Effect of a strong laser field on e+e−e^+ e^- photoproduction by relativistic nuclei

We study the influence of a strong laser field on the Bethe-Heitler photoproduction process by a relativistic nucleus. The laser field propagates in the same direction as the incoming high-energy photon and it is taken into account exactly in the calculations. Two cases are considered in detail. In the first case, the energy of the incoming photon in the nucleus rest frame is much larger than the electron's rest energy. The presence of the laser field may significantly suppress the photoproduction rate at soon available values of laser parameters. In the second case, the energy of the incoming photon in the rest frame of the nucleus is less than and close to the electron-positron pair production threshold. The presence of the laser field allows for the pair production process and the obtained electron-positron rate is much larger than in the presence of only the laser and the nuclear field. In both cases we have observed a strong dependence of the rate on the mutual polarization of the laser field and of the high-energy photon and the most favorable configuration is with laser field and high-energy photon linearly polarized in the same direction. The effects discussed are in principle measurable with presently available proton accelerators and laser systems.Comment: 21 pages, 4 figure

Low field magnetotransport in strained Si/SiGe cavities

Low field magnetotransport revealing signatures of ballistic transport effects in strained Si/SiGe cavities is investigated. We fabricated strained Si/SiGe cavities by confining a high mobility Si/SiGe 2DEG in a bended nanowire geometry defined by electron-beam lithography and reactive ion etching. The main features observed in the low temperature magnetoresistance curves are the presence of a zero-field magnetoresistance peak and of an oscillatory structure at low fields. By adopting a simple geometrical model we explain the oscillatory structure in terms of electron magnetic focusing. A detailed examination of the zero-field peak lineshape clearly shows deviations from the predictions of ballistic weak localization theory.Comment: Submitted to Physical Review B, 25 pages, 7 figure

Barrier control in tunneling e^+ e^- photoproduction

Tunneling electron-positron pair production is studied in a new setup in which a strong low-frequency and a weak high-frequency laser field propagate in the same direction and collide head-on with a relativistic nucleus. The electron-positron pair production rate is calculated analytically in the limit in which in the nucleus rest frame the strong field is undercritical and the frequency of the weak field is below and close to the pair production threshold. By changing the frequency of the weak field one can reduce the tunneling barrier substantially. As a result tunneling pair production is shown to be observable with presently available technology.Comment: 4 pages, 3 figure

Biodiversity in Metal-Contaminated Sites – Problem and Perspective – A Case Study

Summary 1. Introduction. 1.1 Biodiversity in metal-contaminated sites. 1.2 Selecting native fungi and plants for bioremediation. 2. Case study \u2013 Multidisciplinary investigations on biodiversity into a sulphide-rich waste-rock dump. Conclusion: The enormous potential of native fungi and plants that are able to colonize metal-contaminated soils need to be studied in-depth in order to preserve the natural genetic resources of metalliferous habitats and to increase our basic knowledge about the natural adaptation mechanisms of hyperaccumulators in order to employ them in phytoremediation purposes

Light diffraction by a strong standing electromagnetic wave

The nonlinear quantum interaction of a linearly polarized x-ray probe beam with a focused intense standing laser wave is studied theoretically. Because of the tight focusing of the standing laser pulse, diffraction effects arise for the probe beam as opposed to the corresponding plane wave scenario. A quantitative estimate for realistic experimental conditions of the ellipticity and the rotation of the main polarization plane acquired by the x-ray probe after the interaction shows that the implementation of such vacuum effects is feasible with future X-ray Free Electron Laser light.Comment: 5 pages, 2 figures. Published versio

Quale analisi cefalometrica per la chirurgia maxillo-mandibolare in pazienti con sindrome delle apnee ostruttive notturne?

L’avanzamento maxillo-mandibolare (AMM) è un trattamento efficace per pazienti affetti da sindrome delle apnee ostruttive notturne (OSAS) di grado severo. Sebbene il miglioramento dell’OSAS sia l’obiettivo principale di tale chirurgia, è necessario evitare un avanzamento maxillo-mandibolare eccessivo per garantire un gradevole risultato in termini di estetica facciale. A tale scopo, è necessario programmare preoperatoriamente l’entità dell’AMM mediante un’analisi estetica e cefalometrica. Le analisi cefalometriche di Steiner e Delaire vengono comunemente impiegate nella programmazione della chirurgia ortognatica per deformità dentofaciali, tuttavia resta controverso il ruolo di tali analisi nei pazienti con OSAS candidati a AMM. Quarantotto pazienti con OSAS severa sono stati sottoposti a AMM. Abbiamo effettuato le analisi cefalometriche di Steiner e Delaire in tutti i soggetti. Per il tracciato di Steiner, abbiamo misurato la variazione degli angoli SNA e SNB, mentre per l’analisi di Delaire, abbiamo misurato la variazione degli angoli C3/FM-CPA e C3/ FM-Me. L’AMM medio è stato di 6,9 + 3,8 mm per il mascellare superiore e 13,6 + 5 mm per la mandibola. Dopo l’intervento abbiamo riscontrato un miglioramento dell’Indice di Apnea-Ipopnea (40,47 + 7,64 preoperatoriamente vs. 12,56 + 5,78 postoperatoriamente). In tutti i pazienti, entrambe le tecniche cefalometriche hanno dimostrato una retrusione bimascellare preoperatoria. Dopo l’intervento, l’angolo SNA medio è aumentato da 78,18° a 85,58° (p < 0,001), mentre l’angolo C3/FM-CPA medio è aumentato da 81,19° a 89,71° (p < 0,001). Il valore medio dell’angolo SNB è aumentato da 74,33° a 80,73° (p < 0,001), mentre l’angolo medio C3/FM-CPA è passato da 80,10° a 87,29° (p < 0,001). Postoperatoriamente, sia il mascellare superiore che la mandibola risultavano in una posizione più protrusa (p < 0,001) se analizzati secondo l’analisi di Steiner rispetto al tracciato di Delaire. L’utilizzo dell’analisi cefalometrica di Delaire nella programmazione dell’AMM in pazienti con OSAS comporta un avanzamento maxillo-mandibolare superiore rispetto al tracciato di Steiner. È opportuno considerare le conseguenze di tale risulto sull’estetica facciale durante la programmazione chirurgica e nel consenso informato preoperatorio in pazienti con OSAS candidati a AMM

Hydraulic characterization of the full scale mock-up of the demo divertor outer vertical target

In the frame of the pre-conceptual design activities of the DEMO work package DIV-1 “Divertor Cassette Design and Integration” of the EUROfusion program, a mock-up of the divertor outer vertical target (OVT) was built, mainly in order to: (i) demonstrate the technical feasibility of manufacturing procedures; (ii) verify the hydraulic design and its capability to ensure a uniform and proper cooling for the plasma facing units (PFUs) with an acceptable pressure drop; and (iii) experimentally validate the computational fluid-dynamic (CFD) model developed by the University of Palermo. In this context, a research campaign was jointly carried out by the University of Palermo and ENEA to experimentally and theoretically assess the hydraulic performances of the OVT mock-up, paying particular attention to the coolant distribution among the PFUs and the total pressure drop across the inlet and outlet sections of the mock-up. The paper presents the results of the steady-state hydraulic experimental test campaign performed at ENEA Brasimone Research Center as well as the relevant numerical analyses performed at the Department of Engineering at the University of Palermo. The test facility, the experimental apparatus, the test matrix and the experimental results, as well as the theoretical model, its assumptions, and the analyses outcomes are herewith reported and critically discussed