The random-motion theorem in a local cosmology with dark energy

It is shown that the random-motion theorem in cosmology proven in the early 1960s can be generalized to take into account the presence of a uniform dark-energy background. The role of the dark energy is substantial: its repulsive force exceeds the gravitational force due to darkmatter and baryons, both on the scale of the Universe as a whole and on local scales of about 1 Mpc. The generalized random-motion theorem has the form of a differential equation relating the kinetic energy of the random motion and the potential energy of the particles due to their own gravitational field and the repulsive dark-energy field. One consequence of the generalized theorem is a virial relation containing the potential energy in the repulsive field.     

Dark matter and dark energy in dwarf galaxy systems

Quantitative estimates of themaximumallowed totalmasses and sizes of the dark-matter halos in groups and associations of dwarf galaxies—special types of metagalactic populations identified in recent astronomical observations with the Hubble Space Telescope—are presented. Dwarf-galaxy systems are formed of isolated dark-matter halos with a small number of dark galaxies embedded in them. Data on the sizes of these systems and the velocity dispersions of the embedded galaxies can be used to determine lower limits on the total dark-halo masses using the virial theorem. Upper limits follow from the conditions that the systems immersed in the cosmic dark-energy background be gravitationally bound. The median maximum masses are close to 10¹² M _⊙ for both groups and associations of dwarf galaxies, although the median virial masses for these two types of systems differ by approximately a factor of ten.     

Strong Shock in the Uniformly Expanding Universe with a Spherical Void

Astronomy Reports - Propagation of a strong shock wave in the expanding universe is studied using approximate analytic and exact numerical solution of self-similar equations. Both solutions have...     

The interaction factor method for energy pile groups

Prior to this study, no simplified yet rational methods were available for estimating the vertical displacements of energy pile groups subjected to thermal loads. Observing such a challenge, the goal of this study has been threefold: (i) to extend the interaction factor concept from the framework of conventional pile groups to that of energy pile groups, (ii) to present charts for the analysis of the displacement interaction between two identical energy piles over a broad range of design conditions, and (iii) to propose, apply and validate the interaction factor method for the displacement analysis of energy pile groups.     

The uniform expansion of the Universe

The standard equations of general relativity admit extension so that they can be supplemented, not only with Einsteinian cosmological repulsive forces described by the Λ term, but also with other forces. Accordingly, we suggest a model of a uniformly expanding Universe (an S model). In this model, the cosmological forces of attraction and repulsion precisely balance each other. This S model is a good approximation for describing the Universe’s evolution over a wide range of redshifts (up to z ∼ 1000). The S model can explain in a simple way observational data on the age of the Universe, the apparent magnitude-redshift relation for Type Ia supernovae, and the angular separation between the centers of neighboring bright spots against the uniform background of the cosmic microwave background radiation.     

Outer parts of large galactic clusters in the presence of dark energy

Dark energy limits a radius of big clusters of galaxies, and may accelerate hot gas outflowing from the cluster as a wind. Collision of accelerated winds, in presence of a magnetic field, produce a situation favorable for acceleration of EHECR.     

Mean Square Geodesic Deviation in the Zeldovich Problem on Light Propagation in a Universe with Inhomogeneities

Astronomy Reports - In 1964, Ya.B. Zeldovich formulated the problem of light propagation in the Universe under the influence of inhomogeneities. It is reduced to describing the divergence of two...     

基于尺度因素的地下水随机分析

针对小尺度的各态历经假设的失效,研究了小尺度上多孔介质特性参数统计特征。利用基于K-L(Karhunen-Loeve)展开和混沌展开的谱模型,分析了尺度大小对地下水流动的影响。结果表明,尺度大小导致了特征值系列和特征函数系列的变化,尺度的变化对水头、含水量、流速影响程度不同;水头和流速方差与尺度相关,尺度越大,水头和流速方差越大;研究尺度的变化对水头、含水量、流速均值产生的影响较小。     

The activation energy values estimated by the Arrhenius equation as a controlling factor of platinum-group mineral formation

In ophiolite complexes and Ural/Alaskan-type intrusions the platinum-group element minerals (PGM) occur as laurite (RuS₂), erlichmanite (OsS₂), irarsite (IrAsS) and alloys (Os-Ir-Ru and Pt-Fe). They are commonly found as small inclusions (normally less than 10 μm, occasionally up to 100 μm) in chromite. The origin of coarse-grained PGM, in the form of 0.5-10 mm nuggets, in placer deposits related with mafic/ultramafic complexes remains still unclear. Literature data on grain size (r) of platinum-group minerals (PGM) and their formation temperature (range of temperatures between 700 and 1100 °C), revealed an Arrhenius temperature dependence. Correlation of the rate of crystal formation that depends on temperature (T) with the size (r) of the grain results in a linear relationship between ln(r) and 1/T. From the slope of the line n × ln(r) = −const. + E_act/RT the activation energy for the formation of IPGM (Ir-platinum-group minerals) was estimated, for the first time in the present study, to be approximately 450 ± 45 kJ mol⁻¹. Applying the Arrhenius equation, the corresponding formation temperature for extremely large IPGM grains (up to 1.3 mm) in chromite ores related to ophiolites was found to be approximately 740 °C. It seems to be consistent with a lower formation temperature than with the typical formation temperature of small PGM grains associated with ophiolitic chromitites. This suggests that coarse-grained PGM in mafic/ultramafic complexes, along the permeable shear zones, may have been re-crystallized during plastic deformation at relatively lower temperatures (700-800 °C), under appropriate pressure, temperature, redox conditions and an increased H₂O content. Thus, applying the plot of ln(r) versus 1/T on large Os-Ir-Ru-minerals (sulfides or alloys), characterized by an r value falling into the linear part of the graph and having evidence supporting their formation at relatively high temperatures, then the corresponding formation temperature of those IPGM can be found.     

Institutional scale operational symbiosis of photovoltaic and cogeneration energy systems

Due to the negative environmental effects of fossil fuel combustion, there is a growing interest in both improved efficiency in energy management and a large-scale transition to renewable energy systems. Using both of these strategies, a large institutional-scale hybrid energy system is proposed here, which incorporates both solar photovoltaic energy conversion to supply renewable energy and cogeneration to improve efficiency. In this case, the photovoltaic reduces the run time for the cogeneration to meet load, particularly in peaking air conditioning times. In turn, however, the cogeneration system is used to provide power back up for the photovoltaic during the night and adverse weather conditions. To illustrate the operational symbiosis between these two technical systems, this study provides a case study of a hybrid photovoltaic and cogeration system for the Taleghani hospital in Tehran. Three design scenarios using only existing technologies for such a hybrid system are considered here:1) single cogeneration + photovoltaic, 2) double cogeneration + photovoltaic, 3) single cogeneration + photovoltaic + storage. Numerical simulations for photovoltaic and cogeneration performance both before and after incorporating improved thermal energy management and high efficiency lighting were considered. The results show that the total amount of natural gas required to provide for the hospitals needs could be lowered from the current status by 55 % for scenario 1 and 62 % for both scenarios 2 and 3, respectively. This significant improvement in natural gas consumption illustrates the potential of hybridizing solar photovoltaic systems and cogeneration systems on a large scale.     

Dynamics of gaseous disks in a non-axisymmetric dark halo

The dynamics of a galactic disk in a non-axisymmetric (triaxial) dark halo is studied in detail using high-resolution, numerical, hydrodynamical models. A long-lived, two-armed spiral pattern is generated for a wide range of parameters. The spiral structure is global, and the number of turns can be two or three, depending on the model parameters. The morphology and kinematics of the spiral pattern are studied as functions of the halo and disk parameters. The spiral structure rotates slowly, and its angular velocity varies quasi-periodically. Models with differing relative halo masses, halo semi-axis ratios, distributions of matter in the disk, Mach numbers in the gaseous component, and angular rotational velocities of their halos are considered.     

Rectangular tank surface aerators: scale up criteria and energy conservation

Surface aeration experiments were conducted in two types of rectangular tanks of aspect ratios i.e., length to width ratio (L/W) of 1.5 and 2 and developed simulation equations to correlate the oxygen transfer coefficient, k and power number, P₀ with a parameter governing theoretical power per unit volume X. The parameter X is defined as equal to F^4/3R^1/3, where F and R are impellers’ Froude and Reynolds numbers respectively). Results have shown that the P₀ can not be simulated singularly with either Reynolds number, R or Froude number, F, which results in scale-effects; there appears to be a need to incorporate the effects of both F and R. It was found that P⁰ is uniquely related to X for rectangular aeration tanks of both aspect ratios, however, such relationships are different depending upon the aspect ratios. It has been demonstrated that energy can be saved substantially if the aeration tanks are run at relatively higher input powers. It is also demonstrated that smaller sized tanks are more energy conservative and economical when compared to big sized tanks, while aerating the same volume of water, and at the same time by maintaining a constant input power in all the tanks irrespective of their size.     

Modelling crack propagation in concrete structures with a two scale approach

A simplified computational technique based on a refined global–local method is applied to the failure analysis of concrete structures. The technique distinguishes the scale of the structure, modelled with large size finite elements, from the scale at which material non‐linearity occurs due to progressive cracking and macro‐crack propagation. The finite element solution is split into two parts: a linear elastic analysis on a coarse mesh over the entire structure and a non‐linear analysis over a small part of the structure where a dense finite element grid is employed. In the non‐linear calculation, a non‐local damage model is implemented. These two computations are coupled with the help of an iterative scheme. The size and location of the region where a non‐linear analysis is performed, is adapted to follow the development of the damage zone. Numerical examples of mode I fracture of concrete specimens with straight and curved cracks are presented. Copyright © 2003 John Wiley & Sons, Ltd.     

Cosmological magnetic dynamo in the early Universe

We study the behavior of large-scale magnetic fields in the early Universe influenced by an instability associated with breaking of mirror symmetry in weak interactions. It is shown that the magnetic field, whose present scale reaches about 500 m, which is negligible for galactic sizes, increases considerably if we correctly take into account the dynamics of the Universe. We conclude that this magnetic field is unlikely to provide the seed field for galactic dynamos, nearly independent of the particular instability considered.     

Erratum to: Mean Square Geodesic Deviation in the Zeldovich Problem on Light Propagation in a Universe with Inhomogeneities

Astronomy Reports - An Erratum to this paper has been published: https://doi.org/10.1134/S1063772921340035     

The influence of ultrahigh-energy cosmic rays on star formation in the early Universe

The presence of ultrahigh-energy (UHE) cosmic rays results in an increase in the degree of ionization in the post-recombination Universe, which stimulates the efficiency of the production of H₂ molecules and the formation of the first stellar objects. As a result, the onset of the formation of the first stars is shifted to higher redshifts, and the masses of the first stellar systems decrease. As a consequence, a sufficient increase in the ionizing radiation providing the reionization of the Universe can occur. We discuss the possible observational manifestations of these effects and their dependence on the parameters of UHE cosmic rays.     

The mass function of dark halos in superclusters and voids

A modification of the Press-Schechter model for the mass function of the dark halos, whose population develops in the presence of a supercluster or a cosmological void, is proposed. The large-scale structure is specified as a set of statistical constraints in the form of linear functionals that are applied to the initial overdensity field. The parameters and values of these functionals are related to properties of the large-scale structure: its mean density, spatial scales, and shape. The model is applied to the simple case of a spherically symmetric background structure to demonstrate a procedure for recovering these parameters by fitting the halo mass function.     

抛掷型岩爆震源体能量动态释放机制与几何尺度特征

为了进一步理解岩爆的机制并解释岩爆发生的过程,通过对抛掷型岩爆能量来源、去处及大小的分析,提出了抛掷型岩爆的震源两体模型。抛掷型岩爆本质上是释能体-岩爆体相互作用下岩石裂纹动态扩展和能量快速释放的过程。从岩爆体张拉断裂机制出发,采用脆性内聚裂纹阵列扩展动力学模型分析了裂纹间距与应变率对岩爆体能量释放速率的影响。据此得出释能体对岩爆体的作用可归结为应变率效应,释能体能量释放速率越大,对岩爆体的动态加载速率就越大,使得岩爆体能量释放速率加快。岩爆体破裂能量释放速率越大,作用于释能体的动态卸载速率就越大,又使得释能体的能量释放速率增大,两体相互作用形成的动态加、卸载效应构成了岩爆能量释放的正反馈机制。基于上述理论推导得出岩爆震源体的几何尺度是岩爆体的几倍到几十倍,理论结果与现场实际监测分析基本吻合。     

Does the LMC possess a dark bulge?

A series of numerical dynamical models for the LMC are constructed in order to fit the observed rotational velocities and stellar velocity dispersions at various galactocentric distances. The models include a three-dimensional spherical disk and nonevolving spherical components with various relative masses. The two LMC rotation curves presented by Kim et al. (1998) and Sofue (2000), which differ strongly in the inner region of the galaxy, are compared. The latter curve requires the presence of a massive dark bulge. Models based on the rotation curve of Sofue (2000) cannot account for the observed velocity dispersion or the presence of a long-lived bar in the galaxy. A model with no dark bulge is in good agreement with the observations if we assume that the disk dominates over the halo in terms of the mass within the optical radius (about 7 kpc).     

A point source of radiation in the early Universe: Solution in a one-dimensional approximation

The radiation field of a point source with a specified power in the early Universe acting for a specified time in the radiation-dominated epoch after the annihilation of electron-positron pairs is considered. A three-component model for this period is adopted. The equations of radiative transfer for the source are formulated, taking into account polarization arising during scattering of the radiation by free electrons. Analytical, numerical, and asymptotic solutions of the transfer equation are obtained for a flat model in a one-dimensional approximation, which describe the evolution of the intensity and flux of scattered radiation of the source in periods close to the onset of its action. Intervals of redshift corresponding to these periods are estimated. The behavior of the linear polarization near the source is traced. It is shown that the source radiation can be comparable to the thermal background only if the source energy is very high or we consider regions in its immediate vicinity. More optimistic estimates will require that we take into account the decrease in the degree of ionization of matter in the epoch of recombination.