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¹H NMR of Conformationally Flexible Molecules: Variable-Temperature NMR01:15

¹H NMR of Conformationally Flexible Molecules: Variable-Temperature NMR

1.1K
The axial and equatorial protons in cyclohexane can be distinguished by performing a variable-temperature NMR experiment. In this process, except for one proton, the remaining eleven protons are replaced by deuterium. The deuterium substitution avoids the possible peak splitting caused by the spin-spin coupling between the adjacent protons. The remaining proton flips between the axial and equatorial positions.
1.1K
Temperature Dependent Deformation01:12

Temperature Dependent Deformation

140
In a nonhomogeneous rod made up of steel and brass, restrained at both ends and subjected to a temperature change, several steps are involved in calculating the stress and compressive load. Due to the problem's static indeterminacy, one end support is disconnected, allowing the rod to experience the temperature change freely. Next, an unknown force is applied at the free end, triggering deformations in the rod's steel and brass portions. These deformations are then calculated and added...
140
Temperature Measurement Sites01:14

Temperature Measurement Sites

1.6K
A thermometer measures body temperature. The common sites for measuring body temperature are the oral cavity, axillary region, temporal artery, and skin surface, such as the forehead, abdomen, and axilla. True core body temperature is assessed in the rectum, tympanic membrane, pulmonary artery, esophagus, and urinary bladder.
Oral: When assessing oral temperature, the thermometer tip should be placed under the tongue in the posterior sublingual pocket. It offers accurate readings and can be...
1.6K
¹H NMR of Conformationally Flexible Molecules: Temporal Resolution00:52

¹H NMR of Conformationally Flexible Molecules: Temporal Resolution

807
At room temperature, the chair conformer of cyclohexane undergoes rapid ring flipping between two equivalent chair conformers at a rate of approximately 105 times per second. These two chair conformers are in equilibrium. The rapid ring flipping results in the interconversion of the axial proton to an equatorial proton and an equatorial to the axial proton. Such interconversions are too rapid and cannot be detected on the NMR timescale. Hence, the NMR spectrometer cannot distinguish between the...
807
Gas Thermometers and the Kelvin Scale01:22

Gas Thermometers and the Kelvin Scale

4.4K
The definition of temperature in terms of molecular motion suggests that there should be a lowest possible temperature, where the average kinetic energy of molecules is zero (or the minimum allowed by quantum mechanics). Experiments confirm the existence of such a temperature, called absolute zero. An absolute temperature scale is one whose zero point is absolute zero. Such scales are convenient in science because several physical quantities, such as the volume of an ideal gas, are directly...
4.4K
IR Spectroscopy: Hooke's Law Approximation of Molecular Vibration01:16

IR Spectroscopy: Hooke's Law Approximation of Molecular Vibration

1.2K
A covalently bonded heteronuclear diatomic molecule can be modeled as two vibrating masses connected by a spring. The vibrational frequency of the bond can be expressed using an equation derived from Hooke's law, which describes how the force applied to stretch or compress a spring is proportional to the displacement of the spring. In this case, the atoms behave like masses, and the bond acts like a spring.
According to Hooke's law, the vibrational frequency is directly proportional to...
1.2K

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相关实验视频

Updated: Jun 6, 2025

Exploring Caspase Mutations and Post-Translational Modification by Molecular Modeling Approaches
05:56

Exploring Caspase Mutations and Post-Translational Modification by Molecular Modeling Approaches

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在具有刚性约束的分子动力学模拟中测量局部温度.

Stephen Sanderson1, Shern R Tee1,2, Debra J Searles1,3,4

  • 1Australian Institute for Bioengineering and Nanotechnology, The University of Queensland, St. Lucia, QLD 4072, Australia.

Journal of chemical theory and computation
|November 21, 2024
PubMed
概括
此摘要是机器生成的。

在模拟中准确计算局部温度需要考虑受限制的自由度 (DoF). 这种方法正确评估受约束原子的DoF,确保可靠的温度计算和检测模拟工件.

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Thermal Measurement Techniques in Analytical Microfluidic Devices
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Near-Infrared Temperature Measurement Technique for Water Surrounding an Induction-heated Small Magnetic Sphere
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Near-Infrared Temperature Measurement Technique for Water Surrounding an Induction-heated Small Magnetic Sphere

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Near-Infrared Temperature Measurement Technique for Water Surrounding an Induction-heated Small Magnetic Sphere
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科学领域:

  • 计算化学是一种计算化学.
  • 分子动力学模拟的模拟.
  • 统计力学就是统计力学.

背景情况:

  • 分子模拟通常使用约束 (例如固定键长) 来降低计算成本.
  • 这些约束改变了系统的自由度 (DoF),影响了温度计算.
  • 错误的DoF计算可能会导致动能均分的非物理违规.

研究的目的:

  • 开发一种方法来准确计算分子模拟中的局部温度,使用任意的几何约束.
  • 为了自主一致地评估受约束原子的自由度 (DoF),以正确确定温度.
  • 在模拟中提供可靠的方法来评估动能等分的有效性.

主要方法:

  • 开发了一种自相一致的方法来评估在一般几何约束下对原子的自由度 (DoF).
  • 从任意的笛卡儿元件动能计算局部温度.
  • 在各种系统上验证了该方法,包括具有温度梯度和有限几何形状的系统.

主要成果:

  • 该方法通过正确考虑受限制的自由度 (DoF) 准确计算局部温度.
  • 在各种系统中得到验证,在复杂的场景中展示了稳定性.
  • 识别了动能配分分解作为数值整合问题或不充分平衡的敏感指标.
  • 在2 fs时间步骤中,C和H原子之间具有刚性键的均等分离的违反,表明了配置过热.

结论:

  • 在受约束的分子模拟中,通过自相一致的DoF评估,可以实现准确的局部温度计算.
  • 该方法为模拟质量提供了敏感的诊断工具,揭示了诸如数值集成错误或不充分平衡等问题.
  • 观察到的设备分区违规行为可以作为模拟中配置过热的有用指标.