[en] We discuss astrophysical implications of the modified gravity model in which the two matter components, ordinary and dark, couple to separate gravitational fields that mix to each other through small mass terms. There are two spin-2 eigenstates: the massless graviton, which induces universal Newtonian attraction, and the massive one, which gives rise to the Yukawa-like potential which is repulsive between the ordinary and dark bodies. As a result for distances much smaller than the Yukawa radius r_m the gravitation strength between the two types of matter becomes vanishing. If r_m∝10 kpc, the typical size of a galaxy, there are interesting implications for the nature of dark matter. In particular, one can avoid the problem of the cusp that is typical for the cold dark matter halos. Interestingly, the flat shape of the rotational curves can be explained even in the case of the collisional and dissipative dark matter (as e.g. mirror matter), which cannot give the extended halos but instead must form galactic discs similarly to the visible matter. The observed rotational curves for the large, medium-size and dwarf galaxies can be nicely reproduced. We also briefly discuss possible implications for the direct search of dark matter. (orig.)

[en] The nature of the gravitational interaction between ordinary and dark matter is still open. Any deviation from universality or the Newtonian law also modifies the standard assumption of collisionless dark matter. On the other hand, obtaining a Yukawa-like large-distance modification of the gravitational potential is a nontrivial problem, that has so far eluded a consistent realization even at linearized level. We propose here a theory providing a Yukawa-like potential, by coupling non-derivatively the two metric fields related respectively to the visible and dark matter sectors, in the context of massive gravity theories where the local Lorentz invariance is broken by the different coexisting backgrounds. This gives rise to the appropriate mass pattern in the gravitational sector, producing a healthy theory with the Yukawa potential. Our results are of a special relevance in the scenario of dark matter originated from the mirror world, an exact duplicate of the ordinary particle sector.

[en] Simultaneous multi-variable gradient-based optimization is performed on a 300 MWe wet-recycling pressurized oxy-coal combustion process with carbon capture and sequestration. A direct contact separation column is utilized for practical and reliable low-temperature thermal recovery. The models for the components include realistic behavior like heat losses, steam leaks, pressure drops, and cycle irreversibilities. Moreover, constraints are used for technoeconomical considerations. Optimization involves 17 optimization variables and 10 constraints, with the objective of maximizing the thermal efficiency. The optimization procedure utilizes recent design rules and optimization procedures for optimal Rankine cycle performance speeding up the plant optimization process by eliminating variables and avoiding constraint violations. Moreover, the procedure partially alleviates convergence to suboptimal local optima. The basecase of the study is a comprehensively optimized cycle that utilizes a surface heat exchanger, a more thermodynamically-effective form of thermal recovery which however bears significant materials challenges. Upon optimization, the cycle utilizing the direct column is seen to be very attractive regarding efficiency and performance. Moreover, the optimization results unveil potential for reducing capital costs by eliminating the first carbon sequestration intercooled compressor and by showing possibilities of process intensification between the separation column and the carbon sequestration purification columns. -- Highlights: ► Direct contact column is viable technology for acid removal and heat recovery. ► Direct contact column results in higher optimal operating pressure than surface heat exchanger. ► Direct contact column allows for reduction of capital costs.