arXiv subjects

Yue Sun

Publications and source records attributed to Yue Sun.

At least 199 records · Page 11Linked to original sources

arXiv2018

Statistical Software for Psychology: Comparing Development Practices Between CRAN and Other Communities

Different communities rely heavily on software, but use quite different software development practices. {\bf Objective}: We wanted to measure the state of the practice in the area of statistical software for psychology to understand how it compares to best practices. {\bf Method}: We compared and ranked 30 software tools with respect to adherence to best software engineering practices on items that could be measured by end-users. {\bf Results} We found that R packages use quite good practices, that while commercial packages were quite usable, many aspects of their development is too opaque to be measures, and that research projects vary a lot in their practices. {\bf Conclusion} We recommend that more organizations adopt practices similar to those used by CRAN to facilitate success, even for small teams. We also recommend close coupling of source code and documentation, to improve verifiability.

cs.SE↗

arXiv2018

Optimize transfer learning for lung diseases in bronchoscopy using a new concept: sequential fine-tuning

Bronchoscopy inspection as a follow-up procedure from the radiological imaging plays a key role in lung disease diagnosis and determining treatment plans for the patients. Doctors needs to make a decision whether to biopsy the patients timely when performing bronchoscopy. However, the doctors also needs to be very selective with biopsies as biopsies may cause uncontrollable bleeding of the lung tissue which is life-threaten. To help doctors to be more selective on biopsies and provide a second opinion on diagnosis, in this work, we propose a computer-aided diagnosis (CAD) system for lung diseases including cancers and tuberculosis (TB). The system is developed based on transfer learning. We propose a novel transfer learning method: sentential fine-tuning . Compared to traditional fine-tuning methods, our methods achieves the best performance. We obtained a overall accuracy of 77.0% a dataset of 81 normal cases, 76 tuberculosis cases and 277 lung cancer cases while the other traditional transfer learning methods achieve an accuracy of 73% and 68%. . The detection accuracy of our method for cancers, TB and normal cases are 87%, 54% and 91% respectively. This indicates that the CAD system has potential to improve lung disease diagnosis accuracy in bronchoscopy and it also might be used to be more selective with biopsies.

cs.CV↗

arXiv2018

Denoising of 3D magnetic resonance images with multi-channel residual learning of convolutional neural network

The denoising of magnetic resonance (MR) images is a task of great importance for improving the acquired image quality. Many methods have been proposed in the literature to retrieve noise free images with good performances. Howerever, the state-of-the-art denoising methods, all needs a time-consuming optimization processes and their performance strongly depend on the estimated noise level parameter. Within this manuscript we propose the idea of denoising MRI Rician noise using a convolutional neural network. The advantage of the proposed methodology is that the learning based model can be directly used in the denosing process without optimization and even without the noise level parameter. Specifically, a ten convolutional layers neural network combined with residual learning and multi-channel strategy was proposed. Two training ways: training on a specific noise level and training on a general level were conducted to demonstrate the capability of our methods. Experimental results over synthetic and real 3D MR data demonstrate our proposed network can achieve superior performance compared with other methods in term of both of the peak signal to noise ratio and the global of structure similarity index. Without noise level parameter, our general noise-applicable model is also better than the other compared methods in two datasets. Furthermore, our training model shows good general applicability.

cs.CV↗

arXiv2018

Spatial Modulation Aided Layered Division Multiplexing: A Spectral Efficiency Perspective

In this paper, spatial modulation (SM) is introduced to layered division multiplexing (LDM) systems for enlarging the spectral efficiency over broadcasting transmission. Firstly, the SM aided LDM (SM-LDM) system is proposed, in which different layered services utilize SM for terrestrial broadcasting transmission with different power levels. Then a spectral efficiency (SE) analysis framework for SM-LDM systems is proposed, which is suitable for the SM-LDM systems with linear combining. Moreover, the closed-form SE lower bound of SM-LDM systems with maximum ratio combining (MRC) is derived, which is based on this framework. Since the theoretical SE analysis of single transmit antenna (TA) LDM systems with MRC and spatial multiplexing (SMX) aided LDM systems with MRC lacks a closed-form expression, the closed-form SE is also derived for these systems. Monte Carlo simulations are provided to verify the tightness of our proposed SE lower bound. Furthermore, it can be shown via simulations that our proposed SM-LDM systems always have a better SE performance than single-TA LDM systems, which can even outperform the SE of SMX aided LDM (SMX-LDM) systems.

cs.IT↗

arXiv2017

Gap structure of FeSe determined by field-angle-resolved specific heat measurements

Quasiparticle excitations in FeSe were studied by means of specific heat ($C$) measurements on a high-quality single crystal under rotating magnetic fields. The field dependence of $C$ shows three-stage behavior with different slopes, indicating the existence of three gaps ($Δ_1$, $Δ_2$, and $Δ_3$). In the low-temperature and low-field region, the azimuthal-angle ($ϕ$) dependence of $C$ shows a four-fold symmetric oscillation with sign change. On the other hand, the polar-angle ($θ$) dependence manifests as an anisotropy-inverted two-fold symmetry with unusual shoulder behavior. Combining the angle-resolved results and the theoretical calculation, the smaller gap $Δ_1$ is proved to have two vertical-line nodes or gap minima along the $k_z$ direction, and is determined to reside on the electron-type $\varepsilon$ band. $Δ_2$ is found to be related to the electron-type $δ$ band, and is isotropic in the $ab$-plane but largely anisotropic out of the plane. $Δ_3$ residing on the hole-type $α$ band shows a small out-of-plane anisotropy with a strong Pauli-paramagnetic effect.

cond-mat.supr-con↗

arXiv2017

Symmetry-unprotected nodes or gap minima in $s_{++}$ state of FeSe single crystal

We report the study on superconducting pairing mechanism of FeSe via the pair-breaking effects induced by H$^+$-irradiation combined with low-temperature specific heat measurements. A multi-gap structure with nodes or gap minima is suggested in a clean FeSe by the specific heat results. The suppression of critical temperature $T_c$ with increasing the defect density manifests a two-step behavior. When the increase in the residual resistivity is small, $Δρ_0$ $<$ $\sim$4.5 $μΩ$cm, $T_c$ is gradually suppressed with increasing the density of scattering centers, suggesting the presence of symmetry-unprotected nodes or gap minima. However, for $Δρ_0$ $>$ $\sim$4.5 $μΩ$cm, $T_c$ is almost independent of the scattering, which indicates that the nodes or gap minima are lifted and the order parameter becomes almost isotropic without sign change. Thus, the superconductivity in FeSe is found to be realized in symmetry-unprotected nodal or highly anisotropic $s_{++}$ state.

cond-mat.supr-con↗

arXiv2017

Direct Evidence of Spontaneous Abrikosov Vortex State in Ferromagnetic Superconductor EuFe$_2$(As$_{1-x}$P$_x$)$_2$ with $x=0.21$

Using low-temperature Magnetic Force Microscopy (MFM) we provide direct experimental evidence for spontaneous vortex phase (SVP) formation in EuFe$_2$(As$_{0.79}$P$_{0.21}$)$_2$ single crystal with the superconducting $T^{\rm 0}_{\rm SC}=23.6$~K and ferromagnetic $T_{\rm FM}\sim17.7$~K transition temperatures. Spontaneous vortex-antivortex (V-AV) pairs are imaged in the vicinity of $T_{\rm FM}$. Also, upon cooling cycle near $T_{\rm FM}$ we observe the first-order transition from the short period domain structure, which appears in the Meissner state, into the long period domain structure with spontaneous vortices. It is the first experimental observation of this scenario in the ferromagnetic superconductors. Low-temperature phase is characterized by much larger domains in V-AV state and peculiar branched striped structures at the surface, which are typical for uniaxial ferromagnets with perpendicular magnetic anisotropy (PMA). The domain wall parameters at various temperatures are estimated.

cond-mat.supr-con↗

arXiv2017

Effects of heavy-ion irradiation on FeSe

We report the effects of heavy-ion irradiation on FeSe single crystals by irradiating Uranium up to a dose equivalent matching field of $B_ϕ$ = 16 T. Almost continuous columnar defects along the $c$-axis with a diameter $\sim$10 nm are confirmed by high-resolution transmission electron microscopy. $T_c$ is found to be suppressed by introducing columnar defects at a rate of d$T_c$/d$B_ϕ$ $\sim$ -0.29KT$^{-1}$, which is much larger than those observed in iron pnictides. This unexpected large suppression of $T_c$ in FeSe is discussed in relation to the large diameter of the columnar defects as well as its unique band structure with a remarkably small Fermi energy. The critical current density is first dramatically enhanced with irradiation reaching a value over $\sim$2$\times$10$^5$ A/cm$^2$ ($\sim$5 times larger than that of the pristine sample) at 2 K (self-field) with $B_ϕ$ = 2 T, then gradually suppressed with increasing $B_ϕ$. The $δ$$l$-pinning associated with charge-carrier mean free path fluctuations, and the $δ$$T_c$-pinning associated with spatial fluctuations of the transition temperature are found to coexist in the pristine FeSe, while the irradiation increases the contribution from $δ$$l$-pinning, and makes it dominant over $B_ϕ$ = 4 T.

cond-mat.supr-con↗

arXiv2017

Visualization of Magnetic Flux Structure in Phosphorus-Doped EuFe$_2$As$_2$ Single Crystals

Magnetic flux structure on the surface of EuFe$_2$(As$\rm_{1-x}$P$\rm_x$)$_2$ single crystals with nearly optimal phosphorus doping levels $x=0.20$, and $x=0.21$ is studied by low-temperature magnetic force microscopy and decoration with ferromagnetic nanoparticles. The studies are performed in a broad temperature range. It is shown that the single crystal with $x=0.21$ in the temperature range between the critical temperatures $T_{\rm SC}=22$ K and $T_{\rm C}=17.7$ K of the superconducting and ferromagnetic phase transitions, respectively, has the vortex structure of a frozen magnetic flux, typical for type-II superconductors. The magnetic domain structure is observed in the superconducting state below $T_{\rm C}$. The nature of this structure is discussed.

cond-mat.supr-con↗

arXiv2017

Spectral Efficiency Analysis for Spatial Modulation in Massive MIMO Uplink over Dispersive Channels

Flat-fading channel models are usually invoked for analyzing the performance of massive spatial modulation multiple-input multiple-output (SM-MIMO) systems. However, in the context of broadband SM transmission, the severe inter-symbol-interference (ISI) caused by the frequency-selective fading channels can not be ignored, which leads to very detrimental effects on the achievable system performance, especially for single-carrier SM (SC-SM) transmission schemes. To the best of the author's knowledge, none of the previous researchers have been able to provide a thorough analysis on the achievable spectral efficiency (SE) of the massive SC-SM MIMO uplink transmission. In this context, the uplink SE of single-cell massive SC-SM MIMO system is analyzed, and a tight closed-form lower bound is proposed to quantify the SE when the base station (BS) uses maximum ratio (MR) combining for multi-user detection. The impacts of imperfect channel estimation and transmit correlation are all considered. Monte Carlo simulations are performed to verify the tightness of our proposed SE lower bound. Both the theoretical analysis and simulation results show that the SE of uplink single-cell massive SC-SM MIMO system has the potential to outperform the uplink SE achieved by single-antenna UEs.

cs.IT↗

arXiv2017

High-Q microcavity enhanced optical properties of CuInS$_{2}$/ZnS colloidal quantum dots towards non-photodegradation

We report on a temporal evolution of photoluminescence (PL) spectroscopy of CuInS$_{2}$/ZnS colloidal quantum dots (QDs) by drop-casting on SiO$_{2}$/Si substrates and high quality factor microdisks (MDs) under different atmospheric conditions. Fast PL decay, peak blueshift and linewidth broadening due to photooxidation have been observed at low excitation power. With further increasing of the excitation power, the PL peak position shows a redshift and linewidth becomes narrow, which is ascribed to the enhanced F$\ddot{o}$rster resonant energy transfer between different QDs by photoinduced agglomeration. The oxygen plays an important role in optically induced PL decay which is verified by reduced photobleaching effect in vacuum. When the QDs drop-casted on MDs, photooxidation and photobleaching are accelerated because the excitation efficiency is greatly enhanced with coupling the pumping laser with the cavity modes. However, when the emitted photons couple with cavity modes, a PL enhancement by more than 20 times is achieved because of the increased extraction efficiency and Purcell effects of MDs at room temperature (RT), and 35 times at 20 K. The photobleaching can be avoided with a small excitation power but with a strong PL intensity by taking advantages of high quality factor cavities. The high efficient PL emission without photodegradation is very promising for using CuInS$_{2}$ QDs as high efficient photon emitters at RT, where the photodegradation has always been limiting the practical applications of colloidal quantum dots.

physics.optics↗

arXiv2016

Gain enhanced Fano resonance in a coupled photonic crystal cavity-waveguide structure

Systems with coupled cavities and waveguides have been demonstrated as optical switches and optical sensors. To optimize the functionalities of these optical devices, Fano resonance with asymmetric and steep spectral line shape has been used. We theoretically propose a coupled photonic crystal cavity-waveguide structure to achieve Fano resonance by placing partially reflecting elements in waveguide. To enhance Fano resonance, optical gain material is introduced into the cavity. As the gain increases, the transmission line shape becomes steepened and the transmissivity can be six times enhanced, giving a large contrast by a small frequency shift. It is prospected that the gain enhanced Fano resonance is very useful for optical switches and optical sensors.

physics.optics↗

arXiv2016

Structural-transition-induced quasi two-dimensional Fermi surface in FeSe

We report detailed study of angular-dependent magnetoresistance (AMR) with tilting angel $θ$ from $c$-axis ranging from 0$^\circ$ to 360$^\circ$ on a high-quality FeSe single crystal. A pronounced AMR with twofold symmetry is observed, which is caused by the quasi two-dimensional (2D) Fermi surface. The pronounced AMR is observed only in the orthorhombic phase, indicating that the quasi-2D Fermi surface is induced by the structural transition. Details about the influence of the multiband effect to the AMR are also discussed. Besides, the angular response of a possible Dirac-cone-like band structure is investigated by analyzing the detailed magnetoresistance at different $θ$. The obtained characteristic field ($B^*$) can be also roughly scaled in the 2D approximation, which indicates that the Dirac-cone-like state is also 2D in nature.

cond-mat.supr-con↗

arXiv2016

Effects of Iodine Annealing on Fe1+yTe0.6Se0.4

Effects of iodine annealing to induce bulk superconductivity in Fe1+yTe0.6Se0.4 have been systematically studied by changing the molar ratio of iodine to the sample and annealing temperature. The optimal condition to induce bulk superconductivity with Tc ~14.5 K and self-field Jc(2 K) ~ 5x10^5 A/cm2 is found to be a molar ratio of iodine of 5-7 % at the annealing temperature of 400 C. Furthermore, the fact that no compounds containing iodine are detected in the crystal and a significant amount of FeTe2 is produced after the iodine annealing strongly indicate that the excess iron is consumed to form FeTe2 and iodine works as a catalyst in this process.

cond-mat.supr-con↗

arXiv2016

Influence of interstitial Fe to the phase diagram of Fe$_{1+y}$Te$_{1-x}$Se$_x$ single crystals

Superconductivity (SC) with the suppression of long-range antiferromagnetic (AFM) order is observed in the parent compounds of both iron-based and cuprate superconductors. The AFM wave vectors are bicollinear ($π$, 0) in the parent compound FeTe different from the collinear AFM order ($π$, $π$) in most iron pnictides. Study of the phase diagram of Fe$_{1+y}$Te$_{1-x}$Se$_x$ is the most direct way to investigate the competition between bicollinear AFM and SC. However, presence of interstitial Fe affects both magnetism and SC of Fe$_{1+y}$Te$_{1-x}$Se$_x$, which hinders the establishment of the real phase diagram. Here, we report the comparison of doping-temperature ($x$-$T$) phase diagrams for Fe$_{1+y}$Te$_{1-x}$Se$_x$ (0 $\leq$ $x$ $\leq$ 0.43) single crystals before and after removing interstitial Fe. Without interstitial Fe, the AFM state survives only for $x$ $<$ 0.05, and bulk SC emerges from $x$ = 0.05, and does not coexist with the AFM state. The previously reported spin glass state, and the coexistence of AFM and SC may be originated from the effect of the interstitial Fe. The phase diagram of Fe$_{1+y}$Te$_{1-x}$Se$_x$ is found to be similar to the case of the "1111" system such as LaFeAsO$_{1-x}$F$_x$, and is different from that of the "122" system.

cond-mat.supr-con↗

arXiv2016

Low-Rank Positive Semidefinite Matrix Recovery from Corrupted Rank-One Measurements

We study the problem of estimating a low-rank positive semidefinite (PSD) matrix from a set of rank-one measurements using sensing vectors composed of i.i.d. standard Gaussian entries, which are possibly corrupted by arbitrary outliers. This problem arises from applications such as phase retrieval, covariance sketching, quantum space tomography, and power spectrum estimation. We first propose a convex optimization algorithm that seeks the PSD matrix with the minimum $\ell_1$-norm of the observation residual. The advantage of our algorithm is that it is free of parameters, therefore eliminating the need for tuning parameters and allowing easy implementations. We establish that with high probability, a low-rank PSD matrix can be exactly recovered as soon as the number of measurements is large enough, even when a fraction of the measurements are corrupted by outliers with arbitrary magnitudes. Moreover, the recovery is also stable against bounded noise. With the additional information of an upper bound of the rank of the PSD matrix, we propose another non-convex algorithm based on subgradient descent that demonstrates excellent empirical performance in terms of computational efficiency and accuracy.

cs.IT↗

arXiv2016

Electron carriers with possible Dirac-cone-like dispersion in FeSe$_{1-x}$S$_x$ ($x$ = 0 and 0.14) single crystals triggered by structural transition

We report detailed study of the transport properties of FeSe$_{1-x}$S$_x$ ($x$ = 0 and 0.14) single crystals grown by vapor transport method. 14\% S doping is found significantly suppress the structural transition from $T_s$ $\sim$ 86 K in FeSe to $\sim$ 49 K, although the superconducting transition temperature, $T_c$, is only slightly affected. A pronounced linear magnetoresistance (MR) is observed in both FeSe and FeSe$_{0.86}$S$_{0.14}$ single crystals, which is found to be triggered by the structural transition. The linear MR and related discussion indicate the possible existence of Dirac-cone-like state, which may come from the band shift induced by ferro-orbital order. The mobility of the Dirac-cone-like band is found to decrease after S doping. Besides, the invalid Kohler's scaling of MR is found for temperature below $T_s$ in both crystals, however the re-establishment of the Kohler's scaling at temperatures below 30 K is observed in FeSe, but not in FeSe$_{0.86}$S$_{0.14}$. All these observations above support that the orbital ordering causes the band reconstruction in FeSe, and also that the orbital ordering in FeSe is suppressed by the chemical pressure from S doping.

cond-mat.supr-con↗

arXiv2016

Observation of nonlinear thermal optical dynamics in a chalcogenide nanobeam cavity

We present a theoretical and experimental analysis of nonlinear thermo-optic effects in suspended chalcogenide glass nanobeam cavities. We measure the power dependent resonance peaks and characterise the dynamic nonlinear thermo-optic response of the cavity under modulated light input. Several distinct nonlinear characteristics are identified, including a modified spectral response containing periodic fringes, a critical wavelength jump and saturated time delay for modulation frequency faster than the thermal characteristic time. We reveal that the coupling to a parasitic Fabry-Perot cavity enables isolated thermal equilibrium states resulting in the discontinuous thermo-optic critical point.

physics.optics↗