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Official page of #ScienceSunday and #ScienceEveryday (brought to you by Robby Bowles, Allison Sekuler, Rajini Rao, Chad Haney, Buddhini Samarasinghe, Aubrey Francisco, and Carissa Braun)
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You have found the official page for #ScienceSunday (co-curated by Robby Bowles, Allison Sekuler, Rajini Rao, Chad HaneyBuddhini SamarasingheAubrey Francisco, and +Carissa Braun)! Post anything related to science and tag it with #ScienceSunday, +ScienceSunday, and each curator to ensure we see your post. If you are a photographer, post a science related image and explain why it relates to science to you - doesn't need to be too specific (science is all around us!). If you are not a photographer, simply post anything related to science - drawings, movies, songs, and text are all welcome. Regardless of the type of post, feel free to add your 2 cents into a discussion in the comments. We always have some great posts with amazing images, great science information, and a lot of interesting conversations, and we're looking forward to even more in the weeks to come. If you miss the "Sunday" in #ScienceSunday, feel free to tag with #ScienceEveryday - we try to monitor those posts as well.

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What is Near Infrared Spectroscopy?

Getting down to spectral basics with some cool GIFs for #ScienceSunday

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Inferring from Infrared

Imagine if there was a way to know which watermelon is sweeter? When is that avocado going to ripen? How many calories, carbs or protein is in that shake? How your plants are doing? What's in those pills your taking? A new low-cost handheld sensor on the market promises all those answers and more, in real time (https://www.consumerphysics.com/myscio/scio). The technology is based on near infrared spectroscopy. How does it work?

Calorific Rays: We all know that a prism can separate ordinary light into the vibrant colors of the rainbow. Back in 1800, musician and astronomer William Herschel wanted to know the temperature of each color. By placing a thermometer with a blackened bulb along the spectrum, he discovered that the red end was warmer than the blue. To his surprise, a thermometer placed just beyond the visible red part of the spectrum was even warmer. He had discovered infrared rays, although he didn't realize it at the time. This is the same heat that you feel when you hold your hand near a fire.

Bond. Covalent Bond. Shaken and Stirred: Chemicals are arrangements of atoms, held together by bonds. You can think of these bonds as tiny springs in motion. They stretch, wiggle, rotate and twist. When they absorb energy, the natural vibrations of bonds increase. Because of quantum mechanical constraints, these increases occur only to discrete energy levels. Different bond types (C-O, or C-H) and different vibration modes result in a series of absorptions at different wavelengths. By looking at which wavelengths of light were absorbed by a compound, we can deduce what types of chemical bonds are in the sample. Absorbances in the near infrared region of the spectrum can be so complex that they give rise to unique fingerprints of different chemicals.

Citizen Science: Spectrometers built with near infrared technology used to be large, expensive and restricted to universities. That's changing! The handheld spectrometer transmits chemical signatures to a smartphone which checks the pattern against a huge library of compounds in the "cloud" and returns the analysis to you within seconds. When you use it, not only will you be learning more about the chemical world around you but you'll also be helping to build a database of knowledge of the stuff around us. Now that's citizen science! 

REF: An introduction to near infrared (NIR) spectroscopy. A.M.C. Davies. https://www.impublications.com/content/introduction-near-infrared-nir-spectroscopy

GIFS: All gifs are from Wikipedia and are in the public domain.
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Immunotherapy in Cancer: HOA!
#ScienceEveryday   when it isn't #ScienceSunday  
 
What does the immune system have to do with cancer? What exactly is immunotherapy? Join us for a +Cancer Research UK and +Science on Google+ Hangout on Air as we speak to Professor +Frances Balkwill and Professor +Ben Willcox about cancer immunotherapy. 

Fran is a Professor of Cancer Biology at Queen Mary University in London and is a fantastic science communicator. Her research focuses on the links between cancer and inflammation. Ben is a Professor of Molecular Immunology at the University of Birmingham and his work focuses on understanding immune receptor recognition. 
 
This HOA will be hosted by Dr +Buddhini Samarasinghe  and Dr +Kat Arney . You can tune in on Friday July 24th at 4 PM UK time. The hangout will be available for viewing on our YouTube channel (https://www.youtube.com/ScienceHangouts) after the event.
This Hangout On Air is hosted by Science on Google+. The live video broadcast will begin soon.
Q&A
Preview
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Cancer Immunotherapy
Fri, July 24, 11:00 AM
Hangouts On Air - Broadcast for free

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+God Emperor Lionel Lauer wouldn't be a science HOA without it! 
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SciTech Digest for 19 July 2015
Thanks as usual +Mark Bruce.

#ScienceSunday   #SciSunCH  
 
SciTech #ScienceSunday Digest - 29/2015.
Permalink here: http://www.scitechdigest.net/2015/07/gene-therapy-hearing-single-molecule.html 

Gene therapy hearing, Single molecule transistor, Better metamaterials, Crystal light traps, Optofluidic neural probe, Synthetic foods, New particle phenomena, New CRISPR tools, Memory tracking, Regenerating neuronal axons. 

1. Restoring Hearing with Gene Therapy
Deaf mice have had their hearing restored via a gene therapy that used a standard engineered adeno-associated virus to deliver a correct version of a single gene to sensory hair cells in the cochlea http://vector.childrenshospital.org/2015/07/gene-therapy-restores-hearing-in-deaf-mice/. The mechanistic insights into sound perception are equally nice to consider: the gene encodes a channel protein that sits on the microvilli of sensory hair cells whose deformation due to pressure waves causes the channels to open and allow calcium ions to enter the cell. There are a number of different genes that can cause deafness and this platform might be tailored to correct all of them as needed depending on the genetics of each patient. 

2. Single Molecule Transistor
A basic experimental transistor has been demonstrated that consists of a single phthalocyanine molecule surrounded by a hexagon of 12 indium atoms http://phys.org/news/2015-07-transistor-molecule-atoms.html. At this scale structures are hypersensitive to single electron hops and in this case fabricated with a scanning tunnelling microscope; it turns out that electron flow across the molecule is coupled to the orientation of the surface-bound molecule and is capable of generating large conductance gaps. 

3. Improvements in Metamaterial Designs
A few interesting new metamaterial designs this week. First, a new and incredibly thin carpet cloak has been designed to incorporate periodic teflon and ceramic dielectric structures that can effectively bend light to shield anything beneath the cloak to give the appearance of a flat surface http://spectrum.ieee.org/tech-talk/semiconductors/materials/a-slender-bright-invisbility-cloak. This is a two-dimensional metamaterial design and now they just need to make the thing to prove that it works. Second, a new metamaterial design is able to accurately preserve the phase of light while guiding it around sharp corners and abrupt bumps http://phys.org/news/2015-07-clever-cloaks-unique-metamaterials-phase.html. Third, progress towards lossless perfect lenses http://www.mtu.edu/news/stories/2015/july/bringing-back-magic-metamaterials.html

4. Trapping Light in Crystal Granules 
Tiny crystals of hexagonal boron nitride can effectively trap light within their structures http://phys.org/news/2015-07-orbits-intriguing-material.html. Incident light becomes trapped within the material in a form known as a phonon polariton, and at certain resonant frequencies the light adopts simple closed orbits and this produces hot spots of electric fields that form elaborate geometric patterns. The resonant frequencies depend on the physical shape of the crystal and this is an instance of storing light inside a tiny piece of material for extended periods. A nice, elegant new phenomena that we’ll have to wait to see applications for. 

5. Tiny Optofluidic Neural Probe
A tiny flexible neural probe has been developed, a tenth the diameter of a human hair, wirelessly controllable, and able to both deliver drugs to deep inside the brain and also turn on LED lights to switch on optogenetically activated neurons http://neurosciencenews.com/optogenetics-device-neurons-2253/. This new device causes far less damage and displacement compared to existing devices. In experiments it was able to effectively deliver multiple different drugs including gene delivery vectors to the brains of mice and was also able to influence and control behaviour via light activation. Seems to be a great new platform tool for pushing this space forward. 

6. Better “Synthetic” Foods
At some point we’re going to have to drop that “synthetic” label for these new food technologies. First this week was presentations about the ongoing development of 3D printing with foods and the economic and personalised sensation benefits that might accrue http://www.ift.org/newsroom/news-releases/2015/july/13/3d-printers-poised-to-have-major-implications-for-food-manufacturing.aspx. Second, the cost of cultured lab-grown burger meat continues to build on the advance announced in 2013 and is currently projected to decline from $300,000 down to $65 per kilogram http://phys.org/news/2015-07-scientist-texture-lab-produced-hamburger.html

7. Experimental Confirmation of Weyl Point Phenomena
In a nice reduction of theory to practice massless particles with a single point in their energy spectrum , called Weyl points, have been proven to exist experimentally with the aid of new photonic crystal designs http://newsoffice.mit.edu/2015/Weyl-points-detected-0716. This work was done with microwave light in order to simplify the crystal fabrication but there is no reason visible light couldn’t be used in future. Possible future applications include optical devices, high-power single-mode lasers, and bulk materials or lenses that only allow a certain angle and a certain frequency of light to pass through. 

8. CRISPR with Non-Homologous Insertions and Light Activation
A new CRISPR system can achieve targeted insertion of genetic sequences up to 5,000 base pairs long into mammalian cells via non-homologous end-joining, i.e. without the need to include lengthy homologous sequence arms on each side of the genetic sequence / gene of interest and DNA cut or insertion site http://nextbigfuture.com/2015/07/over-5000-base-pairs-were-inserted-into.html. Other benefits include simpler, cheaper plasmid vectors and while the efficiency of integration was not high there is scope to improve this if needed in future. Another newly engineered form of CRISPR now allows light-activation of the CRISPR machinery for applications such as regulating genes with light for example http://www.the-scientist.com/?articles.view/articleNo/43255/title/Optogenetics-Meets-CRISPR/

9. Measuring Memory, Improving Memory, and Altering Neuronal Firing
Electrodes implanted into rat brains and measuring activity from place cells in the hippocampus suggest that there are definite gaps in certain types of normal memory, far from the smooth flow that typically characterises memory http://www.hopkinsmedicine.org/news/media/releases/scientists_watch_rats_string_memories_together. A new type of transcranial direct current stimulation known as transcranial pulsed current stimulation appears to boost neuronal excitability and muscle skill acquisition while transcranial magnetic stimulation appears to show good results in dampening neuronal excitability and associated tinnitus symptoms http://www.kurzweilai.net/could-this-new-electrical-brain-zap-method-help-you-learn-muscle-skills-faster

10. Regenerating Neuronal Axons in Severed Spines
I missed this a couple of weeks ago but switching off or deleting one particular gene was sufficient to induce neuronal regeneration and axon growth in the spines of mice with severed spines http://neurosciencenews.com/corticospinal-axon-regeneration-paralysis-2189/. The neurons were able to bridge the site of injury regardless of whether gene inactivation happened immediately, four months post injury, or one year post injury and are able to form tentative synaptic connections. As a candidate treatment the gene inactivation might be targeted to certain neurons or the specific region of interest. 

Archive: http://www.scitechdigest.net/2015/07/gene-therapy-hearing-single-molecule.html
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Lynx and Assassin bugs
Read the lynx to learn how assassin bugs can help conservation efforts.

#ScienceSunday   #SciSunCH  
 
Smart conservation
Another #ScienceEveryday  meets #Caturday . Conservationists were able to determine if endangered Iberian lynxes were pregnant or not by getting blood samples from triatominae, aka assassin bugs. Read the short lynx to find out more.
Researchers used the insects to keep tabs on population growth in the threatened species
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SciTech Digest 14 June 2015
Thanks as always, +Mark Bruce 

#ScienceSunday   #SciSunCH  
 
SciTech #ScienceSunday Digest - 24/2015.
Permalink here: http://www.scitechdigest.net/2015/06/advanced-brain-interfaces-seawater.html

Advanced brain interfaces, Seawater lithium mining, Better streaming gaming, Body on chip, Portable lab tests, Synthetic immune organoids, Quantum random numbers, Faster tissue regeneration, Pushing Moore’s Law, Vagus nerve stimulators.

1. Brain Interface via Injectable Nanoparticles & Meshes
Magnetoelectric nanoparticles can be injected into the brains of mice (each receiving 20 billion nanoparticle in the experiment) and when stimulated by an external magnetic field they induce an electric field that interacts with neuronal networks and the electric field they produce, as confirmed via EEG http://www.newscientist.com/article/dn27676-20-billion-nanoparticles-talk-to-the-brain-using-electricity.html. Very interesting platform for interfacing with the brain, especially if it can be shown to work in reverse to pick up discrete brain signals. In related news nanoscale electronic meshes can be injected into the body and brain as intimate sensors and interfaces able to connect to other devices http://news.harvard.edu/gazette/story/2015/06/injectable-electronics-promise-sharper-view-of-brain/

2. Mining Lithium from Seawater
A new, early prototype system is able to efficiently extract lithium from seawater using a dialysis-like system with a superconducting membrane that only lets lithium ions pass through http://www.technologyreview.com/news/538036/quest-to-mine-seawater-for-lithium-advances/. If it scales it could be timely given the projected demand for lithium batteries against current reserves. Interesting that this was from Japan, which has previously demonstrated a similar uranium-from-seawater system. 

3. Improving Streaming Gaming Bandwidth
A new collaborative rendering process called Kahawai shares rendering between the server and the user’s device to cut down the required network bandwidth by 83% http://www.techspot.com/news/60792-duke-university-microsoft-researchers-create-tool-reduces-online.html?google_editors_picks=true, and is mainly applicable to interactive game-streaming in which a remote server does most of the number-crunching and sends updated video to the user, which enables very “light” user device hardware but suffers with poor bandwidth. 

4. The Latest Body on a Chip
The latest human-on-a-chip or body-on-a-chip device comprises specific spherical micro-tissues loaded into microfluidic compartments that are connected by tiny tubes, allowing circulation of nutrients, drugs, and importantly drug metabolites throughout the system http://cordis.europa.eu/result/rcn/165278_en.html. It was tested with (i) liver and tumour tissue, (ii) liver, tumour, heart, nervous tissue, and (iii) developed an eight tissue system for future testing; such devices will transform drug development in future. 

5. Portable Handheld Lab Tests
The latest portable handheld laboratory testing device is the Sceptre from a company called Qloudlab, spun out of the EPFL and currently testing the device at a major hospital http://phys.org/news/2015-06-pocket-sized-medical-lab-chuv.html. The device will use interchangeable connectors to take small patient blood, urine, and saliva samples and will be able to run a battery of tests before sending the data to a mobile phone or cloud service; the first test application will be for certain lipids but if successful will expand to others. Once mature we’d all ideally have one of these devices at home. 

6. Synthetic Functional Immune Organs
A synthetic immune system organoid has been produced out of gelatin-based hydrogels reinforced with silica nanoparticles and seeded with immune cells; mimicking the microenvironment of lymphoid tissue the organoid and demonstrated the ability to proliferate and activate B cells and induce the production of antibodies against invaders http://www.news.cornell.edu/stories/2015/06/engineers-synthetic-immune-organ-produces-antibodies. Such organoids might be used in future to rescue a patient’s immune system or otherwise employed industrially to optimise production of therapeutic antibodies. 

7. Quantum Random Number Generator
The fastest quantum random number generator has been unveiled, able to generate 68 billion random numbers per second (compared to only 1 million per second with current systems) by creating a highly sensitive interferometer that that converts fluctuations in the phase of emitted photons into intensity changes and so allowing conventional faster photodetectors to be used http://www.technologyreview.com/view/538406/worlds-fastest-quantum-random-number-generator-unveiled-in-china/. Immediate applications include quantum cryptography. 

8. Triggering Faster Tissue Regeneration
A new drug shows promise in inducing latent tissue stem cells to repair damaged tissues more quickly and across many different tissues at once and hopes to soon enter human trials https://www.fightaging.org/archives/2015/06/a-drug-candidate-to-trigger-faster-regeneration.php. Animal models showed massively damaged livers healing twice as fast as normal, while a model of chronic ulcers was healed and further ulcerative symptoms prevented. We could all do with this at various points in our lives, even if just to heal scrapes and strains. 

9. Pushing Moore’s Law with Better Semiconductors
New work from IBM has successfully fabricated single crystal nanostructures and 3D stacked nanowires with III-V materials (indium, gallium, & arsenide alloys) and for the first time integrated these with silicon in an economically viable process compatible with standard chip fabrication technology http://www.aip.org/publishing/journal-highlights/futuristic-components-silicon-chips-fabricated-successfully. Such materials are considered important for enabling further Moore’s Law style performance gains from conventional silicon chips. 

10. Vagus Nerve Stimulator for Brain Health
A company called Microtransponder has developed an implanted vagus-nerve stimulator to induce targeted relearning in the brain, for example, to treat tinnitus and stroke by retraining the brain to route around damage that causes these diseases http://spectrum.ieee.org/tech-talk/biomedical/devices/implant-fights-stroke-tinnitus-by-retraining-the-brain. Future targets will include post-traumatic stress disorder and obsessive-compulsive disorder, while others are pursuing epilepsy and migraine. 

Archive: http://www.scitechdigest.net/2015/06/advanced-brain-interfaces-seawater.html
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Sitting Down With Science

We always appreciate a combination of art and science. Thanks for finding this one, +Justin Chung!

#ScienceSunday #SciSunCB
 
#ScienceSunday + #SundayPunday = Periodic Table!

This visual pun is pure awesome! "Periodic Table of Elements" made by Nazila Alimohammadi and Anna Clark in 2003 at Wake Forest University. Actinide and lanthanide series are the bench. (Photo: Larry WFU)

If you like science news, check out my "Science" collection: https://plus.google.com/collection/gLLpR

#chemistry #periodictable #elements #geek #humor #pundaysunday #pundayeveryday #punday #visualpun #pun #science #sciencepunday #scienceeveryday
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Weekly Science Roundup

In case you missed them, here are the top news stories in science and technology curated by +Mark Bruce . Thanks, Mark!

#ScienceSunday   #SciSunRR  
 
SciTech #ScienceSunday Digest - 30/2015.
Permalink here: http://www.scitechdigest.net/2015/07/brain-inspired-networking-scene.html 

Brain inspired networking, Scene description, Bacteria vs cancer, Deep learning genetics, Sophisticated DNA origami, Graphene on silicon, Viral immune aging, Stretchy conducting fibers, Biomimicking solar cells, Useful metal foams. 

1. Better Brain-Inspired Networking
New fundamental insights into how the growing brain develops neural networks through variable rates of synaptic pruning have led to the development of algorithms for building efficient computer networking architectures http://www.salk.edu/news/pressrelease_details.php?press_id=2096. Simulations of such networks suggest that they are more efficient than current computer networks, allowing more direct information flows, multiple paths to reach destinations, and reduced risk of network failure. 

2. Image Recognition and Scene Description
Here’s an interesting and accessible update article on Stanford’s NeuralTalk algorithm that can analyse images, recognise objects in them, and describe the scene in natural language with regards to the relation between different objects and their number http://www.theverge.com/2015/7/17/8985699/stanford-neural-networks-image-recognition-google-study. This work continues to be developed and there are now far more examples of its use; it isn’t perfect and doesn’t yet work in all situations reliably but the results are impressive nonetheless and realtime relevant applications such as for autonomous vehicle operation are also being explored. In related news object recognition for robots takes a step forward http://newsoffice.mit.edu/2015/object-recognition-robots-0724

3. Bacteria that Kill Cancer Cells
An interesting twist on modern cancer immunotherapies involves the use of engineered bacterial strains that attack tumour cells by entering them and subsequently thrive and replicate in the low-oxygen environments that are usually present http://www.newsweek.com/programming-bacteria-kill-cancer-cells-355474. This whole field began with the observation that surgical tumour-removal patients were more likely to recover if they developed post-surgical infection. Engineered bacterial strains are designed to retain efficiency while reducing overall human toxicity. It’s also interesting to think about this in the sense of a lethal form of endosymbiosis. 

4. Deep Learning: Genetics and Sketching
A couple of interesting deep learning advances this week. First, Deep Genomics launches to offer advanced personalised medicine and genome analysis services to better predict the consequences of certain mutations on a person’s health http://www.deepgenomics.com/news/2015/7/22/meet-deep-genomics-a-start-up-bringing-the-power-of-deep-learning-to-genomics. Second, the Sketch-a-Net system demonstrated that it can correctly identify the subject of a line-drawn sketch better than a human can http://www.qmul.ac.uk/media/news/items/se/159633.html. In related news deep learning can recognise faces from just thermal images http://www.technologyreview.com/view/539656/deep-neural-nets-can-now-recognize-your-face-in-thermal-images/

5. Increasing Sophistication of DNA Origami
Improvements in computer aided design of 3D DNA origami structures now make it easier than ever to create custom, atomically-precise, 3D DNA origami materials http://www.theverge.com/2015/7/22/9013851/dna-nanotechnology-origami-3d-printing-automation-bunny. The algorithms will take an arbitrary 3D shape, optimise the interlocking DNA scaffolding to realise the shape at the nanoscale and determine the best DNA sequences that need to be produced in order to form the structures; in the example demonstration these included bunny rabbits, nanotubes, toruses, humanoids, icosahedra and other things. In the same week another group also pushed the boundaries with their 2D and 3D DNA origami patterns http://phys.org/news/2015-07-rare-built-dna-emerge.html.

6. Graphene-on-Silicon Innovations
A new wafer-scale ion-implantation synthesis method has demonstrated a simple and scalable way to produce uniform graphene sheets on silicon, potentially enabling integrated circuits that can more readily dissipate heat http://phys.org/news/2015-07-easy-scalable-method-graphene-silicon.html. In other work graphene on silicon creates a near frictionless surface in which two surfaces can slide past each other smoothly when separated by nanodiamond clusters that encase themselves in graphene nanoscrolls http://phys.org/news/2015-07-simulations-near-frictionless-material.html

7. Why Tackle a Virus that Causes No Symptoms
Infection and its recurrence by cytomegalovirus (CMV), which is prevalent throughout most of the population, causes few if any symptoms and so might be innocuous. But chronic life-long infection by this virus activates the immune system on an on-going basis and this leads to aging of the immune system, the accumulation of damage, and contributes to the reduction of immune efficiency with age https://www.fightaging.org/archives/2015/07/immune-profiling-the-contribution-of-cytomegalovirus-to-aging.php. So there are good reasons for developing therapies and interventions towards such a seemingly harmless virus. 

8. Stretchy, Electrically-Conducting Fibers
A new fiber material has been developed that can reversibly stretch to over 14 times its length while electrical conductivity increases by 200 times when fully stretched http://www.utdallas.edu/news/2015/7/23-31627_Scientists-Stretch-Electrically-Conducting-Fibers-_story-wide.html?WT.mc_id=NewsHomePageCenterColumn. The base fibers consist of a rubber core wrapped in carbon nanotube fibers, and these are engineered with a deliberate buckled structure that helps provide the beneficial properties. The group hope to develop applications in artificial muscles and machine actuators. 

9. Biomimicry Improves Solar Cells
A new solar cell design utilises a surface that mimics the texture and structure of the compound eyes of moths, albeit at much smaller feature sizes of 20nm, in order to exploit anti-reflective properties http://phys.org/news/2015-07-artificial-moth-eyes-silicon-solar.html. The surfaces are self-assembled from block copolymers and effectively reduce light reflections to less than 1% across all visible and near-infrared wavelengths of light. The self-assembly process appears scalable; hopefully this can be applied to commercial grade solar cells and other materials. 

10. Useful Properties for Metal Foams
Lightweight composite metal foam materials are effective at both blocking a range of radiation sources (x-rays, gamma rays, neutrons) and also absorbing high-impact collision energy https://news.ncsu.edu/2015/07/rabiei-foam-rays-2015/. Initial tests were very promising but the group believe further optimisation and improvements are possible, mainly with their lead candidate comprising stainless steel with small amounts of tungsten. Applications include nuclear safety and transportation, space exploration, and medical devices - particularly those that utilise radiation. 

Archive: http://www.scitechdigest.net/2015/07/brain-inspired-networking-scene.html
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Super post about Supernovas
Wow, thanks +Jonah Miller for an example of how a science post should be done: clear, concise, and with references.

#ScienceSunday   #SciSunCH  
 
Type 1a: The Other Type of Supernova

When people hear “supernova” they usually think of a star that runs out of fuel. Without the engine of nuclear fusion to heat it, the star collapses under its own weight, which triggers a huge explosion. This is a “core-collapse supernova,” one of the most energetic events in the universe. The result is usually a neutron star or a black hole.

However, there’s another type of supernova, one in which a star whose nuclear fires long ago petered out is reignited, causing a catastrophic explosion. This is the type Ia supernova. We start our story with the type of star that explodes: the white dwarf.

(Those who wish to read this post in blog form can find it here: http://www.thephysicsmill.com/2015/06/29/type-1a-the-other-type-of-supernova/)

White Dwarfs

A star is a balancing act. On the one hand, these massive objects exert an enormous gravitational pull on themselves, driving all the gas to collapse towards the centre of the star. On the other hand, the nuclear fusion reaction at the core of the star heats it up, and hot gas likes to expand, holding the star apart. Paradoxically, the driver of this nuclear reaction is the gravitational pull of the star itself. The weight of the star pushes the stuff in the core together so much that the atoms fuse together, releasing huge amounts of energy.

(Surprisingly, stars need quantum mechanics to burn. When atoms fuse together in a star, the fusion only occurs because the atoms quantum tunnel together. Astrophysicist +Brian Koberlein  has  a nice article on this: https://briankoberlein.com/2014/06/10/chain-reaction/)

The eventual fate of a main sequence star like our sun depends on its mass. If the star is more than about 1.4 times the mass of our sun (this is called the Chandrasekhar limit: https://en.wikipedia.org/wiki/Chandrasekhar_limit) then, once the nuclear reaction stops, the star collapses under its own weight, triggering a core-collapse supernova explosion. However, if the star is less massive, something amazing happens: the star collapses down to a tiny fraction of its original size–a white dwarf star might have a radius only 4 times or so larger than that of the Earth–but it doesn’t explode. Now the star isn’t held up by heat or nuclear fusion. It’s held up by a quantum-mechanical effect called Pauli exclusion principle (See: http://www.thephysicsmill.com/2013/01/27/binary-unity-the-pauli-exclusion-principle/).

Basically, a white dwarf is a hot, ultradense fluid made of electrons and atomic nuclei, packed together so tightly that the only thing holding them apart is their inability to occupy the same physical space. This means white dwarfs are incredibly dense. A tablespoon white dwarf starstuff would weigh about 100 tonnes [1]. Figure 2 shows a white dwarf star next to a larger type A main sequence star on the left and our sun on the right. Keep in mind: that tiny little white dwarf star has the same amount of mass as our sun.

(Neutron stars [2]  are very much like white dwarfs, and they are held apart by similar principles. However neutron stars are, unsurprisingly, made mostly of neutrons, and can be about ten times denser and smaller than white dwarfs.)

But sometimes, a white dwarf can reignite. And the results are explosive.

Reignition

The nuclear fires of a white dwarf have died down. But these fires were first produced by intense pressure. So if the pressure in the core of the white dwarf is ever high enough, then the carbon atoms in the core of the star will start fusing and, temporarily, the nuclear furnace will reignite. Figure 3 shows a computer simulation of the beginning of this process. The core of the star becomes hot due to nuclear fusion and this spreads across the star.

The end results of stellar nuclear fusion are carbon and oxygen. So a white dwarf is made up of carbon and oxygen nuclei… and as we know, oxygen reactions are what make fire. So once the nuclear fires reignite, the star doesn’t just become hotter or expand. The entire star literally burns. That’s what figure 3 is showing. The bright orange stuff in the images is actually ash.

Rocket Star

Although the fusion reaction ignites the star, it doesn’t produce enough energy to make the star explode completely. Instead, all of the fire that spread across the star eventually concentrates on one side of the star in a concentrated burst, which can accelerate the star up to thousands of kilometres per second like a rocket. Stars moving this fast are, awesomely, called hypervelocity stars [3]. Figure 4 shows the next part of the simulation in figure 3, where now one side of the star explodes in a pulse.

After the burning in figure 3 and the explosion in figure 4, things calm down. The nuclear fusion in the star stops, and it returns to normal... albeit with a very different velocity.

Before the Explosion

So now I’ve described how the star explodes… but I still haven’t told you why it explodes. I said that if the pressure in the core of the star becomes high enough, it can re-ignite. But how does that happen? Quite simply, the star has to put on weight. Usually, this means that the white dwarf in question has a companion star–another star nearby such that the two stars orbit each other. And over time, the white dwarf steals material from the companion until it gains enough mass that the weight of the star on the core causes it to reignite.

It’s not known what type of star the companion must be [4]. One possibility is that it must be a massive star near the end of its life. Figure 5 shows the stellar evolution process that might result in a white dwarf stealing from a massive companion. Another possibility is that two white dwarfs might collide. Distinguishing between these models, or perhaps some combination of the two, and identifying which stars will become supernovae is a long-standing problem in astrophysics.

Different Models and The Ignition Problem

It is worth noting that the precise mechanism by which the nuclear fusion restarts in the star is not completely known. There are also a number of models that describe the details of the supernova explosion. The simulation I showed is one such model, but there are others. However, all models are qualitatively the same and they all produce predictions that match the supernovae we observe in the sky.

Further Reading

As we’ve learned, core-collapse supernovae are not the only kind of supernovae. Indeed, the study of white dwarfs and type 1a supernovae is an active field of research with a rich history. Here I include some resources for your reading enjoyment.

1. Measurements of type 1a supernovae were used to measure the accelerated expansion of the universe. I wrote about this in my article on the expanding universe:
http://www.thephysicsmill.com/2013/03/24/receding-horizons-dark-energy-and-the-expanding-universe/

2. Imagine the Universe! by NASA has a great article on white dwarfs with some cool pictures:
http://imagine.gsfc.nasa.gov/science/objects/dwarfs1.html

3. Universe Today has a nice article on the Chandrasekhar limit, which defines how massive a white dwarf can be before it collapses into a black hole:
http://www.universetoday.com/40852/chandrasekhar-limit/

4. For the experts, this is the simulation by Jordan et al. that I showed you above:
http://dx.doi.org/10.1088/0004-637X/759/1/53

5. This is is a review article of various models of type 1a supernova explosions:
http://arxiv.org/abs/astro-ph/0006305

6. And this is a review article on the physics of white dwarf stars:
http://iopscience.iop.org/0034-4885/53/7/001

7. Finally, this is a review of the supernova progenitor problem:
http://dx.doi.org/10.1071/AS11052

Related Reading

If you enjoyed this post, you might enjoy some of my other posts on astrophysics.

1. In this post, I discuss how planets are formed:
http://www.thephysicsmill.com/2014/06/01/planets-form/

2. In this post, I describe simulations of what happens when a black hole eats a neutron star:
http://www.thephysicsmill.com/2015/05/03/simulating-gamma-ray-bursts/

3. In this post, I describe one speculative idea that says black holes can explode:
http://www.thephysicsmill.com/2015/06/14/speculative-sunday-can-a-black-hole-explode/

References
[1] https://en.wikipedia.org/wiki/White_dwarf#Composition_and_structure
[2] https://en.wikipedia.org/wiki/Neutron_star
[3] https://en.wikipedia.org/wiki/Stellar_kinematics#Hypervelocity_stars
[4] https://en.wikipedia.org/wiki/Type_Ia_supernova#Formation

#ScienceEveryDay #physics #astrophysics #science #supernova #astronomy #spaceporn +ScienceSunday 
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+Jonah Miller It's all good. Cool that you're an astrophysicist! 
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Apollo 11 Anniversary
Thanks +Michael Interbartolo for sharing this great post about the Apollo 11 anniversary.

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AMERICA LEAVES FOR THE MOON - Apollo 11 Anniversary
previous day - https://plus.google.com/116992234810067730471/posts/HKpyDBTND3p

July 16, 1969, 9:32am EDT
T- 4 days, 6 hours, 45 minutes
(until man sets foot on the Moon)
It is before dawn on the eastern coast of Florida. Throughout the night radio and television reports link the American nation and the world with a tiny strip of land on the Florida coast. There high atop a liquid rocket three humans from middle America were to be hurtled into space this day on the most unusual undertaking in the history of exploration: voyage to the Moon and land upon it. It has been 11 years since the Space Age was born. It has been eight years since the 35th President of the United States, John Fitzgerald Kennedy, set the lunar landing as a national goal of the United States of America.

Now on this date everyone the world over will get to see if that boast can be made real. The countdown is at T-5 hours, 32 minutes and counting. This is launch day for the United States’ 21st manned space mission: Apollo 11, the spacecraft known as Columbia and Eagle, aboard Saturn V no. AS-506. ..All systems are GO. ...and you are there to witness the event --

4:00am EDT -
Astronaut Donald K. “Deke” Slayton enters the crew quarters at the Operations and Checkout Building at Kennedy Space Center. Outside in the pre-dawn darkness it is pitch black except for one object glowing on the horizon: searchlights play on the gigantic Saturn V.

4:15am EDT -
Slayton awakens each Apollo 11 astronaut: Neil Alden Armstrong, Edwin Buzz Aldrin, and Michael Collins. The crew showers and shaves, then moves to the nearby exercise room. There they are measured, weighed and given their final examinations.

Then it was time for breakfast. The astronauts set down to steak, scrambled eggs, white-bread toast, orange juice and coffee. While the crew ate, Slayton took a call from the launch pad. Back-up crew member Fred Haise was in the white room outside Columbia. Haise reported there were no problems with either rocket or spacecraft.

From breakfast the crew moved to the suit room. There suit technician Joe Schmitt helped the three astronauts don their bulky pressure suits. Armstrong and Aldrin’s suits were the first designed for Moonwalking, and sported gold helmet visors. The visors, however were inside the Lunar Module Eagle out atop the waiting Saturn


6:27am EDT -
Armstrong, Aldrin and Collins along with Deke Slayton leave the Operations and Checkout building and emerge onto the walkway to enter their transfer van and head to Saturn V. Over 100 photographers and press are there to catch a glimpse of the flyers. This marks the public’s last chance to see the crew before they leave for the Moon.
The van turns and heads out to Launch Complex 39A in the darkness using a special traffic lane set aside for them. All along the adjacent roads thousands of cars are already backed up in traffic.The trip to the pad takes 24 minutes.

Now the CBS News television network comes on live, the first U.S. broadcast outlet to go live this day. CBS anchorman Walter Cronkite narrates taped footage of the crew’s walkout. “No matter where you are,” Cronkite says, “you will remember this day: the day Man left for the Moon.” The sun now is rising over the Kennedy Space Center.
At the pad, Armstrong is first out of the van, followed by Aldrin and Collins. They enter the elevator at the base of the pad and ride to Service Arm 9 at the 320 foot level. The crew walks across the swing arm to the entrance to the white room.Walking across the gantry to the Saturn V. There pad technician Guenter Wendt is waiting for them with a gift- a mounted trout! Following the “exchange” of the gift (Wendt actually takes it back with him), the crew grasps an overhead rail mounted inside the capsule’s hatch and board Columbia. Armstrong crosses the sill first and settles into his left-hand couch. Next is Collins, who would normally occupy the center seat but for launch moves over to the right. Last is Aldrin. Ten minutes after arriving, Wendt’s crew starts to strap the astronauts into place. A fourth astronaut- Fred Haise, now crawls out of the craft and bids the astronauts good-bye. Wendt closes the hatch, latches it and the boost protective cover on its exterior. For the next 30 minutes the Command ship is tested for leakage. There is none. Wendt signals his crew it’s time to leave. And they do. Armstrong, Aldrin and Collins are now alone atop pad 39A.
For the next hour and a half the astronauts check out their booster and pair of spaceships. All is well with the duo. Test conductor Norm Carlson puts the big Saturn through a series of power transfer tests, and at T-15 minutes the spacecraft go on internal power.
At T-5 minutes Armstrong reports the crew access arm where they boarded Columbia has now retracted.
At T-50 seconds all three stages of the rocket are pressurized. The other two television networks are on live, as is nearly every radio station in America. They hear the voice of Launch Control Commentator Jack King count the last seconds. And then, at T-8.9 seconds, the firing command enters Saturn V’s first stage. And the flight to the Moon begins. ..it is 9:32 am EDT July 16, 1969.

9:32am EDT -

“Lift-off. ..we have lift-off, lift-off on Apollo 11!” cries Jack King from the launch control center. Fire and smoke have erupted from the bottom of the launch pad as the countdown reaches zero. Columns of flame rise on either side of the Saturn V. At the press and V.I.P. viewings sites, the spectacle unfolds in silence. From three miles away sound waves have not yet reached the viewers. But on television and radio microphones capture the thundering sound of the liquid engines as they roar to full thrust- 7.5 million pounds unleashed.

Now, slowly and majestically Saturn V rises into the air above the pad, with the great five F-1 rocket engines steering the booster away from the launch tower to avoid a collision. It is the heaviest and biggest object ever to leave the Earth, and it does so now riding a tail of flame 1,000 feet long. As the bottom of the F-1 engines clear the top of the hammerhead crane on the tower, the call goes out “tower clear!” Control of the mission now passes seamlessly to the Manned Space Center in Houston, Texas.

Inside Columbia Neil Armstrong follows the rocket’s progress carefully. He would later report that the Saturn was a series of vibrations rather than loud noise-with the great booster steering itself into the sky in a series of small, jerky movements. For the first 450 feet of the flight the rocket was vertical. Then it pitches over into a tilt and roll program to line up the rocket’s center of mass with the thrusting engines. The guidance computer inside the Instrument Unit holds Saturn in a tilt arrest profile for the remainder of the first stage’s burn. The computer is compensating for the wind conditions average for late July.Heading skyward to make the journey from the Earth to the Moon.
From the observation stands the sound now hits the viewers. It is rolling, rhythmic sound that rattles pocket change and makes speech difficult. The crowd is on its feet now cheering, and all along the beaches millions roar their approval-Go! At one minute five seconds into the flight Saturn V hits the Sound Barrier and goes supersonic- from zero to 760 MPH in 65 seconds.

Stage one fires perfectly and drops away, followed some six minutes later by stage two. Stage three fires briefly to insert the rocket unit and the two spacecraft into a parking Earth orbit. At cut-off, it has been just over 11 minutes since lift-off.

12:02pm EDT -
After a two hour and twenty-one minute checkout in orbit, the third stage fires up for about six more minutes. Apollo 11 becomes the third manned craft to leave Earth orbit.

12:52pm EDT -
After the engine shuts down, Mike Collins takes control of Columbia. Explosive bolts detonate and four panels holding the Command and Service Modules to the top of the third stage fall away. Using his hand controls, Collins fires thrusters around the side of the Service Module, and Columbia moves out and away from the rocket, then turns around and doubles back. A probe in the nose of Columbia links with a receptacle atop the Lunar Module Eagle, nestled inside of the third stage rocket.

When latched together, Collins slowly pulls Eagle free of the now-spent rocket and the docked Apollo 11 spacecraft begin their three day voyage to the Moon. It has been four and a half hours now since lift-off.
next day - https://plus.google.com/116992234810067730471/posts/2A9nJUuHDod
#apollo11  
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Harry the tiger shark is quite the traveler
+Sam Andrews reports the results of tracking tiger sharks using satellite technology. Read on to learn about Harry and tracking his movements.

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The travelling life of the tiger shark

At 9 foot long, not including the tail, tiger shark (Galeocerdo cuvier) Harry Lindo is not exactly on the small side.  It’s not Harry’s size that is exciting scientists and shark enthusiasts, nor a photograph taken in 2009 by Ian Card showing a shark – suspected to be Harry, trying to eat a 150 lb juvenile tiger shark off the coast of Bermuda.  Between 2009 and 2012 researchers tagged 24 tiger sharks with satellite transmitters in the Challenger Bank, which lies just off Bermuda in the Atlantic Ocean.  In study lead by James Lea (The Guy Harvey Research Institute, +Nova Southeastern University Oceanographic Center) and team of international collaborators, those shark movements have been compiled and analysed.  Harry, it turns out, is one heck of an ocean wanderer.  In just over 3 years Harry swam over 44,000 kilometres – that’s more than the circumference of the Earth (just over 40,000 kilometres).  Harry’s track is the longest recorded for a tiger shark, and probably the longest ever published for any shark species.  

Unexpected movements
Tiger sharks are often spotted in coastal waters in temperate warm and tropical seas, but they also wander out into the open ocean.  The tagging study is just one of a few multi-year studies tracking individual shark migrations.  The researcher’s hard work was well rewarded when it revealed previously unknown shark movements in the Atlantic.  Most of the sharks in this study were male, but there were a few juvenile and females too.  Adult males, females, and juveniles of both sexes spent the winter months in the Caribbean.  When it came to the summer, all the adult males and just one adult female headed out into the open ocean of the North Atlantic in the summer.  The repeated use of these two vastly different types of habitats up to some 3,500 kilometres or so apart was surprising for a species previously thought to be primarily coastal.  The researchers think that repeated returns to the same sights may be better for the fish than constantly looking for new habitat.  They know where their food is, so why take a risk looking elsewhere only to find none?

How do you track a shark anyway?
Sharks, being a marine species, can’t simply be watched by people.  In this study, the sharks with tagged with something called Argos satellite platform terminal transmitters, also known as PTTs.  Every time a shark goes to the surface, these little tags send location to a receiving satellite.  The researchers can then grab this data from the satellites.  The raw data itself is not 100% usable and goes through processing to ensure that the information is accurate and suitable for analysis.  You can read more about this process in the methods section of the paper (see link below).  As for getting the tags on the shark in the first place, well you have to go fishing.  Once the shark is caught, the tracker device is fixed onto the shark’s fin and then it is released to go about its business.  There is a video showing shark tagging here http://youtu.be/HDUHwLg_RMQ (start at 1:07 if you don’t want to watch the whole thing)

Why is this work important?
Like many shark species, the tiger shark is an at risk species.  It is currently listed as ‘near threatened’ on the IUCN Red List, primarily threatened because it is targeted by fisheries, and caught as bycatch.  If we want to help look after these sharks, understanding their movement is really useful.  For example, earlier work by the Guy Harvey Research Institute highlighted how important the waters around Bermuda were for the sharks.  The Bahamas government responded by establishing a ‘shark sanctuary’ in 2011, in which all commercial fishing was banned in their territorial waters.  Looking after sharks isn’t just important for the sharks themselves either.  They are an apex predator, and considered to be a ‘keystone’ species, playing an essential role in ecosystem health.  One impact is to alter the predator-prey ratio, with alterations via the food web.  Lose too many predators can cause herbivore populations grow.  If there are too many herbivores, you could lose plant-based habitat, like sea grass beds – and the species that depend on them. 

Read the research for yourself
The paper was published in Nature Scientific Reports, and has been made open access.  You can have a read of the research yourself by heading here http://dx.doi.org/10.1038/srep11202 

Fancy following a shark?  
Head over to the Guy Harvey Research Institute Tracking Site where you can see movements of tiger sharks and other species, like blue marlin, sailfish, and mako sharks http://www.nova.edu/ocean/ghri/tracking/

Image: This image was published in +National Geographic  and taken by photographer Brian Skerry.  It depicts a tiger shark in the northern Bahamas at a location known as ‘Tiger Beach’.  National Geographic also have an excellent article looking at Brian’s work on sharks which you can read here http://ow.ly/Oi0tG.  To see more of Brian’s work, have a look at his website http://www.brianskerry.com/ 

#marinescience #movementecology #marinespatialecology #sciencesunday #sharks #tigersharks
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A Disaster-Response Challenge

In a competition inspired by the Fukushima nuclear meltdown, robots were run through an obstacle course of eight tasks which included driving, going through a door, opening a valve, punching through a wall, and dealing with rubble and stairs. Of the 24 robots to make it to the finals, it was HUBO (HUmanoid roBOT) that won. Read on at the link graciously provided by +Ciro Villa.

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South Koreans triumph in US robot challenge

"South Korean boffins carried home the $2 million top prize Saturday after their robot triumphed in a disaster-response challenge inspired by the 2011 Fukushima nuclear meltdown in Japan.

Team KAIST and its DRC-Hubo robot took the honor ahead of Team IHMC Robotics and Tartan Rescue, both from the United States, at the DARPA Robotics Challenge (DRC) after a two-day competition in California.

The runners-up win $1 million and $500,000 respectively, in a field of more than 20 competitors."

Read more: http://phys.org/news/2015-06-south-koreans-triumph-robot.html

#ScienceSunday

Image: The humanoid robot 'DRC-Hubo' developed by Team KAIST from South Korea completes a task before winning the finals of the DARPA Robotics Challenge at the Fairplex complex in Pomona, California on June 6, 2015 
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That is cool
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Floodplain Fundamentals

+Carissa Braun explains why flood prone zones are so important for the health of a river. Also, thanks Carissa, for rescuing that crayfish! ♥

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"The plants in a floodplain slow the floodwaters and prevent much damage downstream. The deep clay soils here store water, reducing flooding. Without intact floodplains, rivers, streams, and the land around them suffer increased erosion and more damaging floods."

Simply put, a floodplain is an area of land prone to flooding. It is often flat with higher elevation on both sides and may be either very small or very large. While it can be a problem for houses build on floodplains, they play an extremely important role. The floods that occur carry sediment rich in nutrients past banks and into surrounding areas. This in turn makes for fertile land ripe for agriculture and is where some of the world's earliest civilizations arose. 

Rather than be labeled as an aquatic or terrestrial ecosystem, some ecologist label floodplains as "pulsed" ecosystems - an intermediate habitat. With exception to extreme events, the "pulse" and reach of a floodplain can be predicted. The flat, fertile, predictable land is therefore considered ideal for building, but often at the cost of the health of the floodplain.

There are six criteria used to determine floodplain health:
1. The ecosystem supports habitats and viable native animal and plant populations similar to those present prior to any disturbances.
2. The ecosystem is able to return to its pre-existing condition after a disturbance, whether natural or human-induced.
3. The ecosystem is able to sustain itself.
4. The river can function as part of a healthy basin.
5. The annual flood pulse "connects" the main channel to its floodplain.
6. Infrequent natural events - floods and droughts - are able to maintain ecological structure and processes within the reach.

A healthy floodplain results in a healthy river. It is also important to understand when developing on a floodplain. Otherwise the result benefits no one.

A quick #ScienceSunday  post and, for the first time, #SignSunday . With all the flooding we've been having in Texas, I wasn't going to miss an opportunity to visit a favorite floodplain not that the trail could actually be walked since it's flooded. Still, the parts I could walk I took pictures to give some sense of a floodplain, and yes, I will be going back this week since the rain hasn't stopped yet!

Sources and Further Reading
Flood Plain | NatGeo
http://goo.gl/TKSpTq (website)
Floodplain River Ecology and the Concept of River Ecological Health
http://goo.gl/EPTCFP (pdf | USGS)
Trail at the +Heard Natural Science Museum & Wildlife Sanctuary.
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I was told I should have saved her for dinner, but alas, I'm not really a big fan of crayfish ;)
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