Observations of atmospheric water vapor with the SAGE 2 instrument

The Stratospheric Aerosol and Gas Experiment 2 (SAGE 2) is discussed. The SAGE 2 instrument was a multichannel spectrometer that inferred the vertical distribution of water vapor, aerosols, nitrogen dioxide, and ozone by measuring the extinction of solar radiation at spacecraft sunrise/sunset. At altitudes above 20 km, the SAGE 2 and LIMS (Limb Infrared Monitor of the Stratosphere) data are in close agreement. The discrepancies below this altitude may be attributed to differences in the instruments' field of view and time of data acquisition

Debra Franks and Karen Claiborne in a Joint Junior Recital

This is the program for the joint junior recital of Debra Franks and Karen Claiborne. Pianist Jane Chu accompanied Franks, who performed on the flute; pianist Dr. Jack W. Jones accompanied Claiborne, who performed on the alto saxophone. The recital took place on December 4, 1975, at 5:00, in the Mabee Fine Arts Center Recital Hall

A high performance zero-crossing based pipelined analog-to-digital converter

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2008.Includes bibliographical references (leaves 46-47).In this thesis, I describe a zero-crossing based pipelined ADC. Unlike traditional pipelined ADCs, this work does not use any op-amps in the signal path. The use of zero-crossing based circuits made it possible to achieve a much better figure of merit. The ADC is design to operate at 200MS/s with a resolution of 12 bits. The simulated results suggest that the target performance is achievable with less than 10 mW of power. This design's figure of merit is at least an order of magnitude better than any existing designs that have comparable speed and accuracy performance. The design will be fabricated later to be tested in silicon.by Yue Jack Chu.S.M

High performance zero-crossing based pipelined analog-to-digital converters

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2011.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from student submitted PDF version of thesis.Includes bibliographical references (p. 133-137).As CMOS processes continue to scale to smaller dimensions, the increased fT of the devices and smaller parasitic capacitance allow for more power ecient and faster digital circuits to be made. But at the same time, output impedance of transistors has gone down, as have the power supply voltages, and leakage currents have increased. These changes in the technology have made analog design more difficult. More specifically, the design of a high gain op-amp, a fundamental analog building block, has become more difficult in scaled processes. In this work, op-amps in pipelined ADCs are replaced with zero-crossing detectors(ZCD). Without the closed-loop feedback provided by the op-amp, a new set of design constraints for Zero-Crossing Based Circuits (ZCBC) is explored.by Yue Jack Chu.Ph.D

The Canonical Structure of Wess-Zumino-Witten Models

The phase space of the Wess-Zumino-Witten model on a circle with target space a compact, connected, semisimple Lie group $G$ is defined and the corresponding symplectic form is given. We present a careful derivation of the Poisson brackets of the Wess-Zumino-Witten model. We also study the canonical structure of the supersymmetric and the gauged Wess-Zumino-Witten models.Comment: 16pp (revised version - two new sections added and relation with other recent work discussed

Investigation of the Augmin Complex, the Template Dependent Microtubule Nucleator, in Drosophila Melanogaster

In order for life to continue, proper segregation of genetic materials by the process of mitosis is essential. Mitosis is facilitated by a bipolar spindle, usually composed of a symmetrical array of microtubules (MTs). MTs consist of Tubulin polymers, and are generated in vivo with the aid of nucleators. The most predominant nucleator is the γ-Tubulin Ring Complex (γ-TuRC). During mitosis, multiple pathways contribute to proper spindle formation, including centrosome-dependent, kinetochore-dependent, and a recently discovered pathway in which new MTs are nucleated from the sides of existing MTs. This last pathway relies on the Augmin complex, a template-dependent MT nucleator which recruits γ-TuRC to the spindle. Mitotic cells lacking Augmin have weak spindles due to a lower density of MTs and in human cells, Augmin reduction also causes centrosome fragmentation. To date, very little is known about the functional properties of Augmin. I have purified individual Augmin subunits and examined their properties in vitro. I show that the Augmin subunits Dgt4 and Wac are responsible for interaction with MTs and that Dgt6, Dgt3 and Dgt5 interact with the γ-TuRC subunit Dgp71WD. I have also shown that Wac protects MTs from destabilisation. Interestingly, the Augmin complex promotes MT assembly in the absence of γ-TuRC, suggesting a novel function for Augmin. I have also successfully purified intact Augmin complex. With this, I determined some of the relationships between Augmin subunits and generated a model of how Augmin might recruit γ-TuRC to MTs. Lastly, I have determined that at least one subunit, Wac, plays a role in MT organisation beyond mitosis. This work significantly improves our understanding of the Augmin complex and provides an excellent complement of tools for further investigation.University of Exeter President's Taiwan Scholarship Awar

Impact-Actuated Digging Tool for Lunar Excavation

NASA s plans for a lunar outpost require extensive excavation. The Lunar Surface Systems Project Office projects that thousands of tons of lunar soil will need to be moved. Conventional excavators dig through soil by brute force, and depend upon their substantial weight to react to the forces generated. This approach will not be feasible on the Moon for two reasons: (1) gravity is 1/6th that on Earth, which means that a kg on the Moon will supply 1/6 the down force that it does on Earth, and (2) transportation costs (at the time of this reporting) of $50K to$100K per kg make massive excavators economically unattractive. A percussive excavation system was developed for use in vacuum or nearvacuum environments. It reduces the down force needed for excavation by an order of magnitude by using percussion to assist in soil penetration and digging. The novelty of this excavator is that it incorporates a percussive mechanism suited to sustained operation in a vacuum environment. A percussive digger breadboard was designed, built, and successfully tested under both ambient and vacuum conditions. The breadboard was run in vacuum to more than 2..times the lifetime of the Apollo Lunar Surface Drill, throughout which the mechanism performed and held up well. The percussive digger was demonstrated to reduce the force necessary for digging in lunar soil simulant by an order of magnitude, providing reductions as high as 45:1. This is an enabling technology for lunar site preparation and ISRU (In Situ Resource Utilization) mining activities. At transportation costs of $50K to$100K per kg, reducing digging forces by an order of magnitude translates into billions of dollars saved by not launching heavier systems to accomplish excavation tasks necessary to the establishment of a lunar outpost. Applications on the lunar surface include excavation for habitats, construction of roads, landing pads, berms, foundations, habitat shielding, and ISRU