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.