arXiv subjects

Xuan Luo

Publications and source records attributed to Xuan Luo.

At least 145 records · Page 8Linked to original sources

arXiv2019

Machine Learning Techniques for Brand-Influencer Matchmaking on the Instagram Social Network

The social media revolution has changed the way that brands interact with consumers. Instead of spending their advertising budget on interstate billboards, more and more companies are choosing to partner with so-called Internet "influencers" --- individuals who have gained a loyal following on online platforms for the high quality of the content they post. Unfortunately, it's not always easy for small brands to find the right influencer: someone who aligns with their corporate image and has not yet grown in popularity to the point of unaffordability. In this paper we sought to develop a system for brand-influencer matchmaking, harnessing the power and flexibility of modern machine learning techniques. The result is an algorithm that can predict the most fruitful brand-influencer partnerships based on the similarity of the content they post.

cs.SI↗

arXiv2018

Characterization of Lattice Thermal Transport in Two-Dimensional BAs, BP, and BSb: A First-Principles Study

Ever since the high thermal conductivity in cubic boron arsenide (c-BAs) was predicted theoretically by Lindsay et. al in 2013, countless studies have zeroed in on this particular material. Most recently, c-BAs has been confirmed experimentally to have a thermal conductivity of around 1,100 W/m-K. In this study, we investigate the seldom studied two dimensional hexagonal form of boron arsenide (h-BAs) using a first-principles approach and by solving the Boltzmann Transport Equation for phonons. Traditionally, a good indicator of a high thermal conductivity material is its high Debye temperature and high phonon group velocity. However, we determine h-BAs to have a much lower Debye temperature and average phonon group velocity compared to the other monolayer boron-V compounds of boron nitride (h-BN) and boron phosphide (h-BP), yet curiously it possesses a higher thermal conductivity. Further investigation reveals that this is due to the phonon frequency gap caused by large mass imbalances, which results in a restricted Umklapp phonon-phonon scattering channel and consequently a higher thermal conductivity. We determine the intrinsic lattice thermal conductivity of monolayer h-BAs to be 362.62 W/m-K at room temperature, which is considerably higher compared to the other monolayer boron-V compounds of h-BN (231.96 W/m-K), h-BP (187.11 W/m-K), and h-BSb (87.15 W/m-K). This study opens the door for investigation into a new class of monolayer structures and the properties they possess.

cond-mat.mtrl-sci↗

arXiv2018

Origin of magnetoresistance suppression in thin $γ$-MoTe$_2$

We use both classical magnetotransport and quantum oscillation measurements to study the thickness evolution of the extremely large magnetoresistance (XMR) material and type-II Weyl semimetal candidate, $γ$-MoTe$_2$, protected from oxidation. We find that the magnetoresistance is systematically suppressed with reduced thickness. This occurs concomitantly with both a decrease in carrier mobility and increase in electron-hole imbalance. We model the two effects separately and conclude that the XMR effect is more sensitive to the former.

cond-mat.mtrl-sci↗

arXiv2018

Exploring the Anomalous Top-Higgs FCNC Couplings at the electron proton colliders

We perform an updated analysis on the searches for the anomalous FCNC Yukawa interactions between the top quark, the Higgs boson, and either an up or charm quark ($\rm tqh,\ q=u,\ c$). We probe the observability of the FCNC top-Higgs couplings through the processes $\rm e^- p\rightarrow ν_e \bar{t} \rightarrow ν_e h \bar{q}$ (signal.I) and $\rm \ e^- p \to ν_e h b$ (singal.II) at the proposed electron proton (ep) colliders, where the Higgs boson decays to a $\rm b\bar{b}$ pair. We find that at the high luminosity (1 $\rm ab^{-1}$) ep colliders where the electrons have a polarisation of $\rm 80\%$ and electron energy is typical 60 GeV, the 2$σ$ upper limit on $\rm Br(t\to uh)$ are $0.15\times 10^{-2}$($2.9\times 10^{-4}$) at the 7TeV@LHeC(50TeV@FCC-eh) for signal.I and $0.15\times 10^{-2}$($2.2\times 10^{-4}$) for signal.II. We also give an estimate on how the sensitivity (take signal.I as examples) would change when we reduce the electron beam energy from 60 GeV to 50 GeV or even 40 GeV due to the cost reason. The conclusion is that the discovery potential reduce $8.7\%$($29.4\%$) if the electron beam change from 60GeV to 50(40) GeV at the 7TeV LHeC, and $16.8\%$($19.8\%$) at the 50 TeV FCC-eh.

hep-ph↗

arXiv2018

Multiple structure and symmetry types in narrow temperature and magnetic field ranges in two-dimensional Cr2Ge2Te6 crystal

Multiple structure and symmetry types and their transformations are discovered in quasi-two-dimensional (quasi-2D) Cr2Ge2Te6 crystal in surprisingly very narrow temperature range of 2 K and magnetic field range of 0.07 T using a homebuilt magnetic force microscope (MFM). A series of basic domain patterns are extracted from the MFM images. Some of them seem unique to 2-D materials as they are not observed in 3-D materials, such as self-fitting disks, and fine ladder structure within Y-connected walls. Based on these findings, a phase map is drawn for the magnetic phase structures. The symmetry of the patterns are discussed. The results are not only important in developing new theories but also highly desirable in applications.

cond-mat.mtrl-sci↗

arXiv2018

Visualization of electronic topology in ZrSiSe by scanning tunneling microscopy

As emerging topological nodal-line semimetals, the family of ZrSiX (X = O, S, Se, Te) has attracted broad interests in condensed matter physics due to their future applications in spintonics. Here, we apply a scanning tunneling microscopy (STM) to study the structural symmetry and electronic topology of ZrSiSe. The glide mirror symmetry is verified by quantifying the lattice structure of the ZrSe bilayer based on bias selective topographies. The quasiparticle interference analysis is used to identify the band structure of ZrSiSe. The nodal line is experimentally determined at $\sim$ 250 meV above the Fermi level. An extra surface state Dirac point at $\sim$ 400 meV below the Fermi level is also determined. Our STM measurement provides a direct experimental evidence of the nodal-line state in the family of ZrSiX.

cond-mat.mtrl-sci↗

arXiv2018

Dimensionality-driven orthorhombic MoTe2 at room temperature

We use a combination of Raman spectroscopy and transport measurements to study thin flakes of the type-II Weyl semimetal candidate MoTe2 protected from oxidation. In contrast to bulk crystals, which undergo a phase transition from monoclinic to the inversion symmetry breaking, orthorhombic phase below ~250 K, we find that in moderately thin samples below ~12 nm, a single orthorhombic phase exists up to and beyond room temperature. This could be due to the effect of c-axis confinement, which lowers the energy of an out-of-plane hole band and stabilizes the orthorhombic structure. Our results suggest that Weyl nodes, predicated upon inversion symmetry breaking, may be observed in thin MoTe2 at room temperature.

cond-mat.mtrl-sci↗

arXiv2017

Searching for the doubly-charged Higgs bosons in the Georgi-Machacek model at the ep colliders

The Georgi-Machacek model is one of many beyond Standard Model scenarios with an extended scalar sector which can group under the custodial $\rm SU(2)_C$ symmetry. There are 5-plet, 3-plet and singlet Higgs bosons under the classification of such symmetry in addition to the Standard Model Higgs boson. Here we study the prospects for detecting the doubly-charged Higgs boson ($\rm H_5^{\pm\pm}$) through the vector boson fusion production at the electron-proton colliders. Typically, we concentrate on our analysis through $μ$-lepton pair production via pair of same-sign W bosons decay. The discovery significance are calculated as the functions of the triplet vacuum expectation value and necessary luminosity.

hep-ph↗

arXiv2017

Searching for the doubly-charged Higgs bosons in the Georgi-Machacek model at the electron-proton colliders

The Georgi-Machacek model is one of many beyond Standard Model scenarios with an extended scalar sector which can group under the custodial $\rm SU(2)_C$ symmetry. There are 5-plet, 3-plet and singlet Higgs bosons under the classification of such symmetry in addition to the Standard Model Higgs boson. In this paper, we study the prospects for detecting the doubly-charged Higgs boson ($\rm H_5^{\pm\pm}$) through the vector boson fusion production at the electron-proton (ep) colliders. We concentrate on our analysis through $μ$-lepton pair production via pair of same-sign W bosons decay. The $\rm H_5^{\pm\pm}$ discovery potentials at the ep colliders are presented.

hep-ph↗

arXiv2017

Searching for the heavy custodial fiveplet Higgs in the Georgi-Machacek model at the International Linear Collider

The Georgi-Machacek (GM) model is one of many Beyond Standard Model scenarios with an extended scalar sector which can group under the custodial $\rm SU(2)_C$ symmetry into a fiveplet, a triplet, and two singlets. The heavy charged custodial fiveplet Higgs $\rm H_5^{\pm}$ are typical particles in GM model which couple to the electroweak gauge bosons, therefore provide a good testing ground for the detection of the $\rm H^\pm W^\mp Z$ vertex. The neutral custodial fiveplet Higgs $\rm H_5^{0}$ in the GM model has the same mass with $\rm H_5^{\pm}$ and couples to the electroweak gauge bosons $\rm W^+ W^-$ and ZZ both. We study the discovery prospects of the exotic scalar bosons $\rm H_5^{\pm}$ and $\rm H_5^{0}$ at the International Linear Collider(ILC) via the vector boson associated production processes, and discuss two different decay modes for both charged and neutral scalars. The discovery potential is discussed. Testing the mass degeneracy of charged and neutral scalar bosons in the GM model is also considered.

hep-ph↗

arXiv2017

Searches for the Anomalous FCNC Top-Higgs Couplings with Polarized Electron Beam at the LHeC

In this paper, we study the single top and Higgs associated production $\rm e^- p\rightarrow ν_e \bar{t} \rightarrow ν_e h \bar{q}(h\rightarrow b\bar{b})$ in the top-Higgs FCNC couplings at the LHeC with the electron beam energy of $E_{e}$ = 60 GeV and $E_{e}$ = 120 GeV, combination of a 7 TeV and 50 TeV proton beam. With the possibility of e-beam polarization ($p_{e}$ = 0, $\pm0.6$), we distinct the Cut-based method and the Multivariate Analysis (MVA) based method, and compare with the current experimental and theoretical limits. It is shown that the branching ratio Br $\rm(t\to uh)$ can be probed to 0.113 (0.093) $\%$, 0.071 (0.057) $\%$, 0.030 (0.022) $\%$ and 0.024 (0.019) $\%$ with the Cut-based (MVA-based) analysis at ($E_{p}$, $E_{e}$) = (7 TeV, 60 GeV), ($E_{p}$, $E_{e}$) = (7 TeV, 120 GeV), ($E_{p}$, $E_{e}$) = (50 TeV, 60 GeV) and ($E_{p}$, $E_{e}$) = (50 TeV, 120 GeV) beam energy and 1$σ$ level. With the possibility of e-beam polarization, the expected limits can be probed down to 0.090 (0.073) $\%$, 0.056 (0.045) $\%$, 0.024 (0.018) $\%$ and 0.019 (0.015) $\%$, respectively.

hep-ph↗

arXiv2015

Fast Non-local Stereo Matching based on Hierarchical Disparity Prediction

Stereo matching is the key step in estimating depth from two or more images. Recently, some tree-based non-local stereo matching methods have been proposed, which achieved state-of-the-art performance. The algorithms employed some tree structures to aggregate cost and thus improved the performance and reduced the coputation load of the stereo matching. However, the computational complexity of these tree-based algorithms is still high because they search over the entire disparity range. In addition, the extreme greediness of the minimum spanning tree (MST) causes the poor performance in large areas with similar colors but varying disparities. In this paper, we propose an efficient stereo matching method using a hierarchical disparity prediction (HDP) framework to dramatically reduce the disparity search range so as to speed up the tree-based non-local stereo methods. Our disparity prediction scheme works on a graph pyramid derived from an image whose disparity to be estimated. We utilize the disparity of a upper graph to predict a small disparity range for the lower graph. Some independent disparity trees (DT) are generated to form a disparity prediction forest (HDPF) over which the cost aggregation is made. When combined with the state-of-the-art tree-based methods, our scheme not only dramatically speeds up the original methods but also improves their performance by alleviating the second drawback of the tree-based methods. This is partially because our DTs overcome the extreme greediness of the MST. Extensive experimental results on some benchmark datasets demonstrate the effectiveness and efficiency of our framework. For example, the segment-tree based stereo matching becomes about 25.57 times faster and 2.2% more accurate over the Middlebury 2006 full-size dataset.

cs.CV↗

arXiv2015

Probing Anomalous FCNC Top-Higgs Yukawa Couplings at the Large Hadron Electron Collider

In this paper, we study the anomalous flavor changing neutral current Yukawa interactions between the top quark, the Higgs boson, and either an up or charm quark ($\rm tqH, q=u, c$). We probe these couplings in $\rm e^- p\rightarrow ν_e \bar{t} \rightarrow ν_e H \bar{q}$ and the channel $\rm e^- p \rightarrow ν_e H b$. Both channels are induced by charged current interactions through $\rm e^- p$ collision at the Large Hadron Electron Collider(LHeC). We study the signatures with the Higgs decay modes $\rm H\rightarrow γγ, b\bar{b}$ and $τ^+τ^-$. Our results show that the flavor changing couplings $\rm κ_{tqH}$ can be probed down to a value of 0.0162 in $\rm e^- p \rightarrow ν_e \bar{t} \rightarrow ν_e H \bar{q}$ with $\rm H\rightarrow b \bar{b}$ at a 14 TeV LHeC with a 150 GeV electron beam and 200 $\rm fb^{-1}$ luminosity. This value of the coupling corresponds to the branching ratio $\rm Br(t\rightarrow qH)=1.34 \times 0^{-4}$.

hep-ph↗

arXiv2015

Purine: A bi-graph based deep learning framework

In this paper, we introduce a novel deep learning framework, termed Purine. In Purine, a deep network is expressed as a bipartite graph (bi-graph), which is composed of interconnected operators and data tensors. With the bi-graph abstraction, networks are easily solvable with event-driven task dispatcher. We then demonstrate that different parallelism schemes over GPUs and/or CPUs on single or multiple PCs can be universally implemented by graph composition. This eases researchers from coding for various parallelization schemes, and the same dispatcher can be used for solving variant graphs. Scheduled by the task dispatcher, memory transfers are fully overlapped with other computations, which greatly reduce the communication overhead and help us achieve approximate linear acceleration.

cs.NE↗

arXiv2014

Experimental demonstration of hybrid improper ferroelectricity and presence of abundant charged walls in (Ca,Sr)$_{3}$Ti$_{2}$O$_{7}$ crystals

Standing on successful first principles predictions for new functional ferroelectric materials, a number of new ferroelectrics have been experimentally discovered. Utilizing trilinear coupling of two types of octahedron rotations, hybrid improper ferroelectricity has been theoretically predicted in ordered perovskites and the Ruddlesden-Popper compounds (Ca$_{3}$Ti$_{2}$O$_{7}$, Ca$_{3}$Mn$_{2}$O$_{7}$, and (Ca/Sr/Ba)$_{3}$(Sn/Zr/Ge)$_{2}$O$_{7}$). However, the ferroelectricity of these compounds has never been experimentally confirmed and even their polar nature has been under debate. Here we provide the first experimental demonstration of room-temperature switchable polarization in the bulk crystals of Ca$_{3}$Ti$_{2}$O$_{7}$ as well as Sr-doped Ca$_{3}$Ti$_{2}$O$_{7}$. In addition, (Ca,Sr)$_{3}$Ti$_{2}$O$_{7}$ is found to exhibit an intriguing ferroelectric domain structure resulting from orthorhombic twins and (switchable) planar polarization. The planar domain structure accompanies abundant charged domain walls with conducting head-to-head and insulating tail-to-tail configurations, which exhibit two-order-of-magnitude conduction difference. These discoveries provide new research opportunities not only on new stable ferroelectrics of Ruddlesden-Popper compounds, but also on meandering conducting domain walls formed by planar polarization.

cond-mat.mtrl-sci↗

arXiv2014

55~Tesla coercive magnetic field in frustrated Sr$_3$NiIrO$_6$

We have measured extremely large coercive magnetic fields of up to 55~T in Sr$_3$NiIrO$_6$, with a switched magnetic moment $\approx 0.8~μ_{\rm B}$ per formula unit. As far as we are aware, this is the largest coercive field observed thus far. This extraordinarily hard magnetism has a completely different origin from that found in conventional ferromagnets. Instead, it is due to the evolution of a frustrated antiferromagnetic state in the presence of strong magnetocrystalline anisotropy due to the overlap of spatially-extended Ir$^{4+}$ 5$d$ orbitals with oxygen 2$p$ and Ni$^{2+}$ 3$d$ orbitals. This work highlights the unusual physics that can result from combining the extended $5d$ orbitals in Ir$^{4+}$ with the frustrated behaviour of triangular lattice antiferromagnets.

cond-mat.mtrl-sci↗

arXiv2014

Magnetic Structure of Hexagonal Mn-doped LuFeO$_{3}$

Neutron scattering techniques are used to investigate the crystalline and magnetic structure of LuFe$_{0.75}$Mn$_{0.25}$O$_{3}$ in bulk polycrystalline form. We find that the crystalline structure is described by the hexagonal P6$_{3}$cm space group similar to that of thin-film LuFeO$_{3}$, and that the system orders antiferromagnetically below T$_{N}$ = 134 K. Inelastic neutron scattering reveals nearest-neighbor superexchange parameters that are enhanced relative to LuMnO$_{3}$. The observation of significant diffuse scattering above T$_{N}$ demonstrates the frustrated nature of the system; comparisons with similar materials suggest the ground state magnetic configuration is sensitive to local crystallographic distortions.

cond-mat.mtrl-sci↗

arXiv2014

Color theorems, chiral domain topology and magnetic properties of FexTaS2

Common mathematical theory can have profound applications in understanding real materials. The intrinsic connection between aperiodic orders observed in the Fibonacci sequence, Penrose tiling, and quasicrystals is a well-known example. Another example is the self-similarity in fractals and dendrites. From transmission electron microscopy experiments, we found that FexTaS2 crystals with x=1/4 and 1/3 exhibit complicated antiphase and chiral domain structures related to ordering of intercalated Fe ions with 2a*2a and sqrt3a*sqrt3a superstructures, respectively. These complex domain patterns are found to be deeply related with the four color theorem, stating that four colors are sufficient to identify the countries on a planar map with proper coloring, and its variations for two-step proper coloring. Furthermore, the domain topology is closely relevant to their magnetic properties. Our discovery unveils the importance of understanding the global topology of domain configurations in functional materials.

cond-mat.mtrl-sci↗