Slashdot stories can be listened to in audio form via an RSS feed, as read by our own robotic overlord.

 



Forgot your password?
typodupeerror

Slashdot videos: Now with more Slashdot!

  • View

  • Discuss

  • Share

We've improved Slashdot's video section; now you can view our video interviews, product close-ups and site visits with all the usual Slashdot options to comment, share, etc. No more walled garden! It's a work in progress -- we hope you'll check it out (Learn more about the recent updates).

×

Comment: kW or kWh? (Score 2) 245

by Framboise (#48751469) Attached to: Bill Gates Endorses Water From Human Waste

From BG blog one can conclude that the author belongs to the category of people unclear about the difference between a quantity of energy and a rate of energy production. To his excuse the common poor choice of kWh instead of the SI J (Joule J, 1 kWh = 3.6 MJ) as energy unit is just making energy discussions more confusing.

 

Comment: Mean and fluctuations (Score 2, Informative) 222

by Framboise (#48604295) Attached to: Linking Drought and Climate Change: Difficult To Do

The climate has always been a highly fluctuating system where extreme temperatures oscillate over seasons and location by, say typically +/-20K (Kelvin), around a mean value around 287K, slowly growing. In some countries the fluctuations are larger, in some others smaller. All the discussion about the human-induced warming is about the effect of changing this mean value by a couple of K (now +0.5K, in the next century by +2-4K). So even in the most pessimistic scenarios the warming remains in amplitude a small fraction of the typical annual fluctuations. No wonder that it will be difficult to prove that any extreme fluctuations will result from the warming.

Comment: Real advantage (Score 2) 108

by Framboise (#48495979) Attached to: Who Needs NASA? Exoplanet Detected Using a DSLR

One cannot escape the fact that bigger apperture telescopes can record fainter
stars, and/or perfom the photometry of bright stars with more precision than a simple camera.

To detect exoplanets one needs both large samples of stars recorded as continuously as
possible over several years and high precision photometry. Besides being cheap, the advantage
of a small camera is than the field is larger. But with a larger telescope in space like Kepler one
can target regions of the sky with density of stars optimal for the CCD/camera combination, and
observe continuously for months with the same instruments, which is crucial for differential
photometry. Thousands of amateurs worldwide detecting as many new exoplantes as Kepler
would face the problem of coordinating the analysis of huge amounts of heterogeneous and
incomplete data (due to day/night and weather interruptions in differently dark and transparent skies).

The real question is wether crowdsourcing planet detection is cheaper for global economy at equal scientific return than with state sponsored research. Perhaps the most important benefit of such an
activity is educational and promotional for research in general.

   

Comment: Re:Lua[0]? (Score 1) 729

The discussion is not on measuring continuous quantities
  but counting discrete objects. Physicists and mathematicians have indexed, say, vectors, starting with 1 for ages, except in recent times where sometimes they use 0 for very special reason (like chapter 0 in a book).

Comment: Assignement in Python (Score 2) 729

Assigning a number or a list in Python and many other languages (Julia) is a different operation. Such as

>>> a = 2
>>> b = a
>>> a = 1
>>> b
2

>>> a = [2]
>>> b = a
>>> a[0] = 1
>>> b
[1]

Octave (Matlab) is more consistent on this point, every assignement is a memory copy.

Comment: Neutrino temperature (Score 5, Interesting) 80

by Framboise (#47072873) Attached to: The Big Bang's Last Great Prediction

The orginal article keeps quoting the temperature of 1.96K as the neutrino background temperature, as found in most textbooks on the topic. This is a relic of the time people were assuming massless neutrinos. The confusion is maintained by people using the temperature as a synonym of energy. Actually the non-zero rest mass energy must be subtracted, providing the real kinetic energy of these particles (moving now at 100-1000 km/s) that would be exchanged with a super large thermometer (in view of the tiny interaction cross section). The effective neutrino temperature would then be measured in the milliKelvin range.

 

Real Users never know what they want, but they always know when your program doesn't deliver it.

Working...