Search

We present a study of social networks based on the analysis of Brazilian and Portuguese family names (surnames). We construct networks whose nodes are names of families and whose edges represent parental relations between two families. From these networks we extract the connectivity distribution, clustering coefficient, shortest path and centrality. We find that the connectivity distribution follows an approximate power law. We associate the number of hubs, centrality and entropy to the degree of miscegenation in the societies in both countries. Our results show that Portuguese society has a higher miscegenation degree than Brazilian society. All networks analyzed lead to approximate inverse square power laws in the degree distribution. We conclude that the thermodynamic limit is reached for small networks (3 or 4 thousand nodes). The assortative mixing of all networks is negative, showing that the more connected vertices are connected to vertices with lower connectivity. Finally, the network of surnames presents some small world characteristics.

We propose a random walk model with q -exponentially decaying memory profile. The q -exponential function is a generalization of the ordinary exponential function. In the limit q → 1 , the q -exponential becomes the ordinary exponential function. This model presents a Markovian diffusive regime that is characterized by finite memory correlations. It is well known, that central limit theorems prohibit superdiffusion for Markovian walks with finite variance of step sizes. In this problem we report the outcome of a transient superdiffusion for finite sized walks.

We analyze the diffusion of a system on a backbone structure, by considering the presence of reaction terms. We start our analysis by considering an irreversible reaction process, where the particles are removed from the system. After, we consider the diffusion subjected to a reversible reaction process. The behavior for the system in this scenario depends on the relative rates of diffusion and reaction. For these cases, we obtain exact solutions in terms of the Green function approach and show a rich class of behavior which can be related to anomalous diffusion.

One of the most important quantities of interest in the theory of diffusion and transport is the random walk propagator. For Markovian processes, such as the standard Brownian random walk and Levy flights, the functional form of the random walk propagator is well understood. Similarly, for certain kinds of simple non-Markovian processes, such as Levy walks, the problem can be mapped to a solvable Markovian model. However, more complicated non-Markovian walks pose a challenge. Here we study a non-Markovian model that is rich enough to exhibit superdiffusion, normal diffusion and subdiffusion regimes (Kumar, Harbola, and Lindenberg (2010)). We numerically estimate propagators for this model and obtain good fits with a family of non-Levy propagators based on the Tsallis q -exponential function. We conclude that stops and restrictions play similar roles in the long time limit of the propagator.

Deep connections are known to exist between scale-free networks and non-Gibbsian statistics. For example, typical degree distributions at the thermodynamical limit are of the form "Equation missing", where the q-exponential form "Equation missing" optimizes the nonadditive entropy Sq (which, for q → 1, recovers the Boltzmann-Gibbs entropy). We introduce and study here d-dimensional geographically-located networks which grow with preferential attachment involving Euclidean distances through "Equation missing". Revealing the connection with q-statistics, we numerically verify (for d = 1, 2, 3 and 4) that the q-exponential degree distributions exhibit, for both q and k, universal dependences on the ratio αA/d. Moreover, the q = 1 limit is rapidly achieved by increasing αA/d to infinity.

We investigate a fractional diffusion equation with a nonlocal reaction term by using the Green function approach. We also consider a modified spatial operator in order to cover situations characterized by a noninteger dimension. The results show a nonusual spreading of the initial condition which can be connected to a rich class of anomalous diffusive processes.

Here we study how a traffic jam spreads on complex networks when driven by an increasing flux between certain initial and final points. For that purpose, we developed two new traffic models based on vehicular traffic and applied them on the Apollonian network and the Swiss road network. The first model is an electrical analog, using ohmic and non-ohmic resistors which is a classical approach in Physics while the second one which we call the herding model, is based on human driving behavior. For both models, we study the sequence of clogged roads up to the traffic gridlock and display the fragilities of the network. In the electrical model, by increasing the external potential, resistors burn out, as the voltage drop between the ends increases above a certain threshold. Analyzing both models, we observed some power-law functions that occur only near a traffic gridlock as well as the dependence on topological features of the network and influence on flux and the robustness in Apollonian networks of different generations.

We analyze the absorbing state phase transition exhibited by two distinct unidimensional delayed contact process (CP). The first is characterized by the introduction of an infection period and the second by an immune period in the dynamics of the original model. We characterize these CP by the quantities t d (infection or disease period) and t i (immune period). The quantity t d corresponds to the period interval an individual remains infected after being contaminated, while the period t i is the time interval an individual remains immune after being cured. We used Monte Carlo simulations to compute the critical parameters associated with the absorbing state phase transition exhibited by these models. We find two distinct power-law scale relations for the critical infection rate [Formula: see text] and the critical cure rate [Formula: see text]. For the CP delayed by the minimum infection period we find μd = 0.98, while we obtained μi = 0.80 for the case of a delay due to immunity. In addition, we used a finite-size scaling analysis to estimate the critical exponents β/ν and ν, and found that these models belong to the universality class of directed percolation irrespective to the time delay.

The solutions of a nonlinear diffusion equation by considering the radially symmetric \({\mathcal{N}}\)-dimensional case are investigated. This equation has the nonlinearity present in the diffusive term and external force. The solutions are obtained by using a similarity method and connected to the q-exponential and q-logarithmic functions which emerge from the Tsallis formalism. In addition, the results obtained here may be useful to investigate a rich class of situations related to anomalous diffusion.

We investigate solutions, by using the Green function approach, for a system governed by a non-Markovian Fokker-Planck equation and subjected to a Comb structure. This structure consists of the axis of structure as the backbone and fingers which are attached perpendicular to the axis. For this system, we consider an arbitrary initial condition, in the presence of time dependent diffusion coefficients and spatial fractional derivative, and analyze the connection to the anomalous diffusion.

We investigate an N -dimensional fractional diffusion equation with radial symmetry by taking a spatial and time dependent diffusion coefficient into account, i.e., D ˜ ( r , t ) = D ( t ) r − η with D ( t ) = D δ ( t ) + D ¯ ( t ) . The equation is considered in a confined region and subjected to time dependent boundary conditions which may be related to inhomogeneous characteristics of the surfaces confining the system. The results show an anomalous spreading of the solutions and an unusual behavior of the survival probability.

We consider the low-temperature specific heat spectra of long-range correlated quasiperiodic DNA molecules using a q -gaussian distribution, and compare them with those considering the Boltzmann-Gibbs distribution. The energy spectra are calculated using the one-dimensional Schrodinger equation in a tight-binding approximation with the on-site energy exhibiting long-range disorder and non-random hopping amplitudes. We focus our attention at the low temperature region, where the specific heat spectra presents a logarithmic-periodic oscillations as a function of the temperature T around a mean value given by a characteristic dimension of the energy spectrum.

We obtain time dependent solutions for a fractional diffusion equation containing a nonlocal term by considering the spherical symmetry and using the Green function approach. The nonlocal term incorporated in the diffusion equation may also be related to the spatial and time fractional derivative and introduces different regimes of spreading of the solution with the time evolution. In addition, a rich class of anomalous diffusion processes may be described from the results obtained here.

The one-dimensional Domany-Kinzel cellular automaton is investigated by two numerical approaches: (i) the spontaneous-search method, which is a method appropriated for a search of criticality; (ii) short-time dynamics. Both critical frontiers of the system are investigated, namely, the one separating the frozen and active phases, as well as the critical line determined by damage spreading between two cellular automata, that splits the active phase into the nonchaotic and chaotic phases. The efficiency of the spontaneous-search method is established herein through a precise estimate of both critical frontiers, and in addition to that, it is shown that this method may also be used in the determination of the critical exponent ν⊥. Using the critical frontiers obtained, other exponents are estimated through short-time dynamics. It is verified that the critical exponents of both critical frontiers fall in the universality class of directed percolation.

We investigate the solutions of the Burgers equation ∂ t u ( x , t ) = D ∂ x 2 u ( x , t ) − ∂ x [ F ( x , t ) u ( x , t ) ] − κ u ( x , t ) ∂ x u ( x , t ) + Φ ( x , t ) , where F ( x , t ) is an external force and Φ ( x , t ) represents a forcing term. This equation is first analyzed in the absence of the forcing term by taking F ( x , t ) = k 1 ( t ) − k 2 ( t ) x into account. For this case, the solution obtained extends the usual one present in the Ornstein–Uhlenbeck process and depending on the choice of k 1 ( t ) and k 2 ( t ) it can present a stationary state or an anomalous spreading. Afterwards, the forcing terms Φ ( x , t ) = Φ 1 ( t ) + Φ 2 ( t ) x and Φ ( x , t ) = Φ 3 x − Φ 4 / x 3 are incorporated in the previous analysis and exact solutions are obtained for both cases.

This work is devoted to investigate the solutions of the one-dimensional diffusion equation by taking the nonlinear external force F ( x , t ; ρ ) = − k ( t ) x + K / x + κ x | x | α − 1 [ ρ ( x , t ) ] η into account. Our investigation is first performed by considering the case α = 0 and η = 1 , which results in a Burgers like equation with a spatial and time dependent external force. After, we consider the case α ≠ 0 and η = α + 1 and show that the solution found may be expressed in terms of the q-exponential functions present in the Tsallis formalism. In addition, we also discuss the stationary solution for α and η arbitraries.

We obtain solutions for a fractional diffusion equation by taking the spherical symmetry into account and using the Green function approach. These solutions are found in a confined region by considering a spatial and time dependent boundary conditions, i.e, inhomogeneous surfaces. In our analysis, we also consider the diffusion coefficient given by D ( r ¯ ) = D r - η , the presence of the external force F ¯ ( r ) = K / r 1 + η r ˆ and a source (or absorbent) term. They show us an anomalous behavior due to the presence of the fractional derivative and the surface which for this case is inhomogeneous.

High signal to noise, high resolution spectra were obtained for a sample of normal, mild barium, and barium giants. Atmospheric parameters were determined from the FeI and FeII lines. Abundances for Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Sr, Y, Zr, Ba, La, Ce, Nd, Sm, Eu, and Gd, were determined from equivalent widths and model atmospheres in a differential analysis, with the red giant Eps Vir as the standard star. The different levels of s-process overabundances of barium and mild barium stars were earlier suggested to be related to the stellar metallicity. Contrary to this suggestion, we found in this work no evidence of barium and mild barium to having different range in metallicity. However, comparing the ratio of abundances of heavy to light s-process elements, we found some evidence that they do not share the same neutron exposure parameter. The exact mechanism controlling this difference is still not clear. As a by-product of this analysis we identify two normal red giants misclassified as mild barium stars. The relevance of this finding is discussed. Concerning the suggested nucleosynthetic effects possibly related to the s-process, for elements like Cu, Mn, V and Sc, we found no evidence for an anomalous behavior in any of the s-process enriched stars analyzed here. However, further work is still needed since a clear [Cu/Fe] vs. [Ba/H] anticorrelation exists for other s-process enriched objects., 34 pages, 18 figures, A&A accepted (revised version)

Aims: To investigate the prevalence and characteristics of Shiga toxin-producing Escherichia coli (STEC) in cattle from Parana State, southern Brazil. Methods and Results: One hundred and seven faeces cattle samples were cultured on Sorbitol-MacConkey agar. Escherichia coli colonies were tested for production of Shiga toxin using Vero-cell assay. A high prevalence (57%) of STEC was found. Sixty-four STEC were serotyped and examined for the presence of stx1, stx2, eae, ehxA and saa genes and stx2 variants. The isolates belonged to 31 different serotypes, of which three (O152:H8, O175:H21 and O176:H18) had not previously been associated with STEC. A high prevalence of stx2-type genes was found (62 strains, 97%). Variant forms found were stx2, stx2c, stx2vhb, stx2vO111v/OX393 and a form nonclassifiable by PCR-RFLP. The commonest genotypes were stx2ehxA saa and stx1stx2ehxA saa. Conclusions: A high frequency of STEC was observed. Several strains belong to serotypes previously associated with human disease and carry stx2 and other virulence factors, thus potentially representing a risk to human health. Significance and Impact of the Study: This is the first study of STEC in Parana State, and its findings emphasize the need for proper cattle handling to prevent human contamination.

We devote this work to investigate the solutions of a generalized diffusion equation which contains spatial fractional derivatives and nonlinear terms. The presence of external forces and absorbent terms is also considered. The solutions found here can have a compact or long tail behavior and, in particular, for the last case in the asymptotic limit, we relate these solutions to the Levy or Tsallis distributions. In addition, from the results presented here a rich class of diffusive processes, including normal and anomalous ones, can be obtained.

We investigate the solutions of a fractional diffusion equation with radial symmetry by using the Green function approach and by taking the N -dimensional case into account. In our analysis, a spatial time-dependent diffusion coefficient is considered, i.e., D ( r , t ) = D t δ - 1 r - θ / Γ ( α ) . The presence of external forces F ( r ) = K r e with e = - 1 - θ and F ( r ) = - kr + K r e is also taken into account. In particular, we discuss the results obtained by employing boundary conditions defined on a finite interval, and afterwards the analysis is extended to a semi-infinite interval. Finally, we also discuss a rich class of diffusive processes that can be obtained from the results presented in this work.

This work is devoted to investigate the solutions of a generalized diffusion equation which contains spatial fractional derivatives and nonlinear terms. The presence of external forces and absorbent terms is also considered. The solutions found here can have a compact or long tail behavior and, in particular, for the last case in the asymptotic limit, we relate these solutions to the Levy distributions. In addition, from the results presented here a rich class of diffusive processes, including normal and anomalous ones, can be obtained.

Dynamical thermostatting constitutes a procedure for computing thermodynamical mean values of classical dynamical systems that is of interest both from the practical and from the conceptual points of view. Here we extend and unify previous partial results, showing that the dynamical thermostatting approach can be implemented in order to simulate a wide family of statistical ensembles of general dynamical systems with a vanishing divergence and admitting an integral of motion. As a particular illustration, the thermostatting procedure is applied to power law-like maximum entropy ensembles.

We analyze a multidimensional nonlinear diffusion equation taking a spatial time dependent diffusion coefficient and external forces into account. We obtain new exact classes of solutions and investigate the transverse effects induced by an external force applied in the system. We also connect the solutions found here with the distribution that emerges from the nonextensive statistics.

The thermodynamics for systems of non-interacting bosons with multifractal energy spectrum is considered. The critical attractors of one-dimensional generalized logistic and circular maps are used to generate multifractal bounded spectra with well defined scaling exponents. The specific heat is then calculated for both cases of conserved and non-conserved particle number, showing a power-law behaviour which is modulated by log-periodic oscillations when the energy spectrum is not dense. The occurrence of Bose–Einstein condensation for systems with conserved particle number, at which the specific heat is discontinuous, is also analyzed.

We discuss the method of automatic search of critical point (MASCP) in the context of self-organizing criticality (SOC). The system analyzed is a contact process that presents a non-equilibrium phase transition between two states: active state and inactive state (the so-called absorbing state). The lattice sites represent infected and healthy individuals. We apply the technique MASCP to the propagation of epidemy in an unidimensional lattice at the criticality (space-domain). We take the thechnique MASCP to study SOC behavior. The time-series of density of infected individuals is analyzed using two complementary tools: Fourier analysis and detrended fluctuation analysis. We find numeric evidence that the time evolution that drives the system to the critical point in MASCP is not a SOC problem, but Gaussian noise. A SOC problem is characterized by an interaction-dominated system that goes spontaneously to the critical point. In fact MASCP goes by itself to a stationary point but it is not an interaction-dominated process, but a mean-field interaction process.

We analyze an anisotropic fractional diffusion equation that extends some known diffusion equations by considering a diffusion coefficient with spatial and time dependence, the presence of external forces and time fractional derivatives. We obtain new exact classes of solutions for a linear anisotropic fractional diffusion equation and investigate the time scaling behavior and an asymptotic solution for a nonlinear anisotropic fractional diffusion equation. We connect the asymptotic solution obtained with the distribution that emerges from the nonextensive statistics to the nonlinear case. We also verify different diffusive behavior, for instance, subdiffusion and superdiffusion, in each direction.

We investigate the solutions of a generalized diffusion equation which extends some known equations such as the fractional diffusion equation and the porous medium equation. We start our study by considering the linear case and the nonlinear case afterward. The linear case is analyzed taking fractional time and spatial derivatives into account. In this context, we also discuss the modifications that emerge by considering a diffusion coefficient given by D (x)∝|x| −θ . For the nonlinear case accomplishing the fractional time derivative, we discuss scaling behavior of the time and the asymptotic for the solution of the nonlinear fractional diffusion equation. In this case, the connection between the asymptotic solution found here and the nonextensive Tsallis statistics is performed.

In this work we investigate the distribution of shortest paths in percolation systems at the percolation threshhold in two dimensions (2D). We study paths from one given point to multiple other points. In oil recovery terminology, the given single point can be mapped to an injection well (injector) and the multiple other points to production wells (producers). In the previously studied standard case of one injection well and one production well separated by Euclidean distance r , the distribution of shortest paths l , P ( l | r ), shows a power-law behavior with exponent g l =2.14 in 2D. Here we analyze the situation of one injector and an array A of producers. Symmetric arrays of producers lead to one peak in the distribution P ( l | A ), the probability that the shortest path between the injector and any of the producers is l , while the asymmetric configurations lead to several peaks in the distribution. We analyze configurations in which the injector is outside and inside the set of producers. The peak in P ( l | A ) for the symmetric arrays decays faster than for the standard case. For very long paths all the studied arrays exhibit a power-law behavior with exponent g ≃ g l .

In this work, we extend the recursive search method to locate the critical point and to obtain the relevant critical exponents of a nonequilibrium phase transition. In particular, the method is applied to the contact process which presents a nonequilibrium phase transition between a steady active to a single inactive absorbing state belonging to the directed percolation universality class. We present the appropriate scaling analysis which allows for precise estimates of the critical parameters with a relatively small computational effort. The proposed scheme can be directly applied to general model systems presenting nonequilibrium transitions into absorbing states including reaction–diffusion and pair contact processes.

The effects of the dilution of sites (with an occupancy probability ps for an active site) on the long-range bond-percolation problem, on a linear chain (d=1), are analyzed by means of a Monte Carlo simulation. The occupancy probability for a bond between two active sites i and j, separated by a distance rij is given by pij=p/rijα (α⩾0), where p represents the usual occupancy probability between nearest-neighbor sites. The percolation order parameter, P∞, is investigated numerically for different values of α and ps, in such a way that a crossover between a nonextensive regime and an extensive regime is observed.

We report evidence of a low-mass companion around the K1III giant star HD 47536. This star belongs to our sample of 83 subgiant and giant stars studied for their radial velocity variations using the FEROS spectrograph at the 1.52 m-ESO telescope on La Silla. We find that the radial velocity of HD 47536 exhibits a periodic variation of about 712 days with a semi-amplitude of 113 m s - 1 . These variations are not accompanied by variations in either Ca II emission or in the spectral line shapes. A Keplerian orbit due to a sub-stellar companion is thus the most viable explanation for the radial velocity variation. Assuming a moderate stellar mass of m 1 = 1.1-3.0 M we obtain a minimum mass for the companion of m 2 sin i = 5.0-9.7 M J u p , an orbital semi-major axis of 1.6-2.3 AU, and an eccentricity of e = 0.2.

We present the first results of our precise radial velocity ( RV ) measurements of G and K giants. A number of stars from our list of 80 targets have been observed for 14 months using the fibre-fed echelle spectrograph FEROS at the 1.52 m ESO telescope in La Silla, Chile. This sample increases the number of giants surveyed with precise stellar radial velocity measurements at least by a factor of 10. During this period we are able to estimate the long-term accuracy of our measurement as better than 11 ${\rm m\,s}^{-1}$. We use the simultaneous Th-Ar calibration and cross-correlation technique to compute the radial velocity by applying a numerical template for K-type stars. Standard deviation σ of mean radial velocity variations between 3 ${\rm m\,s}^{-1}$ and 4 k${\rm m\,s}^{-1}$ with timescales between several days and years are measured for 21 of G and K giants which are presented in this paper. Fifteen stars show definite variability above 3 σ of our measurement uncertainties. Two stars with RV variations above 800 ${\rm m\,s}^{-1}$ are tentatively identified as new binaries. Although definitive trends between RV variations and stellar evolutionary status cannot yet be established, all the luminous cool giants of our sample seem to have significant radial velocity variations, while those stars in the giant's clump region can be either variable or constant.

e14558 Background: Immunotherapy is a procedure to boost the patient's own immune system to fight diseases such as cancer. In some types of cancer, it has been found that the programmed cell death receptor PD-1 impedes the body's immune defenses from functioning at full strength. Therefore drugs, like pembrolizumab, which prevent the interaction between this protein and the T-cells, may be a key tool to avoid the onset of cancer tumors. Methods: The aim of this work is to describe the interaction energies between the protein PD-1 and its drug inhibitor pembrolizumab by using a quantum biochemistry calculations, taking advantage of the X-ray crystal structure of the protein PD-1 in complex with its inhibitor. The protonation state of the drug was obtained using the Marvin Sketch code (Marvin Beans Suite). The optimization procedure was performed using the parametrization tool for organic molecules CHARMM (Chemistry at Harvard Macromolecular Mechanics). Afterwards, simulations within the density functional theory (DFT) framework were carried out by using the Gaussian code to provide a detailed energy profile of the interactions between the inhibitor and the receptor. Results: The interaction energy between each PD-1 molecule and the drug was calculated considering any significant attractive and repulsive drug’s amino acid residues. A searchfor an optimal binding pocket radius was done, looking for no significantvariation in the total binding energy. The converged binding pocket radius was found to be 1.5 nm, comprising a total of 145 amino acids residues displayed in a BIRD (Binding site, Interaction energy and Residues Domain) graphic panel. Although it was observed few repulsive interactions, the attractive ones were predominant, pointing out to a strong inhibition of the programmed cell death receptor. Conclusions: Immunotherapy is ranked nowadays as an important alternative to treat cancer. Among the drugs been tested, those blocking the protein PD-1 and its ligands have been considered an efficient way to trigger the T-cells. In this context, the computational method used in this work is a low cost efficient first step to unveil the drug’s amino-acids residues that play the most important role on the binding affinity of the receptor-ligand complex.

The quenched site-diluted Ising ferromagnet, with a probability p for site occupation, is studied on a square lattice. A method, based on self-organized criticality, drives the system spontaneously to the critical point, providing an efficient way to estimate critical properties for different values of p. In spite of the small lattice sizes used, the method yields critical temperatures and exponents in fairly good agreement with recent extensive numerical analyses. In particular, the slope of the ferromagnetic–paramagnetic boundary near p=1 is very close to the well-known exact value. Our critical-exponent estimates follow, within the error bars, in the same universality class of the pure Ising ferromagnet.

Clusters of parallel spins in the square-lattice Ising model are defined as groups of traders acting together on the Cont-Bouchaud stock market model. As in the random percolation case, we see a crossover from a power-law behaviour to a more Gaussian distribution for the market fluctuations.

A method for obtaining critical properties is presented. Based on self-organized criticality, it drives the system spontaneously to the critical point, providing an efficient way to estimate critical properties. The method is illustrated for Ising spin systems, and despite the small lattice sizes used, it yields critical temperatures and β exponents in good agreement with those available in the literature.

We present a Monte Carlo study in dimension d=1 of the two-species reaction-diffusion process A+B-->2B and B-->A. Below a critical value rho(c) of the conserved total density rho the system falls into an absorbing state without B particles. Above rho(c) the steady state B particle density rho(st)(B) is the order parameter. This system is related to directed percolation but in a different universality class identified by Kree et al. [Phys. Rev. A 39, 2214 (1989)]. We present an algorithm that enables us to simulate simultaneously the full range of densities rho between zero and some maximum density. From finite-size scaling we obtain the steady state exponents beta=0.435(10), nu=2.21(5), and eta=-0.606(4) for the order parameter, the correlation length, and the critical correlation function, respectively. Independent simulation indicates that the critical initial increase exponent takes the value straight theta(')=0.30(2), in agreement with the theoretical relation straight theta(')=-eta/2 due to Van Wijland et al. [Physica A 251, 179 (1998)].

In this work we show that it is possible to obtain a generalized statistical mechanics (thermostatistics) based on Renyi entropy, to be maximized with adequate constraints. The equilibrium probability distribution thus obtained has a very interesting property. Indeed, it reminds us the statistical distribution proposed by Tsallis, known to conveniently describe a variety of phenomena in nonextensive systems. Moreover, some examples are worked out in order to illustrate the main features of the herein introduced formalism.

We prove that the specific heat C q / q is nonnegative for q ∉[0,1) in the Tsallis generalized canonical ensemble with normalized q -expectation values. In this way, we show the thermodynamic stability for this ensemble. We also analyze the behavior of some thermodynamic functions such as internal energy and specific heat in the classical and quantum cases considering a spectrum of energy E n = e | n | r ( e , r >0).

We extend to general divergenceless systems the dynamical thermostatting approach to statistical ensembles proposed by Kusnezov, Bulgac and Bauer (KBB). Furthermore, a new family of dynamical systems inspired by the KBB method is introduced, and some of its properties considered.

Hundreds of millions of adults have high cholesterol, which has generated a billionaire market of drugs. Patents covering the leading statins have expired recently, pressuring the development of new drugs. Statins act by inhibiting the HMG-CoA reductase in the process of converting HMG-CoA to mevalonate, a committed step in the biosynthesis of cholesterol. It is observed in clinical trials that this action decreases by 20 to 60% the low density protein (LDL) cholesterol levels, reducing coronary events by up to one-third over a five years period. In this work, considering the crystallographic data of HMGR complexed with statins, we perform a computer simulation within an ab-initio quantum mechanical approach, based on the density functional theory, to investigate the details of the binding interaction energies of the statins atorvastatin, rosuvastatin, fluvastatin, and simvastatin to the HMGR enzyme. Our purpose is to elucidate why statins have differences in their efficiency to reduce cholesterol levels, by obtaining and comparing the interaction energy between the HMGR residues and the ligand atoms. The main advantage of our methodology is the possibility to evaluate what amino acid residues contribute more intensely to the stabilization of the statin-HMGR complex, a very helpful information for drug design.

The focus of this work is on the numerical investigation of the charge transport properties of the de novo-designed alpha3 polypeptide, a 21-residue with three repeats of the seven-residue sequence Leu-Glu-Thr-Leu-Ala-Lys-Ala, as well as its variants (the so-called 5Q-alpha3 and 7Q-alpha3 peptides), all of them probed by gene engineering. The theoretical model makes use of a tight-binding Hamiltonian within the density functional theory approach. We investigate if the biased alpha3 polypeptide and its variants can be identified by charge transport measurements through current-voltage (IxV) curves, as a pattern to characterize their fibrous assemblies. We found that, from their IxV profiles, the alpha3 peptide, that has the most fibrous assemblies, shows the smaller current saturation; the 5Q-alpha3 variant, which forms fibrous assemblies more attenuated than those of the alpha3 peptide, has a current saturation higher than alpha3, but smaller than 7Q-alpha3; finally, the 7Q-alpha3 variant does not form fibrils and shows the highest current saturation, suggesting that charge transport in peptides can turn out to be a useful tool for the development of biosensors to probe the onset of amyloidosis-like diseases. We hope that this biomedical application of the charge transport in proteins and polypeptides should stimulate experimental and engineering technological developments.

The effects of an external force on a diffusive process subjected to a backbone structure are investigated by considering the system governed by a Fokker-Planck equation with drift terms. Our results show an anomalous spreading which may present different diffusive regimes connected to anomalous diffusion and stationary states.

We investigate transport properties of percolating clusters generated by irreversible cooperative sequential adsorption (CSA) on square lattices with Arrhenius rates given by ki= q^(ni), where ni is the number of occupied neighbors of the site i, and q a controlling parameter. Our results show a dependence of the prefactors on q and a strong finite size effect for small values of this parameter, both impacting the size of the backbone and the global conductance of the system. These results might be pertinent to practical applications in processes involving adsorption of particles., Comment: 4 pages, 5 figures