Adatoms and nanoengineering of carbon

We present a new and general mechanism for inter-conversion of carbon structures via a catalytic exchange process, which operates under conditions of Frenkel pair generation. The mechanism typically lowers reaction barriers by a factor of four compared to equivilent uncatalysed reactions. We examine the relevance of this mechanism for fullerene growth, carbon onions and nanotubes, and dislocations in irradiated graphite.Comment: 3 Figures, 5 Page letter accepted for publication in Chemical Physics Letter

Four groups of type 2 diabetes contribute to the etiological and clinical heterogeneity in newly diagnosed individuals: An IMI DIRECT study

The presentation and underlying pathophysiology of type 2 diabetes (T2D) is complex and heterogeneous. Recent studies attempted to stratify T2D into distinct subgroups using data-driven approaches, but their clinical utility may be limited if categorical representations of complex phenotypes are suboptimal. We apply a soft-clustering (archetype) method to characterize newly diagnosed T2D based on 32 clinical variables. We assign quantitative clustering scores for individuals and investigate the associations with glycemic deterioration, genetic risk scores, circulating omics biomarkers, and phenotypic stability over 36 months. Four archetype profiles represent dysfunction patterns across combinations of T2D etiological processes and correlate with multiple circulating biomarkers. One archetype associated with obesity, insulin resistance, dyslipidemia, and impaired β cell glucose sensitivity corresponds with the fastest disease progression and highest demand for anti-diabetic treatment. We demonstrate that clinical heterogeneity in T2D can be mapped to heterogeneity in individual etiological processes, providing a potential route to personalized treatments

ENERGY LEVELS AND PROPERTIES OF DEFECTS ON RECONSTRUCTED DISLOCATIONS IN SILICON

Nous présentons les résultats de calculs, dans le silicium, des niveaux d'énergie de défauts d'antiphase (soliton) et d'un complexe lacune-soliton sur les dislocations partielles 90° et 30° reconstruites. Pour calculer ces niveaux et explorer l'effet de la relaxation des atomes voisins, nous avons utilisé un hamiltonien de Phillips-Pandey et une méthode recursive. Ces calculs devraient s'appliquer soit à des échantillons de silicium déformés plastiquement et bien recuits, soit à des échantillons déformés suffisamment lentement pour que des amas de défauts ponctuels ne soient pas introduits. De tels échantillons sont diamagnétiques et ont des niveaux donneur-accepteur proches de Ev + 0,3 ev et Ev + 0,8 ev respectivement. Le diamagnétisme d'un défaut ayant une seule liaison pendante, peut être expliqué par le mécanisme de centres U négatifs d'Anderson. Nos estimations suggèrent que le défaut d'anti-phase (soliton) est réellement de ce type, et nous discutons les implications qui en résultent.The results of calculations of the energy levels of anti-phase (soliton) defects and a vacancy-soliton complex on reconstructed 90° and 30° partials in silicon are given. A Phillips - Pandey Hamiltonian and the recursion method were used to evaluate these levels and explore the effect of relaxation of surrounding atoms. These calculations should have relevance to either well-annealed samples of plastically deformed silicon or to samples deformed sufficiently slowly that point defect clusters are not introduced. Such samples are diamagnetic and have donor-acceptor 'levels' around Ev + 0.3 eV and Ev + 0.8 eV respectively. The diamagnetism of a defect with a single dangling bond can be explained by the Anderson negative-U mechanism and estimates are given which suggest the anti-phase defect (soliton) is indeed of this type. Some implications of this are included

Structures of dislocations in GaAs and their modification by impurities

Local density functional theory is used to show that both α and β dislocations in GaAs are reconstructed. This is done by relaxing large 158-atom H-terminated clusters of GaAs containing 90° partial dislocations. The reconstruction is strongly influenced by impurities: acceptor pairs destroy the reconstruction of β partials but strengthen it for α dislocations. Donors have opposite effects. The implication of these results for the pinning of dislocations in GaAs is discussed.Godkänd; 1994; 20080425 (ysko

An Ab Initio{\it Ab}~{\it Initio} Study of the 90° Partial Dislocation Core in Diamond

The electronic and structural properties of the 90° glide partial dislocation in diamond are investigated using an ab initio local density functional cluster method. The core C–C bond is found to be reconstructed with a bond length 5% longer than that in bulk diamond. The formation and migration energy of the kink on the dislocation are calculated to be 0.32 and 2.97 eV respectively. Further, the shift of the gap levels during kink motion suggests that p-type doping will lead to an increase in the mobility of the partial

DFT study of the chemistry of sulfur in graphite, including interactions with defects, edges and folds

Sulfur has several roles, desirable and undesirable, in graphitization. We perform density functional theory calculations within the local density approximation to define the structures and energetics of sulphur in graphite, including its interactions with point defects and edges, in order to understand its role in the later stages of graphitization. We find sulphur does not cross-link layers, except where there are defects. It reacts very strongly with vacancies in neighbouring layers to form a six coordinate split vacancy structure, analogous to that found in diamond. It is also highly stable at basal edge sites, where, as might be expected, the size and valency of sulfur can be easily accommodated. This suggests a role for sulphur in stabilizing graphene edges, and following from this, we show that sulfur dimers can open, i.e. unzip, folds in graphite rapidly and exothermically

Comment On "a/[110] Stacking Fault Model For Platelets In Diamond"

[No abstract available]951

Interaction of Oxygen with Threading Dislocations in GaN

oisoning of growth centres on the walls of nanopipes. 1. Introduction Dislocations in hexagonal GaN are quite unlike those in other IIIV materials like cubic GaAs. For example, the screw dislocation in GaN [1 to 3] lies along [0001] with a full Burgers vector b c0001, whereas in Si or GaAs [4 to 6], it lies along 1 10 and is dissociated into 30 partials with b a=62 1 1. The core structures of the dislocations are also quite different. In the case of GaAs, dislocations are believed to lie on the glide set of planes with a non-stoichiometric core structure consisting of two adjacent chains of chemically identical atoms. Previous calculations [7] indicate that, in the 90 partial, bonds between atoms of the same type are formed in a similar way with the recons

Understanding travel behaviour Final report to the Social Science Research Council

SIGLELD:8318.172(SSRC-HR--2937/4801). / BLDSC - British Library Document Supply CentreGBUnited Kingdo