Xueba's Sea of ​​Stars

Chapter 314 Green's Function
"Come on, have a cup of coffee and continue practicing tonight."

In the laboratory, Wu Bin put the coffee he just bought on Lin Ziqi's table and said.

Facing this sudden surprise, Lin Ziqi happily held up the coffee cup and said, "Thank you~ Where did you buy it?"

"Winter Story at the door, the coffee tastes pretty good." Wu Bin replied casually.

"Why did you suddenly want to go to the coffee shop?" Lin Ziqi asked curiously.

"Talk about patents."

"Oh, how did the talk go?"

"All the preliminary preparations have been discussed, and all that's left is to wait for the results."

"That's great~" Lin Ziqi had an envious expression on her face, then picked up the phone and looked at it, and suddenly said in a hurry: "Oh, I have to go to class, thank you for the coffee."

"Remember to come back and write your paper in the evening." Wu Bin warned Lin Ziqi's back.

"Got it, Professor Wu!" After making a face at Wu Bin, Lin Ziqi ran out of the laboratory.

"Well... I almost have to go to the classroom." Wu Bin looked at the time, then walked back to his seat and picked up his schoolbag.

The courses assigned to him by Academician Chen Xianhui are comprehensive, ranging from advanced quantum mechanics, quantum field theory, electrodynamics, and introduction to condensed matter physics in superconductivity theory to engineering, electromagnetism, heat transfer, fluid mechanics, etc. that apply superconductivity. Wait.

A while ago, because Wu Bin was mostly in the laboratory, he hadn't attended a few classes until now. Now, taking advantage of the gap in the patent application, Wu Bin happened to make up these classes.

But for Wu Bin, it is not so much that he is going to class, it is better to say that he wants to hear more insights and ideas about superconductivity. After all, in terms of his self-learning ability, he has learned these related courses as early as his freshman year I have already learned a lot, and after that, I have read hundreds of documents from various countries.

Based on his current understanding of superconductivity, he can clearly feel that applied superconductivity research is much friendlier than theoretical superconductivity research, because the content of applied superconductivity can still be seen at any rate, and everyone can gather together to review the results during the experiment. discuss.

But theoretical superconductivity is completely different. If you learn a little bit more about this thing, you will see darkness, and the masters of physics all over the world are walking in the dark, and whenever this group of people discusses together, they slam the door And going there is light, and it is common for two friends to suddenly escalate to a Facebook scolding battle while chatting.

As for why this is so, a simple analogy is that the blind man feels the elephant. No one knows where the future of superconductivity is, so some say it is long, some say it is thick, and some say it can spray water.

In short, everyone firmly believes that what they are walking is the path to the truth, otherwise how can they persist.

After arriving in the classroom, Wu Bin sat in the relatively empty third row. Just as he put down his schoolbag, he found an acquaintance of his walking in from outside the classroom.

'It turns out that Professor Cheng is teaching this class. '

Professor Cheng's full name is Cheng Guangji. He is a doctoral student in the Department of Physics and Astronomy at the University of Pittsburgh.

When Wu Bin saw Cheng Guangji, Cheng Guangji also saw him, so he smiled and raised his hand to greet him, and Wu Bin immediately waved his hand and smiled at him.

After about half of the classroom was filled, Professor Cheng stood on the podium and picked up a piece of chalk.

【Green's function】

After writing four big words on the blackboard, Cheng Guangji turned around and asked with a smile: "Which student can explain the physical meaning of Green's function?"

"..."

The students below all looked puzzled, wondering what happened to Professor Cheng today, and asked what the hell was the question as soon as the class started?Haven't talked about it yet!

However, when everyone was lost in confusion, Wu Bin frowned, realizing that things were not simple.

Sure enough, after a brief silence, Cheng Guangji smiled and said, "Come on, the male student in blue who is sitting in the middle of the third row, please get up and talk."

"..."

Wu Bin, who was speechless for a while, slowly stood up, not knowing how he had offended this Professor Cheng, who was smiling and greeting him just now, why did he suddenly get into trouble! ?

When Wu Bin stood up, the students around him couldn't help but focus their attention on him, wanting to see who was so unlucky. However, the first reaction of most people was.

"I don't think I've seen this one before..."

But there were also quite a few people who exclaimed in low voices: "Isn't this God Wu!?"

This made everyone around me think of it.

'This is the boss who graduated from the sophomore year. '

Whether it is the Guo Award or the graduation ceremony alone, Wu Bin has gained a strong sense of presence in HKUST this year, making it difficult for others to know him or not.

"Okay, be quiet, be quiet!" Cheng Guangji patted the podium and shouted.

Suddenly, after the classroom became quiet, Cheng Guangji looked at Wu Bin again and smiled, "Student, please answer."

After showing a dumbfounding expression, Wu Bin said: "In physics, there are a large number of inhomogeneous differential equations with boundary conditions or initial conditions."

"And these differential equations are essentially describing the relationship between the source and the field, and there is a good method called the Green's function method. The function obtained by using it is called the Green's function. In fact, the Green's function is the corresponding A field."

"Well, well said." Standing on the podium, Cheng Guangji clapped his hands twice, and continued: "The rest... I guess it's troublesome to use words alone, so you'd better go on stage and explain it."

"???"

Wu Bin, who fell into confusion again, had no choice but to walk up to the podium slowly under the gaze of the whole class, and took the chalk handed over by Cheng Guangji with a smile.

Taking a deep breath, Wu Bin wrote on the blackboard and said: "Generally speaking, a definite solution is equal to a general solution plus boundary conditions, and finding a general solution is equal to an integral. But if you use Green's function to solve it, a new way of thinking will appear."

As he spoke, Wu Bin drew a line on the blackboard, and then drew an irregular shape on the line.

"In the unbounded space, if there is an irregular charged body, the charge density is rho(r'), it should be noted that this is the field source of any branch."

"Then it will excite an electric field in space, and the TV generated in space r will be wirelessly divided and then superimposed."

Saying this, Wu Bin began to list the formulas on the blackboard.

[(r→)=4πε/1∫∫∫r→-r→'/p(r→')dr→']

"The dr'→ represents not only a vector, but also a volume element, and the potential at a certain point in space is uniquely determined by the distribution of charge density."

Looking at the students who were taking notes at the bottom, Wu Bin said: "We know that the problem without boundary conditions has a solution but is not unique. Given the boundary conditions, the problem can have a unique solution. Then how to find Can we get the charge density with arbitrary distribution, and the electric potential under arbitrary boundary conditions?"

"Then the question arises, what kind of boundary conditions do we need?"

But when everyone was looking at Wu Bin curiously, Wu Bin suddenly turned around and said to Cheng Guangji: "Professor Cheng, I don't understand the next part, so I ask you for advice."

Cheng Guangji was taken aback after hearing this, and then laughed loudly and said: "Yes, you are slippery enough." After laughing, he took the chalk from Wu Bin's hand and said: "Okay, go on, go on, if there is anything you don't understand, you will learn more." Come to class, you know?"

"understood."

Relieved, Wu Bin returned to his seat, and he almost knew why this professor Cheng suddenly targeted him. It was probably just a small expression of dissatisfaction with him for taking so long to come to class, and there was no malice.

After Wu Bin sat back in his seat, Cheng Guangji picked up the chalk and wrote under Wu Bin's formula: "The first half of this student has already explained very well, so for the definite solution problem, we can give a general Poisson equation... ..."

……

As a piece of soft music played, Cheng Guangji, who had written on several blackboards, announced that "get out of class is over."

Just as Wu Bin was packing his schoolbag, two girls sitting in the front row suddenly walked over to him.

"That... hello." The taller girl stepped forward and waved to Wu Bin.

"Hello." Wu Bin nodded towards her.

"We think your explanation of Green's function was very good in the first class." After finishing speaking, he lowered his voice and said, "Actually, you know how to continue explaining."

After hearing this, Wu Bin quickly waved his hands and said, "No, no, I really don't know, otherwise how could I come to Professor Cheng's class."

The two girls laughed lightly after hearing this, with obvious expressions of disbelief on their faces.

After laughing, the tall girl said again: "Actually...we came here to learn from the scriptures and ask the great god for some learning experience."

"My god, I'll save it. If I can help, I will definitely answer."

The tall slender girl clapped her hands and said happily: "The Great God is really close to the people. In fact, the two of us have been abused by graduate courses for a few weeks since we started school! I don't know if it's because of the large span of undergraduate majors or the large span of professional levels. Anyway, I really listen to the class. don't know."

"Some great instructors often use Chinese and English to tell us about the frontiers of their respective fields or the research progress of their own laboratories. It sounds very advanced... But after the class, I feel that I have learned nothing, and my IQ is ready. Being crushed, I have recently doubted whether choosing graduate school was the right choice... Now I feel like a fake antique mixed into a museum, no matter how I look at it, I don't fit in."

The other girl nodded violently, looking very troubled.

"This..." Wu Bin thought for a while, "Which classes do you find difficult to understand?"

"Well... high quantity, field theory, group theory, quantum physics..."

As she spoke, the tall slender girl blushed because she seemed to have holes all over her body...

In order to break the embarrassment, Wu Bin first replied: "Well... You two should also want to understand superconductivity in these courses, right? In this case, I suggest that you read more literature. The scope of this field is too large, and every part of it The courses are not easy, if you really feel that you can't keep up, you can also start the semester of applied superconductivity, the difficulty of entry will actually be slightly lower."

PS: I just got home, code out a chapter first, and continue later.

(End of this chapter)