acta physica slovaca

Abstract: Properties of the Reissner-Nordstrom black-hole and naked-singularity spacetimes with a nonzero cosmological constant $\Lambda$ are represented by their geodetical structure and embedding diagrams of the central planes of both the ordinary geometry and associated optical reference geometry. Both the asymptotically de Sitter ($\Lambda > 0$) and anti-de Sitter ($\Lambda <0$) spacetimes are considered and compared with the asymptotically flat ($\Lambda = 0$) spacetimes. Motion of test particles (timelike geodesics for uncharged particles) and photons (null geodesics) is described in terms of an appropriate `effective potential.' Circular geodesics are discussed and photon escape cones are determined. The spacetimes are divided in their parameter space into separated parts according to different character of the effective potential and properties of the circular geodesics. In all asymptotically anti-de Sitter black-hole spacetimes and some asymptotically de Sitter black-hole spacetimes a region containing stable circular geodesics exists, which allows accretion processes in the disk regime. On the other hand, around some naked singularities, both asymptotically de Sitter and anti-de Sitter, even two separated regions with stable circular geodesics exist. The inner region is limited from below by particles with zero angular momentum that are located in stable equilibrium positions. The inertial and gravitational forces related to the optical reference geometry are introduced and specified for the circular motion. It is shown how the properties of the centrifugal force are closely related to the properties of the optical reference geometry embedding diagrams.

Abstract: Quantum information encoded in a pure state of a single qubit is very fragile in a sense that under the errors induced by the environment the original information is deteriorated. In this paper the protection of unknown states of qubits via symmetrisation with the help of the universal quantum entangler is discussed. It is shown, that for certain values of parameters $p_{x}$,$p_{y}$,$p_{z}$ of a Pauli channel it is useful first to entangle the original state with $N-1$ ancillas so that the output state is in a completely symmetric state of $N$ qubits and only then let the Pauli channel to act.

Abstract: The Milburn equation is solved exactly for multi-quanta Jaynes-Cummings model (JCM) in the presence of Stark shift. The influence of intrinsic decoherence and Stark shift on nonclassical properties (such as collapses and revivals of the population inversion and squeezing of the field modes) of the system is studied. The dynamical behaviour is adjusted in the presence of Stark shift. It is shown that the dynamic Stark shift plays an important role in nonclassical effects in multi-quanta processes. Also, even in the presence of Stark shift the revivals of the population inversion and squeezing of the field are destroyed in the decoherence process.

Abstract: The behavior of mortars with blends consisting of sulfoaluminate-belite (SAB) cements and ordinary Portland cement (OPC) made with cement to sand ratio of 1:3 by weight and w/c = 0.5 maintained for 90 days at 20$^\mathrm{o}$C either at 60% relative humidity (RH) - dry air or 100% RH - wet air. The results show insufficient character of hydraulic activity of SAB cements. Their quality has been improved. The replacement of 15 wt % of SAB cement by OPC influences strength positively and elasticity modulus values as well as hydrated phases and pore structure development of SAB/OPC blends relative to pure SAB cement systems. The above statements confirm the possible making technologies, when improvements in SAB cements quality will be achieved. One would then anticipate the competition in usages between SAB/OPC and blast furnace-slag Portland cement (BFSPC) systems in the practice. It is important to consider because SAB cements are of great advantage from the viewpoint of energy savings and quantity of CO$_{2}$ released during their production. Thermal characteristics of the samples were studied by thermogravimetry (TG) and differential thermal analysis (DTA) from room temperature to 1000$^\mathrm{o}$C in air atmosphere. Generally, four significant temperature regions on TG curves with the respective DTA peak temperature for all types of samples are observed.

Abstract: In the case of applied distorted pulse, the single pulse echo in amorphous magnets, caused by the tunneling two-level systems located inside 180$^\cir$ Bloch walls has been studied. It is shown that in case of TLS the single-pulse echo formation is characterized by some specificity due to the wide distribution of the TLS splitting energy.

Abstract: The 1D Kane oscillator is analysed. It is defined by the Schrodinger-Wannier equation in which the potential-energy term represents the zero-centred quadratic well and in which the `kinetic-energy' term is chosen as an operator corresponding to the conduction-electron dispersion function of the Kane two-band theory. The author considers the approximate form of the Kane function for the conduction band well-known in the theory of narrow-gap semiconductors. Employing the momentum representation, he calculates the eigen-energies of the electrons in frame of the WKB approach. The eigen-energies are roots of a transcendental equation involving the complete elliptic integrals of the first and second kind. The author presents a detailed discussion of the dependence of the eigen-energies of the electrons on the Kane nonparabolicity of the conduction band.

Abstract: Hydrogenated amorphous carbon (a-C:H) films have been prepared by a combined magnetron sputtering-CVD deposition method in argon/methane atmosphere. The most critical process parameter determining the film properties is the ion bombardment occurring during deposition. In the presented deposition method the ion bombardment during deposition can be studied and controlled over a wide range. The effect of the deposition parameters (gas pressure, discharge power, applied bias voltage) on the deposition rate were investigated. The reactive radicals generated in the plasma were identified and monitored by optical emission spectrometry (OES).