Resonant coupling of bound excitons with LO phonons in ZnO: Excitonic polaron states and Fano interference

We report on a photoluminescence observation of robust excitonic polarons due to resonant coupling of exciton and longitudinal optical (LO) phonon as well as Fano-type interference in high quality ZnO crystal. At low enough temperatures, resonant coupling of excitons and LO phonons leads to not only traditional Stokes lines (SLs) but also up to second-order anti-Stokes lines (ASLs) besides the zero-phonon line (ZPL). The SLs and ASLs are found to be not mirror symmetric with respect to the ZPL, strongly suggesting that they are from different coupling states of exciton and phonons. Besides these spectral features showing the quasiparticle properties of exciton-phonon coupling system, the first-order SL is found to exhibit characteristic Fano lineshape, caused by quantum interference between the LO components of excitonic polarons and the continuous phonon bath. These findings lead to a new insight into fundamental effects of exciton-phonon interactions. © 2005 American Institute of Physics.published_or_final_versio

Determination of effective mass of heavy hole from phonon-assisted excitonic luminescence spectra in ZnO

Longitudinal optical (LO) phonon-assisted luminescence spectra of free excitons in high-quality ZnO crystal were investigated both experimentally and theoretically. By using the rigorous Segall-Mahan model based on the Green's function, good agreement between the experimental emission spectra involving one or two LO phonons and theoretical spectra can be achieved when only one adjustable parameter (effective mass of heavy hole) was adopted. This leads to determination of the heavy-hole effective mass m h⊥ (0.8 m 0 and m h∥ 5.0 m 0) in ZnO. Influence of anisotropic effective masses of heavy holes on the phonon sidebands is also discussed. © 2011 American Institute of Physics.published_or_final_versio

Fano resonance in the luminescence spectra of donor bound excitons in polar semiconductors

An unusual response in the luminescence measurements of GaN thin film and ZnO bulk crystal is observed at low temperatures. The authors demonstrate theoretically that such an unusual response is due to the longitudinal optical phonon mediated Fano resonance involved in the recombination process of the donor bound exciton. The line shapes obtained by the calculation in the present mechanism are in excellent agreement with the experimental results. © 2007 American Institute of Physics.published_or_final_versio

Interpretation of anomalous temperature dependence of anti-Stokes photoluminescence at GaInP2/GaAs interface

The anomalous temperature dependence of anti-Stokes photoluminescence (ASPL) at the GaInP2/GaAs interface was studied. A localized state luminescence model was employed to interpret the temperature-dependence of the peak position of the ASPL. The results show that the localization of the up-converted carriers plays an important role in radiative recombination producing the ASPL. The studies also show that the microscopic mechanism of thermal quenching of ASPL at GaInP2/GaAs interface is unmasked.published_or_final_versio

Two-electron-satellite transition of donor bound exciton in ZnO: Radiative Auger effect

Two-electron-satellite (TES) transition of donor bound exciton (D 0X) is an interesting many-body quantum process. In this letter, precise luminescence spectra and temperature behaviors of the TES transition of aluminum bound exciton in two kinds of zinc oxide single crystals were investigated in detail. It is found that the TES transition can be treated as a radiative Auger process in which the temperature dependence of the emission intensity of the transition can be fitted very well with a model taking into account the temperature dependent Auger term and thermal dissociation of the D0X excitons. © 2013 AIP Publishing LLC.published_or_final_versio

Influence of capping layer and atomic interdiffusion on the strain distribution in single and double self-assembled InAs/GaAs quantum dots

The strain distribution in single and double self-assembled InAsGaAs quantum dots is theoretically investigated by using a valence-force-field model. The results show strong influence of the capping conditions on the strain distribution in individual and stacked dots with wetting layers. In particular, the intermixing of atoms is incorporated into the strain calculations, leading to a conclusion that the atomic intermixing can notably modify the strain profiles near the interfaces of the stacked dot system. © 2008 American Institute of Physics.published_or_final_versio

Service-Oriented Reference Architecture for Smart Cities

The trend towards turning existing cities into smart cities is growing. Facilitated by advances in computing such as Cloud services and Internet of Things (IoT), smart cities propose to bring integrated, autonomous systems together to improve quality of life for their inhabitants. Systems such as autonomous vehicles, smart grids and intelligent traffic management are in the initial stages of development. However, as of yet there, is no holistic architecture on which to integrate these systems into a smart city. Additionally, the existing systems and infrastructure of cities is extensive and critical to their operation. We cannot simply replace these systems with smarter versions, instead the system intelligence must augment the existing systems. In this paper we propose a service oriented reference architecture for smart cities which can tackle these problems and identify some related open research questions. The abstract architecture encapsulates the way in which different aspects of the service oriented approach span through the layers of existing city infrastructure. Additionally, the extensible provision of services by individual systems allows for the organic growth of the smart city as required

Analysis and optimization of inventory variance and bullwhip in a manufacturing/remanufacturing system

This is the author accepted manuscript.Quantitative analysis of closed-loop supply chains is often based on a specified cost function; dynamical performance of the system is rarely considered. This paper adopted a control theory approach to build a simple dynamic model of a hybrid manufacturing/remanufacturing system. It highlights the effect of remanufacturing (and return) lead-time and the return rate on the inventory variance and bull whip produced by the ordering policy. The results show that a larger return rate leads to less bullwhip and less inventory variance. Thus returns can be used to improve dynamic performance by absorbing some of the demand fluctuations. Longer remanufacturing (and return) lead-times have less impact on reducing inventory variance and bullwhip than shorter lead-times. It is concluded that within our specified system the inventory variance and bullwhip is always less in supply chain with returns than that without returns

Massive-Scale Automation in Cyber-Physical Systems: Vision & Challenges

The next era of computing is the evolution of the Internet of Things (IoT) and Smart Cities with development of the Internet of Simulation (IoS). The existing technologies of Cloud, Edge, and Fog computing as well as HPC being applied to the domains of Big Data and deep learning are not adequate to handle the scale and complexity of the systems required to facilitate a fully integrated and automated smart city. This integration of existing systems will create an explosion of data streams at a scale not yet experienced. The additional data can be combined with simulations as services (SIMaaS) to provide a shared model of reality across all integrated systems, things, devices, and individuals within the city. There are also numerous challenges in managing the security and safety of the integrated systems. This paper presents an overview of the existing state-of-the-art in automating, augmenting, and integrating systems across the domains of smart cities, autonomous vehicles, energy efficiency, smart manufacturing in Industry 4.0, and healthcare. Additionally the key challenges relating to Big Data, a model of reality, augmentation of systems, computation, and security are examined

n-Dimensional QoS Framework for Real-Time Service-Oriented Architectures

Service-Orientation has long provided an effective mechanism to integrate heterogeneous systems in a loosely coupled fashion as services. However, with the emergence of Internet of Things (IoT) there is a growing need to facilitate the integration of real-time services executing in non-controlled, non-real-time, environments such as the Cloud. With the need to integrate both cyberphysical systems as hardware-in-the-loop (HIL) components and also with Simulation as a Service (SIMaaS) the execution performance and response-times of the services must be managed. This paper presents a mathematical framework that captures the relationship between the host execution environment and service performance allowing the estimation of Quality of Service (QoS) under dynamic Cloud workloads. A formal mathematical definition is provided and this is evaluated against existing techniques from both the Cloud and Real-Time Service Oriented Architecture (RT-SOA) domains. The proposed approach is evaluated against the existing techniques through simulation and demonstrates a reduction of QoS violation percentage by 22% with respect to response-times as well as reducing the number of Micro-Service (uS) instances with QoS violations by 27%