Wenbin Lu

Wenbin Lu
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Wenbin Lu
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High Energy Astrophysical Phenomena (9)
 
Statistics - Methodology (3)
 
Statistics - Machine Learning (2)
 
Astrophysics of Galaxies (2)
 
Statistics - Theory (2)
 
Mathematics - Statistics (2)
 
Statistics - Applications (1)
 
Solar and Stellar Astrophysics (1)

Publications Authored By Wenbin Lu

We use the observed properties of fast radio bursts (FRBs) and a number of general physical considerations to provide a broad-brush model for the physical properties of FRB sources and the radiation mechanism. We show that the magnetic field in the source region should be at least 10^{14} Gauss. This strong field is required to ensure that the electrons have sufficiently high ground state Landau energy so that particle collisions, instabilities, and strong electric and magnetic fields associated with the FRB radiation do not perturb electrons' motion in the direction transverse to the magnetic field and destroy their coherent motion; coherence is required by the high observed brightness temperature of FRB radiation. Read More

Many black hole (BH) candidates have been discovered in X-ray binaries and in the nuclei of galaxies. The prediction of Einstein's general relativity is that BHs have an event horizon --- a one-way membrane through which particles fall into the BH but cannot exit. However, except for the very few nearby supermassive BH candidates, our telescopes are unable to resolve and provide a direct proof of the event horizon. Read More

We present hydrodynamic simulations of the hot cocoon produced when a relativistic jet passes through the gamma-ray burst (GRB) progenitor star and its environment, and we compute the lightcurve and spectrum of the radiation emitted by the cocoon. The radiation from the cocoon has a nearly thermal spectrum with a peak in the X-ray band, and it lasts for a few minutes in the observer frame; the cocoon radiation starts at roughly the same time as when $\gamma$-rays from a burst trigger detectors aboard GRB satellites. The isotropic cocoon luminosity ($\sim 10^{47}$ erg s$^{-1}$) is of the same order of magnitude as the X-ray luminosity of a typical long-GRB afterglow during the plateau phase. Read More

We study the spectra of photospheric emission from highly relativistic gamma-ray burst outflows using a Monte Carlo (MC) code. We consider the Comptonization of photons with a fast cooled synchrotron spectrum in a relativistic jet with photon to electron number ratio $N_{\gamma}/N_e = 10^5$. For all our simulations, we use mono-energetic protons which interact with thermalised electrons through the Coulomb interaction. Read More

The divide and conquer method is a common strategy for handling massive data. In this article, we study the divide and conquer method for cubic-rate estimators under the massive data framework. We develop a general theory for establishing the asymptotic distribution of the aggregated M-estimators using a simple average. Read More

Assuming: fast radio bursts (FRBs) are produced by neutron stars at cosmological distances; FRB rate tracks core-collapse supernova rate; and all FRBs repeat with a universal energy distribution function (EDF) dN/dE ~ E^(-beta) with a high-end cutoff at burst energy E_max. We find that observations so far are consistent with a universal EDF with a power-law index 1.5 < beta < 2. Read More

Within the first 10 days after Swift discovered the jetted tidal disruption event (TDE) Sw J1644+57, simultaneous observations in the radio, near-infrared, optical, X-ray and gamma-ray bands were carried out. These multiwavelength data provide a unique opportunity to constrain the emission mechanism and make-up of a relativistic super-Eddington jet. We consider an exhaustive variety of radiation mechanisms for the generation of X-rays in this TDE, and rule out many processes such as SSC, photospheric and proton synchrotron. Read More

Because different patients may response quite differently to the same drug or treatment, there is increasing interest in discovering individualized treatment rule. In particular, people are eager to find the optimal individualized treatment rules, which if followed by the whole patient population would lead to the "best" outcome. In this paper, we propose new estimators based on robust regression with general loss functions to estimate the optimal individualized treatment rules. Read More

The recent discoveries of Swift J1644+57 and J2058+05 show that tidal disruption events (TDEs) can launch relativistic jets. Super-Eddington accretion produces a strong radiation field of order Eddington luminosity. In a jetted TDE, electrons in the jet will inverse-Compton scatter the external radiation field from the accretion disk and wind. Read More

Recent UV-optical surveys have been successful in finding tidal disruption events (TDEs), in which a star is tidally disrupted by a supermassive black hole (BH). These TDEs release a huge amount of radiation energy ~ 10^51-52 erg into the circum-nuclear medium. If the medium is dusty, most of the radiation energy will be absorbed by dust grains within ~ 1 pc from the BH and re-radiated in the infrared. Read More

In order to identify important variables that are involved in making optimal treatment decision, Lu et al. (2013) proposed a penalized least squared regression framework for a fixed number of predictors, which is robust against the misspecification of the conditional mean model. Two problems arise: (i) in a world of explosively big data, effective methods are needed to handle ultra-high dimensional data set, for example, with the dimension of predictors is of the non-polynomial (NP) order of the sample size; (ii) both the propensity score and conditional mean models need to be estimated from data under NP dimensionality. Read More

Long Gamma-Ray Bursts (GRBs) are produced by ultra-relativistic jets launched from core collapse of massive stars. Most massive stars form in binaries and/or in star clusters, which means that there may be a significant external photon field (EPF) around the GRB progenitor. We calculate the inverse-Compton scattering of EPF by the hot electrons in the GRB jet. Read More

Gene/pathway-based methods are drawing significant attention due to their usefulness in detecting rare and common variants that affect disease susceptibility. The biological mechanism of drug responses indicates that a gene-based analysis has even greater potential in pharmacogenetics. Motivated by a study from the Vitamin Intervention for Stroke Prevention (VISP) trial, we develop a gene-trait similarity regression for survival analysis to assess the effect of a gene or pathway on time-to-event outcomes. Read More

A treatment regime is a deterministic function that dictates personalized treatment based on patients' individual prognostic information. There is a fast-growing interest in finding optimal treatment regimes to maximize expected long-term clinical outcomes of patients for complex diseases, such as cancer and AIDS. For many clinical studies with survival time as a primary endpoint, a main goal is to maximize patients' survival probabilities given treatments. Read More

Variable selection for optimal treatment regime in a clinical trial or an observational study is getting more attention. Most existing variable selection techniques focused on selecting variables that are important for prediction, therefore some variables that are poor in prediction but are critical for decision-making may be ignored. A qualitative interaction of a variable with treatment arises when treatment effect changes direction as the value of this variable varies. Read More