Van der Waals-corrected density functional theory: benchmarking for hydrogen-nanotube and nanotube-nanotube interactions

Density functional theory (DFT) is a powerful approach to electronic structure calculations in extended systems, but suffers currently from inadequate incorporation of long-range dispersion, or Van der Waals (VdW) interactions. VdW-corrected DFT is tested for interactions involving molecular hydrogen, graphite, single-walled carbon nanotubes (SWCNTs), and SWCNT bundles. The energy correction, based on an empirical London dispersion term with a damping function at short range, allows a reasonable physisorption energy and equilibrium distance to be obtained for H-2 on a model graphite surface. The VdW-corrected DFT calculation for an (8, 8) nanotube bundle reproduces accurately the experimental lattice constant. For H-2 inside or outside an (8, 8) SWCNT, we find the binding energies are respectively higher and lower than that on a graphite surface, correctly predicting the well known curvature effect. We conclude that the VdW correction is a very effective method for implementing DFT calculations, allowing a reliable description of both short-range chemical bonding and long-range dispersive interactions. The method will find powerful applications in areas of SWCNT research where empirical potential functions either have not been developed, or do not capture the necessary range of both dispersion and bonding interactions.

Van der Waals interactions between two parallel infinitely long single-walled nanotubes

The potential energies of van der Waals (VDW) interactions between two parallel, infinitely long and perfect SWNTs with identical, and different sizes were studied based on the continuum Lennard-Jones model. The conclusion of Girifalco's work on (n, n) SWNTs that the potentials of SWNT-SWNT fell on a single curve, is also applicable to SWNTs with different sizes. We further obtained the corresponding constants of the well depth phi(0) and equilibrium VDW gap g(0) for SWNTs with a radius from 2 to 25 Angstrom. (C) 2005 Elsevier B.V. All rights reserved.

Simple approach to estimating the van der Waals interaction between carbon nanotubes

The van der Waals (vdW) interactions between carbon nanotubes (CNTs) were studied based on the continuum Lennard-Jones model. It was found that all the vdW potentials between two arbitrary CNTs fall on the same curve when plotted in terms of certain reduced parameters, the well depth, and the equilibrium vdW gap. Based on this observation, an approximate approach is developed to obtain the vdW potential between two CNTs without time-consuming computations. The vdW potential estimated by this approach is close to that obtained from complex integrations. Therefore, the developed approach can greatly simplify the calculation of vdW interactions between CNTs.

London-van der Waals adhesiveness of rough particles

Van der Waals forces often dominate interactions and adhesion between fine particles and, in turn, decisively influence the bulk behaviour of powders. However, so far there is no effective means to characterize the adhesive behaviour of such particles. A complication is that most powder particles have rough surfaces, and it is the asperities on the surfaces that touch, confounding the actual surface that is in contact. Conventional approaches using surface energy provide limited information regarding adhesion, and pull-off forces measured through atomic force microscope (AFM) are highly variable and difficult to interpret. In this paper we develop a model which combines the Rumpf-Rabinovich and the JKR-DMT theories to account simultaneously for the effects of surface roughness and deformation on adhesion. This is applied to a 'characteristic asperity' which may be easily obtained from AFM measurements. The concept of adhesiveness, a material property reflecting the influences of elastic deformability, surface roughness, and interfacial surface energy, is introduced as an efficient and quantitative measure of the adhering tendency of a powder. Furthermore, a novel concept of specific adhesiveness is proposed as a convenient tool for characterizing and benchmarking solid materials. This paper provides an example to illustrate the use of the proposed theories. (c) 2005 Elsevier B.V. All rights reserved.

Prosody of tone Sandhi in Vietnamese reduplications

In this paper we take advantage of the segmental control afforded by full and partial Vietnamese reduplication on a constant carrier phrase to obtain acoustic evidence of assymetrical prominence relations (van der Hulst 2005), in support of a hypothesis that Vietnamese reduplications are phonetically right headed and that tone sandhi is a reduction phenomenon occurring on prosodically weak positions (Shih 2005). Acoustic parameters of syllable duration (onset, nucleus and coda), F0 range, F0 contour, vowel intensity, spectral tilt and vowel formant structure are analyzed to determine: (1) which syllable of the two (base or reduplicant) is more prominent and (2) how the tone sandhi forms differ from their full reduplicated counterparts. Comparison of full and partial reduplicant syllables in tone sandhi forms provide additional support for this analysis.

BIO Logical Agents: Norms, Beliefs, Intentions in Defeasible Logic

In this paper we follow the BOID (Belief, Obligation, Intention, Desire) architecture to describe agents and agent types in Defeasible Logic. We argue, in particular, that the introduction of obligations can provide a new reading of the concepts of intention and intentionality. Then we examine the notion of social agent (i.e., an agent where obligations prevail over intentions) and discuss some computational and philosophical issues related to it. We show that the notion of social agent either requires more complex computations or has some philosophical drawbacks.

Interaction between Normative Systems and Cognitive Agents in Temporal Modal Defeasible Logic

While some recent frameworks on cognitive agents addressed the combination of mental attitudes with deontic concepts, they commonly ignore the representation of time. An exception is [1]that manages also some temporal aspects both with respect to cognition and normative provisions. We propose in this paper an extension of the logic presented in [1]with temporal intervals.

Contextual Deliberation of Cognitive Agents in Defeasible Logic

This article extends Defeasible Logic to deal with the contextual deliberation process of cognitive agents. First, we introduce meta-rules to reason with rules. Meta-rules are rules that have as a consequent rules for motivational components, such as obligations, intentions and desires. In other words, they include nested rules. Second, we introduce explicit preferences among rules. They deal with complex structures where nested rules can be involved.

(FAB12_1_002) 'Would you know the new, you must search the old': William Lethaby's 'Architecture, Mysticism and Myth' (1891) and the 'Hypnerotomachia Poliphili' (1499)

Published in the final months of 1891, Architecture, Mysticism and Myth was the first architectural treatise written by the late nineteenth-century English architect and theorist William Richard Lethaby (1857-1931).' Documenting the characteristic attributes of the architectural myth of the "temple idea", and its presence amongst architectures of multiple ancient cultures, the text was endowed with a distinctly historical tone. In examining the motives behind myth, which Lethaby defined as the interaction and reaction between the natural universe and the built environment, Lethaby also injected a series of theoretical considerations into the text. It is clear that Lethaby's interest in the temple idea was not limited to its curious, prolific presence in past architectures, hut also embraced a consideration of what lessons the temple idea may contribute to the struggle of the late nineteenth-century English architect to define an "art of the future".

Increased expression of mitochondrial genes in human alcoholic brain revealed by differential display

Polymerase chain reaction (PCR)-based differential display was used to screen for alterations in gene expression in the mesolimbic system of the human alcoholic brain. Total RNA was extracted from the nucleus accumbens of five alcoholic and five control brains. A selected subpopulation of mRNA was reverse-transcribed to cDNA and amplified by PCR. A differentially expressed cDNA fragment was recovered, cloned, and sequenced. Full sequence analysis of this 467 bp fragment revealed 98.2% homology with the human mitochondrial 12S rRNA gene. Dot-blot analysis showed increased expression of this gem in nucleus accumbens and hippocampus, but not in the superior frontal cortex, primary motor cortex, caudate, and pallidus/putamen In a total of eight human alcoholic brains, compared with seven control brains. A similar increased expression was observed by dot-blot analysis, using RNA from the cerebral cortex of rats chronically treated with alcohol vapor. Hybridization of a 16S rRNA oligonucleotide probe indicated that the expression of both rRNAs genes was significantly increased in nucleus accumbens. These results indicate that chronic alcohol consumption induces alteration in expression of mitochondrial genes in selected brain regions. The altered gene expression may reflect mitochondrial dysfunction In the alcohol-affected brain.