The measurement of science and technology in China.

This paper introduced the background about the measurement of science and technology in China and selectively introduced the most recent statistic results released by the Institute of Scientific and Technical Information of China.China; Science and technology; Measurement;

Conductivity of Dirac fermions with phonon induced topological crossover

We study the Hall conductivity in single layer gapped Dirac fermion materials including coupling to a phonon field, which not only modifies the quasi-particle dynamics through the usual self-energy term but also renormalizes directly the gap. Consequently the Berry curvature is modified. As the temperature is increased the sign of the renormalized gap can change and the material can cross over from a band insulator to a topological insulator at higher temperature (T). The effective Chern numbers defined for valley and spin Hall conductivity show a rich phase diagram with increasing temperature. While the spin and valley DC Hall conductivity is no longer quantized at elevated temperature a change in sign with increasing T is a clear indication of a topological crossover. The chirality of the circularly polarized light which is dominantly absorbed by a particular valley can change with temperature as a result of a topological crossover.Comment: 6 pages, 5 figures, to appear in Phys. Rev.

Electron-phonon correlations on spin texture of gapped helical Dirac Fermions

The metallic surface states of a topological insulator support helical Dirac fermions protected by topology with their spin locked perpendicular to their momentum. They can acquire mass through magnetic doping or through hybridization of states on opposite faces of a thin sample. In this case there can be a component of electron spin oriented perpendicular to the surface plane. The electron-phonon interaction renormalizes the dynamics of the charge carriers through their spectral density. It also modifies the gap channel and a second spectral function enters which, not only determines the out of plane spin component, but also comes into in-plane properties. While the out of plane spin component is decreased below the Fermi momentum ($k_F$), the in plane component increases. There are also correlation tails extending well beyond $k_F$. The angular resolved photo-emission line shapes aquire Holstein side bands. The effective gap in the density of states is reduced and the optical conductivity aquires distinct measurable phonon structure even for modest value of the electron-phonon coupling.Comment: 9pages, 9 figure

Longitudinal and spin/valley Hall optical conductivity in single layer MoS2MoS_{2}

A monolayer of $MoS_{2}$ has a non-centrosymmetric crystal structure, with spin polarized bands. It is a two valley semiconductor with direct gap falling in the visible range of the electromagnetic spectrum. Its optical properties are of particular interest in relation to valleytronics and possible device applications. We study the longitudinal and the transverse Hall dynamical conductivity which is decomposed into charge, spin and valley contributions. Circular polarized light associated with each of the two valleys separately is considered and results are filtered according to spin polarization. Temperature can greatly change the spin admixture seen in the frequency window where they are not closely in balance.Comment: 8 pages, 5 figures, accepted by Phys. Rev.

Early Turn-taking Prediction with Spiking Neural Networks for Human Robot Collaboration

Turn-taking is essential to the structure of human teamwork. Humans are typically aware of team members' intention to keep or relinquish their turn before a turn switch, where the responsibility of working on a shared task is shifted. Future co-robots are also expected to provide such competence. To that end, this paper proposes the Cognitive Turn-taking Model (CTTM), which leverages cognitive models (i.e., Spiking Neural Network) to achieve early turn-taking prediction. The CTTM framework can process multimodal human communication cues (both implicit and explicit) and predict human turn-taking intentions in an early stage. The proposed framework is tested on a simulated surgical procedure, where a robotic scrub nurse predicts the surgeon's turn-taking intention. It was found that the proposed CTTM framework outperforms the state-of-the-art turn-taking prediction algorithms by a large margin. It also outperforms humans when presented with partial observations of communication cues (i.e., less than 40% of full actions). This early prediction capability enables robots to initiate turn-taking actions at an early stage, which facilitates collaboration and increases overall efficiency.Comment: Submitted to IEEE International Conference on Robotics and Automation (ICRA) 201

Phonon structure in dispersion curves and density of states of massive Dirac Fermions

Dirac fermions exist in many solid state systems including graphene, silicene and other two dimensional membranes such as are found in group VI dichalcogenides, as well as on the surface of some insulators where such states are protected by topology. Coupling of those fermions to phonons introduces new structures in their dispersion curves and, in the case of massive Dirac fermions, can shift and modify the gap. We show how these changes present in angular-resolved photoemission spectroscopy of the dressed charge carrier dispersion curves and scanning tunneling microscopy measurements of their density of states. In particular we focus on the region around the band gap. In this region the charge carrier spectral density no longer consists of a dominant quasiparticle peak and a smaller incoherent phonon related background. The quasiparticle picture has broken down and this leads to important modification in both dispersion curves and density of states.Comment: 12 pages, 6 figures, to appear in PR

Hexagonal warping on spin texture, Hall conductivity and circular dichroism of Topological Insulator

The topological protected electronic states on the surface of a topological insulator can progressively change their Fermi cross-section from circular to a snowflake shape as the chemical potential is increased above the Dirac point because of an hexagonal warping term in the Hamiltonian. Another effect of warping is to change the spin texture which exists when a finite gap is included by magnetic doping, although the in-plane spin component remains locked perpendicular to momentum. It also changes the orbital magnetic moment, the matrix element for optical absorption and the circular dichroism. We find that the Fermi surface average of z-component of spin is closely related to the value of the Berry phase. This holds even when the Hamiltonian includes a subdominant non-relativistic quadratic in momentum term (which provides particle-hole asymmetry) in addition to the dominant relativistic Dirac term. There is also a qualitative correlation between $\left\langle S_z \right\rangle$ and the dichroism. For the case when the chemical potential falls inside the gap between valence and conduction band, the Hall conductivity remains quantized and unaffected in value by the hexagonal warping term.Comment: 10 figures, accepted in PR