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Results for “ASPECT RATIO”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Direct synthesis of high-aspect ratio zeolite nanosheets

An example material includes a planar layer of MFI zeolite. The planar layer has a thickness in a range between 4 nm and 10 nm for at least 70% of a basal area of the planar layer. In one embodiment, the planar layer includes an embedded particle of an MFI zeolite.

Tsapatsis, Michael↗
DOE OSTI2015

A widefield fluorescence microscope with a linear image sensor for image cytometry of biospecimens: Considerations for image quality optimization

Linear image sensors have been widely used in numerous research and industry applications to provide continuous imaging of moving objects. Here, we present a widefield fluorescence microscope with a linear image sensor used to image translating objects for image cytometry. First, a calibration curve was characterized for a custom microfluidic chamber over a span of volumetric pump rates. Image data were also acquired using 15 μm fluorescent polystyrene spheres on a slide with a motorized translation stage in order to match linear translation speed with line exposure periods to preserve the image aspect ratio. Aspect ratios were then calculated after imaging to ensure quality control of image data. Fluorescent beads were imaged in suspension flowing through the microfluidics chamber being pumped by a mechanical syringe pump at 16 μl min{sup −1} with a line exposure period of 150 μs. The line period was selected to acquire images of fluorescent beads with a 40 dB signal-to-background ratio. A motorized translation stage was then used to transport conventional glass slides of stained cellular biospecimens. Whole blood collected from healthy volunteers was stained with 0.02% (w/v) proflavine hemisulfate was imaged to highlight leukocyte morphology with a 1.56 mm × 1.28 mm field of view (1540 ms total acquisition time). Oral squamous cells were also collected from healthy volunteers and stained with 0.01% (w/v) proflavine hemisulfate to demonstrate quantifiable subcellular features and an average nuclear to cytoplasmic ratio of 0.03 (n = 75), with a resolution of 0.31 μm pixels{sup −1}.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2016

Cost-Benefit Analysis of High-Strength Materials for Safety-Related Nuclear Reinforced Concrete Shear Walls

A numerical parametric investigation was conducted to determine the economic benefits of utilizing high-strength concrete and high-strength steel reinforcing bar (rebar) in reinforced concrete (RC) shear walls for nuclear power plant structures. Thick RC shear walls with low height-to-length aspect ratios (i.e., aspect ratios, h{sub w}/l{sub w}≤2.0, where h{sub w} is the wall height and l{sub w} is the wall length) are the most common lateral load resisting members in non-containment, safety-related nuclear structures. Typically, the walls are reinforced with multiple layers of overlapping, large-diameter vertical and horizontal rebar on each face. These heavily-reinforced walls provide large lateral stiffness and strength to prevent significant deformations and/or cracking that could compromise the integrity of the nuclear facility. However, this design adversely affects constructability as the rebar cages become highly congested. The time, labor, and materials required for this construction lead to high overall project costs. There has been a recent research thrust in the U.S. to allow high-strength rebar in non-nuclear building structures. While some of this research (e.g., steel properties, bond, anchorage) is applicable to RC structures in general, there are important differences specific to nuclear structures, such as much thicker walls (often controlled by radiation and thermal cycling), larger reinforcement ratios, and increased susceptibility to shear-controlled behavior (due to low aspect ratios). An important limiting factor for non-nuclear structures in seismic regions is the reduced deformation capacity of high-strength rebar as compared with normal-strength rebar used in current practice. Differences in seismic design philosophy lessen this limitation for nuclear structures (i.e., nuclear structures are designed more conservatively and allowed to undergo significantly smaller nonlinear displacements), making high-strength rebar a promising alternative to reinforcement currently permissible in the ACI 349-13 code requirements, which govern the design of nuclear safety-related concrete structures. To improve constructability and economy, this study investigates the benefits of using high-strength rebar [i.e., ASTM A615 Grade 550 (U.S. Grade 80); ASTM A1035 Grades 690 and 830 (U.S. Grades 100 and 120), where the grade indicates the specified yield strength of the steel in MPa (ksi)] together with high-strength concrete [compression strengths up to 138 MPa (20.0 ksi)] in RC nuclear shear walls. These strength ranges represent steel and concrete materials that are commercially available in the U.S. High-strength rebar can significantly reduce the required steel areas, thereby reducing material/fabrication costs, reducing rebar congestion (fewer/smaller bars and bar layers), and facilitating concrete consolidation and placement. Previous research on the use of high-strength rebar and/or high-strength concrete in nuclear RC structures does not exist in North America. A recent study assessed the potential of high-strength steel to reduce the rebar volume in non-nuclear building construction. In Japan, researchers investigated the use of high-strength materials in safety-related nuclear RC structures, but did not explore the economic benefits of these materials. To address this knowledge gap, the current paper describes a numerical parametric investigation on the potential cost savings of nuclear shear walls with high-strength rebar and/or concrete through comparisons against state-of-practice walls with normal-strength materials. Overall, the results demonstrate that significant economic benefits can be realized by implementing high-strength rebar and concrete in these structures. (authors)

36 MATERIALS SCIENCE↗
DOE OSTI2020

Hydrometeor Shape Variability in Snowfall as Retrieved from Polarimetric Radar Measurements

A polarimetric radar–based method for retrieving atmospheric ice particle shapes is applied to snowfall measurements by a scanning Ka-band radar deployed at Oliktok Point, Alaska (70.495°N, 149.883°W). The mean aspect ratio, which is defined by the hydrometeor minor-to-major dimension ratio for a spheroidal particle model, is retrieved as a particle shape parameter. The radar variables used for aspect ratio profile retrievals include reflectivity, differential reflectivity, and the copolar correlation coefficient. The retrievals indicate that hydrometeors with mean aspect ratios below 0.2–0.3 are usually present in regions with air temperatures warmer than approximately from –17° to –15°C, corresponding to a regime that has been shown to be favorable for growth of pristine ice crystals of planar habits. Radar reflectivities corresponding to the lowest mean aspect ratios are generally between –10 and 10 dBZ. For colder temperatures, mean aspect ratios are typically in a range between 0.3 and 0.8. There is a tendency for hydrometeor aspect ratios to increase as particles transition from altitudes in the temperature range from –17° to –15°C toward the ground. Furthermore, this increase is believed to result from aggregation and riming processes that cause particles to become more spherical and is associated with areas demonstrating differential reflectivity decreases with increasing reflectivity. Aspect ratio retrievals at the lowest altitudes are consistent with in situ measurements obtained using a surface-based multiangle snowflake camera. Pronounced gradients in particle aspect ratio profiles are observed at altitudes at which there is a change in the dominant hydrometeor species, as inferred by spectral measurements from a vertically pointing Doppler radar.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2015

Metallic nanoparticle shape and size effects on aluminum oxide-induced enhancement of exciton-plasmon coupling and quantum dot emission

We investigate the shape and size effects of gold metallic nanoparticles on the enhancement of exciton-plasmon coupling and emission of semiconductor quantum dots induced via the simultaneous impact of metal-oxide and plasmonic effects. This enhancement occurs when metallic nanoparticle arrays are separated from the quantum dots by a layered thin film consisting of a high index dielectric material (silicon) and aluminum oxide. Our results show that adding the aluminum oxide layer can increase the degree of polarization of quantum dot emission induced by metallic nanorods by nearly two times, when these nanorods have large aspect ratios. We show when the aspect ratio of these nanorods is reduced to half, the aluminum oxide loses its impact, leading to no improvement in the degree of polarization. These results suggest that a silicon/aluminum oxide layer can significantly enhance exciton-plasmon coupling when quantum dots are in the vicinity of metallic nanoantennas with high aspect ratios.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

A unified description of ordering in HCP Mg-RE alloys

High throughput first-principles calculations were employed to unravel the thermodynamic stability of two sets of hierarchical phases, β P ''' and β S ''' , in Mg-RE (rare-earth) alloys. The β P ''' orderings (with compositions greater than x RE =0.125) are predicted to form in the Mg-{La,Ce,Pr,Nd,Pm,Sm} binary alloys, thus explaining experimental observations of RE atoms arranged as hexagonal rings in these alloys. Mg-{Sc,Y,Tb,Dy,Ho,Er,Tm,Lu} alloys are predicted to form β S ' (x RE =0.125) precipitates without hexagonal ring arrangements. The calculated misfit strains are used to infer the qualitative shapes of the precipitates and their relative aspect ratios. High aspect-ratio precipitates may be formed using alloying elements that encourage the formation of β P ''' . The predictions in this study can be used to inform alloy design of precipitation strengthened magnesium alloys.

36 MATERIALS SCIENCE↗
DOE OSTI2019

A General Method for Estimating Bulk 2D Projections of Ice Particle Shape: Theory and Applications

The orientation of falling ice particles directly influences estimates of microphysical and radiative bulk quantities as well as in situ retrievals of size, shape, and mass. However, retrieval efforts and bulk calculations often incorporate very basic orientations or ignore these effects altogether. To address this deficiency, this study develops a general method for projecting bulk distributions of particle shape for arbitrary orientations. The Amoroso distribution provides the most general bulk aspect ratio distribution for gamma-distributed particle axis lengths. The parameters that govern the behavior of this aspect ratio distribution depend on the assumed relationship between mass, maximum dimension, and aspect ratio. Individual spheroidal geometry allows for eccentricity quantities to linearly map onto ellipse analogs, whereas aspect ratio quantities map nonlinearly. For particles viewed from their side, this analytic distinction leads to substantially larger errors in projected aspect ratio than for projected eccentricity. Distribution transformations using these mapping equations and numerical integration of projection kernels show that both truncation of size distributions and changes in Gaussian dispersion can alter the modality and shape of projection distributions. As a result, the projection process can more than triple the relative entropy between the spheroidal and projection distributions for commonly assumed model and orientation parameters. This shape uncertainty is maximized for distributions of highly eccentric particles and for particles like aggregates that are thought to fall with large canting-angle deviations. As a result, the methods used to report projected aspect ratios and the corresponding values should be questioned.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Evolution of ion-induced nanoparticle arrays on GaAs surfaces

We have examined the evolution of irradiation-induced Ga nanoparticle (NP) arrays on GaAs surfaces. Focused-ion-beam irradiation of pre-patterned GaAs surfaces induces monotonic increases in the NP volume and aspect ratio up to a saturation ion dose, independent of NP location within the array. Beyond the saturation ion dose, the NP volume continues to increase monotonically while the NP aspect ratio decreases monotonically. In addition, the NP volumes (aspect ratios) are highest (lowest) for the corner NPs. We discuss the relative influences of bulk and surface diffusion on the evolution of Ga NP arrays.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Gas breakdown in atmospheric pressure microgaps with a surface protrusion on the cathode

Gas breakdown in atmospheric pressure microgaps with a cathode surface protrusion is highly sensitive to the protrusion geometry. The breakdown voltage is identified when the discharge enters the subnormal region, according to voltage-current curves calculated by a two-dimensional fluid model. The effects of the protrusion size and the aspect ratio on the gap breakdown voltage are examined. It is found that the protrusion size can have a more profound effect on the breakdown voltage than the protrusion's aspect ratio. The breakdown voltage versus the protrusion aspect ratio will show a minimum value if the aspect ratio varies in a wider range. Shrinking the size of cathode protrusion can increase the breakdown voltage faster than enlarging the gap distance in the absence of a protrusion in the same scale. As a result, the effect of the aspect ratio of the microgap on the breakdown voltage is also presented.

42 ENGINEERING↗