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Search Results: 1 - 10 of 47781 matches for " Si Wu "
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Computational neuroscience in China
Si Wu,PeiJi Liang
Science China Life Sciences , 2010, DOI: 10.1007/s11427-010-0063-y
Abstract: The ultimate goal of Computational Neuroscience (CNS) is to use and develop mathematical models and approaches to elucidate brain functions. CNS is a young and highly multidisciplinary field. It heavily interacts with experimental neuroscience and such other research areas as artificial intelligence, robotics, computer vision, information science and machine learning. This paper reviews the history of CNS in China, its current status and the prospects for its future development. Examples of CNS research in China are also presented.
Soliton Wall Superlattice in Quasi-One-Dimensional Conductor (Per)2Pt(mnt)2
A. G. Lebed,Si Wu
Physics , 2007, DOI: 10.1103/PhysRevLett.99.026402
Abstract: We suggest a model to explain the appearance of a high resistance high magnetic field charge-density-wave (CDW) phase, discovered by D. Graf et al. [Phys. Rev. Lett. v. 93, 076406 (2004)] in (Per)2Pt(mnt)2. In particular, we show that the Pauli spin-splitting effects improve the nesting properties of a realistic quasi-one-dimensional electron spectrum and, therefore, a high resistance Peierls CDW phase is stabilized in high magnetic fields. In low and very high magnetic fields, a periodic soliton wall superlattice (SWS) phase is found to be a ground state. We suggest experimental studies of the predicted phase transitions between the Peierls and SWS CDW phases in (Per)2Pt(mnt)2 to discover a unique SWS phase.
Unification Theory of Angular Magnetoresistance Oscillations in Quasi-One-Dimensional Conductors
Si Wu,A. G. Lebed
Physics , 2010, DOI: 10.1103/PhysRevB.82.075123
Abstract: We present a unification theory of angular magnetoresistance oscillations, experimentally observed in quasi-one-dimensional organic conductors, by solving the Boltzmann kinetic equation in the extended Brillouin zone. We find that, at commensurate directions of a magnetic field, resistivity exhibits strong minima. In two limiting cases, our general solution reduces to the results, previously obtained for the Lebed Magic Angles and Lee-Naughton-Lebed oscillations. We demonstrate that our theoretical results are in good qualitative and quantitative agreement with the existing measurements of resistivity in (TMTSF)$_2$ClO$_4$ conductor.
Soliton Wall Superlattice Charge-Density-Wave Phase in Quasi-One-Dimensional Conductor (Per)$_2$Pt(mnt)$_2$
Si Wu,A. G. Lebed
Physics , 2009, DOI: 10.1103/PhysRevB.80.035128
Abstract: We demonstrate that the Pauli spin-splitting effects in a magnetic field improve nesting properties of a realistic quasi-one-dimensional electron spectrum. As a result, a high resistance Peierls charge-density-wave (CDW) phase is stabilized in high enough magnetic fields in (Per)$_2$Pt(mnt)$_2$ conductor. We show that, in low and very high magnetic fields, the Pauli spin-splitting effects lead to a stabilization of a soliton wall superlattice (SWS) CDW phase, which is characterized by periodically arranged soliton and anti-soliton walls. We suggest experimental studies of the predicted first order phase transitions between the Peierls and SWS phases to discover a unique SWS phase. It is important that, in the absence of a magnetic field and in a limit of very high magnetic fields, the suggested model is equivalent to the exactly solvable model of Brazovskii, Dzyaloshinskii, and Kirova.
Larkin-Ovchinnikov-Fulde-Ferrell phase in the superconductor (TMTSF)2ClO4: Theory versus experiment
A. G. Lebed,Si Wu
Physics , 2010, DOI: 10.1103/PhysRevA.82.012504
Abstract: We consider a formation of the Larkin-Ovchinnikov-Fulde-Ferrell (LOFF) phase in a quasi-one-dimensional (Q1D) conductor in a magnetic field, parallel to its conducting chains, where we take into account both the paramagnetic spin-splitting and orbital destructive effects against superconductivity. We show that, due to a relative weakness of the orbital effects in a Q1D case, the LOFF phase appears in (TMTSF)$_2$ClO$_4$ superconductor for real values of its Q1D band parameters. We compare our theoretical calculations with the recent experimental data by Y. Maeno's group [S. Yonezawa et al., Phys. Rev. Lett. \textbf{100}, 117002 (2008)] and show that there is a good qualitative and quantitative agreement between the theory and experimental data.
Reflection into China’s Business English Teaching Practices Based on GDUFS Graduates’ Employment Status
Wenzhong Zhu,Si Wu,Tingting Guo
International Education Studies , 2009, DOI: 10.5539/ies.v2n3p30
Abstract: GDUFS, as one of China’s top three foreign language universities with the longest history in business English teaching, has accumulated over 20-year experiences in this discipline. This research reflects into its business English teaching practices based on its graduates’ employment status in recent years, and concludes that the students of business English major tend to have higher level of employment status than those of other majors, and their employers are more likely to be consultancy MNCs, commercial banks and other firms. It is suggested that new efforts for reform should be made in disciplinary development, teaching development, curriculum designs and teaching methods.
Graphene: Kinks, Superlattices, Landau levels, and Magnetotransport
Matthew Killi,Si Wu,Arun Paramekanti
Physics , 2012, DOI: 10.1142/S0217979212420076
Abstract: We review recent work on superlattices in monolayer and bilayer graphene. We highlight the role of the quasiparticle chirality in generating new Dirac fermion modes with tunable anisotropic velocities in one dimensional (1D) superlattices in both monolayer and bilayer graphene. We discuss the structure of the Landau levels and magnetotransport in such superlattices over a wide range of perpendicular (orbital) magnetic fields. In monolayer graphene, we show that an orbital magnetic field can reverse the anisotropy of the transport imposed by the superlattice potential, suggesting possible switching-type device applications. We also consider topological modes localized at a kink in an electric field applied perpendicular to bilayer graphene, and show how interactions convert these modes into a two-band Luttinger liquid with tunable Luttinger parameters. The band structures of electric field superlattices in bilayer graphene (with or without a magnetic field) are shown to arise naturally from a coupled array of such topological modes. We briefly review some bandstructure results for 2D superlattices. We conclude with a discussion of recent tunneling and transport experiments and point out open issues.
Non-Abelian toplogical superconductors from topological semimetals and related systems under superconducting proximity effect
Jian-Hua Jiang,Si Wu
Physics , 2011, DOI: 10.1088/0953-8984/25/5/055701
Abstract: Non-Abelian toplogical superconductors are characterized by the existence of {zero-energy} Majorana fermions bound in the quantized vortices. This is a consequence of the nontrivial bulk topology characterized by an {\em odd} Chern number. It is found that in topological semimetals with a single two-bands crossing point all the gapped superconductors are non-Abelian ones. Such a property is generalized to related but more generic systems which will be useful in the search of non-Abelian superconductors and Majorana fermions.
Finite temperature spin dynamics in a perturbed quantum critical Ising chain with an $E_8$ symmetry
Jianda Wu,Márton Kormos,Qimiao Si
Physics , 2014, DOI: 10.1103/PhysRevLett.113.247201
Abstract: A spectrum exhibiting $E_8$ symmetry is expected to arise when a small longitudinal field is introduced in the transverse-field Ising chain at its quantum critical point. Evidence for this spectrum has recently come from neutron scattering measurements in cobalt niobate, a quasi one-dimensional Ising ferromagnet. Unlike its zero-temperature counterpart, the finite-temperature dynamics of the model has not yet been determined. We study the dynamical spin structure factor of the model at low frequencies and nonzero temperatures, using the form factor method. Its frequency dependence is singular, but differs from the diffusion form. The temperature dependence of the nuclear magnetic resonance (NMR) relaxation rate has an activated form, whose prefactor we also determine. We propose NMR experiments as a means to further test the applicability of the $E_8$ description for CoNb$_2$O$_6$.
Band structures of bilayer graphene superlattices
Matthew Killi,Si Wu,Arun Paramekanti
Physics , 2011, DOI: 10.1103/PhysRevLett.107.086801
Abstract: We formulate a low energy effective Hamiltonian to study superlattices in bilayer graphene (BLG) using a minimal model which supports quadratic band touching points. We show that a one dimensional (1D) periodic modulation of the chemical potential or the electric field perpendicular to the layers leads to the generation of zero energy anisotropic massless Dirac fermions and finite energy Dirac points with tunable velocities. The electric field superlattice maps onto a coupled chain model comprised of 'topological' edge modes. 2D superlattice modulations are shown to lead to gaps on the mini-Brillouin zone boundary but do not, for certain symmetries, gap out the quadratic band touching point. Such potential variations, induced by impurities and rippling in biased BLG, could lead to subgap modes which are argued to be relevant to understanding transport measurements.
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