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Denford Berriman
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Something to watch out for as we approach the closing stages of polio eradication: long-term shedders of the poliovirus. "Long-term shedders of poliovirus have been identified before. It’s a rare phenomenon, and for it to occur, several things have to happen: Someone has to be vaccinated as an infant with the oral polio vaccine, which contains a weakened live virus; has to have an immune-system deficiency that keeps the body from eliminating the vaccine virus after immunity develops; and, usually, has to live in an industrialized country where medical care is good enough to keep children with immune-system deficiencies alive.

That has happened a number of times—more than 70—since polio vaccination began in the 1950s, but only a few people shed virus long enough to make public health planners concerned.
[...]
If the world switched from the oral vaccine to the injectable, which the international eradication campaign is planning for, the risk of random outbreaks from mutated virus would go away. The risk of existing shedders continuing to pump out virus would not—not unless vaccination continued indefinitely. The entire goal of the campaign, though, is to vaccinate the world until polio is eradicated, and then stop."
At the end of the decades-long global battle to eradicate polio from the planet, there is what looks like a simple goal: Render every person immune, by vaccination, for long enough that the disease...
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The tale of creation. One of the oldest and most amazing stories ever told.
 
#Goodread   #Linux   #GNU   #God  ;)
Linux is 24 years old today. In 1996, he told me how it all started.
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24 years ago Linux Project was publicly announced.

Happy birthday Linux.
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The collision of Prometheus and Pandora

Prometheus and Pandora were characters in a Greek myth, but now they are moons of Saturn.  They both orbit close to Saturn's F ring, zipping around this planet once every 15 hours or so.

Here you can see Prometheus carving strange slots in the F ring!  This ring is made of ice boulders, maybe up to 3 meters across.  Sometimes these chunks of ice form temporary clumps up to 10 kilometers in size.  At other times, these clumps get pulled apart.   Prometheus steals boulders from the F ring with its gravitational pull.  And each time it comes as close as possible to Saturn, it carves a new slot in the F ring.

Why does this happen?  It's complicated, and people keep learning more about it.  I'm certainly no expert!

People used to call Prometheus and Pandora shepherd moons.  The idea was that they help stabilize the F ring.  It's a cool idea.  The singer Enya even made an album with this title.

But more recent work casts doubt on this theory.  Last month Emily Lakdawalla of the Planetary Society wrote:

The most surprising thing I've learned: You know how Prometheus and Pandora are the F ring shepherds? Prometheus on the inside, and Pandora on the outside, herding the billions of tiny particles that make up the ring into place? It's not true. Pandora is not involved in controlling the F ring's tight shape.

The first paper I looked at was written by Jeff Cuzzi and seven coauthors: "Saturn's F Ring core: Calm in the midst of chaos." (Let's pause for a moment to appreciate the quality of that paper title, which is both interesting and accurate, not boring or silly.) The paper seeks to explain why the central core of Saturn's F ring is so consistently shaped, even though various things are constantly acting to perturb it. In particular, Prometheus periodically plunges into the F ring, drawing out dramatic streamers and fans. In fact, Prometheus and Pandora, far from behaving as shepherds, actually act to stir up the motions of particles in most of the region near the F ring. Furthermore, there are other bodies that Cassini has spotted in the F ring region whose behavior is so chaotic that it's been hard to follow them; these things have "violent collisional interactions with the F ring core," so, all in all, it's really difficult to explain why the core of the F ring generally looks the same as it has ever since the Voyagers passed by.

According to her account of some recent papers, the key is a kind of resonance.  Resonant frequencies shape Saturn's rings in many ways, but here the key is something called a 'Lindblad resonance'.

The orbit of Prometheus precesses.  In other words, its point of closest approach to Saturn keeps slowly moving around.  So, the period with which this moon orbits Saturn is slightly different than the period with which it moves in and out from Saturn.  A Lindblad resonance happens when a chunk of ice goes around Saturn exactly once each time Prometheus goes in and out!  Lakdawalla writes:

So: consider a moon and a ring particle orbiting Saturn. We don't care (for the moment) what the orbital periods of the moon and ring particles are; what we do care about is the "in-and-out" period of the ring particle in its orbit. You have a Lindblad resonance if, every time the moon passes by the ring particle, the ring particle happens to be on the same position in its in-and-out motion.

The full story is even more complicated than that - obviously, since it has to explain all the weird patterns in the picture here.  The F ring consists of several strands, and these even braid around each other.  But I'll let you read her blog for more:

http://www.planetary.org/blogs/emily-lakdawalla/2014/07010001-ringmoons-shepherds.html

What I really want to tell you is some other news: how the F ring was formed in the first place!

It's in an interesting place.  Any moon too close to Saturn would be broken up by tidal forces unless it was held together by forces stronger than gravity.  The Roche limit says how close is too close: it's 147,000 kilometers from the center of Saturn.  The F ring is 140,180 kilometers from the center of Saturn.  So it's just within the Roche limit.

That could be a clue.  But how did the F ring actually form?  A new paper says it was created by a collision between Prometheus and Pandora!   The authors write:

Saturn’s F ring is a narrow ring of icy particles, located 3,400 km beyond the outer edge of the main ring system. Enigmatically, the F ring is accompanied on either side by two small satellites, Prometheus and Pandora, which are called shepherd satellites. The inner regular satellites of giant planets are thought to form by the accretion of particles from an ancient massive ring and subsequent outward migration. However, the origin of a system consisting of a narrow ring and shepherd satellites remains poorly understood. Here we present N-body numerical simulations to show that a collision of two of the small satellites that are thought to accumulate near the main ring’s outer edge can produce a system similar to the F ring and its shepherd satellites. We find that if the two rubble-pile satellites have denser cores, such an impact results in only partial disruption of the satellites and the formation of a narrow ring of particles between two remnant satellites. Our simulations suggest that the seemingly unusual F ring system is a natural outcome at the final stage of the formation process of the ring–satellite system of giant planets.

If so, the F ring and these moons have been engaged in a drama for millions of years, starting with the very formation of Saturn's rings.   We missed the beginning of the show.

The paper is here, but it ain't free:

• Ryuki Hyodo and Keiji Ohtsuki , Saturn’s F ring and shepherd satellites a natural outcome of satellite system formation, Nature Geoscience (2015), http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo2508.html.

The other paper I mentioned is free:

• J. N. Cuzzi, A. D. Whizin, R. C. Hogan, A. R. Dobrovolskis, L. Dones, M. R. Showalter, J. E. Colwell and J. D. Scargle, Saturn’s F Ring core: Calm in the midst of chaos, http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20140011651.pdf

Abstract: The long-term stability of the narrow F Ring core has been hard to understand. Instead of acting as 'shepherds', Prometheus and Pandora together stir the vast preponderance of the region into a chaotic state, consistent with the orbits of newly discovered objects like S/2004 S 6. We show how a comb of very narrow radial locations of high stability in semimajor axis is embedded within this otherwise chaotic region. The stability of these semimajor axes relies fundamentally on the unusual combination of rapid apse precession and long synodic period which characterizes the region. This situation allows stable 'antiresonances' to fall on or very close to traditional Lindblad resonances which, under more common circumstances, are destabilizing. We present numerical integrations of tens of thousands of test particles over tens of thousands of Prometheus orbits that map out the effect. The stable antiresonance zones are most stable in a subset of the region where Prometheus first-order resonances are least cluttered by Pandora resonances. This region of optimum stability is paradoxically closer to Prometheus than a location more representative of 'torque balance', helping explain a longstanding paradox. One stable zone corresponds closely to the currently observed semimajor axis of the F Ring core. While the model helps explain the stability of the narrow F Ring core, it does not explain why the F Ring material all shares a common apse longitude; we speculate that collisional damping at the preferred semimajor axis (not included in the current simulations) may provide that final step. Essentially, we find that the F Ring core is not confined by a combination of Prometheus and Pandora, but a combination of Prometheus and precession.

Whew - complicated!  S/2004 S 6 is a weird little thing they've discovered in the F ring.  Nobody even knows if it's solid or just a clump of dust.  You can see it here:

https://en.wikipedia.org/wiki/S/2004_S_6

#spnetwork #saturn #prometheus #pandora #rings doi:10.1038/ngeo2508
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Tired of feeding his cat in the usual way, Ben Millam created a primal, yet techie alternative for his cat, Monkey. Millam said the project started when he began to read about why cats repeatedly explore the same areas. He…
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A Neural Algorithm of Artistic Style.
"In fine art, especially painting, humans have mastered the skill to create unique visual experiences through composing a complex interplay between the content and style of an image. Thus far the algorithmic basis of this process is unknown and there exists no artificial system with similar capabilities. However, in other key areas of visual perception such as object and face recognition near-human performance was recently demonstrated by a class of biologically inspired vision models called Deep Neural Networks. Here we introduce an artificial system based on a Deep Neural Network that creates artistic images of high perceptual quality. The system uses neural representations to separate and recombine content and style of arbitrary images, providing a neural algorithm for the creation of artistic images. Moreover, in light of the striking similarities between performance-optimised artificial neural networks and biological vision, our work offers a path forward to an algorithmic understanding of how humans create and perceive artistic imagery."

"Images that combine the content of a photograph with the style of several wellknown artworks. The images were created by finding an image that simultaneously matches the content representation of the photograph and the style representation of the artwork. The original photograph depicting the Neckarfront in Tubingen, Germany, is shown in A. The painting that provided the style for the respective generated image is shown in the bottom left corner of each panel. B The Shipwreck of the Minotaur by J.M.W. Turner, 1805. C The Starry Night by Vincent van Gogh, 1889. D Der Schrei by Edvard Munch, 1893. E Femme nue assise by Pablo Picasso, 1910. F Composition VII by Wassily Kandinsky, 1913."
Sources:
http://arxiv.org/abs/1508.06576
http://arxiv.org/pdf/1508.06576v1.pdf

Related: https://www.youtube.com/watch?v=-R9bJGNHltQ (Deep Neural Network Learns Van Gogh's Art)
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This is what happens when your dad is a sysadmin or security conscious ;)

#Funny   #Sysadmin   #IT   #Life   #humor  
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Wowza.
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Sydney on a beautiful day...
by Col Jung
Sydney, Australia

 (1024 x 683)

Copyright © 2015 –  Col Jung

#cityscape  #australia
#aerial-view  #sydney  
#aircraft  #aerial  #city
#airplane-view  #skyline
#NSW  #window-seat    
#Col-Jung  #boats  #AU    

Location: 
Sydney, New South Wales, Australia

Uploaded: January 1, 2015

Camera Data
Camera: Sony ILCA-7
Lens: 50mm ASPH Summilux
Exposure: 1/6400 s
ISO Speed: 100
Flash: Off, did not fire

© Col Jung's website: https://goo.gl/YAtidf

File: (1643) 

(Click on slideshow to see full resolution)
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Great talk. Sort of..
 
The thing that's fascinating about the most recent Der Spiegel leaks about the NSA is that it makes a lot of the things that seemed unrealistic in spy TV shows and movies now seem positively mundane.

I never considered that if I bought a $2 USB cable online, I should expect the NSA to intercept the package and install a circuit board into the plug that turned the USB cable into a wifi device. Or that if I bought off-the-shelf Ethernet RJ45 plugs, they might be delivered after the NSA has installed MITM hardware in them. Or that the NSA might be illuminating my house with 1kW radar to power wireless microphones and keyboard loggers.
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Radioactive is the word, is the word that you heard. It's got groove it's got meaning. Radioactive is the time, is the place, is the motion. Radioactive is the way we are feeling.
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