Dynamical Franz-Keldysh effect

We introduce and analyze the properties of dynamical Franz-Keldysh effect, i.e. the change of density-of-states, or absorption spectra, of semiconductors under the influence of {\it time-dependent} electric fields. In the case of a harmonic time-dependence, we predict the occurence of significant fine structure, both below and above the zero-field band-gap, which should be experimentally observable.Comment: 4 pages, REVTEX 3.0, uses epsf, 5 figures attached as Z-compressed .tar fil

Probing Bose-Einstein Condensation of Excitons with Electromagnetic Radiation

We examine the absorption spectrum of electromagnetic radiation from excitons, where an exciton in the $1s$ state absorbs a photon and makes a transition to the $2p$ state. We demonstrate that the absorption spectrum depends strongly on the quantum degeneracy of the exciton gas, and that it will generally manifest many-body effects. Based on our results we propose that absorption of infrared radiation could resolve recent contradictory experimental results on excitons in Cu$_2$O.Comment: 4 pages, RevTex, 8 ps figures, submitted to PR

A class of well-posed parabolic final value problems

This paper focuses on parabolic final value problems, and well-posedness is proved for a large class of these. The clarification is obtained from Hilbert spaces that characterise data that give existence, uniqueness and stability of the solutions. The data space is the graph normed domain of an unbounded operator that maps final states to the corresponding initial states. It induces a new compatibility condition, depending crucially on the fact that analytic semigroups always are invertible in the class of closed operators. Lax--Milgram operators in vector distribution spaces constitute the main framework. The final value heat conduction problem on a smooth open set is also proved to be well posed, and non-zero Dirichlet data are shown to require an extended compatibility condition obtained by adding an improper Bochner integral.Comment: 16 pages. To appear in "Applied and numerical harmonic analysis"; a reference update. Conference contribution, based on arXiv:1707.02136, with some further development

Spin-dynamic field coupling in strongly THz driven semiconductors : local inversion symmetry breaking

We study theoretically the optics in undoped direct gap semiconductors which are strongly driven in the THz regime. We calculate the optical sideband generation due to nonlinear mixing of the THz field and the near infrared probe. Starting with an inversion symmetric microscopic Hamiltonian we include the THz field nonperturbatively using non-equilibrium Green function techniques. We find that a self induced relativistic spin-THz field coupling locally breaks the inversion symmetry, resulting in the formation of odd sidebands which otherwise are absent.Comment: 8 pages, 6 figure

Relationship and Network Approach to Innovation and Capabilities Building in Small and Medium-Sized UK Organic Food and Drink Suppliers: A Literature Review

Both business and consumer markets of food and drink are increasingly changing, concomitant with changing consumer habits and lifestyles. Particularly in industrialised countries, there has been a tremendous growth in consumer interest for organic food in the last fifteen years, largely driven by the need for healthy food. These market changes have implications for the way firms in the food and drink industry conduct their business. Nevertheless, unlike large firms, small suppliers tend to be constrained in terms of innovations and capabilities, for instance to enable them keep pace with market changes. Based on the literature review, this paper develops a framework that suggests that market-driven innovations may be developed and implemented through augmentation of small and medium-sized suppliers’ (SMEs) own capabilities with those of their larger customers. This consequently would enable SMEs to keep pace with market changes and hence sustain their survival