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Search Results: 1 - 10 of 223997 matches for " R. Svoboda "
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The study of triple systems V819 Her, V2388 Oph, and V1031 Ori
P. Zasche,R. Uhlar,P. Svoboda
Physics , 2014,
Abstract: The systems V819 Her, V2388 Oph, and V1031 Ori are triples comprised of an eclipsing binary orbiting with a distant visual component on a longer orbit. A detailed analysis of these interesting systems, combining the two observational techniques: interferometry and apparent period variation, was performed. The interferometric data for these three systems obtained during the last century determine the visual orbits of the distant components in the systems. The combined analysis of the positional measurements together with the analysis of apparent period changes of the eclipsing binary (using the minima timings) can be used to study these systems in a combined approach, resulting in a set of parameters otherwise unobtainable without the radial velocities. The main advantage of the technique presented here is the fact that one needs no spectroscopic monitoring of the visual orbits, which have rather long periods: 5.5 yr for V819 Her, 9.0 yr for V2388 Oph, and 31.3 yr for V1031 Ori, respectively. The eccentricities of the outer orbits are 0.69, 0.33, and 0.92, respectively. Moreover, the use of minima timings of the eclipsing pairs help us to derive the orientation of the orbit in space with no ambiguity around the celestial plane. And finally, the combined analysis yielded also an independent determination of the distance of V819 Her (68.7 +/- 1.8 pc), and V2388 Oph (70.6 +/- 8.9 pc). We also present a list of similar systems, which would be suitable for a combined analysis like this one.
A potential sterile neutrino search utilizing spectral distortion in a two-reactor/one-detector configuration
M. Bergevin,C. Grant,R. Svoboda
Physics , 2013,
Abstract: There is an observed deficit of about 6\% in the expected rate of anti-neutrino interactions when averaging over many different reactor experiments. While the significance of the deficit is low (98.6 \% CL), there is speculation that a non-interacting "sterile" neutrino could be the cause. In this paper we explore the possibility of a two-reactor/one-detector experiment at intermediate distances (100-500 meters) to look for a sterile neutrino in the mass range implied by this deficit. A method for probing $\Delta m^2$ phase space is developed using interference patterns between two oscillated spectra at different baselines. This method is used to investigate the potential sensitivity of the Double Chooz experiment, which has a single Near Detector at distances of 351 m and 465 m from two reactors of identical design. We conclude that Double Chooz could investigate sterile neutrino in the $\Delta m^{2}$ range of 0.002 to 0.5 eV$^2$ over 5 years of near detector running.
GK Boo and AE For: Two low-mass eclipsing binaries with dwarf companions
P. Zasche,P. Svoboda,R. Uhlar
Physics , 2012, DOI: 10.1051/0004-6361/201117417
Abstract: A study of late-type low-mass eclipsing binaries provides us with important information about the most common stars in the Universe. We obtain the first light curves and perform period analyses of two neglected eclipsing binaries GK Boo and AE For to reveal their basic physical properties. We performed both a period analysis of the times of the minima and a BVR light curve analysis. Many new times of minima for both the systems were derived and collected from the data obtained by automatic and robotic telescopes. This allowed us to study the long-term period changes in these systems for the first time. From the light curve analysis, we derived the first rough estimates of the physical properties of these systems. We find that the analyzed systems are somewhat similar to each other. Both contain low-mass components of similar types, both are close to the Sun, both have short orbital period, and both contain another low-mass companions on longer orbits of a few years. In the case of GK Boo, both components are probably of K3 spectral type, while the distant companion is probably a late M star. The light curve of GK Boo is asymmetric, which probably causes the shift in the secondary minima in the O-C diagram. System AE For comprises two K7 stars, and the third body is a possible brown dwarf with a minimal mass of only about 47 Jupiter Mass. We succeed in completing period and light curve analyses of both systems, although a more detailed spectroscopic analysis is needed to confirm the physical parameters of the components to a higher accuracy.
The Potential Regulation of L1 Mobility by RNA Interference
Shane R. Horman,Petr Svoboda,Eline T. Luning Prak
Journal of Biomedicine and Biotechnology , 2006, DOI: 10.1155/jbb/2006/32713
Abstract: The hypothesis that RNA interference constrains L1 mobility seems inherently reasonable: L1 mobility can be dangerous and L1 RNA, the presumed target of RNAi, serves as a critical retrotransposition intermediate. Despite its plausibility, proof for this hypothesis has been difficult to obtain. Studies attempting to link the L1 retrotransposition frequency to alterations in RNAi activity have been hampered by the long times required to measure retrotransposition frequency, the pleiotropic and toxic effects of altering RNAi over similar time periods, and the possibility that other cellular machinery may contribute to the regulation of L1s. Another problem is that the commonly used L1 reporter cassette may serve as a substrate for RNAi. Here we review the L1-RNAi hypothesis and describe a genetic assay with a modified reporter cassette that detects approximately 4 times more L1 insertions than the conventional retrotransposition assay.
The Potential Regulation of L1 Mobility by RNA Interference
Shane R. Horman,Petr Svoboda,Eline T. Luning Prak
Journal of Biomedicine and Biotechnology , 2006,
Abstract: The hypothesis that RNA interference constrains L1 mobility seems inherently reasonable: L1 mobility can be dangerous and L1 RNA, the presumed target of RNAi, serves as a critical retrotransposition intermediate. Despite its plausibility, proof for this hypothesis has been difficult to obtain. Studies attempting to link the L1 retrotransposition frequency to alterations in RNAi activity have been hampered by the long times required to measure retrotransposition frequency, the pleiotropic and toxic effects of altering RNAi over similar time periods, and the possibility that other cellular machinery may contribute to the regulation of L1s. Another problem is that the commonly used L1 reporter cassette may serve as a substrate for RNAi. Here we review the L1-RNAi hypothesis and describe a genetic assay with a modified reporter cassette that detects approximately 4 times more L1 insertions than the conventional retrotransposition assay.
The Feasibility of Fuzzy Sets Utilization in Quantifying the Results of Company Self-evaluation in Accordance With the EFQM Excellence Model
Chodúr Miroslav,Svoboda Ji?í,Pálka P?emysl
Journal of Competitiveness , 2011,
Abstract: This paper elaborates on the possibility of utilizing fuzzy set methods in order to quantify the results of company self-evaluation in accordance with the EFQM model criteria. The general aim is to modify the self-evaluation method from the EFQM model with statistical utilization of fuzzy set methods in order to improve the aggregation of the indicators (criteria) and evaluate the self-evaluation results.
Measurements of cross-sections of (n,xn) threshold reactions in various materials
Vrzalová J.,Svoboda O.,Kugler A.,Suchopár M.
EPJ Web of Conferences , 2012, DOI: 10.1051/epjconf/20122110007
Abstract: Experimental cross-section data for (n,xn) reactions with x higher than four and neutron energies over ~30 MeV are very scarce. We performed seven successful (n,xn) cross-section measurements in two campaigns exploiting the quasi-monoenergetic neutron source at The Svedberg Laboratory in Uppsala, Sweden. Neutron energies from the 7Li(p,n)7Be based source were in the region 22 to 94 MeV. We carried out additional five irradiations with neutron energies from 17 up to 34 MeV using the quasi-monoenergetic neutron source of the Nuclear Physics Institute in e . We have irradiated Al, Au, Bi, I, In, Ta and Y materials in the form of thin foils. We observed good agreement with the few existing experimental data about corresponding cross-sections in EXFOR database and also with the calculations performed in deterministic code TALYS.
Role of emission angular directionality in spin determination of accreting black holes with broad iron line
J. Svoboda,M. Dovciak,R. W. Goosmann,V. Karas
Physics , 2009, DOI: 10.1051/0004-6361/200911941
Abstract: Spin of an accreting black hole can be determined by spectroscopy of the emission and absorption features produced in the inner regions of an accretion disc. We discuss the method employing the relativistic line profiles of iron in the X-ray domain, where the emergent spectrum is blurred by general relativistic effects. Precision of spectra fitting procedure could be compromised by inappropriate account of the angular distribution of the disc emission. Often a unique profile is assumed, invariable over the entire range of radii in the disc and energy in the spectral band. We study how sensitive the spin determination is to the assumptions about the intrinsic angular distribution of the emitted photons. We find that the uncertainty of the directional emission distribution translates to 20% uncertainty in determination of the marginally stable orbit. By assuming a rotating black hole in the centre of an accretion disc, we perform radiation transfer computations of an X-ray irradiated disc atmosphere to determine the directionality of outgoing X-rays in the 2-10 keV energy band. We implemented the simulation results as a new extension to the KY software package for X-ray spectra fitting of relativistic accretion disc models. Although the parameter space is rather complex, leading to a rich variety of possible outcomes, we find that on average the isotropic directionality reproduces our model data to the best precision. Our results also suggest that an improper usage of limb darkening can partly mimic a steeper profile of radial emissivity. We demonstrate these results on the case of XMM-Newton observation of the Seyfert galaxy MCG-6-30-15, for which we construct confidence levels of chi squared statistics, and on the simulated data for the future X-ray IXO mission.
Transparency of 0.2% GdCl3 Doped Water in a Stainless Steel Test Environment
W. Coleman,A. Bernstein,S. Dazeley,R. Svoboda
Physics , 2008, DOI: 10.1016/j.nima.2008.06.049
Abstract: The possibility of neutron and neutrino detection using water Cerenkov detectors doped with gadolinium holds the promise of constructing very large high-efficiency detectors with wide-ranging application in basic science and national security. This study addressed a major concern regarding the feasibility of such detectors: the transparency of the doped water to the ultraviolet Cerenkov light. We report on experiments conducted using a 19-meter water transparency measuring instrument and associated materials test tank. Sensitive measurements of the transparency of water doped with 0.2% GdCl3 at 337nm, 400nm and 420nm were made using this instrument. These measurements indicate that GdCl3 is not an appropriate dopant in stainless steel constructed water Cerenkov detectors.
Observation of Neutrons with a Gadolinium Doped Water Cerenkov Detector
S. Dazeley,A. Bernstein,N. S. Bowden,R. Svoboda
Physics , 2008, DOI: 10.1016/j.nima.2009.03.256
Abstract: Spontaneous and induced fission in Special Nuclear Material (SNM) such as 235U and 239Pu results in the emission of neutrons and high energy gamma-rays. The multiplicities of and time correlations between these particles are both powerful indicators of the presence of fissile material. Detectors sensitive to these signatures are consequently useful for nuclear material monitoring, search, and characterization. In this article, we demonstrate sensitivity to both high energy gamma-rays and neutrons with a water Cerenkov based detector. Electrons in the detector medium, scattered by gamma-ray interactions, are detected by their Cerenkov light emission. Sensitivity to neutrons is enhanced by the addition of a gadolinium compound to the water in low concentrations. Cerenkov light is similarly produced by an 8 MeV gamma-ray cascade following neutron capture on the gadolinium. The large solid angle coverage and high intrinsic efficiency of this detection approach can provide robust and low cost neutron and gamma-ray detection with a single device.
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