Josephson effect in MgB_2 break junctions

We present the first observation of the DC and AC Josephson effect in MgB_2 break junctions. The junctions, obtained at 4.2 K in high-quality, high-density polycrystalline metallic MgB_2 samples, show a non-hysteretic DC Josephson effect. By irradiating the junctions with microwaves we observe clear Shapiro steps spaced by the ideal $\Delta V$ value. The temperature dependence of the DC Josephson current and the dependence of the height of the steps on the microwave power are obtained. These results are a direct prove for the existence of pairs with charge 2e in this new metallic superconductor and give evidence of the superconductor-normal metal-superconductor weak link character of these junctions.Comment: 4 RevTEX pages, 4 eps figure

GHItaly19: Research Perspectives on Game Human Interaction

This is a short introduction to the papers presented at the 3rd Workshop on Games-Human Interaction - GHItaly19, that was held in connection with CHItaly 2019. This series of workshops focuses on the multifaceted issues related to the design and development of human-game interfaces. This entails multidisciplinary competences and skills, and the final quality of the User eXperience depends on how consistently and smartly they are exploited. As a matter of fact, users\u2019 engagement and satisfaction rely on the wise design and skilled evaluation of the produced (multidimensional) artifacts. This gains even more critical importance since the application of video games has long overcome the borders of amusement, to spur new possibilities for, e.g., continuous healthcare and education

Detection of the Vortex Dynamic Regimes in MgB2 by Third Harmonic AC Susceptibility Measurements

In a type-II superconductor the generation of higher harmonics in the magnetic response to an alternating magnetic field is a consequence of the non-linearity in the I-V relationship. The shape of the current-voltage (I-V) curve is determined by the current dependence of the thermal activation energy U(J) and is thus related to the dynamical regimes governing the vortex motion. In order to investigate the vortex dynamics in MgB2 bulk superconductors we have studied the fundamental (chi1) and third (chi3) harmonics of the ac magnetic susceptibility. Measurements have been performed as a function of the temperature and the dc magnetic field, up to 9 T, for various frequencies and amplitudes of the ac field. We show that the analysis of the behaviour in frequency of chi3(T) and chi3(B) curves can provide clear information about the non-linearity in different regions of the I-V characteristic. By comparing the experimental curves with numerical simulations of the non-linear diffusion equation for the magnetic field we are able to resolve the crossover between a dissipative regime governed by flux creep and one dominated by flux flow phenomena.Comment: to be published in "Horizons in Superconductivity Research" (Nova Science Publishers, Inc., NY, 2003

GHItaly19: Research Perspectives on Game Human Interaction

This is a short introduction to the papers presented at the 3rd Workshop on Games-Human Interaction - GHItaly19, that was held in connection with CHItaly 2019. This series of workshops focuses on the multifaceted issues related to the design and development of human-game interfaces. This entails multidisciplinary competences and skills, and the final quality of the User eXperience depends on how consistently and smartly they are exploited. As a matter of fact, users’ engagement and satisfaction rely on the wise design and skilled evaluation of the produced (multidimensional) artifacts. This gains even more critical importance since the application of video games has long overcome the borders of amusement, to spur new possibilities for, e.g., continuous healthcare and education

On a semiclassical formula for non-diagonal matrix elements

Let $H(\hbar)=-\hbar^2d^2/dx^2+V(x)$ be a Schr\"odinger operator on the real line, $W(x)$ be a bounded observable depending only on the coordinate and $k$ be a fixed integer. Suppose that an energy level $E$ intersects the potential $V(x)$ in exactly two turning points and lies below $V_\infty=\liminf_{|x|\to\infty} V(x)$. We consider the semiclassical limit $n\to\infty$, $\hbar=\hbar_n\to0$ and $E_n=E$ where $E_n$ is the $n$th eigen-energy of $H(\hbar)$. An asymptotic formula for $$, the non-diagonal matrix elements of $W(x)$ in the eigenbasis of $H(\hbar)$, has been known in the theoretical physics for a long time. Here it is proved in a mathematically rigorous manner.Comment: LaTeX2

Dust remobilization in fusion plasmas under steady state conditions

The first combined experimental and theoretical studies of dust remobilization by plasma forces are reported. The main theoretical aspects of remobilization in fusion devices under steady state conditions are analyzed. In particular, the dominant role of adhesive forces is highlighted and generic remobilization conditions - direct lift-up, sliding, rolling - are formulated. A novel experimental technique is proposed, based on controlled adhesion of dust grains on tungsten samples combined with detailed mapping of the dust deposition profile prior and post plasma exposure. Proof-of-principle experiments in the TEXTOR tokamak and the EXTRAP-T2R reversed-field pinch are presented. The versatile environment of the linear device Pilot-PSI allowed for experiments with different magnetic field topologies and varying plasma conditions that were complemented with camera observations.Comment: 16 pages, 11 figures, 3 table