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Sökning: WFRF:(Sergeev V. A.)

  • Resultat 1-10 av 44
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  • Soloviev, A. A., et al. (författare)
  • Fast electron generation using PW-class PEARL facility
  • 2011
  • Ingår i: Nuclear Instruments and Methods in Physics Research Section A : Accelerators, Spectrometers, Detectors and Associated Equipment. - Saunders Elsevier. - 0168-9002 .- 1872-9576. ; 653:1, s. 35-41
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>We use a PW-class PEARL facility to study fast electron beam generation during high intensity laser pulse interaction with a supersonic gas jet. We show that electron beams with several hundreds of MeV and relatively large charges, of hundreds of pC and more, can be effectively produced without any guiding structures. PIC simulations also confirm the obtained experimental data and provide optimized conditions of laser–plasma interaction for high-charged beam production.</p>
  • Kann, D. A., et al. (författare)
  • 2010
  • Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 720:2, s. 1513-1558
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>We have gathered optical photometry data from the literature on a large sample of Swift-era gamma-ray burst (GRB) afterglows including GRBs up to 2009 September, for a total of 76 GRBs, and present an additional three pre-Swift GRBs not included in an earlier sample. Furthermore, we publish 840 additional new photometry data points on a total of 42 GRB afterglows, including large data sets for GRBs 050319, 050408, 050802, 050820A, 050922C, 060418, 080413A, and 080810. We analyzed the light curves of all GRBs in the sample and derived spectral energy distributions for the sample with the best data quality, allowing us to estimate the host-galaxy extinction. We transformed the afterglow light curves into an extinction-corrected z = 1 system and compared their luminosities with a sample of pre-Swift afterglows. The results of a former study, which showed that GRB afterglows clustered and exhibited a bimodal distribution in luminosity space, are weakened by the larger sample. We found that the luminosity distribution of the two afterglow samples (Swift-era and pre-Swift) is very similar, and that a subsample for which we were not able to estimate the extinction, which is fainter than the main sample, can be explained by assuming a moderate amount of line-of-sight host extinction. We derived bolometric isotropic energies for all GRBs in our sample, and found only a tentative correlation between the prompt energy release and the optical afterglow luminosity at 1 day after the GRB in the z = 1 system. A comparative study of the optical luminosities of GRB afterglows with echelle spectra (which show a high number of foreground absorbing systems) and those without, reveals no indication that the former are statistically significantly more luminous. Furthermore, we propose the existence of an upper ceiling on afterglow luminosities and study the luminosity distribution at early times, which was not accessible before the advent of the Swift satellite. Most GRBs feature afterglows that are dominated by the forward shock from early times on. Finally, we present the first indications of a class of long GRBs, which form a bridge between the typical high-luminosity, high-redshift events and nearby low-luminosity events (which are also associated with spectroscopic supernovae) in terms of energetics and observed redshift distribution, indicating a continuous distribution overall.</p>
  • Crenshaw, D. M., et al. (författare)
  • Multiwavelength observations of short-timescale variability in NGC 4151. I. Ultraviolet observations
  • 1996
  • Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 470:1, s. 322-335335
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>Presents the results of an intensive ultraviolet monitoring campaign on the Seyfert 1 galaxy NGC 4151, as part of an effort to study its short-timescale variability over a broad range in wavelength. The nucleus of NGC 4151 was observed continuously with the International Ultraviolet Explorer for 9.3 days, yielding a pair of LWP and SWP spectra every ~70 minutes, and during 4 hr periods for 4 days prior to and 5 days after the continuous-monitoring period. The sampling frequency of the observations is an order of magnitude higher than that of any previous UV monitoring campaign on a Seyfert galaxy. The continuum fluxes in bands from 1275 to 2688 Aring went through four significant and well-defined ldquoeventsrdquo of duration 2-3 days during the continuous-monitoring period. The authors find that the amplitudes of the continuum variations decrease with increasing wavelength, which extends a general trend for this and other Seyfert galaxies to smaller timescales (i.e., a few days). The continuum variations in all the UV bands are simultaneous to within an accuracy of ~0.15 days, providing a strict constraint on continuum models. The emission-line light curves show only one major event during the continuous monitoring (a slow rise followed by a shallow dip) and do not correlate well with continuum light curves over the short duration of the campaign, because the timescale for continuum variations is apparently smaller than the response times of the emission lines</p>
  • De Rosa, G., et al. (författare)
  • Velocity-resolved Reverberation Mapping of Five Bright Seyfert 1 Galaxies
  • 2018
  • Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 866:2
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>We present the first results from a reverberation-mapping campaign undertaken during the first half of 2012, with additional data on one active galactic nucleus (AGN) (NGC 3227) from a 2014 campaign. Our main goals are (1) to determine the black hole masses from continuum-H beta reverberation signatures, and (2) to look for velocity-dependent time delays that might be indicators of the gross kinematics of the broad-line region. We successfully measure H beta time delays and black hole masses for five AGNs, four of which have previous reverberation mass measurements. The values measured here are in agreement with earlier estimates, though there is some intrinsic scatter beyond the formal measurement errors. We observe velocity-dependent H beta lags in each case, and find that the patterns have changed in the intervening five years for three AGNs that were also observed in 2007.</p>
  • Khomutov, G.B., et al. (författare)
  • Interfacial nanofabrication strategies in development of new functional nanomaterials and planar supramolecular nanostructures for nanoelectronics and nanotechnology
  • 2003
  • Ingår i: Microelectronic Engineering. - Elsevier. - 1873-5568. ; 69, s. 373-383
  • Tidskriftsartikel (refereegranskat)abstract
    • Clusters, nanoparticles, nanowires, long molecules as nanotubes and polynucleotides, and functional supramolecular nanostructures are currently considered as potential building blocks for nanotechnology and nanoelectronic devices and circuits, and development and introduction of new methods to control effectively their structure, composition and nanoscale organization are necessary. Here we describe a number of new nanofabrication methods which are based on the monolayer techniques, biomimetic principles, interfacial reactions and interactions. The methods allowed to produce new stable reproducible planar one-dimensional and two-dimensional arrays of ligand-stabilized nanoclusters and nanoparticles on solid substrates, ultrathin polymeric nanoscale-ordered mono- and multilayer quasi-crystalline and nanocomposite films, planar polymeric complex films with integrated DNA and inorganic building blocks as semiconductor and iron oxide nanoparticle quasi-linear arrays and nanowires. Transmission electron microscopy, STM and AFM techniques were used to characterize the fabricated nanostructures. Effects related to discrete electron tunneling were observed in the monolayers of nanoclusters and small gold nanoparticles at room temperature using STM.
  • Khomutov, G.B., et al. (författare)
  • Organized planar nanostructures from ligand-stabilized nanoclusters: a route to molecular nanoelectronic devices
  • 2004
  • Ingår i: Applied Surface Science. - Elsevier. - 1873-5584. ; 226, s. 149-154
  • Tidskriftsartikel (refereegranskat)abstract
    • In present work, we describe the formation and deposition of mixed Langmuir monolayers composed of inert amphiphile molecular matrix and guest ligand-stabilized metal-core nanoclusters. Such approach allowed obtaining the ordered stable reproducible planar monolayer and multilayer nanocluster nanostructures on solid substrates. The use of novel polymeric Langmuir monolayers formed by amphiphilic polyelectrolytes and nanoclusters resulted in fabrication of ultimately thin monomolecular nanoscale-ordered stable planar polymeric nanocomposite films. Morphology and electron transport in fabricated nanostructures were studied experimentally using AFM and STM. The perspectives for nanoelectronic applications of organized planar nanostructures from ligand-stabilized nanoclusters are discussed.
  • Varsani, A., et al. (författare)
  • Simultaneous Remote Observations of Intense Reconnection Effects by DMSP and MMS Spacecraft During a Storm Time Substorm
  • 2017
  • Ingår i: Journal of Geophysical Research - Space Physics. - AMER GEOPHYSICAL UNION. - 2169-9380 .- 2169-9402. ; 122:11, s. 10891-10909
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>During a magnetic storm on 23 June 2015, several very intense substorms took place, with signatures observed by multiple spacecraft including DMSP and Magnetospheric Multiscale (MMS). At the time of interest, DMSP F18 crossed inbound through a poleward expanding auroral bulge boundary at 23.5 h magnetic local time (MLT), while MMS was located duskward of 22 h MLT during an inward crossing of the expanding plasma sheet boundary. The two spacecraft observed a consistent set of signatures as they simultaneously crossed the reconnection separatrix layer during this very intense reconnection event. These include (1) energy dispersion of the energetic ions and electrons traveling earthward, accompanied with high electron energies in the vicinity of the separatrix; (2) energy dispersion of polar rain electrons, with a high-energy cutoff; and (3) intense inward convection of the magnetic field lines at the MMS location. The high temporal resolution measurements by MMS provide unprecedented observations of the outermost electron boundary layer. We discuss the relevance of the energy dispersion of the electrons, and their pitch angle distribution, to the spatial and temporal evolution of the boundary layer. The results indicate that the underlying magnetotail magnetic reconnection process was an intrinsically impulsive and the active X-line was located relatively close to the Earth, approximately at 16-18 R-E.</p>
  • Nakamura, R., et al. (författare)
  • Transient, small-scale field-aligned currents in the plasma sheet boundary layer during storm time substorms
  • 2016
  • Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 43:10, s. 4841-4849
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>We report on field-aligned current observations by the four Magnetospheric Multiscale (MMS) spacecraft near the plasma sheet boundary layer (PSBL) during two major substorms on 23 June 2015. Small-scale field-aligned currents were found embedded in fluctuating PSBL flux tubes near the separatrix region. We resolve, for the first time, short-lived earthward (downward) intense field-aligned current sheets with thicknesses of a few tens of kilometers, which are well below the ion scale, on flux tubes moving equatorward/earthward during outward plasma sheet expansion. They coincide with upward field-aligned electron beams with energies of a few hundred eV. These electrons are most likely due to acceleration associated with a reconnection jet or high-energy ion beam-produced disturbances. The observations highlight coupling of multiscale processes in PSBL as a consequence of magnetotail reconnection.</p>
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