Photonic crystal thin films of GaAs prepared by atomic layer deposition

Photonic crystal thin films were fabricated via the self-assembly of a lattice of silica spheres on silicon (100) substrates. Progressive infilling of the air spaces within the structure with GaAs was achieved using trimethylgallium and arsine under atomic-layer-deposition conditions. Samples with the highest levels of GaAs infill were subsequently inverted using selective etching. Reflectance spectra are interpreted via the Bragg expression and calculated photonic band structure diagrams. For GaAs infilled and inverted samples, the relative positions of the first and second order Bragg reflections are strongly influenced by the wavelength dependent refractive index

Topography and Tilt at Volcanoes

For optimal monitoring of the deformation of a volcano, instrumentation should be deployed at the location most sensitive to changes at the suspected deformation source. The topographic effect on tilt depends strongly on the orientation of the deformation field relative to the surface on which the instrument is deployed. This fact has long been understood and corrected for in tilt measurements related to body tides and referred to as “cavity” or “topographic effects” (Harrison, 1976). Despite this, and whilst topography at volcanoes is often significant, until now the topographic effect on tilt at volcanoes has not been systematically explored. Here, we investigate the topographic effect on tilt produced by either the pressurization of a reservoir or conduit, or shear stress as magma ascends through a conduit, using 2D axisymmetric and 3D finite element deformation modeling. We show that topography alone can amplify or reduce the tilt by more than an order of magnitude, and control the orientation of the maximum tilt. Therefore, a decrease in tilt can even be caused by an increase in deformation at the source. Hence, inverting for the source stress using simple analytical models that neglect topography could potentially lead to a misinterpretation of how the volcanic system is evolving. Since topographic features can amplify the tilt signal, they can be exploited when deciding upon an installation site

Influence of Post-Welding Heat Treatment on the Corrosion Behavior of a 2050-T3 Aluminum-Copper-Lithium Alloy Friction Stir Welding Joint

The corrosion behavior of a Friction Stir Welding joint in 2050-T3 Al-Cu-Li alloy was studied in 1 M NaCl solution and the influence of T8 post-welding heat treatment on its corrosion susceptibility was analyzed. After exposure to 1 M NaCl solution, the heat affected zone (HAZ) of the weld without post-welding heat treatment was found to be the most extensively corroded zone with extended intergranular corrosion damage while, following T8 post-welding heat treatment, no intergranular corrosion was observed in the HAZ and the global corrosion behavior of the weld was significantly improved. The corrosion damage observed on the welded joints after immersion in 1 M NaCl solution was compared to that obtained after 750 h Mastmaasis Wet Bottom tests. The same corrosion damage was observed. Various stationary electrochemical tests were carried out on the global welded joint and/or each of the metallurgical zones of the welded joint to understand the corrosion damage observed. TEM observations helped in bringing meaningful elements to analyze the intrinsic electrochemical behavior of the different zones of the weld related to their microstructure. However, galvanic coupling tests showed that galvanic coupling effects between the different zones of the weld were at least partially responsible for its corrosion behavior

Rats distinguish between absence of events and lack of evidence in contingency learning.

The goal of three experiments was to study whether rats are aware of the difference between absence of events and lack of evidence. We used a Pavlovian extinction paradigm in which lights consistently signaling sucrose were suddenly paired with the absence of sucrose. The crucial manipulation involved the absent outcomes in the extinction phase. Whereas in the Cover conditions, access to the drinking receptacle was blocked by a metal plate, in the No Cover conditions, the drinking receptacle was accessible. The Test phase showed that in the Cover conditions, the measured expectancies of sucrose were clearly at a higher level than in the No Cover conditions. We compare two competing theories potentially explaining the findings. A cognitive theory interprets the observed effect as evidence that the rats were able to understand that the cover blocked informational access to the outcome information, and therefore the changed learning input did not necessarily signify a change of the underlying contingency in the world. An alternative associationist account, renewal theory, might instead explain the relative sparing of extinction in the Cover condition as a consequence of context change. We discuss the merits of both theories as accounts of our data and conclude that the cognitive explanation is in this case preferred

Combining Magma Flow and Deformation Modeling to Explain Observed Changes in Tilt

The understanding of magma ascent dynamics is essential in forecasting the scale, style and timing of volcanic eruptions. The monitoring of near-field deformation is widely used to gain insight into these dynamics, and has been linked to stress changes in the upper conduit. The ascent of magma through the conduit exerts shear stress on the conduit wall, pulling up the surrounding edifice, whilst overpressure in the upper conduit pushes the surrounding edifice outwards. How much shear stress and pressure is produced during magma ascent, and the relative contribution of each to the deformation, has until now only been explored conceptually. By combining flow and deformation modeling using COMSOL Multiphysics, we for the first time present a quantitative model that links magma ascent to deformation. We quantify how both shear stress and pressure vary spatially within a cylindrical conduit, and show that shear stress generally dominates observed changes in tilt close to the conduit. However, the relative contribution of pressure is not insignificant, and both pressure and shear stress must be considered when interpreting deformation data. We demonstrate that significant changes in tilt can be driven by changes in the driving pressure gradient or volatile content of the magma. The relative contribution of shear stress and pressure to the tilt varies considerably depending on these parameters. Our work provides insight into the range of elastic moduli that should be considered when modeling edifice-scale rock masses, and we show that even where the edifice is modeled as weak, shear stress generally dominates the near field deformation over pressurization of the conduit. While our model addresses cyclic tilt changes observed during activity at Tungurahua volcano, Ecuador, between 2013 and 2014, it is also applicable to silicic volcanoes in general

Decadal-scale onset and termination of Antarctic ice-mass loss during the last deglaciation.

Emerging ice-sheet modeling suggests once initiated, retreat of the Antarctic Ice Sheet (AIS) can continue for centuries. Unfortunately, the short observational record cannot resolve the tipping points, rate of change, and timescale of responses. Iceberg-rafted debris data from Iceberg Alley identify eight retreat phases after the Last Glacial Maximum that each destabilized the AIS within a decade, contributing to global sea-level rise for centuries to a millennium, which subsequently re-stabilized equally rapidly. This dynamic response of the AIS is supported by (i) a West Antarctic blue ice record of ice-elevation drawdown >600 m during three such retreat events related to globally recognized deglacial meltwater pulses, (ii) step-wise retreat up to 400 km across the Ross Sea shelf, (iii) independent ice sheet modeling, and (iv) tipping point analysis. Our findings are consistent with a growing body of evidence suggesting the recent acceleration of AIS mass loss may mark the beginning of a prolonged period of ice sheet retreat and substantial global sea level rise

Identificación de epítopes T citotóxicos restringidos a la molécula HLA-A2.1 en la proteína HSP70 de T. cruzi.

El análisis de la capacidad de unión a células T2 realizado con 31 péptidos correspondientes a distintas regiones dela proteína HSP70 de Trypanosoma cruzi, muestra que 14 de estos péptidos tienen una alta o media afinidad por lamolécula presentadora A2.1. Interesantemente, el presente manuscrito pone de manifiesto que la inmunización deratones transgénicos A2/Kb con la proteína recombinante HSP70 de T. cruzi induce CTLs que reconocen células EL4-A2/Kb cargadas de forma independiente con tres de los péptidos con afinidad de unión a moléculas A2. Estospéptidos presentan una homología menor del 65% con sus homólogos de la proteína HSP70 humana. Los resultadosobtenidos permiten sugerir la posibilidad de que la HSP70 de T. cruzi pueda ser usada como diana para induciractividad inmune citotóxica en humanos

Quantitative phosphoproteomic analysis of plasma membrane proteins reveals regulatory mechanisms of plant innate immune responses

Advances in proteomic techniques have allowed the large-scale identification of phosphorylation sites in complex protein samples, but new biological insight requires an understanding of their in vivo dynamics. Here, we demonstrate the use of a stable isotope-based quantitative approach for pathway discovery and structure–function studies in Arabidopsis cells treated with the bacterial elicitor flagellin. The quantitative comparison identifies individual sites on plasma membrane (PM) proteins that undergo rapid phosphorylation or dephosphorylation. The data reveal both divergent dynamics of different sites within one protein and coordinated regulation of homologous sites in related proteins, as found for the PM H+-ATPases AHA1, 2 and 3. Strongly elicitor-responsive phosphorylation sites may reflect direct regulation of protein activity. We confirm this prediction for RbohD, an NADPH oxidase that mediates the rapid production of reactive oxygen species (ROS) in response to elicitors and pathogens. Plant NADPH oxidases are structurally distinct from their mammalian homologues, and regulation of the plant enzymes is poorly understood. On RbohD, we found both unchanging and strongly induced phosphorylation sites. By complementing an RbohD mutant plant with non-phosphorylatable forms of RbohD, we show that only those sites that undergo differential regulation are required for activation of the protein. These experiments demonstrate the potential for use of quantitative phosphoproteomics to determine regulatory mechanisms at the molecular level and provide new insights into innate immune responses