New findings have revealed that there may be a piece of real nervy truth in the phrase “the body electric.”
Experiments with liposomes – cell-like “water balloons” composed of artificially created phospholipid bilayers, similar to natural cell membranes – have revealed unexpected behavior in the presence of electrical fields.
The findings could provide a paradigm-shifting change in science’s understanding of biomembrane function in operating living systems.
ASU chemists Mark Hayes and Michele Pysher have found that liposomes have a tendency to form tube-like extensions in their membranes through the influence of local electrical fields. In particular, the surprising finding of such electrically caused bionanotubule formation could reveal a previously unknown process involved in the development of structures like axons and dendrites in nerve cells.
Hayes presented the results of the experiments March 15 in a session titled “Colloids in Complex Fluids” at the American Chemical Society meeting in San Diego.
In the experiments, the researchers placed liposomes in a droplet of water and applied very low electric fields (five to 10 volts per centimeter), much lower than the fields present in operating neurons (a fraction of a volt but operating over a very short distance – less than a micron – to produce a field up to 1,000 times stronger). In images achieved through optical and scanning electron microscopy, microtubules were observed to immediately form and extend from the phospholipid balloon, like a seed putting forth a stalk or root.
Hayes believes that the phenomena may have significant implications for cellular biology and for nanotechnology.
“This finding might not only be important in its application to understanding life processes, but it has a potentially exciting practical application in the fabrication of bionanotubes,” he says.
Retrieved: http://www.sciencedaily.com/releases/2005/03/050329140648.htm
Thursday, December 18, 2008
New Way To Study Nanostructures Discovered
ScienceDaily (July 30, 2007) — Scientists at the Georgia Institute of Technology have discovered a phenomenon which allows measurement of the mechanical motion of nanostructures by using the AC Josephson effect. The findings, which may be used to identify and characterize structural and mechanical properties of nanoparticles, including materials of biological interest, appear online in the journal Nature Nanotechnology.
The AC Josephson effect refers to work that Brian Josephson published in 1962 regarding the flow of an electrical current between superconductors. In this work, for which he shared a 1973 Nobel Prize, Josephson predicted that when a constant voltage difference is maintained across two weakly linked superconductors separated by a thin insulating barrier (an arrangement now known as a Josephson junction), an alternating electrical current would flow through the junction (imagine turning on a water faucet and having the water start flowing up as well as down once it leaves the spigot). The frequency of the current oscillations is directly related to the applied voltage.
These predictions were fully confirmed by an immense number of experiments, and the standard volt is now defined in terms of the frequency of the Josephson AC current. The Josephson effect has numerous applications in physics, computing and sensing technologies. It can be used for ultra high sensitive detection of electromagnetic radiation, extremely weak magnetic fields and in superconducting quantum computing bits.
Now, experimental physicist Alexei Marchenkov and theoretician Uzi Landman at Georgia Tech have discovered that the AC Josephson effect can be used to detect mechanical motion of atoms placed in the Josephson junction.
"We show here that in addition to being able to detect the effects of electromagnetic radiation on the AC Josephson current, one can also use it to probe mechanical motions of atoms or molecules placed in the junction,” said Landman, director of the Center for Computational Materials Science, Regents and Institute professor, and Callaway Chair of Physics at Georgia Tech. “The prospect of being able to explore, and perhaps utilize, atomic-scale phenomena using this effect is very exciting.”
In January 2007, Marchenkov and Landman published a paper in Physical Review Letters detailing their discovery that fluctuations in the conductance of ultra-thin niobium nanowires are caused by a pair of atoms, known as a dimer, shuttling back and forth between the bulk electrical leads.
In this latest research, Marchenkov and Landman, along with their collaborators Zhenting Dai, Brandon Donehoo and Robert Barnett, report that when a microfabricated junction assembly is held below its superconducting transition temperature, unusual features are found in traces of the electrical conductance measured as a function of the applied voltage.
“In our experiments, only nanowires - which we know now to contain a single dimer have consistently shown a series of additional peaks in the conductance versus voltage curves. Since a peak in such measurements signifies a resonance and knowing that we have intrinsic high-frequency Josephson current oscillations, we started looking into the possible physical mechanisms,” said Marchenkov, assistant professor in the School of Physics.
The team hypothesized that the new measured peaks likely originate from mechanical motions of the dimer, which causes enhancement of the electrical current at particular values of the applied voltage. At each of the peak voltages, the frequency of the AC Josephson current would resonate with the vibrational frequency of the nanostructure in the junction.
Subsequent first principles calculations by Landman’s team predicted that such peaks would occur at three different frequencies, or voltages, and their integer multiples. One corresponds to a back and forth vibration of the dimer suspended between the two niobium electrode tips, a second corresponds to motion in the direction perpendicular to the axis connecting the two tips, and the remaining corresponds to a wagging, or rocking, vibration of the dimer about the inter-tip axis.
Ensuing targeted experiments demonstrated that the resonance peaks disappear gradually as one approaches the superconducting transition temperature from below, while their positions do not change. These observations, exhaustive qualitative and quantitative agreement between experimental measurements and theoretical predictions confirm that vibrational motions of the nanowire atoms are indeed the cause for the newly observed conductance peaks.
Marchenkov and Landman plan to further explore vibrational effects in weak link junctions, using the information obtained through these studies for determining vibrational characteristics, atomic arrangements, and transport mechanisms in metallic, organic and biomolecular nanostructures.
“One of our aims is the development of devices and sensing methodologies that utilize the insights gained from our research,” said Landman.
These predictions were fully confirmed by an immense number of experiments, and the standard volt is now defined in terms of the frequency of the Josephson AC current. The Josephson effect has numerous applications in physics, computing and sensing technologies. It can be used for ultra high sensitive detection of electromagnetic radiation, extremely weak magnetic fields and in superconducting quantum computing bits.
Now, experimental physicist Alexei Marchenkov and theoretician Uzi Landman at Georgia Tech have discovered that the AC Josephson effect can be used to detect mechanical motion of atoms placed in the Josephson junction.
"We show here that in addition to being able to detect the effects of electromagnetic radiation on the AC Josephson current, one can also use it to probe mechanical motions of atoms or molecules placed in the junction,” said Landman, director of the Center for Computational Materials Science, Regents and Institute professor, and Callaway Chair of Physics at Georgia Tech. “The prospect of being able to explore, and perhaps utilize, atomic-scale phenomena using this effect is very exciting.”
In January 2007, Marchenkov and Landman published a paper in Physical Review Letters detailing their discovery that fluctuations in the conductance of ultra-thin niobium nanowires are caused by a pair of atoms, known as a dimer, shuttling back and forth between the bulk electrical leads.
In this latest research, Marchenkov and Landman, along with their collaborators Zhenting Dai, Brandon Donehoo and Robert Barnett, report that when a microfabricated junction assembly is held below its superconducting transition temperature, unusual features are found in traces of the electrical conductance measured as a function of the applied voltage.
“In our experiments, only nanowires - which we know now to contain a single dimer have consistently shown a series of additional peaks in the conductance versus voltage curves. Since a peak in such measurements signifies a resonance and knowing that we have intrinsic high-frequency Josephson current oscillations, we started looking into the possible physical mechanisms,” said Marchenkov, assistant professor in the School of Physics.
The team hypothesized that the new measured peaks likely originate from mechanical motions of the dimer, which causes enhancement of the electrical current at particular values of the applied voltage. At each of the peak voltages, the frequency of the AC Josephson current would resonate with the vibrational frequency of the nanostructure in the junction.
Subsequent first principles calculations by Landman’s team predicted that such peaks would occur at three different frequencies, or voltages, and their integer multiples. One corresponds to a back and forth vibration of the dimer suspended between the two niobium electrode tips, a second corresponds to motion in the direction perpendicular to the axis connecting the two tips, and the remaining corresponds to a wagging, or rocking, vibration of the dimer about the inter-tip axis.
Ensuing targeted experiments demonstrated that the resonance peaks disappear gradually as one approaches the superconducting transition temperature from below, while their positions do not change. These observations, exhaustive qualitative and quantitative agreement between experimental measurements and theoretical predictions confirm that vibrational motions of the nanowire atoms are indeed the cause for the newly observed conductance peaks.
Marchenkov and Landman plan to further explore vibrational effects in weak link junctions, using the information obtained through these studies for determining vibrational characteristics, atomic arrangements, and transport mechanisms in metallic, organic and biomolecular nanostructures.
“One of our aims is the development of devices and sensing methodologies that utilize the insights gained from our research,” said Landman.
Sadi Carnot
Nicolas Léonard Sadi Carnot (1 June 1796 – 24 August 1832) was a French physicist and military engineer who, in his 1824 Reflections on the Motive Power of Fire, gave the first successful theoretical account of heat engines, now known as the Carnot cycle, thereby laying the foundations of the second law of thermodynamics. He is often described as the "Father of thermodynamics", being responsible for such concepts as Carnot efficiency, Carnot theorem, Carnot heat engine, and others.
Born in Paris, Sadi Carnot was the first son of the eminent military leader and geometer, Lazare Nicholas Marguerite Carnot, elder brother of Hippolyte Carnot, and uncle of Marie François Sadi Carnot (President of the French Republic (1887-1894), son of Hippolyte Carnot). His father named him for the Persian poet Sadi of Shiraz (Carnot 1960, p. xi), and he was always known by this third given name.
From age 16 (1812), he lived in Paris and attended the École polytechnique where he and his contemporaries, Claude-Louis Navier and Gaspard-Gustave Coriolis, were taught by professors such as Joseph Louis Gay-Lussac, Siméon Denis Poisson and André-Marie Ampère. After graduation, he became an officer in the French army before committing himself to scientific research, becoming the most celebrated of Fourier's contemporaries who were interested in the theory of heat. Since 1814, he served in the military. Following the final defeat of Napoleon in 1815, his father went into exile. He later obtained permanent leave of absence from the French army. Subsequently, he spent time to write his book.
From age 16 (1812), he lived in Paris and attended the École polytechnique where he and his contemporaries, Claude-Louis Navier and Gaspard-Gustave Coriolis, were taught by professors such as Joseph Louis Gay-Lussac, Siméon Denis Poisson and André-Marie Ampère. After graduation, he became an officer in the French army before committing himself to scientific research, becoming the most celebrated of Fourier's contemporaries who were interested in the theory of heat. Since 1814, he served in the military. Following the final defeat of Napoleon in 1815, his father went into exile. He later obtained permanent leave of absence from the French army. Subsequently, he spent time to write his book.
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