Mechanisms of fragmentation of Al-W granular composites under dynamic loading

Numerical simulations of Aluminum (Al) and Tungsten (W) granular composite rings under various dynamic loading conditions caused by explosive loading were examined. Three competing mechanisms of fragmentation were observed: a continuum level mechanism generating large macrocracks described by the Grady-Kipp fragmentation mechanism, a mesoscale mechanism generating voids and microcracks near the initially unbonded Al/W interfaces due to tensile strains, and a mesoscale jetting due to the development of large velocity gradients between the W particles and adjacent Al. These mesoscale mechanisms can be used to tailor the size of the fragments by selecting an appropriate initial mesostructure for a given loading condition.Comment: 10 pages, 3 figures, submitted to AP

Ancient Cosmic Dust from Triassic Halite

We describe the discovery of fossil micrometeorites in ancient Triassic rock salt; the first to be found in salt and the oldest complete micrometeorites found to date. We present an estimated flux rate of micrometeorites to Earth at this time

Cryptoendolith colonization of diverse substrates (1): cultivation and characterization

We are investigating whether cryptoendolithic microorganisms are able to colonize diverse substrates through biogenic weathering. This first part of the study involves the cultivation and characterization of microbial consortia from Antarctic sandstone habitats

UV-Vis spectroscopy of stardust

NASA's Stardust mission flew through the coma of comet Wild 2 in January 2004, capturing dust grains as it did so. The grains were returned safely to Earth in January 2006, and are in the process of being distributed to investigators. As members of the Spectroscopy Preliminary Examination Team, we are preparing to analyse Stardust grains. Our contribution is to measure the spectrum of the grains between 200 nm (in the near ultraviolet) and 800 nm (near infrared). The purpose of the measurement is to provide an additional technique for characterizing the grains, one that is complementary to other spectroscopic techniques and one that produces results that can be matched directly with spectra acquired remotely (with telescope or spacecraft instrumentation). As part of the preparation for analysis of Stardust materials, we are producing a database of spectra from appropriate minerals, and are honing the technique through analysis of primitive meteorites

CODA: visual studies now

The intention of this critical project is to foster a conversation that foregrounds, and builds from, the complexities of interdisciplinary collaboration, its strengths and weaknesses, contributions and gaps. Our aim is to provide an international forum for the development of visual research; provoke more acceptance, understanding and discussion of a wide range of methods, approaches, theories and paradigms that constitute image-based research; reduce the disparity in emphasis between visual and written studies in scholarly research; and bridge the gap between empirically grounded visually- based research across the spectrum of the social sciences, arts, and humanities

LkHα\alpha 330: Evidence for dust clearing through resolved submillimeter imaging

Mid-infrared spectrophotometric observations have revealed a small sub-class of circumstellar disks with spectral energy distributions (SEDs) suggestive of large inner gaps with low dust content. However, such data provide only an indirect and model dependent method of finding central holes. We present here the direct characterization of a 40 AU radius inner gap in the disk around LkHa 330 through 340 GHz (880 micron) dust continuum imaging with the Submillimeter Array (SMA). This large gap is fully resolved by the SMA observations and mostly empty of dust with less than 1.3 x 10^-6 M_solar of solid particles inside of 40 AU. Gas (as traced by accretion markers and CO M-band emission) is still present in the inner disk and the outer edge of the gap rises steeply -- features in better agreement with the underlying cause being gravitational perturbation than a more gradual process such as grain growth. Importantly, the good agreement of the spatially resolved data and spectrophometry-based model lends confidence to current interpretations of SEDs with significant dust emission deficits as arising from disks with inner gaps or holes. Further SED-based searches can therefore be expected to yield numerous additional candidates that can be examined at high spatial resolution.Comment: 11 pages, 3 figures, accepted to ApJ

Cholinergic Modulation of Locomotion and Striatal Dopamine Release Is Mediated by α6α4* Nicotinic Acetylcholine Receptors

Dopamine (DA) release in striatum is governed by firing rates of midbrain DA neurons, striatal cholinergic tone, and nicotinic ACh receptors (nAChRs) on DA presynaptic terminals. DA neurons selectively express α6* nAChRs, which show high ACh and nicotine sensitivity. To help identify nAChR subtypes that control DA transmission, we studied transgenic mice expressing hypersensitive α6^(L9’S*) receptors. α6^(L9’S) mice are hyperactive, travel greater distance, exhibit increased ambulatory behaviors such as walking, turning, and rearing, and show decreased pausing, hanging, drinking, and grooming. These effects were mediated by α6 α4* pentamers, as α6^(L9’S) mice lacking α4 subunits displayed essentially normal behavior. In α6^(L9’S) mice, receptor numbers are normal, but loss of α4 subunits leads to fewer and less sensitive α6* receptors. Gain-of-function nicotine-stimulated DA release from striatal synaptosomes requires α4 subunits, implicating α6α4β2* nAChRs in α6^(L9’S) mouse behaviors. In brain slices, we applied electrochemical measurements to study control of DA release by α6^(L9’S) nAChRs. Burst stimulation of DA fibers elicited increased DA release relative to single action potentials selectively in α6^(L9’S), but not WT or α4KO/ α6^(L9’S), mice. Thus, increased nAChR activity, like decreased activity, leads to enhanced extracellular DA release during phasic firing. Bursts may directly enhance DA release from α6^(L9’S) presynaptic terminals, as there was no difference in striatal DA receptor numbers or DA transporter levels or function in vitro. These results implicate α6α4β2* nAChRs in cholinergic control of DA transmission, and strongly suggest that these receptors are candidate drug targets for disorders involving the DA system

Environmental Barrier Coating (EBC) Durability Modeling; An Overview and Preliminary Analysis

A study outlining a fracture mechanics based model that is being developed to investigate crack growth and spallation of environmental barrier coating (EBC) under thermal cycling conditions is presented. A description of the current plan and a model to estimate thermal residual stresses in the coating and preliminary fracture mechanics concepts for studying crack growth in the coating are also discussed. A road map for modeling life and durability of the EBC and the results of FEA model(s) developed for predicting thermal residual stresses and the cracking behavior of the coating are generated and described. Further initial assessment and preliminary results showed that developing a comprehensive EBC life prediction model incorporating EBC cracking, degradation and spalling mechanism under stress and temperature gradients typically seen in turbine components is difficult. This is basically due to mismatch in thermal expansion difference between sub-layers of EBC as well as between EBC and substrate, diffusion of moisture and oxygen though the coating, and densification of the coating during operating conditions as well as due to foreign object damage, the EBC can also crack and spall from the substrate causing oxidation and recession and reducing the design life of the EBC coated substrate

Tree-based Coarsening and Partitioning of Complex Networks

Many applications produce massive complex networks whose analysis would benefit from parallel processing. Parallel algorithms, in turn, often require a suitable network partition. For solving optimization tasks such as graph partitioning on large networks, multilevel methods are preferred in practice. Yet, complex networks pose challenges to established multilevel algorithms, in particular to their coarsening phase. One way to specify a (recursive) coarsening of a graph is to rate its edges and then contract the edges as prioritized by the rating. In this paper we (i) define weights for the edges of a network that express the edges' importance for connectivity, (ii) compute a minimum weight spanning tree $T^m$ with respect to these weights, and (iii) rate the network edges based on the conductance values of $T^m$'s fundamental cuts. To this end, we also (iv) develop the first optimal linear-time algorithm to compute the conductance values of \emph{all} fundamental cuts of a given spanning tree. We integrate the new edge rating into a leading multilevel graph partitioner and equip the latter with a new greedy postprocessing for optimizing the maximum communication volume (MCV). Experiments on bipartitioning frequently used benchmark networks show that the postprocessing already reduces MCV by 11.3%. Our new edge rating further reduces MCV by 10.3% compared to the previously best rating with the postprocessing in place for both ratings. In total, with a modest increase in running time, our new approach reduces the MCV of complex network partitions by 20.4%