Studying electronic properties in GaN without electrical contacts using γ-γ vs e--γ Perturbed Angular Correlations.

The potential use of combined e--γ vs γ-γ Perturbed Angular Correlations (PAC) experiments as a possible alternative to study electronic properties of materials and/or samples where Hall effect measurements are difficult to perform due to low-quality ohmic contacts is here demonstrated using Si- and Zn-doped GaN samples as a showcase example. To do so, the lattice site of implanted 181Hf/181Ta and the recombination of Ta ionized and excited electronic states were studied as a function of temperature and sample doping in GaN. By combining the γ-γ and e--γ PAC results with Density Functional Theory simulations, it was possible to assign a single stable site with a double-donor character for Ta in GaN. A metastable charge state was also identified at particular temperatures using e--γ PAC. A thermally activated process was observed for the electronic recombination at high temperatures with activation energies of 15(2) meV and 12(1) meV for the Si- and Zn-doped samples, respectively, and attributed to Si shallow donors present in both samples. A reduced number of available electrons was observed in the Zn-doped sample due to donor compensation by the Zn acceptors. At low temperatures, it is suggested that the recombination process occurs via Variable Range Hopping. The doping characteristics of both samples were successfully distinguished.

Inferring Lévy walks from curved trajectories: A rescaling method.

An important problem in the study of anomalous diffusion and transport concerns the proper analysis of trajectory data. The analysis and inference of Lévy walk patterns from empirical or simulated trajectories of particles in two and three-dimensional spaces (2D and 3D) is much more difficult than in 1D because path curvature is nonexistent in 1D but quite common in higher dimensions. Recently, a new method for detecting Lévy walks, which considers 1D projections of 2D or 3D trajectory data, has been proposed by Humphries et al. The key new idea is to exploit the fact that the 1D projection of a high-dimensional Lévy walk is itself a Lévy walk. Here, we ask whether or not this projection method is powerful enough to cleanly distinguish 2D Lévy walk with added curvature from a simple Markovian correlated random walk. We study the especially challenging case in which both 2D walks have exactly identical probability density functions (pdf) of step sizes as well as of turning angles between successive steps. Our approach extends the original projection method by introducing a rescaling of the projected data. Upon projection and coarse-graining, the renormalized pdf for the travel distances between successive turnings is seen to possess a fat tail when there is an underlying Lévy process. We exploit this effect to infer a Lévy walk process in the original high-dimensional curved trajectory. In contrast, no fat tail appears when a (Markovian) correlated random walk is analyzed in this way. We show that this procedure works extremely well in clearly identifying a Lévy walk even when there is noise from curvature. The present protocol may be useful in realistic contexts involving ongoing debates on the presence (or not) of Lévy walks related to animal movement on land (2D) and in air and oceans (3D).

Determinação dos limiares de percepção sensorial e de resposta motora nas diferentes fases do ciclo menstrual / Determination of sensory perception and motor response thresholds in different phases of the menstrual cycle

OBJETIVO: Identificar a variação de percepção sensorial e resposta motora nas diferentes fases do ciclo menstrual (CM). MÉTODO: 30 mulheres com idade entre 18 e 40 anos (23,7 ± 3,60), com índice de massa corporal entre 18,5 e 25kg/m² (21,15 ± 2,32) e CM entre 21-35 dias participaram do estudo. Utilizou-se um gerador de pulso com correntes elétricas pulsadas, freqüência de 50Hz e fases variando em 20 (B20), 50 (B50), 100 (B100), 300 (B300), 500 (B500), 1000 (B1000) e 3000µs (B3000). O limiar de percepção sensorial (LPS) foi identificado como a primeira sensação de corrente ao aumento da intensidade e o limiar de resposta motora (LRM) como a mínima contração muscular detectada. Realizaram-se cinco coletas, sendo uma em cada fase: fase 1- menstrual (F1), fase 2- proliferativa (F2), fase 3- ovulatória (F3), fase 4- lútea (F4) e fase 5- pré-menstrual (F5). A análise dos dados constou do teste de Friedman seguido do teste de Rank, realizados no programa Bioestat 4.0®, com nível de significância de 5 por cento. Resultados: O LPS foi menor na F5 quando comparado às demais fases menstruais, para as correntes B20, B300, B500, B1000, B3000. Para o LRM houve diferença nas correntes B20, B50, B500 e B1000 entre todas as fases com a F5; na corrente B100, entre a F1 e F5; e nas correntes B300 e B3000 entre F1, F2 e F3 com a F5. CONCLUSÕES: O limiar de percepção sensorial e a resposta motora variaram sistematicamente através das fases do CM, influenciando o comportamento sensório-motor.

OBJECTIVE: To identify the variation of sensory perception and motor response in the different phases of the menstrual cycle. METHOD: Thirty women aged 18 to 40 years old (23.7 ± 3.60), with body mass index between 18.5 and 25kg/m² (21.15 ± 2.32) and menstrual cycle of 21-35 days, participated in this study. A pulse generator was used, with pulsed electric current frequency of 50Hz and variable phases of 20 (L20), 50 (L50), 100 (L100), 300 (L300), 500 (L500), 1000 (L1000) and 3000µs (L3000). The threshold of sensory perception (TSP) was identified as the first sensation of increased current intensity and the threshold of motor response (TMR) as the minimum muscle contraction detected. Five collections were done, at each of the following phases: phase 1- menstrual (P1), phase 2- follicular (P2), phase 3- ovulatory (P3), phase 4- luteal (P4) and phase 5- premenstrual (P5). The data analysis consisted of the Friedman test followed by the Rank test, carried out in the BioStat 4.0® software, with a significance level of 5 percent. RESULTS: The TSP was lower in P5 than in the other menstrual phases, for the L20, L300, L500, L1000 and L3000 currents. For the TMR, there was difference in the L20, L50, L500 and L1000 currents between P5 and all other phases; in the L100 current, between P1 and P5; and in the L300 and L3000 currents for P1, P2 and P3 versus P5. CONCLUSIONS: The thresholds of sensory perception and motor response varied systematically through the phases of the menstrual cycle, thus influencing motor-sensory behavior.

[Persistent primitive trigeminal artery: critical review of the clinical significance]. / Persistência da artéria trigeminal primitiva. Revisão crítica do significado clínico.

The authors report three cases of persistence of primitive trigeminal artery with no evidence of a relationship between its presence and any specific clinical syndrome. They discuss embryological aspects and establish the correlation between the presence of this malformation and other intracranial pathologies, such as "tic douloureux" and morphologic alteration of the circle of Willis. A critical review of the literature is also presented.