The Dynamical Dipole Mode in Fusion Reactions with Exotic Nuclear Beams

We report the properties of the prompt dipole radiation, produced via a collective bremsstrahlung mechanism, in fusion reactions with exotic beams. We show that the gamma yield is sensitive to the density dependence of the symmetry energy below/around saturation. Moreover we find that the angular distribution of the emitted photons from such fast collective mode can represent a sensitive probe of its excitation mechanism and of fusion dynamics in the entrance channel.Comment: 5 pages, 3 figures, to appear in Phys.Rev.

Multiscale lattice Boltzmann approach to modeling gas flows

For multiscale gas flows, kinetic-continuum hybrid method is usually used to balance the computational accuracy and efficiency. However, the kinetic-continuum coupling is not straightforward since the coupled methods are based on different theoretical frameworks. In particular, it is not easy to recover the non-equilibrium information required by the kinetic method which is lost by the continuum model at the coupling interface. Therefore, we present a multiscale lattice Boltzmann (LB) method which deploys high-order LB models in highly rarefied flow regions and low-order ones in less rarefied regions. Since this multiscale approach is based on the same theoretical framework, the coupling precess becomes simple. The non-equilibrium information will not be lost at the interface as low-order LB models can also retain this information. The simulation results confirm that the present method can achieve model accuracy with reduced computational cost

Quiet Sun magnetic fields from space-borne observations: simulating Hinode's case

We examine whether or not it is possible to derive the field strength distribution of quiet Sun internetwork regions from very high spatial resolution polarimetric observations in the visible. In particular, we consider the case of the spectropolarimeter attached to the Solar Optical Telescope aboard Hinode. Radiative magneto-convection simulations are used to synthesize the four Stokes profiles of the \ion{Fe}{1} 630.2 nm lines. Once the profiles are degraded to a spatial resolution of 0\farcs32 and added noise, we infer the atmospheric parameters by means of Milne-Eddington inversions. The comparison of the derived values with the real ones indicates that the visible lines yield correct internetwork field strengths and magnetic fluxes, with uncertainties smaller than $\sim$150 G, when a stray light contamination factor is included in the inversion. Contrary to the results of ground-based observations at 1\arcsec, weak fields are retrieved wherever the field is weak in the simulation.Comment: Accepted for publication in ApJ Letter

Pulse-like and crack-like ruptures in experiments mimicking crustal earthquakes

Theoretical studies have shown that the issue of rupture modes has important implications for fault constitutive laws, stress conditions on faults, energy partition and heat generation during earthquakes, scaling laws, and spatiotemporal complexity of fault slip. Early theoretical models treated earthquakes as crack-like ruptures, but seismic inversions indicate that earthquake ruptures may propagate in a self-healing pulse-like mode. A number of explanations for the existence of slip pulses have been proposed and continue to be vigorously debated. This study presents experimental observations of spontaneous pulse-like ruptures in a homogeneous linear-elastic setting that mimics crustal earthquakes; reveals how different rupture modes are selected based on the level of fault prestress; demonstrates that both rupture modes can transition to supershear speeds; and advocates, based on comparison with theoretical studies, the importance of velocity-weakening friction for earthquake dynamics

The Dynamical Dipole Mode in Dissipative Heavy Ion Collisions

We study the effect of a direct Giant Dipole Resonance ($GDR$) excitation in intermediate dinuclear systems with exotic shape and charge distributions formed in charge asymmetric fusion entrance channels. A related enhancement of the $GDR$ gamma yield in the evaporation cascade of the fused nucleus is expected. The dynamical origin of such $GDR$ extra strength will show up in a characteristic anisotropy of the dipole gamma-emission. A fully microscopic analysis of the fusion dynamics is performed with quantitative predictions of the $GDR$ photon yield based on a dynamics- statistics coupling model. In particular we focus our attention on the energy and mass dependence of the effect. We suggest a series of new experiments, in particular some optimal entrance channel conditions. We stress the importance of using the new available radioactive beams.Comment: 20 pages (Latex), 14 Postscript figure

Helicopter tail rotor thrust and main rotor wake coupling in crosswind flight

The tail rotor of a helicopter with a single main rotor configuration can experience a significant reduction in thrust when the aircraft operates in crosswind flight. Brown’s vorticity transport model has been used to simulate a main rotor and tail rotor system translating at a sideslip angle that causes the tail rotor to interact with the main rotor tip vortices as they propagate downstream at the lateral extremities of the wake. The tail rotor is shown to exhibit a distinct directionally dependent mode during which tail rotors that are configured so that the blades travel forward at the top of the disk develop less thrust than tail rotors with the reverse sense of rotation. The range of flight speeds over which this mode exists is shown to vary considerably with the vertical location of the tail rotor. At low flight speeds, the directionally dependent mode occurs because the tail rotor is immersed within not only the downwash from the main rotor but also the rotational flow associated with clusters of largely disorganized vorticity within the main rotor wake. At higher flight speeds, however, the tail rotor is immersed within a coherent supervortex that strongly influences the velocity field surrounding the tail rotor

Constructing the Tree-Level Yang-Mills S-Matrix Using Complex Factorization

A remarkable connection between BCFW recursion relations and constraints on the S-matrix was made by Benincasa and Cachazo in 0705.4305, who noted that mutual consistency of different BCFW constructions of four-particle amplitudes generates non-trivial (but familiar) constraints on three-particle coupling constants --- these include gauge invariance, the equivalence principle, and the lack of non-trivial couplings for spins >2. These constraints can also be derived with weaker assumptions, by demanding the existence of four-point amplitudes that factorize properly in all unitarity limits with complex momenta. From this starting point, we show that the BCFW prescription can be interpreted as an algorithm for fully constructing a tree-level S-matrix, and that complex factorization of general BCFW amplitudes follows from the factorization of four-particle amplitudes. The allowed set of BCFW deformations is identified, formulated entirely as a statement on the three-particle sector, and using only complex factorization as a guide. Consequently, our analysis based on the physical consistency of the S-matrix is entirely independent of field theory. We analyze the case of pure Yang-Mills, and outline a proof for gravity. For Yang-Mills, we also show that the well-known scaling behavior of BCFW-deformed amplitudes at large z is a simple consequence of factorization. For gravity, factorization in certain channels requires asymptotic behavior ~1/z^2.Comment: 35 pages, 6 figure

MARMOSET: The Path from LHC Data to the New Standard Model via On-Shell Effective Theories

We describe a coherent strategy and set of tools for reconstructing the fundamental theory of the TeV scale from LHC data. We show that On-Shell Effective Theories (OSETs) effectively characterize hadron collider data in terms of masses, production cross sections, and decay modes of candidate new particles. An OSET description of the data strongly constrains the underlying new physics, and sharply motivates the construction of its Lagrangian. Simulating OSETs allows efficient analysis of new-physics signals, especially when they arise from complicated production and decay topologies. To this end, we present MARMOSET, a Monte Carlo tool for simulating the OSET version of essentially any new-physics model. MARMOSET enables rapid testing of theoretical hypotheses suggested by both data and model-building intuition, which together chart a path to the underlying theory. We illustrate this process by working through a number of data challenges, where the most important features of TeV-scale physics are reconstructed with as little as 5 inverse femtobarns of simulated LHC signals