Analysis of intrapulse chirp in CO2 oscillators

Pulsed single-frequency CO2 laser oscillators are often used as transmitters for coherent lidar applications. These oscillators suffer from intrapulse chirp, or dynamic frequency shifting. If excessive, such chirp can limit the signal-to-noise ratio of the lidar (by generating excess bandwidth), or limit the velocity resolution if the lidar is of the Doppler type. This paper describes a detailed numerical model that considers all known sources of intrapulse chirp. Some typical predictions of the model are shown, and simple design rules to minimize chirp are proposed

Hard-wall and non-uniform lattice Monte Carlo approaches to one-dimensional Fermi gases in a harmonic trap

We present in detail two variants of the lattice Monte Carlo method aimed at tackling systems in external trapping potentials: a uniform-lattice approach with hard-wall boundary conditions, and a non-uniform Gauss-Hermite lattice approach. Using those two methods, we compute the ground-state energy and spatial density profile for systems of N=4 - 8 harmonically trapped fermions in one dimension. From the favorable comparison of both energies and density profiles (particularly in regions of low density), we conclude that the trapping potential is properly resolved by the hard-wall basis. Our work paves the way to higher dimensions and finite temperature analyses, as calculations with the hard-wall basis can be accelerated via fast Fourier transforms, the cost of unaccelerated methods is otherwise prohibitive due to the unfavorable scaling with system size

Strong coupling between single photons in semiconductor microcavities

We discuss the observability of strong coupling between single photons in semiconductor microcavities coupled by a chi(2) nonlinearity. We present two schemes and analyze the feasibility of their practical implementation in three systems: photonic crystal defects, micropillars and microdisks, fabricated out of GaAs. We show that if a weak coherent state is used to enhance the chi(2) interaction, the strong coupling regime between two modes at different frequencies occupied by a single photon is within reach of current technology. The unstimulated strong coupling of a single photon and a photon pair is very challenging and will require an improvement in mirocavity quality factors of 2-4 orders of magnitude to be observable.Comment: 4 page

STITCHER: Dynamic assembly of likely amyloid and prion β-structures from secondary structure predictions

The supersecondary structure of amyloids and prions, proteins of intense clinical and biological interest, are difficult to determine by standard experimental or computational means. In addition, significant conformational heterogeneity is known or suspected to exist in many amyloid fibrils. Previous work has demonstrated that probability-based prediction of discrete β-strand pairs can offer insight into these structures. Here, we devise a system of energetic rules that can be used to dynamically assemble these discrete β-strand pairs into complete amyloid β-structures. The STITCHER algorithm progressively ‘stitches’ strand-pairs into full β-sheets based on a novel free-energy model, incorporating experimentally observed amino-acid side-chain stacking contributions, entropic estimates, and steric restrictions for amyloidal parallel β-sheet construction. A dynamic program computes the top 50 structures and returns both the highest scoring structure and a consensus structure taken by polling this list for common discrete elements. Putative structural heterogeneity can be inferred from sequence regions that compose poorly. Predictions show agreement with experimental models of Alzheimer's amyloid beta peptide and the Podospora anserina Het-s prion. Predictions of the HET-s homolog HET-S also reflect experimental observations of poor amyloid formation. We put forward predicted structures for the yeast prion Sup35, suggesting N-terminal structural stability enabled by tyrosine ladders, and C-terminal heterogeneity. Predictions for the Rnq1 prion and alpha-synuclein are also given, identifying a similar mix of homogenous and heterogeneous secondary structure elements. STITCHER provides novel insight into the energetic basis of amyloid structure, provides accurate structure predictions, and can help guide future experimental studies. Proteins 2011

Evaluation of in vitro penetration of fluticasone propionate from MP-AzeFlu and fluticasone propionate nasal spray through EpiAirway (TM) 606 tissues using vertical diffusion cells

Purpose: Most patients with allergic rhinitis (AR) have moderate-to-severe disease, requiring complete and prompt relief when symptoms occur. The time course of fluticasone propionate (FP) penetration into nasal tissues after intranasal administration is not well characterized. The goal of this proof-of-concept study was to evaluate the mucosal penetration of FP from fixed-combination FP-azelastine nasal spray (MP-AzeFlu) compared with an FP-only nasal spray in an in vitro, 3-dimensional human bronchial tissue model. Materials and Methods: Absorption of FP from MP-AzeFlu and FP nasal spray was modeled using EpiAirway (TM) 606 (MatTek Corporation; Ashland, MA, USA) tissue cultured in vertical diffusion cells. The dosing amount of MP-AzeFlu was optimized in a pilot study. Based on the results of the pilot study, 10 mu L of MP-AzeFlu (3.65 mu g; n = 8) and 10 mu L of FP nasal spray (5.00 mu g; n = 8) were evaluated for penetration of tissue. Tissue integrity was monitored with Lucifer yellow. FP in the receiving media was quantified for each sample using liquid chromatography with tandem mass spectrometry. Results: MP-AzeFlu and FP nasal spray were associated with similar FP accumulation profiles in the receiving media, but the permeability of FP was greater for MP-AzeFlu during hours 0 to 6, suggesting faster absorption for MP-AzeFlu. No indications of compromised tissue integrity were found in any of the tested cells. Conclusion: The higher and more rapid penetration of FP from MP-AzeFlu supports the use of MP-AzeFlu for patients with AR, particularly when prioritizing fast and pronounced symptom relief

Development of extinction imagers for the determination of atmospheric optical extinction: final report

The primary goals of this project for JTO and ONR (Grant N00014-07-1-1060) were to further develop Extinction Imagers for use in the ocean environment, and to extend the capabilities into the Short Wave IR (SWIR). Extinction Imaging is a method for determining the effective extinction coefficient over an extended path using a sensor at one end of the path. It uses calibrated imagers to acquire the relative radiance of a dark target near the other the end of the path and the horizon sky in the direction of the dark target. It is completely passive and thus covert, and the hardware is robust and relatively inexpensive. It uses rigorous equations, which determine the extinction coefficient from the measured apparent contrast of the radiance of the dark target with respect to the horizon sky. The project was very successful. We found that the ocean surface could readily be used as a dark target in red and SWIR wavelengths. Both the red and the SWIR measurement results were excellent for daytime. Comparisons with standard instruments, as well as uncertainty analysis, indicated that extinction imagers provide better measurements of the atmospheric extinction losses over extended paths than other methods of which we are aware. Our secondary goals were to address the night regime, and to address slanted paths above the horizontal. Regarding night, we found that the visible sensor acquired excellent data, but the ocean surface was not a good dark target in our wavelengths. Recommendations on the handling of night are given in the report. Regarding the lines of sight above the horizon, we developed a slant path algorithm that determines beam transmittance. It performed very well. Recommendations are made regarding integration of these techniques for military applications.Joint Technology Office via Office of Naval ResearchGrant N00014-07-1-106