2,067 research outputs found
Model Tests of Jet Induced Lift Effects on a VTOL Aircraft in Hover
Lift loss and jet decay measurements on hovering vertical takeoff aircraft model
Roles of Free Electrons and H2O2 in the Optical Breakdown-Induced Photochemical Reduction of Aqueous [AuCl4]-
Free electrons and H2O2 formed in an optical breakdown plasma are found to directly control the kinetics of [AuCl4]− reduction to form Au nanoparticles (AuNPs) during femtosecond laser-assisted synthesis of AuNPs. The formation rates of both free electrons and H2O2 strongly depend on the energy and duration of the 800 nm laser pulses over the ranges of 10−2400 μJ and 30−1500 fs. By monitoring the conversion of [AuCl4]− to AuNPs using in situ UV−vis spectroscopy during laser irradiation, the first- and second-order rate constants in the autocatalytic rate law, k1 and k2, were extracted and compared to the computed free electron densities and experimentally measured H2O2 formation rates. For laser pulse energies of 600 μJ and lower at all pulse durations, the first-order rate constant, k1, was found to be directly proportional to the theoretically calculated plasma volume, in which the electron density exceeds the threshold value of 1.8 × 1020 cm−3. The second-order rate constant, k2, was found to correlate with the measured H2O2 formation rate at all pulse energies and durations, resulting in the empirical relationship k2 ≈ H2O20.5. We have demonstrated that the relative composition of free electrons and H2O2 in the optical breakdown plasma may be controlled by changing the pulse energy and duration, which may make it possible to tune the size and dispersity of AuNPs and other metal nanoparticle products synthesized with femtosecond laser-based methods
An investigation of shoreline change at Sandy Hook, New Jersey utilizing the Shoreline Modeling System
Radical Chemistry in a Femtosecond Laser Plasma: Photochemical Reduction of Ag+ in Liquid Ammonia Solution
Plasmas with dense concentrations of reactive species such as hydrated electrons and hydroxyl radicals are generated from focusing intense femtosecond laser pulses into aqueous media. These radical species can reduce metal ions such as Au3+ to form metal nanoparticles (NPs). However, the formation of H2O2 by the recombination of hydroxyl radicals inhibits the reduction of Ag+ through back-oxidation. This work has explored the control of hydroxyl radical chemistry in a femtosecond laser-generated plasma through the addition of liquid ammonia. The irradiation of liquid ammonia solutions resulted in a reaction between NH3 and OH·, forming peroxynitrite and ONOO−, and significantly reducing the amount of H2O2 generated. Varying the liquid ammonia concentration controlled the Ag+ reduction rate, forming 12.7 ± 4.9 nm silver nanoparticles at the optimal ammonia concentration. The photochemical mechanisms underlying peroxynitrite formation and Ag+ reduction are discussed
Noise characteristics of upper surface blown configurations: Analytical Studies
Noise and flow results of upper surface blown configurations were analyzed. The dominant noise source mechanisms were identified from experimental data. From far-field noise data for various geometric and operational parameters, an empirical noise prediction program was developed and evaluated by comparing predicted results with experimental data from other tests. USB aircraft compatibility studies were conducted using the described noise prediction and a cruise performance data base. A final design aircraft was selected and theory was developed for the noise from the trailing edge wake assuming it as a highly sheared layer
Chandra Observation of 3C 212: a New Look at the X-ray and UV Absorbers
The red quasar 3C 212 (z=1.049) is one of the most distant and most luminous
AGN which has shown evidence of an X-ray warm absorber. In order to further
investigate this unusual quasar, we used Chandra/ACIS-S to observe 3C 212 for
19.5 ksec, resulting in a net detection of ~4000 counts. The Chandra data
confirm the presence of an excess absorbing column N_H ~ 4 x 10^21 cm^-2 at the
quasar redshift, but we find no compelling evidence for a warm absorber. Using
both the Chandra and archival ROSAT PSPC data, we obtain very good fits for
both a partially covered neutral absorber and a low-ionization (U = 0.03)
photo-ionized absorber. In the ultraviolet, 3C 212 shows a strong associated
MgII absorber. Based on a moderate resolution (80 km/s) MMT spectrum we show
that the absorber is highly saturated and has a covering fraction less than
60%, implying that the absorber is truly intrinsic to the quasar.
Photo-ionization modeling of the MgII absorber yields a constraint on the
ionization parameter of U < 0.03, inconsistent with a warm UV/X-ray absorber.
In addition to our spectral analysis, we find evidence in the ACIS image data
for weak extended emission surrounding the quasar as well as emission
corresponding to the radio lobes at a distance of 5 arcsec from 3C 212. The
statistical significance of these features is low, but we briefly explore the
implications if the detections are valid.Comment: 8 pages, 6 figures, Accepted for publication in the Astrophysical
Journa
Generation of Nanomaterials by Reactive Laser Synthesis in Liquid
Nanomaterials with tailored structures and surface chemistry are in high demand, as these materials play increasingly important roles in biology, catalysis, energy storage, and manu- facturing. Their heightened demand has attracted attention towards the development of syn- thesis routes, particularly, laser-synthesis techniques. These efforts drove the refinement of laser ablation in liquid (LAL) and related methods over the past two decades, and have led to the emergence of reactive laser-synthesis techniques that exploit these methods’ character- istic, non-equilibrium conditions. Reactive laser-synthesis approaches foster unique chemical reactions that enable the formation of composite products like multimetallic nanoparticles, supported nanostructures, and complex minerals. This review will examine emerging reac- tive laser-synthesis methods in the context of established methods like LAL. The focus will be on the chemical reactions initiated within the laser plasma, with the goal of understanding how these reactions lead to the formation of unique nanomaterials. We will provide the first systematic review of laser reaction in liquid (LRL) in the literature, and bring a focus to the chemical reaction mechanisms in LAL and reactive-LAL techniques that have not yet been em- phasized in reviews. Discussion of the current challenges and future investigative opportunities into reactive laser-synthesis will impart guidance for researchers interested in designing reactive laser-synthesis approaches to novel nanomaterial production
Detection of KPC-2 in a clinical isolate of Proteus mirabilis and first reported description of carbapenemase resistance caused by a KPC β-lactamase in P. mirabilis
Evaluation of advanced lift concepts and fuel conservative short-haul aircraft, volume 1
The performance and economics of a twin-engine augmentor wing airplane were evaluated in two phases. Design aspects of the over-the-wing/internally blown flap hybrid, augmentor wing, and mechanical flap aircraft were investigated for 910 m. field length with parametric extension to other field lengths. Fuel savings achievable by application of advanced lift concepts to short-haul aircraft were evaluated and the effect of different field lengths, cruise requirements, and noise levels on fuel consumption and airplane economics at higher fuel prices were determined. Conclusions and recommendations are presented
Evaluation of advanced lift concepts and fuel conservative short-haul aircraft, volume 2
For abstract, see N75-20291
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