Quantifying the influence of sea ice on ocean microseism using observations from the Bering Sea, Alaska

Microseism is potentially affected by all processes that alter ocean wave heights. Because strong sea ice prevents large ocean waves from forming, sea ice can therefore significantly affect microseism amplitudes. Here we show that this link between sea ice and microseism is not only a robust one but can be quantified. In particular, we show that 75–90% of the variability in microseism power in the Bering Sea can be predicted using a fairly crude model of microseism damping by sea ice. The success of this simple parameterization suggests that an even stronger link can be established between the mechanical strength of sea ice and microseism power, and that microseism can eventually be used to monitor the strength of sea ice, a quantity that is not as easily observed through other means

The electrochemical generation of useful chemical species from lunar materials

Electrochemical cells have been fabricated for the simultaneous generation of oxygen and lithium from a Li2O containing molten salt (Li2O-LiCl-LiF). The cell utilizes an oxygen vacancy conducting solid electrolyte, yttria-stabilized zirconia (YSZ), to effect separation between oxygen evolving and lithium reduction half-cell reactions. The cell, which operates at 700 to 850 C, possesses rapid electrode kinetics at the lithium-alloy electrode with exchange current density (i sub o) values being greater than 60mA sq cm. When used in the electrolytic mode, lithium produced at the negative electrode would be continuously removed from the cell for later use (under lunar conditions) as an easily storable reducing agent (compared to H2) for the chemical refining of lunar ores. Because of the high reversibility of this electrochemical system, it has also formed tha basis for the lithium oxygen secondary battery system which possesses the highest theoretical energy density yet investigated

The electrochemical generation of useful chemical species from lunar materials

The current status of work on an electrochemical technology for the simultaneous generation of oxygen and lithium from a Li2O containing molten salt (Li2O-LiCl-LiF) is discussed. The electrochemical cell utilizes an oxygen vacancy conducting solid electrolyte, yttria-stabilized zirconia, to effect separation between the oxygen evolving and lithium reduction half-cell reactions. The cell, which operates at 700 to 800 C, possesses rapid electrode kinetics at the lithium-alloy electrode with exchange current density values being greater than 60 mA/sq cm, showing high reversibility for this reaction. When used in the electrolytic mode, lithium produced at the negative electrode would be continuously removed from the cell for later use (under lunar conditions) as an easily storable reducting agent (compared to H2) for the chemical refining of lunar ores via the general reaction: 2Li + MO yields Li2O + M where MO represents a lunar ore. Emphasis to this time has been on the simulated lunar ore ilmenite (FeTiO3), which we have found becomes chemically reduced by Li at 432 C. Furthermore, both Fe2O3 and TiO2 have been reduced by Li to give the corresponding metal. This electrochemical approach provides a convenient route for producing metals under lunar conditions and oxygen for the continuous maintenance of human habitats on the Moon's surface. Because of the high reversibility of this electrochemical system, it has also formed the basis for the lithium-oxygen secondary battery. This secondary lithium-oxygen battery system posses the highest theoretical energy density yet investigated

Earthquake ground motion amplification for surface waves

Surface waves from earthquakes are known to cause strong damage, especially for larger structures such as skyscrapers and bridges. However, common practice in characterizing seismic hazard at a specific site considers the effect of near-surface geology on only vertically propagating body waves. Here we show that surface waves have a unique and different frequency-dependent response to known geologic structure and that this amplification can be analytically calculated in a manner similar to current hazard practices. Applying this framework to amplification in the Los Angeles Basin, we find that peak ground accelerations for certain large regional earthquakes are underpredicted if surface waves are not properly accounted for and that the frequency of strongest ground motion amplification can be significantly different. Including surface-wave amplification in hazards calculations is therefore essential for accurate predictions of strong ground motion for future San Andreas Fault ruptures

Jenga: Harnessing Heterogeneous Memories through Reconfigurable Cache Hierarchies

Conventional memory systems are organized as a rigid hierarchy, with multiple levels of progressively larger and slower memories. Hierarchy allows a simple, fixed design to benefit a wide range of applications, because working sets settle at the smallest (and fastest) level they fit in. However, rigid hierarchies also cause significant overheads, because each level adds latency and energy even when it does not capture the working set. In emerging systems with heterogeneous memory technologies such as stacked DRAM, these overheads often limit performance and efficiency. We propose Jenga, a reconfigurable cache hierarchy that avoids these pathologies and approaches the performance of a hierarchy optimized for each application. Jenga monitors application behavior and dynamically builds virtual cache hierarchies out of heterogeneous, distributed cache banks. Jenga uses simple hardware support and a novel software runtime to configure virtual cache hierarchies. On a 36-core CMP with a 1 GB stacked-DRAM cache, Jenga outperforms a combination of state-of-the-art techniques by 10% on average and by up to 36%, and does so while saving energy, improving system-wide energy-delay product by 29% on average and by up to 96%

Explaining Extreme Ground Motion in Osaka Basin during the 2011 Tohoku Earthquake

Despite being 770 km away from the epicenter, observed ground motions due to the Tohoku earthquake in the Osaka Basin were unexpectedly large, with an amplification of more than a factor of 20 compared to immediately outside the basin, and including 2.7 m peak-to-peak roof displacements at one high-rise building. The local ground motions exceeded expectations based on standard computations of site response by a factor of 3, predicted frequencies of peak acceleration were off by at least 50%, and such discrepancies have not yet been explained quantitatively. Here we show that utilizing semianalytic theory for surface-wave amplification, we are able to accurately predict both the amplitudes and frequencies of large ground amplification in the Osaka Basin using only knowledge of the local one-dimensional structure. Comparison between this simple prediction and observed amplification was not expected to be so favorable and suggests that simple one-dimensional surface-wave site amplification factors can be useful in the absence of full three-dimensional wave propagation simulations. Such surface-wave amplification factors can be included in addition to the standard measures of site-specific site amplification and should help explain strong ground motion variability in future large earthquakes that shake Osaka Basin and elsewhere in the world

Scaling Distributed Cache Hierarchies through Computation and Data Co-Scheduling

Cache hierarchies are increasingly non-uniform, so for systems to scale efficiently, data must be close to the threads that use it. Moreover, cache capacity is limited and contended among threads, introducing complex capacity/latency tradeoffs. Prior NUCA schemes have focused on managing data to reduce access latency, but have ignored thread placement; and applying prior NUMA thread placement schemes to NUCA is inefficient, as capacity, not bandwidth, is the main constraint. We present CDCS, a technique to jointly place threads and data in multicores with distributed shared caches. We develop novel monitoring hardware that enables fine-grained space allocation on large caches, and data movement support to allow frequent full-chip reconfigurations. On a 64-core system, CDCS outperforms an S-NUCA LLC by 46% on average (up to 76%) in weighted speedup and saves 36% of system energy. CDCS also outperforms state-of-the-art NUCA schemes under different thread scheduling policies.National Science Foundation (U.S.) (Grant CCF-1318384)Massachusetts Institute of Technology. Department of Electrical Engineering and Computer Science (Jacobs Presidential Fellowship)United States. Defense Advanced Research Projects Agency (PERFECT Contract HR0011-13-2-0005