4,819 research outputs found
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
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Probing Bose-Einstein Condensation of Excitons with Electromagnetic Radiation
We examine the absorption spectrum of electromagnetic radiation from
excitons, where an exciton in the state absorbs a photon and makes a
transition to the 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 CuO.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
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