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  • Organic Chemistry  (4,034)
  • Aerodynamics
  • Elasticity
  • 2010-2014  (591)
  • 1950-1954  (2,157)
  • 1935-1939  (1,981)
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  • 1
    Publication Date: 2021-05-19
    Description: Se elaboraron películas a partir de disoluciones a 3 % (m/v) de quitosana en ácido láctico a 1% (v/v), empleando glicerina, sorbitol o polietilenglicol como plastificante en concentraciones de 0,25 a 0,50 mL/g de quitosana. Se midieron el esfuerzo tensil, elongación, fuerza de ruptura, deformación y el espesor de las películas, con el objetivo de evaluar la influencia de la masa molar y concentración de plastificante sobre sus propiedades mecánicas. Se obtuvieron los modelos matemáticos que relacionan estos factores. Las películas con polietilenglicol, presentaron mayor esfuerzo tensil y fuerza de ruptura normalizada que las plastificadas con glicerina o sorbitol, pero resultaron menos elásticas y deformables, además, mientras mayor fue la concentración de plastificante, más elásticas resultaron las películas y menor fue el esfuerzo necesario para su rup- tura.
    Description: Films were obtained preparing 3% (w/v) chitosan solutions in 1% (v/v) lactic acid using glycerol, sorbitol or polyethylene glycol at 0.25 to 0.50 mL/g of polymer as plasticizers. Film thickness, tensile strength, force at break, deformation and elongation were measured in order to evaluate the effect of molar mass and plasticizers concentration on mechanical properties values. Mathematical models with these factors were proposed. Films with polyethylene glycol had higher tensile strength and normalized force at break than those which glycerol or sorbitol, but less elongation or normalized deformation. In addition, the films were more elastic and with lesser force at break with the increase of plasticizer concentration.
    Description: Published
    Description: plasticizer
    Description: edible film
    Keywords: Chitosan ; Biopolymers ; Elasticity ; Mechanical properties
    Repository Name: AquaDocs
    Type: Journal Contribution , Refereed , Article
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  • 2
    Publication Date: 2022-05-25
    Description: Author Posting. © Ecological Society of America, 2005. This article is posted here by permission of Ecological Society of America for personal use, not for redistribution. The definitive version was published in Ecological Applications 15 (2005): 1036–1052, doi:10.1890/04-0434.
    Description: Boltonia decurrens is an endangered plant restricted to the Illinois River Valley. Its complex life cycle has evolved in response to the dynamics of the historic flood regime, which has changed dramatically in the last century due to the construction of navigation dams and agricultural levees. To explore the effects of these changes, we developed deterministic and stochastic matrix population models of the demography of Boltonia. We used periodic matrix models to incorporate intra-annual seasonal variation. We estimated parameters as a function of the timing of spring flood recession (early or late) and of growing season precipitation (high or low). Late floods and/or low precipitation reduce population growth (λ). Early floods and high precipitation lead to explosive population growth. Elasticity analysis shows that changes in floods and precipitation alter the life history pathways responsible for population growth, from annual to biennial and eventually clonal pathways. We constructed and analyzed a stochastic model in which flood timing and precipitation vary independently, and we computed the stochastic growth rate (log λs) and the variance growth rate (σ2) as functions of the frequency of late floods and low precipitation. Using historical data on floods and rainfall over the last 100 years, we found that log λs has declined as a result of hydrological changes accompanying the regulation of the river. Stochastic elasticity analysis showed that over that time the contribution of annual life history pathways to log λs has declined as the contributions of biennial and clonal pathways have increased. Over the same time period, σ2 has increased, in agreement with observations of large fluctuations in local B. decurrens populations. Undoubtedly, many plant and animal species evolved in concert with dynamic habitats and are now threatened by anthropogenic changes in those dynamics. The data and analyses used in this study can be applied to management and development strategies to preserve other dynamic systems.
    Description: This work was supported by grants to M. Smith from NSF (DEB 9509763, DED 9321517), USACE, Illinois Groundwater Consortium and USFWS, and an EPA STAR grant (U- 91578101-2) to P. Mettler. H. Caswell also received support from NSF grant OCE-9983976 and EPA grant R-82908901, and a Maclaurin Fellowship from the New Zealand Institute of Mathematics and its Applications.
    Keywords: Boltonia decurrens ; Conservation ; Elasticity ; Floodplain ; Flood regime ; LTRE ; Matrix population model ; Periodic matrix model ; Stochastic elasticity ; Stochastic environment ; Stochastic matrix model ; Threatened species
    Repository Name: Woods Hole Open Access Server
    Type: Article
    Format: application/pdf
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  • 3
    Publication Date: 2022-05-25
    Description: Author Posting. © Ecological Society of America, 2005. This article is posted here by permission of Ecological Society of America for personal use, not for redistribution. The definitive version was published in Ecological Applications 15 (2005): 2097–2108, doi:10.1890/04-1762.
    Description: We investigated the effects of fire on population growth rate and invasive spread of the perennial tussock grass Molinia caerulea. During the last decades, this species has invaded heathland communities in Western Europe, replacing typical heathland species such as Calluna vulgaris and Erica tetralix. M. caerulea is considered a major threat to heathland conservation. In 1996, a large and unintended fire destroyed almost one-third of the Kalmthoutse Heide, a large heathland area in northern Belgium. To study the impact of this fire on the population dynamics and invasive spread of M. caerulea, permanent monitoring plots were established both in burned and unburned heathland. The fate of each M. caerulea individual in these plots was monitored over four years (1997–2000). Patterns of seed dispersal were inferred from a seed germination experiment using soil cores sampled one month after seed rain at different distances from seed-producing plants. Based on these measures, we calculated projected rates of spread for M. caerulea in burned and unburned heathland. Elasticity and sensitivity analyses were used to determine vital rates that contributed most to population growth rate, and invasion speed. Invasion speed was, on average, three times larger in burned compared to unburned plots. Dispersal distances on the other hand, were not significantly different between burned and unburned plots indicating that differences in invasive spread were mainly due to differences in demography. Elasticities for fecundity and growth of seedlings and juveniles were higher for burned than for unburned plots, whereas elasticities for survival were higher in unburned plots. Finally, a life table response experiment (LTRE) analysis revealed that the effect of fire was mainly contributed by increases in sexual reproduction (seed production and germination) and growth of seedlings and juveniles. Our results clearly showed increased invasive spread of M. caerulea after fire, and call for active management guidelines to prevent further encroachment of the species and to reduce the probability of large, accidental fires in the future. Mowing of resprouted plants before flowering is the obvious management tactic to halt massive invasive spread of the species after fire.
    Description: This work was supported by the Flemish Fund for Scientific Research (FWO) to HJ, the U.S. National Science foundation (DEB-0235692, OCE-0083976), and the U.S. Environmental Protection Agency (R-8290891) to MGN.
    Keywords: Disturbance ; Elasticity ; Fire ; Integrodifference equations ; Invasive spread ; LTRE ; Matrix population model ; Molinia caerulea ; Sensitivity
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 4
    Publication Date: 2022-05-26
    Description: Author Posting. © American Geophysical Union, 2007. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 112 (2007): B04106, doi:10.1029/2006JB004484.
    Description: The mechanical behavior of hydrate-bearing sediments subjected to large strains has relevance for the stability of the seafloor and submarine slopes, drilling and coring operations, and the analysis of certain small-strain properties of these sediments (for example, seismic velocities). This study reports on the results of comprehensive axial compression triaxial tests conducted at up to 1 MPa confining pressure on sand, crushed silt, precipitated silt, and clay specimens with closely controlled concentrations of synthetic hydrate. The results show that the stress-strain behavior of hydrate-bearing sediments is a complex function of particle size, confining pressure, and hydrate concentration. The mechanical properties of hydrate-bearing sediments at low hydrate concentration (probably 〈 40% of pore space) appear to be determined by stress-dependent soil stiffness and strength. At high hydrate concentrations (〉50% of pore space), the behavior becomes more independent of stress because the hydrates control both stiffness and strength and possibly the dilative tendency of sediments by effectively increasing interparticle coordination, cementing particles together, and filling the pore space. The cementation contribution to the shear strength of hydrate-bearing sediments decreases with increasing specific surface of soil minerals. The lower the effective confining stress, the greater the impact of hydrate formation on normalized strength.
    Description: This research was sponsored by a contract to C.R. and J.C.S. from the Joint Industry Project for Methane Hydrate, administered by ChevronTexaco with funding from award DE-FC26- 01NT41330 from DOE’s National Energy Technology Laboratory. The Goizueta Foundation at Georgia Tech also provided support for this work. The research was completed while C.R. was on assignment at and wholly supported by the National Science Foundation (NSF).
    Keywords: Gas hydrate ; Sediment strength ; Elasticity ; Mechanical behavior ; Stiffness
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 5
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    In:  Physics, Luxembourg, Conseil de l'Europe, vol. 7, no. B4, pp. 195-202, pp. B04202, (ISSN: 1340-4202)
    Publication Date: 1936
    Keywords: Source ; Dislocation ; Elasticity
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  • 6
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    In:  Phil. Mag., Bonn, Pergamon, vol. 7, no. 2, pp. 1017-1032, pp. B05S04, (ISBN: 0534351875, 2nd edition)
    Publication Date: 1937
    Keywords: Elasticity ; temperature
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  • 7
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    Springer
    In:  Professional Paper, Landolt Börnstein (6. Edition) III. Band: Astronomie und Geophysik, Berlin, Springer, vol. 7, no. XVI:, pp. 326-330, (ISBN: 3-540-23712-7)
    Publication Date: 1952
    Keywords: Elasticity ; Rock mechanics ; Physical properties of rocks
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  • 8
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    In:  J. Geophys. Res., Warszawa, Elsevier, vol. 57, no. 2, pp. 227-286, pp. L02307, (ISBN: 0-12-018847-3)
    Publication Date: 1952
    Keywords: Earth model, also for more shallow analyses ! ; Review article ; Elasticity ; Physical properties of rocks ; Velocity depth profile ; incompressibility ; shear ; modulus ; DENS ; JGR
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  • 9
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    In:  Bull. Am. Ass. Petroleum Geologists, Milano, Gustav Fischer, vol. 19, no. 3, pp. 1842, pp. L24306, (ISBN: 0534351875, 2nd edition)
    Publication Date: 1935
    Keywords: Elasticity ; Velocity analysis ; Laboratory measurements
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  • 10
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    In:  Science, Milano, Gustav Fischer, vol. 82, no. 3, pp. 52, pp. L24306, (ISBN: 0534351875, 2nd edition)
    Publication Date: 1935
    Keywords: Earth model, also for more shallow analyses ! ; Elasticity ; Geothermics ; Physical properties of rocks
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  • 11
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    In:  Trans., Am. Geophys. Union, Milano, California Institute of Technology Pasadena, vol. 32, no. 6, pp. 497-543, pp. L24306, (ISBN: 0534351875, 2nd edition)
    Publication Date: 1951
    Keywords: Elasticity ; Rock mechanics ; Rheology ; Fluids ; Earth model, also for more shallow analyses ! ; EOS ; BIBTEX? ; ENDNOTE?
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  • 12
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    In:  Proc. Koninkl. Ned. Akad. Wetenschap., Hannover, FU Berlin, vol. 42, no. 3, pp. 293, pp. 5091692, (ISBN: 0-12-018847-3)
    Publication Date: 1939
    Keywords: Stress ; Dislocation ; Rock mechanics ; Elasticity
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  • 13
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    Dover Publ.
    In:  Professional Paper, Internal constitution of the earth - Physic of the earth, Dover, 439 pp., Dover Publ., vol. 7, no. VIII:, pp. 167-177, (ISBN: 3-540-23712-7)
    Publication Date: 1951
    Keywords: Earth model, also for more shallow analyses ! ; Elasticity ; TIDES ; (The Earth's free) oscillations ; Geothermics
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  • 14
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    Dover Publ.
    In:  Professional Paper, Internal constitution of the earth - Physic of the earth, Dover, 439 pp., Dover Publ., vol. 7, no. XIV:, pp. 364-381, (ISBN: 3-540-23712-7)
    Publication Date: 1951
    Keywords: Elasticity ; Seismology
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  • 15
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    In:  Monthly Notices Roy. astr. Soc., Geophys. Suppl., Kunming, China, D. Reidel Publishing Company, vol. 3, no. 7, pp. 380-388, pp. L09303, (ISSN: 1340-4202)
    Publication Date: 1936
    Keywords: Crustal deformation (cf. Earthquake precursor: deformation or strain) ; Elasticity ; Dislocation
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  • 16
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    McGraw-Hill
    In:  New York, McGraw-Hill, vol. 7, no. XIV:, pp. 345-360, (ISBN 0-12-305355-2)
    Publication Date: 1939
    Keywords: Earth model, also for more shallow analyses ! ; Elasticity
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  • 17
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    McGraw-Hill
    In:  New York, McGraw-Hill, vol. 7, no. XV:, pp. 361-384, (ISBN 0-12-305355-2)
    Publication Date: 1939
    Keywords: Earth model, also for more shallow analyses ! ; Stress ; Strength ; Elasticity ; Inelastic
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  • 18
    Publication Date: 2010-05-07
    Description: The passive elasticity of muscle is largely governed by the I-band part of the giant muscle protein titin, a complex molecular spring composed of a series of individually folded immunoglobulin-like domains as well as largely unstructured unique sequences. These mechanical elements have distinct mechanical properties, and when combined, they provide the desired passive elastic properties of muscle, which are a unique combination of strength, extensibility and resilience. Single-molecule atomic force microscopy (AFM) studies demonstrated that the macroscopic behaviour of titin in intact myofibrils can be reconstituted by combining the mechanical properties of these mechanical elements measured at the single-molecule level. Here we report artificial elastomeric proteins that mimic the molecular architecture of titin through the combination of well-characterized protein domains GB1 and resilin. We show that these artificial elastomeric proteins can be photochemically crosslinked and cast into solid biomaterials. These biomaterials behave as rubber-like materials showing high resilience at low strain and as shock-absorber-like materials at high strain by effectively dissipating energy. These properties are comparable to the passive elastic properties of muscles within the physiological range of sarcomere length and so these materials represent a new muscle-mimetic biomaterial. The mechanical properties of these biomaterials can be fine-tuned by adjusting the composition of the elastomeric proteins, providing the opportunity to develop biomaterials that are mimetic of different types of muscles. We anticipate that these biomaterials will find applications in tissue engineering as scaffold and matrix for artificial muscles.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Lv, Shanshan -- Dudek, Daniel M -- Cao, Yi -- Balamurali, M M -- Gosline, John -- Li, Hongbin -- Canadian Institutes of Health Research/Canada -- England -- Nature. 2010 May 6;465(7294):69-73. doi: 10.1038/nature09024.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Chemistry, University of British Columbia, Vancouver, British Columbia V6T 1Z1, Canada.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/20445626" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Biocompatible Materials/chemical synthesis/*chemistry ; Biomechanical Phenomena ; Biomimetics/methods ; Biopolymers/*chemistry ; Connectin ; Drosophila melanogaster/genetics ; Elasticity ; Muscle Proteins/*chemistry ; Polyproteins/chemistry ; Protein Kinases/*chemistry ; Stress, Mechanical
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
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  • 19
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    Nature Publishing Group (NPG)
    Publication Date: 2010-05-07
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Chaikof, Elliot L -- England -- Nature. 2010 May 6;465(7294):44-5. doi: 10.1038/465044a.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/20445620" target="_blank"〉PubMed〈/a〉
    Keywords: Biomimetic Materials/*chemistry ; Connectin ; Elasticity ; Muscle Proteins/chemistry ; Polymers/*chemistry ; Protein Kinases/chemistry
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
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  • 20
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    American Association for the Advancement of Science (AAAS)
    Publication Date: 2010-08-28
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Bhatia, Mickie -- New York, N.Y. -- Science. 2010 Aug 27;329(5995):1024-5. doi: 10.1126/science.1194919.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Stem Cell and Cancer Research Institute, McMaster University, Hamilton, Ontario L8N 3Z5, Canada. mbhatia@mcmaster.ca〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/20798306" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Cell Culture Techniques/*methods ; Cell Differentiation ; Cell Division ; Cells, Cultured ; Elasticity ; Humans ; Hydrogels ; Mice ; Muscle Fibers, Skeletal/*cytology/physiology ; Myoblasts, Skeletal/cytology/physiology ; Regeneration ; Stem Cell Niche/*physiology ; Stem Cell Transplantation ; Stem Cells/*physiology
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 21
    Publication Date: 2010-08-07
    Description: Using optical trapping and fluorescence imaging techniques, we measured the step size and stiffness of single skeletal myosins interacting with actin filaments and arranged on myosin-rod cofilaments that approximate myosin mechanics during muscle contraction. Stiffness is dramatically lower for negatively compared to positively strained myosins, consistent with buckling of myosin's subfragment 2 rod domain. Low stiffness minimizes drag of negatively strained myosins during contraction at loaded conditions. Myosin's elastic portion is stretched during active force generation, reducing apparent step size with increasing load, even though the working stroke is approximately constant at about 8 nanometers. Taking account of the nonlinear nature of myosin elasticity is essential to relate myosin's internal structural changes to physiological force generation and filament sliding.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Kaya, Motoshi -- Higuchi, Hideo -- New York, N.Y. -- Science. 2010 Aug 6;329(5992):686-9. doi: 10.1126/science.1191484.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Physics, Graduate School of Science, University of Tokyo, 7-3-1 Hongo, Bunkyou-ku, Tokyo, 113-0033 Japan.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/20689017" target="_blank"〉PubMed〈/a〉
    Keywords: Actin Cytoskeleton/*physiology ; Actomyosin/chemistry/physiology ; Adenosine Diphosphate/metabolism ; Adenosine Triphosphate/metabolism ; Animals ; Compliance ; Elasticity ; Models, Biological ; *Muscle Contraction ; Muscle Fibers, Skeletal/chemistry/physiology ; Muscle, Skeletal ; Myosin Subfragments/physiology ; Myosins/chemistry/*physiology ; Quantum Dots ; Rabbits
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 22
    Publication Date: 2011-09-24
    Description: We studied the mechanical process of seed pods opening in Bauhinia variegate and found a chirality-creating mechanism, which turns an initially flat pod valve into a helix. We studied con fi gurations of strips cut from pod valve tissue and from composite elastic materials that mimic its structure. The experiments reveal various helical con fi gurations with sharp morphological transitions between them. Using the mathematical framework of "incompatible elasticity," we modeled the pod as a thin strip with a flat intrinsic metric and a saddle-like intrinsic curvature. Our theoretical analysis quantitatively predicts all observed con fi gurations, thus linking the pod's microscopic structure and macroscopic conformation. We suggest that this type of incompatible strip is likely to play a role in the self-assembly of chiral macromolecules and could be used for the engineering of synthetic self-shaping devices.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Armon, Shahaf -- Efrati, Efi -- Kupferman, Raz -- Sharon, Eran -- New York, N.Y. -- Science. 2011 Sep 23;333(6050):1726-30. doi: 10.1126/science.1203874.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Racah Institute of Physics, Hebrew University of Jerusalem, Jerusalem 91904, Israel.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/21940888" target="_blank"〉PubMed〈/a〉
    Keywords: Bauhinia/*anatomy & histology/physiology ; Biomimetic Materials ; Elasticity ; *Latex ; Mathematical Concepts ; Models, Biological ; Physical Phenomena ; Seeds/*anatomy & histology/*physiology
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 23
    Publication Date: 2011-03-18
    Description: Inelastic light scattering spectroscopy has, since its first discovery, been an indispensable tool in physical science for probing elementary excitations, such as phonons, magnons and plasmons in both bulk and nanoscale materials. In the quantum mechanical picture of inelastic light scattering, incident photons first excite a set of intermediate electronic states, which then generate crystal elementary excitations and radiate energy-shifted photons. The intermediate electronic excitations therefore have a crucial role as quantum pathways in inelastic light scattering, and this is exemplified by resonant Raman scattering and Raman interference. The ability to control these excitation pathways can open up new opportunities to probe, manipulate and utilize inelastic light scattering. Here we achieve excitation pathway control in graphene with electrostatic doping. Our study reveals quantum interference between different Raman pathways in graphene: when some of the pathways are blocked, the one-phonon Raman intensity does not diminish, as commonly expected, but increases dramatically. This discovery sheds new light on the understanding of resonance Raman scattering in graphene. In addition, we demonstrate hot-electron luminescence in graphene as the Fermi energy approaches half the laser excitation energy. This hot luminescence, which is another form of inelastic light scattering, results from excited-state relaxation channels that become available only in heavily doped graphene.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Chen, Chi-Fan -- Park, Cheol-Hwan -- Boudouris, Bryan W -- Horng, Jason -- Geng, Baisong -- Girit, Caglar -- Zettl, Alex -- Crommie, Michael F -- Segalman, Rachel A -- Louie, Steven G -- Wang, Feng -- England -- Nature. 2011 Mar 31;471(7340):617-20. doi: 10.1038/nature09866. Epub 2011 Mar 16.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Physics, University of California at Berkeley, Berkeley, California 94720, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/21412234" target="_blank"〉PubMed〈/a〉
    Keywords: Elasticity ; Electrons ; Graphite/*chemistry ; *Light ; Luminescence ; Photons ; *Quantum Theory ; *Scattering, Radiation ; Spectrum Analysis, Raman ; Static Electricity
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
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  • 24
    Publication Date: 2012-09-08
    Description: Hydrogels are used as scaffolds for tissue engineering, vehicles for drug delivery, actuators for optics and fluidics, and model extracellular matrices for biological studies. The scope of hydrogel applications, however, is often severely limited by their mechanical behaviour. Most hydrogels do not exhibit high stretchability; for example, an alginate hydrogel ruptures when stretched to about 1.2 times its original length. Some synthetic elastic hydrogels have achieved stretches in the range 10-20, but these values are markedly reduced in samples containing notches. Most hydrogels are brittle, with fracture energies of about 10 J m(-2) (ref. 8), as compared with approximately 1,000 J m(-2) for cartilage and approximately 10,000 J m(-2) for natural rubbers. Intense efforts are devoted to synthesizing hydrogels with improved mechanical properties; certain synthetic gels have reached fracture energies of 100-1,000 J m(-2) (refs 11, 14, 17). Here we report the synthesis of hydrogels from polymers forming ionically and covalently crosslinked networks. Although such gels contain approximately 90% water, they can be stretched beyond 20 times their initial length, and have fracture energies of approximately 9,000 J m(-2). Even for samples containing notches, a stretch of 17 is demonstrated. We attribute the gels' toughness to the synergy of two mechanisms: crack bridging by the network of covalent crosslinks, and hysteresis by unzipping the network of ionic crosslinks. Furthermore, the network of covalent crosslinks preserves the memory of the initial state, so that much of the large deformation is removed on unloading. The unzipped ionic crosslinks cause internal damage, which heals by re-zipping. These gels may serve as model systems to explore mechanisms of deformation and energy dissipation, and expand the scope of hydrogel applications.〈br /〉〈br /〉〈a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3642868/" target="_blank"〉〈img src="https://static.pubmed.gov/portal/portal3rc.fcgi/4089621/img/3977009" border="0"〉〈/a〉   〈a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3642868/" target="_blank"〉This paper as free author manuscript - peer-reviewed and accepted for publication〈/a〉〈br /〉〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Sun, Jeong-Yun -- Zhao, Xuanhe -- Illeperuma, Widusha R K -- Chaudhuri, Ovijit -- Oh, Kyu Hwan -- Mooney, David J -- Vlassak, Joost J -- Suo, Zhigang -- R01 DE013033/DE/NIDCR NIH HHS/ -- R37 DE013033/DE/NIDCR NIH HHS/ -- England -- Nature. 2012 Sep 6;489(7414):133-6. doi: 10.1038/nature11409.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/22955625" target="_blank"〉PubMed〈/a〉
    Keywords: Acrylic Resins/chemistry ; Alginates/chemistry ; Carbohydrate Sequence ; Elasticity ; Glucuronic Acid/chemistry ; Hexuronic Acids/chemistry ; Hydrogels/chemical synthesis/*chemistry ; Materials Testing ; Molecular Sequence Data ; Polymers/chemical synthesis/chemistry
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  • 25
    Publication Date: 2012-02-03
    Description: Natural materials are renowned for exquisite designs that optimize function, as illustrated by the elasticity of blood vessels, the toughness of bone and the protection offered by nacre. Particularly intriguing are spider silks, with studies having explored properties ranging from their protein sequence to the geometry of a web. This material system, highly adapted to meet a spider's many needs, has superior mechanical properties. In spite of much research into the molecular design underpinning the outstanding performance of silk fibres, and into the mechanical characteristics of web-like structures, it remains unknown how the mechanical characteristics of spider silk contribute to the integrity and performance of a spider web. Here we report web deformation experiments and simulations that identify the nonlinear response of silk threads to stress--involving softening at a yield point and substantial stiffening at large strain until failure--as being crucial to localize load-induced deformation and resulting in mechanically robust spider webs. Control simulations confirmed that a nonlinear stress response results in superior resistance to structural defects in the web compared to linear elastic or elastic-plastic (softening) material behaviour. We also show that under distributed loads, such as those exerted by wind, the stiff behaviour of silk under small deformation, before the yield point, is essential in maintaining the web's structural integrity. The superior performance of silk in webs is therefore not due merely to its exceptional ultimate strength and strain, but arises from the nonlinear response of silk threads to strain and their geometrical arrangement in a web.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Cranford, Steven W -- Tarakanova, Anna -- Pugno, Nicola M -- Buehler, Markus J -- England -- Nature. 2012 Feb 1;482(7383):72-6. doi: 10.1038/nature10739.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Laboratory for Atomistic and Molecular Mechanics, Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/22297972" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Biomechanical Phenomena ; Elasticity ; Hardness ; Models, Biological ; Silk/*chemistry ; *Spiders/physiology ; *Tensile Strength ; Wind
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  • 26
    Publication Date: 2011-04-29
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Huck, Wilhelm T S -- England -- Nature. 2011 Apr 28;472(7344):425-6. doi: 10.1038/472425a.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/21525922" target="_blank"〉PubMed〈/a〉
    Keywords: Biosensing Techniques ; Drug Delivery Systems ; Elasticity ; Elastomers/chemistry ; Molecular Conformation/radiation effects ; Pliability ; Polymers/*chemistry/*radiation effects ; Tissue Engineering
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  • 27
    Publication Date: 2011-08-05
    Description: The developing vertebrate gut tube forms a reproducible looped pattern as it grows into the body cavity. Here we use developmental experiments to eliminate alternative models and show that gut looping morphogenesis is driven by the homogeneous and isotropic forces that arise from the relative growth between the gut tube and the anchoring dorsal mesenteric sheet, tissues that grow at different rates. A simple physical mimic, using a differentially strained composite of a pliable rubber tube and a soft latex sheet is consistent with this mechanism and produces similar patterns. We devise a mathematical theory and a computational model for the number, size and shape of intestinal loops based solely on the measurable geometry, elasticity and relative growth of the tissues. The predictions of our theory are quantitatively consistent with observations of intestinal loops at different stages of development in the chick embryo. Our model also accounts for the qualitative and quantitative variation in the distinct gut looping patterns seen in a variety of species including quail, finch and mouse, illuminating how the simple macroscopic mechanics of differential growth drives the morphology of the developing gut.〈br /〉〈br /〉〈a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3335276/" target="_blank"〉〈img src="https://static.pubmed.gov/portal/portal3rc.fcgi/4089621/img/3977009" border="0"〉〈/a〉   〈a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3335276/" target="_blank"〉This paper as free author manuscript - peer-reviewed and accepted for publication〈/a〉〈br /〉〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Savin, Thierry -- Kurpios, Natasza A -- Shyer, Amy E -- Florescu, Patricia -- Liang, Haiyi -- Mahadevan, L -- Tabin, Clifford J -- R01 HD047360/HD/NICHD NIH HHS/ -- R01 HD047360-07/HD/NICHD NIH HHS/ -- England -- Nature. 2011 Aug 3;476(7358):57-62. doi: 10.1038/nature10277.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/21814276" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Biomechanical Phenomena ; Chick Embryo ; Computer Simulation ; Elasticity ; Female ; Finches/embryology ; Intestines/*anatomy & histology/*embryology ; Mesentery/anatomy & histology/embryology ; Mice ; *Models, Anatomic ; *Models, Biological ; Quail/embryology ; Rotation ; Rubber
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  • 28
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    Unknown
    Nature Publishing Group (NPG)
    Publication Date: 2011-02-19
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Hersen, Pascal -- Ladoux, Benoit -- England -- Nature. 2011 Feb 17;470(7334):340-1. doi: 10.1038/470340a.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/21331032" target="_blank"〉PubMed〈/a〉
    Keywords: Biomechanical Phenomena ; Cell Adhesion/physiology ; Cell Movement/*physiology ; Dictyostelium/*cytology ; Elasticity ; Single-Cell Analysis/*methods
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  • 29
    facet.materialart.
    Unknown
    Nature Publishing Group (NPG)
    Publication Date: 2013-01-16
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Jonietz, Erika -- England -- Nature. 2012 Nov 22;491(7425):S56-7.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/23320288" target="_blank"〉PubMed〈/a〉
    Keywords: Biomechanical Phenomena ; Biophysics/methods ; Cell Communication ; *Cell Physiological Processes ; Drug Resistance, Neoplasm ; Elasticity ; Hardness ; Humans ; Medical Oncology ; *Models, Biological ; Neoplasm Invasiveness ; Neoplasm Metastasis ; Neoplasms/diagnosis/drug therapy/genetics/*pathology ; Rheology ; Tumor Microenvironment ; Viscosity
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  • 30
    Publication Date: 2014-05-16
    Description: Groundwater use in California's San Joaquin Valley exceeds replenishment of the aquifer, leading to substantial diminution of this resource and rapid subsidence of the valley floor. The volume of groundwater lost over the past century and a half also represents a substantial reduction in mass and a large-scale unburdening of the lithosphere, with significant but unexplored potential impacts on crustal deformation and seismicity. Here we use vertical global positioning system measurements to show that a broad zone of rock uplift of up to 1-3 mm per year surrounds the southern San Joaquin Valley. The observed uplift matches well with predicted flexure from a simple elastic model of current rates of water-storage loss, most of which is caused by groundwater depletion. The height of the adjacent central Coast Ranges and the Sierra Nevada is strongly seasonal and peaks during the dry late summer and autumn, out of phase with uplift of the valley floor during wetter months. Our results suggest that long-term and late-summer flexural uplift of the Coast Ranges reduce the effective normal stress resolved on the San Andreas Fault. This process brings the fault closer to failure, thereby providing a viable mechanism for observed seasonality in microseismicity at Parkfield and potentially affecting long-term seismicity rates for fault systems adjacent to the valley. We also infer that the observed contemporary uplift of the southern Sierra Nevada previously attributed to tectonic or mantle-derived forces is partly a consequence of human-caused groundwater depletion.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Amos, Colin B -- Audet, Pascal -- Hammond, William C -- Burgmann, Roland -- Johanson, Ingrid A -- Blewitt, Geoffrey -- England -- Nature. 2014 May 22;509(7501):483-6. doi: 10.1038/nature13275. Epub 2014 May 14.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Geology Department, Western Washington University, Bellingham, Washington 98225-9080, USA. ; Department of Earth Sciences, University of Ottawa, Ottawa, Ontario K1N 6N5, Canada. ; Nevada Geodetic Laboratory, Nevada Bureau of Mines and Geology and Nevada Seismological Laboratory, University of Nevada, Reno, Nevada 89557, USA. ; 1] Berkeley Seismological Laboratory, University of California, Berkeley, California 94720-4760, USA [2] Department of Earth and Planetary Science, University of California, Berkeley, California 97720-4767, USA. ; Berkeley Seismological Laboratory, University of California, Berkeley, California 94720-4760, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/24828048" target="_blank"〉PubMed〈/a〉
    Keywords: *Altitude ; California ; Earthquakes/*statistics & numerical data ; Elasticity ; Environmental Monitoring ; Geographic Information Systems ; Groundwater/*analysis ; *Models, Theoretical ; Seasons ; Water Supply/analysis/*statistics & numerical data
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  • 31
    facet.materialart.
    Unknown
    American Association for the Advancement of Science (AAAS)
    Publication Date: 2010-03-27
    Description: Recent advances in mechanics and materials provide routes to integrated circuits that can offer the electrical properties of conventional, rigid wafer-based technologies but with the ability to be stretched, compressed, twisted, bent, and deformed into arbitrary shapes. Inorganic and organic electronic materials in microstructured and nanostructured forms, intimately integrated with elastomeric substrates, offer particularly attractive characteristics, with realistic pathways to sophisticated embodiments. Here, we review these strategies and describe applications of them in systems ranging from electronic eyeball cameras to deformable light-emitting displays. We conclude with some perspectives on routes to commercialization, new device opportunities, and remaining challenges for research.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Rogers, John A -- Someya, Takao -- Huang, Yonggang -- New York, N.Y. -- Science. 2010 Mar 26;327(5973):1603-7. doi: 10.1126/science.1182383.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign, 1304 West Green Street, Urbana, IL 61801, USA. jrogers@illinois.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/20339064" target="_blank"〉PubMed〈/a〉
    Keywords: Biocompatible Materials ; Diagnostic Equipment ; Elasticity ; Elastomers ; *Electrical Equipment and Supplies ; Equipment Design ; Humans ; Mechanical Phenomena ; Nanostructures ; *Semiconductors ; Therapeutics/instrumentation
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  • 32
    facet.materialart.
    Unknown
    American Association for the Advancement of Science (AAAS)
    Publication Date: 2011-09-24
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Forterre, Yoel -- Dumais, Jacques -- New York, N.Y. -- Science. 2011 Sep 23;333(6050):1715-6. doi: 10.1126/science.1210734.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉IUSTI, CNRS, Aix-Marseille Universite, 13453 Marseille Cedex 13, France. yoel.forterre@polytech.univ-mrs.fr〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/21940886" target="_blank"〉PubMed〈/a〉
    Keywords: Bauhinia/*anatomy & histology ; Biomimetic Materials ; Elasticity ; Seeds/*anatomy & histology
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  • 33
    Publication Date: 2012-03-17
    Description: Various plants and fungi have evolved ingenious devices to disperse their spores. One such mechanism is the cavitation-triggered catapult of fern sporangia. The spherical sporangia enclosing the spores are equipped with a row of 12 to 13 specialized cells, the annulus. When dehydrating, these cells induce a dramatic change of curvature in the sporangium, which is released abruptly after the cavitation of the annulus cells. The entire ejection process is reminiscent of human-made catapults with one notable exception: The sporangia lack the crossbar that arrests the catapult arm in its returning motion. We show that much of the sophistication and efficiency of the ejection mechanism lies in the two very different time scales associated with the annulus closure.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Noblin, X -- Rojas, N O -- Westbrook, J -- Llorens, C -- Argentina, M -- Dumais, J -- New York, N.Y. -- Science. 2012 Mar 16;335(6074):1322. doi: 10.1126/science.1215985.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Universite de Nice Sophia Antipolis (UNS), Laboratoire de Physique de la Matiere Condensee, CNRS UMR 7336, Nice, France. xavier.noblin@unice.fr〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/22422975" target="_blank"〉PubMed〈/a〉
    Keywords: Cell Shape ; Elasticity ; Polypodium/cytology/*physiology ; Sporangia/cytology/*physiology ; Spores/*physiology ; Water
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  • 34
    Publication Date: 2012-03-03
    Description: Although genetic control of morphogenesis is well established, elaboration of complex shapes requires changes in the mechanical properties of cells. In plants, the first visible sign of leaf formation is a bulge on the flank of the shoot apical meristem. Bulging results from local relaxation of cell walls, which causes them to yield to internal hydrostatic pressure. By manipulation of tissue tension in combination with quantitative live imaging and finite-element modeling, we found that the slow-growing area at the shoot tip is substantially strain-stiffened compared with surrounding fast-growing tissue. We propose that strain stiffening limits growth, restricts organ bulging, and contributes to the meristem's functional zonation. Thus, mechanical signals are not just passive readouts of gene action but feed back on morphogenesis.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Kierzkowski, Daniel -- Nakayama, Naomi -- Routier-Kierzkowska, Anne-Lise -- Weber, Alain -- Bayer, Emmanuelle -- Schorderet, Martine -- Reinhardt, Didier -- Kuhlemeier, Cris -- Smith, Richard S -- New York, N.Y. -- Science. 2012 Mar 2;335(6072):1096-9. doi: 10.1126/science.1213100.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Institute of Plant Sciences, University of Bern, Bern, Switzerland.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/22383847" target="_blank"〉PubMed〈/a〉
    Keywords: Cell Wall/physiology/ultrastructure ; Elasticity ; Hydrostatic Pressure ; Lycopersicon esculentum/cytology/*growth & development ; Meristem/cytology/*growth & development ; Models, Biological ; *Morphogenesis ; Osmolar Concentration ; Osmotic Pressure ; Plant Shoots/cytology/*growth & development
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  • 35
    Publication Date: 2014-04-05
    Description: When mounted on the skin, modern sensors, circuits, radios, and power supply systems have the potential to provide clinical-quality health monitoring capabilities for continuous use, beyond the confines of traditional hospital or laboratory facilities. The most well-developed component technologies are, however, broadly available only in hard, planar formats. As a result, existing options in system design are unable to effectively accommodate integration with the soft, textured, curvilinear, and time-dynamic surfaces of the skin. Here, we describe experimental and theoretical approaches for using ideas in soft microfluidics, structured adhesive surfaces, and controlled mechanical buckling to achieve ultralow modulus, highly stretchable systems that incorporate assemblies of high-modulus, rigid, state-of-the-art functional elements. The outcome is a thin, conformable device technology that can softly laminate onto the surface of the skin to enable advanced, multifunctional operation for physiological monitoring in a wireless mode.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Xu, Sheng -- Zhang, Yihui -- Jia, Lin -- Mathewson, Kyle E -- Jang, Kyung-In -- Kim, Jeonghyun -- Fu, Haoran -- Huang, Xian -- Chava, Pranav -- Wang, Renhan -- Bhole, Sanat -- Wang, Lizhe -- Na, Yoon Joo -- Guan, Yue -- Flavin, Matthew -- Han, Zheshen -- Huang, Yonggang -- Rogers, John A -- New York, N.Y. -- Science. 2014 Apr 4;344(6179):70-4. doi: 10.1126/science.1250169.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Materials Science and Engineering and Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/24700852" target="_blank"〉PubMed〈/a〉
    Keywords: Adult ; Elasticity ; Electrocardiography/instrumentation/methods ; Electrocardiography, Ambulatory/instrumentation/methods ; Electroencephalography/instrumentation/methods ; Electromyography/instrumentation/methods ; Electrooculography ; Equipment Design ; Humans ; Male ; Microfluidics/*instrumentation ; Monitoring, Ambulatory/*instrumentation/methods ; Monitoring, Physiologic/*instrumentation/methods ; Remote Sensing Technology ; Silicone Elastomers ; *Skin ; Wireless Technology ; Young Adult
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  • 36
    Publication Date: 2018-06-06
    Description: Motivation - Higher loading on Low-Pressure Turbine (LPT) airfoils: Reduce airfoil count, weight, cost. Increase efficiency, and Limited by suction side separation. Growing understanding of transition, separation, wake effects: Improved models. Take advantage of wakes. Higher lift airfoils in use. Further loading increases may require flow control: Passive: trips, dimples, etc. Active: plasma actuators, vortex generator jets (VGJs). Can increased loading offset higher losses on high lift airfoils. Objectives: Advance knowledge of boundary layer separation and transition under LPT conditions. Demonstrate, improve understanding of separation control with pulsed VGJs. Produce detailed experimental data base. Test and develop computational models.
    Keywords: Aerodynamics
    Type: Minnowbrook VI: 2009 Workshop on Flow Physics and Control for Internal and External Aerodynamics; 473-494; NASA/CP-2010-216112
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  • 37
    Publication Date: 2018-06-06
    Description: In assessing the results please recall that the Mach number regimes and model geometries differ considerably. Selection of the radius of curvature at the 10% chord location is consistent but arbitrary, although it does seem representative for most blades and gives a good fit for the results. Measured spanwise wavelengths of the periodic vortex arrays on blading are predicted well by the Kestin and Wood theory. If this behavior is at all common it could have implications for turbine aerodynamic and blade cooling design. The outcome is to establish that organized streamwise vorticity may occur more frequently on convex surfaces, such as turbine blade suction surfaces, than hitherto appreciated. Investigations and predictions of flow behavior should be extended to encompass that possibility.
    Keywords: Aerodynamics
    Type: Minnowbrook VI: 2009 Workshop on Flow Physics and Control for Internal and External Aerodynamics; 61-92; NASA/CP-2010-216112
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  • 38
    Publication Date: 2018-06-06
    Description: Active Flow Control increases the permissible aerodynamic loading. Curved surface near the trailing edge ("Coanda surface"): a) increases turning -〉 higher pressure ratio. b) controls boundary layer separation -〉 increased surge margin. Objective: Reduce the number of vanes or compressor stages. Constraints: 1. In a real compressor, the vane must still function entirely without blowing. 2. Maintain the flow exit angle of the reference stator despite the resulting increase in stator loading.
    Keywords: Aerodynamics
    Type: Minnowbrook VI: 2009 Workshop on Flow Physics and Control for Internal and External Aerodynamics; 417-434; NASA/CP-2010-216112
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  • 39
    facet.materialart.
    Unknown
    In:  CASI
    Publication Date: 2018-06-06
    Description: Effects of roughness in boundary layers have to be addressed. Until adverse pressure gradient effects are understood, roughness will not significantly drive design. Mechanisms responsible for separation not understood. Effects on Zero Pressure Gradient boundary layers (shear stress). Effects on separation in pressure gradient (prediction of separation). Effect on scalar transport (heat transfer) not understood. Model for skin friction needed in simulations - first grid point likely to be in buffer layer. Definition of roughness important for useful experiments. A lot of validation experiments will be needed. How to get to ks for roughness of engineering interest? - depends on wavelength height, etc. for engineering interest? Re-discovering the wheel should be avoided: existing knowledge (theoretical and experimental) should find its way into the engineering models. It is a task of the industry to filter out the existing information in the literature for results relevant to its application, being external or internal.
    Keywords: Aerodynamics
    Type: Minnowbrook VI: 2009 Workshop on Flow Physics and Control for Internal and External Aerodynamics; 589-600; NASA/CP-2010-216112
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  • 40
    Publication Date: 2018-06-28
    Description: Challenges to computational aerothermodynamic (CA) simulation and validation of hypersonic flow over planetary entry vehicles are discussed. Entry, descent, and landing (EDL) of high mass to Mars is a significant driver of new simulation requirements. These requirements include simulation of large deployable, flexible structures and interactions with reaction control system (RCS) and retro-thruster jets. Simulation of radiation and ablation coupled to the flow solver continues to be a high priority for planetary entry analyses, especially for return to Earth and outer planet missions. Three research areas addressing these challenges are emphasized. The first addresses the need to obtain accurate heating on unstructured tetrahedral grid systems to take advantage of flexibility in grid generation and grid adaptation. A multi-dimensional inviscid flux reconstruction algorithm is defined that is oriented with local flow topology as opposed to grid. The second addresses coupling of radiation and ablation to the hypersonic flow solver--flight- and ground-based data are used to provide limited validation of these multi-physics simulations. The third addresses the challenges of retro-propulsion simulation and the criticality of grid adaptation in this application. The evolution of CA to become a tool for innovation of EDL systems requires a successful resolution of these challenges.
    Keywords: Aerodynamics
    Type: Aerothermodynamic Design, Review on Ground Testing and CFD; 11-1 - 11-44; RTO-EN-AVT-186
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  • 41
    Publication Date: 2018-06-28
    Description: The Electric Arc Shock Tube (EAST) facility and the Hypervelocity Free Flight Aerodynamic Facility (HFFAF) at NASA Ames Research Center are described. These facilities have been in operation since the 1960s and have supported many NASA missions and technology development initiatives. The facilities have world-unique capabilities that enable experimental studies of real-gas aerothermal, gas dynamic, and kinetic phenomena of atmospheric entry.
    Keywords: Aerodynamics
    Type: Aerothermodynamic Design, Review on Ground Testing and CFD; 4-1 - 4-24; RTO-EN-AVT-186
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  • 42
    Publication Date: 2019-06-28
    Description: No abstract available
    Keywords: Aerodynamics
    Type: NACA-RM-SL54F28
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  • 43
    Publication Date: 2019-06-28
    Description: The transonic similarity rules have been applied to the correlation of experimental data for a series of 22 rectangular wings having symmetrical NACA 63A-series sections, aspect ratios from 1/2 to 6, and thicknesses from 2 to 10 percent. The data were obtained by use of the transonic bump technique over a Mach number range from 0.40 to 1.10, corresponding to a Reynolds number range from 1.25 to 2.05 million. The results show that it is possible to correlate experimental data throughout the subsonic, transonic, and moderate supersonic regimes by using the transonic similarity parameters in forms which are consistent with the Prandtl-Glauert rule of linearized theory. The multiple families of basic data curves for the various aspect ratios and thickness ratios have been summarized in single presentations involving only one geometric variable - the product of the aspect ratio and the l/3 power of the thickness ratio.
    Keywords: Aerodynamics
    Type: NACA-RM-A51L17b
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  • 44
    Publication Date: 2019-06-28
    Description: Experiments have been made at Stanford University to determine the performance characteristics of plane-wall, two-dimensional diffusers which were so proportioned as to insure reasonable approximation of two-dimensional flow. All of the diffusers had identical entrance cross sections and discharged directly into a large plenum chamber; the test program included wide variations of divergence angle and length. During all tests a dynamic pressure of 60 pounds per square foOt was maintained at the diffuser entrance and the boundary layer there was thin and fully turbulent. The most interesting flow characteristics observed were the occasional appearance of steady, unseparated, asymmetric flow - which was correlated with the boundary-layer coalescence - and the rapid deterioration of flow steadiness - which occurred as soon as the divergence angle for maximum static pressure recovery was exceeded. Pressure efficiency was found to be controlled almost exclusively by divergence angle, whereas static pressure recovery was markedly influenced by area ratio (or length) as well as divergence angle. Volumetric efficiency. diminished as area ratio increased, and at a greater rate with small lengths than with large ones. Large values of the static-pressure-recovery coefficient were attained only with long diffusers of large area ratio; under these conditions pressure efficiency was high and. volumetric efficiency low. Auxiliary tests with asymmetric diffusers demonstrated that longitudinal pressure gradient, rather than wall divergence angle, controlled flow separation. Others showed that the addition of even a short exit duct of uniform section augmented pressure recovery. Finally, it was found that the installation of a thin, central, longitudinal partition suppressed flow separation in short diffusers and thereby improved pressure recovery
    Keywords: Aerodynamics
    Type: NACA-TN-2888
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  • 45
    Publication Date: 2019-06-28
    Description: Recent developments in airfoil-testing methods and fundamental air-flow investigations, as applied to airfoils, are discussed. Preliminary test results, obtained under conditions relatively free from stream turbulence and other disturbances, are presented. Suitable airfoils and airfoil-design principles were developed to take advantage of the unusually extensive laminar boundary layers that may be maintained under the improved testing conditions. The results are of interest mainly in range of below 6,000,000.
    Keywords: Aerodynamics
    Type: NACA-WR-L-345
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  • 46
    facet.materialart.
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    In:  CASI
    Publication Date: 2019-06-28
    Description: Simultaneous air-flow photographs and pressure-distribution measurements have been made of the NACA 4412 airfoil at high speeds in order to determine the physical nature of the compressibility burble. The flow photographs were obtained by the Schlieren method and the pressures were simultaneously measured for 54 stations on the 5-inch-chord wing by means of a multiple-tube photographic manometer. Pressure-measurement results and typical Schlieren photographs are presented. The general nature of the phenomenon called the "compressibility burble" is shown by these experiments. The source of the increased drag is the compression shock that occurs, the excess drag being due to the conversion of a considerable amount of the air-stream kinetic energy into heat at the compression shock.
    Keywords: Aerodynamics
    Type: NACA-TN-543
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  • 47
    Publication Date: 2019-06-28
    Description: A method is presented for the estimation of the subsonic-flight-speed characteristics of sharp-lip inlets applicable to supersonic aircraft. The analysis, based on a simple momentum balance consideration, permits the computation of inlet pressure recovery - mass-flow relations and additive-drag coefficients for forward velocities from zero to the speed of sound. The penalties for operation of a sharp-lip inlet at velocity ratios other than 1.0 may be severe; at lower velocity ratios an additive drag is incurred that is not cancelled by lip suction, while at higher velocity ratios, unavoidable losses in inlet total pressure will result. In particular, at the take-off condition, the total pressure and the mass flow for a choked inlet are only 79 percent of the values ideally attainable with a rounded lip. Experimental data obtained at zero speed with a sharp-lip supersonic inlet model were in substantial agreement with the theoretical results.
    Keywords: Aerodynamics
    Type: NACA-TN-3004
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  • 48
    Publication Date: 2019-06-28
    Description: Wake development behind circular cylinders at Reynolds numbers from 40 to 10,000 was investigated in a low-speed wind tunnel. Standard hotwire techniques were used to study the velocity fluctuations. The Reynolds number range of periodic vortex shedding is divided into two distinct subranges. At R = 40 to 150, called the stable range, regular vortex streets are formed and no turbulent motion is developed. The range R = 150 to 300 is a transition range to a regime called the irregular range, in which turbulent velocity fluctuations accompany the periodic formation of vortices. The turbulence is initiated by laminar-turbulent transition in the free layers which spring from the separation points on the cylinder. This transition first occurs in the range R = 150 to 300. Spectrum and statistical measurements were made to study the velocity fluctuations. In the stable range the vortices decay by viscous diffusion. In the irregular range the diffusion is turbulent and the wake becomes fully turbulent in 40 to 50 diameters downstream. It was found that in the stable range the vortex street has a periodic spanwise structure. The dependence of shedding frequency on velocity was successfully used to measure flow velocity. Measurements in the wake of a ring showed that an annular vortex street is developed.
    Keywords: Aerodynamics
    Type: NACA-TN-2913
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  • 49
    Publication Date: 2019-06-28
    Description: A supersonic inlet with supersonic deceleration of the flow entirely outside of the inlet is considered. A particular arrangement with fixed geometry having a central body with a circular annular intake is analyzed, and it is shown theoretically that this arrangement gives high pressure recovery for a large range of Mach number and mass flow and therefore is practical for use on supersonic airplanes and missiles. For some Mach numbers the drag coefficient for this type of inlet is larger than the drag coefficient for the type of inlet with supersonic compression entirely inside, but the pressure recovery is larger for all flight conditions. The differences in drag can be eliminated for the design Mach number. Experimental results confirm the results of the theoretical analysis and show that pressure recoveries of 95 percent for Mach numbers of 1.33 and 1.52, 92 percent for a Mach number of 1.72, and 86 percent for a Mach number of 2.10 are possible, with the configurations considered. If the mass flow decreases, the total drag coefficient increases gradually and the pressure recovery does not change appreciably. The results of this work were first presented in a classified document issued in 1946.
    Keywords: Aerodynamics
    Type: NACA-TN-2286
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  • 50
    Publication Date: 2019-06-28
    Description: The hypersonic similarity law as derived by Tsien has been investigated by comparing the pressure distributions along bodies of revolution at zero angle of attack. In making these comparisons, particular attention was given to determining the limits of Mach number and fineness ratio for which the similarity law applies. For the purpose of this investigation, pressure distributions determined by the method of characteristics for ogive cylinders for values of Mach numbers and fineness ratios varying from 1.5 to 12 were compared. Pressures on various cones and on cone cylinders were also compared in this study. The pressure distributions presented demonstrate that the hypersonic similarity law is applicable over a wider range of values of Mach numbers and fineness ratios than might be expected from the assumptions made in the derivation. This is significant since within the range of applicability of the law a single pressure distribution exists for all similarly shaped bodies for which the ratio of free-stream Mach number to fineness ratio is constant. Charts are presented for rapid determination of pressure distributions over ogive cylinders for any combination of Mach number and fineness ratio within defined limits.
    Keywords: Aerodynamics
    Type: NACA-TN-2250
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  • 51
    Publication Date: 2019-06-28
    Description: No abstract available
    Keywords: Aerodynamics
    Type: NACA-TN-2211
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  • 52
    Publication Date: 2018-06-06
    Description: Time varying control of CL is necessary for integrating AFC and Flight Control (Biasing allows for +/- changes in lift) Time delays associated with actuation are long (APPROX.5.8 c/U) and must be included in controllers. Convolution of input signal with single pulse kernel gives reasonable prediction of lift response.
    Keywords: Aerodynamics
    Type: Minnowbrook VI: 2009 Workshop on Flow Physics and Control for Internal and External Aerodynamics; 363-374; NASA/CP-2010-216112
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  • 53
    Publication Date: 2018-06-06
    Description: DNS is a powerful tool with high potential for investigating unsteady heat transfer and fluid flow phenomena, in particular for cases involving transition to turbulence and/or large coherent structures. - DNS of idealized configurations related to turbomachinery components is already possible. - For more realistic configurations and the inclusion of more effects, reduction of computational cost is key issue (e.g., hybrid methods). - Approach pursued here: Embedded DNS ( segregated coupling of DNS with LES and/or RANS). - Embedded DNS is an enabling technology for many studies. - Pre-transitional heat transfer and trailing-edge cutback film-cooling are good candidates for (embedded) DNS studies.
    Keywords: Aerodynamics
    Type: Minnowbrook VI: 2009 Workshop on Flow Physics and Control for Internal and External Aerodynamics; 93-116; NASA/CP-2010-216112
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  • 54
    Publication Date: 2018-06-06
    Description: Exploiting instabilities rather than forcing the flow is advantageous. Simple 2D concepts may not always work. Nonlinear effects may result in first order effect. Interaction between spanwise and streamwise vortices may have a paramount effect on the mean flow, but this interaction may not always be beneficial.
    Keywords: Aerodynamics
    Type: Minnowbrook VI: 2009 Workshop on Flow Physics and Control for Internal and External Aerodynamics; 1-36; NASA/CP-2010-216112
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  • 55
    Publication Date: 2018-06-06
    Description: Broad Flow Control Issues: a) Understanding flow physics. b) Specific control objective(s). c) Actuation. d) Sensors. e) Integrated active flow control system. f) Development of design tools (CFD, reduced order models, controller design, understanding and utilizing instabilities and other mechanisms, e.g., streamwise vorticity).
    Keywords: Aerodynamics
    Type: Minnowbrook VI: 2009 Workshop on Flow Physics and Control for Internal and External Aerodynamics; 585-587; NASA/CP-2010-216112
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  • 56
    Publication Date: 2018-06-06
    Description: To develop New Flow Control Techniques: a) Knowledge of the Flow Physics with and without control. b) How does Flow Control Effect Flow Physics (What Works to Optimize the Design?). c) Energy or Work Efficiency of the Control Technique (Cost - Risk - Benefit Analysis). d) Supportability, e.g. (size of equipment, computational power, power supply) (Allows Designer to include Flow Control in Plans).
    Keywords: Aerodynamics
    Type: Minnowbrook VI: 2009 Workshop on Flow Physics and Control for Internal and External Aerodynamics; 349-361; NASA/CP-2010-216112
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  • 57
    facet.materialart.
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    In:  CASI
    Publication Date: 2018-06-06
    Description: Issues & Topics Discussed: a) Aviation Week reported shortfall In LPT efficiency due to the application of "high lift airfoils". b) Progress in the design technologies in LPTs during the last 20 years: 1) Application of RANS based CFD codes. 2) Integration of recent experimental data and modeling of LPT airfoil specific flows into design methods. c) Opportunities to further enhance LPT efficiency for commercial aviation and military transport application and to impact emissions, noise, weight & cost.
    Keywords: Aerodynamics
    Type: Minnowbrook VI: 2009 Workshop on Flow Physics and Control for Internal and External Aerodynamics; 601-604; NASA/CP-2010-216112
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  • 58
    Publication Date: 2018-06-06
    Description: The main objective is to develop effective control strategies for separation control of an airfoil with a single hinge flap. The specific objectives are: Develop an active control architecture for flow control around an airfoil with flap. Design, fabricate, a wind tunnel test of a high lift wing (with flap) with integrated actuators and sensors. Design, development and fabrication of synthetic jet actuators. Develop appropriate control strategy for application to the airfoil. Wind tunnel testing of the high lift wing at various angles of attack and flap positions with closed loop control.
    Keywords: Aerodynamics
    Type: Minnowbrook VI: 2009 Workshop on Flow Physics and Control for Internal and External Aerodynamics; 151-180; NASA/CP-2010-216112
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  • 59
    Publication Date: 2018-06-06
    Description: New ideas are forthcoming to break existing bottlenecks in using CFD during design. CAD-based automated grid generation. Multi-disciplinary use of embedded, overset grids to eliminate complex gridding problems. Use of time-averaged detached-eddy simulations as norm instead of "steady" RANS to include effects of self-excited unsteadiness. Combined GPU/Core parallel computing to provide over an order of magnitude increase in performance/price ratio. Gas-turbine applications are shown here but these ideas can be used for other Air Force, Navy, and NASA applications.
    Keywords: Aerodynamics
    Type: Minnowbrook VI: 2009 Workshop on Flow Physics and Control for Internal and External Aerodynamics; 43-60; NASA/CP-2010-216112
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  • 60
    Publication Date: 2018-06-06
    Description: We finally go back to the four swirl cases and see how the flow responds to either forcing m = -1 or m = -2. On the left we see the flow forced at m = -1 We see that the PVC locks onto the applied forcing also for lower swirl number causing this high TKE at the jet center. The amplification of this instability causes VB to occur at a lower swirl number. The opposite can be seen when forcing the flow at m=-2 which is basically growing in the outer shear layer causing VB to move downstream . There is no energy at the center of the vortex showing that the precessing has been damped. The mean flow is most altered at the swirl numbers were VB is unstable.
    Keywords: Aerodynamics
    Type: Minnowbrook VI: 2009 Workshop on Flow Physics and Control for Internal and External Aerodynamics; 557-583; NASA/CP-2010-216112
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  • 61
    Publication Date: 2018-06-06
    Description: Effects of variable-frequency forcing. Relation to linear theory. Effects of three-dimensional forcing. Relation between instability mechanisms. Future work includes open-loop control and feedback control.
    Keywords: Aerodynamics
    Type: Minnowbrook VI: 2009 Workshop on Flow Physics and Control for Internal and External Aerodynamics; 531-556; NASA/CP-2010-216112
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  • 62
    facet.materialart.
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    In:  CASI
    Publication Date: 2018-06-06
    Description: The details: a) Need stable numerical methods; b) Round off error can be considerable; c) Not convinced modes are correct for incompressible flow. Nonetheless, can derive compact and accurate reduced-order models. Can be used to generate actuator models or full flow-field models
    Keywords: Aerodynamics
    Type: Minnowbrook VI: 2009 Workshop on Flow Physics and Control for Internal and External Aerodynamics; 495-507; NASA/CP-2010-216112
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  • 63
    facet.materialart.
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    In:  CASI
    Publication Date: 2018-06-06
    Description: Let s start with the report - as you know - when we are talking about flow control it is a multi-disciplinary type of work. So it involves many people and disciplines. This group first discussed the important issues associated with flow control. As you start doing flow control what are the issues to which you really have to start paying attention? That is the first part I am going to present. Then in the second part I will present some challenges - problems that we should really be looking at. So as far as the issues - if you want to control a flow, you really need to understand the flow physics, because anything that you do comes from the flow physics. The design of the controllers, your decisions on the actuators, sensors, reduced order modeling and all of that, would be helped if you understand flow physics. And you have to have a specific objective - what exactly are you controlling? Are you trying to reduce drag, eliminate separation, reduce noise, enhance mixing? So you have to have very specific control objectives. From all the talks we have seen here actuation is extremely important and it is very problem specific. It depends on what problem you are dealing with so you have to design and build actuators for that specific problem. Sensors obviously are very important, especially when you are dealing with feedback control. Consensus was that when you dealing with flow control, you must take an integrated approach; from the beginning you have to take into account every aspect of it and even maybe to modify your experiment, your geometry, to go along with the actuation, sensors and control models. Development of tools is very important in this multi-disciplinary problem. The tools include CFD, reduced order modeling, controller design, understanding and utilizing the instabilities of the flow, etc. So, in order to have success in flow control, we really need to develop these tools.
    Keywords: Aerodynamics
    Type: Minnowbrook VI: 2009 Workshop on Flow Physics and Control for Internal and External Aerodynamics; 623-638; NASA/CP-2010-216112
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  • 64
    Publication Date: 2018-06-06
    Description: HPT blade unsteadiness in the presence of a downstream vane consistent with contra-rotation is characterized by strong interaction at the first harmonic of downstream vane passing. E An existing stage-and-one-half transonic turbine rig design was used as a baseline to investigate means of reducing such a blade-vane interaction. E Methods assessed included: Aerodynamic shaping of HPT blades 3D stacking of the downstream vane Steady pressure-side blowing E Of the methods assessed, a combination of vane bowing and steady pressure-side blowing produced the most favorable result. E Transonic turbine experiments are planned to assess predictive accuracy for the baseline turbine and any design improvements.
    Keywords: Aerodynamics
    Type: Minnowbrook VI: 2009 Workshop on Flow Physics and Control for Internal and External Aerodynamics; 399-416; NASA/CP-2010-216112
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  • 65
    Publication Date: 2018-06-06
    Description: Objectives: Measure the flow structure and turbulence within a Naval, axial waterjet pump. Create a database for benchmarking and validation of parallel computational efforts. Address flow and turbulence modeling issues that are unique to this complex environment. Measure and model flow phenomena affecting cavitation within the pump and its effect on pump performance. This presentation focuses on cavitation phenomena and associated flow structure in the tip region of a rotor blade.
    Keywords: Aerodynamics
    Type: Minnowbrook VI: 2009 Workshop on Flow Physics and Control for Internal and External Aerodynamics; 117-133; NASA/CP-2010-216112
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  • 66
    Publication Date: 2018-06-06
    Description: Structural skeleton of high Reynolds number flow gives insight into smooth and rough walls. (modeling implications not yet clear) Dynamic roughness as a model of "designer" roughness: a) Impose length scale(s) and dominant frequency. b) Irregular roughness well-represented by first "few" POD modes (Christensen, 2009). Experiments and simple model demonstrate: a) Harmonics associated with forcing (and w) important. b) Change to the mean profile (skin friction).
    Keywords: Aerodynamics
    Type: Minnowbrook VI: 2009 Workshop on Flow Physics and Control for Internal and External Aerodynamics; 259-271; NASA/CP-2010-216112
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  • 67
    Publication Date: 2018-06-06
    Description: Methodology similar to that used for our closed-loop control of Separation over NACA 0012 Airfoil (Pinier et al, AIAA Journal 2007) Synthetic Jet Actuators, Miniature Pressure Transducers Split POD with and without Actuations Flow state estimation from Pressure signature
    Keywords: Aerodynamics
    Type: Minnowbrook VI: 2009 Workshop on Flow Physics and Control for Internal and External Aerodynamics; 509-529; NASA/CP-2010-216112
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  • 68
    Publication Date: 2018-06-06
    Description: In order to phase lock the flow at the desired shedding cycle, particularly at Phi,best, We designed a feedback compensator. (Even though the open-loop forcing at Wf below Wn can lead to phase-locked limit cycles with a high average lift,) This feedback controller resulted in the phase-locked limit cycles that the open-loop control could not achieve for alpha=30 and 40 Particularly for alpha=40, the feedback was able to stabilize the limit cycle that was not stable with any of the open-loop periodic forcing. This results in stable phase-locked limit cycles for a larger range of forcing frequencies than the open-loop control. Also, it was shown that the feedback achieved the high-lift unsteady flow states that open-loop control could not sustain even after the states have been achieved for a long period of time.
    Keywords: Aerodynamics
    Type: Minnowbrook VI: 2009 Workshop on Flow Physics and Control for Internal and External Aerodynamics; 181-204; NASA/CP-2010-216112
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  • 69
    facet.materialart.
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    In:  CASI
    Publication Date: 2018-06-06
    Description: Open loop edge blowing was demonstrated as an effective method for reducing the broad band and tonal components of the fluctuating surface pressure in open cavities. Closed loop has been successfully applied to low Mach number open cavities. Need to push actuators that are viable for closed loop control in bandwidth and output. Need a better understanding of the effects of control on the flow through detailed measurements so better actuation strategies can be developed.
    Keywords: Aerodynamics
    Type: Minnowbrook VI: 2009 Workshop on Flow Physics and Control for Internal and External Aerodynamics; 289-303; NASA/CP-2010-216112
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  • 70
    Publication Date: 2018-06-06
    Description: Active flow control is often used to manipulate flow instabilities to achieve a desired goal (e.g. prevent separation, enhance mixing, reduce noise, etc.). Instability frequencies normally scale with flow velocity scale and inversely with flow length scale (U/l). In a laboratory setting for such flow experiments, U is high, but l is low, resulting in high instability frequency. In addition, high momentum and high background noise & turbulence in the flow necessitate high amplitude actuation. Developing a high amplitude and high frequency actuator is a major challenge. Ironically, these requirements ease up in application (but other issues arise).
    Keywords: Aerodynamics
    Type: Minnowbrook VI: 2009 Workshop on Flow Physics and Control for Internal and External Aerodynamics; 135-150; NASA/CP-2010-216112
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  • 71
    Publication Date: 2018-06-06
    Description: Four examples of flow control: 1) Passive control of LP turbine blades (Laminar separation control). 2) Aspiration of a conventional axial compressor blade (Turbulent separation control). 3) Compressor blade designed for aspiration (Turbulent separation control). 4.Control of intakes in crosswinds (Turbulent separation control).
    Keywords: Aerodynamics
    Type: Minnowbrook VI: 2009 Workshop on Flow Physics and Control for Internal and External Aerodynamics; 435-472; NASA/CP-2010-216112
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  • 72
    Publication Date: 2018-06-06
    Description: Evaluate the efficacy of Microjets Can we eliminate/minimize flow separation? Is the flow unsteadiness reduced? Guidelines for an active control Search for an appropriate sensor. Examine for means to develop a flow model for identifying the state of flow over the surface Guidelines toward future development of a Simple and Robust control methodology
    Keywords: Aerodynamics
    Type: Minnowbrook VI: 2009 Workshop on Flow Physics and Control for Internal and External Aerodynamics; 375-398; NASA/CP-2010-216112
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  • 73
    facet.materialart.
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    In:  CASI
    Publication Date: 2018-06-06
    Description: Environmental issues are a key driver. The need for better mechanisms to enable discipline hopping/crossover (materials (MEMS), control, fluids). Better sensors and actuators and better communication for these to be developed. Better understanding of the needs of the turbomachinery industry, especially in identifying where flow control can be beneficial (e.g., variable intake geometry). Challenge for flow control to be fail-safe, or to be developed for non-critical control gains (e.g., noise). more detailed information on stage through-flow behaviour (with/without control) increased use of laser interrogation (PIV, PTV, MTV).
    Keywords: Aerodynamics
    Type: Minnowbrook VI: 2009 Workshop on Flow Physics and Control for Internal and External Aerodynamics; 605-621; NASA/CP-2010-216112
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  • 74
    Publication Date: 2018-06-06
    Description: Three existing and two new excitation magnitude scaling options for active separation control at Reynolds numbers below one Million. The physical background for the scaling options was discussed and their relevance was evaluated using two different sets of experimental data. For F+ approx. 1, 2D excitation: a) The traditional VR and C(mu) - do not scale the data. b) Only the Re*C(mu) is valid. This conclusion is also limited for positive lift increment.. For F+ 〉 10, 3D excitation, the Re corrected C(mu), the St corrected velocity ratio and the vorticity flux coefficient, all scale the amplitudes equally well. Therefore, the Reynolds weighted C(mu) is the preferred choice, relevant to both excitation modes. Incidence also considered, using Ue from local Cp.
    Keywords: Aerodynamics
    Type: Minnowbrook VI: 2009 Workshop on Flow Physics and Control for Internal and External Aerodynamics; 305-347; NASA/CP-2010-216112
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  • 75
    Publication Date: 2019-06-28
    Description: The performance of NACA 65-series compressor blade section in cascade has been investigated systematically in a low-speed cascade tunnel. Porous test-section side walls and for high-pressure-rise conditions, porous flexible end walls were employed to establish conditions closely simulating two-dimensional flow. Blade sections of design lift coefficients from 0 to 2.7 were tested over the usable angle-of-attack range for various combinations of inlet-flow angle. A sufficient number of combinations were tested to permit interpolation and extrapolation of the data to all conditions within the usual range of application. The results of this investigation indicate a continuous variation of blade-section performance as the major cascade parameters, blade camber, inlet angle, and solidity were varied over the test range. Summary curves of the results have been prepared to enable compressor designers to select the proper blade camber and angle of attack when the compressor velocity diagram and desired solidity have been determined.
    Keywords: Aerodynamics
    Type: NACA-TR-1368 , NACA-RM-L51G31
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  • 76
    Publication Date: 2019-06-27
    Description: An investigation of the isothermal wake-flow characteristics of several flame-holder shapes was carried out in a 4- by 4-inch flow chamber. The effects of flame-holder-shape changes on the characteristics of the Karman vortices and thus on the recirculation zones to which experimenters have related the combustion process were obtained for several flame holders. The results may furnish a basis of correlation, of combustion efficiency and stability for similarly shaped flame holders in combustion studies. Values of the spacing ratio-(ratio of lateral spacing to longitudinal spacing of vortices] obtained for the various shapes approximated the theoretical value of 0.36 given by the Karman stability analysis. Variations in vortex strength of more than 200 percent and in frequency of more than 60 percent were accomplished by varying flame-holder shape. A maximum increase in the recirculation parameter of 56 percent over that for a conventional V-gutter was also obtained. Varying flameholder shape and size enables the designer to select many schedules of variations in vortex strength and frequency- not obtainable by changing size only and may make it possible to approach theoretical maximum vortex strength for any given frequency.
    Keywords: Aerodynamics
    Type: NACA-RM-E51K07 , E-2403
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  • 77
    Publication Date: 2019-07-27
    Description: In response to the fourth AIAA CFD Drag Prediction Workshop (DPW-IV), the NASA Common Research Model (CRM) wing-body and wing-body-tail configurations are analyzed using the Reynolds-averaged Navier-Stokes (RANS) flow solvers CFL3D and OVERFLOW. Two families of structured, overset grids are built for DPW-IV. Grid Family 1 (GF1) consists of a coarse (7.2 million), medium (16.9 million), fine (56.5 million), and extra-fine (189.4 million) mesh. Grid Family 2 (GF2) is an extension of the first and includes a superfine (714.2 million) and an ultra-fine (2.4 billion) mesh. The medium grid anchors both families with an established build process for accurate cruise drag prediction studies. This base mesh is coarsened and enhanced to form a set of parametrically equivalent grids that increase in size by a factor of roughly 3.4 from one level to the next denser level. Both CFL3D and OVERFLOW are run on GF1 using a consistent numerical approach. Additional OVERFLOW runs are made to study effects of differencing scheme and turbulence model on GF1 and to obtain results for GF2. All CFD results are post-processed using Richardson extrapolation, and approximate grid-converged values of drag are compared. The medium grid is also used to compute a trimmed drag polar for both codes.
    Keywords: Aerodynamics
    Type: AIAA Paper 2010-4219 , NF1676L-10897 , 28th AIAA Applied Aerodynamics Conference; 28 Jun. 1 Jul. 2010; Chicago, IL; United States
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  • 78
    Publication Date: 2019-07-27
    Description: An Aeroelastic Prediction Workshop (AePW) was held in April 2012 using three aeroelasticity case study wind tunnel tests for assessing the capabilities of various codes in making aeroelasticity predictions. One of these case studies was known as the HIRENASD model that was tested in the European Transonic Wind Tunnel (ETW). This paper summarizes the development of a standardized enhanced analytical HIRENASD structural model for use in the AePW effort. The modifications to the HIRENASD finite element model were validated by comparing modal frequencies, evaluating modal assurance criteria, comparing leading edge, trailing edge and twist of the wing with experiment and by performing steady and unsteady CFD analyses for one of the test conditions on the same grid, and identical processing of results.
    Keywords: Aerodynamics
    Type: AIAA Paper 2013-1801 , NF1676L-15290 , 54th AIAA/ASME/ASCE/AHS/ASC, Structures, Structural Dynamics, and Materials Conference; 8-1` Apr. 2013; Boston, MA; United States
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  • 79
    Publication Date: 2019-07-27
    Description: A source-term model that simulates the effects of vortex generators was implemented into the Wind-US Navier-Stokes code. The source term added to the Navier-Stokes equations simulates the lift force that would result from a vane-type vortex generator in the flowfield. The implementation is user-friendly, requiring the user to specify only three quantities for each desired vortex generator: the range of grid points over which the force is to be applied and the planform area and angle of incidence of the physical vane. The model behavior was evaluated for subsonic flow in a rectangular duct with a single vane vortex generator, subsonic flow in an S-duct with 22 corotating vortex generators, and supersonic flow in a rectangular duct with a counter-rotating vortex-generator pair. The model was also used to successfully simulate microramps in supersonic flow by treating each microramp as a pair of vanes with opposite angles of incidence. The validation results indicate that the source-term vortex-generator model provides a useful tool for screening vortex-generator configurations and gives comparable results to solutions computed using gridded vanes.
    Keywords: Aerodynamics
    Type: AIAA Paper 2010-0032 , E-17922 , AIAA Journal; 49; 4; 748-759|48th AIAA Aerospace Sciences Meeting; 4?7 Jan. 2010; Orlando, FL; United States
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  • 80
    Publication Date: 2019-07-27
    Description: Nonlinear parabolized stability equations and secondary instability analyses are used to provide a computational assessment of the potential use of the discrete roughness elements (DRE) technology for extending swept-wing natural laminar flow at chord Reynolds numbers relevant to transport aircraft. Computations performed for the boundary layer on a natural laminar flow airfoil with a leading-edge sweep angle of 34.6deg, free-stream Mach number of 0.75 and chord Reynolds numbers of 17 x 10(exp 6), 24 x 10(exp 6) and 30 x 10(exp 6) suggest that DRE could delay laminar-turbulent transition by about 20% when transition is caused by stationary crossflow disturbances. Computations show that the introduction of small wavelength stationary crossflow disturbances (i.e., DRE) also suppresses the growth of most amplified traveling crossflow disturbances.
    Keywords: Aerodynamics
    Type: AIAA Paper 2013-0412 , NF1676L-14855 , 51st AIAA Aerospace Sciences Meeting; 7-110 Jan. 2013; Grapevine, TX; United States
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  • 81
    Publication Date: 2019-06-27
    Description: An investigation has been conducted in the Langley 20-foot free spinning tunnel to study the relative behavior in descent of a number of homogeneous balsa bodies of revolution simulating anti-personnel bombs with a small cylindrical exploding device suspended approximately 10 feet below the bomb. The bodies of revolution included hemispherical, near-hemispherical, and near-paraboloid shapes. The ordinates of one near-paraboloid shape were specified by the Office of the Chief of Ordnance, U. S. Army. The behavior of the various bodies without the cylinder was also investigated. The results of the investigation indicated that several of the bodies descended vertically with their longitudinal axis, suspension line, and small cylinder in a vertical attitude,. However, the body, the ordinates of which had been specified by the Office of the Chief of Ordnance, U. S. Army, oscillated considerably from a vertical attitude while descending and therefore appeared unsuitable for its intended use. The behavior of this body became satisfactory when its center of gravity was moved well forward from its original position. In general, the results indicated that the descent characteristics of the bodies of revolution become more favorable as their shapes approached that of a hemisphere.
    Keywords: Aerodynamics
    Type: NACA-RM-SL51L13
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  • 82
    Publication Date: 2019-07-13
    Description: Separated flow over a bluff body is analyzed via large eddy simulations. The turbulent flow around a square cylinder features a variety of complex flow phenomena such as highly unsteady vortical structures, reverse flow in the near wall region, and wake turbulence. The formation of spanwise vortices is often times artificially suppressed in computations by either insufficient depth or a coarse spanwise resolution. As the resolution is refined and the domain extended, the artificial turbulent energy exchange between spanwise and streamwise turbulence is eliminated within the wake region. A parametric study is performed highlighting the effects of spanwise vortices where the spanwise computational domain's resolution and depth are varied. For Re=22,000, the mean and turbulent statistics computed from the numerical large eddy simulations (NLES) are in good agreement with experimental data. Von-Karman shedding is observed in the wake of the cylinder. Mesh independence is illustrated by comparing a mesh resolution of 2 million to 16 million. Sensitivities to time stepping were minimized and sampling frequency sensitivities were nonpresent. While increasing the spanwise depth and resolution can be costly, this practice was found to be necessary to eliminating the artificial turbulent energy exchange.
    Keywords: Aerodynamics
    Type: AIAA Paper 2014-2089 , E-663992 , AIAA Fluid Dynamics Conference; Jun 16, 2014 - Jun 20, 2014; Atlanta, GA; United States
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  • 83
    Publication Date: 2019-07-13
    Description: Fundamental research for sonic boom reduction is needed to quantify the interaction of shock waves generated from the aircraft wing or tail surfaces with the nozzle exhaust plume. Aft body shock waves that interact with the exhaust plume contribute to the near-field pressure signature of a vehicle. The plume and shock interaction was studied using computational fluid dynamics and compared with experimental data from a coaxial convergent-divergent nozzle flow in an open jet facility. A simple diamond-shaped wedge was used to generate the shock in the outer flow to study its impact on the inner jet flow. Results show that the compression from the wedge deflects the nozzle plume and shocks form on the opposite plume boundary. The sonic boom pressure signature of the nozzle exhaust plume was modified by the presence of the wedge. Both the experimental results and computational predictions show changes in plume deflection.
    Keywords: Aerodynamics
    Type: E-663895 , AIAA SciTech 2014; Jan 13, 2014 - Jan 17, 2014; National Harbor, MD; United States
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  • 84
    Publication Date: 2019-07-13
    Description: We discuss thrust measurements of Dielectric Barrier Discharge (DBD) plasma actuators devices used for aerodynamic active flow control. After a review of our experience with conventional thrust measurement and significant non-repeatability of the results, we devised a suspended actuator test setup, and now present a methodology of thrust measurements with decreased uncertainty. The methodology consists of frequency scans at constant voltages. The procedure consists of increasing the frequency in a step-wise fashion from several Hz to the maximum frequency of several kHz, followed by frequency decrease back down to the start frequency of several Hz. This sequence is performed first at the highest voltage of interest, then repeated at lower voltages. The data in the descending frequency direction is more consistent and selected for reporting. Sample results show strong dependence of thrust on humidity which also affects the consistency and fluctuations of the measurements. We also observed negative values of thrust or "anti-thrust", at low frequencies between 4 Hz and up to 64 Hz. The anti-thrust is proportional to the mean-squared voltage and is frequency independent. Departures from the parabolic anti-thrust curve are correlated with appearance of visible plasma discharges. We propose the anti-thrust hypothesis. It states that the measured thrust is a sum of plasma thrust and anti-thrust, and assumes that the anti-thrust exists at all frequencies and voltages. The anti-thrust depends on actuator geometry and materials and on the test installation. It enables the separation of the plasma thrust from the measured total thrust. This approach enables more meaningful comparisons between actuators at different installations and laboratories. The dependence on test installation was validated by surrounding the actuator with a large diameter, grounded, metal sleeve.
    Keywords: Aerodynamics
    Type: AIAA Paper 2014-0486 , E-18857-1 , AIAA SciTech 2014; Jan 13, 2014 - Jan 17, 2014; National Harbor, MD; United States
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  • 85
    Publication Date: 2019-07-13
    Description: Determining the adverse aerodynamic effects due to ice accretion often relies on dry-air wind-tunnel testing of artificial, or simulated, ice shapes. Recent developments in ice accretion documentation methods have yielded a laser-scanning capability that can measure highly three-dimensional features of ice accreted in icing wind tunnels. The objective of this paper was to evaluate the aerodynamic accuracy of ice-accretion simulations generated from laser-scan data. Ice-accretion tests were conducted in the NASA Icing Research Tunnel using an 18-inch chord, 2-D straight wing with NACA 23012 airfoil section. For six ice accretion cases, a 3-D laser scan was performed to document the ice geometry prior to the molding process. Aerodynamic performance testing was conducted at the University of Illinois low-speed wind tunnel at a Reynolds number of 1.8 x 10(exp 6) and a Mach number of 0.18 with an 18-inch chord NACA 23012 airfoil model that was designed to accommodate the artificial ice shapes. The ice-accretion molds were used to fabricate one set of artificial ice shapes from polyurethane castings. The laser-scan data were used to fabricate another set of artificial ice shapes using rapid prototype manufacturing such as stereolithography. The iced-airfoil results with both sets of artificial ice shapes were compared to evaluate the aerodynamic simulation accuracy of the laser-scan data. For four of the six ice-accretion cases, there was excellent agreement in the iced-airfoil aerodynamic performance between the casting and laser-scan based simulations. For example, typical differences in iced-airfoil maximum lift coefficient were less than 3% with corresponding differences in stall angle of approximately one degree or less. The aerodynamic simulation accuracy reported in this paper has demonstrated the combined accuracy of the laser-scan and rapid-prototype manufacturing approach to simulating ice accretion for a NACA 23012 airfoil. For several of the ice-accretion cases tested, the aerodynamics is known to depend upon the small, three dimensional features of the ice. These data show that the laser-scan and rapid-prototype manufacturing approach is capable of replicating these ice features within the reported accuracies of the laser-scan measurement and rapid-prototyping method; thus providing a new capability for high-fidelity ice-accretion documentation and artificial ice-shape fabrication for icing research.
    Keywords: Aerodynamics
    Type: GRC-E-DAA-TN14961 , AIAA Atmospheric and Space Environments Conference; Jun 16, 2014 - Jun 20, 2014; Atlanta, GA; United States
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  • 86
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    In:  CASI
    Publication Date: 2019-07-13
    Description: Reliable prediction of contra-rotating open rotor (CROR) noise is an essential element of any strategy for the development of low-noise open rotor propulsion systems that can meet both the community noise regulations and the cabin noise limits. Since CROR noise spectra typically exhibits a preponderance of tones, significant efforts have been directed towards predicting their tone spectra. To that end, there has been an ongoing effort at NASA to assess various in-house open rotor tone noise prediction tools using a benchmark CROR blade set for which significant aerodynamic and acoustic data had been acquired in wind tunnel tests. In the work presented here, the focus is on the near-field noise of the benchmark open rotor blade set at the cruise condition. Using an analytical CROR tone noise model with input from high-fidelity aerodynamic simulations, detailed tone noise spectral predictions have been generated and compared with the experimental data. Comparisons indicate that the theoretical predictions are in good agreement with the data, especially for the dominant CROR tones and their overall sound pressure level. The results also indicate that, whereas individual rotor tones are well predicted by the linear sources (i.e., thickness and loading), for the interaction tones it is essential that the quadrupole sources be included in the analysis.
    Keywords: Aerodynamics
    Type: GRC-E-DAA-TN15607 , AIAA/CEAS Aeroacoustics Conference; Jun 16, 2014 - Jun 20, 2014; Atlanta, GA; United States
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  • 87
    Publication Date: 2019-07-13
    Description: Several minimum-mass aeroelastic optimization problems are solved to evaluate the effectiveness of a variety of novel tailoring schemes for subsonic transport wings. Aeroelastic strength and panel buckling constraints are imposed across a variety of trimmed maneuver loads. Tailoring with metallic thickness variations, functionally graded materials, composite laminates, tow steering, and distributed trailing edge control effectors are all found to provide reductions in structural wing mass with varying degrees of success. The question as to whether this wing mass reduction will offset the increased manufacturing cost is left unresolved for each case.
    Keywords: Aerodynamics
    Type: NF1676L-17757 , AIAA Aviation and Aeronautics Forum and Exposition (AVIATION 2014); Jun 16, 2014 - Jun 20, 2014; Atlanta, GA; United States
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  • 88
    Publication Date: 2019-07-13
    Description: This paper presents results from computational fluid dynamic (CFD) simulations of a three-stream plug nozzle. Time-accurate, Euler, quasi-1D and 2D-axisymmetric simulations were performed as part of an effort to provide a CFD-based approach to modeling nozzle dynamics. The CFD code used for the simulations is based on the space-time Conservation Element and Solution Element (CESE) method. Steady-state results were validated using the Wind-US code and a code utilizing the MacCormack method while the unsteady results were partially validated via an aeroacoustic benchmark problem. The CESE steady-state flow field solutions showed excellent agreement with solutions derived from the other methods and codes while preliminary unsteady results for the three-stream plug nozzle are also shown. Additionally, a study was performed to explore the sensitivity of gross thrust computations to the control surface definition. The results showed that most of the sensitivity while computing the gross thrust is attributed to the control surface stencil resolution and choice of stencil end points and not to the control surface definition itself.Finally, comparisons between the quasi-1D and 2D-axisymetric solutions were performed in order to gain insight on whether a quasi-1D solution can capture the steady and unsteady nozzle phenomena without the cost of a 2D-axisymmetric simulation. Initial results show that while the quasi-1D solutions are similar to the 2D-axisymmetric solutions, the inability of the quasi-1D simulations to predict two dimensional phenomena limits its accuracy.
    Keywords: Aerodynamics
    Type: GRC-E-DAA-TN16144 , AIAA Joint Propulsion Conference; Jul 28, 2014 - Jul 30, 2014; Cleveland, OH; United States
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  • 89
    Publication Date: 2019-07-13
    Description: Supersonic inlets with external compression, having a good level performance at the critical operating point, exhibit a marked instability of the flow in some subcritical operation below a critical value of the capture mass flow ratio. This takes the form of severe oscillations of the shock system, commonly known as "buzz". The underlying purpose of this study is to indicate how Detached Eddy Simulation (DES) analysis of supersonic inlets will alter how we envision unsteady inlet aerodynamics, particularly inlet buzz. Presented in this paper is a discussion regarding the physical explanation underlying inlet buzz as indicated by DES analysis. It is the normal shock wave boundary layer separation along the spike surface which reduces the capture mass flow that is the controlling mechanism which determines the onset of inlet buzz, and it is the aerodynamic characteristics of a choked nozzle that provide the feedback mechanism that sustains the buzz cycle by imposing a fixed mean corrected inlet weight flow. Comparisons between the DES analysis of the Lockheed Martin Corporation (LMCO) N+2 inlet and schlieren photographs taken during the test of the Gulfstream Large Scale Low Boom (LSLB) inlet in the NASA 8x6 ft. Supersonic Wind Tunnel (SWT) show a strong similarity both in turbulent flow field structure and shock wave formation during the buzz cycle. This demonstrates the value of DES analysis for the design and understanding of supersonic inlets.
    Keywords: Aerodynamics
    Type: GRC-E-DAA-TN15470 , Joint Propulsion Conference; Jul 28, 2014 - Jul 30, 2014; Cleveland, OH; United States
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  • 90
    Publication Date: 2019-07-13
    Description: A second wind tunnel test of the FAST-MAC circulation control semi-span model was recently completed in the National Transonic Facility at the NASA Langley Research Center. The model allowed independent control of four circulation control plenums producing a high momentum jet from a blowing slot near the wing trailing edge that was directed over a 15% chord simple-hinged flap. The model was configured for transonic testing of the cruise configuration with 0deg flap deflection to determine the potential for drag reduction with the circulation control blowing. Encouraging results from analysis of wing surface pressures suggested that the circulation control blowing was effective in reducing the transonic drag on the configuration, however this could not be quantified until the thrust generated by the blowing slot was correctly removed from the force and moment balance data. This paper will present the thrust removal methodology used for the FAST-MAC circulation control model and describe the experimental measurements and techniques used to develop the methodology. A discussion on the impact to the force and moment data as a result of removing the thrust from the blowing slot will also be presented for the cruise configuration, where at some Mach and Reynolds number conditions, the thrust-removed corrected data showed that a drag reduction was realized as a consequence of the blowing.
    Keywords: Aerodynamics
    Type: AIAA Paper-2014-2402 , NF1676L-17629 , AIAA Applied Aerodynamics Conference; Jun 16, 2014 - Jun 20, 2014; Atlanta, GA.; United States
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  • 91
    Publication Date: 2019-07-13
    Description: The continued design, certification and safe operation of swept-wing airplanes in icing conditions rely on the advancement of computational and experimental simulation methods for higher fidelity results over an increasing range of aircraft configurations and performance, and icing conditions. The current stateof- the-art in icing aerodynamics is mainly built upon a comprehensive understanding of two-dimensional geometries that does not currently exist for fundamentally three-dimensional geometries such as swept wings. The purpose of this report is to describe what is known of iced-swept-wing aerodynamics and to identify the type of research that is required to improve the current understanding. Following the method used in a previous review of iced-airfoil aerodynamics, this report proposes a classification of swept-wing ice accretion into four groups based upon unique flowfield attributes. These four groups are: ice roughness, horn ice, streamwise ice and spanwise-ridge ice. In the case of horn ice it is shown that a further subclassification of "nominally 3D" or "highly 3D" horn ice may be necessary. For all of the proposed ice-shape classifications, relatively little is known about the three-dimensional flowfield and even less about the effect of Reynolds number and Mach number on these flowfields. The classifications and supporting data presented in this report can serve as a starting point as new research explores swept-wing aerodynamics with ice shapes. As further results are available, it is expected that these classifications will need to be updated and revised.
    Keywords: Aerodynamics
    Type: NASA/TM-2013-216556 , E-18753 , GRC-E-DAA-TN9727 , AIAA Atmospheric and Space Enviroments Conference; Jun 24, 2013 - Jun 27, 2013; San Diego, CA; United States
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  • 92
    Publication Date: 2019-07-13
    Description: NASA, FAA, ONERA, the University of Illinois and Boeing have embarked on a significant, collaborative research effort to address the technical challenges associated with icing on large-scale, three-dimensional swept wings. The overall goal is to improve the fidelity of experimental and computational simulation methods for swept-wing ice accretion formation and resulting aerodynamic effect. A seven-phase research effort has been designed that incorporates ice-accretion and aerodynamic experiments and computational simulations. As the baseline, full-scale, swept-wing-reference geometry, this research will utilize the 65% scale Common Research Model configuration. Ice-accretion testing will be conducted in the NASA Icing Research Tunnel for three hybrid swept-wing models representing the 20%, 64% and 83% semispan stations of the baseline-reference wing. Three-dimensional measurement techniques are being developed and validated to document the experimental ice-accretion geometries. Artificial ice shapes of varying geometric fidelity will be developed for aerodynamic testing over a large Reynolds number range in the ONERA F1 pressurized wind tunnel and in a smaller-scale atmospheric wind tunnel. Concurrent research will be conducted to explore and further develop the use of computational simulation tools for ice accretion and aerodynamics on swept wings. The combined results of this research effort will result in an improved understanding of the ice formation and aerodynamic effects on swept wings. The purpose of this paper is to describe this research effort in more detail and report on the current results and status to date. 1
    Keywords: Aerodynamics
    Type: NASA/TM-2013-216555 , AIAA Paper 2013-28 , E-18752 , GRC-E-DAA-TN9726 , AIAA Atmospheric and Space Enviroment Conference; Jun 24, 2013 - Jun 27, 2013; San Diego, CA; United States
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  • 93
    Publication Date: 2019-07-13
    Description: Reduced-order modeling (ROM) methods are applied to the CFD-based aeroelastic analysis of the AGARD 445.6 wing in order to gain insight regarding well-known discrepancies between the aeroelastic analyses and the experimental results. The results presented include aeroelastic solutions using the inviscid CAP-TSD code and the FUN3D code (Euler and Navier-Stokes). Full CFD aeroelastic solutions and ROM aeroelastic solutions, computed at several Mach numbers, are presented in the form of root locus plots in order to better reveal the aeroelastic root migrations with increasing dynamic pressure. Important conclusions are drawn from these results including the ability of the linear CAP-TSD code to accurately predict the entire experimental flutter boundary (repeat of analyses performed in the 1980's), that the Euler solutions at supersonic conditions indicate that the third mode is always unstable, and that the FUN3D Navier-Stokes solutions stabilize the unstable third mode seen in the Euler solutions.
    Keywords: Aerodynamics
    Type: AIAA Paper 2014-0496 , NF1676-16636 , AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference; Jan 13, 2014 - Jan 17, 2014; National Harbor, MD; United States
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  • 94
    Publication Date: 2019-07-13
    Description: This paper describes a computational fluid dynamic method used for modelling changes in aircraft geometry due to icing. While an aircraft undergoes icing, the accumulated ice results in a geometric alteration of the aerodynamic surfaces. In computational simulations for icing, it is necessary that the corresponding geometric change is taken into consideration. The method used, herein, for the representation of the geometric change due to icing is a non-cut cell Immersed Boundary Method (IBM). Computational cells that are in a body fitted grid of a clean aerodynamic geometry that are inside a predicted ice formation are identified. An IBM is then used to change these cells from being active computational cells to having properties of viscous solid bodies. This method has been implemented in the NASA developed node centered, finite volume computational fluid dynamics code, FUN3D. The presented capability is tested for two-dimensional airfoils including a clean airfoil, an iced airfoil, and an airfoil in harmonic pitching motion about its quarter chord. For these simulations velocity contours, pressure distributions, coefficients of lift, coefficients of drag, and coefficients of pitching moment about the airfoil's quarter chord are computed and used for comparison against experimental results, a higher order panel method code with viscous effects, XFOIL, and the results from FUN3D's original solution process. The results of the IBM simulations show that the accuracy of the IBM compares satisfactorily with the experimental results, XFOIL results, and the results from FUN3D's original solution process.
    Keywords: Aerodynamics
    Type: NASA/TM-2013-217881 , E-18692 , AIAA Paper 2012-1204 , AIAA Aerospace Sciences Meeting; Jan 09, 2012 - Jan 12, 2012; Nashville, TN; United States
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  • 95
    Publication Date: 2019-07-13
    Description: In support of NASA's Entry, Descent, and Landing technology development efforts, testing of Langley's Trim Tab Parametric Models was conducted in Test Section 2 of NASA Langley's Unitary Plan Wind Tunnel. The objectives of these tests were to generate quantitative aerodynamic data and qualitative surface pressure data for experimental and computational validation and aerodynamic database development. Six component force-and-moment data were measured on 38 unique, blunt body trim tab configurations at Mach numbers of 2.5, 3.5, and 4.5, angles of attack from -4deg to +20deg, and angles of sideslip from 0deg to +8deg. Configuration parameters investigated in this study were forebody shape, tab area, tab cant angle, and tab aspect ratio. Pressure Sensitive Paint was used to provide qualitative surface pressure mapping for a subset of these flow and configuration variables. Over the range of parameters tested, the effects of varying tab area and tab cant angle were found to be much more significant than varying tab aspect ratio relative to key aerodynamic performance requirements. Qualitative surface pressure data supported the integrated aerodynamic data and provided information to aid in future analyses of localized phenomena for trim tab configurations.
    Keywords: Aerodynamics
    Type: NF1676L-15681 , AIAA Applied Aerodynamics Conference; Jun 24, 2013 - Jun 27, 2013; San Diego, CA; United States
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  • 96
    Publication Date: 2019-07-13
    Description: This is the presentation related to the paper of the same name describing Reynolds Averaged Navier Stokes (RANS) computational Fluid Dynamics (CFD) analysis of low speed stall aerodynamics of a swept wing with a laminar flow wing glove.
    Keywords: Aerodynamics
    Type: DFRC-E-DAA-TN9982 , DFRC-E-DAA-TN10986 , Applied Aerodynamics Conference; Jun 24, 2013 - Jun 27, 2013; San Diego, CA; United States
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  • 97
    Publication Date: 2019-07-13
    Description: The boundary-layer transition characteristics and convective aeroheating levels on mid lift-to-drag ratio entry vehicle configurations have been studied through wind-tunnel testing. Several configurations were investigated, including elliptically blunted cylinders with both circular and elliptically flattened cross sections, biconic geometries based on launch vehicle dual-use shrouds, and parametrically optimized analytic geometries. Vehicles of this class have been proposed for high-mass Mars missions, such as sample return and crewed exploration, for which the conventional sphere-cone entry-vehicle geometries of previous Mars missions are insufficient. Testing was conducted at Mach 6 over a range of Reynolds numbers sufficient to generate laminar, transitional, and turbulent flow. Transition onset locations, both straight-line and cross-flow, and heating rates were obtained through global phosphor thermography. Supporting computations were performed to obtain heating rates for comparison with the data. Laminar data and predictions agreed to well within the experimental uncertainty. Fully turbulent data and predictions also agreed well. However, in transitional flow regions, greater differences were observed.
    Keywords: Aerodynamics
    Type: NF1676L-22328 , Journal of Spacecraft and Rockets; 50; 5; 937-959|AIAA Fluid Dynamics Conference and Exhibit; Jun 25, 2012 - Jun 28, 2012; New Orleans, LA; United States
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  • 98
    Publication Date: 2019-07-13
    Description: No abstract available
    Keywords: Aerodynamics
    Type: E-667806 , Aviation Safety Program Annual Technical Meeting; May 10, 2011 - May 12, 2011; Saint Louis, MO; United States
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  • 99
    Publication Date: 2019-07-13
    Description: No abstract available
    Keywords: Aerodynamics
    Type: E-664455 , NASA Advisory Council Aeronautics Committee Meeting; Oct 25, 2012 - Oct 26, 2012; Cleveland, OH; United States
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  • 100
    Publication Date: 2019-07-13
    Description: A second wind tunnel test of the FAST-MAC circulation control model was recently completed in the National Transonic Facility at the NASA Langley Research Center. The model was equipped with four onboard flow control valves allowing independent control of the circulation control plenums, which were directed over a 15% chord simple-hinged flap. The model was configured for low-speed high-lift testing with flap deflections of 30 and 60 degrees, along with the transonic cruise configuration with zero degree flap deflection. Testing was again conducted over a wide range of Mach numbers up to 0.88, and Reynolds numbers up to 30 million based on the mean chord. The first wind tunnel test had poor transonic force and moment data repeatability at mild cryogenic conditions due to inadequate thermal conditioning of the balance. The second test demonstrated that an improvement to the balance heating system significantly improved the transonic data repeatability, but also indicated further improvements are still needed. The low-speed highlift performance of the model was improved by testing various blowing slot heights, and the circulation control was again demonstrated to be effective in re-attaching the flow over the wing at off-design transonic conditions. A new tailored spanwise blowing technique was also demonstrated to be effective at transonic conditions with the benefit of reduced mass flow requirements.
    Keywords: Aerodynamics
    Type: NF1676L-15676 , AIAA Fluid Dynamics Conference and Exhibit; Jun 24, 2013 - Jun 27, 2013; San Diego, CA; United States
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