João Patrício firstname.lastname@example.org
I’m a child. Like books, movies, music, aikido, comics and games. “When a man thinks of the past, he becomes kinder.” (Stalker, 1979, Andrey Tarkovskiy)
Astronomy Picture of the Day for 2017-03-20 12:30:01.760103
Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.
The Aurora Tree
Image Credit & Copyright: Alyn Wallace Photography
Explanation: Yes, but can your tree do this? Pictured is a visual coincidence between the dark branches of a nearby tree and bright glow of a distant aurora. The beauty of the aurora -- combined with how it seemed to mimic a tree right nearby -- mesmerized the photographer to such a degree that he momentarily forgot to take pictures. When viewed at the right angle, it seemed that this tree had aurora for leaves! Fortunately, before the aurora morphed into a different overall shape, he came to his senses and capture the awe-inspiring momentary coincidence. Typically triggered by solar explosions, aurora are caused by high energy electrons impacting the Earth's atmosphere around 150 kilometers up. The unusual Earth-sky collaboration was witnessed earlier this month in Iceland.
Follow APOD on: Facebook, Google Plus, Instagram, or Twitter
Tomorrow's picture: kinetic orion
I tink most people here have been there at one point or another
Dealing with non-technical people: The Expert
Pump.io community meeting today 2017/3/17 at 20:00 UTC
Pump.io community meeting today 2017/3/17 at 20:00 UTC !
Our monthly community meeting will be on the #pump.io channel on the Freenode IRC network, which is also mirrored to the email@example.com jabber/XMPP MUC room.
Agenda is here: https://github.com/pump-io/pump.io/wiki/Meeting-2017-03-17
You're all welcome to join us!
Panko shared this.
Kontalk circle definitely missing from here: https://m.xkcd.com/1810/
Q&A: Dark matter next door?
"Q&A: Dark matter next door?"
Astrophysicists Eric Charles and Mattia Di Mauro discuss the surprising glow of our neighbor galaxy.
Astronomers recently discovered a stronger-than-expected glow of gamma rays at the center of the Andromeda galaxy, the nearest major galaxy to the Milky Way. The signal has fueled hopes that scientists are zeroing in on a sign of dark matter, which is five times more prevalent than normal matter but has never been detected directly.
Researchers believe that gamma rays—a very energetic form of light—could be produced when hypothetical dark matter particles decay or collide and destroy each other. However, dark matter isn’t the only possible source of the gamma rays. A number of other cosmic processes are known to produce them.
So what do Andromeda’s gamma rays really tell us about dark matter? To find out, Symmetry’s Manuel Gnida talked with Eric Charles and Mattia Di Mauro, two members of the Fermi-LAT collaboration—an international team of researchers that found the Andromeda gamma-ray signal using the Large Area Telescope, a sensitive “eye” for dark matter on NASA’s Fermi Gamma-ray Space Telescope.
Both researchers are based at the Kavli Institute for Particle Astrophysics and Cosmology, a joint institute of Stanford University and the Department of Energy’s SLAC National Accelerator Laboratory. The LAT was conceived of and assembled at SLAC, which also hosts its operations center.
Have you discovered dark matter?MD:
No, we haven’t. In the study, the LAT team looked at the gamma-ray emissions of the Andromeda galaxy and found something unexpected, something we don’t fully understand yet. But there are other potential astrophysical explanations than dark matter.
It’s also not the first time that the LAT collaboration has studied Andromeda with Fermi, but in the old data the galaxy only looked like a big blob. With more data and improved data processing, we have now obtained a much clearer picture of the galaxy’s gamma-ray glow and how it’s distributed.
What’s so unusual about the results?EC:
As a spiral galaxy, Andromeda is similar to the Milky Way. Therefore, we expected the emissions of both galaxies to look similar. What we discovered is that they are, in fact, quite different.
In our galaxy, gamma rays come from all kinds of locations—from the center and the spiral arms in the outer regions. For Andromeda, on the other hand, the signal is concentrated at the center.
Why do galaxies glow in gamma rays?EC:
The answer depends on the type of galaxy. There are active galaxies called blazars. They emit gamma rays when matter in close orbit around supermassive black holes generates jets of plasma. And then there are “normal” galaxies like Andromeda and the Milky Way that produce gamma rays in other ways.
When we look at the emissions of the Milky Way, the galaxy appears like a bright disk, with the somewhat brighter galactic center at the center of the disk. Most of this glow is diffuse and comes from the gas between the stars that lights up when it’s hit by cosmic rays—energetic particles spit out by star explosions or supernovae.
Other gamma-ray sources are the remnants of such supernovae and pulsars—extremely dense, magnetized, rapidly rotating neutron stars. These sources show up as bright dots in the gamma-ray map of the Milky Way, except at the center where the density of gamma-ray sources is high and the diffuse glow of the Milky Way is brightest, which prevents the LAT from detecting individual sources.
Andromeda is too far away to see individual gamma-ray sources, so it only has a diffuse glow in our images. But we expected to see most of the emissions to come from the disk as well. Its absence suggests that there is less interaction between gas and cosmic rays in our neighbor galaxy. Since this interaction is tied to the formation of stars, this also suggests that Andromeda had a different history of star formation than the Milky Way.
What does all this have to do with dark matter?MD:
When we carefully analyze the gamma-ray emissions of the Milky Way and model all the gas and point-like sources to the best of our knowledge, then we’re left with an excess of gamma rays at the galactic center. Some people have argued this excess could be a telltale sign of dark matter particles.
We know that the concentration of dark matter is largest at the galactic center, so if there were a dark matter signal, we would expect it to come from there. The localization of gamma-ray emissions at Andromeda’s center seems to have renewed the interest in the dark matter interpretation in the media.
Is dark matter the most likely interpretation?EC:
No, there are other explanations. There are so many gamma-ray sources at the galactic center that we can’t really see them individually. This means that their light merges into an extended, diffuse glow.
In fact, two recent studies from the US and The Netherlands have suggested that this glow in the Milky Way could be due to unresolved point sources such as pulsars. The same interpretation could also be true for Andromeda’s signal.http://www.symmetrymagazine.org/feed )
What would it take to know for certain?MD:
To identify a dark matter signal, we would need to exclude all other possibilities. This is very difficult for a complex region like the galactic center, for which we don’t even know all the astrophysical processes. Of course, this also means that, for the same reason, we can’t completely rule out the dark matter interpretation.
But what’s really important is that we would want to see the same signal in a few different places. However, we haven’t detected any gamma-ray excesses in other galaxies that are consistent with the ones in the Milky Way and Andromeda.
This is particularly striking for dwarf galaxies, small companion galaxies of the Milky Way that only have few stars. These objects are only held together because they are dominated by dark matter. If the gamma-ray excess at the galactic center were due to dark matter, then we should have already seen similar signatures in the dwarf galaxies. But we don’t.
Stephen Sekula shared this.
identi.ca is back!
now to return to your regularly scheduled programming of cwebber complaining about themselves
Claes Wallin (韋嘉誠) shared this.
The life of an accelerator
"The life of an accelerator"
As it evolves, the SLAC linear accelerator illustrates some important technologies from the history of accelerator science.
Tens of thousands of accelerators exist around the world, producing powerful particle beams for the benefit of medical diagnostics, cancer therapy, industrial manufacturing, material analysis, national security, and nuclear as well as fundamental particle physics. Particle beams can also be used to produce powerful beams of X-rays.
Many of these particle accelerators rely on artfully crafted components called cavities.
The world’s longest linear accelerator (also known as a linac) sits at the Department of Energy’s SLAC National Accelerator Laboratory. It stretches two miles and accelerates bunches of electrons to very high energies.
The SLAC linac has undergone changes in its 50 years of operation that illustrate the evolution of the science of accelerator cavities. That evolution continues and will determine what the linac does next.
An accelerator cavity is a mostly closed, hollow chamber with an opening on each side for particles to pass through. As a particle moves through the cavity, it picks up energy from an electromagnetic field stored inside. Many cavities can be lined up like beads on a string to generate higher and higher particle energies.
When SLAC’s linac first started operations, each of its cavities was made exclusively from copper. Each tube-like cavity consisted of a 1-inch-long, 4-inch-wide cylinder with disks on either side. Technicians brazed together more than 80,000 cavities to form a straight particle racetrack.
Scientists generate radiofrequency waves in an apparatus called a klystron that distributes them to the cavities. Each SLAC klystron serves a 10-foot section of the beam line. The arrival of the electron bunch inside the cavity is timed to match the peak in the accelerating electric field. When a particle arrives inside the cavity at the same time as the peak in the electric field, then that bunch is optimally accelerated.
“Particles only gain energy if the variable electric field precisely matches the particle motion along the length of the accelerator,” says Sami Tantawi, an accelerator physicist at Stanford University and SLAC. “The copper must be very clean and the shape and size of each cavity must be machined very carefully for this to happen.”
In its original form, SLAC’s linac boosted electrons and their antimatter siblings, positrons, to an energy of 50 billion electronvolts. Researchers used these beams of accelerated particles to study the inner structure of the proton, which led to the discovery of fundamental particles known as quarks.
Today almost all accelerators in the world—including smaller systems for medical and industrial applications—are made of copper. Copper is a good electric conductor, which is important because the radiofrequency waves build up an accelerating field by creating electric currents in the cavity walls. Copper can be machined very smoothly and is cheaper than other options, such as silver.
“Copper accelerators are very robust systems that produce high acceleration gradients of tens of millions of electronvolts per meter, which makes them very attractive for many applications,” says SLAC accelerator scientist Chris Adolphsen.
Today, one-third of SLAC’s original copper linac is used to accelerate electrons for the Linac Coherent Light Source, a facility that turns energy from the electron beam into what is currently the world’s brightest X-ray laser light.
Researchers continue to push the technology to higher and higher gradients—that is, larger and larger amounts of acceleration over a given distance.
“Using sophisticated computer programs on powerful supercomputers, we were able to develop new cavity geometries that support almost 10 times larger gradients,” Tantawi says. “Mixing small amounts of silver into the copper further pushes the technology toward its natural limits.” Cooling the copper to very low temperatures helps as well. Tests at 45 Kelvin—negative 384 degrees Fahrenheit—have shown to increase acceleration gradients 20-fold compared to SLAC’s old linac.
Copper accelerators have their limitations, though. SLAC’s historic linac produces 120 bunches of particles per second, and recent developments have led to copper structures capable of firing 80 times faster. But for applications that need much higher rates, Adolphsen says, “copper cavities don’t work because they would melt.”
For this reason, crews at SLAC are in the process of replacing one-third of the original copper linac with cavities made of niobium.
Niobium can support very large bunch rates, as long as it is cooled. At very low temperatures, it is what’s known as a superconductor.
“Below the critical temperature of 9.2 Kelvin, the cavity walls conduct electricity without losses, and electromagnetic waves can travel up and down the cavity many, many times, like a pendulum that goes on swinging for a very long time,” says Anna Grassellino, an accelerator scientist at Fermi National Accelerator Laboratory. “That’s why niobium cavities can store electromagnetic energy very efficiently and can operate continuously.”
You can find superconducting niobium cavities in modern particle accelerators such as the Large Hadron Collider at CERN and the CEBAF accelerator at Thomas Jefferson National Accelerator Facility. The European X-ray Free-Electron Laser in Germany, the European Spallation Source at CERN, and the Facility for Rare Isotope Beams at Michigan State University are all being built using niobium technology. Niobium cavities also appear in designs for the next-generation International Linear Collider.
At SLAC, the niobium cavities will support LCLS-II, an X-ray laser that will produce up to a million ultrabright light flashes per second. The accelerator will have 280 cavities, each about three feet long with a 3-inch opening for the electron beam to fly through. Sets of eight cavities will be strung together into cryomodules that keep the cavities at a chilly 2 Kelvin, which is colder than interstellar space.
Each niobium cavity is made by fusing together two halves stamped from a sheet of pure metal. The cavities are then cleaned very thoroughly because even the tiniest impurities would degrade their performance.
The shape of the cavities is reminiscent of a stack of shiny donuts. This is to maximize the cavity volume for energy storage and to minimize its surface area to cut down on energy dissipation. The exact size and shape also depends on the type of accelerated particle.
“We’ve come a long way since the first development of superconducting cavities decades ago,” Grassellino says. “Today’s niobium cavities produce acceleration gradients of up to about 50 million electronvolts per meter, and R&D work at Fermilab and elsewhere is further pushing the limits.”
Over the past few years, SLAC accelerator scientists have been working on a way to push the limits of particle acceleration even further: accelerating particles using bubbles of ionized gas called plasma.
Plasma wakefield acceleration is capable of creating acceleration gradients that are up to 1000 times larger than those of copper and niobium cavities, promising to drastically shrink the size of particle accelerators and make them much more powerful.
“These plasma bubbles have certain properties that are very similar to conventional metal cavities,” says SLAC accelerator physicist Mark Hogan. “But because they don’t have a solid surface, they can support extremely high acceleration gradients without breaking down.”
Hogan’s team at SLAC and collaborators from the University of California, Los Angeles, have been developing their plasma acceleration method at the Facility for Advanced Accelerator Experimental Tests, using an oven of hot lithium gas for the plasma and an electron beam from SLAC’s copper linac.
Researchers create bubbles by sending either intense laser light or a high-energy beam of charged particles through plasma. They then send beams of particles through the bubbles to be accelerated.
When, for example, an electron bunch enters a plasma, its negative charge expels plasma electrons from its flight path, creating a football-shaped cavity filled with positively charged lithium ions. The expelled electrons form a negatively charged sheath around the cavity.
This plasma bubble, which is only a few hundred microns in size, travels at nearly the speed of light and is very short-lived. On the inside, it has an extremely strong electric field. A second electron bunch enters that field and experiences a tremendous energy gain. Recent data show possible energy boosts of billions of electronvolts in a plasma column of just a little over a meter.
“In addition to much higher acceleration gradients, the plasma technique has another advantage,” says UCLA researcher Chris Clayton. “Copper and niobium cavities don’t keep particle beams tightly bundled and require the use of focusing magnets along the accelerator. Plasma cavities, on the other hand, also focus the beam.”
Much more R&D work is needed before plasma wakefield accelerator technology can be turned into real applications. But it could represent the future of particle acceleration at SLAC and of accelerator science as a whole.
João Patrício likes this.
- Gentoo-Based #exGENT Linux OS Launches with #Xfce 4.12.1 and #Linux #Kernel 4.10.1 http://news.softpedia.com/news/gentoo-based-exgent-linux-os-launches-with-xfce-4-12-1-and-linux-kern... #gentoo
João Patrício likes this.
Plasma 5.8.5 and Applications 16.12 by KDE now available in ChakraLots of changes introduced with this move, as all the latest updates by KDE hit the ChakraLinux repositories. Make sure to read through all the announcement!
This radioactive life
Shared from RSS:
"This radioactive life"
Radiation is everywhere. The question is: How much?
An overly plump atomic nucleus just can’t keep itself together.
When an atom has too many protons or neutrons, it’s inherently unstable. Although it might sit tight for a while, eventually it can’t hold itself together any longer and it spontaneously decays, spitting out energy in the form of waves or particles.
The end result is a smaller, more stable nucleus. The spit-out waves and particles are known as radiation, and the process of nuclear decay that produces them is called radioactivity.
Radiation is a part of life. There are radioactive elements in most of the materials we encounter on a daily basis, which constantly spray us with radiation. For the average American, this adds up to a dose of about 620 millirem of radiation every year. That’s roughly equivalent to 10 abdominal X-rays.
Scientists use the millirem unit to express how much a radiation dose damages the human body. A person receives 1 millirem during an airline flight from one U.S. coast to the other.
But where exactly does our annual dose of radiation come from? Looking at sources, we can split the dosage in two nearly equal parts: About half comes from natural background radiation and half comes from manmade sources.Infographic by Sandbox Studio, Chicago with Ana Kova
Natural background radiation originates from outer space, the atmosphere, the ground, and our own bodies. There’s radon in the air we breathe, radium in the water we drink and miscellaneous radioactive elements in the food we eat. Some of these pass through our bodies without much ado, but some get incorporated into our molecules. When the nuclei eventually decay, our own bodies expose us to tiny doses of radiation.
“We’re exposed to background radiation whether we like it or not,” says Sayed Rokni, radiation safety officer and radiation protection department head at SLAC National Accelerator Laboratory. “That exists no matter what we do. I wouldn’t advise it, but we could choose not to have dental X-rays. But we can’t choose not to be exposed to terrestrial radiation—radiation that is in the crust of the earth, or from cosmic radiation.”
It’s no reason to panic, though.
“The human species, and everything around us, has evolved over the ages while receiving radiation from natural sources. It has formed us. So clearly there is an acceptable level of radiation,” Rokni says.
Any radiation not considered background comes from manmade sources, primarily through diagnostic or therapeutic medical procedures. In the early 1980s, medical procedures accounted for 15 percent of an American’s yearly radiation exposure—they now account for 48 percent.
“The amount of natural background radiation has stayed the same,” says Don Cossairt, Fermilab radiation protection manager. “But radiation from medical procedures has blossomed, perhaps with corresponding dramatic improvements in treating many diseases and ailments.”
Growth in the use of medical imaging has raised the average American’s yearly exposure from its 1980s' average of 360 millirems to 620 millirems. Today’s annual average is not regarded as harmful to health by any regulatory authority.
While medical procedures make up most of the manmade radiation we receive, about 2 percent of the overall annual dose comes from radiation emitted by some consumer products. Most of these products are probably in your home right now. Simply examining the average kitchen, one finds a cornucopia of items that emit enough radiation to detect it with a Geiger counter, in both manmade consumer products and natural foods.
Are there Brazil nuts in your pantry? They’re the most radioactive food there is. A Brazil nut tree’s roots reach far down into the soil to deep underground where there’s more radium, absorb this radioactive element, and pass it on to the nuts. Brazil nuts also contain potassium, which occurs in tandem with potassium-40, a naturally occurring radioactive isotope.
Potassium-40 is the most prevalent radioactive element in the food we eat. Potassium-packed bananas are well known for their radioactivity, so much so that a banana’s worth of radioactivity is used as an informal measurement of radiation. It’s called the Banana Equivalent Dose. One BED is equal to 0.01 millirem. A typical chest x-ray is somewhere around 200 to 1000 BED. A fatal dose of radiation is about 50 million BED in one sitting.
Some other potassium-40-containing munchies that emit radiation include carrots, potatoes, lima and kidney beans and red meat. From food and water alone, the average person receives an annual internal dose of about 30 millirem. That’s 3000 bananas!
Even the dish off of which you’re eating may be giving you a slight dose of radiation. The glaze of some older ceramics contains uranium, thorium or good ol’ potassium-40 to make it a certain color, especially red-orange pottery made pre-1960s. Likewise, some yellowish and greenish antique glassware contains uranium as a colorant. Though this dinnerware might make a Geiger counter click, it’s still safe to eat with.
Your smoke detector, which usually hangs silently on the ceiling until its batteries go dead, is radioactive too. That’s how it can save you from a burning building: A small amount of americium-241 in the device allows it to detect when there’s smoke in the air.
“It’s not dangerous unless you take it out in the garage and beat it up with a hammer to release the radioactivity,” Cossairt says. The World Nuclear association notes that the americium dioxide found in smoke detectors is insoluble and would “pass through the digestive tract without delivering a significant radiation dose.”
Granite countertops also contain uranium and thorium, which decays into radon gas. Most of the gas gets trapped in the countertop, but some can be released and add a small amount to the radon level in a home—which primarily comes from the soil a structure sits on.
Granite doesn’t just emit radiation inside the home. People living in areas with more granite rock receive an extra boost of radiation per year.
Yearly radiation exposure varies significantly depending on where you live. People at higher altitudes receive a greater dose of radiation showered from space per year.
But not to worry if you live in a locale with lots of altitude and granite, like Denver, Colorado. “No health effect due to radiation exposure has ever been correlated with people living at higher altitudes,” Cossairt says. Similarly, no one has noted a correlation between health and the increased dose of radiation from environmental granite rock.
It doesn’t matter if you’re living at altitude or sea level, in the Rocky Mountains or on Maryland’s Eastern Shore—radiation is everywhere. But annual doses from background and manmade sources aren’t enough to worry about. So enjoy your banana and feel free to grab another handful of Brazil nuts.
Check out our printable poster about radioactivity.
João Patrício likes this.
João Patrício shared this.
- Reclaiming the Computing Commons: Resisting the commodification of information is a political struggle, not a technical one → https://www.jacobinmag.com/2016/02/free-software-movement-richard-stallman-linux-open-source-enclosure/
#FreeSoftware #OpenSource #Software #Computers #Computing #IT #Information #Politics #Technology #Freedom
João Patrício shared this.
New blogpost: "Family games: Robots"
New blogpost: "Family games: Robots" https://larjona.wordpress.com/2015/07/19/family-games-robots/ #freesoftwareforkids
João Patrício likes this.Loved it! Will try it with my daughter. We love games, specially board games. This is a good one to start introducing some concepts that will help the transition to roleplay. Did you invent it? I would love to write this notes/rules down in Portuguese and spread the idea.
Edward Snowden will kick off LibrePlanet 2016: Will you be there?
This is huge: the opening keynote for LibrePlanet 2016: Fork the System is a conversation with National Security Agency (NSA) whistleblower Edward Snowden and American Civil Liberties Union (ACLU) Technologist Daniel Kahn Gillmor.
LaTeX para trabajos administrativos. Libro.
Interesante libro que he visto en tug.org.
En él se reseña y explica, con ejemplos prácticos, típicos trabajos administrativos como correspondencia, facturas, CV, notas de prensa, presentaciones, tarjetas de presentación, flyers... ¡de todo! Muy recomendable.
LaTeX, para mi al menos, tiene una curva de aprendizaje alto pero es cierto que facilita enormemente el trabajo.