Exciton-phonon scattering and photo-excitation dynamics in J-aggregate microcavities

We have developed a model accounting for the photo-excitation dynamics and the photoluminescence of strongly coupled J-aggregate microcavities. Our model is based on a description of the J-aggregate film as a disordered Frenkel exciton system in which relaxation occurs due to the presence of a thermal bath of molecular vibrations. In a strongly coupled microcavity exciton-polaritons are formed, mixing superradiant excitons and cavity photons. The calculation of the microcavity steady-state photoluminescence, following a CW non resonant pumping, is carried out. The experimental photoluminescence intensity ratio between upper and lower polariton branches is accurately reproduced. In particular both thermal activation of the photoluminescence intensity ratio and its Rabi splitting dependence are a consequence of the bottleneck in the relaxation, occurring at the bottom of the excitonic reservoir. The effects due to radiative channels of decay of excitons and to the presence of a paritticular set of discrete optical molecular vibrations active in relaxation processes are investigared.Comment: 8 pages, 6 figure

Organic-inorganic heterostructures for nonlinear optics

We consider a hybrid heterostructure made of an inorganic quantum well in close proximity with an organic material overlayer, whereby the latter is used to funnel excitation energy to the former in order to exploit the optical nonlinearities of the two-dimensional Wannier excitons. The resonant optical pumping of the Frenkel excitons and their diffusion to the organic-inorganic interface can lead to an efficient indirect pumping of the inorganic quantum well turning on the corresponding nonlinearities. As organic material we consider a layer of anthracene or of tetracene. In the latter case, the singlet exciton has an energy which is close to twice the one of a triplet exciton and singlet exciton fission into two triplets can be efficient. In tetracene based hybrid heterostructures, the temperature dependence of fission opens the possibility to turn on and off the indirect pumping due to energy transfer from the organic into the inorganic subsystem. Finally, we show how a generic mechanism of dipole-dipole hybridization may lead to the formation of virtual heterodimers of organic molecules with an enhanced nonlinear optical response. Elsevier B.V. All rights reserved

On-site Experimental Study of HCFC-22 Substitution with HFCs Refrigerants

Abstract The European Regulation no 2037/2000 has banned manufacturing HCFC refrigerants from January 1st 2010, although its use is allowed up to 2015 if the fluids come from a recycling process. This situation creates the need for developing new working fluids to replace the HCFC in the refrigeration plants now in operation. Among all the HCFCs the R22 is the most widely used in a wide range of applications, especially in air conditioning. This paper presents the results of an experimental analysis comparing the performance of a vapour compression refrigerating unit operating with R22, and its performance in comparison to some HFCs fluids, substituting the former. In particular, the plant working efficiency was first tested with R22 and then with three HFC fluids: R417A, R407C and R404A. The investigation verified that the performance with HFCs refrigerants did not result as efficient as when using R2

Parity-time-antisymmetric atomic lattices without gain

Lossy atomic photonic crystals can be suitably tailored so that the real and imaginary parts of the susceptibility are, respectively, an odd and an even function of position. Such a parity-time (PT) space antisymmetry in the susceptibility requires neither optical gain nor negative refraction, but is rather attained by a combined control of the spatial modulation of both the atomic density and their dynamic level shift. These passive photonic crystals made of dressed atoms are characterized by a tunable unidirectional reflectionlessness accompanied by an appreciable degree of transmission. Interestingly, such peculiar properties are associated with non-Hermitian degeneracies of the crystal scattering matrix, which can then be directly observed through reflectivity measurements via a straightforward phase modulation of the atomic dynamic level shift and even off resonance

Neuromodulation of Vegetative State through Spinal Cord Stimulation: Where Are We Now and Where Are We Going?

Background: Vegetative state (VS) is a complex condition that represents a challenging frontier for medicine and neuroscience research. Nowadays there is no scientifically validated treatment for VS patients, and their chronic long-term assistance is very demanding for healthcare systems worldwide. Objectives: The present paper is a systematic review of the role of spinal cord stimulation (SCS) as a treatment of patients with VS. Methods: Published literature on this topic was analyzed systematically. Clinical and epidemiological characteristics of VS, present therapeutic options and social costs of VS were also evaluated. Results: Only 10 papers have been published since 1988, and overall 308 VS patients have been treated with SCS worldwide; 51.6% displayed a clinical improvement and an amelioration of the environmental interaction. These effects are probably mediated by the stimulation of the reticular formation-thalamus-cortex pathway and by cerebral blood flow augmentation induced by SCS. Conclusions: The experience on this topic is still very limited, and on this basis it is still hard to make any rigorous assessment. However, the most recent experiments represent significant progress in the research on this topic and display SCS as a possible therapeutic tool in the treatment of VS

Spin-dependent resonant tunneling in semiconductor nanostructures

The spin-dependent quantum transport of electrons in non magnetic III-V semiconductor nanos-tructures is studied theoretically within the envelope function approximation and the Kane model for the bulk. It is shown that an unpolarized beam of conducting electrons can be strongly polarized in zero magnetic field by resonant tunneling across asymmetric double-barrier structures, as an effect of the spin-orbit interaction. The electron transmission probability is calculated as a function of energy and angle of incidence. Specific results for tunneling across lattice matched politype Ga0.47In0.53As / InP/Ga0.47In0.53As / GaAs0.5Sb0.5 / Ga0.47In0.53 As double barrier heterostructures show sharp spin split resonances, corresponding to resonant tunneling through spin-orbit split quasi-bound electron states. The polarization of the transmitted beam is also calculated and is shown to be over 50%

The role of CD133 in the identification and characterisation of tumour-initiating cells in non-small-cell lung cancer☆☆☆

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Effective g-factor tensor for carriers in IV-VI semiconductor quantum wells

A theory for the electron (and hole) g factor in multivalley lead-salt IV-VI semiconductor quantum wells (QWs) is presented. An effective Hamiltonian for theQWelectronic states in the presence of an external magnetic field is introduced within the envelope-function approximation, based on the multiband kp Dimmock model for the bulk. The mesoscopic spin-orbit (Rashba-type) and Zeeman interactions are taken into account on an equal footing and the effective g factor in symmetric quantum wells (g*(QW)) is calculated analytically for each nonequivalent conduction-band (and valence-band) valley, and for QWs grown along different crystallographic directions

Strumenti di analisi per esplorare reti di collaborazione scientifica

The study of the scientific collaboration networks is one of the traditional areas of interest in Network Analysis framework. The aim of the paper is to explore co-authorship networks, where researchers are connected according to the number of papers published together, in order to assess the attitude to collaborate and to identify peculiar styles of collaboration. Starting from the data base of the published papers in the period 1998-2006 produced by the members of the Department of Economics and Statistics at the University of Salerno, collaboration networks are described both by means of network measures (density, actors centrality and presence of cohesive groups) and exploratory multidimensional techniques

Un approccio GIS-BIM per il governo delle trasformazioni urbane. Il caso del comune di Aversa

Lo studio ha l’obiettivo di definire e sperimentare un metodo semiautomatizzato basato sull’integrazione GIS-BIM che rappresenti uno strumento di supporto per le pubbliche amministrazioni nel processo di rilascio dei titoli abilitativi per interventi sul patrimonio edilizio. Se l’apporto innovativo dello studio è il tentativo di integrare ambienti di conoscenza; il limite è la necessità di una forte interazione tra la lungimiranza della ricerca scientifica e la lentezza dell’apparato burocratic