.2% on public benchmark datasets. Moreover, CorDEL yields a 2.4% improvement over the current best DL model on the real-world dataset, while reducing the number of training parameters by 97.6%.

cs.DB↗

arXiv2020

Cosmological Time Crystals From Einstein-Cubic Gravities

By including appropriate Riemman cubic invariants, we find that the dynamics of classical time crystals can be straightforwardly realized in Einstein gravity on the FLRW metric. The time reflection symmetry is spontaneously broken in the two vacua with the same scale factor $a$, but opposite $\dot a$. The tunneling from one vacuum to the other provides a robust mechanism for bounce universes; it always occurs for systems with positive energy density. For suitable matter energy-momentum tensor we also construct cyclic universes. Cosmological solutions that resemble the classical time crystals can be constructed in massive gravity.

hep-th↗

arXiv2020

Lemaitre-Tolman-Bondi Static Universe in Rastall-like Gravity

In this work, we try to obtain a stable Lemaitre-Tolman-Bondi (LTB) static universe, which is spherically symmetric and radially inhomogeneous. However, this is not an easy task, and fails in general relativity (GR) and various modified gravity theories, because the corresponding LTB static universes must reduce to the Friedmann-Robertson-Walker (FRW) static universes. We find a way out in a new type of modified gravity theory, in which the conservation of energy and momentum is broken. In this work, we have proposed a novel modification to the original Rastall gravity. In some sense, our Rastall-like gravity is essentially different from GR and the original Rastall gravity. In this Rastall-like gravity, LTB static solutions have been found. The stability of LTB static universe against both the homogeneous and the inhomogeneous scalar perturbations is also discussed in details. We show that a LTB static universe can be stable in this Rastall-like gravity.

gr-qc↗

arXiv2020

Neutron Star as a Mirror for Gravitational Waves

Gravitational wave (GW) has become one of the most active fields in physics and astronomy since the first direct detection of GW event in 2015. As is well known, multiple images of GW events are possible through the gravitational lenses. Here, we propose a novel mirror imaging mechanism for GW events different from the gravitational lens. In the literature, the superconductor was predicted to be highly reflective mirror for GWs. It is well known that neutron stars exhibit superconductivity and superfluidity. In this work, we predict that there are two types of GW mirror imaging phenomena caused by the neutron star located in Milky Way or the same host galaxy of GW source, which might be detected within a life period of man (namely the time delay $Δt$ can be a few years to a few tens of years). It is expected to witness this predicted GW mirror imaging phenomenon in the near future. In the long term, the observations of this novel GW mirror imaging phenomenon might help us to find numerous neutron stars unseen by other means, and learn more about the complicated internal structures of neutron stars, as well as their equations of state.

gr-qc↗

arXiv2020

Cosmic Anisotropy and Fast Radio Bursts

In the recent years, the field of fast radio bursts (FRBs) is thriving and growing rapidly. It is of interest to study cosmology by using FRBs with known redshifts. In the present work, we try to test the possible cosmic anisotropy with the simulated FRBs. In particular, we only consider the possible dipole in FRBs, rather than the cosmic anisotropy in general, while the analysis is only concerned with finding the rough number of necessary data points to distinguish a dipole from a monopole structure through simulations. Noting that there is no a large sample of actual data of FRBs with known redshifts by now, simulations are necessary to this end. We find that at least 2800, 190, 100 FRBs are competent to find the cosmic dipole with amplitude 0.01, 0.03, 0.05, respectively. Unfortunately, even 10000 FRBs are not competent to find the tiny cosmic dipole with amplitude of ${\cal O}(10^{-3})$. On the other hand, at least 20 FRBs with known redshifts are competent to find the cosmic dipole with amplitude 0.1. We expect that such a big cosmic dipole could be ruled out by using only a few tens of FRBs with known redshifts in the near future.

astro-ph.CO↗

arXiv2020

The Possible Electromagnetic Counterparts of the First High-Probability NSBH Merger LIGO/Virgo S190814bv

LIGO/Virgo S190814bv is the first high-probability neutron star - black hole (NSBH) merger candidate, whose gravitational waves (GWs) triggered LIGO/Virgo detectors at 21:10:39.012957 UT, 14 August 2019. It has a probability $>99\%$ of being an NSBH merger, with a low false alarm rate (FAR) of 1 per 1.559e+25 years. For an NSBH merger, electromagnetic counterparts (especially short gamma-ray bursts (GRBs)) are generally expected. However, no electromagnetic counterpart has been found in the extensive follow-up observing campaign. In the present work, we propose a novel explanation to this null result. In our scenario, LIGO/Virgo S190814bv is just a GW mirror image of the real NSBH merger which should be detected before 14 September 2015, but at that time we had no ability to detect its GW signals. The electromagnetic counterparts associated with the real NSBH merger should be found in the archive data before 14 September 2015. In this work, we indeed find 9 short GRBs as the possible electromagnetic counterparts.

astro-ph.HE↗

arXiv2020

Reconstructing the Fraction of Baryons in the Intergalactic Medium with Fast Radio Bursts via Gaussian Processes

Fast radio bursts (FRBs) are a promising new probe for astronomy and cosmology. Thanks to their extragalactic and cosmological origin, FRBs could be used to study the intergalactic medium (IGM) and the cosmic expansion. It is expected that numerous FRBs with identified redshifts will be available in the near future through the identification of their host galaxies or counterparts. $\rm DM_{IGM}$, the contribution from IGM to the observed dispersion measure (DM) of FRB, carries the key information about IGM and the cosmic expansion history. We can thus study the evolution of the universe by using FRBs with identified redshifts. In the present work, we are interested in the fraction of baryon mass in the IGM, $f_{\rm IGM}$, which is useful to study the cosmic expansion and the problem of the "missing baryons". We propose to reconstruct the evolution of $f_{\rm IGM}$ as a function of redshift $z$ with FRBs via a completely model-independent method, namely Gaussian processes. Since there is not a large sample of FRBs with identified redshifts, we use simulated FRBs instead. Through various simulations, we show that this methodology works well.

astro-ph.CO↗

arXiv2019

DS-GCNs: Connectome Classification Using Dynamic Spectral Graph Convolution Networks with Assistant Task Training

Functional Connectivity (FC) matrices measure the regional interactions in the brain and have been widely used in neurological brain disease classification. However, a FC matrix is neither a natural image which contains shape and texture information, nor a vector of independent features, which renders the extracting of efficient features from matrices as a challenging problem. A brain network, also named as connectome, could forma a graph structure naturally, the nodes of which are brain regions and the edges are interregional connectivity. Thus, in this study, we proposed novel graph convolutional networks (GCNs) to extract efficient disease-related features from FC matrices. Considering the time-dependent nature of brain activity, we computed dynamic FC matrices with sliding-windows and implemented a graph convolution based LSTM (long short term memory) layer to process dynamic graphs. Moreover, the demographics of patients were also used to guide the classification. However, unlike in conventional methods where personal information, i.e., gender and age were added as extra inputs, we argue that this kind of approach may not actually improve the classification performance, for such personal information given in dataset was usually balanced distributed. In this paper, we proposed to utilize the demographic information as extra outputs and to share parameters among three networks predicting subject status, gender and age, which serve as assistant tasks. We tested the performance of the proposed architecture in ADNI II dataset to classify Alzheimer's disease patients from normal controls. The classification accuracy, sensitivity and specificity reach 0.90, 0.92 and 0.89 on ADNI II dataset.

physics.med-ph↗

arXiv2019

AutoBlock: A Hands-off Blocking Framework for Entity Matching

Entity matching seeks to identify data records over one or multiple data sources that refer to the same real-world entity. Virtually every entity matching task on large datasets requires blocking, a step that reduces the number of record pairs to be matched. However, most of the traditional blocking methods are learning-free and key-based, and their successes are largely built on laborious human effort in cleaning data and designing blocking keys. In this paper, we propose AutoBlock, a novel hands-off blocking framework for entity matching, based on similarity-preserving representation learning and nearest neighbor search. Our contributions include: (a) Automation: AutoBlock frees users from laborious data cleaning and blocking key tuning. (b) Scalability: AutoBlock has a sub-quadratic total time complexity and can be easily deployed for millions of records. (c) Effectiveness: AutoBlock outperforms a wide range of competitive baselines on multiple large-scale, real-world datasets, especially when datasets are dirty and/or unstructured.

cs.DB↗

arXiv2019

Observational Constraints on Growth Index with Cosmography

In the literature, it was proposed that the growth index $γ$ is useful to distinguish the scenarios of dark energy and modified gravity. In the present work, we consider the constraints on the growth index $γ$ by using the latest observational data. To be model-independent, we use cosmography to describe the cosmic expansion history, and also expand the general $γ(z)$ as a Taylor series with respect to redshift $z$ or $y$-shift, $y=z/(1+z)$. We find that the present value $γ_0=γ(z=0)\simeq 0.42$ (for most of viable $f(R)$ theories) is inconsistent with the latest observational data at high confidence level (C.L.). On the other hand, $γ_0\simeq 0.55$ (for dark energy models in GR) can be consistent with the latest observational data at $1σ$ C.L. in 5 of the 9 cases under consideration, but is inconsistent beyond $2σ$ C.L. in the other 4 cases (while it is still consistent within the $3σ$ region). Thus, we can say nothing firmly about $γ_0\simeq 0.55$. We also find that a varying $γ(z)$ is favored.

astro-ph.CO↗

arXiv2019

Emergent Universe Scenario, Bouncing and Cyclic Universes in Degenerate Massive Gravity

We consider alternative inflationary cosmologies in massive gravity with degenerate reference metrics and study the feasibilities of the emergent universe scenario, bouncing and cyclic universes. We focus on the construction of the Einstein static universe, classes of exact solutions of bouncing and cyclic universes in degenerate massive gravity. We further study the stabilities of the Einstein static universe against both homogeneous and inhomogeneous scalar perturbations and give the parameters region for a stable Einstein static universe.

gr-qc↗

arXiv2019

Non-parametric Reconstruction of Growth Index via Gaussian Processes

The accelerated cosmic expansion could be due to dark energy within general relativity (GR), or modified gravity. It is of interest to differentiate between them, by using both the expansion history and the growth history. In the literature, it was proposed that the growth index $γ$ is useful to distinguish these two scenarios. In this work, we consider the non-parametric reconstruction of the growth index $γ$ as a function of redshift $z$ from the latest observational data as of July 2018 via Gaussian Processes. We find that $f(R)$ theories and dark energy models within GR (especially $Λ$CDM) are inconsistent with the results in the moderate redshift range far beyond $3σ$ confidence level. A modified gravity scenario different from $f(R)$ theories is favored. However, these results can also be due to other non-trivial possibilities, in which dark energy models within GR (especially $Λ$CDM) and $f(R)$ theories might still survive. In all cases, our results suggest that new physics is required.

astro-ph.CO↗

arXiv2019

Holographic Entanglement Entropy and Van der Waals transitions in Einstein-Maxwell-dilaton theory

According to the gauge/gravity duality, the Van der Waals transition of charged AdS black holes in extended phase space is conjectured to be dual to a renormalization group flow on the space of field theories. So exploring the Van der Waals transition is potentially valuable for studying holographic properties of charged black hole thermodynamics. There are different transition behaviors for charged dilatonic AdS black holes in Einstein-Maxwell-dilaton (EMD) theory with string-inspired potential with different dilaton coupling constants in diverse dimensions. In this work, we find a special class of charged dilatonic AdS black holes which have the standard Van der Waals transition. We study the extended thermodynamics of the special class of black holes, which, in the extremal limit, have near-horizon geometry conformal to AdS$_2 \times S^{D-2}$. We find that, for these black holes, both the pressure-volume transition in fixed charge ensemble and the inverse temperature-entropy transition in fixed pressure ensemble have the standard Van der Waals behaviors. We also find the holographic entanglement entropy undergoes the same transition behaviors for the same critical temperature in fixing the thermodynamic pressure ensemble.

gr-qc↗

arXiv2019

${\cal P}-v$ Criticality in Gauged Supergravities

AdS black holes show richer transition behaviors in extended phase space by assuming the cosmological constant and its conjugate quantity to behave like thermodynamic pressure and thermodynamic volume. We study the extended thermodynamics of charged dilatonic AdS black holes in a class of Einstein-Maxwell-dilaton theories that can be embedded in gauged supergravities in various dimensions. We find that the transition behaviors of higher dimensional dilatonic AdS black holes are different from the four dimensional counterparts, and new transition behaviors emerges in higher dimensions. First, there exists standard Van der Waals transition only in a five dimensional dilatonic AdS black hole with two equal charges. Second, there emerge a new phase transition branch in negative pressure region in six and seven dimensional dilatonic black holes with two equal charges. Third, there emerge transition behaviors in higher dimensional black hole with single charge cases, which are absent in four dimensions.

gr-qc↗

arXiv2018

Structural and optoelectronic properties of the inorganic perovskites AGeX3 (A = Cs, Rb; X = I, Br, Cl) for solar cell application

We predict the structural, electronic and optic properties of the inorganic Ge-based halide perovskites AGeX3 (A = Cs, Rb; X = I, Br, Cl) by using first-principles method. In particular, absolute electronic energy band levels are calculated using two different surface terminations of each compound, reproducing the experimental band alignment.

cond-mat.mtrl-sci↗

arXiv2018

Null Signal for the Cosmic Anisotropy in the Pantheon Supernovae Data

The cosmological principle assumes that the universe is homogeneous and isotropic on cosmic scales. There exist many works testing the cosmic homogeneity and/or the cosmic isotropy of the universe in the literature. In fact, some observational hints of the cosmic anisotropy have been claimed. However, we note that the paucity of the data considered in the literature might be responsible for the `found' cosmic anisotropy. So, it might disappear in a large enough sample. Very recently, the Pantheon sample consisting of 1048 type Ia supernovae (SNIa) has been released, which is the largest spectroscopically confirmed SNIa sample to date. In the present work, we test the cosmic anisotropy in the Pantheon SNIa sample by using three methods, and hence the results from different methods can be cross-checked. All the results obtained by using the hemisphere comparison (HC) method, the dipole fitting (DF) method and HEALPix suggest that no evidence for the cosmic anisotropy is found in the Pantheon SNIa sample.

astro-ph.CO↗

arXiv2018

Testing the Cosmic Anisotropy with Supernovae Data: Hemisphere Comparison and Dipole Fitting

The cosmological principle is one of the cornerstones in modern cosmology. It assumes that the universe is homogeneous and isotropic on cosmic scales. Both the homogeneity and the isotropy of the universe should be tested carefully. In the present work, we are interested in probing the possible preferred direction in the distribution of type Ia supernovae (SNIa). To our best knowledge, two main methods have been used in almost all of the relevant works in the literature, namely the hemisphere comparison (HC) method and the dipole fitting (DF) method. However, the results from these two methods are not always approximately coincident with each other. In this work, we test the cosmic anisotropy by using these two methods with the Joint Light-Curve Analysis (JLA) and simulated SNIa datasets. In many cases, both methods work well, and their results are consistent with each other. However, in the cases with two (or even more) preferred directions, the DF method fails while the HC method still works well. This might shed new light on our understanding of these two methods.

astro-ph.CO↗