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

Impact of Coronavirus Disease-19 Lockdown on Egyptian Children and Adolescents: Dietary Pattern Changes Health Risk

BACKGROUND: Lockdown and school closure related to the coronavirus disease 2019 (COVID-19) have unfavorable effects on children and adolescents. AIM: This study was conducted to survey the changes in dietary pattern and related health factors in Egyptian children and adolescents during the COVID-19 outbreak closure. MATERIALS AND METHODS: Data were collected through a dietary pattern, eating behavior, and physical activity electronic questionnaire conducted through social media sites, targeting parents of children and adolescents after two whole months of lockdown and school closure in Egypt. RESULTS: This study included 765 participants, 31.8% noted increased appetite, 45.6% reported increased sweets and unhealthy food consumption, and 37.6% showed increased frequent snacking between meals. Alongside 53.1% showed increase in late snacks during night after COVID-19 closure. The majority of our participants 82.0% noted associative change in eating behavior with boring and 94.6% revealed increased usage of electronics and screen time. This study showed significant positive correlation between increased appetite and mobile screen time, laptop screen time, and video gaming. Increased sweets and unhealthy food consumption was positively correlated with TV watching and mobile screen time. A significant positive correlation was revealed between uncaring about eating fruits and vegetables and increase screen time for each of mobile, and laptop and remote learning. Furthermore, there was positive correlation between decreased protein serving intake and each of mobile screen time and remote learning. TV watching and laptop screen times showed positively significantly association with frequent snacking between meals. Mobile screen time, TV screen time, and video gaming were positively significantly correlated with late night snacking. CONCLUSIONS: The present study concluded prolonged lockdown leads to changes in eating patterns, related to contributing factors of physical inactivity and prolonged screen time

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

On the presence of humpback whales in the Persian Gulf: rare or rarely documented? Report of the IWC Scientific Committee Meeting SC/67A/CMP/14, Bled, Slovenia, May 2017

We critically review the evidence for humpback whale presence in the Persian Gulf. Five specimen records, assumed to belong to the endangered Arabian Sea population, are confirmed in the period 1883- 2017: Bassore Bay, Iraq; Doha, Qatar; Kuwait Inner harbour, Kuwait; Qeshm Island, Iran; and Akhtar, Bushehr Province, Iran. The two Iranian cases, both juveniles, are newly recorded. With accumulating reports, an alternate hypothesis to 'rare stragglers' deserves consideration, one in which Arabian Sea humpback whales may enter the Persian Gulf with some regularity, perhaps as normal visitors, if not permanent residents. Deficiency of records may reflect a general sparsity of whale research effort in the Persian Gulf. The historical description of Megaptera indica Gervais, 1883 is translated from French

Channel equalization for indoor lighting communications networks

We consider indoors communications networks using modulated LEDs to transmit the information packets. A generic indoor channel equalization formulation is proposed assuming the existence of both line of sight and diffuse emitters. The proposed approach is of relevance to emergent indoors distributed sensing modalities for which various lighting based network communications protocols are considered