84 research outputs found
Monitoring and prediction of natural disasters
The problems of natural disaster predicting and accomplishing a synthesis of environmental monitoring systems to collect, store, and process relevant
information for their solution are analyzed. A three-level methodology is proposed for making decisions concerning the natural disaster dynamics. The methodology is based on the assessment of environmental indicators and the use of numerical models of the environment
Some New Reactions and Properties of Xanthane Hydride (5-Amino-1,2,4-dithiazole-3-thione)
Aminomethylation of xanthane hydride (5-amino-1,2,4-dithiazole-3-thione) with the RNH2–HCHO system has resulted in the formation of the derivatives of new heterocyclic system (3,7-dihydro-5H-[1,2,4]-dithiazolo[4,3-a][1,3,5]triazine) in low yields. The reaction of xanthane hydride with dicyandiamide has led to thioammeline [4,6-diamino-1,3,5-triazine-2(5Н)-thione]. Some practically important properties of xanthane hydride and its derivatives have been investigated. Xanthane hydride has efficiently exhibited carbon steel corrosion in neutral aqueous media. The prepared compounds have not exhibited growth-regulating or antidote activity to herbicide 2,4-D
"Head-to-head" and "tail-to-tail" 180-degree domain walls in an isolated ferroelectric
"Head-to-head" and "tail-to-tail" 180-degree domain-walls in a finite
isolated ferroelectric sample are theoretically studied using Landau theory.
The full set of equations, suitable for numerical calculations is developed.
The explicit expressions for the polarization profile across the walls are
derived for several limiting cases and wall-widths are estimated. It is shown
analytically that different regimes of screening and different dependences for
width of charged domain walls on the temperature and parameters of the system
are possible, depending on spontaneous polarization and concentration of
carriers in the material. It is shown that the half-width of charged domain
walls in typical perovskites is about the nonlinear Thomas-Fermi
screening-length and about one order of magnitude larger than the half-width of
neutral domain-walls. The formation energies of "head-to-head" walls under
different regimes of screening are obtained, neglecting the poling ability of
the surface. It is shown that either "head-to-head" or "tail-to-tail"
configuration can be energetically favorable in comparison with the monodomain
state of the ferroelectric if the poling ability of the surface is large
enough. If this is not the case, the existence of charged domain walls in bulk
ferroelectrics is merely a result of the domain-growth kinetics. Size-effect
corresponding to the competition between state with charged domain wall, single
domain state, multidomain state, and the state with the zero polarization is
considered. The results obtained for the case of an isolated ferroelectric
sample were compared with the results for an electroded sample. It was shown
that charged domain wall in electroded sample can be either metastable or
stable, depends on the work function difference between electrodes and
ferroelectric and the poling ability of the electrode/ferroelectric interface.Comment: 47 pages, 10 figure
Quenched lattice fluctuations in optically driven SrTiO3
Many functionally relevant ferroic phenomena in quantum materials can be
manipulated by driving the lattice coherently with optical and terahertz
pulses. New physical phenomena and non-equilibrium phases that have no
equilibrium counterpart have been discovered following these protocols. The
underlying structural dynamics has been mostly studied by recording the average
atomic position along dynamical structural coordinates with elastic scattering
methods. However, crystal lattice fluctuations, which are known to influence
phase transitions in equilibrium, are also expected to determine these dynamics
but have rarely been explored. Here, we study the driven dynamics of the
quantum paraelectric SrTiO3, in which mid-infrared drives have been shown to
induce a metastable ferroelectric state. Crucial in these physics is the
competition between the polar instability and antiferrodistortive rotations,
which in equilibrium frustrate the formation of long-range ferroelectricity. We
make use of high intensity mid-infrared optical pulses to resonantly drive a
Ti-O stretching mode at 17 THz, and we measure the resulting change in lattice
fluctuations using time-resolved x-ray diffuse scattering at a free electron
laser. After a prompt increase, we observe a long-lived quench in R-point
antiferrodistortive lattice fluctuations. The enhancement and reduction in
lattice fluctuations are explained theoretically by considering fourth-order
nonlinear phononic interactions and third-order coupling to the driven optical
phonon and to lattice strain, respectively. These observations provide a number
of new and testable hypotheses for the physics of light-induced
ferroelectricity
Hygienic literacy among students of grades 7-11 about the adverse effect of fast food on the body
The purpose of the study is to assess the attitude and awareness about fast food (fast food) among schoolchildren of grades 7-11.Цель исследования – оценить отношение и информированность о фаст-фуде (быстром питании) среди школьников 7-11 классов
ИСПОЛЬЗОВАНИЕ ПРОГРАММЫ ФИДЕСИС ДЛЯ МОДЕЛИРОВАНИЯ РАЗВИТИЯ БОЛЬШИХ ПЛАСТИЧЕСКИХ ДЕФОРМАЦИЙ ВО ВРАЩАЮЩЕМСЯ ДИСКЕ
The paper presents a finite element analysis of the localization of plastic deformations in the region of fracture of the model disk during rotation. At a certain angular velocity of rotation of the disk, an "ejection"is observed experimentally. This effect occurs when the material stability is lost, is analogous to the known "necking"in the specimen tension. In view of the finiteness of the observed experimental displacements and for the detection of the "tightening"effect in a numerical experiment, the equilibrium equations are integrated taking into account the finite deformations. The model calculation was carried out in a quasi-static setting with a step-by-step increase in the rotational speed. The plastic behavior of the metal alloy of the disk material is described according to the Huber-Mises limit surface. The material parameters used in the calculation are determined from the experimental tension curve of the sample. Elasto-plastic governing relations are used in finite deformations with a multiplicative decomposition of the deformation gradient into the elastic and plastic components. In fully plastic deformation of metals, due to the constancy of the first invariant of plastic deformations, the process of deformation is close to isochoric. In such cases, linear isoparametric finite elements show the effect of “volumetric locking which distorts the numerical result. Therefore, in calculations we use twenty-node volume finite elements of the second order, which have no specific feature. The calculations were carried out on the IMERS-Fidesis hardware-software complex. The energy and noise efficiency of a cluster in distributed computations is studied. The article concludes by comparing the numerical results with the experimental data and the energy efficiency level of the cluster.В статье приводится конечно-элементный анализ локализации пластических деформаций в области разрушения модельного диска при вращении. При определенной угловой скорости вращения диска экспериментально замечается «утяжка». Данный эффект возникает при потери материальной устойчивости, является аналогом известного образования «шейки» при растяжении образцов. В силу конечности наблюдаемых экспериментальных перемещений и для обнаружения эффекта «утяжки» в численном эксперименте уравнения равновесия интегрируются с учетом конечности деформаций. Модельный расчет проведен в квазистатической постановке с пошаговым увеличением частоты вращения. Пластическое поведение металллического сплава материала диска описывается согласно предельной поверхности Губера-Мизеса. Материальные параметры, используемые в расчете определены из экспериментальной кривой растяжения образца. Определяющие упругопластические соотношения записаны в конечных деформациях с мультипликативной декомпозицией деформационного градиента на упругую и пластическую компоненты. При полностью пластическом деформировании металлов в силу постоянства первого инварианта пластических деформаций процесс деформирования близок к изохорному. В таких случаях линейные изопараметрические конечные элементы проявляют эффект «объемного локинга», искажающий численный результат. В силу этого в вычислениях используем двадцати-узловые объемные конечные элементы второго порядка, которые указанной особенностью не обладают Вычисления проведены на аппаратно — программном комплексе ИММЕРС — Фидесис. Исследована энерго- и шумо- эффективность кластера в распределенных вычислениях. В заключении статьи приводятся сравнение численных результатов с экспериментальными данными и уровень энерго-эффективности кластера
Normative productivity of the global vegetation
<p>Abstract</p> <p>Background</p> <p>The biosphere models of terrestrial productivity are essential for projecting climate change and assessing mitigation and adaptation options. Many of them have been developed in connection to the International Geosphere-Biosphere Program (IGBP) that backs the work of the Intergovernmental Panel on Climate Change (IPCC). In the end of 1990s, IGBP sponsored release of a data set summarizing the model outputs and setting certain norms for estimates of terrestrial productivity. Since a number of new models and new versions of old models were developed during the past decade, these normative data require updating.</p> <p>Results</p> <p>Here, we provide the series of updates that reflects evolution of biosphere models and demonstrates evolutional stability of the global and regional estimates of terrestrial productivity. Most of them fit well the long-living Miami model. At the same time we call attention to the emerging alternative: the global potential for net primary production of biomass may be as high as 70 PgC y<sup>-1</sup>, the productivity of larch forest zone may be comparable to the productivity of taiga zone, and the productivity of rain-green forest zone may be comparable to the productivity of tropical rainforest zone.</p> <p>Conclusion</p> <p>The departure from Miami model's worldview mentioned above cannot be simply ignored. It requires thorough examination using modern observational tools and techniques for model-data fusion. Stability of normative knowledge is not its ultimate goal – the norms for estimates of terrestrial productivity must be evidence-based.</p
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