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1. chinaXiv:202006.00241 [pdf]
LI Yangyang; CHEN Jiacun; AI Shaoshui; SHI HuiSubjects: Physics >> General Physics: Statistical and Quantum Mechanics, Quantum Information, etc.
| Regulation of leaf gas exchange plays an important role in the survival of trees and shrubs under future climate change. However, the responses of leaf water potential and gas exchange of shrubs in semi-arid areas to the precipitation alteration are not clear. Here, we conducted a manipulated experiment with three levels of precipitation, i.e., a control with ambient precipitation, 50% above ambient precipitation (irrigation treatment), and 50% below ambient precipitation (drought treatment), with two common shrubs, Salix psammophila C. Wang & C. Y. Yang (isohydric plant, maintaining a constant leaf water potential by stomatal regulation) and Caragana korshinskii Kom. (anisohydric plant, having more variable leaf water potential), on the Chinese Loess Plateau in 2014 and 2015. We measured the seasonal variations of predawn and midday leaf water potential (?pd and ?md), two parameters of gas exchange, i.e., light-saturated assimilation (An) and stomatal conductance (gs), and other foliar and canopy traits. The isohydric S. psammophila had a similar An and a higher gs than the anisohydric C. korshinskii under drought treatment in 2015, inconsistent with the view that photosynthetic capacity of anisohydric plants is higher than isohydric plants under severe drought. The two shrubs differently responded to precipitation manipulation. ?pd, An and gs were higher under irrigation treatment than control for S. psammophila, and these three variables and ?md were significantly higher under irrigation treatment and lower under drought treatment than control for C. korshinskii. Leaf water potential and gas exchange responded to manipulated precipitation more strongly for C. korshinskii than for S. psammophila. However, precipitation manipulation did not alter the sensitivity of leaf gas exchange to vapor-pressure deficit and soil moisture in these two shrubs. Acclimation to long-term changes in soil moisture in these two shrubs was primarily attributed to the changes in leaf or canopy structure rather than leaf gas exchange. These findings will be useful for modeling canopy water-carbon exchange and elucidating the adaptive strategies of these two shrubs to future changes in precipitation. |
submitted time 2020-06-22 From cooperative journals:《Journal of Arid Land》 Hits2338， Downloads122， Comment 0
2. chinaXiv:202006.00200 [pdf]
史志强Subjects: Physics >> General Physics: Statistical and Quantum Mechanics, Quantum Information, etc.
| 本文是对《中国科学》一个编者按的商榷和讨论。文章指出手性是手性对称性的破缺，并举例说明了手性对称性和手性的本质区别。手性化合物的一对对映体有不同的生物活性和药物活性，这决不是个别极端的例子，而是非常普遍存在的。生物体内参与蛋白质组成的氨基酸是手性的，但它们既不全都是左旋的，也不全都是右旋的，只能说它们全部都是L构型的。蛋白质的结构是复杂的，我们不能笼统地说蛋白质是右旋的，只能说蛋白质二级结构中的α-螺旋结构是右旋的。最后，我们分析了对手性定义的几种错误表述，并指出产生这些错误的原因。 |
3. chinaXiv:202007.00012 [pdf]
史志强Subjects: Physics >> Interdisciplinary Physics and Related Areas of Science and Technology
| 手性对称性与手性是两个不同的概念，前者研究对称性，后者是手性不对称的简称，它研究对称性的破缺。我们关注手性实际上是研究自然界的手性不对称性，而不是手性对称性。手性可分为结构手性和功能手性两种。结构手性是“互为镜像”的两个物体在自然界存在的数量不同，它强调的是几何结构，手形手性、螺旋手性和旋转手性都是结构手性。功能手性强调的是功能，即它们的几何结构或者坐标系是手性对称的，但其功能（物理性质、化学性质、数学意义、生物活性、药物活性、生物的行为和习性等）不是“互为镜像”的。功能手性是结构手性的拓展，它使手性的表现形式更为多样化。手性分子绝大多数是一种功能手性分子。 |
4. chinaXiv:201607.00046 [pdf]
Exact Solution for Three-Dimensional Ising Model
Zhang, DegangSubjects: Physics >> General Physics: Statistical and Quantum Mechanics, Quantum Information, etc.
| Three-dimensional Ising model in zero external field is exactly solved by operator algebras, similar to the Onsager's approach in two dimensions. The partition function of the simple cubic crystal imposed by the periodic boundary condition along both $(0 1 0)$ and $(0 0 1)$ directions and the screw boundary condition along the $(1 0 0)$ direction is calculated rigorously. In the thermodynamic limit an integral replaces a sum in the formula of the partition function. A order-disorder transition in the infinite crystal occurs at a temperature $T=T_c$ determined by the condition: $\sinh\frac{2J}{k_BT_c}\sinh\frac{2(J_1+J_2)}{k_BT_c}=1$, where $(J_1 J_2 J)$ are the interaction energies in three directions, respectively. The analytical expressions for the internal energy and the specific heat are also given. It is also shown that the thermodynamic properties of 3D Ising model with $J_1=J_2$ are connected to those in 2D Ising model with the interaction energies $(J_1 J_{2D})$ by the relation $(\frac{J_{2D}}{k_BT})^*=(\frac{J}{k_BT})^*-\frac{J_1}{k_BT}$, where $x^*=\frac{1}{2}{\rm ln coth} x={\rm tanh}^{-1}(e^{-2x})$. |
submitted time 2020-05-12 Hits20337， Downloads1966， Comment 0
5. chinaXiv:201802.00685 [pdf]
An Explanation of the Interactions between Waves and Electrons: Discussion of Electromagnetic Fields
Weiye XuSubjects: Physics >> The Physics of Elementary Particles and Fields
| The interactions between waves and electrons are the basis of vacuum tubes and particle accelerators. In order to further understand the interactions, we proposed a new electromagnetic model. In this model, the photon is composed of two elementary particles – ephoton and mphoton, which are the basic particles that form the electric fields and magnetic fields, respectively. There are many ephotons around the electrons and the electrons can absorb the ephotons. The proposed electromagnetic model can well explain the electromagetic phenomena and the interactions between waves and electrons. |
submitted time 2020-03-13 Hits17238， Downloads1803， Comment 0
6. chinaXiv:202002.00069 [pdf]
王基庆; 李志国Subjects: Physics >> Interdisciplinary Physics and Related Areas of Science and Technology
| 由于春运出湖北省高峰和全国各地管控开始之间的时间差，使得在这个时间段内，除湖北外的国内地区是个输入一代到感染二代之间独立自然连续传播体系。基于此，我们使用正态分布的线性叠加来拟合全国除湖北外每日新增的数据，简单模型预测和实际新增结果的高度吻合验证了除湖北外是个近似理想系统。拟合计算得到的新冠病毒可再生系数R0=2.2，一代到二代的峰值传播时间是7天。我们还讨论了偏离理想传播体系的原因并分析了一些省的特殊情况。 |
submitted time 2020-02-25 Hits10424， Downloads1015， Comment 0
7. chinaXiv:202001.00047 [pdf]
Review of the high-power vacuum tube microwave sources
徐伟业Subjects: Electronics and Communication Technology >> Electron Technology
| Since the first vacuum tube (X-ray tube) was invented by Wilhelm R?ntgen in Germany, after more than one hundred years of development, the average power density of the vacuum tube microwave source has reached the order of 108 [MW][GHz]2. The maximum power density record was created by the Free Electron Lasers. In the high-power microwave field, the vacuum devices are still the mainstream microwave sources for applications such as scientific instruments, communications, radars, magnetic confinement fusion heating, microwave weapons, etc. The principles of microwave generation by vacuum tube microwave sources include Cherenkov or Smith-Purcell radiation, transition radiation, and Bremsstrahlung. In this paper, the vacuum tube microwave sources were reviewed in order according to the three radiation principles. Among them, the Vircators can produce 22 GW output power in P-band. Vacuum tubes that can achieve continuous-wave operation include Traveling Wave Tubes, Klystrons, Free Electron Lasers, and Magnetrons, with output power up to 1MW. Vacuum tubes that can generate frequencies of the order of 100 GHz and above include Klystrons, Traveling Wave Tubes, Gyrotrons, Backward Wave Oscillators, Magnetrons, Surface Wave Oscillators, Free Electron Lasers, Orotrons, etc. Gyrotrons are very attractive in the millimeter wave and THz fields. The Gyrotrons can output power at the MW level with 3000s pulse width at millimeter wavelengths. |
8. chinaXiv:202001.00062 [pdf]
李杰彪; 苏锐; 周志超; 郭永海; 季瑞利; 张明; 王洪斌Subjects: Physics >> General Physics: Statistical and Quantum Mechanics, Quantum Information, etc.
| 地下水补给研究是高放废物深地质处置库选址和场址评价的重要研究内容之一。甘肃北山地区是我国高放废物地质处置库场址首选预选区，为查明该区地下水补给特征，基于环境示踪剂氯查明了北山地区浅部地下水补给量。结果表明：（1） 总体而言，氯质量平衡方法在北山地区应用效果较好。（2） 基于包气带的氯质量平衡方法计算得出的浅部地下水垂向补给量在渗透性较大的沟谷盆地中为0.07~2.03 mm·a-1，平均值约1.0 mm·a-1。（3） 基于饱和带的氯质量平衡方法计算得出北山地区浅部地下水多年平均入渗补给量为0.25 mm·a-1，不足多年平均降水量的0.5%。相关结果可为我国高放废物地质处置库选址和场址评价提供依据。 |
submitted time 2020-01-06 From cooperative journals:《干旱区地理》 Hits9128， Downloads516， Comment 0
9. chinaXiv:201911.00009 [pdf]
胡锦文Subjects: Physics >> Geophysics, Astronomy, and Astrophysics
| 在洛伦兹破缺模型中，彩虹模型通常被讨论，因为彩虹模型可以使一个粒子的能量有一个极限，而不是由洛伦兹变换中得到的无限大，这在量子引力理论中被认为是必要的。然而,本文表明一开始并没有必要限制光速是一个常数,当我们约定如下三个原则:(1)我们可以用校准的时钟定义整个空间的同时性,(2)时空是均匀的,空间各向同性和(3)所有的惯性系统是等价的。基于上述三原则,我们可以构造一个通用坐标变换来满足惯性系统的对称性，并可以在惯性系统之间构建一个non-Lorentz变换使得粒子的能量有一个极限值,就像和彩虹模型一样。此外，在最近的论文中，作为一种超高能量尺度的测试，彩虹模型被用来研究伽马射线爆发，如GRB 160509A事件，它强烈地表明了光速的变化与光子能量之间存在线性关系。所以我们也分析了同样的事件，我们发现我们的模型也支持彩虹模型的结论，我们的模型和彩虹模型之间有一定的相关性。最后，我们简要讨论了如何在未来的高能粒子实验中验证这两个模型。 |
10. chinaXiv:201910.00053 [pdf]
Effects of biochar on water movement characteristics in sandy soil under drip irrigation
PU Shenghai; LI Guangyong1; TANG Guangmu; ZHANG Yunshu ; XU Wanli; LI Pan; FENG Guangping; DING FengSubjects: Physics >> General Physics: Statistical and Quantum Mechanics, Quantum Information, etc.
| Biochar addition can improve the physical and hydraulic characteristics of sandy soil. This study investigated the effects of biochar on water holding capacity and water movement in sandy soil under drip irrigation. By indoor simulation experiments, the effects of biochar application at five levels (0%, 1%, 2%, 4% and 6%) on the soil water retention curve, infiltration characteristics of drip irrigation and water distribution were tested and analyzed. The results showed that biochar addition rate was positively correlated with water holding capacity of sandy soil and soil available water. Within the same infiltration time, with an increasing amount of added biochar, the diffusion distance of the horizontal wetting front (HWF) tended to decrease, while the infiltration distance of vertical wetting front (VWF) initially declined and then rose. The features of wetted bodies changed from "broad-shallow" to "narrow-deep" type. The relationship between the transport distances of HWF and VWF and the infiltration time was described by a power function. At the same distance from the point source, the larger the amount of added biochar, the higher the soil water content. Biochar had a great influence on the water content of the layer with biochar (0–200 mm) and had some effects at 200–250 mm without biochar; but it had less influence on the soil water content deeper than 250 mm. For the application rate of biochar of 4%, most water was retained within 0–250 mm soil layer. However, when biochar application amount was high (6%), it would be helpful for water infiltration. During the improvement of sandy soil, biochar application rate of 4% in the plow layer had the best effect. |
submitted time 2019-10-26 From cooperative journals:《Journal of Arid Land》 Hits11686， Downloads711， Comment 0
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