Perfect bell nozzle parametric and optimization curves

Nozzle contour data for untruncated Bell nozzles with expansion area ratios to 6100 and a specific heat ratio of 1.2 are provided. Curves for optimization of nozzles for maximum thrust coefficient within a given length, surface area, or area ratio are included. The nozzles are two dimensional axisymmetric and calculations were performed using the method of characteristics. Drag due to wall friction was included in the final thrust coefficient

Compression creep of filamentary composites

Axial and transverse strain fields induced in composite laminates subjected to compressive creep loading were compared for several types of laminate layups. Unidirectional graphite/epoxy as well as multi-directional graphite/epoxy and graphite/PEEK layups were studied. Specimens with and without holes were tested. The specimens were subjected to compressive creep loading for a 10-hour period. In-plane displacements were measured using moire interferometry. A computer based data reduction scheme was developed which reduces the whole-field displacement fields obtained using moire to whole-field strain contour maps. Only slight viscoelastic response was observed in matrix-dominated laminates, except for one test in which catastrophic specimen failure occurred after a 16-hour period. In this case the specimen response was a complex combination of both viscoelastic and fracture mechanisms. No viscoelastic effects were observed for fiber-dominated laminates over the 10-hour creep time used. The experimental results for specimens with holes were compared with results obtained using a finite-element analysis. The comparison between experiment and theory was generally good. Overall strain distributions were very well predicted. The finite element analysis typically predicted slightly higher strain values at the edge of the hole, and slightly lower strain values at positions removed from the hole, than were observed experimentally. It is hypothesized that these discrepancies are due to nonlinear material behavior at the hole edge, which were not accounted for during the finite-element analysis

Theoretical study of Si+(2PJ)-RG complexes and transport of Si+(2PJ) in RG (RG = He – Ar)

We calculate accurate interatomic potentials for the interaction of a singly-charged silicon cation with a rare gas atom of helium, neon or argon. We employ the RCCSD(T) method, and basis sets of quadruple- and quintuple- quality; each point is counterpoise corrected and extrapolated to the basis set limit. We consider the lowest electronic state of the silicon atomic cation, Si+(2P), and calculate the interatomic potentials for the terms that arise from this: 2and 2+. We additionally calculate the interatomic potentials for the respective spin-orbit levels, and examine the effect on the spectroscopic parameters; we also derive effective ionic radii for C+ and Si+. Finally, we employ each set of potentials to calculate transport coefficients, and compare these to available data for Si+ in He

Mass production of volume phase holographic gratings for the VIRUS spectrograph array

The Visible Integral-field Replicable Unit Spectrograph (VIRUS) is a baseline array of 150 copies of a simple, fiber-fed integral field spectrograph that will be deployed on the Hobby-Eberly Telescope (HET). VIRUS is the first optical astronomical instrument to be replicated on an industrial scale, and represents a relatively inexpensive solution for carrying out large-area spectroscopic surveys, such as the HET Dark Energy Experiment (HETDEX). Each spectrograph contains a volume phase holographic (VPH) grating with a 138 mm diameter clear aperture as its dispersing element. The instrument utilizes the grating in first-order for 350-550 nm. Including witness samples, a suite of 170 VPH gratings has been mass produced for VIRUS. Here, we present the design of the VIRUS VPH gratings and a discussion of their mass production. We additionally present the design and functionality of a custom apparatus that has been used to rapidly test the first-order diffraction efficiency of the gratings for various discrete wavelengths within the VIRUS spectral range. This device has been used to perform both in-situ tests to monitor the effects of adjustments to the production prescription as well as to carry out the final acceptance tests of the gratings' diffraction efficiency. Finally, we present the as-built performance results for the entire suite of VPH gratings.Comment: 16 pages, 11 figures, 2 tables. To be published in Proc. SPIE, 2014, "Advances in Optical and Mechanical Technologies for Telescopes and Instrumentation", 9151-53. The work presented in this article follows from arXiv:1207:448

Local design optimization for composite transport fuselage crown panels

Composite transport fuselage crown panel design and manufacturing plans were optimized to have projected cost and weight savings of 18 percent and 45 percent, respectively. These savings are close to those quoted as overall NASA ACT program goals. Three local optimization tasks were found to influence the cost and weight of fuselage crown panels. This paper summarizes the effect of each task and describes in detail the task associated with a design cost model. Studies were performed to evaluate the relationship between manufacturing cost and design details. A design tool was developed to aid in these investigations. The development of the design tool included combining cost and performance constraints with a random search optimization algorithm. The resulting software was used in a series of optimization studies that evaluated the sensitivity of design variables, guidelines, criteria, and material selection on cost. The effect of blending adjacent design points in a full scale panel subjected to changing load distributions and local variations was shown to be important. Technical issues and directions for future work were identified

Amphotericin forms an extramembranous and fungicidal sterol sponge.

For over 50 years, amphotericin has remained the powerful but highly toxic last line of defense in treating life-threatening fungal infections in humans with minimal development of microbial resistance. Understanding how this small molecule kills yeast is thus critical for guiding development of derivatives with an improved therapeutic index and other resistance-refractory antimicrobial agents. In the widely accepted ion channel model for its mechanism of cytocidal action, amphotericin forms aggregates inside lipid bilayers that permeabilize and kill cells. In contrast, we report that amphotericin exists primarily in the form of large, extramembranous aggregates that kill yeast by extracting ergosterol from lipid bilayers. These findings reveal that extraction of a polyfunctional lipid underlies the resistance-refractory antimicrobial action of amphotericin and suggests a roadmap for separating its cytocidal and membrane-permeabilizing activities. This new mechanistic understanding is also guiding development of what are to our knowledge the first derivatives of amphotericin that kill yeast but not human cells

Interaction potentials, spectroscopy and transport properties of C+(2PJ) and C+(4PJ) with helium

We calculate accurate interatomic potentials for the interaction of a singly-charged carbon cation with a helium atom. We employ the RCCSD(T) method, and basis sets of quadruple-zeta and quintuple-zeta quality; each point is counterpoise corrected and extrapolated to the basis set limit. We consider the two lowest C+(2P) and C+(4P) electronic states of the carbon cation, and calculate the interatomic potentials for the terms that arise from these: 2-PI and 2-SIG+, and 4-PI and 4-SIG- , respectively. We additionally calculate the interatomic potentials for the respective spin-orbit levels, and examine the effect on the spectroscopic parameters. Finally, we employ each set of potentials to calculate transport coefficients, and compare these to available data. Critical comments are made in the cases where there are discrepancies between the calculated values and measured data

Dedicated Three-dimensional Breast Computed Tomography: Lesion Characteristic Perception by Radiologists

Objectives: To assess radiologist confidence in the characterization of suspicious breast lesions with a dedicated three-dimensional breast computed tomography (DBCT) system in comparison to diagnostic two-dimensional digital mammography (dxDM). Materials and Methods: Twenty women were recruited who were to undergo a breast biopsy for a Breast Imaging-Reporting and Data System (BI-RADS) 4 or 5 lesion evaluated with dxDM in this Institutional Review Board-approved study. The enrolled subjects underwent imaging of the breast(s) of concern using DBCT. Seven radiologists reviewed the cases. Each reader compared DBCT to the dxDM and was asked to specify the lesion type and BI-RADS score for each lesion and modality. They also compared lesion characteristics: Shape for masses or morphology for calcifications; and margins for masses or distribution for calcifications between the modalities using confidence scores (0-100). Results: Twenty-four biopsied lesions were included in this study: 17 (70.8%) masses and 7 (29.2%) calcifications. Eight (33.3%) lesions were malignant, and 16 (66.7%) were benign. Across all lesions, there was no significant difference in the margin/distribution (Δ = -0.99, P = 0.84) and shape/morphology (Δ = -0.10, P = 0.98) visualization confidence scores of DBCT in relation to dxDM. However, analysis by lesion type showed a statistically significant increase in reader shape (Δ =11.34, P = 0.013) and margin (Δ =9.93, P = 0.023) visualization confidence with DBCT versus dxDM for masses and significant decrease in reader morphology (Δ = -29.95, P = 0.001) and distribution (Δ = -28.62, P = 0.002) visualization confidence for calcifications. Conclusion: Reader confidence in the characterization of suspicious masses is significantly improved with DBCT, but reduced for calcifications. Further study is needed to determine whether this technology can be used for breast cancer screening

Surface waves in photonic crystal slabs

Photonic crystals with a finite size can support surface modes when appropriately terminated. We calculate the dispersion curves of surface modes for different terminations using the plane wave expansion method. These non-radiative surface modes can be excited with the help of attenuated total reflection technique. We did experiments and simulations to trace the surface band curve, both in good agreement with the numerical calculations