Coherent Radio Emission from a Twisted Magnetosphere after a Magnetar-quake

Magnetars are a class of highly magnetized, slowly rotating neutron stars, only a small fraction of which exhibit radio emission. We propose that the coherent radio curvature emission is generated by net charge fluctuations from a twist-current-carrying bundle (the j-bundle) in the scenario of magnetar-quake. Two-photon pair production is triggered, which requires a threshold voltage not too much higher than 109 V in the current-carrying bundle, and which can be regarded as the open field lines of a magnetar. Continued untwisting of the magnetosphere maintains change fluctuations, and hence coherent radio emission, in the progressively shrinking j-bundle, which lasts for years until the radio beam is too small to be detected. The modeled peak flux of radio emission and the flat spectrum are generally consistent with the observations. We show that this time-dependent, conal-beam, radiative model can interpret the variable radio pulsation behaviors and the evolution of the X-ray hot spot of the radio-transient magnetar XTE J1810−197 and the high-B pulsar/anomalous X-ray pulsar PSR J1622−4950. Radio emission with luminosity of and high-frequency oscillations are expected to be detected for a magnetar after an X-ray outburst. Differences of radio emission between magnetars and ordinary pulsars are discussed

Comparative study of pre⁃column derivatization liquid chromatography and post-column derivatization liquid chromatography for the determination of free formaldehyde residues in vaccines

Objective: To establish a pre⁃column derivatization liquid chromatography method and a post⁃column derivatization liquid chromatography method for the determination of residual amount of free formaldehyde in vaccines. Consistency of the results of two methods was investigated. Methods: The pre⁃column derivatization liq⁃ uid chromatography was performed on a Shimadzu LC⁃20AT liquid chromatograph (SPD⁃20A UV detector). Sepa⁃ ration was accomplished on a Kromasil 100⁃5⁃C18(250mm×4.6mm) column with a mobile phase of 60% acetoni⁃ trile solution at a flow rate of 0. 8 mL·min-1 at 40℃ and the detection wavelength was 360 nm. The post⁃column derivatization liquid chromatography was performed on a Shimadzu LC⁃20AT liquid chromatograph (SPD⁃M20A diode array detector and vector derivative device). Separation was accomplished on a Chrom Core AQ⁃C18 (250mm ×4.6mm) column with a mobile phase of 0.2% (V/V) phosphoric acid solution at a flow rate of 1.0 mL·min-1 at 25℃ and the detection wavelength was 412 nm. The derivatization solution was acetate buffer, the flow rate was 0. 5 mL·min-1, and the temperature was 100℃. The precision, repeatability and sample recovery of the two methods were investigated, and the experiment results were tested for significance by F⁃test and t⁃test. Results: The precolumn derivatization liquid chromatography had good linearity in the range of 0. 025 -100μg· mL-1(R =0. 999 9, n =12). RSD values of precision and repeatability were 0. 06 % and 0.3%-1.4%, respectively. The average recoveries were 97. 3%-104. 8 % with RSD of 0. 7%-2. 9 %. The limit of quantitation was 0. 02μg·mL-1, and the limit of detection was 0. 01μg·mL-1. The post⁃column derivatization liquid chromatog⁃ raphy had good linearity in the range of 0.025-100μg·mL-1 (R =0. 9999, n=12). RSD values of precision and repeatability were 0. 02% and 0. 0.7%-3.5 %, respectively. The average recoveries were 105. 6%-114. 6% with RSD of 0.3% - 1.9%. The limit of quantitation was 0. 02μg·mL-1, and the limit of detection was 0. 006μg·mL-1. The F⁃test and the t⁃test results showed there was no significant difference between two methods. Conclusion: Two methods are simple and accurate with high sensitivity and good specificity, which can be applicable to the determination of free formaldehyde residues in vaccines

Root-MUSIC Based Angle Estimation for MIMO Radar with Unknown Mutual Coupling

Direction of arrival (DOA) estimation problem for multiple-input multiple-output (MIMO) radar with unknown mutual coupling is studied, and an algorithm for the DOA estimation based on root multiple signal classification (MUSIC) is proposed. Firstly, according to the Toeplitz structure of the mutual coupling matrix, output data of some specified sensors are selected to eliminate the influence of the mutual coupling. Then the reduced-dimension transformation is applied to make the computation burden lower as well as obtain a Vandermonde structure of the direction matrix. Finally, Root-MUSIC can be adopted for the angle estimation. The angle estimation performance of the proposed algorithm is better than that of estimation of signal parameters via rotational invariance techniques (ESPRIT)-like algorithm and MUSIC-like algorithm. Furthermore, the proposed algorithm has lower complexity than them. The simulation results verify the effectiveness of the algorithm, and the theoretical estimation error of the algorithm is also derived