Optical Properties of Collective Excitations for Finite Chains of Trapped Atoms

Resonant dipole-dipole interaction modifies the energy and decay rate of electronic excitations for finite one dimensional chains of ultracold atoms in an optical lattice. We show that collective excited states of the atomic chain can be divided into dark and bright modes, where a superradiant mode with an enhanced collective effective dipole dominates the optical scattering. Studying the generic case of two chain segments of different length and position exhibits an interaction blockade and spatially structured light emission. Ultimately, an extended system of several interfering segments models a long chain with randomly distributed defects of vacant sites. The corresponding emission pattern provides a sensitive tool to study structural and dynamical properties of the system.Comment: 8 pages, 12 figure

Collective Light Emission of a Finite Size Atomic Chain

Radiative properties of collective electronic states in a one dimensional atomic chain are investigated. Radiative corrections are included with emphasize put on the effect of the chain size through the dependence on both the number of atoms and the lattice constant. The damping rates of collective states are calculated in considering radiative effects for different values of the lattice constant relative to the atomic transition wave length. Especially the symmetric state damping rate as a function of the number of the atoms is derived. The emission pattern off a finite linear chain is also presented. The results can be adopted for any chain of active material, e.g., a chain of semiconductor quantum dots or organic molecules on a linear matrix.Comment: 10 pages, 20 figure

Hybrid Quantum System of a Nanofiber Mode Coupled to Two Chains of Optically Trapped Atoms

A tapered optical nanofiber simultaneously used to trap and optically interface of cold atoms through evanescent fields constitutes a new and well controllable hybrid quantum system. The atoms are trapped in two parallel 1D optical lattices generated by suitable far blue and red detuned evanescent field modes very close to opposite sides of the nanofiber surface. Collective electronic excitations (excitons) of each of the optical lattices are resonantly coupled to the second lattice forming symmetric and antisymmetric common excitons. In contrast to the inverse cube dependence of the individual atomic dipole-dipole interaction, we analytically find an exponentially decaying coupling strength with distance between the lattices. The resulting symmetric (bright) excitons strongly interact with the resonant nanofiber photons to form fiber polaritons, which can be observed through linear optical spectra. For large enough wave vectors the polariton decay rate to free space is strongly reduced, which should render this system ideal for the realization of long range quantum communication between atomic ensembles.Comment: 9 pages, 9 figure

Collective Electronic Excitation Coupling between Planar Optical Lattices using Ewald's Method

Using Ewald's summation method we investigate collective electronic excitations (excitons) of ultracold atoms in parallel planar optical lattices including long range interactions. The exciton dispersion relation can then be suitably rewritten and efficiently calculated for long range resonance dipole-dipole interactions. Such in-plane excitons resonantly couple for two identical optical lattices, with an energy transfer strength decreasing exponentially with the distance between the lattices. This allows a restriction of the transfer to neighboring planes and gives rise to excitons delocalized between the lattices. In general equivalent results will hold for any planar system containing lattice layers of optically active and dipolar materials.Comment: 6 pages, and 7 figure

Exciton-Polariton scattering for defect detection in cold atom Optical Lattices

We study the effect of defects in the Mott insulator phase of ultracold atoms in an optical lattice on the dynamics of resonant excitations. Defects, which can either be empty sites in a Mott insulator state with one atom per site or a singly occupied site for a filling factor two, change the dynamics of Frenkel excitons and cavity polaritons. While the vacancies in first case behave like hard sphere scatters for excitons, singly occupied sites in the latter case can lead to attractive or repulsive scattering potentials. We suggest cavity polaritons as observation tool of such defects, and show how the scattering can be controlled in changing the exciton-photon detuning. In the case of asymmetric optical lattice sites we present how the scattering effective potential can be detuned by the cavity photon polarization direction, with the possibility of a crossover from a repulsive into an attractive potential.Comment: 9 pages, 10 figure

Bright and dark excitons in an atom--pair filled optical lattice within a cavity

We study electronic excitations of a degenerate gas of atoms trapped in pairs in an optical lattice. Local dipole-dipole interactions produce a long lived antisymmetric and a short lived symmetric superposition of individual atomic excitations as the lowest internal on-site excitations. Due to the much larger dipole moment the symmetric states couple efficiently to neighbouring lattice sites and can be well represented by Frenkel excitons, while the antisymmetric dark states stay localized. Within a cavity only symmetric states couple to cavity photons inducing long range interactions to form polaritons. We calculate their dispersion curves as well as cavity transmission and reflection spectra to observe them. For a lattice with aspherical sites bright and dark states get mixed and their relative excitation energies depend on photon polarizations. The system should allow to study new types of solid state phenomena in atom filled optical lattices

THE PROCESSES OF MANAGEMENT ACCOUNTING CHANGE IN LIBYAN PRIVATISED COMPANIES: AN INSTITUTIONAL PERSPECTIVE

Abstract: This study explains the management accounting process in two privatised Libyan manufacturing companies. In addition, it investigates the perception of managers regarding the emergence of new management accounting systems and/or practices. Moreover, it explores the effect of institutional factors on management accounting systems. The research is based on a case study of two privatised Libyan companies. It uses triangulation of data collection methods and multiple sources of evidence, including interviews, observation and documentation. Using an institutional framework from new institutional sociology (NIS), old institutional economics (OIE) and power mobilisation are used to help clarify the processes of change in Libyan companies. The hybrid-institutional framework utilised in this study has aided in explaining, interpreting and understanding effects which have occurred within the organisations, which involve rules and routines and/or external-organisation, including terms of coercive, mimetic and normative isomorphism. The position as mentioned above cannot be described in terms of quantitative approaches. So the main reason behind the selection of a qualitative approach for this was that the important aim of the qualitative approach is to provide an in-depth understanding of particular phenomena, such as management accounting change. Also, the case study strategy has been chosen from among qualitative strategies; this was appropriate as the researcher wished to provide a fuller understanding of the topics of the research. Triangulation data collection methods have been drawn on. The case studies were carried out during two stages of data collection in 2008-2009. The researcher relied on multiple sources of evidence, including interviews, observations and documents and archival records. Semi-structured interviews were adopted. In this context, the researcher had a list of themes and questions, as well as responses of interviewees which were recorded. Participant observation was converged as it is related to qualitative approach and case study strategy as well. The results of the case studies showed that the objectives of the companies have changed completely from social to economic. The study found that there were institutional factors which affected management accounting systems and practice before, during and after the privatisation process. Also, the case studies affirmed that the changes were incremental or evolutionary. Furthermore, the findings showed that there is no current revolutionary change within the management accounting systems and practices in the companies under the study. It was also found that there was resistance to change when the company attempted to introduce an Information Technology (IT) system

Effects of sewage sludge on heavy metal accumulation in soil and plants and on crop productivity in Aleppo governorate

Sewage sludgeHeavy metalsCrop productionCropsOrganic matterSoil

Solar PV power forecasting at Yarmouk University using machine learning techniques

Renewable energy sources are considered ubiquitous and drive the energy revolution. Energy producers suffer from inconsistent electricity generation. They often struggled with the unpredictability of the weather. Thus, making it challenging to balance supply and demand. Technologies like artificial intelligence (AI) and machine learning are effective ways to forecast, distribute, andmanage renewable photovoltaic (PV) solar supplies. AI will make the energy forecasting system more connected, intelligent, reliable, and sustainable. AI can innovate how energy is used and help find solutions for decarbonizing energy systems. There are potential advantages to total energy forecasting. AI can support the growth and integration of PV solar energy. The article’s main objective is to use AI to forecast the output consumed power of the Yarmouk University PV solar system in Jordan. The total actual yield is 5548.96 MW h, and the performance ratio (PR) is 95.73%. Many techniques are used to predict the consumed solar power. The random forest model obtains the best results of root mean squared error and mean absolute error are 172.07 and 68.7, respectively. This accurate prediction allows for the maximum use of solar power and the minimal use of grid power. This work guides the operators to learn trends embedded in Yarmouk University’s historical data. These understood trends can be used to predict the consumption of solar power output. Thus, the control system and grid operators have advanced knowledge of the expected consumption of solar power at each hour of the day