Acme Shern

Freedom is always free will
腊肉共和国
广场上福尔马林侵泡的腊肉已经遗臭半个世纪
传统工艺制作的腊肉永远飘香世界

[Math Files @Math_files]

When two heavy metal balls collide, their energy is concentrated in a very small area. The temperature can become high enough to burn through paper.

To make the reaction hotter, one ball can be covered with rust, which is iron oxide. The other ball is wrapped in aluminum foil. When the balls collide, the impact can provide enough heat to start a thermite reaction.

In this reaction, aluminum reacts with the iron oxide. It produces aluminum oxide, iron, and a large amount of additional heat. The molten material produced can reach temperatures above 4,500°F (about 2,500°C).

This is an example of an exothermic redox reaction.

[Dr. M.F. Khan @Dr_TheHistories]

During WWI, some British and American warships were painted in wild patterns of contrasting stripes and geometric shapes. Known as “dazzle camouflage,” the designs were not intended to hide the ships at all. Instead, they were meant to confuse German U-boat crews trying to target them.

Submarine crews had to estimate a ship’s distance, speed, and direction before firing a torpedo. The unusual patterns broke up the outline of a vessel, potentially making it harder to tell which way it was moving or even distinguish its bow from its stern.

Thousands of ships received dazzle patterns during the war, with many given their own unique designs. Although historians still debate how effective the technique actually was, it produced some of the most distinctive-looking warships ever sent to sea.

The idea is most closely associated with British artist Norman Wilkinson, who proposed dazzle camouflage in 1917. Rather than making ships less visible, Wilkinson believed confusing a submarine crew's perception could make accurate torpedo targeting more difficult.

#drthehistories

[Wonder of Science @wonderofscience]

Wave tank showing the impact of coastal defences on flood risk.

📽: JBA Trust

[Analysis Fact @AnalysisFact]

Why is cos(200!) harder to compute than log(200!)?

https://t.co/TBtLVxRML3

[Amazing Physics @amazing_physics]

This is so important! It's a 'Heimlich Maneuver' and everyone should know it!

[易富贤Yi Fuxian《大国空巢》 @fuxianyi]

2017年我在北京大学的研讨会上发言指出中国人口存在严重水分，这是惊天大新闻。研讨会邀请了二十多家中国大陆媒体和香港《南华早报》，凤凰网直播。但是大陆媒体对我的发言无感，是《南华早报》报道出来，然后《金融时报》《纽约时报》《华盛顿邮报》《费加罗报》等数十家国际主流媒体报道。

[易富贤Yi Fuxian《大国空巢》 @fuxianyi]

《当代中国评论》 2026 夏季刊的“学者专辑”专栏发表我的5篇文章：
1、人口数据：国运所系，决策所依
2、2000 年中国人口普查：数据造假始末
3、2010、2020 年普查：篡改如故
4、出生数和教育数据的循环上调
5、户籍人口、分娩和死亡数据的失真
下面是第2篇

[Mens_Corner__ @Mens_Corner__]

This would have kept me occupied for the summer as a child

[Fermat's Library @fermatslibrary]

FUN FACT: a toilet roll that looks half used has only 38% of the paper left

[Julia Gomez @MaureenNeesp6k]

Prove that

[Interesting things @awkwardgoogle]

bro unlocked a feeling he didn't know existed

[Time Capsule Tales @timecaptales]

Home video footage taken by Eva Braun, Adolf Hitler's mistress, at the Eagle's Nest in the Bavarian Alps, 1940s.

[Fermat's Library @fermatslibrary]

John Tukey the Fast Fourier Transform (FFT) inventor, who coined both "bit" and "software" died exactly 26 years ago today.

The Fast Fourier Transform (FFT), one of the most important algorithms in signal processing and data analysis, was introduced by Tukey & Cooley in 1965.

In 1805, Gauss - studying the orbits of asteroids Pallas and Juno - came up with a method to interpolate their trajectories from discrete samples. What he came up with was mathematically very close to the modern FFT but Gauss never published that work, and didn’t analyze its computational complexity. It predated even Fourier’s 1822 work on heat diffusion - but without the framing or generalization that Cooley & Tukey would bring 160 years later.

In 1965, Cooley & Tukey published their now-famous algorithm that reduced the cost of computing a Discrete Fourier Transform from 𝑂(𝑛²) to 𝑂(𝑛 log⁡𝑛). This leap made real-time signal processing and digital media compression feasible.

From radio telescopes to JPEGs, from audio codecs to quantum mechanics - the FFT is everywhere. It’s one of the most important (and elegant) algorithms of the 20th century - rooted in the genius of Gauss, but brought to life in the computer age.

[Dreams N Science @dreamsNscience]

Brand new baby kangaroo 🦘, smaller than a jelly bean!

It's blind, deaf and has no fur yet. Arms, legs & take are all fused to body…
Over the next 5 to 9 months this baby will fully develop inside its mom's pouch before coming out and hopping around the world...

🎥 animaledventures

[Cosmos Archive @cosmosarcive]

A Riemannian metric tensor is the mathematical tool that tells us how to measure distances and angles on curved surfaces and spaces.

In flat space, measuring distance is straightforward. But when space is curved, the rules change from point to point. The Riemannian metric tensor, written as ds² = gᵢⱼ dxⁱ dxʲ, provides the local geometry needed to calculate lengths, angles, areas, and volumes accurately.

This idea became the foundation of modern differential geometry and later helped Einstein describe gravity as the curvature of spacetime itself.

[Dreams N Science @dreamsNscience]

🌊 Meet the ultimate reef badass: The Neon Sea Slug (Nembrotha kubaryana)

No shell.
No armor.
No speed.
And yet… nothing dares to eat it.

Why? This nudibranch is a master of chemical warfare. It hunts toxic sea squirts (ascidians) that other fish won’t touch, steals their powerful toxins, and stores them in its own body. When threatened, it releases a slimy, nasty mucus loaded with those stolen weapons.
Predators take one bite and nope out immediately.
Nature’s version of “I’m not fast, I’m poisonous.” 😎

🎥 naturesdeepsecret

[Cosmos Archive @cosmosarcive]

Tensor calculus is the language that lets mathematics work on curved surfaces, spacetime, and complex geometries.

• Tensor
T^(i₁...iₘ)_(j₁...jₙ)

A mathematical object that keeps its meaning even when coordinates change. It generalizes scalars and vectors.

• Metric Tensor
gᵢⱼ = eᵢ · eⱼ

Measures distances and angles in a space. It defines the geometry locally.

• Connection (Christoffel Symbol)

Γᵏᵢⱼ = ½ gᵏˡ (∂ᵢgⱼˡ + ∂ⱼgᵢˡ − ∂ˡgᵢⱼ)

Describes how vectors change as they move through curved space.

• Covariant Derivative

∇ₖTⁱⱼ = ∂ₖTⁱⱼ + ΓⁱₖˡTˡⱼ − ΓˡₖⱼTⁱˡ

Extends differentiation so it remains valid in curved coordinates and curved spaces.

• Einstein Field Equation

Gᵢⱼ = Rᵢⱼ − ½gᵢⱼR = (8πG/c⁴)Tᵢⱼ

Relates the curvature of spacetime to the distribution of matter and energy.

From measuring distances and angles to describing gravity itself, tensor calculus provides the mathematical framework behind differential geometry, general relativity, continuum mechanics, and much of modern physics.

[SKG @sonukg4india]

The figure of mathematics

[Interesting World @_fluxfeeds]

They built a creative ball run entirely out of sand at the beach. So cool!

📹John A. Bandstra

[Math Files @Math_files]

Karl Marx attempted to disprove the concept of the derivative.