6,789 research outputs found

    Fast aquatic escape with a jet thruster

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    The ability to collect water samples rapidly with aerial–aquatic robots would increase the safety and efficiency of water health monitoring and allow water sample collection from dangerous or inaccessible areas. An aquatic micro air vehicle (AquaMAV) able to dive into the water offers a low cost and robust means of collecting samples. However, small-scale flying vehicles generally do not have sufficient power for transition to flight from water. In this paper, we present a novel jet propelled AquaMAV able to perform jumpgliding leaps from water and a planar trajectory model that is able to accurately predict aquatic escape trajectories. Using this model, we are able to offer insights into the stability of aquatic takeoff to perturbations from surface waves and demonstrate that an impulsive leap is a robust method of flight transition. The AquaMAV uses a CO 2 powered water jet to escape the water, actuated by a custom shape memory alloy gas release. The 100 g robot leaps from beneath the surface, where it can deploy wings and glide over the water, achieving speeds above 11 m/s

    Critical currents in weakly textured MgB2: Nonlinear transport in anisotropic heterogeneous media

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    A model for highly non-linear transport in heterogeneous media consisting of anisotropic particles with a preferred orientation is proposed and applied to the current transport in weakly textured magnesium diboride, MgB2. It essentially explains why, unlike in conventional superconductors, a significant macroscopic anisotropy of the critical currents can be induced by the preparation of MgB2 tapes. The field and angular dependence of the critical current is calculated for various degrees of texture and compared to experimental data

    Nonparametric Regression, Confidence Regions and Regularization

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    In this paper we offer a unified approach to the problem of nonparametric regression on the unit interval. It is based on a universal, honest and non-asymptotic confidence region which is defined by a set of linear inequalities involving the values of the functions at the design points. Interest will typically centre on certain simplest functions in that region where simplicity can be defined in terms of shape (number of local extremes, intervals of convexity/concavity) or smoothness (bounds on derivatives) or a combination of both. Once some form of regularization has been decided upon the confidence region can be used to provide honest non-asymptotic confidence bounds which are less informative but conceptually much simpler

    Digital Offset Calibration of an OPAMP Towards Improving Static Parameters of 90 nm CMOS DAC

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    In this paper, an on-chip self-calibrated 8-bit R-2R digital-to-analog converter (DAC) based on digitally compensated input offset of the operational amplifier (OPAMP) is presented. To improve the overall DAC performance, a digital offset cancellation method was used to compensate deviations in the input offset voltage of the OPAMP caused by process variations. The whole DAC as well as offset compensation circuitry were designed in a standard 90 nm CMOS process. The achieved results show that after the self-calibration process, the improvement of 48% in the value of DAC offset error is achieved

    Large scale structure in the HI Parkes All-Sky Survey: Filling the Voids with HI galaxies?

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    We estimate the two-point correlation function in redshift space of the recently compiled HIPASS neutral hydrogen (HI) sources catalogue, which if modeled as a power law, ξ(r)=(r0/r)γ\xi(r)=(r_{0}/r)^{\gamma}, the best-fitting parameters for the HI selected galaxies are found to be r0=3.3±0.3h1r_{0}=3.3 \pm 0.3 h^{-1} Mpc with γ=1.38±0.24\gamma=1.38 \pm 0.24. Fixing the slope to its universal value γ=1.8\gamma=1.8, we obtain r0=3.2±0.2h1r_{0}= 3.2\pm 0.2 h^{-1} Mpc. Comparing the measured two point correlation function with the predictions of the concordance cosmological model, we find that at the present epoch the HI selected galaxies are anti-biased with respect to the underlying matter fluctuation field with their bias value being b00.68b_{0}\simeq 0.68. Furthermore, dividing the HI galaxies into two richness subsamples we find that the low mass HI galaxies have a very low present bias factor (b00.48b_{0}\simeq 0.48), while the high mass HI galaxies trace the underlying matter distribution as the optical galaxies (b01b_{0}\simeq 1). Using our derived present-day HI galaxy bias we estimate their redshift space distortion parameter, and correct accordingly the correlation function for peculiar motions. The resulting real-space correlation length is r0re=1.8±0.2h1r^{\rm re}_{0}=1.8 \pm 0.2 h^{-1}Mpc and r0re=3.9±0.6h1r^{\rm re}_{0}=3.9 \pm 0.6 h^{-1}Mpc for the low and high mass HI galaxies, respectively. The low-mass HI galaxies appear to have the lowest correlation length among all extragalactic populations studied to-date. Also, we have correlated the IRAS-PSCz reconstructed density field, smoothed over scales of 5h1h^{-1} Mpc, with the positions of the HI galaxies, to find that indeed the HI galaxies are typically found in negative overdensity regions (\delta\rho/\rho_{\rm PSCz} \mincir 0).Comment: 9 pages, 8 figures, MNRAS in pres

    The Influence of Task Type on Perceived Fluency

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    In foreign language teaching it is necessary to employ a variety of tasks with a different degree of narrative structure to influence learners’ performance in anticipated ways, thus enhancing overall fluency as a significant aspect of successful communication. This study examines how different task types influence the perceived fluency of EFL learners. The obtained results confirm that the perception of speakers’ fluency varied across tasks. The worst perception of fluency was achieved in the task based on the formulation of unrelated utterances, that is, the most unstructured task led to the least fluent performance. A frequent introduction of new topics demands a great amount of attention. Therefore, in foreign language teaching emphasis should be laid on tasks including frequent introductions of new topics, due to the observed decrease in perceived fluency
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