Exact diagonalization for spin-1/2 chains and the first order quantum phase transitions of the XXX chain in a uniform transverse field

A simple Mathematica code based on the differential realization of hard-core boson operators for finding exact solutions of the periodic-N spin-1/2 systems with or beyond nearest neighbor interactions is proposed; it can easily be used to study general spin-1/2 interaction systems. As an example, the code is applied to study XXX spin-1/2 chains with nearest neighbor interaction in a uniform transverse field. It shows that there are [N/2] level-crossing points in the ground state, where N is the periodic number of the system and [x] stands for the integer part of x, when the interaction strength and magnitude of the magnetic field satisfy certain conditions. The quantum phase transitional behavior in the ground state of the system in the thermodynamic limit is also studied. © IOP Publishing Ltd

Movable Fiber-Integrated Hybrid Plasmonic Waveguide on Metal Film

A waveguide structure consisting of a tapered nanofiber on a metal film is proposed and analyzed to support highly localized hybrid plasmonic modes. The hybrid plasmonic mode can be efficiently excited through the in-line tapered fiber based on adiabatic conversion and collected by the same fiber, which is very convenient in the experiment. Due to the ultrasmall mode area of plasmonic mode, the local electromagnetic field is greatly enhanced in this movable waveguide, which is potential for enhanced coherence light emitter interactions, such as waveguide quantum electrodynamics, single emitter spectrum and nonlinear optics

Secondary Grouting Pressure Limit of Shield Tunnels in Loess Strata Based on Bolt Shear Behavior

A loess stratum was selected as the research object, assuming that the slurry diffuses in a hemispherical shape during secondary grouting. Based on the unified strength theory describing the failure characteristics of loess and the critical condition of bolt shear failure, the critical pressure value of the secondary grouting in loess strata was determined theoretically. The reliability of the theoretical analysis was verified by the numerical modeling realizing the large deformation of formation and the dynamic injection of slurry. The critical grouting pressure of 821.80 kPa of theoretical calculation was obtained. Comparing the results of the numerical simulation analysis, it was found that the critical grouting pressure calculated using the theoretical equation had a safety index of 1.14. Bounded by βu (the ratio of expansion radius RP of soil plastic zone to the expansion radius Ru of the slurry) equal to 2.65, the water pressure at the grouting port is the main factor affecting the upper limit of critical grouting pressure when it is less than 2.65, and the effective internal friction angle of soil layer is the main factor when it is greater than 2.65. The influence of matric suction on the upper limit of the critical grouting pressure can be ignored

Electrocatalytic oxidation of ethanol and ethylene glycol on cubic, octahedral and rhombic dodecahedral palladium nanocrystals

Cubic, octahedral and rhombic dodecahedral Pd nanocrystals were synthesized and examined as nanocatalysts for electro-oxidation of ethanol and ethylene glycol. Combined electrochemical measurements and density functional theory calculations reveal that nanofacet-dependent affinity and reactivity of OHads and COads are closely linked to the C2 alcohol oxidation activities, with the highest reactivity found on the Pd nanocubes bounded by {100} facets

3D LiDAR Aided GNSS NLOS Mitigation for Reliable GNSS-RTK Positioning in Urban Canyons

GNSS and LiDAR odometry are complementary as they provide absolute and relative positioning, respectively. Their integration in a loosely-coupled manner is straightforward but is challenged in urban canyons due to the GNSS signal reflections. Recent proposed 3D LiDAR-aided (3DLA) GNSS methods employ the point cloud map to identify the non-line-of-sight (NLOS) reception of GNSS signals. This facilitates the GNSS receiver to obtain improved urban positioning but not achieve a sub-meter level. GNSS real-time kinematics (RTK) uses carrier phase measurements to obtain decimeter-level positioning. In urban areas, the GNSS RTK is not only challenged by multipath and NLOS-affected measurement but also suffers from signal blockage by the building. The latter will impose a challenge in solving the ambiguity within the carrier phase measurements. In the other words, the model observability of the ambiguity resolution (AR) is greatly decreased. This paper proposes to generate virtual satellite (VS) measurements using the selected LiDAR landmarks from the accumulated 3D point cloud maps (PCM). These LiDAR-PCM-made VS measurements are tightly-coupled with GNSS pseudorange and carrier phase measurements. Thus, the VS measurements can provide complementary constraints, meaning providing low-elevation-angle measurements in the across-street directions. The implementation is done using factor graph optimization to solve an accurate float solution of the ambiguity before it is fed into LAMBDA. The effectiveness of the proposed method has been validated by the evaluation conducted on our recently open-sourced challenging dataset, UrbanNav. The result shows the fix rate of the proposed 3DLA GNSS RTK is about 30% while the conventional GNSS-RTK only achieves about 14%. In addition, the proposed method achieves sub-meter positioning accuracy in most of the data collected in challenging urban areas