Searcharxiv⌕ Search

arXiv subjects

Yuan Wang

Publications and source records attributed to Yuan Wang.

At least 289 records · Page 16Linked to original sources
arXiv2016

Measuring Asymmetric Opinions on Online Social Interrelationship with Language and Network Features

Instead of studying the properties of social relationship from an objective view, in this paper, we focus on individuals' subjective and asymmetric opinions on their interrelationships. Inspired by the theories from sociolinguistics, we investigate two individuals' opinions on their interrelationship with their interactive language features. Eliminating the difference of personal language style, we clarify that the asymmetry of interactive language feature values can indicate individuals' asymmetric opinions on their interrelationship. We also discuss how the degree of opinions' asymmetry is related to the individuals' personality traits. Furthermore, to measure the individuals' asymmetric opinions on interrelationship concretely, we develop a novel model synthetizing interactive language and social network features. The experimental results with Enron email dataset provide multiple evidences of the asymmetric opinions on interrelationship, and also verify the effectiveness of the proposed model in measuring the degree of opinions' asymmetry.

cs.SI↗
arXiv2016

Structure vs. Language: Investigating the Multi-factors of Asymmetric Opinions on Online Social Interrelationship with a Case Study

Though current researches often study the properties of online social relationship from an objective view, we also need to understand individuals' subjective opinions on their interrelationships in social computing studies. Inspired by the theories from sociolinguistics, the latest work indicates that interactive language can reveal individuals' asymmetric opinions on their interrelationship. In this work, in order to explain the opinions' asymmetry on interrelationship with more latent factors, we extend the investigation from single relationship to the structural context in online social network. We analyze the correlation between interactive language features and the structural context of interrelationships. The structural context of vertex, edges and triangles in social network are considered. With statistical analysis on Enron email dataset, we find that individuals' opinions (measured by interactive language features) on their interrelationship are related to some of their important structural context in social network. This result can help us to understand and measure the individuals' opinions on their interrelationship with more intrinsic information.

cs.SI↗
arXiv2016

Study on flexible and organizable time-resolved measurement system and technology for multi-pulsed electron beam parameter

The proof test and debugging of the multi-pulsed electron accelerator, Dragon-2,requires a thorough comprehension of the quality of the beams. This puts forward a rigid requirement on the measurement system that it should have the ability that not only differentiates the three pulses on the whole but also tells the details of each pulse.In the measurements, beam energy is converted by a target to the Optical Transition Radiation (OTR) light, the information carried by which provides a good approach to measure beam profile and divergence simultaneously. Combining with this characteristic of OTR light, the concept of dual-imaging method is adopted in the design of optical imaging system. To avoid interference of the system optical parameters with one another, the original system is separated into two parts by functions, one for beam profile measurements and the other for divergence measurements. Correspondingly a splitter is interposed immediately after the OTR target which splits the light into two parts in perpendicular directions, one part forming a beam spot, and the remaining becoming polarized through a polarizer and imaged by an OTR lens and forming a beam divergence pattern. Again the use of splitters helps the light beam enter different framing camera for different use.With a time resolution of 2ns, the system can provide 8 frames of beam details within any one of the three pulses,at the same time as acquiring the quality of the three pulses on the whole.

physics.acc-ph↗
arXiv2016

Heart Rate Variability and Respiration Signal as Diagnostic Tools for Late Onset Sepsis in Neonatal Intensive Care Units

Apnea-bradycardia is one of the major clinical early indicators of late-onset sepsis occurring in approximately 7% to 10% of all neonates and in more than 25% of very low birth weight infants in NICU. The objective of this paper was to determine if HRV, respiration and their relationships help to diagnose infection in premature infants via non-invasive ways in NICU. Therefore, we implement Mono-Channel (MC) and Bi-Channel (BC) Analysis in two groups: sepsis (S) vs. non-sepsis (NS). Firstly, we studied RR series not only by linear methods: time domain and frequency domain, but also by non-linear methods: chaos theory and information theory. The results show that alpha Slow, alpha Fast and Sample Entropy are significant parameters to distinguish S from NS. Secondly, the question about the functional coupling of HRV and nasal respiration is addressed. Local linear correlation coefficient r2t,f has been explored, while non-linear regression coefficient h2 was calculated in two directions. It is obvious that r2t,f within the third frequency band (0.2<f<0.4 Hz) and h2 in two directions were complementary approaches to diagnose sepsis. Thirdly, feasibility study is carried out on the candidate parameters selected from MC and BC respectively. We discovered that the proposed test based on optimal fusion of 6 features shows good performance with the largest AUC and a reduced probability of false alarm (PFA).

q-bio.QM↗
arXiv2016

Achieving translational symmetry in trapped cold ion rings

Spontaneous symmetry breaking is a universal concept throughout science. For instance, the Landau-Ginzburg paradigm of translational symmetry breaking underlies the classification of nearly all quantum phases of matter and explains the emergence of crystals, insulators, and superconductors. Usually, the consequences of translational invariance are studied in large systems to suppress edge effects which cause undesired symmetry breaking. While this approach works for investigating global properties, studies of local observables and their correlations require access and control of the individual constituents. Periodic boundary conditions, on the other hand, could allow for translational symmetry in small systems where single particle control is achievable. Here, we crystallize up to fifteen 40Ca+ ions in a microscopic ring with inherent periodic boundary conditions. We show the ring's translational symmetry is preserved at millikelvin temperatures by delocalizing the Doppler laser cooled ions. This establishes an upper bound for undesired symmetry breaking at a level where quantum control becomes feasible. These findings pave the way towards studying quantum many-body physics with translational symmetry at the single particle level in a variety of disciplines from simulation of Hawking radiation to exploration of quantum phase transitions.

quant-ph↗
arXiv2016

Thresholded Multivariate Principal Component Analysis for Multi-channel Profile Monitoring

Monitoring multichannel profiles has important applications in manufacturing systems improvement, but it is non-trivial to develop efficient statistical methods due to two main challenges. First, profiles are high-dimensional functional data with intrinsic inner- and inter-channel correlations, and one needs to develop a dimension reduction method that can deal with such intricate correlations for the purpose of effective monitoring. The second, and probably more fundamental, challenge is that the functional structure of multi-channel profiles might change over time, and thus the dimension reduction method should be able to automatically take into account the potential unknown change. To tackle these two challenges, we propose a novel thresholded multivariate principal component analysis (PCA) method for multi-channel profile monitoring. Our proposed method consists of two steps of dimension reduction: It first applies the functional PCA to extract a reasonable large number of features under the normal operational (in-control) state, and then use the soft-thresholding techniques to further select significant features capturing profile information in the out-of-control state. The choice of tuning parameter for soft-thresholding is provided based on asymptotic analysis, and extensive simulation studies are conducted to illustrate the efficacy of our proposed thresholded PCA methodology.

stat.AP↗
arXiv2016

Large-Scale Multi-Stream Quickest Change Detection via Shrinkage Post-Change Estimation

The quickest change detection problem is considered in the context of monitoring large-scale independent normal distributed data streams with possible changes in some of the means. It is assumed that for each individual local data stream, either there are no local changes, or there is a "big" local change that is larger than a pre-specified lower bound. Two different kinds of scenarios are studied: one is the sparse post-change case when the unknown number of affected data streams is much smaller than the total number of data streams, and the other is when all local data streams are affected simultaneously although not necessarily identically. We propose a systematic approach to develop efficient global monitoring schemes for quickest change detection by combining hard thresholding with linear shrinkage estimators to estimating all post-change parameters simultaneously. Our theoretical analysis demonstrates that the shrinkage estimation can balance the tradeoff between the first-order and second-order terms of the asymptotic expression on the detection delays, and our numerical simulation studies illustrate the usefulness of shrinkage estimation and the challenge of Monte Carlo simulation of the average run length to false alarm in the context of online monitoring large-scale data streams.

math.ST↗
arXiv2016

Coherence-Driven Topological Transition in Quantum Metamaterials

We introduce and theoretically demonstrate a quantum metamaterial made of dense ultracold neutral atoms loaded into an inherently defect-free artificial crystal of light, immune to well-known critical chal- lenges inevitable in conventional solid-state platforms. We demonstrate an all-optical control on ultrafast time scales over the photonic topological transition of the isofrequency contour from an open to close topology at the same frequency. This atomic lattice quantum metamaterial enables a dynamic manipula- tion of the decay rate of a probe quantum emitter by more than an order of magnitude. This proposal may lead to practically lossless, tunable and topologically-reconfigurable quantum metamaterials, for single- or few-photon-level applications as varied as quantum sensing, quantum information processing, and quantum simulations using metamaterials.

quant-ph↗
arXiv2015

Chemical assembly of atomically thin transistors and circuits in a large scale

Next-generation electronics calls for new materials beyond silicon for increased functionality, performance, and scaling in integrated circuits. Carbon nanotubes and semiconductor nanowires are at the forefront of these materials, but have challenges due to the complex fabrication techniques required for large-scale applications. Two-dimensional (2D) gapless graphene and semiconducting transition metal dichalcogenides (TMDCs) have emerged as promising electronic materials due to their atomic thickness, chemical stability and scalability. Difficulties in the assembly of 2D electronic structures arise in the precise spatial control over the metallic and semiconducting atomic thin films. Ultimately, this impedes the maturity of integrating atomic elements in modern electronics. Here, we report the large-scale spatially controlled synthesis of the single-layer semiconductor molybdenum disulfide (MoS2) laterally in contact with conductive graphene. Transition electron microscope (TEM) studies reveal that the single-layer MoS2 nucleates at the edge of the graphene, creating a lateral 2D heterostructure. We demonstrate such chemically assembled 2D atomic transistors exhibit high transconductance (10 uS), on-off ratios (10^6), and mobility (20 cm^2 V^-1 s^-1). We assemble 2D logic circuits, such as a heterostructure NMOS inverter with a high voltage gain, up to 70, enabled by the precise site selectivity from atomically thin conducting and semiconducting crystals. This scalable chemical assembly of 2D heterostructures may usher in a new era in two-dimensional electronic circuitry and computing.

cond-mat.mtrl-sci↗
arXiv2015

Ongoing star formation in the proto-cluster IRAS 22134+5834

IRAS 22134+5834 was observed in the centimeter with (E)VLA, 3~mm with CARMA, 2~mm with PdBI, and 1.3~mm with SMA, to study the continuum emission as well as the molecular lines, that trace different physical conditions of the gas to study the influence of massive YSOs on nearby starless cores, and the possible implications in the clustered star formation process. The multi-wavelength centimeter continuum observations revealed two radio sources within the cluster, VLA1 and VLA2. VLA1 is considered to be an optically thin UCHII region with a size of 0.01~pc and sits at the edge of the near-infrared (NIR) cluster. The flux of ionizing photons of the VLA1 corresponds to a B1 ZAMS star. VLA2 is associated with an infrared point source and has a negative spectral index. We resolved six millimeter continuum cores at 2~mm, MM2 is associated with the UCHII region VLA1, and other dense cores are distributed around the UCH{\sc ii} region. Two high-mass starless clumps (HMSC), HMSC-E (east) and HMSC-W (west), are detected around the NIR cluster with N$_2$H$^+$(1--0) and NH$_3$ emission, and show different physical and chemical properties. Two N$_2$D$^+$ cores are detected on an NH$_3$ filament close to the UCHII region, with a projected separation of $\sim$8000~AU at the assumed distance of 2.6~kpc. The kinematic properties of the molecular line emission confirm the expansion of the UCHII region and that the molecular cloud around the near infrared (NIR) cluster is also expanding. Our multi-wavelength study has revealed different generations of star formation in IRAS 22134+5834. The formed intermediate- to massive stars show strong impact on nearby starless clumps. We propose that while the stellar wind from the UCHII region and the NIR cluster drives the large scale bubble, the starless clumps and HMPOs formed at the edge of the cluster.

astro-ph.SR↗
arXiv2015

Research on Brightness Measurement of Intense Electron Beam

The mostly research fasten on high emission density of injector to study electron beam's brightness in LIA. Using the injector(2MeV) was built to research brightness of multi-pulsed high current(KA) electron beam, and researchs three measurement method (the pepper-pot method, beam collimator without magnetic field, beam collimator with magnetic field method) to detect beam's brightness with time-resolved measurement system.

physics.acc-ph↗
arXiv2015

Subspace selection for projection maximization with matroid constraints

Suppose that there is a ground set which consists of a large number of vectors in a Hilbert space. Consider the problem of selecting a subset of the ground set such that the projection of a vector of interest onto the subspace spanned by the vectors in the chosen subset reaches the maximum norm. This problem is generally NP-hard, and alternative approximation algorithms such as forward regression and orthogonal matching pursuit have been proposed as heuristic approaches. In this paper, we investigate bounds on the performance of these algorithms by introducing the notions of elemental curvatures. More specifically, we derive lower bounds, as functions of these elemental curvatures, for performance of the aforementioned algorithms with respect to that of the optimal solution under uniform and non-uniform matroid constraints, respectively. We show that if the elements in the ground set are mutually orthogonal, then these algorithms are optimal when the matroid is uniform and they achieve at least $1/2$-approximations of the optimal solution when the matroid is non-uniform.

cs.IT↗
arXiv2015

Optical Selection Rule based on Valley-Exciton Locking for 2D Valleytronics

Optical selection rule fundamentally determines the optical transition between energy states in a variety of physical systems from hydrogen atoms to bulk crystals such as GaAs. It is important for optoelectronic applications such as lasers, energy-dispersive X-ray spectroscopy and quantum computation. Recently, single layer transition metal dichalcogenide (TMDC) exhibits valleys in momentum space with nontrivial Berry curvature and excitons with large binding energy. However, it is unclear how the unique valley degree of freedom combined with the strong excitonic effect influences the optical excitation. Here we discover a new set of optical selection rules in monolayer WS2,imposed by valley and exciton angular momentum. We experimentally demonstrated such a principle for second harmonic generation (SHG) and two-photon luminescence (TPL). Moreover, the two-photon induced valley populations yield net circular polarized photoluminescence after a sub-ps interexciton relaxation (2p->1s) and last for 8 ps. The discovery of this new optical selection rule in valleytronic 2D system not only largely extend information degrees but sets a foundation in control of optical transitions that is crucial to valley optoeletronic device applications such as 2D valley-polarized light emitting diodes (LED), optical switches and coherent control for quantum computing.

cond-mat.mtrl-sci↗
arXiv2015

Monolayer Excitonic Laser

Recently, two-dimensional (2D) materials have opened a new paradigm for fundamental physics explorations and device applications. Unlike gapless graphene, monolayer transition metal dichalcogenide (TMDC) has new optical functionalities for next generation ultra-compact electronic and opto-electronic devices. When TMDC crystals are thinned down to monolayers, they undergo an indirect to direct bandgap transition, making it an outstanding 2D semiconductor. Unique electron valley degree of freedom, strong light matter interactions and excitonic effects were observed. Enhancement of spontaneous emission has been reported on TMDC monolayers integrated with photonic crystal and distributed Bragg reflector microcavities. However, the coherent light emission from 2D monolayer TMDC has not been demonstrated, mainly due to that an atomic membrane has limited material gain volume and is lack of optical mode confinement. Here, we report the first realization of 2D excitonic laser by embedding monolayer tungsten disulfide (WS2) in a microdisk resonator. Using a whispering gallery mode (WGM) resonator with a high quality factor and optical confinement, we observed bright excitonic lasing in visible wavelength. The Si3N4/WS2/HSQ sandwich configuration provides a strong feedback and mode overlap with monolayer gain. This demonstration of 2D excitonic laser marks a major step towards 2D on-chip optoelectronics for high performance optical communication and computing applications.

cond-mat.mtrl-sci↗
arXiv2015

Active coupling control in densely packed subwavelength waveguides via dark mode

The ever growing need for energy-efficient and fast communications is driving the development of highly integrated photonic circuits where controlling light at the nanoscale becomes the most critical aspect of information transfer . Directional couplers, two interacting optical waveguides placed in close proximity, are important building blocks in these integrated photonics circuits and have been employed as optical modulators and switches for high speed communication, data processing and integrated quantum operations. However, active control over the coupling between closely packed waveguides is highly desirable and yet remains a critical barrier towards ultra small footprint devices. A general approach to achieve active control in waveguide systems is to exploit optical nonlinearities enabled by a strong control pulse. However these devices suffer from the nonlinear absorption induced by the intense control pulse as the signal and its control propagate in the same waveguide. Here we experimentally demonstrate a unique scheme based on adiabatic elimination (AE) concept that effectively manipulates the coupling between densely packed waveguides. We demonstrate active coupling control between two closely packed waveguides by tuning the mode index of an in-between decoupled waveguide. This is achieved via a dark mode and thus leaves the signal unaffected by the induced losses. Such a scheme is a promising candidate for ultra-dense integrated nano-photonics such as on-chip ultrafast modulators and tunable filters for optical communication and quantum computing.

physics.optics↗
arXiv2014

Parity-Time Synthetic Laser

Parity-time (PT) symmetry is a fundamental notion in quantum field theories. It has opened a new paradigm for non-Hermitian Hamiltonians ranging from quantum mechanics, electronics, to optics. In the realm of optics, optical loss is responsible for power dissipation, therefore typically degrading device performance such as attenuation of a laser beam. By carefully exploiting optical loss in the complex dielectric permittivity, however, recent exploration of PT symmetry revolutionizes our understandings in fundamental physics and intriguing optical phenomena such as exceptional points and phase transition that are critical for high-speed optical modulators. The interplay between optical gain and loss in photonic PT synthetic matters offers a new criterion of positively utilizing loss to efficiently manipulate gain and its associated optical properties. Instead of simply compensating optical loss in conventional lasers, for example, it is theoretically proposed that judiciously designed delicate modulation of optical loss and gain can lead to PT synthetic lasing that fundamentally broadens laser physics. Here, we report the first experimental demonstration of PT synthetic lasers. By carefully exploiting the interplay between gain and loss, we achieve degenerate eigen modes at the same frequency but with complex conjugate gain and loss coefficients. In contrast to conventional ring cavity lasers with multiple modes, the PT synthetic micro-ring laser exhibits an intrinsic single mode lasing: the non-threshold PT broken phase inherently associated in such a photonic system squeezes broadband optical gain into a single lasing mode regardless of the gain spectral bandwidth. This chip-scale semiconductor platform provides a unique route towards fundamental explorations of PT physics and next generation of optoelectronic devices for optical communications and computing.

physics.optics↗
arXiv2014

Observation of Piezoelectricity in Monolayer Molybdenum Disulfide

Piezoelectricity offers precise and robust conversion between electricity and mechanical force. Here we report the first experimental evidence of piezoelectricity in a single layer of molybdenum disulfide (MoS2) crystal as a result of inversion symmetry breaking of the atomic structure, with measured piezoelectric coefficient e11 = 2.9e-10 C/m. Through the angular dependence of electro-mechanical coupling, we uniquely determined the two-dimensional (2D) crystal orientation. We observed that only MoS2 membranes with odd number of layers exhibited piezoelectricity, in sharp contrast to the conventional materials. The piezoelectricity discovered in single molecular membrane promises scaling down of nano-electro-mechanical systems (NEMS) to single atomic unit cell - the ultimate material limit.

cond-mat.mtrl-sci↗