A note on the effective medium theory of random resistive-reactive medium

The effective medium theory for a system with randomly distributed point conductivity and polarisability is reformulated, with attention to cross-terms involving the two disorder parameters. The treatment reveals a certain inconsistency of the conventional theory owing to the neglect of the Maxwell-Wagner effect. The results are significant for the critical resistivity and dielectric anomalies of a binary liquid mixture at the phase separation point.

Effective-mass theory for hierarchical self-assembly of GaAs/AlxGa1-xAs quantum dots

The electronic structures in the hierarchical self-assembly of GaAs/AlxGa1-xAs quantum dots are investigated theoretically in the framework of effective-mass envelope function theory. The electron and hole energy levels and optical transition energies are calculated. In our calculation, the effect of finite offset, valence-band mixing, the effects due to the different effective masses of electrons and holes in different regions, and the real quantum dot structures are all taken into account. The results show that (1) electronic energy levels decrease monotonically, and the energy difference between the energy levels increases as the GaAs quantum dot (QD) height increases; (2) strong state mixing is found between the different energy levels as the GaAs QD width changes; (3) the hole energy levels decrease more quickly than those of the electrons as the GaAs QD size increases; (4) in excited states, the hole energy levels are closer to each other than the electron ones; (5) the first heavy- and light-hole transition energies are very close. Our theoretical results agree well with the available experimental data. Our calculated results are useful for the application of the hierarchical self-assembly of GaAs/AlxGa1-xAs quantum dots to photoelectric devices.

Effective-mass theory for coupled quantum dots grown on (11N)-oriented substrates

The electronic structures of coupled quantum dots grown on (11N)-oriented substrates are studied in the framework of effective-mass envelope-function theory. The results show that the all-hole subbands have the smallest widths and the optical properties are best for the (113), (114), and (115) growth directions. Our theoretical results agree with the available experimental data. Our calculated results are useful for the application of coupled quantum dots in photoelectric devices.

EFFECTIVE-MASS THEORY FOR GAAS/GA1-XALXAS QUANTUM WIRES AND CORRUGATED SUPERLATTICES GROWN ON (311)-ORIENTED SUBSTRATES

The electronic structures of GaAs/Ga1-xAlxAs quantum wires (corrugated superlattices) grown on (311)-oriented substrates are studied in the framework of the effective-mass envelope-function method. The electron and hole subband structure and optical transition matrix elements are calculated. When x=1, the results are compared with experiments, and it is found that the direct transition becomes an indirect transition as the widths of well and barrier become smaller.

EFFECTIVE-MASS THEORY FOR SUPERLATTICES GROWN ON (11N)-ORIENTED SUBSTRATES

An effective-mass formulation for superlattices grown on (11N)-oriented substrates is given. It is found that, for GaAs/AlxGa1-xAs superlattices, the hole subband structure and related properties are sensitive to the orientation because of the large anisotropy of the valence band. The energy-level positions for the heavy hole and the optical transition matrix elements for the light hole apparently change with orientation. The heavy- and light-hole energy levels at k parallel-to = 0 can be calculated separately by taking the classical effective mass in the growth direction. Under a uniaxial stress along the growth direction, the energy levels of the heavy and light holes shift down and up, respectively; at a critical stress, the first heavy- and light-hole energy levels cross over. The energy shifts caused by the uniaxial stress are largest for the (111) case and smallest for the (001) case. The optical transition matrix elements change substantially after the crossover of the first heavy- and light-hole energy has occurred.

Effective-mass theory for InAs/GaAs strained superlattices

By using the recently developed exact effective-mass envelope-function theory, the electronic structures of InAs/GaAs strained superlattices grown on GaAs (100) oriented substrates are studied. The electron and hole subband structures, distribution of electrons and holes along the growth direction, optical transition matrix elements, exciton states, and absorption spectra are calculated. In our calculations, the effects due to the different effective masses of electrons and holes in different materials and the strain are included. Our theoretical results are in agreement with the available experimental data.

Effective-mass theory for InAs/GaAs strained coupled quantum dots

In the framework of effective-mass envelope-function theory, the optical transitions of InAs/GaAs strained coupled quantum dots grown on GaAs (100) oriented substrates are studied. At the Gamma point, the electron and hole energy levels, the distribution of electron and hole wave functions along the growth and parallel directions, the optical transition-matrix elements, the exciton states, and absorption spectra are calculated. In calculations, the effects due to the different effective masses of electrons and holes in different materials are included. Our theoretical results are in good agreement with the available experimental data.

Effects of new nonlinear couplings in relativistic effective field theory

We extend the relativistic mean field theory model of Sugahara and Toki by adding new couplings suggested by modern effective field theories. An improved set of parameters is developed with the goal to test the ability of the models based on effective field theory to describe the properties of finite nuclei and, at the same time, to be consistent with the trends of Dirac-Brueckner-Hartree-Fock calculations at densities away from the saturation region. We compare our calculations with other relativistic nuclear force parameters for various nuclear phenomena.

The inadequacy of Western media theory in third world internal conflicts : the case of military censorship in Sri Lanka

The literature of communication and conflict is long and deep. However, it has focused primarily on cross-border conflict in the northern hemisphere. Not much academic research has been done on intra-state conflicts in general or on Asian conflicts in particular. This research on the Sri Lankan separatist conflict contributes towards filling this void.Newspaper reports in three languages on Operation Jayasikurui (1997) as well as on the capture of Elephant Pass (2000) were analyzed by trained coders with high reliability. In-depth interviews were conducted with Sri Lankan journalists and military personnel who participated in these incidents. Triangulation sources include Sri Lanka Army materials and the Sri Lanka Government Gazette.

Results clearly show that despite stringent governmental regulations, censorship had no effect on these Sri Lankan newspapers, which employed unique cultural techniques to circumvent these restrictions. Despite their apparent divergent ethnic backgrounds, all newspaper samples are consensual in their depiction of the conflict all the time while managing to set different agendas for their individual readerships. Media regulations could not impose censorship as proposed by Western theoretical constructs. Results show no correspondence between media samples and imposition of government or military policy. The press enjoyed freedom to convey war information to the public and exhibited a distinct streak of social responsibility in their watchdog instincts.Dominant Western propaganda models and theoretical perspectives do not apply to the Sri Lankan context. Understanding the cultural dimensions is essential before theorizing on media behaviour. No particular theoretical framework from the literature could be used to make inferences. One further interesting finding suggested from this research: Internal conflict within the Asian region may have its own unique theoretical perspective. The study concludes by proposing an alternative model.

The inadequacy of Western media theory in third world internal conflicts : the case of military censorship in Sri Lanka

Research on media production and on media effects under military censorship has centred primarily on cross-border conflicts being waged by Western regimes. There is a noticeable void in understanding internal conflicts, particularly so within the Asian region. To help address this lacuna, we content-analyse Sri Lankan newspaper samples of two critical military campaigns within the Sri Lankan separatist conflict to gain insight into an Asian internal conflict within the context of military censorship and culture. We discover that supposedly stringent censorship regulations and the rules of the official communication systems have almost no effect on Sri Lankan newspapers, which demonstrate a unique talent to circumvent these strictures. During these bloody internal conflicts, the Sri Lankan press enjoyed freedom of expression, flaunted social responsibility and their watchdog instincts, and, most interestingly for us, demonstrated the failure of the Western propaganda model and other theoretical perspectives. The importance of understanding cultural dimensions before theorizing media behaviour in order to obtain a more rational understanding of the sociology of media is posited by this study. We conclude with discussion of a new model of media censorship which has more relevance in Asian internal conflicts.

Weak-field approximation of effective gravitational theory with local Galilean invariance

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

alpha alpha scattering in halo effective field theory

We study the two-alpha-particle (alpha alpha) system in an Effective Field Theory (EFT) for halo-like systems. We propose a power Counting that incorporates the subtle interplay of strong and electromagnetic forces leading to a narrow resonance at an energy of about 0.1 MeV. We investigate the EFT expansion in detail, and compare its results with existing low-energy aa phase shifts and previously determined effective-range parameters. Good description of the data is obtained with a surprising amount of fine-tuning. This scenario can be viewed as an expansion around the limit where, when electromagnetic interactions are turned off, the (8)Be ground state is at threshold and exhibits conformal invariance. We also discuss possible extensions to systems with more than two alpha particles. (c) 2008 Elsevier B.V. All rights reserved.

Effective field theory methods to model compact binaries

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)