Nonuniversality of the dispersion interaction: analytic benchmarks for van der Waals energy functionals

We highlight the non-universality of the asymptotic behavior of dispersion forces, such that a sum of inverse sixth power contributions is often inadequate. We analytically evaluate the cross-correlation energy Ec between two pi-conjugated layers separated by a large distance D within the electromagnetically non-retarded Random Phase Approximation, via a tight-binding model. For two perfect semimetallic graphene sheets at T=0K we find Ec = C D^{-3}, in contrast to the "insulating" D^{-4} dependence predicted by currently accepted approximations. We also treat the case where one graphene layer is replaced by a thin metal, a model relevant to the exfoliation of graphite. Our general considerations also apply to nanotubes, nanowires and layered metals.Comment: 4 pages, 0 fig

Enhanced dispersion interaction between quasi-one dimensional conducting collinear structures

Recent investigations have highlighted the failure of a sum of $R^{-6}$ terms to represent the dispersion interaction in parallel metallic, anisotropic, linear or planar nanostructures [J. F. Dobson, A. White, and A. Rubio, Phys. Rev. Lett. 96, 073201 (2006) and references therein]. By applying a simple coupled plasmon approach and using electron hydrodynamics, we numerically evaluate the dispersion (non-contact van der Waals) interaction between two conducting wires in a collinear pointing configuration. This case is compared to that of two insulating wires in an identical geometry, where the dispersion interaction is modelled both within a pairwise summation framework, and by adding a pinning potential to our theory leading to a standard oscillator-type model of insulating dielectric behavior. Our results provide a further example of enhanced dispersion interaction between two conducting nanosystems compared to the case of two insulating ones. Unlike our previous work, this calculation explores a region of relatively close coupling where, although the electronic clouds do not overlap, we are still far from the asymptotic region where a single power law describes the dispersion energy. We find that strong differences in dispersion attraction between metallic and semiconducting / insulating cases persist into this non-asymptotic region. While our theory will need to be supplemented with additional short-ranged terms when the electronic clouds overlap, it does not suffer from the short-distance divergence exhibited by purely asymptotic theories, and gives a natural saturation of the dispersion energy as the wires come into contact.Comment: 10 pages, 5 figures. Added new extended numerical calculations, new figures, extra references and heavily revised tex

Access to and use of marine genetic resources : understanding the legal framework

This article is licensed under a Creative Commons Attribution 3.0 Unported Licence. Acknowledgements This work was supported by the PharmaSea project funded by the EU Seventh Framework Programme, and reects only the authors' views. Contract number 312184. www.pharma-sea.eu.Peer reviewedPublisher PD

Scalable Asymptotically-Optimal Multi-Robot Motion Planning

Finding asymptotically-optimal paths in multi-robot motion planning problems could be achieved, in principle, using sampling-based planners in the composite configuration space of all of the robots in the space. The dimensionality of this space increases with the number of robots, rendering this approach impractical. This work focuses on a scalable sampling-based planner for coupled multi-robot problems that provides asymptotic optimality. It extends the dRRT approach, which proposed building roadmaps for each robot and searching an implicit roadmap in the composite configuration space. This work presents a new method, dRRT* , and develops theory for scalable convergence to optimal paths in multi-robot problems. Simulated experiments indicate dRRT* converges to high-quality paths while scaling to higher numbers of robots where the naive approach fails. Furthermore, dRRT* is applicable to high-dimensional problems, such as planning for robot manipulatorsComment: 8 pages, 12 figures, submitted to the first International Symposium on Multi-Robot and Multi-Agent Systems (MRS

Asymptotically exact dispersion relations for collective modes in a confined charged Fermi liquid

Using general local conservations laws we derive dispersion relations for edge modes in a slab of electron liquid confined by a symmetric potential. The dispersion relations are exact up to $\lambda^{2} q^{2}$, where $q$ is a wave vector and $\lambda$ is an effective screening length. For a harmonic external potential the dispersion relations are expressed in terms of the {\em exact} static pressure and dynamic shear modulus of a homogeneous liquid with the density taken at the slab core. We also derive a simple expression for the frequency shift of the dipole (Kohn) modes in nearly parabolic quantum dots in a magnetic field.Comment: RevTeX4, 4 pages. Revised version with new results on quantum qots and wires. Published in Phys.Rev.

Boom

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Architecture, 2000.Includes bibliographical references (leaf 33).This thesis is about my relationship to technology through the medium of my body. By implication it is about how our culture and society view and interact with technology's various manifestations. I use my voice as the medium of this exploration. Boom is a sound and video insertion embodying and re-presenting my vocal arguments and mergings with the machines of a cement pour at the Big Dig in Boston in the spring of the year 2000. Boom offers noise, physical auditive immersion, and hopefully a provocative and meaningful perspective on relating with machines. It creates temptations and in draughts of air around the metaphysical ideas it conjures with the humor and poetry of anarchy. By merging and falling out, struggling and capturing, losing and regaining, the machines and I are negotiating our relationship, our take on each other, our roles, our positions relative to each other. Each machine becomes an extension of my body, as I am resonating within its cavities and it is resonating within me. There is a constant arbitration of who is driving whom, my voice driving the machine's motor and/or the machine's vibrations moving my body, feelings, and perceptions of self within space. As I follow a machine's vibratory lead, try to keep up, to match, to catch, through matching vocalizations, I access previously unacknowledged places within myself. Something like the mantras of other cultures - magical brutal mysterious consonance expressed in broad daylight. Communication occurs through the correspondence of internal and external vibrations. Emanating and absorbing. The tones have an acupunctural precision, able to vibrate certain organs, interstitial tissues, cells, thereby accessing the body's warehouses. The performances of myself with the construction machines in the city throw new perspectives on how we conceive of not only the gigantic machines in our environments, but of other elements of technology as well, such as the intimate integration with small electronic devices being cultivated everywhere within our reach.by Kelly E. Dobson.S.M

Correction: Meta-Analysis of the Relationship between Multiple Sclerosis and Migraine.

This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.PMCID: PMC3613438PMCID: PMC3613438PMCID: PMC3613438PMCID: PMC3613438[This corrects the article on p. e45295 in vol. 7.]