Progress Report, Project 6751, March 1 to October 1, 1951

Progress report by project Whirlwind I research teams on Project 6751.During this period we have been working on problems proposed by the Carter Oil Company and by the Humble Oil Company. We have had personal visits and inquiries from members of these companies and of the Magnolia Petroleum Company (Socony-Vacuum), the Continental Oil Company, and the Gulf Research and Development Company. At the Industrial Liaison Office Conference on May 2 and 3, many of the participants exhibited interest and requested copies of R-196, a report on programming for WWI. These reports have been sent out by our librarian

Re-entrant resonant tunneling

We study the effect of electron-electron interactions on the resonant-tunneling spectroscopy of the localized states in a barrier. Using a simple model of three localized states, we show that, due to the Coulomb interactions, a single state can give rise to two resonant peaks in the conductance as a function of gate voltage, G(Vg). We also demonstrate that an additional higher-order resonance with Vg-position in between these two peaks becomes possibile when interactions are taken into account. The corresponding resonant-tunneling process involves two-electron transitions. We have observed both these effects in GaAs transistor microstructures by studying the time evolution of three adjacent G(Vg) peaks caused by fluctuating occupation of an isolated impurity (modulator). The heights of the two stronger peaks exibit in-phase fluctuations. The phase of fluctuations of the smaller middle peak is opposite. The two stronger peaks have their origin in the same localized state, and the third one corresponds to a co-tunneling process.Comment: 9 pages, REVTeX, 4 figure

Enhanced fluctuations of the tunneling density of states near bottoms of Landau bands measured by a local spectrometer

We have found that the local density of states fluctuations (LDOSF) in a disordered metal, detected using an impurity in the barrier as a spectrometer, undergo enhanced (with respect to SdH and dHvA effects) oscillations in strong magnetic fields, omega _c\tau > 1. We attribute this to the dominant role of the states near bottoms of Landau bands which give the major contribution to the LDOSF and are most strongly affected by disorder. We also demonstrate that in intermediate fields the LDOSF increase with B in accordance with the results obtained in the diffusion approximation.Comment: 4 pages, 4 figure

Non Linear Current Response of a Many-Level Tunneling System: Higher Harmonics Generation

The fully nonlinear response of a many-level tunneling system to a strong alternating field of high frequency $\omega$ is studied in terms of the Schwinger-Keldysh nonequilibrium Green functions. The nonlinear time dependent tunneling current $I(t)$ is calculated exactly and its resonance structure is elucidated. In particular, it is shown that under certain reasonable conditions on the physical parameters, the Fourier component $I_{n}$ is sharply peaked at $n=\frac {\Delta E} {\hbar \omega}$, where $\Delta E$ is the spacing between two levels. This frequency multiplication results from the highly nonlinear process of $n$ photon absorption (or emission) by the tunneling system. It is also conjectured that this effect (which so far is studied mainly in the context of nonlinear optics) might be experimentally feasible.Comment: 28 pages, LaTex, 7 figures are available upon request from [email protected], submitted to Phys.Rev.

Quantum Transport in Semiconductor Nanostructures

I. Introduction (Preface, Nanostructures in Si Inversion Layers, Nanostructures in GaAs-AlGaAs Heterostructures, Basic Properties). II. Diffusive and Quasi-Ballistic Transport (Classical Size Effects, Weak Localization, Conductance Fluctuations, Aharonov-Bohm Effect, Electron-Electron Interactions, Quantum Size Effects, Periodic Potential). III. Ballistic Transport (Conduction as a Transmission Problem, Quantum Point Contacts, Coherent Electron Focusing, Collimation, Junction Scattering, Tunneling). IV. Adiabatic Transport (Edge Channels and the Quantum Hall Effect, Selective Population and Detection of Edge Channels, Fractional Quantum Hall Effect, Aharonov-Bohm Effect in Strong Magnetic Fields, Magnetically Induced Band Structure).Comment: 111 pages including 109 figures; this review from 1991 has retained much of its usefulness, but it was not yet available electronicall

Anon is Not Dead: Towards a History of Anonymous Authorship in Early-Twentieth-Century Britain

In 1940, Virginia Woolf blamed the printing press for killing the oral tradition that had promoted authorial anonymity: “Anon is dead,” she pronounced. Scholarship on the printed word has abundantly recognized that, far from being dead, Anon remained very much alive in Britain through the end of the nineteenth century. Even in the twentieth century, Anon lived on, among particular groups and particular genres, yet little scholarship has addressed this endurance. Here, after defining anonymity and sketching its history in the late nineteenth and early twentieth century, I offer three findings. First, women had less need for anonymity as they gained civil protections elsewhere, but anonymity still appealed to writers made vulnerable by their marginalized identities or risky views. Second, in the early twentieth century the genre most likely to go unsigned was autobiography, in all its forms. Third, on rare occasions, which I enumerate, strict anonymity achieves what pseudonymity cannot. I conclude by suggesting that among British modernist authors, the decline of practiced anonymity stimulated desired anonymity and the prizing of anonymity as an aesthetic ideal.En 1940, Virginia Woolf écrivait « Anon est mort », et attribuait la disparition de l’anonymat de l’auteur qu’avait favorisé la tradition orale à l’apparition de l’imprimerie. La recherche portant sur l’oeuvre imprimée indique au contraire qu’Anon était encore bien vivant en Angleterre à la fin du xixe siècle. On le retrouve même au xxe siècle, chez certains groupes ou dans certains genres littéraires. Or cette persistance n’a fait l’objet que de peu d’études. Après avoir défini le concept d’anonymat et évoqué la manière dont il se déployait à la fin du xixe siècle et au début du xxe, j’aborderai trois constats que mes travaux m’ont permis de faire. Premièrement, les femmes ont moins recours à l’anonymat dès lors que leur statut juridique s’améliore dans d’autres sphères; l’anonymat reste néanmoins courant parmi les auteurs juridiquement vulnérables du fait de leur appartenance à un groupe marginalisé ou de leurs opinions transgressives. Deuxièmement, au début du xxe siècle, le genre pour lequel l’usage de l’anonymat est le plus répandu est l’autobiographie, quelle que soit sa forme. Troisièmement, en de rares circonstances, que j’énumérerai, l’usage de l’anonymat permet plus que celui d’un pseudonyme. Enfin, je suggérerai que le déclin de l’usage de l’anonymat a suscité le désir d'être anonyme chez les auteurs modernes britanniques, et l'idéalisation esthétique de l'anonymat en littérature

The Architecture of Ernest Hemingway’s The Three-Day Blow

Discusses symmetrical structures, framing around central counterpoints, chiastic forms, and mirrored imagery