Evidence of resonant surface-wave excitation in the relativistic regime through measurements of proton acceleration from grating targets.

The interaction of laser pulses with thin grating targets, having a periodic groove at the irradiated surface, is experimentally investigated. Ultrahigh contrast (~10(12)) pulses allow us to demonstrate an enhanced laser-target coupling for the first time in the relativistic regime of ultrahigh intensity >10(19) W/cm(2). A maximum increase by a factor of 2.5 of the cutoff energy of protons produced by target normal sheath acceleration is observed with respect to plane targets, around the incidence angle expected for the resonant excitation of surface waves. A significant enhancement is also observed for small angles of incidence, out of resonance.

Observation of magnetized soliton remnants in the wake of intense laser pulse propagation through plasmas.

Slowly evolving, regularly spaced patterns have been observed in proton projection images of plasma channels drilled by intense (≳10¹9 W cm⁻²) short (∼1 ps) laser pulses propagating in an ionized gas jet. The nature and geometry of the electromagnetic fields generating such patterns have been inferred by simulating the laser-plasma interaction and the following plasma evolution with a two-dimensional particle-in-cell code and the probe proton deflections by particle tracing. The analysis suggests the formation of rows of magnetized soliton remnants, with a quasistatic magnetic field associated with vortexlike electron currents resembling those of magnetic vortices.

Corporal oscillation during static biped posture in children with cerebral palsy.

This previous study was performed to compare the antero-posterior and medium-lateral displacements and the speed of displacement of the COP of healthy children and compare them to children with cerebral palsy type spastic diparesy. This study had the participation of 10 healthy children (6 girls and 4 boys), between 5 and 10 (7,6 +/- 2,1) years old, and other 10 children, all diagnosed as CP type spastic diparesy, (5 girls and 5 boys), between 5 e 10 (7,3 +/- 1,8) years old. To collect the data, we used the antero-posterior (AP) e medium-lateral (ML) displacements of the COP The parameters were compared by the variance analysis (ANOVA), and the post hoc test was Tukey's HSD. The level of significance adopted was p < 0,05. After the collect of data and statistical analysis, it was observed that the medium amplitude of the AP and ML displacements was higher in CP children, related to the healthy children: AP-F(I,18)= 1,66 (p = 0,002), ML-F1,18)= 3,36 (p = 0,002). As the amplitude, the speed of the displacements was also different among the children. The speed of the displacements, AP and ML was higher in CP children - F(1,36) = 0,009 (p = 0,00). There were no differences between the speed of AP and ML displacements, neither in the healthy children, nor in CP ones - F(1,36)= 0,00 (p = 0,87). The sensorial deficit found in CP children is an important issue in the increase of the amplitude and speed of displacement of the COP.

Steady magnetic-field generation via surface-plasma-wave excitation.

The possibility of inducing a magnetic field via surface plasma-wave excitation is investigated with a simple nonrelativistic hydrodynamic model. A static magnetic field is predicted at the plasma surface, scaling with the square of the surface-wave field amplitude, and the influence of the electron plasma density is studied. In the case of resonant surface-wave excitation by laser this result can be applied to low intensities such that the electron quiver velocity in the field of the surface wave is less than its thermal velocity.