Dynamics of the kink effect in InAlAs/InGaAs/InP HEMTs

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1997.Includes bibliographical references (leaves 68-72).by Alexander N. Ernst.M.Eng

Temporal and spatial control of transgene expression using laser induction of the hsp70 promoter

BACKGROUND: Precise temporal and spatial regulation of transgene expression is a critical tool to investigate gene function in developing organisms. The most commonly used technique to achieve tight control of transgene expression, however, requires the use of specific DNA enhancers that are difficult to characterize in non-model organisms. Here, we sought to eliminate the need for this type of sequence-based gene regulation and to open the field of functional genetics to a broader range of organisms. RESULTS: We have developed a new laser mediated method to heat shock groups of cells that provides precise spatio-temporal control of gene expression without requiring knowledge of specific enhancer sequences. We tested our laser-system in a transgenic line of Bicyclus anynana butterflies containing the EGFP reporter gene attached to the heat sensitive hsp70 promoter of Drosophila melanogaster. Whole organismal heat shocks demonstrated that this Drosophila promoter can drive gene expression in butterflies, and the subsequent laser heat shocks showed that it was possible to activate cell-specific gene expression in very precise patterns on developing pupal wings. CONCLUSION: This laser-mediated gene expression system will enable functional genetic investigations, i.e., the ectopic expression of genes and their knock-down in targeted groups of cells in model and non-model organisms with little or no available regulatory data, as long as a compatible heat-shock promoter is used and the target tissue is accessible to a laser beam. This technique will also be useful in evolutionary developmental biology as it will enable the study of the evolution of gene function across a variety of organisms

Physics of InAIAs/InGaAs Heterostructure Field-Effect Transistors

Contains an introduction, reports on three research projects, research conclusions and a list of publications.Joint Services Electronics Program Contract DAAHO4-95-1-003

Physics of InAIAs/InGaAs Heterostructure Field-Effect Transistors

Contains an introduction, a report on one research project and a list of publications and conference papers.Joint Services Electronics Program Contract DAAH04-95-1-0038Texas Instrument

Physics of Hemterostructure Field-Effect Transistors

Contains an introduction, report on one research project and a list of publications.Joint Services Electronics Program Contract DAAH04-95-1-0038Texas Instruments Agreement dated 11/23/9

Aluminum-, Calcium- And Titanium-Rich Oxide Stardust In Ordinary Chondrite Meteorites

We report isotopic data for a total of 96 presolar oxide grains found in residues of several unequilibrated ordinary chondrite meteorites. Identified grain types include Al2O3, MgAl2O4, hibonite (CaAl12O19) and Ti oxide. This work greatly increases the presolar hibonite database, and is the first report of presolar Ti oxide. O-isotopic compositions of the grains span previously observed ranges and indicate an origin in red giant and asymptotic giant branch (AGB) stars of low mass (<2.5 MSun) for most grains. Cool bottom processing in the parent AGB stars is required to explain isotopic compositions of many grains. Potassium-41 enrichments in hibonite grains are attributable to in situ decay of now-extinct 41Ca. Inferred initial 41Ca/40Ca ratios are in good agreement with model predictions for low-mass AGB star envelopes, provided that ionization suppresses 41Ca decay. Stable Mg and Ca isotopic ratios of most of the hibonite grains reflect primarily the initial compositions of the parent stars and are generally consistent with expectations for Galactic chemical evolution, but require some local interstellar chemical inhomogeneity. Very high 17O/16O or 25Mg/24Mg ratios suggest an origin for some grains in binary star systems where mass transfer from an evolved companion has altered the parent star compositions. A supernova origin for the hitherto enigmatic 18O-rich Group 4 grains is strongly supported by multi-element isotopic data for two grains. The Group 4 data are consistent with an origin in a single supernova in which variable amounts of material from the deep 16O-rich interior mixed with a unique end-member mixture of the outer layers. The Ti oxide grains primarily formed in low-mass AGB stars. They are smaller and rarer than presolar Al2O3, reflecting the lower abundance of Ti than Al in AGB envelopes.Comment: Accepted for publication in ApJ; 47 pages, 13 figure

Markov chain analysis of random walks on disordered medium

We study the dynamical exponents $d_{w}$ and $d_{s}$ for a particle diffusing in a disordered medium (modeled by a percolation cluster), from the regime of extreme disorder (i.e., when the percolation cluster is a fractal at $p=p_{c}$) to the Lorentz gas regime when the cluster has weak disorder at $p>p_{c}$ and the leading behavior is standard diffusion. A new technique of relating the velocity autocorrelation function and the return to the starting point probability to the asymptotic spectral properties of the hopping transition probability matrix of the diffusing particle is used, and the latter is numerically analyzed using the Arnoldi-Saad algorithm. We also present evidence for a new scaling relation for the second largest eigenvalue in terms of the size of the cluster, $|\ln{\lambda}_{max}|\sim S^{-d_w/d_f}$, which provides a very efficient and accurate method of extracting the spectral dimension $d_s$ where $d_s=2d_f/d_w$.Comment: 34 pages, REVTEX 3.

Dilepton production in proton-proton collisions at BEVALAC energies

The dilepton production in elementary ${pp\to e^{+}e^{-}X}$ reactions at BEVALAC energies $T_{lab}=1\div 5$ GeV is investigated. The calculations include direct ${e^{+}e^{-}}$ decays of the vector mesons $\rho ^{0}$, $\omega$, and $\phi$, Dalitz decays of the $\pi ^{0}$-, $\eta$-, $$-, $\omega$-, and $\phi$-mesons, and of the baryon resonances $$ $...$ . The subthreshold vector meson production cross sections in $pp$ collisions are treated in a way sufficient to avoid double counting with the inclusive vector meson production. The vector meson dominance model for the transition form factors of the resonance Dalitz decays $R\to e^{+}e^{-}N$ is used in an extended form to ensure correct asymptotics which are in agreement with the quark counting rules. Such a modification gives an unified and consistent description of both $R\to N\gamma$ radiative decays and $R\to N\rho (\omega)$ meson decays. The effect of multiple pion production on the experimental efficiency for the detection of the dilepton pairs is studied. We find the dilepton yield in reasonable agreement with the experimental data for the set of intermediate energies whereas at the highest energy $T_{lab}=4.88$ GeV the number of dilepton pairs is likely to be overestimated experimentally in the mass range $M=300\div 700$ MeV.Comment: 25 pages (IOP style), 5 figures, revised manuscript accepted for publication in JP