First principles calculation of electron-phonon and alloy scattering in strained SiGe

First-principles electronic structure methods are used to predict the mobility of n-type carrier scattering in strained SiGe. We consider the effects of strain on the electron-phonon deformation potentials and the alloy scattering parameters. We calculate the electron-phonon matrix elements and fit them up to second order in strain. We find, as expected, that the main effect of strain on mobility comes from the breaking of the degeneracy of the six Δ and L valleys, and the choice of transport direction. The non-linear effects on the electron-phonon coupling of the Δ valley due to shear strain are found to reduce the mobility of Si-like SiGe by 50% per % strain. We find increases in mobility between 2 and 11 times that of unstrained SiGe for certain fixed Ge compositions, which should enhance the thermoelectric figure of merit in the same order, and could be important for piezoresistive applications.

First-principles calculation of carrier-phonon scattering in n-type Si1−xGex alloys

First-principles electronic structure methods are used to find the rates of inelastic intravalley and intervalley n-type carrier scattering in Si1-xGex alloys. Scattering parameters for all relevant Delta and L intra- and intervalley scattering are calculated. The short-wavelength acoustic and the optical phonon modes in the alloy are computed using the random mass approximation, with interatomic forces calculated in the virtual crystal approximation using density functional perturbation theory. Optical phonon and intervalley scattering matrix elements are calculated from these modes of the disordered alloy. It is found that alloy disorder has only a small effect on the overall inelastic intervalley scattering rate at room temperature. Intravalley acoustic scattering rates are calculated within the deformation potential approximation. The acoustic deformation potentials are found directly and the range of validity of the deformation potential approximation verified in long-wavelength frozen phonon calculations. Details of the calculation of elastic alloy scattering rates presented in an earlier paper are also given. Elastic alloy disorder scattering is found to dominate over inelastic scattering, except for almost pure silicon (x approximate to 0) or almost pure germanium (x approximate to 1), where acoustic phonon scattering is predominant. The n-type carrier mobility, calculated from the total (elastic plus inelastic) scattering rate, using the Boltzmann transport equation in the relaxation time approximation, is in excellent agreement with experiments on bulk, unstrained alloys..

First-principles calculation of P-type alloy scattering in Si1-xGex

The p-type carrier scattering rate due to alloy disorder in Si1-xGex alloys is obtained from first principles. The required alloy scattering matrix elements are calculated from the energy splitting of the valence bands, which arise when one average host atom is replaced by a Ge or Si atom in supercells containing up to 128 atoms. Alloy scattering within the valence bands is found to be characterized by a single scattering parameter. The hole mobility is calculated from the scattering rate using the Boltzmann transport equation in the relaxation time approximation. The results are in good agreement with experiments on bulk, unstrained alloys..

First-principles calculation of alloy scattering in GexSi1-x

First-principles electronic structure methods are used to find the rates of intravalley and intervalley n-type carrier scattering due to alloy disorder in Si1-xGex alloys. The required alloy scattering matrix elements are calculated from the energy splitting of nearly degenerate Bloch states which arises when one average host atom is replaced by a Ge or Si atom in supercells containing up to 128 atoms. Scattering parameters for all relevant Delta and L intravalley and intervalley alloy scattering are calculated. Atomic relaxation is found to have a substantial effect on the scattering parameters. f-type intervalley scattering between Delta valleys is found to be comparable to other scattering channels. The n-type carrier mobility, calculated from the scattering rate using the Boltzmann transport equation in the relaxation time approximation, is in excellent agreement with experiments on bulk, unstrained alloys.

Reframing Chinese animation: from classicism to postmodernism in post-1949 non-commercial Chinese animated films

This thesis focuses on Chinese non-commercial animated films produced from 1949 to date, with the aim of remapping and reframing Chinese animation in the light of existing theories, critiques, and frameworks drawn from studies in animation, film, and screen media. I suggest that Chinese animation has experienced three aesthetic transformations since 1949, primarily influenced by traditional Chinese culture, by Western modernist art and literature and, most recently, by postmodernism, respectively. Thus, the research traces and thoroughly investigates these three distinctive phases of Chinese animation in chronological order, from the classical period (1950s– 1980s) to modernism (1980s–2000s) and postmodernism (after 2000s). More in detail, I first rethink and re-evaluate the success of classical Chinese animation and the Chinese school of animation and, at the same time, I explore the influence of the political situation of the time on Chinese animation. Through careful analysis of A Da (1934–87) and other Chinese animators’ practices and theory, then, I argue that a remarkable modernist transformation took place in Chinese animation between the 1980s and 2000s, mainly driven by Western modernism and the Chinese “cultural fever” movement. Finally, through a discussion of the latest non-commercial animations produced after 2005, and especially those of Bu Hua (1973– ), for the first time I classify and theorize contemporary Chinese animations within a postmodern framework. By reframing existing views and broadening the scope of the analysis to encompass new areas and frameworks, this thesis aims to provide the reader with a comprehensive and systematic understanding of post-1949 Chinese animation and to offer an original contribute to scholarship, also working as a starting point for further research in this area.

Resigning: a classic grounded theory of working within constraints when caring for stroke patients in the acute general care setting

This research aims to explore the challenges nurses face, when caring for stroke patients on a general medical/surgical ward, in the acute care setting and identify how nurses resolve or process this challenge. Healthcare environments continue to face the pressures of constraints such as reduced staffing levels, budgets, resources and less time, which influence care provision. Patient safety is central in care provision where nurses face the challenge of delivering best quality care when working within constraints. The incidence of stroke is increasing worldwide and internationally stroke units are the recognised minimum standard of care. In Ireland with few designated stroke units in operation many stroke patients are cared for in the acute general care setting. A classic grounded theory methodology was utilised for this study. Data was collected and analysed simultaneously through coding, constant comparison, theoretical sampling and memoing. Individual unstructured interviews with thirty two nurses were carried out. Twenty hours of non-participant observations in the acute general care setting were undertaken. The main concern that emerged was working within constraints. This concern is processed by nurses through resigning which consists of three phases; idealistic striving, resourcing and care accommodation. Through the process of resigning nurses engage in an energy maintenance process enabling them to continue working within constraints. The generation of the theory of resigning explains how nurses’ resolve or process working within constraints. This theory adds to the body of knowledge on stroke care provision. This theory has the potential to enhance nursing care, minimise burnout and make better use of resources while advocating for best care of stroke patients.