589 research outputs found

    Analysis of negative magnetoresistance. Statistics of closed paths. I. Theory

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    Statistics of closed paths in two-dimensional (2D) systems, which just determines the interference quantum correction to conductivity and anomalous magnetoconductance, has been studied by computer simulation of a particle motion over the plane with randomly distributed scatterers. Both ballistic and diffusion regimes have been considered. The results of simulation have been analyzed in the framework of diffusion approximation. They are used for calculation of the magnetic field dependence of magnetoconductance in the model 2D system. It is shown that the anomalous magnetoconductance can be in principle described by the well known expression, obtained in the diffusion approximation, but with the prefactor less than unity and phase breaking length which differs from true value.Comment: 10 pages, 12 figures, to be published in Phys.Rev.

    The Outburst of the Blazar AO 0235+164 in 2006 December: Shock-in-Jet Interpretation

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    We present the results of polarimetric (RR band) and multicolor photometric (BVRIJHKBVRIJHK) observations of the blazar AO 0235+16 during an outburst in 2006 December. The data reveal a short timescale of variability (several hours), which increases from optical to near-IR wavelengths; even shorter variations are detected in polarization. The flux density correlates with the degree of polarization, and at maximum degree of polarization the electric vector tends to align with the parsec-scale jet direction. We find that a variable component with a steady power-law spectral energy distribution and very high optical polarization (30-50%) is responsible for the variability. We interpret these properties of the blazar withina model of a transverse shock propagating down the jet. In this case a small change in the viewing angle of the jet, by 1o\lesssim 1^o, and a decrease in the shocked plasma compression by a factor of \sim1.5 are sufficient to account for the variability.Comment: 22 pages, 8 figures, accepted for Ap

    Economic Aspects of Emergency Transition to Distance Education, or The Price of Going Online in Higher Education

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    As Russian universities switched to distance education in March 2020 to prevent COVID-19 from spreading, self‑paying students started questioning the fairness of tuition fees during the pandemic. They fled petitions, emphasizing that distance learning could not be equated to traditional classroom‑based learning, that educational services were not delivered to the full extent, and that educational quality had decreased. On those grounds, students required cutting tuition fees down to the size of those in part‑time or extramural education. To understand whether universities can afford making this step, we undertake to measure the price that they have paid for the transition to distance learning. For this purpose, we use data from a survey of faculty teaching and curriculum organization practices carried out at a federal university between March 23, 2020 and June 21, 2020, which involved 4,099 faculty members, as well as financial records of some departments within that university. Findings show that teaching workload reduced by 15% with distance learning during the pandemic, and the number of contact hours decreased 1.7 times. However, the overall amount of faculty workload increased by 50%, first of all due to a 2.4-time rise in curriculum organization activities. Therefore, the transition to distance education led to a significant increase in faculty workload, given that contact hours were preserved. Furthermore, the university invested heavily in the transition to distance learning and continuity of educational processes during the pandemic, in particular by financing the establishment of a new department for digitalization of learning processes. An inference is made that distance education imposed by the pandemic has not been reduced to part‑time or extramural studies. Decisions about cutting tuition fees for self‑paying students should be made at the institutional level, with due regard for faculty workload and digitization costs. © 202

    Diffusion and ballistic contributions of the interaction correction to the conductivity of a two-dimensional electron gas

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    The results of an experimental study of interaction quantum correction to the conductivity of two-dimensional electron gas in A3_3B5_5 semiconductor quantum well heterostructures are presented for a wide range of TτT\tau-parameter (Tτ0.030.8T\tau\simeq 0.03-0.8), where τ\tau is the transport relaxation time. A comprehensive analysis of the magnetic field and temperature dependences of the resistivity and the conductivity tensor components allows us to separate the ballistic and diffusion parts of the correction. It is shown that the ballistic part renormalizes in the main the electron mobility, whereas the diffusion part contributes to the diagonal and does not to the off-diagonal component of the conductivity tensor. We have experimentally found the values of the Fermi-liquid parameters describing the electron-electron contribution to the transport coefficients, which are found in a good agreement with the theoretical results.Comment: 11 pages, 11 figure

    Risk Assessment at the Cosmetic Product Manufacturer by Expert Judgment Method

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    A case study was performed in a cosmetic product manufacturer. We have identified the main risk factors of occupational accidents and their causes. Risk of accidents is assessed by the expert judgment method. Event tree for the most probable accident is built and recommendations on improvement of occupational health and safety protection system at the cosmetic product manufacturer are developed. The results of this paper can be used to develop actions to improve the occupational safety and health system in the chemical industry
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