Science.gov

Sample records for high-angle twist grain

  1. Effect of interatomic potential on the calculated energy and structure of high-angle coincident site grain boundaries. I. (100) twist boundaries in aluminum

    SciTech Connect

    Wolf, D.

    1984-01-01

    A new computer code is described which permits the investigation of the energy and structure of coincident-site lattice (CSL) grain boundaries in metals. As an improvement over computer programs used by other workers, the full second-derivative (force-constant) matrix associated with a given interatomic potential is applied for the iterative energy minimization. Using this extremely efficient and reliable procedure the effect of the form of the interatomic potential and its truncation radius on the predicted grain-boundary energy and structure is investigated. Six different potentials for aluminum, ranging from a Morse potential to a pseudopotential, are applied to the simulation of the energy and structure (100) CSL twist boundaries with values of ..sigma.., the inverse density of CSL sites, ranging between ..sigma.. = 5 and ..sigma.. = 73. It is found that not only do both the energy and structure of a given boundary vary greatly from one potential to another, but also that the relative energies of different boundaries, i.e. the boundary-energy vs misfit-angle curves, depend on the potential. In contrast to recent claims of Brokman and Balluffi, no cusps in these curves are found for potentials which ignore the charge-density oscillations. The two basic assumptions of the Brokman-Balluffi cusp model are found to be valid only for extremely simple potentials with very short cutoff radii. It is suggested that (1) charge-density oscillations may be important for predicting grain-boundary properties, and (2) no obvious relationship exists between grain-boundary geometry (..sigma..) and the energy. 39 references, 18 figures, 1 table.

  2. Dislocation structures in high angle 001 twist boundaries in magnesium oxide

    NASA Astrophysics Data System (ADS)

    Sun, C. P.

    1980-12-01

    A systematic transmission electron microscope (TEM) investigation of possible secondary grain boundary dislocation (GBD) structures in 001 high angle twist boundaries in MgO was carried out using bicrystals of controlled geometry. Techniques were developed to fabricate an extensive series of MgO bicrystals containing 001 twist boundaries with twist angle, theta, covering the entire possible range, 0 theta less than or equal to 45 deg. Tables of MgO single crystals with cleaved 100 faces were welded together by hot pressing. The TEM specimens were prepared by a combination of mechanical and chemical jet polishing using phosphoric acid. Weak beam microscopy was used extensively since this technique is capable of producing a characteristic narrow defect image width, and hence allows complicated GBD networks to be resolved more readily than by use of conventional microscopy.

  3. Characterizing twist grain boundaries in BCC Nb by molecular simulation: Structure and shear deformation

    NASA Astrophysics Data System (ADS)

    Liu, Zeng-Hui; Feng, Ya-Xin; Shang, Jia-Xiang

    2016-05-01

    Atomic scale modeling was used to study the structure, energy and shear behaviors of (110) twist grain boundaries (TWGBs) in body-centered cubic Nb. The relation between grain boundary energy (GBE) and the twist angle θ agrees well with the Read-Shockley equation in low-angle range. At higher angles, the GBEs show no distinct trend with the variation of the twist angle or the density of coincident lattice sites. All (110) twist boundaries can be classified into two types: low-angle grain boundaries (LAGBs) and high-angle grain boundaries (HAGBs). LAGBs contain a hexagonal dislocation network (HDN) which is composed of 1/2 [ 111 ], 1/2 [ 1 bar 1 bar 1 ] and [001] screw dislocations. HAGBs can be classified into three sub-types further: special boundaries with low Σ, boundaries in the vicinity of special boundaries with similar structures and ordinary HAGBs consisting of periodic patterns. Besides, a dependence of grain boundary shear response vs the twist angle over the entire twist angle range is obtained. Pure sliding behavior is found at all TWGBs. When θ < 12°, the flow stress of LAGBs is found to be correlated with the HDNs and decreases with the increasing twist angle. For ordinary HAGBs, the magnitude of flow stress is around 0.8-1.0 GPa and the twist angle has little effect on the anisotropy mobility. For special grain boundaries with low Σ, the boundary structures govern the GBEs and shear motion behavior significantly.

  4. Microstructural Modeling of Intergranular Fracture in Tricrystals With Random Low- and High-Angle Grain Boundaries

    NASA Astrophysics Data System (ADS)

    Bond, David M.; Zikry, Mohammed A.

    2017-03-01

    Intergranular (IG) fracture behavior near triple junctions (TJs) in f.c.c. tricrystals with a variety of grain boundary (GB) misorientations has been investigated. Based on a dislocation-density GB interaction scheme, critical fracture conditions were coupled to evolving dislocation-density pileups and local stresses by using a dislocation-density-based crystalline plasticity formulation within a nonlinear finite-element framework to elucidate the effects of local GB structure, dislocation-GB interactions, and misorientations on IG crack propagation in f.c.c. crystalline materials. Tricrystals with low-angle GBs had higher fracture toughness than tricrystals with high-angle GBs. In TJs with a combination of random low- and high-angle GBs, the formation of dislocation-density pileups in the high-angle GB led to IG crack propagation along the high-angle GB rather than along the low-angle GB. These predictions, which are consistent with experimental observations, indicate that fracture behavior near TJs is controlled by highly local, evolving, and interrelated events, such as dislocation-density pileups and GB misorientations.

  5. Migration and nucleation of helium atoms at (110) twist grain boundaries in tungsten

    NASA Astrophysics Data System (ADS)

    Feng, Ya-Xin; Shang, Jia-Xiang; Lu, Guang-Hong

    2017-04-01

    The migration and nucleation of He atoms at three typical (110) twist grain boundaries (TGBs): the low-angle grain boundary (LAGB), the ordinary high-angle grain boundary (HAGB) and the Σ 3 TGB in W are investigated using molecular dynamics simulations. The presence of TGBs can absorb He atoms from bulk and impede the growth of He bubbles. Moreover, different grain boundary (GB) structures behave differently when interacting with He atoms. The LAGB can control the He distribution on the GB plane through its screw dislocation network, suggesting a promising approach for design of radiation tolerant materials. The ordinary HAGB presents a strong trap effect due to its disordered GB structure, which may induce a large He retention at the GB and embrittlement. The Σ 3 TGB can provide a diffusion path for He atoms, although the diffusion rate is not as fast as it in bulk.

  6. Energetics and structural properties of twist grain boundaries in Cu

    NASA Technical Reports Server (NTRS)

    Karimi, Majid

    1992-01-01

    Structural and energetics properties of atoms near a grain boundary are of great importance from theoretical and experimental standpoints. From various experimental work it is concluded that diffusion at low temperatures at polycrystalline materials take place near grain boundary. Experimental and theoretical results also indicate changes of up to 70 percent in physical properties near a grain boundary. The Embedded Atom Method (EAM) calculations on structural properties of Au twist grain boundaries are in quite good agreement with their experimental counterparts. The EAM is believed to predict reliable values for the single vacancy formation energy as well as migration energy. However, it is not clear whether the EAM functions which are fitted to the bulk properties of a perfect crystalline solid can produce reliable results on grain boundaries. One of the objectives of this work is to construct the EAM functions for Cu and use them in conjunction with the molecular static simulation to study structures and energetics of atoms near twist grain boundaries in Cu. This provides tests of the EAM functions near a grain boundary. In particular, we determine structure, single vacancy formation energy, migration energy, single vacancy activation energy, and interlayer spacing as a function of distance from grain boundary. Our results are compared with the available experimental and theoretical results from grain boundaries and bulk.

  7. Possible model of an antiferroelectric twist grain boundary phase

    SciTech Connect

    Meier, J. G.; Carlsson, T.; Rudquist, P.; Lagerwall, S. T.; Nobili, M.; Brunet, M.

    2007-07-15

    Using x-ray and optical methods we have probed the structural organization of an antiferroelectric twist grain boundary phase (TGBC{sub a}) lying between the regular antiferroelectric smectic-C (SmC{sub a}{sup *}) and the smectic-Q (SmQ) or isotropic phase. We find that the twist axis is everywhere perpendicular to the local smectic layer normal and that the helical superstructure is incommensurate with the smectic layer structure. The twist grain boundaries consist of a periodic lattice of alternating +1/2 and -1/2 dispirations, i.e., unit screw dislocations in combination with half unit disclinations. The molecular tilt plane is alternatingly parallel and perpendicular to the twist axis. We find that the optically measured tilt angle in the SmC{sub a}{sup *} phase is smaller than that measured by x rays, which is the opposite to what is found in the SmC{sup *} phase. This means that the core part tilts less than the end chains in the SmC{sub a}{sup *} phase, while it tilts more in the SmC{sup *} phase. On entering the TGB phase a clear decrease is measured in the tilt angle. This is explained by the elastic influence from the disclinations, which appear in this phase.

  8. Simulation of the structure of vacancies in high angle grain boundaries

    SciTech Connect

    Bristowe, P.D.; Brokman, A.; Spaepen, F.; Balluffi, R.W.

    1980-06-01

    Since the modeling approach used in an earlier work is used at an atomic level, this is the most appropriate and reliable technique available. To complement this study, however, we have also employed a hard sphere dynamic model and a bubble raft model because in the past they have provided useful qualitative insight into the structure of a variety of defects in two-dimensional crystalline and amorphous systems. The computed results form part of a wider investigation of vacancies and interstitials in various grain boundaries in which the binding energies are analyzed and related to the defect structure and form of the interatomic potential.

  9. Characteristics of grain boundaries in YBCO and BSCCO-2212 bicrystals lying in the low angle to high angle crossover regime

    NASA Astrophysics Data System (ADS)

    Larbalestier, David C.

    1996-03-01

    The characteristics of grain boundaries lying in the low angle to high angle crossover regime in thin film and bulk scale YBCO and bulk BSCCO-2212 bicrystals have been studied. Such grain boundaries can be considered as periodic or quasi-periodic structures consisting of grain boundary dislocation barriers separated by channels of strong coupling. This description is valid up to some critical cut off angle at which the whole grain boundary becomes a weak link. The cutoff occurs at lower angles for thin films than for bulk samples and also varies somewhat from one sample to another and from one material to another. Recent study of BSCCO-2212 bicrystals has shown that [100] tilt boundaries containing basal plane facets can be distinguished from those without them because the former have linear components characteristic of c axis transport in them. Both the electromagnetic and the microstructural aspects of our recent studies will be reviewed. My principal collaborators are S. Babcock, X. Y. Cai, M. Field, D. L. Kaiser (NIST), A. Gurevich, N. Heinig, J.E. Nordman, I-Fei Tsu, J. L. Vargas and Jyh-Lih Wang Work primarily supported by NSF Materials Research Group Program with additional support by EPRI and ARPA.

  10. The Potential Link Between High Angle Grain Boundary Morphology and Grain Boundary Deformation in a Nickel-Based Superalloy (Postprint)

    DTIC Science & Technology

    2015-06-01

    mechanism that controls this deformation is the interaction of dislocations with the γ′ precipitate distribution, while ultimate creep life is...poses. ISE images were used for this study because ISE images displayed significant channeling contrast that accentuated the crystallographic...acquired at an oblique angle of 74° to the surface to maximize the channeling contrast differences between adjacent grains. These images were post

  11. Rheology of twist-grain-boundary-A liquid crystals

    NASA Astrophysics Data System (ADS)

    Sahoo, Rasmita; Ananthaiah, J.; Dabrowski, R.; Dhara, Surajit

    2014-07-01

    We report studies on the rheological properties of a liquid crystalline analog of Abrikosov phase in type-II superconductors known as twist-grain-boundary-A (TGBA) phase. The TGBA phase shows a large apparent yield stress compared to the cholesteric (N*) phase. The storage modulus (G') of the TGBA phase is significantly larger than the loss modulus (G''). The dynamic relaxation measurements indicate a solid-like behavior of N*, TGBA, and smectic-C* phases. The complex shear modulus of the TGBA phase exhibits a power-law behavior G*(ω) ˜ ωα with α ≃0.5. The relative amplitude of G' and G'' at various temperatures indicate that the enhanced elasticity of TGBA phase is due to the structural defects.

  12. Atomic simulations of twist grain boundary structures and deformation behaviors in aluminum

    NASA Astrophysics Data System (ADS)

    Yin, Qing; Wang, Zhiqiang; Mishra, Rajiv; Xia, Zhenhai

    2017-01-01

    The structures and behaviors of grain boundaries (GBs) have profound effects on the mechanical properties of polycrystalline materials. In this paper, twist GBs in aluminum were investigated with molecular dynamic simulations to reveal their atomic structures, energy and interactions with dislocations. One hundred twenty-six twist GBs were studied, and the energy of all these twist GBs were calculated. The result indicates that <001> and <111> twist GBs have lower energy than <101> twist GBs because of their higher interplanar spacing. In addition, 12 types of <001> twist GBs in aluminum were chosen to explore the deformation behaviors. Low angle twist GBs with high density of network structures can resist greater tension because mutually hindering behaviors between partial dislocations increase the twist GB strength.

  13. Defects in crystalline packings of twisted filament bundles. II. Dislocations and grain boundaries

    NASA Astrophysics Data System (ADS)

    Azadi, Amir; Grason, Gregory M.

    2012-03-01

    Twisted and ropelike assemblies of filamentous molecules are common and vital structural elements in cells and tissues of living organisms. We study the intrinsic frustration occurring in these materials between the two-dimensional organization of filaments in cross section and out-of-plane interfilament twist in bundles. Using nonlinear continuum elasticity theory of columnar materials, we study the favorable coupling of twist-induced stresses to the presence of edge dislocations in the lattice packing of bundles, which leads to a restructuring of the ground-state order of these materials at intermediate twist. The stability of dislocations increases as both the degree of twist and lateral bundle size grow. We show that in ground states of large bundles, multiple dislocations pile up into linear arrays, radial grain boundaries, whose number and length grows with bundle twist, giving rise to a rich class of “polycrystalline” packings.

  14. Unconfined twist : a simple method to prepare ultrafine grained metallic materials.

    SciTech Connect

    Zhao, Y.; Liao, Xiaozhou; Zhu, Y. T.

    2004-01-01

    A new simple method - unconfined twist was employed to prepare ultrafine grained (UFG) Fe,wire. A coarse grained (CG) Fe wire with a diameter of 0.85 mm was fixed at one end, and twisted at the other end. After maximum twist before fracture, in the cross-sectional plane, concentrically deformed layers with a width of several micrometers formed surrounding the center axis of the wire. The near-surface deformed layers consist of lamella grains with a width in submicrometer range. In the longitudinal plane, deformed bands (with a width of several micrometers) formed uniformly, which were composed of lamella crystallites (with a width in submicrometer range). The tensile yield strength and ultimate strength of the twisted Fe wire are increased by about 150% and 100% compared with the values of its CG counterpart.

  15. On the small angle twist sub-grain boundaries in Ti3AlC2

    PubMed Central

    Zhang, Hui; Zhang, Chao; Hu, Tao; Zhan, Xun; Wang, Xiaohui; Zhou, Yanchun

    2016-01-01

    Tilt-dominated grain boundaries have been investigated in depth in the deformation of MAX phases. In stark contrast, another important type of grain boundaries, twist grain boundaries, have long been overlooked. Here, we report on the observation of small angle twist sub-grain boundaries in a typical MAX phase Ti3AlC2 compressed at 1200 °C, which comprise hexagonal screw dislocation networks formed by basal dislocation reactions. By first-principles investigations on atomic-scale deformation and general stacking fault energy landscapes, it is unequivocally demonstrated that the twist sub-grain boundaries are most likely located between Al and Ti4f (Ti located at the 4f Wyckoff sites of P63/mmc) layers, with breaking of the weakly bonded Al–Ti4f. The twist angle increases with the increase of deformation and is estimated to be around 0.5° for a deformation of 26%. This work may shed light on sub-grain boundaries of MAX phases, and provide fundamental information for future atomic-scale simulations. PMID:27034075

  16. Hydrogen behaviour at twist {110} grain boundaries in α-Fe

    NASA Astrophysics Data System (ADS)

    McEniry, Eunan J.; Hickel, Tilmann; Neugebauer, Jörg

    2017-06-01

    The behaviour of hydrogen at structural defects such as grain boundaries plays a critical role in the phenomenon of hydrogen embrittlement. However, characterization of the energetics and diffusion of hydrogen in the vicinity of such extended defects using conventional ab initio techniques is challenging due to the relatively large system sizes required when dealing with realistic grain boundary geometries. In order to be able to access the required system sizes, as well as high-throughput testing of a large number of configurations, while remaining within a quantum-mechanical framework, an environmental tight-binding model for the iron-hydrogen system has been developed. The resulting model is applied to study the behaviour of hydrogen at a class of low-energy {110}-terminated twist grain boundaries in α-Fe. We find that, for particular Σ values within the coincidence site lattice description, the atomic geometry at the interface plane provides extremely favourable trap sites for H, which also possess high escape barriers for diffusion. By contrast, via simulated tensile testing, weakly trapped hydrogen at the interface plane of the bulk-like Σ3 boundary acts as a `glue' for the boundary, increasing both the energetic barrier and the elongation to rupture. This article is part of the themed issue 'The challenges of hydrogen and metals'.

  17. Interaction of run-in edge dislocations with twist grain boundaries in Al-a molecular dynamics study

    NASA Astrophysics Data System (ADS)

    Chandra, S.; Naveen Kumar, N.; Samal, M. K.; Chavan, V. M.; Patel, R. J.

    2016-06-01

    Grain boundaries play an important role in outlining the mechanical properties of crystalline materials. They act as sites for absorption/nucleation of dislocations, which are the main carriers of plastic deformation. In view of this, the interactions between edge dislocations and twist grain boundaries-dislocation pileup, dislocation absorption and dislocation emission were explored by performing molecular dynamics simulations in face-centered cubic Al using embedded atom method. The ?1 1 0? twist grain boundaries with various misorientation angles were selected for this purpose. It was found that the misorientation angle of boundary and stress anomalies arising from repeated dislocation absorption at the grain boundaries are the important parameters in determining the ability of the boundary to emit dislocations. Complex network of dislocations results in later stages of deformation, which may have a significant effect on the mechanical properties of the material. The peculiarities of dislocation nucleation, their emission from twist grain boundaries and the ramifications of this study towards development of higher length scale material models are discussed.

  18. Uranium vacancy mobility at the Σ5 symmetric tilt and Σ5 twist grain boundaries in UO₂

    DOE PAGES

    Uberuaga, Blas Pedro; Andersson, David A.

    2015-10-01

    Ionic transport at grain boundaries in oxides dictates a number of important phenomena, from ionic conductivity to sintering to creep. For nuclear fuels, it also influences fission gas bubble nucleation and growth. Here, using a combination of atomistic calculations and object kinetic Monte Carlo (okMC) simulations, we examine the kinetic pathways associated with uranium vacancies at two model grain boundaries in UO2. The barriers for vacancy motion were calculated using the nudged elastic band method at all uranium sites at each grain boundary and were used as the basis of the okMC simulations. For both boundaries considered – a simplemore » tilt and a simple twist boundary – the mobility of uranium vacancies is significantly higher than in the bulk. For the tilt boundary, there is clearly preferred migration along the tilt axis as opposed to in the perpendicular direction while, for the twist boundary, migration is essentially isotropic within the boundary plane. These results show that cation defect mobility in fluorite-structured materials is enhanced at certain types of grain boundaries and is dependent on the boundary structure with the tilt boundary exhibiting higher rates of migration than the twist boundary.« less

  19. Uranium vacancy mobility at the Σ5 symmetric tilt and Σ5 twist grain boundaries in UO₂

    SciTech Connect

    Uberuaga, Blas Pedro; Andersson, David A.

    2015-10-01

    Ionic transport at grain boundaries in oxides dictates a number of important phenomena, from ionic conductivity to sintering to creep. For nuclear fuels, it also influences fission gas bubble nucleation and growth. Here, using a combination of atomistic calculations and object kinetic Monte Carlo (okMC) simulations, we examine the kinetic pathways associated with uranium vacancies at two model grain boundaries in UO2. The barriers for vacancy motion were calculated using the nudged elastic band method at all uranium sites at each grain boundary and were used as the basis of the okMC simulations. For both boundaries considered – a simple tilt and a simple twist boundary – the mobility of uranium vacancies is significantly higher than in the bulk. For the tilt boundary, there is clearly preferred migration along the tilt axis as opposed to in the perpendicular direction while, for the twist boundary, migration is essentially isotropic within the boundary plane. These results show that cation defect mobility in fluorite-structured materials is enhanced at certain types of grain boundaries and is dependent on the boundary structure with the tilt boundary exhibiting higher rates of migration than the twist boundary.

  20. Molecular dynamics simulations of grain boundary migration during recrystallization employing tilt and twist dislocation boundaries to provide the driving pressure

    NASA Astrophysics Data System (ADS)

    Godiksen, R. B. N.; Schmidt, S.; Jensen, D. Juul

    2008-09-01

    Molecular dynamics simulations of grain boundary migration, where the driving pressure P is the excess stored energy due to dislocation structures, have been performed. This represents recrystallization in metals. Two types of dislocation structures have been simulated: (a) tilt dislocation boundaries, where edge dislocations are arranged as parallel arrays, (b) twist dislocation boundaries, where screw dislocations are arranged in interconnected dislocation networks. The velocity v and mobility M of the migrating grain boundaries have been calculated from the simulations. v and M are higher in twist-type simulations than in tilt-type simulations, although the activation energies are similar in the two cases. v ~ P is observed for tilt simulations where the driving pressure is changed by varying the density of dislocation boundaries and for twist simulations where the driving pressure is changed by varying the misorientation across dislocation boundaries. When the misorientations across edge dislocation boundaries are varied, however, the simulations show v ~ P2. It is suggested that this deviation from the usual v ~ P-relationship is due to local interactions between the grain boundary and nearby individual dislocations. Misorientation variations across grain boundaries have also been simulated, but the mobilities show little dependence on this. The present simulations result in mobilities and activation energies that are, respectively, significantly higher and somewhat lower than experimental values. A direct mimic of experimental observations is, however not the purpose of this study. Rather the present simulations are based on idealized dislocation structures and suggest that variations in the dislocation structures may play a dominant role in recrystallization dynamics and that local effects are very important phenomena, essential for the interpretation of recrystallization mechanisms.

  1. Kinetic processes at grain boundaries. Progress report, 15 August 1979-14 August 1980

    SciTech Connect

    Balluffi, R.W.

    1980-05-01

    A broad investigation was made of kinetic processes at grain boundaries and the relationship between these kinetic processes and the boundary structure. The approach was both experimental and theoretical. Extensive use was made of high resolution experimental methods of investigating grain boundaries in specimens containing boundaries of controlled geometry. Computer simulation was also employed. Elements of the following projects were completed: a study of intrinsic and extrinsic secondary grain boundary dislocation structure in (001) high angle twist boundaries in MgO; a study of grain boundary dislocations in plane matching grain boundaries; an analysis and review of high angle grain boundaries as sources or sinks for point defects; an analysis and review of grain boundary structure in metals and ceramic oxides; and simulation of the structure of vacancies in high angle grain boundaries. Progress was made: in the development of a model for diffusion induced grain boundary migration; and the determination of the mechanism for grain boundary diffusion in metals.

  2. High Angle of Attack Aerodynamics

    DTIC Science & Technology

    1979-01-01

    describe the behaviour of the air. The Symposium made it clear that the present state of knowledge in the area of high angle-of-attack aerodynamics...TESTING EXPERIENCE by C.W. Smith and C.A.Anderson S FOREBODY-WING VORTEX INTERACTIONS AND THEIR INFLUENCE ON DEPARTURE AND SPIN RESISTANCE by A.MSkow...Figure 6) caused by asymmetric flow conditions. ., s already mentioned, asymmetric flow occurs not only when an air- craft flies at non-zero sideslip

  3. Strengthening effects of various grain boundaries with nano-spacing as barriers of dislocation motion from molecular dynamics simulations

    NASA Astrophysics Data System (ADS)

    Yuan, FuPing

    2017-03-01

    Strengthening in metals is traditionally achieved through the controlled creation of various grain boundaries (GBs), such as low-angle GBs, high-angle GBs, and twin boundaries (TBs). In the present study, a series of large-scale molecular dynamics simulations with spherical nanoindentation and carefully designed model were conducted to investigate and compare the strengthening effects of various GBs with nano-spacing as barriers of dislocation motion. Simulation results showed that high-angle twist GBs and TBs are similar barriers and low-angle twist GBs are less effective in obstructing dislocation motion. Corresponding atomistic mechanisms were also given. At a certain indentation depth, dislocation transmission and dislocation nucleation from the other side of boundaries were observed for low-angle twist GBs, whereas dislocations were completely blocked by high-angle twist GBs and TBs at the same indentation depth. The current findings should provide insights for comprehensive understanding of the strengthening effects of various GBs at nanoscale.

  4. Long-period helical structures and twist-grain boundary phases induced by chemical substitution in the Mn1 -x(Co,Rh ) xGe chiral magnet

    NASA Astrophysics Data System (ADS)

    Martin, N.; Deutsch, M.; Chaboussant, G.; Damay, F.; Bonville, P.; Fomicheva, L. N.; Tsvyashchenko, A. V.; Rössler, U. K.; Mirebeau, I.

    2017-07-01

    We study the evolution of helical magnetism in MnGe chiral magnet upon partial substitution of Mn for 3 d -Co and 4 d -Rh ions. At high doping levels, we observe spin helices with very long periods—more than ten times larger than in the pure compound—and sizable ordered moments. This behavior calls for a change in the energy balance of interactions leading to the stabilization of the observed magnetic structures. Strikingly, neutron scattering unambiguously shows a double periodicity in the observed spectra at x =0.5 and >0.2 for Co- and Rh-doping, respectively. In analogy with observations made in smectic liquid crystals, we suggest that it may reveal the presence of magnetic "twist grain boundary" phases, involving a dense short-range correlated network of magnetic screw dislocations. The dislocation cores are here tentatively described as smooth textures, made of nonradial double-core skyrmions.

  5. High angle conveyors climb to the top

    SciTech Connect

    Mitchell, J.J.

    1984-11-01

    A major objective in the design of a storage facility is to have the least handling over the shortest distances and to optimize land usage by attaining the highest tons-per-acre value. The advantages of high angle conveyors become apparent when the height of lift is compared with the surface area. High angle conveyors achieve high capacities in the least amount of space. Continental Conveyor and Equipment Co., has conducted several studies that evaluate the technical and economic feasibility of using high angle conveyors in conveyor systems. A few of the high angle conveying concepts reviewed are the bucket ladder or pocket belt, belts with partitions or fin belt, and the sandwich type belt conveyors.

  6. High angle conveyors climb to the top

    SciTech Connect

    Mitchell, J.J.

    1984-11-01

    Descriptions are presented of various types of high angle conveyors, including pocket belt, fin belt, sandwich belt, snake sandwich conveyor, mechanically pressed sandwich conveyor, and pneumatically pressed sandwich conveyors. 10 references.

  7. Atomistic simulations of grain boundary migration in copper

    NASA Astrophysics Data System (ADS)

    Schönfelder, B.; Gottstein, G.; Shvindlerman, L. S.

    2006-06-01

    While the motion of twist boundaries can be readily studied by atomistic simulations with molecular dynamics (MD) under the action of an elastic driving force, the approach fails for tilt boundaries. This is due to the interaction of the elastic stress with the grain boundary (GB) structure, which causes plastic strain by GB sliding. A novel concept, the orientation correlated driving force, is introduced to circumvent this problem. It is shown that this concept can be successfully applied to the study of the migration of tilt boundaries. The migration behavior of several twist and tilt GBs was investigated. The transition from low-to high-angle boundaries can be captured, and a structural transition of tilt boundaries was found at high temperatures, which also affected the migration behavior. The results compare well with experimental results of the motion high-angle boundaries, but for low-angle boundaries, the agreement is poor.

  8. On the relationship between grain-boundary migration and grain-boundary diffusion by molecular-dynamics simulation

    SciTech Connect

    Schoenfelder, B. |; Keblinski, P.; Wolf, D.; Phillpot, S.R.

    1998-07-01

    A molecular-dynamics method for the simulation of the intrinsic migration behavior of individual, flat grain boundaries is presented. A constant driving force for grain-boundary migration is generated by imposing an anisotropic elastic strain on a bicrystal such that the elastic-energy densities in its two halves are different. For the model case of the large-planar-unit-cell, high-angle (001) twist boundary in Cu the authors demonstrate that the drift velocity is proportional to the applied driving force, thus enabling determination of the boundary mobility. The activation energy for grain-boundary migration is found to be distinctly lower than that for grain-boundary self-diffusion. A decrease in the related activation energies with increasing temperature is shown to arise from a crossover in the underlying mechanisms, from solid-like at low temperatures to liquid-like at high-temperatures that is accompanied by an underlying grain-boundary structural transition.

  9. Twist Positivity

    NASA Astrophysics Data System (ADS)

    Jaffe, Arthur

    1999-11-01

    We study a heat kernel e-βH defined by a self-adjoint Hamiltonian H acting on a Hilbert space H, and a unitary representation U(g) of a symmetry group G of H, normalized so that the ground vector of H is invariant under U(g). The triple {H, U(g), H} defines a twisted partition function Zg and a twisted Gibbs expectation <·>g, Zg=TrH(U(g-1) e-βH) and <·>g=TrH(U(g-1)·e-βH)/TrH(U(g-1) e-βH). We say that {H, U(g), H} is twist positive if Zg>0. We say that {H, U(g), H} has a Feynman-Kac representation with a twist U(g), if one can construct a function space and a probability measure dμg on that space yielding (in the usual sense on products of coordinates) <·>g=∫·dμg. Bosonic quantum mechanics provides a class of specific examples that we discuss. We also consider a complex bosonic quantum field ϕ(x) defined on a spatial s-torus Ts and with a translation-invariant Hamiltonian. This system has an (s+1)-parameter abelian twist group Ts×R that is twist positive and that has a Feynman-Kac representation. Given τ∈Ts and θ∈R, the corresponding paths are random fields Φ(x, t) that satisfy the twist relationΦ(x, t+β)=eiΩθΦ(x-τ, t). We also utilize the twist symmetry to understand some properties of "zero-mass" limits, when the twist τ, θ lies in the complement of a set ϒsing of singular twists.

  10. Grain boundary motion and grain rotation in aluminum bicrystals: recent experiments and simulations

    NASA Astrophysics Data System (ADS)

    Molodov, D. A.; Barrales-Mora, L. A.; Brandenburg, J.-E.

    2015-08-01

    The results of experimental and computational efforts over recent years to study the motion of geometrically different grain boundaries and grain rotation under various driving forces are briefly reviewed. Novel in-situ measuring techniques based on orientation contrast imaging and applied simulation techniques are described. The experimental results obtained on specially grown aluminum bicrystals are presented and discussed. Particularly, the faceting and migration behavior of low angle grain boundaries under the curvature force is addressed. In contrast to the pure tilt boundaries, which remained flat/faceted and immobile during annealing at elevated temperatures, mixed tilt-twist boundaries readily assumed a curved shape and steadily moved under the capillary force. Computational analysis revealed that this behavior is due to the inclinational anisotropy of grain boundary energy, which in turn depends on boundary geometry. The shape evolution and shrinkage kinetics of cylindrical grains with different tilt and mixed boundaries were studied by molecular dynamics simulations. The mobility of low angle <100> boundaries with misorientation angles higher than 10°, obtained by both the experiments and simulations, was found not to differ from that of the high angle boundaries, but decreases essentially with further decrease of misorientation. The shape evolution of the embedded grains in simulations was found to relate directly to results of the energy computations. Further simulation results revealed that the shrinkage of grains with pure tilt boundaries is accompanied by grain rotation. In contrast, grains with the tilt-twist boundaries composed of dislocations with the mixed edge-screw character do not rotate during their shrinkage. Stress driven boundary migration in aluminium bicrystals was observed to be coupled to a tangential translation of the grains. The activation enthalpy of high angle boundary migration was found to vary non-monotonically with

  11. Light's twist

    PubMed Central

    Padgett, Miles

    2014-01-01

    That light travels in straight lines is a statement of the obvious. However, the energy and momentum flow within light beams can twist to form vortices such as eddies in a stream. These twists carry angular momentum, which can make microscopic objects spin, be used to encode extra information in communication systems, enable the design of novel imaging systems and allow new tests of quantum mechanics. PMID:25484612

  12. Twisting Plasma

    NASA Image and Video Library

    2016-06-08

    A close-up of twisting plasma above the Sun's surface produced a nice display of turbulence by caused combative magnetic forces (June 7-8, 2016) over a day and a half. The plasma does not break away, but just spins and twists the entire period. Images were taken in extreme ultraviolet light. The mass we observed is part of a longer, darkish filament angling down from the upper left of the frame. Filaments are unstable clouds of plasma suspended above the Sun by magnetic forces. http://photojournal.jpl.nasa.gov/catalog/PIA20739

  13. Twisted baskets.

    PubMed

    Hermann, Keith; Pratumyot, Yaowalak; Polen, Shane; Hardin, Alex M; Dalkilic, Erdin; Dastan, Arif; Badjić, Jovica D

    2015-02-23

    A preparative procedure for obtaining a pair of twisted molecular baskets, each comprising a chiral framework with either right ((P)-1syn) or left ((M)-1syn) sense of twist and six ester groups at the rim has been developed and optimized. The racemic (P/M)-1syn can be obtained in three synthetic steps from accessible starting materials. The resolution of (P/M)-1syn is accomplished by its transesterification with (1R,2S,5R)-(-)-menthol in the presence of a Ti(IV) catalyst to give diastereomeric 8(P) and 8(M). It was found that dendritic-like cavitands 8(P) and 8(M), in CD2Cl2, undergo self-inclusion ((1)H NMR spectroscopy) with a menthol moiety occupying the cavity of each host. Importantly, the degree of inclusion of the menthol group was ((1)H NMR spectroscopy) found to be greater in the case of 8(P) than 8(M). Accordingly, it is suggested that different folding characteristic of 8(P) and 8(M) ought to affect the physicochemical characteristics of the hosts to permit their effective separation by column chromatography. The absolute configuration of 8(P)/8(M), encompassing right- and left-handed "cups", was determined with the exciton chirality method and also verified in silico (DFT: B3LYP/TZVP). Finally, the twisted baskets are strongly fluorescent due to three naphthalene chromophores, having a high fluorescence quantum yield within the rigid framework of 8(P)/8(M). © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  14. Generalizing twisted gauge invariance

    SciTech Connect

    Duenas-Vidal, Alvaro; Vazquez-Mozo, Miguel A.

    2009-05-01

    We discuss the twisting of gauge symmetry in noncommutative gauge theories and show how this can be generalized to a whole continuous family of twisted gauge invariances. The physical relevance of these twisted invariances is discussed.

  15. HOUSTON - EARTH VIEWS - LOW-ALTITUDE - HIGH-ANGLE - TX

    NASA Image and Video Library

    1975-01-01

    Low-altitude, high-angle view of Houston downtown area. This view was photographed to show convention central part of downtown to promote facilities here for hosting large conventions, etc. 1. JSC PROTOCOL - CONVENTIONS HOUSTON, TX

  16. Design of Nonlinear Autopilots for High Angle of Attack Missiles

    DTIC Science & Technology

    1996-01-01

    Copyright 1996 by Optimal Synthesis . All Rights Reserved. 1 Design of Nonlinear Autopilots for High Angle of Attack Missiles By P. K. Menon* and...M. Yousefpor† Optimal Synthesis Palo Alto, CA 94306, USA Abstract Two nonlinear autopilot design approaches for a tail-controlled high angle of...Prescribed by ANSI Std Z39-18 © Copyright 1996 by Optimal Synthesis . All Rights Reserved. 2 better agility from tactical missiles. In air-to-air

  17. Twisted dust acoustic waves in dusty plasmas

    SciTech Connect

    Shukla, P. K.

    2012-08-15

    We examine linear dust acoustic waves (DAWs) in a dusty plasma with strongly correlated dust grains, and discuss possibility of a twisted DA vortex beam carrying orbital angular momentum (OAM). For our purposes, we use the Boltzmann distributed electron and ion density perturbations, the dust continuity and generalized viscoelastic dust momentum equations, and Poisson's equation to obtain a dispersion relation for the modified DAWs. The effects of the polarization force, strong dust couplings, and dust charge fluctuations on the DAW spectrum are examined. Furthermore, we demonstrate that the DAW can propagate as a twisted vortex beam carrying OAM. A twisted DA vortex structure can trap and transport dust particles in dusty plasmas.

  18. Aerodynamic characteristics of airplanes at high angles of attack

    NASA Technical Reports Server (NTRS)

    Chambers, J. R.; Grafton, S. B.

    1977-01-01

    An introduction to, and a broad overiew of, the aerodynamic characteristics of airplanes at high angles of attack are provided. Items include: (1) some important fundamental phenomena which determine the aerodynamic characteristics of airplanes at high angles of attack; (2) static and dynamic aerodynamic characteristics near the stall; (3) aerodynamics of the spin; (4) test techniques used in stall/spin studies; (5) applications of aerodynamic data to problems in flight dynamics in the stall/spin area; and (6) the outlook for future research in the area. Although stalling and spinning are flight dynamic problems of importance to all aircraft, including general aviation aircraft, commercial transports, and military airplanes, emphasis is placed on military configurations and the principle aerodynamic factors which influence the stability and control of such vehicles at high angles of attack.

  19. How ARCO drills high-angle wells offshore Indonesia

    SciTech Connect

    Tjondrodiputro, B.; Eddyarso, H.; Jones, K. )

    1993-03-01

    Atlantic Richfield Indonesia, Inc. (ARII) drilled and completed 28 high-angle wells since early 1986 in Bima, Papa and FF fields in the Offshore North West Java Sea (ONWJ) contract area. Early wells were drilled with conventional rotary bottomhole assemblies (BHAs); introduction of a steerable tool and MWD subsequently increased efficiency and reduced drilling costs. Both lignosulfonate and dispersed pac polymer muds have been used with good success. Cost to drill a high-angle well has been only marginally more than that of a 45[degree] directional well. Elimination of open hole logging and use of preperforated liners have reduced drilling costs by 10%. Production performance for wells has been higher than for vertical or low-angle wells. High-angle wells in Bima have outperformed offset vertical wells and are classified as a success. However, horizontal wells in Papa, which has a strong bottom-water drive, have not shown any improved recovery over conventional wells. The new well in FF field is still being evaluated. In this first of a two-part report, high-angle drilling operations including well planning, BHA selection, casing and mud programs, hole cleaning and logging are described. Specific wells in the Bima area are discussed as examples.

  20. ELECTROMAGNETIC AND MICROSTRUCTURAL PROPERTIES OF PURE C-AXIS TWIST Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} BICRYSTAL JUNCTIONS

    SciTech Connect

    TSAY,Y.; LI,Q.; ZHU,Y.; SUENAGA,M.; GU,G.D.; KOSHIZUKA,N.

    1998-07-18

    Bulk Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} (Bi2212) bicrystals containing a single high quality [001] twist grain boundary junction were prepared in order to investigate the orbital symmetry of the superconducting order parameter in highly anisotropic Bi-based high temperature superconductors. The misorientation angles of the bicrystals ranged from 0 to 180{degree}. The microstructure in the vicinity of the junction was characterized using high-resolution, nano-probe analytical microscopy. The authors found that some high angle twist junctions were able to carry a critical current density similar to their constituent single crystals. These results cannot be interpreted in terms of a pure d{sub x{sup 2}-y{sup 2}}-wave order parameter for superconducting Bi2212.

  1. Electromagnetic and microstructural properties of pure c-axis twist Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} bicrystal junctions

    SciTech Connect

    Tsay, Y.N.; Li, Q.; Zhu, Y.; Suenaga, M.; Gu, G.D.; Koshizuka, N.

    1998-08-01

    Bulk Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} (Bi2212) bicrystals containing a single high quality [001] twist grain boundary junction were prepared in order to investigate the orbital symmetry of the superconducting order parameter in highly anisotropic Bi-based high temperature superconductors. The misorientation angles of the bicrystals ranged from 0 to 180{degree}. The microstructure in the vicinity of the junction was characterized using high-resolution, nano-probe analytical microscopy. The authors found that some high angle twist junctions were able to carry a critical current density similar to their constituent single crystals. These results cannot be interpreted in terms of a pure d{sub x{sup 2}{minus}y{sup 2}}-wave order parameter for superconducting Bi2212.

  2. Cable-Twisting Machine

    NASA Technical Reports Server (NTRS)

    Kurnett, S.

    1982-01-01

    New cable-twisting machine is smaller and faster than many production units. Is useful mainly in production of short-run special cables. Already-twisted cable can be fed along axis of machine. Faster operation than typical industrial cable-twisting machines possible by using smaller spools of wire.

  3. X-31 high angle of attack control system performance

    NASA Technical Reports Server (NTRS)

    Huber, Peter; Seamount, Patricia

    1994-01-01

    The design goals for the X-31 flight control system were: (1) level 1 handling qualities during post-stall maneuvering (30 to 70 degrees angle-of-attack); (2) thrust vectoring to enhance performance across the flight envelope; and (3) adequate pitch-down authority at high angle-of-attack. Additional performance goals are discussed. A description of the flight control system is presented, highlighting flight control system features in the pitch and roll axes and X-31 thrust vectoring characteristics. The high angle-of-attack envelope clearance approach will be described, including a brief explanation of analysis techniques and tools. Also, problems encountered during envelope expansion will be discussed. This presentation emphasizes control system solutions to problems encountered in envelope expansion. An essentially 'care free' envelope was cleared for the close-in-combat demonstrator phase. High angle-of-attack flying qualities maneuvers are currently being flown and evaluated. These results are compared with pilot opinions expressed during the close-in-combat program and with results obtained from the F-18 HARV for identical maneuvers. The status and preliminary results of these tests are discussed.

  4. Simulation of xenon, uranium vacancy and interstitial diffusion and grain boundary segregation in UO2

    SciTech Connect

    Andersson, Anders D.; Tonks, Michael R.; Casillas, Luis; Nerikar, Pankaj; Vyas, Shyam; Uberuaga, Blas P.; Stanek, Christopher R.

    2014-10-31

    In light water reactor fuel, gaseous fission products segregate to grain boundaries, resulting in the nucleation and growth of large intergranular fission gas bubbles. Based on the mechanisms established from density functional theory (DFT) and empirical potential calculations 1, continuum models for diffusion of xenon (Xe), uranium (U) vacancies and U interstitials in UO2 have been derived for both intrinsic conditions and under irradiation. Segregation of Xe to grain boundaries is described by combining the bulk diffusion model with a model for the interaction between Xe atoms and three different grain boundaries in UO2 ( Σ5 tilt, Σ5 twist and a high angle random boundary),as derived from atomistic calculations. All models are implemented in the MARMOT phase field code, which is used to calculate effective Xe and U diffusivities as well as redistribution for a few simple microstructures.

  5. Mesoscale mechanics of twisting carbon nanotube yarns

    NASA Astrophysics Data System (ADS)

    Mirzaeifar, Reza; Qin, Zhao; Buehler, Markus J.

    2015-03-01

    Fabricating continuous macroscopic carbon nanotube (CNT) yarns with mechanical properties close to individual CNTs remains a major challenge. Spinning CNT fibers and ribbons for enhancing the weak interactions between the nanotubes is a simple and efficient method for fabricating high-strength and tough continuous yarns. Here we investigate the mesoscale mechanics of twisting CNT yarns using full atomistic and coarse grained molecular dynamics simulations, considering concurrent mechanisms at multiple length-scales. To investigate the mechanical response of such a complex structure without losing insights into the molecular mechanism, we applied a multiscale strategy. The full atomistic results are used for training a coarse grained model for studying larger systems consisting of several CNTs. The mesoscopic model parameters are updated as a function of the twist angle, based on the full atomistic results, in order to incorporate the atomistic scale deformation mechanisms in larger scale simulations. By bridging across two length scales, our model is capable of accurately predicting the mechanical behavior of twisted yarns while the atomistic level deformations in individual nanotubes are integrated into the model by updating the parameters. Our results focused on studying a bundle of close packed nanotubes provide novel mechanistic insights into the spinning of CNTs. Our simulations reveal how twisting a bundle of CNTs improves the shear interaction between the nanotubes up to a certain level due to increasing the interaction surface. Furthermore, twisting the bundle weakens the intertube interactions due to excessive deformation in the cross sections of individual CNTs in the bundle.

  6. Probing grain boundary sink strength at the nanoscale: Energetics and length scales of vacancy and interstitial absorption by grain boundaries in α-Fe

    SciTech Connect

    Tschopp, Mark A.; Solanki, K. N.; Gao, Fei; Sun, Xin; Khaleel, Mohammad A.; Horstemeyer, Mark

    2012-02-10

    The energetics and length scales associated with the interaction between point defects (vacancies and self-interstitial atoms) and grain boundaries in bcc Fe was explored. Molecular statics simulations were used to generate a grain boundary structure database that contained {approx}170 grain boundaries with varying tilt and twist character. Then, vacancy and self-interstitial atom formation energies were calculated at all potential grain boundary sites within 15 {angstrom} of the boundary. The present results provide detailed information about the interaction energies of vacancies and self-interstitial atoms with symmetric tilt grain boundaries in iron and the length scales involved with absorption of these point defects by grain boundaries. Both low- and high-angle grain boundaries were effective sinks for point defects, with a few low-{Sigma} grain boundaries (e.g., the {Sigma}3{l_brace}112{r_brace} twin boundary) that have properties different from the rest. The formation energies depend on both the local atomic structure and the distance from the boundary center. Additionally, the effect of grain boundary energy, disorientation angle, and {Sigma} designation on the boundary sink strength was explored; the strongest correlation occurred between the grain boundary energy and the mean point defect formation energies. Based on point defect binding energies, interstitials have {approx}80% more grain boundary sites per area and {approx}300% greater site strength than vacancies. Last, the absorption length scale of point defects by grain boundaries is over a full lattice unit larger for interstitials than for vacancies (mean of 6-7 {angstrom} versus 10-11 {angstrom} for vacancies and interstitials, respectively).

  7. Wire harness twisting aid

    NASA Technical Reports Server (NTRS)

    Casey, E. J.; Commadore, C. C.; Ingles, M. E.

    1980-01-01

    Long wire bundles twist into uniform spiral harnesses with help of simple apparatus. Wires pass through spacers and through hand-held tool with hole for each wire. Ends are attached to low speed bench motor. As motor turns, operator moves hand tool away forming smooth twists in wires between motor and tool. Technique produces harnesses that generate less radio-frequency interference than do irregularly twisted cables.

  8. Wire harness twisting aid

    NASA Technical Reports Server (NTRS)

    Casey, E. J.; Commadore, C. C.; Ingles, M. E.

    1980-01-01

    Long wire bundles twist into uniform spiral harnesses with help of simple apparatus. Wires pass through spacers and through hand-held tool with hole for each wire. Ends are attached to low speed bench motor. As motor turns, operator moves hand tool away forming smooth twists in wires between motor and tool. Technique produces harnesses that generate less radio-frequency interference than do irregularly twisted cables.

  9. Reynolds Number Effects at High Angles of Attack

    NASA Technical Reports Server (NTRS)

    Fisher, David F.; Cobleigh, Brent R.; Banks, Daniel W.; Hall, Robert M.; Wahls, Richard A.

    1998-01-01

    Lessons learned from comparisons between ground-based tests and flight measurements for the high-angle-of-attack programs on the F-18 High Alpha Research Vehicle (HARV), the X-29 forward-swept wing aircraft, and the X-31 enhanced fighter maneuverability aircraft are presented. On all three vehicles, Reynolds number effects were evident on the forebodies at high angles of attack. The correlation between flight and wind tunnel forebody pressure distributions for the F-18 HARV were improved by using twin longitudinal grit strips on the forebody of the wind-tunnel model. Pressure distributions obtained on the X-29 wind-tunnel model at flight Reynolds numbers showed excellent correlation with the flight data up to alpha = 50 deg. Above (alpha = 50 deg. the pressure distributions for both flight and wind tunnel became asymmetric and showed poorer agreement, possibly because of the different surface finish of the model and aircraft. The detrimental effect of a very sharp nose apex was demonstrated on the X-31 aircraft. Grit strips on the forebody of the X-31 reduced the randomness but increased the magnitude of the asymmetry. Nose strakes were required to reduce the forebody yawing moment asymmetries and the grit strips on the flight test noseboom improved the aircraft handling qualities.

  10. Forebody tangential blowing for control at high angles of attack

    NASA Technical Reports Server (NTRS)

    Kroo, I.; Rock, S.; Roberts, L.

    1991-01-01

    A feasibility study to determine if the use of tangential leading edge blowing over the forebody could produce effective and practical control of the F-18 HARV aircraft at high angles of attack was conducted. A simplified model of the F-18 configuration using a vortex-lattice model was developed to obtain a better understanding of basic aerodynamic coupling effects and the influence of forebody circulation on lifting surface behavior. The effect of tangential blowing was estimated using existing wind tunnel data on normal forebody blowing and analytical studies of tangential blowing over conical forebodies. Incorporation of forebody blowing into the flight control system was investigated by adding this additional yaw control and sideforce generating actuator into the existing F-18 HARV simulation model. A control law was synthesized using LQG design methods that would schedule blowing rates as a function of vehicle sideslip, angle of attack, and roll and yaw rates.

  11. Influence of twist angle on crack propagation of nanoscale bicrystal nickel film based on molecular dynamics simulation

    NASA Astrophysics Data System (ADS)

    Zhang, Yanqiu; Jiang, Shuyong; Zhu, Xiaoming; Zhao, Yanan

    2017-03-01

    Tensile deformation of nanoscale bicrystal nickel film with twist grain boundary, which includes various twist angles, is investigated via molecular dynamics simulation to obtain the influence of twist angle on crack propagation. The twist angle has a significant influence on crack propagation. At the tensile strain of 0.667, as for the twist angles of 0°, 3.54° and 7.05°, the bicrystal nickel films are subjected to complete fracture, while as for the twist angles of 16.1° and 33.96°, no complete fracture occurs in the bicrystal nickel films. When the twist angles are 16.1° and 33.96°, the dislocations emitted from the crack tip are almost unable to go across the grain boundary and enter into the other grain along the slip planes {111}. There should appear a critical twist angle above which the crack propagation is suppressed at the grain boundary. The higher energy in the grain boundary with larger twist angle contributes to facilitating the movement of the glissile dislocation along the grain boundary rather than across the grain boundary, which leads to the propagation of the crack along the grain boundary.

  12. Analysis of lead twist in modern high-performance grinding methods

    NASA Astrophysics Data System (ADS)

    Kundrák, J.; Gyáni, K.; Felhő, C.; Markopoulos, AP; Deszpoth, I.

    2016-11-01

    According to quality requirements of road vehicles shafts, which bear dynamic seals, twisted-pattern micro-geometrical topography is not allowed. It is a question whether newer modern grinding methods - such as quick-point grinding and peel grinding - could provide twist- free topography. According to industrial experience, twist-free surfaces can be made, however with certain settings, same twist occurs. In this paper it is proved by detailed chip-geometrical analysis that the topography generated by the new procedures is theoretically twist-patterned because of the feeding motion of the CBN tool. The presented investigation was carried out by a single-grain wheel model and computer simulation.

  13. Effect of twisting on microstructure, critical current, and AC losses of Bi-2223 superconductor tape

    NASA Astrophysics Data System (ADS)

    Lim, Jun Hyung; Jang, Seok Hern; Kim, Ho Jin; Joo, Jinho; Nah, Wansoo; Kim, Chang Wan; Ryu, Kyung-Woo; Ha, Hong-Soo; Oh, Sang-Soo

    2002-08-01

    We evaluated the effect of twisting on microstructure, critical current, and AC losses of Bi-2223 superconductor tapes. It was observed that grain size and grain alignment were reduced with decreasing twist pitch probably due to the formation of an irregular interface between Ag and filaments. The critical current of the tapes decreased with decreasing pitch. For the tape having a twist pitch of 10 mm, ≈50% of the critical current was maintained compared to that of the non-twisted tape. The reduction of critical current is believed to be due to irregular interface, poor grain alignment, small grain size, and existence of second phases, etc. In addition, it was observed that AC losses of the tapes were reduced as the pitch decreased probably due to the combined effect of lower critical current and electrically decoupled filament of twisted tape.

  14. Apollo 11 Launched Via Saturn V Rocket - High Angle View

    NASA Technical Reports Server (NTRS)

    1969-01-01

    The Apollo 11 mission, the first manned lunar mission, launched from the Kennedy Space Center, Florida via the Saturn V launch vehicle on July 16, 1969 and safely returned to Earth on July 24, 1969. The Saturn V vehicle produced a holocaust of flames as it rose from its pad at Launch complex 39. The 363 foot tall, 6,400,000 pound rocket hurled the spacecraft into Earth parking orbit and then placed it on the trajectory to the moon. This high angle view of the launch was provided by a `fisheye' camera mounted on the launch tower. The Saturn V was developed by the Marshall Space Flight Center (MSFC) under the direction of Dr. Wernher von Braun. Aboard the spacecraft were astronauts Neil A. Armstrong, commander; Michael Collins, Command Module (CM) pilot; and Edwin E. Aldrin Jr., Lunar Module (LM) pilot. With the success of Apollo 11, the national objective to land men on the Moon and return them safely to Earth had been accomplished.

  15. Twisted partially pure spinors

    NASA Astrophysics Data System (ADS)

    Herrera, Rafael; Tellez, Ivan

    2016-08-01

    Motivated by the relationship between orthogonal complex structures and pure spinors, we define twisted partially pure spinors in order to characterize spinorially subspaces of Euclidean space endowed with a complex structure.

  16. Twisted multifilament superconductor

    NASA Technical Reports Server (NTRS)

    Coles, W. D. (Inventor)

    1973-01-01

    Masking selected portions of a ribbon and forming an intermetallic compound on the unmasked portions by a controlled diffusion reaction produces a twisted filamentary structure. The masking material prohibits the formation of superconductive material on predetermined areas of the substrate.

  17. TWIST User Presentation

    EPA Pesticide Factsheets

    The Wastewater Information System Tool (TWIST) is downloadable, user-friendly management tool that will allow state and local health departments to effectively inventory and manage small wastewater treatment systems in their jurisdictions.

  18. Twisted radio waves and twisted thermodynamics.

    PubMed

    Kish, Laszlo B; Nevels, Robert D

    2013-01-01

    We present and analyze a gedanken experiment and show that the assumption that an antenna operating at a single frequency can transmit more than two independent information channels to the far field violates the Second Law of Thermodynamics. Transmission of a large number of channels, each associated with an angular momenta 'twisted wave' mode, to the far field in free space is therefore not possible.

  19. High-Angle Backscatter from Snow on the Ground

    NASA Astrophysics Data System (ADS)

    Knox, Joseph E.

    1983-09-01

    In January and February of 1981 and 1982, the Ballistic Research Laboratory (BRL) participated in SNOW-ONE at Camp Ethan Allen, VT, sponsored by the US Army Cold Regions Research and Engineering Laboratory (CRREL). The BRL conducted high-angle radar measurements there, measuring backscatter at 35 GHz. from various areas of undisturbed snow, acquiring time series data under varied weather conditions. A dual-polarized, 35 GHz radar was used to make the snow backscatter measurements. Polarity of the transmitted signal, vertical or horizontal, was controlled by means of an R.F. switch. The received signal was passed through an orthomode transducer to two receivers, allowing both parallel and cross polarized components to be recorded simultaneously. The sensor was supported 15 meters above the ground on an elevation-over-azimuth antenna mount. Elevation angle was adjusted so that radar beam angle was 30-degrees from vertical. Azimuth angle was varied so as to scan areas of undisturbed snow around the base of the support. The sensor was enclosed in an insulated box and heated to a fixed temperature. Signal returned to the sensor by the snow was, in large part, dependent upon the condition of the surface snow as it was affected by air temperature. When the temperature was well below freezing, sigma-zero was around -7dB with parallel polarization (-13dB, cross polarization). When the temperature increased to the freezing point, the snow became wet, packed easily, and had a lower sigma-zero (-17dB, parallel, and -22dB, cross polarization). The condition of the snow surface had a secondary effect upon the value of sigma-zero. A smoothed surface reflected less energy back to the sensor than a roughened surface. The combined effect of these two variables produced the changes that were measured in sigma-zero.

  20. Multiscale simulation of xenon diffusion and grain boundary segregation in UO₂

    DOE PAGES

    Andersson, David A.; Tonks, Michael R.; Casillas, Luis; ...

    2015-07-01

    In light water reactor fuel, gaseous fission products segregate to grain boundaries, resulting in the nucleation and growth of large intergranular fission gas bubbles. The segregation rate is controlled by diffusion of fission gas atoms through the grains and interaction with the boundaries. Based on the mechanisms established from earlier density functional theory (DFT) and empirical potential calculations, diffusion models for xenon (Xe), uranium (U) vacancies and U interstitials in UO₂ have been derived for both intrinsic (no irradiation) and irradiation conditions. Segregation of Xe to grain boundaries is described by combining the bulk diffusion model with a model formore » the interaction between Xe atoms and three different grain boundaries in UO₂ (Σ5 tilt, Σ5 twist and a high angle random boundary), as derived from atomistic calculations. The present model does not attempt to capture nucleation or growth of fission gas bubbles at the grain boundaries. The point defect and Xe diffusion and segregation models are implemented in the MARMOT phase field code, which is used to calculate effective Xe and U diffusivities as well as to simulate Xe redistribution for a few simple microstructures.« less

  1. Multiscale simulation of xenon diffusion and grain boundary segregation in UO₂

    SciTech Connect

    Andersson, David A.; Tonks, Michael R.; Casillas, Luis; Vyas, Shyam; Nerikar, Pankaj; Uberuaga, Blas P.; Stanek, Christopher R.

    2015-07-01

    In light water reactor fuel, gaseous fission products segregate to grain boundaries, resulting in the nucleation and growth of large intergranular fission gas bubbles. The segregation rate is controlled by diffusion of fission gas atoms through the grains and interaction with the boundaries. Based on the mechanisms established from earlier density functional theory (DFT) and empirical potential calculations, diffusion models for xenon (Xe), uranium (U) vacancies and U interstitials in UO₂ have been derived for both intrinsic (no irradiation) and irradiation conditions. Segregation of Xe to grain boundaries is described by combining the bulk diffusion model with a model for the interaction between Xe atoms and three different grain boundaries in UO₂ (Σ5 tilt, Σ5 twist and a high angle random boundary), as derived from atomistic calculations. The present model does not attempt to capture nucleation or growth of fission gas bubbles at the grain boundaries. The point defect and Xe diffusion and segregation models are implemented in the MARMOT phase field code, which is used to calculate effective Xe and U diffusivities as well as to simulate Xe redistribution for a few simple microstructures.

  2. Multiscale simulation of xenon diffusion and grain boundary segregation in UO2

    NASA Astrophysics Data System (ADS)

    Andersson, David A.; Tonks, Michael R.; Casillas, Luis; Vyas, Shyam; Nerikar, Pankaj; Uberuaga, Blas P.; Stanek, Christopher R.

    2015-07-01

    In light water reactor fuel, gaseous fission products segregate to grain boundaries, resulting in the nucleation and growth of large intergranular fission gas bubbles. The segregation rate is controlled by diffusion of fission gas atoms through the grains and interaction with the boundaries. Based on the mechanisms established from earlier density functional theory (DFT) and empirical potential calculations, diffusion models for xenon (Xe), uranium (U) vacancies and U interstitials in UO2 have been derived for both intrinsic (no irradiation) and irradiation conditions. Segregation of Xe to grain boundaries is described by combining the bulk diffusion model with a model for the interaction between Xe atoms and three different grain boundaries in UO2 (Σ 5 tilt, Σ 5 twist and a high angle random boundary), as derived from atomistic calculations. The present model does not attempt to capture nucleation or growth of fission gas bubbles at the grain boundaries. The point defect and Xe diffusion and segregation models are implemented in the MARMOT phase field code, which is used to calculate effective Xe and U diffusivities as well as to simulate Xe redistribution for a few simple microstructures.

  3. The role of atomic structure on grain boundary-defect interactions in Cu

    SciTech Connect

    Xian-Ming Bai; Louis J. Vernon; Richard G. Hoagland; Arthur F. Voter; Michael Nastasi; Blas Pedro Uberuaga

    2012-06-01

    We investigate the role that the atomic structure of grain boundaries in Cu has in the interaction with point defects produced during irradiation. We focus on three aspects of defect-boundary interaction: how defects interact with pristine boundaries, how boundaries modify defect production during collision cascades, and how defects interact with damaged boundaries. We find that there are generic features common to most boundaries, including biased absorption of interstitials over vacancies during collision cascades and strong interactions with vacancies for interstitial-loaded boundaries. However, we find that the magnitude of these behaviors depends strongly on the atomic structure of the boundary. In particular, the biased absorption is much stronger for a high angle twist boundary and smallest for a more general twist-asymmetric tilt boundary. Further, the strength of defect-boundary interactions is also sensitive to the boundary structure. We conclude that the sink strength of grain boundaries for interacting with point defects is not an intrinsic property of the boundary but rather depends on the irradiation condition through the absorbed defect content at the boundary.

  4. Mesozoic pre-thrusting high-angle faults and stratigraphic variations, Plomosa Mountains, W. Arizona

    SciTech Connect

    Richard, S.M.; Spencer, J.E. )

    1993-04-01

    Three contrasting stratigraphic assemblages characterize fault-bounded terranes in the Southern Plomosa Mtns. (1) The Six Price sequence (SPS) consists of Proterozoic coarse-grained granitoid overlain by Paleozoic and Mesozoic strata. (2) The Apache Wash sequence consists of a basal mega-breccia and conglomerate unit overlain by sandstone in a fining-upward sequence. Paleozoic blocks in the mega-breccia include a Cambrian Muav-like lithology not present in the SPS Paleozoic section. The thickness and clast size in conglomerate associated with the mega-breccia increases the S suggesting a source in that direction. (3) The Crystal Hill sequence consists of strata correlated with the lower McCoy Mountains Formation deposited across a previously tilted unconformity between Jurassic volcanic rocks and the Proterozoic Scadden Mountain quartz monzonite. The lower McCoy Mountain Formation consists of basal quartz-arenite that grades up into fine-grained volcanic-lithic sandstones, and then into lithic-feldspathic sandstone and locally conglomerate, forming a coarsening-upward sequence. Because the Apache Wash sequence is cut by the Poorman thrust, the breccias at its base are not related to the Poorman thrust. Derivation of these creccias entirely from the SPS Paleozoic section is precluded by the presence of the Muav-lithology blocks; their source is not exposed. Thrusting in the area, correlated with deformation in the Maria Fold and Thrust Belt, was preceded by faulting to produce the megabreccias, tilting, and formation of NW-trending high-angle fault one of which forms the major lithotectonic boundary in the range.

  5. Double twist helical nanofilaments in bent-core liquid crystals

    NASA Astrophysics Data System (ADS)

    Zhang, Cuiyu; Diorio, Nicholas; Lavrentovich, Oleg D.; Jakli, Antal

    2014-03-01

    Cryo-TEM observations on 40-150 nm films of four bent-core liquid crystal materials in their helical nanofilament (HNF) phase show that the filaments get deformed near the substrate, and the subsequent arrays of nanofilaments are not parallel, but twisted with respect to each other. The effect can explain the mysterious properties of the HNF materials, such as structural color and ambidextrous optical activity. The observed double twist structure was not expected in the previous models of this phase. Being principally different from the packing of molecules in the twist grain boundary (TGB) and blue (BP) phases, the double-twist structure of HNF expands the rich word of nanostructured organic materials. This work was financially supported by NSF DMR-0964765 and DMR 1104850. The cryo-TEM facility was supported by the Ohio Research Scholars Program. We are grateful for Prof. G. Heppke and Dr. D. Lotsch for providing the PnOPIMB materials for us.

  6. Twisted Yangians of small rank

    NASA Astrophysics Data System (ADS)

    Guay, Nicolas; Regelskis, Vidas; Wendlandt, Curtis

    2016-04-01

    We study quantized enveloping algebras called twisted Yangians associated with the symmetric pairs of types CI, BDI, and DIII (in Cartan's classification) when the rank is small. We establish isomorphisms between these twisted Yangians and the well known Olshanskii's twisted Yangians of types AI and AII, and also with the Molev-Ragoucy reflection algebras associated with symmetric pairs of type AIII. We also construct isomorphisms with twisted Yangians in Drinfeld's original presentation.

  7. Twist Propagation in Dinucleosome Arrays

    PubMed Central

    Dobrovolskaia, Irina V.; Kenward, Martin; Arya, Gaurav

    2010-01-01

    We present a Monte Carlo simulation study of the distribution and propagation of twist from one DNA linker to another for a two-nucleosome array subjected to externally applied twist. A mesoscopic model of the array that incorporates nucleosome geometry along with the bending and twisting mechanics of the linkers is employed and external twist is applied in stepwise increments to mimic quasistatic twisting of chromatin fibers. Simulation results reveal that the magnitude and sign of the imposed and induced twist on contiguous linkers depend strongly on their relative orientation. Remarkably, the relative direction of the induced and applied twist can become inverted for a subset of linker orientations—a phenomenon we refer to as “twist inversion”. We characterize the twist inversion, as a function of relative linker orientation, in a phase diagram and explain its key features using a simple model based on the geometry of the nucleosome/linker complex. In addition to twist inversion, our simulations reveal “nucleosome flipping”, whereby nucleosomes may undergo sudden flipping in response to applied twist, causing a rapid bending of the linker and a significant change in the overall twist and writhe of the array. Our findings shed light on the underlying mechanisms by which torsional stresses impact chromatin organization. PMID:21081084

  8. A Transformation Called "Twist"

    ERIC Educational Resources Information Center

    Hwang, Daniel

    2010-01-01

    The transformations found in secondary mathematics curriculum are typically limited to stretches and translations (e.g., ACARA, 2010). Advanced students may find the transformation, twist, to be of further interest. As most available resources are written for professional-level readers, this article is intended to be an introduction accessible to…

  9. Twistors to twisted geometries

    SciTech Connect

    Freidel, Laurent; Speziale, Simone

    2010-10-15

    In a previous paper we showed that the phase space of loop quantum gravity on a fixed graph can be parametrized in terms of twisted geometries, quantities describing the intrinsic and extrinsic discrete geometry of a cellular decomposition dual to the graph. Here we unravel the origin of the phase space from a geometric interpretation of twistors.

  10. Use of Piloted Simulation for High-Angle-of-Attack Agility Research and Design Criteria Development

    NASA Technical Reports Server (NTRS)

    Ogburn, Marilyn E.; Foster, John V.; Hoffler, Keith D.

    1991-01-01

    The use of piloted simulation at Langley Research Center as part of the NASA High-Angle-of-Attack Technology Program (HATP) to provide methods and concepts for the design of advanced fighter aircraft is discussed. A major focus is to develop the design process required to fully exploit the benefits from advanced control concepts for high-angle-of attack agility.

  11. A numerical analysis applied to high angle of attack three-dimensional inlets

    NASA Technical Reports Server (NTRS)

    Hwang, D. P.

    1986-01-01

    The three-dimensional analytical methods used to analyze subsonic high angle of attack inlets are described. The methods are shown to be in good agreement with experimental results for various three-dimensional high angle of attack inlets. The methods are used to predict aerodynamic characteristics of scarf and slotted-lip inlets.

  12. An Atomistic Modeling Study of Alloying Element Impurity Element, and Transmutation Products on the cohesion of A Nickel E5 {l_brace}001{r_brace} Twist Grain Boundary

    SciTech Connect

    G.A. Young Jr.; R. Najafabadi; W. Strohmayer; D.G. Baldrey; B. Hamm; J. Harris; J. Sticht; E. Wimmer

    2003-06-16

    Atomistic modeling methods were employed to investigate the effects of impurity elements on the metallurgy, irradiation embrittlement, and environmentally assisted cracking of nickel-base alloys exposed to nuclear environments. Calculations were performed via ab initio atomistic modeling methods to ensure the accuracy and reliability of the results. A Griffith-type fracture criterion was used to quantitatively assess the effect of elements or element pairs on the grain boundary cohesive strength. In order of most embrittling to most strengthening, the elements are ranked as: He, Li, S, H, C, Zr, P, Fe, Mn, Nb, Cr, and B. Helium is strongly embrittling (-2.04 eV/atom lowering of the Griffith energy), phosphorus has little effect on the grain boundary (0.1 eV/atom), and boron offers appreciable strengthening (1.03 eV/atom increase in the Griffith energy). Calculations for pairs of elements (H-Li, H-B, H-C, H-P, and H-S) show little interaction on the grain boundary cohesive energy, so that for the conditions studied, linear superposition of elemental effects is a good approximation. These calculations help explain metallurgical effects (e.g. why boron can strengthen grain boundaries), irradiation embrittlement (e.g. how boron transmutation results in grain boundary embrittlement), as well as how grain boundary impurity elements can affect environmentally assisted cracking (i.e. low temperature crack propagation and stress corrosion cracking) of nickel-base alloys.

  13. Effect of filament twist on the structure and properties of Ag-sheathed Bi2223 tape

    NASA Astrophysics Data System (ADS)

    Nakamura, Y.; Kurihara, C.; Machida, T.; Inada, R.; Oota, A.

    2009-10-01

    Ag-sheathed Bi2223 tapes show good performances and are ready for many prototype applications. However, drastic reduction of AC loss is strongly required for practical AC power applications. To reduce the AC loss under AC external magnetic field, the introduction of filament twisting with high resistive barrier is effective, but the filament twisting tends to decrease the Jc value. This decrease in Jc is a problem to balance low AC loss with high Ic value. In this study, the effect of filament twisting on the microstructure and Jc property was investigated to overcome the Jc reduction. The Bi2223 tapes sheathed with Ag-Cu alloy were fabricated with a standard PIT method. Although the formation of Bi2223 phase was not affected by filament twisting from the XRD analysis and SEM observation, the Jc values of the twisted tapes decreased about 30% compared to that of non-twisted tape. In the case of the same twist pitch, the sample rolled under large pass reduction ratio showed relatively high Jc value. This high Jc would be caused by the high aspect ratio of the filament of those tapes, in which the grain alignment along the filament interface would be well. On the other hand, a reason for the Jc reduction of twist tapes is proposed to be the misorientation at grain boundaries of Bi2223 grains in the transference region near the edges of the tape, where the filaments move up and down in the thickness direction.

  14. Twisting perturbed parafermions

    NASA Astrophysics Data System (ADS)

    Belitsky, A. V.

    2017-07-01

    The near-collinear expansion of scattering amplitudes in maximally supersymmetric Yang-Mills theory at strong coupling is governed by the dynamics of stings propagating on the five sphere. The pentagon transitions in the operator product expansion which systematize the series get reformulated in terms of matrix elements of branch-point twist operators in the two-dimensional O(6) nonlinear sigma model. The facts that the latter is an asymptotically free field theory and that there exists no local realization of twist fields prevents one from explicit calculation of their scaling dimensions and operator product expansion coefficients. This complication is bypassed making use of the equivalence of the sigma model to the infinite-level limit of WZNW models perturbed by current-current interactions, such that one can use conformal symmetry and conformal perturbation theory for systematic calculations. Presently, to set up the formalism, we consider the O(3) sigma model which is reformulated as perturbed parafermions.

  15. Twisted aspirin crystals.

    PubMed

    Cui, Xiaoyan; Rohl, Andrew L; Shtukenberg, Alexander; Kahr, Bart

    2013-03-06

    Banded spherulites of aspirin have been crystallized from the melt in the presence of salicylic acid either generated from aspirin decomposition or added deliberately (2.6-35.9 mol %). Scanning electron microscopy, X-ray diffraction analysis, and optical polarimetry show that the spherulites are composed of helicoidal crystallites twisted along the <010> growth directions. Mueller matrix imaging reveals radial oscillations in not only linear birefringence, but also circular birefringence, whose origin is explained through slight (∼1.3°) but systematic splaying of individual lamellae in the film. Strain associated with the replacement of aspirin molecules by salicylic acid molecules in the crystal structure is computed to be large enough to work as the driving force for the twisting of crystallites.

  16. Gravity in twisted space

    NASA Technical Reports Server (NTRS)

    Farrar, Kelly A.; Melott, Adrian L.

    1990-01-01

    Numerical simulations with periodic boundary conditions are widely used in cosmology. These have a multiply connected topology known as a three-torus. Such nontrivial topologies for the actual universe may have arisen in the Big Bang. A two-dimensional numerical model with a twisted topology, sometimes a Klein bottle, is shown as well as the fact that local properties of the model are not dependent on topology.

  17. Adaptive continuous twisting algorithm

    NASA Astrophysics Data System (ADS)

    Moreno, Jaime A.; Negrete, Daniel Y.; Torres-González, Victor; Fridman, Leonid

    2016-09-01

    In this paper, an adaptive continuous twisting algorithm (ACTA) is presented. For double integrator, ACTA produces a continuous control signal ensuring finite time convergence of the states to zero. Moreover, the control signal generated by ACTA compensates the Lipschitz perturbation in finite time, i.e. its value converges to the opposite value of the perturbation. ACTA also keeps its convergence properties, even in the case that the upper bound of the derivative of the perturbation exists, but it is unknown.

  18. Twist planet drive

    NASA Technical Reports Server (NTRS)

    Vranish, John M. (Inventor)

    1996-01-01

    A planetary gear system includes a sun gear coupled to an annular ring gear through a plurality of twist-planet gears, a speeder gear, and a ground structure having an internal ring gear. Each planet gear includes a solid gear having a first half portion in the form of a spur gear which includes vertical gear teeth and a second half portion in the form of a spur gear which includes helical gear teeth that are offset from the vertical gear teeth and which contact helical gear teeth on the speeder gear and helical gear teeth on the outer ring gear. One half of the twist planet gears are preloaded downward, while the other half are preloaded upwards, each one alternating with the other so that each one twists in a motion opposite to its neighbor when rotated until each planet gear seats against the sun gear, the outer ring gear, the speeder gear, and the inner ring gear. The resulting configuration is an improved stiff anti-backlash gear system.

  19. Special Grain Boundaries in Ultrafine-Grained Tungsten

    NASA Astrophysics Data System (ADS)

    Dudka, O. V.; Ksenofontov, V. A.; Sadanov, E. V.; Starchenko, I. V.; Mazilova, T. I.; Mikhailovskij, I. M.

    2016-07-01

    Field ion microscopy and computer simulation were used for the study of an atomic structure high-angle grain boundary in hard-drawn ultrafine-grained tungsten wire. These boundaries with special misorientations are beyond the scope of the coincident site lattice model. It was demonstrated that the special non-coincident grain boundaries are the plane-matching boundaries, and rigid-body displacements of adjacent nanograins are normal to the <110> misorientation axis. The vectors of rigid-body translations of grains are described by broad asymmetric statistical distribution. Mathematical modeling showed that special incommensurate boundaries with one grain oriented along the {211} plane have comparatively high cohesive energies. The grain-boundary dislocations ½<110> were revealed and studied at the line of local mismatch of {110} atomic planes of adjacent grains.

  20. Investigation of Flying Qualities of Military Aircraft at High Angles of Attack. Volume 2. Appendices

    DTIC Science & Technology

    1974-06-01

    IWP^P^WW»» .1 9« »iitfUumiimm^mw^mMini^ ’mi AD-A015 830 INVESTIGATION OF FLYING QUALITIES OF MILITARY AIRCRAFT AT HIGH ANGLES OF ATTACK ...l l I ITTI \\ AFFDLre-7*61 \\- 296063 e CO 00 INVESTIGATION OF FLYING QUALITIES OF tO MILITARY AIRCRAFT AT HIGH ANGLES OF ^ ATTACK ^ Volume II...high Angles of Attack , Vol. II: Appendices 1. *UTMORf.J Donald E. Johnston Jeffrey R. Hogge Gary L. Teper ». PERFORMING ORGANIZATION NAME

  1. Analysis of diffraction from (001) twist boundaries in cubic metals

    SciTech Connect

    Brokman, A.; Balluffi, R.W.

    1983-02-01

    An analysis of the diffraction from (001) twist boundaries in cubic metals has been made using analytical methods. A relatively simple model for boundary structure involving rotational relaxations around O lattice elements in the boundary core was employed. The results yielded grain boundary diffracted intensity on a grain boundary diffraction lattice in reciprocal space. This lattice consisted of an array of line elements running parallel to the twist axis in a square pattern corresponding to the reciprocal lattice of the Coincidence Site Lattice lying parallel to the grain boundary plane. The analytical model predicted the presently available main features of experimentally observed diffracted intensities and also those obtained by computer simulation calculations and clearly revealed the physical origins of the diffraction effects. The generalization of the analytical model to include any type of boundary was indicated. 9 figures.

  2. Analysis of diffraction from (001) twist boundaries in cubic metals

    SciTech Connect

    Brokman, A.; Balluffi, R.W.

    1983-10-01

    An analysis of the diffraction from (001) twist boundaries in cubic metals has been made using analytical methods. A simple model for boundary structure involving rotational relaxations around O lattice elements in the boundary core was employed. The results yielded grain boundary diffracted intensity on a grain boundary diffraction lattice in reciprocal space. This lattice consisted of an array of line elements running parallel to the twist axis in a square pattern corresponding to the reciprocal lattice of the coincidence site lattice lying parallel to the grain boundary plane. The analytical model predicted the main features of experimentally observed diffracted intensities and also those obtained by computer simulation and revealed the physical origins of the diffraction effects. The generalization of the analytical model to include any type of boundary was indicated.

  3. Development of an engineering level prediction method for high angle of attack aerodynamics

    NASA Technical Reports Server (NTRS)

    Reisenthel, Patrick H.; Rodman, Laura C.; Nixon, David

    1993-01-01

    The present work is concerned with predicting the unsteady flow considered to be the cause of the structural failure of twin vertical tail aircraft. An engineering tool has been produced for high angle of attack aerodynamics using the simplest physical models. The main innovation behind this work is its emphasis on the modeling of two key aspects of the dominant physics associated with high angle-of-attack airflows, namely unsteady separation and vortex breakdown.

  4. Economic Recovery of Oil Trapped at Fan Margins Using High Angle Wells and Multiple Hydraulic Fractures

    SciTech Connect

    Mike L. Laue

    1998-02-05

    This project attempts to demonstrate the effectivensss of exploiting thin-layered, low energy deposits at the distal margin of a propagating turbinite complex through u se of hydraulically fractgured horizontal of high-angle wells. TGhe combinaton of a horizontal or high-angle weoo and hydraulic fracturing will allow greater pay exposure than can be achieved with conventional vertical wells while maintaining vertical communication between thin interbedded layers and the wellbore.

  5. Economic Recovery of Oil Trapped at Fan Margins Using High Angle Wells and Multiple Hydraulic Fractures

    SciTech Connect

    Mike L. Laue

    1998-05-29

    This project attempts to demonstrate the effectiveness of exploiting thin-layered, low energy deposits at the distal end of a protruding turbidite complex through use of hydraulically fractured horizontal of high-angle wells. The combination of a horizontal or high-angle well and hydraulic fracturing will allow greater pay exposure than conventional vertical wells while maintaining vertical communication between thin interbedded layers and the well bore.

  6. Economic Recovery of Oil Trapped at Fan Margins Using High Angle Wells and Multiple Hydraulic Fractures

    SciTech Connect

    Mike L. Laue

    1997-05-08

    This project attempts to demonstrate the effectiveness of exploiting thin-layered, low-energy deposits at the distal margin of a propagating turbidite complex through the use of hydraulically-fractured horizontal or high-angle wells. The combination of a horizontal or high-angled well and hydraulic fracturing will allow greater pay exposure than can be achieved with conventional vertical wells while maintaining vertical communication between thininterbedded layers and the well bore.

  7. Twisting Plasma Interactions

    NASA Image and Video Library

    2017-06-19

    Several short stalks of cooler, darker plasma spun and twisted as they interacted with each other at the sun's edge (June 14-15, 2017). The row of strands, which together form a prominence, were being pulled back and forth by magnetic forces. The dynamic action was observed for just over one day. Also noteworthy is the rapid development of a bright active region in the upper right about halfway through the clip. Movies are available at https://photojournal.jpl.nasa.gov/catalog/PIA21761

  8. Twisted bialgebroids versus bialgebroids from a Drinfeld twist

    NASA Astrophysics Data System (ADS)

    Borowiec, Andrzej; Pachoł, Anna

    2017-02-01

    Bialgebroids (respectively Hopf algebroids) are bialgebras (Hopf algebras) over noncommutative rings. Drinfeld twist techniques are particularly useful in the (deformation) quantization of Lie algebras as well as the underlying module algebras (=quantum spaces). A smash product construction combines both of them into the new algebra which, in fact, does not depend on the twist. However, we can turn it into a bialgebroid in a twist-dependent way. Alternatively, one can use Drinfeld twist techniques in a category of bialgebroids. We show that both the techniques indicated in the title—the twisting of a bialgebroid or constructing a bialgebroid from the twisted bialgebra—give rise to the same result in the case of a normalized cocycle twist. This can be useful for the better description of a quantum deformed phase space. We argue that within this bialgebroid framework one can justify the use of deformed coordinates (i.e. spacetime noncommutativity), which are frequently postulated in order to explain quantum gravity effects.

  9. Flight test of the X-29A at high angle of attack: Flight dynamics and controls

    NASA Technical Reports Server (NTRS)

    Bauer, Jeffrey E.; Clarke, Robert; Burken, John J.

    1995-01-01

    The NASA Dryden Flight Research Center has flight tested two X-29A aircraft at low and high angles of attack. The high-angle-of-attack tests evaluate the feasibility of integrated X-29A technologies. More specific objectives focus on evaluating the high-angle-of-attack flying qualities, defining multiaxis controllability limits, and determining the maximum pitch-pointing capability. A pilot-selectable gain system allows examination of tradeoffs in airplane stability and maneuverability. Basic fighter maneuvers provide qualitative evaluation. Bank angle captures permit qualitative data analysis. This paper discusses the design goals and approach for high-angle-of-attack control laws and provides results from the envelope expansion and handling qualities testing at intermediate angles of attack. Comparisons of the flight test results to the predictions are made where appropriate. The pitch rate command structure of the longitudinal control system is shown to be a valid design for high-angle-of-attack control laws. Flight test results show that wing rock amplitude was overpredicted and aileron and rudder effectiveness were underpredicted. Flight tests show the X-29A airplane to be a good aircraft up to 40 deg angle of attack.

  10. Perversions with a twist

    PubMed Central

    Silva, Pedro E. S.; Trigueiros, Joao L.; Trindade, Ana C.; Simoes, Ricardo; Dias, Ricardo G.; Godinho, Maria Helena; de Abreu, Fernao Vistulo

    2016-01-01

    Perversions connecting two helices with symmetric handedness are a common occurrence in nature, for example in tendrils. These defects can be found in our day life decorating ribbon gifts or when plants use tendrils to attach to a support. Perversions arise when clamped elastic filaments coil into a helical shape but have to conserve zero overall twist. We investigate whether other types of perversions exist and if they display different properties. Here we show mathematically and experimentally that a continuous range of different perversions can exist and present different geometries. Experimentally, different perversions were generated using micro electrospun fibres. Our experimental results also confirm that these perversions behave differently upon release and adopt different final configurations. These results also demonstrate that it is possible to control on demand the formation and shape of microfilaments, in particular, of electrospun fibres by using ultraviolet light. PMID:27025549

  11. NanoARPES of twisted bilayer graphene on SiC: absence of velocity renormalization for small angles

    PubMed Central

    Razado-Colambo, I.; Avila, J.; Nys, J.-P.; Chen, C.; Wallart, X.; Asensio, M.-C.; Vignaud, D.

    2016-01-01

    The structural and electronic properties of twisted bilayer graphene (TBG) on SiC(000) grown by Si flux-assisted molecular beam epitaxy were investigated using scanning tunneling microscopy (STM) and angle-resolved photoelectron spectroscopy with nanometric spatial resolution. STM images revealed a wide distribution of twist angles between the two graphene layers. The electronic structure recorded in single TBG grains showed two closely-spaced Dirac π bands associated to the two stacked layers with respective twist angles in the range 1–3°. The renormalization of velocity predicted in previous theoretical calculations for small twist angles was not observed. PMID:27264791

  12. NanoARPES of twisted bilayer graphene on SiC: absence of velocity renormalization for small angles.

    PubMed

    Razado-Colambo, I; Avila, J; Nys, J-P; Chen, C; Wallart, X; Asensio, M-C; Vignaud, D

    2016-06-06

    The structural and electronic properties of twisted bilayer graphene (TBG) on SiC(000) grown by Si flux-assisted molecular beam epitaxy were investigated using scanning tunneling microscopy (STM) and angle-resolved photoelectron spectroscopy with nanometric spatial resolution. STM images revealed a wide distribution of twist angles between the two graphene layers. The electronic structure recorded in single TBG grains showed two closely-spaced Dirac π bands associated to the two stacked layers with respective twist angles in the range 1-3°. The renormalization of velocity predicted in previous theoretical calculations for small twist angles was not observed.

  13. Influence of SiC grain boundary character on fission product transport in irradiated TRISO fuel

    SciTech Connect

    Lillo, T. M.; Rooyen, I. J.

    2016-02-26

    The relationship between grain boundary character and fission product migration is identified as an important knowledge gap in order to advance the understanding of fission product release from TRISO fuel particles. Precession electron diffraction (PED), a TEM-based technique, was used in this study to quickly and efficiently provide the crystallographic information needed to identify grain boundary misorientation, grain boundary type (low or high angle) and whether the boundary is coincident site lattice (CSL) – related, in irradiated SiC. Analysis of PED data showed the grain structure of the SiC layer in an irradiated TRISO fuel particle from the AGR-1 experiment to be composed mainly of twin boundaries with a small fraction of low angle grain boundaries (<10%). In general, fission products favor precipitation on random, high angle grain boundaries but can precipitate out on low angle and CSL-related grain boundaries to a limited degree. Pd is capable of precipitating out on all types of grain boundaries but most prominently on random, high angle grain boundaries. Pd-U and Pd-Ag precipitates were found on CSL-related as well as random high angle grain boundaries but not on low angle grain boundaries. In contrast, precipitates containing only Ag were found only on random, high angle grain boundaries but not on either low angle or CSL-related grain boundaries.

  14. Influence of SiC grain boundary character on fission product transport in irradiated TRISO fuel

    DOE PAGES

    Lillo, T. M.; Rooyen, I. J.

    2016-02-26

    The relationship between grain boundary character and fission product migration is identified as an important knowledge gap in order to advance the understanding of fission product release from TRISO fuel particles. Precession electron diffraction (PED), a TEM-based technique, was used in this study to quickly and efficiently provide the crystallographic information needed to identify grain boundary misorientation, grain boundary type (low or high angle) and whether the boundary is coincident site lattice (CSL) – related, in irradiated SiC. Analysis of PED data showed the grain structure of the SiC layer in an irradiated TRISO fuel particle from the AGR-1 experimentmore » to be composed mainly of twin boundaries with a small fraction of low angle grain boundaries (<10%). In general, fission products favor precipitation on random, high angle grain boundaries but can precipitate out on low angle and CSL-related grain boundaries to a limited degree. Pd is capable of precipitating out on all types of grain boundaries but most prominently on random, high angle grain boundaries. Pd-U and Pd-Ag precipitates were found on CSL-related as well as random high angle grain boundaries but not on low angle grain boundaries. In contrast, precipitates containing only Ag were found only on random, high angle grain boundaries but not on either low angle or CSL-related grain boundaries.« less

  15. Twist Helicity in Classical Vortices

    NASA Astrophysics Data System (ADS)

    Scheeler, Martin W.; Kedia, Hridesh; Kleckner, Dustin; Irvine, William T. M.

    2015-11-01

    Recent experimental work has demonstrated that a partial measure of fluid Helicity (the sum of linking and writhing of vortex tubes) is conserved even as those vortices undergo topology changing reconnections. Measuring the total Helicity, however, requires additional information about how the vortex lines are locally twisted inside the vortex core. To bridge this gap, we have developed a novel technique for experimentally measuring twist Helicity. Using this method, we are able to measure the production and eventual decay of twist for a variety of vortex evolutions. Remarkably, we observe twist dynamics capable of conserving total Helicity even in the presence of rapidly changing writhe. This work was supported by the NSF MRSEC shared facilities at the University of Chicago (DMR-0820054) and an NSF CAREER award (DMR-1351506). W.T.M.I. further acknowledges support from the A.P. Sloan Foundation and the Packard Foundation.

  16. Oscillatory growth for twisting crystals.

    PubMed

    Ibaraki, Shunsuke; Ise, Ryuta; Ishimori, Koichiro; Oaki, Yuya; Sazaki, Gen; Yokoyama, Etsuro; Tsukamoto, Katsuo; Imai, Hiroaki

    2015-05-18

    We demonstrate the oscillatory phenomenon for the twisting growth of a triclinic crystal through in situ observation of the concentration field around the growing tip of a needle by high-resolution phase-shift interferometry.

  17. High angle of attack flying qualities criteria for longitudinal rate command systems

    NASA Technical Reports Server (NTRS)

    Wilson, David J.; Citurs, Kevin D.; Davidson, John B.

    1994-01-01

    This study was designed to investigate flying qualities requirements of alternate pitch command systems for fighter aircraft at high angle of attack. Flying qualities design guidelines have already been developed for angle of attack command systems at 30, 45, and 60 degrees angle of attack, so this research fills a similar need for rate command systems. Flying qualities tasks that require post-stall maneuvering were tested during piloted simulations in the McDonnell Douglas Aerospace Manned Air Combat Simulation facility. A generic fighter aircraft model was used to test angle of attack rate and pitch rate command systems for longitudinal gross acquisition and tracking tasks at high angle of attack. A wide range of longitudinal dynamic variations were tested at 30, 45, and 60 degrees angle of attack. Pilot comments, Cooper-Harper ratings, and pilot induced oscillation ratings were taken from five pilots from NASA, USN, CAF, and McDonnell Douglas Aerospace. This data was used to form longitudinal design guidelines for rate command systems at high angle of attack. These criteria provide control law design guidance for fighter aircraft at high angle of attack, low speed flight conditions. Additional time history analyses were conducted using the longitudinal gross acquisition data to look at potential agility measures of merit and correlate agility usage to flying qualities boundaries. This paper presents an overview of this research.

  18. Aerodynamic surface distension system for high angle of attack forebody vortex control

    NASA Technical Reports Server (NTRS)

    Zell, Peter T. (Inventor)

    1994-01-01

    A deployable system is introduced for assisting flight control under certain flight conditions, such as at high angles of attack, whereby two inflatable membranes are located on the forebody portion of an aircraft on opposite sides thereof. The members form control surfaces for effecting lateral control forces if one is inflated and longitudinal control forces if both are inflated.

  19. Wing-Alone Aerodynamic Characteristics to High Angles of Attack at Subsonic and Transonic Speeds.

    DTIC Science & Technology

    1982-11-01

    indicators of symmetry since the wings were unbanked within the limits of tolerances and flow angularity. Longitudinal, spanwise, and vertical... unbanked wings at subsonic and transonic speeds from low to high angles of attack. The wing planforms varied in aspect ratio and taper ratio with

  20. Twisting Neutron Waves

    NASA Astrophysics Data System (ADS)

    Pushin, Dmitry

    Most waves encountered in nature can be given a ``twist'', so that their phase winds around an axis parallel to the direction of wave propagation. Such waves are said to possess orbital angular momentum (OAM). For quantum particles such as photons, atoms, and electrons, this corresponds to the particle wavefunction having angular momentum of Lℏ along its propagation axis. Controlled generation and detection of OAM states of photons began in the 1990s, sparking considerable interest in applications of OAM in light and matter waves. OAM states of photons have found diverse applications such as broadband data multiplexing, massive quantum entanglement, optical trapping, microscopy, quantum state determination and teleportation, and interferometry. OAM states of electron beams have been used to rotate nanoparticles, determine the chirality of crystals and for magnetic microscopy. Here I discuss the first demonstration of OAM control of neutrons. Using neutron interferometry with a spatially incoherent input beam, we show the addition and conservation of quantum angular momenta, entanglement between quantum path and OAM degrees of freedom. Neutron-based quantum information science heretofore limited to spin, path, and energy degrees of freedom, now has access to another quantized variable, and OAM modalities of light, x-ray, and electron beams are extended to a massive, penetrating neutral particle. The methods of neutron phase imprinting demonstrated here expand the toolbox available for development of phase-sensitive techniques of neutron imaging. Financial support provided by the NSERC Create and Discovery programs, CERC and the NIST Quantum Information Program is acknowledged.

  1. Economic Recovery of Oil Trapped at Fan Margins Using High Angle Wells and Multiple Hydraulic Fractures

    SciTech Connect

    Mike L. Laue

    1997-05-30

    The distal fan margin in the northeast portion of the Yowlumne field contains significant reserves but is not economical to develop using vertical wells. Numerous interbedded shales and deteriorating rock properties limit producibility. In addition, extreme depths (13,000 ft) present a challenging environment for hydraulic fracturing and artificial lift. Lastly, a mature waterflood increases risk because of the uncertainty with size and location of flood fronts. This project attempts to demonstrate the effectiveness of exploiting the distal fan margin of this slope-basin clastic reservoir through the use of a high-angle well completed with multiple hydraulic-fracture treatments. The combination of a high-angle (or horizontal) well and hydraulic fracturing will allow greater pay exposure than can be achieved with conventional vertical wells while maintaining vertical communication between thin interbedded layers and the wellbore. The equivalent production rate and reserves of three vertical wells are anticipated at one-half to two-thirds the cost.

  2. Reconfigurable flight control for high angle of attack fighter aircraft, with wind tunnel study

    NASA Astrophysics Data System (ADS)

    Siddiqui, Bilal Ahmed

    In this work we studied Reconfigurable Flight Control Systems to achieve acceptable performance of a fighter aircraft, even in the event of wing damage to the aircraft at low speeds and high angle of attack, which is typical of many combat maneuvers. Equations of motion for the damaged aircraft were derived, which helped in building simulators. A new methodology combining experimental and numerical aerodynamic prediction was proposed and implemented. For this a wind-tunnel study of a similar configuration was carried out to study the aerodynamics at low speeds and high angle of attack. A baseline control system for undamaged aircraft was developed, and finally a reconfigurable flight control scheme was implemented to keep the aircraft flyable even after the damage.

  3. Robust, nonlinear, high angle-of-attack control design for a supermaneuverable vehicle

    NASA Technical Reports Server (NTRS)

    Adams, Richard J.

    1993-01-01

    High angle-of-attack flight control laws are developed for a supermaneuverable fighter aircraft. The methods of dynamic inversion and structured singular value synthesis are combined into an approach which addresses both the nonlinearity and robustness problems of flight at extreme operating conditions. The primary purpose of the dynamic inversion control elements is to linearize the vehicle response across the flight envelope. Structured singular value synthesis is used to design a dynamic controller which provides robust tracking to pilot commands. The resulting control system achieves desired flying qualities and guarantees a large margin of robustness to uncertainties for high angle-of-attack flight conditions. The results of linear simulation and structured singular value stability analysis are presented to demonstrate satisfaction of the design criteria. High fidelity nonlinear simulation results show that the combined dynamics inversion/structured singular value synthesis control law achieves a high level of performance in a realistic environment.

  4. Remarks on simple interpolation between Jordanian twists

    NASA Astrophysics Data System (ADS)

    Meljanac, Stjepan; Meljanac, Daniel; Pachoł, Anna; Pikutić, Danijel

    2017-06-01

    In this paper, we propose a simple generalization of the locally r-symmetric Jordanian twist, resulting in the one-parameter family of Jordanian twists. All the proposed twists differ by the coboundary twists and produce the same Jordanian deformation of the corresponding Lie algebra. They all provide the κ-Minkowski spacetime commutation relations. Constructions from noncommutative coordinates to the star product and coproduct, and from the star product to the coproduct and the twist are presented. The corresponding twist in the Hopf algebroid approach is given. Our results are presented symbolically by a diagram relating all of the possible constructions.

  5. Phonons in twisted bilayer graphene

    NASA Astrophysics Data System (ADS)

    Cocemasov, Alexandr I.; Nika, Denis L.; Balandin, Alexander A.

    2013-07-01

    We theoretically investigate phonon dispersion in AA-stacked, AB-stacked, and twisted bilayer graphene with various rotation angles. The calculations are performed using the Born-von Karman model for the intralayer atomic interactions and the Lennard-Jones potential for the interlayer interactions. It is found that the stacking order affects the out-of-plane acoustic phonon modes the most. The difference in the phonon densities of states in the twisted bilayer graphene and in AA- or AB-stacked bilayer graphene appears in the phonon frequency range 90-110 cm-1. Twisting bilayer graphene leads to the emergence of different phonon branches—termed hybrid folded phonons—which originate from the mixing of phonon modes from different high-symmetry directions in the Brillouin zone. The frequencies of the hybrid folded phonons depend strongly on the rotation angle and can be used for noncontact identification of the twist angles in graphene samples. The obtained results and the tabulated frequencies of phonons in twisted bilayer graphene are important for the interpretation of experimental Raman data and in determining the thermal conductivity of these material systems.

  6. Aerial, high-angle view of Apollo 10 on Pad B, Launch Complex 39, KSC

    NASA Image and Video Library

    1969-05-04

    S69-33854 (4 May 1969) --- Aerial (high-angle, clasp) view of the Apollo 10 (Spacecraft 106/Lunar Module 4/Saturn 505) space vehicle on Pad B, Launch Complex 39, Kennedy Space Center. This photograph of the 363-feet tall Apollo/Saturn V stack was taken during pull back of the mobile service structure. The Apollo 10 crew will be astronauts Thomas P. Stafford, John W. Young, and Eugene A. Cernan.

  7. Pitch control margin at high angle of attack - Quantitative requirements (flight test correlation with simulation predictions)

    NASA Technical Reports Server (NTRS)

    Lackey, J.; Hadfield, C.

    1992-01-01

    Recent mishaps and incidents on Class IV aircraft have shown a need for establishing quantitative longitudinal high angle of attack (AOA) pitch control margin design guidelines for future aircraft. NASA Langley Research Center has conducted a series of simulation tests to define these design guidelines. Flight test results have confirmed the simulation studies in that pilot rating of high AOA nose-down recoveries were based on the short-term response interval in the forms of pitch acceleration and rate.

  8. Pitch control margin at high angle of attack - Quantitative requirements (flight test correlation with simulation predictions)

    NASA Technical Reports Server (NTRS)

    Lackey, J.; Hadfield, C.

    1992-01-01

    Recent mishaps and incidents on Class IV aircraft have shown a need for establishing quantitative longitudinal high angle of attack (AOA) pitch control margin design guidelines for future aircraft. NASA Langley Research Center has conducted a series of simulation tests to define these design guidelines. Flight test results have confirmed the simulation studies in that pilot rating of high AOA nose-down recoveries were based on the short-term response interval in the forms of pitch acceleration and rate.

  9. Development of a pneumatic high-angle-of-attack flush airdata sensing system

    NASA Technical Reports Server (NTRS)

    Whitmore, Stephen A.

    1991-01-01

    A nonintrusive high-angle-of-attack flush airdata sensing system was installed and flight tested in the F-18 High Alpha Research Vehicle. This system consists of a matrix of 25 pressure orifices arranged in concentric circles on the nose of the vehicle to determine angles of attack and sideslip, Mach number, and pressure altitude. During the course of the flight tests, it was determined that satisfactory results could be achieved using a subset of just nine ports.

  10. Development of a pneumatic high-angle-of-attack flush airdata sensing (HI-FADS) system

    NASA Technical Reports Server (NTRS)

    Whitmore, Stephen A.

    1991-01-01

    A nonintrusive high-angle-of-attack flush airdata sensing system was installed and flight tested in the F-18 High Alpha Research Vehicle. This system consists of a matrix of 25 pressure orifices arranged in concentric circles on the nose of the vehicle to determine angles of attack and sideslip, Mach number, and pressure altitude. During the course of the flight tests, it was determined that satisfactory results could be achieved using a subset of just nine ports.

  11. Experimental Flight Characterization of Spin Stabilized Projectiles at High Angle of Attack

    DTIC Science & Technology

    2017-08-07

    of downrange travel ) is also evident in the horizontal data. Fig. 3 Center-of-gravity motion The rolling motion is captured in Fig. 4. These...data are strongly linear with distance travelled because the launch spin rate is around 90 Hz and roll decelerates slightly due to aerodynamic damping...This vehicle rolls about 70 times over 200 m of downrange travel . For some of the high-angle-of-attack flights a significant amount of roll data

  12. Computational Investigation of Incompressible Airfoil Flows at High Angles of Attack

    DTIC Science & Technology

    1988-12-01

    Incompressible Airfoil Flows at High Angles of Attack by John Mark Mathre Lieutenant, United States Navy B.S., United States Naval Academy, 1978 Submitted...Similarly, in the y-direction the Navier-Stokes equation is ODv v 3v I P Z) v 32v - + U- + v- =- - + V(- + -). (2.24) Zt Zx zy p Dy x 2 Y2 11 III. STEADY

  13. Differential Game Based Guidance Law for High Angle of Attack Missiles

    DTIC Science & Technology

    1996-01-01

    Copyright 1996 by Optimal Synthesis . All Rights Reserved. Differential Game Based Guidance Law for High Angle of Attack Missiles By P. K. Menon and...G.B. Chatterji* Optimal Synthesis 450 San Antonio Road, Suite 53 Palo Alto, CA 94303 Abstract A nonlinear differential game theoretic intercept...Scientists, Optimal Synthesis Inc. Report Documentation Page Form ApprovedOMB No. 0704-0188 Public reporting burden for the collection of information is

  14. Development of a pneumatic high-angle-of-attack flush airdata sensing system

    NASA Technical Reports Server (NTRS)

    Whitmore, Stephen A.

    1991-01-01

    A nonintrusive high-angle-of-attack flush airdata sensing system was installed and flight tested in the F-18 High Alpha Research Vehicle. This system consists of a matrix of 25 pressure orifices arranged in concentric circles on the nose of the vehicle to determine angles of attack and sideslip, Mach number, and pressure altitude. During the course of the flight tests, it was determined that satisfactory results could be achieved using a subset of just nine ports.

  15. High angle-of-attack aerodynamic characteristics of crescent and elliptic wings

    NASA Technical Reports Server (NTRS)

    Vandam, C. P.

    1989-01-01

    Static longitudinal and lateral-directional forces and moments were measured for elliptic- and crescent-wing models at high angles-of-attack in the NASA Langley 14 by 22-Ft Subsonic Tunnel. The forces and moments were obtained for an angle-of-attack range including stall and post-stall conditions at a Reynolds number based on the average wing chord of about 1.8 million. Flow-visualization photographs using a mixture of oil and titanium-dioxide were also taken for several incidence angles. The force and moment data and the flow-visualization results indicated that the crescent wing model with its highly swept tips produced much better high angle-of-attack aerodynamic characteristics than the elliptic model. Leading-edge separation-induced vortex flow over the highly swept tips of the crescent wing is thought to produce this improved behavior at high angles-of-attack. The unique planform design could result in safer and more efficient low-speed airplanes.

  16. Economic Recovery of Oil Trapped at Fan Margins Using High Angle Wells Multiple Hydraulic Fractures

    SciTech Connect

    Mike L. Laue

    1997-10-30

    This project attempts to demonstrate the effectiveness of exploiting thin-layered, low-energy deposits at the distal margin of a prograding turbidite complex through the use of hydraulically fractured horizontal or high-angle wells. The combination of a horizontal or high-angle well and hydraulic fracturing will allow greater pay exposure than can be achieved with conventional vertical wells while maintaining vertical communication between thin interbedded layers and the wellbore. A high-angle well will be drilled in the fan-margin portion of a slope-basin clastic reservoir and will be completed with multiple hydraulic-fracture treatments. Geologic modeling, reservoir characterization, and fine-grid reservoir simulation will be used to select the well location and orientation. Design parameters for the hydraulic-fracture treatments will be determined, in part, by fracturing an existing test well. Fracture azimuth will be predicted by passive seismic monitoring of a fracture-stimulation treatment in the test well using logging tools in an offset well.

  17. Twisted Van der Waals Systems

    NASA Astrophysics Data System (ADS)

    Gani, Satrio; Rossi, Enrico

    Van der Waals systems formed by two-dimensional (2D) crystals and nanostructures possess electronic properties that make them extremely interesting for basic science and for possible technological applications. By tuning the relative angle (the twist angle) between the layers, or nanostructures, forming the Van der Waals systems experimentalists have been able to control the stacking configuration of such systems. We study the dependence on the twist angle of the electronic properties of two classes of Van der Waals systems: double layers formed by two, one-atom thick, layers of a metal dichalcogenide such as molybdenum disulfide (MoS2), and graphene nanoribbons on a hexagonal boron nitride substrate. We present results that show how, for both classes of systems, the electronic properties can be strongly tuned via the twist angle. Work supported by ACS-PRF-53581-DNI5 and NSF-DMR-1455233.

  18. The transient roll moment response due to forebody tangential blowing at high angles of attack

    NASA Astrophysics Data System (ADS)

    Chow, Jonathan Kwokching

    The sustained ability for controlled flight at high angles of attack is desirable for future aircraft. For combat aircraft, enhancing maneuverability is important to increasing its survivability. For future supersonic commercial aircraft, an increase in lift at high angles of attack leads to improved performance during take-offs and landing, and a reduction in noise pollution. However, nonlinear and unsteady phenomena, such as flow separation and vortex shedding dominate the aerodynamics in the high angle of attack regime. These phenomena cause the onset of lateral loads and decrease the effectiveness of conventional control surfaces. For conventional aircraft, controlled flight at high angle of attack is difficult or unfeasible without augmented means of control and a good understanding of their impact on vehicle characteristics and dynamics. The injection of thin sheets of air tangentially to the forebody of the vehicle has been found to be an extremely promising method for augmenting the control of a flight vehicle at high angles of attack. Forebody Tangential Blowing (FTB) allows the flow structure to be altered in a rational manner and increase the controllability of the vehicle under these flight conditions. The feasibility of using FTB to control the roll-yaw motion of flight vehicles has been demonstrated. Existing knowledge of FTB's nonlinear impact on the aerodynamic moment responses is limited. Currently available dynamic models predict the general trends in the behavior but do not capture important transient effects that dominate the responses when small amounts of blowing is used. These transients can be large in comparison to the steady-state values. This thesis summarizes the experimental and theoretical results of an investigation into the transient effects of Forebody Tangential Blowing. The relationship between the aerodynamic roll moment, vortical flowfield, and blowing strength is examined to obtain a fundamental understanding of the physics of

  19. Influence of SiC grain boundary character on fission product transport in irradiated TRISO fuel

    NASA Astrophysics Data System (ADS)

    Lillo, T. M.; van Rooyen, I. J.

    2016-05-01

    In this study, the fission product precipitates at silicon carbide grain boundaries from an irradiated TRISO particle were identified and correlated with the associated grain boundary characteristics. Precession electron diffraction in the transmission electron microscope provided the crystallographic information needed to identify grain boundary misorientation and boundary type (i.e., low angle, random high angle or coincident site lattice (CSL)-related). The silicon carbide layer was found to be composed mainly of twin boundaries and small fractions of random high angle and low angle grain boundaries. Most fission products were found at random, high-angle grain boundaries, with small fractions at low-angle and CSL-related grain boundaries. Palladium (Pd) was found at all types of grain boundaries while Pd-uranium and Pd-silver precipitates were only associated with CSL-related and random, high-angle grain boundaries. Precipitates containing only Ag were found only at random, high-angle grain boundaries, but not at low angle or CSL-related grain boundaries.

  20. Drinfeld J Presentation of Twisted Yangians

    NASA Astrophysics Data System (ADS)

    Belliard, Samuel; Regelskis, Vidas

    2017-03-01

    We present a quantization of a Lie coideal structure for twisted half-loop algebras of finite-dimensional simple complex Lie algebras. We obtain algebra closure relations of twisted Yangians in Drinfeld J presentation for all symmetric pairs of simple Lie algebras and for simple twisted even half-loop Lie algebras. We provide the explicit form of the closure relations for twisted Yangians in Drinfeld J presentation for the sl_3 Lie algebra.

  1. Drinfeld twisting elements on Hom-bialgebras

    NASA Astrophysics Data System (ADS)

    Makhlouf, A.; Torrecillas, B.

    2014-09-01

    The purpose of this paper is to introduce the concept of a twisting element based on a Hom- bialgebra and to use it to provide twists or deformations of Hom-associative algebras. Moreover we review the module theory in Hom-setting and show that a twisting element based on a bialgebra gives rise to a twisting element based on a Hom-bialgebra.

  2. Universal teleportation with a twist

    PubMed

    Braunstein; D'Ariano; Milburn; Sacchi

    2000-04-10

    We give a transfer theorem for teleportation based on twisting the entanglement measurement. This allows one to say what local unitary operation must be performed to complete the teleportation in any situation, generalizing the scheme to include overcomplete measurements, non-Abelian groups of local unitary operations (e.g., angular momentum teleportation), and the effect of nonmaximally entangled resources.

  3. Helically twisted photonic crystal fibres.

    PubMed

    Russell, P St J; Beravat, R; Wong, G K L

    2017-02-28

    Recent theoretical and experimental work on helically twisted photonic crystal fibres (PCFs) is reviewed. Helical Bloch theory is introduced, including a new formalism based on the tight-binding approximation. It is used to explore and explain a variety of unusual effects that appear in a range of different twisted PCFs, including fibres with a single core and fibres with N cores arranged in a ring around the fibre axis. We discuss a new kind of birefringence that causes the propagation constants of left- and right-spinning optical vortices to be non-degenerate for the same order of orbital angular momentum (OAM). Topological effects, arising from the twisted periodic 'space', cause light to spiral around the fibre axis, with fascinating consequences, including the appearance of dips in the transmission spectrum and low loss guidance in coreless PCF. Discussing twisted fibres with a single off-axis core, we report that optical activity in a PCF is opposite in sign to that seen in a step-index fibre. Fabrication techniques are briefly described and emerging applications reviewed. The analytical results of helical Bloch theory are verified by an extensive series of 'numerical experiments' based on finite-element solutions of Maxwell's equations in a helicoidal frame.This article is part of the themed issue 'Optical orbital angular momentum'. © 2017 The Authors.

  4. Helically twisted photonic crystal fibres

    PubMed Central

    Beravat, R.; Wong, G. K. L.

    2017-01-01

    Recent theoretical and experimental work on helically twisted photonic crystal fibres (PCFs) is reviewed. Helical Bloch theory is introduced, including a new formalism based on the tight-binding approximation. It is used to explore and explain a variety of unusual effects that appear in a range of different twisted PCFs, including fibres with a single core and fibres with N cores arranged in a ring around the fibre axis. We discuss a new kind of birefringence that causes the propagation constants of left- and right-spinning optical vortices to be non-degenerate for the same order of orbital angular momentum (OAM). Topological effects, arising from the twisted periodic ‘space’, cause light to spiral around the fibre axis, with fascinating consequences, including the appearance of dips in the transmission spectrum and low loss guidance in coreless PCF. Discussing twisted fibres with a single off-axis core, we report that optical activity in a PCF is opposite in sign to that seen in a step-index fibre. Fabrication techniques are briefly described and emerging applications reviewed. The analytical results of helical Bloch theory are verified by an extensive series of ‘numerical experiments’ based on finite-element solutions of Maxwell's equations in a helicoidal frame. This article is part of the themed issue ‘Optical orbital angular momentum’. PMID:28069771

  5. Helically twisted photonic crystal fibres

    NASA Astrophysics Data System (ADS)

    Russell, P. St. J.; Beravat, R.; Wong, G. K. L.

    2017-02-01

    Recent theoretical and experimental work on helically twisted photonic crystal fibres (PCFs) is reviewed. Helical Bloch theory is introduced, including a new formalism based on the tight-binding approximation. It is used to explore and explain a variety of unusual effects that appear in a range of different twisted PCFs, including fibres with a single core and fibres with N cores arranged in a ring around the fibre axis. We discuss a new kind of birefringence that causes the propagation constants of left- and right-spinning optical vortices to be non-degenerate for the same order of orbital angular momentum (OAM). Topological effects, arising from the twisted periodic `space', cause light to spiral around the fibre axis, with fascinating consequences, including the appearance of dips in the transmission spectrum and low loss guidance in coreless PCF. Discussing twisted fibres with a single off-axis core, we report that optical activity in a PCF is opposite in sign to that seen in a step-index fibre. Fabrication techniques are briefly described and emerging applications reviewed. The analytical results of helical Bloch theory are verified by an extensive series of `numerical experiments' based on finite-element solutions of Maxwell's equations in a helicoidal frame. This article is part of the themed issue 'Optical orbital angular momentum'.

  6. "Oliver Twist": A Teacher's Guide.

    ERIC Educational Resources Information Center

    Cashion, Carol; Fischer, Diana

    This teacher's guide for public television's 3-part adaptation of Charles Dickens's "Oliver Twist" provides information that will help enrich students' viewing of the series, whether or not they read the novel. The guide includes a wide range of discussion and activity ideas; there is also a series Web site and a list of Web resources.…

  7. ECONOMIC RECOVERY OF OIL TRAPPED AT FAN MARGINS USING HIGH ANGLE WELLS AND MULTIPLE HYDRAULIC FRACTURES

    SciTech Connect

    Mike L. Laue

    2001-09-28

    This project attempts to demonstrate the effectiveness of exploiting thin-layered, low-energy deposits at the distal margin of a prograding turbidite complex through the use of hydraulically fractured horizontal or high-angle wells. The combination of a horizontal or high-angle well and hydraulic fracturing will allow greater pay exposure than can be achieved with conventional vertical wells while maintaining vertical communication between thin interbedded layers and the wellbore. A high-angle well will be drilled in the fan-margin portion of a slope-basin clastic reservoir and will be completed with multiple hydraulic-fracture treatments. Geologic modeling, reservoir characterization, and fine-grid reservoir simulation will be used to select the well location and orientation. Design parameters for the hydraulic-fracture treatments will be determined, in part, by fracturing an existing test well. Fracture azimuth will be predicted by passive seismic monitoring of a fracture-stimulation treatment in the test well using logging tools in an offset well. The long radius, near horizontal well was drilled during the first quarter of 1996. Well conditions resulted in the 7 in. production liner sticking approximately 900 ft off bottom. Therefore, a 5 in. production liner was necessary to case this portion of the target formation. Swept-out sand intervals and a poor cement bond behind the 5 in. liner precluded two of the three originally planned hydraulic fracture treatments. As a result, all pay intervals behind the 5 in. liner were perforated and stimulated with a non-acid reactive fluid. Following a short production period, the remaining pay intervals in the well (behind the 7 in. liner) were perforated. The well was returned to production to observe production trends and pressure behavior and assess the need to stimulate the new perforations.

  8. Long-term evolution of nourished beaches under high angle wave conditions

    NASA Astrophysics Data System (ADS)

    van den Berg, Niels; Falqués, Albert; Ribas, Francesca

    2011-10-01

    A nonlinear numerical model for large-scale dynamics of shoreline and nearshore bathymetry under wave action is applied to investigate the long-term evolution of a rectilinear coast dominated by high angle wave incidence, which is perturbed by a nourishment or an offshore borrow pit. Previous studies show that a coastline can be unstable due to high angle wave instability, which results from the feedback between shoreline changes and the wave field. In contrast to traditional one-line shoreline models, which always predict a diffusional behaviour, this instability can lead to the growth of shoreline perturbations. Model results suggest that due to high angle wave instability a nourishment or a borrow pit could trigger the formation of a shoreline sand wave train (alternating accretional and erosional zones). Its formation is a self-organised response of the morphodynamic system and can be seen as a spatial-temporal instability. New sand waves are formed downdrift while the old sand waves migrate downdrift and increase in amplitude and wavelength. Instability develops only if the bathymetric changes related to shoreline perturbations extend to a depth where the wave angle is greater than the critical angle of 42°. The potential for coastline instability is therefore limited by the wave incidence angle at the depth of closure and not the angle at deep water as suggested in previous studies. Including a fraction of low angle waves to the wave climate causes saturation of the amplitudes of the sand waves and limits the formation of the sand wave train. Even on a stable coast dominated by low angle waves, the feedback between morphology and the wave field can be crucial for the prediction of nourishment evolution. This feedback leads to relatively slow diffusion of shoreline perturbations and it can lead to downdrift migration. While some existing observations describe downdrift advection, no satisfactory explanation had been provided previously.

  9. Frictional controls on high-angle reverse faulting during compressional basin inversion

    NASA Astrophysics Data System (ADS)

    Smith, S. A. F.; Alder, S.; Tesei, T.; Collettini, C.

    2015-12-01

    Large normal faults are often reactivated as high-angle reverse faults during compressional basin inversion. Prevailing models to explain steep reverse slip call upon significant fluid overpressure. Though such models are consistent with some seismological data and field observations from incipient (low-displacement) reverse faults, they remain largely untested in the case of basin-scale faults. We present field and experimental data from the >200 km long Moonlight Fault Zone in New Zealand, an Oligocene basin-bounding normal fault that reactivated in the Miocene as a high-angle reverse fault (present dip angle 65°-75°). Excellent exposures of the fault zone exhumed from c. 4-8 km depth are found in creek sections along the entire strike length. Wall rocks are mainly quartz-albite-muscovite-chlorite schists with a strong foliation that is everywhere sub-parallel to the Moonlight Fault (i.e. dip angle 65°-75°). Although the overall structure of the fault zone changes significantly along strike in response to wall rock composition, the <5 metre thick fault core everywhere contains interconnected layers of foliated cataclasite rich in authigenically-grown chlorite and muscovite/illite. Microstructural evidence suggests deformation in the fault core by a combination of cataclasis, frictional slip along phyllosilicate seams and dissolution-precipitation. Single-direct and double-direct friction experiments were performed with the BRAVA apparatus (INGV, Rome) on saturated wafers (e.g. with intact foliation) of foliated cataclasite at normal stresses up to 75 MPa. The foliated cataclasites have a friction coefficient of <0.25 and negligible frictional healing. In combination with dissolution-precipitation mechanisms, a friction coefficient of <0.25 can account for slip on high-angle reverse faults if accompanied by only moderately high fluid pressures. Our results indicate that friction may be equally as important as fluid pressure during compressional basin inversion.

  10. Twist Buckling Behavior of Arteries

    PubMed Central

    Garcia, Justin R.; Lamm, Shawn D.; Han, Hai-Chao

    2012-01-01

    Arteries are often subjected to torsion due to body movement and surgical procedures. While it is essential that arteries remain stable and patent under twisting loads, the stability of arteries under torsion is poorly understood. The goal of this work was to experimentally investigate the buckling behavior of arteries under torsion and to determine the critical buckling torque, the critical buckling twist angle, and the buckling shape. Porcine common carotid arteries were slowly twisted in vitro until buckling occurred while subjected to a constant axial stretch ratio (1.1, 1.3, 1.5 (in vivo level), and 1.7) and lumen pressure (20, 40, 70, and 100 mmHg). Upon buckling, the arteries snapped to form a kink. For a group of six arteries, the axial stretch ratio significantly affected the critical buckling torque (p < 0.002) and the critical buckling twist angle (p < 0.001). Lumen pressure also significantly affected the critical buckling torque (p < 0.001) but had no significant effect on the critical twist angle (p = 0.067). Convex material constants for a Fung strain energy function were determined and fit well with the axial force, lumen pressure, and torque data measured pre-buckling. The material constants are valid for axial stretch ratios, lumen pressures, and rotation angles of 1.3 – 1.5, 20 – 100 mmHg, and 0 – 270 degrees, respectively. The current study elucidates the buckling behavior of arteries under torsion and provides new insight into mechanical instability of blood vessels. PMID:23160845

  11. Twist buckling behavior of arteries.

    PubMed

    Garcia, Justin R; Lamm, Shawn D; Han, Hai-Chao

    2013-10-01

    Arteries are often subjected to torsion due to body movement and surgical procedures. While it is essential that arteries remain stable and patent under twisting loads, the stability of arteries under torsion is poorly understood. The goal of this work was to experimentally investigate the buckling behavior of arteries under torsion and to determine the critical buckling torque, the critical buckling twist angle, and the buckling shape. Porcine common carotid arteries were slowly twisted in vitro until buckling occurred while subjected to a constant axial stretch ratio (1.1, 1.3, 1.5 (in vivo level) and 1.7) and lumen pressure (20, 40, 70 and 100 mmHg). Upon buckling, the arteries snapped to form a kink. For a group of six arteries, the axial stretch ratio significantly affected the critical buckling torque ([Formula: see text]) and the critical buckling twist angle ([Formula: see text]). Lumen pressure also significantly affected the critical buckling torque ([Formula: see text]) but had no significant effect on the critical twist angle ([Formula: see text]). Convex material constants for a Fung strain energy function were determined and fit well with the axial force, lumen pressure, and torque data measured pre-buckling. The material constants are valid for axial stretch ratios, lumen pressures, and rotation angles of 1.3-1.5, 20-100 mmHg, and 0-270[Formula: see text], respectively. The current study elucidates the buckling behavior of arteries under torsion and provides new insight into mechanical instability of blood vessels.

  12. Magnus effects at high angles of attack and critical Reynolds numbers

    NASA Technical Reports Server (NTRS)

    Seginer, A.; Ringel, M.

    1983-01-01

    The Magnus force and moment experienced by a yawed, spinning cylinder were studied experimentally in low speed and subsonic flows at high angles of attack and critical Reynolds numbers. Flow-field visualization aided in describing a flow model that divides the Magnus phenomenon into a subcritical region, where reverse Magnus loads are experienced, and a supercritical region where these loads are not encountered. The roles of the spin rate, angle of attack, and crossflow Reynolds number in determining the boundaries of the subcritical region and the variations of the Magnus loads were studied.

  13. High angle view of Apollo 14 space vehicle on way to Pad A

    NASA Image and Video Library

    1970-11-09

    S70-54127 (9 Nov. 1970) --- A high-angle view at Launch Complex 39, Kennedy Space Center (KSC), showing the Apollo 14 (Spacecraft 110/Lunar Module 8/Saturn 509) space vehicle on the way from the Vehicle Assembly Building (VAB) to Pad A. The Saturn V stack and its mobile launch tower sit atop a huge crawler-transporter. The Apollo 14 crewmen will be astronauts Alan B. Shepard Jr., commander; Stuart A. Roosa, command module pilot; and Edgar D. Mitchell, lunar module pilot.

  14. High angle view of Apollo 14 space vehicle on way to Pad A

    NASA Image and Video Library

    1970-11-09

    S70-54119 (9 Nov. 1970) --- A high-angle view at Launch Complex 39, Kennedy Space Center (KSC), showing the Apollo 14 (Spacecraft 110/Lunar Module 8/Saturn 509) space vehicle on the way from the Vehicle Assembly Building (VAB) to Pad A. The Saturn V stack and its mobile launch tower sit atop a huge crawler-transporter. The Apollo 14 crewmen will be astronauts Alan B. Shepard Jr., commander; Stuart A. Roosa, command module pilot; and Edgar D. Mitchell, lunar module pilot.

  15. Prediction of forces and moments on finned bodies at high angle of attack in transonic flow

    SciTech Connect

    Oberkampf, W. L.

    1981-04-01

    This report describes a theoretical method for the prediction of fin forces and moments on bodies at high angle of attack in subsonic and transonic flow. The body is assumed to be a circular cylinder with cruciform fins (or wings) of arbitrary planform. The body can have an arbitrary roll (or bank) angle, and each fin can have individual control deflection. The method combines a body vortex flow model and lifting surface theory to predict the normal force distribution over each fin surface. Extensive comparisons are made between theory and experiment for various planform fins. A description of the use of the computer program that implements the method is given.

  16. Prediction of Aerodynamic Characteristics of Fighter Wings at High Angles of Attack.

    DTIC Science & Technology

    1984-03-01

    method coupled with iterative routines for wake location, viscous effects and vortex flows. Applications of the techniques to a number of...AD-A145 1@7 PREDICTION OF AERODYNAMIC CHARACTERISTICS OF FIGHTER i/2 WIINGS AT HIGH ANGLES OF ATTACK(U) ANALYTICAL METHODS INC REDMOND WA B MASKEW ET...ATTACK I B. !4askew T.S. Vaidyanathan J.K. Nathman F.A. Dvorak Analytical Methods , Inc. 2047 - 152nd Avenue N.E. Redmond, Washington 98052 CONTRACT

  17. Nonlinear light-matter interaction with femtosecond high-angle Bessel beams

    NASA Astrophysics Data System (ADS)

    Faccio, D.; Rubino, E.; Lotti, A.; Couairon, A.; Dubietis, A.; Tamošauskas, G.; Papazoglou, D. G.; Tzortzakis, S.

    2012-03-01

    We show that high-angle Bessel beams may significantly reduce nonlinear pulse distortions due, for example, to nonlinear Kerr effects (self-phase-modulation and self-focusing) yet enhance ionization and plasma generation. Holographic reconstruction of Bessel beams in water show intensity clamping at increased intensities and evidence of nontrivial plasma dynamics as the input energy is increased. The solvated electron density increases significantly and the cavitation-induced bubbles are ejected from the focal region indicating a significant excess plasma heating in the Bessel-pulse wake.

  18. Global Stability and Control Analysis of Aircraft at High Angles-of-Attack.

    DTIC Science & Technology

    1979-08-31

    6601ISOSLT 70 / .. ,.-j4tY CLASSIrIgCATION OF THIS PAGlVt’Whg Doea Knta.e) 20. (cont.) standing of the dynamic instabilities at high angles-of-attack. A basic...and this agrees with flight test results. The other groups have Cnr > 0 for high a, and so are less realistic. In addition to Cnr, the effects on...Silver Spring, MD 20910 Dover, NJ 07801 J. Wingate , Code R44 1 N. Coleman, DRDAR-SCFCC 1 ""Naval Air Test Center NASA Langley Research Center

  19. Magnus effects at high angles of attack and critical Reynolds numbers

    NASA Technical Reports Server (NTRS)

    Seginer, A.; Ringel, M.

    1983-01-01

    The Magnus force and moment experienced by a yawed, spinning cylinder were studied experimentally in low speed and subsonic flows at high angles of attack and critical Reynolds numbers. Flow-field visualization aided in describing a flow model that divides the Magnus phenomenon into a subcritical region, where reverse Magnus loads are experienced, and a supercritical region where these loads are not encountered. The roles of the spin rate, angle of attack, and crossflow Reynolds number in determining the boundaries of the subcritical region and the variations of the Magnus loads were studied.

  20. Side-force alleviation on slender, pointed forebodies at high angles of attack

    NASA Technical Reports Server (NTRS)

    Rao, D. M.

    1978-01-01

    A new device was proposed for alleviating high angle-of-attack side force on slender, pointed forebodies. A symmetrical pair of separation strips in the form of helical ridges are applied to the forebody to disrupt the primary lee-side vortices and thereby avoid the instability that produces vortex asymmetry. Preliminary wind tunnel tests at Mach 0.3 and Reynolds no. 5,250,000 on a variety of forebody configurations and on a wing-body combination at angles of attack up to 56 degrees, demonstrated the effectiveness of the device.

  1. The electronic structure of grain boundaries in Nb

    SciTech Connect

    Sowa, E.C.; Gonis, A. ); Zhang, X.G. )

    1990-11-01

    We present first-principles calculations of the electronic structure of Nb grain boundaries. These are the first such calculations for a bcc metal using the real-space multiple-scattering theory (RSMST). Local densities of states near a {Sigma}5 twist grain boundary are compared to those for bulk Nb. 5 refs., 1 fig.

  2. Twist: a molecular target in cancer therapeutics.

    PubMed

    Khan, Md Asaduzzaman; Chen, Han-chun; Zhang, Dianzheng; Fu, Junjiang

    2013-10-01

    Twist, the basic helix-loop-helix transcription factor, is involved in the process of epithelial to mesenchymal transitions (EMTs), which play an essential role in cancer metastasis. Overexpression of Twist or its promoter methylation is a common scenario in metastatic carcinomas. Twist is activated by a variety of signal transduction pathways, including Akt, signal transducer and activator of transcription 3, mitogen-activated protein kinase, Ras, and Wnt signaling. Activated Twist upregulates N-cadherin and downregulates E-cadherin, which are the hallmarks of EMT. Moreover, Twist plays an important role in some physiological processes involved in metastasis, like angiogenesis, invadopodia, extravasation, and chromosomal instability. Twist also protects cancer cells from apoptotic cell death. In addition, Twist is responsible for the stemness of cancer cells and the generation of drug resistance. Recently, targeting Twist has gained significant interests in cancer therapeutics. The inactivation of Twist by small RNA technology or chemotherapeutic approach has been proved successful. Moreover, several inhibitors which are antagonistic to the upstream or downstream molecules of Twist signaling pathways have also been identified. Development of potential treatment strategies by targeting Twist has a great promise in cancer therapeutics.

  3. Mathematical modeling of the aerodynamics of high-angle-of-attack maneuvers

    NASA Technical Reports Server (NTRS)

    Schiff, L. B.; Tobak, M.; Malcolm, G. N.

    1980-01-01

    This paper is a review of the current state of aerodynamic mathematical modeling for aircraft motions at high angles of attack. The mathematical model serves to define a set of characteristic motions from whose known aerodynamic responses the aerodynamic response to an arbitrary high angle-of-attack flight maneuver can be predicted. Means are explored of obtaining stability parameter information in terms of the characteristic motions, whether by wind-tunnel experiments, computational methods, or by parameter-identification methods applied to flight-test data. A rationale is presented for selecting and verifying the aerodynamic mathematical model at the lowest necessary level of complexity. Experimental results describing the wing-rock phenomenon are shown to be accommodated within the most recent mathematical model by admitting the existence of aerodynamic hysteresis in the steady-state variation of the rolling moment with roll angle. Interpretation of the experimental results in terms of bifurcation theory reveals the general conditions under which aerodynamic hysteresis must exist.

  4. Full-scale high angle-of-attack tests of an F/A-18

    NASA Technical Reports Server (NTRS)

    Meyn, Larry A.; Lanser, Wendy R.; James, Kevin D.

    1992-01-01

    This paper presents an overview of high angle-of-attack tests of a full-scale F/A-18 in the 80- by 120-Foot Wind Tunnel of the National Full-Scale Aerodynamic Complex at NASA Ames Research Center at Moffett Field, California. A production aircraft was tested over an angle-of-attack range of 18 to 50 deg and at wind speeds of up to 100 knots. These tests had three primary test objectives. Pneumatic and mechanical forebody flow control devices were tested at full-scale and shown to produce significant yawing moments for lateral control of the aircraft at high angles of attack. Mass flow requirements for the pneumatic system were found to scale with freestream density and speed rather than freestream dynamic pressure. Detailed measurements of the pressures buffeting the vertical tail were made and spatial variations in the buffeting frequency were found. The LEX fence was found to have a significant effect on the frequency distribution on the outboard surface of the vertical fin. In addition to the above measurements, an extensive set of data was acquired for the validation of computational fluid dynamics codes and for comparison with flight test and small-scale wind tunnel test results.

  5. High-angle-of-attack pneumatic lag and upwash corrections for a hemispherical flow direction sensor

    NASA Technical Reports Server (NTRS)

    Whitmore, Stephen A.; Heeg, Jennifer; Larson, Terry J.; Ehernberger, L. J.; Hagen, Floyd W.; Deleo, Richard V.

    1987-01-01

    As part of the NASA F-14 high angle of attack flight test program, a nose mounted hemispherical flow direction sensor was calibrated against a fuselage mounted movable vane flow angle sensor. Significant discrepancies were found to exist in the angle of attack measurements. A two fold approach taken to resolve these discrepancies during subsonic flight is described. First, the sensing integrity of the isolated hemispherical sensor is established by wind tunnel data extending to an angle of attack of 60 deg. Second, two probable causes for the discrepancies, pneumatic lag and upwash, are examined. Methods of identifying and compensating for lag and upwash are presented. The wind tunnel data verify that the isolated hemispherical sensor is sufficiently accurate for static conditions with angles of attack up to 60 deg and angles of sideslip up to 30 deg. Analysis of flight data for two high angle of attack maneuvers establishes that pneumatic lag and upwash are highly correlated with the discrepancies between the hemispherical and vane type sensor measurements.

  6. Specialized drilling systems set new world records in high-angle holes

    SciTech Connect

    Gates, R.L.; Schwab, G.A.

    1984-02-01

    Sound well planning and carefully chosen drilling systems have proved successful in completing two high-angle holes through troublesome formations in the Gippsland basin offshore Victoria, Australia. Located about 60 miles (97 km) out in the Bass Strait, Mackerel Wells A-14 and A-16 set new records for being the longest horizontal displacement wells drilled to an angle of up to 72/sup 0/ (1.26 rad) to the vertical. Both wells are producing oil from a previously fault-isolated reservoir southwest of the platform. The use of invert oil emulsion and aluminum drill pipe represented a significant change from normal Bass Strait drilling operations. This, in conjunction with tightly controlled angle buildup and directional control, ensured that the projected well paths were achieved. Completion procedures peculiar to highly deviated holes also were employed to bring the wells on stream successfully. A ''controlled activity'' oil-continuous mud system was chosen to alleviate problems associated with shale hydration and to increase wellbore lubricity. Rig modifications for cuttings disposal were essential before mud systems could be changed over. In combination with aluminum drill pipe for reduced string weight (Well A-16), the oil mud helped minimize torque, drag, and wall-sticking tendencies. With similar drilling systems and well-planned completion techniques, the drilling of high-angle holes will play a vital role in deepwater development.

  7. Renormalization constants for 2-twist operators in twisted mass QCD

    SciTech Connect

    Alexandrou, C.; Constantinou, M.; Panagopoulos, H.; Stylianou, F.; Korzec, T.

    2011-01-01

    Perturbative and nonperturbative results on the renormalization constants of the fermion field and the twist-2 fermion bilinears are presented with emphasis on the nonperturbative evaluation of the one-derivative twist-2 vector and axial-vector operators. Nonperturbative results are obtained using the twisted mass Wilson fermion formulation employing two degenerate dynamical quarks and the tree-level Symanzik improved gluon action. The simulations have been performed for pion masses in the range of about 450-260 MeV and at three values of the lattice spacing a corresponding to {beta}=3.9, 4.05, 4.20. Subtraction of O(a{sup 2}) terms is carried out by performing the perturbative evaluation of these operators at 1-loop and up to O(a{sup 2}). The renormalization conditions are defined in the RI{sup '}-MOM scheme, for both perturbative and nonperturbative results. The renormalization factors, obtained for different values of the renormalization scale, are evolved perturbatively to a reference scale set by the inverse of the lattice spacing. In addition, they are translated to MS at 2 GeV using 3-loop perturbative results for the conversion factors.

  8. The twist box domain is required for Twist1-induced prostate cancer metastasis.

    PubMed

    Gajula, Rajendra P; Chettiar, Sivarajan T; Williams, Russell D; Thiyagarajan, Saravanan; Kato, Yoshinori; Aziz, Khaled; Wang, Ruoqi; Gandhi, Nishant; Wild, Aaron T; Vesuna, Farhad; Ma, Jinfang; Salih, Tarek; Cades, Jessica; Fertig, Elana; Biswal, Shyam; Burns, Timothy F; Chung, Christine H; Rudin, Charles M; Herman, Joseph M; Hales, Russell K; Raman, Venu; An, Steven S; Tran, Phuoc T

    2013-11-01

    Twist1, a basic helix-loop-helix transcription factor, plays a key role during development and is a master regulator of the epithelial-mesenchymal transition (EMT) that promotes cancer metastasis. Structure-function relationships of Twist1 to cancer-related phenotypes are underappreciated, so we studied the requirement of the conserved Twist box domain for metastatic phenotypes in prostate cancer. Evidence suggests that Twist1 is overexpressed in clinical specimens and correlated with aggressive/metastatic disease. Therefore, we examined a transactivation mutant, Twist1-F191G, in prostate cancer cells using in vitro assays, which mimic various stages of metastasis. Twist1 overexpression led to elevated cytoskeletal stiffness and cell traction forces at the migratory edge of cells based on biophysical single-cell measurements. Twist1 conferred additional cellular properties associated with cancer cell metastasis including increased migration, invasion, anoikis resistance, and anchorage-independent growth. The Twist box mutant was defective for these Twist1 phenotypes in vitro. Importantly, we observed a high frequency of Twist1-induced metastatic lung tumors and extrathoracic metastases in vivo using the experimental lung metastasis assay. The Twist box was required for prostate cancer cells to colonize metastatic lung lesions and extrathoracic metastases. Comparative genomic profiling revealed transcriptional programs directed by the Twist box that were associated with cancer progression, such as Hoxa9. Mechanistically, Twist1 bound to the Hoxa9 promoter and positively regulated Hoxa9 expression in prostate cancer cells. Finally, Hoxa9 was important for Twist1-induced cellular phenotypes associated with metastasis. These data suggest that the Twist box domain is required for Twist1 transcriptional programs and prostate cancer metastasis. Targeting the Twist box domain of Twist1 may effectively limit prostate cancer metastatic potential. ©2013 AACR.

  9. Highly transparent twist polarizer metasurface

    NASA Astrophysics Data System (ADS)

    Faniayeu, Ihar; Khakhomov, Sergei; Semchenko, Igor; Mizeikis, Vygantas

    2017-09-01

    A twist polarizer metasurface for polarization rotation by an angle of 90 ° is proposed and realized at microwave frequencies. The metasurface consists of sub-wavelength metallic helices arranged periodically in a single layer and operates in transmission geometry with a nearly unity cross-polarization conversion coefficient at resonance. The structure exhibits low reflectivity R <0.06 within a decade-spanning frequency range of 0.1-5.5 GHz and is insensitive to the polarization orientation of the incident wave. Moreover, it can operate with high efficiency at oblique incidence angles of up to 35 ° . Such twist polarizer metasurfaces are potentially applicable as electromagnetic/optical isolators and frequency-selective polarization antennas.

  10. Vibrations of twisted rotating blades

    NASA Technical Reports Server (NTRS)

    Leissa, A. W.; Lee, J. K.; Wang, A. J.

    1981-01-01

    The literature dealing with vibrations of turbomachinery blades is voluminous, but the vast majority of it treats the blades as beams. In a previous paper a two-dimensional analytical procedure was developed and demonstrated on simple models of blades having camber. The procedure utilizes shallow shell theory along with the classical Ritz method for solving the vibration problem. Displacement functions are taken as algebraic polynomials. In the present paper the method is demonstrated on blade models having camber. Comparisons are first made with results in the literature for nonrotating twisted plates and various disagreements between results are pointed out. A method for depicting mode shape information is demonstrated, permitting one to examine all three components of displacement. Finally, the analytical procedure is demonstrated on rotating twisted blade modes, both without and with camber.

  11. Polarization twist in perovskite ferrielectrics

    PubMed Central

    Kitanaka, Yuuki; Hirano, Kiyotaka; Ogino, Motohiro; Noguchi, Yuji; Miyayama, Masaru; Moriyoshi, Chikako; Kuroiwa, Yoshihiro

    2016-01-01

    Because the functions of polar materials are governed primarily by their polarization response to external stimuli, the majority of studies have focused on controlling polar lattice distortions. In some perovskite oxides, polar distortions coexist with nonpolar tilts and rotations of oxygen octahedra. The interplay between nonpolar and polar instabilities appears to play a crucial role, raising the question of how to design materials by exploiting their coupling. Here, we introduce the concept of ‘polarization twist’, which offers enhanced control over piezoelectric responses in polar materials. Our experimental and theoretical studies provide direct evidence that a ferrielectric perovskite exhibits a large piezoelectric response because of extended polar distortion, accompanied by nonpolar octahedral rotations, as if twisted polarization relaxes under electric fields. The concept underlying the polarization twist opens new possibilities for developing alternative materials in bulk and thin-film forms. PMID:27586824

  12. Evolution of twisted magnetic fields

    SciTech Connect

    Zweibel, E.G.; Boozer, A.H.

    1985-02-01

    The magnetic field of the solar corona evolves quasistatically in response to slowly changing photospheric boundary conditions. The magnetic topology is preserved by the low resistivity of the solar atmosphere. We show that a magnetic flux coordinate system simplifies the problem of calculating field evolution with invariant topology. As an example, we calculate the equilibrium of a thin magnetic flux tube with small twist per unit length.

  13. Aerodynamic control of slender bodies from low to high angles of attack through flow manipulation

    NASA Astrophysics Data System (ADS)

    Lopera, Javier

    2007-12-01

    This dissertation presents experimental investigations of several novel active flow control methodologies that have been implemented for aerodynamic control and maneuvering of slender bodies at low and high angles of attack through flow manipulation. For low angles of attack, a U.S. Army Smart Cargo projectile was examined. For high angles of attack a U.S. Air Force countermeasure concept projectile termed DEX (Destructive Expendable) was examined. Low angle of attack control was attempted using two novel separation control techniques: reconfigurable porosity and miniature deployable spoilers. Results show that significant aerodynamic forces are generated by implementing reconfigurable porosity and can be effectively used to steer and maneuver air vehicles. Porous patterns with a "saw-tooth" configuration seem to be the most effective in generating consistent control forces over a wide range of angles of attack. Miniature deployable spoilers successfully demonstrated their ability in producing both positive and negative pitch and yaw controls by modulating the spoiler height and length when used on the boattail and Aero Control Fins (ACFs) of a projectile. The effect of aftbody strake parameters such as shape, locations (axial and azimuthal), deployment height, and number of strakes implemented was examined on a short blunt-nose projectile. Large yaw control authority was attained for alpha > 40 deg. The largest yaw control authority was produced by a rectangular-shaped strake. A robust closed-loop feedback controller was successfully tested using dynamic wind tunnel experiments to control the coning motion of a projectile. The controller showed good control authority and was capable of attaining and maintaining the commanded roll angle with a tolerance of +/-10 deg. A study was conducted to gain some insights into the fluid mechanics of short blunt-nose bodies of revolution at high angles of attack. Off- and on-surface flow visualization records are collected to

  14. New twist on artificial muscles

    PubMed Central

    Haines, Carter S.; Li, Na; Spinks, Geoffrey M.; Aliev, Ali E.; Di, Jiangtao; Baughman, Ray H.

    2016-01-01

    Lightweight artificial muscle fibers that can match the large tensile stroke of natural muscles have been elusive. In particular, low stroke, limited cycle life, and inefficient energy conversion have combined with high cost and hysteretic performance to restrict practical use. In recent years, a new class of artificial muscles, based on highly twisted fibers, has emerged that can deliver more than 2,000 J/kg of specific work during muscle contraction, compared with just 40 J/kg for natural muscle. Thermally actuated muscles made from ordinary polymer fibers can deliver long-life, hysteresis-free tensile strokes of more than 30% and torsional actuation capable of spinning a paddle at speeds of more than 100,000 rpm. In this perspective, we explore the mechanisms and potential applications of present twisted fiber muscles and the future opportunities and challenges for developing twisted muscles having improved cycle rates, efficiencies, and functionality. We also demonstrate artificial muscle sewing threads and textiles and coiled structures that exhibit nearly unlimited actuation strokes. In addition to robotics and prosthetics, future applications include smart textiles that change breathability in response to temperature and moisture and window shutters that automatically open and close to conserve energy. PMID:27671626

  15. Higher level twisted Zhu algebras

    NASA Astrophysics Data System (ADS)

    van Ekeren, Jethro

    2011-05-01

    The study of twisted representations of graded vertex algebras is important for understanding orbifold models in conformal field theory. In this paper, we consider the general setup of a vertex algebra V, graded by Γ /{Z} for some subgroup Γ of {R} containing {Z}, and with a Hamiltonian operator H having real (but not necessarily integer) eigenvalues. We construct the directed system of twisted level p Zhu algebras operatorname{Zhu}_{p, Γ }(V), and we prove the following theorems: For each p, there is a bijection between the irreducible operatorname{Zhu}_{p, Γ }(V)-modules and the irreducible Γ-twisted positive energy V-modules, and V is (Γ, H)-rational if and only if all its Zhu algebras operatorname{Zhu}_{p, Γ }(V) are finite dimensional and semisimple. The main novelty is the removal of the assumption of integer eigenvalues for H. We provide an explicit description of the level p Zhu algebras of a universal enveloping vertex algebra, in particular of the Virasoro vertex algebra operatorname{Vir}^c and the universal affine Kac-Moody vertex algebra V^k({g}) at non-critical level. We also compute the inverse limits of these directed systems of algebras.

  16. New twist on artificial muscles.

    PubMed

    Haines, Carter S; Li, Na; Spinks, Geoffrey M; Aliev, Ali E; Di, Jiangtao; Baughman, Ray H

    2016-10-18

    Lightweight artificial muscle fibers that can match the large tensile stroke of natural muscles have been elusive. In particular, low stroke, limited cycle life, and inefficient energy conversion have combined with high cost and hysteretic performance to restrict practical use. In recent years, a new class of artificial muscles, based on highly twisted fibers, has emerged that can deliver more than 2,000 J/kg of specific work during muscle contraction, compared with just 40 J/kg for natural muscle. Thermally actuated muscles made from ordinary polymer fibers can deliver long-life, hysteresis-free tensile strokes of more than 30% and torsional actuation capable of spinning a paddle at speeds of more than 100,000 rpm. In this perspective, we explore the mechanisms and potential applications of present twisted fiber muscles and the future opportunities and challenges for developing twisted muscles having improved cycle rates, efficiencies, and functionality. We also demonstrate artificial muscle sewing threads and textiles and coiled structures that exhibit nearly unlimited actuation strokes. In addition to robotics and prosthetics, future applications include smart textiles that change breathability in response to temperature and moisture and window shutters that automatically open and close to conserve energy.

  17. Flight validation of ground-based assessment for control power requirements at high angles of attack

    NASA Technical Reports Server (NTRS)

    Ogburn, Marilyn E.; Ross, Holly M.; Foster, John V.; Pahle, Joseph W.; Sternberg, Charles A.; Traven, Ricardo; Lackey, James B.; Abbott, Troy D.

    1994-01-01

    A review is presented in viewgraph format of an ongoing NASA/U.S. Navy study to determine control power requirements at high angles of attack for the next generation high-performance aircraft. This paper focuses on recent flight test activities using the NASA High Alpha Research Vehicle (HARV), which are intended to validate results of previous ground-based simulation studies. The purpose of this study is discussed, and the overall program structure, approach, and objectives are described. Results from two areas of investigation are presented: (1) nose-down control power requirements and (2) lateral-directional control power requirements. Selected results which illustrate issues and challenges that are being addressed in the study are discussed including test methodology, comparisons between simulation and flight, and general lessons learned.

  18. Use of piloted simulation for high-angle-of-attack agility research and design criteria development

    NASA Technical Reports Server (NTRS)

    Ogburn, Marilyn E.; Foster, John V.; Hoffler, Keith D.

    1991-01-01

    The application of piloted simulations in the development of advanced fighter aircraft is reviewed in the context of the NASA High-Angle-of-Attack Technology Program (HATP). The HATP combines wind-tunnel experiments, computational aerodynamics, piloted simulations, and flight tests on a modified F-18 testbed aircraft and utilizes the experience and facilities of several NASA centers. Consideration is given to the role of simulation in the overall research process, simulation capabilities and software requirements, simulation flexibility and fidelity, evaluation maneuvers, the role of simulator pilots in evaluations, the analysis of simulation results, flight validation of maneuvers and rating approaches, and the use of simulations to define design criteria. Extensive diagrams, graphs, and flow charts are included.

  19. Simulating Effects of High Angle of Attack on Turbofan Engine Performance

    NASA Technical Reports Server (NTRS)

    Liu, Yuan; Claus, Russell W.; Litt, Jonathan S.; Guo, Ten-Huei

    2013-01-01

    A method of investigating the effects of high angle of attack (AOA) flight on turbofan engine performance is presented. The methodology involves combining a suite of diverse simulation tools. Three-dimensional, steady-state computational fluid dynamics (CFD) software is used to model the change in performance of a commercial aircraft-type inlet and fan geometry due to various levels of AOA. Parallel compressor theory is then applied to assimilate the CFD data with a zero-dimensional, nonlinear, dynamic turbofan engine model. The combined model shows that high AOA operation degrades fan performance and, thus, negatively impacts compressor stability margins and engine thrust. In addition, the engine response to high AOA conditions is shown to be highly dependent upon the type of control system employed.

  20. An EnKF-based Flow State Estimator for Airfoils at High Angles of Attack

    NASA Astrophysics Data System (ADS)

    de Castro da Silva, Andre Fernando; Colonius, Tim

    2016-11-01

    Robust flow estimation from available measurements remains a major obstacle to successful flow control applications. Although several estimation methodologies have been developed in the past decades, the high dimensionality of fluid systems renders many of them computationally intractable. In this work, we employ the Ensemble Kalman Filter (EnKF) and the two-dimensional incompressible Navier-Stokes equations to estimate the state of the flow past a NACA 0009 airfoil at high angles of attack and moderate Reynolds number. The pressure distribution on the airfoil and the velocity field in the wake, both randomized by synthetic noise, are sampled as measurement data. In order to evaluate the relative importance of each sensor location to the estimate correction, their influence fields (also known as representers) are analyzed. The performance of the estimator is then assessed for different choices of ensemble size, noise levels, and number/location of sensors. Graduate Student.

  1. Optimization of lateral-directional dynamics for an aircraft operating at high angle of attack

    NASA Technical Reports Server (NTRS)

    Snell, S. A.; Garrard, William L., Jr.; Enns, Dale F.

    1991-01-01

    In this paper, the control laws for the lateral-directional dynamics of a supermaneuverable aircraft is analyzed with a view to reducing the levels of lateral acceleration and sideslip, which are encountered during aggressive rolling maneuvers at high angles of attack. The analysis uses a linearized model of the lateral-directional dynamics and thus H-free-flow techniques can be applied. It is shown that trade-offs exist between simultaneously minimizing lateral acceleration measured at the pilot's station, ny(p), minimizing sideslip and minimizing tracking errors between the roll-rate about the velocity vector and its command. The paper concludes that a significant reduction in ny(p) is only attainable by compromising the roll-rate performance.

  2. Unscrambling Mixed Elements using High Angle Annular Dark Field Scanning Transmission Electron Microscopy

    NASA Astrophysics Data System (ADS)

    van den Bos, Karel H. W.; De Backer, Annick; Martinez, Gerardo T.; Winckelmans, Naomi; Bals, Sara; Nellist, Peter D.; Van Aert, Sandra

    2016-06-01

    The development of new nanocrystals with outstanding physicochemical properties requires a full three-dimensional (3D) characterization at the atomic scale. For homogeneous nanocrystals, counting the number of atoms in each atomic column from high angle annular dark field scanning transmission electron microscopy images has been shown to be a successful technique to get access to this 3D information. However, technologically important nanostructures often consist of more than one chemical element. In order to extend atom counting to heterogeneous materials, a new atomic lensing model is presented. This model takes dynamical electron diffraction into account and opens up new possibilities for unraveling the 3D composition at the atomic scale. Here, the method is applied to determine the 3D structure of Au@Ag core-shell nanorods, but it is applicable to a wide range of heterogeneous complex nanostructures.

  3. Calculation of the flow on a blunted cone at high angle of attack

    NASA Technical Reports Server (NTRS)

    Lubard, S. C.; Rakich, J. V.

    1975-01-01

    A new technique for calculating the entire flow-field on spherically blunted circular cones at high angles of attack and high Reynolds numbers is described. The calculations are based on a single-layer system of three-dimensional parabolic equations which are approximations to the full steady Navier-Stokes equations. Initial conditions at the sphere-cone tangency plane are provided by using an inviscid time-dependent solution added to a viscous nonsimilar boundary layer solution. Calculated results are compared with experimental heat transfer and pressure data for a 15 deg half-angle cone with a 1-in. spherical nose at 15 deg angle of attack. The free-stream Mach number is 10.6, and the free-stream Reynolds number is 1,200,000 per foot. Excellent agreement between the calculated and experimental data for both pressure and heat transfer is obtained.

  4. A study of roll attractor and wing rock of delta wings at high angles of attack

    NASA Technical Reports Server (NTRS)

    Niranjana, T.; Rao, D. M.; Pamadi, Bandu N.

    1993-01-01

    Wing rock is a high angle of attack dynamic phenomenon of limited cycle motion predominantly in roll. The wing rock is one of the limitations to combat effectiveness of the fighter aircraft. Roll Attractor is the steady state or equilibrium trim angle (phi(sub trim)) attained by the free-to-roll model, held at some angle of attack, and released form rest at a given initial roll (bank) angle (phi(sub O)). Multiple roll attractors are attained at different trim angles depending on initial roll angle. The test facility (Vigyan's low speed wind tunnel) and experimental work is presented here along with mathematical modelling of roll attractor phenomenon and analysis and comparison of predictions with experimental data.

  5. Separation control over an airfoil at high angles of attack by sound emanating from the surface

    NASA Technical Reports Server (NTRS)

    Huang, L. S.; Maestrello, L.; Bryant, T. D.

    1987-01-01

    Active control by sound emanating from a narrow gap in the vicinity of the leading edge of a symmetrical airfoil is used to study the influence of sound on the pressure distribution and the wake at high angles of attack. The results from experiments conducted at a Reynolds number based on the chord of 35,000 show that, with injection of sound at twice the shedding frequency of the shear layer, the region of separation becomes drastically reduced. The shear layer is found to be very sensitive to sound excitation in the vicinity of the separation point. The excitation sufficiently alters the global circulation to cause an increase in lift and reduction in drag. Furthermore, experimental results describing stall and post-stall conditions compare well with the limited data available and indicate that stall is delayed by sound injection into the separated region.

  6. Apollo 11 Launched Via the Saturn V Rocket-High Angle View

    NASA Technical Reports Server (NTRS)

    1969-01-01

    The Apollo 11 mission, the first lunar landing mission, launched from the Kennedy Space Center, Florida via the Marshall Space Flight Center (MSFC) developed Saturn V launch vehicle on July 16, 1969 and safely returned to Earth on July 24, 1969. The Saturn V vehicle produced a holocaust of flames as it rose from its pad at Launch complex 39. The 363 foot tall, 6,400,000 pound rocket hurled the spacecraft into Earth parking orbit and then placed it on the trajectory to the moon for man's first lunar landing. This high angle view of the launch was provided by a `fisheye' camera mounted on the launch tower. Aboard the space craft were astronauts Neil A. Armstrong, commander; Michael Collins, Command Module pilot; and Edwin E. Aldrin Jr., Lunar Module pilot. With the success of Apollo 11, the national objective to land men on the Moon and return them safely to Earth had been accomplished.

  7. High-angle-of-attack stability and control improvements for the EA-6B Prowler

    NASA Technical Reports Server (NTRS)

    Jordan, Frank L.; Hahne, David E.; Masiello, Matthew F.; Gato, William

    1987-01-01

    The factors involved in high-angle-of-attack directional divergence phenomena for the EA-6B ECM aircraft have been investigated in NASA-Langley wind tunnel facilities in order to evaluate airframe modifications which would eliminate or delay such divergence to angles-of-attack farther removed from the operational flight envelope of the aircraft. The results obtained indicate that an adverse sidewash at the aft fuselage and vertical tail location is responsible for the directional stability loss, and that the sidewash is due to a vortex system generated by the fuselage-wing juncture. Modifications encompassing a wing inboard leading edge droop, a wing glove strake, and a vertical fin extension, have significantly alleviated the stability problem.

  8. The F-18 High Alpha Research Vehicle: A High-Angle-of-Attack Testbed Aircraft

    NASA Technical Reports Server (NTRS)

    Regenie, Victoria; Gatlin, Donald; Kempel, Robert; Matheny, Neil

    1992-01-01

    The F-18 High Alpha Research Vehicle is the first thrust-vectoring testbed aircraft used to study the aerodynamics and maneuvering available in the poststall flight regime and to provide the data for validating ground prediction techniques. The aircraft includes a flexible research flight control system and full research instrumentation. The capability to control the vehicle at angles of attack up to 70 degrees is also included. This aircraft was modified by adding a pitch and yaw thrust-vectoring system. No significant problems occurred during the envelope expansion phase of the program. This aircraft has demonstrated excellent control in the wing rock region and increased rolling performance at high angles of attack. Initial pilot reports indicate that the increased capability is desirable although some difficulty in judging the size and timing of control inputs was observed. The aircraft, preflight ground testing and envelope expansion flight tests are described.

  9. A three dimensional vortex wake model for missiles at high angles on attack

    NASA Technical Reports Server (NTRS)

    Sheffield, J. S.; Deffenbaugh, F. D.

    1980-01-01

    A three dimensional model for the steady flow past missile and aircraft nose shaped bodies is presented based on augmenting a potential solution with a wake composed of vortex filaments. The vortex positions are determined by the requirement that they, in some sense, align with the flow. The aerodynamic loads on the body are compared with experimental values and used to evaluate the model. The vortex positions compare well with flow visualization results for slender bodies at high angles of attack. The approximations in the wake near the body cause peaks in the force distributions more severe than in the measured values. For given vortex strengths and body attachment points multiple steady vortex positions were not found.

  10. Unscrambling Mixed Elements using High Angle Annular Dark Field Scanning Transmission Electron Microscopy.

    PubMed

    van den Bos, Karel H W; De Backer, Annick; Martinez, Gerardo T; Winckelmans, Naomi; Bals, Sara; Nellist, Peter D; Van Aert, Sandra

    2016-06-17

    The development of new nanocrystals with outstanding physicochemical properties requires a full three-dimensional (3D) characterization at the atomic scale. For homogeneous nanocrystals, counting the number of atoms in each atomic column from high angle annular dark field scanning transmission electron microscopy images has been shown to be a successful technique to get access to this 3D information. However, technologically important nanostructures often consist of more than one chemical element. In order to extend atom counting to heterogeneous materials, a new atomic lensing model is presented. This model takes dynamical electron diffraction into account and opens up new possibilities for unraveling the 3D composition at the atomic scale. Here, the method is applied to determine the 3D structure of Au@Ag core-shell nanorods, but it is applicable to a wide range of heterogeneous complex nanostructures.

  11. Calculation of aerodynamic characteristics of airplane configurations at high angles of attack

    NASA Technical Reports Server (NTRS)

    Tseng, J. B.; Lan, C. Edward

    1988-01-01

    Calculation of longitudinal and lateral directional aerodynamic characteristics of airplanes by the VORSTAB code is examined. The numerical predictions are based on the potential flow theory with corrections of high angle of attack phenomena; namely, vortex flow and boundary layer separation effects. To account for the vortex flow effect, vortex lift, vortex action point, augmented vortex lift and vortex breakdown effect through the method of suction analogy are included. The effect of boundary layer separation is obtained by matching the nonlinear section data with the three dimensional lift characteristics iteratively. Through correlation with results for nine fighter configurations, it is concluded that reasonably accurate prediction of longitudinal and static lateral directional aerodynamics can be obtained with the VORSTAB code up to an angle of attack at which wake interference and forebody vortex effect are not important. Possible reasons for discrepancy at higher angles of attack are discussed.

  12. A review of some Reynolds number effects related to bodies at high angles of attack

    NASA Technical Reports Server (NTRS)

    Polhamus, E. C.

    1984-01-01

    A review of some effects of Reynolds number on selected aerodynamic characteristics of two- and three-dimensional bodies of various cross sections in relation to fuselages at high angles of attack at subsonic and transonic speeds is presented. Emphasis is placed on the Reynolds number ranges above the subcritical and angles of attack where lee side vortex flow or unsteady wake type flows predominate. Lists of references, arranged in subject categories, are presented with emphasis on those which include data over a reasonable Reynolds number range. Selected Reynolds number data representative of various aerodynamic flows around bodies are presented and analyzed and some effects of these flows on fuselage aerodynamic parameters are discussed.

  13. Quasi-periodic dynamics of a high angle of attack aircraft

    NASA Astrophysics Data System (ADS)

    Rohith, G.; Sinha, Nandan K.

    2017-01-01

    High angle of attack maneuvers closer to stall is a commonly accessed flight regime especially in case of fighter aircrafts. Stall and post-stall dynamics are dominated by nonlinearities which make the analysis difficult. Presence of external factors such as wind makes the system even more complex. Rich nonlinearities point to the possibility of existence of chaotic solutions. Past studies in this area confirm the development of such solutions. These studies are mainly concentrated on very high angle of attack regimes, which may not be practically easily accessible. This paper examines the possibility of existence of chaotic solutions in the lower, more accessible areas in the post stall domain. The analysis is composed of the study of effect of external wind as an agent to drive the system towards the possibility of a chaotic solution. Investigations reveal presence of quasi-periodic solutions, which are characterized by two incommensurate frequencies. This solution appears in the time simulation by varying the control parameter viz., wind. The solutions correspond to the values in the lower region of the angle of attack versus elevator bifurcation curve in the post-stall region. A steady wind is considered for the analysis and explores the possibility of chaotic motion by increasing the wind in a step wise manner. It is found that wind adds extra energy to the system which in turn drives the system in to chaos. The analysis is done with the help of phase portrait, Poincare map and amplitude spectrum and a quasi-periodic route to chaos via torus doubling is also presented.

  14. Twisted complex superfluids in optical lattices

    PubMed Central

    Jürgensen, Ole; Sengstock, Klaus; Lühmann, Dirk-Sören

    2015-01-01

    We show that correlated pair tunneling drives a phase transition to a twisted superfluid with a complex order parameter. This unconventional superfluid phase spontaneously breaks the time-reversal symmetry and is characterized by a twisting of the complex phase angle between adjacent lattice sites. We discuss the entire phase diagram of the extended Bose—Hubbard model for a honeycomb optical lattice showing a multitude of quantum phases including twisted superfluids, pair superfluids, supersolids and twisted supersolids. Furthermore, we show that the nearest-neighbor interactions lead to a spontaneous breaking of the inversion symmetry of the lattice and give rise to dimerized density-wave insulators, where particles are delocalized on dimers. For two components, we find twisted superfluid phases with strong correlations between the species already for surprisingly small pair-tunneling amplitudes. Interestingly, this ground state shows an infinite degeneracy ranging continuously from a supersolid to a twisted superfluid. PMID:26345721

  15. Twisted complex superfluids in optical lattices.

    PubMed

    Jürgensen, Ole; Sengstock, Klaus; Lühmann, Dirk-Sören

    2015-09-08

    We show that correlated pair tunneling drives a phase transition to a twisted superfluid with a complex order parameter. This unconventional superfluid phase spontaneously breaks the time-reversal symmetry and is characterized by a twisting of the complex phase angle between adjacent lattice sites. We discuss the entire phase diagram of the extended Bose-Hubbard model for a honeycomb optical lattice showing a multitude of quantum phases including twisted superfluids, pair superfluids, supersolids and twisted supersolids. Furthermore, we show that the nearest-neighbor interactions lead to a spontaneous breaking of the inversion symmetry of the lattice and give rise to dimerized density-wave insulators, where particles are delocalized on dimers. For two components, we find twisted superfluid phases with strong correlations between the species already for surprisingly small pair-tunneling amplitudes. Interestingly, this ground state shows an infinite degeneracy ranging continuously from a supersolid to a twisted superfluid.

  16. Modeling and control of active twist aircraft

    NASA Astrophysics Data System (ADS)

    Cramer, Nicholas Bryan

    The Wright Brothers marked the beginning of powered flight in 1903 using an active twist mechanism as their means of controlling roll. As time passed due to advances in other technologies that transformed aviation the active twist mechanism was no longer used. With the recent advances in material science and manufacturability, the possibility of the practical use of active twist technologies has emerged. In this dissertation, the advantages and disadvantages of active twist techniques are investigated through the development of an aeroelastic modeling method intended for informing the designs of such technologies and wind tunnel testing to confirm the capabilities of the active twist technologies and validate the model. Control principles for the enabling structural technologies are also proposed while the potential gains of dynamic, active twist are analyzed.

  17. Component twist method for higher twists in D1-D5 CFT

    NASA Astrophysics Data System (ADS)

    Carson, Zaq; Jardine, Ian T.; Peet, Amanda W.

    2017-07-01

    The deformation operator of the D1-D5 orbifold CFT, a twist-2 operator, drives the CFT towards the black hole dual, and its physics is key to understanding thermalization in the D1-D5 system. To further study this deformation, we extend previous work on the effect of twist-2 operators to a method that works for higher orders, in the continuum limit. Our component twist method works by building higher-twist operators out of twist-2 operators, together with knowledge of Bogoliubov transformations. Consequently, this method sidesteps limitations in Lunin-Mathur technology by avoiding lifts to the covering space. We verify the method by reproducing results obtainable with Lunin-Mathur technology. Going further, our method upholds a previously conjectured scaling law in the continuum limit that applies to any generic configuration of twists. We illustrate this with computations for a new configuration of two twist-2 operators that twists three copies together.

  18. The Twist Limit for Bipolar Active Regions

    NASA Technical Reports Server (NTRS)

    Moore, Ron; Falconer, David; Gary, Allen

    2008-01-01

    We present new evidence that further supports the standard idea that active regions are emerged magnetic-flux-rope omega loops. When the axial magnetic twist of a cylindrical flux rope exceeds a critical amount, the flux rope becomes unstable to kinking, and the excess axial twist is converted into writhe twist by the kinking. This suggests that, if active regions are emerged omega loops, then (1) no active region should have magnetic twist much above the limit set by kinking, (2) active regions having twist near the limit should often arise from kinked omega loops, and (3) since active regions having large delta sunspots are outstandingly twisted, these arise from kinked omega loops and should have twist near the limit for kinking. From each of 36 vector magnetograms of bipolar active regions, we have measured (1) the total flux of the vertical field above 100 G, (2) the area covered by this flux, and (3) the net electric current that arches over the polarity inversion line. These three quantities yield an estimate of the axial magnetic twist in a simple model cylindrical flux rope that corresponds to the top of the active region s hypothetical omega loop prior to emergence. In all 36 cases, the estimated twist is below the critical limit for kinking. The 11 most twisted active regions (1) have estimated twist within a factor of approx.3 of the limit, and (2) include all of our 6 active regions having large delta sunspots. Thus, our observed twist limit for bipolar active regions is in good accord with active regions being emerged omega loops.

  19. The Twist Limit for Bipolar Active Regions

    NASA Technical Reports Server (NTRS)

    Moore, Ron; Falconer, David; Gary, Allen

    2008-01-01

    We present new evidence that further supports the standard idea that active regions are emerged magnetic-flux-rope omega loops. When the axial magnetic twist of a cylindrical flux rope exceeds a critical amount, the flux rope becomes unstable to kinking, and the excess axial twist is converted into writhe twist by the kinking. This suggests that, if active regions are emerged omega loops, then (1) no active region should have magnetic twist much above the limit set by kinking, (2) active regions having twist near the limit should often arise from kinked omega loops, and (3) since active regions having large delta sunspots are outstandingly twisted, these arise from kinked omega loops and should have twist near the limit for kinking. From each of 36 vector magnetograms of bipolar active regions, we have measured (1) the total flux of the vertical field above 100 G, (2) the area covered by this flux, and (3) the net electric current that arches over the polarity inversion line. These three quantities yield an estimate of the axial magnetic twist in a simple model cylindrical flux rope that corresponds to the top of the active region s hypothetical omega loop prior to emergence. In all 36 cases, the estimated twist is below the critical limit for kinking. The 11 most twisted active regions (1) have estimated twist within a factor of approx.3 of the limit, and (2) include all of our 6 active regions having large delta sunspots. Thus, our observed twist limit for bipolar active regions is in good accord with active regions being emerged omega loops.

  20. The Twist Box Domain is Required for Twist1-induced Prostate Cancer Metastasis

    PubMed Central

    Gajula, Rajendra P.; Chettiar, Sivarajan T.; Williams, Russell D.; Thiyagarajan, Saravanan; Kato, Yoshinori; Aziz, Khaled; Wang, Ruoqi; Gandhi, Nishant; Wild, Aaron T.; Vesuna, Farhad; Ma, Jinfang; Salih, Tarek; Cades, Jessica; Fertig, Elana; Biswal, Shyam; Burns, Timothy F.; Chung, Christine H.; Rudin, Charles M.; Herman, Joseph M.; Hales, Russell K.; Raman, Venu; An, Steven S.; Tran, Phuoc T.

    2013-01-01

    Twist1, a basic helix-loop-helix transcription factor, plays a key role during development and is a master regulator of the epithelial-mesenchymal transition (EMT) that promotes cancer metastasis. Structure-function relationships of Twist1 to cancer-related phenotypes are underappreciated, so we studied the requirement of the conserved Twist box domain for metastatic phenotypes in prostate cancer (PCa). Evidence suggests that Twist1 is overexpressed in clinical specimens and correlated with aggressive/metastatic disease. Therefore, we examined a transactivation mutant, Twist1-F191G, in PCa cells using in vitro assays which mimic various stages of metastasis. Twist1 overexpression led to elevated cytoskeletal stiffness and cell traction forces at the migratory edge of cells based on biophysical single-cell measurements. Twist1 conferred additional cellular properties associated with cancer cell metastasis including increased migration, invasion, anoikis resistance, and anchorage-independent growth. The Twist box mutant was defective for these Twist1 phenotypes in vitro. Importantly, we observed a high frequency of Twist1-induced metastatic lung tumors and extra-thoracic metastases in vivo using the experimental lung metastasis assay. The Twist box was required for PCa cells to colonize metastatic lung lesions and extra-thoracic metastases. Comparative genomic profiling revealed transcriptional programs directed by the Twist box that were associated with cancer progression, such as Hoxa9. Mechanistically, Twist1 bound to the Hoxa9 promoter and positively regulated Hoxa9 expression in PCa cells. Finally, Hoxa9 was important for Twist1-induced cellular phenotypes associated with metastasis. These data suggest that the Twist box domain is required for Twist1 transcriptional programs and PCa metastasis. PMID:23982216

  1. Twisted Gaussian Schell-model beams

    SciTech Connect

    Simon, R. ); Mukunda, N. Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore )

    1993-01-01

    The authors introduce a new class of partially coherent axially symmetric Gaussian Schell-model (GSM) beams incorporating a new twist phase quadratic in configuration variables. This phase twists the beam about its axis during propagation and is shown to be bounded in strength because of the positive semidefiniteness of the cross-spectral density. Propagation characteristics and invariants for such beams are derived and interpreted, and two different geometric representations are developed. Direct effects of the twist phase on free propagation as well as in parabolic index fibers are demonstrated. Production of such twisted GSM beams, starting with Li-Wolf anisotropic GSM beams, is described. 34 refs., 3 figs.

  2. Viscous Nonlinear Dynamics of Twist and Writhe

    NASA Astrophysics Data System (ADS)

    Goldstein, Raymond E.; Powers, Thomas R.; Wiggins, Chris H.

    1998-06-01

    Exploiting the ``natural'' frame of space curves, we formulate an intrinsic dynamics of a twisted elastic filament in a viscous fluid. Coupled nonlinear equations describing the temporal evolution of the filament's complex curvature and twist density capture the dynamic interplay of twist and writhe. These equations are used to illustrate a remarkable nonlinear phenomenon: geometric untwisting of open filaments, whereby twisting strains relax through a transient writhing instability without axial rotation. Experimentally observed writhing motions of fibers of the bacterium B. subtilis [N. H. Mendelson et al., J. Bacteriol. 177, 7060 (1995)] may be examples of this untwisting process.

  3. DVCS amplitude with kinematical twist-3 terms

    SciTech Connect

    Radyushkin, A.V.; Weiss, C.

    2000-08-01

    The authors compute the amplitude of deeply virtual Compton scattering (DVCS) using the calculus of QCD string operators in coordinate representation. To restore the electromagnetic gauge invariance (transversality) of the twist-2 amplitude they include the operators of twist-3 which appear as total derivatives of twist-2 operators. The results are equivalent to a Wandzura-Wilczek approximation for twist-3 skewed parton distributions. They find that this approximation gives a finite result for the amplitude of a longitudinally polarized virtual photon, while the amplitude for transverse polarization is divergent, i.e., factorization breaks down in this term.

  4. Friction spinning - Twist phenomena and the capability of influencing them

    NASA Astrophysics Data System (ADS)

    Lossen, Benjamin; Homberg, Werner

    2016-10-01

    The friction spinning process can be allocated to the incremental forming techniques. The process consists of process elements from both metal spinning and friction welding. The selective combination of process elements from these two processes results in the integration of friction sub-processes in a spinning process. This implies self-induced heat generation with the possibility of manufacturing functionally graded parts from tube and sheets. Compared with conventional spinning processes, this in-process heat treatment permits the extension of existing forming limits and also the production of more complex geometries. Furthermore, the defined adjustment of part properties like strength, grain size/orientation and surface conditions can be achieved through the appropriate process parameter settings and consequently by setting a specific temperature profile in combination with the degree of deformation. The results presented from tube forming start with an investigation into the resulting twist phenomena in flange processing. In this way, the influence of the main parameters, such as rotation speed, feed rate, forming paths and tool friction surface, and their effects on temperature, forces and finally the twist behavior are analyzed. Following this, the significant correlations with the parameters and a new process strategy are set out in order to visualize the possibility of achieving a defined grain texture orientation.

  5. Facial Soft Tissue Changes after Maxillary Impaction and Mandibular Advancement in High Angle Class II Cases

    PubMed Central

    Aydil, Barış; Özer, Nedim; Marşan, Gülnaz

    2012-01-01

    The aim of this study was to determine the vertical and anteroposterior alterations in the soft, the dental and the skeletal tissues associated with the facial profile after Le Fort I maxillary impaction in conjunction with sagittal split osteotomy for mandibular advancement performed in patients with a high angle Class II skeletal deformity. The study population consists of 21 patients (11 females and 10 males, mean age 24.5±1.6 years) who underwent Le Fort I maxillary impaction in conjunction with sagittal split osteotomy for mandibular advancement. Lateral cephalograms were obtained prior to the surgery and 1.3±0.2 years postoperatively. Wilcoxon test was performed to compare the pre- and postsurgical cephalometric measurements. Pearson correlation test was carried out to determine the relative changes in skeletal, dental and the facial soft tissues. The insignificant decrease in the nasolabial angle was correlated with the significant decrease in the vertical position of the nose due to the nasal protraction noticed after bimaxillary surgery. The retraction of both the upper lip and the upper incisors was correlated with the insignificant decrease in the columella-lobular angle. The insignificant decrease in both the vertical height of the mandibular B point and the lower incisors was correlated with the insignificant decrease in vertical height of the soft tissue pogonion, attributable to the resulting superior movement of the soft tissues of the chin and the counter clockwise rotation of the mandible after maxillary impaction and bilateral sagittal split osteotomy, respectively. Le Fort I maxillary impaction in conjunction with mandibular sagittal split osteotomy for mandibular advancement significantly affected the vertical and anteroposterior positions of the maxilla and the mandible, respectively. When performed in combination, these surgical techniques may efficiently alter the position of upper incisor and the nasal position in both vertical and

  6. Mandibular advancement surgery in high-angle and low-angle class II patients: different long-term skeletal responses.

    PubMed

    Mobarak, K A; Espeland, L; Krogstad, O; Lyberg, T

    2001-04-01

    The objective of this cephalometric study was to compare skeletal stability and the time course of postoperative changes in high-angle and low-angle Class II patients after mandibular advancement surgery. The subjects were 61 consecutive mandibular retrognathism patients whose treatment included bilateral sagittal split osteotomy and rigid fixation. The patients were divided according to the preoperative mandibular plane angle; the 20 patients with the lowest mandibular plane angle (20.8 degrees +/- 4.9 degrees ) constituted the low-angle group, while the 20 cases with the highest mandibular plane angle (43.0 degrees +/- 4.0 degrees ) represented the high-angle group. Lateral cephalograms were taken on 6 occasions: immediately before surgery, immediately after surgery, 2 and 6 months after surgery, and 1 and 3 years after surgery. Results demonstrated that the high-angle and low-angle groups had different patterns of surgical and postoperative changes. High-angle patients were associated with both a higher frequency and a greater magnitude of horizontal relapse. While 95% of the total relapse took place during the first 2 months after surgery in the low-angle group, high-angle patients demonstrated a more continuous relapse pattern, with a significant proportion (38%) occurring late in the follow-up period. Possible reasons for the different postsurgical response are discussed.

  7. Longitudinal-control design approach for high-angle-of-attack aircraft

    NASA Technical Reports Server (NTRS)

    Ostroff, Aaron J.; Proffitt, Melissa S.

    1993-01-01

    This paper describes a control synthesis methodology that emphasizes a variable-gain output feedback technique that is applied to the longitudinal channel of a high-angle-of-attack aircraft. The aircraft is a modified F/A-18 aircraft with thrust-vectored controls. The flight regime covers a range up to a Mach number of 0.7; an altitude range from 15,000 to 35,000 ft; and an angle-of-attack (alpha) range up to 70 deg, which is deep into the poststall region. A brief overview is given of the variable-gain mathematical formulation as well as a description of the discrete control structure used for the feedback controller. This paper also presents an approximate design procedure with relationships for the optimal weights for the selected feedback control structure. These weights are selected to meet control design guidelines for high-alpha flight controls. Those guidelines that apply to the longitudinal-control design are also summarized. A unique approach is presented for the feed-forward command generator to obtain smooth transitions between load factor and alpha commands. Finally, representative linear analysis results and nonlinear batch simulation results are provided.

  8. Quantitative atomic resolution mapping using high-angle annular dark field scanning transmission electron microscopy.

    PubMed

    Van Aert, S; Verbeeck, J; Erni, R; Bals, S; Luysberg, M; Van Dyck, D; Van Tendeloo, G

    2009-09-01

    A model-based method is proposed to relatively quantify the chemical composition of atomic columns using high angle annular dark field (HAADF) scanning transmission electron microscopy (STEM) images. The method is based on a quantification of the total intensity of the scattered electrons for the individual atomic columns using statistical parameter estimation theory. In order to apply this theory, a model is required describing the image contrast of the HAADF STEM images. Therefore, a simple, effective incoherent model has been assumed which takes the probe intensity profile into account. The scattered intensities can then be estimated by fitting this model to an experimental HAADF STEM image. These estimates are used as a performance measure to distinguish between different atomic column types and to identify the nature of unknown columns with good accuracy and precision using statistical hypothesis testing. The reliability of the method is supported by means of simulated HAADF STEM images as well as a combination of experimental images and electron energy-loss spectra. It is experimentally shown that statistically meaningful information on the composition of individual columns can be obtained even if the difference in averaged atomic number Z is only 3. Using this method, quantitative mapping at atomic resolution using HAADF STEM images only has become possible without the need of simultaneously recorded electron energy loss spectra.

  9. Actuator and aerodynamic modeling for high-angle-of-attack aeroservoelasticity

    NASA Technical Reports Server (NTRS)

    Brenner, Martin J.

    1993-01-01

    Accurate prediction of airframe/actuation coupling is required by the imposing demands of modern flight control systems. In particular, for agility enhancement at high angle of attack and low dynamic pressure, structural integration characteristics such as hinge moments, effective actuator stiffness, and airframe/control surface damping can have a significant effect on stability predictions. Actuator responses are customarily represented with low-order transfer functions matched to actuator test data, and control surface stiffness is often modeled as a linear spring. The inclusion of the physical properties of actuation and its installation on the airframe is therefore addressed using detailed actuator models which consider the physical, electrical, and mechanical elements of actuation. The aeroservoelastic analysis procedure is described in which the actuators are modeled as detailed high-order transfer functions and as approximate low-order transfer functions. The impacts of unsteady aerodynamic modeling on aeroservoelastic stability are also investigated by varying the order of approximation, or number of aerodynamic lag states, in the analysis. Test data from a thrust-vectoring configuration of an F/A-l8 aircraft are compared to predictions to determine the effects on accuracy as a function of modeling complexity.

  10. Experimental study of effects of forebody geometry on high angle of attack static and dynamic stability

    NASA Technical Reports Server (NTRS)

    Brandon, J. M.; Nguyen, L. T.

    1986-01-01

    A series of low speed wind tunnel tests on a generic fighter model with a cylindrical fuselage were made to investigate the effects of forebody shape on static and dynamic lateral/directional stability. Five forebodies, including a chine nose of unconventional cross-sectional shape, were tested. Conventional force tests were conducted to determine static stability characteristics and single degree-of-freedom free-to-roll tests were used to study the wing rock susceptibility of the model with the various forebodies. Flow visualization data were obtained to aid in analysis of the complex flow phenomena involved. The results show that forebody cross-sectional shape can strongly effect both static and dynamic (roll) stability at high angles of attack. Large variations in stability were obtained for the various forebody geometries. These characteristics result from the impact of cross-sectional shape on forebody vortex development, the behavior of the vortices at sideslip conditions, and their interaction with the wing and empennage flow fields.

  11. Influence of spatial and temporal coherences on atomic resolution high angle annular dark field imaging.

    PubMed

    Beyer, Andreas; Belz, Jürgen; Knaub, Nikolai; Jandieri, Kakhaber; Volz, Kerstin

    2016-10-01

    Aberration-corrected (scanning) transmission electron microscopy ((S)TEM) has become a widely used technique when information on the chemical composition is sought on an atomic scale. To extract the desired information, complementary simulations of the scattering process are inevitable. Often the partial spatial and temporal coherences are neglected in the simulations, although they can have a huge influence on the high resolution images. With the example of binary gallium phosphide (GaP) we elucidate the influence of the source size and shape as well as the chromatic aberration on the high angle annular dark field (HAADF) intensity. We achieve a very good quantitative agreement between the frozen phonon simulation and experiment for different sample thicknesses when a Lorentzian source distribution is assumed and the effect of the chromatic aberration is considered. Additionally the influence of amorphous layers introduced by the preparation of the TEM samples is discussed. Taking into account these parameters, the intensity in the whole unit cell of GaP, i.e. at the positions of the different atomic columns and in the region between them, is described correctly. With the knowledge of the decisive parameters, the determination of the chemical composition of more complex, multinary materials becomes feasible.

  12. A Tail Buffet Loads Prediction Method for Aircraft at High Angles of Attack

    NASA Technical Reports Server (NTRS)

    Pototzky, Anthony S.; Moses, Robert W.

    2005-01-01

    Aircraft designers commit significant resources to the design of aircraft in meeting performance goals. Despite fulfilling traditional design requirements, many fighter aircraft have encountered buffet loads when demonstrating their high angle-of-attack maneuver capabilities. As a result, during test or initial production phases of fighter development programs, many new designs are impacted, usually in a detrimental way, by resulting in reassessing designs or limiting full mission capability. These troublesome experiences usually stem from overlooking or completely ignoring the effects of buffet during the design phase of aircraft. Perhaps additional requirements are necessary that addresses effects of buffet in achieving best aircraft performance in fulfilling mission goals. This paper describes a reliable, fairly simple, but quite general buffet loads analysis method to use in the initial design phases of fighter-aircraft development. The method is very similar to the random gust load analysis that is now commonly available in a commercial code, which this analysis capability is based, with some key modifications. The paper describes the theory and the implementation of the methodology. The method is demonstrated on a JSF prototype example problem. The demonstration also serves as a validation of the method, since, in the paper, the analysis is shown to nearly match the flight data. In addition, the paper demonstrates how the analysis method can be used to assess candidate design concepts in determining a satisfactory final aircraft configuration.

  13. Aerodynamic parameters of High-Angle-of attack Research Vehicle (HARV) estimated from flight data

    NASA Technical Reports Server (NTRS)

    Klein, Vladislav; Ratvasky, Thomas R.; Cobleigh, Brent R.

    1990-01-01

    Aerodynamic parameters of the High-Angle-of-Attack Research Aircraft (HARV) were estimated from flight data at different values of the angle of attack between 10 degrees and 50 degrees. The main part of the data was obtained from small amplitude longitudinal and lateral maneuvers. A small number of large amplitude maneuvers was also used in the estimation. The measured data were first checked for their compatibility. It was found that the accuracy of air data was degraded by unexplained bias errors. Then, the data were analyzed by a stepwise regression method for obtaining a structure of aerodynamic model equations and least squares parameter estimates. Because of high data collinearity in several maneuvers, some of the longitudinal and all lateral maneuvers were reanalyzed by using two biased estimation techniques, the principal components regression and mixed estimation. The estimated parameters in the form of stability and control derivatives, and aerodynamic coefficients were plotted against the angle of attack and compared with the wind tunnel measurements. The influential parameters are, in general, estimated with acceptable accuracy and most of them are in agreement with wind tunnel results. The simulated responses of the aircraft showed good prediction capabilities of the resulting model.

  14. Technical Evaluation Report, Part A - Vortex Flow and High Angle of Attack

    NASA Technical Reports Server (NTRS)

    Luckring, James M.

    2003-01-01

    A symposium entitled Vortex Flow and High Angle of Attack was held in Loen, Norway, from May 7 through May 11, 2001. The Applied Vehicle Technology (AVT) panel, under the auspices of the Research and Technology Organization (RTO), sponsored this symposium. Forty-eight papers, organized into nine sessions, addressed computational and experimental studies of vortex flows pertinent to both aircraft and maritime applications. The studies also ranged from fundamental fluids investigations to flight test results, and significant results were contributed from a broad range of countries. The principal emphasis of this symposium was on "the understanding and prediction of separation-induced vortex flows and their effects on military vehicle performance, stability, control, and structural design loads." It was further observed by the program committee that "separation- induced vortex flows are an important part of the design and off-design performance of conventional fighter aircraft and new conventional or unconventional manned or unmanned advanced vehicle designs (UAVs, manned aircraft, missiles, space planes, ground-based vehicles, and ships)." The nine sessions addressed the following topics: vortical flows on wings and bodies, experimental techniques for vortical flows, numerical simulations of vortical flows, vortex stability and breakdown, vortex flows in maritime applications, vortex interactions and control, vortex dynamics, flight testing, and vehicle design. The purpose of this paper is to provide brief reviews of these papers along with some synthesizing perspectives toward future vortex flow research opportunities. The paper includes the symposium program. (15 refs.)

  15. Twisting the N=2 string

    NASA Astrophysics Data System (ADS)

    Ketov, Sergei V.; Lechtenfeld, Olaf; Parkes, Andrew J.

    1995-03-01

    The most general homogeneous monodromy conditions in N=2 string theory are classified in terms of the conjugacy classes of the global symmetry group U(1,1)⊗openZ2. For classes which generate a discrete subgroup Γ, the corresponding target space backgrounds openC1,1/Γ include half spaces, complex orbifolds, and tori. We propose a generalization of the intercept formula to matrix-valued twists, but find massless physical states only for Γ=open1 (untwisted) and Γ=openZ2 (in the manner of Mathur and Mukhi), as well as for Γ being a parabolic element of U(1,1). In particular, the 16 openZ2-twisted sectors of the N=2 string are investigated, and the corresponding ground states are identified via bosonization and BRST cohomology. We find enough room for an extended multiplet of ``spacetime'' supersymmetry, with the number of supersymmetries being dependent on global ``spacetime'' topology. However, world-sheet locality for the chiral vertex operators does not permit interactions among all massless ``spacetime'' fermions.

  16. STOUT SMEARING FOR TWISTED FERMIONS.

    SciTech Connect

    SCHOLZ,W.; JANSEN, K.; McNEILE, C.; MONTVAY, I.; RICHARDS, C.; URBACH, C.; WENGER, U.

    2007-07-30

    The effect of Stout smearing is investigated in numerical simulations with twisted mass Wilson quarks. The phase transition near zero quark mass is studied on 12{sup 3} x 24, 16{sup 3} x 32 and 24{sup 3} x 48 lattices at lattice spacings a {approx_equal} 0.1-0.125 fm. The phase structure of Wilson fermions with twisted mass ({mu}) has been investigated in [1,2]. As it is explained there, the observed first order phase transition limits the minimal pion mass which can be reached in simulations at a given lattice spacing: m{sub k}{sup min} {approx_equal} {theta}(a). The phase structure is schematically depicted in the left panel of Fig. I . The phase transition can be observed in simulations with twisted mass fermions, for instance, as a ''jump'' or even metastabilities in the average plaquette value as a function of the hopping parameter ({kappa}). One possibility to weaken the phase transition and therefore allow for lighter pion masses at a given lattice spacing is to use an improved gauge action like the DBW2, Iwasaki, or tree-level Symanzik (tlSym) improved gauge action instead of the simple Wilson gauge action. This has been successfully demonstrated in [3,4,5]. Here we report on our attempts to use a smeared gauge field in the fermion lattice Dirac operator to further reduce the strength of the phase transition. This is relevant in simulations with N{sub f} = 2 + 1 + 1 (u,d,s,c) quark flavors [6] where the first order phase transition becomes stronger compared to N{sub f} = 2 simulations. The main impact of the above mentioned improved gauge actions on the gauge fields occurring in simulations is to suppress short range fluctuations (''dislocations'') and the associated ''exceptionally small'' eigenvalues of the fermion matrix. The same effect is expected from smearing the gauge field links in the fermion action. The cumulated effect of the improved gauge action and smeared links should allow for a smaller pion mass at a given lattice spacing and volume. Our

  17. Twisting of glycosidic bonds by hydrolases

    USDA-ARS?s Scientific Manuscript database

    Patterns of scissile bond twisting have been found in crystal structures of glycoside hydrolases (GHs) that are complexed with substrates and inhibitors. To estimate the increased potential energy in the substrates that results from this twisting, we have plotted torsion angles for the scissile bond...

  18. Twist-stretch profiles of DNA chains

    NASA Astrophysics Data System (ADS)

    Zoli, Marco

    2017-06-01

    Helical molecules change their twist number under the effect of a mechanical load. We study the twist-stretch relation for a set of short DNA molecules modeled by a mesoscopic Hamiltonian. Finite temperature path integral techniques are applied to generate a large ensemble of possible configurations for the base pairs of the sequence. The model also accounts for the bending and twisting fluctuations between adjacent base pairs along the molecules stack. Simulating a broad range of twisting conformation, we compute the helix structural parameters by averaging over the ensemble of base pairs configurations. The method selects, for any applied force, the average twist angle which minimizes the molecule’s free energy. It is found that the chains generally over-twist under an applied stretching and the over-twisting is physically associated to the contraction of the average helix diameter, i.e. to the damping of the base pair fluctuations. Instead, assuming that the maximum amplitude of the bending fluctuations may decrease against the external load, the DNA molecule first over-twists for weak applied forces and then untwists above a characteristic force value. Our results are discussed in relation to available experimental information albeit for kilo-base long molecules.

  19. Stress effects in twisted highly birefringent fibers

    NASA Astrophysics Data System (ADS)

    Wolinski, Tomasz R.

    1994-03-01

    Hydrostatic pressure and uniaxial longitudinal strain effects in twisted highly birefringent optical fibers have been investigated from the point of the Marcuse mode-coupling theory. The problem is analyzed in terms of local normal modes of the ideal fiber and in the limit of weak twist, where large linear birefringence dominates over twist effect, and therefore twist coupling between local modes is not effective. The authors present the results of birefringence measurements in highly birefringent bow-tie fibers influenced simultaneously by hydrostatic pressure up to 100 MPa and twisting the result for highly birefringent elliptical-core fibers influenced by uniaxial longitudinal strain up to 4000 (mu) (epsilon) and twisting effect. The birefringence measurement method is based on twist-induced effects and has been successfully applied in a stress environment. The experiment was conducted with a specially designed stress generating device that makes it possible to simultaneously generate various mechanical perturbations such as hydrostatic and radial pressure, axial strain and twist, allowing study of their influence on mode propagation in optical fibers. A comparison with theoretical results as well as with pervious experimental data on stress influence on the beat length parameter in highly birefringent fibers is also provided.

  20. Domain Wall Motion Across Various Grain Boundaries in Ferroelectric Thin Films

    DOE PAGES

    Marincel, Daniel M.; Zhang, Huairuo; Jesse, Stephen; ...

    2015-03-21

    Domain wall movement at and near engineered 10°, 15°, and 24° tilt and 10° and 30° twist grain boundaries was measured by band excitation piezoresponse force microscopy for Pb(Zr,Ti)O3 films with Zr/Ti ratio of 45/55 and 52/48. A minimum in nonlinear response was observed at the grain boundary for the highest angle twist and tilt grain boundaries, while a maximum in nonlinear response was observed at the 10° tilt grain boundaries. Lastly, the observed nonlinear response was correlated to the domain structure imaged in cross section by transmission electron microscopy.

  1. Domain Wall Motion Across Various Grain Boundaries in Ferroelectric Thin Films

    SciTech Connect

    Marincel, Daniel M.; Zhang, Huairuo; Jesse, Stephen; Belianinov, Alex; Okatan, Mahmut B.; Kalinin, Sergei V.; Rainforth, W. Mark; Reaney, Ian M.; Randall, Clive A.; Trolier-McKinstry, Susan

    2015-03-21

    Domain wall movement at and near engineered 10°, 15°, and 24° tilt and 10° and 30° twist grain boundaries was measured by band excitation piezoresponse force microscopy for Pb(Zr,Ti)O3 films with Zr/Ti ratio of 45/55 and 52/48. A minimum in nonlinear response was observed at the grain boundary for the highest angle twist and tilt grain boundaries, while a maximum in nonlinear response was observed at the 10° tilt grain boundaries. Lastly, the observed nonlinear response was correlated to the domain structure imaged in cross section by transmission electron microscopy.

  2. Grain boundary phase equilibrium in metallic systems

    SciTech Connect

    Deymier, P.A.

    1991-04-01

    Progresses in the structural and chemical characterization of grain boundaries in metals are reported. We have developed a solid state method for fabrication of a variety of important grain boundaries. This method is based on a sequence of heavy deformation of single crystals followed by controlled recrystallization. The structure of complex grain boundaries such as the quasiperiodic 45{degree}(100) twist in pure aluminum or the periodic {Sigma}5(310) in aluminum-5%Mg alloy has been elucidated. We have found the structural unit (SU) model to be very powerful for the description of quasiperiodic interfaces. The applicability of the SU model to heterophase interfaces is verified for Si-Al interfaces. Further advances have been achieved in the understanding of the driving forces for grain boundary segregation including elastic and electronic effects. Chemical effects on grain boundary core structure are observed in the case of Al-Mg alloys and Sr doped Si.

  3. Cyclic Cocycles on Twisted Convolution Algebras

    NASA Astrophysics Data System (ADS)

    Angel, Eitan

    2013-01-01

    We give a construction of cyclic cocycles on convolution algebras twisted by gerbes over discrete translation groupoids. For proper étale groupoids, Tu and Xu (Adv Math 207(2):455-483, 2006) provide a map between the periodic cyclic cohomology of a gerbe-twisted convolution algebra and twisted cohomology groups which is similar to the construction of Mathai and Stevenson (Adv Math 200(2):303-335, 2006). When the groupoid is not proper, we cannot construct an invariant connection on the gerbe; therefore to study this algebra, we instead develop simplicial techniques to construct a simplicial curvature 3-form representing the class of the gerbe. Then by using a JLO formula we define a morphism from a simplicial complex twisted by this simplicial curvature 3-form to the mixed bicomplex computing the periodic cyclic cohomology of the twisted convolution algebras.

  4. Application of Piloted Simulation to High-Angle-of-Attack Flight-Dynamics Research for Fighter Aircraft

    NASA Technical Reports Server (NTRS)

    Ogburn, Marilyn E.; Foster, John V.; Hoffler, Keith D.

    2005-01-01

    This paper reviews the use of piloted simulation at Langley Research Center as part of the NASA High-Angle-of-Attack Technology Program (HATP), which was created to provide concepts and methods for the design of advanced fighter aircraft. A major research activity within this program is the development of the design processes required to take advantage of the benefits of advanced control concepts for high-angle-of-attack agility. Fundamental methodologies associated with the effective use of piloted simulation for this research are described, particularly those relating to the test techniques, validation of the test results, and design guideline/criteria development.

  5. Identification of an unsteady aerodynamic model up to high angle of attack regime

    NASA Astrophysics Data System (ADS)

    Fan, Yigang

    1997-12-01

    those from references, a state-space model is developed to describe the unsteady aerodynamic characteristics up to the high angle of attack regime. A nondimensional coordinate is introduced as the state variable describing the flow separation or vortex burst. First-order differential equation is used to govern the dynamics of flow separation or vortex bursting through this state variable. To be valid for general configurations, Taylor series expansions in terms of the input variables are used in the determination of aerodynamic characteristics, resembling the current approach of the stability derivatives. However, these derivatives are longer constant. They are dependent on the state variable of flow separation or vortex burst. In this way, the changes in stability derivatives with the angle of attack are included dynamically. The performance of the model is then validated by the wind-tunnel measurements of an NACA 0015 airfoil, a 70sp° delta wing and, finally two F-18 aircraft configurations. The results obtained show that within the framework of the proposed model, it is possible to obtain good agreement with different unsteady wind tunnel data in high angle-of-attack regime.

  6. Effect of grain orientation on mechanical properties and thermomechanical response of Sn-based solder interconnects

    SciTech Connect

    Chen, Hongtao; Yan, Bingbing; Yang, Ming; Ma, Xin; Li, Mingyu

    2013-11-15

    The thermomechanical response of Sn-based solder interconnects with differently oriented grains was investigated by electron backscattered diffraction technique under thermal cycling and thermal shock testing in this study. The results showed that deformation and cracking of solder interconnects have a close relationship with the unique characteristics of grain orientation and boundaries in each solder interconnect, and deformation was frequently confined within the high-angle grain boundaries. The micro Vickers hardness testing results showed that the hardness varied significantly depending on the grain orientation and structure, and deformation twins can be induced around the indents by the indentation testing. - Highlights: • Thermomechanical response shows a close relationship with the grain structure. • Deformation was frequently confined within the high-angle grain boundaries. • Different grain orientations exhibit different hardness. • Deformation twins can be induced around the indents in SAC105 solder interconnects.

  7. Folded supersymmetry with a twist

    SciTech Connect

    Cohen, Timothy; Craig, Nathaniel; Lou, Hou Keong; Pinner, David

    2016-03-30

    Folded supersymmetry (f-SUSY) stabilizes the weak scale against radiative corrections from the top sector via scalar partners whose gauge quantum numbers differ from their Standard Model counterparts. This non-trivial pairing of states can be realized in extra-dimensional theories with appropriate supersymmetry-breaking boundary conditions. We present a class of calculable f-SUSY models that are parametrized by a non-trivial twist in 5D boundary conditions and can accommodate the observed Higgs mass and couplings. Although the distinctive phenomenology associated with the novel folded states should provide strong evidence for this mechanism, the most stringent constraints are currently placed by conventional supersymmetry searches. As a result, these models remain minimally fine-tuned in light of LHC8 data and provide a range of both standard and exotic signatures accessible at LHC13.

  8. Folded supersymmetry with a twist

    DOE PAGES

    Cohen, Timothy; Craig, Nathaniel; Lou, Hou Keong; ...

    2016-03-30

    Folded supersymmetry (f-SUSY) stabilizes the weak scale against radiative corrections from the top sector via scalar partners whose gauge quantum numbers differ from their Standard Model counterparts. This non-trivial pairing of states can be realized in extra-dimensional theories with appropriate supersymmetry-breaking boundary conditions. We present a class of calculable f-SUSY models that are parametrized by a non-trivial twist in 5D boundary conditions and can accommodate the observed Higgs mass and couplings. Although the distinctive phenomenology associated with the novel folded states should provide strong evidence for this mechanism, the most stringent constraints are currently placed by conventional supersymmetry searches. Asmore » a result, these models remain minimally fine-tuned in light of LHC8 data and provide a range of both standard and exotic signatures accessible at LHC13.« less

  9. Twisting cracks in Bouligand structures.

    PubMed

    Suksangpanya, Nobphadon; Yaraghi, Nicholas A; Kisailus, David; Zavattieri, Pablo

    2017-06-10

    The Bouligand structure, which is found in many biological materials, is a hierarchical architecture that features uniaxial fiber layers assembled periodically into a helicoidal pattern. Many studies have highlighted the high damage-resistant performance of natural and biomimetic Bouligand structures. One particular species that utilizes the Bouligand structure to achieve outstanding mechanical performance is the smashing Mantis Shrimp, Odontodactylus Scyllarus (or stomatopod). The mantis shrimp generates high speed, high acceleration blows using its raptorial appendage to defeat highly armored preys. The load-bearing part of this appendage, the dactyl club, contains an interior region [16] that consists of a Bouligand structure. This region is capable of developing a significant amount of nested twisting microcracks without exhibiting catastrophic failure. The development and propagation of these microcracks are a source of energy dissipation and stress relaxation that ultimately contributes to the remarkable damage tolerance properties of the dactyl club. We develop a theoretical model to provide additional insights into the local stress intensity factors at the crack front of twisting cracks formed within the Bouligand structure. Our results reveal that changes in the local fracture mode at the crack front leads to a reduction of the local strain energy release rate, hence, increasing the necessary applied energy release rate to propagate the crack, which is quantified by the local toughening factor. Ancillary 3D simulations of the asymptotic crack front field were carried out using a J-integral to validate the theoretical values of the energy release rate and the local stress intensity factors. Copyright © 2017 Elsevier Ltd. All rights reserved.

  10. A demonstration of passive blade twist control using extension-twist coupling

    NASA Technical Reports Server (NTRS)

    Lake, Renee C.; Nixon, Mark W.; Wilbur, Matthew L.; Singleton, Jeffrey D.; Mirick, Paul H.

    1992-01-01

    The results from a study aimed at improving the dynamic and aerodynamic characteristics of composite rotor blades through the use of extension-twist coupling are presented. A set of low twist model-scale helicopter rotor blades was manufactured with a view towards demonstrating the passive blade twist control concept. Hover testing of the blades was conducted to measure the change in blade twist as a function of rotor speed. The blades were spun through the 0-800 rpm range, with a corresponding sweep of collective pitch to determine the effect on the blade elastic twist. Hover data were obtained for both a ballasted and unballasted blade configuration in atmospheric conditions, where maximum twist changes of 2.54 and 5.24 degrees were respectively observed. These results compared well with those from a finite element analysis of the blade, which yielded maximum twists of 3.01 and 5.61 degrees for the unballasted and ballasted blade configurations, respectively. The aerodynamic-induced effects on the blade elastic twist, determined by testing a ballasted blade configuration in a near-vacuum condition, were found to be minimal with a maximum twist difference of 0.17 degrees observed between the two test environments. The effect of collective pitch sweep on the elastic twist was minimal.

  11. Search for Mechanically-Induced Grain Morphology Changes in Oxygen Free Electrolytic (OFE) Copper

    SciTech Connect

    Sanders, Jennifer; /SLAC

    2006-08-18

    The deformation of the microscopic, pure metal grains (0.1 to > 1 millimeter) in the copper cells of accelerator structures decreases the power handling capabilities of the structures. The extent of deformation caused by mechanical fabrication damage is the focus of this study. Scanning electron microscope (SEM) imaging of a bonded test stack of six accelerating cells at magnifications of 30, 100, 1000 were taken before simulated mechanical damage was done. After a 2{sup o}-3{sup o} twist was manually applied to the test stack, the cells were cut apart and SEM imaged separately at the same set magnifications (30, 100, and 1000), to examine any effects of the mechanical stress. Images of the cells after the twist were compared to the images of the stack end (cell 60) before the twist. Despite immense radial damage to the end cell from the process of twisting, SEM imaging showed no change in grain morphology from images taken before the damage: copper grains retained shape and the voids at the grain boundaries stay put. Likewise, the inner cells of the test stack showed similar grain consistency to that of the end cell before the twist was applied. Hence, there is no mechanical deformation observed on grains in the aperture disk, either for radial stress or for rotational stress. Furthermore, the high malleability of copper apparently absorbed stress and strain very well without deforming the grain structure in the surface.

  12. DYNAMICS OF STRONGLY TWISTED RELATIVISTIC MAGNETOSPHERES

    SciTech Connect

    Parfrey, Kyle; Beloborodov, Andrei M.; Hui, Lam

    2013-09-10

    Magnetar magnetospheres are believed to be strongly twisted due to shearing of the stellar crust by internal magnetic stresses. We present time-dependent axisymmetric simulations showing in detail the evolution of relativistic force-free magnetospheres subjected to slow twisting through large angles. When the twist amplitude is small, the magnetosphere moves quasi-statically through a sequence of equilibria of increasing free energy. At some twist amplitude the magnetosphere becomes tearing-mode unstable to forming a resistive current sheet, initiating large-scale magnetic reconnection in which a significant fraction of the magnetic free energy can be dissipated. This ''critical'' twist angle is insensitive to the resistive length scale. Rapid shearing temporarily stabilizes the magnetosphere beyond the critical angle, allowing the magnetosphere of a rapidly differentially rotating star to store and dissipate more free energy. In addition to these effects, shearing the surface of a rotating star increases the spindown torque applied to the star. If shearing is much slower than rotation, the resulting spikes in spindown rate can occur on timescales anywhere from the long twisting timescale to the stellar spin period or shorter, depending both on the stellar shear distribution and the existing distribution of magnetospheric twists. A model in which energy is stored in the magnetosphere and released by a magnetospheric instability therefore predicts large changes in the measured spindown rate before soft gamma repeater giant flares.

  13. Low-energy, Mobile Grain Boundaries in Magnesium

    NASA Astrophysics Data System (ADS)

    Liu, Xiangli; Wang, Jian

    2016-02-01

    The strong basal texture that is commonly developed during the rolling of magnesium alloy and can even increase during annealing motivates atomic-level study of dislocation structures of both <0001> tilt and twist grain boundaries (GBs) in Magnesium. Both symmetrical tilt and twist GBs over the entire range of rotation angles θ between 0° and 60° are found to have an ordered atomic structure and can be described with grain boundary dislocation models. In particular, 30° tilt and twist GBs are corresponding to energy minima. The 30° tilt GB is characterized with an array of Shockley partial dislocations bp:-bp on every basal plane and the 30° twist GB is characterized with a stacking faulted structure. More interesting, molecular dynamics simulations explored that both 30° tilt and twist GBs are highly mobile associated with collective glide of Shockley partial dislocations. This could be responsible for the formation of the strong basal texture and a significant number of 30° misorientation GBs in Mg alloy during grain growth.

  14. Low-energy, Mobile Grain Boundaries in Magnesium

    PubMed Central

    Liu, Xiangli; Wang, Jian

    2016-01-01

    The strong basal texture that is commonly developed during the rolling of magnesium alloy and can even increase during annealing motivates atomic-level study of dislocation structures of both <0001> tilt and twist grain boundaries (GBs) in Magnesium. Both symmetrical tilt and twist GBs over the entire range of rotation angles θ between 0° and 60° are found to have an ordered atomic structure and can be described with grain boundary dislocation models. In particular, 30° tilt and twist GBs are corresponding to energy minima. The 30° tilt GB is characterized with an array of Shockley partial dislocations bp:-bp on every basal plane and the 30° twist GB is characterized with a stacking faulted structure. More interesting, molecular dynamics simulations explored that both 30° tilt and twist GBs are highly mobile associated with collective glide of Shockley partial dislocations. This could be responsible for the formation of the strong basal texture and a significant number of 30° misorientation GBs in Mg alloy during grain growth. PMID:26891595

  15. Comparison of X-31 Flight and Ground-Based Yawing Moment Asymmetries at High Angles of Attack

    NASA Technical Reports Server (NTRS)

    Cobleigh, Brent R.; Croom, Mark A.

    2001-01-01

    Significant yawing moment asymmetries were encountered during the high-angle-of-attack envelope expansion of the two X-31 aircraft. These asymmetries caused position saturations of the thrust-vectoring vanes and trailing-edge flaps during some stability-axis rolling maneuvers at high angles of attack. The two test aircraft had different asymmetry characteristics, and ship two has asymmetries that vary as a function of Reynolds number. Several aerodynamic modifications have been made to the X-31 forebody with the goal of minimizing the asymmetry. These modifications include adding transition strips on the forebody and noseboom, using two different length strakes, and increasing nose bluntness. Ultimately, a combination of forebody strakes, nose blunting, and noseboom transition strips reduced the yawing moment asymmetry enough to fully expand the high-angle-of-attack envelope. Analysis of the X-31 flight data is reviewed and compared to wind-tunnel and water-tunnel measurements. Several lessons learned are outlined regarding high-angle-of-attack configuration design and ground testing.

  16. Crack-grain boundary interactions in zinc bicrystals

    NASA Astrophysics Data System (ADS)

    Catoor, D.; Kumar, K. S.

    2011-06-01

    In polycrystalline materials that fail by transgranular cleavage, it is known that crystallographic misorientation of preferred fracture planes across grain boundaries can provide crack growth resistance; despite this, the micromechanisms associated with crack transmission across grain boundaries and their role in determining the overall fracture resistance are not well understood. Recent studies on diverse structural materials such as steels, aluminum alloys and intermetallics have shown a correlation between fracture resistance and the twist component of grain misorientation. However, the lack of control over the degree and type of misorientation in experimental studies, combined with a dearth of analytical and computational investigations that fully account for the three-dimensional nature of the problem, have precluded a systematic analysis of this phenomenon. In this study, this phenomenon was investigated through in situ crack propagation experiments across grain boundaries of controlled twist misorientation in zinc bicrystals. Extrinsic toughening mechanisms that activate upon crack stagnation at the grain boundary deter further crack propagation. The mechanical response and crack growth behavior were observed to be dependent on the twist angle, and several accommodation mechanisms such as twinning, strain localization and slip band blocking contribute to fracture resistance by competing with crack propagation. Three-dimensional finite element analyses incorporating crystal plasticity were performed on a stagnant crack at the grain boundary that provide insight into crack-tip stress and strain fields in the second grain. These analyses qualitatively capture the overall trends in mechanical response as well as strain localization around stagnant crack-tips.

  17. Euclidean supersymmetry, twisting and topological sigma models

    NASA Astrophysics Data System (ADS)

    Hull, C. M.; Lindström, U.; Melo dos Santos, L.; von Unge, R.; Zabzine, M.

    2008-06-01

    We discuss two dimensional N-extended supersymmetry in Euclidean signature and its R-symmetry. For N = 2, the R-symmetry is SO(2) × SO(1, 1), so that only an A-twist is possible. To formulate a B-twist, or to construct Euclidean N = 2 models with H-flux so that the target geometry is generalised Kahler, it is necessary to work with a complexification of the sigma models. These issues are related to the obstructions to the existence of non-trivial twisted chiral superfields in Euclidean superspace.

  18. Twisted spectral geometry for the standard model

    NASA Astrophysics Data System (ADS)

    Martinetti, Pierre

    2015-07-01

    In noncommutative geometry, the spectral triple of a manifold does not generate bosonic fields, for fluctuations of the Dirac operator vanish. A Connes-Moscovici twist forces the commutative algebra to be multiplied by matrices. Keeping the space of spinors untouched, twisted-fluctuations then yield perturbations of the spin connection. Applied to the spectral triple of the Standard Model, a similar twist yields the scalar field needed to stabilize the vacuum and to make the computation of the Higgs mass compatible with its experimental value.

  19. Contrasting fault fluids along high-angle faults: a case study from Southern Apennines (Italy)

    NASA Astrophysics Data System (ADS)

    Sinisi, Rosa; Petrullo, Angela Vita; Agosta, Fabrizio; Paternoster, Michele; Belviso, Claudia; Grassa, Fausto

    2016-10-01

    This work focuses on two fault-controlled deposits, the Atella and Rapolla travertines, which are associated with high-angle extensional faults of the Bradano Trough, southern Apennines (Italy). The Atella travertine is along a NW-SE striking, deep-seated extensional fault, already described in literature, which crosscuts both Apulian carbonates and the overlying foredeep basin infill. The Rapolla travertine is on top of a NE-SW striking, shallow-seated fault, here described for the first time, which is interpreted as a tear fault associated with a shallow thrust displacing only the foredeep basin infill. The results of structural, sedimentological, mineralogical, and C and O isotope analyses are here reported and discussed to assess the provenance of mineralizing fluids, and to evaluate the control exerted by the aforementioned extensional faults on deep, mantle-derived and shallow, meteoric fluids. Sedimentological analysis is consistent with five lithofacies in the studied travertines, which likely formed in a typical lacustrine depositional environment. Mineralogical analysis show that travertines mainly consist of calcite, and minor quartz, feldspar and clay minerals, indicative of a terrigenous supply during travertine precipitation. The isotope signature of the two studied travertines shows different provenance for the mineralizing fluids. At the Atella site, the δ13CPDB values range between + 5.2 and + 5.7‰ and the δ18OPDB values between - 9.0 and - 7.3‰, which are consistent with a mantle-derived CO2 component in the fluid. In contrast, at the Rapolla site the δ13CPDB values vary from - 2.7 to + 1.5‰ and the δ18OPDB values from - 6.8 to - 5.4‰, suggesting a mixed CO2 source with both biogenic-derived and mantle-derived fluids. The results of structural analyses conducted along the footwall damage zone of the fault exposed at the Rapolla site, show that the whole damage zone, in which fractures and joints likely channeled the mixed fluids, acted

  20. Fluid-structure interaction of a rolling restrained body of revolution at high angles of attack

    NASA Astrophysics Data System (ADS)

    Degani, D.; Ishay, M.; Gottlieb, O.

    2017-03-01

    The current work investigates numerically rolling instabilities of a free-to-roll slender rigid-body of revolution placed in a wind tunnel at a high angle of attack. The resistance to the roll moment is represented by a linear torsion spring and equivalent linear damping representing friction in the bearings of a simulated wind tunnel model. The body is subjected to a three-dimensional, compressible, laminar flow. The full Navier-Stokes equations are solved using the second-order implicit finite difference Beam-Warming scheme, adapted to a curvilinear coordinate system, whereas the coupled structural second order equation of motion for roll is solved by a fourth-order Runge-Kutta method. The body consists of a 3.5-diameter tangent ogive forebody with a 7.0-diameter long cylindrical afterbody extending aft of the nose-body junction to x/D = 10.5. We describe in detail the investigation of three angles of attack 20°, 40°, and 65°, at a Reynolds number of 30 000 (based on body diameter) and a Mach number of 0.2. Three distinct configurations are investigated as follows: a fixed body, a free-to-roll body with a weak torsion spring, and a free-to-roll body with a strong torsion spring. For each angle of attack the free-to-roll configuration portrays a distinct and different behavior pattern, including bi-stable limit-cycle oscillations. The bifurcation structure incorporates both large and small amplitude periodic roll oscillations where the latter lose their periodicity with increasing stiffness of the restraining spring culminating with distinct quasiperiodic oscillations. We note that removal of an applied upstream disturbance for a restrained body does not change the magnitude or complexity of the oscillations or of the flow patterns along the body. Depending on structure characteristics and flow conditions even a small rolling moment coefficient at the relatively low angle of attack of 20° may lead to large amplitude resonant roll oscillations.

  1. Twist1 Is Essential for Tooth Morphogenesis and Odontoblast Differentiation*

    PubMed Central

    Meng, Tian; Huang, Yanyu; Wang, Suzhen; Zhang, Hua; Dechow, Paul C.; Wang, Xiaofang; Qin, Chunlin; Shi, Bing; D'Souza, Rena N.; Lu, Yongbo

    2015-01-01

    Twist1 is a basic helix-loop-helix-containing transcription factor that is expressed in the dental mesenchyme during the early stages of tooth development. To better delineate its roles in tooth development, we generated Twist1 conditional knockout embryos (Twist2Cre/+;Twist1fl/fl) by breeding Twist1 floxed mice (Twist1fl/fl) with Twist2-Cre recombinase knockin mice (Twist2Cre/+). The Twist2Cre/+;Twist1fl/fl embryos formed smaller tooth germs and abnormal cusps during early tooth morphogenesis. Molecular and histological analyses showed that the developing molars of the Twist2Cre/+;Twist1fl/fl embryos had reduced cell proliferation and expression of fibroblast growth factors 3, 4, 9, and 10 and FGF receptors 1 and 2 in the dental epithelium and mesenchyme. In addition, 3-week-old renal capsular transplants of embryonic day 18.5 Twist2Cre/+;Twist1fl/fl molars showed malformed crowns and cusps with defective crown dentin and enamel. Immunohistochemical analyses revealed that the implanted mutant molars had defects in odontoblast differentiation and delayed ameloblast differentiation. Furthermore, in vitro ChIP assays demonstrated that Twist1 was able to bind to a specific region of the Fgf10 promoter. In conclusion, our findings suggest that Twist1 plays crucial roles in regulating tooth development and that it may exert its functions through the FGF signaling pathway. PMID:26487719

  2. Twist1 Is Essential for Tooth Morphogenesis and Odontoblast Differentiation.

    PubMed

    Meng, Tian; Huang, Yanyu; Wang, Suzhen; Zhang, Hua; Dechow, Paul C; Wang, Xiaofang; Qin, Chunlin; Shi, Bing; D'Souza, Rena N; Lu, Yongbo

    2015-12-04

    Twist1 is a basic helix-loop-helix-containing transcription factor that is expressed in the dental mesenchyme during the early stages of tooth development. To better delineate its roles in tooth development, we generated Twist1 conditional knockout embryos (Twist2(Cre) (/+);Twist1(fl/fl)) by breeding Twist1 floxed mice (Twist1(fl/fl)) with Twist2-Cre recombinase knockin mice (Twist2(Cre) (/+)). The Twist2(Cre) (/+);Twist1(fl/fl) embryos formed smaller tooth germs and abnormal cusps during early tooth morphogenesis. Molecular and histological analyses showed that the developing molars of the Twist2(Cre) (/+);Twist1(fl/fl) embryos had reduced cell proliferation and expression of fibroblast growth factors 3, 4, 9, and 10 and FGF receptors 1 and 2 in the dental epithelium and mesenchyme. In addition, 3-week-old renal capsular transplants of embryonic day 18.5 Twist2(Cre) (/+);Twist1(fl/fl) molars showed malformed crowns and cusps with defective crown dentin and enamel. Immunohistochemical analyses revealed that the implanted mutant molars had defects in odontoblast differentiation and delayed ameloblast differentiation. Furthermore, in vitro ChIP assays demonstrated that Twist1 was able to bind to a specific region of the Fgf10 promoter. In conclusion, our findings suggest that Twist1 plays crucial roles in regulating tooth development and that it may exert its functions through the FGF signaling pathway. © 2015 by The American Society for Biochemistry and Molecular Biology, Inc.

  3. Mathematical Modeling of Yarn Dynamics in a Generalized Twisting System

    PubMed Central

    Yin, R.; Tao, X. M.; Xu, B. G.

    2016-01-01

    Twisting is an important process to form a continuous yarn from short fibres and to determine the structure and properties of the resultant yarn. This paper proposes a new theoretical model of yarn dynamics in a generalized twisting system, which deals with two important phenomena simultaneously, that is, twist generation and twist propagation. Equations of yarn motion are established and the boundary value problems are numerically solved by Newton-Raphson method. The simulation results are validated by experiments and a good agreement has been demonstrated for the system with a moving rigid cylinder as the twisting element. For the first time, influences of several parameters on the twisting process have been revealed in terms of twist efficiency of the moving rigid cylinder, propagation coefficients of twist trapping and congestion. It was found that the wrap angle and yarn tension have large influence on the twisting process, and the yarn torsional rigidity varies with the twisting parameters. PMID:27079187

  4. A Twist in fate: evolutionary comparison of Twist structure and function.

    PubMed

    Castanon, Irinka; Baylies, Mary K

    2002-04-03

    The general requirement to induce mesoderm and allocate cells into different mesodermal tissues such as body muscle or heart is common in many animal embryos. Since the discovery of the twist gene, there has been great progress toward unraveling the molecular mechanisms that control mesoderm specification and differentiation. Twist was first identified in Drosophila as a gene crucial for proper gastrulation and mesoderm formation. In the fly embryo, Twist continues to play additional roles, allocating mesodermal cells into the body wall muscle fate and patterning a subset of these muscles. Twist is also required for proper differentiation of the adult musculature. Twist homologues have been identified in a great variety of organisms, which span the phylogenetic tree. These organisms include other invertebrates such as jellyfish, nematode, leech and lancelet as well as vertebrates such as frog, chick, fish, mouse and human. The Twist family shares both homology in structure across the basic helix-loop-helix domain and in expression during mesoderm and muscle development in most species. Here we review the current state of knowledge of the Twist family and consider how Twist functions during development. Moreover, we highlight experimental evidence that shows common themes that Twist employs during specification and patterning of the mesoderm among evolutionarily distant organisms. Conserved principles and the molecular mechanisms underlying them are discussed.

  5. Deformed and twisted black holes with NUTs

    NASA Astrophysics Data System (ADS)

    Krtouš, Pavel; Kubizňák, David; Frolov, Valeri P.; Kolář, Ivan

    2016-06-01

    We construct a new class of vacuum black hole solutions whose geometry is deformed and twisted by the presence of NUT charges. The solutions are obtained by ‘unspinning’ the general Kerr-NUT-(A)dS spacetimes, effectively switching off some of their rotation parameters. The resulting geometry has a structure of warped space with the Kerr-like Lorentzian part warped to a Euclidean metric of a deformed and/or twisted sphere, with the deformation and twist characterized by the ‘Euclidean NUT’ parameters. In the absence of NUTs, the solution reduces to a well known Kerr-(A)dS black hole with several rotations switched off. New geometries inherit the original symmetry of the Kerr-NUT-(A)dS family, namely, they possess the full Killing tower of hidden and explicit symmetries. As expected, for vanishing NUT, twist, and deformation parameters, the symmetry is further enlarged.

  6. Thermal conductivity of twisted bilayer graphene

    NASA Astrophysics Data System (ADS)

    Li, Hongyang; Ying, Hao; Chen, Xiangping; Nika, Denis L.; Cocemasov, Alexandr I.; Cai, Weiwei; Balandin, Alexander A.; Chen, Shanshan

    2014-10-01

    We have investigated experimentally the thermal conductivity of suspended twisted bilayer graphene. The measurements were performed using an optothermal Raman technique. It was found that the thermal conductivity of twisted bilayer graphene is lower than that of monolayer graphene and the reference, Bernal stacked bilayer graphene in the entire temperature range examined (~300-700 K). This finding indicates that the heat carriers - phonons - in twisted bilayer graphene do not behave in the same manner as that observed in individual graphene layers. The decrease in the thermal conductivity found in twisted bilayer graphene was explained by the modification of the Brillouin zone due to plane rotation and the emergence of numerous folded phonon branches that enhance the phonon Umklapp and normal scattering. The results obtained are important for understanding thermal transport in two-dimensional systems.

  7. Twists and rotations of solar magnetic fields

    NASA Astrophysics Data System (ADS)

    Piddington, J. H.

    1981-04-01

    A detailed review is given of evidence for the emergence of solar magnetic fields as helically twisted flux ropes, made up of hundreds of thousands of individually twisted flux fibers and reaching concentrations greater than 4000 gauss. The initial pitch angle of the twists is estimated as less than 10 deg in the submerged flux ropes and 1 deg in the fibers, with large-factor increases during (and following) emergence. The upward transmission of magnetic stresses and motions from submerged flux rope sections are major factors in solar physics, with the helical twists accounting for the creation of sunspots and for their stability, fine structure, and mode of decay. They are basic features of solar atmospheric structures, from the largest flare events and prominences to arch filaments and the smallest network components.

  8. New twisted intermetallic compound superconductor: A concept

    NASA Technical Reports Server (NTRS)

    Coles, W. D.; Brown, G. V.; Laurence, J. C.

    1972-01-01

    Method for processing Nb3Sn and other intermetallic compound superconductors produces a twisted, stabilized wire or tube which can be used to wind electromagnetics, armatures, rotors, and field windings for motors and generators as well as other magnetic devices.

  9. Ghost imaging with twisted Gaussian Schell-model beam.

    PubMed

    Cai, Yangjian; Lin, Qiang; Korotkova, Olga

    2009-02-16

    Based on the classical optical coherence theory, ghost imaging with twisted Gaussian Schell-model (GSM) beams is analyzed. It is found that the twist phase of the GSM beam has strong influence on ghost imaging. As the absolute value of the twist factor increases, the ghost image disappears gradually, but its visibility increases. This phenomenon is caused by the fact that the twist phase enhances the transverse spatial coherence of the twisted GSM beam on propagation.

  10. Means for controlling aerodynamically induced twist

    NASA Technical Reports Server (NTRS)

    Elber, W. (Inventor)

    1982-01-01

    A control mechanism which provides active compensation for aerodynamically induced twist deformation of high aspect ratio wings consists of a torque tube, internal to each wing and rigidly attached near the tip of each wing, which is moved by an actuator located in the aircraft fuselage. As changes in the aerodynamic loads on the wings occur the torque tube is rotated to compensate for the induced wing twist.

  11. Twisted covariant noncommutative self-dual gravity

    SciTech Connect

    Estrada-Jimenez, S.; Garcia-Compean, H.; Obregon, O.; Ramirez, C.

    2008-12-15

    A twisted covariant formulation of noncommutative self-dual gravity is presented. The formulation for constructing twisted noncommutative Yang-Mills theories is used. It is shown that the noncommutative torsion is solved at any order of the {theta} expansion in terms of the tetrad and some extra fields of the theory. In the process the first order expansion in {theta} for the Plebanski action is explicitly obtained.

  12. Large-Vortex Capture by a Wing at Very High Angles of Attack

    NASA Technical Reports Server (NTRS)

    Wu, J. M.; Wu, J. Z.; Denny, G. A.; Lu, X. Y.

    1996-01-01

    In generating the lift on a wing, the static stall is a severe barrier. As the angle of attack, alpha, increases to the stall angle, alpha(sub stall) the flow separation point on the upper surface of the wing moves to the leading edge, so that on a two-dimensional airfoil or a large-aspect-ratio wing, the lift abruptly drops to a very low level. Therefore, the first generation of aeronautical flow type, i.e., the attached steady flow, has been limited to alpha less than alpha(sub stall). Owing to the obvious importance in applications, therefore, a great effort has been made in the past two decades to enlarge the range of usable angles of attack by various flow controls for a large-aspect-ratio wing. Basically, relevant works fall into two categories. The first category is usually refereed to as separation control, which concentrates on partially separated flow at alpha less than alpha(sub stall). Since the first experimental study of Collins and Zelenevitz, there has been ample literature showing that a partially separated flow can be turned to almost fully attached by flow controls, so that the lift is recovered and the stall is delayed (for a recent work see Seifert et al.). It has been well established that, in this category, unsteady controls are much more effective than steady ones and can be realized at a very low power-input level (Wu et al.; Seifert et al.). The second and more ambitious category of relevant efforts is the post-stall lift enhancement. Its possibility roots at the existence of a second lift peak at a very high angle of attack. In fact, As alpha further increases from alpha(sub stall), the completely separated flow develops and gradually becomes a bluff-body flow. This flow gives a normal force to the airfoil with a lift component, which reaches a peak at a maximum utilizable angle of attack, alpha(sub m) approx.= 40 deg. This second peak is of the same level as the first lift peak at alpha(sub stall). Meanwhile, the drag is also quickly

  13. Fluctuation Modes of a Twist-Bend Nematic Liquid Crystal

    NASA Astrophysics Data System (ADS)

    Parsouzi, Z.; Shamid, S. M.; Borshch, V.; Challa, P. K.; Baldwin, A. R.; Tamba, M. G.; Welch, C.; Mehl, G. H.; Gleeson, J. T.; Jakli, A.; Lavrentovich, O. D.; Allender, D. W.; Selinger, J. V.; Sprunt, S.

    2016-04-01

    We report a dynamic light-scattering study of the fluctuation modes in a thermotropic liquid crystalline mixture of monomer and dimer compounds that exhibits the twist-bend nematic (NTB ) phase. The results reveal a spectrum of overdamped fluctuations that includes two nonhydrodynamic modes and one hydrodynamic mode in the NTB phase, and a single nonhydrodynamic mode plus two hydrodynamic modes (the usual nematic optic axis or director fluctuations) in the higher temperature, uniaxial nematic phase. The properties of these fluctuations and the conditions for their observation are comprehensively explained by a Landau-de Gennes expansion of the free-energy density in terms of heliconical director and helical polarization fields that characterize the NTB structure, with the latter serving as the primary order parameter. A "coarse-graining" approximation simplifies the theoretical analysis and enables us to demonstrate quantitative agreement between the calculated and experimentally determined temperature dependence of the mode relaxation rates.

  14. Wind-tunnel research comparing lateral control devices, particularly at high angles of attack VI : skewed ailerons on rectangular wings

    NASA Technical Reports Server (NTRS)

    Weick, Fred E; Harris, Thomas A

    1934-01-01

    This report covers the sixth of a series of investigations in which various lateral control devices are compared with particular reference to their effectiveness at high angles of attack. The present report deals with flap-type ailerons hinged about axes having an angle with respect to the leading and trailing edges of the wing. Tests were made on four different skewed ailerons, including two different angles of skew and two sizes of ailerons. At the high angles of attack, all the skewed ailerons tested were slightly inferior with respect to rolling and yawing moments to straight ailerons having the same span and average chord. Computations indicate that the skewed ailerons are also inferior with respect to hinge moments.

  15. Effect of nose perturbation on asymmetric vortices over a blunt-nose body at high angle of attack

    NASA Astrophysics Data System (ADS)

    Sha, Y. X.; Wang, Y. K.; Qi, Z. Y.

    2017-04-01

    To improve the maneuverability, the modern missiles of blunt-nose slender body configuration are required to flight at high angle of attack where many research show complex asymmetric vortices flow will develop over the slender body. The effect of artificial perturbation located on the nose of a blunt slender body at high angle of attack(α=50°) on asymmetric vortices has been investigated with low speed wind tunnel test. The Reynolds number(ReD) of the experiment was 1.48×105. The experimental results are shown to be the following: Asymmetric flow over blunt-nose body was extremely sensitive to the machining tolerances of the nose and can be governed by the artificial perturbation; with the circumferential angle of artificial perturbation varied a period, asymmetric vortices present a behavior of single-period.

  16. Convergence behavior that controls adaptive wind tunnel walls near the test section in the high angle of attack range

    NASA Technical Reports Server (NTRS)

    Ziemann, J.

    1982-01-01

    The NACA 0012 profile at Mach 0.5 was investigated in a wind tunnel with adaptive walls. It is found that adaptation of the flexible walls is possible in the high angle of attack range on both sides of maximum lift. Oil film photographs of the flow at the profile surface show three dimensional effects in the region of the corners between the profile and the sidewall. It is concluded that pure two dimensional separated flow is not possible.

  17. AEROX: Computer program for transonic aircraft aerodynamics to high angles of attack. Volume 1: Aerodynamic methods and program users' guide

    NASA Technical Reports Server (NTRS)

    Axelson, J. A.

    1977-01-01

    The AEROX program estimates lift, induced-drag and pitching moments to high angles (typ. 60 deg) for wings and for wingbody combinations with or without an aft horizontal tail. Minimum drag coefficients are not estimated, but may be input for inclusion in the total aerodynamic parameters which are output in listed and plotted formats. The theory, users' guide, test cases, and program listing are presented.

  18. Flutter Clearance of the F-18 High-angle-of-attack Research Vehicle with Experimental Wingtip Instrumentation Pods

    NASA Technical Reports Server (NTRS)

    Freudinger, Lawrence C.

    1989-01-01

    An F-18 aircraft was modified with wingtip instrumentation pods for use in NASA's high-angle-of-attack research program. Ground vibration and flight flutter testing were performed to clear an acceptable flight envelope for the aircraft. Flight test utilized atmospheric turbulence for structural excitation; the aircraft displayed no adverse aeroelastic trends within the envelope tested. The data presented in this report include mode shapes from the ground vibration and estimates of frequency and damping as a function of Mach number.

  19. Status of the Validation of High-Angle-Of-Attack Nose-Down Pitch Control Margin Design Guidelines

    NASA Technical Reports Server (NTRS)

    Ogburn, Marilyn E.; Foster, John V.; Pahle, Joseph W.; Wilson, R. Joe; Lackey, James B.

    1992-01-01

    This paper presents a summary of results obtained to date in an ongoing cooperative research program between NASA and the U.S. Navy to develop design criteria for high-angle-of-attack nose- down pitch control for combat aircraft. A fundamental design consideration for aircraft incorporating relaxed static stability in pitch is the level of stability which achieves a proper balance between high- speed performance considerations and low-speed requirements for maneuvering at high angles of attack. A comprehensive data base of piloted simulation results was generated for parametric variations of critical parameters affecting nose-down control capability. The results showed a strong correlation of pilot rating to the short-term pitch response for nose-down commands applied at high- angle-of-attack conditions. Using these data, candidate design guidelines and flight demonstration requirements were defined. Full- scale flight testing to validate the research methodology and proposed guidelines is in progress, some preliminary results of which are reviewed.

  20. Evaluation of importance of lateral acceleration derivatives in extraction of lateral-directional derivatives at high angles of attack

    NASA Technical Reports Server (NTRS)

    Nguyen, L. T.

    1974-01-01

    A theoretical investigation was conducted to determine the importance of the lateral acceleration (beta) derivatives in the extraction of lateral-directional stability derivatives for swept wing airplanes at high angles of attack. Representative values of lateral acceleration derivatives in yaw and roll (Cn beta and Cl beta) were used in a computer program to generate representative flight motions at several angles of attack and altitudes. The computer-generated motions were then subjected to a parameter identification process based on a modified Newton-Raphson method. Two identification techniques were evaluated, one which included the beta derivatives and one which neglected them. The results of the study indicate that omission of the beta derivatives from mathematical models used in the derivative-extraction techniques can produce erroneous values for the lateral-directional stability derivatives particularly at high angles of attack, where the beta derivatives are large. The largest errors occur in the dynamic derivatives, but large errors may also occur in the static derivatives for cases in which the beta derivatives have large effects on the flight motions of the airplane. In addition, the resulting identified mathematical models provide poor motion prediction as well as erroneous predictions of dynamic modal characteristics. These results strongly indicate that the effects of beta derivatives should be considered in any attempt to extract lateral-directional aerodynamic parameters at high angles of attack.

  1. Hybrid structured/unstructured grid computations for the F/A-18 at high angle of attack

    NASA Technical Reports Server (NTRS)

    Biedron, Robert T.; Whitaker, David L.

    1994-01-01

    At high angles of attack, vortical flows play a crucial role in the maintenance of lift for fighter aircraft. However, under certain conditions, the vortical flow can have an adverse effect on the aircraft. On the F/A-18 the LEX vortex can impinge on the tail; at high angles of attack the unsteady flow from vortex bursting can cause structural fatigue on the vertical tails. At high angles of attack, the flow field can be quite complex, and a computational analysis challenging. A full configuration analysis with viscous structured grids can be computationally expensive and the task of generating the requisite grids can be quite difficult. To mitigate these difficulties and provide a medium-fidelity analysis tool, a hybrid structured/unstructured approach was adopted for this work. In this analysis, the formation and roll-up of the LEX vortex is computed with a structured Navier-Stokes solver, and the resulting vortex propagated downstream with an unstructured Euler solver.

  2. Grain boundary distribution and texture in ultrafine-grained copper produced by severe plastic deformation

    SciTech Connect

    Mishin, O.V. |; Gertsman, V.Y. |; Valiev, R.Z.; Gottstein, G.

    1996-10-01

    Ultrafine-grained (UFG), i.e., nano- and submicrocrystalline materials have attracted great attention in recent years. This interest is caused by the unusual mechanical and physical properties of these materials. The extremely high volume fraction of grain boundaries (GBs) and triple junctions in UFG materials contribute to their unusual properties. However, other important parameters describing polycrystalline aggregate, namely, grain boundary misorientation and character distributions have not yet been studied in UFG materials, though they are conceived to influence mechanical and physical properties as well. Some studies indicated that mainly high-angle GBs were formed during severe plastic deformation; however, no direct proof of this suggestion has been obtained so far. The current paper deals with a statistical study of GB distributions and texture in UFG-materials. Pure copper was chosen for this study, since many results on microstructure and properties of the ultrafine-grained state produced in this material are available.

  3. SILICON CARBIDE GRAIN BOUNDARY DISTRIBUTIONS, IRRADIATION CONDITIONS, AND SILVER RETENTION IN IRRADIATED AGR-1 TRISO FUEL PARTICLES

    SciTech Connect

    Lillo, T. M.; Rooyen, I. J.; Aguiar, J. A.

    2016-11-01

    Precession electron diffraction in the transmission electron microscope was used to map grain orientation and ultimately determine grain boundary misorientation angle distributions, relative fractions of grain boundary types (random high angle, low angle or coincident site lattice (CSL)-related boundaries) and the distributions of CSL-related grain boundaries in the SiC layer of irradiated TRISO-coated fuel particles. Two particles from the AGR-1 experiment exhibiting high Ag-110m retention (>80%) were compared to a particle exhibiting low Ag-110m retention (<19%). Irradiated particles with high Ag-110m retention exhibited a lower fraction of random, high angle grain boundaries compared to the low Ag-110m retention particle. An inverse relationship between the random, high angle grain boundary fraction and Ag-110m retention is found and is consistent with grain boundary percolation theory. Also, comparison of the grain boundary distributions with previously reported unirradiated grain boundary distributions, based on SEM-based EBSD for similarly fabricated particles, showed only small differences, i.e. a greater low angle grain boundary fraction in unirradiated SiC. It was, thus, concluded that SiC layers with grain boundary distributions susceptible to Ag-110m release were present prior to irradiation. Finally, irradiation parameters were found to have little effect on the association of fission product precipitates with specific grain boundary types.

  4. Exotic Twisted Equivariant Cohomology of Loop Spaces, Twisted Bismut-Chern Character and T-Duality

    NASA Astrophysics Data System (ADS)

    Han, Fei; Mathai, Varghese

    2015-07-01

    We define exotic twisted - equivariant cohomology for the loop space LZ of a smooth manifold Z via the invariant differential forms on LZ with coefficients in the (typically non-flat) holonomy line bundle of a gerbe, with differential an equivariantly flat superconnection. We introduce the twisted Bismut-Chern character form, a loop space refinement of the twisted Chern character form in Bouwknegt et al. (Commun Math Phys 228:17-49, 2002) and Mathai and Stevenson (Commun Math Phys 236:161-186, 2003), which represents classes in the completed periodic exotic twisted -equivariant cohomology of LZ.We establish a localisation theorem for the completed periodic exotic twisted -equivariant cohomology for loop spaces and apply it to establish T-duality in a background flux in type II String Theory from a loop space perspective.

  5. A twist of insight - the role of Twist-family bHLH factors in development

    PubMed Central

    BARNES, RALSTON M.; FIRULLI, ANTHONY B.

    2009-01-01

    Members of the Twist-family of bHLH proteins play a pivotal role in a number of essential developmental programs. Twist-family bHLH proteins function by dimerizing with other bHLH members and binding to cis- regulatory elements, called E-boxes. While Twist-family members may simply exhibit a preference in terms of high-affinity binding partners, a complex, multilevel cascade of regulation creates a dynamic role for these bHLH proteins. We summarize in this review information on each Twist-family member concerning expression pattern, function, regulation, downstream targets, and interactions with other bHLH proteins. Additionally, we focus on the phospho-regulatory mechanisms that tightly control posttranslational modification of Twist-family member bHLH proteins. PMID:19378251

  6. Improvement in performance of heat exchanger fitted with twisted tape

    SciTech Connect

    Sivashanmugam, P.; Sundaram, S.

    1999-04-01

    The improvement in performance of a double pipe heat exchanger fitted with twisted tape as a turbulence promoter with twist ratios of 15.649, 8.54, 5.882, 4.95, and 4.149 was experimentally studied. A maximum percentage gain of 44.7% in energy transfer rate was obtained for the twisted tape of twist ratio 4.149. For all twist ratios, the gain decreases with the Reynolds number and becomes constant for Reynolds numbers greater than 3,000. The smaller the twist ratio is, the larger the gain in energy for a specific Reynolds number.

  7. Gated Raman Spectroscopy of Twisted Bilayer Graphene

    NASA Astrophysics Data System (ADS)

    Huang, Shengqiang; Chattrakun, Kanokporn; Yankowitz, Matthew; Sandhu, Arvinder; Leroy, Brian

    2014-03-01

    The interaction of charge carriers with lattice vibrations in graphene exhibits many intriguing physical phenomena. Raman spectroscopy is a powerful non-destructive technique to probe these interactions. In twisted bilayer graphene, the electronic band structure and phonon dispersion depend on the rotation angle between the layers. Here we present a systematic Raman spectroscopy study of twisted bilayer graphene, using a 532 nm laser, with controllable charge densities up to 2 ×1013cm-2. The twist angle is first identified by the observation of a moire pattern in STM measurements. In the angle range between 5 and 8 degrees, the R' peak softens and weakens with increasing charge density. Near 12 degrees, the G peak is enhanced due to the increased density of states in twisted bilayer graphene. However, the G peak area quickly decreases with increasing charge density. Lastly, we observed several unusual effects for the G peak for all angles from 2 to 10 degrees as a function of increasing charge density. We found that the G peak broadened, split and oscillated in position. All these results demonstrate that twisted bilayer graphene has rich optoelectronic properties.

  8. Twisted electron-acoustic waves in plasmas

    NASA Astrophysics Data System (ADS)

    Aman-ur-Rehman, Ali, S.; Khan, S. A.; Shahzad, K.

    2016-08-01

    In the paraxial limit, a twisted electron-acoustic (EA) wave is studied in a collisionless unmagnetized plasma, whose constituents are the dynamical cold electrons and Boltzmannian hot electrons in the background of static positive ions. The analytical and numerical solutions of the plasma kinetic equation suggest that EA waves with finite amount of orbital angular momentum exhibit a twist in its behavior. The twisted wave particle resonance is also taken into consideration that has been appeared through the effective wave number qeff accounting for Laguerre-Gaussian mode profiles attributed to helical phase structures. Consequently, the dispersion relation and the damping rate of the EA waves are significantly modified with the twisted parameter η, and for η → ∞, the results coincide with the straight propagating plane EA waves. Numerically, new features of twisted EA waves are identified by considering various regimes of wavelength and the results might be useful for transport and trapping of plasma particles in a two-electron component plasma.

  9. Spatially resolved electronic structure of twisted graphene

    NASA Astrophysics Data System (ADS)

    Yao, Qirong; van Bremen, Rik; Slotman, Guus J.; Zhang, Lijie; Haartsen, Sebastiaan; Sotthewes, Kai; Bampoulis, Pantelis; de Boeij, Paul L.; van Houselt, Arie; Yuan, Shengjun; Zandvliet, Harold J. W.

    2017-06-01

    We have used scanning tunneling microscopy and spectroscopy to resolve the spatial variation of the density of states of twisted graphene layers on top of a highly oriented pyrolytic graphite substrate. Owing to the twist a moiré pattern develops with a periodicity that is substantially larger than the periodicity of a single layer graphene. The twisted graphene layer has electronic properties that are distinctly different from that of a single layer graphene due to the nonzero interlayer coupling. For small twist angles (˜1∘-3 .5∘) the integrated differential conductivity spectrum exhibits two well-defined Van Hove singularities. Spatial maps of the differential conductivity that are recorded at energies near the Fermi level exhibit a honeycomb structure that is comprised of two inequivalent hexagonal sublattices. For energies | E -EF |>0.3 eV the hexagonal structure in the differential conductivity maps vanishes. We have performed tight-binding calculations of the twisted graphene system using the propagation method, in which a third graphene layer is added to mimic the substrate. This third layer lowers the symmetry and explains the development of the two hexagonal sublattices in the moiré pattern. Our experimental results are in excellent agreement with the tight-binding calculations.

  10. Twisting microfluidics in a planetary centrifuge.

    PubMed

    Yasuda, Shoya; Hayakawa, Masayuki; Onoe, Hiroaki; Takinoue, Masahiro

    2017-03-15

    This paper reports a twisting microfluidic method utilising a centrifuge-based fluid extruding system in a planetary centrifuge which simultaneously generates an orbital rotation and an axial spin. In this method, fluid extrusion from a micro-scale capillary to an 'open-space' solution or air enables release of the fluid from the capillary-based microchannel, which physically means that there is a release of fluids from a confined low-Reynolds-number environment to an open non-low-Reynolds-number environment. As a result, the extruded fluids are separated from the axial spin of the capillary, and the difference in the angular rates of the axial spin between the capillary and the extruded fluids produces the 'twisting' of the fluid. In this study, we achieve control of the twist of highly viscous fluids, and we construct a simple physical model for the fluid twist. In addition, we demonstrate the formation of twisted hydrogel microstructures (stripe-patterned microbeads and multi-helical microfibres) with control over the stripe pattern and the helical pitch length. We believe that this method will enable the generation of more sophisticated microstructures which cannot easily be formed by usual channel-based microfluidic devices. This method can also provide advanced control of microfluids, as in the case of rapid mixing of highly viscous fluids. This method can contribute to a wide range of applications in materials science, biophysics, biomedical science, and microengineering in the future.

  11. Dual-twist fiber long period gratings

    NASA Astrophysics Data System (ADS)

    Churikov, Victor M.; Kopp, Victor I.; Genack, A. Z.

    2009-02-01

    Long period fiber gratings couple core and co-propagating cladding modes to produce dips in the transmission spectrum and have been widely utilized as sensors and filters. We have recently developed a new approach to long period fiber gratings utilizing optical fibers, which are uniformly twisted at elevated temperatures to produce double or single helices. Because these fibers are not manufactured by exposing photosensitive glass to patterned UV illumination, as is the case for traditional fiber Bragg gratings (FBGs) or long period gratings (LPGs), they are more robust in harsh thermal and chemical environments. Double helix fibers are polarization sensitive and are fabricated by twisting fiber preforms with high-index noncircular cores while single helix gratings are polarization insensitive and are created by twisting standard optical fibers with cores that are not perfectly centered. Here, we present a new approach to single-helix chiral long-period gratings (CLPGs). The CLPG is created in a glassforming process in which two optical fibers are twisted together to form a helix in the signal fiber as the fibers pass through a miniature oven. "Dual-twist" CLPGs may be fabricated from any conventional or specialty fiber and provide reproducible spectra that may be tailored to specific applications.

  12. Ergodic properties of linked-twist maps

    NASA Astrophysics Data System (ADS)

    Springham, James

    2008-12-01

    We study a class of homeomorphisms of surfaces collectively known as linked-twist maps. We introduce an abstract definition which enables us to give a precise characterisation of a property observed by other authors, namely that such maps fall into one of two classes termed co- and counter-twisting. We single out three specific linked-twist maps, one each on the two-torus, in the plane and on the two-sphere and for each prove a theorem concerning its ergodic properties with respect to the invariant Lebesgue measure. For the map on the torus we prove that there is an invariant, zero-measure Cantor set on which the dynamics are topologically conjugate to a full shift on the space of symbol sequences. Such features are commonly known as topological horseshoes. For the map in the plane we prove that there is a set of full measure on which the dynamics are measure-theoretically isomorphic to a full shift on the space of symbol sequences. This is commonly known as the Bernoulli property and verifies, under certain conditions, a conjecture of Wojtkowski's. We introduce the map on the sphere and prove that it too has the Bernoulli property. We conclude with some conjectures, drawn from our experience, concerning how one might extend the results we have for specific linked-twist maps to the abstract linked-twist maps we have defined.

  13. Twisted electron-acoustic waves in plasmas

    SciTech Connect

    Aman-ur-Rehman; Ali, S.; Khan, S. A.; Shahzad, K.

    2016-08-15

    In the paraxial limit, a twisted electron-acoustic (EA) wave is studied in a collisionless unmagnetized plasma, whose constituents are the dynamical cold electrons and Boltzmannian hot electrons in the background of static positive ions. The analytical and numerical solutions of the plasma kinetic equation suggest that EA waves with finite amount of orbital angular momentum exhibit a twist in its behavior. The twisted wave particle resonance is also taken into consideration that has been appeared through the effective wave number q{sub eff} accounting for Laguerre-Gaussian mode profiles attributed to helical phase structures. Consequently, the dispersion relation and the damping rate of the EA waves are significantly modified with the twisted parameter η, and for η → ∞, the results coincide with the straight propagating plane EA waves. Numerically, new features of twisted EA waves are identified by considering various regimes of wavelength and the results might be useful for transport and trapping of plasma particles in a two-electron component plasma.

  14. Direct observation of individual dislocation interaction processes with grain boundaries

    PubMed Central

    Kondo, Shun; Mitsuma, Tasuku; Shibata, Naoya; Ikuhara, Yuichi

    2016-01-01

    In deformation processes, the presence of grain boundaries has a crucial influence on dislocation behavior; these boundaries drastically change the mechanical properties of polycrystalline materials. It has been considered that grain boundaries act as effective barriers for dislocation glide, but the origin of this barrier-like behavior has been a matter of conjecture for many years. We directly observe how the motion of individual dislocations is impeded at well-defined high-angle and low-angle grain boundaries in SrTiO3, via in situ nanoindentation experiments inside a transmission electron microscope. Our in situ observations show that both the high-angle and low-angle grain boundaries impede dislocation glide across them and that the impediment of dislocation glide does not simply originate from the geometric effects; it arises as a result of the local structural stabilization effects at grain boundary cores as well, especially for low-angle grain boundaries. The present findings indicate that simultaneous consideration of both the geometric effects and the stabilization effects is necessary to quantitatively understand the dislocation impediment processes at grain boundaries. PMID:27847862

  15. Twist transition of nematic hyperbolic hedgehogs.

    PubMed

    James, Richard; Fukuda, Jun-ichi

    2014-04-01

    Stability of an idealized hyperbolic hedgehog in a nematic liquid crystal against a twist transition is investigated by extending the methodology of Rüdinger and Stark [Liq. Cryst. 26, 753 (1999)], where the hedgehog is confined between two concentric spheres. In the ideal hyperbolic-hedgehog the molecular orientation is assumed to rotate proportionally with respect to the inclination angle, θ (and in the opposite sense). However, when splay, k11, and bend, k33, moduli differ this proportionality is lost and the liquid crystal deforms relative to the ideal with bend and splay. Although slight, these deformations are shown to significantly shift the transition if k11/k33 is small. By increasing the degree of confinement the twist transition can be inhibited, a characteristic both hyperbolic and radial hedgehogs have in common. The twist transition of a hyperbolic defect that accompanies a particle is found to be well predicted by the earlier stability analysis of a thick shell.

  16. On reweighting for twisted boundary conditions

    NASA Astrophysics Data System (ADS)

    Bussone, Andrea; Della Morte, Michele; Hansen, Martin; Pica, Claudio

    2017-10-01

    We consider the possibility of using reweighting techniques in order to correct the breaking of unitarity when twisted boundary conditions are imposed on valence fermions in simulations of lattice gauge theories. We start by studying the properties of reweighting factors and their variances at tree-level. This leads us to the introduction of a factorization for the fermionic reweighting determinant. In the numerical, stochastic implementation of the method, we find that the effect of reweighting is negligible in the case of large volumes but it is sizeable when the volumes are small and the twisting angles are large. More importantly, we find that for un-improved Wilson fermions, and in small volumes, the dependence of the critical quark mass on the twisting angle is quite pronounced and results in large violations of the continuum dispersion relation.

  17. Matrix theory compactifications on twisted tori

    NASA Astrophysics Data System (ADS)

    Chatzistavrakidis, Athanasios; Jonke, Larisa

    2012-05-01

    We study compactifications of Matrix theory on twisted tori and noncommutative versions of them. As a first step, we review the construction of multidimensional twisted tori realized as nilmanifolds based on certain nilpotent Lie algebras. Subsequently, matrix compactifications on tori are revisited, and the previously known results are supplemented with a background of a noncommutative torus with nonconstant noncommutativity and an underlying nonassociative structure on its phase space. Next, we turn our attention to three- and six-dimensional twisted tori, and we describe consistent backgrounds of Matrix theory on them by stating and solving the conditions which describe the corresponding compactification. Both commutative and noncommutative solutions are found in all cases. Finally, we comment on the correspondence among the obtained solutions and flux compactifications of 11-dimensional supergravity, as well as on relations among themselves, such as Seiberg-Witten maps and T-duality.

  18. Analysis of gun barrel rifling twist

    NASA Astrophysics Data System (ADS)

    Sun, Jia; Chen, Guangsong; Qian, Linfang; Liu, Taisu

    2017-05-01

    Aiming at the problem of gun barrel rifling twist, the constraint relation between rifling and projectile is investigated. The constraint model of rifling and projectile is established and the geometric relation between the twist and the motion of projectile is analyzed. Based on the constraint model, according to the rotating band that is fired, the stress and the motion law of the rotating band in bore are analyzed. The effects to rotating band (double rotating band or wide driving band) caused by different rifling (rib rifling, increasing rifling and combined rifling) are also investigated. The model is demonstrated by several examples. The results of numerical examples and the constraint mode show that the uncertainty factors will be brought in the increasing rifling and combined rifling during the projectile move in the bore. According to the amplitude and the strength of the twist acting on rotating band, the steady property of rotational motion of the projectile, the rib rifling is a better choose.

  19. Unraveling cellulose microfibrils: a twisted tale.

    PubMed

    Hadden, Jodi A; French, Alfred D; Woods, Robert J

    2013-10-01

    Molecular dynamics (MD) simulations of cellulose microfibrils are pertinent to the paper, textile, and biofuels industries for their unique capacity to characterize dynamic behavior and atomic-level interactions with solvent molecules and cellulase enzymes. While high-resolution crystallographic data have established a solid basis for computational analysis of cellulose, previous work has demonstrated a tendency for modeled microfibrils to diverge from the linear experimental structure and adopt a twisted conformation. Here, we investigate the dependence of this twisting behavior on computational approximations and establish the theoretical basis for its occurrence. We examine the role of solvent, the effect of nonbonded force field parameters [partial charges and van der Waals (vdW) contributions], and the use of explicitly modeled oxygen lone pairs in both the solute and solvent. Findings suggest that microfibril twisting is favored by vdW interactions, and counteracted by both intrachain hydrogen bonds and solvent effects at the microfibril surface.

  20. Electrically Controllable Magnetism in Twisted Bilayer Graphene.

    PubMed

    Gonzalez-Arraga, Luis A; Lado, J L; Guinea, Francisco; San-Jose, Pablo

    2017-09-08

    Twisted graphene bilayers develop highly localized states around AA-stacked regions for small twist angles. We show that interaction effects may induce either an antiferromagnetic or a ferromagnetic (FM) polarization of said regions, depending on the electrical bias between layers. Remarkably, FM-polarized AA regions under bias develop spiral magnetic ordering, with a relative 120° misalignment between neighboring regions due to a frustrated antiferromagnetic exchange. This remarkable spiral magnetism emerges naturally without the need of spin-orbit coupling, and competes with the more conventional lattice-antiferromagnetic instability, which interestingly develops at smaller bias under weaker interactions than in monolayer graphene, due to Fermi velocity suppression. This rich and electrically controllable magnetism could turn twisted bilayer graphene into an ideal system to study frustrated magnetism in two dimensions.

  1. Resonance Raman spectroscopy in twisted bilayer graphene

    NASA Astrophysics Data System (ADS)

    Righi, A.; Venezuela, P.; Chacham, H.; Costa, S. D.; Fantini, C.; Ruoff, R. S.; Colombo, L.; Bacsa, W. S.; Pimenta, M. A.

    2013-12-01

    In this work we study the Raman spectra of twisted bilayer graphene samples, with different twisting angles, by changing the incident laser energy between 2.54 and 4.14 eV. The spectra exhibit a number of extra peaks, classified in different families, each one associated with bilayer graphenes with different twisting rotational angles. We theoretically analyze the laser energy dependence of these extra peaks considering a set of discrete wavevectors within the interior of the Brillouin zone of graphene, which activate special double-resonance Raman processes. Our result show a nice qualitative agreement between the experimental and simulated spectra, demonstrating that these extra peaks are indeed ascribed to an umklapp double-resonance process in graphene systems.

  2. On Supermultiplet Twisting and Spin-Statistics

    NASA Astrophysics Data System (ADS)

    Hübsch, T.

    2013-10-01

    Twisting of off-shell supermultiplets in models with (1+1)-dimensional spacetime has been discovered in 1984, and was shown to be a generic feature of off-shell representations in worldline supersymmetry two decades later. It is shown herein that in all supersymmetric models with spacetime of four or more dimensions, this off-shell supermultiplet twisting, if nontrivial, necessarily maps regular (non-ghost) supermultiplets to ghost supermultiplets. This feature is shown to be ubiquitous in all fully off-shell supersymmetric models with (BV/BRST-treated) constraints.

  3. Factorising the 3D topologically twisted index

    NASA Astrophysics Data System (ADS)

    Cabo-Bizet, Alejandro

    2017-04-01

    We explore the path integration — upon the contour of hermitian (non-auxliary) field configurations — of topologically twisted N=2 Chern-Simons-matter theory (TTCSM) on {S}_2 times a segment. In this way, we obtain the formula for the 3D topologically twisted index, first as a convolution of TTCSM on {S}_2 times halves of {S}_1 , second as TTCSM on {S}_2 times {S}_1 — with a puncture, — and third as TTCSM on {S}_2× {S}_1 . In contradistinction to the first two cases, in the third case, the vector multiplet auxiliary field D is constrained to be anti-hermitian.

  4. Natural frequencies of twisted rotating plates

    NASA Astrophysics Data System (ADS)

    Ramamurti, V.; Kielb, R.

    1984-12-01

    A detailed comparison is presented of the predicted eigenfrequencies of twisted rotating plates as obtained by using two different shape functions. Primarily, rotating twisted plates of two different aspect ratios and two different thickness ratios are considered. The effects of rotation are included by using a "stress smoothing" technique when calculating the augmented stiffness matrix. In addition, the effects of Coriolis acceleration, contributions from membrane behaviour, setting angle and sweep angle are considered. The effects of geometric non-linearity are briefly discussed. Finally, results of a brief study of cambered plates are presented.

  5. Natural frequencies of twisted rotating plates

    NASA Technical Reports Server (NTRS)

    Ramamurti, V.; Kielb, R.

    1984-01-01

    A detailed comparison is presented of the predicted eigenfrequencies of twisted rotating plates as obtained by using two different shape functions. Primarily, rotating twisted plates of two different aspect ratios and two different thickness ratios are considered. The effects of rotation are included by using a 'stress smoothing' technique when calculating the augmented stiffness matrix. In addition, the effects of Coriolis acceleration, contributions from membrane behavior, setting angle and sweep angle are considered. The effects of geometric nonlinearity are briefly discussed. Finally, results of a brief study of cambered plates are presented.

  6. Effects Of Twist On Ceramic Threads

    NASA Technical Reports Server (NTRS)

    Sawko, Paul M.; Tran, Huy Kim

    1989-01-01

    Report describes study of effects of yarn twist and other manufacturing parameters on strength of ceramic sewing threads. Three types of thread considered; silica, aluminoborosilicate (ABS) with 14 percent boria, and ABS with 2 percent boria. For silica thread, best twist found 300 turns per meter. Produced highest break strength at temperatures up to about 540 degree C. Overall strengths of both ABS threads higher than silica thread. Threads used to stitch insulating blankets for reusable spacraft; must resist high temperatures and high aerodynamic loads of reentry into atmosphere of Earth.

  7. Shrink, twist, ripple and melt: Studies of frustrated liquid crystals

    NASA Astrophysics Data System (ADS)

    Fernsler, Jonathan G.

    Complex structures can arise out of a simple system with more than one competing influence on its behavior. The protypical example of this is the two-dimensional triangular lattice Ising model. The ferromagnetic model has two simple degenerate ground states of all spins up or down, but the antiferromagnetic model is a frustrated system. Its geometry does not allow satisfaction of the antiferro condition everywhere, which produces complex ordered structures with dimerization of the spins [1]. Without frustration, the complex structures and phase behavior are lost. All of the topics discussed in this thesis concern smectic liquid crystals. Liquid crystals are perhaps uniquely adept at manifesting frustrated phases. Their combination of periodicity in one or more dimensions allows ordered structures, yet their fluid nature in remaining dimensions allows creation of defects and extraordinarily complex structures in ways that a normal crystal could not tolerate. Liquid crystals contain a huge menagerie of frustrated phases and effects including the polarization modulated [2], vortex lattice [3], twist grain boundary [4], and blue [5] phases, as well as frustrated structures such as cholesteric or SmC* helix unwinding [6], defect lattices in thin films [7], and bend melted grain boundary defects [8], arising from boundary conditions and field effects. In this thesis, we study four liquid crystal systems that show unusual phase behavior or complex structures, deriving from the effects of frustration. Frustration, despite some human prejudices against the word, leaves nature all the more interesting and beautiful.

  8. A Toolbox for Geometric Grain Boundary Characterization

    NASA Astrophysics Data System (ADS)

    Glowinski, Krzysztof; Morawiec, Adam

    Properties of polycrystalline materials are affected by grain boundary networks. The most basic aspect of boundary analysis is boundary geometry. This paper describes a package of computer programs for geometric boundary characterization based on macroscopic boundary parameters. The program allows for determination whether a boundary can be classified as near-tilt, -twist, -symmetric et cetera. Since calculations on experimental, i.e., error affected data are assumed, the program also provides distances to the nearest geometrically characteristic boundaries. The software has a number of other functions helpful in grain boundary analysis. One of them is the determination of planes of all characteristic boundaries for a given misorientation. The resulting diagrams of geometrically characteristic boundaries can be linked to experimentally determined grain boundary distributions. In computations, all symmetrically equivalent representations of boundaries are taken into account. Cubic and hexagonal holohedral crystal symmetries are allowed.

  9. Energetics of DNA twisting. I. Relation between twist and cyclization probability.

    PubMed

    Shore, D; Baldwin, R L

    1983-11-15

    The twisting potential of DNA has been determined directly by a method that measures the cyclization probability or j-factor of EcoRI restriction fragments as a function of DNA twist. The cyclization probability is proportional to Kc, the equilibrium constant for cyclization of the restriction fragment via its cohesive ends (Shore et al., 1981). Here we vary the twist of the DNA by making small internal additions to or deletions from a 242 bp EcoRI restriction fragment. A series of 12 DNA molecules has been studied, which range in length from 237 to 254 bp. The cyclization probability is measured from the rates of covalent closure by phage T4 DNA ligase of two systems: (1) a linear restriction fragment in equilibrium with its cyclized form and (2) half molecules (cut by a blunt-end endonuclease) in equilibrium with joined half molecules. The striking result is that, in this DNA size range, the j-factor depends strongly on the fractional twist: the difference between the total helical twist and the nearest integer. Thus j depends in an oscillatory manner on DNA length between 237 and 254 bp with a period of about 10 bp. These data give the free energy of DNA twisting as a function of twist. The curve of j versus DNA length can be fitted to a harmonic twisting potential with a torsional constant of C = 2.4 X 10(-19) erg cm. This value is in reasonable agreement with different estimates of C made by Barkley & Zimm (1979: C = 1.8 X 10(-19) to 4.1 X 10(-19) erg cm) and is somewhat larger than the value obtained resulting from the kinetics of DNA twisting measured by fluorescence depolarization of ethidium intercalated into DNA (C = 1.4 X 10(-19) erg cm; Millar et al., 1982; Thomas et al., 1980) or from spin label studies (Hurley et al., 1982). Our experiments provide a direct measurement of the torsional free energy and they show that the DNA twisting potential is symmetric. Our experiments also indicate that the DNA helix is continuous, or nearly so, in a nicked circle

  10. Grain dissection as a grain size reducing mechanism during ice microdynamics

    NASA Astrophysics Data System (ADS)

    Steinbach, Florian; Kuiper, Ernst N.; Eichler, Jan; Bons, Paul D.; Drury, Martin R.; Griera, Albert; Pennock, Gill M.; Weikusat, Ilka

    2017-04-01

    Ice sheets are valuable paleo-climate archives, but can lose their integrity by ice flow. An understanding of the microdynamic mechanisms controlling the flow of ice is essential when assessing climatic and environmental developments related to ice sheets and glaciers. For instance, the development of a consistent mechanistic grain size law would support larger scale ice flow models. Recent research made significant progress in numerically modelling deformation and recrystallisation mechanisms in the polycrystalline ice and ice-air aggregate (Llorens et al., 2016a,b; Steinbach et al., 2016). The numerical setup assumed grain size reduction is achieved by the progressive transformation of subgrain boundaries into new high angle grain boundaries splitting an existing grain. This mechanism is usually termed polygonisation. Analogue experiments suggested, that strain induced grain boundary migration can cause bulges to migrate through the whole of a grain separating one region of the grain from another (Jessell, 1986; Urai, 1987). This mechanism of grain dissection could provide an alternative grain size reducing mechanism, but has not yet been observed during ice microdynamics. In this contribution, we present results using an updated numerical approach allowing for grain dissection. The approach is based on coupling the full field theory crystal visco-plasticity code (VPFFT) of Lebensohn (2001) to the multi-process modelling platform Elle (Bons et al., 2008). VPFFT predicts the mechanical fields resulting from short strain increments, dynamic recrystallisation process are implemented in Elle. The novel approach includes improvements to allow for grain dissection, which was topologically impossible during earlier simulations. The simulations are supported by microstructural observations from NEEM (North Greenland Eemian Ice Drilling) ice core. Mappings of c-axis orientations using the automatic fabric analyser and full crystallographic orientations using electron

  11. Grain Spectroscopy

    NASA Technical Reports Server (NTRS)

    Allamandola, L. J.

    1992-01-01

    Our fundamental knowledge of interstellar grain composition has grown substantially during the past two decades thanks to significant advances in two areas: astronomical infrared spectroscopy and laboratory astrophysics. The opening of the mid-infrared, the spectral range from 4000-400 cm(sup -1) (2.5-25 microns), to spectroscopic study has been critical to this progress because spectroscopy in this region reveals more about a materials molecular composition and structure than any other physical property. Infrared spectra which are diagnostic of interstellar grain composition fall into two categories: absorption spectra of the dense and diffuse interstellar media, and emission spectra from UV-Vis rich dusty regions. The former will be presented in some detail, with the latter only very briefly mentioned. This paper summarized what we have learned from these spectra and presents 'doorway' references into the literature. Detailed reviews of many aspects of interstellar dust are given.

  12. Presolar Grains

    NASA Astrophysics Data System (ADS)

    Zinner, E. K.

    2003-12-01

    Traditionally, astronomers have studied the stars by using, with rare exception, electromagnetic radiation received by telescopes on and above the Earth. Since the mid-1980s, an additional observational window has been opened in the form of microscopic presolar grains found in primitive meteorites. These grains had apparently formed in stellar outflows of late-type stars and in the ejecta of stellar explosions and had survived the formation of the solar system. They can be located in and extracted from their parent meteorites and studied in detail in the laboratory. Their stellar origin is recognized by their isotopic compositions, which are completely different from those of the solar system and, for some elements, cover extremely wide ranges, leaving little doubt that the grains are ancient stardust.By the 1950s it had been conclusively established that the elements from carbon on up are produced by nuclear reactions in stars and the classic papers by Burbidge et al. (1957) and Cameron (1957) provided a theoretical framework for stellar nucleosynthesis. According to these authors, nuclear processes produce elements with very different isotopic compositions, depending on the specific stellar source. The newly produced elements are injected into the interstellar medium (ISM) by stellar winds or as supernova (SN) ejecta, enriching the galaxy in "metals" (all elements heavier than helium) and after a long galactic history the solar system is believed to have formed from a mix of this material. In fact, the original work by Burbidge et al. and Cameron was stimulated by the observation of regularities in the abundance of the nuclides in the solar system as obtained by the study of meteorites (Suess and Urey, 1956). Although providing only a grand average of many stellar sources, the solar system abundances of the elements and isotopes ( Anders and Grevesse, 1989; Grevesse et al., 1996; see Chapter 1.03; Lodders, 2003) remained an important test for nucleosynthesis

  13. Grain Spectroscopy

    NASA Technical Reports Server (NTRS)

    Allamandola, L. J.

    1992-01-01

    Our fundamental knowledge of interstellar grain composition has grown substantially during the past two decades thanks to significant advances in two areas: astronomical infrared spectroscopy and laboratory astrophysics. The opening of the mid-infrared, the spectral range from 4000-400 cm(sup -1) (2.5-25 microns), to spectroscopic study has been critical to this progress because spectroscopy in this region reveals more about a materials molecular composition and structure than any other physical property. Infrared spectra which are diagnostic of interstellar grain composition fall into two categories: absorption spectra of the dense and diffuse interstellar media, and emission spectra from UV-Vis rich dusty regions. The former will be presented in some detail, with the latter only very briefly mentioned. This paper summarized what we have learned from these spectra and presents 'doorway' references into the literature. Detailed reviews of many aspects of interstellar dust are given.

  14. Twist-ing cell fate: mechanistic insights into the role of twist in lineage specification/differentiation and tumorigenesis.

    PubMed

    Cakouros, D; Raices, R M; Gronthos, S; Glackin, C A

    2010-08-15

    Bone marrow-derived mesenchymal stem cells (MSC), are multipotent cells that give rise to multiple lineages including osteoblasts, adipocytes, muscle, and fibroblasts. MSCs are useful for clinical applications such as cell therapy because they can be isolated from an individual and expanded for use in tissue repair, as well as other therapeutic applications, without immune rejection. However, one of the key problems in the use of MSCs for these applications is the efficiency of these cells to engraft and fully regenerate damaged tissues. Therefore, to optimize this process, a comprehensive understanding of the key regulators of MSCs self-renewal and maintenance are critical to the success of future cell therapy as well as other clinical applications. The basic helix loop helix transcription factor, Twist, plays a master regulatory role in all of these processes and, therefore, a thorough understanding of the mechanistic insights in the role of Twist in lineage specification/differentiation and tumorigenesis is vital to the success of future clinical applications for the therapeutic use of MSCs. In this article, we highlight the basic mechanisms and signaling pathways that are important to MSC fate, maintenance, and differentiation, as well as the critical role that Twist plays in these processes. In addition, we review the known literature suggesting a critical role for Twist in the generation of cancer stem cells, as this information may contribute to a broader understanding of stem cell biology and stem-cell-based therapeutics.

  15. High angle of attack control law development for a free-flight wind tunnel model using direct eigenstructure assignment

    NASA Technical Reports Server (NTRS)

    Wendel, Thomas R.; Boland, Joseph R.; Hahne, David E.

    1991-01-01

    Flight-control laws are developed for a wind-tunnel aircraft model flying at a high angle of attack by using a synthesis technique called direct eigenstructure assignment. The method employs flight guidelines and control-power constraints to develop the control laws, and gain schedules and nonlinear feedback compensation provide a framework for considering the nonlinear nature of the attack angle. Linear and nonlinear evaluations show that the control laws are effective, a conclusion that is further confirmed by a scale model used for free-flight testing.

  16. High angle of attack control law development for a free-flight wind tunnel model using direct eigenstructure assignment

    NASA Technical Reports Server (NTRS)

    Wendel, Thomas R.; Boland, Joseph R.; Hahne, David E.

    1991-01-01

    Flight-control laws are developed for a wind-tunnel aircraft model flying at a high angle of attack by using a synthesis technique called direct eigenstructure assignment. The method employs flight guidelines and control-power constraints to develop the control laws, and gain schedules and nonlinear feedback compensation provide a framework for considering the nonlinear nature of the attack angle. Linear and nonlinear evaluations show that the control laws are effective, a conclusion that is further confirmed by a scale model used for free-flight testing.

  17. Survey of needs and capabilities for wind tunnel testing of dynamic stability of aircraft at high angles of attack

    NASA Technical Reports Server (NTRS)

    Orlik-Ruckemann, K. J.

    1973-01-01

    A survey was conducted relative to future requirements for dynamic stability information for such aerospace vehicles as the space shuttle and advanced high performance military aircraft. High-angle-of-attack and high-Reynolds number conditions were emphasized. A review was made of the wind-tunnel capabilities in North America for measuring dynamic stability derivatives, revealing an almost total lack of capabilities that could satisfy these requirements. Recommendations are made regarding equipment that should be constructed to remedy this situation. A description is given of some of the more advanced existing capabilities, which can be used to at least partly satisfy immediate demands.

  18. Detection of large thermal vibration for Cu atoms in tetrahedrite by high-angle annular dark-field imaging

    NASA Astrophysics Data System (ADS)

    Prasad Mishra, Tara; Koyano, Mikio; Oshima, Yoshifumi

    2017-04-01

    Tetrahedrite (Cu12Sb4S13) is a new type of thermoelectric material with an extremely low thermal conductivity attributed to the anomalous large thermal vibration of specific Cu sites. The tetrahedrite crystal was observed from the [111] direction by high-angle annular dark-field (HAADF) imaging and the image intensity was found to be 64% lower at specific sites. This could be explained by the blurring of the intensity distribution owing to a large atomic displacement, suggesting that anomalous large thermal vibrations at specific sites in the crystal can be distinguished in HAADF images.

  19. Viscous shock-layer predictions of three-dimensional nonequilibrium flows past the space shuttle at high angle of attack

    NASA Technical Reports Server (NTRS)

    Kim, M. D.; Swaminathan, S.; Lewis, C. H.

    1983-01-01

    Computational solutions were obtained for chemically reacting flowfields over the entire windward surface of the Space Shuttle at high angle of attack. The recently developed computational method for the Space Shuttle is capable of treating three dimensional viscous nonequilibrium air flow as well as equilibrium air and perfect gas flows. A general nonorthogonal computational grid system is used to treat the nonaxisymmetric geometry. Boundary conditions take into account noncatalytic wall, equilibrium with noncatalytic wall condition are compared to the fully catalytic wall solutions, the equilibrium air solutions, the perfect gas solutions, and also the Shuttle flight heating and pressure data. The comparisons show good agreement and correlations in most cases.

  20. Improvements to tilt rotor performance through passive blade twist control

    NASA Technical Reports Server (NTRS)

    Nixon, Mark W.

    1988-01-01

    A passive blade twist control is presented in which the twist distribution of a tilt rotor blade is elastically changed as a function of rotor speed. The elastic twist deformation is used to achieve two different blade twist distributions corresponding to the two rotor speeds used on conventional tilt rotors in hover and forward flight. By changing the blade twist distribution, the aerodynamic performance can be improved in both modes of flight. The concept presented obtains a change in twist distribution with extension-twist-coupled composite blade structure. This investigation first determines the linear twists which are optimum for each flight mode. Based on the optimum linear twist distributions, three extension-twist-coupled blade designs are developed using coupled-beam and laminate analyses integrated with an optimization analysis. The designs are optimized for maximum twist deformation subject to material strength limitations. The aerodynamic performances of the final designs are determined which show that the passive blade twist control concept is viable, and can enhance conventional tilt rotor performance.

  1. Geometric somersaults of a polymer chain through cyclic twisting motions.

    PubMed

    Yanao, Tomohiro; Hino, Taiko

    2017-01-01

    This study explores the significance of geometric angle shifts, which we call geometric somersaults, arising from cyclic twisting motions of a polymer chain. A five-bead polymer chain serves as a concise and minimal model of a molecular shaft throughout this study. We first show that this polymer chain can change its orientation about its longitudinal axis largely, e.g., 120^{∘}, under conditions of zero total angular momentum by changing the two dihedral angles in a cyclic manner. This phenomenon is an example of the so-called "falling cat" phenomenon, where a falling cat undergoes a geometric somersault by changing its body shape under conditions of zero total angular momentum. We then extend the geometric somersault of the polymer chain to a noisy and viscous environment, where the polymer chain is steered by external driving forces. This extension shows that the polymer chain can achieve an orientation change keeping its total angular momentum and total external torque fluctuating around zero in a noisy and viscous environment. As an application, we argue that the geometric somersault of the polymer chain by 120^{∘} may serve as a prototypical and coarse-grained model for the rotary motion of the central shaft of ATP synthase (F_{O}F_{1}-ATPase). This geometric somersault is in clear contrast to the standard picture for the rotary motion of the central shaft as a rigid body, which generally incurs nonzero total angular momentum and nonzero total external torque. The power profile of the geometric somersault implies a preliminary mechanism for elastic power transmission. The results of this study may be of fundamental interest in twisting and rotary motions of biomolecules.

  2. Geometric somersaults of a polymer chain through cyclic twisting motions

    NASA Astrophysics Data System (ADS)

    Yanao, Tomohiro; Hino, Taiko

    2017-01-01

    This study explores the significance of geometric angle shifts, which we call geometric somersaults, arising from cyclic twisting motions of a polymer chain. A five-bead polymer chain serves as a concise and minimal model of a molecular shaft throughout this study. We first show that this polymer chain can change its orientation about its longitudinal axis largely, e.g., 120∘, under conditions of zero total angular momentum by changing the two dihedral angles in a cyclic manner. This phenomenon is an example of the so-called "falling cat" phenomenon, where a falling cat undergoes a geometric somersault by changing its body shape under conditions of zero total angular momentum. We then extend the geometric somersault of the polymer chain to a noisy and viscous environment, where the polymer chain is steered by external driving forces. This extension shows that the polymer chain can achieve an orientation change keeping its total angular momentum and total external torque fluctuating around zero in a noisy and viscous environment. As an application, we argue that the geometric somersault of the polymer chain by 120∘ may serve as a prototypical and coarse-grained model for the rotary motion of the central shaft of ATP synthase (FOF1 -ATPase). This geometric somersault is in clear contrast to the standard picture for the rotary motion of the central shaft as a rigid body, which generally incurs nonzero total angular momentum and nonzero total external torque. The power profile of the geometric somersault implies a preliminary mechanism for elastic power transmission. The results of this study may be of fundamental interest in twisting and rotary motions of biomolecules.

  3. Twisted Pair Of Insulated Wires Senses Moisture

    NASA Technical Reports Server (NTRS)

    Laue, Eric G.; Stephens, James B.

    1989-01-01

    Sensitivity of electronic moisture sensor to low levels of moisture increased by new electrode configuration. Moisture-sensing circuit described in "Low-Cost Humidity Sensor" (NPO-16544). New twisted pair of wires takes place of flat-plate capacitor in circuit. Configuration allows for thermal expansion and contraction of polymer while maintaining nearly constant area of contact between polymer and wires.

  4. The Physics of Somersaulting and Twisting.

    ERIC Educational Resources Information Center

    Frohlich, Cliff

    1980-01-01

    This is a discussion of the conservation of angular momentum of the human body engaged in somersaults and twists. The principle is also applied to a cat turning over in midair. The events occur in the absence of torques. Application of the maneuvers are suggested for astronauts. (SA)

  5. The Physics of Somersaulting and Twisting.

    ERIC Educational Resources Information Center

    Frohlich, Cliff

    1980-01-01

    This is a discussion of the conservation of angular momentum of the human body engaged in somersaults and twists. The principle is also applied to a cat turning over in midair. The events occur in the absence of torques. Application of the maneuvers are suggested for astronauts. (SA)

  6. Self-Portraits with a Twist

    ERIC Educational Resources Information Center

    DeMarco, Frederick

    2010-01-01

    This article describes an art activity on self-portraiture inspired by artist Tim Hawkinson. Hawkinson created a sculpture titled "Emoter" in which his face, moved by motors, twisted and contorted based on random signals from a TV. This art activity incorporates technology into the art room, brings the work of practicing artists alive, and is a…

  7. Twisted Ribbons: Theory, Experiment and Applications

    NASA Astrophysics Data System (ADS)

    Chopin, Julien; Davidovitch, Benjamin; Silva, Flavio A.; Toledo Filho, Romildo D.; Kudrolli, Arshad

    2014-03-01

    We investigate, experimentally and theoretically, the buckling and wrinkling instabilities of a pre-stretched ribbon upon twisting and propose strategies for the fabrication of structured yarns. Our experiment consists in a thin elastic sheet in the form of a ribbon which is initially stretched by a fixed load and then subjected to a twist by rotating the ends through a prescribed angle. We show that a wide variety of shapes and instabilities can be obtained by simply varying the applied twist and tension. The observed structures which include helicoids with and without longitudinal and transverse wrinkles, and spontaneous creases, can be organized in a phase diagram with the tension and twist angle as control parameters [J. Chopin and A. Kudrolli, PRL (2013)]. Using a far-from-threshold analysis and a slender body approximation, we provide a comprehensive understanding of the longitudinal and transverse instabilities and show that several regimes emerge depending on subtle combinations of loading and geometrical parameters. Further, we show that the wrinkling instabilities can be manipulated to fabricate structured yarns which may be used to encapsulate amorphous materials or serve as efficient reinforcements for cement-based composites. COPPETEC / CNPq - Science Without Border Program

  8. Energy Release in Driven Twisted Coronal Loops

    NASA Astrophysics Data System (ADS)

    Bareford, M. R.; Gordovskyy, M.; Browning, P. K.; Hood, A. W.

    2016-01-01

    We investigate magnetic reconnection in twisted magnetic fluxtubes, representing coronal loops. The main goal is to establish the influence of the field geometry and various thermodynamic effects on the stability of twisted fluxtubes and on the size and distribution of heated regions. In particular, we aim to investigate to what extent the earlier idealised models, based on the initially cylindrically symmetric fluxtubes, are different from more realistic models, including the large-scale curvature, atmospheric stratification, thermal conduction and other effects. In addition, we compare the roles of Ohmic heating and shock heating in energy conversion during magnetic reconnection in twisted loops. The models with straight fluxtubes show similar distribution of heated plasma during the reconnection: it initially forms a helical shape, which subsequently becomes very fragmented. The heating in these models is rather uniformly distributed along fluxtubes. At the same time, the hot plasma regions in curved loops are asymmetric and concentrated close to the loop tops. Large-scale curvature has a destabilising influence: less twist is needed for instability. Footpoint convergence normally delays the instability slightly, although in some cases, converging fluxtubes can be less stable. Finally, introducing a stratified atmosphere gives rise to decaying wave propagation, which has a destabilising effect.

  9. Generalized Weyl modules for twisted current algebras

    NASA Astrophysics Data System (ADS)

    Makedonskyi, I. A.; Feigin, E. B.

    2017-08-01

    We introduce the notion of generalized Weyl modules for twisted current algebras. We study their representation-theoretic and combinatorial properties and also their connection with nonsymmetric Macdonald polynomials. As an application, we compute the dimension of the classical Weyl modules in the remaining unknown case.

  10. Self-Portraits with a Twist

    ERIC Educational Resources Information Center

    DeMarco, Frederick

    2010-01-01

    This article describes an art activity on self-portraiture inspired by artist Tim Hawkinson. Hawkinson created a sculpture titled "Emoter" in which his face, moved by motors, twisted and contorted based on random signals from a TV. This art activity incorporates technology into the art room, brings the work of practicing artists alive, and is a…

  11. UHE neutrinos: higher twists, scales, saturation

    SciTech Connect

    Fiore, R.; Zoller, V. R.

    2011-07-15

    It is shown that in the ultra-high energy neutrino interactions the higher twist corrections brought about by the non-conservation of the top-bottom current dramatically change the longitudinal structure function, F{sub L}. To the Double Leading Log Approximation simple and numerically accurate formulas for F{sub L} and {sigma}{sup {nu}N} are derived.

  12. Evaluation of High-Angle-of-Attack Handling Qualities for the X-31A Using Standard Evaluation Maneuvers

    NASA Technical Reports Server (NTRS)

    Stoliker, Patrick C.; Bosworth, John T.

    1996-01-01

    The X-31A aircraft gross-acquisition and fine-tracking handling qualities have been evaluated using standard evaluation maneuvers developed by Wright Laboratory, Wright-Patterson Air Force Base. The emphasis of the testing is in the angle-of-attack range between 30 deg and 70 deg. Longitudinal gross-acquisition handling qualities results show borderline Level 1/Level 2 performance. Lateral gross-acquisition testing results in Level 1/Level 2 ratings below 45 deg angle of attack, degrading into Level 3 as angle of attack increases. The fine-tracking performance in both longitudinal and lateral axes also receives Level 1 ratings near 30 deg angle of attack, with the ratings tending towards Level 3 at angles of attack greater than 50 deg. These ratings do not match the expectations from the extensive close-in combat testing where the X-31A aircraft demonstrated fair to good handling qualities maneuvering for high angles of attack. This paper presents the results of the high-angle-of-attack handling qualities flight testing of the X-31A aircraft. Discussion of the preparation for the maneuvers, the pilot ratings, and selected pilot comments are included. Evaluation of the results is made in conjunction with existing Neal-Smith, bandwidth, Smith-Geddes, and military specifications.

  13. Experimental study of effects of forebody geometry on high angle of attack static and dynamic stability and control

    NASA Technical Reports Server (NTRS)

    Brandon, J. M.; Murri, D. G.; Nguyen, L. T.

    1986-01-01

    A series of low-speed wind tunnel tests on a generic airplane model with a cylindrical fuselage were made to investigate the effects of forebody shape and fitness ratio, and fuselage/wing proximity on static and dynamic lateral/directional stability. In addition, some preliminary testing to determine the effectiveness of deflectable forebody strakes for high angle of attack yaw control was conducted. During the stability investigation, 11 forebodies were tested including three different cross-sectional shapes with fineness ratios of 2, 3, and 4. In addition, the wing was tested at two longitudinal positions to provide a substantial variation in forebody/wing proximity. Conventional force tests were conducted to determine static stability characteristics, and single-degree-of-freedom free-to-roll tests were conducted to study the wing rock characteristics of the model with the various forebodies. Flow visualization data were obtained to aid in the analysis of the complex flow phenomena involved. The results show that the forebody cross-sectional shape and fineness ratio and forebody/wing proximity can strongly affect both static and dynamic (roll) stability at high angles of attack. These characteristics result from the impact of these factors on forebody vortex development, the behavior of the vortices in sideslip, and their interaction with the wing flow field. Preliminary results from the deflectable strake investigation indicated that forebody flow control using this concept can provide very large yaw control moments at stall and post-stall angles of attack.

  14. Evaluation of High-Angle-of-Attack Handling Qualities for the X-31A Using Standard Evaluation Maneuvers

    NASA Technical Reports Server (NTRS)

    Stoliker, Patrick C.; Bosworth, John T.

    1997-01-01

    The X-31A aircraft gross-acquisition and fine-tracking handling qualities have been evaluated using standard evaluation maneuvers developed by Wright Laboratory, Wright Patterson Air Force Base. The emphasis of the testing is in the angle-of-attack range between 30 deg. and 70 deg. Longitudinal gross-acquisition handling qualities results show borderline Level l/Level 2 performance. Lateral gross-acquisition testing results in Level l/Level 2 ratings below 45 deg. angle of attack, degrading into Level 3 as angle of attack increases. The fine tracking performance in both longitudinal and lateral axes also receives Level 1 ratings near 30 deg. angle of attack, with the ratings tending towards Level 3 at angles of attack greater than 50 deg. These ratings do not match the expectations from the extensive close-in combat testing where the X-31A aircraft demonstrated fair to good handling qualities maneuvering for high angles of attack. This paper presents the results of the high-angle-of-attack handling qualities flight testing of the X-31A aircraft. Discussion of the preparation for the maneuvers, the pilot ratings, and selected pilot comments are included. Evaluation of the results is made in conjunction with existing Neal Smith, bandwidth, Smith-Geddes, and military specifications.

  15. Structural Dependence of Grain Boundary Resistivity in Copper Nanowires

    SciTech Connect

    Evans III, Boyd Mccutchen; Kenik, Edward A; Kim, Tae Hwan; Kulkarni, Nagraj S; Li, An-Ping; Meyer III, Harry M; Nicholson, Don M; Radhakrishnan, Bala; Zhang, Xiaoguang

    2011-01-01

    We report the direct measurement of individual grain boundary (GB) resistances and the critical role of GB structure in the increased resistivity in copper nanowires. By measuring both intra- and inter-grain resistance with a four-probe scanning tunneling microscope, large resistance jumps are revealed owing to successive scattering across high-angle random GBs, while the resistance changes at twin and other coincidence boundaries are negligibly small. The impurity distributions in the nanowires are characterized in correlating to the microstructures. The resistance of high symmetry coincidence GBs and the impurity contributions are then calculated using a first-principle method which confirms that the coincidence GBs have orders of magnitude smaller resistance than the high-angle random GBs.

  16. New grain formation during warm deformation of ferritic stainless steel

    SciTech Connect

    Belyakov, A.; Sakai, Taku; Kaibyshev, R.

    1998-01-01

    Microstructural evolution accompanied by localization of plastic flow was studied in compression of a ferritic stainless steel with high stacking fault energy (SFE) at 873 K ({approx} 0.5 Tm). The structure evolution is characterized by the formation of dense dislocation walls at low strains and subsequently of microbands and their clusters at moderate strains, followed by the evolution of fragmented structure inside the clusters of microbands at high strains. The misorientations of the fragmented boundaries and the fraction of high-angle grain boundaries increase substantially with increasing strain. Finally, further straining leads to the formation of new fine grains with high-angle boundaries, which become more equiaxed than the previous fragmented structure. The mechanisms operating during such structure changes are discussed in detail.

  17. Interstellar grains within interstellar grains

    NASA Technical Reports Server (NTRS)

    Bernatowicz, Thomas J.; Amari, Sachiko; Zinner, Ernst K.; Lewis, Roy S.

    1991-01-01

    Five interstellar graphite spherules extracted from the Murchison carbonaceous meteorite are studied. The isotopic and elemental compositions of individual particles are investigated with the help of an ion microprobe, and this analysis is augmented with structural studies of ultrathin sections of the grain interiors by transmission electron microscopy. As a result, the following procedure for the formation of the interstellar graphite spherule bearing TiC crystals is inferred: (1) high-temperature nucleation and rapid growth of the graphitic carbon spherule in the atmosphere of a carbon-rich star, (2) nucleation and growth of TiC crystals during continued growth of the graphitic spherule and the accretion of TiC onto the spherule, (3) quenching of the graphite growth process by depletion of C or by isolation of the spherule before other grain types could condense.

  18. Interstellar grains within interstellar grains

    NASA Technical Reports Server (NTRS)

    Bernatowicz, Thomas J.; Amari, Sachiko; Zinner, Ernst K.; Lewis, Roy S.

    1991-01-01

    Five interstellar graphite spherules extracted from the Murchison carbonaceous meteorite are studied. The isotopic and elemental compositions of individual particles are investigated with the help of an ion microprobe, and this analysis is augmented with structural studies of ultrathin sections of the grain interiors by transmission electron microscopy. As a result, the following procedure for the formation of the interstellar graphite spherule bearing TiC crystals is inferred: (1) high-temperature nucleation and rapid growth of the graphitic carbon spherule in the atmosphere of a carbon-rich star, (2) nucleation and growth of TiC crystals during continued growth of the graphitic spherule and the accretion of TiC onto the spherule, (3) quenching of the graphite growth process by depletion of C or by isolation of the spherule before other grain types could condense.

  19. Grain Boundary Specific Segregation in Nanocrystalline Fe(Cr).

    PubMed

    Zhou, Xuyang; Yu, Xiao-Xiang; Kaub, Tyler; Martens, Richard L; Thompson, Gregory B

    2016-10-06

    A cross-correlative precession electron diffraction - atom probe tomography investigation of Cr segregation in a Fe(Cr) nanocrystalline alloy was undertaken. Solute segregation was found to be dependent on grain boundary type. The results of which were compared to a hybrid Molecular Dynamics and Monte Carlo simulation that predicted the segregation for special character, low angle, and high angle grain boundaries, as well as the angle of inclination of the grain boundary. It was found that the highest segregation concentration was for the high angle grain boundaries and is explained in terms of clustering driven by the onset of phase separation. For special character boundaries, the highest Gibbsain interfacial excess was predicted at the incoherent ∑3 followed by ∑9 and ∑11 boundaries with negligible segregation to the twin and ∑5 boundaries. In addition, the low angle grain boundaries predicted negligible segregation. All of these trends matched well with the experiment. This solute-boundary segregation dependency for the special character grain boundaries is explained in terms of excess volume and the energetic distribution of the solute in the boundary.

  20. Grain Boundary Specific Segregation in Nanocrystalline Fe(Cr)

    PubMed Central

    Zhou, Xuyang; Yu, Xiao-xiang; Kaub, Tyler; Martens, Richard L.; Thompson, Gregory B.

    2016-01-01

    A cross-correlative precession electron diffraction – atom probe tomography investigation of Cr segregation in a Fe(Cr) nanocrystalline alloy was undertaken. Solute segregation was found to be dependent on grain boundary type. The results of which were compared to a hybrid Molecular Dynamics and Monte Carlo simulation that predicted the segregation for special character, low angle, and high angle grain boundaries, as well as the angle of inclination of the grain boundary. It was found that the highest segregation concentration was for the high angle grain boundaries and is explained in terms of clustering driven by the onset of phase separation. For special character boundaries, the highest Gibbsain interfacial excess was predicted at the incoherent ∑3 followed by ∑9 and ∑11 boundaries with negligible segregation to the twin and ∑5 boundaries. In addition, the low angle grain boundaries predicted negligible segregation. All of these trends matched well with the experiment. This solute-boundary segregation dependency for the special character grain boundaries is explained in terms of excess volume and the energetic distribution of the solute in the boundary. PMID:27708360

  1. Grain orientations and grain boundaries in tungsten nonotendril fuzz grown under divertor-like conditions

    DOE PAGES

    Parish, Chad M.; Wang, Kun; Doerner, Russel P.; ...

    2016-09-19

    We grew nanotendril “fuzz” on tungsten via plasma exposure and performed transmission Kikuchi diffraction (tKD) in scanning electron microscopy of isolated nanotendrils. 900 °C, 1023 He/m2sec, 4 × 1026 He/m2 exposure of tungsten produced a deep and fully developed nanotendril mat. tKD of isolated nanotendrils indicated that there was no preferred crystallographic direction oriented along the long axes of the tendrils, and the grain boundary character showed slightly preferential orientations. In conclusion, tendril growth is sufficiently non-equilibrium to prevent any preference of growth direction to manifest measurably, and that new high-angle boundaries (with new grains and grain-growth axes) nucleate randomlymore » along the tendrils during growth.« less

  2. Grain orientations and grain boundaries in tungsten nonotendril fuzz grown under divertor-like conditions

    SciTech Connect

    Parish, Chad M.; Wang, Kun; Doerner, Russel P.; Baldwin, Matthew J.

    2016-09-19

    We grew nanotendril “fuzz” on tungsten via plasma exposure and performed transmission Kikuchi diffraction (tKD) in scanning electron microscopy of isolated nanotendrils. 900 °C, 1023 He/m2sec, 4 × 1026 He/m2 exposure of tungsten produced a deep and fully developed nanotendril mat. tKD of isolated nanotendrils indicated that there was no preferred crystallographic direction oriented along the long axes of the tendrils, and the grain boundary character showed slightly preferential orientations. In conclusion, tendril growth is sufficiently non-equilibrium to prevent any preference of growth direction to manifest measurably, and that new high-angle boundaries (with new grains and grain-growth axes) nucleate randomly along the tendrils during growth.

  3. Grain orientations and grain boundaries in tungsten nonotendril fuzz grown under divertor-like conditions

    SciTech Connect

    Parish, Chad M.; Wang, Kun; Doerner, Russel P.; Baldwin, Matthew J.

    2016-09-19

    We grew nanotendril “fuzz” on tungsten via plasma exposure and performed transmission Kikuchi diffraction (tKD) in scanning electron microscopy of isolated nanotendrils. 900 °C, 1023 He/m2sec, 4 × 1026 He/m2 exposure of tungsten produced a deep and fully developed nanotendril mat. tKD of isolated nanotendrils indicated that there was no preferred crystallographic direction oriented along the long axes of the tendrils, and the grain boundary character showed slightly preferential orientations. In conclusion, tendril growth is sufficiently non-equilibrium to prevent any preference of growth direction to manifest measurably, and that new high-angle boundaries (with new grains and grain-growth axes) nucleate randomly along the tendrils during growth.

  4. Operator constraints for twist-3 functions and Lorentz invariance properties of twist-3 observables

    SciTech Connect

    Kanazawa, Koichi; Pitonyak, Daniel; Koike, Yuji; Metz, Andreas; Schlegel, Marc

    2016-03-14

    We investigate the behavior under Lorentz transformations of perturbative coefficient functions in a collinear twist-3 formalism relevant for high-energy observables including transverse polarization of hadrons. We argue that those perturbative coefficient functions can, a priori, acquire quite different yet Lorentz-invariant forms in various frames. This somewhat surprising difference can be traced back to a general dependence of the perturbative coefficient functions on light cone vectors which are introduced by the twist-3 factorization formulas and which are frame-dependent. One can remove this spurious frame dependence by invoking so-called Lorentz invariance relations (LIRs) between twist-3 parton correlation functions. Some of those relations for twist-3 distribution functions were discussed in the literature before. In this paper we derive the corresponding LIRs for twist-3 fragmentation functions. We explicitly demonstrate that these LIRs remove the light cone vector dependence by considering transverse spin observables in the single-inclusive production of hadrons in lepton-nucleon collisions, ℓN→hX. Furthermore, with the LIRs in hand, we also show that twist-3 observables in general can be written solely in terms of three-parton correlation functions.

  5. Operator constraints for twist-3 functions and Lorentz invariance properties of twist-3 observables

    DOE PAGES

    Kanazawa, Koichi; Pitonyak, Daniel; Koike, Yuji; ...

    2016-03-14

    We investigate the behavior under Lorentz transformations of perturbative coefficient functions in a collinear twist-3 formalism relevant for high-energy observables including transverse polarization of hadrons. We argue that those perturbative coefficient functions can, a priori, acquire quite different yet Lorentz-invariant forms in various frames. This somewhat surprising difference can be traced back to a general dependence of the perturbative coefficient functions on light cone vectors which are introduced by the twist-3 factorization formulas and which are frame-dependent. One can remove this spurious frame dependence by invoking so-called Lorentz invariance relations (LIRs) between twist-3 parton correlation functions. Some of those relationsmore » for twist-3 distribution functions were discussed in the literature before. In this paper we derive the corresponding LIRs for twist-3 fragmentation functions. We explicitly demonstrate that these LIRs remove the light cone vector dependence by considering transverse spin observables in the single-inclusive production of hadrons in lepton-nucleon collisions, ℓN→hX. Furthermore, with the LIRs in hand, we also show that twist-3 observables in general can be written solely in terms of three-parton correlation functions.« less

  6. Operator constraints for twist-3 functions and Lorentz invariance properties of twist-3 observables

    NASA Astrophysics Data System (ADS)

    Kanazawa, Koichi; Koike, Yuji; Metz, Andreas; Pitonyak, Daniel; Schlegel, Marc

    2016-03-01

    We investigate the behavior under Lorentz transformations of perturbative coefficient functions in a collinear twist-3 formalism relevant for high-energy observables including transverse polarization of hadrons. We argue that those perturbative coefficient functions can, a priori, acquire quite different yet Lorentz-invariant forms in various frames. This somewhat surprising difference can be traced back to a general dependence of the perturbative coefficient functions on light cone vectors which are introduced by the twist-3 factorization formulas and which are frame-dependent. One can remove this spurious frame dependence by invoking so-called Lorentz invariance relations (LIRs) between twist-3 parton correlation functions. Some of those relations for twist-3 distribution functions were discussed in the literature before. In this paper we derive the corresponding LIRs for twist-3 fragmentation functions. We explicitly demonstrate that these LIRs remove the light cone vector dependence by considering transverse spin observables in the single-inclusive production of hadrons in lepton-nucleon collisions, ℓN →h X . With the LIRs in hand, we also show that twist-3 observables in general can be written solely in terms of three-parton correlation functions.

  7. The Strength-Grain Size Relationship in Ultrafine-Grained Metals

    NASA Astrophysics Data System (ADS)

    Balasubramanian, N.; Langdon, Terence G.

    2016-12-01

    Metals processed by severe plastic deformation (SPD) techniques, such as equal-channel angular pressing (ECAP) and high-pressure torsion (HPT), generally have submicrometer grain sizes. Consequently, they exhibit high strength as expected on the basis of the Hall-Petch (H-P) relationship. Examples of this behavior are discussed using experimental data for Ti, Al, and Ni. These materials typically have grain sizes greater than 50 nm where softening is not expected. An increase in strength is usually accompanied by a decrease in ductility. However, both high strength and high ductility may be achieved simultaneously by imposing high strain to obtain ultrafine-grain sizes and high fractions of high-angle grain boundaries. This facilitates grain boundary sliding, and an example is presented for a cast Al-7 pct Si alloy processed by HPT. In some materials, SPD may result in a weakening even with a very fine grain size, and this is due to microstructural changes during processing. Examples are presented for an Al-7034 alloy processed by ECAP and a Zn-22 pct Al alloy processed by HPT. In some SPD-processed materials, it is possible that grain boundary segregation and other features are present leading to higher strengths than predicted by the H-P relationship.

  8. Torque correlation length and stochastic twist dynamics of DNA.

    PubMed

    Banigan, Edward J; Marko, John F

    2014-06-01

    We introduce a short correlation length for torque in twisting-stiff biomolecules, which is necessary for the physical property that torque fluctuations be finite in amplitude. We develop a nonequilibrium theory of dynamics of DNA twisting which predicts two crossover time scales for temporal torque correlations in single-molecule experiments. Bending fluctuations can be included, and at linear order we find that they do not affect the twist dynamics. However, twist fluctuations affect bending, and we predict the spatial inhomogeneity of twist, torque, and buckling arising in nonequilibrium "rotor-bead" experiments.

  9. The torque correlation length and stochastic twist dynamics of DNA

    PubMed Central

    Banigan, Edward J.; Marko, John F.

    2014-01-01

    We introduce a short correlation length for torque in twisting-stiff biomolecules, which is necessary for the physical property that torque fluctuations be finite in amplitude. We develop a nonequilibrium theory of dynamics of DNA twisting which predicts two crossover time scales for temporal torque correlations in single-molecule experiments. Bending fluctuations can be included, and at linear order we find that they do not affect the twist dynamics. However, twist fluctuations affect bending, and we predict the spatial inhomogeneity of twist, torque, and buckling arising in nonequilibrium “rotor-bead” experiments. PMID:25019813

  10. Mechanical properties and failure behavior of phosphorene with grain boundaries

    NASA Astrophysics Data System (ADS)

    Sorkin, V.; Zhang, Y. W.

    2017-02-01

    Using the density-functional tight-binding method, we studied the effect of grain boundaries on the mechanical properties and failure behavior of phosphorene. We found that the high-angle tilt boundaries with a higher density of (5∣7) defect pairs (oriented along the armchair direction) are stronger than the low-angle tilt boundaries with a lower defect density, and similarly the high-angle boundaries with a higher density of (4∣8) defect pairs (oriented along the zigzag direction) are stronger than the low-angle boundaries with a lower defect density. The failure is due to the rupture of the most pre-strained bonds in the heptagons of the (5∣7) defect pair or octagons of the (4∣8) pairs. The high-angle grain boundaries are better at accommodating the pre-strained bonds in heptagon and octagon defects, leading to a higher failure stress and strain. The results cannot be described by a Griffith-type fracture mechanics criterion, since this does not take into account the bond pre-stretching. Interestingly, these anomalous mechanical and failure characteristics of tilt grain boundaries in phosphorene are also shared by graphene and hexagonal boron nitride, signifying that they may be universal for 2D materials. The findings revealed here may be useful in tuning the mechanical properties of phosphorene via defect engineering for specific applications.

  11. Multiply-Twisted Helices of Various Inter-Round Couplings

    NASA Astrophysics Data System (ADS)

    Ugajin, R.; Watanabe, Y.; Mori, Y.

    Multiply-twisted helices in which a helical chain of components, i.e. atoms or nanoclusters, is twisted, producing a doubly-twisted helix, which if itself is twisted produces a triply-twisted helix, and so on, are characterized by inter-round couplings, through which electrons in the structure transit between adjacent rounds. The multiply-twisted helix of inter-round couplings via a chain of sites and that of inter-round couplings through a single site are compared with that of the direct inter-round couplings previously reported by R. Ugajin [J. Nanosci. Nanotechnol. 1, 227 (2001)]. Monte Carlo simulations of classical spins suggest that the multiply-twisted helix of inter-round couplings through a single site, in which the Curie temperature of ferromagnetic transition is robust against the change of a basal helix, might be critical among these three types.

  12. The prediction of pressure distributions on an arrow-wing configuration including the effect of camber, twist, and a wing fin

    NASA Technical Reports Server (NTRS)

    Bobbitt, P. J.; Manro, M. E.; Kulfan, R. M.

    1980-01-01

    Wind tunnel tests of an arrow wing body configuration consisting of flat, twisted, and cambered twisted wings were conducted at Mach numbers from 0.40 to 2.50 to provide an experimental data base for comparison with theoretical methods. A variety of leading and trailing edge control surface deflections were included in these tests, and in addition, the cambered twisted wing was tested with an outboard vertical fin to determine its effect on wing and control surface loads. Theory experiment comparisons show that current state of the art linear and nonlinear attached flow methods were adequate at small angles of attack typical of cruise conditions. The incremental effects of outboard fin, wing twist, and wing camber are most accurately predicted by the advanced panel method PANAIR. Results of the advanced panel separated flow method, obtained with an early version of the program, show promise that accurate detailed pressure predictions may soon be possible for an aeroelasticity deformed wing at high angles of attack.

  13. Development of microprocessor-based laser velocimeter and its application to measurement of jet exhausts and flows over missiles at high angles of attack

    NASA Astrophysics Data System (ADS)

    Harwell, K. E.; Farmer, W. M.; Hornkohl, J. O.; Stallings, E.

    1981-03-01

    During the past three years, personnel have developed a unique three-component laser velocimeter for the in situ measurement of particle and/or gas velocities in flow fields produced behind bodies at high angles of attack and in jet exhaust plumes. This report describes the development of the laser velocimeter and its subsequent application of the measurement of the velocity distribution and vortex structure in free jets and in flows over missiles at high angles of attack.

  14. High-angle annular dark field scanning transmission electron microscopy on carbon-based functional polymer systems.

    PubMed

    Sourty, Erwan; van Bavel, Svetlana; Lu, Kangbo; Guerra, Ralph; Bar, Georg; Loos, Joachim

    2009-06-01

    Two purely carbon-based functional polymer systems were investigated by bright-field conventional transmission electron microscopy (CTEM) and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). For a carbon black (CB) filled polymer system, HAADF-STEM provides high contrast between the CB agglomerates and the polymer matrix so that details of the interface organization easily can be revealed and assignment of the CB phase is straightforward. For a second system, the functional polymer blend representing the photoactive layer of a polymer solar cell, details of its nanoscale organization could be observed that were not accessible with CTEM. By varying the camera length in HAADF-STEM imaging, the contrast can be enhanced between crystalline and amorphous compounds due to diffraction contrast so that nanoscale interconnections between domains are identified. In general, due to its incoherent imaging characteristics HAADF-STEM allows for reliable interpretation of the data obtained.

  15. Experimental investigations on airfoils with different geometries in the domain of high angles of attack-flow separation

    NASA Technical Reports Server (NTRS)

    Keil, J.

    1985-01-01

    Wind tunnel tests were conducted on airfoil models in order to study the flow separation phenomena occurring for high angles of attack. Pressure distribution on wings of different geometries were measured. Results show that for three-dimensional airfoils layout and span lift play a role. Separation effects on airfoils with moderate extension are three-dimensional. The flow domains separated from the air foil must be treated three-dimensionally. The rolling-up of separated vortex layers increases with angle in intensity and induction effect and shows strong nonlinearities. Boundary layer material moves perpendicularly to the flow direction due to the pressure gradients at the airfoil; this has a stabilizing effect. The separation starts earlier with increasing pointed profiles.

  16. In-flight flow visualization characteristics of the NASA F-18 high alpha research vehicle at high angles of attack

    NASA Technical Reports Server (NTRS)

    Fisher, David F.; Delfrate, John H.; Richwine, David M.

    1991-01-01

    Surface and off-surface flow visualization techniques were used to visualize the 3-D separated flows on the NASA F-18 high alpha research vehicle at high angles of attack. Results near the alpha = 25 to 26 deg and alpha = 45 to 49 deg are presented. Both the forebody and leading edge extension (LEX) vortex cores and breakdown locations were visualized using smoke. Forebody and LEX vortex separation lines on the surface were defined using an emitted fluid technique. A laminar separation bubble was also detected on the nose cone using the emitted fluid technique and was similar to that observed in the wind tunnel test, but not as extensive. Regions of attached, separated, and vortical flow were noted on the wing and the leading edge flap using tufts and flow cones, and compared well with limited wind tunnel results.

  17. Estimation of parameters involved in high angle-of-attack aerodynamic theory using spin flight test data

    NASA Technical Reports Server (NTRS)

    Taylor, L. W., Jr.; Pamadi, B. N.

    1983-01-01

    The difficulty in applying parameter estimation techniques to spinning airplanes is due in part to the unwieldy number of possible combinations of terms in the equations of motion, when the model structure is unknown. The combination of high angle of attack and high rotation rate results in aerodynamic functions which are quite complex. For wing dominated configurations it is advantageous to use aerodynamic theory to generate the model structure. In this way, the number of unknown parameters is reduced and the model accuracy may be increased. Under conditions for which the theory is inadequate, however, model accuracy may be reduced. Strip theory, for example, is incapable of predicting autorotative rolling moments indicated by wind tunnel tests at angles of attack exceeding 40 degrees. An improved aerodynamic theory would be necessary to successfully apply the technique advanced for such regions.

  18. Quantitative Chemical Mapping of InGaN Quantum Wells from Calibrated High-Angle Annular Dark Field Micrographs.

    PubMed

    Carvalho, Daniel; Morales, Francisco M; Ben, Teresa; García, Rafael; Redondo-Cubero, Andrés; Alves, Eduardo; Lorenz, Katharina; Edwards, Paul R; O'Donnell, Kevin P; Wetzel, Christian

    2015-08-01

    We present a simple and robust method to acquire quantitative maps of compositional fluctuations in nanostructures from low magnification high-angle annular dark field (HAADF) micrographs calibrated by energy-dispersive X-ray (EDX) spectroscopy in scanning transmission electron microscopy (STEM) mode. We show that a nonuniform background in HAADF-STEM micrographs can be eliminated, to a first approximation, by use of a suitable analytic function. The uncertainty in probe position when collecting an EDX spectrum renders the calibration of HAADF-STEM micrographs indirect, and a statistical approach has been developed to determine the position with confidence. Our analysis procedure, presented in a flowchart to facilitate the successful implementation of the method by users, was applied to discontinuous InGaN/GaN quantum wells in order to obtain quantitative determinations of compositional fluctuations on the nanoscale.

  19. Experimental study of the effects of Reynolds number on high angle of attack aerodynamic characteristics of forebodies during rotary motion

    NASA Technical Reports Server (NTRS)

    Pauley, H.; Ralston, J.; Dickes, E.

    1995-01-01

    The National Aeronautics and Space Administration and the Defense Research Agency (United Kingdom) have ongoing experimental research programs in rotary-flow aerodynamics. A cooperative effort between the two agencies is currently underway to collect an extensive database for the development of high angle of attack computational methods to predict the effects of Reynolds number on the forebody flowfield at dynamic conditions, as well as to study the use of low Reynolds number data for the evaluation of high Reynolds number characteristics. Rotary balance experiments, including force and moment and surface pressure measurements, were conducted on circular and rectangular aftbodies with hemispherical and ogive noses at the Bedford and Farnborough wind tunnel facilities in the United Kingdom. The bodies were tested at 60 and 90 deg angle of attack for a wide range of Reynolds numbers in order to observe the effects of laminar, transitional, and turbulent flow separation on the forebody characteristics when rolling about the velocity vector.

  20. A study of prediction methods for the high angle-of-attack aerodynamics of straight wings and fighter aircraft

    NASA Technical Reports Server (NTRS)

    Mcmillan, O. J.; Mendenhall, M. R.; Perkins, S. C., Jr.

    1984-01-01

    Work is described dealing with two areas which are dominated by the nonlinear effects of vortex flows. The first area concerns the stall/spin characteristics of a general aviation wing with a modified leading edge. The second area concerns the high-angle-of-attack characteristics of high performance military aircraft. For each area, the governing phenomena are described as identified with the aid of existing experimental data. Existing analytical methods are reviewed, and the most promising method for each area used to perform some preliminary calculations. Based on these results, the strengths and weaknesses of the methods are defined, and research programs recommended to improve the methods as a result of better understanding of the flow mechanisms involved.

  1. Operating characteristics of an inlet model tested with a 0.5m powered fan at high angles of attack

    NASA Technical Reports Server (NTRS)

    Koncsek, J. L.; Shaw, R. J.

    1977-01-01

    An inlet model designed for high angle of attack capability, coupled to a .508 m tip diameter turbofan simulator, was tested in the NASA-Lewis Research Center's 9-by 15-ft low speed wind tunnel. The test variables were: tunnel velocity, 0 to 75 m/s; inlet angle of attack, 0 to 120 deg; and fan face corrected airflow per unit area, 75 to 200 kg/s sqm. The inlet flow separation boundaries, the fan face total pressure recovery and distortion characteristics, and the fan blade vibratory stresses were determined. The recovery, distortion, and stress levels showed no abrupt changes at the onset of separation, but became gradually more unfavorable as the size and intensity of the separation increased as induced by increasingly severe operating conditions. Performance characteristics for a large scale model of the inlet were estimated from these test results.

  2. Twisted, multifilament Nb3Sn superconductive ribbon

    NASA Technical Reports Server (NTRS)

    Coles, W. D.

    1972-01-01

    An experimental study of superconductor stabilization has resulted in the successful application of the concepts of filamentary structure and conductor twist to Nb3Sn ribbon. The Nb3Sn is formed in parallel, helical paths, which are continuous around the ribbon. Short lengths (12-18cm) of 1.27 cm wide superconductive ribbon were produced. The filamentary and twist characteristics are incorporated in the ribbon by means of an inert mask formed on the ribbon surface early in the fabrication process. Diffusion reaction of the niobium and tin is prevented at the filament boundaries. Described are the conductor methods of fabrication, and test results obtained. The technology required to adapt the processes for the production of long lengths of ribbon is available.

  3. A New Twisting Somersault: 513XD

    NASA Astrophysics Data System (ADS)

    Tong, William; Dullin, Holger R.

    2017-07-01

    We present the mathematical framework of an athlete modelled as a system of coupled rigid bodies to simulate platform and springboard diving. Euler's equations of motion are generalised to non-rigid bodies and are then used to innovate a new dive sequence that in principle can be performed by real-world athletes. We begin by assuming that shape changes are instantaneous so that the equations of motion simplify enough to be solved analytically, and then use this insight to present a new dive (513XD) consisting of 1.5 somersaults and five twists using realistic shape changes. Finally, we demonstrate the phenomenon of converting pure somersaulting motion into pure twisting motion by using a sequence of impulsive shape changes, which may have applications in other fields such as space aeronautics.

  4. Magnetic Field Twisting by Intergranular Downdrafts

    NASA Astrophysics Data System (ADS)

    Taroyan, Youra; Williams, Thomas

    2016-10-01

    The interaction of an intergranular downdraft with an embedded vertical magnetic field is examined. It is demonstrated that the downdraft may couple to small magnetic twists leading to an instability. The descending plasma exponentially amplifies the magnetic twists when it decelerates with depth due to increasing density. Most efficient amplification is found in the vicinity of the level, where the kinetic energy density of the downdraft reaches equipartition with the magnetic energy density. Continual extraction of energy from the decelerating plasma and growth in the total azimuthal energy occurs as a consequence of the wave-flow coupling along the downdraft. The presented mechanism may drive vortices and torsional motions that have been detected between granules and in simulations of magnetoconvection.

  5. Twisted black hole is Taub-NUT

    NASA Astrophysics Data System (ADS)

    Ong, Yen Chin

    2017-01-01

    Recently a purportedly novel solution of the vacuum Einstein field equations was discovered: it supposedly describes an asymptotically flat twisted black hole in 4-dimensions whose exterior spacetime rotates in a peculiar manner—the frame dragging in the northern hemisphere is opposite from that of the southern hemisphere, which results in a globally vanishing angular momentum. Furthermore it was shown that the spacetime has no curvature singularity. We show that the geometry of this black hole spacetime is nevertheless not free of pathological features. In particular, it harbors a rather drastic conical singularity along the axis of rotation. In addition, there exist closed timelike curves due to the fact that the constant r and constant t surfaces are not globally Riemannian. In fact, none of these are that surprising since the solution is just the Taub-NUT geometry. As such, despite the original claim that the twisted black hole might have observational consequences, it cannot be.

  6. Ferromagnetic nanoparticles suspensions in twisted nematic

    NASA Astrophysics Data System (ADS)

    Cîrtoaje, Cristina; Petrescu, Emil; Stan, Cristina; Creangă, Dorina

    2016-05-01

    Ferromagnetic nanoparticles insertions in nematic liquid crystals (NLC) in twisted configuration are studied and a theoretical model is proposed to explain the results. Experimental observation revealed that nanoparticles tend to overcrowd in long strings parallel to the rubbing direction of the alignment substrate of the LC cell. Their behavior under external field was studied and their interaction with their nematic host is described using elastic continuum theory.

  7. On rectangular HOMFLY for twist knots

    NASA Astrophysics Data System (ADS)

    Kononov, Ya.; Morozov, A.

    2016-11-01

    As a new step in the study of rectangularly-colored knot polynomials, we reformulate the prescription [A. Morozov, arXiv:1606.06015v8] for twist knots in the double-column representations R = [rr] in terms of skew Schur polynomials. These, however, are mysteriously shifted from the standard topological locus, which makes further generalization to arbitrary R = [rs] not quite straightforward.

  8. Twist-boat conformation in graphene oxides.

    PubMed

    Samarakoon, Duminda K; Wang, Xiao-Qian

    2011-01-01

    We have investigated the structural, electronic, and vibrational properties of graphene oxide based on first-principles density-functional calculations. A twist-boat conformation is identified as the energetically most favorable nonmetallic configuration for fully oxidized graphene. The calculated Raman G-band blue shift is in very good agreement with experimental observations. Our results provide important insight into structural and electronic characteristics that are useful for further development of graphene-based nanodevices.

  9. Overlap fermions on a twisted mass sea

    NASA Astrophysics Data System (ADS)

    Schaefer, Stefan

    2006-12-01

    We present first results of a mixed action project. We analyze gauge configurations generated with two flavors of dynamical twisted mass fermions. Neuberger's overlap Dirac operator is used for the valence sector. The various choices in the setup of the simulation are discussed. We employ chiral perturbation theory to describe the effects of using different actions in the sea and valence sector at non-zero lattice spacing.

  10. Control load envelope shaping by live twist

    NASA Technical Reports Server (NTRS)

    Tarzanin, F. J., Jr.; Mirick, P. H.

    1974-01-01

    Rotor control systems experience a rapid load growth resulting from retreating blade stall during flight conditions of high blade loading or airspeeds. An investigation was undertaken to determine the effect of changing blade torsional properties over the rotor flight envelope. The results of this study show that reducing the blade stiffness to introduce more blade live twist significantly reduces the large retreating blade control loads, while expanding the flight envelope and reducing retreating blade stall loads.

  11. Vacuum expectation value of twist fields

    NASA Astrophysics Data System (ADS)

    Belitsky, A. V.

    2017-09-01

    Twist fields emerge in a number of physical applications ranging from entanglement entropy to scattering amplitudes in four-dimensional gauge theories. In this work, their vacuum expectation values are studied in the path integral framework. By performing a gauge transformation, their correlation functions are reduced to field theory of matter fields in external Aharonov-Bohm vortices. The resulting functional determinants are then analyzed within the zeta-function regularization for the spectrum of Bessel zeros, and concise formulas are derived.

  12. Twist transition of nematic hyperbolic hedgehogs

    NASA Astrophysics Data System (ADS)

    James, Richard; Fukuda, Jun-ichi

    2014-04-01

    Stability of an idealized hyperbolic hedgehog in a nematic liquid crystal against a twist transition is investigated by extending the methodology of Rüdinger and Stark [Liq. Cryst. 26, 753 (1999), 10.1080/026782999204840], where the hedgehog is confined between two concentric spheres. In the ideal hyperbolic-hedgehog the molecular orientation is assumed to rotate proportionally with respect to the inclination angle, θ (and in the opposite sense). However, when splay, k11, and bend, k33, moduli differ this proportionality is lost and the liquid crystal deforms relative to the ideal with bend and splay. Although slight, these deformations are shown to significantly shift the transition if k11/k33 is small. By increasing the degree of confinement the twist transition can be inhibited, a characteristic both hyperbolic and radial hedgehogs have in common. The twist transition of a hyperbolic defect that accompanies a particle is found to be well predicted by the earlier stability analysis of a thick shell.

  13. TWISTED MAGNETIC FLUX TUBES IN THE SOLAR WIND

    SciTech Connect

    Zaqarashvili, Teimuraz V.; Vörös, Zoltán; Narita, Yasuhito; Bruno, Roberto

    2014-03-01

    Magnetic flux tubes in the solar wind can be twisted as they are transported from the solar surface, where the tubes are twisted due to photospheric motions. It is suggested that the twisted magnetic tubes can be detected as the variation of total (thermal+magnetic) pressure during their passage through the observing satellite. We show that the total pressure of several observed twisted tubes resembles the theoretically expected profile. The twist of the isolated magnetic tube may explain the observed abrupt changes of magnetic field direction at tube walls. We have also found some evidence that the flux tube walls can be associated with local heating of the plasma and elevated proton and electron temperatures. For the tubes aligned with the Parker spiral, the twist angle can be estimated from the change of magnetic field direction. Stability analysis of twisted tubes shows that the critical twist angle of the tube with a homogeneous twist is 70°, but the angle can further decrease due to the motion of the tube with respect to the solar wind stream. The tubes with a stronger twist are unstable to the kink instability, therefore they probably cannot reach 1 AU.

  14. Thermal resistance of twist boundaries in silicon nanowires by nonequilibrium molecular dynamics

    NASA Astrophysics Data System (ADS)

    Bohrer, Jan K.; Schröer, Kevin; Brendel, Lothar; Wolf, Dietrich E.

    2017-04-01

    The thermal boundary resistance (Kapitza resistance) of (001) twist boundaries in silicon is investigated by nonequilibrium molecular dynamics simulations. In order to enable continuous adjustment of the mismatch angle, a cylindrical geometry with fixed atomic positions at the boundaries is devised. The influence of the boundary conditions on the Kapitza resistance is removed by means of a finite size analysis. Due to the diamond structure of silicon, twist boundaries with mismatch angles ϕ and 90 ° - ϕ are not equivalent, whereas those with ± ϕ or with 90 ° ± ϕ are. The Kapitza resistance increases with mismatch angle up to 45 ° , where it reaches a plateau around 1.56 ± 0.05 K m 2 / GW . Between 80 ° and the 90 ° Σ 1 grain boundary it drops by about 30%. Surprisingly, lattice coincidence at other angles ( Σ 5 , Σ 13 , Σ 27 , Σ 25 ) has no noticable effect on the Kapitza resistance. However, there is a clear correlation between the Kapitza resistance and the width of a non-crystalline layer at the twist boundaries.

  15. Design optimization for active twist rotor blades

    NASA Astrophysics Data System (ADS)

    Mok, Ji Won

    This dissertation introduces the process of optimizing active twist rotor blades in the presence of embedded anisotropic piezo-composite actuators. Optimum design of active twist blades is a complex task, since it involves a rich design space with tightly coupled design variables. The study presents the development of an optimization framework for active helicopter rotor blade cross-sectional design. This optimization framework allows for exploring a rich and highly nonlinear design space in order to optimize the active twist rotor blades. Different analytical components are combined in the framework: cross-sectional analysis (UM/VABS), an automated mesh generator, a beam solver (DYMORE), a three-dimensional local strain recovery module, and a gradient based optimizer within MATLAB. Through the mathematical optimization problem, the static twist actuation performance of a blade is maximized while satisfying a series of blade constraints. These constraints are associated with locations of the center of gravity and elastic axis, blade mass per unit span, fundamental rotating blade frequencies, and the blade strength based on local three-dimensional strain fields under worst loading conditions. Through pre-processing, limitations of the proposed process have been studied. When limitations were detected, resolution strategies were proposed. These include mesh overlapping, element distortion, trailing edge tab modeling, electrode modeling and foam implementation of the mesh generator, and the initial point sensibility of the current optimization scheme. Examples demonstrate the effectiveness of this process. Optimization studies were performed on the NASA/Army/MIT ATR blade case. Even though that design was built and shown significant impact in vibration reduction, the proposed optimization process showed that the design could be improved significantly. The second example, based on a model scale of the AH-64D Apache blade, emphasized the capability of this framework to

  16. Modeling and Characterization of Texture Evolution in Twist Extrusion

    NASA Astrophysics Data System (ADS)

    Latypov, Marat I.; Lee, Myoung-Gyu; Beygelzimer, Yan; Prilepo, Denis; Gusar, Yuri; Kim, Hyoung Seop

    2016-03-01

    Twist extrusion (TE) is a severe plastic deformation method with a potential for commercialization. Deformation during the TE process is non-uniform and non-monotonic, which is expected to result in significant and non-trivial microstructural changes in metallic materials. In this study, texture evolution during TE of pre-textured copper was investigated. Experimental characterization of textures after various numbers of passes demonstrated that TE can be used for producing uniformly weak textures in pre-textured copper. Crystal plasticity simulations were found to run into the problem known as strain reversal texture. In particular, crystal plasticity simulations predicted the return of initial texture upon strain reversal in the first pass of TE, whereas the experimental texture was not reversed and had components related to simple shear. Grain refinement, imperfect strain reversal, and material asymmetry are proposed to be responsible for the occurrence of strain reversal texture in TE. Effects of the non-random initial texture on the microstructure and texture evolution are also discussed.

  17. Thermally induced twist in graphite-epoxy tubes

    NASA Technical Reports Server (NTRS)

    Hyer, M. W.; Rousseau, C. Q.; Tompkins, S. S.

    1988-01-01

    This paper discusses an analytical and experimental study to investigate the thermally induced twist in laminated angle-ply graphite-epoxy tubes. Attention is focused on balanced laminates which, contrary to intuition, exhibit twist when the temperature is changed. The twisting is due to the fact that a lamina with ( a + phi) orientation and a lamina with (a - phi) orientation must be at slightly different radial positions in the twist. The lamina with the greater radial position determines the sense of the twist. Classical lamination theory does not predict this phenomenon, and so as more sophisticated theory must be employed. This paper outlines such as theory, which is based on an generalized plane-deformation elasticity analysis, and presents experimental data to confirm the predictions of the theory. A brief description of the experimental apparatus and procedure used to measure twist is presented.

  18. Thermally induced twist in graphite-epoxy tubes

    NASA Technical Reports Server (NTRS)

    Hyer, M. W.; Rousseau, C. Q.; Tompkins, S. S.

    1988-01-01

    This paper discusses an analytical and experimental study to investigate the thermally induced twist in laminated angle-ply graphite-epoxy tubes. Attention is focused on balanced laminates which, contrary to intuition, exhibit twist when the temperature is changed. The twisting is due to the fact that a lamina with ( a + phi) orientation and a lamina with (a - phi) orientation must be at slightly different radial positions in the twist. The lamina with the greater radial position determines the sense of the twist. Classical lamination theory does not predict this phenomenon, and so as more sophisticated theory must be employed. This paper outlines such as theory, which is based on an generalized plane-deformation elasticity analysis, and presents experimental data to confirm the predictions of the theory. A brief description of the experimental apparatus and procedure used to measure twist is presented.

  19. Measuring mechanical strain and twist using helical photonic crystal fiber.

    PubMed

    Xi, Xiaoming; Wong, Gordon K L; Weiss, Thomas; Russell, Philip St J

    2013-12-15

    Solid-core photonic crystal fiber (PCF) with a permanent helical twist exhibits dips in its transmission spectrum at certain wavelengths. These are associated with the formation of orbital angular momentum states in the cladding. Here we investigate the tuning of these states with mechanical torque and axial tension. The dip wavelengths are found to scale linearly with both axial strain and mechanical twist rate. Analysis shows that the tension-induced shift in resonance wavelength is determined both by the photoelastic effect and by the change in twist rate, while the torsion-induced wavelength shift depends only on the change in twist rate. Twisted PCF can act as an effective optically monitored torque-tension transducer, twist sensor, or strain gauge.

  20. Twisted Vanes Would Enhance Fuel/Air Mixing In Turbines

    NASA Technical Reports Server (NTRS)

    Nguyen, H. Lee; Micklow, Gerald J.; Dogra, Anju S.

    1994-01-01

    Computations of flow show performance of high-shear airblast fuel injector in gas-turbine engine enhanced by use of appropriately proportioned twisted (instead of flat) dome swirl vanes. Resultant more nearly uniform fuel/air mixture burns more efficiently, emitting smaller amounts of nitrogen oxides. Twisted-vane high-shear airblast injectors also incorporated into paint sprayers, providing advantages of low pressure drop characteristic of airblast injectors in general and finer atomization of advanced twisted-blade design.

  1. Twisted polymeric microfiber formed by structured light illumination

    NASA Astrophysics Data System (ADS)

    Lee, Junhyung; Toyoshima, Shunsuke; Miyamoto, Katsuhiko; Arita, Yoshihiko; Dholakia, Kishan; Omatsu, Takashige

    2017-04-01

    We presented the irradiation of optical vortex to ultraviolet (UV) curing resin structures a twisted polymer fiber. A continuous-wave ultraviolet optical vortex, focused at a glass cell containing the cure resin, allowed us to shape a twisted polymeric fiber with a diameter of a few micrometer and a length of 160 μm with an exposure time of < 1 second. Twisted direction of the fiber was also controlled by inverting the handedness of the optical vortex.

  2. Mechanical properties and radiation tolerance of ultrafine grained and nanocrystalline metals

    NASA Astrophysics Data System (ADS)

    Sun, Cheng

    Austenitic stainless steels are commonly used in nuclear reactors and have been considered as potential structural materials in fusion reactors due to their excellent corrosion resistance, good creep and fatigue resistance at elevated temperatures, but their relatively low yield strength and poor radiation tolerance hinder their applications in high dose radiation environments. High angle grain boundaries have long been postulated as sinks for radiation-induced defects, such as bubbles, voids, and dislocation loops. Here we provide experimental evidence that high angle grain boundaries can effectively remove radiation-induced defects. The equal channel angular pressing (ECAP) technique was used to produce ultrafine grained Fe-Cr-Ni alloy. Mechanical properties of the alloy were studied at elevated temperature by tensile tests and in situ neutron scattering measurements. Enhanced dynamic recovery process at elevated temperature due to dislocation climb lowers the strain hardening rate and ductility of ultrafine grained Fe-Cr-Ni alloy. Thermal stability of the ultrafine grained Fe-Cr-Ni alloy was examined by ex situ annealing and in situ heating within a transmission electron microscope. Abnormal grain growth at 827 K (600°C) is attributed to deformation-induced martensite, located at the triple junctions of grains. Helium ion irradiation studies on Fe-Cr-Ni alloy show that the density of He bubbles, dislocation loops, as well as irradiation hardening are reduced by grain refinement. In addition, we provide direct evidence, via in situ Kr ion irradiation within a transmission electron microscope, that high angle grain boundaries in nanocrystalline Ni can effectively absorb irradiation-induced dislocation loops and segments. The density and size of dislocation loops in irradiated nanocrystalline Ni were merely half of those in irradiated coarse grained Ni. The results imply that irradiation tolerance in bulk metals can be effectively enhanced by microstructure

  3. Nematic twist cell: Strong chirality induced at the surfaces

    NASA Astrophysics Data System (ADS)

    Lin, Tzu-Chieh; Nemitz, Ian R.; Pendery, Joel S.; Schubert, Christopher P. J.; Lemieux, Robert P.; Rosenblatt, Charles

    2013-04-01

    A nematic twist cell having a thickness gradient was filled with a mixture containing a configurationally achiral liquid crystal (LC) and chiral dopant. A chiral-based linear electrooptic effect was observed on application of an ac electric field. This "electroclinic effect" varied monotonically with d, changing sign at d =d0 where the chiral dopant exactly compensated the imposed twist. The results indicate that a significant chiral electrooptic effect always exists near the surfaces of a twist cell containing molecules that can be conformationally deracemized. Additionally, this approach can be used to measure the helical twisting power (HTP) of a chiral dopant in a liquid crystal.

  4. Transonic Navier-Stokes wing solutions using a zonal approach. Part 2: High angle-of-attack simulation

    NASA Technical Reports Server (NTRS)

    Chaderjian, Neal M.

    1986-01-01

    A computer code is under development whereby the thin-layer Reynolds-averaged Navier-Stokes equations are to be applied to realistic fighter aircraft configurations. This transonic Navier-Stokes code (TNS) utilizes a zonal approach in order to treat complex geometries and satisfy in-core computer memory constraints. The zonal approach was applied to isolated wing geometries in order to facilitate code development. The TNS finite difference algorithm, zonal methodology, and code validation with experimental data is addressed. Also addressed are some numerical issues such as code robustness, efficiency, and accuracy at high angles of attack. Special free-stream-preserving metrics proved an effective way to treat H-mesh singularities over a large range of severe flow conditions, including strong leading edge flow gradients, massive shock induced separation, and stall. Furthermore, lift and drag coefficients were computed for a wing up through CLmax. Numerical oil flow patterns and particle trajectories are presented both for subcritical and transonic flow. These flow simulations are rich with complex separated flow physics and demonstrate the efficiency and robustness of the zonal approach.

  5. High-angle wave instability and emergent shoreline shapes: 2. Wave climate analysis and comparisons to nature

    NASA Astrophysics Data System (ADS)

    Ashton, Andrew D.; Murray, A. Brad

    2006-12-01

    Recent research has revealed that the plan view evolution of a coast due to gradients in alongshore sediment transport is highly dependant upon the angles at which waves approach the shore, giving rise to an instability in shoreline shape that can generate different types of naturally occurring coastal landforms, including capes, flying spits, and alongshore sand waves. This instability merely requires that alongshore sediment flux is maximized for a given deepwater wave angle, a maximum that occurs between 35° and 50° for several common alongshore sediment transport formulae. Here we introduce metrics that sum over records of wave data to quantify the long-term stability of wave climates and to investigate how wave climates change along a coast. For Long Point, a flying spit on the north shore of Lake Erie, Canada, wave climate metrics suggest that unstable waves have shaped the spit and, furthermore, that smaller-scale alongshore sand waves occur along the spit at the same locations where the wave climate becomes unstable. A shoreline aligned along the trend of the Carolina Capes, United States, would be dominated by high-angle waves; numerical simulations driven by a comparable wave climate develop a similarly shaped cuspate coast. Local wave climates along these simulated capes and the Carolina Capes show similar trends: Shoreline reorientation and shadowing from neighboring capes causes most of the coast to experience locally stable wave climates despite regional instability.

  6. Transonic Navier-Stokes wing solutions using a zonal approach. Part 2: High angle-of-attack simulation

    NASA Technical Reports Server (NTRS)

    Chaderjian, N. M.

    1986-01-01

    A computer code is under development whereby the thin-layer Reynolds-averaged Navier-Stokes equations are to be applied to realistic fighter-aircraft configurations. This transonic Navier-Stokes code (TNS) utilizes a zonal approach in order to treat complex geometries and satisfy in-core computer memory constraints. The zonal approach has been applied to isolated wing geometries in order to facilitate code development. Part 1 of this paper addresses the TNS finite-difference algorithm, zonal methodology, and code validation with experimental data. Part 2 of this paper addresses some numerical issues such as code robustness, efficiency, and accuracy at high angles of attack. Special free-stream-preserving metrics proved an effective way to treat H-mesh singularities over a large range of severe flow conditions, including strong leading-edge flow gradients, massive shock-induced separation, and stall. Furthermore, lift and drag coefficients have been computed for a wing up through CLmax. Numerical oil flow patterns and particle trajectories are presented both for subcritical and transonic flow. These flow simulations are rich with complex separated flow physics and demonstrate the efficiency and robustness of the zonal approach.

  7. Modelling of AlAs/GaAs interfacial structures using high-angle annular dark field (HAADF) image simulations.

    PubMed

    Robb, Paul D; Finnie, Michael; Craven, Alan J

    2012-07-01

    High angle annular dark field (HAADF) image simulations were performed on a series of AlAs/GaAs interfacial models using the frozen-phonon multislice method. Three general types of models were considered-perfect, vicinal/sawtooth and diffusion. These were chosen to demonstrate how HAADF image measurements are influenced by different interfacial structures in the technologically important III-V semiconductor system. For each model, interfacial sharpness was calculated as a function of depth and compared to aberration-corrected HAADF experiments of two types of AlAs/GaAs interfaces. The results show that the sharpness measured from HAADF imaging changes in a complicated manner with thickness for complex interfacial structures. For vicinal structures, it was revealed that the type of material that the probe projects through first of all has a significant effect on the measured sharpness. An increase in the vicinal angle was also shown to generate a wider interface in the random step model. The Moison diffusion model produced an increase in the interface width with depth which closely matched the experimental results of the AlAs-on-GaAs interface. In contrast, the interface width decreased as a function of depth in the linear diffusion model. Only in the case of the perfect model was it possible to ascertain the underlying structure directly from HAADF image analysis.

  8. Extraction of structural and chemical information from high angle annular dark-field image by an improved peaks finding method.

    PubMed

    Yin, Wenhao; Huang, Rong; Qi, Ruijuan; Duan, Chungang

    2016-09-01

    With the development of spherical aberration (Cs) corrected scanning transmission electron microscopy (STEM), high angle annular dark filed (HAADF) imaging technique has been widely applied in the microstructure characterization of various advanced materials with atomic resolution. However, current qualitative interpretation of the HAADF image is not enough to extract all the useful information. Here a modified peaks finding method was proposed to quantify the HAADF-STEM image to extract structural and chemical information. Firstly, an automatic segmentation technique including numerical filters and watershed algorithm was used to define the sub-areas for each atomic column. Then a 2D Gaussian fitting was carried out to determine the atomic column positions precisely, which provides the geometric information at the unit-cell scale. Furthermore, a self-adaptive integration based on the column position and the covariance of statistical Gaussian distribution were performed. The integrated intensities show very high sensitivity on the mean atomic number with improved signal-to-noise (S/N) ratio. Consequently, the polarization map and strain distributions were rebuilt from a HAADF-STEM image of the rhombohedral and tetragonal BiFeO3 interface and a MnO2 monolayer in LaAlO3 /SrMnO3 /SrTiO3 heterostructure was discerned from its neighbor TiO2 layers. Microsc. Res. Tech. 79:820-826, 2016. © 2016 Wiley Periodicals, Inc.

  9. PIV-based estimation of unsteady loads on a flat plate at high angle of attack using momentum equation approaches

    NASA Astrophysics Data System (ADS)

    Guissart, A.; Bernal, L. P.; Dimitriadis, G.; Terrapon, V. E.

    2017-05-01

    This work presents, compares and discusses results obtained with two indirect methods for the calculation of aerodynamic forces and pitching moment from 2D Particle Image Velocimetry (PIV) measurements. Both methodologies are based on the formulations of the momentum balance: the integral Navier-Stokes equations and the "flux equation" proposed by Noca et al. (J Fluids Struct 13(5):551-578, 1999), which has been extended to the computation of moments. The indirect methods are applied to spatio-temporal data for different separated flows around a plate with a 16:1 chord-to-thickness ratio. Experimental data are obtained in a water channel for both a plate undergoing a large amplitude imposed pitching motion and a static plate at high angle of attack. In addition to PIV data, direct measurements of aerodynamic loads are carried out to assess the quality of the indirect calculations. It is found that indirect methods are able to compute the mean and the temporal evolution of the loads for two-dimensional flows with a reasonable accuracy. Nonetheless, both methodologies are noise sensitive, and the parameters impacting the computation should thus be chosen carefully. It is also shown that results can be improved through the use of dynamic mode decomposition (DMD) as a pre-processing step.

  10. The geometry of high angle of attack maneuvers and the implications for Gy-induced neck injuries.

    PubMed

    Newman, David G; Ostler, David

    2011-08-01

    Modern super agile fighter aircraft have significantly expanded maneuverability envelopes, often involving very high angles of attack (AOA) in the post-stall region. One such maneuver is the high AOA velocity vector roll. The geometry of this flight maneuver is such that during the roll there is a significant lateral C load imposed on the unrestrained head-neck complex of the pilot. A mathematical analysis of the geometric relationship determining the magnitude of +/- Gy acceleration during high AOA maneuvering was conducted. This preliminary mathematical model is able to predict the Gy load imposed on the head-neck complex of the pilot for a given set of flight maneuver parameters. The analysis predicts that at an AOA of 700 and with a roll rate of 100 degrees x s(-1), the lateral G developed will be approximately 3.5 Gy. Increasing the roll rate increases the lateral G component: at 200 degrees x s(-1) the Gy, load is more than 6 Gy. There are serious potential implications of super agile maneuvers on the neck of the pilot. The G environment experienced by the pilot of super agile aircraft is increasingly multiaxial, involving +/- Gx, +/- Gy, and +/- Gz. The level of lateral G developed during these dynamic flight maneuvers should not be underestimated, as such G loads can potentially lead to neck injuries. While aircraft become ever more capable, a full understanding of the biodynamic effects on the pilot while exploiting the agility of the aircraft still needs to be developed.

  11. Effect of time-dependent 3-D electron density gradients on high angle of incidence HF radiowave propagation

    NASA Astrophysics Data System (ADS)

    Zawdie, K. A.; Drob, D. P.; Huba, J. D.; Coker, C.

    2016-07-01

    One of the challenges for the utilization of HF radiowaves in practical applications is to understand how the signals propagate in time- and range-dependent multipath environments. For typical quiescent ionospheric conditions it is often reasonably straightforward to interpret received HF signals. For disturbed ionospheric conditions, however, such as in the presence of large tilts, irregularities, and medium-scale traveling ionospheric disturbances (MSTIDs), data interpretation and utilization often becomes challenging. This paper presents a theoretical HF propagation modeling study that exploits the capabilities of a first principles, mesoscale resolution ionosphere code, SAMI3 (Sami3 is Another Model of the Ionosphere) and a new implementation of the 3-D ray trace equations, MoJo-15 (Modernized Jones Code) in order to examine the relationship between various HF propagation observables and MSTID characteristics. This paper demonstrates the implications of MSTIDS on high angle of incidence HF propagation during typical low-latitude, postsunset ionospheric conditions and examines the spatiotemporal evolution of multiple propagation paths that may connect a given source and receiver.

  12. Twisting and Writhing with George Ellery Hale

    NASA Astrophysics Data System (ADS)

    Canfield, Richard C.

    2013-06-01

    Early in his productive career in astronomy, George Ellery Hale developed innovative solar instrumentation that allowed him to make narrow-band images. Among the solar phenomena he discovered were sunspot vortices, which he attributed to storms akin to cyclones in our own atmosphere. Using the concept of magnetic helicity, physicists and mathematicians describe the topology of magnetic fields, including twisting and writhing. Our contemporary understanding of Hale's vortices as a consequence of large-scale twist in sunspot magnetic fields hinges on a key property of helicity: conservation. I will describe the critical role that this property plays, when applied to twist and writhe, in a fundamental aspect of global solar magnetism: the hemispheric and solar cycle dependences of active region electric currents with respect to magnetic fields. With the advent of unbroken sequences of high-resolution magnetic images, such as those presently available from the Helioseismic and Magnetic Imager on Solar Dynamics Observatory, the flux of magnetic helicity through the photosphere can be observed quantitatively. As magnetic flux tubes buoy up through the convection zone, buffeted and shredded by turbulence, they break up into fragments by repeated random bifurcation. We track these rising flux fragments in the photosphere, and calculate the flux of energy and magnetic helicity there. Using a quantitative model of coronal currents, we also track connections between these fragments to calculate the energy and magnetic helicity stored at topological interfaces that are in some ways analogous to the storage of stress at faults in the Earth's crust. Comparison of these values to solar flares and interplanetary coronal mass ejections implies that this is the primary storage mechanism for energy and magnetic helicity released in those phenomena, and suggests a useful tool for quantitative prediction of geomagnetic storms.

  13. Symmetries and Boundary Conditions with a Twist

    NASA Astrophysics Data System (ADS)

    Zawadzki, Krissia; D'Amico, Irene; Oliveira, Luiz N.

    2017-10-01

    Interest in finite-size systems has risen in the last decades, due to the focus on nanotechnological applications and because they are convenient for numerical treatment that can subsequently be extrapolated to infinite lattices. Independently of the envisioned application, special attention must be given to boundary condition, which may or may not preserve the symmetry of the infinite lattice. Here, we present a detailed study of the compatibility between boundary conditions and conservation laws. The conflict between open boundary conditions and momentum conservation is well understood, but we examine other symmetries, as well: we discuss gauge invariance, inversion, spin, and particle-hole symmetry and their compatibility with open, periodic, and twisted boundary conditions. In the interest of clarity, we develop the reasoning in the framework of the one-dimensional half-filled Hubbard model, whose Hamiltonian displays a variety of symmetries. Our discussion includes analytical and numerical results. Our analytical survey shows that, as a rule, boundary conditions break one or more symmetries of the infinite-lattice Hamiltonian. The exception is twisted boundary condition with the special torsion Θ = πL/2, where L is the lattice size. Our numerical results for the ground-state energy at half-filling and the energy gap for L = 2-7 show how the breaking of symmetry affects the convergence to the L → ∞ limit. We compare the computed energies and gaps with the exact results for the infinite lattice drawn from the Bethe-Ansatz solution. The deviations are boundary-condition dependent. The special torsion yields more rapid convergence than open or periodic boundary conditions. For sizes as small as L = 7, the numerical results for twisted condition are very close to the L → ∞ limit. We also discuss the ground-state electronic density and magnetization at half filling under the three boundary conditions.

  14. Twisted geometries, twistors, and conformal transformations

    NASA Astrophysics Data System (ADS)

    Lângvik, Miklos; Speziale, Simone

    2016-07-01

    The twisted geometries of spin network states are described by simple twistors, isomorphic to null twistors with a timelike direction singled out. The isomorphism depends on the Immirzi parameter γ and reduces to the identity for γ =∞ . Using this twistorial representation, we study the action of the conformal group SU(2,2) on the classical phase space of loop quantum gravity, described by twisted geometry. The generators of translations and conformal boosts do not preserve the geometric structure, whereas the dilatation generator does. It corresponds to a one-parameter family of embeddings of T*SL(2,C) in twistor space, and its action preserves the intrinsic geometry while changing the extrinsic one—that is the boosts among polyhedra. We discuss the implication of this action from a dynamical point of view and compare it with a discretization of the dilatation generator of the continuum phase space, given by the Lie derivative of the group character. At leading order in the continuum limit, the latter reproduces the same transformation of the extrinsic geometry, while also rescaling the areas and volumes and preserving the angles associated with the intrinsic geometry. Away from the continuum limit, its action has an interesting nonlinear structure but is in general incompatible with the closure constraint needed for the geometric interpretation. As a side result, we compute the precise relation between the extrinsic geometry used in twisted geometries and the one defined in the gauge-invariant parametrization by Dittrich and Ryan and show that the secondary simplicity constraints they posited coincide with those dynamically derived in the toy model of [Classical Quantum Gravity 32, 195015 (2015)].

  15. Spin Squeezing: Transforming One-Axis Twisting into Two-Axis Twisting

    SciTech Connect

    Liu, Y. C.; Jin, G. R.; Xu, Z. F.; You, L.

    2011-07-01

    Squeezed spin states possess unique quantum correlation or entanglement and are significantly promising for advancing quantum information processing and quantum metrology. In recent back-to-back publications [C. Gross et al., Nature (London) 464, 1165 (2010) and Max F. Riedel et al., Nature (London) 464, 1170 (2010)], reduced spin fluctuations are observed leading to spin squeezing at -8.2 and -2.5 dB, respectively, in two-component atomic condensates exhibiting one-axis-twisting interactions. The noise reduction limit for the one-axis twisting scales as {proportional_to}1/N{sup 2/3}, which for a condensate with N{approx}10{sup 3} atoms is about 100 times below the standard quantum limit. We present a scheme using repeated Rabi pulses capable of transforming the one-axis-twisting spin squeezing into the two-axis-twisting type, leading to Heisenberg limited noise reduction {proportional_to}1/N or an extra tenfold improvement for N{approx}10{sup 3}.

  16. Low-speed wind-tunnel study of the high-angle-of-attack stability and control characteristics of a cranked-arrow-wing fighter configuration

    NASA Technical Reports Server (NTRS)

    Grafton, S. B.

    1984-01-01

    The low-speed, high-angle-of-attack stability and control characteristics of a fighter configuration incorporating a cranked arrow wing were investigated in the Langley 30- by 60-foot tunnel as part of a NASA/General Dynamics cooperative research program to investigate the application of advanced wing designs to combat aircraft. Tests were conducted on a baseline configuration and on several modified configurations. The results show that the baseline configuration exhibited a high level of maximum lift but displayed undesirable longitudinal and lateral-directional stability characteristics at high angles of attack. Various wing modifications were made which improved the longitudinal and lateral-directional stability characteristics of the configuration at high angles of attack. However, most of the modifications were detrimental to maximum lift.

  17. Electronic structure studies of nanocrystalline diamond grain boundaries

    SciTech Connect

    Zapol, P.; Sternberg, M.; Frauenheim, T.; Gruen, D. M.; Curtiss, L. A.

    1999-11-29

    Diamond growth from hydrogen-poor plasmas results in diamond structures that are profoundly different from conventionally CVD-grown diamond. High concentration of carbon dimers in the microwave plasma results in a high rate of heterogeneous renucleation leading to formation of nanocrystalline diamond with a typical grain size of 3--10 nm. Therefore, up to 10% of carbon atoms are located in the grain boundaries. In this paper the authors report on density-functional based tight-binding molecular dynamics calculations of the structure of a {Sigma}13 twist (100) grain boundary in diamond. Beginning with a coincidence site lattice model, simulated annealing of the initial structure was performed at 1,500 K followed by relaxation toward lower temperatures. About one-half of the carbons in the grain boundary are found to be three-coordinated. Coordination numbers, bond length and bond angle distributions are analyzed and compared to those obtained in previous studies.

  18. Modes of a twisted optical cavity

    SciTech Connect

    Habraken, Steven J. M.; Nienhuis, Gerard

    2007-03-15

    An astigmatic optical resonator consists of two astigmatic mirrors facing each other. The resonator is twisted when the symmetry axes of the mirrors are nonparallel. We present an algebraic method to obtain the complete set of the paraxial eigenmodes of such a resonator. Basic ingredients are the complex eigenvectors of the four-dimensional transfer matrix that describes the transformation of a ray of light over a roundtrip of the resonator. The relation between the fundamental mode and the higher-order modes is expressed in terms of raising operators in the spirit of the ladder operators of the quantum harmonic oscillator.

  19. Twisting and Writhing with George Ellery Hale

    NASA Astrophysics Data System (ADS)

    Canfield, Richard C.

    2013-07-01

    Early in his productive career in astronomy, George Ellery Hale developed innovative instrumentation that allowed him to image the magnetically-dominated solar chromosphere. Among the solar phenomena he discovered were sunspot vortices, which he attributed to storms akin to cyclones in our own atmosphere. Much more recently, physicists discovered a quantity that is very well conserved in ideal magnetohydrodynamics: magnetic helicity. Our contemporary understanding of Hale's vortices as a consequence of large-scale twist in sunspot magnetic fields hinges on this conservation. I will review the crucial role that this property plays in the hemispheric and solar cycle dependences of Hales vortices, as well as solar flares and CMEs.

  20. Superlubricity in quasicrystalline twisted bilayer graphene

    NASA Astrophysics Data System (ADS)

    Koren, Elad; Duerig, Urs

    2016-05-01

    The unique atomic positions in quasicrystals lead to peculiar self-similarity and fractal-like structural morphology. Accordingly, many of the material properties are supposed to manifest exceptional characteristics. In this Rapid Communication, we explain through numerical simulations the fundamental and peculiar aspects of quasicrystals wearless friction manifested in a 30° twisted bilayer graphene system. In particular, the sliding force exhibits a fractal structure with distinct area correlations due to the natural mixture between both periodic and aperiodic lateral modulations. In addition, zero power scaling of the sliding force with respect to the contact area is demonstrated for a geometric sequence of dodecagonal elements.

  1. Interaction of twisted curved flux tubes

    NASA Astrophysics Data System (ADS)

    Selwa, Malgorzata; Parnell, Clare; Priest, Eric

    Most solar eruptions are initiated from sigmoidal structures. We perform 3D MHD numerical experiments of the interaction of force-free dipolar flux tubes. The magnetic configuration is initialized as either a potential or a force-free dipole with a constant density. Next we perturb the dipoles by twisting or rotating them leading to reconnection in a resistive MHD regime. We compare the connectivity, energetics and topological features in both models, vary the contact angle of the dipoles and check if the initial configuration (sigmoidal or not) affects flares and eruption initiation leading to faster and stronger reconnection.

  2. Non-destructive identification of twisted light.

    PubMed

    Li, Pengyun; Wang, Bo; Song, Xinbing; Zhang, Xiangdong

    2016-04-01

    The non-destructive identification of the orbital angular momentum (OAM) is essential to various applications in the optical information processing. Here, we propose and demonstrate experimentally an efficient method to identify non-destructively the OAM by using a modified Mach-Zehnder interferometer. Our schemes are applicable not only to the case with integer charges, but also to optical vortices with noninteger charges. Our Letter presents the first experimental demonstration of the non-destructive identification of twisted light with integer or noninteger topological charges, which has potential applications in the OAM-based data transmission for optical communications.

  3. Microstructural Features Leading to Enhanced Resistance to Grain Boundary Creep Cracking in ALLVAC 718Plus

    NASA Astrophysics Data System (ADS)

    Unocic, Kinga A.; Hayes, Robert W.; Mills, Michael J.; Daehn, Glenn S.

    2010-02-01

    This study focuses on the microstructural features that enhance the resistance of ALLVAC 718Plus to grain boundary creep cracking during testing of samples at 704 °C in both dry and moist air. Fully recrystallized structures were found to be susceptible to brittle grain boundary cracking in both environments. Detailed transmission electron microscopy (TEM) microstructural characterization reveals features that are believed to lead to resistance to grain boundary cracking in the resistant microstructures. It is suggested that dislocation substructures found within the grains of resistant structures compete with the high-angle grain boundaries for oxygen, thereby reducing the concentration of oxygen on the grain boundaries and subsequent embrittlement. In addition, electron backscatter diffraction (EBSD) misorientation maps reveal that special boundaries ( i.e., Σ3 boundaries) resist cracking. This is in agreement with previous findings on the superalloy INCONEL 718. Furthermore, it is observed that cracks propagate along high-angle boundaries. This study also shows that in this case, the presence of delta phase at the grain boundaries does not by itself produce materials that are resistant to grain boundary cracking.

  4. An experimental study of an airfoil with a bio-inspired leading edge device at high angles of attack

    NASA Astrophysics Data System (ADS)

    Mandadzhiev, Boris A.; Lynch, Michael K.; Chamorro, Leonardo P.; Wissa, Aimy A.

    2017-09-01

    Robust and predictable aerodynamic performance of unmanned aerial vehicles at the limits of their design envelope is critical for safety and mission adaptability. Deployable aerodynamic surfaces from the wing leading or trailing edges are often used to extend the aerodynamic envelope (e.g. slats and flaps). Birds have also evolved feathers at the leading edge (LE) of their wings, known as the alula, which enables them to perform high angles of attack maneuvers. In this study, a series of wind tunnel experiments are performed to quantify the effect of various deployment parameters of an alula-like LE device on the aerodynamic performance of a cambered airfoil (S1223) at stall and post stall conditions. The alula relative angle of attack, measured from the mean chord of the airfoil, is varied to modulate tip-vortex strength, while the alula deflection angle is varied to modulate the distance between the tip vortex and the wing surface. Integrated lift force measurements were collected at various alula-inspired device configurations. The effect of the alula-inspired device on the boundary layer velocity profile and turbulence intensity were investigated through hot-wire anemometer measurements. Results show that as alula deflection angle increases, the lift coefficient also increase especially at lower alula relative angles of attack. Moreover, at post stall wing angles of attack, the wake velocity deficit is reduced in the presence of alula device, confirming the mitigation of the wing adverse pressure gradient. The results are in strong agreement with measurements taken on bird wings showing delayed flow reversal and extended range of operational angles of attack. An engineered alula-inspired device has the potential to improve mission adaptability in small unmanned air vehicles during low Reynolds number flight.

  5. Tuning bilayer twist using chiral counterions

    NASA Astrophysics Data System (ADS)

    Oda, R.; Huc, I.; Schmutz, M.; Candau, S. J.; Mackintosh, F. C.

    1999-06-01

    From seashells to DNA, chirality is expressed at every level of biological structures. In self-assembled structures it may emerge cooperatively from chirality at the molecular scale. Amphiphilic molecules, for example, can form a variety of aggregates and mesophases that express the chirality of their constituent molecules at a supramolecular scale of micrometres (refs 1-3). Quantitative prediction of the large-scale chirality based on that at themolecular scale remains a largely unsolved problem. Furthermore, experimental control over the expression of chirality at the supramolecular level is difficult to achieve: mixing of different enantiomers usually results in phase separation. Here we present an experimental and theoretical description of a system in which chirality can be varied continuously and controllably (`tuned') in micrometre-scale structures. We observe the formation of twisted ribbons consisting of bilayers of gemini surfactants (two surfactant molecules covalently linked at their charged head groups). We find that the degree of twist and the pitch of the ribbons can be tuned by the introduction of opposite-handed chiral counterions in various proportions. This degree of control might be of practical value; for example, in the use of thehelical structures as templates for helical crystallization of macromolecules,.

  6. Structure of twisted and buckled bilayer graphene

    NASA Astrophysics Data System (ADS)

    Jain, Sandeep K.; Juričić, Vladimir; Barkema, Gerard T.

    2017-03-01

    We study the atomic structure of twisted bilayer graphene, with very small mismatch angles (θ ∼ {0.28}0), a topic of intense recent interest. We use simulations, in which we combine a recently presented semi-empirical potential for single-layer graphene, with a new term for out-of-plane deformations, (Jain et al 2015 J. Phys. Chem. C 119 9646) and an often-used interlayer potential (Kolmogorov et al 2005 Phys. Rev. B 71 235415). This combination of potentials is computationally cheap but accurate and precise at the same time, allowing us to study very large samples, which is necessary to reach very small mismatch angles in periodic samples. By performing large scale atomistic simulations, we show that the vortices appearing in the Moiré pattern in the twisted bilayer graphene samples converge to a constant size in the thermodynamic limit. Furthermore, the well known sinusoidal behavior of energy no longer persists once the misorientation angle becomes very small (θ \\lt {1}0). We also show that there is a significant buckling after the relaxation in the samples, with the buckling height proportional to the system size. These structural properties have direct consequences on the electronic and optical properties of bilayer graphene.

  7. Strong CP, Flavor, and Twisted Split Fermions

    SciTech Connect

    Harnik, Roni; Perez, Gilad; Schwartz, Matthew D.; Shirman, Yuri

    2004-11-10

    We present a natural solution to the strong CP problem in the context of split fermions. By assuming CP is spontaneously broken in the bulk, a weak CKM phase is created in the standard model due to a twisting in flavor space of the bulk fermion wavefunctions. But the strong CP phase remains zero, being essentially protected by parity in the bulk and CP on the branes. As always in models of spontaneous CP breaking, radiative corrections to theta bar from the standard model are tiny, but even higher dimension operators are not that dangerous. The twisting phenomenon was recently shown to be generic, and not to interfere with the way that split fermions naturally weaves small numbers into the standard model. It follows that out approach to strong CP is compatible with flavor, and we sketch a comprehensive model. We also look at deconstructed version of this setup which provides a viable 4D model of spontaneous CP breaking which is not in the Nelson-Barr class.

  8. Needleless electrospinning with twisted wire spinneret

    NASA Astrophysics Data System (ADS)

    Holopainen, Jani; Penttinen, Toni; Santala, Eero; Ritala, Mikko

    2015-01-01

    A needleless electrospinning setup named ‘Needleless Twisted Wire Electrospinning’ was developed. The polymer solution is electrospun from the surface of a twisted wire set to a high voltage and collected on a cylindrical collector around the wire. Multiple Taylor cones are simultaneously self-formed on the downward flowing solution. The system is robust and simple with no moving parts aside from the syringe pump used to transport the solution to the top of the wire. The structure and process parameters of the setup and the results on the preparation of polyvinyl pyrrolidone (PVP), hydroxyapatite (HA) and bioglass fibers with the setup are presented. PVP fiber sheets with areas of 40 × 120 cm2 and masses up to 1.15 g were prepared. High production rates of 5.23 g h-1 and 1.40 g h-1 were achieved for PVP and HA respectively. The major limiting factor of the setup is drying of the polymer solution on the wire during the electrospinning process which will eventually force to interrupt the process for cleaning of the wire. Possible solutions to this problem and other ways to develop the setup are discussed. The presented system provides a simple way to increase the production rate and area of fiber sheet as compared with the conventional needle electrospinning.

  9. Simulations of twisted bilayer orthorhombic black phosphorus

    NASA Astrophysics Data System (ADS)

    Pan, Douxing; Wang, Tzu-Chiang; Xiao, Wende; Hu, Dongmei; Yao, Yugui

    2017-07-01

    We identified, by means of coincidence site lattice theory, an evaluative stacking phase with a wavelike Moiré pattern, denoted as 2 O -t α P , from all potentially twisted bilayer orthorhombic black phosphorus. Such a twisted stacking comes with a low formation energy of -162.8 meV , very close to existing AB stacking, according to first-principles calculations. Particularly, classic molecular dynamic simulations verified that the stacking can be directly obtained in an in situ cleavage. The stability of 2 O -t α P stacking can be directly attributed to the corrugated configuration of black phosphorus leading to the van der Waals constraining forces, where the top layer can get stuck to the bottom when one layer rotates in plane relative to the other by ˜70 .5∘ . Tribological analysis further revealed that the interlayer friction of 2 O -t α P stacking reaches up to 1.3 nN, playing a key role in the origin of 2 O -t α P .

  10. Quantization by cochain twists and nonassociative differentials

    SciTech Connect

    Beggs, E. J.; Majid, S.

    2010-05-15

    We show that several standard associative quantizations in mathematical physics can be expressed as cochain module-algebra twists in the spirit of Moyal products at least to O(({Dirac_h}/2{pi}){sup 3}), but to achieve this we twist not by a 2-cocycle but by a 2-cochain. This implies a hidden nonassociativity not visible in the algebra itself but present in its deeper noncommutative differential geometry, a phenomenon first seen in our previous work on semiclassicalization of differential structures. The quantizations are induced by a classical group covariance and include enveloping algebras U(g) as quantizations of g*, a Fedosov-type quantization of the sphere S{sup 2} under a Lorentz group covariance, the Mackey quantization of homogeneous spaces, and the standard quantum groups C{sub q}[G]. We also consider the differential quantization of R{sup n} for a given symplectic connection as part of our semiclassical analysis and we outline a proposal for the Dirac operator.

  11. Terahertz conductivity of twisted bilayer graphene

    NASA Astrophysics Data System (ADS)

    Chia, Elbert E. M.; Zou, Xingquan; Shang, Jingzhi; Leaw, Jianing; Luo, Zhiqiang; Luo, Liyan; Cheong, Siew Ann; Su, Haibin; Zhu, Jian-Xin; Castro Neto, A. H.; Yu, Ting

    2013-03-01

    Using terahertz time-domain spectroscopy, the real part of optical conductivity [σ1 (ω) ] of twisted bilayer graphene was obtained at different temperatures (10 - 300 K) in the frequency range 0.3 - 3 THz. On top of a Drude-like response, we see a strong and narrow peak in σ1 (ω) at ~2.7 THz. We analyze the overall Drude-like response using a disorder-dependent (unitary scattering) model, then attribute the peak at 2.7 THz to an enhanced density of states at that energy, that is caused by the presence of van Hove singularities arising from a commensurate twisting of the two graphene layers. Singapore MOE AcRF Tier 2 (ARC 23/08), NRF-CRP (NRF-CRP4-2008-04), NNSA of the U.S. DOE at LANL (DE-AC52-06NA25396), LANL LDRD Program, NRF-CRP (R-144-000-295-281), DOE DE-FG02-08ER46512, ONR MURI N00014-09-1-1063.

  12. Twisting Fluorescence through Extrinsic Chiral Antennas.

    PubMed

    Yan, Chen; Wang, Xiaolong; Raziman, T V; Martin, Olivier J F

    2017-04-12

    Plasmonic antennas and planar structures have been undergoing intensive developments in order to control the scattering and absorption of light. One specific class, extrinsic chiral surfaces, that does not possess 2-fold rotational symmetry exhibits strong asymmetric transmission for different circular polarizations under obliquely incident illumination. In this work, we show that the design of those surfaces can be optimized with complex multipolar resonances in order to twist the fluorescence emission from nearby molecules. While this emission is usually dipolar and linearly polarized, the interaction with these resonances twists it into a multipolar radiation pattern with opposite helicity in different directions. The proposed structure maximizes this effect and provides control over the polarization of light. Splitting of left- and right-handed circularly polarized light is experimentally obtained in the backward direction. These results highlight the intricate interplay between the near-field absorption and the far-field scattering of a plasmonic nanostructure and are further used for modifying the emission of incoherent quantum sources. Our finding can potentially lead to the development of polarization- and angle-resolved ultracompact optical devices.

  13. Needleless electrospinning with twisted wire spinneret.

    PubMed

    Holopainen, Jani; Penttinen, Toni; Santala, Eero; Ritala, Mikko

    2015-01-16

    A needleless electrospinning setup named 'Needleless Twisted Wire Electrospinning' was developed. The polymer solution is electrospun from the surface of a twisted wire set to a high voltage and collected on a cylindrical collector around the wire. Multiple Taylor cones are simultaneously self-formed on the downward flowing solution. The system is robust and simple with no moving parts aside from the syringe pump used to transport the solution to the top of the wire. The structure and process parameters of the setup and the results on the preparation of polyvinyl pyrrolidone (PVP), hydroxyapatite (HA) and bioglass fibers with the setup are presented. PVP fiber sheets with areas of 40 × 120 cm(2) and masses up to 1.15 g were prepared. High production rates of 5.23 g h(-1) and 1.40 g h(-1) were achieved for PVP and HA respectively. The major limiting factor of the setup is drying of the polymer solution on the wire during the electrospinning process which will eventually force to interrupt the process for cleaning of the wire. Possible solutions to this problem and other ways to develop the setup are discussed. The presented system provides a simple way to increase the production rate and area of fiber sheet as compared with the conventional needle electrospinning.

  14. Holographic generation of highly twisted electron beams.

    PubMed

    Grillo, Vincenzo; Gazzadi, Gian Carlo; Mafakheri, Erfan; Frabboni, Stefano; Karimi, Ebrahim; Boyd, Robert W

    2015-01-23

    Free electrons can possess an intrinsic orbital angular momentum, similar to those in an electron cloud, upon free-space propagation. The wave front corresponding to the electron's wave function forms a helical structure with a number of twists given by the angular speed. Beams with a high number of twists are of particular interest because they carry a high magnetic moment about the propagation axis. Among several different techniques, electron holography seems to be a promising approach to shape a conventional electron beam into a helical form with large values of angular momentum. Here, we propose and manufacture a nanofabricated phase hologram for generating a beam of this kind with an orbital angular momentum up to 200ℏ. Based on a novel technique the value of orbital angular momentum of the generated beam is measured and then compared with simulations. Our work, apart from the technological achievements, may lead to a way of generating electron beams with a high quanta of magnetic moment along the propagation direction and, thus, may be used in the study of the magnetic properties of materials and for manipulating nanoparticles.

  15. How the embryonic brain tube twists

    NASA Astrophysics Data System (ADS)

    Chen, Zi; Guo, Qiaohang; Forsch, Nickolas; Taber, Larry

    2014-03-01

    During early development, the tubular brain of the chick embryo undergoes a combination of progressive ventral bending and rightward torsion. This deformation is one of the major organ-level symmetry-breaking events in development. Available evidence suggests that bending is caused by differential growth, but the mechanism for torsion remains poorly understood. Since the heart almost always loops in the same direction that the brain twists, researchers have speculated that heart looping affects the direction of brain torsion. However, direct evidence is virtually nonexistent, nor is the mechanical origin of such torsion understood. In our study, experimental perturbations show that the bending and torsional deformations in the brain are coupled and that the vitelline membrane applies an external load necessary for torsion to occur. In addition, the asymmetry of the looping heart gives rise to the chirality of the twisted brain. A computational model is used to interpret these findings. Our work clarifies the mechanical origins of brain torsion and the associated left-right asymmetry, reminiscent of D'Arcy Thompson's view of biological form as ``diagram of forces''.

  16. Improve sensitization and corrosion resistance of an Al-Mg alloy by optimization of grain boundaries

    NASA Astrophysics Data System (ADS)

    Yan, Jianfeng; Heckman, Nathan M.; Velasco, Leonardo; Hodge, Andrea M.

    2016-05-01

    The sensitization and subsequent intergranular corrosion of Al-5.3 wt.% Mg alloy has been shown to be an important factor in stress corrosion cracking of Al-Mg alloys. Understanding sensitization requires the review of grain boundary character on the precipitation process which can assist in developing and designing alloys with improved corrosion resistance. This study shows that the degree of precipitation in Al-Mg alloy is dependent on grain boundary misorientation angle, adjacent grain boundary planes and grain boundary types. The results show that the misorientation angle is the most important factor influencing precipitation in grain boundaries of the Al-Mg alloy. Low angle grain boundaries (≤15°) have better immunity to precipitation and grain boundary acid attack. High angle grain boundaries (>15°) are vulnerable to grain boundary acid attack. Grain boundaries with adjacent plane orientations near to {100} have potential for immunity to precipitation and grain boundary acid attack. This work shows that low Σ (Σ ≤ 29) coincident site lattice (CSL) grain boundaries have thinner β precipitates. Modified nitric acid mass loss test and polarization test demonstrated that the global corrosion resistance of sputtered Al-Mg alloy is enhanced. This may be attributed to the increased fractions of low Σ (Σ ≤ 29) CSL grain boundaries after sputtering.

  17. Improve sensitization and corrosion resistance of an Al-Mg alloy by optimization of grain boundaries.

    PubMed

    Yan, Jianfeng; Heckman, Nathan M; Velasco, Leonardo; Hodge, Andrea M

    2016-05-27

    The sensitization and subsequent intergranular corrosion of Al-5.3 wt.% Mg alloy has been shown to be an important factor in stress corrosion cracking of Al-Mg alloys. Understanding sensitization requires the review of grain boundary character on the precipitation process which can assist in developing and designing alloys with improved corrosion resistance. This study shows that the degree of precipitation in Al-Mg alloy is dependent on grain boundary misorientation angle, adjacent grain boundary planes and grain boundary types. The results show that the misorientation angle is the most important factor influencing precipitation in grain boundaries of the Al-Mg alloy. Low angle grain boundaries (≤15°) have better immunity to precipitation and grain boundary acid attack. High angle grain boundaries (>15°) are vulnerable to grain boundary acid attack. Grain boundaries with adjacent plane orientations near to {100} have potential for immunity to precipitation and grain boundary acid attack. This work shows that low Σ (Σ ≤ 29) coincident site lattice (CSL) grain boundaries have thinner β precipitates. Modified nitric acid mass loss test and polarization test demonstrated that the global corrosion resistance of sputtered Al-Mg alloy is enhanced. This may be attributed to the increased fractions of low Σ (Σ ≤ 29) CSL grain boundaries after sputtering.

  18. Improve sensitization and corrosion resistance of an Al-Mg alloy by optimization of grain boundaries

    PubMed Central

    Yan, Jianfeng; Heckman, Nathan M.; Velasco, Leonardo; Hodge, Andrea M.

    2016-01-01

    The sensitization and subsequent intergranular corrosion of Al-5.3 wt.% Mg alloy has been shown to be an important factor in stress corrosion cracking of Al-Mg alloys. Understanding sensitization requires the review of grain boundary character on the precipitation process which can assist in developing and designing alloys with improved corrosion resistance. This study shows that the degree of precipitation in Al-Mg alloy is dependent on grain boundary misorientation angle, adjacent grain boundary planes and grain boundary types. The results show that the misorientation angle is the most important factor influencing precipitation in grain boundaries of the Al-Mg alloy. Low angle grain boundaries (≤15°) have better immunity to precipitation and grain boundary acid attack. High angle grain boundaries (>15°) are vulnerable to grain boundary acid attack. Grain boundaries with adjacent plane orientations near to {100} have potential for immunity to precipitation and grain boundary acid attack. This work shows that low Σ (Σ ≤ 29) coincident site lattice (CSL) grain boundaries have thinner β precipitates. Modified nitric acid mass loss test and polarization test demonstrated that the global corrosion resistance of sputtered Al-Mg alloy is enhanced. This may be attributed to the increased fractions of low Σ (Σ ≤ 29) CSL grain boundaries after sputtering. PMID:27230299

  19. Influence of grain boundary character on point defect formation energies in BCC Fe

    SciTech Connect

    Tschopp, Mark A.; Horstemeyer, Mark; Gao, Fei; Sun, Xin; Khaleel, Mohammad A.

    2012-03-01

    The objective of this research is to understand how grain boundary character influences formation of vacancies and interstitials to grain boundaries in BCC Fe. In this study, molecular statics simulations were used to obtain a large number of minimum energy grain boundary structures in the <100> and <110> symmetric tilt grain boundary system. Then, simulations were used to calculate the formation energies associated with vacancies and self-interstitial atoms at atomic positions within 20 Angstroms of the boundary. As a first analysis, the vacancy formation energies are examined here. The simulation results show how the vacancy formation energies are influenced by grain boundary structure. Low angle boundaries are found to be an effective sink for vacancies along planes adjacent to grain boundary dislocations, while high angle low sigma grain boundaries are less effective sinks for vacancies. The grain boundary sink strength is postulated to depend upon the minimum vacancy formation energy and the influence of grain boundary character on this is shown. Interestingly, low sigma boundaries in the <100> symmetric tilt grain boundary system have higher minimum vacancy formation energies, while this quantity does not seem to be influenced by misorientation angle or grain boundary energy. The significance of this research is that atomistic simulations of this kind may ultimately help inform damage evolution via grain boundaries in multiscale models for irradiated materials as well as its implications for grain boundary engineering.

  20. Incompressible magnetohydrodynamic modes in the thin magnetically twisted flux tube

    NASA Astrophysics Data System (ADS)

    Cheremnykh, O. K.; Fedun, V.; Kryshtal, A. N.; Verth, G.

    2017-08-01

    Context. Observations have shown that twisted magnetic fields naturally occur, and indeed are omnipresent in the Sun's atmosphere. It is therefore of great theoretical interest in solar atmospheric waves research to investigate the types of magnetohydrodynamic (MHD) wave modes that can propagate along twisted magnetic flux tubes. Aims: Within the framework of ideal MHD, the main aim of this work is to investigate small amplitude incompressible wave modes of twisted magnetic flux tubes with m ≥ 1. The axial magnetic field strength inside and outside the tube will be allowed to vary, to ensure the results will not be restricted to only cold plasma equilibria conditions. Methods: The dispersion equation for these incompressible linear MHD wave modes was derived analytically by implementing the long wavelength approximation. Results: It is shown, in the long wavelength limit, that both the frequency and radial velocity profile of the m = 1 kink mode are completely unaffected by the choice of internal background magnetic twist. However, fluting modes with m ≥ 2 are sensitive to the particular radial profile of magnetic twist chosen. Furthermore, due to background twist, a low frequency cut-off is introduced for fluting modes that is not present for kink modes. From an observational point of view, although magnetic twist does not affect the propagation of long wavelength kink modes, for fluting modes it will either work for or against the propagation, depending on the direction of wave travel relative to the sign of the background twist.

  1. Landau quantization and Fermi velocity renormalization in twisted graphene bilayers

    NASA Astrophysics Data System (ADS)

    Yin, Long-Jing; Qiao, Jia-Bin; Wang, Wen-Xiao; Zuo, Wei-Jie; Yan, Wei; Xu, Rui; Dou, Rui-Fen; Nie, Jia-Cai; He, Lin

    2015-11-01

    Currently there is a lively discussion concerning Fermi velocity renormalization in twisted bilayers and several contradicted experimental results are reported. Here we study electronic structures of the twisted bilayers by scanning tunneling microscopy (STM) and spectroscopy (STS). The interlayer coupling strengths between the adjacent bilayers are measured according to energy separations of two pronounced low-energy van Hove singularities (VHSs) in the STS spectra. We demonstrate that there is a large range of values for the interlayer interaction not only in different twisted bilayers, but also in twisted bilayers with the same rotation angle. Below the VHSs, the observed Landau quantization in the twisted bilayers is identical to that of massless Dirac fermions in graphene monolayer, which allows us to measure the Fermi velocity directly. Our result indicates that the Fermi velocity of the twisted bilayers depends remarkably on both the twisted angles and the interlayer coupling strengths. This removes the discrepancy about the Fermi velocity renormalization in the twisted bilayers and provides a consistent interpretation of all current data.

  2. Design optimization of a twist compliant mechanism with nonlinear stiffness

    NASA Astrophysics Data System (ADS)

    Tummala, Y.; Frecker, M. I.; Wissa, A. A.; Hubbard, J. E., Jr.

    2014-10-01

    A contact-aided compliant mechanism called a twist compliant mechanism (TCM) is presented in this paper. This mechanism has nonlinear stiffness when it is twisted in both directions along its axis. The inner core of the mechanism is primarily responsible for its flexibility in one twisting direction. The contact surfaces of the cross-members and compliant sectors are primarily responsible for its high stiffness in the opposite direction. A desired twist angle in a given direction can be achieved by tailoring the stiffness of a TCM. The stiffness of a compliant twist mechanism can be tailored by varying thickness of its cross-members, thickness of the core and thickness of its sectors. A multi-objective optimization problem with three objective functions is proposed in this paper, and used to design an optimal TCM with desired twist angle. The objective functions are to minimize the mass and maximum von-Mises stress observed, while minimizing or maximizing the twist angles under specific loading conditions. The multi-objective optimization problem proposed in this paper is solved for an ornithopter flight research platform as a case study, with the goal of using the TCM to achieve passive twisting of the wing during upstroke, while keeping the wing fully extended and rigid during the downstroke. Prototype TCMs have been fabricated using 3D printing and tested. Testing results are also presented in this paper.

  3. Theoretical and experimental study of twisted and cambered delta wings designed for a Mach number of 3.5

    NASA Technical Reports Server (NTRS)

    Sorrells, R. B., III; Landrum, E. J.

    1976-01-01

    Data are provided for the evaluation of the aerodynamic performance of a series of twisted and cambered delta wings designed for a Mach number of 3.5. Systematic force and pressure data are also presented for comparison with theory. Force tests were made at Mach numbers of 2.3, 3.0, 3.5, 4.0, and 4.6. Design lift coefficients of 0.0 and 0.1 were employed on the 55 deg and 68 deg sweep wings, and design lift coefficients of 0.0, 0.05, and 0.1 were employed on the 76 deg sweep wings. Pressure tests were conducted on the 55 deg and 76 deg sweep flat wings and on the 0.1 design lift coefficient 76 deg sweep wing. The results indicate that for the sweep angles tested, an increase in the zero-lift pitching-moment coefficient is the primary benefit of twist and camber at a Mach number of 3.5. Comparison of the experimental results with results obtained from several lift theories indicates that the Carlson-Middleton linear theory method gave the best overall agreement. The pressure data indicate, however, that there is a cancellation of error at high angle of attack where the lower surface pressures are significantly underpredicted over the inboard region of the wing and where the upper and lower surface pressures are overpredicted over the outboard region of the wing.

  4. Grain Handling and Storage.

    ERIC Educational Resources Information Center

    Harris, Troy G.; Minor, John

    This text for a secondary- or postecondary-level course in grain handling and storage contains ten chapters. Chapter titles are (1) Introduction to Grain Handling and Storage, (2) Elevator Safety, (3) Grain Grading and Seed Identification, (4) Moisture Control, (5) Insect and Rodent Control, (6) Grain Inventory Control, (7) Elevator Maintenance,…

  5. Grain Grading and Handling.

    ERIC Educational Resources Information Center

    Rendleman, Matt; Legacy, James

    This publication provides an introduction to grain grading and handling for adult students in vocational and technical education programs. Organized in five chapters, the booklet provides a brief overview of the jobs performed at a grain elevator and of the techniques used to grade grain. The first chapter introduces the grain industry and…

  6. Landau damping of Langmuir twisted waves with kappa distributed electrons

    SciTech Connect

    Arshad, Kashif Aman-ur-Rehman; Mahmood, Shahzad

    2015-11-15

    The kinetic theory of Landau damping of Langmuir twisted modes is investigated in the presence of orbital angular momentum of the helical (twisted) electric field in plasmas with kappa distributed electrons. The perturbed distribution function and helical electric field are considered to be decomposed by Laguerre-Gaussian mode function defined in cylindrical geometry. The Vlasov-Poisson equation is obtained and solved analytically to obtain the weak damping rates of the Langmuir twisted waves in a nonthermal plasma. The strong damping effects of the Langmuir twisted waves at wavelengths approaching Debye length are also obtained by using an exact numerical method and are illustrated graphically. The damping rates of the planar Langmuir waves are found to be larger than the twisted Langmuir waves in plasmas which shows opposite behavior as depicted in Fig. 3 by J. T. Mendoça [Phys. Plasmas 19, 112113 (2012)].

  7. Twisted Fock representations of noncommutative Kähler manifolds

    NASA Astrophysics Data System (ADS)

    Sako, Akifumi; Umetsu, Hiroshi

    2016-09-01

    We introduce twisted Fock representations of noncommutative Kähler manifolds and give their explicit expressions. The twisted Fock representation is a representation of the Heisenberg like algebra whose states are constructed by applying creation operators to a vacuum state. "Twisted" means that creation operators are not Hermitian conjugate of annihilation operators in this representation. In deformation quantization of Kähler manifolds with separation of variables formulated by Karabegov, local complex coordinates and partial derivatives of the Kähler potential with respect to coordinates satisfy the commutation relations between the creation and annihilation operators. Based on these relations, we construct the twisted Fock representation of noncommutative Kähler manifolds and give a dictionary to translate between the twisted Fock representations and functions on noncommutative Kähler manifolds concretely.

  8. Acoustic Aspects of Active-Twist Rotor Control

    NASA Technical Reports Server (NTRS)

    Booth, Earl R., Jr.; Wilbur, Matthew L.

    2002-01-01

    The use of an Active Twist Rotor system to provide both vibration reduction and performance enhancement has been explored in recent analytical and experimental studies. Effects of active-twist control on rotor noise, however, had not been determined. During a recent wind tunnel test of an active-twist rotor system, a set of acoustic measurements were obtained to assess the effects of active-twist control on noise produced by the rotor, especially blade-vortex interaction (BVI) noise. It was found that for rotor operating conditions where BVI noise is dominant, active-twist control provided a reduction in BVI noise level. This BVI noise reduction was almost, but not quite, as large as that obtained in a similar test using HHC. However, vibration levels were usually adversely affected at operating conditions favoring minimum BVI noise. Conversely, operating conditions favoring minimum vibration levels affected BVI noise levels, but not always adversely.

  9. A twisted disk equation that describes warped galaxy disks

    NASA Technical Reports Server (NTRS)

    Barker, K.

    1994-01-01

    Warped H1 gas layers in the outer regions of spiral galaxies usually display a noticeably twisted structure. This structure is thought to arise primarily as a result of differential precession in the H1 disk as it settles toward a 'preferred orientation' in an underlying dark halo potential well that is not spherically symmetric. In an attempt to better understand the structure and evolution of these twisted, warped disk structures, we have utilized the 'twist-equation' formalism. Specifically, we have generalized the twist equation to allow the treatment of non-Keplerian disks and from it have derived the steady-state structure of twisted disks that develop from free precession in a nonspherical, logarithmic halo potential. This generalized equation can also be used to examine the time-evolutionary behavior of warped galaxy disks.

  10. Twist1 activity thresholds define multiple functions in limb development.

    PubMed

    Krawchuk, Dayana; Weiner, Shoshana J; Chen, You-Tzung; Lu, Benson C; Costantini, Frank; Behringer, Richard R; Laufer, Ed

    2010-11-01

    The basic helix-loop-helix transcription factor Twist1 is essential for normal limb development. Twist1(-/-) embryos die at midgestation. However, studies on early limb buds found that Twist1(-/-) mutant limb mesenchyme has an impaired response to FGF signaling from the apical ectodermal ridge, which disrupts the feedback loop between the mesenchyme and AER, and reduces and shifts anteriorly Shh expression in the zone of polarizing activity. We have combined Twist1 null, hypomorph and conditional alleles to generate a Twist1 allelic series that survives to birth. As Twist1 activity is reduced, limb skeletal defects progress from preaxial polydactyly to girdle reduction combined with hypoplasia, aplasia or mirror symmetry of all limb segments. With reduced Twist1 activity there is striking and progressive upregulation of ectopic Shh expression in the anterior of the limb, combined with an anterior shift in the posterior Shh domain, which is expressed at normal intensity, and loss of the posterior AER. Consequently limb outgrowth is initially impaired, before an ectopic anterior Shh domain expands the AER, promoting additional growth and repatterning. Reducing the dosage of FGF targets of the Etv gene family, which are known repressors of Shh expression in anterior limb mesenchyme, strongly enhances the anterior skeletal phenotype. Conversely this and other phenotypes are suppressed by reducing the dosage of the Twist1 antagonist Hand2. Our data support a model whereby multiple Twist1 activity thresholds contribute to early limb bud patterning, and suggest how particular combinations of skeletal defects result from differing amounts of Twist1 activity. Copyright © 2010 Elsevier Inc. All rights reserved.

  11. Aeromechanical Evaluation of Smart-Twisting Active Rotor

    NASA Technical Reports Server (NTRS)

    Lim, Joon W.; Boyd, D. Douglas, Jr.; Hoffman, Frauke; van der Wall, Berend G.; Kim, Do-Hyung; Jung, Sung N.; You, Young H.; Tanabe, Yasutada; Bailly, Joelle; Lienard, Caroline; Delrieux, Yves

    2014-01-01

    An investigation of Smart-Twisting Active Rotor (STAR) was made to assess potential benefits of the current active twist rotor concept for performance improvement, vibration reduction, and noise alleviation. The STAR rotor is a 40% Mach-scaled, Bo105 rotor with an articulated flap-lag hinge at 3.5%R and no pre-cone. The 0-5 per rev active twist harmonic inputs were applied for various flight conditions including hover, descent, moderate to high speed level flights, and slowed rotor high advance ratio. For the analysis, the STAR partners used multiple codes including CAMRAD II, S4, HOST, rFlow3D, elsA, and their associated software. At the high thrust level in hover, the 0 per rev active twist with 80% amplitude increased figure of merit (FM) by 0.01-0.02 relative to the baseline. In descent, the largest BVI noise reduction was on the order of 2 to 5 dB at the 3 per rev active twist. In the high speed case (mu = 0.35), the 2 per rev actuation was found to be the most effective in achieving a power reduction as well as a vibration reduction. At the 2 per rev active twist, total power was reduced by 0.65% at the 60 deg active twist phase, and vibration was reduced by 47.6% at the 45 deg active twist phase. The use of the 2 per rev active twist appears effective for vibration reduction. In the high advance ratio case (mu = 0.70), the 0 per rev actuation appeared to have negligible impact on performance improvement. In summary, computational simulations successfully demonstrated that the current active twist concept provided a significant reduction of the maximum BVI noise in descent, a significant reduction of the vibration in the high speed case, a small improvement on rotor performance in hover, and a negligible impact on rotor performance in forward flight.

  12. Twist1 activity thresholds define multiple functions in limb development

    PubMed Central

    Krawchuk, Dayana; Weiner, Shoshana J.; Chen, You-Tzung; Lu, Benson; Costantini, Frank; Behringer, Richard R.; Laufer, Ed

    2010-01-01

    Summary The basic helix-loop-helix transcription factor Twist1 is essential for normal limb development. Twist1−/− embryos die at midgestation. However, studies on early limb buds found that Twist1−/− mutant limb mesenchyme has an impaired response to FGF signaling from the apical ectodermal ridge, which disrupts the feedback loop between the mesenchyme and AER, and reduces and shifts anteriorly Shh expression in the zone of polarizing activity. We have combined Twist1 null, hypomorph and conditional alleles to generate a Twist1 allelic series that survives to birth. As Twist1 activity is reduced, limb skeletal defects progress from preaxial polydactyly to girdle reduction combined with hypoplasia, aplasia or mirror symmetry of all limb segments. With reduced Twist1 activity there is striking and progressive upregulation of ectopic Shh expression in the anterior of the limb, combined with an anterior shift in the posterior Shh domain, which is expressed at normal intensity, and loss of the posterior AER. Consequently limb outgrowth is initially impaired, before an ectopic anterior Shh domain expands the AER, promoting additional growth and repatterning. Reducing the dosage of FGF targets of the Etv gene family, which are known repressors of Shh expression in the anterior limb mesenchyme, strongly enhances the anterior skeletal phenotype. Conversely this and other phenotypes are suppressed by reducing the dosage of the Twist1 antagonist Hand2. Our data support a model whereby multiple Twist1 activity thresholds contribute to early limb bud patterning, and suggest how particular combinations of skeletal defects result from differing amounts of Twist1 activity. PMID:20732316

  13. Economic recovery of oil trapped at fan margins using high angle wells and multiple hydraulic fractures. Quarterly report, October 1--December 31, 1996

    SciTech Connect

    Laue, M.L.

    1997-02-13

    This project attempts to demonstrate the effectiveness of exploiting thin-layered, low-energy deposits at the distal margin of a prograding turbidite complex through the use of hydraulically- fractured horizontal or high-angle wells. The combination of a horizontal or high-angle well and hydraulic fracturing will allow greater pay exposure than can be achieved with conventional vertical wells while maintaining vertical communication between thin interbedded layers and the wellbore. A high-angle well will be drilled in the fan-margin portion of a slope-basin clastic reservoir and will be completed with multiple hydraulic-fracture treatments. Geologic modeling, reservoir characterization, and fine-grid reservoir simulation will be used to select the well location and orientation. Design parameters for the hydraulic-fracture treatments will be determined, in part, by fracturing an existing test well. Fracture azimuth will be predicted by passive seismic monitoring of a fracture-stimulation treatment in the test well using logging tools in an offset well. The Unites States Department of Energy granted approval of the continuation application to implement Budget Period Two effective November 21, 1996. The only Budget Period One activities for the quarter involved project administration. Budget Period Two activities were initiated with the development of a drilling program for the high-angle slant well. The well was spud on December 4, 1996 and was drilling at 10,830 ft in the vertical section of the hole as of the end of the month.

  14. Do twisted laser beams evoke nuclear hyperpolarization?

    NASA Astrophysics Data System (ADS)

    Schmidt, A. B.; Andrews, D. L.; Rohrbach, A.; Gohn-Kreuz, C.; Shatokhin, V. N.; Kiselev, V. G.; Hennig, J.; von Elverfeldt, D.; Hövener, J.-B.

    2016-07-01

    The hyperpolarization of nuclear spins promises great advances in chemical analysis and medical diagnosis by substantially increasing the sensitivity of nuclear magnetic resonance (NMR). Current methods to produce a hyperpolarized sample, however, are arduous, time-consuming or costly and require elaborate equipment. Recently, a much simpler approach was introduced that holds the potential, if harnessed appropriately, to revolutionize the production of hyperpolarized spins. It was reported that high levels of hyperpolarization in nuclear spins can be created by irradiation with a laser beam carrying orbital angular momentum (twisted light). Aside from these initial reports however, no further experimental verification has been presented. In addition, this effect has so far evaded a critical theoretical examination. In this contribution, we present the first independent attempt to reproduce the effect. We exposed a sample of immersion oil or a fluorocarbon liquid that was placed within a low-field NMR spectrometer to Laguerre-Gaussian and Bessel laser beams at a wavelength of 514.5 nm and various topological charges. We acquired 1H and 19F NMR free induction decay data, either during or alternating with the irradiation that was parallel to B0. We observed an irregular increase in NMR signal in experiments where the sample was exposed to beams with higher values of the topological charge. However, at no time did the effect reach statistical significance of 95%. Given the measured sensitivity of our setup, we estimate that a possible effect did not exceed a hyperpolarization (at 5 mT) of 0.14-6%, depending on the assumed hyperpolarized volume. It should be noted though, that there were some differences between our setup and the previous implementation of the experiment, which may have inhibited the full incidence of this effect. To approach a theoretical description of this effect, we considered the interaction of an electron with a plane wave, which is known to be

  15. Magnetic field twist driven by remote convective motions: Characteristics and twist rates

    NASA Technical Reports Server (NTRS)

    Wang, Zheng-Zhi; Hassam, A. B.

    1987-01-01

    It is generally believed that convective motions below the solar photosphere induce a twist in the coronal magnetic field as a result of frozen-in physics. A question of interest is how much twist can one expect from a persistent convective motion, given the fact that dissipative effects will eventually figure. This question is examined by considering a model problem: two conducting plates, with finite resistivity, are set in sheared motion and forced at constant relative speed. A resistive plasma is between the plates and an initially vertical magnetic field connects the plates. The time rate of tilt experienced by the field is obtained as a function of Hartmann number and the resistivity ratio. Both analytical and numerical approaches are considered.

  16. Twist-joints and double twist-joints in RNA structure.

    PubMed

    Boutorine, Yury I; Steinberg, Sergey V

    2012-12-01

    Analysis of available RNA crystal structures has allowed us to identify a new family of RNA arrangements that we call double twist-joints, or DTJs. Each DTJ is composed of a double helix that contains two bulges incorporated into different strands and separated from each other by 2 or 3 bp. At each bulge, the double helix is over-twisted, while the unpaired nucleotides of both bulges form a complex network of stacking and hydrogen-bonding with nucleotides of helical regions. In total, we identified 14 DTJ cases, which can be combined in three groups based on common structural characteristics. One DTJ is found in a functional center of the ribosome, another DTJ mediates binding of the pre-tRNA to the RNase P, and two more DTJs form the sensing domains in the glycine riboswitch.

  17. Geometry and crystallographic configuration of grain boundaries

    NASA Astrophysics Data System (ADS)

    Eichler, Jan; Weikusat, Ilka; Kipfstuhl, Sepp; Binder, Tobias

    2015-04-01

    Ice cores provide a unique opportunity to study fundamental mechanisms which control the internal flow of ice sheets. Different kinds of deformation processes acting on the micro-scale are responsible for the viscoplastic behavior on large scale. Careful interpretation of microstructural features such as grain size, shape, lattice orientation and the occurrence of subgrain boundaries can help us to follow these processes and to improve our understanding of ice rheology. Polarized light microscopy experienced a quick development in the last decade. A new generation of automatic fabric analyzers enables to measure c-axis orientations in µm-resolution. This high amount and quality of fabric data motivates to apply digital-image-processing routines (DIP) for the recognition and quantification of microstructural patterns. Here we present a study on grain boundaries based on the acquisition of more than 700 fabric images recorded along the NEEM ice core (Greenland). Geometrical characteristics of grain boundaries are studied as well as their cross-sectional orientations in relation to the c-axis orientations of the corresponding adjacent grains. We could follow the evolution from the initial N-type and P-type low-angle boundaries (Weikusat et al., 2011) to high angle boundaries during rotation recrystallization. In agreement with some previous studies we confirm that the established three-stage-recrystallization model may be an oversimplification. According to our results, rotation recrystallization as well as grain boundary migration are actually present in all depths with varying intensities at NEEM. I. Weikusat, A. Miyamoto, S. H. Faria, S. Kipfstuhl, N. Azuma, and T. Hondoh: Subgrain boundaries in Antarctic ice quantified by X-ray Laue diffraction. J. Glaciol., 57(201):85-94, 2011. doi: 10013/epic.36402.

  18. A new twist on surgical guides.

    PubMed

    Bavar, Trevor

    2008-01-01

    Surgical guides have evolved to the point that they can be created with the aid of computer-assisted tomography (CT) technology. Surgical guides also are used in construction of the prosthesis prior to implant surgery. With existing guide techniques, the prosthesis is screw retained, or cone-shaped temporary abutments may be used to overcome the lack of parallelism of the implants. With the New Twist technique, we are able to create the surgical guide in such a way that optimum bone may be used and the rotational position of the implant may be established for the surgeon and for the laboratory. Custom abutments are inserted at the time of surgery, as is an esthetic, functionally provisional cemented prosthesis. Castings for the finished ceramo-metal bridge are fabricated before surgery is performed. The final prosthesis then is easily constructed by the restorative dentist during just 3 simple patient visits.

  19. Optical Twist Induced by Plasmonic Resonance

    NASA Astrophysics Data System (ADS)

    Chen, Jun; Wang, Neng; Cui, Liyong; Li, Xiao; Lin, Zhifang; Ng, Jack

    2016-06-01

    Harvesting light for optical torque is of significant importance, owing to its ability to rotate nano- or micro-objects. Nevertheless, applying a strong optical torque remains a challenging task: angular momentum must conserve but light is limited. A simple argument shows the tendency for two objects with strong mutual scattering or light exchange to exhibit a conspicuously enhanced optical torque without large extinction or absorption cross section. The torque on each object is almost equal but opposite, which we called optical twist. The effect is quite significant for plasmonic particle cluster, but can also be observed in structures with other morphologies. Such approach exhibits an unprecedentedly large torque to light extinction or absorption ratio, enabling limited light to exert a relatively large torque without severe heating. Our work contributes to the understanding of optical torque and introduces a novel way to manipulate the internal degrees of freedom of a structured particle cluster.

  20. Bounds on tensor wave and twisted inflation

    SciTech Connect

    Panda, Sudhakar; Sami, M.; Ward, John

    2010-11-15

    We study the bounds on tensor wave in a class of twisted inflation models, where D(4+2k)-branes are wrapped on cycles in the compact manifold and wrap the Kaluza-Klein direction in the corresponding effective field theory. While the lower bound is found to be analogous to that in type IIB models of brane inflation, the upper bound turns out to be significantly different. This is argued for a range of values for the parameter g{sub s}M satisfying the self-consistency relation and the WMAP data. Further, we observe that the wrapped D8-brane appears to be the most attractive from a cosmological perspective.

  1. Terahertz twisted beams generation in plasma

    NASA Astrophysics Data System (ADS)

    Sobhani, Hassan; Vaziri (Khamedi), Mohammad; Rooholamininejad, Hossien; Bahrampour, Alireza

    2016-08-01

    The resonant vortex terahertz beam generation by the cross-focusing of two twisted coaxial laser beams is investigated. For the resonant excitation of terahertz radiation, the rippled density in plasma and the ripple wave number is suitably chosen to satisfy the phase matching condition. The nonlinear current density at terahertz frequency arises due to the spatial variation of two Laguerre-Gaussian coupled field. The terahertz intensity scales as the ponderomotive force of laser beams which imparts an oscillatory velocity to the electrons and, in fact, input Laguerre-Gaussian laser beams properties such as vortex charge number and beam waist. Various laser and plasma parameters are employed to yield vortex terahertz radiation with higher efficiency. Also, it is shown that when the beating frequency approaches plasma frequency, the amplitude of THz radiation increases.

  2. Optical Twist Induced by Plasmonic Resonance

    PubMed Central

    Chen, Jun; Wang, Neng; Cui, Liyong; Li, Xiao; Lin, Zhifang; Ng, Jack

    2016-01-01

    Harvesting light for optical torque is of significant importance, owing to its ability to rotate nano- or micro-objects. Nevertheless, applying a strong optical torque remains a challenging task: angular momentum must conserve but light is limited. A simple argument shows the tendency for two objects with strong mutual scattering or light exchange to exhibit a conspicuously enhanced optical torque without large extinction or absorption cross section. The torque on each object is almost equal but opposite, which we called optical twist. The effect is quite significant for plasmonic particle cluster, but can also be observed in structures with other morphologies. Such approach exhibits an unprecedentedly large torque to light extinction or absorption ratio, enabling limited light to exert a relatively large torque without severe heating. Our work contributes to the understanding of optical torque and introduces a novel way to manipulate the internal degrees of freedom of a structured particle cluster. PMID:27291860

  3. A Solvable Twisted One-Plaquette Model

    NASA Astrophysics Data System (ADS)

    Billó, M.; D'Adda, A.

    We solve a hot twisted Eguchi-Kawai model with only timelike plaquettes in the deconfined phase, by computing the quadratic quantum fluctuations around the classical vacuum. The solution of the model has some novel features: the eigenvalues of the timelike link variable are separated in L bunches, if L is the number of links of the original lattice in the time direction, and each bunch obeys a Wigner semicircular distribution of eigenvalues. This solution becomes unstable at a critical value of the coupling constant, where it is argued that a condensation of classical solutions takes place. This can be inferred by comparison with the heat-kernel model in the Hamiltonian limit, and the related Douglas-Kazakov phase transition in QCD2. As a byproduct of our solution, we can reproduce the dependence of the coupling constant from the parameter describing the asymmetry of the lattice, and compare it to previous results by Karsch.

  4. Twists and turns: a scientific journey.

    PubMed

    Tilghman, Shirley M

    2014-01-01

    In this perspective I look back on the twists and turns that influenced the direction of my scientific career over the past 40 years. From my early ambition to be a chemist to my training in Philadelphia and Bethesda as a molecular biologist, I benefited enormously from generous and valuable mentoring. In my independent career in Philadelphia and Princeton, I was motivated by a keen interest in the changes in gene expression that direct the development of the mammalian embryo and inspired by the creativity and energy of my students, fellows, and research staff. After twelve years as President of Princeton University, I have happily returned to the faculty of the Department of Molecular Biology.

  5. Twist deformation of rotationally invariant quantum mechanics

    SciTech Connect

    Chakraborty, B.; Kuznetsova, Z.; Toppan, F.

    2010-11-15

    Noncommutative quantum mechanics in 3D is investigated in the framework of an abelian Drinfeld twist which deforms a given Hopf algebra structure. Composite operators (of coordinates and momenta) entering the Hamiltonian have to be reinterpreted as primitive elements of a dynamical Lie algebra which could be either finite (for the harmonic oscillator) or infinite (in the general case). The deformed brackets of the deformed angular momenta close the so(3) algebra. On the other hand, undeformed rotationally invariant operators can become, under deformation, anomalous (the anomaly vanishes when the deformation parameter goes to zero). The deformed operators, Taylor-expanded in the deformation parameter, can be selected to minimize the anomaly. We present the deformations (and their anomalies) of undeformed rotationally invariant operators corresponding to the harmonic oscillator (quadratic potential), the anharmonic oscillator (quartic potential), and the Coulomb potential.

  6. Twisted Trace Formula for Hecke Correspondences

    NASA Astrophysics Data System (ADS)

    Shokranian, Salahoddin

    2004-12-01

    By the twisted trace formula for the Hecke correspondences we understand the trace formulas for Hecke operators for a non-connected algebraic group acting on certain cohomology spaces. The traces of Hecke operators developed by Selberg in 1957 and the work of Arthur on the traces of Hecke operators of 1989 on L2 -cohomology are in some sense application of analysis and representation theory. On the other hand the work of Eichler in 1957 and of Goresky-MacPherson, Harder and Kottwitz from 1993 to present, reflects more geometric and topological applications. These may be seen as different solutions to the same problem, the calculation of the traces of Hecke operators. The present paper intends to be an introductory note about these operators and their applications.

  7. Radially dependent angular acceleration of twisted light.

    PubMed

    Webster, Jason; Rosales-Guzmán, Carmelo; Forbes, Andrew

    2017-02-15

    While photons travel in a straight line at constant velocity in free space, the intensity profile of structured light may be tailored for acceleration in any degree of freedom. Here we propose a simple approach to control the angular acceleration of light. Using Laguerre-Gaussian modes as our twisted beams carrying orbital angular momentum, we show that superpositions of opposite handedness result in a radially dependent angular acceleration as they pass through a focus (waist plane). Due to conservation of orbital angular momentum, we find that propagation dynamics are complex despite the free-space medium: the outer part of the beam (rings) rotates in an opposite direction to the inner part (petals), and while the outer part accelerates, the inner part decelerates. We outline the concepts theoretically and confirm them experimentally. Such exotic structured light beams are topical due to their many applications, for instance in optical trapping and tweezing, metrology, and fundamental studies in optics.

  8. Bioinspired twisted composites based on Bouligand structures

    NASA Astrophysics Data System (ADS)

    Pinto, F.; Iervolino, O.; Scarselli, G.; Ginzburg, D.; Meo, M.

    2016-04-01

    The coupling between structural support and protection makes biological systems an important source of inspiration for the development of advanced smart composite structures. In particular, some particular material configurations can be implemented into traditional composites in order to improve their impact resistance and the out-of-plane properties, which represents one of the major weakness of commercial carbon fibres reinforced polymers (CFRP) structures. Based on this premise, a three-dimensional twisted arrangement shown in a vast multitude of biological systems (such as the armoured cuticles of Scarabei, the scales of Arapaima Gigas and the smashing club of Odontodactylus Scyllarus) has been replicated to develop an improved structural material characterised by a high level of in-plane isotropy and a higher interfacial strength generated by the smooth stiffness transition between each layer of fibrils. Indeed, due to their intrinsic layered nature, interlaminar stresses are one of the major causes of failure of traditional CFRP and are generated by the mismatch of the elastic properties between plies in a traditional laminate. Since the energy required to open a crack or a delamination between two adjacent plies is due to the difference between their orientations, the gradual angle variation obtained by mimicking the Bouligand Structures could improve energy absorption and the residual properties of carbon laminates when they are subjected to low velocity impact event. Two different bioinspired laminates were manufactured following a double helicoidal approach and a rotational one and were subjected to a complete test campaign including low velocity impact loading and compared to a traditional quasi-isotropic panel. Fractography analysis via X-Ray tomography was used to understand the mechanical behaviour of the different laminates and the residual properties were evaluated via Compression After Impact (CAI) tests. Results confirmed that the biological

  9. Twisted hierarchies associated with the generalized sine-Gordon equation

    NASA Astrophysics Data System (ADS)

    Ma, Hui; Wu, Derchyi

    2011-09-01

    Twisted U- and twisted U/K-hierarchies are soliton hierarchies introduced by Terng to find higher flows of the generalized sine-Gordon equation. Twisted O(J,J)/O(J)× O(J)-hierarchies are among the most important classes of twisted hierarchies. In this paper, we derive explicit interesting first and higher flows of twisted O(J,J)/O(J)× O(J)-hierarchies, justify that the one-dimensional systems of twisted O(J,J)/O(J)× O(J)-hierarchies for J = Iq, n - q(1 ⩽ q ⩽ n - 1), called the generalized sinh-Gordon equations, are the Gauss-Codazzi equations for n-dimensional timelike submanifolds with constant sectional curvature 1 and index q in pseudo-Euclidean (2n - 1)-dimensional space {R}^{2n-1}_{2q-1} with index 2q - 1. Furthermore, a unified treatment of the inverse scattering theory for twisted O(J,J)/O(J)× O(J)-hierarchies is provided.

  10. A Computational Investigation of Random Angle Grain Boundaries for CdTe Solar Cells

    NASA Astrophysics Data System (ADS)

    Buurma, Christopher; Chan, Maria; Klie, Robert; Sivananthan, Sivalingam; DOE Bridge Collaboration

    2015-03-01

    Grain boundaries (GB) in poly-CdTe solar cells play an important role in species diffusion, segregation, defect formation, and carrier recombination. Many studies on GBs in CdTe focus on either entire grain-boundary networks found in complete poly-CdTe devices, those exhibiting high symmetry such as the coincident site lattice (CSL) or symmetric tilt or twist, or on very small scale Scanning-Tunneling Electron Microscopse (STEM) viewable interfaces and dislocations. The topic of this talk is a comprehensive survey of the grain boundary parameter space regardless of the degree of symmetry found and whether the STEM channeling condition is satisfied. Our survey encompasses both near-CSL or vicinal grain boundaries decorated with nearby dislocations, as well as mixed tilt and twist interfaces with all possible symmetrically inequivalent grain boundary planes. Atomistic calculations using a Stillinger-Weber potential will be presented on a large representative sample of random-angle GBs. Trends in interfacial energies and atomistic structures as a function of tilt/twist/displacement parameters will be investigated. First principles density functional theory (DFT) calculations will be performed on a subset of these GBs to reveal their electronic structures and their implications towards PV performance. DoE Sunshot program contract DOE DEEE005956. Use of the Center for Nanoscale Materials was supported by the USDoE, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.

  11. Twist1 regulates keratinocyte proliferation and skin tumor promotion.

    PubMed

    Srivastava, Jaya; Rho, Okkyung; Youssef, Ronnie M; DiGiovanni, John

    2016-05-01

    In the present study, we evaluated the effect of deleting Twist1 on keratinocyte proliferation and on skin tumor development using the two-stage chemical carcinogenesis model. BK5.Cre × Twist1(flox/flox) mice, which have a keratinocyte-specific Twist1 knockout (Twist1 KO), developed significantly reduced numbers of papilloma (70% reduction) and squamous cell carcinoma (75% reduction) as well as delayed tumor latency compared to wild-type (WT) mice. Interestingly, knockdown of Twist1 in primary keratinocytes impeded cell cycle progression at the G1/S transition that coincided with reduced levels of the cell cycle proteins c-Myc, Cyclin E1, and E2F1 and increased levels of p53 and p21. Furthermore, ChIP analyses revealed that Twist1 bound to the promoter regions of Cyclin E1, E2F1, and c-Myc at the canonical E-box binding motif suggesting a direct transcriptional regulation. Further analyses of Twist1 KO mice revealed a significant reduction in the number of label-retaining cells as well as the number of α6-integrin(+) /CD34(+) cells in the hair follicles of untreated mice compared to WT mice. These mice also exhibited significantly reduced epidermal proliferation in response to TPA treatment that again correlated with reduced levels of cell cycle regulators and increased levels of p53 and p21. Finally, Twist1 deficiency in keratinocytes led to an upregulation of p53 via its stabilization and nuclear localization, which is responsible for the increased expression of p21 in these cells. Collectively, these findings indicate that Twist1 has a novel role in epithelial carcinogenesis by regulating proliferation of keratinocytes, including keratinocyte stem cells during tumor promotion. © 2015 Wiley Periodicals, Inc.

  12. Aerodynamic Design Study of an Advanced Active Twist Rotor

    NASA Technical Reports Server (NTRS)

    Sekula, Martin K.; Wilbur, Matthew L.; Yeager, William T., Jr.

    2003-01-01

    An Advanced Active Twist Rotor (AATR) is currently being developed by the U.S. Army Vehicle Technology Directorate at NASA Langley Research Center. As a part of this effort, an analytical study was conducted to determine the impact of blade geometry on active-twist performance and, based on those findings, propose a candidate aerodynamic design for the AATR. The process began by creating a baseline design which combined the dynamic design of the original Active Twist Rotor and the aerodynamic design of a high lift rotor concept. The baseline model was used to conduct a series of parametric studies to examine the effect of linear blade twist and blade tip sweep, droop, and taper on active-twist performance. Rotor power requirements and hub vibration were also examined at flight conditions ranging from hover to advance ratio = 0.40. A total of 108 candidate designs were analyzed using the second-generation version of the Comprehensive Analytical Model of Rotorcraft Aerodynamics and Dynamics (CAMRAD II) code. The study concluded that the vibration reduction capabilities of a rotor utilizing controlled, strain-induced twisting are enhanced through the incorporation of blade tip sweep, droop, and taper into the blade design, while they are degraded by increasing the nose-down linear blade twist. Based on the analysis of rotor power, hub vibration, and active-twist response, a candidate aerodynamic design for the AATR consisting of a blade with approximately 10 degrees of linear blade twist and a blade tip design with 30 degree sweep, 10 degree droop, and 2.5:1 taper ratio over the outer five percent of the blade is proposed.

  13. The Small C-terminal Domain Phosphatase 1 Inhibits Cancer Cell Migration and Invasion by Dephosphorylating Ser(P)68-Twist1 to Accelerate Twist1 Protein Degradation*

    PubMed Central

    Sun, Tong; Fu, Junjiang; Shen, Tao; Lin, Xia; Liao, Lan; Feng, Xin-Hua; Xu, Jianming

    2016-01-01

    Twist1 is a basic helix-loop-helix transcription factor that strongly promotes epithelial-to-mesenchymal transition, migration, invasion, and metastasis of cancer cells. The MAPK-phosphorylated Twist1 on its serine 68 (Ser(P)68-Twist1) has a significantly enhanced stability and function to drive cancer cell invasion and metastasis. However, the phosphatase that dephosphorylates Ser(P)68-Twist1 and destabilizes Twist1 has not been identified and characterized. In this study, we screened a serine/threonine phosphatase cDNA expression library in HEK293T cells with ectopically coexpressed Twist1. We found that the small C-terminal domain phosphatase 1 (SCP1) specifically dephosphorylates Ser(P)68-Twist1 in both cell-free reactions and living cells. SCP1 uses its amino acid residues 43–63 to interact with the N terminus of Twist1. Increased SCP1 expression in cells decreased Ser(P)68-Twist1 and total Twist1 proteins, whereas knockdown of SCP1 increased Ser(P)68-Twist1 and total Twist1 proteins. Furthermore, the levels of SCP1 are negatively correlated with Twist1 protein levels in several cancer cell lines. SCP1-dephosphorylated Twist1 undergoes fast degradation via the ubiquitin-proteasome pathway. Importantly, an increase in SCP1 expression in breast cancer cells with either endogenous or ectopically expressed Twist1 largely inhibits the Twist1-induced epithelial-to-mesenchymal transition phenotype and the migration and invasion capabilities of these cells. These results indicate that SCP1 is the phosphatase that counterregulates the MAPK-mediated phosphorylation of Ser68-Twist1. Thus, an increase in SCP1 expression and activity may be a useful strategy for eliminating the detrimental roles of Twist1 in cancer cells. PMID:26975371

  14. The Small C-terminal Domain Phosphatase 1 Inhibits Cancer Cell Migration and Invasion by Dephosphorylating Ser(P)68-Twist1 to Accelerate Twist1 Protein Degradation.

    PubMed

    Sun, Tong; Fu, Junjiang; Shen, Tao; Lin, Xia; Liao, Lan; Feng, Xin-Hua; Xu, Jianming

    2016-05-27

    Twist1 is a basic helix-loop-helix transcription factor that strongly promotes epithelial-to-mesenchymal transition, migration, invasion, and metastasis of cancer cells. The MAPK-phosphorylated Twist1 on its serine 68 (Ser(P)(68)-Twist1) has a significantly enhanced stability and function to drive cancer cell invasion and metastasis. However, the phosphatase that dephosphorylates Ser(P)(68)-Twist1 and destabilizes Twist1 has not been identified and characterized. In this study, we screened a serine/threonine phosphatase cDNA expression library in HEK293T cells with ectopically coexpressed Twist1. We found that the small C-terminal domain phosphatase 1 (SCP1) specifically dephosphorylates Ser(P)(68)-Twist1 in both cell-free reactions and living cells. SCP1 uses its amino acid residues 43-63 to interact with the N terminus of Twist1. Increased SCP1 expression in cells decreased Ser(P)(68)-Twist1 and total Twist1 proteins, whereas knockdown of SCP1 increased Ser(P)(68)-Twist1 and total Twist1 proteins. Furthermore, the levels of SCP1 are negatively correlated with Twist1 protein levels in several cancer cell lines. SCP1-dephosphorylated Twist1 undergoes fast degradation via the ubiquitin-proteasome pathway. Importantly, an increase in SCP1 expression in breast cancer cells with either endogenous or ectopically expressed Twist1 largely inhibits the Twist1-induced epithelial-to-mesenchymal transition phenotype and the migration and invasion capabilities of these cells. These results indicate that SCP1 is the phosphatase that counterregulates the MAPK-mediated phosphorylation of Ser(68)-Twist1. Thus, an increase in SCP1 expression and activity may be a useful strategy for eliminating the detrimental roles of Twist1 in cancer cells. © 2016 by The American Society for Biochemistry and Molecular Biology, Inc.

  15. Tri-bimaximal mixing from twisted Friedberg-Lee symmetry

    NASA Astrophysics Data System (ADS)

    Araki, Takeshi; Takahashi, Ryo

    2009-10-01

    We investigate the Friedberg-Lee (FL) symmetry and its promotion to include the μ- τ symmetry, and call this the twisted FL symmetry. Based on the twisted FL symmetry, two possible schemes are presented toward the realistic neutrino mass spectrum and the tri-bimaximal mixing. In the first scheme, we suggest the semi-uniform translation of the FL symmetry. The second one is based on the S 3 permutation family symmetry. The breaking terms, which are twisted FL symmetric, are introduced. Some viable models in each scheme are also presented.

  16. Topological suppression of optical tunneling in a twisted annular fiber

    SciTech Connect

    Ornigotti, M.; Valle, G. Della; Gatti, D.; Longhi, S.

    2007-08-15

    A classical wave-optics analog of topological (Aharonov-Bohm) suppression of tunneling in a double-well potential on a ring threaded by a magnetic flux is proposed. The optical system consists of a uniformly twisted optical fiber with a structured annular core, in which the fiber twist mimics the role of the magnetic flux in the corresponding quantum-mechanical problem. Light waves trapped in the annular core of the fiber experience an additional topological (Aharonov-Bohm) phase, which may lead to the destruction of optical tunneling at certain values of the twist rate.

  17. Assembly and Folding of Twisted Baskets in Organic Solvents.

    PubMed

    Pratumyot, Yaowalak; Chen, Shigui; Hu, Lei; Polen, Shane M; Hadad, Christopher M; Badjić, Jovica D

    2016-09-02

    A synthetic method for obtaining enantiopure and twisted baskets of type (P)-3 is described. These chiral cavitands were found to fold quinoline gates, at the rim of their twisted platform, in acetonitrile and give molecular capsules that assemble into large unilamellar vesicles. In a less polar dichloromethane, however, cup-shaped (P)-3 packed into vesicles but with the quinoline gates in an unfolded orientation. The ability of twisted baskets to form functional nanostructured materials could be of interest for building stereoselective sensors and catalysts.

  18. Development of twisted high-temperature superconductor composite conductors

    SciTech Connect

    Christopherson, C.J.; Riley, G.N. Jr.

    1995-04-24

    Multifilamentary high-temperature superconductor (HTS) composite conductors have been developed for alternating current (ac) applications. A twisted HTS conductor containing the Bi-2223 phase fabricated using a modified powder-in-tube technique is reported. Transport critical current densities of 13 800 and 10 900 A/cm {sup 2} (77 K, self-field, 1 {mu}V/cm) have been achieved for twisted tape and wire conductors with twist pitches of 3.7 and 3.6 mm, respectively. These conductors are strongly linked and are thus suitable for use in ac applications.

  19. Development of twisted high-temperature superconductor composite conductors

    NASA Astrophysics Data System (ADS)

    Christopherson, C. J.; Riley, G. N., Jr.

    1995-04-01

    Multifilamentary high-temperature superconductor (HTS) composite conductors have been developed for alternating current (ac) applications. A twisted HTS conductor containing the Bi-2223 phase fabricated using a modified powder-in-tube technique is reported. Transport critical current densities of 13 800 and 10 900 A/cm 2 (77 K, self-field, 1 μV/cm) have been achieved for twisted tape and wire conductors with twist pitches of 3.7 and 3.6 mm, respectively. These conductors are strongly linked and are thus suitable for use in ac applications.

  20. Twisted conformal algebra related to κ -Minkowski space

    NASA Astrophysics Data System (ADS)

    Meljanac, Stjepan; Pachoł, Anna; Pikutić, Danijel

    2015-11-01

    Twisted deformations of the conformal symmetry in the Hopf algebraic framework are constructed. The first one is obtained by a Jordanian twist built up from dilatation and momenta generators. The second is the lightlike κ -deformation of the Poincaré algebra extended to the conformal algebra, obtained by a twist corresponding to the extended Jordanian r -matrix. The κ -Minkowski spacetime is covariant quantum space under both of these deformations. The extension of the conformal algebra by the noncommutative coordinates is presented in two cases. The differential realizations for κ -Minkowski coordinates, as well as their left-right dual counterparts, are also included.

  1. Effect of the grain boundary on the evolution of deformation in a bicrystal

    SciTech Connect

    Ziegler, A; Campbell, G H; Kumar, M; Stolken, J S

    2004-09-08

    The role of grain boundary constraint in strain localization and concomitant constitutive response was examined by performing a series of uniaxial compression tests on a tantalum bicrystal. Tantalum single crystals were diffusion bonded to form a (011) 90 twist boundary that was compressed along the common [011] direction. The plastic deformation resulted in the creation of deformation bands away from the highly constraining grain boundary, resembling those bands known from single crystal plastic deformation. Near the grain boundary, such deformation band formation could not be detected. Instead a distinctive pattern of crystal lattice rotation was observed that filled a rather large volume (several millimeters in size) around the bicrystal grain boundary. The internal deformation band structure as well as the crystal lattice rotation pattern near the bicrystal grain boundary were characterized and found to give greater rates of work hardening in the neighborhood of the grain boundary.

  2. Testing mixed action approaches to meson spectroscopy with twisted mass sea quarks

    NASA Astrophysics Data System (ADS)

    Berlin, J.; Palao, D.; Wagner, M.

    We explore and compare three mixed action setups with Wilson twisted mass sea quarks and different valence quark actions: (1) Wilson twisted mass, (2) Wilson twisted mass + clover and (3) Wilson + clover. Our main goal is to reduce lattice discretization errors in mesonic spectral quantities, in particular to reduce twisted mass parity and isospin breaking.

  3. Ultrafast microscopy captures the dynamics of bound excitons in twisted bilayer van der Waals materials

    NASA Astrophysics Data System (ADS)

    Patel, Hiral; Vogt, Kyle T.; Huang, Lujie; Park, Jiwoong; Graham, Matt W.

    2017-05-01

    Stacking and twisting 2D van der Walls (vdW) materials can create unique electronic properties that are not accessible in a single sheet of material. When two sheets of van der Waals material such as graphene are stacked in an off-axis angle, in a twisted bilayer graphene (tBLG) configuration, electronic properties are modified from interlayer orbital hybridization effects. For instance, in tBLG we can access both massless and massive chiral quasiparticles characteristics of graphene and bilayer graphene, as well as angle tunable optical resonances that are not present in graphene or bilayer graphene. In addition, first principle simulation predicts that upon optical resonant excitation of tBLG, bound exciton formation is a possibility due to cancelation of exciton-continuum coupling from anti-symmetric superposition of degenerate resonant transitions. In order to study possible bound exciton formation, we map out the electronic structure of single grain tBLG using multi-photon transient absorption microscopy. Surprisingly, upon resonant optical excitations, tBLG shows enhanced transient response with longer carrier compared to AB stacked bilayer graphene. Further, we find that the origin of this unexpected optical response can be best explained by the presence of a lower lying bound exciton state predicted by recent theoretical simulations. This suggests that tBLG is a novel 2D hybrid material that enables the creation of both strongly-bound excitons along-side highly-conductive continuum states. Recently, the family of 2D vdW materials has grown appreciably. As such, there are countless possibilities for stacking and twisting 2D vDw materials to produce similar interlayer electronic states for next generation optoelectronics.

  4. Strain softening mechanism at meso scale during micro-compression in an ultrafine-grained pure copper

    SciTech Connect

    Xu, Jie; Li, Jianwei; Shan, Debin; Guo, Bin

    2015-09-15

    Strain softening behavior has been found at meso scale using micro-compression testing in an ultrafine-grained (UFG) pure copper by comparison with the typical strain hardening in conventional coarse-grained (CG) material. Microstructural observations show that grain size remains nearly the same including the fraction of high-angle grain boundaries during micro-compression in UFG pure copper. The Kernel average misorientation(KAM) distribution measured by electron backscatter diffraction (EBSD), as a statistical method, is applied to qualitatively evaluate dislocation density in the interior of the grains. It is suggested that the deformation mechanisms are dominated by grain boundary sliding and grain rotation accompanied by dislocation slip in UFG pure copper, which demonstrates that the strain softening behavior is primarily caused by dislocation annihilation during micro-compression.

  5. Randomized Grain Boundary Liquid Crystal Phase

    NASA Astrophysics Data System (ADS)

    Chen, D.; Wang, H.; Li, M.; Glaser, M.; Maclennan, J.; Clark, N.

    2012-02-01

    The formation of macroscopic, chiral domains, in the B4 and dark conglomerate phases, for example, is a feature of bent-core liquid crystals resulting from the interplay of chirality, molecular bend and molecular tilt. We report a new, chiral phase observed in a hockey stick-like liquid crystal molecule. This phase appears below a smectic A phase and cools to a crystal phase. TEM images of the free surface of the chiral phase show hundreds of randomly oriented smectic blocks several hundred nanometers in size, similar to those seen in the twist grain boundary (TGB) phase. However, in contrast to the TGB phase, these blocks are randomly oriented. The characteristic defects in this phase are revealed by freeze-fracture TEM images. We will show how these defects mediate the randomized orientation and discuss the intrinsic mechanism driving the formation of this phase. This work is supported by NSF MRSEC Grant DMR0820579 and NSF Grant DMR0606528.

  6. Grain Boundary Character Distribution of TLM Titanium Alloy During Deformation

    NASA Astrophysics Data System (ADS)

    Bai, X. F.; Zhao, Y. Q.; Jia, Z. Q.; Zhang, Y. S.; Li, B.

    2016-06-01

    The grain boundary character distribution of TLM titanium alloy (with a nominal chemical composition of Ti-3Zr-2Sn-3Mo-25Nb) was studied under the deformation condition with different strain rates and compression reductions. The experimental results showed that the evolution and character distribution of grain boundaries structure during deformation were both related to grain boundary coupling, sliding, migration, and the grain rotating in nature. In TLM titanium alloy, the type of grain boundaries under different deformation condition included high-angle boundaries, low-angle boundaries, and the CSL boundaries of Σ3, Σ13, Σ29, and Σ39. Under the strain rate of 1 s-1, the numbers of grain boundaries with misorientation angle of 3°, 30°, and 60° all decreased obviously with the increasing compression reduction to 4.5%, comparing to those obtained under the strain rate of 0.001 s-1. Under the strain rate of 1 s-1, the numbers of Σ29 boundaries greatly increased with the compression reductions of 3 to 4.5% comparing to those obtained under the strain rate of 0.001 s-1, and the numbers of Σ3 boundaries increased firstly and then stabilized with the compression reduction increasing from 0 to 4%, while the numbers of Σ39 boundaries decreased with the compression reduction increasing to 4.5%.

  7. Grain-boundary plane crystallography and energy in austenitic steel

    SciTech Connect

    Caul, M.; Randle, V.; Fiedler, J.

    1996-10-01

    The presence of grain boundaries in polycrystalline materials affects the materials properties and performance. Recently it has been realized that boundaries can be manipulated to give better properties, and the design and control of grain boundaries is now an area of strong research interest in the search for high performance engineering materials. Grain boundaries can be classified using the Coincident Site Lattice Model (CSL), which defines the periodicity, i.e., the degree of fit between the two lattices which constitute the boundary. Using this model it is possible to divide boundaries into categories: low angle (up to 15{degree} misorientation), CSL and random i.e., high angle non-CSL. Some CSL boundaries have been shown to have special properties: an example from recent research in the same program as that currently reported has shown that twin boundaries ({Sigma} = 3 in CSL notation) in High Nitrogen Austenitic Stainless Steels do not favor the formation of Cr{sub 2}N precipitates. The research presented here examines grain boundary inclinations of surface grains in austenitic steel specimens which have been isothermally aged at higher 700 C or 800 C. Grain boundary plane crystallography has also been obtained for the 800 C aged sample.

  8. Renormalization of quark propagator, vertex functions, and twist-2 operators from twisted-mass lattice QCD at Nf=4

    NASA Astrophysics Data System (ADS)

    Blossier, Benoît.; Brinet, Mariane; Guichon, Pierre; Morénas, Vincent; Pène, Olivier; Rodríguez-Quintero, Jose; Zafeiropoulos, Savvas

    2015-06-01

    We present a precise nonperturbative determination of the renormalization constants in the mass independent RI'-MOM scheme. The lattice implementation uses the Iwasaki gauge action and four degenerate dynamical twisted-mass fermions. The gauge configurations are provided by the ETM Collaboration. Renormalization constants for scalar, pseudoscalar, vector and axial operators, as well as the quark propagator renormalization, are computed at three different values of the lattice spacing, two volumes and several twisted-mass parameters. The method we developed allows for a precise cross-check of the running, thanks to the particular proper treatment of hypercubic artifacts. Results for the twist-2 operator O44 are also presented.

  9. Wind-tunnel static and free-flight investigation of high-angle-of-attack stability and control characteristics of a model of the EA-6B airplane

    NASA Technical Reports Server (NTRS)

    Jordan, Frank L., Jr.; Hahne, David E.

    1992-01-01

    An investigation was conducted in the Langley 30- by 60-Foot Tunnel and the Langley 12-Foot Low-Speed Tunnel to identify factors contributing to a directional divergence at high angles of attack for the EA-6B airplane. The study consisted of static wind-tunnel tests, smoke and tuft flow-visualization tests, and free-flight tests of a 1/8.5-scale model of the airplane. The results of the investigation indicate that the directional divergence of the airplane is brought about by a loss of directional stability and effective dihedral at high angles of attack. Several modifications were tested that significantly alleviate the stability problem. The results of the free-flight study show that the modified configuration exhibits good dynamic stability characteristics and could be flown at angles of attack significantly higher than those of the unmodified configuration.

  10. Economic recovery of oil trapped at fan margins using high angle wells and multiple hydraulic fractures. Annual report, September 28, 1995--September 27, 1996

    SciTech Connect

    Niemeyer, B.L.

    1997-09-01

    The digital fan margin in the northeast portion of the Yowlumne field contains significant reserves but is not economic to develop using verticle wells. Numerous interbedded shales and deteriorating rock properties limit producibility. In addition, extreme depths (13,000 ft) present a challenging environment for hydraulic fracturing and artificial lift. Lastly, a mature waterflood increases risk because of the uncertainty with size and location of flood fronts. This project attempts to demonstrate the effectiveness of exploiting the distal fan margin of this slope-basin clastic reservoir through the use of a high-angle well completed with multiple hydraulic-fracture treatments. The combination of a high-angle (or horizontal) well and hydraulic fracturing will allow greater pay exposure than can be achieved with conventional verticle wells while maintaining verticle communication between thin interbedded layers and the wellbore. The equivalent production rate and reserves of three verticle wells are anticipated at one-half to two-thirds the cost.

  11. Marketing Farm Grain Crops.

    ERIC Educational Resources Information Center

    Ridenour, Harlan E.

    This vocational agriculture curriculum on grain marketing contains three parts: teacher guide, student manual, and student workbook. All three are coordinated and cross-referenced. The course is designed to give students of grain marketing a thorough background in the subject and provide practical help in developing grain marketing strategies for…

  12. 14. DETAIL OF GUSSET WITH CURVE ANGLE IRON AND TWISTED ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    14. DETAIL OF GUSSET WITH CURVE ANGLE IRON AND TWISTED STRIPS, FORMING SUN RAY PATTERN. LATTICE RAILING AT LOWER RIGHT. - River Road Bridge, Spanning Spring Creek in Spring Creek Township, Hallton, Elk County, PA

  13. Determination of Elastic Twist in Horizontal Axis Wind Turbines (HAWTs)

    SciTech Connect

    Stoddard, F.; Nelson, V.; Starcher, K.; Andrews, B.

    2006-06-01

    This report presents the results of a project at the Alternative Energy Institute (AEI) which measured and calculated the elastic twist of three representative composite horizontal-axis blades: Carter 300, Gougeon ESI 54, and UTRC 8 kW.

  14. 6. DETAIL OF GUSSET WITH CURVE ANGLE IRON AND TWISTED ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    6. DETAIL OF GUSSET WITH CURVE ANGLE IRON AND TWISTED STRIPS, FORMING SUN RAY PATTERN. LATTICE RAILING AT LOWER RIGHT. - River Road Bridge, Spanning Spring Creek in Spring Creek Township, Hallton, Elk County, PA

  15. Whittaker modules for the twisted Heisenberg-Virasoro algebra

    SciTech Connect

    Liu Dong; Wu Yuezhu; Zhu Linsheng

    2010-02-15

    We define Whittaker modules for the twisted Heisenberg-Virasoro algebra and obtain several results from the classical setting, including a classification of simple Whittaker modules by central characters.

  16. Applying twisted boundary conditions for few-body nuclear systems

    NASA Astrophysics Data System (ADS)

    Körber, Christopher; Luu, Thomas

    2016-05-01

    We describe and implement twisted boundary conditions for the deuteron and triton systems within finite volumes using the nuclear lattice EFT formalism. We investigate the finite-volume dependence of these systems with different twist angles. We demonstrate how various finite-volume information can be used to improve calculations of binding energies in such a framework. Our results suggests that with appropriate twisting of boundaries, infinite-volume binding energies can be reliably extracted from calculations using modest volume sizes with cubic length L ≈8 -14 fm. Of particular importance is our derivation and numerical verification of three-body analogs of "i-periodic" twist angles that eliminate the leading-order finite-volume effects to the three-body binding energy.

  17. DNA Twist Stability Changes with Magnesium(2 + ) Concentration

    NASA Astrophysics Data System (ADS)

    Broekmans, Onno D.; King, Graeme A.; Stephens, Greg J.; Wuite, Gijs J. L.

    2016-06-01

    To understand DNA elasticity at high forces (F >30 pN ), its helical nature must be taken into account, as a coupling between twist and stretch. The prevailing model, the wormlike chain, was previously extended to include this twist-stretch coupling. Motivated by DNA's charged nature, and the known effects of ionic charges on its elasticity, we set out to systematically measure the impact of buffer ionic conditions on twist-stretch coupling. After developing a robust fitting approach, we show, using our new data set, that DNA's helical twist is stabilized at high concentrations of the magnesium divalent cation. DNA's persistence length and stretch modulus are, on the other hand, relatively insensitive to the applied range of ionic strengths.

  18. Packing with a twist: from Wrinkles to Scrolls

    NASA Astrophysics Data System (ADS)

    Kudrolli, Arshad; Chopin, Julien

    2012-02-01

    We discuss an experimental investigation of a thin elastic sheet in the form of a ribbon with clamped boundary conditions at both ends which is then subjected to a twist by rotating the ends through a prescribed angle. We find that a wrinkling instability appears even at a small twist angle which depends on the aspect ratio of the ribbon, its bending modulus and initial tension. Using x-ray tomography, we show that the pattern of this first instability has an impact on the folding at larger twist angles which can result in ordered configurations including Fermat scrolls. Still further twisting results in a highly compressive packing as in wringing a towel without application of direct radial compression. Implications for developing yarns with novel mechanical and transport properties [Lima, et al., Science 331, 51 (2011)] will be discussed.

  19. AC loss measurements of twisted and untwisted BSCCO multifilamentary tapes

    NASA Astrophysics Data System (ADS)

    Jiang, Zhenan; Amemiya, Naoyuki; Nishioka, Takamasa; Oh, Sang-Soo

    2005-01-01

    AC losses in twisted and untwisted BSCCO multifilamentary superconducting tapes with Ag matrix developed in DAPAS program were measured by an electrical method. Magnetization and transport losses were measured by a pick-up coil and by a voltage taps. Total AC loss during simultaneous application of AC transport current and an AC transverse magnetic field was given by the sum of the magnetization and transport losses measured during this simultaneous application. The magnetization loss without transport current of untwisted and twisted tapes was measured first to evaluate the effect of twisting to decouple filaments. Then, the total AC loss of the twisted tape was measured in transverse magnetic fields with various amplitudes and orientations, while the amplitude of the transport current was fixed. The measured total AC loss in a parallel transverse magnetic field was compared with some theoretical models to study the detailed characteristics of the measured total AC loss of the sample.

  20. Transmission characteristics of a twisted nematic liquid-crystal layer

    NASA Technical Reports Server (NTRS)

    Grinberg, J.; Jacobson, A. D.

    1976-01-01

    An approximate analytical expression is calculated for the transmission of thin twisted nematic layers situated between a polarizer/analyzer pair. The approximation assumes that the twist angle of the nematic liquid crystal is smaller than the maximum retardation of the cell. The direction of the incident light is assumed to be parallel to the normal of the electrode. This configuration is analyzed for a general arrangement of polarizer and analyzer; the general result is evaluated for the case of the polarizer parallel and analyzer perpendicular to the liquid-crystal optical axis on the input and output electrodes, respectively. The results show that in the case of a thin twisted nematic layer the transmission depends on the thickness of the layer, on the birefringence of the liquid crystal, and on the wavelength of the light. This is a departure from the well-known independence of the transmission on these parameters for a thick twisted nematic layer.

  1. Solar Material Twists on Sun’s Surface

    NASA Image and Video Library

    Solar material twists above the sun’s surface in this close-up captured by NASA’s Solar Dynamics Observatory on June 7-8, 2016, showcasing the turbulence caused by combative magnetic forces on the ...

  2. Pure gravitational radiation with twisting rays in the linear approximation

    NASA Astrophysics Data System (ADS)

    Nita, Bogdan G.; MacAlevey, Paul; Downes, Phillip T.

    2005-11-01

    Solutions of types N and III with twisting rays are derived in the linear approximation by means of complex coordinate transformations. Some solutions are shown to have Riemann tensors which vanish asymptotically and are everywhere regular.

  3. Geometry and evolution of low-angle normal faults (LANF) within a Cenozoic high-angle rift system, Thailand: Implications for sedimentology and the mechanisms of LANF development

    NASA Astrophysics Data System (ADS)

    Morley, Chris K.

    2009-10-01

    At least eight examples of large (5-35 km heave), low-angle normal faults (LANFs, 20°-30° dip) occur in the Cenozoic rift basins of Thailand and laterally pass into high-angle extensional fault systems. Three large-displacement LANFs are found in late Oligocene-Miocene onshore rift basins (Suphan Buri, Phitsanulok, and Chiang Mai basins), they have (1) developed contemporaneous with, or after the onset of, high-angle extension, (2) acted as paths for magma and associated fluids, and (3) impacted sedimentation patterns. Displacement on low-angle faults appears to be episodic, marked by onset of lacustrine conditions followed by axial progradation of deltaic systems that infilled the lakes during periods of low or no displacement. The Chiang Mai LANF is a low-angle (15°-25°), high-displacement (15-35 km heave), ESE dipping LANF immediately east of the late early Miocene Doi Inthanon and Doi Suthep metamorphic core complexes. Early Cenozoic transpressional crustal thickening followed by the northward motion of India coupled with Burma relative to east Burma and Thailand (˜40-30 Ma) caused migmatization and gneiss dome uplift in the late Oligocene of the core complex region, followed by LANF activity. LANF displacement lasted 4-6 Ma during the early Miocene and possibly transported a late Oligocene-early Miocene high-angle rift system 35 km east. Other LANFs in Thailand have lower displacements and no associated metamorphic core complexes. The three LANFs were initiated as low-angle faults, not by isostatic rotation of high-angle faults. The low-angle dips appear to follow preexisting low-angle fabrics (thrusts, shear zones, and other low-angle ductile foliations) predominantly developed during Late Paleozoic and early Paleogene episodes of thrusting and folding.

  4. High Quality Image Formation by Nonlocal Means Applied to High-Angle Annular Darkfield Scanning Transmission Electron Microscopy (HAADF-STEM)

    DTIC Science & Technology

    2010-12-31

    sample enables certain electron imaging and spectroscopic techniques such as mapping by energy dispersive X-ray (EDX) spectroscopy , electron energy...loss spectroscopy (EELS) and annular dark-field imaging (ADF). These signals can be obtained simultane- ously, allowing direct correlation of image and...spectroscopic data. By using a STEM and a high-angle annular detector, it is possible to obtain atomic resolution images where the contrast is

  5. Non-geometric fluxes, quasi-Hopf twist deformations, and nonassociative quantum mechanics

    SciTech Connect

    Mylonas, Dionysios Szabo, Richard J.; Schupp, Peter

    2014-12-15

    We analyse the symmetries underlying nonassociative deformations of geometry in non-geometric R-flux compactifications which arise via T-duality from closed strings with constant geometric fluxes. Starting from the non-abelian Lie algebra of translations and Bopp shifts in phase space, together with a suitable cochain twist, we construct the quasi-Hopf algebra of symmetries that deforms the algebra of functions and the exterior differential calculus in the phase space description of nonassociative R-space. In this setting, nonassociativity is characterised by the associator 3-cocycle which controls non-coassociativity of the quasi-Hopf algebra. We use abelian 2-cocycle twists to construct maps between the dynamical nonassociative star product and a family of associative star products parametrized by constant momentum surfaces in phase space. We define a suitable integration on these nonassociative spaces and find that the usual cyclicity of associative noncommutative deformations is replaced by weaker notions of 2-cyclicity and 3-cyclicity. Using this star product quantization on phase space together with 3-cyclicity, we formulate a consistent version of nonassociative quantum mechanics, in which we calculate the expectation values of area and volume operators, and find coarse-graining of the string background due to the R-flux.

  6. Structural reorganization of parallel actin bundles by crosslinking proteins: Incommensurate states of twist

    NASA Astrophysics Data System (ADS)

    Shin, Homin; Grason, Gregory M.

    2010-11-01

    We construct a coarse-grained model of parallel actin bundles crosslinked by compact globular bundling proteins, such as fascin and espin, necessary components of filopodial and mechanosensory bundles. Consistent with structural observations of bundles, we find that the optimal geometry for crosslinking is overtwisted, requiring a coherent structural change of the helical geometry of the filaments. We study the linker-dependent thermodynamic transition of bundled actin filaments from their native state to the overtwisted state and map out the “twist-state” phase diagram in terms of the availability as well as the flexibility of crosslinker proteins. We predict that the transition from the uncrosslinked to fully crosslinked state is highly sensitive to linker flexibility: flexible crosslinking smoothly distorts the twist state of bundled filaments, while rigidly crosslinked bundles undergo a phase transition, rapidly overtwisting filaments over a narrow range of free crosslinker concentrations. Additionally, we predict a rich spectrum of intermediate structures, composed of alternating domains of sparsely bound (untwisted) and strongly bound (overtwisted) filaments. This model reveals that subtle differences in crosslinking agents themselves modify not only the detailed structure of parallel actin bundles, but also the thermodynamic pathway by which they form.

  7. Grain and grain boundary characters in surface layer of untreated and plasma nitrocarburized 18Ni maraging steel with nanocrystalline structure

    NASA Astrophysics Data System (ADS)

    Yan, M. F.; Wu, Y. Q.; Liu, R. L.

    2013-05-01

    The nanocrystallized 18Ni maraging steel was plasma nitrocarburized at 460 °C for 4 h in a mixture gas of N2, H2 and C2H5OH. The surface phase compositions of the specimens were analyzed using X-ray diffractometer. The grain shape and size, and grain boundaries in the subsurface layers of the samples were characterized by electron backscattering diffraction and transmission electron microscopy. The results show that the nitrocarburized layers are composed of α-Fe, γ‧-Fe4N and FeN0.049 phases. Most α-Fe and γ‧-Fe4N grains show in columnar shape. The major and minor axes of some α-Fe grains are elongated and shortened after nitrocarburizing, respectively. In the subsurface layers of the untreated and nitrocarburized specimens, the average areas of γ‧-Fe4N and α-Fe grains both with a dimension of nanometer are 0.395 μm2 and 0.397 μm2, respectively. The γ‧-Fe4N grain boundaries are mainly high angle boundaries with a very small fraction of low angle boundaries. Coincidence site lattice boundaries in the subsurface layer of the untreated specimen are composed mainly of Σ3, Σ11 and Σ13b, and their fraction decreases after nitrocarburizing.

  8. The Algebra of Formal Twisted Pseudodifferential Symbols and a Noncommutative Residue

    NASA Astrophysics Data System (ADS)

    Zadeh, Farzad Fathi; Khalkhali, Masoud

    2010-10-01

    Motivated by Connes-Moscovici’s notion of a twisted spectral triple, we define an algebra of formal twisted pseudodifferential symbols with respect to a twisting of the base algebra. We extend the Adler-Manin trace and the logarithmic cocycle on the algebra of pseudodifferential symbols to our twisted setting. We also give a general method to construct twisted pseudodifferential symbols on crossed product algebras.

  9. Heat transfer enhancement through a square duct fitted with twisted tape inserts

    NASA Astrophysics Data System (ADS)

    Patil, S. V.; Vijaybabu, P. V.

    2012-10-01

    Experimental investigations of friction factor and heat transfer characteristics of a square duct fitted with twisted tapes of different twist ratios have been reported at nearly uniform wall temperature conditions. The experimental results indicate that the friction factor and Nusselt number increases with decreasing twist ratio. The maximum heat transfer enhancement was observed for a minimum twist ratio. The thermohydraulic performance analysis is made to identify potential benefits of using a twisted tape.

  10. Simulator study of the effectiveness of an automatic control system designed to improve the high-angle-of-attack characteristics of a fighter airplane

    NASA Technical Reports Server (NTRS)

    Gilbert, W. P.; Nguyen, L. T.; Vangunst, R. W.

    1976-01-01

    A piloted, fixed-base simulation was conducted to study the effectiveness of some automatic control system features designed to improve the stability and control characteristics of fighter airplanes at high angles of attack. These features include an angle-of-attack limiter, a normal-acceleration limiter, an aileron-rudder interconnect, and a stability-axis yaw damper. The study was based on a current lightweight fighter prototype. The aerodynamic data used in the simulation were measured on a 0.15-scale model at low Reynolds number and low subsonic Mach number. The simulation was conducted on the Langley differential maneuvering simulator, and the evaluation involved representative combat maneuvering. Results of the investigation show the fully augmented airplane to be quite stable and maneuverable throughout the operational angle-of-attack range. The angle-of-attack/normal-acceleration limiting feature of the pitch control system is found to be a necessity to avoid angle-of-attack excursions at high angles of attack. The aileron-rudder interconnect system is shown to be very effective in making the airplane departure resistant while the stability-axis yaw damper provided improved high-angle-of-attack roll performance with a minimum of sideslip excursions.

  11. Economic reocvery of oil trapped at fan margins using high angle wells and multiple hydraulic fractures. Quarterly report, July 1 - September 30, 1996

    SciTech Connect

    Niemeyer, B.L.

    1996-10-01

    This project attempts to demonstrate the effectiveness of exploiting thin-layered, low-energy deposits at the distal margin of a prograding turbitide complex through the use of hydraulically- fractured, horizontal, or high-angle wells. The combination of horizontal or high-angle well and hydraulic fracturing will allow greater pay exposure than can be achieved with conventional vertical wells while maintaining vertical communication between thin interbedded layers and the wellbore. A high-angle well will be drilled in the fan-margin portion of a slope-basin clastic reservoir and will be completed with multiple hydraulic-fracture treatments. Geologic modeling, reservoir characterization, and fine-grid reservoir simulation will be used to select the well location and orientation. Design parameters for the hydraulic-fracture treatments will be determined by fracturing an existing test well. Fracture azimuth will be predicted, in part, by passive seismic monitoring from an offset well during fracture stimulation of the test well. The fine-grid reservoir simulation of the northeast fan-margin region of the Yowlumne field was completed during third quarter 1996. A variety of development alternatives were investigated aimed at optimizing project economics. Model forecasts, compared slant well performance to more conventional development options and quantified rate impacts due to changes in well location, orientation, and completion technique. Project economics were then updated with the production forecasts from the simulation model.

  12. Economic recovery of oil trapped at fan margins using high angle wells and multiple hydraulic fractures. Quarterly report, July 1--September 30, 1997

    SciTech Connect

    Laue, M.L.

    1997-10-30

    This project attempts to demonstrate the effectiveness of exploiting thin-layered, low-energy deposits at the distal margin of a prograding turbidite complex through the use of hydraulically fractured horizontal or high-angle wells. The combination of a horizontal or high-angle well and hydraulic fracturing will allow greater pay exposure than can be achieved with conventional vertical wells while maintaining vertical communication between thin interbedded layers and the wellbore. A high-angle well will be drilled in the fan-margin portion of a slope-basin clastic reservoir and will be completed with multiple hydraulic-fracture treatments. Geologic modeling, reservoir characterization, and fine-grid reservoir simulation will be used to select the well location and orientation. Design parameters for the hydraulic-fracture treatments will be determined, in part, by fracturing an existing test well. Fracture azimuth will be predicted by passive seismic monitoring of a fracture-stimulation treatment in the test well using logging tools in an offset well. The long radius, near horizontal well has been drilled. After pumping a remedial cement squeeze, all pay behind the 5 in. liner was perforated and stimulated. Once wellwork is complete for the existing perforations, a hydraulic fracture treatment will be pumped through a short interval of clustered perforations in the 7 in. liner. Following this frac, all pay behind the 7 in. liner will be perforated and completion operations will be final.

  13. Creep cavitation and grain boundary structure in type 304 stainless steel

    SciTech Connect

    Don, J.; Majumdar, S.

    1986-05-01

    Grain boundary cavitation in Type 304 stainless steel under creep loading was investigated. Scanning electron microscopy observations showed that cavitation varied among different grain boundaries even when similarly oriented to stress direction. Changes in cavitation were also observed across twin boundaries intersecting a grain boundary facet. The correlation between cavity density and boundary structure was characterized by high voltage electron microscopy and Kikuchi patterns. The results are analyzed in the light of modern grain boundary models. In general, cavities were found on most random high-angle boundaries, whereas coincident site lattice (CSL) boundaries tended to resist cavitation. Of the total boundaries (excluding twins), 53% were CSL boundaries; this percentage greatly exceeds available theoretical predictions based on random grain orientation.

  14. Polarisation of microwave emission from reconnecting twisted coronal loops

    NASA Astrophysics Data System (ADS)

    Gordovskyy, M.; Browning, P. K.; Kontar, E. P.

    2017-08-01

    Context. Magnetic reconnection and particle acceleration due to the kink instability in twisted coronal loops can be a viable scenario for confined solar flares. Detailed investigation of this phenomenon requires reliable methods for observational detection of magnetic twist in solar flares, which may not be possible solely through extreme UV and soft X-ray thermal emission. Polarisation of microwave emission in flaring loops can be used as one of the detection criteria. Aims: The aim of this study is to investigate the effect of magnetic twist in flaring coronal loops on the polarisation of gyro-synchrotron microwave (GSMW) emission, and determine whether it could provide a means for magnetic twist detection. Methods: We consider time-dependent magnetohydrodynamic and test-particle models developed using the LARE3D and GCA codes to investigate twisted coronal loops that relax after kink instability. Synthetic GSMW emission maps (I and V Stokes components) are calculated using GX simulator. Results: It is found that flaring twisted coronal loops produce GSMW radiation with a gradient of circular polarisation across the loop. However, these patterns may be visible only for a relatively short period of time owing to fast magnetic reconfiguration after the instability. Their visibility also depends on the orientation and position of the loop on the solar disk. Typically, it would be difficult to see these characteristic polarisation patterns in a twisted loop seen from the top (i.e. close to the centre of the solar disk), but easier in a twisted loop seen from the side (i.e. observed very close to the limb).

  15. Blade tip vortex measurements on actively twisted rotor blades

    NASA Astrophysics Data System (ADS)

    Bauknecht, André; Ewers, Benjamin; Schneider, Oliver; Raffel, Markus

    2017-05-01

    Active rotor control concepts, such as active twist actuation, have the potential to effectively reduce the noise and vibrations of helicopter rotors. The present study focuses on the experimental investigation of active twist for the reduction of blade-vortex interaction (BVI) effects on a model rotor. Results of a large-scale smart-twisting active rotor test under hover conditions are described. This test investigated the effects of individual blade twist control on the blade tip vortices. The rotor blades were actuated with peak torsion amplitudes of up to 2° and harmonic frequencies of 1-5/rev with different phase angles. Time-resolved stereoscopic particle image velocimetry was carried out to study the effects of active twist on the strength and trajectories of the tip vortices between ψ _ {v}= 3.6° and 45.7° of vortex age. The analysis of the vortex trajectories revealed that the 1/rev active twist actuation mainly caused a vertical deflection of the blade tip and the corresponding vortex trajectories of up to 1.3% of the rotor radius R above and -1%R below the unactuated condition. An actuation with frequencies of 2 and 3/rev significantly affected the shapes of the vortex trajectories and caused negative vertical displacements of the vortices relative to the unactuated case of up to 2%R within the first 35° of wake age. The 2 and 3/rev actuation also had the most significant effects on the vortex strength and altered the initial peak swirl velocity by up to -34 and +31% relative to the unactuated value. The present aerodynamic investigation reveals a high control authority of the active twist actuation on the strength and trajectories of the trailing blade tip vortices. The magnitude of the evoked changes indicates that the active twist actuation constitutes an effective measure for the mitigation of BVI-induced noise on helicopters.

  16. Liberations and twists of real and complex spheres

    NASA Astrophysics Data System (ADS)

    Banica, Teodor

    2015-10-01

    We study the 10 noncommutative spheres obtained by liberating, twisting, and liberating +twisting the real and complex spheres SRN-1, SCN-1. At the axiomatic level, we show that, under very strong axioms, these 10 spheres are the only ones. Our main results concern the computation of the quantum isometry groups of these 10 spheres, taken in an affine real/complex sense. We formulate as well a proposal for an extended formalism, comprising 18 spheres.

  17. Active-Twist Rotor Control Applications for UAVs

    NASA Technical Reports Server (NTRS)

    Wilbur, Matthew L.; Wilkie, W. Keats

    2004-01-01

    The current state-of-the-art in active-twist rotor control is discussed using representative examples from analytical and experimental studies, and the application to rotary-wing UAVs is considered. Topics include vibration and noise reduction, rotor performance improvement, active blade tracking, stability augmentation, and rotor blade de-icing. A review of the current status of piezoelectric fiber composite actuator technology, the class of piezoelectric actuators implemented in active-twist rotor systems, is included.

  18. Twisted Single Crystals in Nonbiological Main-Chain Chiral Polyesters

    NASA Astrophysics Data System (ADS)

    Cheng, S.; Li, Y.; Bai, F.; Harris, F.; Yan, D.; Chen, L.

    1998-03-01

    A series of chiral Poly(R)-(-)-4-(w)-[2-(p-hydroxy-o-nitrophenyloxy)-1-propyloxy]-1- nonyloxy-4-biphenyl carboxylic acid has been synthesized. Singe crystals were grown from the melt. Two very distinct morphological habits can be observed: an elongated flat-on morphology and a helical twist along its long axis. The twisted single crystals show a unique left-handed helical habit with typical pitch length of about 1-2 micrometers. It is expected that this twisted morphology results from a slight deviation of a 21 symmetry in chain packing. In the past, helical morphologies were report in two classes of materials: liquid crystals from the melt and biopolymers in solutions. Liquid crystals only show this kind of morphology when their order is lower than smectic F or I phase, while biopolmers, such as bombyx mori silk fibroin, exhibit similar morphology from solutions due to the existence of the twisted b-sheets. In this case, however, the twisted morphology was identified as crystals via ED and WAXD experiments. Furthermore, neither H-bonding nor b-sheet structure exists in the chemical structure. It is believed that our observation in the twisted single crystals from the melt may represent a class of phases which has not been fully classified.

  19. Twist decomposition of Drell-Yan structure functions: phenomenological implications

    NASA Astrophysics Data System (ADS)

    Brzemiński, Dawid; Motyka, Leszek; Sadzikowski, Mariusz; Stebel, Tomasz

    2017-01-01

    The forward Drell-Yan process in pp scattering at the LHC at √{S} = 14 TeV is considered. We analyze the Drell-Yan structure functions assuming the dominance of a Compton-like emission of a virtual photon from a fast quark scattering off the small x gluons. The color dipole framework is applied to perform quantitatively the twist decomposition of all the Drell-Yan structure functions. Two models of the color dipole scattering are applied: the Golec-Biernat-Wüsthoff model and the dipole cross section obtained from the Balitsky-Fadin-Kuraev-Lipatov evolution equation. The two models have essentially different higher twist content and the gluon transverse momentum distribution and lead to different significant effects beyond the collinear leading twist description. It is found that the gluon transverse momentum effects are significant in the Drell-Yan structure functions for all Drell-Yan pair masses M, and the higher twist effects become important for M ≲ 10GeV. It is found that the structure function W TT related to the A 2 angular coefficient and the Lam-Tung observable A 0 - A 2 are particularly sensitive to the gluon k T effects and to the higher twist effects. A procedure is suggested how to disentangle the higher twist effects from the gluon transverse momentum effects.

  20. Twist-induced Magnetosphere Reconfiguration for Intermittent Pulsars

    NASA Astrophysics Data System (ADS)

    Huang, Lei; Yu, Cong; Tong, Hao

    2016-08-01

    We propose that the magnetosphere reconfiguration induced by magnetic twists in the closed field line region can account for the mode switching of intermittent pulsars. We carefully investigate the properties of axisymmetric force-free pulsar magnetospheres with magnetic twists in closed field line regions around the polar caps. The magnetosphere with twisted closed lines leads to enhanced spin-down rates. The enhancement in spin-down rate depends on the size of the region with twisted closed lines. Typically, it is increased by a factor of ˜2, which is consistent with the intermittent pulsars’ spin-down behavior during the “off” and “on” states. We find that there is a threshold of maximal twist angle {{Δ }}{φ }{{thres}}˜ 1. The magnetosphere is stable only if the closed line twist angle is less than {{Δ }}{φ }{{thres}}. Beyond this value, the magnetosphere becomes unstable and gets untwisted. The spin-down rate would reduce to its off-state value. The quasi-periodicity in spin-down rate change can be explained by long-term activities in the star’s crust and the untwisting induced by MHD instability. The estimated duration of on-state is about 1 week, consistent with observations. Due to the MHD instability, there exists an upper limit for the spin-down ratio (f˜ 3) between the on-state and the off-state, if the Y-point remains at the light cylinder.

  1. A new twist on the geometry of gravitational plane waves

    NASA Astrophysics Data System (ADS)

    Shore, Graham M.

    2017-09-01

    The geometry of twisted null geodesic congruences in gravitational plane wave spacetimes is explored, with special focus on homogeneous plane waves. The rôle of twist in the relation of the Rosen coordinates adapted to a null congruence with the fundamental Brinkmann coordinates is explained and a generalised form of the Rosen metric describing a gravitational plane wave is derived. The Killing vectors and isometry algebra of homogeneous plane waves (HPWs) are described in both Brinkmann and twisted Rosen form and used to demonstrate the coset space structure of HPWs. The van Vleck-Morette determinant for twisted congruences is evaluated in both Brinkmann and Rosen descriptions. The twisted null congruences of the Ozsváth-Schücking, `anti-Mach' plane wave are investigated in detail. These developments provide the necessary geometric toolkit for future investigations of the rôle of twist in loop effects in quantum field theory in curved spacetime, where gravitational plane waves arise generically as Penrose limits; in string theory, where they are important as string backgrounds; and potentially in the detection of gravitational waves in astronomy.

  2. Determination of the relative misorientation of two grains in YBa 2Cu 3O 7-δ by twin pattern analysis

    NASA Astrophysics Data System (ADS)

    Schindler, G.; Sarma, C.

    1994-06-01

    In this paper we describe a method for the determination of the relative misorientation of two grains in bulk YBa 2Cu 3O 7-δ. Our method uses an analysis of the twin patterns of both grains and is based on the Eulerian angles. In the second part we describe how to extract rotational components like ab-plane rotation, c-axis tilt and ab-twist from the rotational matrix.

  3. Twisted light transmission over 143 km.

    PubMed

    Krenn, Mario; Handsteiner, Johannes; Fink, Matthias; Fickler, Robert; Ursin, Rupert; Malik, Mehul; Zeilinger, Anton

    2016-11-29

    Spatial modes of light can potentially carry a vast amount of information, making them promising candidates for both classical and quantum communication. However, the distribution of such modes over large distances remains difficult. Intermodal coupling complicates their use with common fibers, whereas free-space transmission is thought to be strongly influenced by atmospheric turbulence. Here, we show the transmission of orbital angular momentum modes of light over a distance of 143 km between two Canary Islands, which is 50× greater than the maximum distance achieved previously. As a demonstration of the transmission quality, we use superpositions of these modes to encode a short message. At the receiver, an artificial neural network is used for distinguishing between the different twisted light superpositions. The algorithm is able to identify different mode superpositions with an accuracy of more than 80% up to the third mode order and decode the transmitted message with an error rate of 8.33%. Using our data, we estimate that the distribution of orbital angular momentum entanglement over more than 100 km of free space is feasible. Moreover, the quality of our free-space link can be further improved by the use of state-of-the-art adaptive optics systems.

  4. Flow around a helically twisted elliptic cylinder

    SciTech Connect

    Kim, Woojin; Lee, Jungil; Choi, Haecheon

    2016-05-15

    In the present study, we conduct unsteady three-dimensional simulations of flows around a helically twisted elliptic (HTE) cylinder at the Reynolds numbers of 100 and 3900, based on the free-stream velocity and square root of the product of the lengths of its major and minor axes. A parametric study is conducted for Re = 100 by varying the aspect ratio (AR) of the elliptic cross section and the helical spanwise wavelength (λ). Depending on the values of AR and λ, the flow in the wake contains the characteristic wavelengths of λ, 2λ, 6λ, or even longer than 60λ, showing a wide diversity of flows in the wake due to the shape change. The drag on the optimal (i.e., having lowest drag) HTE cylinder (AR = 1.3 and λ = 3.5d) is lower by 18% than that of the circular cylinder, and its lift fluctuations are zero owing to complete suppression of vortex shedding in the wake. This optimal HTE configuration reduces the drag by 23% for Re = 3900 where the wake is turbulent, showing that the HTE cylinder reduces the mean drag and lift fluctuations for both laminar and turbulent flows.

  5. Resonant Raman spectroscopy of twisted multilayer graphene

    NASA Astrophysics Data System (ADS)

    Wu, Jiang-Bin; Zhang, Xin; Ijäs, Mari; Han, Wen-Peng; Qiao, Xiao-Fen; Li, Xiao-Li; Jiang, De-Sheng; Ferrari, Andrea C.; Tan, Ping-Heng

    2014-11-01

    Graphene and other two-dimensional crystals can be combined to form various hybrids and heterostructures, creating materials on demand with properties determined by the interlayer interaction. This is the case even for a single material, where multilayer stacks with different relative orientation have different optical and electronic properties. Probing and understanding the interface coupling is thus of primary importance for fundamental science and applications. Here we study twisted multilayer graphene flakes with multi-wavelength Raman spectroscopy. We find a significant intensity enhancement of the interlayer coupling modes (C peaks) due to resonance with new optically allowed electronic transitions, determined by the relative orientation of the layers. The interlayer coupling results in a Davydov splitting of the C peak in systems consisting of two equivalent graphene multilayers. This allows us to directly quantify the interlayer interaction, which is much smaller compared with Bernal-stacked interfaces. This paves the way to the use of Raman spectroscopy to uncover the interface coupling of two-dimensional hybrids and heterostructures.

  6. Dark Matter in a twisted bottle

    NASA Astrophysics Data System (ADS)

    Arbey, Alexandre; Cacciapaglia, Giacomo; Deandrea, Aldo; Kubik, Bogna

    2013-01-01

    The real projective plane is a compact, non-orientable orbifold of Euler characteristic 1 without boundaries, which can be described as a twisted Klein bottle. We shortly review the motivations for choosing such a geometry among all possible two-dimensional orbifolds, while the main part of the study will be devoted to dark matter study and limits in Universal Extra Dimensional (UED) models based on this peculiar geometry. In the following we consider such a UED construction based on the direct product of the real projective plane with the standard four-dimensional Minkowski space-time and discuss its relevance as a model of a weakly interacting Dark Matter candidate. One important difference with other typical UED models is the origin of the symmetry leading to the stability of the dark matter particle. This symmetry in our case is a remnant of the six-dimensional Minkowski space-time symmetry partially broken by the compactification. Another important difference is the very small mass splitting between the particles of a given Kaluza-Klein tier, which gives a very important role to co-annihilation effects. Finally the role of higher Kaluza-Klein tiers is also important and is discussed together with a detailed numerical description of the influence of the resonances.

  7. Twisted light transmission over 143 km

    PubMed Central

    Krenn, Mario; Handsteiner, Johannes; Fink, Matthias; Fickler, Robert; Ursin, Rupert; Zeilinger, Anton

    2016-01-01

    Spatial modes of light can potentially carry a vast amount of information, making them promising candidates for both classical and quantum communication. However, the distribution of such modes over large distances remains difficult. Intermodal coupling complicates their use with common fibers, whereas free-space transmission is thought to be strongly influenced by atmospheric turbulence. Here, we show the transmission of orbital angular momentum modes of light over a distance of 143 km between two Canary Islands, which is 50× greater than the maximum distance achieved previously. As a demonstration of the transmission quality, we use superpositions of these modes to encode a short message. At the receiver, an artificial neural network is used for distinguishing between the different twisted light superpositions. The algorithm is able to identify different mode superpositions with an accuracy of more than 80% up to the third mode order and decode the transmitted message with an error rate of 8.33%. Using our data, we estimate that the distribution of orbital angular momentum entanglement over more than 100 km of free space is feasible. Moreover, the quality of our free-space link can be further improved by the use of state-of-the-art adaptive optics systems. PMID:27856744

  8. Equivalent Thermal Conductivities for Twisted Flat Windings

    NASA Astrophysics Data System (ADS)

    Glises, R.; Bernard, R.; Chamagne, D.; Kauffmann, J. M.

    1996-10-01

    The authors of this paper intend to develop a method of determination of equivalent thermal conductivities for twisted flat windings. The conductivities determined are radial and parallel to the principal directions of the windings. A design has been realized thanks to the thermal modulus of the computation software Flux2D using a finite elements method. Following that phase, numerical correlations permitting to express the radial conductivities as a function of temperature, filling rate and insulation conductivities are proposed. Les auteurs de cet article se proposent de développer une étude de détermination de conductivités thermiques équivalentes d'empilements de bobinages plats torsadés. Les conductivités sont déterminées dans le plan radial (perpendiculaire à l'axe des bobinages) et parallèlement aux directions principales de la structure. La méthode utilisée est exclusivement numérique et est réalisée à l'aide du logiciel de calculs bidimensionnels par éléments finis Flux2D. Des corrélations numériques exploitables permettent d'obtenir directement les conductivités radiales en fonction du taux de remplissage, de la température du milieu et des conductivités des isolants électriques.

  9. Twisted light transmission over 143 km

    NASA Astrophysics Data System (ADS)

    Krenn, Mario; Handsteiner, Johannes; Fink, Matthias; Fickler, Robert; Ursin, Rupert; Malik, Mehul; Zeilinger, Anton

    2016-11-01

    Spatial modes of light can potentially carry a vast amount of information, making them promising candidates for both classical and quantum communication. However, the distribution of such modes over large distances remains difficult. Intermodal coupling complicates their use with common fibers, whereas free-space transmission is thought to be strongly influenced by atmospheric turbulence. Here, we show the transmission of orbital angular momentum modes of light over a distance of 143 km between two Canary Islands, which is 50× greater than the maximum distance achieved previously. As a demonstration of the transmission quality, we use superpositions of these modes to encode a short message. At the receiver, an artificial neural network is used for distinguishing between the different twisted light superpositions. The algorithm is able to identify different mode superpositions with an accuracy of more than 80% up to the third mode order and decode the transmitted message with an error rate of 8.33%. Using our data, we estimate that the distribution of orbital angular momentum entanglement over more than 100 km of free space is feasible. Moreover, the quality of our free-space link can be further improved by the use of state-of-the-art adaptive optics systems.

  10. TWIST1 and TWIST2 promoter methylation and protein expression in tumor stroma influence the epithelial-mesenchymal transition-like tumor budding phenotype in colorectal cancer.

    PubMed

    Galván, José A; Helbling, Melina; Koelzer, Viktor H; Tschan, Mario P; Berger, Martin D; Hädrich, Marion; Schnüriger, Beat; Karamitopoulou, Eva; Dawson, Heather; Inderbitzin, Daniel; Lugli, Alessandro; Zlobec, Inti

    2015-01-20

    Tumor budding in colorectal cancer is likened to an epithelial-mesenchymal transition (EMT) characterized predominantly by loss of E-cadherin and up-regulation of E-cadherin repressors like TWIST1 and TWIST2. Here we investigate a possible epigenetic link between TWIST proteins and the tumor budding phenotype. TWIST1 and TWIST2 promoter methylation and protein expression were investigated in six cell lines and further correlated with tumor budding in patient cohort 1 (n = 185). Patient cohort 2 (n = 112) was used to assess prognostic effects. Laser capture microdissection (LCM) of tumor epithelium and stroma from low- and high-grade budding cancers was performed. In colorectal cancers, TWIST1 and TWIST2 expression was essentially restricted to stromal cells. LCM results of a high-grade budding case show positive TWIST1 and TWIST2 stroma and no methylation, while the low-grade budding case was characterized by negative stroma and strong hypermethylation. TWIST1 stromal cell staining was associated with adverse features like more advanced pT (p = 0.0044), lymph node metastasis (p = 0.0301), lymphatic vessel invasion (p = 0.0373), perineural invasion (p = 0.0109) and worse overall survival time (p = 0.0226). Stromal cells may influence tumor budding in colorectal cancers through expression of TWIST1. Hypermethylation of the tumor stroma may represent an alternative mechanism for regulation of TWIST1.

  11. Determination of the five parameter grain boundary character distribution of nanocrystalline alpha-zirconium thin films using transmission electron microscopy

    DOE PAGES

    Ghamarian, I.; Colorado School of Mines, Golden, CO; Samani, P.; ...

    2017-03-24

    Grain boundary engineering and other fundamental materials science problems (e.g., phase transformations and physical properties) require an improvement in the understanding of the type and population of grain boundaries in a given system – yet, databases are limited in number and spare in detail, including for hcp crystals such as zirconium. One way to rapidly obtain databases to analyze is to use small-grained materials and high spatial resolution orientation microscopy techniques, such as ASTAR™/precession electron diffraction. To demonstrate this, a study of grain boundary character distributions was conducted for α-zirconium deposited at room temperature on fused silica substrates using physicalmore » vapor deposition. The orientation maps of the nanocrystalline thin films were acquired by the ASTARα/precession electron diffraction technique, a new transmission electron microscope based orientation microscopy method. The reconstructed grain boundaries were classified as pure tilt, pure twist, 180°-twist and 180°-tilt grain boundaries based on the distribution of grain boundary planes with respect to the angle/axis of misorientation associated with grain boundaries. The results of the current study were compared to the results of a similar study on α-titanium and the molecular dynamics results of grain boundary energy for α-titanium.« less

  12. Grain Refinement of Magnesium

    NASA Astrophysics Data System (ADS)

    Lee, Y. C.; Dahle, A. K.; StJohn, D. H.

    Grain formation during solidification of magnesium and Mg-Al alloys has been studied with a focus on grain refinement mechanisms, solute and particle effects. The variation in grain size with increased aluminium content in hypoeutectic Mg-Al alloys showed a continuous decrease in grain size up to 5 wt% Al, and a stabilisation at higher Al contents (above 5 wt%). Strontium additions to both low- and high-aluminium content magnesium alloys showed that Sr had a significant grain refining effect in low-aluminium containing alloys. However, strontium had a negligible effect on grain size in the Mg-9Al alloy. Additions of Zr, Si, or Ca to pure magnesium produced significant grain refinement, probably because these elements have high growth restriction effects during solidification. An attempt was made to identify the grain refinement effect of particles added directly to the melt that are considered to be powerful nucleants in Al based alloys (TiC) and in Mg based alloys (AlN, Al4C3). Most of these particles produced grain refinement, probably because of enhanced nucleation due to the small lattice disregistry between their crystal structures and that of magnesium. However, it is not clear whether the grain refining mechanism of the effective particles was catalysis of primary crystal nucleation or simply restriction of crystal growth during solidification.

  13. Secondary recrystallization in non-sag W filament wires -- On the possible role of relative grain boundary character distribution

    SciTech Connect

    Samajdar, I.; Verlinden, B.; Watte, P.; Mertens, F.

    1999-05-07

    Non-Sag tungsten (W) wire is indispensable for the lighting industry. For the necessary creep resistance, large elongated grains are considered as the desired microstructure. These large grains are obtained by primary and secondary recrystallization. In the present study an effort has been made to characterize and to understand the origin of such large elongated grains. In secondary recrystallization, often called abnormal grain growth, a few of the grains grow massive. The mechanisms of normal and abnormal grain growth are essentially the same, involving high angle boundary migration and driven by the reduction of surface energy. The abnormal grain growth can be visualized as a growth advantage for a few of the grains or growth disadvantage for the majority. Such an advantage/disadvantage may be caused by (1) differences in grain size and/or (2) differences in grain boundary character distribution (GBCD). In other words, a grain may grow massive if it has large size and/or possibilities of more favorable (i.e., of higher mobility) grain boundaries with the matrix grains.

  14. Bend-twist-stretch model for coarse elastic network simulation of biomolecular motion.

    PubMed

    Stember, Joseph N; Wriggers, Willy

    2009-08-21

    The empirical harmonic potential function of elastic network models (ENMs) is augmented by three- and four-body interactions as well as by a parameter-free connection rule. In the new bend-twist-stretch (BTS) model the complexity of the parametrization is shifted from the spatial level of detail to the potential function, enabling an arbitrary coarse graining of the network. Compared to distance cutoff-based Hookean springs, the approach yields a more stable parametrization of coarse-grained ENMs for biomolecular dynamics. Traditional ENMs give rise to unbounded zero-frequency vibrations when (pseudo)atoms are connected to fewer than three neighbors. A large cutoff is therefore chosen in an ENM (about twice the average nearest-neighbor distance), resulting in many false-positive connections that reduce the spatial detail that can be resolved. More importantly, the required three-neighbor connectedness also limits the coarse graining, i.e., the network must be dense, even in the case of low-resolution structures that exhibit few spatial features. The new BTS model achieves such coarse graining by extending the ENM potential to include three-and four-atom interactions (bending and twisting, respectively) in addition to the traditional two-atom stretching. Thus, the BTS model enables reliable modeling of any three-dimensional graph irrespective of the atom connectedness. The additional potential terms were parametrized using continuum elastic theory of elastic rods, and the distance cutoff was replaced by a competitive Hebb connection rule, setting all free parameters in the model. We validate the approach on a carbon-alpha representation of adenylate kinase and illustrate its use with electron microscopy maps of E. coli RNA polymerase, E. coli ribosome, and eukaryotic chaperonin containing T-complex polypeptide 1, which were difficult to model with traditional ENMs. For adenylate kinase, we find excellent reproduction (>90% overlap) of the ENM modes and B factors

  15. Extension-twist coupling optimization in composite rotor blades

    NASA Astrophysics Data System (ADS)

    Ozbay, Serkan

    2005-07-01

    For optimal rotor performance in a tiltrotor aircraft the difference in the inflow and the rotor speeds between the hover and cruise flight modes suggests different blade twist and chord distributions. The blade twist rates in current tiltrotor applications are defined based upon a compromise between the figure of merit in hover and propeller efficiency in airplane mode. However, when each operation mode is considered separately the optimum blade distributions are found to be considerably different. Passive blade twist control, which uses the inherent variation in centrifugal forces on a rotor blade to achieve optimum blade twist distributions in each flight mode through the use of extension-twist coupled composite rotor blades, has been considered for performance improvement of tiltrotor aircraft over the last two decades. The challenge for this concept is to achieve the desired twisting deformations in the rotor blade without altering the aeroelastic characteristics of the vehicle. A concept referred to as the sliding mass concept is proposed in this work in order to increase the twist change with rotor speed for a closed-cell composite rotor blade cross-section to practical levels for performance improvement in a tiltrotor aircraft. The concept is based on load path changes for the centrifugal forces by utilizing non-structural masses readily available on a conventional blade, such as the leading edge balancing mass. A multilevel optimization technique based on the simulated annealing method is applied to improve the performance of the XV15 tiltrotor aircraft. A cross-sectional analysis tool, VABS together with a multibody dynamics code, DYMORE are integrated into the optimization process. The optimization results revealed significant improvements in the power requirement in hover while preserving cruise efficiency. It is also shown that about 21% of the improvement is provided through the sliding mass concept pointing to the additional flexibility the concept

  16. Homozygous Nonsense Mutations in TWIST2 Cause Setleis Syndrome

    PubMed Central

    Tukel, Turgut; Šošić, Dražen; Al-Gazali, Lihadh I.; Erazo, Mónica; Casasnovas, Jose; Franco, Hector L.; Richardson, James A.; Olson, Eric N.; Cadilla, Carmen L.; Desnick, Robert J.

    2010-01-01

    The focal facial dermal dysplasias (FFDDs) are a group of inherited developmental disorders in which the characteristic diagnostic feature is bitemporal scar-like lesions that resemble forceps marks. To date, the genetic defects underlying these ectodermal dysplasias have not been determined. To identify the gene defect causing autosomal-recessive Setleis syndrome (type III FFDD), homozygosity mapping was performed with genomic DNAs from five affected individuals and 26 members of the consanguineous Puerto Rican (PR) family originally described by Setleis and colleagues. Microsatellites D2S1397 and D2S2968 were homozygous in all affected individuals, mapping the disease locus to 2q37.3. Haplotype analyses of additional markers in the PR family and a consanguineous Arab family further limited the disease locus to ∼3 Mb between D2S2949 and D2S2253. Of the 29 candidate genes in this region, the bHLH transcription factor, TWIST2, was initially sequenced on the basis of its known involvement in murine facial development. Homozygous TWIST2 nonsense mutations, c.324C>T and c.486C>T, were identified in the affected members of the Arab and PR families, respectively. Characterization of the expressed mutant proteins, p.Q65X and p.Q119X, by electrophoretic mobility shift assays and immunoblot analyses indicated that they were truncated and unstable. Notably, Setleis syndrome patients and Twist2 knockout mice have similar facial features, indicating the gene's conserved role in mammalian development. Although human TWIST2 and TWIST1 encode highly homologous bHLH transcription factors, the finding that TWIST2 recessive mutations cause an FFDD and dominant TWIST1 mutations cause Saethre-Chotzen craniocynostosis suggests that they function independently in skin and bone development. PMID:20691403

  17. Exact special twist method for quantum Monte Carlo simulations

    NASA Astrophysics Data System (ADS)

    Dagrada, Mario; Karakuzu, Seher; Vildosola, Verónica Laura; Casula, Michele; Sorella, Sandro

    2016-12-01

    We present a systematic investigation of the special twist method introduced by Rajagopal et al. [Phys. Rev. B 51, 10591 (1995), 10.1103/PhysRevB.51.10591] for reducing finite-size effects in correlated calculations of periodic extended systems with Coulomb interactions and Fermi statistics. We propose a procedure for finding special twist values which, at variance with previous applications of this method, reproduce the energy of the mean-field infinite-size limit solution within an adjustable (arbitrarily small) numerical error. This choice of the special twist is shown to be the most accurate single-twist solution for curing one-body finite-size effects in correlated calculations. For these reasons we dubbed our procedure "exact special twist" (EST). EST only needs a fully converged independent-particles or mean-field calculation within the primitive cell and a simple fit to find the special twist along a specific direction in the Brillouin zone. We first assess the performances of EST in a simple correlated model such as the three-dimensional electron gas. Afterwards, we test its efficiency within ab initio quantum Monte Carlo simulations of metallic elements of increasing complexity. We show that EST displays an overall good performance in reducing finite-size errors comparable to the widely used twist average technique but at a much lower computational cost since it involves the evaluation of just one wave function. We also demonstrate that the EST method shows similar performances in the calculation of correlation functions, such as the ionic forces for structural relaxation and the pair radial distribution function in liquid hydrogen. Our conclusions point to the usefulness of EST for correlated supercell calculations; our method will be particularly relevant when the physical problem under consideration requires large periodic cells.

  18. Performance of twist-coupled blades on variable speed rotors

    SciTech Connect

    Lobitz, D.W.; Veers, P.S.; Laino, D.J.

    1999-12-07

    The load mitigation and energy capture characteristics of twist-coupled HAWT blades that are mounted on a variable speed rotor are investigated in this paper. These blades are designed to twist toward feather as they bend with pretwist set to achieve a desirable twist distribution at rated power. For this investigation, the ADAMS-WT software has been modified to include blade models with bending-twist coupling. Using twist-coupled and uncoupled models, the ADAMS software is exercised for steady wind environments to generate C{sub p} curves at a number of operating speeds to compare the efficiencies of the two models. The ADAMS software is also used to generate the response of a twist-coupled variable speed rotor to a spectrum of stochastic wind time series. This spectrum contains time series with two mean wind speeds at two turbulence levels. Power control is achieved by imposing a reactive torque on the low speed shaft proportional to the RPM squared with the coefficient specified so that the rotor operates at peak efficiency in the linear aerodynamic range, and by limiting the maximum RPM to take advantage of the stall controlled nature of the rotor. Fatigue calculations are done for the generated load histories using a range of material exponents that represent materials from welded steel to aluminum to composites, and results are compared with the damage computed for the rotor without twist-coupling. Results indicate that significant reductions in damage are achieved across the spectrum of applied wind loading without any degradation in power production.

  19. An unexpected twist in viral capsid maturation

    SciTech Connect

    Gertsman, Ilya; Gan, Lu; Guttman, Miklos; Lee, Kelly; Speir, Jeffrey A.; Duda, Robert L.; Hendrix, Roger W.; Komives, Elizabeth A.; Johnson, John E.

    2009-04-14

    Lambda-like double-stranded (ds) DNA bacteriophage undergo massive conformational changes in their capsid shell during the packaging of their viral genomes. Capsid shells are complex organizations of hundreds of protein subunits that assemble into intricate quaternary complexes that ultimately are able to withstand over 50 atm of pressure during genome packaging. The extensive integration between subunits in capsids requires the formation of an intermediate complex, termed a procapsid, from which individual subunits can undergo the necessary refolding and structural rearrangements needed to transition to the more stable capsid. Although various mature capsids have been characterized at atomic resolution, no such procapsid structure is available for a dsDNA virus or bacteriophage. Here we present a procapsid X-ray structure at 3.65 {angstrom} resolution, termed prohead II, of the lambda-like bacteriophage HK97, the mature capsid structure of which was previously solved to 3.44 {angstrom}. A comparison of the two largely different capsid forms has unveiled an unprecedented expansion mechanism that describes the transition. Crystallographic and hydrogen/deuterium exchange data presented here demonstrate that the subunit tertiary structures are significantly different between the two states, with twisting and bending motions occurring in both helical and -sheet regions. We also identified subunit interactions at each three-fold axis of the capsid that are maintained throughout maturation. The interactions sustain capsid integrity during subunit refolding and provide a fixed hinge from which subunits undergo rotational and translational motions during maturation. Previously published calorimetric data of a closely related bacteriophage, P22, showed that capsid maturation was an exothermic process that resulted in a release of 90 kJ mol{sup -1} of energy. We propose that the major tertiary changes presented in this study reveal a structural basis for an exothermic

  20. Grain boundary phase equilibrium in metallic systems. Final report, December 1, 1986--May 31, 1991

    SciTech Connect

    Deymier, P.A.

    1991-04-01

    Progresses in the structural and chemical characterization of grain boundaries in metals are reported. We have developed a solid state method for fabrication of a variety of important grain boundaries. This method is based on a sequence of heavy deformation of single crystals followed by controlled recrystallization. The structure of complex grain boundaries such as the quasiperiodic 45{degree}[100] twist in pure aluminum or the periodic {Sigma}5[310] in aluminum-5%Mg alloy has been elucidated. We have found the structural unit (SU) model to be very powerful for the description of quasiperiodic interfaces. The applicability of the SU model to heterophase interfaces is verified for Si-Al interfaces. Further advances have been achieved in the understanding of the driving forces for grain boundary segregation including elastic and electronic effects. Chemical effects on grain boundary core structure are observed in the case of Al-Mg alloys and Sr doped Si.

  1. DNA elasticity from coarse-grained simulations: The effect of groove asymmetry

    NASA Astrophysics Data System (ADS)

    Skoruppa, Enrico; Laleman, Michiel; Nomidis, Stefanos K.; Carlon, Enrico

    2017-06-01

    It is well established that many physical properties of DNA at sufficiently long length scales can be understood by means of simple polymer models. One of the most widely used elasticity models for DNA is the twistable worm-like chain (TWLC), which describes the double helix as a continuous elastic rod with bending and torsional stiffness. An extension of the TWLC, which has recently received some attention, is the model by Marko and Siggia, who introduced an additional twist-bend coupling, expected to arise from the groove asymmetry. By performing computer simulations of two available versions of oxDNA, a coarse-grained model of nucleic acids, we investigate the microscopic origin of twist-bend coupling. We show that this interaction is negligible in the oxDNA version with symmetric grooves, while it appears in the oxDNA version with asymmetric grooves. Our analysis is based on the calculation of the covariance matrix of equilibrium deformations, from which the stiffness parameters are obtained. The estimated twist-bend coupling coefficient from oxDNA simulations is G =30 ±1 nm. The groove asymmetry induces a novel twist length scale and an associated renormalized twist stiffness κt≈80 nm, which is different from the intrinsic torsional stiffness C ≈110 nm. This naturally explains the large variations on experimental estimates of the intrinsic stiffness performed in the past.

  2. Twist phase-induced reduction in scintillation of a partially coherent beam in turbulent atmosphere.

    PubMed

    Wang, Fei; Cai, Yangjian; Eyyuboğlu, Halil T; Baykal, Yahya

    2012-01-15

    The scintillation index of a Gaussian Schell-model beam with twist phase (i.e., twisted GSM beam) in weak turbulent atmosphere is formulated with the help of a tensor method. Variations of the scintillation index of a twisted GSM beam on propagation in turbulent atmosphere are studied in detail. It is interesting to find that the scintillation index of a twisted GSM beam can be smaller than that without twist phase in weak turbulent atmosphere. Thus, modulation of the twist phase of a partially coherent beam provides a new way to reduce turbulence-induced scintillation.

  3. Seismology of Oscillating Flux Tube with Twisted Magnetic Field and Plasma Flow

    NASA Astrophysics Data System (ADS)

    Bahari, Karam

    2017-08-01

    Transverse oscillations of a thin coronal loop in a zero-beta plasma in the presence of a twisted magnetic field and flow are investigated. The dispersion relation is obtained in the limit of weak twist. The twisted magnetic field modifies the phase difference and asymmetry of standing kink oscillations caused by the flow. Using data from observations the kink speed and flow speed have been determined. The presence of the twisted magnetic field can cause underestimation or overestimation of the flow speed in coronal loops depending on the direction of the flow and twisted magnetic field, but a twisted magnetic field has little effect on the estimated value of the kink speed.

  4. Extension-twist coupling of composite circular tubes with application to tilt rotor blade design

    NASA Technical Reports Server (NTRS)

    Nixon, Mark W.

    1987-01-01

    This investigation was conducted to determine if twist deformation required for the design of full-scale extension-twist-coupled tilt-rotor blades can be achieved within material design limit loads, and to demonstrate the accuracy of a coupled-beam analysis in predicting twist deformations. Two extension-twist-coupled tilt-rotor blade designs were developed based on theoretically optimum aerodynamic twist distributions. The designs indicated a twist rate requirement of between .216 and .333 deg/in. Agreement between axial tests and analytical predictions was within 10 percent at design limit loads. Agreement between the torsion tests and predictions was within 11 percent.

  5. R-twist gene expression during rat palatogenesis.

    PubMed

    Bloch-Zupan, A; Hunter, N; Manthey, A; Gibbins, J

    2001-04-01

    Palatal clefting is often associated with premature fusion of cranial sutures in human craniosynostosis syndromes, many of which are characterised by mutations affecting the fibroblast growth factor receptor (FGFR) gene family. In palatal fusion, epithelio-mesenchymal transition (EMT) contributes to the dispersion of the midline epithelial seam. EMT has also been observed in neoplastic epithelial cells in relation to the acquisition of malignant characteristics where morphological changes are accompanied by rapid switching in the expression of fgfr2 from the epithelial type (kgfr) to the mesenchymal type (bek). The twist gene codes for a basic helix-loop-helix transcription factor putatively involved in regulation of transcription of fgfr2. Mutations in the TWIST gene have been described as being responsible for the Saethre-Chotzen syndrome, an autosomal dominant craniosynostosis associated with cleft palate as well as other disturbances of the facial skeleton. In this study we have analysed the distribution of twist transcripts during rat palatogenesis in vivo from 14.5 to 17.5 days post coitum by in situ hybridisation with digoxygenin-labelled ssDNA probes. twist transcripts were found to be concentrated in mesenchymal cells beneath the epithelium at the tip of the palatal shelves immediately prior to, and during fusion as well as in a localised epithelial area at the tip of the shelves prior to fusion, thereby implicating twist gene expression in the process of palatogenesis. This pattern of expression illuminates the disturbances of maxillary growth that occur in human craniosynostotic syndromes.

  6. Atomic form factor for twisted vortex photons interacting with atoms

    NASA Astrophysics Data System (ADS)

    Guthrey, Pierson; Kaplan, Lev; McGuire, J. H.

    2014-04-01

    The relatively new atomic form factor for twisted (vortex) beams, which carry orbital angular momentum (OAM), is considered and compared to the conventional atomic form factor for plane-wave beams that carry only spin angular momentum. Since the vortex symmetry of a twisted photon is more complex that that of a plane wave, evaluation of the atomic form factor is also more complex for twisted photons. On the other hand, the twisted photon has additional parameters, including the OAM quantum number, ℓ, the nodal radial number, p, and the Rayleigh range, zR, which determine the cone angle of the vortex. This Rayleigh range may be used as a variable parameter to control the interaction of twisted photons with matter. Here we address (i) normalization of the vortex atomic form factor, (ii) displacement of target atoms away from the center of the beam vortex, and (iii) formulation of transition probabilities for a variety of photon-atom processes. We attend to features related to experiments that can test the range of validity and accuracy of calculations of these variations of the atomic form factor. Using the absolute square of the form factor for vortex beams, we introduce a vortex factor that can be directly measured.

  7. THE NONLINEAR EVOLUTION OF A TWIST IN A MAGNETIC SHOCKTUBE

    SciTech Connect

    Williams, Thomas; Taroyan, Youra; Fedun, Viktor

    2016-02-01

    The interaction between a small twist and a horizontal chromospheric shocktube is investigated. The magnetic flux tube is modeled using 1.5-D magnetohydrodynamics. The presence of a supersonic yet sub-Alfvénic flow along the flux tube allows the Alfvénic pulse driven at the photospheric boundary to become trapped and amplified between the stationary shock front and photosphere. The amplification of the twist leads to the formation of slow and fast shocks. The pre-existing stationary shock is destabilized and pushed forward as it merges with the slow shock. The propagating fast shock extracts the kinetic energy of the flow and launches rapid twists of 10–15 km s{sup −1} upon each reflection. A cavity is formed between the slow and fast shocks where the flux tube becomes globally twisted within less than an hour. The resultant highly twisted magnetic flux tube is similar to those prone to kink instabilities, which may be responsible for solar eruptions. The generated torsional flux is calculated.

  8. Interfacial Atomic Structure of Twisted Few-Layer Graphene.

    PubMed

    Ishikawa, Ryo; Lugg, Nathan R; Inoue, Kazutoshi; Sawada, Hidetaka; Taniguchi, Takashi; Shibata, Naoya; Ikuhara, Yuichi

    2016-02-18

    A twist in bi- or few-layer graphene breaks the local symmetry, introducing a number of intriguing physical properties such as opening new bandgaps. Therefore, determining the twisted atomic structure is critical to understanding and controlling the functional properties of graphene. Combining low-angle annular dark-field electron microscopy with image simulations, we directly determine the atomic structure of twisted few-layer graphene in terms of a moiré superstructure which is parameterized by a single twist angle and lattice constant. This method is shown to be a powerful tool for accurately determining the atomic structure of two-dimensional materials such as graphene, even in the presence of experimental errors. Using coincidence-site-lattice and displacement-shift-complete theories, we show that the in-plane translation state between layers is not a significant structure parameter, explaining why the present method is adequate not only for bilayer graphene but also a few-layered twisted graphene.

  9. The trouble with twisting (2,0) theory

    NASA Astrophysics Data System (ADS)

    Anderson, Louise; Linander, Hampus

    2014-03-01

    We consider a twisted version of the abelian (2, 0) theory placed upon a Lorentzian six-manifold with a product structure, M 6 = C × M 4. This is done by an investigation of the free tensor multiplet on the level of equations of motion, where the problem of its formulation in Euclidean signature is circumvented by letting the time-like direction lie in the two-manifold C and performing a topological twist along M 4 alone. A compactification on C is shown to be necessary to enable the possibility of finding a topological field theory. The hypothetical twist along a Euclidean C is argued to amount to the correct choice of linear combination of the two supercharges scalar on M 4. This procedure is expected and conjectured to result in a topological field theory, but we arrive at the surprising conclusion that this twisted theory contains no Q-exact and covariantly conserved stress tensor unless M 4 has vanishing curvature. This is to our knowledge a phenomenon which has not been observed before in topological field theories. In the literature, the setup of the twisting used here has been suggested as the origin of the conjectured AGT-correspondence, and our hope is that this work may somehow contribute to the understanding of it.

  10. Comments on twisted indices in 3d supersymmetric gauge theories

    NASA Astrophysics Data System (ADS)

    Closset, Cyril; Kim, Heeyeon

    2016-08-01

    We study three-dimensional {N} = 2 supersymmetric gauge theories on Σ g × S 1 with a topological twist along Σ g , a genus- g Riemann surface. The twisted supersymmetric index at genus g and the correlation functions of half-BPS loop operators on S 1 can be computed exactly by supersymmetric localization. For g = 1, this gives a simple UV computation of the 3d Witten index. Twisted indices provide us with a clean derivation of the quantum algebra of supersymmetric Wilson loops, for any Yang-Mills-Chern-Simons-matter theory, in terms of the associated Bethe equations for the theory on {{R}}^2× {S}^1 . This also provides a powerful and simple tool to study 3d {N} = 2 Seiberg dualities. Finally, we study A- and B-twisted indices for {N} = 4 supersymmetric gauge theories, which turns out to be very useful for quantitative studies of three-dimensional mirror symmetry. We also briefly comment on a relation between the S 2 × S 1 twisted indices and the Hilbert series of {N} = 4 moduli spaces.

  11. Curvature regulation of the ciliary beat through axonemal twist

    NASA Astrophysics Data System (ADS)

    Sartori, Pablo; Geyer, Veikko F.; Howard, Jonathon; Jülicher, Frank

    2016-10-01

    Cilia and flagella are hairlike organelles that propel cells through fluid. The active motion of the axoneme, the motile structure inside cilia and flagella, is powered by molecular motors of the axonemal dynein family. These motors generate forces and torques that slide and bend the microtubule doublets within the axoneme. To create regular waveforms, the activities of the dyneins must be coordinated. It is thought that coordination is mediated by stresses due to radial, transverse, or sliding deformations, and which build up within the moving axoneme and feed back on dynein activity. However, which particular components of the stress regulate the motors to produce the observed waveforms of the many different types of flagella remains an open question. To address this question, we describe the axoneme as a three-dimensional bundle of filaments and characterize its mechanics. We show that regulation of the motors by radial and transverse stresses can lead to a coordinated flagellar motion only in the presence of twist. We show that twist, which could arise from torque produced by the dyneins, couples curvature to transverse and radial stresses. We calculate emergent beating patterns in twisted axonemes resulting from regulation by transverse stresses. The resulting waveforms are similar to those observed in flagella of Chlamydomonas and sperm. Due to the twist, the waveform has nonplanar components, which result in swimming trajectories such as twisted ribbons and helices, which agree with observations.

  12. Probing Viscoelasticity of Cholesteric Liquid Crystals in a Twisting Cell

    NASA Astrophysics Data System (ADS)

    Angelo, Joseph; Moheghi, Alireza; Diorio, Nick; Jakli, Antal

    2013-03-01

    Viscoelastic properties of liquid crystals are typically studied either using Poiseuille flow, which can be produced by a pressure gradient in a capillary tube,[2] or Couette flow, which can be generated by a shear between concentric cylinders.[3] We use a different method in which we twist the liquid crystal sandwiched between two cylindrical glass plates, one of which can rotate about its center, the other of which is fixed. When the cell is twisted, there is a force proportional to the twist angle and the twist elastic constant, and inversely proportional to the pitch and sample thickness, normal to the substrates due to the change in pitch in the cholesteric liquid crystal (CLC). Measuring this force on various CLCs with known pitch we could obtain the twist elastic constants. In addition to the equilibrium force, we observed a transient force during the rotation, which is related to the flow of the material, thus allowing us to determine the Leslie viscosity component α1, which typically cannot be assessed by other methods. We expect this apparatus to be a useful tool to study the visco-elastic properties of liquid crystals. The authors acknowledge support from NSF grant DMR-0907055.

  13. AKT-ions with a TWIST between EMT and MET

    PubMed Central

    Tang, Huifang; Massi, Daniela; Hemmings, Brian A.; Mandalà, Mario; Hu, Zhengqiang; Wicki, Andreas; Xue, Gongda

    2016-01-01

    The transcription factor Twist is an important regulator of cranial suture during embryogenesis. Closure of the neural tube is achieved via Twist-triggered cellular transition from an epithelial to mesenchymal phenotype, a process known as epithelial-mesenchymal transition (EMT), characterized by a remarkable increase in cell motility. In the absence of Twist activity, EMT and associated phenotypic changes in cell morphology and motility can also be induced, albeit moderately, by other transcription factor families, including Snail and Zeb. Aberrant EMT triggered by Twist in human mammary tumour cells was first reported to drive metastasis to the lung in a metastatic breast cancer model. Subsequent analysis of many types of carcinoma demonstrated overexpression of these unique EMT transcription factors, which statistically correlated with worse outcome, indicating their potential as biomarkers in the clinic. However, the mechanisms underlying their activation remain unclear. Interestingly, increasing evidence indicates they are selectively activated by distinct intracellular kinases, thereby acting as downstream effectors facilitating transduction of cytoplasmic signals into nucleus and reprogramming EMT and mesenchymal-epithelial transition (MET) transcription to control cell plasticity. Understanding these relationships and emerging data indicating differential phosphorylation of Twist leads to complex and even paradoxical functionalities, will be vital to unlocking their potential in clinical settings. PMID:27623213

  14. Non-Euclidean geometry of twisted filament bundle packing

    PubMed Central

    Bruss, Isaac R.; Grason, Gregory M.

    2012-01-01

    Densely packed and twisted assemblies of filaments are crucial structural motifs in macroscopic materials (cables, ropes, and textiles) as well as synthetic and biological nanomaterials (fibrous proteins). We study the unique and nontrivial packing geometry of this universal material design from two perspectives. First, we show that the problem of twisted bundle packing can be mapped exactly onto the problem of disc packing on a curved surface, the geometry of which has a positive, spherical curvature close to the center of rotation and approaches the intrinsically flat geometry of a cylinder far from the bundle center. From this mapping, we find the packing of any twisted bundle is geometrically frustrated, as it makes the sixfold geometry of filament close packing impossible at the core of the fiber. This geometrical equivalence leads to a spectrum of close-packed fiber geometries, whose low symmetry (five-, four-, three-, and twofold) reflect non-Euclidean packing constraints at the bundle core. Second, we explore the ground-state structure of twisted filament assemblies formed under the influence of adhesive interactions by a computational model. Here, we find that the underlying non-Euclidean geometry of twisted fiber packing disrupts the regular lattice packing of filaments above a critical radius, proportional to the helical pitch. Above this critical radius, the ground-state packing includes the presence of between one and six excess fivefold disclinations in the cross-sectional order. PMID:22711799

  15. Eshelby twist and correlation effects in diffraction from nanocrystals

    SciTech Connect

    Leonardi, A.; Scardi, P.; Ryu, S.; Pugno, N. M.

    2015-04-28

    Molecular dynamics simulations were used to model the Eshelby dislocation inside Pd and Ir nanowires and to predict the powder diffraction pattern using the Debye scattering equation. We find that the ideal dislocation solution by Eshelby is in good agreement with the observed twist angle and deviatoric strain, even though it ignores both the splitting of the Eshelby dislocation into two partials and surface stress. Surface stress plays a significant role only for nanorods with small aspect ratio (∼1:1). We also find that Wilson's prediction on the diffraction peak broadening for the Eshelby dislocation is overestimated because it ignores the fact that the Eshelby twist relaxes the deviatoric strain. Moreover, the twist loosens the correlation along the nanorod, causing additional line profile broadening, which is read by diffraction as a decrease of coherent domain size when the total twist angle is bigger than 1.5°. Overall, our findings suggest a novel way to predict and analyze the dislocations as well as the resulting strain fields in the twisted nanocrystalline rods.

  16. "Twisted Beam" SEE Observations of Ionospheric Heating from HAARP

    NASA Astrophysics Data System (ADS)

    Briczinski, S. J.; Bernhardt, P. A.; Siefring, C. L.; Han, S.-M.; Pedersen, T. R.; Scales, W. A.

    2015-10-01

    Nonlinear interactions of high power HF radio waves in the ionosphere provide aeronomers with a unique space-based laboratory capability. The High-Frequency Active Auroral Research Program (HAARP) in Gakona, Alaska is the world's largest heating facility, yielding effective radiated powers in the gigawatt range. New results are present from HAARP experiments using a "twisted beam" excitation mode. Analysis of twisted beam heating shows that the SEE results obtained are identical to more traditional patterns. One difference in the twisted beam mode is the heating region produced is in the shape of a ring as opposed to the more traditional "solid spot" region from a pencil beam. The ring heating pattern may be more conducive to the creation of stable artificial airglow layers because of the horizontal structure of the ring. The results of these runs include artificial layer creation and evolution as pertaining to the twisted beam pattern. The SEE measurements aid the interpretation of the twisted beam interactions in the ionosphere.

  17. The Equivariant Cohomology Theory of Twisted Generalized Complex Manifolds

    NASA Astrophysics Data System (ADS)

    Lin, Yi

    2008-07-01

    It has been shown recently by Kapustin and Tomasiello that the mathematical notion of Hamiltonian actions on twisted generalized Kähler manifolds is in perfect agreement with the physical notion of general (2, 2) gauged sigma models with three-form fluxes. In this article, we study the twisted equivariant cohomology theory of Hamiltonian actions on H-twisted generalized complex manifolds. If the manifold satisfies the {overline{partial} partial}-lemma, we establish the equivariant formality theorem. If in addition, the manifold satisfies the generalized Kähler condition, we prove the Kirwan injectivity in this setting. We then consider the Hamiltonian action of a torus on an H-twisted generalized Calabi-Yau manifold and extend to this case the Duistermaat-Heckman theorem for the push-forward measure. As a side result, we show in this paper that the generalized Kähler quotient of a generalized Kähler vector space can never have a (cohomologically) non-trivial twisting. This gives a negative answer to a question asked by physicists whether one can construct (2, 2) gauged linear sigma models with non-trivial fluxes.

  18. Longitudinal magnetization loss in twisted multifilamentary Bi2223 tape

    NASA Astrophysics Data System (ADS)

    Amemiya, N.; Rabbers, J.-J.; Krooshoop, B. E.; ten Haken, B.; ten Kate, H.; Ayai, N.; Hayashi, K.

    2002-08-01

    Multifilamentary Bi2223 tapes are exposed to the longitudinal magnetic field as well as the transverse one in some electrical power apparatuses such as multilayer power transmission cables. Here, we define the longitudinal and transverse magnetic fields as the field components parallel and perpendicular to the tape axis, respectively. If the filament-bundle is twisted, it can couple to the AC longitudinal magnetic field to generate the longitudinal magnetization loss. Furthermore, the AC transport current flowing spirally in the twisted filament-bundle possibly influences the longitudinal magnetization. The longitudinal magnetization loss was measured in a twisted multifilamentary Bi2223 tape exposed to longitudinal magnetic field and carrying the transport current. The measured longitudinal magnetization loss in the twisted tape exposed to the longitudinal magnetic field is larger than that in another untwisted tape. Supplying the AC transport current changes the longitudinal magnetization loss in the twisted tape exposed to the AC longitudinal magnetic field. The influence of the transport current depends on the phase relation between the longitudinal magnetic field and the transport current. If their phase difference is 0°, the longitudinal magnetization loss decreases remarkably with increasing amplitude of the transport current. It means that the change in the current distribution due to the transport current results in the decrease in the power flow from the magnet power supply. But, a preliminary measurement of the transport loss shows that the total loss increases with increasing transport current.

  19. Curvature regulation of the ciliary beat through axonemal twist.

    PubMed

    Sartori, Pablo; Geyer, Veikko F; Howard, Jonathon; Jülicher, Frank

    2016-10-01

    Cilia and flagella are hairlike organelles that propel cells through fluid. The active motion of the axoneme, the motile structure inside cilia and flagella, is powered by molecular motors of the axonemal dynein family. These motors generate forces and torques that slide and bend the microtubule doublets within the axoneme. To create regular waveforms, the activities of the dyneins must be coordinated. It is thought that coordination is mediated by stresses due to radial, transverse, or sliding deformations, and which build up within the moving axoneme and feed back on dynein activity. However, which particular components of the stress regulate the motors to produce the observed waveforms of the many different types of flagella remains an open question. To address this question, we describe the axoneme as a three-dimensional bundle of filaments and characterize its mechanics. We show that regulation of the motors by radial and transverse stresses can lead to a coordinated flagellar motion only in the presence of twist. We show that twist, which could arise from torque produced by the dyneins, couples curvature to transverse and radial stresses. We calculate emergent beating patterns in twisted axonemes resulting from regulation by transverse stresses. The resulting waveforms are similar to those observed in flagella of Chlamydomonas and sperm. Due to the twist, the waveform has nonplanar components, which result in swimming trajectories such as twisted ribbons and helices, which agree with observations.

  20. Twinning and twisting of tri- and bilayer graphene.

    PubMed

    Brown, Lola; Hovden, Robert; Huang, Pinshane; Wojcik, Michal; Muller, David A; Park, Jiwoong

    2012-03-14

    The electronic, optical, and mechanical properties of bilayer and trilayer graphene vary with their structure, including the stacking order and relative twist, providing novel ways to realize useful characteristics not available to single layer graphene. However, developing controlled growth of bilayer and trilayer graphene requires efficient large-scale characterization of multilayer graphene structures. Here, we use dark-field transmission electron microscopy for rapid and accurate determination of key structural parameters (twist angle, stacking order, and interlayer spacing) of few-layer CVD graphene. We image the long-range atomic registry for oriented bilayer and trilayer graphene, find that it conforms exclusively to either Bernal or rhombohedral stacking, and determine their relative abundances. In contrast, our data on twisted multilayers suggest the absence of such long-range atomic registry. The atomic registry and its absence are consistent with the two different strain-induced deformations we observe; by tilting the samples to break mirror symmetry, we find a high density of twinned domains in oriented multilayer graphene, where multiple domains of two different stacking configurations coexist, connected by discrete twin boundaries. In contrast, individual layers in twisted regions continuously stretch and shear independently, forming elaborate Moiré patterns. These results, and the twist angle distribution in our CVD graphene, can be understood in terms of an angle-dependent interlayer potential model.