In this classical paper Pople and Walmsley introduced concept of solitons in polyacetylene. The neutral soliton is a radical misfit which exists in the middle of a long polyene chain containing an odd number of conjugated carbons and which consists of several successive bonds of similar lengths near which the unpaired electron is localized. Authors suggested that such a defect could be mobile and, if charged, could be responsible of an high electrical conductivity.

This idea is eventually lead to development Su-Schrieffer-Heeger model [2] and experimental discovery of conducting polymers in the late-70s. Finally, in 2000 Heegler, MacDiarmid and Heeger were awarded by the Nobel Prize in Chemistry for the discovery and development of conductive polymers. Unfortunately, the work by Pople and Walmsley is not even mentioned.

Today, almost 50 years later things are drastically different. The attitude of experimentalists is largely changed, we are working together and both benefit from it. Take, for example, this week issue of Nature, theoretical calculations made small but valuable contribution to describe physics behind the first organic superconductors [3]!

Efforts to identify and develop new superconducting materials continue apace, motivated by both fundamental science and the prospects for application. For example, several new superconducting material systems have been developed in the recent past, including calcium-intercalated graphite compounds, boron-doped diamond and—most prominently—iron arsenides such as LaO_1-xF_xFeAs. In the case of organic superconductors, however, no new material system with a high superconducting transition temperature (Tc) has been discovered in the past decade. Here we report that intercalating an alkali metal into picene, a wide-bandgap semiconducting solid hydrocarbon, produces metallic behaviour and superconductivity. Solid potassium-intercalated picene (K_xpicene) shows Tc values of 7 K and 18 K, depending on the metal content. The drop of magnetization in K_xpicene solids at the transition temperature is sharp (<2 K), similar to the behaviour of Ca-intercalated graphite. The Tc of 18 K is comparable to that of K-intercalated C₆₀. This discovery of superconductivity in Kxpicene shows that organic hydrocarbons are promising candidates for improved Tc values.

Superconductivity has been discovered in the materials that form when alkali metals react with a solid hydrocarbon. Now the discovery of superconductivity at temperatures up to 18 K is reported in crystals of a simple hydrocarbon molecule doped with potassium or rubidium. The basis for the new compound is picene (C₂₂H₁₄), a molecule consisting of five benzene rings sharing edges with one another, which crystallizes into an ordered molecular solid. Intercalation of the alkali metals into the crystal lattice induces metallic behaviour and superconductivity in what is normally a semiconducting material. The Tc of 18 K in potassium-doped picene is high for an organic superconductor — only alkali-metal-doped C₆₀ achieves higher. And as picene is one of a large family of molecules based on fused benzene rings, other superconducting hydrocarbons may be awaiting discovery.

The electronic structure of a pristine picene molecule is shown. The LUMO and LUMO+1 are not degenerate, but the levels are very close to each other, suggesting a high density of states, in the Fermi level as in A_xC₆₀. If three electrons are transferred from three K atoms to picene in K₃picene, the LUMO+1 level is half occupied. The phonon mode responsible for electron-phonon coupling is probably the molecular vibration of picene, judging from the phonon mode in the electron-phonon coupling of C₆₀ superconductors [3].

References:

1. Pople, J., & Walmsley, S. (1962). Bond alternation defects in long polyene molecules Molecular Physics, 5 (1), 15–20 DOI: 10.1080/00268976200100021
2. Su, W., Schrieffer, J., & Heeger, A. (1980). Soliton excitations in polyacetylene Physical Review B, 22 (4), 2099–2111 DOI: 10.1103/PhysRevB.22.2099
3. Mitsuhashi, R., Suzuki, Y., Yamanari, Y., Mitamura, H., Kambe, T., Ikeda, N., Okamoto, H., Fujiwara, A., Yamaji, M., Kawasaki, N., Maniwa, Y., & Kubozono, Y. (2010). Superconductivity in alkali-metal-doped picene Nature, 464 (7285), 76–79 DOI: 10.1038/nature08859

• Christmas Disease. Biggs, R, Douglas, A, Macfarlane, R, Dacie, J, Pitney, W, Merskey, C & O’Brien, J, 1952, BMJ, vol. 2, no. 4799, pp. 1378–1382.
  DOI: http://dx.doi.org/10.1136/bmj.2.4799.1378





• More Than a Labor of Love: Gender Roles and Christmas Gift Shopping. Fischer, E & Arnold, S, 1990, Journal of Consumer Research, vol. 17, no. 3, p. 333. DOI: http://dx.doi.org/10.1086/208561




• Looking at Christmas trees in the nucleolus. Scheer, U, Xia, B, Merkert, H & Weisenberger, D, 1997, Chromosoma, vol. 105, no. 7–8, pp. 470–480.
  DOI: http://dx.doi.org/10.1007/s004120050209




• The Vela glitch of Christmas 1988. McCulloch, P, Hamilton, P, McConnell, D & King, E, 1990, Nature, vol. 346, no. 6287, pp. 822–824.
  DOI: http://dx.doi.org/10.1038/346822a0




• Cardiac Mortality Is Higher Around Christmas and New Year’s Than at Any Other Time: The Holidays as a Risk Factor for Death. Phillips, D, 2004, Circulation, vol. 110, no. 25, pp. 3781–3788. DOI: http://dx.doi.org/10.1161/01.CIR.0000151424.02045.F7




• Red Crabs in Rain Forest, Christmas Island: Biotic Resistance to Invasion by an Exotic Snail. Lake, P & O’Dowd, D, 1991, Oikos, vol. 62, no. 1, p. 25.
  DOI: http://dx.doi.org/10.2307/3545442




• The Carvedilol Hibernation Reversible Ischaemia Trial, Marker of Success (CHRISTMAS) study Methodology of a randomised, placebo controlled, multicentre study of carvedilol in hibernation and heart failure. Pennell, D, 2000, International Journal of Cardiology, vol. 72, no. 3, pp. 265–274.
  DOI: http://dx.doi.org/10.1016/S0167-5273(99)00198–9

[via Crossref blog & PhD Comics]

a) Idealized schematic illustrating the structure of the device (l_d) linkage, with A’, D’ and B’ recognition sequences. b) A bcc unit cell representation of a bulk three-dimensional superlattice consisting of nanoparticles A–p and B–p interconnected by l_d. © Nature Publishing Group.

Such responsiveness to changes in environmental conditions and the ability to adopt new forms are hallmarks of living systems. In that way, these new nanomaterials more closely mimic biological systems than any previous nanostructures. Though far from any form of truly “artificial life,” these materials could lead to the design of nanoscale machines that, at a very simple level, mimic cellular processes such as converting sunlight into useful energy, or sensing the presence of other molecules. Responsive materials would also have benefits in the field of optics or to produce regulated porous materials for molecular separations, Gang says. The scientists achieved the goal of responsiveness by creating structures where the distance between nanoparticles could be carefully controlled with nanometer accuracy.

Nanoscale components can be self-assembled into static three-dimensional structures arrays and clusters using biomolecular motifs. The structural plasticity of biomolecules and the reversibility of their interactions can also be used to make nanostructures that are dynamic, reconfigurable and responsive. DNA has emerged as an ideal biomolecular motif for making such nanostructures, partly because its versatile morphology permits in situ conformational changes using molecular stimuli. This has allowed DNA nanostructures to exhibit reconfigurable topologies and mechanical movement. Recently, researchers have begun to translate this approach to nanoparticle interfaces where, for example, the distances between nanoparticles can be modulated, resulting in a distance-dependent plasmonic response. Here, we report the assembly of nanoparticles into three-dimensional superlattices and dimer clusters, using a reconfigurable DNA device that acts as an interparticle linkage. The interparticle distances in the superlattices and clusters can be modified, while preserving structural integrity, by adding molecular stimuli (simple DNA strands) after the self-assembly processes has been completed. Both systems were found to switch between two distinct rigid states, but a transition to a flexible device configuration within a superlattice showed a significant hysteresis.

The presented approach may potentially offer the post-assembly regulation of systems with useful optoelectronic, energy conversion and bio-diagnostic properties. In addition, the ability to manipulate a nanostructure global system state opens new opportunities for the formation of dynamically self-assembled structures that more closely mimic biological systems.

Maye, M., Kumara, M., Nykypanchuk, D., Sherman, W., & Gang, O. (2009). Switching binary states of nanoparticle superlattices and dimer clusters by DNA strands Nature Nanotechnology DOI: 10.1038/nnano.2009.378

Tip #2: Remind your colleagues how many students you teach, how many exams you have to grade, how frightfully many hours it will take you to grade them, and how grading exams really cuts down the time you can be available for scholarship, service activities, friends or family.

Tip #3: Send an e-mail informing your dean or colleagues that you have been invited to speak at the local Rotary Club or the neighboring town’s PTA meeting.

Tip #4: Bring massive amounts of work to talks by outsiders and student events, and make sure to visibly mark on documents — as if editing your own paper or making comments on student work — in full sight of everyone else in the room.

Tip #5: Get ticked off and behave badly at faculty meetings.

Tip #6: Do not timely answer e-mails from anyone who may be relying on you to show up to an event, help review applications or schedule a meeting, then get huffy when the meeting takes place before you respond to the e-mail.

[via The Chronicle ]

Scientists, at IBM Research — Almaden, in collaboration with colleagues from Lawrence Berkeley National Lab, have performed the first near real-time cortical simulation of the brain that exceeds the scale of a cat cortex and contains 1 billion spiking neurons and 10 trillion individual learning synapses.

The figure presents the results of our weak scaling study, where the problem size is increased with increasing amount of memory. The plot demonstrates nearly perfect weak scaling in terms of memory, since twice the model size could be simulated when the amount of memory is doubled. The largest simulated model corresponds to a scale larger than the cat cerebral cortex, reaching 4.5% of the human cerebral cortex.

Scaling of Cortical Simulations. Copyright © 2009, ACM, Inc.

Using a state-of-the-art Blue Gene/P with 147,456 processors and 144 TB of main memory, authors were able to simulate a thalamocortical model at an unprecedented scale of 10⁹ neurons and 10¹³ synapses. Compared to the human cortex, this simulation has a scale that is roughly 1–2 orders smaller and has a speed that is 2–3 orders slower than real-time. This work opens the doors for bottom-up, actual-scale models of the thalamocortical system derived from biologically-measured data. Moreover, further progress in supercomputing, realtime human-scale simulations are not only within reach, but indeed appear inevitable:

Growth of Top500 supercomputers overlaid with obtained result and a projection for realtime human-scale cortical simulation. Copyright © 2009, ACM, Inc.

Finally, this isn’t a simulation of a cat brain, it’s a simulation of a brain structure that has the scale and connection complexity of a cat brain. It doesn’t include the actual structures of a cat brain, nor its actual connections; the various experiments in the project filled the memory of the cortical simulation with a bunch of data, and let the system create its own signals and connections. Put simply, it’s not an artificial intelligence, it’s a platform upon which an AI could conceivably be built. The same team created a mouse-scale brain simulation a few years ago. One of the researchers, Dharmendra Modha, runs a blog on cognitive computing, and has posted a PDF of the research paper on this project.

R. Ananthanarayanan, S. K. Esser, H. D. Simon, & D. S. Modha (2009). The Cat is Out of the Bag: Cortical Simulations with 109 Neurons, 1013 Synapses Proceedings of the Conference on High Performance Computing Networking, Storage and Analysis , 1–12 DOI: 10.1145/1654059.1654124

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string article = "Lee_Xi_Wang_2009.pdf";
int rejected = 0;
int ii=0;

until (rejected)
{ rejected = submit(journal[ii], article);
ii++; }

It’s Called… THERAPY

Q: What made you want to be a chemist?

A: My junior high school teacher in Mexico was an inspiration. He was a biochemist with a passion for the inner workings of proteins and enzymes. I later had the opportunity of representing Mexico at the International Chemistry Olympiad held in Oslo, Norway, in 1994. By then, I had a a tough choice between studying computer science or chemistry. The inclination for computer science, however, never faded away. For my Ph.D., I carried out large-scale computing using quantum Monte Carlo. During my postdoc years, I began working at the interface between quantum computation and chemistry, and this is still one of my current research topics as an independent faculty.

Q: If you weren’t a chemist and could do any other job, what would it be — and why?

A: If I were not a scientist, I can imagine many other possible alter egos. On dreamy days, I see myself as a film maker, doing independent film, or as a (very) progressive politician.

Read full interview at Sceptical Chymist.

The Sceptical Chymist is a blog by the editors of Nature and the Research journals — and a forum for readers, authors and the entire chemical community. Authors discuss what’s new and exciting in chemistry and chemical biology, be it in Nature journals or elsewhere.