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KVN SOURCE-FREQUENCY PHASE-REFERENCING OBSERVATION OF 3C 66A AND 3C 66B
ZHAO, GUANG-YAO,JUNG, TAEHYUN,DODSON, RICHARD,RIOJA, MARIA,SOHN, BONG WON The Korean Astronomical Society 2015 天文學論叢 Vol.30 No.2
In this proceedings, preliminary results of the KVN Source-Frequency Phase-Referencing (SFPR) observation of 3C 66A and 3C 66B are presented. The motivation of this work is to measure the core-shift of these 2 sources and study the temporal evolution of the jet opacity. Two more sources were observed as secondary reference calibrators and each source was observed at 22, 43, and 86 GHz simultaneously. Our preliminary results show that after using the observations at the lower frequency to calibrate those at the higher frequency of the same source, the residual visibility phases for each source at the higher frequencies became more aligned, and the coherence time became much longer; also, the residual phases for different sources, within 10 degrees angular separations, follow similar trends. After reference to the nearby calibrator, the SFPRed maps were obtained as well as the astrometric measurements, i.e. the combined coreshift. The measurements were found to be affected by structural blending effects because of the large beamsize of KVN, but this can be corrected with higher resolution maps (e.g. KAVA maps).
The Power of Simultaneous Multi-frequency Observations for mm-VLBI: Beyond Frequency Phase Transfer
Guang-Yao Zhao,Juan Carlos Algaba,Sang Sung Lee,Taehyun Jung,Richard Dodson,Maria Rioja,Do-Young Byun,Jeffrey Hodgson,Sincheol Kang,Dae-Won Kim,Jae-Young Kim,Jeong-Sook Kim,Soon-Wook Kim,Motoki Kino,A 한국천문학회 2017 天文學會報 Vol.42 No.1
The Power of Simultaneous Multi-frequency Observations for mm-VLBI: Beyond Frequency Phase Transfer
Zhao, Guang-Yao,Algaba, Juan Carlos,Lee, Sang Sung,Jung, Taehyun,Dodson, Richard,Rioja, Marí,a,Byun, Do-Young,Hodgson, Jeffrey,Kang, Sincheol,Kim, Dae-Won,Kim, Jae-Young,Kim, Jeong-Sook,Kim, Soo American Institute of Physics 2018 The Astronomical journal Vol.155 No.1
<P>Atmospheric propagation effects at millimeter wavelengths can significantly alter the phases of radio signals and reduce the coherence time, putting tight constraints on high-frequency Very Long Baseline Interferometry (VLBI) observations. In previous works, it has been shown that non-dispersive (e.g., tropospheric) effects can be calibrated with the frequency phase transfer (FPT) technique. The coherence time can thus be significantly extended. Ionospheric effects, which can still be significant, remain however uncalibrated after FPT as well as the instrumental effects. In this work, we implement a further phase transfer between two FPT residuals (i.e., so-called FPT-square) to calibrate the ionospheric effects based on their frequency dependence. We show that after FPT-square, the coherence time at 3 mm can be further extended beyond 8 hr and the residual phase errors can be sufficiently canceled by applying the calibration of another source, which can have a large angular separation from the target (> 20 degrees) and significant temporal gaps. Calibrations for all-sky distributed sources with a few calibrators are also possible after FPT-square. One of the strengths and uniqueness of this calibration strategy is the suitability for high-frequency all-sky survey observations including very weak sources. We discuss the introduction of a pulse calibration system in the future to calibrate the remaining instrumental effects, allowing the possibility of imaging the source structure at high frequencies with FPT-square, where all phases are fully calibrated without involving any additional sources.</P>
MULTI-EPOCH MULTI-FREQUENCY VLBI STUDY OF THE PARSEC-SCALE JET IN THE BLAZAR 3C 66A
Zhao, Guang-Yao,Chen, Yong-Jun,Shen, Zhi-Qiang,Sudou, Hiroshi,Iguchi, Satoru American Institute of Physics 2015 The Astronomical journal Vol.149 No.2
<P>We present observational results of the &ggr;-ray blazar 3C 66A at 2.3, 8.4, and 22 GHz at four epochs during 2004–2005 with the VLBA. The resulting images show an overall core-jet structure extending roughly to the south, with two intermediate breaks occurring in the region near the core. By model-fitting to the visibility data, the northmost component, which is also the brightest, is identified as the core according to its relatively flat spectrum and its compactness. Combining our results with previous results to investigate the proper motions of the jet components, we found the kinematics of 3C 66A to be quite complicated, with components of inward and outward, subluminal and superluminal motions all detected in the radio structure. The superluminal motions indicate strong Doppler boosting exists in the jet. The apparent inward motions of the innermost components last for at least 10 years and could not be caused by newborn components. A possible reason could be non-stationarity of the core due to opacity change.</P>
Guang-Yao Zhao,Taehyun Jung,Bong Won Sohn,Motoki Kino,Mareki Honma,Richard Dodson,Maria Rioja,Seog-Tae Han,Katsunori Shibata,Do-Young Byun,Kazunori Akiyama,Juan-Carlos Algaba,Tao An,Xiaopeng Cheng,Ilj 한국천문학회 2019 Journal of The Korean Astronomical Society Vol.52 No.1
The KVN(Korean VLBI Network)-style simultaneous multi-frequency receiving mode is demonstrated to be promising for mm-VLBI observations. Recently, other Very long baseline interferometry (VLBI) facilities all over the globe start to implement compatible optics systems. Simultaneous dual/multi-frequency VLBI observations at mm wavelengths with international baselines are thus possible. In this paper, we present the results from the first successful simultaneous 22/43 GHz dualfrequency observation with KaVA(KVN and VERA array), including images and astrometric results. Our analysis shows that the newly implemented simultaneous receiving system has brought a significant extension of the coherence time of the 43 GHz visibility phases along the international baselines. The astrometric results obtained with KaVA are consistent with those obtained with the independent analysis of the KVN data. Our results thus confirm the good performance of the simultaneous receiving systems for the non-KVN stations. Future simultaneous observations with more global stations bring even higher sensitivity and micro-arcsecond level astrometric measurements of the targets.
Failure characteristics of combined coal-rock with different interfacial angles
Zhao, Tong-Bin,Guo, Wei-Yao,Lu, Cai-Ping,Zhao, Guang-Ming Techno-Press 2016 Geomechanics & engineering Vol.11 No.3
In order to investigate the influence of the interfacial angel on failure characteristics and mechanism of combined coal-rock mass, 35 uniaxial/biaxial compressive simulation tests with 5 different interfacial angels of combined coal-rock samples were conducted by PFC2D software. The following conclusions are drawn: (1) The compressive strength and cohesion decrease with the increase of interfacial angle, which is defined as the angle between structure plane and the exterior normal of maximum principal plane, while the changes of elastic modulus and internal friction angle are not obvious; (2) The impact energy index $K_E$ decreases with the increase of interfacial angle, and the slip failure of the interface can be predicted based on whether the number of acoustic emission (AE) hits has multiple peaks or not; (3) There are four typical failure patterns for combined coal-rock samples including I (V-shaped shear failure of coal), II (single-fracture shear failure of coal), III (shear failure of rock and coal), and IV (slip rupture of interface); and (4) A positive correlation between interfacial angle and interface effect is shown obviously, and the interfacial angle can be divided into weak-influencing scope ($0-15^{\circ}$), moderate-influencing scope ($15-45^{\circ}$), and strong-influencing scope (> $45^{\circ}$), respectively. However, the confining pressure has a certain constraint effect on the interface effect.
Zhao, Cheng-Xiao,Liu, Ming,Xu, Yong,Yang, Kuo,Wei, Dong,Shi, Xiao-Hong,Yang, Fan,Zhang, Yao-Guang,Wang, Xin,Liang, Si-Ying,Zhao, Fan,Zhang, Yu-Rong,Wang, Na-Na,Chen, Xin,Sun, Liang,Zhu, Xiao-Quan,Yuan Asian Pacific Journal of Cancer Prevention 2014 Asian Pacific journal of cancer prevention Vol.15 No.19
Background: Evidence supporting an association between the 8q24 rs4242382-A polymorphism and prostate cancer (PCa) risk has been reported in North American and Europe populations, though data from Asian populations remain limited. We therefore investigated this association by clinical detection in China, and meta-analysis in Asian, Caucasian and African-American populations. Materials and Methods: Blood samples and clinical information were collected from ethnically Chinese men from Northern China with histologically-confirmed PCa (n=335) and from age-matched normal controls (n=347). The 8q24 (rs4242382) gene polymorphism was genotyped by polymerase chain reaction-high-resolution melting analysis. We initially analyzed the associations between the risk allele and PCa and clinical covariates. A meta-analysis was then performed using genotyping data from a total of 1,793 PCa cases and 1,864 controls from our study and previously published studies in American and European populations, to determine the association between PCa and risk genotype. Results: The incidence of the risk allele was higher in PCa cases than controls (0.222 vs 0.140, $P=7.3{\times}10^{-5}$), suggesting that the 8q24 rs4242382-A polymorphism was associated with PCa risk in Chinese men. The genotypes in subjects were in accordance with a dominant genetic model (ORadj=2.03, 95%CI: 1.42-2.91, $Padj=1.1{\times}10^{-4}$). Presence of the risk allele rs4242382-A at 8q24 was also associated with clinical covariates including age at diagnosis ${\geq}65$ years, prostate specific antigen >10 ng/ml, Gleason score <8, tumor stage and aggressive PCa, compared with the non-risk genotype ($P=4.6{\times}10^{-5}-3.0{\times}10^{-2}$). Meta-analysis confirmed the association between 8q24 rs4242382-A polymorphism and PCa risk (OR=1.62, 95%CI: 1.39-1.88, $P=1.0{\times}10^{-5}$) across Asian, Caucasian and African American populations. Conclusions: The replicated data suggest that the 8q24 rs4242382-A variation might be associated with increased PCa susceptibility in Asian, Caucasian and African American populations. These results imply that this polymorphism may be a useful risk biomarker for PCa in multi-ethnic populations.