Dynamic analysis and non-standard continualization of a Timoshenko beam lattice

In this paper, a Timoshenko beam lattice, made up of a chain of masses and straight segments, is proposed, considering bending and shear deformation by means of linear rotational and transverse springs, respectively. Different standard and non-standard continualization methods are applied to it, highlighting here for the first time the suitability of taking the coupled discrete governing equations as a starting point for deriving new continuum models. Several novel low order non-classical continuum models are obtained, with the aim of reliably capturing size-effects and reflecting the dispersive behaviour of the discrete system. Low order governing equations prevents the need for extra boundary conditions when finite (bounded) solids are treated. An extensive analysis of the transition frequency, which initiates the shear propagation spectrum, has been carried out, examining its influence for the discrete and non-standard continuum models. The natural frequencies of a finite solid with two different boundary conditions are obtained through an edge treatment applied here for the first time to this kind of lattices, thus making it possible to solve the clamped-free edges configuration. The reliability of these approaches is evaluated by comparing their dynamic behaviours with that of the discrete system (taken as a reference), through both dispersion and vibration analyses, some of the new proposed continuum models successfully capturing the behaviour of the discrete one, even for high wavenumbers. Moreover, the appearance of physical inconsistencies is examined.The authors acknowledge support from MCIN/ AEI /10.13039/501100011033 under Grants numbers PGC2018-098218-B-I00 and PRE2019-088002. FEDER: A way to make Europe. ESF invests in your future

Low-order continualization of an anisotropic membrane lattice with next-nearest interactions. Enhanced prediction of its dynamic behaviour

In this paper, a novel anisotropic membrane lattice with nearest and next-nearest interactions (long-range forces) has been continualized through different standard and non-standard continualization procedures, which enables the development of new non-classical continuum models capable of accurately capturing the scale effects, present in the matter due to its discrete nature. The performance of these continuum models is assessed by means of both dispersion and natural frequencies analyses, where the discrete model is considered as a reference. In addition, the appearance of certain physical inconsistencies in some of the developed models is analysed, concluding that these only appear for those developed with continualizations based on Taylor expansion. Interestingly, the non-standard models suitably capture the dispersive behaviour of the discrete one, without both physical inconsistencies and higher-order spatial derivatives, thus avoiding the need for extra boundary conditions when finite solids are involved.The authors acknowledge support from MCIN/AEI /10.13039/501100011033 under Grants numbers PGC2018-098218-B-I00 and PRE2019-088002. FEDER: A way to make Europe. ESF invests in your future

On the mechanism for the reduction of nitrogen monoxide on Rh(111) single-crystal surfaces

Isothermal kinetic experiments were carried out with isotopically-labeled molecular beams in order to characterize the surface reactions involved in the reduction of nitrogen monoxide with carbon monoxide on Rh(111) single-crystal surfaces. The new data reported here offers support for the basic model advanced previously where N2 production takes place via the formation of N-NO intermediates at the periphery of atomic nitrogen surface islands. However, they also highlight a few additional subtle complications. In particular, the rapid desorption of a small amount of 14N14N upon switching from 14NO+CO to 15NO+CO mixtures points to the role of additional adsorbates nearby the reaction surface site in facilitating the dissociation of the N-NO intermediates. In addition, the results from experiments with mixed 14NO+15NO+CO indicate a combination of reactions at the edges of previously deposited 14N islands and the growth of new mixed 14N+15N surface clusters

Novel Enriched Kinetic Energy continuum model for the enhanced prediction of a 1D lattice with next-nearest interactions

In this paper, a novel Enriched Kinetic Energy model is proposed for an enhanced prediction of the dynamic behaviour of a one-dimensional lattice with next-nearest interactions playing an important role. The lattice system here considered is made up of a chain formed by particles equally spaced and connected with nearest and next-nearest neighbours, through linear springs with different stiffness. The ability of the novel model proposed in this work in capturing the dynamic behaviour of the lattice system is compared with that of others presented in the literature, concluding that it is the one that shows the best performance around the limit of the Irreducible Brillouin Zone (small wavelengths) when next-nearest interactions are relevant. For this purpose, natural frequencies provided by the continuum models for the finite solid are compared with those provided by the discrete system, considered as a reference. Moreover, the novel Enriched Kinetic Energy model does not present physical inconsistencies, nor higher-order spatial derivatives in its governing equation, so it does not need non-classical boundary conditions to be solved when finite solids are treated.The authors acknowledge MCIN/ AEI /10.13039/501100011033 for the financial support under Grants numbers PGC2018-098218-B-I00 and PRE2019-088002. FEDER: A way to make Europe. ESF invests in your future

Molecular-Level Design of Heterogeneous Chiral Catalysis

The following is a proposal to continue our multi-institutional research on heterogeneous chiral catalysis. Our team combines the use of surface-sensitive analytical techniques for the characterization of model systems with quantum and statistical mechanical calculations to interpret experimental data and guide the design of future research. Our investigation focuses on the interrelation among the three main mechanisms by which enantioselectivity can be bestowed to heterogeneous catalysts, namely: (1) by templating chirality via the adsorption of chiral supramolecular assemblies, (2) by using chiral modifiers capable of forming chiral complexes with the reactant and force enantioselective surface reactions, and (3) by forming naturally chiral surfaces using imprinting chiral agents. Individually, the members of our team are leaders in these various aspects of chiral catalysis, but the present program provides the vehicle to generate and exploit the synergies necessary to address the problem in a comprehensive manner. Our initial work has advanced the methodology needed for these studies, including an enantioselective titration procedure to identify surface chiral sites, infrared spectroscopy in situ at the interface between gases or liquids and solids to mimic realistic catalytic conditions, and DFT and Monte Carlo algorithms to simulate and understand chirality on surfaces. The next step, to be funded by the monies requested in this proposal, is to apply those methods to specific problems in chiral catalysis, including the identification of the requirements for the formation of supramolecular surface structures with enantioselective behavior, the search for better molecules to probe the chiral nature of the modified surfaces, the exploration of the transition from supramolecular to one-to-one chiral modification, the correlation of the adsorption characteristics of one-to-one chiral modifiers with their physical properties, in particular with their configuration, and the development of ways to imprint chiral centers on achiral solid surfaces. Chiral catalysis is not only a problem of great importance in its own right, but also the ultimate test of how to control selectivity in catalysis. The time is ripe for fundamental work in heterogeneous chiral catalysis to provide the U.S. with a leadership role in developing the next generation of catalytic processes for medicinal and agrochemical manufacturing. Our team provides the required expertise for a synergistic and comprehensive integration of physical and chemical experimentation with solid state and molecular reactivity theories to solve this problem

Surface Chemistry of Copper Precursors in Connection with Atomic Layer Deposition (ALD) Processes

Chemistry and Chemical Biolog

Nonstandard continualization of 1D lattice with next-nearest interactions. Low order ODEs and enhanced prediction of the dispersive behavior

In this article, different standard and nonstandard continualization techniques are applied to a one-dimensional solid consisting in a chain of masses interacting with nearest and next-nearest neighbors through linear springs. The study focuses on the reliability of the different continua in capturing the dispersive behavior of the discrete, on the order of the continuous governing equation because of its effect on the need for including nonclassical boundary conditions, as well as on the physical inconsistencies that appear for short wavelengths. The Regularization method, used by Bacigalupo and Gambarotta for a lattice with nearest interactions, presents advantages over the others.The authors wish to acknowledge the Ministerio de Economía y Competitividad de España for the financial support [Grant no. PGC2018-098218-B-I00]

An Approach to Global Rovibrational Analysis Based on Anharmonic Ladder Operators: Application to Hydrogen Selenide (H80 2 Se)

An algebraic approach to perform global rovibrational analysis of molecular spectra is presented. The approach combines the onedimensional limit of the vibron model with rotational degrees of freedom. The model is based on the expression of the phase space Hamiltonian in terms of anharmonic ladder operators and the use of a symmetry-adapted basis set given by the linear combination of products of local vibrational and rotational wavefunctions. As an example we model the rovibrational spectra of a bent triatomic molecule, providing a global analysis for vibrational bands up to polyad 12 and Jmax=5 of Hydrogen Selenide (H2Se). Satisfactory fits of vibrational and rovibrational energies are obtained. A prediction of 2579 rovibrational energies up to J ≤ 5 and polyad 12 for the 140 lowest vibrational bands is also obtained. A possible extension of the model to reach spectroscopic quality results in larger molecular systems is also given

Surface Chemistry of Copper(I) Acetamidinates in Connection with Atomic Layer Deposition (ALD) Processes

The thermal chemistry of copper(I)-N,N′-di-sec-butylacetamidinate on Ni(110) single-crystal and cobalt polycrystalline surfaces was characterized under ultrahigh vacuum (UHV) conditions by X-ray photoelectron spectroscopy (XPS) and temperature-programmed desorption (TPD). A complex network of reactions were identified, starting with the dissociative adsorption of the precursor, from its dimeric form in its free state to a monomer once bonded to the nickel surface. The dissociation of a C–N bond in the acetamidinate ligand at 200K leads to the formation of adsorbed 2-butene and N-sec-butylacetamidinate. Some of the latter intermediates hydrogenate around 300K to release N-sec-butylacetamidine into the gas phase, while the remaining adsorbed species dissociate further around 400K, as the copper atoms become reduced to a metallic state, possibly to form acetonitrile and a sec-butylamido surface species that reacts further at 485 K to release 2-butene. By 800K, only copper and a small amount of carbon can be seen on the surface by XPS. The implications of this chemistry to the growth of metal films by atomic layer deposition (ALD) are discussed.Chemistry and Chemical Biolog

Excited state quantum phase transitions in the bending spectra of molecules

European Union’s Horizon 2020 research and innovation program under the Marie Skłodowska-Curie grant agreement No 87208