Solid bulk cargoes – defined as granular materials loaded directly into a ship’s hold – can suddenly turn from a solid state into a liquid state, a process known as liquefaction. And this can be disastrous for any ship carrying them – and their crew. 10 “solid bulk cargo” carriers have been lost at sea each year for the last 10 years. Solid bulk cargoes are typically “2-phase” materials as they contain water between the solid particles. When the particles can touch, the friction between them makes the material act like a solid (even though there is liquid present). But when the water pressure rises, these inter-particle forces reduce and the strength of the material decreases. When the friction is reduced to zero, the material acts like a liquid (even though the solid particles are still present). A solid bulk cargo that is apparently stable on the quayside can liquefy because pressures in the water between the particles build up as it is loaded onto the ship. This is especially likely if, as is common practice, the cargo is loaded with a conveyor belt from the quayside into the hold, which can involve a fall of significant height. The vibration and motion of the ship from the engine and the sea during the voyage can also increase the water pressure and lead to liquefaction of the cargo. When a solid bulk cargo liquefies, it can shift or slosh inside a ship’s hold, making the vessel less stable. A liquefied cargo can shift completely to one side of the hold. If it regains its strength and reverts to a solid state, the cargo will remain in the shifted position, causing the ship to permanently tilt or “list” in the water. The cargo can then liquefy again and shift further, increasing the angle of list. At some point, the angle of list becomes so great that water enters the hull through the hatch covers, or the vessel is no longer stable enough to recover from the rolling motion caused by the waves. Water can also move from within the cargo to its surface as a result of liquefaction and subsequent sloshing of this free water can further impact the vessel’s stability. Unless the sloshing can be stopped, the ship is in danger of sinking.
Tag: science
Recursive parasites
Scientists studying wasps that target oak leaves found that a second parasite, a vine, can get its tendrils into the homes set up by the wasps, called galls, subverting their diversion of the host’s resources. After that, things don’t go so well for the wasp. When the researchers dissected 51 love-vine-infested galls from 1 wasp species, they found that 45% contained a mummified adult wasp, compared with only 2% of uninfested galls. That suggests that the love vine interferes with the wasp’s nutrition such that it develops fully but is not able to leave. And the host tissue within dissected galls was twisted toward the vine’s entry points, hinting that it was co-opting the gall’s nutrients.
Sabercat extinction
Sabercat extinction has been understood in terms of top-down ecological stress, a victim of ‘trophic cascade’, just as the top predators of the ocean today are dying off because populations of prey fishes are collapsing beneath them. The plight of today’s big cats also seems to echo the downfall of Smilodon: we know that leopards, tigers, jaguars and other big cats require large swathes of habitat that are connected through ecological corridors, providing them with plenty of ground to stalk, and enough prey to survive. Decrease the habitat and food supply, and the cats suffer. But what if we could trace the clues back the other way? What if the extinction of Smilodon could help us understand what wiped out so many of the species it relied upon for food? New research on this question could help us untangle the frighteningly mysterious nature of extinction — in the past and future — itself. For now, the exact reason why Smilodon disappeared remains unknown. Loss of food is a likely cause, but that answer only moves the question a step back to why Smilodon’s prey died out. The sabercat was a casualty in a wider extinction at the end of the Pleistocene that marked the end of the Ice Age and the beginning of a world over which our species has disproportionate influence. Some researchers like to call this the Anthropocene, but whether or not such a designation truly fits depends on how long our species lasts. What might the fossil record look like 100m years from now? The Pleistocene extinction could come to shade into the modern biodiversity crisis with little or no break in between. The close of the Ice Age might have been the beginning of a new age, or it could have been one dramatic blip in an ongoing mass extinction, tracking the rise of human dominance. Some of the garbage that ends up preserved in La Brea’s asphalt might help future archaeologists untangle this mystery.
What killed the Dinosaurs?
The greatest area of consensus between the volcanists and the impacters seems to be on what insults to sling. Both sides accuse the other of ignoring data. Each side dismisses the other as unscientific: “It’s not science. It sometimes seems to border on religious fervor, basically”. Both sides contend that the other is so stubborn, the debate will be resolved only when the opposition croaks. “You don’t convince the old people about a new idea. You wait for them to die,” jokes Courtillot, the volcanism advocate, paraphrasing Max Planck. Smit agrees: “You just have to let them get extinct.”
Memory leak debugging
Guided by BLeak, we identify and fix over 50 memory leaks in popular libraries and apps including Airbnb, AngularJS, Google Analytics, Google Maps SDK, and jQuery. BLeak’s median precision is 100%; fixing the leaks it identifies reduces heap growth by an average of 94%, saving from 0.5MB to 8MB per round trip.
Kolmogorov Complexity
Now our understanding of our search for meaning is starting to come together. We abhor randomness and love patterns. We are biologically programmed to find some patterns that explain what they see. But we can never be certain that the pattern we’ve identified is the right one. Even if we could somehow be assured that we haven’t made a mistake, and we are exhibiting a computer-like perfection, there may always still be a deeper truth to unearth. This tension helps drive our love of literature, theater, and the cinema. When we read a novel, or watch a play, the author or director is presenting us with a sequence of events that has a common theme, pattern, or moral. Literature, plays, and the cinema offer us a delightful escape from the usual unintelligible, meaningless chaos that we find in the real world around us. Really good literature goes further, and leaves us with the possibility of many interpretations. We come face to face with the incomputability of the Kolmogorov complexity.
Since time-bounded Kolmogorov complexity is computable, a natural next question is how hard it is to compute. And this is the question that Liu and Pass proved holds the key to whether one-way functions exist. Suppose you’ve set your sights on a less lofty goal than calculating the exact time-bounded Kolmogorov complexity of every possible string — suppose you’re content to calculate it approximately, and just for most strings. If there’s an efficient way to do this, then true 1-way functions cannot exist. In that case, all our candidate 1-way functions would be instantly breakable, not just in theory but in practice. “Bye-bye to cryptography”.
Conversely, if calculating the approximate time-bounded Kolmogorov complexity is too hard to solve efficiently for many strings, then true 1-way functions must exist. If that’s the case, their paper even provides a specific way to make one. The 1-way function that they describe in their paper is too complicated to use in real-world applications, but in cryptography, practical constructions often quickly follow a theoretical breakthrough. And if their function can be made practical, it should be used in preference to the candidate 1-way functions based on multiplication and other mathematical operations.
Ancient Footprints
Dinosaurs, elephants, and giraffes were all exciting enough. More personal than stone tools, more dynamic than skeletal remains, human footprints create an unparalleled link to the distant past. The analysis of preserved human and animal footprints—known as ichnology, from the Greek word for track—allows us to imagine people not so different from us, standing, running, and playing, 100s or 1000s or even millions of years ago. “Tracks are more exciting than body fossils. They can tell a story.”
Hours of 3D photogrammetry work reveal the tracks of ancient humans on the South African coast.
Human tracks encode a startling amount of information, enough for scientists to create a brief, but illuminating, biography of a person or group of people. The average person takes an estimated 224m steps over the course of a lifetime. When preserved, footprints are a library of clues about a human’s activities, speed of travel, height, weight, and sometimes even sex. They are, however, remarkably rare in the archaeological record. In the past few years, researchers have found them in unexpected places scattered around the world: modern beaches. Finding ancient footprints in such a dynamic environment seems counterintuitive. Is there anything more ephemeral, after all, than footprints in the sand? You’d think that the action of waves and wind would wipe footprints away quickly. But, in 2012, massive storms in Wales revealed fossilized forests—and the footprints of a child, facing a prehistoric sea. In 2013, researchers stumbled across the 800 ka tracks left behind by children and adults, a small family perhaps, playing on a windswept English beach. The following year, researchers working on British Columbia’s Calvert Island found footprints dating back to the earliest days of human presence in the Americas. The one thing they all have in common is proximity to the ocean.
2023-02-26: Towards more children in Archaeology
Finding evidence of Ice Age children is difficult. It’s not just that their small, fragile bones are hard to locate. To understand why we forget about them in our reconstructions of prehistory, we also need to consider our modern assumptions about children. Why do we imagine them as ‘naive’ figures ‘free of responsibility’? Why do we assume that children couldn’t contribute meaningfully to society? Researchers who make these assumptions about children in the present are less likely to seek evidence that things were different in the past.
But using new techniques, and with different assumptions, the children of the Ice Age are being given a voice. And what they’re saying is surprising: they’re telling us different stories, not only about the roles they played in the past, but also about the evolution of human culture itself.
Human bones are fragile things, but some are more fragile than others. The larger, denser bones of adults tend to be better preserved in the archaeological record than those of children, whose bones are more like a bird’s than an elephant’s: they are smaller, more porous and less mineralized, lack tensile and compressive strength, and may not be fully fused to their shafts (in the case of long bones). These skeletons are more vulnerable to both sedimentary pressure (when buried underground) and erosion from acidic soil and biodegrading organic matter. This is one of the main reasons why telling the stories of prehistoric children has been so difficult.
Conservation of Threat
as the environment becomes safer we manufacture new threats. To study how concepts change when they become less common, we brought volunteers into our laboratory and gave them a simple task — to look at a series of computer-generated faces and decide which ones seem “threatening.” The faces had been carefully designed by researchers to range from very intimidating to very harmless. As we showed people fewer and fewer threatening faces over time, we found that they expanded their definition of “threatening” to include a wider range of faces. When they ran out of threatening faces to find, they started calling faces threatening that they used to call harmless. Rather than being a consistent category, what people considered “threats” depended on how many threats they had seen lately.
Computation & time travel
Consider a science-fiction scenario wherein you go back in time and dictate Shakespeare’s plays to him. Shakespeare thanks you for saving him the effort, publishes verbatim the plays that you dictated, and centuries later the plays come down to you, whereupon you go back in time and dictate them to Shakespeare, etc. Notice that, in contrast to the grandfather paradox, here there is no logical contradiction: the story as we told it is entirely consistent. But most people find the story “paradoxical” anyway. After all, somehow Hamlet gets written, without anyone ever doing the work of writing it! As Deutsch perceptively observed, if there is a “paradox” here, then it is not one of logic but of computational complexity. Now, some people have asked how such a claim could possibly be consistent with modern physics. For didn’t Einstein teach us that space and time are merely 2 aspects of the same structure? 1 immediate answer is that, even within relativity theory, space and time are not interchangeable: space has a positive signature whereas time has a negative signature. In complexity theory, the difference between space and time manifests itself in the straightforward fact that you can reuse the same memory cells over and over, but you can’t reuse the same moments of time. Yet, as trivial as that observation sounds, it leads to an interesting thought. Suppose that the laws of physics let us travel backwards in time. In such a case, it’s natural to imagine that time would become a “reusable resource” just like space is—and that, as a result, arbitrary PSPACE computations would fall within our grasp. But is that just an idle speculation, or can we rigorously justify it?
Carbon Nanotube Production
Vanderbilt University researchers have discovered a technique to cost-effectively convert carbon dioxide from the air into a type of carbon nanotubes that is “more valuable than any other material ever made.” Carbon nanotubes are super-materials that can be stronger than steel and more conductive than copper. So despite much research, why aren’t they used in applications ranging from batteries to tires? Answer: The high manufacturing costs and extremely expensive price.
The price ranges from $100–200 per kilogram for the “economy class” carbon nanotubes with larger diameters and poorer properties, up to $100K per kilogram and above for the “first class” carbon nanotubes — ones with a single wall, the smallest diameters, and the most amazing properties.
Nanocomp Technologies is producing sheets of carbon nanotubes that measure 1m by 2m and promising slabs 10m2 in area. The first applications will probably be as electrical conductors in planes and satellites to replace copper wire and save weight. Saving weight would save fuel. Nanocomp’s materials possess a unique combination of high strength-to-weight ratio, electrical and thermal conductivity, as well as flame resistance that exceeds those of many other advanced materials by orders of magnitude.
2022-10-28: Behold Carbon Nano Onions
By microwaving fish waste, you can quickly and efficiently create carbon nano-onions (CNOs)—a unique nanoform of carbon that has applications in energy storage and medicine. CNOs are nanostructures with spherical carbon shells in a concentric layered structure similar to an onion. They have “drawn extensive attention worldwide in terms of energy storage and conversion” because of their “exceptionally high electrical and thermal conductivity, as well as large external surface area”
Though CNOs were first reported in the 1980s, conventional methods of manufacturing them have required high temperatures, a vacuum and a lot of time and energy. Other techniques are expensive and call for complex catalysts or dangerous acidic or basic conditions. The newly discovered method requires only 1 step—microwave pyrolysis of fish scales extracted from fish waste—and can be done within 10 seconds.How exactly the fish scales are converted into CNOs is unclear, though the team thinks it has to do with how collagen in the fish scales can absorb enough microwave radiation to quickly increase in temperature. This leads to pyrolysis, or thermal decomposition, which causes the collagen to break down into gasses. These gasses then support the creation of CNOs.
Gregor J. Rothfuss 