Relaxation time

Overview

This system can be specific or abstract.

This can be referred to as relaxation time, and, for example, the time period of the photovoltaic effect from light is also referred to as relaxation time, and the policy is also called relaxation. Yu time.

wherein the procedure of the atomic physics:

atomic nucleation is replied to the balanced arrangement state. The time it needs to be relaxed. There are two kinds of T1 and T2, T1, which are called T1 and T2, T1, and T2 is a spin or lateral relaxation time.

The quasi-equilibrium process is a sufficiently slow limit. The "slow" here is the time in thermodynamic sense, that is, the time used by imbalance to balanced relaxation time is smaller than the process. It can be considered enough to slow enough.

Relaxation Time:

The system is in a balanced state, after instantaneous disturbance of the outside world, will be able to reply to the original equilibrium state, the system experienced Give time for a while. Expressed in τ. In fact, relaxation time is the time required to adjust its own changes with the environment. This condition is more apparent using the relaxation time. This condition is "sufficiently slow" in the predominant process. As long as the system status change experience is always satisfied with the relaxation time τ, this process can be considered as quasi-static process. Relaxation time is related to the size of the system, the large system has time long, and the relaxation time is long. Relaxation time is also related to the type (mechanical, thermal or chemical balance) that reaches balance. In general, pure mechanical balance conditions destroy the desired relaxation time to be shorter than pure thermal balance or chemical balance destruction. For example, the pressure in the gas tends to have frequent collision exchange momentum between the phases. Since the collision between gas molecules is generally more frequent (1 air molecular balance collision frequency is 6.6 × 109 times / sec under standard condition), in order to always accompany the flow of gas when the pressure is unequal, τ is generally small, for volume A small system τ is approximately

s, and even smaller. For example, the entire compression stroke of the four-stroke internal combustion engine of the rotational speed N = 150 rpm is less than 0.2 s, and it is more than 2 orders of magnitude compared to

S, which can be considered to be slow enough, so it can be approximately It will look at the static process. However, due to diffusion in the mixed gas, the concentration homogenization requires molecular displacement, which relaxation time can be extended to a few minutes or even greater.

We can use the sound velocity to easily discriminate the order of τ, since the system is transmitted back and forth in the system in the system after the system is subjected to the external mechanical disturbance, we can expect the sound wave to transfer several rounds It can reach a new balance state. If the linence of the system is L, the sound speed is c, then

relaxation time , if l = 0.3m, C = 300m / s, τ is

The order of the

.

Analysis

In classic physics, the particles in the electric field can be accelerated under the electric field, that is,

, Free electrons do not meet this simple relationship under the external electric field. First, the free electron is stationary mass and the quality of motion, the quality of the formula is Einstein's relative quality

; additionally, the electrons will eventually collide with atoms in the crystal, and change the motion state. This collision tends to reduce the acceleration obtained from the external electric field, but the final speed of electrons is always increased.

The time interval between each collision is average, we call the cycling time г; each collision speed increase average, we call the drift speed.

Effects

A nuclear spin system in a stable outer magnetic field is subject to two functions, one is that the magnetic field power map enables the magnetic moment of the nucleus along the magnetic field, and the other is The thermal motion chart of the molecule hinders the nuclear magnetic moment adjustment position. The last magnetic moment overlaps and reaches the stabilized magnetic field, and the magnetization intensity in the magnetic field direction is the largest direction, and the magnetization intensity in the vertical direction of the magnetic field is zero. If the primary nuclear system is reached again - the electromagnetic field in different directions, the magnetization intensity deviates from the original balance position, generates a lateral magnetization intensity perpendicular to the raw magnetic field, while the longitudinal magnetization intensity parallel to the raw magnetic field will also be reduced. When this electromagnetic field is removed, the unbalanced state of the nuclear system cannot be maintained, and the balance state is restored. The process of recovering to balanced state is called a relaxation process. The procedure of the atomic nucleus replies to the balanced array state from the state of the activated state. This process follows the rules of exponential, and its time constant is called relaxation time.

The time required for the relaxation process is relaxed. That is to achieve the time required for the thermal balance. Thermal balance is caused by heat, which is caused by heat.

relaxation time has two types T1 and T2

T1 is a spin or The longitudinal cycle time, the longitudinal magnetization intensity recovery time constant T1 is referred to as longitudinal relaxation time (also known as spin - crystal relaxation time),

T2 is a spin or lateral relaxation Time, the time constant T2 of the lateral magnetization disappears is referred to as a horizontal relaxation time (also known as spin-self-awaiting time).

Nuclear magnetic tubes are mainly to understand the reservoir properties of rocks by studying the relaxation process of fluid in rock pores. Therefore, relaxation time is the main parameters of nuclear magnetic measuring studies.