APC Science Union · Online Library

Author: 赖渊   An Android app called “For the Best One,” with the package name com.sgzh.dt, recently spread like wildfire online. Universities across the country were said to have been hit, leaving victims distraught in what became known as the “September 27 app” incident. Online rumors even claimed that merely installing the app would leave harmful files behind after uninstallation, causing endless trouble.   Could it really be that powerful? Did it somehow have even higher privileges than TWRP??   In the spirit of scientific rigor, I tracked down this so-called “Sounds of Nature” APK to find out exactly what it did.   To understand how an APK works, we first have to strip off its “outer clothing.” Only by examining the code underneath can we make sense of how it operates.   Developers o ...

Author: Congyu   Across the ages, the Sun, Moon, and stars have stirred the imagination and inspired poets and writers. Let us explore the poetry in the night sky—and the night sky in poetry. “The Fisherman's Pride” Li Qingzhao The sky meets waves of cloud joined with the dawn mist; the River of Stars begins to turn, and a thousand sails dance. My dreaming soul seems to return to Heaven's court. I hear Heaven speak, asking kindly where I am bound. I answer that the road is long and daylight is fading; though I have studied poetry, my startling lines are of no use. The great roc now rises on a wind of ninety thousand li. Wind, do not cease—carry my reed boat to the three immortal isles.   When a poet known for restrained, delicate verse writes with grandeur and abandon, the result is a w ...

Author: 神州 Reviewer: A Millisecond of Eternity   In “Five-Minute Immunology: How Do Antibodies Adapt?”, we caught a glimpse of a few of the immune system’s many mechanisms. Now let’s take a closer look at another part of that system.   Last time, we saw how important antibodies are to immunity. But antibodies cannot do every job on their own. They usually bind to antigens, neutralizing their toxicity or keeping them from attaching to cells. Antibodies can also clump antigens together so that phagocytes can engulf them. Against an intact pathogen such as a bacterium, however, binding to antigens on its membrane does not kill the whole cell outright. That job calls for help from another part of the immune system: the complement system.   Unlike an antibody, complement is not a single large ...

Author: phy Dongxi Reviewer: Congyu   To most noncubers and beginners, solving a cube blindfolded looks like an extraordinary feat, so it has always attracted plenty of attention. I have even been asked, “Hey, can you do that thing where you solve a Rubik’s Cube with your eyes closed?” Blindfolded solving is not as mysterious as it seems, however. This article explains the basic idea without going too deeply into any particular method. I am not an expert blindfolded solver, so I may miss a few details; please treat this as an overview.   Every algorithm in this article can be entered in the Moves field at https://alg.cubing.net/ for a demonstration. Be sure to distinguish Chinese punctuation from English punctuation when typing. We will begin with two pieces of notation: [A:B] and [A,B]. ...

Author: A Millisecond of Eternity 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, India lost contact with Vikram, the lander carried by Chandrayaan-2—the second lunar probe developed by the Indian Space Research Organisation (ISRO)—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. Instead, the failure dealt a severe blow to the country’s confidence. The previous article described a similar fate for Beresheet, the lander built by the Israeli nonprofit Space ...

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 by hand. 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 will therefore use the foll ...

Author: Millisecond Reviewed by: Dongda Liftoff   At 12:11 p.m. on August 17, 2019, the Smart Dragon-1 (SD-1) carrier rocket lifted off successfully from the Jiuquan Satellite Launch Center, placing 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, and its success opened a new chapter in the country’s commercial space sector.   Recent developments show that China’s commercial space sector is beginning to take off. One month before Smart Dragon-1’s maiden flight, iSpace became the first private Chinese company to place a satellite into its planned orbit. Just a week before the Smart Dragon launch, another Chinese company, LinkSpace, conducted a test flight an ...

Author: Shenzhou Reviewer: Dongda   We know that evolution results from the combined effects of genetic mutation and natural selection. If we ask which living things mutate fastest, bacteria and viruses are obvious candidates. Here I am using Schrödinger’s much-debated idea that life “feeds on negative entropy”; there is still no universally accepted definition of life, but that is not our subject. The status of viruses as living things also remains disputed. Bacteria and viruses are small, reproduce quickly, and in some cases carry genetic material that is structurally unstable. Most 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 indi ...

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 effort to imitate aspects of human intelligence by artificial means. Those means are largely mathematical and involve many different formulas. We generally call the resulting methods “algorithms.” Imitation   Before we can imitate human intelligence, we need some idea of how people process a problem. Take the task of recognizing handwritten digits.   First, the eyes receive an image, such as the two crooked handwritten digits shown on the right. Neurons carry that visual information to the brain’s processing centers, and the brain assigns meaning to what it sees.   In short, a person rea ...

Author: Abaiter   Everything has a life cycle, and a typhoon is no exception. This article follows a typhoon from birth through growth and maturity to its eventual demise. The birth of a typhoon   A typhoon is a tropical cyclone that forms in the western North 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, cyclones; and those in the western North Pacific, typhoons. The names differ, but these storms form and function through the same mechanisms and belong to the same class of weather system. So how is a tropical cyclone born?   Over the vast tropical ocean, intense sunlight warms a deep layer of seawater. Water evaporates rapidly from the warm surface, ...