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Potential Due to a Magnetized Object01:24

Potential Due to a Magnetized Object

285
Magnetic dipoles in magnetic materials are aligned when placed under an external magnetic field. For paramagnets and ferromagnets, dipole alignment occurs in the direction of the magnetic field. However, the dipoles align opposite to the field in the case of diamagnets. This state of magnetic polarization due to the external field is called magnetization. Magnetization is defined as the dipole moment per unit volume. It plays a similar role to polarization in electrostatics.
The vector...
285
Atomic Nuclei: Magnetic Resonance01:05

Atomic Nuclei: Magnetic Resonance

657
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...
657
Atomic Nuclei: Nuclear Relaxation Processes01:23

Atomic Nuclei: Nuclear Relaxation Processes

654
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.
654
Paramagnetism01:30

Paramagnetism

2.5K
Paramagnets are materials with unpaired electrons that possess a finite magnetic moment. In the absence of a magnetic field, these moments are randomly oriented, and thus the net moment is zero. Under an external field, a torque acting on the moments tends to align them along the field's direction. However, the random thermal motion of electrons produces a torque opposite to the external field and tries to disorient the moments. These two competing effects align only a few moments along the...
2.5K
NMR Spectrometers: Resolution and Error Correction01:14

NMR Spectrometers: Resolution and Error Correction

695
When magnetic nuclei in a sample achieve resonance and undergo relaxation, the signal detected in NMR is an approximately exponential free induction decay. Fourier transform of an exponential decay yields a Lorentzian peak in the frequency domain. Lorentzian peaks in an NMR spectrum are defined by their amplitude, full width at half maximum, and position, where the peak width is governed by the spin-spin relaxation time alone. In real experiments, however, the applied magnetic field is rendered...
695
Diamagnetism01:26

Diamagnetism

2.4K
Materials consisting of paired electrons have zero net magnetic moments. However, when these materials are placed under an external magnetic field, the moments opposite to the field are induced. Such materials are called diamagnets. Diamagnetism is the response of the diamagnets when placed in an external magnetic field.
Diamagnetism was discovered by Anton Brugmans in 1778 when he observed that bismuth gets repelled by magnetic fields, thus theorizing that diamagnets get repelled by magnets....
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相关实验视频

Updated: Jul 1, 2025

Spectral and Angle-Resolved Magneto-Optical Characterization of Photonic Nanostructures
08:01

Spectral and Angle-Resolved Magneto-Optical Characterization of Photonic Nanostructures

Published on: November 21, 2019

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适应性多极模型的光学磁计数据数据.

Tim M Tierney1, Zelekha Seedat2, Kelly St Pier2

  • 1Department of Imaging Neuroscience, UCL Queen Square Institute of Neurology, University College London, London, UK.

Human brain mapping
|March 4, 2024
PubMed
概括
此摘要是机器生成的。

适应式多极模型 (AMM) 为光磁力计 (OPM) 数据提供了强大的干扰拒绝,适应多极扩展用于各种OPM系统,并改善信号噪声比.

关键词:
磁性脑电图 (MEG) 是一种磁性脑电图.干扰纠正 干扰纠正有光学的磁力计,用光学的磁力计.

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Optimizing Magnetic Force Microscopy Resolution and Sensitivity to Visualize Nanoscale Magnetic Domains
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Optimizing Magnetic Force Microscopy Resolution and Sensitivity to Visualize Nanoscale Magnetic Domains

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Optimized Setup and Protocol for Magnetic Domain Imaging with In Situ Hysteresis Measurement
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Optimized Setup and Protocol for Magnetic Domain Imaging with In Situ Hysteresis Measurement

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相关实验视频

Last Updated: Jul 1, 2025

Spectral and Angle-Resolved Magneto-Optical Characterization of Photonic Nanostructures
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Spectral and Angle-Resolved Magneto-Optical Characterization of Photonic Nanostructures

Published on: November 21, 2019

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Optimizing Magnetic Force Microscopy Resolution and Sensitivity to Visualize Nanoscale Magnetic Domains
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Optimizing Magnetic Force Microscopy Resolution and Sensitivity to Visualize Nanoscale Magnetic Domains

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Optimized Setup and Protocol for Magnetic Domain Imaging with In Situ Hysteresis Measurement
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Optimized Setup and Protocol for Magnetic Domain Imaging with In Situ Hysteresis Measurement

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科学领域:

  • 神经成像是一种神经成像.
  • 生物物理学的生物物理.
  • 信号处理 信号处理

背景情况:

  • 多极扩张在磁脑电图 (MEG) 中对于干扰缓解和脑信号建模至关重要.
  • 由于传感器和阵列设计的多样性,将这些模型适应光磁力计 (OPM) 系统是具有挑战性的.

研究的目的:

  • 在各种OPM系统中适应多极模型以获得稳定的大脑信号和干扰建模.
  • 在OPM数据中引入一种强大的干扰拒绝和信号增强的新方法.

主要方法:

  • 利用前置球形波来在头皮表面上进行紧的大脑信号表示.
  • 开发了自适应多极模型 (AMM),使用直角投影来拒绝干扰.
  • 在稳定性,噪声和非线性误差强度方面,AMM与信号空间隔离 (SSS) 相比.

主要成果:

  • 普罗拉特球形波器提供了紧的大脑信号表示,只有100个通道.
  • 在OPM系统中,AMM表现出强大的干扰拒绝,即使存在非线性错误.
  • 在128通道的OPM系统中,AMM在视觉唤起的响应中实现了高达40dB的软件屏蔽.

结论:

  • 在基于OPM的神经成像中,AMM提供了一种稳定有效的干扰拒绝和信号增强方法.
  • 与传统的SSS相比,AMM为传感器非线性错误提供了更高的稳定性.
  • 该方法成功地最大化了视觉唤起反应的真实OPM数据中的信号噪声比.