Archive for the ‘Chemistry’ Category

Mystery of car battery’s current solved

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Chemists have solved the 150 year-old mystery of what gives the lead-acid battery, found under the bonnet of most cars, its unique ability to deliver a surge of current.

lead acid battery

Lead-acid batteries are able to deliver the very large currents needed to start a car engine because of the exceptionally high electrical conductivity of the battery anode material, lead dioxide. However, even though this type of battery was invented in 1859, up until now the fundamental reason for the high conductivity of lead dioxide has eluded scientists.
A team of researchers from Oxford University, the University of Bath, Trinity College Dublin, and the ISIS neutron spallation source, have explained for the first time the fundamental reason for the high conductivity of lead dioxide.
A report of the research appears in this week’s Physical Review Letters.
‘The unique ability of lead acid batteries to deliver surge currents in excess of 100 amps to turn over a starter motor in an automobile depends critically on the fact that the lead dioxide which stores the chemical energy in the battery anode has a very high electrical conductivity, thus allowing large current to be drawn on demand,’ said Professor Russ Egdell of Oxford University’s Department of Chemistry, an author of the paper.
‘However the origin of conductivity in lead oxide has remained a matter of controversy. Other oxides with the same structure, such as titanium dioxide, are electrical insulators.’
Through a combination of computational chemistry and neutron diffraction, the team has demonstrated that lead dioxide is intrinsically an insulator with a small electronic band gap, but invariably becomes electron rich due to the loss of oxygen from the lattice, causing the material to be transformed from an insulator into a metallic conductor.
The researchers believe these insights could open up new avenues for the selection of improved materials for modern battery technologies.
Professor Egdell said: ‘The work demonstrates the power of combining predictive materials modelling with state-of-the-art experimental measurements.’

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December 19, 2011 at 1:58 pm

Posted in Chemistry, PHYSICS

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Early Black Holes Grew Big Eating Cold, Fast Food

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The large scale cosmological mass distribution in the simulation volume of the MassiveBlack. The projected gas density over the whole volume ('unwrapped' into 2D) is shown in the large scale (background) image. The two images on top show two zoom-in of increasing factor of 10, of the regions where the most massive black hole - the first quasars - is formed. The black hole is at the center of the image and is being fed by cold gas streams. Image Courtesy of Yu Feng.

PITTSBURGH — Researchers at Carnegie Mellon University’s Bruce and Astrid McWilliams Center for Cosmology have discovered what caused the rapid growth of early supermassive black holes – a steady diet of cold, fast food.

Computer simulations, completed using supercomputers at the National Institute for Computational Sciences and the Pittsburgh Supercomputing Center and viewed using GigaPan Time Machine technology, show that thin streams of cold gas flow uncontrolled into the center of the first black holes, causing them to grow faster than anything else in the universe.  The findings will be published in the Astrophysical Journal Letters.

In the early days of the universe, a mere 700 to 800 million years after the Big Bang, most things were small. The first stars and galaxies were just beginning to form and grow in isolated parts of the universe.  According to astrophysical theory, black holes found during this era also should be small in proportion with the galaxies in which they reside. Recent observations from the Sloan Digital Sky Survey (SDSS) have shown that this isn’t the case — enormous supermassive black holes existed as early as 700 million years after the Big Bang.

“The Sloan Digital Sky Survey found supermassive black holes at less than 1 billion years.  They were the same size as today’s most massive black holes, which are 13.6 billion years old,” said Tiziana Di Matteo, associate professor of physics at Carnegie Mellon.  “It was a puzzle.  Why do some black holes form so early when it takes the whole age of the universe for others to reach the same mass?”

Supermassive black holes are the largest black holes, with masses billions of times larger than that of the sun.  Typical black holes have masses only up to 30 times larger than the sun’s. Astrophysicists have determined that supermassive black holes can form when two galaxies collide and their two black holes merge into one.  These galaxy collisions happened in the later years of the universe, but not in the early days.  In the first few millions of years after the Big Bang, galaxies were too few and too far apart to merge.

“If you write the equations for how galaxies and black holes form, it doesn’t seem possible that these huge masses could form that early,” said Rupert Croft, an associate professor of physics at Carnegie Mellon.   “But we look to the sky and there they are.”

To find out exactly how these supermassive black holes came to be, Di Matteo, Croft and Carnegie Mellon post-doctoral researcher Nishikanta Khandai created the largest cosmological simulation to-date.  Called MassiveBlack, the simulation focused on recreating the first billion years after the Big Bang.

“This simulation is truly gigantic.  It’s the largest in terms of the level of physics and the actual volume.  We did that because we were interested in looking at rare things in the universe, like the first black holes.  Because they are so rare, you need to search over a large volume of space,” said Di Matteo.

They began by running the simulation under conditions laid out under the standard model of cosmology – the accepted theories and laws of modern day physics governing the formation and growth of the universe.

“We didn’t put anything crazy in.  There’s no magic physics, no extra stuff. It’s the same physics that forms galaxies in simulations of the later universe,” said Croft. “But magically, these early quasars, just as had been observed, appear.  We didn’t know they were going to show up.  It was amazing to measure their masses and go ‘Wow! These are the exact right size and show up exactly at the right point in time.’  It’s a success story for the modern theory of cosmology.”

Their simulation data was incorporated into a new technology developed by Carnegie Mellon computer scientists called GigaPan Time Machine. The technology allowed the researchers to view their simulation as if it was a movie.  They could easily pan across the simulated universe as it formed, and zoom in to events that looked interesting, allowing them to see greater detail than what could be seen using a telescope.

As they zoomed in to the creation of the first supermassive black holes, they saw something unexpected.  Normally, when cold gas flows toward a black hole it collides with other gas in the surrounding galaxy. This causes the cold gas to heat up and then cool back down before it enters the black hole. This process, called shock heating, would stop black holes in the early universe from growing fast enough to reach the masses we see. Instead, Di Matteo and Croft saw in their simulation thin streams of cold dense gas flowing along the filaments that give structure to the universe and straight into the center of the black holes at breakneck speed, making for cold, fast food for the black holes.  This uncontrolled consumption caused the black holes to grow exponentially faster than the galaxies in which they reside.

And since when a galaxy forms when a black hole forms, the results could also shed light on how the first galaxies formed, giving more clues to how the universe came to be.  Di Matteo and Croft hope to push the limits of their simulation a bit more, creating even bigger simulations that cover more space and time.
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December 12, 2011 at 5:09 pm

Posted in ASTROPHYSICS, Chemistry

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Single molecule nanocar takes its first spin

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THE tiniest car in the world has gone for a drive. Made of a single molecule, the “vehicle” has four wheel-like paddles that rotate in the same direction when zapped with a beam of electrons.

“The molecule is autonomous,” says Syuzanna Harutyunyan, a chemist at the University of Groningen in the Netherlands who worked on the mini motor vehicle. “You don’t need to touch it. Just give it energy and it’s capable of converting that energy into movement.”

The nanocar could be used to transport miniature loads of cargo and to help unravel why tiny motors in nature tend to be so much more efficient than large-scale ones.

To create the nanocar, Harutyunyan and her team designed a molecule with a long central body and one pivoted paddle at each of four corners. The paddles are free to swing around in circles, not unlike wheels.

Ordinarily they arrange themselves so as to minimise crowding with the central body, as this costs the molecule the least amount of energy. But when the team applies a pulse of electrons to the “wheels”, some gain energy and move a quarter turn.

In this new position, the wheels experience overcrowding against the body of the nanocar and will move to a more spacious position as soon as possible. They get this opportunity when the bonds holding the wheels to the body stretch, prompting the wheels to move another quarter turn in the same direction, to a more “comfortable” position. A further pulse of electrons repeats the process (see diagram).

Frigid temperatures of 7 kelvin (-266 °C) help this clunky forward motion by effectively freezing the wheels in place except when excited by the electron pulse and during their subsequent self-adjustment. This keeps them from rolling backwards.

nanocar had been built before but its wheels only spun in place, equivalent to placing a car on blocks to test it. By contrast, the new vehicle moves in a straight line (NatureDOI: 10.1038/nature10587).

It’s a slow road trip: it takes 10 pulses of electric fuel to move the vehicle 6 nanometres. The head of a pin is about a million nanometres wide.

Nonetheless, nanocar team member Karl-Heinz Ernst at the University of Zurich, Switzerland, is anxious to put it to work. “We have a locomotive,” he says, “but it’s time to put some cars at the back and pull them along.”

Paul Weiss at the University of California, Los Angeles, says the car can help us unravel why tiny motors in nature, such as the motor proteins that move material around in cells, are so highly efficient. “The reason we work at these small scales is so that we can really understand the motion and efficient energy conversion.” He hopes this will lead to more efficient large-scale motors.

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November 9, 2011 at 10:01 pm

Posted in Chemistry, TECHNOLOGY

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Pumpkin Chemistry

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So Halloween is over, what to do with all those pumpkins rotting on your doorstep?
Three chemists do their best to destroy pumpkins using all the tricks up their lab coat sleeves!

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November 1, 2011 at 9:04 am

Posted in Chemistry, HUMOR

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New Thermodynamic Paradigm of Chemical Equilibria

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B. Zilbergleyt

The paper presents new thermodynamic paradigm of chemical equilibrium, setting forth comprehensive basics of Discrete Thermodynamics of Chemical Equilibria (DTd).
Along with previous results by the author during the last decade, this work contains also some new developments of DTd.
Based on the Onsager’s constitutive equations, reformulated by the author thermodynamic affinity and reaction extent, and Le Chatelier’s principle, DTd brings forward a notion of chemical equilibrium as a balance of internal and external thermodynamic forces (TdF), acting against a chemical system.
Basic expression of DTd is the chemical system logistic map of thermodynamic states that ties together energetic characteristics of chemical reaction, occurring in the system, the system shift from “true” thermodynamic equilibrium (TdE), and causing that shift external thermodynamic forces.
Solutions to the basic map are pitchfork bifurcation diagrams in coordinates “shift from TdE – growth factor (or TdF)”; points, corresponding to the system thermodynamic states, are dwelling on its branches.
The diagrams feature three typical areas: true thermodynamic equilibrium and open equilibrium along the thermodynamic branch before the threshold of its stability, i.e. bifurcation point, and bifurcation area with bistability and chaotic oscillations after the point.
The set of solutions makes up the chemical system domain of states.
The new paradigm complies with the correspondence principle: in isolated chemical system external TdF vanish, and the basic map turns into traditional expression of chemical equilibrium via thermodynamic affinity.
The theory binds together classical and contemporary thermodynamics of chemical equilibria on a unique conceptual basis.
The paper is essentially reworked and refocused version of the earlier preprint on the DTd basics, supplemented with new results…….
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October 31, 2011 at 1:52 pm

Astronomers discover complex organic matter in the universe

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This is a spectrum from the Infrared Space Observatory superimposed on an image of the Orion Nebula where these complex organics are found

In today’s issue of the journal Nature, astronomers report that organic compounds of unexpected complexity exist throughout the Universe. The results suggest that complex organic compounds are not the sole domain of life but can be made naturally by stars.
Prof. Sun Kwok and Dr. Yong Zhang of the University of Hong Kong show that an organic substance commonly found throughout the Universe contains a mixture of aromatic (ring-like) and aliphatic (chain-like) components. The compounds are so complex that their chemical structures resemble those of coal and petroleum. Since coal and oil are remnants of ancient life, this type of organic matter was thought to arise only from living organisms. The team’s discovery suggests that complex organic compounds can be synthesized in space even when no life forms are present.
The researchers investigated an unsolved phenomenon: a set of infrared emissions detected in stars, interstellar space, and galaxies. These spectral signatures are known as “Unidentified Infrared Emission features”. For over two decades, the most commonly accepted theory on the origin of these signatures has been that they come from simple organic molecules made of carbon and hydrogen atoms, called polycyclic aromatic hydrocarbon (PAH) molecules. From observations taken by the Infrared Space Observatory and the Spitzer Space Telescope, Kwok and Zhang showed that the astronomical spectra have features that cannot be explained by PAH molecules. Instead, the team proposes that the substances generating these infrared emissions have chemical structures that are much more complex. By analyzing spectra of star dust formed in exploding stars called novae, they show that stars are making these complex organic compounds on extremely short time scales of weeks.
Not only are stars producing this complex organic matter, they are also ejecting it into the general interstellar space, the region between stars. The work supports an earlier idea proposed by Kwok that old stars are molecular factories capable of manufacturing organic compounds. “Our work has shown that stars have no problem making complex organic compounds under near-vacuum conditions,” says Kwok. “Theoretically, this is impossible, but observationally we can see it happening.”
Most interestingly, this organic star dust is similar in structure to complex organic compounds found in meteorites. Since meteorites are remnants of the early Solar System, the findings raise the possibility that stars enriched the early Solar System with organic compounds. The early Earth was subjected to severe bombardments by comets and asteroids, which potentially could have carried organic star dust. Whether these delivered organic compounds played any role in the development of life on Earth remains an open question.
Provided by The University of Hong Kong

Read also: Stars concoct complex molecules

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October 26, 2011 at 6:24 pm

Ergodic theorem passes the test

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This composite image illustrates both methods used to track dye molecules through the channels in the nanoporous material (grey background). Individual molecules (ball and stick figures) can be tracked using the light (orange glow) that they give off. Meanwhile, the collective motion of all the dye molecules is measured using NMR, which focuses on the magnetic moments (blue arrows) of the molecules

For more than a century scientists have relied on the “ergodic theorem” to explain diffusive processes such as the movement of molecules in a liquid. However, they had not been able to confirm experimentally a central tenet of the theorem – that the average of repeated measurements of the random motion of an individual molecule is the same as the random motion of the entire ensemble of those molecules. Now, however, researchers in Germany have measured both parameters in the same system – making them the first to confirm experimentally the ergodic theorem.
The experiments developed from the work of Christoph Bräuchle and a team at Ludwig-Maximilians University in Munich, who developed a technique for tracking individual dye molecules dissolved in alcohol that then pass through a nanoporous material. Such diffusion is of more than just academic interest because it plays an important role in a number of technologies, including molecular sieves, catalysis and drug delivery.
Pinpoints of light
To confirm the ergodic theorem, Bräuchle’s team tracked the molecules by illuminating the sample with light. This makes the molecules fluoresce so that they appear as pinpoints of light when viewed using a high-powered optical microscope. By using dye molecules at very low concentration, the researchers ensured that each point of light corresponded to just one molecule. So, by measuring the intensity profile of a point and finding its centroid, the Munich team was able to determine the position of a dye molecule to within about 5 nm. Individual molecules could then be followed as they moved through the sample by taking a series of snapshots.
Meanwhile, a team led by Jörg Kärger at the University of Leipzig used a nuclear magnetic resonance (NMR) technique to track the diffusion of all the dye molecules in a similar sample. The pulsed-field-gradient NMR method is sensitive only to the collective motion of all the dye molecules and cannot determine individual molecules. Comparing the results from the two groups showed that the average of many measurements of the diffusivity of individual dye molecules (as measured in Munich) was identical to the collective diffusivity of the dye molecules (as measured in Leipzig). Given that diffusion involves the random motions of molecules, the study therefore confirms the ergodic theorem.
Conflicting requirements
Bräuchle told that the main challenge was to find a system that could be studied using both techniques. The fluorescence method works best when the dye concentration is extremely low and the molecules move very slowly – whereas the NMR measurements need much higher concentrations and faster motion. The compromise involved using a special microporous material that slowed down the molecules and constrained them to a plane so that they were easier to track with the microscope. In addition, the dye concentration in the NMR experiments was about 10 times greater than that used for the fluorescence measurements.
Now that the researchers have worked out a way to confirm the ergodic theorem, they are keen to use the technique to search for systems that do not obey the theorem. Bräuchle believes that this could occur when some molecules diffuse through living cells – something that could have important implications for how drugs are designed.
The research is described in Angewandte Chemie
Hamish Johnston –

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October 20, 2011 at 5:42 pm

Posted in Chemistry

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Watching electrons in molecules

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A research group led by ETH Zurich has now, for the first time, visualized the motion of electrons during a chemical reaction. The new findings in the experiment are of fundamental importance for photochemistry and could also assist the design of more efficient solar cells.

The picture shows the conical intersection and the two possible electronic states of the NO2 molecule before it dissociates

In 1999, Ahmed Zewail was awarded the nobel prize in chemistry for his studies of chemical reactions using ultrashort laser pulses. Zewail was able to watch the motion of atoms and thus visualize transition states on the molecular level. Watching the dynamics of single electrons was still considered a dream at that time. Thanks to the latest developments in laser technology and intense research in the field of attosecond spectroscopy (1 attosecond = 10-18 s) the research has developed fast. For the first time, Prof. Hans Jakob Wörner from the Laboratory of Physical Chemistry at ETH Zurich, together with colleagues from Canada and France, was able to record electronic motion during a complete chemical reaction. The experiment is described in the latest issue of Science….. Read the rest of this entry »

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October 14, 2011 at 1:24 pm

Posted in ATOMIC PHYSICS, Chemistry

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