Accelerating cosmologies in Lovelock gravity with dilaton

For the description of the Universe expansion, compatible with observational data, a model of modified gravity - Lovelock gravity with dilaton - is investigated. D-dimensional space with 3- and (D-4)-dimensional maximally symmetric subspaces is considered. Space without matter and space with perfect fluid are under test. In various forms of the theory under way (third order without dilaton and second order - Einstein-Gauss-Bonnet gravity - with dilaton and without it) stationary, power-law, exponential and exponent-of-exponent form cosmological solutions are obtained. Last two forms include solutions which are clear to describe accelerating expansion of 3-dimensional subspace. Also there is a set of solutions describing cosmological expansion which does not tend to isotropization in the presence of matter.Comment: 23 page

Portfolio diversification on a global scale

The research is aimed to analyze different types of portfolios and identify the one with the lowest level of risk. The first portfolio included US and EU securities. The other one studies crypto currency impact on portfolio riskiness

Nanotechnologies in crop cultivation: Ecotoxicological aspects

The European Commission has recognized nanotechnologies as extremely promising for increasing competitiveness of different sectors of the economy. On account of climate changes and the quest for food security, they are an effective way of solving key problems in the agrarian sector. Nowadays nanotechnologies are widely used for creating nanofertilizers, nanoinsecticides, nanofungicides, nanoherbicides and other nanopreparations. Numerous researches affirm advantages of nanopreparations, which has helped them find a wide use in agricultural practice. At the same time, nanopreparations are the source of entry into the environment of nanoparticles (size less than 100 nm) which are characterized by large active surface and specific physical-chemical properties different from ordinary chemical substances. It is precisely this which determines their bioaccessibility, bioaccumulation and toxicity. Recently, data about toxicity of nanoparticles for human and natural ecosystems have been accumulated. The results of a great deal of research affirm that they break the processes of photosynthesis, transpiration, mitosis, miosis and have a negative influence on colouring agents, proteins and carbohydrates. Under their action, physiological processes of plant growth and development are disturbed, which take place mainly in root system. Nanoparticles are characterized by high bioaccessibility for soil organisms, they are toxic to earthworms and microorganisms and they influence circulation of carbon and nitrogen. Aquatic organisms have been shown to have high sensitivity to nanoparticles; toxic effect has been registered for fish, daphnids, water plants and microorganisms. Taking into consideration the high level of potential danger of nanopreparations used in crop cultivation, special notice should be paid to the development of eco toxicological research. At present, nanoecotoxicological approaches to assessment of the danger of nanomaterials and nanoparticles are absent. Development of reports on elaboration of quantitative and qualitative methods of analysis, and methods of modeling and prognostication of risks is only at the initial stage. The objective of this review is attracting attention to solving the problem of nanoecotoxicology, nanoagrochemicals and nanopesticides, which needs consolidated efforts of scientists, governmental organizations and business and is an obligatory condition for preventing the negative impact of nanomaterials on humans and the environment

Non-linear water waves generated by impulsive motion of submerged obstacles

A fully non-linear problem on unsteady water waves generated by an impulsively moving obstacle is studied analytically. Our method involves reduction of the Euler equations to the integral-differential system for the wave elevation together with normal and tangential fluid velocities at a free surface. Exact model equations are derived in explicit form in a case where an isolated obstacle is presented by a totally submerged elliptic cylinder. A small-time asymptotic solution is constructed for a cylinder which starts with constant acceleration from rest. It is demonstrated that the leading-order solution terms describe several wave regimes such as the formation of non-stationary splash jets by vertical rising or vertical submersion of the obstacle; the generation of diverging waves is also observed

Bounce Loop Quantum Cosmology Corrected Gauss-Bonnet Gravity

We develop a Gauss-Bonnet extension of Loop Quantum Cosmology, by introducing holonomy corrections in modified $F(\mathcal{G})$ theories of gravity. Within the context of our formalism, we provide a perturbative expansion in the critical density, a parameter characteristic of Loop Quantum Gravity theories, and we result in having leading order corrections to the classical $F(\mathcal{G})$ theories of gravity. After extensively discussing the formalism, we present a reconstruction method that makes possible to find the Loop Quantum Cosmology corrected $F(\mathcal{G})$ theory that can realize various cosmological scenarios. Specifically, we studied exponential and power-law bouncing cosmologies, emphasizing on the behavior near the bouncing point and in some cases, the behavior for all the values of the cosmic time is obtained. We exemplify our theoretical constructions by using bouncing cosmologies, and we investigate which Loop Quantum Cosmology corrected Gauss-Bonnet modified gravities can successfully realize such cosmologies.Comment: Revised version, to appear in PR