Plasma ion evolution in the wake of a high-intensity ultrashort laser pulse

Experimental investigations of the late-time ion structures formed in the wake of an ultrashort, intense laser pulse propagating in a tenuous plasma have been performed using the proton imaging technique. The pattern found in the wake of the laser pulse shows unexpectedly regular modulations inside a long, finite width channel. On the basis of extensive particle in cell simulations of the plasma evolution in the wake of the pulse, we interpret this pattern as due to ion modulations developed during a two-stream instability excited by the return electric current generated by the wakefield.

Reentry as a Rite of Passage

Mary Douglas argues that, ‘There are some things we cannot experience without ritual.’ Ex-prisoner reintegration may be one of them. The punishment process involves an inordinate amount of ritual behavior, from the drama of the courtroom to the elaborate de-individuation processes involved in institutionalization. Durkheim argues that these rituals served a distinct purpose for society: engendering social solidarity and shaping penal sensibilities. Like the commission of a crime, the reintegration of the former outcast back into society represents a challenge to the moral order, a delicate transition fraught with danger and possibility. However, unlike punishment, reintegration is not a process characterized by well-orchestrated and familiar rituals. This lack might explain the failings of prisoner reentry in contemporary society. This article reviews the sociological and anthropological literature on rituals, explaining what they are and what they do, focusing in particular on the role of status degradation ceremonies in criminal justice work. Drawing on this literature, the core elements that would be needed to develop rituals of reintegration powerful enough to counteract these degradation effects are discussed, and the potential impact of such hypothetical rituals is explored.

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 (greater than or similar to 10(19) W cm(-2)) short (similar to 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.

Field testing a full-scale tidal turbine Part 2: In-line Wake Effects

Recent research has shown that higher ambient turbulence leads to better wake recovery, so turbines could be installed in closer proximity in real tidal flows than might be assumed from typical towing tank tests that do not take into account turbulent inflow conditions. The standard tools to assess flow velocities in field conditions are Doppler based sonar devices, such as Acoustic Doppler Profilers (ADPs) or Acoustic Doppler Velocimeters (ADVs). The use of these devices poses some challenges when assessing the wake of a tidal turbine. While ADPs allow the three-dimensional measurement of a velocity profile over a distance, the data is calculated as a mean of three diverging beams and with low temporal resolution. ADVs can measure with higher sampling frequency but only at a single point in the flow. During the MaRINET testing of the SCHOTTELSIT turbine at the QUB tidal test site in Portaferry, Northern Ireland, ADP and ADV measurements were successfully tested.Two methods were employed for measuring the wake: firstly, with a rigidly mounted ADP and secondly, with a submerged ADV which was streamed behind the turbine. This paper presents the experimental set-up and results and discusses limitations and challenges of the two methods used.