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相关概念视频

Fluid Mosaic Model01:34

Fluid Mosaic Model

The fluid mosaic model was first proposed as a visual representation of research observations. The model comprises the composition and dynamics of membranes and serves as a foundation for future membrane-related studies. The model depicts the structure of the plasma membrane with a variety of components, which include phospholipids, proteins, and carbohydrates. These integral molecules are loosely bound, defining the cell’s border and providing fluidity for optimal function.LipidsThe most...
Fluid Mosaic Model01:19

Fluid Mosaic Model

Scientists identified the plasma membrane in the 1890s and its principal chemical components (lipids and proteins) by 1915. The model for plasma membrane structure, proposed in 1935 by Hugh Davson and James Danielli, was the first model to be widely accepted in the scientific community. The model was based on the plasma membrane's "railroad track" appearance in early electron micrographs. Davson and Danielli theorized that the plasma membrane's structure resembled a sandwich with the analogy of...
Atomic Nuclei: Nuclear Spin State Overview01:03

Atomic Nuclei: Nuclear Spin State Overview

NMR-active nuclei have energy levels called 'spin states' that are associated with the orientations of their nuclear magnetic moments. In the absence of a magnetic field, the nuclear magnetic moments are randomly oriented, and the spin states are degenerate. When an external magnetic field is applied, the spin states have only 2 + 1 orientations available to them. A proton with = ½ has two available orientations. Similarly, for a quadrupolar nucleus with a nuclear spin value of one, the...
Atomic Nuclei: Magnetic Resonance01:05

Atomic Nuclei: Magnetic Resonance

The number of nuclear spins aligned in the lower energy state is slightly greater than those in the higher energy state. In the presence of an external magnetic field, as the spins precess at the Larmor frequency, the excess population results in a net magnetization oriented along the z axis. When a pulse or a short burst of radio waves at the Larmor frequency is applied along the x axis, the coupling of frequencies causes resonance and flips the nuclear spins of the excess population from the...
Atomic Nuclei: Nuclear Relaxation Processes01:23

Atomic Nuclei: Nuclear Relaxation Processes

In the absence of an external magnetic field, nuclear spin states are degenerate and randomly oriented. When a magnetic field is applied, the spins begin to precess and orient themselves along (lower energy) or against (higher energy) the direction of the field. At equilibrium, a slight excess population of spins exists in the lower energy state. Because the direction of the magnetic field is fixed as the z-axis,  the precessing magnetic moments are randomly oriented around the z-axis. This...
Atomic Nuclei: Types of Nuclear Relaxation01:28

Atomic Nuclei: Types of Nuclear Relaxation

Nuclear relaxation restores the equilibrium population imbalance and can occur via spin–lattice or spin–spin mechanisms, which are first-order exponential decay processes.
In spin–lattice or longitudinal relaxation, the excited spins exchange energy with the surrounding lattice as they return to the lower energy level. Among several mechanisms that contribute to spin–lattice relaxation, magnetic dipolar interactions are significant. Here, the excited nucleus transfers energy to a nearby...

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相关实验视频

Updated: Jun 21, 2026

Magnetically Induced Rotating Rayleigh-Taylor Instability
06:42

Magnetically Induced Rotating Rayleigh-Taylor Instability

Published on: March 3, 2017

液态水中的旋转运动是异构的:一个核磁共振和分子动力学模拟研究.

J Ropp1, C Lawrence, T C Farrar

  • 1Department of Chemistry, University of Wisconsin, Madison, Wisconsin 53706, USA.

Journal of the American Chemical Society
|August 17, 2001
PubMed
概括
此摘要是机器生成的。

实验性NMR揭示了液态水中的异构旋转运动. 和氧-17的放松时间表明不同温度的分子重定向动态.

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相关实验视频

Last Updated: Jun 21, 2026

Magnetically Induced Rotating Rayleigh-Taylor Instability
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An Analog Macroscopic Technique for Studying Molecular Hydrodynamic Processes in Dense Gases and Liquids
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科学领域:

  • 物理化学 物理化学
  • 化学物理 化学物理
  • 频谱学是一种光谱学.

背景情况:

  • 核磁共振 (NMR) 光谱是一种用于探测分子动态的强大工具.
  • 由于水在化学和生物过程中无处不在的作用,了解水的旋转动力学至关重要.
  • 之前的研究已经提供了对水的结构和动态的见解,但精确的旋转相关时间仍然是一个活跃的研究领域.

研究的目的:

  • 用NMR放松测量实验确定水分子的旋转相关时间.
  • 为了研究水的旋转动态的温度依赖性.
  • 为了评估水的旋转运动的异构性.

主要方法:

  • 实验性核磁共振 (NMR) 测量 (T1) 和氧-17 (T1) 在丰富液体水中的放松时间.
  • 从水的初始计算和实验化学转移测量中确定四极合常量和不对称性参数.
  • 对放松数据的分析,以提取旋转相关时间.

主要成果:

  • 在D2 ((16) O中OD键向量的旋转相关时间从275K的5.8ps降低到350K的0.86ps,从275K的5.8ps降低到0.86ps.
  • 在D2(16) O中稀释D2(17) O的外平面向量的旋转相关时间从275K的4.4ps降低到350K的0.64ps.
  • 实验结果表明,水分子的反旋运动是异构的.

结论:

  • 这项研究提供了关于液态水中的异型旋转动态的实验证据.
  • 核磁共振放松测量为特征分子重定向提供了一种可靠的方法.
  • 在较低温度下实验数据和分子动力学模拟之间的差异突出了模拟模型的精细化领域.