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Channeling light into quantum-scale gaps

Physical Review B - Condensed Matter and Materials Physics

Kekatpure, Rohan D.; Davids, Paul

We develop a discrete plasmonic mode-matching technique to investigate the ultimate limits to plasmonic light concentration down to the length scales required for observation of quantum-mechanical phenomena, including plasmon-assisted electron tunneling. Our mode-matching calculations, verified by direct numerical solution of Maxwell's equations, indicate achievable coupling efficiencies of >20% into symmetric bound gap plasmon modes in sub-10-nm gaps. For a given operating wavelength and a choice of material parameters, we demonstrate the existence of a specific width that maximizes enhancement of the electromagnetic field coupled into the gap. More generally, our calculations establish an intuitive and a computationally efficient framework for determining coupling efficiencies in and out of quantum-scale waveguides. © 2011 American Physical Society.

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TYPE Journal Article YEAR 2011
OSTIScopus

Targeting proteins to liquid-ordered domains in lipid membranes

Langmuir

Stachowiak, Jeanne C.; Hayden, Carl C.; Sanchez, Mari A.; Wang, Julia W.; Bunker, B.C.; Voigt, James A.; Sasaki, Darryl Y.

We demonstrate the construction of novel protein-lipid assemblies through the design of a lipid-like molecule, DPIDA, endowed with tail-driven affinity for specific lipid membrane phases and head-driven affinity for specific proteins. In studies performed on giant unilamellar vesicles (GUVs) with varying mole fractions of dipalymitoylphosphatidylcholine (DPPC), cholesterol, and diphytanoylphosphatidyl choline (DPhPC), DPIDA selectively partitioned into the more ordered phases, either solid or liquid-ordered (Lo) depending on membrane composition. Fluorescence imaging established the phase behavior of the resulting quaternary lipid system. Fluorescence correlation spectroscopy confirmed the fluidity of the Lo phase containing DPIDA. In the presence of CuCl2, the iminodiacetic acid (IDA) headgroup of DPIDA forms the Cu(II)-IDA complex that exhibits a high affinity for histidine residues. His-tagged proteins were bound specifically to domains enriched in DPIDA, demonstrating the capacity to target protein binding selectively to both solid and Lo phases. Steric pressure from the crowding of surface-bound proteins transformed the domains into tubules with persistence lengths that depended on the phase state of the lipid domains. © 2010 American Chemical Society.

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TYPE Journal Article YEAR 2011
ScopusOSTI

Advanced optical imaging reveals the dependence of particle geometry on interactions between CdSe quantum dots and immune cells

Small

Aaron, Jesse S.; Greene, Adrienne C.; Kotula, Paul G.; Bachand, George D.; Timlin, Jerilyn A.

The biocompatibility and possible toxicological consequences of engineered nanomaterials, including quantum dots (QDs) due to their unique suitability for biomedical applications, remain intense areas of interest. We utilized advanced imaging approaches to characterize the interactions of CdSe QDs of various sizes and shapes with live immune cells. Particle diffusion and partitioning within the plasma membrane, cellular uptake kinetics, and sorting of particles into lysosomes were all independantly characterized. Using high-speed total internal reflectance fluorescence (TIRF) microscopy, we show that QDs with an average aspect ratio of 2.0 (i.e., rod-shaped) diffuse nearly an order of magnitude slower in the plasma membrane than more spherical particles with aspect ratios of 1.2 and 1.6, respectively. Moreover, more rod-shaped QDs were shown to be internalized into the cell 2-3 fold more slowly. Hyperspectral confocal fluorescence microscopy demonstrates that QDs tend to partition within the cell membrane into regions containing a single particle type. Furthermore, data examining QD sorting mechanisms indicate that endocytosis and lysosomal sorting increases with particle size. Together, these observations suggest that both size and aspect ratio of a nanoparticle are important characteristics that significantly impact interactions with the plasma membrane, uptake into the cell, and localization within intracellular vesicles. Thus, rather than simply characterizing nanoparticle uptake into cells, we show that utilization of advanced imaging approaches permits a more nuanced and complete examination of the multiple aspects of cell-nanoparticle interactions that can ultimately aid understanding possible mechanisms of toxicity, resulting in safer nanomaterial designs. Using hyperspectral confocal fluorescence (HCF) microscopy, it is shown that quantum dots of various sizes and shapes partition themselves into distinct regions within the cell membrane of RBL-2H3 rat mast cells. HCF microscopy allows for deconvolving the signal from multiple, overlapping fluorophores in the sample in order to reveal precise concentrations and distributions of nanoparticles in the cell. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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TYPE Journal Article YEAR 2011
ScopusOSTI

Soot volume fraction and morphology of conventional and surrogate jet fuel sprays at 1000-K and 6.7-MPa ambient conditions

Proceedings of the Combustion Institute

Kook, Sanghoon; Pickett, Lyle M.

This paper presents soot processes of a blend of 23% m-xylene and 77% n-dodecane, which has been selected by several working groups as a surrogate for jet fuel. Fuel sprays were injected into high-temperature, high-pressure ambient conditions that are representative of practical engine combustion. Simultaneous laser extinction (KL) measurement and planar laser-induced incandescence imaging were performed to derive the in situ soot volume fraction. Also, soot particles were extracted from different positions within the reacting jet by means of a thermophoretic probe, and analyzed using transmission electron microscopy (TEM) to clarify the soot structure and its correlation with the measured soot volume fraction. The same measurements were repeated for the conventional jet fuel to understand the overall performance of the selected surrogate fuel. The soot volume fraction results show that, at fixed ambient conditions, the surrogate fuel produces more soot than the conventional jet fuel. The TEM images show that the soot aggregates are more agglomerated, which may not be easily eliminated by in-cylinder oxidation. The total number of primary particles and the mean primary particle size are higher for the surrogate fuel, consistent with the soot volume fraction trend. Considering that there is similar lift-off length between fuels, the differences in soot level and morphology are caused by molecular structure effects, such as a higher aromatic content. The quantitative soot database obtained from the present study offers data for the validation of soot kinetic models, particularly at high temperature and pressure conditions where little fundamental data exist. © 2010 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

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TYPE Conference YEAR 2011
ScopusOSTI

Time harmonic two-dimensional cavity scar statistics: Convex mirrors and bowtie

Electromagnetics

Warne, Larry K.; Jorgenson, Roy E.; Kotulski, Joseph D.; Lee, K.S.H.

This article examines the localization of time harmonic high-frequency modal fields in two-dimensional cavities along periodic paths between opposing sides of the cavity. The cases where these orbits lead to unstable localized modes are known as scars. This article examines the enhancements for these unstable orbits when the opposing mirrors are convex, constructing the high-frequency field in the scar region using elliptic cylinder coordinates in combination with a random reflection phase from the outer chaotic region. The enhancements when the cavity is symmetric as well as asymmetric about the orbit are examined. © Taylor & Francis Group, LLC.

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TYPE Journal Article YEAR 2011
ScopusOSTIDOI

Permittivity scaling in Ba1-xSrxTiO3 thin films and ceramics

Journal of Applied Physics

Aygün, Seymen M.; Ihlefeld, Jon F.; Borland, William J.; Maria, Jon P.

A dramatic enhancement in the electromechanical response of barium titanate thin films is demonstrated by understanding and optimizing the relationship between organic removal, crystallization, and microstructure, which therefore results in pore elimination, larger grain sizes, and superior densification. The combination enables one to produce bulk-like dielectric properties in a thin film with a room temperature permittivity value above 3000. This advancement in complex oxide thin film processing science creates a new perspective from which to compare, parameterize, and better understand a collection of literature data concerning the manner in which the dielectric response of BaTiO3 depends upon physical dimensions. We are consequently able to apply a single physical model to bulk ceramic and thin film systems, and so demonstrate that the existence of parasitic interfacial layers are not needed to explain dielectric scaling. This work is instrumental in illustrating that extrinsic contributions to scaling are predominant, and that a fundamental understanding of material synthesis provides important opportunities to broaden the spectrum of nonlinear electromechanical properties that can be achieved in ferroelectric thin films. © 2011 American Institute of Physics.

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TYPE Journal Article YEAR 2011
ScopusOSTI

Laser-induced incandescence measurements of soot in turbulent pool fires

Applied Optics

Frederickson, Kraig; Kearney, Sean P.; Grasser, Thomas

We present what we believe to be the first application of the laser-induced incandescence (LII) technique to large-scale fire testing. The construction of an LII instrument for fire measurements is presented in detail. Soot volume fraction imaging from 2m diameter pool fires burning blended toluene/methanol liquid fuels is demonstrated along with a detailed report of measurement uncertainty in the challenging pool fire environment. Our LII instrument relies upon remotely located laser, optical, and detection systems and the insertion of water-cooled, fiber-bundle-coupled collection optics into the fire plume. Calibration of the instrument was performed using an ethylene/air laminar diffusion flame produced by a Santoro-type burner, which allowed for the extraction of absolute soot volume fractions from the LII images. Single-laser-shot two-dimensional images of the soot layer structure are presented with very high volumetric spatial resolution of the order of 10 -5 cm3. Probability density functions of the soot volume fraction fluctuations are constructed from the large LII image ensembles. The results illustrate a highly intermittent soot fluctuation field with potentially large macroscale soot structures and clipped soot probability densities. © 2010 Optical Society of America.

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TYPE Journal Article YEAR 2011
ScopusOSTIDOI

Advances in process intensification through multifunctional reactor engineering

Gill, Walter; O'Hern, Timothy J.; Cooper, Marcia; Miller, James E.

A multifunctional reactor is a chemical engineering device that exploits enhanced heat and mass transfer to promote production of a desired chemical, combining more than one unit operation in a single system. The main component of the reactor system under study here is a vertical column containing packing material through which liquid(s) and gas flow cocurrently downward. Under certain conditions, a range of hydrodynamic regimes can be achieved within the column that can either enhance or inhibit a desired chemical reaction. To study such reactors in a controlled laboratory environment, two experimental facilities were constructed at Sandia National Laboratories. One experiment, referred to as the Two-Phase Experiment, operates with two phases (air and water). The second experiment, referred to as the Three-Phase Experiment, operates with three phases (immiscible organic liquid and aqueous liquid, and nitrogen). This report describes the motivation, design, construction, operational hazards, and operation of the both of these experiments. Data and conclusions are included.

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TYPE SAND Report YEAR 2011
DOIOSTI
Results 69801–69900 of 99,299
Results 69801–69900 of 99,299