Energetic Topography Research Articles

Connectivity and Mobility Awake Efficient Routing In MWSN

Mobile Wireless Sensor Networks (MWSNs) have established their applications in various streams, particularly in agriculture, forest fire detection, and military applications. However, insufficient bandwidth, communication faults, energetic topography, energy restraints, and stability of connection variations guide to node movement. However, the major problem is to link failures between sensor nodes. As s result, make the rerouting process create an additional delay. To solve the connectivity and Mobility Awake Efficient Routing in MWSNis introduced. We design this paper is mainly for monitoring crop agriculture also produce the supervise information to base stations. In this strategy, the dynamic connectivity is used to measure the node connectivity among nodes. Average encounter rate and the route encounter rate is applied to evaluate the node mobility. These three parameters are used to choose the best forwarder node in MWSN. Simulation results illustrate that improve the network performance equate to the baseline approach.

Adsorption on Heterogeneous Surfaces with Simple Topographies

The localized monolayer adsorption of interacting particles onto heterogeneous surfaces has been studied through Monte Carlo simulation in the framework of the lattice-gas model. The substrate was modelled as a collection of finite homotatic patches, each one characterized by an adsorption energy arising from a discrete energy density function. Patches were distributed spatially, either in a deterministic alternate way (ordered topography) or in a non-overlapping random way (random topography). The adsorption process was analyzed by following the behaviour of surface coverage versus chemical potential (adsorption isotherm) and the differential heat of adsorption as a function of the coverage. These quantities depend on the size of the patch as well as on the topological distribution of the patches on the surface. The consequences of these findings are discussed for the determination of the energetic topography of the surface from adsorption measurements.

Stochastic Ensembles, Conformationally Adaptive Teamwork, and Enzymatic Detoxification

It has been appreciated for a long time that enzymes exist as conformational ensembles throughout multiple stages of the reactions they catalyze, but there is renewed interest in the functional implications. The energy landscape that results from conformationlly diverse poteins is a complex surface with an energetic topography in multiple dimensions, even at the transition state(s) leading to product formation, and this represents a new paradigm. At the same time there has been renewed interest in conformational ensembles, a new paradigm concerning enzyme function has emerged, wherein catalytic promiscuity has clear biological advantages in some cases. "Useful", or biologically functional, promiscuity or the related behavior of "multifunctionality" can be found in the immune system, enzymatic detoxification, signal transduction, and the evolution of new function from an existing pool of folded protein scaffolds. Experimental evidence supports the widely held assumption that conformational heterogeneity promotes functional promiscuity. The common link between these coevolving paradigms is the inherent structural plasticity and conformational dynamics of proteins that, on one hand, lead to complex but evolutionarily selected energy landscapes and, on the other hand, promote functional promiscuity. Here we consider a logical extension of the overlap between these two nascent paradigms: functionally promiscuous and multifunctional enzymes such as detoxification enzymes are expected to have an ensemble landscape with more states accessible on multiple time scales than substrate specific enzymes. Two attributes of detoxification enzymes become important in the context of conformational ensembles: these enzymes metabolize multiple substrates, often in substrate mixtures, and they can form multiple products from a single substrate. These properties, combined with complex conformational landscapes, lead to the possibility of interesting time-dependent, or emergent, properties. Here we demonstrate these properties with kinetic simulations of nonequilibrium steady state (NESS) behavior resulting from energy landscapes expected for detoxification enzymes. Analogous scenarios with other promiscuous enzymes may be worthy of consideration.

Determination of the energetic topography of bivariate heterogeneous surfaces from adsorption isotherms

The reversible adsorption process occurring on patchwise heterogeneous bivariate surfaces is studied by Monte Carlo simulation and mean-field approximation. These surfaces are characterized by a collection of deep and shallow adsorbing patches with a typical length scale l. Patches can be either arranged in a deterministic chessboard structure or in a random way. Previous studies showed that the topography of a given surface can be obtained from the knowledge of the corresponding adsorption isotherm and a reference curve. In the present work, we discuss the advantages and disadvantages of using different reference curves. One of the main consequences of this analysis is to provide an improved method for the determination of the energetic topography of the surface from adsorption measurements.

Energetic Topography in Adsorption onto Heterogeneous Surfaces

The adsorption of gases onto heterogeneous surfaces has been reviewed, highlighting models capable of taking energetic topography effects into account. The basic ideas are contained in the fundamental Generalized Gaussian Model (GGM) developed to represent mobile adsorption onto heterogeneous surfaces at low coverage, where the energetic topography is considered through an adsorptive energy distribution with a spatial correlation function. Adsorbate molecules interact amongst them via Lennard-Jones interactions. Model predictions have been compared to Monte Carlo simulations of adsorption onto heterogeneous solids obtained by doping a pure crystalline solid with different concentrations of impurities. Energetic topography effects were shown to be important, being predicted correctly by the model at low coverage. In addition, a simplified patchwise model was also considered. The adsorption of particles with nearest-neighbour attractive and repulsive interactions was studied using Monte Carlo simulation on bivariant surfaces characterized by patches of weak and strong adsorbing sites of size “i”. Patches were considered to have either a square or a strip geometry, arranged either in a deterministic ordered structure or in a random way. Quantities have been identified which scale obeying power laws as a function of the scale length “l”. The consequences of this finding for the determination of the energetic topography of a surface from adsorption measurements were discussed.

Aggregation on heterogeneous surface

Chessboard-like substrates are introduced in this paper, in order to study the diffusion-limited aggregation (DLA) and the motion of poly-atoms on heterogeneous surfaces. The effect of morphology of such substrates upon the cluster aggregation is investigated using the Monte Carlo simulation. It is found that the growth process and the cluster morphology are governed by the energetic topography of the substrates. Our simulation also indicate that the island density and the fractal dimension of the clusters depend strongly on the substrate topography and the activation energy.

Energetic Topography Effects on Mobile Adsorption on Heterogeneous Surfaces at Low Coverage

Mobile adsorption on heterogeneous surfaces at low coverage is modeled via a gas-solid virial expansion, following the ideas of the generalized Gaussian model 6 , 1 2 to incorporate energetic topography effects. Adsorbatemolecules interact among them via Lennard-Jones interactions. Model predictions are compared to Monte Carlo simulations of adsorption on heterogeneous solids obtained by doping a pure crystalline solid with different concentrations of impurities. Energetic topography effects are shown to be important and they are correctly predicted by the model at low coverage.

Temperature dependence of scaling laws in adsorption on bivariate surfaces

The adsorption of particles with nearest-neighbor repulsive interactions is studied through Monte Carlo simulation on bivariate surfaces characterized by patches of weak and strong adsorbing sites of size l. Patches are considered to have a square geometry and they can be either arranged in a deterministic ordered structure or in a random way. Quantities are identified which scale obeying power laws as a function of the scale length l and its dependence on the temperature is determined. Consequences of this finding are discussed for the determination of the energetic topography of the surface from adsorption measurements.

Kinetics of Multisite-Occupancy Adsorption on Heterogeneous Solid Surfaces: A Statistical Rate Theory Approach

The theoretical approach to kinetics of adsorption on heterogeneous surfaces, developed recently by using the statistical rate theory (Rudzinski, W.; Panczyk, T. J. Phys. Chem. B 2000, 104, 9149) is generalized here for the case of multisite-occupancy adsorption. Theoretical kinetic isotherms are developed for the systems with quasi-Gaussian distribution of adsorption energies and when all of the segments (mers) of the adsorbing molecule are identical. The two extreme cases of surface topography, that is, patchwise and random topography, are considered. The obtained theoretical equations are used to correlate successfully experimental data for kinetics of oxygen adsorption on polycrystalline tungsten. Six experimental isotherms, measured at different pressures, can be successfully fitted by appropriate choice of only three parameters. The analysis of the estimated best-fit parameters makes drawing certain conclusions possible, concerning the energetic topography of the polycrystalline tungsten surface.

Adsorption of dimers on heterogeneous surfaces: scaling behavior for the adsorption isotherms

The localized monolayer adsorption of homonuclear dimers on heterogeneous surfaces with simple topographies is analyzed by combining theoretical modeling and Monte Carlo (MC) simulations. The heterogeneous surfaces are represented by lattices with two kinds of sites, the so-called bivariate heterogeneous surface. Shallow and deep sites with energies ε S and ε D , respectively, form l× l patches distributed at random or in chessboard-like ordered domains on two-dimensional square, honeycomb and triangular lattices. The adsorption process is monitored by following the adsorption isotherms. The scope of the present work is to determine, via MC simulation and a theoretical model, the general properties of the adsorption of non-interacting dimers on bivariate surfaces with a characteristic correlation length, l. These findings are discussed for the determination of the energetic topography of the surface, from adsorption measurements.

Scaling laws in adsorption on bivariate surfaces.

The adsorption of particles with nearest-neighbor attractive and repulsive interactions is studied through Monte Carlo simulation on bivariate surfaces characterized by patches of weak and strong adsorbing sites of size l. Patches are considered to have either a square or a strip geometry and they can be either arranged in a deterministic ordered structure or in a random way. Quantities are identified that scale obeying power laws as a function of the scale length l. The consequences of this finding are discussed for the determination of the energetic topography of the surface from adsorption measurements.

On the characterization of heterogeneous surfaces through the dual site–bond model

Abstract The statistical description of the energetic topography of heterogeneous solid surfaces and the problem of its determination from experimental results are discussed in terms of the dual site–bond model. The effects of the topography on surface processes such as adsorption and thermal desorption, as predicted by the model, are obtained through Monte Carlo simulations. It is shown that adsorbate–adsorbate interactions and adsorptive energy topography may compete with each other in such a way as to produce an indetermination in the characterization from experimental adsorption isotherms and that such an indetermination can be overcome through the analysis of thermal desorption experiments.

Characterization of energetic topography of heterogeneous surfaces through the analysis of thermal desorption spectra

Monte Carlo simulations of thermal programmed desorption spectra (TPDS) are obtained and analyzed for general heterogeneous surfaces characterized by a dual-site-bond model, where the adsorptive energy topography is described in terms of a correlation length l 0. It is shown that the behavior of TPDS is such that the ambiguity arising in the characterization of the energetic topography through adsorption isotherms, where adsorbate–adsorbate interactions and topography effects compete with each other, is resolved in such a way that TPDS provide a more powerful characterization method.

Scaling behavior in adsorption on bivariate surfaces and the determination of energetic topography

Adsorption of particles with repulsive nearest-neighbor interactions is studied through Monte Carlo simulation on bivariate surfaces characterized by patches of weak and strong adsorbing sites of size l. Patches can be either arranged in a deterministic chessboard structure or in a random way. Quantities are identified which scale obeying power laws as a function of the scale length l. Consequences of this finding are discussed for the determination of the energetic topography of the surface from adsorption measurements.

Power Laws in Adsorption and the Characterization of Heterogeneous Substrates

The adsorption of particles with repulsive nearest-neighbour interactions was studied through Monte Carlo simulation on bivariate surfaces characterized by patches of weak and strong adsorbing sites of size l. Patches were either arranged in a deterministic chessboard structure or in a random way. Quantities were identified which scale obeying power laws as a function of the scale length l. The consequences of these findings were discussed for the determination of the energetic topography of the surface from adsorption measurements.

Effects of the heterogeneous energetic topography on the collective motion of adsorbed particles

Collective surface diffusion of adsorbed particles on correlated heterogeneous surfaces is studied by Monte Carlo simulation, in the framework of the Kubo–Green theory. The energetic disordered surface is described through the dual site-bond model (DSBM) introduced by Mayagoitia et al. [Surf. Sci. 221, 394 (1989)]. The influence of the energetic correlation on the jump (DJ) and collective (D) diffusion coefficients is analyzed by simulating the coverage fluctuations in the grand canonical ensemble and the mean-square displacements of particles in the canonical ensemble. The topography is shown to strongly affect the coverage dependence of the transport coefficient. The effects of nearest-neighbor lateral interactions is also discussed.

NO DECOMPOSITION ON TRANSITION METALS: A MONTE CARLO SIMULATION

The kinetics of NO decomposition on transition metals is studied through Monte Carlo simulation, including the effects of adsorbate-adsorbate interactions and of surface energetic heterogeneity. For a homogeneous surface, it is found that previous quasi-chemical approximation calculations are reasonably in agreement with Monte Carlo results except for strong repulsive interactions. In this last case, quasi-chemical predictions largely overestimate the decomposition rate. It is found that energetic heterogeneity introduces interesting behaviors which depend on the energetic topography considered.

Energetic Topography Effects on Surface Diffusion

The chemical diffusion coefficient D for noninteracting particles on heterogeneous surfaces with different energetic topographies is studied by Monte Carlo simulation. Two kinds of topographies are considered: strongly correlated patches and weakly correlated amorphous surfaces. Topography effects are clearly identified due to the fact that no adsorbate-adsorbate interactions are competing. These effects are strong and depend on the trap-barrier feature and on the spatial correlation length for adsorptive energy. The dependence ofD on the temperature T does not follow, in general, the Arrhenius law. The relation between the values of D at coverage near 1 and near 0 appears as a useful tool to characterize the energetic topography.

Collective diffusion on strongly correlated heterogeneous surfaces

Collective diffusion coefficients are studied for heterogeneous bivariate surfaces with two different topographies, namely the random patches and the chessboard-like ordered distributions. The topography is shown to affect strongly the coverage dependence of the transport coefficients. Various diffusion quantities like the chemical D, jump D J and tracer D∗ diffusion coefficients are analyzed by means of Monte Carlo simulations in the framework of the fluctuation and the Kubo–Green theory. The behavior of diffusion coefficients in small patches is mainly affected by the mobility of the particles in the border vacancies, and a simple law is obtained for the ratio D(1)/ D(0). For large patches the behavior is dominated by the mobility of particles in the central vacancies. In the limit of very large patches the diffusion coefficients become independent of the energetic topography.

The effect of energetic topography on the structure of the adsorbate

The distributions of potential energy for particles adsorbed on heterogeneous surfaces with different energetic topographies have been obtained by Monte Carlo simulation. The surfaces themselves were constructed using Monte Carlo simulations. The energy distributions are analyzed to give information about the roles of heterogeneity and lateral interactions in the adsorption process. In addition, these distributions are shown to be closely related to the conventional local adsorption isotherm.