There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

This paper presents control and coordination algorithms for groups of vehicles. The focus is on autonomous vehicle networks performing distributed sensing tasks where each vehicle plays the role of a mobile tunable sensor. The paper proposes gradient descent algorithms for a class of utility functions which encode optimal coverage and sensing policies. The resulting closed-loop behavior is adaptive, distributed, asynchronous, and verifiably correct.

Coverage control for mobile sensing networks

Self-assembled monolayers (SAMs) of alkanethiols and dialkanethiols on gold are key elements for building many systems and devices with applications in the wide field of nanotechnology. Despite the progress made in the knowledge of these fascinating two-dimensional molecular systems, there are still several “hot topics” that deserve special attention in order to understand and to control their physical and chemistry properties at the molecular level. This critical review focuses on some of these topics, including the nature of the molecule–gold interface, whose chemistry and structure remain elusive, the self-assembly process on planar and irregular surfaces, and on nanometre-sized objects, and the chemical reactivity and thermal stability of these systems in ambient and aqueous solutions, an issue which seriously limits their technological applications (375 references).

Self-assembled monolayers of thiols and dithiols on gold: new challenges for a well-known system

The transferable potentials for phase equilibria-united atom (TraPPE-UA) force field for hydrocarbons is extended to primary, secondary, and tertiary alcohols by introducing the following (pseudo-)atoms:  common hydroxyl O and H for all alcohols, α-CH3, α-CH2, α-CH, and α-C for methanol, primary, secondary, and tertiary alcohols, respectively. In the TraPPE-UA force field, the nonbonded interactions of these sites are governed by Lennard−Jones 12−6 potentials and Coulombic interactions of fixed partial charges. The values of these partial charges were borrowed from the optimized potentials for liquid simulations-united atom (OPLS−UA) force field [Jorgensen, W. L. J. Phys. Chem. 1986, 90, 1276]. The Lennard−Jones well depth and size parameters for the new interaction sites were determined by fitting to the single-component vapor−liquid-phase equilibria of a few selected model compounds. Although the well-depth parameters for the α-carbons could be taken directly from the TraPPE-UA parameters for the corres...

Monte Carlo Calculations for Alcohols and Their Mixtures with Alkanes. Transferable Potentials for Phase Equilibria. 5. United-Atom Description of Primary, Secondary, and Tertiary Alcohols

We review the use of kinetically constrained models (KCMs) for the study of dynamics in glassy systems. The characteristic feature of KCMs is that they have trivial, often non-interacting, equilibrium behaviour but interesting slow dynamics due to restrictions on the allowed transitions between configurations. The basic question which KCMs ask is therefore how much glassy physics can be understood without an underlying ‘equilibrium glass transition’. After a brief review of glassy phenomenology, we describe the main model classes, which include spin-facilitated (Ising) models, constrained lattice gases, models inspired by cellular structures such as soap froths, models obtained via mappings from interacting systems without constraints, and finally related models such as urn, oscillator, tiling and needle models. We then describe the broad range of techniques that have been applied to KCMs, including exact solutions, adiabatic approximations, projection and mode-coupling techniques, diagrammatic approaches and mappings to quantum systems or effective models. Finally, we give a survey of the known results for the dynamics of KCMs both in and out of equilibrium, including topics such as relaxation time divergences and dynamical transitions, nonlinear relaxation, ageing and effective temperatures, cooperativity and dynamical heterogeneities, and finally non-equilibrium stationary states generated by external driving. We conclude with a discussion of open questions and possibilities for future work.

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Glassy dynamics of kinetically constrained models

New experimental results for the full intermolecular pair correlation function for liquid carbon tetrachloride have been obtained from analysis of structure factors measured using reactor and pulsed neutron sources. A brief comparison between the results derived from both techniques is presented. The liquid structure is discussed within the framework of the site-site Ornstein-Zernike equation with the hypernetted chain (HNC) and Percus-Yevick (PY) like closures. The Coulomb potentials are handled using Ng's method. The predictions show that the octupolar interactions have a small effect on the radial distribution functions.

How well do we know the structure of simple molecular liquids? CCl4 revisited

Heavily damped excitations are found in molten ${\mathrm{Li}}_{4}\mathrm{Pb}$ by inelastic neutron scattering. The experiment covered a kinematic range which enabled an unambiguous characterization of such excitations by means of the study of the wave vector dependence of their frequencies, lifetimes, and signal amplitudes. It is shown that the excitations being sampled exhibit features which substantially deviate from those expected for the propagation of an acoustic mode (which should involve in-phase atomic displacements).

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High-frequency dynamics in a molten binary alloy

The effects of a minor chemical modification on the microscopic structure of a material in its glass and crystal phases are investigated by the concurrent use of neutron diffraction and computer simulation. Significant changes in short-, intermediate-, and long-range order are found, resulting from the change in molecular structure. These differences are explainable by a shift in the balance between directional and excluded-volume interactions.

Chemical Isomerism as a Key to Explore Free-Energy Landscapes in Disordered Matter

Absence of anomalous dispersion features in the inelastic neutron scattering spectra of water at both sides of the melting transition.

We have studied two simple approaches to consider thermodynamic state dependent electrostatic interactions for molecular modeling of different phases of ethanol: the addition of an isotropic point polarizability located in the oxygen, and a self-consistent calculation of the effective dipole moment at each thermodynamic state. We have performed molecular dynamics simulations in order to investigate the thermodynamic properties, structure and dynamics of the liquid phase at three experimental densities, as well as in the monoclinic crystal and at critical conditions. In order to rationalize the effects of changing the dipole moment of the molecules, simulations with a nonpolarizable model for ethanol were also performed. The results show that a nonpolarizable model with an effective dipole moment is able to reproduce most of the static and dynamic properties of the condensed phases of ethanol, while the need to take into account the real dipole moment of the isolated molecule by using a polarizable model i...

F. J. Bermejo

Papers

How well do we know the structure of simple molecular liquids? CCl4 revisited

High-frequency dynamics in a molten binary alloy

Chemical Isomerism as a Key to Explore Free-Energy Landscapes in Disordered Matter

Absence of anomalous dispersion features in the inelastic neutron scattering spectra of water at both sides of the melting transition.

Ethanol force fields: A molecular dynamics study of polarization effects on different phases