He-like x-ray line emission from laser irradiated sources

Photon yields for the 1s(2)-1s2p (He-alpha) transition of He- like ions have been measured for laser irradiated, thin foils of Ti, V and Fe. The laser pulses were of 0.527 mum wavelength and of either 80 or 300 ps duration. The data shows significant shot-to-shot variation but the Ti data is broadly consistent with previous results. In this work, we extend the previous results to include, new elements, longer pulse lengths and yields measured for emission from both surfaces of the foils. We compare our data to simulations using a hydrodynamic code and a collisional radiative model.

Finite temperature dense matter studies on next-generation light sources

The construction of short-pulse tunable soft x-ray free electron laser sources based on the self-amplified spontaneous emission process will provide a major advance in capability for dense plasma-related and warm dense matter (WDM) research. The sources will provide 10(13) photons in a 200-fs duration pulse that is tunable from approximately 6 to 100 nm. Here we discuss only two of the many applications made possible for WDM that has been severely hampered by the fact that laser-based methods have been unavailable because visible light will not propagate at electron densities of n(e) greater than or equal to 10(22) cm(-3). The next-generation light sources will remove these restrictions.

Fast Heating scalable to laser fusion ignition

Rapid heating of a compressed fusion fuel by a short-duration laser pulse is a promising route to generating energy by nuclear fusion1, and has been demonstrated on an experimental scale using a novel fast-ignitor geometry2. Here we describe a refinement of this system in which a much more powerful, pulsed petawatt (1015 watts) laser creates a fastheated core plasma that is scalable to fullscale ignition, significantly increasing the number of fusion events while still maintaining high heating efficiency at these substantially higher laser energies. Our findings bring us a step closer to realizing the production of relatively inexpensive, full-scale fast-ignition laser facilities.

'Superluminal' tunnelling as a weak measurement effect

We exploit the analogy between the transfer of a pulse across a scattering medium and Aharonov's weak measurements to resolve the long standing paradox between the impossibility to exceed the speed of light and the seemingly "superluminal" behavior of a tunneling particle in the barrier or a photon in a "fast-light" medium. We demonstrate that superluminality occurs when the value of the duration tau spent in the barrier is uncertain, whereas when tau is known accurately, no superluminal behavior is observed. In all cases only subluminal durations contribute to the transmission which precludes faster-than-light information transfer, as observed in a recent experiment.

Effects of plastic coating on K-alpha yield from ultra-short pulse

A study of the K-alpha radiation emitted from Ti foils irradiated with intense, similar to0.2 J, 67 fs, 800 nm laser pulses, scanning a range of intensities (similar to10(15)-10(18) W cm(-2)), is reported. The brightness of single-shot K-alpha line emission from the front of the targets is recorded. The yield from bare titanium (Ti) is compared to that from plastic (parylene-E) coated Ti. It is demonstrated that, for a defocused beam, a thin layer of plastic increases the yield.

Scale-length optimising of short pulse Cu K-alpha laser plasma sources

The authors present experimental results showing how the use of a high contrast femtosecond laser system allows better optimization of K emission from a Cu target. The shorter scale-length preformed plasma is better optimized for resonance absorption of the laser light when the laser is moved away from best focus. The experimental data show a central peak of K emission at tight focus with strong secondary peaks at large offset. The use of these secondary peaks results in a much reduced hard x-ray background and should lead to shorter K pulses than at tight focus.

Problems with identifying the '8200-year cold event' in terrestrial records of the Atlantic seaboard: a case study from Dooagh, Achill Island, Ireland.

The Northern Hemisphere cooling event 8200 years ago is believed to represent the last known major freshwater pulse into the North Atlantic as a result of the final collapse of the North American Laurentide ice sheet. This pulse of water is generally believed to have occurred independently of orbital variations and provides an analogue for predicted increases in high-latitude precipitation and ice melt as a result of anthropogenically driven future climate change. The precise timing, duration and magnitude of this event, however, are uncertain, with suggestions that the 100-yr meltwater cooling formed part of a longer-term cold period in the early Holocene. Here we undertook a multiproxy, high-resolution investigation of a peat sequence at Dooagh, Achill Island, on the west coast of Ireland, to determine whether the 8200-year cold event impacted upon the terrestrial vegetation immediately downwind of the proposed changes in the North Atlantic. We find clear evidence for an oscillation in the early Holocene using various measures of pollen, indicating a disruption in the vegetation leading to a grassland-dominated landscape, most probably driven by changes in precipitation rather than temperature. Radiocarbon dating was extremely problematic, however, with bulk peat samples systematically too young for the North Atlantic event, suggesting significant contamination from downward root penetration. The sustained disruption to vegetation over hundreds of years at Dooagh indicates the landscape was impacted by a long-term cooling event in the early Holocene, and not the single century length 8200-year meltwater event proposed in many other records in the North Atlantic region.

How Does the Unemployment Insurance System Shape the Time Profile of Jobless Duration?

This paper updates a sparse literature on the effects of unemployment benefits (UB) on the time profile of escape rates from unemployment. These effects, as well as those of other regressors, are found to vary profoundly over the course of unemployment.

Unemployment Duration: Competing and Defective Risks

This paper examines the determinants of unemployment duration in a competing risks framework with two destination states: inactivity and employment. The innovation is the recognition of defective risks. A polynomial hazard function is used to differentiate between two possible sources of infinite durations. The first is produced by a random process of unlucky draws, the second by workers rejecting a destination state. The evidence favors the mover-stayer model over the search model. Refinement of the former approach, using a more flexible baseline hazard function, produces a robust and more convincing explanation for positive and zero transition rates out of unemployment.