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相关概念视频

States of Matter and Phase Changes00:59

States of Matter and Phase Changes

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The internal energy of a substance—the total kinetic energy of all its molecules and the potential energy of their associated forces—depends on the strength of the intermolecular forces in the condensed phases and the pressure exerted on the substance. The internal energy of a substance is the highest in the gaseous state, the lowest in the solid state, and intermediate in the liquid state. Phase transitions are caused by changes in physical conditions, such as temperature and...
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Gyroscope: Precession01:24

Gyroscope: Precession

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Precession can be demonstrated effectively through a spinning top. If a spinning top is placed on a flat surface near the surface of the Earth at a vertical angle and is not spinning, it will fall over due to the force of gravity producing a torque acting on its center of mass. However, if the top is spinning on its axis, it precesses about the vertical direction, rather than topple over due to this torque. Precessional motion is a combination of a steady circular motion of the axis and the...
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Classifying Matter by Composition03:35

Classifying Matter by Composition

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Matter: Pure Substances and Mixtures
According to its composition, the matter can be classified into two broad categories — pure substances and mixtures. 
A pure substance is a form of matter that has a constant composition throughout with uniform properties. For example, any sample of sucrose has the same composition and same physical properties, such as melting point, color, and sweetness, regardless of the source from which it is isolated. 
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Classifying Matter by State02:49

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Chemistry is the study of matter and the changes it undergoes. Matter is anything that has mass and occupies space. Matter is all around us; the air, water, soil, mountains, even our bodies are all examples of matter. Matter is divided into three states — solid, liquid, and gas — that are commonly found on earth. The fourth state of matter, plasma, occurs naturally in the interiors of stars. 
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Phase Transitions02:31

Phase Transitions

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Whether solid, liquid, or gas, a substance's state depends on the order and arrangement of its particles (atoms, molecules, or ions). Particles in the solid pack closely together, generally in a pattern. The particles vibrate about their fixed positions but do not move or squeeze past their neighbors. In liquids, although the particles are closely spaced, they are randomly arranged. The position of the particles are not fixed—that is, they are free to move past their neighbors to...
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The most common elements in organic molecules, carbon, hydrogen, oxygen, nitrogen, sulfur, and phosphorus, are only available in the ecosystem in limited amounts. Therefore, these nutrients must be recycled through both biotic and abiotic components of the ecosystem, in processes generally called biogeochemical cycles.
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Updated: Jan 25, 2026

A Versatile Murine Model of Subcortical White Matter Stroke for the Study of Axonal Degeneration and White Matter Neurobiology
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场强度依赖的白物质R1和R2是相循环平衡稳定状态自由偏移放松计的异构性.

Florian Birk1,2, Hamzeh Tesh1, Ali Aghaeifar1

  • 1High-Field Magnetic Resonance, Max Planck Institute for Biological Cybernetics, Tübingen, Germany.

Magnetic resonance in medicine
|January 23, 2026
PubMed
概括
此摘要是机器生成的。

白质 (WM) 中的放松率 (R2) 和不对称指数 (AI) 显示出强烈的方向依赖,随着场强度的增加而增加. 灵敏性效应在超高电场上驱动R2异质性,在较低电场上有其他机制的贡献.

关键词:
大脑组织的异构性.导向依赖性 导向依赖性阶段循环 bSSFPFP 的情况.放松计放松计放松计.旋转走路 走路 旋转走路白质是白色物质的组成部分.

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科学领域:

  • 磁共振成像 (MRI) 是一种磁共振成像技术.
  • 神经成像是一种神经成像.
  • 生物物理学的生物物理.

背景情况:

  • 阶段循环平衡稳定状态自由前行 (pc-bSSFP) 是一种有价值的MRI技术.
  • 了解白质 (WM) 微观结构对于诊断神经疾病至关重要.
  • 放松率 (R1,R2) 和不对称指数 (AI) 提供了对组织特性的洞察力.

研究的目的:

  • 研究R1,R2和AI在WM光纤通道中的方向依赖性.
  • 确定这种依赖如何随磁场强度 (3T和9.4T) 而变化.
  • 探索潜在的机制,包括易感效应和魔法角度效应.

主要方法:

  • 在健康的人类大脑中获得的pc-bSSFP数据在3T和9.4T.
  • 使用运动不敏感的快速配置放松计 (MIRACLE) 和频率响应分析处理的数据.
  • 从扩散张力成像 (DTI) 估计的分数异构 (FA) 和光纤到场角 (θ).

主要成果:

  • R2和AI表现出显著的方向依赖,而R1表现出较弱但明显的依赖.
  • 异构性从3T系统地增加到9.4T.
  • 发现灵敏性效应是R2异构性在超高场 (9.4T) 中的主要驱动因素.

结论:

  • 微结构驱动的放松异质性显著影响pc-bSSFP放松度,特别是R2.
  • R2异质性主要是由超高电场的敏感性驱动的.
  • 其他机制可能会在较低场强度下导致R2异构.