Structure, Thermodynamics and Kinetics of Chemically Heterogeneous Interfaces

In this work we have used atomistic computer simulations to examine the structure, thermodynamics and transport properties, for two models of chemically heterogeneous interfaces: an ideal model (repulsive soft spheres against a potential wall), and a metal alloy interface (Cu-Pb). In both systems, interfacial prefreezing (crystal formation above the melting point of the fluid) was observed and this prefreezing was seen to promote heterogeneous nucleation, when the systems were cooled below the melting temperature. In our study of inverse-power repulsive soft spheres, we found that the soft-sphere fluid exhibited prefreezing at the wall surface. Similar behavior was previously observed in hard-sphere fluids at hard wall [17, 18, 20], however, to our knowledge, this the first time that prefreezing is reported for soft spheres. The prediction of prefreezing is based on the calculation of interfacial free energies wall-crystal (g_wc) and wall-fluid (g_wf ) using a variant of the cleaving wall method. With the calculated, g_wc and g_wf together with g_cf , previously computed [79], the tendency to prefreeze was quantified by the wetting angle formed between the metastable crystal phase on the wall and the soft-sphere fluid. We found that all the closest packing orientations [(111) FCC and (110) BCC] developed prefreezing (complete wetting). A detailed atomic-level characterization of the structure, energetics and transport properties of the planar Cu/Pb solid-liquid interface in equilibrium was performed at a several temperatures (625K and 750K) above the melting point of Pb and for two Cu crystal orientations [(111) and (100)]. Among the most relevant findings are that the Cu(100)/Pb interfaces presents surfaces alloying and the Cu(111)/Pb exhibits a prefreezing layer of Pb crystal. It was also observed that both interfaces have a nucleation barrier that prevents heterogeneous nucleation and that the mechanisms by which each structure promotes heterogeneous nucleation are different. Both models, the inverse-power soft spheres and the EAM Cu-Pb, showed the connection between atomistic behavior and prefreezing. The crystalline layer formed above the melting point of the fluids showed to be influential in heterogeneous nucleation in both cases. In this way, the study of basic properties shed new light on the atomistic underlying nature of macroscopic events, such as wetting and nucleatio

Effects of lattice mismatch on interfacial structures of liquid and solidified Al in contact with hetero-phase substrates: MD simulations

Published under licence in IOP Conference Series: Material Science and Engineering by IOP Publishing Ltd. Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.In this study, the effects of the misfit on in-plane structures of liquid Al and interfacial structure of solidified Al in contact with the heterophase substrates have been investigated, using molecular dynamics (MD) simulations. The MD simulations were conducted for Al/fcc (111) substrates with varied misfits. The order parameter and atomic arrangement indicated that the in-plane ordering of the liquid at the interface decreases significantly with an increase of the misfit, i.e., solid-like for small misfit and liquid-like for large misfit. Further, our MD simulation results revealed that a perfect orientation relationship forms at the interface between the substrate and the solidified Al for a misfit of less than -3% and the boundary is coherent. With an increase in the misfit, Shockley partial and extended dislocations form at the interface, and the boundary becomes a semi-coherent or low-angle twist boundary.EPSR

Detecting affective states in virtual rehabilitation

Virtual rehabilitation supports motor training following stroke by means of tailored virtual environments. To optimize therapy outcome, virtual rehabilitation systems automatically adapt to the different patients' changing needs. Adaptation decisions should ideally be guided by both the observable performance and the hidden mind state of the user. We hypothesize that some affective aspects can be inferred from observable metrics. Here we present preliminary results of a classification exercise to decide on 4 states; tiredness, tension, pain and satisfaction. Descriptors of 3D hand movement and finger pressure were collected from 2 post-stroke participants while they practice on a virtual rehabilitation platform. Linear Support Vector Machine models were learnt to unfold a predictive relation between observation and the affective states considered. Initial results are promising (ROC Area under the curve (mean±std): 0.713 ± 0.137). Confirmation of these opens the door to incorporate surrogates of mind state into the algorithm deciding on therapy adaptation

Unobtrusive inference of affective states in virtual rehabilitation from upper limb motions: a feasibility study

Virtual rehabilitation environments may afford greater patient personalization if they could harness the patient's affective state. Four states: anxiety, pain, engagement and tiredness (either physical or psychological), were hypothesized to be inferable from observable metrics of hand location and gripping strength -relevant for rehabilitation-. Contributions are; (a) multiresolution classifier built from Semi-Naïve Bayesian classifiers, and (b) establishing predictive relations for the considered states from the motor proxies capitalizing on the proposed classifier with recognition levels sufficient for exploitation. 3D hand locations and gripping strength streams were recorded from 5 post-stroke patients whilst undergoing motor rehabilitation therapy administered through virtual rehabilitation along 10 sessions over 4 weeks. Features from the streams characterized the motor dynamics, while spontaneous manifestations of the states were labelled from concomitant videos by experts for supervised classification. The new classifier was compared against baseline support vector machine (SVM) and random forest (RF) with all three exhibiting comparable performances. Inference of the aforementioned states departing from chosen motor surrogates appears feasible, expediting increased personalization of virtual motor neurorehabilitation therapies

Tourism and water as axes of accumulation, in Ixtapan de la Sal, México

Artículo científicoEl agua es un recurso natural, al que por ley todos los seres humanos tienen derecho, sin embargo, la accesibilidad del mismo está condicionada por factores tales como la privatización, proceso mediante el cual se concesiona a empresas del sector privado quien se encarga de su manejo, convirtiéndola en mercancía a la que se le añade un valor, de manera que se vuelve objeto de apropiación y a su vez en un mecanismo de administración peligroso desde el momento en que se establecen precios diferenciados, condicionando así la oferta de servicios. Por ello, en el presente trabajo se analizaron las dinámicas de dominación a partir del uso del agua para la actividad turística de Ixtapan de la Sal, México; con la finalidad de explicar el proceso de acumulación por parte de las empresas privadas. La propuesta teórico metodológica que se siguió, se sustentó en la Economía Política mediante el materialismo histórico con la interpretación de tres dinámicas de dominación y su relación con el turismo. En la dinámica de penetración se observó que los agentes externos privan de los recursos naturales a los habitantes del lugar, modificando y sustituyendo las actividades productivas. Lo anterior debido a la concesión del agua termal en 1944 y el agua dulce en 1951 con vigencia al 2021, beneficiando a un único propietario y concesionario. El recurso hídrico a partir de 2016 se paga al sustituirse el canal a cielo abierto por tubería subterránea, hecho determinado en la dinámica de subsunción. En la dinámica de acumulación se detectó que el agua es ofertada como mercancía y los beneficios por la explotación de ésta dejan de ser para el municipio. Se concluye que la privatización del agua o del manejo del recurso va en contra del buen funcionamiento de la actividad turística, dejando como resultado la insatisfacción de las principales necesidades de la población local

Densidad poblacional y uso del hábitat de la codorniz Moctezuma (Cyrtonyx montezumae) en Hualtepec, Hidalgo

El presente estudio se realizó para determinar la densidad poblacional y el uso del hábitat de la codorniz Moctezuma (Cyrtonyx montezumae) en Hualtepec, Hidalgo, México, en tres tipos de vegetación: bosque, pastizal y zona de transición (ecotono). Dicho sitio se localiza en el extremo oeste de Hidalgo, con área de muestreo de 5 715 ha. Se realizó un muestreo en 55 unidades, para evaluar el uso del hábitat por medio de indicios (excretas, rascaderos, plumas y nidos), y densidad de población, con transectos convencionales (6 km de longitud por 50 m de ancho), con el apoyo de perros de muestra. En cada sitio se registraron los indicios y se contaron las codornices observadas. La densidad (codornices/ha) varió de 0.1341 a 0.2318. No se encontraron diferencias en la densidad de codornices en los diferentes tipos de vegetación (bosque, 0.1765; pastizal, 0.2318; ecotono, 0.1341); sin embargo, el hábitat más usado fue el ecotono, seguido por el pastizal y el bosque. Los rascaderos y bulbos de Oxalis disponibles fueron más altos (P < 0.05) en el pastizal. El número de individuos, plumas, excretas (P < 0.10) y de nidos y rascaderos fueron mayores (P < 0.05) en el pastizal. Este estudio constituye la primera estimación de densidad poblacional de la codorniz Moctezuma en Hidalgo, México

PS447 Environmental Politics & Policy Zoom Presentations - Session #1

Over the spring quarter 2021, students from PS447 Environmental Politics and Policy have been researching a substantial environmental issue of their choice, defining a problem found within the issue, and devising and implementing an awareness campaign focused on a solution to the problem. During the Academic Excellence Showcase zoom presentation they will be presenting their environmental issue, creating awareness and proposing a solution for the audience. Students will present on a wide range of environmental themes such plastic waste, air pollution, deforestation and climate change

Facet selectivity in gold binding peptides: exploiting interfacial water structure

Peptide sequences that can discriminate between gold facets under aqueous conditions offer a promising route to control the growth and organisation of biomimetically-synthesised gold nanoparticles. Knowledge of the interplay between sequence, conformations and interfacial properties is essential for predictable manipulation of these biointerfaces, but the structural connections between a given peptide sequence and its binding affinity remain unclear, impeding practical advances in the field. These structural insights, at atomic-scale resolution, are not easily accessed with experimental approaches, but can be delivered via molecular simulation. A current unmet challenge lies in forging links between predicted adsorption free energies derived from enhanced sampling simulations with the conformational ensemble of the peptide and the water structure at the surface. To meet this challenge, here we use an in situ combination of Replica Exchange with Solute Tempering with Metadynamics simulations to predict the adsorption free energy of a gold-binding peptide sequence, AuBP1, at the aqueous Au(111), Au(100)(1 &times; 1) and Au(100)(5 &times; 1) interfaces. We find adsorption to the Au(111) surface is stronger than to Au(100), irrespective of the reconstruction status of the latter. Our predicted free energies agree with experiment, and correlate with trends in interfacial water structuring. For gold, surface hydration is predicted as a chief determining factor in peptide-surface recognition. Our findings can be used to suggest how shaped seed-nanocrystals of Au, in partnership with AuBP1, could be used to control AuNP nanoparticle morphology

Aqueous peptide-TiO2 interfaces: iso-energetic binding via either entropically- or enthalpically-driven mechanisms

A major barrier to the systematic improvement of biomimetic peptide-mediated strategies for the controlled growth of inorganic nanomaterials in environmentally benign conditions lies in the lack of clear conceptual connections between the sequence of the peptide and its surface binding affinity, with binding being facilitated by non-covalent interactions. Peptide conformation, both in the adsorbed and non-adsorbed state, is the key relationship that connects peptide-materials binding with peptide sequence. Here, we combine experimental peptide–titania binding characterization with state-of-the-art conformational sampling via molecular simulations to elucidate these structure/binding relationships for two very different titania-binding peptide sequences. The two sequences (Ti-1: QPYLFATDSLIK and Ti-2: GHTHYHAVRTQT) differ in their overall hydropathy, yet via quartz-crystal microbalance measurements and predictions from molecular simulations, we show these sequences both support very similar, strong titania-binding affinities. Our molecular simulations reveal that the two sequences exhibit profoundly different modes of surface binding, with Ti-1 acting as an entropically-driven binder while Ti-2 behaves as an enthalpically-driven binder. The integrated approach presented here provides a rational basis for peptide sequence engineering to achieve the in-situ growth and organization of titania nanostructures in aqueous media and for the design of sequences suitable for a range of technological applications that involve the interface between titania and biomolecules