Directional excitation of graphene surface plasmons

We propose a scheme to directionally couple light into graphene plasmons by placing a graphene sheet on a magneto-optical substrate. When a magnetic field is applied parallel to the surface, the graphene plasmon dispersion relation becomes asymmetric in the forward and backward directions. It is possible to achieve unidirectional excitation of graphene plasmons with normally incident illumination by applying a grating to the substrate. The directionality can be actively controlled by electrically gating the graphene, or by varying the magnetic bias. This scheme may have applications in graphene-based opto-electronics and sensing

Performance of Cross-layer Design with Multiple Outdated Estimates in Multiuser MIMO System

By combining adaptive modulation (AM) and automatic repeat request (ARQ) protocol as well as user scheduling, the cross-layer design scheme of multiuser MIMO system with imperfect feedback is presented, and multiple outdated estimates method is proposed to improve the system performance. Based on this method and imperfect feedback information, the closed-form expressions of spectral efficiency (SE) and packet error rate (PER) of the system subject to the target PER constraint are respectively derived. With these expressions, the system performance can be effectively evaluated. To mitigate the effect of delayed feedback, the variable thresholds (VTs) are also derived by means of the maximum a posteriori method, and these VTs include the conventional fixed thresholds (FTs) as special cases. Simulation results show that the theoretical SE and PER are in good agreement with the corresponding simulation. The proposed CLD scheme with multiple estimates can obtain higher SE than the existing CLD scheme with single estimate, especially for large delay. Moreover, the CLD scheme with VTs outperforms that with conventional FTs

High Fill-Out, Extreme Mass Ratio Overcontact Binary Systems. X. The new discovered binary XY Leonis Minoris

The new discovered short-period close binary star, XY LMi, was monitored photometrically since 2006. It is shown that the light curves are typical EW-type and show complete eclipses with an eclipse duration of about 80 minutes. By analyzing the complete B, V, R, and I light curves with the 2003 version of the W-D code, photometric solutions were determined. It is discovered that XY LMi is a high fill-out, extreme mass ratio overcontact binary system with a mass ratio of q=0.148 and a fill-out factor of f=74.1%, suggesting that it is on the late evolutionary stage of late-type tidal-locked binary stars. As observed in other overcontact binary stars, evidence for the presence of two dark spots on both components are given. Based on our 19 epoches of eclipse times, it is found that the orbital period of the overcontact binary is decreasing continuously at a rate of dP/dt=-1.67\times10^{-7}\,days/year, which may be caused by the mass transfer from the primary to the secondary or/and angular momentum loss via magnetic stellar wind. The decrease of the orbital period may result in the increase of the fill-out, and finally, it will evolve into a single rapid-rotation star when the fluid surface reaching the outer critical Roche Lobe.Comment: 19 pages, 4 figures, 9 table

Phase locked-loop with decaying DC transient removal for three-phase grids

Frequency and phase of the power grid, which are critical for reliable control and protection of grid-tied devices, are generally detected by the closed-loop phase locked-loop (PLL). In highly inductive high-voltage transmission systems, decaying DC (DDC) components with large amplitude can be easily introduced by load disturbances and/or grid abnormalities, leading to severe performance degradation of the PLL during the transient. Focusing on this issue, in this paper, modifications to the conventional synchronous reference frame (SRF)-PLL have been made to address the short-term disturbances including the DDC component, and the system operation is divided into the normal state and the DDC-transient state. The SRF-PLL is only adopted for the normal state where the DDC component is negligible. In the presence of a significant DDC component, as well as disturbances including negative-/zero-sequence components and harmonics, the weak effectiveness of the conventional SRF-PLL is proved, and an efficient DDC component extraction method, with a detection time of 0.5 grid cycle, is introduced for the three-phase system. The real-time amplitude and phase of the positive-sequence component can be efficiently extracted via the proposed scheme, by exploiting the transient signal properties in the dq-frame and assuming a constant grid frequency during the short transient. Finally, a proper design of switching logic has been proposed to allow for the fast and precise transition between the normal and the DDC-transient state, thereby ensuring high steady-state accuracy as well as short-term DDC transient immunity. Hardware-in-the-loop based experiments have been used to verify the effectiveness of the proposed PLL technique

A Circumbinary Planet in Orbit Around the Short-Period White-Dwarf Eclipsing Binary RR Cae

By using six new determined mid-eclipse times together with those collected from the literature, we found that the Observed-Calculated (O-C) curve of RR Cae shows a cyclic change with a period of 11.9 years and an amplitude of 14.3s, while it undergoes an upward parabolic variation (revealing a long-term period increase at a rate of dP/dt =+4.18(+-0.20)x10^(-12). The cyclic change was analyzed for the light-travel time effect that arises from the gravitational influence of a third companion. The mass of the third body was determined to be M_3*sin i' = 4.2(+-0.4) M_{Jup} suggesting that it is a circumbinary giant planet when its orbital inclination is larger than 17.6 degree. The orbital separation of the circumbinary planet from the central eclipsing binary is about 5.3(+-0.6)AU. The period increase is opposite to the changes caused by angular momentum loss via magnetic braking or/and gravitational radiation, nor can it be explained by the mass transfer between both components because of its detached configuration. These indicate that the observed upward parabolic change is only a part of a long-period (longer than 26.3 years) cyclic variation, which may reveal the presence of another giant circumbinary planet in a wide orbit.Comment: It will be published in the MNRA

Insulator-metal transition shift related to magnetic polarons in La0.67-xYxCa0.33MnO3

The magnetic transport properties have been measured for La0.67-xYxCa0.33MnO3 (0 <= x <= 0.14) system. It was found that the transition temperature Tp almost linearly moves to higher temperature as H increases. Electron spin resonance confirms that above Tp, there exist ferromagnetic clusters. From the magnetic polaron point of view, the shift of Tp vs. H was understood, and it was estimated that the size of the magnetic polaron is of 9.7~15.4 angstrom which is consistent with the magnetic correlation length revealed by the small-angle neutron-scattering technique. The transport properties at temperatures higher than Tp conform to the variable-range hopping mechanism.Comment: 22 pages, 6 figures, pdf, to be published in Euro. Phys. J.

Effects of hadronic loops on the direct CP violation of BcB_{c}

It is well known that the final state interaction plays an important role in the decays of $B$-meson. The contribution of the final state interaction which is supposed to be long-distance effects, to the concerned processes can interfere with that of the short-distance effects produced via the tree and/or loop diagrams at quark-gluon level. The interference may provide a source for the direct CP violation $\mathcal{A}_{CP}$ in the process $B_{c}^{+}\to D^{0}\pi^{+}$. We find that a typical value of $\mathcal{A}_{CP}$ when the final state interaction effect is taken into account can be about -22% which is different from that without the final state interaction effect. Therefore, when we extract information on CP violation from the data which will be available at LHCb and the new experiments in $B$-factories, the contribution from the final state interaction must be included. This study may be crucial for searching new physics in the future.Comment: 15 pages, 3 figures, 2 tables. More discussion adde

Reverse k-Ranks Queries on Large Graphs

published_or_final_versio

Three-Dimensional Modeling of Transport Properties in Hardened Cement Paste Using Metal Centrifugation-Based Pore Network

Accurate prediction of transport properties for cementitious materials remains a challenge since it is difficult to experimentally obtain the realistic three-dimensional (3D) pore network of cement paste. In this study, the 3D pore network of cement paste is quantitatively characterized using nano X-ray microtomography coupled with the metal centrifugation porosimetry (MCP). First, the MCP technique is carried out to impel the liquid metal into the pore network of cement paste. Subsequently, the 3D pore network of cement paste with the intruded metal is reconstructed using high-resolution X-ray microtomography. Finally, based on the X-ray microtomography images, the transport properties of cement paste including ionic diffusivity and fluid permeability are simulated using a set of lattice Boltzmann transport models. The results show that the metal alloy can significantly enhance the contrast between the pore network and solid phase, and the realistic 3D pore network can be successfully reproduced. For the cement pastes with water-to-cement (w/c) ratios of 0.5 and 0.6, the transport properties are dramatically increased with the improving w/c ratio. A similarly dramatic growth evolution of transport properties also occurs when the effective porosity of cement pastes raises from 27.56% to 36.11%