Microscopic Scenario Research Articles

Atypical Case of the Dielectric Relaxation Responses and its Fractional Kinetic Equation

Abstract We present a probabilistic model of the microscopic scenario of dielectric relaxation relating to the atypical case of two-power-law responses.The surveyed approach extends the cluster model concept used for the description of the typical, Havriliak-Negami (HN) law. Within the proposed framework, all empirical two-power-law relaxation patterns may be derived. Their relaxation functions are expressed in terms of the three-parameter Mittag-Leffler function, and the kinetic equation takes the pseudodifferential form generalizing the Riemann-Louiville fractional calculus. This provides a clue to explain the universality observed in relaxation phenomena.

Self-similarity of strangeness production in pp collisions at RHIC

New experimental data on transverse momentum spectra of strange particles (K0S,K–, K*, ϕ, …) produced in pp collisions at √s = 200 GeV obtained by the STAR and PHENIX collaborations at RHIC are analysed in the framework of z-scaling approach. Scaling properties of the data z-presentation are illustrated. Self-similarity of strange particle production is discussed. A microscopic scenario of constituent interactions developed within the z-scaling approach is used to study constituent energy loss, proton momentum fraction and recoil mass in dependence on the transverse momentum, strangeness, and mass of the inclusive particle. The obtained results can be useful for understanding strangeness origin, for searching for new physics with strange probes and can serve as a benchmark for complex analyses of self-similar features of strange production in heavy ion collisions.

Density functional study on positively charged six-coordinate FeO2 porphyrin complex for a trigger of O2 dissociation

Properties on electronic structure in an Fe-porphyrin (FeP) complex with the proximal imidazole (Im) ligand, a model of active moiety of hemeprotein for analyzing bonding- and separating-processes of dioxygen molecule (O2), were studied by means of spin-polarized density functional theory. It was found that in the ionized model, the bonding stability of O2 was reduced by one order in energy compared with that of the neutral model, implying existence of the state having a large fluctuation between bonded and separated configurations. We proposed a microscopic scenario on O2 dissociation phenomenon in terms of spin-crossover and allosteric mechanism.

Evolution through the stochastic dyadic Cantor Set: the uniqueness of mankind in the Universe

AbstractThe search for intelligent life or any type of life involves processes with nonlinear chaotic behaviours throughout the Universe. Through the sensitive dependence condition, chaotic dynamics are also difficult or impossible to duplicate, forecast and predict. Similar evolution patterns will result in completely different outcomes. Even, the intelligent life evolution pattern, based on carbon, DNA–RNA–protein, will differ from all possible sequences. In the present paper, the stochastic dyadic Cantor set models the many possible variations of such chaotic behaviours in the Universe, yielding to a tendency to zero, for any scenario of intelligent life evolution. The probability of the development of the exact microscopic and macroscopic scenario that is capable of supporting intelligent life or any other type of life in any planet is vanishingly small. Thus, the present analysis suggests that mankind, as an extremely statistically uncommon occurrence, is unique and alone in the Universe.

Enhancement of superconductivity at the onset of charge-density-wave order in a metal

We analyze superconductivity in the cuprates near the onset of an incommensurate charge density wave (CDW) order with momentum ${\bf Q} = (Q,0)/(0,Q)$, as observed in the experiments. We first consider a semi-phenomenological charge-fermion model in which hot fermions, separated by ${\bf Q}$, attract each other by exchanging soft CDW fluctuations. We find that in a quantum-critical region near CDW transition, $T_c = A {\bar g}_c$, where ${\bar g}_c$ is charge-fermion coupling and $A$ is the prefactor which we explicitly compute. We then consider the particular microscopic scenario in which CDW order parameter emerges as a composite field made out of primary spin-density-wave fields. We show that charge-fermion coupling ${\bar g}_c$ is of order of spin-fermion coupling ${\bar g}_s$. As the consequence, superconducting $T_c$ is substantially enhanced near the onset of CDW order. Finally we analyze the effect of an external magnetic field $H$. We show that, as $H$ increases, optimal $T_c$ decreases and the superconducting dome becomes progressively more confined to the CDW quantum-critical point. These results are consistent with the experiments.

Molecular Na-channel excitability from statistical physics

The excitable properties of the neural cell membrane is the driving mechanism of the neural pulses. Coordinated ionic fluxes across Na and K channels are the devices responsible of this function. Here we present a simple microscopic physical scenario which accounts for this phenomenology. The main elements are ions and channel doors that obey the standard formulation of statistical physics (overdamped Langevin equations) with appropriate nonlinear interacting potentials. From these equations we obtain the ionic flux and the dynamics of the membrane potential. We show that the excitable properties of the membrane are present in a single and simple Na channel. From this framework, additional microscopic information can be obtained, such as statistics of single-channels dynamics or the energetics of action potential events.

Thermodynamics of the 2-D Ising Model From a Random Path Sampling Method

We explore the thermodynamics of the 2-D Ising model from a random path sampling method. We show how convergence of free energy and magnetization is obtained in a number of sweeps orders of magnitude below the number of total configurations. The effects of external parameters, such as magnetic field (H) and temperature (T) are accounted in a computationally simple way, allowing very detailed (H, T)-dependent calculations. The effects of more complex interactions can also be considered, particularly magnetovolume coupling, which has proven to be difficult to tackle using traditional approaches. We show its effect on magnetic entropy change (magnetocaloric effect) in this microscopic scenario. As magnetic refrigeration technology matures, the microscopic optimization of magnetovolume effects to enhance the magnetocaloric properties may become a valuable tool in the search of new magnetic refrigerants.

Self-similarity of Low-p T cumulative pion production in proton-nucleus collisions at U70

The data on inclusive momentum spectra of π± mesons produced in p + A collisions over the range pL =15–65 GeV/c and θlab = 159° at U70 are analyzed in the framework of z-scaling approach. Self-similarity of the pion production in the low-pT cumualtive region is verified. Scaling function ψ(z) for Be, C, Al, Ti, Mo, W nuclei is constructed. It is expressed via the invariant cross section and the average multiplicity density of charged particles. Results of the analysis are compared with data obtained by J. Cronin, R. Sulyaev, and D. Jaffe groups at pL = 70, 400 GeV/c, pT > 1 GeV/c and θcms − 90°. A microscopic scenario of p + A interactions in terms of momentum fractions x1, x2 is discussed. Indication on self-similarity of the low-pT cumulative pion production in p + A collisions was found. Universality of the shape of the scaling function is used to predict inclusive cross sections of π+ and π− pions produced in p + A collisions on Be, C, Al, Ti, Mo, W targets in the deep-cumulative region (x2 ≫ 1/A).

Self-similarity of high-p T cumulative hadron production in p + A collisions at high energies at U70

New data on inclusive transverse momentum spectra of charged hadrons produced in p + A collisions at U70 are analyzed in the framework of the z-scaling approach. Self-similarity of the hadron production in the high-pT cumualtive region is verified. Scaling function ψ(z) for C, Al, Cu, W nuclei is constructed. It is expressed via the invariant cross section and the average multiplicity density of charged particles. Results of analysis are compared with the data obtained by J. Cronin, R. Sulyaev and D.Jaffe groups. Self-similarity of the hadron production in p + A collisions over a wide kinematical range is verified. A microscopic scenario of p + A interactions in terms of momentum fractions x1, x2 is discussed. Indication on self-similarity of the high-pT cumulative hadron production in p + A collisions over a wide kinematical range has been found. Based on the universality of the shape of the scaling function the inclusive cross sections of h− and h+ hadrons produced in p + A collisions on C, Al, Cu, W targets in the high-pT deep-cumulatice region are predicted.

Interaction of a long alkyl chain protic ionic liquid and water.

A combined experimental/theoretical approach has been used to investigate the role of water in modifying the microscopic interactions characterizing the optical response of 1-butyl-ammonium nitrate (BAN) water solutions. Raman spectra, dominated by the signal from the protic ionic liquid, were collected as a function of the water content, and the corresponding spatial organization of the ionic couples, as well as their local arrangement with water molecules, was studied exploiting classical molecular dynamics calculations. High quality spectroscopic data, combined with a careful analysis, revealed that water affects the vibrational spectrum BAN in solution: as the water concentration is increased, peaks assigned to stretching modes show a frequency hardening together with a shape narrowing, whereas the opposite behavior is observed for peaks assigned to bending modes. Calculation results clearly show a nanometric spatial organization of the ionic couples that is not destroyed on increasing the water content at least within an intermediate range. Our combined results show indeed that small water concentrations even increase the local order. Water molecules are located among ionic couples and are closer to the anion than the cation, as confirmed by the computation of the number of H-bonds which is greater for water-anion than for water-cation. The whole results set thus clarifies the microscopic scenario of the BAN-water interaction and underlines the main role of the extended hydrogen bond network among water molecules and nitrate anions.

Self-similarity of low-p T cumulative pion production in proton-nucleus collisions at high energies

The experimental data on inclusive spectra of the π+ mesons produced in p + A collisions at the incident proton momentum of 400 GeV/c obtained by G. Leksin group at FNAL are analyzed in the framework of z-scaling. Self-similarity of the hadron production in the low-pT cumulative region is verified. Scaling function ψ(z) for the Li, Be, C, Al, Cu, Ta nuclei is constructed. It is expressed via the invariant cross section and average multiplicity density of charged particles. Results of the analysis of the low-pT data are compared with the high-pT data sets obtained by J. Cronin, R. Sulyaev and D. Jaffe groups. A microscopic scenario of p + A interactions in terms of momentum fractions x1, x2 is discussed. Indication on self-similarity of the cumulative pion production in p + A collisions over a wide kinematical range has been found. Based on the universality of the shape of the scaling function the inclusive cross sections of the π+ mesons produced in p + A collisions on the Li, Be, C, Al, Cu, Ta targets in deep-cumulative region (x2 ≫ 1/A) are predicted.

Beam Energy Scan at RHIC and z-Scaling

Beam Energy Scan (BES) data obtained at RHIC are briefly reviewed. Method of data analysis (z-scaling approach) based on self-similarity and locality of constituent interactions in hadron and nucleus collisions at high energy is described. The method is applied for analysis of BES data to search for signatures of phase transition and Critical Point (CP). Some results of analysis of hadron spectra measured in heavy ion collisions (HIC) at RHIC over a wide range of the energy sNN=7.7–200 GeV are presented. Microscopic scenario of constituent interactions in the framework of this approach is discussed. Dependence of the energy loss on the momentum of the produced hadron, energy and centrality of the collision is studied. Self-similarity of the constituent interactions in terms of momentum fractions is used to characterize the nuclear medium by a “specific heat” and the colliding nuclei by fractal dimensions. Kinematic regions which are assumed to be most preferable for search for signatures of phase transition of nuclear matter produced in HIC in BES are discussed.

Lithium Ion Transport Mechanism in Ternary Polymer Electrolyte-Ionic Liquid Mixtures: A Molecular Dynamics Simulation Study.

The lithium transport mechanism in ternary polymer electrolytes, consisting of PEO20LiTFSI and various fractions of the ionic liquid PYR13TFSI, is investigated by means of MD simulations. This is motivated by recent experimental findings (Passerini et al. Electrochim. Acta2012, 86, 330), which demonstrated that these materials display an enhanced lithium mobility relative to their binary counterpart PEO20LiTFSI. In order to grasp the underlying microscopic scenario giving rise to these observations, we employ an analytical, Rouse-based cation transport model (Maitra et al. Phys. Rev. Lett.2007, 98, 227802), which has originally been devised for conventional polymer electrolytes. This model describes the cation transport via three different mechanisms, each characterized by an individual time scale. It turns out that also in the ternary electrolytes essentially all lithium ions are coordinated by PEO chains, thus, ruling out a transport mechanism enhanced by the presence of ionic-liquid molecules. Rather, the plasticizing effect of the ionic liquid contributes to the increased lithium mobility by enhancing the dynamics of the PEO chains and consequently also the motion of the attached ions. Additional focus is laid on the prediction of lithium diffusion coefficients from the simulation data for various chain lengths and the comparison with experimental data, thus demonstrating the broad applicability of our approach.

Ferroelectricity enhanced by disorder in collinear-magnetism-induced multiferroic state

To understand the fantastic static-disorder-enhanced ferroelectricity observed in Ca3Co2−xMnxO6 compound, the multiferroic state originated from the up-up-down-down spin order in different conditions of disorder is simulated by using Monte Carlo algorithm on a three-dimensional elastic Ising model with dilution. The spin structure factor and the correlation of ionic displacements are calculated to show the detailed variations of microscopic magnetic and ferroelectric structures. It is indicated that in the pure system without disorder the frustration from the long-ranged interchain interaction disrupts the up-up-down-down spin order and the corresponding ferroelectric domain, and hence suppresses the ferroelectric polarization (P). When disorder is introduced by doping a few spin defects, the frustration can be relaxed around these defects. Then the disturbance upon ferroelectric domain is lessened and hereby P is recovered effectively. The result obtained gives a clear microscopic scenario of the static-disorder-enhanced ferroelectricity observed in Ca3Co2−xMnxO6 compound.

Energy scan in heavy-ion collisions and search for a critical point

Experimental data on inclusive spectra measured in heavy-ion collisions at RHIC and SPS over a wide range of the energy \(\sqrt {s_{NN} } = 9 - 200\) GeV are analyzed in the framework of z scaling. A microscopic scenario of constituent interactions in the framework of this approach is discussed. Dependence of the energy loss on the momentum of the produced hadron, energy, and centrality of the collision, is studied. Self-similarity of the constituent interactions in terms of momentum fractions is used to characterize the nuclear medium by “specific heat” and colliding nuclei by fractal dimensions. Preferable kinematical regions for search for signatures of the phase transition of the nuclearmatter produced inHIC are discussed. Discontinuity of “specific heat” is assumed to be a signature of the phase transition and the Critical Point.

Abrikosov vortex escape from a columnar defect as a topological electronic transition in a vortex core

The microscopic scenario of vortex escape from a columnar defect under the influence of a transport current has been studied. For defect radii smaller than the superconducting coherence length the depinning process is shown to be a consequence of two subsequent topological electronic transitions in a trapped vortex core. The first transition at a critical current j L is associated with the opening of Fermi surface segments corresponding to the creation of a vortex-antivortex pair bound to the defect. The second transition at a certain current j d > j L is caused by merging of different Fermi surface segments, which accompanies the formation of a freely moving vortex.

Molecular theory of smectic ordering in liquid crystals with nanoscale segregation of different molecular fragments

A molecular statistical theory of the smectic A phase is developed taking into account specific interactions between different molecular fragments which enables one to describe different microscopic scenario of the transition into the smectic phase. The effects of nanoscale segregation are described using molecular models with different combinations of attractive and repulsive sites. These models have been used to calculate numerically coefficients in the mean filed potential as functions of molecular model parameters and the period of the smectic structure. The same coefficients are calculated also for a conventional smectic with standard Gay-Berne interaction potential which does not promote the segregation. The free energy is minimized numerically to calculate the order parameters of the smectic A phases and to study the nature of the smectic transition in both systems. It has been found that in conventional materials the smectic order can be stabilized only when the orientational order is sufficiently high, In contrast, in materials with nanosegregation the smectic order develops mainly in the form of the orientational-translational wave while the nematic order parameter remains relatively small. Microscopic mechanisms of smectic ordering in both systems are discussed in detail, and the results for smectic order parameters are compared with experimental data for materials of various molecular structure.

Search for signatures of phase transition and critical point in heavy-ion collisions

The general concepts in the critical phenomena related with the notions of “scaling” and “universality” are considered. Behavior of various systems near a phase transition is displayed. Search for clear signatures of the phase transition of the nuclear matter and location of the critical point in heavy-ion collisions (HIC) is discussed. The experimental data on inclusive spectra measured in HIC at RHIC and SPS over a wide range of energies s 1/2 = 9–200 GeV are analyzed in the framework of z-scaling. A microscopic scenario of the constituent interactions is presented. Dependence of the energy loss on the momentum of the produced hadron, energy and centrality of the collision is studied. Self-similarity of the constituent interactions described in terms of momentum fractions is used to characterize the nuclear medium by “specific heat” and colliding nuclei by fractal dimensions. Preferable kinematical regions to search for signatures of the phase transition of the nuclear matter produced in HIC are discussed. Discontinuity of the “specific heat” is assumed to be a signature of the phase transition and the critical point.

On saturation of charged hadron production in pp collisions at LHC

First results on charged hadron transverse momentum spectra in pp collisions obtained by the CMS Collaboration at the LHC are analyzed in the z-scaling approach. These LHC data confirm z-scaling. The saturation regime of the scaling function ψ(z) observed in pp and interactions at lower energies GeV is verified. The saturation of ψ(z) for charged hadrons is found down to a value of z ≃ 0.05 at the highest energy GeV currently reached by the colliders. A microscopic scenario of hadron production is discussed in connection with the search for new signatures of phase transitions in hadron matter. Constituent energy loss and its dependences on the transverse momentum and collision energy are estimated. We suggest that the beam energy scan program in the saturation region at the LHC could be of interest.

Self-similarity of pion production in AA collisions at RHIC

Experimental data on inclusive spectra of pions produced in heavy-ion collisions at RHIC are analyzed in the framework of z-scaling. The data indicate similarity as a characteristic feature of the mechanism of pion production at high energies. It is argued that this property includes structure of the colliding objects, interaction of their constituents, and character of the fragmentation process. A microscopic scenario of nucleus interactions at a constituent level in terms of momentum fractions is developed. The centrality dependence of the shape of the scaling function Ψ(z) and the fractal dimention ɛ AA of the fragmentation process is studied. Energy losses of particles in the final state as a function of the collision energy, transverse momentum, and centrality are estimated. The scale dependence of the energy losses is discussed. A decreasing tendency of specific heat of the produced medium with the system size is established. The obtained results may be exploited to search for and study new physics phenomena in pion production in pp and AA collisions at high multiplicities.