Michigan Technological University

About: Michigan Technological University is a education organization based out in Houghton, Michigan, United States. It is known for research contribution in the topics: Population & Volcano. The organization has 8023 authors who have published 17422 publications receiving 481780 citations. The organization is also known as: MTU & Michigan Tech.

Integrating retrievals of volcanic cloud characteristics from satellite remote sensors: a summary

Abstract: Volcanic eruptions are events that rapidly and suddenly disperse gases and fine particles into the atmosphere, a process most conveniently studied from the synoptic satellite perspective, where remote sensing offers a practical tool for spatial and temporal measurements. Meteorological satellites offer approximately 20 years of archived data, which can be analysed for measurements of masses of SO 2 and fine volcanic ash in spatial two–dimensional arrays and integrated with other meteorological data. The satellite data offer a tool to study volcano–atmosphere interactions in a quantitative way. They provide information of unique value for understanding the fate and transport of fine silicates with significant health hazards and for addressing the problem of volcanic cloud hazards to jet aircraft. Studies of satellite data have demonstrated the following. (1) Volcanic clouds from convergent plate boundary volcanoes contain large and variable excesses of SO 2 . (2) The second day of atmospheric residence for volcanic clouds has significantly higher SO 2 than the first, suggesting that early volcanic H 2 S may be converting to SO 2 . (3) Complete conversion of SO 2 to sulphate in the stratosphere occurs at an efolding rate of approximately 120 days. SO 2 loss from stratospheric volcanic clouds occurs at an e–folding rate of approximately 35 days, and the SO 2 loss rate for volcanic clouds which only barely reach the stratosphere is rapid (efolding only a few days). The latter limits the stratospheric aerosol build–up from smaller eruptions. (4) Fine volcanic ash (with diameters of less than ca .25μm) in drifting volcanic clouds retrieved after 10 h or more appear to represent a small fraction (less than 2% of the total mass) of the total mass of magma erupted, and also a small fraction (less than 20%) of the total mass of fine ash erupted. This is probably explained by the fact that the total mass is greatly reduced by aggregation processes within the volcanic cloud. (5) The amounts of fine ash decrease faster in volcanic clouds of larger eruptions, supporting the self–removal processes suggested by Pinto et al. in 1989. (6) Evidence for a strong role of ice in the fallout and aggregation of volcanic cloud ash is considerable. (7) In many cases, volcanic clouds separate into higher SO 2 –rich portions and lower ash–rich portions. The two portions follow different trajectories and the lower, ash–rich portions are affected by interactions with moist tropospheric air.

Stratigraphy of the Toba Tuffs and the evolution of the Toba Caldera Complex, Sumatra, Indonesia

Abstract: During the past 1.2 m.y., a magma chamber of batholithic proportions has developed under the 100 by 30 km Toba Caldera Complex. Four separate eruptions have occurred from vents within the present collapse structure, which formed from eruption of the 2800 km3 Youngest Toba Tuff (YTT) at 74 ka. Eruption of the three older Toba Tuffs alternated from calderas situated in northern and southern portions of the present caldera. The northern caldera apparently developed upon a large andesitic stratovolcano. The calderas associated with the three older tuffs are obscured by caldera collapse and resurgence resulting from eruption of the YTT. Samosir Island and the Uluan Block are two sides of a single resurgent dome that has resurged since eruption of the YTT. Samosir Island is composed of thick YTT caldera fill, whereas the Uluan Block consists mainly of the Oldest Toba Tuff (OTT). In the past 74000 years lava domes have been extruded on Samosir Island and along the caldera's western ring fracture. This part of the ring fracture is the site of the only current activity at Toba: updoming and fumarolic activity. The Toba eruptions document the growth of the laterally continuous magma body which eventually erupted the YTT. Repose periods between the four Toba Tuffs range between 0.34 and 0.43 m.y. and give insights into pluton emplacement and magmatic evolution at Toba.

A Burst Scheduling Access Reordering Mechanism

Abstract: Utilizing the nonuniform latencies of SDRAM devices, access reordering mechanisms alter the sequence of main memory access streams to reduce the observed access latency. Using a revised M5 simulator with an accurate SDRAM module, the burst scheduling access reordering mechanism is proposed and compared to conventional in order memory scheduling as well as existing academic and industrial access reordering mechanisms. With burst scheduling, memory accesses to the same rows of the same banks are clustered into bursts to maximize bus utilization of the SDRAM device. Subject to a static threshold, memory reads are allowed to preempt ongoing writes for reduced read latency, while qualified writes are piggybacked at the end of bursts to exploit row locality in writes and prevent write queue saturation. Performance improvements contributed by read preemption and write piggybacking are identified. Simulation results show that burst scheduling reduces the average execution time of selected SPEC CPU2000 benchmarks by 21% over conventional bank in order memory scheduling. Burst scheduling also outperforms Intel's patented out of order memory scheduling and the row hit access reordering mechanism by 11% and 6% respectively

Flow-induced calcium oscillations in rat osteoblasts are age, loading frequency, and shear stress dependent.

Abstract: Bone adaptation to mechanical loading is dependent on age and the frequency and magnitude of loading. It is believed that load-induced fluid flow in the porous spaces of bone is an important signal that influences bone cell metabolism and bone adaptation. We used fluid flow-induced shear stress as a mechanical stimulus to study intracellular calcium (Ca) signaling in rat osteoblastic cells (ROB) isolated from young, mature, and old animals. Fluid flow produced higher magnitude and more abundant [Ca(2+)](i) oscillations than spontaneous oscillations, suggesting that flow-induced Ca signaling encodes a different cellular message than spontaneous oscillations. ROB from old rats showed less basal [Ca(2+)](i) activity and were less responsive to fluid flow. Cells were more responsive to 0.2 Hz than to 1 or 2 Hz and to 2 Pa than to 1 Pa. These data suggest that the frequency and magnitude of mechanical loading may be encoded by the percentage of cells displaying [Ca(2+)](i) oscillations but that the ability to transduce this information may be altered with age.