Improved graphene blisters by ultrahigh pressure sealing

Graphene is a very attractive material for nanomechanical devices and membrane applications. Graphene blisters based on silicon oxide micro-cavities are a simple but relevant example of nanoactuators. A drawback of this experimental set up is that gas leakage through the graphene-SiO2 interface contributes significantly to the total leak rate. Here we study the diffusion of air from pressurized graphene drumheads on SiO2 micro-cavities and propose a straightforward method to improve the already strong adhesion between graphene and the underlying SiO2 substrate, resulting in reduced leak rates. This is carried out by applying controlled and localized ultrahigh pressure (> 10 GPa) with an Atomic Force Microscopy diamond tip. With this procedure, we are able to significantly approach the graphene layer to the SiO2 surface around the drumheads, thus enhancing the interaction between them allowing us to better seal the graphene-SiO2 interface, which is reflected in up to ~ 4 times lower leakage rates. Our work opens an easy way to improve the performance of graphene as a gas membrane on a technological relevant substrate such as SiO2.Comment: pages 19, 4 figures + supplementary informatio

Optimization of pulsed thermoelectric materials using simulated annealing and non-linear finite elements

[EN] The objective of this work is to determine the optimal shape, gains and duration of an electric pulse applied to a Peltier cell, together with the length of the thermoelectric to maximize cooling while min- imizing electric consumption. For this purpose, a fully coupled, multiphysics, dynamic finite-element model, which solves for the thermal, electric and mechanical fields is used. Because of the demanding computing requirements of the optimization process, a special mesh is designed and a convergence anal- ysis is carried out before using the multiphysics model. The highly non-linear optimization is done by simulated annealing, a heuristic algorithm in the Markov chain Monte-Carlo family. A preliminary para- metric investigation is presented, analyzing the impact of some of the parameters. The results of this pre- liminary analysis help to understand the effect of the different shapes in the evolution of the cold face temperature. Some of these results are expected and have already been discussed elsewhere, but others can only be explained after further analysis and a full system modeling. Pulse optimization is multiobjec- tive and multiparametric, i.e., it can consider several targets such as maximizing the cooling temperature, the cooling duration or others. The trade-offs between the different targets are studied. In all cases, stres- ses inside the thermoelement are examined at all points, and the pulses must meet the restriction that an equivalent stress is not above the allowable value.This research was partially supported by the grants, Haut-de-France Region (CR Picardie, 120-2015-RDISTRUCT-000010), EU funding (FEDER, RDISTRUCT-000010) for Chaire-de-Mecanique, and Spanish Ministry of Economy and Competitiveness grant CGL2014-59841-P. These supports are gratefully acknowledgedMoreno-Navarro, P.; Pérez-Aparicio, JL.; Gómez-Hernández, JJ. (2017). Optimization of pulsed thermoelectric materials using simulated annealing and non-linear finite elements. Applied Thermal Engineering. 120:603-613. https://doi.org/10.1016/j.applthermaleng.2017.04.036S60361312

Analytical and multicoupled methods for optimal steady-state thermoelectric solutions

[EN] Peltier cells have low efficiency, but they are becoming attractive alternatives for affordable and environmentally clean cooling. In this line, the current article develops closed-form and semianalytical solutions to improve the temperature distribution of Bi2Te3 thermoelements. From the distribution, the main objective of the current work-the optimal electric intensity to maximize cooling-is inferred. The general one-dimensional differential coupled equation is integrated for linear and quadratic geometry of thermoelements, under temperature constant properties. For a general shape, a piece-wise solution based on heat flux continuity among virtual layers gives accurate analytical solutions. For variable properties, another piece-wise solution is developed but solved iteratively. Taking advantage of the formulae, the optimal intensity is directly derived with a minimal computational cost; its value will be of utility for more advanced designs. Finally, a parametric study including straight, two linear, barrel, hourglass and vase geometries is presented, drawing conclusions on how the shape of the thermoelement affects the coupled phenomena. A specially developed coupled and non-linear finite element research code is run taking into account all the materials of the cell and using symmetries and repetitions. These accurate results are used to validate the analytical ones.This work was supported by the Generalitat Valenciana research programmes PROMETEO/2020/016: Applications de Topologic Isolators in Spintronics and Thermoelectricity (TOP-TERM) and BEST/2021/079. The support is gratefully acknowledged.Moreno-Navarro, P.; Pérez-Aparicio, JL.; Gómez-Hernández, JJ. (2022). Analytical and multicoupled methods for optimal steady-state thermoelectric solutions. Coupled Systems Mechanics, an international journal. 11(2):151-166. https://doi.org/10.12989/csm.2022.11.2.15115116611

THE ADVANTAGES OF EVAPORATION IN MICRO-SCALE CHANNELS TO COOL MICROELETRONIC DEVICES

In this paper, the importance of the development of new high power density thermal management systems for electronic devices is assessed. It is described the new heat sink technologies under development to be used in the cooling of microprocessors. The main difficulties to be overcome before the spreading of one specific heat sink configuration are identified. At the end, it is concluded that a heat sink based on flow boiling in micro-scale channels is the most promising approach

Is the Fast Evolution Scenario for Virialized Compact Groups Really Compelling? The Role of a Dark Massive Group Halo

We report on results of N-body simulations aimed at testing the hypothesis that galaxies in X-ray emitting (i.e., virialized) Compact Groups are not tidally stripped when they are embedded in a common, massive, quiescent dark matter halo. To disentangle the effects of interactions from spurious effects due to an incorrect choice of the initial galaxy model configurations, these have been chosen to be tidally-limited King spheres, representing systems in quasi-equilibrium within the tidal field of the halo. The potential of the halo has been assumed to be frozen and the braking due to dynamical friction neglected. Our results confirm the hypothesis of low rates of tidal stripping and suggest a scenario for virialized Compact Group evolution in their quiescent phases with only very moderate tidally induced galaxy evolution can be generally expected. This implies the group stability, provided that the dynamical friction timescales in these systems are not much shorter than the Hubble time. We discuss briefly this possibility, in particular taking account of the similarity between the velocity dispersions of a typical virialized Compact Groups and the internal velocity dispersion of typical member galaxies. A number of puzzling observational data on Compact Groups can be easily explained in this framework. Other observations would be better understood as the result of enhanced merging activity in the proto-group environment, leading to virialized Compact Group formation through mergers of lower mass halos, as predicted by hierarchical scenarios of structure formation.Comment: 18 pages, 1 postscript file, 2 tables, to be published in ApJLet

Small-Scale Abiotic Factors Influencing the Spatial Distribution of Phytophthora cinnamomi under Declining Quercus ilex Trees

Phytophthora root rot is considered one of the main factors associated with holm oak (Quercus ilex L.) mortality. The effectiveness and accuracy of soilborne pathogen and management could be influenced by soil spatial heterogeneity. This factor is of special relevance in many afforestation of southwestern Spain, which were carried out without phytosanitary control of the nursery seedlings. We selected a study area located in a 15 year-old afforestation of Q. ilex, known to be infested by Phytophthora cinnamomi Rands. Soil samples (ntotal = 132) were taken systematically from a grid under 4 trees, and analysed to quantify 12 variables, the colony forming units (cfu) of P. cinnamomi plus 11 physical and chemical soil properties. The combined analysis of all variables was performed with linear mixed models (GLMM), and the spatial patterns of cfu were characterised using an aggregation index (Ia) and a clustering index (ν) by SADIE. Cfu values ranged from 0 to 211 cfu g−1, and the GLMM built with the variables silt, P, K and soil moisture explained the cfu distribution to the greatest extent. The spatial analysis showed that 9 of the 12 variables presented spatial aggregation (Ia > 1), and the clustering of local patches (νi≥1.5) for organic matter, silt, and Ca. The spatial patterns of the P. cinnamomi cfu under planted holm oak trees are related to edaphic variables and canopy cover. Small-scale spatial analysis of microsite variability can predict which areas surrounding trees can influence lower oomycetes cfu availability

Anthropometric Characteristics, Body Composition and Somatotype of Elite Pan-American Race Walking 20K

The anthropometric and somatotype evaluation is an essential tool in the selection and control of high-performance athletes. The aim of this study was to describe the somatotype and body composition of male elite race walkers (20 k modality), and its relationship with athletic performance. Twenty-four race walkers participated in this study. The sample was divided into two groups: the race walkers with the best performance (upper 25 percentile; n=7) and the second group (n=17) that corresponds to the rest of the participants. Weight (kg), height (cm), seven skinfolds, two diameters and five perimeters were measured. Body fat percentage (BF%) were estimated with the Yuhasz formula, and the somatotype was used applying the Heath-Carter method. The best performing athletes were taller (178.3 +/- 4.4 cm vs. 173.7 +/- 5.6 cm, p<0.05) and showed a greater ectomorphic component (p<0.05) than the rest of the participants. The somatotype of the best performance athletes was 2.2-2.8-4.1 against the 2.5-3.8-2.9 of the lowest performing athletes. The average time (hours, minute, seconds) of execution of the race in athletes of better performances was 1: 22:40, in comparison with the athletes of lower performances with 1: 32: 41 (p<0.02). The ectomorphic component and height are morphological characteristics that can determine athletic performance of race walkers. It is suggested to consider these factors in the selection of the race walkers. La evaluación antropométrica y del somatotipo es una importante herramienta en la selección y control de los atletas de alto rendimiento. El objetivo de este estudio fue describir el somatotipo y composición corporal de hombres marchistas olímpicos, modalidad 20 k, y su relación con el rendimiento atlético. Veinticuatro atletas de marcha participaron en este estudio. La muestra fue dividida en dos grupos: los marchistas de mejores rendimientos p25 superior (n=7) y el segundo grupo (n=17) que corresponde al resto de los participantes. Se registró el peso (kg), talla (cm), siete pliegues cutáneos, dos diámetros y cinco perímetros. Se estimó el porcentaje de grasa corporal (%GC) con la fórmula de Yuhasz y se describió el somatotipo utilizando el método de Heath-Carter. Se reporta una mayor altura en los atletas de mejor rendimiento (178,3±4,4 cm vs. 173,7±5,6 cm; p<0,05) y mayor componente ectomorfico (p<0,05) que el resto de los participantes. El somatotipo de los atletas de mejor rendimiento fue de 2.2-2.8-4.1 frente al 2.5-3.8-2.9 de los atletas de menor rendimiento. El tiempo promedio (hora, minuto, segundo) de ejecución de la carrera en atletas de mejores rendimientos fue de 1:22:40, en comparación con los atletas de menores rendimientos con 1:32:41 (p <0,02). El componente ectomórfico y altura serian características morfológicas que pueden determinar el rendimiento deportivo de atletas de marcha. Se sugiere considerar estos factores en la selección de los marchistas olímpicos

Establishment of a network of monitoring stations using lichens as indicators. Base for the assessment of human impact and air quality on the vegetation in the Aigüestortes i Estany de Sant Maurici National Park

Com a primera part de la monitorització, mitjançant el líquens com a indicadors, del Parc Nacional d’Aigüestortes i Estany de Sant Maurici, hem seleccionat, marcat i caracteritzat 20 estacions de seguiment. Les estacions han quedat establertes en els següents ambients: rouredes amb boix, bosc caducifoli mixt, fagedes, fagedes amb avet, pinedes de pi roig, avetosa, avetosa amb neret, pinedes de pi negre amb neret o amb ginebró, i roquissars, tant en roques carbonatades com àcides. Donem, com a exemple de l’estudi d’aquestes estacions, el cas d’una estació establerta a la comunita d’avetosa amb neret. El seguiment de l’evolució, en el temps, de les diferents comunitats, ens haurà de permetre correlacionar les modificacions observades en les estacions amb els canvis produïts en la qualitat de l’aire o a causa de l’impacte humà.As a first part of the monitoring project, using lichens as indicators of the Aigüestortes and Estany de Sant Maurici National Park, 20 monitoring stations have been selected, marked and characterised. The stations were included in the following plant communities: Buxo-Quercetum pubescentis, Helleboro-Fagetum, Luzulo-Fagetum, Hylocomio- Pinetum catalaunicae, Goodyero-Abietetum, Saxifrago-Rhododendretum abietetosum albae, Saxifrago-Rhododendretum pinetosum uncinatae and Arctostaphylo-Pinetum uncinatae, and in rocky places on carbonated and siliceous rocks. As an example of study of these stations, we give the information of one station located in Saxifrago- Rhododendretum abietetosum albae. The changes of the different communities through time allow us to correlate these observed modifications with changes in the air quality or due to the human impact