Kinetika neizotermne kristalizacije kalkogenidnog stakla Sb10Ge10Se80

A differential scanning calorimetry technique was used to study the crystallization kinetics of Sb10Ge10Se80 chalcogenide glass under non-isothermal conditions. The crystallization parameters such as the order parameter (n), the frequency factor (k0), the activation energy of crystallization (Ec), the activation energy of glass transition (Eg) and the activation energy of nucleation (En) were determined. The value of Ec was deduced by means of six methods and the average value was found to be equal to (76.10±1.10) kJmol−1 . The most suitable method for crystallization kinetic studies was the Augis–Bennett approximated method at different heating rates, while the method of Coats–Redfern–Sestak was the most suitable one at constant heating rate. The results have been discussed on the basis of theoretical principles.Primijenili smo diferencijalnu pretražnu kalorimetriju za proučavanje kinetike kristalizacije kalkogenidnog stakla Sb10Ge10Se80 u neizotermnim uvjetima. Odredili smo sljedeće parametre kristalizacije: parametar reda (n), faktor frekvencije (k0), aktivacijsku energiju kristalizacije (Ec), aktivacijsku energiju staklenog prijelaza (Eg) i aktivacijsku energiju nukleacije. Ec smo izveli na osnovi šest metoda i našli srednju vrijednost (76.10 ± 1.10) kJmol−1 . Najpogodnija metoda za proučavanje kinetike kristalizacije za različite brzine grijanja je Augis–Bennettova približna metoda, dok se metoda Coats–Redfern–Sestak-a pokazala najbolja za stalnu brzinu grijanja. Postignuti ishodi raspravljaju se na osnovi teorijskih postavki

Kinetika neizotermne kristalizacije kalkogenidnog stakla Sb10Ge10Se80

A differential scanning calorimetry technique was used to study the crystallization kinetics of Sb10Ge10Se80 chalcogenide glass under non-isothermal conditions. The crystallization parameters such as the order parameter (n), the frequency factor (k0), the activation energy of crystallization (Ec), the activation energy of glass transition (Eg) and the activation energy of nucleation (En) were determined. The value of Ec was deduced by means of six methods and the average value was found to be equal to (76.10±1.10) kJmol−1 . The most suitable method for crystallization kinetic studies was the Augis–Bennett approximated method at different heating rates, while the method of Coats–Redfern–Sestak was the most suitable one at constant heating rate. The results have been discussed on the basis of theoretical principles.Primijenili smo diferencijalnu pretražnu kalorimetriju za proučavanje kinetike kristalizacije kalkogenidnog stakla Sb10Ge10Se80 u neizotermnim uvjetima. Odredili smo sljedeće parametre kristalizacije: parametar reda (n), faktor frekvencije (k0), aktivacijsku energiju kristalizacije (Ec), aktivacijsku energiju staklenog prijelaza (Eg) i aktivacijsku energiju nukleacije. Ec smo izveli na osnovi šest metoda i našli srednju vrijednost (76.10 ± 1.10) kJmol−1 . Najpogodnija metoda za proučavanje kinetike kristalizacije za različite brzine grijanja je Augis–Bennettova približna metoda, dok se metoda Coats–Redfern–Sestak-a pokazala najbolja za stalnu brzinu grijanja. Postignuti ishodi raspravljaju se na osnovi teorijskih postavki

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

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

The role of demand uncertainty in materials selection : a case study on aluminum recycling

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2007."June 2007."Includes bibliographical references (leaves 53-54).Aluminum is a versatile material that is used frequently in transportation and packaging, two industries with substantial recent growth. The increase in demand for aluminum, however, has outpaced the growth of primary aluminum production. One way to meet this shortfall is the use of secondary, or recycled, materials which provides both economic and environmental benefits. The increased use of secondary materials is limited by numerous factors; one such factor of concern is uncertainty. One form of uncertainty that all producers face is consumer demand; this will be the focus of this study. The two stage recourse optimization model presented in this thesis aims to provide batch planners with a tool to effectively manage raw materials in an uncertain demand environment. This model enhances existing research by increasing the number of demand scenarios considered by an increase in the model's resolution. The two metrics evaluated are scrap purchased and production cost. The batch planning process is affected by a number of assumptions about factor inputs including the model resolution, salvage value, coefficient of variation, scrap cost and compositional constraints. Results show that understanding the influence of these factors provides producers with the insight and ability to effectively manage and mitigate the effects of demand uncertainty in a cost minimization framework.by Hashem H. Dabbas.S.B