Electrochemistry of Supramolecular Systems

What is the role of electrochemistry in supramolecular chemistry? On one hand, it provides information on energy and kinetics that is not available with spectroscopic and mass spectrometric techniques; on the other, it can be used to alter the electronic states and thus the interactions between molecules, resulting in new compounds and materials. A typical cyclic voltammogram of the complex shown is depicted on the right; only the first three reductions are presented, although a total of six electrons can be transferred to the bipyridine units sequentially (E in V vs. ferrocene/ferrocenium).     

Hydrodynamic limit for the velocity-flip model

We study the diffusive scaling limit for a chain of N$N$ coupled oscillators. In order to provide the system with good ergodic properties, we perturb the Hamiltonian dynamics with random flips of velocities, so that the energy is locally conserved. We derive the hydrodynamic equations by estimating the relative entropy with respect to the local equilibrium state, modified by a correction term.     

The effects of charge transfer on the aqueous solvation of ions

Ab initio-based charge partitioning of ionic systems results in ions with non-integer charges. This charge-transfer (CT) effect alters both short- and long-range interactions. Until recently, the effects of CT have been mostly neglected in molecular dynamics (MD) simulations. The method presented in this paper for including charge transfer between ions and water is consistent with ab initio charge partitioning and does not add significant time to the simulation. The ions of sodium, potassium, and chloride are parameterized to reproduce dimer properties and aqueous structures. The average charges of the ions from MD simulations (0.900, 0.919, and -0.775 for Na(+), K(+), and Cl(-), respectively) are consistent with quantum calculations. The hydration free energies calculated for these ions are in agreement with experimental estimates, which shows that the interactions are described accurately. The ions also have diffusion constants in good agreement with experiment. Inclusion of CT results in interesting properties for the waters in the first solvation shell of the ions. For all ions studied, the first shell waters acquire a partial negative charge, due to the difference between water-water and water-ion charge-transfer amounts. CT also reduces asymmetry in the solvation shell of the chloride anion, which could have important consequences for the behavior of chloride near the air-water interface.     

Hybrid heuristics for a short sea inventory routing problem

We consider a short sea fuel oil distribution problem where an oil company is responsible for the routing and scheduling of ships between ports such that the demand for various fuel oil products is satisfied during the planning horizon. The inventory management has to be considered at the demand side only, and the consumption rates are given and assumed to be constant within the planning horizon. The objective is to determine distribution policies that minimize the routing and operating costs, while the inventory levels are maintained within their limits. We propose an arc-load flow formulation for the problem which is tightened with valid inequalities. In order to obtain good feasible solutions for planning horizons of several months, we compare different hybridization strategies. Computational results are reported for real small-size instances.     

Reversible Topochemical Exsolution of Iron in BaFe2+2(PO4)2

BaFe²⁺₂(PO₄)₂ was recently prepared and identified as the first 2D‐Ising ferromagnetic oxide with an original reentrant structural transition driven by high‐spin Fe²⁺ ions arranged in honeycomb layers. Both long‐term air exposure and moderate temperature (T>375 °C) leads to topochemical oxidation into iron‐depleted compounds with mixed Fe²⁺/Fe³⁺ valence. This process is unique, as the exsolution is effective even from single crystal with preservation of the initial crystallinity, and the structure of the deficient BaFe_2?x(PO₄)₂ (xx=2/7 and 1/3 with creation of novel original depleted triangular lattices. Under flowing H₂/Ar, Fe is reincorporated in the structure above 480 °C, as reproduced under the electron beam in a transmission microscope. After Fe exsolution, the insulating ferromagnetic compound turns into an antiferromagnetic semiconductor.     

Nonlinear saturation of hot beam-plasma instability

The wave-particle interactions in a beam-plasma system in the presence of finite but small thermal motions of the particles are investigated in the linear as well as nonlinear regime. During the linear growth, the thermal motions are found to have a stabilizing effect. The nonlinear evolution is studied by using the Perturbed Orbit Formalism. Due to the thermal motions the nonlinear saturation of growth is found to take place at a level lower than that of the cold case. A detailed study of the energy balance shows that nonresonant particles pick up a bigger fraction of the energy lost by the streaming motion of the beam, thus leading to more efficient ‘heating’.