Effect of the Spatial Dispersion on the Shape of a Light Pulse in a Quantum Well

Reflectance, transmittance and absorbance of a symmetric light pulse, the carrying frequency of which is close to the frequency of interband transitions in a quantum well, are calculated. Energy levels of the quantum well are assumed discrete, and two closely located excited levels are taken into account. A wide quantum well (the width of which is comparable to the length of the light wave, corresponding to the pulse carrying frequency) is considered, and the dependance of the interband matrix element of the momentum operator on the light wave vector is taken into account. Refractive indices of barriers and quantum well are assumed equal each other. The problem is solved for an arbitrary ratio of radiative and nonradiative lifetimes of electronic excitations. It is shown that the spatial dispersion essentially affects the shapes of reflected and transmitted pulses. The largest changes occur when the radiative broadening is close to the difference of frequencies of interband transitions taken into account.Comment: 7 pages, 5 figure

Elastic Light Scattering by Semiconductor Quantum Dots

Elastic light scattering by low-dimensional semiconductor objects is investigated theoretically. The differential cross section of resonant light scattering on excitons in quantum dots is calculated. The polarization and angular distribution of scattered light do not depend on the quantum-dot form, sizes and potential configuration if light wave lengths exceed considerably the quantum-dot size. In this case the magnitude of the total light scattering cross section does not depend on quantum-dot sizes. The resonant total light scattering cross section is about a square of light wave length if the exciton radiative broadening exceeds the nonradiative broadening. Radiative broadenings are calculated

Cosmology with running parameters

The experimental evidence that the equation of state (EOS) of the dark energy (DE) could be evolving with time/redshift (including the possibility that it might behave phantom-like near our time) suggests that there might be dynamical DE fields that could explain this behavior. We propose, instead, that a variable cosmological term (including perhaps a variable Newton's gravitational coupling too) may account in a natural way for all these features.Comment: Talk given at TAUP 2005, Zaragoza, Spain, 10-14 Sep 200

Transmission of a Symmetric Light Pulse through a Wide QW

The reflection, transmission and absorption of a symmetric electromagnetic pulse, which carrying frequency is close to the frequency of an interband transition in a QW (QW), are obtained. The energy levels of a QW are assumed discrete, one exited level is taken into account. The case of a wide QW is considered when a length of the pulse wave, appropriate to the carrying frequency, is comparable to the QW's width. In figures the time dependencies of the dimensionless reflection, absorption are transmission are represented. It is shown, that the spatial dispersion and a distinction in refraction indexes influence stronger reflection.Comment: 8 pages,8 figures with caption

Exposing the dressed quark's mass

This snapshot of recent progress in hadron physics made in connection with QCD's Dyson-Schwinger equations includes: a perspective on confinement and dynamical chiral symmetry breaking (DCSB); a pre'cis on the physics of in-hadron condensates; results on the hadron spectrum, including dressed-quark-core masses for the nucleon and Delta, their first radial excitations, and the parity-partners of these states; an illustration of the impact of DCSB on the electromagnetic pion form factor, thereby exemplifying how data can be used to chart the momentum-dependence of the dressed-quark mass function; and a prediction that F_1^{p,d}/F_1^{p,u} passes through zero at Q^2\approx 5m_N^2 owing to the presence of nonpointlike scalar and axial-vector diquark correlations in the nucleon.Comment: 10 pages, 4 figures, 2 tables. Contribution to the Proceedings of the 4th Workshop on Exclusive Reactions at High Momentum Transfer, Thomas Jefferson National Accelerator Facility Newport News, Virginia, 18-21 May 201

On Site

Contemporary debates on the transformation of building methods, the structure of the building industry, and the introduction of new technologies (informational, material and structural) in professional literature and in the architectural humanities tend to ignore the realities of work on construction sites. This follows a long history of failure to recognise the importance of workers’ experience and knowledge of building as a process by the key professions in the industry. The absence of the working process in accounts of historical development is exacerbated by abstract reflection on building know-how, categories of expertise, and the structure of the industry, when these are not supported by direct observation and engagement with building work and workers. Key assumptions about the relation between structural and technological changes in the industry and the knowledge, skills, composition, and requirements of the workforce can be challenged by paying attention to day-to-day activities and conditions of site work

Sequential inverse problems Bayesian principles and the\ud logistic map example

Bayesian statistics provides a general framework for solving inverse problems, but is not without interpretation and implementation problems. This paper discusses difficulties arising from the fact that forward models are always in error to some extent. Using a simple example based on the one-dimensional logistic map, we argue that, when implementation problems are minimal, the Bayesian framework is quite adequate. In this paper the Bayesian Filter is shown to be able to recover excellent state estimates in the perfect model scenario (PMS) and to distinguish the PMS from the imperfect model scenario (IMS). Through a quantitative comparison of the way in which the observations are assimilated in both the PMS and the IMS scenarios, we suggest that one can, sometimes, measure the degree of imperfection

Dynamical breaking of gauge symmetry in supersymmetric quantum electrodynamics in three-dimensional spacetime

The dynamical breaking of gauge symmetry in the supersymmetric quantum electrodynamics in three-dimensional spacetime is studied at two-loop approximation. At this level, the effective superpotential is evaluated in a supersymmetric phase. At one-loop order, we observe a generation of the Chern-Simons term due to a parity violating term present in the classical action. At two-loop order, the scalar background superfield acquires a nonvanishing vacuum expectation value, generating a mass term $A^{\alpha}A_{\alpha}$ through Coleman-Weinberg mechanism. It is observed that the mass of gauge superfield is predominantly an effect of the topological Chern-Simons term.Comment: 10 pages, 2 figures, PRD versio