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Positron Emission Tomography01:29

Positron Emission Tomography

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Positron emission tomography (PET) is a medical imaging technique involving radiopharmaceuticals — substances that emit short-lived radiation. Although the first PET scanner was introduced in 1961, it took 15 more years before radiopharmaceuticals were combined with the technique and revolutionized its potential.
One of the main requirements of a PET scan is a positron-emitting radioisotope, which is produced in a cyclotron and then attached to a substance used by the part of the body...
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Atomic Structure01:33

Atomic Structure

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Overview
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Emission Spectra02:39

Emission Spectra

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When solids, liquids, or condensed gases are heated sufficiently, they radiate some of the excess energy as light. Photons produced in this manner have a range of energies, and thereby produce a continuous spectrum in which an unbroken series of wavelengths is present.
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Electron Behavior01:09

Electron Behavior

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Electrons are negatively charged subatomic particles attracted to and orbit around the positively-charged nucleus of an atom. They reside in spaces associated with energy levels called shells and are further organized into subshells and orbitals within each shell.
Electrons Orbit the Nucleus
Electrons are found in specific locations outside of the nucleus. The shell in which an electron resides indicates the general energy level of the electron: those closer to the nucleus have less energy,...
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¹H NMR of Labile Protons: Temporal Resolution01:10

¹H NMR of Labile Protons: Temporal Resolution

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Protons bonded to heteroatoms such as nitrogen and oxygen exhibit a range of chemical shift values. This is due to the varying degree of hydrogen bonding between the proton and the heteroatom in other molecules. The extent of hydrogen bonding affects the electron density around the proton, thereby giving different chemical shift values for the protons in the proton NMR spectrum.
The –OH proton in alcohols typically appears in the range of δ 2 to 5 ppm but can vary depending on the specific...
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π Electron Effects on Chemical Shift: Aromatic and Antiaromatic Compounds01:14

π Electron Effects on Chemical Shift: Aromatic and Antiaromatic Compounds

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In aromatic compounds, such as benzene, the circulation of (4n + 2) π-electrons sets up a diamagnetic or diatropic ring current around the perimeter of the molecule. This current induces a magnetic field that opposes the external field inside the ring and reinforces it on the outside. The protons in benzene are deshielded and exhibit high chemical shifts in the range 6.5–8.5 ppm. The shielding effect at the center of the ring is evident in complex aromatic molecules, such as...
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质子光谱中的时间结构和银河系宇宙射线中的电荷信号效应.

M Aguilar1, G Ambrosi2, H Anderson3

  • 1Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas (CIEMAT), 28040 Madrid, Spain.

Physical review letters
|October 28, 2023
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概括
此摘要是机器生成的。

通过阿尔法磁谱仪 (AMS) 测量的宇宙正子流显示了与电子和质子相比在11年内独特的变化. 阳位子比质子更容易被调节,为宇宙射线行为提供了新的见解.

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科学领域:

  • 天体物理学 天体物理学
  • 粒子物理学 粒子物理学
  • 太空科学 太空科学

背景情况:

  • 由带电粒子组成的宇宙射线穿越太空,受到太阳活动的影响.
  • 了解不同宇宙射线组件的行为,如正子,电子和质子,对于日球物理学至关重要.

研究的目的:

  • 在11年的太阳周期中对宇宙正子流的精确测量.
  • 为了比较正电子流的时间变化与电子和质子的时间变化.
  • 为了研究宇宙射线在日球中的电荷信号和质量依赖性.

主要方法:

  • 利用了国际空间站的Alpha磁谱仪 (AMS) 收集的3.4×10^6个正子事件.
  • 分析了1.00至41.9GV的刚性范围内的每日宇宙正子子流.
  • 在11年的时间里,比较了正电子流量变化与电子和质子流量数据.

主要成果:

  • 在短时间和长时间尺度上,正电子流表与电子流表表现出明显的时间变化.
  • 在8.5GV以下观察到电子和正电子流之间的统计学上显著的hysteresis (>5σ).
  • 质子流表现出与质子流相似的时间变化,但其调制更为显著 (<7 GV).

结论:

  • 每天的正子流量测量为了解宇宙射线调制提供了独特的数据.
  • 在宇宙射线组成部分之间的时间变化和调制中观察到的差异突出了复杂的日球过程.
  • 这些发现有助于更深入地了解宇宙射线传播中的电荷信号和质量依赖.