Phase transformations induced by spherical indentation in ion-implanted amorphous silicon

The deformation behavior of ion-implanted (unrelaxed) and annealed ion-implanted (relaxed) amorphous silicon(a-Si) under spherical indentation at room temperature has been investigated. It has been found that the mode of deformation depends critically on both the preparation of the amorphous film and the scale of the mechanical deformation.Ex situmeasurements, such as Raman microspectroscopy and cross-sectional transmission electron microscopy, as well as in situ electrical measurements reveal the occurrence of phase transformations in all relaxed a-Si films. The preferred deformation mode of unrelaxed a-Si is plastic flow, only under certain high load conditions can this state of a-Si be forced to transform. In situ electrical measurements have revealed more detail of the transformation process during both loading and unloading. We have used ELASTICA simulations to obtain estimates of the depth of the metallic phase as a function of load, and good agreement is found with the experiment. On unloading, a clear change in electrical conductivity is observed to correlate with a “pop-out” event on load versus penetration curves

Effect of oxygen concentration on nanoindentation-induced phase transformations in ion-implanted amorphous silicon

The effect of the local oxygen concentration in ion-implanted amorphous Si (a-Si) on nanoindentation-inducedphase transformations has been investigated. Implantation of oxygen into the a-Sifilms has been used to controllably introduce an approximately constant concentration of oxygen, ranging from ∼10¹⁸ to ∼10²¹ cm⁻³, over the depth range of the phase transformed zones. Nanoindentation was performed under conditions that ensure a phase transformed zone composed completely of Si-III/XII in the nominally oxygen-free a-Si. The effect of the local oxygen concentration has been investigated by analysis of the unloading curves, Raman microspectroscopy, and cross-sectional transmission electron microscopy (XTEM). The formation of Si-III/XII is suppressed with increasing oxygen concentration, favoring a greater volume of a-Si within the zones. The Raman microspectroscopy and XTEM verify that the volume of Si-III/XII decreases with increasing O concentration. With the smaller volumes of Si-III/XII, the pop-out normally observed on load versus penetration depth curves during unloading decreases in magnitude, becoming more kinklike and is barely discernable at high concentrations of oxygen. The probability of forming any high pressure phases is reduced from 1 to ∼0.1 for a concentration of 10²¹ cm⁻³. We suggest that the bonding of O with Si reduces the formation of Si-III/XII during unloading through a similar mechanism to that of oxygen-retarded solid phase crystallization of a-Si.This project is funded by the Australian Research Council and WRiota Pty Ltd

The nonequilibrium Ehrenfest gas: a chaotic model with flat obstacles?

It is known that the non-equilibrium version of the Lorentz gas (a billiard with dispersing obstacles, electric field and Gaussian thermostat) is hyperbolic if the field is small. Differently the hyperbolicity of the non-equilibrium Ehrenfest gas constitutes an open problem, since its obstacles are rhombi and the techniques so far developed rely on the dispersing nature of the obstacles. We have developed analytical and numerical investigations which support the idea that this model of transport of matter has both chaotic (positive Lyapunov exponent) and non-chaotic steady states with a quite peculiar sensitive dependence on the field and on the geometry, not observed before. The associated transport behaviour is correspondingly highly irregular, with features whose understanding is of both theoretical and technological interest

Nitrate uptake across biomes and the influence of elemental stoichiometry: A new look at LINX II

Considering recent increases in anthropogenic N loading, it is essential to identify the controls on N removal and retention in aquatic ecosystems because the fate of N has consequences for water quality in streams and downstream ecosystems. Biological uptake of nitrate (NO3−) is a major pathway by which N is removed from these ecosystems. Here we used data from the second Lotic Intersite Nitrogen eXperiment (LINX II) in a multivariate analysis to identify the primary drivers of variation in NO3− uptake velocity among biomes. Across 69 study watersheds in North America, dissolved organic carbon:NO3− ratios and photosynthetically active radiation were identified as the two most important predictor variables in explaining NO3− uptake velocity. However, within a specific biome the predictor variables of NO3− uptake velocity varied and included various physical, chemical, and biological attributes. Our analysis demonstrates the broad control of elemental stoichiometry on NO3− uptake velocity as well as the importance of biome-specific predictors. Understanding this spatial variation has important implications for biome-specific watershed management and the downstream export of NO3−, as well as for development of spatially explicit global models that describe N dynamics in streams and rivers

The citizen scientific method: tapping a human natural resource in ecosystem restoration

Citizen science forms a nexus point between research and education, between social outreach and project implementation, and between local knowledge (traditional ecological knowledge) and scientific knowledge. For this reason, citizen science can be a valuable tool to integrate the many different players in ecosystem restoration projects and help projects succeed. Citizen science can increase civic engagement in ecosystem restoration, fill in data gaps, and help make adaptive ecosystem management a real community process. However, significant challenges often impede the ability of citizen science projects to reach their full potential. Here, we discuss trends and insights gained through examining three citizen science case studies on Vashon Island, WA where citizen scientists monitor watershed and shoreline restoration (Salmonwatchers, Vashon Stream Bugs, BeachNET bulkhead removal monitoring). Some challenges found include: long-term sustainability, quality of volunteer training, data management, scientific credibility, and communicating project effectiveness to resource managers, funding organizations, and the public. Preliminary findings indicate four main factors crucial to success: strong local leadership and organization of volunteers; common vision and ambitious goals shared between volunteers, resource managers, and scientists; involvement of resource managers and scientists in the creation of citizen science projects and in the volunteer training process; and the use of multiple creative forums (like science pub talks, school-based TED talks, citizen stewardship committees) that promote communication between volunteers, resource managers, scientists, and the community. We describe some “citizen scientific methods” or tools that put the above factors for success into play

Students can sort stream bugs and change watershed management: a case study from Shinglemill Creek, Vashon Island

Building on 7 previous years of data collected by King County and available on the Puget Sound Stream Benthos website, Vashon Nature Center LLC, worked with King County Groundwater Protection Committee, and local middle and high school students to solve the mystery: why does Shinglemill Creek have low B-IBI scores? Testing the hypothesis that erosion may be affecting stream scores, scientists from VNC took aquatic invertebrate samples in two tributaries of Shinglemill Creek—one tributary with high erosion and landslide activity and one with very little erosion. With the help of 6 expert scientists, over 100 students sorted samples to order, calculated a rough B-IBI score, and explored the samples for differences in the invertebrate communities. There were some signs of impacts due to erosion. However, surprisingly, students found a large difference in mayfly richness and composition between the two tributaries leading to the discovery that one tributary drained ¼ of downtown Vashon (including a parking lot popular for student held car washes) and that low mayfly richness could indicate impact from heavy metal run-off. Students presented their findings to the KCGWPC and instigated a cascade of management discussions and actions the first of which is purchasing car wash kits to filter water before it is released to Shinglemill Creek. With the right level of support, students thrive when presented with real life science problems and can make a difference in watershed management

Capacity Bounded Grammars and Petri Nets

A capacity bounded grammar is a grammar whose derivations are restricted by assigning a bound to the number of every nonterminal symbol in the sentential forms. In the paper the generative power and closure properties of capacity bounded grammars and their Petri net controlled counterparts are investigated

Charge Orbits of Extremal Black Holes in Five Dimensional Supergravity

We derive the U-duality charge orbits, as well as the related moduli spaces, of "large" and "small" extremal black holes in non-maximal ungauged Maxwell-Einstein supergravities with symmetric scalar manifolds in d=5 space-time dimensions. The stabilizer groups of the various classes of orbits are obtained by determining and solving suitable U-invariant sets of constraints, both in "bare" and "dressed" charges bases, with various methods. After a general treatment of attractors in real special geometry (also considering non-symmetric cases), the N=2 "magic" theories, as well as the N=2 Jordan symmetric sequence, are analyzed in detail. Finally, the half-maximal (N=4) matter-coupled supergravity is also studied in this context.Comment: 1+63 pages, 6 Table

Habitat structure and alarm call dialects in Gunnison\u27s prairie dog (Cynomys gunnisoni)

We examined the relationship between habitat structure and alarm call characteristics in six colonies of Gunnison’s prairie dogs (Cynomys gunnisoni) near Flagstaff, Arizona, before and after a mid-summer vegetation change. We found significant differences in alarm call characteristics between colonies, confirming the existence of alarm call dialects. Differences in frequency components but not temporal components of calls were associated with differences in habitat structure. Playback experiments revealed that differences in alarm call structure affected acoustic transmission of calls through the local habitat. Thus, we identify habitat structure as one factor that may contribute to alarm call differences between colonies of Gunnison’s prairie dogs. Relationships between call characteristics and habitat structure changed over seasons. Playback experiments suggested that this changing relationship could reflect a change in the purpose of the alarm call between early and late summer. Some components of alarm calls seem tailored for attenuation over short distances in the early summer but for long-distance transmission at summer’s end. These differences might arise because pups stay close to their natal burrows in the early summer and disperse throughout a colony in late summer. Alternatively, these differences in alarm call transmission between seasons could be caused by the increase in vegetation in the mid-summer. At the end of the summer prairie dogs could be more dependent on long-distance antipredator calls to offset the loss of visibility caused by the increase in vegetation in the late summe