natural philosophy

Stellamedusa ventana

2004-02-09T21:05:00.000Z

"Researchers have discovered a new species of jellyfish so different from its fellow creatures that it merits a new subfamily." Read all about it in Nature

Cold molecules

2003-12-12T20:27:00.000Z

"Using a method usually more suitable to billiards than atomic physics, researchers from Sandia National Laboratories and Columbia University have created extremely cold molecules that could be used as the first step in creating Bose-Einstein molecular condensates." in Physlink.com

History of the 2.7 K temperature prior to Penzias and Wilson

2003-12-02T20:23:00.000Z

I've found an article ( Apeiron 2, 79 (1995)) by A. K. T. Assis and M. C. D. Neves that reveals the history of the prediction of the temperature of the Universe. I'll try to give some main points:

1879 - Stefan found experimentaly that the total bolometric flux of radiation emitted by a black body is proportional to the 4th power of its temperature.

1884 - Boltzmann derived theoretically Stefan's law.

1896 - Guillaume estimated the temperature of "space" to be between 5 K and 6 K. This estimate is restricted to the effect due to stars belonging to our own galaxy.

1924 - Hubble established that the nebulae are stellar systems outside the Milky Way.

1926 - Eddington, also restricting himself to stars belonging to our own galaxy, estimated a temperature of 3.18 K

1928 - R. A. Millikan and Cameron found that the total energy of cosmic rays at the top of the atmosphere was one-tenth of that due to starlight and heat.
They also infered that the major part of the cosmic rays components originated from outside our galaxy.

1928 - Walther Nernst developed the idea of an Universe in a stationary state: " The Universe is in a stationary condition, that is, the present fixed stars cool continually and new ones are being formed".

1929 - Hubble obtained his redshift-distance law

1933 - Regener estimated that the charateristic temperature of the intergalatic space would be 2.8 K.

1937 - Nernst developed his model of a Universe in a stationary state and proposed a tired light explanation of the cosmological redshift.

1938 - Nernst discusses the radiation temperature in the Universe arriving at a temperature in intergalatic space as 0.75 K.

1941 - Herzberg based on the observations made by A. McKellar found a temperature of 2.3 K characterizing the observed degree of excitation of the cyanogen molecules if they were in equilibrium in a heat bath.

1953 - Gamow, using the Big Bang model, predicted that the temperature of the Universe should be 7 K.

1953-1954 - Finlay-Freundlich proposed a tired light model to explain the redshift of solar lines and some anomalous redshifts of several stars, as wel as the cosmological redshift. According to his theory the redshift is proportional to the 4th power of the temperature and inverselly proportional to the length of path traversed through the radiation field. By proposing an alternative to the Doppler interpretation of the cosmological redshift he arrived at 1.9K < T < 6.0K for the temperature of the intergalatic space.

1954 - Max Born discussing Finlay-Freundlich's proposal that this new effect might be due to a photon-photon interaction predicted that the resulting radiation should be of the order of radar waves.

1961 - Gamow in his book The Creation of the Universe predicts a present temperature of the Universe of 50 K.

1965 - Penzias and Wilson discovered the Cosmic Background Radiation using a horn reflector antenna built to study radio astronomy. They found a temperature of 3.5+/- 1.0K observing background radiation at 7.3 cm wavelength.

Want to know more about String Theory?

2003-11-14T21:08:00.000Z

For those that want to have a simple view of what String Theory is, go to NOVA and watch the program hosted by Brian Greene, an expert on the subject. You can believe the theory or not, but i'm sure you will be eager to search for more info. The movies are in QuickTime and RealOne format. I'm not sure if those using Linux are able to watch these.

The little things that we sometimes forget ...

2003-11-14T20:51:00.000Z

We are all humans (hopefully). And as humans we may forget some small details. Here are some i found importante to revise. I first start to state two "laws".

Weak Law of Action and Reaction (Also known as Newton's 3rd law of motion): the forces that two particles exert on each other are equal and opposite.

Strong Law of Action and Reaction(Central forces): The forces that two particles exert on each other are equal, opposite and lie along the line joining the particles.

Now for the details one must keep in mind (and i'm sure that all of you that do physics have these in mind):

(1) The conservation of the linear momentum of a system of particles is only valid if all internal forces are in agreement with the weak law.

(2) The conservation of the total angular momentum is only valid if all internal forces are in agreement with the strong law, i.e. if internal forces are central forces.

The conditions on external contributions were assumed to be known.

The top 30 problems with the Big Bang (featuring the first 10)

2003-11-11T20:25:00.000Z

In a work published last year (Apeiron 9, 72 (2002)) Tom van Flandern points out a list of problems with the Big Bang. In order to avoid violation of the copyrights of the article i will just point out the problems and if you are interested in justification i suggest you download the article at Apeiron. The problems that van Flandern points out are:

(1) "Static universe models fit the observational data better than expanding universe models"

(2)"The microwave 'background' makes more sense as the limiting temperature of space heated by starlight than as the remnant of a fireball."

(3)"Element abundance predictions using the Big Bang require too many adjustable parameters to make them work."

(4)"The universe has too much large scale structure (interspersed 'walls' and voids) to form in a time as short as 10-20 billion years."

(5)"The average luminosity of quasars must decrease with time in just the right way so that their average apparent brightness is the same at all redshifts, which is exceedingly unlikely."

(6)"The ages of globular clusters appear older than the universe."

(7)"The local streaming motions of galaxies are too high for a finite universe that is supposed to be everywhere uniform."

(8)"Invisible dark matter of an unknown but non-baryonic nature must be the dominant ingridient of the entire universe."

(9)"The most distant galaxies in the Hubble Deep Field show insufficient evidence of evolution, with some of them having higher redshifts (z=6-7) than the highest-redshift quasars."

(10)"If the open universe we see today is extrapolated back near the beginning the ratio of the actual density of matter in the universe to the critical density must differ from unity by just a part in 10^59. Any larger deviation would result in a universe already collapsed on itself or already dissipated."

Big Bang or Big Fantasy?

2003-11-10T23:19:00.000Z

In this blog you can find a minipoll about the Big Bang. Please state your opinion. The subject will be dealt with in the near future. Thanks! :)

The influence of disclinations in crystals

2003-11-05T14:49:00.000Z

"There is a class of topological defects analogous to twist and bend distortions ... that involve rotations of the lattice..."; they "...are called disclinations." These topological defects "...are energetically very costly and accur only under special circumstances in the solid phase."

Nonetheless, they "... play a very important role in determining the strength of materials."

" Freely mobile dislocations reduce the strength of a material. To make a material strong, one needs either to reduce the density of disclinations or inhibit dislocation motion. This can be accomplished by pinning dislocations to impurity sites or by putting in so many dislocations that they inhibit each other's motion. The latter process is called work hardening."

Come Lightning! .... Come Thunder!

2003-10-30T22:15:00.000Z

Without a doubt one of the most beautiful (though deadly) phenomena on Earth. Generated in electrically charged storms, the lightning bolt can reach temperatures higher than the Sun's surface.

«During thunderstorms, static electricity builds up within the clouds. A positive charge builds in the upper part of the cloud, while a large negative charge builds in the lower portion. When the difference between the positive and negative charges becomes great, the electrical charge jumps from one area to another; creating a lightning bolt.

Most lightning bolts strike from one cloud to another; but they also can strike the ground. These bolts occur when positive charges build up on the ground. A negative charge called the "faintly luminous streamer" or "leader" flows from the cloud toward the ground. Then a positively charged leader, called the "return stroke", leaves the ground and runs into the cloud.

What is seen as a lightning bolt is actually a series of downward-striking leaders and upward-striking return strokes, all taking place in less than a second.»

More online experiments

2003-10-30T15:30:00.001Z

For those that enjoy discovering the life of Albert Einstein

2003-10-30T15:05:00.000Z

Radio waves from your screen monitor

2003-10-30T14:47:00.000Z

As probably you should know, your computer gives off a fair amount of radio waves. Supposely these shouldn't interfere too much with radios, TVs, cordless phones , ect. However, they do interfere and you can detect them in an easy way. Take a small radio and switch it to AM. Tune it to some non-taken frequency and turn the volume up. If you put the radio near your computer you should hear sound coming from it. Try tunning it! Your monitor is a big producer of radio waves, and if you try turning it on and off you can hear some changes. Your hard drive also produces some radio waves. How can you pick them up? Try opening some program will you detect the interference. Your processor can also be detected through radio waves. Tune in the frequency of your processor it should be in the FM dial. (yes i know, some are too fast to detect in the FM dial!)

Experiments to show in your class

2003-10-30T14:20:00.000Z

Those that know physics will tell you that this science is very important and that everyone should have some knowledge of the subject. Nevertheless, sometimes it is hard to teach this science to young students. Why? Mainly because they think it is to hard to understand the subject and also because their minds are some place elsewhere. So teachers have to make an effort to show how funny physics can be. Here are some ideas that i found on Littleshop

X-ray solar flare

2003-10-30T12:18:00.000Z

Learn about this, and much more, at ESA portal

Pendulums

2003-10-29T16:49:00.000Z

I followed luke's link to The Pendulum Lab and found some nice things about pendulums. Check it out and enjoy the experiments

Chaos and Fractals

2003-10-29T16:35:00.000Z

TCA is showing us the way to the world of Chaos and Fractals.

How does the Immunitary system works?

2003-10-29T16:11:00.000Z

Great animations!

The Waldegrave Higgs challenge

2003-10-28T23:52:00.000Z

"In 1993, the then UK Science Minister, William Waldegrave, issued a challence to physicists to answer the questions 'What is the Higgs boson, and why do we want to find it?' on one side of a single sheet of paper.
Bottles of champagne were awarded to the five winning entries at the annual meeting of the British Association for the Advancement of Science."

The Higgs mechanism

2003-10-28T20:16:00.000Z

I saw this in A Metamorfose where jhj tells us how the british scientists tried to explain the so called Higgs Mechanism to 1993 UK Minister of Science, Mr Waldegrave.

New species found ... for how long can it survive?

2003-10-28T15:31:00.001Z

A new species of seedeater was found in Venezuela. The blue-flecked, seed-eating finch was named CARRIZAL SEEDEATER. According to BirdLife the spicies was first spotted on Carrizal Island in southeastern Venezuela. "The bird had a larger bill than other finches and small plumage differences. The male was gray with splashes of blue and the female was varying shades of brown." Venezuela's state electricity company destroyed its only known habitat to make way for a hydroelectric dam.
"It was not clear what had happened to the three Carrizal Seedeaters that were found."

Are they still alive?

Dino's brain tumor

2003-10-27T15:02:00.000Z

So it seems that it already had happen a long time ago! A brain tumor was discovered in the fossilized remains of a 7.6 meter predator called Gorgosaurus, a meat-eater closely related to Tyrannosaurus Rex, that lived 72 000 000 years ago. This discovery shows that the brain tumor problem has been around "forever".

The flapping of wings and tails

2003-10-21T20:01:00.000+01:00

Animals such as birds and fish depend greatly on their ability to beat their wings, or tails. Recent research ( Nature, 425, 707 - 711 (2003)) tells us that there is a certain quantity that " ... describes the beating of animal wings and tails...".

When a bird (or a fish) flaps its wings (or tail) it gives rise to small vortices. This indeed nead to be left behind because turbulence creates resistence to movement. But the animal cannot simply flat too quickly. Otherwise turbulence will form in front of it.

"A quantity called the Strouhal number measures how efficiently an animal cruises. The number describes how much up-and-down movement a wing or tail makes relative to a creature's forward speed. It is calculated as stroke speed multiplied by size, divided by forward speed."

"Flying and swimming is most efficient at Strouhal numbers of 0.2-0.4. The cruising speeds of everything from bumble-bees to blue whales, via mackerel, locusts, pigeons and bats, fall in this range..."

Check out Nature's web site

Colloidal particles

2003-10-14T15:27:00.000+01:00

Colloids are substances with size ranging from a few micrometers to several tens of micrometers immersed in some medium where the host particles are a few nanometers in size (therefore the word colloid). Nevertheless they are still small enough to perform random walks, originated from the thermal fluctuations of the host medium, usually named Brownian motion. Colloidal particles dispersions are essential for some every-day-life products, such as: toothpaste, jelly, meat , modelling clay , chocolate, house paint, hair conditioner, cheese, ketchup, pastry, icecream, and drilling mud for crude oil recovery.

Water closet experiments

2003-10-12T20:48:00.000+01:00

The world is full of interesting stuff for one to explore. Sometimes they are wright in front of you, and then one day ...
I was once in a water closet washing my hands when i realized that there was this very interesting phenomenon that one could study. If you open a water tab, not too much unless you want to wet your pants, and with your finger start to control the flux (again be carefull with the pants), you can see that the water that drops makes this sort of chains

.
It is known that sometimes one can get out of the W.C. with some ideas on how to do some given task, but this time i came out with the knowledge that there is this "W.C. phenomenon" that one can explore.
After talking with may superviser it came to me as a surprise that already someone had been interested in doing this "W.C. experiment" and found out extremely interesting stuff.
John W.M. Bush did some studies on the collision of equal jets at an oblique angle. They used glycerol-water solutions in order to make the viscosities greater. When the flow rate is low they observed the steady fluid chains. However, when increasing the flow rate one can generate instabilities

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The naked eye cannot see how beautifull these instabilities are. So they used strobe illumination to discover a "... remarkably regular and striking flow instability"

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"Droplets form from the sheet rims but remain attached to the fluid sheet by tendrils of fluid that thin and eventually break. The resulting flow takes the form of fluid fishbones, with the fluid sheet being the fish head and the tendrils its bones."

For more information check this web page.

The letter that Einstein wrote to President Roosevelt and started the Nuclear Era

2003-10-08T15:51:00.000+01:00

The Solvay Congress

2003-10-08T15:45:00.000+01:00

A team from MIT is trying to achieve 0 Kelvin

2003-10-08T15:39:00.000+01:00

MIT scientists have cooled a sodium gas to the lowest temperature ever recorded. The work bests the previous record by a factor of six, and is the first time that a gas was cooled below 1 nanoKelvin (nK). For more info check the article on Physlink.com.

The Nobel Prize in Chemistry

2003-10-08T13:33:00.000+01:00

This prize was given to Peter Agre and Roderick MacKinnon, "... for discoveries concerning channels in cell membranes", "... structural and mechanism studies of ion channels". For more information check the Nobel Foundation web site.

Is there a way of predicting the outcome of a soccer match?

2003-10-07T17:44:00.000+01:00

Recently, Gilberto Ramalho (portuguese physicist) studied the statistical distribution of goals for both home and visiting soccer team, using the results of the Super Liga (portuguese soccer league) 2002/2003. He found that the have some simple distributions. Being a down to earth person, Gilberto Ramalho tells us that you shouldn't use this distributions to gamble. Why? Simply because these are not very usefull for predictions, since that he doesn't take into account the fact that a good team can win any game as the home team and as the visiting team, or a not so good team can have a strike of luck and score many goals to a normally good team. Nevertheless, one can predict that in a certain year there should be a game with a soccer of 0-0 (for example). Gilberto has published his study in SUPERFOOT magazine. His work can also be found in is personal web site.

The Nobel Prize in Literature

2003-10-07T16:30:00.000+01:00

The nobel for literature was given to John Maxwell Coetzee "...who in innumerable guises portrays the surprising involvement of the outsider." For more information on this prize check the Nobel Foundation web site.

The Nobel Prize in Physiology or Medicine

2003-10-07T16:26:00.000+01:00

The nobel in physiology or medicine was given to Paul C. Lauterbur and Sir Peter Mansfield "...for their discoveries concerning magnetic resonance imaging". For more information on this prize see the Nobel Foundation web site.

The Nobel Prize in Physics

2003-10-07T13:09:00.000+01:00

This year the Nobel prize in physics was attributed to Alexei A. Abrikosov, Vitaly L. Ginzburg and Anthony J. Leggett ".. for pioneering contributions to the theory of superconductors and superfluids." For more information check the Nobel Foundation web site.

Not every choice is made scientifically

2003-10-06T16:59:00.000+01:00

Nanotubes as superconductors

2003-10-06T16:17:00.000+01:00

"Tiny tubes of carbon may conduct electricity without any resistance, at temperatures stretching up past the boiling point of water. The tubes would be the first superconductors to work at room temperature.", in New Scientist

Experimental proof of the dipolar interaction in nematic lc

2003-10-02T20:08:00.000+01:00

The movie is showing two water droplets imersed in a nematic liquid crystal.

The surfaces of the two particles induce strong homeotropic anchoring; i.e, the lc molecules want to be perpendicular to the surfaces of the two particles. The nematic at the bounds of the experimental set is parallel to the bottom/top side of you screen (if you are using it correctly). This boundary conditions induce two topological defects near each particle (they are left to the particle).

In this experiment, done by Philippe Poullin and co-workers, they have filled the water droplets with a ferrofluid, which are superparamagnetic. So they can apply a magnetic field (weak enough not to disturb the nematic molecules. It takes a lot to do it, ~10kG) in order to separate the particles. Then they turn of the field and observe the behaviour of the colloids.

In this manner they have proven the dipolar interaction of the two particles, which is mainly due to the existence of the defect.

For more information go to Prof. Weitz experimental group site

Nematic LC tensor order parameter

2003-10-02T19:57:00.000+01:00

In liquid crystals the magnetic response, the susceptibility, is a second rank tensor. For an uniaxial nematic phase one can diagonalize this tensor retaining only its eingenvalues. Since liquid crystals are known to have anisotropic magnetic response, one has an eigenvalue that corresponds to the response along the applied field and the other two (which are equal) correspond to the response perpendicular to the applied field.

If we want to define the order parameter for this material, one has to insure that it will be zero in the isotropic phase. This meaning that the orientational order, characteristic of the nematic phase, is lost. Thus one has to extract the anisotropic part of the magnetic susceptibility. Remember that this will certainly be zero in the isotropic phase. In this manner a tensor order parameter Q_ij is defined.

For more information see The physics of liquid crystals, by P.-G. de Gennes and J. Prost.

Lotus effect

2003-10-02T14:31:00.000+01:00

The Lotus effect is the best example for non-wetting. A drop of water when in contact with the Lotus leaf wiil not wet it, assuming a spherical shape.

For those who want to know more about defects

2003-10-01T16:16:00.000+01:00

There is a somewhat elegant book about defects "Vortices in nonlinear fields: From liquid crystals to superfluids,from non-equilibrium patterns to cosmics strings" by L.M. Pismen, Oxford Science Publications. Check it out! I should say i don't find it simple, but it's really elegant.

When you have to explain to outsiders!

2003-10-01T15:04:00.000+01:00

Preparing a seminar for a group of people that don't work in your area it really is challenging! If have to take into account that they really no nothing of what your are working on. So you first have to give a solid base befor going on to the most exciting topics that you have been working on. Otherwise you will loose the audience. Doing science is very exciting. But sometimes you loose touch on how to explain it to common people! Don't you think so?

Topological defects

2003-10-01T15:00:00.000+01:00

The so called topological defects seem to be every where in nature. You can see them mainly in liquid crystals (LCs). I think that's why liquid crystals can be compared with women they both "... are beautiful and mysterious" (de Gennes, in The physics of liquid crystals). It seems strange though that there are some physicists that extrapolate what happens in LCs to the so called cosmic strings! That's really science fiction. Or not?