Durant M.,University of Florida |
Kargaltsev O.,University of Florida |
Pavlov G.G.,Pennsylvania State University |
Pavlov G.G.,St Petersburg Polytechnical University
Astrophysical Journal | Year: 2011
We report broadband Hubble Space Telescope imaging of the field of soft γ-ray repeater SGR 0418+5729 with Advanced Camera for Surveys/Wide Field Channel and Wide Field Camera 3/IR. Observing in two wide filters, F606W and F110W, we find no counterpart within the positional error circle derived from Chandra observations, to limiting magnitudes m F606W > 28.6 and m F110W > 27.4 (Vega system), equivalent to reddening-corrected luminosity limits L F606W < 5 × 1028 and L F110W < 6 × 1028ergs-1 for a distance d = 2kpc, at 3σ confidence. This, in turn, imposes lower limits on the contemporaneous X-ray/optical flux ratio of ≃1100 and the X-ray/near-infrared flux ratio of ≃1000. We derive an upper limit on the temperature and/or size of any fall-back disk around the magnetar. We also compare the detection limits with observations of other magnetars. © 2011. The American Astronomical Society. All rights reserved.
Durant M.,University of Florida |
Kargaltsev O.,University of Florida |
Pavlov G.G.,Pennsylvania State University |
Pavlov G.G.,St Petersburg Polytechnical University |
And 5 more authors.
Astrophysical Journal | Year: 2012
We present extensive spectral and photometric observations of the recycled pulsar/white dwarf binary containing PSR J0437-4715, which we analyzed together with archival X-ray and gamma-ray data, to obtain the complete mid-infrared to gamma-ray spectrum. We first fit each part of the spectrum separately, and then the whole multi-wavelength spectrum. We find that the optical-infrared part of the spectrum is well fit by a cool white dwarf atmosphere model with pure hydrogen composition. The model atmosphere (T eff = 3950 150K, log g = 6.98 ± 0.15, R WD = (1.9 ± 0.2) × 10 9cm) fits our spectral data remarkably well for the known mass and distance (M = 0.25 ± 0.02 M, d = 156.3 ± 1.3pc), yielding the white dwarf age (τWD = 6.0 ± 0.5Gyr). In the UV, we find a spectral shape consistent with thermal emission from the bulk of the neutron star surface, with surface temperature between 1.25 × 105 and 3.5 × 105K. The temperature of the thermal spectrum suggests that some heating mechanism operates throughout the life of the neutron star. The temperature distribution on the neutron star surface is non-uniform. In the X-rays, we confirm the presence of a high-energy tail which is consistent with a continuation of the cutoff power-law component (Γ = 1.56 ± 0.01, E cut = 1.1 ± 0.2GeV) that is seen in gamma rays and perhaps even extends to the near-UV. © 2012. The American Astronomical Society. All rights reserved.
Zegzhda P.D.,St Petersburg Polytechnical University |
Zegzhda D.P.,St Petersburg Polytechnical University |
Kalinin M.O.,St Petersburg Polytechnical University |
Konoplev A.S.,St Petersburg Polytechnical University
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) | Year: 2012
The paper reviews the security problem with computing and information resources in Grid systems. It discusses security relative characteristics of Grid architecture and provides a common threat model of Grid. It summarizes methods being applied to improve security of Grid systems and discusses their disadvantages. There is proposed the Petri-net-based model of access control for Grid systems. That model enhances Grid security with trusted 'job' submission (in strict accordance with security policy constraints) and verification of the security implementation in Grid systems. © 2012 Springer-Verlag Berlin Heidelberg.
Schrange-Kashenock G.,St Petersburg Polytechnical University
Journal of Physics B: Atomic, Molecular and Optical Physics | Year: 2016
The first theoretical investigation of the inner-shell single-photodetachment from the Si- (1s22s22p63s23p3 4So) negative ion is presented. The partial and total cross sections, the photoelectron phaseshifts, and the parameters of angular anisotropy are calculated in the framework of the many-body theory for L-shell photodetachment from Si- ion in the experimentally accessible range of photon energies (7.5-14 Ry). Comparison is made between the calculations of the response of the ionic many-electron system Si- to an electromagnetic field at the different levels of approximation: the 'frozen-field' random phase approximation with exchange (RPAE), and the static relaxation approximation. The optimal analysis is made when the dynamic relaxation and polarization are included within the Dyson equation method (DEM) simultaneously with the RPAE corrections (the RPAE&DEM approach). It is predicted that the photoexcitation to a resonance state of complex 'shape-Feschbach' nature in the open p-shell reveals itself as a prominent resonance structure in the photodetachment cross sections in the energy range of the 2s and 2p inner shell thresholds similar to that in 1s inner-shell photodetachment from C- (2006 J. Phys. B: At. Mol. Opt. Phys. 39 1379). The photodetachment dynamical characteristics clearly demonstrate the significance of all the considered many-electron correlations within the RPAE&DEM approach, however the total photodetachment cross section is dominated by a strong resonance peak just after the 2s threshold. Dynamical relaxation (screening) is identified as a decisive factor in the formation of this resonance. © 2016 IOP Publishing Ltd.
Kalinin M.O.,St Petersburg Polytechnical University
SIN'10 - Proceedings of the 3rd International Conference of Security of Information and Networks | Year: 2010
Information security is very important nowadays. Every IT system needs protection mechanisms for stability and safety of work. To solve this task, there are proposed a variety of securityproviding solutions, but most of them are very expensive and nonsystematic. The paper discusses up-to-date techniques implemented for security aims and addresses to the technique of security control based on settings monitoring of variable program components of the trusted information environment. There is proposed a formal basis of security control based on finding the security settings which provide the system with stability and integrity. The specified technique allows proposing a schema of dynamic Security and Integrity Control System which provides an automated process of security assurance and management. These security control technique and system extend security-relevant approaches making security reachable, permanent, and effective. Copyright 2010 ACM.
Strocov V.N.,Paul Scherrer Institute |
Petrov V.N.,St Petersburg Polytechnical University |
Dil J.H.,Paul Scherrer Institute |
Dil J.H.,Ecole Polytechnique Federale de Lausanne
Journal of Synchrotron Radiation | Year: 2015
The concept of a multichannel electron spin detector based on optical imaging principles and Mott scattering (iMott) is presented. A multichannel electron image produced by a standard angle-resolving (photo) electron analyzer or microscope is re-imaged by an electrostatic lens at an accelerating voltage of 40kV onto the Au target. Quasi-elastic electrons bearing spin asymmetry of the Mott scattering are imaged by magnetic lenses onto position-sensitive electron CCDs whose differential signals yield the multichannel spin asymmetry image. Fundamental advantages of this concept include acceptance of inherently divergent electron sources from the electron analyzer or microscope focal plane as well as small aberrations achieved by virtue of high accelerating voltages, as demonstrated by extensive ray-tracing analysis. The efficiency gain compared with the single-channel Mott detector can be a factor of more than 104 which opens new prospects of spin-resolved spectroscopies in application not only to standard bulk and surface systems (Rashba effect, topological insulators, etc.) but also to buried heterostructures. The simultaneous spin detection combined with fast CCD readout enables efficient use of the iMott detectors at X-ray free-electron laser facilities.
Stepanova T.,St Petersburg Polytechnical University |
Zegzhda D.,St Petersburg Polytechnical University
ACM International Conference Proceeding Series | Year: 2014
Lots of upcoming IT trends are based on the concept of heterogeneous networks: Internet of Things is amongst them. Modern heterogeneous networks are characterized by hardly predictable behavior, hundreds of parameters of network nodes and connections and lack of single basis for development of control methods and algorithms. To overcome listed problems one need to implement topological modeling of dynamically changing structures. In this paper authors propose basic theoretical framework that will allow estimation of controllability, resiliency, scalability and other determinant parameters of complex heterogeneous networks. Copyright is held by the owner/author(s).
Tsendin L.D.,St Petersburg Polytechnical University
Plasma Sources Science and Technology | Year: 2011
Combined experimental, numerical and analytical approaches are presented to address actual problems of glow discharge physics. Such a synthesis is able to clarify relatively simple, qualitative, self-consistent phenomena, and should allow improvement of the existing paradigms and/or formulation of novel approaches. The following illustrative examples are discussed: Linear and non-linear diffusion in multispecies, currentless and current-carrying low-temperature plasmas. Both ambipolar diffusion and ambipolar mobility are considered. Non-local electron kinetics in radio frequency and direct current glows. Structures of the cathode and anode regions in direct current glows. © 2011 IOP Publishing Ltd.
Shevkunov S.V.,St Petersburg Polytechnical University
Doklady Physics | Year: 2011
The phenomenon of domain formation in a liquid film on a polarizable substrate was investigated. A relatively large dipole moment of water molecules in combination with a relatively high polarizability of iodine ions entering the composition of silver iodide determine the considerable contribution of polarization interactions to the mechanism of adhesion with the surface. The interaction of water vapors with the crystalline surface of silver iodide was simulated by the Monte Carlo method. The calculation was performed in a system with periodic boundary conditions in the adsorption plane. The number of water molecules in the periodicity cell over the substrate surface sequentially rose from 1 to 8961. The Ag+ ions were arranged in the surface layer of the substrate, and I- ions were arranged in the next crystalline layer into the substrate depth. The electrostatic interactions with the ions and molecules arranged out of the limits of the proper cell were summed by the two-dimensional Ewald method.
Hanin L.,Idaho State University |
Pavlova L.,St Petersburg Polytechnical University
Journal of Theoretical Biology | Year: 2016
Background: Metastatic relapse is the principal source of breast cancer mortality. This work seeks to uncover unobservable, yet clinically important, aspects of post-surgery metastatic relapse of breast cancer and to quantify effects of surgery on metastatic progression. Methods: We classified metastases into three categories: (1) solitary cancer cells that were formed before or during surgery and either circulate in blood or are lodged at various secondary sites; (2) dormant or slowly growing avascular metastases; and (3) vascular secondary tumors. We developed a general mathematical model aimed at describing post-surgery dynamics of these three metastatic states. One parametric version of the model assumed that sojourn times of metastases in the three states are exponentially distributed while another was based on Erlang distribution. Model parameters were estimated from a sample of metastatic relapse or censoring times for 673 breast cancer patients treated with surgery. Results: We estimated the expected number of metastases at surgery and mean sojourn times for the three states and found that both are decreasing with state number. We also computed the probability that metastatic relapse resulted from a metastasis in a given state at surgery. The values of these attribution probabilities suggest that under the Erlang model all three states have a considerable effect on metastatic relapse while in the case of exponential model this is true for states 1 and 2 only. Conclusions: (1) In some patients metastasis occurred before surgery; (2) our results confirm significance of metastatic dormancy; (3) according to the model surgery stimulates escape from dormancy, promotes angiogenesis and accelerates metastatic growth in a fraction of breast cancer patients. Taken summarily, these findings call into question the benefits of primary tumor resection for certain categories of breast cancer patients. © 2016 Elsevier Ltd.