Anomalous dephasing of bosonic excitons interacting with phonons in the vicinity of the Bose-Einstein condensation

The dephasing and relaxation kinetics of bosonic excitons interacting with a thermal bath of acoustic phonons is studied after coherent pulse excitation. The kinetics of the induced excitonic polarization is calculated within Markovian equations both for subcritical and supercritical excitation with respect to a Bose-Einstein condensation (BEC). For excited densities n below the critical density n_c, an exponential polarization decay is obtained, which is characterized by a dephasing rate G=1/T_2. This dephasing rate due to phonon scattering shows a pronounced exciton-density dependence in the vicinity of the phase transition. It is well described by the power law G (n-n_c)^2 that can be understood by linearization of the equations around the equilibrium solution. Above the critical density we get a non-exponential relaxation to the final condensate value p^0 with |p(t)|-|p^0| ~1/t that holds for all densities. Furthermore we include the full self-consistent Hartree-Fock-Bogoliubov (HFB) terms due to the exciton-exciton interaction and the kinetics of the anomalous functions F_k= . The collision terms are analyzed and an approximation is used which is consistent with the existence of BEC. The inclusion of the coherent x-x interaction does not change the dephasing laws. The anomalous function F_k exhibits a clear threshold behaviour at the critical density.Comment: European Physical Journal B (in print

Destination image in travel magazines: A textual and pictorial analysis of Hong Kong and Macau

Based on the analyses of texts and pictures in the top six outbound travel magazines in Mainland China, this article presents an evaluation of the destination images of Hong Kong and Macau as portrayed in 88 travel articles over a three-year period. The results showed that the projected destination images of Hong Kong and Macau were dominated by attributes related to culture, history, and art and leisure and recreation. Hong Kong was often described by image attributes such as places and attractions, shopping, cuisine and food, hotels, and the creative industries. For Macau, history and heritage, places and attractions, gambling, cuisine and food, and hotels were the most often reported. During the study period, Hong Kong and Macau witnessed several significant changes in the image attributes featured in both texts and pictures. These changes were partly influenced by news and events over the period. In this article, implications for destination marketing organizations and directions for future research were suggested

Polarons in semiconductor quantum-dots and their role in the quantum kinetics of carrier relaxation

While time-dependent perturbation theory shows inefficient carrier-phonon scattering in semiconductor quantum dots, we demonstrate that a quantum kinetic description of carrier-phonon interaction predicts fast carrier capture and relaxation. The considered processes do not fulfill energy conservation in terms of free-carrier energies because polar coupling of localized quantum-dot states strongly modifies this picture.Comment: 6 pages, 6 figures, accepted for publication in Phys.Rev.

Applications of thermal energy storage in the cement industry

In the manufacture of cement, literally trillions of Btu's are rejected to the environment each year. The purpose of this feasibility study program was to determine whether thermal energy storage could be used to conserve or allow alternative uses of this rejected energy. This study identifies and quantifies the sources of rejected energy in the cement manufacturing process, established use of this energy, investigates various storage system concepts, and selects energy conservation systems for further study. Thermal performance and economic analyses are performed on candidate storage systems for four typical cement plants representing various methods of manufacturing cement. Through the use of thermal energy storage in conjunction with waste heat electric power generation units, an estimated 2.4 x 10 to the 13th power Btu/year, or an equivalent on investment of the proposed systems are an incentive for further development

Optical properties of self-organized wurtzite InN/GaN quantum dots: A combined atomistic tight-binding and full configuration interaction calculation

In this work we investigate the electronic and optical properties of self-assembled InN/GaN quantum dots. The one-particle states of the low-dimensional heterostructures are provided by a tight-binding model that fully includes the wurtzite crystal structure on an atomistic level. Optical dipole and Coulomb matrix elements are calculated from these one-particle wave functions and serve as an input for full configuration interaction calculations. We present multi-exciton emission spectra and discuss in detail how Coulomb correlations and oscillator strengths are changed by the piezoelectric fields present in the structure. Vanishing exciton and biexciton ground state emission for small lens-shaped dots is predicted.Comment: 3 pages, 2 figure

RE: Does Snus use have a harm reduction effect in Sweden?

Eletter to Tobacco Control in response to an eletter published in the same journal about whether snus (Swedish moist oral snuff) was responsible for a decline in smoking prevalence among men in Sweden

The two-level atom laser: analytical results and the laser transition

The problem of the two-level atom laser is studied analytically. The steady-state solution is expressed as a continued fraction, and allows for accurate approximation by rational functions. Moreover, we show that the abrupt change observed in the pump dependence of the steady-state population is directly connected with the transition to the lasing regime. The condition for a sharp transition to Poissonian statistics is expressed as a scaling limit of vanishing cavity loss and light-matter coupling, $\kappa \to 0$, $g \to 0$, such that $g^2/\kappa$ stays finite and $g^2/\kappa > 2 \gamma$, where $\gamma$ is the rate of atomic losses. The same scaling procedure is also shown to describe a similar change to Poisson distribution in the Scully-Lamb laser model too, suggesting that the low-$\kappa$, low-$g$ asymptotics is of a more general significance for the laser transition.Comment: 23 pages, 3 figures. Extended discussion of the paper aim (in the Introduction) and of the results (Conclusions and Discussion). Results unchange