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No tribute to the legacy of Stan Ulam would be complete without a discussion of " nonlinear science, " a growing collection of interdisciplinary studies that in the past two decades has excited and challenged researchers from nearly every discipline of the natural sciences, engineering, and mathematics. Through his own research Stan played a major role in… (More)

- D K Campbell, A R Bishop
- 2011

Using recent results on a model relativistic field theory, we find explicitly a new solitonlike solution, essentially the conventional strong polaron, in the continuum interacting electron-phonon model of a Peierls-dimerized chain such as polyacetylene [(CH} " ].This solution is in good agreement with recent numerical simulations in a discrete model of (CH)… (More)

n solid-state physics, the phenomenon of localization is usually perceived as arising from extrinsic disorder that breaks the discrete translational invariance of the perfect crystal lattice. Familiar examples include the localized vibrational phonon modes around impurities or defects (such as atomic vacancies or interstitial atoms) in crystals and Anderson… (More)

- D. K. CAMPBELL
- 2002

A continuum model of a Peierls-dimerized chain, as described generally by Brazovskii and discussed for the case of polyacetylene by Takayama, Lin-Liu and Maki (TLM), is considered. The continuum (Bogliubov-de Gennes) equations arising in this model of interacting electrons and phonons are shown to be equivalent to the static, semiclassical equations for a… (More)

- S.-W. Tsai, A. H. Castro Neto, R. Shankar, D. K. Campbell
- 2005

We develop an asymptotically exact renormalization-group approach that treats electron-electron and electron-phonon interactions on an equal footing. The approach allows an unbiased study of the instabilities of Fermi liquids without the assumption of a broken symmetry. We apply our method to the problem of strongly coupled superconductors and find the… (More)

We report three surprising results regarding the nature of the spatial broken symmetries in the two-dimensional ͑2D͒, quarter-filled band with strong electron-electron interactions that provides a microscopic model of the 2:1 cationic organic charge-transfer solids ͑CTS's͒. First, in direct contradiction to the predictions of one-electron theory, we find a… (More)

This thesis describes the design and implementation of a 4-channel microphone array that is an adaptive beamformer used for hands-free telephony in a noisy environment. The microphone signals are amplified, then sent to an A/D converter. The microprocessor board takes the data from the 4 channels and utilizes digital signal processing to determine the… (More)

- Ka-Ming Tam, S.-W. Tsai, D. K. Campbell, H. Castro Neto
- 2007

The ground-state phase diagram of the half filled one-dimensional Holstein-Hubbard model contains a charge-density-wave ͑CDW͒ phase, driven by the electron-phonon ͑e-ph͒ coupling, and a spin-density-wave ͑SDW͒ phase, driven by the on-site electron-electron ͑e-e͒ repulsion. Recently, the existence of a third phase, which is metallic and lies in a finite… (More)

- Michel Peyrardt, David K Campbell
- 2002

We study numerically the interactions of a kink (K) and an antikink (I~) in a parametrically modified sine-Gordon model with potential V(~)= (1-r)2(!-cos t#)/(1 + r2+ 2r cos ~b). As the parameter r is varied from from the pure sine-Gordon case (r = 0) to values for which the model is not completely integrable (r ~ 0), we find that a rich structure arises in… (More)

- K Fesser, A R Bishop, D K Campbell
- 2011

We present a theoretical calculation, within a continuum electron-phonon-coupled model, of the optical absorption due to polarons in polyacetylene [{CH), ]. Our results can be applied to both trans-and cis-(CH) " , as well as potentially to other polymers (polypyroles, po-lyparaphenylenes) in which polarons are present. We establish that the essential… (More)