Papers by Bruno Escribano
Langmuir, 2013
We establish that the nonlinear dynamics of collisions between particles favors the charging of a... more We establish that the nonlinear dynamics of collisions between particles favors the charging of an insulating, friable, self-replicating granular material that undergoes nucleation, growth, and fission processes; we demonstrate with a minimal dynamical model that secondary nucleation produces a positive feedback in an electrification mechanism that leads to runaway charging. We discuss ice as an example of such a self-replicating granular material: We confirm with laboratory experiments in which we grow ice from the vapor phase in situ within an environmental scanning electron microscope that charging causes fast-growing and easily breakable palm-like structures to form, which when broken off may form secondary nuclei. We propose that
thunderstorms, both terrestrial and on other planets, and lightning in the solar nebula are instances of such runaway charging arising from this nonlinear dynamics in self-replicating granular matter.
Chemical reviews, Jan 15, 2015
Journal of Computational Physics, 2015
Langmuir, 2013
We establish that the nonlinear dynamics of collisions between particles favors the charging of a... more We establish that the nonlinear dynamics of collisions between particles favors the charging of an insulating, friable, self-replicating granular material that undergoes nucleation, growth, and fission processes; we demonstrate with a minimal dynamical model that secondary nucleation produces a positive feedback in an electrification mechanism that leads to runaway charging. We discuss ice as an example of such a selfreplicating granular material: We confirm with laboratory experiments in which we grow ice from the vapor phase in situ within an environmental scanning electron microscope that charging causes fast-growing and easily breakable palmlike structures to form, which when broken off may form secondary nuclei. We propose that thunderstorms, both terrestrial and on other planets, and lightning in the solar nebula are instances of such runaway charging arising from this nonlinear dynamics in self-replicating granular matter.
Journal of Molecular Modeling, 2014
Adaptation and implementation of the Generalized Shadow Hybrid Monte Carlo (GSHMC) method for mol... more Adaptation and implementation of the Generalized Shadow Hybrid Monte Carlo (GSHMC) method for molecular simulation at constant pressure in the NPT ensemble are discussed. The resulting method, termed NPT-GSHMC, combines Andersen barostat with GSHMC to enable molecular simulations in the environment natural for biological applications, namely, at constant pressure and constant temperature. Generalized Hybrid Monte Carlo methods are designed to maintain constant temperature and volume and extending their functionality to preserving pressure is not trivial. The theoretical formulation of NPT-GSHMC was previously introduced. Our main contribution is the implementation of this methodology in the GROMACS molecular simulation package and the evaluation of properties of NPT-GSHMC, such as accuracy, performance, effectiveness for real physical systems in comparison with well-established molecular simulation techniques. Benchmarking tests are presented and the obtained preliminary results are promising. For the first time, the generalized hybrid Monte Carlo simulations at constant pressure are available within the popular open source molecular dynamics software package.
Abstract Chemical gardens are biomimetic structures in the form of plants formed by a combination... more Abstract Chemical gardens are biomimetic structures in the form of plants formed by a combination of salts which precipitate by a combination of convection forced by osmosis, free convection and chemical reactions. Chemical gardens may be implicated in other phenomena of industrial interest which involve precipitation across a colloidal gel membrane which separates two different aqueous solutions, for example, in cement technology and metal corrosion process. However, the variation in chemical composition, ...
Complex Systems, 2008
Ice, the solid phase of water, is ubiquitous. A knowledge of ice helps us to comprehend water, a ... more Ice, the solid phase of water, is ubiquitous. A knowledge of ice helps us to comprehend water, a simple molecule, but one with much complex behaviour. Our aim is to understand the morphologies and physics of thin icy films. To treat this complex system we have developed new experimental capabilities with an environmental scanning electron microscope (ESEM) capable of working with ice films, at the same time as new simulation approaches to understanding the physics of ice morphology. A comprehension of the ...
MRS Proceedings, 2008
The sequence of formation of the organic and inorganic components of nacre in bivalves and gastro... more The sequence of formation of the organic and inorganic components of nacre in bivalves and gastropods is re-studied. We reach the conclusion that interlamellar membranes are formed well in advance of the other elements. In this way, we support and refine the compartment theory for the formation of nacre. We explain the arrangement of chitin crystallites within a single interlamellar membrane and the layering of interlamellar membranes as a process of formation of a liquid crystal.
The Astrophysical Journal, 2008
We present the results of experiments in which we grow submicrometer-to millimeter-thick ice film... more We present the results of experiments in which we grow submicrometer-to millimeter-thick ice films at temperatures of 6Y220 K at low pressures in situ in a cryo environmental scanning electron microscope. We find that ice films show pronounced morphologies at the mesoscale similar to those previously described in films of ceramics, semiconductors, and metals; materials with quite different material properties to ice. Our experiments are aimed at revealing the mesoscale morphologies of amorphous and crystalline ice with regard to astrophysical environments, as the conditions in which the ice films grow in our experiments are those under which exists most extraterrestrial ice. The porosity on the mesoscale of many of the morphologies is notable in this regard; a further intriguing finding is that these ice films can emulate biological forms.
Proceedings of the National Academy of Sciences, 2009
Nacre is an exquisitely structured biocomposite of the calcium carbonate mineral aragonite with s... more Nacre is an exquisitely structured biocomposite of the calcium carbonate mineral aragonite with small amounts of proteins and the polysaccharide chitin. For many years, it has been the subject of research, not just because of its beauty, but also to discover how nature can produce such a superior product with excellent mechanical properties from such relatively weak raw materials. Four decades ago, Wada [Wada K (1966) Spiral growth of nacre. Nature 211:1427] proposed that the spiral patterns in nacre could be explained by using the theory Frank [Frank F (1949) The influence of dislocations on crystal growth. Discuss Faraday Soc 5:48-54] had put forward of the growth of crystals by means of screw dislocations. Frank's mechanism of crystal growth has been amply confirmed by experimental observations of screw dislocations in crystals, but it is a growth mechanism for a single crystal, with growth fronts of molecules. However, the growth fronts composed of many tablets of crystalline aragonite visible in micrographs of nacre are not a molecular-scale but a mesoscale phenomenon, so it has not been evident how the Frank mechanism might be of relevance. Here, we demonstrate that nacre growth is organized around a liquid-crystal core of chitin crystallites, a skeleton that the other components of nacre subsequently flesh out in a process of hierarchical self-assembly. We establish that spiral and target patterns can arise in a liquid crystal formed layer by layer through the Burton-Cabrera-Frank [Burton W, Cabrera N, Frank F (1951) The growth of crystals and the equilibrium structure of their surfaces. Philos Trans R Soc London Ser A 243:299-358] dynamics, and furthermore that this layer growth mechanism is an instance of an important class of physical systems termed excitable media. Artificial liquid crystals grown in this way may have many technological applications.
Physical Review E, 2008
We take a dynamical-systems approach to study the qualitative dynamical aspects of the tidal lock... more We take a dynamical-systems approach to study the qualitative dynamical aspects of the tidal locking of the rotation of secondary celestial bodies with their orbital motion around the primary. We introduce a minimal model including the essential features of gravitationally induced elastic deformation and tidal dissipation that demonstrates the details of the energy transfer between the orbital and rotovibrational degrees of freedom. Despite its simplicity, our model can account for both synchronization into the 1:1 spin-orbit resonance and the circularization of the orbit as the only true asymptotic attractors, together with the existence of relatively long-lived metastable orbits with the secondary in p : q synchronous rotation.
Physical Chemistry Chemical Physics, 2011
We have compared the behaviour of the chloride salts of the cations Ca 2+ , Sr 2+ and Ba 2+ of Gr... more We have compared the behaviour of the chloride salts of the cations Ca 2+ , Sr 2+ and Ba 2+ of Group 2 of the Periodic Table in the formation of chemical gardens in silicate solutions. We performed analyses of morphology, composition and microstructure using environmental scanning electron microscopy (ESEM), X-ray diffraction (XRD) and energy dispersive X-ray analysis (EDX). We have identified different growth regimes in these salts (jetting and budding), which are dependent on the concentration of the silicate solution. The behaviour is similar for all the cations but reactivity decreases down the group and is directly proportional to the solubility of the salts: Ca 2+ > Sr 2+ > Ba 2+ .
Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 2012
Crystal growth has been widely studied for many years, and, since the pioneering work of Burton, ... more Crystal growth has been widely studied for many years, and, since the pioneering work of Burton, Cabrera, and Frank, spirals and target patterns on the crystal surface have been understood as forms of tangential crystal growth mediated by defects and by two-dimensional nucleation. Similar spirals and target patterns are ubiquitous in physical systems describable as excitable media. Here we demonstrate that this is not merely a superficial resemblance; that the physics of crystal growth can be set within the framework of an excitable medium, and that appreciating this correspondence may prove useful to both fields. Apart from solid crystals, we discuss how our model applies to the biomaterial nacre, formed by layer growth of a biological liquid crystal.
Langmuir, 2011
We studied the growth of metal-ion silicate chemical gardens under Earth gravity (1 g) and microg... more We studied the growth of metal-ion silicate chemical gardens under Earth gravity (1 g) and microgravity (μg) conditions. Identical sets of reaction chambers from an automated system (the Silicate Garden Habitat or SGHab) were used in both cases. The μg experiment was performed on board the International Space Station (ISS) within a temperature-controlled setup that provided still and video images of the experiment downlinked to the ground. Calcium chloride, manganese chloride, cobalt chloride, and nickel sulfate were used as seed salts in sodium silicate solutions of several concentrations. The formation and growth of osmotic envelopes and microtubes was much slower under μg conditions. In 1 g, buoyancy forces caused tubes to grow upward, whereas a random orientation for tube growth was found under μg conditions.
Langmuir, 2013
Brinicles are hollow tubes of ice from centimeters to meters in length that form under floating s... more Brinicles are hollow tubes of ice from centimeters to meters in length that form under floating sea ice in the polar oceans when dense, cold brine drains downward from sea ice to seawater close to its freezing point. When this extremely cold brine leaves the ice, it freezes the water it comes into contact with: a hollow tube of icea briniclegrowing downward around the plume of descending brine. We show that brinicles can be understood as a form of the self-assembled tubular precipitation structures termed chemical gardens, which are plantlike structures formed on placing together a soluble metal salt, often in the form of a seed crystal, and an aqueous solution of one of many anions, often silicate. On one hand, in the case of classical chemical gardens, an osmotic pressure difference across a semipermeable precipitation membrane that filters solutions by rejecting the solute leads to an inflow of water and to its rupture. The internal solution, generally being lighter than the external solution, flows up through the break, and as it does so, a tube grows upward by precipitation around the jet of internal solution. Such chemical-garden tubes can grow to many centimeters in length. In the case of brinicles, on the other hand, in floating sea ice we have porous ice in a mushy layer that filters out water, by freezing it, and allows concentrated brine through. Again there is an osmotic pressure difference leading to a continuing ingress of seawater in a siphon pump mechanism that is sustained as long as the ice continues to freeze. Because the brine that is pumped out is denser than the seawater and descends rather than rises, a brinicle is a downward-growing tube of ice, an inverse chemical garden.
… Assembly 2010, held …, 2010
We show with laboratory experiments in which we grow ice films in situ from the vapour phase with... more We show with laboratory experiments in which we grow ice films in situ from the vapour phase within an environmental scanning electron microscope that there are two positive feedback effects that favour the charging of a thundercloud by the collisions ...
Central European Journal of Mathematics, 2013
Generalized Shadow Hybrid Monte Carlo (GSHMC) is a method for molecular simulations that rigorous... more Generalized Shadow Hybrid Monte Carlo (GSHMC) is a method for molecular simulations that rigorously alternates Monte Carlo sampling from a canonical ensemble with integration of trajectories using Molecular Dynamics (MD). While conventional hybrid Monte Carlo methods completely re-sample particle's velocities between MD trajectories, our method suggests a partial velocity update procedure which keeps a part of the dynamic information throughout the simulation. We use shadow (modified) Hamiltonians, the asymptotic expansions in powers of the discretization parameter corresponding to timestep, which are conserved by symplectic integrators to higher accuracy than true Hamiltonians. We present the implementation of this method into the highly efficient MD code GROMACS and demonstrate its performance and accuracy on computationally expensive systems like proteins in comparison with the molecular dynamics techniques already available in GROMACS. We take advantage of the state-of-the-art algorithms adopted in the code, leading to an optimal implementation of the method. Our implementation introduces virtually no overhead and can accurately recreate complex biological processes, including rare event dynamics, saving much computational time compared with the conventional simulation methods.
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Papers by Bruno Escribano
thunderstorms, both terrestrial and on other planets, and lightning in the solar nebula are instances of such runaway charging arising from this nonlinear dynamics in self-replicating granular matter.
thunderstorms, both terrestrial and on other planets, and lightning in the solar nebula are instances of such runaway charging arising from this nonlinear dynamics in self-replicating granular matter.