Late December in Huizhou brought one cold front after another.
The laboratory, located two floors underground in Keda’s Institute of Applied Physics, had no windows. It was illuminated by several rows of cool white fluorescent lights.
A costly vacuum chamber testing apparatus occupied the center of the lab.
Intricate pipelines, thick load-bearing alloy supports, and a dense web of sensor wires formed what looked like a giant metal spiderweb, tightly enveloping the core instrument.
Two mobile whiteboards stood against a wall, covered in partial differential equations, matrix derivations, and Fourier transform expansions written in black marker. Some areas had been erased and rewritten so many times they were now just dark, messy smudges.
PhD student Zhao Peng clutched a broken whiteboard marker, his brow furrowed in concentration. He stared intently at the last equation on the board, motionless for what felt like an eternity.
Nearby, another PhD student, Zheng Nan, walked over holding two disposable paper cups of freshly made instant coffee.
He handed one cup to Zhao Peng and took a large gulp from his own, hissing as the hot liquid burned his tongue.
"Old Zhao, take a break."
Zheng Nan glanced at the whiteboard.
"We checked the boundary conditions for this set of partial differential equations three times last night. We didn’t find any holes in the derivation."
Zhao Peng took the cup but didn’t drink. He irritably tossed the marker onto a table and ran a hand through his hair in frustration.
"If the derivation is solid, then how do you explain the data on the monitor?"
Zhao Peng spun around and pointed at a monitor on a console nearby.
A green, real-time data curve scrolled slowly to the left across the screen.
It was the background noise data from inside the vacuum chamber. According to their theoretical calculations, the line should have been perfectly smooth and straight, with fluctuations of no more than 0.5 percent.
But now, a distinct, sawtooth-like spike appeared on the green line at regular intervals.
Zhao Peng walked over to the monitor and tapped his finger on the jarring spikes on the screen.
"This background noise is drifting way too predictably. Fifty hertz. A very stable, periodic, low-frequency interference peak at 50 Hz. It’s stuck to our valid signal like glue, and no amount of software filtering can get it off."
Zheng Nan came over too. He stared at the screen for a moment before sighing and hazarding a guess.
"Power supply ripple? Or maybe a bad ground? Fifty hertz is the exact AC frequency for the mains electricity in our country. Could the electromagnetic shielding on one of the power cords have degraded, causing a magnetic flux leakage?"
"I took a Gauss meter yesterday afternoon and measured the magnetic field around the entire machine, inch by inch."
"The magnetic shielding is perfectly intact. The chassis’s ground resistance is well below the standard value, and we’ve even added a top-of-the-line active filter to the power supply. We’ve cut off every possible physical path for electromagnetic interference."
"Then that’s just bizarre."
Zheng Nan set down his paper cup and put his hands on his hips.
"If we’ve ruled out electromagnetic interference, what else could it be? Quantum fluctuations on a macroscopic scale could never manifest with such a large amplitude, let alone at a fixed frequency."
The two theoretical physics doctoral students, from one of the nation’s top universities, were plunged into profound self-doubt.
They had already pulled several all-nighters over this background noise issue, trying to find a solution in electromagnetic field theory, quantum mechanical wave equations, and even complex signal processing algorithms. All they wanted was to write a piece of code to filter out this 50-hertz ghost.
"The weighting in the algorithm must be wrong."
Zhao Peng gritted his teeth and turned back to the whiteboard.
"Let’s change the window function for the Fourier transform. We can try a Hamming window and set a much stricter cutoff frequency for the low-frequency component."
The two gathered around the whiteboard again, picked up their markers, and began a new round of derivations.
Meanwhile, less than five meters away, Wang Dayong sat at a metal table.
The underground lab was a bit stuffy, so he had casually pushed his sleeves up his arms.
A copy of *Materials Physics* lay open on the table. Beside it was a stack of scratch paper. The top sheet was covered in pencil drawings: various crude force-body diagrams—their arrows, however, were exceptionally clear—and a few scattered equations.
Dayong twirled a ballpoint pen, silently listening to Zhao Peng and Zheng Nan’s conversation.
As a student in the Prodigy Class, he naturally recognized the long partial differential equations on the whiteboard. He also fully understood the mathematical logic behind their attempt to sever the specific frequency signal at the software level.
But he thought, ’His seniors were probably a little muddled from all the late nights.’
He had just caught a number.
Fifty hertz.
Dayong stopped twirling his pen.
’Fifty hertz.’ That number didn’t require any complex analysis in his mind. ’The standard operating frequency for all AC motors in the country was 50 hertz.’
He closed his copy of *Materials Physics* and stood up. Without disturbing the two seniors locked in their fierce debate, he walked around the console and headed for the communal storage shelves against the wall.
The shelves were a chaotic mess of spare parts, wires, and shared tools.
Dayong rummaged through a pile of junk and pulled out a palm-sized scrap of high-density, shock-absorbing rubber. He also grabbed a wrench.
Carrying these two items, Dayong walked over to the massive vacuum chamber.
The equipment’s operating noise was a chaotic mix of the WHOOSH from the ventilation ducts and the WHIR of the cooling fans.

Comments

Loading...