Band 9, Heft 4

The aim of this paper is to investigate, by means of a numerical simulation, the effect of the half-life of cytoskeletal elements (CEs) on superposition of several waves representing concentrations of running, pausing, and off-track anterograde and retrograde CE populations. The waves can be induced by simultaneous microinjections of radiolabeled CEs in different locations in the vicinity of a neuron body; alternatively, the waves can be induced by microinjecting CEs at the same location several times, with a time interval between the injections. Since the waves spread out as they propagate downstream, unless their amplitude decreases too fast, they eventually superimpose. As a result of superposition and merging of several waves, for the case with a large half-life of CEs, a single wave is formed. For the case with a small half-life the waves vanish before they have enough time to merge.

In eukaryotic cells, the mRNA-protein interplay can be dramatically influenced by non-coding RNAs (ncRNAs). Although this new paradigm is now widely accepted, an understanding of the effect of ncRNAs on complex genetic networks is lacking. To clarify what may happen in this case, we propose a mean-field kinetic model describing the influence of ncRNA on a complex genetic network with a distributed architecture including mutual protein-mediated regulation of many genes transcribed into mRNAs. ncRNA is considered to associate with mRNAs and inhibit their translation and/or facilitate degradation. Our results are indicative of the richness of the kinetics under consideration. The main complex features are found to be bistability and oscillations. One could expect to find kinetic chaos as well. The latter feature has however not been observed in our calculations. In addition, we illustrate the difference in the regulation of distributed networks by mRNA and ncRNA.

The exact solutions of the Einstein field equations for dark energy in Kantowski-Sachs metric under the assumption on the anisotropy of the fluid are obtained for exponential and power-law volumetric expansions. The isotropy of the fluid, space and expansion are examined.

We find simple expressions for velocity of massless particles with dependence on the distance, r, in Schwarzschild coordinates. For massive particles these expressions give an upper bound for the velocity. Our results apply to static spherically symmetric metrics. We use these results to calculate the velocity for different cases: Schwarzschild, Schwarzschild-de Sitter and Reissner-Nordström with and without the cosmological constant. We emphasize the differences between the behavior of the velocity in the different metrics and find that in cases with naked singularity there always exists a region where the massless particle moves with a velocity greater than the velocity of light in vacuum. In the case of Reissner-Nordström-de Sitter we completely characterize the velocity and the metric in an algebraic way. We contrast the case of classical naked singularities with naked singularities emerging from metric inspired by noncommutative geometry where the radial velocity never exceeds one. Furthermore, we solve the Einstein equations for a constant and polytropic density profile and calculate the radial velocity of a photon moving in spaces with interior metric. The polytropic case of radial velocity displays an unexpected variation bounded by a local minimum and maximum.

Within the framework of a Bianchi type-II (BII) cosmological model the behavior of matter distribution has been considered. It is shown that the non-zero off-diagonal component of the Einstein tensor implies some severe restrictions on the choice of matter distribution. In particular, for a locally rotationally symmetric Bianchi type-II (LRS BII) space-time, it is proved that the matter distribution should be strictly isotropic if the corresponding matter field possesses only non-zero diagonal components of the energy-momentum tensor.

Fully differential cross sections are calculated for the ionization of helium by negatively charged fast projectiles using a semiclassical model developed previously for the ionization of atoms by positive projectiles. The method is tested in the case of 1 keV electron and 500 keV antiproton projectiles. The semiclassical results show reasonable agreement with the experiments and other theories. The origin of the obtained structures has been investigated by a partial wave analysis.

We present the results of spectroscopic and polarization studies of dilute rubidium vapor exposed to a single-frequency linearly polarized diode laser radiation in a spectral range of atomic D2 line. We report the origin of a circularly polarized radiation on V-type transitions of 87Rb F g = 2 → F e = 3 and 85Rb F g = 3 → F e = 4, and amplification of this radiation in backward direction caused by a partial population inversion among magnetic sublevels of the ground and excited levels. This is confirmed experimentally by high directivity of backward radiation, absence in its spectrum of 85Rb F g = 2 → F e = 1 (Λ-type) radiation, as well as by different nature of intensity dependences of backward and fluorescence radiations.

In this work, the femtosecond time-resolved photoelectron spectra and the coupling between the A2Σ+ and B2Π states of the NO molecule in a strong laser field have been investigated by the time-dependent wave packet method. We demonstrate that the weak coupling between the A2Σ+ and B2Π states of NO plays a key role on the peak centered at 0.37 eV of the photoelectron spectra in the 2+1’ channel.

The scope of this work is to estimate the effective mass-transfer coefficient in a two-phase system of oil and water fluid droplets, both being in a porous medium. To this end, a tracer is advected from the flowing aqueous phase to the immobile non-aqueous one. Partitioning at the fluid-fluid interface and surface diffusion are also taken into account. By using spatial/volume-averaging techniques, the appropriately simplified boundary-value problems are described and numerically solved for the flow velocity field and for the transport problem. The problem was found to be controlled by the Peclet number of the flowing phase, the dimensionless parameter Λ, containing both diffusion and partition in the two phases, as well as the geometrical properties of the porous structure. It is also verified that the usually involved unit cell-configurations underestimate the mass transport to the immobile phase.

Tomographic Diffractive Microscopy is a technique, which permits to image transparent living specimens in three dimensions without staining. It is commonly implemented in two configurations, by either rotating the sample illumination keeping the specimen fixed, or by rotating the sample using a fixed illumination. Under the first-order Born approximation, the volume of the frequency domain that can be mapped with the rotating illumination method has the shape of a “doughnut”, which exhibits a so-called “missing cone” of non-captured frequencies, responsible for the strong resolution anisotropy characteristic of transmission microscopes. When rotating the sample, the resolution is almost isotropic, but the set of captured frequencies still exhibits a missing part, the shape of which resembles that of an apple core. Furthermore, its maximal extension is reduced compared to tomography with rotating illumination. We propose various configurations for tomographic diffractive microscopy, which combine both approaches, and aim at obtaining a high and isotropic resolution. We illustrate with simulations the expected imaging performances of these configurations.

Eu3+-doped CaZrO3 phosphor with perovskite-type structure was synthesized by the high temperature solid-state method. The samples were characterized by X-ray diffraction, scanning electron microscopy, fluorescence spectrophotometer and UV-vis spectrophotometer, respectively. XRD analysis showed that the formation of CaZrO3 was at the calcinations temperature of 1400°C. The average diameter of CaZrO3 with 4 mol% doped-Eu3+ was 2µm. The PL spectra demonstrated that CaZrO3:Eu3+ phosphor could be excited effectively in the near ultraviolet light region (397 nm) and emitted strong red-emission lines at 616 nm corresponding to the forced electric dipole 5 D 0 → 7 F 2 transitions of Eu3+. Meanwhile, the light-emitting diode was fabricated with the Ca0.96ZrO3:Eu0.043+ phosphor, which can efficiently absorb ∼ 400 nm irradiation and emit red light. Therefore Ca0.96ZrO3:Eu0.043+ may have applications for a near ultraviolet InGaN chip-based white light-emitting diode.

Laser-driven Plasma Accelerators (LPA) have successfully generated high energy, high charge electron bunches which can reach many kA peak current, over short distances. Space charge issues, even in transport lines as simple as a drift section, have to be carefully taken into account since they can degrade the beam quality, preventing any further application of such electron beams. We analyse the space charge effects within an electron bunch with numerical simulations in order to assess their effect on the beam. We use LPA beam parameters published in previous experimental studies. These studies can give an indication of the working point where space charge can dominate the beam dynamics and has to be taken into account in the application of such beams.

The interplay between spectator and participant matter in heavy-ion collisions is investigated within the isospin-dependent quantum molecular dynamics (IQMD) model in terms of the rapidity distribution of light charged particles. The effect of different types and sizes of rapidity distributions is studied in elliptical flow. The elliptical-flow patterns show the important role of nearby spectator matter on the participant zone. This role is further explained on the basis of the passing time of the spectator and the expansion time of the participant zone. The transition from in-plane to out-of-plane emission is observed only when the mid-rapidity region is included into the rapidity bin. Otherwise no transition occurs. The transition energy is found to be highly sensitive to the size of the rapidity bin, while it is only weakly dependent on the type of the rapidity distribution. These theoretical findings are found to be in agreement with experimental results.

We present an algebra generated by a single pair of creation and annihilation operators b and b*. We prove that the algebra has a unique d-dimensional representation. Physically this algebra corresponds to a system where there are at most d − 1 particles in a state with otherwise same quantum numbers.

A simple one-dimensional spring-block chain with asymmetric interactions is considered to model an idealized single-lane highway traffic. The main elements of the system are blocks (modeling cars), springs with unidirectional interactions (modeling distance-keeping interactions between neighbors), static and kinetic friction (modeling inertia of drivers and cars) and spatiotemporal disorder in the values of these friction forces (modeling differences in the driving attitudes). The traveling chain of cars correspond to the dragged spring-block system. Contrary to most of the studies in the field of highway traffic here we focus on a measure characteristic for one car in the row. Our statistical analysis for the spring-block chain predicts a non-trivial and rich complex behavior. As a function of the disorder level in the system a dynamic phase-transition is observed. For low disorder levels uncorrelated slidings of blocks are revealed while for high disorder levels correlated avalanches dominates.

The transport of Brownian particles moving along a three-dimensional fluctuating tube is investigated in the presence of a load. The tube wall can fluctuate between two states. Coarsening the description of a process for the sake of simplifying the dynamic will result in an entropic barrier and an effective diffusion coefficient. It is found that we can control the asymmetric parameter and the load force to control the current direction and there is an optimized transition rate at which the current takes a maximum value.

In a certain sense a perfect fluid is a generalization of a point particle. This leads to the question as to what is the corresponding generalization for extended objects. Here the lagrangian formulation of a perfect fluid is much generalized by replacing the product of the co-moving vector which is a first fundamental form by higher dimensional first fundamental forms; this has as a particular example a fluid which is a classical generalization of a membrane; however there is as yet no indication of any relationship between their quantum theories.

Using the exact propagators in a constant magnetic field, the effective electromagnetic lagrangian at finite temperature and density is calculated to all orders in the field strength B within the framework of the complete electroweak model, in the weak coupling limit. The partition function and free energy are obtained explicitly and the finite temperature effective coupling is derived in closed form. Some implications of this result, potentially interesting to astrophysics and cosmology, are discussed.

We report a new metric of quantum states. This metric is built up from super-fidelity, which has a deep connection with the Uhlmann-Jozsa fidelity and plays an important role in quantum information processing. We find that the new metric possesses some interesting properties.

Group field theories whose Feynman diagrams describe 3d gravity with a varying configuration of Wilson loop observables and 3d gravity with volume observables at each vertex are defined. The volume observables are created by the usual spin network grasping operators which require the introduction of vector fields on the group. We then use this to define group field theories that give a previously defined spin foam model for fermion fields coupled to gravity, and the simpler “quenched” approximation, by using tensor fields on the group. The group field theory naturally includes the sum over fermionic loops at each order of the perturbation theory.

Within a generalized non-relativistic Fermi-liquid approach we have found general analytical formulae for phase-transition temperatures T c,1(n, H) and T c,2(n, H) (which are nonlinear functions of density, n, and linear of magnetic field, H) for phase transitions in spatially uniform, dense, pure neutron matter from normal to superfluid states with spin-triplet p-wave pairing (similar to anisotropic superfluid phases 3He - A1 and 3He - A2) in steady and homogeneous sufficiently strong magnetic field (but |µn|H ≪ E c < ɛ F(n), where µn is the magnetic dipole moment of a neutron, E c is the cutoff energy and ɛ F(n)is the Fermi energy in neutron matter). General formulae for T c,1,2(n,H) are valid for arbitrary parameterization of the effective Skyrme forces in neutron matter. We have used for definiteness the so-called SLy2, Gs and RATP parameterizations of the Skyrme forces with different exponents in their power dependence on density n (at sub- and supranuclear densities) from the interval 0.7 n 0 ≲ n < n c(Skyrme)< 2 n 0, where n 0 =0.17 fm−3 is the nuclear density and n c(Skyrme)is the the critical density of the ferromagnetic instability in superfluid neutron matter. These phase transitions might exist in the liquid outer core of magnetized neutron stars.

This article investigates the zone strong coupling two-channel totally asymmetric simple exclusion processes (TASEPs). The study is based on Pronina and Kolomeisky’s work [J. Phys. A-Math. Gen. 37, 9907 (2004)], in which the coupling exists within two whole parallel channels. Zone strong coupling two-channel TASEPs focuses on the behavior and the effect of a particular segment rather than the whole channel. The study shows that there are five possible stationary phases; LD/LD, HD/HD, MC/LD, LD/HD, and MC/HD. The phase diagrams and the density profiles are investigated using computer Monte Carlo simulations and mean-field approximation. The outcomes of the simulations match agreeably with the analytical predictions.

Within effective field theory (EFT), the critical properties of a random transverse crystal field Ising model with bond dilution are studied on a square lattice. Under both weak and strong bond dilution conditions, we consider three cases (α = 0,±0.5) of a transverse crystal field ratio, obtaining global phase diagrams in T−D x space for changes in the random transverse crystal field concentration. The phase diagrams obtained for a weak bond dilution are very similar in shape to those of pure bond but with decreases in corresponding ordered phases and critical values. However, the phase diagrams for a strong bond dilution exhibit varieties, including a change in reentrant phenomenon, the occurrence of transverse crystal field degeneration, and the opposite direction crossover of temperature peak value.

Using Foreman’s method, the core structure and Peierls stress of dislocations in bubble rafts have been investigated within the framework of the modified Peierls-Nabarro (P-N) model in which the discrete lattice effect is taken into account. The core width obtained from the modified P-N model is much wider than that from the P-N model owing to the discrete lattice effect. It is found that the core width of dislocation increases with a decrease of the bubble radius. The elastic strain energy associated with the discrete effect is considered while calculating the Peierls stress. The new expression of the Peierls stress obtained in this paper is not explicitly dependent on the particular form of the restoring force law, which is only related to the core structure parameter and can be used expediently to predict the Peierls stress of dislocations. The Peierls stress decreases rapidly with the decrease of the bubble radius.

The magnetic domain structure and Raman scattering have been studied in NiO single-crystals with three different (100), (110) and (111) orientations. Twin-domain structure was observed in NiO(100) and NiO(110) single-crystals using cross-polarized optical microscopy. We found that the ratio of the two-magnon (at 1500 cm−1) to the two-phonon (2LO, at 1100 cm−1) Raman bands intensity is sensitive in a particular way to the type of the twin-domain pattern.

We show how to simulate the equatorial section of the Schwarzschild metric through a flowing liquid crystal in its nematic phase. Inside a liquid crystal in the nematic phase, a traveling light ray feels an effective metric, whose properties are linked to perpendicular and parallel refractive indexes, n o and n e respectively, of the rod-like molecule of the liquid crystal. As these indexes depend on the scalar order parameter of the liquid crystal, the Beris-Edwards hydrodynamic theory is used to connect the order parameter with the velocity of a liquid crystal flow at each point. This way we calculate a radial velocity profile that simulates the equatorial section of the Schwarzschild metric, in the region outside of Schwarzschild’s radius, in the nematic phase of the liquid crystal. In our model, the higher flow velocity can be on the order of some meters per second.

This paper compares the luminescence of different modifications of silicon dioxide — silica glass, α-quartz crystal and dense octahedron structured stishovite crystal. Under x-ray irradiation of pure silica glass and pure α-quartz crystal, only the luminescence of self-trapped exciton (STE) is detected, excitable only in the range of intrinsic absorption. No STE luminescence was detected in stishovite since, even though its luminescence is excitable below the optical gap, it could not be ascribed to a self-trapped exciton. Under ArF laser excitation of pure α-quartz crystal, luminescence of a self-trapped exciton was detected under two-photon excitation. In silica glass and stishovite mono crystal, we spectrally detected mutually similar luminescences under single-photon excitation of ArF laser. In silica glass, the luminescence of an oxygen deficient center is presented by the so-called twofold coordinated silicon center (L.N. Skuja et al., Solid State Commun. 50, 1069 (1984)). This center is modified with an unknown surrounding or localized states of silica glass (A.N. Trukhin et al., J. Non-Cryst. Solids 248, 40 (1999)). In stishovite, that same luminescence was ascribed to some defect existing after crystal growth. For α-quartz crystal, similar to silica and stishovite, luminescence could be obtained only by irradiation with a lattice damaging source such as a dense electron beam at a temperature below 80 K, as well as by neutron or -irradiation at 290 K. In spite of a similarity in the luminescence of these three materials (silica glass, stishovite mono crystal and irradiated α-quartz crystal), there are differences that can be explained by the specific characteristics of these materials. In particular, the nature of luminescence excited in the transparency range of stishovite is ascribed to a defect existing in the crystal after-growth. A similarity between stishovite luminescence and that of oxygen-deficient silica glass and radiation induced luminescence of α-quartz crystal presumes a similar nature of the centers in those materials.

Heterojunction bipolar phototransistors, based on GaAs technology, are widely used in optoelectronic integrated circuits. One of the methods to improve phototransistor performance is applying a delta-doped thin base, which causes both a higher current gain and a better time response. There is a lack of information about this kind of device in the literature. Our work presents the results of computer simulations of AlGaAs/GaAs n-p-n phototransistors, with a bulk-doped and delta-doped base working as two- and threeterminal devices. The characteristics and device parameters obtained clearly show that phototransistors with delta-doped base have higher sensitivity and a better time response compared to the structures with a bulk-doped base. Based on simulation results, we modified the epitaxial phototransistor structure with a double delta-doped base that should improve device performance.

Mechanical tests of PVD coatings made on steel 310S were carried out within this study by the scratch test method. It was found that the additions of Al and Ir caused lower critical load values compared to the coating without additions. Despite the reduction of the critical load of the coating by the aluminium addition, the effect of aluminium was considered advantageous owing to the refinement of the structure causing the coating to become more plastic and reducing the number and sizes of micro-cracks. The addition of iridium results in an embrittlement of the coating structure and its poorer adhesion to the substrate. Comparison of the findings from the scratch test with the observations from an optical and a scanning microscopes was also made.

Some new applications of the time resonances (explosions) to new experimental data on high-energy nuclear processes are presented. These new experimental data are fitted rather well by the approach of the time resonances for the compound nuclei and clots.