Science.gov

Sample records for properties in-canopy gradients

  1. Fluxes and In-Canopy Gradients of Biogenic Volatile Organic Compounds Above Contrasting South East Asian Land Uses

    NASA Astrophysics Data System (ADS)

    Nemitz, E.; Misztal, P.; Langford, B.; Oram, D.; Phillips, G.; di Marco, C.; Davison, B.; Hewitt, N.; Cape, N.

    2008-12-01

    Fluxes of volatile organic compounds were measured above tropical rainforest and oil palm plantation in the Malaysian state of Sabah on the island of Borneo. During April and July 2008 an Ionikon proton transfer reaction mass spectrometer (ptrms) was operated at the 100 m Global Atmospheric Watch (GAW) tower at Bukit Atur, at the edge of the Danum Valley conservation area. An ultrasonic anemometer and air inlet were mounted at 76 m, with the ptrms housed in a laboratory building at the foot of the tower, measuring fluxes over tropical rainforest (selectively logged in 1989) with a typical canopy height of 30 to 40 m. In addition, during the July period, a second ptrms was coupled to a lift system which automatically moved an inlet to sample in-canopy gradients inside the forest canopy, between 2 and 30 m. During May 2008, the ptrms was moved to an oil palm plantation, north of the town of Lahad Datu, were fluxes were measured at a height of 15 m above the 12 m tall canopy, together with concentrations and fluxes of ozone and aerosols. These measurements formed part of two major UK projects: OP3-Danum-2008 (Oxidant and Particle Production Processes above South East Asian Rainforest) was aimed at quantifying biogenic emissions and evaluating their impact on air chemistry and the production of photo-oxidants and biogenic secondary organic aerosol, while ACES (Aerosol Coupling in the Earth System) studies the role of primary biogenic emissions, in-canopy processes and the effect of land-use change on aerosols. Initial results indicate that fluxes of isoprene above forest averaged 1.4 mg m-2 s-1 which is somewhat smaller than previous measurements in Amazonia and than previous estimates derived from leaf- level measurements, reflecting uncertainties in the assumed plant species composition. Concentrations peaked at the top of the canopy during midday. With an average of 5.5 mg m-2s-1, isoprene fluxes above the oil palm plantation were four times larger. Average fluxes

  2. In-canopy gradients, composition, and sources of optically active aerosols over the Amazon forest

    NASA Astrophysics Data System (ADS)

    Guyon, P.; Graham, B.; Roberts, G. C.; Mayol-Bracero, O. L.; Andreae, M. O.; Artaxo, P.; Maenhaut, W.

    2003-04-01

    As part of the European contribution to the Large-Scale Biosphere-Atmosphere Experiment in Amazonia (LBA-EUSTACH), size-fractionated aerosol samples were collected at a primary rainforest site in the Brazilian Amazon during the wet and dry seasons. Daytime-nighttime segregated sampling was carried out at three different heights (above, within and below canopy level) on a 54 m meteorological tower. The samples were analyzed for up to 19 trace elements, equivalent black carbon (BCe) and mass concentrations. Additionally, measurements of scattering and absorption coefficients were performed. Absolute principal component analysis revealed that the wet and dry season aerosols contained the same three main aerosol components, namely a natural biogenic, a pyrogenic, and a soil dust component, but that these were present in different (absolute and relative) amounts. The elements related to biomass burning and soil dust generally exhibited highest concentrations above the canopy and during daytime, whilst forest-derived aerosol was more concentrated underneath the canopy and during nighttime. These variations can be largely attributed to daytime convective mixing and the formation of a shallow nocturnal boundary layer, along with the possibility of enhanced nighttime release of biogenic aerosol particles. All three components contributed significantly to light extinction, suggesting that, in addition to pyrogenic particles, biogenic and soil dust aerosols must be taken into account when modeling the physical and optical properties of aerosols in forested regions such the Amazon Basin.

  3. Species-specific Variation in the Importance of the Spectral Quality Gradient in Canopies as a Signal for Photosynthetic Resource Partitioning

    PubMed Central

    PONS, THIJS L.; de JONG-VAN BERKEL, YVONNE E. M.

    2004-01-01

    • Background and Aims Plants adjust the distribution of photosynthetic capacity and chlorophyll to canopy density. The importance of the gradient in the red : far-red ratio (R : FR) relative to the irradiance gradient was studied for its perception with respect to this partitioning of photosynthetic resources. Whether the relative importance of these two signals varied between six species of different growth habit (Phaseolus vulgaris, Lysimachia vulgaris, Hedera helix, Ficus benjamina, Carex acutiformis and Brachypodium pinnatum) was investigated further. • Methods Single leaves of plants were shaded in daylight by a spectrally neutral filter or a leaf. In another experiment, leaves were treated with supplemental FR. In most cases, treatment effects were evaluated after 2 weeks. • Key Results Nitrogen and photosynthetic capacity (Amax) per leaf area, parameters pertaining to between-leaf resource partitioning, were strongly reduced in neutral shade but not additionally by spectral leaf shade. Supplemental FR reduced these parameters also, except in Carex. Acceleration of induction of senescence was observed in spectral leaf shade in primary bean leaves. Amax per unit chlorophyll, a parameter pertaining to within-leaf resource partitioning, was reduced in neutral shade, but not in spectral leaf shade or supplemental FR. • Conclusions Signalling mechanisms associated with perception of the R : FR gradient in canopies were less important than those associated with the irradiance gradient for between-leaf and within-leaf partitioning of photosynthetic resources. The relative importance of the signals differed between species because Carex was the only species for which no indications were found for an involvement of the spectral gradient in perception of canopy density. PMID:15374835

  4. Sources of variability in canopy reflectance and the convergent properties of plants.

    PubMed

    Ollinger, S V

    2011-01-01

    How plants interact with sunlight is central to the existence of life and provides a window to the functioning of ecosystems. Although the basic properties of leaf spectra have been known for decades, interpreting canopy-level spectra is more challenging because leaf-level effects are complicated by a host of stem- and canopy-level traits. Progress has been made through empirical analyses and models, although both methods have been hampered by a series of persistent challenges. Here, I review current understanding of plant spectral properties with respect to sources of uncertainty at leaf to canopy scales. I also discuss the role of evolutionary convergence in plant functioning and the difficulty of identifying individual properties among a suite of interrelated traits. A pattern that emerges suggests a synergy among the scattering effects of leaf-, stem- and canopy-level traits that becomes most apparent in the near-infrared (NIR) region. This explains the widespread and well-known importance of the NIR region in vegetation remote sensing, but presents an interesting paradox that has yet to be fully explored: that we can often gain more insight about the functioning of plants by examining wavelengths that are not used in photosynthesis than by examining those that are. © 2010 The Author. New Phytologist © 2010 New Phytologist Trust.

  5. Simple chromatic properties of gradient flow

    NASA Astrophysics Data System (ADS)

    DeGrand, Thomas

    2017-06-01

    It has become customary to use a smoothing algorithm called "gradient flow" to fix the lattice spacing in a simulation, through a parameter called t0. It is shown that, in order to keep the length t0 fixed with respect to mesonic or gluonic observables as the number of colors Nc is varied, the fiducial point for the flow parameter must be scaled nearly linearly in Nc. In simulations with dynamical fermions, the dependence of t0 on the pseudoscalar meson mass flattens as the number of colors rises, in a way which is consistent with large Nc expectations.

  6. Mechanical Properties of Gradient Structure Mg Alloy

    NASA Astrophysics Data System (ADS)

    Chen, Hongliang; Yang, Jiang; Zhou, Hao; Moering, Jordan; Yin, Zhe; Gong, Yulan; Zhao, KunYu

    2017-09-01

    In this work, a surface mechanical attrition treatment (SMAT) process was applied to AZ31B magnesium alloy at room temperature. This method produced a gradient structure on the treated AZ31B, in which the grains of the topmost layer are refined to nanoscale sizes. A combination of nanocrystallites at the surface and coarse-grains in the center are the main features of this structure. This structure results in an excellent combination of both strength and ductility. The highest yield strength for the 30 minutes SMAT AZ31B samples increased to 249 ± 5 MPa and the uniform elongation decreased to 9.3 ± 0.8 pct, whereas the original yield strength was only 147 ± 4 MPa and the uniform elongation was 15.4 ± 1.1 pct. Microstructural observations, stress relaxation tests, and hardness tests were used to verify the results. Additionally, there is a specific volume fraction of gradient structure to achieve the best mechanical performance, which is shown to be in the range of 9.3 to 14 pct for the AZ31B alloy.

  7. Mechanical Properties of Gradient Structure Mg Alloy

    NASA Astrophysics Data System (ADS)

    Chen, Hongliang; Yang, Jiang; Zhou, Hao; Moering, Jordan; Yin, Zhe; Gong, Yulan; Zhao, KunYu

    2017-07-01

    In this work, a surface mechanical attrition treatment (SMAT) process was applied to AZ31B magnesium alloy at room temperature. This method produced a gradient structure on the treated AZ31B, in which the grains of the topmost layer are refined to nanoscale sizes. A combination of nanocrystallites at the surface and coarse-grains in the center are the main features of this structure. This structure results in an excellent combination of both strength and ductility. The highest yield strength for the 30 minutes SMAT AZ31B samples increased to 249 ± 5 MPa and the uniform elongation decreased to 9.3 ± 0.8 pct, whereas the original yield strength was only 147 ± 4 MPa and the uniform elongation was 15.4 ± 1.1 pct. Microstructural observations, stress relaxation tests, and hardness tests were used to verify the results. Additionally, there is a specific volume fraction of gradient structure to achieve the best mechanical performance, which is shown to be in the range of 9.3 to 14 pct for the AZ31B alloy.

  8. The global convergence properties of a conjugate gradient method

    NASA Astrophysics Data System (ADS)

    Omer, Osman; Mamat, Mustafa; Abashar, Abdelrhaman; Rivaie, Mohd

    2014-06-01

    Conjugate gradient methods are the most famous methods for solving nonlinear unconstrained optimization problems, especially large scale problems. That is, for its simplicity and low memory requirement. The strong Wolfe line search are usually used in practice for the analyses and implementations of conjugate gradient methods. In this paper, we present a new method of nonlinear conjugate gradient method with strong Wolfe line search for unconstrained optimization problems. Under some assumptions, the sufficient descent property and the global convergence are given. The numerical results show that our new method is efficient for some unconstrained optimization problems.

  9. A note on spectral properties of some gradient methods

    NASA Astrophysics Data System (ADS)

    di Serafino, Daniela; Ruggiero, Valeria; Toraldo, Gerardo; Zanni, Luca

    2016-10-01

    Starting from the work by Barzilai and Borwein, gradient methods have gained a great amount of attention, and efficient low-cost schemes are available nowadays. The acceleration strategies used by these methods are based on the definition of effective steplength updating rules, which capture spectral properties of the Hessian of the objective function. The methods arising from this idea represent effective computational tools, extremely appealing for a variety of large-scale optimization problems arising in applications. In this work we discuss the spectral properties of some recently proposed gradient methods with the aim of providing insight into their computational effectiveness. Numerical experiments supporting and illustrating the theoretical analysis are provided.

  10. Gradient-modulus materials: Preparation, physical properties and application

    NASA Astrophysics Data System (ADS)

    Askadskii, Andrey; Goleneva, Lidiya; Afanas'ev, Egor; Petunova, Margarita; Serenko, Ol'ga; Jiang, Shengling

    2017-05-01

    The theoretical analysis of relationship of the chemical structure for polymeric networks on the modulus of elasticity fitting within the broad range from 3 to 2000 MPa has been produced. These networks contain bulky cross-linked points, connected by short flexible chains of controlled length. In this paper we prepared the networks derived from polyurethane-iso-cyan urates as well as a combination of polyurethane-iso-cyan urate and polyurethane. The materials possess elastic properties and high wear resistance due to polyurethane component. The polyurethane-iso-cyan urates and polyurethanes of various chemical structures were used for preparation of gradient-modulus materials with the elasticity modulus controlled in the broad range within the same sample or material. The gradient identified as a change in the concentration of monomers per unit distance in a specified direction. This involves creation of molecular gradient regarding the chemical structure of the sample.

  11. Gradient Mechanical Properties Facilitate Arabidopsis Trichome as Mechanosensor.

    PubMed

    Liu, Han; Zhou, Li Hong; Jiao, Jiaojiao; Liu, Shaobao; Zhang, Zhanming; Lu, Tian Jian; Xu, Feng

    2016-04-20

    It has been reported that Arabidopsis thaliana leaf trichome can act as a mechanosensory switch, transducing mechanical stimuli into physiological signals, mainly through a buckling instability to focus external force (e.g., exerted by insects) on the base of trichome. The material and structural properties of trichomes remain largely unknown in this buckling instability. In this report, we mainly focused on material standpoint to explore the possible mechanism facilitating the buckling instability. We observed that the Young's modulus of trichome cell wall decreased gradually from branch to the base region of trichome. Interestingly, we also found a corresponding decline of calcium concentration on the trichome cell wall. Results of finite element method (FEM) simulation suggested that such a gradient distribution of Young's modulus significantly promotes force focusing and buckling instability on the base of trichome. It is indicated that Arabidopsis trichome has developed into an active mechanosensor benefiting from gradient cell wall mechanical properties.

  12. Process design of press hardening with gradient material property influence

    SciTech Connect

    Neugebauer, R.; Schieck, F.; Rautenstrauch, A.

    2011-05-04

    Press hardening is currently used in the production of automotive structures that require very high strength and controlled deformation during crash tests. Press hardening can achieve significant reductions of sheet thickness at constant strength and is therefore a promising technology for the production of lightweight and energy-efficient automobiles. The manganese-boron steel 22MnB5 have been implemented in sheet press hardening owing to their excellent hot formability, high hardenability, and good temperability even at low cooling rates. However, press-hardened components have shown poor ductility and cracking at relatively small strains. A possible solution to this problem is a selective increase of steel sheet ductility by press hardening process design in areas where the component is required to deform plastically during crash tests. To this end, process designers require information about microstructure and mechanical properties as a function of the wide spectrum of cooling rates and sequences and austenitizing treatment conditions that can be encountered in production environments. In the present work, a Continuous Cooling Transformation (CCT) diagram with corresponding material properties of sheet steel 22MnB5 was determined for a wide spectrum of cooling rates. Heating and cooling programs were conducted in a quenching dilatometer. Motivated by the importance of residual elasticity in crash test performance, this property was measured using a micro-bending test and the results were integrated into the CCT diagrams to complement the hardness testing results. This information is essential for the process design of press hardening of sheet components with gradient material properties.

  13. Phenological changes in morphological, physiological and optical properties of single-leaves in canopy trees of a cool-temperate deciduous forest in Japan

    NASA Astrophysics Data System (ADS)

    Noda, H. M.; Muraoka, H.

    2013-12-01

    Phenology of forest canopy has been focused in carbon cycle studies, but still we need further understandings on its ecophysiological dynamics, to link them to the ecosystem function. For example, combined analysis of yearly NEP (net ecosystem production) by eddy covariance and NPP (net primary production) by biometric measurements in a cool-temperate deciduous broadleaf forest in Japan showed that the interannual variability of NEP is mostly explained by the NPP in tree biomass, rather than those by NPP in foliage nor heterotrophyic respiration (Ohtsuka et al. 2009; Glob. Chan. Ecol.). This result suggests the possible influence of interannual variations in either the length of growing season, phenology and the yearly maximum of leaf photosynthetic capacity, which largely affects GPP (gross primary production). In present study, in order to reveal the phenological pattern and its interannual variation of the leaf ecophysiological properties, leaf mass per area (LMA), chlorophyll contents and photosynthetic traits (Vcmax and Jmax) were measured for dominant canopy tree species Quercus crispla and Betula ermanii in Takayama site (AsiaFlux, JaLTER) for nine years during 2003 and 2012. In addition, to link such ecophysiological traits to the remote sensing of canopy dynamics, the optical properties (reflectance and transmittance spectra) of single leaf were also measured in spring (early June), summer (mid August) and autumn (October) in 2010 and 2012. Leaf budbreak occurred in mid to late May, after two to three weeks of snowmelt, and the photosynthetic capacity increased gradually in Quercus crispla but quickly in Betula ermanii. Seasonal developmental rate, the timing of leaf photosynthetic maturation and its maximum values varied year by year. Photosynthetic capacity was largely correlated with chlorophyll contents throughout the growing season. From spring to summer, i.e., in developing period, both chlorophyll content and LMA increased almost in parallel

  14. Properties of soils and tree wood tissue across a Lake States sulfate deposition gradient.

    Treesearch

    Lewis F. Ohmann; David F. Grigal

    1991-01-01

    Presents the soil and tree wood tissue properties (mostly chemical) of the plots that were remeasured and sampled for a study of the relation between forest condition and wet sulfate deposition along the Lake States acidic deposition gradient.

  15. Photoelectric and passivation properties of atomic layer deposited gradient AZO thin film

    NASA Astrophysics Data System (ADS)

    Zhao, Bin; Tang, Li-dan; Wang, Bing; Jia, Yi; Feng, Jia-heng

    2017-02-01

    Gradient Al-doped ZnO (AZO) thin films were deposited at 150 °C by atomic layer deposition (ALD) with different Al concentration gradient, and their photoelectric and passivation properties were investigated. With increasing Al concentration gradient from 0.09 to 1.21%/nm, Hall-effect showed that the resistivity of gradient AZO thin films deteriorates. The minimal resistivity (2.81 × 10-3 Ω cm), the maximum mobility (9.03 cm2/Vs) and the maximum carrier concentration (2.46 × 1020 cm-3) were obtained at 0.09%/nm Al concentration gradient. The average transmittance of all the gradient AZO films can be more than 85% in the visible region. In addition, gradient AZO thin films demonstrated excellent passivation properties. The maximum minority carrier lifetime (120.6 μs) and the minimal surface recombination velocity (≤208.3 cm/s) were obtained at 0.71%/nm Al concentration gradient.

  16. Bending efficiency through property gradients in bamboo, palm, and wood-based composites.

    PubMed

    Wegst, Ulrike G K

    2011-07-01

    Nature, to a greater extent than engineering, takes advantage of hierarchical structures. These allow for optimization at each structural level to achieve mechanical efficiency, meaning mechanical performance per unit mass. Palms and bamboos do this exceptionally well; both are fibre-reinforced cellular materials in which the fibres are aligned parallel to the stem or culm, respectively. The distribution of these fibres is, however, not uniform: there is a density and modulus gradient across the section. This property gradient increases the flexural rigidity of the plants per unit mass, mass being a measure of metabolic investment made into an organism's construction. An analytical model is presented with which a 'gradient shape factor' can be calculated that describes by how much a plant's bending efficiency is increased through gradient structures. Combining the 'gradient shape factor' with a 'microstructural shape factor' that captures the efficiency gained through the cellular nature of the fibre composite's matrix, and a 'macroscopical shape factor' with which the tubular shape of bamboo can be described, for example, it is possible to explore how much each of these three structural levels of the hierarchy contributes to the overall bending performance of the stem or culm. In analogy, the bending efficiency of the commonly used wood-based composite medium-density fibreboard can be analysed; its property gradient is due to its manufacture by hot pressing. A few other engineered materials exist that emulate property gradients; new manufacturing routes to prepare them are currently being explored. It appears worthwhile to pursue these further.

  17. Small scale vertical gradients of Arctic ice algal photophysiological properties.

    PubMed

    Manes, Sarah Story; Gradinger, Rolf

    2009-10-01

    Photosynthetic parameters of phytoplankton and sea ice algae from landfast sea ice of the Chukchi Sea off Point Barrow, Alaska, were assessed in spring 2005 and winter through spring 2006 using Pulse Amplitude Modulated (PAM) fluorometry including estimates of maximum quantum efficiency (F(v)/F(m)), maximum relative electron transport rate (rETR(max)), photosynthetic efficiency (alpha), and the photoadaptive index (E(k)). The use of centrifuged brine samples allowed to document vertical gradients in ice algal acclimation with 5 cm vertical resolution for the first time. Bottom ice algae (0-5 cm from ice-water interface) expressed low F(v)/F(m) (0.331-0.426) and low alpha (0.098-0.130 (micromol photons m(-2)s(-1))(-1)) in December. F(v)/F(m) and alpha increased in March and May (0.468-0.588 and 0.141-0.438 (micromol photons m(-2)s(-1))(-1), respectively) indicating increased photosynthetic activity. In addition, increases in rETR(max) (3.3-16.4 a.u.) and E(k) (20-88 micromol photons m(-2) s(-1)) from December to May illustrates a higher potential for primary productivity as communities become better acclimated to under-ice light conditions. In conclusion,photosynthetic performance by ice algae (as assessed by PAM fluorometry) was tightly linked to sea ice salinity, temperature, and inorganic nutrient concentrations (mainly nitrogen).

  18. Methods for Fabricating Gradient Alloy Articles with Multi-Functional Properties

    NASA Technical Reports Server (NTRS)

    Hofmann, Douglas C. (Inventor); Borgonia, John Paul C. (Inventor); Dillon, Robert P. (Inventor); Suh, Eric J. (Inventor); Mulder, Jerry L. (Inventor); Gardner, Paul B. (Inventor)

    2015-01-01

    Systems and methods for fabricating multi-functional articles comprised of additively formed gradient materials are provided. The fabrication of multi-functional articles using the additive deposition of gradient alloys represents a paradigm shift from the traditional way that metal alloys and metal/metal alloy parts are fabricated. Since a gradient alloy that transitions from one metal to a different metal cannot be fabricated through any conventional metallurgy techniques, the technique presents many applications. Moreover, the embodiments described identify a broad range of properties and applications.

  19. Research of Mechanical Property Gradient Distribution of Al-Cu Alloy in Centrifugal Casting

    NASA Astrophysics Data System (ADS)

    Sun, Zhi; Sui, Yanwei; Liu, Aihui; Li, Bangsheng; Guo, Jingjie

    Al-Cu alloy castings are obtained using centrifugal casting. The regularity of mechanical property gradient distribution of Al-Cu alloy castings with the same centrifugal radius at different positions is investigated. The result shows that the tensile strength, yield strength, elongation and microscope hardness exhibit the following gradient distribution characteristic — high on both sides and low on the center. The trend of mechanical property gradient distribution of Al-Cu alloy increases with the increase in the rotation speed. Moreover, the mechanical properties of casting centerline two sides have asymmetry. The reason is that the grain size of casting centerline two sides and Al2Cu phase and Cu content change correspondingly.

  20. Measured and theoretical characterization of the RF properties of stacked, high-gradient insulator material

    SciTech Connect

    Houck, T. L., LLNL

    1997-05-09

    Recent high-voltage breakdown experiments of periodic metallic-dielectric insulating structures have suggested several interesting high-gradient applications. One such area is the employment of high-gradient insulators in high-current, electron-beam, accelerating induction modules. For this application, the understanding of the rf characteristics of the insulator plays an important role in estimating beam-cavity interactions. In this paper, we examine the rf properties of the insulator comparing simulation results with experiment. Different insulator designs are examined to determine their rf transmission properties in gap geometries.

  1. Response of forest soil properties to urbanization gradients in three metropolitan areas

    Treesearch

    Richard V. Pouyat; Ian D. Yesilonis; Katalin Szlavecz; Csaba Csuzdi; Elizabeth Hornung; Zoltan Kors& #243; s; Jonathan Russell-Anelli; Vincent Giorgio

    2008-01-01

    We investigated the effects of urban environments on the chemical properties of forest soils in the metropolitan areas of Baltimore, New York, and Budapest. We hypothesized that soils in forest patches in each city will exhibit changes in chemistry corresponding to urbanization gradients, but more strongly with various urban metrics than distance to the urban core....

  2. Combined use of heat and saline tracer to estimate aquifer properties in a forced gradient test

    NASA Astrophysics Data System (ADS)

    Colombani, N.; Giambastiani, B. M. S.; Mastrocicco, M.

    2015-06-01

    Usually electrolytic tracers are employed for subsurface characterization, but the interpretation of tracer test data collected by low cost techniques, such as electrical conductivity logging, can be biased by cation exchange reactions. To characterize the aquifer transport properties a saline and heat forced gradient test was employed. The field site, located near Ferrara (Northern Italy), is a well characterized site, which covers an area of 200 m2 and is equipped with a grid of 13 monitoring wells. A two-well (injection and pumping) system was employed to perform the forced gradient test and a straddle packer was installed in the injection well to avoid in-well artificial mixing. The contemporary continuous monitor of hydraulic head, electrical conductivity and temperature within the wells permitted to obtain a robust dataset, which was then used to accurately simulate injection conditions, to calibrate a 3D transient flow and transport model and to obtain aquifer properties at small scale. The transient groundwater flow and solute-heat transport model was built using SEAWAT. The result significance was further investigated by comparing the results with already published column experiments and a natural gradient tracer test performed in the same field. The test procedure shown here can provide a fast and low cost technique to characterize coarse grain aquifer properties, although some limitations can be highlighted, such as the small value of the dispersion coefficient compared to values obtained by natural gradient tracer test, or the fast depletion of heat signal due to high thermal diffusivity.

  3. Tuning Surface Microstructure and Gradient Property of Polymer by Photopolymerizable Polysiloxane-modified Nanogels

    PubMed Central

    Chen, Cong; Liu, JianCheng; Sun, Fang; Stansbury, Jeffrey W.

    2014-01-01

    This paper reports a series of photopolymerizable polysiloxane-modified nanogels for regulating surface microstructure and gradient property of polymers, which were synthesized by solution polymerization under different feed ratios of a methacrylate-modified polysiloxane, urethane dimethacrylate (UDMA) and isobornyl methacrylate (IBMA) in the presence of a thiol chain transfer agent. The nanogel structure and composition were characterized by proton nuclear magnetic resonance (1H-NMR), Fourier transform-infrared spectroscopy (FT-IR), transmission electron microscope (TEM), gel permeation chromatography (GPC) and differential scanning calorimetry (DSC). The dispersion of these nanogels in triethylene glycol dimethacrylate (TEGDMA) can reduce the onset and magnitude of shrinkage stress during polymerization without compromise to mechanical properties of the resulting polymers. Most importantly, as demonstrated by elemental analysis and X-ray photoelectron spectroscopy (XPS), the nanogels exhibit good self-floating ability in the monomer/polymer matrix and the increase of polysiloxane content in the nanogel can enhance the self-floating capability due to the lower surface tension and energy associated with the polysiloxane component. As a result, the polysiloxane-modified nanogels can spontaneously form a concentration gradient that can be locked in upon photopolymerization leading to a well-controlled heterogeneous polymer that presents a gradient change in thermal stability. With the increase of polysiloxane content, the thermal stability of the polymer was improved significantly. Furthermore, the enrichment of the nanogel on the surface resulting from the good self-floating ability can reduce the dispersion surface energy of gradient polymer film and generate a more hydrophobic surface with altered surface microstructure. These photopolymerizable polysiloxane-modified nanogels are demonstrated to have potential broad application in the preparation of gradient

  4. Convergence of soil microbial properties after plant colonization of an experimental plant diversity gradient.

    PubMed

    Steinauer, Katja; Jensen, Britta; Strecker, Tanja; de Luca, Enrica; Scheu, Stefan; Eisenhauer, Nico

    2016-04-07

    Several studies have examined the effects of plant colonization on aboveground communities and processes. However, the effects of plant colonization on soil microbial communities are less known. We addressed this gap by studying effects of plant colonization within an experimental plant diversity gradient in subplots that had not been weeded for 2 and 5 years. This study was part of a long-term grassland biodiversity experiment (Jena Experiment) with a gradient in plant species richness (1, 2, 4, 8, 16, and 60 sown species per plot). We measured plant species richness and productivity (aboveground cover and biomass) as well as soil microbial basal respiration and biomass in non-weeded subplots and compared the results with those of weeded subplots of the same plots. After 2 and 5 years of plant colonization, the number of colonizing plant species decreased with increasing plant diversity, i.e., low-diversity plant communities were most vulnerable to colonization. Plant colonization offset the significant relationship between sown plant diversity and plant biomass production. In line with plant community responses, soil basal respiration and microbial biomass increased with increasing sown plant diversity in weeded subplots, but soil microbial properties converged in non-weeded subplots and were not significantly affected by the initial plant species richness gradient. Colonizing plant species change the quantity and quality of inputs to the soil, thereby altering soil microbial properties. Thus, plant community convergence is likely to be rapidly followed by the convergence of microbial properties in the soil.

  5. A conjugate gradient method with descent properties under strong Wolfe line search

    NASA Astrophysics Data System (ADS)

    Zull, N.; ‘Aini, N.; Shoid, S.; Ghani, N. H. A.; Mohamed, N. S.; Rivaie, M.; Mamat, M.

    2017-09-01

    The conjugate gradient (CG) method is one of the optimization methods that are often used in practical applications. The continuous and numerous studies conducted on the CG method have led to vast improvements in its convergence properties and efficiency. In this paper, a new CG method possessing the sufficient descent and global convergence properties is proposed. The efficiency of the new CG algorithm relative to the existing CG methods is evaluated by testing them all on a set of test functions using MATLAB. The tests are measured in terms of iteration numbers and CPU time under strong Wolfe line search. Overall, this new method performs efficiently and comparable to the other famous methods.

  6. Modifying gradient theory to predict the surface properties of halogenated hydrocarbons

    NASA Astrophysics Data System (ADS)

    Shestova, T. D.; Lozovsky, T. L.; Zhelezny, V. P.

    2014-05-01

    A new method is proposed for predicting the surface tension, density profile, and thickness of the surface layer of a liquid near an interface using gradient theory. The objects of study are halogenated hydrocarbons. The algorithm for calculating surface properties includes a new modification of the Peng-Robinson cubic equation of state (EoS) that does not require information on the critical parameters, and a new procedure for calculating the influence parameter. Validation of the procedure for predicting the surface properties of liquids shows that the agreement between the calculated surface tension of halogenated hydrocarbons and the existing literature data is sufficient for practical use.

  7. Oscillator strengths, first-order properties, and nuclear gradients for local ADC(2)

    SciTech Connect

    Schütz, Martin

    2015-06-07

    We describe theory and implementation of oscillator strengths, orbital-relaxed first-order properties, and nuclear gradients for the local algebraic diagrammatic construction scheme through second order. The formalism is derived via time-dependent linear response theory based on a second-order unitary coupled cluster model. The implementation presented here is a modification of our previously developed algorithms for Laplace transform based local time-dependent coupled cluster linear response (CC2LR); the local approximations thus are state specific and adaptive. The symmetry of the Jacobian leads to considerable simplifications relative to the local CC2LR method; as a result, a gradient evaluation is about four times less expensive. Test calculations show that in geometry optimizations, usually very similar geometries are obtained as with the local CC2LR method (provided that a second-order method is applicable). As an exemplary application, we performed geometry optimizations on the low-lying singlet states of chlorophyllide a.

  8. Oscillator strengths, first-order properties, and nuclear gradients for local ADC(2)

    NASA Astrophysics Data System (ADS)

    Schütz, Martin

    2015-06-01

    We describe theory and implementation of oscillator strengths, orbital-relaxed first-order properties, and nuclear gradients for the local algebraic diagrammatic construction scheme through second order. The formalism is derived via time-dependent linear response theory based on a second-order unitary coupled cluster model. The implementation presented here is a modification of our previously developed algorithms for Laplace transform based local time-dependent coupled cluster linear response (CC2LR); the local approximations thus are state specific and adaptive. The symmetry of the Jacobian leads to considerable simplifications relative to the local CC2LR method; as a result, a gradient evaluation is about four times less expensive. Test calculations show that in geometry optimizations, usually very similar geometries are obtained as with the local CC2LR method (provided that a second-order method is applicable). As an exemplary application, we performed geometry optimizations on the low-lying singlet states of chlorophyllide a.

  9. Gradients of stellar population properties and evolution clues in a nearby galaxy M101

    SciTech Connect

    Lin, Lin; Kong, Xu; Lin, Xuanbin; Mao, Yewei; Cheng, Fuzhen; Zou, Hu; Jiang, Zhaoji; Zhou, Xu E-mail: xkong@ustc.edu.cn

    2013-06-01

    Multiband photometric images from ultraviolet and optical to infrared are collected to derive spatially resolved properties of the nearby Scd-type galaxy M101. With evolutionary stellar population synthesis models, two-dimensional distributions and radial profiles of age, metallicity, dust attenuation, and star formation timescale in the form of the Sandage star formation history are obtained. When fitting with the models, we use the IRX-A {sub FUV} relation, found to depend on a second parameter of birth rate b (ratio of present- and past-averaged star formation rates), to constrain the dust attenuation. There are obvious parameter gradients in the disk of M101, which supports the theory of an 'inside-out' disk growth scenario. Two distinct disk regions with different gradients of age and color are discovered, similar to another late-type galaxy, NGC 628. The metallicity gradient of the stellar content is flatter than that of H II regions. The stellar disk is optically thicker inside than outside and the global dust attenuation of this galaxy is lower compared with galaxies of similar and earlier morphological type. We note that a variational star formation timescale describes the real star formation history of a galaxy. The timescale increases steadily from the center to the outskirt. We also confirm that the bulge in this galaxy is a disk-like pseudobulge, whose evolution is likely to be induced by some secular processes of the small bar which is relatively young, metal-rich, and contains much dust.

  10. Gradients of Stellar Population Properties and Evolution Clues in a Nearby Galaxy M101

    NASA Astrophysics Data System (ADS)

    Lin, Lin; Zou, Hu; Kong, Xu; Lin, Xuanbin; Mao, Yewei; Cheng, Fuzhen; Jiang, Zhaoji; Zhou, Xu

    2013-06-01

    Multiband photometric images from ultraviolet and optical to infrared are collected to derive spatially resolved properties of the nearby Scd-type galaxy M101. With evolutionary stellar population synthesis models, two-dimensional distributions and radial profiles of age, metallicity, dust attenuation, and star formation timescale in the form of the Sandage star formation history are obtained. When fitting with the models, we use the IRX-A FUV relation, found to depend on a second parameter of birth rate b (ratio of present- and past-averaged star formation rates), to constrain the dust attenuation. There are obvious parameter gradients in the disk of M101, which supports the theory of an "inside-out" disk growth scenario. Two distinct disk regions with different gradients of age and color are discovered, similar to another late-type galaxy, NGC 628. The metallicity gradient of the stellar content is flatter than that of H II regions. The stellar disk is optically thicker inside than outside and the global dust attenuation of this galaxy is lower compared with galaxies of similar and earlier morphological type. We note that a variational star formation timescale describes the real star formation history of a galaxy. The timescale increases steadily from the center to the outskirt. We also confirm that the bulge in this galaxy is a disk-like pseudobulge, whose evolution is likely to be induced by some secular processes of the small bar which is relatively young, metal-rich, and contains much dust.

  11. Thermoelectric properties of gradient polymer composites with nano-inclusions fabricated by laser assisted sintering

    NASA Astrophysics Data System (ADS)

    Shishkovsky, I. V.; Scherbakov, V. I.; Saraeva, I. N.; Ionin, A. A.

    2017-03-01

    Selective laser sintering (SLS) was used to prepare porous gradient polymer nanocomposites consisting of a polyetheretherketone (PEEK) matrix doped with alternating layers of Ni and Cu nanoparticles. Optimal regimes of such 3D-fabrication were determined. The functional graded (FG) structure of sintered parts was observed by optical and scanning electron microscopy and EDX microanalysis. Temperature dependence of electro-physical properties was studied for alternating ferromagnetic/non-magnetic layers (up to 10 layers) into 3D-graded samples derived from Ni-PEEK-Cu powders. Temperature dependences for the real part of the dielectric permeability and loss tangent were found to have a hysteresis character.

  12. Speed and convergence properties of gradient algorithms for optimization of IMRT.

    PubMed

    Zhang, Xiaodong; Liu, Helen; Wang, Xiaochun; Dong, Lei; Wu, Qiuwen; Mohan, Radhe

    2004-05-01

    Gradient algorithms are the most commonly employed search methods in the routine optimization of IMRT plans. It is well known that local minima can exist for dose-volume-based and biology-based objective functions. The purpose of this paper is to compare the relative speed of different gradient algorithms, to investigate the strategies for accelerating the optimization process, to assess the validity of these strategies, and to study the convergence properties of these algorithms for dose-volume and biological objective functions. With these aims in mind, we implemented Newton's, conjugate gradient (CG), and the steepest decent (SD) algorithms for dose-volume- and EUD-based objective functions. Our implementation of Newton's algorithm approximates the second derivative matrix (Hessian) by its diagonal. The standard SD algorithm and the CG algorithm with "line minimization" were also implemented. In addition, we investigated the use of a variation of the CG algorithm, called the "scaled conjugate gradient" (SCG) algorithm. To accelerate the optimization process, we investigated the validity of the use of a "hybrid optimization" strategy, in which approximations to calculated dose distributions are used during most of the iterations. Published studies have indicated that getting trapped in local minima is not a significant problem. To investigate this issue further, we first obtained, by trial and error, and starting with uniform intensity distributions, the parameters of the dose-volume- or EUD-based objective functions which produced IMRT plans that satisfied the clinical requirements. Using the resulting optimized intensity distributions as the initial guess, we investigated the possibility of getting trapped in a local minimum. For most of the results presented, we used a lung cancer case. To illustrate the generality of our methods, the results for a prostate case are also presented. For both dose-volume and EUD based objective functions, Newton's method far

  13. Biogenic gradients in algal density affect the emergent properties of spatially self-organized mussel beds.

    PubMed

    Liu, Quan-Xing; Weerman, Ellen J; Gupta, Rohit; Herman, Peter M J; Olff, Han; van de Koppel, Johan

    2014-07-06

    Theoretical models highlight that spatially self-organized patterns can have important emergent effects on the functioning of ecosystems, for instance by increasing productivity and affecting the vulnerability to catastrophic shifts. However, most theoretical studies presume idealized homogeneous conditions, which are rarely met in real ecosystems. Using self-organized mussel beds as a case study, we reveal that spatial heterogeneity, resulting from the large-scale effects of mussel beds on their environment, significantly alters the emergent properties predicted by idealized self-organization models that assume homogeneous conditions. The proposed model explicitly considers that the suspended algae, the prime food for the mussels, are supplied by water flow from the seaward boundary of the bed, which causes in combination with consumption a gradual depletion of algae over the simulated domain. Predictions of the model are consistent with properties of natural mussel patterns observed in the field, featuring a decline in mussel biomass and a change in patterning. Model analyses reveal a fundamental change in ecosystem functioning when this self-induced algal depletion gradient is included in the model. First, no enhancement of secondary productivity of the mussels comparing with non-patterns states is predicted, irrespective of parameter setting; the equilibrium amount of mussels is entirely set by the input of algae. Second, alternate stable states, potentially present in the original (no algal gradient) model, are absent when gradual depletion of algae in the overflowing water layer is allowed. Our findings stress the importance of including sufficiently realistic environmental conditions when assessing the emergent properties of self-organized ecosystems.

  14. Surface chemistry, morphological analysis and properties of cellulose nanocrystals with gradiented sulfation degrees

    NASA Astrophysics Data System (ADS)

    Lin, Ning; Dufresne, Alain

    2014-04-01

    The process of sulfuric acid-hydrolysis of cellulose fibers for the preparation of cellulose nanocrystals (CNs) includes an esterification reaction between acid and cellulose molecules, which induces the covalent coupling of sulfate groups on the surface of prepared CNs. Negatively charged sulfate groups play an important role in both surface chemistry and physical properties of CNs. This study explored the strategy of introducing a gradient of sulfate groups on the surface of CNs, and further investigated the effect of the sulfation degree on surface chemistry, morphology, dimensions, and physical properties of different CN samples. Based on the discussion of their surface chemistry, the selection of different cross-section models was reported to significantly affect the calculation of the degree of substitution of sulfate groups on CNs. A new ellipsoid cross-section model was proposed on the basis of AFM observations. The effect of sulfate groups on crystal properties and thermal stability was discussed and validated, and the birefringence behavior of nanocrystal suspensions was observed.The process of sulfuric acid-hydrolysis of cellulose fibers for the preparation of cellulose nanocrystals (CNs) includes an esterification reaction between acid and cellulose molecules, which induces the covalent coupling of sulfate groups on the surface of prepared CNs. Negatively charged sulfate groups play an important role in both surface chemistry and physical properties of CNs. This study explored the strategy of introducing a gradient of sulfate groups on the surface of CNs, and further investigated the effect of the sulfation degree on surface chemistry, morphology, dimensions, and physical properties of different CN samples. Based on the discussion of their surface chemistry, the selection of different cross-section models was reported to significantly affect the calculation of the degree of substitution of sulfate groups on CNs. A new ellipsoid cross-section model was

  15. The effects of temperature gradient and growth rate on the morphology and fatigue properties of MAR-M246(Hf)

    NASA Technical Reports Server (NTRS)

    Schmidt, D. D.; Alter, W. S.; Hamilton, W. D.; Parr, R. A.

    1989-01-01

    MAR-M246(Hf) is a nickel based superalloy used in the turbopump blades of the Space Shuttle main engines. The effects are considered of temperature gradient (G) and growth rate (R) on the microstructure and fatigue properties of this superalloy. The primary dendrite arm spacings were found to be inversely proportional to both temperature gradient and growth rate. Carbide and gamma - gamma prime morphology trends were related to G/R ratios. Weibull analysis of fatigue results shows the characteristic life to be larger by a factor of 10 for the low gradient/fast rate pairing of G and R, while the reliability (beta) was lower.

  16. Estimation of in-canopy ammonia sources and sinks in a fertilized Zea mays field.

    PubMed

    Bash, Jesse O; Walker, John T; Katul, Gabriel G; Jones, Matthew R; Nemitz, Eiko; Robarge, Wayne P

    2010-03-01

    An analytical model was developed to describe in-canopy vertical distribution of ammonia (NH(3)) sources and sinks and vertical fluxes in a fertilized agricultural setting using measured in-canopy mean NH(3) concentration and wind speed profiles. This model was applied to quantify in-canopy air-surface exchange rates and above-canopy NH(3) fluxes in a fertilized corn (Zea mays) field. Modeled air-canopy NH(3) fluxes agreed well with independent above-canopy flux estimates. Based on the model results, the urea fertilized soil surface was a consistent source of NH(3) one month following the fertilizer application, whereas the vegetation canopy was typically a net NH(3) sink with the lower portion of the canopy being a constant sink. The model results suggested that the canopy was a sink for some 70% of the estimated soil NH(3) emissions. A logical conclusion is that parametrization of within-canopy processes in air quality models are necessary to explore the impact of agricultural field level management practices on regional air quality. Moreover, there are agronomic and environmental benefits to timing liquid fertilizer applications as close to canopy closure as possible. Finally, given the large within-canopy mean NH(3) concentration gradients in such agricultural settings, a discussion about the suitability of the proposed model is also presented.

  17. Effects of para-fluorine substituent of polystyrene on gradient-index fiber-optic properties

    NASA Astrophysics Data System (ADS)

    Koike, Kotaro; Suzuki, Akifumi; Makino, Kenji; Koike, Yasuhiro

    2015-01-01

    To study the effects of fluorine substituent of polystyrene (PSt) on gradient-index fiber-optic properties, a poly(para-fluorostyrene) (P(p-FSt))-based graded-index plastic optical fiber (GI POF) is fabricated, and its properties are compared with those of a PSt-based GI POF. The para-fluorine substitution positively affects the glass transition temperature (Tg) of the core, wavelength dispersion of the optimum refractive index profile, bandwidth, and attenuation. The core Tg of the P(p-FSt)-based GI POF is 88 °C, which is higher than that of the PSt-based GI POF by 9 °C when both fibers have an identical numerical aperture (NA = 0.2). The optimum refractive index profile coefficient for the P(p-FSt)-based GI POF varies from 2.2 to 2.1 in the 600-800 nm range, whereas that for the PSt-based GI POF varies from 2.6 to 2.3 in the same wavelength region. The bandwidth of the P(p-FSt)-based GI POF is intrinsically higher than that of PSt-based GI POF. Moreover, the fiber attenuation of the P(p-FSt)-based GI POF was significantly smaller than that of the PSt-based GI POF over the source wavelength range. Our study demonstrates that P(p-FSt) has favorable properties as a GI POF base material.

  18. Scaling properties of the mean wall-normal velocity in zero-pressure-gradient boundary layers

    NASA Astrophysics Data System (ADS)

    Wei, Tie; Klewicki, Joseph

    2016-12-01

    The scaling properties of the mean wall-normal velocity V (x ,y ) in zero-pressure-gradient laminar and turbulent boundary-layer flows are investigated using numerical simulation data, physical experiment data, and integral analyses of the governing equations. The maximum mean wall-normal velocity V∞ and the boundary-layer thickness δ are evidenced to be the proper scaling for V over most if not all of the boundary layer. This is different from the behavior of the mean streamwise velocity U or the turbulent shear stress T =-ρ , which depend on different characteristic length scales in the regions near and away from the surface, respectively. The reason for this apparent difference in scaling behaviors is described physically relative to the downstream development of the U velocity profile and the mechanisms of boundary-layer growth. Insights pertaining to this are further surmised from an analytical relationship for the ratio of the displacement to momentum thickness, i.e., shape factor H . Integral analyses using the continuity and mean momentum equation show that U∞V∞/uτ2=H , where uτ is the friction velocity. Both the laminar similarity solution and direct numerical simulation data in post-transitional flows convincingly support this relation. Over the transitional regime, data of sufficiently high quality are lacking to check if this relation remains valid.

  19. Scaling properties of the mean wall-normal velocity in the zero pressure gradient boundary layer

    NASA Astrophysics Data System (ADS)

    Wei, Tie; Klewicki, Joseph

    2016-11-01

    The scaling properties of the mean wall-normal velocity, V (x , y) , in zero-pressure-gradient laminar and turbulent boundary layer flows is investigated using numerical simulation data, physical experiment data, and integral analyses of governing equations. The maximum mean wall-normal velocity, V∞, and the boundary layer thickness, δ, are evidenced to be the proper scaling for V over most if not the entire boundary layer. This is different from the behavior of the mean streamwise velocity (U) or the turbulent shear stress (T = - ρ < uv >), which depend on different characteristic length scales in the regions near to and away from the surface. Insights pertaining to this are further surmised from an analytical relationship for the ratio of the displacement to momentum thickness, i.e., shape factor, H. Integral analyses using the continuity and mean momentum equation show that (U∞V∞) /uτ2 = H , where uτ is the friction velocity. Both the laminar similarity solution and DNS data in post-transitional flows convincingly support this relation. Over the transitional regime, sufficiently high quality data is still lacking to check if this relation remains valid.

  20. Soil Properties Drive Changes in Water Use efficiency Across a Climatic Gradient

    NASA Astrophysics Data System (ADS)

    Maxwell, T.; Silva, L. C. R.; Horwath, W. R.

    2015-12-01

    This research uses a series of physiological models and empirical measurements to evaluate biogeochemical controls over coupled carbon-water cycles in forest systems from the individual plant to the ecosystem scale. Cellulosic biomarkers, and bulk tissue of leaf, litter, and soil organic matter have been analyzed for specific stable isotope ratios of oxygen and carbon to examine causal links between plant to ecosystem scale productivity and water balance. A series of latitudinal and altitudinal transects established across the California Sierra Nevada was used to study the effects of climatic and edaphic gradients on the formation and preservation of these plant isotopic signals. Changes in plant-soil-atmosphere relations are related to productivity and water use efficiency in an attempt to elucidate how plant material reflects ecosystem scale processes in response to variation in climate and soil properties. The use of a dual isotopic approach constrains the role of environmental variables on stable isotope values, allowing for nutritive vs hydrologic limitations over water use efficiency to be assessed. The result of this work is to promote a framework for tracing plant-soil water relations across scales to better understand and more precisely predict the impacts of climate change on forest ecosystems.

  1. Skin Membrane Electrical Impedance Properties under the Influence of a Varying Water Gradient

    PubMed Central

    Björklund, Sebastian; Ruzgas, Tautgirdas; Nowacka, Agnieszka; Dahi, Ihab; Topgaard, Daniel; Sparr, Emma; Engblom, Johan

    2013-01-01

    The stratum corneum (SC) is an effective permeability barrier. One strategy to increase drug delivery across skin is to increase the hydration. A detailed description of how hydration affects skin permeability requires characterization of both macroscopic and molecular properties and how they respond to hydration. We explore this issue by performing impedance experiments on excised skin membranes in the frequency range 1 Hz to 0.2 MHz under the influence of a varying gradient in water activity (aw). Hydration/dehydration induces reversible changes of membrane resistance and effective capacitance. On average, the membrane resistance is 14 times lower and the effective capacitance is 1.5 times higher when the outermost SC membrane is exposed to hydrating conditions (aw = 0.992), as compared to the case of more dehydrating conditions (aw = 0.826). Molecular insight into the hydration effects on the SC components is provided by natural-abundance 13C polarization transfer solid-state NMR and x-ray diffraction under similar hydration conditions. Hydration has a significant effect on the dynamics of the keratin filament terminals and increases the interchain spacing of the filaments. The SC lipids are organized into lamellar structures with ∼ 12.6 nm spacing and hexagonal hydrocarbon chain packing with mainly all-trans configuration of the acyl chains, irrespective of hydration state. Subtle changes in the dynamics of the lipids due to mobilization and incorporation of cholesterol and long-chain lipid species into the fluid lipid fraction is suggested to occur upon hydration, which can explain the changes of the impedance response. The results presented here provide information that is useful in explaining the effect of hydration on skin permeability. PMID:23790372

  2. Skin membrane electrical impedance properties under the influence of a varying water gradient.

    PubMed

    Björklund, Sebastian; Ruzgas, Tautgirdas; Nowacka, Agnieszka; Dahi, Ihab; Topgaard, Daniel; Sparr, Emma; Engblom, Johan

    2013-06-18

    The stratum corneum (SC) is an effective permeability barrier. One strategy to increase drug delivery across skin is to increase the hydration. A detailed description of how hydration affects skin permeability requires characterization of both macroscopic and molecular properties and how they respond to hydration. We explore this issue by performing impedance experiments on excised skin membranes in the frequency range 1 Hz to 0.2 MHz under the influence of a varying gradient in water activity (aw). Hydration/dehydration induces reversible changes of membrane resistance and effective capacitance. On average, the membrane resistance is 14 times lower and the effective capacitance is 1.5 times higher when the outermost SC membrane is exposed to hydrating conditions (aw = 0.992), as compared to the case of more dehydrating conditions (aw = 0.826). Molecular insight into the hydration effects on the SC components is provided by natural-abundance (13)C polarization transfer solid-state NMR and x-ray diffraction under similar hydration conditions. Hydration has a significant effect on the dynamics of the keratin filament terminals and increases the interchain spacing of the filaments. The SC lipids are organized into lamellar structures with ∼ 12.6 nm spacing and hexagonal hydrocarbon chain packing with mainly all-trans configuration of the acyl chains, irrespective of hydration state. Subtle changes in the dynamics of the lipids due to mobilization and incorporation of cholesterol and long-chain lipid species into the fluid lipid fraction is suggested to occur upon hydration, which can explain the changes of the impedance response. The results presented here provide information that is useful in explaining the effect of hydration on skin permeability. Copyright © 2013 Biophysical Society. Published by Elsevier Inc. All rights reserved.

  3. Study of coherent structures of turbulence with large wall-normal gradients in thermophysical properties using direct numerical simulation

    NASA Astrophysics Data System (ADS)

    Reinink, Shawn K.; Yaras, Metin I.

    2015-06-01

    Forced-convection heat transfer in a heated working fluid at a thermodynamic state near its pseudocritical point is poorly predicted by correlations calibrated with data at subcritical temperatures and pressures. This is suggested to be primarily due to the influence of large wall-normal thermophysical property gradients that develop in proximity of the pseudocritical point on the concentration of coherent turbulence structures near the wall. The physical mechanisms dominating this influence remain poorly understood. In the present study, direct numerical simulation is used to study the development of coherent vortical structures within a turbulent spot under the influence of large wall-normal property gradients. A turbulent spot rather than a fully turbulent boundary layer is used for the study, for the coherent structures of turbulence in a spot tend to be in a more organized state which may allow for more effective identification of cause-and-effect relationships. Large wall-normal gradients in thermophysical properties are created by heating the working fluid which is near the pseudocritical thermodynamic state. It is found that during improved heat transfer, wall-normal gradients in density accelerate the growth of the Kelvin-Helmholtz instability mechanism in the shear layer enveloping low-speed streaks, causing it to roll up into hairpin vortices at a faster rate. It is suggested that this occurs by the baroclinic vorticity generation mechanism which accelerates the streamwise grouping of vorticity during shear layer roll-up. The increased roll-up frequency leads to reduced streamwise spacing between hairpin vortices in wave packets. The density gradients also promote the sinuous instability mode in low-speed streaks. The resulting oscillations in the streaks in the streamwise-spanwise plane lead to locally reduced spanwise spacing between hairpin vortices forming over adjacent low-speed streaks. The reduction in streamwise and spanwise spacing between

  4. The structure and tribological properties of gradient layers prepared by plasma-based ion implantation on 2024 Al alloy

    NASA Astrophysics Data System (ADS)

    Liao, J. X.; Xia, L. F.; Sun, M. R.; Liu, W. M.; Xu, T.; Xue, Q. J.

    2004-02-01

    Using plasma-based ion implantation, two types of gradient layers have been prepared on 2024 Al alloy. One is prepared by N-implantation then C-deposition, the other adds an interlayer composed of a Ti layer and a Ti-N layer between N-implantation and C-deposition. C-deposition is carried out at various implanting voltages or C2H2/H2 ratios. The composition depth profiles of these layers were characterized by x-ray photoelectron spectroscopy. The structure, morphologies and microstructure of the C layers were studied using Raman spectroscopy, atomic force microscope and transmission electron microscope, respectively. The surface hardness was measured with a Knoop tester and a mechanical property microprobe. The dry ball-on-disc wear tests were performed in ambient air. The gradient layer without interlayer is composed of an N-implanted layer rich in AlN and a diamond-like carbon (DLC) layer (film), and the two layers are connected with a C-Al transition layer containing Al4C3. The Ti layer rich in agr -Ti and the N-implanted layer are connected by a Ti-Al transition layer containing TiAl3, while the Ti-N layer rich in TiN and the DLC film are connected by a C-Ti transition layer containing TiC, TiCN, etc. Thus, the gradient layer with interlayers has optimized the gradient structure. DLC films are compact and amorphous, contain high sp3/sp2 ratios and depend on the implanting voltage and the C2H2/H2 ratio. Similarly, these gradient layers exhibit significant improvement in morphologies, surface hardness and tribological properties; the interlayer, the implanting voltage and the C2H2/H2 ratio all have prominent effects on these properties.

  5. Study of coherent structures of turbulence with large wall-normal gradients in thermophysical properties using direct numerical simulation

    SciTech Connect

    Reinink, Shawn K.; Yaras, Metin I.

    2015-06-15

    Forced-convection heat transfer in a heated working fluid at a thermodynamic state near its pseudocritical point is poorly predicted by correlations calibrated with data at subcritical temperatures and pressures. This is suggested to be primarily due to the influence of large wall-normal thermophysical property gradients that develop in proximity of the pseudocritical point on the concentration of coherent turbulence structures near the wall. The physical mechanisms dominating this influence remain poorly understood. In the present study, direct numerical simulation is used to study the development of coherent vortical structures within a turbulent spot under the influence of large wall-normal property gradients. A turbulent spot rather than a fully turbulent boundary layer is used for the study, for the coherent structures of turbulence in a spot tend to be in a more organized state which may allow for more effective identification of cause-and-effect relationships. Large wall-normal gradients in thermophysical properties are created by heating the working fluid which is near the pseudocritical thermodynamic state. It is found that during improved heat transfer, wall-normal gradients in density accelerate the growth of the Kelvin-Helmholtz instability mechanism in the shear layer enveloping low-speed streaks, causing it to roll up into hairpin vortices at a faster rate. It is suggested that this occurs by the baroclinic vorticity generation mechanism which accelerates the streamwise grouping of vorticity during shear layer roll-up. The increased roll-up frequency leads to reduced streamwise spacing between hairpin vortices in wave packets. The density gradients also promote the sinuous instability mode in low-speed streaks. The resulting oscillations in the streaks in the streamwise-spanwise plane lead to locally reduced spanwise spacing between hairpin vortices forming over adjacent low-speed streaks. The reduction in streamwise and spanwise spacing between

  6. Microplatforms for gradient field generation of various properties and biological applications.

    PubMed

    Kim, Sung-Hwan; Lee, Gi-Hun; Park, Joong Yull; Lee, Sang-Hoon

    2015-04-01

    Well-designed microfluidic platforms can be excellent tools to eliminate bottleneck problems or issues that have arisen in biological fields by providing unprecedented high-resolution control of mechanical and chemical microenvironments for cell culture. Among such microtechnologies, the precise generation of biochemical concentration gradients has been highly regarded in the biorelated scientific fields; even today, the principles and mechanisms for gradient generation continue to be refined, and the number of applications for this technique is growing. Here, we review the current status of the concentration gradient generation technologies achieved in various microplatforms and how they have been and will be applied to biological issues, particularly those that have arisen from cancer research, stem cell research, and tissue engineering. We also provide information about the advances and future challenges in the technological aspects of microscale concentration gradient generation.

  7. Interfacial properties of water/CO2: a comprehensive description through a Gradient Theory-SAFT-VR Mie approach.

    PubMed

    Lafitte, Thomas; Mendiboure, Bruno; Piñeiro, Manuel M; Bessières, David; Miqueu, Christelle

    2010-09-02

    The Gradient Theory of fluid interfaces is for the first time combined with the SAFT-VR Mie EOS to model the interfacial properties of the water/CO(2) mixture. As a preliminary test of the performance of the coupling between both theories, liquid-vapor interfacial properties of pure water have been determined. The complex temperature dependence of the surface tension of water can be accurately reproduced, and the interfacial thickness is in good agreement with experimental data and simulation results. The water/CO(2) mixture presents several types of interfaces as the liquid water may be in contact with gaseous, liquid, or supercritical CO(2). Here, the interfacial tension of the water/CO(2) mixture is modeled accurately by the gradient theory with a unique value of the crossed influence parameter over a broad range of thermodynamic conditions. The interfacial density profiles show a systematic adsorption of CO(2) in the interface. Moreover, when approaching the saturation pressure of CO(2), a prewetting transition is highlighted. The adsorption isotherm of CO(2) is computed as well in the case of a gas/liquid interface and compared with experimental data. The good agreement obtained is an indirect proof of the consistency of interfacial density profiles computed with the gradient theory for this mixture and confirms that the gradient theory is suitable and reliable to describe the microstructure of complex fluid interfaces.

  8. Dynamics of absorption properties along a latitudinal gradient: sources of absorption in Australian inland waters

    NASA Astrophysics Data System (ADS)

    Hestir, E. L.; Campbell, G.; Malthus, T. J.; Dekker, A.; Botha, E.

    2013-12-01

    Australian inland waters are optically complex and vary spatially and temporally. Inversion of optical remote sensing data for the retrieval of optically active water quality constituents (chlorophyll, colored dissolved organic matter and total suspended solids) is impeded by the scarcity of inherent optical property (IOP) data sets. In 2012 a major measurement program commenced to improve understanding of IOPs in Australia. Seven large lakes were sampled along a latitudinal gradient in Eastern Australia; in situ observations were made of the absorption properties of the water quality during two epochs (wet and dry season). This study documents the seasonal, inter & intra lake variability of the absorption budget of Australian lakes. These data reveal the sources of biogeochemical constituents determining the light climate of lakes. Optically active water quality constituents (total suspended solids, chlorophyll-a, and colored dissolved organic matter) varied significantly between wet and dry season and between lakes. The primary contribution to the absorption budget was from non-algal particulate matter (NAP; 10-60%), followed by colored dissolved organic matter (CDOM; 20-80%). Absorption from phytoplankton contributed only 0-30% of the total budget. This indicates that these lakes are primarily light limited, though the limitation comes from multiple sources. The contribution of NAP to the total absorption budget showed the greatest amount of variance between wet and dry seasons. Examination of the organic matter and estimated phytoplankton biomass contributions to TSS reveal that chlorophyll is not the primary source of organic matter in Australian lakes: allochthonous inputs are the primary trophic driver. Finally, there is strong regional and seasonal variation in the IOPs of the lakes, with the exception of the slope of CDOM. The slope of CDOM was not significantly different between seasons (p=0.94). Non-parametric stepwise multiple comparisons showed the

  9. Gradient-index crystalline lens model: A new method for determining the paraxial properties by the axial and field rays

    NASA Astrophysics Data System (ADS)

    Rama, María. Angeles; Pérez, María. Victoria; Bao, Carmen; Flores-Arias, María. Teresa; Gómez-Reino, Carlos

    2005-05-01

    Gradient-index (GRIN) models of the human lens have received wide attention in optometry and vision sciences for considering the effect of inhomogeneity of the refractive index on the optical properties of the lens. This paper uses the continuous asymmetric bi-elliptical model to determine analytically cardinal elements, magnifications and refractive power of the lens by the axial and field rays in order to study the paraxial light propagation through the human lens from its GRIN nature.

  10. Modification of the structure and properties of gradient nanocrystalline coatings Ti-Al-Si-Cu-N by annealing in vacuum

    NASA Astrophysics Data System (ADS)

    Ovchinnikov, Stanislav; Pinzhin, Yurii

    2016-11-01

    The nanocrystalline gradient coatings system Ti-Al-Si-Cu-N were annealed in the temperature range of 500- 1100°C. Their composition, structure, and mechanical properties were studied by methods of scanning and transmission electron microscopy, scratch test, and measurement of nanohardness. It is shown that the diffusion of substrate elements has a crucial impact on the heat-activated processes of structure recovery, the growth of crystal size and the properties of materials. This results in nanocomposite structure with high adhesion characteristics of the coatings.

  11. Finite Element Analysis of Multilayered and Functionally Gradient Tribological Coatings With Measured Material Properties (Preprint)

    DTIC Science & Technology

    2006-11-01

    gradient coatings with diamond like carbon (DLC) coating on 440C stainless steel substrate were assumed as a series of perfectly bonded layers with...resistance and low friction. Ti1-xCx (0≤ x ≤1) gradient coatings with diamond like carbon (DLC) coating on 440C stainless steel substrate were...indenter tip was used for the FEA model. Each coating sample consists of 1 μm thick coating and 440C stainless steel substrate. The area function for

  12. Gradient Films of Pristine Graphene/Pyrene-Functional Copolymers with Janus Electrical Properties.

    PubMed

    Parviz, Dorsa; Yu, Ziniu; Verkhoturov, Stanislav; Green, Micah J; Hedden, Ronald C

    2016-11-23

    We describe the first preparation of polymer-supported pristine graphene thin films with dramatically different electrical conductivities on the top and bottom surfaces. Pyrene-functional stabilizers based on polystyrene or poly(methyl methacrylate) were first synthesized by copolymerization of their monomers with 1-pyrenemethyl methacrylate. Stable dispersions of pristine graphene nanosheets were prepared by sonication of graphite in chloroform solutions of the pyrene-functional copolymers. Vacuum filtration of the polymer-stabilized graphene dispersions through a porous PTFE filter produces films with an internal gradient in nanosheet concentration. This gradient graphene concentration results in an electrically conductive, graphene-rich surface on one side of the composite film and a nonconductive, polymer-rich surface on its other side. Electrical conductivities ranging from 60 to 194 S/m are measured on the graphene-rich surface, which are among the highest conductivities reported for pristine graphene/polymer composites. Through scanning electron microscopy and secondary ion mass spectrometry characterization, these films were found to contain three distinct layers: a polymer-rich top surface, a transition layer with a gradient in nanosheet concentration, and a buckypaper-like bottom layer consisting of densely packed, highly oriented graphene nanosheets. The gradient structure of these films and their Janus-like electrical conductivity has potential applications in graded coatings for radiofrequency and optical devices.

  13. Chromatic Properties of Horizontal and Ganglion Cell Responses Follow a Dual Gradient in Cone Opsin Expression

    PubMed Central

    Yin, Lu; Smith, Robert G; Sterling, Peter; Brainard, David H.

    2007-01-01

    In guinea pig retina, immunostaining reveals a dual gradient of opsins: cones expressing opsin sensitive to medium wavelengths (M) predominate in the upper retina, whereas cones expressing opsin sensitive to shorter wavelengths (S) predominate in the lower retina. Whether these gradients correspond to functional gradients in postreceptoral neurons is essentially unknown. Using monochromatic flashes, we measured the relative weights with which M, S, and rod signals contribute to horizontal cell responses. For a background that produced 4.76 log10 photoisomerizations per rod per second (Rh*/rod/s), mean weights in superior retina were 52% (M), 2% (S), and 46% (rod). Mean weights in inferior retina were 9% (M), 50% (S), and 41% (rod). In superior retina, cone opsin weights agreed quantitatively with relative pigment density estimates from immunostaining. In inferior retina, cone opsin weights agreed qualitatively with relative pigment density estimates, but quantitative comparison was impossible because individual cones coexpress both opsins to varying and unquantifiable degrees. We further characterized the functional gradients in horizontal and brisk-transient ganglion cells using flickering stimuli produced by various mixtures of blue and green primary lights. Cone weights for both cell types resembled those obtained for horizontal cells using monochromatic flashes. Because the brisk-transient ganglion cell is thought to mediate behavioral detection of luminance contrast, our results are consistent with the hypothesis that the dual gradient of cone opsins assists achromatic contrast detection against different spectral backgrounds. In our preparation, rod responses did not completely saturate, even at background light levels typical of outdoor sunlight (5.14 log10 Rh*/rod/s). PMID:17122060

  14. Properties of bubbled gases transportation in a bromothymol blue aqueous solution under gradient magnetic fields

    NASA Astrophysics Data System (ADS)

    Iwasaka, M.; Kurita, S.; Owada, N.

    2012-04-01

    A new system for the observation of the transport process of dissolved oxygen and carbon-dioxide gases is proposed that utilizes a water-containing column with an optical monitoring unit under gradient magnetic fields of up to 5 T. The system consists of a column for liquid chromatography with "branching flow" tubing at the center of a vertical bore of a superconducting magnet of 5 T. By utilizing bromothymol blue (BTB) as a CO2 concentration indicator, CO2 concentration in the bifurcated liquid stream from the gradient magnetic fields was measured by a time-resolved spectrophotometer in the range of 550 nm-660 nm. The results indicated that the gradient magnetic fields of up to 5 T accelerated the pushing-out of the CO2-rich BTB solution from the branched inlet of the column. Comparing the effects of O2-gas bubbling with He-gas bubbling, it was found that the oxygen gases dissolved in a BTB aqueous solution controlled the transport of CO2 gases in the solution under gradient magnetic fields of up to 5 T. By monitoring the chromatogram pattern of oxygen-gas-bubbled water flow in a straight flow system at the UV band, it was indicated that the paramagnetic oxygen-gas-bubbles stay longer in the magnetic field center of the magnet. The proposed method with the branch flow can enhance the condensation of carbon dioxide gases in a room temperature liquid by the assistance of oxygen-gas in water under gradient magnetic fields of up to 5 T.

  15. Gradient-based Electrical Properties Tomography (gEPT): a Robust Method for Mapping Electrical Properties of Biological Tissues In Vivo Using Magnetic Resonance Imaging

    PubMed Central

    Liu, Jiaen; Zhang, Xiaotong; Schmitter, Sebastian; Van de Moortele, Pierre-Francois; He, Bin

    2014-01-01

    Purpose To develop high-resolution electrical properties tomography (EPT) methods and investigate a gradient-based EPT (gEPT) approach which aims to reconstruct the electrical properties (EP), including conductivity and permittivity, of an imaged sample from experimentally measured B1 maps with improved boundary reconstruction and robustness against measurement noise. Theory and Methods Using a multi-channel transmit/receive stripline head coil, with acquired B1 maps for each coil element, by assuming negligible Bz component compared to transverse B1 components, a theory describing the relationship between B1 field, EP value and their spatial gradient has been proposed. The final EP images were obtained through spatial integration over the reconstructed EP gradient. Numerical simulation, physical phantom and in vivo human experiments at 7 T have been conducted to evaluate the performance of the proposed methods. Results Reconstruction results were compared with target EP values in both simulations and phantom experiments. Human experimental results were compared with EP values in literature. Satisfactory agreement was observed with improved boundary reconstruction. Importantly, the proposed gEPT method proved to be more robust against noise when compared to previously described non-gradient-based EPT approaches. Conclusion The proposed gEPT approach holds promises to improve EP mapping quality by recovering the boundary information and enhancing robustness against noise. PMID:25213371

  16. Gradient networks

    NASA Astrophysics Data System (ADS)

    Toroczkai, Zoltán; Kozma, Balázs; Bassler, Kevin E.; Hengartner, N. W.; Korniss, G.

    2008-04-01

    Gradient networks are defined (Toroczkai and Bassler 2004 Nature 428 716) as directed graphs formed by local gradients of a scalar field distributed on the nodes of a substrate network G. We present the derivation for some of the general properties of gradient graphs and give an exact expression for the in-degree distribution R(l) of the gradient network when the substrate is a binomial (Erd{\\;\\kern -0.10em \\raise -0.35ex \\{{^{^{\\prime\\prime}}}}\\kern -0.57em \\o} s-Rényi) random graph, G_{N,p} , and the scalars are independent identically distributed (i.i.d.) random variables. We show that in the limit N \\to \\infty, p \\to 0, z = pN = \\mbox{const} \\gg 1, R(l)\\propto l^{-1} for l < l_c = z , i.e., gradient networks become scale-free graphs up to a cut-off degree. This paper presents the detailed derivation of the results announced in Toroczkai and Bassler (2004 Nature 428 716).

  17. Growth Structure and Properties of Gradient Nanocrystalline Coatings of the Ti-Al-Si-Cu-N System

    NASA Astrophysics Data System (ADS)

    Ovchinnikov, S. V.; Pinzhin, Yu. P.

    2016-10-01

    Methods of electron microprobe analysis, X-ray structure analysis and electron microscopy were used to study the element composition and features of the structure-phase, elastic stress state of nanocrystalline coatings of the Ti- Al- Si- Cu- N system with gradient of copper concentration across their thickness. The authors established the effects of element composition modification, non-monotonous behavior of the lattice constant of alloyed nitride and rise in the bending-torsion value of the crystalline lattice in individual nanocrystals to values of around 400 degrees/μm with increase in copper concentration, whereas the sizes of alloyed nitride crystals remained practically unchanged. Mechanical (hardness), adhesion and tribological properties of coatings were examined. Comparative analysis demonstrates higher values of adhesion characteristics in the case of gradient coatings of the Ti- Al- Si- Cu- N system than in the case of single-layer (with constant element concentration) analogues.

  18. Estimation of In-Canopy Ammonia Sources and Sinks in a Fertilized Zea mays Field

    EPA Science Inventory

    An analytical model was developed that describes the in-canopy vertical distribution of NH3 source and sinks and vertical fluxes in a fertilized agricultural setting using measured in-canopy concentration and wind speed profiles.

  19. Estimation of In-Canopy Ammonia Sources and Sinks in a Fertilized Zea mays Field

    EPA Science Inventory

    An analytical model was developed that describes the in-canopy vertical distribution of NH3 source and sinks and vertical fluxes in a fertilized agricultural setting using measured in-canopy concentration and wind speed profiles.

  20. Calcium gradients in conifer pollen tubes; dynamic properties differ from those seen in angiosperms.

    PubMed

    Lazzaro, Mark D; Cardenas, Luis; Bhatt, Aadra P; Justus, Charles D; Phillips, Monique S; Holdaway-Clarke, Terena L; Hepler, Peter K

    2005-10-01

    Pollen tubes are an established model system for examining polarized cell growth. The focus here is on pollen tubes of the conifer Norway spruce (Picea abies, Pinaceae); examining the relationship between cytosolic free Ca2+, tip elongation, and intracellular motility. Conifer pollen tubes show important differences from their angiosperm counterparts; they grow more slowly and their organelles move in an unusual fountain pattern, as opposed to reverse fountain, in the tip. Ratiometric ion imaging of growing pollen tubes, microinjected with fura-2-dextran, reveals a tip-focused [Ca2+]i gradient extending from 450 nM at the extreme apex to 225 nM at the base of the tip clear zone. Injection of 5,5' dibromo-BAPTA does not dissipate the apical gradient, but stops cell elongation and uniquely causes rapid, transient increases of apical free Ca2+. The [Ca2+]i gradient is, however, dissipated by reversible perfusion of extracellular caffeine. When the basal cytosolic free Ca2+ concentration falls below 150 nM, again a large increase in apical [Ca2+]i occurs. An external source of calcium is not required for germination but significantly enhances elongation. However, both germination and elongation are significantly inhibited by the inclusion of calcium channels blockers, including lanthanum, gadolinium, or verapamil. Modulation of intracellular calcium also affects organelle position and motility. Extracellular perfusion of lanthanides reversibly depletes the apical [Ca2+]i gradient, altering organelle positioning in the tip. Later, during recovery from lanthanide perfusion, organelle motility switches direction to a reverse fountain. When taken together these data show a unique interplay in Picea abies pollen tubes between intracellular calcium and the motile processes controlling cellular organization.

  1. Analytical applications and effective properties of a second gradient isotropic elastic material model

    NASA Astrophysics Data System (ADS)

    Enakoutsa, Koffi

    2014-09-01

    Recently, the works by Toupin, Mindlin, Sokolowski and Germain have been developed following two research streams. In the first one, higher-order gradient continuum models were developed based on the Cauchy tetrahedron argument (see, e.g., dell'Isola and Seppecher in Comptes Rendus de l Academie de Sciences 17 Serie IIb: Mecanique, Physique, Chimie, Astronomie 321:303-308, 1995, Meccanica 32:33-52 1997, Zeitschrift fr Angewandte Mathematik und Physik 63(6):1119-1141, 2012). In the second one, the structure of higher-order gradient models is developed with a view to the applications. In particular in the model of linear isotropic solids proposed by Dell'Isola, Sciarra and Vidoli (DSV), the main constitutive equation is obtained for the case of second gradient models. This model introduces in addition to the two well-known Lame's elastic constants five constitutive constants. The practical applications of this model remain in its infancy since the issue of determining the new moduli it introduces is not yet completely addressed. Also, analytical solutions of simple boundary value problems that can be helpful to grasp some of the physical foundations of this model are missing. This paper aims to address these two issues by providing the analytical solutions for two model problems, a spherical shell subjected to axisymmetric loading conditions and the circular bending of a beam in plane strain, both the beam and the shell obeying the DSV second gradient isotropic elastic model. The solution of the circular bending of a beam has served to grasp some of the physical soundness of the model. A framework based on homogenization under inhomogeneous boundary conditions is also suggested to determine the unknown constitutive constants, which are provided in the particular case of elastic porous heterogeneous materials.

  2. Investigating the Thermophysical Properties of the Ice-Snow Interface Under a Controlled Temperature Gradient

    NASA Astrophysics Data System (ADS)

    Hammonds, Kevin; Lieb-Lappen, Ross; Baker, Ian; Wang, Xuan; Courville, Zoe

    2015-04-01

    Of critical importance for avalanche forecasting, is the ability to draw meaningful conclusions from a handful of field observations. To this end, it is common for avalanche forecasters to not only have to rely on these sparse data, but also to use their own intuitive understanding of how these observations are correlated with the complex physical processes that produce mechanical instabilities within a snowpack. One such example of this is the long-held notion that kinetic snow metamorphism does not occur at bulk temperature gradients of less than -10°C/m. Although this may be true for the homogeneous case, it has become a point of contention as to whether or not this guideline should be applied to the more representative case of a heavily stratified and anisotropic snowpack. As an idealized case for our initial laboratory investigations, we have studied how an artificially created ice layer or "lens" would affect the thermophysical state of the snow layers adjacent to the ice lens and the ice lens itself, while being held under a controlled temperature gradient. Our findings have shown, via in-situ micro-thermocouple measurements, that a super-temperature gradient many times greater than the imposed bulk temperature gradient can exist within a millimeter above and below the surface of the ice lens. Furthermore, microstructural analysis via time-lapse X-ray Micro-Computed Tomography and environmental SEM imaging has been performed. Results from this analysis show new ice crystal growth and kinetic snow metamorphism occurring simultaneously on or near the ice lens itself with the connectivity density at the ice-snow interface increasing markedly more below the ice lens than above.

  3. Optical Properties of a Bio-Inspired Gradient Refractive Index Polymer Lens

    DTIC Science & Technology

    2008-07-21

    crystalline lens. GRIN lenses found in nature typically consist of approximately 22,000 nonplanar layers of proteins with different refractive...indices [5]. Systematic variation in protein and water concentration in different layers provides the index gradient [6]. The refractive index range (Δn...typically composed of tens of thousands of protein layers. Attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) can confirm

  4. Analytical applications and effective properties of a second gradient isotropic elastic material model

    NASA Astrophysics Data System (ADS)

    Enakoutsa, Koffi

    2015-06-01

    Recently, the works by Toupin, Mindlin, Sokolowski and Germain have been developed following two research streams. In the first one, higher-order gradient continuum models were developed based on the Cauchy tetrahedron argument (see, e.g., dell'Isola and Seppecher in Comptes Rendus de l Academie de Sciences 17 Serie IIb: Mecanique, Physique, Chimie, Astronomie 321:303-308, 1995, Meccanica 32:33-52 1997, Zeitschrift fr Angewandte Mathematik und Physik 63(6):1119-1141, 2012). In the second one, the structure of higher-order gradient models is developed with a view to the applications. In particular in the model of linear isotropic solids proposed by Dell'Isola, Sciarra and Vidoli (DSV), the main constitutive equation is obtained for the case of second gradient models. This model introduces in addition to the two well-known Lame's elastic constants five constitutive constants. The practical applications of this model remain in its infancy since the issue of determining the new moduli it introduces is not yet completely addressed. Also, analytical solutions of simple boundary value problems that can be helpful to grasp some of the physical foundations of this model are missing. This paper aims to address these two issues by providing the analytical solutions for two model problems, a spherical shell subjected to axisymmetric loading conditions and the circular bending of a beam in plane strain, both the beam and the shell obeying the DSV second gradient isotropic elastic model. The solution of the circular bending of a beam has served to grasp some of the physical soundness of the model. A framework based on homogenization under inhomogeneous boundary conditions is also suggested to determine the unknown constitutive constants, which are provided in the particular case of elastic porous heterogeneous materials.

  5. Formation Mechanisms and Properties of Semifluorinated Molecular Gradients on Silica Surfaces

    SciTech Connect

    Genzer,J.; Efimenko, K.; Fischer, D.

    2006-01-01

    The goal of this study is to elucidate the formation of molecular gradients made of semifluorinated organosilanes (SFOs) on flat substrates by using a methodology developed by Chaudhury and Whitesides (Science 1992, 256, 1539). We use surface-sensitive combinatorial near-edge X-ray absorption fine structure (combi-NEXAFS) spectroscopy to measure the position-dependent concentration and orientation of SFO molecules in SFO molecular gradients on flat silica surfaces. Using the combi-NEXAFS data, we establish the correlation between the fraction of the F(CF{sub 2}){sub 8}(CH{sub 2}){sub 2{sup -}} species on the substrate and the average tilt angle of the -(CF{sub 2}){sub 8}F group in the SFO as a function of the deposition gas medium (air vs nitrogen) and the end group around the silicon atom (monofunctional vs trifunctional). In addition, we utilize the gradient geometry to comprehend the mechanism of formation of SFO self-assembled monolayers (SAMs). Specifically, we provide evidence that depending on the nature of the end group in the SFO and the vapor phase the SFO molecules add themselves into the existing SAMs either as individual molecules or as multimolecular complexes.

  6. Large Deformation Properties of Red Blood Cell Membrane Based on a Higher Order Gradient Quasi-continuum Model.

    PubMed

    Wang, X Y; Wang, J B; Qiu, B B; Hu, L F

    2015-12-01

    Based on the proposed higher order gradient quasi-continuum model, the numerical investigations of the basic mechanical properties and deformation behaviors of human red blood cell (RBC) membrane under large deformation at room temperature (i.e., 300 K) are carried out in the present paper. The results show that RBC membrane is a nonlinear hyperelastic material. The mechanical properties of RBC membrane is dominated by isotropic nature at the stage of initial deformation, however, its anisotropic material properties emerge clearly with the loading increasing. The out-of-plane wrinkling of RBC membrane upon shear loading can be reproduced numerically. With the use of the so-called higher order Cauchy-Born rule as the kinematic description, the bending stiffness of RBC membrane can be considered conveniently.

  7. Estimation of in-canopy ammonia sources and sinks in a fertilized Zea mays field

    EPA Science Inventory

    An analytical model was developed that describes the in-canopy vertical distribution of NH3 source and sinks and vertical fluxes in a fertilized agricultural setting using measured in-canopy concentration and wind speed profiles. This model was applied to quantify in-canopy air-s...

  8. Estimation of in-canopy ammonia sources and sinks in a fertilized Zea mays field

    EPA Science Inventory

    An analytical model was developed that describes the in-canopy vertical distribution of NH3 source and sinks and vertical fluxes in a fertilized agricultural setting using measured in-canopy concentration and wind speed profiles. This model was applied to quantify in-canopy air-s...

  9. Reactive combinatorial synthesis and characterization of a gradient Ag-Ti oxide thin film with antibacterial properties.

    PubMed

    Unosson, Erik; Rodriguez, Daniel; Welch, Ken; Engqvist, Håkan

    2015-01-01

    The growing demand for orthopedic and dental implants has spurred researchers to develop multifunctional coatings, combining tissue integration with antibacterial features. A possible strategy to endow titanium (Ti) with antibacterial properties is by incorporating silver (Ag), but designing a structure with adequate Ag(+) release while maintaining biocompatibility has been shown difficult. To further explore the composition-structure-property relationships between Ag and Ti, and its effects against bacteria, this study utilized a combinatorial approach to manufacture and test a single sample containing a binary Ag-Ti oxide gradient. The sample, sputter-deposited in a reactive (O2) environment using a custom-built combinatorial physical vapor deposition system, was shown to be effective against Staphylococcus aureus with viability reductions ranging from 17 to above 99%, depending on the amount of Ag(+) released from its different parts. The Ag content along the gradient ranged from 35 to 62 wt.%, but it was found that structural properties such as varied porosity and degree of crystallinity, rather than the amount of incorporated Ag, governed the Ag(+) release and resulting antibacterial activity. The coating also demonstrated in vitro apatite-forming abilities, where structural variety along the sample was shown to alter the hydrophilic behavior, with the degree of hydroxyapatite deposition varying accordingly. By means of combinatorial synthesis, a single gradient sample was able to display intricate compositional and structural features affecting its biological response, which would otherwise require a series of coatings. The current findings suggest that future implant coatings incorporating Ag as an antibacterial agent could be structurally enhanced to better suit clinical requirements.

  10. Designing Waveform Sets with Good Correlation and Stopband Properties for MIMO Radar via the Gradient-Based Method

    PubMed Central

    Tang, Liang; Zhu, Yongfeng; Fu, Qiang

    2017-01-01

    Waveform sets with good correlation and/or stopband properties have received extensive attention and been widely used in multiple-input multiple-output (MIMO) radar. In this paper, we aim at designing unimodular waveform sets with good correlation and stopband properties. To formulate the problem, we construct two criteria to measure the correlation and stopband properties and then establish an unconstrained problem in the frequency domain. After deducing the phase gradient and the step size, an efficient gradient-based algorithm with monotonicity is proposed to minimize the objective function directly. For the design problem without considering the correlation weights, we develop a simplified algorithm, which only requires a few fast Fourier transform (FFT) operations and is more efficient. Because both of the algorithms can be implemented via the FFT operations and the Hadamard product, they are computationally efficient and can be used to design waveform sets with a large waveform number and waveform length. Numerical experiments show that the proposed algorithms can provide better performance than the state-of-the-art algorithms in terms of the computational complexity. PMID:28468308

  11. Designing Waveform Sets with Good Correlation and Stopband Properties for MIMO Radar via the Gradient-Based Method.

    PubMed

    Tang, Liang; Zhu, Yongfeng; Fu, Qiang

    2017-05-01

    Waveform sets with good correlation and/or stopband properties have received extensive attention and been widely used in multiple-input multiple-output (MIMO) radar. In this paper, we aim at designing unimodular waveform sets with good correlation and stopband properties. To formulate the problem, we construct two criteria to measure the correlation and stopband properties and then establish an unconstrained problem in the frequency domain. After deducing the phase gradient and the step size, an efficient gradient-based algorithm with monotonicity is proposed to minimize the objective function directly. For the design problem without considering the correlation weights, we develop a simplified algorithm, which only requires a few fast Fourier transform (FFT) operations and is more efficient. Because both of the algorithms can be implemented via the FFT operations and the Hadamard product, they are computationally efficient and can be used to design waveform sets with a large waveform number and waveform length. Numerical experiments show that the proposed algorithms can provide better performance than the state-of-the-art algorithms in terms of the computational complexity.

  12. Study of adhesion and friction properties on a nanoparticle gradient surface: transition from JKR to DMT contact mechanics.

    PubMed

    Ramakrishna, Shivaprakash N; Nalam, Prathima C; Clasohm, Lucy Y; Spencer, Nicholas D

    2013-01-08

    We have previously investigated the dependence of adhesion on nanometer-scale surface roughness by employing a roughness gradient. In this study, we correlate the obtained adhesion forces on nanometer-scale rough surfaces to their frictional properties. A roughness gradient with varying silica particle (diameter ≈ 12 nm) density was prepared, and adhesion and frictional forces were measured across the gradient surface in perfluorodecalin by means of atomic force microscopy with a polyethylene colloidal probe. Similarly to the pull-off measurements, the frictional forces initially showed a reduction with decreasing particle density and later an abrupt increase as the colloidal sphere began to touch the flat substrate beneath, at very low particle densities. The friction-load relation is found to depend on the real contact area (A(real)) between the colloid probe and the underlying particles. At high particle density, the colloidal sphere undergoes large deformations over several nanoparticles, and the contact adhesion (JKR type) dominates the frictional response. However, at low particle density (before the colloidal probe is in contact with the underlying surface), the colloidal sphere is suspended by a few particles only, resulting in local deformations of the colloid sphere, with the frictional response to the applied load being dominated by long-range, noncontact (DMT-type) interactions with the substrate beneath.

  13. Importance of Gradients in Membrane Properties and Electrical Coupling in Sinoatrial Node Pacing

    PubMed Central

    Inada, Shin; Zhang, Henggui; Tellez, James O.; Shibata, Nitaro; Nakazawa, Kazuo; Kamiya, Kaichiro; Kodama, Itsuo; Mitsui, Kazuyuki; Dobrzynski, Halina; Boyett, Mark R.; Honjo, Haruo

    2014-01-01

    The sinoatrial node (SAN) is heterogeneous in terms of cell size, ion channels, current densities, connexins and electrical coupling. For example, Nav1.5 (responsible for INa) and Cx43 (responsible for electrical coupling) are absent from the centre of the SAN (normally the leading pacemaker site), but present in the periphery (at SAN-atrial muscle junction). To test whether the heterogeneity is important for the functioning of the SAN, one- and two-dimensional models of the SAN and surrounding atrial muscle were created. Normal functioning of the SAN (in terms of cycle length, position of leading pacemaker site, conduction times, activation and repolarization sequences and space constants) was observed when, from the centre to the periphery, (i) cell characteristics (cell size and ionic current densities) were changed in a gradient fashion from a central-type (lacking INa) to a peripheral-type (possessing INa) and (ii) coupling conductance was increased in a gradient fashion. We conclude that the heterogeneous nature of the node is important for its normal functioning. The presence of Nav1.5 and Cx43 in the periphery may be essential for the node to be able to drive the atrial muscle: Nav1.5 provides the necessary depolarizing current and Cx43 delivers it to the atrial muscle. PMID:24759974

  14. Propagation properties of Airy-Gaussian vortex beams through the gradient-index medium.

    PubMed

    Zhao, Ruihuang; Deng, Fu; Yu, Weihao; Huang, Jiayao; Deng, Dongmei

    2016-06-01

    Propagation of Airy-Gaussian vortex (AiGV) beams through the gradient-index medium is investigated analytically and numerically with the transfer matrix method. Deriving the analytic expression of the AiGV beams based on the Huygens diffraction integral formula, we obtain the propagate path, intensity and phase distributions, and the Poynting vector of the first- and second-order AiGV beams, which propagate through the paraxial ABCD system. The ballistic trajectory is no longer conventional parabolic but trigonometric shapes in the gradient-index medium. Especially, the AiGV beams represent the singular behavior at the propagation path and the light intensity distribution. The phase distribution and the Poynting vector exhibit in reverse when the AiGV beams through the singularity. As the order increases, the main lobe of the AiGV beams is gradually overlapped by the vortex core. Further, the sidelobe weakens when the AiGV beams propagate nearly to the singularity. Additionally, the figure of the Poynting vector of the AiGV beams proves the direction of energy flow corresponding to the intensity distribution. The vortex of the second-order AiGV beams is larger, and the propagation velocity is faster than that of the first order.

  15. Lie symmetry properties of nonlinear reaction-diffusion equations with gradient-dependent diffusivity

    NASA Astrophysics Data System (ADS)

    Cherniha, Roman; King, John R.; Kovalenko, Sergii

    2016-07-01

    Complete descriptions of the Lie symmetries of a class of nonlinear reaction-diffusion equations with gradient-dependent diffusivity in one and two space dimensions are obtained. A surprisingly rich set of Lie symmetry algebras depending on the form of diffusivity and source (sink) in the equations is derived. It is established that there exists a subclass in 1-D space admitting an infinite-dimensional Lie algebra of invariance so that it is linearisable. A special power-law diffusivity with a fixed exponent, which leads to wider Lie invariance of the equations in question in 2-D space, is also derived. However, it is shown that the diffusion equation without a source term (which often arises in applications and is sometimes called the Perona-Malik equation) possesses no rich variety of Lie symmetries depending on the form of gradient-dependent diffusivity. The results of the Lie symmetry classification for the reduction to lower dimensionality, and a search for exact solutions of the nonlinear 2-D equation with power-law diffusivity, also are included.

  16. NMR and pulsed field gradient NMR approach of water sorption properties in Nafion at low temperature.

    PubMed

    Guillermo, Armel; Gebel, Gérard; Mendil-Jakani, Hakima; Pinton, Eric

    2009-05-14

    The water uptake and the water self-diffusion coefficient were measured in Nafion membranes at subzero temperatures. NMR spectroscopy was used to precisely quantify the actual concentration of water in membranes as a function of the temperature and their hydration rates at room temperature. We find that below 273 K the water concentration decreases with temperature to reach, at around 220 K, a limit value independent of the initial concentration. This regime is observed if the concentration at room temperature is higher than 10%. Below this concentration no membrane deswelling was observed. The water self-diffusion coefficient, measured by pulsed field gradient NMR in function of the temperature, is determined by the actual concentration C(T) whatever the concentration at room temperature. The concentration variation is attributed to a decrease in the relative humidity RH(T) of the water vapor surrounding the membrane induced by the simultaneous presence of supercooled water inside the membrane and ice outside the membrane.

  17. Leaf ultraviolet optical properties along a latitudinal gradient in the Arctic-Alpine life zone

    SciTech Connect

    Robberecht, R.; Caldwell, M.M.; Billings, W.D.

    1980-06-01

    Leaf epidermal transmittance of terrestrial solar ultraviolet-B radiation (295 to 320 nm) was examined along a latitudinal gradient of solar uv-B radiation. In high uv-B radiation zones, e.g., equatorial and tropical regions, mean epidermal transmittance for the species examined was less than 2%. At higher latitudes, mean epidermal transmittance exceeded 5%. Although this latitudinal solar uv-B gradient represents more than a seven-fold difference in daily integrated uv-B irradiance, the calculated mean effective uv-B irradiance at the mesophyll of low-latitude species is not substantially different from that of species at higher latitudes. Species in high uv-B radiation environments appear to attenuate this radiation more effectively than those in lower irradiance environments. In most cases, absorption of uv-B in the epidermis is the major parameter effecting low transmittance. Reflectance from glabrous leaves is generally less than 10%. In some species, pubescent or glaucous leaf surfaces can reflect more than 40% of the uv-B radiation incident on a horizontal leaf, although such surface characteristics do not necessarily indicate high uv-B reflectance. Under controlled conditions, epidermal transmittance in Pisum sativum L. decreased in response to uv-B irradiation. The modification of epidermal transmittance, resulting in lower uv-B irradiance at the mesophyll, may represent a mechanism of plant acclimation to uv-B radiation. Such acclimation may have occurred in several wildland species of temperate-latitude origin that have invaded high uv-B irradiance equatorial and tropical regions.

  18. Interfacial and biological properties of the gradient coating on polyamide substrate for bone substitute.

    PubMed

    Huang, Di; Niu, Lulu; Wei, Yan; Guo, Meiqing; Zuo, Yi; Zou, Qin; Hu, Yinchun; Chen, Weiyi; Li, Yubao

    2014-10-06

    Fabrication of bioactive and mechanical matched bone substitutes is crucial for clinical application in bone defects repair. In this study, nano-hydroxyapatite/polyamide (nHA/PA) composite was coated on injection-moulded PA by a chemical corrosion and phase-inversion technique. The shear strength, gradient composition and pore structure of the bioactive coating were characterized. Osteoblast-like MG63 cells were cultured on pure PA and composite-coated PA samples. The cells' adhesion, spread and proliferation were determined using MTT assay and microscopy. The results confirm that the samples with the nHA/PA composite coating have better cytocompatibility and have no negative effects on cells. To investigate the in vivo biocompatibility, both pure PA and composite-coated PA cylinders were implanted in the trochlea of rabbit femurs and studied histologically, and the bonding ability with bone were determined using push-out tests. The results show that composite-coated implants exhibit better biocompatibility and the shear strength of the composite-coated implants with host bone at 12 weeks can reach 3.49±0.42 MPa, which is significantly higher than that of pure PA implants. These results indicate that composite-coated PA implants have excellent biocompatibility and bonding abilities with host bone and they have the potential to be applied in repair of bone defects.

  19. Interfacial and biological properties of the gradient coating on polyamide substrate for bone substitute

    PubMed Central

    Huang, Di; Niu, Lulu; Wei, Yan; Guo, Meiqing; Zuo, Yi; Zou, Qin; Hu, Yinchun; Chen, Weiyi; Li, Yubao

    2014-01-01

    Fabrication of bioactive and mechanical matched bone substitutes is crucial for clinical application in bone defects repair. In this study, nano-hydroxyapatite/polyamide (nHA/PA) composite was coated on injection-moulded PA by a chemical corrosion and phase-inversion technique. The shear strength, gradient composition and pore structure of the bioactive coating were characterized. Osteoblast-like MG63 cells were cultured on pure PA and composite-coated PA samples. The cells' adhesion, spread and proliferation were determined using MTT assay and microscopy. The results confirm that the samples with the nHA/PA composite coating have better cytocompatibility and have no negative effects on cells. To investigate the in vivo biocompatibility, both pure PA and composite-coated PA cylinders were implanted in the trochlea of rabbit femurs and studied histologically, and the bonding ability with bone were determined using push-out tests. The results show that composite-coated implants exhibit better biocompatibility and the shear strength of the composite-coated implants with host bone at 12 weeks can reach 3.49 ± 0.42 MPa, which is significantly higher than that of pure PA implants. These results indicate that composite-coated PA implants have excellent biocompatibility and bonding abilities with host bone and they have the potential to be applied in repair of bone defects. PMID:25121648

  20. Microstructure development, compositional/physical gradient formation and related mechanical properties of gas-pressure-sintered silicon nitride ceramics

    NASA Astrophysics Data System (ADS)

    Tiegs, Terry Norman

    Three inter-related aspects in the fabrication of silicon nitride ceramics were performed for the thesis work. The topics included: (1) an analysis of the composition and physical gradients in bulk silicon nitride, (2) the effect of sintering parameters on microstructure development and the resulting mechanical properties, and (3) an investigation of ss-Sisb3Nsb4 nucleation and initial stage microstructure development. The composition and physical gradients in bulk silicon nitride are due to the furnace conditions and the environment adjacent to the samples. Loss of SiO from the exposed surfaces results in the formation of nitrogen-rich phases, such as melilite on the as-sintered surfaces. The high nitrogen concentration in the near-surface region promotes ss-Sisb3Nsb4 grain growth. Along with the compositional gradients, mechanical property differences also exist between the as-sintered surfaces and the bulk materials. For example, the strengths of as-sintered surfaces of Sisb3Nsb4-Ysb2Osb3-Alsb2Osb3 were observed to be reduced by more than 30% compared to the bulk material. Gas-pressure sintering (GPS) was used to densify silicon nitride two types of sintering additives: Sisb3Nsb4-6% Ysb2Osb3-2% Alsb2Osb3 and Sisb3Nsb4-Srsb2Lasb4Ybsb4(SiOsb4)sb6Osb2. For both compositions a lower densification temperature (1900sp°C in the present tests) was the most significant factor affecting the fracture toughness and promoting a bimodal grain structure. The low significance of the other process parameters implies the microstructure (and therefore properties) are essentially 'locked-in' during the densification stage. The kinetics of the alpha-to-ss Sisb3Nsb4 transformation are dependent on several characteristics of the starting silicon nitride powder. Most importantly, are the silicon nitride powder surface area and initial ss-Sisb3Nsb4 content which both tend to increase the transformation rate. Other factors, such as lattice oxygen or carbon contents, appear to contribute

  1. Planar gradient metamaterials

    NASA Astrophysics Data System (ADS)

    Xu, Yadong; Fu, Yangyang; Chen, Huanyang

    2016-12-01

    Metamaterials possess exotic properties that do not exist in nature. Gradient metamaterials, which are characterized by a continuous spatial variation of their properties, provide a promising approach to the development of both bulk and planar optics. In particular, planar gradient metamaterials can be classified into three categories: gradient metasurfaces, gradient index metamaterials and gradient metallic gratings. In this Review, we summarize the progress made in the theoretical modelling of these materials, in their experimental implementation and in the design of functional devices. We discuss the use of planar gradient metamaterials for wave bending and focusing in free space, for supporting surface plasmon polaritons and for the realization of trapped rainbows. We also focus on the implementation of these materials in waveguide systems, which can enable electromagnetic cloaking, Fano resonances, asymmetric transmission and guided mode conversion. Finally, we discuss promising trends, such as the use of dielectric rather than metallic unit elements and the use of planar gradient metamaterials in 3D systems.

  2. Vibrational-rotational dependence of molecular properties. Electric field gradients for HCl, LiCl, NaCl and KCl

    NASA Astrophysics Data System (ADS)

    Seth, Michael; Pernpointner, Markus; Bowmaker, Graham A.; Schwerdtfeger, Peter

    The vibrational-rotational dependence of the nuclear quadrupole coupling constant (NQCC) for the isotopes 2H, 7Li, 23Na, 39K, and 35Cl is analysed in detail for the diatomic Group 1 chlorides HCl, LiCl, NaCl and KCl. The potential energy curves were calculated pointwise by using coupled cluster techniques. The electric field gradients (EFGs) and dipole moments were obtained analytically from a QCISD procedure using the Z vector method. Generally the calculated spectroscopic properties are in very good agreement with experimental data. Relativistic effects taken into account by a coupled cluster Douglas-Kroll procedure can safely be neglected for the electric field gradients up to potassium. The Inglis model which explains the trend and magnitudes of EFGs within an ionic model of weakly polarized atoms is analysed. According to this model the derivatives of the EFG, ∂nq (R)/∂Rn , with respect to the internuclear distance R should show alternating sign behaviour with increasing power n. Hence, the mechanical anharmonicity (deviation from Hooke's law potential) and the electrical anharmonicity (curvature of q(R)) are of different sign, and we expect partial cancellation of anharmonicity effects in the vibrational dependence of the NQCCs. Nevertheless, a perturbative vibrational-rotational analysis reveals a strong dependence of the chlorine and Group 1 element NQCCs on the vibrational level due to dominating mechanical anharmonicity.

  3. Hydraulic properties and fine root mass of Larix sibirica along forest edge-interior gradients

    NASA Astrophysics Data System (ADS)

    Chenlemuge, Tselmeg; Dulamsuren, Choimaa; Hertel, Dietrich; Schuldt, Bernhard; Leuschner, Christoph; Hauck, Markus

    2015-02-01

    At its southernmost distribution limit in Inner Asia, the boreal forest disintegrates into forest fragments on moist sites (e.g. north-facing slopes), which are embedded in grasslands. This landscape mosaic is characterized by a much higher forest edge-to-interior ratio than in closed boreal forests. Earlier work in the forest-steppe ecotone of Mongolia has shown that Larix sibirica trees at forest edges grow faster than in the forest interior, as the more xeric environment at the edge promotes self-thinning and edges are preferentially targeted by selective logging and livestock grazing. Lowered stand density reduces competition for water in these semi-arid forests, where productivity is usually limited by summer drought. We studied how branch and coarse root hydraulic architecture and xylem conductivity, fine root biomass and necromass, and fine root morphology of L. sibirica respond to sites differing in water availability. Studying forest edge-interior gradients in two regions of western Mongolia, we found a significant reduction of branch theoretical (Kp) and empirical conductivity (Ks) in the putatively more drought-affected forest interior in the Mongolian Altai (mean precipitation: 120 mm yr-1), while no branch xylem modification occurred in the moister Khangai Mountains (215 mm yr-1). Kp and Ks were several times larger in roots than in branches, but root hydraulics were not influenced by stand density or mean annual precipitation. Very low fine root biomass: necromass ratios at all sites, and in the forest interior in particular, suggest that L. sibirica seeks to maintain a relatively high root conductivity by producing large conduits, which results in high root mortality due to embolism during drought. Our results suggest that L. sibirica is adapted to the semi-arid climate at its southernmost distribution limit by considerable plasticity of the branch hydraulic system and a small but apparently dynamic fine root system.

  4. Investigation of trace metal binding properties of lignin by diffusive gradients in thin films.

    PubMed

    Hojaji, Elahe

    2012-09-01

    The binding behavior of lignin for Pb, Cu, Co, Mn, Cd and Ni was studied using the diffusive gradients in thin films technique (DGT). Samplers with different structures of diffusive gel were used in the well-stirred systems containing known concentrations of metals along with (a) 10, 20 and 40 μM lignin and; (b) 0.64 and 6.47 μM Suwannee river fulvic acid+40 μM lignin at an ionic strength of 0.01 M (NaNO(3)) and pH=7. Diffusion coefficients of lignin complexes in acrylamide gels were estimated and found to be less than 5% of the equivalent coefficients for the uncomplexed metal ions. These values were used to calculate concentrations of labile metals from DGT measurements in solutions, where lignin could discriminate metals in the order of Pb(+2)>Cu(+2)>Cd(+2)>Ni(+2)>Co(+2)>Mn(+2). Stability constants (LogK) were calculated using Visual MINTEQ II and WHAM V software. The K values were compared with the stability constants from titration of Pb and Cd with 10 μM lignin aqueous samples and with those of humic substances in natural waters. The constants obtained from measurement of complexing capacities might bias the real corresponding values unless two line regression analyses on titration data are considered. The DGT study of fractionation of metal species at varying ratios indicated that the proportion of organic complexes decreased with increasing ratios and gradually more metals were exchanged with inorganic phases. Speciation of Pb and Cd is affected by the concentrations of FA, Cd is dominantly bound with FA while Pb is evenly partitioned between the ligands. The comprehensive knowledge of metal-lignin complexes sheds some light on in situ operational speciation information that can be achieved by DGT.

  5. Improvement of laser molecular beam epitaxy grown SrTiO3 thin film properties by temperature gradient modulation growth

    NASA Astrophysics Data System (ADS)

    Li, Jin Long; Hao, J. H.; Li, Y. R.

    2007-09-01

    Oxygen diffusion at the SrTiO3/Si interface was analyzed. A method called temperature gradient modulation growth was introduced to control oxygen diffusion at the interface of SrTiO3/Si. Nanoscale multilayers were grown at different temperatures at the initial growing stage of films. Continuous growth of SrTiO3 films was followed to deposit on the grown sacrificial layers. The interface and crystallinity of SrTiO3/Si were investigated by in situ reflection high energy electron diffraction and x-ray diffraction measurements. It has been shown that the modulated multilayers may help suppress the interfacial diffusion, and therefore improve SrTiO3 thin film properties.

  6. Pyrogenic Carbon in forest soils across climate and soil property gradients in Switzerland

    NASA Astrophysics Data System (ADS)

    Reisser, Moritz; González Domínguez, Beatriz R.; Hagedorn, Frank; Abiven, Samuel

    2016-04-01

    Soil organic carbon (SOC) is an important measure for soil quality. Usually a high organic matter content in soils is favourable for most ecosystems. As a very stable component, pyrogenic organic carbon (PyC) can be of major interest to investigate to potential of organic matter, to persist very long in soils. Recent studies have shown, that the mean residence time of organic matter is not only due to its intrinsic chemical nature, but also to a variety of abiotic and biotic variables set by the ecosystem. Especially for PyC it is unclear, whether its content is related to fire regime, soil properties or other climatic conditions. In this study we wanted to investigate, how climatic and soil-related conditions are influencing the persistence of PyC in soils. Therefore we used a sample set from Swiss forest soil (n = 54), which was designed for the purpose of having most differing climatic conditions (aridity and temperature) and a large range of soil properties (pH between 3.4 and 7.6; clay content between 4.7 % and 60 %). The soils were sampled in the first 20 cm of the mineral horizon on a representative plot area of 40 x 40 m. The soils were sieved to 2 mm and dried prior to the analysis. We used the benzene polycarboxylic acids (BPCA) molecular marker method to quantify and characterize PyC in these soil samples. Despite the large span in environmental conditions, we observed rather small differences in the contribution of PyC to SOC between warmer and colder, as well as between wetter and dryer soils. The PyC content in SOC lies well in range with a global average for forest soils estimated in other studies. Stocks of PyC vary more than the content, because of the large range of SOC contents in the samples. The influence of other parameters like soil properties is still under investigation. Qualitative investigation of the BPCAs showed that the degree of condensation, defined by the relative amount of B6CA in the total BPCA, was higher in warmer soils. This

  7. Gradient moduli lens models: how material properties and application of forces can affect deformation and distributions of stress

    PubMed Central

    Wang, Kehao; Venetsanos, Demetrios; Wang, Jian; Pierscionek, Barbara K.

    2016-01-01

    The human lens provides one-third of the ocular focussing power and is responsible for altering focus over a range of distances. This ability, termed accommodation, defines the process by which the lens alters shape to increase or decrease ocular refractive power; this is mediated by the ciliary muscle through the zonule. This ability decreases with age such that around the sixth decade of life it is lost rendering the eye unable to focus on near objects. There are two opponent theories that provide an explanation for the mechanism of accommodation; definitive support for either of these requires investigation. This work aims to elucidate how material properties can affect accommodation using Finite Element models based on interferometric measurements of refractive index. Gradients of moduli are created in three models from representative lenses, aged 16, 35 and 48 years. Different forms of zonular attachments are studied to determine which may most closely mimic the physiological form by comparing stress and displacement fields with simulated shape changes to accommodation in living lenses. The results indicate that for models to mimic accommodation in living eyes, the anterior and posterior parts of the zonule need independent force directions. Choice of material properties affects which theory of accommodation is supported. PMID:27507665

  8. Gradient moduli lens models: how material properties and application of forces can affect deformation and distributions of stress

    NASA Astrophysics Data System (ADS)

    Wang, Kehao; Venetsanos, Demetrios; Wang, Jian; Pierscionek, Barbara K.

    2016-08-01

    The human lens provides one-third of the ocular focussing power and is responsible for altering focus over a range of distances. This ability, termed accommodation, defines the process by which the lens alters shape to increase or decrease ocular refractive power; this is mediated by the ciliary muscle through the zonule. This ability decreases with age such that around the sixth decade of life it is lost rendering the eye unable to focus on near objects. There are two opponent theories that provide an explanation for the mechanism of accommodation; definitive support for either of these requires investigation. This work aims to elucidate how material properties can affect accommodation using Finite Element models based on interferometric measurements of refractive index. Gradients of moduli are created in three models from representative lenses, aged 16, 35 and 48 years. Different forms of zonular attachments are studied to determine which may most closely mimic the physiological form by comparing stress and displacement fields with simulated shape changes to accommodation in living lenses. The results indicate that for models to mimic accommodation in living eyes, the anterior and posterior parts of the zonule need independent force directions. Choice of material properties affects which theory of accommodation is supported.

  9. Explaining the convector effect in canopy turbulence by means of large-eddy simulation

    DOE PAGES

    Banerjee, Tirtha; De Roo, Frederik; Mauder, Matthias

    2017-06-20

    Semi-arid forests are found to sustain a massive sensible heat flux in spite of having a low surface to air temperature difference by lowering the aerodynamic resistance to heat transfer (rH) – a property called the canopy convector effect (CCE). In this work large-eddy simulations are used to demonstrate that the CCE appears more generally in canopy turbulence. It is indeed a generic feature of canopy turbulence: rH of a canopy is found to reduce with increasing unstable stratification, which effectively increases the aerodynamic roughness for the same physical roughness of the canopy. This relation offers a sufficient condition to constructmore » a general description of the CCE. In addition, we review existing parameterizations for rH from the evapotranspiration literature and test to what extent they are able to capture the CCE, thereby exploring the possibility of an improved parameterization.« less

  10. Explaining the convector effect in canopy turbulence by means of large-eddy simulation

    NASA Astrophysics Data System (ADS)

    Banerjee, Tirtha; De Roo, Frederik; Mauder, Matthias

    2017-06-01

    Semi-arid forests are found to sustain a massive sensible heat flux in spite of having a low surface to air temperature difference by lowering the aerodynamic resistance to heat transfer (rH) - a property called the canopy convector effect (CCE). In this work large-eddy simulations are used to demonstrate that the CCE appears more generally in canopy turbulence. It is indeed a generic feature of canopy turbulence: rH of a canopy is found to reduce with increasing unstable stratification, which effectively increases the aerodynamic roughness for the same physical roughness of the canopy. This relation offers a sufficient condition to construct a general description of the CCE. In addition, we review existing parameterizations for rH from the evapotranspiration literature and test to what extent they are able to capture the CCE, thereby exploring the possibility of an improved parameterization.

  11. Structure and properties of metal-exchanged zeolites studied using gradient-corrected and hybrid functionals. I. Structure and energetics

    NASA Astrophysics Data System (ADS)

    Göltl, Florian; Hafner, Jürgen

    2012-02-01

    The structural and energetic properties of purely siliceous, proton-, and Cu- and Co-exchanged chabazite have been studied using periodic density-functional (DFT) calculations with both conventional gradient-corrected exchange-correlation functionals and hybrid functionals mixing exact (i.e., Hartree-Fock) and DFT exchange. Spin-polarized and fixed-moment calculations have been performed to determine the equilibrium and excited spin-configurations of the metal-exchanged chabazites. For the purely siliceous chabazite, hybrid functionals predict a slightly more accurate cell volume and lattice geometry. For isolated Al/Si substitution sites, gradient-corrected functionals predict that the lattice distortion induced by the substitution preserves the local tetrahedral symmetry, whereas hybrid functionals lead to a distorted Al coordination with two short and two long Al-O bonds. Hybrid functionals yield a stronger cation-framework binding that conventional functionals in metal-exchanged zeolites, they favor shorter cation-oxygen bonds and eventually also a higher coordination of the cation. Both types of functionals predict the same spin in the ground-state. The structural optimization of the excited spin-states shows that the formation of a high-spin configuration leads to a strong lattice relaxation and a weaker cation-framework bonding. For both Cu- and Co-exchanged chabazite, the prediction of a preferred location of the cation in a six-membered ring of the zeolite agrees with experiment, but the energy differences between possible cation locations and the lattice distortion induced by the Al/Si substitution and the bonding of the cation depends quite significantly on the choice of the functional. All functionals predict similar energy differences for excited spin states. Spin-excitations are shown to be accompanied by significant changes in the cation coordination, which are more pronounced with hybrid functionals. The consequences of electronic spectra and

  12. Effects of glycerol and moisture gradient on thermomechanical properties of white bread.

    PubMed

    Baik, M Y; Chinachoti, P

    2001-08-01

    The thermomechanical properties of breadcrumb were investigated using dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC). The main transition (T(1), near 0 degrees C) shifted to lower temperature with added glycerol due to freezing point depression. The low-temperature transition (T(3), approximately -50 degrees C), found only in high-glycerol (8.8%) bread, suggested that of excess or phase-separated glycerol. The high-temperature transition (T(2), 60-85 degrees C) appeared only in aged breadcrumbs; its temperature range was correlated well with the amylopectin melting transition (DSC) but its tan delta amplitude did not correlate well with the amylopectin melting enthalpy (r(2) = 0.72). On the other hand, the change of E' ' (viscous behavior) suggested that T(2) might be related to the change in the amorphous region. Domain-to-domain (amorphous) and crumb-to-crust moisture migrations are two critical phenomenological changes associated with aging and could lead to significant local dehydration of some amorphous regions contributing to mechanical firming during storage.

  13. Bacterial adaptation to sublethal antibiotic gradients can change the ecological properties of multitrophic microbial communities.

    PubMed

    Friman, Ville-Petri; Guzman, Laura Melissa; Reuman, Daniel C; Bell, Thomas

    2015-05-07

    Antibiotics leak constantly into environments due to widespread use in agriculture and human therapy. Although sublethal concentrations are well known to select for antibiotic-resistant bacteria, little is known about how bacterial evolution cascades through food webs, having indirect effect on species not directly affected by antibiotics (e.g. via population dynamics or pleiotropic effects). Here, we used an experimental evolution approach to test how temporal patterns of antibiotic stress, as well as migration within metapopulations, affect the evolution and ecology of microcosms containing one prey bacterium, one phage and two protist predators. We found that environmental variability, autocorrelation and migration had only subtle effects for population and evolutionary dynamics. However, unexpectedly, bacteria evolved greatest fitness increases to both antibiotics and enemies when the sublethal levels of antibiotics were highest, indicating positive pleiotropy. Crucially, bacterial adaptation cascaded through the food web leading to reduced predator-to-prey abundance ratio, lowered predator community diversity and increased instability of populations. Our results show that the presence of natural enemies can modify and even reverse the effects of antibiotics on bacteria, and that antibiotic selection can change the ecological properties of multitrophic microbial communities by having indirect effects on species not directly affected by antibiotics.

  14. Bacterial adaptation to sublethal antibiotic gradients can change the ecological properties of multitrophic microbial communities

    PubMed Central

    Friman, Ville-Petri; Guzman, Laura Melissa; Reuman, Daniel C.; Bell, Thomas

    2015-01-01

    Antibiotics leak constantly into environments due to widespread use in agriculture and human therapy. Although sublethal concentrations are well known to select for antibiotic-resistant bacteria, little is known about how bacterial evolution cascades through food webs, having indirect effect on species not directly affected by antibiotics (e.g. via population dynamics or pleiotropic effects). Here, we used an experimental evolution approach to test how temporal patterns of antibiotic stress, as well as migration within metapopulations, affect the evolution and ecology of microcosms containing one prey bacterium, one phage and two protist predators. We found that environmental variability, autocorrelation and migration had only subtle effects for population and evolutionary dynamics. However, unexpectedly, bacteria evolved greatest fitness increases to both antibiotics and enemies when the sublethal levels of antibiotics were highest, indicating positive pleiotropy. Crucially, bacterial adaptation cascaded through the food web leading to reduced predator-to-prey abundance ratio, lowered predator community diversity and increased instability of populations. Our results show that the presence of natural enemies can modify and even reverse the effects of antibiotics on bacteria, and that antibiotic selection can change the ecological properties of multitrophic microbial communities by having indirect effects on species not directly affected by antibiotics. PMID:25833854

  15. Relationships between soil properties and community structure of soil macroinvertebrates in oak-history forests along an acidic deposition gradient

    SciTech Connect

    Kuperman, R.G.

    1996-02-01

    Soil macroinvertebrate communities were studied in ecologically analogous oak-hickory forests across a three-state atmospheric pollution gradient in Illinois, Indiana, and Ohio. The goal was to investigate changes in the community structure of soil fauna in study sites receiving different amounts of acidic deposition for several decades and the possible relationships between these changes and physico-chemical properties of soil. The study revealed significant differences in the numbers of soil animals among the three study sites. The sharply differentiated pattern of soil macroinvertebrate fauna seems closely linked to soil chemistry. Significant correlations of the abundance of soil macroinvertebrates with soil parameters suggest that their populations could have been affected by acidic deposition in the region. Abundance of total soil macroinvertebrates decreased with the increased cumulative loading of acidic deposition. Among the groups most sensitive to deposition were: earthworms gastropods, dipteran larvae, termites, and predatory beetles. The results of the study support the hypothesis that chronic long-term acidic deposition could aversely affect the soil decomposer community which could cause lower organic matter turnover rates leading to an increase in soil organic matter content in high deposition sites.

  16. The renaturation of procarboxypeptidase B by urea gradient gel filtration and some properties of recombinant carboxypeptidase B.

    PubMed

    Xiao-Yan, Zhang; Su-Xia, Li; Qin-Sheng, Yuan

    2005-10-01

    A new pro-carboxypeptidase (pCPB) gene was cloned by RT-PCR from SD rat pancreas and its overexpression in Escherichia coli resulted in the formation of inclusion bodies (IBs). The IBs of pCPB were solubilized in 8 M urea and successively refolded by urea gradient gel filtration. Subsequently, the renatured pCPB was digested by trypsin. Recombinant active CPB was obtained by passing through DEAE-FF ion exchange and Sephadex-G100 chromatographic column. Capillary electrophoresis assay showed that the purity of the recombinant CPB (rCPB) exceeded 90%. Further, some properties of rCPB were characterized. The optimum of activity was achieved at pH 7-9. The activity of rCPB was inhibited by typical metal chelating agents (EDTA) and Hg2+, and was activated by Co2+ and heat treatment at 40 degrees C. The two-dimension electrophoresis map of rCPB showed that the pI value of rCPB was 5.35. UV absorbance spectrum of the enzyme showed that an absorbance maximum was at 277 nm.

  17. Systems Analysis of the Dynamic Inflammatory Response to Tissue Damage Reveals Spatiotemporal Properties of the Wound Attractant Gradient.

    PubMed

    Weavers, Helen; Liepe, Juliane; Sim, Aaron; Wood, Will; Martin, Paul; Stumpf, Michael P H

    2016-08-08

    In the acute inflammatory phase following tissue damage, cells of the innate immune system are rapidly recruited to sites of injury by pro-inflammatory mediators released at the wound site. Although advances in live imaging allow us to directly visualize this process in vivo, the precise identity and properties of the primary immune damage attractants remain unclear, as it is currently impossible to directly observe and accurately measure these signals in tissues. Here, we demonstrate that detailed information about the attractant signals can be extracted directly from the in vivo behavior of the responding immune cells. By applying inference-based computational approaches to analyze the in vivo dynamics of the Drosophila inflammatory response, we gain new detailed insight into the spatiotemporal properties of the attractant gradient. In particular, we show that the wound attractant is released by wound margin cells, rather than by the wounded tissue per se, and that it diffuses away from this source at rates far slower than those of previously implicated signals such as H2O2 and ATP, ruling out these fast mediators as the primary chemoattractant. We then predict, and experimentally test, how competing attractant signals might interact in space and time to regulate multi-step cell navigation in the complex environment of a healing wound, revealing a period of receptor desensitization after initial exposure to the damage attractant. Extending our analysis to model much larger wounds, we uncover a dynamic behavioral change in the responding immune cells in vivo that is prognostic of whether a wound will subsequently heal or not. VIDEO ABSTRACT.

  18. Self-assembling gradient copolymers of vinylimidazol and (acrylic)ibuprofen with anti-inflammatory and zinc chelating properties.

    PubMed

    Suárez, Patricia; Rojo, Luis; González-Gómez, Álvaro; Román, Julio San

    2013-09-01

    Novel gradient copolymers of hydrophilic 1-vinylimidazol and hydrophobic methacrylic derivative of ibuprofen prepared by free radical polymerization are described. The heterogeneous distribution of monomeric units along the polymeric chains leads to a gradient distribution of the hydrophobic and hydrophilic sequences responsible of nanoparticles formation through a self-assembling mechanism, capable of tune the water permeation due to the ionizable imidazole moieties and their gradient profile along the macromolecules, exhibiting pH and composition dependent effect in terms of diameter, zeta potential, acid-base buffering, ibuprofen release and chelating capacities, responsible of matrix metalloproteinase dysfunction showing anti-inflammatory activity in a nitric oxide inhibition assay.

  19. Functional gradients in the pericarp of the green coconut inspire asymmetric fibre-composites with improved impact strength, and preserved flexural and tensile properties.

    PubMed

    Graupner, Nina; Labonte, David; Humburg, Heide; Buzkan, Tayfun; Dörgens, Anna; Kelterer, Wiebke; Müssig, Jörg

    2017-02-28

    Here we investigate the mechanical properties and structural design of the pericarp of the green coconut (Cocos nucifera L.). The pericarp showed excellent impact characteristics, and mechanical tests of its individual components revealed gradients in stiffness, strength and elongation at break from the outer to the inner layer of the pericarp. In order to understand more about the potential effect of such gradients on 'bulk' material properties, we designed simple, graded, cellulose fibre-reinforced polylactide (PLA) composites by stacking layers reinforced with fibres of different mechanical properties. Tensile properties of the graded composites were largely determined by the 'weakest' fibre, irrespective of the fibre distribution. However, a graded design led to pronounced asymmetric bending and impact properties. Bio-inspired, asymmetrically graded composites showed a flexural strength and modulus comparable to that of the strongest reference samples, but the elongation at maximum load was dependent on the specimen orientation. The impact strength of the graded composites showed a similar orientation-dependence, and peak values exceeded the impact strength of a non-graded reference composite containing identical fibre fractions by up to a factor of three. In combination, our results show that an asymmetric, systematic variation of fibre properties can successfully combine desirable properties of different fibre types, suggesting new routes for the development of high-performance composites, and improving our understanding of the structure-function relationship of the coconut pericarp.

  20. Transport in Halobacterium Halobium: Light-Induced Cation-Gradients, Amino Acid Transport Kinetics, and Properties of Transport Carriers

    NASA Technical Reports Server (NTRS)

    Lanyi, Janos K.

    1977-01-01

    Cell envelope vesicles prepared from H. halobium contain bacteriorhodopsin and upon illumination protons are ejected. Coupled to the proton motive force is the efflux of Na(+). Measurements of Na-22 flux, exterior pH change, and membrane potential, Delta(psi) (with the dye 3,3'-dipentyloxadicarbocyanine) indicate that the means of Na(+) transport is sodium/proton exchange. The kinetics of the pH changes and other evidence suggests that the antiport is electrogenic (H(+)/Na(++ greater than 1). The resulting large chemical gradient for Na(+) (outside much greater than inside), as well as the membrane potential, will drive the transport of 18 amino acids. The I9th, glutamate, is unique in that its accumulation is indifferent to Delta(psi): this amino acid is transported only when a chemical gradient for Na(+) is present. Thus, when more and more NaCl is included in the vesicles glutamate transport proceeds with longer and longer lags. After illumination the gradient of H+() collapses within 1 min, while the large Na(+) gradient and glutamate transporting activity persists for 10- 15 min, indicating that proton motive force is not necessary for transport. A chemical gradient of Na(+), arranged by suspending vesicles loaded with KCl in NaCl, drives glutamate transport in the dark without other sources of energy, with V(sub max) and K(sub m) comparable to light-induced transport. These and other lines of evidence suggest that the transport of glutamate is facilitated by symport with Na(+), in an electrically neutral fashion, so that only the chemical component of the Na(+) gradient is a driving force.

  1. Transport in Halobacterium Halobium: Light-Induced Cation-Gradients, Amino Acid Transport Kinetics, and Properties of Transport Carriers

    NASA Technical Reports Server (NTRS)

    Lanyi, Janos K.

    1977-01-01

    Cell envelope vesicles prepared from H. halobium contain bacteriorhodopsin and upon illumination protons are ejected. Coupled to the proton motive force is the efflux of Na(+). Measurements of Na-22 flux, exterior pH change, and membrane potential, Delta(psi) (with the dye 3,3'-dipentyloxadicarbocyanine) indicate that the means of Na(+) transport is sodium/proton exchange. The kinetics of the pH changes and other evidence suggests that the antiport is electrogenic (H(+)/Na(++ greater than 1). The resulting large chemical gradient for Na(+) (outside much greater than inside), as well as the membrane potential, will drive the transport of 18 amino acids. The I9th, glutamate, is unique in that its accumulation is indifferent to Delta(psi): this amino acid is transported only when a chemical gradient for Na(+) is present. Thus, when more and more NaCl is included in the vesicles glutamate transport proceeds with longer and longer lags. After illumination the gradient of H+() collapses within 1 min, while the large Na(+) gradient and glutamate transporting activity persists for 10- 15 min, indicating that proton motive force is not necessary for transport. A chemical gradient of Na(+), arranged by suspending vesicles loaded with KCl in NaCl, drives glutamate transport in the dark without other sources of energy, with V(sub max) and K(sub m) comparable to light-induced transport. These and other lines of evidence suggest that the transport of glutamate is facilitated by symport with Na(+), in an electrically neutral fashion, so that only the chemical component of the Na(+) gradient is a driving force.

  2. Gradient Driven Fluctuations

    NASA Technical Reports Server (NTRS)

    Cannell, David

    2005-01-01

    We have worked with our collaborators at the University of Milan (Professor Marzio Giglio and his group-supported by ASI) to define the science required to measure gradient driven fluctuations in the microgravity environment. Such a study would provide an accurate test of the extent to which the theory of fluctuating hydrodynamics can be used to predict the properties of fluids maintained in a stressed, non-equilibrium state. As mentioned above, the results should also provide direct visual insight into the behavior of a variety of fluid systems containing gradients or interfaces, when placed in the microgravity environment. With support from the current grant, we have identified three key systems for detailed investigation. These three systems are: 1) A single-component fluid to be studied in the presence of a temperature gradient; 2) A mixture of two organic liquids to be studied both in the presence of a temperature gradient, which induces a steady-state concentration gradient, and with the temperature gradient removed, but while the concentration gradient is dying by means of diffusion; 3) Various pairs of liquids undergoing free diffusion, including a proteidbuffer solution and pairs of mixtures having different concentrations, to allow us to vary the differences in fluid properties in a controlled manner.

  3. Exchange-Correlation Functional with Good Accuracy for Both Structural and Energetic Properties while Depending Only on the Density and Its Gradient.

    PubMed

    Peverati, Roberto; Truhlar, Donald G

    2012-07-10

    The generalized gradient approximation (GGA) has been a workhorse exchange-correlation functional for electronic structure studies of extended systems (liquid-phase reactions, solids, heterogeneous and enzymatic catalysis, biopolymers) because its dependence on only the spin-labeled electron densities and their reduced gradients makes it the most affordable choice that produces realistic results for thermochemistry. However, much recent research has focused on its poor performance for solid-state lattice constants; the results for lattice constants can be improved but only at the cost of making the energetic predictions worse. In the present article, we propose a new density functional, called N12, which may be thought of as a generalization of range-separated functionals. The N12 functional depends only on the spin-labeled electron densities and their reduced gradients, but with a new kind of nonseparable term that gives it much greater flexibility. The N12 functional is the first exchange-correlation functional depending only on the spin-labeled electron densities and their reduced gradients that simultaneously provides good accuracy for the four key energetic and structural properties of solids and molecules, namely, solid-state cohesive energies and lattice constants and molecular atomization energies and bond lengths.

  4. Magnetic properties and high-frequency characteristics of FeCoAlO gradient composition thin films

    NASA Astrophysics Data System (ADS)

    Zheng, Fu; Luo, Feilong; Lou, Yuanfu; Wang, Ying; Bai, Jianmin; Wei, Dan; Liu, Xiaoxi; Wei, Fulin

    2012-04-01

    5 × 25 mm FeCoAlO gradient composition thin film was prepared with composite target by using RF magnetron sputtering. The Al-O composition gradient along the length direction of the film was introduced by Al2O3 chips asymmetrically arrayed on a Fe70Co30 target disk. The film was divided into five equal segments. All samples showed a low coercive force Hc of 4 - 8 Oe. The saturation magnetization 4πMs increased continuously from 17.3 kGs for sample 1 (has more Al-O content) to 19.7 kGs for sample 5 and it was consistent with the increasing of Fe-Co composition. Meanwhile, these samples showed different anisotropy behaviors relating with Al-O composition. The sample 1 exhibited the same magnetization curve along the directions of G‖ and G⊥ (G‖ and G⊥ are parallel and perpendicular to the direction of the Al-O composition gradient, respectively). In both of G‖ & G⊥ directions, the sample 1 showed a resonance frequency (fr) of around 2.6 - 3.0 GHz, while, in G‖ direction, it showed a high value of real permeability μ'. The sample 5 exhibited a distinct in-plane uniaxial anisotropy and a good high-frequency response of 3.0 GHz resonance frequency. So these films having gradient composition exhibit are suggested for the use in integrated magnetic devices working in the GHz frequency range.

  5. Compressible boundary layer with normal pressure gradients: Quasi-similarity equations - Their properties at the wall and at sharp and blunt leading edges.

    NASA Technical Reports Server (NTRS)

    Seginer, A.

    1972-01-01

    The failure of most viscous-inviscid interaction methods at strong interactions is attributed to the presence of a normal pressure gradient. A new theory is proposed for supersonic laminar boundary layers that can generate normal pressure gradients. The Navier-Stokes equations are reexamined by an order of magnitude analysis and all first and second order terms are retained. The approximation is found to be dependent not only on the boundary layer thickness but also on the ratio of the dimensionless viscosity and density. The equations are transformed into two quasi-similar, nonlinear, third order, ordinary integro-differential equations for the velocity and pressure as functions of a single transverse variable. The properties of the equations at the boundaries are discussed.

  6. Laser-Doppler acoustic probing of granular media with in-depth property gradient and varying pore pressures

    SciTech Connect

    Bodet, L.; Dhemaied, A.; Mourgues, R.; Tournat, V.; Rejiba, F.

    2012-05-24

    Non-contacting ultrasonic techniques recently proved to be efficient in the physical modeling of seismic-wave propagation at various application scales, as for instance in the context of geological analogue and seismic modeling. An innovative experimental set-up is proposed here to perform laser-Doppler acoustic probing of unconsolidated granular media with varying pore pressures. The preliminary experiments presented here provide reproducible results and exploitable data, thus validating both the proposed medium preparation and pressure gradient generation procedure.

  7. Shell properties of commercial clam Chamelea gallina are influenced by temperature and solar radiation along a wide latitudinal gradient

    PubMed Central

    Gizzi, Francesca; Caccia, Maria Giulia; Simoncini, Ginevra Allegra; Mancuso, Arianna; Reggi, Michela; Fermani, Simona; Brizi, Leonardo; Fantazzini, Paola; Stagioni, Marco; Falini, Giuseppe; Piccinetti, Corrado; Goffredo, Stefano

    2016-01-01

    Phenotype can express different morphologies in response to biotic or abiotic environmental influences. Mollusks are particularly sensitive to different environmental parameters, showing macroscale shell morphology variations in response to environmental parameters. Few studies concern shell variations at the different scale levels along environmental gradients. Here, we investigate shell features at the macro, micro and nanoscale, in populations of the commercially important clam Chamelea gallina along a latitudinal gradient (~400 km) of temperature and solar radiation in the Adriatic Sea (Italian cost). Six populations of clams with shells of the same length were analyzed. Shells from the warmest and the most irradiated population were thinner, with more oval shape, more porous and lighter, showing lower load fracture. However, no variation was observed in shell CaCO3 polymorphism (100% aragonite) or in compositional and textural shell parameters, indicating no effect of the environmental parameters on the basic processes of biomineralization. Because of the importance of this species as commercial resource in the Adriatic Sea, the experimentally quantified and significant variations of mass and fracture load in C. gallina shells along the latitudinal gradient may have economic implications for fisheries producing different economical yield for fishermen and consumers along the Adriatic coastline. PMID:27805037

  8. The structure and properties of single-layer and gradient-layered coatings of the Ti–Al–Si–Cr–Mo–S–N system

    SciTech Connect

    Ovchinnikov, Stanislav Pinzhin, Yurii

    2015-10-27

    Using the method of microprobe analysis and transmission electron microscopy, the influence of obtaining conditions upon particular elemental composition and growth structure coatings of Ti–Al–Si–Mo–S–N system was studied. The possibility of formation and characteristics of the structural and elastic-stress state single-layer coatings with nanoscale columnar or equiaxed grains and gradient-layered, combining two types of selected structure, was defined. On the basis of hardness, tribological properties and coating hardness, a conclusion was made about the relative prospects of its use as wear-resistant coatings with a nanocrystalline structure.

  9. Physicochemical properties and carbon density of alpine sod layer with their variation across habitat gradients in the Zoige Plateau

    NASA Astrophysics Data System (ADS)

    Peixi, Su; Zijuan, Zhou; Rui, Shi; tingting, Xie

    2017-04-01

    The alpine sod layer is a soft, tough and resistant to shifting surface soil layer under the formation of the natural vegetation in the plateau cold region, understanding its ecological function is a prerequisite to promote grass and animal husbandry production for recuperation and protection, and the active use of project construction. Based on the extensive investigation on the alpine vegetation of the Zoige Plateau in the Eastern Qinghai-Tibetan Plateau of China, set up moisture gradient community sample plots: swamp, degraded swamp, swampy meadow, wet meadow, dry meadow and degraded meadow, and the elevation gradient community sample plots: subalpine meadow, subalpine shrub meadow, alpine shrub meadow and alpine meadow were set up. The sod layer bulk density, soil particle composition and soil organic carbon (SOC) content of different types of community plots were analyzed and to compare its carbon sequestration capacity on the moisture and elevation gradients. The results showed that the average thickness of the sod layer was 30 cm, the bulk density of the swamp was the smallest, and the SOC content was above 300 g/kg. The bulk density of degraded meadow was the highest while its SOC content was decreased significantly. The SOC density of sod layer in different communities was between 10 and 24 kg C/m2, and decreased with the decreasing of soil water availability, and meadow degradation significantly decreased the soil organic carbon storage in sod layer. The sod layer SOC density of alpine shrub meadow was 15% higher than that of meadow on the altitudinal gradient. It was concluded that the mass water content threshold value for maintaining the sod layer stable is 30%. In the degraded succession of alpine vegetation from swamp to meadow, the bulk density and compactness of sod layer became larger, while the organic carbon content, carbon density and carbon storage decreased. The higher the gravel content of swamp, the more easily degraded, and the higher the

  10. Gradient-index POF without dopants: how the optical properties can be controlled by sole temperature treatment

    NASA Astrophysics Data System (ADS)

    Bunge, C.-A.; Schüppert, M.; Beckers, M.; Stepniak, G.; Vad, T.; Seide, G.; Gries, T.

    2016-09-01

    In this paper we present a novel melt-spinning fabrication process for graded-index polymer optical fibers that completely avoids additional dopants for the formation of the refractive-index profile. In the presented process the meltspun fiber is rapidly cooled down so that the inner and outer parts of the fiber solidify at different speeds resulting in a density gradient. This density variation leads to a refractive-index profile without any further dopants. We present achieved results for fibers made of PMMA, and also first preliminary results for bio polymers such as TPU.

  11. A linear gradient line source facilitates the use of diffusion models with high order approximation for efficient, accurate turbid sample optical properties recovery.

    PubMed

    Lee, Ming-Wei; Hung, Cheng-Hung; Liao, Jung-Li; Cheng, Nan-Yu; Hou, Ming-Feng; Tseng, Sheng-Hao

    2014-10-01

    In this paper, we demonstrate that a scanning MEMS mirror can be employed to create a linear gradient line source that is equivalent to a planar source. This light source setup facilitates the use of diffusion models of increased orders of approximation having closed form solution, and thus enhance the efficiency and accuracy in sample optical properties recovery. In addition, compared with a regular planar light source, the linear gradient line source occupies much less source area and has an elevated measurement efficiency. We employed a δ-P1 diffusion equation with a closed form solution and carried out a phantom study to understand the performance of this new method in determining the absorption and scattering properties of turbid samples. Moreover, our Monte Carlo simulation results indicated that this geometry had probing depths comparable to those of the conventional diffuse reflectance measurement geometry with a source-detector separation of 3 mm. We expect that this new source setup would facilitate the investigating of superficial volumes of turbid samples in the wavelength regions where tissue absorption coefficients are comparable to scattering coefficients.

  12. An experimental study of the properties of surface pressure fluctuations in strong adverse pressure gradient turbulent boundary layers

    NASA Technical Reports Server (NTRS)

    Simpson, R. L.

    1984-01-01

    Experimental data were obtained on blade self-noise generation by strong adverse-pressure-gradient attached boundary layers and by separated turbulent boundary layers that accompany stall. Two microphones were calibrated, placed in plastic housing, and installed in a wind tunnel where observations of acoustic and turbulent signals permitted decomposition of the surface pressure fluctuation signals into the propagated acoustic part and the turbulent-flow generated portion. To determine the convective wave speed of the turbulent contributions, the microphones were spaced a small distance apart in the streamwise direction and correlations were obtained. The turbulent surface pressure spectra upstream of detachment and downstream of the beginning of separation are discussed as well as measurements of turbulent velocity spectra and wavespeeds.

  13. Bar-coded pyrosequencing reveals shared bacterial community properties along the temperature gradients of two alkaline hot springs in Yellowstone National Park.

    PubMed

    Miller, Scott R; Strong, Aaron L; Jones, Kenneth L; Ungerer, Mark C

    2009-07-01

    An understanding of how communities are organized is a fundamental goal of ecology but one which has historically been elusive for microbial systems. We used a bar-coded pyrosequencing approach targeting the V3 region of the bacterial small-subunit rRNA gene to address the factors that structure communities along the thermal gradients of two alkaline hot springs in the Lower Geyser Basin of Yellowstone National Park. The filtered data set included a total of nearly 34,000 sequences from 39 environmental samples. Each was assigned to one of 391 operational taxonomic units (OTUs) identified by their unique V3 sequence signatures. Although the two hot springs differed in their OTU compositions, community resemblance and diversity changed with strikingly similar dynamics along the two outflow channels. Two lines of evidence suggest that these community properties are controlled primarily by environmental temperature. First, community resemblance decayed exponentially with increasing differences in temperature between samples but was only weakly correlated with physical distance. Second, diversity decreased with increasing temperature at the same rate along both gradients but was uncorrelated with other measured environmental variables. This study also provides novel insights into the nature of the ecological interactions among important taxa in these communities. A strong negative association was observed between cyanobacteria and the Chloroflexi, which together accounted for approximately 70% of the sequences sampled. This pattern contradicts the longstanding hypothesis that coadapted lineages of these bacteria maintain tightly cooccurring distributions along these gradients as a result of a producer-consumer relationship. We propose that they instead compete for some limiting resource(s).

  14. Bar-Coded Pyrosequencing Reveals Shared Bacterial Community Properties along the Temperature Gradients of Two Alkaline Hot Springs in Yellowstone National Park▿ †

    PubMed Central

    Miller, Scott R.; Strong, Aaron L.; Jones, Kenneth L.; Ungerer, Mark C.

    2009-01-01

    An understanding of how communities are organized is a fundamental goal of ecology but one which has historically been elusive for microbial systems. We used a bar-coded pyrosequencing approach targeting the V3 region of the bacterial small-subunit rRNA gene to address the factors that structure communities along the thermal gradients of two alkaline hot springs in the Lower Geyser Basin of Yellowstone National Park. The filtered data set included a total of nearly 34,000 sequences from 39 environmental samples. Each was assigned to one of 391 operational taxonomic units (OTUs) identified by their unique V3 sequence signatures. Although the two hot springs differed in their OTU compositions, community resemblance and diversity changed with strikingly similar dynamics along the two outflow channels. Two lines of evidence suggest that these community properties are controlled primarily by environmental temperature. First, community resemblance decayed exponentially with increasing differences in temperature between samples but was only weakly correlated with physical distance. Second, diversity decreased with increasing temperature at the same rate along both gradients but was uncorrelated with other measured environmental variables. This study also provides novel insights into the nature of the ecological interactions among important taxa in these communities. A strong negative association was observed between cyanobacteria and the Chloroflexi, which together accounted for ∼70% of the sequences sampled. This pattern contradicts the longstanding hypothesis that coadapted lineages of these bacteria maintain tightly cooccurring distributions along these gradients as a result of a producer-consumer relationship. We propose that they instead compete for some limiting resource(s). PMID:19429553

  15. Validating spatial structure in canopy water content using geostatistics

    NASA Technical Reports Server (NTRS)

    Sanderson, E. W.; Zhang, M. H.; Ustin, S. L.; Rejmankova, E.; Haxo, R. S.

    1995-01-01

    Heterogeneity in ecological phenomena are scale dependent and affect the hierarchical structure of image data. AVIRIS pixels average reflectance produced by complex absorption and scattering interactions between biogeochemical composition, canopy architecture, view and illumination angles, species distributions, and plant cover as well as other factors. These scales affect validation of pixel reflectance, typically performed by relating pixel spectra to ground measurements acquired at scales of 1m(exp 2) or less (e.g., field spectra, foilage and soil samples, etc.). As image analysis becomes more sophisticated, such as those for detection of canopy chemistry, better validation becomes a critical problem. This paper presents a methodology for bridging between point measurements and pixels using geostatistics. Geostatistics have been extensively used in geological or hydrogeolocial studies but have received little application in ecological studies. The key criteria for kriging estimation is that the phenomena varies in space and that an underlying controlling process produces spatial correlation between the measured data points. Ecological variation meets this requirement because communities vary along environmental gradients like soil moisture, nutrient availability, or topography.

  16. Sedimentation properties in density gradients correspond with levels of sperm DNA fragmentation, chromatin compaction and binding affinity to hyaluronic acid.

    PubMed

    Torabi, Forough; Binduraihem, Adel; Miller, David

    2017-03-01

    Mature spermatozoa bind hyaluronic acid in the extracellular matrix via hyaladherins. Immature spermatozoa may be unable to interact because they do not express the appropriate hyaladherins on their surface. Fresh human semen samples were fractionated using differential density gradient centrifugation (DDGC) and the ability of these fractions to bind hyaluronic acid was evaluated. The presence of sperm hyaladherins was also assessed. CD44 was located mainly on the acrosome and equatorial segment and became more restricted to the equatorial segment in capacitated spermatozoa. Hyaluronic acid-TRITC (hyaluronic acid conjugated with tetramethylrhodamine isothiocyanante), a generic hyaluronic-acid-binding reagent, labelled the membrane and the neck region, particularly after capacitation. Sperm populations obtained after DDGC or after interaction with hyaluronic acid were assessed for DNA fragmentation and chromatin maturity. Strong relationships between both measures and sperm sedimentation and hyaluronic-acid-binding profiles were revealed. Capacitation enhanced hyaluronic acid binding of both DDGC-pelleted sperm and sperm washed free of seminal fluid. In conclusion, hyaladherins were detected on human sperm and a higher capacity for sperm hyaluronic-acid-binding was shown to correspond with their DDGC sedimentation profiles and with lower levels of DNA fragmentation and better chromatin maturity. Capacitation induced changes in the distribution and presence of hyaladherins may enhance hyaluronic-acid-binding.

  17. Gradient shape-persistent pi-conjugated dendrimers for light-harvesting: synthesis, photophysical properties, and energy funneling.

    PubMed

    Wang, Jin-Liang; Yan, Jing; Tang, Zheng-Ming; Xiao, Qi; Ma, Yuguo; Pei, Jian

    2008-07-30

    A new class of pi-conjugated dendrimers G0, G1, and G2 was developed through a double-stage divergent/convergent growth approach, in which 5,5,10,10,15,15-hexahexyltruxene was employed as the node and oligo(thienylethynylene)s (OTEs) with different lengths as the branching moieties. The dendrimers were fully characterized by (1)H and (13)C NMR, elemental analysis, gel permeation chromatography, and MALDI-TOF MS. Also, by using atomic force microscopy, it was observed that dendrimer G2 laid nearly flat on the mica surface as a single molecule. Dynamic light scattering results showed that the molecule retained its relatively flat shape in solution. To our best knowledge, dendrimer G2, with a radius approaching 10 nm and a molecular weight of 27 072 Da, was the largest among reported second generation dendrimers. The energy gradient in G2 was constructed by linking OTEs of increasing effective conjugation lengths from the dendritic rim to the core. The intramolecular energy transfer process was studied using steady-state UV-vis absorption and photoluminescent spectroscopies, as well as time-resolved fluorescence spectroscopy. Our structurally extended dendrimers showed an excellent energy funneling ability (their energy transfer efficiencies were all over 95%). All results demonstrate that these dendrimers are promising candidates as light-harvesting materials for optoelectronic devices.

  18. Bias-graded deposition and tribological properties of Ti-contained a-C gradient composite film on Ti6Al4V alloy

    NASA Astrophysics Data System (ADS)

    Cai, J. B.; Wang, X. L.; Bai, W. Q.; Zhao, X. Y.; Wang, T. Q.; Tu, J. P.

    2013-08-01

    Ti-contained a-C gradient composite film with a thickness 1.5 μm was deposited on medical Ti6Al4V alloy substrate using a closed field unbalanced magnetron sputtering with bias-graded voltage through -20 V to -150 V. The mechanical and tribological properties were evaluated from nanoindentation, scratch test and ball-on-disk tribometer. Compared with the constant-bias film deposited at -150 V, the bias-graded film has the approximate hardness (19 GPa) but high toughness and adhesion strength. At a normal load of 10 N, the bias-graded composite film shows a low friction coefficient of 0.08 and wear rate of 2.89 × 10-16 m3 N-1 m-1 in ambient air. While in Hanks’ solution, the film has the same low friction coefficient but low wear rate of 4.63 × 10-17 m3 N-1 m-1. Excellent wear resistance in Hanks’ solution may bring about a biological application for the Ti-contained a-C gradient composite film.

  19. Changes in canopy fuels and fire behavior after ponderosa pine restoration treatments: A landscape perspective

    Treesearch

    J. P. Roccaforte; P. Z. Fule

    2008-01-01

    (Please note, this is an abstract only) We modeled crown fire behavior and assessed changes in canopy fuels before and after the implementation of restoration treatments in a ponderosa pine landscape at Mt. Trumbull, Arizona. We measured 117 permanent plots before (1996/1997) and after (2003) thinning and burning treatments. The plots are evenly distributed across the...

  20. High Gradient Accelerator Research

    SciTech Connect

    Temkin, Richard

    2016-07-12

    The goal of the MIT program of research on high gradient acceleration is the development of advanced acceleration concepts that lead to a practical and affordable next generation linear collider at the TeV energy level. Other applications, which are more near-term, include accelerators for materials processing; medicine; defense; mining; security; and inspection. The specific goals of the MIT program are: • Pioneering theoretical research on advanced structures for high gradient acceleration, including photonic structures and metamaterial structures; evaluation of the wakefields in these advanced structures • Experimental research to demonstrate the properties of advanced structures both in low-power microwave cold test and high-power, high-gradient test at megawatt power levels • Experimental research on microwave breakdown at high gradient including studies of breakdown phenomena induced by RF electric fields and RF magnetic fields; development of new diagnostics of the breakdown process • Theoretical research on the physics and engineering features of RF vacuum breakdown • Maintaining and improving the Haimson / MIT 17 GHz accelerator, the highest frequency operational accelerator in the world, a unique facility for accelerator research • Providing the Haimson / MIT 17 GHz accelerator facility as a facility for outside users • Active participation in the US DOE program of High Gradient Collaboration, including joint work with SLAC and with Los Alamos National Laboratory; participation of MIT students in research at the national laboratories • Training the next generation of Ph. D. students in the field of accelerator physics.

  1. Joint analysis of GOCE gravity gradients data of gravitational potential and of gravity with seismological and geodynamic observations to infer mantle properties

    NASA Astrophysics Data System (ADS)

    Greff-Lefftz, Marianne; Métivier, Laurent; Panet, Isabelle; Caron, Lambert; Pajot-Métivier, Gwendoline; Bouman, Johannes

    2016-04-01

    Joint analysis of the seismic velocities and geoid, gravity and gravity gradients are used to constrain the viscosity profile within the mantle as well as the lateral density variations. Recent ESA's Gravity field and steady-state Ocean Circulation Explorer measurements of the second-order derivatives of the Earth's gravity potential give new possibilities to determine these mantle properties. Using a simple mantle model and seismic tomography results, we investigate how the gravitational potential, the three components of the gravity vector and the gravity gradients can bring information on the radial viscosity profile and on the mantle mass anomalies. We start with lateral density variations in the Earth's mantle based either on slab history or deduced from seismic tomography. The main uncertainties are: for the latter case, the relationship between seismic velocity and density-the so-called density/velocity scaling factor-and for the former case, the variation with depth of the density contrast between the cold slabs and the surrounding mantle. We perform a Monte Carlo search for the viscosity and the density/velocity scaling factor profiles within the mantle, which allows to fit the observed geoid, gravity and gradients of gravity. We compute the posterior probability distribution of the unknown parameters, and find that the gravity gradients improve the estimate of the scaling factor within the upper mantle, because of their sensitivity to the masses within the upper mantle, whereas the geoid and the gravity better constrain the scaling factor in the lower mantle. In the upper mantle, it is less than 0.02 in the upper part and about 0.08-0.14 in the lower part, and it is significantly larger for depths greater than 1200 km (about 0.32-0.34). In any case, the density/velocity scaling factor between 670 and 1150 km depth is not well constrained. We show that the viscosity of the upper part of the mantle is strongly correlated with the viscosity of the lower part

  2. Low Thermal Gradient Czochralski growth of large CdWO4 crystals and electronic properties of (010) cleaved surface

    NASA Astrophysics Data System (ADS)

    Atuchin, V. V.; Galashov, E. N.; Khyzhun, O. Y.; Bekenev, V. L.; Pokrovsky, L. D.; Borovlev, Yu. A.; Zhdankov, V. N.

    2016-04-01

    The crystal growth of large high-quality inclusion-free CdWO4 crystals, 110 mm in diameter and mass up to 20 kg, has been carried out by the Low Thermal Gradient Czochralski (LTG Cz) technique. The high-purity CdWO4(010) surface has been prepared by cleavage and high structural quality of the surface has been verified by RHEED, revealing a system of Kikuchi lines. The chemical state and electronic structure of the surface have been studied using X-ray photoelectron spectroscopy (XPS) and X-ray emission spectroscopy (XES). The total and partial densities of states of the CdWO4 tungstate were calculated employing the first-principles full potential linearized augmented plane wave (FP-LAPW) method. The results indicate that the principal contributors to the valence band of CdWO4 are the Cd 4d, W 5d and O 2p states which contribute mainly at the bottom, in the central portion and at the top of the valence band, respectively, with also significant contributions of the mentioned states throughout the whole CdWO4 valence-band region. With respect to the occupation of the O 2p states, the results of the FP-LAPW calculations are confirmed by comparison on a common energy scale of the XPS valence-band spectrum and the XES band representing the energy distribution of the O 2p states in this compound. Additionally, the FP-LAPW data allow us to conclude that the CdWO4 tungstate is a non-direct semiconductor.

  3. Responses of plant species diversity and soil physical-chemical-microbial properties to Phragmites australis invasion along a density gradient.

    PubMed

    Uddin, M D Nazim; Robinson, Randall William

    2017-09-08

    The invasion of ecosystems by strongly colonising plants such as Phragmites australis is viewed as one of the greatest threats to plant diversity and soil properties. This study compared a range of diversity measures including soil properties and mycorrhizal potential under different degrees of Phragmites density among three populations in coastal wetland, Victoria, Australia. Species richness, evenness and Shanon-Wiener index had significantly higher values in low degree of Phragmites density in all populations. Higher densities had the lowest diversity, with Shannon-Wiener index = 0 and Simpson's index = 1 indicating its mono-specificity. Significant alterations in soil properties associated with different degrees of Phragmites density were noticed. These had interactive effects (population × density) on water content, dehydrogenase activity, microbial biomass (C, N and P) but not on pH, electrical conductivity, phenolics, organic carbon, and spore density. Furthermore, the study elucidated decrease of competitive abilities of native plants, by interfering with formation of mycorrhizal associations and biomass. Overall, our results suggest that significant ecological alterations in vegetation and soil variables (including mycorrhizal potential) were strongly dependent on Phragmites density. Such changes may lead to an important role in process of Phragmites invasion through disruption of functional relationships amongst those variables.

  4. Low Thermal Gradient Czochralski growth of large CdWO{sub 4} crystals and electronic properties of (010) cleaved surface

    SciTech Connect

    Atuchin, V.V.; Galashov, E.N.; Khyzhun, O.Y.; Bekenev, V.L.; Pokrovsky, L.D.; Borovlev, Yu.A.; Zhdankov, V.N.

    2016-04-15

    The crystal growth of large high-quality inclusion-free CdWO4 crystals, 110 mm in diameter and mass up to 20 kg, has been carried out by the Low Thermal Gradient Czochralski (LTG Cz) technique. The high-purity CdWO{sub 4}(010) surface has been prepared by cleavage and high structural quality of the surface has been verified by RHEED, revealing a system of Kikuchi lines. The chemical state and electronic structure of the surface have been studied using X-ray photoelectron spectroscopy (XPS) and X-ray emission spectroscopy (XES). The total and partial densities of states of the CdWO{sub 4} tungstate were calculated employing the first-principles full potential linearized augmented plane wave (FP-LAPW) method. The results indicate that the principal contributors to the valence band of CdWO{sub 4} are the Cd 4d, W 5d and O 2p states which contribute mainly at the bottom, in the central portion and at the top of the valence band, respectively, with also significant contributions of the mentioned states throughout the whole CdWO{sub 4} valence-band region. With respect to the occupation of the O 2p states, the results of the FP-LAPW calculations are confirmed by comparison on a common energy scale of the XPS valence-band spectrum and the XES band representing the energy distribution of the O 2p states in this compound. Additionally, the FP-LAPW data allow us to conclude that the CdWO{sub 4} tungstate is a non-direct semiconductor. - Highlights: • Large high-quality CdWO{sub 4} crystals, up to 115 mm in diameter and mass up to 20 kg, have been grown. • The high-purity cleaved CdWO{sub 4}(010) surface has been studied by the XPS and XES methods. • The principal contributors to the CdWO{sub 4} valence band are the Cd 4d, W 5d and O 2p states.

  5. Buckling and free vibration of shallow curved micro/nano-beam based on strain gradient theory under thermal loading with temperature-dependent properties

    NASA Astrophysics Data System (ADS)

    Rahmani, O.; Hosseini, S. A. H.; Ghoytasi, I.; Golmohammadi, H.

    2017-01-01

    In this study, influences of a uniform thermomechanical loading in buckling and free vibration of a curved FG microbeam have been investigated, based on strain gradient theory (SGT) theory and Timoshenko beam model. Distribution of structural materials varies continuously in thickness direction due to power-law exponent. Unlike classical models, this novel model employs three length scale parameters which can capture the size effect. This work is based on SGT theory and Timoshenko beam model. Governing equation of motion and associated boundary condition have been developed based on Hamilton's principle, which is the specified case of virtual work theorem. In continuance, final differential equations were solved by Navier's solution method and the results have been presented. Moreover, influences of dimensionless length-to-thickness ratio (aspect ratio), dimensionless length scale parameter, power-law exponent, temperature difference and arc angle for various values of mode numbers on natural frequency and critical temperature by considering temperature-dependent material properties have been investigated. In order to validate accomplished study, some of the results were compared with those of previous works. It has been concluded that applying a thermomechanical loading on a FG microbeam causes the natural frequency to become more sensitive about variations of geometrical, physical and mechanical properties and characteristics.

  6. Generalized gradient calculations of magneto-electronic properties for diluted magnetic semiconductors ZnMnS and ZnMnSe

    NASA Astrophysics Data System (ADS)

    Méçabih, S.; Benguerine, K.; Benosman, N.; Abbar, B.; Bouhafs, B.

    2008-10-01

    Using the first-principles method, we investigate the electronic and magnetic properties of the diluted magnetic semiconductors Zn 1-xMn xS and Zn 1-xMn xSe with 25% of Mn. The calculations are performed by a developed full-potential augmented plane wave plus local orbitals (FP-L/APW+lo) method within the spin density functional theory. As exchange-correlation potential we used the new generalized gradient approximation GGA form. Structural properties are determined from the total energy calculations. We show that the cohesive energy of ZnMnS and ZnMnSe exceeds that of the parent elements ZnS and ZnSe. We discuss the electronic structures, total and partial densities of states and local moments. We have calculated the Mn 3d spin-exchange splitting energies Δ x( d), which reflect the effective potential of the majority and the minority spin. From the charge spin densities calculations, we study the nature of the bonding and the effect of the Mn 3d states on these densities. Furthermore, we found that p-d hybridization reduces the local moment of Mn from its free space value of 5.0 μB.

  7. Linking biochemical properties of particles to particle-attached and free-living bacterial community structure along the particle density gradient from freshwater to open ocean

    NASA Astrophysics Data System (ADS)

    Zhang, Yao; Xiao, Wei; Jiao, Nianzhi

    2016-08-01

    To test the hypothesis that particle composition has a stronger influence on the community structure of particle-attached than free-living bacteria, elemental (C/N, δ13C, and δ15N) and chemical composition of particles and the size-fractionated bacterial community composition were examined along the particle density gradient from the Pearl River to the open basin in the South China Sea. Microbial communities were collected at the three size fractions of 0.2-0.8, 0.8-3, and >3 µm, and the community composition was analyzed using high-throughput sequencing of the 16S rRNA gene (V3-V4 regions). Multivariate analysis evaluating the similarities of bacterial community composition and chemical composition of particles revealed their general consistent spatial variations along the particle density gradient from freshwater to the sea basin. However, compositions of particulate organic matter were more strongly related to the free living than to the particle-attached bacterial community composition, which was composed of relatively abundant anaerobic bacteria and those taxa preferring low-oxygen conditions. This latter result might be caused by low-oxygen microzones in particles. Community network models further revealed tighter interactions within the particle-attached than in free-living bacterial communities, suggesting that a relatively confined space in particles is more favorable for interactions within the community. These analyses indicated that particle microniche properties might be important in shaping particle-attached community structure. In contrast, particulate organic matter compositions significantly influenced the free-living bacterial community probably through the release of labile or semilabile organic matter from particles contributing to the bioavailability of dissolved organic carbon.

  8. Tailoring the magnetic properties and thermal stability of FeSiAl-Al2O3 thin films fabricated by hybrid oblique gradient-composition sputtering

    NASA Astrophysics Data System (ADS)

    Zhong, Xiaoxi; Phuoc, Nguyen N.; Soh, Wee Tee; Ong, C. K.; Peng, Long; Li, Lezhong

    2017-05-01

    In this study, we systematically investigate the dynamic magnetic properties of FeSiAl-Al2O3 thin films fabricated by hybrid oblique gradient-composition sputtering technique with respect to temperature ranging from 300 K to 420 K. The magnetic anisotropy field HK and ferromagnetic resonance frequency fFMR can be tuned from 14.06 to 110.18 Oe and 1.05-3.05 GHz respectively, by changing the oblique angle, which can be interpreted in terms of the contribution of stress-induced anisotropy and shape anisotropy. In addition, the thermal stability of FeSiAl-Al2O3 films in terms of magnetic anisotropy HK and ferromagnetic resonance frequency fFMR are enhanced with the increase of oblique angle up to 35° while the thermal stability of effective Gilbert damping factor αeff and the maximum imaginary permeability μ''max are improved with the increase of oblique angle up to 45°.

  9. Nitrogen cycling in canopy soils of tropical montane forests responds rapidly to indirect N and P fertilization.

    PubMed

    Matson, Amanda L; Corre, Marife D; Veldkamp, Edzo

    2014-12-01

    Although the canopy can play an important role in forest nutrient cycles, canopy-based processes are often overlooked in studies on nutrient deposition. In areas of nitrogen (N) and phosphorus (P) deposition, canopy soils may retain a significant proportion of atmospheric inputs, and also receive indirect enrichment through root uptake followed by throughfall or recycling of plant litter in the canopy. We measured net and gross rates of N cycling in canopy soils of tropical montane forests along an elevation gradient and assessed indirect effects of elevated nutrient inputs to the forest floor. Net N cycling rates were measured using the buried bag method. Gross N cycling rates were measured using (15) N pool dilution techniques. Measurements took place in the field, in the wet and dry season, using intact cores of canopy soil from three elevations (1000, 2000 and 3000 m). The forest floor had been fertilized biannually with moderate amounts of N and P for 4 years; treatments included control, N, P, and N + P. In control plots, gross rates of NH4 (+) transformations decreased with increasing elevation; gross rates of NO3 (-) transformations did not exhibit a clear elevation trend, but were significantly affected by season. Nutrient-addition effects were different at each elevation, but combined N + P generally increased N cycling rates at all elevations. Results showed that canopy soils could be a significant N source for epiphytes as well as contributing up to 23% of total (canopy + forest floor) mineral N production in our forests. In contrast to theories that canopy soils are decoupled from nutrient cycling in forest floor soil, N cycling in our canopy soils was sensitive to slight changes in forest floor nutrient availability. Long-term atmospheric N and P deposition may lead to increased N cycling, but also increased mineral N losses from the canopy soil system.

  10. Calculation of turbulent boundary layers with heat transfer and pressure gradient utilizing a compressibility transformation. Part 2: Constant property turbulent boundary layer flow with simultaneous mass transfer and pressure gradient

    NASA Technical Reports Server (NTRS)

    Boccio, J.; Economos, C.

    1972-01-01

    An analysis of the incompressible turbulent boundary layer, developing under the combined effects of mass transfer and pressure gradient, is presented in this paper. A strip-integral method is employed whereby two of the three governing equations are obtained by integrating the combined momentum and continuity equation to 50 percent and 100 percent, respectively, of the boundary-layer height. The latter equation is the usual momentum-integral equation; the former equation requires specification of shear. Accordingly, Clauser's equilibrium eddy-viscosity law is assumed valid at this point. The third and final equation is obtained by specifying that Stevenson's velocity profiles apply throughout the domain of interest, from which a skin-friction law can be derived. Comparisons of the numerical results with the experiments of McQuaid, which include combined effects of variable pressure gradient and mass transfer, show good agreement.

  11. Soil phosphorus mobility and solid-to-solution phase resupply studied by diffusive gradients in thin films: background soil properties driving their variation

    NASA Astrophysics Data System (ADS)

    Menezes-Blackburn, Daniel; Zhang, Hao; Giles, Courtney; George, Timothy; Shand, Charlie; Lumsdon, David; Cooper, Patricia; Wendler, Renate; Brown, Lawrie; Stutter, Marc; Blackwell, Martin; Darch, Tegan; Wearing, Catherine; Philip, Haygarth

    2015-04-01

    The mobility and resupply of inorganic phosphorus (P) from the solid phase was studied in 32 representative soils from the UK. The objective was to identify the background soil properties driving the variation of soil inorganic P desorption kinetics across different soil types. Diffusive gradients in thin films (DGT), diffusive equilibration in thin films (DET) and the DGT-induced fluxes in sediments model (DIFS) were used as tools for exploring solid-to-solution desorption kinetics. Previously characterized physicochemical properties of the same soils were used for correlation analysis. On average and across soil types, the inorganic P maximum distance of depletion was 0.42±0.10 cm, the equilibration time (Tc) was 3.63 h, the desorption rate constant (k-1) was 0.0046 h-1, and the desorption rate was 4.71 nmol l-1 s-1. The correlation between P in Olsen extractcs (POlsen) with PDGT, PDET and phosphorus effective concentration (PE) was enhanced when similar soils were isolated and used in the comparison, clearly showing that these parameters are affected differently by soil types. The PE was better correlated to Ptot, POlsen, PFeO, and PNaOH/EDTA than PDGT. This may indicate that PE is a better representation of P availability across soil types than PDGT. While the relative DGT-induced inorganic P flux in the first hour is mainly a function of soil wetting properties and % Corg, at longer times it is a function of the resupply capacity (R-Rdiff) of the soil solid phase. In general, resupply of P from the solid phase was less than that for other chemical elements, as shown by high Tc and low k-1 values. Desorption rates and resupply from the solid phase were fundamentally influenced by P saturation status, as reflected by their strong correlation with P concentration in water, FeO strips, Olsen and NaOH-EDTA extracts. Soil pH and particle size distribution had little or no effect on the evaluated parameters. The DGT and DET techniques, along with the DIFS model

  12. On gradient field theories: gradient magnetostatics and gradient elasticity

    NASA Astrophysics Data System (ADS)

    Lazar, Markus

    2014-09-01

    In this work, the fundamentals of gradient field theories are presented and reviewed. In particular, the theories of gradient magnetostatics and gradient elasticity are investigated and compared. For gradient magnetostatics, non-singular expressions for the magnetic vector gauge potential, the Biot-Savart law, the Lorentz force and the mutual interaction energy of two electric current loops are derived and discussed. For gradient elasticity, non-singular forms of all dislocation key formulas (Burgers equation, Mura equation, Peach-Koehler stress equation, Peach-Koehler force equation, and mutual interaction energy of two dislocation loops) are presented. In addition, similarities between an electric current loop and a dislocation loop are pointed out. The obtained fields for both gradient theories are non-singular due to a straightforward and self-consistent regularization.

  13. Graded/Gradient Porous Biomaterials

    PubMed Central

    Miao, Xigeng; Sun, Dan

    2009-01-01

    Biomaterials include bioceramics, biometals, biopolymers and biocomposites and they play important roles in the replacement and regeneration of human tissues. However, dense bioceramics and dense biometals pose the problem of stress shielding due to their high Young’s moduli compared to those of bones. On the other hand, porous biomaterials exhibit the potential of bone ingrowth, which will depend on porous parameters such as pore size, pore interconnectivity, and porosity. Unfortunately, a highly porous biomaterial results in poor mechanical properties. To optimise the mechanical and the biological properties, porous biomaterials with graded/gradient porosity, pores size, and/or composition have been developed. Graded/gradient porous biomaterials have many advantages over graded/gradient dense biomaterials and uniform or homogenous porous biomaterials. The internal pore surfaces of graded/gradient porous biomaterials can be modified with organic, inorganic, or biological coatings and the internal pores themselves can also be filled with biocompatible and biodegradable materials or living cells. However, graded/gradient porous biomaterials are generally more difficult to fabricate than uniform or homogenous porous biomaterials. With the development of cost-effective processing techniques, graded/gradient porous biomaterials can find wide applications in bone defect filling, implant fixation, bone replacement, drug delivery, and tissue engineering.

  14. SPIDER. IV. OPTICAL AND NEAR-INFRARED COLOR GRADIENTS IN EARLY-TYPE GALAXIES: NEW INSIGHT INTO CORRELATIONS WITH GALAXY PROPERTIES

    SciTech Connect

    La Barbera, F.; De Carvalho, R. R.; Gal, R. R.; Swindle, R.; Lopes, P. A. A.

    2010-11-15

    We present an analysis of stellar population gradients in 4546 early-type galaxies (ETGs) with photometry in grizYHJK along with optical spectroscopy. ETGs were selected as bulge-dominated systems, displaying passive spectra within the SDSS fibers. A new approach is described which utilizes color information to constrain age and metallicity gradients. Defining an effective color gradient, {nabla}{sub *}, which incorporates all of the available color indices, we investigate how {nabla}{sub *} varies with galaxy mass proxies, i.e., velocity dispersion, stellar (M{sub *}) and dynamical (M{sub dyn}) masses, as well as age, metallicity, and [{alpha}/Fe]. ETGs with M{sub dyn} larger than 8.5 x 10{sup 10} M{sub sun} have increasing age gradients and decreasing metallicity gradients with respect to mass, metallicity, and enhancement. We find that velocity dispersion and [{alpha}/Fe] are the main drivers of these correlations. ETGs with 2.5 x 10{sup 10} M{sub sun} {<=} M{sub dyn} {<=} 8.5 x 10{sup 10} M{sub sun} show no correlation of age, metallicity, and color gradients with respect to mass, although color gradients still correlate with stellar population parameters, and these correlations are independent of each other. In both mass regimes, the striking anti-correlation between color gradient and {alpha}-enhancement is significant at {approx}5{sigma} and results from the fact that metallicity gradient decreases with [{alpha}/Fe]. This anti-correlation may reflect the fact that star formation and metallicity enrichment are regulated by the interplay between the energy input from supernovae, and the temperature and pressure of the hot X-ray gas in ETGs. For all mass ranges, positive age gradients are associated with old galaxies (>5-7 Gyr). For galaxies younger than {approx}5 Gyr, mostly at low mass, the age gradient tends to be anti-correlated with the Age parameter, with more positive gradients at younger ages.

  15. Gradient Index Lens Research

    DTIC Science & Technology

    1981-10-19

    Finally, an assessment of the current technologies in gradient index has been made. This includes a series of recommendations w’iich will be...17 III. Ray Tracing in Anamorphic Gradient Index Media ......... 20 IV. Fabrication of Six Gradient Index Samples ............. 27 V. Technology ...for a basic understanding of what can and cannot be done with gradient index lenses, aside from any lack of technology for making a paricular gradient

  16. Responses of leaf structure and photosynthetic properties to intra-canopy light gradients: a common garden test with four broadleaf deciduous angiosperm and seven evergreen conifer tree species.

    PubMed

    Wyka, Tomasz P; Oleksyn, J; Zytkowiak, R; Karolewski, P; Jagodziński, A M; Reich, P B

    2012-09-01

    Spectra of leaf traits in northern temperate forest canopies reflect major differences in leaf longevity between evergreen conifers and deciduous broadleaf angiosperms, as well as plastic modifications caused by within-crown shading. We investigated (1) whether long-lived conifer leaves exhibit similar intra-canopy plasticity as short-lived broadleaves, and (2) whether global interspecific relationships between photosynthesis, nitrogen, and leaf structure identified for sun leaves adequately describe leaves differentiated in response to light gradients. We studied structural and photosynthetic properties of intra-tree sun and shade foliage in adult trees of seven conifer and four broadleaf angiosperm species in a common garden in Poland. Shade leaves exhibited lower leaf mass-per-area (LMA) than sun leaves; however, the relative difference was smaller in conifers than in broadleaves. In broadleaves, LMA was correlated with lamina thickness and tissue density, while in conifers, it was correlated with thickness but not density. In broadleaves, but not in conifers, reduction of lamina thickness was correlated with a thinner palisade layer. The more conservative adjustment of conifer leaves could result from a combination of phylogenetic constraints, contrasting leaf anatomies and shoot geometries, but also from functional requirements of long-lived foliage. Mass-based nitrogen concentration (N(mass)) was similar between sun and shade leaves, and was lower in conifers than in deciduous broadleaved species. Given this, the smaller LMA in shade corresponded with a lower area-based N concentration (N(area)). In evergreen conifers, LMA and N(area) were less powerful predictors of area-based photosynthetic rate (A (max(area))) in comparison with deciduous broadleaved angiosperms. Multiple regression for sun and shade leaves showed that, in each group, A (max(mass)) was related to N(mass) but not to LMA, whereas LMA became a significant codeterminant of A (max(mass)) in

  17. The Evolution of Strain Gradient and Anisotropy in Gradient-Structured Metal

    NASA Astrophysics Data System (ADS)

    Bian, Xiangde; Yuan, Fuping; Wu, Xiaolei; Zhu, Yuntian

    2017-09-01

    Gradient-structured metals have been reported to possess superior mechanical properties, which were attributed to their mechanical heterogeneity. Here we report in-situ observation of the evolution of strain gradient and anisotropy during tensile testing of a gradient-structured metal. Strain gradients and anisotropy in the lateral directions were observed to increase with increasing applied tensile strain. In addition, the equivalent Poisson's ratio showed gradient, which evolved with applied strain. The gradient structure produced higher deformation anisotropy than coarse-grained homogeneous structure, and the anisotropy increased with increasing tensile strain. The strain gradient and anisotropy resulted in strong back-stress hardening, large strain gradients, and a high density of geometrically necessary dislocations, which helped with increasing the ductility.

  18. The Evolution of Strain Gradient and Anisotropy in Gradient-Structured Metal

    NASA Astrophysics Data System (ADS)

    Bian, Xiangde; Yuan, Fuping; Wu, Xiaolei; Zhu, Yuntian

    2017-07-01

    Gradient-structured metals have been reported to possess superior mechanical properties, which were attributed to their mechanical heterogeneity. Here we report in-situ observation of the evolution of strain gradient and anisotropy during tensile testing of a gradient-structured metal. Strain gradients and anisotropy in the lateral directions were observed to increase with increasing applied tensile strain. In addition, the equivalent Poisson's ratio showed gradient, which evolved with applied strain. The gradient structure produced higher deformation anisotropy than coarse-grained homogeneous structure, and the anisotropy increased with increasing tensile strain. The strain gradient and anisotropy resulted in strong back-stress hardening, large strain gradients, and a high density of geometrically necessary dislocations, which helped with increasing the ductility.

  19. Microinstabilities in weak density gradient tokamak systems

    SciTech Connect

    Tang, W.M.; Rewoldt, G.; Chen, L.

    1986-04-01

    A prominent characteristic of auxiliary-heated tokamak discharges which exhibit improved (''H-mode type'') confinement properties is that their density profiles tend to be much flatter over most of the plasma radius. Depsite this favorable trend, it is emphasized here that, even in the limit of zero density gradient, low-frequency microinstabilities can persist due to the nonzero temperature gradient.

  20. Seepage and seepage gradients in an homogeneous, isotropic aquifer with drains as a function of soil properties and flow region geometry

    USDA-ARS?s Scientific Manuscript database

    Seepage and seepage gradients are important parameters in soil erosion processes and water quality problems on agricultural land. Traditionally, surface overland flow is viewed as one of the major soil erosive agents on those areas. In recent years, the role of the subsurface flow regime is increasi...

  1. Non Linear Conjugate Gradient

    SciTech Connect

    Newman, Gregory A.; Commer, Michael

    2006-11-17

    Software that simulates and inverts electromagnetic field data for subsurface electrical properties (electrical conductivity) of geological media. The software treats data produced by a time harmonic source field excitation arising from the following antenna geometery: loops and grounded bipoles, as well as point electric and magnetic dioples. The inversion process is carried out using a non-linear conjugate gradient optimization scheme, which minimizes the misfit between field data and model data using a least squares criteria. The software is an upgrade from the code NLCGCS_MP ver 1.0. The upgrade includes the following components: Incorporation of new 1 D field sourcing routines to more accurately simulate the 3D electromagnetic field for arbitrary geologic& media, treatment for generalized finite length transmitting antenna geometry (antennas with vertical and horizontal component directions). In addition, the software has been upgraded to treat transverse anisotropy in electrical conductivity.

  2. Gradient copolymers - a new class of materials

    SciTech Connect

    Greszta, D.; Matyjaszewski, K.

    1996-10-01

    In this work preparation of a new class of copolymers, namely gradient copolymers via controlled Atom Transfer Radical Polymerization (ATRP) is described. Due to the compositional gradient along the chain, gradient copolymers are expected to exhibit unique physical characteristics as compared to block and random copolymers with similar composition and molecular weight. These include unusual phase separation behavior, and mechanical and thermal properties. Using ATRP one can prepare gradient copolymers via two routes. The first one is the one-pot copolymerization of monomers with different reactitvity ratios r{sub 1}{much_gt}r{sub 2}. The second one is a copolymerization while continuously changing the comonomers feed composition.

  3. Biomimetic Gradient Polymers with Enhanced Damping Capacities.

    PubMed

    Wang, Dong; Zhang, Huan; Guo, Jing; Cheng, Beichen; Cao, Yuan; Lu, Shengjun; Zhao, Ning; Xu, Jian

    2016-04-01

    Designing gradient structures, mimicking biological materials, such as pummelo peels and tendon, is a promising strategy for developing advanced materials with superior energy damping capacities. Here a facile and effective approach for fabricating polymers with composition gradients at millimeter length scale is presented. The gradient thiol-ene polymers (TEPs) are created by the use of density difference of ternary thiol-ene-ene precursors and the subsequent photo-crosslinking via thiol-ene reaction. The compositional gradients are analyzed via differential scanning calorimeter (DSC), compressive modulus testing, atomic force microscopy (AFM) indentation, and swelling measurements. In contrast to homogeneous TEPs networks, the resultant gradient polymer shows a broader effective damping temperature range combining with good mechanical properties. The present result provides an effective route toward high damping materials by the fabrication of gradient structures.

  4. A model to describe the surface gradient-nanograin formation and property of friction stir processed laser Co-Cr-Ni-Mo alloy

    NASA Astrophysics Data System (ADS)

    Li, Ruidi; Yuan, Tiechui; Qiu, Zili

    2014-07-01

    A gradient-nanograin surface layer of Co-base alloy was prepared by friction stir processing (FSP) of laser-clad coating in this work. However, it is lack of a quantitatively function relationship between grain refinement and FSP conditions. Based on this, an analytic model is derived for the correlations between carbide size, hardness and rotary speed, layer depth during in-situ FSP of laser-clad Co-Cr-Ni-Mo alloy. The model is based on the principle of typical plastic flow in friction welding and dynamic recrystallization. The FSP experiment for modification of laser-clad Co-based alloy was conducted and its gradient nanograin and hardness were characterized. It shows that the model is consistent with experimental results.

  5. Landscape-scale quantification of fire-induced change in canopy cover following mountain pine beetle outbreak and timber harvest

    Treesearch

    T. Ryan McCarley; Crystal A. Kolden; Nicole M. Vaillant; Andrew T. Hudak; Alistair M. S. Smith; Jason Kreitler

    2017-01-01

    Across the western United States, the three primary drivers of tree mortality and carbon balance are bark beetles, timber harvest, and wildfire. While these agents of forest change frequently overlap, uncertainty remains regarding their interactions and influence on specific subsequent fire effects such as change in canopy cover. Acquisition of pre- and post-fire Light...

  6. Modification of the melting properties of duplex DNA by attachment of a GC-rich DNA sequence as determined by denaturing gradient gel electrophoresis.

    PubMed Central

    Myers, R M; Fischer, S G; Maniatis, T; Lerman, L S

    1985-01-01

    The melting behavior of a DNA fragment carrying the mouse beta maj-globin promoter was investigated as a means of establishing procedures for separating DNA fragments differing by any single base substitution using the denaturing gradient gel electrophoresis procedure of Fischer and Lerman (1,2). We find that attachment of a 300 base pair GC-rich DNA sequence, termed a GC-clamp, to a 135 bp DNA fragment carrying the mouse beta-globin promoter significantly alters the pattern of DNA melting within the promoter. When the promoter is attached to the clamp, the promoter sequences melt without undergoing strand dissociation. The calculated distribution of melting domains within the promoter differs markedly according to the relative orientation of the clamp and promoter sequences. We find that the behavior of DNA fragments containing the promoter and clamp sequences on denaturing gradient polyacrylamide gels is in close agreement with the theoretical melting calculations. These studies provide the basis for critical evaluation of the parameters for DNA melting calculations, and they establish conditions for determining whether all single base substitutions within the promoter can be separated on denaturing gradient gels. Images PMID:2987873

  7. Tectorial Membrane Stiffness Gradients

    PubMed Central

    Richter, Claus-Peter; Emadi, Gulam; Getnick, Geoffrey; Quesnel, Alicia; Dallos, Peter

    2007-01-01

    The mammalian inner ear processes sound with high sensitivity and fine resolution over a wide frequency range. The underlying mechanism for this remarkable ability is the “cochlear amplifier”, which operates by modifying cochlear micromechanics. However, it is largely unknown how the cochlea implements this modification. Although gradual improvements in experimental techniques have yielded ever-better descriptions of gross basilar membrane vibration, the internal workings of the organ of Corti and of the tectorial membrane have resisted exploration. Although measurements of cochlear function in mice with a gene mutation for α-tectorin indicate the tectorial membrane's key role in the mechanoelectrical transformation by the inner ear, direct experimental data on the tectorial membrane's physical properties are limited, and only a few direct measurements on tectorial micromechanics are available. Using the hemicochlea, we are able to show that a tectorial membrane stiffness gradient exists along the cochlea, similar to that of the basilar membrane. In artificial perilymph (but with low calcium), the transversal and radial driving point stiffnesses change at a rate of –4.0 dB/mm and −4.9 dB/mm, respectively, along the length of the cochlear spiral. In artificial endolymph, the stiffness gradient for the transversal component was –3.4 dB/mm. Combined with the changes in tectorial membrane dimensions from base to apex, the radial stiffness changes would be able to provide a second frequency-place map in the cochlea. Young's modulus, which was obtained from measurements performed in the transversal direction, decreased by −2.6 dB/mm from base to apex. PMID:17496047

  8. Moving thermal gradients in gas chromatography.

    PubMed

    Tolley, H Dennis; Tolley, Samuel E; Wang, Anzi; Lee, Milton L

    2014-12-29

    This paper examines the separation effects of a moving thermal gradient on a chromatographic column in gas chromatography. This movement of the gradient has a focusing effect on the analyte bands, limiting band broadening in the column. Here we examine the relationship between the slope of this gradient, the velocity of the gradient and the resulting band width. Additionally we examine how transport of analytes along the column at their analyte specific constant temperatures, determined by the gradient slope and velocity, affects resolution. This examination is based primarily on a theoretical model of partitioning and transport of analyte under low concentration conditions. Preliminary predictions indicate that analytes reach near constant temperatures, relative positions and resolutions in less than 100cm of column transport. Use of longer columns produces very little improvement in resolution for any fixed slope. Properties of the thermal gradient determine a fixed solute band width for each analyte. These widths are nearly reached within the first 40-70cm, after which little broadening or narrowing of the bands occur. The focusing effect of the thermal gradient corrects for broad injections, reduces effects of irregular stationary phase coatings and can be used with short columns for fast analysis. Thermal gradient gas chromatographic instrumentation was constructed and used to illustrate some characteristics predicted from the theoretical results.

  9. Vertical gradient solution growth of N-type Si0.73Ge0.27 bulk crystals with homogeneous composition and its thermoelectric properties

    NASA Astrophysics Data System (ADS)

    Omprakash, M.; Arivanandhan, M.; Sabarinathan, M.; Koyama, T.; Momose, Y.; Ikeda, H.; Tatsuoka, H.; Aswal, D. K.; Bhattacharya, S.; Inatomi, Y.; Hayakawa, Y.

    2016-05-01

    Compositionally homogeneous Sb-doped (5×1018 and 1×1019 cm-3) Si0.73Ge0.27 bulk crystals were grown by a vertical gradient solution growth method. The sandwich sample Si (seed)/Sb-doped Ge/ Si(feed) was set up inside a furnace under a mild temperature gradient 0.57 °C/mm for homogeneous growth. The Si composition was analyzed by electron probe micro- analysis (EPMA). It revealed that the Si composition was homogeneous and the lengths of the Sb-doped (5×1018 and 1×1019 cm-3) Si0.73Ge0.27 bulk crystals were 18.3 and 15.1 mm, respectively. Grain distribution was investigated by electron backscattered diffraction spectrum (EBSD). The Seebeck coefficients (-440 and -426 μV/K) of Sb-doped (5×1018 and 1×1019 cm-3) Si0.73Ge0.27 were higher than the reported value (-211 μV/K) of P-doped (5×1019 cm-3) Si0.8Ge0.2 at room temperature. Thermal conductivity of Ga and Sb-doped SiGe was decreased with temperature due to scattering of phonon at the temperature range between 313 and 913 K. The maximum ZT values of Ga and Sb-doped SiGe were 0.34 and 0.44 at 820 K, respectively. The ZT values of Ga and Sb-doped SiGe were higher (0.07 and 0.13) than the reported value of Ga-doped Si0.81Ge0.19 (0.05) and P-doped (5×1019 cm-3) Si0.8Ge0.2 bulk crystals at room temperature. The improvement in ZT value was caused by a decrease of thermal conductivity which related to a composition of the alloy and doping concentration in the crystal.

  10. Near-surface remote sensing of spatial and temporal variation in canopy phenology.

    PubMed

    Richardson, Andrew D; Braswell, Bobby H; Hollinger, David Y; Jenkins, Julian P; Ollinger, Scott V

    2009-09-01

    There is a need to document how plant phenology is responding to global change factors, particularly warming trends. "Near-surface" remote sensing, using radiometric instruments or imaging sensors, has great potential to improve phenological monitoring because automated observations can be made at high temporal frequency. Here we build on previous work and show how inexpensive, networked digital cameras ("webcams") can be used to document spatial and temporal variation in the spring and autumn phenology of forest canopies. We use two years of imagery from a deciduous, northern hardwood site, and one year of imagery from a coniferous, boreal transition site. A quantitative signal is obtained by splitting images into separate red, green, and blue color channels and calculating the relative brightness of each channel for "regions of interest" within each image. We put the observed phenological signal in context by relating it to seasonal patterns of gross primary productivity, inferred from eddy covariance measurements of surface-atmosphere CO2 exchange. We show that spring increases, and autumn decreases, in canopy greenness can be detected in both deciduous and coniferous stands. In deciduous stands, an autumn red peak is also observed. The timing and rate of spring development and autumn senescence varies across the canopy, with greater variability in autumn than spring. Interannual variation in phenology can be detected both visually and quantitatively; delayed spring onset in 2007 compared to 2006 is related to a prolonged cold spell from day 85 to day 110. This work lays the foundation for regional- to continental-scale camera-based monitoring of phenology at network observatory sites, e.g., National Ecological Observatory Network (NEON) or AmeriFlux.

  11. Mechanical Properties and Real-Time Damage Evaluations of Environmental Barrier Coated SiC/SiC CMCs Subjected to Tensile Loading Under Thermal Gradients

    NASA Technical Reports Server (NTRS)

    Appleby, Matthew; Zhu, Dongming; Morscher, Gregory

    2015-01-01

    SiC/SiC ceramic matrix composites (CMCs) require new state-of-the art environmental barrier coatings (EBCs) to withstand increased temperature requirements and high velocity combustion corrosive combustion gasses. The present work compares the response of coated and uncoated SiC/SiC CMC substrates subjected to simulated engine environments followed by high temperature mechanical testing to asses retained properties and damage mechanisms. Our focus is to explore the capabilities of electrical resistance (ER) measurements as an NDE technique for testing of retained properties under combined high heat-flux and mechanical loading conditions. Furthermore, Acoustic Emission (AE) measurements and Digital Image Correlation (DIC) were performed to determine material damage onset and accumulation.

  12. High Gradient Induction Cell

    SciTech Connect

    Caporaso, G J

    2004-11-29

    A concept being developed for high current electron beams may have application to HEDP and is described here. It involves the use of planar Blumlein stacks placed inside an induction cell. The output end of the Blumlein stack is applied across a high gradient insulator (HGI). These insulators have been used successfully in the presence of kilo Ampere-level electron beam currents for tens of nanoseconds at gradients of 20 MV/meter.

  13. Self-organization of intracellular gradients during mitosis.

    PubMed

    Fuller, Brian G

    2010-01-29

    Gradients are used in a number of biological systems to transmit spatial information over a range of distances. The best studied are morphogen gradients where information is transmitted over many cell lengths. Smaller mitotic gradients reflect the need to organize several distinct events along the length of the mitotic spindle. The intracellular gradients that characterize mitosis are emerging as important regulatory paradigms. Intracellular gradients utilize intrinsic auto-regulatory feedback loops and diffusion to establish stable regions of activity within the mitotic cytosol. We review three recently described intracellular mitotic gradients. The Ran GTP gradient with its elaborate cascade of nuclear transport receptors and cargoes is the best characterized, yet the dynamics underlying the robust gradient of Ran-GTP have received little attention. Gradients of phosphorylation have been observed on Aurora B kinase substrates both before and after anaphase onset. In both instances the phosphorylation gradient appears to result from a soluble gradient of Aurora B kinase activity. Regulatory properties that support gradient formation are highlighted. Intracellular activity gradients that regulate localized mitotic events bare several hallmarks of self-organizing biologic systems that designate spatial information during pattern formation. Intracellular pattern formation represents a new paradigm in mitotic regulation.

  14. Self-organization of intracellular gradients during mitosis

    PubMed Central

    2010-01-01

    Gradients are used in a number of biological systems to transmit spatial information over a range of distances. The best studied are morphogen gradients where information is transmitted over many cell lengths. Smaller mitotic gradients reflect the need to organize several distinct events along the length of the mitotic spindle. The intracellular gradients that characterize mitosis are emerging as important regulatory paradigms. Intracellular gradients utilize intrinsic auto-regulatory feedback loops and diffusion to establish stable regions of activity within the mitotic cytosol. We review three recently described intracellular mitotic gradients. The Ran GTP gradient with its elaborate cascade of nuclear transport receptors and cargoes is the best characterized, yet the dynamics underlying the robust gradient of Ran-GTP have received little attention. Gradients of phosphorylation have been observed on Aurora B kinase substrates both before and after anaphase onset. In both instances the phosphorylation gradient appears to result from a soluble gradient of Aurora B kinase activity. Regulatory properties that support gradient formation are highlighted. Intracellular activity gradients that regulate localized mitotic events bare several hallmarks of self-organizing biologic systems that designate spatial information during pattern formation. Intracellular pattern formation represents a new paradigm in mitotic regulation. PMID:20181052

  15. Convection driven generation of long-range material gradients

    PubMed Central

    Du, Yanan; Hancock, Matthew J.; He, Jiankang; Villa-Uribe, Jose; Wang, Ben; Cropek, Donald M.; Khademhosseini, Ali

    2009-01-01

    Natural materials exhibit anisotropy with variations in soluble factors, cell distribution, and matrix properties. The ability to recreate the heterogeneity of the natural materials is a major challenge for investigating cell-material interactions and for developing biomimetic materials. Here we present a generic fluidic approach using convection and alternating flow to rapidly generate multi-centimeter gradients of biomolecules, polymers, beads and cells and cross-gradients of two species in a microchannel. Accompanying theoretical estimates and simulations of gradient growth provide design criteria over a range of material properties. A poly(ethyleneglycol) hydrogel gradient, a porous collagen gradient and a composite material with a hyaluronic acid/gelatin cross-gradient were generated with continuous variations in material properties and in their ability to regulate cellular response. This simple yet generic fluidic platform should prove useful for creating anisotropic biomimetic materials and high-throughput platforms for investigating cell-microenvironment interaction. PMID:20035990

  16. Property Improvement in CZT via Modeling and Processing Innovations . Te-particles in vertical gradient freeze CZT: Size and Spatial Distributions and Constitutional Supercooling

    SciTech Connect

    Henager, Charles H.; Alvine, Kyle J.; Bliss, Mary; Riley, Brian J.; Stave, Jean A.

    2014-10-01

    A section of a vertical gradient freeze CZT boule approximately 2100-mm3 with a planar area of 300-mm2 was prepared and examined using transmitted IR microscopy at various magnifications to determine the three-dimensional spatial and size distributions of Te-particles over large longitudinal and radial length scales. The boule section was approximately 50-mm wide by 60-mm in length by 7-mm thick and was doubly polished for TIR work. Te-particles were imaged through the thickness using extended focal imaging to locate the particles in thickness planes spaced 15-µm apart and then in plane of the image using xy-coordinates of the particle center of mass so that a true three dimensional particle map was assembled for a 1-mm by 45-mm longitudinal strip and for a 1-mm by 50-mm radial strip. Te-particle density distributions were determined as a function of longitudinal and radial positions in these strips, and treating the particles as vertices of a network created a 3D image of the particle spatial distribution. Te-particles exhibited a multi-modal log-normal size density distribution that indicated a slight preference for increasing size with longitudinal growth time, while showing a pronounced cellular network structure throughout the boule that can be correlated to dislocation network sizes in CZT. Higher magnification images revealed a typical Rayleigh-instability pearl string morphology with large and small satellite droplets. This study includes solidification experiments in small crucibles of 30:70 mixtures of Cd:Te to reduce the melting point below 1273 K (1000°C). These solidification experiments were performed over a wide range of cooling rates and clearly demonstrated a growth instability with Te-particle capture that is suggested to be responsible for one of the peaks in the size distribution using size discrimination visualization. The results are discussed with regard to a manifold Te-particle genesis history as 1) Te

  17. Flow field thermal gradient gas chromatography.

    PubMed

    Boeker, Peter; Leppert, Jan

    2015-09-01

    Negative temperature gradients along the gas chromatographic separation column can maximize the separation capabilities for gas chromatography by peak focusing and also lead to lower elution temperatures. Unfortunately, so far a smooth thermal gradient over a several meters long separation column could only be realized by costly and complicated manual setups. Here we describe a simple, yet flexible method for the generation of negative thermal gradients using standard and easily exchangeable separation columns. The measurements made with a first prototype reveal promising new properties of the optimized separation process. The negative thermal gradient and the superposition of temperature programming result in a quasi-parallel separation of components each moving simultaneously near their lowered specific equilibrium temperatures through the column. Therefore, this gradient separation process is better suited for thermally labile molecules such as explosives and natural or aroma components. High-temperature GC methods also benefit from reduced elution temperatures. Even for short columns very high peak capacities can be obtained. In addition, the gradient separation is particularly beneficial for very fast separations below 1 min overall retention time. Very fast measurements of explosives prove the benefits of using negative thermal gradients. The new concept can greatly reduce the cycle time of high-resolution gas chromatography and can be integrated into hyphenated or comprehensive gas chromatography setups.

  18. A new nonlinear conjugate gradient method

    NASA Astrophysics Data System (ADS)

    Abdelrahman, Awad; Mamat, Mustafa; Mohd, Ismail bin; Rivaie, Mohd; Omer, Osman

    2015-02-01

    Conjugate gradient (CG) methods are essential for solving large-scale unconstrained optimization problems. Many of studies and modifications have been practiced to improve this method. In this paper, a new class of conjugate gradient coefficients (βk) with a new parameter m = ‖g/k‖ ‖dk-1‖ that possess global convergence properties is presented. The global convergence and sufficient decent property result is established using inexact line searches to determine the step size of CG, denoted as ∝k. Numerical result shows that the new formula is superior and more efficient when compared to other CG coefficients.

  19. Development and application of the High resolution VOC Atmospheric Chemistry in Canopies (Hi-VACC) model

    NASA Astrophysics Data System (ADS)

    Kenny, W.; Bohrer, G.; Chatziefstratiou, E.

    2013-12-01

    We have been working to develop a new post-processing model - High resolution VOC Atmospheric Chemistry in Canopies (Hi-VACC) - which will be able to resolve the dispersion and chemistry of reacting chemical species given their emission rates from the vegetation and soil, driven by high resolution meteorological forcing and wind fields from various high resolution atmospheric regional and large-eddy simulations. Hi-VACC reads in fields of pressure, temperature, humidity, air density, short-wave radiation, wind (3-D u, v and w components) and sub-grid-scale turbulence that were simulated by a high resolution atmospheric model. This meteorological forcing data is provided as snapshots of 3-D fields. Presently, the advection-diffusion portion of the model is fully developed, and we have tested it using a number of RAMS-based Forest Large Eddy Simulation (RAFLES) runs. Here, we present results from utilizing Hi-VACC in a few different contexts where it performs smoke and particle dispersion well. These include simulations of smoke dispersion from a theoretical forest fire in a domain in The Pine Barrens in New Jersey, as well as simulations to test the effects of heat flux on a scalar plume dispersing over a vegetative windbreak in an agricultural setting. Additional, we show initial results from testing the coupled chemistry component of Hi-VACC. One of the primary benefits of Hi-VACC is that users of other models can utilize this tool with only minimal work on their part -- processing their output fields into the appropriate HI-VACC input format. We have developed our model such that for whatever atmospheric model is being used with it, a MATLAB function must be written to extract the necessary information from the output files of that model and shape it into the proper format. This is the only model-specific work required. As such, this sort of smoke dispersion modeling performed by Hi-VACC - as well as its other capabilities - can be easily performed in other

  20. Assessing the mechanical properties of tissue-mimicking phantoms at different depths as an approach to measure biomechanical gradient of crystalline lens

    PubMed Central

    Wang, Shang; Aglyamov, Salavat; Karpiouk, Andrei; Li, Jiasong; Emelianov, Stanislav; Manns, Fabrice; Larin, Kirill V.

    2013-01-01

    We demonstrate the feasibility of using the dominant frequency of the sample surface response to a mechanical stimulation as an effective indicator for sensing the depthwise distribution of elastic properties in transparent layered phantom samples simulating the cortex and nucleus of the crystalline lens. Focused ultrasound waves are used to noninvasively interrogate the sample surface. A phase-sensitive optical coherence tomography system is utilized to capture the surface dynamics over time with nanometer scale sensitivity. Spectral analysis is performed on the sample surface response to ultrasound stimulation and the dominant frequency is calculated under particular loading parameters. Pilot experiments were conducted on homogeneous and layered tissue-mimicking phantoms. Results indicate that the mechanical layers located at different depths introduce different frequencies to the sample surface response, which are correlated with the depth-dependent elasticity of the sample. The duration and the frequency of the ultrasound excitation are also investigated for their influences on this spectrum-based detection. This noninvasive method may be potentially applied for localized and rapid assessment of the depth dependence of the mechanical properties of the crystalline lens. PMID:24409379

  1. Coast-to-interior gradients and recent trends in physical and chemical properties of near-surface snow and firn in northwest Greenland

    NASA Astrophysics Data System (ADS)

    Wong, G. J.; Osterberg, E. C.; Hawley, R. L.; Caughey, S. K.; Courville, Z.; Howley, J.; Lutz, E.; Overly, T. B.

    2013-12-01

    The Greenland Ice Sheet (GIS), which holds enough ice to raise global sea levels by approximately 7 m, is a major driver of Arctic and global climate. Observations over the past two decades have documented changes including notable increases in ice discharge, significant warming in coastal regions, and expanded areal extent of annual surface melt (e.g., Rignot and Thomas, 2002; Mote, 2007; Hanna and others, 2008). In contrast, observations document little change in temperature or accumulation in the central regions of the ice sheet (Hanna and others, 2008, 2011). The 1120 km-long Greenland Inland Traverse (GrIT), between Thule Air Base in northwest Greenland and Summit Station in central Greenland, is a logistics traverse that follows a nearly identical route taken by Carl Benson and the US Army Snow, Ice and Permafrost Research Establishment (SIPRE) between 1952 and 1955 (Benson, 1962). Observations from the SIPRE and GrIT traverses provide two snapshots of surface conditions across the northwest region of the GIS separated by 56 years. Hawley and others (in review) observe an increase in snow accumulation rates along the GrIT traverse route based on internal reflecting horizons in radar data dated with firn cores, with larger accumulation increases observed in the coastal region near Thule. Here we expand upon the analysis of Hawley and others (in review) by determining coast-to-interior gradients in snow accumulation, density, hardness (Rammsonde), and snow chemistry using samples from 18 snow pits and 3 firn cores collected during the 2010 and 2011 GrIT traverses. Snow pit and firn core samples were analyzed for trace element (23Na, 24Mg, 27Al, 32S, 39K, 44Ca, 47Ti, 51V, 52Cr, 55Mn, 56Fe, 59Co, 63Cu, 66Zn, 75As, 88Sr, 111Cd, 133Cs, 138Ba, 139La, 140Ce, 141Pr, 208Pb, 209Bi, 238U) concentrations and stable water isotope ratios (δD, δ18O), and were dated by seasonal oscillations in chemical concentrations and isotope ratios. We compare the GrIT data to those of

  2. [Microbial community and its activities in canopy- and understory humus of two montane forest types in Ailao Mountains, Northwest China].

    PubMed

    Liu, Yong-jie; Liu, Wen-yao; Chen, Lin; Zhang, Han-bo; Wang, Gao-sheng

    2010-09-01

    Mid-montane moist evergreen broadleaved forest (MMF) and top-montane dwarf mossy forest (DMF) are the two major natural forest types in subtropical mountainous area of Ailao Mountains, Northwest China. In this paper, a comparative study was made on the microbial composition, quantity, biochemical activity, metabolic activity, and their seasonal dynamics in the canopy- and understory humus of the two forest types. The composition, quantity, and metabolic activity of the microbes in the canopy humus of dominant tree species in MMF and DMF were also analyzed. In the canopy humus of the two forest types, the amounts of fungi and actinomycetes, microbial biomass C and N, and intensities of nitrogen fixation and cellulose decomposition were significantly higher than those in understory humus. Meanwhile, the amount of cellulose-decomposing microbes (ACDM), cellulose decomposition intensity, microbial biomass C and N, and metabolic activity in the canopy humus of MMF were significantly higher than those of DMF. The amounts of bacteria, fungi, and aerobic nitrogen-fixing bacteria (ANFB) and the metabolic activity in the canopy humus of MMF and DMF were significantly higher in wet season than in dry season, while a contradictory trend was observed on the amount of actinomycetes. No significant difference was observed on the amount of ACDM between wet season and dry season. For the two forest types, the amounts of microbes and their biochemical activities in canopy humus had a larger seasonal variation range than those in understory humus. There was a significant difference in the amounts of the microbes in canopy humus among the dominant tree species in MMF and DMF, especially in wet season. The microbes in canopy humus played important roles in maintaining the biodiversity of epiphytes in the canopy, and in supplying the needed nutrients for the vigorous growth of the epiphytes.

  3. Restoring the density-gradient expansion for exchange in solids and surfaces.

    PubMed

    Perdew, John P; Ruzsinszky, Adrienn; Csonka, Gábor I; Vydrov, Oleg A; Scuseria, Gustavo E; Constantin, Lucian A; Zhou, Xiaolan; Burke, Kieron

    2008-04-04

    Popular modern generalized gradient approximations are biased toward the description of free-atom energies. Restoration of the first-principles gradient expansion for exchange over a wide range of density gradients eliminates this bias. We introduce a revised Perdew-Burke-Ernzerhof generalized gradient approximation that improves equilibrium properties of densely packed solids and their surfaces.

  4. Shoot biomass growth is related to the vertical leaf nitrogen gradient in Salix canopies.

    PubMed

    Weih, Martin; Rönnberg-Wästjung, Ann-Christin

    2007-11-01

    Plant canopy optimization models predict that leaf nitrogen (N) distribution in the canopy will parallel the vertical light gradient, and numerous studies with many species have confirmed this prediction. Further, it is predicted that for a given canopy leaf area, a low vertical light extinction coefficient will promote rapid growth. Therefore, the ideal canopy of fast-growing plants should combine high leaf area index with a low light extinction coefficient; the latter being reflected in a flat vertical leaf N gradient throughout the canopy. Based on data from an experimental Salix stand (six varieties) grown on agricultural land in central Sweden, we tested the hypothesis that shoot growth is correlated with vertical leaf N gradient in canopies of hybrid willows bred for biomass production, which could have implications for Salix breeding. Tree improvement research requires screening of growth-related traits in large numbers of plants, but assessment of canopy leaf N gradients by chemical analysis is expensive, time-consuming and destructive. An alternative to analytical methods is to estimate leaf N gradients nondestructively with an optical chlorophyll meter (SPAD method). Here we provide a specific calibration for interpreting SPAD data measured in hybrid willows grown in biomass plantations on fertile agricultural land. Based on SPAD measurements, a significant and inverse relationship (r(2) = 0.88) was found between shoot biomass growth and vertical leaf N gradient across canopies of six Salix varieties.

  5. Momentum-weighted conjugate gradient descent algorithm for gradient coil optimization.

    PubMed

    Lu, Hanbing; Jesmanowicz, Andrzej; Li, Shi-Jiang; Hyde, James S

    2004-01-01

    MRI gradient coil design is a type of nonlinear constrained optimization. A practical problem in transverse gradient coil design using the conjugate gradient descent (CGD) method is that wire elements move at different rates along orthogonal directions (r, phi, z), and tend to cross, breaking the constraints. A momentum-weighted conjugate gradient descent (MW-CGD) method is presented to overcome this problem. This method takes advantage of the efficiency of the CGD method combined with momentum weighting, which is also an intrinsic property of the Levenberg-Marquardt algorithm, to adjust step sizes along the three orthogonal directions. A water-cooled, 12.8 cm inner diameter, three axis torque-balanced gradient coil for rat imaging was developed based on this method, with an efficiency of 2.13, 2.08, and 4.12 mT.m(-1).A(-1) along X, Y, and Z, respectively. Experimental data demonstrate that this method can improve efficiency by 40% and field uniformity by 27%. This method has also been applied to the design of a gradient coil for the human brain, employing remote current return paths. The benefits of this design include improved gradient field uniformity and efficiency, with a shorter length than gradient coil designs using coaxial return paths.

  6. High gradient electron guns

    SciTech Connect

    Fant, K.S.; Caryotakis, G.; Koontz, R.F.; Vlieks, A.E. ); Miram, G. , Atherton, CA )

    1990-08-01

    Experiments have been conducted to determine peak operating gradients attainable in thermionic electron guns. These tests are part of a study of high-current-density, long-life cathodes suitable for use in high power klystrons. We also investigated the use of chromium oxide coating as a means of inhibiting electronic breakdown across the focus electrode anode gap. Field gradients in excess of 280 kV/cm have been achieved for a gun operating at 240 kV with a beam current of 228 A, at pulse widths of the order of 1 {mu}s. 3 refs., 5 figs.

  7. HIGH GRADIENT INDUCTION ACCELERATOR

    SciTech Connect

    Caporaso, G J; Sampayan, S; Chen, Y; Blackfield, D; Harris, J; Hawkins, S; Holmes, C; Krogh, M; Nelson, S; Nunnally, W; Paul, A; Poole, B; Rhodes, M; Sanders, D; Selenes, K; Sullivan, J; Wang, L; Watson, J

    2007-06-21

    A new type of compact induction accelerator is under development at the Lawrence Livermore National Laboratory that promises to increase the average accelerating gradient by at least an order of magnitude over that of existing induction machines. The machine is based on the use of high gradient vacuum insulators, advanced dielectric materials and switches and is stimulated by the desire for compact flash x-ray radiography sources. Research describing an extreme variant of this technology aimed at proton therapy for cancer will be described. Progress in applying this technology to several applications will be reviewed.

  8. High-gradient continuous-casting furnace

    NASA Technical Reports Server (NTRS)

    Scheuermann, C. M.; Flemings, M. C.; Neff, M. A.; Rickinson, B. A.; Young, K. P.

    1979-01-01

    High gradient allows rapid growth rates in directionally-solidified eutectic alloys. Furnace design permits cost reductions in directional solidification process through its increased solidification rates, which reduces melt/mold interaction. It produces structural engineering materials for any application requiring properties directionally-solidified eutectic materials.

  9. Gradient Refractive Index Lenses.

    ERIC Educational Resources Information Center

    Morton, N.

    1984-01-01

    Describes the nature of gradient refractive index (GRIN) lenses, focusing on refraction in these materials, focal length of a thin Wood lens, and on manufacturing of such lenses. Indicates that GRIN lenses of small cross section are in limited production with applications suggested for optical communication and photocopying fields. (JN)

  10. Manipulating the Gradient

    ERIC Educational Resources Information Center

    Gaze, Eric C.

    2005-01-01

    We introduce a cooperative learning, group lab for a Calculus III course to facilitate comprehension of the gradient vector and directional derivative concepts. The lab is a hands-on experience allowing students to manipulate a tangent plane and empirically measure the effect of partial derivatives on the direction of optimal ascent. (Contains 7…

  11. Spectroscopic Gradients in Early-type Galaxies

    NASA Astrophysics Data System (ADS)

    Buzzoni, A.; Battistini, C.; Carrasco, L.; Recillas, E.

    2009-11-01

    We review some relevant properties of the observed changes of Hβ, Mg_2, and FeI Lick indices across the surface of 25 bright elliptical galaxies. The impact of these spectroscopic gradients is briefly discussed, in the framework of the leading physical mechanisms that led to galaxy formation. In particular, three relevant evolutionary scenarios are sketched, each one able, in principle, to consistently match galaxy spectral properties and effectively constrain the composing stellar populations in these systems.

  12. Gradient Sun [still

    NASA Image and Video Library

    2017-09-27

    To view a video of the Gradient Sun go to: www.flickr.com/photos/gsfc/8103212817 Looking at a particularly beautiful image of the sun helps show how the lines between science and art can sometimes blur. But there is more to the connection between the two disciplines: science and art techniques are often quite similar, indeed one may inform the other or be improved based on lessons from the other arena. One such case is a technique known as a "gradient filter" – recognizable to many people as an option available on a photo-editing program. Gradients are, in fact, a mathematical description that highlights the places of greatest physical change in space. A gradient filter, in turn, enhances places of contrast, making them all the more obviously different, a useful tool when adjusting photos. Scientists, too, use gradient filters to enhance contrast, using them to accentuate fine structures that might otherwise be lost in the background noise. On the sun, for example, scientists wish to study a phenomenon known as coronal loops, which are giant arcs of solar material constrained to travel along that particular path by the magnetic fields in the sun's atmosphere. Observations of the loops, which can be more or less tangled and complex during different phases of the sun's 11-year activity cycle, can help researchers understand what's happening with the sun's complex magnetic fields, fields that can also power great eruptions on the sun such as solar flares or coronal mass ejections. The still here shows an unfiltered image from the sun next to one that has been processed using a gradient filter. Note how the coronal loops are sharp and defined, making them all the more easy to study. On the other hand, gradients also make great art. NASA/Goddard Space Flight Center To download this video go to: svs.gsfc.nasa.gov/goto?11112 NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics

  13. Design of Gradient Index Optical Thin Films

    NASA Astrophysics Data System (ADS)

    Druessel, Jeffrey J.

    Gradient index thin films provide greater flexibility for the design of optical coatings than the more conventional "layer" films. In addition, gradient index films have higher damage thresholds and better adhesion properties. In this dissertation I present an enhancement to the existing inverse Fourier transform gradient index design method, and develop a new optimal design method for gradient index films using a generalized Fourier series approach. The inverse Fourier transform method is modified to include use of the phase of the index profile as a variable in rugate filter design. Use of an optimal phase function in Fourier-based filter designs reduces the product of index contrast and thickness for desired reflectance spectra. The shape of the reflectance spectrum is recovered with greater fidelity by suppression of Gibbs oscillations and shifting of side-lobes into desired wavelength regions. A new method of gradient index thin film design using generalized Fourier series extends the domain of problems for which gradient index solutions can be found. The method is analogous to existing techniques for layer based coating design, but adds the flexibility of gradient index films. A subset of the coefficients of a generalized Fourier series representation of the gradient index of refraction profile are used as variables in a nonlinear constrained optimization formulation. The optimal values of the design coefficients are determined using a sequential quadratic programming algorithm. This method is particularly well suited for the design of coatings for laser applications, where only a few widely separated wavelength requirements exist. The generalized Fourier series method is extended to determine the minimum film thickness needed, as well as the index of refraction profile for the optimal film.

  14. Critical gradient response of the Weiland model

    NASA Astrophysics Data System (ADS)

    Asp, E.; Weiland, J.; Garbet, X.; Parail, V.; Strand, P.; JET EFDA contributors, the

    2007-08-01

    The success the Weiland model has had in reproducing modulation experiments prompted this in-depth investigation into its behaviour as a critical gradient model (CGM). The critical gradient properties of the Weiland model is examined analytically and numerically and compared with the empirical CGM commonly used in experiment. A simplified Weiland CGM is derived in which the height-above-threshold dependence is not necessarily linear. Simultaneously, the validity of the empirical CGM was examined. It is shown that an effective threshold, which is higher than the instability threshold, can be obtained if pinches influence the diffusivity.

  15. Thermal Stability of the Dynamic Magnetic Properties of FeSiAl-Al2O3 and FeSiAl-SiO2 Films Grown by Gradient-Composition Sputtering Technique

    NASA Astrophysics Data System (ADS)

    Zhong, Xiaoxi; Phuoc, Nguyen N.; Soh, Wee Tee; Ong, C. K.; Peng, Long; Li, Lezhong

    2017-01-01

    We carry out a systematic investigation of the dynamic magnetic properties of FeSiAl-Al2O3 and FeSiAl-SiO2 thin films prepared by gradient-composition deposition technique with respect to temperature in the range of 300 K to 420 K. It was found that the magnetic anisotropy field ( H K) and ferromagnetic resonance frequency ( f FMR) are increased with increasing deposition angle ( β) due to the enhancement of stress ( σ) when concentrations of Al and O or Si and O are increased. The thermal stability of FeSiAl-Al2O3 films show a very interesting behavior with the magnetic anisotropy increasing with temperature when the deposition angle is increased. In contrast, when the deposition angle is lower, the usual trend of decreasing magnetic anisotropy with increasing temperature is observed. Moreover, the temperature-dependent behaviors of the dynamic permeability and effective Gilbert damping coefficient ( α eff) for FeSiAl-Al2O3 and FeSiAl-SiO2 films at different deposition angles are discussed in detail.

  16. Bigravity from gradient expansion

    SciTech Connect

    Yamashita, Yasuho; Tanaka, Takahiro

    2016-05-04

    We discuss how the ghost-free bigravity coupled with a single scalar field can be derived from a braneworld setup. We consider DGP two-brane model without radion stabilization. The bulk configuration is solved for given boundary metrics, and it is substituted back into the action to obtain the effective four-dimensional action. In order to obtain the ghost-free bigravity, we consider the gradient expansion in which the brane separation is supposed to be sufficiently small so that two boundary metrics are almost identical. The obtained effective theory is shown to be ghost free as expected, however, the interaction between two gravitons takes the Fierz-Pauli form at the leading order of the gradient expansion, even though we do not use the approximation of linear perturbation. We also find that the radion remains as a scalar field in the four-dimensional effective theory, but its coupling to the metrics is non-trivial.

  17. Stress-gradient plasticity

    PubMed Central

    Chakravarthy, Srinath S.; Curtin, W. A.

    2011-01-01

    A new model, stress-gradient plasticity, is presented that provides unique mechanistic insight into size-dependent phenomena in plasticity. This dislocation-based model predicts strengthening of materials when a gradient in stress acts over dislocation source–obstacle configurations. The model has a physical length scale, the spacing of dislocation obstacles, and is validated by several levels of discrete-dislocation simulations. When incorporated into a continuum viscoplastic model, predictions for bending and torsion in polycrystalline metals show excellent agreement with experiments in the initial strengthening and subsequent hardening as a function of both sample-size dependence and grain size, when the operative obstacle spacing is proportional to the grain size. PMID:21911403

  18. Gradient magnetometer system balloons

    NASA Astrophysics Data System (ADS)

    Korepanov, Valery; Tsvetkov, Yury

    2005-08-01

    Earth's magnetic field study still remains one of the leading edges of experimental geophysics. Thus study is executed on the Earth surface, including ocean bottom, and on satellite heights using component, mostly flux-gate magnetometers. But balloon experiments with component magnetometers are very seldom, first of all because of great complexity of data interpretation. This niche still waits for new experimental ideology, which will allow to get the measurements results with high accuracy, especially in gradient mode. The great importance of precise balloon-borne component magnetic field gradient study is obvious. Its technical realization is based both on the available at the marked high-precision non-magnetic tiltmeters and on recent achievements of flux-gate magnetometry. The scientific goals of balloon-borne magnetic gradiometric experiment are discussed and its practical realization is proposed.

  19. Lightness, illumination, and gradients.

    PubMed

    Todorović, Dejan

    2006-01-01

    The illumination interpretation approach claims that lightness illusions can be explained as misapplications of lightness constancy mechanisms, processes which usually enable veridical extraction of surface reflectance from luminance distributions by discounting illumination. In particular, luminance gradients are thought to provide cues about the interactions of light and surfaces. Several examples of strong lightness illusions are discussed for which explanations based on illumination interpretation can be proposed. In criticisms of this approach, a variety of demonstrations of similarly structured control displays are presented, which involve equivalent lightness effects that cannot readily be accounted for by illumination interpretation mechanisms. Furthermore, a number of known and novel displays are presented that demonstrate effects of gradients on the qualitative appearance of uniform regions. Finally, some simple simulations of neural effects of luminance distributions are discussed.

  20. Gradient Index Lens Research.

    DTIC Science & Technology

    1982-11-25

    over six to nine readings at two to three input polarizations each. The first set of index values is calculated assuming ei = 450 These values are...TECHNICAL REPORT RG-CR-84-2 Sli GRADIENT INDEX LENS RESEARCH Prepared by: Duncan T. Moore The Institute of Optics University of Rochester Rochester...CLASSIFICATION OF THIS PAGE (Miten Data Fntered) READ INSTRUCTIONSREPORT DOCUMENTATION PAGE BEFORE COMPLETING FORM 1. REPORT NU14MU R GOVT ACCESSION No. 3

  1. Multiscale architectured materials with composition and grain size gradients manufactured using high-pressure torsion

    PubMed Central

    Kang, Ji Yun; Kim, Jung Gi; Park, Hyo Wook; Kim, Hyoung Seop

    2016-01-01

    The concept of multiscale architectured materials is established using composition and grain size gradients. Composition-gradient nanostructured materials are produced from coarse grained interstitial free steels via carburization and high-pressure torsion. Quantitative analyses of the dislocation density using X-ray diffraction and microstructural studies clearly demonstrate the gradients of the dislocation density and grain size. The mechanical properties of the gradient materials are compared with homogeneous nanostructured carbon steel without a composition gradient in an effort to investigate the gradient effect. Based on the above observations, the potential of multiscale architecturing to open a new material property is discussed. PMID:27229160

  2. Gradient structure-induced temperature responsiveness in styrene/methyl methacrylate gradient copolymers micelles.

    PubMed

    Zheng, Chao; Huang, Haiying; He, Tianbai

    2014-02-01

    In this work, micelles are formed by gradient copolymer of styrene and methyl methacrylate in acetone-water mixture and their temperature responsiveness is investigated in a narrow range near room temperature. Three different kinds of structural transitions could be induced by temperature: unimers to micelle transition, shrinkage/stretching of micelles, and morphological transition from spherical micelles to vesicles. In addition, a model analysis on the interface of gradient copolymer micelle is made to better understand these phenomena. It is found that both position and composition of the interface could alter in response to the change in temperature. According to the experiments and model analysis, it is proposed that temperature responsiveness might be an intrinsic and universal property of gradient copolymer micelles, which only originates from the gradient structure.

  3. Chronological changes in canopy hydrometeorological dynamics may aid invasion of a globally invasive species (Ailanthus altissima Mill. tree of heaven)

    NASA Astrophysics Data System (ADS)

    Van Stan, J. T., II; Sadeghi, S. M. M.; Pypker, T. G.; Friesen, J.

    2016-12-01

    We examined the effect of a globally-invasive species, Ailanthus altissima, on canopy hydrometeorological processes. Throughfall (TF), stemflow (SF) and interception loss (I) were measured in a chronosequence of three A. altissima stands (planted 1975, 1985, 1995). Canopy structural and ecohydrological parameters varied with age: woody area index (WAI), ratio of wet canopy evaporation and rainfall rates, and stem drainage coefficient increased; while leaf area index (LAI), canopy water storage, and gap fraction declined. This corresponded to increased SF and decreased TF across annual, seasonal, and inter-storm scales. Changes in canopy hydrologic flow paths (TF v. SF) may be advantageous to invasive species as the promotion of SF with canopy age may increase water supply to the roots and help distribute allelopathic chemicals through the soil. Further research is needed on the correlation between canopy architecture of A. altissima invasion and the distribution of water and chemicals to soils.

  4. Landscape-scale quantification of fire-induced change in canopy cover following mountain pine beetle outbreak and timber harvest

    USGS Publications Warehouse

    McCarley, T. Ryan; Kolden, Crystal A.; Vaillant, Nicole M.; Hudak, Andrew T.; Smith, Alistair M.S.; Kreitler, Jason R.

    2017-01-01

    Across the western United States, the three primary drivers of tree mortality and carbon balance are bark beetles, timber harvest, and wildfire. While these agents of forest change frequently overlap, uncertainty remains regarding their interactions and influence on specific subsequent fire effects such as change in canopy cover. Acquisition of pre- and post-fire Light Detection and Ranging (LiDAR) data on the 2012 Pole Creek Fire in central Oregon provided an opportunity to isolate and quantify fire effects coincident with specific agents of change. This study characterizes the influence of pre-fire mountain pine beetle (MPB; Dendroctonus ponderosae) and timber harvest disturbances on LiDAR-estimated change in canopy cover. Observed canopy loss from fire was greater (higher severity) in areas experiencing pre-fire MPB (Δ 18.8%CC) than fire-only (Δ 11.1%CC). Additionally, increasing MPB intensity was directly related to greater canopy loss. Canopy loss was lower for all areas of pre-fire timber harvest (Δ 3.9%CC) than for fire-only, but among harvested areas, the greatest change was observed in the oldest treatments and the most intensive treatments [i.e., stand clearcut (Δ 5.0%CC) and combination of shelterwood establishment cuts and shelterwood removal cuts (Δ 7.7%CC)]. These results highlight the importance of accounting for and understanding the impact of pre-fire agents of change such as MPB and timber harvest on subsequent fire effects in land management planning. This work also demonstrates the utility of multi-temporal LiDAR as a tool for quantifying these landscape-scale interactions.

  5. Discrete gradient methods for solving variational image regularisation models

    NASA Astrophysics Data System (ADS)

    Grimm, V.; McLachlan, Robert I.; McLaren, David I.; Quispel, G. R. W.; Schönlieb, C.-B.

    2017-07-01

    Discrete gradient methods are well-known methods of geometric numerical integration, which preserve the dissipation of gradient systems. In this paper we show that this property of discrete gradient methods can be interesting in the context of variational models for image processing, that is where the processed image is computed as a minimiser of an energy functional. Numerical schemes for computing minimisers of such energies are desired to inherit the dissipative property of the gradient system associated to the energy and consequently guarantee a monotonic decrease of the energy along iterations, avoiding situations in which more computational work might lead to less optimal solutions. Under appropriate smoothness assumptions on the energy functional we prove that discrete gradient methods guarantee a monotonic decrease of the energy towards stationary states, and we promote their use in image processing by exhibiting experiments with convex and non-convex variational models for image deblurring, denoising, and inpainting.

  6. Nickel gradient electrode

    SciTech Connect

    Zimmerman, A.H.

    1988-03-31

    This invention relates generally to rechargeable batteries, and, in particular, relates to batteries that use nickel electrodes. It provides an improved nickel electrode with a selected gradient of additive materials. The concentration of additives in the impregnating solution are controlled during impregnation such that an additive gradient is generated. In the situation where the highest ionic conductivity is needed at the current collector boundary with the active material, the electrochemical impregnating solution is initially high in additive, and at the end of impregnation has been adjusted to significantly lower additive concentration. For chemical impregnation, the electrodes are similarly dipped in solutions that are initially high in additive. This invention is suitable for conventional additives such as cobalt, cadmium, barium, manganese, and zinc. It is therefore one objective of the invention to provide an improved nickel electrode of a battery cell with an additive in the active material to increase the life of the battery cell. Another objective is to provide for an improved nickel electrode having a greater concentration of additive near the current collector of nickel.

  7. Energy in density gradient

    SciTech Connect

    Vranjes, J.; Kono, M.

    2015-01-15

    Inhomogeneous plasmas and fluids contain energy stored in inhomogeneity and they naturally tend to relax into lower energy states by developing instabilities or by diffusion. But the actual amount of energy in such inhomogeneities has remained unknown. In the present work, the amount of energy stored in a density gradient is calculated for several specific density profiles in a cylindrical configuration. This is of practical importance for drift wave instability in various plasmas, and, in particular, in its application in models dealing with the heating of solar corona because the instability is accompanied with stochastic heating, so the energy contained in inhomogeneity is effectively transformed into heat. It is shown that even for a rather moderate increase of the density at the axis in magnetic structures in the corona by a factor 1.5 or 3, the amount of excess energy per unit volume stored in such a density gradient becomes several orders of magnitude greater than the amount of total energy losses per unit volume (per second) in quiet regions in the corona. Consequently, within the life-time of a magnetic structure such energy losses can easily be compensated by the stochastic drift wave heating.

  8. Density Gradient Dependent Helicon Modes

    NASA Astrophysics Data System (ADS)

    Panevsky, Martin; Bengtson, Roger

    2002-11-01

    Radially localized helicon modes have been proposed to provide a fuller description of helicon discharges over a wide span of operating conditions and gas types [1]. These plasma modes could be of vital importance to the VASIMR engine. They depend on a radial density gradient and appear to operate over a range of frequencies inaccessible to traditional helicon discharges. Our work focuses on confirming experimentally the existence and properties of these helicon modes in Argon, Helium, and Hydrogen. We investigate the density profile, power deposition, wavefields, and dispersion relation of the new helicon modes which differ substantially from the properties of the traditional helicon plasma. We are using a set of dual half-turn helical antennas driven at 13.56 MHz. Our diagnostics includes a system for monitoring the plasma impedance, a set of Langmuir probes, a set of magnetic probes, as well as sensors for monitoring the pressure and DC magnetic field. *Work supported in part by Advanced Space Propulsion Lab, Johnson Space Center, NASA [1] B. N. Breizman and A. V. Arefiev, Phys. Rev. 84, 3863 (2000)

  9. Controlled Temperature Gradient Improves Freezing Alloy

    NASA Technical Reports Server (NTRS)

    Schmidt, Deborah; Alter, Wendy S.; Hamilton, William D.

    1991-01-01

    Controlled gradient of temperature in advancing zone of solidification increases fatigue life of directionally solidified nickel-base superalloy. Improved solidification process eliminates, reduces, or controls microstructure of deleterious brittle phases, including carbides and gamma/gamma prime eutectic. Also reduces microsegregation and makes discrete carbides (if present) become fine and blocky. Expected to improve properties of other alloys, of both directionally-solidified polycrystalline and single-crystal forms.

  10. Formation of actin networks in microfluidic concentration gradients

    NASA Astrophysics Data System (ADS)

    Strelnikova, Natalja; Herren, Florian; Schoenenberger, Cora-Ann; Pfohl, Thomas

    2016-05-01

    The physical properties of cytoskeletal networks are contributors in a number of mechanical responses of cells including cellular deformation and locomotion, and are crucial for the proper action of living cells. Local chemical gradients modulate cytoskeletal functionality including the interactions of the cytoskeleton with other cellular components. Actin is a major constituent of the cytoskeleton. Introducing a microfluidic-based platform, we explored the impact of concentration gradients on the formation and structural properties of actin networks. Microfluidics-controlled flow-free steady state experimental conditions allow for the generation of chemical gradients of different profiles, such as linear or step-like. We discovered specific features of actin networks emerging in defined gradients. In particular, we analyzed the effects of spatial conditions on network properties, bending rigidities of network links, and the network elasticity.

  11. Generalized conjugate gradient squared

    SciTech Connect

    Fokkema, D.R.; Sleijpen, G.L.G.

    1994-12-31

    In order to solve non-symmetric linear systems of equations, the Conjugate Gradient Squared (CGS) is a well-known and widely used iterative method. In practice the method converges fast, often twice as fast as the Bi-Conjugate Gradient method. This is what you may expect, since CGS uses the square of the BiCG polynomial. However, CGS may suffer from its erratic convergence behavior. The method may diverge or the approximate solution may be inaccurate. BiCGSTAB uses the BiCG polynomial and a product of linear factors in an attempt to smoothen the convergence. In many cases, this has proven to be very effective. Unfortunately, the convergence of BiCGSTAB may stall when a linear factor (nearly) degenerates. BiCGstab({ell}) is designed to overcome this degeneration of linear factors. It generalizes BiCGSTAB and uses both the BiCG polynomial and a product of higher order factors. Still, CGS may converge faster than BiCGSTAB or BiCGstab({ell}). So instead of using a product of linear or higher order factors, it may be worthwhile to look for other polynomials. Since the BiCG polynomial is based on a three term recursion, a natural choice would be a polynomial based on another three term recursion. Possibly, a suitable choice of recursion coefficients would result in method that converges faster or as fast as CGS, but less erratic. It turns out that an algorithm for such a method can easily be formulated. One particular choice for the recursion coefficients leads to CGS. Therefore one could call this algorithm generalized CGS. Another choice for the recursion coefficients leads to BiCGSTAB. It is therefore possible to mix linear factors and some polynomial based on a three term recursion. This way one may get the best of both worlds. The authors will report on their findings.

  12. Nanoparticle manipulation by thermal gradient

    PubMed Central

    2012-01-01

    A method was proposed to manipulate nanoparticles through a thermal gradient. The motion of a fullerene molecule enclosed inside a (10, 10) carbon nanotube with a thermal gradient was studied by molecular dynamics simulations. We created a one-dimensional potential valley by imposing a symmetrical thermal gradient inside the nanotube. When the temperature gradient was large enough, the fullerene sank into the valley and became trapped. The escaping velocities of the fullerene were evaluated based on the relationship between thermal gradient and thermophoretic force. We then introduced a new way to manipulate the position of nanoparticles by translating the position of thermostats with desirable thermal gradients. Compared to nanomanipulation using a scanning tunneling microscope or an atomic force microscope, our method for nanomanipulation has a great advantage by not requiring a direct contact between the probe and the object. PMID:22364240

  13. Step-gradient capillary electrochromatography.

    PubMed

    Euerby, M R; Gilligan, D; Johnson, C M; Bartle, K D

    1997-10-01

    The analytical benefits of using a step-gradient in capillary electrochromatography (CEC) are demonstrated. The application of step-gradient CEC to the analysis of six diuretics of widely differing lipophilicities was evaluated and shown to result in a marked reduction in the analysis time and an improvement in the peak shape for later-eluting lipophilic components. When the step-gradient approach was performed in an automated mode, the retention time RSD for repeated injections was below 1%.

  14. Escalation of polymerization in a thermal gradient.

    PubMed

    Mast, Christof B; Schink, Severin; Gerland, Ulrich; Braun, Dieter

    2013-05-14

    For the emergence of early life, the formation of biopolymers such as RNA is essential. However, the addition of nucleotide monomers to existing oligonucleotides requires millimolar concentrations. Even in such optimistic settings, no polymerization of RNA longer than about 20 bases could be demonstrated. How then could self-replicating ribozymes appear, for which recent experiments suggest a minimal length of 200 nt? Here, we demonstrate a mechanism to bridge this gap: the escalated polymerization of nucleotides by a spatially confined thermal gradient. The gradient accumulates monomers by thermophoresis and convection while retaining longer polymers exponentially better. Polymerization and accumulation become mutually self-enhancing and result in a hyperexponential escalation of polymer length. We describe this escalation theoretically under the conservative assumption of reversible polymerization. Taking into account the separately measured thermophoretic properties of RNA, we extrapolate the results for primordial RNA polymerization inside a temperature gradient in pores or fissures of rocks. With a dilute, nanomolar concentration of monomers the model predicts that a pore length of 5 cm and a temperature difference of 10 K suffice to polymerize 200-mers of RNA in micromolar concentrations. The probability to generate these long RNAs is raised by a factor of >10(600) compared with polymerization in a physical equilibrium. We experimentally validate the theory with the reversible polymerization of DNA blocks in a laser-driven thermal trap. The results confirm that a thermal gradient can significantly enlarge the available sequence space for the emergence of catalytically active polymers.

  15. Proton gradients at the origin of life.

    PubMed

    Lane, Nick

    2017-06-01

    Chemiosmotic coupling - the harnessing of electrochemical ion gradients across membranes to drive metabolism - is as universally conserved as the genetic code. As argued previously in these pages, such deep conservation suggests that ion gradients arose early in evolution, and might have played a role in the origin of life. Alkaline hydrothermal vents harbour pH gradients of similar polarity and magnitude to those employed by modern cells, one of many properties that make them attractive models for life's origin. Their congruence with the physiology of anaerobic autotrophs that use the acetyl CoA pathway to fix CO2 gives the alkaline vent model broad appeal to biologists. Recently, however, a paper by Baz Jackson criticized the hypothesis, concluding that natural pH gradients were unlikely to have played any role in the origin of life. Unfortunately, Jackson mainly criticized his own interpretations of the theory, not what the literature says. This counterpoint is intended to set the record straight. © 2017 WILEY Periodicals, Inc.

  16. Escalation of polymerization in a thermal gradient

    PubMed Central

    Mast, Christof B.; Schink, Severin; Gerland, Ulrich; Braun, Dieter

    2013-01-01

    For the emergence of early life, the formation of biopolymers such as RNA is essential. However, the addition of nucleotide monomers to existing oligonucleotides requires millimolar concentrations. Even in such optimistic settings, no polymerization of RNA longer than about 20 bases could be demonstrated. How then could self-replicating ribozymes appear, for which recent experiments suggest a minimal length of 200 nt? Here, we demonstrate a mechanism to bridge this gap: the escalated polymerization of nucleotides by a spatially confined thermal gradient. The gradient accumulates monomers by thermophoresis and convection while retaining longer polymers exponentially better. Polymerization and accumulation become mutually self-enhancing and result in a hyperexponential escalation of polymer length. We describe this escalation theoretically under the conservative assumption of reversible polymerization. Taking into account the separately measured thermophoretic properties of RNA, we extrapolate the results for primordial RNA polymerization inside a temperature gradient in pores or fissures of rocks. With a dilute, nanomolar concentration of monomers the model predicts that a pore length of 5 cm and a temperature difference of 10 K suffice to polymerize 200-mers of RNA in micromolar concentrations. The probability to generate these long RNAs is raised by a factor of >10600 compared with polymerization in a physical equilibrium. We experimentally validate the theory with the reversible polymerization of DNA blocks in a laser-driven thermal trap. The results confirm that a thermal gradient can significantly enlarge the available sequence space for the emergence of catalytically active polymers. PMID:23630280

  17. Gradient optimization and nonlinear control

    NASA Technical Reports Server (NTRS)

    Hasdorff, L.

    1976-01-01

    The book represents an introduction to computation in control by an iterative, gradient, numerical method, where linearity is not assumed. The general language and approach used are those of elementary functional analysis. The particular gradient method that is emphasized and used is conjugate gradient descent, a well known method exhibiting quadratic convergence while requiring very little more computation than simple steepest descent. Constraints are not dealt with directly, but rather the approach is to introduce them as penalty terms in the criterion. General conjugate gradient descent methods are developed and applied to problems in control.

  18. Gradient forests: calculating importance gradients on physical predictors.

    PubMed

    Ellis, Nick; Smith, Stephen J; Pitcher, C Roland

    2012-01-01

    In ecological analyses of species and community distributions there is interest in the nature of their responses to environmental gradients and in identifying the most important environmental variables, which may be used for predicting patterns of biodiversity. Methods such as random forests already exist to assess predictor importance for individual species and to indicate where along gradients abundance changes. However, there is a need to extend these methods to whole assemblages, to establish where along the range of these gradients the important compositional changes occur, and to identify any important thresholds or change points. We develop such a method, called "gradient forest," which is an extension of the random forest approach. By synthesizing the cross-validated R2 and accuracy importance measures from univariate random forest analyses across multiple species, sampling devices, and surveys, gradient forest obtains a monotonic function of each predictor that represents the compositional turnover along the gradient of the predictor. When applied to a synthetic data set, the method correctly identified the important predictors and delineated where the compositional change points occurred along these gradients. Application of gradient forest to a real data set from part of the Great Barrier Reef identified mud fraction of the sediment as the most important predictor, with highest compositional turnover occurring at mud fraction values around 25%, and provided similar information for other predictors. Such refined information allows for more accurate capturing of biodiversity patterns for the purposes of bioregionalization, delineation of protected areas, or designing of biodiversity surveys.

  19. Canonical trivialization of gravitational gradients

    NASA Astrophysics Data System (ADS)

    Niedermaier, Max

    2017-06-01

    A one-parameter family of canonical transformations is constructed that reduces the Hamiltonian form of the Einstein-Hilbert action to its strong coupling limit where dynamical spatial gradients are absent. The parameter can alternatively be viewed as the overall scale of the spatial metric or as a fractional inverse power of Newton’s constant. The generating function of the canonical transformation is constructed iteratively as a powerseries in the parameter to all orders. The algorithm draws on Lie-Deprit transformation theory and defines a ‘trivialization map’ with several bonus properties: (i) Trivialization of the Hamiltonian constraint implies that of the action while the diffeomorphism constraint is automatically co-transformed. (ii) Only a set of ordinary differential equations needs to be solved to drive the iteration via a homological equation where no gauge fixing is required. (iii) In contrast to (the classical limit of) a Lagrangian trivialization map the algorithm also produces series solutions of the field equations. (iv) In the strong coupling theory temporal gauge variations are abelian, nevertheless the map intertwines with the respective gauge symmetries on the action, the field equations, and their solutions.

  20. A Study of Stress Distribution in Layered and Gradient Tribological Coatings (Preprint)

    DTIC Science & Technology

    2006-11-01

    distribution in the layered and gradient coatings and the 440C steel substrate. Layered and gradient Ti/TiC coatings consisted of a titanium bond...applied load, material properties, and interfacial friction on the stress distribution in the layered and gradient coatings and the 440C steel...and gradient Ti/TiC/DLC coating displaying the compositional variation of the Ti/TiC/DLC coating deposited on the top of the 440C steel substrate

  1. Leaf Spectra and Weight of Species in Canopy, Subcanopy, and Understory Layers in a Venezuelan Andean Cloud Forest

    PubMed Central

    Acevedo, Miguel F.; Ataroff, Michele

    2012-01-01

    We characterize the leaf spectra of tree species of an Andean cloud forest in Venezuela, grouped according to position in canopy, subcanopy and understory. We measured leaf reflectance and transmittance spectra in the 400–750 nm range using a high-resolution spectrometer. Both signals were subtracted from unity to calculate the absorbance signal. Nine spectral variables were calculated for each signal, three based on wide-bands and six based on features. We measured leaf mass per unit area of all species, and calculated efficiency of absorbance, as ratio of absorbance in photosynthetic range over leaf mass. Differences among groups were significant for several absorbance and transmittance variables, leaf mass, and efficiency of absorbance. The clearest differences are between canopy and understory species. There is strong correlation for at least one pair of band variables for each signal, and each band variable is strongly correlated with at least one feature variable for most signals. High canonical correlations are obtained between pairs of the three canonical axes for bands and the first three canonical axes for features. Absorbance variables produce species clusters having the closest correspondence to the species groups. Linear discriminant analysis shows that species groups can be sorted by all signals, particularly absorbance. PMID:24278746

  2. Improving and validating 3D models for the leaf energy balance in canopy-scale problems with complex geometry

    NASA Astrophysics Data System (ADS)

    Bailey, B.; Stoll, R., II; Miller, N. E.; Pardyjak, E.; Mahaffee, W.

    2014-12-01

    Plants cover the majority of Earth's land surface, and thus play a critical role in the surface energy balance. Within individual plant communities, the leaf energy balance is a fundamental component of most biophysical processes. Absorbed radiation drives the energy balance and provides the means by which plants produce food. Available energy is partitioned into sensible and latent heat fluxes to determine surface temperature, which strongly influences rates of metabolic activity and growth. The energy balance of an individual leaf is coupled with other leaves in the community through longwave radiation emission and advection through the air. This complex coupling can make scaling models from leaves to whole-canopies difficult, specifically in canopies with complex, heterogeneous geometries. We present a new three-dimensional canopy model that simultaneously resolves sub-tree to whole-canopy scales. The model provides spatially explicit predictions of net radiation exchange, boundary-layer and stomatal conductances, evapotranspiration rates, and ultimately leaf surface temperature. The radiation model includes complex physics such as anisotropic emission and scattering. Radiation calculations are accelerated by leveraging graphics processing unit (GPU) technology, which allows canopy-scale problems to be performed on a standard desktop workstation. Since validating the three-dimensional distribution of leaf temperature can be extremely challenging, we used several independent measurement techniques to quantify errors in measured and modeled values. When compared with measured leaf temperatures, the model gave a mean error of about 2°C, which was close to the estimated measurement uncertainty.

  3. Leaf spectra and weight of species in canopy, subcanopy, and understory layers in a venezuelan andean cloud forest.

    PubMed

    Acevedo, Miguel F; Ataroff, Michele

    2012-01-01

    We characterize the leaf spectra of tree species of an Andean cloud forest in Venezuela, grouped according to position in canopy, subcanopy and understory. We measured leaf reflectance and transmittance spectra in the 400-750 nm range using a high-resolution spectrometer. Both signals were subtracted from unity to calculate the absorbance signal. Nine spectral variables were calculated for each signal, three based on wide-bands and six based on features. We measured leaf mass per unit area of all species, and calculated efficiency of absorbance, as ratio of absorbance in photosynthetic range over leaf mass. Differences among groups were significant for several absorbance and transmittance variables, leaf mass, and efficiency of absorbance. The clearest differences are between canopy and understory species. There is strong correlation for at least one pair of band variables for each signal, and each band variable is strongly correlated with at least one feature variable for most signals. High canonical correlations are obtained between pairs of the three canonical axes for bands and the first three canonical axes for features. Absorbance variables produce species clusters having the closest correspondence to the species groups. Linear discriminant analysis shows that species groups can be sorted by all signals, particularly absorbance.

  4. Property.

    ERIC Educational Resources Information Center

    Piele, Philip K.

    Several court cases involving acquisition, use, and disposal of property by institutions of higher education are briefly summarized in this chapter. Cases discussed touch on such topics as municipal annexation of university property; repurchase of properties temporarily allocated to faculty members; implications of zoning laws and zoning board…

  5. Property.

    ERIC Educational Resources Information Center

    Piele, Philip K.

    Several court cases involving acquisition, use, and disposal of property by institutions of higher education are briefly summarized in this chapter. Cases discussed touch on such topics as municipal annexation of university property; repurchase of properties temporarily allocated to faculty members; implications of zoning laws and zoning board…

  6. Multilayer High-Gradient Insulators

    SciTech Connect

    Harris, J R

    2006-08-16

    Multilayer High-Gradient Insulators are vacuum insulating structures composed of thin, alternating layers of dielectric and metal. They are currently being developed for application to high-current accelerators and related pulsed power systems. This paper describes some of the High-Gradient Insulator research currently being conducted at Lawrence Livermore National Laboratory.

  7. Empirical equation estimates geothermal gradients

    SciTech Connect

    Kutasov, I.M. )

    1995-01-02

    An empirical equation can estimate geothermal (natural) temperature profiles in new exploration areas. These gradients are useful for cement slurry and mud design and for improving electrical and temperature log interpretation. Downhole circulating temperature logs and surface outlet temperatures are used for predicting the geothermal gradients.

  8. Density Gradients in Chemistry Teaching

    ERIC Educational Resources Information Center

    Miller, P. J.

    1972-01-01

    Outlines experiments in which a density gradient might be used to advantage. A density gradient consists of a column of liquid, the composition and density of which varies along its length. The procedure can be used in analysis of solutions and mixtures and in density measures of solids. (Author/TS)

  9. Density Gradients in Chemistry Teaching

    ERIC Educational Resources Information Center

    Miller, P. J.

    1972-01-01

    Outlines experiments in which a density gradient might be used to advantage. A density gradient consists of a column of liquid, the composition and density of which varies along its length. The procedure can be used in analysis of solutions and mixtures and in density measures of solids. (Author/TS)

  10. Effects of degree correlation on scale-free gradient networks

    NASA Astrophysics Data System (ADS)

    Pan, Gui-Jun; Yan, Xiao-Qing; Ma, Wei-Chuan; Luo, Yi-Hui; Huang, Zhong-Bing

    2010-05-01

    We have studied the effects of degree correlation on congestion pressure in scale-free gradient networks. It is observed that the jamming coefficient J is insensitive to the degree correlation coefficient r for assortative and strongly disassortative scale-free networks, and J markedly decreases with an increase in r for weakly disassortative scale-free networks. We have also investigated the effects of degree correlation on the topology structure of scale-free gradient networks, and discussed the relation between the topology structure properties and transport efficiency of gradient networks.

  11. Kerosene wick lamp flame deformation in gradient magnetic fields

    NASA Astrophysics Data System (ADS)

    Saeedi, A.; Moghiman, M.

    2014-03-01

    The behavior of a kerosene wick lamp flame in the presence of non-uniform DC magnetic fields has been investigated and the results of this experimental study are presented. It has long been recognized that magnetic fields can influence the behavior of diffusion flames as a result of the paramagnetic and diamagnetic properties of the constituent gases. Using an electromagnet consisting of two coils and cores to generate a horizontal magnetic field, a non-uniform upward increasing and decreasing magnetic field was applied to a kerosene wick lamp flame. The experimental results show that the influence of DC gradient magnetic field on diffusion flame structure deformation depends on the flame position in the increasing or decreasing magnetic field, the flame situation relative to the maximum of the absolute value of the gradient and the quantity of the gradient magnetic field. It was also observed that both flame front area and flame height decrease in the positive and negative gradient field below the maximum of the absolute value of the gradient. Also, increasing the absolute of the gradient of the square magnetic induction in the positive and negative gradient field above the maximum of the absolute value of the gradient cause to elongate the flame and increase in the flame front area and then the flame height and front area decrease.

  12. Gradient zone boundary control in salt gradient solar ponds

    DOEpatents

    Hull, John R.

    1984-01-01

    A method and apparatus for suppressing zone boundary migration in a salt gradient solar pond includes extending perforated membranes across the pond at the boundaries, between the convective and non-convective zones, the perforations being small enough in size to prevent individual turbulence disturbances from penetrating the hole, but being large enough to allow easy molecular diffusion of salt thereby preventing the formation of convective zones in the gradient layer. The total area of the perforations is a sizable fraction of the membrane area to allow sufficient salt diffusion while preventing turbulent entrainment into the gradient zone.

  13. Comparing species interaction networks along environmental gradients.

    PubMed

    Pellissier, Loïc; Albouy, Camille; Bascompte, Jordi; Farwig, Nina; Graham, Catherine; Loreau, Michel; Maglianesi, Maria Alejandra; Melián, Carlos J; Pitteloud, Camille; Roslin, Tomas; Rohr, Rudolf; Saavedra, Serguei; Thuiller, Wilfried; Woodward, Guy; Zimmermann, Niklaus E; Gravel, Dominique

    2017-09-22

    Knowledge of species composition and their interactions, in the form of interaction networks, is required to understand processes shaping their distribution over time and space. As such, comparing ecological networks along environmental gradients represents a promising new research avenue to understand the organization of life. Variation in the position and intensity of links within networks along environmental gradients may be driven by turnover in species composition, by variation in species abundances and by abiotic influences on species interactions. While investigating changes in species composition has a long tradition, so far only a limited number of studies have examined changes in species interactions between networks, often with differing approaches. Here, we review studies investigating variation in network structures along environmental gradients, highlighting how methodological decisions about standardization can influence their conclusions. Due to their complexity, variation among ecological networks is frequently studied using properties that summarize the distribution or topology of interactions such as number of links, connectance, or modularity. These properties can either be compared directly or using a procedure of standardization. While measures of network structure can be directly related to changes along environmental gradients, standardization is frequently used to facilitate interpretation of variation in network properties by controlling for some co-variables, or via null models. Null models allow comparing the deviation of empirical networks from random expectations and are expected to provide a more mechanistic understanding of the factors shaping ecological networks when they are coupled with functional traits. As an illustration, we compare approaches to quantify the role of trait matching in driving the structure of plant-hummingbird mutualistic networks, i.e. a direct comparison, standardized by null models and hypothesis

  14. High field gradient particle accelerator

    DOEpatents

    Nation, John A.; Greenwald, Shlomo

    1989-01-01

    A high electric field gradient electron accelerator utilizing short duration, microwave radiation, and capable of operating at high field gradients for high energy physics applications or at reduced electric field gradients for high average current intermediate energy accelerator applications. Particles are accelerated in a smooth bore, periodic undulating waveguide, wherein the period is so selected that the particles slip an integral number of cycles of the r.f. wave every period of the structure. This phase step of the particles produces substantially continuous acceleration in a traveling wave without transverse magnetic or other guide means for the particle.

  15. High field gradient particle accelerator

    DOEpatents

    Nation, J.A.; Greenwald, S.

    1989-05-30

    A high electric field gradient electron accelerator utilizing short duration, microwave radiation, and capable of operating at high field gradients for high energy physics applications or at reduced electric field gradients for high average current intermediate energy accelerator applications is disclosed. Particles are accelerated in a smooth bore, periodic undulating waveguide, wherein the period is so selected that the particles slip an integral number of cycles of the r.f. wave every period of the structure. This phase step of the particles produces substantially continuous acceleration in a traveling wave without transverse magnetic or other guide means for the particle. 10 figs.

  16. Use of Ground Penetrating Radar to Study Gradient Media

    NASA Astrophysics Data System (ADS)

    Titov, A.

    2016-12-01

    Nowadays Ground Penetrating Radar (GPR) is often used to solve different problems of applied geophysics including the hydrological ones. This work was motivated by detection of weak reflections in the body of water observed during the surveys on the freshwater lakes using GPR. The same reflections were first analyzed by John Bradford in 2007. These reflections can arise from the thermal gradient layer or thermocline due to different dielectric permittivity of cold and warm water. We employed physical and mathematical modeling to identify the properties of such thermoclines. We have constructed a special GPR stand to study the gradient media in our laboratory. The stand consists of a water-filled plastic tank and plastic tubes, which gather the cold water under the warm water. Our stand allows for changing parameters of the gradient layer, such as limits of dielectric permittivity and the thickness of the gradient layer. GPR antenna was placed slightly under the water surface to remove the parasitic reflections. To visualize the thermal distribution, an infrared camera and thermal sensors were used. Analysis of the GPR traces after physical modeling, performed in the MATLAB environment, allows us to locate the weak reflection from the gradient layer. We observed that (i) the change of the gradient boundary values alters the amplitude of the signal, (ii) the arrival time of the impulse reflected from the gradient layer corresponds to the arrival time of the impulse reflected from the top boundary of this layer, and (iii) the shape of the signal reflected from the gradient layer coincides with the shape of the signal reflected from the non-gradient boundary between two bodies. The quantitative properties of thermocline can be determined using amplitude analysis of GPR signals. Finally, the developed methods were successfully applied to real field data.

  17. Property.

    ERIC Educational Resources Information Center

    Goldblatt, Steven M.; Piele, Philip K.

    This chapter reviews 1982 cases related to school property. Cases involving citizen efforts to overturn school board decisions to close schools dominate the property chapter, and courts continue to uphold school board authority to close schools, transfer students, and sell or lease the buildings. Ten cases involving detachment and attachment of…

  18. Property.

    ERIC Educational Resources Information Center

    Piele, Philip K.; Johnson, Margaret M.

    This chapter deals with 1981 cases involving disputes over property. Cases involving the detachment and attachment of land continue to dominate the property chapter with 11 cases reported, the same number summarized in last year's chapter. One case involving school board referenda raised the interesting question of whether or not a state could…

  19. Property.

    ERIC Educational Resources Information Center

    Piele, Philip K.

    Chapter 7 of a book on school law, this chapter deals with 1979 cases involving disputes over property. Cases involving taxpayer attempts to prevent the construction of school buildings dominate this year's property chapter, as they did last year's. Yet, paradoxically, there is also a significant increase in cases in which taxpayers tried to…

  20. Property.

    ERIC Educational Resources Information Center

    Bickel, Robert D.; Zeller, Trisha A.

    A number of cases related to property issues involving institutions of higher education are examined in this chapter. Cases discussed touch on such topics as funding for property and equipment acquisition; opposition to building construction or demolition; zoning issues; building construction and equipment contracts; and lease agreements. Current…

  1. Property.

    ERIC Educational Resources Information Center

    Bickel, Robert D.; Zeller, Trisha A.

    A number of cases related to property issues involving institutions of higher education are examined in this chapter. Cases discussed touch on such topics as funding for property and equipment acquisition; opposition to building construction or demolition; zoning issues; building construction and equipment contracts; and lease agreements. Current…

  2. Property.

    ERIC Educational Resources Information Center

    Piele, Philip K.; Johnson, Margaret M.

    This chapter deals with 1981 cases involving disputes over property. Cases involving the detachment and attachment of land continue to dominate the property chapter with 11 cases reported, the same number summarized in last year's chapter. One case involving school board referenda raised the interesting question of whether or not a state could…

  3. Property.

    ERIC Educational Resources Information Center

    Piele, Philip K.

    Chapter 7 of a book on school law, this chapter deals with 1979 cases involving disputes over property. Cases involving taxpayer attempts to prevent the construction of school buildings dominate this year's property chapter, as they did last year's. Yet, paradoxically, there is also a significant increase in cases in which taxpayers tried to…

  4. JPRS Report Science & Technology, Japan; Functionally Gradient Materials Symposium

    DTIC Science & Technology

    2007-11-02

    Reaction Method 48 Research on Si3N4-M0 Ceramic With Gradient Composition 54 Research on FGM Thermal Property Evaluation Technique 62 Research on FGM...high strength and good reliability. In solid state bonding the most important factor which reduces these properties is the edge effect. In this area...cooling is also important. Recently the active brazing alloys used in Si3NA joining can present some brittle properties which can lower the interface

  5. Gravity Gradients Frame Oceanus Procellarum

    NASA Image and Video Library

    2014-10-01

    Topography of Earth moon generated from data NASA LRO, with the gravity anomalies bordering the Procellarum region superimposed in blue. The border structures are shown using gravity gradients calculated with data from NASA GRAIL mission.

  6. Parameter-exploring policy gradients.

    PubMed

    Sehnke, Frank; Osendorfer, Christian; Rückstiess, Thomas; Graves, Alex; Peters, Jan; Schmidhuber, Jürgen

    2010-05-01

    We present a model-free reinforcement learning method for partially observable Markov decision problems. Our method estimates a likelihood gradient by sampling directly in parameter space, which leads to lower variance gradient estimates than obtained by regular policy gradient methods. We show that for several complex control tasks, including robust standing with a humanoid robot, this method outperforms well-known algorithms from the fields of standard policy gradients, finite difference methods and population based heuristics. We also show that the improvement is largest when the parameter samples are drawn symmetrically. Lastly we analyse the importance of the individual components of our method by incrementally incorporating them into the other algorithms, and measuring the gain in performance after each step.

  7. High-thermal-gradient Superalloy Crystal Growth

    NASA Technical Reports Server (NTRS)

    Pearson, D. D.; Anton, D. L.; Giamei, A. F.

    1985-01-01

    Single, (001)-oriented crystals of PWA 1480 were processed in alumina/silica shell molds in a laboratory high gradient furnace. The furnace employs a graphite resistance heated element, a radiation baffle, and a water cooled radiation trap below the baffle. All crystals were grown in vacuum (10 torr) and all heat transfer was radiative. The element is constructed with a variable cross section that is tapered just above the baffle to maximize heat input and therefore thermal gradient. A maximum alloy temperature of 1600 C was used. A thermal gradient of 130 deg C/cm was recorded at 1370 C just above the solidus of the PWA 1480 alloys. Crystal bars with 14.4 and 17.5 mm diameters were grown in alumina/silica shell molds. Each crystal was started from a 1.6 mm pencil seed at a rate of 76 mm/hr and slowly accelerated to a rate of 200 mm/hr under computer control. Volume percent porosity and average pore size were measured as functions of distance in representative bars. Low cycle fatigue behavior and stress rupture properties were determined.

  8. Gradient expansion, curvature perturbations, and magnetized plasmas

    SciTech Connect

    Giovannini, Massimo; Rezaei, Zahra

    2011-04-15

    The properties of magnetized plasmas are always investigated under the hypothesis that the relativistic inhomogeneities stemming from the fluid sources and from the geometry itself are sufficiently small to allow for a perturbative description prior to photon decoupling. The latter assumption is hereby relaxed and predecoupling plasmas are described within a suitable expansion where the inhomogeneities are treated to a given order in the spatial gradients. It is argued that the (general relativistic) gradient expansion shares the same features of the drift approximation, customarily employed in the description of cold plasmas, so that the two schemes are physically complementary in the large-scale limit and for the low-frequency branch of the spectrum of plasma modes. The two-fluid description, as well as the magnetohydrodynamical reduction, is derived and studied in the presence of the spatial gradients of the geometry. Various solutions of the coupled system of evolution equations in the anti-Newtonian regime and in the quasi-isotropic approximation are presented. The relation of this analysis to the so-called separate universe paradigm is outlined. The evolution of the magnetized curvature perturbations in the nonlinear regime is addressed for the magnetized adiabatic mode in the plasma frame.

  9. Low-gradient aortic stenosis.

    PubMed

    Clavel, Marie-Annick; Magne, Julien; Pibarot, Philippe

    2016-09-07

    An important proportion of patients with aortic stenosis (AS) have a 'low-gradient' AS, i.e. a small aortic valve area (AVA <1.0 cm(2)) consistent with severe AS but a low mean transvalvular gradient (<40 mmHg) consistent with non-severe AS. The management of this subset of patients is particularly challenging because the AVA-gradient discrepancy raises uncertainty about the actual stenosis severity and thus about the indication for aortic valve replacement (AVR) if the patient has symptoms and/or left ventricular (LV) systolic dysfunction. The most frequent cause of low-gradient (LG) AS is the presence of a low LV outflow state, which may occur with reduced left ventricular ejection fraction (LVEF), i.e. classical low-flow, low-gradient (LF-LG), or preserved LVEF, i.e. paradoxical LF-LG. Furthermore, a substantial proportion of patients with AS may have a normal-flow, low-gradient (NF-LG) AS: i.e. a small AVA-low-gradient combination but with a normal flow. One of the most important clinical challenges in these three categories of patients with LG AS (classical LF-LG, paradoxical LF-LG, and NF-LG) is to differentiate a true-severe AS that generally benefits from AVR vs. a pseudo-severe AS that should be managed conservatively. A low-dose dobutamine stress echocardiography may be used for this purpose in patients with classical LF-LG AS, whereas aortic valve calcium scoring by multi-detector computed tomography is the preferred modality in those with paradoxical LF-LG or NF-LG AS. Although patients with LF-LG severe AS have worse outcomes than those with high-gradient AS following AVR, they nonetheless display an important survival benefit with this intervention. Some studies suggest that transcatheter AVR may be superior to surgical AVR in patients with LF-LG AS.

  10. Reconstructing global overturning from meridional density gradients

    NASA Astrophysics Data System (ADS)

    Butler, E. D.; Oliver, K. I. C.; Hirschi, J. J.-M.; Mecking, J. V.

    2016-04-01

    Despite the complexity of the global ocean system, numerous attempts have been made to scale the strength of the meridional overturning circulation (MOC), principally in the North Atlantic, with large-scale, basin-wide hydrographic properties. In particular, various approaches to scaling the MOC with meridional density gradients have been proposed, but the success of these has only been demonstrated under limited conditions. Here we present a scaling relationship linking overturning to twice vertically-integrated meridional density gradients via the hydrostatic equation and a "rotated" form of the geostrophic equation. This provides a meridional overturning streamfunction as a function of depth for each basin. Using a series of periodically forced experiments in a global, coarse resolution configuration of the general circulation model NEMO, we explore the timescales over which this scaling is temporally valid. We find that the scaling holds well in the upper Atlantic cell (at 1000 m) for multi-decadal (and longer) timescales, accurately reconstructing the relative magnitude of the response for different frequencies and explaining over 85 % of overturning variance on timescales of 64-2048 years. Despite the highly nonlinear response of the Antarctic cell in the abyssal Atlantic, between 76 and 94 % of the observed variability at 4000 m is reconstructed on timescales of 32 years (and longer). The scaling law is also applied in the Indo-Pacific. This analysis is extended to a higher resolution, stochastically forced simulation for which correlations of between 0.79 and 0.99 are obtained with upper Atlantic MOC variability on timescales >25 years. These results indicate that meridional density gradients and overturning are linked via meridional pressure gradients, and that both the strength and structure of the MOC can be reconstructed from hydrography on multi-decadal and longer timescales provided that the link is made in this way.

  11. Predicting global overturning from meridional density gradients

    NASA Astrophysics Data System (ADS)

    Butler, Edward; Oliver, Kevin; Hirschi, Joel

    2015-04-01

    Numerous attempts have been made to scale the strength of the meridional overturning circulation (MOC), principally in the North Atlantic, with large-scale, basin-wide hydrographic properties. In particular, various approaches to scaling the MOC with meridional density gradients have been proposed, but the success of these has only been demonstrated under limited conditions. Here we present a scaling relationship linking overturning to twice vertically-integrated meridional density gradients via the hydrostatic equation and a "rotated" form of the geostrophic equation. This provides a meridional overturning streamfunction as a function of depth for each basin. Using a series of periodically forced experiments in a global, coarse resolution configuration of the general circulation model NEMO, we explore the timescales over which this scaling is temporally valid. We find that the scaling holds well in the upper Atlantic cell (at 1000m) on decadal and longer timescales, explaining at least 94% of overturning variance for timescales of 128 to 2048 years and accurately predicting the relative magnitude of the response for different frequencies. Despite the highly nonlinear response of the Antarctic cell in the abyssal Atlantic, over 77% of the observed variability at 4000m is predicted on timescales of 32 years and longer. The scaling law is also successful in the Indo-Pacific, thus demonstrating its generality. This analysis is extended to a higher resolution, stochastically forced simulation for which correlations of at least 0.79 are obtained with upper Atlantic MOC variance on all timescales greater than 25 years. These results demonstrate that meridional density gradients and overturning are linked via meridional pressure gradients, and that both the strength and structure of the MOC can be predicted from hydrography on multi-decadal and longer timescales provided that the link is made in this way.

  12. Learning from nature: synthesis and characterization of longitudinal polymer gradient materials inspired by mussel byssus threads.

    PubMed

    Claussen, Kai U; Giesa, Reiner; Scheibel, Thomas; Schmidt, Hans-Werner

    2012-02-13

    Marine mussels use their threads for attachment to any substratum and these biopolymer gradient fibers show an excellent combination of stiff and soft mechanical properties. A straightforward approach for the preparation of macroscopic longitudinal polymer gradient materials on the centimeter scale based on a poly(dimethyl siloxane) system is presented. Compositional gradients are realized by using three syringe pumps feeding different prepolymers capable to undergo thermal cross-linking. Within the gradient samples, the stiffness between the hard and soft part can be varied up to a factor of four. The gradients are analyzed by UV-Vis spectroscopy as well as compressive and tensile modulus testing.

  13. Effect of neglecting geothermal gradient on calculated oil recovery

    NASA Astrophysics Data System (ADS)

    Safari, Mehdi; Mohammadi, Majid; Sedighi, Mehdi

    2017-03-01

    Reduced recovery rate with time is a common challenge for most of the oil producing reservoirs. Water flooding is one of the most common methods used for enhanced oil recovery. Simulating water-flooding process is sometimes carried out without considering the effect of geothermal gradient, and an average temperature is assumed for all the grid blocks. However, the gradient plays a significant role on the reservoir fluid properties. So neglecting its effect might result in a large error in the calculated oil recovery results, especially for the thick reservoirs, which in theory can show significant variations in temperature with depth. In this paper, first, advancing the waterfront during injection into a geothermal oil reservoir is discussed. Then, the performance of considering either an average temperature or gradient temperature, are considered and compared with each other. The results suggest that assuming a fixed average reservoir temperature with no geothermal gradient, can lead to a pronounced error for calculated oil recovery.

  14. Estimation of coastal density gradients

    NASA Astrophysics Data System (ADS)

    Howarth, M. J.; Palmer, M. R.; Polton, J. A.; O'Neill, C. K.

    2012-04-01

    Density gradients in coastal regions with significant freshwater input are large and variable and are a major control of nearshore circulation. However their measurement is difficult, especially where the gradients are largest close to the coast, with significant uncertainties because of a variety of factors - spatial and time scales are small, tidal currents are strong and water depths shallow. Whilst temperature measurements are relatively straightforward, measurements of salinity (the dominant control of spatial variability) can be less reliable in turbid coastal waters. Liverpool Bay has strong tidal mixing and receives fresh water principally from the Dee, Mersey, Ribble and Conwy estuaries, each with different catchment influences. Horizontal and vertical density gradients are variable both in space and time. The water column stratifies intermittently. A Coastal Observatory has been operational since 2002 with regular (quasi monthly) CTD surveys on a 9 km grid, an situ station, an instrumented ferry travelling between Birkenhead and Dublin and a shore-based HF radar system measuring surface currents and waves. These measurements are complementary, each having different space-time characteristics. For coastal gradients the ferry is particularly useful since measurements are made right from the mouth of Mersey. From measurements at the in situ site alone density gradients can only be estimated from the tidal excursion. A suite of coupled physical, wave and ecological models are run in association with these measurements. The models, here on a 1.8 km grid, enable detailed estimation of nearshore density gradients, provided appropriate river run-off data are available. Examples are presented of the density gradients estimated from the different measurements and models, together with accuracies and uncertainties, showing that systematic time series measurements within a few kilometres of the coast are a high priority. (Here gliders are an exciting prospect for

  15. Photosynthetic characteristics in canopies of Quercus rubra, Quercus prinus and Acer rubrum differ in response to soil water availability.

    PubMed

    Turnbull, Matthew H; Whitehead, David; Tissue, David T; Schuster, William S; Brown, Kim J; Engel, Victor C; Griffin, Kevin L

    2002-02-01

    Photosynthesis and related leaf characteristics were measured in canopies of co-occurring Quercus rubra L. (red oak), Quercus prinus L. (chestnut oak) and Acer rubrum L. (red maple) trees. Mature (20+ m tall) trees were investigated at sites of differing soil water availability within a catchment (a drier upper site and a wetter lower site). Leaf photosynthetic characteristics differed significantly between species and in response to site and position in the canopy. Photosynthetic capacity (A max) was significantly greater at the wetter site in all canopy strata in A. rubrum but not in Q. rubra or Q. prinus. Our findings for A. rubrum are generally consistent with those predicting that species with higher specific leaf area (SLA) will have higher A max per unit leaf nitrogen (N) and that species with leaves with lower SLA (e.g. Q. rubra and Q. prinus) will have shallower slopes of the A max-N relationship. Importantly, the relationships between A max and N area (and by implication photosynthetic nitrogen-use efficiency, PNUE) differed in A. rubrum between the sites, with PNUE significantly lower at the drier site. The lower photosynthetic capacity and PNUE must substantially reduce carbon acquisition capacity in A. rubrum under these field conditions. Maximum stomatal conductance (g smax) differed significantly between species, with g smax greatest in Q. rubra and Q. prinus. In Q. rubra and Q. prinus, g smax was significantly lower at the upper site than the lower site. There was no significant response of g smax to site in A. rubrum. These stomatal responses were consistent with the C i/C a ratio, which was significantly lower in leaves of Q. rubra and Q. prinus at the upper site, but did not differ between sites in A. rubrum. Leaf δ(13)C was significantly lower in A. rubrum than in either Q. rubra or Q. prinus at both sites. These findings indicate differences in stomatal behaviour in A. rubrum which are likely to contribute to lower water use efficiency at

  16. Depth Image Inpainting: Improving Low Rank Matrix Completion With Low Gradient Regularization.

    PubMed

    Xue, Hongyang; Zhang, Shengming; Cai, Deng

    2017-09-01

    We address the task of single depth image inpainting. Without the corresponding color images, previous or next frames, depth image inpainting is quite challenging. One natural solution is to regard the image as a matrix and adopt the low rank regularization just as color image inpainting. However, the low rank assumption does not make full use of the properties of depth images. A shallow observation inspires us to penalize the nonzero gradients by sparse gradient regularization. However, statistics show that though most pixels have zero gradients, there is still a non-ignorable part of pixels, whose gradients are small but nonzero. Based on this property of depth images, we propose a low gradient regularization method in which we reduce the penalty for small gradients while penalizing the nonzero gradients to allow for gradual depth changes. The proposed low gradient regularization is integrated with the low rank regularization into the low rank low gradient approach for depth image inpainting. We compare our proposed low gradient regularization with the sparse gradient regularization. The experimental results show the effectiveness of our proposed approach.

  17. Depth Image Inpainting: Improving Low Rank Matrix Completion With Low Gradient Regularization

    NASA Astrophysics Data System (ADS)

    Xue, Hongyang; Zhang, Shengming; Cai, Deng

    2017-09-01

    We consider the case of inpainting single depth images. Without corresponding color images, previous or next frames, depth image inpainting is quite challenging. One natural solution is to regard the image as a matrix and adopt the low rank regularization just as inpainting color images. However, the low rank assumption does not make full use of the properties of depth images. A shallow observation may inspire us to penalize the non-zero gradients by sparse gradient regularization. However, statistics show that though most pixels have zero gradients, there is still a non-ignorable part of pixels whose gradients are equal to 1. Based on this specific property of depth images , we propose a low gradient regularization method in which we reduce the penalty for gradient 1 while penalizing the non-zero gradients to allow for gradual depth changes. The proposed low gradient regularization is integrated with the low rank regularization into the low rank low gradient approach for depth image inpainting. We compare our proposed low gradient regularization with sparse gradient regularization. The experimental results show the effectiveness of our proposed approach.

  18. Rapid Gradient-Echo Imaging

    PubMed Central

    Hargreaves, Brian

    2012-01-01

    Gradient echo sequences are widely used in magnetic resonance imaging (MRI) for numerous applications ranging from angiography to perfusion to functional MRI. Compared with spin-echo techniques, the very short repetition times of gradient-echo methods enable very rapid 2D and 3D imaging, but also lead to complicated “steady states.” Signal and contrast behavior can be described graphically and mathematically, and depends strongly on the type of spoiling: fully balanced (no spoiling), gradient spoiling, or RF-spoiling. These spoiling options trade off between high signal and pure T1 contrast while the flip angle also affects image contrast in all cases, both of which can be demonstrated theoretically and in image examples. As with spin-echo sequences, magnetization preparation can be added to gradient-echo sequences to alter image contrast. Gradient echo sequences are widely used for numerous applications such as 3D perfusion imaging, functional MRI, cardiac imaging and MR angiography. PMID:23097185

  19. Dynamic thermal gradient gas chromatography.

    PubMed

    Contreras, Jesse A; Wang, Anzi; Rockwood, Alan L; Tolley, H Dennis; Lee, Milton L

    2013-08-09

    The use of negative axial thermal gradients in gas chromatography (TGGC) has intrigued chromatographers since the early 1950s because of the dramatic narrowing of analyte bands and concomitant raised expectations for improving resolving power. However, technical difficulties experienced in construction of TGGC instrumentation and control of the temperature along the column have made its implementation and, hence, detailed study difficult. In this work, we describe a TGGC system capable of rapidly producing and varying thermal gradient profiles by simultaneous use of resistive heating and convective cooling. Heating and cooling rates as high as 1200 and 2500°C/min, respectively, allowed the creation of dynamic temperature gradients. The separation characteristics of TGGC with dynamically changing temperature gradients are demonstrated. A gradient velocity of 2.22cm/s provided repetitive separations every 45s, and injection band widths of 45s duration were transformed into approximately 1-s peak widths. Peak tailing for basic compounds was nearly eliminated. Dynamic TGGC allows unique control over separations, oftentimes improving resolution and detection signal-to-noise. Thermally controlled elution in TGGC holds great promise for performing smart separations in which the separation time window is most efficiently utilized, and optimized separations can be quickly achieved. Rapid adjustment of relative compound elution can be used to greatly reduce GC method development time. Copyright © 2013 Elsevier B.V. All rights reserved.

  20. Property.

    ERIC Educational Resources Information Center

    Piele, Philip K.

    The author notes that controversies over construction bids and contracts continue to represent the largest number of property cases reported in this year's chapter. Most of these cases are routine disputes between colleges or universities and contractors over such issues as the return of bid bonds, recovery of additional costs for construction…

  1. Property.

    ERIC Educational Resources Information Center

    Piele, Philip K.

    Numerous cases in this year's chapter dealt with the same topics of previous years--contracts and bids for building construction, and detachment and annexation of a portion of a school district. The courts continued to attribute board discretionary authority to school boards in school property matters. Intergovernmental disputes over ownership or…

  2. Property.

    ERIC Educational Resources Information Center

    Piele, Philip K.; Forsberg, James R.

    This chapter summarizes and analyze all state supreme court and federal court decisions as well as other significant court decisions involving school property. The cases discussed are generally limited to those decided during 1974 and reported in the General Digest on or before March 1, 1975. In their discussion, the authors attempt to integrate…

  3. Property.

    ERIC Educational Resources Information Center

    Piele, Philip K.; Forsberg, James R.

    This chapter summarizes recent state supreme court and federal court decisions involving school property. The cases discussed are generally limited to those decided during 1975 and reported in the General Digest as of March 1976. In their discussion, the authors attempt to integrate related cases and to illuminate any unifying legal principles…

  4. Property.

    ERIC Educational Resources Information Center

    Piele, Philip K.

    A review of cases involving higher education property matters shows that many are concerned with building construction, equipment installation, or repair contracts. A number of other cases involve routine conflicts between colleges or universities and other governmental entities over matters such as requests for special exceptions to zoning…

  5. Property.

    ERIC Educational Resources Information Center

    Piele, Philip K.

    Numerous cases in this year's chapter dealt with the same topics of previous years--contracts and bids for building construction, and detachment and annexation of a portion of a school district. The courts continued to attribute board discretionary authority to school boards in school property matters. Intergovernmental disputes over ownership or…

  6. Property.

    ERIC Educational Resources Information Center

    Piele, Philip K.; Forsberg, James R.

    This chapter summarizes and analyze all state supreme court and federal court decisions as well as other significant court decisions involving school property. The cases discussed are generally limited to those decided during 1974 and reported in the General Digest on or before March 1, 1975. In their discussion, the authors attempt to integrate…

  7. Property.

    ERIC Educational Resources Information Center

    Piele, Philip K.

    A review of cases involving higher education property matters shows that many are concerned with building construction, equipment installation, or repair contracts. A number of other cases involve routine conflicts between colleges or universities and other governmental entities over matters such as requests for special exceptions to zoning…

  8. Property.

    ERIC Educational Resources Information Center

    Piele, Philip K.; Forsberg, James R.

    This chapter summarizes recent state supreme court and federal court decisions involving school property. The cases discussed are generally limited to those decided during 1975 and reported in the General Digest as of March 1976. In their discussion, the authors attempt to integrate related cases and to illuminate any unifying legal principles…

  9. Property.

    ERIC Educational Resources Information Center

    Piele, Philip K.

    Reflecting widespread unhappiness with the growing tax burdens in this country, the most active area of litigation reported in the property chapter this year involves various attempts by taxpayers to prevent the construction or remodeling of public school facilities. While some taxpayers fought to keep schools from being built, others in New York…

  10. Property.

    ERIC Educational Resources Information Center

    Piele, Philip K.

    The author notes that controversies over construction bids and contracts continue to represent the largest number of property cases reported in this year's chapter. Most of these cases are routine disputes between colleges or universities and contractors over such issues as the return of bid bonds, recovery of additional costs for construction…

  11. Property.

    ERIC Educational Resources Information Center

    Piele, Philip K.; Johnson, Margaret M.

    While the number of cases dealing with school property issues was significantly lower than in previous years, a significant number of cases involving the detachment and attachment of land to school districts arose. Eight of the eleven cases dealing with land detachment come from Illinois. The cases concerned requests from parents that their…

  12. Property.

    ERIC Educational Resources Information Center

    Piele, Philip K.; Forsberg, James R.

    While the types of cases reported in this year's chapter are essentially the same as those reported in last year's, the number of certain types of cases have changed--in some instances significantly. For example, the number of cases raising constitutional issues in the areas of school construction, location, and property use have declined. On the…

  13. Multilayer High-Gradient Insulators

    SciTech Connect

    Harris, J R; Anaya, R M; Blackfield, D; Chen, Y -; Falabella, S; Hawkins, S; Holmes, C; Paul, A C; Sampayan, S; Sanders, D M; Watson, J A; Caporaso, G J; Krogh, M

    2006-11-15

    High voltage systems operated in vacuum require insulating materials to maintain spacing between conductors held at different potentials, and may be used to maintain a nonconductive vacuum boundary. Traditional vacuum insulators generally consist of a single material, but insulating structures composed of alternating layers of dielectric and metal can also be built. These ''High-Gradient Insulators'' have been experimentally shown to withstand higher voltage gradients than comparable conventional insulators. As a result, they have application to a wide range of high-voltage vacuum systems where compact size is important. This paper describes ongoing research on these structures, as well as the current theoretical understanding driving this work.

  14. Templating Surfaces with Gradient Assemblies

    SciTech Connect

    Genzer,J.

    2005-01-01

    One of the most versatile and widely used methods of forming surfaces with position-dependent wettability is that conceived by Chaudhury and Whitesides more than a decade ago. In this paper we review several projects that utilize this gradient-forming methodology for: controlled of deposition of self-assembled monolayers on surfaces, generating arrays of nanoparticles with number density gradients, probing the mushroom-to-brush transition in surface-anchored polymers, and controlling the speed of moving liquid droplets on surfaces.

  15. Conjugate gradient method - Electromagnetism applications

    NASA Astrophysics Data System (ADS)

    Mosig, Juan R.

    1987-10-01

    This paper presents a brief but rigorous description of the conjugate gradient technique as applied to the solution of algebraic linear systems with complex coefficients. The relationships between conjugate gradient techniques and other commonly used methods are established. A normalized algorithm is introduced which optimally exploits the computer capabilities. Its performance is compared with that of Gaussian elimination by numerical tests on Hilbert matrices of more than a thousand unknowns. As a practical application, the problem of electrostatic screening by a finite ground plane has been solved with this technique.

  16. A new convergent conjugate gradient method under the exact line search

    NASA Astrophysics Data System (ADS)

    Omer, Osman; Mamat, Mustafa; Rivaie, Mohd

    2015-05-01

    Conjugate gradient methods are widely used for unconstrained optimization problems, especially large scale problems. That is, for its simplicity, low memory requirement, and global convergence properties. In this paper, we study the global convergence properties of a new conjugate gradient method under the exact line search. Under some assumptions, the proofs of the sufficient descent property and the global convergence are given. The numerical results show that our new method is efficient for some unconstrained optimization problems.

  17. Spatiotemporal polarization gradients in phase-bearing light

    SciTech Connect

    Lembessis, V. E.; Babiker, M.

    2010-03-15

    It is shown how the interference of two circularly polarized laser beams endowed with orbital angular momentum can give rise to spatial and temporal polarization gradients, displaying axial as well as angular symmetry properties. Illustrations are given with reference to circularly polarized Laguerre-Gaussian beams as typical light beams carrying orbital angular momentum.

  18. Morphogengineering roots: comparing mechanisms of morphogen gradient formation

    PubMed Central

    2012-01-01

    Background In developmental biology, there has been a recent focus on the robustness of morphogen gradients as possible providers of positional information. It was shown that functional morphogen gradients present strong biophysical constraints and lack of robustness to noise. Here we explore how the details of the mechanism which underlies the generation of a morphogen gradient can influence those properties. Results We contrast three gradient-generating mechanisms, (i) a source-decay mechanism; and (ii) a unidirectional transport mechanism; and (iii) a so-called reflux-loop mechanism. Focusing on the dynamics of the phytohormone auxin in the root, we show that only the reflux-loop mechanism can generate a gradient that would be adequate to supply functional positional information for the Arabidopsis root, for biophysically reasonable kinetic parameters. Conclusions We argue that traits that differ in spatial and temporal time-scales can impose complex selective pressures on the mechanism of morphogen gradient formation used for the development of the particular organism. PMID:22583698

  19. Quantitative results for square gradient models of fluids

    NASA Astrophysics Data System (ADS)

    Kong, Ling-Ti; Vriesinga, Dan; Denniston, Colin

    2011-03-01

    Square gradient models for fluids are extensively used because they are believed to provide a good qualitative understanding of the essential physics. However, unlike elasticity theory for solids, there are few quantitative results for specific (as opposed to generic) fluids. Indeed the only numerical value of the square gradient coefficients for specific fluids have been inferred from attempts to match macroscopic properties such as surface tensions rather than from direct measurement. We employ all-atom molecular dynamics, using the TIP3P and OPLS force fields, to directly measure the coefficients of the density gradient expansion for several real fluids. For all liquids measured, including water, we find that the square gradient coefficient is negative, suggesting the need for some regularization of a model including only the square gradient, but only at wavelengths comparable to the molecular separation of molecules. The implications for liquid-gas interfaces are also examined. Remarkably, the square gradient model is found to give a reasonably accurate description of density fluctuations in the liquid state down to wavelengths close to atomic size.

  20. Influence of Groundwater Hydraulic Gradient on Bank Storage Metrics.

    PubMed

    Welch, Chani; Harrington, Glenn A; Cook, Peter G

    2015-01-01

    The hydraulic gradient between aquifers and rivers is one of the most variable properties in a river/aquifer system. Detailed process understanding of bank storage under hydraulic gradients is obtained from a two-dimensional numerical model of a variably saturated aquifer slice perpendicular to a river. Exchange between the river and the aquifer occurs first at the interface with the unsaturated zone. The proportion of total water exchanged through the river bank compared to the river bed is a function of aquifer hydraulic conductivity, partial penetration, and hydraulic gradient. Total exchange may be estimated to within 50% using existing analytical solutions provided that unsaturated zone processes do not strongly influence exchange. Model-calculated bank storage is at a maximum when no hydraulic gradient is present and increases as the hydraulic conductivity increases. However, in the presence of a hydraulic gradient, the largest exchange flux or distance of penetration does not necessarily correspond to the highest hydraulic conductivity, as high hydraulic conductivity increases the components of exchange both into and out of an aquifer. Flood wave characteristics do not influence ambient groundwater discharge, and so in large floods, hydraulic gradients must be high to reduce the volume of bank storage. Practical measurement of bank storage metrics is problematic due to the limitations of available measurement technologies and the nested processes of exchange that occur at the river-aquifer interface. Proxies, such as time series concentration data in rivers and groundwater, require further development to be representative and quantitative.

  1. Variable metric conjugate gradient methods

    SciTech Connect

    Barth, T.; Manteuffel, T.

    1994-07-01

    1.1 Motivation. In this paper we present a framework that includes many well known iterative methods for the solution of nonsymmetric linear systems of equations, Ax = b. Section 2 begins with a brief review of the conjugate gradient method. Next, we describe a broader class of methods, known as projection methods, to which the conjugate gradient (CG) method and most conjugate gradient-like methods belong. The concept of a method having either a fixed or a variable metric is introduced. Methods that have a metric are referred to as either fixed or variable metric methods. Some relationships between projection methods and fixed (variable) metric methods are discussed. The main emphasis of the remainder of this paper is on variable metric methods. In Section 3 we show how the biconjugate gradient (BCG), and the quasi-minimal residual (QMR) methods fit into this framework as variable metric methods. By modifying the underlying Lanczos biorthogonalization process used in the implementation of BCG and QMR, we obtain other variable metric methods. These, we refer to as generalizations of BCG and QMR.

  2. Gradient Tempering Of Bearing Races

    NASA Technical Reports Server (NTRS)

    Parr, Richardson A.

    1991-01-01

    Gradient-tempering process increases fracture toughness and resistance to stress-corrosion cracking of ball-bearing races made of hard, strong steels and subject to high installation stresses and operation in corrosive media. Also used in other applications in which local toughening of high-strength/low-toughness materials required.

  3. Geothermal gradients in Mississippi embayment

    SciTech Connect

    Staub, W.P.; Treat, N.L.

    1983-09-01

    A statistical analysis of bottom-hole temperatures from oil and gas wells in the northern Mississippi embayment suggests that the geothermal gradient below a depth of 1 km is low (22.2/sup 0/C/km) and for the New Madrid seismic zone, it is even lower (15.7/sup 0/C/km). These data support the tentative conclusion of Swanberg et al that ground-water convection is the source of near-surface heat in shallow water wells of the region. Research by Mitchell et al had suggested a high geothermal gradient in the crust and upper mantel beneath the New Madrid seismic zone as a plausible explanation for the lower than average compressional wave velocities observed there. Warmer than normal wells in the northern Mississippi embayment are scattered at random and may be attributed to random error in the data. Deep wells in the southern Mississippi embayment are substantially hotter than wells at a comparable depth farther north. The regional geothermal gradient below a depth of 1 km from northern Louisiana to central Mississippi is 26.9/sup 0/C/km. From central Mississippi to central Alabama, the geothermal gradient (23.1/sup 0/C/km) is comparable to that of the northern Mississippi embayment.

  4. Reinforcement Learning Through Gradient Descent

    DTIC Science & Technology

    1999-05-14

    Reinforcement learning is often done using parameterized function approximators to store value functions. Algorithms are typically developed for...practice of existing types of algorithms, the gradient descent approach makes it possible to create entirely new classes of reinforcement learning algorithms

  5. Low-gradient aortic stenosis

    PubMed Central

    Clavel, Marie-Annick; Magne, Julien; Pibarot, Philippe

    2016-01-01

    An important proportion of patients with aortic stenosis (AS) have a ‘low-gradient’ AS, i.e. a small aortic valve area (AVA <1.0 cm2) consistent with severe AS but a low mean transvalvular gradient (<40 mmHg) consistent with non-severe AS. The management of this subset of patients is particularly challenging because the AVA-gradient discrepancy raises uncertainty about the actual stenosis severity and thus about the indication for aortic valve replacement (AVR) if the patient has symptoms and/or left ventricular (LV) systolic dysfunction. The most frequent cause of low-gradient (LG) AS is the presence of a low LV outflow state, which may occur with reduced left ventricular ejection fraction (LVEF), i.e. classical low-flow, low-gradient (LF-LG), or preserved LVEF, i.e. paradoxical LF-LG. Furthermore, a substantial proportion of patients with AS may have a normal-flow, low-gradient (NF-LG) AS: i.e. a small AVA—low-gradient combination but with a normal flow. One of the most important clinical challenges in these three categories of patients with LG AS (classical LF-LG, paradoxical LF-LG, and NF-LG) is to differentiate a true-severe AS that generally benefits from AVR vs. a pseudo-severe AS that should be managed conservatively. A low-dose dobutamine stress echocardiography may be used for this purpose in patients with classical LF-LG AS, whereas aortic valve calcium scoring by multi-detector computed tomography is the preferred modality in those with paradoxical LF-LG or NF-LG AS. Although patients with LF-LG severe AS have worse outcomes than those with high-gradient AS following AVR, they nonetheless display an important survival benefit with this intervention. Some studies suggest that transcatheter AVR may be superior to surgical AVR in patients with LF-LG AS. PMID:27190103

  6. Single-Image Vignetting Correction from Gradient Distribution Symmetries

    PubMed Central

    Zheng, Yuanjie; Lin, Stephen; Kang, Sing Bing; Xiao, Rui; Gee, James C.; Kambhamettu, Chandra

    2014-01-01

    We present novel techniques for single-image vignetting correction based on symmetries of two forms of image gradients: semicircular tangential gradients (SCTG) and radial gradients (RG). For a given image pixel, an SCTG is an image gradient along the tangential direction of a circle centered at the presumed optical center and passing through the pixel. An RG is an image gradient along the radial direction with respect to the optical center. We observe that the symmetry properties of SCTG and RG distributions are closely related to the vignetting in the image. Based on these symmetry properties we develop an automatic optical center estimation algorithm by minimizing the asymmetry of SCTG distributions, and also present two methods for vignetting estimation based on minimizing the asymmetry of RG distributions. In comparison to prior approaches to single-image vignetting correction, our methods do not rely on image segmentation and they produce more accurate results. Experiments show our techniques to work well for a wide range of images while achieving a speed-up of 3-5 times compared to a state-of-the-art method. PMID:23599060

  7. Single-image vignetting correction from gradient distribution symmetries.

    PubMed

    Zheng, Yuanjie; Lin, Stephen; Kang, Sing Bing; Xiao, Rui; Gee, James C; Kambhamettu, Chandra

    2013-06-01

    We present novel techniques for single-image vignetting correction based on symmetries of two forms of image gradients: semicircular tangential gradients (SCTG) and radial gradients (RG). For a given image pixel, an SCTG is an image gradient along the tangential direction of a circle centered at the presumed optical center and passing through the pixel. An RG is an image gradient along the radial direction with respect to the optical center. We observe that the symmetry properties of SCTG and RG distributions are closely related to the vignetting in the image. Based on these symmetry properties, we develop an automatic optical center estimation algorithm by minimizing the asymmetry of SCTG distributions, and also present two methods for vignetting estimation based on minimizing the asymmetry of RG distributions. In comparison to prior approaches to single-image vignetting correction, our methods do not rely on image segmentation and they produce more accurate results. Experiments show our techniques to work well for a wide range of images while achieving a speed-up of 3-5 times compared to a state-of-the-art method.

  8. Corrosion in a temperature gradient

    SciTech Connect

    Covino, Bernard S., Jr.; Holcomb, Gordon R.; Cramer, Stephen D.; Bullard, Sophie J.; Ziomek-Moroz, Margaret; White, M.L.

    2003-01-01

    High temperature corrosion limits the operation of equipment used in the Power Generation Industry. Some of the more destructive corrosive attack occurs on the surfaces of heat exchangers, boilers, and turbines where the alloys are subjected to large temperature gradients that cause a high heat flux through the accumulated ash, the corrosion product, and the alloy. Most current and past corrosion research has, however, been conducted under isothermal conditions. Research on the thermal-gradient-affected corrosion of various metals and alloys is currently being studied at the Albany Research Center’s SECERF (Severe Environment Corrosion and Erosion Research Facility) laboratory. The purpose of this research is to verify theoretical models of heat flux effects on corrosion and to quantify the differences between isothermal and thermal gradient corrosion effects. The effect of a temperature gradient and the resulting heat flux on corrosion of alloys with protective oxide scales is being examined by studying point defect diffusion and corrosion rates. Fick’s first law of diffusion was expanded, using irreversible thermodynamics, to include a heat flux term – a Soret effect. Oxide growth rates are being measured for the high temperature corrosion of cobalt at a metal surface temperature of 900ºC. Corrosion rates are also being determined for the high temperature corrosion of carbon steel boiler tubes in a simulated waste combustion environment consisting of O2, CO2, N2, and water vapor. Tests are being conducted both isothermally and in the presence of a temperature gradient to verify the effects of a heat flux and to compare to isothermal oxidation.

  9. Ants of three adjacent habitats of a transition region between the cerrado and caatinga biomes: the effects of heterogeneity and variation in canopy cover.

    PubMed

    Neves, F S; Queiroz-Dantas, K S; da Rocha, W D; Delabie, J H C

    2013-06-01

    Habitat heterogeneity and complexity associated with variations in climatic conditions are important factors determining the structure of ant communities in different terrestrial ecosystems. The objective of this study was to describe the horizontal and vertical distribution patterns of the ant community associated with three adjacent habitats in a transition area between the Cerrado and Caatinga biomes at the Pandeiros River, state of Minas Gerais, Brazil. We tested the following hypotheses: (1) the richness and composition of ant species and functional group structure changes between different habitats and strata; (2) habitats with higher tree species richness and density support higher ant species richness; and (3) habitats with lower variation in canopy cover support higher ant species richness. Sampling was conducted in three adjacent habitats and at three vertical strata. Ant species richness was significantly different among vertical strata. Ant species composition was different among both habitats and vertical strata and functional group structure was divergent among habitats. Partitioning of the diversity revealed that the diversity for the three components was statistically different from the one expected by the null model; α and β 2 were higher and β 1 was lower than the values expected by chance. Tree density and variation in canopy cover negatively affected ant species richness. The occurrence of different species and the changing of functional group structures in different habitats and strata suggest an ecological-evolutionary relationship between ants and their habitats and emphasize the need to implement local conservation strategies in the ecotones between biomes.

  10. Chemical transport models: the combined non-local diffusion and mixing schemes, and calculation of in-canopy resistance for dry deposition fluxes.

    PubMed

    Mihailovic, Dragutin T; Alapaty, Kiran; Podrascanin, Zorica

    2009-03-01

    Improving the parameterization of processes in the atmospheric boundary layer (ABL) and surface layer, in air quality and chemical transport models. To do so, an asymmetrical, convective, non-local scheme, with varying upward mixing rates is combined with the non-local, turbulent, kinetic energy scheme for vertical diffusion (COM). For designing it, a function depending on the dimensionless height to the power four in the ABL is suggested, which is empirically derived. Also, we suggested a new method for calculating the in-canopy resistance for dry deposition over a vegetated surface. The upward mixing rate forming the surface layer is parameterized using the sensible heat flux and the friction and convective velocities. Upward mixing rates varying with height are scaled with an amount of turbulent kinetic energy in layer, while the downward mixing rates are derived from mass conservation. The vertical eddy diffusivity is parameterized using the mean turbulent velocity scale that is obtained by the vertical integration within the ABL. In-canopy resistance is calculated by integration of inverse turbulent transfer coefficient inside the canopy from the effective ground roughness length to the canopy source height and, further, from its the canopy height. This combination of schemes provides a less rapid mass transport out of surface layer into other layers, during convective and non-convective periods, than other local and non-local schemes parameterizing mixing processes in the ABL. The suggested method for calculating the in-canopy resistance for calculating the dry deposition over a vegetated surface differs remarkably from the commonly used one, particularly over forest vegetation. In this paper, we studied the performance of a non-local, turbulent, kinetic energy scheme for vertical diffusion combined with a non-local, convective mixing scheme with varying upward mixing in the atmospheric boundary layer (COM) and its impact on the concentration of pollutants

  11. Separation of colloidal two dimensional materials by density gradient ultracentrifugation

    SciTech Connect

    Kuang, Yun; Song, Sha; Huang, Jinyang; Sun, Xiaoming

    2015-04-15

    Two-dimensional (2D) materials have been made through various approaches but obtaining monodispersed simply by synthesis optimization gained little success, which highlighted the need for introducing nanoseparation methods. Density gradient ultracentrifugation method has emerged as a versatile and scalable method for sorting colloidal 2D nanomaterials. Isopycnic separation was applied on thickness-dependent separation of graphene nanosheets. And rate-zonal separation, as a more versatile separation method, demonstrated its capability in sorting nanosheets of chemically modified single layered graphene, layered double hydroxide, and even metallic Ag. Establishing such density gradient ultracentrifugation method not only achieves monodispersed nanosheets and provides new opportunities for investigation on size dependent properties of 2D materials, but also makes the surface modification possible by introducing “reaction zones” during sedimentation of the colloids. - Graphical abstract: Two-dimensional (2D) materials have been made through various approaches but obtaining monodispersed simply by synthesis optimization gained little success, which highlighted the need for introducing nanoseparation methods. Density gradient ultracentrifugation method has emerged as a versatile and scalable method for sorting colloidal 2D nanomaterials according to their size of thickness difference. Establishing such density gradient ultracentrifugation method not only achieves monodispersed nanosheets and provides new opportunities for investigation on size dependent properties of 2D materials, but also makes the surface modification possible by introducing “reaction zones” during sedimentation of the colloids. - Highlights: • Density gradient ultracentrifugation was applied on size separation of 2D material. • Isopycnic separation was applied on separation of low density materials. • Rate-zonal separation was applied on separation of large density materials. • Size

  12. The composition gradient across M81

    NASA Astrophysics Data System (ADS)

    Garnett, D. R.; Shields, G. A.

    1987-06-01

    Spectrophotometric observations are presented for 18 H II regions in the galaxy M81 (type SAab). M81 is the earliest type galaxy for which extensive H II region observations have been made. The observed emission-line intensities have been analyzed by the empirical calibration method and by the use of photoionization models. Strong radial gradients are seen in (forbidden O II + forbidden O III)/H-beta and in the derived oxygen abundance. M81 has an abundance gradient and an overall metallicity similar to those of late-type galaxies of similar mass, luminosity, and gas fraction. This suggests that the chemical properties of galaxies are governed more by these physical characteristics than by the morphological type. There appears to be little systematic variation of N/O with radius in M81. The outlying H II region Muench 1, located 15 kpc from the nucleus, has about solar N/O but O/H about 0.2 times the solar value; in contrast, much lower N/O values occur in comparably oxygen-poor H II regions in other galaxies. The oxygen abundance and gas fraction as a function of radius in M81 are roughly consistent with a 'simple' model of chemical evolution (Searle and Sargent, 1972) with the same heavy-element yield as found for dwarf irregular galaxies. However, the low oxygen abundance in Muench 1 agrees only if the dynamically inferred 'dark mass' is excluded in computing the gas fraction.

  13. Gradient navigation model for pedestrian dynamics

    NASA Astrophysics Data System (ADS)

    Dietrich, Felix; Köster, Gerta

    2014-06-01

    We present a microscopic ordinary differential equation (ODE)-based model for pedestrian dynamics: the gradient navigation model. The model uses a superposition of gradients of distance functions to directly change the direction of the velocity vector. The velocity is then integrated to obtain the location. The approach differs fundamentally from force-based models needing only three equations to derive the ODE system, as opposed to four in, e.g., the social force model. Also, as a result, pedestrians are no longer subject to inertia. Several other advantages ensue: Model-induced oscillations are avoided completely since no actual forces are present. The derivatives in the equations of motion are smooth and therefore allow the use of fast and accurate high-order numerical integrators. At the same time, the existence and uniqueness of the solution to the ODE system follow almost directly from the smoothness properties. In addition, we introduce a method to calibrate parameters by theoretical arguments based on empirically validated assumptions rather than by numerical tests. These parameters, combined with the accurate integration, yield simulation results with no collisions of pedestrians. Several empirically observed system phenomena emerge without the need to recalibrate the parameter set for each scenario: obstacle avoidance, lane formation, stop-and-go waves, and congestion at bottlenecks. The density evolution in the latter is shown to be quantitatively close to controlled experiments. Likewise, we observe a dependence of the crowd velocity on the local density that compares well with benchmark fundamental diagrams.

  14. Preparation and characterization of gradient polymer films

    SciTech Connect

    Smith, S.C.

    1987-01-01

    Gradient polymers are multicomponent polymers whose chemical constitution varies with depth in the sample. Although these polymers may possess unique mechanical, optical, and barrier properties they remain relatively unexplored. This work is a study of the preparation of gradient polymers by sequential exposure of films to a diffusing monomer followed by electron beam irradiation. Initial experiments involved immersion of poly(vinyl chloride) (PVC) films in styrene or n-butyl methacrylate (BMA) for various time periods followed by irradiation with 1 or 10 megarads of accelerated electrons. A significant amount of poly(n-butyl methacrylate) (PBMA) formed in PVC/BMA systems, but little polystyrene could be found in the PVC/styrene films. A second set of experiments involved immersion of PVC and polyethylene (PE) films in BMA for 20, 40, 60, and 720 minutes followed by irradiation with 10 megarads of electrons. These films were then characterized using optical microscopy, quantitative transmission Fourier transform infrared spectroscopy (FTIR), and a depth profiling procedure based on quantitative attenuated total reflection (ATR) FTIR. It was concluded that the mechanism of PBMA formation in the polyethylene films was a result of events immediately following irradiation. Atmospheric oxygen diffusing into irradiated films trapped free radicals at the film surfaces. This was followed by storage in an evacuated desiccator where unintentional exposure to BMA vapor took place. This BMA reacted with free radicals that remained within the film cores, polymerizing to PBMA.

  15. Biocompatible gradient ceramic coatings for metal implants

    NASA Astrophysics Data System (ADS)

    Sharkany, Josif P.; Sichka, Mikhail J.; Potapchuk, Anatolij M.; Lemko, Ivan S.; Pintye, Josif L.

    2001-08-01

    For the acceleration of the osteointegration processes of the metals implants we deposit on their surface the biokompotible ceramic coatings on the basis of hydroxyapatite. However such coatings have a certain deficiency connected with the absence of the necessary strength characteristics for a such kind of the implant. That's why it actual to create the coatings having beside biological compatibility the necessary strength and springy- elastic properties. We have developed the method of the receiving of the new biocompatible coatings with gradient structure over width on the titanium substrate. The essence of the developed method is in plasma coatings deposition within beforehand given supply of the powder consisting of two components (oxyde aluminum and hydroxyapatite) in the process of the deposition. It's showed that the received gradient coatings are the mixture of the crystals Al2O3 and HA, the concentrations of which change over the width. The topological investigation of the surface and the coating cross-sections was performed from which the chemical composition distribution over width was studied and found the absense of the chemical interaktion between Al2O3 and HA. By regulation of the distribution of the initial components over the coating widths it is possible to set the phase comsposition and crystal sizes in the biocompatible coatings. In the process of etching in the solutions imitating the physiological ones it is found the formation of the pores having dendritic structure. The performed investigations show the possibility of the usage of the developed coatings in medicine particularly in stomatolgoy.

  16. Ultrasonic characterization of functionally gradient materials with leaky Rayleigh wave

    SciTech Connect

    Kawashima, Koichiro; Takenouchi, Naoki; Awaji, Hideo; Nishikawa, Tadahiro

    1999-12-02

    Young's modulus of functionally gradient Al{sub 2}O{sub 3}/Ni ceramics, which was formed by centrifugal casting and has gradient of the elastic properties along a particular direction on the surface, is estimated by velocity measurement of the leaky Rayleigh and longitudinal waves. Those velocities were measured every 1mm with a line focused PVDF transducer, of which central frequency, focal length and width are 36MHz, 5mm and 8mm. Thus measured Young's modulus varies from 370GPa (Al{sub 2}O{sub 3} rich side) to 200GPa (Ni rich side)

  17. Soil moisture gradients and controls on a southern Appalachian hillslope from drought through recharge

    Treesearch

    J.A. Yeakley; W.T. Swank; L.W. Swift; G.M. Hornberger; H.H. Shugart

    1998-01-01

    Soil moisture gradients along hillslopes in humid watersheds, although indicated by vegetation gradients and by studies using models, have been difficult to confirm empirically. While soil properties and topographic features are the two general physiographic factors controlling soil moisture on hillslopes, studies have shown conflicting results regarding which factor...

  18. Carbon and Oxygen Galactic Gradients

    NASA Astrophysics Data System (ADS)

    Carigi, L.; Peimbert, M.; Esteban, C.; García-Rojas, J.

    2006-06-01

    A chemical evolution model of the Galaxy has been computed to reproduce the O/H gradients from Galactic HII regions. This model solves the C enrichment problem because it fits the C/H and C/O gradients and the C and O histories of the solar vicinity. The model is based on C yields dependent on metallicity (Z) owing to stellar winds. The C yields of massive stars (MS) increase with Z and those of low and intermediate mass stars (LIMS) decrease with Z. An important result is that the fraction of carbon in the interstellar medium (ISM) due to MS and LIMS is strongly dependent on Z of the ISM, therefore, that fraction depends on time and on the Galactocentric distance. At present and in the solar vicinity about half of the C in the interstellar medium has been produced by MS and half by LIMS.

  19. High gradient directional solidification furnace

    NASA Technical Reports Server (NTRS)

    Aldrich, B. R.; Whitt, W. D. (Inventor)

    1985-01-01

    A high gradient directional solidification furnace is disclosed which includes eight thermal zones throughout the length of the furnace. In the hot end of the furnace, furnace elements provide desired temperatures. These elements include Nichrome wire received in a grooved tube which is encapsulated y an outer alumina core. A booster heater is provided in the hot end of the furnace which includes toroidal tungsten/rhenium wire which has a capacity to put heat quickly into the furnace. An adiabatic zone is provided by an insulation barrier to separate the hot end of the furnace from the cold end. The old end of the furnace is defined by additional heating elements. A heat transfer plate provides a means by which heat may be extracted from the furnace and conducted away through liquid cooled jackets. By varying the input of heat via the booster heater and output of heat via the heat transfer plate, a desired thermal gradient profile may be provided.

  20. Bacterial accumulation in viscosity gradients

    NASA Astrophysics Data System (ADS)

    Waisbord, Nicolas; Guasto, Jeffrey

    2016-11-01

    Cell motility is greatly modified by fluid rheology. In particular, the physical environments in which cells function, are often characterized by gradients of viscous biopolymers, such as mucus and extracellular matrix, which impact processes ranging from reproduction to digestion to biofilm formation. To understand how spatial heterogeneity of fluid rheology affects the motility and transport of swimming cells, we use hydrogel microfluidic devices to generate viscosity gradients in a simple, polymeric, Newtonian fluid. Using video microscopy, we characterize the random walk motility patterns of model bacteria (Bacillus subtilis), showing that both wild-type ('run-and-tumble') cells and smooth-swimming mutants accumulate in the viscous region of the fluid. Through statistical analysis of individual cell trajectories and body kinematics in both homogeneous and heterogeneous viscous environments, we discriminate passive, physical effects from active sensing processes to explain the observed cell accumulation at the ensemble level.

  1. THE GRADIENT OF VASCULAR PERMEABILITY

    PubMed Central

    Smith, Frederick; Rous, Peyton

    1931-01-01

    A mounting gradient of permeability exists along the capillaries of frog muscle. In chicken muscle on the other hand none has been demonstrated; but the close-knit vascularization is arranged in duplicate in such manner that the blood runs in opposite directions through the capillaries of nearly adjacent fibres. In a flight muscle of the pigeon there exists in addition to this artifice what appears to be a special collecting system of venous capillaries. In the mammalian diaphragm indications of such a system are also to be found, and a gradient of capillary permeability like that in the other skeletal muscles is probably present. These vascular conditions are briefly considered in terms of function. PMID:19869836

  2. Stellar Population Gradients in WLM

    NASA Astrophysics Data System (ADS)

    Noriega-Mendoza, H.; Holtzman, J.

    2001-12-01

    WLM is one of the most isolated galaxies in the Local Group. From archival HST frames, we look for population gradients using star count ratios from distinct regions of the Color-Magnitude diagram. We find clear evidence for a central concentration of the younger stars. This scenario supports the two-component disk/halo-like structure suggested for dwarf irregular galaxies (Martinez-Delgado, Gallart & Aparicio, 1999).

  3. Biomimetic Gradient Index (GRIN) Lenses

    DTIC Science & Technology

    2006-01-01

    optics include single lenses inspired by cephalopod (octopus) eyes and a three-lens, wide field of view, optical system for a surveillance sensor...camera. Details are easily resolv- able with the polymer lens. This lens system was installed on an Evolution unmanned aerial vehicle (UAV) with a...lens system was installed in an NRL Evolution UAV and used to record video images at a height of up to 1000 ft. The index gradients in the polymer

  4. Programming the gradient projection algorithm

    NASA Technical Reports Server (NTRS)

    Hargrove, A.

    1983-01-01

    The gradient projection method of numerical optimization which is applied to problems having linear constraints but nonlinear objective functions is described and analyzed. The algorithm is found to be efficient and thorough for small systems, but requires the addition of auxiliary methods and programming for large scale systems with severe nonlinearities. In order to verify the theoretical results a digital computer is used to simulate the algorithm.

  5. Two New PRP Conjugate Gradient Algorithms for Minimization Optimization Models

    PubMed Central

    Yuan, Gonglin; Duan, Xiabin; Liu, Wenjie; Wang, Xiaoliang; Cui, Zengru; Sheng, Zhou

    2015-01-01

    Two new PRP conjugate Algorithms are proposed in this paper based on two modified PRP conjugate gradient methods: the first algorithm is proposed for solving unconstrained optimization problems, and the second algorithm is proposed for solving nonlinear equations. The first method contains two aspects of information: function value and gradient value. The two methods both possess some good properties, as follows: 1)βk ≥ 0 2) the search direction has the trust region property without the use of any line search method 3) the search direction has sufficient descent property without the use of any line search method. Under some suitable conditions, we establish the global convergence of the two algorithms. We conduct numerical experiments to evaluate our algorithms. The numerical results indicate that the first algorithm is effective and competitive for solving unconstrained optimization problems and that the second algorithm is effective for solving large-scale nonlinear equations. PMID:26502409

  6. Two New PRP Conjugate Gradient Algorithms for Minimization Optimization Models.

    PubMed

    Yuan, Gonglin; Duan, Xiabin; Liu, Wenjie; Wang, Xiaoliang; Cui, Zengru; Sheng, Zhou

    2015-01-01

    Two new PRP conjugate Algorithms are proposed in this paper based on two modified PRP conjugate gradient methods: the first algorithm is proposed for solving unconstrained optimization problems, and the second algorithm is proposed for solving nonlinear equations. The first method contains two aspects of information: function value and gradient value. The two methods both possess some good properties, as follows: 1) βk ≥ 0 2) the search direction has the trust region property without the use of any line search method 3) the search direction has sufficient descent property without the use of any line search method. Under some suitable conditions, we establish the global convergence of the two algorithms. We conduct numerical experiments to evaluate our algorithms. The numerical results indicate that the first algorithm is effective and competitive for solving unconstrained optimization problems and that the second algorithm is effective for solving large-scale nonlinear equations.

  7. Future of gradient index optics

    NASA Astrophysics Data System (ADS)

    Hashizume, Hideki; Hamanaka, Kenjiro; Graham, Alan C., III; Zhu, X. Frank

    2001-11-01

    First developed over 30 years ago, gradient index lenses play an important role not only in telecommunications technology, but also in applications such as information interface and biomedical technology. Traditional manufacturing consists of doping a certain ion, A+ into the mother glass, drawing the glass into rods and then immersing the rods into s molten salt bath containing another certain ion B+. During a thermal ion exchange process, the original ion migrates out of the mother glass, and is replaced by the alternate ion, creating a refractive index variation. Current research is being conducted to improve the thermal ion exchange technology, and open new applications. This research includes extending working distances to greater than 100mm, decreasing the lens diameter, increasing the effective radius, and combining the technology with other technologies such as photolithographically etched masks to produce arrays of gradient index lenses. As a result of this ongoing research, the gradient index lens is expected to continue to be the enabling optical technology in the first decade of the new millennium and beyond.

  8. Seismic Velocity Gradients Across the Transition Zone

    NASA Astrophysics Data System (ADS)

    Escalante, C.; Cammarano, F.; de Koker, N.; Piazzoni, A.; Wang, Y.; Marone, F.; Dalton, C.; Romanowicz, B.

    2006-12-01

    One-D elastic velocity models derived from mineral physics do a notoriously poor job at predicting the velocity gradients in the upper mantle transition zone, as well as some other features of models derived from seismological data. During the 2006 CIDER summer program, we computed Vs and Vp velocity profiles in the upper mantle based on three different mineral physics approaches: two approaches based on the minimization of Gibbs Free Energy (Stixrude and Lithgow-Bertelloni, 2005; Piazzoni et al., 2006) and one obtained by using experimentally determined phase diagrams (Weidner and Wang, 1998). The profiles were compared by assuming a vertical temperature profile and two end-member compositional models, the pyrolite model of Ringwood (1979) and the piclogite model of Anderson and Bass (1984). The predicted seismic profiles, which are significantly different from each other, primarily due to different choices of properties of single minerals and their extrapolation with temperature, are tested against a global dataset of P and S travel times and spheroidal and toroidal normal mode eigenfrequencies. All the models derived using a potential temperature of 1600K predict seismic velocities that are too slow in the upper mantle, suggesting the need to use a colder geotherm. The velocity gradient in the transition zone is somewhat better for piclogite than for pyrolite, possibly indicating the need to increase Ca content. The presence of stagnant slabs in the transition zone is a possible explanation for the need for 1) colder temperature and 2) increased Ca content. Future improvements in seismic profiles obtained from mineral physics will arise from better knowledge of elastic properties of upper mantle constituents and aggregates at high temperature and pressure, a better understanding of differences between thermodynamic models, and possibly the effect of water through and on Q. High resolution seismic constraints on velocity jumps at 400 and 660 km also need to be

  9. Spatially-distributed pulsed gradient spin echo NMR using single-wire proximity

    NASA Astrophysics Data System (ADS)

    Callaghan, Paul T.; Stepisnik, Janez

    1995-12-01

    NMR microimaging may be used to observe the effect of molecular diffusion in the vicinity of a thin wire subjected to current pulses. By this means the pulsed gradient spin echo technique can utilize very large pulsed magnetic field gradients, on the order of 100 T m-1. The quadratic dependence of gradient amplitude on distance from the wire leads to large dynamic range while the distribution of local gradient vectors makes it possible to image anisotropic diffusion. We demonstrate these properties in measurements on polymer solutions and liquid crystals.

  10. Positive Contrast Visualization of Nitinol Devices using Susceptibility Gradient Mapping

    PubMed Central

    Vonken, Evert-jan P.A.; Schär, Michael; Stuber, Matthias

    2008-01-01

    MRI visualization of devices is traditionally based on the signal loss due to T2* effects originating from the local susceptibility differences. To visualize nitinol devices with positive contrast a recently introduced post processing method is adapted to map the induced susceptibility gradients. This method operates on regular gradient echo MR images and maps the shift in k-space in a (small) neighborhood of every voxel by Fourier analysis followed by a center of mass calculation. The quantitative map of the local shifts generates the positive contrast image of the devices, while areas without susceptibility gradients render a background with noise only. The positive signal response of this method depends only on the choice of the voxel neighborhood size. The properties of the method are explained and the visualization of a nitinol wire and two stents are shown for illustration. PMID:18727096

  11. Propagation of microwaves in gradient transmission lines: exactly solvable model

    NASA Astrophysics Data System (ADS)

    Shvartsburg, A. B.; Silin, N. V.

    2015-08-01

    Propagation of microwaves along the transmission line with smoothly continuously distributed capacitance and inductance (gradient transmission line) is considered in the framework of an exactly solvable model. The appearance of strong heterogeneity-induced plasma-like dispersion in gradient transmission line determined by the sizes and shapes of these distributions, is visualized by means of this model. Owing to this dispersion the energy transport in the line discussed can be ensured by both travelling and evanescent microwave modes, characterized by the real and imaginary wave numbers, respectively. The reflectance spectra for microwaves, incident on this heterogeneous transition section located between two homogeneous sections of transmission line are presented, the antireflection properties of this section are demonstrated. The interference of evanescent and anti-evanescent microwave modes is shown to provide the effective weakly attenuated energy transfer in the tunneling regime. The analogy between this microwave system and gradient nano-optical photonic barrier in revealed.

  12. Exploring chemical space with discrete, gradient, and hybrid optimization methods.

    PubMed

    Balamurugan, D; Yang, Weitao; Beratan, David N

    2008-11-07

    Discrete, gradient, and hybrid optimization methods are applied to the challenge of discovering molecules with optimized properties. The cost and performance of the approaches were studied using a tight-binding model to maximize the static first electronic hyperpolarizability of molecules. Our analysis shows that discrete branch and bound methods provide robust strategies for inverse chemical design involving diverse chemical structures. Based on the linear combination of atomic potentials, a hybrid discrete-gradient optimization strategy significantly improves the performance of the gradient methods. The hybrid method performs better than dead-end elimination and competes with branch and bound and genetic algorithms. The branch and bound methods for these model Hamiltonians are more cost effective than genetic algorithms for moderate-sized molecular optimization.

  13. Gradient networks on uncorrelated random scale-free networks

    NASA Astrophysics Data System (ADS)

    Pan, Gui-Jun; Yan, Xiao-Qing; Huang, Zhong-Bing; Ma, Wei-Chuan

    2011-03-01

    Uncorrelated random scale-free (URSF) networks are useful null models for checking the effects of scale-free topology on network-based dynamical processes. Here, we present a comparative study of the jamming level of gradient networks based on URSF networks and Erdős-Rényi (ER) random networks. We find that the URSF networks are less congested than ER random networks for the average degree langkrang>kc (kc ≈ 2 denotes a critical connectivity). In addition, by investigating the topological properties of the two kinds of gradient networks, we discuss the relations between the topological structure and the transport efficiency of the gradient networks. These findings show that the uncorrelated scale-free structure might allow more efficient transport than the random structure.

  14. A magnetic gradient induced force in NMR restricted diffusion experiments

    SciTech Connect

    Ghadirian, Bahman; Stait-Gardner, Tim; Castillo, Reynaldo; Price, William S.

    2014-03-28

    We predict that the phase cancellation of a precessing magnetisation field carried by a diffusing species in a bounded geometry under certain nuclear magnetic resonance pulsed magnetic field gradient sequences results in a small force over typically micrometre length scales. Our calculations reveal that the total magnetisation energy in a pore under the influence of a pulsed gradient will be distance-dependent thus resulting in a force acting on the boundary. It is shown that this effect of the magnetisation of diffusing particles will appear as either an attractive or repulsive force depending on the geometry of the pore and magnetic properties of the material. A detailed analysis is performed for the case of a pulsed gradient spin-echo experiment on parallel planes. It is shown that the force decays exponentially in terms of the spin-spin relaxation. The proof is based on classical electrodynamics. An application of this effect to soft matter is suggested.

  15. A shift from arbuscular mycorrhizal to dark septate endophytic colonization in Deschampsia flexuosa roots occurs along primary successional gradient.

    PubMed

    Huusko, K; Ruotsalainen, A L; Markkola, A M

    2017-02-01

    Soil fungal community and dominant mycorrhizal types are known to shift along with plant community changes during primary succession. However, it is not well understood how and why root fungal symbionts and colonization types vary within the plant host when the host species is able to thrive both at young and at old successional stages with different light and nutrient resource availability. We asked (i) how root fungal colonization of Deschampsia flexuosa (Poaceae) by arbuscular mycorrhizal (AM) fungi and dark septate endophytes (DSE) changes along a postglacial primary successional land uplift gradient. As neighboring vegetation may play a role in root fungal colonization, we also asked (ii) whether removal of the dominant neighbor, Empetrum nigrum ssp. hermaphroditum (Ericaceae), affects root fungal colonization of Deschampsia. We also studied whether (iii) foliar carbon (C) and nitrogen (N) concentration of Deschampsia is related to successional changes along a land uplift gradient. AM colonization decreased (-50 %), DSE colonization increased (+200 %), and foliar C declined in Deschampsia along with increasing successional age, whereas foliar N was not affected. Empetrum removal did not affect AM colonization but increased DSE sclerotial colonization especially at older successional stages. The observed decrease in foliar C coincides with an increase in canopy closure along with increasing successional age. We suggest that the shift from an AM-dominated to a DSE-dominated root fungal community in Deschampsia along a land uplift successional gradient may be related to different nutritional benefits gained through these root fungal groups.

  16. Cell, isoform, and environment factors shape gradients and modulate chemotaxis.

    PubMed

    Chang, S Laura; Cavnar, Stephen P; Takayama, Shuichi; Luker, Gary D; Linderman, Jennifer J

    2015-01-01

    Chemokine gradient formation requires multiple processes that include ligand secretion and diffusion, receptor binding and internalization, and immobilization of ligand to surfaces. To understand how these events dynamically shape gradients and influence ensuing cell chemotaxis, we built a multi-scale hybrid agent-based model linking gradient formation, cell responses, and receptor-level information. The CXCL12/CXCR4/CXCR7 signaling axis is highly implicated in metastasis of many cancers. We model CXCL12 gradient formation as it is impacted by CXCR4 and CXCR7, with particular focus on the three most highly expressed isoforms of CXCL12. We trained and validated our model using data from an in vitro microfluidic source-sink device. Our simulations demonstrate how isoform differences on the molecular level affect gradient formation and cell responses. We determine that ligand properties specific to CXCL12 isoforms (binding to the migration surface and to CXCR4) significantly impact migration and explain differences in in vitro chemotaxis data. We extend our model to analyze CXCL12 gradient formation in a tumor environment and find that short distance, steep gradients characteristic of the CXCL12-γ isoform are effective at driving chemotaxis. We highlight the importance of CXCL12-γ in cancer cell migration: its high effective affinity for both extracellular surface sites and CXCR4 strongly promote CXCR4+ cell migration. CXCL12-γ is also more difficult to inhibit, and we predict that co-inhibition of CXCR4 and CXCR7 is necessary to effectively hinder CXCL12-γ-induced migration. These findings support the growing importance of understanding differences in protein isoforms, and in particular their implications for cancer treatment.

  17. The properties of the star-forming interstellar medium at z = 0.84-2.23 from HiZELS: mapping the internal dynamics and metallicity gradients in high-redshift disc galaxies

    NASA Astrophysics Data System (ADS)

    Swinbank, A. M.; Sobral, D.; Smail, Ian; Geach, J. E.; Best, P. N.; McCarthy, I. G.; Crain, R. A.; Theuns, T.

    2012-10-01

    We present adaptive optics assisted, spatially resolved spectroscopy of a sample of nine Hα-selected galaxies at z = 0.84-2.23 drawn from the HiZELS narrow-band survey. These galaxies have star formation rates of 1-27 M⊙ yr-1 and are therefore representative of the typical high-redshift star-forming population. Our ˜kpc-scale resolution observations show that approximately half of the sample have dynamics suggesting that the ionized gas is in large, rotating discs. We model their velocity fields to infer the inclination-corrected, asymptotic rotational velocities. We use the absolute B-band magnitudes and stellar masses to investigate the evolution of the B-band and stellar-mass Tully-Fisher relationships. By combining our sample with a number of similar measurements from the literature, we show that, at fixed circular velocity, the stellar mass of star-forming galaxies has increased by a factor of 2.5 between z = 2 and 0, whilst the rest-frame B-band luminosity has decreased by a factor of ˜ 6 over the same period. Together, these demonstrate a change in mass-to-light ratio in the B band of Δ(M/LB)/(M/LB)z=0 ˜ 3.5 between z = 1.5 and 0, with most of the evolution occurring below z = 1. We also use the spatial variation of [N II]/Hα to show that the metallicity of the ionized gas in these galaxies declines monotonically with galactocentric radius, with an average Δ log(O/H)/ΔR = -0.027 ± 0.005 dex kpc-1. This gradient is consistent with predictions for high-redshift disc galaxies from cosmologically based hydrodynamic simulations.

  18. Development of New Gradient Index Glasses for Optical Imaging Systems.

    NASA Astrophysics Data System (ADS)

    Kindred, Douglas Scott

    1991-02-01

    Previous research has shown that many imaging systems can benefit from the use of gradient index (GRIN) materials. The required number of lens elements can often be reduced or the system performance can be improved. The use of gradient index lenses has not become widespread, however, largely due to three major problems. The first is that there is a lack of available gradient index materials. Lens designers require glasses with a wide range of refractive index and dispersions in both homogeneous and gradient index systems. Very few GRIN glasses have been developed and only small diameter (1-3 mm) gradient index rods are commercially available, leaving virtually nothing for the lens designer. The second problem is that adequate control of the index of refraction profile must be achieved. This is necessary in order to control the aberrations of the systems in question. The last problem is that the mathematical representation of the index of refraction profile is not currently linked to the fabrication parameters, thus making it difficult to manufacture a lens once it has been designed. This work concentrates largely on the first of these problems. Several new glasses have been developed which are suitable for fabricating both axial and radial gradients by Ag^{+}-Na ^{+} and Li^ {+}-Na^{+} ion exchange. New crown glasses, flint glasses and high index crowns with both positive and negative index changes are presented. A variety of refractive index profiles with different index changes (Deltan), and dispersive properties are also shown. The ion exchange properties of the glasses were investigated using conventional Fickian diffusion models and the refractive index profiles were modeled using Fantone's adaption of the Gladstone -Dale equation. The usefulness of these glasses in optical systems is assessed and a procedure for designing lenses with manufacturable index profiles is also demonstrated.

  19. Geomorphic controls on elevational gradients of species richness

    PubMed Central

    Bertuzzo, Enrico; Carrara, Francesco; Mari, Lorenzo; Altermatt, Florian; Rodriguez-Iturbe, Ignacio; Rinaldo, Andrea

    2016-01-01

    Elevational gradients of biodiversity have been widely investigated, and yet a clear interpretation of the biotic and abiotic factors that determine how species richness varies with elevation is still elusive. In mountainous landscapes, habitats at different elevations are characterized by different areal extent and connectivity properties, key drivers of biodiversity, as predicted by metacommunity theory. However, most previous studies directly correlated species richness to elevational gradients of potential drivers, thus neglecting the interplay between such gradients and the environmental matrix. Here, we investigate the role of geomorphology in shaping patterns of species richness. We develop a spatially explicit zero-sum metacommunity model where species have an elevation-dependent fitness and otherwise neutral traits. Results show that ecological dynamics over complex terrains lead to the null expectation of a hump-shaped elevational gradient of species richness, a pattern widely observed empirically. Local species richness is found to be related to the landscape elevational connectivity, as quantified by a newly proposed metric that applies tools of complex network theory to measure the closeness of a site to others with similar habitat. Our theoretical results suggest clear geomorphic controls on elevational gradients of species richness and support the use of the landscape elevational connectivity as a null model for the analysis of the distribution of biodiversity. PMID:26831107

  20. Geomorphic controls on elevational gradients of species richness.

    PubMed

    Bertuzzo, Enrico; Carrara, Francesco; Mari, Lorenzo; Altermatt, Florian; Rodriguez-Iturbe, Ignacio; Rinaldo, Andrea

    2016-02-16

    Elevational gradients of biodiversity have been widely investigated, and yet a clear interpretation of the biotic and abiotic factors that determine how species richness varies with elevation is still elusive. In mountainous landscapes, habitats at different elevations are characterized by different areal extent and connectivity properties, key drivers of biodiversity, as predicted by metacommunity theory. However, most previous studies directly correlated species richness to elevational gradients of potential drivers, thus neglecting the interplay between such gradients and the environmental matrix. Here, we investigate the role of geomorphology in shaping patterns of species richness. We develop a spatially explicit zero-sum metacommunity model where species have an elevation-dependent fitness and otherwise neutral traits. Results show that ecological dynamics over complex terrains lead to the null expectation of a hump-shaped elevational gradient of species richness, a pattern widely observed empirically. Local species richness is found to be related to the landscape elevational connectivity, as quantified by a newly proposed metric that applies tools of complex network theory to measure the closeness of a site to others with similar habitat. Our theoretical results suggest clear geomorphic controls on elevational gradients of species richness and support the use of the landscape elevational connectivity as a null model for the analysis of the distribution of biodiversity.

  1. An education gradient in health, a health gradient in education, or a confounded gradient in both?

    PubMed

    Lynch, Jamie L; von Hippel, Paul T

    2016-04-01

    There is a positive gradient associating educational attainment with health, yet the explanation for this gradient is not clear. Does higher education improve health (causation)? Do the healthy become highly educated (selection)? Or do good health and high educational attainment both result from advantages established early in the life course (confounding)? This study evaluates these competing explanations by tracking changes in educational attainment and Self-rated Health (SRH) from age 15 to age 31 in the National Longitudinal Study of Youth, 1997 cohort. Ordinal logistic regression confirms that high-SRH adolescents are more likely to become highly educated. This is partly because adolescent SRH is associated with early advantages including adolescents' academic performance, college plans, and family background (confounding); however, net of these confounders adolescent SRH still predicts adult educational attainment (selection). Fixed-effects longitudinal regression shows that educational attainment has little causal effect on SRH at age 31. Completion of a high school diploma or associate's degree has no effect on SRH, while completion of a bachelor's or graduate degree have effects that, though significant, are quite small (less than 0.1 points on a 5-point scale). While it is possible that educational attainment would have greater effect on health at older ages, at age 31 what we see is a health gradient in education, shaped primarily by selection and confounding rather than by a causal effect of education on health.

  2. Derivative Free Gradient Projection Algorithms for Rotation

    ERIC Educational Resources Information Center

    Jennrich, Robert I.

    2004-01-01

    A simple modification substantially simplifies the use of the gradient projection (GP) rotation algorithms of Jennrich (2001, 2002). These algorithms require subroutines to compute the value and gradient of any specific rotation criterion of interest. The gradient can be difficult to derive and program. It is shown that using numerical gradients…

  3. Synthesis and characterization of functionally gradient materials obtained by frontal polymerization.

    PubMed

    Nuvoli, Daniele; Alzari, Valeria; Pojman, John A; Sanna, Vanna; Ruiu, Andrea; Sanna, Davide; Malucelli, Giulio; Mariani, Alberto

    2015-02-18

    Functionally gradient materials (FGMs) with gradual and continuous changes of their properties in one or more dimensions are useful in a wide range of applications. However, obtaining such materials with accurate control of the gradient, especially when the gradient is nonlinear, is not easy. In this work, frontal polymerization (FP) was exploited to synthesize polymeric FGMs. We demonstrated that the use of ascending FP with continuous feeding of monomers with computer-controlled peristaltic pumps provided an excellent method for the preparation of functionally gradient materials with programmed gradients. To test the effectiveness of the method, copolymers made from triethylene glycol dimethacrylate/hexyl methacrylate with linear and hyperbolic gradient in composition were synthesized. Differential scanning calorimetry (DSC), Shore A hardness measurements, compression tests, and swelling studies were performed along the length of the materials to assess the relationship between the gradients and the material properties. Glass transition temperatures, determined by DSC, showed a linear dependence on the composition and were in agreement with theoretical values. The other properties showed different and specific behaviors as a function of the compositional gradient.

  4. Solution of the Eshelby problem in gradient elasticity for multilayer spherical inclusions

    NASA Astrophysics Data System (ADS)

    Volkov-Bogorodskii, D. B.; Lurie, S. A.

    2016-03-01

    We consider gradient models of elasticity which permit taking into account the characteristic scale parameters of the material. We prove the Papkovich-Neuber theorems, which determine the general form of the gradient solution and the structure of scale effects. We derive the Eshelby integral formula for the gradient moduli of elasticity, which plays the role of the closing equation in the self-consistent three-phase method. In the gradient theory of deformations, we consider the fundamental Eshelby-Christensen problem of determining the effective elastic properties of dispersed composites with spherical inclusions; the exact solution of this problem for classical models was obtained in 1976. This paper is the first to present the exact analytical solution of the Eshelby-Christensen problem for the gradient theory, which permits estimating the influence of scale effects on the stress state and the effective properties of the dispersed composites under study.We also analyze the influence of scale factors.

  5. Oxygen Gradients in the Microcirculation

    PubMed Central

    Pittman, Roland N.

    2010-01-01

    Early in the last century August Krogh embarked on a series of seminal studies to understand the connection between tissue metabolism and mechanisms by which the cardiovascular system supplied oxygen to meet those needs. Krogh recognized that oxygen was supplied from blood to the tissues by passive diffusion and that the most likely site for oxygen exchange was the capillary network. Studies of tissue oxygen consumption and diffusion coefficient, coupled with anatomical studies of capillarity in various tissues, led him to formulate a model of oxygen diffusion from a single capillary. Fifty years after the publication of this work, new methods were developed which allowed the direct measurement of oxygen in and around microvessels. These direct measurements have confirmed the predictions by Krogh and have led to extensions of his ideas resulting in our current understanding of oxygenation within the microcirculation. Developments during the last 40 years are reviewed, including studies of oxygen gradients in arterioles, capillaries, venules, microvessel wall and surrounding tissue. These measurements were made possible by the development and use of new methods to investigate oxygen in the microcirculation, so mention is made of oxygen microelectrodes, microspectrophotometry of haemoglobin and phosphorescence quenching microscopy. Our understanding of oxygen transport from the perspective of the microcirculation has gone from a consideration of oxygen gradients in capillaries and tissue to the realization that oxygen has the ability to diffuse from any microvessel to another location under the conditions that there exists a large enough PO2 gradient and that the permeability for oxygen along the intervening pathway is sufficient. PMID:21281453

  6. Structure of the velocity gradient tensor in turbulent shear flows

    NASA Astrophysics Data System (ADS)

    Pumir, Alain

    2017-07-01

    The expected universality of small-scale properties of turbulent flows implies isotropic properties of the velocity gradient tensor in the very large Reynolds number limit. Using direct numerical simulations, we determine the tensors formed by n =2 and 3 velocity gradients at a single point in turbulent homogeneous shear flows and in the log-layer of a turbulent channel flow, and we characterize the departure of these tensors from the corresponding isotropic prediction. Specifically, we separate the even components of the tensors, invariant under reflexion with respect to all axes, from the odd ones, which identically vanish in the absence of shear. Our results indicate that the largest deviation from isotropy comes from the odd component of the third velocity gradient correlation function, especially from the third moment of the derivative along the normal direction of the streamwise velocity component. At the Reynolds numbers considered (Reλ≈140 ), we observe that these second- and third-order correlation functions are significantly larger in turbulent channel flows than in homogeneous shear flow. Overall, our work demonstrates that a mean shear leads to relatively simple structure of the velocity gradient tensor. How isotropy is restored in the very large Reynolds limit remains to be understood.

  7. Cytokinin Import Rate as a Signal for Photosynthetic Acclimation to Canopy Light Gradients1[W][OA

    PubMed Central

    Boonman, Alex; Prinsen, Els; Gilmer, Frank; Schurr, Ulrich; Peeters, Anton J.M.; Voesenek, Laurentius A.C.J.; Pons, Thijs L.

    2007-01-01

    Plants growing in dense canopies are exposed to vertical light gradients and show photosynthetic acclimation at the whole-plant level, resulting in efficient photosynthetic carbon gain. We studied the role of cytokinins transported through the transpiration stream as one of probably multiple signals for photosynthetic acclimation to light gradients using both tobacco (Nicotiana tabacum) and Arabidopsis (Arabidopsis thaliana). We show that substantial variation in leaf transpiration parallels the light gradient in tobacco canopies and experimental reduction of the transpiration rate of a leaf, independent of light, is sufficient to reduce photosynthetic capacity in both species, as well as transcript levels of the small subunit of Rubisco (rbcS) gene in Arabidopsis. Mass spectrometric analysis of xylem sap collected from intact, transpiring tobacco plants revealed that shaded leaves import less cytokinin than leaves exposed to high light. In Arabidopsis, reduced transpiration rate of a leaf in the light is associated with lower cytokinin concentrations, including the bioactive trans-zeatin and trans-zeatin riboside, as well as reduced expression of the cytokinin-responsive genes ARR7 and ARR16. External application of cytokinin to shaded leaves rescued multiple shade effects, including rbcS transcript levels in both species, as did locally induced cytokinin overproduction in transgenic tobacco plants. From these data, we conclude that light gradients over the foliage of a plant result in reduced cytokinin activity in shaded leaves as a consequence of reduced import through the xylem and that cytokinin is involved in the regulation of whole-plant photosynthetic acclimation to light gradients in canopies. PMID:17277095

  8. Autonomous pump against concentration gradient

    PubMed Central

    Xu, Zhi-cheng; Zheng, Dong-qin; Ai, Bao-quan; Zhong, Wei-rong

    2016-01-01

    Using non-equilibrium molecular dynamics and Monte Carlo methods, we have studied the molecular transport in asymmetric nanochannels. The efficiency of the molecular pump depends on the angle and apertures of the asymmetric channel, the environmental temperature and average concentration of the particles. The pumping effect can be explained as the competition between the molecular force field and the thermal disturbance. Our results provide a green approach for pumping fluid particles against the concentration gradient through asymmetric nanoscale thin films without any external forces. It indicates that pumping vacuum can be a spontaneous process. PMID:26996204

  9. Temperature Gradient in Hall Thrusters

    SciTech Connect

    D. Staack; Y. Raitses; N.J. Fisch

    2003-11-24

    Plasma potentials and electron temperatures were deduced from emissive and cold floating probe measurements in a 2 kW Hall thruster, operated in the discharge voltage range of 200-400 V. An almost linear dependence of the electron temperature on the plasma potential was observed in the acceleration region of the thruster both inside and outside the thruster. This result calls into question whether secondary electron emission from the ceramic channel walls plays a significant role in electron energy balance. The proportionality factor between the axial electron temperature gradient and the electric field is significantly smaller than might be expected by models employing Ohmic heating of electrons.

  10. Generalized Gradient Approximation Made Simple

    SciTech Connect

    Perdew, J.P.; Burke, K.; Ernzerhof, M.

    1996-10-01

    Generalized gradient approximations (GGA{close_quote}s) for the exchange-correlation energy improve upon the local spin density (LSD) description of atoms, molecules, and solids. We present a simple derivation of a simple GGA, in which all parameters (other than those in LSD) are fundamental constants. Only general features of the detailed construction underlying the Perdew-Wang 1991 (PW91) GGA are invoked. Improvements over PW91 include an accurate description of the linear response of the uniform electron gas, correct behavior under uniform scaling, and a smoother potential. {copyright} {ital 1996 The American Physical Society.}

  11. Stringy bounces and gradient instabilities

    NASA Astrophysics Data System (ADS)

    Giovannini, Massimo

    2017-04-01

    Bouncing solutions are obtained from a generally covariant action characterized by a potential which is a nonlocal functional of the dilaton field at two separated space-time points. Gradient instabilities are shown to arise in this context but they are argued to be nongeneric. After performing a gauge-invariant and a frame-invariant derivation of the evolution equations of the fluctuations, a heuristic criterion for the avoidance of pathological instabilities is proposed and corroborated by a number of explicit examples that turn out to be compatible with a quasiflat spectrum of curvature inhomogeneities for large wavelengths.

  12. Mechanisms of FGF gradient formation during embryogenesis.

    PubMed

    Balasubramanian, Revathi; Zhang, Xin

    2016-05-01

    Fibroblast growth factors (FGFs) have long been attributed to influence morphogenesis in embryonic development. Signaling by FGF morphogen encodes positional identity of tissues by creating a concentration gradient over the developing embryo. Various mechanisms that influence the development of such gradient have been elucidated in the recent past. These mechanisms of FGF gradient formation present either as an extracellular control over FGF ligand diffusion or as a subcellular control of FGF propagation and signaling. In this review, we describe our current understanding of FGF as a morphogen, the extracellular control of FGF gradient formation by heparan sulfate proteoglycans (HSPGs) and mechanisms of intracellular regulation of FGF signaling that influence gradient formation.

  13. Compositional gradients in photopolymer films utilizing kinetic driving forces

    NASA Astrophysics Data System (ADS)

    Cook, Clinton John

    Independent control of the surface and bulk properties is advantageous for many applications such as adhesives, release coatings, and antimicrobial films. Traditional methods for achieving independent control typically require multiple processing steps such as wet-on-wet or wet-on-dry coating methods. Independent control over the surface properties can achieved in a single step utilizing the temporal and spatial control inherent to photopolymerization. Specifically, a co-photopolymerization of monomers with different reactivities in the presence of a light gradient is capable of producing a polymer film with a surface chemistry that differs from the bulk chemistry. The light gradient, produced via the concentration of photoinitiator in the formulation, results in a reaction gradient through the film with the higher rates of reaction occurring in the high light intensity regions of the film. The preferentially reacting monomer adds at a greater rate in the high light intensity regions resulting in non-uniform consumption yielding a concentration gradient. Consequently, diffusion of the preferentially reacting monomer from the bulk to the surface of the film and a counter-diffusion of the other monomer from the surface to the bulk of the film occurs from the non-uniform monomer consumption thus producing a film with a concentration gradient through the depth of the film with the preferentially reacting monomer enriching the high light intensity regions. A variety of kinetic differences capable of producing a stratified film will be presented including inherent monomer reactivity, number of functional groups per monomer, oxygen inhibition, thiol-ene chemistry, and Norrish type two initiation. Additionally, parameters that control the degree of stratification, such as methods of varying polymerization rate and the light gradient, will be examined. Changes in surface properties (such as contact angle, surface hardness, adhesion) and bulk properties (such as mechanical

  14. Bicrystals with strain gradient effects

    SciTech Connect

    Shu, J.Y.

    1997-01-09

    Boundary between two perfectly bonded single crystals plays an important role in determining the deformation of the bicrystals. This work addresses the role of the grain boundary by considering the elevated hardening of a slip system due to a slip gradient. The slip gradients are associated with geometrically necessary dislocations and their effects become pronounced when a representative length scale of the deformation field is comparable to the dominant microstructural length scale of a material. A new rate-dependent crystal plasticity theory is presented and has been implemented within the finite element method framework. A planar bicrystal under uniform in-plane loading is studied using the new crystal theory. The strain is found to be continuous but nonuniform within a boundary layer around the interface. The lattice rotation is also nonuniform within the boundary layer. The width of the layer is determined by the misorientation of the grains, the hardening of slip systems, and most importantly by the characteristic material length scales. The overall yield strength of the bicrystal is also obtained. A significant grain-size dependence of the yield strength, the Hall- Petch effect is predicted.

  15. Gradient-Modulated PETRA MRI.

    PubMed

    Kobayashi, Naoharu; Goerke, Ute; Wang, Luning; Ellermann, Jutta; Metzger, Gregory J; Garwood, Michael

    2015-12-01

    Image blurring due to off-resonance and fast T 2(*) signal decay is a common issue in radial ultrashort echo time MRI sequences. One solution is to use a higher readout bandwidth, but this may be impractical for some techniques like pointwise encoding time reduction with radial acquisition (PETRA), which is a hybrid method of zero echo time and single point imaging techniques. Specifically, PETRA has severe specific absorption rate (SAR) and radiofrequency (RF) pulse peak power limitations when using higher bandwidths in human measurements. In this study, we introduce gradient modulation (GM) to PETRA to reduce image blurring artifacts while keeping SAR and RF peak power low. Tolerance of GM-PETRA to image blurring was evaluated in simulations and experiments by comparing with the conventional PETRA technique. We performed inner ear imaging of a healthy subject at 7T. GM-PETRA showed significantly less image blurring due to off-resonance and fast T2(*) signal decay compared to PETRA. In in vivo imaging, GM-PETRA nicely captured complex structures of the inner ear such as the cochlea and semicircular canals. Gradient modulation can improve the PETRA image quality and mitigate SAR and RF peak power limitations without special hardware modification in clinical scanners.

  16. NIF optics phase gradient specfication

    SciTech Connect

    Williams, W.; Auerbach, J.; Hunt, J.; Lawson, L.; Manes, K.; Orth, C.; Sacks, R.; Trenholme, J.; Wegner, P.

    1997-05-02

    A root-mean-square (rms) phase gradient specification seems to allow a good connection between the NIP optics quality and focal spot requirements. Measurements on Beamlet optics individually, and as a chain, indicate they meet the assumptions necessary to use this specification, and that they have a typical rms phase gradient of {approximately}80 {angstrom}/cm. This may be sufficient for NIP to meet the proposed Stockpile Stewardship Management Program (SSMP) requirements of 80% of a high- power beam within a 200-250 micron diameter spot. Uncertainties include, especially, the scale length of the optics phase noise, the ability of the adaptive optic to correct against pump-induced distortions and optics noise, and the possibility of finding mitigation techniques against whole-beam self-focusing (e.g. a pre- correction optic). Further work is needed in these areas to better determine the NIF specifications. This memo is a written summary of a presentation on this topic given by W. Williams 24 April 1997 to NIP and LS&T personnel.

  17. Interhemispheric thermal gradient and tropical Pacific climate

    NASA Astrophysics Data System (ADS)

    Chiang, John C. H.; Fang, Yue; Chang, P.

    2008-07-01

    We explore the impact of interhemispheric thermal gradients forcing on the tropical Pacific ocean-atmosphere climate in an intermediate coupled model. The equatorial zonal sea surface temperature (SST) gradient strengthens with an increased northward interhemispheric thermal gradient, the increase arising from earlier onset and later retreat of the seasonal cold tongue, and intensification during the peak cold season. When the mean interhemispheric thermal gradient is reversed, the central equatorial Pacific SST annual cycle abruptly reverses in phase, with its cold season in Mar-May rather than Sep-Nov. While startling, this response is consistent with a prevailing hypothesis that ties the cold tongue SST annual cycle phase to the hemispheric mean asymmetry of the Intertropical Convergence Zone. El Niño-Southern Oscillation activity is also sensitive to the interhemispheric thermal gradient, with peak activity occurring when the mean gradient is small, reducing rapidly as the mean gradient increases in either direction.

  18. Extraordinary strain hardening by gradient structure.

    PubMed

    Wu, XiaoLei; Jiang, Ping; Chen, Liu; Yuan, Fuping; Zhu, Yuntian T

    2014-05-20

    Gradient structures have evolved over millions of years through natural selection and optimization in many biological systems such as bones and plant stems, where the structures change gradually from the surface to interior. The advantage of gradient structures is their maximization of physical and mechanical performance while minimizing material cost. Here we report that the gradient structure in engineering materials such as metals renders a unique extra strain hardening, which leads to high ductility. The grain-size gradient under uniaxial tension induces a macroscopic strain gradient and converts the applied uniaxial stress to multiaxial stresses due to the evolution of incompatible deformation along the gradient depth. Thereby the accumulation and interaction of dislocations are promoted, resulting in an extra strain hardening and an obvious strain hardening rate up-turn. Such extraordinary strain hardening, which is inherent to gradient structures and does not exist in homogeneous materials, provides a hitherto unknown strategy to develop strong and ductile materials by architecting heterogeneous nanostructures.

  19. Biomolecular gradients in cell culture systems

    PubMed Central

    Keenan, Thomas M.

    2013-01-01

    Biomolecule gradients have been shown to play roles in a wide range of biological processes including development, inflammation, wound healing, and cancer metastasis. Elucidation of these phenomena requires the ability to expose cells to biomolecule gradients that are quantifiable, controllable, and mimic those that are present in vivo. Here we review the major biological phenomena in which biomolecule gradients are employed, traditional in vitro gradient-generating methods developed over the past 50 years, and new microfluidic devices for generating gradients. Microfluidic gradient generators offer greater levels of precision, quantitation, and spatiotemporal gradient control than traditional methods, and may greatly enhance our understanding of many biological phenomena. For each method, we outline the salient features, capabilities, and applications. PMID:18094760

  20. A Review on Functionally Gradient Materials (FGMs) and Their Applications

    NASA Astrophysics Data System (ADS)

    Bhavar, Valmik; Kattire, Prakash; Thakare, Sandeep; patil, Sachin; Singh, RKP, Dr.

    2017-09-01

    Functionally gradient materials (FGM) are innovative materials in which final properties varies gradually with dimensions. It is the recent development in traditional composite materials which retains their strengths and eliminates their weaknesses. It can be formed by varying chemical composition, microstructure or design attributes from one end to other as per requirement. This feature allows FGM to have best material properties in required quantities only where it is needed. Though there are several methods available for manufacturing FGMs, additive based metal deposition (by laser, electron beam, plasma etc.) technologies are reaping particular interest owing to their recent developments. This paper presents evolution, current status and challenges of functionally gradient materials (FGMs). Various manufacturing processes of different types of FGMs are also presented. In addition, applications of FGMs in various fields including aerospace, defence, mining, power and tools manufacturing sectors are discussed in detail.

  1. Dispersion and optical gradient force from high-order mode coupling between two hyperbolic metamaterial waveguides

    NASA Astrophysics Data System (ADS)

    Wang, Guanghui; Zhang, Weifeng; Lu, Jiahui; Zhao, Huijun

    2016-08-01

    We analytically study dispersion properties and optical gradient forces of different-order transverse magnetic (TM) modes in two coupled hyperbolic metamaterial waveguides (HMMWs). According to Maxwell's equations, we obtain the dispersion relation of symmetric and antisymmetric modes, and calculate optical gradient forces of different-order modes by using Maxwell stress tensor. Numerical results show that the dispersion properties are dependent on the filling ratio, and the optical gradient forces of high-order TM modes are larger than the fundamental mode when the gap between two HMMWs is very narrow, but they weaken much faster than the case of low-order TM modes with the gap width increasing. In addition, the effects of the dielectric surrounding of waveguides on the coupling effect and optical gradient force are clarified. These properties offer an avenue for various optomechanical applications in optical sensors and actuators.

  2. A new conjugate gradient method with sufficient descent without any line search for unconstrained optimization

    NASA Astrophysics Data System (ADS)

    Omer, Osman; Rivaie, Mohd; Mamat, Mustafa; Amani, Zahrahtul

    2015-02-01

    Conjugate gradient methods are one of the most used methods for solving nonlinear unconstrained optimization problems, especially of large scale. Their wide applications are due to their simplicity and low memory requirement. The sufficient descent property is an important issue in the analyses and implementations of conjugate gradient methods. In this paper, a new conjugate gradient method is proposed for unconstrained optimization problems. The theoretical analysis shows that the directions generated by the new method are always satisfy the sufficient descent property, and this property is independent of the line search used. Furthermore, a numerical experiment based on comparing the new method with other known conjugate gradient methods shows that the new is efficient for some unconstrained optimization problems.

  3. Fabrication and evaluation of uniform and gradient density epoxies

    SciTech Connect

    Domeier, L.A.; Skala, D.M.; Goods, S.H.

    1997-11-01

    Filled epoxy materials which vary in density in a designed manner have been fabricated and their mechanical properties evaluated. Density variations were produced by incorporating different volume fractions of either glass microballoons (GMB) or alumina. Several different sample types were evaluated including uniform density (0.8 g/cm{sup 3} < {rho} < 2.0 g/cm{sup 3}) samples and gradient density samples (GMB only, 0.8 g/cm{sup 3} < {rho} < 1.2 g/cm{sup 3}). The uniform density specimens were evaluated for the effects of filler type and concentration on modulus and toughness. Results indicated that addition of alumina filler significantly increased the resulting modulus while addition of GMB had little measurable effect. These differences could be understood in terms of the differing moduli of the additives relative to that of the epoxy matrix. In the former case the alumina particulates had a modulus much greater than that of the epoxy while in the latter case, the modulus of the GMB additive was only slightly greater than that of the matrix. Addition of either filler significantly degraded the toughness of the composite specimens and precluded the use of gradients to enhance toughness performance. Discontinuous {open_quotes}block{close_quotes} gradients used for testing were fabricated by simple sequential pours of formulations with different GMB loadings and were evaluated for modulus, strength and ductility. Continuous gradients were fabricated in process studies by programmed shifts in the peristaltic pumping/mixing ratio of epoxies filled with either alumina or GMB. None of the continuous gradient materials were mechanically tested. These results suggest that applications utilizing gradient materials containing alumina and similar high modulus fillers to provide designed stiffness rather than improved toughness are the most appropriate targets for future investigation.

  4. Combinational concentration gradient confinement through stagnation flow.

    PubMed

    Alicia, Toh G G; Yang, Chun; Wang, Zhiping; Nguyen, Nam-Trung

    2016-01-21

    Concentration gradient generation in microfluidics is typically constrained by two conflicting mass transport requirements: short characteristic times (τ) for precise temporal control of concentration gradients but at the expense of high flow rates and hence, high flow shear stresses (σ). To decouple the limitations from these parameters, here we propose the use of stagnation flows to confine concentration gradients within large velocity gradients that surround the stagnation point. We developed a modified cross-slot (MCS) device capable of feeding binary and combinational concentration sources in stagnation flows. We show that across the velocity well, source-sink pairs can form permanent concentration gradients. As source-sink concentration pairs are continuously supplied to the MCS, a permanently stable concentration gradient can be generated. Tuning the flow rates directly controls the velocity gradients, and hence the stagnation point location, allowing the confined concentration gradient to be focused. In addition, the flow rate ratio within the MCS rapidly controls (τ ∼ 50 ms) the location of the stagnation point and the confined combinational concentration gradients at low flow shear (0.2 Pa < σ < 2.9 Pa). The MCS device described in this study establishes the method for using stagnation flows to rapidly generate and position low shear combinational concentration gradients for shear sensitive biological assays.

  5. Strength gradient enhances fatigue resistance of steels

    PubMed Central

    Ma, Zhiwei; Liu, Jiabin; Wang, Gang; Wang, Hongtao; Wei, Yujie; Gao, Huajian

    2016-01-01

    Steels are heavily used in infrastructure and the transportation industry, and enhancing their fatigue resistance is a major challenge in materials engineering. In this study, by introducing a gradient microstructure into 304 austenitic steel, which is one of the most widely used types of stainless steel, we show that a strength gradient substantially enhances the fatigue life of the material. Pre-notched samples with negative strength gradients in front of the notch’s tip endure many more fatigue cycles than do samples with positive strength gradients during the crack initiation stage, and samples with either type of gradient perform better than do gradient-free samples with the same average yield strength. However, as a crack grows, samples with positive strength gradients exhibit better resistance to fatigue crack propagation than do samples with negative gradients or no gradient. This study demonstrates a simple and promising strategy for using gradient structures to enhance the fatigue resistance of materials and complements related studies of strength and ductility. PMID:26907708

  6. Why do high-redshift galaxies show diverse gas-phase metallicity gradients?

    NASA Astrophysics Data System (ADS)

    Ma, Xiangcheng; Hopkins, Philip F.; Feldmann, Robert; Torrey, Paul; Faucher-Giguère, Claude-André; Kereš, Dušan

    2017-01-01

    Recent spatially resolved observations of galaxies at z ˜ 0.6-3 reveal that high-redshift galaxies show complex kinematics and a broad distribution of gas-phase metallicity gradients. To understand these results, we use a suite of high-resolution cosmological zoom-in simulations from the Feedback in Realistic Environments (FIRE) project, which include physically motivated models of the multi-phase ISM, star formation, and stellar feedback. Our simulations reproduce the observed diversity of kinematic properties and metallicity gradients, broadly consistent with observations at z ˜ 0-3. Strong negative metallicity gradients only appear in galaxies with a rotating disk, but not all rotationally supported galaxies have significant gradients. Strongly perturbed galaxies with little rotation always have flat gradients. The kinematic properties and metallicity gradient of a high-redshift galaxy can vary significantly on short time-scales, associated with starburst episodes. Feedback from a starburst can destroy the gas disk, drive strong outflows, and flatten a pre-existing negative metallicity gradient. The time variability of a single galaxy is statistically similar to the entire simulated sample, indicating that the observed metallicity gradients in high-redshift galaxies reflect the instantaneous state of the galaxy rather than the accretion and growth history on cosmological time-scales. We find weak dependence of metallicity gradient on stellar mass and specific star formation rate (sSFR). Low-mass galaxies and galaxies with high sSFR tend to have flat gradients, likely due to the fact that feedback is more efficient in these galaxies. We argue that it is important to resolve feedback on small scales in order to produce the diverse metallicity gradients observed.

  7. Why do high-redshift galaxies show diverse gas-phase metallicity gradients?

    NASA Astrophysics Data System (ADS)

    Ma, Xiangcheng; Hopkins, Philip F.; Feldmann, Robert; Torrey, Paul; Faucher-Giguère, Claude-André; Kereš, Dušan

    2017-04-01

    Recent spatially resolved observations of galaxies at z ˜ 0.6-3 reveal that high-redshift galaxies show complex kinematics and a broad distribution of gas-phase metallicity gradients. To understand these results, we use a suite of high-resolution cosmological zoom-in simulations from the Feedback in Realistic Environments project, which include physically motivated models of the multiphase interstellar medium, star formation and stellar feedback. Our simulations reproduce the observed diversity of kinematic properties and metallicity gradients, broadly consistent with observations at z ˜ 0-3. Strong negative metallicity gradients only appear in galaxies with a rotating disc, but not all rotationally supported galaxies have significant gradients. Strongly perturbed galaxies with little rotation always have flat gradients. The kinematic properties and metallicity gradient of a high-redshift galaxy can vary significantly on short time-scales, associated with starburst episodes. Feedback from a starburst can destroy the gas disc, drive strong outflows and flatten a pre-existing negative metallicity gradient. The time variability of a single galaxy is statistically similar to the entire simulated sample, indicating that the observed metallicity gradients in high-redshift galaxies reflect the instantaneous state of the galaxy rather than the accretion and growth history on cosmological time-scales. We find weak dependence of metallicity gradient on stellar mass and specific star formation rate (sSFR). Low-mass galaxies and galaxies with high sSFR tend to have flat gradients, likely due to the fact that feedback is more efficient in these galaxies. We argue that it is important to resolve feedback on small scales in order to produce the diverse metallicity gradients observed.

  8. Gradient scaling for nonuniform meshes

    SciTech Connect

    Margolin, L.G.; Ruppel, H.M.; Demuth, R.B.

    1985-01-01

    This paper is concerned with the effect of nonuniform meshes on the accuracy of finite-difference calculations of fluid flow. In particular, when a simple shock propagates through a nonuniform mesh, one may fail to model the jump conditions across the shock even when the equations are differenced in manifestly conservative fashion. We develop an approximate dispersion analysis of the numerical equations and identify the source of the mesh dependency with the form of the artificial viscosity. We then derive an algebraic correction to the numerical equations - a scaling factor for the pressure gradient - to essentially eliminate the mesh dependency. We present several calculations to illustrate our theory. We conclude with an alternate interpretation of our results. 14 refs., 5 figs.

  9. Spin-wave propagation and transformation in a thermal gradient

    NASA Astrophysics Data System (ADS)

    Obry, Björn; Vasyuchka, Vitaliy I.; Chumak, Andrii V.; Serga, Alexander A.; Hillebrands, Burkard

    2012-11-01

    The influence of a thermal gradient on the propagation properties of externally excited dipolar spin waves in a magnetic insulator waveguide is investigated. It is shown that spin waves propagating towards a colder region along the magnetization direction continuously reduce their wavelength. The wavelength increase of a wave propagating into a hotter region was utilized to realize its decomposition in the partial waveguide modes which are reflected at different locations. This influence of temperature on spin-wave properties is mainly caused by a change in the saturation magnetization and yields promising opportunities for the manipulation of spin waves in spin-caloritronic applications.

  10. Interspecific variation of photosynthesis and leaf characteristics in canopy trees of five species of Dipterocarpaceae in a tropical rain forest.

    PubMed

    Kenzo, Tanaka; Ichie, Tomoaki; Yoneda, Reiji; Kitahashi, Yoshinori; Watanabe, Yoko; Ninomiya, Ikuo; Koike, Takayoshi

    2004-10-01

    Photosynthetic rate, nitrogen concentration and morphological properties of canopy leaves were studied in 18 trees, comprising five dipterocarp species, in a tropical rain forest in Sarawak, Malaysia. Photosynthetic rate at light saturation (Pmax) differed significantly across species, varying from 7 to 18 micro mol m(-2) s(-1). Leaf nitrogen concentration and morphological properties, such as leaf blade and palisade layer thickness, leaf mass per area (LMA) and surface area of mesophyll cells per unit leaf area (Ames/A), also varied significantly across species. Among the relationships with leaf characteristics, Pmax had the strongest correlation with leaf mesophyll parameters, such as palisade cell layer thickness (r2 = 0.76, P < 0.001) and Ames/A (r2 = 0.73, P < 0.001). Leaf nitrogen concentration and Pmax per unit area also had a significant but weaker correlation (r2 = 0.46, P < 0.01), whereas Pmax had no correlation, or only weakly significant correlations, with leaf blade thickness and LMA. Shorea beccariana Burck, which had the highest P(max) of the species studied, also had the thickest palisade layer, with up to five or more layers. We conclude that interspecific variation in photosynthetic capacity in tropical rain forest canopies is influenced more by leaf mesophyll structure than by leaf thickness, LMA or leaf nitrogen concentration.

  11. Half conformally flat gradient Ricci almost solitons

    PubMed Central

    Brozos-Vázquez, M.; Valle-Regueiro, X.

    2016-01-01

    The local structure of half conformally flat gradient Ricci almost solitons is investigated, showing that they are locally conformally flat in a neighbourhood of any point where the gradient of the potential function is non-null. In opposition, if the gradient of the potential function is null, then the soliton is a steady traceless κ-Einstein soliton and is realized on the cotangent bundle of an affine surface. PMID:27279774

  12. Testing the limits of gradient sensing

    PubMed Central

    Lakhani, Vinal

    2017-01-01

    The ability to detect a chemical gradient is fundamental to many cellular processes. In multicellular organisms gradient sensing plays an important role in many physiological processes such as wound healing and development. Unicellular organisms use gradient sensing to move (chemotaxis) or grow (chemotropism) towards a favorable environment. Some cells are capable of detecting extremely shallow gradients, even in the presence of significant molecular-level noise. For example, yeast have been reported to detect pheromone gradients as shallow as 0.1 nM/μm. Noise reduction mechanisms, such as time-averaging and the internalization of pheromone molecules, have been proposed to explain how yeast cells filter fluctuations and detect shallow gradients. Here, we use a Particle-Based Reaction-Diffusion model of ligand-receptor dynamics to test the effectiveness of these mechanisms and to determine the limits of gradient sensing. In particular, we develop novel simulation methods for establishing chemical gradients that not only allow us to study gradient sensing under steady-state conditions, but also take into account transient effects as the gradient forms. Based on reported measurements of reaction rates, our results indicate neither time-averaging nor receptor endocytosis significantly improves the cell’s accuracy in detecting gradients over time scales associated with the initiation of polarized growth. Additionally, our results demonstrate the physical barrier of the cell membrane sharpens chemical gradients across the cell. While our studies are motivated by the mating response of yeast, we believe our results and simulation methods will find applications in many different contexts. PMID:28207738

  13. Morpheus unbound: reimagining the morphogen gradient.

    PubMed

    Lander, Arthur D

    2007-01-26

    The theory that the spatial organization of cell fate is orchestrated by gradients of diffusing molecules was a major contribution to 20th century developmental biology. Although the existence of morphogens is no longer in doubt, studies on the formation and function of their gradients have yielded far more puzzles than answers. On close inspection, every morphogen gradient seems to use a rich array of regulatory mechanisms, suggesting that the tasks carried out by such systems are far more extensive than previously thought.

  14. Gas-phase detonation propagation in mixture composition gradients.

    PubMed

    Kessler, D A; Gamezo, V N; Oran, E S

    2012-02-13

    The propagation of detonations through several fuel-air mixtures with spatially varying fuel concentrations is examined numerically. The detonations propagate through two-dimensional channels, inside of which the gradient of mixture composition is oriented normal to the direction of propagation. The simulations are performed using a two-component, single-step reaction model calibrated so that one-dimensional detonation properties of model low- and high-activation-energy mixtures are similar to those observed in a typical hydrocarbon-air mixture. In the low-activation-energy mixture, the reaction zone structure is complex, consisting of curved fuel-lean and fuel-rich detonations near the line of stoichiometry that transition to decoupled shocks and turbulent deflagrations near the channel walls where the mixture is extremely fuel-lean or fuel-rich. Reactants that are not consumed by the leading detonation combine downstream and burn in a diffusion flame. Detonation cells produced by the unstable reaction front vary in size across the channel, growing larger away from the line of stoichiometry. As the size of the channel decreases relative to the size of a detonation cell, the effect of the mixture composition gradient is lessened and cells of similar sizes form. In the high-activation-energy mixture, detonations propagate more slowly as the magnitude of the mixture composition gradient is increased and can be quenched in a large enough gradient.

  15. Gradient-Stable Linear Time Steps for Phase Field Models

    NASA Astrophysics Data System (ADS)

    Vollmayr-Lee, Benjamin

    2013-03-01

    Phase field models, which are nonlinear partial-differential equations, are a widely used for modeling the dynamics and equilibrium properties of materials. Unfortunately, time marching the equations of motion by explicit methods is usually numerically unstable unless the size of the time step is kept below a lattice-dependent threshold. Consequently, the amount of numerical computation is determined by avoidance of the instability rather than by the natural time scale of the dynamics. This can be a severe overhead. In contrast, a gradient stable method ensures a decreasing free energy, consistent with the relaxational dynamics of the continuous time model. Eyre's theorem proved that gradient stable schemes are possible, and Eyre presented a framework for constructing gradient-stable, semi-implicit time steps for a given phase-field model. Here I present a new theorem that provides a broader class of gradient-stable steps, in particular ones in which the implicit part of the equation is linear. This enables use of fast Fourier transforms to solve for the updated field, providing a considerable advantage in speed and simplicity. Examples will be presented for the Allen-Cahn and Cahn-Hilliard equations, an Ehrlich-Schwoebel-type interface growth model, and block copolymers.

  16. Development of morphogen gradient: The role of dimension and discreteness

    SciTech Connect

    Teimouri, Hamid; Kolomeisky, Anatoly B.

    2014-02-28

    The fundamental processes of biological development are governed by multiple signaling molecules that create non-uniform concentration profiles known as morphogen gradients. It is widely believed that the establishment of morphogen gradients is a result of complex processes that involve diffusion and degradation of locally produced signaling molecules. We developed a multi-dimensional discrete-state stochastic approach for investigating the corresponding reaction-diffusion models. It provided a full analytical description for stationary profiles and for important dynamic properties such as local accumulation times, variances, and mean first-passage times. The role of discreteness in developing of morphogen gradients is analyzed by comparing with available continuum descriptions. It is found that the continuum models prediction about multiple time scales near the source region in two-dimensional and three-dimensional systems is not supported in our analysis. Using ideas that view the degradation process as an effective potential, the effect of dimensionality on establishment of morphogen gradients is also discussed. In addition, we investigated how these reaction-diffusion processes are modified with changing the size of the source region.

  17. Microfluidic chip containing porous gradient for chemotaxis study

    NASA Astrophysics Data System (ADS)

    Al-Abboodi, Aswan; Tjeung, Ricky; Doran, Pauline; Yeo, Leslie; Friend, James; Chan, Peggy

    2011-12-01

    We have developed a new porous gradient microfluidic device based on in situ Gtn-HPA/CMC-Tyr hydrogel that comprises gelatin hydroxyphenylpropionic acid (Gtn-HPA) conjugate and carboxymethyl cellulose tyramine (CMC-Tyr) conjugate. The device is fabricated using a soft lithographic technique, in which microstructures were patterned on a thin layer of polydimethylsiloxane (PDMS) using a polymeric mold. Human fibrosarcoma cells (HT1080) were employed as invasive cancer cell model. Porosity gradients were generated by flowing pore etching fluid in the gradient generator network. Results suggested that spatial control of the porosity can be obtained, which mimics the 3-dimensional microenvironment in vivo for cell-based screening applications including real time chemotaxis, cytotoxicity, and continuous drug-response monitoring. A chemoattractant gradient is then generated and cell migration is monitored in real time using fluorescence microscopy. The viability of cells was evaluated using calcien AM stain. Herein, we successfully monitored the chemotactic responses of cancer cells, confirmed the validity of using in situ porous hydrogels as a construction material for a microchemotaxis device, and demonstrated the potential of the hydrogel with tunable porosity based microfluidic device in biological experiments. This device will also be practical in controlling the chemical and mechanical properties of the surroundings during the formation of tissue engineered constructs.

  18. Wettability-gradient-driven micropump for transporting discrete liquid drops

    NASA Astrophysics Data System (ADS)

    Bardaweel, Hamzeh K.; Zamuruyev, Konstantin; Delplanque, Jean-Pierre; Davis, Cristina E.

    2013-03-01

    In this paper, we report our efforts toward building a microelectromechanical system-based micropump. The micropump is driven by a wettability gradient and used to transport discrete drops. The gradient in wettability is distributed axisymmetrically, with hydrophobicity of the micropump surface decreasing radially toward the center. Both physical and chemical properties of the surface are altered to obtain the wettability gradient needed for driving the drops. The surface of the micropump is, first, patterned with pre-designed micro-features that define the roughness of the surface and, then, coated with a low-energy interface film. Results show that drops deposited on the surface of the micropump move, in a directional way, along the wettability gradient. The average velocity of the deposited drops is 5 mm s-1. Measured contact angles decrease gradually from 157.0° to 124.2° toward the center of the micropump surface. Maximum driving force exerted by the solid surface on the drops is 12.82 µN. The average size of the drops transported on the surface of the micropump is 2 µL.

  19. Directional motion of evaporating droplets on gradient surfaces

    NASA Astrophysics Data System (ADS)

    Yao, Shuhuai; Xu, Li; Li, Zhigang

    2012-11-01

    Droplet evaporation on surfaces has various applications in drying problems such as ink-jet printing, pesticide spraying, chemical or biological detection, and DNA microarray spotting technology. Controlling evaporating droplets via substrate morphology and/or wetting properties allows for efficient deposition of sample molecules in these applications. In this work, evaporation of sessile water droplets on surfaces with wettability gradients was studied. The wettability gradient was generated by fabricating non-uniformly distributed cylindrical micropillars on silicon surfaces. During the evaporation, it was found, along the wettability gradient, that the contact line on one side was strongly pinned, while the contact line on the other side depinned and gradually receded, making the center of mass of the droplet move either in or against the direction the wettability gradient, depending on the configuration of the micropillars. The theoretical criterion predicting the moving direction was derived based on the excess free energy and the energy barrier during the evaporation. The theoretical predications agreed well with the experimental observations. The results provide a parametric design basis to control the contact line dynamics and directional transport of evaporating droplets. This work was supported by the Research Grants Council of Hong Kong under General Research Fund (Grant No. 621110).

  20. Engineering functionality gradients by dip coating process in acceleration mode.

    PubMed

    Faustini, Marco; Ceratti, Davide R; Louis, Benjamin; Boudot, Mickael; Albouy, Pierre-Antoine; Boissière, Cédric; Grosso, David

    2014-10-08

    In this work, unique functional devices exhibiting controlled gradients of properties are fabricated by dip-coating process in acceleration mode. Through this new approach, thin films with "on-demand" thickness graded profiles at the submillimeter scale are prepared in an easy and versatile way, compatible for large-scale production. The technique is adapted to several relevant materials, including sol-gel dense and mesoporous metal oxides, block copolymers, metal-organic framework colloids, and commercial photoresists. In the first part of the Article, an investigation on the effect of the dip coating speed variation on the thickness profiles is reported together with the critical roles played by the evaporation rate and by the viscosity on the fluid draining-induced film formation. In the second part, dip-coating in acceleration mode is used to induce controlled variation of functionalities by playing on structural, chemical, or dimensional variations in nano- and microsystems. In order to demonstrate the full potentiality and versatility of the technique, original graded functional devices are made including optical interferometry mirrors with bidirectional gradients, one-dimensional photonic crystals with a stop-band gradient, graded microfluidic channels, and wetting gradient to induce droplet motion.

  1. Enhanced protective role in materials with gradient structural orientations: Lessons from Nature.

    PubMed

    Liu, Zengqian; Zhu, Yankun; Jiao, Da; Weng, Zhaoyong; Zhang, Zhefeng; Ritchie, Robert O

    2016-10-15

    Living organisms are adept at resisting contact deformation and damage by assembling protective surfaces with spatially varied mechanical properties, i.e., by creating functionally graded materials. Such gradients, together with multiple length-scale hierarchical structures, represent the two prime characteristics of many biological materials to be translated into engineering design. Here, we examine one design motif from a variety of biological tissues and materials where site-specific mechanical properties are generated for enhanced protection by adopting gradients in structural orientation over multiple length-scales, without manipulation of composition or microstructural dimension. Quantitative correlations are established between the structural orientations and local mechanical properties, such as stiffness, strength and fracture resistance; based on such gradients, the underlying mechanisms for the enhanced protective role of these materials are clarified. Theoretical analysis is presented and corroborated through numerical simulations of the indentation behavior of composites with distinct orientations. The design strategy of such bioinspired gradients is outlined in terms of the geometry of constituents. This study may offer a feasible approach towards generating functionally graded mechanical properties in synthetic materials for improved contact damage resistance. Living organisms are adept at resisting contact damage by assembling protective surfaces with spatially varied mechanical properties, i.e., by creating functionally-graded materials. Such gradients, together with multiple length-scale hierarchical structures, represent the prime characteristics of many biological materials. Here, we examine one design motif from a variety of biological tissues where site-specific mechanical properties are generated for enhanced protection by adopting gradients in structural orientation at multiple length-scales, without changes in composition or microstructural

  2. Improving generalization performance of natural gradient learning using optimized regularization by NIC.

    PubMed

    Park, Hyeyoung; Murata, Noboru; Amari, Shun-Ichi

    2004-02-01

    Natural gradient learning is known to be efficient in escaping plateau, which is a main cause of the slow learning speed of neural networks. The adaptive natural gradient learning method for practical implementation also has been developed, and its advantage in real-world problems has been confirmed. In this letter, we deal with the generalization performances of the natural gradient method. Since natural gradient learning makes parameters fit to training data quickly,the overfitting phenomenon may easily occur, which results in poor generalization performance. To solve the problem, we introduce the regularization term in natural gradient learning and propose an efficient optimizing method for the scale of regularization by using a generalized Akaike information criterion (network information criterion). We discuss the properties of the optimized regularization strength by NIC through theoretical analysis as well as computer simulations. We confirm the computational efficiency and generalization performance of the proposed method in real-world applications through computational experiments on benchmark problems.

  3. Fibrillar adhesion with no clusterisation: Functional significance of material gradient along adhesive setae of insects.

    PubMed

    Gorb, Stanislav N; Filippov, Alexander E

    2014-01-01

    It has been recently demonstrated that adhesive tarsal setae of beetles possess material gradients along their length. These gradients presumably represent an evolutionary optimization enhancing the adaptation to rough surfaces while simultaneously preventing clusterisation of the setae by lateral collapse. The numerical experiment of the present study has clearly demonstrated that gradient-bearing fibers with short soft tips and stiff bases have greater advantage in maximizing adhesion and minimizing clusterisation in multiple attachment-detachment cycles, if compared to the fibers with longer soft tips on the stiff bases and fibers with stiff tips on the soft bases. This study not only manifests the crucial role of gradients in material properties along the setae in beetle fibrillar adhesive system, but predicts that similar gradients must have been convergently evolved in various lineages of arthropods.

  4. A second gradient formulation for a 2D fabric sheet with inextensible fibres

    NASA Astrophysics Data System (ADS)

    Placidi, Luca; Greco, Leopoldo; Bucci, Sara; Turco, Emilio; Rizzi, Nicola Luigi

    2016-10-01

    We present numerical simulations of rectangular woven fabrics made of two, initially orthogonal, families of inextensible fibres. We consider an energy functional which includes both first and second gradients of the displacement. The energy density is expressed in terms of the angles between the fibres directions, using trigonometric functions and their gradients. In particular, we focus on an energy density depending on the squared tangent of the shear angle, which automatically satisfies some natural properties of the energy. The numerical results show that final configurations obtained by the second gradient energies are smoother than the first gradient ones. Moreover, we show that if a second gradient energy is considered, the shear energy is better uniformly distributed.

  5. Self-Assembled Monolayers with Molecular Gradients

    NASA Astrophysics Data System (ADS)

    Schäferling, Michael; Riepl, Michael; Liedberg, Bo

    In recent years, biosensors and sensor arrays have developed into very important analytical tools, which found applications in many fields such as pharmaceutical (high-throughput) screening, medical diagnosis, or industrial process control. One of the major challenges for material research is the preparation of appropriate sensor surfaces, providing an interface with a high sensitivity and selectivity toward a given analyte. This chapter discusses some straightforward and flexible approaches to study structure and/or composition-function relationships and response characteristics of polymeric and molecular sensor materials. The controlled continuous deposition of self-assembled monolayers (SAMs), e.g. of substituted thiols or silanes, paves the way for the generation of molecular gradients on solid surfaces. These are useful for the preparation of interfaces with spatially controlled chemical composition and/ or physical properties. These tools can help to improve the selectivity and specificity of surfaces for biosensors and biochips. They can also be utilized for the study of fundamental protein adsorption and exchange phenomena.

  6. Electron transfer across a thermal gradient

    PubMed Central

    Craven, Galen T.

    2016-01-01

    Charge transfer is a fundamental process that underlies a multitude of phenomena in chemistry and biology. Recent advances in observing and manipulating charge and heat transport at the nanoscale, and recently developed techniques for monitoring temperature at high temporal and spatial resolution, imply the need for considering electron transfer across thermal gradients. Here, a theory is developed for the rate of electron transfer and the associated heat transport between donor–acceptor pairs located at sites of different temperatures. To this end, through application of a generalized multidimensional transition state theory, the traditional Arrhenius picture of activation energy as a single point on a free energy surface is replaced with a bithermal property that is derived from statistical weighting over all configurations where the reactant and product states are equienergetic. The flow of energy associated with the electron transfer process is also examined, leading to relations between the rate of heat exchange among the donor and acceptor sites as functions of the temperature difference and the electronic driving bias. In particular, we find that an open electron transfer channel contributes to enhanced heat transport between sites even when they are in electronic equilibrium. The presented results provide a unified theory for charge transport and the associated heat conduction between sites at different temperatures. PMID:27450086

  7. Vertical gradients of mineral elements in Pinus sylvestris crown in alkalised soil.

    PubMed

    Mandre, Malle

    2009-12-01

    Alkalisation of soil has been assumed to be the principal cause of changes in vertical gradients of nutrients in Pinus sylvestris crown. The long-term influence of alkaline dust pollution (pHH2O 12.3-12.6) emitted from a cement plant on the element composition of soil and needles of Scots pine in different canopy layers was studied. In the polluted area, the pH of soils was >7, and high amounts of Ca, K and Mg were measured in the upper layers of soil (0-30 cm), while the mobility and solubility of some contaminants have decreased, nutrition processes have become complicated, and imbalance of mineral composition of trees was revealed. Reduced N and increased K, Ca and Mg concentrations in needles were observed in the heavily polluted area. Vertical gradients of elements and their ratios in canopies varied depending on the alkalisation level of soil. Needles on the upper-crown shoots had higher concentrations of N, C, Ca and Mg and lower concentrations of P and K compared to the lower layer of the crown. In the unpolluted area, higher concentrations of N, P, K and Ca were found in lower-crown needles and of C and Mg in needles at the top of the canopy. The P/N ratio below 0.125 indicated P deficiency in pines. The ratios N/Ca, N/Mg and N/K had significantly decreased, while the ratios Ca/Mg, K/Mg and K/Ca had a tendency to increase in heavily polluted sample plots. Magnitude of changes of element ratios indicates on the disbalances of availability and translocation of nutrients in the crown of trees.

  8. Intra prediction with spatial gradient

    NASA Astrophysics Data System (ADS)

    Matsuo, Shohei; Takamura, Seishi; Kamikura, Kazuto; Yashima, Yoshiyuki

    2009-01-01

    Spatial intra prediction has been added recently to the latest video coding standard H.264/AVC. In the intra prediction of H.264/AVC, there are 9, 9 and 4 prediction modes for 4×4, 8×8 and 16×16 blocks, respectively. Prediction signals are generated by using one or several reference pixels. The value of a reference pixel is copied as the prediction value. In some prediction modes, we calculate a weighted mean by averaging several pixels. The same prediction value is copied to several of the pixels lying in the prediction direction. However, if original image has patterns like gradations, the residual energy could increase which would result in low coding efficiency. In this paper, we propose a new intra prediction that generates prediction signals with a spatial gradient to deal with this problem. Simulation results show that it improves the picture quality and reduce the bit-rate by about 0.14 dB and 1.0 % on average for CIF sequences, respectively. It is also confirmed that our method is effective at high bit-rates.

  9. Pumpernickel Valley Geothermal Project Thermal Gradient Wells

    SciTech Connect

    Z. Adam Szybinski

    2006-01-01

    The Pumpernickel Valley geothermal project area is located near the eastern edge of the Sonoma Range and is positioned within the structurally complex Winnemucca fold and thrust belt of north-central Nevada. A series of approximately north-northeast-striking faults related to the Basin and Range tectonics are superimposed on the earlier structures within the project area, and are responsible for the final overall geometry and distribution of the pre-existing structural features on the property. Two of these faults, the Pumpernickel Valley fault and Edna Mountain fault, are range-bounding and display numerous characteristics typical of strike-slip fault systems. These characteristics, when combined with geophysical data from Shore (2005), indicate the presence of a pull-apart basin, formed within the releasing bend of the Pumpernickel Valley – Edna Mountain fault system. A substantial body of evidence exists, in the form of available geothermal, geological and geophysical information, to suggest that the property and the pull-apart basin host a structurally controlled, extensive geothermal field. The most evident manifestations of the geothermal activity in the valley are two areas with hot springs, seepages, and wet ground/vegetation anomalies near the Pumpernickel Valley fault, which indicate that the fault focuses the fluid up-flow. There has not been any geothermal production from the Pumpernickel Valley area, but it was the focus of a limited exploration effort by Magma Power Company. In 1974, the company drilled one exploration/temperature gradient borehole east of the Pumpernickel Valley fault and recorded a thermal gradient of 160oC/km. The 1982 temperature data from five unrelated mineral exploration holes to the north of the Magma well indicated geothermal gradients in a range from 66 to 249oC/km for wells west of the fault, and ~283oC/km in a well next to the fault. In 2005, Nevada Geothermal Power Company drilled four geothermal gradient wells, PVTG-1

  10. Role of gradients in vocal fold elastic modulus on phonation.

    PubMed

    Bhattacharya, Pinaki; Kelleher, Jordan E; Siegmund, Thomas

    2015-09-18

    New studies show that the elastic properties of the vocal folds (VFs) vary locally. In particular strong gradients exist in the distribution of elastic modulus along the length of the VF ligament, which is an important load-bearing constituent of the VF tissue. There is further evidence that changes in VF health are associated with alterations in modulus gradients. The role of VF modulus gradation on VF vibration and phonation remains unexplored. In this study the magnitude of the gradient in VF elastic modulus is varied, and sophisticated computational simulations are performed of the self-oscillation of three-dimensional VFs with realistic modeling of airflow physical properties. Results highlight that phonation frequency, characteristic modes of deformation and phase differences, glottal airflow rate, spectral-width of vocal output, and glottal jet dynamics are dependent on the magnitude of VF elastic modulus gradation. The results advance the understanding of how VF functional gradation can lead to perceptible changes in speech quality. Copyright © 2015 Elsevier Ltd. All rights reserved.

  11. Role of gradients in vocal fold elastic modulus on phonation

    PubMed Central

    Bhattacharya, Pinaki; Kelleher, Jordan E.; Siegmund, Thomas

    2015-01-01

    New studies show that the elastic properties of the vocal folds (VFs) vary locally. In particular strong gradients exist in the distribution of elastic modulus along the length of the VF ligament, which is an important load-bearing constituent of the VF tissue. There is further evidence that changes in VF health are associated with alterations in modulus gradients. The role of VF modulus gradation on VF vibration and phonation remains unexplored. In this study the magnitude of the gradient in VF elastic modulus is varied, and sophisticated computational simulations are performed of the self-oscillation of three-dimensional VFs with realistic modeling of airflow physical properties. Results highlight that phonation frequency, characteristic modes of deformation and phase differences, glottal airflow rate, spectral-width of vocal output, and glottal jet dynamics are dependent on the magnitude of VF elastic modulus gradation. The results advance the understanding of how VF functional gradation can lead to perceptible changes in speech quality. PMID:26159059

  12. Light gradients and optical microniches in coral tissues

    PubMed Central

    Wangpraseurt, Daniel; Larkum, Anthony W. D.; Ralph, Peter J.; Kühl, Michael

    2012-01-01

    Light quantity and quality are among the most important factors determining the physiology and stress response of zooxanthellate corals. Yet, almost nothing is known about the light field that Symbiodinium experiences within their coral host, and the basic optical properties of coral tissue are unknown. We used scalar irradiance microprobes to characterize vertical and lateral light gradients within and across tissues of several coral species. Our results revealed the presence of steep light gradients with photosynthetically available radiation decreasing by about one order of magnitude from the tissue surface to the coral skeleton. Surface scalar irradiance was consistently higher over polyp tissue than over coenosarc tissue in faviid corals. Coral bleaching increased surface scalar irradiance by ~150% (between 500 and 700 nm) relative to a healthy coral. Photosynthesis peaked around 300 μm within the tissue, which corresponded to a zone exhibiting strongest depletion of scalar irradiance. Deeper coral tissue layers, e.g., ~1000 μm into aboral polyp tissues, harbor optical microniches, where only ~10% of the incident irradiance remains. We conclude that the optical microenvironment of corals exhibits strong lateral and vertical gradients of scalar irradiance, which are affected by both tissue and skeleton optical properties. Our results imply that zooxanthellae populations inhabit a strongly heterogeneous light environment and highlight the presence of different optical microniches in corals; an important finding for understanding the photobiology, stress response, as well as the phenotypic and genotypic plasticity of coral symbionts. PMID:22969755

  13. Computation of the gravity field and its gradient: Some applications

    NASA Astrophysics Data System (ADS)

    Dubey, C. P.; Tiwari, V. M.

    2016-03-01

    New measuring instruments of Earth's gravity gradient tensors (GGT) have offered a fresh impetus to gravimetry and its application in subsurface exploration. Several efforts have been made to provide a thorough understanding of the complex properties of the gravity gradient tensor and its mathematical formulations to compute GGT. However, there is not much open source software available. Understanding of the tensor properties leads to important guidelines in the development of real three dimensional geological models. We present a MATLAB computational algorithm to calculate the gravity field and full gravity gradient tensor for an undulated surface followed by regular geometries like an infinite horizontal slab, a vertical sheet, a solid sphere, a vertical cylinder, a normal fault model and a rectangular lamina or conglomerations of such bodies and the results are compared with responses using professional software based on different computational schemes. Real subsurface geometries of complex geological structures of interest are approximated through arrangements of vertical rectangular laminas. The geological application of this algorithm is demonstrated over a horst-type structure of Oklahoma Aulacogen, USA and Vredefort Dome, South Africa, where measured GGT data are available.

  14. Algorithm for ion beam figuring of low-gradient mirrors.

    PubMed

    Jiao, Changjun; Li, Shengyi; Xie, Xuhui

    2009-07-20

    Ion beam figuring technology for low-gradient mirrors is discussed. Ion beam figuring is a noncontact machining technique in which a beam of high-energy ions is directed toward a target workpiece to remove material in a predetermined and controlled fashion. Owing to this noncontact mode of material removal, problems associated with tool wear and edge effects, which are common in conventional contact polishing processes, are avoided. Based on the Bayesian principle, an iterative dwell time algorithm for planar mirrors is deduced from the computer-controlled optical surfacing (CCOS) principle. With the properties of the removal function, the shaping process of low-gradient mirrors can be approximated by the linear model for planar mirrors. With these discussions, the error surface figuring technology for low-gradient mirrors with a linear path is set up. With the near-Gaussian property of the removal function, the figuring process with a spiral path can be described by the conventional linear CCOS principle, and a Bayesian-based iterative algorithm can be used to deconvolute the dwell time. Moreover, the selection criterion of the spiral parameter is given. Ion beam figuring technology with a spiral scan path based on these methods can be used to figure mirrors with non-axis-symmetrical errors. Experiments on SiC chemical vapor deposition planar and Zerodur paraboloid samples are made, and the final surface errors are all below 1/100 lambda.

  15. SDSS-IV MaNGA: stellar population gradients as a function of galaxy environment

    NASA Astrophysics Data System (ADS)

    Goddard, D.; Thomas, D.; Maraston, C.; Westfall, K.; Etherington, J.; Riffel, R.; Mallmann, N. D.; Zheng, Z.; Argudo-Fernández, M.; Bershady, M.; Bundy, K.; Drory, N.; Law, D.; Yan, R.; Wake, D.; Weijmans, A.; Bizyaev, D.; Brownstein, J.; Lane, R. R.; Maiolino, R.; Masters, K.; Merrifield, M.; Nitschelm, C.; Pan, K.; Roman-Lopes, A.; Storchi-Bergmann, T.

    2017-02-01

    We study the internal radial gradients of stellar population properties within 1.5 Re and analyse the impact of galaxy environment. We use a representative sample of 721 galaxies with masses ranging between 109 M⊙ and 1011.5 M⊙ from the SDSS-IV survey MaNGA. We split this sample by morphology into early-type and late-type galaxies. Using the full spectral fitting code FIREFLY, we derive the light and mass-weighted stellar population properties, age and metallicity, and calculate the gradients of these properties. We use three independent methods to quantify galaxy environment, namely the Nth nearest neighbour, the tidal strength parameter Q and distinguish between central and satellite galaxies. In our analysis, we find that early-type galaxies generally exhibit shallow light-weighted age gradients in agreement with the literature and mass-weighted median age gradients tend to be slightly positive. Late-type galaxies, instead, have negative light-weighted age gradients. We detect negative metallicity gradients in both early- and late-type galaxies that correlate with galaxy mass, with the gradients being steeper and the correlation with mass being stronger in late-types. We find, however, that stellar population gradients, for both morphological classifications, have no significant correlation with galaxy environment for all three characterizations of environment. Our results suggest that galaxy mass is the main driver of stellar population gradients in both early and late-type galaxies, and any environmental dependence, if present at all, must be very subtle.

  16. Engineering optical gradient force from coupled surface plasmon polariton modes in nanoscale plasmonic waveguides

    NASA Astrophysics Data System (ADS)

    Lu, Jiahui; Wang, Guanghui

    2016-11-01

    We explore the dispersion properties and optical gradient forces from mutual coupling of surface plasmon polariton (SPP) modes at two interfaces of nanoscale plasmonic waveguides with hyperbolic metamaterial cladding. With Maxwell’s equations and Maxwell stress tensor, we calculate and compare the dispersion relation and optical gradient force for symmetric and antisymmetric SPP modes in two kinds of nanoscale plasmonic waveguides. The numerical results show that the optical gradient force between two coupled hyperbolic metamaterial waveguides can be engineered flexibly by adjusting the waveguide structure parameters. Importantly, an alternative way to boost the optical gradient force is provided through engineering the hyperbolic metamaterial cladding of suitable orientation. These special optical properties will open the door for potential optomechanical applications, such as optical tweezers and actuators. Project supported by the National Natural Science Foundation of China (Grant No. 11474106) and the Natural Science Foundation of Guangdong Province, China (Grant No. 2016A030313439).

  17. Statistics of concentration gradients in porous media

    NASA Astrophysics Data System (ADS)

    Le Borgne, Tanguy; Huck, Peter; Dentz, Marco; Villermaux, Emmanuel

    2017-04-01

    In subsurface environments, concentration gradients develop at interfaces between surface water and groundwater bodies, such as hyporheic zones, saline wedges or recharge areas, as well as around contaminant plumes and fluids injected in subsurface operations. These areas generally represent hotspots of biogeochemical reactions, such as redox, dissolution and precipitation reactions, as concentration gradients create opportunities for reactive agents to mix and generate chemical disequilibrium. While macrodispersion theories predict smooth gradients, decaying in time due to dispersive dissipation, we show that concentration gradients can be broadly distributed since they are enhanced by velocity gradients induced by medium heterogeneity. We thus present a stochastic theory linking the Probability Density Function (PDF) of concentration gradients to flow heterogeneity (Le Borgne et al., 2017). Analytical predictions are validated from high resolution simulations of transport in heterogeneous Darcy fields ranging from small to large permeability variances and low to high Peclet numbers. This modelling framework hence opens new perspectives for quantifying the dynamics of chemical gradient distributions and the kinetics of associated biogeochemical reactions in a stochastic framework. References: Le Borgne T., P.D. Huck, M. Dentz and E. Villermaux (2017) Scalar gradients in stirred mixtures and the deconstruction of random fields, J. of Fluid Mech. 812, pp. 578-610. doi: 10.1017/jfm.2016.799

  18. The gradient deformation criterion for brittle fracture

    NASA Astrophysics Data System (ADS)

    Kuliev, V. D.; Morozov, E. M.

    2016-10-01

    A new fracture criterion based on the assumption that brittle fracture occurs when the strain gradient reaches its limiting value is formulated. The presence of a strain gradient at the boundary of a body's temperature drop is shown analytically. The results of an experiment with specimens under an abrupt change in temperature are presented.

  19. Geothermal gradient map of the United States

    SciTech Connect

    Kron, A.; Heiken, G.

    1980-01-01

    A geothermal gradient map is needed in order to determine the hot dry rock (HDR) geothermal resource of the United States. Based on published and unpublished data (including new measurements) the HDR program will produce updated gradient maps annually, to be used as a tool for resource evaluation and exploration. The 1980 version of this map is presented.

  20. An Inexpensive Digital Gradient Controller for HPLC.

    ERIC Educational Resources Information Center

    Brady, James E.; Carr, Peter W.

    1983-01-01

    Use of gradient elution techniques in high performance liquid chromatography (HPLC) is often essential for direct separation of complex mixtures. Since most commercial controllers have features that are of marginal value for instructional purposes, a low-cost controller capable of illustrating essential features of gradient elution was developed.…

  1. An Inexpensive Digital Gradient Controller for HPLC.

    ERIC Educational Resources Information Center

    Brady, James E.; Carr, Peter W.

    1983-01-01

    Use of gradient elution techniques in high performance liquid chromatography (HPLC) is often essential for direct separation of complex mixtures. Since most commercial controllers have features that are of marginal value for instructional purposes, a low-cost controller capable of illustrating essential features of gradient elution was developed.…

  2. Calculation of exit gradients at drainage ditches

    USDA-ARS?s Scientific Manuscript database

    Seepage gradients play an important role in the detachment of soil particles from the side walls of stream channels and drainage ditches. Most seepage studies have focused on water losses. Relatively few have addressed the determination of these gradients as causes of soil loss and incipient gully d...

  3. Patterns of macromycete community assemblage along an elevation gradient: options for fungal gradient and metacommunity analyse

    Treesearch

    Marko Gómez-Hernández; Guadalupe Williams-Linera; Roger Guevara; D. Jean Lodge

    2012-01-01

    Gradient analysis is rarely used in studies of fungal communities. Data on macromycetes from eight sites along an elevation gradient in central Veracruz, Mexico, were used to demonstrate methods for gradient analysis that can be applied to studies of communities of fungi. Selected sites from 100 to 3,500 m altitude represent tropical dry forest, tropical montane cloud...

  4. Dual fuel gradients in uranium silicide plates

    SciTech Connect

    Pace, B.W.

    1997-08-01

    Babcock & Wilcox has been able to achieve dual gradient plates with good repeatability in small lots of U{sub 3}Si{sub 2} plates. Improvements in homogeneity and other processing parameters and techniques have allowed the development of contoured fuel within the cladding. The most difficult obstacles to overcome have been the ability to evaluate the bidirectional fuel loadings in comparison to the perfect loading model and the different methods of instilling the gradients in the early compact stage. The overriding conclusion is that to control the contour of the fuel, a known relationship between the compact, the frames and final core gradient must exist. Therefore, further development in the creation and control of dual gradients in fuel plates will involve arriving at a plausible gradient requirement and building the correct model between the compact configuration and the final contoured loading requirements.

  5. A new family of conjugate gradient methods

    NASA Astrophysics Data System (ADS)

    Shi, Zhen-Jun; Guo, Jinhua

    2009-02-01

    In this paper we develop a new class of conjugate gradient methods for unconstrained optimization problems. A new nonmonotone line search technique is proposed to guarantee the global convergence of these conjugate gradient methods under some mild conditions. In particular, Polak-Ribiére-Polyak and Liu-Storey conjugate gradient methods are special cases of the new class of conjugate gradient methods. By estimating the local Lipschitz constant of the derivative of objective functions, we can find an adequate step size and substantially decrease the function evaluations at each iteration. Numerical results show that these new conjugate gradient methods are effective in minimizing large-scale non-convex non-quadratic functions.

  6. Approximate error conjugation gradient minimization methods

    DOEpatents

    Kallman, Jeffrey S

    2013-05-21

    In one embodiment, a method includes selecting a subset of rays from a set of all rays to use in an error calculation for a constrained conjugate gradient minimization problem, calculating an approximate error using the subset of rays, and calculating a minimum in a conjugate gradient direction based on the approximate error. In another embodiment, a system includes a processor for executing logic, logic for selecting a subset of rays from a set of all rays to use in an error calculation for a constrained conjugate gradient minimization problem, logic for calculating an approximate error using the subset of rays, and logic for calculating a minimum in a conjugate gradient direction based on the approximate error. In other embodiments, computer program products, methods, and systems are described capable of using approximate error in constrained conjugate gradient minimization problems.

  7. Nonchaotic stagnant motion in a marginal quasiperiodic gradient system.

    PubMed

    Mitsui, Takahito

    2008-08-01

    A one-dimensional dynamical system with a marginal quasiperiodic gradient is presented as a mathematical extension of a nonuniform oscillator. The system exhibits a nonchaotic stagnant motion, which is reminiscent of intermittent chaos. In fact, the density function of residence times near stagnation points obeys an inverse-square law, due to a mechanism similar to type-I intermittency. However, unlike intermittent chaos, in which the alternation between long stagnant phases and rapid moving phases occurs in a random manner, here the alternation occurs in a quasiperiodic manner. In particular, in the case of a gradient with the golden ratio, the renewal of the largest residence time occurs at positions corresponding to the Fibonacci sequence. Finally, the asymptotic long-time behavior, in the form of a nested logarithm, is theoretically derived. Compared with the Pomeau-Manneville intermittency, a significant difference in the relaxation property of the long-time average of the dynamical variable is found.

  8. Size-separation of silver nanoparticles using sucrose gradient centrifugation

    SciTech Connect

    Suresh, Anil K.; Pelletier, Dale A.; Moon, Ji Won; Phelps, Tommy; Doktycz, Mitchel John

    2015-08-28

    Size and shape distributions of nanoparticles can drastically contribute to the overall properties of nanoparticles, thereby influencing their interaction with different chemotherapeutic molecules, biological organisms and or materials and cell types. Therefore, to exploit the proper use of nanoparticles for various biomedical and biosensor applications, it is important to obtain well-separated monodispersed nanoparticles. However, gaining precise control over the morphological characteristics of nanoparticles during their synthesis is often a challenging task. Consequently, post-synthesis separation of nanoparticles is necessary. In the present study, we demonstrate the successful one-pot post-synthesis separation of anisotropic silver nanoparticles to near modispersities using sucrose density gradient sedimentation. The separation of the nanoparticles was evidenced based on optical confirmation, and spectrophotometric and transmission electron microscopy measurements. Our results clearly demonstrate the facile separation of anisotropic silver nanoparticles using sucrose density gradient sedimentation and can enable the use of nanoparticles for various biomedical applications.

  9. Developing gradient metal alloys through radial deposition additive manufacturing.

    PubMed

    Hofmann, Douglas C; Roberts, Scott; Otis, Richard; Kolodziejska, Joanna; Dillon, R Peter; Suh, Jong-ook; Shapiro, Andrew A; Liu, Zi-Kui; Borgonia, John-Paul

    2014-06-19

    Interest in additive manufacturing (AM) has dramatically expanded in the last several years, owing to the paradigm shift that the process provides over conventional manufacturing. Although the vast majority of recent work in AM has focused on three-dimensional printing in polymers, AM techniques for fabricating metal alloys have been available for more than a decade. Here, laser deposition (LD) is used to fabricate multifunctional metal alloys that have a strategically graded composition to alter their mechanical and physical properties. Using the technique in combination with rotational deposition enables fabrication of compositional gradients radially from the center of a sample. A roadmap for developing gradient alloys is presented that uses multi-component phase diagrams as maps for composition selection so as to avoid unwanted phases. Practical applications for the new technology are demonstrated in low-coefficient of thermal expansion radially graded metal inserts for carbon-fiber spacecraft panels.

  10. Separation of colloidal two dimensional materials by density gradient ultracentrifugation

    NASA Astrophysics Data System (ADS)

    Kuang, Yun; Song, Sha; Huang, Jinyang; Sun, Xiaoming

    2015-04-01

    Two-dimensional (2D) materials have been made through various approaches but obtaining monodispersed simply by synthesis optimization gained little success, which highlighted the need for introducing nanoseparation methods. Density gradient ultracentrifugation method has emerged as a versatile and scalable method for sorting colloidal 2D nanomaterials. Isopycnic separation was applied on thickness-dependent separation of graphene nanosheets. And rate-zonal separation, as a more versatile separation method, demonstrated its capability in sorting nanosheets of chemically modified single layered graphene, layered double hydroxide, and even metallic Ag. Establishing such density gradient ultracentrifugation method not only achieves monodispersed nanosheets and provides new opportunities for investigation on size dependent properties of 2D materials, but also makes the surface modification possible by introducing "reaction zones" during sedimentation of the colloids.

  11. Developing Gradient Metal Alloys through Radial Deposition Additive Manufacturing

    PubMed Central

    Hofmann, Douglas C.; Roberts, Scott; Otis, Richard; Kolodziejska, Joanna; Dillon, R. Peter; Suh, Jong-ook; Shapiro, Andrew A.; Liu, Zi-Kui; Borgonia, John-Paul

    2014-01-01

    Interest in additive manufacturing (AM) has dramatically expanded in the last several years, owing to the paradigm shift that the process provides over conventional manufacturing. Although the vast majority of recent work in AM has focused on three-dimensional printing in polymers, AM techniques for fabricating metal alloys have been available for more than a decade. Here, laser deposition (LD) is used to fabricate multifunctional metal alloys that have a strategically graded composition to alter their mechanical and physical properties. Using the technique in combination with rotational deposition enables fabrication of compositional gradients radially from the center of a sample. A roadmap for developing gradient alloys is presented that uses multi-component phase diagrams as maps for composition selection so as to avoid unwanted phases. Practical applications for the new technology are demonstrated in low-coefficient of thermal expansion radially graded metal inserts for carbon-fiber spacecraft panels. PMID:24942329

  12. Strong solutions and instability for the fitness gradient system in evolutionary games between two populations

    NASA Astrophysics Data System (ADS)

    Xu, Qiuju; Belmonte, Andrew; deForest, Russ; Liu, Chun; Tan, Zhong

    2017-04-01

    In this paper, we study a fitness gradient system for two populations interacting via a symmetric game. The population dynamics are governed by a conservation law, with a spatial migration flux determined by the fitness. By applying the Galerkin method, we establish the existence, regularity and uniqueness of global solutions to an approximate system, which retains most of the interesting mathematical properties of the original fitness gradient system. Furthermore, we show that a Turing instability occurs for equilibrium states of the fitness gradient system, and its approximations.

  13. Acupuncture needles and the Seebeck effect: do temperature gradients produce electrostimulation?

    PubMed

    Cohen, M; Kwok, G; Cosic, I

    1997-01-01

    Acupuncture may act through modifying bioelectric events and this may occur through different mechanisms including the application of external currents. According to the Seebeck effect which produces a potential difference when a temperature gradient is placed across a conductor, the physical properties of acupuncture needles may produce internal currents due to the temperature gradient across the needle when placed insitu. Such currents were detected when needles were differentially heated and these currents were found to be in the range capable of producing biological effects. The traditional design of acupuncture needles and traditional needle manipulations seem to maintain a temperature gradient across the needle and thus enhance the Seebeck effect.

  14. Predicting Chemical Reactivity from the Charge Density through Gradient Bundle Analysis: Moving beyond Fukui Functions.

    PubMed

    Morgenstern, Amanda; Wilson, Timothy R; Eberhart, M E

    2017-06-08

    Predicting chemical reactivity is a major goal of chemistry. Toward this end, atom condensed Fukui functions of conceptual density functional theory have been used to predict which atom is most likely to undergo electrophilic or nucleophilic attack, providing regioselectivity information. We show that the most probable regions for electrophilic attack within each atom can be predicted through analysis of gradient bundle volumes, a property that depends only on the charge density of the neutral molecules. We also introduce gradient bundle condensed Fukui functions to compare the stereoselectivity information obtained from gradient bundle volume analysis. We demonstrate this method using the test set of molecular fluorine, oxygen, nitrogen, carbon monoxide, and hydrogen cyanide.

  15. An investigation on directionally dependent fracture toughness behavior of monolithic nickel gradient material synthesized from electroplating

    NASA Astrophysics Data System (ADS)

    Farooq, Ahmad; El-Aty, Ali Abd; Ahmed, Tauseef; Tai-Chi, Chang

    2017-07-01

    Bulk sized continuous and monolithic pure Nickel gradient material is successfully developed using electroplating method. Great emphasis is given on controlling the direction of the gradient for the samples. The gradient belt for each Nickel gradient material consisted of grain size from maximum 4 µm to minimum 20nm, with the belt transcending from coarse towards ultrafine to finally nano-grain structure. Crack is propagated from Coarse to Nano-grain gradient Nickel and vice versa in order to procure the J-integral (Jic) for each sample according to ASTM standard E-1820 and deduce the fracture properties under each condition. Under such conditions when crack propagated from coarse to nano direction, Jmax is found to be 215kJ/m2 while crack propagating from Nano to Coarse direction, Jmax is found to be 62kJ/m2. Such dual polarized Jic within a single material is unique, especially for nickel whose Jicin literature for coarse grain (95 µm) was around 225kJ/m2 and ultrafine grain (300nm) was 100 kJ/m2, meaning the nickel gradient material consisting the grain gradient belt between 4 µm-20nm exhibits similar fracture toughness as pure coarse grain almost 20 times larger. Such gradient material exhibiting directionally dependent fracture toughness behavior can most certainly be much stronger under tensile conditions while keeping high fracture toughness.

  16. Stratospheric Balloon Gradient Geomagnetic Measurements

    NASA Astrophysics Data System (ADS)

    Filippov, Sergey; Tsvetkov, Yury

    The study of the interior structure of the Earth and laws of its evolution is one of the most difficult problems of natural science. Among the geophysical fields the anomaly magnetic field is one of the most informational in questions of the Earth's crust structure. Many important parameters of an environment are expedient for measuring at lower altitudes, than satellite ones. So, one of the alternatives is stratospheric balloon survey. The balloon flight altitudes cover the range from 20 to 50 km. At such altitudes there are steady zone air flows due to which the balloon flight trajectories can be of any direction, including round-the-world (round-the-pole). One of the examples of such sounding system have been designed, developed and maintained at IZMIRAN during already about 20 years. This system consists of three instrumental con-tainers uniformly placed along a vertical 6 km line. System allows measuring a module and vertical gradient of the geomagnetic field along the whole flight trajectory and so one's name is -stratospheric balloon magnetic gradiometer (SMBG). The GPS-receivers, located in each instrumental container, fix the flight coordinates to within several tens meters. Data trans-mission is carried out by Globalstar satellite link. The obtained data are used in solving the problems of deep sounding of the Earth's crust magnetic structure -an extraction of magnetic anomalies, determination of a depth of bedding of magnetoactive rocks and others. The developed launching technology, deployment in flight, assembly, data processing, transfer and landing the containers with the equipment can be used for other similar problems of monitoring and sounding an environment. Useful flight weights of each instrumental container may be reaching 50 kg. More than ten testing flights (1986-2009) at stratospheric altitudes (20-30 km) have proven the reliability of this system.

  17. Gradient Approximation on Uniform Meshes by Finite Differences and Cubic Spline Interpolation

    NASA Astrophysics Data System (ADS)

    Sablonnière, P.

    For the approximation of gradients from data values at vertices of a uniform grid, we compare two methods based on cubic spline interpolation with a classical method based on finite differences. For univariate cubic splines, we use the so-called de Boor’s Not a Knot property and a new method giving pretty good slopes. Then these methods are used on parallels to the axes for estimating gradients on bivariate grids. They are illustrated by several numerical examples.

  18. Novel concepts in weld metal science: Role of gradients and composite structure

    SciTech Connect

    Matlock, D.K.; Olson, D.L.

    1991-12-01

    The effects of compositional and microstructural gradients on weld metal properties are being investigated. Crack propagation is solidified alloy structures is being characterized as to solidification orientation and the profile of the compositional variations. The effects of compositional gradients, are considered based on a thermodynamic analysis, referred to as the Cahn-Hillard analysis, which describes the degree to which a local surface energy is modified by the presence of a compositional gradient. The analysis predicts that both ductile and brittle fracture mechanisms are enhanced by the presence of a composition gradient. Special techniques to produce laboratory samples with microstructures which simulate the composition and microstructure gradients in solidified weld metal are used, along with appropriate mathematical models, to evaluate the properties of the composite weld metals. The composite modeling techniques are being applied to describe the effects of compositional and microstructural gradients on weld metal properties in Ni-Cu alloys. The development of metal matrix composition weld deposits on austenitic stainless steels has been studied. The particulate metal matrix composites were produced with ceramic or refractory metal powder filled cored wire, which was gas tungsten arc and gas metal arc welded.

  19. Measurement of Gravity-Induced Concentration Gradients in the Presence of Perturbing Thermal Gradients.

    NASA Astrophysics Data System (ADS)

    Hicks, F. B.; van Vechten, Thomas C.; Franck, Carl

    1996-03-01

    As noted by Kayser, Moldover, and Schmidt, the varying thicknesses of gravity thinned wetting layers reported in the literature may be due to the presence of perturbing forces, such as accidental temperature gradients. In order to study the effect of such forces, we observed the long time evolution of gravity-induced concentration gradients in the presence of small perturbing horizontal temperature gradients (<= 50 mK/cm) in a system of aniline and cyclohexane near its consolute critical point. These measurements are unique since previous studies of gravity-induced concentration gradients in binary liquid mixtures have focused only on fast developing gradients created by sedimentation or on the measurement of the equilibrium barodiffusion gradient. Our results reveal large variations in the steady state concentration gradients which arise, even in the absence of applied temperature gradients. Furthermore, in the presence of nonzero temperature gradients, we observe the formation of concentration gradients which are significantly larger than the equilibrium barodiffusion gradient. No theory currently exists which explains these surprising results. Supported by the NSF under DMR-9320910 and by the central facilities of the Materials Science Center at Cornell University.

  20. Satellite gravity gradient grids for geophysics.

    PubMed

    Bouman, Johannes; Ebbing, Jörg; Fuchs, Martin; Sebera, Josef; Lieb, Verena; Szwillus, Wolfgang; Haagmans, Roger; Novak, Pavel

    2016-02-11

    The Gravity field and steady-state Ocean Circulation Explorer (GOCE) satellite aimed at determining the Earth's mean gravity field. GOCE delivered gravity gradients containing directional information, which are complicated to use because of their error characteristics and because they are given in a rotating instrument frame indirectly related to the Earth. We compute gravity gradients in grids at 225 km and 255 km altitude above the reference ellipsoid corresponding to the GOCE nominal and lower orbit phases respectively, and find that the grids may contain additional high-frequency content compared with GOCE-based global models. We discuss the gradient sensitivity for crustal depth slices using a 3D lithospheric model of the North-East Atlantic region, which shows that the depth sensitivity differs from gradient to gradient. In addition, the relative signal power for the individual gradient component changes comparing the 225 km and 255 km grids, implying that using all components at different heights reduces parameter uncertainties in geophysical modelling. Furthermore, since gravity gradients contain complementary information to gravity, we foresee the use of the grids in a wide range of applications from lithospheric modelling to studies on dynamic topography, and glacial isostatic adjustment, to bedrock geometry determination under ice sheets.

  1. Satellite gravity gradient grids for geophysics

    NASA Astrophysics Data System (ADS)

    Bouman, Johannes; Ebbing, Jörg; Fuchs, Martin; Sebera, Josef; Lieb, Verena; Szwillus, Wolfgang; Haagmans, Roger; Novak, Pavel

    2016-02-01

    The Gravity field and steady-state Ocean Circulation Explorer (GOCE) satellite aimed at determining the Earth’s mean gravity field. GOCE delivered gravity gradients containing directional information, which are complicated to use because of their error characteristics and because they are given in a rotating instrument frame indirectly related to the Earth. We compute gravity gradients in grids at 225 km and 255 km altitude above the reference ellipsoid corresponding to the GOCE nominal and lower orbit phases respectively, and find that the grids may contain additional high-frequency content compared with GOCE-based global models. We discuss the gradient sensitivity for crustal depth slices using a 3D lithospheric model of the North-East Atlantic region, which shows that the depth sensitivity differs from gradient to gradient. In addition, the relative signal power for the individual gradient component changes comparing the 225 km and 255 km grids, implying that using all components at different heights reduces parameter uncertainties in geophysical modelling. Furthermore, since gravity gradients contain complementary information to gravity, we foresee the use of the grids in a wide range of applications from lithospheric modelling to studies on dynamic topography, and glacial isostatic adjustment, to bedrock geometry determination under ice sheets.

  2. Extraordinary strain hardening by gradient structure

    PubMed Central

    Wu, XiaoLei; Jiang, Ping; Chen, Liu; Yuan, Fuping; Zhu, Yuntian T.

    2014-01-01

    Gradient structures have evolved over millions of years through natural selection and optimization in many biological systems such as bones and plant stems, where the structures change gradually from the surface to interior. The advantage of gradient structures is their maximization of physical and mechanical performance while minimizing material cost. Here we report that the gradient structure in engineering materials such as metals renders a unique extra strain hardening, which leads to high ductility. The grain-size gradient under uniaxial tension induces a macroscopic strain gradient and converts the applied uniaxial stress to multiaxial stresses due to the evolution of incompatible deformation along the gradient depth. Thereby the accumulation and interaction of dislocations are promoted, resulting in an extra strain hardening and an obvious strain hardening rate up-turn. Such extraordinary strain hardening, which is inherent to gradient structures and does not exist in homogeneous materials, provides a hitherto unknown strategy to develop strong and ductile materials by architecting heterogeneous nanostructures. PMID:24799688

  3. Satellite gravity gradient grids for geophysics

    PubMed Central

    Bouman, Johannes; Ebbing, Jörg; Fuchs, Martin; Sebera, Josef; Lieb, Verena; Szwillus, Wolfgang; Haagmans, Roger; Novak, Pavel

    2016-01-01

    The Gravity field and steady-state Ocean Circulation Explorer (GOCE) satellite aimed at determining the Earth’s mean gravity field. GOCE delivered gravity gradients containing directional information, which are complicated to use because of their error characteristics and because they are given in a rotating instrument frame indirectly related to the Earth. We compute gravity gradients in grids at 225 km and 255 km altitude above the reference ellipsoid corresponding to the GOCE nominal and lower orbit phases respectively, and find that the grids may contain additional high-frequency content compared with GOCE-based global models. We discuss the gradient sensitivity for crustal depth slices using a 3D lithospheric model of the North-East Atlantic region, which shows that the depth sensitivity differs from gradient to gradient. In addition, the relative signal power for the individual gradient component changes comparing the 225 km and 255 km grids, implying that using all components at different heights reduces parameter uncertainties in geophysical modelling. Furthermore, since gravity gradients contain complementary information to gravity, we foresee the use of the grids in a wide range of applications from lithospheric modelling to studies on dynamic topography, and glacial isostatic adjustment, to bedrock geometry determination under ice sheets. PMID:26864314

  4. A conjugate gradient method with descent direction for unconstrained optimization

    NASA Astrophysics Data System (ADS)

    Yuan, Gonglin; Lu, Xiwen; Wei, Zengxin

    2009-11-01

    A modified conjugate gradient method is presented for solving unconstrained optimization problems, which possesses the following properties: (i) The sufficient descent property is satisfied without any line search; (ii) The search direction will be in a trust region automatically; (iii) The Zoutendijk condition holds for the Wolfe-Powell line search technique; (iv) This method inherits an important property of the well-known Polak-Ribière-Polyak (PRP) method: the tendency to turn towards the steepest descent direction if a small step is generated away from the solution, preventing a sequence of tiny steps from happening. The global convergence and the linearly convergent rate of the given method are established. Numerical results show that this method is interesting.

  5. Computational analysis of frp composite under different temperature gradient

    NASA Astrophysics Data System (ADS)

    Gunasekar, P.; Manigandan, S.

    2017-05-01

    Composite material strength depends on the stiffness of fiber and the resin which is used for reinforcement. The strength of the laminate can be increased by applying good manufacturing practices. The strength is directly depending on the property of resin. The property of the any compound subjected to changed when they exposed to the temperature. This paper investigates the strength of laminate when they subjected to different temperature gradient of resin while manufacturing. The resin is preheated before adding hardener with them. These types of laminate reinforced with resin at different levels of temperature 20c, 40c, and 60c. These different temperature resin are used for reinforcement and the specimen tested. The comparative results are made to find how the stiffness of laminate changes with respect to the thermal property of resin. The results are helpful to obtain high strength laminate.

  6. Speciation gradients and the distribution of biodiversity.

    PubMed

    Schluter, Dolph; Pennell, Matthew W

    2017-05-31

    Global patterns of biodiversity are influenced by spatial and environmental variations in the rate at which new species form. We relate variations in speciation rates to six key patterns of biodiversity worldwide, including the species-area relationship, latitudinal gradients in species and genetic diversity, and between-habitat differences in species richness. Although they sometimes mirror biodiversity patterns, recent rates of speciation, at the tip of the tree of life, are often highest where species richness is low. Speciation gradients therefore shape, but are also shaped by, biodiversity gradients and are often more useful for predicting future patterns of biodiversity than for interpreting the past.

  7. Sound beam manipulation based on temperature gradients

    SciTech Connect

    Qian, Feng; Quan, Li; Liu, Xiaozhou Gong, Xiufen

    2015-10-28

    Previous research with temperature gradients has shown the feasibility of controlling airborne sound propagation. Here, we present a temperature gradients based airborne sound manipulation schemes: a cylindrical acoustic omnidirectional absorber (AOA). The proposed AOA has high absorption performance which can almost completely absorb the incident wave. Geometric acoustics is used to obtain the refractive index distributions with different radii, which is then utilized to deduce the desired temperature gradients. Since resonant units are not applied in the scheme, its working bandwidth is expected to be broadband. The scheme is temperature-tuned and easy to realize, which is of potential interest to fields such as noise control or acoustic cloaking.

  8. Gradient fiber electrospinning of layered scaffolds using controlled transitions in fiber diameter.

    PubMed

    Grey, Casey P; Newton, Scott T; Bowlin, Gary L; Haas, Thomas W; Simpson, David G

    2013-07-01

    We characterize layered, delamination resistant, tissue engineering scaffolds produced by gradient electrospinning using computational fluid dynamics, measurements of fiber diameter with respect to dynamic changes in polymer concentration, SEM analysis, and materials testing. Gradient electrospinning delivers a continuously variable concentration of polymer to the electrospinning jet, resulting in scaffolds that exhibit controlled transitions in fiber diameter across the Z-axis. This makes it possible to produce scaffolds that exhibit very different fiber sizes and material properties on opposing surfaces while eliminating the boundary layers that lead to delamination failures. In materials testing bi-layered laminated electrospun scaffolds (layer 1 = <250 nm, layer 2 = 1000 nm diameter polycaprolactone fibers) exhibit ductile properties and undergo multiphasic failure. In contrast, scaffolds, produced by gradient electrospinning fabricated with fibers of this type on opposing surfaces fracture and fail as unified, and mechanically integrated, structures. Gradient electrospinning also eliminates the anisotropic strain properties observed in scaffolds composed of highly aligned fibers. In burst testing, scaffolds composed of aligned fibers produced using gradient electrospinning exhibit superior material properties with respect to scaffolds composed of random or aligned fibers produced from a single polymer concentration or as bi-layered, laminated structures.

  9. Effects of roads on alpine and subalpine plant species distribution along an altitudinal gradient on Mount Norikura, central Japan.

    PubMed

    Takahashi, Koichi; Miyajima, Yutaka

    2010-11-01

    We investigated the effects of roads on alpine and subalpine plant species distribution along an altitudinal gradient on Mount Norikura (3026 m a.s.l.), Japan. We examined the vegetation of herb and tree species shorter than 1.3 m along roadsides and adjacent natural vegetation at 200 m intervals between 1600 and 3000 m a.s.l. The timberline was at 2500 m a.s.l. Although the canopy opening was greater at the roadsides than in the natural vegetation, it was similar above the timberline. Soil cover and litter depth of the soil surface were less at roadsides than the natural vegetation, and gravel and rock cover were greater at roadsides. Species composition changed in similar directions from natural vegetation to roadsides along the altitudinal gradient. This direction was related to canopy opening and litter depth. Liliaceae, Ericaceae and Pinaceae were dominant families in the natural vegetation, and Asteraceae and Poaceae were greatest at the roadsides. Roadside plants were mostly herb species, while tree species increased in natural vegetation. Five exotic species were also observed at the roadsides. Sunny plant species gradually increased with altitude in the natural vegetation, indicated by the increase in canopy opening. By contrast, roadside plants were mostly sunny plant species irrespective of altitude. The number of lowland and montane species increased at the roadsides in the subalpine zone. Thus, roads strongly altered species composition of the natural vegetation along the altitudinal gradient probably because of changes in light and soil-surface conditions for growth and seedling establishment.

  10. Stability of gradient semigroups under perturbations

    NASA Astrophysics Data System (ADS)

    Aragão-Costa, E. R.; Caraballo, T.; Carvalho, A. N.; Langa, J. A.

    2011-07-01

    In this paper we prove that gradient-like semigroups (in the sense of Carvalho and Langa (2009 J. Diff. Eqns 246 2646-68)) are gradient semigroups (possess a Lyapunov function). This is primarily done to provide conditions under which gradient semigroups, in a general metric space, are stable under perturbation exploiting the known fact (see Carvalho and Langa (2009 J. Diff. Eqns 246 2646-68)) that gradient-like semigroups are stable under perturbation. The results presented here were motivated by the work carried out in Conley (1978 Isolated Invariant Sets and the Morse Index (CBMS Regional Conference Series in Mathematics vol 38) (RI: American Mathematical Society Providence)) for groups in compact metric spaces (see also Rybakowski (1987 The Homotopy Index and Partial Differential Equations (Universitext) (Berlin: Springer)) for the Morse decomposition of an invariant set for a semigroup on a compact metric space).

  11. Coreless Concept for High Gradient Induction Cell

    SciTech Connect

    Krasnykh, Anatoly; /SLAC

    2008-01-07

    An induction linac cell for a high gradient is discussed. The proposed solid state coreless approach for the induction linac topology (SLIM{reg_sign}) is based on nanosecond mode operation. This mode may have an acceleration gradient comparable with gradients of rf- accelerator structures. The discussed induction system has the high electric efficiency. The key elements are a solid state semiconductor switch and a high electric density dielectric with a thin section length. The energy in the induction system is storied in the magnetic field. The nanosecond current break-up produces the high voltage. The induced voltage is used for acceleration. This manner of an operation allows the use of low voltage elements in the booster part and achieves a high accelerating gradient. The proposed topology was tested in POP (proof of principle) experiments.

  12. SW New Mexico BHT geothermal gradient calculations

    DOE Data Explorer

    Shari Kelley

    2015-07-24

    This file contains a compilation of BHT data from oil wells in southwestern New Mexico. Surface temperature is calculated using the collar elevation. An estimate of geothermal gradient is calculated using the estimated surface temperature and the uncorrected BHT data.

  13. The gradient filter test to assess amblyopia.

    PubMed

    Keech, R V; Kutschke, P J

    1990-07-15

    A new technique, the gradient filter test, was developed for evaluating changes in the visual acuity of preverbal children undergoing treatment for amblyopia. The gradient filter test consists of a series of calibrated photographic fog filter and prism lenses. The combined prism-filter lenses are placed in front of the normal fixing eye. The greatest density (fogging value) filter that causes a switch in fixation from the amblyopic to the normal eye is noted. In both normal eyes of 20 nonamblyopic patients and the fellow (non-amblyopic) eyes of 20 amblyopic patients, visual acuity decreased as the density of the prism-filter lens increased. The gradient filter test accurately detected an improvement in visual acuity when compared with optotype measurements in eight patients undergoing occlusion therapy. The gradient filter test is a useful clinical tool that can assess changes in visual acuity in preverbal children who are being treated for amblyopia.

  14. Continuous spray forming of functionally gradient materials

    SciTech Connect

    McKechnie, T.N.; Richardson, E.H.

    1995-12-01

    Researchers at Plasma Processes Inc. have produced a Functional Gradient Material (FGM) through advanced vacuum plasma spray processing for high heat flux applications. Outlined in this paper are the manufacturing methods used to develop a four component functional gradient material of copper, tungsten, boron, and boron nitride. The FGM was formed with continuous gradients and integral cooling channels eliminating bondlines and providing direct heat transfer from the high temperature exposed surface to a cooling medium. Metallurgical and x-ray diffraction analyses of the materials formed through innovative VPS (vacuum plasma spray) processing are also presented. Applications for this functional gradient structural material range from fusion reactor plasma facing components to missile nose cones to boilers.

  15. Full Gradient Solution to Adaptive Hybrid Control

    NASA Technical Reports Server (NTRS)

    Bean, Jacob; Schiller, Noah H.; Fuller, Chris

    2016-01-01

    This paper focuses on the adaptation mechanisms in adaptive hybrid controllers. Most adaptive hybrid controllers update two filters individually according to the filtered-reference least mean squares (FxLMS) algorithm. Because this algorithm was derived for feedforward control, it does not take into account the presence of a feedback loop in the gradient calculation. This paper provides a derivation of the proper weight vector gradient for hybrid (or feedback) controllers that takes into account the presence of feedback. In this formulation, a single weight vector is updated rather than two individually. An internal model structure is assumed for the feedback part of the controller. The full gradient is equivalent to that used in the standard FxLMS algorithm with the addition of a recursive term that is a function of the modeling error. Some simulations are provided to highlight the advantages of using the full gradient in the weight vector update rather than the approximation.

  16. Full Gradient Solution to Adaptive Hybrid Control

    NASA Technical Reports Server (NTRS)

    Bean, Jacob; Schiller, Noah H.; Fuller, Chris

    2017-01-01

    This paper focuses on the adaptation mechanisms in adaptive hybrid controllers. Most adaptive hybrid controllers update two filters individually according to the filtered reference least mean squares (FxLMS) algorithm. Because this algorithm was derived for feedforward control, it does not take into account the presence of a feedback loop in the gradient calculation. This paper provides a derivation of the proper weight vector gradient for hybrid (or feedback) controllers that takes into account the presence of feedback. In this formulation, a single weight vector is updated rather than two individually. An internal model structure is assumed for the feedback part of the controller. The full gradient is equivalent to that used in the standard FxLMS algorithm with the addition of a recursive term that is a function of the modeling error. Some simulations are provided to highlight the advantages of using the full gradient in the weight vector update rather than the approximation.

  17. Improving GOCE cross-track gravity gradients

    NASA Astrophysics Data System (ADS)

    Siemes, Christian

    2017-07-01

    The GOCE gravity gradiometer measured highly accurate gravity gradients along the orbit during GOCE's mission lifetime from March 17, 2009, to November 11, 2013. These measurements contain unique information on the gravity field at a spatial resolution of 80 km half wavelength, which is not provided to the same accuracy level by any other satellite mission now and in the foreseeable future. Unfortunately, the gravity gradient in cross-track direction is heavily perturbed in the regions around the geomagnetic poles. We show in this paper that the perturbing effect can be modeled accurately as a quadratic function of the non-gravitational acceleration of the satellite in cross-track direction. Most importantly, we can remove the perturbation from the cross-track gravity gradient to a great extent, which significantly improves the accuracy of the latter and offers opportunities for better scientific exploitation of the GOCE gravity gradient data set.

  18. Velocity gradients and microturbulence in Cepheids

    NASA Technical Reports Server (NTRS)

    Karp, A. H.

    1972-01-01

    Variations of the microturbulent velocity with phase and height in the atmosphere were reported in classical Cepheids. It is shown that these effects can be understood in terms of variations of the velocity gradient in the atmospheres of these stars.

  19. Establishing positional information through gradient dynamics

    PubMed Central

    Nahmad, Marcos

    2010-01-01

    A long standing question in developmental biology is how morphogen gradients establish positional information during development. Although the existence of gradients and their role in developmental patterning is no longer in doubt, the ability of cells to respond to different morphogen concentrations has been controversial. In the Drosophila wing disc, Hedgehog (Hh) forms a concentration gradient along the anterior-posterior axis and establishes at least three different gene expression patterns. In a recent study, we challenged the prevailing idea that Hh establishes positional information in a dose-dependent manner and proposed a model in which dynamics of the gradient, resulting from the Hh gene network architecture, determines pattern formation in the wing disc. In this Extra View, we discuss further the methodology used in this study, highlight differences between this and other models of developmental patterning, and also present some questions that remain to be answered in this system. PMID:20699656

  20. Pollution Gradients on a Fine Spatial Scale

    NASA Astrophysics Data System (ADS)

    Wardlaw, K. D.; Ramos, M. A.; Nation, H. E.; Mah, D. A.; Nickolaisen, S. L.

    2002-12-01

    Gas phase tropospheric oxidants in photochemical smog are measured with a mobile unit to determine if localized concentration gradients exist. Species sampled include ozone, hydrocarbons, and nitrogen oxides. The study was conducted in the area immediately surrounding the California State University Los Angeles campus, with sampling sites between 200 to 1000 meters apart. Pollutant concentrations are correlated with variables such as local topography, land use, meteorological conditions, and traffic patterns. Meteorological sampling at each measurement site consists of temperature, humidity, dew point, barometric pressure, wind speed and direction. Preliminary sampling suggest no strong correlations between concentration gradients and meteorological factors, rather they are weak determinants. Stronger correlation is shown with land use; sites in close proximity to busy freeways tend towards lower ozone concentration. The largest gradients are seen when pollutant concentrations are moderate to high. The possible causes for these trends and gradients will be discussed.

  1. Gradient systems on coupled cell networks

    NASA Astrophysics Data System (ADS)

    Manoel, Miriam; Roberts, Mark

    2015-10-01

    For networks of coupled dynamical systems we characterize admissible functions, that is, functions whose gradient is an admissible vector field. The schematic representation of a gradient network dynamical system is of an undirected cell graph, and we use tools from graph theory to deduce the general form of such functions, relating it to the topological structure of the graph defining the network. The coupling of pairs of dynamical systems cells is represented by edges of the graph, and from spectral graph theory we detect the existence and nature of equilibria of the gradient system from the critical points of the coupling function. In particular, we study fully synchronous and 2-state patterns of equilibria on regular graphs. These are two special types of equilibrium configurations for gradient networks. We also investigate equilibrium configurations of {{\\mathbf{S}}1} -invariant admissible functions on a ring of cells.

  2. Quantitative analysis of the effects of biofunctional and physical gradients on cell behavior in poly (ethylene glycol) diacrylate hydrogels

    NASA Astrophysics Data System (ADS)

    Turturro, Michael

    The continued enhancement of tissue engineered scaffolds relies on their ability to stimulate the formation of a stable microvascular network within the biomaterial. In vivo, the spatial presentation of immobilized extracellular matrix cues and matrix mechanical properties play an important role in directed and guided cell behavior and neovascularization. The overall goals of this thesis are to develop a technique for the generation of gradients of physical properties and incorporated biofunctionality within poly(ethylene glycol) diacrylate (PEGDA) scaffolds and to investigate the effects of these gradients on 3D cell invasion and neovascularization. To this end, a novel photopolymerization technique for generating spatial variations in matrix properties and incorporated biofunctionality within synthetic PEGDA hydrogels, perfusion-based frontal polymerization (PBFP), was developed. This technique relies on the controlled perfusion of a photoinitiator to a reaction chamber containing a precursor solution and results in the propagation of a polymer reaction front that travels through the monomer solution creating a gradient in hydrogel crosslinking. Manipulation of the magnitude of the gradient can be achieved through alterations in the polymerization conditions. Scaffolds with embedded gradients were designed and optimized based on a range of properties shown to support 2D cell adhesion, proliferation, and 3D vascular cell invasion in bulk photopolymerized hydrogels with homogeneous properties. An in vitro model of neovascularization was used to evaluate the effect of these gradients on vascular sprout formation. Sprout invasion in gradient hydrogels occurred bi-directionally with sprout alignment observed in the direction parallel to the gradient while control hydrogels with homogeneous properties resulted in uniform invasion. In PBFP gradient hydrogels, sprout length was found to be twice as long in the direction parallel to the gradient as compared to the

  3. Vandenberg Air Force Base Pressure Gradient Wind Study

    NASA Technical Reports Server (NTRS)

    Shafer, Jaclyn A.

    2013-01-01

    Warning category winds can adversely impact day-to-day space lift operations at Vandenberg Air Force Base (VAFB) in California. NASA's Launch Services Program and other programs at VAFB use wind forecasts issued by the 30 Operational Support Squadron Weather Flight (30 OSSWF) to determine if they need to limit activities or protect property such as a launch vehicle. The 30 OSSWF tasked the AMU to develop an automated Excel graphical user interface that includes pressure gradient thresholds between specific observing stations under different synoptic regimes to aid forecasters when issuing wind warnings. This required the AMU to determine if relationships between the variables existed.

  4. Ion imaging in a high-gradient magnetic guide

    SciTech Connect

    Vaidya, V. D.; Traxler, M.; Mhaskar, R. R.; Raithel, G.; Hempel, C.

    2010-04-15

    We study a photoionization method to detect and image a narrow beam of cold atoms traveling along a high-gradient two-wire magnetic guide that is continuously on. Ions are accelerated in a compact acceleration region, directed through a drift region several centimeters in length, and detected using a position-sensitive ion detector. The potentials of several electrodes can be varied to adjust the imaging properties. Using ion trajectory simulations as well as experiments, we study the passage of the ions through the detection system, the magnification of the detection system, and the time-of-flight characteristics.

  5. Ion imaging in a high-gradient magnetic guide.

    PubMed

    Vaidya, V D; Traxler, M; Hempel, C; Mhaskar, R R; Raithel, G

    2010-04-01

    We study a photoionization method to detect and image a narrow beam of cold atoms traveling along a high-gradient two-wire magnetic guide that is continuously on. Ions are accelerated in a compact acceleration region, directed through a drift region several centimeters in length, and detected using a position-sensitive ion detector. The potentials of several electrodes can be varied to adjust the imaging properties. Using ion trajectory simulations as well as experiments, we study the passage of the ions through the detection system, the magnification of the detection system, and the time-of-flight characteristics.

  6. Star formation rates and abundance gradients in disk galaxies

    NASA Technical Reports Server (NTRS)

    Wyse, Rosemary F. G.; Silk, Joseph

    1989-01-01

    Analytic models for the evolution of disk galaxies are presented, placing special emphasis on the radial properties. These models are straightforward extensions of the original Schmidt (1959, 1963) models, with a dependence of star formation rate on gas density. The models provide successful descriptions of several measures of galactic disk evolution, including solar neighborhood chemical evolution, the presence and amplitude of metallicity and color gradients in disk galaxies, and the global rates of star formation in disk galaxies, and aid in the understanding of the apparent connection between young and old stellar populations in spiral galaxies.

  7. An Adaptive Mesh Refined Gradient-Augmented Level Set Method

    NASA Astrophysics Data System (ADS)

    Nave, Jean-Christophe; Seibold, Benjamin; Rosales, Ruben

    2010-11-01

    The Gradient-Augmented Level Set method (GA-LS) was introduced at the 62^nd annual APS-DFD meeting by Nave et al. (arXiv:0905.3409). Leveraging the optimal locality and unconditional stability of the method, we present a natural extension to adaptive quad-tree meshes. The new method possesses many desirable features such as improved mass conservation, reduced computational effort, and is, due to the optimal locality property of the underlying GA-LS, very easy to implement. Several key benchmark tests will be presented to help demonstrate the benefits of the approach, and the overall simplicity of the algorithm.

  8. Generation and interpretation of FGF morphogen gradients in vertebrates.

    PubMed

    Bökel, Christian; Brand, Michael

    2013-08-01

    Signalling via fibroblast growth factors (FGFs) is involved in multiple aspects of vertebrate development. In several instances FGFs act as morphogens, that is secreted signalling molecules that encode positional information in their graded distribution throughout their target tissue. In recent years, work in the zebrafish model system has been instrumental in addressing the cell biological basis of FGF morphogen gradient formation and interpretation. These experiments have benefitted from the optical properties of the zebrafish embryo that render this vertebrate organism particularly suited for advanced microscopic and biophysical approaches. Copyright © 2013 Elsevier Ltd. All rights reserved.

  9. Density gradient electrophoresis of cultured human embryonic kidney cells

    NASA Technical Reports Server (NTRS)

    Plank, L. D.; Kunze, M. E.; Giranda, V.; Todd, P. W.

    1985-01-01

    Ground based confirmation of the electrophoretic heterogeneity of human embryonic kidney cell cultures, the general characterization of their electrophoretic migration, and observations on the general properties of cultures derived from electrophoretic subpopulations were studied. Cell migration in a density gradient electrophoresis column and cell electrophoretic mobility was determined. The mobility and heterogeneity of cultured human embryonic kidney cells with those of fixed rat erythrocytes as model test particle was compared. Electrophoretically separated cell subpopulations with respect to size, viability, and culture characteristics were examined.

  10. Intratumoral oxygen gradients mediate sarcoma cell invasion

    PubMed Central

    Lewis, Daniel M.; Park, Kyung Min; Tang, Vitor; Xu, Yu; Pak, Koreana; Eisinger-Mathason, T. S. Karin; Simon, M. Celeste; Gerecht, Sharon

    2016-01-01

    Hypoxia is a critical factor in the progression and metastasis of many cancers, including soft tissue sarcomas. Frequently, oxygen (O2) gradients develop in tumors as they grow beyond their vascular supply, leading to heterogeneous areas of O2 depletion. Here, we report the impact of hypoxic O2 gradients on sarcoma cell invasion and migration. O2 gradient measurements showed that large sarcoma mouse tumors (>300 mm3) contain a severely hypoxic core [≤0.1% partial pressure of O2 (pO2)] whereas smaller tumors possessed hypoxic gradients throughout the tumor mass (0.1–6% pO2). To analyze tumor invasion, we used O2-controllable hydrogels to recreate the physiopathological O2 levels in vitro. Small tumor grafts encapsulated in the hydrogels revealed increased invasion that was both faster and extended over a longer distance in the hypoxic hydrogels compared with nonhypoxic hydrogels. To model the effect of the O2 gradient accurately, we examined individual sarcoma cells embedded in the O2-controllable hydrogel. We observed that hypoxic gradients guide sarcoma cell motility and matrix remodeling through hypoxia-inducible factor-1α (HIF-1α) activation. We further found that in the hypoxic gradient, individual cells migrate more quickly, across longer distances, and in the direction of increasing O2 tension. Treatment with minoxidil, an inhibitor of hypoxia-induced sarcoma metastasis, abrogated cell migration and matrix remodeling in the hypoxic gradient. Overall, we show that O2 acts as a 3D physicotactic agent during sarcoma tumor invasion and propose the O2-controllable hydrogels as a predictive system to study early stages of the metastatic process and therapeutic targets. PMID:27486245

  11. Bragg interferometer for gravity gradient measurements

    NASA Astrophysics Data System (ADS)

    D'Amico, G.; Borselli, F.; Cacciapuoti, L.; Prevedelli, M.; Rosi, G.; Sorrentino, F.; Tino, G. M.

    2016-06-01

    We report on the characterization of a dual cloud atom interferometer for gravity gradient measurements using third-order Bragg diffraction as atom optical elements. We study the dependence of the contrast and the gradiometer phase angle against the relevant experimental parameters and characterize the instrument sensitivity. We achieve a sensitivity to gravity gradient measurements of 2.6 ×10-8s-2 (26 E) after 2000 s of integration time.

  12. Ultimate gradient in solid-state accelerators

    SciTech Connect

    Whittum, D.H.

    1998-08-01

    The authors recall the motivation for research in high-gradient acceleration and the problems posed by a compact collider. They summarize the phenomena known to appear in operation of a solid-state structure with large fields, and research relevant to the question of the ultimate gradient. They take note of new concepts, and examine one in detail, a miniature particle accelerator based on an active millimeter-wave circuit and parallel particle beams.

  13. Fast Deconvolution with Color Constraints on Gradients

    DTIC Science & Technology

    2013-01-01

    deconvolution approach for color images that combines a sparse regularization cost on the magnitudes of gradients with constraints on their direction in color...Research Office P.O. Box 12211 Research Triangle Park, NC 27709-2211 15. SUBJECT TERMS computer vision, deblurring, spatio-spectral image model Ayan...approach for color images that combines a sparse regularization cost on the magnitudes of gradients with constraints on their direction in color space. We

  14. Interplay between transport barriers and density gradient

    NASA Astrophysics Data System (ADS)

    Sarazin, Y.; Grandgirard, V.; Dif-Pradalier, G.; Garbet, X.; Ghendrih, Ph.

    2006-09-01

    The present paper addresses two critical issues of zonal flows: the evidence of control parameters of their driving term, namely the Reynolds stress, and how they back-react on turbulence and transport. Kinetic nonlinear simulations are performed with the GYSELA code [V. Grandgirard et al., J. Comput. Phys. (to be published)], which models the slab branch of the ion temperature gradient driven instability in the four-dimensional drift-kinetic regime. First, the numerical results show that the gradient of the guiding center density, related to the general potential vorticity, is stabilizing both linearly, by increasing the instability threshold, and nonlinearly, by activating zonal flows. Accordingly, the Reynolds stress is found to scale like LΩ-2 in the quasilinear regime, LΩ being the gradient length of the guiding center density. Second, the local temperature gradient appears to increase linearly with the curvature of the zonal flows, regardless of its sign. Such behavior agrees qualitatively with a perturbative theory. Indeed, while linear eigenmodes are localized at the maximum of the temperature gradient in the absence of zonal flows, they tend to be expelled if both exhibit a maximum at the same location. In this case, the reduction mechanism of the turbulent transport results from the ability of large zonal flow curvatures to render strong temperature gradients stable with respect to perturbations.

  15. Quantitative analysis of mRNA translation in mammalian spermatogenic cells with sucrose and Nycodenz gradients.

    PubMed

    Kleene, Kenneth C; Bagarova, Jana; Hawthorne, Sabrina K; Catado, Leah M

    2010-12-25

    Developmental and global regulation of mRNA translation plays a major role in regulating gene expression in mammalian spermatogenic cells. Sucrose gradients are widely used to analyze mRNA translation. Unfortunately, the information from sucrose gradient experiments is often compromised by the absence of quantification and absorbance tracings, and confusion about the basic properties of sucrose gradients. The Additional Materials contain detailed protocols for the preparation and analysis of sucrose and Nycodenz gradients, obtaining absorbance tracings of sucrose gradients, aligning tracings and fractions, and extraction of equal proportions of RNA from all fractions. The techniques described here have produced consistent measurements despite changes in personnel and minor variations in RNA extraction, gradient analysis, and mRNA quantification, and describes for the first time potential problems in using gradients to analyze mRNA translation in purified spermatogenic cells. Accurate quantification of the proportion of polysomal mRNA is useful in comparing translational activity at different developmental stages, different mRNAs, different techniques and different laboratories. The techniques described here are sufficiently accurate to elucidate the contributions of multiple regulatory elements of variable strength in regulating translation of the sperm mitochondria associated cysteine-rich protein (Smcp) mRNA in transgenic mice.

  16. Quantitative analysis of mRNA translation in mammalian spermatogenic cells with sucrose and Nycodenz gradients

    PubMed Central

    2010-01-01

    Background Developmental and global regulation of mRNA translation plays a major role in regulating gene expression in mammalian spermatogenic cells. Sucrose gradients are widely used to analyze mRNA translation. Unfortunately, the information from sucrose gradient experiments is often compromised by the absence of quantification and absorbance tracings, and confusion about the basic properties of sucrose gradients. Methods The Additional Materials contain detailed protocols for the preparation and analysis of sucrose and Nycodenz gradients, obtaining absorbance tracings of sucrose gradients, aligning tracings and fractions, and extraction of equal proportions of RNA from all fractions. Results The techniques described here have produced consistent measurements despite changes in personnel and minor variations in RNA extraction, gradient analysis, and mRNA quantification, and describes for the first time potential problems in using gradients to analyze mRNA translation in purified spermatogenic cells. Conclusions Accurate quantification of the proportion of polysomal mRNA is useful in comparing translational activity at different developmental stages, different mRNAs, different techniques and different laboratories. The techniques described here are sufficiently accurate to elucidate the contributions of multiple regulatory elements of variable strength in regulating translation of the sperm mitochondria associated cysteine-rich protein (Smcp) mRNA in transgenic mice. PMID:21184686

  17. An improved equivalent magnetization current method applied to the design of local breast gradient coils

    NASA Astrophysics Data System (ADS)

    Lopez, Hector Sanchez; Poole, Michael; Crozier, Stuart

    2009-07-01

    Magnetic resonance imaging (MRI) is an important tool in the diagnosis of breast cancer. Increased gradient strengths and slew rates assist in terms of the potential to image with increased spatial and/or temporal resolution. Strong gradients also facilitate diffusion studies; one well-known method of increasing gradient strength is to design local gradient coils, those with reduced diameter where the gradient conductors are closer to the region of interest. In the case of breast imaging, this necessitates the use of coil geometries that lack the symmetry (e.g. cylindrical) required by some standard coil design techniques. Therefore a symmetry-free, inverse boundary element method (BEM) was employed to design a set of local breast gradient coils which would allow simultaneous imaging of both breasts. This BEM is a modified version of a previously reported equivalent magnetisation current method that now incorporates a piecewise-linear magnetisation rather than piecewise-constant. It is demonstrated that coil geometries more closely encompassing the sample shape, hence possessing wire windings located close the sample, produce superior coil performances. The use of two regions of interest instead one that covers the two samples produces superior high performance breast gradient coils. Additionally, it was demonstrated that this inverse BEM produced standard cylindrical coils with comparable properties and that the method is robust when challenged with difficult coil design problems in two other examples.

  18. Nonlinear Interaction of Shear Alfven Waves with Gradient Driven Instabilities

    NASA Astrophysics Data System (ADS)

    Auerbach, David William

    An experimental study of the interactions between gradient-driven instabilities (GDI) and beat waves driven between two Alfven waves is presented. A cylindrical density depletion is imposed on the otherwise uniform plasma in the Large Plasma Device (LAPD) by selectively blocking the electron beam that produces the plasma. Coherent, single mode fluctuations in density, temperature, plasma potential, and magnetic field are observed to be unstable on the gradient. Measurements of the relative cross-phase between the density and potential fluctuations indicate that the fluctuations are not likely to drive significant cross field transport. Comparisons of the properties of the modes to theoretical predictions for Kelvin-Helmholtz (KH) and drift wave modes indicate that the fluctuations are likely to be a hybrid of the two instabilities. Analytic eigenmode solutions to the linearized Braginskii fluid equations using the experimentally measured gradient profiles support the conclusion that both instabilities are active. A beat wave between two driven Alfven waves is broadcast into the gradient region using a pair of loop antennas with independently controlled frequency and power. This beat wave is observed to resonantly drive the unstable mode, as well as a second otherwise stable mode slightly higher in frequency and azimuthal mode number. During the drive of the secondary stable mode, the growth of the primary instability is suppressed. The broadcast of the Alfven waves and the beat wave is also observed to drive other fluctuations in the plasma at frequencies higher than either the spontaneous instability or the second, stable mode. Both the resonant drive of the modes and the control of the mode number are observed to have non-linear threshold and saturation behavior.

  19. Bioactive polyacrylamide hydrogels with gradients in mechanical stiffness.

    PubMed

    Diederich, Vincent E G; Studer, Peter; Kern, Anita; Lattuada, Marco; Storti, Giuseppe; Sharma, Ram I; Snedeker, Jess G; Morbidelli, Massimo

    2013-05-01

    We propose a novel, single step method for the production of polyacrylamide hydrogels with a gradient in mechanical properties. In contrast to already existing techniques such as UV photo-polymerization with photomasks (limited penetration depth) or microfluidic gradient mixers (complex microfluidic chip), this technique is not suffering such limitations. Young's modulus of the hydrogels was varied by changing the total monomer concentration of the hydrogel precursor solution. Using programmable syringe pumps, the total monomer concentration in the solution fed to the hydrogel mold was varied from 16 wt% down to 5 wt% over the feeding time to obtain a gradient in compliance ranging from 150 kPa down to 20 kPa over a length of 10 mm down to 2.5 mm. Polymerization was achieved with the dual initiation system composed of ammonium persulfate and N,N,N',N'-tetramethylethylenediamine, which were both fed through separate capillaries to avoid premature polymerization. Functionalized with the model ligand collagen I, the substrates were bioactive and supported the attachment of human foreskin fibroblasts (around 30% of the cells seeded attached after 1 h). A kinetic morphology study on homogeneous hydrogels of different stiffness's indicated that fibroblasts tend to spread to their final size within 2 h on stiff substrates, while the spreading time was much longer (ca. 4-5 h) on soft substrates. These trends were confirmed on hydrogels with compliance gradients, showing well spread fibroblasts on the stiff end of the hydrogel after 2 h, while the cells on the soft end still had small area and rounded morphology.

  20. Facile Fabrication of Gradient Surface Based on (meth)acrylate Copolymer Films

    NASA Astrophysics Data System (ADS)

    Zhang, Y.; Yang, H.; Wen, X.-F.; Cheng, J.; Xiong, J.

    2016-08-01

    This paper describes a simple and economic approach for fabrication of surface wettability gradient on poly(butyl acrylate - methyl methacrylate) [P (BA-MMA)] and poly(butyl acrylate - methyl methacrylate - 2-hydroxyethyl methacrylate) [P (BA-MMA-HEMA)] films. The (meth)acrylate copolymer [including P (BA-MMA) and P (BA-MMA-HEMA)] films are hydrolyzed in an aqueous solution of NaOH and the transformation of surface chemical composition is achieved by hydrolysis in NaOH solution. The gradient wetting properties are generated based on different functional groups on the P (BA-MMA) and P (BA-MMA-HEMA) films. The effects of both the surface chemical and surface topography on wetting of the (meth)acrylate copolymer film are discussed. Surface chemical composition along the materials length is determined by XPS, and surface topography properties of the obtained gradient surfaces are analyzed by FESEM and AFM. Water contact angle system (WCAs) results show that the P (BA-MMA-HEMA) films provide a larger slope of the gradient wetting than P (BA-MMA). Moreover, this work demonstrates that the gradient concentration of chemical composition on the poly(meth) acrylate films is owing to the hydrolysis processes of ester group, and the hydrolysis reactions that have negligible influence on the surface morphology of the poly(meth) acrylate films coated on the glass slide. The gradient wettability surfaces may find broad applications in the field of polymer coating due to the compatibility of (meth) acrylate polymer.

  1. Global convergence analysis of a new nonlinear conjugate gradient coefficient with strong Wolfe line search

    NASA Astrophysics Data System (ADS)

    Abdelrahman, Awad; Mamat, Mustafa; Rivaie, Mohd; Omer, Osman

    2015-05-01

    Nonlinear conjugate gradient (CG) methods are the most important method for solving large-scale unconstrained optimization problems. Many studies and modifications have been conducted recently to improve this method. In this paper, a new class of conjugate gradient coefficients (βk ) with a new parameter m =‖gk ‖ /‖gk -1 ‖ that possess global convergence properties is presented. The global convergence and sufficient decent property result is established using inexact line searches to determine the (αk>0 ) is a step size of CG methods. Numerical result shows that the new formula is superior and more efficient when compared to other CG coefficients.

  2. Boundary detection in medical images using edge following algorithm based on intensity gradient and texture gradient features.

    PubMed

    Somkantha, Krit; Theera-Umpon, Nipon; Auephanwiriyakul, Sansanee

    2011-03-01

    Finding the correct boundary in noisy images is still a difficult task. This paper introduces a new edge following technique for boundary detection in noisy images. Utilization of the proposed technique is exhibited via its application to various types of medical images. Our proposed technique can detect the boundaries of objects in noisy images using the information from the intensity gradient via the vector image model and the texture gradient via the edge map. The performance and robustness of the technique have been tested to segment objects in synthetic noisy images and medical images including prostates in ultrasound images, left ventricles in cardiac magnetic resonance (MR) images, aortas in cardiovascular MR images, and knee joints in computerized tomography images. We compare the proposed segmentation technique with the active contour models (ACM), geodesic active contour models, active contours without edges, gradient vector flow snake models, and ACMs based on vector field convolution, by using the skilled doctors' opinions as the ground truths. The results show that our technique performs very well and yields better performance than the classical contour models. The proposed method is robust and applicable on various kinds of noisy images without prior knowledge of noise properties.

  3. Stiffness gradient of the beetle penis facilitates propulsion in the spiraled female spermathecal duct.

    PubMed

    Filippov, Alexander E; Matsumura, Yoko; Kovalev, Alexander E; Gorb, Stanislav N

    2016-06-23

    It is well known that sexual selection is the main driving force of substantial diversity of genitalia found in animals. However, how it facilitates the diversity is still largely unknown, because genital morpho/physical features and motions/functional morphology of the structures in sexual intercourse are not linked for the vast majority of organisms. Here we showed the presence of material gradient and numerically studied an effect of stiffness gradient of the beetle penis during its propulsion through the female duct. We found that stiffness gradient on the penis essentially affects its propulsion. Microscopic investigation suggests the possibility that the tip of the hyper-elongated penis is softer than the rest of it, and our numerical model confirms that this type of distribution of stiffness gradient aids in faster propulsion than other types. This result indicates that previously ignored physical properties of genital materials are of crucial importance in evolutionary studies of genitalia.

  4. Microsphere-based gradient implants for osteochondral regeneration: a long-term study in sheep

    PubMed Central

    Mohan, Neethu; Gupta, Vineet; Sridharan, Banu Priya; Mellott, Adam J; Easley, Jeremiah T; Palmer, Ross H; Galbraith, Richard A; Key, Vincent H; Berkland, Cory J; Detamore, Michael S

    2015-01-01

    Background: The microfracture technique for cartilage repair has limited ability to regenerate hyaline cartilage. Aim: The current study made a direct comparison between microfracture and an osteochondral approach with microsphere-based gradient plugs. Materials & methods: The PLGA-based scaffolds had opposing gradients of chondroitin sulfate and β-tricalcium phosphate. A 1-year repair study in sheep was conducted. Results: The repair tissues in the microfracture were mostly fibrous and had scattered fissures with degenerative changes. Cartilage regenerated with the gradient plugs had equal or superior mechanical properties; had lacunated cells and stable matrix as in hyaline cartilage. Conclusion: This first report of gradient scaffolds in a long-term, large animal, osteochondral defect demonstrated potential for equal or better cartilage repair than microfracture. PMID:26418471

  5. Experimental analysis of the boundary layer transition with zero and positive pressure gradient

    NASA Technical Reports Server (NTRS)

    Arnal, D.; Jullen, J. C.; Michel, R.

    1980-01-01

    The influence of a positive pressure gradient on the boundary layer transition is studied. The mean velocity and turbulence profiles of four cases are examined. As the intensity of the pressure gradient is increased, the Reynolds number of the transition onset and the length of the transition region are reduced. The Tollmein-Schlichting waves disturb the laminar regime; the amplification of these waves is in good agreement with the stability theory. The three dimensional deformation of the waves leads finally to the appearance of turbulence. In the case of zero pressure gradient, the properties of the turbulent spots are studied by conditional sampling of the hot-wire signal; in the case of positive pressure gradient, the turbulence appears in a progressive manner and the turbulent spots are much more difficult to characterize.

  6. Characterization and simulation on antireflective coating of amorphous silicon oxide thin films with gradient refractive index

    NASA Astrophysics Data System (ADS)

    Huang, Lu; Jin, Qi; Qu, Xingling; Jin, Jing; Jiang, Chaochao; Yang, Weiguang; Wang, Linjun; Shi, Weimin

    2016-08-01

    The optical reflective properties of silicon oxide (SixOy) thin films with gradient refractive index are studied both theoretically and experimentally. The thin films are widely used in photovoltaic as antireflective coatings (ARCs). An effective finite difference time domain (FDTD) model is built to find the optimized reflection spectra corresponding to structure of SixOy ARCs with gradient refractive index. Based on the simulation analysis, it shows the variation of reflection spectra with gradient refractive index distribution. The gradient refractive index of SixOy ARCs can be obtained in adjustment of SiH4 to N2O ratio by plasma-enhanced chemical vapor deposition (PECVD) system. The optimized reflection spectra measured by UV-visible spectroscopy confirms to agree well with that simulated by FDTD method.

  7. Turbulence measurements in axisymmetric supersonic boundary layer flow in adverse pressure gradients

    NASA Technical Reports Server (NTRS)

    Gootzait, E.; Childs, M. E.

    1977-01-01

    Mean flow and turbulence measurements are presented for adiabatic compressible turbulent boundary layer flow in adverse pressure gradients. The gradients were induced on the wall of an axially symmetric wind tunnel by contoured centerbodies mounted on the wind tunnel centerline. The boundary layer turbulence downstream of a boundary layer bleed section in a zero pressure gradient was also examined. The measurements were obtained using a constant temperature hot-wire anemometer. The adverse pressure gradients were found to significantly alter the turbulence properties of the boundary layer. With flow through the bleed holes there was a measureable decrease in the rms longitudinal velocity fluctuations near the wall and the turbulent shear stress in the boundary layer was reduced.

  8. Perspectives in flow-based microfluidic gradient generators for characterizing bacterial chemotaxis.

    PubMed

    Wolfram, Christopher J; Rubloff, Gary W; Luo, Xiaolong

    2016-11-01

    Chemotaxis is a phenomenon which enables cells to sense concentrations of certain chemical species in their microenvironment and move towards chemically favorable regions. Recent advances in microbiology have engineered the chemotactic properties of bacteria to perform novel functions, but traditional methods of characterizing chemotaxis do not fully capture the associated cell motion, making it difficult to infer mechanisms that link the motion to the microbiology which induces it. Microfluidics offers a potential solution in the form of gradient generators. Many of the gradient generators studied to date for this application are flow-based, where a chemical species diffuses across the laminar flow interface between two solutions moving through a microchannel. Despite significant research efforts, flow-based gradient generators have achieved mixed success at accurately capturing the highly subtle chemotactic responses exhibited by bacteria. Here we present an analysis encompassing previously published versions of flow-based gradient generators, the theories that govern their gradient-generating properties, and new, more practical considerations that result from experimental factors. We conclude that flow-based gradient generators present a challenge inherent to their design in that the residence time and gradient decay must be finely balanced, and that this significantly narrows the window for reliable observation and quantification of chemotactic motion. This challenge is compounded by the effects of shear on an ellipsoidal bacterium that causes it to preferentially align with the direction of flow and subsequently suppresses the cross-flow chemotactic response. These problems suggest that a static, non-flowing gradient generator may be a more suitable platform for chemotaxis studies in the long run, despite posing greater difficulties in design and fabrication.

  9. Strategies and Applications for Incorporating Physical and Chemical Signal Gradients in Tissue Engineering

    PubMed Central

    Singh, Milind; Berkland, Cory

    2008-01-01

    From embryonic development to wound repair, concentration gradients of bioactive signaling molecules guide tissue formation and regeneration. Moreover, gradients in cellular and extracellular architecture as well as in mechanical properties are readily apparent in native tissues. Perhaps tissue engineers can take a cue from nature in attempting to regenerate tissues by incorporating gradients into engineering design strategies. Indeed, gradient-based approaches are an emerging trend in tissue engineering, standing in contrast to traditional approaches of homogeneous delivery of cells and/or growth factors using isotropic scaffolds. Gradients in tissue engineering lie at the intersection of three major paradigms in the field—biomimetic, interfacial, and functional tissue engineering—by combining physical (via biomaterial design) and chemical (with growth/differentiation factors and cell adhesion molecules) signal delivery to achieve a continuous transition in both structure and function. This review consolidates several key methodologies to generate gradients, some of which have never been employed in a tissue engineering application, and discusses strategies for incorporating these methods into tissue engineering and implant design. A key finding of this review was that two-dimensional physicochemical gradient substrates, which serve as excellent high-throughput screening tools for optimizing desired biomaterial properties, can be enhanced in the future by transitioning from two dimensions to three dimensions, which would enable studies of cell–protein–biomaterial interactions in a more native tissue–like environment. In addition, biomimetic tissue regeneration via combined delivery of graded physical and chemical signals appears to be a promising strategy for the regeneration of heterogeneous tissues and tissue interfaces. In the future, in vivo applications will shed more light on the performance of gradient-based mechanical integrity and signal

  10. Strategies and applications for incorporating physical and chemical signal gradients in tissue engineering.

    PubMed

    Singh, Milind; Berkland, Cory; Detamore, Michael S

    2008-12-01

    From embryonic development to wound repair, concentration gradients of bioactive signaling molecules guide tissue formation and regeneration. Moreover, gradients in cellular and extracellular architecture as well as in mechanical properties are readily apparent in native tissues. Perhaps tissue engineers can take a cue from nature in attempting to regenerate tissues by incorporating gradients into engineering design strategies. Indeed, gradient-based approaches are an emerging trend in tissue engineering, standing in contrast to traditional approaches of homogeneous delivery of cells and/or growth factors using isotropic scaffolds. Gradients in tissue engineering lie at the intersection of three major paradigms in the field-biomimetic, interfacial, and functional tissue engineering-by combining physical (via biomaterial design) and chemical (with growth/differentiation factors and cell adhesion molecules) signal delivery to achieve a continuous transition in both structure and function. This review consolidates several key methodologies to generate gradients, some of which have never been employed in a tissue engineering application, and discusses strategies for incorporating these methods into tissue engineering and implant design. A key finding of this review was that two-dimensional physicochemical gradient substrates, which serve as excellent high-throughput screening tools for optimizing desired biomaterial properties, can be enhanced in the future by transitioning from two dimensions to three dimensions, which would enable studies of cell-protein-biomaterial interactions in a more native tissue-like environment. In addition, biomimetic tissue regeneration via combined delivery of graded physical and chemical signals appears to be a promising strategy for the regeneration of heterogeneous tissues and tissue interfaces. In the future, in vivo applications will shed more light on the performance of gradient-based mechanical integrity and signal delivery

  11. Perspectives in flow-based microfluidic gradient generators for characterizing bacterial chemotaxis

    PubMed Central

    Wolfram, Christopher J.; Rubloff, Gary W.; Luo, Xiaolong

    2016-01-01

    Chemotaxis is a phenomenon which enables cells to sense concentrations of certain chemical species in their microenvironment and move towards chemically favorable regions. Recent advances in microbiology have engineered the chemotactic properties of bacteria to perform novel functions, but traditional methods of characterizing chemotaxis do not fully capture the associated cell motion, making it difficult to infer mechanisms that link the motion to the microbiology which induces it. Microfluidics offers a potential solution in the form of gradient generators. Many of the gradient generators studied to date for this application are flow-based, where a chemical species diffuses across the laminar flow interface between two solutions moving through a microchannel. Despite significant research efforts, flow-based gradient generators have achieved mixed success at accurately capturing the highly subtle chemotactic responses exhibited by bacteria. Here we present an analysis encompassing previously published versions of flow-based gradient generators, the theories that govern their gradient-generating properties, and new, more practical considerations that result from experimental factors. We conclude that flow-based gradient generators present a challenge inherent to their design in that the residence time and gradient decay must be finely balanced, and that this significantly narrows the window for reliable observation and quantification of chemotactic motion. This challenge is compounded by the effects of shear on an ellipsoidal bacterium that causes it to preferentially align with the direction of flow and subsequently suppresses the cross-flow chemotactic response. These problems suggest that a static, non-flowing gradient generator may be a more suitable platform for chemotaxis studies in the long run, despite posing greater difficulties in design and fabrication. PMID:27917249

  12. Age and metallicity gradients in fossil ellipticals

    NASA Astrophysics Data System (ADS)

    Eigenthaler, P.; Zeilinger, W. W.

    2013-05-01

    Context. Fossil galaxy groups are speculated to be old and highly evolved systems of galaxies that formed early in the universe and had enough time to deplete their L∗ galaxies through successive mergers of member galaxies, building up one massive central elliptical, but retaining the group X-ray halo. Aims: Considering that fossils are the remnants of mergers in ordinary groups, the merger history of the progenitor group is expected to be imprinted in the fossil central galaxy (FCG). We present for the first time radial gradients of single-stellar population (SSP) ages and metallicites in a sample of FCGs to constrain their formation scenario. We also measure line-strength gradients for the strongest absorption features in these galaxies. Methods: We took deep spectra with the long-slit spectrograph ISIS at the William Herschel Telescope (WHT) for six FCGs. The obtained spectra are fit with Pegase HR SSP models within the full-spectrum fitting package ULySS yielding SSP ages and metallicities of the stellar populations. We measure radial gradients of SSP ages and metallicities along the major axes. Lick indices are measured for the strongest absorption features to determine line-strength gradients and compare with the full-spectrum fitting results. Results: Our sample comprises some of the most massive galaxies in the universe exhibiting an average central velocity dispersion of σ0 = 271 ± 28 km s-1. Metallicity gradients are throughout negative with comparatively flat slopes of ∇[Fe/H] = -0.19 ± 0.08 while age gradients are found to be insignificant (∇age = 0.00 ± 0.05). All FCGs lie on the fundamental plane, suggesting that they are virialised systems. We find that gradient strengths and central metallicities are similar to those found in cluster ellipticals of similar mass. Conclusions: The comparatively flat metallicity gradients with respect to those predicted by monolithic collapse (∇Z = -0.5) suggest that fossils are indeed the result of

  13. Control of vortex breakdown by temperature gradients

    NASA Astrophysics Data System (ADS)

    Herrada, Miguel Angel; Shtern, Vladimir

    2003-11-01

    An axial gradient of temperature can either suppress or enhance vortex breakdown (VB). The underlying mechanism of such VB control is centrifugal or/and gravitational convection. An additional thermal-convection flow directed oppositely to the base flow suppresses VB while a co-flow enhances VB. Our numerical simulations of a compressible flow in a sealed cylinder induced by a rotating bottom disk clearly reveal these effects. We vary the temperature gradient (ɛ), Mach (Ma), Froude (Fr), and Reynolds (Re) numbers, and the aspect ratio (h). As ɛ increases (ɛ>0 corresponding to a temperature gradient parallel to the downward near-axis flow), the VB "bubble," which occurs at ɛ=0, diminishes and then totally disappears. The opposite temperature gradient (ɛ<0) enlarges the VB bubble and makes the flow unsteady. These effects of centrifugal convection become more prominent with increasing Ma and Re. Density variations induced by the temperature gradients are more important for VB control than those induced by the increase in Ma. A new efficient time-evolution code for axisymmetric flows of an ideal gas has facilitated these simulations.

  14. Polarisation effects in gradient nano-optics

    SciTech Connect

    Erokhin, N S; Shvartsburg, A B; Zueva, Yu M

    2013-09-30

    The spectra of reflection of s- and p-polarised waves from gradient nanocoatings at arbitrary angles of incidence are found within the framework of two exactly solvable models of such coatings. To use the detected spectra in the visible and IR ranges, for different frequencies and coating thicknesses we present the wave reflection coefficients as functions of dimensionless frequencies related to the refractive index gradient of the coating material. It is shown that reflection from the gradient coatings in question is an order of magnitude weaker than reflection from uniform coatings, other parameters of radiation and the reflection system being equal. We report a new exactly solvable model illustrating the specific effect of gradient film optics – the possibility of non-reflective propagation of an s-wave through such a film (an analogue of the Brewster effect). The prospects are shown for the use of gradient nanostructures with different refractive index profiles to fabricate broadband non-reflective coatings. (nanogradient dielectric coatings and metamaterials)

  15. MEMS cantilever based magnetic field gradient sensor

    NASA Astrophysics Data System (ADS)

    Dabsch, Alexander; Rosenberg, Christoph; Stifter, Michael; Keplinger, Franz

    2017-05-01

    This paper describes major contributions to a MEMS magnetic field gradient sensor. An H-shaped structure supported by four arms with two circuit paths on the surface is designed for measuring two components of the magnetic flux density and one component of the gradient. The structure is produced from silicon wafers by a dry etching process. The gold leads on the surface carry the alternating current which interacts with the magnetic field component perpendicular to the direction of the current. If the excitation frequency is near to a mechanical resonance, vibrations with an amplitude within the range of 1-103 nm are expected. Both theoretical (simulations and analytic calculations) and experimental analysis have been carried out to optimize the structures for different strength of the magnetic gradient. In the same way the impact of the coupling structure on the resonance frequency and of different operating modes to simultaneously measure two components of the flux density were tested. For measuring the local gradient of the flux density the structure was operated at the first symmetrical and the first anti-symmetrical mode. Depending on the design, flux densities of approximately 2.5 µT and gradients starting from 1 µT mm-1 can be measured.

  16. Importance of Ionospheric Gradients for error Correction

    NASA Astrophysics Data System (ADS)

    Ravula, Ramprasad

    Importance of Ionospheric Gradients for error Correction R. Ram Prasad1, P.Nagasekhar2 1Sai Spurthi Institute of Technology-JNTU Hyderabad,2Sai Spurthi Institute of Technology-JNTU Hyderabad Email ID:rams.ravula@gmail.com In India, Indian Space Research Organization (ISRO) has established with an objective to develop space technology and its application to various national tasks. To cater to the needs of civil aviation applications, GPS Aided Geo Augmented Navigation (GAGAN) system is being jointly implemented along with Airports Authority of India (AAI) over the Indian region. The most predominant parameter affecting the navigation accuracy of GAGAN is ionospheric delay which is a function of total number of electrons present in one square meter cylindrical cross sectional area in the line of site direction between the satellite and the user on the earth i.e. Total Electron Content (TEC).The irregular distribution of electron densities i.e. rate of TEC variation, causes Ionospheric gradients such as spatial gradients (Expressed in TECu/km) and temporal gradients (Expressed in TECu /minute). Among the satellite signals arriving to the earth in multiple directions, the signals which suffer from severe ionospheric gradients can be estimated i.e. Rate of TEC Index (ROTI) and Rate of TEC (ROT). These aspects which contribute to errors can be treated for improving GAGAN positional accuracy.

  17. Income inequality and socioeconomic gradients in mortality.

    PubMed

    Wilkinson, Richard G; Pickett, Kate E

    2008-04-01

    We investigated whether the processes underlying the association between income inequality and population health are related to those responsible for the socioeconomic gradient in health and whether health disparities are smaller when income differences are narrower. We used multilevel models in a regression analysis of 10 age- and cause-specific US county mortality rates on county median household incomes and on state income inequality. We assessed whether mortality rates more closely related to county income were also more closely related to state income inequality. We also compared mortality gradients in more- and less-equal states. Mortality rates more strongly associated with county income were more strongly associated with state income inequality: across all mortality rates, r= -0.81; P=.004. The effect of state income inequality on the socioeconomic gradient in health varied by cause of death, but greater equality usually benefited both wealthier and poorer counties. Although mortality rates with steep socioeconomic gradients were more sensitive to income distribution than were rates with flatter gradients, narrower income differences benefit people in both wealthy and poor areas and may, paradoxically, do little to reduce health disparities.

  18. Population Gradients in Stellar Halos from GHOSTS

    NASA Astrophysics Data System (ADS)

    Bailin, Jeremy; Monachesi, Antonela; Bell, Eric F.; de Jong, Roelof S.; Ghosts Survey

    2015-01-01

    We report on recent results from the Galaxy Halos, Outer disks, Substructure, Thick disks, and Star clusters (GHOSTS) survey, an HST ACS+WFC3 imaging survey to study stellar populations in and around 16 nearby spiral galaxies. By using HST resolution to resolve the stellar halos into individual red giant branch (RGB) stars, we are able to detect distinct stellar populations at several points throughout the halo of the half dozen massive highly-inclined galaxies in the sample. In approximately half of these galaxies, we detect a gradient in the color of the RGB; which we interpret as a metallicity gradient. Stellar halo formation models predict a wide variety of metallicity gradients: those in which the halos are dominated by stars formed in situ predict stronger gradients than we observe, while accretion-dominated halo models predict weaker or nonexistent gradients. Our measurements therefore provide a useful discriminator between stellar halo models, and at first look appear most consistent with the accretion-based model of Cooper et al. (2010).

  19. A circuit for gradient climbing in C. elegans chemotaxis

    PubMed Central

    Larsch, Johannes; Flavell, Steven W.; Liu, Qiang; Gordus, Andrew; Albrecht, Dirk R.; Bargmann, Cornelia I.

    2016-01-01

    Animals have a remarkable ability to track dynamic sensory information. For example, the nematode Caenorhabditis elegans can locate a diacetyl odor source across a 100,000-fold concentration range. Here, we relate neuronal properties, circuit implementation, and behavioral strategies underlying this robust navigation. Diacetyl responses in AWA olfactory neurons are concentration- and history-dependent; AWA integrates over time at low odor concentrations, but as concentrations rise it desensitizes rapidly through a process requiring cilia transport. After desensitization, AWA retains sensitivity to small odor increases. The downstream AIA interneuron amplifies weak odor inputs and desensitizes further, resulting in a stereotyped response to odor increases over three orders of magnitude. The AWA-AIA circuit drives asymmetric behavioral responses to odor increases that facilitate gradient climbing. The adaptation-based circuit motif embodied by AWA and AIA shares computational properties with bacterial chemotaxis and the vertebrate retina, each providing a solution for maintaining sensitivity across a dynamic range. PMID:26365196

  20. High-gradient, pulsed operation of superconducting niobium cavities

    SciTech Connect

    Campisi, I.E.; Farkas, Z.D.

    1984-02-01

    Tests performed on several Niobium TM/sub 010/ cavities at frequencies of about 2856 MHz using a high-power, pulsed method indicate that, at the end of the charging pulse, peak surface magnetic fields of up to approx. 1300 Oe, corresponding to a peak surface electric field of approx. 68 MV/m, can be reached at 4.2/sup 0/K without appreciable average losses. Further studies of the properties of superconductors under pulsed operation might shed light on fundamental properties of rf superconductivity, as well as lead to the possibility of applying the pulse method to the operation of high-gradient linear colliders. 7 references, 30 figures, 2 tables.

  1. Tubing-Electrospinning: A One-Step Process for Fabricating Fibrous Matrices with Spatial, Chemical, and Mechanical Gradients.

    PubMed

    Kim, Jung-Suk; Im, Byung Gee; Jin, Gyuhyung; Jang, Jae-Hyung

    2016-08-31

    Guiding newly generated tissues in a gradient pattern, thereby precisely mimicking inherent tissue morphology and subsequently arranging the intimate networks between adjacent tissues, is essential to raise the technical levels of tissue engineering and facilitate its transition into the clinic. In this study, a straightforward electrospinning method (the tubing-electrospinning technique) was developed to create fibrous matrices readily with diverse gradient patterns and to induce patterned cellular responses. Gradient fibrous matrices can be produced simply by installing a series of polymer-containing lengths of tubing into an electrospinning circuit and sequentially processing polymers without a time lag. The loading of polymer samples with different characteristics, including concentration, wettability, and mechanical properties, into the tubing system enabled unique features in fibrous matrices, such as longitudinal gradients in fiber density, surface properties, and mechanical stiffness. The resulting fibrous gradients were shown to arrange cellular migration and residence in a gradient manner, thereby offering efficient cues to mediate patterned tissue formation. The one-step process using tubing-electrospinning apparatus can be used without significant modifications regardless of the type of fibrous gradient. Hence, the tubing-electrospinning system can serve as a platform that can be readily used by a wide-range of users to induce patterned tissue formation in a gradient manner, which will ultimately improve the functionality of tissue engineering scaffolds.

  2. Investigation of Cu2ZnSnS4 thin-film solar cells with carrier concentration gradient

    NASA Astrophysics Data System (ADS)

    Xu, Jiaxiong

    2016-11-01

    To investigate the effect of carrier concentration gradient on Cu2ZnSnS4 (CZTS) thin-film solar cells, the properties of CZTS solar cells were studied by numerical method. The photovoltaic performances of carrier concentration gradient CZTS solar cells were calculated by the solutions of Poisson's equation, continuity equation, and current density equation using AFors-Het v2.4 program. The carrier concentration gradient was changed to analyze its effect. Compared with CZTS solar cells without carrier concentration gradient, the photovoltaic performances of CZTS solar cells can be enhanced by using carrier concentration gradient absorber. The carrier concentration gradient can extend the distribution region of built-in electric field, which is beneficial to the drift of photo-generated carriers. However, the carrier concentration gradient also affects the recombination and series resistances of solar cells. When the defect density of CZTS layer is high, the photo-generated carriers are affected significantly by recombination, resulting in slight effect of carrier concentration gradient. Therefore, the defect density should be reduced to enhance the effect of carrier concentration gradient on improving conversion efficiency of CZTS thin-film solar cells.

  3. Evidence of counter-gradient growth in western pond turtles (Actinemys marmorata) across thermal gradients

    Treesearch

    Melissa L. Snover; Michael J. Adams; Donald T. Ashton; Jamie B. Bettaso; Hartwell H. Welsh

    2015-01-01

    Summary1. Counter-gradient growth, where growth per unit temperature increases as temperature decreases, can reduce the variation in ectothermic growth rates across environmental gradients. Understanding how ectothermic species respond to changing temperatures is essential to their conservation and management due to human-altered habitats and changing...

  4. A transient FGM interlayer based approach to joining ceramics. [Functionally gradient materials

    SciTech Connect

    Glaeser, A.M.; Shalz, M.L.; Dalgleish, B.J.; Tomsia, A.P.

    1993-01-01

    In most cases, functionally gradient materials have been designed to produce a desirable property gradient in a material or in a joint region. In this paper, the concept of a transient gradient structure is introduced. The function of the intentional property discontinuities in these multilayer interlayers is to facilitate processing of assemblies and materials combinations that would be difficult to process using conventional bonding approaches. Specifically, the methods make use of a thin or partial layer of a low melting point transient liquid phase to facilitate bonding via brazing, yet produce refractory joints. Several mechanisms for consuming the transient liquid former are outlined, and examples of interlayer designs that exploit these mechanisms are presented. Specific results from experiments joining alumina to alumina via Cu/Pt/Cu, Cu/Ni/Cu, Cu/Nb/Cu and Sn/Nb/Sn interlayers are presented.

  5. Gradient Calculation Methods on Arbitrary Polyhedral Unstructured Meshes for Cell-Centered CFD Solvers

    NASA Technical Reports Server (NTRS)

    Sozer, Emre; Brehm, Christoph; Kiris, Cetin C.

    2014-01-01

    A survey of gradient reconstruction methods for cell-centered data on unstructured meshes is conducted within the scope of accuracy assessment. Formal order of accuracy, as well as error magnitudes for each of the studied methods, are evaluated on a complex mesh of various cell types through consecutive local scaling of an analytical test function. The tests highlighted several gradient operator choices that can consistently achieve 1st order accuracy regardless of cell type and shape. The tests further offered error comparisons for given cell types, leading to the observation that the "ideal" gradient operator choice is not universal. Practical implications of the results are explored via CFD solutions of a 2D inviscid standing vortex, portraying the discretization error properties. A relatively naive, yet largely unexplored, approach of local curvilinear stencil transformation exhibited surprisingly favorable properties

  6. Design of objectives consisting of cemented radial gradient-index lenses

    NASA Astrophysics Data System (ADS)

    Greisukh, Grigoriy I.; Ezhov, Evgeniy G.; Stepanov, Sergei A.

    1999-08-01

    Aberration properties and correction capabilities of objectives containing two or three cemented radial gradient- index lenses are analyzed. It is shown that the simplest radial gradient-index system, which can be corrected for all third-order monochromatic aberrations, is the cemented doublet with flat external and spherical cemented surfaces. Aberration properties of the cemented component made of two different inhomogeneous materials and having only four flat surfaces are analogous. It is also shown that the simplest radial gradient-index system, which can be simultaneously corrected for all third- and fifth-order monochromatic aberrations, is the cemented triplet made of three different inhomogeneous materials and having spherical surfaces. The methods and examples of aberrations-free objectives design are given.

  7. Conjugate gradient algorithms using multiple recursions

    SciTech Connect

    Barth, T.; Manteuffel, T.

    1996-12-31

    Much is already known about when a conjugate gradient method can be implemented with short recursions for the direction vectors. The work done in 1984 by Faber and Manteuffel gave necessary and sufficient conditions on the iteration matrix A, in order for a conjugate gradient method to be implemented with a single recursion of a certain form. However, this form does not take into account all possible recursions. This became evident when Jagels and Reichel used an algorithm of Gragg for unitary matrices to demonstrate that the class of matrices for which a practical conjugate gradient algorithm exists can be extended to include unitary and shifted unitary matrices. The implementation uses short double recursions for the direction vectors. This motivates the study of multiple recursion algorithms.

  8. Gradients in Planarian Regeneration and Homeostasis

    PubMed Central

    Adell, Teresa; Cebrià, Francesc; Saló, Emili

    2010-01-01

    Planarian regeneration was one of the first models in which the gradient concept was developed. Morphological studies based on the analysis of the regeneration rates of planarian fragments from different body regions, the generation of heteromorphoses, and experiments of tissue transplantation led T.H. Morgan (1901) and C.M Child (1911) to postulate different kinds of gradients responsible for the regenerative process in these highly plastic animals. However, after a century of research, the role of morphogens in planarian regeneration has yet to be demonstrated. This may change soon, as the sequencing of the planarian genome and the possibility of performing gene functional analysis by RNA interference (RNAi) have led to the isolation of elements of the bone morphogenetic protein (BMP), Wnt, and fibroblast growth factor (FGF) pathways that control patterning and axial polarity during planarian regeneration and homeostasis. Here, we discuss whether the actions of these molecules could be based on morphogenetic gradients. PMID:20182600

  9. Dynamics of gradient formation by intracellular shuttling

    NASA Astrophysics Data System (ADS)

    Berezhkovskii, Alexander M.; Shvartsman, Stanislav Y.

    2015-08-01

    A number of important cellular functions rely on the formation of intracellular protein concentration gradients. Experimental studies discovered a number of mechanisms for the formation of such gradients. One of the mechanisms relies on the intracellular shuttling of a protein that interconverts between the two states with different diffusivities, under the action of two enzymes, one of which is localized to the plasma membrane, whereas the second is uniformly distributed in the cytoplasm. Recent work reported an analytical solution for the steady state gradient in this mechanism, obtained in the framework of a one-dimensional reaction-diffusion model. Here, we study the dynamics in this model and derive analytical expressions for the Laplace transforms of the time-dependent concentration profiles in terms of elementary transcendental functions. Inverting these transforms numerically, one can obtain time-dependent concentration profiles of the two forms of the protein.

  10. Image restoration by matching gradient distributions.

    PubMed

    Cho, Taeg Sang; Zitnick, C Lawrence; Joshi, Neel; Kang, Sing Bing; Szeliski, Richard; Freeman, William T

    2012-04-01

    The restoration of a blurry or noisy image is commonly performed with a MAP estimator, which maximizes a posterior probability to reconstruct a clean image from a degraded image. A MAP estimator, when used with a sparse gradient image prior, reconstructs piecewise smooth images and typically removes textures that are important for visual realism. We present an alternative deconvolution method called iterative distribution reweighting (IDR) which imposes a global constraint on gradients so that a reconstructed image should have a gradient distribution similar to a reference distribution. In natural images, a reference distribution not only varies from one image to another, but also within an image depending on texture. We estimate a reference distribution directly from an input image for each texture segment. Our algorithm is able to restore rich mid-frequency textures. A large-scale user study supports the conclusion that our algorithm improves the visual realism of reconstructed images compared to those of MAP estimators.

  11. Texturing of REBCO using temperature gradient.

    SciTech Connect

    Salama, K.; Athur, S. P.; Balachandran, U.; Energy Technology; Univ. of Houston

    2001-01-01

    Isothermal melt texturing is currently a well-established technique for manufacturing superconducting materials with high trapped magnetic field and levitation forces. For conductor applications, however, a temperature gradient needs to be employed in order to align the oriented domains with the a-b planes where the current will be flowing over long lengths. Melt-textured Y-123 bars of length 100 mm with Jc values of 70,000 A/cm2 at 77 K in self-field have been routinely manufactured by directional solidification. The presence of temperature gradient also lends itself to faster texturing rates. Recently, Ag-clad Yb-123 tapes made by the powder-in-tube process were successfully melt textured in the presence of a temperature gradient and controlled oxygen partial pressure. These tapes exhibit the potential to be an alternative to BSCCO tapes, for relatively high temperature and magnetic field applications.

  12. Temperature gradient formation while axial gas compression

    NASA Astrophysics Data System (ADS)

    Geyko, V. I.; Fisch, N. J.

    2015-11-01

    A spinning gas in equilibrium has a rotation-dependent heat capacity. However, as equilibrium is approached, such as after sudden heating, significant variations in temperature appear. Surprisingly, when fast axial compression or instantaneous gas heating occurs, the temperature does not grow homogeneously in radial direction, but instead has a gradient towards to the maximum of potential energy of external or self potential. The gradient monotonically grows with compression rate and the amplitude of the potential. The gradient builds up due to change of equilibrium density distribution, yet, not due to acoustic waves created by the compression. This result was checked in numerical simulations for particles in an external constant gravitational potential and also for rotating gas in the cylinder with perfect slip boundary conditions on the walls. This work was supported by the U.S. Defense Threat Reduction Agency, and by the NNSA SSAA Program through DOE Research Grant No. DE-FG52-08NA28553.

  13. Relativistic klystrons for high-gradient accelerators

    SciTech Connect

    Westenskow, G.A.; Aalberts, D.P.; Boyd, J.K.; Deis, G.A.; Houck, T.L.; Orzechowski, T.J.; Ryne, R.D.; Yu, S.S. ); Allen, M.A.; Callin, R.S.; Deruyter, H.; Eppley, K.R.; Fant, K.S.; Fowkes, W.R.; Hoag, H.A.; Koontz, R.F.; Lavine, T.L.; Loew, G.A.; Miller, R.H.; Ruth, R.D.; Vlieks, A.E.; Wang, J.W. ); Haimson, J.; Mecklen

    1990-09-05

    Experimental work is being performed by collaborators at LLNL, SLAC, and LBL to investigate relativistic klystrons as a possible rf power source for future high-gradient accelerators. We have learned how to overcome or previously reported problem of high power rf pulse shortening and have achieved peak rf power levels of 330 MW using an 11.4-GHz high-gain tube with multiple output structures. In these experiments the rf pulse is of the same duration as the beam current pulse. In addition, experiments have been performed on two short sections of a high-gradient accelerator using the rf power from a relativistic klystron. An average accelerating gradient of 84 MV/m has been achieved with 80-MW of rf power.

  14. Using Spatial Gradients to Model Localization Phenomena

    SciTech Connect

    D.J.Bammann; D.Mosher; D.A.Hughes; N.R.Moody; P.R.Dawson

    1999-07-01

    We present the final report on a Laboratory-Directed Research and Development project, Using Spatial Gradients to Model Localization Phenomena, performed during the fiscal years 1996 through 1998. The project focused on including spatial gradients in the temporal evolution equations of the state variables that describe hardening in metal plasticity models. The motivation was to investigate the numerical aspects associated with post-bifurcation mesh dependent finite element solutions in problems involving damage or crack propagation as well as problems in which strain Localizations occur. The addition of the spatial gradients introduces a mathematical length scale that eliminates the mesh dependency of the solution. In addition, new experimental techniques were developed to identify the physical mechanism associated with the numerical length scale.

  15. Preparation of gradient polyacrylate brushes in microchannels.

    PubMed

    Lee, Seongyeol; Youm, Sang Gil; Song, Yeari; Yi, Whikum; Sohn, Daewon

    2012-05-01

    Gradient poly(2-hydroxyethyl methacrylate) brushes were synthesized by surface-initiated atom transfer radical polymerization (ATRP) confined within a microfluidic system on a silicon wafer. For ATRP, surface initiator, 11-((2-bromo, 2-methyl) propionyloxy) undecyltrichlorosilane (BUC), was synthesized, and allowed to self-assemble in a monolayer on the Si wafer, as analyzed by XPS to confirm the presence of an ester group of BUC. A solution containing 2-hydroxyethylmethacrylate, Cu catalyst, and bipyridin was allowed to flow in a microchannel and polymerize, resulting in the brushes with a gradient of thickness on the Si wafer. Using ellipsometry and ATR-IR, we verified the gradients of well established brushes on the Si wafer. AFM and contact angle data showed that wettability of the brushes did not exhibit a linear relationship with hydrophilicity.

  16. Transverse gradient in Apple-type undulators

    PubMed Central

    Calvi, M.; Camenzuli, C.; Prat, E.; Schmidt, Th.

    2017-01-01

    Apple-type undulators are globally recognized as the most flexible devices for the production of variable polarized light in the soft X-ray regime, both at synchrotron and free-electron laser facilities. Recently, the implementation of transverse gradient undulators has been proposed to enhance the performance of new generation light sources. In this paper it is demonstrated that Apple undulators do not only generate linear and elliptical polarized light but also variable transverse gradient under certain conditions. A general theoretical framework is introduced to evaluate the K-value and its transverse gradient for an Apple undulator, and formulas for all regular operational modes and different Apple types (including the most recent Delta type and Apple X) are calculated and critically discussed. PMID:28452751

  17. Dynamics of gradient formation by intracellular shuttling

    SciTech Connect

    Berezhkovskii, Alexander M.; Shvartsman, Stanislav Y.

    2015-08-21

    A number of important cellular functions rely on the formation of intracellular protein concentration gradients. Experimental studies discovered a number of mechanisms for the formation of such gradients. One of the mechanisms relies on the intracellular shuttling of a protein that interconverts between the two states with different diffusivities, under the action of two enzymes, one of which is localized to the plasma membrane, whereas the second is uniformly distributed in the cytoplasm. Recent work reported an analytical solution for the steady state gradient in this mechanism, obtained in the framework of a one-dimensional reaction-diffusion model. Here, we study the dynamics in this model and derive analytical expressions for the Laplace transforms of the time-dependent concentration profiles in terms of elementary transcendental functions. Inverting these transforms numerically, one can obtain time-dependent concentration profiles of the two forms of the protein.

  18. Motion Driven by Strain Gradient Fields

    PubMed Central

    Wang, Chao; Chen, Shaohua

    2015-01-01

    A new driving mechanism for direction-controlled motion of nano-scale objects is proposed, based on a model of stretching a graphene strip linked to a rigid base with linear springs of identical stiffness. We find that the potential energy difference induced by the strain gradient field in the graphene strip substrate can generate sufficient force to overcome the static and kinetic friction forces between the nano-flake and the strip substrate, resulting in the nanoscale flake motion in the direction of gradient reduction. The dynamics of the nano-flake can be manipulated by tuning the stiffness of linear springs, stretching velocity and the flake size. This fundamental law of directional motion induced by strain gradient could be very useful for promising designs of nanoscale manipulation, transportation and smart surfaces. PMID:26323603

  19. Gradients of signalling in the developing limb.

    PubMed

    Towers, Matthew; Wolpert, Lewis; Tickle, Cheryll

    2012-04-01

    The developing limb is one of the first systems where it was proposed that a signalling gradient is involved in pattern formation. This gradient for specifying positional information across the antero-posterior axis is based on Sonic hedgehog signalling from the polarizing region. Recent evidence suggests that Sonic hedgehog signalling also specifies positional information across the antero-posterior axis by a timing mechanism acting in parallel with graded signalling. The progress zone model for specifying proximo-distal pattern, involving timing to provide cells with positional information, continues to be challenged, and there is further evidence that graded signalling by retinoic acid specifies the proximal part of the limb. Other recent papers present the first evidence that gradients of signalling by Wnt5a and FGFs govern cell behaviour involved in outgrowth and morphogenesis of the developing limb.

  20. Exploring Nf=2 +1 QCD thermodynamics from the gradient flow

    NASA Astrophysics Data System (ADS)

    Taniguchi, Yusuke; Ejiri, Shinji; Iwami, Ryo; Kanaya, Kazuyuki; Kitazawa, Masakiyo; Suzuki, Hiroshi; Umeda, Takashi; Wakabayashi, Naoki; WHOT-QCD Collaboration

    2017-07-01

    The energy-momentum tensor plays an important role in QCD thermodynamics. Its expectation value contains information of the pressure and the energy density as its diagonal part. Further properties like viscosity and specific heat can be extracted from its correlation function. A nonperturbative evaluation of it on the lattice is called. Recently, a new method based on the gradient flow was introduced to calculate the energy-momentum tensor on the lattice and has been successfully applied to quenched QCD. In this paper, we apply the gradient flow method to calculate the energy-momentum tensor in (2 +1 )-flavor QCD adopting a nonperturbatively O (a )-improved Wilson quark action and the renormalization group-improved Iwasaki gauge action. As the first application of the method with dynamical quarks, we study at a single but fine lattice spacing a ≃0.07 fm with heavy u and d quarks (mπ/mρ≃0.63 ) and approximately physical s quark (mηss/mϕ≃0.74 ). With the fixed-scale approach, temperature is varied by the temporal lattice size Nt at a fixed lattice spacing. Performing simulations on lattices with Nt=16 to 4, the temperature range of T ≃174 - 697 MeV is covered. We find that the results of the pressure and the energy density by the gradient flow method are consistent with the previous results using the T -integration method at T ≲280 MeV (Nt≳10 ), while the results show disagreement at T ≳350 MeV (Nt≲8 ), presumably due to the small-Nt lattice artifact of O ((a T )2) =O (1 /Nt2) . We also apply the gradient flow method to evaluate the chiral condensate taking advantage of the gradient flow method that renormalized quantities can be directly computed avoiding the difficulty of explicit chiral violation with lattice quarks. We compute the renormalized chiral condensate in the MS ¯ scheme at renormalization scale μ =2 GeV with a high precision to study the temperature dependence of the chiral condensate and its disconnected susceptibility. Even with

  1. Efficient gradient calibration based on diffusion MRI

    PubMed Central

    Teh, Irvin; Maguire, Mahon L.

    2016-01-01

    Purpose To propose a method for calibrating gradient systems and correcting gradient nonlinearities based on diffusion MRI measurements. Methods The gradient scaling in x, y, and z were first offset by up to 5% from precalibrated values to simulate a poorly calibrated system. Diffusion MRI data were acquired in a phantom filled with cyclooctane, and corrections for gradient scaling errors and nonlinearity were determined. The calibration was assessed with diffusion tensor imaging and independently validated with high resolution anatomical MRI of a second structured phantom. Results The errors in apparent diffusion coefficients along orthogonal axes ranged from −9.2% ± 0.4% to + 8.8% ± 0.7% before calibration and −0.5% ± 0.4% to + 0.8% ± 0.3% after calibration. Concurrently, fractional anisotropy decreased from 0.14 ± 0.03 to 0.03 ± 0.01. Errors in geometric measurements in x, y and z ranged from −5.5% to + 4.5% precalibration and were likewise reduced to −0.97% to + 0.23% postcalibration. Image distortions from gradient nonlinearity were markedly reduced. Conclusion Periodic gradient calibration is an integral part of quality assurance in MRI. The proposed approach is both accurate and efficient, can be setup with readily available materials, and improves accuracy in both anatomical and diffusion MRI to within ±1%. Magn Reson Med 77:170–179, 2017. © 2016 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine. PMID:26749277

  2. Stereo transparency and the disparity gradient limit

    NASA Technical Reports Server (NTRS)

    McKee, Suzanne P.; Verghese, Preeti

    2002-01-01

    Several studies (Vision Research 15 (1975) 583; Perception 9 (1980) 671) have shown that binocular fusion is limited by the disparity gradient (disparity/distance) separating image points, rather than by their absolute disparity values. Points separated by a gradient >1 appear diplopic. These results are sometimes interpreted as a constraint on human stereo matching, rather than a constraint on fusion. Here we have used psychophysical measurements on stereo transparency to show that human stereo matching is not constrained by a gradient of 1. We created transparent surfaces composed of many pairs of dots, in which each member of a pair was assigned a disparity equal and opposite to the disparity of the other member. For example, each pair could be composed of one dot with a crossed disparity of 6' and the other with uncrossed disparity of 6', vertically separated by a parametrically varied distance. When the vertical separation between the paired dots was small, the disparity gradient for each pair was very steep. Nevertheless, these opponent-disparity dot pairs produced a striking appearance of two transparent surfaces for disparity gradients ranging between 0.5 and 3. The apparent depth separating the two transparent planes was correctly matched to an equivalent disparity defined by two opaque surfaces. A test target presented between the two transparent planes was easily detected, indicating robust segregation of the disparities associated with the paired dots into two transparent surfaces with few mismatches in the target plane. Our simulations using the Tsai-Victor model show that the response profiles produced by scaled disparity-energy mechanisms can account for many of our results on the transparency generated by steep gradients.

  3. Stereo transparency and the disparity gradient limit

    NASA Technical Reports Server (NTRS)

    McKee, Suzanne P.; Verghese, Preeti

    2002-01-01

    Several studies (Vision Research 15 (1975) 583; Perception 9 (1980) 671) have shown that binocular fusion is limited by the disparity gradient (disparity/distance) separating image points, rather than by their absolute disparity values. Points separated by a gradient >1 appear diplopic. These results are sometimes interpreted as a constraint on human stereo matching, rather than a constraint on fusion. Here we have used psychophysical measurements on stereo transparency to show that human stereo matching is not constrained by a gradient of 1. We created transparent surfaces composed of many pairs of dots, in which each member of a pair was assigned a disparity equal and opposite to the disparity of the other member. For example, each pair could be composed of one dot with a crossed disparity of 6' and the other with uncrossed disparity of 6', vertically separated by a parametrically varied distance. When the vertical separation between the paired dots was small, the disparity gradient for each pair was very steep. Nevertheless, these opponent-disparity dot pairs produced a striking appearance of two transparent surfaces for disparity gradients ranging between 0.5 and 3. The apparent depth separating the two transparent planes was correctly matched to an equivalent disparity defined by two opaque surfaces. A test target presented between the two transparent planes was easily detected, indicating robust segregation of the disparities associated with the paired dots into two transparent surfaces with few mismatches in the target plane. Our simulations using the Tsai-Victor model show that the response profiles produced by scaled disparity-energy mechanisms can account for many of our results on the transparency generated by steep gradients.

  4. Gradient Learning Algorithms for Ontology Computing

    PubMed Central

    Gao, Wei; Zhu, Linli

    2014-01-01

    The gradient learning model has been raising great attention in view of its promising perspectives for applications in statistics, data dimensionality reducing, and other specific fields. In this paper, we raise a new gradient learning model for ontology similarity measuring and ontology mapping in multidividing setting. The sample error in this setting is given by virtue of the hypothesis space and the trick of ontology dividing operator. Finally, two experiments presented on plant and humanoid robotics field verify the efficiency of the new computation model for ontology similarity measure and ontology mapping applications in multidividing setting. PMID:25530752

  5. The effect of density gradients on hydrometers

    NASA Astrophysics Data System (ADS)

    Heinonen, Martti; Sillanpää, Sampo

    2003-05-01

    Hydrometers are simple but effective instruments for measuring the density of liquids. In this work, we studied the effect of non-uniform density of liquid on a hydrometer reading. The effect induced by vertical temperature gradients was investigated theoretically and experimentally. A method for compensating for the effect mathematically was developed and tested with experimental data obtained with the MIKES hydrometer calibration system. In the tests, the method was found reliable. However, the reliability depends on the available information on the hydrometer dimensions and density gradients.

  6. 17 GHz High Gradient Accelerator Research

    SciTech Connect

    Temkin, Richard J.; Shapiro, Michael A.

    2013-07-10

    This is a report on the MIT High Gradient Accelerator Research program which has included: Operation of the 17 GHz, 25 MeV MIT/Haimson Research Corp. electron accelerator at MIT, the highest frequency, stand-alone accelerator in the world; collaboration with members of the US High Gradient Collaboration, including the design and test of novel structures at SLAC at 11.4 GHz; the design, construction and testing of photonic bandgap structures, including metallic and dielectric structures; the investigation of the wakefields in novel structures; and the training of the next generation of graduate students and postdoctoral associates in accelerator physics.

  7. Relativistic klystron research for high gradient accelerators

    SciTech Connect

    Allen, M.A.; Callin, R.S.; Deruyter, H.; Eppley, K.R.; Fowkes, W.R.; Herrmannsfeldt, W.B.; Higo, T.; Hoag, H.A.; Lavine, T.L.; Lee, T.G.

    1988-06-01

    Relativistic klystrons are being developed as a power source for high gradient accelerator applications which include large linear electron--positron colliders, compact accelerators, and FEL sources. We have attained 200MW peak power at 11.4 GHz from a relativistic klystron, and 140 MV/m longitudinal gradient in a short 11.4 GHz accelerator section. We report here on the design of our first klystrons, the results of our experiments so far, and some of our plans for the near future. 5 refs., 7 figs.

  8. CARS thermometry in high temperature gradients

    NASA Astrophysics Data System (ADS)

    Zhu, J. Y.; Dunn-Rankin, D.

    1993-01-01

    CARS is an effective non-intrusive technique for measuring gas temperature in combustion environments. In regions of high temperature gradient, however, the CARS signal is complicated by contributions from gas at different temperature. This paper examines theoretically the uncertainty associated with CARS thermometry in steep temperature gradients. In addition, the work compares the temperature predicted from CARS with the adiabatic mixed temperature of the gas resident in the measurement volume. This comparison helps indicate the maximum sample volume size allowed for accurate temperature measurements.

  9. Alumina Concentration Gradients in Aluminium Reduction Cells

    NASA Astrophysics Data System (ADS)

    Lavoie, Pascal; Taylor, Mark P.

    The length of aluminium electrolysis cells have constantly increased over the last decades. The drive to increase productivity resulted in the need to feed and dissolve more alumina in less electrolyte. There is mounting evidence that these two trends are pushing the electrolysis cells above their capability to maintain alumina concentration, through time and space, at levels preventing both conventional and non-propagating anode effects. Alumina concentration gradient measurements were performed within large industrial cells and showed that large gradients occurred between locations in cells.

  10. Imbibition Driven by a Temperature Gradient

    NASA Astrophysics Data System (ADS)

    Medina, A.; Pineda, A.; Treviño, C.

    2003-05-01

    In this work, we have theoretically studied the imbibition process in a cylindrical capillary under a constant, longitudinal temperature gradient, G. A closed-form analytical solution has been obtained and the Washburn law (valid for the isothermal case) has been found to hold for G=0. The space and time evolution of the interface is strongly dependent on surface tension and the viscosity with temperature. By using reported data for an organic oil (squalene), we showed how imbibition can be accelerated when the temperature gradient is negative.

  11. High pressure liquid chromatographic gradient mixer

    DOEpatents

    Daughton, Christian G.; Sakaji, Richard H.

    1985-01-01

    A gradient mixer which effects the continuous mixing of any two miscible solvents without excessive decay or dispersion of the resultant isocratic effluent or of a linear or exponential gradient. The two solvents are fed under low or high pressure by means of two high performance liquid chromatographic pumps. The mixer comprises a series of ultra-low dead volume stainless steel tubes and low dead volume chambers. The two solvent streams impinge head-on at high fluxes. This initial nonhomogeneous mixture is then passed through a chamber packed with spirally-wound wires which cause turbulent mixing thereby homogenizing the mixture with minimum "band-broadening".

  12. Enhancement of chest radiographs with gradient operators.

    PubMed

    Daponte, J S; Fox, M D

    1988-01-01

    Reference is made to the Sobel and Roberts gradient operators used to enhance image edges. Overall, the Sobel operator was found to be superior to the Roberts operator in edge enhancement. A theoretical explanation for the superior performance of the Sobel operator was developed based on the concept of analyzing the x and y Sobel masks as linear filters. By applying pill-box, Gaussian, or median filtering prior to applying a gradient operator, noise was reduced. The pill-box and Gaussian filters were more computationally efficient than the median filter with approximately equal effectiveness in noise reduction.

  13. High-pressure liquid chromatographic gradient mixer

    DOEpatents

    Daughton, C.G.; Sakaji, R.H.

    1982-09-08

    A gradient mixer effects the continuous mixing of any two miscible solvents without excessive decay or dispersion of the resultant isocratic effluent or of a linear or exponential gradient. The two solvents are fed under low or high pressure by means of two high performance liquid chromatographic pumps. The mixer comprises a series of ultra-low dead volume stainless steel tubes and low dead volume chambers. The two solvent streams impinge head-on at high fluxes. This initial nonhomogeneous mixture is then passed through a chamber packed with spirally-wound wires which cause turbulent mixing thereby homogenizing the mixture with minimum band-broadening.

  14. A seismological determination of the temperature gradient in D″ beneath the western Pacific

    NASA Astrophysics Data System (ADS)

    Kuo, Ban-Yuan; Chen, Chin-Wu

    2005-05-01

    The temperature gradient of the thermal boundary layer in the D″ region is one of the basic properties of the mantle that remains difficult to evaluate. We characterize this quantity for a region in the western Pacific using gradient-sensitive seismological probes. First, both the amplitudes and travel times of the diffracted P and S phases (Pdiff, Sdiff) were analyzed to constrain the regional-scale vertical gradients of VP and VS. Acceptable models were grid-searched using synthetic waveforms for trial models that employ only one velocity gradient zone in D″. The VS models were searched over the parameter space of the thickness (H) and the gradient. Solutions show negative deviation from Preliminary Reference Earth Model and a trade-off between gradient and H from -0.00088 s-1, for190 km to -0.00049 s-1, for 240 km with a typical error of ±0.00015 s-1. Rather than pinning down the best solution, we consider two sets of solutions for VS with H = 190 and 240 km. For these two H values, the gradients of VP were determined solely by amplitude to be -0.00032 s-1 for 190 km and 0.00015 s-1 for 240 km, shrouded in relatively large errors of 0.0002-0.0003 s-1. We derive the temperature gradient from the resolved velocity gradients using the seismological-thermodynamic equation of Doornbos et al. (1986) and arrive at 9.0 ± 5.8 K/km and 5.7 ± 4.1 K/km over 190 and 240 km, respectively. The difference in gradient between these two models is statistically significant at the 99% confidence level, and the odds that the apparent steeper gradient is caused by squeezing energy of diffracted waves into a thinner zone can also be rejected with high confidence. The combination of the two models is thus consistent with a nonlinear temperature profile that steepens toward the core-mantle boundary. Both models detect the superadiabatic gradient of temperature in the lowermost mantle.

  15. An Introduction to the Conjugate Gradient Method that Even an Idiot Can Understand

    DTIC Science & Technology

    1994-03-07

    and Jorge Nocedal , Global convergence properties of conjugate gradient methods for optimization, SIAM Journal of Optimization 2 (1992), no. 1, 21-42...line searches was analyzed by Daniel [3]. The choice of t3 for nonlinear CG is discussed by Gilbert and Nocedal [81.. A history and extensive

  16. Gradient-index microlenses: numerical investigation of different spherical index profiles with the wave propagation method.

    PubMed

    Singer, W; Testorf, M; Brenner, K H

    1995-05-01

    Ion-exchange microlenses are available with different gradient-index profiles. We investigate the dependence of the imaging properties on the steepness of the index profiles. Therefore we model the index distribution by the Fermi function as radial distribution with spherical symmetry. The results are compared to index profiles according to the Doremus model.

  17. Nonisothermal flow of a polymeric liquid under a pulsating pressure gradient

    SciTech Connect

    Shul'man, Z.P.; Khusid, B.M.; Shabunina, Z.A.

    1987-03-01

    Increasing flow rates is a major problem in transporting petroleum as well as polymer solutions and melts. Industrial methods are often directed to reducing the effective viscosity: heating and pulsation. The latter is related to the nonlinearity in the properties. This paper studies the effects of pressure-gradient pulsations on the nonisothermal flow of a nonlinear liquid with memory in an annular channel.

  18. Light and competition gradients fail to explain the coexistence of shade-tolerant Fagus sylvatica and shade-intermediate Quercus petraea seedlings

    PubMed Central

    Van Couwenberghe, Rosalinde; Gégout, Jean-Claude; Lacombe, Eric; Collet, Catherine

    2013-01-01

    Background and Aims The coexistence of forest tree species has often been linked to differences among species in terms of their response to light availability during the regeneration stage. From this perspective, species coexistence results from growth–growth or mortality–growth trade-offs along spatial light gradients. Experimental evidence of growth–growth trade-offs in natural conditions is sparse due to various confounding factors that potentially hinder the relationship. This study examined growth hierarchies along light gradients between two tree species with contrasting shade tolerance by controlling potential confounding factors such as seedling size, seedling status, seedling density and species composition. Methods Natural regenerated shade-tolerant Fagus sylvatica and shade-intermediate Quercus petraea seedlings were used, and growth rankings over a 4-year period were compared in 8- to 10-year-old tree seedlings. Key results No rank reversal occurs between the two species along the light gradient, or along the density, mixture or seedling size gradients. The shade-tolerant species was always the more competitive of the two. Pronounced effects of initial size on seedling growth were observed, whereas the effects of light and competition by neighbours were of secondary importance. The paramount effect of size, which results from the asymmetric nature of interseedling competition, gives a strong advantage to tall seedlings over the long term. Conclusions This study extends previous efforts to identify potential drivers of rank reversals in young tree mixtures. It does not support the classical assumption that spatial heterogeneity in canopy opening explains the coexistence of the two species studied. It suggests that spatial variation in local size hierarchies among seedlings that may be caused by seedling emergence time or seedling initial performance is the main driver of the dynamics of these mixed stands. PMID:24036670

  19. Ordered Micro/Nanostructures with Geometric Gradient: From Integrated Wettability "Library" to Anisotropic Wetting Surface.

    PubMed

    Xue, Peihong; Nan, Jingjie; Wang, Tieqiang; Wang, Shuli; Ye, Shunsheng; Zhang, Junhu; Cui, Zhanchen; Yang, Bai

    2017-01-01

    Geometric gradients within ordered micro/nanostructures exhibit unique wetting properties. Well-defined and ordered microsphere arrays with geometric gradient (OMAGG) are successfully fabricated through combining colloidal lithography and inclined reactive ion etching (RIE). During the inclined RIE, the graded etching rates in vertical direction of etcher chamber are the key to generating a geometric gradient. The OMAGG can be used as an effective mask for the preparation of micro/nanostructure arrays with geometric gradient by selective RIE. Through this strategy, a well-defined wettability "library" with graded silicon cone arrays is fabricated, and the possibility of screening one desired "book" from the designated wettability "library" is demonstrated. Meanwhile, the silicon cone arrays with geometric gradient (SCAGG) can be applied to control the wetting behavior of water after being modified by hydrophilic or hydrophobic chemical groups. Based on this result, a temperature-responsive wetting substrate is fabricated by modifying poly n-isopropyl acrylamide (PNIPAM) on the SCAGG. These wettability gradients have great potential in tissue engineering, microfluidic devices, and integrated sensors. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  20. Shape and function of the Bicoid morphogen gradient in dipteran species with different sized embryos

    PubMed Central

    Gregor, Thomas; McGregor, Alistair P.; Wieschaus, Eric F.

    2008-01-01

    The Bicoid morphogen evolved approximately 150 MYA from a Hox3 duplication and is only found in higher dipterans. A major difference between dipteran species, however, is the size of the embryo, which varies up to 5 fold. Although the expression of developmental factors scale with egg length, it remains unknown how this scaling is achieved. To test whether scaling is accounted for by the properties of Bicoid, we expressed eGFP fused to the coding region of bicoid from three dipteran species in transgenic Drosophila embryos using the Drosophila bicoid cis-regulatory and mRNA localization sequences. In such embryos, we find that Lucilia sericata and Calliphora vicina Bicoid produce gradients very similar to the endogenous Drosophila gradient and much shorter than what they would have produced in their own respective species. The common shape of the Drosophila, Lucilia and Calliphora Bicoid gradients appears to be a conserved feature of the Bicoid protein. Surprisingly, despite their similar distributions, we find that Bicoid from Lucilia and Calliphora do not rescue Drosophila bicoid mutants, suggesting that that Bicoid proteins have evolved species-specific functional amino acid differences. We also found that maternal expression and anteriorly localization of proteins other than Bcd does not necessarily give rise to a gradient; eGFP produced a uniform protein distribution. However, a shallow gradient was observed using eGFP-NLS, suggesting nuclear localization may be necessary but not sufficient for gradient formation. PMID:18328473

  1. Numerical Study of the Shape Irregularity Gradient in Metallic Foams Under Different Impact Velocities

    NASA Astrophysics Data System (ADS)

    Wu, Yidong; Tang, Liqun; Liu, Zejia; Liu, Yiping; Jiang, Zhenyu; Zhang, Xiaoyang

    2017-08-01

    The properties of metallic foams are closely related to the average pore size, relative density and degree of the shape irregularity in the meso-structure. In this paper, gradient metallic foams with Voronoi structures based on different degrees of shape irregularity are constructed and numerically tested under different impact velocities. We combine three types of metallic foams with identical relative density but different degrees of shape irregularity in a specific sequence (from large to small or from small to large) to construct the new gradient models. A series of impact tests at different velocities are performed on the gradient metallic foams to acquire deformation characteristics and stress states. According to the results from the inertia effect and the energy absorption capacity, a gradient metallic foam with a shape irregularity that changes from large to small (negative gradient) is the optimal design. The simulation results provide a fresh perspective and methodology to design gradient metallic foams at the meso-structure scale for use as energy absorption materials.

  2. Calcium transport driven by a proton gradient and inverted membrane vesicles of Escherichia coli.

    PubMed

    Tsuchiya, T; Rosen, B P

    1976-02-25

    Calcium transport into inverted vesicles of Escherichia coli was observed to occur without an exogenous energy source when an artificial proton gradient was used. The orientation of the proton gradient was acid inside and alkaline outside. Either phosphate or oxalate was necessary for transport, as was found for respiratory-driven or ATP-driven uptake (Tsuchiya, T., and Rosen, B.P. (1975) J. Biol. Chem. 250, 7687-7692). Phosphate accumulation was found to occur in conjunction with calcium accumulation. Calcium transport driven by an artificial proton gradient was stimulated by dicyclohexylcarbodiimide, an inhibitor of the Mg2+ATPase (EC 3.6.1.3). Valinomycin, which catalyzes electrogenic potassium movement, stimulated calcium accumulation, while nigericin, which catalyzes electroneutral exchange of potassium and protons, inhibited both artificial proton gradient-driven transport and respiratory-driven transport. Other properties of the proton gradient-driven system and the previously reported energy-linked calcium transport system are similar, indicating that calcium is transported by the same carrier whether energy is supplied through an artificial proton gradient or an energized membrane state. These results suggest the existence of a calcium/proton antiport.

  3. Which processes shape stellar population gradients of massive galaxies at large radii?

    NASA Astrophysics Data System (ADS)

    Hirschmann, Michaela

    2016-08-01

    We investigate the differential impact of physical mechanisms, mergers (stellar accretion) and internal energetic phenomena, on the evolution of stellar population gradients in massive, present-day galaxies employing a set of high-resolution, cosmological zoom simulations. We demonstrate that negative metallicity and color gradients at large radii (>2Reff) originate from the accretion of metal-poor stellar systems. At larger radii, galaxies become typically more dominated by stars accreted from satellite galaxies in major and minor mergers. However, only strong galactic winds can sufficiently reduce the metallicity content of the accreted stars to realistically steepen the outer metallicity and colour gradients in agreement with present-day observations. In contrast, the gradients of the models without winds are inconsistent with observations (too flat). In the wind model, colour and metallicity gradients are significantly steeper for systems which have accreted stars in minor mergers, while galaxies with major mergers have relatively flat gradients, confirming previous results. This analysis greatly highlights the importance of both energetic processes and merger events for stellar population properties of massive galaxies at large radii. Our results are expected to significantly contribute to the interpretation of current and up-coming IFU surveys (like MaNGA and Califa), which in turn can help to better constrain still uncertain models for energetic processes in simulations.

  4. Linear and nonlinear effects of temperature and precipitation on ecosystem properties in tidal saline wetlands

    USGS Publications Warehouse

    Feher, Laura C.; Osland, Michael J.; Griffith, Kereen T.; Grace, James B.; Howard, Rebecca J.; Stagg, Camille L.; Enwright, Nicholas M.; Krauss, Ken W.; Gabler, Christopher A.; Day, Richard H.; Rogers, Kerrylee

    2017-01-01

    comparatively large changes in canopy height. However, there are scant data to evaluate the influence of precipitation on other ecosystem properties. There is a need for more decomposition data across climatic gradients, and to advance understanding of the influence of changes in precipitation and freshwater availability, additional ecological data are needed from tidal saline wetlands in arid climates. Collectively, our results can help scientists and managers better anticipate the linear and nonlinear ecological consequences of climate change for coastal wetlands.

  5. Examining the Education Gradient in Chronic Illness

    ERIC Educational Resources Information Center

    Chatterji, Pinka; Joo, Heesoo; Lahiri, Kajal

    2015-01-01

    We examine the education gradient in diabetes, hypertension, and high cholesterol. We take into account diagnosed as well as undiagnosed cases and use methods accounting for the possibility of unmeasured factors that are correlated with education and drive both the likelihood of having illness and the propensity to be diagnosed. Data come from the…

  6. Plant reproduction: GABA gradient, guidance and growth.

    PubMed

    Ma, Hong

    2003-10-28

    How a pollen tube manages to navigate through the female tissues during plant reproduction has been a mystery. A new analysis of an Arabidopsis mutant has provided the strongest evidence yet that a GABA gradient may be a critical signal for correct targeting of the pollen tube.

  7. HOT PRESSING WITH A TEMPERATURE GRADIENT

    DOEpatents

    Hausner, H.H.

    1958-05-20

    A method is described for producing powder metal compacts with a high length to width ratio, which are of substantially uniform density. The process consists in arranging a heating coil around the die and providing a temperature gradient along the length of the die with the highest temperature at the point of the compact farthest away from the ram or plunger.

  8. Density Gradient Columns for Chemical Displays.

    ERIC Educational Resources Information Center

    Guenther, William B.

    1986-01-01

    Procedures for preparing density gradient columns for chemical displays are presented. They include displays illustrating acid-base reactions, metal ion equilibria, and liquid density. The lifetime of these metastable displays is surprising, some lasting for months in display cabinets. (JN)

  9. Integral Field Spectroscopy Surveys: Oxygen Abundance Gradients

    NASA Astrophysics Data System (ADS)

    Sánchez, S. F.; Sánchez-Menguiano, L.

    2017-07-01

    We present here the recent results on our understanding of oxygen abundance gradients derived using Integral Field Spectroscopic surveys. In particular we analyzed more than 2124 datacubes corresponding to individual objects observed by the CALIFA (˜ 734 objects) and the public data by MaNGA (˜ 1390 objects), deriving the oxygen abundance gradient for each galaxy. We confirm previous results that indicate that the shape of this gradient is very similar for all galaxies with masses above 109.5M⊙, presenting in average a very similar slope of ˜ -0.04 dex within 0.5-2.0 re, with a possible drop in the inner regions (r<0.5re) and a flattennig in the outer regions. For lower masses (>109.5M⊙) the gradient seems to be flatter than for more massive ones. All these results agree with an inside-out growth of massive galaxies and indicate that low mass ones may still be growing in an outside in phase.

  10. Marine submicron aerosol gradients, sources and sinks

    NASA Astrophysics Data System (ADS)

    Ceburnis, Darius; Rinaldi, Matteo; Ovadnevaite, Jurgita; Martucci, Giovanni; Giulianelli, Lara; O'Dowd, Colin D.

    2016-10-01

    Aerosol principal sources and sinks over eastern North Atlantic waters were studied through the deployment of an aerosol chemistry gradient sampling system. The chemical gradients of primary and secondary aerosol components - specifically, sea salt (SS), water-insoluble organic matter (WIOM), water-soluble organic matter (WSOM), nitrate, ammonium, oxalate, amines, methanesulfonic acid (MSA) and water-soluble organic nitrogen (WSON) - were examined in great detail. Sea salt fluxes were estimated by the boundary layer box model and ranged from 0.3 to 3.5 ng m-2 s-1 over the wind speed range of 5-12 m s-1 and compared well with the derived fluxes from existing sea salt source parameterisations. The observed seasonal pattern of sea salt gradients was mainly driven by wind stress in addition to the yet unquantified effect of marine OM modifying fractional contributions of SS and OM in sea spray. WIOM gradients were a complex combination of rising and waning biological activity, especially in the flux footprint area, and wind-driven primary sea spray production supporting the coupling of recently developed sea spray and marine OM parameterisations.

  11. Examining the Education Gradient in Chronic Illness

    ERIC Educational Resources Information Center

    Chatterji, Pinka; Joo, Heesoo; Lahiri, Kajal

    2015-01-01

    We examine the education gradient in diabetes, hypertension, and high cholesterol. We take into account diagnosed as well as undiagnosed cases and use methods accounting for the possibility of unmeasured factors that are correlated with education and drive both the likelihood of having illness and the propensity to be diagnosed. Data come from the…

  12. Velocity gradients and microturbulence in Cepheids.

    NASA Technical Reports Server (NTRS)

    Karp, A. H.

    1973-01-01

    Variations of the microturbulent velocity with phase and height in the atmosphere have been reported in classical Cepheids. It is shown that these effects can be understood in terms of variations of the velocity gradient in the atmospheres of these stars.

  13. Annular beam with segmented phase gradients

    SciTech Connect

    Cheng, Shubo; Wu, Liang; Tao, Shaohua

    2016-08-15

    An annular beam with a single uniform-intensity ring and multiple segments of phase gradients is proposed in this paper. Different from the conventional superposed vortices, such as the modulated optical vortices and the collinear superposition of multiple orbital angular momentum modes, the designed annular beam has a doughnut intensity distribution whose radius is independent of the phase distribution of the beam in the imaging plane. The phase distribution along the circumference of the doughnut beam can be segmented with different phase gradients. Similar to a vortex beam, the annular beam can also exert torques and rotate a trapped particle owing to the orbital angular momentum of the beam. As the beam possesses different phase gradients, the rotation velocity of the trapped particle can be varied along the circumference. The simulation and experimental results show that an annular beam with three segments of different phase gradients can rotate particles with controlled velocities. The beam has potential applications in optical trapping and optical information processing.

  14. Analysis of magnetic gradients to study gravitropism.

    PubMed

    Hasenstein, Karl H; John, Susan; Scherp, Peter; Povinelli, Daniel; Mopper, Susan

    2013-01-01

    Gravitropism typically is generated by dense particles that respond to gravity. Experimental stimulation by high-gradient magnetic fields provides a new approach to selectively manipulate the gravisensing system. The movement of corn, wheat, and potato starch grains in suspension was examined with videomicroscopy during parabolic flights that generated 20 to 25 s of weightlessness. During weightlessness, a magnetic gradient was generated by inserting a wedge into a uniform, external magnetic field that caused repulsion of starch grains. The resultant velocity of movement was compared with the velocity of sedimentation under 1 g conditions. The high-gradient magnetic fields repelled the starch grains and generated a force of at least 0.6 g. Different wedge shapes significantly affected starch velocity and directionality of movement. Magnetic gradients are able to move diamagnetic compounds under weightless or microgravity conditions and serve as directional stimulus during seed germination in low-gravity environments. Further work can determine whether gravity sensing is based on force or contact between amyloplasts and statocyte membrane system.

  15. On-chip temperature gradient interaction chromatography.

    PubMed

    Shih, Chi-Yuan; Chen, Yang; Xie, Jun; He, Qing; Tai, Yu-Chong

    2006-04-14

    This paper reports the first integrated microelectromechanical system (MEMS) HPLC chip that consists of a parylene high-pressure LC column, an electrochemical sensor, a resistive heater and a thermal-isolation structure for on-chip temperature gradient interaction chromatography application. The separation column was 8 mm long, 100 microm wide, 25 microm high and was packed with 5 microm sized, C18-coated beads using conventional slurry-packing technique. A novel parylene-enhanced, air-gap thermal isolation technology was used to reduce heater power consumption by 58% and to reduce temperature rise in the off-column area by 67%. The fabricated chip consumed 400 mW when operated at 100 degrees C. To test the chromatography performance of the fabricated system, a mixture of derivatized amino acids was chosen for separation. A temporal temperature gradient scanning from 25 to 65 degrees C with a ramping rate of 3.6 degrees C/min was applied to the column during separation. Successful chromatographic separation of derivatized amino acids was carried out using our chip. Compared with conventional temperature gradient HPLC system which incorporates "macro oven" to generate temporal temperature gradient on the column, our chip's thermal performance, i.e., power consumption and thermal response, is greatly improved without sacrificing chromatography quality.

  16. CMB anisotropies from a gradient mode

    NASA Astrophysics Data System (ADS)

    Mirbabayi, Mehrdad; Zaldarriaga, Matias

    2015-03-01

    A linear gradient mode must have no observable dynamical effect on short distance physics. We confirm this by showing that if there was such a gradient mode extending across the whole observable Universe, it would not cause any hemispherical asymmetry in the power of CMB anisotropies, as long as Maldacena's consistency condition is satisfied. To study the effect of the long wavelength mode on short wavelength modes, we generalize the existing second order Sachs-Wolfe formula in the squeezed limit to include a gradient in the long mode and to account for the change in the location of the last scattering surface induced by this mode. Next, we consider effects that are of second order in the long mode. A gradient mode Φ = qṡx generated in Single-field inflation is shown to induce an observable quadrupole moment. For instance, in a matter-dominated model it is equal to Q = 5(qṡx)2/18. This quadrupole can be canceled by superposition of a quadratic perturbation. The result is shown to be a nonlinear extension of Weinberg's adiabatic modes: a long-wavelength physical mode which looks locally like a coordinate transformation.

  17. Consideration of Gravity Gradient Stabilization for Orion

    DTIC Science & Technology

    1989-03-01

    generating devices are necessary to auiment the gravityN aradient effect. Control moment gyros, reaction wheels , and magnetic torquers will be...generating devices are necessary to augment the gravity gradient effect. Control moment gyros, reaction wheels , and magnetic torquers will be investi...32 a. Reaction wheels ...................................... 33 3. C M G (s

  18. The microfluidic lighthouse: an omnidirectional gradient generator.

    PubMed

    Nakajima, A; Ishida, M; Fujimori, T; Wakamoto, Y; Sawai, S

    2016-11-01

    Studies of chemotactic cell migration rely heavily on various assay systems designed to evaluate the ability of cells to move in response to attractant molecules. In particular, the development of microfluidics-based devices in recent years has made it possible to spatially distribute attractant molecules in graded profiles that are sufficiently stable and precise to test theoretical predictions regarding the accuracy and efficiency of chemotaxis and the underlying mechanism of stimulus perception. However, because the gradient is fixed in a direction orthogonal to the laminar flow and thus the chamber geometry, conventional devices are limited for the study of cell re-orientation to gradients that move or change directions. Here, we describe the development of a simple radially symmetric microfluidics device that can deliver laminar flow in 360°. A stimulant introduced either from the central inlet or by photo uncaging is focused into the laminar flow in a direction determined by the relative rate of regulated flow from multiple side channels. Schemes for flow regulation and an extended duplexed device were designed to generate and move gradients in desired orientations and speed, and then tested to steer cell migration of Dictyostelium and neutrophil-like HL60 cells. The device provided a high degree of freedom in the positioning and orientation of attractant gradients, and thus may serve as a versatile platform for studying cell migration, re-orientation, and steering.

  19. Gradient mechanism in a communication network

    NASA Astrophysics Data System (ADS)

    Mukherjee, Satyam; Gupte, Neelima

    2008-03-01

    We study the efficiency of the gradient mechanism of message transfer in a two-dimensional communication network of regular nodes and randomly distributed hubs. Each hub on the network is assigned some randomly chosen capacity and hubs with lower capacities are connected to the hubs with maximum capacity. The average travel times of single messages traveling on the lattice decrease rapidly as the number of hubs increase. The functional dependence of the average travel times on the hub density shows q -exponential behavior with a power-law tail. We also study the relaxation behavior of the network when a large number of messages are created simultaneously at random locations and travel on the network toward their designated destinations. For this situation, in the absence of the gradient mechanism, the network can show congestion effects due to the formation of transport traps. We show that if hubs of high betweenness centrality are connected by the gradient mechanism, efficient decongestion can be achieved. The gradient mechanism is less prone to the formation of traps than other decongestion schemes. We also study the spatial configurations of transport traps and propose minimal strategies for their elimination.

  20. Velocity gradients and microturbulence in Cepheids.

    NASA Technical Reports Server (NTRS)

    Karp, A. H.

    1973-01-01

    Variations of the microturbulent velocity with phase and height in the atmosphere have been reported in classical Cepheids. It is shown that these effects can be understood in terms of variations of the velocity gradient in the atmospheres of these stars.