Long-Lived Non-Equilibrium Interstitial-Solid-Solutions in Binary Mixtures

We perform particle resolved experimental studies on the heterogeneous crystallisation process of two compo- nent mixtures of hard spheres. The components have a size ratio of 0.39. We compared these with molecular dynamics simulations of homogenous nucleation. We find for both experiments and simulations that the final assemblies are interstitial solid solutions, where the large particles form crystalline close-packed lattices, whereas the small particles occupy random interstitial sites. This interstitial solution resembles that found at equilibrium when the size ratios are 0.3 [Filion et al., Phys. Rev. Lett. 107, 168302 (2011)] and 0.4 [Filion, PhD Thesis, Utrecht University (2011)]. However, unlike these previous studies, for our system sim- ulations showed that the small particles are trapped in the octahedral holes of the ordered structure formed by the large particles, leading to long-lived non-equilibrium structures in the time scales studied and not the equilibrium interstitial solutions found earlier. Interestingly, the percentage of small particles in the crystal formed by the large ones rapidly reaches a maximum of around 14% for most of the packing fractions tested, unlike previous predictions where the occupancy of the interstitial sites increases with the system concentration. Finally, no further hopping of the small particles was observed

Inelastic Quantum Transport and Peierls-like Mechanism in Carbon Nanotubes

We report on a theoretical study of inelastic quantum transport in $(3m,0)$ carbon nanotubes. By using a many-body description of the electron-phonon interaction in Fock space, a novel mechanism involving optical phonon emission (absorption) is shown to induce an unprecedented energy gap opening at half the phonon energy, $\hbar\omega_{0}/2$, above (below) the charge neutrality point. This mechanism, which is prevented by Pauli blocking at low bias voltages, is activated at bias voltages in the order of $\hbar\omega_{0}$.Comment: 4 pages, 4 figure

Wannier-Stark ladders in one-dimensional elastic systems

The optical analogues of Bloch oscillations and their associated Wannier-Stark ladders have been recently analyzed. In this paper we propose an elastic realization of these ladders, employing for this purpose the torsional vibrations of specially designed one-dimensional elastic systems. We have measured, for the first time, the ladder wave amplitudes, which are not directly accessible either in the quantum mechanical or optical cases. The wave amplitudes are spatially localized and coincide rather well with theoretically predicted amplitudes. The rods we analyze can be used to localize different frequencies in different parts of the elastic systems and viceversa.Comment: 10 pages, 6 figures, accepted in Phys. Rev. Let

The energy-water nexus: Renewable energy and water desalination

The essential connection between energy and water, also defined as the energy-water nexus, has been recognized by scientists and policy makers worldwide. Integrated solutions and policies that consider both energy and water aspects into future planning have been developing at a fast pace. In this paper, we review the state of the art of the energy-water nexus, with particular focus on the integration between renewable energy and desalination technologies. We also model the integration of reverse osmosis (RO) desalination and solar photovoltaics in an edge-of-grid coastal town in Western Australia. The current literature agrees on the sustainable use of renewable energy sources to improve the water-energy nexus in the context of water desalination. Although the integration of solar and wind energy with desalination technologies is a mature and well-proven solution at both small and large scales, the intermittency and fluctuating nature of wind and solar power still constitute the main technical challenge that has limited the diffusion of renewable energy powered desalination on a large scale. Several successful applications of renewable energy powered desalination in remote, off the grid, locations have tackled the issue of power intermittency by the use of batteries and diesel generators. Such systems often couple reverse osmosis desalination with solar photovoltaic energy. Large desalination plants have been successfully connected to wind farms and grid electricity to secure uninterrupted plant operations, thus meeting water targets in large-scale systems. Our review identifies a knowledge gap in the integration of decentralized energy systems, e.g. rooftop solar photovoltaic, with small scale RO desalination. Such configuration would benefit those regional towns that have historically suffered from weak and unreliable connections to the electricity grid, thus helping them secure both their energy and water requirements. The modelling exercise on a renewable energy powered RO plant in an edge-of-grid town in Western Australia has identified an operating strategy that maximizes the renewable energy fraction and secures the annual supply of water. The system involves operating the RO unit for six months of the year at a daily variable load and integrating solar energy with grid electricity. Careful evaluation of the RO performance under such operating conditions is necessary to ensure a safe and reliable water treatment process. A niche in the literature of the energy-water nexus has been identified in the integration of rooftop solar photovoltaic, grid electricity and desalination technologies applied in a regional context. A future study will consider the rollout of rooftop solar photovoltaic installations across the whole town, thus enabling the active engagement of the community by integrating the households’ energy demand response patterns to the operations of both rooftop photovoltaics and the desalination unit

The energy-water nexus: Renewable energy and water desalination

The essential connection between energy and water, also defined as the energy-water nexus, has been recognized by scientists and policy makers worldwide. Integrated solutions and policies that consider both energy and water aspects into future planning have been developing at a fast pace. In this paper, we review the state of the art of the energy-water nexus, with particular focus on the integration between renewable energy and desalination technologies. We also model the integration of reverse osmosis (RO) desalination and solar photovoltaics in an edge-of-grid coastal town in Western Australia. The current literature agrees on the sustainable use of renewable energy sources to improve the water-energy nexus in the context of water desalination. Although the integration of solar and wind energy with desalination technologies is a mature and well-proven solution at both small and large scales, the intermittency and fluctuating nature of wind and solar power still constitute the main technical challenge that has limited the diffusion of renewable energy powered desalination on a large scale. Several successful applications of renewable energy powered desalination in remote, off the grid, locations have tackled the issue of power intermittency by the use of batteries and diesel generators. Such systems often couple reverse osmosis desalination with solar photovoltaic energy. Large desalination plants have been successfully connected to wind farms and grid electricity to secure uninterrupted plant operations, thus meeting water targets in large-scale systems. Our review identifies a knowledge gap in the integration of decentralized energy systems, e.g. rooftop solar photovoltaic, with small scale RO desalination. Such configuration would benefit those regional towns that have historically suffered from weak and unreliable connections to the electricity grid, thus helping them secure both their energy and water requirements. The modelling exercise on a renewable energy powered RO plant in an edge-of-grid town in Western Australia has identified an operating strategy that maximizes the renewable energy fraction and secures the annual supply of water. The system involves operating the RO unit for six months of the year at a daily variable load and integrating solar energy with grid electricity. Careful evaluation of the RO performance under such operating conditions is necessary to ensure a safe and reliable water treatment process. A niche in the literature of the energy-water nexus has been identified in the integration of rooftop solar photovoltaic, grid electricity and desalination technologies applied in a regional context. A future study will consider the rollout of rooftop solar photovoltaic installations across the whole town, thus enabling the active engagement of the community by integrating the households’ energy demand response patterns to the operations of both rooftop photovoltaics and the desalination unit

Dynamic instabilities in resonant tunneling induced by a magnetic field

We show that the addition of a magnetic field parallel to the current induces self sustained intrinsic current oscillations in an asymmetric double barrier structure. The oscillations are attributed to the nonlinear dynamic coupling of the current to the charge trapped in the well, and the effect of the external field over the local density of states across the system. Our results show that the system bifurcates as the field is increased, and may transit to chaos at large enough fields.Comment: 4 pages, 3 figures, accepted in Phys. Rev. Letter

Switchable Membrane Remodeling and Antifungal Defense by Metamorphic Chemokine XCL1

Antimicrobial peptides (AMPs) are a class of molecules which generally kill pathogens via preferential cell membrane disruption. Chemokines are a family of signaling proteins that direct immune cell migration and share a conserved α–β tertiary structure. Recently, it was found that a subset of chemokines can also function as AMPs, including CCL20, CXCL4, and XCL1. It is therefore surprising that machine learning based analysis predicts that CCL20 and CXCL4’s α-helices are membrane disruptive, while XCL1’s helix is not. XCL1, however, is the only chemokine known to be a metamorphic protein which can interconvert reversibly between two distinct native structures (a β-sheet dimer and the α–β chemokine structure). Here, we investigate XCL1’s antimicrobial mechanism of action with a focus on the role of metamorphic folding. We demonstrate that XCL1 is a molecular “Swiss army knife” that can refold into different structures for distinct context-dependent functions: whereas the α–β chemokine structure controls cell migration by binding to G-Protein Coupled Receptors (GPCRs), we find using small angle X-ray scattering (SAXS) that only the β-sheet and unfolded XCL1 structures can induce negative Gaussian curvature (NGC) in membranes, the type of curvature topologically required for membrane permeation. Moreover, the membrane remodeling activity of XCL1’s β-sheet structure is strongly dependent on membrane composition: XCL1 selectively remodels bacterial model membranes but not mammalian model membranes. Interestingly, XCL1 also permeates fungal model membranes and exhibits anti-Candida activity in vitro, in contrast to the usual mode of antifungal defense which requires Th17 mediated cell-based responses. These observations suggest that metamorphic XCL1 is capable of a versatile multimodal form of antimicrobial defense

Switchable Membrane Remodeling and Antifungal Defense by Metamorphic Chemokine XCL1

Antimicrobial peptides (AMPs) are a class of molecules which generally kill pathogens via preferential cell membrane disruption. Chemokines are a family of signaling proteins that direct immune cell migration and share a conserved α–β tertiary structure. Recently, it was found that a subset of chemokines can also function as AMPs, including CCL20, CXCL4, and XCL1. It is therefore surprising that machine learning based analysis predicts that CCL20 and CXCL4’s α-helices are membrane disruptive, while XCL1’s helix is not. XCL1, however, is the only chemokine known to be a metamorphic protein which can interconvert reversibly between two distinct native structures (a β-sheet dimer and the α–β chemokine structure). Here, we investigate XCL1’s antimicrobial mechanism of action with a focus on the role of metamorphic folding. We demonstrate that XCL1 is a molecular “Swiss army knife” that can refold into different structures for distinct context-dependent functions: whereas the α–β chemokine structure controls cell migration by binding to G-Protein Coupled Receptors (GPCRs), we find using small angle X-ray scattering (SAXS) that only the β-sheet and unfolded XCL1 structures can induce negative Gaussian curvature (NGC) in membranes, the type of curvature topologically required for membrane permeation. Moreover, the membrane remodeling activity of XCL1’s β-sheet structure is strongly dependent on membrane composition: XCL1 selectively remodels bacterial model membranes but not mammalian model membranes. Interestingly, XCL1 also permeates fungal model membranes and exhibits anti-Candida activity in vitro, in contrast to the usual mode of antifungal defense which requires Th17 mediated cell-based responses. These observations suggest that metamorphic XCL1 is capable of a versatile multimodal form of antimicrobial defense

Waterborne outbreak of tularemia associated with crayfish fishing.

In 1997, an outbreak of human tularemia associated with hare-hunting in central Spain affected 585 patients. We describe the identification of Francisella tularensis biovar palaearctica in a second outbreak of ulceroglandular tularemia associated with crayfish (Procambarus clarkii) fishing in a contaminated freshwater stream distant from the hare-associated outbreak. The second outbreak occurred 1 year after the first

Independence in CLP Languages

Studying independence of goals has proven very useful in the context of logic programming. In particular, it has provided a formal basis for powerful automatic parallelization tools, since independence ensures that two goals may be evaluated in parallel while preserving correctness and eciency. We extend the concept of independence to constraint logic programs (CLP) and prove that it also ensures the correctness and eciency of the parallel evaluation of independent goals. Independence for CLP languages is more complex than for logic programming as search space preservation is necessary but no longer sucient for ensuring correctness and eciency. Two additional issues arise. The rst is that the cost of constraint solving may depend upon the order constraints are encountered. The second is the need to handle dynamic scheduling. We clarify these issues by proposing various types of search independence and constraint solver independence, and show how they can be combined to allow dierent optimizations, from parallelism to intelligent backtracking. Sucient conditions for independence which can be evaluated \a priori" at run-time are also proposed. Our study also yields new insights into independence in logic programming languages. In particular, we show that search space preservation is not only a sucient but also a necessary condition for ensuring correctness and eciency of parallel execution