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1. chinaXiv:202206.00139 [pdf]

Commissioning of Laser Electron Gamma Beamline SLEGS at SSRF

王宏伟; 范功涛; 刘龙祥; 许杭华; 沈文庆; 马余刚; Hiroaki Utsunomiya; 宋龙龙; 曹喜光; 郝子锐; 陈开杰; 金晟; 杨宇萱; 胡新荣; 李鑫祥; 匡攀
Subjects: Physics >> Nuclear Physics

Shanghai Laser Electron Gamma Source (SLEGS) is a powerful gamma source to provide MeV gamma-ray beams for nuclear science and technology. It is developed as one of the sixteen beamline stations in Phase II Project of the Shanghai Synchrotron Radiation Facility (SSRF). The slant-scattering mode is for the first time systematically employed in the laser Compton scattering (LCS) at SLEGS to produce energy-tunable quasi-monoenergetic gamma-ray beams.  SLEGS officially completed its commissioning from July to December 2021. Gamma-rays in energy range of 0.25 - 21.7 MeV with the flux of 2.1 × 104 - 1.2 × 107 photons/s and the energy spread of  2 – 15 % are produced during the test. This paper reports results of the commissioning of the SLEGS beamline.

submitted time 2022-06-13 Hits635Downloads179 Comment 0

2. chinaXiv:202206.00131 [pdf]

正常老化对视觉早期注意的影响—来自ERP的证据

丁玉珑; 叶丽群; 谭欣; 姚堃
Subjects: Psychology >> Cognitive Psychology
Subjects: Psychology >> Developmental Psychology

选择性注意能够作用于视觉信息加工的不同阶段。各个注意阶段均受到老化过程的影响,其中注意早期阶段的老化研究对于理解认知老化的发生机制有重要意义。本文系统地梳理了刺激前的注意预期阶段以及刺激后200ms内的早期感知注意阶段的正常老年人和青年人ERP比较研究,以探讨正常老化对视觉早期注意的影响。现有证据表明,相对于青年人,正常老年人:(1)多个早期ERP注意效应(包括注意预期ADAN,早期空间注意N1,以及特征注意SP和SN)在潜伏期上都存在显著延迟;(2)在振幅上,不同ERP注意效应的老化表现存在差异:某些ERP成分(包括注意预期EDAN,以及早期空间注意P1)的注意效应没有明显减弱,而某些ERP成分(包括注意预期alpha,早期空间注意N1,以及特征注意SN)的注意效应受到老化调控;(3)一些注意效应(包括特征注意SP成分,以及客体注意P1和N1成分)的目标增强机制保留,而干扰抑制机制缺损。目前已有研究在老化对注意效应振幅的调控上还存在不一致,这可能与研究的信噪比、任务难度、注意机制分离以及老年人的个体差异有关。未来研究应考虑这些因素以更好地探究正常老化对视觉早期注意的影响。

submitted time 2022-06-13 Hits1191Downloads192 Comment 0

3. chinaXiv:202206.00143 [pdf]

束团压缩

朱雄伟
Subjects: Physics >> Nuclear Physics

本文提出了束团压缩物理的产生背景,束团压缩的基本原理、种类。运用束流光学的基本理论,给出了
束团压缩的基本理论公式,论证了束团压缩的高阶限制。分析讨论了单级压缩、两级压缩中存在的设计
物理问题,总结了束团压缩设计中经常遇见的一些物理问题。关于束团压缩的束流动力学问题,给出了
束团压缩器中的粒子运动方程,以及完整的动力学方程-Vlasov方程。讨论了相干同步辐射效应和微束团
不稳定性。最后,分析了磁压缩器中的误差问题。

submitted time 2022-06-13 Hits800Downloads167 Comment 0

4. chinaXiv:202206.00133 [pdf]

Application of biocementation technique using Bacillus sphaericus for stabilization of soil surface and dust storm control

Davood NAMDAR-KHOJASTEH; Masoud BAZGIR; Seyed Abdollah HASHEMI BABAHEIDARI; Akwasi B ASUMADU-SAKYI
Subjects: Environmental Sciences, Resource Sciences >> Basic Disciplines of Environmental Science and Technology

Abstract: Dust emission and wind erosion are widespread phenomena in arid and semi-arid regions, which have far-reaching harmful effects to the environment. This study aimed to use microbial induced carbonate precipitation (MICP) method with Bacillus sphaericus to reduce soil losses that occur in a dust-producing area due to wind erosion in the Ilam Province, Iran. Soil samples at the 0–30 cm depth were used and sterilized in an autoclave for 2 h at 121°C and 103 kPa. Approximately 3 kg soils were weighed and poured in the 35 cm×35 cm×3 cm trays. Different treatments included two levels of B. sphaericus (0.0 and 0.5 OD), three levels of suspension volume (123, 264, and 369 mL), two levels of urea-chloride cementation solution (0.0 and 0.5 M), and two levels of bacterial spray (once and twice spray). After 28 d, soil properties such as soil mass loss, penetration resistance, and aggregate stability were measured. The results showed a low soil mass loss (1 g) in F14 formulation (twice bacterial spray+264 mL suspension volume+without cementation solution) and a high soil mass loss (246 g) in F5 formulation (without bacteria+264 mL suspension volume+0.5 M cementation solution). The highest (42.55%) and the lowest (19.47%) aggregate stabilities were observed in F16 and F7 formulations, respectively, and the highest penetration resistance (3.328 kg/cm2) was observed in F18 formulation. According to the final results, we recommended the formulation with twice bacterial spray, 0.5 M cementation solution, and 269 mL suspension volume as the best combination for soil surface stabilization. Furthermore, this method is environmentally friendly because it has no adverse effects on soil, water, and plants, thus, it would be an efficient approach to stabilize soil surface.

submitted time 2022-06-13 Cooperative journals:《Journal of Arid Land》 Hits876Downloads132 Comment 0

5. chinaXiv:202206.00134 [pdf]

Grazing alters sandy soil greenhouse gas emissions in a sand-binding area of the Hobq Desert, China

WANG Bo; LI Yuwei; BAO Yuhai
Subjects: Environmental Sciences, Resource Sciences >> Basic Disciplines of Environmental Science and Technology

Abstract: Deserts are sensitive to environmental changes caused by human interference and are prone to degradation. Revegetation can promote the reversal of desertification and the subsequent formation of fixed sand. However, the effects of grazing, which can cause the ground-surface conditions of fixed sand to further deteriorate and result in re-desertification, on the greenhouse gas (GHG) fluxes from soils remain unknown. Herein, we investigated GHG fluxes in the Hobq Desert, Inner Mongolia Autonomous Region of China, at the mobile (desertified), fixed (vegetated), and grazed (re-desertified) sites from January 2018 to December 2019. We analyzed the response mechanism of GHG fluxes to micrometeorological factors and the variation in global warming potential (GWP). CO2 was emitted at an average rate of 4.2, 3.7, and 1.1 mmol/(m2•h) and N2O was emitted at an average rate of 0.19, 0.15, and 0.09 µmol/(m2•h) at the grazed, fixed, and mobile sites, respectively. Mean CH4 consumption was as follows: fixed site (2.9 µmol/(m2•h))>grazed site (2.7 µmol/(m2•h))>mobile site (1.1 µmol/(m2•h)). GHG fluxes varied seasonally, and soil temperature (10 cm) and soil water content (30 cm) were the key micrometeorological factors affecting the fluxes. The changes in the plant and soil characteristics caused by grazing resulted in increased soil CO2 and N2O emissions and decreased CH4 absorption. Grazing also significantly increased the GWP of the soil (P<0.05). This study demonstrates that grazing on revegetated sandy soil can cause re-desertification and significantly increase soil carbon and nitrogen leakage. These findings could be used to formulate informed policies on the management and utilization of desert ecosystems.

submitted time 2022-06-13 Cooperative journals:《Journal of Arid Land》 Hits505Downloads153 Comment 0

6. chinaXiv:202206.00136 [pdf]

Seed rain and soil seed bank compensatory roles on Nassella tenuis (Phil.) Barkworth seedling recruitment in ungrazed and grazed sites

Cintia Vanesa LEDER; Dianela Alejandra CALVO; Guadalupe PETER
Subjects: Environmental Sciences, Resource Sciences >> Basic Disciplines of Environmental Science and Technology

In semi-arid lands, vegetation is distributed in shrub patches immersed in a less vegetated interpatch matrix. Grazing affects perennial grass seed bank through a decrease in seed rain and an increase in seed predation and soil compaction. Nevertheless, some species with anchorage mechanisms in their seeds might overcome this, such as Nassella tenuis (Phil.) Barkworth. This is an important species in grazing paddocks because it has an intermediate palatability and its relatively tolerant to grazing. These characteristics allow N. tenuis to increase its abundance in grazed sites. Our objective was to assess how grazing affects the key palatable species from seeds to seedlings: i.e., seed rain, soil seed bank, and seedling recruitment in different microsites along a windward-leeward transect across shrub canopy. We hypothesized that: (1) the negative effects of grazing on N. tenuis fructification are reflected in its seed rain, soil seed bank, and seedling recruitment, especially in interpatches; (2) Nassella tenuis seed rain reduction, soil compaction by cattle in grazed sites, and removal of seeds by wind decrease its soil seed bank, especially in microsites exposed to the predominant wind; and (3) the decrease in N. tenuis soil seed bank and cover increase in annual species in grazed sites have negative effects on its seedling recruitment, especially in microsites exposed to predominant wind. We placed seed traps, collected soil samples, and monitored seedling recruitment in different locations around shrub canopy to address our hypotheses. Also, we established a manipulative experiment in which we sow N. tenuis seeds and followed its recruitment in different microsites. We compared the seed rain, soil seed bank, natural seedling recruitment, and sown seeds recruitment of N. tenuis between grazed and ungrazed sites. We analyzed differences between microsites along a windward-leeward transect across shrubs patches. Seed rain and soil seed bank had the same density in patches and interpatches both in ungrazed and grazed sites. But seed rain was higher, and soil seed bank was lower in ungrazed sites than in grazed sites. Almost all under-canopy microsites showed greater soil seed bank abundance and natural seedling recruitment in ungrazed sites. Sown seeds recruitment was the same between grazed and ungrazed sites, but it showed protective effects of shrubs in leeward microsites under grazed sites. As a conclusion, seed rain and soil seed bank are complementary under grazed sites.

submitted time 2022-06-13 Cooperative journals:《Journal of Arid Land》 Hits296Downloads105 Comment 0

7. chinaXiv:202206.00135 [pdf]

Changes in diversity, composition and assembly processes of soil microbial communities during Robinia pseudoacacia L. restoration on the Loess Plateau, China

WANG Kun; WANG Xiaoxia; FEI Hongyan; WAN Chuanyu; HAN Fengpeng
Subjects: Biology >> Ecology

Abstract: Robinia pseudoacacia L. (RP) restoration has increased vegetation cover in semi-arid regions on the Loess Plateau of China, but ecological problems have also occurred due to RP restoration, such as reduced soil moisture. Further, it is still uncertain how microbial diversity, composition and assembly processes change with RP restoration in semi-arid regions. Therefore, amplicon sequencing of small subunit ribosomal ribonucleic acid (16S rRNA) and internal transcribed spacer (ITS) genes was performed to study soil bacterial and fungal diversity, composition and assembly processes at four study sites with different stand ages of RP plantations (Y10, RP plantation with stand ages less than 10 a; Y15, RP plantation with stand ages approximately 15 a; Y25, RP plantation with stand ages approximately 25 a; and Y40, RP plantation with stand ages approximately 40 a) along a 40-a chronosequence on the Loess Plateau. The diversity of soil bacteria and fungi increased significantly during the restoration period from 10 to 15 a (P<0.05). However, compared with Y15, bacterial diversity was lower at Y25 and Y40, and fungal diversity remained stable during the restoration period between 25 and 40 a. The relative abundances of Proteobacteria and Ascomycota increased during the restoration period from 10 to 15 a. Conversely, after 15 a of restoration, they both decreased, whereas the relative abundances of Actinomycetes, Acidobacteria and Basidiomycota gradually increased. The variations in soil bacterial communities were mainly related to changes in soil total nitrogen, nitrate nitrogen and moisture contents, while soil fungal communities were mainly shaped by soil organic carbon and nitrate nitrogen contents. Bacterial communities were structured by the heterogeneous selection and stochastic process, while fungal communities were structured primarily by the stochastic process. The RP restoration induced an increase in the relative importance of heterogeneous selection on bacterial communities. Overall, this study reveals the changes in microbial diversity, community composition and assembly processes with RP restoration on the Loess Plateau and provides a new perspective on the effects of vegetation restoration on soil microbial communities in semi-arid regions.

submitted time 2022-06-13 Cooperative journals:《Journal of Arid Land》 Hits1175Downloads180 Comment 0

8. chinaXiv:202206.00130 [pdf]

运算动量效应的理论解释及其发展性预测因素

张雯; 董亓易如; 龚丽娟; 尚琪; 程琛; 丁雪辰
Subjects: Psychology >> Developmental Psychology

了解运算偏差的形成与发展对探索算数运算系统的内在机制具有重要意义,早期的算数运算能力是儿童理解和进行复杂数学运算的基础。运算动量偏差是指个体在进行基本数学运算时倾向于高估加法运算结果而低估减法运算结果的一种运算偏差,主要包括三种理论解释,即注意转移假说、启发式解释和压缩解释。鉴于运算动量效应在成年群体中的相对稳定性以及在不同发展阶段儿童中发现的不一致证据,数学能力的提高与空间注意的成熟可结合不同的理论解释来阐明儿童发展过程中运算动量效应的变化趋势。未来可以进一步整合多种研究任务以揭示运算动量效应的发展轨迹,考察数量表征系统与运算动量效应间的关联,探究运算动量效应在不同运算符号中的稳定性,探讨不同因素共同作用对运算动量效应的影响,并设计有关数学能力的干预措施以减少运算动量效应这一运算偏差。

submitted time 2022-06-13 Hits1165Downloads210 Comment 0

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