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.

Temporal trends in lava dome extrusion at Santiaguito 1922–2000

Abstract: We present a means of extracting lava dome extrusion rates from data provided by the Thematic Mapper and Enhanced Thematic Mapper Plus instruments flown on the Landsat satellites Extrusion rates derived from the Landsat data for Santiaguito dome complex (Guatemala) during November 1987 and January 2000 of 072±008 and 048±009 m3 s–1 compare favorably with ground-based estimates of 063±028 and 048±017 m3 s–1 A satellite-data-derived set of 18 extrusion rate estimates between 1987 and 2000, along with ground-based volume estimates prior to 1987, allow us to infer volumes of magma erupted since 1922 These data reveal cyclic extrusion at Santiaguito Each cycle begins with a 3–6-year-long phase of high extrusion rate (05–21 m3 s–1), followed by a longer (3–11 years) phase of low extrusion rate (≤02 m3 s–1) The 8th cycle began in 1996 and was still in its high extrusion rate phase during January 2000 With time, however, the durations of the low extrusion rate phases have increased, peak extrusion and time-averaged extrusion rates for each cycle have decreased, and the difference between extrusion rates during the high and low extrusion rate phases of each cycle has decreased These trends may be the result of depressurization and exhaustion of the source In this case, the current eruption may be expected to end around 2020 Alternatively, Santiaguito may be entering a period of persistent activity maintained by a stable magma supply In this case, we may expect extrusion to become less cyclic and to stabilize at 02–04 m3 s–1 However, a 2 wt% decrease in SiO2 content of erupted products since 1970 appears to be consistent with chamber exhaustion, as well as an increase in block lava flow lengths during 1970–2000

Hydrometeor-enhanced tephra sedimentation: Constraints from the 18 May 1980 eruption of Mount St. Helens

Abstract: [1] Uncertainty remains on the origin of distal mass deposition maxima observed in many recent tephra fall deposits. In this study the link between ash aggregation and the formation of distal mass deposition maxima is investigated through reanalysis of tephra fallout from the Mount St. Helens 18 May 1980 (MSH80) eruption. In addition, we collate all the data needed to model distal ash sedimentation from the MSH80 eruption cloud. Four particle size subpopulations were present in distal fallout with modes at 2.2 Φ, 4.2 Φ, 5.9 Φ, and 8.3 Φ. Settling rates of the coarsest subpopulation closely matched predicted single-particle terminal fall velocities. Sedimentation of particles <100 μm was greatly enhanced, predominantly through aggregation of a particle subpopulation with modal diameter 5.9 ± 0.2 Φ (19 ± 3 μm). Mammatus on the MSH80 cloud provided a mechanism to transport very fine ash particles, with predicted atmospheric lifetimes of days to weeks, from the upper troposphere to the surface in a matter of hours. In this mechanism, ash particles initiate ice hydrometeor formation high in the troposphere. Subsequently, the volcanic cloud rapidly subsides as mammatus develop from increased particle loading and cloud base sublimation. Rapid fallout occurs as the cloud passes through the melting level in a process analogous to snowflake aggregation. Aggregates sediment en masse and form the distal mass deposition maxima observed in many recent volcanic ash fall deposits. This work provides a data resource that will facilitate tephra sedimentation modeling and allow model intercomparisons.

An All-DC Offshore Wind Farm With Series-Connected Turbines: An Alternative to the Classical Parallel AC Model?

Abstract: In this paper, the concept of an all-dc wind park with series-connected turbines is investigated as an alternative to the classical ac parallel or radial wind park. This paper presents a literature overview of all-dc wind park concepts with series connection. A three-phase conversion system with permanent magnet machine, ac-ac converter, high-frequency transformer, and diode bridge rectifier is suggested in this paper for the series connection of dc turbines. The dc series park with the suggested conversion system is compared in terms of losses, cost, and reliability to the state-of-the-art park configuration which is the ac radial park with HVDC transmission. It is found that the dc series park becomes comparable with the ac radial design for high ratings of the dc turbines. Furthermore, the comparison shows that emphasis must be put on reducing the losses in the conversion system of the dc turbine and, particularly, the ac-ac converter. Therefore, the efficiency of the ac-ac converter is compared for three different topologies: the direct matrix converter, the indirect matrix converter, and the conventional back-to-back converter. The direct matrix converter is found to be the most efficient, suitable for the suggested conversion system.

A xylem-specific cellulose synthase gene from aspen (Populus tremuloides) is responsive to mechanical stress.

Abstract: Angiosperm trees accumulate an elevated amount of highly crystalline cellulose with a concomitant decrease in lignin in the cell walls of tension-stressed tissues. To investigate the molecular basis of this tree stress response, we cloned a full-length cellulose synthase (PtCesA) cDNA from developing xylem of aspen (Populus tremuloides). About 90% sequence similarity was found between the predicted PtCesA and cotton GhCesA proteins. Northern blot and in situ hybridization analyses of PtCesA gene transcripts in various aspen tissues, and PtCesA gene promoter-beta-glucuronidase (GUS) fusion analysis in transgenic tobacco, demonstrated conclusively that PtCesA expression is confined to developing xylem cells during normal plant growth. During mechanical stress induced by stem bending, GUS expression remained in xylem and was induced in developing phloem fibers undergoing tension stress, but was turned off in tissues undergoing compression on the opposite side of the bend. Our results suggest a unique role for PtCesA in cellulose biosynthesis in both tension-stressed and normal tissues in aspen, and that the on/off control of PtCesA expression may be a part of a signaling mechanism triggering a stress-related compensatory deposition of cellulose and lignin that is crucial to growth and development in trees.