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Search Results: 1 - 10 of 256540 matches for " V. B. Filippov "
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Wire GEM detector
B. M. Ovchinnikov,V. I. Razin,A. I. Reshetin,S. N. Filippov
Physics , 2009,
Abstract: A wire GEM (WGEM) detector with a gas gap between meshes was constructed. The detector provides the amplification 5x10E5 for the gas mixture of Ar +20% CO2 at atmospheric pressure. As compared with well-known GEM detectors produced by perforation the plastic plate metalized on both sides the WGEM does not suffer from breakdowns between its electrodes and the effect of accumulation of charges on holes walls is absent. As a result the WGEM has high reliability and stability.
RETGEM with polyvinylchloride (PVC) electrodes
V. I. Razin,B. M. Ovchinnikov,A. I. Reshetin,S. N. Filippov
Physics , 2009,
Abstract: This paper presents a new design of the RETGEM (Resistive Electrode Thick GEM) based on electrodes made of a polyvinylchloride material (PVC). Our device can operate with gains of 10E5 as a conventional TGEM at low counting rates and as RPC in the case of high counting rates without of the transit to the violent sparks. The distinct feature of present RETGEM is the absent of the metal coating and lithographic technology for manufacturing of the protective dielectric rms. The electrodes from PVC permit to do the holes by a simple drilling machine. Detectors on a RETGEM basis could be useful in many fields of an application requiring a more cheap manufacturing and safe operation, for example, in a large neutrino experiments, in TPC, RICH systems.
Observation of Kink Instability as Driver of Recurrent Flares in AR 10960
A. K. Srivastava,Pankaj Kumar,T. V. Zaqarashvili,B. P. Filippov,M. L. Khodachenko,Wahab Uddin
Physics , 2011,
Abstract: We study the active region NOAA 10960, which produces two flare events (B5.0, M8.9) on 04 June 2007. We find the observational signature of right handed helical twists in the loop system associated with this active region. The first B5.0 flare starts with the activation of helical twist showing ~3 turns. However, after ~20 minutes another helical twist (with ~2 turns) appears, which triggers M8.9 flare. Both helical structures were closely associated with a small positive polarity sunspot in the AR. We interpret these observations as evidence of kink instability, which triggers the recurrent solar flares.
Specific heat, magnetic susceptibility, resistivity and thermal expansion of the superconductor ZrB12
R. Lortz,Y. Wang,S. Abe,C. Meingast,Yu. B. Paderno,V. Filippov,A. Junod
Physics , 2005, DOI: 10.1103/PhysRevB.72.024547
Abstract: In an attempt to clarify conflicting published data, we report new measurements of specific heat, resistivity, magnetic susceptibility, and thermal expansivity up to room temperature for the 6 K superconductor ZrB12, using well-characterized single crystals with a residual resistivity ratio >9. The specific heat gives the bulk result 2*delta(0)/(k_B*Tc)=3.7 for the superconducting gap ratio, and excludes multiple gaps and d-wave symmetry for the Cooper pairs. The Sommerfeld constant gamma_n = 0.34 mJ K-2 gat-1 and the magnetic susceptibility xsi = -2.1 x 10^-5 indicate a low density of states at the Fermi level. The Debye temperature theta_D is in the range 1000-1200 K near zero and room temperature, but decreases by a factor of ~2 at ~35 K. The specific heat and resistivity curves are inverted to yield approximations of the phonon density of states F(omega) and the spectral electron-phonon scattering function alpha_tr^2 F(omega), respectively. Both unveil a 15 meV mode, attributed to Zr vibrations in oversized B cages, which gives rise to electron-phonon coupling. The thermal expansivity further shows that this mode is anharmonic, while the vanishingly small discontinuity at Tc establishes that the cell volume is nearly optimal with respect to Tc.
Study of the Electric Explosion of Titanium Foils in Uranium Salts  [PDF]
Leonid I. Urutskoev, Dmitry V. Filippov
Journal of Modern Physics (JMP) , 2010, DOI: 10.4236/jmp.2010.14034
Abstract: The results of experiments on electroexplosion titanic foil in water solutions of salts of uranium are presented in this paper. It is shown, that as a result of electroexplosion occurs appreciable (to 20%) distortion of an initial isotope parity of uranium. In the most solution parts, observable isotope distortion occurs in favour of enrichment by 235U. At the moment of electroexplosion it was not observed an appreciable stream of the neutrons. By means of Cs label and by methods by α, β, γ-spectrometry and mass-spectrometry it have been shown, that isotope distortion occurs at the expense of non-uniform “disappearance” of both isotopes from a solution. The isotope distortion leads to infringement of the 234Th secular equilibrium in the uranyl solution. The equilibrium infringement between the 234Th and 234mPa, i.e. within the proper thorium decay chain, was observed also. The assumption about that the effects are caused of low-energy nuclear reactions at the moment of electroexplosion is suggested.
A Challenging Solar Eruptive Event of 18 November 2003 and the Causes of the 20 November Geomagnetic Superstorm. I. Unusual History of an Eruptive Filament
V. V. Grechnev,A. M. Uralov,V. A. Slemzin,I. M. Chertok,B. P. Filippov,G. V. Rudenko,M. Temmer
Physics , 2013, DOI: 10.1007/s11207-013-0316-6
Abstract: This is the first of four companion papers, which analyze a complex eruptive event of 18 November 2003 in AR 10501 and the causes of the largest Solar Cycle 23 geomagnetic storm on 20 November 2003. Analysis of a complete data set, not considered before, reveals a chain of eruptions to which hard X-ray and microwave bursts responded. A filament in AR 10501 was not a passive part of a larger flux rope, as usually considered. The filament erupted and gave origin to a CME. The chain of events was as follows: i) an eruption at 07:29 accompanied by a not reported M1.2 class flare associated with the onset of a first southeastern CME1, which is not responsible for the superstorm; ii) a confined eruption at 07:41 (M3.2 flare) that destabilized the filament; iii) the filament acceleration (07:56); iv) the bifurcation of the eruptive filament that transformed into a large cloud; v) an M3.9 flare in AR 10501 associated to this transformation. The transformation of the filament could be due to its interaction with the magnetic field in the neighborhood of a null point, located at a height of about 100 Mm above the complex formed by ARs 10501, 10503, and their environment. The CORONAS-F/SPIRIT telescope observed the cloud in 304 A as a large Y-shaped darkening, which moved from the bifurcation region to the limb. The masses and kinematics of the cloud and the filament were similar. Remnants of the filament were not observed in the second southwestern CME2, previously regarded as a source of the 20 November superstorm. These facts do not support a simple scenario, in which the interplanetary magnetic cloud is considered as a flux rope formed from a structure initially associated with the pre-eruption filament in AR 10501. Observations suggest a possible additional eruption above the bifurcation region close to solar disk center between 08:07 and 08:17 that could be the source of the superstorm.
Optical properties and electronic structure of ZrB$_{12}$
J. Teyssier,A. B. Kuzmenko,D. van der Marel,F. Marsiglio,A. B. Liashchenko,V. Filippov,N. Shitsevalova
Physics , 2006, DOI: 10.1103/PhysRevB.75.134503
Abstract: We report optical (6 meV - 4 eV) properties of a boride superconductor ZrB$_{12}$ ($T_c$ = 6 K) in the normal state from 20 to 300 K measured on high-quality single crystals by a combination of reflectivity and ellipsometry. The Drude plasma frequency and interband optical conductivity calculated by self-consistent full-potential LMTO method agree well with experimental data. The Eliashberg function $\alpha_{tr}^2F(\omega)$ extracted from optical spectra features two peaks at about 25 and 80 meV, in agreement with specific heat data. The total coupling constant is $\lambda_{tr}=1.0\pm0.35$. The low energy peak presumably corresponds to the displacement mode of Zr inside $B_{24}$ cages, while the second one involves largely boron atoms. In addition to the usual narrowing of the Drude peak with cooling down, we observe an unexpected removal of about 10 % of the Drude spectral weight which is partially transferred to the region of the lowest-energy interband transition ($\sim$ 1 eV). This effect may be caused by the delocalization of the metal ion from the center of the $B_{24}$ cluster.
A Challenging Solar Eruptive Event of 18 November 2003 and the Causes of the 20 November Geomagnetic Superstorm. IV. Unusual Magnetic Cloud and Overall Scenario
V. V. Grechnev,A. M. Uralov,I. M. Chertok,A. V. Belov,B. P. Filippov,V. A. Slemzin,B. V. Jackson
Physics , 2014, DOI: 10.1007/s11207-014-0596-5
Abstract: The geomagnetic superstorm of 20 November 2003 with Dst = -422 nT, one of the most intense in history, is not well understood. The superstorm was caused by a moderate solar eruptive event on 18 November, comprehensively studied in our preceding Papers I-III. The analysis has shown a number of unusual and extremely complex features, which presumably led to the formation of an isolated right-handed magnetic-field configuration. Here we analyze the interplanetary disturbance responsible for the 20 November superstorm, compare some of its properties with the extreme 28-29 October event, and reveal a compact size of the magnetic cloud (MC) and its disconnection from the Sun. Most likely, the MC had a spheromak configuration and expanded in a narrow angle of < 14 degree. A very strong magnetic field in the MC up to 56 nT was due to the unusually weak expansion of the disconnected spheromak in an enhanced-density environment constituted by the tails of the preceding ICMEs. Additional circumstances favoring the superstorm were (i) the exact impact of the spheromak on the Earth's magnetosphere and (ii) the almost exact southward orientation of the magnetic field, corresponding to the original orientation in its probable source region near the solar disk center.
Magnetic reconnection processes induced by a CME expansion
B. Filippov,S. Koutchmy
Annales Geophysicae (ANGEO) , 2008,
Abstract: A close association between eruptive prominences and CMEs, both slow and fast CMEs, was reported in many studies. Sometimes it was possible to follow the material motion starting from the prominence (filament) activation to the CME in the high corona. Remnants of the prominence were found in the bright core of the CME. However, detailed comparisons of the two phenomena reveal problems in explaining CMEs as a continuation of filament eruptions in the upper corona. For example, the heliolatitudes of the disappeared filaments and subsequent coronal ejections sometimes differ by tens of degrees. In order to clear up the problems appearing when considering this association EP-CME, we tentatively analyse the more general question of the dynamics of the generic magnetic flux rope. Prominences and filaments are the best tracers of the flux ropes in the corona long before the beginning of the eruption. A twisted flux rope is held by the tension of field lines of photospheric sources until parameters of the system reach critical values and a catastrophe happens. We suggest that the associated flux rope height above the photosphere is one of these parameters and that it is revealed by the measured height of the filament. 80 filaments were analysed and we found that eruptive prominences were near the so-called limit of stability a few days before their eruptions. We suggest that a comparison of actual heights of prominences with the calculated critical heights from magnetograms could be systematically used to predict filament eruptions and the corresponding CMEs.
A Challenging Solar Eruptive Event of 18 November 2003 and the Causes of the 20 November Geomagnetic Superstorm. III. Catastrophe of the Eruptive Filament at a Magnetic Null Point and Formation of an Opposite-Handedness CME
A. M. Uralov,V. V. Grechnev,G. V. Rudenko,I. I. Myshyakov,I. M. Chertok,B. P. Filippov,V. A. Slemzin
Physics , 2014, DOI: 10.1007/s11207-014-0536-4
Abstract: Our analysis in Papers I and II (Grechnev et al., 2014, Solar Phys. 289, 289 and 1279) of the 18 November 2003 solar event responsible for the 20 November geomagnetic superstorm has revealed a complex chain of eruptions. In particular, the eruptive filament encountered a topological discontinuity located near the solar disk center at a height of about 100 Mm, bifurcated, and transformed into a large cloud, which did not leave the Sun. Concurrently, an additional CME presumably erupted close to the bifurcation region. The conjectures about the responsibility of this compact CME for the superstorm and its disconnection from the Sun are confirmed in Paper IV (Grechnev et al., Solar Phys., submitted), which concludes about its probable spheromak-like structure. The present paper confirms the presence of a magnetic null point near the bifurcation region and addresses the origin of the magnetic helicity of the interplanetary magnetic clouds and their connection to the Sun. We find that the orientation of a magnetic dipole constituted by dimmed regions with the opposite magnetic polarities away from the parent active region corresponded to the direction of the axial field in the magnetic cloud, while the pre-eruptive filament mismatched it. To combine all of the listed findings, we come to an intrinsically three-dimensional scheme, in which a spheromak-like eruption originates via the interaction of the initially unconnected magnetic fluxes of the eruptive filament and pre-existing ones in the corona. Through a chain of magnetic reconnections their positive mutual helicity was transformed into the self-helicity of the spheromak-like magnetic cloud.
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