Nonlinear Induction Detection of Electron Spin Resonance

We present a new approach to the induction detection of electron spin resonance (ESR) signals exploiting the nonlinear properties of a superconducting resonator. Our experiments employ a yttrium barium copper oxide (YBCO) superconducting stripline microwave (MW) resonator integrated with a microbridge. A strong nonlinear response of the resonator is thermally activated in the microbridge when exceeding a threshold in the injected MW power. The responsivity factor characterizing the ESR-induced change in the system's output signal is about 100 times larger when operating the resonator near the instability threshold, compared to the value obtained in the linear regime of operation. Preliminary experimental results, together with a theoretical model of this phenomenon are presented. Under appropriate conditions nonlinear induction detection of ESR can potentially improve upon the current capabilities of conventional linear induction detection ESR

Experimentally induced helper dispersal in colonially breeding cooperative cichlids

The ‘benefits of philopatry' hypothesis states that helpers in cooperatively breeding species derive higher benefits from remaining home, instead of dispersing and attempting to breed independently. We tested experimentally whether dispersal options influence dispersal propensity in the cooperatively breeding Lake Tanganyika cichlids Neolamprologus pulcher and N. savoryi. Cooperative groups of these fishes breed in densely packed colonies, surrounded by unoccupied, but apparently suitable breeding habitat. Breeding inside colonies and living in groups seems to benefit individuals, for example by early detection and deterrence of predators. We show that despite a slight preference of both species for habitat with a higher stone cover, 40% of the preferred habitat remained unoccupied. On average, the colonies contained a higher number of (1) predators of adults, juveniles and eggs, (2) shelter competitors, and (3) other species including potential food competitors, compared to the outside colony habitat. Apparently, habitat differences cannot explain why these cichlids breed in colonies. Accordingly, dispersal may not be limited by a lack of suitable breeding shelters, but by the relatively higher risk of establishing an outside- compared to a within-colony breeding territory. To test whether cichlids prefer within- to outside-colony breeding territories, we provided breeding shelters inside the colony and at the colony edge and studied helper dispersal. As expected, significantly more shelters were occupied within the colony compared to the edge. New breeding pairs with several helpers occupied these shelters. We conclude that although breeding habitat is plentiful outside the colonies, helpers delay dispersal to obtain a higher quality breeding position within the group or colony eventually, or they disperse in groups. Our results suggest that (1) group augmentation and Allee effects are generally important for dispersal decisions in cooperatively breeding cichlids, consistent with the ‘benefits of philopatry hypothesis', and (2) habitat saturation cannot fully explain delayed dispersal in these specie

Selection of pomegranate (Punica granatum L.) in south-eastern Tunisia

Tunisia is one of the main producers and exporters of pomegranate (Punica granatum L.) in the world. Due to its international importance, the selection of both quantitative and qualitative most desirable varieties has become a necessity. To select new cultivars that are most appropriate for commercial use, 21 accessions were collected from different regions of south-east Tunisia. 24 morphological characters of the tree and fruit were studied for each accession. This study has revealed considerable diversity especially concerning the tree vigor, the fruit size and color and the acidity of juice. Taking into account all comments, some trees are considered particularly efficient in south-eastern Tunisia.Key words: South-east Tunisia, Punica granatum L., selection, morphological characters

Evidence of a subenergy gap in the overdoped regime of Y_{1-x}Ca_{x}Ba_{2}Cu_{3}O_{7-\delta} thin films from THz Spectroscopy

We measured the terahertz (THz) complex conductivity of Ca doped YBa_{2}Cu_{3}O_{7-\delta} thin films in the frequency range of 0.1 to 3 THz (3 to 100 cm^{-1}) and at a temperature range of 20 to 300 K. The films were measured using both time domain and frequency domain THz methods. We showed evidence for the existence of a sub-gap in overdoped Y_{1-x}Ca_{x}Ba_{2}Cu_{3}O_{7-\delta} samples doped with 5% and 10% Ca. Evidence for the opening of this sub-gap appears as a sharp decrease in the spectrum of the real part of conductivity at frequencies equivalent to a gap energy of 1 meV and is more prominent with increased doping. This decrease in conductivity can be explained by using d-wave pairing symmetry with an imaginary part of is or id_{xy} which suggests node removal.Comment: 7 pages, 7 figure

Optical signatures of the superconducting Goldstone mode in granular aluminum: experiments and theory

Recent advances in the experimental growth and control of disordered thin films, heterostructures, and interfaces provide a fertile ground for the observation and characterisation of the collective superconducting excitations emerging below $T_c$ after breaking the $U(1)$ gauge symmetry. Here we combine THz experiments in a nano-structured granular Al thin film and theoretical calculations to demonstrate the existence of optically-active phase modes, which represent the Goldstone excitations of the broken gauge symmetry. By measuring the complex transmission trough the sample we identify a sizeable and temperature-dependent optical sub-gap absorption, which cannot be ascribed to quasiparticle excitations. A quantitative modelling of this material as a disordered Josephson array of nano-grains allows us to determine, with no free parameters, the structure of the spatial inhomogeneities induced by shell effects. Besides being responsible for the enhancement of the critical temperature with respect to bulk Al, already observed in the past, this spatial inhomogeneity provides a mechanism for the optical visibility of the Goldstone mode. By computing explicitly the optical spectrum of the superconducting phase fluctuations we obtain a good quantitative description of the experimental data. Our results demonstrate that nanograins arrays are a promising setting to study and control the collective superconducting excitations via optical means

Synthesis of benzimidazole-cyclohexanone derivatives

This work reports the synthesis and characterization of new benzimidazole-cyclohexanone derivatives 3a-d, 4a-d and 5a-d under different reaction conditions. The intermediates and final compounds were purified and their  chemical structures were elucidated using 1H-NMR, 13C-NMR and mass spectral data.Keywords: Benzimidazole, Cyclohexanone, NMR, Reaction intermediate

Les Difficultés D’apprentissage En Éducation Physique Et Sportive: Une Étude De Trois Cas D’enseignement De La Course De Haies Au Bénin

This study explored the functioning of the in-situ didactic system to highlight the difficulties experienced by students in the third year of the secondary school level when performing the activities suggested by their Sport and Physical Education Teachers. Based on the logic of the ternarity of the didactic system (Amade-Escot, 2008; 2003), the interactions between the teachers and students during the teaching/learning of the race were the subjects of study. A triangulation method was utilized whereby data was collected by extracting information from various sources including (Leutenegger, 2009; Van Der Maren, 1996): documentary analysis, interviews conducted pre-session, post-session, and post-cycle, as well as audio-visual recording of the class sessions. Central concepts within the anthropological theory of didactic (Chevallard, 1992) and didactic joint action theory (Sensevy, 2007) were used to analyze and interpret the results of which the most salient revealed that the students have difficulty with crossing and resuming the race after the hurdle. The inter-hurdle race does not occur at regular intervals. These are difficulties previously noted by Lamote (2002) and Aubert (1994). Within the context of our investigation, the agglomeration of the contents of the program, the number of sessions (03) devoted to the teaching/learning cycle of this physical activity, the quality of the material used, and the personal interactions between the participants, were all factors shown to account for the difficulties experienced by the students

Noise Induced Intermittency in a Superconducting Microwave Resonator

We experimentally and numerically study a NbN superconducting stripline resonator integrated with a microbridge. We find that the response of the system to monochromatic excitation exhibits intermittency, namely, noise-induced jumping between coexisting steady-state and limit-cycle responses. A theoretical model that assumes piecewise linear dynamics yields partial agreement with the experimental findings