Structural Transitions in a Classical Two-Dimensional Molecule System

The ground state of a classical two-dimensional (2D) system with finite number of charged particles, trapped by two positive impurities charges localized at a distance (zo) from the 2D plane and separated from each other by a distance xp are obtained. The impurities are allowed to carry more than one positive charge. This classical system can form a 2D-like classical molecule that exhibits structural transitions and spontaneous symmetry breaking as a function of the separation between the positive charges before it transforms into two independent 2D-like classical atoms. We also observe structural transitions as a function of the dielectric constant of the substrate which supports the charged particles, in addition to broken symmetry states and unbinding of particles.Comment: 9 pages, 7 figure

Periodical evaluation of photovoltaic modules and diode parameter extraction method using multiple linear regression models

The stability and performance of photovoltaic modules can be assessed by outdoor testing where external conditions such as illumination and module temperature are measured at regular time intervals together with the jV curve of the module. However, the fluctuation and seasonal variation of external conditions can make it difficult to trace changes such as degradation in PV module properties at e.g. STC . This contribution demonstrates the use of multiple linear regressions MLR to overcome these difficulties. The data gathered over large periods are condensed into a set of few predictors, which reproduce the jV parameters at infrequently encountered conditions that are required for comparison. Furthermore, the parameters of a physical device model are calculated directly from MLR predictors, validating our procedure two fold, by applying the MLR method to simulated data, replicating the original input parameters, and by comparing monthly parameter averages between the MLR method and a known parameter extraction metho

Electron mobility in Si δ-doped GaAs with spatial correlationsin the distribution of charged impurities

We present a theoretical study of electron mobility in heavily Si d-doped GaAs in the presence of applied hydrostatic pressure. At low temperature the electron-ionized impurity scattering is the most important scattering mechanism. The presence of DX centers in Si-doped GaAs results in spatial correlations of the charged impurities, which increase the electron mobility through the structure factor of the charged-impurity distribution and/or a decrease in the density of the charged dopants. A Monte Carlo approach has been developed to simulate this distribution in two dimensions for the d+/DX0 and d+/DX- models. In the mobility calculation, both intrasubband and intersubband scatterings are considered with the electron-electron screening within the random-phase approximation. A detailed comparison between experiment and theory shows that theory excluding the correlation effects underestimates the electron mobility systematically. In cooperation with other mechanisms, e.g., self-compensation of Si dopants, in the d layer, both DX-center models can explain the experimental results well. This indicates that in order to effectively study the electronic properties of DX centers via the electron mobility in d-doped structures, the samples must have a relatively low doping concentration in order to prevent self-compensation

Path Integral Description of a Semiclassical Su-Schrieffer-Heeger Model

The electron motion along a chain is described by a continuum version of the Su-Schrieffer-Heeger Hamiltonian in which phonon fields and electronic coordinates are mapped onto the time scale. The path integral formalism allows us to derive the non local source action for the particle interacting with the oscillators bath. The method can be applied for any value of the {\it e-ph} coupling. The path integral dependence on the model parameters has been analysed by computing the partition function and some thermodynamical properties from $T= 1K$ up to room temperature. A peculiar upturn in the low temperature {\it heat capacity over temperature} ratio (pointing to a glassy like behavior) has been ascribed to the time dependent electronic hopping along the chain

Mass Renormalization in the Su-Schrieffer-Heeger Model

This study of the one dimensional Su-Schrieffer-Heeger model in a weak coupling perturbative regime points out the effective mass behavior as a function of the adiabatic parameter $\omega_{\pi}/J$, $\omega_{\pi}$ is the zone boundary phonon energy and $J$ is the electron band hopping integral. Computation of low order diagrams shows that two phonons scattering processes become appreciable in the intermediate regime in which zone boundary phonons energetically compete with band electrons. Consistently, in the intermediate (and also moderately antiadiabatic) range the relevant mass renormalization signals the onset of a polaronic crossover whereas the electrons are essentially undressed in the fully adiabatic and antiadiabatic systems. The effective mass is roughly twice as much the bare band value in the intermediate regime while an abrupt increase (mainly related to the peculiar 1D dispersion relations) is obtained at $\omega_{\pi}\sim \sqrt{2}J$.Comment: To be published in Phys.Rev.B - 3 figure

Neoctangium travassosi (Digenea: Microscaphidiidae) in sea turtles from South America

ABSTRACT Sea turtles are endangered animals that present cosmopolitan distribution. Anthropic actions have been considered important causes for the reduction of sea turtle population, but natural aspects such as parasitism may also contribute to their decline. This study aimed to report the occurrence of parasites in stranded dead sea turtles found in an area known as Potiguar Basin, northeastern Brazil, from 2010 to 2019. They were identified and classified according to the carapace length. At post-mortem analyses all organs were examined, parasites collected and morphologically identified. Ecological parasitic indexes as prevalence (P), mean intensity (MI) and mean abundance (MA) were calculated. A total of 80 Chelonia mydas and 5 Eretmochelys imbricata were assessed. Neoctangium travassosi was detected in both species presenting P = 20%, MI = 4.19 and MA = 0.84 for C. mydas and P = 60%, MI = 1.67 and MA = 1.0 for E. imbricata. This is the first report of N. travassosi parasitizing E. imbricata in South America. Finally, the retrieval of these parasites is a warning regarding the need for further studies to assess the impact of this parasitism on the health and conservation of sea turtles

Laser based series interconnection of chalcopyrite und perovskite solar cells Analysis of material modifications and implications for achieving small dead area widths

Both nanosecond pulses and picosecond laser pulses are used for P2 patterning of chalcopyrite Cu In,Ga Se2, CIGSe and metal halide perovskite solar cell absorber layers. For CIGSe, the range of the modified material visualized by photoluminescence imaging is significantly wider than the actual physical linewidth, since energy input by the laser pulses leads to material modification in the vicinity of the scribed lines. This effect does not occur with the perovskite absorber layers, where there is no apparent influence on the edge regions. From numerical calculations of the temperature depth profiles and the surface temperature distributions it is concluded that this effect is due to the significantly lower perovskite absorber layer thickness compared to CIGSe and the nevertheless significantly higher laser fluence required for perovskite ablation. The unaffected edge regions around the P2 line in the perovskite enabled a reduction of the dead area width in the fabrication of 3 segmented mini modules, which could be significantly reduced from 430 to 230 m, while increasing the aperture area power conversion efficiency and also the geometric fill factor, which could be increased up to 94.