Д о п о л н и т е л ь н ы е т е к с т ы. для перевода со словарем HOW 3D PRINTERS WORK
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AT FIRST, 3D printing was known as stereolithography, a process invented in 1986 by Chuck Hull of 3D Systems. Variations of this process are still used. It begins, like all 3D printing, with software that takes a series of digital slices through a computer model of an object. The shape of each slice is used selectively to harden a layer of light-sensitive liquid, usually with ultraviolet light, to form the required shape. After each layer has been made, the build tray lowers by a fraction, another layer of liquid is added and the process is repeated until the object is complete.
Many other approaches have since been developed. Laser-sintering involves zapping layers of powdered plastic or metal with a laser to harden the powder in some places, but not others. Other machines use an electron beam in a similar way. An alternative process melts a metallic powder as it is deposited. This can be used to repair worn parts, such as turbine blades. Some machines operate a bit like 2D inkjet printers, jetting light-sensitive liquid materials to form layers and then hardening them. Some machines can print a dozen different materials in a single pass of the print head.
One of the most popular techniques is fused deposition modelling (FDM), which is akin to a computer-controlled glue gun (pictured below). A heated nozzle extrudes a filament of thermoplastic, which sets as it cools. Multiple heads can extrude different colours. FDM is the mechanism used in many of the small 3D printers used by hobbyists, some of which now cost less than $1,000. More capable 3D printers cost tens of thousands of dollars, and big industrial systems, like the laser-sintering machines capable of printing aerospace parts in titanium, cost as much as $1m.
It is the light we think we see that counts. Optical illusions designed to seem brighter than they are make your pupils constrict a little more. This suggests that we have evolved systems for anticipating dazzling light to protect our eyes.
Our pupils’ fast response to light appears to occur even without input from the brain. For example, it is seen in people with damage to the visual cortex. Appearances can be deceptive, though.
Bruno Laeng of the University of Oslo in Norway measured tiny changes in pupil size as volunteers viewed various illusions that were all identical in brightness, though did not look so. If light levels alone dictated pupil size, they would have reacted identically whichever image a person viewed. Instead, people’s pupils constricted more when they viewed the illusions designed to appear brightest.
What’s surprising is that even something as simple as how bright we think our environment is will be affected by our expectations.
Previous studies snow that the brain controls pupil size in other situations: our pupils dilate when we make decisions, for instance.
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At the moment, none of us can reliably improve the biological hardware involved in memory, though it is comparatively easy to damage it via drug and alcohol abuse or injury. So-called “smart drugs” and neurochemical agents claim to improve the functioning of our memory circuits, but although some treatements have been shown to help people with impaired memory due to brain damage or illness, their effect seem to be unreliable and insubstantial in healthy people.
We can ensure that we make the best possible use of our memory by living and eating healthily, and by using a range of mnemonics, some of which have been known for thousands of years. Most mnemonics are based on the principles of reduction or elaboration. As the name suggests, a reduction code reduces the information to be remembered, through an acronym like the words Roy G Biv, which helps children to remember the colours of the rainbow. An elaboration code increases the information to be retained, perhaps through a catchy phrase like “Richard of York gave battle in vain”, which again is used to remember a rainbow’s colours. There are some more detailed systems too, like peg word system. This involves assigning a memorable rhyming word to a number: “one is bun”, “two is shoe”, “three is tree”. A list can then be remembered by linking each item in the sequence to each peg word, through a memorable image.
There are many other ways of increasing you chances of recall, such as actively elaborating or rehearsing information, organizing it in a new way, or attempting to explain what you are studying to someone else. Timing your study so that you attempt to remember a piece of information after steadily increasing intervals can also help to lay the foundations for effective long-term recall.
That Greek fire was one of the most terrifying weapons ever made is known to everyone. But the secret ingredients and technology required to make the incendiary substance “Greek fire” has defeated scientific minds ever since the 12th century.
Greek fire was a flaming mixture fired from the ships of the Byzantine Empire from the 7th century. The fire would cling to flesh and was impossible to extinguish with water. This deadly concoction was created by a family of chemists and engineers from Constantinople, and the secret recipe died with them.
John Haldon from Princeton University has a hunch though: he suspects it was a petroleum-based liquid stuff modified to increase its potency. He thinks the key ingredients were a highly flammable light crude oil called naphtha, and pine resin, which is sticky and would have made the mixture burn hotter and longer.
But there was more to the mystery of Greek fire that its ingredients alone. “Whenever enemies captured elements of the equipment, they just weren’t able to work out how to use it to recreate the same effects,” explains Haldon. Historians have the same problem, but they’ve deduced that a bronze pump probably pressurized heated oil which was then ejected through a nozzle and ignited. The reconstruction was built for a National Geographic TV programme, using a mixture of light crude oil and pine resin. Their fame destroyed a ship in minutes.
Uncertainties remain because the secret was never written down, but the power of Greek fire is beyond doubt. “It was definitely an effective weapon of terror,” says Haldon.
A solid solution
LITHIUM-ION batteries are hot stuff. Affordable, relatively lightweight and packing a lot of energy, they are the power source of choice for everything from mobile phones to electric cars. Unfortunately, the heat can be more than figurative. Occasionally, such batteries suffer malfunctions that lead to smoke, flames and even explosions. In gadgets, such meltdowns can be distressing and dangerous. In aircraft, they can be fatal. Earlier this year airlines grounded their entire fleet of Boeing’s next-generation 787 passenger jet after the lithium-ion batteries installed in two planes caught fire. Last month they have been permitted back in the air after being retrofitted with a protection system in the form of a tough steel box that vents directly outside in the event of a fire.
A more comforting solution, of course, would be to build a lithium-ion battery that could not burst into flames in the first place. Katie Zhong at Washington State University might have just such a device. For the last few years, she has been working on battery technology for flexible and bendable electronic gadgets. By blending a polymer called polyethylene oxide (PEO) with natural soy protein, she had made a solid electrolyte for lithium ion batteries that could be bent or stretched to twice its normal size without affecting its performance.
Like all batteries, lithium-ion rechargeables consist of two electrodes separated by an electrolyte. In a typical lithium-ion cell, the electrolyte is a solution of lithium salts and organic solvents. Charging drives lithium ions from the electrolyte into a graphite anode. On discharge, the reverse happens, with a balancing flow of electrons through the device being powered.
This process is not perfectly efficient, however, and any energy left over is released as heat. While managing that heat is usually straightforward, the risks rise when something goes wrong. Overcharging the battery or applying too high a charging voltage can cause the electrodes to become dangerously reactive. Moreover, short circuits can occur if the battery is contaminated with tiny metal particles during manufacturing, has microscopic flaws that allow lithium crystals to build up, or is physically damaged.
All of these situations can generate more heat than the battery is capable of dissipating, ultimately leading to a thermal runaway in which the electrolyte releases gases or even ignites. Once lit, a lithium-ion fire is hard to extinguish: a single 787 battery accidentally ignited during testing in 2006 sparked a fire that destroyed a 10,000-square-foot (925-square-metre) building in Arizona.
In the wake of such incidents Dr Zhong realized that her biomaterial electrolyte might also be suitable for use in aircraft. The soy-based electrolyte is reassuringly inert, thermally stable and not prone to explosion. As a solid, it resists the kind of physical damage that can cause short circuits. It is also lighter than an equivalent liquid electrolyte, and does not require the same heavy protection against corrosive leaks (or explosions).
But there are reasons why solid electrolytes are not already used. It is usually much harder for ions to travel through solids than liquids, which reduces the amount of power they can deliver. It can also be tricky for a solid electrolyte to form a good contact with the electrodes to transfer those ions. Ms Zhong’s bio-electrolyte makes progress on both counts.
First, the soy protein is chemically denatured to disrupt its folded structure and make it attractive to the lithium ions. It is then blended with the PEO to form an amorphous structure with uneven distribution of electrons, which facilitates the movement of ions. The tacky biomaterial also adheres easily to the electrodes.
Ms Zhong’s battery is still some way from take-off. While its ionic conductivity is much better than other solid electrolytes, it lags that of most liquid electrolytes. With funding from Washington State’s Joint Centre for Aerospace Technology Innovation, Dr Zhong is now developing an electrolyte with, she claims, the performance of a liquid and the safety of a solid. If that proves to be the case, Ms Zhong should expect to find aircraft manufacturers blazing a trail to her door. Hopefully, not literally.
STEGANOGRAPHY, the art of hiding things in plain sight, is a trick as old as espionage. Unlike its cousin, cryptography, which makes no attempt to disguise the existence of a message, but rather hides its meaning, a steganographic message need not be encyphered. What it does need to be is invisible – at least to those who are not the intended recipients. And that, in the modern world of the internet, is a crucial distinction. A censor can block a message he mistrusts, even if he cannot read it, thus putting the onus on the recipient to justify both the message and the fact it is encrypted. A well-crafted steganographic message, though, will never come to the censors’ attention in the first place. Which is the purpose of Collage, a system devised by Nick Feamster and his colleagues at the Georgia Institute of Technology.
Traditional steganography hides its message as, say, every 20th word in a letter, or as the colour of every hundredth pixel in an electronic image. Sophisticated analysis of such things might, though, notice something odd and thus flag a document for closer examination. Collage escapes notice by dividing the message into pieces, and then hiding these in electronic files posted to public websites, such as Twitter and YouTube.
Scattering the message among multiple files and websites offers a number of advantages. For instance, the small amount of data in each file makes it difficult for a censor to notice anything odd unless all traffic on the network is subjected to advanced analysis techniques. Though possible in theory, the cost and effort of doing so makes this unfeasible in practice. More importantly, Collage’s design allows reconstruction of the original message even if only 60-80% of the files hiding it are recovered. Thus, even if a censor manages to block some of the files, users are still able to communicate.
To pull a message together requires the execution of what Dr Feamster refers to as a “task sequence” – a series of actions, chosen not to arouse suspicion, that must be performed to locate the files hiding the message. For example, if images of the Himalayas are used as cover media, the associated task sequence might be to search specific sites for images tagged with the words “mountain” and “glacier” and download a defined number of images in a set amount of time.
Although much of Collage’s design focuses on avoiding detection, it also provides a measure of deniability should detection occur. The cover media used to hide data and the actions performed to locate and recover messages mimic those of innocent users, allowing Collage users to argue that they were unaware of the presence of hidden data. Collage also aims to mimic the traffic patterns of legitimate users, so that digital fingerprints which may suggest illegal behaviour are not produced.
Finally, hiding messages among otherwise-legitimate content makes it difficult for a censor to block communication effectively without also causing significant disruption to innocuous users. For governments trying to walk the fine line between access and censorship, this reluctance to block large quantities of legitimate content in the hope of also blocking prohibited content can be crucial. Even if the hidden messages are known to be present, there may be little the censor can do about it.
 PCB – Printed Circuit Board – печатная плата
 potting (n) – зд. герметизация
 abandon (v) – отказываться от, прекращать что-либо делать
 printout (n) – распечатка (из компьютера)
 package (n) – зд. пакет офисных программ
 annular magnet – кольцевой магнит
 laminated (a) – листовой
 challenge (n) – вызов, запрос
 retina (n) – сетчатка глаза
 social pattern – социальный уклад
 CCD – charge-couple device – прибор с зарядовой связью
 skirmish (n) – перестрелка, схватка
 algae (n) - водоросли
 ski run – горнолыжная трасса
 indiscretion (n) – неосмотрительность, неосторожность
 scanning pattern – развертка
 exploring element – развертывающий элемент
 cheerleader (n) - обычно участник группы поддержки
 intricate (a) – сложный, замысловатый
 all but – почти, едва не
 isoperimetric quotient – изопериметрическое частное
 Holy Grail – Святой Грааль (чаша Грааля)
 owe (v) – быть обязанным (чем-либо), приписывать (открытие)
 Министерство бизнеса, инноваций и ремесел Великобритании
 Макронутриенты (питательные вещества, необходимые для жизнедеятельности организма – белки, жиры, углеводы)
 spawn [spɔːn] (v) – порождать
 recipe for disaster – верный путь к беде, катастрофе
 onset (n) – наступление, начало, возникновение
 Министерство окружающей среды, продовольствия и сельского хозяйства
 toss (v) – бросать, кидать, швырять
 crops (n, pl) – зерновые культуры
 livestock (n) – домашний скот
 obesity (n) – ожирение, тучность
 "углеродный след" (выброс диоксида углерода в атмосферу, связанный с деятельностью отдельного человека или организации: например, в результате поездки на автомобиле, полёта на самолёте, производства товаров)
 mnemonics (n) - мнемоника, мнемотехника (совокупность приёмов и способов, облегчающих запоминание)