58: Chapter 58 Is this even a high school student?!

"Shut down the machine and save all raw data. Meng Che, turn off the laser power supply, cut off all high-voltage control lines for the PZT, and sever all feedback loops."

He finally looked at Jiang Lin, his gaze completely devoid of any condescending, mentor-like tolerance.

"You are right, Jiang Lin. The physical world doesn't lie; it's simply punishing our arrogance," Professor Lu Zhixing slowly said. "Now, based on your diagnosis, let's redefine the boundary conditions of the physical world for this system. What do we need to do?"

Jiang Lin did not decline.

On the battlefield of resolving mechanical failures, modesty is a blasphemy against engineering.

"Take it apart," Jiang Lin said, looking at Yin Hang. "Level it, and then reassemble it by the book."

A few minutes later.

Yin Hang fetched a 5mm hex bit and a common short-handled ratchet wrench from the tool cart.

Standing in front of the optical table, his fingers trembled and stiffened uncontrollably.

As a top student specializing in precision measurement at Jiangcheng University, he was accustomed to typing elegant Python code on a mechanical keyboard and searching for optimal mathematical solutions within complex covariance matrices.

But now, at this critical moment, he had to manually dismantle an aluminum alloy plate under the stern gaze of his mentor and the almost penetrating stare of an outsider.

This intense sense of contrast felt like a top cardiothoracic surgeon accustomed to using the da Vinci surgical system being suddenly asked to perform an amputation using a rusty nail clipper.

He took a deep breath and put on a fresh pair of cleanroom nitrile gloves.

He inserted the hex end of the wrench into the counterbore of the first bolt on the upper-left corner of the adapter plate.

Tensing his wrist muscles, he exerted force abruptly.

"Clack—"

A crisp, almost jarring metallic friction sound rang out abruptly in the eerily quiet constant-temperature room.

It sounded like the agonizing scream of the massive static friction formed by long-term engagement between threads being instantly shattered by an external force.

Jiang Lin stood one meter away from the table, his hands hanging naturally at the sides of his fleece jacket in a relaxed posture.

He had no intention of stepping forward to take the wrench and do it himself.

In the engineering field, a workstation, tools, and running equipment belong to the operator's absolute personal territory.

Touching someone else's equipment without permission is not only a violation of the operator's boundaries, but also a sign of unprofessionalism.

"The initial tightening torque of this bolt in the upper-left corner was at least over forty percent too high," Jiang Lin said, listening to the crisp metallic sound as he instantly estimated the stress in his brain. "The moment you loosened it, didn't your wrist feel a distinct sense of sluggishness and rebound? That's because near the edge of the counterbore and the contact surface, slight irreversible plastic deformation had already occurred under immense pressure."

Yin Hang did not refute.

His wrists were still sore and numb; he had indeed used almost enough force to snap the wrench just to loosen this bolt that seemed rooted in the iron plate.

He turned to dismantle the second one on the diagonal.

This time, after inserting the wrench, it met almost no decent resistance. With just a gentle twist of his wrist, the bolt loosened effortlessly, as if it had merely been placed there symbolically.

"Obviously too loose," Jiang Lin calmly delivered the final physical verdict, sounding like a coroner reading an autopsy report. "The normal tension provided by the right side is far less than that of the left. This is the source of the initial stress that caused your aluminum alloy adapter plate to warp microscopically. Keep dismantling; take them all off."

A minute later, four M6 socket head cap screws of the same specification were removed one by one and neatly placed into a tray.

Yin Hang first removed the half-wave plate and the upper adjustment mount, sealing them into a clean component box, leaving only the aluminum alloy adapter plate body itself.

The subsequent red lead testing and deburring were performed exclusively on the adapter plate body.

"Get the red lead paste," Jiang Lin said, turning his head to look at Meng Che standing aside.

Meng Che was momentarily stunned.

Red lead paste is an indicator used in traditional heavy machining workshops to check the contact area between two mating metal surfaces.

In modern ultra-high-end optical laboratories that constantly use coordinate measuring machines and laser interferometry, this messy red ointment has all but vanished.

Meng Che ran out and actually managed to dig up a small, nearly expired and dried-up tube of red lead paste from somewhere.

Jiang Lin looked at Meng Che and still didn't take it. "Wipe the exposed bottom surface of the adapter plate and the mounting area on the optical table that was just covered with high-purity absolute ethanol. Use a cleanroom wipe. Remember, not even a single speck of dust invisible to the naked eye can remain, or it will ruin the test."

Not daring to slack off, Meng Che immediately followed suit.

High-purity absolute ethanol was sprayed onto the cold stainless steel surface, evaporating rapidly and carrying away any potentially remaining grease and particles, leaving behind a clean metallic luster.

"Now, evenly apply a layer of red lead paste on the stainless steel mounting area of the table using a scraper," Jiang Lin outputted operational instructions to the two doctoral students with the precision of an emotionless industrial CNC machine. "The red lead paste cannot be thick; if it's thick, you aren't testing contact, you're testing an oil film. As long as there is an extremely faint layer of red shadow capable of catching the high points, that's enough."

Professor Lu Zhixing frowned, had Meng Che take the adapter plate to the nearby mechanical repair workbench, and brought over a cleaned steel inspection surface plate.

This was an emergency troubleshooting step, not a formal assembly and alignment procedure.

Afterward, this area would need to be re-cleaned according to cleanroom protocols.

Meng Che put on brand-new nitrile gloves, dipped a special cleanroom wipe into a bit of red lead paste, and carefully smeared it across the area previously covered by the adapter plate.

Under the cold white fluorescent light, that small area that was originally silver turned into a pale dark red layer.

"Put the adapter plate on," Jiang Lin stared at Yin Hang's hands. "Don't put bolts in, place it down gently and flatly, and then apply a little vertical downward pressure with your finger at the center. Do not let it slide horizontally at all."

Yin Hang took a deep breath, held the aluminum plate with both hands, and lowered it vertically.

Metal met metal, producing a dull clashing sound.

He pressed down on the exact center of the aluminum plate with his index finger for three seconds.

"Pick it up and flip it over."

Complying with the instruction, Yin Hang lifted the aluminum plate vertically, flipped it over, and displayed the bottom surface to everyone present.

The sound of breathing in the laboratory stagnated for that fraction of a second.

According to the subconscious understanding of Yin Hang and Meng Che previously, this aluminum plate was milled piece by piece using high-precision carbide cutting tools by the vertical machining center in the school-run factory that had been in use for many years.

The roughness requirements on the blueprint were clearly marked.

In the eyes of these Physics PhDs who were accustomed to using differential geometry and tensor analysis to describe the world, the bottom surface of this aluminum plate, baptized by modern industrial machinery, should at least be flat enough in their subconscious.

Just like the ideal plane in Euclidean geometry, it didn't possess any macroscopic undulations.

Therefore, when pressed onto the equally flat optical table, this thin layer of red lead paste should uniformly coat the entire bottom surface without any dead angles.

Logically speaking, once flipped over, this plate should be a uniform, reassuring red.

Yet now, these red marks looked like chaotic scribbles.

The cruel reality was like a resounding slap across the face of believers in modern precision machining superstition.

On the bottom surface of the aluminum plate, only the upper-left and lower-right corners were stained with distinct red patches.

Especially the upper-left corner, where the red was extremely deep, and the red lead paste even exhibited a viscous dark purplish-red due to excessive compression.

In the jargon of mechanical scraping, this is called a "hard point." It cruelly demonstrated that at the exact moment of the previous press, nearly all the weight and normal pressure of this seemingly flat aluminum plate were concentrated on an area smaller than a fingernail.

Meanwhile, at the upper-right and lower-left corners, the metal surfaces still displayed the original cool tone of the aluminum alloy—clean and spotless, without a trace of red lead.

This meant that at a microscopic level, those two corners hadn't touched the reference table underneath at all.

They were suspended in mid-air.

How was this possible?

Yin Hang's pupils contracted sharply, his brain went blank for a brief moment, and he subconsciously brought the aluminum plate closer to his eyes, trying to find an illusion of light refraction.

Meng Che beside him also pushed up the black-rimmed glasses on the bridge of his nose, his eyes filled with disbelief.

"This is a local high point," Jiang Lin said. "When the bolts are screwed down, the force travels through here. Everywhere else that didn't get stained with red is floating and unsupported."

Jiang Lin raised his hand and drew a crude force analysis diagram in mid-air.

"The physical world doesn't reason with you. Do you think that by tightening the bolts at the four corners, the force will be evenly distributed? Impossible. Force is like water flow; it will frantically pour down the path of least resistance. When the upper-left corner is the highest point, the dozen or so Newton-meters of torque you applied is converted into axial clamping force through the threads, and finally concentrated by this local high point into extremely high contact pressure."

He stepped forward, extended his finger, and pointed vaguely next to the deepest red patch in the upper-left corner of the aluminum plate.

There was a through-hole used for passing through the M6 fixing bolt.

Several pairs of eyes in the laboratory focused along his finger.

"This is a machining defect. After this through-hole is drilled, a countersink tool is needed for chamfering to remove burrs. However, on this hole, due to severe wear and blunting of the countersink tool, or because the workers pushed the feed rate too fast to rush progress during a shift change, the metal wasn't cleanly and crisply cut away, but rather brutally extruded and torn."

"At the edge of the through-hole, a ring of metal burrs as tiny as rolling mountain ranges flipped outward. Judging by the depth of this indentation, the height of this burr is probably only 0.02 millimeters."

"When you were assembling and used immense force to tighten the bolt in the upper-left corner, this ring of invisible burrs became a hard fulcrum that couldn't be completely flattened. The entire aluminum plate, which should have lain flat against the base, was stubbornly propped up by this fulcrum."

"Consequently, this adapter plate, which bore the heavy responsibility of fixing the beamsplitter, turned into a microscopic seesaw. The upper-left and lower-right corners barely touched the ground, while the upper-right and lower-left corners were actually suspended in mid-air."

Jiang Lin turned his head to look at the air outlet of the temperature control system, which emitted a low hum due to year-round operation.

"The control precision of this laboratory's temperature control system is nominally plus or minus 0.1 degrees, right?"

"Yes, this is to ensure that the overall thermal expansion and contraction of the table remain within a controllable range," Yao Siyu said.

Jiang Lin nodded. "For an ideally rigid body subjected to uniform force, this temperature fluctuation is indeed sufficient. But in a suspended state, the cold air periodically blown out by the temperature control system causes the surface of the aluminum plate to contract rapidly, whereas the steel table at the bottom has a large heat capacity and drops in temperature slowly."

"This tiny temperature difference causes microscopic warping and deformation in the aluminum plate. This ridiculous seesaw begins to twist through thermal expansion and contraction, invisible to the naked eye with a cycle lasting up to forty minutes, inside this 0.02-millimeter suspended gap as the temperature control system's compressor starts and stops."

"You tried using Kalman Filtering, trying to use endless adaptive algorithms and matrix operations to filter out a seesaw that twists incessantly at the physical level. Do you think that's possible?"

Yin Hang's fingers were still holding that aluminum plate, but he felt that the few hundred grams of metal now weighed thousands of catties.

Especially that ring of tiny burrs, which could barely be seen unless illuminated obliquely with a magnifying glass, made his cheeks burn with a fiery heat.

As a prestigious university PhD cultivated in Jiangcheng University's top laboratory, he could fluently derive up to three pages of tensor calculus formulas on a blackboard.

He could skillfully use Python and MATLAB to write tens of thousands of lines of signal processing code.

He could rattle off the power spectral density distributions of various noise models with his eyes closed.

Yet he was thoroughly and solidly defeated by metal debris casually left behind by a workshop worker.

The nights he stayed up, the hair he lost over these three weeks, and those elegant algorithms he had modified countless times turned into an absurd farce in the face of this crudest and most primitive physical reality.

"A scraper, or fine sandpaper."

Professor Lu Zhixing's voice came from behind.

This thirty-nine-year-old young professor displayed the resolution expected of a top-tier scientific researcher at this moment.

He asked no further redundant questions.

Physics is like this: when the correct logical chain is laid out before one's eyes, and when data and phenomena complete a closed loop, any argument is pale and feeble.

He had completely accepted Jiang Lin's diagnostic logic.

The low-frequency drift phantom that had tormented their entire team for three weeks was finally nailed to this aluminum plate at this very moment by this foul-smelling red lead paste and a pair of naked eyes.

"I'll get it!" Meng Che reacted extremely quickly, turning around and striding toward the tool cabinet in the corner of the laboratory.

In less half a minute, he brought back a sharp deburring knife and several sheets of black 2000-grit metallographic sandpaper.

Yin Hang placed the aluminum plate on the workbench, took a deep breath, and forcefully suppressed the sense of frustration in his heart. He picked up the deburring knife, his fingers turning slightly white from tension.

He leaned in extremely close, almost pressing his face against the aluminum plate.

The blade cautiously cut into the edge of that through-hole in the upper-left corner, his wrist rotating slightly.

Accompanied by a slight hiss, a hair-thin, silvery-white aluminum shaving curled up and was peeled away.

That was the culprit that had tortured him for three weeks.

Next, he meticulously scraped flat the potential burrs on the edges of the other three through-holes one by one.

But this was not enough.

"Lay the sandpaper flat on that optical glass surface plate," Jiang Lin directed.

Meng Che immediately followed suit.

"Add a few drops of water; water can carry away the cut-off debris and prevent the aluminum powder from scratching the surface a second time."

Yin Hang picked up the aluminum plate, bottom-facing down, and pressed it flatly onto the moistened 2000-grit sandpaper.

He didn't grind randomly, but instead followed Jiang Lin's brief instructions, applying even force with both hands and drawing slow figure-eights on the glass surface plate.

"Swish—swish—swish—"

The subtle sound of friction echoed in the laboratory.

This was a very pure sound of machining, carrying a rhythm that smoothed away trauma.

After grinding for about two minutes, Yin Hang stopped his hands, rinsed the bottom surface thoroughly with absolute ethanol, and finally wiped it dry with a cleanroom wipe.

Re-cleaning the table and re-applying an extremely thin layer of red lead paste.

Yin Hang picked up the aluminum plate once more, repeating the previous actions of suspended dropping and pressing.

This time, when the aluminum plate was flipped over again, the atmosphere in the laboratory noticeably relaxed.

Yin Hang exhaled a long breath of stale air trapped in his chest.

On the bottom surface, there was no longer that kind of extreme polarization.

The area that was originally largely blank now presented four or five relatively evenly distributed red patches.

Although the area was still not large, at least it was no longer a dangerous seesaw supported by only two points.

Jiang Lin looked at those patches, his brows furrowed slightly, but they quickly relaxed again.

If it were in the Wasteland, in that terrible environment where the yaw bearing had to forcefully withstand lateral shear forces in a sandstorm, this kind of contact surface would simply be life-threatening garbage.

He would have to use a scraper, scraping it stroke by stroke, using fifteen years of mastery to trim the entire surface until within every 25-millimeter square area, more than 20 tiny contact points appeared evenly, which would only then meet his perverted precision baseline.

But this was, after all, just a temperature-controlled optical laboratory.

This was just an adapter plate used to temporarily fix a small lens, and it did not need to bear any perverted alternating loads.

Polished to this extent, although far from reaching a perfect plane, it was already enough to eliminate that 0.02-millimeter local high point and eliminate the vast majority of over-constraints and stress concentrations.

That thermodynamic seesaw effect had been greatly weakened.

"It is ready." Jiang Lin nodded. "Prepare for assembly, and pay attention to the sequence; this is more important than polishing."

Yin Hang felt a great sense of relief, washed away the residual red lead oil with alcohol, and carefully placed the aluminum plate back into its original position in the interferometry system.

He picked up the torque-set Allen wrench, preparing to tighten it directly as usual.

"Put down the wrench." Professor Lu Zhixing's voice suddenly turned cold.

Yin Hang's hand shook and stopped mid-air.

"Use your hands." Jiang Lin took a step closer, his eyes staring at the four bolt holes. "First put the four bolts into the holes and tighten them all with your fingers. Only use the pads of your thumbs and index fingers."

Yin Hang did not understand why, but he still followed the instructions, pinching the edge of the screw cap and screwing it down circle by circle.

"Feel the resistance of the thread engagement, screw it all the way down until the bottom surface of the screw just touches the metal surface of the aluminum plate—that is, the moment your finger feels the first trace of obvious resistance—and stop immediately. Do not apply any extra torque, not even a tiny bit." Jiang Lin provided rigorous verbal guidance from the side.

All four bolts entered a standby state.

At this time, the aluminum plate was only loosely fixed.

"Now, pick up the wrench and set the torque value to thirty percent of the design torque."

"Pay attention to the sequence."

Jiang Lin's voice seemed to carry a unique beat, a rhythm he had summarized from countless Wasteland assemblies that conformed to the internal temperament of metal materials.

"Top left, then the diagonal bottom right, then top right, and finally the diagonal bottom left. You must cross-pre-tighten them."

Yin Hang held the wrench and inserted the wrench head into the socket head cap screw at the top left corner.

With a very soft click, the wrench reached the preset tiny torque.

Then bottom right, top right, bottom left.

Four slight clicks sounded in succession.

"Why do it this way?" Meng Che couldn't help asking in a low voice from the side.

"The first round of thirty percent torque is not for locking down, but to let the four bolts enter the stressed state simultaneously." Jiang Lin's eyes did not leave the aluminum plate. "Metal is not a dead object, and the contact surface is not an ideal plane in mathematics. If you lock down one corner right at the beginning, it is equivalent to nailing the error there first. Tightening the other three corners later will only force the plate into a posture with internal stress."

"Cross-pre-tightening is to let the contact surface settle down bit by bit. Thirty percent, seventy percent, full torque—doing it in three rounds is to let the threads, counterbores, contact surface, and the platform below gradually establish the same stress benchmark, rather than letting a certain corner bear all the mistakes for the entire plate first."

"Second round, set to seventy percent of the design torque, with the same diagonal crossing sequence."

Yin Hang executed mechanically; his hands were no longer casual, and his movements became slow and pious.

The click of the wrench became a bit duller, which meant that firm normal constraints were being established between the metal surfaces.

"Third round, design torque, still the crossing sequence."

The four bolts were locked down in turn.

"Finally, recheck it." Jiang Lin said, "Do not apply extra force, just confirm that every bolt trips at the same torque point. Whichever one can still turn means the contact surface has settled down again, and it must be made up to the same state."

But Jiang Lin did not call to stop.

His gaze swept past the side of the aluminum plate, where there was a black coaxial cable used to transmit piezoelectric ceramic drive signals.

Because of the previous disassembly, this cable was now draped somewhat casually over the edge of the aluminum plate.

"Take that wire away." Jiang Lin pointed at the cable. "Fix it again in the adjacent cable management slot and tie it tight with a zip tie. Leave an arc for the wire, and do not let it produce any direct dangling pull on this aluminum plate."

"This wire is very light." Yin Hang subconsciously retorted, but he immediately shut his mouth.

Because he remembered the 0.02 millimeters from just now.

"The gravity of a wire is indeed very small." Jiang Lin looked at him. "But in a sub-nanometer-level interferometer, the slight thermal expansion and contraction of this wire with temperature changes is just a restless rubber band hanging on this structure. It will pull. What you need to do now is to cut off all unnecessary parasitic stress transmission paths."

Yin Hang honestly found a nylon zip tie and properly fixed the cable in the cable slot far away from the optical motherboard, ensuring that the cable routing presented a relaxed U-shape.

The entire process of disassembly, deburring, cleaning, and reassembly actually took nearly forty minutes.

Professor Lu Zhixing, Yin Hang, and Meng Che present all felt as if they had gone through a microscopic surgery that could not tolerate the slightest mistake.

When everything was ready, Yin Hang took two steps back and gave up his position.

Professor Lu Zhixing walked to the front of the main control console and took a deep breath.

"Power on."

Meng Che quickly pressed the row of green buttons on the control cabinet.

"Hum—"

The low roar of the vacuum pump sounded again, and the laser's warm-up indicator light began to flash red.

"Wait for the system thermal balance." Professor Lu Zhixing stared at the screen.

The constant temperature room returned to that drowsy fan hum.

Yet none of the people present felt drowsy.

The system had its original thermodynamic state broken by the previous toss and turn, and it needed some time to absorb the heat generated by the machine running again, thereby re-establishing the locking balance of the interference fringes at the microscopic level.

Time passed minute by minute.

Ten minutes.

Twenty minutes.

Thirty minutes.

On the computer screen, the colorful data stream representing the real-time phase of the interference signal began to roll again like a waterfall.

In the first few minutes, because of the violent fluctuations in the internal temperature gradient and the piezoelectric ceramic searching for the locking point at full scale, the curve oscillated violently, jumping up and down like a crazy roller coaster.

Gradually, as the heat conduction stabilized, the powerful PID control loop began to intervene.

The amplitude of that crazy curve became smaller and smaller, gradually converging, and finally turned into a thin line crawling within a very small range near the baseline.

One hour passed.

This was only enough to cover one and a half periods of the original forty-minute drift, far from enough to serve as a final conclusion.

But it was enough to explain one thing: for the first time, that most glaring low-frequency hump did not appear on time.

The PZT compensation voltage dropped from the previous 80% approaching full scale to small-range fluctuations around 15%.

This wasn't about the paper being saved already.

This meant they had finally found the correct troubleshooting direction.

You must know that over the past three days, no matter how Yin Hang modified the filtering algorithm, that blue curve representing system stability, in the region where the horizontal axis represented smoothing time, would always bulge high like a desperate hump in the low-frequency interval of 10⁻³ to 10⁻⁴ Hz in the frequency domain.

That hump was the ghostly manifestation of the thermal cycle hysteresis effect in the frequency domain.

It declared that the long-term stability of the system was completely finished.

But now.

That solid blue line extending continuously to the right on the screen.

It was as smooth as a sharp sword swung by an unrivaled master, without the slightest hesitation, directly cutting off that damn bulging hump with a single sword stroke.

On the log-log coordinate system, with a standard −1/2 slope, it madly dived all the way toward the bottom right of the chart like a fighter jet that had lost lift.

It directly pierced through the residual baseline that they could never reach no matter how they modified the code or optimized the circuit, plunging deeply into the suffocating low-noise interval.

There were no periodic slow undulations, no low-frequency ghosts, and no hysteresis asymmetry.

At least in this short one-hour data, the main noise terms had retreated back to near photon shot noise, electronic white noise, and residual thermal noise.

In a monitoring window next to it, the mechanical compensation voltage, which originally required the piezoelectric ceramic to output a high voltage of 80% of full scale to forcibly pull it back and resist stubbornly, now stayed quietly and fluctuated in a tiny range of about 15% like an old man who had unloaded a heavy burden.

This indicated that the entire huge interference optical path was already in a stable stressed state at the physical and mechanical underlying architecture.

The electronic system and feedback control loop now only needed to handle the real environmental micro-noise in space with ease, instead of acting like firefighters taking the blame for the constantly twisting microscopic seesaw.

The data not only met the standard.

Moreover, it was a full order of magnitude lower than the long-term residual level required by that sharp-eyed second reviewer of PRL.

This was simply a miraculous number.

"Is the filtering algorithm turned off?" Meng Che's voice trembled slightly.

"Off, it's been off." Yin Hang swallowed a mouthful of saliva and gently tapped the keyboard to call up the background settings. "I swear, this is the sampling data coming straight out of the ADC converter. No moving average, no Kalman Filtering, no fucking software smoothing."

Professor Lu Zhixing did not speak.

He dragged the mouse over and pulled up three windows on the screen.

The leftmost was the original drift chart with a hump from three days ago, the middle was the rough displacement chart magnified and verified by the optical lever principle, and the rightmost was the current reinstalled residual chart with a smooth dive.

The three charts placed side by side had a strong visual impact.

Professor Lu Zhixing slowly straightened his waist.

He knew that this painstaking work was saved.

His youth talent application plan was saved.

More importantly, he saved this multi-million-dollar interferometry system from subsequent meaningless electronic disassembly and destruction due to looking in the wrong direction.

He turned around.

Several students of the research group were on the verge of ecstasy, but Professor Lu Zhixing looked at Jiang Lin, who had quietly retreated to the edge of the optical platform and seemed to be out of the picture ever since the assembly was completed.

Jiang Lin was quietly looking at the downward diving curve on the screen.

There was no surprise in his eyes, only a matter-of-course calmness, as if he had long known where that line would go.

Professor Lu Zhixing's gaze did not look at Jiang Lin's young face, but slowly moved down, falling on Jiang Lin's hands hanging casually at his sides.

That was a pair of very young hands.

The fingers were slender and distinct in joints, with some yellowish thin calluses on the finger pads and the web of the thumb.

The nails were trimmed very neatly, without leaving a single bit of white edge.

They looked clean and tidy, without any of the rough marks common in machining workshops.

But Professor Lu Zhixing was very clear that it was these hands just now that pointed virtually in mid-air and precisely cut off the root of chaotic stress in a microscopic world.

"Have you done precision assembly and adjustment before?" Professor Lu Zhixing's tone carried a hint of probing.

Jiang Lin withdrew his gaze looking at the screen, turned his head, and met Professor Lu Zhixing's gaze.

"Done some rough things, not counting as precision."

"Rough?"

Professor Lu Zhixing couldn't help sneering. There was no malice in this laugh, only a kind of self-mockery of an absurd reality.

"Rough mechanical operations probably couldn't train a person's intuition and muscle memory into the way you were just now. Your feel for the torque wrench just now, and your subconscious reaction to troubleshooting parasitic stress, could never be taught by books."

Jiang Lin's eyelids drooped slightly without answering.

He couldn't possibly say that his so-called roughness came from the Wasteland.

Seeing that he did not speak, Professor Lu Zhixing did not continue to ask.

Having stayed in this circle for a long time, he knew that everyone had their own moat and secrets that could not be put on the table immediately to ask about.

No matter what kind of past this young man in front of him was hiding behind those clean hands, to Professor Lu Zhixing and this precision measurement laboratory facing extreme engineering challenges at all times, he was an extremely precious abnormal variable.

"Yin Hang, Meng Che, you stay here and completely save the data of this past hour. Write a preliminary troubleshooting memo and record the 0.02-millimeter burr and the cable matter faithfully."

Professor Lu Zhixing gave a few instructions and turned his head to look at Jiang Lin.

"For today's matter, on behalf of the research group, I thank you. You saved us at least half a month of blind troubleshooting time and a paper that might have been rejected."

"Can I delay you for some more time to talk in my office? I want to learn more about today's judgments regarding contact stiffness and error propagation."

Jiang Lin nodded.

Returning to the office, Professor Lu Zhixing invited Jiang Lin to sit down and personally poured him a glass of purified water.

Professor Lu Zhixing sat back in his swivel chair, picked up the thick stack of materials Jiang Lin brought over just now, and turned directly to the back part about the derivation of the contact stiffness degradation model.

"Your model, the way you estimate the plastic deformation parameters of micro-asperities—I have looked at the logic, and it is very clever. But there is one thing I want to confirm: when you write the contact stress relaxation function here, you use the form of exponential decay. You said that the time constant of decay is estimated using the thermal diffusion length. Where did you get this cross-border processing method that kneads heat conduction and solid mechanics together? Classical textbooks, or did you derive it yourself?"

"Classical advanced heat conduction textbooks have mathematical ways of handling local hot spots similarly, and I referred to those boundary conditions. But specific to the complex situation of your aluminum-steel contact pair, I made modifications. Because on both sides of the contact surface, the thermal diffusivity of aluminum is extremely large, while that of steel is very small, the difference is too huge. If you directly use the parameters of one side to approximate, the error will be ridiculously large. So I constructed an equivalent thermodynamic boundary and reconstructed the time constant using a weighted average method." Jiang Lin answered impeccably.

"What is the basis for weighting?" Professor Lu Zhixing pursued with extreme speed.

"The proportion of the contact area, specifically, the true microscopic contact area proportion at the yield point." Jiang Lin replied fluently, without even any pause for thought.

"Have you verified the accuracy of this weighting coefficient experimentally?"

"There is no precise validation," Jiang Lin admitted candidly, "I have done a rough mathematical sensitivity analysis. That is, continuously changing the weight coefficients to see the variation range of the model's predicted stiffness degradation results. But at the precision level of the extremely terrible measurement data in my hands, the macroscopic result differences given by different weight coefficients were all buried within the error bars. Therefore, I didn't, and couldn't, further refine it."

"When you made this model, was it ultimately to solve a specific engineering problem, or to fundamentally understand this underlying Physics phenomenon?"

Jiang Lin tilted his head slightly, pondered for a moment, and said, "Both. But in the beginning, it was definitely for an engineering problem; I needed to make a key bearing work in a harsh environment. If it didn't work, the system would collapse. I needed to find the cause and fix it, even if it meant using the ugliest method. Understanding the phenomenon came later. It was because after fixing it, I wanted to know why it happened this way, and whether next time I could predict it in advance from the data before a catastrophic problem occurred."

Professor Lu Zhixing fell silent for a moment before speaking again: "The measurement conditions in that set of appendix data can be said to be appallingly poor, and the instruments are unbelievably old. However, your error analysis was done meticulously, even somewhat harshly. You are clear about exactly where the uncertainty of each step comes from, whether it's sensor drift or environmental white noise. How did you develop this habit?"

It was no wonder Professor Lu Zhixing was surprised.

Many graduate students from prestigious universities nowadays, fed by advanced software, only know how to throw data into a black box to run a p-value, completely lacking the literacy to deeply mine the bottom layer of the error chain.

"Because the data conditions are poor, if the uncertainty is not figured out, there is no way to judge what real information this pile of data actually told me, and what flaws it covered up."

There was a clear self-awareness in Jiang Lin's tone.

"I cannot pretend that uncertainty does not exist and deceive myself. But even more so, I cannot simply throw away this only set of data just because there is uncertainty. I can only honestly list the source of each of its items. Then, on this riddled foundation, I tell as much truth as I can, and never cross the line."

Professor Lu Zhixing did not respond immediately.

He was processing everything that had happened overall today.

Not that chokepoint technical problem—that problem now had a perfect answer, and he had already digested it.

What he was processing now was the person sitting opposite him.

This person came with rigorous data, and the data had unreserved descriptions of limitations.

His model had original derivation, and the source of parameters for each step of the derivation was clearly noted.

Estimated values and measured values were strictly labeled separately, and where he was unsure, he even drew circles with a red pen to actively expose them.

When he was recounting what he had done, he always talked about the mistakes he had made, how long it took to find the cause, and where the compromised Physics boundary lay.

Rather than boasting about how good he was at this like many arrogant geniuses.

This pragmatic, even somewhat pessimistic engineering undertone was unlike any type of student he had ever seen.

Professor Lu Zhixing took a deep breath and continued to interrogate the professional details: "In that set of your data, the proxy quantity of contact stiffness is the indentation area distribution. However, what model did you use for the mathematical mapping relationship between this proxy quantity and the true contact stiffness?"

"The Hertzian contact model, but I made a lot of simplifications," Jiang Lin answered without hesitation, "I assumed the asperities were ideal spheres and mainly underwent elastic deformation; I deliberately ignored the influence of early large-scale plastic deformation and the surface oxide layer."

"Does this crude simplification hold true in your case?" Professor Lu Zhixing's gaze was as sharp as a knife.

"For early shallow contact, it basically holds true," Jiang Lin said, staring fixedly, "However, after dozens of harsh thermal cycles, the contact surface inevitably produced slight macroscopic plastic deformation. At this time, the simplified model began to introduce huge errors. This is the most fragile one in my proxy quantity error chain. On the second paragraph of the third page of the appendix, I specifically stated this point."

Professor Lu Zhixing immediately turned the materials to the appendix and quickly found the paragraph circled with a red pen.

After reading it once, the muscles at the corner of his eyes twitched slightly, and he did not pursue this question any further.

Because Jiang Lin's logical closed-loop was already flawlessly impregnable.

Professor Lu Zhixing paused, leaned forward, looked into Jiang Lin's eyes, and asked the core question: "What do you need?"

Jiang Lin heard the context of this question clearly.

It was not the condescending what reward do you want, but rather, you are doing this difficult thing, what weapons are you lacking?

"I need an absolutely reliable Physics reference plane," Jiang Lin said, his speech accelerating slightly, carrying an undisguised desire, "A calibrated zero-grade granite surface plate, a set of gauge blocks with calibration certificates traceable to the national measurement benchmark, and a dial indicator with micron-level resolution."

"In addition, I also need a place where basic machining can be done. Lathes, milling machines, drilling machines are all fine. I don't need expensive five-axis linkage precision equipment; the most traditional manual lathe will do."

"What do you need these things for?" Professor Lu Zhixing was somewhat puzzled.

This request was both high-end to death and crudely baffling.

"At my previous place, I had three cast iron surface plates used as plane benchmarks, which were scraped to the micron level using the Three-Plate Grinding Method process. However, they have never been truly calibrated by a modern system; I don't know what the true flatness number I scraped with my own hands actually is. I want to use a reliable reference plane to check them, and also to verify whether my grinding method at that time went astray."

Jiang Lin said.

"As for the machining equipment, it's because in the previous harsh environment, I made a lot of very crude transition fixtures. I want to redo them using normal equipment in reality. I want to verify what magnitude the absolute error of that physical feeling about cutting force, feed rate, and metal vibration established in that desperate situation actually is under processing conditions without external interference."

"Where are those three cast iron plates now?" Professor Lu Zhixing, who had been shocked, hurriedly asked.

"In another very far place, they can't be brought over," Jiang Lin replied without changing his expression, "But I can buy raw materials and grind a set in your engineering internship workshop here. Then use the autocollimator and electronic level in the school's metrology room, or find a third-party metrological institution to conduct a formal verification. If your interferometry system can provide a local displacement reference, it can also be used as auxiliary cross-validation."

"The Three-Plate Grinding Method, huh? How many times have you done it?"

As someone with a background in Physics, although not proficient in locksmithing, how could Professor Lu Zhixing not know about this hardcore and most agonizing manual stunt from the early Industrial Revolution.

"I did it for a very long time, until between the three plates under a thin oil film and surface adhesion effect, an obvious fit-retardation appeared, making pushing them apart feel like pulling open an invisible film."

Professor Lu Zhixing gasped and instantly became decisive: "You eliminated a fatal error for our research group, which entirely falls under the scope of basic scientific research training in key laboratories. In return, in the name of the research group leader, I can submit an application for your temporary visit and equipment use to the School of Physics. The reference platform and the engineering workshop, I can help you sort them out."

Saying that, he opened the drawer, took out a School of Physics Temporary Experimental Personnel Filing Form printed with the Jiangcheng University school emblem, picked up a black carbon pen, and prepared to fill it out.

"I know your name, Jiang Lin. Send me your ID number on WeChat later," Professor Lu Zhixing looked at the columns on the form and asked casually, "Where is your current student status information?"

Jiang Lin looked at Professor Lu Zhixing's hand about to put down the pen and replied, "Jiangcheng No. 7 High School's."

Professor Lu Zhixing raised his head with a look of confusion: "No. 7 High School? Is there any key laboratory or school called No. 7 High School in our school or the neighboring University of Science and Technology or University of Technology?"

"It's a high school, Jiangcheng No. 7 High School, senior year."

In the office, it suddenly became frighteningly quiet.

Professor Lu Zhixing's hand holding the pen froze in mid-air. He looked at Jiang Lin with his mouth slightly open, not making a sound for a full half minute.

Just moments ago, Professor Lu Zhixing had deduced countless possible identity backgrounds for Jiang Lin in his mind.

He had guessed that this might be a low-key junior undergraduate student in the Physics Strong Base Class of Jiangcheng University.

It might be a competition student who had been privately mentored for many years in an old professor's underground laboratory.

He had even thought that this might be a child from the family of an employee in a military industry or aerospace research institute, who grew up touching precision equipment as toys in a confidential workshop since childhood.

But he never expected the two words senior year of high school.

It was not because Professor Lu Zhixing looked down on high school students. He had seen extremely smart high school students.

Geniuses who had won gold medals in the International Physics Olympiad, who were early-admitted to the USTC Juvenile Class, or who had self-studied the four major mechanics of undergraduate courses in high school were not legends in this circle, but living reality.

Yet what Jiang Lin displayed just now in the constant-temperature room was simply not just good mathematics or cleverness.

That was a morbid obsession with microscopic contact surfaces, a neurotic sensitivity to the pre-tightening force distribution, and the engineering experience that could only be polished out through continuous repeated hammering over long years.

This extremely aged and extremely rational thing should absolutely not, and could not possibly, grow on a high school student.

You must know that even in the senior year of high school, separated from the true Physics frontier and the deep water area of the industrial system, there are still four years of undergraduate foundation, three years of master's research, and four years of doctoral training in between.

And now, this guy who had just used the clever design of the optical lever principle and the partial differential model of underlying stress hysteresis in the constant-temperature room with million-level equipment to rub the cognition of him—an associate professor, plus a Ph.D. and a master's student—into the ground, turned out to be a high school student who still had to carry his schoolbag back to school tomorrow morning to do Five Years of Gaokao, Three Years of Simulation?

This was not just a simple cognitive dissonance.

It was practically a violent deconstruction of the entire educational values and academic career Professor Lu Zhixing had built over thirty-nine years.

Professor Lu Zhixing felt his breathing become heavy.

However, that perfectly diving Allan variance plot was right there on the computer next door.

That aluminum plate smoothed of 0.02mm burrs was running in the system.

All the logically rigorous conversations that happened in this laboratory today were in his head.

The feeling of being convinced deep inside his own heart was also real.

Jiang Lin looked at Professor Lu Zhixing, who was stunned there, and added a little embarrassedly, "Can I register in the name of a high school student?"

Professor Lu Zhixing closed his eyes fiercely, took a deep breath, and replayed the whole matter today, every micro-expression and every response of Jiang Lin, rapidly in his mind like a movie.

When he opened his eyes again, the shock in the depths of his eyes had been replaced by a wild joy as if unearthing an peerless treasure.

"With this level of engineering intuition, this terrifying knowledge reserve of the error chain, plus what you showed here today, the High School Student Basic Scientific Research and Innovation Ability Observation Program—I will use this special name to submit a special report to the School."

Professor Lu Zhixing quickly put pen to paper on the form, his handwriting flying and dancing.

"You are a minor; I cannot make the final decision on this alone. Parental informed consent, school certificate, laboratory safety training, laser safety training—not a single one can be missing. You can only enter the core equipment area and the engineering workshop accompanied by me or a designated doctoral student."

"No problem, I'll abide by the laboratory rules," Jiang Lin agreed very readily.

In the Wasteland, not following the rules meant not living long.

"There is one more thing that is very important," Professor Lu Zhixing raised his head, his gaze returning to a professor's majesty, "Those physical judgments and troubleshooting logic of yours in the constant-temperature room today, you need to write them into a written report for me."

"The error source of the burrs, the verification method of the optical lever, the alternative hypothesis of hysteresis asymmetry, why you could eliminate the interference of electrical noise at the very first moment—every single point must be written clearly and explicitly."

"Are there format requirements?" Jiang Lin asked.

"No format restriction," Professor Lu Zhixing stared at him, "But the underlying logic must be airtight, so that when I bring it out at the regular meeting, half a word of logical loophole cannot be picked out."

Jiang Lin nodded: "No problem."

Only then did Professor Lu Zhixing pick up his thermos cup again, and for the first time since Jiang Lin entered the door, unscrewed the lid and took a large gulp of warm wolfberry tea.

...

At noon, because time was tight and the task was heavy, lunch was eaten at the Jiangda University small cafeteria.

Jiang Lin didn't care where he ate or what he ate.

After finishing his meal, holding the application material checklist for temporary admission and equipment use for high school student scientific research training of the School of Physics, Jiangcheng University given by Teacher Lu, he prepared to leave.

However, as soon as he came down from upstairs, at the cafeteria entrance, he saw Yao Siyu, a graduate student in Teacher Lu's team, standing there holding a lunch box.

Seeing Jiang Lin come out, Yao Siyu's eyes lit up, and she trotted up to meet him.

"Jiang Lin, is it convenient to add WeChat?" she said quickly, with the exhaustion after staying up late still on her face, "It's not a personal matter. For the subsequent set of raw residual data, I might still need to confirm a few annotations with you. Also, the proxy index you mentioned today, I want to go back and reorganize it into the troubleshooting memo."

Jiang Lin nodded and scanned the code to add.

"Send me a copy of the report, and we'll talk after I finish reading it."

Yao Siyu was startled for a moment, then nodded earnestly: "Okay."

Jiang Lin put away his phone, waved, and then walked away briskly.

All the way, the spring breeze brushed his face, carrying the scent of green grass, fresh and moist.