arXiv subjects

Rui Qin

Publications and source records attributed to Rui Qin.

24 records · Page 2Linked to original sources

arXiv2019

Alternative Analysis Methods for Time to Event Endpoints under Non-proportional Hazards: A Comparative Analysis

The log-rank test is most powerful under proportional hazards (PH). In practice, non-PH patterns are often observed in clinical trials, such as in immuno-oncology; therefore, alternative methods are needed to restore the efficiency of statistical testing. Three categories of testing methods were evaluated, including weighted log-rank tests, Kaplan-Meier curve-based tests (including weighted Kaplan-Meier and Restricted Mean Survival Time, RMST), and combination tests (including Breslow test, Lee's combo test, and MaxCombo test). Nine scenarios representing the PH and various non-PH patterns were simulated. The power, type I error, and effect estimates of each method were compared. In general, all tests control type I error well. There is not a single most powerful test across all scenarios. In the absence of prior knowledge regarding the PH or non-PH patterns, the MaxCombo test is relatively robust across patterns. Since the treatment effect changes overtime under non-PH, the overall profile of the treatment effect may not be represented comprehensively based on a single measure. Thus, multiple measures of the treatment effect should be pre-specified as sensitivity analyses to evaluate the totality of the data.

stat.AP↗

arXiv2019

Strong-field nonlinear optical properties of monolayer black phosphorus

Within the past few years, atomically thin black phosphorus (BP) has been demonstrated as a fascinating new 2D material that is promising for novel nanoelectronics and nanophotonics applications, due to its many unique properties such as direct and widely tunable bandgap, high carrier mobility and remarkable intrinsic in-plane anisotropy. However, its important extreme nonlinear behavior and ultrafast dynamics of carriers under strong-field excitation have yet to be revealed to date. Herein, we report nonperturbative high harmonic generation (HHG) in monolayer BP by first-principles simulations. We show that BP exhibits extraordinary HHG properties, with clear advantages over three major types of 2D materials under intensive study, i.e., semimetallic graphene, semiconducting MoS$_2$, and insulating hexagonal boron nitride, in terms of HHG cutoff energy and spectral intensity. This study advances the scope of current research activities of BP into a new regime, suggesting its promising future in applications of extreme-ultraviolet and attosecond nanophotonics, and also opening doors to investigate the strong-field and ultrafast carrier dynamics of this emerging material.

physics.app-ph↗

arXiv2019

Circularly polarized extreme ultraviolet high harmonic generation in graphene

Circularly polarized extreme ultraviolet (XUV) radiation is highly interesting for investigation of chirality-sensitive light-matter interactions. Recent breakthroughs have enabled generation of such light sources via high harmonic generation (HHG) from rare gases. There is a growing interest in extending HHG medium from gases to solids, especially to 2D materials, as they hold great promise to develop ultra-compact solid-state photonic devices and provide insights into electronic properties of the materials themselves. However, HHG in graphene driven by terahertz to mid-infrared fields reported so far only generate low harmonic orders, and furthermore no harmonics driven by circularly polarized lasers. Here, using first-principles simulations within a time-dependent density-functional theory framework, we show that it is possible to generate HHG extending to the XUV spectral region in monolayer extended graphene excited by near-infrared lasers. Moreover, we demonstrate that a single circularly polarized driver is enough to ensure HHG in graphene with circular polarization. The corresponding spectra reflect the six-fold rotational symmetry of the graphene crystal. Extending HHG in graphene to the XUV spectral regime and realizing circular polarization represent an important step towards the development of novel nanoscale attosecond photonic devices and numerous applications such as spectroscopic investigation and nanoscale imaging of ultrafast chiral and spin dynamics in graphene and other 2D materials.

physics.optics↗

arXiv2018

Strain-controlled high harmonic generation with Dirac fermions in silicene

Two-dimensional (2D) materials with zero band gap exhibit remarkable electronic properties with wide tunability. High harmonic generation (HHG) in such materials offers unique platforms to develop novel optoelectronic devices at nanoscale, as well as to investigate strong-field and ultrafast nonlinear behaviour of massless Dirac fermions. However, control of HHG by modulating electronic structure of materials remains largerly unexplored to date. Here we report controllable HHG by tuning the electronic structures via mechanical engineering. Using an \textit{ab initio} approach based on time-dependent density-functional theory (TDDFT), we show that the HHG process is sensitive to the modulation of band structures of monolayer silicene while preserving the Dirac cones under biaxial and uniaxial strains, which can lead to significant enhancement of harmonic intensity up to an order of magnitude. With the additional advantage of silicene in compatibility and integration into the current silicon-based electronic industry, this study may open a new avenue to develop efficient solid-state optoelectronic nano-devices, and provide a valuable tool to understand the strong-field and mechanically induced ultrafast nonlinear response of Dirac carriers in 2D materials.

physics.optics↗

arXiv2018

Holoscopic 3D Micro-Gesture Database for Wearable Device Interaction

With the rapid development of augmented reality (AR) and virtual reality (VR) technology, human-computer interaction (HCI) has been greatly improved for gaming interaction of AR and VR control. The finger micro-gesture is one of the important interactive methods for HCI applications such as in the Google Soli and Microsoft Kinect projects. However, the progress in this research is slow due to the lack of high quality public available database. In this paper, holoscopic 3D camera is used to capture high quality micro-gesture images and a new unique holoscopic 3D micro-gesture (HoMG) database is produced. The principle of the holoscopic 3D camera is based on the fly viewing system to see the objects. HoMG database recorded the image sequence of 3 conventional gestures from 40 participants under different settings and conditions. For the purpose of micro-gesture recognition, HoMG has a video subset with 960 videos and a still image subset with 30635 images. Initial micro-gesture recognition on both subsets has been conducted using traditional 2D image and video features and popular classifiers and some encouraging performance has been achieved. The database will be available for the research communities and speed up the research in this area.

cs.HC↗

arXiv2010

Functionalized Graphene for High Performance Two-dimensional Spintronics Devices

Using first-principles calculations, we explore the possibility of functionalized graphene as high performance two-dimensional spintronics device. Graphene functionalized with O on one side and H on the other side in the chair conformation is found to be a ferromagnetic metal with a spin-filter efficiency up to 85% at finite bias. The ground state of graphene semi-functionalized with F in the chair conformation is an antiferromagnetic semiconductor, and we construct a magnetoresistive device from it by introducing a magnetic field to stabilize its ferromagnetic metallic state. The resulting room-temperature magnetoresistance is up to 5400%, which is one order of magnitude larger than the available experimental values.

cond-mat.mtrl-sci↗