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philippe roux
Works at ENSSAT-Lannion
Attended université de rennes1
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philippe roux

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  #security   since 2006  it is considered that the  MD5 hash function  is vulnerable to collision attack (less that 1 hour is needed to generate such collisions  with pentium4-1,6Ghz processor), now some recent hardware improvements lead to make easier breaking  another well known hash function  :  the SHA-1 .  This still requires huge resource (about 100,000$),  but it seriously undermines the trust in the algorithm ...  it should be replaced by stronger versions like  SHA-2 or SHA-3.
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philippe roux

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#astronomy the evidence of water (or rather a brine) on Mars, seen by #HiRISE camera on #MRO spacecraft.
Water on Mars

Yes, you've heard there's liquid water on Mars.  But have you actually seen it?  Now you have.

This gif shows what's probably salty water flowing in Newton Crater on Mars.   The dark stripes are between 1/2 and 5 meters wide.  Stripes like this appear on steep slopes at several locations in the southern hemisphere of Mars.  They show up in the spring and summer, when the temperature can rise above the freezing point.  They go away when it gets colder. 

The photos here go from the early spring of one Mars year to mid-summer of the next year.  They were taken by the HiRISE camera on NASA's Mars Reconnaissance Orbiter.  That stands for High Resolution Imaging Science Experiment.
These images not new!   Here's a paper about them, written in 2011:

• Alfred S. McEwen et al, Seasonal flows on warm Martian slopes,
Science 333 (August 5, 2011), 740–743.  Available at , free if you register.

So, what made NASA announce now that there is liquid water on Mars?  Could it have anything to do with the new movie, The Martian?  I don't know.

Some puzzles about the movie:

Puzzle 1: why is there no communication apparatus in the living habitat where the Matt Damon character winds up living?  Does the book explain why?

Puzzle 2: what would it actually feel like to be in a dust storm on Mars? 

Puzzle 3: could you really take off in a rocket on Mars with just a tarp on top?

For more about these flows on Mars, see:

#spnetwork   doi:10.1126/science.1204816 #mars #astronomy
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Takaaki Kajita (Japan) and Arthur McDonald (Canada) won the #Nobel Prize in physics for the discovery of #neutrino oscillations.
Sudbury Neutrino Observatory detects neutrinos from the Sun, where only electron-neutrinos are produced. The reactions between neutrinos and the heavy water in the tank yielded the possibility to measure both electron-neutrinos and all three types of neutrinos combined. It was discovered that the electron-neutrinos were fewer than expected, while the total number of all three types of neutrinos combined still corresponded to expectations. The conclusion was that some of the electron-neutrinos had changed into another identity.
Read more about Arthur B. McDonald’s work at Sudbury Neutrino Observatory! Popular information – The 2015 #NobelPrize in Physics:
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hard to find an effective strategy to solve this puzzle, the simplest way seems to compute the sums by simple "blocks" taking into account that the sum never be greater than 2395 . Let S_n be the sum of digits  of pages wit number :
S_0= from 0 to 9  = 45
S_1= from 0 to 19  = 2*S_0+10 = 100
S_2= from 0 to 29  = 3*S_0+10+20 = 165
S_9= from 0 to 99  = 10*S_0 + 10*S_0 =900
S_19= from 0 to 199 = S_9+S_9+100 = 1900
S_20= from 0 to 209 = S_19+S_0+20 = 1965
S_21= from 0 to 219 = S_20+S_0+20+10 =2040
S_22= from 0 to 229 = S_21+S_0+20+20 =2125
S_23= from 0 to 239 = S_22+S_0+20+30 =2220
S_24= from 0 to 249 = S_23+S_0+20+40 =2325
How many pages are in the book if the sum of all digits of the page numbers is equal to 2395?  
384 votes  -  votes visible to Public
more than 400
It's hard to calculate
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Beau travail +philippe roux 
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#astronomy 3D view of #pluto moon #charon 
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#astronomy a first attempt to make an animation of the first part of last night eclipse, they are two difficulties:
1) aligning images, because no details of the lunar surface is visible on all the images
2) find the right progression in the list of images to simulate the visual appearance of the eclipse (as the brightness of the varying moon, the eye adapts continuously what we're trying to simulate changing the exposure time and sensitivity)
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Very nice. I have a little bit of an animation, but think it would be too jumpy to do from the beginning since I didn't time my shots in even intervals.
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#astronomy   what are the mysterious patterns  moving in the accretion disk around the star AU Microscopii ?
Mysterious Ripples Found Racing Through Planet-forming Disc
Hubble and VLT images of the disc around star AU Microscopii
Using images from the NASA/ESA Hubble Space Telescope and ESO’s Very Large Telescope, astronomers have discovered fast-moving wave-like features in the dusty disc around the nearby star AU Microscopii. These odd structures are unlike anything ever observed, or even predicted, before now.

The top row shows a Hubble image of the AU Mic disc from 2010, the middle row Hubble from 2011 and the bottom row is an image taken with the SPHERE instrument, mounted on the Very Large Telescope, from 2014. The black central circles show where the brilliant light of the central star has been blocked off to reveal the much fainter disc, and the position of the star is indicated schematically.

The scale bar at the top of the picture indicates the diameter of the orbit of the planet Neptune in the Solar System (60 AU).

Note that the brightness of the outer parts of the disc has been artificially brightened to reveal the faint structure.

Credit: ESO, NASA & ESA

+European Southern Observatory (ESO) 
+European Space Agency, ESA 
+Hubble Space Telescope 
+NASA Goddard 
+Space Telescope Science Institute 

#NASA #Astronomy #Hubble #Science #Star #Telescope #AUMicroscopii #Cosmos #Universe #ESA #STScI #ESO
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#astronomy morning #conjunction   with #venus #jupiter #mars and the #moon , if you have a clear sky try to see this in the next 3 days 1h hour before sunrise over eastern horizon
The Planets are Aligning at Dawn...Get up and take a look between 6:30am & 7:00am to see the Planets in Leo & this morning the Moon joined them above my backyard Observatory in Dayton, Ohio!
Look East,
Top to Bottom ...M44 Beehive cluster...Waning Moon, The Planet Venus, Brightest star in Leo is Regulus (blue), The Red Planet Mars, The Planet Jupiter. I included an illustrated help you ID them!
Keep watching each day as Jupiter,Mars, and Venus are going to get real close together by the end of the month.
Canon 6D DSLR & 24mm Lens, F4.5, ISO 800, 5 second exposure.
Best Regards,
John Chumack
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#mathematics    a parabola is a good approximation of a Catenary curve as long as it's not too much tightened. You can also see it expanding the Catenary equation in Taylor series : 
y=a*cosh(x/a)= 1+ x^2/(2a)+x^4/(24a^3)+...
so a*cosh(x/a)  stay close to the parabola 1+ x^2/(2a) unless "a" goes to 0 . See also

A rope is supported at its ends. What shape do you think it assumes?
Galileo, some 400 years ago, thought a parabola (red, thin line). He was wrong: the right answer is a so-called catenary (black), which, however, resembles a parabola quite well!

The curve a hanging flexible wire or chain assumes when supported at its ends and acted upon by a uniform gravitational force. The word catenary is derived from the Latin word for "chain". In 1669, Jungius disproved Galileo's claim that the curve of a chain hanging under gravity would be a parabola.
The curve is also called the alysoid and chainette. The equation was obtained by Leibniz, Huygens, and Johann Bernoulli in 1691 in response to a challenge by Jakob Bernoulli.

Huygens was the first to use the term catenary in a letter to Leibniz in 1690, and David Gregory wrote a treatise on the catenary in 1690. If you roll a parabola along a straight line, its focus traces out a catenary.
As proved by Euler in 1744, the catenary is also the curve which, when rotated, gives the surface of minimum surface area (the catenoid) for the given bounding circle.


Animation via mathani>>

#catenary #mathematics #animations
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#mathematics another way to look at primality  testing with the  trail division algorithm 
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#astronomy   an #ISS   transit captured during the #moon #eclipse   last Monday  ones again by Thierry Legault !
First transit of the ISS during a lunar eclipse ever captured !

More details on :

Image Credit : Thierry Legault

#moon   #lunareclipse   #eclipse   #astronomy  
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j'ai rarement eu d'aussi bonnes conditions pour observer une éclipse totale de Lune, je vais avoir besoin de pas mal de temps pour traiter toutes les images :-) je partage celle image prise au début de la totalité (4h25) qui me semble une des plus belle de ma série ...
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#astronomy Beautiful #moon #eclipse   tonight , weather condition were excellent ! I'll need a lot of time to process all the images taken last night, this one is probably one of the best I shot.
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Très belle photo !
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  • université de rennes1
    mathématiques, 1992 - 2001
  • lycée notre dame de campostal
    voie générale, 1989 - 1992
  • collège notre dame de campostal
    voie générale, 1985 - 1989
I like to discover new things every day, learn from other persons and share my experience ... to make it short : I'm an enthusiast :-)
I'm looking for interesting things about mathematics, astronomy, computing, outdoor sports ... do not hesitate to comment or re-share my public stream, then  I'll probably have a look to your profile and circle you if we have common centers of interest.
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on google+ since July 2011, survived to ten years of high-level in athletics, three years phD in mathematics and to being father of two girls! !
mathematics, astronomy, computer science, trail, mountain bike, kayak ...
mathematics, scilab programming
  • ENSSAT-Lannion
    Associate Professor in Mathematics for post graduate engineering students, 2014 - present
    for post graduate engineering students in electronics, optronics and computer science
  • ENSSAT-Lannion
    Professeur agrégé Mathématiques, 2014 - present
    école publique d'ingénieurs en 'électronique, optronique et informatique
  • IUT Lannion-B.Eng. level in Computing
    Associate Professor in Mathematics, 2001 - 2014
  • IUT Lannion-DUT informatique
    Professeur agrégé Mathématiques, 2001 - 2014
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