arXiv subjects

Lu Ma

Publications and source records attributed to Lu Ma.

66 records · Page 4Linked to original sources

arXiv2018

A Weak Modulation Effect Detected in the Light Curves of KIC 5950759: Intrinsic or Instrumental Effect?

In this paper, the high-precision light curves of $Kepler$ target KIC 5950759 are analyzed. The Fourier analysis of the long cadence light curve reveals 3 independent frequencies. Two of them are main pulsation modes: F0 = 14.221373(21) $\rm{d^{-1}}$ and F1 = 18.337249(44) $\rm{d^{-1}}$. The third independent frequency $f_m$ = 0.3193 d$^{-1}$ is found in long cadence data with a signal-to-noise ratio of 6.2. A weak modulation of $f_m$ to F0 and F1 modes (triplet structures centred on F0 and F1) are detected both in long and short cadence data. This is the first detection of the modulation effect in a double-mode HADS star. The most possible cause of the modulation effect in the light curves is amplitude modulation with the star's rotation frequency of 0.3193 d$^{-1}$. The preliminary analysis suggests that KIC 5950759 is in the bottom of the HADS instability strip and likely situated in the main sequence. Spectroscopic observations are necessary to verify the true nature of the modulation terms.

astro-ph.SR↗

arXiv2018

Probing single protein dynamics on liposome surfaces

It is crucial to measure position and conformational changes of a membrane-interacting protein relative to the membrane surface. This is however challenging because the thickness of a membrane is usually only about 4 nm. We developed a fluorescence method which makes use of the principle of FRET between a fluorophore and a cloud of quenchers encapsulated in a liposome, hence the name LipoFRET. LipoFRET can readily locate a fluorophore in different depths inside and at different heights above the membrane. We applied LipoFRET to study α-synuclein, a key player in the pathology of Parkinson's disease. Our approach yielded quantita-tive information about the dynamics of different regions of α-syn in lipid membranes, which has never been explored before.

physics.bio-ph↗

arXiv2018

Satellite-relayed intercontinental quantum network

We perform decoy-state quantum key distribution between a low-Earth-orbit satellite and multiple ground stations located in Xinglong, Nanshan, and Graz, which establish satellite-to-ground secure keys with ~kHz rate per passage of the satellite Micius over a ground station. The satellite thus establishes a secure key between itself and, say, Xinglong, and another key between itself and, say, Graz. Then, upon request from the ground command, Micius acts as a trusted relay. It performs bitwise exclusive OR operations between the two keys and relays the result to one of the ground stations. That way, a secret key is created between China and Europe at locations separated by 7600 km on Earth. These keys are then used for intercontinental quantum-secured communication. This was on the one hand the transmission of images in a one-time pad configuration from China to Austria as well as from Austria to China. Also, a videoconference was performed between the Austrian Academy of Sciences and the Chinese Academy of Sciences, which also included a 280 km optical ground connection between Xinglong and Beijing. Our work points towards an efficient solution for an ultralong-distance global quantum network, laying the groundwork for a future quantum internet.

quant-ph↗

arXiv2017

Pulsations of the High-Amplitude $δ$ Scuti Star YZ Bootis

We present a study on the pulsations of the high-amplitude $δ$ Scuti star YZ Boo based on photometric observations in Johnson $V$ and $R$ bands with both the Nanshan 1-m telescope of Xinjiang Astronomical Observatory (XAO) and the Xinglong 85-cm telescope of National Astronomical Observatories, Chinese Academy of Sciences (NAOC). The Fourier analysis of the light curves reveals the fundamental radial mode and its five harmonics, with the fourth and the fifth newly detected. 39 new times of light maximum are determined from the light curves, and combined with those in the literature, we construct the $O - C$ diagram and derive a new ephemeris and the determination of a new value of the updated period 0.104091579(2). Besides, the $O - C$ diagram reveals an increasing period change rate of YZ Boo. Theoretical models are calculated and constrained with the observationally determined parameters of YZ Boo. The mass and age of YZ Boo are hence derived as $M$ = 1.61 $\pm$ 0.05 $M_\odot$ and $age$ = (1.44 $\pm$ 0.14) $\times$ 10$^9$ yr, respectively. With both the frequency of the fundamental radial mode and the period change rate, YZ Boo is located at the post-main-sequence stage.

astro-ph.SR↗

arXiv2017

Pair production of the Elementary Goldstone Higgs boson at the LHC

The Elementary Goldstone Higgs (EGH) model is a perturbative extension of the standard model (SM), which identifies the EGH boson as the observed Higgs boson. In this paper, we study pair production of the EGH boson via gluon fusion at the LHC and find that the resonant contribution of the heavy scalar is very small and the SM-like triangle diagram contribution is strongly suppressed. The total production cross section mainly comes from the box diagram contribution and its value can be significantly enhanced with respect to the SM prediction.

hep-ph↗

arXiv2017

Satellite-to-ground quantum key distribution

Quantum key distribution (QKD) uses individual light quanta in quantum superposition states to guarantee unconditional communication security between distant parties. In practice, the achievable distance for QKD has been limited to a few hundred kilometers, due to the channel loss of fibers or terrestrial free space that exponentially reduced the photon rate. Satellite-based QKD promises to establish a global-scale quantum network by exploiting the negligible photon loss and decoherence in the empty out space. Here, we develop and launch a low-Earth-orbit satellite to implement decoy-state QKD with over kHz key rate from the satellite to ground over a distance up to 1200 km, which is up to 20 orders of magnitudes more efficient than that expected using an optical fiber (with 0.2 dB/km loss) of the same length. The establishment of a reliable and efficient space-to-ground link for faithful quantum state transmission constitutes a key milestone for global-scale quantum networks.

quant-ph↗

arXiv2015

Layer-Transferred MoS2/GaN PN Diodes

Electrical and optical characterization of two-dimensional/three-dimensional (2D/3D) p-molybdenum disulfide/n-gallium nitride (p-MoS2/n-GaN) heterojunction diodes are reported. Devices were fabricated on high-quality, large-area p-MoS2 grown by chemical vapor deposition (CVD) on hexagonal sapphire substrates. The processed devices were transferred onto GaN/sapphire substrates, and the transferred films were characterized by X-ray diffraction (XRD) and atomic force microscopy (AFM). On-axis XRD spectra and surface topology obtained from AFM scans were consistent with previously grown high-quality, continuous MoS2 films. Current-voltage measurements of these diodes exhibited excellent rectification, and capacitance-voltage measurements were used to extract a conduction band offset of approximately 0.2 eV for the transferred MoS2/GaN heterojunction. This conduction band offset was confirmed by internal photoemission (IPE) measurements. The energy band lineup of the MoS2/GaN heterojunction is proposed here. This work demonstrates the potential of 2D/3D heterojunctions for novel device applications.

cond-mat.mtrl-sci↗

arXiv2014

Simultaneous Localization, Mapping, and Manipulation for Unsupervised Object Discovery

We present an unsupervised framework for simultaneous appearance-based object discovery, detection, tracking and reconstruction using RGBD cameras and a robot manipulator. The system performs dense 3D simultaneous localization and mapping concurrently with unsupervised object discovery. Putative objects that are spatially and visually coherent are manipulated by the robot to gain additional motion-cues. The robot uses appearance alone, followed by structure and motion cues, to jointly discover, verify, learn and improve models of objects. Induced motion segmentation reinforces learned models which are represented implicitly as 2D and 3D level sets to capture both shape and appearance. We compare three different approaches for appearance-based object discovery and find that a novel form of spatio-temporal super-pixels gives the highest quality candidate object models in terms of precision and recall. Live experiments with a Baxter robot demonstrate a holistic pipeline capable of automatic discovery, verification, detection, tracking and reconstruction of unknown objects.

cs.RO↗

arXiv2014

Epitaxial Growth of Large Area Single-Crystalline Few-Layer MoS2 with Room Temperature Mobility of 192 cm2V-1s-1

We report on the vapor-solid growth of single crystalline few-layer MoS2 films on (0001)-oriented sapphire with excellent structural and electrical properties over centimeter length scale. High-resolution X-ray diffraction scans indicated that the films had good out-of-plane ordering and epitaxial registry. A carrier density of ~2 x 1011 cm-2 and a room temperature mobility of 192 cm2/Vs were extracted from space-charge limited transport regime in the films. The electron mobility was found to exhibit in-plane anisotropy with a ratio of ~ 1.8. Theoretical estimates of the temperature-dependent electron mobility including optical phonon, acoustic deformation potential and remote ionized impurity scattering were found to satisfactorily match the measured data. The synthesis approach reported here demonstrates the feasibility of device quality few-layer MoS2 films with excellent uniformity and high quality.

cond-mat.mtrl-sci↗

arXiv2014

Growth and Electrical Characterization of 2D Layered MoS2/SiC Heterojunctions

The growth and electrical characterization of a heterojunction formed between 2D layered p-MoS2 and nitrogen-doped 4H-SiC is reported. Direct growth of p-type MoS2 films on SiC was demonstrated using chemical vapor deposition, and the MoS2 films were found to be crystalline based on x-ray diffraction measurements. The resulting heterojunction was found to display rectification and current-voltage characteristics consistent with a p-n junction diode. Capacitance voltage measurements were used to determine the built-in voltage for the p-MoS2/n-SiC heterojunction p-n diode. The demonstration of heterogeneous material integration between 2D layered semiconductors and 3D SiC enables a new class of heterostructures.

cond-mat.mtrl-sci↗

arXiv2013

Low frequency noise in chemical vapor deposited MoS2

Inherent low frequency noise is a ubiquitous phenomenon, which limits operation and performance of electronic devices and circuits. This limiting factor is very important for nanoscale electronic devices, such as 2D semiconductor devices. In this work, low frequency noise in high mobility single crystal MoS2 grown by chemical vapor deposition (CVD) is investigated. The measured low frequency noise follows an empirical formulation of mobility fluctuations with Hooge' s parameter ranging between 1.44E-3 and 3.51E-2. Small variation of Hooge's parameter suggests superior material uniformity and processing control of CVD grown MoS2 devices than reported single-layer MoS2 FET. The extracted Hooge's parameter is one order of magnitude lower than CVD grown graphene. The Hooge's parameter shows an inverse relationship with the field mobility.

cond-mat.mes-hall↗

arXiv2013

Large Area Single Crystal (0001) Oriented MoS2 Thin Films

Layered metal dichalcogenide materials are a family of semiconductors with a wide range of energy band gaps and properties, and potential to open up new areas of physics and technology applications. However, obtaining high crystal quality thin films over a large area remains a challenge. Here we show that chemical vapor deposition (CVD) can be used to achieve large area electronic grade single crystal Molybdenum Disulfide (MoS2) thin films with the highest mobility reported in CVD grown films so far. Growth temperature and choice of substrate were found to critically impact the quality of film grown, and high temperature growth on (0001) orientated sapphire yielded highly oriented single crystal MoS2 films for the first time. Films grown under optimal conditions were found to be of high structural quality from high-resolution X-ray diffraction, transmission electron microscopy, and Raman measurements, approaching the quality of reference geological MoS2. Photoluminescence and electrical measurements confirmed the growth of optically active MoS2 with a low background carrier concentration, and high mobility. The CVD method reported here for the growth of high quality MoS2 thin films paves the way towards growth of a variety of layered 2D chalcogenide semiconductors and their heterostructures.

cond-mat.mtrl-sci↗