The Hamiltonian formalism of the generalized unimodular gravity theory, which was recently suggested as a model of dark energy, is shown to be a complicated example of constrained dynamical system. ...The set of its canonical constraints has a bifurcation-splitting of the theory into two branches differing by the number and type of these constraints, one of the branches effectively describing a gravitating perfect fluid with the time-dependent equation of state, which can potentially play the role of dark energy in cosmology. The first class constraints in this branch generate local gauge symmetries of the Lagrangian action-two spatial diffeomorphisms-and rule out the temporal diffeomorphism which does not have a realization in the form of the canonical transformation on phase space of the theory and turns out to be either nonlocal in time or violating boundary conditions at spatial infinity. As a consequence, the Hamiltonian reduction of the model enlarges its physical sector from two general relativistic modes to three degrees of freedom including the scalar graviton. This scalar mode is free from ghost and gradient instabilities on the Friedmann background in a wide class of models subject to a certain restriction on time-dependent parameter w of the dark fluid equation of state, p=wϵ. For a special family of models this scalar mode can be ruled out even below the phantom divide line w=−1, but this line cannot be crossed in the course of the cosmological expansion. This is likely to disable the generalized unimodular gravity as a model of the phenomenologically consistent dark energy scenario, but opens the prospects in inflation theory with a scalar graviton playing the role of inflaton.
•Clays can be used as a material for electrokinetic protective reactive barriers.•Alkaline treatment results in a negative charge and acidic treatment cause a positive charge of clay ...particles.•Positively charged clay particles will bind anionic toxicants, and negatively charged ones will adsorb cationic ones.•Clays’ surface charge properties and barrier’s protective characteristics change at the point of zero charge (p.z.c.).•In the raw ‘kaolin/illite clay/montmorillonite clay’ p.z.c. values shift to the alkaline area of pH.
Coupled electrokinetic protective reactive barriers (PRB) are considered as a perspective technology for the treatment of contaminated groundwater. Design of PRB is directly connected with a problem of barrier material choice. Clays can be considered as an appropriate material due to high adsorptive properties and relative cheapness. The barrier internals are formed by clay surface charge properties. We revealed that acidic and alkaline treatment of clay is an effective way to affect its protective properties so that clay can be used to treat various pollutants. Surface charge and electrokinetic properties of clays were characterized by point of zero charge (p.z.c.), point of zero net proton charge (p.z.n.p.c.) and ζ-potential at different pH. Suspensions of 3 main clay types were studied by microelectrophoresis and potentiometric titration methods. At pH > p.z.n.p.c. clayey barrier adsorbs predominantly cationic toxicants and at pH < p.z.c. – anionic ones. The barrier is seemed to be the least effective in pH range between p.z.c. and p.z.n.p.c. Given the physicochemical and electrokinetic parameters, the most efficient clays for barrier design are Cambrian illite and all montmorillonite clays.
We present a detailed derivation of the recently suggested new type of hill-top inflation originating from the microcanonical density matrix initial conditions in cosmology driven by conformal ...field theory (CFT). The cosmological instantons of topology Formula omitted, which set up these initial conditions, have the shape of a garland with multiple periodic oscillations of the scale factor of the spatial Formula omitted-section. They describe underbarrier oscillations of the inflaton and scale factor in the vicinity of the inflaton potential maximum, which gives a sufficient amount of inflation required by the known CMB data. We build the approximation of two coupled harmonic oscillators for these garland instantons and show that they can generate inflation consistent with the parameters of the CMB primordial power spectrum in the non-minimal Higgs inflation model and in Formula omitted gravity. In particular, the instanton solutions provide smallness of inflationary slow-roll parameters Formula omitted and Formula omitted and their relation Formula omitted characteristic of these two models. We present the mechanism of formation of hill-like inflaton potentials, which is based on logarithmic loop corrections to the asymptotically shift-invariant tree-level potentials of these models in the Einstein frame. We also discuss the role of Formula omitted-gravity as an indispensable finite renormalization tool in the CFT driven cosmology, which guarantees the non-dynamical (ghost free) nature of its scale factor and special properties of its cosmological garland-type instantons. Finally, as a solution to the problem of hierarchy between the Planckian scale and the inflation scale we discuss the concept of a hidden sector of conformal higher spin fields.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
For the blends of chlorinated polyethylene and copolymer of ethylene with vinyl acetate, the effect of the introducing filler (fumed silica) on the phase behavior of the blends was investigated. It ...was found that introducing filler in polymer blends depending on its amount lead either to the increase or to the decrease in the temperature of phase separation. At the filler concentration where both components transit into the state of a border layers, the phase separation temperature increases. This effect was explained by the change of the total thermodynamic interaction parameter in the ternary system polymer–polymer–filler. At lower concentration of a filler, the possible effect is the redistribution of the blend components according to their molecular masses between filler surface (in the border layer) and in the bulk that may diminish the phase separation temperature.
Effect of the filler on the phase behavior was explained by the simultaneous action of two mechanisms: by changing the thermodynamics of interaction near the surface due to selective adsorption of one of the components and by the redistribution of components according to their molecular masses between the boundary region (near the surface) and in the matrix.
The measurements of the kinetics of phase separation and calculation of the parameters of the activation energy are in agreement with proposed mechanisms.
The change in properties and structure of clay soils due to electro-osmosis was studied. These alterations were exemplified by mantle loam and kaolin. It is shown that electro-osmotic treatment of ...the soils on the open scheme resulted in the transformations in their moisture content, total and dry density, salinity, pH, and the parameters of their particles. The most notable changes occurred within the diffuse double layers (DDLs) of soil particles such as their recharge in the anodic zone. The transformations of the loam particles DDLs resulted in their aggregation in the cathodic and anodic zones. Also, electro-osmotic flow caused the redistribution of pore sizes within the soils between the electrodes. In the case of the kaolin, electro-osmosis resulted in the formation of the anisotropic, flow-oriented structure. The change in the types of soil particles contacts formed was observed during electro-osmosis as well. The obtained data can be used to study the behavior of soil during electro-osmosis as a function of the soil type.
—In our work, we carry out a structural-spectroscopic study of AlGaN/GaN epitaxial layers grown by molecular-beam epitaxy with nitrogen-plasma activation on a hybrid substrate containing layers of ...silicon carbide and porous silicon. Using X-ray diffractometry, Raman and photoluminescence spectroscopy, it is shown that thin films formed on a hybrid substrate have minimal residual stresses and intense photoluminescence.
A method for preparation of poly(
N
-sulfoethylaminomethylstyrene) with a degree of functionalization up to 0.54 has been developed. The composition and structure of the products of polymer analogous ...transformations were characterized by elemental analysis, FTIR spectroscopy, and thermogravimetric analysis. It has been established that materials with a degree of functionalization of 0.35 and 0.5 are capable of selective sorption of noble metal ions in the presence of transition metals. An increase in the sulfoethyl group content increases the degree of extraction of Pd
II
and reduces the degree of extraction of Pt
IV
. It was also found that the studied sorbent with a degree of functionalization of 0.35 selectively extracts Ag
I
ions from multicomponent systems at pH 5.5–6.0 in an ammonium acetate buffer solution.
Numerical simulation of the interaction of the current layer in the magneto-gasdynamic channel with the induction of external magnetic fields of 1, 2, and 4 T and various load resistance values has ...been carried out. Features of the energy balance and differences in the temperature profiles in the current layers, which were both streamlined by a nonconducting gas flow and completely covered the channel cross section and interacted with the flow like a piston, are revealed. The dependences on the load resistance are obtained for the current, coefficients of current-layer permeability, and enthalpy conversion.
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