Piecewise acceleration of electrons across a periodic solid-state structure irradiated by intense laser pulse

Three-dimensional particle-in-cell simulations show that the periodic solid-state structures irradiated by intense ($\sim 10^{19}$ W/cm${}^2$) laser pulses can generate collimated electron bunches with energies up to 30 MeV (and acceleration gradient of $11.5$ GeV/cm), if the microstructure period is equal to the laser wavelength. A one-dimensional model of piecewise acceleration in the microstructure is proposed and it is in a good agreement with the results of numerical simulations. It shows that the acceleration process for relativistic electrons can be theoretically infinite. In the simulations, the optimal target parameters (the width of the microstructure elements and the microstructure period) are determined. The explored parameters can be used for proof-of-principle experiments demonstrating an ultrahigh gradient acceleration by a number of identical and mutually coherent laser pulses [A. Pukhov et al., Eur. Phys. J. Spec. Top. 223, 1197 (2014)]

In situ dating and investigation of remarkably depleted –27.3‰ SMOW “Slushball” Earth zircons

Paleoproterozoic amphibolites and gneisses - that are remarkably depleted in ^(18)O are found in the Belomorian Belt in Karelia, Russia [1,2]. We mapped their extent to exceed 200x20km and affect metamorphosed mafic intrusions (est. ~2.4 Ga intrusion age) and host 2.6Ga gneisses found in this 1.9 Ga collisional belt. δ^(18)O values of –7 to –27.3‰ characterize minerals and rocks from several of these localities; some of these rocks are also remarkably depleted with respect to δD (-212 to –235‰ amphiboles). All have typical terrestrial Δ^(17)O values of 0‰. Based on previous paleogeographic reconstructions, we attribute the origin of these exotic O and H isotope compositions to the hydrothermal alteration associated with subglacial rifting during the Paleoproterozoic panglobal ice ages, but discuss additional possibilities: extremely low-δ^(18)O Paleo- proterozoic sea water, and excursion of Karelia to polar latitudes. Given that at high-T hydrothermal exchange equilibrium Δ^(18)O(rockwater) is close to zero, but water-rock interaction is rarely 100% efficient, the lowest measured δ^(18)O value in silicates likely gives the upper δ^(18)O bound for the altering meteoric fluid; we thus continues our quest to find the lowest δ^(18)O material such as a mineral assemblage or a tiny zircon fragment that would provide record of δ^(18)Owater

The control system of synchronous movement of the gantry crane supports

The paper presents study findings on synchronization of the gantry crane support movement. Asynchrony moving speed bearings may lead to an emergency mode at the natural rate of deformed metal structure alignment. The use of separate control of asynchronous motors with the vector control method allows synchronizing the movement speed of crane supports and achieving a balance between the motors. Simulation results of various control systems are described. Recommendations regarding the system further application are given

Comparative study of the structural-phase state and mechanical properties of Ni-Cr(X) and Fe-Cr(X) heat-resistant alloys fabricated by additive technologies

Comparative studies of peculiarities of the formation, thermal stability of the structure, and mechanical properties of heat-resistant alloys based on iron and nickel and fabricated using additive technologies (ATs) by laser metal deposition and selective laser melting are performed. It is established that a cellular structure is formed in alloys fabricated by the laser metal deposition and small pores up to 200 nm in size are present. The structure of alloys fabricated by selective laser melting contains elements with a globular and lamellar morphology and incompletely melted regions, as well as large pores on the order of 5 μm in size. The possibility of manifestation of the nanophase hardening effect due to the presence of nanodimensional particles of chromium silicides is show

Performance of ALICE AD modules in the CERN PS test beam

Two modules of the AD detector have been studied with the test beam at the T10 facility at CERN. The AD detector is made of scintillator pads read out by wave-length shifters (WLS) coupled to clean fibres that carry the produced light to photo-multiplier tubes (PMTs). In ALICE the AD is used to trigger and study the physics of diffractive and ultra-peripheral collisions as well as for a variety of technical tasks like beam-gas background monitoring or as a luminometer. The position dependence of the modules' efficiency has been measured and the effect of hits on the WLS or PMTs has been evaluated. The charge deposited by pions and protons has been measured at different momenta of the test beam. The time resolution is determined as a function of the deposited charge. These results are important ingredients to better understand the AD detector, to benchmark the corresponding simulations, and very importantly they served as a baseline for a similar device, the Forward Diffractive Detector (FDD), being currently built and that will be in operation in ALICE during the LHC Runs 3 and 4.Peer reviewe

Global baryon number conservation encoded in net-proton fluctuations measured in Pb–Pb collisions at √sNN = 2.76 TeV

Experimental results are presented on event-by-event net-proton fluctuation measurements in Pb–Pb collisions at √SNN=2.76 TeV, recorded by the ALICE detector at the CERN LHC. These measurements have as their ultimate goal an experimental test of Lattice QCD (LQCD) predictions on second and higher order cumulants of net-baryon distributions to search for critical behavior near the QCD phase boundary. Before confronting them with LQCD predictions, account has to be taken of correlations stemming from baryon number conservation as well as fluctuations of participating nucleons. Both effects influence the experimental measurements and are usually not considered in theoretical calculations. For the first time, it is shown that event-by-event baryon number conservation leads to subtle long-range correlations arising from very early interactions in the collisions.publishedVersio