A Good, Hard Look At Pre-Stressed Concrete

September 29, 2020 by Kristina Panos 43 Comments

From the looks of the average driveway or sidewalk, it may seem as though concrete is just destined to crack. But if concrete is so prone to cracking, how are we able to use it in so many high-stress applications like bridges and skyscrapers? This question came about while I was researching 3D-printed thermite for an article. Thermite is often used in welding railroad tracks, and I linked a video of fresh tracks being welded that had concrete ties. I knew I had to find out how concrete could be made to withstand the pressure of freight trains.

On its own, concrete is brittle and has no give to it at all. But that doesn’t mean it isn’t strong. Although concrete has good compression strength, the tensile strength is quite poor. Around the late 1800s, someone thought to fortify spans of concrete with steel reinforcing bars, better known as rebar. Steel can stretch, adding steel bars gives the concrete some tensile strength to go along with its compressive strength. Rebar also allows for thinner slabs and other members.

Rebar Only Goes So Far

Parking blocks are meant to be replaced occasionally. Image via Checkers Safety

Rebar or mesh-enforced concrete is good for things like parking lot blocks and roads, but it still fails before it ought to. In fact, it usually has to crack before the rebar can chip in any of its tensile strength.

In high-stress concrete applications like bridges and skyscrapers, it’s terrifically important to avoid deflection — that’s when a concrete member flexes and bends under load. Deflection can cause the modern glass skins to pop off of skyscrapers, among other problems.

A solid, rigid bridge is much nicer to walk, drive, and bicycle on than a bridge that sways in the breeze. But how do you do make a rigid bridge? One solution is to apply stresses to the concrete before it ever bears the load of cars and trucks or a steady schedule of freight trains.

Pre-stressed concrete is like rebar-enforced concrete, but with the added power of tension baked in. By adding stress to the concrete before it goes into service, deflection will be reduced or perhaps eliminated altogether. With the addition of tensile strength, more of the concrete’s own strength is able to come into play.

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PC Cases Are Still Stuck In The Dark Ages, But We Can Fix This

September 28, 2020 by Lewin Day 182 Comments

In the dawning of the IBM PC era, the computer case was a heavy, stout thing. These were industrial machines, built with beefy paddle power switches, and weighing as much as a ton of bricks. Painted in only the ugliest beige, they set the tone for PC design for the next couple of decades.

At the turn of the millennium, the winds of change swept through. The Apple iMac redefined the computer as a hip, cool device, and other manufacturers began to reconsider their product aesthetics. Around the same time, the casemodding scene took off in earnest, with adherents building ever wilder battle stations for internet clout and glory.

With all the development that has gone in the last 40 years of the PC platform, we’ve seen great change and improvement in almost every area. But in building a new rig this past month, this writer discovered there’s one element of the modern PC that’s still trapped in the past.

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Exploring The Clouds Of Venus; It’s Not Fantasy, But It Will Take Specialized Spacecraft

September 21, 2020 by Tom Nardi 23 Comments

By now, you’ve likely heard that scientists have found a potential sign of biological life on Venus. Through a series of radio telescope observations in 2017 and 2019, they were able to confirm the presence of phosphine gas high in the planet’s thick atmosphere. Here on Earth, the only way this gas is produced outside of the laboratory is through microbial processes. The fact that it’s detectable at such high concentrations in the Venusian atmosphere means we either don’t know as much as we thought we did about phosphine, or more tantalizingly, that the spark of life has been found on our nearest planetary neighbor.

To many, the idea that life could survive on Venus is difficult to imagine. While it’s technically the planet most like Earth in terms of size, mass, composition, and proximity to the Sun, the surface of this rocky world is absolutely hellish; with a runaway greenhouse effect producing temperatures in excess of 460 C (840 F). Life, at least as we currently know it, would find no safe haven on the surface of Venus. Even the Soviet Venera landers, sent to the planet in the 1980s, were unable to survive the intense heat and pressure for more than a few hours.

While the surface may largely be outside of our reach, the planet’s exceptionally dense atmosphere is another story entirely. At an altitude of approximately 50 kilometers, conditions inside the Venusian atmosphere are far more forgiving. The atmospheric pressure at this altitude is almost identical to surface-level pressures on Earth, and the average temperature is cool enough that liquid water can form. While the chemical composition of the atmosphere is not breathable by Earthly standards, and the clouds of sulfuric acid aren’t particularly welcoming, it’s certainly not out of the realm of possibility that simple organisms could thrive in this CO2-rich environment. If there really is life on Venus, many speculate it will be found hiding in this relatively benign microcosm high in the clouds.

In short, all the pieces seem to be falling into place. Observations confirm a telltale marker of biological life is in the upper levels of the Venusian atmosphere, and we know from previous studies that this region is arguably one of the most Earth-like environments in the solar system. It’s still far too early to claim we’ve discovered extraterrestrial life, but it’s not hard to see why people are getting so excited.

But this isn’t the first time scientists have turned their gaze towards Earth’s twin. In fact, had things gone differently, NASA might have sent a crew out to Venus after the Apollo program had completed its survey of the Moon. If that mission had launched back in the 1970s, it could have fundamentally reshaped our understanding of the planet; and perhaps even our understanding of humanity’s place in the cosmos.

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Targeting Rivers To Keep Plastic Pollution Out Of The Ocean

September 17, 2020 by Lewin Day 49 Comments

Since the widespread manufacture of plastics began in earnest in the early 1950s, plastic pollution in the environment has become a major global problem. Nowhere is this more evident than the Great Pacific Garbage Patch. A large ocean gyre that has become a swirling vortex full of slowly decaying plastic trash, it has become a primary target for ocean cleanup campaigns in recent years.

However, plastic just doesn’t magically appear in the middle of the ocean by magic. The vast majority of plastic in the ocean first passes through river systems around the globe. Thanks to new research, efforts are now beginning to turn to tackling the issue of plastic pollution before it gets out to the broader ocean, where it can be even harder to clean up.
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Otis Boykin’s Precision Passives Propelled The Pacemaker

September 16, 2020 by Kristina Panos 11 Comments

The simplest ideas can be the ones that change the world. For Otis Boykin, it was a new way to make wirewound precision resistors. Just like that, he altered the course of electronics with his ideas about what a resistor could be. Now his inventions are in everything from household appliances and electronics to missile guidance computers.

While we like to geek out about developments in resistor tech, Otis’ most widely notable contribution to electronics is the control unit he designed for pacemakers, which regulate a person’s heartbeat. Pacemakers are a real-time clock for humans, and he made them more precise than ever.

Street Smarts and Book Smarts

Otis Frank Boykin was born August 29th, 1920 in Dallas, Texas to Sarah and Walter Boykin. Otis’ father was a carpenter who later became a preacher. His mother Sarah was a maid, and she died of heart failure when Otis was only a year old.

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GitHub’s Move Away From Passwords: A Sign Of Things To Come?

September 15, 2020 by Maya Posch 69 Comments

Later this month, people who use GitHub may find themselves suddenly getting an error message while trying to authenticate against the GitHub API or perform actions on a GitHub repository with a username and password. The reason for this is the removal of this authentication option by GitHub, with a few ‘brown-out’ periods involving the rejection of passwords to give people warning of this fact.

This change was originally announced by GitHub in November of 2019, had a deprecation timeline assigned in February of 2020 and another blog update in July repeating the information. As noted there, only GitHub Enterprise Server remains unaffected for now. For everyone else, as of November 13th, 2020, in order to use GitHub services, the use of an OAuth token, personal token or SSH key is required.

While this is likely to affect a fair number of people who are using GitHub’s REST API and repositories, perhaps the more interesting question here is whether this is merely the beginning of a larger transformation away from username and password logins in services.

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Floating Spaceports For Future Rockets

September 14, 2020 by Tom Nardi 36 Comments

While early prototypes for SpaceX’s Starship have been exploding fairly regularly at the company’s Texas test facility, the overall program has been moving forward at a terrific pace. The towering spacecraft, which CEO Elon Musk believes will be the key to building a sustainable human colony on Mars, has gone from CGI rendering to flight hardware in just a few short years. That’s fast even by conventional rocket terms, but then, there’s little about Starship that anyone would dare call conventional.

An early Starship prototype being assembled.

Nearly every component of the deep space vehicle is either a technological leap forward or a deviation from the norm. Its revolutionary full-flow staged combustion engines, the first of their kind to ever fly, are so complex that the rest of the aerospace industry gave up trying to build them decades ago. To support rapid reusability, Starship’s sleek fuselage abandons finicky carbon fiber for much hardier (and heavier) stainless steel; a material that hasn’t been used to build a rocket since the dawn of the Space Age.

Then there’s the sheer size of it: when Starship is mounted atop its matching Super Heavy booster, it will be taller and heavier than both the iconic Saturn V and NASA’s upcoming Space Launch System. At liftoff the booster’s 31 Raptor engines will produce an incredible 16,000,000 pounds of thrust, unleashing a fearsome pressure wave on the ground that would literally be fatal for anyone who got too close.

Which leads to an interesting question: where could you safely launch (and land) such a massive rocket? Even under ideal circumstances you would need to keep people several kilometers away from the pad, but what if the worst should happen? It’s one thing if a single-engine prototype goes up in flames, but should a fully fueled Starship stack explode on the pad, the resulting fireball would have the equivalent energy of several kilotons of TNT.

Thanks to the stream of consciousness that Elon often unloads on Twitter, we might have our answer. While responding to a comment about past efforts to launch orbital rockets from the ocean, he casually mentioned that Starship would likely operate from floating spaceports once it started flying regularly:

While history cautions us against looking too deeply into Elon’s social media comments, the potential advantages to launching Starship from the ocean are a bit too much to dismiss out of hand. Especially since it’s a proven technology: the Zenit rocket he references made more than 30 successful orbital launches from its unique floating pad.

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