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Greek Blog November 1, 2010

Posted by dorigo in Blogroll, internet, language, news, personal, physics, science.
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I had forgotten to link it from here, but the internet always provides a chance for redemption. So here I go. A couple of months ago I have opened another wordpress blog, where I write on particle physics – in Greek. This is a rather extravagant choice, and I think I need to spend a few words explaining it.

First of all, there is my love of the language, which I have been studying for two years. It is a difficult language to master, due to the interplay of several factors: the different alphabet, the enormous wealth of words, and the rather quick evolution of rules and uses. Maybe because of these challenges, I have found it quite entertaining to get on top of it.

The second reason for writing in Greek is, in fact, that I have yet a lot to learn, and I think that writing about science is a very good exercise, allowing me to find a solution to the translation problems I may encounter if I discuss about my job – physics – in that language.

The third reason is that I think there is no offer whatsoever in the web for a blog about particle physics in Greek (if you know any, let me know). So I might just try to fill that hole myself.

In short, the new blog is an experiment. I do not know, nor can predict, how long it will last; for now, if you know modern Greek please stop by. Below is a list of my recent efforts:

One million hits June 29, 2009

Posted by dorigo in Blogroll, internet, news, personal, physics.
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While this site has been basically inactive for over two months, it still draws some residual traffic due to google searches and links; so the hit counter has continued to click after April 15th, although at a rate of roughly a third of what it did before.

Today’s news is that we got past the millionth click. Thanks to everybody for your interest in particle physics and in my reports. Please visit www.scientificblogging.com/quantum_diaries_survivor to keep up-to-date with particle physics!

Post summary – April 2009 May 1, 2009

Posted by dorigo in astronomy, Blogroll, cosmology, internet, news, personal, physics, science, social life.
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As the less distracted among you have already figured out, I have permanently moved my blogging activities to www.scientificblogging.com. The reasons for the move are explained here.

Since I know that this site continues to be visited -because the 1450 posts it contains draw traffic regardless of the inactivity- I am providing here monthly updates of the pieces I write in my new blog here. Below is a list of posts published last month at the new site.

The Large Hadron Collider is Back Together – announcing the replacement of the last LHC magnets

Hera’s Intriguing Top Candidates – a discussion of a recent search for FCNC single top production in ep collisions

Source Code for the Greedy Bump Bias – a do-it-yourself guide to study the bias of bump fitting

Bump Hunting II: the Greedy Bump Bias – the second part of the post about bump hunting, and a discussion of a nagging bias in bump fitting

Rita Levi Montalcini: 100 Years and Still Going Strong – a tribute to Rita Levi Montalcini, Nobel prize for medicine

The Subtle Art of Bump Hunting – Part I – a discussion of some subtleties in the search for new particle signals

Save Children Burnt by Caustic Soda! – an invitation to donate to Emergency!

Gates Foundation to Chat with Bloggers About World Malaria Day – announcing a teleconference with bloggers

Dark Matter: a Critical Assessment of Recent Cosmic Ray Signals – a summary of Marco Cirelli’s illuminating talk at NeuTel 2009

A Fascinating New Higgs Boson Search by the DZERO Experiment – a discussion on a search for tth events recently published by the Tevatron experiment

A Banner Worth a Thousand Words – a comment on my new banner

Confirmed for WCSJ 2009 – my first post on the new site

!! Moving !! April 15, 2009

Posted by dorigo in news, personal, travel.
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Effective today: after forty months of service on wordpress, my blogging activity is moving to scientific blogging, an excellent site which collects many top-notch science writers. As soon as I manage to work it out, I will provide here a widget with links to my posts on that site, and possibly I will keep this site from being reported as mature by making a monthly entry with a link to the most interesting read in the new site. Other necessary adjustments are also in order, fixing some external links etcetera. But really, if you love me, please follow me there now.

I know, I can almost hear some of you complaining about this uncalled-for, unanticipated decision: this has indeed been a quick resolution, and quite un-characteristically the idea has not been submitted in advance here, to make a dry run and hear your opinions on the plan before it became a fact.

So, why am I doing it ? There are several answers to this question, and you may pick the one you like the most.

1) Blogging for me is about reaching as large an audience as possible, because I do conceive it as an educational mission. I have repeatedly explained here that I do not feel guilty for the time I invest on blogging, because my research position does not require me to teach, and I am glad to distribute through the internet some of the knowledge I have had the chance to accumulate through my studies and my job. Now, the target site of this move will increase my reach of potential readers, especially ones that might be interested in particle physics but have so far not realized it is not beyond their understanding capabilities. This by itself is a valuable asset.

2) While this blog has served my large ego extremely well, providing me with surprising opportunities and gratifications over the course of these forty months, I have realized that in its present form its further growth is problematic. Moving to scientificblogging.com will supply fresh air, new ideas, and a possibility to interact more closely with a stimulating crew of writers.

3) The real question is, why not ? I am not losing paternity or rights on my writings, the interface and functionalities at the new site are no worse, the freedom to write what I like is assured to stay unchanged. There are paid ads there, that is true; however, I have decided to trust the owner of the site that it will remain as non-invasive and reasonable as it looks now. As for the slight loss of control that the move entails, there are a couple of things to say also against wordpress itself, for instance the obligatory, auto-generated “possibly related” links that are supplied to every post, or the arbitrary taking down of this site I have experienced due to my failure to delete spam comments.

4) As for money, that is really not the reason. No, really. I will indeed get paid in the new site, but the sum I will earn is not going to change appreciably the depth of my pockets. Rather, I see the higher visibility I am expecting there as a reward, which will possibly help any future endeavour I might be entertaining myself with fantasizing about. Like writing a book.

So, it is your turn now to speak up and tell me what you think of this. I know, nobody likes change. But change is a fundamental ingredient of life, and specifically, one associated with growth.

Grow Triops with your kids! April 13, 2009

Posted by dorigo in personal, science.
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Just a short, advertising post to mention a very entertaining “scientific toy” for children. Filippo was given a box for his birthday, “Triassic Triops”, a toy made in USA by Triops Inc., three weeks ago. The box rested untouched for a while, until Filippo asked me to try it. The figure on the cover shows a mean-looking crustacean, and it took me a while to decide to try and grow those creatures in our home.

The box contains a small plastic tank, an envelope with gravel and tiny wood bits to create a reasonable habitat in the tank, a tiny box containing about 20 eggs, a tape-on thermometer, and a parcel of food pellets, plus instructions and a plastic pipette. Instructions are quite precise and easy to follow, but the hard part is to find a place in your home where you can stabilize the temperature: these creatures will hatch and grow only if the temperature is in the 22-29°C range.

We followed instructions carefully by using bottled water and waiting until the temperature had stabilized, but once eggs had to be dropped in the tank I was rather amazed: the little box did not seem to contain anything! Only by looking very carefully could I spot tiny grains smaller than half a millimeter across.

Nothing happened for a couple of days, but then we started to see two or three teeny-tiny little beings swimming around. We started feeding them, and they grew quite fast. I have no idea why only few of the eggs hatched, but I am really not sure whether there were twenty originally in the box, nor whether I managed to drop all of them in the tank…

In ten days, two triops have grown to about two-thirds of an inch in length (see right), probably killing the third one in the process (its carcass is still floating around). They are happily swimming day and night, and they eat all the pellets I put in the tank in the matter of a couple of hours… According to instructions, the life cycle of these amazing creatures is of about one to three months. They should grow to about two inches length -roughly the size of a small shrimp. Then they will die, and -by totally drying the tank, and pouring warm water in again- it should be possible to revive their eggs, if they have produced any.

The interesting thing about these creatures is that they have remained biologically identical to the original beings that populated our earth in the Triassic age. Quoting from the leaflet:

“Millions of years before Tyrannosaurus Rex ruled the earth, Tripos Longicaudatus was evolving a method of reproduction that allowed the developing embryos (developing eggs) to survive the drying up of the temporary ponds. This amazing process is known as suspended animation, or diapause. Scientists have found that Triops eggs can remain dormant for more than 25 years. In other words, the little Tripos slept while the dinosaurs disappeared”.

Regardless of the accuracy of the above reconstruction, I think it is really amazing to drop dried eggs into water and see creatures growing up in it. Try it with your kids: fun is assured!

Ten photons per hour March 23, 2009

Posted by dorigo in astronomy, games, mathematics, personal, physics, science.
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Every working day I walk for about a mile to my physics department in Padova from the train station in the morning. I find it is a healthy habit, but I sometimes fear it also in some sense is a waste of time: if I catched a bus, I could be at work ten minutes earlier. I hate losing time, so I sometimes use the walking time to set physics problems to myself, trying to see whether I can solve them by heart. It is a way to exercise my mind while I exercise my body.

Today I was thinking at the night of stargazing I treated myself with last Saturday. I had gone to Casera Razzo, a secluded place in the Alps, and observed galaxies for four hours in a row with a 16″ dobsonian telescope, in the company of four friends (and three other dobs). One thing we had observed with amazement was a tiny speck of light coming from the halo of an interacting pair of galaxies in Ursa Major, the one pictured below.

The small speck of light shown in the upper left of the picture above, labeled as MGC 10-17-5, is actually a faint galaxy in the field of view of NGC3690. It has a visual magnitude of +15.7: this is a measure of its integrated luminosity as seen from the Earth. It is a really faint object, and barely at the limit of visibility with the instrument I had. The question I arrived at formulating to myself this morning was the following: how many photons did we get to see per second through the eyepiece, from that faint galaxy ?

This is a nice, simple question, but computing its answer by heart took me the best part of my walk. My problem was that I did not have a clue of the relationship between visual magnitude and photon fluxes. So I turned to things I did know.

Some background is needed to those of you who do not know how visual magnitudes are computed, so I will make a small digression here. The scale of visual magnitude is a semi-empirical one, which sets the brightest stars at magnitude zero or so, and defines a decrease of luminosity by a factor 100 per every five magnitudes difference. The faintest stars visible with the naked eye in a moonless night are of magnitude +6, and that means they are about 250 times fainter than the brightest ones. On the other hand, Venus shines at magnitude -4.5 at its brightest -almost 100 times as bright as the brightest stars-, and our Sun shines at a visual magnitude of about -27, more than a billion times brighter than Venus. The magnitude difference between two objects is in a relation with their relative brightness by a power law: L_1/L_2 = 2.5^{-M_1+M_2}; the factor 2.5 is an approximation for the fifth root of 100, and it corresponds to the brigthness ratio of two objects that differ by one unit of visual magnitude.

Ok, so we know how bright is the Sun. Now, if I could get how many photons reach our eye from it every second, I would make some progress. I reasoned that I knew the value of the solar constant: that is the energy radiated by the Sun on an area of 1 square meter on the ground of the Earth. I remembered a value of about 1 kilowatt (it is actually 1.366 kW, as I found out later in wikipedia).

Now, how many photons of visible light arriving per second on that square meter of ground correspond to 1 kilowatt of power ? I reasoned that I did not remember the energy of a single visible photon -I remembered it was in the electron-Volt range but I was not really sure- so I had to compute it.

The energy of a quantum of light is given by the formula E = h \nu, where h is Planck’s constant and \nu is the light frequency. However, all I knew was that visible light has a wavelength of about 500 nanometers (which is 5 \times 10^{-7} m), so I had to use the more involved formula E = hc/\lambda, where now c is the speed of light and \lambda is the wavelength. I remembered that h=6 \times 10^{-34} Js, and that c=3 \times 10^8 m/s, so with some effort I could get E=6 \times 10^{-34} \times 3 \times 10^8 / (5 \times 10^-7) = 4 \times 10^{-19}, more or less.

My brains were a bit strained by the simple calculation above, but I was relieved to get back an energy roughly equal to that I expected -in the eV range (one eV equals 1.6 \times 10^{-19} Joules -that much I do know).

Now, if the Sun radiates 1 kW of power, which is a thousand Joules per second, how many visible photons do we get ? Here there is a subtlety I did not even bother considering in my walk to the physics department: only about half of the power from the Sun is in the form of visible light, so one should divide that power by two. But I was unhindered by this in my order-of-magnitude walk-estimate. Of course, 1 kW divided by 4 \times 10^{-19} makes 2.5 \times 10^{21} visible quanta of light per square meter per second.

Now, visual magnitude is expressed as the amount of light hitting the eye. A human eye has a surface of about 20 square millimeters, which is 20 millionths of a square meter: so the number of photons you get by looking straight at the sun (do not do it) is 1.2 \times 10^{14} per second. That’s a hundred trillions of ’em photons per second!

I was close to my goal now: the magnitude of the speck of galaxy I saw on Saturday is +15.7, the magnitude of the Sun is -27, so the difference is 43 magnitudes. This corresponds to 2.5^{43}, which you might throw up your hands at, until you realize that every 5 units of the exponent the number increases by 100, so you just do 100^{43/5} which is 100^{8.6} which is 10^{17.2}… Simple, isn’t it ?

Now, taking the number of photons reaching the eye from the Sun every second, and dividing by the ratio of apparent luminosities of the Sun and the galaxy, I could get N_{\gamma}=10^{14} / 10^{17} = 10^{-3}. One photon every thousand seconds!

Let me stress this: if you watch that patch of sky at night, the number of photons you get from that source alone is a few per hour! With my dobson telescope, which intensifies light by almost 10,000 times, I could get a rate of a few tens of photons per second, and the detail was indeed detectable!

If you are intested in the exact number, which I worked out after reaching my office and the tables of constants in the PDG booklet, I computed a rate of N_{\gamma}=3.4 \times 10^{-3} photons per second with unaided eye, and 22 per second through the eyepiece of the telescope. Without telescope, that galaxy sends to each of us about 10 photons per hour!

UPDATE: this post will remain as one clear example of how dangerous it is to compute by heart! Indeed, somewhere in my order-of-magnitude conversions above I dropped a factor 10^2 -which, mind you, is not horrible in numbers which have 20 digits or so; but when one wants to get back to reasonable estimates for reasonably small numbers, it does count a lot. So, after taking care of some other (more legitimate) approximations, if one computes things correctly, the number of photons from the galaxy seen with the unaided eye is more like two hundred per hour, and in the telescope it is of about 350 per second.

Be flexible March 18, 2009

Posted by dorigo in personal, physics.
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I was quite surprised to see today a slide from an american CDF colleague, in a talk aimed at a general audience of physicists, containing the picture shown below.

Sure, the message is clear. Be flexible. And I would have nothing to object with regards to the means used to convey that message. However, I have learned the hard way that many -especially in the US- consider sexist things that I consider normal. Thus my surprise. The picture is nice and the girl is pretty, but there is something distinctly sexual in her posture -and please do not even try saying that it feels like that just to me “because I am a sex maniac”.

Neutrino Telescopes XIII March 8, 2009

Posted by dorigo in astronomy, cosmology, news, personal, physics, science, travel.
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The conference “Neutrino Telescopes” has arrived at its XIII edition. It is a very nicely organized workshop, held in Venice every year towards the end of the winter or the start of the spring. For me it is especially pleasing to attend, since the venue, Palazzo Franchetti (see picture below) is located at a ten minute walk from my home: a nice change from my usual hour-long commute with Padova by train.

This year the conference will start on Tuesday, March 10th, and will last until Friday. I will be blogging from there, hopefully describing some new results heard in the several interesting talks that have been scheduled. Let me mention only a few of the talks, pasted from the program:

  • D. Meloni (University of Roma Tre)
    CP Violation in Neutrino Physics and New Physics
  • K. Hoffman (University of Maryland)
    AMANDA and IceCube Results
  • S. Enomoto (Tohoku University)
    Using Neutrinos to study the Earth
  • D.F. Cowen (Penn State University)
    The Physics Potential of IceCube’s Deep Core Sub-Detector
  • S. Katsanevas (Université de Paris 7)
    Toward a European Megaton Neutrino Observatory
  • E. Lisi (INFN, Bari)
    Core-Collapse Supernovae: When Neutrinos get to know Each
  • G. Altarelli (University of Roma Tre & CERN)
    Recent Developments of Models of Neutrino Mixing
  • M. Mezzetto (INFN, Padova)
    Next Challenge in Neutrino Physics: the θ13 Angle
  • M. Cirelli (IPhT-CEA, Saclay)
    PAMELA, ATIC and Dark Matter

The conference will close with a round table: here are the participants:

Chair: N. Cabibbo (University of Roma “La Sapienza”)
B. Barish (CALTECH)
L. Maiani (CNR)
V.A. Matveev (INR of RAS, Moscow)
H. Minakata (Tokyo Metropolitan University)
P.J. Oddone (FNAL)
R. Petronzio (INFN, Roma)
C. Rubbia (CERN)
M. Spiro (CEA, Saclay)
A. Suzuki (KEK)

Needless to say, I look forward to a very interesting week!

The four pawns attack as black likes it March 7, 2009

Posted by dorigo in chess, games, personal.
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The four-pawns attack of the Alechin defense arises after the sequence 1.e4 Nf6 2.e5 Nd5 3.c4 Nb6 4.d4 d6 5.f4. White goes all in for a direct attack, exploiting the wandering black knight to gain space in the center. This variation has received a lot of attention since the early days of the Alechin Defense, and it has seen in particular some interesting developments during the seventies, by the sapient hands of Jugoslav players.

I play the Alechin defense as black, and I often find myself struggling in extremely sharp positions when the four-pawns attack is played. It is white’s choice to enter that variation, and one should be prepared well on the main variations, since one faux pas may be fatal. However, these days I cannot afford the luxury of spending time on chess openings, so I have to rely on my experience on the general ideas of the positions that arise.

This evening I played a game that turned out to be a clear (although most probably not clean) example of the thematic tactical motives of the positions that arise in the four-pawns attack. It was a 5′ blitz game on the ICC, so I should be forgiven (as should my unnamed opponent) for any unchecked blunders -I have not fed the moves to a chess engine yet. So here are the moves of the game, with minimal commentary.

1.e4 Nf6 2.e5 Nd5 3.d4 d6 4.c4 Nb6 5.f4 dxe5 6.fxe5 Nc6 7.Be3 Bf5 8.Nc3 e6 9.Nf3 Be7 (see diagram below)

We have reached a tabiya, a standard position in the four-pawns attack. Here white has the choice of the solid, positional play that arises after 10.Be2 0-0 11.0-0 f6 12.exf6, or the more aggressive, bold play involving a central push and a swift assault on the black kingside. My opponent chose the second way.

10.d5 exd5 11.cxd5 Nb4 12.Nd4 Bd7 13.e6 fxe6 14.dxe6 Bc6 15.Qg4 Bh4+ 16.g3 Bxh1

We are still playing moves that are in most chess textbooks. White has given up the exchange -the difference in value between a rook and a light piece- but he has a positional advantage and the initiative for it.

17.0-0-0 Qf6 18.gxh4 0-0 19.Be2 Qe5!?N 20.Bh6

Here I vaguely remembered a game I played six or seven hundred years ago, at a national tournament, when I was taken by surprise by the last move of the white pieces. The most used move here, I recalled -and the only one I was prepared to answer- is 20.Bg5. I tried to squeeze my brains for the textbook variation, but I only recalled that the black rook used to end invading the second rank. The move 20….Rf2 did not look that bad, so I played it, letting my opponent spend time to think on its merits. However, I was wrong. The move 19….Qe5 was a mix-up of two variations, and turns out to be a novelty in this position: not a bad move, however.

20…. Rf2?! 21.Rxh1 Kh8 22.Bg5?

Black’s twentieth move was not good, since now, instead than 22.Bg5, white could have acquired a sizable advantage by 22.Nf3!, attacking the queen while she is still forced to defend the g7 square. Instead the move chosen by white justifies black’s sortie on the seventh rank: black has free hands to attack now.

I felt pretty sure of what I needed to do. The pivot of the white position is the Nd4: it is an octopus rather than a knight, but kick it away from there, and it causes white more trouble than benefits. The move I played is a thematic push in this position, aimed at taking control of the center, defending the black Nb4 from horizontal attacks by the white queen, and caressing ideas of a pawn storm of the white king. I felt it in my bones that this move should be played. Of course a computer might prove it a blunder: but at blitz, these moves bring home a lot of points.

22…. c5! 23.Nf3?

This move is very bad, and is the cause of white’s loss. Now, disregarding the attack on the his queen, black takes total control.

23…. Nxa2+! 24.Kc2? Rxe2+ 25.Nxe2 Qxe2+ 26.Kb1

And what now ? The black Na2 is under attack. Black is a pawn up, but he needs to be precise. On 26….Nb4 27.Qf5 white seems capable to hold. But here comes a silent killer:

26…. Nc4!

White is powerless: he has no means to defend the b2 square from the simple threat of Qxb2 mate. White played

27.Bc1 Nxc1 28.Kxc1

but after the precise


he had to resign. There is no way to avoid Qb2 mate, other than sacrificing the queen. Note that 28…. Nb4! would also have been an excellent move. Here many continuations win for black.

I was pleased with this short game, which shows that the position arising from the four-pawns attack is dangerous for white just as much as it is for black!

A pretty knight journey February 21, 2009

Posted by dorigo in chess, games, personal.
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I give below the moves of a blitz game I played tonight on the Internet Chess Club. The moves are not accurate, as we had just five minutes each to complete the game, and we are both dilettantes. But the attack I played was so simple it played itself, so maybe this is a good training example… I am white against a first-category player (HerrTrigger his ICC handle).

1.e4 e5 2.Nf3 Nc6 3.d4 exd4 4.Nxd4 Nf6 5.Nxc6 bxc6 6.Nc3 Bb4 7.Bd3 0-0 8.0-0 d5 9.exd5 cxd5 10.Bg5 c6 11.Qf3,
Up to now, nothing of our own making – you can find the above sequence on any chess opening book. It is called “Scotch game”; this particular variation is not known for causing black any particular opening problem, but white’s setup is solid and lends itself to a quick kingside surge, if black does not play the most accurate moves.

Sub-optimal. Black has to be careful of his dark squares, and the pin of the Nf6 required more attention. Now white gets a clear initiative.
The start of a straightforward idea – Ne2-d4-f5 will further weaken the dark squares around the black king.
12…. Rb8 13.Nd4
Now Nxc6 is threatened, and the queen cannot defend the pawn since it is tied to the defence of the Nf6.
But this is surely a mistake. Black places the lightsquared bishop on a passive square, blocking the open b-file for some counterplay by the Rb8, and totally leaves the f5 square undefended.
14.Nf5 Be5

This is the position bfore the  start of the final attack. First of all, the black bishop is targeted, gaining a tempo with the rook.
15.Rfe1 Qc7
Now black threatens Bxh2+, but this is not really a problem for white. Instead, the logical conclusion of the knight manouver is in the air…
If now black takes the N, white wins both by 17.Qf5 and by means of the pretty 17.Rxe5! Qxe5 (17…. hxg5 18.Rxg5+ Kh8 19.Qxf6 mate) 18.Bxf6, and black is soon mated (18…Qe6 19.Qg3+).
16….Kh8 17.Bxf6!

The simplest way to win. Black resigned, since on both 17….Bxf6 and 17….gxf6 there follows 18.Qf5 and there is no way to avert Qxh7 mate, while on 17….Bxh2+ 18.Kh1 Qf4 19.Qh5 Qxf6 (19….Qxh6?20.Qxh6) 20.Nxf7+! Kg8 21.Bxh7+ is mate. The Nc3-e2-d4-f5-h6 manouver is pretty in this game, since all the moves are active, and by threatening in turn the c6 pawn, the d6 bishop, and the king the knight takes the lion’s share of merit for the attack.

One word of warning: the above variations are the result of some thoughts on the game diagram, without even moving pieces on a real chessboard, let alone running a check with Fritz. So I am most likely going to be refuted by deeper silicon analysis… To me, the game and the variations still look quite logical in their development and conclusion!