Posts tagged physics

August 8, 2012

Researchers capture evolutionary dynamics in a new theoretical framework that could help explain some of the mysteries of how and why species change over time.

Although the qualitative description of evolution – its observed behavior and characteristics – is well-established, a comprehensive quantitative theory that captures general evolution dynamics is still lacking. There are also many lingering mysteries surrounding the story of life on Earth, including the question of why sex is such a prevalent reproductive strategy. A team of scientists from the Chinese Academy of Sciences; Jilin University in Jilin, China; and the State University of New York at Stony Brook, led by Prof. Jin Wang, has examined some of these puzzles from a physical science prospective. They propose a new theory of evolution with two ingredients: the underlying emergent “fitness” landscape and an associated evolutionary force called “curl flux,” which causes species to move through the emergent fitness landscape in a spiraling manner.

The researchers captured evolutionary relationships in a system of equations. They then created quantitative pictures that visualized evolutionary pathways as journeys through a mountainous terrain of peaks and valleys of biological fitness. The key breakthrough beyond the conventional quantitative theory of evolution is the emergent curl flux, which is generated by interactions between individuals within or across species. The underlying emergent landscape gradient and the curl flux act together as a “Yin and Yang” duality pair to determine the dynamics of general evolution, says Wang. An example of similar behavior is the particle and wave duality that determines the dynamics of the quantum world, he notes. The researchers also note that this combined effect is analogous to the way electric and magnetic forces both act on electrons.

The new theory provides a physical foundation for general evolution dynamics. The researchers found that interactions between individuals of different species can give rise to the curl flux. This can sustain an endless evolution that does not lead to areas of higher relative fitness, even if the physical environment is unchanged.

This finding offers a theoretical framework to explain the Red Queen Hypothesis, which states that species continually evolve in order to fend off parasites that are themselves continually evolving. The hypothesis, first proposed by evolutionary biologist Leigh Van Valen in 1973, gets its name from the character of the Red Queen in Lewis Carroll’s book Through the Looking-Glass, who observed that in her world it was necessary to keep running just to stay in one place. The idea of endless co-evolution through the maintenance of the genetic variation due to the curl flux could help explain the benefits of sexual reproduction, since the mixing and matching of genes preserves a greater diversity of traits. When a species’ arms race with a co-evolving parasite takes an unexpected twist, a previously unnecessary trait could suddenly turn into the key to surviving. In the co-evolving world, there is no guarantee for “survival of the fittest” and it is often necessary to keep running for survival.

Source: PHYS.ORG

(PhysOrg.com) — Geraldo Barbosa, professor of electrical engineering and computer science at Northwestern University has posed an interesting challenge. He wonders if the human eye and brain together are capable of actually seeing entangled images. This is not a philosophical question, as he has phrased the query as part of a practical experiment that someone with the proper lab could actually carry out. To that end, he’s posted a paper on the preprint server arXiv with the hope that a physics team will take up the challenge.

The whole idea is based on entanglement and the means by which researchers make it come about. What they do is shoot a laser at a non-linear crystal causing the photons in the beam to be converted into lower frequency entangled pairs. Those pairs are then directed to sensors which individually are able to measure a fuzzy or blurred “image”. But when both of the entangled photons are taken together as a single measurement, the image sharpens. These images are of course far too small for the human eye to see, plus they don’t last long enough for them to be seen anyway. To address these issues, researchers have taken to firing lasers that are formed into patterns such as a doughnut shape in a continuous sequence. The result is a steady stream of entangled pairs being created in the shape of a doughnut.

Barbosa wants to know what would happen if instead of forming a doughnut shape, the lasers were made to look like a letter in the alphabet, such as the letter A, and then of course if it were made large enough to be seen by the human eye. Two entangled letter As should be created and seeable albeit in a lower frequency. If that happened, would the human eye when paired with the brain’s abilities, be able to merge the two into a sharp readable image, or would we see just the individual blurred images captured by just one sensor?

Barbosa doesn’t know, and neither does anyone else, thus he suggests someone or some group build an experiment to find out.

The ability to see things differently than we are accustomed to seeing isn’t anything new of course. Some animals can see things in the infrared spectrum for example and evidence has been slowly emerging as described here, here and here, suggesting that some migrating birds are able to “see” the Earth’s magnetic field. So maybe it’s possible that we see entangled images every day, and just don’t know it.

Hopefully someone will take Barbosa up on his challenge, and then we’ll all find out if it’s possible or not.

More information: Can humans see beyond intensity images? by Geraldo A. Barbosa, arXiv:1202.5434v1 [q-bio.NC] http://arxiv.org/abs/1202.5434

Source: PHYSORG.com

February 3, 2012

Schematic drawing of the upright STED microscope used for the experiments. Image: Science, DOI:10.1126/science.1215369

(PhysOrg.com) — Ever since scientists began studying the brain, they’ve wanted to get a better look at what was going on. Researchers have poked and prodded and looked at dead cells under electron microscopes, but never before have they been able to get high resolution microscopic views of actual living brain cells as they function inside of a living animal. Now, thanks to work by physicist Stefan Hell and his colleagues at the Max Planck Institute in Germany, that dream is realized. In a paper published in Science, Hell and his team describe the workings of their marvelous discovery.

Hell (which in German means “bright”) and others at the Institute have been working for years on ultra high resolution microscopes that go by the name “stimulated emission depletion” or STED microscopes. Now, they’ve taken their work to a whole new level by cutting away a small portion of a mouse’s skull and replacing it with a glass window and then placing their latest STED microscope against the glass to peer inside. To make it easier to see what is what, the team first genetically altered the mouse to make certain brain cells fluorescent. Then, to allow for focusing exclusively on just those cells that are lit up, they added software to the microscope to blot out anything that was not lit up. The result is super high resolution real time imagery of the neurons that exist on the exterior part of a living mouse brain. 

(video)

STED time-lapse recording of a single spine at an interval of 10 seconds. The measurement includes 128 z-stacks consisting of 5 slices each. Most of the rapid remodeling of the spine head appears continuous and smooth at this frame rate. No damage is observed at the dendrite or the spine after recording a total of 640 slices. The movie was acquired in a different experiment than the spines in Fig.1. Scale bar = 1µm. Video: DOI:10.1126/science.1215369

The new microscope provides clear resolution down to 70 nanometers, which is four times that ever achieved before and is enough to allow scientists to see the actual movement of dendritic spines, which may help researches understand why they do so.

It is likely that researchers will find many varied uses for the new microscope. One prominent area will almost certainly involve looking into what psychiatric drugs are really doing within synapses, perhaps leading to breakthroughs in pharmaceutical drugs that are better able to target specific illnesses.

One downside to any new scientific breakthrough however, is the natural tendency of many to move from excitation, to wondering about what will come next. In this case, Hell and his team have already started contemplating ideas on ways to allow researchers to study any cell in the living brain at such high resolution, not just those that lie on the surface.

More information: Nanoscopy in a Living Mouse Brain, Science 3 February 2012: Vol. 335 no. 6068 p. 551. DOI: 10.1126/science.1215369

"Renowned physicist invents microscope that can peer at living brain cells." February 3rd, 2012. http://www.physorg.com/news/2012-02-renowned-physicist-microscope-peer-brain.html

February 1st, 2012 in Physics / General Physics 

Scientists have found that the capacity of the human brain to process and record information - and not economic constraints - may constitute the dominant limiting factor for the overall growth of globally stored information. These findings have just been published in an article in EPJ B by Claudius Gros and colleagues from the Institute for Theoretical Physics at Goethe University Frankfurt in Germany.

The authors first looked at the distribution of 633 public internet files by plotting the number of videos, audio and image files against the size of the files. They gathered files which were produced by humans or intended for human use with the spider file search engine Findfiles.net. They chose to focus on files which are hosted on domains pointing from the online encyclopaedia Wikipedia and the open web directory dmoz.

Assuming that economic costs for data production are proportional to the amount of data produced, these costs should be driving the generation of information exponentially. However, the authors found that, in fact, economic costs were not the limiting factors for data production. The absence of exponential tails for the graph representing the number of files indicates this conclusion.

They found that underlying neurophysiological processes influence the brain’s ability to handle information. For example, when a person produces an image and attributes a subjective value to it, for example, a given resolution, he or she is influenced by his or her perception of the quality of that image. Their perception of the amount of information gained when increasing the resolution of a low-quality image is substantially higher than when increasing the resolution of a high-quality photo by the same degree. This relation is known as the Weber-Fechner law.

The authors observed that file-size distributions obey this Weber-Fechner law. This means that the total amount of information cannot grow faster than our ability to digest or handle it.

More information: Gros C., Kaczor G., Markovic D., (2012) Neuropsychological constraints to human data production on a global scale, European Physical Journal B (EPJ B) 85: 28, DOI 10.1140/epjb/e2011-20581-3

Provided by Springer

"Brain capacity limits exponential online data growth." February 1st, 2012.http://www.physorg.com/news/2012-02-brain-capacity-limits-exponential-online.html