Oct 19, 2017

Six degrees of separation: Why it is a small world after all

It's a small world after all.
It's a small world after all -- and now science has explained why.

A study conducted by the University of Leicester and KU Leuven, Belgium, examined how small worlds emerge spontaneously in all kinds of networks, including neuronal and social networks, giving rise to the well-known phenomenon of "six degrees of separation."

Many systems show complex structures, of which a distinctive feature is small-world network organization. They arise in society as well as ecological and protein networks, the networks of the mammalian brain, and even human-built networks such as the Boston subway and the World Wide Web.

The researchers set out to examine whether this is a coincidence that such structures are so wide-spread or is there a common mechanism driving their emergence?

A study recently published in Scientific Reports by an international team of academics from the University of Leicester and KU Leuven showed that these remarkable structures are reached and maintained by the network diffusion, i.e. the traffic flow or information transfer occurring on the network.

The research presents a solution to the long-standing question of why the vast majority of networks around us (WWW, brain, roads, power grid infrastructure) might have a peculiar yet common structure: small-world topology.

The study showed that these structures emerge naturally in systems in which the information flow is accounted for in their evolution.

Nicholas Jarman, who recently completed his PhD degree at the Department of Mathematics, and is first author of the study, said: "Algorithms that lead to small-world networks have been known in scientific community for many decades. The Watts-Strogatz algorithm is a good example. The Watts-Strogatz algorithm, however, was never meant to address the problem of how small-world structure emerges through self-organisation. The algorithm just modifies a network that is already highly organised."

Professor Cees van Leeuwen, who led the research at KU Leuven said: "The network diffusion steers network evolution towards emergence of complex network structures. The emergence is effectuated through adaptive rewiring: progressive adaptation of structure to use, creating short-cuts where network diffusion is intensive while annihilating underused connections. The product of diffusion and adaptive rewiring is universally a small-world structure. The overall diffusion rate controls the system's adaptation, biasing local or global connectivity patterns, the latter providing a preferential attachment regime to adaptive rewiring. The resulting small-world structures shift accordingly between decentralised (modular) and centralised ones. At their critical transition, network structure is hierarchical, balancing modularity and centrality -- a characteristic feature found in, for instance, the human brain."

Dr Ivan Tyukin from the University of Leicester added: "The fact that diffusion over network graph plays crucial role in keeping the system at a somewhat homeostatic equilibrium is particularly interesting. Here we were able to show that it is the diffusion process, however small or big gives rise to small-world network configurations that remain in this peculiar state over long intervals of time. At least as long as we were able to monitor the network development and continuous evolution."

Alexander Gorban, Professor in Applied Mathematics, University of Leicester commented: "Small-world networks, in which most nodes are not neighbours of one another, but most nodes can be reached from every other node by a small number of steps, were described in mathematics and discovered in nature and human society long ago, in the middle of the previous century. The question, how these networks are developing by nature and society remained not completely solved despite of many efforts applied during last twenty years. The work of N. Jarman with co-authors discovers a new and realistic mechanism of emergence of such networks. The answer to the old question became much clearer! I am glad that the University of Leicester is a part of this exciting research."

From Science Daily

New tyrannosaur fossil is most complete found in Southwestern US

Toe bones, the upper jaw and snout of the fossilized remains of a tyrannosaur skeleton found in Grand Staircase-Escalante National Monument. The skeleton is the most complete of its kind found in the Southwest United States.
A remarkable new fossilized skeleton of a tyrannosaur discovered in the Bureau of Land Management's Grand Staircase-Escalante National Monument (GSENM) in southern Utah was airlifted by helicopter Sunday, Oct 15, from a remote field site, and delivered to the Natural History Museum of Utah where it will be uncovered, prepared, and studied. The fossil is approximately 76 million years old and is most likely an individual of the species Teratophoneus curriei, one of Utah's ferocious tyrannosaurs that walked western North America between 66 and 90 million years ago during the Late Cretaceous Period.

"With at least 75 percent of its bones preserved, this is the most complete skeleton of a tyrannosaur ever discovered in the southwestern US," said Dr. Randall Irmis, curator of paleontology at the Museum and associate professor in the Department of Geology and Geophysics at the University of Utah. "We are eager to get a closer look at this fossil to learn more about the southern tyrannosaur's anatomy, biology, and evolution."

GSENM Paleontologist Dr. Alan Titus discovered the fossil in July 2015 in the Kaiparowits Formation, part of the central plateau region of the monument. Particularly notable is that the fossil includes a nearly complete skull. Scientists hypothesize that this tyrannosaur was buried either in a river channel or by a flooding event on the floodplain, keeping the skeleton intact.

"The monument is a complex mix of topography -- from high desert to badlands -- and most of the surface area is exposed rock, making it rich grounds for new discoveries, said Titus. "And we're not just finding dinosaurs, but also crocodiles, turtles, mammals, amphibians, fish, invertebrates, and plant fossils -- remains of a unique ecosystem not found anywhere else in the world," said Titus.

Although many tyrannosaur fossils have been found over the last one hundred years in the northern Great Plains region of the northern US and Canada, until relatively recently, little was known about them in the southern US. This discovery, and the resulting research, will continue to cement the monument as a key place for understanding the group's southern history, which appears to have followed a different path than that of their northern counterparts.

This southern tyrannosaur fossil is thought to be a sub-adult individual, 12-15 years old, 17-20 feet long, and with a relatively short head, unlike the typically longer-snouted look of northern tyrannosaurs.

Collecting such fossils from the monument can be unusually challenging. "Many areas are so remote that often we need to have supplies dropped in and the crew hikes in," said Irmis. For this particular field site, Museum and monument crews back-packed in, carrying all of the supplies they needed to excavate the fossil, such as plaster, water and tools to work at the site for several weeks. The crews conducted a three-week excavation in early May 2017, and continued work during the past two weeks until the specimen was ready to be airlifted out.

Irmis said with the help of dedicated volunteers, it took approximately 2,000-3,000 people hours to excavate the site and estimates at least 10,000 hours of work remain to prepare the specimen for research. "Without our volunteer team members, we wouldn't be able to accomplish this work. We absolutely rely on them throughout the entire process," said Irmis.

Irmis says that this new fossil find is extremely significant. Whether it is a new species or an individual of Teratophoneus, the new research will provide important context as to how this animal lived. "We'll look at the size of this new fossil, it's growth pattern, biology, reconstruct muscles to see how the animal moved, how fast could it run, and how it fed with its jaws. The possibilities are endless and exciting," said Irmis.

Read more at Science Daily

DNA Reveals Link Between Saber-Toothed Cats and Domestic Felines

Reconstructed skeleton of a Saber-tooth Cat (Smilodon californicus)
Saber-toothed cats were among the animal kingdom’s most formidable predators. Their sharp, dagger-like teeth could grow up to seven inches long, and were likely used to slay everything from enormous woolly mammoths to rhinos.

Their evolutionary history has been shrouded in mystery, but a new genetic analysis published in the journal Current Biology reveals many surprising finds. One is the link between these stealthy carnivores and animals that are now residing in many households the world over.

“The two saber-toothed cat mitochondrial lineages we investigated — Smilodon and Homotherium — diverged from all living cat-like species around 20 million years ago,” lead author Johanna Paijmans told Seeker, clarifying that the big, ancient cats were indeed related to today’s common domesticated cats.

Paijmans, a researcher at the University of Potsdam’s Institute for Biochemistry and Biology, has always been interested in extinct mammal lineages. When she was asked to perform DNA analysis on saber-tooth cat remains starting about 5 years ago, she jumped at the chance.

The story behind this particular study began long before then, however.

“It all started with the recovery of a 28,000-year-old Homotherium fossil from the North Sea by Jelle Reumer and colleagues in 2000,” Paijmans explained.

Artist depiction of a Homotherium
Homotherium became extinct in Africa about 1.5 million years ago. It was thought to have gone extinct in Europe 300,000 years ago, so scientists were puzzled by the estimated age of the North Sea fossil.

Paijmans, senior author Michael Hofreiter, and their team analyzed this big cat’s complete mitochondrial genome and compared it to that of Smilodon, the world’s best-known saber-toothed cat that became extinct around 10,000 years ago.

“Our results prove that Homotherium did exist in Europe around 28,000 years ago,” Paijmans said.

“With the current knowledge,” she continued, “it’s not clear whether Homotherium did exist (in Europe) between 300,000 and 30,000 years ago at very low population densities, or if Homotherium re-dispersed from North America during the Late Pleistocene after the earlier populations had already gone extinct.”

The date of Homotherium’s presence in Europe opens up yet another intriguing mystery.

“When the first anatomically modern humans migrated to Europe, there may have been a saber-toothed cat waiting for them,” she said.

There is no question that Neanderthals and other early hominids in Europe and Asia lived in regions where saber-toothed cats lurked.

A few years ago, a team of archaeologists working at the Schöningen site in north-central Germany found saber-toothed cat remains next to an ancient stash of weapons. They included several wooden spears, a lance, a double-pointed stick and another stick that was burnt.

It is then possible that early humans waged battles with saber-toothed cats, attempting to either kill or scare them off with torches and their weapons. Since both humans and these predators were drawn to caves, their paths could easily have crossed often, with each group going after similar prey — not to mention each other.

Saber-toothed cats might have even affected early human migration routes, but more evidence is needed to clarify how our human ancestors could have interacted with these fierce felines.

Paijmans said we need to re-think how and where Homotherium lived during the Late Pleistocene, as it occurred in Europe much later than we previously thought. “This,” she said, “can open up new questions about its extinction that can be addressed in future studies.”

In short, it is now possible that anatomically modern humans migrating from Africa could have killed off this species of saber-toothed cat, and possibly others.

A homotherium fossil recovered from the North Sea
Yet another surprising finding from the study is the conclusion that Smilodon and Homotherium were not very closely related.

“In terms of their mitochondrial DNA, these two saber-toothed cats are more distant from each other than tigers are from housecats,” Paijmans said.

After the cats diverged from their common ancestor, they traveled and evolved into distinct forms. Nonetheless, they shared the similar, very toothy dentition that was lost when they went extinct.

Read more at Seeker

Dog Facial Expressions Are Directed at Humans

Brinks the pit bull sits at home smiling at the camera, taken in New York, August 2016.
Few can resist dogs when they raise their inner brows, making their eyes appear to be larger and like those of a human baby who is sad and desiring attention. A study published a few years ago even found that shelter dogs that produced this pathetic facial expression were consistently adopted faster than those that did not.

Dog owners might do well to watch out for this powerful look, because new research suggests that canines tailor their facial expressions for human viewers, and may even intentionally manipulate us with them. 

“There is quite a bit of research showing that human attention affects dog behavior. Our study is one of them,” lead author Juliane Kaminski of the University of Portsmouth told Seeker.

Kaminski, along with colleagues Jennifer Hynds, Paul Morris and senior author Bridget Waller, came to their conclusions after studying 24 beloved family dogs: 13 males and 11 females of various breeds and ages. Before testing started, each dog was allowed to familiarize itself with the human experimenter and the quiet room in which the testing was conducted.

The dogs were next individually brought to the room to a predetermined spot. Each dog was attached to a lead while a female experimenter positioned herself in front of the canine and behaved according to certain conditions. In some instances, she was attentive and holding up food treats that all of the dogs loved. In others, she was attentive, but had no food, or she simply ignored the dog altogether.

As all of these conditions were enacted, a video camera recorded the dogs’ faces. Their facial movements were then analyzed via the Facial Action Coding System (FACS), which was first developed for humans. It identifies observable facial changes associated with underlying muscle movements, permitting an objective, reliable, and standardized measurement of facial movements.

Kaminski and her team found that the dogs produced significantly more facial movements when the experimenter was facing them than when not. Surprisingly, the presence of food had no effect.

Dogs therefore are not only sensitive to a human’s attention when producing facial expressions, but they also appear to be intentionally using these subtle — and sometimes not so subtle — movements to communicate with the viewer.

The findings, published in the journal Scientific Reports, provide evidence that facial expressions of dogs are not always inflexible and involuntary displays reflecting their emotions. Instead, they also often appear to be used for communication, and likely manipulation, too.

“Humans also have the ability to move facial muscles both voluntarily and spontaneously,” Waller said. “So, in some situations we can control our muscles very carefully, and in others, perhaps when we are overcome with emotion, it can be very difficult.”

She added, “In dogs, it is possible that voluntary movement of facial muscles evolved later and in response to selection pressures during domestication.”

Most mammals have a fairly similar set of facial muscles, she explained, but humans and dogs have a particularly complex network of muscles that are capable of producing very slight, as well as very specific, movements. Dogs have some movements that are uncannily similar to those of humans — and their babies.

“But they also have different movements, like ear movements, that humans don’t have,” Waller said. “Other apes, like chimpanzees, also don’t have many ear movements, but numerous monkey species do.”

Mimi the chimpanzee at Chimp Eden in South Africa
The dogs in the study, such as Dusky the basenji and Paul the golden retriever, exhibited an impressive number of expressions. These included pulling their lip corners towards their ears, dropping their jaws, showing their tongues, puckering their lips and much more.

In some cases, the expressions might have been learned from humans. In others, the expressions could hold meanings that are more dog-centric, as for visual cues using additional parts of their body. For example, dogs often lower their front two paws in an unmistakable bow when they want to play.

It could be that dogs use different facial expressions when communicating with other dogs, but the authors are not sure.

“We do not have a lot of research looking at the sensitivity of dogs to other dogs’ attention,” Kaminski said. “We know dogs follow other dogs’ gazes, so they seem to be sensitive to other dogs’ line of sight.”

The researchers suggest it’s possible that horses and goats also attempt to communicate with humans using facial expressions, given that these animals tend to be sensitive to human gazes and levels of attention.

Read more at Seeker

Oct 18, 2017

Petals produce a 'blue halo' that helps bees find flowers

Ursinia speciosa is a member of the Daisy family. The region at the base of the petals contains a dark pigment, but appears blue due to the presence of disordered floral nanostructures on the cell surface.
Latest research has found that several common flower species have nanoscale ridges on the surface of their petals that meddle with light when viewed from certain angles.

These nanostructures scatter light particles in the blue to ultraviolet colour spectrum, generating a subtle effect that scientists have christened the 'blue halo'.

By manufacturing artificial surfaces that replicated 'blue halos', scientists were able to test the effect on pollinators, in this case foraging bumblebees. They found that bees can see the blue halo, and use it as a signal to locate flowers more efficiently.

While the ridges and grooves on a petal surface line up next to each other "like a packet of dry spaghetti," when analysing different flower species the researchers discovered these striations vary greatly in height, width and spacing -- yet all produce a similar 'blue halo' effect.

In fact, even on a single petal these light-manipulating structures were found to be surprisingly irregular. This is a phenomenon physicists describe as 'disorder'.

The researchers conclude that these "messy" petal nanostructures likely evolved independently many times across flowering plant species, but reached the same luminous outcome that increases visibility to pollinators -- an example of what's known as 'convergent evolution'.

The study was conducted by a multidisciplinary team of scientists from the University of Cambridge's departments of plant sciences, chemistry and physics along with colleagues from the Royal Botanic Gardens Kew and the Adolphe Merkele Institute in Switzerland.

The findings are published today in the journal Nature.

"We had always assumed that the disorder we saw in our petal surfaces was just an accidental by-product of life -- that flowers couldn't do any better," said senior author Prof Beverley Glover, plant scientist and director of Cambridge's Botanic Garden.

"It came as a real surprise to discover that the disorder itself is what generates the important optical signal that allows bees to find the flowers more effectively."

"As a biologist, I sometimes find myself apologising to physicist colleagues for the disorder in living organisms -- how generally messy their development and body structures can seem."

"However, the disorder we see in petal nanostructures appears to have been harnessed by evolution and ends up aiding floral communication with bees," Glover said.

All flowering plants belong to the 'angiosperm' lineage. Researchers analysed some of the earliest diverging plants from this group, and found no halo-producing petal ridges.

However, they found several examples of halo-producing petals among the two major flower groups (monocots and eudicots) that emerged during the Cretaceous period over 100 million years ago -- coinciding with the early evolution of flower-visiting insects, in particular nectar-sucking bees.

"Our findings suggest the petal ridges that produce 'blue halos' evolved many times across different flower lineages, all converging on this optical signal for pollinators," said Glover.

Species which the team found to have halo-producing petals included Oenothera stricta (a type of Evening Primrose), Ursinia speciosa (a member of the Daisy family) and Hibiscus trionum (known as 'Flower-of-the-hour').

All the analysed flowers revealed significant levels of apparent 'disorder' in the dimensions and spacing of their petal nanostructures.

"The huge variety of petal anatomies, combined with the disordered nanostructures, would suggest that different flowers should have different optical properties," said Dr Silvia Vignolini, from Cambridge's Department of Chemistry, who led the study's physics team.

"However, we observed that all these petal structures produce a similar visual effect in the blue-to-ultraviolet wavelength region of the spectrum -- the blue halo."

Previous studies have shown that many species of bee have an innate preference for colours in the violet-blue range. However, plants do not always have the means to produce blue pigments.

"Many flowers lack the genetic and biochemical capability to manipulate pigment chemistry in the blue to ultraviolet spectrum," said Vignolini. "The presence of these disordered photonic structures on their petals provides an alternative way to produce signals that attract insects."

The researchers artificially recreated 'blue halo' nanostructures and used them as surfaces for artificial flowers. In a "flight arena" in a Cambridge lab, they tested how bumblebees responded to surfaces with and without halos.

Their experiments showed that bees can perceive the difference, finding the surfaces with halos more quickly -- even when both types of surfaces were coloured with the same black or yellow pigment.

Using rewarding sugar solution in one type of artificial flower, and bitter quinine solution in the other, the scientists found that bees could use the blue halo to learn which type of surface had the reward.

"Insect visual systems are different to human ones," explains Edwige Moyroud, from Cambridge's Department of Plant Sciences and the study's lead author. "Unlike us, bees have enhanced photoreceptor activity in the blue-UV parts of the spectrum."

"Humans can identify some blue halos -- those emanating from darkly pigmented flowers. For example the 'black' tulip cultivar, known as 'Queen of the night'."

"However, we can't distinguish between a yellow flower with a blue halo and one without -- but our study found that bumblebees can," she said.

Read more at Science Daily

Scientists dig into the origin of organics on dwarf planet Ceres

SwRI scientists are studying the geology associated with the organic-rich areas on Ceres. Dawn spacecraft data show a region around the Ernutet crater where organic concentrations have been discovered (background image). The color coding shows the surface concentration of organics, as inferred from the visible and near infrared spectrometer. The inset shows a higher resolution enhanced color image of the Ernutet crater acquired by Dawn’s framing camera. Regions in red indicate higher concentration of organics.
Since NASA's Dawn spacecraft detected localized organic-rich material on Ceres, Southwest Research Institute (SwRI) has been digging into the data to explore different scenarios for its origin. After considering the viability of comet or asteroid delivery, the preponderance of evidence suggests the organics are most likely native to Ceres.

"The discovery of a locally high concentration of organics close to the Ernutet crater poses an interesting conundrum," said Dr. Simone Marchi, a principal scientist at SwRI. He is discussing his team findings today at a press conference at the American Astronomical Society's 49th Division for Planetary Sciences Meeting in Provo. "Was the organic material delivered to Ceres after its formation? Or was it synthesized and/or concentrated in a specific location on Ceres via internal processes? Both scenarios have shortfalls, so we may be missing a critical piece of the puzzle."

Ceres is believed to have originated about 4.5 billion years ago at the dawn of our solar system. Studying its organics can help explain the origin, evolution, and distribution of organic species across the solar system. The very location of Ceres at the boundary between the inner and outer solar system and its intriguing composition characterized by clays, sodium- and ammonium-carbonates, suggest a very complex chemical evolution. The role of organics in this evolution is not fully understood, but has important astrobiological implications.

"Earlier research that focused on the geology of the organic-rich region on Ceres were inconclusive about their origin," Marchi said. "Recently, we more fully investigated the viability of organics arriving via an asteroid or comet impact."

Scientists explored a range of impact parameters, such as impactor sizes and velocities, using iSALE shock physics code simulations. These models indicated that comet-like projectiles with relatively high impact velocities would lose almost all of their organics due to shock compression. Impacting asteroids, with lower incident velocities, can retain between 20 and 30 percent of their pre-impact organic material during delivery, especially for small impactors at oblique impact angles. However, the localized spatial distribution of organics on Ceres seems difficult to reconcile with delivery from small main belt asteroids.

"These findings indicate that the organics are likely to be native to Ceres," Marchi said.

From Science Daily

Ancient preen oil: Researchers discover 48-million-year-old lipids in a fossil bird

48-million-year old bird fossil excavated at the “Messel Pit“ in Germany. Markings show the uropygial gland.
As a rule, soft parts do not withstand the ravages of time; hence, the majority of vertebrate fossils consist only of bones. Under these circumstances, a new discovery from the UNESCO World Heritage Site "Messel Pit" near Darmstadt in Germany comes as an even bigger surprise: a 48-million-year old skin gland from a bird, containing lipids of the same age. The oldest lipids ever recorded in a fossil vertebrate were used by the bird to preen its plumage. The study is now published in the scientific journal Royal Society Proceedings B.

Birds spend a large amount of time preening their plumage. This makes sense, since the set of feathers adds to each bird's particular appearance, isolates and enables them to fly. In this preening ritual, the uropygial gland, located at the lower end of the bird's back, plays an important role. It produces an oily secretion used by the birds to grease their plumage in order to render it smoother and water-repellent.

Together with a group of international colleagues, Dr. Gerald Mayr, head of the Ornithology Section at the Senckenberg Research Institute, now discovered the oldest occurrence of such preen oils in birds known to date. With an age of 48 million years, this ancient preen oil constitutes a small scientific sensation. "The discovery is one of the most astonishing examples of soft part preservation in animals. It is extremely rare for something like this to be preserved for such a long time," says Mayr.

The organic materials that the soft parts consist of usually decompose within decades, or even just a few years. Several-million-year-old feathers and fur remnants are only known from a small number of fossil sites to date, including the oxygen-poor oil shale deposits of the Messel fossil site. This site also yielded the uropygial gland and the contained lipids examined in the course of this study.

"As shown by our detailed chemical analysis, the lipids have kept their original chemical composition, at least in part, over a span of 48 million years. The long-chain hydrocarbon compounds from the fossil remains of the uropygial gland can clearly be differentiated from the oil shale surrounding the fossil," explains Mayr. The analysis offers proof that the fossil artifact constitutes one of the oldest preserved uropygial glands -- a suspicion which had already been suggested by the arrangement at the fossil bird skeleton, albeit not finally confirmed.

To date, it is not clear why the lipids from the uropygial gland were able to survive for so long. It is possible that hey hardened into nore decomposition-resistant waxes under exclusion of oxygen. In addition, the researchers assume that one of the properties of the preen oil played a role that is still shown by modern birds today -- its antibacterial components. They may have been the reason that after the bird's death only few bacteria were able to settle in, preventing the full-on decomposition.

Read more at Science Daily

Filling the early universe with knots can explain why the world is three-dimensional

This is a computer graphic showing the kind of tight network of flux tubes that the physicists propose may have filled the early universe.
The next time you come across a knotted jumble of rope or wire or yarn, ponder this: The natural tendency for things to tangle may help explain the three-dimensional nature of the universe and how it formed.

An international team of physicists has developed an out-of-the-box theory which proposes that shortly after it popped into existence 13.8 billion years ago the universe was filled with knots formed from flexible strands of energy called flux tubes that link elementary particles together. The idea provides a neat explanation for why we inhabit a three-dimensional world and is described in a paper titled "Knotty inflation and the dimensionality of space time" accepted for publication in the European Physical Journal C.

"Although the question of why our universe has exactly three (large) spatial dimensions is one of the most profound puzzles in cosmology ... it is actually only occasionally addressed in the [scientific] literature," the article begins.

For a new solution to this puzzle, the five co-authors -- physics professors Arjun Berera at the University of Edinburgh, Roman Buniy at Chapman University, Heinrich Päs (author of The Perfect Wave: With Neutrinos at the Boundary of Space and Time) at the University of Dortmund, João Rosa at the University of Aveiro and Thomas Kephart at Vanderbilt University -- took a common element from the standard model of particle physics and mixed it with a little basic knot theory to produce a novel scenario that not only can explain the predominance of three dimensions but also provides a natural power source for the inflationary growth spurt that most cosmologists believe the universe went through microseconds after it burst into existence.

The common element that the physicists borrowed is the "flux tube" composed of quarks, the elementary particles that make up protons and neutrons, held together by another type of elementary particle called a gluon that "glues" quarks together. Gluons link positive quarks to matching negative antiquarks with flexible strands of energy called flux tubes. As the linked particles are pulled apart, the flux tube gets longer until it reaches a point where it breaks. When it does, it releases enough energy to form a second quark-antiquark pair that splits up and binds with the original particles, producing two pairs of bound particles. (The process is similar to cutting a bar magnet in half to get two smaller magnets, both with north and south poles.)

"We've taken the well-known phenomenon of the flux tube and kicked it up to a higher energy level," said Kephart, professor of physics at Vanderbilt.

The physicists have been working out the details of their new theory since 2012, when they attended a workshop that Kephart organized at the Isaac Newton Institute in Cambridge, England. Berera, Buniy and Päs all knew Kephart because they were employed as post-doctoral fellows at Vanderbilt before getting faculty appointments. In discussions at the workshop, the group became intrigued by the possibility that flux tubes could have played a key role in the initial formation of the universe.

According to current theories, when the universe was created it was initially filled with a superheated primordial soup called quark-gluon plasma. This consisted of a mixture of quarks and gluons. (In 2005 the quark-gluon plasma was successfully recreated in a particle accelerator, the Relativistic Heavy Ion Collider at Brookhaven National Laboratory, by an international group of physicists, including three from Vanderbilt: Stevenson Chair in Physics Victoria Greene and Professors of Physics Charles Maguire and Julia Velkovska.)

Kephart and his collaborators realized that a higher energy version of the quark-gluon plasma would have been an ideal environment for flux tube formation in the very early universe. The large numbers of pairs of quarks and antiquarks being spontaneously created and annihilated would create myriads of flux tubes.

Normally, the flux tube that links a quark and antiquark disappears when the two particles come into contact and self-annihilate, but there are exceptions.

If a tube takes the form of a knot, for example, then it becomes stable and can outlive the particles that created it. If one of particles traces the path of an overhand knot, for instance, then its flux tube will form a trefoil knot. As a result, the knotted tube will continue to exist, even after the particles that it links annihilate each other. Stable flux tubes are also created when two or more flux tubes become interlinked. The simplest example is the Hopf link, which consists of two interlinked circles.

In this fashion, the entire universe could have filled up with a tight network of flux tubes, the authors envisioned. Then, when they calculated how much energy such a network might contain, they were pleasantly surprised to discover that it was enough to power an early period of cosmic inflation.

Since the idea of cosmic inflation was introduced in the early 1980s, cosmologists have generally accepted the proposition that the early universe went through a period when it expanded from the size of a proton to the size of a grapefruit in less than a trillionth of a second.

This period of hyper-expansion solves two important problems in cosmology. It can explain observations that space is both flatter and smoother than astrophysicists think it should be. Despite these advantages, acceptance of the theory has been hindered because an appropriate energy source has not been identified.

"Not only does our flux tube network provide the energy needed to drive inflation, it also explains why it stopped so abruptly," said Kephart. "As the universe began expanding, the flux-tube network began decaying and eventually broke apart, eliminating the energy source that was powering the expansion."

When the network broke down, it filled the universe with a gas of subatomic particles and radiation, allowing the evolution of the universe to continue along the lines that have previously been determined.

The most distinctive characteristic of their theory is that it provides a natural explanation for a three-dimensional world. There are a number of higher dimensional theories, such as string theory, that visualize the universe as having nine or ten spatial dimensions. Generally, their proponents explain that these higher dimensions are hidden from view in one fashion or another.

The flux-tube theory's explanation comes from basic knot theory. "It was Heinrich Päs who knew that knots only form in three dimensions and wanted to use this fact to explain why we live in three dimensions," said Kephart.

A two-dimensional example helps explain. Say you put a dot in the center of a circle on a sheet of paper. There is no way to free the circle from the dot while staying on the sheet. But if you add a third dimension, you can lift the circle above the dot and move it to one side until the dot is no longer inside the circle before lowering it back down. Something similar happens to three-dimensional knots if you add a fourth dimension -- mathematicians have shown that they unravel. "For this reason, knotted or linked tubes can't form in higher-dimension spaces," said Kephart.

The net result is that inflation would have been limited to three dimensions. Additional dimensions, if they exist, would remain infinitesimal in size, far too small for us to perceive.

Read more at Science Daily

A Black Butterfly’s Wings Point the Way Toward Better Solar Cells

Black butterfly
A microscopic pattern on the wings of a butterfly has shown scientists how to capture more of the sun’s energy in solar cells.

The scales of the black-colored common rose butterfly are topped with an irregular lattice of chitin and melanin. Those structures drew the attention of Radwan Siddique, an engineer trying to develop a technique for building 3D nanostructures as part of his doctoral work at Germany’s Karlsruhe Institute of Technology.

Siddique told Seeker he came across a description of the butterfly’s wings in the course of his research. The lattice helps the cold-blooded insect regulate its body temperature, keeping it warm enough to fly in cool weather, he said.

“I was so intrigued that I literally went to a lot of butterfly nurseries and gathered several butterflies,” said Siddique, now a post-doctoral researcher at Caltech. “The black butterfly was one of them. I was putting them under SEM [an electron microscope] and looking at the structures.” It openings are less than a millionth of a meter wide, but they scatter light and help the butterfly absorb more of the sun’s heat.

“They use those nanostructures to improve absorption,” he said. “So I asked, ‘Can we use the same nanostructres in this type of solar cell, which is not highly used because the absorption isn’t that good?’”

Scientists from KIT and Caltech utilize the disordered nanoholes of the black butterfly to improve solar cell performance.
By mimicking the butterfly’s structure in a sheet of hydrogenated amorphous silicon, he and his colleagues at Karlsruhe were able to capture more low-frequency light — at wavelengths near the infrared end of the spectrum — that wouldn’t have been converted to energy otherwise. A layer of polymer pockmarked with circular indentations of various sizes, transferred to a silicon base, was able to pick up about double the amount of energy that a smooth surface produced and convert it to electricity. Angling those indentations might improve those efficiencies even more, he said.

The findings were published Oct. 18 in the research journal Science Advances. They’re part of a growing body of research aimed at improving the efficiency and reducing the size of solar cells.

Scanning electron microscope image of bio-inspired nanoholes
The ability to produce solar power with a thin film, as opposed to the larger, more typical crystal-based cells, holds the promise of making them more useful. They could be used to power personal electronics or for larger-scale applications, such as being incorporated into windows or other building materials.

And Siddique and his colleagues aren’t the first to find inspiration in the natural world: Earlier this year, researchers in Australia etched a fractal pattern inspired by the leaves of a fern onto sheets of graphene to increase the surface area available for storing and conducting energy.

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Oct 17, 2017

Archaeologists Unearth Roman Structure at the Foot of Jerusalem’s Western Wall

Reporters visit the recently discovered ancient roman theatre from the second sanctuary that was found by the Israeli Antiquity Authority at the foot of the Western Wall tunnels in Jerusalem's Old City on October 16, 2017. Excavations conducted by the Israel Antiquities Authority have uncovered large portions of the Western Wall that have been hidden for 1,700 years.
Israeli archaeologists in Jerusalem's Old City on Monday unveiled a newly unearthed section of the Western Wall and the first Roman public structure ever discovered in the city, they said.

Archaeologist Joe Uziel said he and his colleagues knew the wall section was there and had expected to find a Roman street at its base.

"But as we excavated and excavated we realized we weren't getting to the street. Instead we have this circular building," he told reporters at the underground site.

"Basically we realized that we were excavating a theatre-like (Roman) structure."

He said that carbon-14 and other dating methods indicated it came from the second or third centuries AD and appeared to be unfinished.

The Israel Antiquities Authority (IAA), which conducted the two-year dig, said that historical sources mentioned such structures but in 150 years of modern archaeological research in the city none had been found.

The section of the 2,000-year-old Western Wall uncovered by the diggers is about 15 meters (yards) in width and eight meters high, with the stones very well preserved.

It had been buried under eight meters of earth for 1,700 years, the IAA said.

The Western Wall is among the last remnants of the retaining structures that surrounded the second Jewish temple until its destruction by the Romans in 70 AD.

It is the holiest site where Jews are permitted to pray.

Previously, the last section to be exposed was in 2007, IAA chief Jerusalem architect Yuval Baruch said.

"Exposing parts of the Western Wall is of course extremely, extremely, extremely exciting, but the structure we are looking at right now we had no idea would be here," Uziel said, pointing to the 200-seat auditorium.

"It's probably the most important archaeological site in the country, the first public structure from the Roman period of Jerusalem," Baruch said.

"We know a lot about dwelling houses, a lot about installations, water systems, roads, streets, but this is the first time we can present to the public a Roman public structure," he added.

Religious tensions

The IAA statement said the building could have been a meeting chamber for Roman administrative officials or a concert venue, but said its location under an ancient arch, which could have served as its roof, gave a clue.

"This is a relatively small structure compared to known Roman theatres," it said.

"This fact, in addition to its location under a roofed space — in this case under Wilson’s Arch — leads us to suggest that this is a theatre-like structure of the type known in the Roman world as an odeon."

"In most cases, such structures were used for acoustic performances. Alternatively, this may have been a structure known as a bouleuterion — the building where the city council met," it said.

Wilson's Arch, named for 19th-century explorer and surveyor Charles Wilson, dates to the second temple period and served as a passageway for people entering the temple compound, the IAA says.

Uziel said that the archaeologists worked with care, mindful of the Jewish, Muslim, and Christian worshippers nearby.

"We did not want to disturb any of the religious activities that were occurring in this area," he said.

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