Energy barriers in three-dimensional micromagnetic models and the physics of thermoviscous magnetization

This article has been accepted for publication in Geophysical Journal International © 2018. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved. Source at https://doi.org/10.1093/gji/ggy285.A first-principle micromagnetic and statistical calculation of viscous remanent magnetization (VRM) in an ensemble of cubic magnetite pseudo-single domain (PSD) particles is presented. The theoretical methods developed apply to all magnetic particle sizes, from single domain to multidomain. The numerical implementation is based on a fast relaxation algorithm for finding optimal transition paths between micromagnetic local energy minima. The algorithm combines a nudged-elastic-band technique with action minimization. Initial paths are obtained by repetitive minimizations of modified energy functions. For a cubic PSD particle, 60 different local energy minima are identified, and all optimal energy barriers between them are numerically calculated for the case of zero external field. These results are used to estimate the energy barriers in weak external fields. Based on these, time-dependent transition matrices are constructed, which fully describe the continuous homogeneous Markov processes of VRM acquisition and decay. By spherical averaging, the acquisition of remanent magnetization in an isotropic PSD ensemble is calculated from laboratory to geological timescales. The modelled particle ensemble shows a physically meaningful overshooting of magnetization during VRM acquisition. The results also clarify why VRM acquisition in PSD particles can occur much faster than VRM decay, and therefore explain occurrence of extremely stable VRM as found in some palaeomagnetic studies

Limit theorems for random point measures generated by cooperative sequential adsorption

We consider a finite sequence of random points in a finite domain of a finite-dimensional Euclidean space. The points are sequentially allocated in the domain according to a model of cooperative sequential adsorption. The main peculiarity of the model is that the probability distribution of a point depends on previously allocated points. We assume that the dependence vanishes as the concentration of points tends to infinity. Under this assumption the law of large numbers, the central limit theorem and Poisson approximation are proved for the generated sequence of random point measures.Comment: 17 page

Обоснование сушки плодов боярышника в барабанной сушилке с использованием лопастного перемешивающего устройства

Perennial provision of high-quality fruits and berries to population is a very important issue. Drying the products is an optimum solution to preserve quality of plant raw materials. This article discusses comparative experimental results of drying hawthorn berries in drying cabinet and drum dryer equipped with rotary cylindrical drum with rigidly fixed blades and internal blade agitator rotating in the contrary direction with respect to the drum. It has been established that drying from initial moisture content of 74.9% to final level of 20% in drying cabinet requires 11 hours at average power consumption of 2.3 kWh/kg of evaporated moisture, whereas drying in drum dryer with agitator requires 7 hours at average power consumption of 1.8 kWh/kg of evaporated moisture to final moisture content of 14%; moreover, it has been experimentally detected that drying in cabinet is heterogeneous over product bulk, the final product moisture content varies from 17.5 to 23.5%. Moisture content as a function of drying time is presented which demonstrates homogeneity of drying resulting in production of high-quality dried berries.El suministro perenne de frutas y bayas de alta calidad a la población es un tema muy importante. El secado de los productos es una solución óptima para preservar la calidad de las materias primas vegetales. Este artículo analiza los resultados experimentales comparativos del secado de bayas de espino en un gabinete de secado y un secador de tambor equipado con un tambor cilíndrico giratorio con cuchillas rígidamente fijas y un agitador interno de cuchillas que gira en la dirección contraria con respecto al tambor. Se ha establecido que el secado desde el contenido de humedad inicial del 74.9% hasta el nivel final del 20% en el gabinete de secado requiere 11 horas con un consumo de energía promedio de 2.3 kWh / kg de humedad evaporada, mientras que el secado en un secador de tambor con agitador requiere 7 horas en promedio consumo de energía de 1.8 kWh / kg de humedad evaporada hasta un contenido de humedad final de 14%; Además, se ha detectado experimentalmente que el secado en el gabinete es heterogéneo sobre el volumen del producto, el contenido de humedad del producto final varía de 17.5 a 23.5%. Se presenta el contenido de humedad en función del tiempo de secado, lo que demuestra la homogeneidad del secado que resulta en la producción de bayas secas de alta calidad.Круглогодичное обеспечение населения плодами и ягодами высокого качества относится к наиболее важному числу задач. Оптимальным решением по сохранению качества растительного сырья является сушка продукта. В статье представлены сравнительные результаты экспериментальных исследований процесса сушки плодов боярышника в сушильном шкафу и барабанной сушильной установке, комплектуемой вращающимся цилиндрическим барабаном с жестко закрепленными на нем лопастями и установленной внутри барабана мешалкой с лопастями, которая вращается в противоположную сторону от барабана. В ходе проведенных исследований установлено, что на сушку при начальной влажности плодов 74,9% до конечной 20% в сушильном шкафу затрачивается 11 часов, при среднем расходе электроэнергии 2,3 кВт/ч испаренной влаги, в то время как сушка в барабанной сушилке с перемешивающим устройством проходит в течение 7 часов при среднем расходе 1,8 кВт/ч испаренной влаги до конечной влажности 14%, кроме того, экспериментально определено, что сушка в сушильном шкафу характеризуется неравномерностью по объему продукта, конечная влажность которого изменяется в пределах от 17,5 до 23,5%. Представлены экспериментальные зависимости снижения уровня влажности от времени сушки, определяющие, что перемешивающее устройство обеспечивает равномерность процесса сушки, позволяя получать высушенные плоды высокого качества

Theoretical analysis of flux amplification by soft magnetic material in a putative biological magnetic-field receptor

Birds are endowed with a magnetic sense that allows them to detectEarth’s magnetic field and to use it for orientation. Physiological andbehavioral experiments have shown the upper beak to host amagnetoreceptor. Putative magnetoreceptive structures in the beak arenerve terminals that each contain a dozen or so of micrometer-sizedclusters of superparamagnetic nanocrystals made of magnetite/maghemiteand numerous electron-opaque platelets filled with a so farunidentified, amorphous ferric iron compound. The platelets typicallyform chainlike structures, which have been proposed to function asmagnetic flux focusers for detecting the intensity of the geomagneticfield. Here, we test that proposition from first principles and developan unconstrained model to determine the equilibrium distribution ofmagnetization along a linear chain of platelets which we assume tobehave magnetically soft and to have no magnetic remanence. Ouranalysis, which is valid for arbitrary values of the intrinsic magneticsusceptibility chi, shows that chi needs to be much greater than unityto amplify the external field by two orders of magnitude in a chain ofplatelets. However, the high amplification is confined to the centralregion of the chain and subsides quadratically toward the ends of thechain. For large values of chi, the possibility opens up of realizingmagnetoreceptor mechanisms on the basis of attraction forces betweenadjacent platelets in a linear chain. The force in the central region ofthe chain may amount to several pN, which would be sufficient to convertmagnetic input energy into mechanical output energy. The strikingfeature of an ensemble of platelets is its ability to organize intotightly spaced chains under the action of an external field of givenstrength. We discuss how this property can be exploited for amagnetoreception mechanism

Almost Periodic and Asymptotically Almost Periodic Solutions of Liénard Equations

The aim of this paper is to study the almost periodic and asymptotically almost periodic solutions on (0,+1) of the Li´enard equation x′′ + f(x)x′ + g(x) = F(t), where F : T ! R (T = R+ or R) is an almost periodic or asymptotically almost periodic function and g : (a, b) ! R is a strictly decreasing function. We study also this problem for the vectorial Li´enard equation. We analyze this problem in the framework of general non-autonomous dynamical systems (cocycles). We apply the general results obtained in our early papers [3, 7] to prove the existence of almost periodic (almost automorphic, recurrent, pseudo recurrent) and asymptotically almost periodic (asymptotically almost automorphic, asymptotically recurrent, asymptotically pseudo recurrent) solutions of Li´enard equations (both scalar and vectorial)

Critical Dynamics of Self-Organizing Eulerian Walkers

The model of self-organizing Eulerian walkers is numerically investigated on the square lattice. The critical exponents for the distribution of a number of steps ($\tau_l$) and visited sites ($\tau_s$) characterizing the process of transformation from one recurrent configuration to another are calculated using the finite-size scaling analysis. Two different kinds of dynamical rules are considered. The results of simulations show that both the versions of the model belong to the same class of universality with the critical exponents $\tau_l=\tau_s=1.75\pm 0.1$.Comment: 3 pages, 4 Postscript figures, RevTeX, additional information available at http://thsun1.jinr.dubna.su/~shche

Prompt emission from tidal disruptions of white dwarfs by intermediate mass black holes

We present a qualitative picture of prompt emission from tidal disruptions of white dwarfs (WD) by intermediate mass black holes (IMBH). The smaller size of an IMBH compared to a supermassive black hole and a smaller tidal radius of a WD disruption lead to a very fast event with high peak luminosity. Magnetic field is generated in situ following the tidal disruption, which leads to effective accretion. Since large-scale magnetic field is also produced, geometrically thick super-Eddington inflow leads to a relativistic jet. The dense jet possesses a photosphere, which emits quasi-thermal radiation in soft X-rays. The source can be classified as a long low-luminosity gamma-ray burst (ll-GRB). Tidal compression of a WD causes nuclear ignition, which is observable as an accompanying supernova. We suggest that GRB060218 and SN2006aj is such a pair of ll-GRB and supernova. We argue that in a flux-limited sample the disruptions of WDs by IMBHs are more frequent then the disruptions of other stars by IMBHs