Strategies for construction and maintenance of rural roads in Cameroon

Thesis (M.C.P.)--Massachusetts Institute of Technology, Dept. of Urban Studies and Planning, 1996.Includes bibliographical references (leaves 79-82).by Veronica Fofang.M.C.P

Optical Properties of Strongly Coupled Plasmon-Exciton Hybrid Nanostructures

Strongly coupled plasmon-exciton hybrid nanostructures are fabricated and their optical properties are studied. The plasmonic and excitonic systems are gold nanoshells and J-aggregates, respectively. Gold nanoshells are tunable plasmonic core-shell nanoparticles which can sustain distinct dipole and quadrupole plasmons with resonant energies dependent on core-size/shell-thickness ratio. J-aggregates are organic semiconducting material with excitons that possess very high oscillator strength making them suitable for coherent interaction with other kinds of excitations. The J-aggregates are formed on the surface of the nanoshells when a water/ethanol (50:50) solution of the dye molecules (2,2'-dimethyl-8-phenyl-5,6,5',6'-dibenzothiacarbocyanine chloride) is added to an aqueous solution of nanoshells. These nanoshell-J-aggregate complexes exhibit coherent coupling between localized plasmons of the nanoshell and excitons of the molecular J-aggregates. Coherent coupling strengths of 120 meV and 100 meV have been measured for dipole and quadrupole plasmon interactions with excitons, respectively. Femtosecond time-resolved transmission spectroscopy studies are carried out in order to understand the possible sources of optical nonlinearities in the nanoshell-J-aggregate hybrid. Transient absorption of the interacting plasmon-exciton system is observed, in dramatic contrast to the photoinduced transmission of the pristine J-aggregate. An additional, transient Fano-shaped modulation within the Fano dip is also observable. The transient behavior of the J-aggregate-Au nanoshell complex is described by a combined one-exciton and two-exciton state model coupled to the nanoshell plasmon

Surface bound waves and optical interactions in excitonic thin films

Excitonic films such as J-aggregate-doped polymer films can exhibit sharp Lorentzian dispersions and thus have various optical features in the visible region. They can even show an optically metallic response and can be considered as alternative plasmonic materials. However, there were no systematic studies on optical interactions in such excitonic films. Here, we perform theoretical investigations on optical modes and interactions in planar excitonic thin films. We gradually vary the dye concentration and the film thickness and study optical coupling to surface bound waves (surface polariton modes and epsilon-near-zero modes). We also investigate thin-film interferences in high-loss and low-loss regimes. Finally, we discuss the freespace impedance matching that can result from the Lorentzian dispersion in excitonic films. Our work enables in-depth understandings on optical interactions in excitonic films and it can provide guidelines for various nanophotonic applications in the visible region

Real-time observation of ultrafast Rabi oscillations between excitons and plasmons in metal nanostructures with J-aggregates

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A synthetic biological quantum optical system

In strong plasmon–exciton coupling, a surface plasmon mode is coupled to an array of localized emitters to yield new hybrid light–matter states (plexcitons), whose properties may in principle be controlled via modification of the arrangement of emitters. We show that plasmon modes are strongly coupled to synthetic light-harvesting maquette proteins, and that the coupling can be controlled via alteration of the protein structure. For maquettes with a single chlorin binding site, the exciton energy (2.06 ± 0.07 eV) is close to the expected energy of the Qy transition. However, for maquettes containing two chlorin binding sites that are collinear in the field direction, an exciton energy of 2.20 ± 0.01 eV is obtained, intermediate between the energies of the Qx and Qy transitions of the chlorin. This observation is attributed to strong coupling of the LSPR to an H-dimer state not observed under weak coupling

Universal surface-enhanced Raman tags : individual nanorods for measurements from the visible to the infrared (514 – 1064 nm)

Surface-enhanced Raman scattering (SERS) is a promising imaging modality for use in a variety of multiplexed tracking and sensing applications in biological environments. However, the uniform production of SERS nanoparticle tags with high yield and brightness still remains a significant challenge. Here, we describe an approach based on the controlled co-adsorption of multiple dye species onto gold nanorods to create tags that can be detected across a much wider range of excitation wavelengths (514 – 1064 nm) compared to conventional approaches that typically focus on a single wavelength. This was achieved without the added complexity of nanoparticle aggregation or growing surrounding metallic shells to further enhance the surface-enhanced resonance Raman scattering (SERRS) signal. Correlated Raman and scanning electron microscopy mapping measurements of individual tags were used to clearly demonstrate that strong and reproducible SERRS signals at high particle yields (>92 %) were readily achievable. The polyelectrolyte-wrapped nanorod-dye conjugates were also found to be highly stable as well as non-cytotoxic. To demonstrate the use of these universal tags for the multimodal optical imaging of biological specimens, confocal Raman and fluorescence maps of stained immune cells following nanoparticle uptake were acquired at several excitation wavelengths and compared with dark-field images. The ability to colocalize and track individual optically encoded nanoparticles across a wide range of wavelengths simultaneously will enable the use of SERS alongside other imaging techniques for the real-time monitoring of cell-nanoparticle interactions

Theoretical Criteria for Scattering Dark States in Nanostructured Particles

Nanostructures with multiple resonances can exhibit a suppressed or even completely eliminated scattering of light, called a scattering dark state. We describe this phenomenon with a general treatment of light scattering from a multiresonant nanostructure that is spherical or nonspherical but subwavelength in size. With multiple resonances in the same channel (i.e., same angular momentum and polarization), coherent interference always leads to scattering dark states in the low-absorption limit, regardless of the system details. The coupling between resonances is inevitable and can be interpreted as arising from far-field or near-field. This is a realization of coupled-resonator-induced transparency in the context of light scattering, which is related to but different from Fano resonances. Explicit examples are given to illustrate these concepts.Massachusetts Institute of Technology. Institute for Soldier Nanotechnologies (Contract W911NF-13-D-0001)National Science Foundation (U.S.). Materials Research Science and Engineering Centers (Program) (Grant DMR-0819762

Reprocessing of line FFI-161 of the Brazos-Galveston area using Pro-MAX 2D to evaluate migration techniques

Due to the character of the original source materials and the nature of batch digitization, quality control issues may be present in this document. Please report any quality issues you encounter to [email protected], referencing the URI of the item.Includes bibliographical references.Issued also on microfiche from Lange Micrographics.ProMAX 2D, a software for the interactive and batch processing of two dimensional seismic data, was used to process approximately 25 km of seismic data from line FFI-161 of the Brazos-Galveston area of the Gulf of Mexico. The main objectives were to process the data to obtain optimum velocities that are good for stacking and migration, and to produce and compare migrated sections using different migration schemes. The dip moveout (DMO) process was incorporated in the processing stream to improve the velocity estimates. The DMO process was not very successful for two main reasons: the velocity gradients at shallow depth were too large and the deeper part of the section lacked large dips and continuous reflectors. Three migration algorithms namely, Memory Stolt F-K (a transform method), Kirchhoff Time (a summation method), and Fast Explicit FD Time (a finite-difference method), were used to migrate the stacked data. All three migration algorithms performed well in broadening the synclines in the section, defining fault ten-ninations and collapsing diffractions from faults. The fault terminations on the section produced by the Fast Explicit FD Time algorithm were better defined but the section suffered from smearing. Comparison of the sections produced by the Kirchhoff Time and the Memory Stolt F-K migration schemes revealed that the performance of the two schemes was the same for the same events on the stacked section except that the section from the Memory Stolt F-K was less noisy. The Memory Stolt F-K algorithm produced a section with the best picture contrast and was found to be the least computationally expensive. It is over 100 times faster than the Kirchhoff Time and over 25 times faster than the Fast Explicit FD Time. The Memory Stolt F-K algorithm using a stretch factor of 0.6 is the most suitable for line FFI-16 1