Monte Carlo simulation of cluster growth in surface defects induced by the tip of a scanning tunnelling microscope

First steps are taken to model the electrochemical deposition of metals in nanometer-sized cavities. In the present work, the electrochemical deposition of Cu atoms in nanometer-sized holes dug on Au(111) is investigated through Monte Carlo simulations using the embedded atom method to represent particle interactions. By sweeping the chemical potential of Cu, a cluster is allowed to grow within the hole rising four atomic layers above the surface. Its lateral extension remains confined to the area defined by the borders of the original defect. (C) 2004 Elsevier B.V. All rights reserved.

Molecular electrostatic properties of ions in an ionic liquid

We have analysed the electronic wave functions from an ab initio simulation of the ionic liquid (room temperature molten salt) dimethyl imidazolium chloride ([dmim][Cl] or [C1mim][Cl]) using localized Wannier orbitals. This allows us to assign electron density to individual ions. The probability distributions of the ionic dipole moments for an isolated ion and for ions in solution are compared. The liquid environment is found to polarize the cation by about 0.7 D and to increase the amplitude of the fluctuations in the dipole moments of both cation and anion. The relative changes in nuclear and electronic contributions are shown. The implications for classical force fields are discussed.

The transfer of energy between electrons and ions in solids

In this review we consider those processes in condensed matter that involve the irreversible flow of energy between electrons and nuclei that follows from a system being taken out of equilibrium. We survey some of the more important experimental phenomena associated with these processes, followed by a number of theoretical techniques for studying them. The techniques considered are those that can be applied to systems containing many nonequivalent atoms. They include both perturbative approaches (Fermi's Golden Rule and non-equilibrium Green's functions) and molecular dynamics based (the Ehrenfest approximation, surface hopping, semi-classical Gaussian wavefunction methods and correlated electron-ion dynamics). These methods are described and characterized, with indications of their relative merits.

X-ray emission from charge exchange of highly-charged ions in atoms and molecules

Charge exchange followed by radiative stabilization are the main processes responsible for the recent observations of X-ray emission from comets in their approach to the Sun. A new apparatus was constructed at JPL to measure, in collisions of HCIs with atoms and molecules, (a) absolute cross sections for single and multiple charge exchange, and (b) normalized X-ray emission cross sections. The ions are produced by the JPL HCI Facility and passed through a neutral-gas target cell. The product charge states are analyzed by a retarding potential difference technique. Results are made absolute by measuring target pressure, and incident and product ion currents. X-rays emitted from the product ions are detected with a Ge solid-state detector having a resolution of approximately 100 eV. X-ray astronomy has taken major steps forward with the recent launch of the high-resolution satellites Chandra and Newton. The cross sections reported herein are essential for the development of the solar wind comet interaction models inspired by these observations.

Dielectronic recombination of He-like to C-like iodine ions

KLL dielectronic recombination resonances, where a free electron is captured into the L shell and at the same time a K shell electron is excited into the L shell, have been measured for open shell iodine ions by measuring the detected yield of escaping ions of various charge states and modeling the charge balance in an electron beam ion trap. In the modeling, the escape from the trap and multiple charge exchange were considered. Extracted ions were used to measure the charge balance in the trap. The different charge states were clearly separated, which along with the correction for artifacts connected with ion escape and multiple charge exchange made the open shell highly charged ion measurements of this type possible for the first time. From the measured spectra resonant strengths were obtained. The results were 4.27(39)x10(-19) cm(2) eV, 2.91(26)x10(-19) cm(2) eV, 2.39(22)x10(-19) cm(2) eV, 1.49(14)x10(-19) cm(2) eV and 7.64(76)x10(-20) cm(2) eV for the iodine ions from He-like to C-like, respectively.

A cluster randomised controlled trial to evaluate a policy of making hip protectors available to residents of nursing homes

Objectives: to evaluate the effectiveness of a policy of making hip protectors available to residents of nursing homes. Design: a cluster randomised controlled trial of the policy in nursing and residential homes, with the home as the unit of randomisation. Setting: 127 nursing and residential homes in the greater Belfast area of Northern Ireland. Participants: 40 homes in the intervention group (representing 1,366 occupied beds) and 87 homes in the control group (representing 2,751 occupied beds). Interventions: a policy of making hip protectors available free of charge to residents of nursing homes and supporting the implementation process by employing a nurse facilitator to encourage staff in the homes to promote their use, over a 72-week period. Main outcome measures: the rate of hip fractures in intervention and control homes, and the level of adherence to use of hip protectors. Results: there were 85 hip fractures in the intervention homes and 163 in the control homes. The mean fracture rate per 100 residents was 6.22 in the intervention homes and 5.92 in the control homes, giving an adjusted rate ratio for the intervention group compared to the control group of 1.05 (95% CI 0.77, 1.43, P = 0.76). Initial acceptance of the hip protectors was 37.2% (508/1,366) with adherence falling to 19.9% (272/1,366) at 72 weeks. Conclusions: making hip protectors available to residents of nursing and residential homes did not reduce the rate of hip fracture.

Observing time-dependent vibrational quantum dynamics in deuterium hydride molecular ions

Few-cycle laser pulses are used to "pump and probe" image the vibrational wavepacket dynamics of a HD+ molecular ion. The quantum dephasing and revival structure of the wavepacket are mapped experimentally with time-resolved photodissociation imaging. The motion of the molecule is simulated using a quantum-mechanical model predicting the observed structure. The coherence of the wavepacket is controlled by varying the duration of the intense laser pulses. By means of a Fourier transform analysis both the periodicity and relative population of the vibrational states of the excited molecular ion have been characterized.

Damage to plasmid DNA induced by low energy carbon ions

The damage induced in supercoiled plasmid DNA molecules by 1-6 keV carbon ions has been investigated as a function of ion exposure, energy and charge state. The production of short linear fragments through multiple double strand breaks has been demonstrated and exponential exposure responses for each of the topoisomers have been found. The cross section for the loss of supercoiling was calculated to be (2.2 +/- 0.5) x 10(-14) cm(2) for 2 keVC(+) ions. For singly charged carbon ions, increased damage was observed with increasing ion energy. In the case of 2 keV doubly charged ions, the damage was greater than for singly charged ions of the same energy. These observations demonstrate that ion induced damage is a function of both the kinetic and potential energies of the ion.

Excited ions in intense femtosecond laser pulses: Laser-induced recombination

Electron-ion recombination in a laser-induced electron recollision is of fundamental importance as the underlying mechanism responsible for the generation of high harmonic radiation, and hence for the production of attosecond pulse trains in the extreme ultraviolet and soft X-ray spectral regions. By using an ion beam target, remotely prepared to be partially in long-lived excited states, the recombination process has for the first time been directly observed and studied.