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18. Transfers thermiques d'énergie

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Hydrogen bonds directly detected for the first time. For the first time, scientists have succeeded in studying the strength of hydrogen bonds in a single molecule using an atomic force microscope.

Hydrogen bonds directly detected for the first time

Researchers from the University of Basel's Swiss Nanoscience Institute network have reported the results in the journal Science Advances. Hydrogen is the most common element in the universe and is an integral part of almost all organic compounds. Molecules and sections of macromolecules are connected to one another via hydrogen atoms, an interaction known as hydrogen bonding.

These interactions play an important role in nature, because they are responsible for specific properties of proteins or nucleic acids and, for example, also ensure that water has a high boiling temperature. To date, it has not been possible to conduct a spectroscopic or electron microscopic analysis of hydrogen and the hydrogen bonds in single molecules, and investigations using atomic force microscopy have also not yielded any clear results.

Dr. Des chercheurs créent une molécule inédite et stable - Science-et-vie.com. Depuis plus de 50 ans les chimistes cherchaient à synthétiser le "triangulène".

Des chercheurs créent une molécule inédite et stable - Science-et-vie.com

Et aujourd'hui, grâce aux techniques modernes, une équipe a réussi à le construire et le stabiliser dans le temps. Une belle promesse pour l'ordinateur quantique et l'électronique de demain. En un siècle, la chimie a changé de nature : jadis art du mélange de millions de molécules afin de les faire réagir massivement entre elles au moyen de leurs propriétés naturelles (réactions chimiques), elle est aujourd'hui devenue un art de la construction atome par atome de molécules individuelles impossibles à obtenir par voie naturelle. L'exemple le plus aboutit a été présenté par des chercheurs d'IBM-Zurich (Suisse) et de l'université de Warwick (GB) dans la revue Nature : la synthèse du "triangulène", une molécule triangulaire prédite en 1953, supposément instable et jamais obtenue. Deux électrons en guise d'antennes Une stabilité inespérée La manipulation par microscope. Au-delà des nuages. Le microscope à effet tunnel. Le microscope à effet tunnel.

First-ever videos show how heat moves through materials at the nanoscale and speed of sound. Using a state-of-the-art ultrafast electron microscope, University of Minnesota researchers have recorded the first-ever videos showing how heat moves through materials at the nanoscale traveling at the speed of sound.

First-ever videos show how heat moves through materials at the nanoscale and speed of sound

The research, published today in Nature Communications, provides unprecedented insight into roles played by individual atomic and nanoscale features that could aid in the design of better, more efficient materials with a wide array of uses, from personal electronics to alternative-energy technologies. Energy in the form of heat impacts all technologies and is a major factor in how electronic devices and public infrastructure are designed and engineered.

It is also the largest form of waste energy in critical applications, including power transmission and especially transportation, where, for example, roughly 70 percent of the energy in gasoline is wasted as heat in automobile engines. Share Video undefined Explore further: Can heat be controlled as waves? Icists measure van der Waals forces of individual atoms for the first time. Physicists at the Swiss Nanoscience Institute and the University of Basel have succeeded in measuring the very weak van der Waals forces between individual atoms for the first time.

icists measure van der Waals forces of individual atoms for the first time

To do this, they fixed individual noble gas atoms within a molecular network and determined the interactions with a single xenon atom that they had positioned at the tip of an atomic force microscope. As expected, the forces varied according to the distance between the two atoms; but, in some cases, the forces were several times larger than theoretically calculated. These findings are reported by the international team of researchers in Nature Communications.

Van der Waals forces act between non-polar atoms and molecules. Although they are very weak in comparison to chemical bonds, they are hugely significant in nature. Van der Waals interactions arise due to a temporary redistribution of electrons in the atoms and molecules. Fixed within the nano-beaker Compared with theory. Atomic force microscope reveals molecular ghosts. To the surprise of chemists, a new technique for taking snapshots of molecules with atomic precision is turning up chemicals they shouldn't be able to see.

Atomic force microscope reveals molecular ghosts

Chemical reactions take place so rapidly - often within picoseconds, or a trillionth of a second - that chemists expect intermediate steps in the reaction to be too brief to observe. Only lasers firing in femtosecond bursts - like a strobe flashing every thousandth of a picosecond - can capture the fleeting molecular structures that reacting chemicals form on their way to a final product. Yet a team of chemists and physicists from the University of California, Berkeley, and Lawrence Berkeley National Laboratory has taken snapshots of two molecules reacting on the surface of a catalyst, and found intermediate structures lasting for the 20 minutes or so it takes to snap a photo. Share Video undefined A paper describing their work appeared online this week in advance of publication in the journal Nature Chemistry.