"Here, have a cup of coffee, and continue practicing tonight."

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

Faced with this sudden surprise, Lin Ziqi happily picked 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 think to go to the café?" Lin Ziqi asked curiously.

"Let's talk about patents."

"Oh, how's the talk?"

"The preparations have been discussed, all that remains is to wait for the results."

"It's so good~" Lin Ziqi had an envious expression, then picked up her phone and looked at it, and suddenly said hurriedly: "Oops, I have to go to class, thank you for your coffee." ”

"Remember to come back in the evening to write your paper."

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

"Hmm...... I'm almost going to the classroom. Wu Bin glanced at the time, then walked back to his place and picked up his schoolbag.

Academician Chen Xianhui gave him a comprehensive curriculum, ranging from advanced quantum mechanics, quantum field theory, electrodynamics, and introduction to condensed matter physics in the field of superconductivity theory to applied superconductivity engineering, electromagnetism, heat transfer, fluid mechanics, and so on.

A while ago, because Wu Bin was basically immersed in the laboratory, he hadn't been to a few classes until now, and at this time, taking advantage of the gap in patent application, Wu Bin happened to make up for these classes.

But for Wu Bin, it's not so much that he is going to class, but that he wants to hear more insights and ideas about superconductivity.

After all, in terms of his self-learning ability, he had already learned these related courses as early as his freshman year, and he had read hundreds of literatures from various countries since then.

As far as his current understanding is concerned, the application of superconductivity is much friendlier than the study of theoretical superconductivity, because the content of the application of superconductivity can still be seen, and everyone can get together to discuss the results during the experiment.

But theoretical superconductivity is completely different, this thing will be seen in the dark if you learn it a little deeper, and the world's physics masters are moving forward in the dark, and whenever this group of people slams the door when they discuss together, it is light, and it is common for two friends to chat and suddenly escalate to Facebook.

As for why this is the case, it is simply a blind man touching an elephant, and no one knows where the future of superconductivity is, so some say it is long, some say it is thick, and some say it will spray water.

In short, everyone firmly believes that they are on the road to the truth, otherwise how can they persevere.

After coming to the classroom, Wu Bin sat in the relatively empty third row, and as soon as he put down his bag, he found an acquaintance of his walking in from outside the classroom.

It turned out that Professor Cheng was teaching this class. ’

Professor Cheng Guangji, a Ph.D. student in the Department of Physics and the Department of Astronomy at the University of Pittsburgh, has been working on quantum nanoelectronics since returning to China.

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

After about half of the classroom was seated, 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 classmate will explain the physical meaning of the Green function?" ”

“……”

The students below were all puzzled, wondering what happened to Professor Cheng today, and asked the question as soon as the class started. I haven't talked about it yet!

However, when everyone was confused, Wu Bin frowned, realizing that things were not simple.

Sure enough, after a short silence, Cheng Guangji smiled and said, "Come, the male classmate in blue sitting in the middle of the third row, get up and talk about it." ”

“……”

Wu Bin, who was speechless for a while, slowly stood up, and he didn't know how he had offended this Professor Cheng, obviously he was smiling and saying hello just now, why did he suddenly get into trouble!?

And when Wu Bin stood up, the surrounding students couldn't help but focus their eyes on him, wanting to see who was so unlucky, but most people's first reaction was.

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

But there are also many people who whispered: "Isn't this Wu God!?" ”

The people around me also remembered this.

"This is the big guy who graduated from his sophomore year." ’

Whether it is the Guo Award or a person's graduation ceremony, Wu Bin has made a sense of presence in the University of Science and Technology this year, and it is difficult for others to know him.

"Alright, quiet, quiet!" Cheng Guangji slapped the podium and shouted.

Suddenly, after the classroom returned to quiet, Cheng Guangji looked at Wu Bin again and smiled: "Classmate, please answer." ”

After showing a crying and laughing expression, Wu Bin spoke: "In physics, there are a large number of non-homogeneous 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 way to do this called the Green's function method, and the function obtained by solving it is called the Green's function, and in fact the Green's function corresponds to a field."

"Well, that's a good point." Cheng Guangji, who was standing on the podium, clapped his hands twice, and then said, "What about the rest of the part...... I guess it's more troublesome to use language alone, so you might as well come on stage and demonstrate. ”

“？？？”

Wu Bin, who fell into confusion again, had to slowly walk up to the podium under the gaze of the whole class, and received the chalk handed by Cheng Guangji with a smile.

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

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

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

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

Say thisWu Bin began to list the formulas on the blackboard.

【? （r→）=4πε/1∫∫∫r→-r→’/p（r→’）dr→’】

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

Glancing at the students who were taking notes below, Wu Bin said again: "We know that there is a solution to the problem without boundary conditions, but it is not unique, and given the boundary conditions, the problem can be uniquely solved, so how to find the charge density of any distribution and the potential under any boundary conditions through the superposition of point charge potentials?" ”

"The question then comes in, what kind of boundary conditions do we need?"

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

Cheng Guangji was stunned for a moment after hearing this, and then laughed and said, "Yes, you are slippery enough." After laughing, he took the chalk in Wu Bin's hand and said, "Okay, go down, go down, if you don't understand, you can come to class more in the future, right?" ”

"Got it."

Wu Bin, who breathed a sigh of relief, returned to his position, and almost knew in his heart why this Professor Cheng suddenly targeted him, and it was estimated that it was a small expression of dissatisfaction with him for coming to class for so long, 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: "For the solution problem, we can give a general Poisson equation ......"

……

As a piece of light music sounded, Cheng Guangji, who had several blackboards written on it, announced the end of class.

While Wu Bin was sorting out his schoolbag, two girls sitting in the front row suddenly walked over to him.

"That...... Hello. The taller girl stepped forward first and beckoned to Wu Bin.

"Hello." Wu Bin nodded at her.

"We think you explained Green's functions well when you first started the class." After speaking, he lowered his voice and said, "Actually, you know how to continue to explain." ”

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

The two girls chuckled twice after hearing this, and the expressions on their faces were obviously unbelieving.

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

"The great god is exempt, if I can help, I will definitely answer."

The tall girl clapped her hands and said happily: "The great god is really close to the people, in fact, the two of us have just been abused by the graduate program for a few weeks!" I don't know if it's because of the large span with the undergraduate major or the professional level, anyway, I really can't understand the class. ”

"Some of the top tutors often tell us about the frontiers of their respective fields or the research progress of their own laboratories in a mixture of Chinese and English, which sounds very high-minded...... But after class, I felt that I hadn't learned anything, and my IQ was crushed, and recently I have wondered if I made the right choice to go to graduate school...... Now I feel like a fake antique in a museum, how out of place. ”

The other girl also nodded on the side, looking very annoyed.

"This ......," Wu Bin thought for a moment, "may I ask what classes you take that find difficult to understand?" ”

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

As she spoke, the tall girl's face turned red, because she seemed to be covered with holes......

In order to break the embarrassment, Wu Bin replied first: "Hmm...... You should also want to enter the field of superconductivity after taking these classes, right? In this case, I actually recommend that you read more literature, the scope of this field is too large, and every course in it is not easy, if you really feel that you can't keep up, I suggest that you can also try applied courses, for example, maybe you will find your own strengths. ”

PS: Just arrived home, code out a chapter first, and continue later.