Search results for "Statistical physics"
showing 10 items of 1402 documents
Surface segregation trends in transition metal alloys
2013
In this work, we revisit the problem of predicting the surface segregation trends in binary transition metal alloys from the knowledge of the basic features of the pure component $d$-band electronic structure within tight-binding approximation. In contrast to previous trend studies, the present one includes, within the fourth-moment approximation (FMA) of the tight-binding scheme, both the difference in the average band energies (diagonal disorder) and the difference in the band widths (off-diagonal disorder) of the two components. We show that treating on the same footing these two effects is essential for a correct prediction of surface segregation. The presented study, giving a natural l…
Quantifying the limits of transition state theory in enzymatic catalysis
2017
Significance Transition state theory (TST) is the most popular theory to calculate the rates of enzymatic reactions. However, in some cases TST could fail due to the violation of the nonrecrossing hypothesis at the transition state. In the present work we show that even for one of the most controversial enzymatic reactions—the hydride transfer catalyzed by dihydrofolate reductase—the error associated to TST represents only a minor correction to the reaction rate. Moreover, this error is actually larger for the reaction in solution than in the enzymatic active site. Based on this finding and on previous studies we propose an “enzymatic shielding” hypothesis which encompasses various aspects …
Reply to "comment on 'Monte Carlo simulations for a Lotka-type model with reactant surface diffusion and interactions' ".
2002
As is well known, a wide class of physical problems, including the kinetics of heterogeneous catalytic reactions, is traditionally described in terms of the master equations ~ME!. The definition of ME allows us not only to perform Monte Carlo ~MC! simulations, but also to develop at the same time appropriate analytical methods @mean field~MF!, cluster approximations, etc. #@ 1#. ME is formally defined when all possible states of a system and the transition rates between these states are specified. This is enough to define only the transition rates K(i! j ) for such elementary processes as particle adsorption, desorption, diffusion, reaction, etc., from the initial state i to the final state…
Electronic structure trends of Möbius graphene nanoribbons from minimal-cell simulations
2014
Investigating topological effects in materials requires often the modeling of material systems as a whole. Such modeling restricts system sizes, and makes it hard to extract systematic trends. Here, we investigate the effect of M\"obius topology in the electronic structures of armchair graphene nanoribbons. Using density-functional tight-binding method and minimum-cell simulations through revised periodic boundary conditions, we extract electronic trends merely by changing cells' symmetry operations and respective quantum number samplings. It turns out that for a minimum cell calculation, once geometric and magnetic contributions are ignored, the effect of the global topology is unexpectedl…
New method for field studies on the parapatric distribution of sibling species
1999
Abstract Spatial segregation (parapatry) often occurs between closely related species. The distributions of the two species are sometimes defined with a small overlapping zone (called a `sympatric area') which generally shifts. Exclusion is necessary to explain the persistence and shift of such a spatial pattern. Field studies are carried out to identify the type of interaction that leads to the required exclusion. This is usually achieved by estimating competition and predation parameters to define the type of interaction strong enough to imply exclusion. But interaction parameters are estimated by quantitative methods which require prolonged observation (5–10 years). These estimations are…
Error Estimates of Theoretical Models: a Guide
2014
This guide offers suggestions/insights on uncertainty quantification of nuclear structure models. We discuss a simple approach to statistical error estimates, strategies to assess systematic errors, and show how to uncover inter-dependencies by correlation analysis. The basic concepts are illustrated through simple examples. By providing theoretical error bars on predicted quantities and using statistical methods to study correlations between observables, theory can significantly enhance the feedback between experiment and nuclear modeling.
Errors in Monte Carlo simulations using shift register random number generators
1996
We report large systematic errors in Monte Carlo simulations of the tricritical Blume-Capel model using single spin Metropolis updating. The error, manifest as a $20\%$ asymmetry in the magnetisation distribution, is traced to the interplay between strong triplet correlations in the shift register random number generator and the large tricritical clusters. The effect of these correlations is visible only when the system volume is a multiple of the random number generator lag parameter. No such effects are observed in related models.
Experimental results for two-particle break-up
1991
In this section we shall review the present status of experiments on two-body photo-disintegration of deuteron up to and above the Δ region. The results of different experiments will be discussed and a guideline will be given for a selection of the experiments to be used in the comparison of experimental data with theoretical results. Moreover, since a large variety of observables exists, which have been studied experimentally, we shall discuss which kind of measured quantities, having a smaller systematic error, can give more accurate information.
Enabling quantum non-Markovian dynamics by injection of classical colored noise
2017
The non-Markovian nature of quantum systems recently turned to be a key subject for investigations on open quantum system dynamics. Many studies, from its theoretical grounding to its usefulness as a resource for quantum information processing and experimental demonstrations, have been reported in the literature. Typically, in these studies, a structured reservoir is required to make non-Markovian dynamics emerge. Here, we investigate the dynamics of a qubit interacting with a bosonic bath and under the injection of a classical stochastic colored noise. A canonical Lindblad-like master equation for the system is derived by using the stochastic wave function formalism. Then, the non-Markovia…
Statistically validated networks in bipartite complex systems.
2011
Many complex systems present an intrinsic bipartite nature and are often described and modeled in terms of networks [1-5]. Examples include movies and actors [1, 2, 4], authors and scientific papers [6-9], email accounts and emails [10], plants and animals that pollinate them [11, 12]. Bipartite networks are often very heterogeneous in the number of relationships that the elements of one set establish with the elements of the other set. When one constructs a projected network with nodes from only one set, the system heterogeneity makes it very difficult to identify preferential links between the elements. Here we introduce an unsupervised method to statistically validate each link of the pr…