155 research outputs found
Relativistic spherical plasma waves
Tightly focused laser pulses as they diverge or converge in underdense plasma
can generate wake waves, having local structures that are spherical waves. Here
we report on theoretical study of relativistic spherical wake waves and their
properties, including wave breaking. These waves may be suitable as particle
injectors or as flying mirrors that both reflect and focus radiation, enabling
unique X-ray sources and nonlinear QED phenomena.Comment: 6 pages; 4 figure
Laser-driven high-power X- and gamma-ray ultra-short pulse source
A novel ultra-bright high-intensity source of X-ray and gamma radiation is
suggested. It is based on the double Doppler effect, where a relativistic
flying mirror reflects a counter-propagating electromagnetic radiation causing
its frequency multiplication and intensification, and on the inverse double
Doppler effect, where the mirror acquires energy from an ultra-intense
co-propagating electromagnetic wave. The role of the flying mirror is played by
a high-density thin plasma slab accelerating in the radiation pressure dominant
regime. Frequencies of high harmonics generated at the flying mirror by a
relativistically strong counter-propagating radiation undergo multiplication
with the same factor as the fundamental frequency of the reflected radiation,
approximately equal to the quadruple of the square of the mirror Lorentz
factor.Comment: 8 pages, 5 figures. Presented at the ELI Workshop and School on
"Fundamental Physics with Ultra-High Fields" 29.09.-02.10.2008, in
Frauenworth Monastery, Bavaria, German
Atomic and electronic structure of a copper/graphene interface as prepared and 1.5 years after
We report the results of X-ray spectroscopy and Raman measurements of
as-prepared graphene on a high quality copper surface and the same materials
after 1.5 years under different conditions (ambient and low humidity). The
obtained results were compared with density functional theory calculations of
the formation energies and electronic structures of various structural defects
in graphene/Cu interfaces. For evaluation of the stability of the carbon cover,
we propose a two-step model. The first step is oxidation of the graphene, and
the second is perforation of graphene with the removal of carbon atoms as part
of the carbon dioxide molecule. Results of the modeling and experimental
measurements provide evidence that graphene grown on high-quality copper
substrate becomes robust and stable in time (1.5 years). However, the stability
of this interface depends on the quality of the graphene and the number of
native defects in the graphene and substrate. The effect of the presence of a
metallic substrate with defects on the stability and electronic structure of
graphene is also discussed.Comment: 18 pages, 6 figures, accepted to Appl. Surf. Sc
Study of the structure of crater at the surface of 12Cr18Ni10Ti steel irradiated by high-power pulsed ion beam
The topography of surface layers of 12Cr18Ni10Ti (AISI 321) steel after pulsed high-power Cn+ ion beams irradiation was investigated by scanning electron microscopy. A thin foil was prepared from the cross section of a crater with the use of a focused ion beam in the column of a two-beam electron-ion microscope. The microstructure and chemical composition of the crater were studied by transmission electron microscop
On the design of experiments to study extreme field limits
We propose experiments on the collision of high intensity electromagnetic
pulses with electron bunches and on the collision of multiple electromagnetic
pulses for studying extreme field limits in the nonlinear interaction of
electromagnetic waves. The effects of nonlinear QED will be revealed in these
laser plasma experiments.Comment: 7 pages, 3 figures, 1 table; 15th Advanced Accelerator Concepts
Workshop (AAC 2012), Austin, Texas, 10-15 June, 201
Test determinations of paleointensity in historical lavas of Kamchatka
© 2017, Pleiades Publishing, Ltd.The reliability of the Thellier method for determining the paleointensity of a geomagnetic field is explored on recent igneous rocks of Kamchatka. The main magnetic mineral in the studied rocks is titanomagnetite with different degree of oxidation. It is obtained that the reliability of the results can be assessed based on the deviations of the check points of the partial thermoremanent magnetization (pTRM) during the Thellier experiment. Besides, for different rocks, it is found that the stability of titanomagnetites to heating during the experiments can be insufficient for validating the reliability of the results of paleointensity determination; however, at the same time, the reliability may depend on the initial (oxidation) state of the magnetic minerals of the studied rocks
CuO-CeO2 nanocomposite catalysts produced by mechanochemical synthesis
Mechanochemical synthesis based on ball-milling of individual oxides was applied as a one-step preparation technique for CuO-CeO2 catalyst for preferential CO oxidation in H2 excess. The mechanical energy dose transferred to the original powder mixture determines both the catalyst composition and activity. It is found that after 90 min of milling (corresponding to a dose of 372 kJ mol-1), a mixture of 10 wt.% CuO-CeO2 powder exhibits a CO conversion of 97% at 423 K. Four active oxygen states, which are not observed in case of pure CeO2, were detected in the nanocomposite lattice and attributed to the presence of Cu in surface sites as well as in subsurface bulk sites of CeO2, in nearest neighbor and next nearest neighbor positions. Correspondingly, oxidation of CO to CO2 was found to occur in a two-stage process with Tmax = 395/460 K, and oxidation of H2 to H2O likewise in a four-stage process with Tmax = 426/448/468/516 K. The milled powder consists of CeO2 crystallites sized 8-10 nm agglomerated to somewhat larger aggregates, with CuO dispersed on the surface of the CeO2 crystallites, and to a lesser extent present as Cu2O. © 2019 Author(s).This work was partially supported by Russian Foundation for Basic Research [Projects n.n. 16-03-00330a and 16-03-00178a] in theoretical studies and part of experimental research and by FASO [program no. AAAA-A18-118012390374-3]. XPS measurements were supported by FASO (Theme “Electron”). The Alexander von Humboldt foundation is gratefully acknowledged for funding. We also would like to thank N. Berezkina for SEM measurements. We acknowledge support by the Open Access Publication Funds of the Göttingen University. Declarations of interest: none
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