Science.gov

Sample records for aspect ratio tokamaks

  1. A low aspect ratio tokamak transmutation system

    NASA Astrophysics Data System (ADS)

    Qiu, L. J.; Wu, Y. C.; Xiao, B. J.; Xu, Q.; Huang, Q. Y.; Wu, B.; Chen, Y. X.; Xu, W. N.; Chen, Y. P.; Liu, X. P.

    2000-03-01

    A low aspect ratio tokamak transmutation system is proposed as an alternative application of fusion energy on the basis of a review of previous studies. This system includes: (1) a low aspect ratio tokamak as fusion neutron driver, (2) a radioactivity-clean nuclear power system as blanket, and (3) a novel concept of liquid metal centre conductor post as part of the toroidal field coils. In the conceptual design, a driver of 100 MW fusion power under 1 MW/m2 neutron wall loading can transmute the amount of high level waste (including minor actinides and fission products) produced by ten standard pressurized water reactors of 1 GW electrical power output. Meanwhile, the system can produce tritium on a self-sustaining basis and an output of about 2 GW of electrical energy. After 30 years of operation, the biological hazard potential level of the whole system will decrease by two orders of magnitude.

  2. Heavy ion beam probe systems for tight aspect ratio tokamaks

    SciTech Connect

    Melnikov, A.V.; Zimeleva, L.G.; Krupnik, L.I.; Nedzelskij, I.S.; Trofimenko, Y.V.; Minaev, V.B.

    1997-01-01

    We discuss the specific features of the application of heavy ion beam probe (HIBP) systems to tight aspect ratio tokamaks. We present and compare the HIBP projects for the TUMAN-3, GLOBUS, and COMPASS, where the inner part of the plasma is not available for regular chord diagnostics, so the HIBP becomes very desirable. All existing tight aspect ratio facilities and projects have a low (less than 1.9 T) toroidal field that requires a comparatively low beam energy range. The natural elongation and triangularity in tight aspect ratio tokamaks require an accurate calculation of the three-dimensional magnetic field for probing optimization. In comparison with traditional tokamaks, the detector grids have a wider energy interval. In general, the trajectories and detector grids for tight aspect ratio tokamaks become similar to the stellarator ones. Traditional and new probing schemes are suggested and discussed. {copyright} {ital 1997 American Institute of Physics.}

  3. Omniclassical Diffusion in Low Aspect Ratio Tokamaks

    SciTech Connect

    H.E. Mynick; R.B. White; D.A. Gates

    2004-03-19

    Recently reported numerical results for axisymmetric devices with low aspect ratio A found radial transport enhanced over the expected neoclassical value by a factor of 2 to 3. In this paper, we provide an explanation for this enhancement. Transport theory in toroidal devices usually assumes large A, and that the ratio B{sub p}/B{sub t} of the poloidal to the toroidal magnetic field is small. These assumptions result in transport which, in the low collision limit, is dominated by banana orbits, giving the largest collisionless excursion of a particle from an initial flux surface. However in a small aspect ratio device one may have B{sub p}/B{sub t} {approx} 1, and the gyroradius may be larger than the banana excursion. Here, we develop an approximate analytic transport theory valid for devices with arbitrary A. For low A, we find that the enhanced transport, referred to as omniclassical, is a combination of neoclassical and properly generalized classical effects, which become dominant in the low-A, B{sub p}/B{sub t} {approx} 1 regime. Good agreement of the analytic theory with numerical simulations is obtained.

  4. Stability of high. beta. large aspect ratio tokamaks

    SciTech Connect

    Cowley, S.C.

    1991-10-01

    High {beta}({beta}{much gt} {epsilon}/q{sup 2}) large aspect ratio ({epsilon} {much gt} 1) tokamak equilibria are shown to be always stable to ideal M.H.D. modes that are localized about a flux surface. Both the ballooning and interchange modes are shown to be stable. This work uses the analytic high {beta} large aspect ratio tokamak equilibria developed by Cowley et.al., which are valid for arbitrary pressure and safety factor profiles. The stability results make no assumption about these profiles or the shape of the boundary. 14 refs., 4 figs.

  5. Prospects and status of low-aspect-ratio tokamaks

    SciTech Connect

    Peng, Y.K.M.

    1994-12-31

    The prospects for the low-aspect-ratio (A) tokamak to fulfill the requirements of viable fusion power plants are considered relative to the present status in data and modeling. Desirable physics and design features for an attractive Blanket Test Facility and power reactors are estimated for low-A tokamaks based on calculations improved with the latest data from small pioneering experiments. While these experiments have confirmed some of the recent predictions for low-A, they also identify the remaining issues that require verification before reliable projections can be made for these deuterium-tritium applications. The results show that the low-A regime of small size, modest field, and high current offers a path complementary to the standard and high A tokamaks in developing the full potential of fusion power.

  6. Configuration studies for a small-aspect-ratio tokamak stellarator hybrid

    SciTech Connect

    Carreras, B.A.; Lynch, V.E.; Ware, A.

    1996-08-01

    The use of modulated toroidal coils offers a new path to the tokamak-stellarator hybrids. Low-aspect-ratio configurations can be found with robust vacuum flux surfaces and rotational transform close to the transform of a reverse-shear tokamak. These configurations have clear advantages in minimizing disruptions and their effect and in reducing tokamak current drive needs. They also allow the study of low-aspect-ratio effects on stellarator confinement in small devices.

  7. Physics Studies of a Proposed Small Aspect Ratio Torsatron-Tokamak Hybrid

    NASA Astrophysics Data System (ADS)

    Valanju, P. M.; Gentle, K. W.; McCool, S.; Miner, W. H., Jr.; Ross, D. W.; Wiley, J. C.; Wootton, A. J.

    1996-11-01

    Physics studies of a proposed small aspect ratio torsatron-tokamak hybrid (SMARTH) are presented. This small aspect ratio configuration attempts to remedy a major drawback of conventional stellarator reactors, viz. the large volume resulting from the large aspect ratio. Considering a small aspect ratio machine with 8 field periods (m=8) and with 8 or 16 modular coils, we investigate vacuum configurations and MHD equilibria to determine the optimum configuration which produces large rotational transform, large plasma volume, large beta, and small field ripple. Implications for particle confinement will also be discussed. Effects of radial electric fields on orbit losses and confinement will also be explored.

  8. All Metal Iron Core For A Low Aspect Ratio Tokamak

    SciTech Connect

    D.A. Gates, C. Jun, I. Zatz, A. Zolfaghari

    2010-06-02

    A novel concept for incorporating a iron core transformer within a axisymmetric toroidal plasma containment device with a high neutron flux is described. This design enables conceptual design of low aspect ratio devices which employ standard transformer-driven plasma startup by using all-metal high resistance separators between the toroidal field windings. This design avoids the inherent problems of a multiturn air core transformer which will inevitably suffer from strong neutron bombardment and hence lose the integrity of its insulation, both through long term material degradation and short term neutron- induced conductivity.. A full 3-dimensional model of the concept has been developed within the MAXWELL program and the resultant loop voltage calculated. The utility of the result is found to be dependent on the resistivity of the high resistance separators. Useful loop voltage time histories have been obtained using achievable resistivities.

  9. Characterization of peeling modes in a low aspect ratio tokamak

    NASA Astrophysics Data System (ADS)

    Bongard, M. W.; Thome, K. E.; Barr, J. L.; Burke, M. G.; Fonck, R. J.; Hinson, E. T.; Redd, A. J.; Schlossberg, D. J.

    2014-11-01

    Peeling modes are observed at the plasma edge in the Pegasus Toroidal Experiment under conditions of high edge current density (Jedge ˜ 0.1 MA m-2) and low magnetic field (B ˜ 0.1 T) present at near-unity aspect ratio. Their macroscopic properties are measured using external Mirnov coil arrays, Langmuir probes and high-speed visible imaging. The modest edge parameters and short pulse lengths of Pegasus discharges permit direct measurement of the internal magnetic field structure with an insertable array of Hall-effect sensors, providing the current profile and its temporal evolution. Peeling modes generate coherent, edge-localized electromagnetic activity with low toroidal mode numbers n ⩽ 3 and high poloidal mode numbers, in agreement with theoretical expectations of a low-n external kink structure. Coherent MHD fluctuation amplitudes are found to be strongly dependent on the experimentally measured Jedge/B peeling instability drive, consistent with theory. Peeling modes nonlinearly generate ELM-like, field-aligned filamentary structures that detach from the edge and propagate radially outward. The KFIT equilibrium code is extended with an Akima spline profile parameterization and an improved model for induced toroidal wall current estimation to obtain a reconstruction during peeling activity with its current profile constrained by internal Hall measurements. It is used to test the analytic peeling stability criterion and numerically evaluate ideal MHD stability. Both approaches predict instability, in agreement with experiment, with the latter identifying an unstable external kink.

  10. Transmutation of nuclear waste with a low-aspect-ratio tokamak neutron source

    NASA Astrophysics Data System (ADS)

    Hong, Bong Guen; Moon, Se Youn

    2014-10-01

    The transmutation characteristics of transuranics (TRUs) in a transmutation reactor based on a LAR (Low-aspect-ratio) tokamak as a neutron source are investigated. The optimum radial build of a transmutation reactor is found by using a coupled analysis of the tokamak systems and the neutron transport. The dependences of the transmutation characteristics on the aspect ratio A in the range of 1.5 to 2.5 and on the fusion power in the range of 150 to 500 MW are investigated. An equilibrium fuel cycle is developed for effective transmutation, and show that with one unit of the transmutation reactor based on the LAR tokamak producing fusion power in the range of a few hundred MWs, up to 3 PWRs (1.0 GWe capacity) can be supported with a burn-up fraction larger than 50%.

  11. Global gyrokinetic stability of collisionless microtearing modes in large aspect ratio tokamaks

    SciTech Connect

    Swamy, Aditya K.; Ganesh, R.; Chowdhury, J.; Brunner, S.; Vaclavik, J.; Villard, L.

    2014-08-15

    Linear full radius gyrokinetic calculations show the existence of unstable microtearing modes (MTMs) in purely collisionless, high temperature, large aspect ratio tokamak plasmas. The present study takes into account fully gyrokinetic highly passing ions and electrons. The global 2-D structures of the collisionless mode with full radius coupling of the poloidal modes is obtained and compared with another electromagnetic mode, namely, the Alfvén Ion Temperature Gradient (AITG) mode (or Kinetic Ballooning Mode, KBM) for the same equilibrium profile. Several important characteristics of the modes are brought out and compared, such as a clear signature in the symmetry properties of the two modes, the plasma–β dependence, and radial and poloidal length scales of the electrostatic and magnetic vector potential fluctuations. Extensive parameter scans for this collisionless microtearing mode reveal the scaling of the growth rate with β and the electron temperature gradient η{sub e}. Scans at different β values show an inverse relationship between the η{sub e} threshold and β, leading to a stability diagram, and implying that the mode might exist at moderate to strong temperature gradients for finite β plasmas in large aspect ratio tokamaks. In contrast to small aspect ratio tokamaks where the trapped electron magnetic drift resonance is found to be important, in large aspect ratio tokamaks, a strong destabilization due to the magnetic drift resonance of passing electrons is observed and is identified as a possible collisionless drive mechanism for the collisionless MTM.

  12. A Novel Demountable TF Joint Design for Low Aspect Ratio Spherical Torus Tokamaks

    SciTech Connect

    R.D. Woolley

    2009-05-29

    A novel shaped design for the radial conductors and demountable electrical joints connecting inner and outer legs of copper TF system conductors in low aspect ratio tokamaks is described and analysis results are presented. Specially shaped designs can optimize profiles of electrical current density, magnetic force, heating, and mechanical stress.

  13. A Novel Demountable TF Joint Design for Low Aspect Ratio Spherical Torus Tokamaks

    SciTech Connect

    Robert D. Woolley

    2009-06-11

    A novel shaped design for the radial conductors and demountable electrical joints connecting inner and outer legs of copper TF system conductors in low aspect ratio tokamaks is described and analysis results are presented. Specially shaped designs can optimize profiles of electrical current density, magnetic force, heating, and mechanical stress.

  14. Transport theory for energetic alpha particles in finite aspect ratio tokamaks with broken symmetry

    NASA Astrophysics Data System (ADS)

    Shaing, K. C.; Schlutt, M.; Lai, A. L.

    2016-02-01

    Transport theory for the energetic alpha particles in finite aspect ratio tokamaks with broken symmetry is developed for the case where the slowing down collision operator dominates. The transport fluxes in the 1 /ν and superbanana plateau regimes are derived. Here, ν is the typical collision frequency. They can be used in modeling the energy loss of the alpha particles in thermonuclear fusion reactors. Numerical realizations of the superbanana orbits of alpha particles in tokamaks with broken symmetry are also presented. The existence of the superbananas corroborates the predictions of the theories presented here and elsewhere.

  15. Corrected Formulation for Estimation of Ripple in Large Aspect Ratio Tokamaks

    NASA Astrophysics Data System (ADS)

    Dini, F.; Khorasani, S.

    2012-04-01

    The finite number of toroidal field coils of a tokamak destroys the perfect axisymmetry of the device. The coils produce a short wavelength ripple in the toroidal magnetic field strength as a field line follows round the torus, which becomes important in transport and confinement properties of plasma. Hence, a quick and accurate estimation of ripple becomes important. We have noticed that a previously reported analytical formulation by Princeton Plasma Physics Laboratory team is not applicable to our large aspect ratio tokamak, and have devised a slightly modified form which has greatly improved the accuracy of the analytical fit.

  16. Configuration, Equilibrium, and Stability Studies for a Small-Aspect-Ratio Tokamak Stellarator Hybrid

    NASA Astrophysics Data System (ADS)

    Ware, A. S.; Batchelor, D. B.; Carreras, B. A.; Hirshman, S. P.; Leboeuf, J. N.; Lynch, V. E.; Whitson, J.

    1996-11-01

    A new class of small-aspect-ratio tokamak stellarator hybrids using modulated toroidal field coils(B. A. Carreras, et al, ORNL/TM-13252 (1996).) is investigated. A comprehensive study is underway to diagnose the vacuum, equilibrium, transport,(D. A. Spong, et al, this meeting.) and stability properties of these devices. These configurations have advantages in minimizing disruptions and reducing tokamak current drive needs, but they must also be optimized to reduce the amount of ripple transport and increase β_critical. Vacuum configurations have been found with robust flux surfaces and rotational transform close to that of a reverse-shear tokamak. With finite plasma current, equilibriums with <β > ~ 9% have been obtained. Results of these configuration and equilibrium studies will be reported along with initial stability studies using a 3D-ballooning code.

  17. Flow shear induced fluctuation suppression in finite aspect ratio shaped tokamak plasma

    SciTech Connect

    Hahm, T.S.; Burrell, K.H.

    1995-01-01

    The suppression of turbulence by the E {times} B flow shear and parallel flow shear is studied in an arbitrary shape finite aspect ratio tokamak plasma using the two point nonlinear analysis previously utilized in a high aspect rat& tokamak plasma. The result shows that only the E {times} B flow shear is responsible for the suppression of flute-like fluctuations. This suppression occurs regardless of the plasma rotation direction and is therefore, relevant for the VH mode plasma core as well as for the H mode plasma edge. Experimentally observed in-out asymmetry of fluctuation reduction behavior can be addressed in the context of flux expansion and magnetic field pitch variation on a given flux surface. The adverse effect of neutral particles on confinement improvement is also discussed in the context of the charge exchange induced parallel momentum damping.

  18. First results from the small tight aspect ratio tokamak multifrequency pulse radar reflectometer

    SciTech Connect

    Shevchenko, V.F.; Walsh, M.J.

    1997-05-01

    A multifrequency pulse radar reflectometer (PRR) has been designed, commissioned, and is operating successfully on the small tight aspect ratio tokamak (START). The data obtained with this technique allow the study of the density profile evolution during the shot, revealing aspects of the plasma behavior during such events as the internal reconnection. A simple and effective profile-reconstruction algorithm using the stepwise profile approximation permits the monitoring of the plasma density profile immediately after each shot. Cross checks between the START hydrogen cyanide (HCN) interferometer and the line integral density determined by integrating the PRR generated data shows good agreement. {copyright} {ital 1997 American Institute of Physics.}

  19. First results from the small tight aspect ratio tokamak multifrequency pulse radar reflectometer

    NASA Astrophysics Data System (ADS)

    Shevchenko, V. F.; Walsh, M. J.

    1997-05-01

    A multifrequency pulse radar reflectometer (PRR) has been designed, commissioned, and is operating successfully on the small tight aspect ratio tokamak (START). The data obtained with this technique allow the study of the density profile evolution during the shot, revealing aspects of the plasma behavior during such events as the internal reconnection. A simple and effective profile-reconstruction algorithm using the stepwise profile approximation permits the monitoring of the plasma density profile immediately after each shot. Cross checks between the START hydrogen cyanide (HCN) interferometer and the line integral density determined by integrating the PRR generated data shows good agreement.

  20. Neoclassical toroidal plasma viscosity with effects of finite banana width for finite aspect ratio tokamaks

    NASA Astrophysics Data System (ADS)

    Shaing, K. C.; Sabbagh, S. A.

    2016-07-01

    Theory for neoclassical toroidal plasma viscosity has been developed to model transport phenomena, especially, toroidal plasma rotation for tokamaks with broken symmetry. Theoretical predictions are in agreement with the results of the numerical codes in the large aspect ratio limit. The theory has since been extended to include effects of finite aspect ratio and finite plasma β. Here, β is the ratio of the plasma thermal pressure to the magnetic field pressure. However, there are cases where the radial wavelength of the self-consistent perturbed magnetic field strength B on the perturbed magnetic surface is comparable to the width of the trapped particles, i.e., bananas. To accommodate those cases, the theory for neoclassical toroidal plasma viscosity is further extended here to include the effects of the finite banana width. The extended theory is developed using the orbit averaged drift kinetic equation in the low collisionality regimes. The results of the theory can now be used to model plasma transport, including toroidal plasma rotation, in real finite aspect ratio, and finite plasma β tokamaks with the radial wavelength of the perturbed symmetry breaking magnetic field strength comparable to or longer than the banana width.

  1. High Confinement Mode and Edge Localized Mode Characteristics in a Near-Unity Aspect Ratio Tokamak.

    PubMed

    Thome, K E; Bongard, M W; Barr, J L; Bodner, G M; Burke, M G; Fonck, R J; Kriete, D M; Perry, J M; Schlossberg, D J

    2016-04-29

    Tokamak experiments at near-unity aspect ratio A≲1.2 offer new insights into the self-organized H-mode plasma confinement regime. In contrast to conventional A∼3 plasmas, the L-H power threshold P_{LH} is ∼15× higher than scaling predictions, and it is insensitive to magnetic topology, consistent with modeling. Edge localized mode (ELM) instabilities shift to lower toroidal mode numbers as A decreases. These ultralow-A operations enable heretofore inaccessible J_{edge}(R,t) measurements through an ELM that show a complex multimodal collapse and the ejection of a current-carrying filament. PMID:27176526

  2. High Confinement Mode and Edge Localized Mode Characteristics in a Near-Unity Aspect Ratio Tokamak

    NASA Astrophysics Data System (ADS)

    Thome, K. E.; Bongard, M. W.; Barr, J. L.; Bodner, G. M.; Burke, M. G.; Fonck, R. J.; Kriete, D. M.; Perry, J. M.; Schlossberg, D. J.

    2016-04-01

    Tokamak experiments at near-unity aspect ratio A ≲1.2 offer new insights into the self-organized H -mode plasma confinement regime. In contrast to conventional A ˜3 plasmas, the L -H power threshold PL H is ˜15 × higher than scaling predictions, and it is insensitive to magnetic topology, consistent with modeling. Edge localized mode (ELM) instabilities shift to lower toroidal mode numbers as A decreases. These ultralow-A operations enable heretofore inaccessible Jedge(R ,t ) measurements through an ELM that show a complex multimodal collapse and the ejection of a current-carrying filament.

  3. High confinement mode and edge localized mode characteristics in a near-unity aspect ratio tokamak

    DOE PAGESBeta

    Thome, Kathreen E.; Bongard, Michael W.; Barr, Jayson L.; Bodner, Grant M.; Burke, Marcus G.; Fonck, Raymond J.; Kriete, David M.; Perry, Justin M.; Schlossberg, David J.

    2016-04-27

    Tokamak experiments at near-unity aspect ratio A ≲ 1.2 offer new insights into the self-organized H-mode plasma confinement regime. In contrast to conventional A ~ 3 plasmas, the L–H power threshold PLH is ~15× higher than scaling predictions, and it is insensitive to magnetic topology, consistent with modeling. Edge localized mode (ELM) instabilities shift to lower toroidal mode numbers as A decreases. Furthermore, these ultralow-A operations enable heretofore inaccessible Jedge(R,t) measurements through an ELM that show a complex multimodal collapse and the ejection of a current-carrying filament.

  4. Free boundary, high beta equilibrium in a large aspect ratio tokamak with nearly circular plasma boundary

    SciTech Connect

    Qin, H.; Reiman, A.

    1996-09-25

    An analytic solution is obtained for free-boundary, high-beta equilibria in large aspect ratio tokamaks with a nearly circular plasma boundary. In the absence of surface currents at the plasma-vacuum interface, the free-boundary equilibrium solution introduces constraints arising from the need to couple to an external vacuum field which is physically realizable with a reasonable set of external field coils. This places a strong constraint on the pressure profiles that are consistent with a given boundary shape at high {epsilon}{beta}{sub p}. The equilibrium solution also provides information on the flux surface topology. The plasma is bounded by a separatrix. Increasing the plasma pressure at fixed total current causes the plasma aperture to decrease in a manner that is described.

  5. Shaping of the plasma column in a small aspect ratio tokamak

    NASA Astrophysics Data System (ADS)

    Herrera, Julio; Arroyo, Ismael; Chavez, Esteban

    2015-11-01

    This is a follow-up to the work presented in last year's meeting, on the conceptual design of a small aspect ratio tokamak of variable configuration. The base parameters for this device would be similar to those in the START tokamak. The shaping of the plasma column is known to have important effects in the plasma performance, including the value of β, bootstrap currents, and intrinsic rotation. The main feature being explored here is the inclusion of independent control coils in the inboard and outboard sides; six in the first case, and up to seven in the latter. By varying the strength in their currents it is possible to achieve a wide variety of shapes: elliptical, conventional D-shape, inverse D-shape, and Bean-shape. As the control coils are activated, the strength of the toroidal magnetic field needs to he weakened, in order to keep reasonable values of the safety factor q . The study presented here is made by means of the 3D-MAPTOR code, which produces the Poincaré maps of the magnetic field lines, given the currents. For this purpose, a seed plasma current must be provided. All studies presented here assume equatorial symmetry, due to limitations in the code.

  6. Collisionless microtearing modes in large aspect ratio Tokamaks with weak reversed shear configurations

    NASA Astrophysics Data System (ADS)

    Krishna Swamy, Aditya; Ganesh, Rajaraman; Brunner, Stephan; Vaclavik, Jan; Villard, Laurent

    2015-11-01

    Gyrokinetic simulations have found Collisionless Microtearing Modes (MTM) to be linearly unstable in sharp temperature gradient regions of tokamaks, typically with high magnetic shear. The collisionless MTM is driven by the magnetic drift resonance of passing electrons, aided by the closeness of Mode Rational Surfaces (MRS) arising due to the high shear. Here, the role of global safety factor profile variation on the MTM instability and global mode structure is studied, in particular in weak reverse shear (WRS) configurations in large aspect ratio tokamaks. At lower shear profiles, multiple MTM branches are found with tearing parity as well as mixed parity. The linear growth rates of MTM is found to be weakened and linearly unstable modes are found whose global mode structures of φ~ and Ã∥ exhibit Mixed Parity. For the same equilibrium profiles and parameters, AITG instability is also studied and global mode structures are compared with MTM. The growth rate spectrum is found to extend to shorter/mesoscale wavelengths in WRS. Several other characteristics of MTMs and AITG are recovered in the WRS configuration, such as the dependency on free energy source and on plasma β.

  7. Advanced Fuels Reactor using Aneutronic Rodless Ultra Low Aspect Ratio Tokamak Hydrogenic Plasmas

    NASA Astrophysics Data System (ADS)

    Ribeiro, Celso

    2015-11-01

    The use of advanced fuels for fusion reactor is conventionally envisaged for field reversed configuration (FRC) devices. It is proposed here a preliminary study about the use of these fuels but on an aneutronic Rodless Ultra Low Aspect Ratio (RULART) hydrogenic plasmas. The idea is to inject micro-size boron pellets vertically at the inboard side (HFS, where TF is very high and the tokamak electron temperature is relatively low because of profile), synchronised with a proton NBI pointed to this region. Therefore, p-B reactions should occur and alpha particles produced. These pellets will act as an edge-like disturbance only (cp. killer pellet, although the vertical HFS should make this less critical, since the unablated part should appear in the bottom of the device). The boron cloud will appear at midplance, possibly as a MARFE-look like. Scaling of the p-B reactions by varying the NBI energy should be compared with the predictions of nuclear physics. This could be an alternative to the FRC approach, without the difficulties of the optimization of the FRC low confinement time. Instead, a robust good tokamak confinement with high local HFS TF (enhanced due to the ultra low aspect ratio and low pitch angle) is used. The plasma central post makes the RULART concept attractive because of the proximity of NBI path and also because a fraction of born alphas will cross the plasma post and dragged into it in the direction of the central plasma post current, escaping vertically into a hole in the bias plate and reaching the direct electricity converter, such as in the FRC concept.

  8. Public Data Set: High Confinement Mode and Edge Localized Mode Characteristics in a Near-Unity Aspect Ratio Tokamak

    DOE Data Explorer

    Thome, Kathreen E. [University of Wisconsin-Madison] (ORCID:0000000248013922); Bongard, Michael W. [University of Wisconsin-Madison] (ORCID:0000000231609746); Barr, Jayson L. [University of Wisconsin-Madison] (ORCID:0000000177685931); Bodner, Grant M. [University of Wisconsin-Madison] (ORCID:0000000324979172); Burke, Marcus G. [University of Wisconsin-Madison] (ORCID:0000000176193724); Fonck, Raymond J. [University of Wisconsin-Madison] (ORCID:0000000294386762); Kriete, David M. [University of Wisconsin-Madison] (ORCID:0000000236572911); Perry, Justin M. [University of Wisconsin-Madison] (ORCID:0000000171228609); Schlossberg, David J. [University of Wisconsin-Madison] (ORCID:0000000287139448)

    2016-04-27

    This data set contains openly-documented, machine readable digital research data corresponding to figures published in K.E. Thome et al., 'High Confinement Mode and Edge Localized Mode Characteristics in a Near-Unity Aspect Ratio Tokamak,' Phys. Rev. Lett. 116, 175001 (2016).

  9. An analytic solution of high. beta. equilibrium in a large aspect ratio tokamak

    SciTech Connect

    Cowley, S.C.; Kaw, P.K.; Kelly, R.S.; Kulsrud, R.M.

    1991-03-01

    An analytic solution of the high {beta} ({epsilon}{bar {beta}}{sub p} {approximately} {beta}q{sup 2}/{epsilon} {much gt} 1) equilibrium of a large aspect ratio tokamak is presented. Two arbitrary flux functions, the pressure profile p({psi}) and the safety factor profile q({psi}), specify the equilibrium. The solution splits into two asymptotic regions: the core region where {psi} is a function of the major radius alone and a narrow boundary layer region adjoining the conducting wall. The solutions in the two regions are asymptotically matched to each other. For monotonic pressure profiles, the Shafranov shift is equal to the minor radius. For {beta} much bigger than one, the solution contains a region (in place of the magnetic axis) of zero magnetic field and constant pressure. At high {beta} the quantity {beta}{sub I}, which is essentially proportional to the pressure over the total current squared, is largely independent of pressure. We discuss the important ramifications of limited {beta}{sub I} for high {beta} reactors. Generalizations to shaped cross sections and hollow pressure profiles are outlined. We also consider the problem of equilibrium reconstruction in the high {beta} regime. 8 refs., 7 figs.

  10. Global two-fluid simulations of geodesic acoustic modes in strongly shaped tight aspect ratio tokamak plasmas

    SciTech Connect

    Robinson, J. R.; Hnat, B.; Thyagaraja, A.; McClements, K. G.; Knight, P. J.; Kirk, A. [EURATOM Collaboration: MAST Team

    2013-05-15

    Following recent observations suggesting the presence of the geodesic acoustic mode (GAM) in ohmically heated discharges in the Mega Amp Spherical Tokamak (MAST) [J. R. Robinson et al., Plasma Phys. Controlled Fusion 54, 105007 (2012)], the behaviour of the GAM is studied numerically using the two fluid, global code CENTORI [P. J. Knight et al. Comput. Phys. Commun. 183, 2346 (2012)]. We examine mode localisation and effects of magnetic geometry, given by aspect ratio, elongation, and safety factor, on the observed frequency of the mode. An excellent agreement between simulations and experimental data is found for simulation plasma parameters matched to those of MAST. Increasing aspect ratio yields good agreement between the GAM frequency found in the simulations and an analytical result obtained for elongated large aspect ratio plasmas.

  11. Collisional Transport in a Low Aspect Ratio Tokamak -- Beyond the Drift Kinetic Formalism

    SciTech Connect

    D.A. Gates; R.B. White

    2004-01-28

    Calculations of collisional thermal and particle diffusivities in toroidal magnetic plasma confinement devices order the toroidal gyroradius to be small relative to the poloidal gyroradius. This ordering is central to what is usually referred to as neoclassical transport theory. This ordering is incorrect at low aspect ratio, where it can often be the case that the toroidal gyroradius is larger than the poloidal gyroradius. We calculate the correction to the particle and thermal diffusivities at low aspect ratio by comparing the diffusivities as determined by a full orbit code (which we refer to as omni-classical diffusion) with those from a gyroaveraged orbit code (neoclassical diffusion). In typical low aspect ratio devices the omni-classical diffusion can be up to 2.5 times the calculated neoclassical value. We discuss the implications of this work on the analysis of collisional transport in low aspect ratio magnetic confinement experiments.

  12. Exploration of low-aspect-ratio tokamak regimes in the CDX-U and TS-3 devices

    SciTech Connect

    Hwang, Y.S.; Yamada, M.; Jones, T.G.

    1994-12-31

    In the low-aspect-ratio tokamak regime, a lower q(a) regime (i.e. q(a) {le} 5, A = R/a {approx} 1.5) has been explored in CDX-U, and the ultra-low-aspect-ratio tokamak regime (1.05 {le} A {le} 1.5) has been explored in TS-3. Using a relatively low toroidal magnetic field, plasma discharges with I{sub p} {le} 53 kA, and q(a) {ge} 4 [q{sub cyl}(a) {ge}1] have been obtained in CDX-U. Low q(a), Ohmic plasmas in CDX-U show increasing MHD activity as the edge safety factor is lowered. These modes appear to reduce the current ramp-up rate and, at present, limit the access to even lower q(a) regimes. An experiment carried out in the ULART regime (A {approx} 1.05 {minus} 1.5) on the TS-3 device identifies a threshold of q(a) {ge} 3 with q{sub cyl}(a) < 1 for stability of global tilt/shift modes.

  13. RCD Large Aspect-Ratio Tokamak Equilibrium with Magnetic Islands: a Perturbed Approach

    NASA Astrophysics Data System (ADS)

    F. L., Braga

    2013-03-01

    Solutions of Grad-Shafranov (GS) equation with Reversed Current Density (RCD) profiles present magnetic islands when the magnetic flux is explicitly dependent on the poloidal angle. In this work it is shown that a typical cylindrical (large aspect-ratio) RCD equilibrium configuration perturbed by the magnetic field of a circular loop (simulating a divertor) is capable of generate magnetic islands, due to the poloidal symmetry break of the GS equilibrium solution.

  14. Kinetic effects in the conversion of fast waves in pre-heated, low aspect ratio tokamak plasmas

    NASA Astrophysics Data System (ADS)

    Kommoshvili, K.; Cuperman, S.; Bruma, C.

    2003-03-01

    Kinetic effects in the conversion of fast waves to Alfvèn waves and their subsequent deposition in low aspect ratio (spherical) tokamaks (LARTs) have been investigated theoretically. More specifically, we have considered the consequences of incorporation of kinetic effects in the electron parallel (to the ambient magnetic field) dynamics derived by following the drift-tearing mode analysis of Chen et al (Chen L, Rutherford P H and Tang W M 1977 Phys. Rev. Lett. 39 460), and particle-conserving Krook collision operator for the passing electrons involved (Mett R R and Mahajan S M 1992 Phys. Fluids B 4 2885). The perpendicular plasma dynamics is described by a quite general resistive two-fluid (2F) model based dielectric tensor-operator (Cuperman S, Bruma C and Komoshvili K 2002 Solution of the resistive 2F wave equations for Alfvènic modes in spherical tokamak plasmas J. Plasma Phys. accepted for publication). The full-wave electromagnetic equations, formulated in terms of the vector and scalar potentials, have been solved by the aid of an advanced finite elements numerical code (Sewell G 1993 Adv. Eng. Software 17 105). Detailed solutions of the full-wave equations are obtained and compared with those corresponding to a pure resistive 2F model, this, for the illustrative pre-heated START-type device (Sykes 1994). Our results quantitatively confirm the general theory of the conversion of fast waves with subsequent power dissipation for the conditions of spherical tokamaks thus providing the required auxilliary energy source for the succesful operation of LARTs. Moreover, these results indicate the absolute necessity of using a full model for the parallel electron dynamics, i.e. including both kinetic and collisional effects.

  15. Comment on 'Continuum modes in rotating plasmas: General equations and continuous spectra for large aspect ratio tokamaks'[Phys. Plasmas 18, 092103 (2011)

    SciTech Connect

    Goedbloed, J. P.

    2012-06-15

    It is shown that some of the main results of the recent paper by Lakhin and Ilgisonis [Phys. Plasmas 18, 092103 (2011)], viz. the derivation of the equations for the continuous spectra of poloidally and toroidally rotating plasmas and their special solution for large aspect ratio tokamaks with large parallel flows were obtained before by Goedbloed, Belieen, van der Holst, and Keppens [Phys. Plasmas 11, 28 (2004)]. A further rearrangement of the system of equations for the coupled Alfven and slow continuous spectra clearly exhibits: (a) coupling through a single tangential derivative, which is a generalization of the geodesic curvature; (b) the 'transonic' transitions of the equilibrium, which need to be carefully examined in order to avoid entering hyperbolic flow regimes where the stability formalism breaks down. A critical discussion is devoted to the implications of this failure, which is generally missed in the tokamak literature, possibly as a result of the wide-spread use of the sonic Mach number of gas dynamics, which is an irrelevant and misleading parameter in 'transonic' magnetohydrodynamics. Once this obstacle in understanding is removed, further application of the theory of trans-slow Alfven continuum instabilities to both tokamaks, with possible implications for the L-H transition, and astrophysical objects like 'fat' accretion disks, with a possible new route to magnetohydrodynamic turbulence, becomes feasible.

  16. High Aspect Ratio Wrinkles

    NASA Astrophysics Data System (ADS)

    Chen, Yu-Cheng; Crosby, Alfred

    2015-03-01

    Buckling-induced surface undulations are widely found in living creatures, for instance, gut villi and the surface of flower petal cells. These undulations provide unique functionalities with their extremely high aspect ratios. For the synthetic systems, sinusoidal wrinkles that are induced by buckling a thin film attached on a soft substrate have been proposed to many applications. However, the impact of the synthetic wrinkles have been restricted by limited aspect ratios, ranging from 0 to 0.35. Within this range, wrinkle aspect ratio is known to increase with increasing compressive strain until a critical strain is reached, at which point wrinkles transition to localizations, such as folds or period doublings. Inspired by the living creatures, we propose that wrinkles can be stabilized in high aspect ratio by manipulating the strain energy in the substrate. We experimentally demonstrate this idea by forming a secondary crosslinking network in the wrinkled surface and successfully achieve aspect ratio as large as 0.8. This work not only provides insights for the mechanism of high aspect ratio structures seen in living creatures, but also demonstrates significant promise for future wrinkle-based applications.

  17. On virial analysis at low aspect ratio

    NASA Astrophysics Data System (ADS)

    Bongard, M. W.; Barr, J. L.; Fonck, R. J.; Reusch, J. A.; Thome, K. E.

    2016-07-01

    The validity of virial analysis to infer global MHD equilibrium poloidal beta βp and internal inductance ℓi from external magnetics measurements is examined for low aspect ratio configurations with A <2 . Numerical equilibrium studies at varied aspect ratio are utilized to validate the technique at finite aspect ratio. The effect of applying high- A approximations to low- A experimental data is quantified and demonstrates significant over-estimation of stored energy (factors of 2-10) in spherical tokamak geometry. Experimental approximations to equilibrium-dependent volume integral terms in the analysis are evaluated at low- A . Highly paramagnetic configurations are found to be inadequately represented through the virial mean radius parameter RT . Alternate formulations for inferring βp and ℓi that are independent of RT to avoid this difficulty are presented for the static isotropic limit. These formulations are suitable for fast estimation of tokamak stored energy components at low aspect ratio using virial analysis.

  18. On virial analysis at low aspect ratio

    DOE PAGESBeta

    Bongard, Michael W.; Barr, Jayson L.; Fonck, Raymond J.; Reusch, Joshua A.; Thome, Kathreen E.

    2016-07-28

    The validity of virial analysis to infer global MHD equilibrium poloidal beta βp and internal inductance ℓi from external magnetics measurements is examined for low aspect ratio configurations with A < 2. Numerical equilibrium studies at varied aspect ratio are utilized to validate the technique at finite aspect ratio. The effect of applying high-A approximations to low-A experimental data is quantified and demonstrates significant over-estimation of stored energy (factors of 2–10) in spherical tokamak geometry. Experimental approximations to equilibrium-dependent volume integral terms in the analysis are evaluated at low-A. Highly paramagnetic configurations are found to be inadequately represented through themore » virial mean radius parameter RT. Alternate formulations for inferring βp and ℓi that are independent of RT to avoid this difficulty are presented for the static isotropic limit. Lastly, these formulations are suitable for fast estimation of tokamak stored energy components at low aspect ratio using virial analysis.« less

  19. ITER physics design guidelines at high aspect ratio

    NASA Astrophysics Data System (ADS)

    Uckan, N. A.

    1991-09-01

    The physics requirements for the International Thermonuclear Experimental Reactor (ITER) design are formulated in a set of physics design guidelines. These guidelines, established by the ITER Physics Group during the Conceptual Design Activity (CDA, 1988--90), were based on credible extrapolations of the tokamak physics database as assessed during the CDA, and defined a class of tokamak designs (with plasma current I is approximately 20 MA and aspect ratio A is approximately 2.5--3.5) that meet the ITER objectives. Recent U.S. studies have indicated that there may be significant benefits if the ITER-CDA design point is moved from the low aspect ratio, high current baseline (A = 2.79, I = 22 MA) to a high aspect ratio machine at Ais approximately 4, I is approximately 15 MA, especially regarding steady-state, technology-testing performance. To adequately assess the physics and technology testing capability of higher aspect ratio design options, several changes are proposed to the original ITER guidelines to reflect the latest developments in physics understanding at higher aspect ratios. The critical issues for higher aspect ratio design options are the uncertainty in scaling of confinement with aspect ratio, the variation of vertical stability with elongation and aspect ratio, plasma shaping requirements, ability to control and maintain plasma current and q-profiles for MHD stability (and volt-second consumption), access for current drive, restrictions on field ripple and divertor plate incident angles, etc.

  20. Extreme Low Aspect Ratio Stellarators

    NASA Astrophysics Data System (ADS)

    Moroz, Paul

    1997-11-01

    Recently proposed Spherical Stellarator (SS) concept [1] includes the devices with stellarator features and low aspect ratio, A <= 3.5, which is very unusual for stellarators (typical stellarators have A ≈ 7-10 or above). Strong bootstrap current and high-β equilibria are two distinguished elements of the SS concept leading to compact, steady-state, and efficient fusion reactor. Different coil configurations advantageous for the SS have been identified and analyzed [1-6]. In this report, we will present results on novel stellarator configurations which are unusual even for the SS approach. These are the extreme-low-aspect-ratio-stellarators (ELARS), with the aspect ratio A ≈ 1. We succeeded in finding ELARS configurations with extremely compact, modular, and simple design compatible with significant rotational transform (ι ≈ 0.1 - 0.15), large plasma volume, and good particle transport characteristics. [1] P.E. Moroz, Phys. Rev. Lett. 77, 651 (1996); [2] P.E. Moroz, Phys. Plasmas 3, 3055 (1996); [3] P.E. Moroz, D.B. Batchelor et al., Fusion Tech. 30, 1347 (1996); [4] P.E. Moroz, Stellarator News 48, 2 (1996); [5] P.E. Moroz, Plasma Phys. Reports 23, 502 (1997); [6] P.E. Moroz, Nucl. Fusion 37, No. 8 (1997). *Supported by DOE Grant No. DE-FG02-97ER54395.

  1. Physics aspects of the Compact Ignition Tokamak

    SciTech Connect

    Post, D.; Bateman, G.; Houlberg, W.; Bromberg, L.; Cohn, D.; Colestock, P.; Hughes, M.; Ignat, D.; Izzo, R.; Jardin, S.

    1986-11-01

    The Compact Ignition Tokamak (CIT) is a proposed modest-size ignition experiment designed to study the physics of alpha-particle heating. The basic concept is to achieve ignition in a modest-size minimum cost experiment by using a high plasma density to achieve the condition of ntau/sub E/ approx. 2 x 10/sup 20/ sec m/sup -3/ required for ignition. The high density requires a high toroidal field (10 T). The high toroidal field allows a large plasma current (10 MA) which improves the energy confinement, and provides a high level of ohmic heating. The present CIT design also has a gigh degree of elongation (k approx. 1.8) to aid in producing the large plasma current. A double null poloidal divertor and a pellet injector are part of the design to provide impurity and particle control, improve the confinement, and provide flexibility for impurity and particle control, improve the confinement, and provide flexibility for improving the plasma profiles. Since auxiliary heating is expected to be necessary to achieve ignition, 10 to 20 MW of Ion Cyclotron Radio Frequency (ICRF) is to be provided.

  2. Effect of particle aspect ratio in magnetorheology

    NASA Astrophysics Data System (ADS)

    Morillas, Jose R.; Carreón-González, Elizabeth; de Vicente, Juan

    2015-12-01

    We investigate the influence of the aspect ratio of the dispersed particles in magnetorheology. Two systems are studied: conventional magnetorheological fluids prepared by dispersion of nickel nanowires, and inverse ferrofluids prepared by dispersion of glass fibers in a ferrofluid. In both cases the apparent yield stress is found to increase with aspect ratio in contradiction to available models in the literature. Experimental observations demonstrate that the particle volume fraction within the aggregates initially increases with increasing the aspect ratio of the dispersed particles. When the aspect ratio is further raised, a gel-like percolating structure forms inhibiting the formation of elongated clusters in the field direction.

  3. Study of Aspect Ratio Effects on Kinetic MHD Instabilities in NSTX and DIII-D

    SciTech Connect

    E.D. Fredrickson; W.W. Heidbrink; C.Z. Cheng; N.N. Gorelenkov; E. Belova; A.W. Hyatt; G.J. Kramer; J. Manickam; J. Menard; R. Nazikian; T.L. Rhodes; E. Ruskov

    2004-10-21

    We report general observations of kinetic instabilities on the low aspect-ratio National Spherical Torus Experiment (NSTX) and describe explicit aspect ratio scaling studies of kinetic instabilities using both the NSTX and the DIII-D tokamak. The NSTX and the DIII-D tokamak are nearly ideal for such experiments, having a factor of two difference in major radius but otherwise similar parameters. We also introduce new theoretical work on the physics of kinetic ballooning modes (KBM), toroidal Alfven eigenmodes (TAE), and compressional Alfven eigenmodes (CAE) with applications to NSTX.

  4. Optimal aspect ratio of endocytosed spherocylindrical nanoparticle

    NASA Astrophysics Data System (ADS)

    Chen, Ying-Bing; Liu, Yan-Hui; Zeng, Yan; Mao, Wei; Hu, Lin; Mao, Zong-Liang; Xu, Hou-Qiang

    2015-02-01

    Recent simulations have demonstrated that bioparticle size and shape modulate the process of endocytosis, and studies have provided more quantitative information that the endocytosis efficiency of spherocylindrical bioparticles is decided by its aspect ratio. At the same time, the dimensions of the receptor-ligand complex have strong effects on the size-dependent exclusion of proteins within the cellular environment. However, these earlier theoretical works including simulations did not consider the effects of ligand-receptor complex dimension on the endocytosis process. Thus, it is necessary to resolve the effects of ligand-receptor complex dimension and determine the optimal aspect ratio of spherocylindrical bioparticles in the process of endocytosis. Accordingly, we proposed a continuum elastic model, of which the results indicate that the aspect ratio depends on the ligand-receptor complex dimension and the radius of the spherocylindrical bioparticle. This model provides a phase diagram of the aspect ratio of endocytosed spherocylindrical bioparticles, the larger aspect ratio of which appears in the phase diagram with increasing ligand density, and highlights the bioparticle design.

  5. Busbar for the low aspect ratio device

    SciTech Connect

    Bromberg, L.; Sidorov, M.

    1996-12-31

    The high current required to drive the toroidal field coil of Low Aspect Ratio reactor-size devices (due to the single turn design) results in difficult choices for the electrical bus. In this paper, the implications of both superconducting and resistive busbar are investigated. Special attention is given to the possibility of using a high-Tc busbar. 14 refs., 5 figs.

  6. Method for nanomachining high aspect ratio structures

    DOEpatents

    Yun, Wenbing; Spence, John; Padmore, Howard A.; MacDowell, Alastair A.; Howells, Malcolm R.

    2004-11-09

    A nanomachining method for producing high-aspect ratio precise nanostructures. The method begins by irradiating a wafer with an energetic charged-particle beam. Next, a layer of patterning material is deposited on one side of the wafer and a layer of etch stop or metal plating base is coated on the other side of the wafer. A desired pattern is generated in the patterning material on the top surface of the irradiated wafer using conventional electron-beam lithography techniques. Lastly, the wafer is placed in an appropriate chemical solution that produces a directional etch of the wafer only in the area from which the resist has been removed by the patterning process. The high mechanical strength of the wafer materials compared to the organic resists used in conventional lithography techniques with allows the transfer of the precise patterns into structures with aspect ratios much larger than those previously achievable.

  7. Noise of Embedded High Aspect Ratio Nozzles

    NASA Technical Reports Server (NTRS)

    Bridges, James E.

    2011-01-01

    A family of high aspect ratio nozzles were designed to provide a parametric database of canonical embedded propulsion concepts. Nozzle throat geometries with aspect ratios of 2:1, 4:1, and 8:1 were chosen, all with convergent nozzle areas. The transition from the typical round duct to the rectangular nozzle was designed very carefully to produce a flow at the nozzle exit that was uniform and free from swirl. Once the basic rectangular nozzles were designed, external features common to embedded propulsion systems were added: extended lower lip (a.k.a. bevel, aft deck), differing sidewalls, and chevrons. For the latter detailed Reynolds-averaged Navier-Stokes (RANS) computational fluid dynamics (CFD) simulations were made to predict the thrust performance and to optimize parameters such as bevel length, and chevron penetration and azimuthal curvature. Seventeen of these nozzles were fabricated at a scale providing a 2.13 inch diameter equivalent area throat." ! The seventeen nozzles were tested for far-field noise and a few data were presented here on the effect of aspect ratio, bevel length, and chevron count and penetration. The sound field of the 2:1 aspect ratio rectangular jet was very nearly axisymmetric, but the 4:1 and 8:1 were not, the noise on their minor axes being louder than the major axes. Adding bevel length increased the noise of these nozzles, especially on their minor axes, both toward the long and short sides of the beveled nozzle. Chevrons were only added to the 2:1 rectangular jet. Adding 4 chevrons per wide side produced some decrease at aft angles, but increased the high frequency noise at right angles to the jet flow. This trend increased with increasing chevron penetration. Doubling the number of chevrons while maintaining their penetration decreased these effects. Empirical models of the parametric effect of these nozzles were constructed and quantify the trends stated above." Because it is the objective of the Supersonics Project that

  8. High aspect ratio, remote controlled pumping assembly

    DOEpatents

    Brown, S.B.; Milanovich, F.P.

    1995-11-14

    A miniature dual syringe-type pump assembly is described which has a high aspect ratio and which is remotely controlled, for use such as in a small diameter penetrometer cone or well packer used in water contamination applications. The pump assembly may be used to supply and remove a reagent to a water contamination sensor, for example, and includes a motor, gearhead and motor encoder assembly for turning a drive screw for an actuator which provides pushing on one syringe and pulling on the other syringe for injecting new reagent and withdrawing used reagent from an associated sensor. 4 figs.

  9. High aspect ratio, remote controlled pumping assembly

    DOEpatents

    Brown, Steve B.; Milanovich, Fred P.

    1995-01-01

    A miniature dual syringe-type pump assembly which has a high aspect ratio and which is remotely controlled, for use such as in a small diameter penetrometer cone or well packer used in water contamination applications. The pump assembly may be used to supply and remove a reagent to a water contamination sensor, for example, and includes a motor, gearhead and motor encoder assembly for turning a drive screw for an actuator which provides pushing on one syringe and pulling on the other syringe for injecting new reagent and withdrawing used reagent from an associated sensor.

  10. Flutter analysis of low aspect ratio wings

    NASA Technical Reports Server (NTRS)

    Parnell, L. A.

    1986-01-01

    Several very low aspect ratio flat plate wing configurations are analyzed for their aerodynamic instability (flutter) characteristics. All of the wings investigated are delta planforms with clipped tips, made of aluminum alloy plate and cantilevered from the supporting vehicle body. Results of both subsonic and supersonic NASTRAN aeroelastic analyses as well as those from another version of the program implementing the supersonic linearized aerodynamic theory are presented. Results are selectively compared with the experimental data; however, supersonic predictions of the Mach Box method in NASTRAN are found to be erratic and erroneous, requiring the use of a separate program.

  11. High aspect ratio silicon etch: A review

    NASA Astrophysics Data System (ADS)

    Wu, Banqiu; Kumar, Ajay; Pamarthy, Sharma

    2010-09-01

    High aspect ratio (HAR) silicon etch is reviewed, including commonly used terms, history, main applications, different technological methods, critical challenges, and main theories of the technologies. Chronologically, HAR silicon etch has been conducted using wet etch in solution, reactive ion etch (RIE) in low density plasma, single-step etch at cryogenic conditions in inductively coupled plasma (ICP) combined with RIE, time-multiplexed deep silicon etch in ICP-RIE configuration reactor, and single-step etch in high density plasma at room or near room temperature. Key specifications are HAR, high etch rate, good trench sidewall profile with smooth surface, low aspect ratio dependent etch, and low etch loading effects. Till now, time-multiplexed etch process is a popular industrial practice but the intrinsic scalloped profile of a time-multiplexed etch process, resulting from alternating between passivation and etch, poses a challenge. Previously, HAR silicon etch was an application associated primarily with microelectromechanical systems. In recent years, through-silicon-via (TSV) etch applications for three-dimensional integrated circuit stacking technology has spurred research and development of this enabling technology. This potential large scale application requires HAR etch with high and stable throughput, controllable profile and surface properties, and low costs.

  12. Stability of Small Aspect Ratio Toroidal Hybrid Devices

    NASA Astrophysics Data System (ADS)

    Ware, A. S.; Batchelor, D. B.; Carreras, B. A.; Hirshman, S. P.; Lynch, V. E.; Spong, D. A.; Whitson, J.

    1997-11-01

    The stability properties of small aspect ratio toroidal hybrid (SMARTH) devices are investigated. SMARTH configurations are a hybrid between a stellarator and a tokamak: the poloidal field is provided by both external modulated coils as well as plasma current. Initial studies of these devices focused on configurations with a simple set of modulated circular toroidal field coils.(B. A. Carreras, V. E. Lynch, and A. S. Ware, ORNL/TM-13252, 1996) These configurations have a magnetic well throughout the plasma volume and β limits for these devices are set by ideal ballooning modes. Here, we focus on the effect of finite plasma current on the ideal ballooning stability limit for SMARTH configurations. Preliminary results indicate that adding plasma current raises the stability β threshhold. More recent investigation have focused on configurations optimized solely for maximal particle confinement.(D. A. Spong, et al., 1997 Sherwood Theory Meeting, Poster 3C08) Confinement optimization, however, was deleterious to stability. We will report on progress to include a `stability criteria' in further confinement optimization studies.

  13. New High Aspect-Ratio Titania Nanotubes

    NASA Astrophysics Data System (ADS)

    Panaitescu, Eugen; Richter, Christiaan; Menon, Latika

    2007-03-01

    Titanium oxide nanotubes show great promise in photocatalytic, gas sensing, biological, and other applications. Techniques for the fabrication of titania nanotubes include electrodeposition in polymer molds starting from alumina templates, anodization of titanium in fluoride containing solutions, and hydrothermal treatment of nano- and micropowders. We have developed a new synthesis route for the production of new ultra-high aspect-ratio (over 1000:1) titania nanotubes by anodization in chloride containing acid solutions. The fabrication process occurs rapidly, in a fraction of the time when compared with other methods such as anodization in the highly toxic fluoride-containing electrolytes. We have demonstrated nanotubes with diameters as small as 25 nm, and lengths of up to 50 μm, and we have produced them with varying carbon content through the addition of organic acids in the electrolyte. This opens up new possibilities for many advanced applications of such nanotubes. Various synthesis conditions (pH, chloride content, electrolyte nature), and their influence on morphology, composition, and crystalline structure will be presented. Preliminary results on photocatalytic and transmission properties will also be discussed.

  14. Key Aspects of EBW Heating and Current Drive in Tokamaks

    NASA Astrophysics Data System (ADS)

    Urban, Jakub; Decker, Joan; Preinhaelter, Josef; Taylor, Gary; Vahala, Linda; Vahala, George

    2010-11-01

    Electron Bernstein wave (EBW) heating and current drive is modeled by coupled mode conversion, ray-tracing (AMR) and Fokker-Planck (LUKE) codes. Deposition and current drive profiles are determined for EBW with various injection parameters under realistic spherical tokamak conditions. There parameters are varied to investigate the robustness of the applied scenarios. The importance of relativistic corrections to EBW absorption is considered. The differences between various relativistic models are explored.

  15. Nuclear aspects of tokamak fusion test reactor (TFTR) diagnostics and instrumentation

    SciTech Connect

    Young, K.M.

    1982-01-01

    There are five principal aspects of the nuclear radiation from the high temperature plasmas of TFTR on its plasma diagnostic equipment. i) Important information about the plasma properties to be obtained from measurement of the neutrons, or other fusion reaction products. ii) Experimental studies to give design data for future tokamak devices and their instrumentation. iii) Transient noise or damage effects on the array of detectors for the collection of physics data about the plasma. iv) The effect of tritium on detectors that necessarily are in vacuum, directly connected to the tokamak vacuum vessel. v) Damage of diagnostic components mounted close to the vacuum vessel. Each of these topics will be addressed after a brief description of the TFTR tokamak and its radiation environment.

  16. Aspect ratio effects on limited scrape-off layer plasma turbulence

    NASA Astrophysics Data System (ADS)

    Jolliet, Sébastien; Halpern, Federico D.; Loizu, Joaquim; Mosetto, Annamaria; Ricci, Paolo

    2014-02-01

    The drift-reduced Braginskii model describing turbulence in the tokamak scrape-off layer is written for a general magnetic configuration with a limiter. The equilibrium is then specified for a circular concentric magnetic geometry retaining aspect ratio effects. Simulations are then carried out with the help of the global, flux-driven fluid three-dimensional code GBS [Ricci et al., Plasma Phys. Controlled Fusion 54, 124047 (2012)]. Linearly, both simulations and simplified analytical models reveal a stabilization of ballooning modes. Nonlinearly, flux-driven nonlinear simulations give a pressure characteristic length whose trends are correctly captured by the gradient removal theory [Ricci and Rogers, Phys. Plasmas 20, 010702 (2013)], that assumes the profile flattening from the linear modes as the saturation mechanism. More specifically, the linear stabilization of ballooning modes is reflected by a 15% increase in the steady-state pressure gradient obtained from GBS nonlinear simulations when going from an infinite to a realistic aspect ratio.

  17. Aspect ratio effects on limited scrape-off layer plasma turbulence

    SciTech Connect

    Jolliet, Sébastien Halpern, Federico D.; Loizu, Joaquim; Mosetto, Annamaria; Ricci, Paolo

    2014-02-15

    The drift-reduced Braginskii model describing turbulence in the tokamak scrape-off layer is written for a general magnetic configuration with a limiter. The equilibrium is then specified for a circular concentric magnetic geometry retaining aspect ratio effects. Simulations are then carried out with the help of the global, flux-driven fluid three-dimensional code GBS [Ricci et al., Plasma Phys. Controlled Fusion 54, 124047 (2012)]. Linearly, both simulations and simplified analytical models reveal a stabilization of ballooning modes. Nonlinearly, flux-driven nonlinear simulations give a pressure characteristic length whose trends are correctly captured by the gradient removal theory [Ricci and Rogers, Phys. Plasmas 20, 010702 (2013)], that assumes the profile flattening from the linear modes as the saturation mechanism. More specifically, the linear stabilization of ballooning modes is reflected by a 15% increase in the steady-state pressure gradient obtained from GBS nonlinear simulations when going from an infinite to a realistic aspect ratio.

  18. Energy confinement scaling in the low aspect ratio National Spherical Torus Experiment (NSTX)

    SciTech Connect

    Kaye, S. M.; Bell, M. G.; Bell, R. E.; Fredrickson, E. D.; LeBlanc, B. P.; Lee, K. C.; Lynch, S.; Sabbagh, S. A.

    2006-10-01

    Statistical and systematic studies have been conducted in order to develop an understanding of the parametric dependences of both the global and thermal energy confinement times at low aspect ratio in high power National Spherical Torus Experiment (NSTX) discharges. The global and thermal confinement times of both L- and H-mode discharges can exceed values given by H-mode scalings developed for conventional aspect ratio. Results of systematic scans in the H-mode indicate that the confinement times exhibit a nearly linear dependence on plasma current and a power degradation weaker than that observed at conventional aspect ratio. In addition, the dependence on the toroidal magnetic field is stronger than that seen in conventional aspect ratio tokamaks. Also, this latter trend is evident in statistical analyses of the available dataset. These statistical studies also indicate a weaker parametric dependence on plasma current than found in the systematic scans, due to correlations among the predictor variables. Regressions based on engineering variables, when transformed to dimensionless physics variables, indicate that the dependence of BτE on βt can range from being negative to null. Regressions based directly on the dimensionless physics variables are inexact because of large correlations among these variables. Scatter in the confinement data, at otherwise fixed operating parameters, is found to be due to variations in ELM activity, low frequency density fluctuations and plasma shaping.

  19. Physics Basis for High-Beta, Low-Aspect-Ratio Stellarator Experiments

    SciTech Connect

    A. Brooks; A.H. Reiman; G.H. Neilson; M.C. Zarnstorff; et al

    1999-11-01

    High-beta, low-aspect-ratio (compact) stellarators are promising solutions to the problem of developing a magnetic plasma configuration for magnetic fusion power plants that can be sustained in steady-state without disrupting. These concepts combine features of stellarators and advanced tokamaks and have aspect ratios similar to those of tokamaks (2-4). They are based on computed plasma configurations that are shaped in three dimensions to provide desired stability and transport properties. Experiments are planned as part of a program to develop this concept. A beta = 4% quasi-axisymmetric plasma configuration has been evaluated for the National Compact Stellarator Experiment (NCSX). It has a substantial bootstrap current and is shaped to stabilize ballooning, external kink, vertical, and neoclassical tearing modes without feedback or close-fitting conductors. Quasi-omnigeneous plasma configurations stable to ballooning modes at beta = 4% have been evaluated for the Quasi-Omnigeneous Stellarator (QOS) experiment. These equilibria have relatively low bootstrap currents and are insensitive to changes in beta. Coil configurations have been calculated that reconstruct these plasma configurations, preserving their important physics properties. Theory- and experiment-based confinement analyses are used to evaluate the technical capabilities needed to reach target plasma conditions. The physics basis for these complementary experiments is described.

  20. Integrable perturbed magnetic fields in toroidal geometry: An exact analytical flux surface label for large aspect ratio

    SciTech Connect

    Kallinikos, N.; Isliker, H.; Vlahos, L.; Meletlidou, E.

    2014-06-15

    An analytical description of magnetic islands is presented for the typical case of a single perturbation mode introduced to tokamak plasma equilibrium in the large aspect ratio approximation. Following the Hamiltonian structure directly in terms of toroidal coordinates, the well known integrability of this system is exploited, laying out a precise and practical way for determining the island topology features, as required in various applications, through an analytical and exact flux surface label.

  1. The unsteady lift of a wing of finite aspect ratio

    NASA Technical Reports Server (NTRS)

    Jones, Robert T

    1940-01-01

    Unsteady-lift functions for wings of finite aspect ratio have been calculated by correcting the aerodynamic inertia and the angle of attack of the infinite wing. The calculations are based on the operational method.

  2. Aeroacoustics of a High Aspect-Ratio Jet

    NASA Technical Reports Server (NTRS)

    Munro, Scott E.; Ahuja, K. K.

    2003-01-01

    Circulation control wings are a type of pneumatic high-lift device that have been extensively researched as to their aerodynamic benefits. However, there has been little research into the possible airframe noise reduction benefits of a circulation control wing. The key element of noise is the jet noise associated with the jet sheet emitted from the blowing slot. This jet sheet is essentially a high aspect-ratio rectangular jet. Thus, to fully understand the noise of a circulation control wing, the noise of high aspect-ratio rectangular jets must also be understood. A high aspect-ratio nozzle was fabricated to study the general characteristics of high aspect-ratio jets with aspect ratios from 100 to 3000. The jet noise of this nozzle was proportional to the 8" power of the jet velocity. It was also found that the jet noise was proportional to the slot height to the 312 power and slot width to the 1/2 power.

  3. Deformation mechanisms in negative Poisson's ratio materials - Structural aspects

    NASA Technical Reports Server (NTRS)

    Lakes, R.

    1991-01-01

    Poisson's ratio in materials is governed by the following aspects of the microstructure: the presence of rotational degrees of freedom, non-affine deformation kinematics, or anisotropic structure. Several structural models are examined. The non-affine kinematics are seen to be essential for the production of negative Poisson's ratios for isotropic materials containing central force linkages of positive stiffness. Non-central forces combined with pre-load can also give rise to a negative Poisson's ratio in isotropic materials. A chiral microstructure with non-central force interaction or non-affine deformation can also exhibit a negative Poisson's ratio. Toughness and damage resistance in these materials may be affected by the Poisson's ratio itself, as well as by generalized continuum aspects associated with the microstructure.

  4. Aspect ratio effect on shock-accelerated elliptic gas cylinders

    NASA Astrophysics Data System (ADS)

    Zou, Liyong; Liao, Shenfei; Liu, Cangli; Wang, Yanping; Zhai, Zhigang

    2016-03-01

    The evolution of an elliptic heavy-gas (SF6) cylinder accelerated by a planar weak shock wave is investigated experimentally using particle image velocimetry (PIV) diagnostics, and the emphasis is on the aspect ratio effect on shock-elliptic cylinder interaction. Experiments are conducted at five different aspect ratios (the ratio of length in streamwise and spanwise directions) varied from 0.25 to 4.0. PIV raw images and quantitative flow field data are obtained at t = 0.6 ms after the shock impact. As the aspect ratio increases, the interface morphology develops faster owing to more vorticity produced along the interface and smaller vortex spacing between the two vortex cores. For each case in this study, the maximal fluctuating velocity locates at the middle point of the two counter-vortices. The histograms of fluctuating velocity reveal that a distinct double-peak structure appears in the largest aspect ratio case in comparison with a single-peak structure in the smallest aspect ratio case. The vortex velocities predicted by the theoretical model [G. Rudinger and L. M. Somers, "Behaviour of small regions of different gases carried in accelerated gas flows," J. Fluid Mech. 7, 161-176 (1960)] agree well with the experimental ones. With the increase of aspect ratio, the maximal value of vorticity increases as well as the circulation, and more low-magnitude quantities are generated, which indicates the formation of multi-scale flow structure in the late mixing process. It is found that the experimental circulation of the vortex motion is reasonably estimated by the ideal point vortex-pair model.

  5. Fabrication and characterization of plasmonic nanorods with high aspect ratios

    NASA Astrophysics Data System (ADS)

    Jiang, Xiaoxiao; Hu, Sheng; Li, Zhigang; Lv, Jiangtao; Si, Guangyuan

    2016-08-01

    Metallic nanostructures with high aspect ratios are important for developing devices in photonics and integrated optics. However, fabricating well-aligned plasmonic arrays is challenging due to the difficulties of etching metals. In this work, we investigate the feasibility of constructing high aspect ratio nanorods with desired shapes and controllable geometric parameters using direct focused ion beam etching. The whole fabrication process only involves a metal-deposition step and a single milling of designed patterns. Detailed characterizations of the fabricated devices are also experimentally demonstrated.

  6. Method of fabricating a high aspect ratio microstructure

    DOEpatents

    Warren, John B.

    2003-05-06

    The present invention is for a method of fabricating a high aspect ratio, freestanding microstructure. The fabrication method modifies the exposure process for SU-8, an negative-acting, ultraviolet-sensitive photoresist used for microfabrication whereby a UV-absorbent glass substrate, chosen for complete absorption of UV radiation at 380 nanometers or less, is coated with a negative photoresist, exposed and developed according to standard practice. This UV absorbent glass enables the fabrication of cylindrical cavities in a negative photoresist microstructures that have aspect ratios of 8:1.

  7. The Vortices Trapped above Low-aspect-ratio Wings

    NASA Astrophysics Data System (ADS)

    Tang, Jian

    2007-11-01

    A stationary vortex trapped above the nondelta, low-aspect-ratio wings was first obtained in 3D unsteady numerical simulation. Flow visualization was conducted in water-channel using hydrogen bubble. The results verify that there is a vortex trapped above the low-aspect-ratio wings and the stationary vortex is consisted of two semi-ball, anti-rotation vortices which are different from the leading edge vortices on the delta wing. This stationary vortex trapped above the nondelta, low-aspect-ratio wings is a new phenomenon, which is different from the leading edge vortex on the delta wing. The numerical results show that lift coefficient increase to 0.8 when incidence increases form 0^o to 30^o, the lift coefficient keeps this value up to 45^o--a very high stall angle. The numerical results indicate that the trapped vortex might be the source of the high stall angle of attack and nonlinear lift at high incidence. Accompanied with the low-aspect-ratio wing, the existence of the stationary vortex is thought to be related to the strong effects of tip vortices. Further experimental and numerical works have been undertaken, the results show that trapped vortices have variant shapes and different critical angels of attack.

  8. Averaged equilibrium and stability in low-aspect-ratio stellarators

    SciTech Connect

    Garcia, L.; Carreras, B.A.; Dominguez, N.

    1989-01-01

    The MHD equilibrium and stability calculations or stellarators are complex because of the intrinsic three-dimensional (3-D) character of these configurations. The stellarators expansion simplifies the equilibrium calculation by reducing it to a two-dimensional (2-D) problem. The classical stellarator expansion includes terms up to order epsilon/sup 2/, and the vacuum magnetic field is also included up to this order. For large-aspect-ratio configurations, the results of the stellarator expansion agree well with 3-D numerical equilibrium results. But for low-aspect-ratio configurations, these are significant discrepancies with 3-D equilibrium calculations. The main reason for these discrepancies is the approximation in the vacuum field contributions. This problem can be avoided by applying the average method in a vacuum flux coordinate system. In this way, the exact vacuum magnetic field contribution is included and the results agree well with 3-D equilibrium calculations even for low-aspect-ratio configurations. Using the average method in a vacuum flux coordinate system also permit the accurate calculation of local stability properties with the Mercier criterion. The main improvement is in the accurate calculation of the geodesic curvature term. In this paper, we discuss the application of the average method in flux coordinates to the calculation of the Mercier criterion for low-aspect-ratio stellarator configurations. 12 refs., 3 figs.

  9. Transitions in Dynamo Modes Controlled by the Domain Aspect Ratio

    NASA Astrophysics Data System (ADS)

    Goudard, L.; Dormy, E.

    2007-12-01

    Magnetic fields of internal origin are observed on many planets in the solar system. The Sun itself acts as a dynamo. While these natural objects are very different in their composition, when it comes to dynamo modeling the governing equations are remarkably similar. One of the controlling parameters to distinguish between these objects is the aspect ratio of the convecting domain. Comparing the Sun to the Earth raises the issue of the nature of reversals. A challenging issue is to determine why the geomagnetic field reverses polarity on an irregular basis, whereas the Sun --which is a much larger object, governed by stronger nonlinearities-- reverses its magnetic polarity on a quasi-periodic timescale of 11 yrs. We use a three-dimensional Boussinesq model (the Parody code) to investigate the transition between these two types of behavior. We show that the aspect ratio of the convecting domain controls the nature of the dynamo field. We report a butterfly-like diagram at large aspect ratio, with magnetic activity near 30° of latitudes, which migrates with time toward the equator. We trace the existence of the dynamo wave solution at various aspect ratio and suggest possible consequences for the geomagnetic secular variation.

  10. Fluid Dynamics of a High Aspect-Ratio Jet

    NASA Technical Reports Server (NTRS)

    Munro, Scott E.; Ahuja, K. K.

    2003-01-01

    Circulation control wings are a type of pneumatic high-lift device that have been extensively researched as to their aerodynamic benefits. However, there has been little research into the possible airframe noise reduction benefits of a circulation control wing. The key element of noise is the jet noise associated with the jet sheet emitted from the blowing slot. High aspect-ratio jet acoustic results (aspect-ratios from 100 to 3,000) from a related study showed that the jet noise of this type of jet was proportional to the slot height to the 3/2 power and slot width to the 1/2 power. Fluid dynamic experiments were performed in the present study on the high aspect-ratio nozzle to gain understanding of the flow characteristics in an effort to relate the acoustic results to flow parameters. Single hot-wire experiments indicated that the jet exhaust from the high aspect-ratio nozzle was similar to a 2-d turbulent jet. Two-wire space-correlation measurements were performed to attempt to find a relationship between the slot height of the jet and the length-scale of the flow noise generating turbulence structure. The turbulent eddy convection velocity was also calculated, and was found to vary with the local centerline velocity, and also as a function of the frequency of the eddy.

  11. CFD assessment of orifice aspect ratio and mass flow ratio on jet mixing in rectangular ducts

    NASA Technical Reports Server (NTRS)

    Bain, D. B.; Smith, C. E.; Holdeman, J. D.

    1994-01-01

    Isothermal CFD analysis was performed on axially opposed rows of jets mixing with cross flow in a rectangular duct. Laterally, the jets' centerlines were aligned with each other on the top and bottom walls. The focus of this study was to characterize the effects of orifice aspect ratio and jet-to-mainstream mass flow ratio on jet penetration and mixing. Orifice aspect ratios (L/W) of 4-to-1, 2-to-1, and 1-to-1, along with circular holes, were parametrically analyzed. Likewise, jet-to-mainstream mass flow ratios (MR) of 2.0, 0.5, and 0.25 were systematically investigated. The jet-to-mainstream momentum-flux ratio (J) was maintained at 36 for all cases, and the orifice spacing-to-duct height (S/H) was varied until optimum mixing was attained for each configuration. The numerical results showed that orifice aspect ratio (and likewise orifice blockage) had little effect on jet penetration and mixing. Based on mixing characteristics alone, the 4-to-1 slot was comparable to the circular orifice. The 4-to-1 slot has a smaller jet wake which may be advantageous for reducing emissions. However, the axial length of a 4-to-1 slot may be prohibitively long for practical application, especially for MR of 2.0. The jet-to-mainstream mass flow ratio had a more significant effect on jet penetration and mixing. For a 4-to-1 aspect ratio orifice, the design correlating parameter for optimum mixing (C = (S/H)(sq. root J)) varied from 2.25 for a mass flow ratio of 2.0 to 1.5 for a mass flow ratio of 0.25.

  12. Evolution of cooling-channel properties for varying aspect ratio

    NASA Astrophysics Data System (ADS)

    Pizzarelli, M.; Nasuti, F.; Onofri, M.

    2016-07-01

    A trade-off analysis is performed on a cooling channel system representative of liquid rocket engine cooling systems. This analysis requires multiple cooling channel flow calculations which are performed by means of a proper numerical approach, referred to as quasi-two-dimensional (2D) model. This model, which is suited to high-aspect-ratio cooling channels (HARCC), permits to have a fast prediction of both the coolant flow evolution and the temperature distribution along the whole cooling channel structure. Before using the quasi-2D model for the trade-off analysis, its validation by comparison with computational fluid dynamics (CFD) results is presented and discussed. The results show that the pump power required to overcome losses in the cooling circuit can be minimized selecting a channel shaped with a suitably high aspect ratio.

  13. Method for fabricating high aspect ratio structures in perovskite material

    DOEpatents

    Karapetrov, Goran T.; Kwok, Wai-Kwong; Crabtree, George W.; Iavarone, Maria

    2003-10-28

    A method of fabricating high aspect ratio ceramic structures in which a selected portion of perovskite or perovskite-like crystalline material is exposed to a high energy ion beam for a time sufficient to cause the crystalline material contacted by the ion beam to have substantially parallel columnar defects. Then selected portions of the material having substantially parallel columnar defects are etched leaving material with and without substantially parallel columnar defects in a predetermined shape having high aspect ratios of not less than 2 to 1. Etching is accomplished by optical or PMMA lithography. There is also disclosed a structure of a ceramic which is superconducting at a temperature in the range of from about 10.degree. K. to about 90.degree. K. with substantially parallel columnar defects in which the smallest lateral dimension of the structure is less than about 5 microns, and the thickness of the structure is greater than 2 times the smallest lateral dimension of the structure.

  14. Nanorod Aspect Ratios Determined by the Nano-Impact Technique.

    PubMed

    Plowman, Blake J; Young, Neil P; Batchelor-McAuley, Christopher; Compton, Richard G

    2016-06-01

    The in situ electrochemical sizing of individual gold nanorods is reported. Through the combination of electrochemical dissolution and the use of a surface-bound redox tag, the volume and surface area of the nanorods are measured, and provide the aspect ratio and the size of the nanorods. Excellent independent agreement is found with electron microscopy analysis of the nanorods, establishing the application of nano-impact experiments for the sizing of anisotropic nanomaterials. PMID:27106096

  15. High-aspect-ratio fine-line metallization

    NASA Astrophysics Data System (ADS)

    Chang, Chienliu; Chang, Peizen; Yen, Kaihsiang; Lu, Sheyshi

    1998-08-01

    This study is aimed at making metallic fine lines characterized with high aspect ratio. There are two methods we have developed. One is the trilevel lift-off method with submicron lithography, and the other is the lift-off method by using the commercial negative photoresist SU-8 made by IBM. First, the trilevel lift-off method is described. A pre- imidized, soluble polyimide layer of OCG Probimide 293 A is spun on a wafer with thickness 4 micrometer. A 120 nm thick layer of silicon oxynitride was formed on the polyimide by PECVD. A layer photoresist layer was applied and patterned. This photoresist layer is used as the etching mask of silicon oxynitride by RIE with the gas CF4 plasma. Similarly, the silicon oxynitride is used as the etching mask of the thick polyimide layers by RIE with the gas O2 plasma. After metallization the pre-imidized polyimide is dissolved in methylene chloride lifting off the oxynitride and metal layers. Following this way, the submicron lithography, such as silylation technology, is suitable to make the aspect ratio up to 10 and the metal line will still have 3 micrometer height. The other is the lift-off method by using negative photoresist SU-8. This SU-8 is originally used as high aspect ratio molding. The linewidth of SU-8 is reduced to 2 micrometer linewidth with 12 micrometer height, and used as the remover to lift off after metallization. This SU-8 makes the fine-line metallization of 2 micrometer linewidth to achieve the aspect- ratio up to 5.

  16. Evolution of turbulent jets in low aspect ratio containers

    NASA Astrophysics Data System (ADS)

    Pol, S.; Nath, C.; Gest, D.; Voropayev, S.; Fernando, H. J. S.; Webb, S.

    2009-11-01

    The evolution of homogeneous and buoyant turbulent jets released into a low aspect ratio (width/height) container was investigated experimentally using PIV, MSCT probing and digital imaging. The motivation was to understand mixing process occurring in U.S. Strategic Petroleum Reserves (SPR), where crude oil is stored in salt caverns of low aspect ratio. During maintenance or filling, oil is introduced as a jet from the top of the caverns. This study is focussed on mean and turbulent flow characteristics as well as global flow instability and periodic oscillations intrinsic to jets in low aspect ratio containers. Scaling arguments were advanced for salient flow parameters, which included the characteristic length (container width D) and velocity (for homogeneous jets, J^1/2D, where J is the momentum flux at the jet exit) scales. For buoyant jets, the buoyancy flux B needs to be introduced as an additional parameter. Such jet flows do not reach a steady state, but bifurcate periodically with a frequency scale J^1/2/ D^2 while enhancing global mixing.

  17. Micromilling of thin ribs with high aspect ratios

    NASA Astrophysics Data System (ADS)

    Li, P.; Zdebski, D.; Langen, H. H.; Hoogstrate, A. M.; Oosterling, J. A. J.; Munnig Schmidt, R. H.; Allen, D. M.

    2010-11-01

    Micro features with high aspect ratios are one of the commonly encountered geometries found in micro products. In the literature, these structures are often used in demonstrator products machined by a micromilling process. In this paper, the challenges in micromilling thin ribs with high aspect ratios have been studied. Due to the scaling effect, micro-ribs have relatively low stiffness but high natural frequency. Therefore, on the one hand, average forces have to be controlled well to avoid structural bending or even damage, while on the other hand, micro features are unlikely to be excited by the dynamic forces. The characteristics of micromilling forces and their relationships to the machining parameters, namely, feed per tooth, depth of cut and width of cut, were studied theoretically by force models. In addition, the effects of different milling strategies (up-/down-milling) and tool paths on the quality of thin features have been investigated using FEM. The results allow measures to be taken to minimize the force effects and support the micro features during machining. The experimental results verify the theoretical studies. Thin ribs about 15 µm wide and with an aspect ratio of more than 50 were machined with good form and surface quality.

  18. Formation of High Aspect Ratio Microcoil Using Dipping Method

    NASA Astrophysics Data System (ADS)

    Noda, Daiji; Yamashita, Shuhei; Matsumoto, Yoshifumi; Setomoto, Masaru; Hattori, Tadashi

    Coils are used in many electronic devices as inductors in mobile units such as mobile phone, digital cameras, etc. Inductance and quality factor of coils are very important value of the performance. Therefore, the requests for coils are small size, high inductance, low power consumption, etc. However, coils are unsuitable for miniaturization because of its structure. Therefore, we have proposed and developed the microcoils of high aspect ratio with the dipping method and an X-ray lithography technique. In dipping method, centrifugal force and highly viscous photoresist solution were key points to evenly apply resist in the form of thick film on metal bar. The film thickness of resist on bar was achieved about 50 μm after single coating. Using these techniques, we succeeded in creating threaded groove structure with 10 μm lines and spaces on 1 mm brass bar. In this case, the aspect ratio was achieved five. It is very expected the high performance microcoil with high aspect ratio lines could be manufactured in spite of the miniature size.

  19. High-aspect ratio magnetic nanocomposite polymer cilium

    NASA Astrophysics Data System (ADS)

    Rahbar, M.; Tseng, H. Y.; Gray, B. L.

    2014-03-01

    This paper presents a new fabrication technique to achieve ultra high-aspect ratio artificial cilia micro-patterned from flexible highly magnetic rare earth nanoparticle-doped polymers. We have developed a simple, inexpensive and scalable fabrication method to create cilia structures that can be actuated by miniature electromagnets, that are suitable to be used for lab-on-a chip (LOC) and micro-total-analysis-system (μ-TAS) applications such as mixers and flow-control elements. The magnetic cilia are fabricated and magnetically polarized directly in microfluidic channels or reaction chambers, allowing for easy integration with complex microfluidic systems. These cilia structures can be combined on a single chip with other microfluidic components employing the same permanently magnetic nano-composite polymer (MNCP), such as valves or pumps. Rare earth permanent magnetic powder, (Nd0.7Ce0.3)10.5Fe83.9B5.6, is used to dope polydimethylsiloxane (PDMS), resulting in a highly flexible M-NCP of much higher magnetization and remanence [1] than ferromagnetic polymers typically employed in magnetic microfluidics. Sacrificial poly(ethylene-glycol) (PEG) is used to mold the highly magnetic polymer into ultra high-aspect ratio artificial cilia. Cilia structures with aspect ratio exceeding 8:0.13 can be easily fabricated using this technique and are actuated using miniature electromagnets to achieve a high range of motion/vibration.

  20. Instability of low viscosity elliptic jets with varying aspect ratio

    NASA Astrophysics Data System (ADS)

    Kulkarni, Varun

    2011-11-01

    In this work an analytical description of capillary instability of liquid elliptic jets with varying aspect ratio is presented. Linear stability analysis in the long wave approximation with negligible gravitational effects is employed. Elliptic cylindrical coordinate system is used and perturbation velocity potential substituted in the Laplace equation to yield Mathieu and Modified Mathieu differential equations. The dispersion relation for elliptical orifices of any aspect ratio is derived and validated for axisymmetric disturbances with m = 0, in the limit of aspect ratio, μ = 1 , i.e. the case of a circular jet. As Mathieu functions and Modified Mathieu function solutions converge to Bessel's functions in this limit the Rayleigh-Plateau instability criterion is met. Also, stability of solutions corresponding to asymmetric disturbances for the kink mode, m = 1 and flute modes corresponding to m >= 2 is discussed. Experimental data from earlier works is used to compare observations made for elliptical orifices with μ ≠ 1 . This novel approach aims at generalizing the results pertaining to cylindrical jets with circular cross section leading to better understanding of breakup in liquid jets of various geometries.

  1. Accuracy of Gradient Reconstruction on Grids with High Aspect Ratio

    NASA Technical Reports Server (NTRS)

    Thomas, James

    2008-01-01

    Gradient approximation methods commonly used in unstructured-grid finite-volume schemes intended for solutions of high Reynolds number flow equations are studied comprehensively. The accuracy of gradients within cells and within faces is evaluated systematically for both node-centered and cell-centered formulations. Computational and analytical evaluations are made on a series of high-aspect-ratio grids with different primal elements, including quadrilateral, triangular, and mixed element grids, with and without random perturbations to the mesh. Both rectangular and cylindrical geometries are considered; the latter serves to study the effects of geometric curvature. The study shows that the accuracy of gradient reconstruction on high-aspect-ratio grids is determined by a combination of the grid and the solution. The contributors to the error are identified and approaches to reduce errors are given, including the addition of higher-order terms in the direction of larger mesh spacing. A parameter GAMMA characterizing accuracy on curved high-aspect-ratio grids is discussed and an approximate-mapped-least-square method using a commonly-available distance function is presented; the method provides accurate gradient reconstruction on general grids. The study is intended to be a reference guide accompanying the construction of accurate and efficient methods for high Reynolds number applications

  2. Study of blade aspect ratio on a compressor front stage

    NASA Technical Reports Server (NTRS)

    Behlke, R. F.; Brooky, J. D.; Canal, E., Jr.

    1980-01-01

    A single stage, low aspect ratio, compressor with a 442.0 m/sec (1450 ft/sec) tip speed and a 0.597 hub/tip ratio typical of an advanced core compressor front stage was tested. The test stage incorporated an inlet duct which was representative of an engine transition duct between fan and high pressure compressors. At design speed, the rotor stator stage achieved a peak adiabatic efficiency of 86.6 percent at a flow of 44.35 kg/sec (97.8 lbm/sec) and a pressure ratio of 1.8. Surge margin was 12.5 percent from the peak stage efficiency point.

  3. Dependence of the ac loss on the aspect ratio in a cable in conduit conductor

    NASA Astrophysics Data System (ADS)

    Cau, F.; Bruzzone, P.

    2010-04-01

    The coupling current loss in rectangular superconducting cables is strictly dependent on their aspect ratio, which has an impact on the area linked by the field variation and consequently on the currents induced between strands. The relation between the ac loss and aspect ratio is studied with reference to the testing of three short cable in conduit conductor (CICC) samples at the SULTAN test facility. The first conductor is a 25 kA NbTi cable for the JT60-SA tokamak; the second is a 20 kA Nb3Sn cable for the HZB hybrid magnet. The last CICC is a 68 kA Nb3Sn cable with layout similar to that of the ITER toroidal field (TF) conductor (called the 'European toroidal field (EUTF) alternate'). All the samples are assembled with two conductor sections differing only in their orientation with respect to the external variable field. In the first and third samples, the cable of one leg is rotated by 90°, while in the HZB sample it is rotated by 45° with respect to the other leg. The ac loss is measured at the SULTAN test facility using a gas flow calorimetric method. A sample length of 39 cm is exposed to a sinusoidal field with an amplitude of ± 0.3 or ± 0.2 T (depending on the superconductor) and frequency variable in the range 0.1-0.8 Hz. A background field of 2 T perpendicular both to the sinusoidal field and to the sample axis is also applied. The ac loss is assessed by measuring the variation of the He enthalpy, assuming the metal enthalpy to be negligible. The loss curve for both legs is discussed in terms of the respective aspect ratios and the results, including data from former test campaigns, are compared with the aim of finding an analytical relation between the loss and the conductor dimensions.

  4. Fluid overpressure estimates from the aspect ratios of mineral veins

    NASA Astrophysics Data System (ADS)

    Philipp, Sonja L.

    2012-12-01

    Several hundred calcite veins and (mostly) normal faults were studied in limestone and shale layers of a Mesozoic sedimentary basin next to the village of Kilve at the Bristol Channel (SW-England). The veins strike mostly E-W (239 measurements), that is, parallel with the associated normal faults. The mean vein dip is 73°N (44 measurements). Field observations indicate that these faults transported the fluids up into the limestone layers. The vein outcrop (trace) length (0.025-10.3 m) and thickness (0.1-28 mm) size distributions are log-normal. Taking the thickness as the dependent variable and the outcrop length as the independent variable, linear regression gives a coefficient of determination (goodness of fit) of R2 = 0.74 (significant with 99% confidence), but natural logarithmic transformation of the thickness-length data increases the coefficient of determination to R2 = 0.98, indicating that nearly all the variation in thickness can be explained in terms of variation in trace length. The geometric mean of the aspect (length/thickness) ratio, 451, gives the best representation of the data set. With 95% confidence, the true geometric mean of the aspect ratios of the veins lies in the interval 409-497. Using elastic crack theory, appropriate elastic properties of the host rock, and the mean aspect ratio, the fluid overpressure (that is, the total fluid pressure minus the normal stress on the fracture plane) at the time of vein formation is estimated at around 18 MPa. From these results, and using the average host rock and water densities, the depth to the sources of the fluids (below the present exposures) forming the veins is estimated at between around 300 m and 1200 m. These results are in agreement to those obtained by independent isotopic studies and indicate that the fluids were of rather local origin, probably injected from sill-like sources (water sills) inside the sedimentary basin.

  5. Aspect ratio dependent cytotoxicity and antimicrobial properties of nanoclay.

    PubMed

    Rawat, Kamla; Agarwal, Shweta; Tyagi, Aakriti; Verma, Anita K; Bohidar, H B

    2014-10-01

    Nanoclays may enter human body through various routes such as through the respiratory and gastrointestinal tract, skin, blood, etc. There is dearth of such studies evaluating the interaction of clay nanoparticles with human cells. In particular, the interaction of proteins and nucleic acids with nanoparticles of different aspect ratio remains a domain that is very poorly probed and understood. In the present study, we address the issue of cytotoxicity and antimicrobial attributes of two distinct nanoclay platelets namely, laponite (diameter = 25 nm and thickness = 1 nm) and montmorillonite (MMT, diameter = 300 nm and thickness = 1 nm), having different aspect ratio (25:1 vs 300:1). Cytotoxicity was assessed in both prokatyotes: Escherichia coli, eukaryotes-human embryonic kidney (HEK), and cervical cancer SiHa cell lines, and a comparative size-based analysis of the toxicity were made at different exposure time points by MTT assay. The antimicrobial activity of the nanoclays was evaluated by disc diffusion method (Kirbey-Bauer protocol). Laponite exhibited maximum efficacy as an antimicrobial agent against E. coli. Comparatively smaller size laponite could preferentially enter the cells, leading to relatively wider or larger zone of inhibition. On contradictory; laponite showed 74.67 % survival while MMT showed 89.02 % survival in eukaryotic cells at 0.00001 % (w/v) concentration. In summary, both MMT and laponite indicated cytotoxicity at 0.05 % concentration within 24 h of exposure on HEK and cervical cancer (SiHa) cell lines. The toxicity was possibly dependent on size, aspect ratio, and concentration. PMID:24894661

  6. Tunable high aspect ratio polymer nanostructures for cell interfaces

    NASA Astrophysics Data System (ADS)

    Beckwith, Kai Sandvold; Cooil, Simon P.; Wells, Justin W.; Sikorski, Pawel

    2015-04-01

    Nanoscale topographies and chemical patterns can be used as synthetic cell interfaces with a range of applications including the study and control of cellular processes. Herein, we describe the fabrication of high aspect ratio nanostructures using electron beam lithography in the epoxy-based polymer SU-8. We show how nanostructure geometry, position and fluorescence properties can be tuned, allowing flexible device design. Further, thiol-epoxide reactions were developed to give effective and specific modification of SU-8 surface chemistry. SU-8 nanostructures were made directly on glass cover slips, enabling the use of high resolution optical techniques such as live-cell confocal, total internal reflection and 3D structured illumination microscopy to investigate cell interactions with the nanostructures. Details of cell adherence and spreading, plasma membrane conformation and actin organization in response to high aspect ratio nanopillars and nanolines were investigated. The versatile structural and chemical properties combined with the high resolution cell imaging capabilities of this system are an important step towards the better understanding and control of cell interactions with nanomaterials.Nanoscale topographies and chemical patterns can be used as synthetic cell interfaces with a range of applications including the study and control of cellular processes. Herein, we describe the fabrication of high aspect ratio nanostructures using electron beam lithography in the epoxy-based polymer SU-8. We show how nanostructure geometry, position and fluorescence properties can be tuned, allowing flexible device design. Further, thiol-epoxide reactions were developed to give effective and specific modification of SU-8 surface chemistry. SU-8 nanostructures were made directly on glass cover slips, enabling the use of high resolution optical techniques such as live-cell confocal, total internal reflection and 3D structured illumination microscopy to investigate cell

  7. Primary response of high-aspect-ratio thermoresistive sensors

    NASA Astrophysics Data System (ADS)

    Majlesein, H. R.; Mitchell, D. L.; Bhattacharya, Pradeep K.; Singh, A.; Anderson, James A.

    1997-07-01

    There is a growing need for sensors in monitoring performance in modern quality products such as in electronics to monitor heat build up, substrate delaminations, and thermal runaway. In processing instruments, intelligent sensors are needed to measure deposited layer thickness and resistivities for process control, and in environmental electrical enclosures, they are used for climate monitoring and control. A yaw sensor for skid prevention utilizes very fine moveable components, and an automobile engine controller blends a microprocessor and sensor on the same chip. An Active-Pixel Image Sensor is integrated with a digital readout circuit to perform most of the functions in a video camera. Magnetostrictive transducers sense and damp vibrations. Improved acoustic sensors will be used in flow detection of air and other fluids, even at subsonic speeds. Optoelectronic sensor systems are being developed for installation on rocket engines to monitor exhaust gases for signs of wear in the engines. With new freon-free coolants being available the problems of A/C system corrosion have gone up in automobiles and need to be monitored more frequently. Defense cutbacks compel the storage of hardware in safe-custody for an indeterminate period of time, and this makes monitoring more essential. Just-in-time customized manufacturing in modern industries also needs dramatic adjustment in productivity of various selected items, leaving some manufacturing equipment idle for a long time, and therefore, it will be prone to more corrosion, and corrosion sensors are needed. In the medical device industry, development of implantable medical devices using both potentiometric and amperometric determination of parameters has, until now, been used with insufficient micro miniaturization, and thus, requires surgical implantation. In many applications, high-aspect- ratio devices, made possible by the use of synchrotron radiation lithography, allow more useful devices to be produced. High-aspect-ratio

  8. Nonconservative dynamics of optically trapped high-aspect-ratio nanowires

    NASA Astrophysics Data System (ADS)

    Toe, Wen Jun; Ortega-Piwonka, Ignacio; Angstmann, Christopher N.; Gao, Qiang; Tan, Hark Hoe; Jagadish, Chennupati; Henry, Bruce I.; Reece, Peter J.

    2016-02-01

    We investigate the dynamics of high-aspect-ratio nanowires trapped axially in a single gradient force optical tweezers. A power spectrum analysis of the dynamics reveals a broad spectral resonance of the order of kHz with peak properties that are strongly dependent on the input trapping power. A dynamical model incorporating linear restoring optical forces, a nonconservative asymmetric coupling between translational and rotational degrees of freedom, viscous drag, and white noise provides an excellent fit to experimental observations. A persistent low-frequency cyclical motion around the equilibrium trapping position, with a frequency distinct from the spectral resonance, is observed from the time series data.

  9. Nonlinear Finite Element Analysis of Shells with Large Aspect Ratio

    NASA Technical Reports Server (NTRS)

    Chang, T. Y.; Sawamiphakdi, K.

    1984-01-01

    A higher order degenerated shell element with nine nodes was selected for large deformation and post-buckling analysis of thick or thin shells. Elastic-plastic material properties are also included. The post-buckling analysis algorithm is given. Using a square plate, it was demonstrated that the none-node element does not have shear locking effect even if its aspect ratio was increased to the order 10 to the 8th power. Two sample problems are given to illustrate the analysis capability of the shell element.

  10. Compressional Alfvin Eigenmode Dispersion in Low Aspect Ratio Plasmas

    SciTech Connect

    N.N. Gorelenkov; C.Z. Cheng; E. Fredrickson

    2002-01-29

    Recent observations of new fast ion beam driven instabilities in MHz frequency range in National Spherical Torus experiments (NSTX) are suggested to be Compressional Alfvin Eigenmodes (CAEs). A new theory of CAEs applicable to low aspect ratio toroidal plasmas is developed based on the ballooning representation for the poloidal dependence of the perturbed quantities. In agreement with observations, the analytical theory predicts that CAEs are discrete modes with frequencies correlated with the characteristic Alfvin velocity of the plasma. Plasma equilibrium structure is essential to determine accurately the dispersion of CAEs. The mode structure is localized in both the minor radius and the poloidal directions on the low magnetic field side.

  11. Masks for high aspect ratio x-ray lithography

    SciTech Connect

    Malek, C.K.; Jackson, K.H.; Bonivert, W.D.; Hruby, J.

    1997-04-01

    Fabrication of very high aspect ratio microstructures, as well as ultra-high precision manufacturing is of increasing interest in a multitude of applications. Fields as diverse as micromechanics, robotics, integrated optics, and sensors benefit from this technology. The scale-length of this spatial regime is between what can be achieved using classical machine tool operations and that which is used in microelectronics. This requires new manufacturing techniques, such as the LIGA process, which combines x-ray lithography, electroforming, and plastic molding.

  12. Method for producing thin graphite flakes with large aspect ratios

    DOEpatents

    Bunnell, L. Roy

    1993-01-01

    A method for making graphite flakes of high aspect ratio by the steps of providing a strong concentrated acid and heating the graphite in the presence of the acid for a time and at a temperature effective to intercalate the acid in the graphite; heating the intercalated graphite at a rate and to a temperature effective to exfoliate the graphite in discrete layers; subjecting the graphite layers to ultrasonic energy, mechanical shear forces, or freezing in an amount effective to separate the layes into discrete flakes.

  13. Aspect ratio effects in turbulent duct flows studied with DNS

    NASA Astrophysics Data System (ADS)

    Vinuesa, R.; Noorani, A.; Lozano-Durán, A.; Schlatter, P.; Fischer, P.; Nagib, H.

    2012-11-01

    Three-dimensional effects present in turbulent duct flows, i.e., side-wall boundary layers and secondary motions, are studied by means of direct numerical simulations (DNS). The spectral element code Nek5000, developed by Fischer et. al. (2008), is used to compute turbulent duct flows with aspect ratios 1 and 3 in streamwise-periodic boxes of length 25 h (long enough to capture the longest streamwise structures). The total number of grid points is 28 and 62 million respectively, and the inflow conditions were adjusted iteratively in order to keep the same bulk Reynolds number at the centerplane (Reb , c = 2800) in both cases. Spanwise variations in wall shear, mean-flow profiles and turbulence statistics were analyzed with aspect ratio, and also compared with the 2D channel. The simulations were started from a laminar duct profile, and transition to turbulence was triggered by means of trip-forcing in the wall-normal direction, applied at the two horizontal walls. In addition, we developed a convergence criterion aimed at assessing the necessary averaging time TA for converged statistics. We find that econdary motions present in duct flows require longer averaging times and the total shear-stress profile is not necessarily linear.

  14. THE LARGE ASPECT RATIO LIMIT OF NEOCLASSICAL TRANSPORT THEORY

    SciTech Connect

    WONG,SK; CHAN,VS

    2002-11-01

    OAK B202 THE LARGE ASPECT RATIO LIMIT OF NEOCLASSICAL TRANSPORT THEORY. This article presents a comprehensive description of neoclassical transport theory in the banana regime for large aspect ratio flux surfaces of arbitrary shapes. The method of matched asymptotic expansions is used to obtain analytical solutions for plasma distribution functions and to compute transport coefficients. The method provides justification for retaining only the part of the Fokker-Planck operator that involves the second derivative with respect to the cosine of the pitch angle for the trapped and barely circulating particles. It leads to a simple equation for the freely circulating particles with boundary conditions that embody a discontinuity separating particles moving in opposite directions. Corrections to the transport coefficients are obtained by generalizing an existing boundary layer analysis. The system of moment and field equations is consistently taken in the cylinder limit, which facilitates discussion of the treatment of dynamical constraints. it is shown that the nonlocal nature of Ohm's law in neoclassical theory renders the mathematical problem of plasma transport with changing flux surfaces nonstandard.

  15. HAREM: high aspect ratio etching and metallization for microsystems fabrication

    NASA Astrophysics Data System (ADS)

    Sarajlic, Edin; Yamahata, Christophe; Cordero, Mauricio; Collard, Dominique; Fujita, Hiroyuki

    2008-07-01

    We report a simple bulk micromachining method for the fabrication of high aspect ratio monocrystalline silicon MEMS (microelectromechanical systems) in a standard silicon wafer. We call this two-mask microfabrication process high aspect ratio etching and metallization or HAREM: it combines double-side etching and metallization to create suspended micromechanical structures with electrically 'insulating walls' on their backside. The insulating walls ensure a proper electrical insulation between the different actuation and sensing elements situated on either fixed or movable parts of the device. To demonstrate the high potential of this simple microfabrication method, we have designed and characterized electrostatically actuated microtweezers that integrate a differential capacitive sensor. The prototype showed an electrical insulation better than 1 GΩ between the different elements of the device. Furthermore, using a lock-in amplifier circuit, we could measure the position of the moving probe with few nanometers resolution for a displacement range of about 3 µm. This work was presented in part at the 21st IEEE MEMS Conference (Tucson, AZ, USA, 13-17 January, 2008) (doi:10.1109/MEMSYS.2008.4443656).

  16. Measuring the aspect ratio renormalization of anisotropic-lattice gluons

    SciTech Connect

    Alford, M.; Drummond, I. T.; Horgan, R. R.; Shanahan, H.; Peardon, M.

    2001-04-01

    Using tadpole-improved actions we investigate the consistency between different methods of measuring the aspect ratio renormalization of anisotropic-lattice gluons for bare aspect ratios {chi}{sub 0}=4,6,10 and inverse lattice spacing in the range a{sub s}{sup -1}=660--840 MeV. The tadpole corrections to the action, which are established self-consistently, are defined for two cases, mean link tadpoles in the Landau gauge and gauge invariant mean plaquette tadpoles. Parameters in the latter case exhibited no dependence on the spatial lattice size L, while in the former, parameters showed only a weak dependence on L easily extrapolated to L={infinity}. The renormalized anisotropy {chi}{sub R} was measured using both the torelon dispersion relation and the sideways potential method. There is general agreement between these approaches, but there are discrepancies which are evidence for the presence of lattice artifact contributions. For the torelon these are estimated to be O({alpha}{sub S}a{sub s}{sup 2}/R{sup 2}), where R is the flux-tube radius. We also present some new data that suggest that rotational invariance is established more accurately for the mean-link action than the plaquette action.

  17. Piezoresistance in polymer nanocomposites with high aspect ratio particles.

    PubMed

    Cattin, Cyrill; Hubert, Pascal

    2014-02-12

    In this paper, we address the problem of positive piezoresistance in high aspect ratio particle based polymer nanocomposites, a hybrid system at the center of research on flexible piezoresistive materials. We introduce a percolation theory based model relating the variation in electrical resistance to compressive strain and show that it gives accurate theoretical fits to experimental data presented in this paper, as well as to much of the available data in the literature. In contrast to existing theories, the model captures the characteristics of the particle network through experimentally definable parameters and does not rely on assumptions regarding the nature of the particles and/or the configuration of the network. It is further demonstrated that the presented theoretical framework is not limited to polymer nanocomposites with high aspect ratio particle but that it can explain piezoresistance in bulk electroconductive polymer nanocomposites in general. We find that the piezoresistive effect in such materials is rooted in a mechanical deformation induced change in the distribution of local conductances within the particle network, and we show that this change in the distribution of local conductances is well described by a strain dependent conductivity exponent, which scales with the magnitude of mechanical deformation. Besides, we demonstrate that these findings can be applied to the experimentally observed concentration dependence of the piezoresistance in polymer nanocomposites and, thus, to predicting the electric response to mechanical deformation at any particle concentration, which is expected to be highly instrumental in applied materials selection and performance evaluation. PMID:24410147

  18. Alternative lithographic methods for variable aspect ratio vias

    NASA Astrophysics Data System (ADS)

    Schepis, Anthony R.

    The foundation of semiconductor industry has historically been driven by scaling. Device size reduction is enabled by increased pattern density, enhancing functionality and effectively reducing cost per chip. Aggressive reductions in memory cell size have resulted in systems with diminishing area between parallel bit/word lines. This affords an even greater challenge in the patterning of contact level features that are inherently difficult to resolve because of their relatively small area, a product of their two domain critical dimension image. To accommodate these trends there has been a shift toward the implementation of elliptical contact features. This empowers designers to maximize the use of free space between bit/word lines and gate stacks while preserving contact area; effectively reducing the minor via axis dimension while maintaining a patternable threshold in increasingly dense circuitry. It is therefore critical to provide methods that enhance the resolving capacity of varying aspect ratio vias for implementation in electronic design systems. This work separately investigates two unique, non-traditional lithographic techniques in the integration of an optical vortex mask as well as a polymer assembly system as means to augment ellipticity while facilitating contact feature scaling. This document affords a fundamental overview of imaging theory, details previous literature as to the technological trends enabling the resolving of contact features and demonstrates simulated & empirical evidence that the described methods have great potential to extend the resolution of variable aspect ratio vias using lithographic technologies.

  19. Aspect Ratio Effects in the Driven, Flux-Core Spheromak

    SciTech Connect

    Hooper, E B; Romero-Talam?s, C A; LoDestro, L L; Wood, R D; McLean, H S

    2009-03-02

    Resistive magneto-hydrodynamic simulations are used to evaluate the effects of the aspect ratio, A (length to radius ratio) in a spheromak driven by coaxial helicity injection. The simulations are benchmarked against the Sustained Spheromak Physics Experiment (SSPX) [R. D. Wood, et al., Nucl. Nucl. Fusion 45, 1582 (2005)]. Amplification of the bias ('gun') poloidal flux is fit well by a linear dependence (insensitive to A) on the ratio of gun current and bias flux above a threshold dependent on A. For low flux amplifications in the simulations the n = 1 mode is coherent and the mean-field geometry looks like a tilted spheromak. Because the mode has relatively large amplitude the field lines are open everywhere, allowing helicity penetration. Strongly-driven helicity injection at A {le} 1.4 in simulations generates reconnection events which open the magnetic field lines; this state is characteristic of SSPX. Near the spheromak tilt-mode limit, A {approx} 1.67 for a cylindrical flux conserver, the tilt approaches 90{sup o}; reconnection events are not generated up to the strongest drives simulated. The time-sequence of these events suggests that they are representative of a chaotic process. Implications for spheromak experiments are discussed.

  20. Vortex Interaction on Low Aspect Ratio Membrane Wings

    NASA Astrophysics Data System (ADS)

    Waldman, Rye M.; Breuer, Kenneth S.

    2013-11-01

    Inspired by the flight of bats and by recent interest in Micro Air Vehicles, we present measurements on the steady and unsteady behavior of low aspect ratio membrane wings. We conduct wind tunnel experiments with coupled force, kinematic, and flow field measurements, both on the wing and in the near wake. Membrane wings interact strongly with the vortices shed from the leading- and trailing-edges and the wing tips, and the details of the membrane support play an important role in the fluid-structure interaction. Membranes that are supported at the wing tip exhibit less membrane flutter, more coherent tip vortices, and enhanced lift. The interior wake can exhibit organized spanwise vortex shedding, and shows little influence from the tip vortex. In contrast, membranes with an unsupported wing tip show exaggerated static deformation, significant membrane fluttering and a diffuse, unsteady tip vortex. The unsteady tip vortex modifies the behavior of the interior wake, disrupting the wake coherence.

  1. Fabrication of high aspect ratio micro electrode by using EDM

    NASA Astrophysics Data System (ADS)

    Mejid Elsiti, Nagwa; Noordin, M. Y.; Umar Alkali, Adam

    2016-02-01

    The electrical discharge machining (EDM) process inherits characteristics that make it a promising micro-machining technique. Micro electrical discharge machining (micro- EDM) is a derived form of EDM, which is commonly used to manufacture micro and miniature parts and components by using the conventional electrical discharge machining fundamentals. Moving block electro discharge grinding (Moving BEDG) is one of the processes that can be used to fabricate micro-electrode. In this study, a conventional die sinker EDM machine was used to fabricate the micro-electrode. Modifications are made to the moving BEDG, which include changing the direction of movements and control gap in one electrode. Consequently current was controlled due to the use of roughing, semi-finishing and finishing parameters. Finally, a high aspect ratio micro-electrode with a diameter of 110.49μm and length of 6000μm was fabricated.

  2. Aerodynamic performance of a transonic low aspect ratio turbine nozzle

    SciTech Connect

    Moustapha, S.H. . Turbine Aerodynamics); Carscallen, W.E. . Combustion and Fluids Engineering Lab.); McGeachy, J.D. . Dept. of Mechanical Engineering)

    1993-07-01

    This paper presents detailed information of the three-dimensional flow field in a realistic turbine nozzle with an aspect ratio of 0.65 and a turning angle of 76 deg. The nozzle has been tested in a large-scale planar cascade over a range of exit Mach numbers from 0.3 to 1.3. The experimental results are presented in the form of nozzle passage Mach number distributions and spanwise distribution of losses and exit flow angle. Details of the flow field inside the nozzle passage are examined by means of surface flow visualization and Schlieren pictures. The performance of the nozzle is compared to the data obtained for the same nozzle tested in an annular cascade and a stage environment. Excellent agreement is found between the measured pressure distribution and the prediction of a three-dimensional Euler flow solver.

  3. Dielectric spectroscopy of high aspect ratio graphene-polyurethane nanocomposites

    NASA Astrophysics Data System (ADS)

    Jan, Rahim; Habib, Amir; Abbassi, Hina; Amir, Shahid

    2015-03-01

    High aspect ratio graphene nanosheets (GNS), prepared via liquid exfoliation, are homogeneously dispersed in thermoplastic polyurethane (TPU). Dielectric spectroscopy results are reported for these nanocomposites (up to 0.55 vol. % GNS) in the frequency range of 100 Hz to 5 MHz. The as-prepared GNS increased the AC conductivity 10-1000 times across the given frequency range. The dielectric constant is increased 5-6 times at 100 Hz for the maximum loading of GNS when compared with the pristine TPU, with subsequently high dielectric loss making them a suitable candidate for high energy dissipation applications such as EMI shielding. The temperature effects on the dielectric characteristics of 0.55 vol. % GNS/TPU nanocomposites beyond 400 K are more pronounced due to the interfacial and orientation polarization. Mechanical characteristics evaluation of GNS/TPU composites shows a marked increase in the ultimate tensile strength without compromising their ductility and stiffness. [Figure not available: see fulltext.

  4. Flexible replication technique for high-aspect-ratio nanostructures.

    PubMed

    Szeghalmi, Adriana; Sklarek, Kornelia; Helgert, Michael; Brunner, Robert; Erfurth, Wilfried; Gosele, Ulrich; Knez, Mato

    2010-12-01

    A flexible, nondestructive, and cost-effective replication technique for nanostructures is presented. The advantages of the process are: 1) it allows for tailoring structural parameters of the replica (e.g., line width) nearly independent of the structural geometry of the master; 2) it allows for replication of high-aspect-ratio structures also in polymer materials from solution (especially noncurable polymers) such as polystyrene and polymethylmethacrylate; 3) it includes an easy separation process, thus preserving the master for repeated use. Linear grating replicas with line widths ranging from 88 to 300 nm are obtained using a single nanostructured master. Nanofibers and complex nanopatterned replicas are achievable. The presented technique and its flexibility show that atomic layer deposition is a unique tool for the preparation of high-efficiency polarizer diffractive optics, photonics, electronics, and catalysts. PMID:21069891

  5. Modular low-aspect-ratio high-beta torsatron

    DOEpatents

    Sheffield, G.V.

    1982-04-01

    A fusion-reactor device is described which the toroidal magnetic field and at least a portion of the poloidal magnetic field are provided by a single set of modular coils. The coils are arranged on the surface of a low-aspect-ratio toroid in planed having the cylindrical coordinate relationship phi = phi/sub i/ + kz, where k is a constant equal to each coil's pitch and phi/sub i/ is the toroidal angle at which the i'th coil intersects the z = o plane. The toroid defined by the modular coils preferably has a race track minor cross section. When vertical field coils and, preferably, a toroidal plasma current are provided for magnetic-field-surface closure within the toroid, a vacuum magnetic field of racetrack-shaped minor cross section with improved stability and beta valves is obtained.

  6. Modular low aspect ratio-high beta torsatron

    DOEpatents

    Sheffield, George V.; Furth, Harold P.

    1984-02-07

    A fusion reactor device in which the toroidal magnetic field and at least a portion of the poloidal magnetic field are provided by a single set of modular coils. The coils are arranged on the surface of a low aspect ratio toroid in planes having the cylindrical coordinate relationship .phi.=.phi..sub.i +kz where k is a constant equal to each coil's pitch and .phi..sub.i is the toroidal angle at which the i'th coil intersects the z=o plane. The device may be described as a modular, high beta torsation whose screw symmetry is pointed along the systems major (z) axis. The toroid defined by the modular coils preferably has a racetrack minor cross section. When vertical field coils and preferably a toroidal plasma current are provided for magnetic field surface closure within the toroid, a vacuum magnetic field of racetrack shaped minor cross section with improved stability and beta valves is obtained.

  7. Photoimageable Polyimide: A Dielectric Material For High Aspect Ratio Structures

    NASA Astrophysics Data System (ADS)

    Cech, Jay M.; Oprysko, Modest M.; Young, Peter L.; Li, Kin

    1986-07-01

    Polyimide has been identified as a useful material for microelectronic packaging because of its low dielectric constant and high temperature stability. Difficulties involved with reactive ion etching (RIE), a conventional technique for patterning thick polyimide films (thickness greater than 5 microns) with vertical walls, can be overcome by using photimageable polyimide precursors. The processing steps are similar to those used with negative photoresists. EM Chemical's HTR-3 photosensitive polyimide has been spun on up to a thickness of 12 microns. Exposure with a dose of 780 mJcm-2 of ultraviolet light, followed by spin development produces clean patterns as small as 5 microns corresponding to an aspect ratio of 2.4. When the patterned precursor is heated, an imidization reaction occurs converting the patterned film to polyimide. Baking to ca. 400 degrees C results in substantial loss in the thickness and in line width. However, shrinkage occurs reproducibly so useful rules for mask design can be formulated. Near vertical wall structures can be fabricated by taking advantage of the optical and shrinkage properties of the polyimide precursor. After development, an undercut wall profile can be produced since the bottom of the film receives less exposure and is hence more soluble in the developer. During heating, lateral shrinkage pulls the top of the film inward producing a vertical wall since the bottom is fixed to the substrate by adhesion. As a result, fully cured polyimide structures with straight walls and aspect ratios greater than one can be obtained. Dielectric properties of the fully imidized films were investigated with capacitor test structures. A relative dielectric constant of 3.3 and a loss tangent of .002 were measured at 20 kHz. It was also found that the dielectric constant increases as a linear function of relative humidity.

  8. Noise Measurements of High Aspect Ratio Distributed Exhaust Systems

    NASA Technical Reports Server (NTRS)

    Bridges, James

    2015-01-01

    This paper covers far-field acoustic measurements of a family of rectangular nozzles with aspect ratio 8, in the high subsonic flow regime. Several variations of nozzle geometry, commonly proposed for embedded exhaust systems, are explored, including bevels, slants, single broad chevrons and notches, and internal septae. Far-field acoustic results, presented previously for the simple rectangular nozzle, showed that increasing aspect ratio increases the high frequency noise, especially directed in the plane containing the minor axis of the nozzle. Detailed changes to the nozzle geometry generally made little difference in the noise, and the differences were greatest at low speed. Having an extended lip on one broad side ('bevel') did produce up to 3dB more noise in all directions, while extending the lip on the narrow side ('slant') produced up to 2dB more noise, primarily on the side with the extension. Adding a single, non-intrusive chevron, made no significant change to the noise, while inverting the chevron ('notch') produced up to 2dB increase in the noise. Having internal walls ('septae') within the nozzle, such as would be required for structural support or when multiple fan ducts are aggregated, reduced the noise of the rectangular jet, but could produce a highly directional shedding tone from the septae trailing edges. Finally, a nozzle with both septae and a beveled nozzle, representative of the exhaust system envisioned for a distributed propulsion aircraft with a common rectangular duct, produced almost as much noise as the beveled nozzle, with the septae not contributing much reduction in noise.

  9. Noise Measurements of High Aspect Ratio Distributed Exhaust Systems

    NASA Technical Reports Server (NTRS)

    Bridges, James E.

    2015-01-01

    This paper covers far-field acoustic measurements of a family of rectangular nozzles with aspect ratio 8, in the high subsonic flow regime. Several variations of nozzle geometry, commonly found in embedded exhaust systems, are explored, including bevels, slants, single broad chevrons and notches, and internal septae. Far-field acoustic results, presented previously for the simple rectangular nozzle, showed that increasing aspect ratio increases the high frequency noise, especially directed in the plane containing the minor axis of the nozzle. Detailed changes to the nozzle geometry generally made little difference in the noise, and the differences were greatest at low speed. Having an extended lip on one broad side (bevel) did produce up to 3 decibels more noise in all directions, while extending the lip on the narrow side (slant) produced up to 2 decibels more noise, primarily on the side with the extension. Adding a single, non-intrusive chevron, made no significant change to the noise, while inverting the chevron (notch) produced up to 2decibels increase in the noise. Having internal walls (septae) within the nozzle, such as would be required for structural support or when multiple fan ducts are aggregated, reduced the noise of the rectangular jet, but could produce a highly directional shedding tone from the septae trailing edges. Finally, a nozzle with both septae and a beveled nozzle, representative of the exhaust system envisioned for a distributed electric propulsion aircraft with a common rectangular duct, produced almost as much noise as the beveled nozzle, with the septae not contributing much reduction in noise.

  10. H-mode Characteristics and ELM Dynamics at Near-Unity Aspect Ratio

    NASA Astrophysics Data System (ADS)

    Thome, K. E.; Bodner, G. M.; Bongard, M. W.; Burke, M. G.; Fonck, R. J.; Schlossberg, D. J.

    2014-10-01

    Ohmic H-mode is achieved at near-unity aspect ratio in the Pegasus Toroidal Experiment through the use of high-field-side fueling in both limited and diverted geometries. This regime is characterized by: increased edge rotation shear; increased central heating; and measured energy confinement consistent with the ITER98pb(y,2) scaling. In limited plasmas the power threshold is ~ 10 × higher than predicted by the high- A empirical tokamak scaling for nG = 0 . 1- 0 . 6 . No significant reduction in the power threshold has been observed in favorable ∇B SN plasma when compared to limited plasmas. Two classes of ELMs have been identified to date by their proximity to the power threshold and measured n spectra. Small, Type III-like ELMs are present at input power POH ~Pth and have n <= 4 . At POH >>Pth , they transition to large, Type-I-like ELMs with intermediate 5 < n < 15. These general mode numbers are opposite those seen at large A and reflect the increased peeling drive present at low A . The unique operating characteristics available at A ~ 1 in Pegasus allow long-sought measurements of the time evolution of the Jedge (R) pedestal collapse during an ELM event. They show a complex, multimodal pedestal collapse and the subsequent ejection of a current-carrying filament. Work supported by US DOE Grant DE-FG02-96ER54375.

  11. Influence of Ground Effect on Low Aspect Ratio Membrane Wings

    NASA Astrophysics Data System (ADS)

    Bleischwitz, Robert; de Kat, Roeland; Ganapathisubramani, Bharathram

    2014-11-01

    Inspired by the current interest of membrane wings for Micro Air Vehicles (MAVs) and hard limits in aerodynamic performance for wings in moderate Reynolds number regimes, an experimental wind tunnel study is conducted at a Reynolds number of approximately 65,000 to determine the aeromechanics of flexible, low aspect ratio (AR) membrane wings (AR <= 2) in the vicinity of the ground. Pitch angle α and height over ground h / c is varied with a traverse system. Flexible membrane wings are compared with rigid flat plates. A rolling road is used to impose the ground effect and the boundary layer leading up to the road is removed using a suction system. Time-averaged lift, drag and pitch moment changes are captured with a 6-axis force transducer and its effects are interpreted in terms of the membrane motions obtained using Direct-Image-Correlation (DIC) technique. Flow-structure-ground interactions are examined and the membrane dynamics are compared to results obtained outside of ground effect. Ultimately, understanding the ground effect on flexible membrane wings at moderate Reynolds numbers could help to design Wing-in-Ground MAVs with extended range and reduced energy consumption.

  12. Double-Diffusive Convection in Low-Aspect Ratio Containers

    NASA Astrophysics Data System (ADS)

    Pol, S.; Fernando, H. J. S.; Webb, S.

    2008-11-01

    Laboratory experiments and phenomenological modeling were undertaken to investigate the influence of container sidewalls on the evolution of diffusive layering in confined double-diffusive systems. Such flow configurations are common in engineering situations, including underground storage caverns of national strategic petroleum reserves. The laboratory flow configuration consisted of a linearly salt stratified fluid subjected to either heating from below or uniform heating from both the bottom and sidewalls. A number of different containers were used, allowing investigations over a range of governing parameters. The growth of the lowest mixed layer as well as multiple convecting layers aloft separated by diffusive interfaces were monitored using LIF, PIV and traversing temperature/conductivity probe techniques. The aspect ratio for side walls to become important was inferred by the bottom-layer growth measurements, which undergoes a transition of the growth law upon onset of side-wall effects. The combined side and bottom wall heating case was strikingly different from the bottom heating case, wherein layers of approximately equal heights are generated rather rapidly in the former as a result of convective plumes rising along the sidewalls and their arrest by the background stable density gradient. Theoretical arguments were advanced to explain and parameterize experimental observations.

  13. Aspect ratio effects on revolving wings with Rossby number consideration.

    PubMed

    Lee, Y J; Lua, K B; Lim, T T

    2016-01-01

    Numerical simulations have been conducted to investigate the effect of aspect ratio (AR) on the mean lift generation of a revolving flat rectangular wing. The purpose of the study is to address some discrepancies reported in the literature regarding the influence of AR on mean lift coefficient. Here, we consider a range of AR from 1 to 10 and Rossby number (Ro) from 0.58 to 7.57, and our results show that different degrees of coupling between AR and Ro yield different trends of a mean lift coefficient with respect to increasing AR. The choice of reference velocity for the normalisation of mean lift forces also has a significant effect on the perceived AR effect. By isolating the effect of Ro, we found that higher AR produces higher mean lift coefficient until it plateaus at a sufficiently high AR. This finding is consistent with conventional fixed wing aerodynamics. Additionally, our results show that increasing AR reduces the three-dimensional wing tip effect and is beneficial to mean lift generation while higher Ro increases leading-edge vortex instability, which is detrimental to mean lift generation. Therefore, mean lift generation on revolving wings is dictated by the competition between these two factors, which represent two fundamentally independent phenomena. PMID:27608653

  14. Determination of sub-micrometer high aspect ratio grating profiles

    NASA Astrophysics Data System (ADS)

    Garnaes, J.; Hansen, P.-E.; Agersnap, N.; Davi, I.; Petersen, J. C.; Kuehle, A.; Holm, J.; Christensen, L. H.

    2005-08-01

    Atomic force microscopy (AFM) and optical diffraction microscopy (ODM) are used to measure the profiles of grating grooves with depths much larger than their widths. Gratings with these features are essential in numerous optical devices such as spectrometers, monochromators and for the production of many fibre Bragg gratings. However, measurement of the physical shape is inherently difficult but necessary for the understanding of their function and in order to improve the manufacturing process. After a thorough calibration of an AFM and by tilting the plane of the grating by up to 17° relative to the symmetry axis of the sensing probe we measured accurately and traceably the sidewall angle and the sidewall profile in a non-destructive way. ODM is a new method where the intensity of the optical field diffracted is measured as a function of the frequency and an inverse algorithm is used to reconstruct the surface profile. It is fast, non-destructive, and it gives height and filling degree of a grating very accurately. As example a high aspect ratio grating with period p of 220 nm, depths d of ≈300 nm, and sidewall angles γ of approximately ≈90° and filling degree f of ≈40 % were examined. Standard uncertainties as low as u(d) = 3 nm, u( α) = 0.4° and u(f) = 3.1 % were achieved. Despite the fact that the AFM responds to the physical surface and ODM responds to the optical properties of the material we find that the results are in very good agreement and consistent with (destructive) scanning electron microscopy measurements of the filling degree.

  15. Capillary force in high aspect-ratio micropillar arrays

    NASA Astrophysics Data System (ADS)

    Chandra, Dinesh

    High aspect-ratio (HAR) micropillar arrays are important for many applications including, mechanical sensors and actuators, tunable wetting surfaces and substrates for living cell studies. However, due to their mechanical compliance and large surface area, the micropillars are susceptible to deformation due to surface forces, such as adhesive force and capillary force. In this thesis we have explored the capillary force driven mechanical instability of HAR micropillar arrays. We have shown that when a liquid is evaporated off the micropillar arrays, the pillars bend and cluster together due to a much smaller capillary meniscus interaction force while still surrounded by a continuous liquid body, rather than due to often reported Laplace pressure difference because of isolated capillary bridges. We have studied both theoretically and experimentally, the capillary force induced clustering behavior of micropillar arrays as a function of their elastic modulus. To this end, we have developed a modified replica molding process to fabricate a wide range of hydrogel micropillar arrays, whose elastic modulus in the wet state could be tuned by simply varying the hydrogel monomer composition. By minimizing the sum of capillary meniscus interaction energy and bending energy of the pillars in a cluster, we have derived a critical micropillar cluster size, which is inversely proportional to elastic modulus of micropillars. The estimated cluster size as a function of elastic modulus agrees well with our experimental observation. We have also explored the utility of the clustered micropillar arrays as ultrathin whitening layers mimicking the structural whitening mechanism found in some insects in nature. Finally, we have theoretically studied the capillary force induced imbibition of a liquid droplet on a model rough surface consisting of micropillar arrays. Our theoretical model suggests that due to shrinking liquid droplet, the imbibition dynamics does not follow the diffusive

  16. Dimensions and aspect ratios of natural ice crystals

    NASA Astrophysics Data System (ADS)

    Um, J.; McFarquhar, G. M.; Hong, Y. P.; Lee, S.-S.; Jung, C. H.; Lawson, R. P.; Mo, Q.

    2015-04-01

    During the 2006 Tropical Warm Pool International Cloud Experiment (TWP-ICE) in the tropics, the 2008 Indirect and Semi-Direct Aerosol Campaign (ISDAC) in the Arctic, and the 2010 Small PARTicles In CirrUS (SPARTICUS) campaign at mid-latitudes, high-resolution images of ice crystals were recorded by a Cloud Particle Imager at temperatures (T) between -87 and 0 °C. The projected maximum dimension (D'), length (L'), and width (W') of pristine columns, plates, and component bullets of bullet rosettes were measured using newly developed software, the Ice Crystal Ruler. The number of bullets in each bullet rosette was also measured. Column crystals were further distinguished as either horizontally oriented columns or columns with other orientations to eliminate any orientation effect on the measured dimensions. The dimensions and aspect ratios (AR, the dimension of the major axis divided by the dimension of the minor axis) of crystals were determined as functions of temperature, geophysical location, and type of cirrus. Dimensions of crystals generally increased with temperature. Columns and bullets had larger dimensions (i.e., W') of the minor axis (i.e., a axis) for a given dimension (i.e., D' orL') of the major axis (i.e., c axis), and thus smaller AR, as T increased, whereas this trend did not occur for plate crystals. The average number of branches in bullet rosettes was 5.50 ± 1.35 during three campaigns and 6.32 ± 1.34 (5.46 ± 1.34; 4.95 ± 1.01) during TWP-ICE (SPARTICUS; ISDAC). The AR of bullets increased with the number of branches in bullet rosettes. Most dimensions of crystals and ARs of columnar crystals measured during SPARTICUS were larger than those measured during TWP-ICE and ISDAC at -67 < T < -35 °C and at -40 < T < -15 °C, respectively. The relative occurrence of varying pristine habits depended strongly on cirrus type (i.e., anvil or non-anvil clouds), with plates especially occurring more frequently in anvils. The L-W relationships of columns

  17. Dimensions and aspect ratios of natural ice crystals

    DOE PAGESBeta

    Um, J.; McFarquhar, G. M.; Hong, Y. P.; Lee, S. -S.; Jung, C. H.; Lawson, R. P.; Mo, Q.

    2015-04-15

    During the 2006 Tropical Warm Pool International Cloud Experiment (TWP-ICE) in the tropics, the 2008 Indirect and Semi-Direct Aerosol Campaign (ISDAC) in the Arctic, and the 2010 Small PARTicles In CirrUS (SPARTICUS) campaign at mid-latitudes, high-resolution images of ice crystals were recorded by a Cloud Particle Imager at temperatures (T) between -87 and 0 °C. The projected maximum dimension (D'), length (L'), and width (W') of pristine columns, plates, and component bullets of bullet rosettes were measured using newly developed software, the Ice Crystal Ruler. The number of bullets in each bullet rosette was also measured. Column crystals were furthermore » distinguished as either horizontally oriented columns or columns with other orientations to eliminate any orientation effect on the measured dimensions. The dimensions and aspect ratios (AR, the dimension of the major axis divided by the dimension of the minor axis) of crystals were determined as functions of temperature, geophysical location, and type of cirrus. Dimensions of crystals generally increased with temperature. Columns and bullets had larger dimensions (i.e., W') of the minor axis (i.e., a axis) for a given dimension (i.e., D' orL') of the major axis (i.e., c axis), and thus smaller AR, as T increased, whereas this trend did not occur for plate crystals. The average number of branches in bullet rosettes was 5.50 ± 1.35 during three campaigns and 6.32 ± 1.34 (5.46 ± 1.34; 4.95 ± 1.01) during TWP-ICE (SPARTICUS; ISDAC). The AR of bullets increased with the number of branches in bullet rosettes. Most dimensions of crystals and ARs of columnar crystals measured during SPARTICUS were larger than those measured during TWP-ICE and ISDAC at −67 < T < -35 °C and at −40 < T < −15 °C, respectively. The relative occurrence of varying pristine habits depended strongly on cirrus type (i.e., anvil or non-anvil clouds), with plates especially occurring more frequently in anvils. The L

  18. Dimensions and aspect ratios of natural ice crystals

    DOE PAGESBeta

    Um, J.; McFarquhar, G. M.; Hong, Y. P.; Lee, S. -S.; Jung, C. H.; Lawson, R. P.; Mo, Q.

    2014-12-10

    During the 2006 Tropical Warm Pool International Cloud Experiment (TWP-ICE) in the Tropics, the 2008 Indirect and Semi-Direct Aerosol Campaign (ISDAC) in the Arctic, and the 2010 Small PARTicles In CirrUS (SPARTICUS) campaign in mid-latitudes, high-resolution images of ice crystals were recorded by a Cloud Particle Imager at temperatures (T) between -87 and 0 °C. The projected maximum dimension (D'), length (L'), and width (W') of pristine columns, plates, and component bullets of bullet rosettes were measured using newly developed software, the Ice Crystal Ruler. The number of bullets in each bullet rosette was also measured. Column crystals were furthermore » distinguished as either horizontally oriented columns or columns with other orientations to eliminate any orientation effect on the measured dimensions. Dimensions and aspect ratios (AR, dimension of major axis divided by dimension of minor axis) of crystals were determined as functions of temperature, geophysical location, and type of cirrus. Dimensions of crystals generally increased as temperature increased. Columns and bullets had larger dimensions (i.e., W') of the minor axis (i.e., a axis) for a given dimension (i.e., D' or L') of the major axis (i.e., c axis), and thus smaller AR, as T increased, whereas this trend did not occur for plate crystals. The average number of branches in bullet rosettes was 5.50±1.35 during three campaigns and 6.32±1.34 (5.46±1.34; 4.95±1.01) during TWP-ICE (SPARTICUS; ISDAC). The AR of bullets increased with the number of branches in bullet rosettes. Most dimensions of crystals and ARs of columnar crystals measured during SPARTICUS were larger than those measured during TWP-ICE and ISDAC at −67 < T < −35 °C and at −40 < T < −15 °C, respectively. The relative occurrence of varying pristine habits depended strongly on cirrus type (i.e., anvil or non-anvil clouds), with plates especially occurring more frequently in anvils. The L–W relationships of columns

  19. High Beta Tokamaks

    SciTech Connect

    Cowley, S.

    1998-11-14

    Perhaps the ideal tokamak would have high {beta} ({beta} {approx}> 1) and classical confinement. Such a tokamak has not been found, and we do not know if one does exist. We have searched for such a possibility, so far without success. In 1990, we obtained analytic equilibrium solutions for large aspect ratio tokamaks at {beta} {approx} {Omicron}(1) [1]. These solutions and the extension at high {beta} poloidal to finite aspect ratio [2] provided a basis for the study of high {beta} tokamaks. We have shown that these configurations can be stable to short scale MHD modes [3], and that they have reduced neoclassical transport [4]. Microinstabilities (such as the {del}T{sub i} mode) seem to be stabilized at high {beta} [5] - this is due to the large local shear [3] and the magnetic well. We have some concerns about modes associated with the compressional branch which may appear at high {beta}. Bill Dorland and Mike Kotschenreuther have studied this issue and our concerns may be unfounded. It is certainly tantalizing, especially given the lowered neoclassical transport values, that these configurations could have no microinstabilities and, one could assume, no anomalous transport. Unfortunately, while this work is encouraging, the key question for high {beta} tokamaks is the stability to large scale kink modes. The MHD {beta} limit (Troyon limit) for kink modes at large aspect ratio is problematically low. There is ample evidence from computations that the limit exists. However, it is not known if stable equilibria exist at much higher {beta}--none have been found. We have explored this question in the asymptotic high {beta} poloidal limit. Unfortunately, we are unable to find stable equilibrium and also unable to show that they don't exist. The results of these calculations will be published when a more definitive answer is found.

  20. Effect of Aspect Ratio on the Low-Speed Lateral Control Characteristics of Untapered Low-Aspect-Ratio Wings Equipped with Flap and with Retractable Ailerons

    NASA Technical Reports Server (NTRS)

    Fischel, Jack; Naeseth, Rodger L; Hagerman, John R; O'Hare, William M

    1952-01-01

    A low-speed wind-tunnel investigation was made to determine the lateral control characteristics of a series of untapered low-aspect-ratio wings. Sealed flap ailerons of various spans and spanwise locations were investigated on unswept wings of aspect ratios 1.13, 1.13, 4.13, and 6.13; and various projections of 0.60-semispan retractable ailerons were investigated on the unsweptback wings of aspect ratios 1.13, 2.13, and 4.13 and on a 45 degree sweptback wing. The retractable ailerons investigated on the unswept wings spanned the outboard stations of each wing; whereas the plain and stepped retractable ailerons investigated on the sweptback wing were located at various spanwise stations. Design charts based on experimental results are presented for estimating the flap aileron effectiveness for low-aspect-ratio, untapered, unswept.

  1. The effect of aspect ratio and fluid flow on crystal growth

    NASA Technical Reports Server (NTRS)

    Barber, Patrick G.

    1986-01-01

    Supersaturated solutions were conditioned at different aspect ratios before crystal growth. The conditioned solutions were poured out into a dish to initiate crystal nucleation and growth. The rate of growth was measured microscopically and found to depend upon the aspect ratio. Secondly, the number and size of crystals formed was found to depend upon the aspect ratio. The data support the above conclusion, but do not prove it.

  2. The effect of aspect ratio on adhesion and stiffness for soft elastic fibres

    PubMed Central

    Aksak, Burak; Hui, Chung-Yuen; Sitti, Metin

    2011-01-01

    The effect of aspect ratio on the pull-off stress and stiffness of soft elastic fibres is studied using elasticity and numerical analysis. The adhesive interface between a soft fibre and a smooth rigid surface is modelled using the Dugdale–Barenblatt model. Numerical simulations show that, while pull-off stress increases with decreasing aspect ratio, fibres get stiffer. Also, for sufficiently low aspect ratio fibres, failure occurs via the growth of internal cracks and pull-off stress approaches the intrinsic adhesive strength. Experiments carried out with various aspect ratio polyurethane elastomer fibres are consistent with the numerical simulations. PMID:21227962

  3. OPTIMUM PLASMA STATES FOR NEXT STEP TOKAMAKS

    SciTech Connect

    LIN-LIU,YR; STAMBAUGH,RD

    2002-11-01

    OAK A271 OPTIMUM PLASMA STATES FOR NEXT STEP TOKAMAKS. The dependence of the ideal ballooning {beta} limit on aspect ratio, A, and elongation {kappa} is systematically explored for nearly 100% bootstrap current driven tokamak equilibria in a wide range of the shape parameters (A = 1.2-7.0, {kappa} = 1.5-6.0 with triangularity {delta} = 0.5). The critical {beta}{sub N} is shown to be optimal at {kappa} = 3.0-4.0 for all A studied and increases as A decreases with a dependence close to A{sup -0.5}. The results obtained can be used as a theoretical basis for the choice of optimum aspect ratio and elongation of next step burning plasma tokamaks or tokamak reactors.

  4. THE RAYLEIGH-TAYLOR INSTABILITY IN SMALL ASPECT RATIO CONTAINERS

    SciTech Connect

    RIVERA, MICHAEL K.; ECKE, ROBERT E.

    2007-01-22

    We present experimental measurements of density and velocity obtained from the mixing zone of buoyancy driven turbulence initiated by the Rayleigh-Taylor instability in a small aspect ration chamber (a chamber who's vertical height is significantly larger than its lateral dimesion). The mixing front propogates at a slightly slower rate than the expected t{sup 2} behavior obtained from earlier experiments and numerics. Once the front has propogated significantly far away, we observe that the mixing zone develops to a statistically stationary state. In this stationary state, the spectral distributions of energy and density deviate from the familiar k{sup -5/3} ubiquitous to turbulence in three dimensions.

  5. Hydrodynamic chromatography and field flow fractionation in finite aspect ratio channels.

    PubMed

    Shendruk, T N; Slater, G W

    2014-04-25

    Hydrodynamic chromatography (HC) and field-flow fractionation (FFF) separation methods are often performed in 3D rectangular channels, though ideal retention theory assumes 2D systems. Devices are commonly designed with large aspect ratios; however, it can be unavoidable or desirable to design rectangular channels with small or even near-unity aspect ratios. To assess the significance of finite-aspect ratio effects and interpret experimental retention results, an ideal, analytical retention theory is needed. We derive a series solution for the ideal retention ratio of HC and FFF rectangular channels. Rather than limiting devices' ability to resolve samples, our theory predicts that retention curves for normal-mode FFF are well approximated by the infinite plate solution and that the performance of HC is actually improved. These findings suggest that FFF devices need not be designed with large aspect ratios and that rectangular HC channels are optimal when the aspect ratio is unity. PMID:24674643

  6. The Effect of Cooling Passage Aspect Ratio on Curvature Heat Transfer Enhancement

    NASA Technical Reports Server (NTRS)

    Meyer, Michael L.

    1997-01-01

    A series of electrically heated tube experiments was performed to investigate the effect of high aspect ratio on curvature heat transfer enhancement in uniformly heated rectangular cooling passages. Three hardware geometries were tested: a baseline straight aspect ratio 10 tube, an aspect ratio 1 (square) tube with a 45 deg. curve, and an aspect ratio 10 tube with a 45 deg. curve. Gaseous nitrogen with the following properties was used as the coolant: ambient inlet temperature, pressures to 8.3 MPa, wall-to-bulk temperature ratios less than two, and Reynolds numbers based on hydraulic diameter ranging from 250,000 to 1,600,000. The measured curvature enhancement factors were compared to values predicted by three previously published models which had been developed for low aspect ratio tubes. The models were shown to be valid for the high aspect ratio tube as well the low aspect ratio tube, indicating that aspect ratio had little impact on the curvature heat transfer enhancement in these tests.

  7. Gelation effect on the synthesis of high-aspect-ratio gold nanorods.

    PubMed

    Takenaka, Yoshiko; Kitahata, Hiroyuki; Yamada, Norifumi L; Seto, Hideki; Hara, Masahiko

    2012-01-01

    The growth process of high-aspect-ratio gold nanorods in gelled surfactant solution was studied. As for the application of gold nanorods, the surface plasmon is quite useful, whose absorption depends on their aspect ratio. Hence it is important to synthesize gold nanorods with favorable aspect ratio in high yield. For shorter nanorods (aspect ratio < -10), the synthesis and the growth mechanism have been studied well. For the longer nanorods (aspect ratio > -30), however, the growth mechanism has not yet been understood well, although it has been known that the high-aspect-ratio gold nanorods could be synthesized in high yield in gelled surfactant solution. In this paper, we studied the relationship between the growth process of high-aspect-ratio gold nanorods and the gelation of surfactant growth-solution. Small angle X-ray scattering (SAXS) revealed the microscopic feature of gelation as the structural transition of self-assembly of surfactant molecules from micellar to lamellar. These results will be helpful for better understanding on the growth mechanism of high-aspect-ratio gold nanorods. PMID:22524045

  8. New Vehicle Detection Method with Aspect Ratio Estimation for Hypothesized Windows

    PubMed Central

    Kim, Jisu; Baek, Jeonghyun; Park, Yongseo; Kim, Euntai

    2015-01-01

    All kinds of vehicles have different ratios of width to height, which are called the aspect ratios. Most previous works, however, use a fixed aspect ratio for vehicle detection (VD). The use of a fixed vehicle aspect ratio for VD degrades the performance. Thus, the estimation of a vehicle aspect ratio is an important part of robust VD. Taking this idea into account, a new on-road vehicle detection system is proposed in this paper. The proposed method estimates the aspect ratio of the hypothesized windows to improve the VD performance. Our proposed method uses an Aggregate Channel Feature (ACF) and a support vector machine (SVM) to verify the hypothesized windows with the estimated aspect ratio. The contribution of this paper is threefold. First, the estimation of vehicle aspect ratio is inserted between the HG (hypothesis generation) and the HV (hypothesis verification). Second, a simple HG method named a signed horizontal edge map is proposed to speed up VD. Third, a new measure is proposed to represent the overlapping ratio between the ground truth and the detection results. This new measure is used to show that the proposed method is better than previous works in terms of robust VD. Finally, the Pittsburgh dataset is used to verify the performance of the proposed method. PMID:26690177

  9. Effect of Stator and Rotor Aspect Ratio on Transonic-Turbine Performance

    NASA Technical Reports Server (NTRS)

    Wong, Robert Y.; Monroe, Daniel E.

    1959-01-01

    The effect of stator and rotor aspect ratio on transonic-turbine performance was experimentally investigated. The stator aspect ratios covered were 1.6. 0.8, and 0.4, while the rotor aspect ratios investigated were 1.46 and 0.73. It was found that the observed variation in turbine design-point efficiency was negligible. Thus, within the range of aspect ratio investigated, these results verify for turbines operating in the transonic flow range the finding of a reference report, which showed analytically that, if blade shape and solidity are held constant, the aspect ratio may be varied over a wide range without appreciable change in turbine efficiency.

  10. Aspect Ratio Effects on Fluid Flow Fluctuations in Rectangular Cavities

    NASA Astrophysics Data System (ADS)

    Kalter, Rudi; Tummers, Mark J.; Wefers Bettink, Jeroen B.; Righolt, Bernhard W.; Kenjereš, Sasa; Kleijn, Chris R.

    2014-12-01

    The flow from a submerged bifurcated nozzle into rectangular liquid-filled cavities with width-to-thickness ratios W/ T = 6.5, 11, and 18 has been studied using free surface visualization and particle tracking. When W/ T = 11 and when W/ T = 18, self-sustained oscillations of the submerged jets and the free surface are present. When W/ T = 6.5, the self-sustained oscillations are no longer present, but oscillations with the frequency of gravity waves occur. We propose a critical value of W/ T above which self-sustained jet oscillations occur, based on the spreading angle of turbulent jets. When W/ T is larger than this critical value, the shear layers of the jet reach the front and back wall of the cavity before the jet can impinge the side wall, resulting in semi two-dimensional flow in the plane between the front and the back wall. Two-dimensional recirculation zones form alongside the jet leading to the jet oscillations. When W/ T is smaller than this critical value, the jet can develop like a free turbulent jet up to an impingement point at the narrow side wall. When the jet impinges the side wall, flow in the directions parallel and perpendicular to the front and back walls is possible, resulting in complex three-dimensional flow patterns. The critical value for W/ T, based on the known 12 deg spreading angle of turbulent jets is W/ T = 10, which is in good agreement with the experimental results.

  11. Three-dimensional numerical simulation of Marangoni instabilities in liquid bridges: influence of geometrical aspect ratio

    NASA Astrophysics Data System (ADS)

    Lappa, M.; Savino, R.; Monti, R.

    2001-05-01

    Oscillatory Marangoni convection in silicone oil-liquid bridges with different geometrical aspect ratios is investigated by three-dimensional and time-dependent numerical simulations, based on control volume methods in staggered cylindrical non-uniform grids. The three-dimensional oscillatory flow regimes are studied and compared with previous experimental and theoretical results. The results show that the critical wavenumber (m), related to the azimuthal spatio-temporal flow structure, is a monotonically decreasing function of the geometrical aspect ratio of the liquid bridge (defined as the ratio of length to diameter). For this function, a general correlation formula is found, which is in agreement with the previous experimental findings. The critical Marangoni number and the oscillation frequency are decreasing functions of the aspect ratio; however, the critical Marangoni number, based on the axial length of the bridge, does not change much with the aspect ratio. For each aspect ratio investigated, the onset of the instability from the axisymmetric steady state to the three-dimensional oscillatory one is characterized by the appearance of a standing wave regime that exhibits, after a certain time, a second transition to a travelling wave regime. The standing wave regime is more stable for lower aspect ratios since it lasts for a long time. This behaviour is explained on the basis of the propagation velocity of the disturbances in the liquid phase. For this velocity, a general correlation law is found as a function of the aspect ratio and of the Marangoni number. Copyright

  12. Performance of a transonic compressor rotor with an aspect ratio of 6.5

    NASA Technical Reports Server (NTRS)

    Reid, L.; Tysl, E. R.

    1974-01-01

    The overall and blade-element performances and the aerodynamic design parameters of a transonic rotor with an aspect ratio of 6.5, designed to investigate the effects of aspect ratio on range and performance are presented. The rotor was designed for a total-pressure ratio of 1.53, an efficiency of 0.898, and a weight flow of 67.76 pounds per second.

  13. Flow visualization study in high aspect ratio cooling channels for rocket engines

    NASA Technical Reports Server (NTRS)

    Meyer, Michael L.; Giuliani, James E.

    1993-01-01

    The structural integrity of high pressure liquid propellant rocket engine thrust chambers is typically maintained through regenerative cooling. The coolant flows through passages formed either by constructing the chamber liner from tubes or by milling channels in a solid liner. Recently, Carlile and Quentmeyer showed life extending advantages (by lowering hot gas wall temperatures) of milling channels with larger height to width aspect ratios (AR is greater than 4) than the traditional, approximately square cross section, passages. Further, the total coolant pressure drop in the thrust chamber could also be reduced, resulting in lower turbomachinery power requirements. High aspect ratio cooling channels could offer many benefits to designers developing new high performance engines, such as the European Vulcain engine (which uses an aspect ratio up to 9). With platelet manufacturing technology, channel aspect ratios up to 15 could be formed offering potentially greater benefits. Some issues still exist with the high aspect ratio coolant channels. In a coolant passage of circular or square cross section, strong secondary vortices develop as the fluid passes through the curved throat region. These vortices mix the fluid and bring lower temperature coolant to the hot wall. Typically, the circulation enhances the heat transfer at the hot gas wall by about 40 percent over a straight channel. The effect that increasing channel aspect ratio has on the curvature heat transfer enhancement has not been sufficiently studied. If the increase in aspect ratio degrades the secondary flow, the fluid mixing will be reduced. Analysis has shown that reduced coolant mixing will result in significantly higher wall temperatures, due to thermal stratification in the coolant, thus decreasing the benefits of the high aspect ratio geometry. A better understanding of the fundamental flow phenomena in high aspect ratio channels with curvature is needed to fully evaluate the benefits of this

  14. Modular Coil Design for the Ultra-low Aspect Ratio Quasi-axially Symmetric Stellarator MHH2

    SciTech Connect

    Ku LP, the ARIES-CS Team

    2005-09-27

    A family of two field-period quasi-axisymmetric stellarators generally known as MHH2 with aspect ratios of only {approx}2.5 was found. These configurations have low field ripples and excellent confinement of {alpha} particles. This discovery raises the hope that a compact stellarator reactor may eventually be designed with the property of tokamak transport and stellarator stability. In this paper we demonstrate that smooth modular coils may be designed for this family of configurations that not only yield plasmas with good physics properties but also possess engineering properties desirable for compact power producing reactors. We show designs featuring 16 modular coils with ratios of major radius to minimum coil-plasma separation {approx}5.5, major radius to minimum coil-coil separation {approx}10 and the maximum field in coil bodies to the field on axis {approx}2 for 0.2 m{sup 2} conductors. These coils is expected to allow plasmas operated at 5% {beta} with {alpha} energy loss < 10% for a reactor of major radius <9 m at 5 T.

  15. High aspect ratio composite structures with 48.5% thermal neutron detection efficiency

    SciTech Connect

    Shao, Q.; Voss, L. F.; Conway, A. M.; Nikolic, R. J.; Dar, M. A.; Cheung, C. L.

    2013-02-11

    The pillar structured thermal neutron detector is based on the combination of high aspect ratio silicon p-i-n pillars surrounded by the neutron converter material {sup 10}B. By etching high aspect ratio pillar structures into silicon, the result is a device that efficiently absorbs the thermal neutron flux by accommodating a large volume fraction of {sup 10}B within the silicon pillar array. Here, we report a thermal neutron detection efficiency of 48.5% using a 50 {mu}m pillar array with an aspect ratio of 25:1.

  16. Effect of tip vortices on flow over NACA4412 aerofoil with different aspect ratios

    NASA Astrophysics Data System (ADS)

    Genç, Mustafa Serdar; Özkan, Gökhan; Hakan Açikel, Halil; Sadık Kiriş, Mehmet; Yildiz, Rahime

    2016-03-01

    Effect of tip vortices on flow and laminar separation bubble over NACA4412 aerofoil at low Reynolds numbers and different angles of attack was investigated in detail by performing force and flow visualization via smoke wire technique. Experiments have been done at Reynolds number of 50000 and the wing model of aspect-ratio was 1 and 3, respectively. From the experimental results, the flow visualization results showed that tip vortices effect on the laminar separation bubble and the bubble reduces over the wing with low aspect ratio as the angle of attack increased. Moreover, it was noticed that stall angles decreased as aspect-ratio increased at the same Reynolds number.

  17. Aspect ratio control and sensing applications for a slot waveguide with a multimode stub

    NASA Astrophysics Data System (ADS)

    He, Zhihui; Peng, Yongyi; Li, Boxun; Chen, Zhiquan; Xu, Hui; Zheng, Mingfei; Li, Hongjian

    2016-07-01

    We report the aspect ratio control and sensing applications for metal–dielectric–metal (MDM) slot waveguides with a multimode stub. By adjusting the aspect ratio r = h/w of the stub, five types of optical evolutions in various aspect ratio r ranges are defined. We can realize a single or double plasmon-induced transparency (PIT) as well as Fano resonances. In addition, the figure of merit (FOM), which can describe the sensing performance of structures, is discussed in our paper. We can find up to three FOM peaks in our proposed structure. These findings provide guidance for the fundamental research of integrated plasmonic sensors.

  18. Distribution over pore radii in random and isotropic systems of polydisperse rods with finite aspect ratios

    NASA Astrophysics Data System (ADS)

    Chatterjee, Avik P.

    2016-06-01

    Excluded-volume arguments are applied toward modeling the pore-size distribution in systems of randomly arranged cylindrical rods with finite and nonuniform aspect ratios. An explicit expression for the pore-size distribution is obtained by way of an analogy to a hypothetical system of fully penetrable objects, through a mapping that is designed to preserve the volume fraction occupied by the particle cores and the specific surface area. Results are presented for the mean value and standard deviation of the pore radius as functions of the rod aspect ratio, volume fraction, and polydispersity (degree of nonuniformity in the aspect ratios of the particles).

  19. Accessibility of second regions of stability in tokamaks

    SciTech Connect

    Manickam, J.

    1985-12-01

    Second regions of stability to the ideal ballooning modes have been shown to exist in large-aspect-ratio circular and small-aspect-ratio bean-shaped tokamaks. We report on the existence of these second stability regions in finite-aspect-ratio dee-shaped tokamaks. We also report on the discovery of a second-stable region with respect to the n = 1 external kink mode in a bean-shaped plasma. The role of the shear and current profile in determining these regions of parameter space are discussed. 13 refs., 6 figs.

  20. Development of a Prediction Scheme for High Aspect-Ratio Jet Noise

    NASA Technical Reports Server (NTRS)

    Munro, Scott E.; Ahuja, K. K.

    2003-01-01

    Circulation control wings are a type of pneumatic high-lift device that have been extensively researched as to their aerodynamic benefits. However, there has been little research into the possible airframe noise reduction benefits of a circulation control wing. The key element of noise is the jet noise associated with the jet sheet emitted from the blowing slot. This jet sheet is essentially a high aspect-ratio rectangular jet. A recent study on high aspect-ratio jet noise was performed on a nozzle with aspect-ratios ranging from 100 to 3,000. In addition to the acoustic data, fluid dynamic measurements were made as well. This paper uses the results of these two studies and attempts to develop a prediction scheme for high aspect-ratio jet noise

  1. Template-mediated Synthesis of Hollow Microporous Organic Nanorods with Tunable Aspect Ratio

    PubMed Central

    Li, Qingyin; Jin, Shangbin; Tan, Bien

    2016-01-01

    Hollow microporous organic nanorods (HMORs) with hypercrosslinked polymer (HCPs) shells were synthesized through emulsion polymerization followed by hypercrosslinking. The HMORs have tunable aspect ratios, high BET surface areas and monodispersed morphologies, showing good performance in gas adsorpion. PMID:27506370

  2. Template-mediated Synthesis of Hollow Microporous Organic Nanorods with Tunable Aspect Ratio

    NASA Astrophysics Data System (ADS)

    Li, Qingyin; Jin, Shangbin; Tan, Bien

    2016-08-01

    Hollow microporous organic nanorods (HMORs) with hypercrosslinked polymer (HCPs) shells were synthesized through emulsion polymerization followed by hypercrosslinking. The HMORs have tunable aspect ratios, high BET surface areas and monodispersed morphologies, showing good performance in gas adsorpion.

  3. Aspect ratio dependent fluorescence quenching of eosin Y by gold nanorods.

    PubMed

    Weng, Guojun; Li, Jianjun; Zhang, Li; Zhao, Junwu

    2014-06-01

    Gold nanorods of different aspect ratios had been synthesized using seed mediated growth method. The formed gold nanorods had been characterized by the absorption and transmission electron microscopy (TEM) measurements. The obtained gold nanorods were used to study the quenched effect on fluorescence of Eosin Y. Experimental results revealed that Eosin Y molecules adsorbed on the metallic surfaces, suffering strong quenching of their fluorescence and the quenching efficiency was different for different aspect ratio. Using dielectric coated gold nanorods model, the probable mechanism of aspect ratio dependent quenching efficiency was obtained by numerical calculation based on fluorescence resonance energy transfer and quasi-static theory. The calculation results showed that the non-monotonic changing of fluorescence quenching was attributed to competing effects of aspect ratio and the dielectric constant of coated shell on surface plasmon resonance. PMID:24738353

  4. Approximate quasi-isodynamicity at a finite aspect ratio in a stellarator vacuum magnetic field

    SciTech Connect

    Mikhailov, M. I.; Nührenberg, J. Zille, R.

    2015-12-15

    A stellarator vacuum field is found in which, at a finite aspect ratio (A ≈ 40), the contours of the second adiabatic invariant of nearly all particles reflected inside that surface are poloidally closed.

  5. Fidelity of reduced and realistic electron mass ratio multi-scale gyrokinetic simulations of tokamak discharges

    NASA Astrophysics Data System (ADS)

    Howard, N. T.; Holland, C.; White, A. E.; Greenwald, M.; Candy, J.

    2015-06-01

    The first study using multi-scale (coupled ITG/TEM/ETG) gyrokinetic simulations at both reduced and realistic electron mass ratios, μ = (mD/me).5 = 20.0, 40.0 and 60.0, has been performed on a standard, Alcator C-Mod, L-mode discharge. Ion-scale (kθρs  ∼  1.0) and multi-scale (up to kθρe  ∼  0.8) gyrokinetic simulations are compared at different simulated mass ratios to investigate the fidelity of reduced electron mass ratio, multi-scale simulation through direct comparison with realistic mass ratio, multi-scale simulation. Detailed description of both the numerical setup and the turbulent scales required to obtain meaningful coupled ITG/TEM/ETG simulation is presented. Significant high-k driven (TEM/ETG) heat flux is found to exist at scales of approximately kθρe  ∼  0.1 at all mass ratios but can only be obtained by simulation capturing turbulence up to kθρe  ∼  1.0. At slightly reduced mass ratio, μ = 40.0, qualitative agreement with realistic mass simulation can be obtained in the studied discharge, consistent with intuition obtained from linear stability analysis. However, realistic electron mass is required for any robust quantitative comparison with experimental heat fluxes for the condition studied, as significant differences are observed at even slightly reduced electron mass ratio. The details of this numerical study are presented to provide a basis for future studies utilizing coupled ITG/TEM/ETG gyrokinetic simulation.

  6. Tractor tire aspect ratio effects on soil bulk density and cone index

    Technology Transfer Automated Retrieval System (TEKTRAN)

    A 580/70R38 tractor drive tire with an aspect ratio of 0.756 and a 650/75R32 tire with an aspect ratio of 0.804 were operated at two dynamic loads and two inflation pressures on a sandy loam and a clay loam with loose soil above a hardpan. Soil bulk density and cone index were measured just above t...

  7. Origin of enhanced photocatalytic activity and photoconduction in high aspect ratio ZnO nanorods.

    PubMed

    Leelavathi, A; Madras, Giridhar; Ravishankar, N

    2013-07-14

    Faceted ZnO nanorods with different aspect ratios were synthesized by a solvothermal method by tuning the reaction time. Increased reaction leads to the formation of high aspect ratio ZnO nanorods largely bound by the prism planes. The high aspect ratio rods showed significantly higher visible light photocatalytic activity when compared to the lower aspect ratio structures. It is proposed that the higher activity is due to better charge separation in the elongated 1D structure. In addition, the fraction of unsaturated Zn(2+) sites is higher on the {1010} facets, leading to better adsorption of oxygen-containing species. These species enhance the production of reactive radicals that are responsible for photodegradation. The photocurrent for these ZnO nanostructures under solar light was measured and a direct correlation between photocurrent and aspect ratio was observed. Since the underlying mechanisms for photodegradation and photocurrent generation are directly related to the efficiency of electron-hole creation and separation, this observation corroborates that the charge separation processes are indeed enhanced in the high aspect ratio structures. The efficiency of photoconduction (electron-hole pair separation) could be further improved by attaching Au nanoparticles on ZnO, which can act as a sink for the electrons. This heterostructure exhibits a high chemisorption of oxygen, which facilitates the production of highly reactive radicals contributing to the high photoreactivity. The suggested mechanisms are applicable to other n-type semiconductor nanostructures with important implications for applications relating to energy and the environment. PMID:23694926

  8. Effect of tip vortices on membrane vibration of flexible wings with different aspect ratios

    NASA Astrophysics Data System (ADS)

    Genç, Mustafa Serdar; Hakan Açikel, Halil; Demir, Hacımurat; Özden, Mustafa; Çağdaş, Mücahit; Isabekov, Iliasbek

    2016-03-01

    In this study, the effect of the aspect ratio on the aerodynamics characteristic of flexible membrane wings with different aspect ratios (AR = 1 and AR = 3) is experimentally investigated at Reynolds number of 25000. Time accurate measurements of membrane deformation using Digital Image Correlation system (DIC) is carried out while normal forces of the wing will be measured by helping a load-cell system and flow on the wing was visualized by means of smoke wire technic. The characteristics of high aspect ratio wings are shown to be affected by leading edge separation bubbles at low Reynolds number. It is concluded that the camber of membrane wing excites the separated shear layer and this situation increases the lift coefficient relatively more as compared to rigid wings. In membrane wings with low aspect ratio, unsteadiness included tip vortices and vortex shedding, and the combination of tip vortices and vortex shedding causes complex unsteady deformations of these membrane wings. The characteristic of high aspect ratio wings was shown to be affected by leading edge separation bubbles at low Reynolds numbers whereas the deformations of flexible wing with low aspect ratio affected by tip vortices and leading edge separation bubbles.

  9. A micro powder injection molding apparatus for high aspect ratio metal micro-structure production

    NASA Astrophysics Data System (ADS)

    Fu, Gang; Tor, Shubeng; Loh, Ngiaphiang; Tay, Beeyen; Hardt, David E.

    2007-09-01

    A new variotherm molding apparatus is presented in this paper for the fabrication of high aspect ratio 316L stainless steel micro-structures using micro powder injection molding (μPIM) technology. The molding apparatus prototype includes an injection mold in which a silicon insert with an array of 24 × 24 (576) microcavities is mounted, a set of rapid tempering systems for the mold and a set of vacuum systems. The key advantage of this molding apparatus lies in the real-time monitoring and rapid adjustment of the mold cavity temperature during injection molding and part ejection, which makes molding and demolding of high aspect ratio green micro-structures possible. For example, incomplete filling occurs while injection molding micro-structures of 60 µm × height 191 µm with an aspect ratio of 3.2 using a conventional mold. In comparison, smaller micro-structures with higher aspect ratio are produced successfully in the case of the new molding apparatus, e.g. micro-structures of 40 µm × height 174 µm with an aspect ratio of 4.35 and 20 µm × height 160 µm with an aspect ratio of 8 were molded successfully.

  10. Vortex formation and drag on low aspect ratio, normal flat plates

    NASA Astrophysics Data System (ADS)

    Ringuette, Matthew James

    Experiments were done to investigate the role of vortex formation in the drag force generation of low aspect ratio, normal flat plates starting from rest. This very simplified case is a first, fundamental step toward understanding the more complicated flow of hovering flight, which relies primarily on drag for propulsion. The relative importance of the plate's free end, or tip, with varying aspect ratio was also studied. Identifying the relationship among aspect ratio, vortex formation, and drag force can provide insight into the wing aspect ratios and kinematics found nature, with the eventual goal of designing man-made flapping wing micro air vehicles. The experiments were carried out using flat plate models in a towing tank at a moderate Reynolds number of 3000. Two aspect ratios, 6 and 2, were considered, the latter in order to have a highly tip-dominated case. A force balance measured the time-varying drag, and multiple, perpendicular sections of the flow velocity were measured quantitatively using digital particle image velocimetry. Vorticity fields were calculated from the velocity data, and features in the drag force for different aspect ratios were related to the vortex dynamics. Finally, since the flow is highly three-dimensional, dye flow visualization was done to characterize its structure and to augment the two-dimensional digital particle image velocimetry data.

  11. Variable aspect ratio method in the Xu-White model for shear-wave velocity estimation

    NASA Astrophysics Data System (ADS)

    Bai, Jun-Yu; Yue, Cheng-Qi; Liang, Yi-Qiang; Song, Zhi-Xiang; Ling, Su; Zhang, Yang; Wu, Wei

    2013-06-01

    Shear-wave velocity logs are useful for various seismic interpretation applications, including bright spot analyses, amplitude-versus-offset analyses and multicomponent seismic interpretations. This paper presents a method for predicting the shear-wave velocity of argillaceous sandstone from conventional log data and experimental data, based on Gassmann's equations and the Xu-White model. This variable aspect ratio method takes into account all the influences of the matrix nature, shale content, porosity size and pore geometry, and the properties of pore fluid of argillaceous sandstone, replacing the fixed aspect ratio assumption in the conventional Xu-White model. To achieve this, we first use the Xu-White model to derive the bulk and shear modulus of dry rock in a sand-clay mixture. Secondly, we use Gassmann's equations to calculate the fluid-saturated elastic properties, including compressional and shear-wave velocities. Finally, we use the variable aspect ratio method to estimate the shear-wave velocity. The numerical results indicate that the variable aspect ratio method provides an important improvement in the application of the Xu-White model for sand-clay mixtures and allows for a variable aspect ratio log to be introduced into the Xu-White model instead of the constant aspect ratio assumption. This method shows a significant improvement in predicting velocities over the conventional Xu-White model.

  12. Neoclassical transport in high [beta] tokamaks

    SciTech Connect

    Cowley, S.C.

    1992-12-01

    Neoclassical, transport in high [beta] large aspect ratio tokamaks is calculated. The variational method introduced by Rosenbluth, et al., is used to calculate the full Onsager matrix in the banana regime. These results are part of a continuing study of the high [beta] large aspect ratio equilibria introduced in Cowley, et al. All the neoclassical coefficients are reduced from their nominal low [beta] values by a factor ([var epsilon]/q[sup 2][beta])[sup [1/2

  13. Static investigation of circular-to-rectangular transition ducts for high-aspect-ratio nonaxisymmetric nozzles

    NASA Technical Reports Server (NTRS)

    Burley, J. R., II; Bangert, L. S.; Carlson, J. R.

    1986-01-01

    An investigation was conducted in the static-test facility of the Langley 16-Foot Transonic Tunnel to determine the internal performance of a high-aspect-ratio nonaxisymmetric nozzle with five circular-to-rectangular transition ducts of varying design. Nozzle pressure ratio was varied from 1.5 to 5.3, and nozzle performance parameters were recorded.

  14. Power reduction and the radial limit of stall delay in revolving wings of different aspect ratio

    PubMed Central

    Kruyt, Jan W.; van Heijst, GertJan F.; Altshuler, Douglas L.; Lentink, David

    2015-01-01

    Airplanes and helicopters use high aspect ratio wings to reduce the power required to fly, but must operate at low angle of attack to prevent flow separation and stall. Animals capable of slow sustained flight, such as hummingbirds, have low aspect ratio wings and flap their wings at high angle of attack without stalling. Instead, they generate an attached vortex along the leading edge of the wing that elevates lift. Previous studies have demonstrated that this vortex and high lift can be reproduced by revolving the animal wing at the same angle of attack. How do flapping and revolving animal wings delay stall and reduce power? It has been hypothesized that stall delay derives from having a short radial distance between the shoulder joint and wing tip, measured in chord lengths. This non-dimensional measure of wing length represents the relative magnitude of inertial forces versus rotational accelerations operating in the boundary layer of revolving and flapping wings. Here we show for a suite of aspect ratios, which represent both animal and aircraft wings, that the attachment of the leading edge vortex on a revolving wing is determined by wing aspect ratio, defined with respect to the centre of revolution. At high angle of attack, the vortex remains attached when the local radius is shorter than four chord lengths and separates outboard on higher aspect ratio wings. This radial stall limit explains why revolving high aspect ratio wings (of helicopters) require less power compared with low aspect ratio wings (of hummingbirds) at low angle of attack and vice versa at high angle of attack. PMID:25788539

  15. Power reduction and the radial limit of stall delay in revolving wings of different aspect ratio.

    PubMed

    Kruyt, Jan W; van Heijst, GertJan F; Altshuler, Douglas L; Lentink, David

    2015-04-01

    Airplanes and helicopters use high aspect ratio wings to reduce the power required to fly, but must operate at low angle of attack to prevent flow separation and stall. Animals capable of slow sustained flight, such as hummingbirds, have low aspect ratio wings and flap their wings at high angle of attack without stalling. Instead, they generate an attached vortex along the leading edge of the wing that elevates lift. Previous studies have demonstrated that this vortex and high lift can be reproduced by revolving the animal wing at the same angle of attack. How do flapping and revolving animal wings delay stall and reduce power? It has been hypothesized that stall delay derives from having a short radial distance between the shoulder joint and wing tip, measured in chord lengths. This non-dimensional measure of wing length represents the relative magnitude of inertial forces versus rotational accelerations operating in the boundary layer of revolving and flapping wings. Here we show for a suite of aspect ratios, which represent both animal and aircraft wings, that the attachment of the leading edge vortex on a revolving wing is determined by wing aspect ratio, defined with respect to the centre of revolution. At high angle of attack, the vortex remains attached when the local radius is shorter than four chord lengths and separates outboard on higher aspect ratio wings. This radial stall limit explains why revolving high aspect ratio wings (of helicopters) require less power compared with low aspect ratio wings (of hummingbirds) at low angle of attack and vice versa at high angle of attack. PMID:25788539

  16. Effects of Aspect Ratio on Water Immersion into Deep Silica Nanoholes.

    PubMed

    Zheng, Jing; Zhang, Junqiao; Tan, Lu; Li, Debing; Huang, Liangliang; Wang, Qi; Liu, Yingchun

    2016-08-30

    Understanding the influence of aspect ratio on water immersion into silica nanoholes is of significant importance to the etching process of semiconductor fabrication and other water immersion-related physical and biological processes. In this work, the processes of water immersion into silica nanoholes with different height/width aspect ratios (ϕ = 0.87, 1.92, 2.97, 4.01, 5.06) and different numbers of water molecules (N = 9986, 19972, 29958, 39944) were studied by molecular dynamics simulations. A comprehensive analysis has been conducted about the detailed process of water immersion and the influence of aspect ratios on water immersion rates. Five distinguishable stages were identified for the immersion process with all studied models. The results reveal that water can easily immerse into the silica nanoholes with larger ϕ and smaller N. The calculation also suggests that aspect ratios have a greater effect on water immersion rates for larger N numbers. The mechanism of the water immersion process is discussed in this work. We also propose a mathematical model to correlate the complete water immersion process for different aspect ratios. PMID:27506253

  17. Hydrodynamic thrust generation and power consumption investigations for piezoelectric fins with different aspect ratios

    NASA Astrophysics Data System (ADS)

    Shahab, S.; Tan, D.; Erturk, A.

    2015-12-01

    Bio-inspired hydrodynamic thrust generation using piezoelectric transduction has recently been explored using Macro-Fiber Composite (MFC) actuators. The MFC technology strikes a balance between the actuation force and structural deformation levels for effective swimming performance, and additionally offers geometric scalability, silent operation, and ease of fabrication. Recently we have shown that mean thrust levels comparable to biological fish of similar size can be achieved using MFC fins. The present work investigates the effect of length-to-width (L/b) aspect ratio on the hydrodynamic thrust generation performance of MFC cantilever fins by accounting for the power consumption level. It is known that the hydrodynamic inertia and drag coefficients are controlled by the aspect ratio especially for L/b< 5. The three MFC bimorph fins explored in this work have the aspect ratios of 2.1, 3.9, and 5.4. A nonlinear electrohydroelastic model is employed to extract the inertia and drag coefficients from the vibration response to harmonic actuation for the first bending mode. Experiments are then conducted for various actuation voltage levels to quantify the mean thrust resultant and power consumption levels for different aspect ratios. Variation of the thrust coefficient of the MFC bimorph fins with changing aspect ratio is also semi-empirically modeled and presented.

  18. Size Dependent Cellular Uptake of Rod-like Bionanoparticles with Different Aspect Ratios.

    PubMed

    Liu, Xiangxiang; Wu, Fengchi; Tian, Ye; Wu, Man; Zhou, Quan; Jiang, Shidong; Niu, Zhongwei

    2016-01-01

    Understanding the cellular internalization mechanism of nanoparticles is essential to study their biological fate. Especially, due to the anisotropic properties, rod-like nanoparticles have attracted growing interest for the enhanced internalization efficiency with respect to spherical nanoparticles. Here, to elucidate the effect of aspect ratio of rod-like nanoparticles on cellular uptake, tobacco mosaic virus (TMV), a typical rod-like bionanoparticle, is developed as a model. Nanorods with different aspect ratios can be obtained by ultrasound treatment and sucrose density gradient centrifugation. By incubating with epithelial and endothelial cells, we found that the rod-like bionanoparticles with various aspect ratios had different internalization pathways in different cell lines: microtubules transport in HeLa and clathrin-mediated uptake in HUVEC for TMV4 and TMV8; caveolae-mediated pathway and microtubules transport in HeLa and HUVEC for TMV17. Differently from most nanoparticles, for all the three TMV nano-rods with different aspect ratios, macropinocytosis takes no effect on the internalization in both cell types. This work provides a fundamental understanding of the influence of aspect ratio on cellular uptake decoupled from charge and material composition. PMID:27080246

  19. Influence of grid aspect ratio on planetary boundary layer turbulence in large-eddy simulations

    NASA Astrophysics Data System (ADS)

    Nishizawa, S.; Yashiro, H.; Sato, Y.; Miyamoto, Y.; Tomita, H.

    2015-10-01

    We examine the influence of the grid aspect ratio of horizontal to vertical grid spacing on turbulence in the planetary boundary layer (PBL) in a large-eddy simulation (LES). In order to clarify and distinguish them from other artificial effects caused by numerical schemes, we used a fully compressible meteorological LES model with a fully explicit scheme of temporal integration. The influences are investigated with a series of sensitivity tests with parameter sweeps of spatial resolution and grid aspect ratio. We confirmed that the mixing length of the eddy viscosity and diffusion due to sub-grid-scale turbulence plays an essential role in reproducing the theoretical -5/3 slope of the energy spectrum. If we define the filter length in LES modeling based on consideration of the numerical scheme, and introduce a corrective factor for the grid aspect ratio into the mixing length, the theoretical slope of the energy spectrum can be obtained; otherwise, spurious energy piling appears at high wave numbers. We also found that the grid aspect ratio has influence on the turbulent statistics, especially the skewness of the vertical velocity near the top of the PBL, which becomes spuriously large with large aspect ratio, even if a reasonable spectrum is obtained.

  20. Size Dependent Cellular Uptake of Rod-like Bionanoparticles with Different Aspect Ratios

    PubMed Central

    Liu, Xiangxiang; Wu, Fengchi; Tian, Ye; Wu, Man; Zhou, Quan; Jiang, Shidong; Niu, Zhongwei

    2016-01-01

    Understanding the cellular internalization mechanism of nanoparticles is essential to study their biological fate. Especially, due to the anisotropic properties, rod-like nanoparticles have attracted growing interest for the enhanced internalization efficiency with respect to spherical nanoparticles. Here, to elucidate the effect of aspect ratio of rod-like nanoparticles on cellular uptake, tobacco mosaic virus (TMV), a typical rod-like bionanoparticle, is developed as a model. Nanorods with different aspect ratios can be obtained by ultrasound treatment and sucrose density gradient centrifugation. By incubating with epithelial and endothelial cells, we found that the rod-like bionanoparticles with various aspect ratios had different internalization pathways in different cell lines: microtubules transport in HeLa and clathrin-mediated uptake in HUVEC for TMV4 and TMV8; caveolae-mediated pathway and microtubules transport in HeLa and HUVEC for TMV17. Differently from most nanoparticles, for all the three TMV nano-rods with different aspect ratios, macropinocytosis takes no effect on the internalization in both cell types. This work provides a fundamental understanding of the influence of aspect ratio on cellular uptake decoupled from charge and material composition. PMID:27080246

  1. Fabrication of high aspect ratio nanogrid transparent electrodes via capillary assembly of Ag nanoparticles.

    PubMed

    Kang, Juhoon; Park, Chang-Goo; Lee, Su-Han; Cho, Changsoon; Choi, Dae-Geun; Lee, Jung-Yong

    2016-06-01

    In this report, we describe the fabrication of periodic Ag nanogrid electrodes by capillary assembly of silver nanoparticles (AgNPs) along patterned nanogrid templates. By assembling the AgNPs into these high-aspect-ratio nanogrid patterns, we can obtain high-aspect-ratio nanogratings, which can overcome the inherent trade-off between the optical transmittance and the sheet resistance of transparent electrodes. The junction resistance between the AgNPs is effectively reduced by photochemical welding and post-annealing. The fabricated high-aspect-ratio nanogrid structure with a line width of 150 nm and a height of 450 nm has a sheet resistance of 15.2 Ω sq(-1) and an optical transmittance of 85.4%. PMID:27187802

  2. On the aspect ratio of Rayleigh-Benard convection cells. [in earth mantle

    NASA Technical Reports Server (NTRS)

    Christensen, Ulrich; Yuen, David

    1988-01-01

    Numerical model calculations of isoviscous bottom-heated convection in a two-dimensional box with aspect ratio twelve are reported. The aim was to determine the preferred aspect ratio of convection cells. Time-dependent runs were started from two widely different initial conditions. At Rayleigh numbers in the range 10 to the 5th to 10 to the 6th about eight cells with a mean aspect ratio of 1.5 formed eventually in each case. Thus neither the preference for approximately square cells nor the stability of very elongated cells could be confirmed. The existence of large-scale convective structures in the earth's mantle must be due to deviations from the simple Rayleigh-Benard model of convection.

  3. SML resist processing for high-aspect-ratio and high-sensitivity electron beam lithography

    NASA Astrophysics Data System (ADS)

    Mohammad, Mohammad Ali; Dew, Steven K.; Stepanova, Maria

    2013-03-01

    A detailed process characterization of SML electron beam resist for high-aspect-ratio nanopatterning at high sensitivity is presented. SML contrast curves were generated for methyl isobutyl ketone (MIBK), MIBK/isopropyl alcohol (IPA) (1:3), IPA/water (7:3), n-amyl acetate, xylene, and xylene/methanol (3:1) developers. Using IPA/water developer, the sensitivity of SML was improved considerably and found to be comparable to benchmark polymethylmethacrylate (PMMA) resist without affecting the aspect ratio performance. Employing 30-keV exposures and ultrasonic IPA/water development, an aspect ratio of 9:1 in 50-nm half-pitch dense grating patterns was achieved representing a greater than two times improvement over PMMA. Through demonstration of 25-nm lift-off features, the pattern transfer performance of SML is also addressed.

  4. Shape matters: synthesis and biomedical applications of high aspect ratio magnetic nanomaterials

    NASA Astrophysics Data System (ADS)

    Fratila, Raluca M.; Rivera-Fernández, Sara; de La Fuente, Jesús M.

    2015-04-01

    High aspect ratio magnetic nanomaterials possess anisotropic properties that make them attractive for biological applications. Their elongated shape enables multivalent interactions with receptors through the introduction of multiple targeting units on their surface, thus enhancing cell internalization. Moreover, due to their magnetic anisotropy, high aspect ratio nanomaterials can outperform their spherical analogues as contrast agents for magnetic resonance imaging (MRI) applications. In this review, we first describe the two main synthetic routes for the preparation of anisotropic magnetic nanomaterials: (i) direct synthesis (in which the anisotropic growth is directed by tuning the reaction conditions or by using templates) and (ii) assembly methods (in which the high aspect ratio is achieved by assembly from individual building blocks). We then provide an overview of the biomedical applications of anisotropic magnetic nanomaterials: magnetic separation and detection, targeted delivery and magnetic resonance imaging.

  5. Mosquitofish (Gambusia affinis) responds differentially to a robotic fish of varying swimming depth and aspect ratio.

    PubMed

    Polverino, Giovanni; Porfiri, Maurizio

    2013-08-01

    In this study, we explore the feasibility of using bioinspired robotics to influence the behaviour of mosquitofish (Gambusia affinis), a social freshwater fish species that is extensively studied for the ecological issues associated with its diffusion in non-native environments. Specifically, in a dichotomous choice test, we investigate the behavioural response of small shoals of mosquitofish to a robotic fish inspired by mosquitofish in its colouration, shape, aspect ratio, and locomotion. Our results indicate that the swimming depth and the aspect ratio of the robotic fish are both determinants of mosquitofish preference. In particular, we find that mosquitofish are never attracted by a robotic fish whose colouration and shape are inspired by live subjects and that the degree of repulsion varies as a function of the swimming depth and the aspect ratio. PMID:23684918

  6. Effects of aspect ratio on the phase diagram of spheroidal particles

    NASA Astrophysics Data System (ADS)

    Kutlu, Songul; Haaga, Jason; Rickman, Jeffrey; Gunton, James

    Ellipsoidal particles occur in both colloidal and protein science. Models of protein phase transitions based on interacting spheroidal particles can often be more realistic than those based on spherical molecules. One of the interesting questions is how the aspect ratio of spheroidal particles affects the phase diagram. Some results have been obtained in an earlier study by Odriozola (J. Chem. Phys. 136:134505 (2012)). In this poster we present results for the phase diagram of hard spheroids interacting via a quasi-square-well potential, for different aspect ratios. These results are obtained from Monte Carlo simulations using the replica exchange method. We find that the phase diagram, including the crystal phase transition, is sensitive to the choice of aspect ratio. G. Harold and Leila Y. Mathers Foundation.

  7. Aspect Ratio Model for Radiation-Tolerant Dummy Gate-Assisted n-MOSFET Layout.

    PubMed

    Lee, Min Su; Lee, Hee Chul

    2014-01-01

    In order to acquire radiation-tolerant characteristics in integrated circuits, a dummy gate-assisted n-type metal oxide semiconductor field effect transistor (DGA n-MOSFET) layout was adopted. The DGA n-MOSFET has a different channel shape compared with the standard n-MOSFET. The standard n-MOSFET has a rectangular channel shape, whereas the DGA n-MOSFET has an extended rectangular shape at the edge of the source and drain, which affects its aspect ratio. In order to increase its practical use, a new aspect ratio model is proposed for the DGA n-MOSFET and this model is evaluated through three-dimensional simulations and measurements of the fabricated devices. The proposed aspect ratio model for the DGA n-MOSFET exhibits good agreement with the simulation and measurement results. PMID:27350975

  8. Aspect Ratio Model for Radiation-Tolerant Dummy Gate-Assisted n-MOSFET Layout

    PubMed Central

    Lee, Min Su; Lee, Hee Chul

    2014-01-01

    In order to acquire radiation-tolerant characteristics in integrated circuits, a dummy gate-assisted n-type metal oxide semiconductor field effect transistor (DGA n-MOSFET) layout was adopted. The DGA n-MOSFET has a different channel shape compared with the standard n-MOSFET. The standard n-MOSFET has a rectangular channel shape, whereas the DGA n-MOSFET has an extended rectangular shape at the edge of the source and drain, which affects its aspect ratio. In order to increase its practical use, a new aspect ratio model is proposed for the DGA n-MOSFET and this model is evaluated through three-dimensional simulations and measurements of the fabricated devices. The proposed aspect ratio model for the DGA n-MOSFET exhibits good agreement with the simulation and measurement results. PMID:27350975

  9. Fabrication of high aspect ratio nanogrid transparent electrodes via capillary assembly of Ag nanoparticles

    NASA Astrophysics Data System (ADS)

    Kang, Juhoon; Park, Chang-Goo; Lee, Su-Han; Cho, Changsoon; Choi, Dae-Geun; Lee, Jung-Yong

    2016-05-01

    In this report, we describe the fabrication of periodic Ag nanogrid electrodes by capillary assembly of silver nanoparticles (AgNPs) along patterned nanogrid templates. By assembling the AgNPs into these high-aspect-ratio nanogrid patterns, we can obtain high-aspect-ratio nanogratings, which can overcome the inherent trade-off between the optical transmittance and the sheet resistance of transparent electrodes. The junction resistance between the AgNPs is effectively reduced by photochemical welding and post-annealing. The fabricated high-aspect-ratio nanogrid structure with a line width of 150 nm and a height of 450 nm has a sheet resistance of 15.2 Ω sq-1 and an optical transmittance of 85.4%.In this report, we describe the fabrication of periodic Ag nanogrid electrodes by capillary assembly of silver nanoparticles (AgNPs) along patterned nanogrid templates. By assembling the AgNPs into these high-aspect-ratio nanogrid patterns, we can obtain high-aspect-ratio nanogratings, which can overcome the inherent trade-off between the optical transmittance and the sheet resistance of transparent electrodes. The junction resistance between the AgNPs is effectively reduced by photochemical welding and post-annealing. The fabricated high-aspect-ratio nanogrid structure with a line width of 150 nm and a height of 450 nm has a sheet resistance of 15.2 Ω sq-1 and an optical transmittance of 85.4%. Electronic supplementary information (ESI) available. See DOI: 10.1039/c6nr01896c

  10. Simultaneous fabrication of very high aspect ratio positive nano- to milliscale structures.

    PubMed

    Chen, Long Qing; Chan-Park, Mary B; Zhang, Qing; Chen, Peng; Li, Chang Ming; Li, Sai

    2009-05-01

    A simple and inexpensive technique for the simultaneous fabrication of positive (i.e., protruding), very high aspect (>10) ratio nanostructures together with micro- or millistructures is developed. The method involves using residual patterns of thin-film over-etching (RPTO) to produce sub-micro-/nanoscale features. The residual thin-film nanopattern is used as an etching mask for Si deep reactive ion etching. The etched Si structures are further reduced in size by Si thermal oxidation to produce amorphous SiO(2), which is subsequently etched away by HF. Two arrays of positive Si nanowalls are demonstrated with this combined RPTO-SiO(2)-HF technique. One array has a feature size of 150 nm and an aspect ratio of 26.7 and another has a feature size of 50 nm and an aspect ratio of 15. No other parallel reduction technique can achieve such a very high aspect ratio for 50-nm-wide nanowalls. As a demonstration of the technique to simultaneously achieve nano- and milliscale features, a simple Si nanofluidic master mold with positive features with dimensions varying continuously from 1 mm to 200 nm and a highest aspect ratio of 6.75 is fabricated; the narrow 200-nm section is 4.5 mm long. This Si master mold is then used as a mold for UV embossing. The embossed open channels are then closed by a cover with glue bonding. A high aspect ratio is necessary to produce unblocked closed channels after the cover bonding process of the nanofluidic chip. The combined method of RPTO, Si thermal oxidation, and HF etching can be used to make complex nanofluidic systems and nano-/micro-/millistructures for diverse applications. PMID:19235805

  11. ECH tokamak

    SciTech Connect

    Firestone, M.A.; Mau, T.K.; Conn, R.W.

    1985-04-01

    A small steady-state tokamak capable of producing power in the 100 to 300 MWe range and relying on electron cyclotron RF heating (ECH) for both heating and current drive is described. Working in the first MHD stability regime for tokamaks, the approach adheres to the recently discovered maximum beta limit. An appropriate figure of merit is the ratio of the fusion power to absorbed RF power. Efficient devices are feasible at both small and large values of fusion power, thereby pointing to a development path for an attractive commercial fusion reactor.

  12. Effect of aspect ratio and surface defects on the photocatalytic activity of ZnO nanorods

    PubMed Central

    Zhang, Xinyu; Qin, Jiaqian; Xue, Yanan; Yu, Pengfei; Zhang, Bing; Wang, Limin; Liu, Riping

    2014-01-01

    ZnO, aside from TiO2, has been considered as a promising material for purification and disinfection of water and air, and remediation of hazardous waste, owing to its high activity, environment-friendly feature and lower cost. However, their poor visible light utilization greatly limited their practical applications. Herein, we demonstrate the fabrication of different aspect ratios of the ZnO nanorods with surface defects by mechanical-assisted thermal decomposition method. The experiments revealed that ZnO nanorods with higher aspect ratio and surface defects show significantly higher photocatalytic performances. PMID:24699790

  13. Contact fatigue mechanisms as a function of crystal aspect ratio in baria-silicate glass ceramics

    NASA Astrophysics Data System (ADS)

    Suputtamongkol, Kallaya

    2003-10-01

    Ceramic materials are potentially useful for dental applications because of their esthetic potential and biocompatibility. However, the existence of fatigue damage in ceramics raises considerable concern regarding its effect on the life prediction of dental prostheses. During normal mastication, dental restorations are subjected to repeated loading more than a thousand times per day and relatively high clinical failure rates for ceramic prostheses have been reported. To simulate the intraoral loads, Hertzian indentation loading was used in this study to characterize the fatigue failure mechanisms of ceramic materials using clinically relevant parameters. The baria-silicate system was chosen because of the nearly identical composition between the crystal and the glass matrix. Little or no residual stress is expected from the elastic modulus and thermal expansion mismatches between the two phases. Crystallites with different aspect ratios can also be produced by controlled heat treatment schedules. The objective of this study was to characterize the effect of crystal morphology on the fatigue mechanisms of bariasilicate glass-ceramics under clinically relevant conditions. The results show that the failure of materials with a low toughness such as baria-silicate glass (0.7 MPa•m1/2) and glass-ceramic with an aspect ratio of 3/1 (1.3 MPa•m1/2) initiated from a cone crack developed during cyclic loading for 103 to 105 cycles. The mean strength values of baria-silicate glass and glass-ceramic with an aspect ratio of 3/1 decreased significantly as a result of the presence of a cone crack. Failure of baria-silicate glass-ceramics with an aspect ratio of 8/1 (Kc = 2.1 MPa•m1/2) was initiated from surface flaws caused by either polishing or cyclic loading. The gradual decrease of fracture stress was observed in specimens with an aspect ratio of 8/1 after loading in air for 103 to 10 5 cycles. A reduction of approximately 50% in fracture stress levels was found for

  14. Simple Systematic Synthesis of Periodic Mesoporous Organosilica Nanoparticles with Adjustable Aspect Ratios

    NASA Astrophysics Data System (ADS)

    Mohanty, Paritosh; Landskron, Kai

    2009-12-01

    One-dimensional periodic mesoporous organosilica (PMO) nanoparticles with tunable aspect ratios are obtained from a chain-type molecular precursor octaethoxy-1,3,5-trisilapentane. The aspect ratio can be tuned from 2:1 to >20:1 simply by variation in the precursor concentration in acidic aqueous solutions containing constant amounts of triblock copolymer Pluronic P123. The mesochannels are highly ordered and are oriented parallel to the longitudinal axis of the PMO particles. No significant Si-C bond cleavage occurs during the synthesis according to 29Si MAS NMR. The materials exhibit surface areas between 181 and 936 m2 g-1.

  15. Effect of aspect ratio and surface defects on the photocatalytic activity of ZnO nanorods

    NASA Astrophysics Data System (ADS)

    Zhang, Xinyu; Qin, Jiaqian; Xue, Yanan; Yu, Pengfei; Zhang, Bing; Wang, Limin; Liu, Riping

    2014-04-01

    ZnO, aside from TiO2, has been considered as a promising material for purification and disinfection of water and air, and remediation of hazardous waste, owing to its high activity, environment-friendly feature and lower cost. However, their poor visible light utilization greatly limited their practical applications. Herein, we demonstrate the fabrication of different aspect ratios of the ZnO nanorods with surface defects by mechanical-assisted thermal decomposition method. The experiments revealed that ZnO nanorods with higher aspect ratio and surface defects show significantly higher photocatalytic performances.

  16. Theory and Observations of High Frequency Alfven Eigenmodes in Low Aspect Ratio Plasma

    SciTech Connect

    N.N. Gorelenkov; E. Fredrickson; E. Belova; C.Z. Cheng; D. Gates; S. Kaye; R. White

    2003-06-27

    New observations of sub-cyclotron frequency instability in low aspect ratio plasma in National Spherical Torus Experiments (NSTX) are reported. The frequencies of observed instabilities correlate with the characteristic Alfven velocity of the plasma. A theory of localized Compressional Alfven Eigenmodes (CAE) and Global shear Alfven Eigenmodes (GAE) in low aspect ratio plasma is presented to explain the observed high frequency instabilities. CAE's/GAE's are driven by the velocity space gradient of energetic super-Alfvenic beam ions via Doppler shifted cyclotron resonances. One of the main damping mechanisms of GAE's, the continuum damping, is treated perturbatively within the framework of ideal MHD. Properties of these cyclotron instabilities ions are presented.

  17. Revealing the nanoparticles aspect ratio in the glass-metal nanocomposites irradiated with femtosecond laser

    PubMed Central

    Chervinskii, S.; Drevinskas, R.; Karpov, D. V.; Beresna, M.; Lipovskii, A. A.; Svirko, Yu. P.; Kazansky, P. G.

    2015-01-01

    We studied a femtosecond laser shaping of silver nanoparticles embedded in soda-lime glass. Comparing experimental absorption spectra with the modeling based on Maxwell Garnett approximation modified for spheroidal inclusions, we obtained the mean aspect ratio of the re-shaped silver nanoparticles as a function of the laser fluence. We demonstrated that under our experimental conditions the spherical shape of silver nanoparticles changed to a prolate spheroid with the aspect ratio as high as 3.5 at the laser fluence of 0.6 J/cm2. The developed approach can be employed to control the anisotropy of the glass-metal composites. PMID:26348691

  18. Revealing the nanoparticles aspect ratio in the glass-metal nanocomposites irradiated with femtosecond laser

    NASA Astrophysics Data System (ADS)

    Chervinskii, S.; Drevinskas, R.; Karpov, D. V.; Beresna, M.; Lipovskii, A. A.; Svirko, Yu. P.; Kazansky, P. G.

    2015-09-01

    We studied a femtosecond laser shaping of silver nanoparticles embedded in soda-lime glass. Comparing experimental absorption spectra with the modeling based on Maxwell Garnett approximation modified for spheroidal inclusions, we obtained the mean aspect ratio of the re-shaped silver nanoparticles as a function of the laser fluence. We demonstrated that under our experimental conditions the spherical shape of silver nanoparticles changed to a prolate spheroid with the aspect ratio as high as 3.5 at the laser fluence of 0.6 J/cm2. The developed approach can be employed to control the anisotropy of the glass-metal composites.

  19. Revealing the nanoparticles aspect ratio in the glass-metal nanocomposites irradiated with femtosecond laser.

    PubMed

    Chervinskii, S; Drevinskas, R; Karpov, D V; Beresna, M; Lipovskii, A A; Svirko, Yu P; Kazansky, P G

    2015-01-01

    We studied a femtosecond laser shaping of silver nanoparticles embedded in soda-lime glass. Comparing experimental absorption spectra with the modeling based on Maxwell Garnett approximation modified for spheroidal inclusions, we obtained the mean aspect ratio of the re-shaped silver nanoparticles as a function of the laser fluence. We demonstrated that under our experimental conditions the spherical shape of silver nanoparticles changed to a prolate spheroid with the aspect ratio as high as 3.5 at the laser fluence of 0.6 J/cm2. The developed approach can be employed to control the anisotropy of the glass-metal composites. PMID:26348691

  20. Visualization of Secondary Flow Development in High Aspect Ratio Channels with Curvature

    NASA Technical Reports Server (NTRS)

    Meyer, Michael L.; Giuliani, James E.

    1994-01-01

    The results of an experimental project to visually examine the secondary flow structure that develops in curved, high aspect-ratio rectangular channels are presented. The results provide insight into the fluid dynamics within high aspect ratio channels. A water flow test rig constructed out of plexiglass, with an adjustable aspect ratio, was used for these experiments. Results were obtained for a channel geometry with a hydraulic diameter of 10.6 mm (0.417 in.), an aspect ratio of 5.0, and a hydraulic radius to curvature radius ratio of 0.0417. Flow conditions were varied to achieve Reynolds numbers up to 5,100. A new particle imaging velocimetry technique was developed which could resolve velocity information from particles entering and leaving the field of view. Time averaged secondary flow velocity vectors, obtained using this velocimetry technique, are presented for 30 degrees, 60 degrees, and 90 degrees into a 180 degrees bend and at a Reynolds number of 5,100. The secondary flow results suggest the coexistence of both the classical curvature induced vortex pair flow structure and the eddies seen in straight turbulent channel flow.

  1. Collisionless microtearing modes in hot tokamaks: Effect of trapped electrons

    SciTech Connect

    Swamy, Aditya K.; Ganesh, R.; Brunner, S.; Vaclavik, J.; Villard, L.

    2015-07-15

    Collisionless microtearing modes have recently been found linearly unstable in sharp temperature gradient regions of large aspect ratio tokamaks. The magnetic drift resonance of passing electrons has been found to be sufficient to destabilise these modes above a threshold plasma β. A global gyrokinetic study, including both passing electrons as well as trapped electrons, shows that the non-adiabatic contribution of the trapped electrons provides a resonant destabilization, especially at large toroidal mode numbers, for a given aspect ratio. The global 2D mode structures show important changes to the destabilising electrostatic potential. The β threshold for the onset of the instability is found to be generally downshifted by the inclusion of trapped electrons. A scan in the aspect ratio of the tokamak configuration, from medium to large but finite values, clearly indicates a significant destabilizing contribution from trapped electrons at small aspect ratio, with a diminishing role at larger aspect ratios.

  2. The neoclassical angular momentum flux in the large aspect ratio limit

    SciTech Connect

    Wong, S.K.; Chan, V.S.

    2005-09-15

    The small rotation version of the neoclassical angular momentum flux is calculated in the large aspect ratio limit and in the banana regime. The method relies on solving an adjoint equation to the customary linearized drift kinetic equation, circumventing the difficulty of obtaining the ion distribution function that is second order in the ratio of poloidal gyroradius over plasma scale length. The result differs significantly from a long-standing result for circular cross-section flux surfaces.

  3. Effect of asymmetrical street aspect ratios on microclimates in hot, humid regions

    NASA Astrophysics Data System (ADS)

    Qaid, Adeb; Ossen, Dilshan R.

    2015-06-01

    Asymmetrical street aspect ratios, i.e. different height-to-width (H1/W-H2/W) ratios, have not received much attention in the study of urban climates. Putrajaya Boulevard (northeast to southwest orientation) in Malaysia was selected to study the influence of six asymmetrical aspect ratio scenarios on the street microclimate using the Envi-met three-dimensional microclimate model (V3.1 Beta). Putrajaya Boulevard suffers from high surface and air temperature during the day due to the orientation, the low aspect ratio and the wide sky view factor. These issues are a common dilemma in many boulevards. Further, low and high symmetrical streets are incompatible with tropical regions as they offer conflicting properties during the day and at night. These scenarios are examined, therefore, to find asymmetrical streets which are able to reduce the impact of the day microclimate on boulevards, and as an alternative strategy fulfilling tropical day and night climatic conditions. Asymmetrical streets are better than low symmetrical streets in enhancing wind flow and blocking solar radiation, when tall buildings confront winds direction or solar altitudes. Therefore, mitigating heat islands or improving microclimates in asymmetrical streets based on tall buildings position which captures wind or caste shades. In northeast to southwest direction, aspect ratios of 0.8-2 reduce the morning microclimate and night heat islands yet the negative effects during the day are greater than the positive effects in the night. An aspect ratio of 2-0.8 reduces the temperature of surfaces by 10 to 14 °C and the air by 4.7 °C, recommended for enhancing boulevard microclimates and mitigating tropical heat islands.

  4. Effect of asymmetrical street aspect ratios on microclimates in hot, humid regions.

    PubMed

    Qaid, Adeb; Ossen, Dilshan R

    2015-06-01

    Asymmetrical street aspect ratios, i.e. different height-to-width (H1/W-H2/W) ratios, have not received much attention in the study of urban climates. Putrajaya Boulevard (northeast to southwest orientation) in Malaysia was selected to study the influence of six asymmetrical aspect ratio scenarios on the street microclimate using the Envi-met three-dimensional microclimate model (V3.1 Beta). Putrajaya Boulevard suffers from high surface and air temperature during the day due to the orientation, the low aspect ratio and the wide sky view factor. These issues are a common dilemma in many boulevards. Further, low and high symmetrical streets are incompatible with tropical regions as they offer conflicting properties during the day and at night. These scenarios are examined, therefore, to find asymmetrical streets which are able to reduce the impact of the day microclimate on boulevards, and as an alternative strategy fulfilling tropical day and night climatic conditions. Asymmetrical streets are better than low symmetrical streets in enhancing wind flow and blocking solar radiation, when tall buildings confront winds direction or solar altitudes. Therefore, mitigating heat islands or improving microclimates in asymmetrical streets based on tall buildings position which captures wind or caste shades. In northeast to southwest direction, aspect ratios of 0.8-2 reduce the morning microclimate and night heat islands yet the negative effects during the day are greater than the positive effects in the night. An aspect ratio of 2-0.8 reduces the temperature of surfaces by 10 to 14 °C and the air by 4.7 °C, recommended for enhancing boulevard microclimates and mitigating tropical heat islands. PMID:25108376

  5. Selecting the aspect ratio of a scatter plot based on its delaunay triangulation.

    PubMed

    Fink, Martin; Haunert, Jan-Henrik; Spoerhase, Joachim; Wolff, Alexander

    2013-12-01

    Scatter plots are diagrams that visualize two-dimensional data as sets of points in the plane. They allow users to detect correlations and clusters in the data. Whether or not a user can accomplish these tasks highly depends on the aspect ratio selected for the plot, i.e., the ratio between the horizontal and the vertical extent of the diagram. We argue that an aspect ratio is good if the Delaunay triangulation of the scatter plot at this aspect ratio has some nice geometric property, e.g., a large minimum angle or a small total edge length. More precisely, we consider the following optimization problem. Given a set Q of points in the plane, find a scale factor s such that scaling the x-coordinates of the points in Q by s and the y-coordinates by 1=s yields a point set P(s) that optimizes a property of the Delaunay triangulation of P(s), over all choices of s. We present an algorithm that solves this problem efficiently and demonstrate its usefulness on real-world instances. Moreover, we discuss an empirical test in which we asked 64 participants to choose the aspect ratios of 18 scatter plots. We tested six different quality measures that our algorithm can optimize. In conclusion, minimizing the total edge length and minimizing what we call the 'uncompactness' of the triangles of the Delaunay triangulation yielded the aspect ratios that were most similar to those chosen by the participants in the test. PMID:24051799

  6. Friction factors and heat transfer coefficients in turbulated cooling passages of different aspect ratios. I - Experimental results

    NASA Astrophysics Data System (ADS)

    Taslim, M. E.; Spring, S. D.

    1987-06-01

    In advanced turbine airfoil cooling designs where multiple-pass cooling circuits are used, a range of cooling passage aspect ratios (height/width) are encountered. The objective of this experimental investigation was to determine the effect that increasing aspect ratios have on friction factors and Nusselt numbers in internal cooling passages with rib-roughened (turbulated) surfaces. Aspect ratios ranging from 0.5 to 3.5 were tested over a Reynolds number range of 30,000 to 190,000. Each aspect ratio was tested at three different turbulator-height/hydraulic-diameter ratios and at a constant turbulator-height/pitch ratio of 0.10.

  7. Computer simulation of transport driven current in tokamaks

    NASA Astrophysics Data System (ADS)

    Nunan, W. J.; Dawson, J. M.

    1994-09-01

    We have investigated transport driven current in tokamaks via 2+1/2 dimensional, electromagnetic, particle-in-cell simulations. These have demonstrated a steady increase of toroidal current in centrally fueled plasmas. Neoclassical theory predicts that the bootstrap current vanishes at large aspect ratio, but we see equal or greater current growth in straight cylindrical plasmas. These results indicate that a centrally fueled and heated tokamak may sustain its toroidal current, even without the ``seed current'' which the neoclassical bootstrap theory requires.

  8. Electrohydrodynamic pressure enhanced by free space charge for electrically induced structure formation with high aspect ratio.

    PubMed

    Tian, Hongmiao; Wang, Chunhui; Shao, Jinyou; Ding, Yucheng; Li, Xiangming

    2014-10-28

    Electrically induced structure formation (EISF) is an interesting and unique approach for generating a microstructured duplicate from a rheological polymer by a spatially modulated electric field induced by a patterned template. Most of the research on EISF have so far used various dielectric polymers (with an electrical conductivity smaller than 10(-10) S/m that can be considered a perfect dielectric), on which the electric field induces a Maxwell stress only due to the dipoles (or bounded charges) in the polymer molecules, leading to a structure with a small aspect ratio. This paper presents a different approach for improving the aspect ratio allowed in EISF by doping organic salt into the perfect dielectric polymer, i.e., turning the perfect dielectric into a leaky dielectric, considering the fact that the free space charges enriched in the leaky dielectric polymer can make an additional contribution to the Maxwell stress, i.e., electrohydrodynamic pressure, which is desirable for high aspect ratio structuring. Our numerical simulations and experimental tests have shown that a leaky dielectric polymer, with a small conductivity comparable to that of deionized water, can be much more effective at being electrohydrodynamically deformed into a high aspect ratio in comparison with a perfect dielectric polymer when both of them have roughly the same dielectric constant. PMID:25268463

  9. The Flow Field Downstream of a Dynamic Low Aspect Ratio Circular Cylinder: A Parametric Study

    NASA Astrophysics Data System (ADS)

    Gildersleeve, Samantha; Dan, Clingman; Amitay, Michael

    2015-11-01

    Flow past a static, low aspect ratio cylinder (pin) has shown the formation of vortical structures, namely the horseshoe and arch-type vortex. These vortical structures may have substantial effects in controlling flow separation over airfoils. In the present experiments, the flow field associated with a low aspect ratio cylinder as it interacts with a laminar boundary layer under static and dynamic conditions was investigated through a parametric study over a flat plate. As a result of the pin being actuated in the wall-normal direction, the structures formed in the wake of the pin were seen to be a strong function of actuation amplitude, driving frequency, and aspect ratio of the cylinder. The study was conducted at a Reynolds number of 1875, based on the local boundary layer thickness, with a free stream velocity of 10 m/s. SPIV data were collected for two aspect ratios of 0.75 and 1.125, actuation amplitudes of 6.7% and 16.7%, and driving frequencies of 175 Hz and 350 Hz. Results indicate that the presence and interactions between vortical structures are altered in comparison to the static case and suggest increased large-scale mixing when the pin is driven at the shedding frequency (350 Hz). Supported by the Boeing Company.

  10. Fine and high-aspect-ratio screen printing combined with an imprinting technique

    NASA Astrophysics Data System (ADS)

    Hokari, Ryohei; Kurihara, Kazuma; Takada, Naoki; Matsumoto, Junichi; Matsumoto, Sohei; Hiroshima, Hiroshi

    2016-03-01

    The development of screen-printing techniques in order to obtain fine patterns with a high aspect ratio is an important task in the advancement of printed electronics. To this end, we propose a new printing concept in this study that consists of a combination of the screen-printing process with an imprinting technique. We show that fine and high-aspect-ratio patterns are realized by the capillary force of parallel-walled structures (PWSs) on the material to be printed. The PWS is fabricated by an imprinting method using an ultra-violet curable resin. In order to obtain finer patterns with a higher aspect ratio, printed patterns according to the pitch and the height of the PWSs were assessed. A printed pattern with a line width of 6.3 μm was obtained at a PWS, with a pitch of 20 μm and at a height of 110 μm, when a screen mask with a 100 μm-wide resist opening was used. The line width of the printed patterns was well controlled by the pitch of the PWSs. Moreover, an aspect ratio of up to 7.4 was achieved. Furthermore, we expect this screen-printing process to implement submicron patterns as well as more complex patterns, including curves and rings, through well-designed microstructures.

  11. Role of substrate aspect ratio on the robustness of capillary alignment

    NASA Astrophysics Data System (ADS)

    Broesch, David J.; Shiang, Edward; Frechette, Joelle

    2014-02-01

    Capillary forces associated with liquid bridges formed across solid substrates are routinely exploited to align and assemble micro- and nanoscale devices. The magnitude of these forces plays a critical role in minimizing substrate misalignment and therefore should be controlled for robust and reliable fabrication process. We explore through simulations and experiments the role of the substrate aspect ratio (L/W) on capillary restoring forces and torques. Simulations show that increasing the aspect ratio of the substrates increases the capillary torques and forces when the substrates are misaligned through either lateral or rotational perturbations. The effect of substrate area, perimeter, and liquid volume are also systematically explored to show that the increase in restoring torque is caused by an increase in aspect ratio. A simple theoretical model based on the geometry of the system shows excellent agreement with Surface Evolver simulations. Finally, parameters from experimental flip-chip devices [Josell, D. Wallace, W.E. Warren, J.A. Wheeler, D. Powell, A.C. J. Electron. Packag. 124, 227, (2002)] are used in our simulations to show how current capillary self-alignment schemes could benefit from using rectangular substrate shapes with aspect ratio greater than one.

  12. ASPECT RATIO DEPENDENCE OF THE FREE-FALL TIME FOR NON-SPHERICAL SYMMETRIES

    SciTech Connect

    Pon, Andy; Johnstone, Doug; Toala, Jesus A.; Heitsch, Fabian E-mail: Douglas.Johnstone@nrc-cnrc.gc.ca E-mail: e.vazquez@crya.unam.mx E-mail: fheitsch@unc.edu

    2012-09-10

    We investigate the collapse of non-spherical substructures, such as sheets and filaments, which are ubiquitous in molecular clouds. Such non-spherical substructures collapse homologously in their interiors but are influenced by an edge effect that causes their edges to be preferentially accelerated. We analytically compute the homologous collapse timescales of the interiors of uniform-density, self-gravitating filaments and find that the homologous collapse timescale scales linearly with the aspect ratio. The characteristic timescale for an edge-driven collapse mode in a filament, however, is shown to have a square-root dependence on the aspect ratio. For both filaments and circular sheets, we find that selective edge acceleration becomes more important with increasing aspect ratio. In general, we find that lower dimensional objects and objects with larger aspect ratios have longer collapse timescales. We show that estimates for star formation rates, based upon gas densities, can be overestimated by an order of magnitude if the geometry of a cloud is not taken into account.

  13. Enhanced electrorheological activity of polyaniline coated mesoporous silica with high aspect ratio.

    PubMed

    Noh, Jungchul; Yoon, Chang-Min; Jang, Jyongsik

    2016-05-15

    Polyaniline-coated mesoporous silica (PANI/mSiO2) materials with different aspect ratios (L/D=1, 5, and 10) were fabricated by a vapor deposition polymerization (VDP) method to investigate the geometric effect on electrorheological (ER) activity. The PANI/mSiO2 materials were dedoped by a facile NH4OH treatment to reduce the conductivity to a level appropriate for ER applications. Notably, the PANI/mSiO2-based ER fluids exhibited enhanced ER performance with increasing aspect ratio. In particular, the PANI/mSiO2 material with the highest aspect ratio manifested the highest ER activity, which was attributed to geometric effects on flow resistance and mechanical stability. Moreover, the ER materials with higher aspect ratios showed improved dielectric properties of large achievable polarizability and short relaxation time. Hence, the synergistic contribution of geometric effects and dielectric properties resulted in enhanced ER activity. Consequently, this study provides insight into an effective method to improve ER performance by simple manipulation of the particle geometry. PMID:26950396

  14. Out-of-plane Block Copolymer Microdomains in High Aspect-Ratio Templates

    NASA Astrophysics Data System (ADS)

    Gadelrab, Karim; Bai, Wubin; Alexander-Katz, Alfredo; Ross, Caroline

    Directed self-assembly DSA of block copolymers BCP proved to be a power approach for nanoscale fabrication. In addition, BCP with highly incompatible blocks (high Flory-Huggins interaction parameter (χ)) offer improvement in resolution of the BCP patterns. Unfortunately, high- χ BCPs usually exhibit large differences in surface affinity between the two blocks, forming a surface layer of the lower surface energy block and favoring in-plane orientation of lamellae or cylindrical microdomains. Here, we explore the conditions under which a high χ BCP creates an out-of-plane lamellar structure using high aspect ratio trenches with preferential walls. We employ self-consistent field theory SCFT and single mode expansion of Ginzburg-Landau free energy expression in the weak segregation limit to analytically construct a phase diagram of the in- and out-of-plane lamellae as a function of aspect ratio and surface affinity. It is found that achieving an out of plane lamellar structure necessitates a coupling between aspect ratio and surface functionality. In particular, strong side wall attraction results in out-of-plane lamellae when the trench aspect ratio is greater than unity. The results are validated for a polystyrene-block-polydimethylsiloxane (PS-b-PDMS) system within trenches made using interference lithography.

  15. Experimental simulation of air quality in street canyon under changes of building orientation and aspect ratio.

    PubMed

    Yassin, Mohamed F; Ohba, Masaake

    2012-09-01

    To assist validation of numerical simulations of urban pollution, air quality in a street canyon was investigated using a wind tunnel as a research tool under neutral atmospheric conditions. We used tracer gas techniques from a line source without buoyancy. Ethylene (C(2)H(4)) was used as the tracer gas. The street canyon model was formed of six parallel building rows of the same length. The flow and dispersion field was analyzed and measured using a hot-wire anemometer with split fiber probe and fast flame ionization detector. The diffusion flow field in the boundary layer within the street canyon was examined at different locations, with varying building orientations (θ=90°, 112.5°, 135° and 157.5°) and street canyon aspect ratios (W/H=1/2, 3/4 and 1) downwind of the leeward side of the street canyon model. Results show that velocity increases with aspect ratio, and with θ>90°. Pollutant concentration increases as aspect ratio decreases. This concentration decreases exponentially in the vertical direction, and decreases as θ increases from 90°. Measured pollutant concentration distributions indicate that variability of building orientation and aspect ratio in the street canyon are important for estimating air quality in the canyon. The data presented here can be used as a comprehensive database for validation of numerical models. PMID:22760437

  16. Simplified lifting-surface theory for flaps on wings of low and moderate aspect ratios

    NASA Technical Reports Server (NTRS)

    Wick, B. H.

    1975-01-01

    A modification of the simplified lifting-surface theory for wings with deflected flaps is presented and evaluated. The modification is simple and straightforward in application, and is shown to overcome the deficiency in the theory that results in an underestimation of flap lift effectiveness for wings that have low or moderate aspect ratios.

  17. Role of substrate aspect ratio on the robustness of capillary alignment

    SciTech Connect

    Broesch, David J.; Shiang, Edward; Frechette, Joelle

    2014-02-24

    Capillary forces associated with liquid bridges formed across solid substrates are routinely exploited to align and assemble micro- and nanoscale devices. The magnitude of these forces plays a critical role in minimizing substrate misalignment and therefore should be controlled for robust and reliable fabrication process. We explore through simulations and experiments the role of the substrate aspect ratio (L/W) on capillary restoring forces and torques. Simulations show that increasing the aspect ratio of the substrates increases the capillary torques and forces when the substrates are misaligned through either lateral or rotational perturbations. The effect of substrate area, perimeter, and liquid volume are also systematically explored to show that the increase in restoring torque is caused by an increase in aspect ratio. A simple theoretical model based on the geometry of the system shows excellent agreement with Surface Evolver simulations. Finally, parameters from experimental flip-chip devices [Josell, D. Wallace, W.E. Warren, J.A. Wheeler, D. Powell, A.C. J. Electron. Packag. 124, 227, (2002)] are used in our simulations to show how current capillary self-alignment schemes could benefit from using rectangular substrate shapes with aspect ratio greater than one.

  18. Nonlinear aeroelastic analysis of high-aspect-ratio wings in low subsonic flow

    NASA Astrophysics Data System (ADS)

    Eskandary, K.; Dardel, M.; Pashaei, M. H.; Moosavi, A. K.

    2012-01-01

    In this study, aeroelastic characteristics of high-aspect-ratio wing models with structural nonlinearities in quasi-steady aerodynamics flows are investigated. The studied wing model is a cantilever wing with double bending and torsional vibrations and with large deflection ability in accordance with Hodges-Dowell wing model. This wing model is valid for long, straight and thin homogeneous isotropic beams. The aerodynamics model is based on quasi-steady aerodynamic which is valid for aerodynamic flows without wake, viscosity and compressibility effects. The effect of different parameters such as mass ratios and stiffness ratios on flutter and divergence velocities and limit cycle oscillation amplitudes are carefully studied.

  19. Study of blade aspect ratio on a compressor front stage aerodynamic and mechanical design report

    NASA Technical Reports Server (NTRS)

    Burger, G. D.; Lee, D.; Snow, D. W.

    1979-01-01

    A single stage compressor was designed with the intent of demonstrating that, for a tip speed and hub-tip ratio typical of an advanced core compressor front stage, the use of low aspect ratio can permit high levels of blade loading to be achieved at an acceptable level of efficiency. The design pressure ratio is 1.8 at an adiabatic efficiency of 88.5 percent. Both rotor and stator have multiple-circular-arc airfoil sections. Variable IGV and stator vanes permit low speed matching adjustments. The design incorporates an inlet duct representative of an engine transition duct between fan and high pressure compressor.

  20. Selective aspect ratio of CNTs based on annealing temperature by TCVD method

    NASA Astrophysics Data System (ADS)

    Yousefi, Amin Termeh; Mahmood, Mohamad Rusop; Ikeda, Shoichiro

    2016-07-01

    Various aspect ratios of CNTs reported based on alteration of annealing temperature using thermal-chemical vapor deposition (TCVD) method. Also the growth dependent and independent parameters of the carbon nanotube (CNTs) array were studied as a function of synthesis method. The FESEM images indicate that the nanotubes are approximately perpendicular to the surface of the silicon substrate and form carbon nanotubes in different aspect ratios according to the applied annealing temperature. Furthermore, due to the optimized results it can be observed that, the mechanism of the CNTs growth is still present in the annealing step as well as deposition process and the most CNTs with crystalline aspect, produced in the annealing temperature, which was optimized at 700 - 900 ˚C. This result demonstrates that the growth rate, mass production, diameter, density, and crystallinity of CNT can be controlled by the annealing temperature.

  1. Blade tip, finite aspect ratio, and dynamic stall effects on the Darrieus rotor

    SciTech Connect

    Paraschivoiu, I.; Desy, P.; Masson, C.

    1988-02-01

    The objective of the work described in this paper was to apply the Boeing-Vertol dynamic stall model in an asymmetric manner to account for the asymmetry of the flow between the left and right sides of the rotor. This phenomenon has been observed by the flow visualization of a two-straight-bladed Darrieus rotor in the IMST water tunnel. Also introduced into the aerodynamic model are the effects of the blade tip and finite aspect ratio on the aerodynamic performance of the Darrieus wind turbine. These improvements are compatible with the double-multiple-streamtube model and have been included in the CARDAAV computer code for predicting the aerodynamic performance. Very good agreement has been observed between the test data (Sandia 17 m) and theoretical predictions; a significant improvement over the previous dynamic stall model was obtained for the rotor power at low tip speed ratios, while the inclusion of the finite aspect ratio effects enhances the prediction of the rotor power for high tip speed ratios. The tip losses and finite aspect ratio effects were also calculated for a small-scale vertical-axis wind turbine, with a two-straight-bladed (NACA 0015) rotor. 15 references.

  2. A 3-dimensional in vitro model of epithelioid granulomas induced by high aspect ratio nanomaterials

    PubMed Central

    2011-01-01

    Background The most common causes of granulomatous inflammation are persistent pathogens and poorly-degradable irritating materials. A characteristic pathological reaction to intratracheal instillation, pharyngeal aspiration, or inhalation of carbon nanotubes is formation of epithelioid granulomas accompanied by interstitial fibrosis in the lungs. In the mesothelium, a similar response is induced by high aspect ratio nanomaterials, including asbestos fibers, following intraperitoneal injection. This asbestos-like behaviour of some engineered nanomaterials is a concern for their potential adverse health effects in the lungs and mesothelium. We hypothesize that high aspect ratio nanomaterials will induce epithelioid granulomas in nonadherent macrophages in 3D cultures. Results Carbon black particles (Printex 90) and crocidolite asbestos fibers were used as well-characterized reference materials and compared with three commercial samples of multiwalled carbon nanotubes (MWCNTs). Doses were identified in 2D and 3D cultures in order to minimize acute toxicity and to reflect realistic occupational exposures in humans and in previous inhalation studies in rodents. Under serum-free conditions, exposure of nonadherent primary murine bone marrow-derived macrophages to 0.5 μg/ml (0.38 μg/cm2) of crocidolite asbestos fibers or MWCNTs, but not carbon black, induced macrophage differentiation into epithelioid cells and formation of stable aggregates with the characteristic morphology of granulomas. Formation of multinucleated giant cells was also induced by asbestos fibers or MWCNTs in this 3D in vitro model. After 7-14 days, macrophages exposed to high aspect ratio nanomaterials co-expressed proinflammatory (M1) as well as profibrotic (M2) phenotypic markers. Conclusions Induction of epithelioid granulomas appears to correlate with high aspect ratio and complex 3D structure of carbon nanotubes, not with their iron content or surface area. This model offers a time- and cost

  3. Comparison of High Aspect Ratio Cooling Channel Designs for a Rocket Combustion Chamber

    NASA Technical Reports Server (NTRS)

    Wadel, Mary F.

    1997-01-01

    An analytical investigation on the effect of high aspect ratio (height/width) cooling channels, considering different coolant channel designs, on hot-gas-side wall temperature and coolant pressure drop for a liquid hydrogen cooled rocket combustion chamber, was performed. Coolant channel design elements considered were: length of combustion chamber in which high aspect ratio cooling was applied, number of coolant channels, and coolant channel shape. Seven coolant channel designs were investigated using a coupling of the Rocket Thermal Evaluation code and the Two-Dimensional Kinetics code. Initially, each coolant channel design was developed, without consideration for fabrication, to reduce the hot-gas-side wall temperature from a given conventional cooling channel baseline. These designs produced hot-gas-side wall temperature reductions up to 22 percent, with coolant pressure drop increases as low as 7.5 percent from the baseline. Fabrication constraints for milled channels were applied to the seven designs. These produced hot-gas-side wall temperature reductions of up to 20 percent, with coolant pressure drop increases as low as 2 percent. Using high aspect ratio cooling channels for the entire length of the combustion chamber had no additional benefit on hot-gas-side wall temperature over using high aspect ratio cooling channels only in the throat region, but increased coolant pressure drop 33 percent. Independent of coolant channel shape, high aspect ratio cooling was able to reduce the hot-gas-side wall temperature by at least 8 percent, with as low as a 2 percent increase in coolant pressure drop. The design with the highest overall benefit to hot-gas-side wall temperature and minimal coolant pressure drop cooling can now be done in relatively short periods of time with multiple iterations.

  4. Critical aspect ratio for tungsten fibers in copper-nickel matrix composites

    NASA Technical Reports Server (NTRS)

    Jech, R. W.

    1975-01-01

    Stress-rupture and tensile tests were conducted at 816 C (1500 F) to determine the effect of matrix composition on the minimum fiber length to diameter ratio (critical aspect ratio) below which fibers in a tungsten fiber/copper-nickel alloy matrix composite could not be stressed to their ultimate load carrying capability. This study was intended to simulate some of the conditions that might be encountered with materials combinations used in high-temperature composites. The critical aspect ratio for stress-rupture was found to be greater than for short-time tension, and it increased as the time to rupture increased. The increase was relatively slight, and calculated fiber lengths for long service appear to be well within practical size limits for effective reinforcement and ease of fabrication of potential gas turbine components.

  5. Geometry effects on aerodynamics performance of a low aspect ratio turbine nozzle

    NASA Astrophysics Data System (ADS)

    Chen, Naixing; Zhang, Hongwu; Xu, Yanji; Huang, Weiguang

    2004-11-01

    This paper describes the influence of some geometric parameters on aerodynamics performance of a low-aspect-ratio turbine blading designed by a novel method developed at the Institute of Engineering Thermophysics, Chinese Academy of Sciences. This is a part of the study on aerodynamics optimization of turbomachinery. It follows the development of the basic ideas in the turbomachinery aerodynamics research project at the institute. The present paper concentrates mainly on the effects of geometry, such as stagger angle, leading and trailing edge thickness, maximum thickness and its location on adiabatic efficiency, total pressure ratio and mass flow rate. The study was performed and assessed for a low-aspect ratio turbine nozzle using 3D steady Reynolds-averaged N.S. solver. Using the knowledge of the flow physics analysis an optimized turbine nozzle was obtained.

  6. Study by the Prandtl-Glauert method of compressibility effects and critical Mach number for ellipsoids of various aspect ratios and thickness ratios

    NASA Technical Reports Server (NTRS)

    Hess, Robert V; Gardner, Clifford S

    1947-01-01

    By using the Prandtl-Glauert method that is valid for three-dimensional flow problems, the value of the maximum incremental velocity for compressible flow about thin ellipsoids at zero angle of attack is calculated as a function of the Mach number for various aspect ratios and thickness ratios. The critical Mach numbers of the various ellipsoids are also determined. The results indicate an increase in critical Mach number with decrease in aspect ratio which is large enough to explain experimental results on low-aspect-ratio wings at zero lift.

  7. Generation of liquid metal structures of high aspect ratio by application of an ac magnetic field

    NASA Astrophysics Data System (ADS)

    Andreev, Oleg; Pothérat, Alban; Thess, André

    2010-06-01

    We study how the shape of parts obtained through the LASER cladding process can be controlled by application of an ac magnetic field by means of two simple physical models: a numerical and an experimental one. More specifically, we show that straight metallic joints of high aspect ratio can be obtained by using inductors of triangular cross-section that concentrate electromagnetic forces at the bottom of the joint. The effect is first demonstrated on a numerical model for an infinitely long joint such as: we illustrate how the joint shape can be controlled by varying the inclination of the inductor and for a magnetic Bond number Bom=60 (which measures the ratio of electromagnetic to capillary forces), we obtain a joint of aspect ratio up to 7.2. We further find that inductor angles in the range 15°-25° lead to joint side faces that are close to vertical. These findings are then verified experimentally by placing a liquid metal drop in a purpose built inductor of triangular cross-section. We find a good agreement between the theoretical prediction of our two-dimensional model and the real three-dimensional drop. For the highest magnetic Bond number our generator could deliver, Bom=20.19, we achieved a drop aspect ratio of 2.73.

  8. Time-dependent large aspect-ratio thermal convection in the earth's mantle

    NASA Astrophysics Data System (ADS)

    Weinstein, Stuart A.; Olson, Peter L.; Yuen, David A.

    Numerical simulations of two-dimensional time-dependent thermal convection in a Boussinesq, isoviscous, infinite Prandtl number fluid with isothermal, stress-free boundaries have been performed in large aspect-ratio configurations, in which the fluid is heated from below as well as internally. The value of the basal heated Rayleigh number ranged from 16000 to 800 000 and the Rayleigh number based on internal heat generation was varied from zero to 4 500 000. Large aspect-ratio cells are found to exist, however, they are time-dependent even at small values of the Rayleigh number. In the absence of internal heating, the onset of time-dependence occurs as a regular oscillation in the flow characteristics (Nusselt number, kinetic energy), and is accompanied by the presence of boundary layer instabilities (BLI) which exist within a large aspect-ratio circulation. At high values of the Rayleigh number the BLI are powerful features which leave the confines of the boundary layer and strongly perturb the large aspect-ratio circulation giving the flow a multi-scale character. Convective mixing of these powerful BLI results in heterogeneity in the cell interior which plays a role in the excitation of new BLI and establishes a negative temperature gradient in the cell interior. We have developed a fluid loop model which gives a qualitative explanation for the variation of the onset of time-dependence with aspect-ratio. The addition of internal heating tends to destabilize the large aspect-ratio cell configuration. Multi-cellular states last longer and occur more frequently with increasing amounts of internal heating. These calculations shed new light on a variety of time-dependent phenomena in geodynamics such as subduction, back-arc spreading, intraplate deformation, and the average geotherm. Recently, Jeanloz and Morris proposed that the seismic inhomogeneity parameter () can be used to measure the importance of internal heating in mantle convection. However, our

  9. On the evolution of the wake structure produced by a low-aspect-ratio pitching panel

    PubMed Central

    BUCHHOLZ, JAMES H. J.; SMITS, ALEXANDER J.

    2009-01-01

    Flow visualization is used to interrogate the wake structure produced by a rigid flat panel of aspect ratio (span/chord) 0.54 pitching in a free stream at a Strouhal number of 0.23. At such a low aspect ratio, the streamwise vorticity generated by the plate tends to dominate the formation of the wake. Nevertheless, the wake has the appearance of a three-dimensional von Kármán vortex street, as observed in a wide range of other experiments, and consists of horseshoe vortices of alternating sign shed twice per flapping cycle. The legs of each horseshoe interact with the two subsequent horseshoes in an opposite-sign, then like-sign interaction in which they become entrained. A detailed vortex skeleton model is proposed for the wake formation. PMID:19746198

  10. High Yield Synthesis of Aspect Ratio Controlled Graphenic Materials from Anthracite Coal in Supercritical Fluids.

    PubMed

    Sasikala, Suchithra Padmajan; Henry, Lucile; Yesilbag Tonga, Gulen; Huang, Kai; Das, Riddha; Giroire, Baptiste; Marre, Samuel; Rotello, Vincent M; Penicaud, Alain; Poulin, Philippe; Aymonier, Cyril

    2016-05-24

    This paper rationalizes the green and scalable synthesis of graphenic materials of different aspect ratios using anthracite coal as a single source material under different supercritical environments. Single layer, monodisperse graphene oxide quantum dots (GQDs) are obtained at high yield (55 wt %) from anthracite coal in supercritical water. The obtained GQDs are ∼3 nm in lateral size and display a high fluorescence quantum yield of 28%. They show high cell viability and are readily used for imaging cancer cells. In an analogous experiment, high aspect ratio graphenic materials with ribbon-like morphology (GRs) are synthesized from the same source material in supercritical ethanol at a yield of 6.4 wt %. A thin film of GRs with 68% transparency shows a surface resistance of 9.3 kΩ/sq. This is apparently the demonstration of anthracite coal as a source for electrically conductive graphenic materials. PMID:27135862

  11. Convergence acceleration of implicit schemes in the presence of high aspect ratio grid cells

    NASA Technical Reports Server (NTRS)

    Buelow, B. E. O.; Venkateswaran, S.; Merkle, C. L.

    1993-01-01

    The performance of Navier-Stokes codes are influenced by several phenomena. For example, the robustness of the code may be compromised by the lack of grid resolution, by a need for more precise initial conditions or because all or part of the flowfield lies outside the flow regime in which the algorithm converges efficiently. A primary example of the latter effect is the presence of extended low Mach number and/or low Reynolds number regions which cause convergence deterioration of time marching algorithms. Recent research into this problem by several workers including the present authors has largely negated this difficulty through the introduction of time-derivative preconditioning. In the present paper, we employ the preconditioned algorithm to address convergence difficulties arising from sensitivity to grid stretching and high aspect ratio grid cells. Strong grid stretching is particularly characteristic of turbulent flow calculations where the grid must be refined very tightly in the dimension normal to the wall, without a similar refinement in the tangential direction. High aspect ratio grid cells also arise in problems that involve high aspect ratio domains such as combustor coolant channels. In both situations, the high aspect ratio cells can lead to extreme deterioration in convergence. It is the purpose of the present paper to address the reasons for this adverse response to grid stretching and to suggest methods for enhancing convergence under such circumstances. Numerical algorithms typically possess a maximum allowable or optimum value for the time step size, expressed in non-dimensional terms as a CFL number or vonNeumann number (VNN). In the presence of high aspect ratio cells, the smallest dimension of the grid cell controls the time step size causing it to be extremely small, which in turn results in the deterioration of convergence behavior. For explicit schemes, this time step limitation cannot be exceeded without violating stability restrictions

  12. High aspect ratio nanochannel machining using single shot femtosecond Bessel beams

    SciTech Connect

    Bhuyan, M. K.; Courvoisier, F.; Lacourt, P. A.; Jacquot, M.; Salut, R.; Furfaro, L.; Dudley, J. M.

    2010-08-23

    We report high aspect ratio nanochannel fabrication in glass using single-shot femtosecond Bessel beams of sub-3 {mu}J pulse energies at 800 nm. We obtain near-parallel nanochannels with diameters in the range 200-800 nm, and aspect ratios that can exceed 100. An array of 230 nm diameter channels with 1.6 {mu}m pitch illustrates the reproducibility of this approach and the potential for writing periodic structures. We also report proof-of-principle machining of a through-channel of 400 nm diameter in a 43 {mu}m thick membrane. These results represent a significant advance of femtosecond laser ablation technology into the nanometric regime.

  13. High aspect ratio tungsten grating on ultrathin Si membranes for extreme UV lithography

    NASA Astrophysics Data System (ADS)

    Peng, Xinsheng; Ying, Yulong

    2016-09-01

    Extreme ultraviolet lithography is one of the modern lithography tools for high-volume manufacturing with 22 nm resolution and beyond. But critical challenges exist to the design and fabrication of large-scale and highly efficient diffraction transmission gratings, significantly reducing the feature sizes down to 22 nm and beyond. To achieve such a grating, the surface flatness, the line edge roughness, the transmission efficiency and aspect ratio should be improved significantly. Delachat et al (2015 Nanotechnology 26 108262) develop a full process to fabricate a tungsten diffraction grating on an ultrathin silicon membrane with higher aspect ratio up to 8.75 that met all the aforementioned requirements for extreme ultraviolet lithography. This process is fully compatible with standard industrial extreme ultraviolet lithography.

  14. Light emitting diode with high aspect ratio submicron roughness for light extraction and methods of forming

    DOEpatents

    Li, Ting

    2013-08-13

    The surface morphology of an LED light emitting surface is changed by applying a reactive ion etch (RIE) process to the light emitting surface. High aspect ratio, submicron roughness is formed on the light emitting surface by transferring a thin film metal hard-mask having submicron patterns to the surface prior to applying a reactive ion etch process. The submicron patterns in the metal hard-mask can be formed using a low cost, commercially available nano-patterned template which is transferred to the surface with the mask. After subsequently binding the mask to the surface, the template is removed and the RIE process is applied for time duration sufficient to change the morphology of the surface. The modified surface contains non-symmetric, submicron structures having high aspect ratio which increase the efficiency of the device.

  15. Rapid fabrication of high aspect ratio silicon nanopillars for chemical analysis

    NASA Astrophysics Data System (ADS)

    Sainiemi, Lauri; Keskinen, Helmi; Aromaa, Mikko; Luosujärvi, Laura; Grigoras, Kestas; Kotiaho, Tapio; Mäkelä, Jyrki M.; Franssila, Sami

    2007-12-01

    In this study, a method for fabrication of high aspect ratio silicon nanopillars is presented. The method combines liquid flame spray production of silica nanoparticle agglomerates with cryogenic deep reactive ion etching. First, the nanoparticle agglomerates, having a diameter of about 100 nm, are deposited on a silicon wafer. Then, during the subsequent cryogenic deep reactive ion etching process, the particle agglomerates act as etch masks and silicon nanopillars are formed. Aspect ratios of up to 20:1 are demonstrated. The masking process is rapid, cheap and has the potential to be scaled up for large areas. Three other structured silicon surfaces were fabricated for comparison. All four surfaces were utilized as desorption/ionization on silicon (DIOS) sample plates. The mass spectrometry results indicate that nanopillar surfaces masked with the liquid flame spray technique are well suited as DIOS sample plates.

  16. High aspect ratio tungsten grating on ultrathin Si membranes for extreme UV lithography.

    PubMed

    Peng, Xinsheng; Ying, Yulong

    2016-09-01

    Extreme ultraviolet lithography is one of the modern lithography tools for high-volume manufacturing with 22 nm resolution and beyond. But critical challenges exist to the design and fabrication of large-scale and highly efficient diffraction transmission gratings, significantly reducing the feature sizes down to 22 nm and beyond. To achieve such a grating, the surface flatness, the line edge roughness, the transmission efficiency and aspect ratio should be improved significantly. Delachat et al (2015 Nanotechnology 26 108262) develop a full process to fabricate a tungsten diffraction grating on an ultrathin silicon membrane with higher aspect ratio up to 8.75 that met all the aforementioned requirements for extreme ultraviolet lithography. This process is fully compatible with standard industrial extreme ultraviolet lithography. PMID:27458188

  17. High-aspect-ratio line focus for an x-ray laser by a deformable mirror

    SciTech Connect

    Yoon, G.; Jitsuno, T.; Kato, Y.; Nakatsuka, M.

    1997-02-01

    A high-aspect-ratio line focus is required on a plane target in x-ray laser experiments for obtaining a high gain-length product. Inherent wave-front aberrations in line-focusing optics, which consist of a cylindrical lens and a spherical lens, are discussed with respect to beam diameter. The nonuniformity of the linewidth that is due to the aberrations is also calculated by the ABCD matrix method. A deformable mirror of a continuous plate type with a diameter of 185 mm provides an adequate wave-front distribution for compensating for the wave-front aberration. The wave-front control by the deformable mirror realizes a fine linewidth of 25 {mu}m and 18.2 mm long, corresponding to the aspect ratio of 728. The linewidth is three times the diffraction limit. The intensity distribution along the line focus is also improved. {copyright} 1997 Optical Society of America

  18. High-aspect-ratio line focus for an x-ray laser by a deformable mirror.

    PubMed

    Yoon, G Y; Jitsuno, T; Kato, Y; Nakatsuka, M

    1997-02-01

    A high-aspect-ratio line focus is required on a plane target in x-ray laser experiments for obtaining a high gain-length product. Inherent wave-front aberrations in line-focusing optics, which consist of a cylindrical lens and a spherical lens, are discussed with respect to beam diameter. The nonuniformity of the linewidth that is due to the aberrations is also calculated by the ABCD matrix method. A deformable mirror of a continuous plate type with a diameter of 185 mm provides an adequate wave-front distribution for compensating for the wave-front aberration. The wave-front control by the deformable mirror realizes a fine linewidth of 25 microm and 18.2 mm long, corresponding to the aspect ratio of 728. The linewidth is three times the diffraction limit. The intensity distribution along the line focus is also improved. PMID:18250748

  19. Fabrication of Very-High-Aspect-Ratio Microstructures in Complex Patterns by Photoelectrochemical Etching

    SciTech Connect

    Sun, GY; Zhao, X; Kim, CJ

    2012-12-01

    We have fabricated very-high-aspect-ratio (VHAR) silicon and metal microstructures in complex geometric patterns. The recently developed surfactant-added tetramethylammonium hydroxide etching allows the formation of V-grooves in any pattern, i.e., not limited by the crystal direction, on a silicon surface. As the resulting sharp pits allow very deep photoelectrochemical etching, VHAR silicon microstructures (4-mu m-wide and over-300-mu m-deep trenches) are successfully fabricated in complex patterns (spiral and zigzag demonstrated), overcoming the prevailing limitations of simple pores and straight trenches. Furthermore, by filling the VHAR silicon mold with nickel and removing the silicon, high-aspect-ratio metal microstructures of complex patterns are also obtained. These VHAR microstructures in complex patterns, which are structurally much stronger than the simple posts and straight plates, overcome the stiction problem even when densely populated. [2012-0042

  20. Cross-sectional aspect ratio modulated electronic properties in Si/Ge core/shell nanowires

    SciTech Connect

    Liu, Nuo; Lu, Ning; Yao, Yong-Xin; Zhang, Gui-Ping; Wang, Cai-Zhuang; Ho, Kai-Ming

    2013-02-28

    Electronic structures of (4, n) and (m, 4) (the NW has m layers parallel to the {1 1 1} facet and n layers parallel to {1 1 0}) Si/Ge core/shell nanowires (NWs) along the [1 1 2] direction with cross-sectional aspect ratio (m/n) from 0.36 to 2.25 are studied by first-principles calculations. An indirect to direct band gap transition is observed as m/n decreases, and the critical values of m/n and diameter for the transition are also estimated. The size of the band gap also depends on the aspect ratio. These results suggest that m/n plays an important role in modulating the electronic properties of the NWs.

  1. Light emitting diode with high aspect ratio submicron roughness for light extraction and methods of forming

    DOEpatents

    Li, Ting

    2011-04-26

    The surface morphology of an LED light emitting surface is changed by applying a reactive ion etch (RIE) process to the light emitting surface. High aspect ratio, submicron roughness is formed on the light emitting surface by transferring a thin film metal hard-mask having submicron patterns to the surface prior to applying a reactive ion etch process. The submicron patterns in the metal hard-mask can be formed using a low cost, commercially available nano-patterned template which is transferred to the surface with the mask. After subsequently binding the mask to the surface, the template is removed and the RIE process is applied for time duration sufficient to change the morphology of the surface. The modified surface contains non-symmetric, submicron structures having high aspect ratio which increase the efficiency of the device.

  2. Convergence acceleration of implicit schemes in the presence of high aspect ratio grid cells

    NASA Astrophysics Data System (ADS)

    Buelow, B. E. O.; Venkateswaran, S.; Merkle, C. L.

    1993-07-01

    The performance of Navier-Stokes codes are influenced by several phenomena. For example, the robustness of the code may be compromised by the lack of grid resolution, by a need for more precise initial conditions or because all or part of the flowfield lies outside the flow regime in which the algorithm converges efficiently. A primary example of the latter effect is the presence of extended low Mach number and/or low Reynolds number regions which cause convergence deterioration of time marching algorithms. Recent research into this problem by several workers including the present authors has largely negated this difficulty through the introduction of time-derivative preconditioning. In the present paper, we employ the preconditioned algorithm to address convergence difficulties arising from sensitivity to grid stretching and high aspect ratio grid cells. Strong grid stretching is particularly characteristic of turbulent flow calculations where the grid must be refined very tightly in the dimension normal to the wall, without a similar refinement in the tangential direction. High aspect ratio grid cells also arise in problems that involve high aspect ratio domains such as combustor coolant channels. In both situations, the high aspect ratio cells can lead to extreme deterioration in convergence. It is the purpose of the present paper to address the reasons for this adverse response to grid stretching and to suggest methods for enhancing convergence under such circumstances. Numerical algorithms typically possess a maximum allowable or optimum value for the time step size, expressed in non-dimensional terms as a CFL number or vonNeumann number (VNN). In the presence of high aspect ratio cells, the smallest dimension of the grid cell controls the time step size causing it to be extremely small, which in turn results in the deterioration of convergence behavior. For explicit schemes, this time step limitation cannot be exceeded without violating stability restrictions

  3. Synthesis of High-Aspect-Ratio Nickel Nanowires by Dropping Method.

    PubMed

    Zhang, Jiaqi; Xiang, Wenfeng; Liu, Yuan; Hu, Minghao; Zhao, Kun

    2016-12-01

    A facile and high-yield route, dropping method, has been used to synthesize Ni nanowires (NWs) with a high aspect ratio. Compared to the conventional chemical reduction method, the diameter of Ni NWs prepared by the dropping method distinctively decreased and the surface roughness was improved. After optimizing the process parameters such as the Ni ion concentration and volume of the dropped NiCl2·6H2O solution, the diameter and aspect ratio of the NWs are 70 nm and ~600, respectively. The possible synthesized process of the dropping method was discussed. This work presents a preferred approach to fabricate high-quality one-dimensional magnetic materials which have potential applications in electrochemical devices, magnetic sensors, and catalytic agents. PMID:26925866

  4. Some Divergence Characteristics of Low-Aspect-Ratio Wings at Transonic and Supersonic Speeds

    NASA Technical Reports Server (NTRS)

    Woolston, Donald S.; Gibson, Frederick W.; Cunningham, Herbert J.

    1960-01-01

    The problem of chordwise, or camber, divergence at transonic and supersonic speeds is treated with primary emphasis on slender delta wings having a cantilever support at the trailing edge. Experimental and analytical results are presented for four wing models having apex half-angles of 5 deg, 10 deg, 15 deg, and 20 deg. A Mach number range from 0.8 to 7.3 is covered. The analytical results include calculations based on small-aspect-ratio theory, lifting-surface theory, and strip theory. A closed-form solution of the equilibrium equation is given, which is based on low-aspect-ratio theory but which applies only to certain stiffness distributions. Also presented is an iterative procedure for use with other aerodynamic theories and with arbitrary stiffness distribution.

  5. Progress in the fabrication of high aspect ratio zone plates by soft x-ray lithography.

    SciTech Connect

    Divan, R.; Mancini, D. C.; Moldovan, N. A.; Lai, B.; Assoufid, L.; Leondard, Q.; Cerrina, F.

    2002-08-13

    Soft x-ray lithography technology has been applied to fabrication of phase shifting Fresnel Zone Plate (FZP's) for hard x-rays. Effects of the exposure conditions, developing system, and electroplating process parameters on line width and aspect ratio have been analyzed. The process has been optimized and an aspect ratio of 11 has been achieved for 110 nm outermost zone width. SEM and AFM have been used for preliminary metrology of the FZPs. The FZP optical performance was characterized at 8 keV photon energy at the 2-ID-D beam line at the Advanced Photon Source. Focusing efficiencies of 23% for FZPs apertures to 100 microns and 18% for 150-micron-diameter apertures have been obtained. The parameters of the fabricated FZP are in good agreement with the predicted values.

  6. Maintaining high-Q in an optical microresonator coated with high-aspect-ratio gold nanorods

    NASA Astrophysics Data System (ADS)

    Ganta, D.; Dale, E. B.; Rosenberger, A. T.

    2013-10-01

    We report methods to coat fused-silica microresonators with solution-grown high-aspect-ratio (AR) gold nanorods (NRs). Microresonators coated using our method maintain an optical quality factor (Q) greater than 107 after coating. The more successful method involves silanization of the surface of the microresonator with 3-mercaptopropylmethyldimethoxysilane (MPMDMS), to enable the adhesion of gold NRs. The high-AR NR-coated microresonator combines the field enhancement of localized surface plasmon resonances with the cavity-enhanced evanescent components of high-Q whispering-gallery modes, making it useful for plasmonic sensing applications in the infrared. By coating with NRs having a different aspect ratio, the enhancement regime can be selected within a wide range of wavelengths.

  7. Dense high aspect ratio hydrogen silsesquioxane nanostructures by 100 keV electron beam lithography

    NASA Astrophysics Data System (ADS)

    Vila-Comamala, Joan; Gorelick, Sergey; Guzenko, Vitaliy A.; Färm, Elina; Ritala, Mikko; David, Christian

    2010-07-01

    We investigated the fabrication of dense, high aspect ratio hydrogen silsesquioxane (HSQ) nanostructures by 100 keV electron beam lithography. The samples were developed using a high contrast developer and supercritically dried in carbon dioxide. Dense gratings with line widths down to 25 nm were patterned in 500 nm-thick resist layers and semi-dense gratings with line widths down to 10 nm (40 nm pitch) were patterned in 250 nm-thick resist layers. The dense HSQ nanostructures were used as molds for gold electrodeposition, and the semi-dense HSQ gratings were iridium-coated by atomic layer deposition. We used these methods to produce Fresnel zone plates with extreme aspect ratio for scanning transmission x-ray microscopy that showed excellent performance at 1.0 keV photon energy.

  8. Dense high aspect ratio hydrogen silsesquioxane nanostructures by 100 keV electron beam lithography.

    PubMed

    Vila-Comamala, Joan; Gorelick, Sergey; Guzenko, Vitaliy A; Färm, Elina; Ritala, Mikko; David, Christian

    2010-07-16

    We investigated the fabrication of dense, high aspect ratio hydrogen silsesquioxane (HSQ) nanostructures by 100 keV electron beam lithography. The samples were developed using a high contrast developer and supercritically dried in carbon dioxide. Dense gratings with line widths down to 25 nm were patterned in 500 nm-thick resist layers and semi-dense gratings with line widths down to 10 nm (40 nm pitch) were patterned in 250 nm-thick resist layers. The dense HSQ nanostructures were used as molds for gold electrodeposition, and the semi-dense HSQ gratings were iridium-coated by atomic layer deposition. We used these methods to produce Fresnel zone plates with extreme aspect ratio for scanning transmission x-ray microscopy that showed excellent performance at 1.0 keV photon energy. PMID:20562479

  9. Effects of Variable Aspect-Ratio Inclusions on the Electrical Impedance of an Alumina Zirconia Composite at Intermediate Temperatures

    NASA Technical Reports Server (NTRS)

    Goldsby, Jon C.

    2010-01-01

    A series of alumina-yttria-stabilized zirconia composites containing either a high aspect ratio (5 and 30 mol%) hexagonal platelet alumina or an alumina low aspect ratio (5 and 30 mol%) spherical particulate was used to determine the effect of the aspect ratio on the temperature-dependent impedance of the composite material. The highest impedance across the temperature range of 373 to 1073 K is attributed to the grain boundary of the hexagonal platelet second phase in this alumina zirconia composite.

  10. Strong geographical variation in wing aspect ratio of a damselfly, Calopteryx maculata (Odonata: Zygoptera).

    PubMed

    Hassall, Christopher

    2015-01-01

    Geographical patterns in body size have been described across a wide range of species, leading to the development of a series of fundamental biological rules. However, shape variables are less well-described despite having substantial consequences for organism performance. Wing aspect ratio (AR) has been proposed as a key shape parameter that determines function in flying animals, with high AR corresponding to longer, thinner wings that promote high manoeuvrability, low speed flight, and low AR corresponding to shorter, broader wings that promote high efficiency long distance flight. From this principle it might be predicted that populations living in cooler areas would exhibit low AR wings to compensate for reduced muscle efficiency at lower temperatures. I test this hypothesis using the riverine damselfly, Calopteryx maculata, sampled from 34 sites across its range margin in North America. Nine hundred and seven male specimens were captured from across the 34 sites (mean = 26.7 ± 2.9 SE per site), dissected and measured to quantify the area and length of all four wings. Geometric morphometrics were employed to investigate geographical variation in wing shape. The majority of variation in wing shape involved changes in wing aspect ratio, confirmed independently by geometric morphometrics and wing measurements. There was a strong negative relationship between wing aspect ratio and the maximum temperature of the warmest month which varies from west-east in North America, creating a positive relationship with longitude. This pattern suggests that higher aspect ratio may be associated with areas in which greater flight efficiency is required: regions of lower temperatures during the flight season. I discuss my findings in light of research of the functional ecology of wing shape across vertebrate and invertebrate taxa. PMID:26336648

  11. Nanoscale-Tipped High-Aspect-Ratio Vertical Microneedle Electrodes for Intracellular Recordings.

    PubMed

    Kubota, Yoshihiro; Oi, Hideo; Sawahata, Hirohito; Goryu, Akihiro; Ando, Yoriko; Numano, Rika; Ishida, Makoto; Kawano, Takeshi

    2016-06-01

    Intracellular recording nanoscale electrode devices provide the advantages of a high spatial resolution and high sensitivity. However, the length of nanowire/nanotube-based nanoelectrodes is currently limited to <10 μm long due to fabrication issues for high-aspect-ratio nanoelectrodes. The concept reported here can address the technological limitations by fabricating >100 μm long nanoscale-tipped electrodes, which show intracellular recording capability. PMID:27062044

  12. Harnessing localized ridges for high-aspect-ratio hierarchical patterns with dynamic tunability and multifunctionality.

    PubMed

    Cao, Changyong; Chan, Hon Fai; Zang, Jianfeng; Leong, Kam W; Zhao, Xuanhe

    2014-03-19

    A simple method for fabricating high-aspect-ratio, hierarchical, and dynamically tunable surface patterns is invented by harnessing localized-ridge instabilities in gold nanofilms coated on elastomer substrates (a); a theoretical model to calculate the critical parameters (e.g., wavelength and amplitude) for designing the new patterns is developed (b); and novel applications of the patterns as super-hydrophobic coatings (c) and biomimetic cell-culture substrates (d) capable of on-demand tunability are demonstrated. PMID:24339233

  13. Fiber angle and aspect ratio influence the shear mechanics of oriented electrospun nanofibrous scaffolds.

    PubMed

    Driscoll, Tristan P; Nerurkar, Nandan L; Jacobs, Nathan T; Elliott, Dawn M; Mauck, Robert L

    2011-11-01

    Fibrocartilages, including the knee meniscus and the annulus fibrosus (AF) of the intervertebral disc, play critical mechanical roles in load transmission across joints and their function is dependent upon well-defined structural hierarchies, organization, and composition. All, however, are compromised in the pathologic transformations associated with tissue degeneration. Tissue engineering strategies that address these key features, for example, aligned nanofibrous scaffolds seeded with mesenchymal stem cells (MSCs), represent a promising approach for the regeneration of these fibrous structures. While such engineered constructs can replicate native tissue structure and uniaxial tensile properties, the multidirectional loading encountered by these tissues in vivo necessitates that they function adequately in other loading modalities as well, including shear. As previous findings have shown that native tissue tensile and shear properties are dependent on fiber angle and sample aspect ratio, respectively, the objective of the present study was to evaluate the effects of a changing fiber angle and sample aspect ratio on the shear properties of aligned electrospun poly(ε-caprolactone) (PCL) scaffolds, and to determine how extracellular matrix deposition by resident MSCs modulates the measured shear response. Results show that fiber orientation and sample aspect ratio significantly influence the response of scaffolds in shear, and that measured shear strains can be predicted by finite element models. Furthermore, acellular PCL scaffolds possessed a relatively high shear modulus, 2-4 fold greater than native tissue, independent of fiber angle and aspect ratio. It was further noted that under testing conditions that engendered significant fiber stretch, the aggregate resistance to shear was higher, indicating a role for fiber stretch in the overall shear response. Finally, with time in culture, the shear modulus of MSC laden constructs increased, suggesting that

  14. Strong geographical variation in wing aspect ratio of a damselfly, Calopteryx maculata (Odonata: Zygoptera)

    PubMed Central

    2015-01-01

    Geographical patterns in body size have been described across a wide range of species, leading to the development of a series of fundamental biological rules. However, shape variables are less well-described despite having substantial consequences for organism performance. Wing aspect ratio (AR) has been proposed as a key shape parameter that determines function in flying animals, with high AR corresponding to longer, thinner wings that promote high manoeuvrability, low speed flight, and low AR corresponding to shorter, broader wings that promote high efficiency long distance flight. From this principle it might be predicted that populations living in cooler areas would exhibit low AR wings to compensate for reduced muscle efficiency at lower temperatures. I test this hypothesis using the riverine damselfly, Calopteryx maculata, sampled from 34 sites across its range margin in North America. Nine hundred and seven male specimens were captured from across the 34 sites (mean = 26.7 ± 2.9 SE per site), dissected and measured to quantify the area and length of all four wings. Geometric morphometrics were employed to investigate geographical variation in wing shape. The majority of variation in wing shape involved changes in wing aspect ratio, confirmed independently by geometric morphometrics and wing measurements. There was a strong negative relationship between wing aspect ratio and the maximum temperature of the warmest month which varies from west-east in North America, creating a positive relationship with longitude. This pattern suggests that higher aspect ratio may be associated with areas in which greater flight efficiency is required: regions of lower temperatures during the flight season. I discuss my findings in light of research of the functional ecology of wing shape across vertebrate and invertebrate taxa. PMID:26336648

  15. Jet-Surface Interaction: High Aspect Ratio Nozzle Test, Nozzle Design and Preliminary Data

    NASA Technical Reports Server (NTRS)

    Brown, Clifford; Dippold, Vance

    2015-01-01

    The Jet-Surface Interaction High Aspect Ratio (JSI-HAR) nozzle test is part of an ongoing effort to measure and predict the noise created when an aircraft engine exhausts close to an airframe surface. The JSI-HAR test is focused on parameters derived from the Turbo-electric Distributed Propulsion (TeDP) concept aircraft which include a high-aspect ratio mailslot exhaust nozzle, internal septa, and an aft deck. The size and mass flow rate limits of the test rig also limited the test nozzle to a 16:1 aspect ratio, half the approximately 32:1 on the TeDP concept. Also, unlike the aircraft, the test nozzle must transition from a single round duct on the High Flow Jet Exit Rig, located in the AeroAcoustic Propulsion Laboratory at the NASA Glenn Research Center, to the rectangular shape at the nozzle exit. A parametric nozzle design method was developed to design three low noise round-to-rectangular transitions, with 8:1, 12:1, and 16: aspect ratios, that minimizes flow separations and shocks while providing a flat flow profile at the nozzle exit. These designs validated using the WIND-US CFD code. A preliminary analysis of the test data shows that the actual flow profile is close to that predicted and that the noise results appear consistent with data from previous, smaller scale, tests. The JSI-HAR test is ongoing through October 2015. The results shown in the presentation are intended to provide an overview of the test and a first look at the preliminary results.

  16. Out-of-plane Block Copolymer Microdomains in High Aspect-Ratio Templates

    NASA Astrophysics Data System (ADS)

    Gadelrab, Karim; Bai, Wubin; Alexander-Katz, Alfredo; Ross, Caroline

    The use of directed self-assembly DSA of block copolymers BCP proved to be a power approach for nanoscale fabrication. It combines the ability of BCPs to self-assemble into nanoscale features with the use of lithographic tools to create controlled long range order. In addition, BCP with highly incompatible blocks (high Flory-Huggins interaction parameter (χ)) offer improvement in resolution, and line edge fluctuations of the self-assembled patterns. Unfortunately, high- χ BCPs usually exhibit large differences in surface affinity between the two blocks, leading to the formation of a surface layer of the lower surface energy block and favoring in-plane orientation of lamellae or cylindrical microdomains. Here, we explore the conditions under which a high χ BCP creates an out-of-plane lamellar structure using functionalized high aspect ratio trenches with preferential walls. We employ the free energy analysis of self-consistent field theory SCFT to identify whether an in-plane or out-of-plane structure is stable for a particular trench width. In addition, we employ the single mode expansion of Ginzburg-Landau free energy expression in the weak segregation limit to analytically construct a phase diagram of the in-plane and out-of-plane lamellae as a function of aspect ratio and surface attraction strength. It is found that achieving an out of plane lamellar structure necessitates a coupling between aspect ratio and surface functionality. In particular, strong side wall attraction results in out-of-plane lamellae when the trench aspect ratio is greater than unity. The results are validated for a lamellar forming polystyrene-block-polydimethylsiloxane (PS-b-PDMS) within trenches made using interference lithography.

  17. Alternative method for variable aspect ratio vias using a vortex mask

    NASA Astrophysics Data System (ADS)

    Schepis, Anthony R.; Levinson, Zac; Burbine, Andrew; Smith, Bruce W.

    2014-03-01

    Historically IC (integrated circuit) device scaling has bridged the gap between technology nodes. Device size reduction is enabled by increased pattern density, enhancing functionality and effectively reducing cost per chip. Exemplifying this trend are aggressive reductions in memory cell sizes that have resulted in systems with diminishing area between bit/word lines. This affords an even greater challenge in the patterning of contact level features that are inherently difficult to resolve because of their relatively small area and complex aerial image. To accommodate these trends, semiconductor device design has shifted toward the implementation of elliptical contact features. This empowers designers to maximize the use of free device space, preserving contact area and effectively reducing the via dimension just along a single axis. It is therefore critical to provide methods that enhance the resolving capacity of varying aspect ratio vias for implementation in electronic design systems. Vortex masks, characterized by their helically induced propagation of light and consequent dark core, afford great potential for the patterning of such features when coupled with a high resolution negative tone resist system. This study investigates the integration of a vortex mask in a 193nm immersion (193i) lithography system and qualifies its ability to augment aspect ratio through feature density using aerial image vector simulation. It was found that vortex fabricated vias provide a distinct resolution advantage over traditionally patterned contact features employing a 6% attenuated phase shift mask (APM). 1:1 features were resolvable at 110nm pitch with a 38nm critical dimension (CD) and 110nm depth of focus (DOF) at 10% exposure latitude (EL). Furthermore, iterative source-mask optimization was executed as means to augment aspect ratio. By employing mask asymmetries and directionally biased sources aspect ratios ranging between 1:1 and 2:1 were achievable, however, this

  18. Evolution of Double-Diffusive Convection in Low-Aspect Ratio Containers

    NASA Astrophysics Data System (ADS)

    Pol, Suhas; Fernando, Harindra; Webb, Stephen

    2010-11-01

    Laboratory experiments and phenomenological modeling were undertaken to investigate the influence of container sidewalls on the evolution of diffusive layering in confined double-diffusive systems. Such flow configurations are common in engineering situations, including underground storage caverns of national strategic petroleum reserves. The laboratory flow configuration consisted of a linearly salt stratified fluid subjected to either heating from below or uniform heating from both the bottom and sidewalls. The growth of the mixed layers separated by diffusive interfaces was monitored using PIV and traversing temperature/conductivity probe techniques. The importance of aspect ratio effects was inferred from the bottom-layer growth measurements, which undergoes a transition upon onset of side-wall effects (aspect ratio ˜ 1). A second transition was noticed at an aspect ratio ˜ 2 when elongated eddies break down in to smaller sizes. The combined side and bottom wall heating case was strikingly different from the bottom heating case, wherein layers of approximately equal heights are generated rather rapidly in the former as a result of convective plumes rising along the sidewalls and their arrest by the background stable density gradient. Theoretical arguments were advanced to explain and parameterize experimental observations.

  19. Is aspect ratio sufficient to classify intra-aneurysmal hemodynamics- a parametric approach

    NASA Astrophysics Data System (ADS)

    Durka, Michael; Robertson, Anne

    2013-11-01

    Intracranial aneurysms are a vascular pathology in which a localized bulge is formed in the arterial wall, most often in a saccular shape. It is believed that the blood flow field within the aneurysm plays a critical role in the degradation of the wall. Aneurysm rupture has a high mortality risk. Since only a small fracture of aneurysms rupture, and common treatments have their own risks, it is desirable to identify a useful means of assessing rupture risk. Therefore, numerous groups have endeavored to identify a correlation between rupture risk and sac geometry or flow dynamics. However, no clinically useful parameters have been identified to date. Prior work has suggested that the aspect ratio (sac height/neck) could be useful for risk stratification due to its influence on the sac hemodynamics. In this work, we make of a previously developed parametric model of the aneurysm geometry to evaluate the influence of aspect ratio (sac height/sac neck) on flow dynamics, using computational fluid dynamics. In particular, we assess the influence of aspect ratio on the number of vortices in the aneurysm sac over a wide range of sac geometries. The conclusions obtained for the parametric model are then assessed in 20 clinical cases.

  20. Jet Surface Interaction Scrubbing Noise from High Aspect-Ratio Rectangular Jets

    NASA Technical Reports Server (NTRS)

    Khavaran, Abbas; Bozak, Richard F.

    2015-01-01

    Concepts envisioned for the future of civil air transport consist of unconventional propulsion systems in the close proximity of the airframe. Distributed propulsion system with exhaust configurations that resemble a high aspect ratio rectangular jet are among geometries of interest. Nearby solid surfaces could provide noise shielding for the purpose of reduced community noise. Interaction of high-speed jet exhaust with structure could also generate new sources of sound as a result of flow scrubbing past the structure, and or scattered noise from sharp edges. The present study provides a theoretical framework to predict the scrubbing noise component from a high aspect ratio rectangular exhaust in proximity of a solid surface. The analysis uses the Greens function (GF) to the variable density Pridmore-Brown equation in a transversely sheared mean flow. Sources of sound are defined as the auto-covariance function of second-rank velocity fluctuations in the jet plume, and are modeled using a RANS-based acoustic analogy approach. Acoustic predictions are presented in an 8:1 aspect ratio rectangular exhaust at three subsonic Mach numbers. The effect of nearby surface on the scrubbing noise component is shown on both reflected and shielded sides of the plate.

  1. Relation between self-organized criticality and grain aspect ratio in granular piles

    NASA Astrophysics Data System (ADS)

    Denisov, D. V.; Villanueva, Y. Y.; Lőrincz, K. A.; May, S.; Wijngaarden, R. J.

    2012-05-01

    We investigate experimentally whether self-organized criticality (SOC) occurs in granular piles composed of different grains, namely, rice, lentils, quinoa, and mung beans. These four grains were selected to have different aspect ratios, from oblong to oblate. As a function of aspect ratio, we determined the growth (β) and roughness (α) exponents, the avalanche fractal dimension (D), the avalanche size distribution exponent (τ), the critical angle (γ), and its fluctuation. At superficial inspection, three types of grains seem to have power-law-distributed avalanches with a well-defined τ. However, only rice is truly SOC if we take three criteria into account: a power-law-shaped avalanche size distribution, finite size scaling, and a universal scaling relation relating characteristic exponents. We study SOC as a spatiotemporal fractal; in particular, we study the spatial structure of criticality from local observation of the slope angle. From the fluctuation of the slope angle we conclude that greater fluctuation (and thus bigger avalanches) happen in piles consisting of grains with larger aspect ratio.

  2. Malignant mesothelioma caused by childhood exposure to long-fiber low aspect ratio tremolite.

    PubMed

    Magee, F; Wright, J L; Chan, N; Lawson, L; Churg, A

    1986-01-01

    A 41-year-old man was found to have a malignant mesothelioma of the pleura. During childhood in Corsica, he had been exposed at home to chrysotile ore from the Canari mine. Analysis of lung mineral content revealed background levels of chrysotile but an elevated level of tremolite and actinolite asbestos. The latter had a geometric mean length of 3.7 microns, a value considerably longer than we have found for tremolite and actinolite from Quebec chrysotile miners but roughly the same as the mean length of amosite and crocidolite in workers with occupational amphibole exposure. No tremolite or actinolite fibers of length greater than 8 microns microns and width less than 0.25 micron were observed. The mean aspect ratio of the tremolite and actinolite fibers was 7, a value similar to that found in chrysotile miners with mesothelioma but considerably less than the mean aspect ratio of amosite and crocidolite from those with occupational exposure. These data suggest that long-fiber tremolite is a potential mesothelial carcinogen in humans, and that fiber length is more important than fiber aspect ratio in this regard. PMID:3017103

  3. Nacre-mimetics with synthetic nanoclays up to ultrahigh aspect ratios.

    PubMed

    Das, Paramita; Malho, Jani-Markus; Rahimi, Khosrow; Schacher, Felix H; Wang, Baochun; Demco, Dan Eugen; Walther, Andreas

    2015-01-01

    Nacre-mimetics hold great promise as mechanical high-performance and functional materials. Here we demonstrate large progress of mechanical and functional properties of self-assembled polymer/nanoclay nacre-mimetics by using synthetic nanoclays with aspect ratios covering three orders in magnitude (25-3,500). We establish comprehensive relationships among structure formation, nanostructuration, deformation mechanisms and mechanical properties as a function of nanoclay aspect ratio, and by tuning the viscoelastic properties of the soft phase via hydration. Highly ordered, large-scale nacre-mimetics are obtained even for low aspect ratio nanoplatelets and show pronounced inelastic deformation with very high toughness, while those formed by ultralarge nanoplatelets exhibit superb stiffness and strength, previously only reachable for highly crosslinked materials. Regarding functionalities, we report formerly impossible glass-like transparency, and excellent gas barrier considerably exceeding earlier nacre-mimetics based on natural nanoclay. Our study enables rational design of future high-performance nacre-mimetic materials and opens avenues for ecofriendly, transparent, self-standing and strong advanced barrier materials. PMID:25601360

  4. Nacre-mimetics with synthetic nanoclays up to ultrahigh aspect ratios

    NASA Astrophysics Data System (ADS)

    Das, Paramita; Malho, Jani-Markus; Rahimi, Khosrow; Schacher, Felix H.; Wang, Baochun; Demco, Dan Eugen; Walther, Andreas

    2015-01-01

    Nacre-mimetics hold great promise as mechanical high-performance and functional materials. Here we demonstrate large progress of mechanical and functional properties of self-assembled polymer/nanoclay nacre-mimetics by using synthetic nanoclays with aspect ratios covering three orders in magnitude (25-3,500). We establish comprehensive relationships among structure formation, nanostructuration, deformation mechanisms and mechanical properties as a function of nanoclay aspect ratio, and by tuning the viscoelastic properties of the soft phase via hydration. Highly ordered, large-scale nacre-mimetics are obtained even for low aspect ratio nanoplatelets and show pronounced inelastic deformation with very high toughness, while those formed by ultralarge nanoplatelets exhibit superb stiffness and strength, previously only reachable for highly crosslinked materials. Regarding functionalities, we report formerly impossible glass-like transparency, and excellent gas barrier considerably exceeding earlier nacre-mimetics based on natural nanoclay. Our study enables rational design of future high-performance nacre-mimetic materials and opens avenues for ecofriendly, transparent, self-standing and strong advanced barrier materials.

  5. A high-output-voltage micro-thermoelectric generator having high-aspect-ratio structure

    NASA Astrophysics Data System (ADS)

    Kouma, N.; Nishino, T.; Tsuboi, O.

    2013-11-01

    A high-output-voltage micro-thermoelectric generator (µTEG) has been developed by fabricating thermocouples having a high aspect ratio (HAR) with a high integration density. They have been made by a novel and simple fabrication method, in which thermoelectric nanopowders are filled in a photosensitive glass mold by using aerosol deposition. It is followed by hot isostatic pressing to improve the thermoelectric property. This method has the possibility of increasing the aspect ratio of thermocouples drastically while increasing their toughness. We have fabricated thermocouples with an aspect ratio of 3.5 and a high integration density of 620 TCs cm-2. Their Seebeck coefficient and electrical resistivity are 290 µV K-1 and 1.5 mΩ cm, respectively, which make them as good as the thermocouples fabricated by hot pressing. By using the method, we have fabricated a µTEG chip having an area of 25 mm2 in which 56 thermocouples are arranged in an area of 9 mm2. The µTEG reaches a thermal resistance of 17.1 K W-1, output voltage efficiency of 0.16 V cm-2 K-1 and output power efficiency of 9.3 µW cm-2 K-2. These HAR thermocouples have an advantage for energy harvesting from a human body because they can result in a high temperature difference because of their high thermal resistance.

  6. Convective heat transfer in a high aspect ratio minichannel heated on one side

    SciTech Connect

    Forrest, Eric C.; Hu, Lin -Wen; Buongiorno, Jacopo; McKrell, Thomas J.

    2015-10-21

    Experimental results are presented for single-phase heat transfer in a narrow rectangular minichannel heated on one side. The aspect ratio and gap thickness of the test channel were 29:1 and 1.96 mm, respectively. Friction pressure drop and Nusselt numbers are reported for the transition and fully turbulent flow regimes, with Prandtl numbers ranging from 2.2 to 5.4. Turbulent friction pressure drop for the high aspect ratio channel is well-correlated by the Blasius solution when a modified Reynolds number, based upon a laminar equivalent diameter, is utilized. The critical Reynolds number for the channel falls between 3500 and 4000, with Nusselt numbers in the transition regime being reasonably predicted by Gnielinski's correlation. The dependence of the heat transfer coefficient on the Prandtl number is larger than that predicted by circular tube correlations, and is likely a result of the asymmetric heating. The problem of asymmetric heating condition is approached theoretically using a boundary layer analysis with a two-region wall layer model, similar to that originally proposed by Prandtl. The analysis clarifies the influence of asymmetric heating on the Nusselt number and correctly predicts the experimentally observed trend with Prandtl number. Furthermore, a semi-analytic correlation is derived from the analysis that accounts for the effect of aspect ratio and asymmetric heating, and is shown to predict the experimental results of this study with a mean absolute error (MAE) of less than 5% for 4000 < Re < 70,000.

  7. Influence of particle aspect ratio on the midinfrared extinction spectra of wavelength-sized ice crystals.

    PubMed

    Wagner, Robert; Benz, Stefan; Möhler, Ottmar; Saathoff, Harald; Schnaiter, Martin; Leisner, Thomas

    2007-12-20

    We have used the T-matrix method and the discrete dipole approximation to compute the midinfrared extinction cross-sections (4500-800 cm(-1)) of randomly oriented circular ice cylinders for aspect ratios extending up to 10 for oblate and down to 1/6 for prolate particle shapes. Equal-volume sphere diameters ranged from 0.1 to 10 microm for both particle classes. A high degree of particle asphericity provokes a strong distortion of the spectral habitus compared to the extinction spectrum of compactly shaped ice crystals with an aspect ratio around 1. The magnitude and the sign (increase or diminution) of the shape-related changes in both the absorption and the scattering cross-sections crucially depend on the particle size and the values for the real and imaginary part of the complex refractive index. When increasing the particle asphericity for a given equal-volume sphere diameter, the values for the overall extinction cross-sections may change in opposite directions for different parts of the spectrum. We have applied our calculations to the analysis of recent expansion cooling experiments on the formation of cirrus clouds, performed in the large coolable aerosol and cloud chamber AIDA of Forschungszentrum Karlsruhe at a temperature of 210 K. Depending on the nature of the seed particles and the temperature and relative humidity characteristics during the expansion, ice crystals of various shapes and aspect ratios could be produced. For a particular expansion experiment, using Illite mineral dust particles coated with a layer of secondary organic matter as seed aerosol, we have clearly detected the spectral signatures characteristic of strongly aspherical ice crystal habits in the recorded infrared extinction spectra. We demonstrate that the number size distributions and total number concentrations of the ice particles that were generated in this expansion run can only be accurately derived from the recorded infrared spectra when employing aspect ratios as high as

  8. Tokamak and RFP ignition requirements

    SciTech Connect

    Werley, K.A.

    1991-01-01

    A plasma model is applied to calculate numerically transport- confinement (n{tau}{sub E}) requirements and steady-state operation tokamak. The CIT tokamak and RFP ignition conditions are examined. Physics differences between RFP and tokamaks, and their consequences for a DT ignition machine, are discussed. The ignition RFP, compared to a tokamak, has many physics advantages, including ohmic heating to ignition (no need for auxiliary heating systems), higher beta, low ignition current, less sensitivity of ignition requirements to impurity effects, no hard disruptions (associated with beta or density limits), and successful operation with high radiation fractions (f{sub RAD} {approximately} 0.95). These physics advantages, coupled with important engineering advantages associated with lower external magnetic fields, larger aspect ratios, and smaller plasma cross sections translate into significant cost reductions for both ignition and power reactor. The primary drawback of the RFP is the uncertainty that the present confinement scaling will extrapolate to reactor regimes. The 4-MA ZTH was expected to extend the n{tau}{sub E} transport scaling data three order of magnitude above ZT-40M results, and if the present scaling held, to achieve a DT-equivalent scientific energy breakeven, Q=1. A basecase RFP ignition point is identified with a plasma current of 8.1 MA and no auxiliary heating. 16 refs., 4 figs., 1 tab.

  9. Effects of fluid behavior around low aspect ratio, low Reynolds number wings on aerodynamic stability

    NASA Astrophysics Data System (ADS)

    Shields, Matthew; Mohseni, Kamran

    2011-11-01

    The innovation of micro aerial vehicles (MAVs) has brought to attention the unique flow regime associated with low aspect ratio (LAR), low Reynolds number fliers. The dominant effects of developing tip vortices and leading edge vortices create a fundamentally different flow regime than that of conventional aircraft. An improved knowledge of low aspect ratio, low Reynolds number aerodynamics can be greatly beneficial for future MAV design. A little investigated but vital aspect of LAR aerodynamics is the behavior of the fluid as the wing yaws. Flow visualization experiments undertaken in the group for the canonical case of varying AR flat plates indicate that the propagation of the tip vortex keeps the flow attached over the upstream portion of the wing, while the downstream vortex is convected away from the wing. This induces asymmetric, destabilizing loading on the wing which has been observed to adversely affect MAV flight. In addition, experimental load measurements indicate significant nonlinearities in forces and moments which can be attributed to the development and propagation of these vortical structures. A non-dimensional analysis of the rigid body equations of motion indicates that these nonlinearities create dependencies which dramatically change the conventional linearization process. These flow phenomena are investigated with intent to apply to future MAV design.

  10. Some Effects of Sweep and Aspect Ratio on the Transonic Flutter Characteristics of a Series of Thin Cantilever Wings Having a Taper Ratio of 0.6

    NASA Technical Reports Server (NTRS)

    Jones, G. W., Jr.; Unangst, J. R.

    1963-01-01

    An investigation of the flutter characteristics of a series of thin cantilever wings having taper ratios of 0.6 was conducted in the Langley transonic blowdown tunnel at Mach numbers between 0.76 and 1.42. The angle of sweepback was varied from 0 degrees to 60 degrees on wings of aspect ratio 4, and the aspect ratio was varied from 2.4 to 6.4 on wings with 45 degrees of sweepback. The results are presented as ratios between the experimental flutter speeds and the reference flutter speeds calculated on the basis of incompressible two-dimensional flow. These ratios, designated the flutter-speed ratios, are given as functions of Mach number for the various wings. The flutter-speed ratios were characterized, in most cases, by values near 1.0 at subsonic speeds with large increases in the speed ratios in the range of supersonic speeds investigated. Increasing the sweep effected increases in the flutter-speed ratios between 0 degrees and 30 degrees followed by progressive reductions of the speed ratios to nearly 1.0 as the sweep was increased from 30 degrees to 60 degrees. Reducing the aspect ratio from 6.4 to 2.4 resulted in progressively larger values of the flutter-speed ratios throughout the Mach number range investigated.

  11. A High Aspect Ratio Microelectrode Array for Mapping Neural Activity in-vitro

    PubMed Central

    Kibler, Andrew B.; Jamieson, Brian G.; Durand, Dominique M.

    2011-01-01

    A novel high-aspect-ratio penetrating microelectrode array was designed and fabricated for the purpose of recording neural activity. The array allows two dimensional recording of 64 sites in vitro with high aspect ratio penetrating electrodes. Traditional surface electrode arrays, although easy to fabricate, do not penetrate to the viable tissue such as central hippocampus slices and thus have a lower signal/noise ratio and lower selectivity than a penetrating array. In the unfolded hippocampus preparation, the CA1–CA3 pyramidal cell layer in the whole unfolded rodent hippocampus preparation is encased by the alveus on one side and the Schaffer tract on the other and requires penetrating electrodes for high signal to noise ratio recording. An array of 64 electrode spikes, each with a target height of 200 μm and diameter of 20μm, was fabricated in silicon on a transparent glass substrate. The impedance of the individual electrodes was measured to be approximately 1.5MΩ± 497kΩ. The signal to noise ratio was measured and found to be 19.4 ± 3 dB compared to 3.9 ± 0.8 dB S/N for signals obtained with voltage sensitive dye RH414. A mouse unfolded hippocampus preparation was bathed in solution containing 50 micro-molar 4-Amino Pyridine and a complex two dimensional wave of activity was recorded using the array. These results indicate that this novel penetrating electrode array is able to obtain data superior to that of voltage sensitive dye techniques for broad field two-dimensional neuronal activity recording. When used with the unfolded hippocampus preparation, the combination forms a uniquely capable tool for imaging hippocampal network activity in the entire hippocampus. PMID:22179041

  12. The effect of aspect ratio on the piezoresistive behavior of the multiwalled carbon nanotubes/thermoplastic elastomer nanocomposites

    NASA Astrophysics Data System (ADS)

    Zha, Jun-Wei; Shehzad, Khurram; Li, Wei-Kang; Dang, Zhi-Min

    2013-01-01

    To explore the effect of aspect ratio (AR) of carbon nanotubes (CNT) on the piezoresistive behavior of the composites, four kinds of multiwalled carbon nanotubes (MWNT) with different nominal aspect ratios (AR = 62, 133, 433, and 833) were well dispersed in a thermoplastic elastomer (TPE) via melt blending. The piezoresistivity of the MWNT/TPE nanocomposites was found to be dependent on the nominal MWNT aspect ratios. However, their relationship is non-linear and non-monotonic. By introducing the effective MWNT aspect ratios which are length-dependent and diameter-dependent, it has been demonstrated that the piezoresistivity will decrease with the increase of effective aspect ratios. The length-dependent increase of aspect ratio results in one hundred-fold or more decrease of piezoresistivity, but the diameter-dependent increase of aspect ratios only leads to a slight marginal change of the piezoresistivity. The proper selection of MWNT aspect ratios could enable their utilization to tailor as well as finely tune the piezoresistivity of the MWNT/TPE nanocomposites.

  13. An Empirical Jet-Surface Interaction Noise Model with Temperature and Nozzle Aspect Ratio Effects

    NASA Technical Reports Server (NTRS)

    Brown, Cliff

    2015-01-01

    An empirical model for jet-surface interaction (JSI) noise produced by a round jet near a flat plate is described and the resulting model evaluated. The model covers unheated and hot jet conditions (1 less than or equal to jet total temperature ratio less than or equal to 2.7) in the subsonic range (0.5 less than or equal to M(sub a) less than or equal to 0.9), surface lengths 0.6 less than or equal to (axial distance from jet exit to surface trailing edge (inches)/nozzle exit diameter) less than or equal to 10, and surface standoff distances (0 less than or equal to (radial distance from jet lipline to surface (inches)/axial distance from jet exit to surface trailing edge (inches)) less than or equal to 1) using only second-order polynomials to provide predictable behavior. The JSI noise model is combined with an existing jet mixing noise model to produce exhaust noise predictions. Fit quality metrics and comparisons to between the predicted and experimental data indicate that the model is suitable for many system level studies. A first-order correction to the JSI source model that accounts for the effect of nozzle aspect ratio is also explored. This correction is based on changes to the potential core length and frequency scaling associated with rectangular nozzles up to 8:1 aspect ratio. However, more work is needed to refine these findings into a formal model.

  14. Nanofabrication of high aspect ratio structures using an evaporated resist containing metal

    NASA Astrophysics Data System (ADS)

    Con, Celal; Zhang, Jian; Cui, Bo

    2014-05-01

    Organic electron beam resists are typically not resistant to the plasma etching employed to transfer the pattern into the underlying layer. Here, the authors present the incorporation of a metal hard mask material into negative resist polystyrene by co-evaporation of the polystyrene and the metal onto a substrate. With a volume ratio of 1:15 between Cr and polystyrene, this nanocomposite resist showed an etching selectivity to silicon one order higher than pure polystyrene resist. Silicon structures of 100 nm width and 3.5 μm height (aspect ratio 1:35) were obtained using a non-switching deep silicon etching recipe with SF6 and C4F8 gas. Moreover, unlike the common spin coating method, evaporated nanocomposite resist can be coated onto irregular and non-flat surfaces such as optical fibers and AFM cantilevers. As a proof of concept, we fabricated high aspect ratio structures on top of an AFM cantilever. Nanofabrication on non-flat surfaces may find applications in the fields of (AFM) tip enhanced Raman spectroscopy for chemical analysis and lab-on-fiber technology.

  15. Nanofabrication of high aspect ratio structures using an evaporated resist containing metal.

    PubMed

    Con, Celal; Zhang, Jian; Cui, Bo

    2014-05-01

    Organic electron beam resists are typically not resistant to the plasma etching employed to transfer the pattern into the underlying layer. Here, the authors present the incorporation of a metal hard mask material into negative resist polystyrene by co-evaporation of the polystyrene and the metal onto a substrate. With a volume ratio of 1:15 between Cr and polystyrene, this nanocomposite resist showed an etching selectivity to silicon one order higher than pure polystyrene resist. Silicon structures of 100 nm width and 3.5 μm height (aspect ratio 1:35) were obtained using a non-switching deep silicon etching recipe with SF6 and C4F8 gas. Moreover, unlike the common spin coating method, evaporated nanocomposite resist can be coated onto irregular and non-flat surfaces such as optical fibers and AFM cantilevers. As a proof of concept, we fabricated high aspect ratio structures on top of an AFM cantilever. Nanofabrication on non-flat surfaces may find applications in the fields of (AFM) tip enhanced Raman spectroscopy for chemical analysis and lab-on-fiber technology. PMID:24717720

  16. High-aspect-ratio and highly ordered 15-nm porous alumina templates.

    PubMed

    Martín, Jaime; Manzano, Cristina V; Caballero-Calero, Olga; Martín-González, Marisol

    2013-01-01

    Ordered anodic aluminum oxide (AAO) templates with pores <15 nm in diameter and an aspect ratio (length-to-diameter ratio) above 3 × 10(3) have been fabricated using a nonlithographic approach; specifically, by anodizing aluminum in an ethylene-glycol-containing sulfuric acid electrolyte. The pores are the smallest in diameter reported for a self-ordered AAO without pore aspect-ratio limitations and good ordering, which opens up the possibility of obtaining nanowire arrays in the quantum confinement regime that is of interest for efficient thermoelectric generators. The effect of the ethylene glycol addition on both the pore diameter and the ordering is evaluated and discussed. Moreover, 15-nm-diameter Bi(2)Te(3) and poly(3-hexyl thiophene) (P3HT) nanowires have been prepared using these AAO templates. As known, Bi(2)Te(3) is currently the most efficient thermoelectric bulk material for room-temperature operations and, according with theory, its Seebeck coefficient should be increased when it is confined to nanowires with diameters close to 10 nm. On the other hand, P3HT is one of the main candidates for integrating organic photovoltaic and thermoelectric devices, and its properties are also proposed to increase when it is confined to nanoscale structures, mainly due to molecular orientation effects. PMID:23215033

  17. Effects of diffusion factor, aspect ratio and solidity on overall performance of 14 compressor middle stages. [the effects of varying both diffusion through the rotor and compressor blades and blade aspect ratio

    NASA Technical Reports Server (NTRS)

    Britsch, W. R.; Osborn, W. M.; Laessig, M. R.

    1979-01-01

    A series of high hub tip radius ratio compressor stages representative of the middle and latter stages of axial flow compressors is discussed. The effects of aspect ratio, diffusion factor, and solidity on rotor and stage performance are determined. Fourteen middle stages are tested to study the effects on performance of varying both diffusion through the rotor and stator blades and blade aspect ratio. The design parameters in the streamline analysis program, the blade geometry program, and the blade coordinate program are presented.

  18. Surface-diffusion-driven decay of high-aspect-ratio gratings: Existence of morphologically related classes

    NASA Astrophysics Data System (ADS)

    Madrid, Marcos A.; Salvarezza, Roberto C.; Castez, Marcos F.

    2013-06-01

    We present numerical and theoretical results concerning the technologically important process of evolution of high-aspect-ratio profiles due to surface diffusion under thermal treatment. We show how a broad class of initial gratings adopt, after a short transient stage, a typical shape that can be accurately described as a curve whose curvature has only two single Fourier modes as a function of the arc-length parameter. Moreover, we introduce a set of evolution equations for the relevant parameters that accounts very accurately for both morphological and kinetic aspects of the transformation processes for these curves in a wide region in parameter space. Regarding the decay of rectangular gratings, our numerical results show the existence of geometrically related classes that asymptotically approach to the same trajectory in parameter space. Gratings belonging to the same class pass through the same sequence of morphologies before reaching the final equilibrium state.

  19. The effect of filler aspect ratio on the electromagnetic properties of carbon-nanofibers reinforced composites

    SciTech Connect

    De Vivo, B.; Lamberti, P.; Spinelli, G. Tucci, V.; Guadagno, L.; Raimondo, M.

    2015-08-14

    The effect of filler aspect ratio on the electromagnetic properties of epoxy-amine resin reinforced with carbon nanofibers is here investigated. A heat treatment at 2500 °C of carbon nanofibers seems to increase their aspect ratio with respect to as-received ones most likely due to a lowering of structural defects and the improvement of the graphene layers within the dixie cup conformation. These morphological differences revealed by Raman's spectroscopy and scanning electron microscopy analyses may be responsible for the different electrical properties of the resulting composites. The DC characterization of the nanofilled material highlights an higher electrical conductivity and a lower electrical percolation threshold for the heat-treated carbon nanofibers based composites. In fact, the electrical conductivity is about 0.107 S/m and 1.36 × 10{sup −3} S/m for the nanocomposites reinforced with heat-treated and as received fibers, respectively, at 1 wt. % of nanofiller loading, while the electrical percolation threshold falls in the range [0.05–0.32]wt. % for the first nanocomposites and above 0.64 wt. % for the latter. Moreover, also a different frequency response is observed since the critical frequency, which is indicative of the transition from a resistive to a capacitive-type behaviour, shifts forward of about one decade at the same filler loading. The experimental results are supported by theoretical and simulation studies focused on the role of the filler aspect ratio on the electrical properties of the nanocomposites.

  20. Convective heat transfer in a high aspect ratio minichannel heated on one side

    DOE PAGESBeta

    Forrest, Eric C.; Hu, Lin -Wen; Buongiorno, Jacopo; McKrell, Thomas J.

    2015-10-21

    Experimental results are presented for single-phase heat transfer in a narrow rectangular minichannel heated on one side. The aspect ratio and gap thickness of the test channel were 29:1 and 1.96 mm, respectively. Friction pressure drop and Nusselt numbers are reported for the transition and fully turbulent flow regimes, with Prandtl numbers ranging from 2.2 to 5.4. Turbulent friction pressure drop for the high aspect ratio channel is well-correlated by the Blasius solution when a modified Reynolds number, based upon a laminar equivalent diameter, is utilized. The critical Reynolds number for the channel falls between 3500 and 4000, with Nusseltmore » numbers in the transition regime being reasonably predicted by Gnielinski's correlation. The dependence of the heat transfer coefficient on the Prandtl number is larger than that predicted by circular tube correlations, and is likely a result of the asymmetric heating. The problem of asymmetric heating condition is approached theoretically using a boundary layer analysis with a two-region wall layer model, similar to that originally proposed by Prandtl. The analysis clarifies the influence of asymmetric heating on the Nusselt number and correctly predicts the experimentally observed trend with Prandtl number. Furthermore, a semi-analytic correlation is derived from the analysis that accounts for the effect of aspect ratio and asymmetric heating, and is shown to predict the experimental results of this study with a mean absolute error (MAE) of less than 5% for 4000 < Re < 70,000.« less

  1. Deposition of a-C:H films on inner surface of high-aspect-ratio microchannel

    NASA Astrophysics Data System (ADS)

    Hirata, Yuki; Choi, Junho

    2016-08-01

    Hydrogenated amorphous carbon (a-C:H) films were prepared on inner surface of 100-μm-width microchannel by using a bipolar-type plasma based ion implantation and deposition. The microchannel was fabricated using a silicon plate, and two kinds of microchannels were prepared, namely, with a bottom layer (open at one end) and without a bottom layer (open at both ends). The distribution of thickness and hardness of films was evaluated by SEM and nanoindentation measurements, respectively, and the microstructures of films were evaluated by Raman spectroscopy. Furthermore, the behavior of ions and radicals was analyzed simultaneously by combining the calculation methods of Particle-In-Cell/Monte Carlo Collision and Direct Simulation Monte Carlo to investigate the coating mechanism for the microchannel. It was found that the film thickness decreased as the depth of the coating position increased in the microchannels where it is open at one end. The uniformity of the film thickness improved by increasing the negative pulse voltage because ions can arrive at the deeper part of the microchannel. In addition, the hardness increased as the depth of the coating position increased. This is because the radicals do not arrive at the deeper part of the microchannel, and the incident proportion of ions relative to that of radicals increases, resulting in a high hardness due to the amorphization of the film. The opening area of the microchannel where the aspect ratio is very small, radicals dominate the incident flux, whereas ions prevail over radicals above an aspect ratio of about 7.5. On the other hand, in the microchannels that are open at both ends, there were great improvements in uniformity of the film thickness, hardness, and the film structure. The a-C:H films were successfully deposited on the entire inner surface of a microchannel with an aspect ratio of 20.

  2. Planar silicon fabrication process for high-aspect-ratio micromachined parts

    SciTech Connect

    Barron, C.C.; Fleming, J.G.

    1997-09-01

    Surface-micromachined silicon inertial sensors are limited to relatively high-G applications in part because of the fundamental limitations on proof mass imposed by the manufacturing technology. At the same time, traditional micromolding technologies such as LIGA do not lend themselves to integration with electronics, a capability which is equally necessary for high-performance inertial sensors. The silicon micromolding processes described in this report promise to offer both larger proof masses and integrability with on-chip electronics. In Sandia`s silicon micromolding process, the proof mass is formed using a mold which is first recessed into the substrate using a deep silicon trench etch, then lined with a sacrificial or etch-stop layer, and filled with mechanical polysilicon. Since the mold is recessed into the substrate, the whole micromechanical structure can be formed, planarized, and integrated with standard silicon microelectronic circuits before the release etch. In addition, unlike surface-micromachined parts, the thickness of the molded parts is limited by the depth of the trench etch (typically 10--50 {micro}m) rather than the thickness of deposited polysilicon (typically 2 {micro}m). The fact that the high-aspect-ratio section of the device is embedded in the substrate enables the monolithic integration of high-aspect-ratio parts with surface-micromachined mechanical parts, and, in the future, also electronics. The authors anticipate that such an integrated mold/surface micromachining/electronics process will offer versatile high-aspect-ratio micromachined structures that can be batch-fabricated and monolithically integrated into complex microelectromechanical systems including high-performance inertial sensing systems.

  3. Performance of two-stage fan having low-aspect-ratio first-stage rotor blading

    NASA Technical Reports Server (NTRS)

    Urasek, D. C.; Gorrell, W. T.; Cunnan, W. S.

    1979-01-01

    The NASA two stage fan was tested with a low aspect ratio first stage rotor having no midspan dampers. At design speed the fan achieved an adiabatic design efficiency of 0.846, and peak efficiencies for the first stage and rotor of 0.870 and 0.906, respectively. Peak efficiency occurred very close to the stall line. In an attempt to improve stall margin, the fan was retested with circumferentially grooved casing treatment and with a series of stator blade resets. Results showed no improvement in stall margin with casing treatment but increased to 8 percent with stator blade reset.

  4. The buffeting pressure field of a high-aspect-ratio swept wing

    NASA Technical Reports Server (NTRS)

    Roos, F. W.

    1985-01-01

    An experimental study of the fluctuating pressure field of a high-aspect-ratio swept transport-type wing model in transonic buffeting flow is examined. A high degree of similarity between the buffet-related features of the wing flowfield and 2-D transonic flowfields is indicated. At several spanwise stations, unsteady lift produced by the pressure fluctuations is evaluated and found to increase in intensity as local flow separation develops. Results show that although the wing does vibrate, the measured lift fluctuations are driving, and not driven by wing vibrations. The influence of tunnel-flow unsteadiness on the data is considered.

  5. Nanometer scale high-aspect-ratio trench etching at controllable angles using ballistic reactive ion etching

    SciTech Connect

    Cybart, Shane; Roediger, Peter; Ulin-Avila, Erick; Wu, Stephen; Wong, Travis; Dynes, Robert

    2012-11-30

    We demonstrate a low pressure reactive ion etching process capable of patterning nanometer scale angled sidewalls and three dimensional structures in photoresist. At low pressure the plasma has a large dark space region where the etchant ions have very large highly-directional mean free paths. Mounting the sample entirely within this dark space allows for etching at angles relative to the cathode with minimal undercutting, resulting in high-aspect ratio nanometer scale angled features. By reversing the initial angle and performing a second etch we create three-dimensional mask profiles.

  6. Morphology and aspect ratio of bismuth nanoparticles embedded in a zinc matrix

    SciTech Connect

    Song, Tae Eun; Wilde, Gerhard; Peterlechner, Martin

    2014-12-15

    Nanoscale Bi particles embedded in a Zn matrix were obtained by casting and melt-spinning, resulting in quenching rate-dependent sizes and shapes. With decreasing Bi particle size, an increasing aspect ratio was observed. Due to high resolution transmission electron microscopy performed for different orientations of the nanoparticles and the matrix, the three-dimensional shape and the respective crystallographic orientations of the Bi nanoparticles as well as the orientation relationship with the matrix have been evaluated. It is suggested that the size-dependence of the nanoparticle morphologies has a strong impact on their thermal stabilities thus affecting the size dependence of the melting temperature.

  7. Characteristics of Low-Aspect-Ratio Wings at Supercritical Mach Numbers

    NASA Technical Reports Server (NTRS)

    Stack, John; Lindsey, W F

    1949-01-01

    The separation of the flow over wings precipitated by the compression shock that forms as speeds are increased into the supercritical Mach number range has imposed serious difficulties in the improvement of aircraft performance. Three difficulties rise principally as a consequence of the rapid drag rise and the loss of lift that causes serious stability changes when the wing shock-stalls. Favorable relieving effects due to the three-dimensional flow around the tips were obtained and these effects were of such magnitude that it is indicated that low-aspect-ratio wings offer a possible solution of the problems encountered.

  8. Three dimensional flow field measurements of a 4:1 aspect ratio subsonic jet

    NASA Technical Reports Server (NTRS)

    Morrison, G. L.; Swan, D. H.

    1989-01-01

    Flow field measurements for a subsonic rectangular cold air jet with an aspect ratio of 4:1 (12.7 x 50.8 mm) at a Mach number of 0.09 and Re of 100,000 have been carried out using a three-dimensional laser Doppler anemometer system. Mean velocity measurements show that the jet width spreads more rapidly along the minor axis than along the major axis. The outward velocities, however, are not significantly different for the two axes, indicating the presence of enhanced mixing along the minor axis. The jet slowly changes from a rectangular jet to a circular jet as the flow progresses downstream.

  9. High aspect ratio nanoneedle probes with an integrated electrode at the tip apex

    NASA Astrophysics Data System (ADS)

    Comstock, David J.; Elam, Jeffrey W.; Pellin, Michael J.; Hersam, Mark C.

    2012-11-01

    Many nanoscale characterization techniques require high aspect ratio nanoneedle probes with an integrated electrode that is electrically insulated everywhere except at the tip apex. We report the utilization of electron beam induced deposition, focused ion beam milling, and atomic layer deposition to fabricate such probes at the sub-100 nm length scale. This fabrication method is highly reproducible and enables precise control of the probe dimensions. Subsequent electrodeposition at the integrated electrode enables customized functionalization of the tip apex. These probes have clear applications in scanning electrochemical microscopy-atomic force microscopy, magnetic force microscopy, apertureless near-field optical microscopy, and tip-enhanced Raman spectroscopy.

  10. Analytic free-form lens design for imaging applications with high aspect ratio

    NASA Astrophysics Data System (ADS)

    Duerr, Fabian; Benítez, Pablo; Miñano, Juan Carlos; Meuret, Youri; Thienpont, Hugo

    2012-10-01

    A new three-dimensional analytic optics design method is presented that enables the coupling of three ray sets with only two free-form lens surfaces. Closely related to the Simultaneous Multiple Surface method in three dimensions (SMS3D), it is derived directly from Fermat's principle, leading to multiple sets of functional differential equations. The general solution of these equations makes it possible to calculate more than 80 coefficients for each implicit surface function. Ray tracing simulations of these free-form lenses demonstrate superior imaging performance for applications with high aspect ratio, compared to conventional rotational symmetric systems.

  11. Effect of wing loading, aspect ratio, and span loading of flight performances

    NASA Technical Reports Server (NTRS)

    Gothert, B

    1940-01-01

    An investigation is made of the possible improvements in maximum, cruising, and climbing speeds attainable through increase in the wing loading. The decrease in wing area was considered for the two cases of constant aspect ratio and constant span loading. For a definite flight condition, an investigation is made to determine what loss in flight performance must be sustained if, for given reasons, certain wing loadings are not to be exceeded. With the aid of these general investigations, the trend with respect to wing loading is indicated and the requirements to be imposed on the landing aids are discussed

  12. Analysis of high aspect ratio jet flap wings of arbitrary geometry.

    NASA Technical Reports Server (NTRS)

    Lissaman, P. B. S.

    1973-01-01

    Paper presents a design technique for rapidly computing lift, induced drag, and spanwise loading of unswept jet flap wings of arbitrary thickness, chord, twist, blowing, and jet angle, including discontinuities. Linear theory is used, extending Spence's method for elliptically loaded jet flap wings. Curves for uniformly blown rectangular wings are presented for direct performance estimation. Arbitrary planforms require a simple computer program. Method of reducing wing to equivalent stretched, twisted, unblown planform for hand calculation is also given. Results correlate with limited existing data, and show lifting line theory is reasonable down to aspect ratios of 5.

  13. Epitaxial growth of quantum rods with high aspect ratio and compositional contrast

    SciTech Connect

    Li, L. H.; Patriarche, G.

    2008-12-01

    The epitaxial growth of quantum rods (QRs) on GaAs was investigated. It was found that GaAs thickness in the GaAs/InAs superlattice used for QR formation plays a key role in improving the QR structural properties. Increasing the GaAs thickness results in both an increased In compositional contrast between the QRs and surrounding layer, and an increased QR length. QRs with an aspect ratio of up to 10 were obtained, representing quasiquantum wires in a GaAs matrix. Due to modified confinement and strain potential, such nanostructure is promising for controlling gain polarization.

  14. Aerodynamic and heat transfer analysis of the low aspect ratio turbine

    NASA Astrophysics Data System (ADS)

    Sharma, O. P.; Nguyen, P.; Ni, R. H.; Rhie, C. M.; White, J. A.

    1987-06-01

    The available two- and three-dimensional codes are used to estimate external heat loads and aerodynamic characteristics of a highly loaded turbine stage in order to demonstrate state-of-the-art methodologies in turbine design. By using data for a low aspect ratio turbine, it is found that a three-dimensional multistage Euler code gives good averall predictions for the turbine stage, yielding good estimates of the stage pressure ratio, mass flow, and exit gas angles. The nozzle vane loading distribution is well predicted by both the three-dimensional multistage Euler and three-dimensional Navier-Stokes codes. The vane airfoil surface Stanton number distributions, however, are underpredicted by both two- and three-dimensional boundary value analysis.

  15. Vortex induction and mass entrainment in a small-aspect-ratio elliptic jet

    NASA Astrophysics Data System (ADS)

    Ho, Chih-Ming; Gutmark, Ephraim

    1987-06-01

    A passive technique of increasing entrainment was found by using a small-aspect-ratio elliptic jet. The entrainment ratio of an elliptic jet was several times greater than that of a circular jet or a plane jet. The self-induction of the asymmetric coherent structure caused azimuthal distortions which were responsible for engulfing large amounts of surrounding fluid into the jet. In an elliptic jet, an interesting feature in the initial stability process is that the thickness of the shear layer varies around the nozzle. The data indicated that instability frequency was scaled with the thinnest initial momentum thickness which was associated with the maximum vorticity. Turbulence properties were also examined and were found to be significantly different in the major- and minor-axis planes.

  16. Pressure drop and heat transfer characteristics of circular and oblong low aspect ratio pin fins

    NASA Astrophysics Data System (ADS)

    Arora, S. C.; Messeh, W. A.

    1985-09-01

    The pressure drop and heat transfer characteristics of circular and oblong pin fins of height-to-diameter ratio of unity used to augment internal cooling of gas turbine airfoils are presented. Data were obtained for an array of 10 rows of staggered pin fins in a 25:1 aspect ratio channel, with both pins and channel endwalls forming the heat transfer surface. Results show that the array average friction factor increases with increasing blockage caused by different arrangement of pin fin geometries in the channel. The local heat transfer coefficient increases up to the 3rd row of pin fins and decreases thereafter. Oblong pin fins with gamma=90 deg (major axis parallel to the direction of flow) result in higher heat transfer rates and lower friction factor than the circular pin fins. For other orientations, oblong pin fins do not offer any advantage over circular pin fins for Re or = 20,000 (typical of small gas turbine engines).

  17. Evaluation of a low aspect ratio small axial compressor stage, volume 1

    NASA Technical Reports Server (NTRS)

    Sawyer, C. W., III

    1977-01-01

    A program was conducted to evaluate the effects of scaling, tip clearance, and IGV reset on the performance of a low aspect ratio compressor stage. Stage design was obtained by scaling an existing single stage compressor by a linear factor of 0.304. The design objective was to maintain the meanline velocity field of the base machine in the smaller size. Adjustments were made to account for predicted blockage differences and to chord lengths and airfoil edge radii to obtain reasonable blade geometries. Meanline velocity diagrams of the base stage were not maintained at the scaled size. At design speed and flowrate the scaled stage achieved a pressure ratio of 1.423, adiabatic efficiency of 0.822, and surge margin of 18.5%. The corresponding performance parameters for the base stage were 1.480, 0.872, and 25.2%, respectively. The base stage demonstrated a peak efficiency at design speed of 0.872; the scaled stage achieved a level of 0.838. When the scaled stage rotor and stator tip clearances were doubled, the stage achieved a pressure ratio of 1.413, efficiency of 0.799, and surge margin of 16.0% at the design flowrate. The peak stage efficiency at design speed was 0.825 with the increased clearance. Increased prewhirl lowered the stage pressure ratio as expected. Stage efficiency was maintained with ten degrees of increased prewhirl and then decreased substantially with ten additional degrees of reset.

  18. Effect of aspect ratio on the hydrodynamics of a self-propelled elliptic foil

    NASA Astrophysics Data System (ADS)

    Zhang, Xing; Ni, Saizhen; Wang, Shizhao; He, Guowei

    2008-11-01

    Flapping wings or fins are commonly used by birds, insects, fishes and some Micro Air Vehicles to generate propulsive force. In most of the studies on flapping wings, the foil is placed in a steady stream and the motion in the horizontal direction is constrained. However, the condition in these studies is completely different from that in real self-propelled locomotion. Alben and Shelly (PNAS, 102, 11163-11166 (2005)) have performed a pioneering study on fundamental hydrodynamics of a self-propelled flapping foil. In this study, we investigate the effect of geometrical shape on the hydrodynamics by varying the aspect ratio of the elliptical foil. Three different dynamic modes of the foil have been identified with the increase of aspect ratio, i.e. fore-aft symmetry, non-periodic motion and unidirectional motion with periodic velocity oscillation. It is observed that the dynamics of the body are closely related to various vortical patterns around the foil. The formation of the vortices during the starting procedure and their subsequent disposition in the wake will be described. The implication of the current study on the optimization of the foil shape in obtaining locomotion is given.

  19. Characterization of the optical parameters of high aspect ratio polymer micro-optical components

    NASA Astrophysics Data System (ADS)

    Krajewski, Rafal; Van Erps, Jurgen; Wissmann, Markus; Kujawinska, Malgorzata; Parriaux, Olivier; Tonchev, S.; Mohr, Jurgen; Thienpont, Hugo

    2008-04-01

    Over the last decades the significant grow of interest of photonics devices is observed in various fields of applications. Due to the market demands, the current research studies are focused on the technologies providing miniaturized, reliable low-cost micro-optical systems, particularly the ones featuring the fabrication of high aspect ratio structures. A high potential of these technologies comes from the fact that fabrication process is not limited to single optical components, but entire systems integrating sets of elements could be fabricated. This could in turn result in a significant saving on the assembly and packaging costs. We present a brief overview of the most common high aspect ratio fabrication technologies for micro-optical components followed by some characterization studies of these techniques. The sidewall quality and internal homogeneity will be considered as the most crucial parameters, having an impact on the wavefront propagation in the fabricated components. We show the characterization procedure and measurement results for components prototyped with Deep Proton Writing and glass micromachining technology replicated with Hot Embossing and Elastomeric Mould Vacuum Casting technology. We discuss the pros and cons for using these technologies for the production of miniaturized interferometers blocks. In this paper we present the status of our research on the new technology chain and we show the concept of microinterferometers to be fabricated within presented technology chain.

  20. High aspect ratio 10-nm-scale nanoaperture arrays with template-guided metal dewetting.

    PubMed

    Wang, Ying Min; Lu, Liangxing; Srinivasan, Bharathi Madurai; Asbahi, Mohamed; Zhang, Yong Wei; Yang, Joel K W

    2015-01-01

    We introduce an approach to fabricate ordered arrays of 10-nm-scale silica-filled apertures in a metal film without etching or liftoff. Using low temperature (<400°C) thermal dewetting of metal films guided by nano-patterned templates, apertures with aspect ratios up to 5:1 are demonstrated. Apertures form spontaneously during the thermal process without need for further processing. Although the phenomenon of dewetting has been well studied, this is the first demonstration of its use in the fabrication of nanoapertures in a spatially controllable manner. In particular, the achievement of 10-nm length-scale patterning at high aspect ratio with thermal dewetting is unprecedented. By varying the nanotemplate design, we show its strong influence over the positions and sizes of the nanoapertures. In addition, we construct a three-dimensional phase field model of metal dewetting on nano-patterned substrates. The simulation data obtained closely corroborates our experimental results and reveals new insights to template dewetting at the nanoscale. Taken together, this fabrication method and simulation model form a complete toolbox for 10-nm-scale patterning using template-guided dewetting that could be extended to a wide range of material systems and geometries. PMID:25858792

  1. Fabrication of ultra-high aspect ratio silicon nanopores by electrochemical etching

    SciTech Connect

    Schmidt, Torsten; Zhang, Miao; Linnros, Jan; Yu, Shun

    2014-09-22

    We report on the formation of ultra-high aspect ratio nanopores in silicon bulk material using photo-assisted electrochemical etching. Here, n-type silicon is used as anode in contact with hydrofluoric acid. Based on the local dissolution of surface atoms in pre-defined etching pits, pore growth and pore diameter are, respectively, driven and controlled by the supply of minority charge carriers generated by backside illumination. Thus, arrays with sub-100 nm wide pores were fabricated. Similar to macropore etching, it was found that the pore diameter is proportional to the etching current, i.e., smaller etching currents result in smaller pore diameters. To find the limits under which nanopores with controllable diameter still can be obtained, etching was performed at very low current densities (several μA cm{sup −2}). By local etching, straight nanopores with aspect ratios above 1000 (∼19 μm deep and ∼15 nm pore tip diameter) were achieved. However, inherent to the formation of such narrow pores is a radius of curvature of a few nanometers at the pore tip, which favors electrical breakdown resulting in rough pore wall morphologies. Lowering the applied bias is adequate to reduce spiking pores but in most cases also causes etch stop. Our findings on bulk silicon provide a realistic chance towards sub-10 nm pore arrays on silicon membranes, which are of great interest for molecular filtering and possibly DNA sequencing.

  2. HCl-Retarded Gold Nanorod Growth for Aspect Ratio and Shape Tuning.

    PubMed

    Wang, Yun; Guo, Yuan; Shen, Yuanyuan; Chen, Rongjun; Wang, Feihu; Zhou, Dejian; Guo, Shengrong

    2016-01-01

    Traditionally, gold nanorods (GNRs) are mostly prepared via a seed-mediated growth approach, which usually produce an initial burst growth followed by slower kinetics and generate dogbone- shaped GNRs with relatively small aspect ratios (ARs). We demonstrate here that the growth of GNRs can be effectively retarded by addition of hydrochloric acid (HCl), leading to the formation of symmetric, long GNRs with high ARs. Furthermore, time-dependent kinetic analysis of GNR growth reveals two completely different growth modalities: in the absence of HCl, the GNR growth is rapid, reaching a concentration of 0.64 nM in 10 min. Its AR also rapidly reaches a maximum value of 4.1 at 2 min and then gradually decreases to 3.3 over 5 h. In sharp contrast, in the presence of HCI additive, the GNR growth happens very slowly, reaching a concentration of 0.33 nM at 7 h, and the AR also grows slowly to reach a maximum value of 5.3 at 3 h. These growth modalities endow different formation mechanisms of GNRs, which determine their aspect ratios and shape. PMID:27398586

  3. Realization of Vertically Aligned, Ultrahigh Aspect Ratio InAsSb Nanowires on Graphite.

    PubMed

    Anyebe, E A; Sanchez, A M; Hindmarsh, S; Chen, X; Shao, J; Rajpalke, M K; Veal, T D; Robinson, B J; Kolosov, O; Anderson, F; Sundaram, R; Wang, Z M; Falko, V; Zhuang, Q

    2015-07-01

    The monolithic integration of InAs(1-x)Sb(x) semiconductor nanowires on graphitic substrates holds enormous promise for cost-effective, high-performance, and flexible devices in optoelectronics and high-speed electronics. However, the growth of InAs(1-x)Sb(x) nanowires with high aspect ratio essential for device applications is extremely challenging due to Sb-induced suppression of axial growth and enhancement in radial growth. We report the realization of high quality, vertically aligned, nontapered and ultrahigh aspect ratio InAs(1-x)Sb(x) nanowires with Sb composition (xSb(%)) up to ∼12% grown by indium-droplet assisted molecular beam epitaxy on graphite substrate. Low temperature photoluminescence measurements show that the InAs(1-x)Sb(x) nanowires exhibit bright band-to-band related emission with a distinct redshift as a function of Sb composition providing further confirmation of successful Sb incorporation in as-grown nanowires. This study reveals that the graphite substrate is a more favorable platform for InAs(1-x)Sb(x) nanowires that could lead to hybrid heterostructures possessing potential device applications in optoelectronics. PMID:26086785

  4. Measuring ion velocity distribution functions through high-aspect ratio holes in inductively coupled plasmas

    NASA Astrophysics Data System (ADS)

    Cunge, G.; Darnon, M.; Dubois, J.; Bezard, P.; Mourey, O.; Petit-Etienne, C.; Vallier, L.; Despiau-Pujo, E.; Sadeghi, N.

    2016-02-01

    Several issues associated with plasma etching of high aspect ratio structures originate from the ions' bombardment of the sidewalls of the feature. The off normal angle incident ions are primarily due to their temperature at the sheath edge and possibly to charging effects. We have measured the ion velocity distribution function (IVDF) at the wafer surface in an industrial inductively coupled plasma reactor by using multigrid retarding field analyzers (RFA) in front of which we place 400 μm thick capillary plates with holes of 25, 50, and 100 μm diameters. The RFA then probes IVDF at the exit of the holes with Aspect Ratios (AR) of 16, 8, and 4, respectively. The results show that the ion flux dramatically drops with the increase in AR. By comparing the measured IVDF with an analytical model, we concluded that the ion temperature is 0.27 eV in our plasma conditions. The charging effects are also observed and are shown to significantly reduce the ion energy at the bottom of the feature but only with a "minor" effect on the ion flux and the shape of the IVDF.

  5. Simulation and investigation of factors affecting high aspect ratio UV embossing.

    PubMed

    Chan-Park, Mary B; Lam, Y C; Laulia, P; Joshi, S C

    2005-03-01

    UV embossing is a replication method whereby an UV-curable polymer is pressed against a patterned mold and cured with UV irradiation, resulting in a patterned polymeric substrate. High aspect ratio UV embossing will find diverse applications in tissue engineering, micro-optics, display technologies, and sensors. Demolding of an UV-embossed polymer pattern with aspect ratio of 5 from the mold has previously been demonstrated experimentally. In this paper, parameters that affect the demolding process have been identified and investigated. They include cross-linking shrinkage during curing by UV irradiation, modulus of cured polymer, interfacial fracture strength and toughness, and loading method during demolding. Shrinkage is an important parameter, and an optimum level of shrinkage to avoid breakage of the embossing during demolding was found to exist. This optimum level is that at which the maximum stress (sigma(1)max) experienced by the polymer during demolding is minimized. The micromechanics of demolding was found to be different for shrinkage values lower or larger than the optimum value. PMID:15723501

  6. Parametrization of the Gay-Berne potential for conjugated oligomer with a high aspect ratio

    NASA Astrophysics Data System (ADS)

    Lee, Cheng K.; Hua, Chi C.; Chen, Show A.

    2010-08-01

    The Gay-Berne (GB) potential has been a popular semiempirical model for describing the short-range intermolecular forces for a wide variety of aspherical molecules, including liquid crystals and anisotropic colloids, with generally small molecular dimensions and low aspect ratios (<5). This study evaluates the parametrization of the GB potential for a high-aspect-ratio (=10) oligomer belonging to a model conjugated polymer. We elaborate that the semiflexibility associated with a large oligomer species demands a variant umbrella-sampling scheme in establishing the potentials of mean force (PMFs) for four pair ellipsoid arrangements typically utilized to parametrize the GB potential. The model ellipsoid so constructed is shown to capture the PMFs of essential intermediate arrangements as well, and, according to the results of simplex optimizations, recommendations are given for the minimum set of parameters to be included in the optimization of a large oligomer or particulate species. To further attest the parametrized GB potential, the coarse-grained (CG) Monte Carlo simulations employing the GB potential and the back-mapped, full-atom atomistic molecular dynamics (AMD) simulations were performed for a dense oligomer system at two representative system temperatures. The results indicated that the CG simulations can capture, with exceptional computational efficiency, the AMD predictions with good thermal transferability. In future perspectives, we remark on potential applications to construct efficient, parameter-free CG models for capturing fundamental material properties of large oligomer/particulate species as well as long-chain conjugated polymers.

  7. Large area UV casting using diverse polyacrylates of microchannels separated by high aspect ratio microwalls.

    PubMed

    Zhou, W X; Chan-Park, Mary B

    2005-05-01

    Large area molding of long and deep microchannels separated by high aspect ratio microwalls is important for high sensitivity and high throughput microfluidic devices. Ultraviolet (UV) casting is a feasible, economical and convenient method of replication of such microstructures in plastics. It is shown that a wide variety of polyacrylates with diverse properties such as those made from epoxy (EP), polyurethane (UR), polyester (ES), poly (ethylene glycol) (EG) and poly(propylene glycol) (PG) can be used for the high aspect ratio (7-9) UV casting of such linear microstructures over a 100 mm diameter, enlarging the range of applications of the replicated microstructures. Some challenges arise. With the EG formulation, wavy microstructures were observed; this can be overcome by stress relaxation. With non-polar PG formulation, poor adhesion between the polyester substrate and resin can lead to delamination of the casting from the substrate during demolding; this can be overcome by pre-coating a partially cured same resin on the polyester substrate. An optimum UV irradiation time was important for cure at the deepest end of the microstructure without excessive crosslinking leading to much increased demolding forces. The viscosity and wetting capability of the formulations were found to affect replication fidelity. PMID:15856087

  8. Fabrication of 3D high aspect ratio PDMS microfluidic networks with a hybrid stamp.

    PubMed

    Kung, Yu-Chun; Huang, Kuo-Wei; Fan, Yu-Jui; Chiou, Pei-Yu

    2015-04-21

    We report a novel methodology for fabricating large-area, multilayer, thin-film, high aspect ratio, 3D microfluidic structures with through-layer vias and open channels that can be bonded between hard substrates. It is realized by utilizing a hybrid stamp with a thin plastic sheet embedded underneath a PDMS surface. This hybrid stamp solves an important edge protrusion issue during PDMS molding while maintaining necessary stamp elasticity to ensure the removal of PDMS residues at through-layer regions. Removing edge protrusion is a significant progress toward fabricating 3D structures since high aspect ratio PDMS structures with flat interfaces can be realized to facilitate multilayer stacking and bonding to hard substrates. Our method also allows for the fabrication of 3D deformable channels, which can lead to profound applications in electrokinetics, optofluidics, inertial microfluidics, and other fields where the shape of the channel cross section plays a key role in device physics. To demonstrate, as an example, we have fabricated a microfluidic channel by sandwiching two 20 μm wide, 80 μm tall PDMS membranes between two featureless ITO glass substrates. By applying electrical bias to the two ITO substrates and pressure to deform the thin membrane sidewalls, strong electric field enhancement can be generated in the center of a channel to enable 3D sheathless dielectrophoretic focusing of biological objects including mammalian cells and bacteria at a flow speed up to 14 cm s(-1). PMID:25710255

  9. Effect of free surface on near-wake flow of elliptic cylinders with different aspect ratios

    NASA Astrophysics Data System (ADS)

    Lee, Sang Joon; Daichin, -

    2003-04-01

    The flow fields behind elliptic cylinders with different aspect ratios adjacent to a free surface were investigated experimentally in a circulating water channel. The elliptic cylinders tested in this study have same cross section area. For each elliptic cylinder, the experiments were carried out under different conditions by varying the submergence depth of the cylinder beneath the free surface. The flow fields were measured using a single-frame double-exposure PIV system. For each experimental condition, 350 instantaneous velocity fields were captured and ensemble-averaged to obtain the mean flow field information and spatial distribution of turbulent statistics. The near-wakes can be basically classified into three typical patterns, which are formation of Coanda effect, generation of substantial jet-like flow, and attachment of jet flow to the free surface. The general flow structures behind the elliptic cylinder are similar to previous results for a circular submerged near to a free surface. However, the wake width and the angle of downward deflection of the shear layer developed from the lower surface of the elliptic cylinder are smaller than those for the circular cylinder. These trends are enhance with increasing of the cylinder aspect ratios.

  10. Numerical simulation of the tip vortex off a low-aspect-ratio wing at transonic speed

    NASA Technical Reports Server (NTRS)

    Mansour, N. N.

    1984-01-01

    The viscous transonic flow around a low aspect ratio wing was computed by an implicit, three dimensional, thin-layer Navier-Stokes solver. The grid around the geometry of interest is obtained numerically as a solution to a Dirichlet problem for the cube. A low aspect ratio wing with large sweep, twist, taper, and camber is the chosen geometry. The topology chosen to wrap the mesh around the wing with good tip resolution is a C-O type mesh. The flow around the wing was computed for a free stream Mach number of 0.82 at an angle of attack of 5 deg. At this Mach number, an oblique shock forms on the upper surface of the wing, and a tip vortex and three dimensional flow separation off the wind surface are observed. Particle path lines indicate that the three dimensional flow separation on the wing surface is part of the roots of the tip vortex formation. The lifting of the tip vortex before the wing trailing edge is observed by following the trajectory of particles release around the wing tip.

  11. Mechanically stable, high aspect ratio, multifilar, wound, ribbon-type conductor and method for manufacturing same

    DOEpatents

    Cottingham, James G.

    1987-01-01

    A mechanically stable, wound, multifilar, ribbon-type conductor having a cross-sectional aspect ratio which may be greater than 12:1, comprising a plurality of conductive strands wound to form a flattened helix containing a plastic strip into which the strands have been pressed so as to form a bond between the strip and the strands. The bond mechanically stabilizes the conductor under tension, preventing it from collapsing into a tubular configuration. In preferred embodiments the plastic strip may be polytetrafluoroethylene, and the conductive strands may be formed from a superconductive material. Conductors in accordance with the present invention may be manufactured by winding a plurality of conductive strands around a hollow mandrel; the cross-section of a hollow mandrel; the cross-section of the mandrel continuously varying from substantially circular to a high aspect ratio elipse while maintaining a constant circumference. The wound conductive strands are drawn from the mandrel as a multifilar helix while simultaneously a plastic strip is fed through the hollow mandrel so that it is contained within the helix as it is withdrawn from the mandrel. The helical conductor is then compressed into a ribbon-like form and the strands are bonded to the plastic strip by a combination of heat and pressure.

  12. Mechanically stable, high aspect ratio, multifilar, wound, ribbon-type conductor and method for manufacturing same

    DOEpatents

    Cottingham, James G.

    1987-11-03

    A mechanically stable, wound, multifilar, ribbon-type conductor having a cross-sectional aspect ratio which may be greater than 12:1, comprising a plurality of conductive strands wound to form a flattened helix containing a plastic strip into which the strands have been pressed so as to form a bond between the strip and the strands. The bond mechanically stabilizes the conductor under tension, preventing it from collapsing into a tubular configuration. In preferred embodiments the plastic strip may be polytetrafluoroethylene, and the conductive strands may be formed from a superconductive material. Conductors in accordance with the present invention may be manufactured by winding a plurality of conductive strands around a hollow mandrel; the cross-section of a hollow mandrel; the cross-section of the mandrel continuously varying from substantially circular to a high aspect ratio elipse while maintaining a constant circumference. The wound conductive strands are drawn from the mandrel as a multifilar helix while simultaneously a plastic strip is fed through the hollow mandrel so that it is contained within the helix as it is withdrawn from the mandrel. The helical conductor is then compressed into a ribbon-like form and the strands are bonded to the plastic strip by a combination of heat and pressure.

  13. High aspect ratio PS-b-PMMA block copolymer masks for lithographic applications.

    PubMed

    Ferrarese Lupi, F; Giammaria, T J; Volpe, F G; Lotto, F; Seguini, G; Pivac, B; Laus, M; Perego, M

    2014-12-10

    The control of the self-assembly (SA) process and nanostructure orientation in diblock copolymer (DBC) thick films is a crucial technological issue. Perpendicular orientation of the nanostructures in symmetric and asymmetric poly(styrene)-b-poly(methyl methacrylate) (PS-b-PMMA) block copolymer films obtained by means of simple thermal treatments was demonstrated to occur in well-defined thickness windows featuring modest maximum values, thus resulting in low aspect ratio (h/d < 2) of the final lithographic mask. In this manuscript, the thickness window corresponding to the perpendicular orientation of the cylindrical structures in asymmetric DBC is investigated at high temperatures (190 °C ≤ T ≤ 310 °C) using a rapid thermal processing machine. A systematic study of the annealing conditions (temperature and time) of asymmetric PS-b-PMMA (Mn = 67.1, polydispersity index = 1.09) films, with thicknesses ranging from 10 to 400 nm, allowed ordered patterns, with a maximum value of orientational correlation length of 350 nm, to be obtained for film thicknesses up to 200 nm. The complete propagation of the cylindrical structures through the whole film thickness in a high aspect ratio PS template (h/d ≈ 7) is probed by lift-off process. Si nanopillars are obtained having the same lateral ordering and characteristic dimensions of the DBC lithographic mask as further confirmed by grazing-incidence small-angle X-ray scattering experiments. PMID:25387131

  14. Parametrization of the Gay-Berne potential for conjugated oligomer with a high aspect ratio.

    PubMed

    Lee, Cheng K; Hua, Chi C; Chen, Show A

    2010-08-14

    The Gay-Berne (GB) potential has been a popular semiempirical model for describing the short-range intermolecular forces for a wide variety of aspherical molecules, including liquid crystals and anisotropic colloids, with generally small molecular dimensions and low aspect ratios (<5). This study evaluates the parametrization of the GB potential for a high-aspect-ratio (=10) oligomer belonging to a model conjugated polymer. We elaborate that the semiflexibility associated with a large oligomer species demands a variant umbrella-sampling scheme in establishing the potentials of mean force (PMFs) for four pair ellipsoid arrangements typically utilized to parametrize the GB potential. The model ellipsoid so constructed is shown to capture the PMFs of essential intermediate arrangements as well, and, according to the results of simplex optimizations, recommendations are given for the minimum set of parameters to be included in the optimization of a large oligomer or particulate species. To further attest the parametrized GB potential, the coarse-grained (CG) Monte Carlo simulations employing the GB potential and the back-mapped, full-atom atomistic molecular dynamics (AMD) simulations were performed for a dense oligomer system at two representative system temperatures. The results indicated that the CG simulations can capture, with exceptional computational efficiency, the AMD predictions with good thermal transferability. In future perspectives, we remark on potential applications to construct efficient, parameter-free CG models for capturing fundamental material properties of large oligomer/particulate species as well as long-chain conjugated polymers. PMID:20707586

  15. Volumetric measurements and simulations of the vortex structures generated by low aspect ratio plunging wings

    NASA Astrophysics Data System (ADS)

    Calderon, D. E.; Wang, Z.; Gursul, I.; Visbal, M. R.

    2013-06-01

    Volumetric three-component velocimetry measurements have been performed on low aspect ratio wings undergoing a small amplitude pure plunging motion. This study focuses on the vortex flows generated by rectangular and elliptical wings set to a fixed geometric angle of attack of α = 20°. An investigation into the effect of Strouhal number illustrates the highly three-dimensional nature of the leading edge vortex as well as its inherent ability to improve lift performance. Computational simulations show good agreement with experimental results, both demonstrating the complex interaction between leading, trailing, and tip vortices generated in each cycle. The leading edge vortex, in particular, may deform significantly throughout the cycle, in some cases developing strong spanwise undulations. These are at least both Strouhal number and planform dependent. One or two arch-type vortical structures may develop, depending on the aspect ratio and Strouhal number. At sufficiently high Strouhal numbers, a tip vortex ring may also develop, propelling itself away from the wing in the spanwise direction due to self-induced velocity.

  16. Etching of Silicon in HBr Plasmas for High Aspect Ratio Features

    NASA Technical Reports Server (NTRS)

    Hwang, Helen H.; Meyyappan, M.; Mathad, G. S.; Ranade, R.

    2002-01-01

    Etching in semiconductor processing typically involves using halides because of the relatively fast rates. Bromine containing plasmas can generate high aspect ratio trenches, desirable for DRAM and MEMS applications, with relatively straight sidewalk We present scanning electron microscope images for silicon-etched trenches in a HBr plasma. Using a feature profile simulation, we show that the removal yield parameter, or number of neutrals removed per incident ion due to all processes (sputtering, spontaneous desorption, etc.), dictates the profile shape. We find that the profile becomes pinched off when the removal yield is a constant, with a maximum aspect ratio (AR) of about 5 to 1 (depth to height). When the removal yield decreases with increasing ion angle, the etch rate increases at the comers and the trench bottom broadens. The profiles have ARs of over 9:1 for yields that vary with ion angle. To match the experimentally observed etched time of 250 s for an AR of 9:1 with a trench width of 0.135 microns, we find that the neutral flux must be 3.336 x 10(exp 17)sq cm/s.

  17. Numerical simulation of the tip vortex off a low-aspect-ratio wing at transonic speed

    NASA Technical Reports Server (NTRS)

    Mansour, N. N.

    1984-01-01

    The viscous transonic flow around a low-aspect-ratio wing has been computed using an implicit, three-dimensional, 'thin-layer' Navier-Stokes solver. The grid around the geometry of interest is obtained numerically as a solution to a Dirichlet problem for the cube. The geometry chosen for this study is a low-aspect-ratio wing with large sweep, twist, taper, and camber. The topology chosen to wrap the mesh around the wing with good tip resolution is a C-O type mesh. Using this grid, the flow around the wing was computed for a free-stream Mach number of 0.82 at an angle of attack of 5 deg. At this Mach number, an oblique shock forms on the upper surface of the wing, and a tip vortex and three-dimensional flow separation off the wing surface are observed. Particle path lines indicate that the three-dimensional flow separation on the wing surface is part of the roots of the tip-vortex formation. The lifting of the tip vortex before the wing trailing edge is clearly observed by following the trajectory of particles released around the wing tip.

  18. FULLY CONVECTIVE MAGNETO-ROTATIONAL TURBULENCE IN LARGE ASPECT-RATIO SHEARING BOXES

    SciTech Connect

    Bodo, G.; Rossi, P.; Cattaneo, F.; Mignone, A.

    2015-01-20

    We present a numerical study of turbulence and dynamo action in stratified shearing boxes with both finite and zero net magnetic flux. We assume that the fluid obeys the perfect gas law and has finite thermal diffusivity. The latter is chosen to be small enough so that vigorous convective states develop. The properties of these convective solutions are analyzed as the aspect ratio of the computational domain is varied and as the value of the mean field is increased. For the cases with zero net flux, we find that a well-defined converged state is obtained for large enough aspect ratios. In the converged state, the dynamo can be extremely efficient and can generate substantial toroidal flux. We identify solutions in which the toroidal field is mostly symmetric about the mid-plane and solutions in which it is mostly anti-symmetric. The symmetric solutions are found to be more efficient at transporting angular momentum and can give rise to a luminosity that is up to an order of magnitude larger than the corresponding value for the anti-symmetric states. In the cases with a finite net flux, the system appears to spend most of the time in the symmetric states.

  19. Planarization of High Aspect Ratio P-I-N Diode Pillar Arrays for Blanket Electrical Contacts

    SciTech Connect

    Voss, L F; Shao, Q; Reinhardt, C E; Graff, R T; Conway, A M; Nikolic, R J; Deo, N; Cheung, C L

    2009-03-05

    Two planarization techniques for high aspect ratio three dimensional pillar structured P-I-N diodes have been developed in order to enable a continuous coating of metal on the top of the structures. The first technique allows for coating of structures with topography through the use of a planarizing photoresist followed by RIE etch back to expose the tops of the pillar structure. The second technique also utilizes photoresist, but instead allows for planarization of a structure in which the pillars are filled and coated with a conformal coating by matching the etch rate of the photoresist to the underlying layers. These techniques enable deposition using either sputtering or electron beam evaporation of metal films to allow for electrical contact to the tops of the underlying pillar structure. These processes have potential applications for many devices comprised of 3-D high aspect ratio structures. Two separate processes have been developed in order to ensure a uniform surface for deposition of an electrode on the {sup 10}Boron filled P-I-N pillar structured diodes. Each uses S1518 photoresist in order to achieve a relatively uniform surface despite the non-uniformity of the underlying detector. Both processes allow for metallization of the final structure and provide good electrical continuity over a 3D pillar structure.

  20. Microscopic silicon-based lateral high-aspect-ratio structures for thin film conformality analysis

    SciTech Connect

    Gao, Feng; Arpiainen, Sanna; Puurunen, Riikka L.

    2015-01-15

    Film conformality is one of the major drivers for the interest in atomic layer deposition (ALD) processes. This work presents new silicon-based microscopic lateral high-aspect-ratio (LHAR) test structures for the analysis of the conformality of thin films deposited by ALD and by other chemical vapor deposition means. The microscopic LHAR structures consist of a lateral cavity inside silicon with a roof supported by pillars. The cavity length (e.g., 20–5000 μm) and cavity height (e.g., 200–1000 nm) can be varied, giving aspect ratios of, e.g., 20:1 to 25 000:1. Film conformality can be analyzed with the microscopic LHAR by several means, as demonstrated for the ALD Al{sub 2}O{sub 3} and TiO{sub 2} processes from Me{sub 3}Al/H{sub 2}O and TiCl{sub 4}/H{sub 2}O. The microscopic LHAR test structures introduced in this work expose a new parameter space for thin film conformality investigations expected to prove useful in the development, tuning and modeling of ALD and other chemical vapor deposition processes.

  1. High aspect ratio 10-nm-scale nanoaperture arrays with template-guided metal dewetting

    PubMed Central

    Wang, Ying Min; Lu, Liangxing; Srinivasan, Bharathi Madurai; Asbahi, Mohamed; Zhang, Yong Wei; Yang, Joel K. W.

    2015-01-01

    We introduce an approach to fabricate ordered arrays of 10-nm-scale silica-filled apertures in a metal film without etching or liftoff. Using low temperature (<400°C) thermal dewetting of metal films guided by nano-patterned templates, apertures with aspect ratios up to 5:1 are demonstrated. Apertures form spontaneously during the thermal process without need for further processing. Although the phenomenon of dewetting has been well studied, this is the first demonstration of its use in the fabrication of nanoapertures in a spatially controllable manner. In particular, the achievement of 10-nm length-scale patterning at high aspect ratio with thermal dewetting is unprecedented. By varying the nanotemplate design, we show its strong influence over the positions and sizes of the nanoapertures. In addition, we construct a three-dimensional phase field model of metal dewetting on nano-patterned substrates. The simulation data obtained closely corroborates our experimental results and reveals new insights to template dewetting at the nanoscale. Taken together, this fabrication method and simulation model form a complete toolbox for 10-nm-scale patterning using template-guided dewetting that could be extended to a wide range of material systems and geometries. PMID:25858792

  2. Ultrasharp high-aspect-ratio probe array for SECM and AFM Analysis

    NASA Astrophysics Data System (ADS)

    Tao, Ye; Fasching, Rainer J.; Prinz, Fritz B.

    2004-07-01

    A powerful experimental tool, ultra-sharp nano-electrode array is designed, fabricated and characterized. The application on a combination of Scanning Electrochemical Microscopy (SECM) and the Atomic Force Microcopy (AFM) is demonstrated. It can measure sample electrochemically initiated by SECM changes of topography while detecting topography using AFM. In order to realize this, a specialized probe system that is composed of a micro-mechanical bending structure necessary for the AFM mode and an electrochemical UME-tip required for a high performance SECM is crucial. The probe array is a row of silicon transducers embedded in silicon nitride cantilever array. The sharp high-aspect ratio (20:1) silicon tips are shaped and a thin layer of silicon nitride is deposited, which embeds the silicon tips in a silicon nitride layer so that they protrude through the nitride. Thus, the embedded silicon tips with a diameter less than 600 nm, the top radius less than 20 nm, and the aspect ratio as high as 20 can be achieved. A metal layer and an insulator layer are deposited on these tip structures to make each probe selectively conductive. Finally, cantilever structures are shaped and released by etching the silicon substrate from the backside. Electrochemical and impedance spectroscopic characterization show electrochemical functionality of the transducer system.

  3. Braiding of submarine channels controlled by aspect ratio similar to rivers

    NASA Astrophysics Data System (ADS)

    Foreman, Brady Z.; Lai, Steven Y. J.; Komatsu, Yuhei; Paola, Chris

    2015-09-01

    The great majority of submarine channels formed by turbidity and density currents are meandering in planform; they consist of a single, sinuous channel that transports a turbid, dense flow of sediment from submarine canyons to ocean floor environments. Braided turbidite systems consisting of multiple, interconnected channel threads are conspicuously rare. Furthermore, such systems may not represent the spontaneous planform instability of true braiding, but instead result from erosive processes or bathymetric variability. In marked contrast to submarine environments, both meandering and braided planforms are common in fluvial systems. Here we present experiments of subaqueous channel formation conducted at two laboratory facilities. We find that density currents readily produce a braided planform for flow aspect ratios of depth to width that are similar to those that produce river braiding. Moreover, we find that stability model theory for river planform morphology successfully describes submarine channels in both experiments and the field. On the basis of these observations, we propose that the rarity of braided submarine channels is explained by the generally greater flow depths in submarine systems, which necessitate commensurately greater widths to achieve the required aspect ratio, along with feedbacks among flow thickness, suspended sediment concentration and channel relief that induce greater levee deposition rates and limit channel widening.

  4. The Effect of Aspect Ratio and Deformability on Nanoparticle Extravasation through Nanopores

    PubMed Central

    Kersey, Farrell R.; Merkel, Timothy J.; Perry, Jillian L.; Napier, Mary E.; DeSimone, Joseph M.

    2012-01-01

    We describe the fabrication of filamentous hydrogel nanoparticles using a unique soft lithography based particle molding process referred to as PRINT (Particle Replication in Non-wetting Templates). The nanoparticles possess a constant width of 80 nm, and we varied their lengths ranging from 180 nm to 5000 nm. In addition to varying the aspect ratio of the particles, the deformability of the particles was tuned by varying the cross-link density within the particle matrix. Size characteristics such as hydrodynamic diameter and persistence length of the particles were analyzed using dynamic light scattering and electron microscopy techniques, respectively, while particle deformability was assessed by atomic force microscopy. Additionally, the ability of the particles to pass through membranes containing 0.2 μm pores was assessed by means of a simple filtration technique, and particle recovery was determined using fluorescence spectroscopy. The results show that particle recovery is mostly independent of aspect ratio at all cross-linker concentrations utilized, with the exception of 96 wt% PEG diacrylate 80 × 5000 nm particles, which showed the lowest percent recovery. PMID:22612428

  5. Different methods to alter surface morphology of high aspect ratio structures

    NASA Astrophysics Data System (ADS)

    Leber, M.; Shandhi, M. M. H.; Hogan, A.; Solzbacher, F.; Bhandari, R.; Negi, S.

    2016-03-01

    In various applications such as neural prostheses or solar cells, there is a need to alter the surface morphology of high aspect ratio structures so that the real surface area is greater than geometrical area. The change in surface morphology enhances the devices functionality. One of the applications of altering the surface morphology is of neural implants such as the Utah electrode array (UEA) that communicate with single neurons by charge injection induced stimulation or by recording electrical neural signals. For high selectivity between single cells of the nervous system, the electrode surface area is required to be as small as possible, while the impedance is required to be as low as possible for good signal to noise ratios (SNR) during neural recording. For stimulation, high charge injection and charge transfer capacities of the electrodes are required, which increase with the electrode surface. Traditionally, researchers have worked with either increasing the roughness of the existing metallization (platinum grey, black) or other materials such as Iridium Oxide and PEDOT. All of these previously investigated methods lead to more complicated metal deposition processes that are difficult to control and often have a critical impact on the mechanical properties of the metal films. Therefore, a modification of the surface underneath the electrode's coating will increase its surface area while maintaining the standard and well controlled metal deposition process. In this work, the surfaces of the silicon micro-needles were engineered by creating a defined microstructure on the electrodes surface using several methods such as laser ablation, focused ion beam, sputter etching, reactive ion etching (RIE) and deep reactive ion etching (DRIE). The surface modification processes were optimized for the high aspect ratio silicon structures of the UEA. The increase in real surface area while maintaining the geometrical surface area was verified using scanning electron

  6. Effect of aspect-ratio on vortex distribution and heat transfer in rotating Rayleigh-Bénard convection

    NASA Astrophysics Data System (ADS)

    Overkamp, J.; Stevens, R. J. A. M.; Lohse, Detlef; Clercx, Herman J. H.

    2011-12-01

    Numerical and experimental data for the heat transfer as function of the Rossby number Ro in rotating Rayleigh-Benard are presented for Pr = 4.38 and up to Ra = 4.52 × 109 . The aspect ratio is varied between Γ = 0.5 and Γ = 2.0. Without rotation, where the aspect ratio influences the global flow structure, we see a small aspect-ratio dependence in the Nusselt number. For stronger rotation, i.e. 1/Ro gg 1/Roc, the heat transport becomes independent of the aspect-ratio. We interpret this finding as follows: In the rotating regime the heat is mainly transported by vertically-aligned vortices. Since these vortices are local, the aspect ratio has a negligible effect on the heat transport in the rotating regime. Indeed, an analysis of the vortex statistics shows that the fraction of the horizontal area that is covered by vortices is aspect-ratio independent when 1/Ro gg 1/Roc. In agreement with the results of Weiss & Ahlers (2011) we find a vortex-depleted area close to the sidewall. Here, we show that there is also an area with enhanced vortex concentration next to the vortex-depleted edge region and that the absolute widths of both regions are independent of the aspect ratio. This proceeding is a summary of Stevens et al. (2011).

  7. The Impact of Aspect Ratio on the Biodistribution and Tumor Homing of Rigid Soft-Matter Nanorods

    PubMed Central

    Shukla, Sourabh; Eber, Fabian J.; Nagarajan, Adithy S.; DiFranco, Nicholas A.; Schmidt, Nora; Wen, Amy M.; Eiben, Sabine; Twyman, Richard M.; Wege, Christina; Steinmetz, Nicole F.

    2016-01-01

    The size and shape of nanocarriers can affect their fate in vivo, but little is known about the effect of nanocarrier aspect ratio on biodistribution in the setting of cancer imaging and drug delivery. The production of nanoscale anisotropic materials is a technical challenge. A unique biotemplating approach based on of rod-shaped nucleoprotein nanoparticles with predetermined aspect ratios (AR 3.5, 7, and 16.5) is used. These rigid, soft-matter nanoassemblies are derived from tobacco mosaic virus (TMV) components. The role of nanoparticle aspect ratio is investigated, while keeping the surface chemistries constant, using either PEGylated stealth nanoparticles or receptor-targeted RGD-displaying formulations. Aspect ratio has a profound impact on the behavior of the nanoparticles in vivo and in vitro. PEGylated nanorods with the lowest aspect ratio (AR 3.5) achieve the most efficient passive tumorhoming behavior because they can diffuse most easily, whereas RGD-labeled particles with a medium aspect ratio (AR 7) are more efficient at tumor targeting because this requires a balance between infusibility and ligand–receptor interactions. The in vivo behavior of nanoparticles can therefore be tailored to control biodistribution, longevity, and tumor penetration by modulating a single parameter: the aspect ratio of the nanocarrier. PMID:25641794

  8. Compact tokamak reactors. Part 1 (analytic results)

    SciTech Connect

    Wootton, A.J.; Wiley, J.C.; Edmonds, P.H.; Ross, D.W.

    1996-09-13

    We discuss the possible use of tokamaks for thermonuclear power plants, in particular tokamaks with low aspect ratio and copper toroidal field coils. Three approaches are presented. First we review and summarize the existing literature. Second, using simple analytic estimates, the size of the smallest tokamak to produce an ignited plasma is derived. This steady state energy balance analysis is then extended to determine the smallest tokamak power plant, by including the power required to drive the toroidal field, and considering two extremes of plasma current drive efficiency. The analytic results will be augmented by a numerical calculation which permits arbitrary plasma current drive efficiency; the results of which will be presented in Part II. Third, a scaling from any given reference reactor design to a copper toroidal field coil device is discussed. Throughout the paper the importance of various restrictions is emphasized, in particular plasma current drive efficiency, plasma confinement, plasma safety factor, plasma elongation, plasma beta, neutron wall loading, blanket availability and recirculating electric power. We conclude that the latest published reactor studies, which show little advantage in using low aspect ratio unless remarkably high efficiency plasma current drive and low safety factor are combined, can be reproduced with the analytic model.

  9. The effect of wing stroke and aspect ratio on the force generation a compliant membrane flapping wing

    NASA Astrophysics Data System (ADS)

    Schunk, Cosima; Swartz, Sharon M.; Breuer, Kenneth S.

    2015-11-01

    Aspect ratio is one parameter used in efforts to predict a bat species' flight performance based on wing shape. Bats with high aspect ratio wings are expected to have superior lift-to-drag ratios and therefore to fly faster or be able to sustain longer flights. In contrast, bats with lower aspect ratio wings are usually thought to exhibit higher maneuverability. These assumptions are often based on fixed-wing aerodynamic theory, and do not take the wide variation in flapping kinematics observed in bats into account. To examine the influence of different stroke patterns, we measure lift and drag of highly compliant membrane wings with different bat-relevant aspect ratios. A two degree of freedom shoulder joint allows for independent control of flapping amplitude and wing sweep. We test five models with the same variations of stroke patterns, flapping frequencies, and wind speeds.

  10. Designed Synthesis of CeO2 Nanorods and Nanowires for Studying Toxicological Effects of High Aspect Ratio Nanomaterials

    PubMed Central

    Ji, Zhaoxia; Wang, Xiang; Zhang, Haiyuan; Lin, Sijie; Meng, Huan; Sun, Bingbing; George, Saji; Xia, Tian; Nel, André E.; Zink, Jeffrey I.

    2012-01-01

    While it has been shown that high aspect ratio nanomaterials like carbon nanotubes and TiO2 nanowires can induce toxicity by acting as fiber-like substances that damage the lysosome, it is not clear what the critical lengths and aspect ratios are that induce this type of toxicity. To answer this question, we synthesized a series of cerium oxide (CeO2) nanorods and nanowires with precisely controlled lengths and aspect ratios. Both phosphate and chloride ions were shown to play critical roles in obtaining these high aspect ratio nanostructures. High resolution TEM analysis shows that single crystalline CeO2 nanorods/nanowires were formed along the [211] direction by an “oriented attachment” mechanism, followed by Ostwald ripening. The successful creation of a comprehensive CeO2 nanorod/nanowire combinatorial library allows, for the first time, the systematic study of the effect of aspect ratio on lysosomal damage, cytoxicity and IL-1β production by the human myeloid cell line (THP-1). This in vitro toxicity study demonstrated that at lengths ≥200 nm and aspect ratios ≥ 22, CeO2 nanorods induced progressive cytotoxicity and pro-inflammatory effects. The relatively low “critical” length and aspect ratio were associated with small nanorod/nanowire diameters (6–10 nm), which facilitates the formation of stacking bundles due to strong van der Waals and dipole-dipole attractions. Our results suggest that both length and diameter components of aspect ratio should be considered when addressing the cytotoxic effects of long aspect ratio materials. PMID:22564147

  11. The Science of Spherical Tokamak Plasmas: Progress and Promise

    NASA Astrophysics Data System (ADS)

    Sykes, Alan

    2008-11-01

    The talk will summarize the development of the low aspect ratio `Spherical' Tokamak (ST) from early linear magnetic confinement devices, through toroidal pinches, to the emergence of the tokamak in the 1960's. Theoretical predictions given by Peng and Strickler of the exciting physics of extreme low aspect ratio tokamaks (supported by early experiments involving centre rods inserted into existing Rotamaks, Spheromaks and other small-scale experiments), led to the pioneering START experiment at Culham which convincingly demonstrated the potential of the ST concept. There are now many STs world-wide. The largest among these are MA-scale devices NSTX and MAST with plasmas of cross-section comparable to DIII-D and Asdex-Upgrade. The major results include development of start-up methods; the refinement of scaling laws; improved understanding of general tokamak phenomena such as Edge Localised Modes and development of heating and current drive schemes. ST research on over 20 devices has extended the tokamak plasma regime in many ways, notably a factor 4 increase in stable toroidal average beta, and large increases in the Alfven Mach number and ExB flow shear. By exploiting such features, joint experiments with tokamaks of conventional aspect ratio are resolving several key degeneracies of interest to ITER, DEMO and larger future ST devices. Present STs have low toroidal fields sufficient for most physics studies, but for high fusion yield or energy production higher fields are required; importantly, studies on both NSTX and MAST indicate a stronger than expected improvement of performance with toroidal field. Both devices are planning exciting upgrades which feature a considerable increase of toroidal field. Recent designs for a D-T Component Test Facility based on the Spherical Tokamak show the promise of low Tritium consumption and minimum build cost. Such a facility would provide valuable R&D on the scientific and technical issues of fusion power.

  12. Design of a Low Aspect Ratio Transonic Compressor Stage Using CFD Techniques

    NASA Technical Reports Server (NTRS)

    Sanger, Nelson L.

    1994-01-01

    A transonic compressor stage has been designed for the Naval Postgraduate School Turbopropulsion Laboratory. The design relied heavily on CFD techniques while minimizing conventional empirical design methods. The low aspect ratio (1.2) rotor has been designed for a specific head ratio of .25 and a tip relative inlet Mach number of 1.3. Overall stage pressure ratio is 1.56. The rotor was designed using an Euler code augmented by a distributed body force model to account for viscous effects. This provided a relatively quick-running design tool, and was used for both rotor and stator calculations. The initial stator sections were sized using a compressible, cascade panel code. In addition to being used as a case study for teaching purposes, the compressor stage will be used as a research stage. Detailed measurements, including non-intrusive LDV, will be compared with the design computations, and with the results of other CFD codes, as a means of assessing and improving the computational codes as design tools.

  13. Design of a low aspect ratio transonic compressor stage using CFD techniques

    SciTech Connect

    Sanger, N.L.

    1996-07-01

    A transonic compressor stage has been designed for the Naval Postgraduate School Turbopropulsion Laboratory. The design relied heavily on CFD techniques while minimizing conventional empirical design methods. The low aspect ratio (1.2) rotor has been designed for a specific head ratio of 0.25 and a tip relative inlet Mach number of 1.3. Overall stage pressure ratio is 1.56. The rotor was designed using a Euler code augmented by a distributed body force model to account for viscous effects. This provided a relatively quick-running design tool, and was used for both rotor and stator calculations. The initial stator sections were sized using a compressible, cascade panel code. In addition to being used as a case study for teaching purposes, the compressor stage will be used as a research stage. Detailed measurements, including nonintrusive LDV, will be compared with the design computations, and with the results of other CFD codes, as a means of assessing and improving the computational codes as design tools.

  14. Emission behavior of sudan red 7B on dogbone-shaped gold nanorods: Aspect ratio dependence of the metallic nanostructures

    NASA Astrophysics Data System (ADS)

    Rahman, Dewan S.; Sharma, Debdulal; Ghosh, Sujit Kumar

    2014-01-01

    Cetyltrimethylammonium bromide-stabilized 'dogbone-shaped' gold nanorods of aspect ratio varying from 1 to 6 have been synthesized by seed-mediated growth method in aqueous medium. Then, sudan red 7B, an alien molecular probe has been used as local probe to elucidate aspect ratio dependence of the nanorods on the photophysical properties of the dye molecules. It is seen that the relative intensity decreases exponentially with increasing aspect ratio and has been attributed to decrease in overall surface area for a particular concentration of the nanorods. The mechanism of fluorescence quenching has been ascribed to the electron and energy transfer processes in the gold-fluorophore hybrid nanostructures.

  15. An advanced AFM sensor for high-aspect ratio pattern profile in-line measurement

    NASA Astrophysics Data System (ADS)

    Watanabe, Masahiro; Baba, Shuichi; Nakata, Toshihiko; Kurenuma, Toru; Kuroda, Hiroshi; Hiroki, Takenori

    2006-03-01

    Design rule shrinkage and the wider adoption of new device structures such as STI, copper damascene interconnects, and deep trench structures have increased the necessity of in-line process monitoring of step heights and profiles of device structures. For monitoring active device patterns, not test patterns as in OCD, AFM is the only non-destructive 3D monitoring tool. The barriers to using AFM in-line monitoring are its slow throughput and the accuracy degradation associated with probe tip wear and spike noise caused by unwanted oscillation on the steep slopes of high-aspect-ratio patterns. Our proprietary AFM scanning method, Step in mode®, is the method best suited to measuring high-aspect-ratio pattern profiles. Because the probe is not dragged on the sample surface as in conventional AFM, the profile trace fidelity across steep slopes is excellent. Because the probe does not oscillate and hit the sample at a high frequency as in AC scanning mode, this mode is free from unwanted spurious noises on steep sample slopes and incurs extremely little probe tip wear. To fully take advantage of the above properties, we have developed an AFM sensor optimized for in-line use, which produces accurate profile data at high speeds. The control scheme we have developed for the AFM sensor, which we call "Smart Step-in", elaborately analyses the contact force signal, enabling efficient probe tip scanning and a low and stable contact force. The mechanism of the AFM sensor has been optimized for the higher scanning rate and has improved the accuracy, such as the scanning planarity, position and height accuracy, and slope angle accuracy. Our prototype AFM sensor can scan high-aspect-ratio patterns while stabilizing the contact force at 3 nN. The step height measurement repeatability was 0.8 nm (3σ). A STI-like test pattern was scanned, and the steep sidewalls with angles of 84° were measured with high fidelity and without spurious noises.

  16. Simulation studies and fabrication of microtraps with long aspect ratio to store high density of positrons

    NASA Astrophysics Data System (ADS)

    Narimannezhad, Alireza

    Conventionally, non-neutral antimatter is stored using a Penning-Malmberg trap, a single tube with aspect ratios being of the order of less than 10:1. Parallel microtubes with aspect ratios of 1000:1 have the potential to store many orders of magnitude more with substantially lower end electrode potential than conventional traps. In this study, the charged particles storage capacity of these microtraps (micro-Penning-Malmberg traps) with radii of the order of tens of microns was explored. Simulation studies of the motions of charged particles were conducted with particle-in-cell plasma code WARP and the Charged Particle Optics (CPO) program. It was presented how to evaluate and lower the numerical noise by controlling the modeling parameters so the simulated plasma evolves toward computational equilibrium. The local equilibrium distribution, where longitudinal force balance is satisfied along each magnetic field line, was attained in 10 μs for plasmas initialized with a uniform density and Boltzmann energy distribution. To reach global equilibrium longer runs were performed using a fast particle mover code. Charge clouds developed the expected radial density distribution (that of a soft edge) and rigid rotation evolved to some extent. The plasma confinement time and its thermalization were independent of the length showing the length-dependency, reported in experiments, is due to fabrication and field asymmetries. Simulation demonstrated each microtrap with 50 microm radius immersed in a 7 T magnetic field could store positrons indefinitely with a density of 1.6x1011 cm-3 while the confinement voltage was only 10 V. For microtraps with radii between 100 μm and 3 μm, the particle density scaled as radius-2. Plasma confinement time was also independent of trap length. A unique approach for the fabrication of long-aspect ratio microtubes was presented for 100 μm microtraps. Standard processes such as photolithography, deep reactive ion etching, sputtering and

  17. Spherical tokamaks with plasma centre-post

    NASA Astrophysics Data System (ADS)

    Ribeiro, Celso

    2013-10-01

    The metal centre-post (MCP) in tokamaks is a structure which carries the total toroidal field current and also houses the Ohmic heating solenoid in conventional or low aspect ratio (Spherical)(ST) tokamaks. The MCP and solenoid are critical components for producing the toroidal field and for the limited Ohmic flux in STs. Constraints for a ST reactor related to these limitations lead to a minimum plasma aspect ratio of 1.4 which reduces the benefit of operation at higher betas in a more compact ST reactor. Replacing the MCP is of great interest for reactor-based ST studies since the device is simplified, compactness increased, and maintenance reduced. An experiment to show the feasibility of using a plasma centre-post (PCP) is being currently under construction and involves a high level of complexity. A preliminary study of a very simple PCP, which is ECR(Electron Cyclotron Resonance)-assisted and which includes an innovative fuelling system based on pellet injection, has recently been reported. This is highly suitable for an ultra-low aspect ratio tokamak (ULART) device. Advances on this PCP ECR-assisted concept within a ULART and the associated fuelling system are presented here, and will include the field topology for the PCP ECR-assisted scheme, pellet ablation modeling, and a possible global equilibrium simulation. VIE-ITCR, IAEA-CRP contr.17592, National Instruments-Costa Rica.

  18. Effect of torsional stiffness and inertia on the dynamics of low aspect ratio flapping wings.

    PubMed

    Xiao, Qing; Hu, Jianxin; Liu, Hao

    2014-03-01

    Micro air vehicle-motivated aerodynamics in biological flight has been an important subject in the past decade. Inspired by the novel flapping wing mechanisms in insects, birds and bats, we have carried out a numerical study systematically investigating a three-dimensional flapping rigid wing with passively actuated lateral and rotational motion. Distinguishing it from the limited existing studies, this work performs a systematic examination on the effects of wing aspect ratio (AR = 1.0 to infinity), inertia (density ratio σ = 4-32), torsional stiffness (frequency ratio F = 1.5-10 and infinity) and pivot point (from chord-center to leading edge) on the dynamics response of a low AR rectangular wing under an initial zero speed flow field condition. The simulation results show that the symmetry breakdown of the flapping wing results in a forward/backward motion with a rotational pitching. When the wing reaches its stable periodic state, the induced pitching frequency is identical to its forced flapping frequency. However, depending on various kinematic and dynamic system parameters, (i.e. flapping frequency, density ratio and pitching axis), the lateral induced velocity shows a number of different oscillating frequencies. Furthermore, compared with a one degree of freedom (DoF) wing in the lateral direction only, the propulsion performance of such a two DoF wing relies very much on the magnitude of torsional stiffness adding on the pivot point, as well as its pitching axis. In all cases examined here, thrust force and moment generated by a long span wing is larger than that of a short wing, which is remarkably linked to the strong reverse von Kármán vortex street formed in the wake of a wing. PMID:24434625

  19. A small perturbation based optimization approach for the frequency placement of high aspect ratio wings

    NASA Astrophysics Data System (ADS)

    Goltsch, Mandy

    Design denotes the transformation of an identified need to its physical embodiment in a traditionally iterative approach of trial and error. Conceptual design plays a prominent role but an almost infinite number of possible solutions at the outset of design necessitates fast evaluations. The corresponding practice of empirical equations and low fidelity analyses becomes obsolete in the light of novel concepts. Ever increasing system complexity and resource scarcity mandate new approaches to adequately capture system characteristics. Contemporary concerns in atmospheric science and homeland security created an operational need for unconventional configurations. Unmanned long endurance flight at high altitudes offers a unique showcase for the exploration of new design spaces and the incidental deficit of conceptual modeling and simulation capabilities. Structural and aerodynamic performance requirements necessitate light weight materials and high aspect ratio wings resulting in distinct structural and aeroelastic response characteristics that stand in close correlation with natural vibration modes. The present research effort evolves around the development of an efficient and accurate optimization algorithm for high aspect ratio wings subject to natural frequency constraints. Foundational corner stones are beam dimensional reduction and modal perturbation redesign. Local and global analyses inherent to the former suggest corresponding levels of local and global optimization. The present approach departs from this suggestion. It introduces local level surrogate models to capacitate a methodology that consists of multi level analyses feeding into a single level optimization. The innovative heart of the new algorithm originates in small perturbation theory. A sequence of small perturbation solutions allows the optimizer to make incremental movements within the design space. It enables a directed search that is free of costly gradients. System matrices are decomposed

  20. Boundary-layer measurements on a transonic low-aspect ratio wing

    NASA Technical Reports Server (NTRS)

    Keener, Earl R.

    1985-01-01

    Tabulations and plots are presented of boundary-layer velocity and flow-direction surveys from wind-tunnel tests of a large-scale (0.90 m semi-span) model of the NASA/Lockheed Wing C. This wing is a generic, transonic, supercritical, highly three-dimensional, low-aspect-ratio configuration designed with the use of a three-dimensional, transonic full-potential-flow wing code (FLO22). Tests were conducted at the design angle of attack of 5 deg over a Mach number range from 0.25 to 0.96 and a Reynolds number range of 3.4x10 to the 6th power. Wing pressures were measured at five span stations, and boundary-layer surveys were measured at the midspan station. The data are presented without analysis.

  1. 6:1 aspect ratio silicon pillar based thermal neutron detector filled with {sup 10}B

    SciTech Connect

    Nikolic, R. J.; Conway, A. M.; Reinhardt, C. E.; Graff, R. T.; Wang, T. F.; Deo, N.; Cheung, C. L.

    2008-09-29

    Current helium-3 tube based thermal neutron detectors have shortcomings in achieving simultaneously high efficiency and low voltage while maintaining adequate fieldability performance. By using a three-dimensional silicon p-i-n diode pillar array filled with boron-10 these constraints can be overcome. The fabricated pillar structured detector reported here is composed of 2 {mu}m diameter silicon pillars with a 4 {mu}m pitch and height of 12 {mu}m. A thermal neutron detection efficiency of 7.3+/-0.6% and a neutron-to-gamma discrimination of 10{sup 5} at 2 V reverse bias were measured for this detector. When scaled to larger aspect ratio, a high efficiency device is possible.

  2. Operational Limits and MHD Activity at Near-Unity Aspect Ratio

    NASA Astrophysics Data System (ADS)

    Unterberg, E. A.; Diem, S. J.; Fonck, R. J.; Garstka, G. D.; Lewicki, B. T.; Ostrander, C. N.; Sontag, A. C.; Thorson, T. A.; Winz, G. R.

    2000-10-01

    Experiments on the PEGASUS Toroidal Experiment are focusing on the limits of plasma operation at ultralow aspect ratio (A<1.2). Plasmas have been produced with I_p/I_TF=1, with q_98 ≈ 4-6; no external kink stability boundary is evident at that level. Studies of the q-limit have been constrained by the incomplete status of the OH power supply; the recent completion of this supply allows further exploration of this limit. Electron densities approaching the Greenwald limit have been observed. An n=1 mode is often observed during startup and is commonly associated with fast current ramps (>30 MA/s). This mode often limits the discharge evolution. There is also evidence that double tearing modes are present during the current ramp. Internal reconnection events have been observed with characteristics similar to those observed on other ST experiments.

  3. Facile Route to Vertically Aligned High-Aspect Ratio Block Copolymer Films via Dynamic Zone Annealing

    NASA Astrophysics Data System (ADS)

    Singh, Gurpreet; Kulkarni, Manish; Yager, Kevin; Smilgies, Detlef; Bucknall, David; Karim, Alamgir

    2012-02-01

    Directed assembly of block copolymers (BCP) can be used to fabricate a diversity of nanostructures useful for nanotech applications. The ability to vertically orient etchable high aspect ratio (˜30) ordered BCP domains on flexible substrates via continuous processing methods are particularly attractive for nanomanufacturing. We apply sharp dynamic cold zone annealing (CZA-S) to create etchable, and predominantly vertically oriented 30nm cylindrical domains in 1 μm thick poly(styrene-b-methylmethacrylate) films on low thermal conductivity rigid (quartz) and flexible (PDMS & Kapton) substrates. Under similar static conditions, temporally stable vertical cylinders form within a narrow zone above a critical temperature gradient. Primary ordering mechanism of CZA-S involves sweeping this vertically orienting zone created at maximum thermal gradient. An optimal speed is needed since the process competes with preferential surface wetting dynamics that favors parallel orientation. GISAXS of etched BCP films confirms internal morphology.

  4. A wearable, highly stable, strain and bending sensor based on high aspect ratio graphite nanobelts

    NASA Astrophysics Data System (ADS)

    Alaferdov, A. V.; Savu, R.; Rackauskas, T. A.; Rackauskas, S.; Canesqui, M. A.; de Lara, D. S.; Setti, G. O.; Joanni, E.; de Trindade, G. M.; Lima, U. B.; de Souza, A. S.; Moshkalev, S. A.

    2016-09-01

    A simple and scalable method was developed for the fabrication of wearable strain and bending sensors, based on high aspect ratio (length/thickness ∼103) graphite nanobelt thin films deposited by a modified Langmuir–Blodgett technique onto flexible polymer substrates. The sensing mechanism is based on the changes in contact resistance between individual nanobelts upon substrate deformation. Very high sensor response stability for more than 5000 strain–release cycles and a device power consumption as low as 1 nW were achieved. The device maximum stretchability is limited by the metal electrodes and the polymer substrate; the maximum strain that could be applied to the polymer used in this work was 40%. Bending tests carried out for various radii of curvature demonstrated distinct sensor responses for positive and negative curvatures. The graphite nanobelt thin flexible films were successfully tested for acoustic vibration and heartbeat sensing.

  5. Three dimensional flow field measurements of a 4:1 aspect ratio subsonic jet

    SciTech Connect

    Morrison, G.L.; Swan, D.H.

    1989-01-01

    Flow field measurements for a subsonic rectangular cold air jet with an aspect ratio of 4:1 (12.7 x 50.8 mm) at a Mach number of 0.09 and Re of 100,000 have been carried out using a three-dimensional laser Doppler anemometer system. Mean velocity measurements show that the jet width spreads more rapidly along the minor axis than along the major axis. The outward velocities, however, are not significantly different for the two axes, indicating the presence of enhanced mixing along the minor axis. The jet slowly changes from a rectangular jet to a circular jet as the flow progresses downstream. 11 references.

  6. Extreme hydrophobicity and omniphilicity of high-aspect-ratio silicon structures

    NASA Astrophysics Data System (ADS)

    Kwak, Moon Kyu; Park, Cheol Woo; Hwang, Kwang-Il; Park, Choon Man; Jeong, Hoon Eui; Choi, Jun Ho

    2015-03-01

    We present an application of high-aspect-ratio (high-AR) silicon structures (black silicon) with high water repellency and good wettability by oils and solvents. The fabrication of black silicon consists of a deep reactive-ion etching process for extremely-high-AR silicon structures and surface treatment with C4F8 gas. Such high-AR structures were found to be highly resistant against wetting by water, but they also have good wetting characteristics with respect to certain liquids such as ethanol, hexane and mineral oil. To determine the relationship between the AR of nanostructures and wetting selectivity, four different black silicon samples with different pattern heights were used. The static contact angles of various liquid were measured for the analysis of wetting properties of the four black silicon samples. To explore feasible applications, ethanol-water separation was performed as a miniaturized experimental simulation of environmental remediation.

  7. Bio-nanotextured high aspect ratio micropillar arrays for high surface area energy storage devices

    NASA Astrophysics Data System (ADS)

    Chu, S.; Gerasopoulos, K.; Ghodssi, R.

    2015-12-01

    This paper presents fabrication and characterization of bio-nanotextured hierarchical nickel oxide (NiO) supercapacitor electrodes. The hierarchical electrode structure is created through self-assembly of Tobacco mosaic viruses (TMVs) on high aspect-ratio micropillar arrays. Enhanced assembly of the bio-nanoparticles was achieved by increasing TMV solution accessibility into the deep microcavities of the pillar arrays. Electrochemical characterization of the hierarchical NiO supercapacitor electrodes revealed a 25-fold increase in charge capacity compared to a planar NiO, and demonstrated excellent cycle stability over 1500 charge/discharge cycles at 2 mA/cm2. This study leverages the unique bio-nanoscaffolds for small scale energy storage devices through further optimization of the hierarchical structures and wetting techniques for significant improvements in micro/nano scale energy storage devices.

  8. Measurement and simulation of jet mass caused by a high-aspect ratio pertubation

    SciTech Connect

    Keiter, Paul A; Cooley, James; Kyrala, George; Wilson, Doug; Blue, Brent; Edwards, John; Robey, Harry; Spears, Brian

    2009-01-01

    Inertial confinement fusion (ICF) capsule performance can be negatively impacted by the presence of hydrodynamic instabilities. To perform a gas fill on an ICF capsule current plans involve drilling a small hole and inserting a fill tube to inject the gas mixture into the capsule. This introduces a perturbation on the capsule, which can seed hydrodynamic instabilities. The small hole can cause jetting of the shell material into the gas, which might adversely affect the capsule performance. We have performed simulations and experiments to study the hydrodynamic evolution of jets from high-aspect ratio holes, such as the fill tube hole. Although simulations using cold materials over predict the amount of mass in the jet, when a reasonable amount of preheat (< 1 eV) is introduced, the simulations are in better agreement with the experiment.

  9. Mineralization and optical characterization of copper oxide nanoparticles using a high aspect ratio bio-template

    SciTech Connect

    Zaman, Mohammed Shahriar; Haberer, Elaine D.

    2014-10-21

    Organized chains of copper oxide nanoparticles were synthesized, without palladium (Pd) activation, using the M13 filamentous virus as a biological template. The interaction of Cu precursor ions with the negatively charged viral coat proteins were studied with Fourier transform infrared spectroscopy, transmission electron microscopy, and energy dispersive x-ray spectroscopy. Discrete nanoparticles with an average diameter of 4.5 nm and narrow size distribution were closely spaced along the length of the high aspect ratio templates. The synthesized material was identified as a mixture of cubic Cu₂O and monoclinic CuO. UV/Vis absorption measurements were completed and a direct optical band gap of 2.87 eV was determined using Tauc's method. This value was slightly larger than bulk, signaling quantum confinement effects within the templated materials.

  10. Initial performance results for high-aspect ratio gold MEMS deformable mirrors

    NASA Astrophysics Data System (ADS)

    Fernández, Bautista; Kubby, Joel

    2009-02-01

    The fabrication and initial performance results of high-aspect ratio 3-dimensional Micro-Electro-Mechanical System (MEMS) Deformable Mirrors (DM) for Adaptive Optics (AO) will be discussed. The DM systems were fabricated out of gold, and consist of actuators bonded to a continuous face sheet, with different boundary conditions. DM mirror displacements vs. voltage have been measured with a white light interferometer and the corresponding results compared to Finite Element Analysis (FEA) simulations. Interferometer scans of a DM have shown that ~9.4um of stroke can be achieved with low voltage, thus showing that this fabrication process holds promise in the manufacturing of future MEMS DM's for the next generation of extremely large telescopes.

  11. On the symmetry of proper orthogonal decomposition modes of a low-aspect-ratio plate

    NASA Astrophysics Data System (ADS)

    Liang, Zongxian; Dong, Haibo

    2015-06-01

    In this paper, the symmetry property and corresponding virtual force contribution of the proper orthogonal decomposition (POD) modes are numerically investigated for the low-Reynolds number flows passing over a low-aspect-ratio pitching-plunging plate. It is found that the flow and its POD modes have the same reflectional symmetry about the spanwise central plane. However, about the crossflow central plane, the spatio-temporal flow symmetry results in a change of symmetry pattern every two POD modes, which corresponds to odd or even multiples of the vortex shedding frequency. Based on a wake survey method for virtual forces, the POD modes are further classified into two groups, thrust- and lift-producing modes, respectively. Results have also shown that the distinct symmetry properties of these modes can be used to identify the correlation between the wake structure and the hydrodynamic force production.

  12. Transmission electron microscopy specimen preparation perpendicular to the long axis of high aspect ratio features

    SciTech Connect

    Irwin, R. B.; Anciso, A.; Jones, P. J.; Glenn, A. L.; Williams, B. L.; Sridhar, S.; Arshad, S.

    2009-11-15

    A new variation of transmission electron microscopy (TEM) specimen preparation is introduced. By thinning a tall high aspect ratio structure perpendicular to the long dimension (i.e., from the side) rather than from perpendicular to the short dimension (either the top or the bottom), it is possible to obtain a more uniformly thin TEM specimen over the entire long dimension of the structure. This article will describe the rational for this variation in specimen preparation. The necessary modifications of four different specimen preparation methods (in situ lift-out, traditional H-bar, ex situ lift-out, and tripod polishing) will be discussed and images of specimens obtained by both of these first two methods will be shown. Additional potential advantages and other applications of this specimen preparation method will be covered.

  13. Measurement and simulation of jet mass caused by a high-aspect ratio hole perturbation

    SciTech Connect

    Keiter, Paul A; Cooley, James H; Wilson, D C; Kyrala, George A; Blue, Brent E; Edwards, J; Elliott, James B; Robey, H F; Spears, B

    2009-01-01

    Inertial confinement fusion (ICF) capsule performance can be negatively impacted by the presence of hydrodynamic instabilities. To perform a gas fill on an ICF capsule, current plans involve drilling a small hole and inserting a fill tube to inject the gas mixture into the capsule. This introduces a perturbation on the capsule, which can seed hydrodynamic instabilities. The small hole can cause jetting of the shell material into the gas, which might adversely affect the capsule performance. We have performed simulations and experiments to study the hydrodynamic evolution of jets from high-aspect ratio holes, such as the fill tube hole. Although simulations using cold materials overpredict the amount of mass in the jet, when a reasonable amount of preheat (<1 eV) is introduced, the simulations are in better agreement with the experiment.

  14. Ultra-low-loss high-aspect-ratio Si3N4 waveguides.

    PubMed

    Bauters, Jared F; Heck, Martijn J R; John, Demis; Dai, Daoxin; Tien, Ming-Chun; Barton, Jonathon S; Leinse, Arne; Heideman, René G; Blumenthal, Daniel J; Bowers, John E

    2011-02-14

    We characterize an approach to make ultra-low-loss waveguides using stable and reproducible stoichiometric Si3N4 deposited with low-pressure chemical vapor deposition. Using a high-aspect-ratio core geometry, record low losses of 8-9 dB/m for a 0.5 mm bend radius down to 3 dB/m for a 2 mm bend radius are measured with ring resonator and optical frequency domain reflectometry techniques. From a waveguide loss model that agrees well with experimental results, we project that 0.1 dB/m total propagation loss is achievable at a 7 mm bend radius with this approach. PMID:21369138

  15. Highly aligned arrays of high aspect ratio barium titanate nanowires via hydrothermal synthesis

    SciTech Connect

    Bowland, Christopher C.; Zhou, Zhi; Malakooti, Mohammad H.; Sodano, Henry A.

    2015-06-01

    We report on the development of a hydrothermal synthesis procedure that results in the growth of highly aligned arrays of high aspect ratio barium titanate nanowires. Using a multiple step, scalable hydrothermal reaction, a textured titanium dioxide film is deposited on titanium foil upon which highly aligned nanowires are grown via homoepitaxy and converted to barium titanate. Scanning electron microscope images clearly illustrate the effect the textured film has on the degree of orientation of the nanowires. The alignment of nanowires is quantified by calculating the Herman's Orientation Factor, which reveals a 58% improvement in orientation as compared to growth in the absence of the textured film. The ferroelectric properties of barium titanate combined with the development of this scalable growth procedure provide a powerful route towards increasing the efficiency and performance of nanowire-based devices in future real-world applications such as sensing and power harvesting.

  16. Large-area thermoelectric high-aspect-ratio nanostructures by atomic layer deposition

    NASA Astrophysics Data System (ADS)

    Ruoho, Mikko; Juntunen, Taneli; Tittonen, Ilkka

    2016-09-01

    We report on the thermoelectric properties of large-area high-aspect-ratio nanostructures. We fabricate the structures by atomic layer deposition of conformal ZnO thin films on track-etched polycarbonate substrate. The resulting structure consists of ZnO tubules which continue through the full thickness of the substrate. The electrical and thermal properties of the structures are studied both in-plane and out-of-plane. They exhibit very low out-of-plane thermal conductivity down to 0.15 W m‑1 K‑1 while the in-plane sheet resistance of the films was found to be half that of the same film on glass substrate, allowing material-independent doubling of output power of any planar thin-film thermoelectric generator. The wall thickness of the fabricated nanotubes was varied within a range of up to 100 nm. The samples show polycrystalline nature with (002) preferred crystal orientation.

  17. Static Footprint Local Forces, Areas, and Aspect Ratios for Three Type 7 Aircraft Tires

    NASA Technical Reports Server (NTRS)

    Howell, William E.; Perez, Sharon E.; Vogler, William A.

    1991-01-01

    The National Tire Modeling Program (NTMP) is a joint NASA/industry effort to improve the understanding of tire mechanics and develop accurate analytical design tools. This effort includes fundamental analytical and experimental research on the structural mechanics of tires. Footprint local forces, areas, and aspect ratios were measured. Local footprint forces in the vertical, lateral, and drag directions were measured with a special footprint force transducer. Measurements of the local forces in the footprint were obtained by positioning the transducer at specified locations within the footprint and externally loading the tires. Three tires were tested: (1) one representative of those used on the main landing gear of B-737 and DC-9 commercial transport airplanes, (2) a nose landing gear tire for the Space Shuttle Orbiter, and (3) a main landing gear tire for the Space Shuttle Orbiter. Data obtained for various inflation pressures and vertical loads are presented for two aircraft tires. The results are presented in graphical and tabulated forms.

  18. Experimental investigation of high aspect ratio tubular microstructuring of glass by means of picosecond Bessel vortices

    NASA Astrophysics Data System (ADS)

    Jedrkiewicz, Ottavia; Bonanomi, Simone; Selva, Marco; Di Trapani, Paolo

    2015-07-01

    We report on experiments on glass material modification using nondiffractive high-order picosecond pulsed Bessel beams, generated by a spatial light phase modulator and then suitably demagnified. We investigate the possibility to generate in single-shot tubular microstructures across 100-μm-thin borosilicate glass, when a suitable energy range is considered, and we highlight the effect of the unstable propagation regime for very high input energies, leading to a breakup of the tubular microstructure. The micromachined glass samples are observed on their top and bottom surfaces as well as longitudinally along their thickness. For the conical beam geometry used, we observe no internal material modification pattern with pulses in the femtosecond range. A comparison with glass machining by means of a focused ring-shaped beam is also presented. The results highlight the role of the conical energy flux for single-shot smooth high aspect ratio material modification in a regime where nonlinear Kerr effects are absent.

  19. Lift due to thickness for low aspect ratio wings in incompressible flow

    NASA Technical Reports Server (NTRS)

    Dodbele, S. S.; Plotkin, A.

    1985-01-01

    The problem under consideration is a numerical study of the effects of thickness on lift for low aspect ratio wings in steady incompressible inviscid flow at moderate angles of attack. At these angles of attack the flow separates along the leading edge giving rise to a lift substantially higher than that computed by classical attached flow potential theory. The problem is treated as a perturbation expansion in a small thickness parameter. The lifting elements of the flow are modeled using a nonlinear vortex lattice method which replaces the leading and trailing edge vortex sheets by segmented straight vortex filaments. The thickness elements of the flow are modeled with a mean plane source distribution and a modification to the wing boundary conditions. Results are obtained for wings with biconvex and NACA 0012 sections which compare well with available experimental data. The important observation that the effect of thickness is to decrease the lift is made.

  20. High-Aspect-Ratio Nanophotonic Components Fabricated by Cl(2) RIBE

    SciTech Connect

    Zubrzycki, W.J.; Vawter, G.A.; Wendt, J.R.

    1999-07-08

    We describe highly anisotropic reactive ion beam etching of nanophotonic structures in AlGaAs based on the ion beam divergence angle and chamber pressure. The divergence angle is shown to influence the shape of the upper portion of the etch while the chamber pressure controls the shape of the lower portion. This predictable region of parameter space resulted in highly anisotropic nanostructures. Deeply etched distributed Bragg reflectors are etched to an aspect ratio of 8:1 with 100 nm trench widths. The profile of the grating etch is straight with smooth sidewalls, flat bottoms, and squared corners. Two-dimensional photonic crystal post arrays are fabricated with smooth and vertical sidewalls, with structures as small as 180 nm in diameter and 2.0 {micro}m in height.

  1. Effects of ground proximity on a low aspect ratio propulsive wing/canard configuration

    NASA Technical Reports Server (NTRS)

    Stewart, V. R.; Kemmerly, G. T.

    1987-01-01

    The effect of near proximity to the ground are investigated on a low aspect ratio propulsive wing/canard concept at STOL conditions. Data were obtained on a wing/body and wing/body/canard configuration at various heights above the ground, ranging from free air to approximately 1/4 of the mean aerodynamic chord (MAC) above the ground. The data presented and discussed include force and moment coefficients, surface pressure distributions, and downwash angles measured one MAC behind the wing. The test technique, model requirements, and special considerations required for testing these configurations are also discussed. Special model requirements included evenly distributed exit nozzle pressures along four separate nozzles of lengths of one and two feet with only one air supply to the model. Test techniques must recognize and deal with the ground boundary layer as well as the air supply pressure measurement and management.

  2. Mineralization and optical characterization of copper oxide nanoparticles using a high aspect ratio bio-template

    NASA Astrophysics Data System (ADS)

    Zaman, Mohammed Shahriar; Haberer, Elaine D.

    2014-10-01

    Organized chains of copper oxide nanoparticles were synthesized, without palladium (Pd) activation, using the M13 filamentous virus as a biological template. The interaction of Cu precursor ions with the negatively charged viral coat proteins were studied with Fourier transform infrared spectroscopy, transmission electron microscopy, and energy dispersive x-ray spectroscopy. Discrete nanoparticles with an average diameter of 4.5 nm and narrow size distribution were closely spaced along the length of the high aspect ratio templates. The synthesized material was identified as a mixture of cubic Cu2O and monoclinic CuO. UV/Vis absorption measurements were completed and a direct optical band gap of 2.87 eV was determined using Tauc's method. This value was slightly larger than bulk, signaling quantum confinement effects within the templated materials.

  3. Analysis of high-aspect-ratio jet-flap wings of arbitrary geometry

    NASA Technical Reports Server (NTRS)

    Lissaman, P. B. S.

    1973-01-01

    An analytical technique to compute the performance of an arbitrary jet-flapped wing is developed. The solution technique is based on the method of Maskell and Spence in which the well-known lifting-line approach is coupled with an auxiliary equation providing the extra function needed in jet-flap theory. The present method is generalized to handle straight, uncambered wings of arbitrary planform, twist, and blowing (including unsymmetrical cases). An analytical procedure is developed for continuous variations in the above geometric data with special functions to exactly treat discontinuities in any of the geometric and blowing data. A rational theory for the effect of finite wing thickness is introduced as well as simplified concepts of effective aspect ratio for rapid estimation of performance.

  4. Millijoule femtosecond micro-Bessel beams for ultra-high aspect ratio machining.

    PubMed

    Mitra, Sambit; Chanal, Margaux; Clady, Raphaël; Mouskeftaras, Alexandros; Grojo, David

    2015-08-20

    We report on a functional experimental design for Bessel beam generation capable of handling high-energy ultrashort pulses (up to 1.2 mJ per pulse of 50 fs duration). This allows us to deliver intensities exceeding the breakdown threshold for air or any dielectric along controlled micro-filaments with lengths exceeding 4 mm. It represents an unprecedented upscaling in comparison to recent femtosecond Bessel beam micromachining experiments. We produce void microchannels through glass substrates to demonstrate that aspect ratios exceeding 1200∶1 can be achieved by using single high-intensity pulses. This demonstration must lead to new methodologies for deep-drilling and high-speed cutting applications. PMID:26368773

  5. A Study of Micro Injection Molding for High-Aspect-Ratio Optical Fiber Ferrules

    NASA Astrophysics Data System (ADS)

    Lin, Zheng-Guan.; Tseng, Shi-Chang; Wang, James; Su, Yi-Chung

    2004-06-01

    This study focused on manufacture of high-aspect-ratio optical fiber ferrules by micro thermoplastic injection molding technique. In the past, the optical fiber connectors were produced by ceramic powder injection molding and subsequent precision grinding process. In this work, plastic micro injection molding technique was attempted to manufacture net-shaped products at once. Each ferrule has a micro through hole in the center. The hole's diameter is 125±1μm, and its length is 9mm. During micro molding, how to keep the micro core pin at the center becomes a critical issue. In this work, a guiding slide system is introduced to hold the micro pin continuously. And the slide movement was controlled by a spring behind it. Such a guiding system can help reduce mis-alignment of the micro core pin and increase its life time. Taguchi's design of experiment was used to evaluate the effects of processing parameters on final properties. Experimental results reveal that the higher the spring force, the larger the product weight and the lower the shrinkage. In order to obtain better uniformity of diameters at different locations, diameters at three locations were measured. Measured data showed the shrinkage of diameter in the middle is greater than those at two ends. It is because the two ends cooled faster than the center region. This can be improved by applying higher mold temperature or appropriate holding pressure or holding time. The new design concept can be applied in molding micro tubes, especially for the high aspect ratio cases.

  6. Ni-Al2O3 and Ni-Al composite high-aspect-ratio microstructures

    NASA Astrophysics Data System (ADS)

    Wang, Tao; Sorrell, Melford; Kelly, Kevin W.; Ma, Evan

    1998-09-01

    High-aspect-ratio microstructures (HARMs) have a variety of potential applications in heat transfer, fluid mechanics, catalysts and other microelectromechanical systems (MEMS). The aim of this work is to demonstrate the feasibility to fabricate high performance particulate metal-matrix composite and intermetallic micromechanical structures using the LIGA process. Well-defined functionally graded Ni-Al2O3 and Ni-Al high-aspect-ratio microposts were electroformed into lithographically patterned PMMA holes from a nickel sulfamate bath containing submicron alumina and a diluted Watts bath containing microsized aluminum particles, respectively. SEM image analysis showed that the volume fraction of the alumina reached up to around 30% in the Ni-Al2O3 deposit. The Vickers microhardness of these composites is in the range of 418 through 545, which is higher than those of nickel microstructures from a similar particle-free bath and other Ni-based electrodeposits. In the work on Ni-Al electroplating, a newly developed diluted Watts bath was used to codeposit micron-sized aluminum particles. The intermetallic compound Ni3Al was formed by the reaction of nickel matrices and aluminum particles through subsequent annealing at 630 degrees Celsius. WDS and XRD analyses confirmed that the annealed coating is a two-phase (Ni-Ni3Al) composite. The maximum aluminum volume fraction reached 19% at a cathode current density of 12 mA cm-2, and the Vickers microhardness of the as-deposited coatings is in the range 392 - 515 depending on the amount of aluminum incorporated.

  7. Plasma Filaments in Dielectric Barrier Discharges Penetrating into High Aspect Ratio Cracks for Sterilization

    NASA Astrophysics Data System (ADS)

    Babaeva, Natalia Yu.; Kushner, Mark J.

    2012-10-01

    The ability of surface-hugging-plasmas, as produced in dielectric barrier discharges (DBDs), to penetrate into crevices, turn corners and navigate geometrical obstructions, is important in plasma-wound healing and sterilization. In this talk, we discuss results from a computational investigation of the plasma filaments produced in an air DBD and impinging on and penetrating into deep, high aspect ratio cracks in the bottom dielectric. The model used in this work, nonPDPSIM, is a plasma hydrodynamics model in which continuity, momentum and energy equations are solved for charged and neutral species with solution of Poisson's equation for the electric potential, concurrent with radiation transport. A Monte Carlo simulation is used to obtain ion energy distributions (IEDs) to surfaces. Cracks are 1 mm deep and 3 μm to 250 μm wide (aspect ratios of 333 to 4). We found that when impinging onto the cracked dielectric, the plasma filament conformally spreads over the surface. The conductive plasma transfers the applied potential to the opening of the crack. The width of the crack, w, then determines the penetration of the plasma. If w is large compared to the filament, the penetration is surface hugging. If w is commensurate with the filament, the plasma fills the crack. If the Debye length is about w or larger, there is not significant penetration. For the conditions investigated, penetration occurred for w > 5-6 μm. IEDs onto the surfaces of the trenches produce transient pulses of ions with energies >150 eV.

  8. Aspect-ratio dependency of Rayleigh-Bénard convection in box-shaped containers

    NASA Astrophysics Data System (ADS)

    Wagner, Sebastian; Shishkina, Olga

    2013-08-01

    We report on a numerical study of the aspect-ratio dependency of Rayleigh-Bénard convection, using direct numerical simulations. The investigated domains have equal height and width while the aspect ratio Γ of depth per height is varied between 1/10 and 1. The Rayleigh numbers textit {Ra} for this study variate between 105 and 109, while the Prandtl number is textit {Pr} = 0.786. The main focus of the study concerns the dependency of the Nusselt number textit {Nu} and the Reynolds number textit {Re} on textit {Ra} and Γ. It turns out that due to Γ, differences to the cubic case (i.e., Γ = 1) in textit {Nu} of up to 55% and in textit {Re} of up to 97% occur, which decrease for increasing textit {Ra}. In particular for small Γ sudden drops in the textit {Ra}-scaling of textit {Nu} and textit {Re} appear for textit {Ra}≈ 10^6. Further analysis reveals that these correspond to the onset of unsteady motion accompanied by changes in the global flow structure. The latter is investigated by statistical analysis of the heat flux distribution on the bottom and top plates and a decomposition of the instantaneous flow fields into two-dimensional modes. For textit {Ra} slightly above the onset of unsteady motion (i.e., textit {Ra}≈ 10^6) for all considered Γ ⩽ 1/3 a four-roll structure is present, which corresponds to thermal plumes moving vertically through the domain's center. For textit {Ra}ge 10^7, also for small Γ, a single-roll structure is dominant, in agreement with two-dimensional simulations and experiments at larger textit {Ra} and textit {Pr}.

  9. Convection-Enhanced Transport into Open Cavities : Effect of Cavity Aspect Ratio.

    PubMed

    Horner, Marc; Metcalfe, Guy; Ottino, J M

    2015-09-01

    Recirculating fluid regions occur in the human body both naturally and pathologically. Diffusion is commonly considered the predominant mechanism for mass transport into a recirculating flow region. While this may be true for steady flows, one must also consider the possibility of convective fluid exchange when the outer (free stream) flow is transient. In the case of an open cavity, convective exchange occurs via the formation of lobes at the downstream attachment point of the separating streamline. Previous studies revealed the effect of forcing amplitude and frequency on material transport rates into a square cavity (Horner in J Fluid Mech 452:199-229, 2002). This paper summarizes the effect of cavity aspect ratio on exchange rates. The transport process is characterized using both computational fluid dynamics modeling and dye-advection experiments. Lagrangian analysis of the computed flow field reveals the existence of turnstile lobe transport for this class of flows. Experiments show that material exchange rates do not vary linearly as a function of the cavity aspect ratio (A = W/H). Rather, optima are predicted for A ≈ 2 and A ≈ 2.73, with a minimum occurring at A ≈ 2.5. The minimum occurs at the point where the cavity flow structure bifurcates from a single recirculating flow cell into two corner eddies. These results have significant implications for mass transport environments where the geometry of the flow domain evolves with time, such as coronary stents and growing aneurysms. Indeed, device designers may be able to take advantage of the turnstile-lobe transport mechanism to tailor deposition rates near newly implanted medical devices. PMID:26577366

  10. Implications of in-vitro dosimetry on toxicological ranking of low aspect ratio engineered nanomaterials

    PubMed Central

    Pal, Anoop K.; Bello, Dhimiter; Cohen, Joel; Demokritou, Philip

    2016-01-01

    In-vitro high throughput screening platforms based on mechanistic injury pathways are been used for hazard assessment of engineered nanomaterials (ENM). Toxicity screening and other in vitro nanotoxicology assessment efforts in essence compare and rank nanomaterials relative to each other. We hypothesize that this ranking of ENM is susceptible to dispersion and dosimetry protocols, which continue to be poorly standardized. Our objective was to quantitate the impact of dosimetry on toxicity ranking of ENM. A set of eight well-characterized and diverse low aspect ratio ENMs, were utilized. The recently developed at Harvard in-vitro dosimetry platform, which includes preparation of fairly monodispersed suspensions, measurement of the effective density of formed agglomerates in culture media and fate and transport modeling was used for calculating the effective dose delivered to cells as a function of time. Changes in the dose-response relationships between the administered and delivered dose were investigated with two representative endpoints, cell viability and IL-8 production, in the human monocytic THP-1 cells. The slopes of administered/delivered dose-response relationships changed 1:4.94 times and were ENM-dependent. The overall relative ranking of ENM intrinsic toxicity also changed considerably, matching notably better the in vivo inflammation data (R2 0.97 vs. 0.64). This standardized dispersion and dosimetry methodology presented here is generalizable to low aspect ratio ENMs. Our findings further reinforce the need to reanalyze and reinterpret in-vitro ENM hazard ranking data published in the nanotoxicology literature in the light of dispersion and dosimetry considerations (or lack thereof) and to adopt these protocols in future in vitro nanotoxicology testing. PMID:25672815

  11. Effects of spoiler surfaces on the aeroelastic behavior of a low-aspect-ratio rectangular wing

    NASA Technical Reports Server (NTRS)

    Cole, Stanley R.

    1990-01-01

    An experimental research study to determine the effectiveness of spoiler surfaces in suppressing flutter onset for a low-aspect-ratio, rectangular wing was conducted in the Langley Transonic Dynamics Tunnel (TDT). The wing model used in this flutter test consisted of a rigid wing mounted to the wind-tunnel wall by a flexible, rectangular beam. The flexible beam was connected to the wing root and cantilever mounted to the wind-tunnel wall. The wing had a 1.5 aspect ratio based on wing semispan and a NACA 64A010 airfoil shape. The spoiler surfaces consisted of thin, rectangular aluminum plates that were vertically mounted to the wing surface. The spoiler surface geometry and location on the wing surface were varied to determine the effects of these parameters on the classical flutter of the wing model. Subsonically, the experiment showed that spoiler surfaces increased the flutter dynamic pressure with each successive increase in spoiler height or width. This subsonic increase in flutter dynamic pressure was approximately 15 percent for the maximum height spoiler configuration and for the maximum width spoiler configuration. At transonic Mach numbers, the flutter dynamic pressure conditions were increased even more substantially than at subsonic Mach numbers for some of the smaller spoiler surfaces. But greater than a certain spoiler size (in terms of either height or width) the spoilers forced a torsional instability in the transonic regime that was highly Mach number dependent. This detrimental torsional instability was found at dynamic pressures well below the expected flutter conditions. Variations in the spanwise location of the spoiler surfaces on the wing showed little effect on flutter. Flutter analysis was conducted for the basic configuration (clean wing with all spoiler surface mass properties included). The analysis correlated well with the clean wing experimental flutter results.

  12. High-Aspect Ratio Bio-Metallic Nanocomposites for Cellular Interactions

    NASA Astrophysics Data System (ADS)

    Deodhar, Sneha; Huckaby, Justin; Delahoussaye, Miles; DeCoster, Mark A.

    2014-08-01

    We synthesized high aspect ratio composites with biological and metal components. Scanning electron microscopy (SEM) and Transmission Electron Microscopy (TEM) revealed linear morphology and smooth surface texture. SEM, TEM and light microscopy showed that composites have scalable dimensions from nano- to micro-, with diameters as low as 60 nm, lengths exceeding 150 pm, and average aspect ratio of 100. The structures are stable, remaining intact for over one year in dried form and in liquid, and did not aggregate, in contrast to metal nanoparticles such as iron and copper. Many metal nanoparticles are toxic to cells, limiting their use for biological applications. The bio-metallic composites characterized here showed lower toxicity compared to their precursor metal nanoparticles in brain tumor cell cultures. Due to these more biocompatible properties, we tested the ability of the composites to interact with cells. Zeta potential analysis indicated that composites carry a net negative charge (-24.3 ± 2.2 mV), while the starting metal nanoparticles measured (43.3 ± 2.4 mV). We labeled the composites with poly-l-lysine fluorescein isothiocyanate (PLL-FITC), which shifted the potential to 3.5 ± 2.9 mV. It was observed by fluorescence microscopy that composites smaller than cells were internalized by some cells and larger composites remained outside. Cells became fluorescent over time due to leakage of PLL-FITC from the composites which lost fluorescence over time. Higher biocompatibility, low aggregation, and ability to control size distribution of the linear composites may make them ideal vehicles to deliver drugs or other materials to cells, and may be used as a scaffolding material for cells.

  13. Clothing polymer fibers with well-aligned and high-aspect ratio carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Sun, Gengzhi; Zheng, Lianxi; An, Jia; Pan, Yongzheng; Zhou, Jinyuan; Zhan, Zhaoyao; Pang, John H. L.; Chua, Chee Kai; Leong, Kah Fai; Li, Lin

    2013-03-01

    It is believed that the crucial step towards preparation of electrical conductive polymer-carbon nanotube (CNT) composites is dispersing CNTs with a high length-to-diameter aspect ratio in a well-aligned manner. However, this process is extremely challenging when dealing with long and entangled CNTs. Here in this study, a new approach is demonstrated to fabricate conductive polymer-CNT composite fibers without involving any dispersion process. Well-aligned CNT films were firstly drawn from CNT arrays, and then directly coated on polycaprolactone fibers to form polymer-CNT composite fibers. The conductivity of these composite fibers can be as high as 285 S m-1 with only 2.5 wt% CNT loading, and reach 1549 S m-1 when CNT loading is 13.4 wt%. As-prepared composite fibers also exhibit 82% retention of conductivity at a strain of 7%, and have improved mechanical properties.It is believed that the crucial step towards preparation of electrical conductive polymer-carbon nanotube (CNT) composites is dispersing CNTs with a high length-to-diameter aspect ratio in a well-aligned manner. However, this process is extremely challenging when dealing with long and entangled CNTs. Here in this study, a new approach is demonstrated to fabricate conductive polymer-CNT composite fibers without involving any dispersion process. Well-aligned CNT films were firstly drawn from CNT arrays, and then directly coated on polycaprolactone fibers to form polymer-CNT composite fibers. The conductivity of these composite fibers can be as high as 285 S m-1 with only 2.5 wt% CNT loading, and reach 1549 S m-1 when CNT loading is 13.4 wt%. As-prepared composite fibers also exhibit 82% retention of conductivity at a strain of 7%, and have improved mechanical properties. Electronic supplementary information (ESI) available. See DOI: 10.1039/c3nr34208e

  14. A study of high-altitude manned research aircraft employing strut-braced wings of high-aspect-ratio

    NASA Technical Reports Server (NTRS)

    Smith, P. M.; Deyoung, J.; Lovell, W. A.; Price, J. E.; Washburn, G. F.

    1981-01-01

    The effect of increased wing aspect ratio of subsonic aircraft on configurations with and without strut bracing. Results indicate that an optimum cantilever configuration, with a wing aspect ratio of approximately 26, has a 19% improvement in cruise range when compared to a baseline concept with a wing aspect ratio of approximately 10. An optimum strut braced configuration, with a wing aspect ratio of approximately 28, has a 31% improvment in cruise range when compared to the same baseline concept. This improvement is mainly due to the estimated reduction in wing weight resulting from use of lifting struts. All configurations assume the same mission payload and fuel. The drag characteristics of the wings are enhanced with the use of laminar flow airfoils. A method for determining the extent of attainable natural laminar flow, and methods for preliminary structural design and for aerodynamic analysis of wings lifting struts are presented.

  15. Scanning electron microscopy imaging of ultra-high aspect ratio hole features

    NASA Astrophysics Data System (ADS)

    Cepler, Aron J.; Bunday, Benjamin; Thiel, Bradley L.; Villarrubia, John S.

    2012-03-01

    In-line, non-destructive process control metrology of high aspect ratio (HAR) holes and trenches has long been a known gap in metrology. Imaging the bottoms of at-node size contact holes in oxide with aspect rations beyond 10:1 has not yet been demonstrated. Nevertheless, holes and trenches of 30:1, 40:1, or even 60:1 will soon enter production, with these etches being applied to various homogeneous and multi-layer stacks of Si and SiO2. The need comes from Moore's Law and increasing functional density on microchips, on which true 3D memory devices will soon be manufactured. These can take many different forms, but a common building block will be these ultra-HAR etched features. In this work, we show experimental results and simulations from the NIST JMONSEL program to assess the feasibility of measuring such features using both conventional low voltage scanning electron microscopy (SEM) and higher beam energies and low vacuum conditions to ameliorate charging. In our measurements, higher voltage SEM did not improve upon conventional critical dimension (CD)-SEM. Simulations suggest the reason is a failure to overcome a negative oxide potential. Although a signal can in principle be detected from the bottom of contact holes in typical imaging conditions in the CD-SEM, it is likely that it will be very small and possibly below the noise floor.

  16. Inlet distortion generated forced response of a low-aspect-ratio transonic fan

    SciTech Connect

    Manwaring, S.R.; Lorence, C.B.; Wadia, A.R.; Rabe, D.C.

    1997-10-01

    This paper describes a portion of an experimental and computational program (ADLARF), which incorporates, for the first time, measurements of all aspects of the forced response of an airfoil row, i.e., the flow defect, the unsteady pressure loadings, and the vibratory response. The purpose of this portion was to extend the knowledge of the unsteady aerodynamics associated with a low-aspect-ratio transonic fan where the flow defects were generated by inlet distortions. Measurements of screen distortion patterns were obtained with total pressure rakes and casing static pressures. The unsteady pressure loadings on the blade were determined from high response pressure transducers. The resulting blade vibrations were measured with strain gages. The steady flow was analyzed using a three-dimensional Navier-Stokes solver while the unsteady flow was determined with a quasi-three-dimensional linearized Euler solver. Experimental results showed that the distortions had strong vortical, moderate entropic, and weak acoustic parts. The three-dimensional Navier-Stokes analyses showed that the steady flow is predominantly two-dimensional, with radially outward flow existing only in the blade surface boundary layers downstream of shocks and in the aft part of the suction surface. At near resonance conditions, the strain gage data showed blade-to-blade motion variations and thus, linearized unsteady Euler solutions showed poorer agreement with the unsteady loading data than comparisons at off-resonance speeds. Data analysis showed that entropic waves generated unsteady loadings comparable to vortical waves in the blade regions where shocks existed.

  17. Ground Effects on the Longitudinal Characteristics of Two Models with Wings Having Low Aspect Ratio and Pointed Tips

    NASA Technical Reports Server (NTRS)

    Buell, Donald A; Tinling, Bruce E

    1957-01-01

    Wind-tunnel tests were conducted to determine the ground effects on a tailless model with a wing of aspect ratio 2 and infinite taper, and on a tailed model with a triangular wing of aspect ratio 3, with flaps. Control-surface hinge moments were measured on the tailless model. The results are compared with the predictions of the theory of Tani, et al.

  18. High Rayleigh number convection in rectangular enclosures with differentially heated vertical walls and aspect ratios between zero and unity

    NASA Technical Reports Server (NTRS)

    Kassemi, Siavash A.

    1988-01-01

    High Rayleigh number convection in a rectangular cavity with insulated horizontal surfaces and differentially heated vertical walls was analyzed for an arbitrary aspect ratio smaller than or equal to unity. Unlike previous analytical studies, a systematic method of solution based on linearization technique and analytical iteration procedure was developed to obtain approximate closed-form solutions for a wide range of aspect ratios. The predicted velocity and temperature fields are shown to be in excellent agreement with available experimental and numerical data.

  19. An asymptotic theory for the interference of large aspect ratio swept wings and multiple propeller slipstreams

    NASA Technical Reports Server (NTRS)

    Prabhu, R. K.; Liu, C. H.; Tiwari, S. N.

    1985-01-01

    This paper presents an asymptotic method for the analysis of the interference of multiple tractor propeller slipstream with large aspect ratio swept wings. It is assumed that the height of the slipstream is of the order of the wing chord and its spanwise extent is of the order of the wing span. Three different flow regions are identified by employing different stretching transformations. Asymptotic expansions are made in each of the three regions, using the chord to span ratio as the small expansion parameter. The details of the nonuniform flow in the slipstream enter into the wing sectional analysis. In the outer limit, the wing shrinks to a swept lifting line, and the slipstream reduces to a thin sheet of jet carrying the momentum gain from the propeller. The curvature of this jet sheet results in a pressure difference which is represented by a vortex sheet. The governing equations are solved by discretization. Several examples are considered for which experimental data are available. Comparison of the present results with the experimental data as well as other numerical solutions showed generally good agreement.

  20. Electronic transport through side-contacted graphene nanoribbons: effects of overlap, aspect ratio and orientation.

    PubMed

    Krompiewski, S

    2011-11-01

    We numerically calculate the conductance and shot noise Fano factor of graphene nanoribbons (GNRs) side-contacted to metallic leads. A tight-binding model and Landauer's formalism are used in combination with a modified recursion method for Green's functions. The interfaces are modeled as a contact region between an infinite metallic electrode and a segment of the GNR put on top of it. The key question to answer in this study is how the size and orientation of the GNR and the GNR/electrode interface area influence the transport properties. It turns out that in general the transport characteristics depend strongly on overlap, meant as the ratio between the electrode-supported GNR length and the unsupported one. Moreover, a speed of convergence (with the overlap length) depends on both the transport direction and the aspect ratio of the GNR. It is shown that a short overlap interface is often, but not always, advantageous in nanoelectronics. These findings reconcile some seemingly conflicting opinions reported in the literature. PMID:21975438

  1. The wake structure and thrust performance of a rigid low-aspect-ratio pitching panel

    PubMed Central

    BUCHHOLZ, JAMES H. J.; SMITS, ALEXANDER J.

    2009-01-01

    Thrust performance and wake structure were investigated for a rigid rectangular panel pitching about its leading edge in a free stream. For ReC = O(104), thrust coefficient was found to depend primarily on Strouhal number St and the aspect ratio of the panel AR. Propulsive efficiency was sensitive to aspect ratio only for AR less than 0.83; however, the magnitude of the peak efficiency of a given panel with variation in Strouhal number varied inversely with the amplitude to span ratio A/S, while the Strouhal number of optimum efficiency increased with increasing A/S. Peak efficiencies between 9 % and 21 % were measured. Wake structures corresponding to a subset of the thrust measurements were investigated using dye visualization and digital particle image velocimetry. In general, the wakes divided into two oblique jets; however, when operating at or near peak efficiency, the near wake in many cases represented a Kármán vortex street with the signs of the vortices reversed. The three-dimensional structure of the wakes was investigated in detail for AR = 0.54, A/S = 0.31 and ReC = 640. Three distinct wake structures were observed with variation in Strouhal number. For approximately 0.20 < St < 0.25, the main constituent of the wake was a horseshoe vortex shed by the tips and trailing edge of the panel. Streamwise variation in the circulation of the streamwise horseshoe legs was consistent with a spanwise shear layer bridging them. For St > 0.25, a reorganization of some of the spanwise vorticity yielded a bifurcating wake formed by trains of vortex rings connected to the tips of the horseshoes. For St > 0.5, an additional structure formed from a perturbation of the streamwise leg which caused a spanwise expansion. The wake model paradigm established here is robust with variation in Reynolds number and is consistent with structures observed for a wide variety of unsteady flows. Movies are available with the online version of the paper. PMID:19746195

  2. Vortices behavior depending on the aspect ratio of an insect-like flapping wing in hover

    NASA Astrophysics Data System (ADS)

    Han, Jong-Seob; Chang, Jo Won; Cho, Hwan-Kee

    2015-09-01

    Force measurements and digital particle image velocimetry (DPIV) were carried out to reveal the effects of the aspect ratio (AR) of an insect-like flapping wing. A total of seven aspect ratios around that of an insect wing including 1.5, 2, 3, 4, 5, 6, and 8 were taken into account for the same hovering configurations. Time-course forces showed that both lift and drag in the translational phase were maximized in the case of AR = 3, which is the closest ratio to that of a living insect. The chordwise cross-sectional DPIV conclusively showed that the leading-edge vortex (LEV) on the wing of AR = 1.5 remained nearly unchanged in all cross sections. In other AR cases, however, the trailing-edge vortices (TEV) were clearly found with LEVs that lifted off the wing surfaces at the outboard cross sections. In each of these cases, the TEV interrupted the downwash, and the overall flows behind the wing became wakes similar to those found over a blunt body. The near-wake flow structures revealed that the tip vortex gradually entered the inner area from the wing tip as the AR increased. Circulations and downwash distributions showed a stretched LEV and asymmetrically developed tip and root vortices as the AR moved away from AR = 3. These results do not only indicate that the AR effects of a flapping wing are characteristics that are definitely distinctive from those of a typical aircraft, but also briefly imply that maintaining an LEV attachment by employing strong rotational accelerations is not the highest priority when attempting to achieve lift enhancements. Among the tested cases, the wing of AR = 3 had a balanced downwash flux as well as the best aerodynamic performance characteristics, including the maximum lift, reasonable efficiency, and a moderate pitching moment. This indirectly explains why the wings of living flyers adept at hovering have this AR, and it also suggests the appropriate AR for a flapping-type micro-air vehicle.

  3. High aspect ratio AFM Probe processing by helium-ion-beam induced deposition.

    PubMed

    Onishi, Keiko; Guo, Hongxuan; Nagano, Syoko; Fujita, Daisuke

    2014-11-01

    A Scanning Helium Ion Microscope (SHIM) is a high resolution surface observation instrument similar to a Scanning Electron Microscope (SEM) since both instruments employ finely focused particle beams of ions or electrons [1]. The apparent difference is that SHIMs can be used not only for a sub-nanometer scale resolution microscopic research, but also for the applications of very fine fabrication and direct lithography of surfaces at the nanoscale dimensions. On the other hand, atomic force microscope (AFM) is another type of high resolution microscopy which can measure a three-dimensional surface morphology by tracing a fine probe with a sharp tip apex on a specimen's surface.In order to measure highly uneven and concavo-convex surfaces by AFM, the probe of a high aspect ratio with a sharp tip is much more necessary than the probe of a general quadrangular pyramid shape. In this paper we report the manufacture of the probe tip of the high aspect ratio by ion-beam induced gas deposition using a nanoscale helium ion beam of SHIM.Gas of platinum organic compound was injected into the sample surface neighborhood in the vacuum chamber of SHIM. The decomposition of the gas and the precipitation of the involved metal brought up a platinum nano-object in a pillar shape on the normal commercial AFM probe tip. A SHIM system (Carl Zeiss, Orion Plus) equipped with the gas injection system (OmniProbe, OmniGIS) was used for the research. While the vacuum being kept to work, we injected platinum organic compound ((CH3)3(CH3C5H4)Pt) into the sample neighborhood and irradiated the helium ion beam with the shape of a point on the apex of the AFM probe tip. It is found that we can control the length of the Pt nano-pillar by irradiation time of the helium ion beam. The AFM probe which brought up a Pt nano-pillar is shown in Figure 1. It is revealed that a high-aspect-ratio Pt nano-pillar of ∼40nm diameter and up to ∼2000 nm length can be grown. In addition, for possible heating

  4. Preliminary design characteristics of a subsonic business jet concept employing an aspect ratio 25 strut braced wing

    NASA Technical Reports Server (NTRS)

    Turriziani, R. V.; Lovell, W. A.; Martin, G. L.; Price, J. E.; Swanson, E. E.; Washburn, G. F.

    1980-01-01

    The advantages of replacing the conventional wing on a transatlantic business jet with a larger, strut braced wing of aspect ratio 25 were evaluated. The lifting struts reduce both the induced drag and structural weight of the heavier, high aspect ratio wing. Compared to the conventional airplane, the strut braced wing design offers significantly higher lift to drag ratios achieved at higher lift coefficients and, consequently, a combination of lower speeds and higher altitudes. The strut braced wing airplane provides fuel savings with an attendant increase in construction costs.

  5. Selective epitaxial growth of Ge(1 1 0) in trenches using the aspect ratio trapping technique

    NASA Astrophysics Data System (ADS)

    Destefanis, V.; Hartmann, J. M.; Baud, L.; Delaye, V.; Billon, T.

    2010-03-01

    The aim of this study was to assess the efficiency of aspect ratio trapping in improving the crystalline quality of relaxed Ge(1 1 0) layers selectively grown in trenches surrounded by SiO 2. The 400 °C growth of a few hundreds of nanometers thick Ge layers has first been studied on blanket Si(1 1 0) surfaces then in recessed areas of Si(1 1 0) patterned wafers. The influence of 1 min H 2 anneals (in-between 600 and 850 °C) on the surface morphology, crystalline quality and strain state of blanket Ge(1 1 0) layers has notably been quantified. Intermediate annealing temperatures (750 °C) have improved the crystalline quality and increased the macroscopic strain relaxation of those layers, without too high a surface roughening. (1 1 0) Si windows (surrounded by shallow trench isolation) of patterned wafers have then been recessed by ≈300 nm using gaseous HCl, with a definite faceting and a slight roughening of the resulting cavities. Epitaxial lateral overgrowth of Ge has then been implemented in those trenches, followed by 1' H 2 bakes at 750 °C. Chemical mechanical polishing has been used afterwards to get rid of the several hundreds of nm thick Ge layer overflowing on the SiO 2 areas (very reduced dishing and flat Ge(1 1 0) surfaces obtained in the end). The efficiency of aspect ratio trapping in reducing the defect density in those Ge(1 1 0) layers is not obvious. Indeed, some trapping of inclined defects in the SiO 2 sidewalls of narrow Ge(1 1 0) patterns (˜80 nm long) has been evidenced. However, the theoretically unexpected appearance of defects at 90° to the surface (i.e. normal to (1 1 0)) that were consequently not trapped was detrimental to defect density reduction. Those 90° defects may have arisen from interactions of inclined defects with one another. The reduction of the high defect density in relaxed (1 1 0) layers is thus still challenging and requires further investigations.

  6. BisGMA/TEGDMA dental composite containing high aspect-ratio hydroxyapatite nanofibers

    PubMed Central

    Chen, Liang; Yu, Qingsong; Wang, Yong; Li, Hao

    2011-01-01

    Objectives The objectives of this study are to investigate the properties of high aspect-ratio hydroxyapatite (HAP) nanofibers and the reinforcing effect of such fibers on bisphenol A glycidyl methacrylate (BisGMA)/triethylene glycol dimethacrylate (TEGDMA) dental resins (without silica microparticle filler) and dental composites (with silica microparticle filler) with various mass fractions (loading rates). Methods HAP nanofibers were synthesized using a wet-chemical method and characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), and thermal gravimetric analysis (TGA). Biaxial flexural strength (BFS) of the HAP nanofibers reinforced dental resins without any microsized filler and dental composites with silica microparticle filler was tested and analysis of variance (ANOVA) was used for the statistically analysis of acquired data. The morphology of fracture surface of tested dental composite samples was examined by SEM. Results The HAP nanofibers with aspect-ratios of 600 to 800 can be successfully fabricated with a simple wet-chemical method in aqueous solution. Impregnation of small mass fractions of the HAP nanofibers (5 wt% or 10 wt%) into the BisGMA/TEGDMA dental resins or impregnation of small mass fractions of the HAP nanofibers (2 wt% or 3 wt%) into the dental composites can substantially improve the biaxial flexural strength of the resulting dental resins and composites. A percolation threshold of HAP nanofibers, beyond which more nanofibers will no longer further increase the mechanical properties of dental composites containing HAP nanofibers, was observed for the dental composites with or without silica microparticle filler. Our mechanical testing and fractographic analysis indicated that the relatively good dispersion of HAP nanofibers at low mass fraction is the key reason for the significantly improved biaxial flexural strength, while higher mass fraction of HAP nanofibers tends to lead to bundles that cannot effectively

  7. A helium-cooled blanket design of the low aspect ratio reactor

    SciTech Connect

    Wong, C.P.; Baxi, C.B.; Reis, E.E.; Cerbone, R.; Cheng, E.T.

    1998-03-01

    An aggressive low aspect ratio scoping fusion reactor design indicated that a 2 GW(e) reactor can have a major radius as small as 2.9 m resulting in a device with competitive cost of electricity at 49 mill/kWh. One of the technology requirements of this design is a high performance high power density first wall and blanket system. A 15 MPa helium-cooled, V-alloy and stagnant LiPb breeder first wall and blanket design was utilized. Due to the low solubility of tritium in LiPb, there is the concern of tritium migration and the formation of V-hydride. To address these issues, a lithium breeder system with high solubility of tritium has been evaluated. Due to the reduction of blanket energy multiplication to 1.2, to maintain a plant Q of > 4, the major radius of the reactor has to be increased to 3.05 m. The inlet helium coolant temperature is raised to 436 C in order to meet the minimum V-alloy temperature limit everywhere in the first wall and blanket system. To enhance the first wall heat transfer, a swirl tape coolant channel design is used. The corresponding increase in friction factor is also taken into consideration. To reduce the coolant system pressure drop, the helium pressure is increased from 15 to 18 MPa. Thermal structural analysis is performed for a simple tube design. With an inside tube diameter of 1 cm and a wall thickness of 1.5 mm, the lithium breeder can remove an average heat flux and neutron wall loading of 2 and 8 MW/m(2), respectively. This reference design can meet all the temperature and material structural design limits, as well as the coolant velocity limits. Maintaining an outlet coolant temperature of 650 C, one can expect a gross closed cycle gas turbine thermal efficiency of 45%. This study further supports the use of helium coolant for high power density reactor design. When used with the low aspect ratio reactor concept a competitive fusion reactor can be projected at 51.9 mill/kWh.

  8. The effect of area aspect ratio on the yawing moments of rudders at large angles of pitch on three fuselages

    NASA Technical Reports Server (NTRS)

    Dryden, Hugh L; Monish, B H

    1933-01-01

    This reports presents the results of measurements made of yawing moments produced by rudder displacement for seven rudders mounted on each of three fuselages at angles of pitch of 0 degree, 8 degrees, 12 degrees, 20 degrees, 30 degrees and 40 degrees. The dimensions of the rudders were selected to cover the range of areas and aspect ratios commonly used, while the ratios of rudder area to fin area and of rudder chord to fin chord were kept approximately constant. An important result of the measurements is to show that increased aspect ratio gives increased yawing moments for a given area, provided the maximum rudder displacement does not exceed 25 degrees. If large rudder displacements are used, the effect of aspect ratio is not so great.

  9. Effect of aspect ratio on vortex distribution and heat transfer in rotating Rayleigh-Bénard convection

    NASA Astrophysics Data System (ADS)

    Stevens, Richard J. A. M.; Overkamp, Jim; Lohse, Detlef; Clercx, Herman J. H.

    2011-11-01

    Numerical and experimental data for the heat transfer as a function of the Rossby number Ro in turbulent rotating Rayleigh-Bénard convection are presented for the Prandtl number Pr=4.38 and the Rayleigh number Ra=2.91×108 up to Ra=4.52×109. The aspect ratio Γ≡D/L, where L is the height and D the diameter of the cylindrical sample, is varied between Γ=0.5 and 2.0. Without rotation, where the aspect ratio influences the global large-scale circulation, we see a small-aspect-ratio dependence in the Nusselt number for Ra=2.91×108. However, for stronger rotation, i.e., 1/Ro≫1/Roc, the heat transport becomes independent of the aspect ratio. We interpret this finding as follows: In the rotating regime the heat is mainly transported by vertically aligned vortices. Since the vertically aligned vortices are local, the aspect ratio has a negligible effect on the heat transport in the rotating regime. Indeed, a detailed analysis of vortex statistics shows that the fraction of the horizontal area that is covered by vortices is independent of the aspect ratio when 1/Ro≫1/Roc. In agreement with the results of Weiss [Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.105.224501 105, 224501 (2010)], we find a vortex-depleted area close to the sidewall. Here we show that there is also an area with enhanced vortex concentration next to the vortex-depleted edge region and that the absolute widths of both regions are independent of the aspect ratio.

  10. Effect of aspect ratio on vortex distribution and heat transfer in rotating Rayleigh-Bénard convection.

    PubMed

    Stevens, Richard J A M; Overkamp, Jim; Lohse, Detlef; Clercx, Herman J H

    2011-11-01

    Numerical and experimental data for the heat transfer as a function of the Rossby number Ro in turbulent rotating Rayleigh-Bénard convection are presented for the Prandtl number Pr=4.38 and the Rayleigh number Ra=2.91×10(8) up to Ra=4.52×10(9). The aspect ratio Γ≡D/L, where L is the height and D the diameter of the cylindrical sample, is varied between Γ=0.5 and 2.0. Without rotation, where the aspect ratio influences the global large-scale circulation, we see a small-aspect-ratio dependence in the Nusselt number for Ra=2.91×10(8). However, for stronger rotation, i.e., 1/Ro>1/Ro(c), the heat transport becomes independent of the aspect ratio. We interpret this finding as follows: In the rotating regime the heat is mainly transported by vertically aligned vortices. Since the vertically aligned vortices are local, the aspect ratio has a negligible effect on the heat transport in the rotating regime. Indeed, a detailed analysis of vortex statistics shows that the fraction of the horizontal area that is covered by vortices is independent of the aspect ratio when 1/Ro>1/Ro(c). In agreement with the results of Weiss et al. [Phys. Rev. Lett. 105, 224501 (2010)], we find a vortex-depleted area close to the sidewall. Here we show that there is also an area with enhanced vortex concentration next to the vortex-depleted edge region and that the absolute widths of both regions are independent of the aspect ratio. PMID:22181504

  11. Long-range forces affecting equilibrium inertial focusing behavior in straight high aspect ratio microfluidic channels

    NASA Astrophysics Data System (ADS)

    Reece, Amy E.; Oakey, John

    2016-04-01

    The controlled and directed focusing of particles within flowing fluids is a problem of fundamental and technological significance. Microfluidic inertial focusing provides passive and precise lateral and longitudinal alignment of small particles without the need for external actuation or sheath fluid. The benefits of inertial focusing have quickly enabled the development of miniaturized flow cytometers, size-selective sorting devices, and other high-throughput particle screening tools. Straight channel inertial focusing device design requires knowledge of fluid properties and particle-channel size ratio. Equilibrium behavior of inertially focused particles has been extensively characterized and the constitutive phenomena described by scaling relationships for straight channels of square and rectangular cross section. In concentrated particle suspensions, however, long-range hydrodynamic repulsions give rise to complex particle ordering that, while interesting and potentially useful, can also dramatically diminish the technique's effectiveness for high-throughput particle handling applications. We have empirically investigated particle focusing behavior within channels of increasing aspect ratio and have identified three scaling regimes that produce varying degrees of geometrical ordering between focused particles. To explore the limits of inertial particle focusing and identify the origins of these long-range interparticle forces, we have explored equilibrium focusing behavior as a function of channel geometry and particle concentration. Experimental results for highly concentrated particle solutions identify equilibrium thresholds for focusing that scale weakly with concentration and strongly with channel geometry. Balancing geometry mediated inertial forces with estimates for interparticle repulsive forces now provide a complete picture of pattern formation among concentrated inertially focused particles and enhance our understanding of the fundamental limits of

  12. Formation and sustainment of a very low aspect ratio tokamak using coaxial helicity injection (the Helicity Injected Torus (HIT) experiment)

    SciTech Connect

    Jarboe, T.R.; Nelson, B.A.

    1992-01-01

    In the paper we will detail the progress of the HIT experiment construction, including the following components: preliminary data and interpretation; diagnostic systems; vacuum vessel and pumping system; helicity source and power supplies; toroidal field coil and power supply; data acquisition system; collaboration with general atomics, with a brief summary given on each.

  13. Microwave dynamics of high aspect ratio superconducting nanowires studied using self-resonance

    NASA Astrophysics Data System (ADS)

    Santavicca, Daniel F.; Adams, Jesse K.; Grant, Lierd E.; McCaughan, Adam N.; Berggren, Karl K.

    2016-06-01

    We study the microwave impedance of extremely high aspect ratio (length/width ≈ 5000) superconducting niobium nitride nanowires. The nanowires are fabricated in a compact meander geometry that is in series with the center conductor of a 50 Ω coplanar waveguide transmission line. The transmission coefficient of the sample is measured up to 20 GHz. At high frequency, a peak in the transmission coefficient is seen. Numerical simulations show that this is a half-wave resonance along the length of the nanowire, where the nanowire acts as a high impedance, slow wave transmission line. This resonance sets the upper frequency limit for these nanowires as inductive elements. Fitting simulations to the measured resonance enables a precise determination of the nanowire's complex sheet impedance at the resonance frequency. The real part is a measure of dissipation, while the imaginary part is dominated by kinetic inductance. We characterize the dependence of the sheet resistance and sheet inductance on both temperature and current and compare the results to recent theoretical predictions for disordered superconductors. These results can aid in the understanding of high frequency devices based on superconducting nanowires. They may also lead to the development of novel superconducting devices such as ultra-compact resonators and slow-wave structures.

  14. Flow development over low aspect ratio cantilevered circular cylinders in the laminar shedding regime

    NASA Astrophysics Data System (ADS)

    Morton, Chris; Saeedi, Mohammad; Martinuzzi, Robert

    2015-11-01

    The flow development over a cantilevered circular cylinder of aspect ratio 4 at Re = 300 has been investigated numerically by employing a laminar flow solution to the Navier-Stokes equations. The results show that two distinct wake modulation frequencies are detectable downstream of the cylinder, differing from higher Reynolds number turbulent flow cases where only one dominant frequency is present. In particular, there is a low frequency modulation with a well-defined narrow-band peak (fm) , and a high frequency contribution from the shedding of vortices (fv) . The fluctuating loading on the cylinder in the streamwise direction is tightly coupled with the low frequency modulation, while the transverse direction forces show only a weak correlation with the vortex shedding frequency. Coherent flow structures have been analyzed using proper orthogonal decomposition (POD) to provide insight into the nature of vortex formation and associated coupling with the detected low frequency modulation. The temporal coefficients obtained from the POD analysis have been used to construct a low order model for the investigation of the overall flow development. While the high frequency component is known to be related to the formation and shedding of vortices, the low frequency component is shown to be associated with a modulation in upwash and downwash intensity.

  15. Mixing characteristics of a moderate aspect ratio screeching supersonic rectangular jet

    NASA Astrophysics Data System (ADS)

    Valentich, Griffin; Upadhyay, Puja; Kumar, Rajan

    2016-05-01

    Flow field characteristics of a moderate aspect ratio supersonic rectangular jet were examined at two overexpanded, a perfectly expanded, and an underexpanded jet conditions. The underexpanded and one overexpanded operating condition were of maximum screech, while the second overexpanded condition was of minimum screech intensity. Streamwise particle image velocimetry was performed along both major and minor axes of the jet and the measurements were made up to 30 nozzle heights, h, where h is the small dimension of the nozzle. Select cross planes were examined using stereoscopic particle image velocimetry to investigate the jet development and the role streamwise vortices play in jet spreading at each operating condition. The results show that streamwise vortices present at the nozzle corners along with vortices excited by screech tones play a major role in the jet evolution. All cases except for the perfectly expanded operating condition exhibited axis switching at streamwise locations ranging from 11 to 16 nozzle heights downstream of the exit. The overexpanded condition of maximum screech showed the most upstream switch over, while the underexpanded case showed the farthest downstream. Both of the maximum screeching cases developed into a diamond cross-sectional profile far downstream of the exit, while the ideally expanded case maintained a rectangular shape. The overexpanded minimum screeching case eventually decayed into an oblong profile.

  16. H-mode Characterization and Edge Stability at Near-Unity Aspect Ratio in PEGASUS Discharges

    NASA Astrophysics Data System (ADS)

    Thome, K. E.; Barr, J. L.; Bongard, M. W.; Burke, M. G.; Fonck, R. J.; Peguero, L. M.; Perry, J. M.; Schlossberg, D. J.; Thompson, D. S.

    2013-10-01

    Unique features of operating at near-unity aspect ratio include: ready access to Ohmic H-mode; operation in the low collisionality regime with strong neoclassical effects; and ELM instabilities driven by peeling and peeling- ballooning modes. Ohmic H-mode is achieved in both limited and diverted configurations by using high-field-side fueling. The access to and characteristics of H-mode regimes as well as various ELM types in PEGASUS is currently being explored. Characteristics of the L-H transition are: formation of an edge current pedestal; reversal of the direction of toroidal flow at the transition; doubling of the stored energy; and the presence of ELMs. Modest temperatures and pulse lengths in PEGASUS allow the use of insertable probes to measure the properties of the edge plasma with high spatial and temporal resolution, even in ELMy H-mode. A current pedestal in the edge J (R , t) profile is observed in H-mode but not in L-mode operation. This pedestal is destroyed during an ELM event cycle, but returns quickly after the ELM. Peeling modes, identified in the edge of L-mode plasmas with strong edge current, drive the formation of an edge current hole and ejection of a current-carrying filament consistent with electromagnetic blob theory. Similar behavior is indicated with ELMs in H-mode plasmas. Work supported by US DOE Grant DE-FG02-96ER54375.

  17. Plasma Characteristics and High-Beta Operation at Near-Unity Aspect Ratio

    NASA Astrophysics Data System (ADS)

    Thorson, T. A.

    2000-10-01

    Research on PEGASUS presently focuses on exploring the extremely low aspect ratio regime of operation (A<1.2) at low toroidal field with ohmic heating. Plasmas are typically created with A = 1.1-1.4 at Bt <= 0.07 T. Relatively high current ramp rates (typically 15-45 MA/s) and high elongation (between 1.5-4) are associated with these low A plasmas. Magnetic equilibrium reconstructions of plasmas at lower toroidal fields (down to Bt = 0.04 T) indicate high normalized currents (>5), normalized beta (>4), and toroidal beta (>20%). These high beta cases are consistent with temperature estimates from spectroscopy, the high densities (up to 10^20 m-3) observed with interferometry, and estimates from confinement models using scalings that best described START results (ITER98pby1). Present experiments are focusing on determining the minimum q required for stability as a function of shape (elongation, A) and beta. In this regime, ohmic plasmas may also challenge beta limits. Beta limit studies will be expanded to both low and high q plasmas with the advent of the 2 MW HHFW heating system.

  18. Self-consistent Equilibrium Model of Low-aspect-ratio Toroidal Plasma with Energetic Beam Ions

    SciTech Connect

    E.V. Belova; N.N. Gorelenkov; C.Z. Cheng

    2003-04-09

    A theoretical model is developed which allows the self-consistent inclusion of the effects of energetic beam ions in equilibrium calculations of low-aspect-ratio toroidal devices. A two-component plasma is considered, where the energetic ions are treated using a kinetic Vlasov description, while a one-fluid magnetohydrodynamic description is used to represent the thermal plasma. The model allows for an anisotropic distribution function and a large Larmor radius of the beam ions. Numerical results are obtained for neutral-beam-heated plasmas in the National Spherical Torus Experiment (NSTX). Self-consistent equilibria with an anisotropic fast-ion distribution have been calculated for NSTX. It is shown for typical experimental parameters that the contribution of the energetic neutral-beam ions to the total current can be comparable to that of the background plasma, and that the kinetic modifications of the equilibrium can be significant. The range of validity of the finite-Larmor-radius expansion and of the reduced kinetic descriptions for the beam ions in NSTX is discussed. The calculated kinetic equilibria can be used for self-consistent numerical studies of beam-ion-driven instabilities in NSTX.

  19. Numerical investigation of flow on NACA4412 aerofoil with different aspect ratios

    NASA Astrophysics Data System (ADS)

    Demir, Hacımurat; Özden, Mustafa; Genç, Mustafa Serdar; Çağdaş, Mücahit

    2016-03-01

    In this study, the flow over NACA4412 was investigated both numerically and experimentally at a different Reynolds numbers. The experiments were carried out in a low speed wind tunnel with various angles of attack and different Reynolds numbers (25000 and 50000). Airfoil was manufactured using 3D printer with a various aspect ratios (AR = 1 and AR = 3). Smoke-wire and oil flow visualization methods were used to visualize the surface flow patterns. NACA4412 aerofoil was designed by using SOLIDWORKS. The structural grid of numerical model was constructed by ANSYS ICEM CFD meshing software. Furthermore, ANSYS FLUENT™ software was used to perform numerical calculations. The numerical results were compared with experimental results. Bubble formation was shown in CFD streamlines and smoke-wire experiments at z / c = 0.4. Furthermore, bubble shrunk at z / c = 0.2 by reason of the effects of tip vortices in both numerical and experimental studies. Consequently, it was seen that there was a good agreement between numerical and experimental results.

  20. Proposal for a risk banding framework for inhaled low aspect ratio nanoparticles based on physicochemical properties.

    PubMed

    Oosterwijk, Mattheus T T; Feber, Maaike Le; Burello, Enrico

    2016-08-01

    We present a conceptual framework that can be used to assign risk bands to inhaled low aspect ratio nanoparticles starting from exposure bands assigned to a specific exposure situation. The framework mimics a basic physiological scheme that captures the essential mechanisms of fate and toxicity of inhaled nanoparticles and is composed of several models and rules that estimate the result of the following processes: the deposition of particles in the respiratory tract, their (de-)agglomeration, lung burden and clearance, their diffusion through the lung mucus layer, translocation and cellular uptake and local and systemic toxicity. Each model is based on a set of particle's physicochemical properties, including the size and size distribution(s), the zeta potential (or net charge at a specific pH), the surface hydrophobicity or hydrophilicity, the conduction band energy (for metals, metal oxides, quantum dots, etc.) and the solubility at a specific pH. The framework takes the exposure bands as input and predicts, using the above-mentioned models, an internal dose band (module 1). Module 2 assigns a relative hazard ranking depending on the region of particle deposition in the respiratory tract, the likelihood of uptake and whether the toxicological effects are assumed to be local and/or systemic. By combining the results of Module 1 and 2, the framework provides a relative risk ranking. PMID:26763369

  1. Investigation of a wind tunnel model high aspect ratio wing fracture

    SciTech Connect

    Gutierrez, W.T.; Tate, R.E.; Fell, H.P.

    1994-06-01

    A preliminary design and feasibility analysis on the aerodynamic performance characteristics of an experimental flight vehicle was conducted by Sandia National Laboratories. During a routine force and moment, static wind tunnel test in a blow down facility, one section of the high aspect ratio wing fractured outboard of the critical static stress location. Initially, a combination of material and aeroelastic analyses provided insight into the problem, but eventually proved inconclusive. After returning to the wind tunnel with a near identical model, instrumented with strain gages and accelerometers, and viewed with high speed video, the definitive mode of failure was discovered. It was determined that the first torsional mode of the wing was excited over a discrete angle of attack band, over the tested Mach number range of 0.5--0.9. Major flow separation on the airfoil occurred at the same time that flutter initiated, and was repeatable with a smaller scale model (geometrically similar, but 22% scale relative to the larger model) tested in a smaller test section wind tunnel. Data acquired during the stall flutter confirmed stress levels and numbers of cycles worked consistent with low cycle fatigue.

  2. Stamping High-Aspect-Ratio Plasmonic Nanoarrays on SERS-Supporting Platforms

    SciTech Connect

    Bhandari, Deepak; Wells, Sabrina M; Polemi, Alessia; Kravchenko, Ivan I; Shuford, Kevin L; Sepaniak, Michael J

    2011-01-01

    The dielectric property of a nanoparticle-supporting film has recently garnered attention in the fabrication of plasmonic surfaces. A few studies have shown that localized surface plasmon resonance (LSPR), and hence SERS, strongly depends on substrate refractive index. In order to create higher efficiency SERS-active surfaces, it is therefore necessary to consider substrate property along with nanoparticle morphology. However, due to certain limitations of conventional lithography, it is often not feasible to create well-defined plasmonic nanoarrays on a substrate of interest. Herein, an additive nanofabrication technique, nanotransfer printing (nTP), is implemented to integrate electron beam lithography (EBL) defined high-aspect-ratio nanofeatures on a variety of SERS-supporting surfaces. With the aid of suitable surface chemistries, a wide range of plasmonic particles were successfully integrated on surfaces of three physically and chemically distinct dielectric materials, viz Polydimethyl siloxane (PDMS), SU-8 photoresist, and glass surfaces, using silicon-based relief pillars. These nTP created metal nanoparticles strongly amplify Raman signal and complement the selection of suitable substrates for better SERS enhancement. Our experimental observations are also supported by the theoretical calculations. The implementation of nTP to stamp out metal nanoparticles on multitude conventional/unconventional substrates has novel applications in designing in-built plasmonic microanalytical devices for SERS sensing and other related photonic studies.

  3. Parallel Operation of Multiple Closely Spaced Small Aspect Ratio Rod Pinches

    DOE PAGESBeta

    Harper-Slaboszewicz, Victor J.; Leckbee, Joshua; Bennett, Nichelle; Madrid, Elizabeth A.; Rose, David V.; Thoma, Carsten; Welch, Dale R.; Lake, Patrick W.; McCourt, Andrew L.

    2014-12-10

    A series of simulations and experiments to resolve questions about the operation of arrays of closely spaced small aspect ratio rod pinches has been performed. Design and post-shot analysis of the experimental results are supported by 3D particle-in-cell simulations. Both simulations and experiments support these conclusions. Penetration of current to the interior of the array appears to be efficient, as the current on the center rods is essentially equal to the current on the outer rods. Current loss in the feed due to the formation of magnetic nulls was avoided in these experiments by design of the feed surface ofmore » the cathode and control of the gap to keep the electric fields on the cathode below the emission threshold. Some asymmetry in the electron flow to the rod was observed, but the flow appeared to symmetrize as it reached the end of the rod. Interaction between the rod pinches can be controlled to allow the stable and consistent operation of arrays of rod pinches.« less

  4. Hummingbird wing efficacy depends on aspect ratio and compares with helicopter rotors

    PubMed Central

    Kruyt, Jan W.; Quicazán-Rubio, Elsa M.; van Heijst, GertJan F.; Altshuler, Douglas L.; Lentink, David

    2014-01-01

    Hummingbirds are the only birds that can sustain hovering. This unique flight behaviour comes, however, at high energetic cost. Based on helicopter and aeroplane design theory, we expect that hummingbird wing aspect ratio (AR), which ranges from about 3.0 to 4.5, determines aerodynamic efficacy. Previous quasi-steady experiments with a wing spinner set-up provide no support for this prediction. To test this more carefully, we compare the quasi-steady hover performance of 26 wings, from 12 hummingbird taxa. We spun the wings at angular velocities and angles of attack that are representative for every species and measured lift and torque more precisely. The power (aerodynamic torque × angular velocity) required to lift weight depends on aerodynamic efficacy, which is measured by the power factor. Our comparative analysis shows that AR has a modest influence on lift and drag forces, as reported earlier, but interspecific differences in power factor are large. During the downstroke, the power required to hover decreases for larger AR wings at the angles of attack at which hummingbirds flap their wings (p < 0.05). Quantitative flow visualization demonstrates that variation in hover power among hummingbird wings is driven by similar stable leading edge vortices that delay stall during the down- and upstroke. A side-by-side aerodynamic performance comparison of hummingbird wings and an advanced micro helicopter rotor shows that they are remarkably similar. PMID:25079868

  5. Cellulosic fibers with high aspect ratio from cornhusks via controlled swelling and alkaline penetration.

    PubMed

    Ma, Zhuanzhuan; Pan, Gangwei; Xu, Helan; Huang, Yiling; Yang, Yiqi

    2015-06-25

    Cellulosic fibers with high aspect ratio have been firstly obtained from cornhusks via controlled swelling in organic solvent and simultaneous tetramethylammonium hydroxide (TMAOH) post treatment within restricted depth. Cornhusks, with around 42% cellulose content, are a copious and inexpensive source for natural fibers. However, cornhusk fibers at 20tex obtained via small-molecule alkaline extraction were too coarse for textile applications. Continuous NaOH treatment would result in fine fibers but with length of about 0.5-1.5mm, too short for textile use. In this research, post treatment using TMAOH and under controlled swelling significantly reduced fineness of cornhusk fibers from 21.3±2.88 to 5.72±0.21tex. Fiber length was reduced from 105.47±10.03 to47.2±27.4mm. The cornhusk fibers had more oriented microstructures and cellulose content increased to 84.47%. Besides, cornhusk fibers had similar tenacity, longer elongation, and lower modulus compared to cotton and linen, which endowed them with durability and flexibility. PMID:25839793

  6. Generation of Scalable, Metallic High-Aspect Ratio Nanocomposites in a Biological Liquid Medium.

    PubMed

    Cotton Kelly, Kinsey; Wasserman, Jessica R; Deodhar, Sneha; Huckaby, Justin; DeCoster, Mark A

    2015-01-01

    The goal of this protocol is to describe the synthesis of two novel biocomposites with high-aspect ratio structures. The biocomposites consist of copper and cystine, with either copper nanoparticles (CNPs) or copper sulfate contributing the metallic component. Synthesis is carried out in liquid under biological conditions (37 °C) and the self-assembled composites form after 24 hr. Once formed, these composites are highly stable in both liquid media and in a dried form. The composites scale from the nano- to micro- range in length, and from a few microns to 25 nm in diameter. Field emission scanning electron microscopy with energy dispersive X-ray spectroscopy (EDX) demonstrated that sulfur was present in the NP-derived linear structures, while it was absent from the starting CNP material, thus confirming cystine as the source of sulfur in the final nanocomposites. During synthesis of these linear nano- and micro-composites, a diverse range of lengths of structures is formed in the synthesis vessel. Sonication of the liquid mixture after synthesis was demonstrated to assist in controlling average size of the structures by diminishing the average length with increased time of sonication. Since the formed structures are highly stable, do not agglomerate, and are formed in liquid phase, centrifugation may also be used to assist in concentrating and segregating formed composites. PMID:26274773

  7. Relationship between the consolidation parameter, porosity and aspect ratio in microporous carbonate rocks

    NASA Astrophysics Data System (ADS)

    de Ceia, Marco A. R.; Misságia, Roseane M.; Neto, Irineu Lima; Archilha, Nathaly

    2015-11-01

    The estimation of dry bulk modulus is required for the successful application of the Biot-Gassmann theory to forecast fluid changes within a reservoir. The Pride model is one of the several models described in the literature for predicting the dry elastic moduli of rocks. However, the accuracy of the Pride model depends on the estimation of the consolidation parameter. In this paper, the consolidation parameter was estimated using the pore stiffness, mineral bulk modulus and porosity. That approach allowed calculating the dry bulk modulus of a set of microporous carbonate rocks according to the Pride model and compare those estimates to the results obtained using the elastic velocities. The change in the consolidation parameter over a range of pressures suggests that the relationship between this parameter and the unconfined porosity increases at high effective pressure. Statistical analyses of the distribution of those consolidation parameter values were performed to verify how the effective pressure influences the mean value and variance. Mean pore aspect ratios were estimated using Kuster-Toksoz methodology to establish a relationship with the consolidation parameter and the unconfined porosity. Such relationship also accounts for pressure-dependence within the studied pressure range. Although only 20 samples were analyzed, those studies can contribute to advise the estimation of the consolidation parameter in this type of carbonate rocks.

  8. Universal scaling law for the aspect ratio of a pancake vortex in a rotating stratified medium

    NASA Astrophysics Data System (ADS)

    Aubert, Oriane; Le Bars, Michael; Le Gal, Patrice; Marcus, Philip S.

    2010-11-01

    The Great Red Spot of Jupiter and the meddies in the Atlantic Ocean are the most famous and puzzling examples of long-lived pancake like anticyclones that take place in a rotating and stably stratified medium. To reproduce and study these vortices in the laboratory, we inject a volume of isodensity dyed fluid in a rotating linearly stratified layer of salt water. Due to the Coriolis force, the injected fluid rapidly forms a pancake vortex whose long term evolution is quantified using PIV measurements and image processing. Three different phases take place: a fast geostrophic adjustment, an axisymmetrization by viscous coupling with the outside and finally a very slow decrease of the motion while preserving the self-similar shape of the vortex. This last regime can be described using a simplified system of equations based on a geostrophic equilibrium, where the energy source maintaining the long-lived vortex is the density anomaly with the outside: the vortex persists as long as the density anomaly remains, maintained by internal recirculations. The non-diffusive version of the equations gives an analytical solution for the self-similar shape of the vortex and the evolution law for the aspect ratio for small Rossby numbers. These theoretical predictions are verified experimentally and also agree with published measurements for the meddies and Jupiter's Great Red Spot.

  9. Adaptive AFM scan speed control for high aspect ratio fast structure tracking

    SciTech Connect

    Ahmad, Ahmad; Schuh, Andreas; Rangelow, Ivo W.

    2014-10-15

    Improved imaging rates in Atomic Force Microscopes (AFM) are of high interest for disciplines such as life sciences and failure analysis of semiconductor wafers, where the sample topology shows high aspect ratios. Also, fast imaging is necessary to cover a large surface under investigation in reasonable times. Since AFMs are composed of mechanical components, they are associated with comparably low resonance frequencies that undermine the effort to increase the acquisition rates. In particular, high and steep structures are difficult to follow, which causes the cantilever to temporarily loose contact to or crash into the sample. Here, we report on a novel approach that does not affect the scanner dynamics, but adapts the lateral scanning speed of the scanner. The controller monitors the control error signal and, only when necessary, decreases the scan speed to allow the z-piezo more time to react to changes in the sample's topography. In this case, the overall imaging rate can be significantly increased, because a general scan speed trade-off decision is not needed and smooth areas are scanned fast. In contrast to methods trying to increase the z-piezo bandwidth, our method is a comparably simple approach that can be easily adapted to standard systems.

  10. Fabrication and characterization of large arrays of mesoscopic gold rings on large-aspect-ratio cantilevers

    SciTech Connect

    Ngo, D. Q.; Petković, I. Lollo, A.; Castellanos-Beltran, M. A.; Harris, J. G. E.

    2014-10-15

    We have fabricated large arrays of mesoscopic metal rings on ultrasensitive cantilevers. The arrays are defined by electron beam lithography and contain up to 10{sup 5} rings. The rings have a circumference of 1 μm, and are made of ultrapure (6N) Au that is deposited onto a silicon-on-insulator wafer without an adhesion layer. Subsequent processing of the SOI wafer results in each array being supported at the end of a free-standing cantilever. To accommodate the large arrays while maintaining a low spring constant, the cantilevers are nearly 1 mm in both lateral dimensions and 100 nm thick. The extreme aspect ratio of the cantilevers, the large array size, and the absence of a sticking layer are intended to enable measurements of the rings' average persistent current in the presence of relatively small magnetic fields. We describe the motivation for these measurements, the fabrication of the devices, and the characterization of the cantilevers' mechanical properties. We also discuss the devices' expected performance in measurements of .

  11. Strong-Field Emission From High Aspect Ratio Si Emitter Arrays

    NASA Astrophysics Data System (ADS)

    Keathley, Phillip; Swanwick, Michael; Sell, Alexander; Putnam, William; Guerrera, Stephen; Velásquez-García, Luis; Kärtner, Franz

    2013-03-01

    We discuss photoelectron emission from an arrays of high aspect ratio, sharp Si emitters both experimentally and theoretically. The structures are prepared from highly doped single-crystal silicon having a pencil-like shape with end radii of curvature of around 10 nm. The tips were illuminated at a grazing incidence of roughly 84deg.with a laser pulse having a center wavelength of 800 nm, and a pulse duration of 35 fs from a regenerative amplifier system. Native oxide coated Si tips were characterized using a time of flight (TOF) electron energy spectrometer. An annealing process was observed, resulting in a red shift of the energy spectra along with an increased electron yield. Total current yield from samples having the oxide stripped were also studied. Apeak total emission of 0.68 pC/bunch, corresponding to around 1.5x103 electrons/tip/pulse was observed at a DC bias of 70 V. Both spectral and current characterization results are consistent with a stong-field photoemission process at the surface of the tip apex. This work was funded by Defense Advanced Research Projects Agency (DARPA)/Microsystems Technology Office and the Space and Naval Warfare Systems Center (SPAWAR) under contract N66001-11-1-4192.

  12. Core/Shell and High Aspect Ratio Magnetic Oxide Nanoparticles for Antenna Applications

    NASA Astrophysics Data System (ADS)

    Ekiert, Thomas F., Jr.; O'Malley, Matthew; Yocum, Brandon; Lippold, Jennifer; Lyle, Mallory; Griner, Angela; Flynn, Cory; Nickel, Anna; Alexander, Max D., Jr.

    2012-02-01

    Improved antenna gain, reduced antenna aperture size, and improved bandwidth are of interest to an increasingly mobile world. To obtain these improvements our efforts are directed at developing new magnetic oxide nanoparticle/polymer composites with modifiable permeability and permittivity and low electrical losses. Our approach consists of producing core/shell and shape controlled magnetic nanoparticles. Methods of synthesis utilize microwave and traditional heating to perform hydrothermal and solvothermal reactions. Decomposition of metal acetylacetonates is performed using various alcohols resulting in spherical nanoparticles with diameters of 8-16 nm and 3-7 nm for Fe3O4 and CoFe2O4, respectively. Microwave methods result in similar particles, but are produced in an hour or less as compared to 48 hrs via the traditional solvothermal method. Successive growths are used to produce larger monolithic particles as well as core/shell systems where exchange coupling between the core and shell is observed. Hexaferrite particles have been produced via hydrothermal synthesis, while high aspect ratio Fe3O4 nanoparticles ( 10-100 nm) produced via hydrothermal synthesis result in nanoneedles with high μr.

  13. Fabrication and characterization of large arrays of mesoscopic gold rings on large-aspect-ratio cantilevers.

    PubMed

    Ngo, D Q; Petković, I; Lollo, A; Castellanos-Beltran, M A; Harris, J G E

    2014-10-01

    We have fabricated large arrays of mesoscopic metal rings on ultrasensitive cantilevers. The arrays are defined by electron beam lithography and contain up to 10(5) rings. The rings have a circumference of 1 μm, and are made of ultrapure (6N) Au that is deposited onto a silicon-on-insulator wafer without an adhesion layer. Subsequent processing of the SOI wafer results in each array being supported at the end of a free-standing cantilever. To accommodate the large arrays while maintaining a low spring constant, the cantilevers are nearly 1 mm in both lateral dimensions and 100 nm thick. The extreme aspect ratio of the cantilevers, the large array size, and the absence of a sticking layer are intended to enable measurements of the rings' average persistent current ⟨I⟩ in the presence of relatively small magnetic fields. We describe the motivation for these measurements, the fabrication of the devices, and the characterization of the cantilevers' mechanical properties. We also discuss the devices' expected performance in measurements of ⟨I⟩. PMID:25362443

  14. Leading-edge vortex burst on a low-aspect-ratio rotating flat plate

    NASA Astrophysics Data System (ADS)

    Medina, Albert; Jones, Anya R.

    2016-08-01

    This study experimentally investigates the phenomenon of leading-edge-vortex burst on rotating flat plate wings. An aspect-ratio-2 wing was driven in pure rotation at a Reynolds number of Re=2500 . Of primary interest is the evolution of the leading-edge vortex along the wing span over a single-revolution wing stroke. Direct force measurements of the lift produced by the wing revealed a single global lift maximum relatively early in the wing stroke. Stereoscopic particle image velocimetry was applied to several chordwise planes to quantify the structure and strength of the leading-edge vortex and its effect on lift production. This analysis revealed opposite-sign vorticity entrainment into the core of the leading-edge vortex, originating from a layer of secondary vorticity along the wing surface. Coincident with the lift peak, there emerged both a concentration of opposite vorticity in the leading-edge-vortex core, as well as axial flow stagnation within the leading-edge-vortex core. Planar control volume analysis was performed at the midspan to quantify the contributions of vorticity transport mechanisms to the leading-edge-vortex circulation. The rate of circulation annihilation by opposite-signed vorticity entrainment was found to be minimal during peak lift production, where convection balanced the flux of vorticity resulting in stagnation and eventually reversal of axial flow. Finally, vortex burst was found to be correlated with swirl number, where bursting occurs at a swirl threshold of Sw<0.6 .

  15. Bubble confinement in flow boiling of FC-72 in a ''rectangular'' microchannel of high aspect ratio

    SciTech Connect

    Barber, Jacqueline; Brutin, David; Tadrist, Lounes; Sefiane, Khellil

    2010-11-15

    Boiling in microchannels remains elusive due to the lack of full understanding of the mechanisms involved. A powerful tool in achieving better comprehension of the mechanisms is detailed imaging and analysis of the two-phase flow at a fundamental level. Boiling is induced in a single microchannel geometry (hydraulic diameter 727 {mu}m), using a refrigerant FC-72, to investigate the effect of channel confinement on bubble growth. A transparent, metallic, conductive deposit has been developed on the exterior of the rectangular microchannel, allowing simultaneous uniform heating and visualisation to be achieved. The data presented in this paper is for a particular case with a uniform heat flux applied to the microchannel and inlet liquid mass flowrate held constant. In conjunction with obtaining high-speed images and videos, sensitive pressure sensors are used to record the pressure drop across the microchannel over time. Bubble nucleation and growth, as well as periodic slug flow, are observed in the microchannel test section. The periodic pressure fluctuations evidenced across the microchannel are caused by the bubble dynamics and instances of vapour blockage during confined bubble growth in the channel. The variation of the aspect ratio and the interface velocities of the growing vapour slug over time, are all observed and analysed. We follow visually the nucleation and subsequent both 'free' and 'confined' growth of a vapour bubble during flow boiling of FC-72 in a microchannel, from analysis of our results, images and video sequences with the corresponding pressure data obtained. (author)

  16. The Orientations of Large Aspect-Ratio Coiled-Coil Proteins Attached to Gold Nanostructures.

    PubMed

    Chang, Jae-Byum; Kim, Yong Ho; Thompson, Evan; No, Young Hyun; Kim, Nam Hyeong; Arrieta, Jose; Manfrinato, Vitor R; Keating, Amy E; Berggren, Karl K

    2016-03-01

    Methods for patterning biomolecules on a substrate at the single molecule level have been studied as a route to sensors with single-molecular sensitivity or as a way to probe biological phenomena at the single-molecule level. However, the arrangement and orientation of single biomolecules on substrates has been less investigated. Here, the arrangement and orientation of two rod-like coiled-coil proteins, cortexillin and tropomyosin, around patterned gold nanostructures is examined. The high aspect ratio of the coiled coils makes it possible to study their orientations and to pursue a strategy of protein orientation via two-point attachment. The proteins are anchored to the surfaces using thiol groups, and the number of cysteine residues in tropomyosin is varied to test how this variation affects the structure and arrangement of the surface-attached proteins. Molecular dynamics studies are used to interpret the observed positional distributions. Based on initial studies of protein attachment to gold post structures, two 31-nm-long tropomyosin molecules are aligned between the two sidewalls of a trench with a width of 68 nm. Because the approach presented in this study uses one of twenty natural amino acids, this method provides a convenient way to pattern biomolecules on substrates using standard chemistry. PMID:26799936

  17. Tunable Ultra-high Aspect Ratio Nanorod Architectures grown on Porous Substrate via Electromigration

    PubMed Central

    Mansourian, Ali; Paknejad, Seyed Amir; Wen, Qiannan; Vizcay-Barrena, Gema; Fleck, Roland A.; Zayats, Anatoly V.; Mannan, Samjid H.

    2016-01-01

    The interplay between porosity and electromigration can be used to manipulate atoms resulting in mass fabrication of nanoscale structures. Electromigration usually results in the accumulation of atoms accompanied by protrusions at the anode and atomic depletion causing voids at the cathode. Here we show that in porous media the pattern of atomic deposition and depletion is altered such that atomic accumulation occurs over the whole surface and not just at the anode. The effect is explained by the interaction between atomic drift due to electric current and local temperature gradients resulting from intense Joule heating at constrictions between grains. Utilizing this effect, a porous silver substrate is used to mass produce free-standing silver nanorods with very high aspect ratios of more than 200 using current densities of the order of 108 A/m2. This simple method results in reproducible formation of shaped nanorods, with independent control over their density and length. Consequently, complex patterns of high quality single crystal nanorods can be formed in-situ with significant advantages over competing methods of nanorod formation for plasmonics, energy storage and sensing applications. PMID:26923553

  18. Tunable Ultra-high Aspect Ratio Nanorod Architectures grown on Porous Substrate via Electromigration

    NASA Astrophysics Data System (ADS)

    Mansourian, Ali; Paknejad, Seyed Amir; Wen, Qiannan; Vizcay-Barrena, Gema; Fleck, Roland A.; Zayats, Anatoly V.; Mannan, Samjid H.

    2016-02-01

    The interplay between porosity and electromigration can be used to manipulate atoms resulting in mass fabrication of nanoscale structures. Electromigration usually results in the accumulation of atoms accompanied by protrusions at the anode and atomic depletion causing voids at the cathode. Here we show that in porous media the pattern of atomic deposition and depletion is altered such that atomic accumulation occurs over the whole surface and not just at the anode. The effect is explained by the interaction between atomic drift due to electric current and local temperature gradients resulting from intense Joule heating at constrictions between grains. Utilizing this effect, a porous silver substrate is used to mass produce free-standing silver nanorods with very high aspect ratios of more than 200 using current densities of the order of 108 A/m2. This simple method results in reproducible formation of shaped nanorods, with independent control over their density and length. Consequently, complex patterns of high quality single crystal nanorods can be formed in-situ with significant advantages over competing methods of nanorod formation for plasmonics, energy storage and sensing applications.

  19. Preparation and Properties of Nanocomposites from Pristine and Modified SWCNTs of Comparable Average Aspect Ratios

    NASA Technical Reports Server (NTRS)

    Smith, Joseph G.; Delozier, Donavon M.; Watson, Kent A.; Connell, John W.; Bekyarova, E.; Haddon, R.; Yu, A.

    2008-01-01

    Low color, flexible, space-durable polyimide films with inherent and robust electrical conductivity to dissipate electrostatic charge (ESC) have been under investigation as part of a materials development activity for future NASA space missions. The use of single-walled carbon nanotubes (SWCNTs) is one means to achieving this goal. Even though the concentration of SWCNTs needed to achieve ESC dissipation is typically low, it is dependent upon purity, size, dispersion, and functionalization. In this study, SWCNTs prepared by the electric arc discharge method were used to synthesize nanocomposites using the LaRC(TradeMark) CP2 backbone as the matrix. Pristine and functionalized SWCNTs were mixed with an alkoxysilane terminated amide acid of LaRC(TradeMark) CP2 and the soluble imide form of the polymer and the resultant nanocomposites evaluated for mechanical, thermal, and electrical properties. Due to the preparative conditions for the pristine and functionalized SWCNTs, the average aspect ratio for both was comparable. This permitted the assessment of SWCNT functionalization with respect to various interactions (e.g. van der Waals, hydrogen bonding, covalent bond formation, etc.) with the matrix and the macroscopic effects upon nanocomposite properties. The results of this study are described herein.

  20. Pressure-distribution measurements on a transonic low-aspect ratio wing

    NASA Technical Reports Server (NTRS)

    Keener, E. R.

    1985-01-01

    Experimental surface pressure distributions and oil flow photographs are presented for a 0.90 m semispan model of NASA/Lockheed Wing C, a generic transonic, supercritical, low aspect ratio, highly 3-dimensional configuration. This wing was tested at the design angle of attack of 5 deg over a Mach number range from 0.25 to 0.96, and a Reynolds number range from 3.4 x 1,000,000 to 10 x 1,000,000. Pressures were measured with both the tunnel floor and ceiling suction slots open for most of the tests but taped closed for some tests to simulate solid walls. A comparison is made with the measured pressures from a small model in high Reynolds number facility and with predicted pressures using two three dimesional, transonic full potential flow wing codes: design code FLO22 (nonconservative) and TWING code (conservative). At the given design condition, a small region of flow separation occurred. At a Mach number of 0.82 the flow was unseparated and the surface flow angles were less than 10 deg, indicating that the boundary layer flow was not 3-D. Evidence indicate that wings that are optimized for mild shock waves and mild pressure recovery gradients generally have small 3-D boundary layer flow at design conditions for unseparated flow.

  1. Parallel Operation of Multiple Closely Spaced Small Aspect Ratio Rod Pinches

    SciTech Connect

    Harper-Slaboszewicz, Victor J.; Leckbee, Joshua; Bennett, Nichelle; Madrid, Elizabeth A.; Rose, David V.; Thoma, Carsten; Welch, Dale R.; Lake, Patrick W.; McCourt, Andrew L.

    2014-12-10

    A series of simulations and experiments to resolve questions about the operation of arrays of closely spaced small aspect ratio rod pinches has been performed. Design and post-shot analysis of the experimental results are supported by 3D particle-in-cell simulations. Both simulations and experiments support these conclusions. Penetration of current to the interior of the array appears to be efficient, as the current on the center rods is essentially equal to the current on the outer rods. Current loss in the feed due to the formation of magnetic nulls was avoided in these experiments by design of the feed surface of the cathode and control of the gap to keep the electric fields on the cathode below the emission threshold. Some asymmetry in the electron flow to the rod was observed, but the flow appeared to symmetrize as it reached the end of the rod. Interaction between the rod pinches can be controlled to allow the stable and consistent operation of arrays of rod pinches.

  2. High aspect ratio iridescent three-dimensional metal–insulator–metal capacitors using atomic layer deposition

    SciTech Connect

    Burke, Micheal Blake, Alan; Djara, Vladimir; O'Connell, Dan; Povey, Ian M.; Cherkaoui, Karim; Monaghan, Scott; Scully, Jim; Murphy, Richard; Hurley, Paul K.; Pemble, Martyn E.; Quinn, Aidan J.

    2015-01-01

    The authors report on the structural and electrical properties of TiN/Al{sub 2}O{sub 3}/TiN metal–insulator–metal (MIM) capacitor structures in submicron three-dimensional (3D) trench geometries with an aspect ratio of ∼30. A simplified process route was employed where the three layers for the MIM stack were deposited using atomic layer deposition (ALD) in a single run at a process temperature of 250 °C. The TiN top and bottom electrodes were deposited via plasma-enhanced ALD using a tetrakis(dimethylamino)titanium precursor. 3D trench devices yielded capacitance densities of 36 fF/μm{sup 2} and quality factors >65 at low frequency (200 Hz), with low leakage current densities (<3 nA/cm{sup 2} at 1 V). These devices also show strong optical iridescence which, when combined with the covert embedded capacitance, show potential for system in package (SiP) anticounterfeiting applications.

  3. Micropatterned Hydrogel Surface with High-Aspect-Ratio Features for Cell Guidance and Tissue Growth.

    PubMed

    Hu, Yuhang; You, Jin-Oh; Aizenberg, Joanna

    2016-08-31

    Surface topography has been introduced as a new tool to coordinate cell selection, growth, morphology, and differentiation. The materials explored so far for making such structural surfaces are mostly rigid and impermeable. Hydrogel, on the other hand, was proved a better synthetic media for cell culture because of its biocompatibility, softness, and high permeability. Herein, we fabricated a poly(2-hydroxyethyl methacrylate) (pHEMA) hydrogel substrate with high-aspect-ratio surface microfeatures. Such structural surface could effectively guide the orientation and shape of human mesenchymal stem cells (HMSCs). Notably, on the flat hydrogel surface, cells rounded up, whereas on the microplate patterned hydrogel surface, cells elongated and aligned along the direction parallel to the plates. The microplates were 2 μm thick, 20 μm tall, and 10-50 μm wide. The interplate spacing was 5-15 μm, and the intercolumn spacing was 5 μm. The elongation of cell body was more pronounced on the patterns with narrower interplate spacing and wider plates. The cells behaved like soft solid. The competition between surface energy and elastic energy defined the shape of the cells on the structured surfaces. The soft permeable hydrogel scaffold with surface structures was also demonstrated as being viable for long-term cell culture, and could be used to generate interconnected tissues with finely tuned cell morphology and alignment across a few centimeter sizes. PMID:27089518

  4. Large-area thermoelectric high-aspect-ratio nanostructures by atomic layer deposition.

    PubMed

    Ruoho, Mikko; Juntunen, Taneli; Tittonen, Ilkka

    2016-09-01

    We report on the thermoelectric properties of large-area high-aspect-ratio nanostructures. We fabricate the structures by atomic layer deposition of conformal ZnO thin films on track-etched polycarbonate substrate. The resulting structure consists of ZnO tubules which continue through the full thickness of the substrate. The electrical and thermal properties of the structures are studied both in-plane and out-of-plane. They exhibit very low out-of-plane thermal conductivity down to 0.15 W m(-1) K(-1) while the in-plane sheet resistance of the films was found to be half that of the same film on glass substrate, allowing material-independent doubling of output power of any planar thin-film thermoelectric generator. The wall thickness of the fabricated nanotubes was varied within a range of up to 100 nm. The samples show polycrystalline nature with (002) preferred crystal orientation. PMID:27454037

  5. Experimental investigation of a large aspect ratio flat plate encountering a steam-wise gust

    NASA Astrophysics Data System (ADS)

    Mulleners, Karen; Mancini, Peter; Jones, Anya

    2015-11-01

    While humans are capable of mimicking, and even outperform, the kinematic capabilities of natural flyers, birds and insects are still way ahead of us when it comes to anticipating and dealing with turbulent and gusty flow conditions. To tailor and improve flight control capabilities of low Reynolds number flyers in real weather, we need to bridge this gap of knowledge. As a first step, we experimentally studied the aerodynamic influence of a simplified stream-wise gust on a large aspect ratio flat plate. The experiments were conduction in the 7 × 1 . 5 × 1 m3 towing tank at UMD which was equipped with a 4-axis computer-controlled motion system. The effect of a stream-wise gust was simulated by accelerating or decelerating the wing to a new constant velocity after an initial constant surge. A high-speed camera and light sheet optics were attached to the tow carriage allowing for time-resolved particle image velocimetry along the entire motion in addition to direct force measurements. A proper orthogonal decomposition of the flow field was carried out to study the time scales related to changes induced by the sudden acceleration or deceleration in addition to analyzing the size, position and trajectory of prominent vortices and associated forces during the gust encounter.

  6. Light extinction and scattering from individual and arrayed high-aspect-ratio trenches in metals

    NASA Astrophysics Data System (ADS)

    Roberts, Alexander S.; Søndergaard, Thomas; Chirumamilla, Manohar; Pors, Anders; Beermann, Jonas; Pedersen, Kjeld; Bozhevolnyi, Sergey I.

    2016-02-01

    We investigate the scattering properties of two-dimensional high-aspect-ratio metal trenches acting as resonators for gap-surface plasmons and show that these resonators are highly efficient scatterers of free waves, reaching at resonance in the perfect-conductor limit the unitary dipolar limit for a two-dimensional scatterer. We construct a simple resonator model which predicts the wavelength-dependent extinction, scattering, and absorption cross section of the trench and compare the model findings with full numerical simulations. Both extinction and scattering cross sections are mainly determined by the wavelength and can reach highly supergeometric values. At wavelengths where the metal exhibits near perfect electrical conductor behavior, such trenches lend themselves to be used as self-normalizing scatterers, as their scattering cross section is independent of their geometry and depend only on the resonance wavelength. For real metals with nonzero absorption, efficient monomaterial absorbers and emitters can be fabricated. We extend the analysis to tapering trenches that can be readily fabricated employing common milling or etching techniques and verify by reflection spectroscopy and two-photon luminescence that the resonant behavior of the vertical trenches is preserved.

  7. Hummingbird wing efficacy depends on aspect ratio and compares with helicopter rotors.

    PubMed

    Kruyt, Jan W; Quicazán-Rubio, Elsa M; van Heijst, GertJan F; Altshuler, Douglas L; Lentink, David

    2014-10-01

    Hummingbirds are the only birds that can sustain hovering. This unique flight behaviour comes, however, at high energetic cost. Based on helicopter and aeroplane design theory, we expect that hummingbird wing aspect ratio (AR), which ranges from about 3.0 to 4.5, determines aerodynamic efficacy. Previous quasi-steady experiments with a wing spinner set-up provide no support for this prediction. To test this more carefully, we compare the quasi-steady hover performance of 26 wings, from 12 hummingbird taxa. We spun the wings at angular velocities and angles of attack that are representative for every species and measured lift and torque more precisely. The power (aerodynamic torque × angular velocity) required to lift weight depends on aerodynamic efficacy, which is measured by the power factor. Our comparative analysis shows that AR has a modest influence on lift and drag forces, as reported earlier, but interspecific differences in power factor are large. During the downstroke, the power required to hover decreases for larger AR wings at the angles of attack at which hummingbirds flap their wings (p < 0.05). Quantitative flow visualization demonstrates that variation in hover power among hummingbird wings is driven by similar stable leading edge vortices that delay stall during the down- and upstroke. A side-by-side aerodynamic performance comparison of hummingbird wings and an advanced micro helicopter rotor shows that they are remarkably similar. PMID:25079868

  8. Identifying the pulmonary hazard of high aspect ratio nanoparticles to enable their safety-by-design.

    PubMed

    Donaldson, Ken; Murphy, Fiona; Schinwald, Anja; Duffin, Rodger; Poland, Craig A

    2011-01-01

    High aspect ratio, or fiber-shaped, nanoparticles (HARNs) represent a growth area in nanotechnology as their useful properties become more apparent. Carbon nanotubes, the best known and studied of the HARNs are handled on an increasingly large scale, with subsequent potential for human inhalation exposure. Their resemblance to asbestos fibers precipitated fears that they might show the same type of pathology as that caused by asbestos and there is emerging evidence to support this possibility. The large number of other HARNs, including nanorods, nanowires and other nanofibers, require similar toxicological scrutiny. In this article we describe the unusual hazard associated with fibers, with special reference to asbestos, and address the features of fibers that dictate their pathogenicity as developed in the fiber pathogenicity paradigm. This paradigm is a robust structure:toxicity model that identifies thin, long, biopersistent fibers as the effective dose for fiber-type pathogenic effects. It is likely that HARNs will in general conform to the paradigm and such an understanding of the features that make fibers pathogenic should enable us to design safer HARNs. PMID:21182425

  9. High Aspect Ratio Sub-15 nm Silicon Trenches From Block Copolymer Templates

    NASA Astrophysics Data System (ADS)

    Gu, Xiaodan; Liu, Zuwei; Gunkel, Ilja; Olynick, Deirdre; Russell, Thomas; University of Massachusetts Amherst Collaboration; Oxford Instrument Collaboration; Lawrence Berkeley National Lab Collaboration

    2013-03-01

    High-aspect-ratio sub-15 nm silicon trenches are fabricated directly from plasma etching of a block copolymer (BCP) mask. Polystyrene-b-poly(2-vinyl pyridine) (PS-b-P2VP) 40k-b-18k was spin coated and solvent annealed to form cylindrical structures parallel to the silicon substrate. The BCP thin film was reconstructed by immersion in ethanol and then subjected to an oxygen and argon reactive ion etching to fabricate the polymer mask. A low temperature ion coupled plasma with sulfur hexafluoride and oxygen was used to pattern transfer block copolymer structure to silicon with high selectivity (8:1) and fidelity. The silicon pattern was characterized by scanning electron microscopy and grazing incidence x-ray scattering. We also demonstrated fabrication of silicon nano-holes using polystyrene-b-polyethylene oxide (PS-b-PEO) using same methodology described above for PS-b-P2VP. Finally, we show such silicon nano-strucutre serves as excellent nano-imprint master template to pattern various functional materials like poly 3-hexylthiophene (P3HT).

  10. Development of a low-aspect ratio fin for flight research experiments

    NASA Technical Reports Server (NTRS)

    Richwine, David M.; Delfrate, John H.

    1994-01-01

    A second-generation flight test fixture, developed at NASA Dryden Flight Research Center, offers a generic testbed for aerodynamic and fluid mechanics research. The new fixture, a low-aspect ratio vertical fin shape mounted on the centerline of an F-15B aircraft lower fuselage, is designed for flight research at Mach numbers up to 2.0. The new fixture is a composite structure with a modular configuration and removable components for functional flexibility. This report describes the multidisciplinary design and analysis approach used to develop the fixture. The approach integrates conservative assumptions with simple analysis techniques to minimize the time and cost associated with its development. Presented are the principal disciplines required for this effort, which include aerodynamics, structures, stability, and operational considerations. In addition, preliminary results from the first phase of flight testing are presented. Acceptable directional stability and flow quality are documented and show agreement with predictions. Future envelope expansion activities will minimize current limitations so that the fixture can be used for a wide variety of high-speed aerodynamic and fluid mechanics research experiments.

  11. On the flow generated by rotating flat plates of low aspect ratio

    NASA Astrophysics Data System (ADS)

    DeVoria, Adam C.

    Low-aspect-ratio propulsors typically allow for high maneuverability at low-to-moderate speeds. This has made them the subject of much recent research aimed at employing such appendages on autonomous vehicles which are required to navigate tumultuous environments. This experimental investigation focuses on the fluid dynamic aspects associated with overly-simplified versions of such biologically-inspired propulsors. In doing so, fundamental contributions are made to the research area. The unsteady, three-dimensional flow of a low-aspect-ratio, trapezoidal flat plate undergoing rotation from rest at a 90° angle of attack and Reynolds numbers of O(103) is investigated experimentally. The objectives are to develop a straightforward protocol for vortex saturation, and to understand the effects of the root-to-tip flow for different velocity programs. The experiments are conducted in a glass-walled tank, and digital particle image velocimetry is used to obtain planar velocity measurements. A formation-parameter definition is investigated and is found to reasonably predict the state corresponding to the pinch-off of the initial tip vortex across the velocity programs tested. The flow in the region near the tip is relatively insensitive to Reynolds number over the range studied. The component normal to the plate is unaffected by total rotational amplitude while the tangential component has dependence on this angle. Also, an estimate of the first tip-vortex pinch-off time is obtained from the near-tip velocity data and agrees very well with values estimated using circulation. The angle of incidence of the bulk root-to-tip flow relative to the plate normal becomes more oblique with increasing rotational amplitude. Accordingly, the peak magnitude of the tangential velocity is also increased and as a result advects fluid momentum away from the plate at a higher rate. The more oblique impingement of the root-to-tip flow for increasing rotational amplitude is shown to have a

  12. The immersed boundary projection method and its application to simulation and control of flows around low-aspect-ratio wings

    NASA Astrophysics Data System (ADS)

    Taira, Kunihiko

    First, we present a new formulation of the immersed boundary method that is algebraically identical to the traditional fractional step algorithm. This method, called the immersed boundary projection method, allows for the simulations of incompressible flows over arbitrarily shaped bodies under motion and/or deformation in both two and three dimensions. The no-slip condition along the immersed boundary is enforced simultaneously with the incompressibility constraint through a single projection. The boundary force is determined implicitly without any constitutive relations for the rigid body formulation, which in turn allows the use of high CFL numbers in our simulations compared to past methods. Next, the above immersed boundary projection method is used to analyze three-dimensional separated flows around low-aspect-ratio flat-plate wings. A number of simulations highlighting the unsteady nature of the separated flows are performed for Re=300 and 500 with various aspect ratios, angles of attack, and planform geometries. The aspect ratio and angle of attack are found to have a large influence on the stability of the wake profile and the force experienced by the low-aspect-ratio wing. At early times, following an impulsive start, topologies of the wake vortices are found to be the same across different aspect ratios and angles of attack. Behind low-aspect-ratio rectangular plates, leading-edge vortices form and eventually separate as hairpin vortices following the start-up. This phenomenon is found to be similar to dynamic stall observed behind pitching plates. The detached structure would then interact with the tip vortices, reducing the downward velocity induced by the tip vortices acting upon the leading-edge vortex. At large time, depending on the aspect ratio and angles of attack, the wakes reach one of the three states: (i) a steady state, (ii) a periodic unsteady state, or (iii) an aperiodic unsteady state. We have observed that the tip effects in three

  13. Numerical modeling on air quality in an urban environment with changes of the aspect ratio and wind direction.

    PubMed

    Yassin, Mohamed F

    2013-06-01

    Due to heavy traffic emissions within an urban environment, air quality during the last decade becomes worse year by year and hazard to public health. In the present work, numerical modeling of flow and dispersion of gaseous emissions from vehicle exhaust in a street canyon were investigated under changes of the aspect ratio and wind direction. The three-dimensional flow and dispersion of gaseous pollutants were modeled using a computational fluid dynamics (CFD) model which was numerically solved using Reynolds-averaged Navier-Stokes (RANS) equations. The diffusion flow field in the atmospheric boundary layer within the street canyon was studied for different aspect ratios (W/H=1/2, 3/4, and 1) and wind directions (θ=90°, 112.5°, 135°, and 157.5°). The numerical models were validated against wind tunnel results to optimize the turbulence model. The numerical results agreed well with the wind tunnel results. The simulation demonstrated that the minimum concentration at the human respiration height within the street canyon was on the windward side for aspect ratios W/H=1/2 and 1 and wind directions θ=112.5°, 135°, and 157.5°. The pollutant concentration level decreases as the wind direction and aspect ratio increase. The wind velocity and turbulence intensity increase as the aspect ratio and wind direction increase. PMID:23192299

  14. On vortex evolution in the wake of axisymmetric and non-axisymmetric low-aspect-ratio accelerating plates

    NASA Astrophysics Data System (ADS)

    Fernando, John N.; Rival, David E.

    2016-01-01

    Impulsively started, low-aspect-ratio elliptical and rectangular flat plates were investigated to determine the role of geometric asymmetries on vortex evolution. Dye visualizations, force measurements, and particle image velocimetry were used throughout to characterize the variation between shapes. For all the shapes studied, aspect ratio was observed to have the largest influence on force production and vortex evolution. Non-uniform curvature and edge discontinuities characteristic of ellipses (with aspect ratios other than one) and rectangles, respectively, play a secondary role. Furthermore, it was shown that stably attached vortex rings form behind the circular and square flat plates, which reduce the instantaneous drag force of each plate until the vortex rings break down. In contrast, all flat plates with aspect ratios other than one are subjected to fast-modulating elliptical vortex rings in the wake. These vortex rings increase the drag force of each plate until pinch-off occurs. Finally, pinch-off was identified with the streamwise pressure-gradient field and compared with formation numbers calculated using the circulation-based methodology, yielding good agreement for all plates with aspect ratios greater than one.

  15. Single-pulse femtosecond laser Bessel beams drilling of high-aspect-ratio microholes based on electron dynamics control

    NASA Astrophysics Data System (ADS)

    Zhao, Weiwei; Li, Xiaowei; Xia, Bo; Yan, Xueliang; Han, Weina; Lu, Yongfeng; Jiang, Lan

    2014-11-01

    Microholes drilling has attracted extensive research efforts for its broad applications in photonics, microfluidics, optical fibers and many other fields. A femtosecond (fs) laser is a promising tool for high-precision materials processing with reduced recast/microcracks and minimized heat affected zones. But there remain many challenges in hole drilling using conventional fs laser with Gaussian beams, such as low aspect ratio and taper effects. We report small-diameter and high-aspect-ratio microholes with taper free drilling in PMMA (polymethyl methacrylate) using single-pulse fs laser Bessel beams. Axicon is used to transform Gaussian beams into Bessel beams, which then irradiate in the sample by a telescope consisting of plano-convex lens and microscope objective. Using this technique, we enhance the aspect ratio of microholes by 55 times as compared with Gaussian beams. We attribute this high aspect ratio and high quality microholes formation to the unique spatial intensity distribution and propagation stability of Bessel beams, which can effectively adjust the transient localized electron density distribution leading to a long and uniform localized-interacted zone. By using the optimized pulse energy and focal depth position, the microholes diameter ranges between 1.4-2.1 μm and the aspect ratio can exceed 460. This efficient technique is of great potentials for fabrication of microphotonics devices and microfluidics.

  16. Enhanced plasticity of bulk metallic glass in different aspect ratios via laser shock peening with multiple impacts

    NASA Astrophysics Data System (ADS)

    Fu, Jie; Zhu, Yunhu; Zheng, Chao; Liu, Ren; Ji, Zhong

    2016-09-01

    In this study laser shock peening (LSP) with multiple laser impacts was used to improve the mechanical properties especially the plasticity of Zr35Ti30Cu8.25Be26.75 bulk metallic glass (BMG) pillars in two aspect ratios (1:1 and 2:1). It was found that, with increasing laser impacts up to 5, the compression plastic strain of BMG pillar with aspect ratio of 1:1 increased from 0 to 1.48% and the compression strength increased significantly from 1569 MPa to 1721 MPa. With further laser impacts beyond 5, the changes in the plasticity and the compression strength were observed to be insignificant. Considering the effect of sample geometry at the same laser impacts, it could be concluded that the BMG pillars with smaller aspect ratio of 1:1 had better mechanical properties than that of the lager BMG pillars with aspect ratio of 2:1. Besides, the elastic strain limit of BMG pillars with LSP was not only independent of the laser impacts, but also irrelevant to the aspect ratio. At last, we discussed the reason for the increase of plasticity in view of the creation of excess free volume during LSP.

  17. The role of spherical torus in clarifying tokamak physics

    SciTech Connect

    Morris, A. W.; Peng, Yueng Kay Martin

    1999-01-01

    The spherical tokamak (ST) provides a unique environment in which to perform complementary and exacting tests of the tokamak physics required for a burning plasma experiment of any aspect ratio, while also having the potential for long-term fusion applications in its own right. New experiments are coming on-line in the UK (MAST), USA (NSTX, Pegasus), Russia (Globus-M), Brazil (ETE) and elsewhere, and the status of these devices will be reported, along with newly-analysed data from START. Those physics issues where the ST provides an opportunity to remove degeneracy in the databases or clarify one s understanding will be emphasized.

  18. Parallel fabrication of high-aspect-ratio all-silicon grooves using femtosecond laser irradiation and wet etching

    NASA Astrophysics Data System (ADS)

    Li, Yanna; Chen, Tao; Pan, An; Li, Cunxia; Tang, Litie

    2015-11-01

    This paper introduces a simple method using 800 nm femtosecond laser irradiation and wet etching with a hydrofluoric (HF) acid solution for the parallel fabrication of high-aspect-ratio all-silicon groove arrays. In this method, one laser beam was divided into five beams by a diffractive optical element. Five laser-induced structure change (LISC) zones were formed in the silicon simultaneously with a single scan of the divided beams, and then the materials in the LISC zones were etched by HF acid solution to form groove arrays. Via this method, all-silicon grooves with aspect ratios up to 39.4 were produced, and the processing efficiency could be increased by five times in contrast with that of the single laser beam irradiation. Furthermore, high-aspect-ratio grooves with near uniform morphologies were fabricated using this method in silicon wafers with different crystal orientations.

  19. Mechanical properties of natural rubber nanocomposites reinforced with high aspect ratio cellulose nanocrystals isolated from soy hulls.

    PubMed

    Flauzino Neto, Wilson Pires; Mariano, Marcos; da Silva, Ingrid Souza Vieira; Silvério, Hudson Alves; Putaux, Jean-Luc; Otaguro, Harumi; Pasquini, Daniel; Dufresne, Alain

    2016-11-20

    Cellulose nanocrystals (CNCs) were isolated from soy hulls by acid sulfuric hydrolysis. The resulting CNCs were characterized using TEM, AFM, WAXS, elemental analysis and TGA. The CNCs have a high crystallinity, specific surface area and aspect ratio. The aspect ratio (around 100) is the largest ever reported in the literature for a plant cellulose source. These CNCs were used as a reinforcing phase to prepare nanocomposite films by casting/evaporation using natural rubber as matrix. The mechanical properties were studied in both the linear and non-linear ranges. The reinforcing effect was higher than the one observed for CNCs extracted from other sources. It may be assigned not only to the high aspect ratio of these CNCs but also to the stiffness of the percolating nanoparticle network formed within the polymer matrix. Moreover, the sedimentation of CNCs during the evaporation step was found to play a crucial role on the mechanical properties. PMID:27561481

  20. Effect of coolant flow ejection on aerodynamic performance of low-aspect-ratio vanes. 2: Performance with coolant flow ejection at temperature ratios up to 2

    NASA Technical Reports Server (NTRS)

    Hass, J. E.; Kofskey, M. G.

    1977-01-01

    The aerodynamic performance of a 0.5 aspect ratio turbine vane configuration with coolant flow ejection was experimentally determined in a full annular cascade. The vanes were tested at a nominal mean section ideal critical velocity ratio of 0.890 over a range of primary to coolant total temperature ratio from 1.0 to 2.08 and a range of coolant to primary total pressure ratio from 1.0 to 1.4 which corresponded to coolant flows from 3.0 to 10.7 percent of the primary flow. The variations in primary and thermodynamic efficiency and exit flow conditions with circumferential and radial position were obtained.

  1. Access to and Characterization of Ohmic H-mode Plasmas at Near-Unity Aspect Ratio

    NASA Astrophysics Data System (ADS)

    Fonck, R. J.; Bongard, M. W.; Thome, K. E.; Burke, M. G.; Peguero, L. M.; Perry, J. M.; Schlossberg, D. J.; Shriwise, P. C.; Thompson, D. S.

    2013-10-01

    The low H-mode transition power threshold at near-unity aspect ratio allows access to H-mode in the PEGASUS experiment with only Ohmic heating. Ohmic H-mode plasmas are achieved in both a limited and a new separatrix-limited magnetic configuration. H-mode is attained with high-field-side centerstack fueling, with densities from 1 to > 3 × 1019 m-3 and Greenwald fractions ~ 0.2-0.7 for Ip ~ 0 . 13 MA. Compared to L-mode plasmas, H-modes show: a doubling of the stored energy; reduced D- α emission; edge current pedestal with characteristic width of ~ 2 cm, with 6 cm for L-mode; reversal of the edge toroidal flow from counter-current to co-current; reduced V-sec consumption due to increased temperatures; and ELM excitation. Operation at A ~1.15 results in strong particle trapping, fT ~ 0.7 - 0.9, and associated neoclassical effects even at modest plasma temperatures so that POH ~ 0.4 MW, which readily surpasses the estimated threshold power of <0.1 MW. Low-field-side fueling appears to degrade access to and quality of the H-mode plasma. Characterization of H-mode access in PEGASUS will provide unique data at near-unity A and guide detailed studies of ELM dynamics, as well as provide a critical tool for exploring the extremely high-βT regime at A ~ 1. Work supported by US DOE Grant DE-FG02-96ER54375.

  2. The flow field in a high aspect ratio cooling duct with and without one heated wall

    NASA Astrophysics Data System (ADS)

    Rochlitz, Henrik; Scholz, Peter; Fuchs, Thomas

    2015-12-01

    The flow in a high aspect ratio generic cooling duct is described for different Reynolds numbers and for adiabatic as well as non-adiabatic conditions. The Reynolds number is varied in a range from 39,000 to 111,000. The generic cooling duct facility allows for applying a constant temperature on the duct's lower wall, and it ensures having well-defined boundary conditions. The high-quality, optical noninvasive measurement methods, namely Particle Image Velocimetry (2C2D-PIV, i.e., two velocity components in a plane), Stereo Particle Image Velocimetry (3C2D-PIV, i.e., three velocity components in a plane) and Volumetric Particle Tracking Velocimetry (3C3D-PTV, i.e., three velocity components in a volume), are used to characterize the flow in detail. Pressure transducers are installed for measuring the pressure losses. The repeatability and the validity of the data are discussed in detail. For that purpose, modifications in the test facility and in the experimental setup as well as comparisons between the different measurement methods are given. A focus lies on the average velocity distribution and on the turbulent statistics. The longitudinal velocity profile is analyzed in detail for Reynolds number variations. Secondary flows are identified with velocities of two orders of magnitude smaller than the longitudinal velocity. Reynolds stress distributions are given for several different cases. The Reynolds number dependency of overline{u'^2} and overline{v'^2} is shown, and a comparison between the adiabatic and the heated case is given. overline{u'^2} changes significantly when the lower wall heat flux is applied, whereas overline{v'^2} and overline{u'v'} almost stay constant.

  3. Effect of Aspect Ratio on H-mode and ELM Characteristics

    NASA Astrophysics Data System (ADS)

    Thome, K. E.; Bodner, G. M.; Bongard, M. W.; Burke, M. G.; Fonck, R. J.; Kriete, D. M.

    2015-11-01

    The H-mode confinement regime is achieved at near-unity aspect ratio (A < 1 . 2) in the Pegasus Toroidal Experiment via high-field-side fueling and low edge recycling. Ohmic H-mode is attained in both limited and diverted magnetic topologies. This regime is characterized by: reduced Dα emissions; increased core rotation; increased central heating; formation of edge current and pressure pedestals; and measured energy confinement consistent with the ITER98pb(y,2) scaling. The H-mode power threshold, PLH , behaves quite differently at low- A when compared with high- A operations. PLH /PLH_ITPA 08 increases sharply as A is lowered and no difference in PLH for limited and diverted plasmas is observed at A ~ 1 . 2 . No minimum in PLH with density is observed. Some of these results are consistent with the FM3 model for the L-H transition. Two classes of ELMs have been observed. Small, Type III-like ELMs are present at low input power and have n <= 4 . At POH >>PLH , they transition to large, Type-I-like ELMs with intermediate 5 < n < 15 . The Type III ELM magnetic structures behave opposite that of high- A plasmas, with n much higher, presumably due to the naturally higher J / B peeling mode drive at low- A . Long-sought measurements of the Jedge (R , t) pedestal collapse during an ELM event show a complex, multimodal pedestal collapse and the subsequent ejection of a current-carrying filament. Work supported by US DOE grant DE-FG02-96ER54375.

  4. Mapping stresses in high aspect ratio polysilicon electrical through-wafer interconnects

    NASA Astrophysics Data System (ADS)

    Sharma, Himani; Krabbe, Joshua D.; Farsinezhad, Samira; van Popta, Andy C.; Wakefield, Nick G.; Fitzpatrick, Glen A.; Shankar, Karthik

    2015-04-01

    Electrical through-wafer interconnect technologies such as vertical through-silicon vias (TSVs) are essential in order to maximize performance, optimize usage of wafer real estate, and enable three-dimensional packaging in leading edge electronic and microelectromechanical systems (MEMS) products. Although copper TSVs have the advantage of low resistance, highly doped polysilicon TSVs offer designers a much larger range of processing options due to the compatibility of polysilicon with high temperatures and also with the full range of traditional CMOS processes. Large stresses are associated with both Cu and polysilicon TSVs, and their accurate measurement is critical for determining the keep-out zone (KOZ) of transistors and for optimizing downstream processes to maintain high yield. This report presents the fabrication and stress characterization of 400-μm deep, 20-Ω resistance, high aspect ratio (25:1) polysilicon TSVs fabricated by deep reactive ion etching (DRIE) followed by low-pressure chemical vapor deposition (LPCVD) of polysilicon with in-situ boron doping. Micro-Raman imaging of the wafer surface showed a maximum stress of 1.2 GPa occurring at the TSV edge and a KOZ of ˜9 to 11 μm. For polysilicon TSVs, the stress distribution in the TSVs far from the wafer surface(s) was not previously well-understood due to measurement limitations. Raman spectroscopy was able to overcome this limitation; a TSV cross section was examined and stresses as a function of both depth and width of the TSVs were collected and are analyzed herein. An 1100°C postanneal was found to reduce average stresses by 40%.

  5. Evaluation of carbonate pore system under texture control for prediction of microporosity aspect ratio and shear wave velocity

    NASA Astrophysics Data System (ADS)

    Lima Neto, Irineu A.; Misságia, Roseane M.; Ceia, Marco A.; Archilha, Nathaly L.; Hollis, Cathy

    2015-06-01

    This work evaluates a suite of carbonate rocks from Albian age in the Campos Basin - Brazil, complemented by data from the literature, totaling 472 samples with detailed description of diagenetic features, quantitative mineralogy analyses, and P- and S-wave velocities (Vp and Vs) measured at three ranges of effective pressure loading: low (5-7.5 MPa), moderate (20 MPa) and high (40-50 MPa) values. Digital image analysis (DIA) was applied on microtomography (μCT) images to quantitatively describe the macro-mesopore system of the Albian carbonates, and was extended to characterize different textures from literature data to estimate reference values for carbonates. The methodology utilized to predict the aspect ratio of microporosity assumes three pore-space scales in two representative scenarios: 1) measured macro-mesopore aspect ratio from DIA, and 2) predicted microporosity aspect ratio, using Vp measurement as the main input parameter. The differential effective medium model (DEMM) is combined with analytical theories of data analysis to characterize microporosity. Shear modulus and microporosity aspect ratio calibrated by this methodology were used to predict Vs, which was compared to experimental data, resulting in a good match for all samples. Polynomial curves are fitted with a variety of carbonate textures by velocities at effective pressure and bulk porosity crossplots, establishing important relationships for velocity prediction. The effects of effective pressure on the pore system within dry plugs of Albian samples were evaluated by combining triaxial measurements at 0-10 MPa, relative pore volume reduction (RPVR) and microporosity aspect ratio prediction. According to the results, micropores that exhibit low aspect ratio tend to close with stress and cause an increase on Vp and Vs. A wide textural heterogeneity of data base and different digital image analysis and resolutions were employed successfully, combining rock physics methodologies and concepts

  6. Single-shot high aspect ratio bulk nanostructuring of fused silica using chirp-controlled ultrafast laser Bessel beams

    SciTech Connect

    Bhuyan, M. K.; Velpula, P. K.; Colombier, J. P.; Olivier, T.; Faure, N.; Stoian, R.

    2014-01-13

    We report single-shot, high aspect ratio nanovoid fabrication in bulk fused silica using zeroth order chirp-controlled ultrafast laser Bessel beams. We identify a unique laser pulse length and energy dependence of the physical characteristics of machined structures over which nanovoids of diameter in the range 200–400 nm and aspect ratios exceeding 1000 can be fabricated. A mechanism based on the axial energy deposition of nonlinear ultrashort Bessel beams and subsequent material densification or rarefaction in fused silica is proposed, intricating the non-diffractive nature with the diffusing character of laser-generated free carriers. Fluid flow through nanochannel is also demonstrated.

  7. Filling high aspect ratio trenches by superconformal chemical vapor deposition: Predictive modeling and experiment

    NASA Astrophysics Data System (ADS)

    Wang, Wenjiao B.; Abelson, John R.

    2014-11-01

    Complete filling of a deep recessed structure with a second material is a challenge in many areas of nanotechnology fabrication. A newly discovered superconformal coating method, applicable in chemical vapor deposition systems that utilize a precursor in combination with a co-reactant, can solve this problem. However, filling is a dynamic process in which the trench progressively narrows and the aspect ratio (AR) increases. This reduces species diffusion within the trench and may drive the component partial pressures out of the regime for superconformal coating. We therefore derive two theoretical models that can predict the possibility for filling. First, we recast the diffusion-reaction equation for the case of a sidewall with variable taper angle. This affords a definition of effective AR, which is larger than the nominal AR due to the reduced species transport. We then derive the coating profile, both for superconformal and for conformal coating. The critical (most difficult) step in the filling process occurs when the sidewalls merge at the bottom of the trench to form the V shape. Experimentally, for the Mg(DMADB)2/H2O system and a starting AR = 9, this model predicts that complete filling will not be possible, whereas experimentally we do obtain complete filling. We then hypothesize that glancing-angle, long-range transport of species may be responsible for the better than predicted filling. To account for the variable range of species transport, we construct a ballistic transport model. This incorporates the incident flux from outside the structure, cosine law re-emission from surfaces, and line-of-sight transport between internal surfaces. We cast the transport probability between all positions within the trench into a matrix that represents the redistribution of flux after one cycle of collisions. Matrix manipulation then affords a computationally efficient means to determine the steady-state flux distribution and growth rate for a given taper angle. The

  8. SUEX process optimization for ultra-thick high-aspect ratio LIGA imaging

    NASA Astrophysics Data System (ADS)

    Johnson, Donald W.; Goettert, Jost; Singh, Varshni; Yemane, Dawit

    2011-04-01

    oven, taken out and cooled to RT then relaxed up to 3 days before development to reduce stress. Development was done in PGMEA for up to 3 hours for the 1000μm thick samples followed by a short IPA rinse and drying in air. Very high aspect ratios of 100 or more have been routinely patterned with nearly perfectly straight sidewalls (~1-1.5μm deviation for a 1mm tall structure) and excellent image fidelity.

  9. Public Data Set: H-mode Plasmas at Very Low Aspect Ratio on the Pegasus Toroidal Experiment

    DOE Data Explorer

    Thome, Kathreen E. [University of Wisconsin-Madison; Oak Ridge Associated Universities] (ORCID:0000000248013922); Bongard, Michael W. [University of Wisconsin-Madison] (ORCID:0000000231609746); Barr, Jayson L. [University of Wisconsin-Madison] (ORCID:0000000177685931); Burke, Marcus G. [University of Wisconsin-Madison] (ORCID:0000000176193724); Fonck, Raymond J. [University of Wisconsin-Madison] (ORCID:0000000294386762); Kriete, David M. [University of Wisconsin-Madison] (ORCID:0000000236572911); Perry, Justin M. [University of Wisconsin-Madison] (ORCID:0000000171228609); Reusch, Joshua A. [University of Wisconsin-Madison] (ORCID:0000000284249422); Schlossberg, David J. [University of Wisconsin-Madison] (ORCID:0000000287139448)

    2016-08-05

    This public data set contains openly-documented, machine readable digital research data accompanying 'H-mode Plasmas at Very Low Aspect Ratio on the Pegasus Toroidal Experiment' by K.E. Thome et al., accepted for publication in Nuclear Fusion.

  10. Surface chemistry but not aspect ratio mediates the biological toxicity of gold nanorods in vitro and in vivo

    PubMed Central

    Wan, Jiali; Wang, Jia-Hong; Liu, Ting; Xie, Zhixiong; Yu, Xue-Feng; Li, Wenhua

    2015-01-01

    Gold nanorods are a promising nanoscale material in clinical diagnosis and treatment. The physicochemical properties of GNRs, including size, shape and surface features, are crucial factors affecting their cytotoxicity. In this study, we investigated the effects of different aspect ratios and surface modifications on the cytotoxicity and cellular uptake of GNRs in cultured cells and in mice. The results indicated that the surface chemistry but not the aspect ratio of GNRs mediates their biological toxicity. CTAB-GNRs with various aspect ratios had similar abilities to induce cell apoptosis and autophagy by damaging mitochondria and activating intracellular reactive oxygen species (ROS). However, GNRs coated with CTAB/PSS, CTAB/PAH, CTAB/PSS/PAH or CTAB/PAH/PSS displayed low toxicity and did not induce cell death. CTAB/PAH-coated GNRs caused minimally abnormal cell morphology compared with CTAB/PSS and CTAB/PSS/PAH coated GNRs. Moreover, the intravenous injection of CTAB/PAH GNRs enabled the GNRs to reach tumor tissues through blood circulation in animals and remained stable, with a longer half-life compared to the other GNRs. Therefore, our results demonstrated that further coating can prevent cytotoxicity and cell death upon CTAB-coated GNR administration, similar to changing the GNR aspect ratio and CTAB/PAH coated GNRs show superior biological properties with better biocompatibility and minimal cytotoxicity. PMID:26096816

  11. Surface chemistry but not aspect ratio mediates the biological toxicity of gold nanorods in vitro and in vivo.

    PubMed

    Wan, Jiali; Wang, Jia-Hong; Liu, Ting; Xie, Zhixiong; Yu, Xue-Feng; Li, Wenhua

    2015-01-01

    Gold nanorods are a promising nanoscale material in clinical diagnosis and treatment. The physicochemical properties of GNRs, including size, shape and surface features, are crucial factors affecting their cytotoxicity. In this study, we investigated the effects of different aspect ratios and surface modifications on the cytotoxicity and cellular uptake of GNRs in cultured cells and in mice. The results indicated that the surface chemistry but not the aspect ratio of GNRs mediates their biological toxicity. CTAB-GNRs with various aspect ratios had similar abilities to induce cell apoptosis and autophagy by damaging mitochondria and activating intracellular reactive oxygen species (ROS). However, GNRs coated with CTAB/PSS, CTAB/PAH, CTAB/PSS/PAH or CTAB/PAH/PSS displayed low toxicity and did not induce cell death. CTAB/PAH-coated GNRs caused minimally abnormal cell morphology compared with CTAB/PSS and CTAB/PSS/PAH coated GNRs. Moreover, the intravenous injection of CTAB/PAH GNRs enabled the GNRs to reach tumor tissues through blood circulation in animals and remained stable, with a longer half-life compared to the other GNRs. Therefore, our results demonstrated that further coating can prevent cytotoxicity and cell death upon CTAB-coated GNR administration, similar to changing the GNR aspect ratio and CTAB/PAH coated GNRs show superior biological properties with better biocompatibility and minimal cytotoxicity. PMID:26096816

  12. Strain-gage bridge calibration and flight loads measurements on a low-aspect-ratio thin wing

    NASA Technical Reports Server (NTRS)

    Peele, E. L.; Eckstrom, C. V.

    1975-01-01

    Strain-gage bridges were used to make in-flight measurements of bending moment, shear, and torque loads on a low-aspect-ratio, thin, swept wing having a full depth honeycomb sandwich type structure. Standard regression analysis techniques were employed in the calibration of the strain bridges. Comparison of the measured loads with theoretical loads are included.

  13. Bulk purification and deposition methods for selective enrichment in high aspect ratio single-walled carbon nanotubes.

    PubMed

    Bhatt, Nidhi P; Vichchulada, Pornnipa; Lay, Marcus D

    2012-06-01

    Aqueous batch processing methods for the concurrent purification of single-walled carbon nanotube (SWNT) soot and enrichment in high aspect ratio nanotubes are essential to their use in a wide variety of electronic, structural, and mechanical applications. This manuscript presents a new route to the bulk purification and enrichment of unbundled SWNTs having average lengths in excess of 2 μm. Iterative centrifugation cycles at low centripetal force not only removed amorphous C and catalyst nanoparticles but also allowed the enhanced buoyancy of surfactant encapsulated, unbundled, high aspect ratio SWNTs to be used to isolate them in the supernatant. UV-vis-NIR and Raman spectroscopy were used to verify the removal of residual impurities from as-produced (AP-grade) arc discharge soot and the simultaneous enrichment in unbundled, undamaged, high aspect ratio SWNTs. The laminar flow deposition process (LFD) used to form two-dimensional networks of SWNTs prevented bundle formation during network growth. Additionally, it further enhanced the quality of deposits by taking advantage of the inverse relationship between the translational diffusion coefficient and length for suspended nanoparticles. This resulted in preferential deposition of pristine, unbundled, high aspect ratio SWNTs over residual impurities, as observed by Raman spectroscopy and atomic force microscopy (AFM). PMID:22571337

  14. Fabrication of micro-pin array with high aspect ratio on stainless steel using nanosecond laser beam machining

    NASA Astrophysics Data System (ADS)

    Lee, Se Won; Shin, Hong Shik; Chu, Chong Nam

    2013-01-01

    In this paper, a micro-pin array with a high aspect ratio was fabricated on AISI 304 using laser beam ablation for attachment to a vertical wall. In recent times, there has been research in various fields, including robotics and bio-MEMS, regarding attachment to vertical walls, and micro-pin arrays may offer the best solution. For vertical wall attachment, the micro-pin should have a high aspect ratio, long length, and sharp tip. The recast layer could be piled due to the chromium oxide with high surface tension and viscosity of chromium oxide, and it composed the micro-pins with high aspect ratio. X-ray photoelectron spectroscopy (XPS) was used to identify the characteristics of the piled recast layer. The machining characteristics for a high aspect ratio micro-pin array were investigated according to laser beam machining parameters. In addition, experiments for attaching force relative to the surface roughness of the subject plane were carried out.

  15. Tunable Microwave Absorption Frequency by Aspect Ratio of Hollow Polydopamine@α-MnO2 Microspindles Studied by Electron Holography.

    PubMed

    She, Wen; Bi, Han; Wen, Zhiwei; Liu, Qinghe; Zhao, Xuebing; Zhang, Jie; Che, Renchao

    2016-04-20

    A tunable response frequency is highly desirable for practical applications of microwave absorption materials but remains a great challenge. Here, hollow lightweight polydopamine@α-MnO2 microspindles were facilely synthesized with the tunable absorption frequency governed by the aspect ratio. The size of the hard template is a key factor to achieve the unique shape; the polymer layer with uniform thickness plays an important role in obtaining spindles with homogeneous size. With the aspect ratio increasing, the maximum reflection loss, as well as the absorption bandwidth (<-10 dB), increases and then decreases; meanwhile, the microwave absorption band shifts to the low frequency. The optimized aspect ratio of the cavity about the hollow polydopamine@α-MnO2 microspindles is ∼2.8. With 3 mm thickness at 9.7 GHz, the strongest reflection reaches -21.8 dB, and the width of the absorbing band (<-10 dB) is as wide as 3.3 GHz. Via electron holography, it is confirmed that strong charge accumulates around the interface between the polydopamine and α-MnO2 layers, which mainly contributes to the dielectric polarization absorption. This study proposes a reliable strategy to tune the absorption frequency via different aspect ratio polymer@α-MnO2 microspindles. PMID:27027922

  16. Direct e-beam writing of dense and high aspect ratio nanostructures in thick layers of PMMA for electroplating

    NASA Astrophysics Data System (ADS)

    Gorelick, Sergey; Guzenko, Vitaliy A.; Vila-Comamala, Joan; David, Christian

    2010-07-01

    Due to the ability of 100 keV electrons to penetrate deep into resist with little scattering, we were able to directly write various dense and high aspect ratio nanostructures in 540 nm and 1.1 µm thick layers of poly(methyl methacrylate) (PMMA) resist. The PMMA molds produced by electron beam lithography were developed using a high contrast developer. The molds were used to transfer the pattern into metallic nanostructures by filling the developed trenches with Au by electroplating. By exposing lines narrower than the target width, we observed improved process latitude and line width control. The obtained aspect ratios of the dense structures are nearly 20 in 1.1 µm PMMA layers and > 16 for structures electroplated into this PMMA mold. The fabrication method was successfully applied to produce Au diffractive x-ray Fresnel zone plates of exceptionally good quality with 50 and 70 nm outermost zones using 540 nm and 1.1 µm thick PMMA molds. In addition, we also produced regular arrays of high aspect ratio and dense Au nanorods with periods down to 100 nm and high aspect ratio split-ring resonators.

  17. Direct e-beam writing of dense and high aspect ratio nanostructures in thick layers of PMMA for electroplating.

    PubMed

    Gorelick, Sergey; Guzenko, Vitaliy A; Vila-Comamala, Joan; David, Christian

    2010-07-23

    Due to the ability of 100 keV electrons to penetrate deep into resist with little scattering, we were able to directly write various dense and high aspect ratio nanostructures in 540 nm and 1.1 microm thick layers of poly(methyl methacrylate) (PMMA) resist. The PMMA molds produced by electron beam lithography were developed using a high contrast developer. The molds were used to transfer the pattern into metallic nanostructures by filling the developed trenches with Au by electroplating. By exposing lines narrower than the target width, we observed improved process latitude and line width control. The obtained aspect ratios of the dense structures are nearly 20 in 1.1 microm PMMA layers and > 16 for structures electroplated into this PMMA mold. The fabrication method was successfully applied to produce Au diffractive x-ray Fresnel zone plates of exceptionally good quality with 50 and 70 nm outermost zones using 540 nm and 1.1 microm thick PMMA molds. In addition, we also produced regular arrays of high aspect ratio and dense Au nanorods with periods down to 100 nm and high aspect ratio split-ring resonators. PMID:20601756

  18. Comparison of High Aspect Ratio Cooling Channel Designs for a Rocket Combustion Chamber with Development of an Optimized Design

    NASA Technical Reports Server (NTRS)

    Wadel, Mary F.

    1998-01-01

    An analytical investigation on the effect of high aspect ratio (height/width) cooling channels, considering different coolant channel designs, on hot-gas-side wall temperature and coolant pressure drop for a liquid hydrogen cooled rocket combustion chamber, was performed. Coolant channel design elements considered were: length of combustion chamber in which high aspect ratio cooling was applied, number of coolant channels, and coolant channel shape. Seven coolant channel designs were investigated using a coupling of the Rocket Thermal Evaluation code and the Two-Dimensional Kinetics code. Initially, each coolant channel design was developed, without consideration for fabrication, to reduce the hot-gas-side wall temperature from a given conventional cooling channel baseline. These designs produced hot-gas-side wall temperature reductions up to 22 percent, with coolant pressure drop increases as low as 7.5 percent from the baseline. Fabrication constraints for milled channels were applied to the seven designs. These produced hot-gas-side wall temperature reductions of up to 20 percent, with coolant pressure drop increases as low as 2 percent. Using high aspect ratio cooling channels for the entire length of the combustion chamber had no additional benefit on hot-gas-side wall temperature over using high aspect ratio cooling channels only in the throat region, but increased coolant pressure drop 33 percent. Independent of coolant channel shape, high aspect ratio cooling was able to reduce the hot-gas-side wall temperature by at least 8 percent, with as low as a 2 percent increase in coolant pressure drop. ne design with the highest overall benefit to hot-gas-side wall temperature and minimal coolant pressure drop increase was the design which used bifurcated cooling channels and high aspect ratio cooling in the throat region. An optimized bifurcated high aspect ratio cooling channel design was developed which reduced the hot-gas-side wall temperature by 18 percent and

  19. Synthesis of Hollow Mesoporous Silica Nanorods with Controllable Aspect Ratios for Intracellular Triggered Drug Release in Cancer Cells.

    PubMed

    Yang, Xue; He, Dinggeng; He, Xiaoxiao; Wang, Kemin; Tang, Jinlu; Zou, Zhen; He, Xing; Xiong, Jun; Li, Liling; Shangguan, Jingfang

    2016-08-17

    Here, we have reported a straightforward and effective synthetic strategy for synthesis of aspect-ratios-controllable mesoporous silica nanorods with hollow structure (hMSR) and its application for transcription factor (TF)-responsive drug delivery intracellular. Templating by an acid-degradable nickel hydrazine nanorods (NHNT), we have first synthesized the hollow dense silica nanorods and then coated on a mesoporous silica layer. Subsequently, the dense silica layer was removed by the surface-protected etching method and the hollow structure of hMSR was finally formed. The aspect ratios of the hMSR can be conveniently controlled by regulating the aspect ratios of NHNT. Four different hMSR with aspect ratios of ca. 2.5, ca. 5.3, ca. 8.1, and ca. 9.0 has been obtained. It was demonstrated that the as-prepared hMSRs have good stability, high drug loading capacity, and fast cell uptake capability, which makes them to a potential nanocarrier for drug delivery. As the paradigm, hMSR with an aspect ratio of ca. 8.1 was then applied for TF-responsive intracellular anticancer drug controlled release by using a Ag(+)-stabilized molecular switch of triplex DNA (TDNA) as capping agents and probes for TFs recognition. In the presence of TF, the pores of hMSR can be unlocked by the TFs induced disassembly of TDNA, leading to the leakage of DOX. The research in vitro displayed that this system has a TFs-triggered DOX release, and the cytotoxicity in L02 normal cells was lower than that of HeLa cells. We hope that this developed hMSR-based system will promote the development of cancer therapy in related fields. PMID:27411575

  20. Finite-span rotating wings: three-dimensional vortex formation and variations with aspect ratio

    NASA Astrophysics Data System (ADS)

    Carr, Z. R.; Chen, C.; Ringuette, M. J.

    2013-02-01

    We investigate experimentally the effect of aspect ratio ( [InlineMediaObject not available: see fulltext.] ) on the time-varying, three-dimensional flow structure of flat-plate wings rotating from rest at 45° angle of attack. Plates of [InlineMediaObject not available: see fulltext.] = 2 and 4 are tested in a 50 % by mass glycerin-water mixture, with a total rotation of ϕ = 120° and a matched tip Reynolds number of 5,000. The time-varying, three-component volumetric velocity field is reconstructed using phase-locked, phase-averaged stereoscopic digital particle image velocimetry in multiple, closely-spaced chordwise planes. The vortex structure is analyzed using the {Q}-criterion, helicity density, and spanwise quantities. For both [InlineMediaObject not available: see fulltext.] s, the flow initially consists of a connected and coherent leading-edge vortex (LEV), tip vortex (TV), and trailing-edge vortex (TEV) loop; the LEV increases in size with span and tilts aft. Smaller, discrete vortices are present in the separated shear layers at the trailing and tip edges, which wrap around the primary TEV and TV. After about ϕ = 20°, the outboard-span LEV lifts off the plate and becomes arch-like. A second, smaller LEV and the formation of corner vortex structures follow. For [InlineMediaObject not available: see fulltext.] = 4, the outboard LEV moves farther aft, multiple LEVs form ahead of it, and after about ϕ = 50° a breakdown of the lifted-off LEV and the TV occurs. However, for [InlineMediaObject not available: see fulltext.] = 2, the outboard LEV lift-off is not progressive, and the overall LEV-TV flow remains more coherent and closer to the plate, with evidence of breakdown late in the motion. Inboard of about 50 % span, the [InlineMediaObject not available: see fulltext.] = 4 LEV is stable for the motion duration. Up to approximately 60 % span, the [InlineMediaObject not available: see fulltext.] = 2 LEV is distinct from the TV and is similarly stable

  1. Distal femoral aspect ratios throughout childhood: an MRI study of normative data and sex comparisons.

    PubMed

    Schwarzkopf, Ran; Bauer, Andrea; Chaurasia, Avinash; Hall, Amber M; Zurakowski, David; Scott, Richard D

    2016-05-01

    The ratio of anteroposterior (AP) to medial-lateral (ML) dimensions of the distal femur in adults differs by sex. The average AP/ML dimension ratios are 0.82 for females and 0.79 for males. How and when this difference develops is not yet understood. In this study, the distal femoral dimensions and physeal development of 345 participants younger than 21 years of age were evaluated by MRI. Regression analysis indicated a significant increase in the AP/ML ratio with increasing age for both sexes. In girls, the ratio increased from 0.63 at ages 0-5 years to 0.76 at 15-20 years. In boys, the ratio increased from 0.61 to 0.73 over the same age groups. Female distal femur dimensions are narrower than that of males from birth. Throughout childhood, both sexes show gradual increases in AP/ML ratios. After closure of the physes, the AP/ML ratio in children approaches adult values, with females continuing to have relatively narrower dimensions than males. PMID:26895290

  2. Nanoimprinting ultrasmall and high-aspect-ratio structures by using rubber-toughened UV cured epoxy resist

    NASA Astrophysics Data System (ADS)

    Shin, Young Jae; Wu, Yi-Kuei; Guo, L. Jay

    2013-06-01

    A simple and robust scheme is proposed for the fabrication of nanoscale (20 nm line width) and high-aspect-ratio (9:1) structures by using modulus-tunable UV curable epoxy resists. Additionally, the ability to control the Young’s modulus of the imprinted material from hard to rigiflex using these epoxy resists is demonstrated. The physical properties of the new epoxy resists were controlled by adjusting the ratio of bisphenol F-type epoxy resin and acrylonitrile-butadiene rubber-based epoxy resin in the formulation of the resist. The mechanical properties of the resist were tuned to obtain various aspect ratios as well as mold flexibility for conformal contact over non-planar surfaces and large areas. In order to reduce the line width of the imprinted patterns, a process to conformally coat the mold structure by atomic layer deposition of alumina was also developed. Narrow lines with high-aspect-ratio features and with very low defect density were achieved via the new approach and the high mechanical strength of the new resist formulation.

  3. The Effect of Relative Submergence and Shape on the Wake of a Low-Aspect-Ratio Wall-Mounted body

    NASA Astrophysics Data System (ADS)

    Hajimirzaie, Seyed Mohammad; Wojcik, Craig; Buchholz, James

    2010-11-01

    Wall-mounted bodies in boundary layer flows are ubiquitous in nature and engineering applications and significantly enhance momentum and scalar transport in their vicinity. In this experimental study we evaluate the role of relative submergence (the ratio of flow depth to obstacle height) and shape on the wakes around four different wall-mounted obstacles. We consider four obstacle geometries: semi-ellipsoids with the major and minor axes of the base ellipses aligned in the streamwise and transverse directions, and two cylinders with matching aspect ratios D/H (where D is the maximum transverse dimension and H is the obstacle height). The aspect ratios considered are 0.67 and 0.89. DPIV was used to interrogate the flow. Streamwise structures observed in the mean wake include tip, base, and horseshoe vortex pairs as well as additional structures apparently not previously observed. The presence of a base vortex for such low-aspect-ratio obstacles is unexpected, and its strength increases with decreasing relative submergence. We will discuss hypotheses on the mechanisms of generation of the base and tertiary structures and their interconnection with the rest of the vortex skeleton.

  4. Nanoimprinting ultrasmall and high-aspect-ratio structures by using rubber-toughened UV cured epoxy resist.

    PubMed

    Shin, Young Jae; Wu, Yi-Kuei; Jay Guo, L

    2013-06-28

    A simple and robust scheme is proposed for the fabrication of nanoscale (20 nm line width) and high-aspect-ratio (9:1) structures by using modulus-tunable UV curable epoxy resists. Additionally, the ability to control the Young's modulus of the imprinted material from hard to rigiflex using these epoxy resists is demonstrated. The physical properties of the new epoxy resists were controlled by adjusting the ratio of bisphenol F-type epoxy resin and acrylonitrile-butadiene rubber-based epoxy resin in the formulation of the resist. The mechanical properties of the resist were tuned to obtain various aspect ratios as well as mold flexibility for conformal contact over non-planar surfaces and large areas. In order to reduce the line width of the imprinted patterns, a process to conformally coat the mold structure by atomic layer deposition of alumina was also developed. Narrow lines with high-aspect-ratio features and with very low defect density were achieved via the new approach and the high mechanical strength of the new resist formulation. PMID:23708317

  5. Effects of orbit squeezing on poloidal mass flow and bootstrap current in tokamak plasmas

    SciTech Connect

    Shaing, K.C. ); Hsu, C.T. ); Hazeltine, R.D. )

    1994-10-01

    It is shown, by solving the drift kinetic equation, that the asymptotic values of the poloidal mass flow and the bootstrap current in the banana regime of large-aspect-ratio tokamak plasmas are not affected by orbit squeezing. However, because the definition of ion collisionality [upsilon][sub *[ital i

  6. A comparative study of different aspects of manipulating ratio spectra applied for ternary mixtures: derivative spectrophotometry versus wavelet transform.

    PubMed

    Salem, Hesham; Lotfy, Hayam M; Hassan, Nagiba Y; El-Zeiny, Mohamed B; Saleh, Sarah S

    2015-01-25

    This work represents a comparative study of different aspects of manipulating ratio spectra, which are: double divisor ratio spectra derivative (DR-DD), area under curve of derivative ratio (DR-AUC) and its novel approach, namely area under the curve correction method (AUCCM) applied for overlapped spectra; successive derivative of ratio spectra (SDR) and continuous wavelet transform (CWT) methods. The proposed methods represent different aspects of manipulating ratio spectra of the ternary mixture of Ofloxacin (OFX), Prednisolone acetate (PA) and Tetryzoline HCl (TZH) combined in eye drops in the presence of benzalkonium chloride as a preservative. The proposed methods were checked using laboratory-prepared mixtures and were successfully applied for the analysis of pharmaceutical formulation containing the cited drugs. The proposed methods were validated according to the ICH guidelines. A comparative study was conducted between those methods regarding simplicity, limitation and sensitivity. The obtained results were statistically compared with those obtained from the reported HPLC method, showing no significant difference with respect to accuracy and precision. PMID:25171050

  7. A comparative study of different aspects of manipulating ratio spectra applied for ternary mixtures: Derivative spectrophotometry versus wavelet transform

    NASA Astrophysics Data System (ADS)

    Salem, Hesham; Lotfy, Hayam M.; Hassan, Nagiba Y.; El-Zeiny, Mohamed B.; Saleh, Sarah S.

    2015-01-01

    This work represents a comparative study of different aspects of manipulating ratio spectra, which are: double divisor ratio spectra derivative (DR-DD), area under curve of derivative ratio (DR-AUC) and its novel approach, namely area under the curve correction method (AUCCM) applied for overlapped spectra; successive derivative of ratio spectra (SDR) and continuous wavelet transform (CWT) methods. The proposed methods represent different aspects of manipulating ratio spectra of the ternary mixture of Ofloxacin (OFX), Prednisolone acetate (PA) and Tetryzoline HCl (TZH) combined in eye drops in the presence of benzalkonium chloride as a preservative. The proposed methods were checked using laboratory-prepared mixtures and were successfully applied for the analysis of pharmaceutical formulation containing the cited drugs. The proposed methods were validated according to the ICH guidelines. A comparative study was conducted between those methods regarding simplicity, limitation and sensitivity. The obtained results were statistically compared with those obtained from the reported HPLC method, showing no significant difference with respect to accuracy and precision.

  8. Solenoid-free plasma start-up in spherical tokamaks

    NASA Astrophysics Data System (ADS)

    Raman, R.; Shevchenko, V. F.

    2014-10-01

    The central solenoid is an intrinsic part of all present-day tokamaks and most spherical tokamaks. The spherical torus (ST) confinement concept is projected to operate at high toroidal beta and at a high fraction of the non-inductive bootstrap current as required for an efficient reactor system. The use of a conventional solenoid in a ST-based fusion nuclear facility is generally believed to not be a possibility. Solenoid-free plasma start-up is therefore an area of extensive worldwide research activity. Solenoid-free plasma start-up is also relevant to steady-state tokamak operation, as the central transformer coil of a conventional aspect ratio tokamak reactor would be located in a high radiation environment but would be needed only during the initial discharge initiation and current ramp-up phases. Solenoid-free operation also provides greater flexibility in the selection of the aspect ratio and simplifies the reactor design. Plasma start-up methods based on induction from external poloidal field coils, helicity injection and radio frequency current drive have all made substantial progress towards meeting this important need for the ST. Some of these systems will now undergo the final stages of test in a new generation of large STs, which are scheduled to begin operations during the next two years. This paper reviews research to date on methods for inducing the initial start-up current in STs without reliance on the conventional central solenoid.

  9. Effects of aspect ratio and specimen size on uniaxial failure stress of iron green bodies at high strain rates

    NASA Astrophysics Data System (ADS)

    Kuroyanagi, Yuki; Nishida, Masahiro; Ogura, Takashi; Häggblad, H.-Å.; Jonsén, P.; Gustafsson, G.

    2015-09-01

    Powder metallurgy is used for the production of a number of mechanical parts and is an essential production method. These are great advantages such as product cost effectiveness and product uniqueness. In general, however parts created by powder metallurgy have low strength because of low density. In order to increase strength as well as density, new techniques such as high-velocity-compaction (HVC) was developed and further investigation has been conducted on improvement of techniques and optimum condition using computer simulation. In this study, the effects of aspect ratio and specimen size of iron green bodies on failure strength of uniaxial compression and failure behavior were examined using a split Hopkinson pressure Bar. The diameters of specimens were 12.5 mm and 25 mm the aspect ratios (thickness/diameter) were 0.8 and 1.2.

  10. Viscoelastic lithography for fabricating self-organizing soft micro-honeycomb structures with ultra-high aspect ratios

    NASA Astrophysics Data System (ADS)

    Jeong, Gi Seok; No, Da Yoon; Lee, Jaeseo; Yoon, Junghyo; Chung, Seok; Lee, Sang-Hoon

    2016-05-01

    High-aspect ratio micro- and nano-structures have been used for the production of a variety of applications. In this paper, we describe a simple and cost-effective approach to fabricate an arrayed microarchitecture with an ultra-high aspect ratio using soft materials. The shapes and sizes of the honeycomb structure can be easily modulated by changing the dimensions and position of the base mould pattern and the pressure. The honeycomb structure is used to prepare a drug delivery patch and a microwell array to form cell spheroids without cell loss. The honeycomb structures prepared using natural ECM (collagen-Matrigel) materials are successfully fabricated. The hepatocytes and endothelial cells are seeded and co-cultured in the ECM-based micro-honeycomb to prepare a 3D liver model successfully mimicking an ultrastructure of liver and providing enhanced liver function.

  11. High aspect ratio nano-fabrication of photonic crystal structures on glass wafers using chrome as hard mask

    NASA Astrophysics Data System (ADS)

    Nazmul Hossain, Md; Justice, John; Lovera, Pierre; McCarthy, Brendan; O'Riordan, Alan; Corbett, Brian

    2014-09-01

    Wafer-scale nano-fabrication of silicon nitride (Si x N y ) photonic crystal (PhC) structures on glass (quartz) substrates is demonstrated using a thin (30 nm) chromium (Cr) layer as the hard mask for transferring the electron beam lithography (EBL) defined resist patterns. The use of the thin Cr layer not only solves the charging effect during the EBL on the insulating substrate, but also facilitates high aspect ratio PhCs by acting as a hard mask while deep etching into the Si x N y . A very high aspect ratio of 10:1 on a 60 nm wide grating structure has been achieved while preserving the quality of the flat top of the narrow lines. The presented nano-fabrication method provides PhC structures necessary for a high quality optical response. Finally, we fabricated a refractive index based PhC sensor which shows a sensitivity of 185 nm per RIU.

  12. Adaptive finite elements with high aspect ratio for the computation of coalescence using a phase-field model

    NASA Astrophysics Data System (ADS)

    Burman, E.; Jacot, A.; Picasso, M.

    2004-03-01

    A multiphase-field model for the description of coalescence in a binary alloy is solved numerically using adaptive finite elements with high aspect ratio. The unknown of the multiphase-field model are the three phase fields (solid phase 1, solid phase 2, and liquid phase), a Lagrange multiplier and the concentration field. An Euler implicit scheme is used for time discretization, together with continuous, piecewise linear finite elements. At each time step, a linear system corresponding to the three phases plus the Lagrange multiplier has to be solved. Then, the linear system pertaining to concentration is solved. An adaptive finite element algorithm is proposed. In order to reduce the number of mesh vertices, the generated meshes contain elements with high aspect ratio. The refinement and coarsening criteria are based on an error indicator which has already been justified theoretically for simpler problems. Numerical results on two test cases show the efficiency of the method.

  13. Numerical Study of the Effect of the Sample Aspect Ratio on the Ductility of Bulk Metallic Glasses (BMGs) Under Compression

    NASA Astrophysics Data System (ADS)

    Jiang, Yunpeng

    2016-05-01

    In this article, a systematic numerical study was conducted to study the detailed shear banding evolution in bulk metallic glasses (BMGs) with various sample aspect ratios under uniaxial compression, and whereby the effect of the sample aspect ratio on the compressive ductility was elucidated. A finite strain viscoelastic model was employed to describe the shear banding nucleation, growth, and coalescence in BMG samples with the help of Anand and Su's theory, which was incorporated into the ABAQUS finite element method code as a user material subroutine VUMAT. The present numerical method was first verified by comparing with the corresponding experimental results, and then parameter analysis was performed to discuss the impact of microstructure parameters on the predicted results. The present modeling will shed some light on enhancing the toughness of BMG structures in the engineering applications.

  14. Configuration design studies and wind tunnel tests of an energy efficient transport with a high-aspect-ratio supercritical wing

    NASA Technical Reports Server (NTRS)

    Henne, P. A.; Dahlin, J. A.; Peavey, C. C.; Gerren, D. S.

    1982-01-01

    The results of design studies and wind tunnel tests of high aspect ratio supercritical wings suitable for a medium range, narrow body transport aircraft flying near M=0.80 were presented. The basic characteristics of the wing design were derived from system studies of advanced transport aircraft where detailed structural and aerodynamic tradeoffs were used to determine the most optimum design from the standpoint of fuel usage and direct operating cost. These basic characteristics included wing area, aspect ratio, average thickness, and sweep. The detailed wing design was accomplished through application of previous test results and advanced computational transonic flow procedures. In addition to the basic wing/body development, considerable attention was directed to nacelle/plyon location effects, horizontal tail effects, and boundary layer transition effects. Results of these tests showed that the basic cruise performance objectives were met or exceeded.

  15. Enhanced photocatalytic activity of ultra-high aspect ratio ZnO nanowires due to Cu induced defects

    NASA Astrophysics Data System (ADS)

    Pasupathi Sugavaneshwar, Ramu; Duy Dao, Thang; Nanda, Karuna Kar; Nagao, Tadaaki; Hishita, Shunichi; Sakaguchi, Isao

    2015-12-01

    We report the synthesis of ZnO nanowires in ambient air at 650°C by a single-step vapor transport method using two different sources Zn (ZnO nanowires-I) and Zn:Cu (ZnO nanowires-II). The Zn:Cu mixed source co-vaporize Zn with a small amount of Cu at temperatures where elemental Cu source does not vaporize. This method provides us a facile route for Cu doping into ZnO. The aspect ratio of the grown ZnO nanowires-II was found to be higher by more than five times compared ZnO nanowires-I. Photocatalytic activity was measured by using a solar simulator and its ultraviolet-filtered light. The ZnO nanowires-II shows higher catalytic activity due to increased aspect ratio and higher content of surface defects because of incorporation of Cu impurities.

  16. Viscoelastic lithography for fabricating self-organizing soft micro-honeycomb structures with ultra-high aspect ratios

    PubMed Central

    Jeong, Gi Seok; No, Da Yoon; Lee, JaeSeo; Yoon, Junghyo; Chung, Seok; Lee, Sang-Hoon

    2016-01-01

    High-aspect ratio micro- and nano-structures have been used for the production of a variety of applications. In this paper, we describe a simple and cost-effective approach to fabricate an arrayed microarchitecture with an ultra-high aspect ratio using soft materials. The shapes and sizes of the honeycomb structure can be easily modulated by changing the dimensions and position of the base mould pattern and the pressure. The honeycomb structure is used to prepare a drug delivery patch and a microwell array to form cell spheroids without cell loss. The honeycomb structures prepared using natural ECM (collagen–Matrigel) materials are successfully fabricated. The hepatocytes and endothelial cells are seeded and co-cultured in the ECM-based micro-honeycomb to prepare a 3D liver model successfully mimicking an ultrastructure of liver and providing enhanced liver function. PMID:27157977

  17. Hydrothermal waves under microgravity in a differentially heated long liquid bridge with aspect ratio near the Rayleigh-limit

    NASA Astrophysics Data System (ADS)

    Schwabe, D.

    2005-08-01

    A liquid bridge of 15.0 mm length L and 3.0 mm radius r (aspect ratio A = L/r = 5) from 2 cSt silicone oil (Pr = 28) was established under microgravity during the flight of the sounding rocket MAXUS-4. Four different temperature differences ΔT = 7K, 9K, 10K, 12K have been applied between the ends, each for sufficient time to reach steady state thermocapillary flow conditions. The aim of the experiment - to observe the onset of hydrothermal waves and to measure their features like the waves phase speed and the angle between the wave vector and the applied temperature gradient - was reached. We used microgravity in this experiment in a twofold manner; (1) a liquid bridge with A = 5 can be established only under microgravity; (2) it was possible to study hydrothermal waves without the influence of gravity and without the aspect ratio restrictions at normal gravity.

  18. Nano-scaled graphene platelets with a high length-to-width aspect ratio

    DOEpatents

    Zhamu, Aruna; Guo, Jiusheng; Jang, Bor Z.

    2010-09-07

    This invention provides a nano-scaled graphene platelet (NGP) having a thickness no greater than 100 nm and a length-to-width ratio no less than 3 (preferably greater than 10). The NGP with a high length-to-width ratio can be prepared by using a method comprising (a) intercalating a carbon fiber or graphite fiber with an intercalate to form an intercalated fiber; (b) exfoliating the intercalated fiber to obtain an exfoliated fiber comprising graphene sheets or flakes; and (c) separating the graphene sheets or flakes to obtain nano-scaled graphene platelets. The invention also provides a nanocomposite material comprising an NGP with a high length-to-width ratio. Such a nanocomposite can become electrically conductive with a small weight fraction of NGPs. Conductive composites are particularly useful for shielding of sensitive electronic equipment against electromagnetic interference (EMI) or radio frequency interference (RFI), and for electrostatic charge dissipation.

  19. Tokamak Startup Using Point-Source dc Helicity Injection

    SciTech Connect

    Battaglia, D. J.; Bongard, M. W.; Fonck, R. J.; Redd, A. J.; Sontag, A. C.

    2009-06-05

    Startup of a 0.1 MA tokamak plasma is demonstrated on the ultralow aspect ratio Pegasus Toroidal Experiment using three localized, high-current density sources mounted near the outboard midplane. The injected open field current relaxes via helicity-conserving magnetic turbulence into a tokamaklike magnetic topology where the maximum sustained plasma current is determined by helicity balance and the requirements for magnetic relaxation.

  20. Tokamak startup using point-source dc helicity injection.

    PubMed

    Battaglia, D J; Bongard, M W; Fonck, R J; Redd, A J; Sontag, A C

    2009-06-01

    Startup of a 0.1 MA tokamak plasma is demonstrated on the ultralow aspect ratio Pegasus Toroidal Experiment using three localized, high-current density sources mounted near the outboard midplane. The injected open field current relaxes via helicity-conserving magnetic turbulence into a tokamaklike magnetic topology where the maximum sustained plasma current is determined by helicity balance and the requirements for magnetic relaxation. PMID:19658871

  1. Wind tunnel tests of high-lift systems for advanced transports using high-aspect-ratio supercritical wings

    NASA Technical Reports Server (NTRS)

    Allen, J. B.; Oliver, W. R.; Spacht, L. A.

    1982-01-01

    The wind tunnel testing of an advanced technology high lift system for a wide body and a narrow body transport incorporating high aspect ratio supercritical wings is described. This testing has added to the very limited low speed high Reynolds number data base for this class or aircraft. The experimental results include the effects on low speed aerodynamic characteristics of various leading and trailing edge devices, nacelles and pylons, ailerons, and spoilers, and the effects of Mach and Reynolds numbers.

  2. Investigation at Low Speeds of the Effect of Aspect Ratio and Sweep on Rolling Stability Derivatives of Untapered Wings

    NASA Technical Reports Server (NTRS)

    Goodman, Alex; Fisher, Lewis R

    1950-01-01

    A low-scale wind-tunnel investigation was conducted in rolling flow to determine the effects of aspect ratio and sweep (when varied independently) on the rolling stability derivatives for a series of untapered wings. The rolling-flow equipment of the Langley stability tunnel was used for the tests. The data of the investigation have been used to develop a method of accounting for the effects of the drag on the yawing moment due to rolling throughout the lift range.

  3. Effects of aspect ratio and concentration on rheology of epoxy suspensions containing model plate-like nanoparticles

    SciTech Connect

    White, K. L.; Takahara, A.; Hawkins, S.; Sue, H.-J.; Miyamoto, M.

    2015-12-15

    Hexagonal 2-dimensional α-zirconium phosphate crystals were prepared with lateral diameters ranging from 110 nm to 1.5 μm to investigate the effect of particle size on suspension rheology. The nanoplatelets were exfoliated to individual sheets with monodisperse thickness and dispersed in a Newtonian epoxy fluid. The steady shear response of dilute and semi-dilute suspensions was measured and compared to expressions obtained from theory for infinitely dilute suspensions. For suspensions containing the smaller nanoplatelets, aspect ratio ∼160, the low shear rate viscosity and transition to shear thinning behavior were well described by theory for loadings up to 0.5 vol. %. The agreement was improved by assuming a moderate polydispersity in lateral diameter, ∼30%–50%, which is consistent with experimental observation. For the higher aspect ratio nanoplatelets, good agreement between theory and experiment was observed only at high shear rates. At lower shear rate, theory consistently over-predicted viscosity, which was attributed to a progressive shift to non-isotropic initial conditions with increasing particle size. The results suggest that at a fixed Peclet number, there is an increasing tendency for the nanoplatelets to form transient, local stacks as particle size increases. The largest particles, aspect ratio ∼2200, showed unusual shear thinning and thickening behaviors that were attributed to particle flexibility. The findings demonstrate the surprising utility of theory for infinitely dilute suspensions to interpret, and in some cases quantitatively describe, the non-Newtonian viscosity of real suspensions containing high aspect ratio plate-like particles. A simple framework is proposed to interpret deviations from ideal behavior based on the local and collective behavior of the suspended nanoplatelets.

  4. Microdevice having interior cavity with high aspect ratio surface features and associated methods of manufacture and use

    DOEpatents

    Morales, Alfredo M.

    2002-01-01

    A microdevice having interior cavity with high aspect ratio features and ultrasmooth surfaces, and associated method of manufacture and use is described. An LIGA-produced shaped bit is used to contour polish the surface of a sacrificial mandrel. The contoured sacrificial mandrel is subsequently coated with a structural material and the mandrel removed to produce microdevices having micrometer-sized surface features and sub-micrometer RMS surface roughness.

  5. Ratio

    NASA Astrophysics Data System (ADS)

    Webster, Nathan A. S.; Pownceby, Mark I.; Madsen, Ian C.; Studer, Andrew J.; Manuel, James R.; Kimpton, Justin A.

    2014-12-01

    Effects of basicity, B (CaO:SiO2 ratio) on the thermal range, concentration, and formation mechanisms of silico-ferrite of calcium and aluminum (SFCA) and SFCA-I iron ore sinter bonding phases have been investigated using an in situ synchrotron X-ray diffraction-based methodology with subsequent Rietveld refinement-based quantitative phase analysis. SFCA and SFCA-I phases are the key bonding materials in iron ore sinter, and improved understanding of the effects of processing parameters such as basicity on their formation and decomposition may assist in improving efficiency of industrial iron ore sintering operations. Increasing basicity significantly increased the thermal range of SFCA-I, from 1363 K to 1533 K (1090 °C to 1260 °C) for a mixture with B = 2.48, to ~1339 K to 1535 K (1066 °C to 1262 °C) for a mixture with B = 3.96, and to ~1323 K to 1593 K (1050 °C to 1320 °C) at B = 4.94. Increasing basicity also increased the amount of SFCA-I formed, from 18 wt pct for the mixture with B = 2.48 to 25 wt pct for the B = 4.94 mixture. Higher basicity of the starting sinter mixture will, therefore, increase the amount of SFCA-I, considered to be more desirable of the two phases. Basicity did not appear to significantly influence the formation mechanism of SFCA-I. It did, however, affect the formation mechanism of SFCA, with the decomposition of SFCA-I coinciding with the formation of a significant amount of additional SFCA in the B = 2.48 and 3.96 mixtures but only a minor amount in the highest basicity mixture. In situ neutron diffraction enabled characterization of the behavior of magnetite after melting of SFCA produced a magnetite plus melt phase assemblage.

  6. Versatile pattern generation of periodic, high aspect ratio Si nanostructure arrays with sub-50-nm resolution on a wafer scale

    PubMed Central

    2013-01-01

    We report on a method of fabricating variable patterns of periodic, high aspect ratio silicon nanostructures with sub-50-nm resolution on a wafer scale. The approach marries step-and-repeat nanoimprint lithography (NIL) and metal-catalyzed electroless etching (MCEE), enabling near perfectly ordered Si nanostructure arrays of user-defined patterns to be controllably and rapidly generated on a wafer scale. Periodic features possessing circular, hexagonal, and rectangular cross-sections with lateral dimensions down to sub-50 nm, in hexagonal or square array configurations and high array packing densities up to 5.13 × 107 structures/mm2 not achievable by conventional UV photolithography are fabricated using this top-down approach. By suitably tuning the duration of catalytic etching, variable aspect ratio Si nanostructures can be formed. As the etched Si pattern depends largely on the NIL mould which is patterned by electron beam lithography (EBL), the technique can be used to form patterns not possible with self-assembly methods, nanosphere, and interference lithography for replication on a wafer scale. Good chemical resistance of the nanoimprinted mask and adhesion to the Si substrate facilitate good pattern transfer and preserve the smooth top surface morphology of the Si nanostructures as shown in TEM. This approach is suitable for generating Si nanostructures of controlled dimensions and patterns, with high aspect ratio on a wafer level suitable for semiconductor device production. PMID:24289275

  7. Effect of shape, size, and aspect ratio on nanoparticle penetration and distribution inside solid tissues using 3D spheroid models.

    PubMed

    Agarwal, Rachit; Jurney, Patrick; Raythatha, Mansi; Singh, Vikramjit; Sreenivasan, Sidlgata V; Shi, Li; Roy, Krishnendu

    2015-10-28

    Efficient penetration and uniform distribution of nanoparticles (NPs) inside solid tissues and tumors is paramount to their therapeutic and diagnostic success. While many studies have reported the effect of NP size and charge on intratissue distribution, role of shape, and aspect ratio on NP transport inside solid tissues remain unclear. Here experimental and theoretical studies are reported on how nanoscale geometry of Jet and Flash Imprint Lithography-fabricated, polyethylene-glycol-based anionic nanohydrogels affect their penetration and distribution inside 3D spheroids, a model representing the intervascular region of solid, tumor-like tissues. Unexpectedly, low aspect ratio cylindrical NPs (H/D ≈0.3; disk-like particles, 100 nm height, and 325 nm diameter) show maximal intratissue delivery (>50% increase in total cargo delivered) and more uniform penetration compared to nanorods or smaller NPs of the same shape. This is in contrast to spherical NPs where smaller NP size resulted in deeper, more uniform penetration. Our results provide fundamental new knowledge on NP transport inside solid tissues and further establish shape and aspect ratio as important design parameters in developing more efficient, better penetrating, nanocarriers for drug, or contrast-agent delivery. PMID:26376024

  8. Fabrication of high aspect ratio tungsten nanostructures on ultrathin c-Si membranes for extreme UV applications

    NASA Astrophysics Data System (ADS)

    Delachat, F.; Le Drogoff, B.; Constancias, C.; Delprat, S.; Gautier, E.; Chaker, M.; Margot, J.

    2016-01-01

    In this work, we demonstrate a full process for fabricating high aspect ratio diffraction optics for extreme ultraviolet lithography. The transmissive optics consists in nanometer scale tungsten patterns standing on flat, ultrathin (100 nm) and highly transparent (>85% at 13.5 nm) silicon membranes (diameter of 1 mm). These tungsten patterns were achieved using an innovative pseudo-Bosch etching process based on an inductively coupled plasma ignited in a mixture of SF6 and C4F8. Circular ultra-thin Si membranes were fabricated through a state-of-the-art method using direct-bonding with thermal difference. The silicon membranes were sputter-coated with a few hundred nanometers (100-300 nm) of stress-controlled tungsten and a very thin layer of chromium. Nanoscale features were written in a thin resist layer by electron beam lithography and transferred onto tungsten by plasma etching of both the chromium hard mask and the tungsten layer. This etching process results in highly anisotropic tungsten features at room temperature. The homogeneity and the aspect ratio of the advanced pattern transfer on the membranes were characterized with scanning electron microscopy after focus ion beam milling. An aspect ratio of about 6 for 35 nm size pattern is successfully obtained on a 1 mm diameter 100 nm thick Si membrane. The whole fabrication process is fully compatible with standard industrial semiconductor technology.

  9. Metal assisted chemical etching for high aspect ratio nanostructures: A review of characteristics and applications in photovoltaics

    SciTech Connect

    Li, XL

    2012-04-01

    Metal assisted chemical etching (MacEtch) is a recently developed anisotropic wet etching method that is capable of producing high aspect ratio semiconductor nanostructures from patterned metal film. In this review article, we highlight the characteristics of MacEtch of silicon (Si) including controllability of the produced sidewall roughness, the inherent high aspect ratio, the weak crystal orientation dependence, impurity doping and solution concentration dependent porosity, as well as the applicability of MacEtch to non-Si based semiconductor materials including III-V compound semiconductors. Also reviewed are applications of MacEtch produced high aspect ratio Si nanostructures in photovoltaics, where the p-n junction can be in the planar Si tray, core-shell, or axial geometry, with nanowire, micropillar, or hole arrays serving as light trapping or carrier collection structures. The prospect of using MacEtch to improve the cost and efficiency of photovoltaic cells is discussed. (c) 2011 Elsevier Ltd. All rights reserved.

  10. Effects of building aspect ratio, diurnal heating scenario, and wind speed on reactive pollutant dispersion in urban street canyons.

    PubMed

    Tong, Nelson Y O; Leung, Dennis Y C

    2012-01-01

    A photochemistry coupled computational fluid dynamics (CFD) based numerical model has been developed to model the reactive pollutant dispersion within urban street canyons, particularly integrating the interrelationship among diurnal heating scenario (solar radiation affections in nighttime, daytime, and sun-rise/set), wind speed, building aspect ratio (building-height-to-street-width), and dispersion of reactive gases, specifically nitric oxide (NO), nitrogen dioxide (NO2) and ozone (O3) such that a higher standard of air quality in metropolitan cities can be achieved. Validation has been done with both experimental and numerical results on flow and temperature fields in a street canyon with bottom heating, which justifies the accuracy of the current model. The model was applied to idealized street canyons of different aspect ratios from 0.5 to 8 with two different ambient wind speeds under different diurnal heating scenarios to estimate the influences of different aforementioned parameters on the chemical evolution of NO, NO2 and O3. Detailed analyses of vertical profiles of pollutant concentrations showed that different diurnal heating scenarios could substantially affect the reactive gases exchange between the street canyon and air aloft, followed by respective dispersion and reaction. Higher building aspect ratio and stronger ambient wind speed were revealed to be, in general, responsible for enhanced entrainment of O3 concentrations into the street canyons along windward walls under all diurnal heating scenarios. Comparatively, particular attention can be paid on the windward wall heating and nighttime uniform surface heating scenarios. PMID:23534205

  11. Large Aspect Ratio Roll Vortices (10 km Wavelength) In Tropical Cyclone Boundary Layers: SAR Evidence and Theoretical Modeling

    NASA Astrophysics Data System (ADS)

    Foster, Ralph; Patoux, Jerome; Horstmann, Jochen; Wackerman, Chris; Graber, Hans

    2013-04-01

    Analysis of synthetic aperture radar (SAR) images of the sea surface underneath tropical cyclones shows clear evidence of organized bands of surface wind convergence and wind stress curl. These patterns are consistent with the effects of planetary boundary roll vortices, except the observed wavelengths are O(10 km), which implies the rolls have aspect ratios (wavelength/PBL depth) many times what has been commonly observed in hurricane boundary layers (typically 2.5). The tropical cyclone boundary layer is a very favorable environment for the formation of roll vortices and observations show that O(1-3 km) wavelength rolls are a very common feature. We present an extension of the Foster (2005) nonlinear theory for hurricane PBL roll formation that posits a nonlinear, wave-wave, upscale energy transfer mechanism for the formation of large aspect ratio rolls. These large-aspect ratio rolls induce a circulation that extends from the sea-surface into the storm interior above the boundary layer and modulates the smaller rolls. Implications for improving SAR surface wind retrievals, hurricane boundary layer parameterization and surface fluxes are presented.

  12. Rapid micromachining of high aspect ratio holes in fused silica glass by high repetition rate picosecond laser

    NASA Astrophysics Data System (ADS)

    Karimelahi, Samira; Abolghasemi, Ladan; Herman, Peter R.

    2014-01-01

    We present multiple methods of high aspect ratio hole drilling in fused silica glass, taking advantage of high power and high repetition rate picosecond lasers and flexible beam delivery methods to excise deep holes with minimal collateral damage. Combinations of static and synchronous scanning of laser focus were explored over a range of laser repetition rates and burst-train profiles that dramatically vary laser plume interaction dynamics, heat-affected zone, and heat accumulation physics. Chemically assisted etching of picosecond laser modification tracks are also presented as an extension from femtosecond laser writing of volume nanograting to form high aspect ratio (77) channels. Processing windows are identified for the various beam delivery methods that optimize the laser exposure over energy, wavelength, and repetition rate to reduce microcracking and deleterious heating effects. The results show the benefits of femtosecond laser interactions in glass extend into the picosecond domain, where the attributes of higher power further yield wide processing windows and significantly faster fabrication speed. High aspect ratio holes of 400 μm depth were formed over widely varying rates of 333 holes per second for mildly cracked holes in static-focal positioning through to one hole per second for low-damage and taper free holes in synchronous scanning.

  13. High-aspect-ratio, high-quality microdrilling by electron density control using a femtosecond laser Bessel beam

    NASA Astrophysics Data System (ADS)

    Xie, Qian; Li, Xiaowei; Jiang, Lan; Xia, Bo; Yan, Xueliang; Zhao, Weiwei; Lu, Yongfeng

    2016-02-01

    We propose an efficient microdrilling method of high-aspect-ratio, high-quality microholes in polymethyl methacrylate by controlling localized transient spatial electron density using single-pulse femtosecond laser Bessel beams. The microholes fabricated with diameters of 1.5-2.4 μm are taper-free, which are of much better quality in the entrances and sidewalls, as compared with those fabricated by Gaussian beams. The aspect ratio of the microholes is up to 330:1. It takes 42 min to fabricate a 501 × 501 microhole array (with 251,001 holes in total, about 100 holes per second under a repetition rate of 100 Hz) in a 1 cm × 1 cm area, which is very uniform in size and shape. For single-pulse drilling of a microhole array, the number of ultrahigh-aspect-ratio microholes processed per second is theoretically determined by the repetition rate. The liquid infiltration method and cross-sectional profile tests confirm hollow microhole drillings rather than material modifications. The theoretical simulation of optical intensity distribution and intensified charge-coupled device detection shows that fabricating such thin, long, uniform microholes using Bessel beams is attributed to electron density control by spatially shaping femtosecond laser pulses.

  14. Fabrication of high aspect ratio tungsten nanostructures on ultrathin c-Si membranes for extreme UV applications.

    PubMed

    Delachat, F; Le Drogoff, B; Constancias, C; Delprat, S; Gautier, E; Chaker, M; Margot, J

    2016-01-15

    In this work, we demonstrate a full process for fabricating high aspect ratio diffraction optics for extreme ultraviolet lithography. The transmissive optics consists in nanometer scale tungsten patterns standing on flat, ultrathin (100 nm) and highly transparent (>85% at 13.5 nm) silicon membranes (diameter of 1 mm). These tungsten patterns were achieved using an innovative pseudo-Bosch etching process based on an inductively coupled plasma ignited in a mixture of SF6 and C4F8. Circular ultra-thin Si membranes were fabricated through a state-of-the-art method using direct-bonding with thermal difference. The silicon membranes were sputter-coated with a few hundred nanometers (100-300 nm) of stress-controlled tungsten and a very thin layer of chromium. Nanoscale features were written in a thin resist layer by electron beam lithography and transferred onto tungsten by plasma etching of both the chromium hard mask and the tungsten layer. This etching process results in highly anisotropic tungsten features at room temperature. The homogeneity and the aspect ratio of the advanced pattern transfer on the membranes were characterized with scanning electron microscopy after focus ion beam milling. An aspect ratio of about 6 for 35 nm size pattern is successfully obtained on a 1 mm diameter 100 nm thick Si membrane. The whole fabrication process is fully compatible with standard industrial semiconductor technology. PMID:26630379

  15. On the structure of cellular solutions in Rayleigh-Benard-Marangoni flows in small-aspect-ratio containers

    NASA Technical Reports Server (NTRS)

    Dijkstra, Henk A.

    1992-01-01

    Multiple steady flow patterns occur in surface-tension/buoyancy-driven convection in a liquid layer heated from below (Rayleigh-Benard-Marangoni flows). Techniques of numerical bifurcation theory are used to study the multiplicity and stability of two-dimensional steady flow patterns (rolls) in rectangular small-aspect-ratio containers as the aspect ratio is varied. For pure Marangoni flows at moderate Biot and Prandtl number, the transitions occurring when paths of codimension 1 singularities intersect determine to a large extent the multiplicity of stable patterns. These transitions also lead, for example, to Hopf bifurcations and stable periodic flows for a small range in aspect ratio. The influence of the type of lateral walls on the multiplicity of steady states is considered. 'No-slip' lateral walls lead to hysteresis effects and typically restrict the number of stable flow patterns (with respect to 'slippery' sidewalls) through the occurrence of saddle node bifurcations. In this way 'no-slip' sidewalls induce a selection of certain patterns, which typically have the largest Nusselt number, through secondary bifurcation.

  16. Versatile pattern generation of periodic, high aspect ratio Si nanostructure arrays with sub-50-nm resolution on a wafer scale

    NASA Astrophysics Data System (ADS)

    Ho, Jian-Wei; Wee, Qixun; Dumond, Jarrett; Tay, Andrew; Chua, Soo-Jin

    2013-12-01

    We report on a method of fabricating variable patterns of periodic, high aspect ratio silicon nanostructures with sub-50-nm resolution on a wafer scale. The approach marries step-and-repeat nanoimprint lithography (NIL) and metal-catalyzed electroless etching (MCEE), enabling near perfectly ordered Si nanostructure arrays of user-defined patterns to be controllably and rapidly generated on a wafer scale. Periodic features possessing circular, hexagonal, and rectangular cross-sections with lateral dimensions down to sub-50 nm, in hexagonal or square array configurations and high array packing densities up to 5.13 × 107 structures/mm2 not achievable by conventional UV photolithography are fabricated using this top-down approach. By suitably tuning the duration of catalytic etching, variable aspect ratio Si nanostructures can be formed. As the etched Si pattern depends largely on the NIL mould which is patterned by electron beam lithography (EBL), the technique can be used to form patterns not possible with self-assembly methods, nanosphere, and interference lithography for replication on a wafer scale. Good chemical resistance of the nanoimprinted mask and adhesion to the Si substrate facilitate good pattern transfer and preserve the smooth top surface morphology of the Si nanostructures as shown in TEM. This approach is suitable for generating Si nanostructures of controlled dimensions and patterns, with high aspect ratio on a wafer level suitable for semiconductor device production.

  17. The residual zonal flow in tokamak plasmas toroidally rotating at arbitrary velocity

    SciTech Connect

    Zhou, Deng

    2014-08-15

    Zonal flows, initially driven by ion-temperature-gradient turbulence, may evolve due to the neoclassic polarization in a collisionless tokamak plasma. In our previous work [D. Zhou, Nucl. Fusion 54, 042002 (2014)], the residual zonal flow in a tokamak plasma rotating toroidally at sonic speed is found to have the same form as that of a static plasma. In the present work, the form of the residual zonal flow is presented for tokamak plasmas rotating toroidally at arbitrary velocity. The gyro-kinetic equation is analytically solved for low speed rotation to give the expression of residual zonal flows, and the expression is then generalized for cases with arbitrary rotating velocity through interpolation. The zonal flow level decreases as the rotating velocity increases. The numerical evaluation is in good agreement with the former simulation result for high aspect ratio tokamaks.

  18. Lift, Drag, and Pitching Moment of Low-Aspect-Ratio Wings at Subsonic and Supersonic Speeds: Triangular Wing of Aspect Ratio 2 with NACA 0005-63 Thickness Distribution, Cambered and Twisted for a Trapezoidal Span Load Distribution

    NASA Technical Reports Server (NTRS)

    Smith, Willard G.; Phelps, E. Ray

    1951-01-01

    A wing-body combination having a plane triangular wing of aspect ratio 2 with NACA 0005-63 thickness distribution in streamwise planes, and twisted and cambered for a trapezoidal span load distribution has been investigated at both subsonic and supersonic Mach numbers. The lift, drag, and pitching moment of the model are presented for Mach numbers from 0.60 to 0.90 and 1.30 to 1.70 at a Reynolds number of 3.0 million. The variations of the characteristics with Reynolds number are also shown for several Mach numbers.

  19. Lift, Drag, and Pitching Moment of Low-aspect-ratio Wings at Subsonic and Supersonic Speeds : Twisted and Cambered Triangular Wing of Aspect Ratio 2 with NACA 0003-63 Thickness Distribution

    NASA Technical Reports Server (NTRS)

    Hall, Charles F; Heitmeyer, John C

    1951-01-01

    This report presents the results of an investigation to ascertain the lift, drag, and pitching moment of a wing-body combination having a triangular wing of aspect ratio 2 with NACA 0003-63 thickness distribution in streamwise planes and twisted and cambered for a nearly elliptical span load distribution. Results are shown for Mach numbers from 0.60 to 0.90 and from 1.30 to 1.70 at Reynolds numbers of 3.0 million and 7.5 million.

  20. Characterization Of High-Stroke High-Aspect Ratio Micro Electro Mechanical Systems Deformable Mirrors For Adaptive Optics

    NASA Astrophysics Data System (ADS)

    Bouchti, Mohamed Amine

    Adaptive optics MEMS deformable mirror, in conjunction with Shack Hartman wave front sensor and real-time controller, is capable of correcting time-varying aberrations in imaging applications through manipulating its mirror surface. Adaptive optics systems in astronomy for next generation large telescopes (30 meter primary mirrors) require a high stroke of 10microm of mechanical displacement. This required stroke would be achieved by MEMS deformable mirrors fabricated with high aspect ratio techniques. This thesis will review the designs of various types of high aspect actuators consisting of folded springs with rectangular and circular membranes as well as X-beam actuators. Finite element analysis (FEA) simulations of these designs have shown the ability of each design to achieve a stroke of approximately 9.4 microm. Also, FEA simulations proved that the X-beam actuators provide the best spring support while preventing tilting. In addition, this thesis will discuss device characterization and voltage vs. displacement test results for the high aspect ratio gold MEMS 16 x 16 X-beam actuators deformable mirror that has been bonded and packaged. The results have shown that the device is capable of achieving approximately 5.5 microm in individual actuator testing and 7microm in dual actuator testing.

  1. The effect of aspect ratio on the leading-edge vortex over an insect-like flapping wing.

    PubMed

    Phillips, Nathan; Knowles, Kevin; Bomphrey, Richard J

    2015-10-01

    Insect wing shapes are diverse and a renowned source of inspiration for the new generation of autonomous flapping vehicles, yet the aerodynamic consequences of varying geometry is not well understood. One of the most defining and aerodynamically significant measures of wing shape is the aspect ratio, defined as the ratio of wing length (R) to mean wing chord (c). We investigated the impact of aspect ratio, AR, on the induced flow field around a flapping wing using a robotic device. Rigid rectangular wings ranging from AR = 1.5 to 7.5 were flapped with insect-like kinematics in air with a constant Reynolds number (Re) of 1400, and a dimensionless stroke amplitude of 6.5c (number of chords traversed by the wingtip). Pseudo-volumetric, ensemble-averaged, flow fields around the wings were captured using particle image velocimetry at 11 instances throughout simulated downstrokes. Results confirmed the presence of a high-lift, separated flow field with a leading-edge vortex (LEV), and revealed that the conical, primary LEV grows in size and strength with increasing AR. In each case, the LEV had an arch-shaped axis with its outboard end originating from a focus-sink singularity on the wing surface near the tip. LEV detachment was observed for AR > 1.5 around mid-stroke at ~70% span, and initiated sooner over higher aspect ratio wings. At AR > 3 the larger, stronger vortex persisted under the wing surface well into the next half-stroke leading to a reduction in lift. Circulatory lift attributable to the LEV increased with AR up to AR = 6. Higher aspect ratios generated proportionally less lift distally because of LEV breakdown, and also less lift closer to the wing root due to the previous LEV's continuing presence under the wing. In nature, insect wings go no higher than AR ~ 5, likely in part due to architectural and physiological constraints but also because of the reducing aerodynamic benefits of high AR wings. PMID:26451802

  2. An Analysis of the Effects of Wing Aspect Ratio and Tail Location on Static Longitudinal Stability Below the Mach Number of Lift Divergence

    NASA Technical Reports Server (NTRS)

    Axelson, John A.; Crown, J. Conrad

    1948-01-01

    An analysis is presented of the influence of wing aspect ratio and tail location on the effects of compressibility upon static longitudinal stability. The investigation showed that the use of reduced wing aspect ratios or short tail lengths leads to serious reductions in high-speed stability and the possibility of high-speed instability.

  3. Length-dependent charge generation from vertical arrays of high-aspect-ratio ZnO nanowires.

    PubMed

    Rivera, Vivian Farías; Auras, Florian; Motto, Paolo; Stassi, Stefano; Canavese, Giancarlo; Celasco, Edvige; Bein, Thomas; Onida, Barbara; Cauda, Valentina

    2013-10-18

    Aqueous chemical growth of zinc oxide nanowires is a flexible and effective approach to obtain dense arrays of vertically oriented nanostructures with high aspect ratio. Herein we present a systematic study of the different synthesis parameters that influence the ZnO seed layer and thus the resulting morphological features of the free-standing vertically oriented ZnO nanowires. We obtained a homogeneous coverage of transparent conductive substrates with high-aspect-ratio nanowire arrays (length/diameter ratio of up to 52). Such nanostructured vertical arrays were examined to assess their electric and piezoelectric properties, and showed an electric charge generation upon mechanical compressive stress. The principle of energy harvesting with these nanostructured ZnO arrays was demonstrated by connecting them to an electronic charge amplifier and storing the generated charge in a series of capacitors. We found that the generated charge and the electrical behavior of the ZnO nanowires are strictly dependent on the nanowire length. We have shown the importance of controlling the morphological properties of such ZnO nanostructures for optimizing a nanogenerator device. PMID:24027171

  4. Large aspect ratio titanate nanowire prepared by monodispersed titania submicron sphere via simple wet-chemical reactions

    SciTech Connect

    Wang Baoxiang Shi Yong; Xue Dongfeng

    2007-03-15

    A facile one-step hydrothermal reaction among monodispersed titania submicron spheres and KOH solution was found to result in potassium titanate nanowires with a large aspect ratio. The diameter of these nanowires falls in the range of 50-200 nm and the length ranges from several micrometers to several tens of micrometers. It is found that the reaction temperature, duration, titanium source and the size distribution of titania raw powders have a great impact on the resultant morphology. Monodispersed TiO{sub 2} submicron sphere is beneficail for the formation and growth of large-area lamellar potassium titanate and consequently it is in favor of the production of nanowires with a large aspect ratio. The nanowires were analyzed by a range of methods including powder X-ray diffraction (XRD), scanning electron microscope (SEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), energy-dispersive X-ray spectrometer (EDX) and UV/Vis spectrophotometer. UV-absorption study showed that these nanowires are wide-band semiconductors with a band gap 3.4 eV. A formation mechanism is proposed on the basis of the dissolving, growth, thickening and splitting of K{sub 2}Ti{sub 6}O{sub 13} nanointermediates. - Graphical abstract: Monodispersed raw titania powders are beneficial to get the long and uniform K{sub 2}Ti{sub 6}O{sub 13} nanowires with a large aspect ratio. A formation mechanism of nanowires is proposed based on the dissolving, growth, thickening and splitting of K{sub 2}Ti{sub 6}O{sub 13} nanointermediates.

  5. Near-wake flow structure of elliptic cylinders close to a free surface: effect of cylinder aspect ratio

    NASA Astrophysics Data System (ADS)

    Daichin, K. V.; Lee, Sang Joon

    The flow fields behind elliptic cylinders adjacent to a free surface were investigated experimentally in a circulating water channel. A range of cylinder aspect ratios (AR=2, 3, 4) were considered, while the cross-sectional area of the elliptical cylinder was kept constant. The main objective of this study was to investigate the effect of cylinder aspect ratio and a free surface on the flow structure in the near-wake behind elliptic cylinders. For each elliptic cylinder, the flow structure was analyzed for various values of the submergence depth of the cylinder beneath the free surface. The flow fields were measured using a single-frame double-exposure PIV (Particle Image Velocimetry) system. For each experimental condition, 350 instantaneous velocity fields were obtained and ensemble-averaged to obtain the mean velocity field and spatial distribution of the mean vorticity statistics. The results show that near-wake can be classified into three typical flow patterns: formation of a Coanda flow, generation of substantial jet-like flow, and attachment of this jet flow to the free surface. The general flow structure observed behind the elliptic cylinders resembles the structure previously reported for a circular cylinder submerged near a free surface. However, the wake width and the angle of downward deflection of the shear layer developed from the lower surface of the elliptic cylinder differ from those observed for a circular cylinder. These trends are enhanced as cylinder aspect ratio is increased. In addition, the free surface distortion is also discussed in the paper.

  6. A Novel Metal-Rich Anneal for In Vacuo Passivation of High-Aspect-Ratio Mercury Cadmium Telluride Surfaces

    NASA Astrophysics Data System (ADS)

    Wan, Chang-Feng; Orent, Thomas; Myers, Thomas; Bhat, Ishwara; Stoltz, Andy; Pellegrino, Joe

    2013-11-01

    A new method for Cd-rich annealing of mercury cadmium telluride (MCT) was developed based on the observation that the deposition of Cd onto MCT by vacuum evaporation became self-limiting whenever the substrate temperature was above 70°C regardless of the Cd evaporation rate. Preliminary results indicated that this new method may be suitable for passivation of high-aspect-ratio MCT surfaces, for passivation at low temperatures, for in vacuo operation, and/or for vacancy annihilation in MCT. Furthermore, the process can be carried out in the conventional open-tube reactors used for molecular beam epitaxy, metalorganic chemical vapor deposition, and physical vapor deposition.

  7. Hydrothermal Synthesis of ZnO Structures Formed by High-Aspect-Ratio Nanowires for Acetone Detection

    NASA Astrophysics Data System (ADS)

    Cao, Zhen; Wang, Yong; Li, Zhanguo; Yu, Naisen

    2016-07-01

    Snowflake-like ZnO structures originating from self-assembled nanowires were prepared by a low-temperature aqueous solution method. The as-grown hierarchical ZnO structures were investigated by X-ray diffraction (XRD) and field-emission scanning electron microscopy (FESEM). The results showed that the snowflake-like ZnO structures were composed of high-aspect-ratio nanowires. Furthermore, gas-sensing properties to various testing gases of 10 and 50 ppm were measured, which confirms that the ZnO structures were of good selectivity and response to acetone and could serve for acetone sensor to detect low-concentration acetone.

  8. UV activation of polymeric high aspect ratio microstructures: ramifications in antibody surface loading for circulating tumor cell selection†

    PubMed Central

    Jackson, Joshua M.; Witek, Małgorzata A.; Hupert, Mateusz L.; Brady, Charles; Pullagurla, Swathi; Kamande, Joyce; Aufforth, Rachel D.; Tignanelli, Christopher J.; Torphy, Robert J.; Yeh, Jen Jen

    2014-01-01

    The need to activate thermoplastic surfaces using robust and efficient methods has been driven by the fact that replication techniques can be used to produce microfluidic devices in a high production mode and at low cost, making polymer microfluidics invaluable for in vitro diagnostics, such as circulating tumor cell (CTC) analysis, where device disposability is critical to mitigate artifacts associated with sample carryover. Modifying the surface chemistry of thermoplastic devices through activation techniques can be used to increase the wettability of the surface or to produce functional scaffolds to allow for the covalent attachment of biologics, such as antibodies for CTC recognition. Extensive surface characterization tools were used to investigate UV activation of various surfaces to produce uniform and high surface coverage of functional groups, such as carboxylic acids in microchannels of different aspect ratios. We found that the efficiency of the UV activation process is highly dependent on the microchannel aspect ratio and the identity of the thermoplastic substrate. Colorimetric assays and fluorescence imaging of UV-activated microchannels following EDC/NHS coupling of Cy3-labeled oligonucleotides indicated that UV-activation of a PMMA microchannel with an aspect ratio of ∼3 was significantly less efficient toward the bottom of the channel compared to the upper sections. This effect was a consequence of the bulk polymer's damping of the modifying UV radiation due to absorption artifacts. In contrast, this effect was less pronounced for COC. Moreover, we observed that after thermal fusion bonding of the device's cover plate to the substrate, many of the generated functional groups buried into the bulk rendering them inaccessible. The propensity of this surface reorganization was found to be higher for PMMA compared to COC. As an example of the effects of material and microchannel aspect ratios on device functionality, thermoplastic devices for the

  9. Oscillating high-aspect-ratio monolithic silicon nanoneedle array enables efficient delivery of functional bio-macromolecules into living cells

    PubMed Central

    Matsumoto, Daisuke; Rao Sathuluri, Ramachandra; Kato, Yoshio; Silberberg, Yaron R.; Kawamura, Ryuzo; Iwata, Futoshi; Kobayashi, Takeshi; Nakamura, Chikashi

    2015-01-01

    Delivery of biomolecules with use of nanostructures has been previously reported. However, both efficient and high-throughput intracellular delivery has proved difficult to achieve. Here, we report a novel material and device for the delivery of biomacromolecules into live cells. We attribute the successful results to the unique features of the system, which include high-aspect-ratio, uniform nanoneedles laid across a 2D array, combined with an oscillatory feature, which together allow rapid, forcible and efficient insertion and protein release into thousands of cells simultaneously. PMID:26471006

  10. Effect of wing aspect ratio and flap span on aerodynamic characteristics of an externally blown jet-flap STOL model

    NASA Technical Reports Server (NTRS)

    Smith, C. C., Jr.

    1973-01-01

    An investigation has been conducted to determine the effects of flap span and wing aspect ratio on the static longitudinal aerodynamic characteristics and chordwise and spanwise pressure distributions on the wing and trailing-edge flap of a straight-wing STOL model having an externally blown jet flap without vertical and horizontal tail surfaces. The force tests were made over an angle-of-attack range for several thrust coefficients and two flap deflections. The pressure data are presented as tabulated and plotted chordwise pressure-distribution coefficients for angles of attack of 1 and 16. Pressure-distribution measurements were made at several spanwise stations.

  11. The Effect of Aspect Ratio and Angle of Attack on the Transition Regions of the Inverted Flag Instability

    NASA Astrophysics Data System (ADS)

    Cosse, Julia; Sader, John; Fan, Boyu; Kim, Daegyoum; Gharib, Mory

    2014-11-01

    The inverted flag instability occurs when a pliable plate is held parallel to a free-stream, with the leading edge free to move and the trailing edge clamped. Large-amplitude flapping is observed across a slim band of non-dimensional wind speeds. This specific boundaries of this flapping band vary greatly, depending on both the aspect ratio and the angle of attack of the plate with respect to the incoming flow. In addition, both periodic and aperiodic flapping modes exist. The frequency of the plate motion was analyzed and was found to be consistent with vortex-induced vibration. This research is supported by the Gordon and Betty Moore Foundation.

  12. Polydimethyl siloxane wet etching for three dimensional fabrication of microneedle array and high-aspect-ratio micropillars

    PubMed Central

    Deng, Yu-Luen; Juang, Yi-Je

    2014-01-01

    Among various transdermal drug delivery (TDD) approaches, utilizing the microneedles (MNs) not only can penetrate the skin but also deliver the drug with reduced tissue damage, reduced pain, and no bleeding. However, the MNs with larger height are required to overcome the skin barrier for effective TDD. Unlike 2D patterning, etching polydimethyl siloxane (PDMS) micropillars for fabrication of 3D microstructures is presented. The PDMS micropillars were first constructed by casting PDMS on the computer numerical control-machined cylindrical microwells, which then went through etching process to obtain the MNs for subsequent fabrication of polymer MNs or high aspect ratio micropillars. PMID:24803970

  13. Effect of aspect ratio on the air forces and moments of harmonically oscillating thin rectangular wings in supersonic potential flow

    NASA Technical Reports Server (NTRS)

    Watkins, Charles E

    1951-01-01

    This report treats the effect of aspect ratio on the air forces and moments of an oscillating flat rectangular wing in supersonic potential flow. The linearized velocity potential for the wing undergoing sinusoidal torsional oscillations simultaneously with sinusoidal vertical translations is derived in the form of a power series in terms of a frequency parameter. The series development is such that the differential equation for the velocity potential is satisfied to the required power of the frequency parameter considered and the linear boundary conditions are satisfied exactly. The method of solution can be utilized for other plan forms, that is, plan forms for which certain steady-state solutions are known.

  14. Subsonic and transonic pressure measurements on a high-aspect-ratio supercritical-wing model with oscillating control surfaces

    NASA Technical Reports Server (NTRS)

    Sandford, M. C.; Ricketts, R. H.; Watson, J. J.

    1981-01-01

    A high aspect ratio supercritical wing with oscillating control surfaces is described. The semispan wing model was instrumented with 252 static orifices and 164 in situ dynamic pressure gases for studying the effects of control surface position and sinusoidal motion on steady and unsteady pressures. Data from the present test (this is the second in a series of tests on this model) were obtained in the Langley Transonic Dynamics Tunnel at Mach numbers of 0.60 and 0.78 and are presented in tabular form.

  15. UV activation of polymeric high aspect ratio microstructures: ramifications in antibody surface loading for circulating tumor cell selection.

    PubMed

    Jackson, Joshua M; Witek, Małgorzata A; Hupert, Mateusz L; Brady, Charles; Pullagurla, Swathi; Kamande, Joyce; Aufforth, Rachel D; Tignanelli, Christopher J; Torphy, Robert J; Yeh, Jen Jen; Soper, Steven A

    2014-01-01

    The need to activate thermoplastic surfaces using robust and efficient methods has been driven by the fact that replication techniques can be used to produce microfluidic devices in a high production mode and at low cost, making polymer microfluidics invaluable for in vitro diagnostics, such as circulating tumor cell (CTC) analysis, where device disposability is critical to mitigate artifacts associated with sample carryover. Modifying the surface chemistry of thermoplastic devices through activation techniques can be used to increase the wettability of the surface or to produce functional scaffolds to allow for the covalent attachment of biologics, such as antibodies for CTC recognition. Extensive surface characterization tools were used to investigate UV activation of various surfaces to produce uniform and high surface coverage of functional groups, such as carboxylic acids in microchannels of different aspect ratios. We found that the efficiency of the UV activation process is highly dependent on the microchannel aspect ratio and the identity of the thermoplastic substrate. Colorimetric assays and fluorescence imaging of UV-activated microchannels following EDC/NHS coupling of Cy3-labeled oligonucleotides indicated that UV-activation of a PMMA microchannel with an aspect ratio of ~3 was significantly less efficient toward the bottom of the channel compared to the upper sections. This effect was a consequence of the bulk polymer's damping of the modifying UV radiation due to absorption artifacts. In contrast, this effect was less pronounced for COC. Moreover, we observed that after thermal fusion bonding of the device's cover plate to the substrate, many of the generated functional groups buried into the bulk rendering them inaccessible. The propensity of this surface reorganization was found to be higher for PMMA compared to COC. As an example of the effects of material and microchannel aspect ratios on device functionality, thermoplastic devices for the

  16. Stability and control characteristics of an airplane model having a 45.1 degree swept-back wing with aspect ratio 2.50 and taper ratio 0.42 and a 42.8 degree swept-back horizontal tail with aspect ratio 3.87 and taper ratio 0.49

    NASA Technical Reports Server (NTRS)

    Schuldenfrei, Marvin; Comisarow, Paul; Goodson, Kenneth W

    1947-01-01

    Tests were made of an airplane model having a 45.1 degree swept-back wing with aspect ratio 2.50 and taper ratio 0.42 and a 42.8 degree swept-back horizontal tail with aspect ratio 3.87 and taper ratio 0.49 to determine its low-speed stability and control characteristics. The test Reynolds number was 2.87 x 10(6) based on a mean aerodynamic chord of 2.47 feet except for some of the aileron tests which were made at a Reynolds number of 2.05 x 10(6). With the horizontal tail located near the fuselage juncture on the vertical tail, model results indicated static longitudinal instability above a lift coefficient that was 0.15 below the lift coefficient at which stall occurred. Static longitudinal stability, however, was manifested throughout the life range with the horizontal tail located near the top of the vertical tail. The use of 10 degrees negative dihedral on the wing had little effect on the static longitudinal stability characteristics. Preliminary tests of the complete model revealed an undesirable flat spot in the yawing-moment curves at low angles of attack, the directional stability being neutral for yaw angles of plus-or-minus 2 degrees. This undesirable characteristic was improved by replacing the thick original vertical tail with a thin vertical tail and by flattening the top of the dorsal fairing.

  17. HIGH ASPECT RATIO ION EXCHANGE RESIN BED - HYDRAULIC RESULTS FOR SPERICAL RESIN BEADS

    SciTech Connect

    Duignan, M; Charles Nash, C; Timothy Punch, T

    2007-09-27

    A principal role of the DOE Savannah River Site is to safely dispose of a large volume of liquid nuclear waste held in many storage tanks. An in-tank ion exchange unit is being considered for cesium removal to accelerate waste processing. This unit is planned to have a relatively high bed height to diameter ratio (10:1). Complicating the design is the need to cool the ion exchange media; therefore, the ion exchange column will have a central cooling core making the flow path annular. To separate cesium from waste the media being considered is made of resorcinol formaldehyde resin deposited on spherical plastic beads and is a substitute for a previously tested resin made of crystalline silicotitanate. This spherical media not only has an advantage of being mechanically robust, but, unlike its predecessor, it is also reusable, that is, loaded cesium can be removed through elution and regeneration. Resin regeneration leads to more efficient operation and less spent resin waste, but its hydraulic performance in the planned ion exchange column was unknown. Moreover, the recycling process of this spherical resorcinol formaldehyde causes its volume to significantly shrink and swell. To determine the spherical media's hydraulic demand a linearly scaled column was designed and tested. The waste simulant used was prototypic of the wastes' viscosity and density. This paper discusses the hydraulic performance of the media that will be used to assist in the design of a full-scale unit.

  18. Acoustic scattering by circular cylinders of various aspect ratios. [pressure gradient microphones

    NASA Technical Reports Server (NTRS)

    Maciulaitis, A.

    1979-01-01

    The effects of acoustic scattering on the useful frequency range of pressure gradient microphones were investigated experimentally between ka values of 0.407 and 4.232 using two circular cylindrical models (L/D = 0.5 and 0.25) having a 25 cm outside diameter. Small condenser microphones, attached to preamplifiers by flexible connectors, were installed from inside the cylindrical bodies, and flush mounted on the exterior surface of the cylinders. A 38 cm diameter woofer in a large speaker enclosure was used as the sound source. Surface pressure augmentation and phase differences were computed from measured data for various sound wave incidence angles. Results are graphically compared with theoretical predictions supplied by NASA for ka = 0.407, 2.288, and 4.232. All other results are tabulated in the appendices. With minor exceptions, the experimentally determined pressure augmentations agreed within 0.75 dB with theoretical predictions. The agreement for relative phase angles was within 5 percent without any exceptions. Scattering parameter variations with ka and L/D ratio, as computed from experimental data, are also presented.

  19. Detailed pressure distribution measurements obtained on several configurations of an aspect-ratio-7 variable twist wing

    NASA Technical Reports Server (NTRS)

    Holbrook, G. T.; Dunham, D. M.

    1985-01-01

    Detailed pressure distribution measurements were made for 11 twist configurations of a unique, multisegmented wing model having an aspect ratio of 7 and a taper ratio of 1. These configurations encompassed span loads ranging from that of an untwisted wing to simple flapped wings both with and without upper-surface spoilers attached. For each of the wing twist configurations, electronic scanning pressure transducers were used to obtain 580 surface pressure measurements over the wing in about 0.1 sec. Integrated pressure distribution measurements compared favorably with force-balance measurements of lift on the model when the model centerbody lift was included. Complete plots and tabulations of the pressure distribution data for each wing twist configuration are provided.

  20. Development of low-fluorescence thick photoresist for high-aspect-ratio microstructure in bio-application

    PubMed Central

    Tamai, H.; Maruo, K.; Ueno, H.; Terao, K.; Kotera, H.; Suzuki, T.

    2015-01-01

    In this study, we propose and evaluate a novel low-auto-fluorescence photoresist (SJI photoresist) for bio-application, e.g., in gene analysis and cell assay. The spin-coated SJI photoresist has a wide thickness range of ten to several hundred micrometers, and photoresist microstructures with an aspect ratio of over 7 and micropatterns of less than 2 μm are successfully fabricated. The emission spectrum intensity of the SJI photoresist is found to be over 80% less than that of the widely used SU-8 photoresist. To evaluate the validity of using the proposed photoresist in bio-application for fluorescence observation, we demonstrate a chromosome extension device composed of the SJI photoresist. The normalized contrast ratio of the SJI photoresist exhibits a 50% improvement over that of the SU-8 photoresist; thus, the SJI photoresist is a versatile tool for bio-application. PMID:25945132