Finite size phase transitions in QCD with adjoint fermions

We perform a lattice investigation of QCD with three colors and 2 flavors of Dirac (staggered) fermions in the adjoint representation, defined on a 4d space with one spatial dimension compactified, and study the phase structure of the theory as a function of the size Lc of the compactified dimension. We show that four different phases take place, corresponding to different realizations of center symmetry: two center symmetric phases, for large or small values of Lc, separated by two phases in which center symmetry is broken in two different ways; the dependence of these results on the quark mass is discussed. We study also chiral properties and how they are affected by the different realizations of center symmetry; chiral symmetry, in particular, stays spontaneously broken at the phase transitions and may be restored at much lower values of the compactification radius. Our results could be relevant to a recently proposed conjecture of volume indepedence of QCD with adjoint fermions in the large Nc limit.Comment: 9 pages, 12 figures; extended discussion about the chiral limit and the chiral properties; 2 figures and references adde

Moderating Political Extremism: Single Round vs Runoff Elections under Plurality Rule

We compare single ballot vs dual ballot elections under plurality rule, assuming sincere voting and allowing for partly endogenous party formation. Under the dual ballot, the number of parties is larger but the influence of extremists voters on equilibrium policy is smaller, because their bargaining power is reduced compared to a single ballot election. The predictions on the number of parties and on policy volatility are consistent with data on municipal elections in Italy, where cities with more (less) than 15,000 inhabitants have dual (single) ballots respectively.political extremism

Moderating Political Extremism: Single Round vs Runoff Elections under Plurality Rule

We compare single ballot vs dual ballot elections under plurality rule, assuming sincere voting and allowing for partly endogenous party formation. Under the dual ballot, the number of parties is larger but the influence of extremist voters on equilibrium policy is smaller, because their bargaining power is reduced compared to a single ballot election. The predictions on the number of parties and on policy volatility are consistent with data on municipal elections in Italy, where cities with more (less) than 15,000 inhabitants have dual (single) ballots respectively.run-off, municipal elections, political bargaining, property

QCD simulations with staggered fermions on GPUs

We report on our implementation of the RHMC algorithm for the simulation of lattice QCD with two staggered flavors on Graphics Processing Units, using the NVIDIA CUDA programming language. The main feature of our code is that the GPU is not used just as an accelerator, but instead the whole Molecular Dynamics trajectory is performed on it. After pointing out the main bottlenecks and how to circumvent them, we discuss the obtained performances. We present some preliminary results regarding OpenCL and multiGPU extensions of our code and discuss future perspectives.Comment: 22 pages, 14 eps figures, final version to be published in Computer Physics Communication

The Roberge-Weiss endpoint in N_f = 2 QCD

We present the results of extensive simulations regarding the critical behavior at the endpoint of the Roberge-Weiss transition for N_f = 2 QCD. We confirm early evidence, presented in arXiv:0909.0254, according to which the Roberge-Weiss endpoint is first order in the limit of large or small quark masses, and second order for intermediate masses. A systematic study of the transition strength as a function of the quark mass in the first order regions, permits us to estimate the tricritical values of the quark mass separating the second order region from the first order ones.Comment: 10 pages, 20 figures. References and figures updated. Matches the published versio

Gyrotactic phytoplankton in laminar and turbulent flows: a dynamical systems approach

Gyrotactic algae are bottom heavy, motile cells whose swimming direction is determined by a balance between a buoyancy torque directing them upwards and fluid velocity gradients. Gyrotaxis has, in recent years, become a paradigmatic model for phytoplankton motility in flows. The essential attractiveness of this peculiar form of motility is the availability of a mechanistic description which, despite its simplicity, revealed predictive, rich in phenomenology, easily complemented to include the effects of shape, feed-back on the fluid and stochasticity (e.g. in cell orientation). In this review we consider recent theoretical, numerical and experimental results to discuss how, depending on flow properties, gyrotaxis can produce inhomogeneous phytoplankton distributions on a wide range of scales, from millimeters to kilometers, in both laminar and turbulent flows. In particular, we focus on the phenomenon of gyrotactic trapping in nonlinear shear flows and in fractal clustering in turbulent flows. We shall demonstrate the usefulness of ideas and tools borrowed from dynamical systems theory in explaining and interpreting these phenomena

Assessment of a Dual-Wavelength Compensation Technique for Displacement Sensors Using Plastic Optical Fibers

The paper analyzes the performance of a dual-wavelength technique devised to compensate power fluctuations in intensity-modulated plastic optical fiber sensors, which were specifically conceived for the measurement of displacements in industrial and civil applications. These sensors retrieve the displacement from the variation of the attenuation along the light path and use two signals at different wavelengths to compensate for the effects of parasitic quantities, such as temperature and strains along the fiber. The theoretical behavior of the compensation technique is presented, and the results of experiments carried out with different combinations of signal wavelengths and plastic fibers are reported. The experimental setup has proved that, by proper choice of the compensation signal wavelength, it is possible to monitor displacements in the range (0 to 10) mm, even for low received power and under severe perturbation conditions, thus significantly improving the long-term stability of the sensor