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# 物理代写|天文学代写Astronomy代写|ASTR101 ENERGIES, SPECTRA,AND COMPOSITION

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## 物理代写|天文学代写Astronomy代写|ENERGIES, SPECTRA,AND COMPOSITION

The solar wind prevents low-energy charged articles from entering the inner solar system due to interaction with the magnetic field in the solar wind, a steady stream of gas going out from the sun into all directions, originally discovered in 1950 from the effect on cometary tails: they all point outward, at all latitudes of the sun, and independent of whether the comet actually comes into the inner solar system or goes outward, in which case the tail actually precedes the head of the comet. This prevents us from knowing anything about interstellar energetic particles with energies lower than about $300 \mathrm{MeV}$. Above about $10 \mathrm{GeV}$ per charge unit $Z$ of the particle, the effect of the solar wind becomes negligible. Since cosmic ray particles are mostly fully ionized nuclei (with the exception of electrons and positrons), this is a strong effect.

Our Galaxy has a magnetic field of about $6 \times 10^{-6} \mathrm{G}$ in the solar neighborhood; the energy density of such a field corresponds approximately to $1 \mathrm{eV} / \mathrm{cm}^{3}$, just like the other components of the interstellar medium. In such a magnetic field charged energetic particles gyrate with a radius of gyration called the Larmor radius, which is proportional to the momentum of the particle perpendicular to the magnetic field direction. For highly relativistic particles this entails that around $3 \times 10^{18}-\mathrm{eV}$ protons, or other nuclei of the same energy-to-charge ratio, no longer gyrate in the disk of the Galaxy, i.e., their radius of gyration is larger than the thickness of the disk. Thus, they cannot possibly originate in the Galaxy, and must come from out-side; indeed, at that energy there is evidence for a change both in chemical composition and in the slope of the spectrum.

The energies of these cosmic ray particles that we observe range from a few hundred $\mathrm{MeV}$ to $300 \mathrm{EeV}$. The integral flux ranges from about $10^{-5}$ per $\mathrm{cm}^{2}$, per sec, per sterad at $1 \mathrm{TeV}$ per nucleus for hydrogen or protons, to 1 particle per sterad per $\mathrm{km}^{2}$ and per century around $10^{20} \mathrm{eV}$, a decrease by a factor of $3 \times 10^{15}$ in integral flux, and a corresponding decrease by a factor of $3 \times 10^{23}$ in the spectrum, i.e., per energy interval, which means in differential flux. Electrons have only been measured to a few $\mathrm{TeV}$.
The total particle spectrum spectrum is about $E^{-2.7}$ below the knee and about $E^{-3.1}$ above the knee, at $5 \mathrm{PeV}$, and flattens again to about $E^{-2.7}$ beyond the ankle, at about $3 \mathrm{EeV}$. Electrons have a spectrum which is similar to that of protons below about $10 \mathrm{GeV}$, and steeper near $E^{-3.3}$ above this energy. The lower energy spectrum of electrons is inferred from radio emission, while the steeper spectrum at the higher energies is measured directly (Fig. 1).

The chemical composition is rather close to that of the interstellar medium, with a few strong peculiarities relative to that of the interstellar medium: (a) hydrogen and helium are less common relative to silicon. Also, the ratio of hydrogen to helium is smaller. (b) lithium, beryllium, and boron, the odd- $Z$ elements, as well as the sub-iron elements (i.e., those with $Z$ somewhat less than iron) are all enhanced relative to the interstellar medium (Fig. 3).
(c) Many isotope ratios are quite different, while some are identical. (d) Among the cosmic ray particles there are radioactive isotopes, which give an age of the particles since acceleration and injection of about $3 \times 10^{7}$ years. (e) Toward the knee and beyond the fraction of heavy elements appears to continuously increase, with moderately heavy to heavy elements almost certainly dominating beyond the knee, all the way to the ankle, where the composition becomes light again. This means that at that energy we observe a transition to what appears to be mostly hydrogen and helium nuclei. At much higher energies we can only show consistency with a continuation of these properties; we cannot prove unambiguously what the nature of these particles is.

## 物理代写|天文学代写Astronomy代写|ORIGIN OF GALACTIC COSMIC RAYS

$1 \mathrm{GeV}$, we cannot yet prove directly that supernova shocks provide the acceleration; only the analogy with electrons can be demonstrated.

However, we observe what ought to be galactic cosmic rays up to energies near the knee, and beyond to the ankle, i.e., $3 \mathrm{EeV}$.

The energies, especially for particles beyond $100 \mathrm{TeV}$, can be provided by several possibilities, with the only theory worked out to a quantitative level suggesting that those particles also get accelerated in supernova shock waves, in those which run through the powerful stellar wind of the predecessor star. Then it can be shown that energies up to $3 \mathrm{EeV}$ per particle are possible (mostly iron). An alternate possibility is that a ping-pong effect between various supernova shock waves occurs, but in this case seen from outside. In either (or any other) such theory it is a problem that we observe a knee, i.e., a downward bend of the spectrum at an energy-to-charge ratio which appears to be fairly sharply defined. The concept that stellar explosions are at the origin entails that all such stars are closely similar in their properties, including their magnetic field, at the time of explosion; this implies a specific length scale in the explosion, connected to the thickness of the matter of the wind snowplowed together by the supernova shock wave. While this is certainly possible, we have too little information on the magnetic field of pre-supernova stars to verify or falsify this. In the case of the other concept it means that the transport through the interstellar gas has change in properties also at a fairly sharply defined energy-to-charge ratio, indicating a special scale in the interstellar gas, for which there is no other evidence.

## 物理代写|天文学代写ASTRONOMY代写|ENERGIES, SPECTRA,AND COMPOSITION

C许多同位素比率是完全不同的，而有些是相同的。d在宇宙线粒子中有放射性同位素，它给出了粒子的年龄，因为加速和注入大约3×107年。和靠近膝盖和更远的地方，重元素的比例似乎在不断增加，几乎可以肯定的是，中等重元素到重元素几乎可以肯定在膝盖之外占主导地位，一直到脚踝，那里的成分再次变轻。这意味着在那个能量下，我们观察到向似乎主要是氢核和氦核的转变。在更高的能量下，我们只能表现出与这些性质的延续的一致性；我们无法明确地证明这些粒子的性质是什么。

## 物理代写|天文学代写ASTRONOMY代写|ORIGIN OF GALACTIC COSMIC RAYS

1G和在，我们还不能直接证明超新星冲击提供了加速度；只能证明与电子的类比。

## Matlab代写

MATLAB 是一种用于技术计算的高性能语言。它将计算、可视化和编程集成在一个易于使用的环境中，其中问题和解决方案以熟悉的数学符号表示。典型用途包括：数学和计算算法开发建模、仿真和原型制作数据分析、探索和可视化科学和工程图形应用程序开发，包括图形用户界面构建MATLAB 是一个交互式系统，其基本数据元素是一个不需要维度的数组。这使您可以解决许多技术计算问题，尤其是那些具有矩阵和向量公式的问题，而只需用 C 或 Fortran 等标量非交互式语言编写程序所需的时间的一小部分。MATLAB 名称代表矩阵实验室。MATLAB 最初的编写目的是提供对由 LINPACK 和 EISPACK 项目开发的矩阵软件的轻松访问，这两个项目共同代表了矩阵计算软件的最新技术。MATLAB 经过多年的发展，得到了许多用户的投入。在大学环境中，它是数学、工程和科学入门和高级课程的标准教学工具。在工业领域，MATLAB 是高效研究、开发和分析的首选工具。MATLAB 具有一系列称为工具箱的特定于应用程序的解决方案。对于大多数 MATLAB 用户来说非常重要，工具箱允许您学习应用专业技术。工具箱是 MATLAB 函数（M 文件）的综合集合，可扩展 MATLAB 环境以解决特定类别的问题。可用工具箱的领域包括信号处理、控制系统、神经网络、模糊逻辑、小波、仿真等。