Polarized Curvature Radiation in Pulsar Magnetosphere

The propagation of polarized emission in pulsar magnetosphere is investigated in this paper. The polarized waves are generated through curvature radiation from the relativistic particles streaming along curved magnetic field lines and co-rotating with the pulsar magnetosphere. Within the 1/{\deg} emission cone, the waves can be divided into two natural wave mode components, the ordinary (O) mode and the extraord nary (X) mode, with comparable intensities. Both components propagate separately in magnetosphere, and are aligned within the cone by adiabatic walking. The refraction of O-mode makes the two components separated and incoherent. The detectable emission at a given height and a given rotation phase consists of incoherent X-mode and O-mode components coming from discrete emission regions. For four particle-density models in the form of uniformity, cone, core and patches, we calculate the intensities for each mode numerically within the entire pulsar beam. If the co-rotation of relativistic particles with magnetosphere is not considered, the intensity distributions for the X-mode and O-mode components are quite similar within the pulsar beam, which causes serious depolarization. However, if the co-rotation of relativistic particles is considered, the intensity distributions of the two modes are very different, and the net polarization of out-coming emission should be significant. Our numerical results are compared with observations, and can naturally explain the orthogonal polarization modes of some pulsars. Strong linear polarizations of some parts of pulsar profile can be reproduced by curvature radiation and subsequent propagation effect.Comment: 12 pages, 9 figures, Accepted for publication in MNRA

Optomechanical Stochastic Resonance in a Macroscopic Torsion Oscillator

Linear mechanical oscillators have been applied to measure very small forces, mostly with the help of noise suppression. In contrast, adding noise to non-linear oscillators can improve the measurement conditions. Here, this effect of stochastic resonance is demonstrated in a macroscopic torsion oscillator, for an optomechanical non-linear potential. The signal output is enhanced for a sub-threshold electronic signal. This non-linear oscillator serves as a model system for the enhancement of signal-to-noise ratio in high precision optomechanical experiments.Comment: 4 pages (double column), 3 figure

Database management and implementation for coal fire detection and monitoring in the Ruijgou Coalfield, Northwest China

Coal fire monitoring by aerospace remote sensing and GIS techniques is an advanced approach, which has been implemented in the Rujigou coalfield, northwest China. A database of several different types of data, including remote sensing images, results of geological surveys, etc., has been collected and assembled in a PC-based information system, which is being developed by the International Institute for Aerospace Survey and Earth Sciences (ITC). This coal fire monitoring and management information system (CoalMan) comprises of two main parts: one is the database with its management tools, and the tools for data processing and analysis form the other. This paper first introduces the structure of the CoalMan information system, presents the data types and contents of CoalMan database, then shows the data management methods. A complex data analysis package is outlined too, as the core of the information system

Jointly optimised iterative source-coding, channel-coding and modulation for transmission over wireless channels

Joint source-coding, channel-coding and modulation schemes based on Variable Length Codes (VLCs), Trellis Coded Modulation (TCM), Turbo TCM (TTCM), Bit-Interleaved Coded Modulation (BICM) and iteratively decoded BICM (BICM-ID) schemes are proposed. A significant coding gain is achieved without bandwidth expansion, when exchanging information between the VLC and the coded modulation decoders with the advent of iterative decoding. With the aid of using independent interleavers for the In-phase and Quadrature phase components of the complex-valued constellation, further diversity gain may be achieved. The performance of the proposed schemes is evaluated over both AWGN and Rayleigh fading channels. Explicitly, at BER = 10-5 most of the proposed schemes have BER curves less than one-dB away from the channel capacity limit

Quantum spin mixing in a binary mixture of spin-1 atomic condensates

We study quantum spin mixing in a binary mixture of spin-1 condensates including coherent interspecies mixing process, using the familiar spinor condensates of $^{87}$Rb and $^{23}$Na atoms in the ground lower hyperfine F=1 manifolds as prototype examples. Within the single spatial mode approximation for each of the two spinor condensates, the mixing dynamics reduce to that of three coupled nonlinear pendulums with clear physical interpretations. Using suitably prepared initial states, it is possible to determine the interspecies singlet-pairing as well as spin-exchange interactions from the subsequent mixing dynamics.Comment: 6 pages, 3 figure

Comparative study of Steel-FRP, FRP and steel reinforced coral concrete beams in their flexural performance

In this paper, a comparative study of Carbon Fiber Reinforced Polymer (CFRP) Bar and Steel-Carbon Fiber Composite Bar (SCFCB) reinforced coral concrete beams are made through a series experimental tests and theoretical analysis. The flexural capacity, crack development and failure modes of CFRP and SCFCB reinforced coral concrete were investigated in detail. They are also compared to ordinary steel reinforced coral concrete beams. The results show that under the same condition of reinforcement ratio, the SCFCB reinforced beam exhibits better performance than those of the CFRP reinforced beams, and its stiffness is slightly lower than that of the steel reinforced beam. Under the same load condition, the crack width of the SCFCB beam is between the steel reinforced beam and the CFRP bar reinforced beam. Before the steel core yields, the crack growth rate of SCFCB beam is similar to the steel reinforced beam. SCFCB has a higher strength utilization rate, about 70% -85% of its ultimate strength. The current design guidance was also examined based on the test results. It was found that the existing design specifications for FRP reinforced normal concrete is not suitable for SCFCB reinforced coral concrete structures