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Nizhniy Novgorod, Russia

Pukhov A.,Heinrich Heine University Dusseldorf | An der Brugge D.,Heinrich Heine University Dusseldorf | Kostyukov I.,Institute for Applied Physics
Plasma Physics and Controlled Fusion | Year: 2010

We consider here a few options to use relativistic laser plasmas for novel sources of short wavelength radiation. Electrons accelerated in underdense plasmas in the bubble regime wiggle in an ion channel. This leads to broadband incoherent synchrotron-like radiation bursts which are of femtosecond duration. The photon energies are in the kiloelectronvolt to megaelectronvolt energy range. However, this radiation is not coherent. To reach coherency, the electron bunch must have structure at the wavelength of the emitted x-rays. This can be achieved in principle by sending the laser-accelerated electron bunch through an external wiggler. However, to reach free electron lasing in the x-ray regime, the energy spread of the laser-accelerated electrons must be reduced dramatically. Another option is to use high harmonic generation at overdense plasma boundaries. The high harmonics are emitted in coherent subfemtosecond flashes. The harmonic spectra decay as a power of the harmonic number, with an exponent that can be as low as -6/5. This can make the high harmonics potentially the brightest laser-driven short wavelength sources with unique properties. © 2010 IOP Publishing Ltd. Source


Henkel C.,Max Planck Institute for Radio Astronomy | Menten K.M.,Max Planck Institute for Radio Astronomy | Murphy M.T.,Swinburne University of Technology | Flambaum V.V.,University of New South Wales | And 4 more authors.
12th Marcel Grossmann Meeting on Recent Dev. in Theoretical and Experimental General Relativity, Astrophysics and Relativistic Field Theories - Proc. of the MG 2009 Meeting on General Relativity | Year: 2012

Observing inversion lines of ammonia (NH3), complemented by rotational lines of NH3 and other molecular species, provides stringent constraints on potential variations of the proton-to-electron mass ratio, μ. While a limit of |Δμ|/μ 10-6 is derived for a lookback time of 7×109 yr, nearby dark clouds might show a significant variation of order (2-3)×10-8, possibly being related to chameleon fields. The detection of radioloud quasars with strong molecular absorption lines at redshifts z > 1 as well as the identification of a larger sample of nearby molecular clouds with exceptionally narrow lines (ΔV < 0.2kms-1) would be essential to improve present limits and to put the acquired results onto a firmer statistical basis. Copyright © 2012 by World Scientific Publishing Co. Pte. Ltd. Source


Levshakov S.A.,Physical Technical Institute | Molaro P.,National institute for astrophysics | Kozlov M.G.,RAS Petersburg Nuclear Physics Institute | Lapinov A.V.,Institute for Applied Physics | And 4 more authors.
Astrophysics and Space Science Proceedings | Year: 2011

Using the 32-m Medicina, 45-m Nobeyama, and 100-m Effelsberg telescopes we found a statistically significant velocity offset ΔV ≈ 27±3 m s-1 .1σ;/between the inversion transition in NH 3(1,1) and low-J rotational transitions in N2H +(1-0) and HC3N(2-1) arising in cold and dense molecular cores in the Milky Way. Systematic shifts of the line centers caused by turbulent motions and velocity gradients, possible non-thermal hyperfine structure populations, pressure and optical depth effects are shown to be lower than or about 1 m s-1 and thus can be neglected in the total error budget. The reproducibility of ΔV at the same facility (Effelsberg telescope) on a year-to-year basis is found to be very good. Since the frequencies of the inversion and rotational transitions have different sensitivities to variations in μ ≡ me/mp, the revealed non-zero ΔV may imply that μ changes when measured at high (terrestrial) and low (interstellar)matter densities as predicted by chameleonlike scalar field models - candidates to the dark energy carrier. Thus we are testing whether scalar field models have chameleon-type interactions with ordinary matter. The measured velocity offset corresponds to the ratio Δμ/μ≡.(μspace - μ lab)/ μlab of .(26±3)×10-9 (1σ;). © Springer-Verlag Berlin Heidelberg 2011. Source


Levshakov S.A.,National institute for astrophysics | Levshakov S.A.,RAS Ioffe Physical - Technical Institute | Molaro P.,National institute for astrophysics | Lapinov A.V.,Institute for Applied Physics | And 3 more authors.
Astronomy and Astrophysics | Year: 2010

Aims. We probe the dependence of the electron-to-proton mass ratio, ì = me/mp, on the ambient matter density by means of radio astronomical observations. Methods. The ammonia method, which has been proposed to explore the electron-to-proton mass ratio, is applied to nearby dark clouds in the Milky Way. This ratio, which is measured in different physical environments of high (terrestrial) and low (interstellar) densities of baryonic matter is supposed to vary in chameleon-like scalar field models, which predict strong dependences of both masses and coupling constant on the local matter density. High resolution spectral observations of molecular cores in lines of NH3 (J, K) = (1, 1), HC3N J = 2.1, and N2H+ J = 1.0 were performed at three radio telescopes to measure the radial velocity offsets, ΔV. Vrot. Vinv, between the inversion transition of NH3 (1,1) and the rotational transitions of other molecules with different sensitivities to the parameter Δμ/μ. (μobs. μlab)/μlab. Results. The measured values of ΔV exhibit a statistically significant velocity offset of 23 ± 4stat ± 3sys m s.1. When interpreted in terms of the electron-to-proton mass ratio variation, this infers that Δμ/μ = (2.2 ± 0.4stat ± 0.3sys) × 10-8. If only a conservative upper bound is considered, then the maximum offset between ammonia and the other molecules is |ΔV| ≤ 30 m s-1. This provides the most accurate reference point at z = 0 for Δμ/μ of |Δμ/μ| ≤ 3 × 10.8. Source


Danilchenko S.N.,Institute for Applied Physics | Kalinkevich O.V.,Institute for Applied Physics | Kuznetsov V.N.,Institute for Applied Physics | Kalinkevich A.N.,Institute for Applied Physics | And 5 more authors.
Crystal Research and Technology | Year: 2010

Composite biomaterials based on chitosan and calcium apatite with different chitosan/apatite ratio were prepared by chemical synthesis of apatite in chitosan solution using one-step co-precipitation method. Initial and annealed samples were characterized by X-ray diffraction, FTIR spectroscopy and scanning electron microscopy coupled to energy-dispersive electron X-ray spectroscopy. The data obtained suggest that the formation of the calcium-phosphate mineral in chitosan solution is substantially modulated by the chemical interaction of the components; apparently, a part of calcium is captured by chitosan and does not participate in the formation of the main mineral phase. The apatite in the composite is calcium-deficient, carbonatesubstituted and is composed of dispersed nano-sized crystallites, i.e. has properties that closely resemble those of bone mineral. Varying synthesis, drying and lyophilization conditions, the composite materials can be produced with the desirable chitosan/apatite ratio, both in the dense and porous form. The structural analysis of composite samples after annealing at certain temperatures is examined as an approach to elucidate the mechanism of co-precipitation by one-step method. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

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