Fermi-edge singularities in linear and non-linear ultrafast spectroscopy

We discuss Fermi-edge singularity effects on the linear and nonlinear transient response of an electron gas in a doped semiconductor. We use a bosonization scheme to describe the low energy excitations, which allows to compute the time and temperature dependence of the response functions. Coherent control of the energy absorption at resonance is analyzed in the linear regime. It is shown that a phase-shift appears in the coherent control oscillations, which is not present in the excitonic case. The nonlinear response is calculated analytically and used to predict that four wave-mixing experiments would present a Fermi-edge singularity when the exciting energy is varied. A new dephasing mechanism is predicted in doped samples that depends linearly on temperature and is produced by the low-energy bosonic excitations in the conduction band.Comment: long version; 9 pages, 4 figure

Ultrafast Coulomb-induced dynamics of 2D magnetoexcitons

We study theoretically the ultrafast nonlinear optical response of quantum well excitons in a perpendicular magnetic field. We show that for magnetoexcitons confined to the lowest Landau levels, the third-order four-wave-mixing (FWM) polarization is dominated by the exciton-exciton interaction effects. For repulsive interactions, we identify two regimes in the time-evolution of the optical polarization characterized by exponential and {\em power law} decay of the FWM signal. We describe these regimes by deriving an analytical solution for the memory kernel of the two-exciton wave-function in strong magnetic field. For strong exciton-exciton interactions, the decay of the FWM signal is governed by an antibound resonance with an interaction-dependent decay rate. For weak interactions, the continuum of exciton-exciton scattering states leads to a long tail of the time-integrated FWM signal for negative time delays, which is described by the product of a power law and a logarithmic factor. By combining this analytic solution with numerical calculations, we study the crossover between the exponential and non-exponential regimes as a function of magnetic field. For attractive exciton-exciton interaction, we show that the time-evolution of the FWM signal is dominated by the biexcitonic effects.Comment: 41 pages with 11 fig

Standardized ultrasound evaluation of carotid stenosis for clinical trials: University of Washington Ultrasound Reading Center

<p>Abstract</p> <p>Introduction</p> <p>Serial monitoring of patients participating in clinical trials of carotid artery therapy requires noninvasive precision methods that are inexpensive, safe and widely available. Noninvasive ultrasonic duplex Doppler velocimetry provides a precision method that can be used for recruitment qualification, pre-treatment classification and post treatment surveillance for remodeling and restenosis. The University of Washington Ultrasound Reading Center (UWURC) provides a uniform examination protocol and interpretation of duplex Doppler velocity measurements.</p> <p>Methods</p> <p>Doppler waveforms from 6 locations along the common carotid and internal carotid artery path to the brain plus the external carotid and vertebral arteries on each side using a Doppler examination angle of 60 degrees are evaluated. The UWURC verifies all measurements against the images and waveforms for the database, which includes pre-procedure, post-procedure and annual follow-up examinations. Doppler angle alignment errors greater than 3 degrees and Doppler velocity measurement errors greater than 0.05 m/s are corrected.</p> <p>Results</p> <p>Angle adjusted Doppler velocity measurements produce higher values when higher Doppler examination angles are used. The definition of peak systolic velocity varies between examiners when spectral broadening due to turbulence is present. Examples of measurements are shown.</p> <p>Discussion</p> <p>Although ultrasonic duplex Doppler methods are widely used in carotid artery diagnosis, there is disagreement about how the examinations should be performed and how the results should be validated. In clinical trails, a centralized reading center can unify the methods. Because the goals of research examinations are different from those of clinical examinations, screening and diagnostic clinical examinations may require fewer velocity measurements.</p

Ultrafast Nonlinear Optical Response of Strongly Correlated Systems: Dynamics in the Quantum Hall Effect Regime

We present a theoretical formulation of the coherent ultrafast nonlinear optical response of a strongly correlated system and discuss an example where the Coulomb correlations dominate. We separate out the correlated contributions to the third-order nonlinear polarization, and identify non-Markovian dephasing effects coming from the non-instantaneous interactions and propagation in time of the collective excitations of the many-body system. We discuss the signatures, in the time and frequency dependence of the four-wave-mixing (FWM) spectrum, of the inter-Landau level magnetoplasmon (MP) excitations of the two-dimensional electron gas (2DEG) in a perpendicular magnetic field. We predict a resonant enhancement of the lowest Landau level (LL) FWM signal, a strong non-Markovian dephasing of the next LL magnetoexciton (X), a symmetric FWM temporal profile, and strong oscillations as function of time delay, of quantum kinetic origin. We show that the correlation effects can be controlled experimentally by tuning the central frequency of the optical excitation between the two lowest LLs.Comment: 21 pages, 10 figure

Propaganda and art in Soviet film: A study of “Alexander Nevsky” and “Ivan the Terrible”

Abstract not availabl

Using PLACE mapping to improve public participation in Tillamook County, Oregon riparian action planning

In the fall and winter of 1999/2000, efforts by federal, state, and local agencies to restore salmon habitat by protecting land adjacent to rivers and streams drew intense responses citizens in the Pacific Northwest. Despite efforts to "involve" citizens in the development of riparian protection policies, many did not believe their knowledge or concerns were considered or addressed. The PLACE (People Learning About Community and Environment) mapping technique was developed and tested as a way to improve the quality of citizen participation by improving their ability to help define the situation to be addressed by policy. The PLACE mapping technique is guided by LINCS (Learning-oriented, Interactive, Non-competitive, Collaborative, Systemic inquiry) theory, which suggests that contentious situations will be improved by increasing learning among community members. Participants in PLACE mapping sessions explore and learn from the knowledge and experiences of community members to appropriately identify the situation and criteria that need to be addressed by policy. The PLACE mapping technique is shown to promote learning among participants, but limitations are revealed in the format of project that restricts learning to isolated groups by limiting interactions among diverse interests

Maximixing Daylight in Lower Level Classrooms using Lightwells

Student and worker performance has been shown to share a correlation with access to natural sources of lighting (Heschong, 2002). Natural lighting also provides environmental benefits through the reduction of a building’s energy dependence (Ihm, P., Nemri, A., Krarti, M., 2008). Lower-level classrooms are particularly troublesome to daylight because skylight strategies are unavailable and relying on exterior glazing increases solar heat gain as well as increased envelope costs. Lightwells offer a potential solution for daylighting without the costs associated with traditional solutions. A lightwell is a vertical shaft extending from an opening in the roof structure to lower level rooms. The main design distinction between a lightwell and a skylight is the method of transmittance. Skylights provide direct sunlight while the lightwell has a highly reflective interior surface material that allows light entering from the roof opening to reflect down providing diffuse light into the space below. Lightwells with horizontal openings are more efficient in bringing in light in than vertical or slanted openings (Bouchet B., Fontoynont M., 1996). This research, in coordination with Thomas Hacker Architects (THA), explores various configurations of lightwell design to maximize daylighting in the proposed classroom building on the Oregon Episcopal School campus. The proposed building design is two levels with an allotted 950ft of useable floor plan in lower level classrooms. The structural allowance for lightwell shafts is limited to 50ft. Ceiling height is limited to 12-½ft. This research focuses on the southern classrooms.https://pdxscholar.library.pdx.edu/research_based_design/1026/thumbnail.jp