Parametric investigation of nonlinear fluctuations in a dc glow discharge plasma

Glow discharge plasmas exhibit various types of self excited oscillations for different initial conditions like discharge voltages and filling pressures. The behavior of such oscillations associated with the anode glow have been investigated using nonlinear techniques like correlation dimension, largest Lyapunov exponent etc. It is seen that these oscillations go to an ordered state from a chaotic state with increase in input energy i.e. with discharge voltages implying occurrence of inverse bifurcations. These results are different from the other observations wherein the fluctuations have been observed to go from ordered to chaotic state.Comment: Submitted to Chao

From Monocular SLAM to Autonomous Drone Exploration

Micro aerial vehicles (MAVs) are strongly limited in their payload and power capacity. In order to implement autonomous navigation, algorithms are therefore desirable that use sensory equipment that is as small, low-weight, and low-power consuming as possible. In this paper, we propose a method for autonomous MAV navigation and exploration using a low-cost consumer-grade quadrocopter equipped with a monocular camera. Our vision-based navigation system builds on LSD-SLAM which estimates the MAV trajectory and a semi-dense reconstruction of the environment in real-time. Since LSD-SLAM only determines depth at high gradient pixels, texture-less areas are not directly observed so that previous exploration methods that assume dense map information cannot directly be applied. We propose an obstacle mapping and exploration approach that takes the properties of our semi-dense monocular SLAM system into account. In experiments, we demonstrate our vision-based autonomous navigation and exploration system with a Parrot Bebop MAV

Structural Stability: On the Prerequisites of Nonviolent Conflict Management

The concept of “structural stability” has been gaining prominence in development policy circles. In the EU’s and the OECD Development Assistance Committee’s (OECD DAC) understanding, it describes the ability of societies to handle intra-societal conflict without resorting to violence. This study investigates the preconditions of structural stability and tests their mutual interconnections. Seven dimensions are analyzed: (1) long-term economic growth, (2) environmental security, (3) social equality, (4) governmental effectiveness, (5) democracy, (6) rule of law, and (7) inclusion of identity groups. The postulated mutual enhancement of the seven dimensions is plausible but cannot be proven. The most significant positive relationship appears between “democracy” and “rule of law,” respectively, on the one hand and the dependent variable “violence/ human security” on the other hand. This points to the usefulness of the political concept of structural stability to promote development policy agendas in this area at least. Applications that reach beyond these initial findings will, however, require further research.Structural stability, violence, human security, development aid, conflict management, prerequisites of nonviolence

Wigner crystalization about ν\nu=3

We measure a resonance in the frequency dependence of the real diagonal conductivity, Re[$\sigma_{xx}$], near integer filling factor, $\nu=3$. This resonance depends strongly on $\nu$, with peak frequency $f_{pk} \approx 1.7$ GHz at $\nu=3.04$ or 2.92 close to integer $\nu$, but $f_{pk} \approx$ 600 MHz at $\nu=3.19$ or 2.82, the extremes of where the resonance is visible. The dependence of $f_{pk}$ upon $n^*$, the density of electrons in the partially filled level, is discussed and compared with similar measurments by Chen {\it et al.}\cite{yong} about $\nu=1$ and 2. We interpret the resonance as due to a pinned Wigner crystal phase with density $n^*$ about the $\nu=3$ state.Comment: for proceedings of EP2DS-15 (Nara) to appear in Physica

The New Old (and Old New) Medical Model:Four Decades Navigating the Biomedical and Psychosocial Understandings of Health and Illness

The importance of how disease and illness are conceptualised lies in the fact that such definition is paramount to understand the boundaries and scope of responsibility associated with medical work. In this paper, we aim to provide an overview of the interplay of these understandings in shaping the nature of medical work, philosophically, and in practice. We first discuss the emergence of the biopsychosocial model as an attempt to both challenge and broaden the traditional biomedical model. Then, we outline the main criticisms associated with the biopsychosocial model and note a range of contributions addressing the shortcomings of the model as initially formulated. Despite recurrent criticisms and uneven uptake, the biopsychosocial model has gone on to influence core aspects of medical practice, education, and research across many areas of medicine. One of these areas is adolescent medicine, which provides a particularly good exemplar to examine the contemporary challenges associated with the practical application of the biopsychosocial model. We conclude that a more optimal use of existing bodies of evidence, bringing together evidence-based methodological advances of the biopsychosocial model and existing evidence on the psychosocial needs associated with specific conditions/populations, can help to bridge the gap between philosophy and practice

Oscillation modes of dc microdischarges with parallel-plate geometry

Two different oscillation modes in microdischarge with parallel-plate geometry has been observed: relaxation oscillations with frequency range between 1.23 and 2.1 kHz and free-running oscillations with 7 kHz frequency. The oscillation modes are induced by increasing power supply voltage or discharge current. For a given power supply voltage, there is a spontaneous transition from one to other oscillation mode and vice versa. Before the transition from relaxation to free-running oscillations, the spontaneous increase of oscillation frequency of relaxation oscillations form 1.3 kHz to 2.1 kHz is measured. Fourier Transform Spectra of relaxation oscillations reveal chaotic behaviour of microdischarge. Volt-Ampere characteristics associated with relaxation oscillations describes periodical transition between low current, diffuse discharge and normal glow. However, free-running oscillations appear in subnormal glow only.Comment: Submitted to: New Journal of Physic

Direct Simulation of Low-Pressure Supersonic Gas Expansions and its Experimental Verification

The use of gas expansions to generate atomic or molecular beams has become a standard technique in nuclear and hadron physics for the production of polarized ion beams and gas targets. A direct simulation Monte Carlo method was used to understand the processes occurring in an expansion of highly dissociated hydrogen or deuterium gas at low densities. The results were verified in several measurements including time-of-flight and beam-profile determinations which showed that the supersonic gas expansions can properly be described by the Monte Carlo calculations. Additionally a new method of beam formation, the hollow carrier jet, was tested under the conditions of the atomic beam source operation

On the jets, kinks, and spheromaks formed by a planar magnetized coaxial gun

Measurements of the various plasma configurations produced by a planar magnetized coaxial gun provide insight into the magnetic topology evolution resulting from magnetic helicity injection. Important features of the experiments are a very simple coaxial gun design so that all observed geometrical complexity is due to the intrinsic physical dynamics rather than the source shape and use of a fast multiple-frame digital camera which provides direct imaging of topologically complex shapes and dynamics. Three key experimental findings were obtained: (1) formation of an axial collimated jet [Hsu and Bellan, Mon. Not. R. Astron. Soc. 334, 257 (2002)] that is consistent with a magnetohydrodynamic description of astrophysical jets, (2) identification of the kink instability when this jet satisfies the Kruskal-Shafranov limit, and (3) the nonlinear properties of the kink instability providing a conversion of toroidal to poloidal flux as required for spheromak formation by a coaxial magnetized source [Hsu and Bellan, Phys. Rev. Lett. 90, 215002 (2003)]. A new interpretation is proposed for how the n=1 central column instability provides flux amplification during spheromak formation and sustainment, and it is shown that jet collimation can occur within one rotation of the background poloidal field.Comment: Physics of Plasmas (accepted

The impact of mixing across the polar vortex edge on Match ozone loss estimates

The Match method for quantification of polar chemical ozone loss is investigated mainly with respect to the impact of mixing across the vortex edge onto this estimate. We show for the winter 2002/03 that significant mixing across the vortex edge occurred and was accurately modeled by the Chemical Lagrangian Model of the Stratosphere. Observations of inert tracers and ozone in-situ from HAGAR on the Geophysica aircraft and sondes and also remote from MIPAS on ENVISAT were reproduced well. The model even reproduced a small vortex remnant that was isolated until June 2003 and was observed in-situ by a balloon-borne whole air sampler. We use this CLaMS simulation to quantify the impact of cross vortex edge mixing on the results of the Match method. It is shown that a time integration of the determined vortex average ozone loss rates as performed in Match results in larger ozone loss than the polar vortex average ozone loss in CLaMS. Also, the determination of the Match ozone loss rates can be influenced by mixing. This is especially important below 430 K, where ozone outside the vortex is lower than inside and the vortex boundary is not a strong transport barrier. This effect and further sampling effects cause an offset between vortex average ozone loss rates derived from Match and deduced from CLaMS with an even sampling for the entire vortex. Both, the time-integration of ozone loss and the determination of ozone loss rates for Match are evaluated using the winter 2002/03 CLaMS simulation. These impacts can explain the differences between CLaMS and Match column ozone loss. While the investigated effects somewhat reduce the apparent discrepancy in January ozone loss rates, a discrepancy between simulations and Match remains. However, its contribution to the accumulated ozone loss over the winter is not large

A conic manifold perspective of elliptic operators on graphs

We give a simple, explicit, sufficient condition for the existence of a sector of minimal growth for second order regular singular differential operators on graphs. We specifically consider operators with a singular potential of Coulomb type and base our analysis on the theory of elliptic cone operators.Comment: 18 page