Elementary Kaluza-Klein Towers revisited

Considering that the momentum squared in the extra dimensions is the physically relevant quantity for the generation of the Kaluza-Klein mass states, we have reanalyzed mathematically the procedure for five dimensional scalar fields within the Arkhani-Ahmed, Dimopoulos and Dvali scenario. We find new sets of physically allowed boundary conditions. Beside the usual results, they lead to new towers with non regular mass spacing, to lonely mass states and to tachyons. We remark that, since the SO(1,4) symmetry is to be broken due to the compactification of the extra dimensions, the speed of light could be different in the fifth dimension. This would lead to the possible appearance of a new universal constant besides $\hbar$ and $c$.Comment: 20 pages, 1 figur

The mechanism of the Einstellung (set) effect: A pervasive source of cognitive bias

Copyright @ The Authors 2010The eye movements of expert players trying to solve a chess problem show that the first idea that comes to mind directs attention towards sources of information consistent with itself and away from inconsistent information. This bias continues unconsciously even when the player believes he is looking for alternatives. The result is that alternatives to the first idea are ignored. This mechanism for biasing attention ensures a speedy response in familiar situations but it can lead to errors when the first thought that comes to mind is not appropriate. We propose that this mechanism is the source of many cognitive biases from phenomena in problem solving and reasoning, to perceptual errors and failures in memory

Visual search in ecological and non-ecological displays: Evidence for a non-monotonic effect of complexity on performance

Copyright @ 2013 PLoSThis article has been made available through the Brunel Open Access Publishing Fund.Considerable research has been carried out on visual search, with single or multiple targets. However, most studies have used artificial stimuli with low ecological validity. In addition, little is known about the effects of target complexity and expertise in visual search. Here, we investigate visual search in three conditions of complexity (detecting a king, detecting a check, and detecting a checkmate) with chess players of two levels of expertise (novices and club players). Results show that the influence of target complexity depends on level of structure of the visual display. Different functional relationships were found between artificial (random chess positions) and ecologically valid (game positions) stimuli: With artificial, but not with ecologically valid stimuli, a “pop out” effect was present when a target was visually more complex than distractors but could be captured by a memory chunk. This suggests that caution should be exercised when generalising from experiments using artificial stimuli with low ecological validity to real-life stimuli.This study is funded by Brunel University and the article is made available through the Brunel Open Access Publishing Fund

A pattern-recognition theory of search in expert problem solving

Understanding how look-ahead search and pattern recognition interact is one of the important research questions in the study of expert problem-solving. This paper examines the implications of the template theory (Gobet & Simon, 1996a), a recent theory of expert memory, on the theory of problem solving in chess. Templates are "chunks" (Chase & Simon, 1973) that have evolved into more complex data structures and that possess slots allowing values to be encoded rapidly. Templates may facilitate search in three ways: (a) by allowing information to be stored into LTM rapidly; (b) by allowing a search in the template space in addition to a search in the move space; and (c) by compensating loss in the "mind's eye" due to interference and decay. A computer model implementing the main ideas of the theory is presented, and simulations of its search behaviour are discussed. The template theory accounts for the slight skill difference in average depth of search found in chess players, as well as for other empirical data

Multiscale mechanical studies of nacre from gastropod mollusk Trochus Nilocitus

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2004.Includes bibliographical references (p. 82-83).(cont.) revealed jagged and branched crack fronts at plate interface, tortuous crack paths, non-uniform angles of polygons (suggesting possible intrinsic deformability and displacement/sliding). The technique of nanoindentation was carried out on individual aragonite tablets using a diamond-coated Berkovich probe tip (end-radius of 70 nm, tip angle of 142.3 degrees), at a rate of indentation of 10 [micro]N/s (load controlled), forces from 10 to 1000 [micro]N and indentation depths from 10 to 97 nm. AFM inspection of the indented region showed the existence of extensive plastic deformation within the tablet and suggested that occluded biomacromolecules may play a significant role in the deformation at loads below 100 [micro]N. Using the contact elastic theory, a Young modulus of 112.3 GPa and a hardness of 10.5 GPa were found for an individual platelet. This study shows that a biocomposite principally composed of a poor ceramic (aragonite) can achieve surprisingly good macroscopic mechanical properties thanks to a complex hierarchical structure allowing an extraordinary variety of energy-dissipating mechanisms. Our aim is to continue to formulate multiscale structure-property relationships to eventually aid in the design and advancement of new synthetic biologically inspired lightweight, hard body armor technologies.The inner columnar nacreous layer of the gastropod mollusk Trochus Niloticus is a nanostructured biocomposite with outstanding and unique mechanical properties. It is composed of [approximately]95% wt of hexagonal aragonite plates (width=5.8±0.4 [micro]m, thickness=0.87±0.07 [micro]m), stacked [approximately]40 nm apart, and [approximately]5% wt of a biomacromolecular "glue" which exists between and within the individual plates. Atomic force microscopy (AFM) revealed a dense array of nanoasperities on the top and sides of the aragonite plates ([approximately]120 nm wide). A multiscale theoretical and experimental approach was taken to identify, understand, and predict the complex deformation mechanisms and mechanical behavior of this fascinating material. Macroscopic 3-point bend tests yielded an in-plane Young modulus of 68.0 ± 11.4 GPa and 65.4 ± 9.6 GPa for freshly cut samples and samples soaked for 10 weeks respectively. A fracture strength of 231 ± 34 MPa and 213 ± 42 MPa respectively were measured. Samples soaked for 10 weeks, even if slightly less strong, exhibited major non-linearities in the stress-strain curves, emphasizing the greater toughness of hydrated nacre. Uniaxial compression yielded Young moduli of 63.8 ± 14.7 GPa for samples with the brick layers oriented parallel to the load, 19.1 ± 3.4 GPa when oriented perpendicular to it and fracture strengths of respectively 225 ± 44 and 663 ± 71 MPa. The discrepancy between the compression moduli emphasizes that very distinct deformation mechanisms prevail during these tests, which is confirmed by the fact that fracture occurs also in three different ways (respectively through thickness, interlaminar and shatter). Scanning electron microscopy (SEM) and AFM of fractured samplesby Benjamin J.F. Bruet.S.M

Multiscale structural and mechanical design of mineralized biocomposites

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2008.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Includes bibliographical references (p. 211-222).Gastropod mollusk nacre tablets and Polypterus senegalus armored scales share common features such as a very complex and changing structure spanning several length scales. The smallest building blocks are single crystals, have dimensions of a from tens of nanometers to several microns and are intimately blended with an organic glue present within pores or between the crystallites. In particular, our results strongly suggest that nacre tablets possess nanoscale porosity in the form of elongated tubules that may contain the intratablet macromolecules. Their unique structure allows these materials deform in a ductile way at the nanoscale, with no cracks observed, and to confine deformation at the microscale so as to impede crack propagation. Gradient in the mechanical properties are ubiquitous at both the microscale (scales) and the nanoscale (nacre tablets), preventing stress concentration and enhancing strain distribution. The armored scales thus exhibit a unique spatial functional form of mechanical properties with regions of differing levels of gradation within and between material layers, as well as layer with an undetectable gradation. Though highly mineralized, these biomaterials also exhibit greater local heterogeneity in their mechanical properties compared to pure minerals. Materials layers have distinct morphology and mechanical properties depending on their role (resistance to abrasion for harder outer layers, resistance to fracture for tougher inner layers) and their interface are reinforced (by anchored organic fiber ligaments and corrugated interfaces that maximize contact surface., preventing propagation of cracks both through and along the interfaces.(cont.) The heterogeneity in size and shape of the crystallites and the pores, as well as the variation in the composition (mineral / organic, crystalline amorphous) are likely responsible for the desirable variations of mechanical properties as observed in these biocomposites at the smallest length scales, resulting in more spatially distributed strains and greater energy dissipation.Benjamin J.F. Bruet.Ph.D

Transition State Spectroscopy of the Photoinduced Ca + CH3F Reaction. 2. Experimental and Ab Initio Studies of the Free Ca***FCH3 Complex

International audienceThe Ca* + CH3F CaF* + CH3 reaction was photoinduced in 1:1 Ca***CH3F complexes formed in a supersonic expansion. The transition state of the reaction was explored by monitoring the electronically excited product, CaF, while scanning the laser that turns on the reaction. Moreover, the electronic structure of the Ca***FCH3 system was studied using ab initio methods by associating a pseudopotential description of the [Ca2+] and [F7+] cores, a core polarization operator on calcium, an extensive Gaussian basis and a treatment of the electronic problem at the CCSD(T) (ground state) and RSPT2 (excited states) level. In this contribution we present experimental results for the free complex and a comparison with the results of a previous experiment where the Ca***CH3F complexes are deposited at the surface of large argon clusters. The ab initio calculations allowed an interpretation of the experimental data in terms of two reaction mechanisms, one involving a partial charge transfer state, the other involving the excitation of the C-F stretch in the CH3F moiety prior to charge transfer