An Introduction to Blindfolded Cubing
Author: phy东西 Reviewer: 丛雨 To most people and novice cubers, blindfolded solving looks like an extraordinary feat, and it has long attracted a great deal of attention. I have even been asked, “Hey, can you do that thing where you solve a Rubik’s Cube with your eyes closed?” In reality, blindfolded solving is not as mysterious as it seems. This article explains its basic logic without going too deeply into specific methods. I am not an expert blindfolded solver, so there will inevitably be omissions; I hope readers will bear with me. Every algorithm mentioned here can be entered in the Moves field at https://alg.cubing.net/ for a demonstration. When entering them, pay attention to the difference between Chinese and English punctuation. We will begin with two forms of notation: [A:B] a ...
India's Lunar Landing Fails, but the Search at the Moon's South Pole Continues
Author: 一毫秒的永恒 If everything had gone to plan, India's Pragyan rover would have emerged from the Vikram lander, as shown, and spent 14 Earth days exploring the Moon | credit: ISRO In the early hours of September 7, 2019, Beijing time, contact was lost with the Vikram lander aboard Chandrayaan-2, the second lunar probe developed by the Indian Space Research Organisation (ISRO), at an altitude of only 2.1 kilometers above the Moon. India had hoped to make history as the fourth country, after the United States, Russia, and China, to achieve a soft lunar landing and the first to land at the Moon’s south pole. The failure dealt a severe blow to the country’s confidence. The Beresheet lander built by the Israeli nonprofit SpaceIL, introduced in the preceding article, had likewise crashed du ...
Why a Rubik's Cube with One Twisted Corner Cannot Be Solved
Author: phy东西 Reviewed by: A Millisecond of Eternity When many people first learn to solve a 3×3 Rubik’s Cube, they reach the top layer, run into a case they do not know how to handle, and twist a few corner pieces into place. But if we accidentally twist a single corner, the top layer may take on a configuration we have never seen before. This raises a question: why does twisting one corner make the cube impossible to solve? To answer it, we first need to define a quantity for the cube: corner orientation. Diagram of Rubik's Cube orientations. The letters abbreviate face names—for example, U stands for Up, the top face. | Credits: wikiHow Most solvers begin with white on the bottom, and the standard color scheme places yellow opposite white. We therefore adopt the following conve ...
Behind Smart Dragon-1's Successful Maiden Flight—Eighteen Months of Relentless Work
Author: Millisecond Reviewed by: Dongda Launch At 12:11 p.m. on August 17, 2019, the Smart Dragon-1 (SD-1) carrier rocket was launched successfully from the Jiuquan Satellite Launch Center and placed three satellites into their planned orbits in a “one rocket, three satellites” mission. This was China’s first commercial space launch conducted entirely under a commercial model. Its success opened a new chapter in the country’s commercial space sector. Recent developments show China’s commercial space sector beginning to take off. One month before Smart Dragon-1’s maiden flight, China’s iSpace became the first private Chinese company to place a satellite into its planned orbit. Only a week before the Smart Dragon launch, another Chinese company, LinkSpace, conducted a test flight and ...
Immunity in Five Minutes | How Do Antibodies Keep Up with Change?
Author: 神州 Reviewer: 东达 We know that evolution results from the combined effects of genetic mutation and natural selection. If we ask which living things mutate fastest—using Schrödinger’s much-debated idea that life “feeds on negative entropy,” since there is still no universally accepted definition of life, though that is not our subject here—bacteria and viruses are obvious candidates, even if the status of viruses as living things remains disputed. They are small, reproduce quickly, and in some cases carry genetic material that is structurally unstable. Many of them also cause disease in plants and animals, so we continually develop drugs to destroy them. Yet the rapid reproduction and high mutation rates of some bacteria and viruses allow drug-resistant individuals or strains to ...
Artificial Intelligence — An Intuitive Introduction
Author: 面皮 (Mepy) Reviewer: 东达 Left: people who know nothing about AI think it will take over the world. Right: my AI neural network identifies a cat as a dog. Artificial intelligence, or AI, is the attempt to reproduce aspects of human intelligence by artificial means. Those means are mainly mathematical and involve many different formulas. We generally call these methods “algorithms.” Imitation Before we can imitate human intelligence, we need to understand how human intelligence processes a problem. Consider the task of recognizing handwritten digits. First, a person receives an image through the eyes—the two crooked handwritten digits shown on the right, for example. Neurons then carry that visual information to the brain’s processing centers. Finally, the brain assigns meani ...
The Life Cycle of a Typhoon
Author: 阿白特尔 Everything has a life cycle, and typhoons are no exception. In this article, we will follow a typhoon through its birth, growth, maturity, and eventual demise. The birth of a typhoon A typhoon is a tropical cyclone that forms in the northwestern Pacific. Tropical cyclones develop over many of the world’s oceans. Those in the eastern Pacific and North Atlantic are called hurricanes; those in the Indian Ocean and South Pacific are called cyclones; and those in the northwestern Pacific are called typhoons. Despite the different names, they form and operate through the same mechanisms and belong to the same type of weather system. How, then, is a tropical cyclone born? Across the vast tropical ocean, intense sunlight has warmed a deep layer of seawater. Water evaporates r ...
A Few Facts About Typhoons
Author: Guanfu · Juntian Every summer and autumn, the northwestern Pacific near China produces many violent storms known as typhoons. Some dissipate over the sea, while others make landfall and bring fierce winds and torrential rain. Where do these typhoons come from, where do they go, and why do they affect China so profoundly? Today, I will offer a brief introduction to typhoons. What is a typhoon? In essence, a typhoon is a tropical cyclone: as the name suggests, a vortex formed by rotating tropical air. Tropical cyclones can be divided by wind strength into tropical storms, severe tropical storms, typhoons, and other categories. How Does a Typhoon Form? Three conditions are required for a typhoon to form. The first is moisture: the ocean provides an inexhaustible supply of w ...
How Do We Measure the Distances to Stars?
Author: Star Life Reviewer: 阿白特尔 When we look up at the night sky under good conditions, we can see a sky full of stars. To understand these celestial objects, people observe and measure them, then use the resulting data in theoretical calculations to reach the conclusions they seek. The branch of astronomy concerned with observing stars, planets, deep-sky objects, and other bodies in the universe to obtain the quantities needed for such calculations is called astrometry. Today, let us look at how astronomers measure the distances to stars. We know that stars lie at different distances from the Sun, but all of them are extremely far away. Ordinary units of length used on Earth are therefore impractical for stellar distances, so we use other units instead. One is the light-year, defin ...
Theory in Natural Science, Seen Through Chemistry
Theory in Natural Science, Seen Through Chemistry Author: Dclean Reviewers: 黍离, 白書, and 一毫秒的永恒 Human understanding of nature begins with the observation of natural phenomena. The immediate impressions formed by those observations became some of the earliest “knowledge” in human history. In pursuit of deeper understanding, people gradually classified, organized, and connected that knowledge through logic. Out of this process came the first rudiments of “theory.” This article discusses how science understands theory, the place of theory in the natural sciences, and its relationship with practice. Part I | How Disciplines Differ: Subject Matter and Method We often ask what really distinguishes physics from chemistry. We also encounter claims that chemistry is merely a branch of physi ...