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Evidence from the northwestern Venezuelan Andes for extraterrestrial impact: The black mat enigma
Mahaney, W.C.,Kalm, V.,Krinsley, D.H.,Tricart, P.,Schwartz, S.,Dohm, J.,Kim, K.J.,Kapran, B.,Milner, M.W.,Beukens, R.,Boccia, S.,Hancock, R.G.V.,Hart, K.M.,Kelleher, B. Elsevier 2010 Geomorphology Vol.116 No.1
<P><B>Abstract</B></P><P>A carbon-rich black layer encrusted on a sandy pebbly bed of outwash in the northern Venezuelan Andes, previously considered the result of an alpine grass fire, is now recognized as a ‘black mat’ candidate correlative with Clovis Age sites in North America, falling within the range of ‘black mat’ dated sites (~12.9ka cal BP). As such, the bed at site MUM7B, which dates to <11.8ka <SUP>14</SUP>C years BP (raw dates) and appears to be contemporaneous with the Younger Dryas (YD) cooling event, marks a possibly much more extensive occurrence than previously identified. No fossils (megafauna) or tool assemblages were observed at this newly identified candidate site (3800a.m.s.l.), as in the case of the North American sites. Here, evidence is presented for an extraterrestrial impact event at ~12.9ka. The impact-related Andean bed, located ~20cm above 13.7–13.3ka cal BP alluvial and glaciolacustrine deposits, falls within the sediment characteristics and age range of ‘black mat’ dated sites (~12.9ka cal BP) in North America. Site sediment characteristics include: carbon, glassy spherules, magnetic microspherules, carbon mat ‘welded’ onto coarse granular material, occasional presence of platinum group metals (Rh and Ru), planar deformation features (pdfs) in fine silt-size fragmental grains of quartz, as well as orthoclase, and monazite (with an abundance of Rare Earth Elements—REEs). If the candidate site is ‘black mat’, correlative with the ‘black mat’ sites of North America, such an extensive occurrence may support the hypothesized airburst/impact over the Laurentide Glacier, which led to a reversal of Allerød warming and the onset of YD cooling and readvance of glaciers. While this finding does not confirm such, it merits further investigation, which includes the reconnaissance for additional sites in South America. Furthermore, if confirmed, such an extensive occurrence may corroborate an impact origin.</P>
Localised nanoscale resistive switching in GaP thin films with low power consumption
Kurnia, F.,Liu, C.,Liu, G.,Vasudevan, R.,Yang, S.,Kalinin, S.,Valanoor, N.,Hart, J. Royal Society of Chemistry 2017 Journal of materials chemistry. C, Materials for o Vol.5 No.8
<P>Nanoscale localisation of the electroforming-free resistive switching (RS) behaviour in polycrystalline GaP thin films has been observed for the first time. A combination of conductive atomic force microscopy and first-order reversal curve current-voltage measurements indicated that the grain boundaries are the preferred sites for the formation of the conductive switching filaments. It is proposed, based on TEM and XPS results, that local electrochemical migration of Ga ions along the grain boundaries plays a critical role in the switching mechanism. In the low-resistance (ON) state, the conduction mechanism was found to be the space-charge-limited current mechanism, while the high-resistance (OFF) state was governed by the Frenkel-Poole mechanism. A high OFF/ON resistance ratio (similar to 10(4)) and lower power consumption than current RS devices, in addition to the easy integration of GaP with silicon substrates, make these GaP films promising for future applications in future non-volatile resistive random access memory (RRAM).</P>