Dynamical symmetry breaking with optimal control: Reducing the number of pieces

We analyze the production of defects during the dynamical crossing of a mean-field phase transition with a real order parameter. When the parameter that brings the system across the critical point changes in time according to a power-law schedule, we recover the predictions dictated by the well-known Kibble-Zurek theory. For a fixed duration of the evolution, we show that the average number of defects can be drastically reduced for a very large but finite system, by optimizing the time dependence of the driving using optimal control techniques. Furthermore, the optimized protocol is robust against small fluctuations.

Long-term mass balance of perennial firn and ice in an Alpine cave (Austria):Constraints from radiocarbon-dated wood fragments

Hundsalm ice cave located at 1520 m altitude in a karst region of western Austria contains up to 7-m-thick deposits of snow, firn and congelation ice. Wood fragments exposed in the lower parts of an ice and firn wall were radiocarbon accelerator mass spectrometry (AMS) dated. Although the local stratigraphy is complex, the 19 individual dates - the largest currently available radiocarbon dataset for an Alpine ice cave - allow to place constraints on the accumulation and ablation history of the cave ice. Most of the cave was either ice free or contained only a small firn and ice body during the 'Roman Warm Period'; dates of three wood fragments mark the onset of firn and ice build-up in the 6th and 7th century ad. In the central part of the cave, the oldest samples date back to the 13th century and record ice growth coeval with the onset of the 'Little Ice Age'. The majority of the ice and firn deposit, albeit compromised by a disturbed stratigraphy, appears to have been formed during the subsequent centuries, supported by wood samples from the 15th to the 17th century. The oldest wood remains found so far inside the ice is from the end of the Bronze Age and implies that local relics of prehistoric ice may be preserved in this cave. The wood record from Hundsalm ice cave shows parallels to the Alpine glacier history of the last three millennia, for example, the lack of preserved wood remains during periods of known glacier minima, and underscores the potential of firn and ice in karst cavities as a long-term palaeoclimate archive, which has been degrading at an alarming rate in recent years. © The Author(s) 2013.

Irradiation of water ice by C+ ions in the cosmic environment

We present a first principles molecular dynamics (FPMD) study of the interaction of low energy, positively charged, carbon (C+) projectiles with amorphous solid water clusters at 30 K. Reactions involving the carbon ion at an initial energy of 11 eV and 1.7 eV with 30-molecule clusters have been investigated. Simulations indicate that the neutral isoformyl radical, COH, and carbon monoxide, CO, are the dominant products of these reactions. All these reactions are accompanied by the transfer of a proton from the reacting water molecule to the ice, where it forms a hydronium ion. We find that COH is formed either via a direct, "knock-out", mechanism following the impact of the C+ projectile upon a water molecule or by creation of a COH_2^+ intermediate. The direct mechanism is more prominent at higher energies. CO is generally produced following the dissociation of COH. More frequent production of the formyl radical, HCO, is observed here than in gas phase calculations. A less commonly occurring product is the dihydroxymethyl, CH(OH)_2, radical. Although a minor result, its existence gives an indication of the increasing chemical complexity which is possible in such heterogeneous environments.

A predictive maintenance system for integral type faults based on support vector machines:An application to ion implantation

In semiconductor fabrication processes, effective management of maintenance operations is fundamental to decrease costs associated with failures and downtime. Predictive Maintenance (PdM) approaches, based on statistical methods and historical data, are becoming popular for their predictive capabilities and low (potentially zero) added costs. We present here a PdM module based on Support Vector Machines for prediction of integral type faults, that is, the kind of failures that happen due to machine usage and stress of equipment parts. The proposed module may also be employed as a health factor indicator. The module has been applied to a frequent maintenance problem in semiconductor manufacturing industry, namely the breaking of the filament in the ion-source of ion-implantation tools. The PdM has been tested on a real production dataset. © 2013 IEEE.

Tephrochronology and the extended intimate (integration of ice‐core, marine and terrestrial records) event stratigraphy 8-128kab2k

The comparison of palaeoclimate records on their own independent timescales is central to the work of the INTIMATE (INTegrating Ice core, MArine and TErrestrial records) network. For the North Atlantic region, an event stratigraphy has been established from the high-precision Greenland ice-core records and the integrated GICC05 chronology. This stratotype provides a palaeoclimate signal to which the timing and nature of palaeoenvironmental change recorded in marine and terrestrial archives can be compared. To facilitate this wider comparison, without assuming synchroneity of climatic change/proxy response, INTIMATE has also focussed on the development of tools to achieve this. In particular the use of time-parallel marker horizons e.g. tephra layers (volcanic ash). Coupled with the recent temporal extension of the Greenland stratotype, as part of this special issue, we present an updated INTIMATE event stratigraphy highlighting key tephra horizons used for correlation across Europe and the North Atlantic. We discuss the advantages of such an approach, and the key challenges for the further integration of terrestrial palaeoenvironmental records with those from ice cores and the marine realm.

A smart load appliance application using a single compressor fridge-freezer to support grid operations

This paper describes a fridge-freezer smart load model, which responds to external signals from the wholesale electricity market to support grid operations while switching the fridge-freezer on and off to maintain optimum operations for the owner. The key parameters of the model are the appliance dimensions, thermal mass, the fridge and freezer thermal time constants and the compressor power consumption. The model demonstrates that control strategies help to minimise load at times when the grid is under stress from high demand, and shift some load to a lower wholesale price or when there is excess renewable power. Three control strategies are proposed, based on peak shaving and valley filling, price signals and wind availability.

Localizationlike effect in two-dimensional alternate quantum walks with periodic coin operations

Exploiting multidimensional quantum walks as feasible platforms for quantum computation and quantum simulation attracts constantly growing attention from a broad experimental physics community. Here, we propose a two-dimensional quantum walk scheme with a single-qubit coin that presents, in the considered regimes, a strong localizationlike effect on the walker. The result could provide new possible directions for the implementation of quantum algorithms or from the point of view of quantum simulation. We characterize the localizationlike effect in terms of the parameters of a step-dependent qubit operation that acts on the coin space after any standard coin operation, showing that a proper choice can guarantee a nonnegligible probability of finding the walker in the origin even for large times. We finally discuss the robustness to imperfections, a qualitative relation with coherences behavior, and possible experimental realizations of this model with the current state-of-the-art settings.

Sputtering of oxygen ice by low energy ions

Naturally occurring ices lie on both interstellar dust grains and on celestial objects, such as those in the outer Solar system. These ices are continuously subjected to irradiation by ions from the solar wind and/or cosmic rays, which modify their surfaces. As a result, new molecular species may form which can be sputtered off into space or planetary atmospheres. We determined the experimental values of sputtering yields for irradiation of oxygen ice at 10 K by singly (He+, C+, N+, O+ and Ar+) and doubly (C2 +, N2 + and O2 +) charged ions with 4 keV kinetic energy. In these laboratory experiments, oxygen ice was deposited and irradiated by ions in an ultra high vacuum chamber at low temperature to simulate the environment of space. The number of molecules removed by sputtering was observed by measurement of the ice thickness using laser interferometry. Preliminary mass spectra were taken of sputtered species and of molecules formed in the ice by temperature programmed desorption (TPD). We find that the experimental sputtering yields increase approximately linearly with the projectile ion mass (or momentum squared) for all ions studied. No difference was found between the sputtering yields for singly and doubly charged ions of the same atom within the experimental uncertainty, as expected for a process dominated by momentum transfer. The experimental sputter yields are in good agreement with values calculated using a theoretical model except in the case of oxygen ions. Preliminary studies have shown molecular oxygen as the dominant species sputtered and TPD measurements indicate ozone formation.