955 research outputs found
Aerodynamic performance investigation of advanced mechanical suppressor and ejector nozzle concepts for jet noise reduction
Advanced Supersonic Transport jet noise may be reduced to Federal Air Regulation limits if recommended refinements to a recently developed ejector shroud exhaust system are successfully carried out. A two-part program consisting of a design study and a subscale model wind tunnel test effort conducted to define an acoustically treated ejector shroud exhaust system for supersonic transport application is described. Coannular, 20-chute, and ejector shroud exhaust systems were evaluated. Program results were used in a mission analysis study to determine aircraft takeoff gross weight to perform a nominal design mission, under Federal Aviation Regulation (1969), Part 36, Stage 3 noise constraints. Mission trade study results confirmed that the ejector shroud was the best of the three exhaust systems studied with a significant takeoff gross weight advantage over the 20-chute suppressor nozzle which was the second best
The Concept of Photozymes: Short Peptides with Photoredox Catalytic Activity for Nucleophilic Additions to α-Phenyl Styrenes
Conventional photoredox catalytic additions of alcohols to olefins require additives, like thiophenol, to promote back electron transfer. The concept of âphotozymesâ assumes that forward and backward electron transfer steps in a photoredox catalytic cycle are controllable by substrate binding to photocatalytically active peptides. Accordingly, we synthesized a short tripeptide modified with 1,7-dicyano-perylene-3,4â:â9,10-tetracarboxylic acid bisimide as photoredox catalyst. This peptide undergoes an unconventional photoredox catalytic cycle with the radical anion and dianion of the perylene bisimide-peptide as intermediates. The photoredox catalytic reactions with α-phenyl styrenes as substrates require remarkably low catalyst loadings (0.5â
mol%) and give the methoxylation products in high yields. The concept of âphotozymesâ for photoredox catalysis has significant potential for other photocatalytic reactions, in particular with respect to enantioselective photocatalysis
Testing for Antiphospholipid Antibody (aPL) Specificities in Retrospective âNormalâ Cerebral Spinal Fluid (CSF)
Antiphospholipid antibodies (aPL) have been found in the blood of patients with systemic and
neurological disease. The rare reports of aPL in cerebral spinal fluid (CSF) have been limited mostly to
IgG and IgM anticardiolipin (aCL). Our published finding of IgA aPE in the CSF of a young stroke
victim prompted us to establish ânormalâ CSF aPL values for a panel of aPL, which included aCL,
antiphosphatidylserine (aPS), antiphosphatidylethanolamine (aPE) and antiphosphatidylcholine (aPC).
CSF samples were tested by ELISA for IgG, IgM and IgA aPL. In addition, the CSF samples were
tested for activity in the presence and absence of phospholipid (PL) binding plasma-proteins. A total of
24 data points were obtained for each CSF sample.We tested 59 CSF samples obtained from 59 patients
who were undergoing evaluation for systemic or neurologic diseases. All CSF samples had normal
protein, glucose and cell counts. Ten of the 59 CSF samples (17%) had elevated aPL optical density
(OD) values an order of magnitude higher than the other 49 CSF samples for one or more aPL
specificity and/or isotype. One CSF sample had both PL-binding protein dependent and independent
IgG aPE activity. Another CSF sample showed both IgG aPE and aPC reactivity. The remaining eight
CSF samples showed single aPL findings; IgG aPE (5), IgG aPC (1), IgG aCL (1) and IgM aPC (1).
Seven of 10 patients with elevated CSF values were females. As expected, most ânormalâ aPL OD
values were substantially lower in CSF than those we have reported in blood samples from volunteer
blood donors
Laser microscopy of tunneling magnetoresistance in manganite grain-boundary junctions
Using low-temperature scanning laser microscopy we directly image electric
transport in a magnetoresistive element, a manganite thin film intersected by a
grain boundary (GB). Imaging at variable temperature allows reconstruction and
comparison of the local resistance vs temperature for both, the manganite film
and the GB. Imaging at low temperature also shows that the GB switches between
different resistive states due to the formation and growth of magnetic domains
along the GB. We observe different types of domain wall growth; in most cases a
domain wall nucleates at one edge of the bridge and then proceeds towards the
other edge.Comment: 5 pages, 4 figures; submitted to Phys. Rev. Let
Unsupervised learning for cross-domain medical image synthesis using deformation invariant cycle consistency networks
Recently, the cycle-consistent generative adversarial networks (CycleGAN) has
been widely used for synthesis of multi-domain medical images. The
domain-specific nonlinear deformations captured by CycleGAN make the
synthesized images difficult to be used for some applications, for example,
generating pseudo-CT for PET-MR attenuation correction. This paper presents a
deformation-invariant CycleGAN (DicycleGAN) method using deformable
convolutional layers and new cycle-consistency losses. Its robustness dealing
with data that suffer from domain-specific nonlinear deformations has been
evaluated through comparison experiments performed on a multi-sequence brain MR
dataset and a multi-modality abdominal dataset. Our method has displayed its
ability to generate synthesized data that is aligned with the source while
maintaining a proper quality of signal compared to CycleGAN-generated data. The
proposed model also obtained comparable performance with CycleGAN when data
from the source and target domains are alignable through simple affine
transformations
Andreev bound states at a cuprate grain boundary junction: A lower bound for the upper critical field
We investigate in-plane quasiparticle tunneling across thin film grain
boundary junctions (GBJs) of the electron-doped cuprate
LaCeCuO in magnetic fields up to T, perpendicular to
the CuO layers. The differential conductance in the superconducting state
shows a zero bias conductance peak (ZBCP) due to zero energy surface Andreev
bound states. With increasing temperature , the ZBCP vanishes at the
critical temperature K if B=0, and at K for B=16 T. As
the ZBCP is related to the macroscopic phase coherence of the superconducting
state, we argue that the disappearance of the ZBCP at a field
must occur below the upper critical field of the superconductor. We
find T which is at least a factor of 2.5 higher than
previous estimates of .Comment: 4 pages, 4 figure
Complementary Photocatalytic Toolbox: Control of Intramolecular endo-versus exo-trig Cyclizations of α-Phenyl Olefins to Oxaheterocyclic Products
The regioselectivity of the intramolecular cyclization of bifunctional α-phenyl alkenes can be controlled simply by the choice of the organic chromophore as the photocatalyst. The central photoredox catalytic reaction in both cases is a nucleophilic addition of the hydroxy function to the olefin function of the substrates. N,N-(4-Diisobutylaminophenyl)phenothiazine catalyzes exo-trig cyclizations, whereas 1,7-dicyanoperylene-3,4,9,10-tetracarboxylic acid bisimides catalyze endo-trig additions to products with anti-Markovnikov regioselectivity. We preliminarily report the photoredox catalytic conversions of 11 representative substrates into 20 oxaheterocycles in order to demonstrate the similarity, but also the complementarity, of these two variants in this photoredox catalytic toolbox
Ponticulin plays a role in the positional stabilization of pseudopods
Ponticulin is a 17-kD glycoprotein that represents a major high affinity link between the plasma membrane and the cortical actin network of Dictyostelium. To assess the role of ponticulin in pseudopod extension and retraction, the motile behavior of two independently generated mutants lacking ponticulin was analyzed using computer-assisted two- and three-dimensional motion analysis systems. More than half of the lateral pseudopods formed off the substratum by ponticulin-minus cells slipped relative to the substratum during extension and retraction. In contrast, all pseudopods formed off the substratum by wild-type cells were positionally fixed in relation to the substratum. Ponticulin-minus cells also formed a greater proportion of both anterior and lateral pseudopods off the substratum and absorbed a greater proportion of lateral pseudopods into the uropod than wild-type cells. In a spatial gradient of cAMP, ponticulin-minus cells were less efficient in tracking the source of chemoattractant. Since ponticulin-minus cells extend and retract pseudopods with the same time course as wild-type cells, these behavioral defects in ponticulin-minus cells appear to be the consequence of pseudopod slippage. These results demonstrate that pseudopods formed off the substratum by wild-type cells are positionally fixed in relation to the substratum, that ponticulin is required for positional stabilization, and that the loss of ponticulin and the concomitant loss of positional stability of pseudopods correlate with a decrease in the efficiency of chemotaxis
VEGETATION FIRE FUELS MAPPING IN THE SAN DIEGO CITY CANYONS â A METHOD COMPARISON
Fire risk is a major threat to life, property and natural resources in southern California. Recent fire disasters occurred in autumn 2003 and 2007. Fire risk management deals with these hazards, input data are collected, analyzed and evaluated. One of the most important input data is the vegetation density in the endangered areas. Here we describe methods to map vegetation density forming five hazard classes. The main objective of this study is to explore the benefits of using remote sensed data for the accurate classification of vegetation in San Diego city canyons. Three very high resolution remote sensing data sets (< 1 m) were used in comparison: scanned color infrared film (CIR) airborne, digital multi-spectral airborne (ADS40) and digital multi-spectral satellite imagery (QuickBird). Different classification approaches (e.g. pixel-based, segment-based and knowledge-based) were tested and analyzed to separate the vegetation into five hazard classes. Accuracy assessment indicated low overall accuracies of 58 % on average. With regard to an optimized classification result in particular unsupervised and segment-based classification can be recommended. The overall accuracy for these two methods reached around 62 %. The use of specially selected reference areas for validation helped to increase the accuracies up to 81 %. Also a separating between three instead of five different hazard classes resulted in accuracies around 80 %. Furthermore it could be shown that all three data sets can be used for successful classification procedures. The resulting fire risk maps can help to reduce or prevent fire hazards. The maps are a basis for the brush management of the Fir
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