Showing posts with label Light Research. Show all posts
Showing posts with label Light Research. Show all posts

Wednesday, December 28, 2016

How many Earth-size planets are orbiting Sun-like stars?

Size and number of Kepler Planet Candidates
Size and number of Kepler Planet Candidates
In the search for planets that may be habitable outside of our own solar system, one of the elements that should be considered is planet size.  Planet size is important for various reasons. There is evidence that suggests that plate tectonic activity on a global level is a necessary factor for supporting life on a planet similar to Earth.  Planets must be of a particular size in order to allow for global plate tectonics.[001] Larger planets (between the range of Mars and Earth) may be necessary to maintain an atmosphere with the right composition to support life.[002] Based on the limited examples available within our own solar system, life may require specific conditions that are associated with Earth's size.

So, how many Earth-size planets exist?  Well, to start with, small terrestrial planets drastically outnumber larger Earth-size and Jupiter-size planets.  That being the case, recent observations suggest that Earth-size planets are fairly common around Sun-like stars.[003] There are so many such planets, the 2013 study Prevalence of Earth-size planets orbiting Sun-like stars states that (given certain circumstances),
...the nearest such planet is expected to orbit a star that is less than 12 light-years from Earth and can be seen by the unaided eye.[003]
That's not only a lot of planets, 12 light-years is a distance that seems at least somewhat reachable with technology that is currently being investigated.  Recently, such a planet seems to have been discovered around the closest star to our own, Proxima Centauri.[004]  Technically, Proxima Centauri cannot be seen with the unaided eye on its own, but rather as part triple star system that appears as one the dot in the Southern Hemisphere sky called Alpha Centauri, but close enough (literally).[005]

Kepler's Small Habitable Zone Planets
Kepler's Small Habitable Zone Planets
Overall based on Kepler space observatory results, it is calculated that about 22% of all Sun-like stars have an Earth-size planet within its Habitable Zone.  Prevalence of Earth-size planets orbiting Sun-like stars seems well informed in its conclusion (2013),
Future instrumentation to image and take spectra of these Earths need only observe a few dozen nearby stars to detect a sample of Earth-size planets residing in the Habitable Zones of their host stars.[003]
The number of Sun-like stars in the Milky Way Galaxy is said to be about 10%.*  The number total stars is a matter of debate, but it often stated as 100 billion stars.[006]  10% of that is 10 billion stars.  Therefore, 22% of 10 billion is 2.2 billion stars.  With that determined, how common are planets that are so similar to Earth that events naturally occur in the right sequence to spark and nurture life?  How likely is that life to evolve to develop the human-level expression of intelligence and curiosity?  What is the likelihood of any of species developing in the same timeframe as us?  Are other species close enough to us to communicate with us?  Should we really trying to reach out to these others?  Some of these questions will be addressed in further articles.

*10% is stated by multiple tertiary sources for "sun-like" stars, and 7.5% is stated for "g-type" stars, but I could not verify these percentages from any original sources.

Primary reference:
E.A. Petigura, A.W. Howard, G.W. Marcya, Proceedings of the National Academy of Sciences of the United States of America, 110 no. 48, (Nov., 2013), 19273-19278, 10.1073/pnas.1319909110,  Prevalence of Earth-size planets orbiting Sun-like stars

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Wednesday, December 21, 2016

Habitable Worlds Around Binary Star Systems might not match Sci-fi

It's hard to talk about planets in binary (dual) star systems without mentioning Star Wars: A New Hope.  The famous scene of Luke Skywalker standing and looking off into the distance while two suns appear near the horizon is iconic.  However, there's a problem with that iconic scene.  The problem is a not full-fledged error, just an unlikelihood: both suns appear as the same size in the sky in very close proximity to each other.  The reason this is unlikely is due to the two types of planetary orbits in binary star systems: s-type and p-type.  A planet in either type of binary system would rarely see both suns as the same size in the sky and that close to each other, even if the suns are the same size.

S-type is the name for the orbit of a planet that revolves around just one of the two stars within a binary system. P-type is the name for the orbit of a planet that revolves around both stars within a binary system, having a common barycenter (or center of mass) with the suns as the suns orbit around each other.[001]

S-type orbits are interesting, but for this article, I'll cover P-type because this is more interesting to me when talking about Habitable Zones, particularly where the suns have similar masses.  Of course, even with p-type orbits, there exist many possible varieties for how the suns can orbit each other.

The ability of a planet to maintain liquid water depends on the interaction between stellar radiation and the top of its atmosphere.  Also, that interaction is complicated in a binary system.  There can be substantial difference in energy received by the dual suns.  Sometimes both suns appear side by side in the sky, providing maximum energy.   However, when one sun is eclipsed by the other, the amount of energy is lessened due to the closer sun blocking the stellar radiation from its partner.[001]

In either case, this variation in stellar radiation can limit how small a planet's orbit can be around the dual suns and still be capable of harboring life.   As stated in Calculating the Habitable Zone of Binary Start Systems II: P-Type Binaries:
This interaction strongly depends on the stellar spectral energy distributions implying that stars with different energy distributions will contribute differently to the absolute incident flux at the top of the planet’s atmosphere.[001]
Even with all of these factors, planet formation within the Habitable Zone of a binary system would be similar to that of a singular star system.[001]


Common binary system and P-type orbit
Two suns of similar mass with elliptical orbits around a common barycenter
Another common binary system and P-type orbit
   Two suns of similar mass in the same orbit around a common barycenter

Where two suns are of the same size, their location to the planet can vary greatly depending on the size of their orbit around their common barycenter.  If there is a wide orbit, it is safe to assume that one sun will provide more energy than the other sun which is farther away.  In this case, the further sun would appear smaller in size within the sky, even though both suns are of the same mass.  The graphics above suggest why the iconic Star Wars scene isn't likely accurate.  The scene is possible maybe one or two times per year if the suns are in similar orbits which are tight and circular; or in rare instances where the suns have elliptical orbits and the planet just happens to be in the right place at the right time.

Sidebar

Close up of Alpha Centauri A and B, NASA photo
Here's a close up of Alpha Centauri A and B. Their distance from each other can be as much as 11 AU's, which would make a p-type planetary orbit so large, that habitable planets would be unlikely.  Planets have been discovered in s-type orbits around Alpha Centauri B and their sibling Proxima Centauri.

HZ reference:
N. Haghighipour, L. Kaltenegger, The Astrophysical Journal, 777 (Nov., 2013) 166, arXiv:1306.2890 [astro-ph.EP], Calculating the Habitable Zone of Binary Star Systems II: P-Type Binaries 

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Tuesday, December 13, 2016

Habitable Planets around White Dwarfs

The white dwarf G29-38 (NASA)
The white dwarf G29-38 (NASA)
Out of all the odd scenarios that might be possible in our Universe, the thought that there might be habitable planets around White Dwarfs is one of the stranger ideas, in my opinion.  Imagine what it would be like to look up to see a White Dwarf dominating the daytime sky.  How close would the planet have to be to the star to receive enough light and energy to support life?  How would a planet find itself within the Habitable Zone around a White Dwarf?

This last question is particularly interesting because White Dwarfs are the remains of a Red Giants.  Red Giants are the last phase of fusion based main sequence stars.  Between White Dwarf, Red Giant and main sequence phases, a star changes so drastically that it is unlikely planets close to the star would survive into the next phase.  Some very interesting things need to happen for a planet to form within the Habitable Zone of a White Dwarf.

With main sequence stars, the Habitable Zone slows moves away from the star because the star slowly gets hotter.  A planet that starts out within the Habitable Zone of a young main sequence stars may not remain within the Habitable Zone for the full length of that star's life-cycle.[001] [002] Oddly enough, White Dwarfs have the exact opposite problem.  White Dwarfs cool down as they age.[003]  Habitable Zones around White Dwarfs will shrink until being too small for any sizable planet to exist within it.

The Habitable Zone around a White Dwarf is very small compared to that of Sun.  The Habitable Zone around Sun is roughly between the orbits of Venus and Mars.  The Habitable Zone around a White Dwarf is much closer than even the orbit of Mercury around Sun.[003]  It seems a planet that close to a White Dwarf cannot exist without some special events.

How do planets get to the Habitable Zone?

A planet could have existed in the previous solar system during the main sequence star phase, but much further out; so far out that it may not have been previously habitable.  When the main sequence star expands to become a Red Giant, then explodes to leave a White Dwarf, the planet would have to move from the outer reaches of the solar system to a stable close orbit.  This sounds incredible, but apparently it is possible since planets have been discovered around Neutron Stars, which go thru even more violence.[003]

Another possible scenario is it the matter ejected from the exploding Red Giant, or other remaining debris within the solar system somehow creates a new accretion disk around the newly formed White Dwarf, from which new planets could form.[003]
Water Cycle
Water Cycle

Even if either of these scenarios do happen, a water related challenge presents itself.  A lot water must somehow remain or be (re)introduced on these special planets.  Water is likely stripped from any existing planet that moves so close to the White Dwarf.[004]  Water is also unlikely to be available on any planet that forms so close to any star, White Dwarf or otherwise.  Maybe these planets could gather new water via the same processes as Earth, possibly "delivered to by a barrage of comets."[003]

If a planet is lucky enough to form around a White Dwarf, what's that White Dwarf going to look like in the sky?  White Dwarfs have a lot of mass, but they are very small in size.  White Dwarfs are about the same size as Earth.[005]  By my rough calculations, the Habitable Zone around a White Dwarf is about 5 times the distance of Earth to the Moon.  So, I image the White Dwarf would appear several times smaller in the sky as the Earth appears to the Moon.  Maintaining habitability of planet around a White Dwarf might be a bit like trying to keep warm outside on a freezing night next to a slowly fading campfire.

Primary reference:
A Loeb, D Maoz, Monthly Notices of the Royal Astronomical Society: Letters, Volume 432, Issue 1, p.11-15, arXiv:1301.4994 [astro-ph.EP], Detecting bio-markers in habitable-zone earths transiting white dwarfs

Monday, December 05, 2016

Small stars may have stable Habitable Zones, but habitable planets might not be common there


Protoplanetary accretion disk around a new star
Protoplanetary accretion disk around a new star
The previous article Limited lifespan of Habitable Zones around other stars (September 2016) covered the topic of Habitable Zones for planets around other solar systems.  However, Habitable Zones are only one of considerations for finding other stars with habitable planets.  Given the lack of data right now, sometimes science has to fall back on simulations.  These simulations do not replace actual observations.  Instead, they offer clues as to how we may be proceed in our search for hard data.

Habitable Zones appear to be more stable and longer lasting around small stars, such as Red Dwarfs.[001]  However, what are the chances of habitable planets appearing in these small zones around these small stars?  It turns out that the chances may not be good.

According to the study A Decreased Probability Of Habitable Planet Formation Around Low-Mass Stars, multiple simulations suggest that low-mass stars are unlikely to have terrestrial planets of sufficient size within their Habitable Zones.  This is due to a several factors.  That's not to say it is impossible nor improbable; just not as common as previous thought.[002]

Other factors

Besides Habitable Zones, another factor to consider is the Habitable Planet Mass Limit.  There is evidence that suggests that plate tectonic activity on a global level is a necessary factor for supporting life on a planet similar to Earth.  Planets must be of a particular size in order to allow for global tectonics.[002]  The lack or presence of global tectonics seems to be a factor in the differences between Venus and Earth.  Though Venus seems to be large enough, its surface heals too quickly to allow for global tectonics.[003]   The examples within our own solar system suggest that even when planets are large enough, there is no guarantee they will have global tectonics.

Another factor is the Protoplanetary Disk.  During the planet formation phase (accretion), there has to be enough material within the disk of matter that forms around very young stars (Protoplanetary Disk) in order produce larger planets.  Though there are a lot of unknowns regarding this factor, the "ratio of disk mass to stellar mass is roughly constant with stellar mass".  Also, planets seem to form much faster around small stars for various reasons.  With less time to form and less mass within the Protoplanetary Disk, planets around low-mass stars may typically be much smaller.  A second issue with fast forming planets is that they are much less likely to have enough time to collect enough water to support life.[002]

Exceptions?

Nothing is absolute.  Gliese 581 is a Red Dwarf that has a number of large planets, and also has a debris disk that appears to have tens times amount of comet debris than our own Solar System.  This suggests low-mass stars can have habitable planets.  That said, Gliese 581 may be an outlier.  Other factors are obviously involved that need further study.

Primary reference:
S. N. Raymond, J. Scalo and V. S. Meadows, The Astrophysical Journal 669 (Nov., 2007) 606–614, arXiv:0707.1711 [astro-ph], A Decreased Probability of Habitable Planet Formation around Low-Mass Stars

Response:
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Friday, September 09, 2016

Limited lifespan of Habitable Zones around other stars [and a loosely held secret finally revealed about me]

Habitable zone around a red dwarf, image © Matthew Lorono, 2016
Habitable Zone around a Red Dwarf star
I've been fascinated by the idea of planets around other stars since I was young.  In fact, I developed several fictional solar systems, one of which became the basis for an online gaming and science fiction club.  That solar system is called Greeop System,[001]  which inspired the development of many more solar systems and formed the basis of many gaming and fictional story plots.[002]

At some point, I stumbled across the book Rare Earth: Why Complex Life Is Uncommon In The Universe (2000), which is one of the earliest sources that discusses the idea of Habitable Zones around stars.  

What's a Habitable Zone?  If a terrestrial planet orbits its sun at just the right distance, that sun provides the right amount of light and other energy to make life more likely, given several other factors.  If a planet is too close to its sun, it is likely too hot.  If a planet is too far from its sun, it is likely too cold.  This is why Habitable Zones are sometimes called Goldilocks Zones, in reference to the fairy tale Goldilocks and the Three Bears and finding options that are "just right" between two extremes.

In the past decade, the concept of Habitable Zone has been refined.  From the study Habitable Zone Lifetimes of Exoplanets around Main Sequence Stars, it is now often defined similar to,
...the circumstellar distance at which surface temperatures allow liquid water to be present on the planet’s surface, assuming variable H2O/CO2/CH4 greenhouse forcings.  The Habitable Zone has a minimum and maximum extent, forming inner (closer to the star) and outer boundaries that are set in part by biogeochemical climate feedback mechanisms and stellar luminosity.[003]
Yeah, Goldilocks metaphor seems to get the point across easier.  The question is, what's "just right" for life?  Star size and age appear to play the substantial roles in setting the limits of a Habitable Zone.  Not only is the Habitable Zone different between large and small stars, it can move over the life-cycle of a star. For example, main sequence stars gradually output more energy over billions of years.  A planet that initially forms within the Habitable Zone of a young star might not remain in the Habitable Zone later in the star's life-span. It is predicted that our Sun will be so hot in 1.75B years, surface water will no longer be possible on Earth, presumably making life on Earth no longer sustainable.[003]

If a planet has the right conditions and resides within the Habitable Zone, life still has to appear and evolve in some sort of sequence.  Taking Earth as the only example we have,
... this stepwise progression began with the origin of life, continued through the transition from replicating molecules to RNA and then DNA [1B years after Earth formation], from prokaryotes to eukaryotes [1.5 to 2.5B yrs after Earth formation] and cell differentiation [3.5 to 4B yrs after Earth formation], and concluded with the final step from primate to human societies [4.54B years after Earth formation].[003]
However, if just one of these steps takes a lot longer, there is a drastically lessened chance of having enough time to develop intelligent life similar to humans; assuming the march toward more intelligent creatures is inherent to the process of evolution on different planets.  Different stars may also extend or reduce the time-frame within which life may appear and develop.  Larger stars will have short Habitable Zone lifespans.  Smaller stars, such as Red Dwarfs may have very long and stable Habitable Zone lifespans.

Of course, a lot of this is based on assumptions that life on other planets will resemble life that formed on Earth.  Maybe life of different kinds exist in the Universe.[004]  The rules may be different for different kinds of life.  Maybe Earth is extremely unusual. Worse, maybe we will not be able to immediately recognize other forms of life simply because it is so different from our experience.  As more information is gathered, these issues will hopefully be addressed.

Pirmary reference:
Andrew J. Rushby, Mark W. Claire, Hugh Osborn, and Andrew J. Watson. Astrobiology. September 2013, 13(9): 833-849. doi:10.1089/ast.2012.0938, Habitable Zone Lifetimes of Exoplanets around Main Sequence Stars.

Response:
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Monday, September 05, 2016

Wind what?

What do you call that giant tower with spinning blades that produces electricity from wind?  Windmill?  Well, kinda, but not really.  The word "mill" that forms the latter portion of the word "windmill" is just that, a mill.  In this context, a mill is a machine that grinds and crushes something, such as grain.MD There isn't a whole lot of grinding and crushing of anything when using a rotor to produce electricity.  It's really the opposite of a mill.

The definition of "turbine" is a bit more broad.  A turbine is a machine that converts the movement of a fluid into rotary motion.TD  With that definition, a mill is a type of turbine.  However, a turbine is not necessarily a mill.

There is no specific word that provides a special name for an electricity producing turbine, so the word turbine itself is used.  Turbine is also used to name machines that make electricity from flowing water, such as those found at Hoover Dam.HD   So, that giant tower with spinning blades that produces electricity is more correctly called a wind turbine.  A collection of wind turbines at one location are frequently referred to as "wind farms".


Another wind powered machine is the windpump, which is used to pump water.  Windpumps and windmills have been in use for about 1500 years, being first developed in the Persian region between A.D. 500 and 900.WP  Wind turbines owe their existence to our long history of windmills and windpumps.  It's somewhat understandable that there is some confusion of terms.

Interesting modern examples of wind power in use


There's even a wind-powered record player!  Well, that's mostly art, but apparently it works well.  Then, there's this guy, William Kamkwamba, who built wind turbines and pumps for his village in Malawi at a time of famine and when such luxaries were only experienced by 2% of their population.

Friday, July 29, 2016

Trouble with Wikileaks emails from DNC: as far as I can tell, no "election manipulation" is actually in the emails

Anyone can go to the Wikileaks page and peruse through the DNC leaked emails.

You know what I've seen no one do? Look through the emails and talk about any actual evidence of election manipulation.  I've seen journalist use rather dicey innuendo regarding email content, but not much else.

Most of emails are just reports.  What conversations I've seen are just people expressing their opinions and/or making strategies in support of those opinions and desires (like how best to get certain points across to their constituents).  I've not seen anyone showing anything from the emails about rigging the primaries.

The party insiders are supposed to be neutral by their own party rules, but I don't really care about DNC or any party's rules.  I'm not a Democrat, Republican, Libertarian, Greenie, etc.  Even if I were, I still wouldn't care because I understand that people are people.  We Americans all have the rights to our own opinions, and the rights to pursue our own interests.  What would've suprized me?  Seeing every person in the DNC expressing complete neutrality regarding who is going to represent their party in the General Election.

The DNC rules aren't laws of the land. The only person that needs to be upset, maybe, is Sanders since he was working under one set of rules, and others where not.  In the end, it still just people expressing their opinions and trying to work towards goals they feel are best for their interests.  None of this has anything to do with me, and none of this is in anyway a "manipulation" of elections.

If someone can dig up something that shows election rigging, then we have a story, as well as an actual crime.  Maybe it is buried somewhere deep in the emails.   I've not see it.  I'd be interested to see if something like that pops up.   The fact that no journalist have dug it up suggests that it's just not there.

At this point, after looking through the emails myself, I'm forming the opinion that anyone that uses the terms "manipulate" or "rigged" in reference to the primary elections based on these emails is being dishonest or honestly doesn't know what they are talking about (which is still a form of dishonesty).

I'm also now of the opinion that Julian Assange, who has made several incendiary statements regarding the content of these emails, is full of nonsense.  What little good he did in the distant past is now been cancelled out by his modern behavior.

Tuesday, May 03, 2016

Killing of the Real-time Strategy game

Real time strategy (RTS) game is often defined by what it is not, rather than what it is.  When looking up real time strategy game, you'll often find it described as a strategy game that is not turned-based.1  I find this tendency as funny.  Normally, something is defined by its characteristics, not the lack thereof.  A real time strategy game is a strategy game played in real time (hence the name) between two or more opposing teams.  Elements of real time strategy games typically include fighting units used for attack, harvesting units used to gather resources, structures of various functions, terrains of various properties that aid or reduce defense, unit spawning, hidden map areas until explored (fog of war), etc.

Generally, real time strategy games allow the player to control position of units on a field of play (map) with various types of terrain. Units can be assigned to act on specified targets.  For example, harvesting units can be assigned to collect resources at a specific location on the map.  Another example, fighting units can be assigned to attack (cause damage) on specified opponent's units.  Typically, units without specified targets will act autonomously in how they attack nearby opposing units or collect nearby resources.

One of the first real time strategy games is The Ancient Art of War, which was initially released in 1984.  I played this game for many hours.  I even also designed many of my own levels for this game.  Many games have followed.  Dune II is often considered the break-thru title that popularized real time strategy.  Prior to online gaming, many releases of real time strategy games supported diverse game-play possibilities.

An alternate viewpoint about real time strategy games can be found in the article What is a real-time strategy game? An exploration and definition.

Currently, real-time strategy games are looking like the proverbial red-headed step child of gaming. Fairly few RTS are being made any more (for a variety of reasons, but that is a topic for another article perhaps) and they tend not to sell particularly well, nor do most of them hold on to viable communities for considerable periods of time...
The author of this article laments that real time strategy games have not been particularly common or successful in recent years.

I found another article, Did the multiplayer online battle arena kill real-time strategy, that claims to explain why real time strategy games aren't be developed anymore, from a perspective of a Blizzard fan.  In this article, the cause is passively blamed on the popularization of massive multiplayer (MMO) online games.  I think this author is wrong.  He references events long after real time strategy games began to falter.  However, the popularization of online gaming is related to the demise of the real time strategy genre, it wasn't related to MMO's, such as World of Warcraft.

Real time strategy games seemed to be an excellent fit for online gaming.  Instead of being pitted against the limited AI, players are able to play against other humans.  However, instead of valuing the challenge of playing against humans with various strategies, a vocal set of players didn't want other humans to use other types of winning strategies against them. They wanted to limit all human players to the same strategies that they chose for themselves.

Developers unfortunately listened to these vocal users too much and reduced real time strategy games down to frantic rushes to resources and frantic rushes on opponent's bases with very repetitive build order of units and structures.  Instead of adding capabilities to increase the number of possible strategies (to better match the real world), developers reduced game play down to focus on one strategy.  The games were still tactical in how you faced units against each other, but they lost all sense of strategy.  With reduced game play possibilities, developers lost their ability to be innovative and bring in new inspiration into the subsequent real time strategy games.  Without the ability to expand playable strategies of real time strategy games, the genre has atrophied.

Thursday, July 09, 2015

Significantly higher rate of foodborne illness and death in cities with plastic bag bans

In 2007, San Francisco, CA became the first county in the US (or anywhere) to ban plastic bags at grocery stores. A 2012 study titled Grocery Bag Bans and Foodborne Illness by Jonathan Klick University of Pennsylvania and Joshua d. Wright of George Mason University stated the following,

We find that the San Francisco County ban is associated with a 46 percent increase in deaths from foodborne illnesses. 

The study not only links deaths to the plastic bag ban, but also the additional costs of illness for those who get sick, but do not die.  What is the reason for more people getting sick?  The study claims it is because we are reusing our reusable shopping bags without cleaning them between uses!

The study goes on to point out that similar increases in illnesses from foodborne diseases have been seen in other communities that have since also banned plastic bags.

Ick!

I pointed out this potential problem about six years ago in my Tuesday Two/Epoch-Fail series, where I stated,

And what of reusable canvas bags? Heh. Guess what. You have to buy them. They get very unsanitary very quickly. Wanna guess how many patrons are not washing them regularly? There are reasons behind our strict food handling guidelines, and canvas bags now represent a very weak link in food safety

The Grocery Bag Bans and Foodborne Illness study isn't perfect, but it does coincide with my statements.  However, it's not just about keeping bags washed.  The study finds that we store the reusable bags in places that tend to breed bacteria, such as car trunks.

The study also points out that the overall cost of the ban doesn't come close to breaking even with the benefit seen to the environment as a result of the ban.  In other words, the cost of plastic bag bans is substantially greater than the cost benefit to the environment!

The problem is that we have local governments making rules about society without proper research in vain attempts at social engineering.  Before the plastic bag bans went into effect, these governments should've found and implemented safe alternatives.  It's been eights years since that original ban, and we still do not have safe alternatives even being proposed!  What we do have is more cities and counties pushing for expansion of the ban, despite the harm it causes us and the lack of actual benefit to the environment.


Saturday, June 27, 2015

Lack of reproducibility of scientific papers getting attention

A lack of reproducibility of published scientific studies is finally getting recognition by the corporations (that seems to me to that could lose millions from bad research).  Academia seems a bit resist.  Source article:
 Reseach uncovering unreproducibility faces backlash