A proposal of an open PET geometry.
Yamaya, Taiga; Inaniwa, Taku; Minohara, Shinichi; Yoshida, Eiji; Inadama, Naoko; Nishikido, Fumihiko; Shibuya, Kengo; Lam, Chih Fung; Murayama, Hideo
2008-02-01
The long patient port of a PET scanner tends to put stress on patients, especially patients with claustrophobia. It also prevents doctors and technicians from taking care of patients during scanning. In this paper, we proposed an 'open PET' geometry, which consists of two axially separated detector rings. A long and continuous field-of-view (FOV) including a 360 degrees opened gap between two detector rings can be imaged enabling a fully 3D image reconstruction of all the possible lines-of-response. The open PET will become practical if iterative image reconstruction methods are applied even though image reconstruction of the open PET is analytically an incomplete problem. First we implemented a 'masked' 3D ordered subset expectation maximization (OS-EM) in which the system matrix was obtained from a long 'gapless' scanner by applying a mask to detectors corresponding to the open space. Next, in order to evaluate imaging performance of the proposed open PET geometry, we simulated a dual HR+ scanner (ring diameter of D = 827 mm, axial length of W = 154 mm x 2) separated by a variable gap. The gap W was the maximum limit to have axially continuous FOV of 3W though the maximum diameter of FOV at the central slice was limited to D/2. Artifacts, observed on both sides of the open space when the gap exceeded W, were effectively reduced by inserting detectors partially into unnecessary open spaces. We also tested the open PET geometry using experimental data obtained by the jPET-D4. The jPET-D4 is a prototype brain scanner, which has 5 rings of 24 detector blocks. We simulated the open jPET-D4 with a gap of 66 mm by eliminating 1 block-ring from experimental data. Although some artifacts were seen at both ends of the opened gap, very similar images were obtained with and without the gap. The proposed open PET geometry is expected to lead to realization of in-beam PET, which is a method for an in situ monitoring of charged particle therapy, by letting the beams pass
Cost Effective Open Geometry HTS MRI System amended to BSCCO 2212 Wire for High Field Magnets
Kennth Marken
2006-08-11
The original goal of this Phase II Superconductivity Partnership Initiative project was to build and operate a prototype Magnetic Resonance Imaging (MRI) system using high temperature superconductor (HTS) coils wound from continuously processed dip-coated BSCCO 2212 tape conductor. Using dip-coated tape, the plan was for MRI magnet coils to be wound to fit an established commercial open geometry, 0.2 Tesla permanent magnet system. New electronics and imaging software for a prototype higher field superconducting system would have added significantly to the cost. However, the use of the 0.2 T platform would allow the technical feasibility and the cost issues for HTS systems to be fully established. Also it would establish the energy efficiency and savings of HTS open MRI compared with resistive and permanent magnet systems. The commercial goal was an open geometry HTS MRI running at 0.5 T and 20 K. This low field open magnet was using resistive normal metal conductor and its heat loss was rather high around 15 kolwatts. It was expected that an HTS magnet would dissipate around 1 watt, significantly reduce power consumption. The SPI team assembled to achieve this goal was led by Oxford Instruments, Superconducting Technology (OST), who developed the method of producing commercial dip coated tape. Superconductive Components Inc. (SCI), a leading US supplier of HTS powders, supported the conductor optimization through powder optimization, scaling, and cost reduction. Oxford Magnet Technology (OMT), a joint venture between Oxford Instruments and Siemens and the world’s leading supplier of MRI magnet systems, was involved to design and build the HTS MRI magnet and cryogenics. Siemens Magnetic Resonance Division, a leading developer and supplier of complete MRI imaging systems, was expected to integrate the final system and perform imaging trials. The original MRI demonstration project was ended in July 2004 by mutual consent of Oxford Instruments and Siemens. Between
Assessment of Geometry and In-Flow Effects on Contra-Rotating Open Rotor Broadband Noise Predictions
NASA Technical Reports Server (NTRS)
Zawodny, Nikolas S.; Nark, Douglas M.; Boyd, D. Douglas, Jr.
2015-01-01
Application of previously formulated semi-analytical models for the prediction of broadband noise due to turbulent rotor wake interactions and rotor blade trailing edges is performed on the historical baseline F31/A31 contra-rotating open rotor configuration. Simplified two-dimensional blade element analysis is performed on cambered NACA 4-digit airfoil profiles, which are meant to serve as substitutes for the actual rotor blade sectional geometries. Rotor in-flow effects such as induced axial and tangential velocities are incorporated into the noise prediction models based on supporting computational fluid dynamics (CFD) results and simplified in-flow velocity models. Emphasis is placed on the development of simplified rotor in-flow models for the purpose of performing accurate noise predictions independent of CFD information. The broadband predictions are found to compare favorably with experimental acoustic results.
Geometry of anterior open bite correction.
Abramson, Zachary R; Susarla, Srinivas M; Lawler, Matthew E; Choudhri, Asim F; Peacock, Zachary S
2015-05-01
Correction of anterior open bite is a frequently encountered and challenging problem for the craniomaxillofacial surgeon and orthodontist. Accurate clinical evaluation, including cephalometric assessment, is paramount for establishing the diagnosis and appropriate treatment plan. The purposes of this technical note were to discuss the basic geometric principles involved in the surgical correction of skeletal anterior open bites and to offer a simple mathematical model for predicting the amount of posterior maxillary impaction with concomitant mandibular rotation required to establish an adequate overbite. Using standard geometric principles, a mathematical model was created to demonstrate the relationship between the magnitude of the open bite and the magnitude of the rotational movements required for correction. This model was then validated using a clinical case. In summary, the amount of open bite closure for a given amount of posterior maxillary impaction depends on anatomic variables, which can be obtained from a lateral cephalogram. The clinical implication of this relationship is as follows: patients with small mandibles and steep mandibular occlusal planes will require greater amounts of posterior impaction. PMID:25950521
Stability analysis of underground mining openings with complex geometry
NASA Astrophysics Data System (ADS)
Cała, Marek; Stopkowicz, Agnieszka; Kowalski, Michał; Blajer, Mateusz; Cyran, Katarzyna; D'obyrn, Kajetan
2016-03-01
Stability of mining openings requires consideration of a number of factors, such as: geological structure, the geometry of the underground mining workings, mechanical properties of the rock mass, changes in stress caused by the influence of neighbouring workings. Long-term prediction and estimation of workings state can be analysed with the use of numerical methods. Application of 3D numerical modelling in stability estimation of workings with complex geometry was described with the example of Crystal Caves in Wieliczka Salt Mine. Preservation of the Crystal Caves reserve is particularly important in view of their unique character and the protection of adjacent galleries which are a part of tourist attraction included in UNESCO list. A detailed 3D model of Crystal Caves and neighbouring workings was built. Application of FLAC3D modelling techniques enabled indication of the areas which are in danger of stability loss. Moreover, the area in which protective actions should be taken as well as recommendations concerning the convergence monitoring were proposed.
ERIC Educational Resources Information Center
Kutluca, Tamer
2013-01-01
The aim of this study is to investigate the effect of dynamic geometry software GeoGebra on Van Hiele geometry understanding level of students at 11th grade geometry course. The study was conducted with pre and posttest control group quasi-experimental method. The sample of the study was 42 eleventh grade students studying in the spring term of…
Effect of geometry on hydrodynamic film thickness
NASA Technical Reports Server (NTRS)
Brewe, D. E.; Hamrock, B. J.; Taylor, C. M.
1978-01-01
The influence of geometry on the isothermal hydrodynamic film separating two rigid solids was investigated. Pressure-viscosity effects were not considered. The minimum film thickness is derived for fully flooded conjunctions by using the Reynolds conditions. It was found that the minimum film thickness had the same speed, viscosity, and load dependence as Kapitza's classical solution. However, the incorporation of Reynolds boundary conditions resulted in an additional geometry effect. Solutions using the parabolic film approximation are compared with those using the exact expression for the film in the analysis. Contour plots are shown that indicate in detail the pressure developed between the solids.
Multiscale Talbot effects in Fibonacci geometry
NASA Astrophysics Data System (ADS)
Ho, I.-Lin; Chang, Yia-Chung
2015-04-01
This article investigates the Talbot effects in Fibonacci geometry by introducing the cut-and-projection construction, which allows for capturing the entire infinite Fibonacci structure in a single computational cell. Theoretical and numerical calculations demonstrate the Talbot foci of Fibonacci geometry at distances that are multiples (τ +2){{({{F}μ }+τ {{F}μ +1})}-1}p/(2q) or (τ +2){{({{L}μ }+τ {{L}μ +1})}-1}p/(2q) of the Talbot distance. Here (p, q) are coprime integers, μ is an integer, τ is the golden mean, and {{F}μ } and {{L}μ } are Fibonacci and Lucas numbers, respectively. The image of a single Talbot focus exhibits a multiscale-interval pattern due to the self-similarity of the scaling Fourier spectrum.
Cloud geometry effects on atmospheric solar absorption
Fu, Q.; Cribb, M.C.; Barker, H.W.; Krueger, S.K.; Grossman, A.
2000-04-15
A 3D broadband solar radiative transfer scheme is formulated by integrating a Monte Carlo photon transport algorithm with the Fu-Liou radiation model. It is applied to fields of tropical mesoscale convective clouds and subtropical marine boundary layer clouds that were generated by a 2D cloud-resolving model. The effects of cloud geometry on the radiative energy budget are examined by comparing the full-resolution Monte Carlo results with those from the independent column approximation (ICA) that applies the plane-parallel radiation model to each column. For the tropical convective cloud system, it is found that cloud geometry effects always enhance atmospheric solar absorption regardless of solar zenith angle. In a large horizontal domain (512 km), differences in domain-averaged atmospheric absorption between the Monte Carlo and the ICA are less than 4 W m{sup {minus}2} in the daytime. However, for a smaller domain (e.g., 75 km) containing a cluster of deep convective towers, domain-averaged absorption can be enhanced by more than 20 W m{sup {minus}2}. For a subtropical marine boundary layer cloud system during the stratus-to-cumulus transition, calculations show that the ICA works very well for domain-averaged fluxes of the stratocumulus cloud fields even for a very small domain (4.8 km). For the trade cumulus cloud field, the effects of cloud sides and horizontal transport of photons become more significant. Calculations have also been made for both cloud systems including black carbon aerosol and a water vapor continuum. It is found that cloud geometry produces no discernible effects on the absorption enhancement due to the black carbon aerosol and water vapor continuum. The current study indicates that the atmospheric absorption enhancement due to cloud-related 3D photon transport is small. This enhancement could not explain the excess absorption suggested by recent studies.
Effective geometry of a white dwarf
Bini, D.; Cherubini, C.; Filippi, S.
2011-03-15
The ''effective geometry'' formalism is used to study the perturbations of a white dwarf described as a self-gravitating fermion gas with a completely degenerate relativistic equation of state of barotropic type. The quantum nature of the system causes an absence of homological properties, manifested instead by polytropic stars, and requires a parametric study of the solutions both at the numerical and analytical level. We have explicitly derived a compact analytical parametric approximate solution of Pade type, which gives density curves and stellar radii in good accordance with already existing numerical results. After validation of this new type of approximate solutions, we use them to construct the effective acoustic metric governing general perturbations following Chebsch's formalism. Even in this quantum case, the stellar surface exhibits a curvature singularity due to the vanishing of density, as already evidenced in past studies on nonquantum self-gravitating polytropic stars. The equations of the theory are finally numerically integrated in the simpler case of irrotational spherical pulsating perturbations, including the effect of backreaction, in order to have a dynamical picture of the process occurring in the acoustic metric.
Effects of flow geometry on blood viscoelasticity.
Thurston, George B; Henderson, Nancy M
2006-01-01
The viscoelastic properties of blood are dominated by microstructures formed by red cells. The microstructures are of several types such as irregular aggregates, rouleaux, and layers of aligned cells. The dynamic deformability of the red cells, aggregation tendency, cell concentration, size of confining vessel and rate of flow are determining factors in the microstructure. Viscoelastic properties, viscosity and elasticity, relate to energy loss and storage in flowing blood while relaxation time and Weissenberg number play a role in assessing the importance of the elasticity relative to the viscosity. These effects are shown herein for flow in a large straight cylindrical tube, a small tube, and a porous medium. These cases approximate the geometries of the arterial system: large vessels, small vessels and vessels with many branches and bifurcations. In each case the viscosity, elasticity, relaxation time and Weissenberg number for normal human blood as well as blood with enhanced cell aggregation tendency and diminished cell deformability are given. In the smaller spaces of the microtubes and porous media, the diminished viscosity shows the possible influence of the Fåhraeus-Lindqvist effect and at high shear rates, the viscoelasticity of blood shows dilatancy. This is true for normal, aggregation enhanced and hardened cells. PMID:17148856
Effects of Liner Geometry on Acoustic Impedance
NASA Technical Reports Server (NTRS)
Jones, Michael G.; Tracy, Maureen B.; Watson, Willie R.; Parrott, Tony L.
2002-01-01
Current aircraft engine nacelles typically contain acoustic liners consisting of perforated sheets bonded onto honeycomb cavities. Numerous models have been developed to predict the acoustic impedance of these liners in the presence of grazing flow, and to use that information with aeroacoustic propagation codes to assess nacelle liner noise suppression. Recent efforts have provided advances in impedance education methodologies that offer more accurate determinations of acoustic liner properties in the presence of grazing flow. The current report provides the results of a parametric study, in which a finite element method was used to assess the effects of variations of the following geometric parameters on liner impedance, with and without the presence of grazing flow: percent open area, sheet thickness, sheet thickness-to-hole diameter ratio and cavity depth. Normal incidence acoustic impedances were determined for eight acoustic liners, consisting of punched aluminum facesheets bonded to hexcell honeycomb cavities. Similar liners were tested in the NASA Langley Research Center grazing incidence tube to determine their response in the presence of grazing flow. The resultant data provide a quantitative assessment of the effects of these perforate, single-layer liner parameters on the acoustic impedance of the liner.
Effectiveness of Multimedia in Teaching Descriptive Geometry.
ERIC Educational Resources Information Center
Rankowski, Charles A.; Galey, Minaruth
1979-01-01
Demonstrates the instructional value of supplementary media presentations using first year engineering students randomly split into 11 descriptive geometry classes; five received multimedia instruction, and six did not. Data compared each study group in relation to competency in the subject, achievement, visualization of spatial relationships, and…
Modelling functional effects of muscle geometry.
van der Linden, B J; Koopman, H F; Grootenboer, H J; Huijing, P A
1998-04-01
Muscle architecture is an important aspect of muscle functioning. Hence, geometry and material properties of muscle have great influence on the force-length characteristics of muscle. We compared experimental results for the gastrocnemius medialis muscle (GM) of the rat to model results of simple geometric models such as a planimetric model and three-dimensional versions of this model. The capabilities of such models to adequately calculate muscle geometry and force-length characteristics were investigated. The planimetric model with elastic aponeurosis predicted GM muscle geometry well: maximal differences are 6, 1, 4 and 6% for fiber length, aponeurosis length, fiber angle and aponeurosis angle respectively. A slanted cylinder model with circular fiber cross-section did not predict muscle geometry as well as the planimetric model, whereas the geometry results of a second slanted cylinder model were identical to the planimetric model. It is concluded that the planimetric model is capable of adequately calculating the muscle geometry over the muscle length range studied. However, for modelling of force-length characteristics more complex models are needed, as none of the models yielded results sufficiently close to experimental data. Modelled force-length characteristics showed an overestimation of muscle optimum length by 2 mm with respect to experimental data, and the force at the ascending limb of the length force curve was underestimated. The models presented neglect important aspects such as non-linear geometry of muscle, certain passive material properties and mechanical interactions of fibers. These aspects may be responsible for short-comings in the modelling. It is argued that, considering the inability to adequately model muscle length-force characteristics for an isolated maximally activated (in situ) muscle, it is to be expected that prediction will fail for muscle properties in conditions of complex movement with many interacting factors. Therefore
The effect of geometry on integrity monitoring performance
NASA Astrophysics Data System (ADS)
Brown, Alison; Sturza, Mark
A geometry parameter which can be utilized to define when receiver autonomous integrity monitoring is effective for each phase of flight is derived. The integrity geometry parameter permits the optimum geometry to be determined for maximizing the probability of failure detection and isolation in the presence of multiple instrument faults. These parameters can also be applied in evaluating the performance of redundant navigation systems in the presence of multiple or single instrument faults.
Phenomenology of effective geometries from quantum gravity
NASA Astrophysics Data System (ADS)
Torromé, Ricardo Gallego; Letizia, Marco; Liberati, Stefano
2015-12-01
In a recent paper [M. Assanioussi, A. Dapor, and J. Lewandowski, Phys. Lett. B 751, 302 (2015)] a general mechanism for the emergence of cosmological spacetime geometry from a quantum gravity setting was devised and a departure from standard dispersion relations for an elementary particle was predicted. We elaborate here on this approach extending the results obtained in that paper and showing that generically such a framework will not lead to higher order modified dispersion relations in the matter sector. Furthermore, we shall discuss possible phenomenological constraints to this scenario showing that spacetime will have to be classical to a very high degree by now in order to be consistent with current observations.
Second Landau level fractional quantum Hall effects in the Corbino geometry
NASA Astrophysics Data System (ADS)
Schmidt, B. A.; Bennaceur, K.; Bilodeau, S.; Gervais, G.; Pfeiffer, L. N.; West, K. W.
2015-09-01
For certain measurements, the Corbino geometry has a distinct advantage over the Hall and van der Pauw geometries, in that it provides a direct probe of the bulk 2DEG without complications due to edge effects. This may be important in enabling detection of the non-Abelian entropy of the 5/2 fractional quantum Hall state via bulk thermodynamic measurements. We report the successful fabrication and measurement of a Corbino-geometry sample in an ultra-high mobility GaAs heterostructure, with a focus on transport in the second and higher Landau levels. In particular, we report activation energy gaps of fractional quantum Hall states, with all edge effects ruled out, and extrapolate σ0 from the Arrhenius fits. Our results show that activated transport in the second Landau level remains poorly understood. The development of this Corbino device opens the possibility to study the bulk of the 5/2 state using techniques not possible in other geometries.
Open-geometry Fourier modal method: modeling nanophotonic structures in infinite domains.
Häyrynen, Teppo; de Lasson, Jakob Rosenkrantz; Gregersen, Niels
2016-07-01
We present an open-geometry Fourier modal method based on a new combination of open boundary conditions and an efficient k-space discretization. The open boundary of the computational domain is obtained using basis functions that expand the whole space, and the integrals subsequently appearing due to the continuous nature of the radiation modes are handled using a discretization based on nonuniform sampling of the k space. We apply the method to a variety of photonic structures and demonstrate that our method leads to significantly improved convergence with respect to the number of degrees of freedom, which may pave the way for more accurate and efficient modeling of open nanophotonic structures. PMID:27409686
Open-geometry Fourier modal method: modeling nanophotonic structures in infinite domains
NASA Astrophysics Data System (ADS)
Häyrynen, Teppo; de Lasson, Jakob Rosenkrantz; Gregersen, Niels
2016-07-01
We present an open geometry Fourier modal method based on a new combination of open boundary conditions and an efficient $k$-space discretization. The open boundary of the computational domain is obtained using basis functions that expand the whole space, and the integrals subsequently appearing due to the continuous nature of the radiation modes are handled using a discretization based on non-uniform sampling of the $k$-space. We apply the method to a variety of photonic structures and demonstrate that our method leads to significantly improved convergence with respect to the number of degrees of freedom, which may pave the way for more accurate and efficient modeling of open nanophotonic structures.
Multi-megampere operation of plasma compression opening switches in planar geometry
Goforth, J.H.; Erickson, D.J.; Williams, A.H.; Greene, A.E.
1985-01-01
Experiments are described in which a plasma compression opening switch is used in planar geometry to sharpen the output pulse of an explosive-driven magnetic flux compression generator. Included are data from tests where peak opening switch currents range from 5.7 to 9.3 MA. The switch is used to transfer current to a static low-inductance load (approx.10 nH) with an efficiency of 50% or better and a risetime as low as 0.45 ..mu..s. Results related to current transfer are interpreted within a simple analytical model.
Nozzle and wing geometry effects on OTW aerodynamic characteristics
NASA Technical Reports Server (NTRS)
Vonglahn, U.; Groesbeck, D.
1976-01-01
The effects of nozzle geometry and wing size on the aerodynamic performance of several 5:1 aspect ratio slot nozzles are presented for over-the-wing (OTW) configurations. Nozzle geometry variables include roof angle, sidewall cutback, and nozzle chordwise location. Wing variables include chord size, and flap deflection. Several external deflectors also were included for comparison. The data indicate that good flow turning may not necessarily provide the best aerodynamic performance. The results suggest that a variable exhaust nozzle geometry offers the best solution for a viable OTW configuration.
Geometry effects on detonation in vapor-deposited hexanitroazobenzene (HNAB)
NASA Astrophysics Data System (ADS)
Tappan, Alexander S.; Wixom, Ryan R.; Knepper, Robert
2015-06-01
Physical vapor deposition is a technique that can be used to produce explosive films with controlled geometry and microstructure. Films of the high explosive hexanitroazobenzene (HNAB) were deposited by vacuum thermal evaporation. HNAB deposits in an amorphous state that crystallizes over time into a polycrystalline material with high density and a consistent porosity distribution. In previous work, we have evaluated detonation critical thickness in HNAB films in an effectively infinite slab geometry with insignificant side losses. In this work, the effect of geometry on detonation failure was investigated by performing experiments on films with different thicknesses, while also changing dimensions such that side losses became significant. Films were characterized with surface profilometry and scanning electron microscopy. The results of these experiments will be discussed in the context of small sample geometry, deposited film microstructure, and density.
Geometry and starvation effects in hydrodynamic lubrication
NASA Technical Reports Server (NTRS)
Brewe, D. E.; Hamrock, B. J.
1982-01-01
Numerical methods were used to determine the effects of lubricant starvation on the minimum film thickness under conditions of a hydrodynamic point contact. Starvation was effected by varying the fluid inlet level. The Reynolds boundary conditions were applied at the cavitation boundary and zero pressure was stipulated at the meniscus or inlet boundary. A minimum-film-thickness equation as a function of both the ratio of dimensionless load to dimensionless speed and inlet supply level was determined. By comparing the film generated under the starved inlet condition with the film generated from the fully flooded inlet, an expression for the film reduction factor was obtained. Based on this factor a starvation threshold was defined as well as a critically starved inlet. The changes in the inlet pressure buildup due to changing the available lubricant supply are presented in the form of three dimensional isometric plots and also in the form of contour plots.
Effects of geometry on slot-jet film cooling performance
Hyams, D.G.; McGovern, K.T.; Leylek, J.H.
1995-10-01
The physics of the film cooling process for shaped, inclined slot-jets with realistic slot-length-to-width ratios (L/s) is studied for a range of blowing ratio (M) and density ratio (DR) parameters typical of gas turbine operations. For the first time in the open literature, the effect of inlet and exit shaping of the slot-jet on both flow and thermal field characteristics is isolated, and the dominant mechanisms responsible for differences in these characteristics are documented. A previously documented computational methodology was applied for the study of four distinct configurations: (1) slot with straight edges and sharp corners (reference case); (2) slot with shaped inlet region; (3) slot with shaped exit region; and (4) slot with both shaped inlet and exit regions. Detailed field results as well as surface phenomena involving adiabatic film effectiveness ({eta}) and heat transfer coefficient (h) are presented. It is demonstrated that both {eta} and h results are vital in the proper assessment of film cooling performance. All simulations were carried out using a multi-block, unstructured/adaptive grid, fully explicit, time-marching solver with multi-grid, local time stepping, and residual smoothing type acceleration techniques. Special attention was paid to and full documentation provided for: (1) proper modeling of the physical phenomena; (2) exact geometry and high quality grid generation techniques; (3) discretization schemes; and (4) turbulence modeling issues. The key parameters M and DR were varied from 1.0 to 2.0 and 1.5 to 2.0, respectively, to show their influence. Simulations were repeated for slot length-to-width ratio (L/s) of 3.0 and 4.5 in order to explain the effects of this important parameter. Additionally, the performance of two popular turbulence models, standard k-F, and RNG k-E, were studied to establish their ability to handle highly elliptic jet/crossflow interaction type processes.
Applied-field MPD thruster geometry effects
NASA Technical Reports Server (NTRS)
Myers, Roger M.
1991-01-01
Eight MPD thruster configurations were used to study the effects of applied field strength, propellant, and facility pressure on thruster performance. Vacuum facility background pressures higher than approx. 0.12 Pa were found to greatly influence thruster performance and electrode power deposition. Thrust efficiency and specific impulse increased monotonically with increasing applied field strength. Both cathode and anode radii fundamentally influenced the efficiency specific impulse relationship, while their lengths influence only the magnitude of the applied magnetic field required to reach a given performance level. At a given specific impulse, large electrode radii result in lower efficiencies for the operating conditions studied. For all test conditions, anode power deposition was the largest efficiency loss, and represented between 50 and 80 pct. of the input power. The fraction of the input power deposited into the anode decreased with increasing applied field and anode radii. The highest performance measured, 20 pct. efficiency at 3700 seconds specific impulse, was obtained using hydrogen propellant.
Applied-field MPD thruster geometry effects
NASA Technical Reports Server (NTRS)
Myers, Roger M.
1991-01-01
Eight MPD thruster configurations were used to study the effects of applied-field strength, propellant, and facility pressure on thruster performance. Vacuum facility background pressures higher than about 0.12 Pa were found to significantly influence thruster performance and electrode power deposition. Thrust efficiency and specific impulse increased monotonically with increasing applied field strength. Both cathode and anode radii fundamentally influenced the efficiency-specific impulse relationship, while their lengths influenced only the magnitude of the applied magnetic field required to reach a given performance level. At a given specific impulse, large electrode radii result in lower efficiencies for the operating conditions studied. For all test conditions, anode power deposition was the largest efficiency loss, and represented between 50 percent and 80 percent of the input power. The fraction of the input power deposited into the anode decreased with increasing applied field and anode radius. The highest performance measured, 20 percent efficiency at 3700 seconds specific impulse, was obtained using hydrogen propellant.
3D Simulation of Velocity Profile of Turbulent Flow in Open Channel with Complex Geometry
NASA Astrophysics Data System (ADS)
Kamel, Benoumessad; Ilhem, Kriba; Ali, Fourar; Abdelbaki, Djebaili
Simulation of open channel flow or river flow presents unique challenge to numerical simulators, which is widely used in the applications of computational fluid dynamics. The prediction is extremely difficult because the flow in open channel is usually transient and turbulent, the geometry is irregular and curved, and the free-surface elevation is varying with time. The results from a 3D non-linear k- ɛ turbulence model are presented to investigate the flow structure, the velocity distribution and mass transport process in a meandering compound open channel and a straight open channel. The 3D numerical model for calculating flow is set up in cylinder coordinates in order to calculate the complex boundary channel. The finite volume method is used to disperse the governing equations and the SIMPLE algorithm is applied to acquire the coupling of velocity and pressure. The non-linear k- ɛ turbulent model has good useful value because of taking into account the anisotropy and not increasing the computational time. The main contributions of this study are developing a numerical method that can be applied to predict the flow in river bends with various bend curvatures and different width-depth ratios. This study demonstrates that the 3D non-linear k- ɛ turbulence model can be used for analyzing flow structures, the velocity distribution and pollutant transport in the complex boundary open channel, this model is applicable for real river and wetland problem.
Cutting Edge Geometry Effect on Plastic Deformation of Titanium Alloy
NASA Astrophysics Data System (ADS)
Korovin, G. I.; Filippov, A. V.; Proskokov, A. V.; Gorbatenko, V. V.
2016-04-01
The paper presents experimental studies of OT4 titanium alloy machining with cutting edges of various geometry parameters. Experiments were performed at a low speed by the scheme of free cutting. Intensity of plastic shear strain was set for defining of cutting edge geometry effect on machining. Images of chip formed are shown. Estimation of strain magnitude was accomplished with digital image correlation method. Effect of rake angle and cutting edge angle has been studied. Depth of deformed layer and the area of the plastic strain is determine. Results showed that increasing the angle of the cutting edge inclination results in a change the mechanism of chip formation.
Effect of detailed surface geometry on riblet drag reduction performance
NASA Technical Reports Server (NTRS)
Walsh, Michael J.
1990-01-01
A comparison is made of the effect of small changes in v-groove geometry, for several riblet films applicable for drag reduction to commercial transport aircraft, whose nominal v-groove dimension is of the order of 0.002 inch. The films were tested in a water towing-tank facility. The results obtained indicate that small riblet peak geometry variations can result in a deterioration of riblet drag-reduction efficacy of as much as 40 percent, while interriblet valley curvature was found not to be critical to riblet performance.
Effect of nanopore geometry on ion current rectification.
Apel, Pavel Yu; Blonskaya, Irina V; Orelovitch, Oleg L; Ramirez, Patricio; Sartowska, Bozena A
2011-04-29
We present the results of systematic studies of ion current rectification performed on artificial asymmetric nanopores with different geometries and dimensions. The nanopores are fabricated by the ion track etching method using surfactant-doped alkaline solutions. By varying the alkali concentration in the etchant and the etching time, control over the pore profile and dimensions is achieved. The pore geometry is characterized in detail using field-emission scanning electron microscopy. The dependence of the ion current rectification ratio on the pore length, tip diameter, and the degree of pore taper is analysed. The experimental data are compared to the calculations based on the Poisson-Nernst-Planck equations. A strong effect of the tip geometry on the diode-like behaviour is confirmed. PMID:21411914
Geometry of the human erythrocyte. I. Effect of albumin on cell geometry.
Jay, A W
1975-01-01
The effects of albumin on the geometry of human erythrocytes have been studied. Individual red cells, hanging on edge from coverslips were photographed. Enlarged cell profiles were digitized using a Gradicon digitizer (Instronics Ltd., Stittsville, Ontario). Geometric parameters including diameter, area, volume, minimum cylindrical diameter, sphericity index, swelling index, maximum and minimum cell thickness, were calculated for each cell using a CDC 6400 computer. Maximum effect of human serum albumin was reached at about 1 g/liter. Studies of cell populations showed decreases in mean cell diameter of up to 6%, area 6%, and volume 15%, varying from sample to sample. The thickness of the rim was increased while that at the dimple was decreased. Studies of single cells showed that area and volume changes do not occur equally in all cells. Cells with lower sphericity indices showed larger effects. In the presence of albumin, up to 50% of the cells assumed cup-shapes (stomatocytes). These cells had smaller volumes but the same area as biconcave cells. Mechanical agitation could reversibly induce biconcave cells to assume cup shapes without area or volume changes. Experiments with de-fatted human albumins showed that the presence of bound fatty acids in varying concentrations does not alter the observed effects. Bovine serum albumin has similar effects on human erythrocytes as human serum albumin. Images FIGURE 2 FIGURE 6 FIGURE 9 PMID:1122337
The effects of solidification on sill propagation dynamics and geometry
NASA Astrophysics Data System (ADS)
Lola, Chanceaux; Thierry, Menand
2015-04-01
The effects of solidification on sill propagation dynamics and geometry are studied by means of analogue laboratory experiments. Hot fluid vegetable oil (a magma analogue), that solidifies during its propagation, is injected as a sill in a colder layered gelatine solid (an elastic host rock analogue). The injection flux and temperature are maintained constant during an experiment. In order to vary the importance of solidification and quantify its effect on sill propagation, the injection flux and temperature are systematically varied between each experiment. Depending on the importance of solidification effects, two extreme behaviours for sill propagation dynamics and geometry are observed. When solidification effects are small (high injection temperatures and fluxes), the propagation is continuous and the sill has a regular and smooth surface. Inversely, when solidification effects are important (low injection temperatures and fluxes), sill propagation is discontinuous and occurs by steps. After each propagation step, the sill stalls, thickens progressively by storing hot fluid vegetable oil beneath the partially solidified intrusion, without growing neither in length nor in breadth, and after a pause, the propagation initiates again, soon followed by a new episode of momentary arrest. The geometry of these sills displays folds, ropy structures on their surface, and lobes with imprints of the leading fronts that correspond to each step of surface creation. These experiments show that for a given, constant injected volume, as solidification effects increase, the surface of the sills decreases, their thickness increases, and the number of propagation steps increases. In the same way lower solidification effects promote larger sill surfaces, lower thicknesses, and a lower number of propagation steps. These results have various geological and geophysical implications. Regarding the geometry of sills, 3D seismic studies in sedimentary basins reveal sills with lobate
DL-FIND: an open-source geometry optimizer for atomistic simulations.
Kästner, Johannes; Carr, Joanne M; Keal, Thomas W; Thiel, Walter; Wander, Adrian; Sherwood, Paul
2009-10-29
Geometry optimization, including searching for transition states, accounts for most of the CPU time spent in quantum chemistry, computational surface science, and solid-state physics, and also plays an important role in simulations employing classical force fields. We have implemented a geometry optimizer, called DL-FIND, to be included in atomistic simulation codes. It can optimize structures in Cartesian coordinates, redundant internal coordinates, hybrid-delocalized internal coordinates, and also functions of more variables independent of atomic structures. The implementation of the optimization algorithms is independent of the coordinate transformation used. Steepest descent, conjugate gradient, quasi-Newton, and L-BFGS algorithms as well as damped molecular dynamics are available as minimization methods. The partitioned rational function optimization algorithm, a modified version of the dimer method and the nudged elastic band approach provide capabilities for transition-state search. Penalty function, gradient projection, and Lagrange-Newton methods are implemented for conical intersection optimizations. Various stochastic search methods, including a genetic algorithm, are available for global or local minimization and can be run as parallel algorithms. The code is released under the open-source GNU LGPL license. Some selected applications of DL-FIND are surveyed. PMID:19639948
Ambient Occlusion Effects for Combined Volumes and Tubular Geometry
Schott, Mathias; Martin, Tobias; Grosset, A.V. Pascal; Smith, Sean T.; Hansen, Charles D.
2013-01-01
This paper details a method for interactive direct volume rendering that computes ambient occlusion effects for visualizations that combine both volumetric and geometric primitives, specifically tube-shaped geometric objects representing streamlines, magnetic field lines or DTI fiber tracts. The algorithm extends the recently presented the directional occlusion shading model to allow the rendering of those geometric shapes in combination with a context providing 3D volume, considering mutual occlusion between structures represented by a volume or geometry. Stream tube geometries are computed using an effective spline-based interpolation and approximation scheme that avoids self-intersection and maintains coherent orientation of the stream tube segments to avoid surface deforming twists. Furthermore, strategies to reduce the geometric and specular aliasing of the stream tubes are discussed. PMID:23559506
Effect of Dust Coagulation Dynamics on the Geometry of Aggregates
NASA Technical Reports Server (NTRS)
Nakamura, R.
1996-01-01
Master equation gives a more fundamental description of stochastic coagulation processes rather than popular Smoluchowski's equation. In order to examine the effect of the dynamics on the geometry of resulting aggregates, we study Master equation with a rigorous Monte Carlo algorithm. It is found that Cluster-Cluster aggregation model is a good approximation of orderly growth and the aggregates have fluffy structures with a fractal dimension approx. 2. A scaling analysis of Smoluchowski's equation also supports this conclusion.
Effects of Sample Geometry and Loading Rate onTensile Ductility of TRIP800 Steel
Sun, Xin; Soulami, Ayoub; Choi, Kyoo Sil; Guzman, O.; Chen, Weinong W.
2012-04-15
The effects of sample geometry and loading rate on the tensile ductility of a commercial grade Transformation Induced Plasticity (TRIP) steel are examined in this paper. Quasistatic tensile tests were performed for the 1.2mm gauge TRIP800 steel sheets with two geometries: sub-sized ASTM E-8 and a custom designed miniature tensile sample. Sample geometry effects on post-uniform elongation are discussed together with other experimental data reported in the open literature. Further discussions on the effects of sample geometry are cast in the context of mesh-size dependent ductility in finite element-based engineering simulations. The quasi-static tensile curve for the miniature sample is then compared with the split Hopkinson bar results at the loading rates of 1700-S-1 and 2650-S-1 with the same sample design. In contrary to the typical strain rate sensitivity results for mild steel where the dynamic strength increase at high strain rate usually occurs at the price of ductility reduction, our results show that the TRIP800 under examination has positive strain rate sensitivity on both strength and ductility. Images of the deformation process captured by high speed camera together with scanning electron microscopy (SEM) near the fracture zone are also used to elucidate the different deformation modes at different loading rates.
Pin Tool Geometry Effects in Friction Stir Welding
NASA Technical Reports Server (NTRS)
Querin, J. A.; Rubisoff, H. A.; Schneider, J. A.
2009-01-01
In friction stir welding (FSW) there is significant evidence that material can take one of two different flow paths when being displaced from its original position in front of the pin tool to its final position in the wake of the weld. The geometry of the pin tool, along with the process parameters, plays an important role in dictating the path that the material takes. Each flow path will impart a different thermomechanical history on the material, consequently altering the material microstructure and subsequent weld properties. The intention of this research is to isolate the effect that different pin tool attributes have on the flow paths imparted on the FSWed material. Based on published weld tool geometries, a variety of weld tools were fabricated and used to join AA2219. Results from the tensile properties and microstructural characterization will be presented.
The effect of realistic antenna geometries on plasma loading predictions
Ryan, P.M.; Baity, F.W.; Batchelor, D.B.; Goulding, R.H.; Hoffman, D.J.; Tolliver, J.S.
1991-01-01
Plasma loading resistances for Ion Cyclotron Resonance Heating (ICRH) antennas are often calculated with sophisticated plasma models and only rudimentary antenna geometries. This paper presents techniques for modifying loading calculations for cavity antennas to account for such realities as return currents in the antenna sidewalls and backplane, the transmission and reflection properties of the Faraday shield, the end effects due to a finite length antenna, the reduction in phase velocity due to strap interaction with the Faraday shield, and the effect of slots in the cavity sidewalls and dividing septa. 4 refs., 4 figs.
Effect of varying internal geometry on the static performance of rectangular thrust-reverser ports
NASA Technical Reports Server (NTRS)
Re, Richard J.; Mason, Mary L.
1987-01-01
An investigation has been conducted to evaluate the effects of several geometric parameters on the internal performance of rectangular thrust-reverser ports for nonaxisymmetric nozzles. Internal geometry was varied with a test apparatus which simulated a forward-flight nozzle with a single, fully deployed reverser port. The test apparatus was designed to simulate thrust reversal (conceptually) either in the convergent section of the nozzle or in the constant-area duct just upstream of the nozzle. The main geometric parameters investigated were port angle, port corner radius, port location, and internal flow blocker angle. For all reverser port geometries, the port opening had an aspect ratio (throat width to throat height) of 6.1 and had a constant passage area from the geometric port throat to the exit. Reverser-port internal performance and thrust-vector angles computed from force-balance measurements are presented.
Reconstructing the open-field magnetic geometry of solar corona using coronagraph images
NASA Astrophysics Data System (ADS)
Uritsky, Vadim M.; Davila, Joseph M.; Jones, Shaela; Burkepile, Joan
2015-04-01
The upcoming Solar Probe Plus and Solar Orbiter missions will provide an new insight into the inner heliosphere magnetically connected with the topologically complex and eruptive solar corona. Physical interpretation of these observations will be dependent on the accurate reconstruction of the large-scale coronal magnetic field. We argue that such reconstruction can be performed using photospheric extrapolation codes constrained by white-light coronagraph images. The field extrapolation component of this project is featured in a related presentation by S. Jones et al. Here, we focus on our image-processing algorithms conducting an automated segmentation of coronal loop structures. In contrast to the previously proposed segmentation codes designed for detecting small-scale closed loops in the vicinity of active regions, our technique focuses on the large-scale geometry of the open-field coronal features observed at significant radial distances from the solar surface. Coronagraph images are transformed into a polar coordinate system and undergo radial detrending and initial noise reduction followed by an adaptive angular differentiation. An adjustable threshold is applied to identify candidate coronagraph features associated with the large-scale coronal field. A blob detection algorithm is used to identify valid features against a noisy background. The extracted coronal features are used to derive empirical directional constraints for magnetic field extrapolation procedures based on photospheric magnetograms. Two versions of the method optimized for processing ground-based (Mauna Loa Solar Observatory) and satellite-based (STEREO Cor1 and Cor2) coronagraph images are being developed.
UEDGE modeling of divertor geometry effects in NSTX
NASA Astrophysics Data System (ADS)
Izacard, Olivier; Soukhanovskii, Vlad; Scotti, Filippo
2015-11-01
We report efforts toward the modeling of divertor geometry effects using the fluid code UEDGE and NSTX experimental equilibria with different X-point heights. A variation of the geometry generates a competition between the poloidal magnetic flux expansion, which reduces the peak of the deposited heat flux and homogenizes its profile at divertor plates, and the proximity of the X-point to the divertor plates, which decreases the connection length and increases the peak heat flux. Our simulations use fixed fraction of carbon impurity, poloidally and radially constant transport coefficients, and high recycling boundary conditions, with a scan of density and pressure boundary conditions, and impurity fraction. Our simulations support the experimental observation that the poloidal flux expansion dominates the deposit heat flux over the parallel connection length effect. In opposite to experimental observation, detachment seems independent to the elevation. Improvement of the model is required. Supported by U.S. Department of Energy Contract No. DE-AC52-07NA27344.
Symmetric airfoil geometry effects on leading edge noise.
Gill, James; Zhang, X; Joseph, P
2013-10-01
Computational aeroacoustic methods are applied to the modeling of noise due to interactions between gusts and the leading edge of real symmetric airfoils. Single frequency harmonic gusts are interacted with various airfoil geometries at zero angle of attack. The effects of airfoil thickness and leading edge radius on noise are investigated systematically and independently for the first time, at higher frequencies than previously used in computational methods. Increases in both leading edge radius and thickness are found to reduce the predicted noise. This noise reduction effect becomes greater with increasing frequency and Mach number. The dominant noise reduction mechanism for airfoils with real geometry is found to be related to the leading edge stagnation region. It is shown that accurate leading edge noise predictions can be made when assuming an inviscid meanflow, but that it is not valid to assume a uniform meanflow. Analytic flat plate predictions are found to over-predict the noise due to a NACA 0002 airfoil by up to 3 dB at high frequencies. The accuracy of analytic flat plate solutions can be expected to decrease with increasing airfoil thickness, leading edge radius, gust frequency, and Mach number. PMID:24116405
Status of geometry effects on structural nuclear composite properties
Will Windes; Y. Katoh; L.L. Snead; E. Lara-Curzio; C. Henagar, Jr.
2005-09-01
structural ceramic composites being considered for control rod applications within the VHTR design. While standard sized (i.e. 150-mm long or longer) test specimens can be used for baseline non-irradiated thermal creep studies, very small, compact, tensile specimens will be required for the irradiated creep studies. Traditionally, it is standard practice to use small, representative test samples in place of full-size components for an irradiated study. However, a real problem exists for scale-up of composite materials. Unlike monolithic materials, these composites are engineered from two distinct materials using complicated infiltration techniques to provide full density and maximum mechanical properties. The material properties may be significantly affected when the component geometry or size is changed. It must be demonstrated that the smaller test samples used in an irradiated study will adequately represent larger composite tubes used for control rod applications. To accomplish this, two different test programs are being implemented to establish that small, flat test specimens are representative of the mechanical response for large, cylindrical composite tubes: a size effect study and a geometry effect study.
Effects of parent vessel geometry on intraaneurysmal flow patterns
NASA Astrophysics Data System (ADS)
Castro, Marcelo A.; Putman, Christopher M.; Cebral, Juan R.
2006-03-01
This study shows the influence of the upstream parent artery geometry on intra-aneurysmal hemodynamics of cerebral aneurysms. Patient-specific models of four cerebral aneurysms at four typical locations were constructed from 3D rotational angiography images. Two geometrical models were constructed for each patient, one with the native parent vessel geometry and another with the parent vessel truncated approximately 1cm upstream from the aneurysm. For one aneurysm, two images were used to construct a model as realistic and large as possible - down to the carotid bifurcation - which was cut at seven different locations. Corresponding finite element grids were generated and computational fluid dynamics simulations were carried out under pulsatile flow conditions. It was found that truncated models tended to underestimate the wall shear stress in the aneurysm and to shift the impaction zone to the neck when compared with the native geometry. In one aneurysm the parent vessel included a tortuous segment close to the neck that strongly influenced the flow pattern entering the aneurysm. Thus, including longer portions of the parent vessel beyond this segment did not have a substantial effect. Depending on the dominant geometrical features the length of the parent artery needed for an accurate representation of the intraaneurysmal hemodynamics may vary among individuals. In conclusion, failure to properly model the inflow stream determined by the upstream parent artery can significantly influence the results of intra-aneurysmal hemodynamic models. The upstream portion of the parent vessel of cerebral aneurysms should be included in order to accurately represent the intraaneurysmal hemodynamics.
NASA Technical Reports Server (NTRS)
Burd, Steven W.; Simon, Terrence W.; Thurman, Douglas (Technical Monitor)
2000-01-01
Experimental measurements are presented in this report to document the sensitivity of film cooling performance to the hole length and coolant delivery plenum geometry. Measurements with hot-wire anemometry detail velocity, local turbulence, and spectral distributions over the exit plane of film cooling holes and downstream of injection in the coolant-freestream interaction zone. Measurements of discharge coefficients and adiabatic effectiveness are also provided. Coolant is supplied to the film cooling holes by means of a large, open plenum and through plenums which force the coolant to approach the holes either co-current or counter-current to the freestream. A single row of film cooling holes with 35 degree-inclined streamwise at two coolant-to-freestream velocity ratios, 0.5 and 1.0, is investigated. The coolant-to-freestream density ratio is maintained in the range 0.96 to 1.0. Measurements were taken under high-freestream (FSTI = 12%) and low-freestream turbulence intensity (FSTI = 0.5%) conditions. The results document the effects of the hole L/D, coolant supply plenum geometry, velocity ratio, and FSTI. In general, hole L/D and the supply plenum geometry play influential roles in the film cooling performance. Hole L/D effects, however, are more pronounced. Film cooling performance is also dependent upon the velocity ratio and FSTI.
Effects of forebody geometry on subsonic boundary-layer stability
NASA Technical Reports Server (NTRS)
Dodbele, Simha S.
1990-01-01
As part of an effort to develop computational techniques for design of natural laminar flow fuselages, a computational study was made of the effect of forebody geometry on laminar boundary layer stability on axisymmetric body shapes. The effects of nose radius on the stability of the incompressible laminar boundary layer was computationally investigated using linear stability theory for body length Reynolds numbers representative of small and medium-sized airplanes. The steepness of the pressure gradient and the value of the minimum pressure (both functions of fineness ratio) govern the stability of laminar flow possible on an axisymmetric body at a given Reynolds number. It was found that to keep the laminar boundary layer stable for extended lengths, it is important to have a small nose radius. However, nose shapes with extremely small nose radii produce large pressure peaks at off-design angles of attack and can produce vortices which would adversely affect transition.
Weld geometry strength effect in 2219-T87 aluminum
NASA Technical Reports Server (NTRS)
Nunes, A. C., Jr.; Novak, H. L.; Mcilwain, M. C.
1981-01-01
A theory of the effect of geometry on the mechanical properties of a butt weld joint is worked out based upon the soft interlayer weld model. Tensile tests of 45 TIG butt welds and 6 EB beads-on-plate in 1/4-in. 2219-T87 aluminum plate made under a wide range of heat sink and power input conditions are analyzed using this theory. The analysis indicates that purely geometrical effects dominate in determining variations in weld joint strength with heat sink and power input. Variations in weld dimensions with cooling rate are significant as well as with power input. Weld size is suggested as a better indicator of the condition of a weld joint than energy input.
Geometry and molecular architecture effects in nanobubble inflation measurements
NASA Astrophysics Data System (ADS)
Xu, Shanhong; Castagnet, Sylvie; McKenna, Gregory
2011-03-01
Confinement effects on the mechanical properties of ultrathin polymer films were investigated by a bubble inflation technique developed in our lab. Prior studies of ultrathin films of poly(vinyl acetate) (PVAc) and linear polystyrene (PS) were performed on circular bubbles of different diameters. Here the creep behaviors of ultrathin films of linear PS were investigated on rectangular bubbles. The modulus of the thin film rectangular bubbles was analyzed by approximation methods. The inflation of rectangular bubbles was simulated by finite element analysis (FEA). The mechanical properties of the thin films with the same thickness for circular and rectangular bubbles are compared and we find that the rubbery plateau compliance is geometry independent. We also investigated the creep behaviors of ultrathin films of 3-arm star PS on circular bubbles. We find the rubbery plateau compliance is molecular architecture independent.
Biosimulation and visualization: effect of cerebrovascular geometry on hemodynamics.
Oshima, Marie; Kobayashi, Toshio; Takagi, Kiyoshi
2002-10-01
Hemodynamics plays an important role in cardiovascular disorders, and the authors are applying numerical and experimental studies of cerebrovascular blood flow to the creation and rupture of cerebral aneurysms. In particular, this study aims to investigate the effects of cerebrovascular geometry on hemodynamics, such as flow pattern, wall shear stress distribution, and pressure. This report consists mainly of two parts: numerical study of blood flow in the artery extracted from computer tomography data, and numerical and experimental studies of a curved pipe model. The simulation was conducted by using a finite element method; the experiment was conducted by particle imaging velocimetry. Numerical and experimental results are compared and both show similar secondary flow behavior. PMID:12496038
ERIC Educational Resources Information Center
DeMarinis, Matthew David
2011-01-01
While many studies examining the effectiveness of using dynamic geometry software exist, few studies exist at the elementary school level. An extensive data analysis of student performance on New York State Math Assessments revealed that students in the fifth grade may not have had a clear understanding of interior angles sums of polygons, more…
Neoclassical viscosity effects on resistive magnetohydrodynamic modes in toroidal geometry
Yang, J.G.; Oh, Y.H.; Choi, D.I. ); Kim, J.Y.; Horton, W. )
1992-03-01
The flux-surface-averaged linearized resistive magnetohydrodynamic (MHD) boundary-layer equations including the compressibility, diamagnetic drift, and neoclassical viscosity terms are derived in toroidal geometry. These equations describe the resistive layer dynamics of resistive MHD modes over the collisionality regime between the banana plateau and the Pfirsch--Schlueter. From the resulting equations, the effects of neoclassical viscosity on the stability of the tearing and resistive ballooning modes are investigated numerically. Also, a study is given for the problem of how the neoclassical resistive MHD mode is generated as the collisionality is reduced. It is shown that the neoclassical viscosity terms give a significant destabilizing effect for the tearing and resistive ballooning modes. This destabilization comes mainly from the reduction of the stabilizing effect of the parallel ion sound compression by the ion neoclassical viscosity. In the banana-plateau collisionality limit, where the compressibility is negligible, the dispersion relations of the tearing and resistive ballooning modes reduce to the same form, with the threshold value of the driving force given by {Delta}{sub {ital c}}=0. On the other hand, with the finite neoclassical effect it is found that the neoclassical resistive MHD instability is generated in agreement with previous results. Furthermore, it is shown that this later instability can be generated in a wide range of the collisionality including near the Pfirsch--Schlueter regime as well as the banana-plateau regime, suggesting that this mode is a probable cause of anomalous transport.
Electrically heated tube investigation of cooling channel geometry effects
NASA Technical Reports Server (NTRS)
Meyer, Michael L.
1995-01-01
The results of an experimental investigation on the combined effects of cooling channel aspect ratio and curvature for rocket engines are presented. Symmetrically heated tubes with average heat fluxes up to 1.7 MW/m(exp 2) were used. The coolant was gaseous nitrogen at an inlet temperature of 280 K (500 R) and inlet pressures up to 1.0 x 10(exp 7) N/m(exp 2) (1500 psia). Two different tube geometries were tested: a straight, circular cross-section tube, and an aspect-ratio 10 cross-section tube with a 45 deg bend. The circular tube results are compared to classical models from the literature as validation of the system. The curvature effect data from the curved aspect-ratio 10 tube compare favorably to the empirical equations available in the literature for low aspect ratio tubes. This latter results suggest that thermal stratification of the coolant due to diminished curvature effect mixing may not be an issue for high aspect-ratio cooling channels.
Schwinger effect and entanglement entropy in confining geometries
NASA Astrophysics Data System (ADS)
Ghodrati, Mahdis
2015-09-01
By using AdS /CFT , we study the critical electric field, the Schwinger pair creation rate and the potential phase diagram for the quark and antiquark in four confining supergravity backgrounds which are the Witten QCD (WQCD), the Maldacena-Nunez (MN), the Klebanov-Tseytlin (KT) and the Klebanov-Strassler (KS) models. We compare the rate of phase transition in these models and compare it also with the conformal case. We then present the phase diagrams of the entanglement entropy of a strip in these geometries and find the predicted butterfly shape in the diagrams. We found that the phase transitions have a higher rate in WQCD and KT relative to MN and KS. Finally we show the effect of turning on an additional magnetic field on the rate of pair creation by using the imaginary part of the Euler-Heisenberg effective Lagrangian. The result is increasing the parallel magnetic field would increase the pair creation rate and increasing the perpendicular magnetic field would decrease the rate.
Effect of fjord geometry on tidewater glacier stability
NASA Astrophysics Data System (ADS)
Åkesson, Henning; Nisancioglu, Kerim H.; Nick, Faezeh M.
2016-04-01
Many marine-terminating glaciers have thinned, accelerated and retreated during the last two decades, broadly consistent with warmer atmospheric and oceanic conditions. However, these patterns involve considerable spatial and temporal variability, with diverse glacier behavior within the same regions. Similarly, reconstructions of marine-terminating glaciers indicate highly asynchronous retreat histories. While it is well known that retrograde slopes can cause marine ice sheet instabilities, the effect of lateral drag and fjord width has received less attention. Here, we test the hypothesis that marine outlet glacier stability is largely controlled by fjord width, and to a less extent by regional climate forcing. We employ a dynamic flowline model on idealized glacier geometries (representative of different outlet glaciers) to investigate geometric controls on decadal and longer times scales. The model accounts for driving and resistive stresses of glacier flow as well as along-flow stress transfer. It has a physical treatment of iceberg calving and a time-adaptive grid allowing for continuous tracking of grounding-line migration. We apply changes in atmospheric and oceanic forcing and show how wide and narrow fjord sections foster glacier (in)stabilities. We also evaluate the effect of including a surface mass balance - elevation feedback in such a setting. Finally, the relevance of these results to past and future marine-terminating glacier stability is discussed.
NASA Astrophysics Data System (ADS)
Guan, Mingfu; Carrivick, Jonathan L.; Wright, Nigel G.; Sleigh, P. Andy; Staines, Kate E. H.
2016-07-01
Effects of flood-induced bed elevation and channel geometry changes on flood hazards are largely unexplored, especially in the case of multiple floods from the same site. This study quantified the evolution of river channel and floodplain geometry during a repeated series of hypothetical extreme floods using a 2D full hydro-morphodynamic model (LHMM). These experiments were designed to examine the consequences of channel geometry changes on channel conveyance capacity and subsequent flood dynamics. Our results revealed that extreme floods play an important role in adjusting a river channel to become more efficient for subsequent propagation of floods, and that in-channel scour and sediment re-distribution can greatly improve the conveyance capacity of a channel for subsequent floods. In our hypothetical sequence of floods the response of bed elevation was of net degradation, and sediment transport successively weakened even with floods of the same magnitude. Changes in river channel geometry led to significant impact on flood hydraulics and thereby flood hazards. We found that flood-induced in-channel erosion can disconnect the channel from its floodplain resulting in a reduction of floodwater storage. Thus, the frequency and extent of subsequent overbank flows and floodplain inundation decreased, which reduced downstream flood attenuation and increased downstream flood hazard. In combination and in summary, these results suggest that changes in channel capacity due to extreme floods may drive changes in flood hazard. The assumption of unchanging of river morphology during inundation modelling should therefore be open to question for flood risk management.
Planar Hall effect bridge geometries optimized for magnetic bead detection
NASA Astrophysics Data System (ADS)
Østerberg, Frederik Westergaard; Rizzi, Giovanni; Henriksen, Anders Dahl; Hansen, Mikkel Fougt
2014-05-01
Novel designs of planar Hall effect bridge sensors optimized for magnetic bead detection are presented and characterized. By constructing the sensor geometries appropriately, the sensors can be tailored to be sensitive to an external magnetic field, the magnetic field due to beads being magnetized by the sensor self-field or a combination thereof. The sensors can be made nominally insensitive to small external magnetic fields, while being maximally sensitive to magnetic beads, magnetized by the sensor self-field. Thus, the sensor designs can be tailored towards specific applications with minimal influence of external variables. Three different sensor designs are analyzed theoretically. To experimentally validate the theoretical signals, two sets of measurements are performed. First, the sensor signals are characterized as function of an externally applied magnetic field. Then, measurements of the dynamic magnetic response of suspensions of magnetic beads with a nominal diameter of 80 nm are performed. Furthermore, a method to amplify the signal by appropriate combinations of multiple sensor segments is demonstrated.
Effects of spaceflight on rat humerus geometry, biomechanics, and biochemistry
NASA Technical Reports Server (NTRS)
Vailas, A. C.; Zernicke, R. F.; Grindeland, R. E.; Kaplansky, A.; Durnova, G. N.; Li, K. C.; Martinez, D. A.
1990-01-01
The effects of a 12.5-day spaceflight (Cosmos 1887 biosatellite) on the geometric, biomechanical, and biochemical characteristics of humeri of male specific pathogen-free rats were examined. Humeri of age-matched basal control, synchronous control, and vivarium control rats were contrasted with the flight bones to examine the influence of growth and space environment on bone development. Lack of humerus longitudinal growth occurred during the 12.5 days in spaceflight. In addition, the normal mid-diaphysial periosteal appositional growth was affected; compared with their controls, the spaceflight humeri had less cortical cross-sectional area, smaller periosteal circumferences, smaller anterior-posterior periosteal diameters, and smaller second moments of area with respect to the bending and nonbending axes. The flexural rigidity of the flight humeri was comparable to that of the younger basal control rats and significantly less than that of the synchronous and vivarium controls; the elastic moduli of all four groups, nonetheless, were not significantly different. Generally, the matrix biochemistry of the mid-diaphysial cross sections showed no differences among groups. Thus, the spaceflight differences in humeral mechanical strength and flexural rigidity were probably a result of the differences in humeral geometry rather than material properties.
Effect of crack surface geometry on fatigue crack closure
Drury, W.J.; Gokhale, A.M.; Antolovich, S.D.
1995-10-01
The geometry of crack faces often plays a critical role in reducing crack extension forces when crack closure occurs during fatigue crack growth. Most previous studies of fatigue crack closure are concerned with mechanical measure of closure as related to the crack growth rate; very little attention has been given to the geometry of the crack surfaces. The objective is to identify those aspects of crack surface geometry that are important in the closure process, to develop quantitative fractographic techniques to estimate such attributes in a statistically significant and robust manner, and to correlate them to the physical process of crack closure. For this purpose, fatigue crack propagation experiments were performed on a Ni-base superalloy and crack growth rates and crack closure loads were measured. Digital image profilometry and software-based analysis techniques were used for statistically reliable and detailed quantitative characterization of fatigue crack profiles. It is shown that the dimensionless, scale-independent attributes, such a height-to-width ratio of asperities, fractal dimensions, dimensionless roughness parameters, etc., do not represent the aspects of crack geometry that are of primary importance in the crack closure phenomena. Furthermore, it is shown that the scale-dependent characteristics, such as average asperity height, do represent the aspects of crack geometry that play an interactive role in the closure process. These observations have implications concerning the validity of geometry-dependent, closure-based models for fatigue crack growth.
Effect of crack surface geometry on fatigue crack closure
NASA Astrophysics Data System (ADS)
Drury, W. J.; Gokhale, Arun M.; Antolovich, S. D.
1995-10-01
The geometry of crack faces often plays a critical role in reducing crack extension forces when crack closure occurs during fatigue crack growth. Most previous studies of fatigue crack closure are concerned with mechanical measures of closure as related to the crack growth rate; very little attention has been given to the geometry of the crack surfaces. Our objective is to identify those aspects of crack surface geometry that are important in the closure process, to develop quantitative fractographic techniques to estimate such attributes in a statistically significant and robust manner, and to correlate them to the physical process of crack closure. For this purpose, fatigue crack propagation experiments were performed on a Ni-base superalloy and crack growth rates and crack closure loads were measured. Digital image profilometry and software-based analysis techniques were used for statistically reliable and detailed quantitative characterization of fatigue crack profiles. It is shown that the dimensionless, scale-independent attributes, such as height-to-width ratio of asperities, fractal dimensions, dimensionless roughness parameters, etc., do not represent the aspects of crack geometry that are of primary importance in the crack closure phenomena. Furthermore, it is shown that the scaledependent characteristics, such as average asperity height, do represent the aspects of crack geometry that play an interactive role in the closure process. These observations have implications concerning the validity of geometry-dependent, closure-based models for fatigue crack growth.
Radio flares of compact binary mergers: the effect of non-trivial outflow geometry
NASA Astrophysics Data System (ADS)
Margalit, Ben; Piran, Tsvi
2015-10-01
The next generation gravitational waves (GW) detectors are most sensitive to GW emitted by compact (neutron star/black hole) binary mergers. If one of those is a neutron star the merger will also emit electromagnetic radiation via three possible channels: gamma-ray bursts and their (possibly orphan) afterglows, Li-Paczynski Macronovae and radio flares. This accompanying electromagnetic radiation is vitally important in confirming the GW detections. It could also reveal a wealth of information regarding the merger and will open a window towards multimessenger astronomy. Identifying and characterizing these counterparts is therefore of utmost importance. In this work, we explore late time radio flares emitted by the dynamically ejected outflows. We build upon previous work and consider the effect of the outflow's non-trivial geometry. Using an approximate method, we estimate the radio light-curves for several ejected matter distributions obtained in numerical simulations. Our method provides an upper limit to the effect of non-sphericity. Together with the spherical estimates, the resulting light curves bound the actual signal. We find that while non-spherical geometries can in principle lead to an enhanced emission, in most cases they result in an increase in the time-scale compared with a corresponding spherical configuration. This would weaken somewhat these signals and might decrease the detection prospects.
Finite-size effects and percolation properties of Poisson geometries.
Larmier, C; Dumonteil, E; Malvagi, F; Mazzolo, A; Zoia, A
2016-07-01
Random tessellations of the space represent a class of prototype models of heterogeneous media, which are central in several applications in physics, engineering, and life sciences. In this work, we investigate the statistical properties of d-dimensional isotropic Poisson geometries by resorting to Monte Carlo simulation, with special emphasis on the case d=3. We first analyze the behavior of the key features of these stochastic geometries as a function of the dimension d and the linear size L of the domain. Then, we consider the case of Poisson binary mixtures, where the polyhedra are assigned two labels with complementary probabilities. For this latter class of random geometries, we numerically characterize the percolation threshold, the strength of the percolating cluster, and the average cluster size. PMID:27575099
Tunneling into microstate geometries: quantum effects stop gravitational collapse
NASA Astrophysics Data System (ADS)
Bena, Iosif; Mayerson, Daniel R.; Puhm, Andrea; Vercnocke, Bert
2016-07-01
Collapsing shells form horizons, and when the curvature is small classical general relativity is believed to describe this process arbitrarily well. On the other hand, quantum information theory based (fuzzball/firewall) arguments suggest the existence of some structure at the black hole horizon. This structure can only form if classical general relativity stops being the correct description of the collapsing shell before it reaches the horizon size. We present strong evidence that classical general relativity can indeed break down prematurely, by explicitly computing the quantum tunneling amplitude of a collapsing shell of branes into smooth horizonless microstate geometries. We show that the amplitude for tunneling into microstate geometries with a large number of topologically non-trivial cycles is parametrically larger than e - S BH , which indicates that the shell can tunnel into a horizonless configuration long before the horizon has any chance to form. We also use this technology to investigate the tunneling of M2 branes into LLM bubbling geometries.
Finite-size effects and percolation properties of Poisson geometries
NASA Astrophysics Data System (ADS)
Larmier, C.; Dumonteil, E.; Malvagi, F.; Mazzolo, A.; Zoia, A.
2016-07-01
Random tessellations of the space represent a class of prototype models of heterogeneous media, which are central in several applications in physics, engineering, and life sciences. In this work, we investigate the statistical properties of d -dimensional isotropic Poisson geometries by resorting to Monte Carlo simulation, with special emphasis on the case d =3 . We first analyze the behavior of the key features of these stochastic geometries as a function of the dimension d and the linear size L of the domain. Then, we consider the case of Poisson binary mixtures, where the polyhedra are assigned two labels with complementary probabilities. For this latter class of random geometries, we numerically characterize the percolation threshold, the strength of the percolating cluster, and the average cluster size.
Effect of electrode geometry on photovoltaic performance of polymer solar cells
NASA Astrophysics Data System (ADS)
Li, Meng; Ma, Heng; Liu, Hairui; Wu, Dongge; Niu, Heying; Cai, Wenjun
2014-10-01
This paper investigates the impact of electrode geometry on the performance of polymer solar cells (PSCs). The negative electrodes with equal area (0.09 cm2) but different shape (round, oval, square and triangular) are evaluated with respect to short-circuit current density, open-circuit voltage, fill factor and power conversion efficiency of PSCs. The results show that the device with round electrodes gives the best photovoltaic performance; in contrast, the device with triangular electrodes reveals the worst properties. A maximum of almost a 19% increase in power conversion efficiency with a round electrode is obtained in the devices compared with that of the triangular electrode. To conclude, the electrode boundary curvature has a significant impact on the performance of PSCs. The larger curvature, i.e. sharper electrodes edges, perhaps has a negative effect on exciton separation and carrier transport in photoelectric conversion processes.
Study of Gasdynamic Effect Upon the Weld Geometry When Concumable Electrode Welding
NASA Astrophysics Data System (ADS)
Chinakhov, D. A.; Grigorieva, E. G.; Mayorova, E. I.
2016-04-01
The paper considers the ways of weld geometry controlling when consumable electrode welding under single-jet and double-jet gas shielding. The authors provide comparative results of experimental studies on the effects of shielding gas supply upon the weld geometry in weld joints produced from construction carbon steel 45. It has been established that gas-dynamic effect of the shielding gas has a significant impact upon shaping and weld geometry when consumable electrode welding under double-jet gas shielding.
Coincidence technique to reduce geometry and matrix effects in assay
Zucker, M.S.; Gozani, T.; Bernatowicz, H.
1983-01-01
Algebraic combinations of coincidence multiplicities can be formed which are relatively independent of detection efficiency, yet proportional to the amount of nuclear material being assayed. Considering these combinations, rather than the coincidence alone as signatures, has the demonstrable advantage that the assay results are comparatively independent of sample geometry or even matrix.
NASA Astrophysics Data System (ADS)
Zha, Guofeng; Wang, Hongqiang; Yang, Zhaocheng; Cheng, Yongqiang; Qin, Yuliang
2016-03-01
As a complementary imaging technology, coincidence imaging radar (CIR) achieves super-resolution in real aperture staring radar imagery via employing the temporal-spatial independent array detecting (TSIAD) signals. The characters of TSIAD signals are impacted by the array geometry and the imaging performance are influenced by the relative imaging position with respect to antennas array. In this paper, the effect of array geometry on CIR system is investigated in detail based on the judgment criteria of the effective rank theory. In course of analyzing of these influences, useful system design guidance about the array geometry is remarked for the CIR system. With the design guidance, the target images are reconstructed based on the Tikhonov regularization algorithm. Simulation results are presented to validate the whole analysis and the efficiency of the design guidance.
Effects of Hip Geometry on Fracture Patterns of Proximal Femur
Kazemi, Seyyed Morteza; Qoreishy, Mohamad; Keipourfard, Ali; Sajjadi, Mohammadreza Minator; Shokraneh, Shahram
2016-01-01
Background: Some studies have previously shown that geometry of proximal femur can affect the probability of fracture and type of fracture. It happens since the geometry of the proximal femur determines how a force is applied to its different parts. In this study, we have compared proximal femur’s geometric characteristics in femoral neck (FNF), intertrochanteric (ITF) and Subtrochanteric (STF) fractures. Methods: In this study, 60 patients who had hip fractures were studied as case studies. They were divided into FNF, ITF and STF groups based on their fracture types (20 patients in each group). Patients were studied with x-ray radiography and CT scans. Radiological parameters including femoral neck length from lateral cortex to center of femoral head (FNL), diameter of femoral head (FHD), diameter of femoral neck (FND), femoral head neck offset (FHNO), neck-shaft angle (alpha), femoral neck anteversion (beta) were measured and compared in all three groups. Results: Amount of FNL was significantly higher in STF group compared to FNF (0.011) while ITF and STF as well as FNT and ITF did not show a significant different. Also, FND in FNF group was significantly lower than the other two groups, i.e. ITF and STF. In other cases there were no instances of significant statistical difference. Conclusion: Hip geometry can be used to identify individuals who are at the risk of fracture with special pattern. Also, it is important to have more studies in different populations and more in men. PMID:27517071
Effect of wafer geometry on lithography chucking processes
NASA Astrophysics Data System (ADS)
Turner, Kevin T.; Sinha, Jaydeep K.
2015-03-01
Wafer flatness during exposure in lithography tools is critical and is becoming more important as feature sizes in devices shrink. While chucks are used to support and flatten the wafer during exposure, it is essential that wafer geometry be controlled as well. Thickness variations of the wafer and high-frequency wafer shape components can lead to poor flatness of the chucked wafer and ultimately patterning problems, such as defocus errors. The objective of this work is to understand how process-induced wafer geometry, resulting from deposited films with non-uniform stress, can lead to high-frequency wafer shape variations that prevent complete chucking in lithography scanners. In this paper, we discuss both the acceptable limits of wafer shape that permit complete chucking to be achieved, and how non-uniform residual stresses in films, either due to patterning or process non-uniformity, can induce high spatial frequency wafer shape components that prevent chucking. This paper describes mechanics models that relate non-uniform film stress to wafer shape and presents results for two example cases. The models and results can be used as a basis for establishing control strategies for managing process-induced wafer geometry in order to avoid wafer flatness-induced errors in lithography processes.
[The Effect of Observation Geometry on Polarized Skylight Spectrum].
Zhang, Ren-bin; Wang, Ling-mei; Gao, Jun; Wang, Chi
2015-03-01
Study on polarized skylight spectral characters while observation geometry changing in different solar zenith angles (SZA), viewing zenith angles (VZA) or relative azimuth angles (RAA). Simulation calculation of cloudless daylight polarimetric spectrum is realized based on the solver, vector discrete ordinate method, of radiative transfer equation. In the Sun's principal and perpendicular plane, the spectral irradiance data, varying at wavelengths in the range between 0.4 and 3 μm, are calculated to extend the atmospheric polarization spectral information under the conditions: the MODTRAN solar reference spectrur is the only illuminant source; the main influencing factors of polarized radiative transfer include underlying surface albedo, aerosol layers and components, and the absorption of trace gases. Simulation analysis results: (1) While the relative azimuth angle is zero, the magnitude of spectrum U/I is lower than 10(-7) and V/I is negligible, the degree of polarization and the spectrum Q/I are shaped like the letter V or mirror-writing U. (2) In twilight, when the Sun is not in FOV of the detector, the polarization of the daytime sky has two maximum near 0.51 and 2.75 μm, and a minimum near 1.5 μm. For arbitrary observation geometry, the spectral signal of V/I may be ignored. According to observation geometry, choosing different spectral bands or polarized signal will be propitious to targets detection. PMID:26117882
Children's Use of Geometry and Landmarks To Reorient in an Open Space.
ERIC Educational Resources Information Center
Gouteux, Stephane; Spelke, Elizabeth S.
2001-01-01
Eight experiments examined abilities of 3- to 4-year-olds to reorient themselves and locate a hidden object in an open circular space furnished with landmark objects. Findings showed that children failed to use geometric configuration of objects to reorient themselves. Children successfully located the object in relation to a geometric…
Effects of Drama-Based Geometry Instruction on Student Achievement, Attitudes, and Thinking Levels
ERIC Educational Resources Information Center
Duatepe-Paksu, Asuman; Ubuz, Behiye
2009-01-01
The authors investigated the effects of drama-based instruction on students' geometry achievement, geometric thinking level, attitudes toward mathematics and geometry, and retention of achievement, in comparison with traditional teaching. The sample involved 102 7th-grade students from a public school. Multivariate analyses of covariance revealed…
ERIC Educational Resources Information Center
Arici, Sevil; Aslan-Tutak, Fatma
2015-01-01
This research study examined the effect of origami-based geometry instruction on spatial visualization, geometry achievement, and geometric reasoning of tenth-grade students in Turkey. The sample ("n" = 184) was chosen from a tenth-grade population of a public high school in Turkey. It was a quasi-experimental pretest/posttest design. A…
ERIC Educational Resources Information Center
Kesan, Cenk; Caliskan, Sevdane
2013-01-01
The aim of this study is to investigate the effect of learning geometry topics of 7th grade in primary education with dynamic geometer's sketchpad geometry software to student's success and retention. The experimental research design with The Posttest-Only Control Group was used in this study. In the experimental group, dynamic geometer's…
ERIC Educational Resources Information Center
Cukier, Mimi; Asdourian, Tony; Thakker, Anand
2012-01-01
Geometry provides a natural window into what it is like to do mathematics. In the world of geometry, playful experimentation is often more fruitful than following a procedure, and logic plus a few axioms can open new worlds. Nonetheless, teaching a geometry course in a way that combines both rigor and play can be difficult. Many geometry courses…
Film stress and geometry effects in chrome photomask cleaning damage
NASA Astrophysics Data System (ADS)
Alpay, H. Ufuk; Wood, James L.; Kalk, Franklin D.
1997-02-01
As design rules shrink, photomask blank material characteristics play a more significant role in successful mask fabrication. Chromium-based absorber film stress is a key material attribute in determining mask quality. A photomask is cleaned several times during manufacture by various techniques incorporating part or all of the following processes: strong acids, bases, high pressure sprays, mechanical brushes, sonic agitation. In such aggressive environments, electrostatic discharge damage (ESD) and mechanical damage can occur. Chromium-based film dependence on sputter deposition parameters was studied here. Photoblank flatness, measured by optical interferometry, was used to quantify the stress. Blanks with various chrome film stresses were patterned with features combining different geometry types. The masks were then subjected to multiple cleaning cycles and inspected after each cycle. The results demonstrate how mask damage is related to the film mechanical properties (which are controllable by sputter deposition parameters) and the pattern itself (which is not controllable).
Effect of geometry in frequency response modeling of nanomechanical resonators
NASA Astrophysics Data System (ADS)
Esfahani, M. Nasr; Yilmaz, M.; Sonne, M. R.; Hattel, J. H.; Alaca, B. Erdem
2016-06-01
The trend towards nanomechanical resonator sensors with increasing sensitivity raises the need to address challenges encountered in the modeling of their mechanical behavior. Selecting the best approach in mechanical response modeling amongst the various potential computational solid mechanics methods is subject to controversy. A guideline for the selection of the appropriate approach for a specific set of geometry and mechanical properties is needed. In this study, geometrical limitations in frequency response modeling of flexural nanomechanical resonators are investigated. Deviation of Euler and Timoshenko beam theories from numerical techniques including finite element modeling and Surface Cauchy-Born technique are studied. The results provide a limit beyond which surface energy contribution dominates the mechanical behavior. Using the Surface Cauchy-Born technique as the reference, a maximum error on the order of 50 % is reported for high-aspect ratio resonators.
NASA Technical Reports Server (NTRS)
Choo, Yung; Vickerman, Mary; Lee, Ki D.; Thompson, David S.
2000-01-01
There are two distinct icing-related problems for airfoils that can be simulated. One is predicting the effects of ice on the aerodynamic performance of airfoils when ice geometry is known ("icing effects" study). The other is simulating ice accretion under specified icing conditions ("ice accretion" simulation). This paper will address development of two different software packages for two-dimensional geometry preparation and grid generation for both "icing effects" and "ice accretion" studies.
EFFECTS OF PLANFORM GEOMETRY ON TIDAL FLUSHING AND MIXING IN MARINAS
Physical hydraulic models of marinas possessing rectangular planforms were tested to determine effects of various geometrical parameters on tidal flushing and internal circulation in small harbors. Parameters investigated were: (1) Planform geometry aspect ratio; (2) ratio of ent...
Effect of Adhesion and Contact Geometry on Scratch Behavior of Polyvinyl Alcohol
NASA Astrophysics Data System (ADS)
Yoder, Karl; Xia, Xinyun; Gerberich, William
2000-03-01
The mechanical response of a material to single-point scratch loading is complex, with contributions from contact geometry, imposed deformation rate, thermomechanical interactions, and constitutive properties. Additionally, the effect of adhesion between scratch tip and specimen is an important, yet poorly understood, variable in deformation response. In particular the effects of adhesion and contact geometry on the mode of deformation and damage morphology are difficult to experimentally separate. Using a Hysitron Triboindenter, which can perform both nanoindentation and nanoscratch tests, in a controlled environmental chamber, the effect of adhesion on scratch response of polyvinyl alcohol is investigated. In addition, by using four different diamond tips, the role of contact geometry as it pertains to adhesion and scratch response is investigated. This talk presents the effects of contact geometry and relative humidity on stylus-PVOH adhesion, and subsequent scratch deformation response in an attempt to elucidate the role played by adhesion.
Update on single-screw expander geometry model integrated into an open-source simulation tool
NASA Astrophysics Data System (ADS)
Ziviani, D.; Bell, I. H.; De Paepe, M.; van den Broek, M.
2015-08-01
In this paper, a mechanistic steady-state model of a single-screw expander is described with emphasis on the geometric description. Insights into the calculation of the main parameters and the definition of the groove profile are provided. Additionally, the adopted chamber model is discussed. The model has been implemented by means of the open-source software PDSim (Positive Displacement SIMulation), written in the Python language, and the solution algorithm is described. The single-screw expander model is validated with a set of steady-state measurement points collected from a 11 kWe organic Rankine cycle test-rig with SES36 and R245fa as working fluid. The overall performance and behavior of the expander are also further analyzed.
The effect of reactor geometry on frontal polymerization spin modes
NASA Astrophysics Data System (ADS)
Pojman, John A.; Masere, Jonathan; Petretto, Enrico; Rustici, Mauro; Huh, Do-Sung; Kim, Min Suk; Volpert, Vladimir
2002-03-01
Using reactors of different sizes and geometries the dynamics of the frontal polymerization of 1,6-hexanediol diacrylate (HDDA) and pentaerythritol tetraacrylate (PETAC), with ammonium persulfate as the initiator were studied. For this system, the frontal polymerization exhibits complex behavior that depends on the ratio of the monomers. For a particular range of monomers concentration, the polymerization front becomes nonplanar, and spin modes appear. By varying the reactor diameter, we experimentally confirmed the expected shift of the system to a greater number of "hot spots" for larger diameters. For square test tubes a "zig-zag" mode was observed for the first time in frontal polymerization. We confirmed the viscosity-dependence of the spin mode instabilities. We also observed novel modes in cylinder-inside-cylinder reactors. Lastly, using a conical reactor with a continuously varying diameter, we observed what may be evidence for bistability depending on the direction of propagation. We discuss these finding in terms of the standard linear stability analysis for propagating fronts.
Effects of hillslope geometry on surface and subsurface flows
NASA Astrophysics Data System (ADS)
Sabzevari, T.; Noroozpour, S.
2014-07-01
Dividing a catchment to subcatchment or hillslope scales allows for better scrutiny of the changes in spatial distribution of rainfall, soil attributes and plant cover across the catchment. An instantaneous unit hydrograph model is suggested for simulating runoff hydrographs for complex hillslopes. This model is able to estimate surface and subsurface flows of the catchment based on the Dunne-Black mechanism. For this purpose, a saturation model is used to separate the saturated and unsaturated zones in complex hillslopes. The profile curvatures (concave, straight and convex) and plan shapes (convergent, parallel and divergent) of complex hillslopes are considered, in order to compute the travel time of surface and subsurface flows. The model was used for prediction of the direct runoff hydrograph and subsurface flow hydrograph of Walnut Gulch No. 125 catchment in Arizona (USA). Based on results, the geometry of hillslopes can change the peak of the direct runoff hydrograph up to two-fold, either higher or lower. The divergent hillslopes show higher peaks in comparison with the parallel and convergent hillslopes. The highest and lowest peak flows correspond to divergent-concave and convergent-straight hillslopes, respectively.
Casimir effects for classical and quantum liquids in slab geometry: A brief review
Biswas, Shyamal
2015-05-15
We analytically explore Casimir effects for confinement of classical and quantum fluctuations in slab (film) geometry (i) for classical (critical) fluctuations over {sup 4}He liquid around the λ point, and (ii) for quantum (phonon) fluctuations of Bogoliubov excitations over an interacting Bose-Einstein condensate. We also briefly review Casimir effects for confinement of quantum vacuum fluctuations confined to two plates of different geometries.
The vacuum geometry effect on neutron transmission and spatial resolution of neutron transmission.
Khanouchi, A; Sabir, A; Boulkheir, M; Ichaoui, R; Ghassoun, J; Jehouani, A
1997-01-01
Frequently, shields used against radiation contain some vacuum channels. We have therefore considered an infinite slab with a fixed thickness (thickness 20 lambda with lambda the mean free path of the neutron in the slab) and an infinite plane source of neutrons which arrived on the left side of the slab; transmitted neutrons through the slab to its right side are detected by finite detectors having windows equal to 2 lambda. This slab contains a vacuum channel. This channel has many legs with several horizontal parts. We used the Monte Carlo method for sampling the neutron history in the slab with a spatial biasing technique in order to accelerate the calculation convergence (Levitt, L. B. (1968) Nuclear Science and Engineering 31, 500-504; Jehouani, A., Ghassoun, J. and Aboubker, A. (1994) In Proceedings of 6th International Symposium on Radiation Physics, Rabat, Morocco). We studied the effects of the angle position and the number of horizontal parts of the channel on the neutron transmission. We have studied the effect of the vacuum channel opening (Artigas, R. and Hungerford, H. E. (1969) Nuclear Science and Engineering 36, 295-303) on the neutron transmission; for several values of this opening we have calculated the neutron transmission probability for each detector position. This study allowed us to determine the optimal conditions of vacuum geometries to improve protection against neutrons. In the second part we considered a shield which consists of a slab and a two-legged vacuum channel with two horizontal parts. The spatial distribution of neutrons transmitted through the protection screen was determined. This distribution shows two peaks. The study was made for different distances between the two horizontal parts. We have determined the smallest distance between the two horizontal parts for which the two peaks can be resolved. PMID:9463882
Toward physical cosmology: focus on inhomogeneous geometry and its non-perturbative effects
NASA Astrophysics Data System (ADS)
Buchert, Thomas
2011-08-01
We outline the key steps toward the construction of a physical, fully relativistic cosmology. The influence of inhomogeneities on the effective evolution history of the Universe is encoded in backreaction terms and expressed through spatially averaged geometrical invariants. These are absent and potential candidates for the missing dark sources in the standard model. Since they can be interpreted as energies of an emerging scalar field (the morphon), we are in a position to propose a strategy of how phenomenological scalar field models for dark energy, dark matter and inflation, that are usually added as fundamental sources to a homogeneous-geometry (FLRW) cosmology, can be potentially traced back to the inhomogeneous geometrical properties of space and its embedding into spacetime. We lay down a line of arguments that is—thus far only qualitatively—conclusive, and we address open problems of quantitative nature, related to the interpretation of observations. We discuss within a covariant framework (i) the foliation problem and invariant definitions of backreaction effects; (ii) the background problem and the notion of an effective cosmology; (iii) generalizations of the cosmological principle and generalizations of the cosmological equations; (iv) dark energies as energies of an effective scalar field; (v) the global gravitational instability of the standard model and basins of attraction for effective states; (vi) multiscale cosmological models and volume acceleration; (vii) effective metrics and strategies for effective distance measurements on the light cone, including observational predictions; (viii) examples of non-perturbative models, including explicit backreaction models for the LTB solution, extrapolations of the relativistic Lagrangian perturbation theory and scalar metric inhomogeneities. The role of scalar metric perturbations is critically examined and embedded into the non-perturbative framework.
Effects of nozzle lip geometry on spray atomization and emissions advanced gas turbine combustors
NASA Technical Reports Server (NTRS)
Micklow, Gerald J.; Roychoudhury, Subir; Nguyen, H. L.
1991-01-01
A parametric study is conducted to investigate the effect of nozzle lip geometry on nozzle fuel distribution, emissions and temperature distribution for a rich burn section of a rich burn/quick quench/lean burn combustor. It is seen that the nozzle lip geometry greatly affects the fuel distribution, emissions and temperature distribution. It is determined that at an equivalence ratio of 1.6 the NO concentration could be lowered by a factor greater than three by changing the nozzle lip geometry.
Modeling of divertor geometry effects in China fusion engineering testing reactor by SOLPS/B2-Eirene
Zhao, M. L.; Chen, Y. P.; Li, G. Q.; Luo, Z. P.; Guo, H. Y.; Institute of Plasma Physics, Chinese Academy of Science, Hefei 230031; General Atomics, P.O. Box 85608, San Diego, California 92186 ; Ye, M. Y.; Institute of Plasma Physics, Chinese Academy of Science, Hefei 230031 ; Tendler, M.
2014-05-15
The China Fusion Engineering Testing Reactor (CFETR) is currently under design. The SOLPS/B2-Eirene code package is utilized for the design and optimization of the divertor geometry for CFETR. Detailed modeling is carried out for an ITER-like divertor configuration and one with relatively open inner divertor structure, to assess, in particular, peak power loading on the divertor target, which is a key issue for the operation of a next-step fusion machine, such as ITER and CFETR. As expected, the divertor peak heat flux greatly exceeds the maximum steady-state heat load of 10 MW/m{sup 2}, which is a limit dictated by engineering, for both divertor configurations with a wide range of edge plasma conditions. Ar puffing is effective at reducing divertor peak heat fluxes below 10 MW/m{sup 2} even at relatively low densities for both cases, favoring the divertor configuration with more open inner divertor structure.
An experimental investigation of film cooling effectiveness for slots of various exit geometries
NASA Astrophysics Data System (ADS)
Taslim, M. E.; Spring, S. D.; Mehlman, B. P.
1990-07-01
The effect different slot geometries have on film effectiveness in the vicinity of slot breakout region is studied. Four different slot lip thickness to height ratios (t/s) and three different slot width to height ratios (w/s) are tested over a blowing ratio range of 0 to 1.3. All geometries are tested at a constant density ratio of 1.4. Slot surface film effectiveness measurements are made over a range of downstream surface distance to slot ratios of 0 to 15. Five different density ratios, spanning the typical engine operating range, are tested for one geometry to determine the effect of density ratio on film effectiveness. The results show that film effectiveness is highly sensitive to t/s but not significantly sensitive to either w/s or density ratio, and that an optimum injection angle of 8.5 deg exists for nondimensionalized downstream distance values less than 60.
Effects of various parameters on hydraulic fracturing geometry
Hanson, M.E.; Shaffer, R.J.; Anderson, G.D.
1981-08-01
Small-scale laboratory experiments are performed to study the effects of frictional characteristics on hydraulic fracture growth across unbonded interfaces in rocks. Various lubricants and mechanical preparations of the interface surfaces are used to vary the coefficients of friction on the interface surfaces. It is found that the frictional shear stress that the interface surface can support determines whether a hydraulically driven crack will cross the interface. Experiments also are being performed to study the effects of pre-existing cracks, which perpendicularly intersect the unbonded interface, on hydraulic crack growth across the interface. 17 refs.
Size and Geometry Effects on the Mechanical Properties of Carrara Marble Under Dynamic Loadings
NASA Astrophysics Data System (ADS)
Zou, Chunjiang; Wong, Louis Ngai Yuen
2016-05-01
The effects of specimen size and geometry on the dynamic mechanical properties of Carrara marble including compressive strength, failure strain and elastic modulus are investigated in this research. Four different groups of specimens of different sizes and cross-sectional geometries are loaded under a wide range of strain rates by the split Hopkinson pressure bar setup. The experimental results indicate that all these mechanical properties are significantly influenced by the specimen size and geometry to different extent, hence highlighting the importance of taking into account of the specimen size and geometry in dynamic tests on rock materials. In addition, the transmission coefficient and the determination of strain rate under dynamic tests are discussed in detail.
Thermoelectric effects in a rectangular Aharonov-Bohm geometry
NASA Astrophysics Data System (ADS)
Pye, A. J.; Faux, D. A.; Kearney, M. J.
2016-04-01
The thermoelectric transport properties of a rectangular Aharonov-Bohm ring at low temperature are investigated using a theoretical approach based on Green's functions. The oscillations in the transmission coefficient as the field is varied can be used to tune the thermoelectric response of the ring. Large magnitude thermopowers are obtainable which, in conjunction with low conductance, can result in a high thermoelectric figure of merit. The effects of single site impurities and more general Anderson disorder are considered explicitly in the context of evaluating their effect on the Fano-type resonances in the transmission coefficient. Importantly, it is shown that even for moderate levels of disorder, the thermoelectric figure of merit can remain significant, increasing the appeal of such structures from the perspective of specialist thermoelectric applications.
Nitriding of Aluminum Extrusion Die: Effect of Die Geometry
NASA Astrophysics Data System (ADS)
Akhtar, S. S.; Arif, A. F. M.; Yilbas, B. S.
2010-04-01
Nitriding of complex-shaped extrusion dies may result in non-uniform nitride layers and hence a required hardness may not be achieved in some regions of the bearing area. The present study is carried out to assess the effect of extrusion die profile on the characteristics and growth behavior of nitride layers so that the critical die design feature can be identified to enhance the uniformity of the nitride layer. For this purpose, AISI H13 steel samples have been manufactured with profiles similar to those of hot extrusion dies. The samples were then gas nitrided under controlled nitriding potential. The uniformity and depth of nitride layers have been investigated in terms of compound layer and total nitride case depth for selected die features. The results of this study indicated the need to include the effect of profile on the nitride layer for the optimal die design with improved service life.
Inflationary back-reaction effects from Relativistic Quantum Geometry
NASA Astrophysics Data System (ADS)
Bellini, Mauricio
2016-03-01
We study the dynamics of scalar metric fluctuations in a non-perturbative variational formalism recently introduced, by which the dynamics of a geometrical scalar field θ, describes the quantum geometrical effects on a Weylian-like manifold with respect to a background Riemannian space-time. In this letter we have examined an example in the framework of inflationary cosmology. The resulting spectral predictions are in very good agreement with observations and other models of inflation.
Effect of Tube Geometry on Regenerative Cooling Performance
NASA Technical Reports Server (NTRS)
Parris, Daniel K.; Landrum, D. Brian
2005-01-01
The flowfield characteristics in a rocket engine coolant channels are analyzed by use of a commercial CFD and multiphysics software developed by the CFD Research Corp. called CFD-ACE+. The channels are characterized by high Reynolds number flow, varying aspect ratio, varying curvature, asymmetric and symmetric heating. The supercritical hydrogen coolant introduces large property variations that have a strong influence on the developing flow and the resulting heat transfer. This paper only shows the effect of aspect ratio and curvature for constant properties.
NASA Astrophysics Data System (ADS)
Kettermann, M.; van Gent, H. W.; Urai, J. L.
2012-04-01
Brittle rocks, such as for example those hosting many carbonate or sandstone reservoirs, are often affected by different kinds of fractures that influence each other. Understanding the effects of these interactions on fault geometries and the formation of cavities and potential fluid pathways might be useful for reservoir quality prediction and production. Analogue modeling has proven to be a useful tool to study faulting processes, although usually the used materials do not provide cohesion and tensile strength, which are essential to create open fractures. Therefore, very fine-grained, cohesive, hemihydrate powder was used for our experiments. The mechanical properties of the material are scaling well for natural prototypes. Due to the fine grain size structures are preserved in in great detail. The used deformation box allows the formation of a half-graben and has initial dimensions of 30 cm width, 28 cm length and 20 cm height. The maximum dip-slip along the 60° dipping predefined basement fault is 4.5 cm and was fully used in all experiments. To setup open joints prior to faulting, sheets of paper placed vertically within the box to a depth of about 5 cm from top. The powder was then sieved into the box, embedding the paper almost entirely. Finally strings were used to remove the paper carefully, leaving open voids. Using this method allows the creation of cohesionless open joints while ensuring a minimum impact on the sensitive surrounding material. The presented series of experiments aims to investigate the effect of different angles between the strike of a rigid basement fault and a distinct joint set. All experiments were performed with a joint spacing of 2.5 cm and the fault-joint angles incrementally covered 0°, 4°, 8°, 12°, 16°, 20° and 25°. During the deformation time lapse photography from the top and side captured every structural change and provided data for post-processing analysis using particle imaging velocimetry (PIV). Additionally
Effect of tool geometry on ultrasonic welding process
NASA Astrophysics Data System (ADS)
Sasaki, Tomohiro; Sakata, Yutaro; Watanabe, Takehiko
2014-08-01
Ultrasonic welding of pure aluminum sheets is performed using two weld tools, one with a knurled surface and one with a cylindrical surface. Relative motion behaviors of each weld tool, with respect to the working materials, during ultrasonic welding tests are analyzed using the digital correlation method. Weld microstructure development is investigated on the basis of transitional weld stages in the context of relative motion behaviors. The dominant relative motion is between the two work materials at the beginning of the weld but changes to be the motion between the weld tool and the work material it is in contact with as weld time increases. Thermo-mechanical effects of the relative motion of the weld tool and the work materials, on the development of weld microstructure, are discussed.
Ultrasonic flowmeters: temperature gradients and transducer geometry effects.
Willatzen, M
2003-03-01
Ultrasonic flowmeter performance is addressed for the case of cylindrically shaped flowmeters employing two reciprocal ultrasonic transducers A and B so as to measure time-of-flight differences between signals transmitted from transducer A towards B followed by an equivalent signal transmitted from transducer B towards A. In the case where a liquid flows through the flowmeter's measuring section ("spoolpiece"), the arrival times of the two signals differ by an amount related to the flow passing between the two transducers. Firstly, a detailed study of flow measurement errors with mean flow in the laminar flow regime is carried out as a function of the mode index and the transducer diameter/cylinder diameter ratio in the case where no temperature gradients are present in the flowmeter sensor. It is shown that all modes except the fundamental mode overestimate the mean flow by a factor of 33.33% while excitation of the fundamental mode solely give error-free measurements. The immediate consequences are that the flowmeter error decreases as the transducer diameter/cylinder diameter ratio approaches 1 from 0 reflecting the fact that the excitation level of the fundamental mode increases from almost 0 to 1 as this ratio approaches 1 from 0. Secondly, the effect on flowmeter performance due to flow-induced temperature gradients is examined. It is shown that the presence of temperature gradients leads to flowmeter errors at the higher-flow values even in the case where the fundamental mode is the only mode excited. It is also deduced that flowmeter errors in general depend on the distance between transducers A and B whether temperature gradients exist or not. This conclusion is not reflected in the usual definition of flowmeter errors given by the so-called mode-dependent deviation of measurement introduced in earlier works. PMID:12565074
Geometry effects on magnetization dynamics in circular cross-section wires
Sturma, M.; Toussaint, J.-C. E-mail: daria.gusakova@cea.fr; Gusakova, D. E-mail: daria.gusakova@cea.fr
2015-06-28
Three-dimensional magnetic memory design based on circular-cross section nanowires with modulated diameter is the emerging field of spintronics. The consequences of the mutual interaction between electron spins and local magnetic moments in such non-trivial geometries are still open to debate. This paper describes the theoretical study of domain wall dynamics within such wires subjected to spin polarized current. We used our home-made finite element software to characterize the variety of domain wall dynamical regimes observed for different constriction to wire diameter ratios d/D. Also, we studied how sizeable geometry irregularities modify the internal micromagnetic configuration and the electron spin spatial distribution in the system, the geometrical reasons underlying the additional contribution to the system's nonadiabaticity, and the specific domain wall width oscillations inherent to fully three-dimensional systems.
The geometry effect on energy transfer rate in a coupled-quantum-wires structure
NASA Astrophysics Data System (ADS)
Rafee, Vahdat
2016-03-01
The geometry effect on energy transfer rate in a coupled cylindrical quantum wires system is investigated. The corrected random phase approximation by the zero-temperature static Hubbard correction is employed to calculate dielectric function of the system. The geometry effect on energy transfer rate is studied for statically and dynamically screened electron-electron interaction. Both the linear and nonlinear regimes correspond respectively to weak and strong external field are considered. The calculations show that increasing wire radius increases energy transfer rate in both the static and dynamic screening approximations for electron-electron interactions. Moreover, the same trend is predicted by the calculations for both the linear and nonlinear regimes.
NASA Technical Reports Server (NTRS)
Kuo, P. S.
1973-01-01
The complexities of turbine engine blade vibration are compounded by blade geometry, temperature gradients, and rotational speeds. Experience indicates that dynamics analysis using the finite element approach provides an effective means for predicting vibration characteristics of compressor and turbine blades whose geometry may be irregular, have curved boundaries, and be subjected to high temperatures and speeds. The NASTRAN program was chosen to help analyze the dynamics of normal modes, rotational stiffening and thermal effects on the normal modes, and forced responses. The program has produced reasonable success. This paper presents the analytical procedures and the NASTRAN results, in comparison with a conventional beam element program and laboratory data.
Effective coupling for open billiards
NASA Astrophysics Data System (ADS)
Pichugin, Konstantin; Schanz, Holger; Šeba, Petr
2001-11-01
We derive an explicit expression for the coupling constants of individual eigenstates of a closed billiard that is opened by attaching a waveguide. The Wigner time delay and the resonance positions resulting from the coupling constants are compared to an exact numerical calculation. Deviations can be attributed to evanescent modes in the waveguide and to the finite number of eigenstates taken into account. The influence of the shape of the billiard and of the boundary conditions at the mouth of the waveguide are also discussed. Finally we show that the mean value of the dimensionless coupling constants tends to the critical value when the eigenstates of the billiard follow random-matrix theory.
Minimizing the effect of automotive pollution in urban geometry using mathematical optimization
NASA Astrophysics Data System (ADS)
Craig, K. J.; de Kock, D. J.; Snyman, J. A.
One of the factors that needs to be considered during the layout of new urban geometry (e.g. street direction, spacing and width, building height restrictions) is the effect of the air pollution associated with the automotive transport that would use routes in this urban area. Although the pollution is generated at street level, its effect can be widespread due to interaction of the pollutant dispersion and diffusion with the wind speed and direction. In order to study the effect of a new urban geometry on the pollutant levels and dispersion, a very time-consuming experimental or parametric numerical study would have to be performed. This paper proposes an alternative approach, that of combining mathematical optimization with the techniques of computational fluid dynamics (CFD). In essence, the meteorological information as represented by a wind rose (wind speed and direction), is used to calculate pollutant levels as a function of urban geometry variables: street canyon depth and street canyon width. The pollutant source specified in conjunction with a traffic scenario with CO is used as pollutant. The main aim of the study is to be able to suggest the most beneficial configuration of an idealized urban geometry that minimizes the peak pollutant levels due to assumed traffic distributions. This study uses two mathematical optimization methods. The first method is implemented through a successive maximization-minimization approach, while the second method determines the location of saddle points of the pollutant level, considered as a function of urban geometry and wind rose. Locally, a saddle point gives the best urban geometry for the worst meteorological scenario. The commercial CFD code, STAR-CD, is coupled with a version of the DYNAMIC-Q optimization algorithm of Snyman, first to successively locate maxima and minima in a min-max approach; and then to locate saddle points. It is shown that the saddle-point method is more cost-effective. The methodology
ERIC Educational Resources Information Center
Nichols, Joe D.; Hall, Neff
In this study, the effects of a form of cooperative group instruction (Student Teams Achievement Divisions) on student motivation and achievement in a high school geometry class were examined. Ninety (mostly 10th-grade) students were randomly assigned to either a control group receiving traditional instruction or one of two treatment groups…
ERIC Educational Resources Information Center
Gambari, Isiaka Amosa; Ezenwa, Victoria Ifeoma; Anyanwu, Romanus Chogozie
2014-01-01
The study examined the effects of two modes of computer-assisted instructional package on solid geometry achievement amongst senior secondary school students in Minna, Niger State, Nigeria. Also, the influence of gender on the performance of students exposed to CAI(AT) and CAI(AN) packages were examined. This study adopted a pretest-posttest…
ERIC Educational Resources Information Center
Babai, Reuven; Zilber, Hanna; Stavy, Ruth; Tirosh, Dina
2010-01-01
This study investigates the effect on student performance in drawing their attention to relevant task variables, focusing on accuracy of responses and reaction times. We chose this methodology in order to better understand how such interventions affect the reasoning process. The study employs a geometry task in which the irrelevant salient…
Comparative studies of the effect of polycyclic aromatic hydrocarbon geometry on the hydrolysis of diol epoxides
The interaction of the diol epoxides (DEs) of both planar and non-planar PAHs with water have been examined using quantum mechanical and molecular dynamics. Th...
Effect of discharge duct geometry on centrifugal fan performance and noise emission
NASA Astrophysics Data System (ADS)
Nelson, David A.; Butrymowicz, William; Thomas, Christopher
2005-09-01
Non-ideal inlet and discharge duct geometries can cause significant changes to both the aerodynamic performance (``fan curve'') and specific sound power emission of a fan. A proper understanding of actual installed performance, as well as a good estimate of the system backpressure curve, is critical to achieving flow and acoustic goals as well as other criteria such as power consumption, mass and volume. To this end a battery of ISO 10302 tests was performed on a blower assembly which supports the Advanced Animal Habitat, being developed by ORBITEC for deployment on the International Space Station. The blower assembly consists of (4) identical centrifugal fans that, amongst themselves and across two prototypes, incorporated several discharge geometries. The inlet geometries were identical in all cases. Thus by comparing the dimensionless pressure-flow and noise emission characteristics across the cases, significant insight into the nature and potential magnitude of these effects is gained.
THE EFFECT OF VARIOUS DETECTOR GEOMETRIES ON THE PERFORMANCE OF CZT USING ONE CRYSTAL
Washington, A.; Duff, M.; Teague, L.
2011-06-21
CdZnTe (CZT) continues to be a major thrust interest mainly due to its potential application as a room temperature radiation detector. The performance of CZT detectors is directly related to the charge collection ability which can be affected by the configuration of the electrical contact. The charge collection efficiency is determined in part by the specific geometry of the anode contact which serves as the readout electrode. In this report, contact geometries including single pixel, planar, coplanar, and dual anode will be systematically explored by comparing the performance efficiencies of the detector using both low and high energy gamma rays. To help eliminate the effect of crystal quality variations, the contact geometries were fabricated on the same crystal detector with minimal polishing between contact placements.
Anderson, Andrew E.; Ellis, Benjamin J.; Maas, Steve A.; Weiss, Jeffrey A.
2010-01-01
Computational models may have the ability to quantify the relationship between hip morphology, cartilage mechanics and osteoarthritis. Most models have assumed the hip joint to be a perfect ball and socket joint and have neglected deformation at the interface between bone/cartilage. The objective of this study was to analyze finite element (FE) models of hip cartilage mechanics with varying degrees of simplified geometry and a model with a rigid bone material assumption to elucidate the effects on predictions of cartilage stress. A previously validated subject-specific FE model of a cadaveric hip joint was used as the basis for the models. Geometry for the bone/cartilage interface was either: 1) subject-specific (i.e. irregular), 2) spherical, or 3) a rotational conchoid. Cartilage was assigned either a varying (irregular) or constant thickness (smoothed). Loading conditions simulated walking, stair climbing and descending stairs. FE predictions of contact stress for the simplified models were compared with predictions from the subject-specific model. Both spheres and conchoids provided a good approximation of native hip joint geometry (average fitting error ~0.5 mm). However, models with spherical/conchoid bone geometry and smoothed articulating cartilage surfaces grossly underestimated peak and average contact pressures (50% and 25% lower, respectively) and overestimated contact area when compared to the subject-specific FE model. Models incorporating subject-specific bone geometry with smoothed articulating cartilage also underestimated pressures and predicted evenly distributed patterns of contact. The model with rigid bones predicted much higher pressures than the subject-specific model with deformable bones. The results demonstrate that simplifications to the geometry of the bone/cartilage interface, cartilage surface and bone material properties can have a dramatic effect on the predicted magnitude and distribution of cartilage contact pressures in the hip
Computer-aided three-dimensional analysis of the small-geometry effects of a MOSFET
Hsueh, K.L.K.
1987-01-01
The 3-D effects of a small-geometry MOSFET can only be analyzed accurately by using a 3-D simulator. A 3-D MOSFET simulator, called MICROMOS, therefore, was developed for this purpose. The history of numerical analysis used to simulate semiconductor devices was reviewed. Numerical methods, their mathematical background, and the iteration techniques commonly used in the semiconductor simulation are also discussed. The three-dimensional graphic results of the numerical analysis give valuable information for the understanding the physics of the small-geometry effects in a VLSI MOSFET. A mutual modulation of the depletion depth underneath the gate is described. This leads to an accurate 3-D analytical model for the prediction of the threshold voltage of a small-geometry MOSFET with a fully-recessed isolation oxide structure. Also, there is a mutual modulation between the transverse electric field and its two perpendicular components. This modulation was proven to be the source of the small-geometry effects of a small-size MOSFET. The enhanced drain-induced barrier lowering (DIBL) due to the scaling of the device is also presented.
The Effect of Tip Geometry on Active-Twist Rotor Response
NASA Technical Reports Server (NTRS)
Wilbur, Matthew L.; Sekula, Martin K.
2005-01-01
A parametric examination of the effect of tip geometry on active-twist rotor system response is conducted. Tip geometry parameters considered include sweep, taper, anhedral, nonlinear twist, and the associated radial initiation location for each of these variables. A detailed study of the individual effect of each parameter on active-twist response is presented, and an assessment offered of the effect of combining multiple tip shape parameters. Tip sweep is shown to have the greatest affect on active-twist response, significantly decreasing the response available. Tip taper and anhedral are shown to increase moderately the active-twist response, while nonlinear twist is shown to have a minimal effect. A candidate tip shape that provides active-twist response equivalent to or greater than a rectangular planform blade is presented.
NASA Astrophysics Data System (ADS)
Liang, M.; Kim, W.; Passalacqua, P.
2015-12-01
Tectonic subsidence and basin topography, both determining the accommodation, are fundamental controls on the basin filling processes. Their effects on the fluvial organization and the resultant subsurface patterns remain difficult to predict due to the lack of understanding about interaction between internal dynamics and external controls. Despite the intensive studies on tectonic steering effects on alluvial architecture, how the self-organization of deltaic channels, especially the distributary channel network, respond to tectonics and basin geometry is mostly unknown. Recently physical experiments and field studies have hinted dramatic differences in fluviodeltaic evolution between ones associated with active differential subsidence and existing basin depth. In this work we designed a series of numerical experiments using a reduced-complexity channel-resolving model for delta formation, and tested over a range of localized subsidence rates and topographic depression in basin geometry. We also used a set of robust delta metrics to analyze: i) shoreline planform asymmetry, ii) channel and lobe geometry, iii) channel network pattern, iv) autogenic timescales, and v) subsurface structure. The modeling results show that given a similar final thickness, active subsidence enhances channel branching with smaller channel sand bodies that are both laterally and vertically connected, whereas existing topographic depression causes more large-scale channel avulsions with larger channel sand bodies. In general, both subsidence and existing basin geometry could steer channels and/or lock channels in place but develop distinct channel patterns and thus stratal architecture.
Quantum spin Hall effect in graphene nanoribbons: Effect of edge geometry
NASA Astrophysics Data System (ADS)
Rhim, Jun-Won; Moon, Kyungsun
2011-07-01
There has been tremendous recent progress in realizing topological insulator initiated by the proposal of Kane and Mele for the graphene system. They have suggested that the odd Z2 index for the graphene manifests the spin-filtered edge states for the graphene nanoribbons, which lead to the quantum spin Hall effect (QSHE). Here, we investigate the role of the spin-orbit interaction both for the zigzag and armchair nanoribbons with special care in the edge geometry. For the pristine zigzag nanoribbons, we have shown that one of the σ edge bands located near E=0 lifts up the energy of the spin-filtered chiral edge states at the zone boundary by warping the π edge bands, and hence the QSHE does not occur. Upon increasing the carrier density above a certain critical value, the spin-filtered edge states are formed leading to the QSHE. We suggest that the hydrogen passivation on the edge can recover the original feature of the QSHE. For the armchair nanoribbon, the QSHE is shown to be stable. We have also derived the real-space effective Hamiltonian, which demonstrates that the on-site energy and the effective spin-orbit coupling strength are strongly enhanced near the ribbon edges. We have shown that the steep rise of the confinement potential thus obtained is responsible for the warping of the π edge bands.
Polarizability of acetanilide and RDX in the crystal: effect of molecular geometry
NASA Astrophysics Data System (ADS)
Tsiaousis, D.; Munn, R. W.; Smith, P. J.; Popelier, P. L. A.
2004-10-01
Density-functional theory with the B3LYP functional at the 6-311++G** level is used to calculate the dipole moment and the static polarizability for acetanilide and 1,3,5-trinitro-1,3,5-triazacyclohexane (RDX) in their in-crystal structures. For acetanilide the dipole moment is 2{1}/{2}% larger than for the gas-phase structure and for RDX (where there is a gross geometry change) it is 15% larger. The polarizability for the in-crystal structure is smaller than for the gas-phase structure by 3% for both species, whereas the in-crystal effective optical polarizability is larger than the gas-phase static polarizability for both crystals. Hence, effects in addition to the molecular geometry change in the crystal must be considered in order to interpret the effective polarizability completely.
Size and Geometry Effects on Rock Fracture Toughness: Mode I Fracture
NASA Astrophysics Data System (ADS)
Ayatollahi, M. R.; Akbardoost, J.
2014-03-01
In this paper, the effects of specimen size and geometry on the apparent mode I fracture toughness ( K c) of an Iranian white marble (Neyriz) are studied. A number of fracture tests were conducted on center-cracked circular disk (CCCD) specimens with different radii to investigate the size effects on K c. The experimental results demonstrate that the apparent fracture toughness increases in bigger specimens. In order to explain the experimental results, the modified maximum tangential stress (MMTS) criterion is used, where higher order terms of the Williams' series expansion are included in the maximum tangential stress criterion. It is shown that the MMTS criterion provides good estimates for the apparent fracture toughness of Neyriz marble, obtained from fracture tests of edge-cracked triangular specimens. It is, therefore, concluded that the proposed criterion is able to account for the size and geometry effects on the fracture resistance of rocks simultaneously.
Specimen geometry effects on graphite/PMR-15 composites during thermo-oxidative aging
NASA Technical Reports Server (NTRS)
Bowles, K. J.; Meyers, A.
1986-01-01
Studies were conducted to establish the effects of specimen geometry on the thermo-oxidative stability and the mechanical properties retention of unidirectional Celion 12000 graphite fiber reinforced PMR-15 polyimide composites. Weight loss, flexural strength and interlaminar shear strength are measured at isothermal aging times as long as 1639 hr at a temperature of 316 C for three different specimen geometries. It is found that the three different types of specimen surfaces exhibit different values of weight loss/unit area. The mechanical properties retention is also found to be dependent on geometry for these composites. The interlaminar shear strength decreases significantly over the complete range of aging times. The flexural strength retention starts showing geometric dependency after about 1000 hr of aging at 316C. Weight loss fluxes, associated with the three different types of exposed surfaces, are calculated and used to develop an empirical mathematical model for predicting the weight loss behavior of unidirectional composites of arbitrary geometries. Data are presented comparing experimentally determined weight loss with weight loss values predicted using the empirical model.
The effects of specimen geometry and size on the fracture toughness of nuclear graphites
Romanoski, G.R.; Burchell, T.D.
1991-01-01
In a joint Oak Ridge National Laboratory (ORNL)/Japan Atomic Energy Research Institute (JAERI) study, various fracture toughness techniques were applied to Toyo Tanso grade IG-110 graphite to establish if specimen geometry influences on fracture toughness. The test geometries investigated were: compact tension (CT), disc compact tension (DCT), short rod (SR), chevron-notched short-red (CNSR), cylindrical bend specimen (BS), and centrally slotted disc (CSD). Specimen geometries which allow slow crack propagation, such as the CNSR and CT, yielded higher fracture toughness values than those where fracture is very rapid, e.g., the CSD. In a further ORNL study, the CNSR specimen geometry was selected to investigate the effect of specimen size on fracture toughness. Three specimen sizes and three grades of graphite were examined: Great Lakes Carbon grade H-451, Stackpole grade 2020, and Toyo Tanso grade IG-110. Grade H-451 was the toughest graphite, while Stackpole 2020 was the least tough. Fracture toughness increased with increasing specimen size for all graphites tested. This result was attributed to rising R-curve behavior. 13 refs., 8 figs., 3 tabs.
Chiral and Achiral Nanodumbbell Dimers: The Effect of Geometry on Plasmonic Properties.
Smith, Kyle W; Zhao, Hangqi; Zhang, Hui; Sánchez-Iglesias, Ana; Grzelczak, Marek; Wang, Yumin; Chang, Wei-Shun; Nordlander, Peter; Liz-Marzán, Luis M; Link, Stephan
2016-06-28
Metal nanoparticles with a dumbbell-like geometry have plasmonic properties similar to those of their nanorod counterparts, but the unique steric constraints induced by their enlarged tips result in distinct geometries when self-assembled. Here, we investigate gold dumbbells that are assembled into dimers within polymeric micelles. A single-particle approach with correlated scanning electron microscopy and dark-field scattering spectroscopy reveals the effects of dimer geometry variation on the scattering properties. The dimers are prepared using exclusively achiral reagents, and the resulting dimer solution produces no detectable ensemble circular dichroism response. However, single-particle circular differential scattering measurements uncover that this dimer sample is a racemic mixture of individual nanostructures with significant positive and negative chiroptical signals. These measurements are complemented with detailed simulations that confirm the influence of various symmetry elements on the overall peak resonance energy, spectral line shape, and circular differential scattering response. This work expands the current understanding of the influence self-assembled geometries have on plasmonic properties, particularly with regard to chiral and/or racemic samples which may have significant optical activity that may be overlooked when using exclusively ensemble characterization techniques. PMID:27172606
On the effects of geometry in discrete element numerical earthquake simulations
NASA Astrophysics Data System (ADS)
McGinnis, Seth Aaron
2001-07-01
Computer simulation is a widely-used component of earthquake research, but while many computer models of earthquakes exist, there are none that simulate both sub-fault activity and three-dimensional geometry. I develop a computer model of earthquakes that simulates activity on fault systems with three-dimensional geometry by calculating stress transfer between fault elements as a three-dimensional tensor quantity. This model is a discrete, quasi-static, cellular-automaton type model that generates failure cascade sequences of all sizes. The fault is represented as a collection of rectangular sub-faults or "fault patches" that are not constrained to a two-dimensional plane. Stress transfer is calculated as a tensor field originating from point sources in a linear elastic whole-space, though the effects of normal stress on the friction holding the surfaces of a fault element in place are neglected. I then develop a procedure for studying the effects of geometry on the evolution of synthetic event histories in a computer model by systematically varying the configuration of a z-shaped or "zig-zag" fault and studying the results using scaling, clustering, correlation, and phase dynamic probability change (PDPC) analysis. I also study the effects of roughness and coupling parameters. I find that, in the absence of normal stress effects, geometry does not act as a barrier to the development and propagation of events, but that differences in the rate of stress accumulation due to tectonic loading forces do; that geometric roughness does not change the dynamics of the system in a qualitative way; and that the PDPC analysis methodology cannot be effectively applied to simulation data of the quality that can be currently generated.
Zhang, Dake; Wang, Qiu; Ding, Yi; Liu, Jeremy Jian
2014-01-01
According to the National Council of Teachers of Mathematics, geometry and spatial sense are fundamental components of mathematics learning. However, learning disabilities (LD) research has shown that many K-12 students encounter particular geometry difficulties (GD). This study examined the effect of an integrated object representation (IOR) accommodation on the test performance of students with GD compared to students without GD. Participants were 118 elementary students who took a researcher-developed geometry problem solving test under both a standard testing condition and an IOR accommodation condition. A total of 36 students who were classified with GD scored below 40% correct in the geometry problem solving test in the standard testing condition, and 82 students who were classified without GD scored equal to or above 40% correct in the same test and condition. All students were tested in both standard testing condition and IOR accommodation condition. The results from both ANOVA and regression discontinuity (RD) analyses suggested that students with GD benefited more than students without GD from the IOR accommodation. Implications of the study are discussed in terms of providing accommodations for students with mathematics learning difficulties and recommending RD design in LD research. PMID:24166208
The effect of nose geometry on the aerothermodynamic environment of shuttle entry configurations
NASA Technical Reports Server (NTRS)
Bertin, J. J.; Martindale, W. R.; Faria, H. T.; Graumann, B. W.; Horn, M. K.; Johnson, G. W.
1973-01-01
The effect was studied of nose geometry on the transition criteria for the windward boundary layer, on the extent of separation, on the heat transfer perturbation due to the canopy, and on the surface pressure and the heat transfer in the separated region. The data for each of these problems is analyzed. A literature review that concentrates on separation and the leeward flow-field is presented.
Effective geometry of the n=1 uniformly rotating self-gravitating polytrope
Bini, D.; Cherubini, C.; Filippi, S.; Geralico, A.
2010-08-15
The ''effective geometry'' formalism is used to study the perturbations of a perfect barotropic Newtonian self-gravitating rotating and compressible fluid coupled with gravitational backreaction. The case of a uniformly rotating polytrope with index n=1 is investigated, due to its analytical tractability. Special attention is devoted to the geometrical properties of the underlying background acoustic metric, focusing, in particular, on null geodesics as well as on the analog light cone structure.
Flow visualization study of the effect of injection hole geometry on an inclined jet in crossflow
NASA Technical Reports Server (NTRS)
Simon, F. F.; Ciancone, M. L.
1985-01-01
A flow visualization was studied by using neutrally buoyant, helium-filled soap bubbles, to determine the effect of injection hole geometry on the trajectory of an air jet in a crossflow and to investigate the mechanisms involved in jet deflection. Experimental variables were the blowing rate, and the injection hole geometry cusp facing upstream (CUS), cusp facing downstream (CDS), round, swirl passage, and oblong. It is indicated that jet deflection is governed by both the pressure drag forces and the entrainment of free-stream fluid into the jet flow. For injection hole geometries with similar cross-sectional areas and similar mass flow rates, the jet configuration with the larger aspect ratio experienced a greater deflection. Entrainment arises from lateral shearing forces on the sides of the jet, which set up a dual vortex motion within the jet and thereby cause some of the main-stream fluid momentum to be swept into the jet flow. This additional momentum forces the jet nearer the surface. Of the jet configurations, the oblong, CDS, and CUS configutations exhibited the largest deflections. The results correlate well with film cooling effectiveness data, which suggests a need to determine the jet exit configuration of optimum aspect ratio to provide maximum film cooling effectiveness.
Flow visualization study of the effect of injection hole geometry on an inclined jet in crossflow
NASA Technical Reports Server (NTRS)
Simon, Frederick F.; Ciancone, Michael L.
1987-01-01
A flow visualization was studied by using neutrally buoyant, helium-filled soap bubbles, to determine the effect of injection hole geometry on the trajectory of an air jet in a crossflow and to investigate the mechanisms involved in jet deflection. Experimental variables were the blowing rate, and the injection hole geometry cusp facing upstream (CUS), cusp facing downstream (CDS), round, swirl passage, and oblong. It is indicated that jet deflection is governed by both the pressure drag forces and the entrainment of free-stream fluid into the jet flow. For injection hole geometries with similar cross-sectional areas and similar mass flow rates, the jet configuration with the larger aspect ratio experienced a greater deflection. Entrainment arises from lateral shearing forces on the sides of the jet, which set up a dual vortex motion within the jet and thereby cause some of the main-stream fluid momentum to be swept into the jet flow. This additional momentum forces the jet nearer the surface. Of the jet configurations, the oblong, CDS, and CUS configurations exhibited the largest deflections. The results correlate well with film cooling effectiveness data, which suggests a need to determine the jet exit configuration of optimum aspect ratio to provide maximum film cooling effectiveness.
Effect of magnetic island geometry on ECRH/ECCD and consequences to the NTM stabilization dynamics
NASA Astrophysics Data System (ADS)
Chatziantonaki, I.; Tsironis, C.; Isliker, H.; Vlahos, L.
2012-09-01
In the majority of codes that model ECCD-based NTM stabilization, the analysis of the EC propagation and absorption is performed in terms of the axisymmetric magnetic field, ignoring effects due to the island topology. In this paper, we analyze the wave propagation, absorption and current drive in the presence of NTMs, as well as the ECCD-driven island growth, focusing on the effect of the island geometry on the wave de-position. A primary evaluation of the consequences of these effects on the NTM evolution is also made in terms of the modified Rutherford equation.
Evaluation of the effect of geometry for measuring section thickness in tomosynthesis.
Fukui, Ryohei; Ishii, Rie; Kishimoto, Junichi; Yamato, Shinichiro; Takahata, Akira; Kohama, Chiyuki
2014-01-01
Our aim in this study was to evaluate the effect of geometry for measuring section thickness in tomosynthesis by using a metal bead device (bead method). Tomosynthesis images were obtained from two types of tomosynthesis equipment, Safire17 (ST, Shimadzu, Kyoto, Japan) and XR650 (GT, GE Healthcare, Milwaukee, WI). After tomosynthesis radiography with each device, the bead tomosynthesis images were obtained by image reconstruction. The digital profile was obtained from the digital value of the bead central coordinate in the perpendicular direction, and we acquired the slice sensitivity profile (SSP). The section thickness was defined with the full width at half maximum obtained from the SSP. We investigated the change in section thickness under different evaluation conditions: the angular range, the height of the bead position, the source-image receptor distance (SID), and image processing. The section thickness decreased when the angular range and height of the bead position increased. Also, the section thickness varied with a change in the SID. The section thickness differed according to the geometry for measuring the section thickness. Thus, the effect of the geometry used for measurement should be considered when the section thickness in tomosynthesis is measured by the bead method. PMID:24254729
Finite element analysis of magnetohydrodynamic effects on blood flow in an aneurysmal geometry
NASA Astrophysics Data System (ADS)
Raptis, Anastasios; Xenos, Michalis; Tzirtzilakis, Efstratios; Matsagkas, Miltiadis
2014-10-01
Blood flow in an aneurysmal geometry, subjected to a static and uniform magnetic field, was studied. Blood was considered as a Newtonian, incompressible, and electrically conducting fluid. The nonlinear system of partial differential equations, describing the blood flow under the presence of a magnetic field, was discretized by the Galerkin weighted residual method. The transformation in generalized curvilinear coordinates facilitates the solution of the governing equations within arbitrary geometries. Pressure and velocity fields along with wall shear stress distributions were obtained for varying magnetic field intensities and directions. The visualization of the blood streamlines in the dilatation region highlights the effect of a magnetic field on the recirculation zones. The application of static magnetic fields can yield spatio-temporal description of blood flow patterns. The current study discusses implications of the hemodynamic properties estimated by respective screening techniques since the static magnetic field might cause alterations that possibly cannot be detected and thus eliminated.
Yilgor, P; Yilmaz, G; Onal, M B; Solmaz, I; Gundogdu, S; Keskil, S; Sousa, R A; Reis, R L; Hasirci, N; Hasirci, V
2013-09-01
The hypothesis of this study was that the extent of bone regeneration could be enhanced by using scaffolds with appropriate geometry, and that such an effect could be further increased by mimicking the natural timing of appearance of bone morphogenetic proteins BMP-2 and BMP-7 after fracture. Bioplotted poly(ε-caprolactone) (PCL) disks with four different fibre organizations were used to study the effect of 3D scaffold architecture on the healing of bone defects in a rat pelvis model. Moreover, one PCL construct was further modified by introducing a nanoparticulate sequential BMP-2/BMP-7 delivery system into this scaffold. Scaffolds and functionalized construct along with free nanocapsules were implanted using a rat iliac crest defect model. Six weeks post-implantation, the defects were evaluated by CT scan and histology. Analysis revealed that the basic architecture, having the highest pore volume for tissue ingrowth, presented the highest bone formation as determined by the bone mineral density (BMD) within the defect (144.2 ± 7.1); about four-fold higher than that of the empty defect (34.9 ± 10.7). It also showed the highest histological analysis scores with a high amount of bone formation within the defect, within the scaffold pores and along the outer surfaces of the scaffold. The basic scaffold carrying the BMP-2/BMP-7 delivery system showed significantly higher bone formation than the growth factor-free basic scaffold at 6 weeks (BMD 206.8 ± 15.7). Histological analysis also revealed new bone formation in close to or in direct contact with the construct interface. This study indicates the importance of open and interconnecting pore geometry on the better healing of bone defects, and that this effect could be further increased by supplying growth factors, as is the case in nature. PMID:22396311
The effect of surface anisotropy and viewing geometry on the estimation of NDVI from AVHRR
Meyer, D.; Verstraete, M.; Pinty, B.
1995-01-01
Since terrestrial surfaces are anisotropic, all spectral reflectance measurements obtained with a small instantaneous field of view instrument are specific to these angular conditions, and the value of the corresponding NDVI, computed from these bidirectional reflectances, is relative to the particular geometry of illumination and viewing at the time of the measurement. This paper documents the importance of these geometric effects through simulations of the AVHRR data acquisition process, and investigates the systematic biases that result from the combination of ecosystem-specific anisotropies with instrument-specific sampling capabilities. Typical errors in the value of NDVI are estimated, and strategies to reduce these effects are explored. -from Authors
Tip geometry effects on the model helicopter rotor low frequency broadband noise
NASA Technical Reports Server (NTRS)
Humbad, N. G.; Harris, W. L.
1981-01-01
The effect of rotor blade tip shapes and performance parameters on the low frequency broadband noise (LFBN) is investigated experimentally. The experimental results show 2 to 5 dB reductions for swept geometries compared with square tip blades at constant blade loading. A theoretical model is formulated which includes a detailed lift response function. For the square tip blades, theoretical results are found to be in good agreement with the experimental results. While the effects of advance ratio and tip speed on the LFBN are explicable, those of blade loading are not clearly understood.
A numerical study of the effect of urban geometry upon the surface energy budget
NASA Astrophysics Data System (ADS)
Sakakibara, Yasushi
This numerical study investigates the effect of urban canyon geometry upon the thermal environment using a parking lot model and an urban canyon model in identical meteorological conditions. The urban canyon model assumes two buildings on opposite sides of a street, no windows or interior anthropogenic heat source, an infinitely long east-west oriented canyon, and waterproof surfaces. The simulated surface temperatures agree well with those obtained by field measurement. The energy balance of the urban canyon is represented by that of the canyon top, which is an imaginary surface. The urban canyon, whose top surface is a plane above the canyon at the same level as the roof surface of the building, absorbs more heat in the daytime and releases more at night than the parking lot. The urban thermal environment depends on an urban geometry which particular to the urban canyon model produces reduced small sky view factors and complicated daytime shadow patterns. The results show that this urban geometry contributes to urban heat island formation.
NASA Astrophysics Data System (ADS)
Bolling, Denzell Tamarcus
A significant amount of research has been devoted to the characterization of new engineering materials. Searching for new alloys which may improve weight, ultimate strength, or fatigue life are just a few of the reasons why researchers study different materials. In support of that mission this study focuses on the effects of specimen geometry and size on the dynamic failure of AA2219 aluminum alloy subjected to impact loading. Using the Split Hopkinson Pressure Bar (SHPB) system different geometric samples including cubic, rectangular, cylindrical, and frustum samples are loaded at different strain rates ranging from 1000s-1 to 6000s-1. The deformation properties, including the potential for the formation of adiabatic shear bands, of the different geometries are compared. Overall the cubic geometry achieves the highest critical strain and the maximum stress values at low strain rates and the rectangular geometry has the highest critical strain and the maximum stress at high strain rates. The frustum geometry type consistently achieves the lowest the maximum stress value compared to the other geometries under equal strain rates. All sample types clearly indicated susceptibility to strain localization at different locations within the sample geometry. Micrograph analysis indicated that adiabatic shear band geometry was influenced by sample geometry, and that specimens with a circular cross section are more susceptible to shear band formation than specimens with a rectangular cross section.
NASA Astrophysics Data System (ADS)
Gockel, Joy; Klingbeil, Nathan; Bontha, Srikanth
2016-04-01
Laser and electron beam-based additive manufacturing of Ti-6Al-4V are under consideration for application to aerospace components. A critical concern for these processes is the ability to obtain a consistent and desirable microstructure and corresponding mechanical properties of the deposit. Based on the Rosenthal solution for a moving point-heat source, recent work has developed simulation-based process maps for the thermal conditions controlling microstructure (grain size and morphology) in beam-based deposition of semi-infinite geometries, where a steady-state melt pool exists away from free edges. In the current study, the Rosenthal solution is modified to include the effects of free edges. This is accomplished by the superposition of two point-heat sources approaching one another, with the line of symmetry representing the free edge. The result is an exact solution for the case of temperature-independent properties. Dimensionless results for melt pool geometry are determined, and plotted as a function of distance from the free edge. Results are plotted on solidification maps to predict trends in microstructure for Ti-6Al-4V. Finite element analysis is used to verify results. Results suggest that melt pool geometry is more sensitive to free edges than solidification microstructure.
NASA Technical Reports Server (NTRS)
Egolf, T. A.; Landgrebe, A. J.
1983-01-01
An analytic investigation to generalize wake geometry of a helicopter rotor in steady level forward flight and to demonstrate the influence of wake deformation in the prediction of rotor airloads and performance is described. Volume 1 presents a first level generalized wake model based on theoretically predicted tip vortex geometries for a selected representative blade design. The tip vortex distortions are generalized in equation form as displacements from the classical undistorted tip vortex geometry in terms of vortex age, blade azimuth, rotor advance ratio, thrust coefficient, and number of blades. These equations were programmed to provide distorted wake coordinates at very low cost for use in rotor airflow and airloads prediction analyses. The sensitivity of predicted rotor airloads, performance, and blade bending moments to the modeling of the tip vortex distortion are demonstrated for low to moderately high advance ratios for a representative rotor and the H-34 rotor. Comparisons with H-34 rotor test data demonstrate the effects of the classical, predicted distorted, and the newly developed generalized wake models on airloads and blade bending moments. Use of distorted wake models results in the occurrence of numerous blade-vortex interactions on the forward and lateral sides of the rotor disk. The significance of these interactions is related to the number and degree of proximity to the blades of the tip vortices. The correlation obtained with the distorted wake models (generalized and predicted) is encouraging.
Study of effects of injector geometry on fuel-air mixing and combustion
NASA Technical Reports Server (NTRS)
Bangert, L. H.; Roach, R. L.
1977-01-01
An implicit finite-difference method has been developed for computing the flow in the near field of a fuel injector as part of a broader study of the effects of fuel injector geometry on fuel-air mixing and combustion. Detailed numerical results have been obtained for cases of laminar and turbulent flow without base injection, corresponding to the supersonic base flow problem. These numerical results indicated that the method is stable and convergent, and that significant savings in computer time can be achieved, compared with explicit methods.
Bao, Y; Guérout, R; Lussange, J; Lambrecht, A; Cirelli, R A; Klemens, F; Mansfield, W M; Pai, C S; Chan, H B
2010-12-17
We measure the Casimir force between a gold sphere and a silicon plate with nanoscale, rectangular corrugations with a depth comparable to the separation between the surfaces. In the proximity force approximation (PFA), both the top and bottom surfaces of the corrugations contribute to the force, leading to a distance dependence that is distinct from a flat surface. The measured Casimir force is found to deviate from the PFA by up to 10%, in good agreement with calculations based on scattering theory that includes both geometry effects and the optical properties of the material. PMID:21231564
The effect of perspective geometry on judged direction in spatial information instruments
NASA Technical Reports Server (NTRS)
Mcgreevy, Michael Wallace; Ellis, Stephen R.
1986-01-01
Attention is given to the methodology and results of an experiment examining design aspects of panel-mounted displays that (1) incorporate a planar grid in their symbology, (2) subtend a narrow visual angle, and (3) are mounted so that they can be viewed face-on rather than obliquely. An analysis of direction judgments in such perspective displays shows that the perspective geometry of the stimulus image has a significant effect on direction judgment accuracy. Target elevation direction is generally overestimated; azimuth error varies sinusoidally with target azimuth direction, and is modulated by field-of-view angle.
Shear-flow Effects in Open Traps
Beklemishev, A. D.
2008-11-01
Interaction between shear flows and plasma instabilities and turbulence in open traps can lead to improved confinement both in experiments and in simulations. Shear flows, driven by biasing end-plates and limiters or by off-axis electron heating, in combination with the finite-larmor-radius (FLR) effects are shown to be efficient in confining plasmas even with unstable flute modes. Interpretation of the observed effects as the ''vortex confinement,'' i.e., confinement of the plasma core in the dead-flow zone of the driven vortex, is shown to agree well with simulations.
NASA Astrophysics Data System (ADS)
Zhou, Jing; Song, Bin; Zhao, Gaoling; Dong, Weixia; Han, Gaorong
2012-05-01
CdS quantum dot (QD) sensitized TiO2 nanorod array (NRA) film electrodes with different rod geometries were fabricated via a solvothermal route followed by a sequentialchemical bath deposition (S-CBD) process. By controlling the solution growth conditions, the rod geometries, especially the tip structures, of the TiO2 NRAs were tuned. The results indicated that the vertically aligned hierarchical NRAs possessed conically shaped tip geometry, which was favorable for film electrodes due to the reduced reflectance, enhanced light harvesting, fast charge-carrier separation and transfer, suppression of carrier recombination, sufficient electrolyte penetration and subsequent efficient QD assembly. CdS QD sensitized TiO2 NRA film electrodes with tapered tips exhibited an enhanced photoelectrochemical (PEC) performance, a photocurrent intensity of 5.13 mA/cm2 at a potential of 0 V vs. saturated calomel electrode, an open-circuit potential of -0.68 V vs. saturated calomel electrode and an incident photon to current conversion efficiency (IPCE) of 22% in the visible-light region from 400 to 500 nm. The effects of rod geometry on the optical absorption, reflectance, hydrophilic properties and PEC performance of bare TiO2 and CdS QD sensitized TiO2 NRA film electrodes were investigated. The mechanism of charge-carrier generation and transfer in these CdS QD sensitized solar cells based on vertically aligned TiO2 nanorods is discussed.
NASA Astrophysics Data System (ADS)
Kim, Goun; Park, Yoon-Cheol; Lee, Younki; Cho, Namung; Kim, Chang-Soo; Jung, Keeyoung
2016-09-01
Two sodium sulfur (NaS) cells, one with a planar design and the other with a tubular design, were subject to discharge-charge cycles in order to investigate the effect of cathode felt geometries on electrochemical characteristics of NaS cells. Their discharge-charge behaviors over 200 cycles were evaluated at the operation temperature of 350 °C with the current densities of 100 mA cm-2 for discharge and 80 mA cm-2 for charge. The results showed that the deviation from theoretical open circuit voltage changes of a planar cell was smaller than those of a tubular cell resulting in potential specific power loss reduction during operation. In order to understand the effect, a three dimensional statistically representative matrix for a cathode felt has been generated using experimentally measured data. It turns out that the area specific fiber number density in the outer side area of a tubular cathode felt is smaller than that of a planar felt resulting in occurrence of larger voltage drops via retarded convection of cathode melts during cell operation.
NASA Astrophysics Data System (ADS)
Sen, Oishik; Udaykumar, H. S.; Jacobs, Gustaaf
Interaction of a shock wave with dust particles is a complex physical phenomenon. A computational model for studying this two-phase system is the Particle-Source in Cell (PSIC) approach. In this method, the dust particles are tracked as point particles in a Lagrangian frame of reference immersed in a compressible fluid. Two-way interaction between the carrier and the dispersed phases is ensured by coupling the momentum and energy transfer between the two phases as source terms in the respective governing equations. These source terms (e.g. drag force on particles) may be computed from resolved numerical simulations by treating each macroscopic point particle as an ensemble of cylinders immersed in a compressed fluid. However the drag so computed must be independent of the geometry of the mesoscale. In this work, the effect of the stochasticity of the microstructural geometry in construction of drag laws from resolved mesoscale computations is studied. Several different arrangement of cylinders are considered and the mean drag law as a function of Mach Number and Volume Fraction for each arrangement is computed using the Dynamic Kriging Method. The uncertainty in the drag forces arising because of the arrangement of the cylinders for a given volume fraction is quantified as 90% credible sets and the effect of the uncertainty on PSIC computations is studied.
Briot, Karine; Benhamou, Claude Laurent; Roux, Christian
2012-01-01
The aims of this study were to assess the relationship between hip geometry and the 5-yr risk of hip fractures in postmenopausal osteoporotic women and the effects of strontium ranelate on these parameters. Using the 5-yr data of a randomized placebo-controlled trial of strontium ranelate (Treatment of Peripheral Osteoporosis Study [TROPOS]), we reanalyzed the hip dual-energy X-ray absorptiometry scans to determine the role of hip geometry in the risk of hip fractures (placebo group, n=636) and to analyze the effects of strontium ranelate (n=483). The outcomes included the hip structure analysis (HSA) parameters: cross-sectional area (CSA), section modulus, cortical thickness, and buckling ratio, measured at femoral neck, intertrochanteric (IT) region, and proximal shaft. The geometric parameters associated with an increased risk of hip fracture over 5yr were IT CSA and femoral shaft cortical thickness independent of age and total-hip bone mineral density (BMD). Using Bonferroni adjustment, IT cortical thickness was associated with the risk of hip fracture. Over 5yr, significant decreases in some femoral dimensions of the placebo group contrast with significant increases in strontium ranelate group after adjustment for age and BMD. Using Bonferroni adjustment, differences between placebo and strontium ranelate groups were no longer significant after adjustment on 5-yr BMD changes. Some HSA parameters have predictive value for hip fracture risk in postmenopausal osteoporotic women. Strontium ranelate improves some HSA parameters, through the BMD increase. PMID:22321661
Monte Carlo simulations on the effect of substrate geometry on adsorption and compression.
Wetzel, T E; Erickson, J S; Donohue, P S; Charniak, C L; Aranovich, G L; Donohue, M D
2004-06-22
Canonical Monte Carlo simulations were used to study the adsorption and compression of fluid layers on model substrates with cubic, (111) fcc, and graphite geometries. The effect of the relative size of the fluid and substrate molecules on adsorption was considered for strong molecule-surface interactions. In the case of monolayer formation, it was found that the surface geometry and the size of the adsorbate molecules had a significant effect on the structure of the adsorbed layer. These structures varied from well-ordered, commensurate layers to liquid-like structures. Lateral compression was observed for certain fluid to substrate molecule sizes. For the interactions studied in this work, it was found that maximum lateral compression occurred on the cubic surface when adsorbate molecules had a diameter approximately 15% larger than the substrate diameter. In the case of multilayer formation, it was found that second and higher adsorbed layers could compress into the adsorbed layers below them. For cubic substrates, the interlayer compression was predicted analytically with reasonable accuracy, with maximum interlayer compression found for fluid diameters approximately 90% the size of substrate molecule diameters. PMID:15268211
The Effect of Geometry Teaching with Cabri to Learning Levels of Fourth Grade Students
ERIC Educational Resources Information Center
Tutak, Tayfun; Turkdogan, Ali; Birgin, Osman
2009-01-01
In the study Cabri was used for teaching geometry at 4th grade. To investigate students' geometry level, a semi-experimental method was used. In the test group, geometry subjects are taught using Cabri. A multiple choice test was used to collect data as pre and post test. Answers were assigned as 1 to correct, 0 to wrong answers. Data were…
The shielding effect of small-scale martian surface geometry on ultraviolet flux
NASA Astrophysics Data System (ADS)
Moores, J. E.; Smith, P. H.; Tanner, R.; Schuerger, A. C.; Venkateswaran, K. J.
2007-12-01
The atmosphere of Mars does little to attenuate incoming ultraviolet (UV) radiation. Large amounts of UV radiation sterilize the hardiest of terrestrial organisms within minutes, and chemically alter the soil such that organic molecules at or near the surface are rapidly destroyed. Thus the survival of any putative martian life near the surface depends to a large extent on how much UV radiation it receives. Variations in small-scale geometry of the surface such as pits, trenches, flat faces and overhangs can have a significant effect on the incident UV flux and may create "safe havens" for organisms and organic molecules. In order to examine this effect, a 1-D radiative transfer sky model with 836 meshed points (plus the Sun) was developed which includes both diffuse and direct components of the surface irradiance. This model derives the variation of UV flux with latitude and an object's Geometric Shielding Ratio (a ratio which describes the geometry of each situation). The best protection is offered by overhangs with flux reduced to a factor of 1.8±0.2×10 of the unprotected value, a reduction which does not vary significantly by latitude. Pits and cracks are less effective with a reduction in UV flux of only up to 4.5±0.5×10 for the modeled scenarios; however, they are more effective for the same geometric shielding ratio than overhangs at high latitudes due to the low height of the Sun in the sky. Lastly, polar faces of rocks have the least effective shielding geometry with at most a 1.1±0.1×10 reduction in UV flux. Polar faces of rocks are most effective at mid latitudes where the Sun is never directly overhead, as at tropical latitudes, and never exposes the back of the rock, as at polar latitudes. In the most favorable cases, UV flux is sufficiently reduced such that organic in-fall could accumulate beneath overhanging surfaces and in pits and cracks. As well, hardy terrestrial microorganisms such as Bacillus pumilus could persist for up to 100 sols on
Friedman, J.M.; Osterkamp, W.R.; Scott, M.L.; Auble, G.T.
1998-01-01
The response of rivers and riparian forests to upstream dams shows a regional pattern related to physiographic and climatic factors that influence channel geometry. We carried out a spatial analysis of the response of channel geometry to 35 dams in the Great Plains and Central Lowlands, USA. The principal response of a braided channel to an upstream dam is channel-narrowing, and the principal response of a meandering channel is a reduction in channel migration rate. Prior to water management, braided channels were most common in the southwestern Plains where sand is abundant, whereas meandering channels were most common in the northern and eastern Plains. The dominant response to upstream dams has been channel-narrowing in the southwestern Plains (e.g., six of nine cases in the High Plains) and reduction in migration rate in the north and east (e.g., all of twelve cases in the Missouri Plateau and Western Lake Regions). Channel-narrowing is associated with a burst of establishment of native and exotic woody riparian pioneer species on the former channel bed. In contrast, reduction in channel migration rate is associated with a decrease in reproduction of woody riparian pioneers. Thus, riparian pioneer forests along large rivers in the southwestern Plains have temporarily increased following dam construction while such forests in the north and east have decreased. These patterns explain apparent contradictions in conclusions of studies that focused on single rivers or small regions and provide a framework for predicting effects of dams on large rivers in the Great Plains and elsewhere. These conclusions are valid only for large rivers. A spatial analysis of channel width along 286 streams ranging in mean annual discharge from 0.004 to 1370 cubic meters per second did not produce the same clear regional pattern, in part because the channel geometries of small and large streams are affected differently by a sandy watershed.
Effect of conductor geometry on source localization: Implications for epilepsy studies
Schlitt, H.; Heller, L.; Best, E.; Ranken, D.; Aaron, R.
1994-07-01
We shall discuss the effects of conductor geometry on source localization for applications in epilepsy studies. The most popular conductor model for clinical MEG studies is a homogeneous sphere. However, several studies have indicated that a sphere is a poor model for the head when the sources are deep, as is the case for epileptic foci in the mesial temporal lobe. We believe that replacing the spherical model with a more realistic one in the inverse fitting procedure will improve the accuracy of localizing epileptic sources. In order to include a realistic head model in the inverse problem, we must first solve the forward problem for the realistic conductor geometry. We create a conductor geometry model from MR images, and then solve the forward problem via a boundary integral equation for the electric potential due to a specified primary source. One the electric potential is known, the magnetic field can be calculated directly. The most time-intensive part of the problem is generating the conductor model; fortunately, this needs to be done only once for each patient. It takes little time to change the primary current and calculate a new magnetic field for use in the inverse fitting procedure. We present the results of a series of computer simulations in which we investigate the localization accuracy due to replacing the spherical model with the realistic head model in the inverse fitting procedure. The data to be fit consist of a computer generated magnetic field due to a known current dipole in a realistic head model, with added noise. We compare the localization errors when this field is fit using a spherical model to the fit using a realistic head model. Using a spherical model is comparable to what is usually done when localizing epileptic sources in humans, where the conductor model used in the inverse fitting procedure does not correspond to the actual head.
Numerical Investigation of the Effects of Channel Geometry on Platelet Activation and Blood Damage
Wu, Jingshu; Yun, B. Min; Fallon, Anna M.; Hanson, Stephen R.; Aidun, Cyrus K.; Yoganathan, Ajit P.
2011-01-01
Thromboembolic complications in Bileaflet mechanical heart valves (BMHVs) are believed to be due to the combination of high shear stresses and large recirculation regions. Relating blood damage to design geometry is therefore essential to ultimately optimize the design of BMHVs. The aim of this research is to quantitatively study the effect of 3D channel geometry on shear-induced platelet activation and aggregation, and to choose an appropriate blood damage index (BDI) model for future numerical simulations. The simulations in this study use a recently developed lattice-Boltzmann with external boundary force (LBM-EBF) method [Wu, J., and C. K. Aidun. Int. J. Numer. Method Fluids 62(7):765–783, 2010; Wu, J., and C. K. Aidun. Int. J. Multiphase flow 36:202–209, 2010]. The channel geometries and flow conditions are re-constructed from recent experiments by Fallon [The Development of a Novel in vitro Flow System to Evaluate Platelet Activation and Procoagulant Potential Induced by Bileaflet Mechanical Heart Valve Leakage Jets in School of Chemical and Biomolecular Engineering. Atlanta: Georgia Institute of Technology] and Fallon et al. [Ann. Biomed. Eng. 36(1):1]. The fluid flow is computed on a fixed regular ‘lattice’ using the LBM, and each platelet is mapped onto a Lagrangian frame moving continuously throughout the fluid domain. The two-way fluid–solid interactions are determined by the EBF method by enforcing a no-slip condition on the platelet surface. The motion and orientation of the platelet are obtained from Newtonian dynamics equations. The numerical results show that sharp corners or sudden shape transitions will increase blood damage. Fallon’s experimental results were used as a basis for choosing the appropriate BDI model for use in future computational simulations of flow through BMHVs. PMID:20976558
NASA Astrophysics Data System (ADS)
Cigala, V.; Kueppers, U.; Dingwell, D. B.
2015-12-01
Explosive volcanic eruptions eject large quantities of gas and particles into the atmosphere. The portion directly above the vent commonly shows characteristics of underexpanded jets. Understanding the factors that influence the initial pyroclast ejection dynamics is necessary in order to better assess the resulting near- and far-field hazards. Field observations are often insufficient for the characterization of volcanic explosions due to lack of safe access to such environments. Fortunately, their dynamics can be simulated in the laboratory where experiments are performed under controlled conditions. We ejected loose natural particles from a shock-tube while controlling temperature (25˚ and 500˚C), overpressure (15MPa), starting grain size distribution (1-2 mm, 0.5-1 mm and 0.125-0.250 mm), sample-to-vent distance and vent geometry. For each explosion we quantified the velocity of individual particles, the jet spreading angle and the production of fines. Further, we varied the setup to allow for different sample-to-gas ratios and deployed four different vent geometries: 1) cylindrical, 2) funnel with a flaring of 30˚, 3) funnel with a flaring of 15˚ and 4) nozzle. The results showed maximum particle velocities up to 296 m/s, gas spreading angles varying from 21˚ to 37˚ and particle spreading angles from 3˚ to 40˚. Moreover we observed dynamically evolving ejection characteristics and variations in the production of fines during the course of individual experiments. Our experiments mechanistically mimic the process of pyroclast ejection. Thus the capability for constraining the effects of input parameters (fragmentation conditions) and conduit/vent geometry on ballistic pyroclastic plumes has been clearly established. These data obtained in the presence of well-documented conduit and vent conditions, should greatly enhance our ability to numerically model explosive ejecta in nature.
Lau, Kevin Ka-Lun; Lindberg, Fredrik; Rayner, David; Thorsson, Sofia
2015-07-01
Future anthropogenic climate change is likely to increase the air temperature (T(a)) across Europe and increase the frequency, duration and magnitude of severe heat stress events. Heat stress events are generally associated with clear-sky conditions and high T(a), which give rise to high radiant heat load, i.e. mean radiant temperature (T(mrt)). In urban environments, T mrt is strongly influenced by urban geometry. The present study examines the effect of urban geometry on daytime heat stress in three European cities (Gothenburg in Sweden, Frankfurt in Germany and Porto in Portugal) under present and future climates, using T(mrt) as an indicator of heat stress. It is found that severe heat stress occurs in all three cities. Similar maximum daytime T(mrt) is found in open areas in all three cities despite of the latitudinal differences in average daytime T(mrt). In contrast, dense urban structures like narrow street canyons are able to mitigate heat stress in the summer, without causing substantial changes in T(mrt) in the winter. Although the T(mrt) averages are similar for the north-south and east-west street canyons in each city, the number of hours when T(mrt) exceeds the threshold values of 55.5 and 59.4 °C-used as indicators of moderate and severe heat stress-in the north-south canyons is much higher than that in the east-west canyons. Using statistically downscaled data from a regional climate model, it is found that the study sites were generally warmer in the future scenario, especially Porto, which would further exacerbate heat stress in urban areas. However, a decrease in solar radiation in Gothenburg and Frankfurt reduces T(mrt) in the spring, while the reduction in T(mrt) is somewhat offset by increasing T(a) in other seasons. It suggests that changes in the T(mrt) under the future scenario are dominated by variations in T(a). Nonetheless, the intra-urban differences remain relatively stable in the future. These findings suggest that dense urban
NASA Astrophysics Data System (ADS)
Lau, Kevin Ka-Lun; Lindberg, Fredrik; Rayner, David; Thorsson, Sofia
2015-07-01
Future anthropogenic climate change is likely to increase the air temperature ( T a ) across Europe and increase the frequency, duration and magnitude of severe heat stress events. Heat stress events are generally associated with clear-sky conditions and high T a , which give rise to high radiant heat load, i.e. mean radiant temperature ( T mrt ). In urban environments, T mrt is strongly influenced by urban geometry. The present study examines the effect of urban geometry on daytime heat stress in three European cities (Gothenburg in Sweden, Frankfurt in Germany and Porto in Portugal) under present and future climates, using T mrt as an indicator of heat stress. It is found that severe heat stress occurs in all three cities. Similar maximum daytime T mrt is found in open areas in all three cities despite of the latitudinal differences in average daytime T mrt . In contrast, dense urban structures like narrow street canyons are able to mitigate heat stress in the summer, without causing substantial changes in T mrt in the winter. Although the T mrt averages are similar for the north-south and east-west street canyons in each city, the number of hours when T mrt exceeds the threshold values of 55.5 and 59.4 °C—used as indicators of moderate and severe heat stress—in the north-south canyons is much higher than that in the east-west canyons. Using statistically downscaled data from a regional climate model, it is found that the study sites were generally warmer in the future scenario, especially Porto, which would further exacerbate heat stress in urban areas. However, a decrease in solar radiation in Gothenburg and Frankfurt reduces T mrt in the spring, while the reduction in T mrt is somewhat offset by increasing T a in other seasons. It suggests that changes in the T mrt under the future scenario are dominated by variations in T a . Nonetheless, the intra-urban differences remain relatively stable in the future. These findings suggest that dense urban structure
NASA Astrophysics Data System (ADS)
Takao, Manabu; Kuma, Hideki; Maeda, Takao; Kamada, Yasunari; Oki, Michiaki; Minoda, Atsushi
2009-03-01
The objective of this study is to show the effect of guide vane geometry on the performance. In order to overcome the disadvantages of vertical axis wind turbine, a straight-bladed vertical axis wind turbine (S-VAWT) with a directed guide vane row has been proposed and tested by the authors. According to previous studies, it was clarified that the performance of the turbine can be improved by means of the directed guide vane row. However, the guide vane geometry of S-VAWT has not been optimized so far. In order to clarify the effect of guide vane geometry, the effects of setting angle and gap between rotor blade and guide vane on power coefficient and starting characteristic were investigated in the experiments. The experimental study of the proposed wind turbine was carried out by a wind tunnel. The wind tunnel with a diameter of 1.8m is open jet type. The wind velocity is 8 m/s in the experiments. The rotor has three straight blades with a profile of NACA0018 and a chord length of 100 mm, a diameter of 0.6 m and a blade height of 0.7 m. The guide vane row consists of 3 arc plates.
Effect of Ripple Geometry on Vortex Generation, Ejection, and Strength in Oscillatory Flow
NASA Astrophysics Data System (ADS)
Smith, H. D.
2012-12-01
Turbulent vortex structures generated around bedforms have a large potential for significant suspended sediment transport. In the nearshore, the flow separation over ripples results in the generation of a lee vortex that can entrain sediment during half of the wave cycle. As the flow reverses, the sediment-laden vortex is ejected into the water column. The vortex is translated with the reversed flow and dissipates, releasing its sediment load back to the bed. The generation and ejection processes are functions of the ripple geometry and the wave acceleration. These same processes are also present for other geometries placed near the sea bed. Studies around bottom-seated cylindrical structures have shown multiple generation and ejection events off of the lee of the cylinder during half of the wave cycle. This generation is a function of Keulegan-Carpenter number, which balances the semi-excursion of the wave to the dominant length scale of the structure. In this work, the flow over rippled beds of various geometries over a range of hydrodynamic forcing will be numerically simulated to investigate the generation, ejection mechanisms, and strength of vortices created by this interaction. The simulations will be performed with the finite-difference CFD model, FLOW-3D. An advantage to this model is its ability to resolve complicated geometries in the flow with cartesian grids. In order to resolve the complex, three-dimensional flow field over an approximately two-dimensional rippled bed, a Smagorinsky Large Eddy Simulation closure scheme will be utilized. This model configuration has been shown to accurately predict the lift and drag force coefficients for bottom-mounted cylinders under linear waves, which are dominated by vortex generation and ejection. The three-dimensional vortex structure and strength will be evaluated with swirling strength criterion. Three-dimensional isosurfaces of the swirling strength will allow for the visual identification of the interaction
Integral-geometry characterization of photobiomodulation effects on retinal vessel morphology
Barbosa, Marconi; Natoli, Riccardo; Valter, Kriztina; Provis, Jan; Maddess, Ted
2014-01-01
The morphological characterization of quasi-planar structures represented by gray-scale images is challenging when object identification is sub-optimal due to registration artifacts. We propose two alternative procedures that enhances object identification in the integral-geometry morphological image analysis (MIA) framework. The first variant streamlines the framework by introducing an active contours segmentation process whose time step is recycled as a multi-scale parameter. In the second variant, we used the refined object identification produced in the first variant to perform the standard MIA with exact dilation radius as multi-scale parameter. Using this enhanced MIA we quantify the extent of vaso-obliteration in oxygen-induced retinopathic vascular growth, the preventative effect (by photobiomodulation) of exposure during tissue development to near-infrared light (NIR, 670 nm), and the lack of adverse effects due to exposure to NIR light. PMID:25071966
NASA Astrophysics Data System (ADS)
Hood, L. L.
1993-04-01
Possible causes of the observed long-term variation of Jovian synchrotron radio emission, including both intrinsic changes in the Jovian radiation belts and apparent changes due to variations in the Jovigraphic declination of the earth, DE, are investigated. An increase in diffusion rate with other parameters held constant results in an inward displacement of the peak emission radial distance that is not observed. Effects of viewing geometry changes are examined. The possible importance of such effects is suggested by a correlation between the total decimetric radio flux and DE, which varies between -3.3 and +3.3 deg during one Jovian orbital period. Because the Jovian central meridian longitudes where the magnetic latitude passes through zero during a given Jovian rotation change substantially with DE and since significant longitudinal asymmetries exist in both the volume emissivity and the latitudinal profile of the beam, the total intensity should be at least a partial function of D sub E.
Effects of frequency, irradiation geometry and polarisation on computation of SAR in human brain.
Zhou, Hongmei; Su, Zhentao; Ning, Jing; Wang, Changzhen; Xie, Xiangdong; Qu, Decheng; Wu, Ke; Zhang, Xiaomin; Pan, Jie; Yang, Guoshan
2014-12-01
The power absorbed by the human brain has possible implications in the study of the central nervous system-related biological effects of electromagnetic fields. In order to determine the specific absorption rate (SAR) of radio frequency (RF) waves in the human brain, and to investigate the effects of geometry and polarisation on SAR value, the finite-difference time-domain method was applied for the SAR computation. An anatomically realistic model scaled to a height of 1.70 m and a mass of 63 kg was selected, which included 14 million voxels segmented into 39 tissue types. The results suggested that high SAR values were found in the brain, i.e. ∼250 MHz for vertical polarisation and 900-1200 MHz both for vertical and horizontal polarisation, which may be the result of head resonance at these frequencies. PMID:24399107
Marquez-Lago, Tatiana T.
2015-01-01
The asymmetrical inheritance of plasmid DNA, as well as other cellular components, has been shown to be involved in replicative aging. In Saccharomyces cerevisiae, there is an ongoing debate regarding the mechanisms underlying this important asymmetry. Currently proposed models suggest it is established via diffusion, but differ on whether a diffusion barrier is necessary or not. However, no study so far incorporated key aspects to segregation, such as dynamic morphology changes throughout anaphase or plasmids size. Here, we determine the distinct effects and contributions of individual cellular variability, plasmid volume and moving boundaries in the asymmetric segregation of plasmids. We do this by measuring cellular nuclear geometries and plasmid diffusion rates with confocal microscopy, subsequently incorporating this data into a growing domain stochastic spatial simulator. Our modelling and simulations confirms that plasmid asymmetrical inheritance does not require an active barrier to diffusion, and provides a full analysis on plasmid size effects. PMID:26468952
Computational Analysis of an effect of aerodynamic pressure on the side view mirror geometry
NASA Astrophysics Data System (ADS)
Murukesavan, P.; Mu'tasim, M. A. N.; Sahat, I. M.
2013-12-01
This paper describes the evaluation of aerodynamic flow effects on side mirror geometry for a passenger car using ANSYS Fluent CFD simulation software. Results from analysis of pressure coefficient on side view mirror designs is evaluated to analyse the unsteady forces that cause fluctuations to mirror surface and image blurring. The fluctuation also causes drag forces that increase the overall drag coefficient, with an assumption resulting in higher fuel consumption and emission. Three features of side view mirror design were investigated with two input velocity parameters of 17 m/s and 33 m/s. Results indicate that the half-sphere design shows the most effective design with less pressure coefficient fluctuation and drag coefficient.
Denton, Jai A; Ghosh, Atiyo; Marquez-Lago, Tatiana T
2015-01-01
The asymmetrical inheritance of plasmid DNA, as well as other cellular components, has been shown to be involved in replicative aging. In Saccharomyces cerevisiae, there is an ongoing debate regarding the mechanisms underlying this important asymmetry. Currently proposed models suggest it is established via diffusion, but differ on whether a diffusion barrier is necessary or not. However, no study so far incorporated key aspects to segregation, such as dynamic morphology changes throughout anaphase or plasmids size. Here, we determine the distinct effects and contributions of individual cellular variability, plasmid volume and moving boundaries in the asymmetric segregation of plasmids. We do this by measuring cellular nuclear geometries and plasmid diffusion rates with confocal microscopy, subsequently incorporating this data into a growing domain stochastic spatial simulator. Our modelling and simulations confirms that plasmid asymmetrical inheritance does not require an active barrier to diffusion, and provides a full analysis on plasmid size effects. PMID:26468952
NASA Astrophysics Data System (ADS)
Limsakul, Praopim; Modchang, Charin
2016-07-01
We investigate the effects of synaptic vesicle geometry on Ca2+ diffusion dynamics in presynaptic terminals using MCell, a realistic Monte Carlo algorithm that tracks individual molecules. By modeling the vesicle as a sphere and an oblate or a prolate spheroid with a reflective boundary, we measure the Ca2+ concentration at various positions relative to the vesicle. We find that the presence of a vesicle as a diffusion barrier modifies the shape of the [Ca2+] microdomain in the vicinity of the vesicle. Ca2+ diffusion dynamics also depend on the distance between the vesicle and the voltage-gated calcium channels (VGCCs) and on the shape of the vesicle. The oblate spheroidal vesicle increases the [Ca2+] up to six times higher than that in the absence of a vesicle, while the prolate spheroidal vesicle can increase the [Ca2+] only 1.4 times. Our results also show that the presence of vesicles that have different geometries can maximally influence the [Ca2+] microdomain when the vesicle is located less than 50 nm from VGCCs.
Geometry, Electronic Structure, and Pseudo Jahn-Teller Effect in Tetrasilacyclobutadiene Analogues
NASA Astrophysics Data System (ADS)
Liu, Yang; Wang, Ya; Bersuker, Isaac B.
2016-03-01
We revealed the origin of the structural features of a series of tetrasilacyclobutadiene analogues based on a detailed study of their electronic structure and the pseudo Jahn-Teller effect (PJTE). Starting with the D4h symmetry of the Si4R4 system with a square four-membered silicon ring as a reference geometry, and employing ab initio calculations of energy profiles along lower-symmetry nuclear displacements in the ground and several excited states, we show that the ground-state boat-like and chair-like equilibrium configurations are produced by the PJT interaction with appropriate excited sates. For Si4F4 a full two-mode b1g‑b2g adiabatic potential energy surface is calculated showing explicitly the way of transformation from the unstable D4h geometry to the two equilibrium C2h configurations via the D2h saddle point. The PJTE origin of these structural features is confirmed also by estimates of the vibronic coupling parameters. For Si4R4 with large substituents the origin of their structure is revealed by analyzing the PJT interaction between the frontier molecular orbitals. The preferred chair-like structures of Si4R4 analogues with amido substituents, and heavier germanium-containing systems Ge4R4 (potential precursors for semiconducting materials) are predicted.
Effect of system compliance and indenter geometry on puncture mechanics of soft materials
NASA Astrophysics Data System (ADS)
Rattan, Shruti; Fakhouri, Sami; Crosby, Alfred
2015-03-01
Puncture mechanics in soft materials is critical for the development of new surgical instruments as well as new materials used in personal protective equipment. However, fundamental knowledge of how geometry and material properties control the nucleation of a crack, i.e. puncture, at large deformations in a soft material is currently limited. We describe a simple experimental method to study the resistive forces and failure of a soft gel being indented and punctured with a small needle. We show that puncture stresses can reach two orders of magnitude greater than the material modulus and that the force-deformation response is insensitive to the geometry of indenter at large indentation depths. We determine a transition between stress-limited and energy-limited failure modes, which is governed by the indenter size and the balance between fracture energy and cohesive stress. In addition, we examine the influence of system compliance on puncture of soft gels. It is well-known that system compliance influences the peak force in adhesion and traditional fracture experiments; however, its effect on crack nucleation is unresolved. We find that as the system becomes more compliant lower peak puncture forces were measured, which is associated with increased energy available for fracture.
Numerical investigation of the effect of blade geometry on blood trauma in a centrifugal blood pump.
Chan, W K; Wong, Y W; Ding, Y; Chua, L P; Yu, S C M
2002-09-01
Fluid dynamic forces in centrifugal blood pump impellers are of key importance in destruction of red blood cells (RBCs) because high rotational speed leads to strong interaction between the impeller and the RBCs. In this paper, three-dimensional models of five different blade geometries are investigated numerically using the commercial software CFX-TASCflow, and the streaklines of RBCs are obtained using the Lagrangian particle tracking method. In reality, RBCs pass through the pump along complicated paths resulting in a highly irregular loading condition for each RBC. In order to enable the prediction of blood damage under the action of these complex-loading conditions, a cumulative damage model for RBCs was adopted in this paper. The numerically simulated percent hemoglobin (%HB) released as RBCs traversed the impeller and volute was examined. It was observed that the residence time of particles in the blade passage is a critical factor in determining hemolytic effects. This, in turn, is a function of the blade geometry. In addition, it was observed that the volute profile is an important influence on the computed HB% released. PMID:12197935
Geometry, Electronic Structure, and Pseudo Jahn-Teller Effect in Tetrasilacyclobutadiene Analogues.
Liu, Yang; Wang, Ya; Bersuker, Isaac B
2016-01-01
We revealed the origin of the structural features of a series of tetrasilacyclobutadiene analogues based on a detailed study of their electronic structure and the pseudo Jahn-Teller effect (PJTE). Starting with the D4h symmetry of the Si4R4 system with a square four-membered silicon ring as a reference geometry, and employing ab initio calculations of energy profiles along lower-symmetry nuclear displacements in the ground and several excited states, we show that the ground-state boat-like and chair-like equilibrium configurations are produced by the PJT interaction with appropriate excited sates. For Si4F4 a full two-mode b1g-b2g adiabatic potential energy surface is calculated showing explicitly the way of transformation from the unstable D4h geometry to the two equilibrium C2h configurations via the D2h saddle point. The PJTE origin of these structural features is confirmed also by estimates of the vibronic coupling parameters. For Si4R4 with large substituents the origin of their structure is revealed by analyzing the PJT interaction between the frontier molecular orbitals. The preferred chair-like structures of Si4R4 analogues with amido substituents, and heavier germanium-containing systems Ge4R4 (potential precursors for semiconducting materials) are predicted. PMID:26996445
NASA Astrophysics Data System (ADS)
Moghaddam, M.; Akbar, R.; West, R. D.; Colliander, A.; Kim, S.; Dunbar, R. S.
2015-12-01
The NASA Soil Moisture Active-Passive Mission (SMAP), launched in January 2015, provides near-daily global surface soil moisture estimates via combined Active Radar and Passive Radiometer observations at various spatial resolutions. The goal of this mission is to enhance our understanding of global carbon and water cycles. This presentation will focus on a comprehensive assessment of the SMAP high resolution radar backscatter data (formally the L1C_S0_HiRes data product) obtained over a 3 km Woody Savanna region in north-central California during a 2.5 month period starting late May 2015. The effects of spacecraft observation geometry (fore- and aft-looks as well as ascending and descending obits) along with regional topography on soil moisture estimation abilities will be examined. Furthermore surface soil moisture retrievals, obtained through utilization of different combinations of observation geometries, will be compared to an existing network of in situsensors. Current electromagnetic scattering and emission models do not properly account for surface topography, therefore physical forward model predictions and observations have unaccounted mismatch errors which also affect soil moisture estimation accuracies. The goal of this study is to quantify these soil moisture prediction errors and highlight the need for new and complete Electromagnetic modeling efforts.
Effects of surface wettability and edge geometry on drop motion through an orifice
NASA Astrophysics Data System (ADS)
Bordoloi, Ankur; Longmire, Ellen
2012-11-01
In geothermal energy recovery and CO2 sequestration, drops move through a porous structure by displacing a surrounding liquid. Both the pore geometry and surface wettability influence the drop motion. We simplify the pore structure to a thin plate with a circular orifice. The plate is held horizontally inside a rectangular tank filled with silicone oil. Drops of water/glycerin with Bond numbers (Bo) of 1-10 are released above and axisymmetric to the orifice, encountering the plate after reaching their terminal speed. We use high speed imaging to examine the effects of orifice-to-drop diameter ratio (d/D), orifice surface wettability (hydrophilic/hydrophobic) and edge geometry on the passage of drop fluid through the orifice. We generate regime maps for d/D and Bo delineating domains of drop capture, passage, and passage with breakup. For d/D < 1, sharp edges are observed to yield contact between the drop and orifice so that surface wettability influences the subsequent dynamics. On the other hand, rounded edges appear to prevent direct contact so that the dynamics are unaffected by the surface wettability. Supported by DOE (DOE EERE-PMC-10EE0002764).
Geometry, Electronic Structure, and Pseudo Jahn-Teller Effect in Tetrasilacyclobutadiene Analogues
Liu, Yang; Wang, Ya; Bersuker, Isaac B.
2016-01-01
We revealed the origin of the structural features of a series of tetrasilacyclobutadiene analogues based on a detailed study of their electronic structure and the pseudo Jahn-Teller effect (PJTE). Starting with the D4h symmetry of the Si4R4 system with a square four-membered silicon ring as a reference geometry, and employing ab initio calculations of energy profiles along lower-symmetry nuclear displacements in the ground and several excited states, we show that the ground-state boat-like and chair-like equilibrium configurations are produced by the PJT interaction with appropriate excited sates. For Si4F4 a full two-mode b1g−b2g adiabatic potential energy surface is calculated showing explicitly the way of transformation from the unstable D4h geometry to the two equilibrium C2h configurations via the D2h saddle point. The PJTE origin of these structural features is confirmed also by estimates of the vibronic coupling parameters. For Si4R4 with large substituents the origin of their structure is revealed by analyzing the PJT interaction between the frontier molecular orbitals. The preferred chair-like structures of Si4R4 analogues with amido substituents, and heavier germanium-containing systems Ge4R4 (potential precursors for semiconducting materials) are predicted. PMID:26996445
Organ and effective dose coefficients for cranial and caudal irradiation geometries: photons.
Veinot, K G; Eckerman, K F; Hertel, N E
2016-02-01
With the introduction of new recommendations of the International Commission on Radiological Protection (ICRP) in Publication 103, the methodology for determining the protection quantity, effective dose, has been modified. The modifications include changes to the defined organs and tissues, the associated tissue weighting factors, radiation weighting factors and the introduction of reference sex-specific computational phantoms. Computations of equivalent doses in organs and tissues are now performed in both the male and female phantoms and the sex-averaged values used to determine the effective dose. Dose coefficients based on the ICRP 103 recommendations were reported in ICRP Publication 116, the revision of ICRP Publication 74 and ICRU Publication 57. The coefficients were determined for the following irradiation geometries: anterior-posterior (AP), posterior-anterior (PA), right and left lateral (RLAT and LLAT), rotational (ROT) and isotropic (ISO). In this work, the methodology of ICRP Publication 116 was used to compute dose coefficients for photon irradiation of the body with parallel beams directed upward from below the feet (caudal) and directed downward from above the head (cranial). These geometries may be encountered in the workplace from personnel standing on contaminated surfaces or volumes and from overhead sources. Calculations of organ and tissue kerma and absorbed doses for caudal and cranial exposures to photons ranging in energy from 10 keV to 10 GeV have been performed using the MCNP6.1 radiation transport code and the adult reference phantoms of ICRP Publication 110. As with calculations reported in ICRP 116, the effects of charged-particle transport are evident when compared with values obtained by using the kerma approximation. At lower energies the effective dose per particle fluence for cranial and caudal exposures is less than AP orientations while above ∼30 MeV the cranial and caudal values are greater. PMID:25935016
Geometry-Induced Memory Effects in Isolated Quantum Systems: Cold-Atom Applications
NASA Astrophysics Data System (ADS)
Lai, Chen-Yen; Chien, Chih-Chun
2016-03-01
Memory effects result from the history-dependent behavior of a system, are abundant in our daily life, and have broad applications. Here, we explore the possibilities of generating memory effects in simple isolated quantum systems. By utilizing geometrical effects from a class of lattices supporting flatbands consisting of localized states, memory effects could be observed in ultracold atoms in optical lattices. As the optical lattice continuously transforms from a triangular lattice into a kagome lattice with a flatband, history-dependent density distributions manifest quantum memory effects even in noninteracting systems, including fermionic as well as bosonic systems, in the proper ranges of temperatures. Rapid growth of ultracold technology predicts a bright future for quantum memory-effect systems, and here two prototypical applications of geometry-induced quantum memory effects are proposed: A cold-atom-based accelerometer using an atomic differentiator to record the mechanical change rate of a coupled probe, and an atomic quantum memory cell for storing information with write-in and readout schemes.
Distribution of air-water mixtures in parallel vertical channels as an effect of the header geometry
Marchitto, Annalisa; Fossa, Marco; Guglielmini, Giovanni
2009-07-15
Uneven phase distribution in heat exchangers is a cause of severe reductions in thermal performances of refrigeration equipment. To date, no general design rules are available to avoid phase separation in manifolds with several outlet channels, and even predicting the phase and mass distribution in parallel channels is a demanding task. In the present paper, measurements of two-phase air-water distributions are reported with reference to a horizontal header supplying 16 vertical upward channels. The effects of the operating conditions, the header geometry and the inlet port nozzle were investigated in the ranges of liquid and gas superficial velocities of 0.2-1.2 and 1.5-16.5 m/s, respectively. Among the fitting devices used, the insertion of a co-axial, multi-hole distributor inside the header confirmed the possibility of greatly improving the liquid and gas flow distribution by the proper selection of position, diameter and number of the flow openings between the supplying distributor and the system of parallel channels connected to the header. (author)
Effects of Viewing Geometry and Temperature on Spectral Reflectance of Planetary-analog Materials
NASA Astrophysics Data System (ADS)
Izenberg, N. R.; Hibbitts, C.; Klima, R. L.; Greenspon, A. S.; Marusiak, A. G.; Sprague, A. L.; Domingue, D. L.; Helbert, J.; Blewett, D. T.
2012-12-01
The MESSENGER spacecraft's Mercury Atmospheric and Surface Composition Spectrometer (MASCS) has obtained over 2 million spectra of Mercury's surface between 300 and 1450 nm. VIRS reflectance spectra have shown no unequivocal evidence of the crystal-field absorption band centered near 1000-nm wavelength associated with the presence of ferrous iron in silicates. The lack of this absorption, and presence of an oxygen-metal charge transfer (OMCT)-like band at 300-400 nm is consistent with low (< 2-4%), but variable Fe contents in surface minerals. Two key factors that may affect the relative breadth, depth, and band center of subtle bands in reflectance spectra measured by MESSENGER are the viewing geometry of MASCS observations and the high temperature of the dayside Mercury surface, which can exceed 400° C. MESSENGER orbital and pointing constraints restrict reflectance observations of Mercury to phase angles between 78° and 102°, with average incidence and emission angles between 39° and 51°, but ranging from near 0° to 90°. A pilot study at Brown University's Reflectance Laboratory (RELAB) and the optics laboratory of the Applied Physics Laboratory (APL) has measured a suite of low-Fe silicates at angles of incidence, emission, and phase, chosen to cover those of the MASCS measurements. The purpose is to provide direct photometric comparisons of known laboratory samples to Mercury observations. We present initial findings that indicate small (~4%) effects of viewing geometry on the 1000-nm band absorption and other spectral features. At APL, we are investigating thermal effects on spectral reflectance of rock-forming minerals from UV through NIR wavelengths under vacuum over a temperature range of -140 to 400°C. Different silicate absorption bands in the 1-4 micron range tend to widen and shallow by up to tens of percent, and shift band center slightly with increasing temperature. In addition, overall reflectance decreases with increasing temperatures
Learning Geometry through Dynamic Geometry Software
ERIC Educational Resources Information Center
Forsythe, Sue
2007-01-01
In this article, the author investigates effective teaching and learning of geometrical concepts using dynamic geometry software (DGS). Based from her students' reactions to her project, the author found that her students' understanding of the concepts was better than if they had learned geometry through paper-based tasks. However, mixing computer…
NASA Astrophysics Data System (ADS)
Lai, Chen-Yen; Chien, Chin-Chun
Memory effects have been of broad interest and particularly relevant in condensate matter systems where dynamical properties depend on history. Here we explore possibilities of observing memory effects in simple isolated quantum systems undergoing geometry transformations. By transforming into lattices supporting flat-bands consisting of localized states, memory effects could be observed in ultracold atoms in optical lattices due to different time scales of localized and mobile atoms. As an optical lattice is continuously transformed from a triangular lattice into a kagome or square lattice, the system reach a non-thermal quasi-steady state. In the absence of interactions and dissipations, the emergence of steady states are highly nontrivial and crucial in identifying memory effects unambiguously. Moreover, when the lattices transform from a triangular lattice into a kagome lattice with a flat band, history-dependent density distributions even in noninteracting systems can be observed in fermionic as well as bosonic systems. Rapid growth of cold atom technology and possibilities of various mechanisms for inducing memory effect promise interesting applications of novel quantum devices utilizing memory effect, especially in the thriving field of atomtronics. (arXiv:1510.08978)
Study of the Effects of Target Geometry on Synthetic Aperture Radar Images using Simulation Studies
NASA Astrophysics Data System (ADS)
Tummala, K.; Jha, A. K.; Kumar, S.
2014-11-01
Synthetic aperture radar technology has revolutionized earth observation with very high resolutions of below 5m, making it possible to distinguish individual urban features like buildings and even cars on the surface of the earth. But, the difficulty in interpretation of these images has hindered their use. The geometry of target objects and their orientation with respect to the SAR sensor contribute enormously to unexpected signatures on SAR images. Geometry of objects can cause single, double or multiple reflections which, in turn, affect the brightness value on the SAR images. Occlusions, shadow and layover effects are present in the SAR images as a result of orientation of target objects with respect to the incident microwaves. Simulation of SAR images is the best and easiest way to study and understand the anomalies. This paper discusses synthetic aperture radar image simulation, with the study of effect of target geometry as the main aim. Simulation algorithm has been developed in the time domain to provide greater modularity and to increase the ease of implementation. This algorithm takes into account the sensor and target characteristics, their locations with respect to the earth, 3-dimensional model of the target, sensor velocity, and SAR parameters. two methods have been discussed to obtain position and velocity vectors of SAR sensor - the first, from the metadata of real SAR image used to verify the simulation algorithm, and the second, from satellite orbital parameters. Using these inputs, the SAR image coordinates and backscatter coefficients for each point on the target are calculated. The backscatter coefficients at target points are calculated based on the local incidence angles using Muhleman's backscatter model. The present algorithm has been successfully implemented on radarsat-2 image of San Francisco bay area. Digital elevation models (DEMs) of the area under consideration are used as the 3d models of the target area. DEMs of different
Quantum geometry and stability of the fractional quantum Hall effect in the Hofstadter model
NASA Astrophysics Data System (ADS)
Bauer, David; Jackson, T. S.; Roy, Rahul
2016-06-01
We study how the stability of the fractional quantum Hall effect is influenced by the geometry of band structure in lattice Chern insulators. We consider the Hofstadter model, which converges to continuum Landau levels in the limit of small flux per plaquette. This gives us a degree of analytic control not possible in generic lattice models, and we are able to obtain analytic expressions for the relevant geometric criteria. These may be differentiated by whether they converge exponentially or polynomially to the continuum limit. We demonstrate that the latter criteria play a dominant role in predicting the physics of interacting particles in Hofstadter bands in this low flux density regime. In particular, we show that the many-body gap depends monotonically on a band-geometric criterion related to the trace of the Fubini-Study metric.
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.
Polarization effect in (e, 2e) reaction process for Ar (3s) in coplanar asymmetric geometry
NASA Astrophysics Data System (ADS)
Zhou, Li-Xia; Wang, Dian-Sheng; Yan, You-Guo; Wang, Cai-Ling
2014-11-01
The (e, 2e) triple differential cross sections (TDCSs) of Ar (3s) are calculated by using distorted-wave Born approximation under coplanar asymmetric geometry. The incident electron energy is 113.5 eV, and the scattering electron angle θ1 is -15°. The ejected electron energy is set at 10 eV, 7.5 eV, 5 eV, and 2 eV, respectively. The polarization effects have been discussed and the polarization potential Vpol changing from a second-order to a fourth-order term has been analyzed. Our calculated TDCSs have been compared with reported experimental and theoretical results, and the calculated TDCSs of polarization potential up to the fourth order could give a good fit with experimental results in the binary region, but fail to predict the correct recoil-to-binary ratio in most cases.
Hybrid RHF/MP2 Geometry Optimizations with the Effective Fragment Molecular Orbital Method
Christensen, Anders S.; Steinmann, Casper; Fedorov, Dmitri G.; Jensen, Jan H.
2014-01-01
The frozen domain effective fragment molecular orbital method is extended to allow for the treatment of a single fragment at the MP2 level of theory. The approach is applied to the conversion of chorismate to prephenate by Chorismate Mutase, where the substrate is treated at the MP2 level of theory while the rest of the system is treated at the RHF level. MP2 geometry optimization is found to lower the barrier by up to 3.5 kcal/mol compared to RHF optimzations and ONIOM energy refinement and leads to a smoother convergence with respect to the basis set for the reaction profile. For double zeta basis sets the increase in CPU time relative to RHF is roughly a factor of two. PMID:24558430
NASA Astrophysics Data System (ADS)
Wada, I.; Wang, K.; He, J.
2013-12-01
In this study, we revisit the effects of along-strike variation in slab geometry and oblique subduction on subduction zone thermal structures. Along-strike variations in slab dip cause changes in the descending rate of the slab and generate trench-parallel pressure gradients that drive trench-parallel mantle flow (e.g., Kneller and van Keken, 2007). Oblique subduction also drives trench-parallel mantle flow. In this study, we use a finite element code PGCtherm3D and examine a range of generic subduction geometries and parameters to investigate the effects of the above two factors. This exercise is part of foundational work towards developing detailed 3-D thermal models for NE Japan, Nankai, and Cascadia to better constrain their 3-D thermal structures and to understand the role of temperature in controlling metamorphic, seismogenic, and volcanic processes. The 3-D geometry of the subducting slabs in the forearc and arc regions are well delineated at these three subduction zones. Further, relatively large compilations of surface heat flow data at these subduction zones make them excellent candidates for this study. At NE Japan, a megathrust earthquake occurred on March 11, 2011; at Nankai and Cascadia, there has been a great effort to constrain the scale of the next subduction thrust earthquake for the purpose of disaster prevention. Temperature influences the slip behavior of subduction faults by (1) affecting the rheology of the interface material and (2) controlling dehydration reactions, which can lead to elevated pore fluid pressure. Beyond the depths of subduction thrust earthquakes, the thermal structure is affected strongly by the pattern of mantle wedge flow. This flow is driven by viscous coupling between the subducting slab and the overriding mantle, and it brings in hot flowing mantle into the wedge. The trench-ward (up-dip) extent of the slab-mantle coupling is thus a key factor that controls the thermal structure. Slab-mantle decoupling at shallow
Welding polarity effects on weld spatters and bead geometry of hyperbaric dry GMAW
NASA Astrophysics Data System (ADS)
Xue, Long; Wu, Jinming; Huang, Junfen; Huang, Jiqiang; Zou, Yong; Liu, Jian
2016-03-01
Welding polarity has influence on welding stability to some extent, but the specific relationship between welding polarity and weld quality has not been found, especially under the hyperbaric environment. Based on a hyperbaric dry welding experiment system, gas metal arc welding(GMAW) experiments with direct current electrode positive(DCEP) and direct current electrode negative(DCEN) operations are carried out under the ambient pressures of 0.1 MPa, 0.4 MPa, 0.7 MPa and 1.0 MPa to find the influence rule of different welding polarities on welding spatters and weld bead geometry. The effects of welding polarities on the weld bead geometry such as the reinforcement, the weld width and the penetration are discussed. The experimental results show that the welding spatters gradually grow in quantity and size for GMAW with DCEP, while GMAW with DCEN can produce fewer spatters comparatively with the increase of the ambient pressure. Compared with DCEP, the welding current and arc voltage waveforms for DCEN is more stable and the distribution of welding current probability density for DCEN is more concentrated under the hyperbaric environment. When the ambient pressure is increased from 0.1 MPa to 1.0 MPa, the effects of welding polarities on the reinforcement, the weld width and the penetration are as follows: an increase of 0.8 mm for the weld reinforcement is produced by GMAW with DCEN and 1.3 mm by GMAW with DCEP, a decrease of 7.2 mm for the weld width is produced by DCEN and 6.1 mm by DCEP; and an increase of 3.9 mm for the penetration is produced by DCEN and 1.9 mm by DCEP. The proposed research indicates that the desirable stability in the welding procedure can be achieved by GMAW with DCEN operation under the hyperbaric environment.
Piston-Liner Crevice Geometry Effect on HCCI Combustion by Multi-Zone Analysis
Aceves, S M; Flowers, D L; Espinosa-Loza, F; Martinez-Frias, J; Dibble, R W; Christensen, M; Johansson, B; Hessel, R P
2002-09-04
A multi-zone model has been developed that accurately predicts HCCI combustion and emissions. The multizone methodology is based on the observation that turbulence does not play a direct role on HCCI combustion. Instead, chemical kinetics dominates the process, with hotter zones reacting first, and then colder zones reacting in rapid succession. Here, the multi-zone model has been applied to analyze the effect of piston crevice geometry on HCCI combustion and emissions. Three different pistons of varying crevice size were analyzed. Crevice sizes were 0.26, 1.3 and 2.1 mm, while a constant compression ratio was maintained (17:1). The results show that the multi-zone model can predict pressure traces and heat release rates with good accuracy. Combustion efficiency is also predicted with good accuracy for all cases, with a maximum difference of 5% between experimental and numerical results. Carbon monoxide emissions are underpredicted, but the results are better than those obtained in previous publications. The improvement is attributed to the use of a 40-zone model, while previous publications used a 10-zone model. Hydrocarbon emissions are well predicted. For cylinders with wide crevices (1.3 and 2.1 mm), HC emissions do not decrease monotonically as the relative air/fuel ratio ({lambda}) increases. Instead, maximum HC emissions are obtained for an intermediate value of {lambda}. The model predicts this relative air/fuel ratio for maximum HC emissions with very good accuracy. The results show that the multi-zone model can successfully predict the effect of crevice geometry on HCCI combustion, and therefore it has applicability to the design of HCCI engines with optimum characteristics for high efficiency, low emissions and low peak cylinder pressure.
NASA Astrophysics Data System (ADS)
Wang, Xiao-feng; Guo, Ming-xing; Cao, Ling-yong; Wang, Fei; Zhang, Ji-shan; Zhuang, Lin-zhong
2015-07-01
The effect of rolling geometry on mechanical properties, microstructure, and recrystallization texture of Al-Mg-Si alloys was studied by means of tensile tests, microstructural observations, and electron backscatter diffraction measurements. The results reveal that the elongation and the average plasticity strain ratio ( r) values of the T4P (pre-aging plus natural aging)-treated alloy sheet with a rolling geometry value between 1 and 3 are somewhat higher than those of the T4P-treated sheet with a rolling geometry value between 3 and 6. The deformation and recrystallization microstructures of the sheet with a rolling geometry value between 1 and 3 are more uniform than those of the sheet with a rolling geometry value between 3 and 6. The former also possesses somewhat higher surface quality. H {001}<110> and Goss {110}<001> orientations are the main recrystallization texture components for the former case, whereas the latter case only includes H{001}<110> orientation. Texture gradients are present in the two alloy sheets. Shear texture component F on the surface of the sheet with a rolling geometry value between 3 and 6 and its higher texture gradients have revealed that non-uniform deformation occurred during cold rolling. The effects of texture on the yield strength and r value were also discussed.
Surface Geometry and Stomatal Conductance Effects on Evaporation From Aquatic Macrophytes
NASA Astrophysics Data System (ADS)
Anderson, Michael G.; Idso, Sherwood B.
1987-06-01
Evaporative water loss rates of several floating and emergent aquatic macrophytes were studied over a 4-year period through comparison of daily evaporative water losses from similar-sized vegetated (E) and open water (E0) surfaces. Two species with planate floating leaves (water fern and water lily) yielded E/E0 values of 0.90 for one and four growing seasons, respectively, and displayed stomatal regulation of potential evaporation. Water hyacinths grown in ponds with different diameters exhibited E/E0 ratios which decreased with increasing pond diameter for both short (0.06-0.36 m) and tall (0.63-0.81 m) plants, producing high linear correlations with amount of peripheral vegetative surface area. The latter relationships suggested an E/E0 value less than unity for a relatively extensive canopy of short water hyacinths and a value of the order of 1.4 for a tall canopy possessing similar two-dimensional surface area characteristics. The latter results were also demonstrated in a separate study utilizing polyurethane foam to insulate the peripheral exposure of tall water hyacinth canopies from advective energy. Finally, simultaneous stomatal conductance and daily E/E0 measurements on cattail and water hyacinth canopies with identical tank diameters indicated that although the mean stomatal conductance of the peripheral exposure of the cattail canopy was 72% less than that of the water hyacinth canopy, its total evaporative water loss was nearly equivalent, due to its greater height. Reducing the surface area of the peripheral cattail exposure by the fractional amount suggested by the stomatal conductance measurements harmonized its surface geometry-evaporation relationship with that of the water hyacinth canopy and once again demonstrated the reality of stomatal control of potential evaporation.
Cooper, Robert F.; Sulai, Yusufu N.; Dubis, Adam M.; Chui, Toco Y.; Rosen, Richard B.; Michaelides, Michel; Dubra, Alfredo; Carroll, Joseph
2016-01-01
Purpose To characterize the effects of intraframe distortion due to involuntary eye motion on measures of cone mosaic geometry derived from adaptive optics scanning light ophthalmoscope (AOSLO) images. Methods We acquired AOSLO image sequences from 20 subjects at 1.0, 2.0, and 5.0° temporal from fixation. An expert grader manually selected 10 minimally distorted reference frames from each 150-frame sequence for subsequent registration. Cone mosaic geometry was measured in all registered images (n = 600) using multiple metrics, and the repeatability of these metrics was used to assess the impact of the distortions from each reference frame. In nine additional subjects, we compared AOSLO-derived measurements to those from adaptive optics (AO)-fundus images, which do not contain system-imposed intraframe distortions. Results We observed substantial variation across subjects in the repeatability of density (1.2%–8.7%), inter-cell distance (0.8%–4.6%), percentage of six-sided Voronoi cells (0.8%–10.6%), and Voronoi cell area regularity (VCAR) (1.2%–13.2%). The average of all metrics extracted from AOSLO images (with the exception of VCAR) was not significantly different than those derived from AO-fundus images, though there was variability between individual images. Conclusions Our data demonstrate that the intraframe distortion found in AOSLO images can affect the accuracy and repeatability of cone mosaic metrics. It may be possible to use multiple images from the same retinal area to approximate a “distortionless” image, though more work is needed to evaluate the feasibility of this approach. Translational Relevance Even in subjects with good fixation, images from AOSLOs contain intraframe distortions due to eye motion during scanning. The existence of these artifacts emphasizes the need for caution when interpreting results derived from scanning instruments. PMID:26933523
THE EFFECTS OF APONEUROSIS GEOMETRY ON STRAIN INJURY SUSCEPTIBILITY EXPLORED WITH A 3D MUSCLE MODEL
Rehorn, Michael R.; Blemker, Silvia S.
2010-01-01
In the musculoskeletal system, some muscles are injured more frequently than others. For example, the biceps femoris longhead (BFLH) is the most commonly injured hamstring muscle. It is thought that acute injuries result from large strains within the muscle tissue, but the mechanism behind this type of strain injury is still poorly understood. The purpose of this study was to build computational models to analyze the stretch distributions within the BFLH muscle and to explore the effects of aponeurosis geometry on the magnitude and location of peak stretches within the model. We created a three-dimensional finite element (FE) model of the BFLH based on magnetic resonance (MR) images. We also created a series of simplified models with a similar geometry to the MR-based model. We analyzed the stretches predicted by the MR-based model during lengthening contractions to determine the region of peak local fiber stretch. The peak along-fiber stretch was 1.64 and was located adjacent to the proximal myotendinous junction (MTJ). In contrast, the average along-fiber stretch across all the muscle tissue was 0.95. By analyzing the simple models, we found that varying the dimensions of the aponeuroses (width, length, and thickness) had a substantial impact on the location and magnitude of peak stretches within the muscle. Specifically, the difference in widths between the proximal and distal aponeurosis in the BFLH contributed most to the location and magnitude of peak stretch, as decreasing the proximal aponeurosis width by 80% increased peak average stretches along the proximal MTJ by greater than 60% while slightly decreasing stretches along the distal MTJ. These results suggest that the aponeurosis morphology of the BFLH plays a significant role in determining stretch distributions throughout the muscle. Furthermore, this study introduces the new hypothesis that aponeurosis widths may be important in determining muscle injury susceptibility. PMID:20541207
NASA Astrophysics Data System (ADS)
Yang, Yi; Mielczarek, Kamil; Zakhidov, Anvar; Hu, Walter
2013-03-01
Among the various organic photovoltaic devices, the conjugated polymer/fullerene approach has drawn the most research interest. The performance of these types of solar cells is greatly determined by the nanoscale morphology of the two components (donor/acceptor) and the molecular orientation/crystallinity in the photoactive layer. This article demonstrates our recent studies on the nanostructure geometry effects on the nanoimprint induced poly(3 hexylthiophene-2,5-diyl) (P3HT) chain alignment and photovoltaic performance. Out-of-plane and in-plane grazing incident X-ray diffractions are employed to characterize the chain orientations in P3HT nanogratings with different widths and heights. It is found that nanoimprint procedure changes the initial edge-on alignment in non-imprinted P3HT thin film to a vertical orientation which favors the hole transport, with an organization height H≥ 170 nm and width in the range of 60 nm<= W< 210 nm. Samples with better aligned molecules lead to a larger crystallite sizes as well. Imprinted P3HT/[6,6]-penyl-C61-butyric-acid-methyl-ester (PCBM) solar cells show an increase in power conversion efficiency (PCE) with the decrease of nanostructure width, and with the increase of height and junction area. Devices with the highest PCE are made by the fully aligned and highest P3HT nanostructures (width w= 60 nm, height h= 170 nm), allowing for the most efficient charge separation, transport and light absorption. We believe this work will contribute to the optimal geometry design of nanoimprinted polymer solar cells.
Effect of Subsonic Inlet Lip Geometry on Predicted Surface and Flow Mach Number Distributions
NASA Technical Reports Server (NTRS)
Albers, J. A.; Miller, B. A.
1973-01-01
The effect of subsonic inlet lip geometry on predicted surface and flow Mach number distributions is illustrated. The theoretical results were obtained from incompressible potential flow calculations corrected for compressibility. The major emphasis of this investigation is on the low-speed (takeoff and landing) operating conditions. The low-speed results were obtained for a range of three geometric variables of interest: contraction ratio, defined as the ratio of highlight area to throat area; internal lip major - to minor-axis ratio; and internal lip shape. The low-speed results were obtained at both static conditions and a free-stream velocity of 42.6m/sec, with incidence angles ranging from 0 deg to 50 deg. The results indicate that of the three geometric variables considered, contraction ratio had the largest effect on the surface Mach number distributions. The effects of inlet diameter ratio and blunting of the external forebody on maximum external surface Mach numbers are illustrated at a cruise Mach number of 0.8.
Effect of AFM probe geometry on visco-hyperelastic characterization of soft materials.
Boccaccio, Antonio; Lamberti, Luciano; Papi, Massimiliano; De Spirito, Marco; Pappalettere, Carmine
2015-08-14
Atomic force microscopy (AFM) nanoindentation is very suited for nano- and microscale mechanical characterization of soft materials. Although the structural response of polymeric networks that form soft matter depends on viscous effects caused by the relative slippage of polymeric chains, the usual assumption made in the AFM-based characterization is that the specimen behaves as a purely elastic material and viscous forces are negligible. However, for each geometric configuration of the AFM tip, there will be a limit indentation rate above which viscous effects must be taken into account to correctly determine mechanical properties. A parametric finite element study conducted on 12 geometric configurations of a blunt cone AFM tip (overall, the study included about 200 finite element analyses) allowed us to determine the limit indentation rate for each configuration. The selected tip dimensions cover commercially available products and account for changes in tip geometry caused by serial measurements. Nanoindentation rates cover typical experimental conditions set in AFM bio-measurements on soft matter. Viscous effects appear to be more significant in the case of sharper tips. This implies that, if quantitative data on sample viscosity are not available, using a rounded indenter and carrying out experiments below the limit indentation rate will allow errors in the determination of mechanical properties to be minimized. PMID:26201503
Lee, Myeong H; Geva, Eitan; Dunietz, Barry D
2016-05-19
The dependence of charge-transfer states on interfacial geometry at the phthalocyanine/fullerene organic photovoltaic system is investigated. The effect of deviations from the equilibrium geometry of the donor-donor-acceptor trimer on the energies of and electronic coupling between different types of interfacial electronic excited states is calculated from first-principles. Deviations from the equilibrium geometry are found to destabilize the donor-to-donor charge transfer states and to weaken their coupling to the photoexcited donor-localized states, thereby reducing their ability to serve as charge traps. At the same time, we find that the energies of donor-to-acceptor charge transfer states and their coupling to the donor-localized photoexcited states are either less sensitive to the interfacial geometry or become more favorable due to modifications relative to the equilibrium geometry, thereby enhancing their ability to serve as gateway states for charge separation. Through these findings, we eludicate how interfacial geometry modifications can play a key role in achieving charge separation in this widely studied organic photovoltaic system. PMID:26237431
On the Effects of Modeling As-Manufactured Geometry: Toward Digital Twin
NASA Technical Reports Server (NTRS)
Cerrone, Albert; Hochhalter, Jacob; Heber, Gerd; Ingraffea, Anthony
2014-01-01
Asimple, nonstandardized material test specimen,which fails along one of two different likely crack paths, is considered herein.The result of deviations in geometry on the order of tenths of amillimeter, this ambiguity in crack pathmotivates the consideration of asmanufactured component geometry in the design, assessment, and certification of structural systems.Herein, finite elementmodels of as-manufactured specimens are generated and subsequently analyzed to resolve the crack-path ambiguity. The consequence and benefit of such a "personalized" methodology is the prediction of a crack path for each specimen based on its as-manufactured geometry, rather than a distribution of possible specimen geometries or nominal geometry.The consideration of as-manufactured characteristics is central to the Digital Twin concept. Therefore, this work is also intended to motivate its development.
Whelan, C.T.; Allan, R.J.; Rasch, J.; Walters, H.R.J.; Zhang, X.; Roeder, J.; Jung, K.; Ehrhardt, H. Daresbury Laboratory, Warrington WA4 4AD Department of Applied Mathematics and Theoretical Physics, The Queen's University of Belfast, BT7 1NN Belfast, Northern Ireland Fachbereich Physik, Universitaet Kaiserslautern, Erwin Schroedinger Strasse, D6750, Kaiserslautern )
1994-11-01
The role of postcollisional and polarization-correlation effects in energy-sharing ([ital e],2[ital e]) collisions is considered. Theoretical and experimental results are presented for the ionization of hydrogen in a symmetric coplanar geometry. A kinematical regime is identified where the triple-differential cross section is sensitive to three-body effects in both the incident and final channels.
NASA Astrophysics Data System (ADS)
Sunil Kumar, S.; Ratna Raju, L.; Nandi, T. K.
2015-12-01
The performance of high effectiveness (high NTU) perforated plate matrix heat exchangers (MHEs) is dependent on the geometry of the flow channels, as well as the longitudinal heat conduction through the outer walls. The effect of the above factors on the performance of MHEs is investigated in this paper numerically. The results obtained with the present model are validated with our own experimental results as well as those in the literature. The results show a strong influence of longitudinal heat conduction through the outer wall on the performance of MHEs. A parametric study has been carried out to arrive at the optimum flow channel geometry under given operating conditions.
Unravelling the geometry of data matrices: effects of water stress regimes on winemaking.
Fushing, Hsieh; Hsueh, Chih-Hsin; Heitkamp, Constantin; Matthews, Mark A; Koehl, Patrice
2015-10-01
A new method is proposed for unravelling the patterns between a set of experiments and the features that characterize those experiments. The aims are to extract these patterns in the form of a coupling between the rows and columns of the corresponding data matrix and to use this geometry as a support for model testing. These aims are reached through two key steps, namely application of an iterative geometric approach to couple the metric spaces associated with the rows and columns, and use of statistical physics to generate matrices that mimic the original data while maintaining their inherent structure, thereby providing the basis for hypothesis testing and statistical inference. The power of this new method is illustrated on the study of the impact of water stress conditions on the attributes of 'Cabernet Sauvignon' Grapes, Juice, Wine and Bottled Wine from two vintages. The first step, named data mechanics, de-convolutes the intrinsic effects of grape berries and wine attributes due to the experimental irrigation conditions from the extrinsic effects of the environment. The second step provides an analysis of the associations of some attributes of the bottled wine with characteristics of either the matured grape berries or the resulting juice, thereby identifying statistically significant associations between the juice pH, yeast assimilable nitrogen, and sugar content and the bottled wine alcohol level. PMID:26468072
Effect of leading-edge geometry on boundary-layer receptivity to freestream sound
NASA Technical Reports Server (NTRS)
Lin, Nay; Reed, Helen L.; Saric, W. S.
1991-01-01
The receptivity to freestream sound of the laminar boundary layer over a semi-infinite flat plate with an elliptic leading edge is simulated numerically. The incompressible flow past the flat plate is computed by solving the full Navier-Stokes equations in general curvilinear coordinates. A finite-difference method which is second-order accurate in space and time is used. Spatial and temporal developments of the Tollmien-Schlichting wave in the boundary layer, due to small-amplitude time-harmonic oscillations of the freestream velocity that closely simulate a sound wave travelling parallel to the plate, are observed. The effect of leading-edge curvature is studied by varying the aspect ratio of the ellipse. The boundary layer over the flat plate with a sharper leading edge is found to be less receptive. The relative contribution of the discontinuity in curvature at the ellipse-flat-plate juncture to receptivity is investigated by smoothing the juncture with a polynomial. Continuous curvature leads to less receptivity. A new geometry of the leading edge, a modified super ellipse, which provides continuous curvature at the juncture with the flat plate, is used to study the effect of continuous curvature and inherent pressure gradient on receptivity.
Effects of 3D geometries on cellular gradient sensing and polarization
NASA Astrophysics Data System (ADS)
Spill, Fabian; Andasari, Vivi; Mak, Michael; Kamm, Roger D.; Zaman, Muhammad H.
2016-06-01
During cell migration, cells become polarized, change their shape, and move in response to various internal and external cues. Cell polarization is defined through the spatio-temporal organization of molecules such as PI3K or small GTPases, and is determined by intracellular signaling networks. It results in directional forces through actin polymerization and myosin contractions. Many existing mathematical models of cell polarization are formulated in terms of reaction–diffusion systems of interacting molecules, and are often defined in one or two spatial dimensions. In this paper, we introduce a 3D reaction–diffusion model of interacting molecules in a single cell, and find that cell geometry has an important role affecting the capability of a cell to polarize, or change polarization when an external signal changes direction. Our results suggest a geometrical argument why more roundish cells can repolarize more effectively than cells which are elongated along the direction of the original stimulus, and thus enable roundish cells to turn faster, as has been observed in experiments. On the other hand, elongated cells preferentially polarize along their main axis even when a gradient stimulus appears from another direction. Furthermore, our 3D model can accurately capture the effect of binding and unbinding of important regulators of cell polarization to and from the cell membrane. This spatial separation of membrane and cytosol, not possible to capture in 1D or 2D models, leads to marked differences of our model from comparable lower-dimensional models.
NASA Astrophysics Data System (ADS)
Valenza, Antonino; Borsellino, Chiara; Calabrese, Luigi; di Bella, Guido
2006-07-01
Composite materials are widely employed in sailing sports, a possible application is for the mast pole or other sail poles. In the paper the attention is focused on the spinnaker poles mechanical performances; in particular the focus is on axial and ring compressive properties of three different carbon fibre/epoxy resin spinnaker poles, to investigate both the diameter and stacking sequence effect on the mechanical performance of the structure. Starting from the stacking sequence used in the production of a particular spinnaker pole, the effect of a lamina at 0° in the middle of wall thickness is investigated with the purpose to obtain a more stiff structure. Moreover to test the proposed stacking sequence on different size products, a prototype with lower diameter is realized. To properly evaluate axial and ring stiffness, axial compression test and ring stiffness one are performed. Then a numerical model is developed to support the design of the finished product: A simple and versatile numerical analysis (FEA with software ANSYS), by simulating ring stiffness and pull-direction compression tests, is carried out in elastic regime. Such model should be suitable for designing and/or verifying the mechanical performance of pole structures, even though differing from those above described, for materials, geometry and stacking sequence.
Effect of pore's geometry on the electroosmotic flow and nanoparticle dynamics in the nanopore
NASA Astrophysics Data System (ADS)
Hulings, Zachery; Melnikov, Dmitriy; Gracheva, Maria
We theoretically study how the electroosmotic fluid velocity in a charged cylindrical nanopore in a solid state membranes depends on the pore's geometry, electrolyte concentration, and applied electrolyte bias. We find that in long pores, the fluid velocity follows the classical von Smoluchowski result for an infinite pore with a maximum along the pore axis. However, when the pore's length is comparable to its diameter, the velocity profile develops a local minimum along the pore axis with a maximum value near the membrane walls. The minimum becomes more pronounced when the electrolyte concentration and/or applied bias become larger. We attribute this effect to the inhomogeneous electric field distribution in the nanopore with the field along the axis of the pore being smaller than along the pore's walls due to the effects of access resistance on each side of the channel. We also investigate repercussions of such a velocity profile on the transport of a nanoparticle through the nanopore. NSF DMR and CBET Grant No. 1352218.
Theoretical investigation of ionic effects in actuation and sensing of IPMCs of various geometries
NASA Astrophysics Data System (ADS)
Stalbaum, Tyler; Nelson, Shelby E.; Palmre, Viljar; Kim, Kwang J.
2015-04-01
Ionic polymer-metal composite (IPMC) electromechanical and mechanoelectrical phenomena for rectangular and tube-shaped IPMC devices have been examined through simulation and experimental investigation. There is a specific focus on investigating the anion and cation effects in actuation versus sensing. Simulations were performed using COMSOL Multiphysics 4.3b. Sample IPMCs were fabricated in lab in the desired geometries by techniques described herein. The sample sizes were roughly 1 mm thick and 20-25 mm in length. Actuation and sensor experiments were performed with the samples and compared to simulation results, which exhibit good agreement for voltage and tip displacement measurements. Fundamental differences in the electromechanical and mechanoelectrical transductions of IPMCs are highlighted in the simulation results. These results display the negligible effect of anion motion in actuation as compared to during sensing. In actuation, the cation motion is dominated by an electric potential flux, and the anions move only slightly in accordance with the deformed polymer membrane. In sensing, the electric potential is induced by the ionic migration in the polymer, and both cation and anion concentration variations are of similar magnitudes.
NASA Technical Reports Server (NTRS)
Brandon, J. M.; Nguyen, L. T.
1986-01-01
A series of low speed wind tunnel tests on a generic fighter model with a cylindrical fuselage were made to investigate the effects of forebody shape on static and dynamic lateral/directional stability. Five forebodies, including a chine nose of unconventional cross-sectional shape, were tested. Conventional force tests were conducted to determine static stability characteristics and single degree-of-freedom free-to-roll tests were used to study the wing rock susceptibility of the model with the various forebodies. Flow visualization data were obtained to aid in analysis of the complex flow phenomena involved. The results show that forebody cross-sectional shape can strongly effect both static and dynamic (roll) stability at high angles of attack. Large variations in stability were obtained for the various forebody geometries. These characteristics result from the impact of cross-sectional shape on forebody vortex development, the behavior of the vortices at sideslip conditions, and their interaction with the wing and empennage flow fields.
Geometry effects on cooling in a standing wave cylindrical thermoacousic resonator
NASA Astrophysics Data System (ADS)
Mohd-Ghazali, Normah; Ghazali, Ahmad Dairobi; Ali, Irwan Shah; Rahman, Muhammad Aminullah A.
2012-06-01
Numerous reports have established the refrigeration applications of thermoacoustic cooling without compressors and refrigerants. Significant cooling effects can be obtained in a thermoacoustic resonator fitted with a heat exchanging stack and operated at resonance frequency. Past studies, however, have hardly referred to the fundamental relationship between resonant frequency and the resonator geometry. This paper reports the thermoacoustic cooling effects at resonance obtained by changing the diameter of the resonator while holding the length constant and vice versa. Experiments were completed at atmospheric pressure with air as the working fluid using a number of pvc tubes having parallel plate stack from Mylar. The temperature difference measured across the stack showed that a volume increase in the working fluid in general increases the temperature gradient for the quarter-and half-wavelength resonators. Doubling the diameter from 30 mm to 60 mm produced the highest temperature difference due to the greater number of stack plates resulting in a higher overall thermoacaoustic cooling. Increasing the resonator length only produced a small increase in temperature gradient since the resonant frequency at operation is only slightly changed. Investigation on the aspect ratio exhibits no influence on the temperature difference across the stack. This study have shown that the resonator length and diameter do affect the temperature difference across the thermoacoustic stack, and further research should be done to consider the contribution of the stack mass on the overall desired thermoacoustic cooling.
NASA Astrophysics Data System (ADS)
Chheda, T. D.; Nevitt, J. M.; Pollard, D. D.
2014-12-01
The formation of monoclinal right-lateral kink bands in Lake Edison granodiorite (central Sierra Nevada, CA) is investigated through field observations and mechanics based numerical modeling. Vertical faults act as weak surfaces within the granodiorite, and vertical granodiorite slabs bounded by closely-spaced faults curve into a kink. Leucocratic dikes are observed in association with kinking. Measurements were made on maps of Hilgard, Waterfall, Trail Fork, Kip Camp (Pollard and Segall, 1983b) and Bear Creek kink bands (Martel, 1998). Outcrop scale geometric parameters such as fault length andspacing, kink angle, and dike width are used to construct a representative geometry to be used in a finite element model. Three orders of fault were classified, length = 1.8, 7.2 and 28.8 m, and spacing = 0.3, 1.2 and 3.6 m, respectively. The model faults are oriented at 25° to the direction of shortening (horizontal most compressive stress), consistent with measurements of wing crack orientations in the field area. The model also includes a vertical leucocratic dike, oriented perpendicular to the faults and with material properties consistent with aplite. Curvature of the deformed faults across the kink band was used to compare the effects of material properties, strain, and fault and dike geometry. Model results indicate that the presence of the dike, which provides a mechanical heterogeneity, is critical to kinking in these rocks. Keeping properties of the model granodiorite constant, curvature increased with decrease in yield strength and Young's modulus of the dike. Curvature increased significantly as yield strength decreased from 95 to 90 MPa, and below this threshold value, limb rotation for the kink band was restricted to the dike. Changing Poisson's ratio had no significant effect. The addition of small faults between bounding faults, decreasing fault spacing or increasing dike width increases the curvature. Increasing friction along the faults decreases slip, so
Karimkhani, Chante; Dellavalle, Robert P
2015-01-01
This commentary explores the fundamentals of network theory, a branch of applied mathematics that has numerous applications in many fields. Maruani et al. (2014) used network theory to analyze the geometry of the evidence base for dermatologic treatments. This is a prime example of the innovative nature of network theory: the mapping of a complex system into an abstract geometry for easier analysis. The interpretation rests upon the two concepts of diversity and co-occurrence. The mathematical foundation of these concepts is briefly reviewed. In addition, examples of the application of network geometry in other dermatologic settings as well as in science and technology are presented. PMID:25501378
Investigation of flaw geometry and loading effects on plane strain fracture in metallic structures
NASA Technical Reports Server (NTRS)
Hall, L. R.; Finger, R. W.
1971-01-01
The effects on fracture and flaw growth of weld-induced residual stresses, combined bending and tension stresses, and stress fields adjacent to circular holes in 2219-T87 aluminum and 5AI-2.5Sn(ELI) titanium alloys were evaluated. Static fracture tests were conducted in liquid nitrogen; fatigue tests were performed in room air, liquid nitrogen, and liquid hydrogen. Evaluation of results was based on linear elastic fracture mechanics concepts and was directed to improving existing methods of estimating minimum fracture strength and fatigue lives for pressurized structure in spacecraft and booster systems. Effects of specimen design in plane-strain fracture toughness testing were investigated. Four different specimen types were tested in room air, liquid nitrogen and liquid hydrogen environments using the aluminum and titanium alloys. Interferometry and holograph were used to measure crack-opening displacements in surface-flawed plexiglass test specimens. Comparisons were made between stress intensities calculated using displacement measurements, and approximate analytical solutions.
ERIC Educational Resources Information Center
Stallings, William M.
It was hypothesized that instruction in descriptive geometry produces an increase in SRT scores. The resultant data do not firmly support this hypothesis. It is suggested that this study be replicated with the use of randomly selected control groups. (MS)
Effects of branched defect geometry on the propagation of Rayleigh waves
NASA Astrophysics Data System (ADS)
Hernandez-Valle, F.; Clough, A. R.; Dutton, B.; Edwards, R. S.
2014-02-01
Rayleigh waves can be used for characterisation of surface-breaking defects, giving a measure of the depth and the angle of propagation of a defect with simple (i.e. single crack) geometry. However, surface breaking defects will often grow with a more complicated geometry. We present here results of experimental measurements using laser generated and detected Rayleigh waves on aluminium samples containing machined slots with varied branched geometries. The signal enhancement found in the near-field, and the reflection and transmission of different wavemodes can be used to position the defect and gain an idea of its geometry. This research can be applied to monitor components prone to developing stress corrosion cracking (branched-like defects). Results are shown of the near-field interactions of Rayleigh waves with this type of cracking in stainless steel pipe samples, in order to resolve the spatial extent and geometric alignment of those defects.
NASA Technical Reports Server (NTRS)
Gordon, Stephen S.
1992-01-01
A mathematical theory was evaluated empirically. This theory predicts weld ultimate tensile strength based on material properties and fusion line angles, mismatch, peaking, and weld widths. Welds were made on 1/4 and 1/2 in. aluminum 2219-T87, their geometries were measured, they were tensile tested, and these results were compared to theoretical predictions. Statistical analysis of results was performed to evaluate correlation of theory to results for many different categories of weld geometries.
NASA Astrophysics Data System (ADS)
Hallock, Ashley Kristin
The effect of inductive coil geometry on the operating characteristics of a pulsed inductive plasma thruster is investigated analytically and experimentally. Coil inductance is measured as a function of the position of a simulated current sheet and modeled using finite element analysis to develop a two-dimensional semi-empirical inductance relation that is used to expand a circuit-based acceleration model from one to two dimensions. The model includes electromagnetic and gas-dynamic forces but excludes any process to translate radial plasma motion into axial motion. Furthermore a magnetically-impermeable current sheet encompassing all the propellant for a pulse is assumed to form immediately at the start of the pulse and at the surface of the inductive coil. The two-dimensional acceleration model is nondimensionalized, yielding a set of dimensionless performance scaling parameters. Model results indicate that the introduction of radial current sheet motion caused by a conical inductive coil geometry (versus a flat circular plate) increases the axial dynamic impedance parameter at which thrust efficiency is maximized and generally decreases the overall achievable thrust efficiency. Operational characteristics of two thrusters with inductive coils of different cone angles are explored through thrust stand measurements and time-integrated, unfiltered photography. Trends in impulse bit measurements indicate that, in the present configuration, the thruster with the inductive coil possessing a smaller cone angle produced larger values of thrust, in apparent contradiction to results of the model. Areas of increased light intensity in photographs of thruster operation are assumed to qualitatively represent locations of increased current density. Light intensity is generally greater in images of the thruster with the smaller cone angle when compared to those of the thruster with the larger half cone angle for the same operating conditions, and generally decreases in both
Effects of soil settlement and deformed geometry on a historical structure
NASA Astrophysics Data System (ADS)
Yardim, Y.; Mustafaraj, E.
2015-05-01
Protecting the historical character of a valued structure during the assessment and damage repair process is a very challenging task for many engineers. Heritage protection is complicated by a lack of design details and restrictions on sample extraction needed to obtain accurate material properties and limited studies on the restoration of certain types of historical structures. This study aims to assess the effects of soil settlement on a structure's stress concentrations and the value of laser scanning techniques on structure analysis in obtaining correct data of settlement vs. deformation. Terrestrial laser scanner (TLS) data are used to analyse the 500-year-old historical structure of Naziresha's Mosque. The obtained TLS data allow an accurate definition of the imperfect geometry patterns lying on every side of the structure. The soil profile and general crack formation together with TLS measurement proves that the structure deformed toward the south facade, where a railway and motorway are also located. Stress concentration and mode period results have a considerable difference, which highlights earthquake vulnerability and failure mechanisms and changes the strategy of possible retrofitting.
Effects of soil settlement and deformed geometry on a historical structure
NASA Astrophysics Data System (ADS)
Yardım, Y.; Mustafaraj, E.
2013-10-01
Protecting the historic character of a valued structure during the assessment and damage repair process is a very challenging task for many engineers. Heritage protection is complicated by a lack of design details and restrictions on sample extraction needed to obtain accurate material properties and limited studies on the restoration of certain types of historical structures. This study aims to assess the effects of soil settlement on a structure's stress concentrations and the value of laser scanning techniques on structure analysis in obtaining correct data of settlement vs. deformation. Terrestrial laser scanner (TLS) data are used to analyse the 500 yr-old historical structure of Naziresha's Mosque. The obtained TLS data allow an accurate definition of the imperfect geometry patterns lying on every side of the structure. The soil profile and general crack formation together with TLS measurement proves that the structure deformed toward the south façade, where a railway and motorway are also located. Stress concentration and mode period results have a considerable difference, which highlights earthquake vulnerability and failure mechanisms and changes the strategy of possible retrofitting.
Holt, Amanda L.; Sweeney, Alison M.; Johnsen, Sönke; Morse, Daniel E.
2011-01-01
Cephalopods possess a sophisticated array of mechanisms to achieve camouflage in dynamic underwater environments. While active mechanisms such as chromatophore patterning and body posturing are well known, passive mechanisms such as manipulating light with highly evolved reflectors may also play an important role. To explore the contribution of passive mechanisms to cephalopod camouflage, we investigated the optical and biochemical properties of the silver layer covering the eye of the California fishery squid, Loligo opalescens. We discovered a novel nested-spindle geometry whose correlated structure effectively emulates a randomly distributed Bragg reflector (DBR), with a range of spatial frequencies resulting in broadband visible reflectance, making it a nearly ideal passive camouflage material for the depth at which these animals live. We used the transfer-matrix method of optical modelling to investigate specular reflection from the spindle structures, demonstrating that a DBR with widely distributed thickness variations of high refractive index elements is sufficient to yield broadband reflectance over visible wavelengths, and that unlike DBRs with one or a few spatial frequencies, this broadband reflectance occurs from a wide range of viewing angles. The spindle shape of the cells may facilitate self-assembly of a random DBR to achieve smooth spatial distributions in refractive indices. This design lends itself to technological imitation to achieve a DBR with wide range of smoothly varying layer thicknesses in a facile, inexpensive manner. PMID:21325315
Effects of reading-oriented tasks on students' reading comprehension of geometry proof
NASA Astrophysics Data System (ADS)
Yang, Kai-Lin; Lin, Fou-Lai
2012-06-01
This study compared the effects of reading-oriented tasks and writing-oriented tasks on students' reading comprehension of geometry proof (RCGP). The reading-oriented tasks were designed with reading strategies and the idea of problem posing. The writing-oriented tasks were consistent with usual proof instruction for writing a proof and applying it. Twenty-two classes of ninth-grade students ( N = 683), aged 14 to 15 years, and 12 mathematics teachers participated in this quasi-experimental classroom study. While the experimental group was instructed to read and discuss the reading tasks in two 45-minute lessons, the control group was instructed to prove and apply the same propositions. Generalised estimating equation (GEE) method was used to compare the scores of the post-test and the delayed post-test with the pre-test scores as covariates. Results showed that the total scores of the delayed post-test of the experimental group were significantly higher than those of the control group. Furthermore, the scores of the experimental group on all facets of reading comprehension except the application facet were significantly higher than those of the control group for both the post-test and delayed post-test.
Holt, Amanda L; Sweeney, Alison M; Johnsen, Sönke; Morse, Daniel E
2011-10-01
Cephalopods possess a sophisticated array of mechanisms to achieve camouflage in dynamic underwater environments. While active mechanisms such as chromatophore patterning and body posturing are well known, passive mechanisms such as manipulating light with highly evolved reflectors may also play an important role. To explore the contribution of passive mechanisms to cephalopod camouflage, we investigated the optical and biochemical properties of the silver layer covering the eye of the California fishery squid, Loligo opalescens. We discovered a novel nested-spindle geometry whose correlated structure effectively emulates a randomly distributed Bragg reflector (DBR), with a range of spatial frequencies resulting in broadband visible reflectance, making it a nearly ideal passive camouflage material for the depth at which these animals live. We used the transfer-matrix method of optical modelling to investigate specular reflection from the spindle structures, demonstrating that a DBR with widely distributed thickness variations of high refractive index elements is sufficient to yield broadband reflectance over visible wavelengths, and that unlike DBRs with one or a few spatial frequencies, this broadband reflectance occurs from a wide range of viewing angles. The spindle shape of the cells may facilitate self-assembly of a random DBR to achieve smooth spatial distributions in refractive indices. This design lends itself to technological imitation to achieve a DBR with wide range of smoothly varying layer thicknesses in a facile, inexpensive manner. PMID:21325315
Field gradient imaging of nanoparticle systems: analysis of geometry and surface coating effects
NASA Astrophysics Data System (ADS)
Pacifico, J.; van Leeuwen, Y. M.; Spuch-Calvar, M.; Sánchez-Iglesias, A.; Rodríguez-Lorenzo, L.; Pérez-Juste, J.; Pastoriza-Santos, I.; Liz-Marzán, L. M.
2009-03-01
In this work we compare the standard imaging of various types of nanoparticles deposited on surfaces by atomic force microscopy (AFM) with a complementary analysis of the same samples by either electrostatic force microscopy (EFM) or magnetic force microscopy (MFM). Experiments were carried out on gold nanoparticles (decahedrons and stars) and two different iron oxide systems: goethite (α-FeOOH) and hematite (α-Fe2O3). Regardless of the particular geometry, the EFM signal appears to be stronger on edges or tips of pure gold nanoparticles. Both EFM and MFM experiments were also carried out on iron oxide particles. Apart from the structural analysis, we analyzed the influence of a shell layer deposited on the gold and iron oxide particles, the shell being amorphous SiO2. Although the silica layer was found to have an insulating effect around the particles, in all cases EFM/MFM measurements could still be performed by the proper choice of the scan lift height (with an eventual slight increase of the sample bias, where applicable).
Field gradient imaging of nanoparticle systems: analysis of geometry and surface coating effects.
Pacifico, J; van Leeuwen, Y M; Spuch-Calvar, M; Sánchez-Iglesias, A; Rodríguez-Lorenzo, L; Pérez-Juste, J; Pastoriza-Santos, I; Liz-Marzán, L M
2009-03-01
In this work we compare the standard imaging of various types of nanoparticles deposited on surfaces by atomic force microscopy (AFM) with a complementary analysis of the same samples by either electrostatic force microscopy (EFM) or magnetic force microscopy (MFM). Experiments were carried out on gold nanoparticles (decahedrons and stars) and two different iron oxide systems: goethite (alpha-FeOOH) and hematite (alpha-Fe(2)O(3)). Regardless of the particular geometry, the EFM signal appears to be stronger on edges or tips of pure gold nanoparticles. Both EFM and MFM experiments were also carried out on iron oxide particles. Apart from the structural analysis, we analyzed the influence of a shell layer deposited on the gold and iron oxide particles, the shell being amorphous SiO(2). Although the silica layer was found to have an insulating effect around the particles, in all cases EFM/MFM measurements could still be performed by the proper choice of the scan lift height (with an eventual slight increase of the sample bias, where applicable). PMID:19417504
Effects of package geometry, materials, and die design on energy dependence of pMOS dosimeters
Brucker, G.J.; Kronenberg, S.; Gentner, F.
1995-02-01
This paper presents the results of further studies enhancement in dual and single-dielectric pMOSFET dosimeters for various package and die designs. Eight different MOSFET designs and package types were investigated over a photon energy range from 14 to 1250 keV. Seven X-ray effective energies and two radioactive sources of cesium and cobalt provided the radiation. As in a previous study Rutherford back-scattered electrons were primarily responsible for the dose enhancement factors which achieved values as high as 20. Packages filled with silicon grease, aluminum oxide, or paraffin eliminated the contribution of back-scatter to the enhanced dose. These modifications allowed measurements of the usual dose enhancement at the aluminum or polysilicon gate-silicon nitride (dual dielectric devices), or silicon dioxide interfaces (single dielectric parts), and at the silicon nitride-silicon dioxide interface. In addition to the primary peak in the DEF (Dose Enhancement Factor) curve versus energy at 45.7 keV, there is a second peak at about 215 keV. This peak might be due to enhancements at the interfaces of a MOSFET. These interface effects were small in the single-insulator parts in standard ceramic packages, and significantly larger in the dual-insulator devices. The effects were reduced by filling the packages with the materials as previously described. The geometry of the package, for example, the size of the air gap between the die`s surface, and the lid of the package impacts the value of the DEF.
Som, S.; Longman, D. E; Ramirez, A. I.; Aggarwal, S. K.
2011-03-01
Diesel engine performance and emissions are strongly coupled with fuel atomization and spray processes, which in turn are strongly influenced by injector flow dynamics. Modern engines employ micro-orifices with different orifice designs. It is critical to characterize the effects of various designs on engine performance and emissions. In this study, a recently developed primary breakup model (KH-ACT), which accounts for the effects of cavitation and turbulence generated inside the injector nozzle is incorporated into a CFD software CONVERGE for comprehensive engine simulations. The effects of orifice geometry on inner nozzle flow, spray, and combustion processes are examined by coupling the injector flow and spray simulations. Results indicate that conicity and hydrogrinding reduce cavitation and turbulence inside the nozzle orifice, which slows down primary breakup, increasing spray penetration, and reducing dispersion. Consequently, with conical and hydroground nozzles, the vaporization rate and fuel air mixing are reduced, and ignition occurs further downstream. The flame lift-off lengths are the highest and lowest for the hydroground and conical nozzles, respectively. This can be related to the rate of fuel injection, which is higher for the hydroground nozzle, leading to richer mixtures and lower flame base speeds. A modified flame index is employed to resolve the flame structure, which indicates a dual combustion mode. For the conical nozzle, the relative role of rich premixed combustion is enhanced and that of diffusion combustion reduced compared to the other two nozzles. In contrast, for the hydroground nozzle, the role of rich premixed combustion is reduced and that of non-premixed combustion is enhanced. Consequently, the amount of soot produced is the highest for the conical nozzle, while the amount of NOx produced is the highest for the hydroground nozzle, indicating the classical tradeoff between them.
The effect of cathode geometry on barium transport in hollow cathode plasmas
Polk, James E. Mikellides, Ioannis G.; Katz, Ira; Capece, Angela M.
2014-05-14
The effect of barium transport on the operation of dispenser hollow cathodes was investigated in numerical modeling of a cathode with two different orifice sizes. Despite large differences in cathode emitter temperature, emitted electron current density, internal xenon neutral and plasma densities, and size of the plasma-surface interaction region, the barium transport in the two geometries is qualitatively very similar. Barium is produced in the insert and flows to the surface through the porous structure. A buildup of neutral Ba pressure in the plasma over the emitter surface can suppress the reactions supplying the Ba, restricting the net production rate. Neutral Ba flows into the dense Xe plasma and has a high probability of being ionized at the periphery of this zone. The steady state neutral Ba density distribution is determined by a balance between pressure gradient forces and the drag force associated with collisions between neutral Ba and neutral Xe atoms. A small fraction of the neutral Ba is lost upstream. The majority of the neutral Ba is ionized in the high temperature Xe plasma and is pushed back to the emitter surface by the electric field. The steady state Ba{sup +} ion density distribution results from a balance between electrostatic and pressure forces, neutral Xe drag and Xe{sup +} ion drag with the dominant forces dependent on location in the discharge. These results indicate that hollow cathodes are very effective at recycling Ba within the discharge and therefore maintain a high coverage of Ba on the emitter surface, which reduces the work function and sustains high electron emission current densities at moderate temperatures. Barium recycling is more effective in the cathode with the smaller orifice because the Ba is ionized in the dense Xe plasma concentrated just upstream of the orifice and pushed back into the hollow cathode. Despite a lower emitter temperature, the large orifice cathode has a higher Ba loss rate through the orifice
The effect of cathode geometry on barium transport in hollow cathode plasmas
NASA Astrophysics Data System (ADS)
Polk, James E.; Mikellides, Ioannis G.; Capece, Angela M.; Katz, Ira
2014-05-01
The effect of barium transport on the operation of dispenser hollow cathodes was investigated in numerical modeling of a cathode with two different orifice sizes. Despite large differences in cathode emitter temperature, emitted electron current density, internal xenon neutral and plasma densities, and size of the plasma-surface interaction region, the barium transport in the two geometries is qualitatively very similar. Barium is produced in the insert and flows to the surface through the porous structure. A buildup of neutral Ba pressure in the plasma over the emitter surface can suppress the reactions supplying the Ba, restricting the net production rate. Neutral Ba flows into the dense Xe plasma and has a high probability of being ionized at the periphery of this zone. The steady state neutral Ba density distribution is determined by a balance between pressure gradient forces and the drag force associated with collisions between neutral Ba and neutral Xe atoms. A small fraction of the neutral Ba is lost upstream. The majority of the neutral Ba is ionized in the high temperature Xe plasma and is pushed back to the emitter surface by the electric field. The steady state Ba+ ion density distribution results from a balance between electrostatic and pressure forces, neutral Xe drag and Xe+ ion drag with the dominant forces dependent on location in the discharge. These results indicate that hollow cathodes are very effective at recycling Ba within the discharge and therefore maintain a high coverage of Ba on the emitter surface, which reduces the work function and sustains high electron emission current densities at moderate temperatures. Barium recycling is more effective in the cathode with the smaller orifice because the Ba is ionized in the dense Xe plasma concentrated just upstream of the orifice and pushed back into the hollow cathode. Despite a lower emitter temperature, the large orifice cathode has a higher Ba loss rate through the orifice because the Xe
ERIC Educational Resources Information Center
Mandaci Sahin, Seher; Kendir, Fatma
2013-01-01
The purpose of this study is to identify the effect of using metacognitive strategies for problem solving in "geometry" on fifth grade students' achievement, metacognitive skills and attitude. Experimental method was used with a pretest/posttest control group design. Firstly, both groups were subject to a pretest that was comprised…
Technology Transfer Automated Retrieval System (TEKTRAN)
Experimental and theoretical studies were undertaken to explore the coupling effects of chemical conditions and pore space geometry on bacteria transport in porous media. The retention of Escherichia coli D21g was investigated in a series of batch and column experiments with solutions of different i...
14 CFR § 1203.401 - Effect of open publication.
Code of Federal Regulations, 2014 CFR
2014-01-01
... 14 Aeronautics and Space 5 2014-01-01 2014-01-01 false Effect of open publication. Â§ 1203.401... SECURITY PROGRAM Guides for Original Classification § 1203.401 Effect of open publication. Public disclosure, regardless of source or form, of information currently classified or being considered...
14 CFR 1203.401 - Effect of open publication.
Code of Federal Regulations, 2012 CFR
2012-01-01
... 14 Aeronautics and Space 5 2012-01-01 2012-01-01 false Effect of open publication. 1203.401 Section 1203.401 Aeronautics and Space NATIONAL AERONAUTICS AND SPACE ADMINISTRATION INFORMATION SECURITY PROGRAM Guides for Original Classification § 1203.401 Effect of open publication. Public...
14 CFR 1203.401 - Effect of open publication.
Code of Federal Regulations, 2011 CFR
2011-01-01
... 14 Aeronautics and Space 5 2011-01-01 2010-01-01 true Effect of open publication. 1203.401 Section 1203.401 Aeronautics and Space NATIONAL AERONAUTICS AND SPACE ADMINISTRATION INFORMATION SECURITY PROGRAM Guides for Original Classification § 1203.401 Effect of open publication. Public...
14 CFR 1203.401 - Effect of open publication.
Code of Federal Regulations, 2013 CFR
2013-01-01
... 14 Aeronautics and Space 5 2013-01-01 2013-01-01 false Effect of open publication. 1203.401 Section 1203.401 Aeronautics and Space NATIONAL AERONAUTICS AND SPACE ADMINISTRATION INFORMATION SECURITY PROGRAM Guides for Original Classification § 1203.401 Effect of open publication. Public...
NASA Astrophysics Data System (ADS)
Zhang, L.; Eskin, D. G.; Miroux, A.; Subroto, T.; Katgerman, L.
2012-07-01
Controlling macrosegregation is one of the major challenges in direct-chill (DC) casting of aluminium alloys. In this paper, the effect of the inlet geometry (which influences the melt distribution) on macrosegregation during the DC casting of 7050 alloy billets was studied experimentally and by using 2D computer modelling. The ALSIM model was used to determine the temperature and flow patterns during DC casting. The results from the computer simulations show that the sump profiles and flow patterns in the billet are strongly influenced by the melt flow distribution determined by the inlet geometry. These observations were correlated to the actual macrosegregation patterns found in the as-cast billets produced by having two different inlet geometries. The macrosegregation analysis presented here may assist in determining the critical parameters to consider for improving the casting of 7XXX aluminium alloys.
Maruani, Annabel; Samimi, Mahtab; Lorette, Gérard; le Cleach, Laurence
2015-01-01
Among the 100 initial priority topics for comparative effectiveness research, three concern topical drugs in the following dermatologic diseases: psoriasis, chronic lower-extremity wounds (CLEWs), and acne vulgaris (AV). Our objective was to explore the geometry of the corresponding networks of randomized controlled trials (RCTs). We performed a review of RCTs on topical drugs in psoriasis, CLEWs, and AV. We searched MEDLINE, Embase, and CENTRAL for published trials from 2007 to 2012 and ClinicalTrials.gov for unpublished trials registered since 2011. RCTs comparing at least one topical treatment with any active or inactive comparator, regardless of RCT design and outcomes, were eligible. We produced network graphs (each node representing a treatment and links between nodes representing trials) and tested for co-occurrence (preference or avoidance of specific comparisons). We included 60 RCTs on psoriasis (14,255 patients) and 19 registered RCTs, 50 of CLEWs (5,916 patients) and 7 registered RCTs, and 90 of AV (22,984 patients) and 21 registered RCTs. Head-to-head comparisons were made in 78%, 32%, and 57% of published RCTs of these conditions, respectively. The co-occurrence test suggested that no specific head-to-head comparison was significantly preferred or avoided (P-value=0.53, 0.20, and 0.57, respectively). This study has limitations, the main being that the search period was restricted to 5 years. In conclusion, more comparative effectiveness trials are needed for CLEWs, for which head-to-head comparisons are fewer than those for psoriasis and AV. PMID:25046338
Boerger, D.M.; Kramer, J.J.; Partain, L.D.
1981-01-01
A rigorous derivation is given to generalize the allowed, Hall effect, sample shapes from the restrictive, rectangular parallelepiped configurations to a much more general class of geometries characterized by mirror symmetry for materials whose mobile carriers have surfaces of constant energy in k-bar space that are well described by ellipsoids. However, this mirror symmetry condition is more restrictive than the almost arbitrary sample shapes proposed with the van der Pauw technique for thin films. Experimental data taken on n-type CdS at liquid-nitrogen temperatures in magnetic field strengths of 8 and 145 kG show that errors ranging from 1 to 600% can result from van der Pauw-type geometries depending on how much the sample shape and/or contact arrangement differs from the mirror symmetry. An empirically derived averaging technique is described that reduces the observed errors to less than 13% even with van der Pauw-type shapes that do not meet the mirror symmetry conditions.
Jiang, Jian-Hua
2014-11-21
We propose a scheme of multilayer thermoelectric engine where one electric current is coupled to two temperature gradients in three-terminal geometry. This is realized by resonant tunneling through quantum dots embedded in two thermal and electrical resisting polymer matrix layers between highly conducting semiconductor layers. There are two thermoelectric effects, one of which is pertaining to inelastic transport processes (if energies of quantum dots in the two layers are different), while the other exists also for elastic transport processes. These two correspond to the transverse and longitudinal thermoelectric effects, respectively, and are associated with different temperature gradients. We show that cooperation between the two thermoelectric effects leads to markedly improved figure of merit and power factor, which is confirmed by numerical calculation using material parameters. Such enhancement is robust against phonon heat conduction and energy level broadening. Therefore, we demonstrated cooperative effect as an additional way to effectively improve performance of thermoelectrics in three-terminal geometry.
Geometry of the quantum Hall effect: An effective action for all dimensions
NASA Astrophysics Data System (ADS)
Karabali, Dimitra; Nair, V. P.
2016-07-01
We present a general formula for the topological part of the effective action for integer quantum Hall systems in higher dimensions, including fluctuations of the gauge field and metric around background fields of a specified topological class. The result is based on a procedure of integrating up from the Dolbeault index density which applies for the degeneracies of Landau levels, combined with some input from the standard descent procedure for anomalies. Features of the topological action in (2 +1 ), (4 +1 ), (6 +1 ) dimensions, including the contribution due to gravitational anomalies, are discussed in some detail.
The Effects of Geometry and Stability of Solid-state Nanopores on Detecting Single DNA molecules
Rollings, Ryan; Graef, Edward; Walsh, Nathan; Nandivada, Santoshi; Benamara, Mourad
2014-01-01
In this work we use a combination of 3D-TEM tomography, energy filtered TEM, single molecule DNA translocation experiments, and numerical modeling to show a more precise relationship between nanopore shape and ionic conductance and show that changes in geometry while in solution can account for most deviations between predicted and measured conductance. We compare the structural stability of Ion Beam Sculpted (IBS), IBS-annealed, and TEM drilled nanopores. We demonstrate that annealing can significantly improve the stability of IBS made pores. Furthermore, the methods developed in this work can be used to predict pore conductance and current drop amplitudes of DNA translocation events for a wide variety of pore geometries. We discuss that chemical dissolution is one mechanism of the geometry change for SiNx nanopores and show that small modification in fabrication procedure can significantly increase the stability of IBS nanopores. PMID:25556317
Effects of the geomagnetic field on the beaming geometry of TGFs
NASA Astrophysics Data System (ADS)
Celestin, Sebastien
2016-04-01
Terrestrial gamma-ray flashes (TGFs) are bursts of high-energy photons originating from the Earth's atmosphere in association with thunderstorm activity [e.g., Briggs et al., JGR, 118, 3805, 2013]. Although TGFs are believed to be produced inside thunderclouds (below 15 km altitude), the underlying physical mechanisms are still debated. Large-scale relativistic runaway electron avalanches (RREAs) along with relativistic feedback caused by positrons and photons have been proposed to occur in thunderclouds and to produce TGFs [e.g., Dwyer et al., Space Sci. Rev., 173, 133, 2012]. It has also been found that the production of thermal runaway electrons by stepping lightning leaders and their further acceleration could explain the TGF spectra and fluences for intracloud (IC) lightning electric potentials above ˜100 MV [Xu et al., GRL, 39, L08801, 2012; Celestin et al., JGR, 120, 2015]. In both scenarios, runaway electron avalanches take place and the related bremsstrahlung produces the TGF. The impact of the geomagnetic field on RREAs has been seldom studied (with the notable exceptions of Lehtinen et al. [JGR, 104, 24699, 1999], Babich et al. [Geom. Aeron., 44, 243, 2004] and Cramer et al. [AGU Fall Meeting, abstract AE33A-0472, San Francisco, USA, 2015]), particularly in view of recent knowledge acquired about TGF sources properties. In this work, we study the effects of the geomagnetic field on the runaway electron beam geometry in large-scale RREAs and in the vicinity of lightning leaders and the corresponding impact on TGF observations using analytical and numerical means.
NASA Astrophysics Data System (ADS)
Mitra, Partha P.; Sen, Pabitra N.
1992-01-01
We derive an expression for the magnetization M(k,Δ) in a pulsed-field-gradient experiment for spins diffusing in a confined space with relaxation at the pore walls. Here k=γδg, δ= pulse width, g= gradient strength, γ= the gyromagnetic ratio, and Δ is the time between gradient pulses. We show that the deviation of -ln[M(k,Δ)/M(0,Δ)] from quadratic behavior in k in experiments in porous media can be a more sensitive probe of the microgeometry (size, connectivity, size distribution, shape, etc.), than either the enhancement of 1/T1 over the bulk water value, or the macroscopic diffusion coefficient, which is derived from the slope of -ln[M(k,Δ)/M(0,Δ)] at small k2, in the limit of large Δ. We propose some simple models of randomly oriented tubes and sheets to interpret the k dependence of the amplitude beyond the leading small-k quadratic behavior. When the macroscopic diffusion coefficient is unobtainable, due to the decay, the present considerations should be useful in extracting geometrical information. The effective diffusion constant derived from NMR exactly equals that derived from electrical conductivity only when the surface relaxivity is zero, but can be close to each other in favorable circumstances even for finite surface relaxivity. Exact solutions with partially absorbing boundary conditions are obtained for a slab and a sphere to infer that the normalized amplitude M(k,Δ,ρ)/M(0,Δ,ρ) depends only weakly on the surface relaxivity ρ for monodisperse convex-shaped pores in the parameter ranges of interest. We also obtain expressions for the mean lifetime of the amplitude in the geometries considered.
Analysis of the Effect of Geometry Generated Turbulence on HCCI Combustion by Multi-Zone Modeling
Aceves, S M; Flowers, D L; Martinez-Frias, J; Espinosa-Loza, F; Christensen, M; Johansson, B; Hessel, R P
2004-12-13
This paper illustrates the applicability of a sequential fluid mechanics, multi-zone chemical kinetics model to analyze HCCI experimental data for two combustion chamber geometries with different levels of turbulence: a low turbulence disc geometry (flat top piston), and a high turbulence square geometry (piston with a square bowl). The model uses a fluid mechanics code to determine temperature histories in the engine as a function of crank angle. These temperature histories are then fed into a chemical kinetic solver, which determines combustion characteristics for a relatively small number of zones (40). The model makes the assumption that there is no direct linking between turbulence and combustion. The results show that the multi-zone model yields good results for both the disc and the square geometries. The model makes good predictions of pressure traces and heat release rates. The experimental results indicate that the high turbulence square geometry has longer burn duration than the low turbulence disc geometry. This difference can be explained by the sequential multi-zone model, which indicates that the cylinder with the square bowl has a thicker boundary layer that results in a broader temperature distribution. This broader temperature distribution tends to lengthen the combustion, as cold mass within the cylinder takes longer to reach ignition temperature when compressed by the expansion of the first burned gases. The multi-zone model, which makes the basic assumption that HCCI combustion is controlled by chemical kinetics, is therefore capable of explaining the experimental results obtained for different levels of turbulence, without considering a direct interaction between turbulence and combustion. A direct connection between turbulence and HCCI combustion may still exists, but it seems to play a relatively minor role in determining burn duration at the conditions analyzed in this paper.
Geometry Effects on Multipole Components and Beam Optics in High-Velocity Multi-Spoke Cavities
Hopper, Christopher S.; Deitrick, Kirsten E.; Delayen, Jean R.
2013-12-01
Velocity-of-light, multi-spoke cavities are being proposed to accelerate electrons in a compact light-source. There are strict requirements on the beam quality which require that the linac have only small non-uniformities in the accelerating field. Beam dynamics simulations have uncovered varying levels of focusing and defocusing in the proposed cavities, which is dependent on the geometry of the spoke in the vicinity of the beam path. Here we present results for the influence different spoke geometries have on the multipole components of the accelerating field and how these components, in turn, impact the simulated beam properties.
Effect of Weld Tool Geometry on Friction Stir Welded AA2219-T87 Properties
NASA Technical Reports Server (NTRS)
Querin, Joseph A.; Schneider, Judy A.
2008-01-01
In this study, flat panels of AA2219-T87 were friction stir welded (FSWed) using weld tools with tapered pins The three pin geometries of the weld tools included: 0 (straight cylinder), 30 , and 60 angles on the frustum. For each weld tool geometry, the FSW process parameters were optimized to eliminate defects. A constant heat input was maintained while varying the process parameters of spindle rpm and travel speed. This provided a constant heat input for each FSW weld panel while altering the hot working conditions imparted to the workpiece. The resulting mechanical properties were evaluated from tensile test results of the FSW joint.
Effective Results of an Open Concept School
ERIC Educational Resources Information Center
Cobos, Irma; Lewallen, Joy
2009-01-01
Open concept schools were a popular architectural design in the 70s. They were built to provide large areas of flexible space for team teaching with small enclosed areas for restrooms, science labs, and special needs classrooms. Because there are no barriers and no closed doors, an attitude of inclusiveness is created merely by the building's…
ERIC Educational Resources Information Center
Guven, Bulent; Kosa, Temel
2008-01-01
Geometry is the study of shape and space. Without spatial ability, students cannot fully appreciate the natural world. Spatial ability is also very important for work in various fields such as computer graphics, engineering, architecture, and cartography. A number of studies have demonstrated that technology has an important potential to develop…
Effects of Polya Questioning Instruction for Geometry Reasoning in Junior High School
ERIC Educational Resources Information Center
Lee, Chun-Yi; Chen, Ming-Jang
2015-01-01
In teaching geometry, most instructors opt for direct demonstration with detailed explanations; however, under this kind of instruction students face considerable difficulties in the development of the reasoning skills required to deal with problems of a geometric nature. This study adopted a nonequivalent pretest-postest quasi-experimental design…
Modeling the Coupled Effects of Pore Space Geometry and Velocity on Colloid Transport and Retention
Technology Transfer Automated Retrieval System (TEKTRAN)
Recent experimental and theoretical work has demonstrated that pore space geometry and hydrodynamics can play an important role in colloid retention under unfavorable attachment conditions. Computer models that only consider the average pore-water velocity and a single attachment rate coefficient a...
ERIC Educational Resources Information Center
Lin, Hao-Chiang Koong; Chen, Mei-Chi; Chang, Chih-Kai
2015-01-01
This study integrates augmented reality (AR) technology into teaching activities to design a learning system that assists junior high-school students in learning solid geometry. The following issues are addressed: (1) the relationship between achievements in mathematics and performance in spatial perception; (2) whether system-assisted learning…
The Effect of Teacher Pedagogical Content Knowledge and the Instruction of Middle School Geometry
ERIC Educational Resources Information Center
Lenhart, Sara Talley
2010-01-01
This study investigated the relationship between middle school math teacher pedagogical content knowledge as gathered from a teacher assessment and student Standards of Learning scores. Nine middle-school math teachers at two rural schools were assessed for their pedagogical content knowledge in geometry and measurement in the specific area of…
ERIC Educational Resources Information Center
Yilmaz, Gül Kaleli; Koparan, Timur
2016-01-01
The aim of this study is to find out how designed Geometry Teaching Lesson affects candidate teachers' Van Hiele Geometric Thinking Levels. For that purpose, 14 weeks long study was performed with 44 candidate teachers who were university students in Turkey. Van Hiele Geometric Thinking Test was applied to candidate teachers before and after…
ERIC Educational Resources Information Center
Zhang, Dake; Ding, Yi; Stegall, Joanna; Mo, Lei
2012-01-01
Students who struggle with learning mathematics often have difficulties with geometry problem solving, which requires strong visual imagery skills. These difficulties have been correlated with deficiencies in visual working memory. Cognitive psychology has shown that chunking of visual items accommodates students' working memory deficits. This…
Effects of detector geometry on measured lineshapes and intensities in surface scattering
NASA Astrophysics Data System (ADS)
Hinch, B. J.; Frankl, D. R.; Allison, W.
1987-02-01
A general expression for the detector response to a given beam flux distribution is given. Illustrative examples are worked out for some simple idealized cases and it is shown that both the measured lineshape and the measured intensity depend on the details of incident beam and detector geometry.
Effect of port corner geometry on the internal performance of a rotating-vane-type thrust reverser
NASA Technical Reports Server (NTRS)
Berrier, B. L.; Capone, F. J.
1986-01-01
An investigation has been conducted in the static-test facility of the Langley 16-Foot Transonic Tunnel to determine the effects of reverser port geometry on the internal performance of a nonaxisymmetric rotating-vane-type thrust reverser. Thrust reverser vane positions representing a spoiled-trust (partially deployed) position and a full-reverse-thrust (fully deployed) position were tested with each port geometry variable. The effects of upstream port corner radius and wall angle on internal performance were determined. In addition, the effect of the length of a simulated cooling liner (blunt-base step) near the reverser port entrance was investigated; five different lengths were tested. All tests were conducted with no external flows, and nozzle pressure ratio was varied from 1.2 to 5.0.
NASA Astrophysics Data System (ADS)
Arciniaga, Michael; Peterson, Michael R.
2016-07-01
We derive the single-particle eigenenergies and eigenfunctions for massless Dirac fermions confined to the surface of a sphere in the presence of a magnetic monopole, i.e., we solve the Landau level problem for electrons in graphene on the Haldane sphere. With the single-particle eigenfunctions and eigenenergies we calculate the Haldane pseudopotentials for the Coulomb interaction in the second Landau level and calculate the effective pseudopotentials characterizing an effective Landau level mixing Hamiltonian entirely in the spherical geometry to be used in theoretical studies of the fractional quantum Hall effect in graphene. Our treatment is analogous to the formalism in the planar geometry and reduces to the planar results in the thermodynamic limit.
Effect of flying activity on capillary-fiber geometry in pigeon flight muscle.
Mathieu-Costello, O; Agey, P J; Logemann, R B; Florez-Duquet, M; Bernstein, M H
1994-02-01
The effect of flying activity on capillary density and geometry was investigated in pectoralis muscle of 4 wild-caught (W) pigeons (BW 233-348 g) perfusion-fixed in situ and processed for electron microscopy. Morphometric analysis revealed both differences and similarities with similar sampling sites (superficial and deep in central area of right or left pectoralis major muscle, approximately midway along cranio-caudal and lateral axis) in sedentary (S) pigeons. Differences were the greater fractional cross-sectional area of aerobic fibers (W, 82 +/- 2%; S, 63 +/- 6%; p = 0.006) and the greater volume density of mitochondria per volume of fiber (W, 22.0 +/- 1.3%; S, 15.7 +/- 1.7%; p = 0.011) in wild-caught pigeons. While glycolytic fibers were significantly narrower in W, the size of the majority of fibers comprising the muscles, i.e. aerobic fibers, was similar in the two groups. Other similarities were found in capillary-to-fiber ratio (W, 2.0 +/- 0.2; S, 2.1 +/- 0.2) and in the degree of orientation of capillaries in the two groups. In addition, both capillary density at a given fractional cross-sectional area of aerobic fibers and capillary length per fiber volume at a given mitochondrial volume density were similar in the two groups, indicating a proportional increase in capillarity and muscle aerobic capacity in W compared with S. Comparison of capillary numbers around aerobic fibers at a given mitochondrial volume per microns length of fiber showed no difference between W and S groups nor with previous data in muscles with wide differences in fiber size and mitochondrial density such as rat soleus, bat muscles and hummingbird flight muscles. This supported the notion of a tight correlation between capillary numbers around individual fibers and mitochondrial volume per unit length of fiber in aerobic muscles. It also supported the idea that it is the number of capillaries around the fibers rather than diffusion distance which determines O2 flux rates in
NASA Astrophysics Data System (ADS)
Yu, Bin; Deng, Jian-Hua; Wang, Zheng; Li, Bao-Hui; Shi, An-Chang
2015-04-01
The self-assembly of symmetric diblock copolymers confined in the channels of variously shaped cross sections (regular triangles, squares, and ellipses) is investigated using a simulated annealing technique. In the bulk, the studied symmetric diblock copolymers form a lamellar structure with period LL. The geometry and surface property of the confining channels have a large effect on the self-assembled structures and the orientation of the lamellar structures. Stacked perpendicular lamellae with period LL are observed for neutral surfaces regardless of the channel shape and size, but each lamella is in the shape of the corresponding channel's cross section. In the case of triangle-shaped cross sections, stacked parallel lamellae are the majority morphologies for weakly selective surfaces, while morphologies including a triangular-prism-shaped B-cylinder and multiple tridentate lamellae are obtained for strongly selective surfaces. In the cases of square-shaped and ellipse-shaped cross sections, concentric lamellae are the signature morphology for strongly selective surfaces, whereas for weakly selective surfaces, stacked parallel lamellae, and several types of folding lamellae are obtained in the case of square-shaped cross sections, and stacked parallel lamellae are the majority morphologies in the case of ellipse-shaped cross sections when the length of the minor axis is commensurate with the bulk lamellar period. The mean-square end-to-end distance, the average contact number between different species and the surface concentration of the A-monomers are computed to elucidate the mechanisms of the formation of the different morphologies. It is found that the resulting morphology is a consequence of competition among the chain stretching, interfacial energy, and surface energy. Our results suggest that the self-assembled morphology and the orientation of lamellae can be manipulated by the shape, the size, and the surface property of the confining channels. Project
NASA Astrophysics Data System (ADS)
Orescanin, M. M.; Elgar, S.; Raubenheimer, B.
2014-12-01
Circulation in bays with one or more connections to the ocean depends on the location and morphology of the inlets. Here, field observations and the numerical model ADCIRC are used to investigate circulation in the small (~7 km2 surface area) and shallow (~2 m deep) Katama Bay, Martha's Vineyard, MA, which is connected to Vineyard Sound in the north by the long (~2.5 km), stable, maintained Edgartown Channel, and to the Atlantic Ocean in the south by the variable and ephemeral Katama Inlet, which changes shape in response to storms, as well as to daily waves and tides. Katama Inlet was initiated by a breach in 2007, and has migrated almost 2.5 km to the east where it is now adjacent to Chappaquiddick Island. In a typical decadal cycle, the inlet eventually closes until another storm breaches the sand barrier. As it migrates, Katama Inlet varies in width, length, depth, and orientation. The bathymetry near the inlet was measured pre- and post Hurricane Irene (2011), and in the summers of 2012-2014. In addition, sea levels, waves, and currents were measured in the ocean, the inlets, and the bay from August until October 2011 (including during Hurricane Irene), and in August 2013. Between 2011 and 2013 the inlet migrated 1 km to the east and changed alignment from roughly north-south to east-west. Pressure data from the Atlantic Ocean and northern Edgartown Channel are used to drive ADCIRC using bathymetry measured (1) pre- and (2) post-Irene in 2011, and (3) in 2013. The model is run over month-long periods using a variable Manning's n for friction and including wetting and drying of the coast. The model simulations are consistent with the observations, including the observed changes to the circulation caused by the evolving inlet channel. The results suggest that changes in the geometry, orientation, and location of one inlet may have significant effects on hydrodynamics throughout the bay and in the other channel. Supported by ASD(R&E), ONR, and NSF.
Aramburu, José Antonio; García-Fernández, Pablo; García-Lastra, Juan María; Moreno, Miguel
2016-07-18
First-principle calculations together with analysis of the experimental data found for 3d(9) and 3d(7) ions in cubic oxides proved that the center found in irradiated CaO:Ni(2+) corresponds to Ni(+) under a static Jahn-Teller effect displaying a compressed equilibrium geometry. It was also shown that the anomalous positive g∥ shift (g∥ -g0 =0.065) measured at T=20 K obeys the superposition of the |3 z(2) -r(2) ⟩ and |x(2) -y(2) ⟩ states driven by quantum effects associated with the zero-point motion, a mechanism first put forward by O'Brien for static Jahn-Teller systems and later extended by Ham to the dynamic Jahn-Teller case. To our knowledge, this is the first genuine Jahn-Teller system (i.e. in which exact degeneracy exists at the high-symmetry configuration) exhibiting a compressed equilibrium geometry for which large quantum effects allow experimental observation of the effect predicted by O'Brien. Analysis of the calculated energy barriers for different Jahn-Teller systems allowed us to explain the origin of the compressed geometry observed for CaO:Ni(+) . PMID:27028895
Effect of particle geometry on triple line motion of nano-fluid drops and deposit nano-structuring.
Askounis, Alexandros; Sefiane, Khellil; Koutsos, Vasileios; Shanahan, Martin E R
2015-08-01
We illustrate the importance of particle geometry on droplet contact line pinning, 'coffee-stain' formation and nano-structuring within the resulting rings. We present the fundamentals of pure liquid droplet evaporation and then discuss the effect of particles on the evaporation process. The resulting coffee-stain patterns and particle structuring within them are presented and discussed. In the second part, we turn our attention to the effect of particle geometry on the evaporation process. A wide range of particle shapes, categorised according to aspect ratio, from the simple shape of a sphere to the highly irregular shapes of platelets and tubes is discussed. Particle geometry effect on evaporation behaviour was quantified in terms of change in contact angle and contact radius for the stick-slip cases. Consequently the hysteretic energy barrier pinning the droplets was estimated, showing an increasing trend with particle aspect ratio. The three-phase contact line (TL) motion kinetics are complemented with analysis of the nano-structuring behaviour of each shape, leading to the identification of the two main parameters affecting nanoparticle self-assembly behaviour at the wedge. Flow velocity and wedge constraints were found to have antagonist effects on particle deposition, although these varied with particle shape. This description should help in understanding the drying behaviour of more complex fluids. Furthermore, knowing the fundamentals of this simple and inexpensive surface patterning technique should permit its tailoring to the needs of many potential applications. PMID:24927853
[Evaluating the effectiveness of "open lung" maneuvre].
Eremenko, A A; Borisov, R Iu; Egorov, V M
2011-01-01
The purpose of this study--a comparative evaluation of the treatment of postoperative acute respiratory insufficiency in cardio surgical patients with lung opening maneuver and conventional mechanical ventilation. The study included 81 patients operated on the heart and magistral vessels in which the immediate postoperative period was complicated by the development of acute lung injury. Patients were divided into 2 groups: 1 (main) group (48 patients), on which the open lung technique was used, 2 (control) group (33 patients) who underwent a standard respiratory support. The initial values of the partial oxygen pressure in arterial blood and the oxygenation index in patients of both groups were significantly reduced, and the fraction of intrapulmonary shunting - significantly increased. Starting with 1 day sharp increase in PaO2 and IE in patients with the first group was noticed, which coincides with the beginning of the opening of the alveoli. At the same time, the dynamics of these indicators in the second group had the reverse tendency. After the recruiting maneuver in all patients significant improvements in the mechanics of breathing were noticed. As a result of the recruiting maneuver in the first group sustained improvement of arterial oxygenation was achieved in 35 patients. In patients with acute postoperative respiratory failure recruiting maneuver led to a significant increase in arterial oxygenation and reduce the fraction of intrapulmonary shunt. Application of "open lung" maneuver leads to the resolution of respiratory failure, which greatly reduces the timing of mechanical ventilation and length of stay of patients in intensive care units in comparison with traditional methods of respiratory therapy. PMID:21851022
Effect of geometry on drug release from 3D printed tablets.
Goyanes, Alvaro; Robles Martinez, Pamela; Buanz, Asma; Basit, Abdul W; Gaisford, Simon
2015-10-30
The aim of this work was to explore the feasibility of combining hot melt extrusion (HME) with 3D printing (3DP) technology, with a view to producing different shaped tablets which would be otherwise difficult to produce using traditional methods. A filament extruder was used to obtain approx. 4% paracetamol loaded filaments of polyvinyl alcohol with characteristics suitable for use in fused-deposition modelling 3DP. Five different tablet geometries were successfully 3D-printed-cube, pyramid, cylinder, sphere and torus. The printing process did not affect the stability of the drug. Drug release from the tablets was not dependent on the surface area but instead on surface area to volume ratio, indicating the influence that geometrical shape has on drug release. An erosion-mediated process controlled drug release. This work has demonstrated the potential of 3DP to manufacture tablet shapes of different geometries, many of which would be challenging to manufacture by powder compaction. PMID:25934428
NASA Astrophysics Data System (ADS)
Goker, Ali Ihsan; Zhu, Zhiyong; Schwingenschlogl, Udo; Manchon, Aurelien
2011-03-01
The time-dependent non-crossing approximation is utilized to investigate the influence of the geometry of contacts made of gold on time dependent current through a quantum dot suddenly shifted into the Kondo regime via a gate voltage. For an asymmetrically coupled system, instantaneous conductance exhibits complex fluctuations. We identify the frequencies participating in these fluctuations and they turn out to be proportional to the separation between the sharp features in the density of states and the Fermi level. Increasing ambient temperature or bias quenches the amplitude of these fluctuations. This suggests that the interference between the emerging Kondo resonance and the van Hove singularities in the density of states is the underlying microscopic mechanism for these fluctuations. Based on these observations, we predict that using different electrode geometries would give rise to drastically different transient currents which can be accessed with state-of-the-art ultrafast pump-probe techniques. King Abdullah University of Science and Technology.
NASA Astrophysics Data System (ADS)
Ebrahimi Khabbazi, A.; Richards, A. J.; Hoorfar, M.
Using COMSOL Multiphysics 3.5, 3D numerical models of different microfluidic fuel cells have been developed in this paper to determine the effect of different modifications which have been implemented in the microfluidic fuel cell since its advent. These modifications include the channel geometry aspect ratio and electrode configuration, the third flow between the anolyte and catholyte in the channel (i.e., multi-stream laminar flow), and multiple periodically placed inlets. To be consistent with the convention, the output power of the device is normalized by the electrode surface area; however, the power density calculations are also performed through normalization by the device volume. It is shown that the latter method is more realistic and providing more information from the design point of view since the ultimate goal in designing the microfluidic fuel cell is to fabricate a compact, yet powerful device. Finally, a novel design of the microfluidic fuel cell with a tapered channel is suggested and compared to the non-tapered geometry through the polarization curves. The steps which have been taken in COMSOL to obtain these polarization curves are clearly and thoroughly explained. The Butler-Volmer equation was implemented to incorporate for the electrochemical reactions at the electrodes. The "Conductive Media DC" module, in COMSOL, is used to model the electric fields within the fuel cell. The concentration distributions of the reactant species are obtained using the "Incompressible Navier-Stokes" and "Convection and Diffusion" modules. Solving these equations together predicts the current density for given cell voltage values. The results demonstrate the cell voltage losses due to activation, ohmic and concentration overpotentials. It is shown that for a fixed value of the cell voltage (say 0.45 V), the fuel cell with multiple periodically placed inlets has the highest fuel utilization (i.e., 62.3%); while the "Simple square" geometry depicts 13.8% fuel
NASA Astrophysics Data System (ADS)
Contreras, Ernesto; Villalba, Fabián D.; Bargueño, Pedro
2016-06-01
In this work we construct several black-hole metrics which are consistent with the generalized uncertainty principle logarithmic correction to the Bekenstein-Hawking entropy formula. After preserving the event horizon at the usual position, a singularity at the Planck scale is found. Finally, these geometries are shown to be realized by certain model of non-linear electrodynamics, which resembles previously studied regular black-hole solutions.
Study of the Effects of Photometric Geometry on Spectral Reflectance Measurements
NASA Technical Reports Server (NTRS)
Helfenstein, Paul
1998-01-01
The objective of this research is to investigate how the spectrophotometric properties of planetary surface materials depend on photometric geometry by refining and applying radiative transfer theory to data obtained from spacecraft and telescope observations of planetary surfaces, studies of laboratory analogs, and computer simulations. The goal is to perfect the physical interpretation of photometric parameters in the context of planetary surface geological properties and processes. The purpose of this report is to document the research achievements associated with this study.
NASA Technical Reports Server (NTRS)
Scallion, William I.
1991-01-01
The effects of varying the exit geometry on the plume shapes of supersonic nozzles exhausting into quiescent air at several exit-to-ambient pressure ratios are given. Four nozzles having circular throat sections and circular, elliptical and oval exit cross sections were tested and the exit plume shapes are compared at the same exit-to-ambient pressure ratios. The resulting mass flows were calculated and are also presented.
Probing bulk physics in the 5/2 fractional quantum Hall effect using the Corbino geometry
NASA Astrophysics Data System (ADS)
Schmidt, Benjamin; Bennaceur, Keyan; Bilodeau, Simon; Gaucher, Samuel; Lilly, Michael; Reno, John; Pfeiffer, Loren; West, Ken; Reulet, Bertrand; Gervais, Guillaume
We present two- and four-point Corbino geometry transport measurements in the second Landau level in GaAs/AlGaAs heterostructures. By avoiding edge transport, we are able to directly probe the physics of the bulk quasiparticles in fractional quantum Hall (FQH) states including 5/2. Our highest-quality sample shows stripe and bubble phases in high Landau levels, and most importantly well-resolved FQH minima in the second Landau level. We report Arrhenius-type fits to the activated conductance, and find that σ0 agrees well with theory and existing Hall geometry data in the first Landau level, but not in the second Landau level. We will discuss the advantages the Corbino geometry could bring to various experiments designed to detect the non-Abelian entropy at 5/2, and our progress towards realizing those schemes. The results of these experiments could complement interferometry and other edge-based measurements by providing direct evidence for non-Abelian behaviour of the bulk quasiparticles. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under Contract DE-AC04-94AL8500.
ERIC Educational Resources Information Center
Desseyn, H. O.; And Others
1985-01-01
Compares linear-nonlinear and planar-nonplanar geometry through the valence-shell electron pairs repulsion (V.S.E.P.R.), Mulliken-Walsh, and electrostatic force theories. Indicates that although the V.S.E.P.R. theory has more advantages for elementary courses, an explanation of the best features of the different theories offers students a better…
NASA Astrophysics Data System (ADS)
Liu, Na; Miao, Wen-Dan; Song, Li-Hua; Duan, Chun-Gui
2015-10-01
Hadron production in semi-inclusive deep-inelastic scattering of leptons from nuclei is an ideal tool to determine and constrain the transport coefficient in cold nuclear matter. The leading-order computations for hadron multiplicity ratios are performed by means of the SW quenching weights and the analytic parameterizations of quenching weights based on BDMPS formalism. The theoretical results are compared to the HERMES positively charged pions production data with the quarks hadronization occurring outside the nucleus. With considering the nuclear geometry effect on hadron production, our predictions are in good agreement with the experimental measurements. The extracted transport parameter from the global fit is shown to be q ˆ = 0.74 ± 0.03 GeV2 /fm for the SW quenching weight without the finite energy corrections. As for the analytic parameterization of BDMPS quenching weight without the quark energy E dependence, the computed transport coefficient is q ˆ = 0.20 ± 0.02 GeV2 /fm. It is found that the nuclear geometry effect has a significant impact on the transport coefficient in cold nuclear matter. It is necessary to consider the detailed nuclear geometry in studying the semi-inclusive hadron production in deep inelastic scattering on nuclear targets.
NASA Technical Reports Server (NTRS)
Jones, D. L.; Poulose, P. K.; Liebowitz, H.
1976-01-01
The effect of subcritical crack growth on the geometry dependence of nonlinear fracture toughness parameters was studied by comparing the toughness values for different specimen geometries at the onset of subcritical crack growth and at the initiation of unstable crack propagation. Center-cracked thin sheet specimens of 2024-T3 and 7075-T6 aluminum alloys were tested by varying the specimen length L, width w, and crack length-to-width ratio c/w. When the onset of unstable crack propagation was selected as the critical point, the nonlinear energy toughness and the R curve toughness increased with increasing w and decreasing L and c/w. However, when the onset of subcritical crack growth was taken as the critical point, energy toughness and the linear toughness values were independent of these geometrical variables.
Baxamusa, S. Field, J.; Dylla-Spears, R.; Kozioziemski, B.; Suratwala, T.; Sater, J.
2014-03-28
Growth of high-quality single-crystal hydrogen in confined geometries relies on the in situ formation of seed crystals. Generation of deuterium-tritium seed crystals in a confined geometry is governed by three effects: self-heating due to tritium decay, external thermal environment, and latent heat of phase change at the boundary between hydrogen liquid and vapor. A detailed computation of the temperature profile for liquid hydrogen inside a hollow shell, as is found in inertial confinement fusion research, shows that seeds are likely to form at the equatorial plane of the shell. Radioactive decay of tritium to helium slowly alters the composition of the hydrogen vapor, resulting in a modified temperature profile that encourages seed formation at the top of the shell. We show that the computed temperature profile is consistent with a variety of experimental observations.
Volcano plumbing system geometry: The result of multi-parametric effects
NASA Astrophysics Data System (ADS)
Tibaldi, Alessandro
2014-05-01
Magma is transported from magma chambers towards the surface through networks of planar structures (intrusive sheets) spanning from vertical dikes to inclined sheets and horizontal sills. This study presents an overview of intrusive sheets at several volcanoes located in different settings in order to contribute to assess the factors controlling the geometry of magma plumbing systems. Data have been mainly acquired in the field and secondarily through a collection and analysis of geophysical publications; data include local lithology and tectonics of the substratum surrounding the volcano with special reference to local fault kinematics and related stress tensor, regional tectonics (general kinematics and far-field stress tensors), crustal thickness, geology and shape of the volcano, topographic setting, and characteristics of the plumbing system. Data from active volcanoes and eroded extinct volcanoes are discussed; the shallow plumbing system of active volcanoes has been reconstructed by combining available geophysical data with field information derived from outcropping sheets, morphometric analyses of pyroclastic cones, and the orientation and location of eruptive fissures. The study of eroded volcanoes enabled to assess the plumbing system geometry at lower levels in the core of the edifice or under the volcano-substratum interface. Key sites are presented in extensional, transcurrent and contractional tectonic settings, and different geodynamic areas have been investigated in North and South-America, Iceland, Southern Tyrrhenian Sea and Africa. The types of sheet arrangements that are illustrated include swarms of parallel dikes, diverging rift patterns, centrally-inclined sheets, radial dikes, bi-modal dike strikes, circum-lateral collapse sheets, and mixed members. This review shows that intrusive sheet emplacement at a volcano depends upon the combination of several local and regional factors, some of which are difficult to be constrained. While much
Experiments on Sphere Cylinder Geometry Dependence in the Electromagnetic Casimir Effect
NASA Astrophysics Data System (ADS)
Mukhopadhyay, Shomeek; Noruzifar, Ehsan; Wagner, Jeffrey; Zandi, Roya; Mohideen, Umar
2013-03-01
We report on ongoing experimental investigations on the geometry dependence of the electromagnetic Casimir force in the sphere-cylinder configuration. A gold coated hollow glass sphere which forms one surface is attached to a Silicon AFM cantilever. The cylinder, which is constructed from tapered optical fiber is also gold coated. The resonance frequency shift of the cantilever is measured as a function of the sphere-cylinder surface separation. The sphere-cylinder electrostatic force is used for alignment of the sphere and the cylinder and also for calibrating the system. The results are compared to numerical simulations in the framework of the Proximity Force Approximation (PFA).
Effects of flameholder geometry on emissions and performance of lean premixed combustors
NASA Technical Reports Server (NTRS)
Venkataramani, K. S.
1979-01-01
Emission levels and performance of twelve flameholder designs were investigated in a lean, premixed propane-air system at inlet conditions of 800K and 10 atm. The flameholder tested represents six design concepts with two values of blockage for each concept. The design concept consists of the following geometries: perforated plate, wire grid, single cone, multiple cone, vee gutter and swirl cone. Measurements were made at reference velocities of 35 m/s, 25 m/s and 20 m/s at combustor stations 10 cm and 30 cm downstream of the flameholder.
Lensless x-ray imaging in reflection geometry
Roy, S.; Parks, D.H.; Seu, K.A.; Turner, J.J.; Chao, W.; Anderson, E.H.; Cabrini, S.; Kevan, S.D.; Su, R.
2011-02-03
Lensless X-ray imaging techniques such as coherent diffraction imaging and ptychography, and Fourier transform holography can provide time-resolved, diffraction-limited images. Nearly all examples of these techniques have focused on transmission geometry, restricting the samples and reciprocal spaces that can be investigated. We report a lensless X-ray technique developed for imaging in Bragg and small-angle scattering geometries, which may also find application in transmission geometries. We demonstrate this by imaging a nanofabricated pseudorandom binary structure in small-angle reflection geometry. The technique can be used with extended objects, places no restriction on sample size, and requires no additional sample masking. The realization of X-ray lensless imaging in reflection geometry opens up the possibility of single-shot imaging of surfaces in thin films, buried interfaces in magnetic multilayers, organic photovoltaic and field-effect transistor devices, or Bragg planes in a single crystal.
Winter, T.C.; Pfannkuch, H.O.
1984-01-01
The interaction of lakes and groundwater is controlled partly by the geologic framework through which the water flows. Two interrelated geometric factors of the groundwater system that affect flow are overall geometry of the system, and anisotropy of the porous media within the system. Numerical simulation analysis was made for variations in the coefficient of anisotropy for each of several lake and groundwater settings having different geometric configurations. These analyses indicate that, for a given geometric setting, as the anisotropy of geologic materials decreases seepage from a lake decreases and depth of the local groundwater flow system associated with the lake increases. Transformation of scale of groundwater systems that have anisotropic media to isotropic equivalents results in a change in the overall geometry. Because of the different slopes of the water table and lakebed resulting from the scale transformations, a series of numerical experiments were made for various geometric configurations for a given anisotropy. These analyses indicate that as thickness of the groundwater system decreases, relative depth of the local flow system increases and seepage from the lake decreases. ?? 1984.
Effect of Weld Tool Geometry on Friction Stir Welded Ti-6Al-4V
NASA Technical Reports Server (NTRS)
Querin, Joseph A.; Schneider, Judy A.
2008-01-01
In this study, flat 0.250" thick Ti-6Al-4V panels were friction stir welded (FSWed) using weld tools with tapered pins. The five different pin geometries of the weld tools included: 0 degree (straight cylinder), 15 degree, 30 degree, 45 degree, and 60 degree angles on the frustum. All weld tools had a smooth 7 degree concave shoulder and were made from microwave sintered tungsten carbide. For each weld tool geometry, the FSW process parameters were optimized to eliminate internal defects. All the welds were produced in position control with a 2.5 degree lead angle using a butt joint configuration for the panels. The process parameters of spindle rpm and travel speed were varied, altering the hot working conditions imparted to the workpiece. Load cells on the FSWing machine allowed for the torque, the plunge force, and the plow force to be recorded during welding. Resulting mechanical properties were evaluated from tensile tests results of the FSWjoints. Variations in the material flow were investigated by use of microstructural analysis including optical microscopy (OM), scanning electron microscopy (SEM), and orientation image mapping (aIM).
The Effects of Magnetic-field Geometry on Longitudinal Oscillaitons of Solar Prominences
NASA Technical Reports Server (NTRS)
Luna, M.; Diaz, A. J.; Karpen, J.
2013-01-01
We investigate the influence of the geometry of the solar filament magnetic structure on the large-amplitude longitudinal oscillations. A representative filament flux tube is modeled as composed of a cool thread centered in a dipped part with hot coronal regions on either side.We have found the normal modes of the system and establish that the observed longitudinal oscillations are well described with the fundamental mode. For small and intermediate curvature radii and moderate to large density contrast between the prominence and the corona, the main restoring force is the solar gravity. In this full wave description of the oscillation a simple expression for the oscillation frequencies is derived in which the pressure-driven term introduces a small correction. We have also found that the normal modes are almost independent of the geometry of the hot regions of the tube. We conclude that observed large-amplitude longitudinal oscillations are driven by the projected gravity along the flux tubes and are strongly influenced by the curvature of the dips of the magnetic field in which the threads reside.
Effects of the geometry of the exit of a tube in an oscillating flow
NASA Astrophysics Data System (ADS)
Echeverría, Elia; Málaga, Carlos; Czitrom, Steven; Olvera, Arturo; Stern, Catalina
2014-11-01
The problem of optimizing the performance of a wave-driven seawater pump - comprising a resonant duct and an exhaust duct joined by a variable volume air-compression chamber - it is explored by studying oscillating flows at the exit of a tube. It is known that the performance of this pump depends on the geometry of the mouth of its intake tube. An inspection of the integral expression of the Navier-Stokes equation along a central streamline of this flow shows that changing the shape of the tube's mouth modifies only the inertia and energy losses terms because both depend on the flow field at the chosen streamline. These changes must be such that the integral relation is preserved. Therefore, by measuring the inertial term (known as added mass), the term for losses can be measured indirectly. We developed a method to measure the added mass for oscillating flows in tubes with different mouth shapes and compared these measurements with those obtained for a model of the flow through the pump. Our results suggest a way to find a criterion for choosing the geometry of the mouth of the tubes in order to minimize dissipation and improve efficiency of the pump. This work was supported by funds provided by DGAPA-UNAM (Project PAPITT-IN1188608).
Effect of geometry on concentration polarization in realistic heterogeneous permselective systems
NASA Astrophysics Data System (ADS)
Green, Yoav; Shloush, Shahar; Yossifon, Gilad
2014-04-01
This study extends previous analytical solutions of concentration polarization occurring solely in the depleted region, to the more realistic geometry consisting of a three-dimensional (3D) heterogeneous ion-permselective medium connecting two opposite microchambers (i.e., a three-layer system). Under the local electroneutrality approximation, the separation of variable methods is used to derive an analytical solution of the electrodiffusive problem for the two opposing asymmetric microchambers. The assumption of an ideal permselective medium allows for the analytic calculation of the 3D concentration and electric potential distributions as well as a current-voltage relation. It is shown that any asymmetry in the microchamber geometries will result in current rectification. Moreover, it is demonstrated that for non-negligible microchamber resistances, the conductance does not exhibit the expected saturation at low concentrations but instead shows a continuous decrease. The results are intended to facilitate a more direct comparison between theory and experiments, as now the voltage drop is across a realistic 3D and three-layer system.
Characterizing the Peano fluidic muscle and the effects of its geometry properties on its behavior
NASA Astrophysics Data System (ADS)
Veale, Allan Joshua; Xie, Sheng Quan; Anderson, Iain Alexander
2016-06-01
In this work, we explore the basic static and dynamic behavior of a hydraulically actuated Peano muscle and how its geometry affects key static and dynamic performance metrics. The Peano muscle, or pouch motor is a fluid powered artificial muscle. Similar to McKibben pneumatic artificial muscles (PAMs), it has the ability to generate the high forces of biological muscles with the low threshold pressure of pleated PAMs, but in a slim, easily distributed form. We found that Peano muscles have similar characteristics to other PAMs, but produce lower free-strains. A test rig capable of measuring high-speed flow rates with a Venturi tube revealed that their efficiency peaks at about 40% during highly dynamic movements. Peano muscles with more tubes and of a greater size do not move faster. Also, their muscle tubes should have an aspect ratio of at least 1:3 and channel width greater than 20% to maximize performance. These findings suggest that finite element modeling be used to optimize more complex Peano muscle geometries.
Effect of casting geometry on mechanical properties of two nickel-base superalloys
NASA Technical Reports Server (NTRS)
Johnston, J. R.; Dreshfield, R. L.; Collins, H. E.
1976-01-01
An investigation was performed to determine mechanical properties of two rhenium-free modifications of alloy TRW, and to evaluate the suitability of the alloy for use in a small integrally cast turbine rotor. The two alloys were initially developed using stress rupture properties of specimens machined from solid gas turbine blades. Properties in this investigation were determined from cast to size bars and bars cut from 3.8 by 7.6 by 17.8 cm blocks. Specimens machined from blocks had inferior tensile strength and always had markedly poorer rupture lives than cast to size bars. At 1,000 C the cast to size bars had shorter rupture lives than those machined from blades. Alloy R generally had better properties than alloy S in the conditions evaluated. The results show the importance of casting geometry on mechanical properties of nickel base superalloys and suggest that the geometry of a component can be simulated when developing alloys for that component.
NASA Astrophysics Data System (ADS)
Cembranos, J. A. R.; Dobado, A.; Maroto, A. L.
Extra-dimensional theories contain additional degrees of freedom related to the geometry of the extra space which can be interpreted as new particles. Such theories allow to reformulate most of the fundamental problems of physics from a completely different point of view. In this essay, we concentrate on the brane fluctuations which are present in brane-worlds, and how such oscillations of the own space-time geometry along curved extra dimensions can help to resolve the Universe missing mass problem. The energy scales involved in these models are low compared to the Planck scale, and this means that some of the brane fluctuations distinctive signals could be detected in future colliders and in direct or indirect dark matter searches.
Marocico, C. A.; Knoester, J.
2011-11-15
We use a Green's tensor method to investigate the spontaneous emission rate of a molecule and the energy-transfer rate between molecules placed in two types of layered geometries: a slab geometry and a planar waveguide. We focus especially on the role played by surface-plasmon polaritons in modifying the spontaneous emission and energy-transfer rates as compared to free space. In the presence of more than one interface, the surface-plasmon polariton modes split into several branches, and each branch can contribute significantly to modifying the electromagnetic properties of atoms and molecules. Enhancements of several orders of magnitude both in the spontaneous emission rate of a molecule and the energy-transfer rate between molecules are obtained and, by tuning the parameters of the geometry, one has the ability to control the range and magnitude of these enhancements. For the energy-transfer rate interference effects between contributions of different plasmon-polariton branches are observed as oscillations in the distance dependence of this rate.
NASA Astrophysics Data System (ADS)
Reshad Seighalani, K.; Besharati Givi, M. K.; Nasiri, A. M.; Bahemmat, P.
2010-10-01
Friction stir welding (FSW) parameters, such as tool material, tool geometry, tilt angle, tool rotational speed, welding speed, and axial force play a major role in the weld quality of titanium alloys. Because of excessive erosion, tool material and geometry play the main roles in FSW of titanium alloys. Therefore, in the present work for the first time, tool material and geometry, tool tilt angle, cooling system and shielding gas effects on macrostructure, microstructure, and mechanical properties of pure titanium weld joint were investigated. Result of this research shows that Ti can be joined by the FSW, using a tool with a shoulder made of tungsten (W) and simple pin made of tungsten carbide (WC). The best conditions for welding were use of compressed air as a cooling system, tool tilt angle of 1°, and a stream of Argon as a shielding medium. Investigation on mechanical properties shows that the tensile strength and the yield strength of the welded joint in the best case could be similar to the corresponding strengths of the base metal.
NASA Astrophysics Data System (ADS)
Wada, Ikuko; He, Jiangheng; Hasegawa, Akira; Nakajima, Junichi
2015-09-01
We develop a 3-D thermal model for the Northeast Japan subduction margin, using a realistic slab geometry for the subducting Pacific plate, and investigate the effects of oblique subduction and 3-D slab geometry on the mantle wedge flow pattern and the thermal structure. In the Tohoku region, the mantle wedge flow pattern is nearly two-dimensional resulting in a thermal structure similar to those obtained by a 2-D model, owing to the simple slab geometry and subduction nearly perpendicular to the margin. However, in Hokkaido, oblique subduction leads to 3-D mantle wedge flow with northerly inflow and west-northwestward outflow and also results in lower temperatures in the shallow part of the mantle wedge than in Tohoku due to lower sinking rate of the slab. Between Hokkaido and Tohoku, the slab has a hinge-like shape due to a relatively sharp change in the dip direction. In this hinge zone, northerly mantle inflow from Hokkaido and westerly mantle inflow from Tohoku converge, discouraging inflow from northwest and resulting in a cooler mantle wedge. The model-predicted mantle wedge flow patterns are consistent with observed seismic anisotropy and may explain the orientations of volcanic cross-chains. The predicted 3-D thermal structure correlates well with the along-arc variations in the location of the frontal arc volcanoes and help to provide new insights into the surface heat flow pattern and the down-dip extent of interplate earthquakes.
NASA Technical Reports Server (NTRS)
Polhamus, Edward C.
1996-01-01
This paper presents a survey of the effects of Reynolds number on the low- speed lift characteristics of wings encountering separated flows at their leading and side edges, with emphasis on the region near the stall. The influence of leading-edge profile and Reynolds number on the stall characteristics of two- dimensional airfoils are reviewed first to provide a basis for evaluating three- dimensional effects associated with various wing planforms. This is followed by examples of the effects of Reynolds number and geometry on the lift characteristics near the stall for a series of three-dimensional wings typical of those suitable for high-speed aircraft and missiles. Included are examples of the effects of wing geometry on the onset and spanwise progression of turbulent reseparation near the leading edge and illustrations of the degree to which simplified theoretical approaches can be useful in defining the influence of the various geometric parameters. Also illustrated is the manner in which the Reynolds number and wing geometry parameters influence whether the turbulent reseparation near the leading edge results in a sudden loss of lift, as in the two-dimensional case, or the formation of a leading-edge vortex with Rs increase in lift followed by a gentle stall as in the highly swept wing case. Particular emphasis is placed on the strong influence of 'induced camber' on the development of turbulent reseparation. R is believed that the examples selected for this report may be useful in evaluating viscous flow solutions by the new computational methods based on the Navier-Stokes equations as well as defining fruitful research areas for the high-Reynolds-number wind tunnels.
Sisniega, A.; Zbijewski, W.; Badal, A.; Kyprianou, I. S.; Stayman, J. W.; Vaquero, J. J.; Siewerdsen, J. H.
2013-01-01
Purpose: The proliferation of cone-beam CT (CBCT) has created interest in performance optimization, with x-ray scatter identified among the main limitations to image quality. CBCT often contends with elevated scatter, but the wide variety of imaging geometry in different CBCT configurations suggests that not all configurations are affected to the same extent. Graphics processing unit (GPU) accelerated Monte Carlo (MC) simulations are employed over a range of imaging geometries to elucidate the factors governing scatter characteristics, efficacy of antiscatter grids, guide system design, and augment development of scatter correction. Methods: A MC x-ray simulator implemented on GPU was accelerated by inclusion of variance reduction techniques (interaction splitting, forced scattering, and forced detection) and extended to include x-ray spectra and analytical models of antiscatter grids and flat-panel detectors. The simulator was applied to small animal (SA), musculoskeletal (MSK) extremity, otolaryngology (Head), breast, interventional C-arm, and on-board (kilovoltage) linear accelerator (Linac) imaging, with an axis-to-detector distance (ADD) of 5, 12, 22, 32, 60, and 50 cm, respectively. Each configuration was modeled with and without an antiscatter grid and with (i) an elliptical cylinder varying 70–280 mm in major axis; and (ii) digital murine and anthropomorphic models. The effects of scatter were evaluated in terms of the angular distribution of scatter incident upon the detector, scatter-to-primary ratio (SPR), artifact magnitude, contrast, contrast-to-noise ratio (CNR), and visual assessment. Results: Variance reduction yielded improvements in MC simulation efficiency ranging from ∼17-fold (for SA CBCT) to ∼35-fold (for Head and C-arm), with the most significant acceleration due to interaction splitting (∼6 to ∼10-fold increase in efficiency). The benefit of a more extended geometry was evident by virtue of a larger air gap—e.g., for a 16 cm
Experimental study of effect of stenosis geometry on pressure loss for periodic flow
NASA Astrophysics Data System (ADS)
Veselý, Ondřej; Nováková, Ludmila; Adamec, Josef
2016-03-01
A stenosis is a narrowing in a tubular organ. In medicine, vessel stenosis poses health risk for people. In the last work, experimental investigation of pressure loss coefficient for varying stenosis eccentricity and shape for steady flow were performed. In this work, experimental investigation of pressure loss for varying stenosis eccentricity and shape under periodic flow were performed. Four models of different geometry were studied, two models are axisymmetric stenoses and two models are eccentric stenoses. All models were stenosis of 75% area reduction. The periodic flow, generated by a controllable pump, has sinus shape in an inlet. The measuring range of medium Reynolds number was from 500 to 1500, range of ratio between an amplitude and medium flow rate was from 0.2 to 0.6 and range of frequency was from 0.2 to 1 Hz. The pressure loss for each conditions was quantified by mean value, amplitude and phase shift against flow rate.
Effect of reentrant cone geometry on energy transport in intense laser-plasma interactions
Lancaster, K. L.; Sherlock, M.; Heathcote, R.; Green, J. S.; Norreys, P. A.; Gregory, C. D.; Hakel, P.; Akli, K. U.; Hey, D. S.; Stephens, R. B.; Beg, F. N.; Chen, S. N.; Wei, M. S.; Yabuuchi, T.; Freeman, R. R.; Highbarger, K.; Van Woerkom, L.; Weber, R. L.; Habara, H.; Key, M. H.
2009-10-15
The energy transport in cone-guided low-Z targets has been studied for laser intensities on target of 2.5x10{sup 20} W cm{sup -2}. Extreme ultraviolet (XUV) imaging and transverse optical shadowgraphy of the rear surfaces of slab and cone-slab targets show that the cone geometry strongly influences the observed transport patterns. The XUV intensity showed an average spot size of 65{+-}10 {mu}m for slab targets. The cone slabs showed a reduced spot size of 44{+-}10 {mu}m. The shadowgraphy for the aforementioned shots demonstrate the same behavior. The transverse size of the expansion pattern was 357{+-}32 {mu}m for the slabs and reduced to 210{+-}30 {mu}m. A transport model was constructed which showed that the change in transport pattern is due to suppression of refluxing electrons in the material surrounding the cone.
Postlethwaite, J.; Nesic, S. . Dept of Chemical Engineering)
1993-10-01
Erosion rates were measured along the length of a tubular flow cell of type 304 (UNS S30400) stainless steel (SS) carrying dilute slurries of silica sand (0.43 mm diam) and smooth glass beads of a similar size. The segmented test cell contained a sudden constriction, a sudden expansion, and a groove to produce disturbed flow conditions. Erosion rates were reduced by changes in the cell wall geometry that resulted from erosion at positions of high local metal loss and from erosion further downstream because of the reduction in turbulence and particle dispersion. Smoothing of the sand particles in the test system halved the erosion rates; however, reduced erosion rates obtained with the sand were 2 orders of magnitude higher than those produced with the glass beads. This difference was attributed to surface microroughness of the particles.
Computational studies of flow through cross flow fans - effect of blade geometry
NASA Astrophysics Data System (ADS)
Govardhan, M.; Sampat, D. Lakshmana
2005-09-01
This present paper describes three dimensional computational analysis of complex internal flow in a cross flow fan. A commercial computational fluid dynamics (CFD) software code CFX was used for the computation. RNG k-ɛ two equation turbulence model was used to simulate the model with unstructured mesh. Sliding mesh interface was used at the interface between the rotating and stationary domains to capture the unsteady interactions. An accurate assessment of the present investigation is made by comparing various parameters with the available experimental data. Three impeller geometries with different blade angles and radius ratio are used in the present study. Maximum energy transfer through the impeller takes place in the region where the flow follows the blade curvature. Radial velocity is not uniform through blade channels. Some blades work in turbine mode at very low flow coefficients. Static pressure is always negative in and around the impeller region.
Effect of nozzle geometry on the performance of laser ablative propulsion thruster
NASA Astrophysics Data System (ADS)
Li, Long; Jiao, Long; Tang, Zhiping; Hu, Xiaojun; Peng, Jie
2016-05-01
The performance of "ablation mode" laser propulsion thrusters can be improved obviously by nozzle constraint. The nozzle geometry of "ablation mode" laser propulsion thrusters has been studied experimentally with CO2 lasers. Experimental results indicate that the propulsion performance of cylindrical nozzle thrusters is better than expansionary nozzle thrusters at the same lengths. The cylindrical nozzle thrusters were optimized by different laser energies. The results show that two important factors, the length-to-diameter ratio α and the thruster diameter to laser-spot diameter ratio β, affect the propulsion performance of the thruster obviously. The momentum coupling coefficient C m increases with the increase of α, while C m increases at first and then decreases with the increase of β.
Effect of geometry on the nose-region flow-field of shuttle entry-configurations
NASA Technical Reports Server (NTRS)
Bertin, J. J.; Faria, H. T.
1973-01-01
In order to determine the convective heat-transfer distribution for the nose region of the space shuttle entry configurations, a three-dimensional flow-field is described which may include extensive regions of separated flow. Because of the complexity of the flow field for the nose region, experimental data are needed to define the relation between the nose geometry and the resultant flow field. According to theoretical solutions of the three-dimensional boundary layer, the boundary layer separates from the leeward generator of a blunted cone at an alpha equal to the cone half-angle. Separation results from the transverse pressure gradient, i.e., the velocity derivative due to crossflow. The boundary layer limiting streamlines converge toward the singular point of sep aration. The separated region is bounded by an ordinary line of separation.
Keller, K S; Olsson, M H M; Yang, M; Stipp, S L S
2015-04-01
Molecular dynamics (MD) simulations were used to explore adsorption on calcite, from a 1:1 mixture of ethanol and water, on planar {10.4} and stepped, i.e. vicinal, surfaces. Varying the surface geometry resulted in different adsorption patterns, which would directly influence the ability of ethanol to control calcite crystal growth, dissolution, and adsorption/desorption of other ions and molecules. Ethanol forms a well-ordered adsorbed layer on planar faces and on larger terraces, such as between steps and defects, providing little chance for water, with its weaker attachment, to displace it. However, on surfaces with steps, adsorption affinity depends on the length of the terraces between the steps. Long terraces allow ethanol to form a well-ordered, hydrophobic layer, but when step density is high, ethanol adsorption is less ordered, allowing water to associate at and near the steps and even displacing pre-existing ethanol. Water adsorbed at steps forms mass transport pathways between the bulk solution and the solid surface. Our simulations confirm the growth inhibiting properties of ethanol, also explaining how certain crystal faces are more stabilized because of their surface geometry. The -O(H) functional group on ethanol forms tight bonds with calcite; the nonpolar, -CH3 ends, which point away from the surface, create a hydrophobic layer that changes surface charge, thus wettability, and partly protects calcite from precipitation and dissolution. These tricks could easily be adopted by biomineralizing organisms, allowing them to turn on and off crystal growth. They undoubtedly also play a role in the wetting properties of mineral surfaces in commercial CaCO3 manufacture, oil production, and contamination remediation. PMID:25790337
Effect of growth plate geometry and growth direction on prediction of proximal femoral morphology.
Yadav, Priti; Shefelbine, Sandra J; Gutierrez-Farewik, Elena M
2016-06-14
Mechanical stimuli play a significant role in the process of endochondral growth. Thus far, approaches to understand the endochondral mechanical growth rate have been limited to the use of approximated location and geometry of the growth plate. Furthermore, growth has been simulated based on the average deflection of the growth plate or of the femoral neck. It has also been reported in the literature that the growth plate lies parallel to one of the principal stresses acting on it, to reduce the shear between epiphysis and diaphysis. Hence the current study objectives were (1) to evaluate the significance of a subject-specific finite element model of the femur and growth plate compared to a simplified growth plate model and (2) to explore the different growth direction models to better understand proximal femoral growth mechanisms. A subject-specific finite element model of an able-bodied 7-year old child was developed. The muscle forces and hip contact force were computed for one gait cycle and applied to a finite element model to determine the specific growth rate. Proximal femoral growth was simulated for two different growth direction models: femoral neck deflection direction and principal stress direction. The principal stress direction model captured the expected tendency for decreasing the neck shaft angle and femoral anteversion for both growth plate models. The results of this study suggest that the subject-specific geometry and consideration of the principal stress direction as growth direction may be a more realistic approach for correct prediction of proximal femoral growth morphology. PMID:27063249
Dietary Pseudopurpurin Effects on Bone Mineral Density and Bone Geometry Architecture in Rats
Wu, Chen-Chen; Li, Xiao-Bing; Han, Tie-Suo; Li, Peng; Liu, Guo-Wen; Wang, Wei-Zhong; Wang, Zhe
2012-01-01
The objective of our study was to evaluate whether feeding pseudopurpurin affects bone mineral density and bone geometry architecture in rats. Pseudopurpurin was extracted, analyzed and purified using an HLPC-ESI-MS. Rats were given 0% and 0.5% pseudopurpurin powder in their diet. Femurs of rats were examined at 0.5, 1 and 2 months after pseudopurpurin feeding. Compared with rats in the group 0%, the bone mineral density, and the calcium, magnesium, zinc and manganese concentrations in the rats femur in the group 0.5% increased significantly at 1 month and 2 months after pseudopurpurin feeding. Analytical results of micro-computed tomography showed that the group 0.5% displayed an increase in the trabecular volume fraction, trabecular thickness and trabecular number of the distal femur at 1 and 2 months after pseudopurpurin feeding, and the mean thickness, inner perimeter, outer perimeter, and area of the femur diaphysis were significantly increased at 2 months after pseudopurpurin feeding compared with the group 0%. In parallel, the trabecular separation and structure model index of the distal femur were decreased, compared with the group 0% at 1 and 2 months after pseudopurpurin feeding. In the 0.5% and 0% groups, there was no damage to kidney and liver by histopathology analysis. The long-term feeding of pseudopurpurin is safe for rats. The feeding of 0.5% pseudopurpurin which has specific chemical affinities for calcium for bone improvement and level of bone mineral density, enhances the geometry architecture compared with the 0% group. PMID:22489160
Open Rotor Aeroacoustic Installation Effects for Conventional and Unconventional Airframes
NASA Technical Reports Server (NTRS)
Czech, Michael J.; Thomas, Russell H.
2013-01-01
As extensive experimental campaign was performed to study the aeroacoustic installation effects of an open rotor with respect to both a conventional tube and wing type airframe and an unconventional hybrid wing body airframe. The open rotor rig had two counter rotating rows of blades each with eight blades of a design originally flight tested in the 1980s. The aeroacoustic installation effects measured in an aeroacoustic wind tunnel included those from flow effects due to inflow distortion or wake interaction and acoustic propagation effects such as shielding and reflection. The objective of the test campaign was to quantify the installation effects for a wide range of parameters and configurations derived from the two airframe types. For the conventional airframe, the open rotor was positioned in increments in front of and then over the main wing and then in positions representative of tail mounted aircraft with a conventional tail, a T-tail and a U-tail. The interaction of the wake of the open rotor as well as acoustic scattering results in an increase of about 10 dB when the rotor is positioned in front of the main wing. When positioned over the main wing a substantial amount of noise reduction is obtained and this is also observed for tail-mounted installations with a large U-tail. For the hybrid wing body airframe, the open rotor was positioned over the airframe along the centerline as well as off-center representing a twin engine location. A primary result was the documentation of the noise reduction from shielding as a function of the location of the open rotor upstream of the trailing edge of the hybrid wing body. The effects from vertical surfaces and elevon deflection were also measured. Acoustic lining was specially designed and inserted flush with the elevon and airframe surface, the result was an additional reduction in open rotor noise propagating to the far field microphones. Even with the older blade design used, the experiment provided
NASA Astrophysics Data System (ADS)
Yellowhair, Julius; Ho, Clifford K.; Ortega, Jesus D.; Christian, Joshua M.; Andraka, Charles E.
2015-09-01
Concentrating solar power receivers are comprised of panels of tubes arranged in a cylindrical or cubical shape on top of a tower. The tubes contain heat-transfer fluid that absorbs energy from the concentrated sunlight incident on the tubes. To increase the solar absorptance, black paint or a solar selective coating is applied to the surface of the tubes. However, these coatings degrade over time and must be reapplied, which reduces the system performance and increases costs. This paper presents an evaluation of novel receiver shapes and geometries that create a light-trapping effect, thereby increasing the effective solar absorptance and efficiency of the solar receiver. Several prototype shapes were fabricated from Inconel 718 and tested in Sandia's solar furnace at an irradiance of ~30 W/cm2. Photographic methods were used to capture the irradiance distribution on the receiver surfaces. The irradiance profiles were compared to results from raytracing models. The effective solar absorptance was also evaluated using the ray-tracing models. Results showed that relative to a flat plate, the new geometries could increase the effective solar absorptance from 86% to 92% for an intrinsic material absorptance of 86%, and from 60% to 73% for an intrinsic material absorptance of 60%.
ERIC Educational Resources Information Center
Al-ebous, Tahani
2016-01-01
This study aimed to investigate the effect of the van Hiele model in Geometric Concepts Acquisition, and the attitudes towards Geometry and learning transfer of the first three grades students in Jordan. Participants of the study consisted of 60 students from the third grade primary school students from the First Directorate, Amman, in the…
NASA Technical Reports Server (NTRS)
Weller, W. H.
1979-01-01
Wind-tunnel tests of an aeroelastically designed helicopter rotor model were carried out to determine the effects on dynamic response and aerodynamic performance of varying the design of the outboard 8 percent of the blade lengths. Four different blade tip geometries or shapes having different amounts of planform sweep, thickness and chordwise taper, and anhedral angle were studied. Each configuration was tested at several shaft angles of attack for advance ratios of 0.20, 0.30, 0.35, and 0.40. For each combination of shaft angle and advance ratio, rotor lift was varied over a wide range to include high lift conditions.
NASA Technical Reports Server (NTRS)
Jegley, Dawn C.
1993-01-01
The behavior of thin laminated flat and curved panels subjected to transverse pressure and inplane loads is considered. The effects of panel geometry, boundary conditions and laminate stacking sequence on the response of panels subjected to transverse pressure loads up to 12.4 N/sq cm is presented. The response of thin laminated panels is evaluated analytically and selected results are compared with test data. A parametric study of the deformation and strain responses of panels with radius of curvature ranging from 20 to 305 cm is presented. The combination of inplane tensile and pressure loads is also considered.
NASA Technical Reports Server (NTRS)
Malila, W. A.; Gleason, J. M.; Cicone, R. C.
1976-01-01
A simulation study was carried out to characterize atmospheric effects in LANDSAT-D Thematic Mapper data. In particular, the objective was to determine if any differences would result from using a linear vs. a conical scanning geometry. Insight also was gained about the overall effect of the atmosphere on Thematic Mapper signals, together with the effects of time of day. An added analysis was made of the geometric potential for direct specular reflections (sun glint). The ERIM multispectral system simulation model was used to compute inband Thematic Mapper radiances, taking into account sensor, atmospheric, and surface characteristics. Separate analyses were carried out for the thermal band and seven bands defined in the reflective spectral region. Reflective-region radiances were computed for 40 deg N, 0 deg, and 40 deg S latitudes; June, Mar., and Dec. days; and 9:30 and 11:00 AM solar times for both linear and conical scan modes. Also, accurate simulations of solar and viewing geometries throughout Thematic Mapper orbits were made. It is shown that the atmosphere plays an important role in determining Thematic Mapper radiances, with atmospheric path radiance being the major component of total radiances for short wavelengths and decreasing in importance as wavelength increases. Path radiance is shown to depend heavily on the direct radiation scattering angle and on haze content. Scan-angle-dependent variations were shown to be substantial, especially for the short-wavelength bands.
Simulating the effects of stellarator geometry on gyrokinetic drift-wave turbulence
NASA Astrophysics Data System (ADS)
Baumgaertel, Jessica Ann
Nuclear fusion is a clean, safe form of energy with abundant fuel. In magnetic fusion energy (MFE) experiments, the plasma fuel is confined by magnetic fields at very high temperatures and densities. One fusion reactor design is the non-axisymmetric, torus-shaped stellarator. Its fully-3D fields have advantages over the simpler, better-understood axisymmetric tokamak, including the ability to optimize magnetic configurations for desired properties, such as lower transport (longer confinement time). Turbulence in the plasma can break MFE confinement. While turbulent transport is known to cause a significant amount of heat loss in tokamaks, it is a new area of research in stellarators. Gyrokinetics is a good mathematical model of the drift-wave instabilities that cause turbulence. Multiple gyrokinetic turbulence codes that had great success comparing to tokamak experiments are being converted for use with stellarator geometry. This thesis describes such adaptations of the gyrokinetic turbulence code, GS2. Herein a new computational grid generator and upgrades to GS2 itself are described, tested, and benchmarked against three other gyrokinetic codes. Using GS2, detailed linear studies using the National Compact Stellarator Experiment (NCSX) geometry were conducted. The first compares stability in two equilibria with different β=(plasma pressure)/(magnetic pressure). Overall, the higher β case was more stable than the lower β case. As high β is important for MFE experiments, this is encouraging. The second compares NCSX linear stability to a tokamak case. NCSX was more stable with a 20% higher critical temperature gradient normalized by the minor radius, suggesting that the fusion power might be enhanced by ˜ 50%. In addition, the first nonlinear, non-axisymmetric GS2 simulations are presented. Finally, linear stability of two locations in a W7-AS plasma were compared. The experimentally-measured parameters used were from a W7-AS shot in which measured heat fluxes
Geometry effects in the magnetoconductance of normal and Andreev Sinai billiards
NASA Astrophysics Data System (ADS)
Fytas, Nikolaos G.
2016-06-01
We study the transport properties of low-energy (quasi)particles ballistically traversing normal and Andreev two-dimensional open cavities with a Sinai-billiard shape. We consider four different geometrical setups and focus on the dependence of transport on the strength of an applied magnetic field. By solving the classical equations of motion for each setup we calculate the magnetoconductance in terms of transmission and reflection coefficients for both the normal and Andreev versions of the billiard, calculating in the latter the critical field value above which the outgoing current of holes becomes zero.
Zhou, Yufeng; Zhong, Pei
2006-06-01
A theoretical model for the propagation of shock wave from an axisymmetric reflector was developed by modifying the initial conditions for the conventional solution of a nonlinear parabolic wave equation (i.e., the Khokhlov-Zabolotskaya-Kuznestsov equation). The ellipsoidal reflector of an HM-3 lithotripter is modeled equivalently as a self-focusing spherically distributed pressure source. The pressure wave form generated by the spark discharge of the HM-3 electrode was measured by a fiber optic probe hydrophone and used as source conditions in the numerical calculation. The simulated pressure wave forms, accounting for the effects of diffraction, nonlinearity, and thermoviscous absorption in wave propagation and focusing, were compared with the measured results and a reasonably good agreement was found. Furthermore, the primary characteristics in the pressure wave forms produced by different reflector geometries, such as that produced by a reflector insert, can also be predicted by this model. It is interesting to note that when the interpulse delay time calculated by linear geometric model is less than about 1.5 micros, two pulses from the reflector insert and the uncovered bottom of the original HM-3 reflector will merge together. Coupling the simulated pressure wave form with the Gilmore model was carried out to evaluate the effect of reflector geometry on resultant bubble dynamics in a lithotripter field. Altogether, the equivalent reflector model was found to provide a useful tool for the prediction of pressure wave form generated in a lithotripter field. This model may be used to guide the design optimization of reflector geometries for improving the performance and safety of clinical lithotripters. PMID:16838506
Zhou, Yufeng; Zhong, Pei
2007-01-01
A theoretical model for the propagation of shock wave from an axisymmetric reflector was developed by modifying the initial conditions for the conventional solution of a nonlinear parabolic wave equation (i.e., the Khokhlov–Zabolotskaya–Kuznestsov equation). The ellipsoidal reflector of an HM-3 lithotripter is modeled equivalently as a self-focusing spherically distributed pressure source. The pressure wave form generated by the spark discharge of the HM-3 electrode was measured by a fiber optic probe hydrophone and used as source conditions in the numerical calculation. The simulated pressure wave forms, accounting for the effects of diffraction, nonlinearity, and thermoviscous absorption in wave propagation and focusing, were compared with the measured results and a reasonably good agreement was found. Furthermore, the primary characteristics in the pressure wave forms produced by different reflector geometries, such as that produced by a reflector insert, can also be predicted by this model. It is interesting to note that when the interpulse delay time calculated by linear geometric model is less than about 1.5 μs, two pulses from the reflector insert and the uncovered bottom of the original HM-3 reflector will merge together. Coupling the simulated pressure wave form with the Gilmore model was carried out to evaluate the effect of reflector geometry on resultant bubble dynamics in a lithotripter field. Altogether, the equivalent reflector model was found to provide a useful tool for the prediction of pressure wave form generated in a lithotripter field. This model may be used to guide the design optimization of reflector geometries for improving the performance and safety of clinical lithotripters. PMID:16838506
NASA Technical Reports Server (NTRS)
Sadler, S. G.
1972-01-01
A mathematical model and computer program were implemented to study the main rotor free wake geometry effects on helicopter rotor blade air loads and response in steady maneuvers. The theoretical formulation and analysis of results are presented.
Nozzle geometry and injection duration effects on diesel sprays measured by x-ray radiography.
Kastengren, A. L.; Powell, C. F.; Riedel, T.; Cheong, S.-K.; Im, K.-S.; Liu, X.; Wang, Y. J.; Wang, J.; Robert Bosch GmbH
2008-04-01
X-ray radiography was used to measure the behavior of four fuel sprays from a light-duty common-rail diesel injector. The sprays were at 250 bar injection pressure and 1 bar ambient pressure. Injection durations of 400 {micro}s and 1000 {micro}s were tested, as were axial single-hole nozzles with hydroground and nonhydroground geometries. The X-ray data provide quantitative measurements of the internal mass distribution of the spray, including near the injector orifice. Such measurements are not possible with optical diagnostics. The 400 {micro}s sprays from the hydroground and nonhydroground nozzles appear qualitatively similar. The 1000 {micro}s spray from the nonhydroground nozzle has a relatively consistent moderate width, while that from the hydroground nozzle is quite wide before transitioning into a narrow jet. The positions of the leading- and trailing-edges of the spray have also been determined, as has the amount of fuel residing in a concentrated structure near the leading edge of the spray.
Jamison, Ryan D.; Shen, Y. -L.
2015-03-19
Two finite element models are used to investigate the behavior of aluminum/silicon carbide thin-film layered composites with imperfect internal geometry when subjected to various loadings. In both models, undulating layers are represented by regular waveforms with various amplitudes, wavelengths, and phase offsets. First, uniaxial compressive loading of the composite is considered. The modulus and stress/strain response of the composite is sensitive to both loading direction and frequency of the undulation. Second, the nanoindentation response of the composite is investigated. The derived hardness and modulus are shown to be sensitive to the presence of undulating layers and the relative size ofmore » the indenter to the undulation. Undulating layers create bands of tensile and compressive stress in the indentation direction that are significantly different from the flat layers. The amount of equivalent plastic strain in the Al layers is increased by the presence of undulating layers. The correlations between the two forms of loading, and the implications to composite property measurement are carefully examined in this study.« less
NASA Astrophysics Data System (ADS)
Han, Shaobing; Zhong, Jingjun; Lu, Huawei; Kan, Xiaoxu; Yang, Ling
2014-08-01
An experimental study is conducted to investigate the influences of blade tip winglet on the flow field of a compressor cascade. The tests are performed in a low speed linear cascade with stationary endwall, with three blade tip configurations, including the baseline tip, the suction-side winglet tip and the pressure-side winglet tip. The flowfield downstream of the cascade is measured using five-hole probe, from which the three-dimensional velocity field, vorticity field and pressure field are obtained. Static pressure measurements are made on the endwall above the blade row using pressure taps embedded in the plywood endwall. All measurements are made at both design and off-design conditions for tip clearance level of about 2 percent of the blade chord. The results revealed the incidence variation significantly affects the secondary flow and the associated loss field downstream of the cascade, where the tip leakage vortex and passage vortex exist as the major contributors on the field. The winglet geometry arrangements can change the trajectory of the tip leakage vortex. The suction-side winglet tip blade provides a lower overall total pressure loss coefficient when compared to the baseline tip blade and pressure-side winglet tip blade at all incidence angles.
Jamison, Ryan D.; Shen, Y. -L.
2015-03-19
Two finite element models are used to investigate the behavior of aluminum/silicon carbide thin-film layered composites with imperfect internal geometry when subjected to various loadings. In both models, undulating layers are represented by regular waveforms with various amplitudes, wavelengths, and phase offsets. First, uniaxial compressive loading of the composite is considered. The modulus and stress/strain response of the composite is sensitive to both loading direction and frequency of the undulation. Second, the nanoindentation response of the composite is investigated. The derived hardness and modulus are shown to be sensitive to the presence of undulating layers and the relative size of the indenter to the undulation. Undulating layers create bands of tensile and compressive stress in the indentation direction that are significantly different from the flat layers. The amount of equivalent plastic strain in the Al layers is increased by the presence of undulating layers. The correlations between the two forms of loading, and the implications to composite property measurement are carefully examined in this study.
Effect of electrode geometry on high energy spark discharges in air
NASA Astrophysics Data System (ADS)
Belmouss, Mounia
The government, aerospace, and transportation industries are deeply invested in developing new technologies to improve the performance and maneuverability of current and future aircraft while reducing aerodynamic noise and environmental impact. One of the key pathways to meet these goals is through aerodynamic flow control, which can involve suppressing or inducing separation, transition and management of turbulence in boundary layers, increasing the lift and reducing the drag of airfoils, and gas mixing to control fluctuating forces and aerodynamic noise [1]. In this dissertation, the complex flow field following a spark discharge is studied for a range of geometries and discharge characteristics, and the possibilities for using the induced flow for aerodynamic control are assessed. This work shows the influence of the electrode configuration on the fluid dynamics following the spark discharge and how the hot gas evolution gives rise to various physical phenomena (i.e. generation of turbulence, inducing vorticity, and gas mixing) that can be used to modify the flow-field structure near the boundary layer on an aerodynamic surface.
Geometry effects on STOL engine-over-the-wing acoustics with 5.1 slot nozzles
NASA Technical Reports Server (NTRS)
Vonglahn, U.; Groesbeck, D.
1975-01-01
The correspondence of far field acoustic trends with changes in the characteristics of the flow field at the wing trailing edge caused by alterations in the nozzle-wing geometry were determined for several STOL-OTW configurations. Nozzle roof angles of 10 to 40 deg were tested with and without cutback of the nozzle sidewalls. Three wing chord sizes were used: baseline (33 cm with flaps retracted), 2/3-baseline, and 3/2-baseline. Flap deflection angles of 20 and 60 deg were used. The nozzle locations were at 21 and 46-percent of chord. With increasing wing size the jet noise shielding benefits increased. With increasing nozzle roof angle, the jet velocity at the trailing edge was decreased, causing a decrease in trailing-edge and fluctuating lift noise. Cutback of the nozzle sides improved flow attachment and reduced far-field noise. The best flow attachment and least trailing-edge noise generally were obtained with a 40 deg external deflector configuration and a cutback nozzle with a 40 deg roof angle.
NASA Technical Reports Server (NTRS)
Zernicke, R. F.; Li, K.-C.; Salem, G. J.; Vailas, A. C.; Grindeland, R. E.
1990-01-01
An investigation was conducted to generate comparative data on the sensitivity of cortical- and vertebral-bone adaptations in two different rat strains maintained at conditions typical for spaceborne experiments conducted by U.S.A. and USSR. The effects of cage environment, diet, and rat-strain on the cortical (humerus) and vertebral (T7) bones of male Taconic-Sprague-Dawley and Czechoslovakian-Wistar rats were investigated using different flight-simulation cages (one rat/cage for U.S.A.; ten rats/cage for USSR conditions) and fed either U.S.A. or USSR diet. The results showed significant effects of these factors on the humeral and vertebral geometry and mechanical properties, as well as significant interactive effects on the mechanical properties of the humerus.
NASA Astrophysics Data System (ADS)
Park, Kyungwha; Barraza-Lopez, Salvador; García-Suárez, Víctor M.; Ferrer, Jaime
2010-03-01
We examine theoretically coherent electron transport through the single-molecule magnet Mn12 , bridged between Au(111) electrodes, using the nonequilibrium Green’s function method and the density-functional theory. We analyze the effects of bonding type, molecular orientation, and geometry relaxation on the electronic properties and charge and spin transport across the single-molecule junction. We consider nine interface geometries leading to five bonding mechanisms and two molecular orientations: (i) Au-C bonding, (ii) Au-Au bonding, (iii) Au-S bonding, (iv) Au-H bonding, and (v) physisorption via van der Waals forces. The two molecular orientations of Mn12 correspond to the magnetic easy axis of the molecule aligned perpendicular [hereafter denoted as orientation (1)] or parallel [orientation (2)] to the direction of electron transport. We find that the electron transport is carried by the lowest unoccupied molecular orbital (LUMO) level in all the cases that we have simulated. Relaxation of the junction geometries mainly shifts the relevant occupied molecular levels toward the Fermi energy as well as slightly reduces the broadening of the LUMO level. As a result, the current slightly decreases at low bias voltage. Our calculations also show that placing the molecule in the orientation (1) broadens the LUMO level much more than in the orientation (2) due to the internal structure of the Mn12 . Consequently, junctions with the former orientation yield a higher current than those with the latter. Among all of the bonding types considered, the Au-C bonding gives rise to the highest current (about one order of magnitude higher than the Au-S bonding), for a given distance between the electrodes. The current through the junction with other bonding types decreases in the order of Au-Au, Au-S, and Au-H. Importantly, the spin-filtering effect in all the nine geometries stays robust and their ratios of the majority-spin to the minority-spin transmission coefficients are
Hu, Jian; Tanabe, Masahiro; Sato, Jun; Uosaki, Kohei; Ikeda, Katsuyoshi
2014-07-23
Surface enhanced Raman scattering (SERS) spectra of organic monolayers were measured on various types of polycrystalline and single crystalline Pt substrates with nanometric or atomic surface features, including heteroepitaxial Pt monolayers, using sphere-plane type nanogap structures. Although atomic geometry and electronic structures of a metal surface significantly influence metal-molecule interactions, such effects are often hindered in conventional SERS measured on a roughened surface because of the spectral information averaging at various adsorption sites. In this study, the use of atomically defined Pt surfaces revealed detailed surface effects; the observed preferential adsorption geometry on each surface was well explained by atomic surface arrangements. The peak shift of the intramolecular vibration in the anchor group was in good agreement with the variation of the d-band center of Pt substrates. Moreover, in electrochemical SERS study the Stark shift of an extramolecular vibrational mode at around 400 cm(-1), which is not accessible in infrared absorption spectroscopy, was monitored on an atomically defined heteroepitaxial Pt monolayer electrode. PMID:24802029
LI, BO; SUN, HUI; ZHOU, SHENGGAO
2015-01-01
The solute-solvent interface that separates biological molecules from their surrounding aqueous solvent characterizes the conformation and dynamics of such molecules. In this work, we construct a solvent fluid dielectric boundary model for the solvation of charged molecules and apply it to study the stability of a model cylindrical solute-solvent interface. The motion of the solute-solvent interface is defined to be the same as that of solvent fluid at the interface. The solvent fluid is assumed to be incompressible and is described by the Stokes equation. The solute is modeled simply by the ideal-gas law. All the viscous force, hydrostatic pressure, solute-solvent van der Waals interaction, surface tension, and electrostatic force are balanced at the solute-solvent interface. We model the electrostatics by Poisson’s equation in which the solute-solvent interface is treated as a dielectric boundary that separates the low-dielectric solute from the high-dielectric solvent. For a cylindrical geometry, we find multiple cylindrically shaped equilibrium interfaces that describe polymodal (e.g., dry and wet) states of hydration of an underlying molecular system. These steady-state solutions exhibit bifurcation behavior with respect to the charge density. For their linearized systems, we use the projection method to solve the fluid equation and find the dispersion relation. Our asymptotic analysis shows that, for large wavenumbers, the decay rate is proportional to wavenumber with the proportionality half of the ratio of surface tension to solvent viscosity, indicating that the solvent viscosity does affect the stability of a solute-solvent interface. Consequences of our analysis in the context of biomolecular interactions are discussed. PMID:26877555
NASA Astrophysics Data System (ADS)
Ruesch, O.; Hiesinger, H.; Cloutis, E.; Le Corre, L.; Kallisch, J.; Mann, P.; Markus, K.; Metzler, K.; Nathues, A.; Reddy, V.
2015-09-01
The howardite, eucrite and diogenite (HED) meteorites are genetically related and represent the most voluminous group of achondrites. They are the closest analog materials to Vesta and V-type asteroids. Many of these meteorites were the focus of intense petrologic and visible to near infrared spectral studies. As ground-based and orbital observations of basaltic asteroids have increased, an improved understanding of HEDs is needed. For this study, we investigated 24 HED samples, mainly new finds from Northwest Africa (NWA). Visible to near infrared (up to 2.5 μm) spectral measurements under varying illumination and observation geometries were acquired for 4 samples. Phase reddening and bluing (i.e., increase and decrease in spectral slope) is observed for the visible slope as phase angle increase. Monotonic phase reddening can occur for the near infrared slope as phase angle increase. Non-systematic changes with phase angle are found for the Band Area Ratio parameter. At phase angles higher than ∼60°, the decrease of reflectance and decrease of pyroxene bands depth are undistinguishable from admixture of low albedo material to HED samples. To assess the precision of empirical equations relating spectral properties and composition, the pyroxenes, feldspar, and olivine chemistry of the samples was determined. Using previous calibrations, systematic overestimations of the ferrosilite (Fs) and wollastonite (Wo) contents are found, especially in the 15-40 Fs range. To overcome such discrepancies, a new set of empirical equations is proposed. For an application of the new calibration, we selected two compositional end-member areas on Vesta on the basis of their iron content. For the iron-poor terrain we found an average pyroxene composition of Fs30Wo5 and for the iron-rich terrain an average of Fs47Wo14.
A cost-effective laser scanning method for mapping stream channel geometry and roughness
NASA Astrophysics Data System (ADS)
Lam, Norris; Nathanson, Marcus; Lundgren, Niclas; Rehnström, Robin; Lyon, Steve
2015-04-01
In this pilot project, we combine an Arduino Uno and SICK LMS111 outdoor laser ranging camera to acquire high resolution topographic area scans for a stream channel. The microprocessor and imaging system was installed in a custom gondola and suspended from a wire cable system. To demonstrate the systems capabilities for capturing stream channel topography, a small stream (< 2m wide) in the Krycklan Catchment Study was temporarily diverted and scanned. Area scans along the stream channel resulted in a point spacing of 4mm and a point cloud density of 5600 points/m2 for the 5m by 2m area. A grain size distribution of the streambed material was extracted from the point cloud using a moving window, local maxima search algorithm. The median, 84th and 90th percentiles (common metrics to describe channel roughness) of this distribution were found to be within the range of measured values while the largest modelled element was approximately 35% smaller than its measured counterpart. The laser scanning system captured grain sizes between 30mm and 255mm (coarse gravel/pebbles and boulders based on the Wentworth (1922) scale). This demonstrates that our system was capable of resolving both large-scale geometry (e.g. bed slope and stream channel width) and small-scale channel roughness elements (e.g. coarse gravel/pebbles and boulders) for the study area. We further show that the point cloud resolution is suitable for estimating ecohydraulic parameters such as Manning's n and hydraulic radius. Although more work is needed to fine-tune our system's design, these preliminary results are encouraging, specifically for those with a limited operational budget.
Substitutional geometry and strain effects in overlayers of phosphorus on Si(111)
NASA Astrophysics Data System (ADS)
Vitali, L.; Ramsey, M. G.; Netzer, F. P.
1998-06-01
The structure and bonding topology of phosphorus adatoms on Si(111) surfaces have been investigated by scanning tunneling microscopy (STM) and scanning tunneling spectroscopy, in conjunction with low-energy electron diffraction and Auger electron spectroscopy. At room temperature P adatoms substitute for the Si adatoms of the Si(111)7×7 surface at low coverages as revealed by the chemical contrast between P and Si adatoms in the filled-state STM images. A statistical evaluation of the STM images within the framework of a simple reaction model suggests that the corner adatoms of the faulted half of the (7×7) unit cell act as primary reaction centers for the P2 molecules from the gas phase, in agreement with theoretical expectation. At elevated temperature (500-650 °C) a (63×63)R30° structure is the prevailing P-induced surface reconstruction. Atomically resolved STM images show that this structure is a domain-wall structure containing hexagonal domains that tesselate the entire surface. The 6% contracted (1×1) phosphorus domains are separated by straight, 4% expanded light domain walls of irregular lengths. The structure displays a complex in-phase-antiphase-stacking fault relationship between adjacent domains, which has been modeled successfully with a P adlayer in a substitutional bonding geometry on an unreconstructed Si(111) surface. The large tensile surface stress introduced by the P-Si bonding is responsible for the domain-wall formation and precludes the formation of a global (1×1)-P structure on Si(111) surfaces.
Effect of ocular shape and vascular geometry on retinal hemodynamics: a computational model.
Dziubek, Andrea; Guidoboni, Giovanna; Harris, Alon; Hirani, Anil N; Rusjan, Edmond; Thistleton, William
2016-08-01
A computational model for retinal hemodynamics accounting for ocular curvature is presented. The model combines (i) a hierarchical Darcy model for the flow through small arterioles, capillaries and small venules in the retinal tissue, where blood vessels of different size are comprised in different hierarchical levels of a porous medium; and (ii) a one-dimensional network model for the blood flow through retinal arterioles and venules of larger size. The non-planar ocular shape is included by (i) defining the hierarchical Darcy flow model on a two-dimensional curved surface embedded in the three-dimensional space; and (ii) mapping the simplified one-dimensional network model onto the curved surface. The model is solved numerically using a finite element method in which spatial domain and hierarchical levels are discretized separately. For the finite element method, we use an exterior calculus-based implementation which permits an easier treatment of non-planar domains. Numerical solutions are verified against suitably constructed analytical solutions. Numerical experiments are performed to investigate how retinal hemodynamics is influenced by the ocular shape (sphere, oblate spheroid, prolate spheroid and barrel are compared) and vascular architecture (four vascular arcs and a branching vascular tree are compared). The model predictions show that changes in ocular shape induce non-uniform alterations of blood pressure and velocity in the retina. In particular, we found that (i) the temporal region is affected the least by changes in ocular shape, and (ii) the barrel shape departs the most from the hemispherical reference geometry in terms of associated pressure and velocity distributions in the retinal microvasculature. These results support the clinical hypothesis that alterations in ocular shape, such as those occurring in myopic eyes, might be associated with pathological alterations in retinal hemodynamics. PMID:26445874
NASA Astrophysics Data System (ADS)
Cigala, Valeria; Kueppers, Ulrich; Dingwell, Donald B.
2016-04-01
The lowermost part of an eruptive plume commonly shows characteristics of an underexpanded jet. The dynamics of this gas-thrust region are likely to be a direct consequence of intrinsic (magma properties, overpressure) and extrinsic (vent geometry, weather) eruption conditions. Additionally, they affect the subsequent evolution of the eruptive column and have, therefore, important hazard assessment implications for both near- and far-field. Direct observation of eruptive events is possible, but often insufficient for complete characterization. Important complementary data can be achieved using controlled and calibrated laboratory experiments. Loose natural particles were ejected from a shock-tube while controlling temperature (25° and 500°C), overpressure (15MPa), starting grain size distribution (1-2 mm, 0.5-1 mm and 0.125-0.250 mm), density (basaltic and phonolitic), gas-particle ratio and vent geometry (nozzle, cylindrical, funnel with a flaring of 15° and 30°, respectively). For each experiment, we quantified the velocity of individual particles, the jet spreading angle, the presence of electric discharges and the production of fines and analysed their dynamic evolution. Data shows velocity of up to 296 m/s and deceleration patterns following nonlinear paths. Gas spreading angles range between 21° and 41° while the particle spreading angles between 3° and 32°. Electric discharges, in the form of lightning, are observed, quantified and described. Moreover, a variation in the production of fines is recognized during the course of single experiments. This experimental investigation, which mechanistically mimics the process of pyroclast ejection, is shown to be capable of constraining the effects of input parameters and conduit/vent geometry on pyroclastic plumes. Therefore, the results should greatly enhance the ability of numerically model explosive ejecta in nature.
Demuth, K; Moatti, N; Hanon, O; Benoit, M O; Safar, M; Girerd, X
1998-12-01
Studies of symptomatic patients have identified hyperhomocysteinemia as an independent risk factor for vascular disease. In case-control studies, a point mutation (C677T) in the gene encoding 5,10-methylenetetrahydrofolate reductase (MTHFR) has also been linked to an increased risk of vascular disease through its effect on homocysteinemia. Our aim was to extend these observations to asymptomatic subjects by studying the influence of both homocysteinemia and its mutation on carotid artery geometry. We examined 144 subjects free of atherosclerotic lesions. Fasting homocysteinemia was measured by high-performance liquid chromatography with fluorometric detection. MTHFR genotype was analyzed by polymerase chain reaction followed by HinfI digestion. Carotid artery geometry was characterized by internal diameter and intima-media thickness, as assessed by a high-resolution echo-tracking system. Subjects in the upper homocysteine tertile had a greater carotid internal diameter than did subjects in the middle and lower tertiles (6516+/-770 versus 6206+/-641 and 5985+/-558 microm, respectively; P<0.001). Subjects homozygous for the mutation had a smaller carotid artery internal diameter than did subjects heterozygous or homozygous for the wild-type allele (5846+/-785 versus 6345+/-673 and 6199+/-671 microm, respectively; P<0.05). Homocysteinemia was not significantly increased in subjects homozygous for the mutation. In multivariate regression analysis, homocysteinemia was independently and positively associated with lumen diameter (P=0.0008) and wall thickness (P=0.020). Conversely, homozygosity for the mutation was negatively associated with internal diameter (P=0.009). These preliminary data suggest that mildly elevated homocysteinemia and homozygosity for the MTHFR C677T mutation are associated with opposite preclinical modifications of carotid artery geometry. If confirmed, these results may have important implications for new treatment strategies for vascular disease
NASA Astrophysics Data System (ADS)
Gui, Jianbao; Zou, Jing; Rong, Junyan; Hu, Zhanli; Zhang, Qiyang; Zheng, Hairong; Xia, Dan
2012-03-01
Based upon a bench-top micro-CT system, propagation-based phase-contrast imaging has been investigated using insects and a thin plastic sheet. The system mainly includes a micro-focus source with focal spot size of 13-20 μm and a cooled X-ray CCD detector with pixel size of 24 μm. The edge-enhancement effect can be found clearly in the acquired images. With a 0.5 mm thickness plastic edge phantom, the effects of X-ray tube voltage and imaging geometry on the phase-contrast imaging were investigated, and quantitative index, edge-enhancement index (EEI), were also calculated. In our study, an interesting phenomenon was observed that the phase-contrast effect becomes more pronounced as the tube voltage increases from 20 kVp to 90 kVp. Further investigation indicates that smaller focal spot size resulting from the reduction of tube current at higher tube voltage, has caused the unexpected phenomenon. Inferred from our results, phase-contrast effect is insensitive to the tube voltage in the range of 20-90 kVp (widely used in medical diagnosis); however, it is sensitive to the focal spot size. In addition, for the investigation of the effect of imaging geometry, an optimal geometric magnification range of 2.5-4.5 is suggested to get a good phase-contrast imaging for a micro-CT system with source-to-detector distance of 720 mm.
EFFECTS OF OPEN-TOP CHAMBERS ON 'VALENCIA' ORANGE TREES
Young 'Valencia' orange trees (Citrus sinensis(L) Osbeck) were grown for four years in large open-top chambers with ambient (nonfiltered) air or in outside air to determine any effects of the chambers on the air pollutant susceptibility of the trees. ong-term ozone average concen...
Dryden, Daniel M; Hopkins, Jaime C; Denoyer, Lin K; Poudel, Lokendra; Steinmetz, Nicole F; Ching, Wai-Yim; Podgornik, Rudolf; Parsegian, Adrian; French, Roger H
2015-09-22
The self-assembly of heterogeneous mesoscale systems is mediated by long-range interactions, including van der Waals forces. Diverse mesoscale architectures, built of optically and morphologically anisotropic elements such as DNA, collagen, single-walled carbon nanotubes, and inorganic materials, require a tool to calculate the forces, torques, interaction energies, and Hamaker coefficients that govern assembly in such systems. The mesoscale Lifshitz theory of van der Waals interactions can accurately describe solvent and temperature effects, retardation, and optically and morphologically anisotropic materials for cylindrical and planar interaction geometries. The Gecko Hamaker open-science software implementation of this theory enables new and sophisticated insights into the properties of important organic/inorganic systems: interactions show an extended range of magnitudes and retardation rates, DNA interactions show an imprint of base pair composition, certain SWCNT interactions display retardation-dependent nonmonotonicity, and interactions are mapped across a range of material systems in order to facilitate rational mesoscale design. PMID:25815562
Arnela, Marc; Guasch, Oriol; Alías, Francesc
2013-10-01
One of the key effects to model in voice production is that of acoustic radiation of sound waves emanating from the mouth. The use of three-dimensional numerical simulations allows to naturally account for it, as well as to consider all geometrical head details, by extending the computational domain out of the vocal tract. Despite this advantage, many approximations to the head geometry are often performed for simplicity and impedance load models are still used as well to reduce the computational cost. In this work, the impact of some of these simplifications on radiation effects is examined for vowel production in the frequency range 0-10 kHz, by means of comparison with radiation from a realistic head. As a result, recommendations are given on their validity depending on whether high frequency energy (above 5 kHz) should be taken into account or not. PMID:24116430
Investigation on the reflector/moderator geometry and its effect on the neutron beam design in BNCT.
Kasesaz, Y; Rahmani, F; Khalafi, H
2015-12-01
In order to provide an appropriate neutron beam for Boron Neutron Capture Therapy (BNCT), a special Beam Shaping Assembly (BSA) must be designed based on the neutron source specifications. A typical BSA includes moderator, reflector, collimator, thermal neutron filter, and gamma filter. In common BSA, the reflector is considered as a layer which covers the sides of the moderator materials. In this paper, new reflector/moderator geometries including multi-layer and hexagonal lattice have been suggested and the effect of them has been investigated by MCNP4C Monte Carlo code. It was found that the proposed configurations have a significant effect to improve the thermal to epithermal neutron flux ratio which is an important neutron beam parameter. PMID:26298435
NASA Astrophysics Data System (ADS)
Wang, H. S.; Honda, Hiroshi
A theoretical study has been made on the effects of tube diameter and tubeside fin geometry on the heat transfer performance of air-cooled condensers. Extensive numerical calculations of overall heat transfer from refrigerant R410A flowing inside a horizontal microfin tube to ambient air were conducted for a typical operating condition of the air-cooled condenser. The tubeside heat transfer coefficient was calculated by applying a modified stratified flow model developed by Wang et al.8). The numerical results show that the effects of tube diameter, fin height, fin number and helix angle of groove are significant, whereas those of the width of flat portion at the fin tip, the radius of round corner at the fin tip and the fin half tip angle are small.
Bryan, W. A.; Stebbings, S. L.; English, E. M. L.; Goodworth, T. R. J.; Newell, W. R.; McKenna, J.; Suresh, M.; Srigengan, B.; Williams, I. D.; Turcu, I. C. E.; Smith, J. M.; Divall, E. J.; Hooker, C. J.; Langley, A. J.
2006-01-15
We report an experimental technique for the comparison of ionization processes in ultrafast laser pulses irrespective of pulse ellipticity. Multiple ionization of xenon by 50 fs 790 nm, linearly and circularly polarized laser pulses is observed over the intensity range 10 TW/cm{sup 2} to 10 PW/cm{sup 2} using effective intensity matching (EIM), which is coupled with intensity selective scanning (ISS) to recover the geometry-independent probability of ionization. Such measurements, made possible by quantifying diffraction effects in the laser focus, are compared directly to theoretical predictions of multiphoton, tunnel and field ionization, and a remarkable agreement demonstrated. EIM-ISS allows the straightforward quantification of the probability of recollision ionization in a linearly polarized laser pulse. Furthermore, the probability of ionization is discussed in terms of the Keldysh adiabaticity parameter {gamma}, and the influence of the precursor ionic states present in recollision ionization is observed.
NASA Astrophysics Data System (ADS)
Georgen, Jennifer E.; Sankar, Ravi D.
2010-09-01
Plate boundary geometry can affect the nature of magmatism along a mid-ocean ridge. The Azores Plateau is located in a complex geological setting that includes a triple junction (TJ), an oblique and recently-formed ultra-slow-spreading ridge, a zone of diffuse seafloor deformation, a major fracture zone, and a postulated hotspot. The precise character of the hotspot is somewhat debated, as some lines of evidence indicate it may not be a classic deep-seated plume. However, seismic and gravity data suggest plateau crustal thicknesses of ˜ 8 km or more, implying some mechanism for excess melting. To assess the role of ridge geometry in creating the Azores Plateau, this study uses a finite element numerical model to isolate the effects of selected aspects of plate boundary configuration on mantle flow and melt production in a TJ kinematically similar to the Azores TJ. The model focuses on the slowest-spreading ridge in the TJ, analogous to the Terceira Rift. The effect of the varying ridge obliquity observed along the Terceira Rift is also assessed using an independent 1-D melting model. In general, relatively little melt production is predicted along the Terceira Rift analogue, except for regions closest to the TJ where the proximity of a faster-spreading ridge increases temperatures within the melting zone. In the 1-D melting model with mantle temperatures of 1350 °C, melt thicknesses of ˜ 2 km are calculated for the least oblique segments, while more oblique segments produce little to no melt. The presence of a long discontinuity (simulating the Gloria FZ) has little effect on mantle dynamics for axial distances < 350 km from the TJ, although crustal production is predicted to diminish to zero within ˜ 150 km of the discontinuity. When several ridge geometrical effects are combined (i.e., a TJ, time-limited spreading, a ridge discontinuity, and depressed spreading rates within ˜ 100 km of the TJ point), ˜ 2.5 km of variability in melt thickness can be produced
Ridgway, Cathy J.; Schoelkopf, Joachim; Matthews, G. Peter; Gane, Patrick A. C.; James, Philip W.
2001-07-15
The absorption (permeation) of alcohols into porous blocks of calcium carbonate has been studied experimentally and with a computer model. The experimental measurement was of change in apparent weight of a block with time after contact with liquid. The modeling used the previously developed 'Pore-Cor' model, based on unit cells of 1000 cubic pores connected by cylindrical throats. To gain some insight into absorption into voids of complex geometry, and to provide a representation of heterogeneities in surface interaction energy, the cylindrical throats were converted to double cones. Relative to cylinders, such geometries caused hold-ups of the percolation of nonwetting fluids with respect to increasing applied pressure, and a change in the rate of absorption of wetting fluids. Both the measured absorption of the alcohols and the simulated absorption of the alcohols and of water showed significant deviations from that predicted by an effective hydraulic radius approximation. The simulation demonstrated the development of a highly heterogeneous wetting front, and of preferred wetting pathways that were perturbed by inertial retardation. The findings are useful in the design of high-performance, low-waste pigments for paper coatings, and environmentally friendly printing inks, as well as in wider industrial, environmental, and geological contexts. Copyright 2001 Academic Press. PMID:11427007
NASA Astrophysics Data System (ADS)
Chooljian, Marc; Paredes, Jacobo; Liepmann, Dorian
2014-11-01
We have developed a method that allows embedding of electrodes in up to 3 walls of a plastic microfluidic channel. Electric field strength and homogeneity of various electrode geometries is analyzed theoretically and experimentally by evaluating the efficiency of on-chip lysis of cells. Electric field-mediated disruption of membranes is an important tool in diagnostics, basic biology, and synthetic biology due to the ability to permeabilize the cell membrane without changing the chemical composition of the buffer. Typically, fields of the required magnitude are applied to the cell by discharging a capacitor through a mixture of cells in a cuvette, resulting in a transient high-voltage pulse. We demonstrate that is possible to substitute a spatially varied DC electric field along a microchannel and to control the timing of the pulses by changing the electrode spacing and the flow rate. Homogeneity of the field with respect to the cross section of the channel is key to achieving critical field strength regardless of the cell's lateral position in the channel. A comparison of 2D versus 3D electrode geometries on the efficiency of electroporation and on side-effects arising due to the electric field (recirculating flows and hydrolysis) is presented.
Renga, Alfredo; Moccia, Antonio
2009-01-01
During the last decade a methodology for the reconstruction of surface relief by Synthetic Aperture Radar (SAR) measurements – SAR interferometry – has become a standard. Different techniques developed before, such as stereo-radargrammetry, have been experienced from space only in very limiting geometries and time series, and, hence, branded as less accurate. However, novel formation flying configurations achievable by modern spacecraft allow fulfillment of SAR missions able to produce pairs of monostatic-bistatic images gathered simultaneously, with programmed looking angles. Hence it is possible to achieve large antenna separations, adequate for exploiting to the utmost the stereoscopic effect, and to make negligible time decorrelation, a strong liming factor for repeat-pass stereo-radargrammetric techniques. This paper reports on design of a monostatic-bistatic mission, in terms of orbit and pointing geometry, and taking into account present generation SAR and technology for accurate relative navigation. Performances of different methods for monostatic-bistatic stereo-radargrammetry are then evaluated, showing the possibility to determine the local surface relief with a metric accuracy over a wide range of Earth latitudes. PMID:22389594
Joint effects of illumination geometry and object shape in the perception of surface reflectance
Olkkonen, Maria; Brainard, David H
2011-01-01
Surface properties provide useful information for identifying objects and interacting with them. Effective utilization of this information, however, requires that the perception of object surface properties be relatively constant across changes in illumination and changes in object shape. Such constancy has been studied separately for changes in these factors. Here we ask whether the separate study of the illumination and shape effects is sufficient, by testing whether joint effects of illumination and shape changes can be predicted from the individual effects in a straightforward manner. We found large interactions between illumination and object shape in their effects on perceived glossiness. In addition, analysis of luminance histogram statistics could not account for the interactions. PMID:23145259
NASA Astrophysics Data System (ADS)
Filatov, Michael; Cremer, Dieter
2003-03-01
For the quasi-relativistic normalized elimination of small component using an effective potential (NESC-EP) method, analytical energy gradients were developed, programmed, and implemented in a standard quantum chemical program package. NESC-EP with analytical gradients was applied to determine geometry, vibrational frequencies, and dissociation enthalpies of ferrocene, tungsten hexafluoride, and tungsten hexacarbonyle. Contrary to non-relativistic calculations and calculations carried out with RECPs for the same compounds, NESC-EP provided reliable molecular properties in good agreement with experiment. The computational power of NESC-EP results from the fact that reliable relativistic corrections are obtained at a cost level only slightly larger than that of a non-relativistic calculation.
NASA Technical Reports Server (NTRS)
Cullom, R. R.; Johnsen, R. L.
1979-01-01
Three afterburner configurations were tested in a low-bypass-ratio turbofan engine to determine the effect of various fuel distributions, inlet conditions, flameholder geometry, and fuel injection location on combustion instability. Tests were conducted at simulated flight conditions of Mach 0.75 and 1.3 at altitudes from 11,580 to 14,020 m (38,000 to 46,000 ft). In these tests combustion instability with frequency from 28 to 90 Hz and peak-to-peak pressure amplitude up to 46.5 percent of the afterburner inlet total pressure level was encountered. Combustion instability was suppressed in these tests by varying the fuel distribution in the afterburner.
Sánchez-Arellano, Enrique; Olivares, Wilmer; Lozada-Cassou, Marcelo; Jiménez-Angeles, Felipe
2009-02-15
The electrokinetic properties (such as capillary conductance, electroviscosity, and the streaming potential) are obtained for a restricted primitive model electrolyte confined in a slitlike nanopore made up of two infinite parallel plates and in a cylindrical cavity of infinite extension. The hypernetted chain/mean spherical approximation (HNC/MSA) is used to obtain the equilibrium ionic concentration profiles inside the pores, which in turn are used to calculate the electrokinetic properties via linear hydrodynamic equations. Our results are compared with those obtained via the classical Poisson-Boltzmann (PB) theory. Important quantitative and qualitative effects, attributed to geometry and to the proper consideration of short-range correlations by HNC/MSA, are discussed. PMID:19062031
NASA Astrophysics Data System (ADS)
Agashe, Janhavi S.; Arnold, David P.
2008-05-01
Kelvin's formula is used to calculate forces acting on a permanent magnet in the presence of an external magnetic field from a second permanent magnet. This approach is used to derive explicit analytical solutions for the axial and lateral forces between cuboidal and cylindrical permanent magnets as functions of magnet dimensions and separation. While exact solutions can be found for cuboidal magnets, a hypergeometric expansion is used to approximate the elliptic integrals in solving for the fields and forces for the cylindrical magnets. The resulting equations are applied over a range of magnet sizes and geometries to explore scaling laws and other geometrical effects. It is shown that cuboidal magnets provide larger forces than equivalently sized cylindrical magnets. Also, the aspect ratio of the magnets significantly affects the forces. These results are intended to benefit the design and optimization of sensors, actuators and systems that rely on magnetic forces, particularly at the microscale.
Geometry of the effective Majorana neutrino mass in the 0νββ decay
NASA Astrophysics Data System (ADS)
Xing, Zhi-zhong; Zhou, Ye-Ling
2015-01-01
The neutrinoless double-beta (0νββ) decay is a unique process used to identify the Majorana nature of massive neutrinos, and its rate depends on the size of the effective Majorana neutrino mass
Mathematical Analysis of the Effect of Rotor Geometry on Cup Anemometer Response
Sanz-Andrés, Ángel; Sorribes-Palmer, Félix
2014-01-01
The calibration coefficients of two commercial anemometers equipped with different rotors were studied. The rotor cups had the same conical shape, while the size and distance to the rotation axis varied. The analysis was based on the 2-cup positions analytical model, derived using perturbation methods to include second-order effects such as pressure distribution along the rotating cups and friction. The comparison with the experimental data indicates a nonuniform distribution of aerodynamic forces on the rotating cups, with higher forces closer to the rotating axis. The 2-cup analytical model is proven to be accurate enough to study the effect of complex forces on cup anemometer performance. PMID:25110735
Mathematical analysis of the effect of rotor geometry on cup anemometer response.
Sanz-Andrés, Ángel; Pindado, Santiago; Sorribes-Palmer, Félix
2014-01-01
The calibration coefficients of two commercial anemometers equipped with different rotors were studied. The rotor cups had the same conical shape, while the size and distance to the rotation axis varied. The analysis was based on the 2-cup positions analytical model, derived using perturbation methods to include second-order effects such as pressure distribution along the rotating cups and friction. The comparison with the experimental data indicates a nonuniform distribution of aerodynamic forces on the rotating cups, with higher forces closer to the rotating axis. The 2-cup analytical model is proven to be accurate enough to study the effect of complex forces on cup anemometer performance. PMID:25110735
Reconstruction of effective cloud field geometry from series of sunshine number
NASA Astrophysics Data System (ADS)
Badescu, Viorel; Paulescu, Marius; Brabec, Marek
2016-07-01
A new method is proposed for extracting the parameters of effective cloud field models from time series of sunshine number (SSN). Data of SSN number and point cloudiness during 2009 and 2010 at Timisoara (Romania, South Eastern Europe; temperate continental climate) are used to illustrate the method. Two procedures of fitting the estimated point cloudiness to the observed point cloudiness data are proposed and tested. Seven simple effective cloud field models are analyzed. All models underestimate the point cloudiness. The MBE ranges between - 0.06 and - 0.23 while RMSE between 0.15 and 0.38, depending on the month and the duration of the SSN data averaging interval. The best model is based on a field of clouds of semicircle form. This agrees with previous results obtained in the semi-arid climate of Great South Plains in US. The dynamics of the effective cloud field is reconstructed during all months of 2010 at Timisoara. The time series of effective cloud fields are dominated by semicircle clouds but short episodes of semielliptic clouds, ellipsoid clouds, truncated cone clouds and cuboidal clouds are included in the series.
Effects of various parameters on hydraulic fracture geometry. [Theoretical and experimental studies
Hanson, M.E.; Anderson, G.D.; Shaffer, R.J.
1980-05-01
Theoretical models have been applied to analyze some aspects of the dynamics of fracturing near material interfaces. Results of these calculations indicate that variation of material properties across a well bonded interface can cause dynamic material response resulting from the fracturing which could enhance propagation across the inerface. Effects of friction have also been analyzed theoretically; however, in the frictional calculations the wave mechanics have been ignored. These calculations have shown that frictional slip along the interface tends to draw a pressurized fracture toward the interface; this motion tends to reduce the chances of penetrating the material across the frictional interface. Small scale laboratory experiments are performed to study the effects of frictional characteristics on hydraulic fracture growth across unbonded interfaces in rocks. Various lubricants and mechanical preparation of the interface surfaces are used to vary the coefficients of friction on the interface surfaces. It is found that the frictional shear stress that the interface surface can support determines whether a hydraulically driven crack will cross the interface. Pre-existing cracks impede the propagation of the hydraulic fracture across the interface. These experimental results on the effects of friction on the interface and the effects of pre-existing cracks on hydraulic fracture penetration of interfaces are consistent with the predictions of the numerical model calculations. 11 figures.
ERIC Educational Resources Information Center
Bokosmaty, Sahar; Sweller, John; Kalyuga, Slava
2015-01-01
Research has demonstrated that instruction that relies heavily on studying worked examples is more effective for less experienced learners compared to instruction emphasizing problem solving. However, the guidance associated with studying some worked examples may reduce the performance of more experienced learners. This study investigated…
Pierson, Jeffery L; Small, Scott R; Rodriguez, Jose A; Kang, Michael N; Glassman, Andrew H
2015-07-01
Design parameters affecting initial mechanical stability of tapered, splined modular titanium stems (TSMTSs) are not well understood. Furthermore, there is considerable variability in contemporary designs. We asked if spline geometry and stem taper angle could be optimized in TSMTS to improve mechanical stability to resist axial subsidence and increase torsional stability. Initial stability was quantified with stems of varied taper angle and spline geometry implanted in a foam model replicating 2cm diaphyseal engagement. Increased taper angle and a broad spline geometry exhibited significantly greater axial stability (+21%-269%) than other design combinations. Neither taper angle nor spline geometry significantly altered initial torsional stability. PMID:25754255
NASA Technical Reports Server (NTRS)
Bangert, Linda S.; Carson, George T., Jr.
1992-01-01
A parametric study was conducted in the Langley 16-Foot Transonic Tunnel on an isolated nonaxisymmetic fuselage model that simulates a twin-engine fighter. The effects of aft-end closure distribution (top/bottom) nozzle-flap boattail angle versus nozzle-sidewall boattail angle) and afterbody and nozzle corner treatment (sharp or radius) were investigated. Four different closure distributions with three different corner radii were tested. Tests were conducted over a range of Mach numbers from 0.40 to 1.25 and over a range of angles of attack from -3 to 9 degrees. Solid plume simulators were used to simulate the jet exhaust. For a given closure distribution in the range of Mach numbers tested, the sharp-corner nozzles generally had the highest drag, and the 2-in. corner-radius nozzles generally had the lowest drag. The effect of closure distribution on afterbody drag was highly dependent on configuration and flight condition.
Ect Simulation of Coil Tilt Effect on 3d Flaws Responses in Planar Geometries
NASA Astrophysics Data System (ADS)
Reboud, C.; Pichenot, G.; Theodoulidis, T.
2009-03-01
Eddy current testing signals are quite sensitive to the probe tilt, which is difficult to adjust in many practical testing configurations. In order to take account of this effect in simulation, a collaborative work between CEA and the University of Western Macedonia has been carried out. This paper presents the modeling approaches that have been used for the primary field computation and its interaction with the flaw, respectively, as well as an experimental validation of the complete model available in the CIVA software.
Effect of geometry and composition on the intraband transitions of holes in quantum dots
Singh, Satish Kumar Kumar, Jitendra
2014-12-28
The effect of shape and size anisotropy on unipolar intraband transitions of holes in quantum dots (QDs) is studied. The optical matrix elements are calculated for transitions of holes in valence band. To get the optical matrix elements, energy eigenvalues and eigenvectors are calculated using 4 × 4 Luttinger Hamiltonian in the effective mass approximation. The formulation is applied to InGaAs/GaAs QD with parabolic confinement potential in xy-plane. The optical matrix elements for intraband hole transitions are calculated for x and y polarised light. The transitions are considered from ground state to other excited states. The effect of In concentration on optical matrix elements is also investigated. It is important to note that the transitions of holes are governed by the character of initial and final states for different light polarisations that give specific transition selection rules. It is found that the polarisation is strongly dependent on the in-plane anisotropy of the QDs.
Luo, Hu-Ping; Al-Dahhan, Muthanna H
2012-04-01
Photosynthetic microorganisms have been attracting world attention for their great potential as renewable energy sources in recent years. Cost effective production in large scale, however, remains a major challenge to overcome. It is known to the field that turbulence could help improving the performance of photobioreactors due to the so-called flashing light effects. Better understanding of the multiphase fluid dynamics and the irradiance distribution inside the reactor that cause the flashing light effects, as well as quantifying their impacts on the reactor performance, thus, are crucial for successful design and scale-up of photobioreactors. In this study, a species of red marine microalgae, Porphyridium sp., was grown in three airlift column photobioreactors (i.e., draft tube column, bubble column, and split column). The physical properties of the culture medium, the local fluid dynamics and the photobioreactor performances were investigated and are reported in this part of the manuscript. Results indicate that the presence of microalgae considerably affected the local multiphase flow dynamics in the studied draft tube column. Results also show that the split column reactor works slightly better than the draft tube and the bubble columns due to the spiral flow pattern inside the reactor. PMID:22068325
Effects of irradiation geometry on treatment plan optimization with linac-based radiosurgery.
Phillips, M H; Stelzer, K J; Mayberg, M R; Winn, H R
1996-08-01
A comparison was made of different treatment plans to determine the effect on the three-dimensional dose distributions of varying the allowed parameters in linac-based stereotactic radiosurgery with circular collimators; these parameters are arc position, length, and weighting, and collimator diameter. For the class of eccentrically shaped target volumes that are not so irregular as to require several separate isocenters, it was found that superior dose distributions could be achieved by varying arc length, arc position, arc weighting, and collimator diameter. An analysis of the results achieved with an automated planning program indicates that, in general, the variables of arc position and arc length are of greater importance than collimator size or beam weighting. However, there are cases where varying these latter two parameters does result in markedly better dose distributions. A deeper investigation into the effects of multiple collimators on the dose distribution in the area of steepest gradient demonstrated that multiple collimator sizes do not significantly degrade the dose falloff, which is in fact mostly determined by the effects of intersecting arcs. PMID:8873037
Hwang, Jong-Min; Baek, Seung-Hak; Choi, Jin-Young
2012-03-01
The purpose of this study was to investigate the effect of the number and the geometry of resorbable screws (RSs; Inion CPS System; Inion Ltd, Tampere, Finland) on the biomechanical stability of the in vitro model with sagittal split ramus osteotomy. The sagittal split ramus osteotomy polyurethane hemimandible (Synbone, Malans, Switzerland) was fixed by 7 osteosynthesis methods after 5 mm advancement of the distal segment (n = 5 for each method): 1TP (1 titanium miniplate and 4 screws), 3RL (3 RSs with linear configuration at the retromolar area [RMA]), 2R1B (2 RSs at RMA and 1 RS at the mandibular body [MB]), 2R1A (2 RSs at the RMA and 1 RS at the mandibular angle [MA]), 3R1B (3 RSs at RMA and 1 RS at the MB), 3R1A (3 RSs at RMA and 1 RS at the MA), and 3R1A1B (3 RSs at the RMA, 1 RS at the MA, and 1 RS at the MB). Values of linear compressive load were measured at 1- to 5-mm displacement of the lower first molar with a 1-mm interval and were statistically analyzed. From 1- to 5-mm displacement, there were significant differences in load values among groups (P < 0.05, P < 0.01, P < 0.01, P < 0.001, and P < 0.001, respectively). When the amount of displacement was increased, the difference in load values between 1TP, 3RL, and 2R1B became significantly prominent. There was a significant difference in total load values according to number and geometry of RSs (P < 0.001). All kinds of geometry with more than 3 RSs were more rigid than 1TP. The 3R1A1B method showed better biomechanical stability than 1TP, 3RL, and 2R1B. In 3 RS and 4 RS groups, fixation in MA (2R1A, 3R1A) exhibited a tendency of better stability than fixation in MB (2R1B, 3R1B). Fixation with 2R1A could provide better biomechanical stability than 1TP and similar rigidity with 3R1A1B. PMID:22421826
Polarization effects in double open-charm production at LHCb
NASA Astrophysics Data System (ADS)
Echevarría, Miguel G.; Kasemets, Tomas; Mulders, Piet J.; Pisano, Cristian
2015-04-01
Double open-charm production is one of the most promising channels to disentangle single from double parton scattering (DPS) and study different properties of DPS. Several studies of the DPS contributions have been made. A missing ingredient so far has been the study of polarization effects, arising from spin correlations between the two partons inside an unpolarized proton. We investigate the impact polarization has on the double open-charm cross section. We show that the longitudinally polarized gluons can give significant contributions to the cross section, but for most of the considered kinematic region only have a moderate effect on the shape. We compare our findings to the LHCb data in the D 0 D 0 final state, identify observables where polarization does have an impact on the distribution of the final state particles, and suggest measurements which could lead to first experimental indications of, or limits on, polarization in DPS.
Haslinger, K.H.
1995-03-01
Fluid film characteristics inside cylindrical steam generator tube support holes and near anti-vibration bar supports were determined experimentally. Test results were evaluated and empirical formulations were developed which adequately represent the observed fluid film phenomena. The empirical formulations are suited for incorporation into the ABAQUS computer code which has been developed by Foster Wheeler for EPRI for prediction of the dynamic behavior and work rates of vibrating steam generator tubes with non-linear support characteristics. A short rigid tube was cycled sinusoidally inside special, instrumented tube support samples. Alignment features enabled accurate positioning of the tube, thereby producing either non-contact or impact conditions with known excitation frequency, tube orbit, and amplitude. The complement of measurements consisted of the instantaneous values for tube motion, tube velocity, tube acceleration, contact condition, and the force exchange between tube and support. These measurements were digitized with high sampling rates and subsequently tabulated and graphed. Review of various 2-D and 3-D collages for a water environment at ambient revealed that the fluid film reaction forces, for reasonably large gaps between tube and support, are primarily dependent on tube acceleration, and to a lesser extent on tube velocity. For smooth cylindrical support surfaces there also exists a strong squeeze film effect for small gaps up to impact, and a suction effect during rebound. The squeeze film effect was found to be dependent on the instantaneous gap and tube velocity values. As influenced by the fluid viscosity, the dependency of the fluid reaction force on tube acceleration and on tube velocity was found to vary and was characterized in the experiments for one support clearance condition.
Sensing (un)binding events via surface plasmons: effects of resonator geometry
NASA Astrophysics Data System (ADS)
Antosiewicz, Tomasz J.; Claudio, Virginia; Käll, Mikael
2016-04-01
The resonance conditions of localized surface plasmon resonances (LSPRs) can be perturbed in any number ways making plasmon nanoresonators viable tools in detection of e.g. phase changes, pH, gasses, and single molecules. Precise measurement via LSPR of molecular concentrations hinge on the ability to confidently count the number of molecules attached to a metal resonator and ideally to track binding and unbinding events in real-time. These two requirements make it necessary to rigorously quantify relations between the number of bound molecules and response of plasmonic sensors. This endeavor is hindered on the one hand by a spatially varying response of a given plasmonic nanosensor. On the other hand movement of molecules is determined by stochastic effects (Brownian motion) as well as deterministic flow, if present, in microfluidic channels. The combination of molecular dynamics and the electromagnetic response of the LSPR yield an uncertainty which is little understood and whose effect is often disregarded in quantitative sensing experiments. Using a combination of electromagnetic finite-difference time-domain (FDTD) calculations of the plasmon resonance peak shift of various metal nanosensors (disk, cone, rod, dimer) and stochastic diffusion-reaction simulations of biomolecular interactions on a sensor surface we clarify the interplay between position dependent binding probability and inhomogeneous sensitivity distribution. We show, how the statistical characteristics of the total signal upon molecular binding are determined. The proposed methodology is, in general, applicable to any sensor and any transduction mechanism, although the specifics of implementation will vary depending on circumstances. In this work we focus on elucidating how the interplay between electromagnetic and stochastic effects impacts the feasibility of employing particular shapes of plasmonic sensors for real-time monitoring of individual binding reactions or sensing low concentrations
Ricard, Mark D; Hills-Meyer, Patrick; Miller, Michael G; Michael, Timothy J
2006-01-01
The purpose of this study was to compare the effects of bicycle seat tube angles (STA) of (72° and 82°) on power production and EMG of the vastus laeralis (VL), vastus medialis (VM), semimembranous (SM), biceps femoris (BF) during a Wingate test (WAT). Twelve experienced cyclists performed a WAT at each STA. Repeated measures ANOVA was used to identify differences in muscular activation by STA. EMG variables were normalized to isometric maximum voluntary contraction (MVC). Paired t-tests were used to test the effects of STA on: peak power, average power, minimum power and percent power drop. Results indicated BF activation was significantly lower at STA 82° (482.9 ± 166.6 %MVC·s) compared to STA 72° (712.6 ± 265.6 %MVC·s). There were no differences in the power variables between STAs. The primary finding was that increasing the STA from 72° to 82° enabled triathletes' to maintain power production, while significantly reducing the muscular activation of the biceps femoris muscle. Key PointsRoad cyclists claim that bicycle seat tube angles between 72° and 76° are most effective for optimal performance in racing.Triathletes typically use seat tube angles greater than 76°. It is thought that a seat tube angle greater than 76° facilitates a smoother bike to run transition in the triathlon.Increasing the seat tube angle from 72 to 82 enabled triathletes' to maintain power production, while significantly reducing the muscular activation of the biceps femoris muscle.Reduced hamstring muscular activation in the triathlon frame (82 seat tube angle) may serve to reduce hamstring tightness following the bike phase of the triathlon, allowing the runner to use a longer stride length. PMID:24198678
Experimental study of the thermodynamic effect in a cavitating flow on a simple Venturi geometry
NASA Astrophysics Data System (ADS)
Petkovšek, M.; Dular, M.
2015-12-01
The thermodynamic effects in cavitating flow are observed on a simple Venturi profile. A thorough experimental investigation of the temperature field on cavitating flow has been performed in water of 100°C at different operating conditions. Temperature measurements were performed with Infra-Red (IR) high-speed camera, while visualisation was made with conventional high-speed camera. Both, average temperature fields and temperature dynamics are presented at different operating conditions and compared with collected data in visual spectrum. In the vicinity of the throat a temperature depression up to 0.5 K was recorded.
Heikkinen, J.A.; Pavlov, I.P.
1996-02-01
The fairly large poloidal directivity of a radiated fast wave spectrum related to the wave polarization relative to the ion gyration can be further enhanced by the nonperpendicular angle between the antenna current strap and the magnetic field. The latter is shown to be responsible also for the asymmetry in the parallel wavenumber spectrum of an unphased antenna, and can lead to deviations of order {le}30{percent} in the corresponding spectrum of a phased antenna array. The consequences of the observed effects to the antenna performance in the current drive applications as well as in excitation of poloidally asymmetric spectra are discussed. {copyright} {ital 1996 American Institute of Physics.}
NASA Technical Reports Server (NTRS)
Fatuzzo, Marco; Melia, Fulvio
1991-01-01
Sheared Alfven waves generated by nonradial crustal disturbances above the polar cap of a strongly magnetized neutron star induce an electric field component parallel to B. An attempt is made to determine the manner in which the strong radial dependence of B affects the propagation of these sheared Alfven waves, and whether this MHD process is still an effective particle accelerator. It is found that although the general field equation is quite complicated, a simple wavelike solution can still be obtained under the conditions of interest for which the Alfven phase velocity decouples from the wave equation. The results may be applicable to gamma-ray burst sources.
Effective two-dimensional frictional contact model for arbitrary curved geometry
NASA Astrophysics Data System (ADS)
Saleeb, A. F.; Chen, K.; Chang, Y. P.
1994-04-01
A finite element model is developed on the basis of a variational formulation of the perturbed Lagrange type and the classical Coulomb law of friction, for the analysis of frictional contact problems in two dimensions. The model accounts for all geometric/ kinematic non-linearities associated with large sliding motions as well as arbitrary contact-surface curvatures. Explicit forms for the contact force and tangent stiffness operators and a penalty-type format is utilized in the implementation. An extensive number of numerical simulations are used to demonstrate the effectiveness and practical usefulness of the model.
Effect of geometry and operating conditions on spur gear system power loss
NASA Technical Reports Server (NTRS)
Anderson, N. E.; Loewenthal, S. H.
1980-01-01
The results of an analysis of the effects of spur gear size, pitch, width, and ratio on total mesh power loss for a wide range of speeds, torques, and oil viscosities are presented. The analysis uses simple algebraic expressions to determine gear sliding, rolling, and windage losses and also incorporates an approximate ball bearing power loss expression. The analysis shows good agreement with published data. Large diameter and fine pitched gears had higher peak efficiencies but low part load efficiency. Gear efficiencies were generally greater than 98 percent except at very low torque levels. Tare (no-load) losses are generally a significant percentage of the full load loss except at low speeds.
Effect of flow and active mixing on bacterial growth in a colon-like geometry
NASA Astrophysics Data System (ADS)
Cremer, Jonas; Segota, Igor; Arnoldini, Markus; Groisman, Alex; Hwa, Terence
The large intestine harbors bacteria from hundreds of species, with bacterial densities reaching up to 1012 cells per gram. Many different factors influence bacterial growth dynamics and thus bacterial density and microbiota composition. One dominant force is flow which can in principle lead to a washout of bacteria from the proximal colon. Active mixing by Contractions of the colonic wall together with bacterial growth might counteract such flow-forces and allow high bacterial densities to occur. As a step towards understanding bacterial growth in the presence of mixing and flow, we constructed an in-vitro setup where controlled wall-deformations of a channel emulate Contractions. We investigate growth along the channel under a steady nutrient inflow. In the limits of no or very frequent Contractions, the device behaves like a plug-flow reactor and a chemostat respectively. Depending on mixing and flow, we observe varying spatial gradients in bacterial density along the channel. Active mixing by deformations of the channel wall is shown to be crucial in maintaining a steady-state bacterial population in the presence of flow. The growth-dynamics is quantitatively captured by a simple mathematical model, with the effect of mixing described by an effective diffusion term.
Effects of the boundary geometry on the edge current in the two dimensional topological insulator
NASA Astrophysics Data System (ADS)
Doh, Hyeonjin; Choi, Hyoung Joon
2015-03-01
We study the effects of the boundary shape on the edge transport of the two dimensional topological insulator described by Kane-Mele model. The edge state is robust against all time-reversal invariant defects. However, when we consider an arbitrary sample, the edge is not straight and consists of various types of boundaries. Actually, the transport property of the edge-state in the Kane-Mele model depends on the boundary type of the edge such as zigzag and armchair edges. Therefore, the edge-transport can be affected by a corner connecting two different types of edges. Here, we investigate the energy spectrum of the various shapes of finite-size honeycomb lattice with corners along the edge. We also calculate the transport properties on the edges by applying an artificial gauge field which drives a persistent current along the edges. Although the corner of the edge seems a geometrical defects and is expected to have a little effect on the transport, our results show that the geometrical defects strongly affect the edge current depending on the corner types. This work was supported by NRF of Korea (Grant No. 2011-0018306) and KISTI supercomputing center (Project No. KSC-2013-C3-062).
The effect of geometry on the particle stress in suspensions of rigid particles in simple shear
NASA Astrophysics Data System (ADS)
Daghooghi, Mohsen; Borazjani, Iman
2014-11-01
The contribution of particles on the total stress of a suspension is known as particle stress, which consists of three sources: moment of stress on the particle surface, inertial term and Reynolds stress term. The symmetric part of the first term, i.e. stresslet, is considered as the most important term in rheological calculation and contribution of other terms is mainly ignored in low Reynolds regimes. For suspensions of rigid spheres at steady state these terms are negligible comparing to stresslet of the suspension, however this might not be the case for complex particle shapes. Using immersed boundary method, we simulate suspensions of complex shaped particles in simple shear flow to investigate the role of other two terms on the total particle stress and effective viscosity. We validated our results against classical analytical results for the low Reynolds-Stokes problem of suspension of ellipsoidal particles by Jeffery. We studied the effect of volume fraction of suspension and particle shape (aspect ratio) on the rheology of suspensions at Reynolds number range of 0 . 01 < Re < 10 . Our study shows that particle shape has an mportant role on all components of the particle stress, and for Re > 1 the budget of inertial term in the total particle stress is not negligible. This work was supported by the American Chemical Society Doctoral New Investigator grant. The computational resources were partly provided by Center for Computational Research (CCR) at University at Buffalo.
Selwyn, Peter A.
2015-01-01
Reviewing his clinic patient schedule for the day, a physician reflects on the history of a young woman he has been caring for over the past 9 years. What starts out as a routine visit then turns into a unique opening for communication and connection. A chance glimpse out the window of the exam room leads to a deeper meditation on parenthood, survival, and healing, not only for the patient but also for the physician. How many missed opportunities have we all had, without even realizing it, to allow this kind of fleeting but profound opening? PMID:26195687
Selwyn, Peter A
2015-01-01
Reviewing his clinic patient schedule for the day, a physician reflects on the history of a young woman he has been caring for over the past 9 years. What starts out as a routine visit then turns into a unique opening for communication and connection. A chance glimpse out the window of the exam room leads to a deeper meditation on parenthood, survival, and healing, not only for the patient but also for the physician. How many missed opportunities have we all had, without even realizing it, to allow this kind of fleeting but profound opening? PMID:26195687
The effect of exercise on bone mass and structural geometry during growth.
Daly, Robin M
2007-01-01
Regular weight-bearing exercise is widely reported to have beneficial effects on bone mineral content and areal bone mineral density during growth, but the structural basis underlying these changes remains uncertain. In young athletic children, participation in high-impact sports has been shown to enhance bone formation on the periosteal and/or endosteal surfaces of long bones at loaded skeletal sites. Participation in moderate physical activity, recreational play or school-based exercise interventions designed to specifically load bone have also been shown to enhance bone mineral accrual. However, few data are available on the surface-specific effects of exercise training or general physical activity on bone. Based on the limited data available, it would appear that the structural response of bone to exercise during growth is maturity dependent and sex specific; prior to puberty exercise appears to increase periosteal apposition in both sexes, whereas during or late in puberty exercise appears to result in periosteal expansion in boys but endocortical contraction in girls. In most cases, these geometric changes lead to an increase in bone bending strength. However, there are contrasting results as to whether the pre- or peripubertal years are an optimal time to intervene for the greatest osteogenic response; it is likely that both periods represent an important time for incorporating physical activity to optimize bone health. There are also many unresolved questions as to the optimal dose of exercise (intensity, frequency, duration and rate of progression) needed to enhance bone strength in children and adolescents. We know that weight-bearing exercise is important, and that activities should be dynamic, variable in nature, applied rapidly and intermittently, and that relatively few loading cycles are required. Although several effective interventions have been designed for improving bone mass, further research is needed to define the specific exercise programs or
Effects of filament geometry on the arc efficiency of a high-intensity He+ ion source.
Kobuchi, T; Kisaki, M; Shinto, K; Okamoto, A; Kitajima, S; Sasao, M; Tsumori, K; Kaneko, O; Sakakita, H; Kiyama, S; Hirano, Y; Wada, M
2008-10-01
A strongly focusing high-intensity He(+) ion source equipped with three concave electrodes has been designed and constructed as the beam source for a high-energy He(0) neutral beam probe system to diagnose fusion-produced alpha particles in thermonuclear fusion plasmas. The reduction of heat load onto the concave extraction electrodes is particularly important for a long pulse operation, as the heat load deforms the electrodes and thus the beam focal length. The effects on the arc efficiency (beam current/arc power) of the ion source due to the discharge filament structure (straight-type and L-shape-type filaments), size (filament diameters of 2 and 1.5 mm), number, and the locations have been studied. Choice of the appropriate filament structure improved the arc efficiency by 17%. PMID:19044629
Effects of road geometry and traffic volumes on rural roadway accident rates.
Karlaftis, Matthew G; Golias, Ioannis
2002-05-01
This paper revisits the question of the relationship between rural road geometric characteristics, accident rates and their prediction, using a rigorous non-parametric statistical methodology known as hierarchical tree-based regression. The goal of this paper is twofold: first, it develops a methodology that quantitatively assesses the effects of various highway geometric characteristics on accident rates and, second, it provides a straightforward, yet fundamentally and mathematically sound way of predicting accident rates on rural roads. The results show that although the importance of isolated variables differs between two-lane and multilane roads, 'geometric design' variables and pavement condition' variables are the two most important factors affecting accident rates. Further, the methodology used in this paper allows for the explicit prediction of accident rates for given highway sections, as soon as the profile of a road section is given. PMID:11939365
Effect of geometry and operating conditions on spur gear system power loss
NASA Technical Reports Server (NTRS)
Anderson, N. E.; Loewenthal, S. H.
1980-01-01
The results of an analysis of the effects of spur gear size, pitch, width and ratio on total mesh power loss for a wide range of speeds, torques and oil viscosities are presented. The analysis uses simple algebraic expressions to determine gear sliding, rolling and windage losses and also incorporates an approximate ball bearing power loss expression. The analysis shows good agreement with published data. Large diameter and fine-pitched gears had higher peak efficiencies but lower part-load efficiency. Gear efficiencies were generally greater than 98 percent except at very low torque levels. Tare (no-load) losses are generally a significant percentage of the full-load loss except at low speeds.
Effects of mold geometry on fiber orientation of powder injection molded metal matrix composites
Ahmad, Faiz Aslam, Muhammad Altaf, Khurram Shirazi, Irfan
2015-07-22
Fiber orientations in metal matrix composites have significant effect on improving tensile properties. Control of fiber orientations in metal injection molded metal composites is a difficult task. In this study, two mold cavities of dimensions 6x6x90 mm and 10x20x180 mm were used for comparison of fiber orientation in injection molded metal composites test parts. In both mold cavities, convergent and divergent flows were developed by modifying the sprue dimensions. Scanning electron microscope (SEM) was used to examine the fiber orientations within the test samples. The results showed highly aligned fiber in injection molded test bars developed from the convergent melt flow. Random orientation of fibers was noted in the composites test bars produced from divergent melt flow.
NASA Astrophysics Data System (ADS)
Chen, F.; Gindre, D.; Nunzi, J.-M.
2007-09-01
Tunable distributed feedback (DFB) lasing output based on reflection grating configuration instead of the traditional transmission grating type was realized from rhodamine 6G (R6G)-doped ethanol and DCM-doped methanol. Pure gain coupling and additional index coupling were obtained in R6G-doped ethanol and DCM-doped methanol, respectively. The tuning which was independent on the refractive index of the lasing media went through all of the tuning data for the two cases. Dual-peak lasing emissions indicative of the existence of the index grating from the DCM-doped methanol were observed. The interval between the dual peaks increased as the increasing of the pump energy. The effect can be used to estimate the resonant nonlinear refractive index of luminescent materials.
Casimir effect for curved geometries: proximity-force-approximation validity limits.
Gies, Holger; Klingmüller, Klaus
2006-06-01
We compute Casimir interaction energies for the sphere-plate and cylinder-plate configuration induced by scalar-field fluctuations with Dirichlet boundary conditions. Based on a high-precision calculation using world-line numerics, we quantitatively determine the validity bounds of the proximity-force approximation (PFA) on which the comparison between all corresponding experiments and theory are based. We observe the quantitative failure of the PFA on the 1% level for a curvature parameter a/R>0.00755. Even qualitatively, the PFA fails to predict reliably the correct sign of genuine Casimir curvature effects. We conclude that data analysis of future experiments aiming at a precision of 0.1% must no longer be based on the PFA. PMID:16803290
Effect of surface interactions and geometry on the motion of micro bio robots
NASA Astrophysics Data System (ADS)
Wong, Denise; Beattie, Elizabeth E.; Steager, Edward B.; Kumar, Vijay
2013-10-01
Micro Bio Robots (MBRs) are synthetic microstructures with a monolayer of flagellated bacteria adhered to the surface. The flagella of the bacteria propel the microstructure causing it to rotate and translate in a fluidic environment on a planar surface in the absence of external forces. This paper investigates the force contributions of bacteria adhered to the edge versus the center of the micro-structure by selectively altering their behavior using near-UV light. In particular, we investigate the forces that cause predominant clockwise MBR rotation when viewed from above. Additionally, asymmetric shapes, particularly gears, are used to compare the effect of the adherent bacteria with that of collisions among free-swimming bacteria and the microstructure. We find that bacteria adhered near the edge of the MBR interact with the glass substrate under the MBR, accounting for statistically biased clockwise rotation of MBRs.
Rawal, B R; Bhatnagar, Naresh
2013-12-15
The optimal surface for a cementless femoral stem has been a subject of debate for the past several years. Several researchers have stressed the need for research on how an implant surface shape contributes to long-term stability after implantation, in the field of orthopaedics. The introduction of optimized grooves on an implant proximal surface may enhance long-term stability of an implant. This study thus analyzes the effect of different groove dimensions and angles in a transverse plane on stress transmission by a constant load at the femur by using Finite Element Analysis (FEA). Results suggest that the tendency of stress transmission differs depending on the size, position and angle of the grooves. An optimized groove size and inclination plays a vital role for long-term stability of cementless femoral stems. PMID:24517034
NASA Technical Reports Server (NTRS)
Maresh, J. L.; Bragg, M. B.
1984-01-01
A method has been developed to predict the contamination of an airfoil by insects and the resultant performance penalty. Insect aerodynamics have been modeled and the impingement of insects on an airfoil are solved by calculating their trajectories. Upon impact, insect rupture and the resulting height of the debris is determined based on experimental data. A boundary layer analysis is performed to determine which insects cause boundary layer transition and the resultant drag penalty. A contaminated airfoil figure of merit is presented to be used to compare airfoil susceptibility. Results show that the insect contamination effects depend on accretion conditions, airfoil angle of attack and Reynolds number. The importance of the stagnation region to designing airfoils for minimum drag penalties is discussed.
Nonradiative Plasmon Decay and Hot Carrier Dynamics: Effects of Phonons, Surfaces, and Geometry.
Brown, Ana M; Sundararaman, Ravishankar; Narang, Prineha; Goddard, William A; Atwater, Harry A
2016-01-26
The behavior of metals across a broad frequency range from microwave to ultraviolet frequencies is of interest in plasmonics, nanophotonics, and metamaterials. Depending on the frequency, losses of collective excitations in metals can be predominantly classical resistive effects or Landau damping. In this context, we present first-principles calculations that capture all of the significant microscopic mechanisms underlying surface plasmon decay and predict the initial excited carrier distributions so generated. Specifically, we include ab initio predictions of phonon-assisted optical excitations in metals, which are critical to bridging the frequency range between resistive losses at low frequencies and direct interband transitions at high frequencies. In the commonly used plasmonic materials, gold, silver, copper, and aluminum, we find that resistive losses compete with phonon-assisted carrier generation below the interband threshold, but hot carrier generation via direct transitions dominates above threshold. Finally, we predict energy-dependent lifetimes and mean free paths of hot carriers, accounting for electron-electron and electron-phonon scattering, to provide insight toward transport of plasmonically generated carriers at the nanoscale. PMID:26654729
Effect of asymmetrical flow field-flow fractionation channel geometry on separation efficiency.
Ahn, Ji Yeon; Kim, Ki Hun; Lee, Ju Yong; Williams, P Stephen; Moon, Myeong Hee
2010-06-11
The separation efficiencies of three different asymmetrical flow field-flow fractionation (AF4) channel designs were evaluated using polystyrene latex standards. Channel breadth was held constant for one channel (rectangular profile), and was reduced either linearly (trapezoidal profile) or exponentially (exponential profile) along the length for the other two. The effective void volumes of the three channel types were designed to be equivalent. Theoretically, under certain flow conditions, the mean channel flow velocity of the exponential channel could be arranged to remain constant along the channel length, thereby improving separation in AF4. Particle separation obtained with the exponential channel was compared with particle separation obtained with the trapezoidal and rectangular channels. We demonstrated that at a certain flow rate condition (outflow/inflow rate=0.2), the exponential channel design indeed provided better performance with respect to the separation of polystyrene nanoparticles in terms of reducing band broadening. While the trapezoidal channel exhibited a little poorer performance than the exponential, the strongly decreasing mean flow velocity in the rectangular channel resulted in serious band broadening, a delay in retention time, and even failure of larger particles to elute. PMID:20439106
Numerical Investigation of the Effect of Stenosis Geometry on the Coronary Diagnostic Parameters
Kamangar, Sarfaraz; Kalimuthu, Govindaraju; Anjum Badruddin, Irfan; Badarudin, A.; Salman Ahmed, N. J.; Khan, T. M. Yunus
2014-01-01
The present study deals with the functional severity of a coronary artery stenosis assessed by the fractional flow reserve (FFR). The effects of different geometrical shapes of lesion on the diagnostic parameters are unknown. In this study, 3D computational simulation of blood flow in three different geometrical shapes of stenosis (triangular, elliptical, and trapezium) is considered in steady and transient conditions for 70% (moderate), 80% (intermediate), and 90% (severe) area stenosis (AS). For a given percentage AS, the variation of diagnostic parameters which are derived from pressure drop across the stenosis was found in three different geometrical shapes of stenosis and it was observed that FFR is higher in triangular shape and lower in trapezium shape. The pressure drop coefficient (CDP) was higher in trapezium shape and lower in triangular model whereas the LFC shows opposite trend. From the clinical perspective, the relationship between percentage AS and FFR is linear and inversely related in all the three models. A cut-off value of 0.75 for FFR was observed at 76.5% AS in trapezium model, 79.5% in elliptical model, and 82.7% AS for the triangular shaped model. The misinterpretation of the functional severity of the stenosis is in the region of 76.5%-82.7 % AS from different shapes of stenosis models. PMID:25258722
A study on geometry effect of transmission coil for micro size magnetic induction coil
NASA Astrophysics Data System (ADS)
Lee, Kyung Hwa; Jun, Byoung Ok; Kim, Seunguk; Lee, Gwang Jun; Ryu, Mingyu; Choi, Ji-Woong; Jang, Jae Eun
2016-05-01
The effects of transmission (Tx) coil structure have been studied for micro-size magnetic induction coil. The size of the receiving (Rx) coil should be shrunk to the micrometer level for the various new applications such as micro-robot and wireless body implanted devices. In case of the macro-scale magnetic induction coil, the power transmission efficiency is generally considered to be higher as the inductance of the transmission coil became larger; however, the large size difference between macro-size Tx coil and micro-size Rx coil can decrease the power transmission efficiency due to the difference of resonance frequency. Here, we study a correlation of the power transmission with the size and distance between the macro-size Tx and micro-size Rx coils using magnetic induction technique. The maximum power efficiency was 0.28/0.23/0.13/0.12% at the distance of 0.3/1/3/5 cm between Rx and Tx coil. In addition, more efficient wireless power transferring method is suggested with a floating coil for the body implantable devices. The voltage output increased up to 5.4 mV than the original one Tx coil system. The results demonstrated the foundational wireless power transferring system with enhanced power efficiency.
Effects of mesh resolution on large eddy simulation of reacting flows in complex geometry combustors
Boudier, G.; Gicquel, L.Y.M.; Poinsot, T.J.
2008-10-15
The power of current parallel computers is becoming sufficient to apply large eddy simulation (LES) tools to reacting flows not only in academic configurations but also in real gas turbine chambers. The most limiting factor in performing LES of real systems is the mesh size, which directly controls the overall cost of the simulation, so that the effects of mesh resolution on LES results become a key issue. In the present work, an unstructured compressible LES solver is used to compute the reacting flow in a domain corresponding to a sector of a realistic helicopter chamber. Three grids ranging from 1.2 to 44 million elements are used for LES and results are compared in terms of mean and fluctuating fields as well as of pressure spectra. Results show that the mean temperature, reaction rate, and velocity fields are almost insensitive to the grid size. The RMS field of the resolved velocity is also reasonably independent of the mesh, while the RMS fields of temperature exhibit more sensitivity to the grid, as expected from the fact that most of the combustion process proceeds at small scales. The acoustic field exhibits a limited sensitivity to the mesh, suggesting that LES is adapted to the computation of combustion instabilities in complex systems. (author)
Effect of Roller Geometry on Roller Bearing Load-Life Relation
NASA Technical Reports Server (NTRS)
Oswald, Fred B.; Zaretsky, Erwin V.; Poplawski, Joseph V.
2015-01-01
Cylindrical roller bearings typically employ roller profile modification to equalize load distribution, minimize stress concentration at roller ends and allow for a small amount of misalignment. The 1947 Lundberg-Palmgren analysis reported an inverse fourth power relation between load and life for roller bearings with line contact. In 1952, Lundberg and Palmgren changed their load-life exponent to 10/3 for roller bearings, assuming mixed line and point contact. The effect of roller-crown profile was reanalyzed in this paper to determine the actual load-life relation for modified roller profiles. For uncrowned rollers (line contact), the load-life exponent is p = 4, in agreement with the 1947 Lundberg-Palmgren value but crowning reduces the value of the exponent, p. The lives of modern roller bearings made from vacuum-processed steels significantly exceed those predicted by the Lundberg-Palmgren theory. The Zaretsky rolling-element bearing life model of 1996 produces a load-life exponent of p = 5 for flat rollers, which is more consistent with test data. For the Zaretsky model with fully crowned rollers p = 4.3. For an aerospace profile and chamfered rollers, p = 4.6. Using the 1952 Lundberg-Palmgren value p = 10/3, the value incorporated in ANSI/ABMA and ISO bearing standards, can create significant life calculation errors for roller bearings.
Solubility Limits in Lennard-Jones Mixtures: Effects of Disparate Molecule Geometries.
Dyer, Kippi M; Perkyns, John S; Pettitt, B Montgomery
2015-07-23
In order to better understand general effects of the size and energy disparities between macromolecules and solvent molecules in solution, especially for macromolecular constructs self-assembled from smaller molecules, we use the first- and second-order exact bridge diagram extensions of the HNC integral equation theory to investigate single-component, binary, ternary, and quaternary mixtures of Lennard-Jones fluids. For pure fluids, we find that the HNCH3 bridge function integral equation (i.e., exact to third order in density) is necessary to quantitatively predict the pure gas and pure liquid sides of the coexistence region of the phase diagram of the Lennard-Jones fluid. For the mixtures, we find that the HNCH2 bridge function integral equation is sufficient to qualitatively predict solubility in the binary, ternary, and quaternary mixtures, up to the nominal solubility limit. The results, as limiting cases, should be useful to several problems, including accurate phase diagram predictions for complex mixtures, design of self-assembling nanostructures via solvent controls, and the solvent contributions to the conformational behavior of macromolecules in complex fluids. PMID:25621892
Solubility Limits in Lennard-Jones Mixtures: Effects of Disparate Molecule Geometries
Dyer, Kippi M.; Perkyns, John S.; Pettitt, B. Montgomery
2016-01-01
In order to better understand general effects of the size and energy disparities between macromolecules and solvent molecules in solution, especially for macromolecular constructs self-assembled from smaller molecules, we use the first- and second-order exact bridge diagram extensions of the HNC integral equation theory to investigate single-component, binary, ternary, and quaternary mixtures of Lennard-Jones fluids. For pure fluids, we find that the HNCH3 bridge function integral equation (i.e., exact to third order in density) is necessary to quantitatively predict the pure gas and pure liquid sides of the coexistence region of the phase diagram of the Lennard-Jones fluid. For the mixtures, we find that the HNCH2 bridge function integral equation is sufficient to qualitatively predict solubility in the binary, ternary, and quaternary mixtures, up to the nominal solubility limit. The results, as limiting cases, should be useful to several problems, including accurate phase diagram predictions for complex mixtures, design of self-assembling nanostructures via solvent controls, and the solvent contributions to the conformational behavior of macromolecules in complex fluids. PMID:25621892
NASA Technical Reports Server (NTRS)
Schnetzler, C. C.
1981-01-01
A computer modeling and simulation study carried out to assess the effects of various sun and sensor geometries and atmospheric conditions on the directional reflected radiance of several vegetated targets is described. Spectral responses at two wavelengths, 0.68 micron and 0.80 micron, are simulated at nine sensor zenith angles, five sensor azimuths, and nine solar zenith angles for six vegetation canopies under three atmspheric conditions. The six canopies comprise two different geometries of grass canopies at low, medium, and high leaf density. The results suggest that off-nadir viewing effects are more pronounced in the red than in the IR. However, the use of such transformations as the normalized difference index is found to reduce much of the variability seen in the bands. The magnitude of off-nadir viewing effects is found to be a function of canopy geometry.
Effects of shoe sole geometry on toe clearance and walking stability in older adults.
Thies, S B; Price, C; Kenney, L P J; Baker, R
2015-07-01
Thirty-five percent of people above age 65 fall each year, and half of their falls are associated with tripping: tripping, an apparently 'mundane' everyday problem, therefore, significantly impacts on older people's health and associated medical costs. To avoid tripping and subsequent falling, sufficient toe clearance during the swing phase is crucial. We previously found that a rocker-shaped shoe sole enhances toe clearance in young adults, thereby decreasing their trip-risk. This study investigates whether such sole design also enhances older adults' toe clearance, without inadvertently affecting their walking stability. Toe clearance and its variability are reported together with measures of walking stability for twelve older adults, walking in shoes with rocker angles of 10°, 15°, and 20°. Surface inclinations (flat, incline, decline) were chosen to reflect a potential real-world environment. Toe clearance increased substantially from the 10° to the 15° rocker angle (p=0.003) without compromising measures of walking stability (p>0.05). A further increase in rocker angle to 20° resulted in less substantial enhancement of toe clearance and came at the cost of a decrease in gait speed on the decline. The novelty of this investigation lies in the exploration of the trade-off between reduction of trip-risk through footwear design and adverse effects on walking stability on real-life relevant surfaces. Our two studies suggest that the current focus on slip-resistance in footwear design may need to be generalised to include other factors that affect trip-risk. PMID:26032398
Effect of nifedipine on coronary capillary geometry in normotensive and hypertensive rats.
Rakusan, K; Cicutti, N; Kazda, S; Turek, Z
1994-08-01
The aim of this study was to describe quantitatively changes in the coronary capillary network resulting from hypertrophy in spontaneously hypertensive rats (SHR) and a potential effect of long-term treatment of these animals with nifedipine. Age-matched male SHR and Wistar-Kyoto (WKY) rats were treated for 27 weeks. Four experimental groups were analyzed: (1) untreated SHR, (2) nifedipine-treated SHR, (3) untreated control WKY rats, and (4) nifedipine-treated WKY rats. Treatment significantly decreased systolic blood pressure in SHR, although normotensive pressures were not reached. SHR had significantly higher cardiac weight, which decreased in nifedipine-treated rats, but values remained above those in control animals. Morphometric evaluation revealed lower capillary density and larger capillary domain area in hearts from SHR, which were partially attenuated by treatment with nifedipine. Capillary domain area was also significantly larger at arteriolar portions compared with domains supplied at venular portions. Capillary segment length was consistently shorter on the venular than arteriolar portion of the capillary, whereas no differences were observed between hearts from WKY rats and SHR. Treatment with nifedipine resulted in a prolongation of segment length. Reconstruction of the three-dimensional capillary supply unit (capillary domain area times capillary segment length) revealed significant differences between the amount of tissue supplied by a capillary at its arteriolar portion than more distally, which was detectable in all experimental groups. In hypertrophic hearts from SHR this tissue volume is increased mainly because of longer intercapillary distances and larger domains, especially on arteriolar portions.(ABSTRACT TRUNCATED AT 250 WORDS) PMID:8039845
Spacetime symmetries, Newton-Cartan geometry and the quantum Hall effect
NASA Astrophysics Data System (ADS)
Son, Dam
2015-03-01
Spacetime symmetries place powerful constraints on the physics of quantum Hall states from spacetime symmetries. These symmetries can be seen by putting the quantum Hall system on a curved manifold. By doing so, one discovers that the action is invariant with respect to time-preserving diffeomorphisms. The diffeomorphism invariance remains nontrivial on the lowest Landau level when inter Landau level mixing is negligible. In the talk we will extract physical consequences of the diffeomorphism invariance for physical observables in flat space. In particular, we relate the leading dependence of the Hall conductivity on wavenumber to the shift. We show how the spectral densities of the components of the stress tensor satisfy several sum rules, one of which involves the static projected structure factor and another involves the shift. From the sum rules one can deduce an inequality between the leading k4 coefficient of the static structure factor and the shift. The inequality is saturated for a large class of trial wavefunctions. The sum rules suggest that if the magneto-roton continues to exist as a sharp resonance at small wavenumber, it should be a ``chiral massive graviton,'' i.e., a particle with spin 2 of one circular polarization. This is demonstrated explicitly in a toy model, where which the sum rules are saturated by one single gapped mode. We argue that the circular polarization of the magneto-roton can be in principle observed by polarized Raman scatterings. The most convenient formalism to write down effective actions satisfying local diffeomorphism invariance turns out to be the Newton-Cartan formalism, introduced by Elie Cartan in 1922-1923 in his attempt to rewrite Newton's gravity in a coordinate-invariant way. We describe the structure of the Newton-Cartan space, including the construction of the connection. Supported by DOE Grant DE-FG02-13ER4195, ARO-MURI Grant 63834-PH-MUR, NSF Grant DMR-0820054, and a Simons Investigator grant from the Simons
NASA Astrophysics Data System (ADS)
Perez-Gussinye, M.; Lowry, A. R.; Phipps Morgan, J.; Tassara, A.
2007-12-01
We present a new map of spatial variations in effective elastic thickness, Te, along the Andes, estimated using Bouguer coherence. The Te variations reflect interactions between subducting slab and pre-existing terrane structure. In the forearc, conductive cooling of the continent by the subducting slab exerts primary control on rigidity, resulting in Te that is highest (~ 40 km) where the oceanic lithosphere is oldest and coldest (~ 20° S). In the central Andes, Te is relatively low (~ 20 km) along the volcanic chain, the Altiplano and Puna plateaus. We interpret this weakening to reflect a high geothermal gradient maintained by advective magmatic processes, a shallow and hot asthenosphere, and a very weak lower crust throughout this region. East of the plateaus, high Te delineates underthrusting of the Brazilian shield. North and south of the plateaus, areas experiencing flat subduction are characterized by high Te, high shear wave velocity, thick thermal boundary layer and low heat flow, indicating that continental lithosphere there is thicker, colder and stronger. Based on these relationships we suggest that variations in slab dip along the margin relate to variations in structure of the continental lithosphere. In particular, we propose that upper plate structure influences the width and viscosity of the asthenospheric wedge, which control the suction moment responsible for the subduction angle at depths ~ 70--100 km. When oceanic lithosphere subducts beneath thin continental lithosphere, the low viscosity asthenosphere allows the slab to detach from the continent and sink into the mantle at normal angles. However, when oceanic lithosphere subducts near or beneath thick and strong continental lithosphere, the asthenospheric wedge narrows and corner flow drags high viscosity mantle from the base of the thick (> 150 km), cold continent into the wedge. Suction forces increase both with narrowing of the wedge and with increasing viscosity. We estimate the
NASA Astrophysics Data System (ADS)
PéRez-Gussinyé, M.; Lowry, A. R.; Phipps Morgan, J.; Tassara, A.
2008-02-01
We present a new map of the spatial variations in effective elastic thickness, Te, along the Andes estimated using Bouguer coherence. The Te variations reflect interactions between subducting slab and preexisting terrane structure. In the forearc, conductive cooling of the continent by the subducting slab exerts primary control on rigidity, resulting in Te that is highest (˜40 km) where the oceanic lithosphere is oldest and coldest (˜20°S). In the central Andes, Te is relatively low (˜20 km) along the volcanic chain and the Altiplano and Puna plateaus. We interpret this weakening to reflect a high geothermal gradient maintained by advective magmatic processes, a shallow and hot asthenosphere, and a very weak lower crust throughout this region. East of the plateaus, high Te delineates underthrusting of the Brazilian shield. Finally, north and south of the plateaus, flat subduction areas are characterized by high Te, high shear wave velocity, thick thermal lithosphere, and low heat flow, indicating that continental lithosphere there is thicker, colder, and stronger. On the basis of these relationships we suggest that variations in slab dip along the margin relate to variations in structure of the continental lithosphere. In particular, we propose that upper plate structure influences the width and viscosity of the asthenospheric wedge, which control the suction moment responsible for the subduction angle at depths ≥70-100 km. For example, when oceanic lithosphere subducts beneath thin continental lithosphere, the low-viscosity asthenosphere allows the slab to detach from the continent and sink into the mantle at normal angles. However, when oceanic lithosphere subducts close or beneath thick and strong continental lithosphere, the asthenospheric wedge narrows and corner flow drags high-viscosity mantle from the base of the thick (>150 km), cold continent into the wedge. Suction forces increase with both narrowing of the wedge and its increasing viscosity. We
Effects of display geometry and pixel structure on stereo display usability
NASA Astrophysics Data System (ADS)
Mulkens, Edwin; Roberts, John W.
2001-06-01
for inconsistencies, so any improvement in stereo realism increases the number of people who can enjoy it. Despite the importance of providing consistent 3-D cues, no existing display system can do a perfect job of displaying any significant variety of stereo images, nor will such a perfect display be created in the next several decades. It is therefore important to look at the sources of 3-D cue inconsistencies in terms of the severity of impact on the viewing experience, and the effort required to minimize the effect of each inconsistency.
Dynamical gauge effects in an open quantum network
NASA Astrophysics Data System (ADS)
Zhao, Jianshi; Price, Craig; Liu, Qi; Gemelke, Nathan
2016-05-01
We describe new experimental techniques for simulation of high-energy field theories based on an analogy between open thermodynamic systems and effective dynamical gauge-fields following SU(2) × U(1) Yang-Mills models. By coupling near-resonant laser-modes to atoms moving in a disordered optical environment, we create an open system which exhibits a non-equilibrium phase transition between two steady-state behaviors, exhibiting scale-invariant behavior near the transition. By measuring transport of atoms through the disordered network, we observe two distinct scaling behaviors, corresponding to the classical and quantum limits for the dynamical gauge field. This behavior is loosely analogous to dynamical gauge effects in quantum chromodynamics, and can mapped onto generalized open problems in theoretical understanding of quantized non-Abelian gauge theories. Additional, the scaling behavior can be understood from the geometric structure of the gauge potential and linked to the measure of information in the local disordered potential, reflecting an underlying holographic principle. We acknowledge support from NSF Award No.1068570, and the Charles E. Kaufman Foundation.
Foudray, A M K; Olcott, P D
2013-01-01
We are studying two new detector technologies that directly measure the three-dimensional coordinates of 511 keV photon interactions for high-resolution positron emission tomography (PET) systems designed for small animal and breast imaging. These detectors are based on (1) lutetium oxyorthosilicate (LSO) scintillation crystal arrays coupled to position-sensitive avalanche photodiodes (PSAPD) and (2) cadmium zinc telluride (CZT). The detectors have excellent measured 511 keV photon energy resolutions (≤12% FWHM for LSO-PSAPD and ≤3% for CZT) and good coincidence time resolutions (2 ns FWHM for LSO-PSAPD and 8 ns for CZT). The goal is to incorporate the detectors into systems that will achieve 1 mm3 spatial resolution (~1 mm3, uniform throughout the field of view (FOV)), with excellent contrast resolution as well. In order to realize 1 mm3 spatial resolution with high signal-to-noise ratio (SNR), it is necessary to significantly boost coincidence photon detection efficiency (referred to as photon sensitivity). To facilitate high photon sensitivity in the proposed PET system designs, the detector arrays are oriented ‘edge-on’ with respect to incoming 511 keV annihilation photons and arranged to form a compact FOV with detectors very close to, or in contact with, the subject tissues. In this paper, we used Monte Carlo simulation to study various factors that limit the photon sensitivity of a high-resolution PET system dedicated to small animal imaging. To optimize the photon sensitivity, we studied several possible system geometries for a fixed 8 cm transaxial and 8 cm axial FOV. We found that using rectangular-shaped detectors arranged into a cylindrical geometry does not yield the best photon sensitivity. This is due to the fact that forming rectangular-shaped detectors into a ring produces significant wedge-shaped inter-module gaps, through which Compton-scattered photons in the detector can escape. This effect limits the center point source photon
Habte, F; Foudray, A M K; Olcott, P D; Levin, C S
2007-07-01
We are studying two new detector technologies that directly measure the three-dimensional coordinates of 511 keV photon interactions for high-resolution positron emission tomography (PET) systems designed for small animal and breast imaging. These detectors are based on (1) lutetium oxyorthosilicate (LSO) scintillation crystal arrays coupled to position-sensitive avalanche photodiodes (PSAPD) and (2) cadmium zinc telluride (CZT). The detectors have excellent measured 511 keV photon energy resolutions (geometries for a fixed 8 cm transaxial and 8 cm axial FOV. We found that using rectangular-shaped detectors arranged into a cylindrical geometry does not yield the best photon sensitivity. This is due to the fact that forming rectangular-shaped detectors into a ring produces significant wedge-shaped inter-module gaps, through which Compton-scattered photons in the detector can escape. This effect limits the center point source
NASA Astrophysics Data System (ADS)
Habte, F.; Foudray, A. M. K.; Olcott, P. D.; Levin, C. S.
2007-07-01
We are studying two new detector technologies that directly measure the three-dimensional coordinates of 511 keV photon interactions for high-resolution positron emission tomography (PET) systems designed for small animal and breast imaging. These detectors are based on (1) lutetium oxyorthosilicate (LSO) scintillation crystal arrays coupled to position-sensitive avalanche photodiodes (PSAPD) and (2) cadmium zinc telluride (CZT). The detectors have excellent measured 511 keV photon energy resolutions (<=12% FWHM for LSO-PSAPD and <=3% for CZT) and good coincidence time resolutions (2 ns FWHM for LSO-PSAPD and 8 ns for CZT). The goal is to incorporate the detectors into systems that will achieve 1 mm3 spatial resolution (~1 mm3, uniform throughout the field of view (FOV)), with excellent contrast resolution as well. In order to realize 1 mm3 spatial resolution with high signal-to-noise ratio (SNR), it is necessary to significantly boost coincidence photon detection efficiency (referred to as photon sensitivity). To facilitate high photon sensitivity in the proposed PET system designs, the detector arrays are oriented 'edge-on' with respect to incoming 511 keV annihilation photons and arranged to form a compact FOV with detectors very close to, or in contact with, the subject tissues. In this paper, we used Monte Carlo simulation to study various factors that limit the photon sensitivity of a high-resolution PET system dedicated to small animal imaging. To optimize the photon sensitivity, we studied several possible system geometries for a fixed 8 cm transaxial and 8 cm axial FOV. We found that using rectangular-shaped detectors arranged into a cylindrical geometry does not yield the best photon sensitivity. This is due to the fact that forming rectangular-shaped detectors into a ring produces significant wedge-shaped inter-module gaps, through which Compton-scattered photons in the detector can escape. This effect limits the center point source photon sensitivity to
NASA Astrophysics Data System (ADS)
Karamooz Ravari, M. R.; Nasr Esfahani, S.; Taheri Andani, M.; Kadkhodaei, M.; Ghaei, A.; Karaca, H.; Elahinia, M.
2016-02-01
Shape memory alloy (such as NiTi) cellular lattice structures are a new class of advanced materials with many potential applications. The cost of fabrication of these structures however is high. It is therefore necessary to develop modeling methods to predict the functional behavior of these alloys before fabrication. The main aim of the present study is to assess the effects of geometry, microstructural imperfections and material asymmetric response of dense shape memory alloys on the mechanical response of cellular structures. To this end, several cellular and dense NiTi samples are fabricated using a selective laser melting process. Both cellular and dense specimens were tested in compression in order to obtain their stress-strain response. For modeling purposes, a three -dimensional (3D) constitutive model based on microplane theory which is able to describe the material asymmetry was employed. Five finite element models based on unit cell and multi-cell methods were generated to predict the mechanical response of cellular lattices. The results show the considerable effects of the microstructural imperfections on the mechanical response of the cellular lattice structures. The asymmetric material response of the bulk material also affects the mechanical response of the corresponding cellular structure.
Moazami, Hamid Reza; Hosseiny Davarani, Saied Saeed; Mohammadi, Jamil; Nojavan, Saeed; Abrari, Masoud
2015-09-01
The distribution of electric field vectors was first calculated for electromembrane extraction (EME) systems in classical and cylindrical electrode geometries. The results showed that supported liquid membrane (SLM) has a general field amplifying effect due to its lower dielectric constant in comparison with aqueous donor/acceptor solutions. The calculated norms of the electric field vector showed that a DC voltage of 50 V can create huge electric field strengths up to 64 kV m(-1) and 111 kV m(-1) in classical and cylindrical geometries respectively. In both cases, the electric field strength reached its peak value on the inner wall of the SLM. In the case of classical geometry, the field strength was a function of the polar position of the SLM whereas the field strength in cylindrical geometry was angularly uniform. In order to investigate the effect of the electrode geometry on the performance of real EME systems, the analysis was carried out in three different geometries including classical, helical and cylindrical arrangements using naproxen and sodium diclofenac as the model analytes. Despite higher field strength and extended cross sectional area, the helical and cylindrical geometries gave lower recoveries with respect to the classical EME. The observed decline of the signal was proved to be against the relations governing migration and diffusion processes, which means that a third driving force is involved in EME. The third driving force is the interaction between the radially inhomogeneous electric field and the analyte in its neutral form. PMID:26388374
NASA Technical Reports Server (NTRS)
Asbury, Scott C.; Hunter, Craig A.
1999-01-01
An investigation was conducted in the model preparation area of the Langley 16-Foot Transonic Tunnel to determine the effects of convoluted divergent-flap contouring on the internal performance of a fixed-geometry, nonaxisymmetric, convergent-divergent exhaust nozzle. Testing was conducted at static conditions using a sub-scale nozzle model with one baseline and four convoluted configurations. All tests were conducted with no external flow at nozzle pressure ratios from 1.25 to approximately 9.50. Results indicate that baseline nozzle performance was dominated by unstable, shock-induced, boundary-layer separation at overexpanded conditions. Convoluted configurations were found to significantly reduce, and in some cases totally alleviate separation at overexpanded conditions. This result was attributed to the ability of convoluted contouring to energize and improve the condition of the nozzle boundary layer. Separation alleviation offers potential for installed nozzle aeropropulsive (thrust-minus-drag) performance benefits by reducing drag at forward flight speeds, even though this may reduce nozzle thrust ratio as much as 6.4% at off-design conditions. At on-design conditions, nozzle thrust ratio for the convoluted configurations ranged from 1% to 2.9% below the baseline configuration; this was a result of increased skin friction and oblique shock losses inside the nozzle.
NASA Technical Reports Server (NTRS)
Groesbeck, D.; Von Glahn, U.
1979-01-01
The effects on acoustic characteristics of nozzle type and location on a wing for STOL engine over-the-wing configurations are assessed at full scale on the basis of model-scale data. Three types of nozzle configurations are evaluated: a circular nozzle with external deflector mounted above the wing, a slot nozzle with external deflector mounted on the wing and a slot nozzle mounted on the wing. Nozzle exhaust plane locations with respect to the wing leading edge are varied from 10 to 46 percent chord (flaps retracted) with flap angles of 20 deg (take-off attitude) and 60 deg (approach attitude). Perceived noise levels (PNL) are calculated as a function of flyover distance at 152 m altitude. From these plots, static EPNL values, defined as flyover relative noise levels, are calculated and plotted as a function of lift and thrust ratios. From such plots the acoustic benefits attributable to variations in nozzle/deflector/wing geometry at full scale are assessed for equal aerodynamic performance.
NASA Technical Reports Server (NTRS)
Groesbeck, D.; Vonglahn, U.
1979-01-01
The effects on acoustic characteristics of nozzle type and location on a wing for STOL engine over-the-wing configurations are assessed at full scale on the basis of model-scale data. Three types of nozzle configurations are evaluated: a circular nozzle with external deflector mounted above the wing, a slot nozzle with external deflector mounted on the wing and a slot nozzle mounted on the wing. Nozzle exhaust plane locations with respect to the wing leading edge are varied from 10 to 46 percent chord (flaps retracted) with flap angles of 20 (takeoff altitude) and 60 (approach attitude). Perceived noise levels (PNL) are calculated as a function of flyover distance at 152 m altitude. From these plots, static EPNL values, defined as flyover relative noise levels, are calculated and plotted as a function of lift and thrust ratios. From such plots the acoustic benefits attributable to variations in nozzle/deflector/wing geometry at full scale are assessed for equal aerodynamic performance.
NASA Technical Reports Server (NTRS)
Font, G. I.
1993-01-01
Explored in this study are the physical effects of the numerical treatment of the aft geometry on the vortex behavior and force production due to a tangential jet on a body at a high angle of attack. The study is conducted numerically by solving the three-dimensional, compressible-flow, Reynolds-averaged Navier-Stokes equations. Two tangent-ogive cylinder configurations are used. The first configuration locates the computational exit plane at the end of the body, while the second caps the end of the body with a hemisphere and locates the exit plane far downstream. In both configurations, a blowing slot is located at the cylinder-ogive junction. Comparisons are made between results for the two configurations for cases with and without the jet present. Results indicate that inclusion of the wake of the body in the computations, while altering the flow in small details, does not change the character of the flow. The vortex behavior remains unaltered and the force distribution, while changing to some degree in magnitude, does not change in shape.
NASA Astrophysics Data System (ADS)
Tseng, Chien-Fu; Tsai, Tsung-Yen; Huang, Yen-Hsiu; Lee, Ming-Tsang; Horng, Ray-Hua
2015-12-01
In this study a numerical simulation was carried out to analyze the transport phenomena in a vertical type metal organic chemical vapor deposition (MOCVD) reactor for Gallium Nitride (GaN) growth. The simulated results were compared and validated by experiment. The effects of showerhead design and chamber height are investigated and discussed. It was found that, by properly adjusting the height of the chamber, both the growth rate and film uniformity could be significantly improved. This is attributed to the suppression of the thermal and mass transfer boundary layers by the injection flow of reacting gas mixtures, as well as the confined vertical vortices caused by the geometry of the reduced space. However, inappropriate design of the distance between the showerhead and the susceptor can result in uneven distribution of the organic source in the vicinity of the substrate surface resulting in an uneven growth rate of the GaN film. Consequently, there exists an optimal chamber height that will give the best growth rate and uniformity to the GaN film as discussed in this study. This study provides comprehensive insight into the transport phenomena of GaN growth that includes coupled heat and mass transfer as well as chemical reactions. The results provide important information in a succinct format and enable decisions to be made about the showerhead and the geometrical design and size of a vertical MOCVD reactor.
NASA Astrophysics Data System (ADS)
Ghazanfarian, J.; Abbassi, A.
2012-03-01
Analytical and numerical solutions of the 2D transient dual-phase-lag (DPL) heat conduction equation are presented in this article. The geometry is that of a simplified metal oxide semiconductor field effect transistor with a heater placed on it. A temperature jump boundary condition is used on all boundaries in order to consider boundary phonon scattering at the micro- and nanoscale. A combination of a Laplace transformation technique and separation of variables is used to solve governing equations analytically, and a three-level finite difference scheme is employed to generate numerical results. The results are illustrated for three Knudsen numbers of 0.1, 1, and 10 at different instants of time. It is seen that the wave characteristic of the DPL model is strengthened by increasing the Knudsen number. It is found that the combination of the DPL model with the proposed mixed-type temperature boundary condition has the potential to accurately predict a 2D temperature distribution not only within the transistor itself but also in the near-boundary region.
Jiang, Shan; Li, Pan; Yu, Yan; Liu, Jun; Yang, Zhiyong
2014-10-17
A thorough understanding of needle-tissue interaction mechanics is necessary to optimize needle design, achieve robotically needle steering, and establish surgical simulation system. It is obvious that the interaction is influenced by numerous variable parameters, which are divided into three categories: needle geometries, insertion methods, and tissue characteristics. A series of experiments are performed to explore the effect of influence factors (material samples n=5 for each factor) on the insertion force. Data were collected from different biological tissues and a special tissue-equivalent phantom with similar mechanical properties, using a 1-DOF mechanical testing system instrumented with a 6-DOF force/torque (F/T) sensor. The experimental results indicate that three basic phases (deformation, insertion, and extraction phase) are existent during needle penetration. Needle diameter (0.7-3.2mm), needle tip (blunt, diamond, conical, and beveled) and bevel angle (10-85°) are turned out to have a great influence on insertion force, so do the insertion velocity (0.5-10mm/s), drive mode (robot-assisted and hand-held), and the insertion process (interrupted and continuous). Different tissues such as skin, muscle, fat, liver capsule and vessel are proved to generate various force cures, which can contribute to the judgement of the needle position and provide efficient insertion strategy. PMID:25169657
Goodsitt, Mitchell M; Chan, Heang-Ping; Schmitz, Andrea; Zelakiewicz, Scott; Telang, Santosh; Hadjiiski, Lubomir; Watcharotone, Kuanwong; Helvie, Mark A; Paramagul, Chintana; Neal, Colleen; Christodoulou, Emmanuel; Larson, Sandra C; Carson, Paul L
2014-10-01
The effect of acquisition geometry in digital breast tomosynthesis was evaluated with studies of contrast-to-noise ratios (CNRs) and observer preference. Contrast-detail (CD) test objects in 5 cm thick phantoms with breast-like backgrounds were imaged. Twelve different angular acquisitions (average glandular dose for each ~1.1 mGy) were performed ranging from narrow angle 16° with 17 projection views (16d17p) to wide angle 64d17p. Focal slices of SART-reconstructed images of the CD arrays were selected for CNR computations and the reader preference study. For the latter, pairs of images obtained with different acquisition geometries were randomized and scored by 7 trained readers. The total scores for all images and readings for each acquisition geometry were compared as were the CNRs. In general, readers preferred images acquired with wide angle as opposed to narrow angle geometries. The mean percent preferred was highly correlated with tomosynthesis angle (R = 0.91). The highest scoring geometries were 60d21p (95%), 64d17p (80%), and 48d17p (72%); the lowest scoring were 16d17p (4%), 24d9p (17%) and 24d13p (33%). The measured CNRs for the various acquisitions showed much overlap but were overall highest for wide-angle acquisitions. Finally, the mean reader scores were well correlated with the mean CNRs (R = 0.83). PMID:25211509
NASA Astrophysics Data System (ADS)
Goodsitt, Mitchell M.; Chan, Heang-Ping; Schmitz, Andrea; Zelakiewicz, Scott; Telang, Santosh; Hadjiiski, Lubomir; Watcharotone, Kuanwong; Helvie, Mark A.; Paramagul, Chintana; Neal, Colleen; Christodoulou, Emmanuel; Larson, Sandra C.; Carson, Paul L.
2014-10-01
The effect of acquisition geometry in digital breast tomosynthesis was evaluated with studies of contrast-to-noise ratios (CNRs) and observer preference. Contrast-detail (CD) test objects in 5 cm thick phantoms with breast-like backgrounds were imaged. Twelve different angular acquisitions (average glandular dose for each ~1.1 mGy) were performed ranging from narrow angle 16° with 17 projection views (16d17p) to wide angle 64d17p. Focal slices of SART-reconstructed images of the CD arrays were selected for CNR computations and the reader preference study. For the latter, pairs of images obtained with different acquisition geometries were randomized and scored by 7 trained readers. The total scores for all images and readings for each acquisition geometry were compared as were the CNRs. In general, readers preferred images acquired with wide angle as opposed to narrow angle geometries. The mean percent preferred was highly correlated with tomosynthesis angle (R = 0.91). The highest scoring geometries were 60d21p (95%), 64d17p (80%), and 48d17p (72%); the lowest scoring were 16d17p (4%), 24d9p (17%) and 24d13p (33%). The measured CNRs for the various acquisitions showed much overlap but were overall highest for wide-angle acquisitions. Finally, the mean reader scores were well correlated with the mean CNRs (R = 0.83).
Goodsitt, Mitchell M.; Chan, Heang-Ping; Schmitz, Andrea; Zelakiewicz, Scott; Telang, Santosh; Hadjiiski, Lubomir; Watcharotone, Kuanwong; Helvie, Mark A.; Paramagul, Chintana; Neal, Colleen; Christodoulou, Emmanuel; Larson, Sandra C.; Carson, Paul L.
2014-01-01
The effect of acquisition geometry in digital breast tomosynthesis (DBT) was evaluated with studies of contrast-to-noise ratios (CNRs) and observer preference. Contrast-detail (CD) test objects in 5 cm thick phantoms with breast-like backgrounds were imaged. Twelve different angular acquisitions (average glandular dose for each ~1.1 mGy) were performed ranging from narrow angle 16° with 17 projection views (16d17p) to wide angle 64d17p. Focal slices of SART-reconstructed images of the CD arrays were selected for CNR computations and the reader preference study. For the latter, pairs of images obtained with different acquisition geometries were randomized and scored by 7 trained readers. The total scores for all images and readings for each acquisition geometry were compared as were the CNRs. In general, readers preferred images acquired with wide angle as opposed to narrow angle geometries. The mean percent preferred was highly correlated with tomosynthesis angle (R=0.91). The highest scoring geometries were 60d21p (95%), 64d17p (80%), and 48d17p (72%); the lowest scoring were 16d17p (4%), 24d9p (17%) and 24d13p (33%). The measured CNRs for the various acquisitions showed much overlap but were overall highest for wide-angle acquisitions. Finally, the mean reader scores were well correlated with the mean CNRs (R=0.83). PMID:25211509
NASA Technical Reports Server (NTRS)
Sadler, S. G.
1972-01-01
A mathematical model and computer program was implemented to study the main rotor free wake geometry effects on helicopter rotor blade air loads and response in steady maneuvers. Volume 1 (NASA CR-2110) contains the theoretical formulation and analysis of results. Volume 2 contains the computer program listing.
Dong, Xue-Hui; Lu, Xiaocun; Ni, Bo; Chen, Ziran; Yue, Kan; Li, Yiwen; Rong, Lixia; Koga, Tadanori; Hsiao, Benjamin S; Newkome, George R; Shi, An-Chang; Zhang, Wen-Bin; Cheng, Stephen Z D
2014-05-14
A series of giant polymer-dendron conjugates with a dendron head and a linear polymer tail were synthesized via"click" chemistry between azide-functionalized polystyrene (PS(N), N: degree-of-polymerization) and t-butyl protected, alkyne-functionalized second generation dendron (tD), followed by a deprotection process to generate a dendron termini possessing nine carboxylic acid groups. The molecular structures were confirmed by nuclear magnetic resonance, size-exclusion chromatographic analyses, and matrix-assisted laser desorption ionization time-of-flight mass spectra. These well-defined conjugates can serve as a model system to study the effects of the molecular geometries on the self-assembly behaviour, as compared with their linear analogues. Four phase morphologies found in flexible linear diblock copolymer systems, including lamellae, bicontinuous double gyroids, hexagonal packed cylinders, and body-centred cubic packed spheres, were observed in this series of conjugates based on the results of small angle X-ray scattering and transmission electron microscopy. All of the domain sizes in these phase separated structures were around or less than 10 nm. A 'half' phase diagram was constructed based on the experimental results. The geometrical effect was found not only to enhance the immiscibility between the PS(N) tail and dendron head, but also systematically shift all of the phase boundaries towards higher volume fractions of the PS(N) tails, resulting in an asymmetrical phase diagram. This study may provide a pathway to the construction of ordered patterns of sub-10 nm feature size using polymer-dendron conjugates. PMID:24718376
Ando, Masatoshi; Eckert, George J; Stookey, George K; Zero, Domenick T
2004-01-01
The objective of this study was to determine the effect of imaging geometry on evaluating natural white-spot lesions with quantitative light-induced fluorescence (QLF). A total of 34 specimens were prepared from extracted human premolars and permanent molars with white spots on the interproximal surface. The specimens were each adjusted to a final thickness of 3.0 mm. Images were acquired with the QLF system perpendicular to the white spots and at 5 degrees intervals up to 30 degrees above and below the perpendicular. The specimens were rotated around the buccolingual axis of the tooth (pitch angle) and around the long axis of the tooth (roll angle). The averages of fluorescence loss (DeltaF, %) and lesion size (mm2) were determined with QLF. Another variable, DeltaQ, which was defined as the fluorescence loss integrated over the lesion size (% x mm2), was also calculated. DeltaF was smaller when lesions were viewed from the cervical direction (angles less than 90 degrees ), and became bigger when viewed from the coronal direction. Roll angle did not significantly affect DeltaF. Apparent lesion size diminished with deviations from 90 degrees in both directions for pitch and roll angles. DeltaQ was affected by pitch and roll angles with the largest value at 90 degrees and values decreasing in both directions from 90 degrees. In general, there were significant differences for angles larger than 20 degrees from the perpendicular for all three QLF variables. This study suggests that angle is an important factor to control when performing QLF studies; however, small changes (deviations within 20 degrees ) have a minimal effect on QLF variables. PMID:14684976
43 CFR 2091.5-4 - Segregative effect and opening: Water power withdrawals.
Code of Federal Regulations, 2012 CFR
2012-10-01
... 43 Public Lands: Interior 2 2012-10-01 2012-10-01 false Segregative effect and opening: Water power withdrawals. 2091.5-4 Section 2091.5-4 Public Lands: Interior Regulations Relating to Public Lands... LAWS AND RULES Segregation and Opening of Lands § 2091.5-4 Segregative effect and opening: Water...
43 CFR 2091.5-4 - Segregative effect and opening: Water power withdrawals.
Code of Federal Regulations, 2013 CFR
2013-10-01
... 43 Public Lands: Interior 2 2013-10-01 2013-10-01 false Segregative effect and opening: Water power withdrawals. 2091.5-4 Section 2091.5-4 Public Lands: Interior Regulations Relating to Public Lands... LAWS AND RULES Segregation and Opening of Lands § 2091.5-4 Segregative effect and opening: Water...
43 CFR 2091.5-4 - Segregative effect and opening: Water power withdrawals.
Code of Federal Regulations, 2011 CFR
2011-10-01
... 43 Public Lands: Interior 2 2011-10-01 2011-10-01 false Segregative effect and opening: Water power withdrawals. 2091.5-4 Section 2091.5-4 Public Lands: Interior Regulations Relating to Public Lands... LAWS AND RULES Segregation and Opening of Lands § 2091.5-4 Segregative effect and opening: Water...
43 CFR 2091.7-2 - Segregative effect and opening: Taylor Grazing Act.
Code of Federal Regulations, 2011 CFR
2011-10-01
... 43 Public Lands: Interior 2 2011-10-01 2011-10-01 false Segregative effect and opening: Taylor Grazing Act. 2091.7-2 Section 2091.7-2 Public Lands: Interior Regulations Relating to Public Lands... LAWS AND RULES Segregation and Opening of Lands § 2091.7-2 Segregative effect and opening:...
Eyes open versus eyes closed - Effect on human rotational responses
NASA Technical Reports Server (NTRS)
Wall, Conrad, III; Furman, Joseph M. R.
1989-01-01
The effect of eyelid closure on the response to rotational vestibular stimulation was assessed by evaluating 16 normal human subjects with both earth vertical axis (EVA) and earth horizontal axis (EHA) yaw rotations with either eyes closed (EC) or eyes open in the dark (EOD). Results indicated that for EVA rotation, the subjects' responses were of larger magnitude and less variable with EOD than with EC. However, for EHA rotation, responses were of larger magnitude and equally variable with EC as compared to EOD. Data also indicated that the quality of the EHA response with EC was altered because eyelid closure influenced the amount of periodic gaze. It is concluded that eyelid closure has an effect upon both canalocular and otolithocular reflexes and it is suggested that both EVA and EHA rotational testing be performed with EOD rather than with EC.
Reed, Matthew P; Ebert-Hamilton, Sheila M; Klinich, Kathleen D; Manary, Miriam A; Rupp, Jonathan D
2013-01-01
more likely to experience poor shoulder belt fit due to outboard and forward D-ring locations when sitting on the booster. Taller children experienced more-outboard shoulder belt fit in conditions without shoulder belt routing by the booster and in the one booster with poor shoulder belt routing. Adjustable shoulder belt routing on three of the highback boosters effectively eliminated stature effects, providing approximately the same shoulder belt fit for all children. Seat back angle did not have a significant effect on shoulder belt fit. The results of this study have broad applicability toward the improvement of occupant restraints for children The data show substantial effects of booster design on belt fit, particularly the effects of alternative lap and torso belt routing approaches. The data quantify the critical importance of belt anchorage location for child belt fit, providing an important foundation for efforts to optimize belt geometry for children. PMID:22703990
ERIC Educational Resources Information Center
Kuntz, Gilles
The first section of this paper on World Wide Web applications related to dynamic geometry addresses dynamic geometry and teaching, including the relationship between dynamic geometry and direct manipulation, key features of dynamic geometry environments, the importance of direct engagement of the learner using construction software for…
Li, Han; Lin, Kexin; Shahmirzadi, Danial
2016-01-01
This study aims to quantify the effects of geometry and stiffness of aneurysms on the pulse wave velocity (PWV) and propagation in fluid–solid interaction (FSI) simulations of arterial pulsatile flow. Spatiotemporal maps of both the wall displacement and fluid velocity were generated in order to obtain the pulse wave propagation through fluid and solid media, and to examine the interactions between the two waves. The results indicate that the presence of abdominal aortic aneurysm (AAA) sac and variations in the sac modulus affect the propagation of the pulse waves both qualitatively (eg, patterns of change of forward and reflective waves) and quantitatively (eg, decreasing of PWV within the sac and its increase beyond the sac as the sac stiffness increases). The sac region is particularly identified on the spatiotemporal maps with a region of disruption in the wave propagation with multiple short-traveling forward/reflected waves, which is caused by the change in boundary conditions within the saccular region. The change in sac stiffness, however, is more pronounced on the wall displacement spatiotemporal maps compared to those of fluid velocity. We conclude that the existence of the sac can be identified based on the solid and fluid pulse waves, while the sac properties can also be estimated. This study demonstrates the initial findings in numerical simulations of FSI dynamics during arterial pulsations that can be used as reference for experimental and in vivo studies. Future studies are needed to demonstrate the feasibility of the method in identifying very mild sacs, which cannot be detected from medical imaging, where the material property degradation exists under early disease initiation. PMID:27478394
Arsalan, Mani; Agricola, Eustachio; Alfieri, Ottavio; Baldus, Stephan; Colombo, Antonio; Filardo, Giovanni; Hammerstingl, Christophe; Huntgeburth, Michael; Kreidel, Felix; Kuck, Karl-Heinz; LaCanna, Giovanni; Messika-Zeitoun, David; Maisano, Francesco; Nickenig, Georg; Pollock, Benjamin D; Roberts, Bradley J; Vahanian, Alec; Grayburn, Paul A
2016-09-01
This study was performed to assess the acute intraprocedural effects of transcatheter direct mitral annuloplasty using the Cardioband device on 3-dimensional (3D) anatomy of the mitral annulus. Of 45 patients with functional mitral regurgitation (MR) enrolled in a single arm, multicenter, prospective trial, 22 had complete pre- and post-implant 3D transesophageal echocardiography (TEE) images stored in native data format that allowed off-line 3D reconstruction. Images with the highest volume rate and best image quality were selected for analysis. Multiple measurements of annular geometry were compared from baseline to post-implant using paired t tests with Bonferroni correction to account for multiple comparisons. The device was successfully implanted in all patients, and MR was reduced to moderate in 2 patients, mild in 17 patients, and trace in 3 patients after final device cinching. Compared with preprocedural TEE, postprocedural TEE showed statistically significantly reductions in annular circumference (137 ± 15 vs 128 ± 17 mm; p = 0.042), intercommissural distance (42.4 ± 4.3 vs 38.6 ± 4.4 mm; p = 0.029), anteroposterior distance (40.0 ± 5.4 vs 37.0 ± 5.7 mm; p = 0.025), and aortic-mitral angle (117 ± 8° vs 112 ± 8°; p = 0.032). This study demonstrates that transcatheter direct mitral annuloplasty with the Cardioband device results in acute remodeling of the mitral annulus with successful reduction of functional MR. PMID:27389565
Therkelsen, Peter L.; Littlejohn, David; Cheng, Robert K.; Portillo, J. Enrique; Martin, Scott M.
2009-11-30
Low Swirl Injector (LSI) technology is a lean premixed combustion method that is being developed for fuel-flexible gas turbines. The objective of this study is to characterize the fuel effects and influences of combustor geometry on the LSI's overall acoustic signatures and flowfields. The experiments consist of 24 flames at atmospheric condition with bulk flows ranging between 10 and 18 m/s. The flames burn CH{sub 4} (at {phi} = 0.6 & 0.7) and a blend of 90% H{sub 2} - 10% CH{sub 4} by volume (at {phi} = 0.35 & 0.4). Two combustor configurations are used, consisting of a cylindrical chamber with and without a divergent quarl at the dump plane. The data consist of pressure spectral distributions at five positions within the system and 2D flowfield information measured by Particle Imaging Velocimetry (PIV). The results show that acoustic oscillations increase with U{sub 0} and {phi}. However, the levels in the 90% H{sub 2} flames are significantly higher than in the CH{sub 4} flames. For both fuels, the use of the quarl reduces the fluctuating pressures in the combustion chamber by up to a factor of 7. The PIV results suggest this to be a consequence of the quarl restricting the formation of large vortices in the outer shear layer. A Generalized Instability Model (GIM) was applied to analyze the acoustic response of baseline flames for each of the two fuels. The measured frequencies and the stability trends for these two cases are predicted and the triggered acoustic mode shapes identified.
Li, Han; Lin, Kexin; Shahmirzadi, Danial
2016-01-01
This study aims to quantify the effects of geometry and stiffness of aneurysms on the pulse wave velocity (PWV) and propagation in fluid-solid interaction (FSI) simulations of arterial pulsatile flow. Spatiotemporal maps of both the wall displacement and fluid velocity were generated in order to obtain the pulse wave propagation through fluid and solid media, and to examine the interactions between the two waves. The results indicate that the presence of abdominal aortic aneurysm (AAA) sac and variations in the sac modulus affect the propagation of the pulse waves both qualitatively (eg, patterns of change of forward and reflective waves) and quantitatively (eg, decreasing of PWV within the sac and its increase beyond the sac as the sac stiffness increases). The sac region is particularly identified on the spatiotemporal maps with a region of disruption in the wave propagation with multiple short-traveling forward/reflected waves, which is caused by the change in boundary conditions within the saccular region. The change in sac stiffness, however, is more pronounced on the wall displacement spatiotemporal maps compared to those of fluid velocity. We conclude that the existence of the sac can be identified based on the solid and fluid pulse waves, while the sac properties can also be estimated. This study demonstrates the initial findings in numerical simulations of FSI dynamics during arterial pulsations that can be used as reference for experimental and in vivo studies. Future studies are needed to demonstrate the feasibility of the method in identifying very mild sacs, which cannot be detected from medical imaging, where the material property degradation exists under early disease initiation. PMID:27478394
Jankovic, Drazenka; Winhofer, Yvonne; Promintzer-Schifferl, Miriam; Wohlschläger-Krenn, Evelyne; Anderwald, Christian Heinz; Wolf, Peter; Scherer, Thomas; Reiter, Gert; Trattnig, Siegfried; Luger, Anton; Krebs, Michael; Krssak, Martin
2012-01-01
Aims/Hypothesis Recent evidence suggests a link between myocardial steatosis and diabetic cardiomyopathy. Insulin, as a lipogenic and growth-promoting hormone, might stimulate intramyocardial lipid (MYCL) deposition and hypertrophy. Therefore, the aim of the present study was to investigate the short-term effects of insulin therapy (IT) on myocardial lipid content and morphology in patients with T2DM. Methods Eighteen patients with T2DM were recruited (age 56±2 years; HbA1c: 10.5±0.4%). In 10 patients with insufficient glucose control under oral medication IT was initiated due to secondary failure of oral glucose lowering therapy (IT-group), while 8 individuals did not require additional insulin substitution (OT-group). In order to assess MYCL and intrahepatic lipid (IHLC) content as well as cardiac geometry and function magnetic resonance spectroscopy (MRS) and imaging (MRI) examinations were performed at baseline (IT and OT) and 10 days after initiation of IT. Follow up measurements took place 181±49 days after IT. Results Interestingly, basal MYCLs were 50% lower in IT- compared to OT-group (0.41±0.12 vs. 0.80±0.11% of water signal; p = 0.034). After 10 days of IT, an acute 80%-rise in MYCL (p = 0.008) was observed, while IHLC did not change. Likewise, myocardial mass (+13%; p = 0.004), wall thickness in end-diastole (+13%; p = 0.030) and concentricity, an index of cardiac remodeling, increased (+28%; p = 0.026). In the long-term MYCL returned to baseline, while IHCL significantly decreased (−31%; p = 0.000). No acute changes in systolic left ventricular function were observed. Conclusions/Interpretation The initiation of IT in patients with T2DM was followed by an acute rise in MYCL concentration and myocardial mass. PMID:23226508
NASA Astrophysics Data System (ADS)
Tung, Yao-Sheng; Olumolade, Yemi; Wang, Shutao; Wu, Shih-Ying; Konofagou, Elisa E.
2012-11-01
Acoustic cavitation has been identified as the main physical mechanism for the focused ultrasound (FUS) induced blood-brain barrier (BBB) opening. In this paper, the mechanism of stable cavitation (SC) and inertial cavitation (IC) responsible for BBB opening was investigated. Thirty-three (n=33) mice were intravenously injected with bubbles of 4-5 μm in diameter. The right hippocampus was then sonicated using focused 1.5-MHz ultrasound and three different studies were carried out. First, pulse lengths (PLs) of 0.1, 0.5, 2, and 5 ms at 0.18- MPa peak rarefactional pressure with 5-Hz pulse repetition frequency (PRF) and 5-minute duration were used to identify the threshold of PL using SC. Second, the effects of the duty cycle and exposure time were investigated. Third, the BBB opening size was compared between the SC and the IC. In the case of IC-induced BBB opening, a burst sequence (3-cycles PL; 5-Hz burst repetition frequency (BRF); 30 s duration) at 0.45 MPa was applied. Passive cavitation detection was performed with each sonication to detect whether a broadband response was obtained, i.e., if IC occurred, during BBB opening. The properties of BBB opening were measured through MRI. The threshold of PL for BBB opening was identified between 0.1 and 0.5 ms using SC, but the BBB can be opened in few cycles using IC. The BBB opening volume and normalized intensity increased with the PL, but reached saturation when the PL was above 2 ms. Once the PL threshold was reached, the same exposure time induced a similar BBB opening volume, but longer sonication duration induced higher MR intensity. The duty cycle was found not to play an important role on the BBB opening. Comparable BBB opening volume (20-25 mm3) could be reached between long PL (7500 cycles, i.e., 5 ms) at 0.18 MPa and 3 cycles at 0.45 MPa. 3-kDa fluorescently tagged dextran may be able to diffuse to the parenchyma after IC-induced BBB opening at 0.45 MPa but not after SC-induced BBB opening at 0.18 MPa.
Single chamber fuel cells: Flow geometry, rate and composition considerations
Stefan, Ionel C.; Jacobson, Craig P.; Visco, Steven J.; De Jonghe, Lutgard C.
2003-11-17
Four different single chamber fuel cell designs were compared using propane-air gas mixtures. Gas flow around the electrodes has a significant influence on the open circuit voltage and the power density of the cell. The strong influence of flow geometry is likely due to its effect on gas composition, particularly on the oxygen chemical potential at the two electrodes as a result of gas mixing. The chamber design which exposes the cathode first to the inlet gas was found to yield the best performance at lower flow rates, while the open tube design with the electrodes equally exposed to the inlet gas worked best at higher flow rates.
Analysis and modeling of photomask edge effects for 3D geometries and the effect on process window
NASA Astrophysics Data System (ADS)
Miller, Marshal A.; Neureuther, Andrew R.
2009-03-01
Simulation was used to explore boundary layer models for 1D and 2D patterns that would be appropriate for fast CAD modeling of physical effects during design. FDTD simulation was used to compare rigorous thick mask modeling to a thin mask approximation (TMA). When features are large, edges can be viewed as independent and modeled as separate from one another, but for small mask features, edges experience cross-talk. For attenuating phase-shift masks, interaction distances as large as 150nm were observed. Polarization effects are important for accurate EMF models. Due to polarization effects, the edge perturbations in line ends become different compared to a perpendicular edge. For a mask designed to be real, the 90o transmission created at edges produces an asymmetry through focus, which is also polarization dependent. Thick mask fields are calculated using TEMPEST and Panoramic Technologies software. Fields are then analyzed in the near field and on wafer CDs to examine deviations from TMA.
Kulkarni, A.K.; Paranjape, S.D.; Kumar, V.; Sahni, D.C.
1994-12-31
Nonmonotonic variation of the {open_quotes}C{close_quotes} eigenvalue (average number of secondaries per collision) with increasing {alpha}, the strength of forward scattering, has been observed earlier for one-dimensional infinite homogeneous slabs and infinitely long homogeneous cylinders. The authors have developed the Integral Transform (IT) method, an accurate semi-analytical method to obtain the C eigenvalue for a homogeneous cylinder (two-dimensional system). They are thus able to detect any nonmonotonic variation of C (with {alpha}) using the Sahni and Sjoestrand criterion. Along with the IT method, the authors also present the results obtained by the well-known numerical techniques like the discrete ordinates method using a high quadrature order and the Monte Carlo method for the same problem. The S{sub N} results show disagreement with the other two methods when one of the dimensions is very small (<0.05{lambda}{sub t}). They believe that even the 16th order quadrature set cannot integrate the angular flux accurately in these extreme situations. 12 refs., 9 tabs.
NASA Technical Reports Server (NTRS)
Smalley, A. J.; Tessarzik, J. M.
1975-01-01
Effects of temperature, dissipation level and geometry on the dynamic behavior of elastomer elements were investigated. Force displacement relationships in elastomer elements and the effects of frequency, geometry and temperature upon these relationships are reviewed. Based on this review, methods of reducing stiffness and damping data for shear and compression test elements to material properties (storage and loss moduli) and empirical geometric factors are developed and tested using previously generated experimental data. A prediction method which accounts for large amplitudes of deformation is developed on the assumption that their effect is to increase temperature through the elastomers, thereby modifying the local material properties. Various simple methods of predicting the radial stiffness of ring cartridge elements are developed and compared. Material properties were determined from the shear specimen tests as a function of frequency and temperature. Using these material properties, numerical predictions of stiffness and damping for cartridge and compression specimens were made and compared with corresponding measurements at different temperatures, with encouraging results.
Radiocarbon dating of open systems with bomb effect
NASA Technical Reports Server (NTRS)
Mckay, C. P.; Long, A.; Friedmann, E. I.
1986-01-01
The application of radiocarbon dating is extended to include systems that are slowly exchanging carbon with the atmosphere. Simple formulae are derived that relate the true age and the exchange rate of carbon to the apparent radiocarbon age. A radiocarbon age determination does not give a unique true age and exchange rate but determines a locus of values bounded by a minimum age and a minimum exchange rate. It is found that for radiocarbon ages as large as 10,000 years it is necessary to correct for the anthropogenic radiocarbon produced in the atmosphere by nuclear weapons testing. A one-term exponential approximation, with an e-folding time of 14.43 years, is used to model this effect and is shown to be accurate to within 3 percent for exchange time constants of 100 years and greater. The approach developed here is not specific to radiocarbon and can be applied to other radioisotopes in open systems.
Radiocarbon dating of open systems with bomb effect
McKay, C.P.; Long, A.; Friedmann, E.I.
1986-03-10
The application of radiocarbon dating is extended to include systems that are slowly exchanging carbon with the atmosphere. Simple formulae are derived that relate the true age and the exchange rate of carbon to the apparent radiocarbon age. A radiocarbon age determination does not give a unique true age and exchange rate but determines a locus of values bounded by a minimum age and a minimum exchange rate. It is found that for radiocarbon ages as large as 10,000 years it is necessary to correct for the anthropogenic radiocarbon produced in the atmosphere by nuclear weapons testing. A one-term exponential approximation, with an e-folding time of 14.43 years, is used to model this effect and is shown to be accurate to within 3% for exchange time constants of 100 years and greater. The approach developed here is not specific to radiocarbon and can be applied to other radioisotopes in open systems.
Kulla, Eliona; Chou, Jie; Simmons, Glennon; Wong, Jorge; McRae, Michael P.; Patel, Rushi; Floriano, Pierre N.; Christodoulides, Nicolaos; Leach, Robin J.; Thompson, Ian M.; McDevitt, John T.
2015-01-01
Measuring low concentrations of clinically-important biomarkers using porous bead-based lab-on-a-chip (LOC) platforms is critical for the successful implementation of point-of-care (POC) devices. One way to meet this objective is to optimize the geometry of the bead holder, referred to here as a micro-container. In this work, two geometric micro-containers were explored, the inverted pyramid frustum (PF) and the inverted clipped pyramid frustum (CPF). Finite element models of this bead array assay system were developed to optimize the micro-container and bead geometries for increased pressure, to increase analyte capture in porous bead-based fluorescence immunoassays. Custom micro-milled micro-container structures containing an inverted CPF geometry resulted in a 28% reduction in flow-through regions from traditional anisotropically-etched pyramidal geometry derived from Si-111 termination layers. This novel “reduced flow-through” design resulted in a 33% increase in analyte penetration into the bead and twofold increase in fluorescence signal intensity as demonstrated with C-Reactive Protein (CRP) antigen, an important biomarker of inflammation. A consequent twofold decrease in the limit of detection (LOD) and the limit of quantification (LOQ) of a proof-of-concept assay for the free isoform of Prostate-Specific Antigen (free PSA), an important biomarker for prostate cancer detection, is also presented. Furthermore, a 53% decrease in the bead diameter is shown to result in a 160% increase in pressure and 2.5-fold increase in signal, as estimated by COMSOL models and confirmed experimentally by epi-fluorescence microscopy. Such optimizations of the bead micro-container and bead geometries have the potential to significantly reduce the LODs and reagent costs for spatially programmed bead-based assay systems of this type. PMID:26097696
Effects of open-top chambers on 'Valencia' orange trees
Olszyk, D.M.; Takemoto, B.K.; Kats, G.; Dawson, P.J.; Morrison, C.L.
1992-01-01
Young 'Valencia' orange trees (Citrus sinensis(L) Osbeck) were grown for four years in large open-top chambers with ambient (nonfiltered) air or in outside air to determine any effects of the chambers on the air pollutant susceptibility of the trees. Long-term ozone average concentrations (12 hours, growing season) were 8% lower, and cumulative ozone dose (hourly values >0.1 microL/L) was 29% lower in ambient chambers compared to outside air. Fruit yields were much higher (>39%) for ambient chamber trees than for outside trees over three harvests, due at least partly to less fruit drop during the growing season for ambient chamber trees. Ambient chamber trees were much larger than outside trees and produced over twice as much leaf material over four years of study. Leaves on ambient chamber trees were larger and less dense than on outside trees. Leaves on ambient chamber trees were under more stress than leaves on outside trees during summer months; with lower stomatal conductances (14% average) and transpiration rates (12%), and more negative leaf water pressure potentials (28%). In contrast, leaves on ambient chamber trees had higher net photosynthetic rates (13%) and higher leaf starch concentrations prior to tree flowering (31%), than leaves on outside trees. While these results indicated large long-term impacts on tree growth which must be considered when using open-top chambers, they did not indicate any net effect of chambers on the air pollutant susceptibility of trees which would limit the usefulness of chamber tree data for air quality impact assessment purposes.
Nishida, Masahiro; Nakayama, Kento; Sakota, Daisuke; Kosaka, Ryo; Maruyama, Osamu; Kawaguchi, Yasuo; Kuwana, Katsuyuki; Yamane, Takashi
2016-06-01
The effect of the flow path geometry of the impeller on the lift-off and tilt of the rotational axis of the impeller against the hydrodynamic force was investigated in a centrifugal blood pump with an impeller supported by a single-contact pivot bearing. Four types of impeller were compared: the FR model with the flow path having both front and rear cutouts on the tip, the F model with the flow path having only a front cutout, the R model with only a rear cutout, and the N model with a straight flow path. First, the axial thrust and the movement about the pivot point, which was loaded on the surface of the impeller, were calculated using computational fluid dynamics (CFD) analysis. Next, the lift-off point and the tilt of the rotational axis of the impeller were measured experimentally. The CFD analysis showed that the axial thrust increased gently in the FR and R models as the flow rate increased, whereas it increased drastically in the F and N models. This difference in axial thrust was likely from the higher pressure caused by the smaller circumferential velocity in the gap between the top surface of the impeller and the casing in the FR and R models than in the F and N models, which was caused by the rear cutout. These results corresponded with the experimental results showing that the impellers lifted off in the F and N models as the flow rate increased, whereas it did not in the FR and R models. Conversely, the movement about the pivot point increased in the direction opposite the side with the pump outlet as the flow rate increased. However, the tilt of the rotational axis of the impeller, which oriented away from the pump outlet, was less than 0.8° in any model under any conditions, and was considered to negligibly affect the rotational attitude of the impeller. These results confirm that a rear cutout prevents lift-off of the impeller caused by a decrease in the axial thrust. PMID:27097844
Turbine engine variable geometry device
NASA Technical Reports Server (NTRS)
Rogo, Casimir (Inventor); Lenz, Herman N. (Inventor)
1985-01-01
A variable geometry device for use with the turbine nozzle of a turbine engine of the type having a support housing and a combustion chamber contained within the support housing. A pair of spaced walls in the support housing define an annular and radially extending nozzle passageway. The outer end of the nozzle passageway is open to the combustion chamber while the inner end of the nozzle passageway is open to one or more turbine stages. A plurality of circumferentially spaced nozzle vanes are mounted to one of the spaced walls and protrude across the nozzle passageway. An annular opening is formed around the opposite spaced wall and an annular ring is axially slidably mounted within the opening. A motor is operatively connected to this ring and, upon actuation, axially displaces the ring within the nozzle passageway. In addition, the ring includes a plurality of circumferentially spaced slots which register with the nozzle vanes so that the vane geometry remains the same despite axial displacement of the ring.
NASA Technical Reports Server (NTRS)
Chyu, Wei J.; Rimlinger, Mark J.; Shih, Tom I.-P.
1993-01-01
A numerical study was performed to investigate 3D shock-wave/boundary-layer interactions on a flat plate with bleed through one or more circular holes that vent into a plenum. This study was focused on how bleed-hole geometry and pressure ratio across bleed holes affect the bleed rate and the physics of the flow in the vicinity of the holes. The aspects of the bleed-hole geometry investigated include angle of bleed hole and the number of bleed holes. The plenum/freestream pressure ratios investigated range from 0.3 to 1.7. This study is based on the ensemble-averaged, 'full compressible' Navier-Stokes (N-S) equations closed by the Baldwin-Lomax algebraic turbulence model. Solutions to the ensemble-averaged N-S equations were obtained by an implicit finite-volume method using the partially-split, two-factored algorithm of Steger on an overlapping Chimera grid.
NASA Technical Reports Server (NTRS)
Ryan, R. M.; Gross, L. A.
1986-01-01
This paper presents the results of an advanced turbine blade test program aimed at improving turbine blade low cycle fatigue (LCF) life. A total of 21 blades were tested in a blade thermal tester. The blades were made of MAR-M-246(Hf)DS and PWA-1480SC in six different geometries. The test results show that the PWA-1480SC material improved life by a factor of 1.7 to 3.0 over the current MAR-M-246(Hf)DS. The geometry changes yielded life improvements as high as 20 times the baseline blade made of PWA-1480SC and 34 times the baseline MAR-M-246DS blade.
View-based strategy for reorientation by geometry.
Pecchia, Tommaso; Vallortigara, Giorgio
2010-09-01
Human and non-human animals can use geometric information (metric information and left-right discrimination sense) to reorient themselves in an environment. The hypothesis that in so doing they rely on allocentric (map-like) representations has received wide consensus. However, theoretical models suggest that egocentric representations may represent efficient strategies for visuo-spatial navigation. Here, we provide, for the first time, evidence that a view-based strategy is effectively used by animals to reorient themselves in an array of landmarks. Domestic chicks were trained to locate a food-reward in a rectangular array of either four indistinguishable or distinctive pipes. In the key experimental series, the pipes had four openings, only one of which allowed the chicks to access the reward. The direction of the open access relative to the array was either maintained stable or it was changed throughout training. The relative position of the pipes in the array was maintained stable in both training conditions. Chicks reoriented according to configural geometry as long as the open access pointed in the same direction during training but failed when the positions of the openings was changed throughout training. When the correct pipe was characterized by a distinctive featural cue, chicks learnt to locate the reward irrespective of the stability of the direction to openings, indicating that place-navigation was dissociated from non-spatial learning. These findings provide evidence that view-based strategies to reorient by geometry could be used by animals. PMID:20709927
Effective Protection of Open Space: Does Planning Matter?
NASA Astrophysics Data System (ADS)
Steelman, Toddi A.; Hess, George R.
2009-07-01
High quality plans are considered a crucial part of good land use planning and often used as a proxy measure for success in plan implementation and goal attainment. We explored the relationship of open space plan quality to the implementation of open space plans and attainment of open space protection goals in Research Triangle, North Carolina, USA. To measure plan quality, we used a standard plan evaluation matrix that we modified to focus on open space plans. We evaluated all open space plans in the region that contained a natural resource protection element. To measure plan implementation and open space protection, we developed an online survey and administered it to open space planners charged with implementing the plans. The survey elicited each planner’s perspective on aspects of open space protection in his or her organization. The empirical results (1) indicate that success in implementation and attaining goals are not related to plan quality, (2) highlight the importance of when and how stakeholders are involved in planning and implementation processes, and (3) raise questions about the relationship of planning to implementation. These results suggest that a technically excellent plan does not guarantee the long-term relationships among local landowners, political and appointed officials, and other organizations that are crucial to meeting land protection goals. A greater balance of attention to the entire decision process and building relationships might lead to more success in protecting open space.
Effective protection of open space: does planning matter?
Steelman, Toddi A; Hess, George R
2009-07-01
High quality plans are considered a crucial part of good land use planning and often used as a proxy measure for success in plan implementation and goal attainment. We explored the relationship of open space plan quality to the implementation of open space plans and attainment of open space protection goals in Research Triangle, North Carolina, USA. To measure plan quality, we used a standard plan evaluation matrix that we modified to focus on open space plans. We evaluated all open space plans in the region that contained a natural resource protection element. To measure plan implementation and open space protection, we developed an online survey and administered it to open space planners charged with implementing the plans. The survey elicited each planner's perspective on aspects of open space protection in his or her organization. The empirical results (1) indicate that success in implementation and attaining goals are not related to plan quality, (2) highlight the importance of when and how stakeholders are involved in planning and implementation processes, and (3) raise questions about the relationship of planning to implementation. These results suggest that a technically excellent plan does not guarantee the long-term relationships among local land owners, political and appointed officials, and other organizations that are crucial to meeting land protection goals. A greater balance of attention to the entire decision process and building relationships might lead to more success in protecting open space. PMID:19219489
Combinatorial Geometry Printer Plotting.
Energy Science and Technology Software Center (ESTSC)
1987-01-05
Picture generates plots of two-dimensional slices through the three-dimensional geometry described by the combinatorial geometry (CG) package used in such codes as MORSE and QAD-CG. These plots are printed on a standard line printer.
NASA Astrophysics Data System (ADS)
Taylor, Marika
2006-03-01
Two charge BPS horizon free supergravity geometries are important in proposals for understanding black hole microstates. In this paper we construct a new class of geometries in the NS1-P system, corresponding to solitonic strings carrying fermionic as well as bosonic condensates. Such geometries are required to account for the full microscopic entropy of the NS1-P system. We then briefly discuss the properties of the corresponding geometries in the dual D1-D5 system.
Kidwell, Mallory C; Lazarević, Ljiljana B; Baranski, Erica; Hardwicke, Tom E; Piechowski, Sarah; Falkenberg, Lina-Sophia; Kennett, Curtis; Slowik, Agnieszka; Sonnleitner, Carina; Hess-Holden, Chelsey; Errington, Timothy M; Fiedler, Susann; Nosek, Brian A
2016-05-01
Beginning January 2014, Psychological Science gave authors the opportunity to signal open data and materials if they qualified for badges that accompanied published articles. Before badges, less than 3% of Psychological Science articles reported open data. After badges, 23% reported open data, with an accelerating trend; 39% reported open data in the first half of 2015, an increase of more than an order of magnitude from baseline. There was no change over time in the low rates of data sharing among comparison journals. Moreover, reporting openness does not guarantee openness. When badges were earned, reportedly available data were more likely to be actually available, correct, usable, and complete than when badges were not earned. Open materials also increased to a weaker degree, and there was more variability among comparison journals. Badges are simple, effective signals to promote open practices and improve preservation of data and materials by using independent repositories. PMID:27171007
Kidwell, Mallory C.; Lazarević, Ljiljana B.; Baranski, Erica; Piechowski, Sarah; Falkenberg, Lina-Sophia; Sonnleitner, Carina; Fiedler, Susann; Nosek, Brian A.
2016-01-01
Beginning January 2014, Psychological Science gave authors the opportunity to signal open data and materials if they qualified for badges that accompanied published articles. Before badges, less than 3% of Psychological Science articles reported open data. After badges, 23% reported open data, with an accelerating trend; 39% reported open data in the first half of 2015, an increase of more than an order of magnitude from baseline. There was no change over time in the low rates of data sharing among comparison journals. Moreover, reporting openness does not guarantee openness. When badges were earned, reportedly available data were more likely to be actually available, correct, usable, and complete than when badges were not earned. Open materials also increased to a weaker degree, and there was more variability among comparison journals. Badges are simple, effective signals to promote open practices and improve preservation of data and materials by using independent repositories. PMID:27171007
NASA Technical Reports Server (NTRS)
Leavitt, L. D.; Yip, L. P.
1978-01-01
A V/STOL tunnel study was performed to determine the effects of spanwise blowing on longitudinal aerodynamic characteristics of a model using a vectored-over-wing powered lift concept. The effects of spanwise nozzle throat area, internal and external nozzle geometry, and vertical and axial location were investigated. These effects were studied at a Mach number of 0.186 over an angle-of-attack range from 14 deg to 40 deg. A high pressure air system was used to provide jet-exhaust simulation. Engine nozzle pressure ratio was varied from 1.0 (jet off) to approximately 3.75.
ERIC Educational Resources Information Center
McDonald, Nathaniel J.
2001-01-01
Chronicles a teacher's first year teaching geometry at the Hershey Montessori Farm School in Huntsburg, Ohio. Instructional methods relied on Euclid primary readings and combined pure abstract logic with practical applications of geometry on the land. The course included geometry background imparted by Montessori elementary materials as well as…
Effects of Land Use Development on Urban Open Spaces
NASA Astrophysics Data System (ADS)
Esbah, Hayriye; Deniz, Bulent
City of Aydin has grown extremely due to immigration from the eastern part of Turkey, immigration from rural areas to urban areas of the city and alterations in economic and social structure of the nation. The rapid expansion of the urban area results in dramatic change in the open space system of the town. Understanding this transformation is important to generate sustainable planning in the area. The purpose of this study is to elaborate the different open space opportunities in Aydin and to detect the change in these areas. Black and white aerial photographs from 1977 and 1993 and Ikonos 2002 images are utilized for the analysis in GIS environment. First, 14 different open space types are defined and the open spaces are delineated from the aerials and satellite images. Second, the change in the area of these patches is analyzed. The results indicate that urban open spaces are negatively affected by historic land use development. The natural and agricultural patches diminished while semi-natural or man made open space patches increased. Opportunities to increase the variability in the open space types should be embraced to promote sustainability in the urban matrix. Ecological design of the man made open spaces is necessary to increase their contribution in this endeavor.
NASA Astrophysics Data System (ADS)
Zhang, X.; Liu, J.; Wang, J.
2016-05-01
The diesel spray characteristics are strongly influenced by the flow dynamics inside the injector nozzle. Moreover, the off-axis oscillation of needle could lead to variation of orifice flow in the nozzle. In this paper, the needle oscillation was investigated using high-speed X-ray phase contrast imaging and quantitative image processing. The effects of fuel, injection pressure and nozzle geometry on the needle oscillation were analyzed. The results showed that the vertical and horizontal oscillation of needle was independent on the injection pressure. The maximum oscillation range of 14μ m was found. Biodiesel application slightly decreased the needle oscillation due to high viscosity. The needle oscillation range increased generally with increasing hole number. The larger needle oscillation in multi-hole injectors was dominated by the geometry problem or production issue at lower needle lift. In addition, the influence of needle oscillation on the spray morphology was also discussed.
NASA Astrophysics Data System (ADS)
Mathew, Sonia Susan
The dye sensitized solar cell (DSSC) is a photoelectrochemical cell that has garnered considerable attention because of its high efficiencies and potentially low production costs. The technology is based on a layer of mesoscopic TiO 2 particles, which significantly increases the optical path of the incident light that is harvested by the surface-anchored sensitizer molecules, whilst keeping an efficient contact with the electrolytic solution. The solar cell configuration that first achieved a high efficiency (˜7.5%) had a randomly connected network of titania nanoparticles, ruthenium polypyridyl complexes as the sensitizer, and an iodide/triiodide redox couple dissolved in an organic electrolyte. While the disordered nanoparticle network has a high surface area which maximizes the photogenerated electron density, the nanostructure also has a large number of surface states. These surface states act as traps and are known to limit the transport of electrons within such electrodes thereby hindering progress in achieving higher efficiencies. The structural disorder at the contact between two crystalline nanoparticles leads to enhanced scattering of free electrons, thus reducing electron mobility. An interconnected photoanode architecture offers the potential for improved electron transport by reducing the degree of disorder. This Thesis investigates the effect of the TiO2 network geometry on electron movement within the DSSC. In this regard, inverse opal structures with hexagonally close-packed pores and macroscopic (˜microm) order are synthesized and evaluated qualitatively and quantitatively (via FFT) with respect to their degree of interconnectedness. An inverse opal TiO2 electrode possesses advantages that supplement those of current disordered electrodes: (a) high surface area for dye adhesion, (b) large area contact between the sensitizer and the electrolyte, which aids electron transfer reactions, and (c) scattering of incident radiation due to the inherent
Nucleus as an Open System: New Effects and Theoretical Challenges
NASA Astrophysics Data System (ADS)
Zelevinsky, Vladimir
2012-10-01
As nuclear science moves in the direction of nuclei far from stability, the studies of nuclear structure and nuclear reactions become more and more interrelated. The main theoretical challenge is to find a consistent description of the nucleus as an open mesoscopic system coupled with continuum through real decay channels and through virtual excitations. The method using the effective non-Hermitian Hamiltonian [see review article: N. Auerbach and V. Zelevinsky, Rep. Prog. Phys. 74, 106301 (2011)] is one of the most promising theoretical approaches; it can be strictly derived from quantum many-body theory, it allows for calculating bound states, resonances and reaction cross sections in the unified framework, and it is quite flexible in practical applications. After explaining the main features of this theory, I will show the method at work (continuum shell model with predictions recently confirmed by the experiments with exotic oxygen isotopes, phenomenon of super-radiance, relation to the idea of doorway states, quantum signal transmission through mesoscopic systems) and discuss new theoretical challenges.
Effective Thermal Conductivity of High Porosity Open Cell Nickel Foam
NASA Technical Reports Server (NTRS)
Sullins, Alan D.; Daryabeigi, Kamran
2001-01-01
The effective thermal conductivity of high-porosity open cell nickel foam samples was measured over a wide range of temperatures and pressures using a standard steady-state technique. The samples, measuring 23.8 mm, 18.7 mm, and 13.6 mm in thickness, were constructed with layers of 1.7 mm thick foam with a porosity of 0.968. Tests were conducted with the specimens subjected to temperature differences of 100 to 1000 K across the thickness and at environmental pressures of 10(exp -4) to 750 mm Hg. All test were conducted in a gaseous nitrogen environment. A one-dimensional finite volume numerical model was developed to model combined radiation/conduction heat transfer in the foam. The radiation heat transfer was modeled using the two-flux approximation. Solid and gas conduction were modeled using standard techniques for high porosity media. A parameter estimation technique was used in conjunction with the measured and predicted thermal conductivities at pressures of 10(exp -4) and 750 mm Hg to determine the extinction coefficient, albedo of scattering, and weighting factors for modeling the conduction thermal conductivity. The measured and predicted conductivities over the intermediate pressure values differed by 13%.
De Jager, N. R.; Pastor, J.; Hodgson, A.L.
2009-01-01
Landscape heterogeneity influences large herbivores by altering their feeding rates, but as herbivores attempt to maximize feeding rates they also create spatial heterogeneity by altering plant growth. Herbivore feeding rates thus provide a quantitative link between the causes and consequences of spatial heterogeneity in herbivore-dominated ecosystems. The fractal geometry of plant canopies determines both the density and mass of twigs available to foraging herbivores. These properties determine a threshold distance between plants (d*) that distinguishes the mechanisms regulating herbivore intake rates. When d* is greater than the actual distance between plants (d), intake is regulated by the rate of food processing in the mouth. But when d* < d, intake is regulated by the rate at which the herbivore encounters new plants. Alterations to plant geometry due to past browsing could change the rate at which herbivores encounter and process bites of plant tissue, modify d* relative to d, and thus change intake rates and the distribution of mechanisms regulating it across landscapes. We measured changes in the geometry of aspen (Populus tremuloides) and balsam fir (Abies balsamea) saplings along gradients of moose browsing from 2001 to 2005 at Isle Royale National Park, Michigan, USA. For aspen saplings, fractal dimension of bite density, bite mass, and forage biomass responded quadratically to increasing moose browsing and were greatest at -3-4 g-g.m-2.yr"1 consumption. For balsam fir, in contrast, these same measures declined steadily with increasing moose browsing. The different responses of plant canopies to increased browsing altered d* around plants. In summer, d* > d for aspen saplings at all prior consumption levels. Food processing therefore regulated summer moose feeding rates across our landscapes. In winter, changes in bite mass due to past browsing were sufficient to cause d* < d for aspen and balsam fir. Therefore, travel velocity and food processing
NASA Astrophysics Data System (ADS)
Trejo, Adrian
Rocket engine fuel alternatives have been an area of discussion for use in high performance engines and deep spaceflight missions. In particular, LCH4 has showed promise as an alternative option in regeneratively cooled rocket engines due to its non-toxic nature, similar storage temperatures to liquid oxygen, and its potential as an in situ resource. However, data pertaining to the heat transfer characteristics of LCH4 is limited. For this reason, a High Heat Transfer Test Facility (HHTTF) at the University of Texas at El Paso's (UTEP) Center for Space Exploration Technology and Research has been developed for the purpose of flowing LCH4 through several heated tube geometry designs subjected to a constant heat flux. In addition, a Methane Condensing Unit (MCU) is integrated to the system setup to supply LCH4 to the test facility. Through the use of temperature and pressure measurements, this experiment will serve not only to study the heat transfer characteristics of LCH4; it serves as a method of simulating the cooling channels of a regeneratively cooled rocket engine at a subscale level. The cross sections for the cooling channels investigated are a 1.8 mm x 1.8 mm square channel, 1.8 mm x 4.1 mm rectangular channel, 3.2 mm and 6.34 mm inside diameter channel, and a 1.8 mm x 14.2 mm high aspect ratio cooling channel (HARCC). The test facility is currently designed for test pressures between 1.03 MPa to 2.06 MPa and heat fluxes up to 5 MW/m2. Results show that at the given test pressures, the Reynolds number reaches up to 140,000 for smaller cooling channels (3.2 mm diameter tube and 1.8 mm x 4.1 mm rectangle) while larger cooling channel geometries (6.35 mm diameter and HARCC) reached Reynolds number around 70,000. Nusselt numbers reached as high as 320 and 265 for a 3.2 mm diameter tube and 1.8 mm x 4.1 mm rectangular channel respectively. For cooling channel geometries with 6.35 mm diameter and HARCC geometry, Nusselt numbers reached 136 (excluding an outlier
Effect of opening helix on flying wire emittance measurements
Pruss, Stan; /Fermilab
1996-04-01
It has been noted for some time that after the protons are injected, when the helix is opened the proton normalized vertical emittance (as measured by the flying wires) increases by about two {pi} mm-mr. The horizontal emittance decreases by about the same amount. This has been recognized as a false result, but there has been uncertainty as to whether it was due to the flying wires not measuring the beam sigma correctly when the beam center moved at the wires or whether the effective beta at the wires changed when the helix was opened and the orbit changed all around the machine. This study attempts to answer that question. The study took place Sunday, Feb. 25, 1996, from 18:30 to 22:30. The study consisted of injecting P1, P2 and P3 as normal, coalesced bunches and P4 and P5 as uncoalesced bunch trains of nominally 11 bunches. The purpose in using more than a single bunch was to increase statistical sampling and to investigate whether there was any significant difference between coalesced and uncoalesced bunches. Because the injection kicker had a long flat-top for 36 bunch studies, P6 could not be injected and when P5 was injected, P1 emittance increased by about two {pi} mm-mr. The flying wires were flown several times, the helix was turned on, the wires flown several times, the helix turned off, and the wires flown several times. The helix cycling was performed by knobbing the power supplies to avoid any possible emittance dilution from a non-adiabatic change. note that during the helix off state during helix cycling, one of the power supplies for the horizontal separators was inadvertently not turned down to zero, leaving the horizontal part of the helix at {approx} 16% of normal. After three cycles of helix on-off, a local horizontal three bump was made to duplicate the horizontal orbit change at the E11 wires and the wires were flown several times. The local bump was removed and the wires flown several times. Finally, the protons were put onto the pbar helix
Convection-Enhanced Transport into Open Cavities : Effect of Cavity Aspect Ratio.
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
Solar Wind Acceleration: Modeling Effects of Turbulent Heating in Open Flux Tubes
NASA Astrophysics Data System (ADS)
Woolsey, Lauren N.; Cranmer, Steven R.
2014-06-01
We present two self-consistent coronal heating models that determine the properties of the solar wind generated and accelerated in magnetic field geometries that are open to the heliosphere. These models require only the radial magnetic field profile as input. The first code, ZEPHYR (Cranmer et al. 2007) is a 1D MHD code that includes the effects of turbulent heating created by counter-propagating Alfven waves rather than relying on empirical heating functions. We present the analysis of a large grid of modeled flux tubes (> 400) and the resulting solar wind properties. From the models and results, we recreate the observed anti-correlation between wind speed at 1 AU and the so-called expansion factor, a parameterization of the magnetic field profile. We also find that our models follow the same observationally-derived relation between temperature at 1 AU and wind speed at 1 AU. We continue our analysis with a newly-developed code written in Python called TEMPEST (The Efficient Modified-Parker-Equation-Solving Tool) that runs an order of magnitude faster than ZEPHYR due to a set of simplifying relations between the input magnetic field profile and the temperature and wave reflection coefficient profiles. We present these simplifying relations as a useful result in themselves as well as the anti-correlation between wind speed and expansion factor also found with TEMPEST. Due to the nature of the algorithm TEMPEST utilizes to find solar wind solutions, we can effectively separate the two primary ways in which Alfven waves contribute to solar wind acceleration: 1) heating the surrounding gas through a turbulent cascade and 2) providing a separate source of wave pressure. We intend to make TEMPEST easily available to the public and suggest that TEMPEST can be used as a valuable tool in the forecasting of space weather, either as a stand-alone code or within an existing modeling framework.
Convection in Slab and Spheroidal Geometries
NASA Technical Reports Server (NTRS)
Porter, David H.; Woodward, Paul R.; Jacobs, Michael L.
2000-01-01
Three-dimensional numerical simulations of compressible turbulent thermally driven convection, in both slab and spheroidal geometries, are reviewed and analyzed in terms of velocity spectra and mixing-length theory. The same ideal gas model is used in both geometries, and resulting flows are compared. The piecewise-parabolic method (PPM), with either thermal conductivity or photospheric boundary conditions, is used to solve the fluid equations of motion. Fluid motions in both geometries exhibit a Kolmogorov-like k(sup -5/3) range in their velocity spectra. The longest wavelength modes are energetically dominant in both geometries, typically leading to one convection cell dominating the flow. In spheroidal geometry, a dipolar flow dominates the largest scale convective motions. Downflows are intensely turbulent and up drafts are relatively laminar in both geometries. In slab geometry, correlations between temperature and velocity fluctuations, which lead to the enthalpy flux, are fairly independent of depth. In spheroidal geometry this same correlation increases linearly with radius over the inner 70 percent by radius, in which the local pressure scale heights are a sizable fraction of the radius. The effects from the impenetrable boundary conditions in the slab geometry models are confused with the effects from non-local convection. In spheroidal geometry nonlocal effects, due to coherent plumes, are seen as far as several pressure scale heights from the lower boundary and are clearly distinguishable from boundary effects.
Meulenberg, Cécil J W; de Groot, Aart; Westerink, Remco H S; Vijverberg, Henk P M
2016-07-01
Exposure to organic solvents may cause narcotic effects. At the cellular level, these narcotic effects have been associated with a reduction in neuronal excitability caused by changes in membrane structure and function. In order to critically test whether changes in membrane geometry contribute to these narcotic effects, cultured human SH-SY5Y neuroblastoma cells have been exposed to selected organic solvents. The solvent-induced changes in cell membrane capacitance were investigated using the whole-cell patch clamp technique for real-time capacitance measurements. Exposure of SH-SY5Y cells to the cyclic hydrocarbons m-xylene, toluene, and cyclohexane caused a rapid and reversible increase of membrane capacitance. The aliphatic, nonpolar n-hexane did not cause a detectable change of whole-cell membrane capacitance, whereas the amphiphiles n-hexanol and n-hexylamine caused an increase of membrane capacitance and a concomitant reduction in membrane resistance. Despite a large difference in dielectric properties, the chlorinated hydrocarbons 1,1,2,2-tetrachoroethane and tetrachloroethylene caused a similar magnitude increase in membrane capacitance. The theory on membrane capacitance has been applied to deduce changes in membrane geometry caused by solvent partitioning. Although classical observations have shown that solvents increase the membrane capacitance per unit area of membrane, i.e., increase membrane thickness, the present results demonstrate that solvent partitioning predominantly leads to an increase in membrane surface area and to a lesser degree to an increase in membrane thickness. Moreover, the present results indicate that the physicochemical properties of each solvent are important determinants for its specific effects on membrane geometry. This implies that the hypothesis that solvent partitioning is associated with a common perturbation of membrane structure needs to be revisited and cannot account for the commonly observed narcotic effects of
NASA Astrophysics Data System (ADS)
Kumar, Jagadeesha; Attridge, Alex; Wood, P. K. C.; Williams, Mark A.
2011-03-01
Industrial x-ray computed tomography (CT) scanners are used for non-contact dimensional measurement of small, fragile components and difficult-to-access internal features of castings and mouldings. However, the accuracy and repeatability of measurements are influenced by factors such as cone-beam system geometry, test object configuration, x-ray power, material and size of test object, detector characteristics and data analysis methods. An attempt is made in this work to understand the measurement errors of a CT scanner over the complete scan volume, taking into account only the errors in system geometry and the object configuration within the scanner. A cone-beam simulation model is developed with the radiographic image projection and reconstruction steps. A known amount of errors in geometrical parameters were introduced in the model to understand the effect of geometry of the cone-beam CT system on measurement accuracy for different positions, orientations and sizes of the test object. Simulation analysis shows that the geometrical parameters have a significant influence on the dimensional measurement at specific configurations of the test object. Finally, the importance of system alignment and estimation of correct parameters for accurate CT measurements is outlined based on the analysis.
NASA Technical Reports Server (NTRS)
Berry, John D.
1988-01-01
A method is described for the analysis of the unsteady, incompressible potential flow associated with a helicopter rotor and it's wake in forward flight. This method is particularly useful in low advance ratio flight due to the major contribution, in the near field, of the deformed wake. The rotor geometry is prescribed and the unsteady wake geometry is computed from the local flow perturbation velocities. The wake is modeled as a full vortex lattice. The rotor geometry is arbitrary and several rotor blades can be represented. The unsteady airloads on the rotor blades are computed in the presence of the deformed rotor wake by a time-stepping technique. Solution for the load distribution on the blade surfaces is found by prescribing boundary conditions in a reference system which rotates with the blade tips. Transformation tensors are used to describe the contribution of the wake in the inertial system to the rotor in the rotating reference system. The effects of blade cyclic pitch variation are computed using a rotation tensor. The deformation of the wake is computed in the inertial frame. The wake is started impulsively from rest, allowing a natural convection of the wake with time.
NASA Technical Reports Server (NTRS)
Hallock, Ashley; Polzin, Kurt; Emsellem, Gregory
2012-01-01
Pulsed inductive plasma thrusters [1-3] are spacecraft propulsion devices in which electrical energy is capacitively stored and then discharged through an inductive coil. The thruster is electrodeless, with a time-varying current in the coil interacting with a plasma covering the face of the coil to induce a plasma current. Propellant is accelerated and expelled at a high exhaust velocity (O(10-100 km/s)) by the Lorentz body force arising from the interaction of the magnetic field and the induced plasma current. While this class of thruster mitigates the life-limiting issues associated with electrode erosion, pulsed inductive plasma thrusters require high pulse energies to inductively ionize propellant. The Microwave Assisted Discharge Inductive Plasma Accelerator (MAD-IPA) [4, 5] is a pulsed inductive plasma thruster that addressees this issue by partially ionizing propellant inside a conical inductive coil via an electron cyclotron resonance (ECR) discharge. The ECR plasma is produced using microwaves and permanent magnets that are arranged to create a thin resonance region along the inner surface of the coil, restricting plasma formation, and in turn current sheet formation, to a region where the magnetic coupling between the plasma and the inductive coil is high. The use of a conical theta-pinch coil is under investigation. The conical geometry serves to provide neutral propellant containment and plasma plume focusing that is improved relative to the more common planar geometry of the Pulsed Inductive Thruster (PIT) [2, 3], however a conical coil imparts a direct radial acceleration of the current sheet that serves to rapidly decouple the propellant from the coil, limiting the direct axial electromagnetic acceleration in favor of an indirect acceleration mechanism that requires significant heating of the propellant within the volume bounded by the current sheet. In this paper, we describe thrust stand measurements performed to characterize the performance
The effect of maximum open height on operating characteristics of polymer injected pump poppet valve
NASA Astrophysics Data System (ADS)
Zhang, S. C.; Chen, X. D.; Deng, H. Y.
2012-11-01
Reciprocating polymer injected pump is the key injection equipment of tertiary oil recovery, the poppet valve in it exists the problem of large vibration noise, low efficiency and short life when transportation high viscosity medium. So the CFD technique is adopted to simulate and analyze the inner flow fields of fluid end poppet valve. According to the practical structure of the poppet valve, a simplified 2D axis-symmetry geometry model of the flow field is established. Combined with pump speed, plunger stroke and plunger diameter, given the boundary condition of the inlet valve, then the numerical simulation of flow field under six different maximum open heights is done depending on software Fluent. The relationship between open height to valve gap flow velocity, hydraulic loss and lag angle is obtained. The results indicate that, with the increase of open height, the valve gap flow velocity decreases, inlet outlet pressure differential decreases and hydraulic loss decreases. But the lag angle is continuously increasing with the increase of maximum open height, the valve has a good work performance when the open height is 1, 1.5, 2, 2.5, 3mm, but when it reaches 3.5mm, the valve performance becomes poor. The study can offer certain reference to understand operating characteristics of poppet valve, help to reduce the hydraulic losses and raise volume efficiency of the pump.
NASA Astrophysics Data System (ADS)
Odette, G. R.; Lucas, G. E.; Maiti, R.; Sheckherd, J. W.
1985-08-01
A two-parameter procedure (TTP) for evaluating cleavage fracture stresses was investigated. The TPP interpolates between linear elastic and fully plastic fracture regimes. Predictions of the TPP were compared to experimental data obtained from bend bars 0.5 to 2.0 cm wide with various crack-to-width ratios, at -73°C and -101°C, and at three displacement rates. Agreement was good. The results suggest that thin-walled components containing shallow cracks will fail near plastic collapse stresses. In such a case, irradiation would probably result in an increase in the fracture stresses. Bend ductilities were low and found to be very sensitive to geometry and strength level.
NASA Astrophysics Data System (ADS)
Wang, Zhi-Yong; Xiong, Cai-Dong; Qiu, Qi; Wang, Yun-Xiang; Shi, Shuang-Jin
2016-06-01
The (1,\\quad 0)\\oplus (0,\\quad 1) representation of the group SL(2, C) provides a six-component spinor equivalent to the electromagnetic field tensor. By means of the (1,\\quad 0)\\oplus (0,\\quad 1) description, one can treat the photon field in curved spacetime via spin connection and the tetrad formalism, which is of great advantage to study the gravitational spin–orbit coupling of photons. Once the gravitational spin–orbit coupling is taken into account, the traditional radius of the circular photon orbit in the Schwarzschild geometry should be replaced with two different radiuses corresponding to the photons with the helicities of +/- 1, respectively. Owing to the splitting of energy levels induced by the spin–orbit coupling, photons (from Hawking radiations, say) escaping from a Schwarzschild black hole are partially polarized, provided that their initial velocities possess nonzero tangential components.
Unusual large-pitch banding in poly(L-lactic acid): Effects of composition and geometry confinement
Woo, Eamor M.; Lugito, Graecia; Hsieh, Ya-Ting; Nurkhamidah, Siti
2014-02-24
Lamellar patterns and orientations in blends of two crystalline polymers: poly(ethylene oxide) (PEO) and low-molecular-weight poly(L-lactic acid) (PLLA) were investigated using polarizing light optical microscopy (POM), and atomic and scanning electron microscopy (AFM, SEM). Specific etching off of PEO was used to reveal the complex earlier-grown PLLA lamellae patterns with various PEO content in blends. Banding of extremely long pitch (50 μm) in crystallized PLLA spherulites was induced by two kinetic factors: geometry confinement by top cover and introduction of diluent such as PEO. The mechanisms and correlation among the lamellar assembly, ring bands, and cracks are exemplified. Lamellar patterns and ring-band types in blends were found to vary with respect to not only blend compositions, but also confinement of top-cover.
Optically defined mechanical geometry
NASA Astrophysics Data System (ADS)
Barasheed, Abeer Z.; Müller, Tina; Sankey, Jack C.
2016-05-01
In the field of optomechanics, radiation forces have provided a particularly high level of control over the frequency and dissipation of mechanical elements. Here we propose a class of optomechanical systems in which light exerts a similarly profound influence over two other fundamental parameters: geometry and mass. By applying an optical trap to one lattice site of an extended phononic crystal, we show it is possible to create a tunable, localized mechanical mode. Owing to light's simultaneous and constructive coupling with the structure's continuum of modes, we estimate that a trap power at the level of a single intracavity photon should be capable of producing a significant effect within a realistic, chip-scale device.
Kristianto, Jasmin; Litscher, Suzanne J.; Johnson, Michael G.; Patel, Forum; Patel, Mital; Fisher, Jacqueline; Zastrow, Ryley K.; Radcliff, Abigail B.; Blank, Robert D.
2016-01-01
A pleiotropic quantitative trait locus (QTL) for bone geometry and mechanical performance in mice was mapped to distal chromosome 4 via an intercross of recombinant congenic mice HcB-8 and HcB-23. To study the QTL in isolation, we have generated C3H.B10-(rs6355453-rs13478087) (C.B.4.3) and C3H.B10-(rs6369860-D4Mit170) (C.B.4.2) congenic strains that harbor ~20 Mb and ~3 Mb, respectively, of chromosome 4 overlapping segments from C57BL/10ScSnA (B10) within the locus on a C3H/DiSnA (C3H) background. Using 3-point bend testing and standard beam equations, we phenotyped these mice for femoral mid-diaphyseal geometry and biomechanical performance. We analyzed the results via 2-way ANOVA, using sex and genotype as factors. In the C.B.4.3 strain, we found that homozygous B10/B10 male mice had smaller cross sectional area (CSA) and reduced total displacement than homozygous C3H/C3H mice. Sex by genotype interaction was also observed for maximum load and stiffness for C3H/C3H and B10/B10 mice, respectively. In C.B.4.2 strain, we found that homozygous B10/B10 mice had lower total displacement, post-yield displacement (PYD), stiffness, yield load and maximum load than mice harboring C3H allele. Sex by genotype interaction was observed in B10/B10 mice for perimeter, outer minor axis (OMA) and CSA. There were no significant differences in tissue level mechanical performance, which suggest that the QTL acts primarily on circumferential bone size. These data confirm the prior QTL mapping data and support other work demonstrating the importance of chromosome 4 QTL on bone modeling and bone responses to mechanical loading. PMID:26849124
NASA Technical Reports Server (NTRS)
Hallock, Ashley K.; Polzin, Kurt A.; Bonds, Kevin W.; Emsellem, Gregory D.
2011-01-01
Results are presented demonstrating the e ect of inductive coil geometry and current sheet trajectory on the exhaust velocity of propellant in conical theta pinch pulsed induc- tive plasma accelerators. The electromagnetic coupling between the inductive coil of the accelerator and a plasma current sheet is simulated, substituting a conical copper frustum for the plasma. The variation of system inductance as a function of plasma position is obtained by displacing the simulated current sheet from the coil while measuring the total inductance of the coil. Four coils of differing geometries were employed, and the total inductance of each coil was measured as a function of the axial displacement of two sep- arate copper frusta both having the same cone angle and length as the coil but with one compressed to a smaller size relative to the coil. The measured relationship between total coil inductance and current sheet position closes a dynamical circuit model that is used to calculate the resulting current sheet velocity for various coil and current sheet con gura- tions. The results of this model, which neglects the pinching contribution to thrust, radial propellant con nement, and plume divergence, indicate that in a conical theta pinch ge- ometry current sheet pinching is detrimental to thruster performance, reducing the kinetic energy of the exhausting propellant by up to 50% (at the upper bound for the parameter range of the study). The decrease in exhaust velocity was larger for coils and simulated current sheets of smaller half cone angles. An upper bound for the pinching contribution to thrust is estimated for typical operating parameters. Measurements of coil inductance for three di erent current sheet pinching conditions are used to estimate the magnetic pressure as a function of current sheet radial compression. The gas-dynamic contribution to axial acceleration is also estimated and shown to not compensate for the decrease in axial electromagnetic acceleration
Gahungu, Godefroid; Zhang, Jingping; Ntakarutimana, Vestine; Gahungu, Nestor
2010-01-14
With the aim of evaluating the combined effect of one 8-hydroxyquinoline (q)/picolinate (p) and "CH"/N substitutions on the molecular geometry, electronic structure, and optical properties of tris-(8-hydroxyquinoline)aluminum [Alq(3)], the density functional theory (B3LYP) and time-dependent density functional theory (TD-B3LYP), using the 6-31G(d) and 3-21+G(d,p) basis sets were applied on Alq(3), Alq(2)p, and its "CH"/N-substitution derivatives. A comparison of the optimized ground-state (S(0)) geometries has shown that the molecular shape is conserved upon such a substitution. On the basis of the frontier molecular orbital and gap energy (E(g)) calculations, it was shown that, comparatively to the pristine Alq(2)p (and to the original parent Alq(3)), the HOMO and LUMO are stabilized, the net effect being an increasing or a decreasing E(g), depending on the position of the substituted group. The substitution of q(B) by p (from Alq(3) to Alq(2)p) was also found to induce the same feature. Starting from the S(0) and S(1) (first excited state) geometries, the effect of the substitution on the absorption (and emission) spectra was evaluated. It was found that the "CH"/N substitution in different positions on the two 8-hydroxyquinoline ligands may also constitute an efficient approach of tuning the Alq(2)p emitting color. In comparison with both Alq(3) and Alq(2)p, an important blue shift was predicted for the 5-substituted derivative, an important red shift being observed for the 4-substituted one. Also, relatively significant blue and red shifts were predicted for the 7- and 2-substituted derivatives. Finally, revisiting the correlation between the spectrum shifts and the metal-ligand bonding, our recent findings (2) were confirmed. PMID:19904976
Yan, Xuzhou; Li, Zhengtao; Wei, Peifa; Huang, Feihe
2013-02-01
A chemically responsive diquaternary salt with π-extended surface was made. The host-guest complexation with chemo-responsiveness between three bis(m-phenylene)-32-crown-10 (BMP32C10) derivatives and this diquaternary salt guest was studied through the sequential addition of basic and acidic reagents (diethylamine and trifluoroacetic acid, respectively). Furthermore, the host-substituent effect on the complexation geometries of these three host-guest complexes, from taco to taco-type threaded to threaded structures by changing the substituent on BMP32C10 as shown by crystal structures, was also addressed. PMID:23320925
LOGO Based Instruction in Geometry.
ERIC Educational Resources Information Center
Yusuf, Mian Muhammad
The objective of this pretest-posttest Quasi-Experimental Design study was to determine the effects of LOGO Based Instruction (LBI) compared to instruction by teacher lecture and pencil-and-paper activities on: (1) students' understanding of the concepts of point, ray, line, and line segment; (2) students' attitudes toward learning geometry,…
Tafra, E; Culo, M; Basletić, M; Korin-Hamzić, B; Hamzić, A; Jacobsen, C S
2012-02-01
We have measured the Hall effect on recently synthesized single crystals of the quasi-one-dimensional organic conductor TTF-TCNQ (tetrathiafulvalene-tetracyanoquinodimethane), a well known charge transfer complex that has two kinds of conductive stacks: the donor (TTF) and the acceptor (TCNQ) chains. The measurements were performed in the temperature interval 30 K < T < 300 K and for several different magnetic field and current directions through the crystal. By applying the equivalent isotropic sample approach, we have demonstrated the importance of the choice of optimal geometry for accurate Hall effect measurements. Our results show, contrary to past belief, that the Hall coefficient does not depend on the geometry of measurements and that the Hall coefficient value is approximately zero in the high temperature region (T > 150 K), implying that there is no dominance of either the TTF or the TCNQ chain. At lower temperatures our measurements clearly prove that all three phase transitions of TTF-TCNQ could be identified from Hall effect measurements. PMID:22214728
NASA Astrophysics Data System (ADS)
Tafra, E.; Čulo, M.; Basletić, M.; Korin-Hamzić, B.; Hamzić, A.; Jacobsen, C. S.
2012-02-01
We have measured the Hall effect on recently synthesized single crystals of the quasi-one-dimensional organic conductor TTF-TCNQ (tetrathiafulvalene-tetracyanoquinodimethane), a well known charge transfer complex that has two kinds of conductive stacks: the donor (TTF) and the acceptor (TCNQ) chains. The measurements were performed in the temperature interval 30 K < T < 300 K and for several different magnetic field and current directions through the crystal. By applying the equivalent isotropic sample approach, we have demonstrated the importance of the choice of optimal geometry for accurate Hall effect measurements. Our results show, contrary to past belief, that the Hall coefficient does not depend on the geometry of measurements and that the Hall coefficient value is approximately zero in the high temperature region (T > 150 K), implying that there is no dominance of either the TTF or the TCNQ chain. At lower temperatures our measurements clearly prove that all three phase transitions of TTF-TCNQ could be identified from Hall effect measurements.
Johnson, C.L.; Franseen, E.K.; Goldstein, R.H.
2005-01-01
This study utilized three-dimensional exposures to evaluate how sea-level position and palaeotopography control the facies and geometries of heterozoan carbonates. Heterozoan carbonates were deposited on top of a Neogene volcanic substrate characterized by palaeotopographic highs, palaeovalleys, and straits that were formed by subaerial erosion, possibly original volcanic topography, and faults prior to carbonate deposition. The depositional sequence that is the focus of this study (DS1B) consists of 7-10 fining upward cycles that developed in response to relative sea-level fluctuations. A complete cycle has a basal erosion surface overlain by deposits of debrisflows and high-density turbidity currents, which formed during relative sea-level fall. Overlying tractive deposits most likely formed during the lowest relative position of sea level. Overlying these are debrites grading upward to high-density turbidites and low-density turbidites that formed during relative sea-level rise. The tops of the cycles consist of hemipelagic deposits that formed during the highest relative position of sea level. The cycles fine upward because upslope carbonate production decreased as relative sea level rose due to less surface area available for shallow-water carbonate production and partial drowning of substrates. The cycles are dominated by two end-member types of facies associations and stratal geometries that formed in response to fluctuating sea-level position over variable substrate palaeotopography. One end-member is termed 'flank flow cycle' because this type of cycle indicates dominant sediment transport down the flanks of palaeovalleys. Those cycles drape the substrate, have more debrites, high-density turbidites and erosion on palaeovalley flanks, and in general, the lithofacies fine down the palaeovalley flanks into the palaeovalley axes. The second end-member is termed 'axial flow cycle' because it indicates a dominance of sediment transport down the axes of
Hexatic undulations in curved geometries.
Lenz, Peter; Nelson, David R
2003-03-01
We discuss the influence of two-dimensional hexatic order on capillary waves and undulation modes in spherical and cylindrical geometries. In planar geometries, extended bond-orientational order has only a minor effect on the fluctuations of liquid surfaces or lipid bilayers. However, in curved geometries, the long-wavelength spectrum of these ripples is altered. We calculate this frequency shift and discuss applications to spherical vesicles, liquid metal droplets, bubbles and cylindrical jets coated with surface-active molecules, and to multielectron bubbles in liquid helium at low temperatures. Hexatic order also leads to a shift in the threshold for the fission instability of charged droplets and bubbles, and for the Plateau-Rayleigh instability of liquid jets. PMID:12689068
Effects of Open Enrollment in Minnesota. ERS Research Digest.
ERIC Educational Resources Information Center
Educational Research Service, Arlington, VA.
In recent years, many policy makers, including officials in the Federal Government and the National Governors' Association, have advocated public school choice as the answer to the problems of public education. In 1987, Minnesota was the first state to pass legislation implementing a statewide, interdistrict, open enrollment plan for public…
The Effect of Reductions in Public Library Opening Hours on Book Issues: A Statistical Analysis.
ERIC Educational Resources Information Center
Loynes, Robert; Proctor, Richard
2000-01-01
Discusses statistical analyses of the effect of reduction in opening hours on book issues, or borrowing, of public library authorities (PLAs) in the United Kingdom. Demonstrates the difficulties involved in using statistical data to make accurate predictions of the impact of opening hour reductions on borrowing. (Author/LRW)
ERIC Educational Resources Information Center
Lovett, Marsha; Meyer, Oded; Thille, Candace
2008-01-01
The Open Learning Initiative (OLI) is an open educational resources project at Carnegie Mellon University that began in 2002 with a grant from The William and Flora Hewlett Foundation. OLI creates web-based courses that are designed so that students can learn effectively without an instructor. In addition, the courses are often used by instructors…
43 CFR 2091.5-4 - Segregative effect and opening: Water power withdrawals.
Code of Federal Regulations, 2014 CFR
2014-10-01
... 43 Public Lands: Interior 2 2014-10-01 2014-10-01 false Segregative effect and opening: Water power withdrawals. 2091.5-4 Section 2091.5-4 Public Lands: Interior Regulations Relating to Public Lands (Continued) BUREAU OF LAND MANAGEMENT, DEPARTMENT OF THE INTERIOR LAND RESOURCE MANAGEMENT (2000) SPECIAL LAWS AND RULES Segregation and Opening...
Fan, Tingting; Lu, Yuan; Gao, Yan; Meng, Jie; Tan, Wenchang; Huo, Yunlong; Kassab, Ghassan S
2016-03-21
Although the left internal mammary artery (LIMA) bypass graft is the best choice for surgical revascularization, its hemodynamics are still complex and can result in long-term graft failure. Here, we performed a hemodynamic analysis of the LIMA-coronary artery with end-to-side/side-to-side anastomoses based on 15 patient-specific CTA images at various postoperative periods. We hypothesize that hemodynamic patterns are determined by the interplay of LIMA geometry, anastomotic configuration, and severity of native coronary artery stenosis, which are strongly affected by the postoperative time. A 3D finite volume method with the inlet pressure wave and outlet resistance boundary conditions was used to compute the distribution of pressure and flow, from which the time-averaged wall shear stress (TAWSS), oscillation shear index (OSI), time-averaged WSS gradient (TAWSSG), and transverse WSS (transWSS) were determined. To characterize the hemodynamic environment, we defined surface area ratios of low TAWSS (≤4dynes/cm(2)), high OSI (≥0.15), TAWSSG (≥500dynes/cm(3)), and transWSS (≥6dynes/cm(2)) in the LIMA graft and at the anastomosis between LIMA graft and coronary artery. These ratios were determined by the interplay of multiple morphometric parameters in the LIMA-coronary artery, but increased with postoperative time. These findings have significant implications for understanding LIMA graft patency. PMID:26900034
Pauly, Hannah M; Kelly, Daniel J; Popat, Ketul C; Trujillo, Nathan A; Dunne, Nicholas J; McCarthy, Helen O; Haut Donahue, Tammy L
2016-08-01
Electrospun nanofibers are a promising material for ligamentous tissue engineering, however weak mechanical properties of fibers to date have limited their clinical usage. The goal of this work was to modify electrospun nanofibers to create a robust structure that mimics the complex hierarchy of native tendons and ligaments. The scaffolds that were fabricated in this study consisted of either random or aligned nanofibers in flat sheets or rolled nanofiber bundles that mimic the size scale of fascicle units in primarily tensile load bearing soft musculoskeletal tissues. Altering nanofiber orientation and geometry significantly affected mechanical properties; most notably aligned nanofiber sheets had the greatest modulus; 125% higher than that of random nanofiber sheets; and 45% higher than aligned nanofiber bundles. Modifying aligned nanofiber sheets to form aligned nanofiber bundles also resulted in approximately 107% higher yield stresses and 140% higher yield strains. The mechanical properties of aligned nanofiber bundles were in the range of the mechanical properties of the native ACL: modulus=158±32MPa, yield stress=57±23MPa and yield strain=0.38±0.08. Adipose derived stem cells cultured on all surfaces remained viable and proliferated extensively over a 7 day culture period and cells elongated on nanofiber bundles. The results of the study suggest that aligned nanofiber bundles may be useful for ligament and tendon tissue engineering based on their mechanical properties and ability to support cell adhesion, proliferation, and elongation. PMID:27082129
Sader, John E.; Lu, Jianing; Mulvaney, Paul
2014-11-15
Calibration of the optical lever sensitivities of atomic force microscope (AFM) cantilevers is especially important for determining the force in AFM measurements. These sensitivities depend critically on the cantilever mode used and are known to differ for static and dynamic measurements. Here, we calculate the ratio of the dynamic and static sensitivities for several common AFM cantilevers, whose shapes vary considerably, and experimentally verify these results. The dynamic-to-static optical lever sensitivity ratio is found to range from 1.09 to 1.41 for the cantilevers studied – in stark contrast to the constant value of 1.09 used widely in current calibration studies. This analysis shows that accuracy of the thermal noise method for the static spring constant is strongly dependent on cantilever geometry – neglect of these dynamic-to-static factors can induce errors exceeding 100%. We also discuss a simple experimental approach to non-invasively and simultaneously determine the dynamic and static spring constants and optical lever sensitivities of cantilevers of arbitrary shape, which is applicable to all AFM platforms that have the thermal noise method for spring constant calibration.
ERIC Educational Resources Information Center
Morris, Barbara H.
2004-01-01
This article describes a geometry project that used the beauty of stained-glass-window designs to teach middle school students about geometric figures and concepts. Three honors prealgebra teachers and a middle school mathematics gifted intervention specialist created a geometry project that covered the curriculum and also assessed students'…
Geometry of multihadron production
Bjorken, J.D.
1994-10-01
This summary talk only reviews a small sample of topics featured at this symposium: Introduction; The Geometry and Geography of Phase space; Space-Time Geometry and HBT; Multiplicities, Intermittency, Correlations; Disoriented Chiral Condensate; Deep Inelastic Scattering at HERA; and Other Contributions.
ERIC Educational Resources Information Center
Kaufmann, Matthew L.; Bomer, Megan A.; Powell, Nancy Norem
2009-01-01
Students enter the geometry classroom with a strong concept of fairness and a sense of what it means to "play by the rules," yet many students have difficulty understanding the postulates, or rules, of geometry and their implications. Although they may never have articulated the properties of an axiomatic system, they have gained a practical…
Euclidean Geometry via Programming.
ERIC Educational Resources Information Center
Filimonov, Rossen; Kreith, Kurt
1992-01-01
Describes the Plane Geometry System computer software developed at the Educational Computer Systems laboratory in Sofia, Bulgaria. The system enables students to use the concept of "algorithm" to correspond to the process of "deductive proof" in the development of plane geometry. Provides an example of the software's capability and compares it to…
ERIC Educational Resources Information Center
Lyublinskaya, Irina; Funsch, Dan
2012-01-01
Several interactive geometry software packages are available today to secondary school teachers. An example is The Geometer's Sketchpad[R] (GSP), also known as Dynamic Geometry[R] software, developed by Key Curriculum Press. This numeric based technology has been widely adopted in the last twenty years, and a vast amount of creativity has been…
NASA Technical Reports Server (NTRS)
Capuano, J. M., Jr.; Thronson, H. A., Jr.; Witt, A. N.
1993-01-01
The presence of substantial amounts of interstellar dust in late-type galaxies affects observable parameters such as the optical surface brightness, the color, and the ratio of far-infrared to optical luminosity of these galaxies. We conducted radiative transfer calculations for late-type galaxy environments to examine two different scenarios: (1) the effects of increasing amounts of dust in two fixed geometries with different star distributions; and (2) the effects of an evolving dust-star geometry in which the total amount of dust is held constant, for three different star distributions. The calculations were done for ten photometric bands, ranging from the far-ultraviolet to the near-infrared (K), and scattered light was included in the galactic surface brightness at each wavelength. The energy absorbed throughout these ten photometric bands was assumed to re-emerge in the far-infrared as thermal dust emission. We also considered the evolutionary contraction of a constant amount of dust relative to pre-existing star distributions.
NASA Astrophysics Data System (ADS)
Alves, M. C.; Santos, W. S.; Lee, Choonsik; Bolch, Wesley E.; Hunt, John G.; Carvalho Júnior, A. B.
2014-12-01
The conversion coefficients (CCs) relate protection quantities, mean absorbed dose (DT) and effective dose (E), with physical radiation field quantities, such as fluence (Φ). The calculation of CCs through Monte Carlo simulations is useful for estimating the dose in individuals exposed to radiation. The aim of this work was the calculation of conversion coefficients for absorbed and effective doses per fluence (DT/ Φ and E/Φ) using a sitting and standing female hybrid phantom (UFH/NCI) exposure to monoenergetic protons with energy ranging from 2 MeV to 10 GeV. The radiation transport code MCNPX was used to develop exposure scenarios implementing the female UFH/NCI phantom in sitting and standing postures. Whole-body irradiations were performed using the recommended irradiation geometries by ICRP publication 116 (AP, PA, RLAT, LLAT, ROT and ISO). In most organs, the conversion coefficients DT/Φ were similar for both postures. However, relative differences were significant for organs located in the abdominal region, such as ovaries, uterus and urinary bladder, especially in the AP, RLAT and LLAT geometries. Anatomical differences caused by changing the posture of the female UFH/NCI phantom led an attenuation of incident protons with energies below 150 MeV by the thigh of the phantom in the sitting posture, for the front-to-back irradiation, and by the arms and hands of the phantom in the standing posture, for the lateral irradiation.
Bengel, F M; Nekolla, S G; Ibrahim, T; Weniger, C; Ziegler, S I; Schwaiger, M
2000-05-01
Thyroid hormones influence cardiac performance directly and indirectly via changes in peripheral circulation. Little, however, is known about the effect on myocardial oxidative metabolism and its relation to cardiac function and geometry. Patients with a history of thyroidectomy for thyroid cancer present a unique model to investigate the cardiac effects of hypothyroidism. Ten patients without heart disease were investigated in the hypothyroid state and again 4-6 weeks later under euthyroid conditions. Myocardial oxidative metabolism was measured by positron emission tomography with [11C]acetate and the clearance constant k(mono). Cine magnetic resonance imaging was applied to determine left ventricular geometry. A stroke work index (SWI = stroke volume x systolic blood pressure/ventricular mass) was calculated. Then, to estimate myocardial efficiency, a work metabolic index [WMI = SWI x heart rate/k(mono)] was obtained. Compared to hormone replacement, systemic vascular resistance and left ventricular mass were significantly higher in hypothyroidism. Ejection fraction and SWI were significantly lower. Despite an additional reduction of k(mono), the WMI was significantly lower, too. In summary, cardiac oxygen consumption is reduced in hypothyroidism. This reduction is associated with increased peripheral resistance and reduced contractility. Estimates of cardiac work are more severely suppressed than those of oxidative metabolism, suggesting decreased efficiency. These findings may provide an explanation for development or worsening of heart failure in hypothyroid patients with preexisting heart disease. PMID:10843159
Diamantopoulos, Stefanos; Butt, Saeed; Katsilieri, Zaira; Kefala, Vasiliki; Zogal, Pawel; Sakas, George; Baltas, Dimos
2011-01-01
Purpose This study investigates the distortion of geometry of catheters and anatomy in acquired U/S images, caused by utilizing various stand-off materials for covering a transrectal bi-planar ultrasound probe in HDR and LDR prostate brachytherapy, biopsy and other interventional procedures. Furthermore, an evaluation of currently established water-bath based quality assurance (QA) procedures is presented. Material and methods Image acquisitions of an ultrasound QA setup were carried out at 5 MHz and 7 MHz. The U/S probe was covered by EA 4015 Silicone Standoff kit, or UA0059 Endocavity balloon filled either with water or one of the following: 40 ml of Endosgel®, Instillagel®, Ultraschall gel or Space OAR™ gel. The differences between images were recorded. Consequently, the dosimetric impact of the observed image distortion was investigated, using a tissue equivalent ultrasound prostate phantom – Model number 053 (CIRS Inc., Norfolk, VA, USA). Results By using the EA 4015 Silicone Standoff kit in normal water with sound speed of 1525 m/s, a 3 mm needle shift was observed. The expansion of objects appeared in radial direction. The shift deforms also the PTV (prostate in our case) and other organs at risk (OARs) in the same way leading to overestimation of volume and underestimation of the dose. On the other hand, Instillagel® and Space OAR™ “shrinks” objects in an ultrasound image for 0.65 mm and 0.40 mm, respectively. Conclusions The use of EA 4015 Silicone Standoff kit for image acquisition, leads to erroneous contouring of PTV and OARs and reconstruction and placement of catheters, which results to incorrect dose calculation during prostate brachytherapy. Moreover, the reliability of QA procedures lies mostly in the right temperature of the water used for accurate simulation of real conditions of transrectal ultrasound imaging. PMID:23346130
Barraclough, B; Lebron, S; Li, J; Fan, Qiyong; Liu, C; Yan, G
2015-06-15
Purpose: A novel convolution-based approach has been proposed to address ion chamber (IC) volume averaging effect (VAE) for the commissioning of commercial treatment planning systems (TPS). We investigate the use of various convolution kernels and its impact on the accuracy of beam models. Methods: Our approach simulates the VAE by iteratively convolving the calculated beam profiles with a detector response function (DRF) while optimizing the beam model. At convergence, the convolved profiles match the measured profiles, indicating the calculated profiles match the “true” beam profiles. To validate the approach, beam profiles of an Elekta LINAC were repeatedly collected with ICs of various volumes (CC04, CC13 and SNC 125) to obtain clinically acceptable beam models. The TPS-calculated profiles were convolved externally with the DRF of respective IC. The beam model parameters were reoptimized using Nelder-Mead method by forcing the convolved profiles to match the measured profiles. We evaluated three types of DRFs (Gaussian, Lorentzian, and parabolic) and the impact of kernel dependence on field geometry (depth and field size). The profiles calculated with beam models were compared with SNC EDGE diode-measured profiles. Results: The method was successfully implemented with Pinnacle Scripting and Matlab. The reoptimization converged in ∼10 minutes. For all tested ICs and DRFs, penumbra widths of the TPS-calculated profiles and diode-measured profiles were within 1.0 mm. Gaussian function had the best performance with mean penumbra width difference within 0.5 mm. The use of geometry dependent DRFs showed marginal improvement, reducing the penumbra width differences to less than 0.3 mm. Significant increase in IMRT QA passing rates was achieved with the optimized beam model. Conclusion: The proposed approach significantly improved the accuracy of the TPS beam model. Gaussian functions as the convolution kernel performed consistently better than Lorentzian and
Spazzin, Aloísio Oro; Costa, Ana Rosa; Correr, Américo Bortolazzo; Consani, Rafael Leonardo Xediek; Correr-Sobrinho, Lourenço; dos Santos, Mateus Bertolini Fernandes
2013-08-01
This study evaluated the influence of cross-section geometry of the bar framework on the distribution of static stresses in an overdenture-retaining bar system simulating horizontal misfit and bone loss. Three-dimensional FE models were created including two titanium implants and three cross-section geometries (circular, ovoid or Hader) of bar framework placed in the anterior part of a severely resorbed jaw. One model with 1.4-mm vertical loss of the peri-implant tissue was also created. The models set were exported to mechanical simulation software, where horizontal displacement (10, 50 or 100 μm) was applied simulating the settling of the framework, which suffered shrinkage during the laboratory procedures. The bar material used for the bar framework was a cobalt--chromium alloy. For evaluation of bone loss effect, only the 50-μm horizontal misfit was simulated. Data were qualitatively and quantitatively evaluated using von Mises stress for the mechanical part and maximum principal stress and μ-strain for peri-implant bone tissue given by the software. Stresses were concentrated along the bar and in the join between the bar and cylinder. In the peri-implant bone tissue, the μ-strain was higher in the cervical third. Higher stress levels and μ-strain were found for the models using the Hader bar. The bone loss simulated presented considerable increase on maximum principal stresses and μ-strain in the peri-implant bone tissue. In addition, for the amplification of the horizontal misfit, the higher complexity of the bar cross-section geometry and bone loss increases the levels of static stresses in the peri-implant bone tissue. PMID:23791086
NASA Astrophysics Data System (ADS)
Braun, H.; Kyriakou, Y.; Kachelrieß, M.; Kalender, W. A.
2010-10-01
For decades, the heel effect has been known to cause an angular dependence of the emitted spectrum of an x-ray tube. In radiography, artifacts were observed and attributed to the heel effect. However, no problems due to the heel effect were discerned in multi-slice computed tomography (MSCT) so far. With flat-detector CT (FDCT), involving larger cone angles and different system geometries, the heel effect might cause new artifacts. These artifacts were analyzed in this paper for system geometries different from the ones widely used nowadays. Simulations and measurements were performed. Simulations included symmetric as well as asymmetric detector layouts and different x-ray tube orientations with respect to the detector plane. The measurements were performed on a micro-CT system in an asymmetric detector layout. Furthermore, an analytical correction scheme is proposed to overcome heel effect artifacts. It was shown that the type of artifact greatly depends on the orientation of the x-ray tube and also on the type of detector alignment (i.e. symmetric or different types of asymmetric alignment). Certain combinations exhibited almost no significant artifact while others greatly influenced the quality of the reconstructed images. The proposed correction scheme showed good results that were further improved when also applying a scatter correction. When designing CT systems, care should be taken when placing the tube and the detector. Orientation of the x-ray tube like in most MSCT systems seems advisable in asymmetric detector layouts. However, a different type of tube orientation can be overcome with suitable correction schemes.
NASA Astrophysics Data System (ADS)
Sessions, John W.; Lindstrom, Dallin L.; Hanks, Brad W.; Hope, Sandra; Jensen, Brian D.
2016-04-01
Connecting technology to biologic discovery is a core focus of non-viral gene therapy biotechnologies. One approach that leverages both the physical and electrical function of microelectromechanical systems (MEMS) in cellular engineering is a technology previously described as lance array nanoinjection (LAN). In brief, LAN consists of a silicon chip measuring 2 cm by 2 cm that has been etched to contain an array of 10 μm tall, solid lances that are spaced every 10 μm in a grid pattern. This array of lances is used to physically penetrate hundreds of thousands of cells simultaneously and to then electrically deliver molecular loads into cells. In this present work, two variables related to the microfabrication of the silicon lances, namely lance geometry and coating, are investigated. The purpose of both experimental variables is to assess these parameters’ effect on propidium iodide (PI), a cell membrane impermeable dye, uptake to injected HeLa 229 cells. For the lance geometry experimentation, three different microfabricated lance geometries were used which include a flat/narrow (FN, 1 μm diameter), flat/wide (FW, 2-2.5 μm diameter), and pointed (P, 1 μm diameter) lance geometries. From these tests, it was shown that the FN lances had a slightly better cell viability rate of 91.73% and that the P lances had the best PI uptake rate of 75.08%. For the lance coating experimentation, two different lances were fabricated, both silicon etched lances with some being carbon coated (CC) in a <100 nm layer of carbon and the other lances being non-coated (Si). Results from this experiment showed no significant difference between lance types at three different nanoinjection protocols (0V, +1.5V DC, and +5V Pulsed) for both cell viability and PI uptake rates. One exception to this is the comparison of CC/5V Pul and Si/5V Pul samples, where the CC/5V Pul samples had a cell viability rate 5% higher. Both outcomes were unexpected and reveal how to better
Arie, H.; Kume, E.; Iguchi, I.
1997-08-01
We present measurements on quasiparticle injection into a YBa{sub 2}Cu{sub 3}O{sub 7{minus}y} (YBCO) film, with double injector-junction geometry free from the parallel overlapping effect of the currents, fabricated by electron-beam coevaporation and photolithographic lift off. The observed injection characteristics are quite symmetric with respect to the relative flow direction between the injection current and the film current, in contrast to previous reports. The film critical current decreases almost linearly with the injection current. The critical current density J{sub c} can be controlled by injection current density much smaller than J{sub c}, indicating that quasiparticle injection is dominant. The estimated effective quasiparticle recombination time at the critical injection is about 2 ns, consistent with previous reports of optical excitation. {copyright} {ital 1997} {ital The American Physical Society}
Periat, Aurélie; Kohler, Isabelle; Bugey, Aurélie; Bieri, Stefan; Versace, François; Staub, Christian; Guillarme, Davy
2014-08-22
In this study, the influence of electrospray ionization (ESI) source design on the overall sensitivity achieved in hydrophilic interaction chromatography (HILIC) and reversed phase liquid chromatography (RPLC), was investigated. State-of-the-art triple quadrupole mass analyzers from AB Sciex, Agilent Technologies and Waters equipped with brand specific source geometries were tested with various mobile phase pH on 53 pharmaceutical compounds. The design of the ESI source showed to strongly influence the gain in sensitivity that can be achieved in HILIC compared to RPLC mode. The 6460 Triple Quadrupole LC/MS system from Agilent Technologies was particularly affected by mobile phase settings. Indeed, compared to RPLC conditions, 92% of the compounds had an increased signal-to-noise ratio at a flow rate of 300 μL/min in HILIC mode at pH 6, while this percentage dropped to only 7% at 1000 μL/min and pH 3. In contrast, the influence of flow rate and mobile phase pH on the gain in sensitivity between RPLC and HILIC was found very limited with the API 5000 LC/MS/MS system from AB Sciex, as only 15 to 36% of the tested compounds showed an enhanced sensitivity in HILIC mode. With the Xevo TQ-S instrument from Waters, superior sensitivity in HILIC was noticed for 85% of the compounds with optimal conditions (i.e., pH 3 and 1000 μL/min), whereas at sub-optimal conditions (i.e. pH 6 and 300 μL/min), it represented less than 50%. The gain in sensitivity observed in HILIC was found less significant with the recent LC-MS platforms used in this study than for old-generation instruments. Indeed, the improved ESI sources equipping the recent mass analyzers allow for enhanced evaporation efficiency, mainly for RPLC mobile phases containing high proportion of water and this even at high flow rates. PMID:25017394
Effects of Increasing Urbanization on the Ecological Integrity of Open Space Preserves
NASA Astrophysics Data System (ADS)
Esbah, Hayriye; Cook, Edward A.; Ewan, Joseph
2009-05-01
This article analyzes the effects of increasing urbanization on open space preserves within the metropolitan area of Phoenix, Arizona, USA. Time series analysis is used in 10-year increments over 40 years to study urban landscape change. Three landscape metrics—(1) matrix utility (measures intensity of adjacent land uses), (2) isolation (measures distances to other open space patches), and (3) connectivity (measures physical links to other open space patches and corridors)—are used to assess changes in landscape patterns and serve as indicators of urban ecological integrity of the open space preserves. Results show that in the case of both open space preserves, general decline in indicators of urban ecological integrity was evident. The matrix utility analysis demonstrated that increasing intensity of land uses adjacent to preserve is likely to increase edge effects, reducing the habitat value of interior or core habitat areas. Isolation analysis showed that both preserves have experienced increasing isolation from other open space elements over time. Also, connectivity analysis indicated that terrestrial connections to other open space elements have also deteriorated. Conclusions of this research demonstrate that while preservation of natural areas as open space is important in an urban context, intense development of surrounding areas reduces the urban ecological integrity significantly.
Hahn, Konstanze R; Seitsonen, Ari P; Baiker, Alfons
2015-11-01
The cinchona alkaloids cinchonidine and cinchonine belong to the most efficient chiral modifiers for the noble metal-catalyzed enantioselective hydrogenation of C=O and C=C bonds. Under reaction conditions these modifiers are coadsorbed on the noble metal surface with hydrogen. Using density functional theory, we studied the effect of coadsorbed hydrogen on the adsorption mode of cinchonidine and cinchonine on a Pt(111) surface at different hydrogen coverages. The theoretical study indicates that the presence of coadsorbed hydrogen affects both the adsorption geometry as well as the stability of the adsorbed cinchona alkaloids. At all hydrogen coverages the cinchona alkaloids are found to be adsorbed via anchoring of the quinoline moiety. In the absence of hydrogen as well as at low hydrogen coverage the quinoline moiety adsorbs nearly parallel to the surface, whereas at higher hydrogen coverage it becomes tilted. Higher hydrogen coverage as well as partial hydrogenation of the quinoline part of the cinchona alkaloid and hydrogen transfer to the C[double bond, length as m-dash]C double bond at 10, 11 position of the quinuclidine moiety destabilize the adsorbed cinchona alkaloid, whereas hydrogen transfer to the nitrogen atom of the quinoline and the quinuclidine moiety stabilizes the adsorbed molecule. The stability as well as the adsorption geometry of the cinchona alkaloids are affected by the coadsorbed hydrogen and are proposed to influence the efficiency of the enantiodifferentiating ability of the chirally modified platinum surface. PMID:26426825
Bandyopadhyay, Debashis
2012-02-01
The present study reports the effect of oxygen addition on small size Ni(n) (n = 1-6) clusters in different spin states within the framework of linear combination of atomic orbital (LCAO) density functional theory (DFT) under spin polarized generalized gradient approximation (GGA) functional. Relative stabilities of the optimized clusters are discussed on the basis of the calculated parameters, such as, binding energy (BE), embedding energy (EE) and fragmentation energy (FE). Other parameters, like ionization potential (IP), electron affinity (EA), etc. show that though the additions of oxygen can affect the chemical properties of Ni(n) clusters with an additional stability to Ni(n)O. In most of the cases the magnetic moment of the stable isomers are geometry dependent for a particular size both in pure and oxidized clusters. Calculated magnetic moments of Ni(n)O (n = 1-6) clusters reveal that the magnetic moment of ground state Ni(4)O isomers in different geometries is same as in pure Ni(4) isomers. Present study also explains the cause of stable magnetic moment in Ni(4)O cluster through the distribution of electrons in different orbitals. PMID:21567288
NASA Astrophysics Data System (ADS)
Jing, Weixuan; Qi, Han; Shi, Jiafan; Jiang, Zhuangde; Zhou, Fan; Cheng, Yanyan; Gao, Kun
2015-11-01
This paper identifies and investigates the influencing factors and their effects on the surface morphologies of ZnO nanorod-based hierarchical structures. With ZnO nanorods hydrothermally synthesized on a piece of planar glass, an optical fiber core, and a SiO2 microsphere, three kinds of ZnO nanorod-based hierarchical structures were fabricated. It is found that not only the synthesizing parameters but also the geometries of the micro-scale substrates affect significantly the nucleation densities of seed layers and the Zn2+ diffusion zones of growth solution upon the substrate surfaces. These two factors further give rise to varied diameters and orientation of the ZnO nanorods as well as different sizes of the pits among the bundles of ZnO nanorods, which eventually result in different surface morphologies of corresponding hierarchical structures. With Zn2+ concentration of the growth solution increasing, side-by-side coalescence among neighboring ZnO nanorods first appears on the optical fiber core. The different curvature radii of the optical fiber core at front and side view lead to the anisotropic surface morphology of the related hierarchical structure. Although their curvature radii are the same, the different geometries of the optical fiber core at side view and the planar glass account for varied surface morphologies of the corresponding hierarchical structures.
Increased Knowledge in Geometry and Instructional Practice.
ERIC Educational Resources Information Center
Swafford, Jane O.; And Others
1997-01-01
Examines the effects on instruction of an intervention program designed to enhance teachers' knowledge of geometry and their knowledge of research on student cognition in geometry. Findings indicate significant gains in content knowledge and in van Hiele level, and marked changes in what was taught, how it was taught, and the characteristics…
The slab geometry laser. I - Theory
NASA Technical Reports Server (NTRS)
Eggleston, J. M.; Kane, T. J.; Kuhn, K.; Byer, R. L.; Unternahrer, J.
1984-01-01
Slab geometry solid-state lasers offer significant performance improvements over conventional rod-geometry lasers. A detailed theoretical description of the thermal, stress, and beam-propagation characteristics of a slab laser is presented. The analysis includes consideration of the effects of the zig-zag optical path, which eliminates thermal and stress focusing and reduces residual birefringence.
Effects of weld residual stresses on crack-opening area analysis of pipes for LBB applications
Dong, P.; Rahman, S.; Wilkowski, G.
1997-04-01
This paper summarizes four different studies undertaken to evaluate the effects of weld residual stresses on the crack-opening behavior of a circumferential through-wall crack in the center of a girth weld. The effect of weld residual stress on the crack-opening-area and leak-rate analyses of a pipe is not well understood. There are no simple analyses to account for these effects, and, therefore, they are frequently neglected. The four studies involved the following efforts: (1) Full-field thermoplastic finite element residual stress analyses of a crack in the center of a girth weld, (2) A comparison of the crack-opening displacements from a full-field thermoplastic residual stress analysis with a crack-face pressure elastic stress analysis to determine the residual stress effects on the crack-opening displacement, (3) The effects of hydrostatic testing on the residual stresses and the resulting crack-opening displacement, and (4) The effect of residual stresses on crack-opening displacement with different normal operating stresses.
ERIC Educational Resources Information Center
Emenaker, Charles E.
1999-01-01
Describes a sixth-grade interdisciplinary geometry unit based on Charles Dickens's "A Christmas Carol". Focuses on finding area, volume, and perimeter, and working with estimation, decimals, and fractions in the context of making gingerbread houses. (ASK)
ERIC Educational Resources Information Center
Chern, Shiing-Shen
1990-01-01
Discussed are the major historical developments of geometry. Euclid, Descartes, Klein's Erlanger Program, Gaus and Riemann, globalization, topology, Elie Cartan, and an application to molecular biology are included as topics. (KR)
Noncommutative Geometry and Physics
NASA Astrophysics Data System (ADS)
Connes, Alain
2006-11-01
In this very short essay we shall describe a "spectral" point of view on geometry which allows to start taking into account the lessons from both renormalization and of general relativity. We shall first do that for renormalization and explain in rough outline the content of our recent collaborations with Dirk Kreimer and Matilde Marcolli leading to the universal Galois symmetry of renormalizable quantum field theories provided by the renormalization group in its cosmic Galois group incarnation. As far as general relativity is concerned, since the functional integral cannot be treated in the traditional perturbative manner, it relies heavily as a "sum over geometries" on the chosen paradigm of geometric space. This will give us the occasion to discuss, in the light of noncommutative geometry, the issue of "observables" in gravity and our joint work with Ali Chamseddine on the spectral action, with a first attempt to write down a functional integral on the space of noncommutative geometries.
Proof in Transformation Geometry
ERIC Educational Resources Information Center
Bell, A. W.
1971-01-01
The first of three articles showing how inductively-obtained results in transformation geometry may be organized into a deductive system. This article discusses two approaches to enlargement (dilatation), one using coordinates and the other using synthetic methods. (MM)