On frequency measurements and resolution

Sine wave frequency measurements and resolutio

Allegory, Gendered Allegory, and Paradise Lost

In Paradise Lost, John Milton's allegorical personifications, Sin and Death exist in a peculiar ontological space. They are not angels like Raphael or Abidel, but they are not human like our "Grand Parents," Adam and Eve. Their existence in the poem has confused and troubled scholars for centuries, but Sin and Death are more than a rhetorical anomaly. In my first chapter I analyze the ontological status and purpose of these characters based on their effect on the poem's internal cosmology. From that analysis, I continue my discussion by focusing on Sin and her gender, which, based on her placement in the narrative and her troubling characterization, has a direct effect on how readers interpret the only other woman in the poem, Eve.No embargoAcademic Major: Englis

The GSFC scientific data storage problem

Scientific data storage problems of telemetry tape

Tunneling Conductance Between Parallel Two Dimensional Electron Systems

We derive and evaluate expressions for the low temperature {\it dc} equilibrium tunneling conductance between parallel two-dimensional electron systems. Our theory is based on a linear-response formalism and on impurity-averaged perturbation theory. The disorder broadening of features in the dependence of tunneling conductance on sheet densities and in-plane magnetic field strengths is influenced both by the finite lifetime of electrons within the wells and by non-momentum-conserving tunneling events. Disorder vertex corrections are important only for weak in-plane magnetic fields and strong interwell impurity-potential correlations. We comment on the basis of our results on the possibility of using tunneling measurements to determine the lifetime of electrons in the quantum wells.Comment: 14 pages, 5 Fig. not included, revtex, IUcm92-00

Experimental and numerical investigations of a thermoplastic composite (carbon/PPS) thermoforming

For lightweight structural components, continuous fibre-reinforced thermoplastic composites have demonstrated success in aerospace and defence applications. Their mechanical behaviour is a result of the possible sliding and interactions between the fibres, but the complex deformation mechanisms of this sheet are a main problem in the practical thermoforming process. In this context, a large experimental work was developed to analyse the behaviour of a 5-harness satin weave carbon–polyphenylenesulfide (PPS) composite. Firstly, we started this work with a microscope observation of the sheet cross section and a thermo-gravimetric analysis of carbon/PPS to understand the thermal condition in the forming process, the reinforcement (fibre and yarn) geometry and dimensions and the textile reinforcement architectures. Secondly, in high temperature conditions (at 320�C), static uniaxial and biaxial tensile tests were carried out. During these mechanical tests, we used a digital image stereo-correlation technique to get full field displacement measurements and an infrared camera to measure the temperature in the surface of sample. The results of the experimental investigation were used with the commercial software ABAQUS to develop a numerical model of stamp thermoforming operation. The stamp thermoforming part was developed using a hemispherical punch and compared with an experimental result. In the deformed part obtained by thermoforming of the carbon/PPS sheet, we analysed the instability phenomena such as wrinkling

Mesoscopic effects in tunneling between parallel quantum wires

We consider a phase-coherent system of two parallel quantum wires that are coupled via a tunneling barrier of finite length. The usual perturbative treatment of tunneling fails in this case, even in the diffusive limit, once the length L of the coupling region exceeds a characteristic length scale L_t set by tunneling. Exact solution of the scattering problem posed by the extended tunneling barrier allows us to compute tunneling conductances as a function of applied voltage and magnetic field. We take into account charging effects in the quantum wires due to applied voltages and find that these are important for 1D-to-1D tunneling transport.Comment: 8 pages, 7 figures, improved Figs., added Refs. and appendix, to appear in Phys. Rev.

Lifetime of Two-Dimensional Electrons Measured by Tunneling Spectroscopy

For electrons tunneling between parallel two-dimensional electron systems, conservation of in-plane momentum produces sharply resonant current-voltage characteristics and provides a uniquely sensitive probe of the underlying electronic spectral functions. We report here the application of this technique to accurate measurements of the temperature dependence of the electron-electron scattering rate in clean two-dimensional systems. Our results are in qualitative agreement with existing calculations.Comment: file in REVTEX format produces 11 pages, 3 figures available from [email protected]

Tunneling Between Two-Dimensional Electron Gases in a Strong Magnetic Field

We have measured the tunneling between two two-dimensional electron gases at high magnetic fields $B$, when the carrier densities of the two electron layers are matched. For filling factors $\nu<1$, there is a gap in the current-voltage characteristics centered about $V=0$, followed by a tunneling peak at $\sim 6$~mV. Both features have been observed before and have been attributed to electron-electron interactions within a layer. We have measured high field tunneling peak positions and fitted gap parameters that are proportional to $B$, and independent of the carrier densities of the two layers. This suggests a different origin for the gap to that proposed by current theories, which predict a $\sqrt{B}$ dependence.Comment: 9 pages, cond-mat/yymmnn