A III Reunião Ibérica de Colóides e Interfaces irá ser realizada em Granada, Espanha, de 13 a 15 de Julho de 2009.
As comunicações abordarão os seguintes temas
Para mais informações visite o site: http://rici3.ugr.es/
Everything should be made as simple as possible, but not simpler.
Albert Einstein
“If your experiment needs statistics, you ought to have done a better experiment.”
Lord Rutherford
This is a video where the paramagnetic properties of oxygen are demonstrated.
NCAR’s Whole Atmosphere Community Climate Model (WACCM)is being used to study the atmospheric response from the surface to the lower thermosphere to changes in solar and geomagnetic forcing over the 11 year solar cycle. WACCM is a new general circulation model developed by scientists at ACD, HAO, and CGD. It incorporates MOZART-3 interactive chemistry that solves for both neutral and ion species.
Energy inputs include solar radiation and energetic particles, which vary significantly over the solar cycle.
Simulations show large changes in composition and dynamical variables such as ozone and temperature, especially in the upper atmosphere, that are in good agreement with observations.
Many of ACD’s models are available to the public. Please visit NCAR’s Community Data Portal to download. Note a short registration is required.
Source: http://www.acd.ucar.edu
By soaking a silica sponge with antimatter, physicists have made the first matter-antimatter molecules. With further refinement, the technique might be used to briefly condense antimatter into fluid or solid states or even to create the first gamma-ray laser.
About 10 years ago, researchers created atoms of antihydrogen by combining antiprotons and positrons, the antimatter equivalents of protons and electrons. By itself, antihydrogen is as stable as hydrogen, though it’s difficult to store in our matter world because of antimatter’s propensity to vanish in a flash of gamma rays as soon as it comes into contact with matter.
For more than 50 years, however, physicists have been able to create nucleus-free “atoms” consisting of one electron and one positron. Attracted by their opposite charges, electrons and positrons will orbit each other, as the stars in a binary system do.
Unlike antihydrogen, however this unusual matter-antimatter hybrid, called positronium, is unstable. It enjoys just a brief dance of death as the two particles spiral in toward mutual annihilation.
Still, positronium can live long enough—up to hundreds of nanoseconds—that physicists had speculated that the atoms might be able to pair up into molecules. Coaxing the atoms to do so would require assembling them in tight quarters and slowing them down enough to allow them to intermingle.
To perform this feat, David Cassidy and Allen Mills of the University of California, Riverside began by trapping millions of positrons—produced by a radioactive source—in an electromagnetic field. By applying brief electric pulses, the team expelled short bursts of positrons, directing them toward a thin, porous silica membrane. Inside the pores, some of the positrons scooped up electrons from the silica to form positronium.
The researchers hoped that some of the atoms would bounce around inside the pores and even temporarily stick to the pores’ inner surfaces, where feeble electrostatic forces might slow them down and allow them to bind to each other as molecules.
All the positrons, whether free or bound in atoms or molecules, eventually annihilated, producing gamma rays. But Cassidy and Mills detected a telltale gamma-ray signal that they had expected the annihilation of molecular positronium to produce. For confirmation, they heated the membrane, creating conditions that would prevent the formation of molecules. Sure enough, the signal disappeared, the team reports in the Sept. 13 Nature. Mills says that the data show “all the hallmarks” of the appearance of positronium molecules.
Clifford M. Surko of the University of California, San Diego says that the evidence for the formation of positronium is convincing, if indirect. “I did not find any obvious potential flaw in it,” he says.
This achievement is only the beginning, Mills says. If the researchers manage to concentrate more positrons into their sponge, more-complex states of matter should appear. In a Bose-Einstein condensate, an exotic gas in which atoms share a quantum state, positrons could be forced to annihilate in sync to produce the first gamma-ray laser, Cassidy says. Even higher densities could lead to the first solid matter–antimatter state.
Source: http://www.sciencenews.org/
Discover8 is a new scientific communications database where registered users can suggest, comment and rate scientific communications. Its also possible to recommend any article with a valid web link (for instance your own articles 
).
A large number of topics related to life sciences are present.
Take a look at it at http://www.discover8.com/
University of Aveiro, Portugal
6 and 7 September 2007
“The aim of the SMARTER meeting is to bring together specialists from the different areas of materials science, such as materials chemists and processing engineers, diffraction and spectroscopy scientists, and computational structuralists, that may contribute to the development of a common language for a SMARTER approach to structure solving, using Geometrical, Diffraction Modeling and NMR Crystallographies.”
workshop homepage: http://www.primarius.pt/smarter/index.php?option=com_content&task=view&id=17&Itemid=1
Thermoelectric materials are special types of semiconductors that, when coupled, function as a “heat pump”.
The discovery of thermoelectricity dates back to Seebeck (1770-1831). Thomas Johann Seebeck was born in Revel (now Tallinn), the capital of Estonia which at that time was part of East Prussia. Seebeck was a member of a prominent merchant family with ancestral roots in Sweden. He studied medicine in Germany and qualified as a doctor in 1802. Seebeck spent most of his life involved in scientific research. In 1821 he discovered that a compass needle deflected when placed in the vicinity of a closed loop formed from two dissimilar metal conductors if the junctions were maintained at different temperatures. He also observed that the magnitude of the deflection was proportional to the temperature difference and depended on the type of conducting material, and does not depend on the temperature distribution along the conductors. Seebeck tested a wide range of materials, including the naturally found semiconductors ZnSb and PbS. It is interesting to note that if these materials had been used at that time to construct a thermoelectric generator, it could have had an efficiency of around 3% - similar to that of contemporary steam engines.
The Seebeck coefficient is defined as the open circuit voltage produced between two points on a conductor, where a uniform temperature difference of 1K exists between those points.
It was later in 1834 that Peltier described thermal effects at the junctions of dissimilar conductors when an electrical current flows between the materials. Peltier failed however to understand the full implications of his findings and it wasn’t until four years later that Lenz concluded that there is heat adsorption or generation at the junctions depending on the direction of current flow.
In 1851, Thomson (later Lord Kelvin) predicted and subsequently observed experimentally the cooling or heating of a homogeneous conductor resulting from the flow of an electrical current in the presence of a temperature gradient. This is know as the Thomson effect and is defined as the rate of heat generated or absorbed in a single current carrying conductor subjected to a temperature gradient.
It was later in 1909 and 1911 that Altenkirch showed that good thermoelectric materials should possess large Seebeck coefficients, high electrical conductivity and low thermal conductivity. A high electrical conductivity is necessary to minimise Joule heating, whilst a low thermal conductivity helps to retain heat at the junctions and maintain a large temperature gradient. These three properties were later embodied in the so-called figure-of-merit, Z. Since Z varies with temperature, a useful dimensionless figure-of-merit can be defined as ZT.
Although the properties favoured for good thermoelectric materials were known, the advantages of semiconductors as thermoelectric materials were neglected and research continued to focus on metals and metal alloys. These materials however have a constant ratio of electrical to thermal conductivity (Widemann-Franz-Lorenz law) so it is not possible to increase one without increasing the other. Metals best suited to thermoelectric applications should therefore possess a high Seebeck coefficient. Unfortunately most possess Seebeck coefficients in the order of 10 microvolts/K, resulting in generating efficiencies of only fractions of a percent.
It was during the 1920’s that the development of synthetic semiconductors with Seebeck coefficients in excess of 100 microvolts/K increased interest in thermoelectricity. At this time it was not apparent that semiconductors were superior thermoelectric materials due to their higher ratio of electricall conductivity to thermal conductivity, when compared to metals.
As early as 1929 when very little was known about semiconductors, Abram Fedorovich Ioffe (1880-1960) showed that a thermoelectric generator utilising semiconductors could achieve a conversion efficiency of 4%, with further possible improvement in its performance. By the 1950’s, Ioffe and his colleagues had developed the theory of thermoelectric conversion, which forms the basis of all modern thermoelectric theory.
A large number of semiconductor materials were being investigated by the late 1950’s and early 1960’s , several of which emerged with Z values significantly higher than in metals or metal alloys. No single compound semiconductor evolved that exhibited a uniform high figure-of-merit over a wide temperature range, so research focused on developing materials with high figure-of-merit values over relatively narrow temperature ranges. Of the great number of materials investigated, those based on bismuth telluride, lead telluride and silicon-germanium alloys emerged as the best for operating to
temperatures of about 450K, 900K and 1400K respectively.
The simplest thermoelectric generator consists of a thermocouple, comprising a p-type and n-type thermoelement connected electrically in series and thermally in parallel. Heat is pumped into one side of the couple and rejected from the opposite side. An electrical current is produced, proportional to the temperature gradient between the hot and cold junctions.
If an electric current is applied to the thermocouple as shown, heat is pumped from the cold junction to the hot junction. The cold junction will rapidly drop below ambient temperature provided heat is removed from the hot side. The temperature gradient will vary according to the magnitude of current applied.
A typical thermoelectric module is shown left. The module consists of pairs of p-type and n-type semiconductor thermoelements forming thermocouples which are connected electrically in series and thermally in parallel.
http://www.its.caltech.edu/~jsnyder/Research.html
http://www.its.caltech.edu/~jsnyder/thermoelectrics/science_page.htm
http://www.americool.com/BeyondBismuthTelluride2003.htm
We all know that an important part of the scientific work is related to communicating your findings to your peers. So here are a couple of texts on the subject (from the “Improbable research” site). I hope you find them useful .
“How to write a scientific paper“, by E. Robert Schulman
” How To Make a Scientific Lecture Unbearable” , by Alexander Khon
jmgs
pgomes
filipefernandes