Explanation and Cognition

These essays draw on work in the history and philosophy of science, the philosophy of mind and language, the development of concepts in children, conceptual.

Explaining Explanation

It is not a particularly hard thing to want or seek explanations. In fact, explanations seem to be a large and natural part of our cognitive lives. Children ask why and how questions very early in development and seem genuinely to want some sort of answer, despite our often being poorly equipped to provide them at the appropriate level of sophistication and detail. We seek and receive explanations in every sphere of our adult lives, whether it be to understand why a friendship has foundered, why a car will not start, or why ice expands when it freezes. Moreover, correctly or incorrectly, most of the time we think we know when we have or have not received a good explanation. There is a sense both that a given, successful explanation satisfies a cognitive need, and that a questionable or dubious explanation does not. There are also compelling intuitions about what make good explanations in terms of their form, that is, a sense of when they are structured correctly

Bosnia and Herzegovina twenty years after Dayton: complexity born of paradoxes

This paper will start with an analysis of the Dayton Peace Agreement, and assess to what extent it focused on peace-building, state-reconstruction and democratization. It will provide an overview of major peace-building, state-reconstruction and democratization initiatives by international and local actors in post-war Bosnia. Following the often-presented argument that “Dayton is a good peace agreement but a bad blueprint for a democratic state,” the paper will ask if the Dayton Peace Agreement has failed in the consolidation of Bosnian statehood and the democratization of the country. In order to do this, an in-depth analysis of the current situation in terms of state consolidation and democratization will be given. The main argument of the paper demonstrates that while the Dayton Agreement had some inherent weaknesses, actions by local elites and international state-builders also explain some of the current issues of the Bosnian state

Adsorption of cobalt on graphene: Electron correlation effects from a quantum chemical perspective

In this work, we investigate the adsorption of a single cobalt atom (Co) on graphene by means of the complete active space self-consistent field approach, additionally corrected by the second-order perturbation theory. The local structure of graphene is modeled by a planar hydrocarbon cluster (C$_{24}$H$_{12}$). Systematic treatment of the electron correlations and the possibility to study excited states allow us to reproduce the potential energy curves for different electronic configurations of Co. We find that upon approaching the surface, the ground-state configuration of Co undergoes several transitions, giving rise to two stable states. The first corresponds to the physisorption of the adatom in the high-spin $3d^74s^2$ ($S=3/2$) configuration, while the second results from the chemical bonding formed by strong orbital hybridization, leading to the low-spin $3d^9$ ($S=1/2$) state. Due to the instability of the $3d^9$ configuration, the adsorption energy of Co is small in both cases and does not exceed 0.35 eV. We analyze the obtained results in terms of a simple model Hamiltonian that involves Coulomb repulsion ($U$) and exchange coupling ($J$) parameters for the 3$d$ shell of Co, which we estimate from first-principles calculations. We show that while the exchange interaction remains constant upon adsorption ($\simeq1.1$ eV), the Coulomb repulsion significantly reduces for decreasing distances (from 5.3 to 2.6$\pm$0.2 eV). The screening of $U$ favors higher occupations of the 3$d$ shell and thus is largely responsible for the interconfigurational transitions of Co. Finally, we discuss the limitations of the approaches that are based on density functional theory with respect to transition metal atoms on graphene, and we conclude that a proper account of the electron correlations is crucial for the description of adsorption in such systems.Comment: 12 pages, 6 figures, 2 table

Interfacial interactions between local defects in amorphous SiO2_2 and supported graphene

We present a density functional study of graphene adhesion on a realistic SiO$_2$ surface taking into account van der Waals (vdW) interactions. The SiO$_2$ substrate is modeled at the local scale by using two main types of surface defects, typical for amorphous silica: the oxygen dangling bond and three-coordinated silicon. The results show that the nature of adhesion between graphene and its substrate is qualitatively dependent on the surface defect type. In particular, the interaction between graphene and silicon-terminated SiO$_2$ originates exclusively from the vdW interaction, whereas the oxygen-terminated surface provides additional ionic contribution to the binding arising from interfacial charge transfer ($p$-type doping of graphene). Strong doping contrast for the different surface terminations provides a mechanism for the charge inhomogeneity of graphene on amorphous SiO$_2$ observed in experiments. We found that independent of the considered surface morphologies, the typical electronic structure of graphene in the vicinity of the Dirac point remains unaltered in contact with the SiO$_2$ substrate, which points to the absence of the covalent interactions between graphene and amorphous silica. The case of hydrogen-passivated SiO$_2$ surfaces is also examined. In this situation, the binding with graphene is practically independent of the type of surface defects and arises, as expected, from the vdW interactions. Finally, the interface distances obtained are shown to be in good agreement with recent experimental studies.Comment: 10 pages, 4 figure

Graphene adhesion on mica: Role of surface morphology

We investigate theoretically the adhesion and electronic properties of graphene on a muscovite mica surface using the density functional theory (DFT) with van der Waals (vdW) interactions taken into account (the vdW-DF approach). We found that irregularities in the local structure of cleaved mica surface provide different mechanisms for the mica-graphene binding. By assuming electroneutrality for both surfaces, the binding is mainly of vdW nature, barely exceeding thermal energy per carbon atom at room temperature. In contrast, if potassium atoms are non uniformly distributed on mica, the different regions of the surface give rise to $n$- or $p$-type doping of graphene. In turn, an additional interaction arises between the surfaces, significantly increasing the adhesion. For each case the electronic states of graphene remain unaltered by the adhesion. It is expected, however, that the Fermi level of graphene supported on realistic mica could be shifted relative to the Dirac point due to asymmetry in the charge doping. Obtained variations of the distance between graphene and mica for different regions of the surface are found to be consistent with recent atomic force microscopy experiments. A relative flatness of mica and the absence of interlayer covalent bonding in the mica-graphene system make this pair a promising candidate for practical use.Comment: 6 pages, 3 figure

Adsorption of diatomic halogen molecules on graphene: A van der Waals density functional study

The adsorption of fluorine, chlorine, bromine, and iodine diatomic molecules on graphene has been investigated using density functional theory with taking into account nonlocal correlation effects by means of vdW-DF approach. It is shown that the van der Waals interaction plays a crucial role in the formation of chemical bonding between graphene and halogen molecules, and is therefore important for a proper description of adsorption in this system. In-plane orientation of the molecules has been found to be more stable than the orientation perpendicular to the graphene layer. In the cases of F$_2$, Br$_2$ and I$_2$ we also found an ionic contribution to the binding energy, slowly vanishing with distance. Analysis of the electronic structure shows that ionic interaction arises due to the charge transfer from graphene to the molecules. Furthermore, we found that the increase of impurity concentration leads to the conduction band formation in graphene due to interaction between halogen molecules. In addition, graphite intercalation by halogen molecules has been investigated. In the presence of halogen molecules the binding between graphite layers becomes significantly weaker, which is in accordance with the results of recent experiments on sonochemical exfoliation of intercalated graphite.Comment: Submitted to PR

Experiment K-6-12. Morphometric studies of atrial or granules and hepatocytes. Part 1: Morphometric study of the liver; Part 2: The atrial granular accumulations

The livers of flight, F, rats from the Cosmos 1887 mission were markedly paler and heavier than those of the synchronous, S, and vivarium, V, controls. In the F group, microscopic study revealed extensive hepatocytic intracytoplasmic vacuolization which was moderate in the S and minimal in the V groups. The vacuoles were not sudanophilic and therefore were regarded as glycogenic in origin. To obtain objective data concerning the extent of the vacuolization, livers were examined by computer assisted morphometry. Measurements of profile area and perimeter of the hepatocyte nuclei and vacuoles were evaluated according to stereological principles. Results indicated that the volume density of the nuclei was less in the F group than in the S(p equal less than 0.0002) and V(p equal less than 0.001) groups. Mean volume of individual nuclei did not differ. Volume density of the vacuoles was greater in the F than in the V group (p equal less than 0.02) while their mean diameter was less (p equal less than 0.05). To ascertain the relationship between increase in liver weight of the flight animals and the results of this study, an assumption was made that the specific gravity of the vacuolar contents was similar to the other extranuclear components of the hepatocyte. On that basis, calculations showed that the elevated vacuolar volume density in the flight group did not cause the increased liver weight in those animals, but that the non-nuclear, non-vacuolar parenchymal compartment did contribute significantly. Factors that may have played a causal role in liver weight and vacuolar compartment increases are discussed