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1. chinaXiv:201711.02259 [pdf]

Probing Primordial Gravitational Waves: Ali CMB Polarization Telescope

Hong Li; Si-Yu Li; Yang Liu; Yong-Ping Li; Yifu Cai; Mingzhe Li; Gong-Bo Zhao; Cong-Zhan Liu; Zheng-Wei Li; He Xu; Di Wu; Yong-Jie Zhang; Zu-Hui Fan; Yong-Qiang Yao; Chao-Lin Kuo; Fang-Jun Lu; Xinmin Zhang
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等

In this paper, we will give a general introduction to the project of Ali CMB Polarization Tele-scope (AliCPT), which is a Sino-US joint project led by the Institute of High Energy Physics (IHEP) and has involved many di erent institutes in China. It is the rst ground-based cosmic microwave background (CMB) polarization experiment in China and an integral part of China's Gravitational Waves Program. The main scienti c goal of AliCPT project is to probe the primor-dial gravitational waves (PGWs) originated from the very early Universe. The AliCPT project includes two stages. The rst stage referred to as AliCPT-1, is to build a telescope in the Ali region of Tibet with an altitude of 5,250 meters. Once completed, it will be the worldwide highest ground-based CMB observatory and open a new window for probing PGWs in northern hemisphere. AliCPT-1 telescope is designed to have about 7,000 TES detectors at 90GHz and 150GHz. The second stage is to have a more sensitive telescope (AliCPT-2) with the number of detectors more than 20,000. Our simulations show that AliCPT will improve the current constraint on the tensor-to-scalar ratio r by one order of magnitude with 3 years' observation. Besides the PGWs, the AliCPT will also enable a precise measurement on the CMB rotation angle and provide a precise test on the CPT symmetry. We show 3 years' observation will improve the current limit by two order of magnitude.

提交时间: 2017-11-10 点击量537下载量320 评论 0

2. chinaXiv:201707.00514 [pdf]

Transcriptome analysis of Hamelia patens (Rubiaceae) anthers reveals candidate genes for tapetum and pollen wall development

Yue, Lin; Twell, David; Kuang, Yanfeng; Liao, Jingping; Zhou, Xianqiang
分类: 生物学 >> 植物学

Studies of the anther transcriptome on non-model plants without a known genome are surprisingly scarce. RNA-Seq and digital gene expression (DGE) profiling provides a comprehensive approach to identify candidate genes contributing to developmental processes in non-model species. Here we built a transcriptome library of developing anthers of Hamelia patens and analysed DGE profiles from each stage to identify genes that regulate tapetum and pollen development. In total 7,720 putative differentially expressed genes across four anther stages were identified. The number of putative stage-specific genes was: 776 at microspore mother cell stage (MMC), 807 at tetrad stage (TET), 322 at uninucleate microspore stage (UNM) and the highest number (1,864) at bicellular pollen stage (BCP). GO enrichment analysis revealed 243 differentially expressed and 108 stage-specific genes that are potentially related to tapetum development, sporopollenin synthesis and pollen wall. The number of expressed genes, their function and expression profiles were all significantly correlated with anther developmental processes. Overall comparisons of anther and pollen transcriptomes with those of rice and Arabidopsis together with the expression profiles of homologs of known anther-expressed genes, revealed conserved patterns and also divergence. The divergence may reflect taxon-specific differences in gene expression, the use RNA-seq as a more sensitive methodology, variation in tissue composition and sampling strategies. Given the lack of genomic sequence, this study succeeded in assigning putative identity to a significant proportion of anther-expressed genes and genes relevant to tapetum and pollen development in H. patens. The anther transcriptome revealed a molecular distinction between developmental stages, serving as a resource to unravel the functions of genes involved in anther development in H. patens and informing the analysis of other members of the Rubiaceae.

提交时间: 2017-07-18 点击量999下载量501 评论 0

3. chinaXiv:201707.00468 [pdf]

Studies on pollen morphology of selected species of Annonaceae from Thailand

Shao, Yunyun; Xu, Fengxia
分类: 生物学 >> 植物学

The pollen morphology of 48 species and two varieties, representing 18 genera of the family Annonaceae from Thailand, is described and illustrated based on observations with scanning electron microscopy (SEM). The results reaffirm the great diversity in Annonaceae at the pollen morphological level, with the size of pollen varying from small, medium-sized to large, the shape of monads being elliptic, spheroidal or triangular with monosulcate, disulculate or no visible aperture, and the shape of tetrads being tetragonal, rhomboidal, tetrahedral, T-shaped or decussate. Ornamentation is echinate, psilate, microreticulate, rugulate, scabrate or verrucate. Decussate tetrads in Goniothalamus, and tetragonal, rhomboidal, T-shaped and decussate tetrads and new tetrad type in Mitrephora are first reported. The pollen grains of Anaxagorea show slightly bilateral and no visible aperture as a result of intine extrusion. The palynological evidence confirms the close relationship of Dasymaschalon, Desmos and Asian Friesodielsia, and shows the high diversity of pollen morphology within genera in Annonaceae.

提交时间: 2017-07-13 点击量677下载量410 评论 0

4. chinaXiv:201703.00303 [pdf]

Single-layer reflectarray antennas with improved bandwidth by attaching phase-delay lines

Han, Chunhui; Zhang, Yunhua; Yang, Qingshan
分类: 地球科学 >> 空间物理学

A novel X-band unit cell structure with improved bandwidth performance for single-layer microstrip reflectarray antenna is proposed. The new element structure consists of two circular rings, each with a pair of gaps, and two phase-delay lines are attached to the outer ring to provide the required phase shift. A 9� center-fed reflectarray antenna operating at 10 GHz is designed to validate the broadband performance of the proposed unit cell. Simulated results show 20% 1-dB gain bandwidth and 38.5% 3-dB gain bandwidth. The maximum gain at 10 GHz is 20.1 dB, which is equivalent to 40 % efficiency.

提交时间: 2017-03-10 点击量5517下载量404 评论 0

5. chinaXiv:201703.00301 [pdf]

A novel deorientation method in PolSAR data processing

Zhu, F.Y.; Zhang, Y.H.; Li, D.
分类: 地球科学 >> 空间物理学

Deorientation plays an important role in polarimetric synthetic aperture radar (PolSAR) target decomposition, terrain classification, and geophysical parameters retrieval. The existing deorientation method roughly rotates the target by an average/mixed orientation angle (OA) about the line of radar sight. However, regarding the complex high-entropy mixed scatterer, which usually comprises several comparable sub-scatterers with different OAs, the average/mixed OA is obviously insufficient to account for the diverse OAs’ reality. To address this, a novel PolSAR data deorientation method is proposed in this letter. The proposed method deorients a mixed scatterer by reconstructing the underlying sub-scatterers using the eigenvalue-based Cloude–Pottier decomposition first, and then compensates the OA of each reconstructed sub-scatterer using Huynen’s desying operation, respectively. One important feature of the proposed method is that it is consistent with Huynen’s desying operation that the real part of the (1, 3) element of the deoriented coherency matrix should be zero. The proposed method provides a fine deorientation for mixed targets, and is especially suitable for the extraction of oriented urban regions. Comparative experiments with the existing method on RADARSAT-2 PolSAR data demonstrate the excellent deorientation performance of the proposed method. © 2016 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group.

提交时间: 2017-03-10 点击量897下载量246 评论 0

6. chinaXiv:201703.00258 [pdf]


Xiaobin Yin; Lanjie Zhang; Hao Liu; Risheng Yun; Lin Wu; Xingou Xu; Di Zhu
分类: 地球科学 >> 空间物理学

A 1-D interferometric system at 1.4GHz, 6.9GHz, 18.7 GHz and 23.8GHz combined with a scatterometer at 1.26GHz, called microwave imager combined active/passive (MICAP), has been proposed to retrieve sea surface salinity (SSS) and to reduce geophysical errors due to surface roughness and sea surface temperature (SST). The MICAP will be a candidate payload onboard the Ocean Salinity Satellite of China. The sensitivity of active/passive microwave observations to SSS, SST and wind is analyzed and the stability requirement of the instruments is estimated, with the objective of designing an optimized satellite instrument, dedicated to an "all-weather" estimate of the SSS with high accuracy from space.

提交时间: 2017-03-10 点击量378下载量203 评论 0

7. chinaXiv:201605.00321 [pdf]

Novel compressive sensing-based Dechirp-Keystone algorithm for synthetic aperture radar imaging of moving target

Yang, Jiefang; Zhang, Yunhua
分类: 地球科学 >> 空间物理学

The authors propose a novel compressive sensing (CS)-based Dechirp-Keystone algorithm (DKA) for synthetic aperture radar (SAR) moving target imaging, which is called the CS-DKA. The DKA can focus on moving targets in range-Doppler domain efficiently through only keystone transform (KT), complex multiplication and Fourier transform (FT)/inverse Fourier transform (IFT) operations. It has been shown that the non-interpolation implementation of KT can be expressed by an orthonormal basis, and it is known that the complex multiplication and FT/IFT are linear and invertible; therefore, the Dechirp-Keystone operator (DKO) is also linear and invertible. In the proposed algorithm, the authors take the inverse of DKO (IDKO) rather than the exact SAR echo model to construct the representation basis in the CS frame owing to its high implementation efficiency. After that, a random transmitting/receiving scheme is considered, to implement the down-sampling operation, and then reconstruct the moving target image by solving a regularisation problem. Both simulated and real SAR data are processed to show that the CS-DKA with down-sampled data can focus the target as well as the conventional DKA does with full data, and at the same time can achieve much lower sidelobes.

提交时间: 2016-05-03 点击量345下载量214 评论 0

8. chinaXiv:201605.00314 [pdf]

Wide-band chaotic noise signal for velocity estimation and imaging of high-speed moving targets

Yang, Qilun; Zhang, Yunhua; Gu, Xiang
分类: 地球科学 >> 空间物理学

This paper proposes a burst model of chaotic noise signals with randomly stepped carrier frequencies for velocity estimation and high-resolution range imaging of high-speed moving targets. The random stepping of carrier frequencies is controlled by a combination chaotic map (CCM), which is generated by embedding a Logistic map into a Bernoulli map. The baseband noise signal adopts the CCM based frequency-modulation (CCM-FM) signal, which has good randomness and a thumbtack ambiguity function as well. The velocity estimation includes a coarse search and a precise search, where the coarse search is conducted with a fixed step to makes the velocity deviation less than the velocity resolution, while the precise search adopts the Golden Section Search (GSS) algorithm to get an accurate estimation of velocity. What should be emphasized is that the velocity estimation process can be completed with just a burst of subpulses. Then the spectra are coherently synthesized to obtain ultra-wide bandwidth and high-resolution range imaging. Finally, numerical simulations demonstrate a good performance of the proposed signal model and the processing algorithm.

提交时间: 2016-05-03 点击量396下载量249 评论 0

9. chinaXiv:201605.00305 [pdf]

Analysis on the azimuth shift of a moving target in SAR image

Yang, Jiefang; Zhang, Yunhua
分类: 地球科学 >> 空间物理学

As we know, a moving target’s azimuth shift in synthetic aperture radar (SAR) image is proportional to the projected velocity of its across-track velocity in the slant-range plane. Therefore, we can relocate the moving target in SAR image after estimating its velocity. However, when the Doppler ambiguity occurs due to the limitation of the SAR system’s pulse repetition frequency (PRF), this relationship will not hold any more, in this case, we cannot relocate the moving target to the right position. The Doppler spectrum of a moving target with arbitrary velocity may entirely situate in a PRF band or span in two neighboring PRF bands. In this paper, we conduct a detailed theoretical analysis on the moving target’s azimuth shift for these two scenarios. According to the derived formulas, one can relocate a moving target with arbitrary velocity to the right position no matter the Doppler ambiguity occurs or not. Simulated data are processed to validate the analysis. © 2015 Electromagnetics Academy. All rights reserved.

提交时间: 2016-05-03 点击量318下载量196 评论 0

10. chinaXiv:201605.00289 [pdf]


Wang, Gang; Dong, Xiaolong; Bao, Qingliu; Zhu, Di; Xu, Xingou
分类: 地球科学 >> 空间物理学

In order to satisfy a high resolution for the measurement of snow water equivalent, we use the system of using the dual frequency(X-band 9.6GHz and Ku-band 17GHz) and full polarization. This paper discusses the various system options(scanning pencil-beam, high PRF, high SNR) and tradeoffs considered for improving the azimuth resolution of scatterometer are required.

提交时间: 2016-05-03 点击量535下载量337 评论 0

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