Magnetic nulls in interacting dipolar fields

The prominence of nulls in reconnection theory is due to the expected singular current density and the indeterminacy of field lines at a magnetic null. Electron inertia changes the implications of both features. Magnetic field lines are distinguishable only when their distance of closest approach exceeds a distance $\varDelta _d$ . Electron inertia ensures $\varDelta _d\gtrsim c/\omega _{pe}$ . The lines that lie within a magnetic flux tube of radius $\varDelta _d$ at the place where the field strength $B$ is strongest are fundamentally indistinguishable. If the tube, somewhere along its length, encloses a point where $B=0$ vanishes, then distinguishable lines come no closer to the null than $\approx (a^2c/\omega _{pe})^{1/3}$ , where $a$ is a characteristic spatial scale of the magnetic field. The behaviour of the magnetic field lines in the presence of nulls is studied for a dipole embedded in a spatially constant magnetic field. In addition to the implications of distinguishability, a constraint on the current density at a null is obtained, and the time required for thin current sheets to arise is derived.

Propagation of weak shocks in cool-core galaxy clusters in two-temperature magnetohydrodynamics with anisotropic thermal conduction

ABSTRACT We investigate how different magnetohydrodynamic models of propagation of a weak (Mach number ∼1.2) shock in the core of a galaxy cluster affect its observational appearance, using the Perseus cluster as our fiducial model. In particular, we study how thermal conduction, both isotropic and anisotropic, and ion–electron temperature equilibration modify a weak shock. Strong thermal conduction is expected to produce an electron temperature precursor. Less prominent pressure and density precursors are formed as well. A longer equilibration time largely reduces the density precursor but does not change the electron temperature precursor much. When thermal conduction becomes anisotropic, the intracluster magnetic field imprints its characteristic spatial scale on the distortions of the shock induced by heat fluxes.

Dynamic path-dependent landslide susceptibility modelling

This contribution tests the added value of including landslide path dependency in statistically based landslide susceptibility modelling. A conventional pixel-based landslide susceptibility model was compared with a model that includes landslide path dependency and with a purely path-dependent landslide susceptibility model. To quantify path dependency among landslides, we used a space–time clustering (STC) measure derived from Ripley's space–time K function implemented on a point-based multi-temporal landslide inventory from the Collazzone study area in central Italy. We found that the values of STC obey an exponential-decay curve with a characteristic timescale of 17 years and characteristic spatial scale of 60 m. This exponential space–time decay of the effect of a previous landslide on landslide susceptibility was used as the landslide path-dependency component of susceptibility models. We found that the performance of the conventional landslide susceptibility model improved considerably when adding the effect of landslide path dependency. In fact, even the purely path-dependent landslide susceptibility model turned out to perform better than the conventional landslide susceptibility model. The conventional plus path-dependent and path-dependent landslide susceptibility model and their resulting maps are dynamic and change over time, unlike conventional landslide susceptibility maps.

Economic assessment of the accidental risk of natural emergencies for train traffic

Aim. The paper is dedicated to the evaluation of the risk of transportation accidents caused by natural emergencies affecting train traffic on a specific line. The ever-growing anthropogenic burden on the environment inevitably causes climate change that, in turn, gives rise to higher numbers of extreme weather events. The latter usually cause industrial accidents and disasters. The assessment of the factors of climate-related risk that quantitatively characterize their effect on the railway infrastructure is the starting point of calamity risk management and adaptation of human activities to the ever-changing climate. Methods. The authors propose a method of risk assessment that takes into consideration the effect of various natural emergencies that affect rolling stock in motion. The method is based on elements of the probability theory and mathematical statistics. The developed method enables the assessment of the risk of a transportation accident caused by natural emergencies specific to not only a line, but a route on a railway network. Results. For the Nevinnomysskaya – Tuapse line that includes 6 sections of the North Caucasus Railway, one of which was damaged due to abundant precipitations on October 24 and 25, 2018, the risk of transportation accident caused by the effects of three types of natural emergencies on the sociotechnical system of this line has been calculated: – flood, – hurricane with wind strength of over 22 mps, – heavy rain. The parameters of such emergencies are characterized by the following factors: – frequency as compared to other types of emergencies, – average annual number of natural emergencies, – characteristic spatial scale of the natural emergency, – characteristic duration of the natural emergency. The conditional probabilities of the effects on the railway sociotechnical system of an event that has characteristic spatial scale and duration and has caused a transportation accident involving a train were estimated based on the assumption that a train flow in space follows the normal Erlang distribution of the k-th kind. The risk of transportation accident involving up and down trains travelling along the i-th line of the j-th railway caused by a hazardous effect of a natural emergency of the m-th type is identified subject to the jointness of events. Using the discounting method, an equation was obtained for estimating the mathematical expectation of economic damage by traffic safety disturbances, which allowed estimating the economic component of the risk. Conclusions. As the result, a method is proposed for estimation of the risk of transportation accidents caused by natural emergencies, an example is provided of such risk estimation, including the economic component, for the Nevinnomysskaya – Tuapse line.

Economic assessment of the accidental risk of natural emergencies for train traffic

Aim. The paper is dedicated to the evaluation of the risk of transportation accidents caused by natural emergencies affecting train traffic on a specific line. The ever-growing anthropogenic burden on the environment inevitably causes climate change that, in turn, gives rise to higher numbers of extreme weather events. The latter usually cause industrial accidents and disasters. The assessment of the factors of climate-related risk that quantitatively characterize their effect on the railway infrastructure is the starting point of calamity risk management and adaptation of human activities to the ever-changing climate. Methods. The authors propose a method of risk assessment that takes into consideration the effect of various natural emergencies that affect rolling stock in motion. The method is based on elements of the probability theory and mathematical statistics. The developed method enables the assessment of the risk of a transportation accident caused by natural emergencies specific to not only a line, but a route on a railway network. Results. For the Nevinnomysskaya – Tuapse line that includes 6 sections of the North Caucasus Railway, one of which was damaged due to abundant precipitations on October 24 and 25, 2018, the risk of transportation accident caused by the effects of three types of natural emergencies on the sociotechnical system of this line has been calculated: – flood, – hurricane with wind strength of over 22 mps, – heavy rain. The parameters of such emergencies are characterized by the following factors: – frequency as compared to other types of emergencies, – average annual number of natural emergencies, – characteristic spatial scale of the natural emergency, – characteristic duration of the natural emergency. The conditional probabilities of the effects on the railway sociotechnical system of an event that has characteristic spatial scale and duration and has caused a transportation accident involving a train were estimated based on the assumption that a train flow in space follows the normal Erlang distribution of the k-th kind. The risk of transportation accident involving up and down trains travelling along the i-th line of the j-th railway caused by a hazardous effect of a natural emergency of the m-th type is identified subject to the jointness of events. Using the discounting method, an equation was obtained for estimating the mathematical expectation of economic damage by traffic safety disturbances, which allowed estimating the economic component of the risk. Conclusions. As the result, a method is proposed for estimation of the risk of transportation accidents caused by natural emergencies, an example is provided of such risk estimation, including the economic component, for the Nevinnomysskaya – Tuapse line.

Ближний порядок, транспорт заряда в SiO-=SUB=-x-=/SUB=-: эксперимент и численное моделирование

The structure of nonstoichiometric silicon oxide (SiO_ x ) has been studied by the methods of highresolution X-ray photoelectron spectroscopy and fundamental optical-absorption spectroscopy. The conductivity of SiO_ x ( x = 1.4 and 1.6) films has been measured in a wide range of electric fields and temperatures. Experimental data are described in terms of the proposed SiO_ x structure model based on the concept of fluctuating chemical composition leading to nanoscale fluctuations in the electric potential. The maximum amplitude of potential fluctuations amounts to 2.6 eV for electrons and 3.8 eV for holes. In the framework of this model, the observed conductivity of SiO_ x is described by the Shklovskii–Efros theory of percolation in inhomogeneous media. The characteristic spatial scale of potential fluctuations in SiO_ x films is about 3 nm. The electron-percolation energy in SiO_1.4 and SiO_1.6 films is estimated to be 0.5 and 0.8 eV, respectively.

Landscape complexity influences route-memory formation in navigating pigeons

Observations of the flight paths of pigeons navigating from familiar locations have shown that these birds are able to learn and subsequently follow habitual routes home. It has been suggested that navigation along these routes is based on the recognition of memorized visual landmarks. Previous research has identified the effect of landmarks on flight path structure, and thus the locations of potentially salient sites. Pigeons have also been observed to be particularly attracted to strong linear features in the landscape, such as roads and rivers. However, a more general understanding of the specific characteristics of the landscape that facilitate route learning has remained out of reach. In this study, we identify landscape complexity as a key predictor of the fidelity to the habitual route, and thus conclude that pigeons form route memories most strongly in regions where the landscape complexity is neither too great nor too low. Our results imply that pigeons process their visual environment on a characteristic spatial scale while navigating and can explain the different degrees of success in reproducing route learning in different geographical locations.

Baroclinic instability of quasi-geostrophic flows localized in a thin layer

This paper examines the baroclinic instability of a quasi-geostrophic flow with vertical shear in a continuously stratified fluid. The flow and density stratification are both localized in a thin upper layer. (i) Disturbances whose wavelength is much smaller than the deformation radius (based on the depth of the upper layer) are demonstrated to satisfy an ‘equivalent two-layer model’ with properly chosen parameters. (ii) For disturbances whose wavelength is of the order of, or greater than, the deformation radius we derive a sufficient stability criterion. The above analysis is applied to the subtropical and subarctic frontal currents in the Northern Pacific. The effective time of growth of disturbances (i) is found to be 16–22 days, the characteristic spatial scale is 130–150 km.