Continuous melting through a hexatic phase in confined bilayer water

Liquid water is not only of obvious importance but also extremely intriguing, displaying many anomalies that still challenge our understanding of such an a priori simple system. The same is true when looking at nanoconfined water: The liquid between constituents in a cell is confined to such dimensions, and there is already evidence that such water can behave very differently from its bulk counterpart. A striking finding has been reported from computer simulations for two-dimensionally confined water: The liquid displays continuous or discontinuous melting depending on its density. In order to understand this behavior, we have analyzed the melting exhibited by a bilayer of nanoconfined water by means of molecular dynamics simulations. At high density we observe the continuous melting to be related to the phase change of the oxygens only, with the hydrogens remaining liquidlike throughout. Moreover, we find an intermediate hexatic phase for the oxygens between the liquid and a triangular solid ice phase, following the Kosterlitz-Thouless-Halperin-Nelson-Young theory for two-dimensional melting. The liquid itself tends to maintain the local structure of the triangular ice, with its two layers being strongly correlated yet with very slow exchange of matter. The decoupling in the behavior of the oxygens and hydrogens gives rise to a regime in which the complexity of water seems to disappear, resulting in what resembles a simple monoatomic liquid. This intrinsic tendency of our simulated water may be useful for understanding novel behaviors in other confined and interfacial water systems

A Century of Arbitrage and Disaster Risk Pricing in the Foreign Exchange Market

A long-standing puzzle in international finance is that a positive interest rate differential systematically forecasts an exchange rate appreciation - the Uncovered Interest Parity (UIP) puzzle. Hence, a carry trade portfolio long in high yield currency bonds funded by borrowing in low yield currencies can be expected to yield positive profits. Following the Great Financial Crisis, however, the sign of the puzzle has changed - positive differentials forecast excessive depreciation - and carry trade has withered after the large losses suffered by investors in 2007-2008. In this paper, we use a century-long time series for the GBP/USD exchange rate to show that a sign switch is neither new, nor, arguably, a new puzzle. First, it is not new in the data|by virtue of a long sample featuring infrequent, non-overlapping currency crashes, we document that switches systematically occur in crises such as the Great Depression in the 1930s and the exchange rate turmoil of the 1990s. However, UIP deviations, sharp in either direction for short - to medium-horizon portfolios, remain small to almost negligible for long-horizon investment portfolios. Second, we argue that our century-long evidence is consistent with models featuring a time-varying probability of disasters or 'Peso events,' specified so to account for the difference in UIP deviations in crisis and normal times, as well as for a decreasing term structure of carry trade returns that on average characterize the data

Enhanced Configurational Entropy in High-Density Nanoconfined Bilayer Ice

A novel kind of crystal order in high-density nanoconfined bilayer ice is proposed from molecular dynamics and density-functional theory simulations. A first-order transition is observed between a low-temperature proton-ordered solid and a high-temperature proton-disordered solid. The latter is shown to possess crystalline order for the oxygen positions, arranged on a close-packed triangular lattice with AA stacking. Uniquely among the ice phases, the triangular bilayer is characterized by two levels of disorder (for the bonding network and for the protons) which results in a configurational entropy twice that of bulk ice.This work was partly funded by Grants No. FIS2012- 37549-C05 from the Spanish Ministry of Science, and Exp. 97/14 (Wet Nanoscopy) from the Programa Red Guipuzcoana de Ciencia, Tecnología e Innovación, Diputación Foral de Gipuzkoa. We thank José M. Soler and M.-V. Fernández-Serra for useful discussions. The calculations were performed on the arina HPC cluster (Universidad del País Vasco/Euskal Herriko Unibertsitatea, Spain). SGIker (UPV/EHU, MICINN, GV/EJ, ERDF and ESF) support is gratefully acknowledged

Structural and configurational properties of nanoconfined monolayer ice from first principles

Understanding the structural tendencies of nanoconfined water is of great interest for nanoscience and biology, where nano/micro-sized objects may be separated by very few layers of water. Here we investigate the properties of ice confined to a quasi-2D monolayer by a featureless, chemically neutral potential, in order to characterize its intrinsic behaviour. We use density-functional theory simulations with a non-local van der Waals density functional. An ab initio random structure search reveals all the energetically competitive monolayer configurations to belong to only two of the previously-identified families, characterized by a square or honeycomb hydrogen-bonding network, respectively. We discuss the modified ice rules needed for each network, and propose a simple point dipole 2D lattice model that successfully explains the energe tics of the square configurations. All identified stable phases for both networks are found to be non-polar (but with a topologically non-trivial texture for the square) and, hence, non-ferroelectric, in contrast to previous predictions from a five-site empirical force-field model. Our results are in good agreement with very recently reported experimental observations.This work was partly funded by grants FIS2012-37549-C05 from the Spanish Ministry of Science, and Exp. 97/14 (Wet Nanoscopy) from the Programa Red Guipuzcoana de Ciencia, Tecnología e Innovación, Diputación Foral de Gipuzkoa. We thank Richard Korytár and Javier Junquera for their work on the SIESTA interface to Wannier90, and Raffaele Resta and M.-V. Fernández-Serra for useful discussions. The calculations were performed on the arina HPC cluster (Universidad del País Vasco/Euskal Herriko Unibertsitatea, Spain). SGIker (UPV/EHU, MICINN, GV/EJ, ERDF and ESF) support is gratefully acknowledged

Malnutrition and Gut Flora dysbiosis: specific therapies for emerging comorbidities in heart failure

Chronic heart failure is a complicated multifactorial disease with wide-spread social-economic consequences. In spite of the recent development of new drugs and therapeutic strategies, CHF-related mortality and morbidity remain high. Recent evidence suggests that changes in organs such as skeletal muscle and gut flora may play an important and independent role in CHF prognosis. This paper illustrates these phenomena, proposing how to identify them and presenting current therapies which treat organs all too often underestimated but which have a fundamental role in worsening CHF

The Euro Crisis in the Mirror of the EMS: How Tying Odysseus to the Mast Avoided the Sirens but Led Him to Charybdi

Why was recovery from the euro area crisis delayed for a decade? The explanation lies in the absence of credible and timely policies to backstop financial intermediaries and sovereign debt markets. In this paper we add light and color to this analysis, contrasting recent experience with the 1992-3 crisis in the European Monetary System, when national central banks and treasuries more successfully provided this backstop. In the more recent episode, the incomplete development of the euro area constrained the ability of the ECB and other European institutions to do likewis

The Euro Crisis in the Mirror of the EMS: How Tying Odysseus to the Mast Avoided the Sirens but Led Him to Charybdis

Why was recovery from the euro area crisis delayed for a decade? The explanation lies in the absence of credible and timely policies to backstop financial intermediaries and sovereign debt markets. In this paper we add light and color to this analysis, contrasting recent experience with the 1992-3 crisis in the European Monetary System, when national central banks and treasuries more successfully provided this backstop. In the more recent episode, the incomplete development of the euro area constrained the ability of the ECB and other European institutions to do likewise.Keynes Fund at Cambridge University. The Making of the Euro-Area Crisis: Lessons from Theory and History (JHLP)

Probing the Evaporation Dynamics of Ethanol/Gasoline Biofuel Blends Using Single Droplet Manipulation Techniques

Peer reviewedPublisher PD

Electronic stopping power in a narrow band gap semiconductor from first principles

© 2015 American Physical Society. The direction and impact parameter dependence of electronic stopping power, along with its velocity threshold behavior, is investigated in a prototypical small-band-gap semiconductor. We calculate the electronic stopping power of H in Ge, a semiconductor with relatively low packing density, using time-evolving time-dependent density-functional theory. The calculations are carried out in channeling conditions with different impact parameters and in different crystal directions for projectile velocities ranging from 0.05 to 0.6 atomic units. The satisfactory comparison with available experiments supports the results and conclusions beyond experimental reach. The calculated electronic stopping power is found to differ in different crystal directions; however, strong impact parameter dependence is observed only in one of these directions. The distinct velocity threshold observed in experiments is well reproduced, and its nontrivial relation with the band gap follows a perturbation theory argument surprisingly well. This simple model is also successful in explaining why different density functionals give the same threshold even with substantially different band gaps.We are thankful to M. A. Zeb, A. Arnau, J. I. Juaristi, J. M. Pitarke, P. Bauer, D. Roth, and A. Correa for useful discussions. The financial support from MINECO-Spain through Plan Nacional Grant No. FIS2012-37549-C05-01, FPI Ph.D. Fellowship Grant No. BES-2013-063728, and Grant No. MAT2013-46593-C6-2-P along with the EU Grant “ElectronStopping” in the Marie Curie CIG Program is duly acknowledged. SGIker (UPV/EHU, MICINN, GV/EJ, ERDF and ESF) support is gratefully acknowledged.

A microbial carbonate response in synchrony with the end-Triassic mass extinction across the SW UK

The eruption of the Central Atlantic Magmatic Province (CAMP)—the largest igneous province known—has been linked to the end-Triassic mass extinction event, however reconciling the response of the biosphere (at local and nonlocal scales) to potential CAMP-induced geochemical excursions has remained challenging. Here we present a combined sedimentary and biological response to an ecosystem collapse in Triassic-Jurassic strata of the southwest United Kingdom (SW UK) expressed as widely distributed carbonate microbialites and associated biogeochemical facies. The microbialites (1) occur at the same stratigraphic level as the mass extinction extinction, (2) host a negative isotope excursion in δ(13)C(org) found in other successions around the world, and (3) co-occur with an acme of prasinophyte algae ‘disaster taxa’ also dominant in Triassic-Jurassic boundary strata of other European sections. Although the duration of microbialite deposition is uncertain, it is likely that they formed rapidly (perhaps fewer than ten thousand years), thus providing a high-resolution glimpse into the initial carbon isotopic perturbation coincident with the end-Triassic mass extinction. These findings indicate microbialites from the SW UK capture a nonlocal biosedimentary response to the cascading effects of massive volcanism and add to the current understanding of paleoecology in the aftermath of the end-Triassic extinction