Breaking out of biogeographical modules: range expansion and taxon cycles in the hyperdiverse ant genus Pheidole

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Ultrafast Hole Trapping and Relaxation Dynamics in p-Type CuS Nanodisks

CuS nanocrystals are potential materials for developing low-cost solar energy conversion devices. Understanding the underlying dynamics of photoinduced carriers in CuS nanocrystals is essential to improve their performance in these devices. In this work, we investigated the photoinduced hole dynamics in CuS nanodisks (NDs) using the combination of transient optical (OTA) and X-ray (XTA) absorption spectroscopy. OTA results show that the broad transient absorption in the visible region is attributed to the photoinduced hot and trapped holes. The hole trapping process occurs on a subpicosecond time scale, followed by carrier recombination (~100 ps). The nature of the hole trapping sites, revealed by XTA, is characteristic of S or organic ligands on the surface of CuS NDs. These results not only suggest the possibility to control the hole dynamics by tuning the surface chemistry of CuS but also represent the first time observation of hole dynamics in semiconductor nanocrystals using XTA

Постать Тараса Шевченка в рецепції Ліни Костенко

У статті розглядається поетика творення Ліною Костенко образу Кобзаря крізь призму власного "я", через пережиті відчуття поета-шістдесятника, що своєю проекцією нагадують душевні терзання великого поета.В статье рассмотрена поэтика создания Линой Костенко образа Тараса Шевченко сквозь призму собственного "я", через пережитые ощущения поэта-шестидесятника, своей проекцией напоминающие душевные терзания великого поэта.The article deals with the problem of the poetics creation by Lina Kostenko Taras Shevchenko’ image through a prism her own mind, through sensations of the poet-sixtier, by the projection reminding sincere torments the great poet is considered

Theory of Pseudomodes in Quantum Optical Processes

This paper deals with non-Markovian behaviour in atomic systems coupled to a structured reservoir of quantum EM field modes, with particular relevance to atoms interacting with the field in high Q cavities or photonic band gap materials. In cases such as the former, we show that the pseudo mode theory for single quantum reservoir excitations can be obtained by applying the Fano diagonalisation method to a system in which the atomic transitions are coupled to a discrete set of (cavity) quasimodes, which in turn are coupled to a continuum set of (external) quasimodes with slowly varying coupling constants and continuum mode density. Each pseudomode can be identified with a discrete quasimode, which gives structure to the actual reservoir of true modes via the expressions for the equivalent atom-true mode coupling constants. The quasimode theory enables cases of multiple excitation of the reservoir to now be treated via Markovian master equations for the atom-discrete quasimode system. Applications of the theory to one, two and many discrete quasimodes are made. For a simple photonic band gap model, where the reservoir structure is associated with the true mode density rather than the coupling constants, the single quantum excitation case appears to be equivalent to a case with two discrete quasimodes

Efficient Auger electron cooling in seemingly unfavourable configurations: hole traps and electrochemical charging

The absence of a phonon bottleneck in the intraband relaxation between p-like and s-like electron states in CdSe nanocrystals is generally ascribed to efficient inelastic scattering with the photogen- erated hole (Auger cooling). However the fast relaxation of electrons observed in the absence of a hole or in the presence of a hole trapped in a surface state have raised serious questions about the suitability of this model. The semiempirical pseudopotential calculations reported here show that electron-electron scattering in chemically reduced or electrochemically charged (i.e., hole-less) CdSe nanocrystals leads to short p electron lifetimes comparable to those calculated in the presence of a photogenerated hole delocalised in the dot core. Furthermore, it is shown that efficient energy transfer can also be achieved between a delocalised electron and a surface-trapped hole leading to short p electron lifetimes in the (sub-) ps range. These results are in quantitative agreement with experiment and consistent with the Auger interpretation of the electron relaxation. The fast sub-ps electron relaxation times calculated in the presence of a hole localised in a shallow surface trap raise the intriguing question of whether in earlier measurements in TOPO-capped nanocrystals the hole was indeed delocalised within the dot core, as it was believed at the time, or whether it could have been in a trap state

Disorder strongly enhances Auger recombination in conductive quantum-dot solids

Auger recombination (AR) can be an important loss mechanism for optoelectronic devices, but it is typically not very efficient at low excitation densities. Here we show that in conductive quantum-dot solids, AR is the dominant charge carrier decay path even at excitation densities as low as 10?3 per quantum dot, and that AR becomes faster as the charge carrier mobility increases. Monte Carlo simulations reveal that this efficient AR results from charge carrier congregation in ‘Auger hot spots’: lower-energy sites that are present because of energy disorder. Disorder-enhanced AR is a general effect that is expected to be active in all disordered materials. The observed efficient AR is an issue of concern for devices that work at charge carrier densities in excess of ~10?3 charge carriers per quantum dot. At the same time, efficient carrier congregation could be exploited for fast optical switching or to achieve optical gain in the near infrared.ChemE/Chemical EngineeringApplied Science