Morphological instability analysis of a misfit strained core-shell nanowire for the growth of quantum dots

Nell'ambito delle nanostrutture, un ruolo primario è svolto dai punti quantici. In questo lavoro siamo interessati all'analisi teorica del processo di creazione dei punti quantici: esso può avvenire per eteroepitassia, in particolare secondo il metodo studiato da Stranski-Krastanov. Un film di Germanio viene depositato su un substrato di Silicio in modo coerente, cioè senza dislocazioni, e, a causa del misfit tra le maglie dei due materiali, c'è un accumulo di energia elastica nel film. A una certa altezza critica questa energia del film può essere ridotta se il film si organizza in isole (punti quantici), dove la tensione può essere rilassata lateralmente. L'altezza critica dipende dai moduli di Young (E, υ), dal misfit tra le maglie (m) e dalla tensione superficiali (γ). Il trasporto di materiale nel film è portato avanti per diffusione superficiale. Il punto focale nell'analisi delle instabilità indotte dal misfit tra le maglie dei materiali è la ricerca delle caratteristiche che individuano il modo di crescita più rapido dei punti quantici. In questo lavoro siamo interessati ad un caso particolare: la crescita di punti quantici non su una superficie piana ma sulla superficie di un nanofilo quantico a geometria cilindrica. L'analisi delle instabilità viene condotta risolvendo le equazioni all'equilibrio: a tal fine sono state calcolate le distribuzioni del tensore delle deformazioni e degli sforzo di un nanofilo core-shell con una superficie perturbata al primo ordine rispetto all'ampiezza della perturbazione. L'analisi è stata condotta con particolari condizioni al contorno ed ipotesi geometriche, e diverse scelte dello stato di riferimento del campo degli spostamenti. Risolto il problema elastico, è stata studiata l'equazione dinamica di evoluzione descrivente la diffusione di superficie. Il risultato dell'analisi di instabilità è il tasso di crescita in funzione del numero d'onda q, con diversi valori del raggio del core, spessore dello shell e modo normale n, al fine di trovare il più veloce modo di crescita della perturbazione.

Classification of thoracolumbar fractures and dislocations

A classification of injuries is necessary in order to develop a common language for treatment indications and outcomes. Several classification systems have been proposed, the most frequently used is the Denis classification. The problem of this classification system is that it is based on an assumption, which is anatomically unidentifiable: the so-called middle column. For this reason, few years ago, a group of spine surgeons has developed a new classification system, which is based on the severity of the injury. The severity is defined by the pathomorphological findings, the prognosis in terms of healing and potential of neurological damage. This classification is based on three major groups: A = isolated anterior column injuries by axial compression, B = disruption of the posterior ligament complex by distraction posteriorly, and group C = corresponding to group B but with rotation. There is an increasing severity from A to C, and within each group, the severity usually increases within the subgroups from .1, .2, .3. All these pathomorphologies are supported by a mechanism of injury, which is responsible for the extent of the injury. The type of injury with its groups and subgroups is able to suggest the treatment modality.

How fit turns into misfit and back: institutional transformations of pastoral commons in African floodplains

We enlarge the notion of institutional fit using theoretical approaches from New Institutionalism, including rational choice and strategic action, political ecology and constructivist approaches. These approaches are combined with ecological approaches (system and evolutionary ecology) focusing on feedback loops and change. We offer results drawn from a comparison of fit and misfit cases of institutional change in pastoral commons in four African floodplain contexts (Zambia, Cameroon, Tanzania (two cases). Cases of precolonial fit and misfit in the postcolonial past, as well as a case of institutional fit in the postcolonial phase, highlight important features, specifically, flexible institutions, leadership, and mutual economic benefit under specific relations of bargaining power of actors. We argue that only by combining otherwise conflicting approaches can we come to understand why institutional fit develops into misfit and back again. Key Words: African floodplains; governance; institutional change; institutional fit; New Institutionalism; pastoral commons

Understanding heterogeneity in post-implementation enterprise system usage: towards a fit/misfit-experience-outcome typology

The overarching objective of this dissertation is to uncover why and how individually experienced fits and misfits translate into different outcomes of user behavior and satisfaction and whether these individual fit/misfit outcomes are in line with organizational intent. In search of patterns and possible archetype users in the context of ES PIPs, this dissertation is the first study that specifically links the theoretical concepts of the aggregated individual fit experiences with the individual and organizational outcome of these experiences (i.e. behavioral reaction, user satisfaction, and alignment with organizational intent). The case study’s findings provide preliminary support for four archetype users characterized by specific fit/misfit experience-outcome patterns.

Assessment of interatomic potentials for atomistic analysis of static and dynamic properties of screw dislocations in W

Screw dislocations in bcc metals display non-planar cores at zero temperature which result in high lattice friction and thermally-activated strain rate behavior. In bcc W, electronic structure molecular statics calculations reveal a compact, non-degenerate core with an associated Peierls stress between 1.7 and 2.8 GPa. However, a full picture of the dynamic behavior of dislocations can only be gained by using more efficient atomistic simulations based on semiempirical interatomic potentials. In this paper we assess the suitability of five different potentials in terms of static properties relevant to screw dislocations in pure W. Moreover, we perform molecular dynamics simulations of stress-assisted glide using all five potentials to study the dynamic behavior of screw dislocations under shear stress. Dislocations are seen to display thermally-activated motion in most of the applied stress range, with a gradual transition to a viscous damping regime at high stresses. We find that one potential predicts a core transformation from compact to dissociated at finite temperature that affects the energetics of kink-pair production and impacts the mechanism of motion. We conclude that a modified embedded-atom potential achieves the best compromise in terms of static and dynamic screw dislocation properties, although at an expense of about ten-fold compared to central potentials.

A practical treatise on fractures and dislocations /

Spine title: Fractures and dislocations.

The medical companion, or family physician; treating of the diseases of the United States, with their symptoms, causes, cure and means of prevention: common cases in surgery, as fractures, dislocations, &c. the management and diseases of women and children. A dispensatory, for preparing family medicine, and a glossary explaining technical terms. To which are added, a brief anatomy and physiology of the human body, shewing, on rational principles, the cause and cure of diseases: an essay on hygiene, or the art of preserving health, without the aid of medicine: an American materia medica, pointing out the virtues and doses of our medicinal plants. Also, the nurse's guide,

Mode of access: Internet.

Les dislocations de l'écorce terrestre. Die dislocationen der erdrinde. Essai de définition et de nomenclature. Versuch einer definition und bezeichnung. Texte en français et en allemand, synonymie en français, allemand et anglais ...

Text in French and German in parallel columns.

A practical treatise on fractures and dislocations /

Includes bibliographical references and index.

Determination of a misfit dislocation complex in SiGe/Si heterostructures by image deconvolution technique in HREM

The core structure of a dislocation complex in SiGe/Si system composed of a perfect 60degrees dislocation and an extended 60 dislocation has been revealed at atomic level. This is attained by applying the image deconvolution technique in combination with dynamical diffraction effect correction to an image taken with a 200 kV field-emission high-resolution electron microscope. The possible configuration of the dislocation complex is analyzed and their Burgers vectors are determined. (C) 2003 Elsevier B.V. All rights reserved.

Comparing Postcolonial Literatures: Dislocations. (review)

Review of book edited by Ashok Berry and Patricia Murray. Copyright 2002 MHRA, and included in the repository with permission.