Radiation-Pressure Acceleration of Ion Beams Driven by Circularly Polarized Laser Pulses

We present experimental studies on ion acceleration from ultrathin diamondlike carbon foils irradiated by ultrahigh contrast laser pulses of energy 0.7 J focused to peak intensities of 5×1019  W/cm2. A reduction in electron heating is observed when the laser polarization is changed from linear to circular, leading to a pronounced peak in the fully ionized carbon spectrum at the optimum foil thickness of 5.3 nm. Two-dimensional particle-in-cell simulations reveal that those C6+ ions are for the first time dominantly accelerated in a phase-stable way by the laser radiation pressure.

A Strain-Driven Morphotropic Phase Boundary in BiFeO3

Piezoelectric materials, which convert mechanical to electrical energy and vice versa, are typically characterized by the intimate coexistence of two phases across a morphotropic phase boundary. Electrically switching one to the other yields large electromechanical coupling coefficients. Driven by global environmental concerns, there is currently a strong push to discover practical lead-free piezoelectrics for device engineering. Using a combination of epitaxial growth techniques in conjunction with theoretical approaches, we show the formation of a morphotropic phase boundary through epitaxial constraint in lead-free piezoelectric bismuth ferrite (BiFeO3) films. Electric field-dependent studies show that a tetragonal-like phase can be reversibly converted into a rhombohedral-like phase, accompanied by measurable displacements of the surface, making this new lead-free system of interest for probe-based data storage and actuator applications.

Actively Tuned Plasmons on Elastomerically Driven Au Nanoparticle Dimers

We demonstrate a novel way to actively tune surface plasmons by fabricating plasmonic nanostructures on stretchable elastomeric films. This allows reversible modification of the metal geometry on the nanometer scale. Using 100 nm scale Au nanoparticle dimers whose spacing is stretch-tuned reveals radically different spectral tuning than previously reported for sub-10-nm nanoparticles, but which can be explained by a revised interpretation of existing models. Tuning plasmons in this way offers a much more robust way than lithography to interrogate the physics of localized plasmons and has applications in optimized surface-enhanced luminescence and Raman scattering.

PIC simulation of a thermal anisotropy-driven Weibel instability in a circular rarefaction wave

The expansion of an initially unmagnetized planar rarefaction wave has recently been shown to trigger a thermal anisotropy-driven Weibel instability (TAWI), which can generate magnetic fields from noise levels. It is examined here whether the TAWI can also grow in a curved rarefaction wave. The expansion of an initially unmagnetized circular plasma cloud, which consists of protons and hot electrons, into a vacuum is modelled for this purpose with a two-dimensional particle-in-cell (PIC) simulation. It is shown that the momentum transfer from the electrons to the radially accelerating protons can indeed trigger a TAWI. Radial current channels form and the aperiodic growth of a magnetowave is observed, which has a magnetic field that is oriented orthogonal to the simulation plane. The induced electric field implies that the electron density gradient is no longer parallel to the electric field. Evidence is presented here that this electric field modification triggers a environments, which are needed to explain the electromagnetic emissions by astrophysical jets. It is outlined how this instability could be examined experimentally.second magnetic instability, which results in a rotational low-frequency magnetowave. The relevance of the TAWI is discussed for the growth of small-scale magnetic fields in astrophysical

Pedometer-driven walking for chronic low back pain:A feasibility randomized controlled trial

OBJECTIVES: To evaluate the feasibility of an RCT of a pedometer-driven walking program and education/advice to remain active compared with education/advice only for treatment of chronic low back pain (CLBP). METHODS: Fifty-seven participants with CLBP recruited from primary care were randomly allocated to either: (1) education/advice (E, n=17) or (2) education/advice plus an 8-week pedometer-driven walking program (EWP, n=40). Step targets, actual daily step counts, and adverse events were recorded in a walking diary over the 8 weeks of intervention for the EWP group only. All other outcomes (eg, functional disability using the Oswestry Disability Questionnaire (ODQ), pain scores, physical activity (PA) measurement etc.) were recorded at baseline, week 9 (immediately post-intervention), and 6 months in both groups. RESULTS: The recruitment rate was 22% and the dropout rate was lower than anticipated (13% to 18% at 6 mo). Adherence with the EWP was high, 93% (n=37/40) walked for =6 weeks, and increased their steps/day [mean absolute increase in steps/d, 2776, 95% confidence interval (CI), 1996-3557] by 59% (95% CI, 40.73%-76.25%) from baseline. Mean percentage adherence with weekly step targets was 70% (95% CI, 62%-77%). Eight (20%) minor-related adverse events were observed in 13% (5/40) of the participants. The EWP group participants demonstrated an 8.2% point improvement [95% CI, -13 to -3.4] on the ODQ at 6 months compared with 1.6% points [95% CI, -9.3 to 6.1) for the E group (between group d=0.44). There was also a larger mean improvement in pain (d=0.4) and a larger increase in PA (d=0.59) at 6 months in EWP. DISCUSSION: This preliminary study demonstrated that a main RCT is feasible. EWP was safe and produced a real increase in walking; CLBP function and pain improved, and participants perceived a greater improvement in their PA levels. These improvements require confirmation in a fully powered RCT.

Towards Utilizing Model-Driven Engineering of Composite Applications for Business Performance Analysis

Composite Applications on top of SAPs implementation of SOA (Enterprise SOA) enable the extension of already existing business logic. In this paper we show, based on a case study, how Model-Driven Engineering concepts are applied in the development of such Composite Applications. Our Case Study extends a back-end business process which is required for the specific needs of a demo company selling wine. We use this to describe how the business centric models specifying the modified business behaviour of our case study can be utilized for business performance analysis where most of the actions are performed by humans. In particular, we apply a refined version of Model-Driven Performance Engineering that we proposed in our previous work and motivate which business domain specifics have to be taken into account for business performance analysis. We additionally motivate the need for performance related decision support for domain experts, who generally lack performance related skills. Such a support should offer visual guidance about what should be changed in the design and resource mapping to get improved results with respect to modification constraints and performance objectives, or objectives for time.

Diffusive shock acceleration at laser-driven shocks: studying cosmic-ray accelerators in the laboratory

The non-thermal particle spectra responsible for the emission from many astrophysical systems are thought to originate from shocks via a first order Fermi process otherwise known as diffusive shock acceleration. The same mechanism is also widely believed to be responsible for the production of high energy cosmic rays. With the growing interest in collisionless shock physics in laser produced plasmas, the possibility of reproducing and detecting shock acceleration in controlled laboratory experiments should be considered. The various experimental constraints that must be satisfied are reviewed. It is demonstrated that several currently operating laser facilities may fulfil the necessary criteria to confirm the occurrence of diffusive shock acceleration of electrons at laser produced shocks. Successful reproduction of Fermi acceleration in the laboratory could open a range of possibilities, providing insight into the complex plasma processes that occur near astrophysical sources of cosmic rays.

TWO-DIMENSIONAL PARTICLE-IN-CELL SIMULATIONS OF THE NONRESONANT, COSMIC-RAY-DRIVEN INSTABILITY IN SUPERNOVA REMNANT SHOCKS

In supernova remnants, the nonlinear amplification of magnetic fields upstream of collisionless shocks is essential for the acceleration of cosmic rays to the energy of the "knee" at 10(15.5) eV. A nonresonant instability driven by the cosmic ray current is thought to be responsible for this effect. We perform two-dimensional, particle-in-cell simulations of this instability. We observe an initial growth of circularly polarized nonpropagating magnetic waves as predicted in linear theory. It is demonstrated that in some cases the magnetic energy density in the growing waves can grow to at least 10 times its initial value. We find no evidence of competing modes, nor of significant modification by thermal effects. At late times, we observe saturation of the instability in the simulation, but the mechanism responsible is an artifact of the periodic boundary conditions and has no counterpart in the supernova-shock scenario.